The Critical Role of Fillers in Composite Polymer Electrolytes for Lithium Battery
填料在锂电池复合聚合物电解质中的关键作用

Highlights 亮点

• The mechanism of the change in lithium-ion transport behavior caused by the incorporation of inorganic fillers into the polymer matrix is reviewed.
  本文综述了聚合物基体中加入无机填料导致锂离子传输行为发生变化的机理。

• The intrinsic factors of inorganic fillers to enhance the ionic conductivity of composite polymer electrolyte (CPEs) are investigated in depth.
  深入研究了无机填料增强复合聚合物电解质（CPE）离子导电性的内在因素。

• The contribution of inorganic fillers to inhibit dendrite growth and side reactions in CPEs is summarized.
  总结了无机填料在 CPE 中抑制枝晶生长和副反应的作用。

Abstract 摘要

With excellent energy densities and highly safe performance, solid-state lithium batteries (SSLBs) have been hailed as promising energy storage devices. Solid-state electrolyte is the core component of SSLBs and plays an essential role in the safety and electrochemical performance of the cells. Composite polymer electrolytes (CPEs) are considered as one of the most promising candidates among all solid-state electrolytes due to their excellent comprehensive performance. In this review, we briefly introduce the components of CPEs, such as the polymer matrix and the species of fillers, as well as the integration of fillers in the polymers. In particular, we focus on the two major obstacles that affect the development of CPEs: the low ionic conductivity of the electrolyte and high interfacial impedance. We provide insight into the factors influencing ionic conductivity, in terms of macroscopic and microscopic aspects, including the aggregated structure of the polymer, ion migration rate and carrier concentration. In addition, we also discuss the electrode–electrolyte interface and summarize methods for improving this interface. It is expected that this review will provide feasible solutions for modifying CPEs through further understanding of the ion conduction mechanism in CPEs and for improving the compatibility of the electrode–electrolyte interface.
固态锂电池（SSLB）具有出色的能量密度和高度安全的性能，被誉为前景广阔的储能设备。固态电解质是固态锂电池的核心成分，对电池的安全性和电化学性能起着至关重要的作用。复合聚合物电解质（CPE）因其优异的综合性能，被认为是所有固态电解质中最有前途的候选者之一。在本综述中，我们将简要介绍 CPE 的组成成分，如聚合物基体和填料种类，以及填料在聚合物中的整合。我们尤其关注影响 CPE 发展的两大障碍：电解质的低离子电导率和高界面阻抗。我们从聚合物的聚集结构、离子迁移率和载流子浓度等宏观和微观方面深入探讨了影响离子电导率的因素。此外，我们还讨论了电极-电解质界面，并总结了改善该界面的方法。通过进一步了解 CPE 中的离子传导机制和改善电极-电解质界面的兼容性，本综述有望为改性 CPE 提供可行的解决方案。

1 Introduction
1 简介

Traditional liquid electrolytes are used with safety issues such as flammability and leakage. Replacing liquid electrolytes with solid-state electrolytes is expected to fundamentally solve the safety problems of lithium-ion batteries [1, 2]. Moreover, solid-state electrolytes exhibit excellent mechanical strength and chemical neutrality, which can reduce the side reactions with lithium metal and inhibit the growth of lithium dendrites [3, 4]. Therefore, solid-state electrolytes are considered as a promising route for the preparation of lithium batteries with high safety performance, high stability and high energy density [5, 6].
传统的液态电解质存在易燃性和泄漏等安全问题。用固态电解质取代液态电解质有望从根本上解决锂离子电池的安全问题 [1, 2] 。此外，固态电解质具有出色的机械强度和化学中性，可减少与锂金属的副反应，抑制锂枝晶的生长 [3, 4] 。因此，固态电解质被认为是制备具有高安全性能、高稳定性和高能量密度的锂电池的一条有前途的途径[5, 6] 。

To date, the solid-state electrolytes have been divided into three categories: solid polymer electrolytes (SPEs), inorganic solid electrolytes (ISEs), and composite polymer electrolytes (CPEs) [7]. Solid-state electrolytes should exhibit high ionic conductivity, a broad electrochemical window, an outstanding lithium-ion transference number (t_Li⁺), enough mechanical strength, and great electrode compatibility [8]. ISEs, such as oxide electrolytes (garnet, NASICON, perovskite), sulfide electrolytes (Li₁₀GeP₂S₁₂, Li₂S–P₂S₅, Li₆PS₅X) and halide electrolytes (Li₃YCl₆, Li₃ScCl₆, Li₃YBr₆), have been widely investigated [9, 10]. ISEs show high mechanical robustness and excellent conductivity, which is even equal to that of liquid electrolytes. However, the commercial application of ISEs is limited by drawbacks such as poor electrode–electrolyte interfaces and processing properties. In contrast, SPEs with good flexibility can solve interface compatibility and processing problems [11, 12]. Due to the good solid–solid contact, the electrolyte can be well fitted to lithium metal for high-performance batteries. Many typical SPEs have been extensively studied, such as polyacrylonitrile (PAN) [13], poly (vinylidene fluoride‐hexafluoropropylene) (PVDF‐HFP) [14], polyethylene oxide (PEO) [15], and poly(ethylene glycol) dimethacrylate (PEGDMA) [16]. However, SPEs always suffer from poor ionic conductivity and low voltage tolerance.
迄今为止，固态电解质分为三类：固态聚合物电解质（SPE）、无机固态电解质（ISE）和复合聚合物电解质（CPE）[7]。固态电解质应具有高离子电导率、宽电化学窗口、出色的锂离子转移数（t_Li⁺）、足够的机械强度和良好的电极兼容性[8]。ISE，如氧化物电解质（石榴石、NASICON、透辉石）、硫化物电解质（Li₁₀GeP₂S₁₂、Li₂S-P₂S₅、Li₆PS₅X) 和卤化物电解质（Li₃YCl₆、Li₃ScCl₆, Li₃YBr₆) 已被广泛研究[9, 10] 。ISE 具有很高的机械坚固性和出色的导电性，甚至与液态电解质的导电性相当。然而，由于电极-电解质界面和加工性能较差等缺点，ISE 的商业应用受到了限制。相比之下，具有良好柔韧性的 SPE 可以解决界面兼容性和加工问题 [11、12]。由于良好的固-固接触，电解质可以很好地与锂金属相匹配，从而制造出高性能电池。 聚氧化乙烯（PEO）[15] 和聚（乙二醇）二甲基丙烯酸酯（PEGDMA）[16] 。然而，SPE 始终存在离子导电性差和耐压性低的问题。

CPEs, which consist of polymers, inorganic fillers and lithium salts, not only succeed in the virtues of processability and flexibility of SPE, but also bridge the discrepancy between SPE and ISEs by incorporating fillers [17]. Usually, the amount of filler is different in CPEs. When the filler content is lower than 50%, the filler can be approximately considered as being incorporated into the polymer. Otherwise, the polymer can be regarded as being incorporated into the filler. In recent years, CPEs have attracted much attention for their excellent electrochemical and safety properties [18,19,20,21]. However, in practical applications, CPEs cannot support the high-performance SSLBs, due to disappointing ionic conductivity and interfacial stability. Consequently, it is necessary to adopt some strategies to enhance the ionic conductivity and alleviate the interfacial issues of CPEs [19, 22].
由聚合物、无机填料和锂盐组成的 CPE 不仅继承了 SPE 的加工性和灵活性，还通过加入填料弥补了 SPE 和 ISE 之间的差异 [17]。通常，CPE 中的填料量是不同的。当填料含量低于 50%时，可近似认为填料已融入聚合物中。否则，聚合物可视为与填料结合在一起。近年来，CPE 因其优异的电化学和安全性能而备受关注[18,19,20,21] 。然而，在实际应用中，CPE 的离子传导性和界面稳定性令人失望，因此无法支持高性能 SSLB。因此，有必要采取一些策略来增强 CPE 的离子传导性并缓解其界面问题[19, 22] 。

Surprisingly, the inorganic fillers have an important effect on several properties of CPEs. Inorganic fillers can be divided into two categories: passive fillers and active fillers. Generally, active fillers (perovskite, garnet, LISICON, etc.), which can form continuous ion channels in the bulk phase and facilitate fast-ion transport, have a superior ionic conductivity. Li_3xLa_(2/3−x)TiO₃ (LLTO) is a representative active filler with a high ionic conductivity of 10^–3 S cm⁻¹ [15, 23, 24]. In regard to passive fillers, SiO₂, Al₂O₃, TiO₂, MgO and ZnO are the most researched. These fillers do not possess ion transport capabilities [25]. Nevertheless, the enhancement of the ionic conductivity of CPEs with passive fillers depends on the filler–polymer interface.
令人惊讶的是，无机填料对氯化聚乙烯的多项性能都有重要影响。无机填料可分为两类：被动填料和主动填料。一般来说，活性填料（透辉石、石榴石、LISICON 等）能在体相中形成连续的离子通道，促进离子的快速传输，因此具有更优越的离子导电性。Li_3xLa_(2/3-x)TiO₃ (LLTO) 是一种具有代表性的活性填料，其离子导电率高达 10^-3 S cm^-1 [15、23, 24] 。在被动填料方面，研究最多的是 SiO₂、Al₂O₃ 、TiO₂ 、MgO 和 ZnO。这些填料不具备离子传输能力 [25]。不过，使用被动填料的氯化聚乙烯离子电导率的增强取决于填料-聚合物界面。

Thanks to the extensive studies of CPEs doped with different fillers, a fundamental understanding of the ion transport mechanisms in CPEs has been obtained. Inorganic fillers can disrupt the aggregated structure of the polymer matrix, reduce the crystallinity and increase the number of polymer chain segments that can be conducted [26]. Meanwhile, structural design and surface modification of inorganic fillers can facilitate the dissociation of lithium salts or establish new ion conduction channels. For example, some vertically aligned structures can minimize the distance of ion movement. The functional groups on the surface of the inorganic fillers will also have an effect on the carrier concentration in CPEs and the motion of polymer chains. Therefore, many factors of the filler can affect the performance of CPEs [27]. These changes in performance are reflected in the intrinsic ion transport. This interaction is mainly attributed to two categories: filler–polymer and filler–lithium salt. In CPEs, ion transport is dominated by polymer chains. Therefore, filler size, concentration and hybridization strategies are key steps in the fabrication of high-performance CPEs. In addition, some fillers can optimize the electrode–electrolyte interface through synergistic effects and reduce the ion transport resistance at the interface [28]. For example, good chemical stability can be matched with high-voltage cathode materials, and excellent mechanical strength can effectively inhibit the growth of lithium dendrites [29]. In addition, the internal Lewis acid–base interaction induces the uniform deposition of lithium ions and uniform ion transport flux and reduces the large accumulation of charges at the electrode–electrolyte.
通过对掺入不同填料的氯化聚乙烯进行广泛研究，人们对氯化聚乙烯中的离子传输机制有了基本的了解。无机填料可以破坏聚合物基体的聚集结构，降低结晶度，增加可传导的聚合物链段数量[26]。同时，无机填料的结构设计和表面改性可促进锂盐的解离或建立新的离子传导通道。例如，一些垂直排列的结构可以最大限度地减少离子移动的距离。无机填料表面的官能团也会对 CPE 中的载流子浓度和聚合物链的运动产生影响。因此，填料的许多因素都会影响氯化聚乙烯的性能[27]。这些性能变化反映在内在离子传输中。这种相互作用主要分为两类：填料-聚合物和填料-锂盐。在 CPE 中，离子传输由聚合物链主导。因此，填料的尺寸、浓度和杂化策略是制造高性能 CPE 的关键步骤。此外，一些填料还能通过协同效应优化电极-电解质界面，降低界面上的离子传输阻力[28]。例如，良好的化学稳定性可与高电压正极材料相匹配，出色的机械强度可有效抑制锂枝晶的生长[29]。 此外，内部路易斯酸碱相互作用促使锂离子均匀沉积，离子传输通量均匀，减少了电极-电解质的大量电荷积累。

In this review, we first introduce the composition of CPEs, including polymer matrix and species of fillers. Second, the contribution of fillers in CPEs is presented in terms of the bulk phase and interface. Regarding the bulk phase, the interactions are focused on the filler–polymer and filler–lithium salt. The former mainly affects the aggregated state structure of the polymer, as reflected by the changes in the crystallinity (Xc), glass transition temperature (Tg) and spherulite morphology of CPEs. The latter influences the ionic conductivity, and t_Li⁺. From the perspective of the basic theory of physical chemistry, all of these factors are responsible for the ionic conductivity. For the electrode–electrolyte interface, the contributions of inorganic fillers at the cathode–electrolyte and anode–electrolyte interface are summarized. Both lowering the HOMO energy level of the CPEs and inducing uniform lithium deposition can effectively regulate the interfacial compatibility. Finally, we offer some suggestions for the development of CPEs with the hope of promoting the industrialization of high-performance solid-state lithium batteries.
在本综述中，我们首先介绍了 CPE 的组成，包括聚合物基体和填料种类。其次，从体相和界面两个方面介绍了填料在 CPE 中的作用。在体相方面，相互作用主要集中在填料-聚合物和填料-锂盐。前者主要影响聚合物的聚集态结构，这体现在氯化聚乙烯的结晶度（Xc）、玻璃化转变温度（Tg）和球粒形态的变化上。后者影响离子电导率和 t_Li⁺ 。从物理化学基本理论的角度来看，所有这些因素都是离子导电性的原因。就电极-电解质界面而言，阴极-电解质和阳极-电解质界面上的无机填料的贡献得到了总结。降低 CPE 的 HOMO 能级和诱导锂均匀沉积都能有效调节界面相容性。最后，我们对 CPE 的发展提出了一些建议，希望能促进高性能固态锂电池的产业化。

2 Overview of Composite Polymer Electrolytes
2 复合聚合物电解质概述

2.1 Polymer Matrices
2.1聚合物矩阵

Polymer electrolytes have been studied for many years. In 1973, Wright et al. [30] revealed that PEO with alkali metal salts possesses ionic conductivity. This finding set a precedent for the development of ion-conducting polymer. PEO, as a typical ion-conducting polymer, contains abundant ether-oxygen groups that can dissolve lithium salts and form complexes with lithium ions [31, 32]. In SPEs, lithium salts and polymers form complexes. Under this condition, the driving force of propulsion generated through the movement of the amorphous polymer chains promotes the jumping of anions and cations at the adjacent coordination sites. Directional motion, which is referred to as an ion-conducting process, is achieved under the external electric field. Therefore, it is generally agreed that ionic conduction mainly happens in the amorphous region of the polymer. Most ion-conducting polymers are semicrystalline at RT, including PAN, polyvinyl carbonate (PVC), polyvinylidene fluoride (PVDF), PVDF-HFP, polymethyl methacrylate (PMMA), polyethylene (glycol) diacrylate (PEGDA), tetraethylene glycol dimethacrylate (TEGDMA), and tetraethylene glycol dimethyl ether (TEGDME) [33, 34]. Common polymer matrices and their chemical structures are summarized in Fig. 1. And the molecular weight of common polymers is listed in Table 1. Due to the semicrystalline nature of these polymers, chain segment movement is difficult at RT. The ionic conductivity of these polymers at RT ranges from only 10^–6 to 10^–8 S cm⁻¹ [35]. The addition of hydrogen bonds or π-conjugated groups in polymer chains is an effective way to enhance the ionic conductivity [36, 37]. Hydrogen bonding can occur through interactions with polar groups to relieve the coordination of strong polar groups with lithium ions to increase the carrier concentration. The π-conjugated groups can form new ion conduction channels [38].
对聚合物电解质的研究已有多年。1973 年，Wright 等人[30] 发现，含有碱金属盐的 PEO 具有离子导电性。这一发现为离子导电聚合物的开发开创了先河。PEO 作为一种典型的离子导电聚合物，含有丰富的醚氧基团，可溶解锂盐并与锂离子形成络合物[31，32]。在 SPE 中，锂盐和聚合物形成复合物。在这种情况下，通过无定形聚合物链的运动产生的推动力会促进阴阳离子在相邻配位点的跳跃。在外部电场的作用下，可实现定向运动，即离子传导过程。因此，人们普遍认为离子传导主要发生在聚合物的无定形区域。大多数离子导电聚合物在 RT 状态下都是半结晶的，包括 PAN、聚碳酸酯（PVC）、聚偏氟乙烯（PVDF）、PVDF-HFP、聚甲基丙烯酸甲酯（PMMA）、聚乙二醇二丙烯酸酯 (PEGDA)、四甘醇二甲基丙烯酸酯 (TEGDMA) 和四甘醇二甲醚 (TEGDME) [33, 34] 。图 1 概括了常见的聚合物基质及其化学结构。表 1 列出了常见聚合物的分子量。由于这些聚合物的半结晶性质，链段在 RT 时很难移动。这些聚合物在 RT 时的离子导电率仅为 10^-6 到 10^-8 S cm^-1 [35]。 在聚合物链中添加氢键或π共轭基团是增强离子导电性的有效方法[36, 37] 。氢键可通过与极性基团的相互作用发生，以缓解强极性基团与锂离子的配位，从而提高载流子浓度。π 共轭基团可形成新的离子传导通道[38]。

Fig. 1 图 1

Chemical structure of commonly polymers [45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64]
常见聚合物的化学结构 [45,46,47,48、49,50,51,52,53、54,55,56,57,58,59、60,61,62,63,64].

However, a few studies have suggested that crystalline polymers can also conduct lithium ions [39, 40]. In contrast to conventional ion conduction, lithium-ion movement in crystalline polymers does not depend on relaxed segments, but on jumps in helical channels. PEO chains fold in an ordered framework to form an interlocking cylinder (channels). Lithium ions are present in the channels and the anions are located outside [41]. In addition to PEO, some plastic crystals are also attracting attention. The plastic crystals are a kind of material with a disordered direction and ordered position due to the rotational motion of molecules or ions at a certain temperature, such as succinonitrile (SN) and sebaconitrile. Because of the special structure, plastic crystals have excellent plasticity and diffusion rate. As a result, this type of solid-state electrolyte has a high ionic conductivity. SN, as a typical molecular plastic crystal, exhibits plastic crystal behavior at − 35∼62 °C [42]. Below − 35 °C, the SN molecule exists only in gauche conformation and all rotational motions are frozen. In contrast, the orientation disorder of the plastic phase of SN at room temperature (RT) is formed by the coexistence of trans and gauche isomers. The trans-isomer increases the defects in the lattice and thus decreases the activation energy for ion migration. Also in trans-gauche isomeric, which includes molecules rotating around the central C–C bond, the SN molecule contributes to increasing the ion mobility [43]. Yet, the mechanical strength of such solid-state electrolytes is not sufficient for their practical applications. Therefore, the incorporation of high-strength polymers is the main way to solve the problem. Zhou et al. [44] prepared a solid-state electrolyte based on nitrile material. Cyanoethyl polyvinyl alcohol (PVA-CN) was polymerized in situ in the SN-based solid-state electrolyte. This solid-state electrolyte was filled in a PAN fiber network. The cross-linked PVA-CN polymer backbone enhances the mechanical strength of the SN. PVA-CN/SN SPEs exhibit appreciable ionic conductivity of 0.3 S cm⁻¹.
不过，一些研究表明，结晶聚合物也能传导锂离子[39, 40] 。与传统的离子传导不同，锂离子在结晶聚合物中的移动并不依赖于松弛的片段，而是依赖于螺旋通道中的跃迁。PEO 链在一个有序的框架中折叠，形成一个交错的圆柱体（通道）。锂离子存在于通道中，阴离子则位于通道外[41]。除 PEO 外，一些塑料晶体也备受关注。塑性晶体是一种由于分子或离子在一定温度下的旋转运动而形成的方向无序、位置有序的物质，如琥珀腈（SN）和癸二腈。由于结构特殊，塑性晶体具有极佳的可塑性和扩散率。因此，这类固态电解质具有很高的离子导电率。SN 作为一种典型的分子塑性晶体，在 - 35∼62 °C [42]时表现出塑性晶体行为。在零下 35 °C以下，SN 分子只存在于凹凸构象中，所有旋转运动都被冻结。与此相反，室温（RT）下 SN 塑性相的取向紊乱是由反式异构体和高斯异构体共存形成的。反式异构体增加了晶格中的缺陷，从而降低了离子迁移的活化能。此外，在反式-高歇异构体（包括围绕中心 C-C 键旋转的分子）中，SN 分子也有助于提高离子迁移率[43]。然而，这种固态电解质的机械强度不足以满足实际应用的需要。 因此，加入高强度聚合物是解决问题的主要途径。Zhou 等人 [44] 制备了一种基于腈材料的固态电解质。氰乙基聚乙烯醇（PVA-CN）在基于 SN 的固态电解质中原位聚合。这种固态电解质被填充在 PAN 纤维网络中。交联的 PVA-CN 聚合物骨架增强了 SN 的机械强度。PVA-CN/SN 固态电解质的离子电导率为 0.3 S cm^-1。

Table 1 The molecular weight of common polymers
表 1 常见聚合物的分子量

Currently, the plastic crystal materials used for SPEs are mostly nitrile materials. However, the compatibility between nitrile and lithium metal is poor. As well, the mechanical strength of nitriles is low. Modified lithium metal, with a supporting membrane, mixed with high-strength polymer can solve the above problems. The research on plastic crystal materials is still in the beginning stage, and more research is needed to succeed.
目前，用于固相萃取的塑料晶体材料主要是腈类材料。然而，腈与金属锂的相容性较差。此外，腈类材料的机械强度也较低。将改性金属锂与高强度聚合物混合，再加上一层支撑膜，可以解决上述问题。塑料晶体材料的研究仍处于起步阶段，需要更多的研究才能取得成功。

2.2 Inorganic Fillers
2.2无机填料

The uniform mixing of inorganic fillers with polymers has been extensively investigated. Inorganic fillers in polymers reduce the tendency of the polymer to crystallize and accelerate the lithium salt dissociation. Furthermore, such an abundant composite solid electrolyte interface may provide multiple transfer routes for lithium ions, resulting in improved ionic conductivity. Inorganic fillers can be grouped into two categories: passive fillers and active fillers.
无机填料与聚合物的均匀混合已得到广泛研究。聚合物中的无机填料可降低聚合物的结晶趋势，加速锂盐的解离。此外，这种丰富的复合固体电解质界面可为锂离子提供多种转移途径，从而提高离子传导性。无机填料可分为两类：被动填料和主动填料。

2.2.1 Passive Fillers
2.2.1 被动填充物

Passive fillers are lithium-ion insulators. They cannot conduct lithium ions by themselves. However, the existence of these fillers can affect the ability of polymer chain segments to transport ions [65]. First, passive filler is added to the polymer matrix as small molecule plasticizers. This can increase the amorphous phase in the polymer matrix, thus inhibiting the polymer crystallization kinetics and reducing the Tg. Moreover, with an increase in the localized amorphous region, the ion transport efficiency is elevated. Second, based on Lewis acid–base theory, the surface groups of passive fillers would interact with ion pairs to promote further dissociation. In recent decades, many passive fillers, including TiO₂ [66], Al₂O₃ [67], SiO₂ [68] and ZrO₂ [69]_, have been widely applied in CPEs owing to their advantages of easy synthesis, controllable size and stable physical and chemical stability. Table 2 shows typical passive fillers and their ionic conductivity. There is another type of passive filler called ferroelectric ceramic fillers, such as BaTiO₃ [70]. Different from oxide fillers, ferroelectric ceramic fillers interact with polymer chains through spontaneous polarization to improve the ionic conductivity in the interfacial region. Besides, clays are also involved. This kind of passive filler can provide a large specific surface area. The free lithium ions are increased at the interfacial area between polymers and fillers. However, the mechanism of this interaction is relatively complex, and there is no clear explanation for this process.
被动填料是锂离子绝缘体。它们本身不能传导锂离子。然而，这些填料的存在会影响聚合物链段传输离子的能力[65]。首先，被动填料作为小分子增塑剂添加到聚合物基体中。这会增加聚合物基体中的无定形相，从而抑制聚合物的结晶动力学并降低 Tg。此外，随着局部无定形区域的增加，离子传输效率也会提高。其次，根据路易斯酸碱理论，被动填料的表面基团会与离子对相互作用，促进离子进一步解离。近几十年来，许多被动填料，包括 TiO₂ [66], Al₂O₃ [67]、SiO₂ [68] 和 ZrO₂ [69]_, 由于其易于合成、尺寸可控、物理和化学稳定性稳定等优点，已广泛应用于 CPE 中。表2显示了典型的无源填料及其离子导电性。还有一种无源填料称为铁电陶瓷填料，如 BaTiO₃ [70]。与氧化物填料不同，铁电陶瓷填料通过自发极化与聚合物链相互作用，从而提高界面区的离子导电性。此外，粘土也参与其中。这种被动填料可提供较大的比表面积。 游离锂离子在聚合物和填料之间的界面区域增加。然而，这种相互作用的机理相对复杂，对这一过程也没有明确的解释。

Table 2 CPEs incorporated with passive fillers
表 2 含有无源填料的氯化聚乙烯

2.2.2 Active Fillers
2.2.2 活性填充物

Compared to passive fillers, lithium fast-ion conductors serving as active fillers can improve the electrochemical performance of CPEs more effectively by facilitating the migration of lithium ions. Table 3 shows the ionic conductivity of typical active fillers incorporated with polymers. Active fillers always exhibit a high ion conductivity (> 10^–4 S cm⁻¹). This can be attributed following factors: The many continuous defects in active fillers with low activation energy enable easy ion hopping. Moreover, active fillers themselves can supply a large number of lithium ions, enhancing the concentration of free lithium ions at the interface between the active filler and the polymer. Therefore, the total ionic conductivity is improved. Generally, active fillers include perovskite, garnet, LISICON, etc. When the percentage of active filler is less than 40 wt%, the CPEs can supply a high concentration of free lithium ions. However, the concentration of active filler exceeds a certain threshold, it forms a fully permeable network. At this moment, the ion transport behavior changes.
与被动填料相比，作为主动填料的锂快离子导体可通过促进锂离子迁移更有效地改善 CPE 的电化学性能。表 3 显示了与聚合物结合的典型活性填料的离子电导率。活性填料总是表现出很高的离子传导性（> 10^-4 S cm^-1 ）。这可归因于以下因素：活性填料中的许多连续缺陷具有较低的活化能，使离子易于跳跃。此外，活性填料本身可提供大量锂离子，从而提高了活性填料与聚合物界面处的游离锂离子浓度。因此，总离子传导性得到了改善。一般来说，活性填料包括透辉石、石榴石、LISICON 等。当活性填料的百分比小于 40 wt% 时，CPE 可以提供高浓度的游离锂离子。然而，当活性填料的浓度超过一定阈值时，就会形成完全渗透的网络。此时，离子传输行为会发生变化。

Table 3 CPEs incorporated with active fillers
表 3 含有活性填料的氯化聚乙烯

2.3 Distribution of Fillers in Polymers
2.3填料在聚合物中的分布

The incorporation of inorganic fillers with polymers can allow one to take full advantage of CPEs. For example, inorganic fillers can be used to elevate the ionic conductivity, t_Li⁺ and electrochemical stability window of SPEs [98]. Besides, they also show excellent performance in alleviating the interfacial stability between the electrolyte and electrode. Therefore, in recent years, CPE has a broad application prospect in the field of lithium batteries and has attracted more and more attention.
在聚合物中加入无机填料可以充分利用 CPE 的优势。例如，无机填料可用于提高 SPE 的离子电导率、t_Li⁺ 和电化学稳定性窗口[98]。此外，它们在缓解电解质与电极之间的界面稳定性方面也表现出色。因此，近年来 CPE 在锂电池领域具有广阔的应用前景，受到越来越多的关注。

In the early phases of research, scholars were devoted to the Lewis acid–base interactions between inorganic fillers and polymers. This model assumes that fast-ion-conducting channels can be constructed on the surface of fillers. Since then, many studies have focused on the construction of fast-ion-conducting channels. This fast-ion transfer percolation channel is related to the orientation (ordered or disordered arrangement) and morphology (1D, 2D, 3D) of the filler in the polymer. Therefore, the main goal of this section is to present the integration method of inorganic fillers in CPEs and their influence on the ionic conductivity.
在研究的早期阶段，学者们致力于研究无机填料与聚合物之间的路易斯酸碱相互作用。这一模型假定可以在填料表面构建快速离子传导通道。此后，许多研究都集中在快速离子传导通道的构建上。这种快速离子传输渗流通道与聚合物中填料的取向（有序或无序排列）和形态（一维、二维、三维）有关。因此，本节的主要目标是介绍 CPE 中无机填料的整合方法及其对离子导电性的影响。

2.3.1 Disordered Fillers in CPEs
2.3.1氯化聚乙烯中的杂乱填料

Usually, inorganic fillers are mainly dispersed disorderly in the polymers. The presence of inorganic fillers disturbs the crystallization of the polymers and thus increases the ionic conductivity of CPE. However, the fillers inevitably prefer to aggregate in the polymer, which hinders the formation of percolation network. Facilitating the dispersion of fillers in polymers is an effective method for forming percolation networks [99].
通常，无机填料主要无序地分散在聚合物中。无机填料的存在会干扰聚合物的结晶，从而增加 CPE 的离子导电性。然而，填料不可避免地倾向于聚集在聚合物中，从而阻碍了渗滤网络的形成。促进填料在聚合物中的分散是形成渗滤网络的有效方法 [99]。

Li et al. [100] prepared HPDA fillers, as shown in Fig. 2a, in which hollow silica was used as a template and covered with a layer of polydopamine. Compared with silica alone, the thin polydopamine layer facilitated the dispersion of HPDA in PEO by providing a surface that was more compatible with the PEO matrix. As a consequence, the ionic conductivity of HPDA-PEO CPEs was 0.189 × 10⁻³ S cm⁻¹ (60 °C), as shown in Fig. 2b. Huang et al. [101] coated a layer of polydopamine (PDA) in situ on the surface of LLZTO. The modified LLZTO with PDA allowed uniform dispersion of LLZTO (80 wt%) in SPEs. PDA lowed the surface energy of LLZTO to promote the dispersion of LLZTO nanoparticles in the polymers (Fig. 2c). Thus, the ionic conductivity of LLZTO@PDA-PEO CPEs was increased to 1.1 × 10^–4 S cm⁻¹ (at 30 °C) (Fig. 2d). Cui and workers [102] introduced a method for the in situ production of inorganic fillers in SPEs (Fig. 2e). Thanks to this in situ polymerization, SiO₂ formed a continuous dispersed phase in the polymer. Thus, more contact area was provided for Lewis acid–base interactions. Moreover, the mono-dispersity SiO₂ effectively inhibited the crystallization of PEO to promote the movement of polymer segments. As a consequence, the SiO₂-PEO CPEs showed a superior ionic conductivity of 4.4 × 10^–5 S cm⁻¹ at 30 °C (Fig. 2f). Moreover, the electrochemical window was broadened to 5.5 V versus Li/Li⁺ (Fig. 2g).
Li 等人[100]制备了 HPDA 填料，如图2a 所示，其中使用空心二氧化硅作为模板，并覆盖一层聚多巴胺。与单纯的二氧化硅相比，薄薄的聚多巴胺层提供了一个与 PEO 基质更相容的表面，从而促进了 HPDA 在 PEO 中的分散。因此，如图 2b 所示，HPDA-PEO CPE 的离子电导率为 0.189 × 10^-3 S cm^-1 (60 °C)。Huang 等人[101]在 LLZTO 表面原位涂覆了一层聚多巴胺 (PDA)。经 PDA 修饰的 LLZTO 可在 SPE 中均匀分散 LLZTO（80 wt%）。PDA 降低了 LLZTO 的表面能，从而促进了 LLZTO 纳米粒子在聚合物中的分散（图 2c ）。因此，LLZTO@PDA-PEO CPE 的离子电导率提高到 1.1 × 10^-4 S cm^-1 （30 °C 时）（图 2d ）。Cui 等人[102]提出了一种在 SPE 中原位生产无机填料的方法（图2e）。通过这种原位聚合，SiO₂ 在聚合物中形成了连续的分散相。因此，路易斯酸碱相互作用有了更大的接触面积。此外，单分散性 SiO₂ 能有效抑制 PEO 的结晶，促进聚合物段的移动。因此，SiO₂-PEO CPE 在 30 °C 时的离子电导率高达 4.4 × 10^-5 S cm^-1 （图2f）。 此外，与 Li/Li⁺ 相比，电化学窗口扩大到 5.5 V（图2g）。

Fig. 2 图 2

a Schematic of HPDA-PEOCPEs; b Arrhenius plots for HPDA-PEO CPEs. Adapted with permission from Ref. [100]. c Schematic of dopamine on the surface of LLZTO particles; d Arrhenius log $\text{σ}\sim$ 1000/T of LLZTO@PDA-PEO and LLZTO/PEO CPEs. Adapted with permission from Ref. [101]. e Schematic diagram illustrating the in situ hydrolysis process and the interaction mechanism between PEO chains and SiO₂; f Arrhenius plots of SiO₂-PEO CPEs; g Electrochemical stability windows of SiO₂-PEO CPEs. Adapted with permission from Ref. [102]
a HPDA-PEOCPE 示意图；b HPDA-PEO CPE 的阿伦尼乌斯图。经授权改编自参考文献。[100]。c LLZTO 颗粒表面的多巴胺示意图；d LLZTO@PDA-PEO 和 LLZTO/PEO CPE 的 Arrhenius log \(\sigma\sim) 1000/T 。经授权改编自参考文献。[101]。e 原位水解过程和 PEO 链与 SiO₂ 之间相互作用机制示意图；f SiO₂-PEO CPE 的阿伦尼乌斯图；g SiO₂-PEO CPE 的电化学稳定性窗口。经授权改编自参考文献。[102] 改编自参考文献。

Chen et al. [103] prepared LLZTO-PEO CPEs by the hot-pressing technique. The CPEs, including fillers incorporated into polymers and polymers incorporated into fillers, were designed by adjusting the content of LLZTO (Fig. 3a). As illustrated in Fig. 3b, Tm of LLZTO- PEO CPEs decreases gradually with the addition of LLZTO particles. When the LLZTO concentration was low enough, the fillers were well dispersed in the polymers causing less crystallization of the polymers. However, when the LLZTO content exceeded the permeation threshold, it could not be dispersed uniformly, which caused a significant increase in the stiffness of LLZTO-PEO CPEs. With the increase in LLZTO content, the ionic conductivity first increased and then decreased, which is due to the serious agglomeration of the additional LLZTO. Figure 3c shows that the ionic conductivity of LLZTO-PEO CPEs got a maximum value of 1.17 × 10^–4 S cm⁻¹ at 10% LLZTO. Croce et al. [104] investigated the mechanism of ionic conductivity enhancement for Al₂O₃ with different surface treatments in PEO. As shown in Fig. 3d, there were three different surface interactions between Al₂O₃ and PEO. It was assumed that a Lewis acid (Li⁺) interacted with a Lewis base (–OH groups of Al₂O₃). The additional interactions weakened the complexation of lithium ions with oxygen atoms on the PEO chain to facilitate the transport of lithium ions. As shown in Fig. 3e, the differences in ionic conductivity were directly related to the different filler surfaces. This can be ascribed to the different microstructural interactions that occurred when varying the type of ceramic surface states. We will discuss this interaction in detail in the next section.
Chen 等人[103]采用热压技术制备了 LLZTO-PEO CPE。通过调整 LLZTO 的含量，设计出了 CPE，其中包括加入聚合物的填料和加入填料的聚合物（图 3a）。如图3b所示，随着 LLZTO 颗粒的加入，LLZTO-PEO CPE 的 Tm 逐渐降低。当 LLZTO 的浓度足够低时，填料能很好地分散在聚合物中，从而减少聚合物的结晶。然而，当 LLZTO 的含量超过渗透阈值时，它就无法均匀分散，从而导致 LLZTO-PEO 氯化聚乙烯的刚度显著增加。随着 LLZTO 含量的增加，离子电导率先升高后降低，这是由于额外的 LLZTO 严重团聚所致。图 3c 显示，LLZTO-PEO CPE 的离子电导率在 10% LLZTO 时达到最大值 1.17 × 10^-4 S cm^-1 。Croce 等人[104]研究了在 PEO 中经过不同表面处理的 Al₂O₃ 离子电导率增强的机理。如图 3d 所示，Al₂O₃ 与 PEO 之间存在三种不同的表面相互作用。假设路易斯酸（Li⁺）与路易斯碱（Al₂O₃ 的 -OH 基团）相互作用。额外的相互作用减弱了锂离子与 PEO 链上氧原子的络合，从而促进了锂离子的传输。如图所示3e，离子传导性的差异与不同的填料表面直接相关。这可以归因于不同类型的陶瓷表面状态所产生的不同微观结构相互作用。我们将在下一节详细讨论这种相互作用。

Fig. 3 图 3

a Schematic illustration for LLZTO- PEO CPEs; b DSC result of different filler contents of LLZTO-PEO CPEs; c Ionic conductivities of different filler contents of LLZTO- PEO CPEs. Adapted with permission from Ref. [103]. d Surface interactions between three different type Al₂O₃ and PEO; e conductivity plots of Al₂O₃-PEO CPEs. Adapted with permission from Ref. [104]
a LLZTO- PEO CPE 的示意图；b LLZTO-PEO CPE 不同填料含量的 DSC 结果；c LLZTO- PEO CPE 不同填料含量的离子电导率。经授权改编自参考文献。[103]。d 三种不同类型的 Al₂O₃ 和 PEO 之间的表面相互作用；e Al₂O₃-PEO CPE 的电导率图。经授权改编自参考文献。[104] 改编自参考文献。

In addition to the above-mentioned 0D inorganic fillers, which are randomly dispersed, there are some 1D inorganic fillers that are also randomly dispersed in the polymers. Liu et al. [105] first fabricated LLTO nanowires by electrostatic spinning and dispersed them in PAN to prepare PAN- LLTO NW CPEs (Fig. 4a). LLTO nanowires with a high length-to-diameter ratio can provide continuous transport channels for lithium ions. Furthermore, they can be uniformly distributed in the polymer matrix as indicated in Fig. 4b. As shown in Fig. 4c, the ionic conductivity of PAN-15LLTO NW CPEs was higher (2.4 × 10^–4 S cm⁻¹) than that of PAN-15LLTO NP CPEs. Subsequently, Chen et al. [106] added Ca–CeO₂ nanotubes into PEO to prepare Ca–CeO₂–PEO CPEs. Ca–CeO₂ nanotubes can inhibit the reorganization and increase the dipole moment of PEO chains. As depicted in Fig. 4d, Ca–CeO₂ nanotubes can accelerate the dissociation of LiTFSI through oxygen vacancies on the surface, resulting in more free lithium ions. The Ca–CeO₂–PEO CPEs offered a high t_Li⁺ of 0.453 (Fig. 4e). Moreover, the Li|Ca–CeO₂–PEO CPEs|LiFePO₄ battery provided an initial discharge capacity of 164 mAh g⁻¹ at 0.1C. Even at a high current density of 2C, 100 mAh g⁻¹ was obtained (Fig. 4f). After 200 cycles, the discharge capacity was maintained at 93 mAh g⁻¹ at 1C.
除了上述随机分散的 0D 无机填料外，还有一些 1D 无机填料也是随机分散在聚合物中的。Liu 等人[105]首先通过静电纺丝制备出 LLTO 纳米线，并将其分散在 PAN 中，制备出 PAN- LLTO NW CPE（图4a）。具有高长径比的 LLTO 纳米线可为锂离子提供连续的传输通道。此外，如图4b所示，它们可以均匀地分布在聚合物基体中。如图 4c 所示，PAN-15LLTO NW CPE 的离子电导率（2.4 × 10^-4 S cm^-1 ）高于 PAN-15LLTO NP CPE。随后，Chen 等人[106]在 PEO 中加入 Ca-CeO₂ 纳米管，制备了 Ca-CeO₂-PEO CPEs。Ca-CeO₂ 纳米管可以抑制 PEO 链的重组并增加偶极矩。如图 4d 所示，Ca-CeO₂ 纳米管可以通过表面的氧空位加速 LiTFSI 的解离，从而产生更多的游离锂离子。Ca-CeO₂-PEO CPE 的 t_Li⁺ 高达 0.453（图4e）。此外，Li|Ca-CeO₂-PEO CPEs|LiFePO₄ 电池在 0.1C 时的初始放电容量为 164 mAh g^-1 。即使在 2C 的高电流密度下，也能获得 100 mAh g^-1 （图4f）。 经过 200 次循环后，放电容量在 1C 时保持在 93 mAh g^-1 的水平。

Fig. 4 图 4

a Lithium-ion pathways in nanowire- and nanoparticle-filled PAN CPEs; b SEM pictures for the PAN-LLTO NWs; c Arrhenius plots of the PAN-LLTO NWs and PAN-LLTO NPs CPEs. Adapted with permission from Ref. [105]. d Diagram of the enhanced mechanism of lithium-ion transport in Ca–CeO₂-PEO CPEs; e Chronoamperometry curves of Ca–CeO₂-PEO CPEs; f Rate performance of PEO-LiTFSI and Ca–CeO₂-PEO CPEs with LiFePO₄ cathode. Adapted with permission from Ref. [106]
a 纳米线和纳米粒子填充的 PAN CPE 中的锂离子路径；b PAN-LLTO NW 的 SEM 照片；c PAN-LLTO NW 和 PAN-LLTO NPs CPE 的 Arrhenius 图。经授权改编自参考文献。[105]。d Ca-CeO₂-PEO CPE 中锂离子传输增强机制示意图；e Ca-CeO₂-PEO CPE 的时变曲线；f 采用 LiFePO₄ 阴极的 PEO-LiTFSI 和 Ca-CeO₂-PEO CPE 的速率性能。经授权改编自参考文献。[106] 改编自参考文献。

In addition, 2D fillers are also of great interest due to their structural characteristics. In practical applications, small-sized 2D nanosheets are more popular among researchers. This is due to the fact that large sizes of 2D nanosheets are difficult to provide continuous ion transport paths. And, the larger size 2D nanosheets offer limited ability to inhibit the crystallization of polymeric matrix. However, 2D fillers are equipped with high specific surface area, ultrathin lamellar structure and large aspect ratio. Once the size of the 2D nanosheet is small enough, a larger contact area can be formed between it and the polymer matrix. A new ionic conductivity will be established between the 2D nanosheet–polymer interfaces, resulting in a higher ionic conductivity. Shi et al. [107] prepared an MXene-based silica nanosheet MXene-mSiO₂. Due to the large specific surface area of MXene-mSiO₂ and the abundance of functional groups on the surface, a large number of Lewis acid–base interactions existed in the MXene-mSiO₂-PPO interface. These interactions promote the rapid conduction of lithium ions. MXene-mSiO₂-PPO CPEs provide an ionic conductivity of 4.6 × 10^–4 S cm⁻¹. Rojaee et al. [108] prepared BP-PEO CPEs using a new 2D material, black phosphorus (BP). The unique curved structure of BP nanosheets allows the ions to be anisotropic at the interface. BP nanosheets can effectively trap TFSI- as well as weaken the bond length of N–Li. Therefore, the dissociation of Li⁺ is promoted. And Li/BP-PEO CPEs/Li cells can be cycled for more than 500 h at RT. Besides, graphene, vermiculite and double hydroxide also have a flake structure. Luo et al. [109] reported an ultrathin vermiculite nanosheet VS. The VS-PEO CPEs could provide ionic conductivity of 1.2 × 10^–3 S cm⁻¹. In addition, the excellent mechanical strength and enhanced dimensions stability of VS-PEO CPEs were favorable to inhibiting the growth of lithium dendrites.
此外，二维填料也因其结构特点而备受关注。在实际应用中，小尺寸的二维纳米片更受研究人员的青睐。这是因为大尺寸的二维纳米片难以提供连续的离子传输路径。而且，尺寸较大的二维纳米片抑制聚合物基质结晶的能力有限。然而，二维填料具有高比表面积、超薄片状结构和大纵横比。一旦二维纳米片的尺寸足够小，就能在其与聚合物基质之间形成较大的接触面积。二维纳米片与聚合物界面之间将形成新的离子传导，从而产生更高的离子传导性。Shi 等人[107]制备了一种基于 MXene 的二氧化硅纳米片 MXene-mSiO₂。由于 MXene-mSiO₂ 具有较大的比表面积和表面官能团的丰富性，MXene-mSiO₂-PPO 界面存在大量的路易斯酸碱相互作用。这些相互作用促进了锂离子的快速传导。MXene-mSiO₂-PPO CPE 的离子电导率为 4.6 × 10^-4 S cm^-1 。Rojaee 等人[108]使用新型二维材料黑磷（BP）制备了 BP-PEO CPE。BP 纳米片独特的曲线结构使离子在界面上具有各向异性。BP 纳米片能有效捕获 TFSI- 并削弱 N-Li 的键长。因此，促进了 Li⁺ 的解离。 锂/BP-PEO CPEs/Li 电池可在实时条件下循环使用 500 小时以上。此外，石墨烯、蛭石和双氢氧化物也具有片状结构。Luo 等人[109]报道了一种超薄蛭石纳米片 VS。VS-PEO CPE 的离子电导率可达 1.2 × 10^-3 S cm^-1。此外，VS-PEO 氯化聚乙烯具有优异的机械强度和更高的尺寸稳定性，有利于抑制锂枝晶的生长。

2.3.2 Ordered Fillers in CPEs
2.3.2 CPE 中的有序填充物

The above-mentioned nanoparticles or nanowires tend to be randomly dispersed in the polymer matrix. This structure is thermodynamically stable, which makes it difficult for the fillers to form a continuous conduction route. The ion-conducting pathways constructed by randomly dispersed microstructures are undesirable. To obtain more efficient ion transport, researchers have focused on CPEs that are prepared with directionally aligned ceramic fillers.
上述纳米颗粒或纳米线往往随机分散在聚合物基体中。这种结构在热力学上是稳定的，因此填料很难形成连续的传导路径。随机分散的微结构所构建的离子传导路径并不理想。为了获得更高效的离子传输，研究人员重点研究了使用定向排列陶瓷填料制备的 CPE。

Liu et al. [110] investigated the influence of LLTO nanowires of different orientations on lithium-ion transport. As shown in Fig. 5a, LLTO nanowires with different orientations (angles of 0° (perpendicular), 45° and 90° (parallel)) were prepared by adjusting different positions of the collector. The ionic conductivities of the LLTO-PAN CPEs made by randomly LLTO nanowires and orientation-ordered LLTO nanowires (angles of 0°, 90° and 45°) were 7.82 × 10^–6, 5.02 × 10^–5, 1.78 × 10^–7 and 2.24 × 10^–5 S cm⁻¹ at 30 °C, respectively (Fig. 5b). The randomly dispersed LLTO nanowires formed a semicontinuous structure in CPEs, which facilitated the transportation of lithium ions. However, the ionic conductivity of CPEs further increased when the orientation was parallel to the current direction, forming a continuous fast-ion transport channel. Thereafter, Zhai et al. [111] added a continuous vertical arrangement of Li_1+xAl_xTi_2−x(PO₄)₃ (LATP) in PEO/PEG (Fig. 5c). The vertically aligned LATPs formed an efficient ionic conductivity structure with an excellent ionic conductivity of 5.2 × 10^–5 S cm⁻¹ at RT. This value is approximately 3.6 times higher than that of LATP NP-PEO/PEG CPEs (1.5 × 10^–5 S cm⁻¹). Zhang et al. [112] also reported CPEs with a vertically continuous structure. As shown in Fig. 5d, surface-modified anodic aluminum oxide (AAO) acted as a ceramic backbone rich in continuous nanoscale channels. PEO was packed in the pore channel. These AAO-PEO CPEs allowed fast lithium-ion transport along the AAO-PEO interface. The ionic conductivity of the AAO-PEO CPEs was 5.82 × 10^–4 S cm⁻¹ (Fig. 5e). Dai et al. [113] exploited highly conductive garnet frameworks equipped with multiscale aligned structures through a top-down method. PEO was doped into the vertically aligned garnet nanostructure to produce flexible LLZO-PEO CPEs (Fig. 5f). The LLTO framework inherited the aligned porous structure of the wood template (Fig. 5g). Moreover, the LLTO-PEO CPEs were flexible (Fig. 5h). They possessed an excellent ionic conductivity of 1.8 × 10^–4 S cm⁻¹ at RT (Fig. 5i).
Liu 等人[110] 研究了不同取向的 LLTO 纳米线对锂离子传输的影响。如图5a 所示，通过调整集电极的不同位置制备了不同取向（0° 角（垂直）、45° 角和 90°角（平行））的 LLTO 纳米线。由随机 LLTO 纳米线和取向有序的 LLTO 纳米线（角度为 0°、90° 和 45°）制备的 LLTO-PAN CPE 的离子电导率分别为 7.82 × 10^-6, 5.02 × 10^-5、1.78 × 10^-7和 2.24 × 10^-5 S cm^-1（图5b）。随机分散的 LLTO 纳米线在 CPE 中形成了半连续结构，从而促进了锂离子的传输。然而，当取向与电流方向平行时，CPE 的离子电导率会进一步提高，从而形成连续的快速离子传输通道。此后，Zhai 等人[111] 添加了连续垂直排列的 Li_1+xAl_x钛_2-x(PO₄)₃ (LATP) 在 PEO/PEG 中的连续垂直排列（图）。5c）。垂直排列的 LATPs 形成了一种高效离子导电结构，在 RT 条件下具有 5.2 × 10^-5 S cm^-1 的出色离子导电率。该值约为 LATP NP-PEO/PEG CPE（1.5 × 10^-5 S cm^-1 ）的 3.6 倍。Zhang et al. [112]也报道了具有垂直连续结构的 CPE。如图5d所示，表面改性的阳极氧化铝（AAO）充当了富含连续纳米级通道的陶瓷骨架。PEO 被填充在孔道中。这些 AAO-PEO CPE 允许锂离子沿着 AAO-PEO 界面快速传输。AAO-PEO CPE 的离子电导率为 5.82 × 10^-4 S cm^-1 （图 5e ）。Dai 等人[113]通过一种自上而下的方法开发了具有多尺度排列结构的高导电性石榴石框架。在垂直排列的石榴石纳米结构中掺入 PEO，生产出柔性 LLZO-PEO CPE（图5f）。LLTO 框架继承了木质模板的对齐多孔结构（图5g）。此外，LLTO-PEO CPE 具有柔韧性（图5h）。在 RT 条件下，它们具有 1.8 × 10^-4 S cm^-1 的出色离子电导率（图 5i）。

Fig. 5 图 5

a CPEs with different aligned LLTO nanowires; b Arrhenius plots of different aligned LLTO-PAN CPEs. Adapted with permission from Ref. [110]. c Schematic diagram of vertically aligned LATP in polymers and the ionic conductivity plots. Adapted with permission from Ref. [111]. d Schematics of AAO-PEO CPEs; e Interfacial ionic conductivities of CPEs based on AAO disks. Adapted with permission from Ref. [112]. f Schematic of multiscale aligned LLZO incorporated with PEO; g SEM images showing the alignment of channels of LLZO-PEO CPEs; h Photograph of the LLZO-PEO CPEs; i Ionic conductivity of LLTO-PEO CPEs and PEO SPEs. Adapted with permission from Ref. [113]
a 不同排列的 LLTO 纳米线 CPE；b 不同排列的 LLTO-PAN CPE 的阿伦尼乌斯图。经授权改编自参考文献。[110]。c 聚合物中垂直排列的 LATP 示意图和离子电导率图。经授权改编自参考文献。[111]。d AAO-PEO CPE 的示意图；e 基于 AAO 磁盘的 CPE 的界面离子电导率。经授权改编自参考文献。[112]。f 加入 PEO 的多尺度排列 LLZO 示意图；g 显示 LLZO-PEO CPE 通道排列的 SEM 图像；h LLZO-PEO CPE 的照片；i LLTO-PEO CPE 和 PEO SPE 的离子电导率。经授权改编自参考文献。[113].

2.3.3 Three‐Dimensional (3D) Fillers in CPEs
2.3.3 CPE 中的三维 (3D) 填充物

The filler is easily clustered in the polymer matrix. The construction of a 3D skeleton structure by controlling the space position of the filler in the polymer is an effective way to solve this dispersion problem. Moreover, the inorganic network has high mechanical strength, which can hinder lithium dendrite growth and promote cyclic stability performance.
填料很容易在聚合物基体中聚集。通过控制填料在聚合物中的空间位置来构建三维骨架结构是解决这一分散问题的有效方法。此外，无机网络具有很高的机械强度，可以阻碍锂枝晶的生长，提高循环稳定性能。

Fu et al. [114] prepared LLZO-PEO CPEs consisting of interconnected LLZO nanowires and PEO. The three-dimensional interconnected LLZO nanowires effectively precluded the agglomeration of nanoparticles and formed a continuous lithium-ion conduction network, as depicted in Fig. 6a. The ionic conductivity of the LLZO-PEO CPEs was 2.5 × 10^–4 S cm⁻¹ at RT. The SiO₂ 3D network structure-enhanced CPEs were fabricated by in situ hydrolysis by Cui et al. [115]. As shown in Fig. 6b, the 3D structure of SiO₂ has a high specific surface area (701 m² g⁻¹) and continuous ion transport channels. This special 3D structure enhanced the Lewis interactions and boosted the t_Li⁺ of SiO₂-PEO CPEs (t_Li⁺ = 0.38) (Fig. 6c). The strong Lewis acid–base interactions promote the separation of anions and cations. As shown in Fig. 6d–e, the dissociation of LiTFSI in SiO₂-PEO CPEs increased from 84.7 to 94.4%. The ionic conductivity of SiO₂-PEO CPEs was 0.6 × 10^–3 S cm⁻¹ at 30 °C (Fig. 6f). The Li|SiO₂-PEO CPEs|LFP cell exhibited a good performance (105 mAh g⁻¹ at 0.4C), even at 15 °C. It is clear that facilitating continuous ion conduction pathways is a good strategy for promoting lithium-ion migration.
Fu 等人[114]制备了由相互连接的 LLZO 纳米线和 PEO 组成的 LLZO-PEO CPE。如图6a所示，三维互连的 LLZO 纳米线有效地防止了纳米颗粒的团聚，并形成了连续的锂离子传导网络。在 RT 条件下，LLZO-PEO CPE 的离子电导率为 2.5 × 10^-4 S cm^-1 。Cui 等人[115]通过原位水解法制备了 SiO₂ 三维网络结构增强的 CPE。如图6b 所示，SiO₂ 的三维结构具有高比表面积（701 m² g^-1 ）和连续的离子传输通道。这种特殊的三维结构增强了路易斯相互作用，提高了 SiO₂-PEO CPE 的 t_Li⁺ (t_Li⁺ = 0.38）（图6c）。强烈的路易斯酸碱相互作用促进了阴阳离子的分离。如图 6d-e 所示，LiTFSI 在 SiO₂-PEO CPE 中的解离率从 84.7% 增加到 94.4%。在 30 °C 时，SiO₂-PEO CPE 的离子电导率为 0.6 × 10^-3 S cm^-1 （图 6f ）。Li|SiO₂-PEO CPEs|LFP 电池表现出良好的性能（0.4℃时为 105 mAh g^-1 ），即使在 15 ℃ 时也是如此。 显然，促进连续的离子传导途径是促进锂离子迁移的良好策略。

Fig. 6 图 6

a Schematic and ionic conductivity of the LLZO-PEO CPEs. Adapted with permission from Ref. [114]. b Schematic of the SiO₂-aerogel-reinforced CPE; c Nyquist plot of electrochemical impedance spectroscopy of Li|SiO₂-PEO CPEs|Li cell; d–e FTIR spectra of the electrolytes without and SiO₂ aerogel; f ionic conductivity plot of CPEs with and without SiO₂ aerogel. Adapted with permission from Ref. [115]. g A diagram of the temples used for the LAGP-PEO CPEs and SEM images. Adapted with permission from Ref. [116]. h Agglomerated nanoparticles and three-dimensional continuous framework of LLTO. Adapted with permission from Ref. [117]
a LLZO-PEO CPE 的示意图和离子电导率。经授权改编自参考文献。[114]。b SiO₂ 气凝胶增强型 CPE 示意图；c Li|SiO₂-PEO CPEs|Li 电池的电化学阻抗光谱奈奎斯特图；d-e 无 SiO₂ 气凝胶和有 SiO₂ 气凝胶的电解质的傅立叶变换红外光谱；f 有 SiO₂ 气凝胶和无 SiO₂ 气凝胶的 CPE 的离子电导率图。经授权改编自参考文献。[115]。g LAGP-PEO CPE 所用的庙宇示意图和 SEM 图像。经授权改编自参考文献。[116]。h LLTO 的团聚纳米颗粒和三维连续框架。经授权改编自参考文献。[117] 。

Bruce et al. [116] designed gyroscopically structured CPEs by 3D printing (Fig. 6g). This structure formed a bi-continuous ion conduction pathway, in which the LAGP ceramic backbone ensured fast Li-ion transport and the polymers guaranteed the efficient dissociation of lithium ions and the flexibility of CPEs. This structure exhibited a promising ionic conductivity of 1.6 × 10^–4 S cm⁻¹ at RT. Bae et al. [117] fabricated a 3D LLTO framework for high-performance CPEs. Figure 6h shows the 3D structure of LLTO with a high content ceramic (44 wt%). In addition, the ionic conductivity was increased to 8.8 × 10^–5 S cm⁻¹ at RT.
Bruce 等人[116]通过三维打印技术设计出了陀螺结构的 CPE（图6g）。这种结构形成了双连续离子传导途径，其中 LAGP 陶瓷骨架确保了锂离子的快速传输，而聚合物则保证了锂离子的高效解离和 CPE 的柔韧性。这种结构在 RT 条件下的离子电导率高达 1.6 × 10^-4 S cm^-1 。Bae 等人[117]为高性能 CPE 制作了三维 LLTO 框架。图6h 显示了具有高含量陶瓷（44 wt%）的 LLTO 三维结构。此外，在 RT 条件下，离子导电率提高到 8.8 × 10^-5 S cm^-1 。

In summary, although disordered nanoparticles can reduce the crystallinity of PEO and promote the conduction of lithium ions through Lewis acid–base interactions, the discontinuous lithium-ion transport path and the tendency of nanoparticles to agglomerate lead to worse ion conduction. In contrast, some ordered structures, especially 1D nanowires aligned parallel to the lithium-ion transport direction, can provide the shortest lithium-ion transport paths. Therefore, the smooth ion conduction in 3D continuous structures is the main direction for future development.
总之，虽然无序纳米粒子可以降低 PEO 的结晶度，并通过路易斯酸碱相互作用促进锂离子的传导，但不连续的锂离子传输路径和纳米粒子的团聚倾向会导致离子传导性变差。相反，一些有序结构，尤其是平行于锂离子传输方向排列的一维纳米线，可以提供最短的锂离子传输路径。因此，在三维连续结构中实现顺畅的离子传导是未来发展的主要方向。

2.4 Filler–Polymer Interface
2.4填料-聚合物界面

As mentioned above, the ionic conductivity of CPEs can be significantly increased by inorganic fillers doped in polymers. This is due to the Lewis acid–base interaction in filler–lithium salt–polymer. Significantly, Lewis acid–base interactions promote further dissociation of the lithium salt and increase the free Li⁺ concentration in the polymer. Moreover, that Lewis acid–base interaction is much more obvious in the interfacial phase of the filler–polymer. This is highly related to the type, size, concentration, morphology and surface properties of the inorganic fillers. Constructing fast-ion conduction channels at the filler–polymer interface is an effective way to enhance the ion transport efficiency.
如上所述，聚合物中掺入无机填料可显著提高氯化聚乙烯的离子导电性。这是由于填料-锂盐-聚合物中的路易斯酸碱相互作用。值得注意的是，路易斯酸碱相互作用会促进锂盐的进一步解离，并增加聚合物中的游离锂⁺ 浓度。此外，路易斯酸碱相互作用在填料-聚合物的界面相中更为明显。这与无机填料的类型、大小、浓度、形态和表面特性有很大关系。在填料-聚合物界面构建快速离子传导通道是提高离子传输效率的有效方法。

In order to enhance the ion transport efficiency at the filler–polymer interface, Cheol et al. [118] used purine-modified MOFs as inorganic fillers to enhance CPEs. First, strong hydrogen bonds exist between –NH₂ on the surface of Bio-MOF11, which promotes the dispersion of Bio-MOF11 in PEO and facilitates to increase the ion transport-specific surface area. Secondly, the open metal sites (Lewis acidic) can effectively trap the anions by electrostatic interaction. Therefore, the multiple Lewis basic/acidic sites in the Bio-MOF11-PEO CPEs effectively enhance the lithium-ion transport efficiency. Zhou et al. [119] prepared a novel amphoteric ion-modified metal–organic framework NH₃⁺–SO₃⁻@ZIFs. At the interface of PEO– NH₃⁺–SO₃⁻@ZIFs, the strong electrostatic interaction between the cation and TFSI⁻ largely inhibited the movement of the anion and enhanced the t_Li⁺. Chen et al. [120] coated a layer of PDA on the surface of Co₃O₄. The PDA coating can act as a multifunctional medium to finely adjust the ion distribution and transport behavior through Lewis acid–base interactions. The phenolic hydroxyl and o-benzoquinone groups on the surface of the Co₃O₄@PDA not only alleviate the coordination of PEO with Li⁺, but also the –NH⁻ can form hydrogen bonding network with PEO chains. This can increase the amorphous region of PEO and form an effective ion migration pathway at the Co₃O₄@PDA-PEO surface to improve the ionic conductivity.
为了提高填料-聚合物界面的离子传输效率，Cheol 等人[118]使用嘌呤修饰的 MOFs 作为无机填料来增强 CPE。首先，Bio-MOF11 表面的 -NH₂ 之间存在强氢键，这促进了 Bio-MOF11 在 PEO 中的分散，有利于增加离子传输特异性比表面积。其次，开放的金属位点（路易斯酸性）可以通过静电作用有效地捕获阴离子。因此，Bio-MOF11-PEO CPE 中的多个路易斯碱性/酸性位点可有效提高锂离子传输效率。Zhou 等人[119] 制备了一种新型两性离子修饰金属有机框架 NH₃⁺-SO₃^-@ZIFs 。在 PEO- NH₃⁺-SO₃^-@ZIFs 的界面上、阳离子与 TFSI^- 之间的强静电作用在很大程度上抑制了阴离子的移动，增强了 t_Li⁺ 的作用。Chen 等人 [120] 在 Co₃O₄ 表面涂上一层 PDA。PDA 涂层可作为一种多功能介质，通过路易斯酸碱相互作用精细调节离子分布和传输行为。 Co₃O₄@PDA 表面的酚羟基和邻苯醌基不仅可以缓解 PEO 与 Li⁺ 的配位，而且 -NH^- 可以与 PEO 链形成氢键网络。这可以增加 PEO 的无定形区域，并在 Co₃O₄@PDA-PEO 表面形成有效的离子迁移通道，从而提高离子导电性。

Apart from the special interactions between the filler–polymer which affect the formation of the ion permeation network, the size and concentration of the inorganic fillers also have a great influence on the properties of the filler–polymer interface. To increase the contact area of filler–polymer, some fillers with smaller particle size and larger specific surface area are often used. Hu et al. [121] compared the effects of different sizes of ZrO₂ (220, 365, and 470 nm in diameter, respectively) on the formation of ion permeation networks in PAN-LiClO₄. The results showed that the ionic conductivity of ZrO₂-PAN CPEs increased with the decrease in the size of ZrO₂. In comparison, ZrO₂ (220 nm) can form more effective ion transport interfaces. So, ZrO₂ (220 nm)-PAN CPEs have the best ionic conductivity of 1.16 × 10^–3 S cm⁻¹. This is for the passive inorganic fillers. At the same time, the filler size has a similar effect on the active filler. For example, Zhang et al. [122] investigated the effect of the active fillers of LLZTO with different sizes (10 um, 400 nm, 40 nm) on ionic conductivity. Excluding the disturbance of lithium salts in CPEs, LLZTO (40 nm)-PEO CPEs exhibited a greater ionic conductivity than LLZTO (10 um)-PEO CPEs. The enhanced ionic conductivity of the smaller LLZTO is attributed to the remarkably high conductive routes along the interface of PEO-LLZTO. And the small particles usually have a relatively large specific surface area, leading to an increase in the coherent conductivity path.
除了填料-聚合物之间的特殊相互作用会影响离子渗透网络的形成外，无机填料的粒度和浓度对填料-聚合物界面的特性也有很大影响。为了增加填料-聚合物的接触面积，通常会使用一些粒径较小、比表面积较大的填料。Hu 等人[121]比较了不同尺寸的 ZrO₂ （直径分别为 220、365 和 470 nm）对 PAN-LiClO₄ 中离子渗透网络形成的影响。结果表明，ZrO₂-PAN CPE 的离子导电率随着 ZrO₂ 尺寸的减小而增加。相比之下，ZrO₂ (220 nm) 可以形成更有效的离子传输界面。因此，ZrO₂ (220 nm)-PAN CPE 的离子电导率最好，达到 1.16 × 10^-3 S cm^-1 。这是针对被动无机填料而言的。同时，填料尺寸对活性填料也有类似的影响。例如，Zhang 等人[122] 研究了不同尺寸（10 um、400 nm、40 nm）的 LLZTO 活性填料对离子导电性的影响。排除氯化聚乙烯中锂盐的干扰，LLZTO（40 nm）-PEO 氯化聚乙烯比 LLZTO（10 um）-PEO 氯化聚乙烯表现出更高的离子电导率。较小的 LLZTO 离子电导率的增强归因于 PEO-LLZTO 界面上显著较高的导电路线。而小颗粒通常具有相对较大的比表面积，从而增加了相干导电路径。

When the size of the filler is certain, the variations in the concentration of the filler also greatly influence the ion transport behavior in CPEs. With a small volume of passive filler in CPEs, the fast ionic conductivity region at the filler–polymer interface increases with the increase in filler. At this time, the ionic conductivity will show the same tendency. However, with the increase in passive filler, especially some nano-sized inert fillers, it tends to agglomerate. The unfavorable dispersion will reduce the filler–polymer contact area and cause a negative growth in ion transport rates. Xu et al. [123] prepared Bi/HMT-MOFs-PEO CPEs. It was found that the ionic conductivity of Bi/HMT-MOFs-PEO CPEs showed a phenomenon of increasing first and then decreasing. When Bi/HMT-MOFs were increased to 10 wt%, Bi/HMT-MOFs-PEO CPEs exhibited the highest ionic conductivity (3.06 × 10^–5 S cm⁻¹, 25 °C). The excess amount of Bi/HMT-MOFs may lead to difficulty in forming continuous lithium-ion transport channels, and thus the ionic conductivity decreases when the filler content exceeds 10 wt%. However, these changes in the active filler are different from the passive filler. At first, the active filler does not create a continuous interfacial phase with the polymer phase, in which ionic transport does not occur in the bulk phase of the active filler. Therefore, the ionic conductivity tends to first increase and then decrease with a change in active filler concentration. But, as the concentration of active filler continues to increase, the new ion pathways will be established inside the CPEs. Therefore, the ionic conductivity will continue to increase again. Wang et al. [124] systematically investigated the influence of LATP content on ion permeation channels. The results indicated that at low content, LATP (4 vol%)-PEO CPEs exhibited a high ionic conductivity of 1.70 × 10^–4 S cm⁻¹. The obvious enhancement of ionic conductivity was attributed to the rapid migration of lithium ions within the LATP-PEO surface. As the LATP increases, the ionic conductivity of LATP-PEO CPEs starts to decrease. However, when the LATP increases to 13 vol%, the volume fraction of the interfacial phase can reach a maximum. At this moment, it was derived that the ionic conductivity of (13 vol%)-PEO CPEs was showing an increasing trend again.
当填料的尺寸一定时，填料浓度的变化也会在很大程度上影响 CPE 中的离子传输行为。当 CPE 中的被动填料体积较小时，填料-聚合物界面上的快速离子传导区域会随着填料的增加而增大。此时，离子电导率将呈现相同的趋势。然而，随着被动填料的增加，特别是一些纳米级惰性填料的增加，它往往会发生团聚。这种不利的分散会减少填料与聚合物的接触面积，导致离子传输速率的负增长。Xu 等人 [123] 制备了 Bi/HMT-MOFs-PEO CPE。研究发现，Bi/HMT-MOFs-PEO CPE 的离子电导率呈现先增大后减小的现象。当 Bi/HMT-MOFs 增加到 10 wt% 时，Bi/HMT-MOFs-PEO CPE 的离子导电率最高（3.06 × 10^-5 S cm^-1, 25 °C）。过量的 Bi/HMT-MOFs 可能导致难以形成连续的锂离子传输通道，因此当填料含量超过 10 wt% 时，离子导电率会降低。然而，活性填料的这些变化与被动填料不同。起初，活性填料不会与聚合物相形成连续的界面相，在这种情况下，离子传输不会在活性填料的体相中发生。因此，随着活性填料浓度的变化，离子电导率呈先上升后下降的趋势。但是，随着活性填料浓度的不断增加，CPE 内部会形成新的离子通道。因此，离子电导率又会继续增加。Wang 等人 [124]系统地研究了 LATP 含量对离子渗透通道的影响。结果表明，在低含量时，LATP（4 vol%）-PEO CPE 的离子电导率高达 1.70 × 10^-4 S cm^-1。离子电导率的明显提高归因于锂离子在 LATP-PEO 表面的快速迁移。随着 LATP 的增加，LATP-PEO CPE 的离子电导率开始下降。然而，当 LATP 增加到 13 Vol% 时，界面相的体积分数可达到最大值。此时，(13 vol%)-PEO CPE 的离子电导率再次呈现上升趋势。

3 Effects of Fillers and the Mechanism in CPEs
3CPE中填充物的效果和机制

CPEs consist of polymer matrix, lithium salt and inorganic filler. In general, SPEs are strongly limited in terms of ionic conductivity by the high crystallinity. Fortunately, CPEs prepared by introducing fillers in SPEs can effectively suppress the crystallization behavior of polymers, which is indicated to be a more promising method for the development of SSLBs [12]. Inorganic fillers can promote the comprehensive electrochemical performance of CPEs, but this mechanism is complex and involves many significant factors such as ionic conductivity, t_Li⁺, and polymer aggregate structure [11]. The complex relationship is shown in Fig. 7.
CPE 由聚合物基体、锂盐和无机填料组成。一般来说，高结晶性会严重限制 SPE 的离子导电性。幸运的是，在 SPE 中引入填料制备的 CPE 能有效抑制聚合物的结晶行为，这被认为是一种更有前景的 SSLB 开发方法 [12]。无机填料可以促进 CPE 的综合电化学性能，但这一机制非常复杂，涉及离子电导率、t_Li⁺ 和聚合物聚合体结构等许多重要因素[11]。复杂的关系如图7所示。

Fig. 7 图 7

Schematic of the effects of fillers in CPEs for lithium batteries
锂电池 CPE 中填料的影响示意图

In CPEs, the polymer, inorganic filler and lithium salt interact with one another. This interaction mainly occurs in two aspects:
在 CPE 中，聚合物、无机填料和锂盐会相互影响。这种相互作用主要体现在两个方面：

• (1) The interaction between the filler and the lithium salt. This involves the alteration of the lithium-ion chemical environment. And reflected mostly in the changes in ionic conductivity and t_Li⁺.
  填料与锂盐之间的相互作用。这涉及锂离子化学环境的改变。这主要体现在离子电导率和 t_Li⁺ 的变化上。

• (2) The interaction between the filler and the polymer. This involves changes in the polymer aggregate structure. It can be characterized by the Xc, Tg and spherulites.
  填料与聚合物之间的相互作用。这涉及聚合物聚合体结构的变化。它可以用 Xc、Tg 和球形物来表征。

In addition to the above two main aspects, some functionalized fillers simultaneously interact with lithium salts and polymers to change the coordination mode between polymers and lithium ions, which is also worthy of further consideration. In the following sections, we will discuss the electrochemical enhancement mechanism of inorganic fillers for CPEs from the two main factors.
除了上述两个主要方面，一些功能化填料同时与锂盐和聚合物发生作用，改变聚合物与锂离子之间的配位模式，也值得进一步考虑。下文将从这两个主要因素出发，探讨无机填料对 CPE 的电化学增强机理。

3.1 Interactions Between Fillers and Lithium Salts
3.1 填充物与锂盐之间的相互作用

The surfaces of inorganic fillers are rich in chemical groups. These fillers exhibit strong Lewis acid–base interactions with the lithium salts. The categories of such interactions include hydrogen bond, hole, and dipole–dipole interactions [125]. On the one hand, the interaction between the lithium ions and fillers could expedite the transportation as well as enhance the ionic conductivity. On the other hand, the filler interactions with anions (TFSI⁻, ClO₄⁻, PF₆⁻, etc.) can enhance t_Li⁺.
无机填料的表面含有丰富的化学基团。这些填料与锂盐表现出强烈的路易斯酸碱相互作用。这种相互作用的类别包括氢键、空穴和偶极-偶极相互作用[125]。一方面，锂离子与填料之间的相互作用可加快传输速度并增强离子导电性。另一方面，填料与阴离子（TFSI^-、ClO₄^-、PF₆^-等）之间的相互作用可增强锂离子的导电性。PF₆^- 等）可以增强 t_Li⁺ 。

3.1.1 Ionic Conductivity
3.1.1离子传导性

Ionic conductivity is one of the standards to measure the ionic conduction of electrolyte and a key factor in determining the electrochemical performance of SSLBs. SPEs exhibit a low ionic conductivity, which is usually in 10^–6–10^–5 S cm⁻¹ or even much lower at RT. However, in practical applications, the ionic conductivity of solid-state electrolytes is expected to be 10^–4 S cm⁻¹. It is obvious that SPEs cannot meet the requirements. Notably, CPEs are expected to satisfy the requirements by improving the ion transport capacity.
离子电导率是衡量电解质离子传导性的标准之一，也是决定固相惰性硫化弹性体电化学性能的关键因素。固相萃取剂的离子电导率很低，通常在 10^-6-10^-5 S cm^-1 或在 RT 时更低。然而，在实际应用中，固态电解质的离子电导率预计为 10^-4 S cm^-1 。显然，SPE 无法满足要求。值得注意的是，CPE 可通过提高离子传输能力来满足要求。

The ionic conductivity of CPEs is given by Eq. 1 [126]:
CPE 的离子电导率由公式 1 [126] 得出：

$$\text{σ}=\sum nq\mu$$

(1)

Here, n is the number of carriers, q is the ionic charge, and u is the carrier mobility. For a given system, q is definite. Therefore, there are two pathways for boosting the ionic conductivity: (1) increase the number of carriers and (2) increase the rate of carrier motion.
这里，n 是载流子数目，q 是离子电荷，u 是载流子迁移率。对于给定的系统，q是确定的。因此，提高离子导电性有两种途径：(1) 增加载流子数量；(2) 提高载流子运动速率。

• (1) Increase the number of carriers (n)
  增加载体数量 (n)

In CPEs, when the lithium salt concentration is sufficiently low, all the lithium ions are soluble in the polymer matrix. In these circumstances, lithium ions and anions both can act as charge carriers. However, with an increasing concentration of lithium salts, the dissolution capacity of the polymer matrix for lithium ions reaches a saturation state. As a result, electrostatic interactions between anions and cations cannot be neglected, which could reduce the number of carriers [36]. As shown in Fig. 8, lithium salt exists in the polymer in the form of ionic clusters. The migration of ionic clusters in the polymer is much more difficult. So, it is necessary to find some solutions to increase the carrier concentration.
在 CPE 中，当锂盐浓度足够低时，所有的锂离子都能溶解在聚合物基质中。在这种情况下，锂离子和阴离子都可以充当电荷载体。然而，随着锂盐浓度的增加，聚合物基体对锂离子的溶解能力达到饱和状态。因此，阴离子和阳离子之间的静电相互作用不容忽视，这可能会减少载流子的数量[36]。如图8所示，锂盐以离子团簇的形式存在于聚合物中。离子簇在聚合物中的迁移要困难得多。因此，有必要找到一些提高载流子浓度的解决方案。

Fig. 8 图 8

Migration of lithium ion in polymers. Adapted with permission from Ref. [127]
聚合物中的锂离子迁移。经授权改编自参考文献。[127] 改编自参考文献。

Inorganic fillers incorporated with polymers are the mainstream method for increasing the ionic conductivity of CPEs. The main reason is that the inorganic filler can promote the lithium salt to dissociate, i.e., increasing the carrier concentration in the CPEs. Sun et al. [128] proposed a strategy of grafting pyridine N in UiO-66 (CMOF) (Fig. 9a). The –N⁺CH₃ on the surface of UiO-66 interacts electrostatically with the lithium salt, which can accelerate the dissociation of the lithium salt to release a large number of carriers. As a result, the dissociation of lithium ions in the CMOF-PEO CPEs was 87.4%, which is higher than PEO-LiTFSI. This high dissociation of lithium salts endowed the CMOF-PEO CPEs with an excellent conductivity of 6.3 × 10^–4 S cm⁻¹ (at 60 °C), as demonstrated in Fig. 9b. Chen and coworkers [129] introduced cations into a COF to split the ion pairs of lithium salts by a stronger dielectric effect. As a result, the free lithium-ion concentration increased sharply at 70 °C, with ionic conductivity up to 2.09 × 10^–4 S cm⁻¹ (Fig. 9c). Cui et al. [115] doped mesoporous SiO₂ in polymers to fabricate SiO₂-CPEs (Fig. 9d). The interconnected SiO₂ network had a high specific surface area and uniformly distributed pores. This maximized the interactions between SiO₂ and lithium salts. The dissociation of LiTFSI increased from ≈ 84.7 to 94.4%. Thus, the SiO₂-PEO CPEs displayed a high ionic conductivity of 1.0 mS cm⁻¹ at 40 °C. Recently, some studies have revealed that oxygen vacancies on inorganic fillers can facilitate the decomposition of lithium salts. Liu et al. [130] reported Y₂O₃-doped ZrO₂ (YSZ)-PAN CPEs, as shown in Fig. 9e. The oxygen vacancy in YSZ is positively charged and it can be used in CPEs as the Lewis acid site. As shown in Fig. 9f, the dissociation of LiClO₄ was maximized with 7 mol% YSZ. Moreover, the conductivity of the YSZ-PAN CPEs also reached a maximum value. Zhang et al. [131] synthesized an ultrasmall Nb₂O₅ (3 nm) nanofiller for Nb₂O₅-PVDF-HFP CPEs. Nb⁵⁺ acted as a Lewis acid center that could release more free charge carriers by interacting with the SO²⁻ group in TFSI⁻. The ionic conductivity of Nb₂O₅-PVDF-HFP CPEs was 6.6 × 10^–5 S cm⁻¹. Sun et al. [132] also confirmed that Al₂O₃ and BaTiO₃ inorganic fillers can effectively enhance the carrier concentration in CPEs, which increased the ionic conductivity of the CPEs.
在聚合物中加入无机填料是提高氯化聚乙烯离子电导率的主流方法。主要原因是无机填料可以促进锂盐离解，即增加 CPE 中的载流子浓度。Sun 等人[128]提出了在 UiO-66 (CMOF) 中接枝吡啶 N 的策略（图9a）。UiO-66 表面的 -N⁺CH₃ 与锂盐发生静电作用，从而加速锂盐的解离，释放出大量载流子。因此，锂离子在 CMOF-PEO CPE 中的解离率为 87.4%，高于 PEO-LiTFSI。如图9b所示，锂盐的高度解离赋予了 CMOF-PEO CPE 6.3 × 10^-4 S cm^-1 （60 °C）的出色导电性。Chen 及其同事[129]在 COF 中引入阳离子，通过更强的介电效应来分裂锂盐的离子对。结果，在 70 °C 时，游离锂离子浓度急剧增加，离子电导率高达 2.09 × 10^-4 S cm^-1 （图 9c ）。Cui 等人[115] 将介孔 SiO₂ 掺杂到聚合物中，制备出 SiO₂-CPE （图9d）。相互连接的 SiO₂ 网络具有高比表面积和均匀分布的孔隙。这最大限度地增强了 SiO₂ 与锂盐之间的相互作用。锂盐的解离度从≈84.0%增加到≈100.0%。7% 到 94.4%。因此，SiO₂-PEO CPE 在 40 °C 时显示出 1.0 mS cm^-1 的高离子电导率。最近的一些研究表明，无机填料上的氧空位可促进锂盐的分解。Liu 等人[130] 报道了 Y₂O₃ 掺杂 ZrO₂ (YSZ)-PAN CPE，如图9e 所示。YSZ 中的氧空位带正电，可在 CPE 中用作路易斯酸位点。如图9f所示，当 YSZ 含量为 7 mol%时，LiClO₄ 的解离度最大。此外，YSZ-PAN CPE 的电导率也达到了最大值。Zhang 等人[131] 为 Nb₂O₅ (3 nm) 纳米填料合成了超小的 Nb₂O₅-PVDF-HFP CPE。Nb⁵⁺ 充当路易斯酸中心，通过与 TFSI^- 中的 SO^2- 基团相互作用，释放出更多的自由电荷载流子。Nb₂O₅-PVDF-HFP CPE 的离子电导率为 6.6 × 10^-5 S cm^-1 。Sun 等人[132]还证实，Al₂O₃ 和 BaTiO₃ 无机填料能有效提高 CPE 中的载流子浓度，从而提高 CPE 的离子导电率。

Fig. 9 图 9

a Schematic diagram of Li-ion transport in CMOF; b the ionic conductivities of P@CMOF with different temperature. Adapted with permission from Ref. [128]. c Schematic illustrations of ion association in COFs with neutral and cationic frameworks, respectively. Adapted with permission from Ref. [129]. d LiTFSI was dissolved in PEGDA/SCN and SiO₂ aerogel is the backbone. Adapted with permission from Ref. [115]. e Schematic of lithium-ion transport in YSZ; f FTIR spectra from filler-free electrolyte to the 2–7 mol% YSZ. Adapted with permission from Ref. [130]
a CMOF 中的锂离子传输示意图；b 不同温度下 P@CMOF 的离子电导率。经授权改编自参考文献。[128]。c 离子分别与中性和阳离子框架中的 COF 关联示意图。经授权改编自参考文献[c] 。[129]。d LiTFSI 溶于 PEGDA/SCN 中，SiO₂ 气凝胶为骨架。经授权改编自参考文献。[115]。e YSZ 中的锂离子传输示意图；f 从无填料电解质到 2-7 mol% YSZ 的傅立叶变换红外光谱。经允许改编自参考文献。[130].

Ideally, all lithium ions are complexed with the polymers. Therefore, both anions and cations are carriers. Unfortunately, as the concentration increases, the lithium salt hardly dissociates due to the electrostatic effect. Inorganic fillers in polymers can increase the concentration of carriers in the composite system. In addition, some inorganic fillers that contain lithium sources can also contribute to carriers.
理想情况下，所有锂离子都与聚合物复合。因此，阴离子和阳离子都是载体。遗憾的是，随着浓度的增加，由于静电效应，锂盐很难解离。聚合物中的无机填料可以增加复合体系中载体的浓度。此外，一些含有锂源的无机填料也会成为载流子。

• (B) Increasing the motion rate of carriers (u)
  提高运载工具的移动速度 (u)

According to Eq. (1), as the ion transport rate increases, the ionic conductivity also increases. However, the strong polar groups in the polymer chains, such as –CN and –C–O–C, are able to form strong complexes with lithium ions. This lowers the movement ability of lithium ions. The main reason why inorganic fillers can increase the ion movement rate is that the special groups on the surface of inorganic fillers can coordinate with lithium ions to weaken the interactions between lithium ions and polymers to accelerate the movement of lithium ions [77, 115]. Moreover, some long-term continuous inorganic fillers can form interconnected conductive ion channels, which significantly increases the ion migration rate. In addition, the 3D ion-conductive framework can accelerate the ion transport rate.
根据公式（1），随着离子传输速率的增加，离子导电率也会增加。然而，聚合物链中的强极性基团（如 -CN和 -C-O-C）能够与锂离子形成强络合物。这就降低了锂离子的移动能力。无机填料之所以能提高离子移动速度，主要是因为无机填料表面的特殊基团能与锂离子配位，从而削弱锂离子与聚合物之间的相互作用，加速锂离子的移动[77，115]。此外，一些长期连续的无机填料可以形成相互连接的导电离子通道，从而显著提高离子迁移率。此外，三维离子导电框架还能加快离子传输速率。

Wang et al. [133] reported an MOF functionalized with –NH₂ for PEO@N-MC CPEs (Fig. 10a). In this case, hydrogen bonds were formed between the ether oxygen of PEO and –NH₂, which effectively connected the adjacent MOF nanosheets. This particular interaction accelerated ion transport and promoted structural stability. The ionic conductivity of the PEO@N-MC CPEs was significantly increased by 253% compared to that of PEO-LiTFSI. Chen et al. [134] designed an inorganic filler with an MB-LLZTO molecular brush. It was introduced into PEO, as shown in Fig. 10b. The molecular brush with a special structure extends the diffusion pathway of lithium ions in MB-LLZTO PEO CPEs. As shown in Fig. 10c, on the surface of the MB-LLZTO CPEs, a third component with a value of 0.05 ppm was observed, which was introduced by the molecular brush on the LLZTO nanoparticles (Fig. 10c, bottom). Moreover, the resonance of Li in MB-LLZTO CPEs was significantly narrower than that in PEO, which suggested an irregular structure at the interface. This irregular structure provides a rapid pathway for lithium ions. Therefore, the MB-LLZTO CPEs exhibited a high ionic conductivity of 3.11 × 10⁻⁴ S cm⁻¹ at 45 °C (Fig. 10d). Zheng et al. [135] changed the amount of inorganic filler in the polymer matrix, as presented in Fig. 10e. As LLZO content increases, the ion transfer route gradually shifts from PEO to the percolation network of interconnected LLZO particles. This continuous ion conduction channel accelerated ion transport. In Fig. 10f, Liu et al. [136] initiated the ring-opening reaction of ethylene carbonate (EC) on the LLZTO surface to form oligomers containing ether-oxygen chains. This oligomer provided an ultra-dense and fast conduction pathway for lithium ions between LLZTO and PEO substrates. The delicate design endowed LLZTO-PEO CPEs with a high ionic conductivity of 1.43 × 10^–3 S cm⁻¹. Tian et al. [77] filled CeO₂ nanowires with SPEs, as shown in Fig. 10g. The CeO₂ nanowires produced extended continuous ion transfer pathways, which further improved the ionic conductivity (1.1 × 10^–3 S cm⁻¹ at 60 °C).
Wang 等人[133]报道了用 -NH₂ 官能化的 MOF 用于 PEO@N-MC CPE（图10a）。在这种情况下，PEO 的醚氧和 -NH₂ 之间形成了氢键，从而有效地连接了相邻的 MOF 纳米片。这种特殊的相互作用加速了离子传输，提高了结构稳定性。与 PEO-LiTFSI 相比，PEO@N-MC CPE 的离子电导率显著提高了 253%。Chen 等人[134]设计了一种带有 MB-LLZTO 分子刷的无机填料。如图10b 所示，它被引入到 PEO 中。具有特殊结构的分子刷扩展了锂离子在 MB-LLZTO PEO CPE 中的扩散途径。如图10c 所示，在 MB-LLZTO 氯化聚乙烯的表面，观察到了由 LLZTO 纳米粒子上的分子刷引入的第三种成分，其值为 0.05 ppm（图10c，底部）。此外，MB-LLZTO CPE 中 Li 的共振明显窄于 PEO 中的共振，这表明界面上存在不规则结构。这种不规则结构为锂离子提供了一条快速通道。因此，MB-LLZTO CPE 在 45 °C 时表现出 3.11 × 10^-4 S cm^-1 的高离子电导率（图10d）。Zheng 等人[135]改变了聚合物基体中无机填料的含量，如图10e 所示。随着 LLZO 含量的增加，离子转移路线逐渐从 PEO 转向相互连接的 LLZO 粒子的渗滤网络。 这种连续的离子传导通道加速了离子传输。在图10f中，Liu等人[136]在LLZTO表面引发了碳酸乙烯（EC）的开环反应，形成了含有醚氧链的低聚物。这种低聚物为 LLZTO 和 PEO 基底之间的锂离子提供了超密集和快速的传导途径。精巧的设计使 LLZTO-PEO CPE 具有 1.43 × 10^-3 S cm^-1 的高离子电导率。Tian等人[77]用SPE填充了CeO₂纳米线，如图10g所示。CeO₂ 纳米线产生了延伸的连续离子转移途径，从而进一步提高了离子导电率（60 °C 时为 1.1 × 10^-3 S cm^-1 ）。

Fig. 10 图 10

a Schematic diagram of the lithium-ion transfer in PEO@N-MC. Adapted with permission from Ref. [133]. b Figure of diffusion route of lithium ions in MB-LLZTO CPE; c ⁶Li NMR spectra of LLZTO CPEs and MB-LLZTO CPEs; d Ionic conductivity of MB-LLZTO CPEs. Adapted with permission from Ref. [100]. e Schematic representation of the lithium-ion route within LLZO (5–50 wt%)-PEO (LiTFSI). Adapted with permission from Ref. [135]. f Intermolecular interact on mechanism of LLZTO with in PEO. Adapted with permission from Ref. [136]. g Illustration of CeO₂NW-CPEs. Adapted with permission from Ref. [77]
a PEO@N-MC 中的锂离子转移示意图。经授权改编自参考文献。[133]。b 锂离子在 MB-LLZTO CPE 中的扩散路线图；c⁶ LLZTO CPE 和 MB-LLZTO CPE 的锂 NMR 光谱；d MB-LLZTO CPE 的离子电导率。经允许改编自参考文献。[100]。e LLZO (5-50 wt%)-PEO (LiTFSI) 内的锂离子路线示意图。经授权改编自参考文献。[135]。f LLZTO 在 PEO 中的分子间相互作用机理。经允许改编自参考文献。[136]。g CeO₂NW-CPEs 图示。经授权改编自参考文献。[77] 改编自参考文献。

The addition of such a surface-functionalized inorganic filler contributes to the formation of a fast lithium-ion pathway. Therefore, the inorganic filler which has a high specific surface area allows more flow area. The more continuous the ion conduction path is, the faster the ion transfer. However, some nanofillers may lead to serious phase separation, resulting in a lower ion transfer rate and a negative increase in ionic conductivity. This interfacial effect of ionic conductivity depends on the size, shape and content of the embedded filler and the relevant filler/polymer interfacial region.
加入这种表面功能化的无机填料有助于形成快速的锂离子通路。因此，具有高比表面积的无机填料可以提供更大的流动面积。离子传导路径越连续，离子传输速度就越快。然而，某些纳米填料可能会导致严重的相分离，从而降低离子传输速率，并使离子导电率出现负增长。离子传导性的这种界面效应取决于嵌入填料的尺寸、形状和含量以及相关的填料/聚合物界面区域。

3.1.2 Lithium-Ion Transference Number t _Li ⁺
3.1.2 锂离子转移数 t_Li⁺

The t_Li⁺ is another vital parameter of CPEs, which reflects the contribution of lithium ions to the total ionic conductivity. Both lithium ions and anions can move in the battery, but the anions prefer to migrate in the opposite direction to the lithium ions. Consequently, a large concentration gradient of lithium ions is formed, which blocks lithium-ion transport and produces uneven lithium-ion deposition. The relevant theoretical calculations suggest that the higher t_Li⁺ is, the more uniform the lithium deposition. In this way, the generation of lithium dendrites can be avoided [137, 138]. However, t_Li⁺ of CPEs is only 0.1–0.2. The calculation formula is as follows [139]:
t_Li⁺ 是 CPE 的另一个重要参数，它反映了锂离子对总离子导电率的贡献。锂离子和阴离子都可以在电池中移动，但阴离子更倾向于以与锂离子相反的方向移动。因此，会形成较大的锂离子浓度梯度，从而阻碍锂离子的传输并产生不均匀的锂离子沉积。相关理论计算表明，t_Li⁺ 越高，锂沉积越均匀。这样就可以避免产生锂枝晶[137, 138] 。然而，CPE 的 t_Li⁺ 仅为 0.1-0.2。计算公式如下[139]：

$${\text{t}}_{\text{L}{\text{i}}^{+}}\text{=}\frac{{\text{I}}_{\text{s}}\text{(}\text{V}-{\text{I}}_0{\text{R}}_0\text{)}}{{\text{I}}_0\text{(}\text{V}-{\text{I}}_{\text{s}}{\text{R}}_{\text{s}}\text{)}}$$

(2)

As illustrated in Eq. (2), R₀ and I₀ are the initial interfacial impedance and the first current response of the cells, respectively. Rs and Is are the interfacial impedance and current, respectively. V is the potential used for constant-potential polarization.
如公式 (2) 所示，R₀ 和 I₀ 分别是电池的初始界面阻抗和第一电流响应。Rs 和 Is 分别是界面阻抗和电流。V 是用于恒电位极化的电位。

ZIF-8-PEO CPEs were prepared by Wang et al. [79], as shown in Fig. 11a. ZIF-8, which has a surface with an abundance of Lewis acid sites, has a strong interaction with TFSI⁻. It can inhibit the movement of anion and decrease concentration polarization, resulting in a high t_Li⁺ of 0.35. Wang and coworkers [140] reported BNN-PEGDA-MPEGA CPEs prepared with 2D boron nitride nanosheets (BNN) as inorganic nanofillers, as shown in Fig. 11b. The interpenetrating network of BNNs efficiently blocked anions. It exhibited an excellent t_Li⁺ of 0.79, as illustrated in Fig. 11c. Zhang et al. [141] studied a series of single ion-conducted ICOFs based on imidazolium, as presented in Fig. 11d. The negatively charged groups within the ICOFs shielded the anions and permitted only lithium ions to migrate. Therefore, it showed a high t_Li⁺ of 0.81 in Fig. 11e. Shi et al. [142] used Fe-MOFs to optimize the electrochemical properties of SPEs (Fig. 11f). The ultrafine pores of Fe-MOFs block down the anions and the free lithium-ion concentration is increased. The t_Li⁺ increased to 0.6. Moreover, the Lewis acid–base interactions between PEO and Fe-MOFs enhanced the lithium-ion migration rate. Thus, the Fe-MOFs-PEO CPEs displayed an appreciable ionic conductivity of 2.3 × 10^–5 S cm⁻¹. Zhang et al. [143] prepared LiMNT-PEC CPEs by mixing layer-structured lithium montmorillonite (LiMNT) with PEC. 2D LiMNT has an enriched Lewis acid center that anchors the anion and releases more lithium ions, as illustrated in Fig. 11g. The intercalation structure released lithium ions rapidly, allowing the t_Li⁺ of the LiMNT-PEC CPEs to increase to 0.83.
Wang 等人[79]制备了 ZIF-8-PEO CPE，如图11a 所示。ZIF-8 表面有大量路易斯酸位点，与 TFSI^- 有很强的相互作用。它能抑制阴离子的移动，降低浓度极化，从而使 t_Li⁺ 达到 0.35 的高水平。Wang 和同事[140]报道了以二维氮化硼纳米片（BNN）作为无机纳米填料制备的 BNN-PEGDA-MPEGA CPE，如图11b 所示。BNN 的互穿网络能有效阻隔阴离子。如图11c所示，它的t_Li⁺ 为 0.79。Zhang 等人[141]研究了一系列基于咪唑的单离子传导 ICOF，如图11d 所示。ICOF 内带负电的基团屏蔽了阴离子，只允许锂离子迁移。因此，在图 _{Li⁺11e 中显示了 0.81 的高 tLi⁺ 。Shi 等人[142]使用 Fe-MOFs 优化了 SPE 的电化学性能（图11f）。Fe-MOFs 的超细孔隙阻挡了阴离子，从而提高了游离锂离子的浓度。tLi⁺ 增加到 0.6。此外，PEO 和 Fe-MOFs 之间的路易斯酸碱相互作用提高了锂离子迁移率。因此，Fe-MOFs-PEO CPE 的离子电导率达到了 2。3 × 10^-5 S cm^-1。Zhang 等人[143]通过将层结构锂蒙脱石（LiMNT）与 PEC 混合，制备了 LiMNT-PEC CPE。如图11g所示，二维锂蒙脱石具有丰富的路易斯酸中心，可锚定阴离子并释放更多的锂离子。插层结构能迅速释放锂离子，使 LiMNT-PEC CPE 的 tLi⁺ 增加到 0.83。}

Fig. 11 图 11

a Lithium-ion conductive mechanism of ZIF-8-PEO CPEs. Adapted with permission from Ref. [79]. b Transport pathway of lithium-ion in BNN-CPEs; c transference number of different content of BNN. Adapted with permission from Ref. [140]. d Li-ion transfer in Li-ImCOFs; e t_Li⁺ of LiImCOF-PEO CPEs. Adapted with permission from Ref. [141]. f Mechanism of ion transport in Fe-MOFs-PEO CPEs. Adapted with permission from Ref. [142]. g Intercalation LiMNT-PEC CPEs with enhanced t_Li⁺ mechanism. Adapted with permission from Ref. [143]
a ZIF-8-PEO CPE 的锂离子传导机制。经授权改编自参考文献。[79].b 锂离子在 BNN-CPE 中的传输途径；c 不同含量 BNN 的传输数。经授权改编自参考文献。[140]。d LiImCOF 中的锂离子转移；e LiImCOF-PEO CPE 的 t_Li⁺ 。经授权改编自参考文献。[141]。f Fe-MOFs-PEO CPE 中的离子传输机制。经授权改编自参考文献。[142]。g 具有增强 t_Li⁺ 机制的互掺 LiMNT-PEC CPE。经授权改编自参考文献。[143] 改编自参考文献。

In general, t_Li⁺ increases mainly due to the improvement in lithium-ion mobility, the decrease in anion mobility, or both. Inorganic fillers may increase t_Li⁺ by immobilizing anions through abundant Lewis acid sites. In addition, the t_Li⁺ can also be boosted by the special structures of CPEs. For example, ceramic/polymer/ceramic CPEs use a ceramic layer to block the transport of anions.
一般来说，t_Li⁺ 的增加主要是由于锂离子迁移率的提高、阴离子迁移率的降低或两者兼而有之。无机填料可通过丰富的路易斯酸位点固定阴离子，从而增加 t_Li⁺ 。此外，CPE 的特殊结构也能提高 t_Li⁺ 的浓度。例如，陶瓷/聚合物/陶瓷 CPE 使用陶瓷层阻止阴离子的传输。

3.2 Interactions Between Fillers and Polymers
3.2填料与聚合物之间的相互作用

As mentioned previously, fillers can significantly increase the ionic conductivity and t_Li⁺ of CPEs by interacting with lithium salts. However, the transport of lithium ion is mainly dependent on polymer chain segments. However, polymers exhibit a semicrystalline aggregated structure at RT. Spherulites are the most common crystal form of polymers [144]. The behavior of ion conduction in CPEs is strongly influenced by this aggregated structure. The most evident change is ionic conductivity. Introducing inorganic fillers into polymers has proven to be an effective method for decreasing the crystalline regions of polymers and improving ionic conductivity. Therefore, the effects of fillers on the aggregated structures of polymers are mainly reflected in the changes in crystallinity Xc, glass transition temperature Tg and spherulite shape [145]. In the following chapters, we will discuss the effects of inorganic fillers on the aggregated structures of polymers in terms of these three factors.
如前所述，填料可通过与锂盐相互作用，显著提高氯化聚乙烯的离子电导率和 t_Li⁺ 。然而，锂离子的传输主要取决于聚合物链段。然而，聚合物在实时状态下会呈现半晶体聚集结构。球晶是聚合物最常见的晶体形式[144]。CPE 中的离子传导行为受到这种聚集结构的强烈影响。最明显的变化是离子传导性。事实证明，在聚合物中引入无机填料是减少聚合物结晶区域和提高离子传导性的有效方法。因此，填料对聚合物聚集结构的影响主要体现在结晶度 Xc、玻璃化转变温度 Tg 和球粒形状的变化上 [145]。在接下来的章节中，我们将从这三个因素来讨论无机填料对聚合物聚集结构的影响。

3.2.1 Glass Transition Temperature Tg
3.2.1 玻璃转化温度 Tg

Tg is an important parameter for the motion of polymer chain segments. Below the Tg, molecules, atoms or groups vibrate only at their respective equilibrium positions. The polymer chains are frozen, and the molecules can hardly flow. When T > Tg, the polymer segments begin to move but the molecular chains do not. The migration of lithium ions in polymers matrix happens mostly in the amorphous phase, while migration in the crystalline phase is limited. A majority of polymers are semicrystalline in character. Such polymers have a high Tg. It leads to a decrease in the amorphous region of the polymer, which has a detrimental effect on ion migration. Therefore, desirable electrolyte materials should exhibit at least two characteristics: a high amorphous ratio and low Tg. A number of recent studies suggested that the addition of nano additives into a polymer matrix can reduce the Tg.
Tg 是聚合物链段运动的一个重要参数。低于 Tg 时，分子、原子或基团只能在各自的平衡位置振动。聚合物链被冻结，分子几乎无法流动。当 T > Tg 时，聚合物段开始移动，但分子链不会移动。锂离子在聚合物基体中的迁移主要发生在无定形相中，而在结晶相中的迁移是有限的。大多数聚合物都具有半结晶特性。此类聚合物的 Tg 较高。这导致聚合物的无定形区域减少，从而对离子迁移产生不利影响。因此，理想的电解质材料至少应具备两个特点：高非晶比例和低 Tg。最近的一些研究表明，在聚合物基体中添加纳米添加剂可以降低 Tg。

Li et al. [146] designed SiO₂-Cs-PEO CPEs for high-performance CPEs. With the increasing SiO₂, Tg of the SiO₂-Cs-PEO CPEs (1–4 wt% SiO₂) decreased to − 40.5, − 41.2, − 43 and − 41.7 °C, respectively. It is evident that the introduction of SiO₂ may increase the amorphous phase in the polymer matrix. In addition, it facilitates the movement of polymer chains, which provides a significant increase in ionic conductivity. Guo et al. [147] first introduced hydroxide (2D LDH) nanosheets into PEO. These 2D LDH fillers were rich in hydroxide radicals, forming hydrogen bonds with PEO chains to inhibit them toward the crystalline phase. Therefore, the 2D LDH-PEO CPEs showed a decrease in Tg. Xie et al. [81] doped ZnO quantum dots into PEO by vapor phase infiltration (VPI). The Tg of ZnO-PEO CPEs was significantly reduced to − 37.6 °C (compared to − 34.8 °C for PEO-LiTFSI). Guo et al. [148] prepared ZIF-67-PEO CPEs. Compared to PEO-LiTFSI (− 37.6 °C), the ZIF-67-PEO CPEs showed a significant decrease in Tg (− 40.0 °C).
Li 等人[146]设计了用于高性能 CPE 的 SiO₂-Cs-PEO CPE。随着 SiO₂ 的增加，SiO₂-Cs-PEO CPE（1-4 wt% SiO₂ ）的 Tg 分别降至 - 40.5、 - 41.2、 - 43 和 - 41.7 °C。显然，SiO₂ 的引入可能会增加聚合物基体中的无定形相。此外，它还能促进聚合物链的运动，从而显著提高离子传导性。Guo 等人[147] 首次将氢氧化物（二维 LDH）纳米片引入 PEO。这些二维 LDH 填料富含氢氧自由基，可与 PEO 链形成氢键，抑制其向结晶相移动。因此，二维 LDH-PEO CPE 的 Tg 有所下降。Xie 等[81]通过气相渗透（VPI）将氧化锌量子点掺杂到 PEO 中。ZnO-PEO CPE 的 Tg 显著降至 - 37.6 °C（PEO-LiTFSI 的 Tg 为 - 34.8 °C）。Guo 等人 [148] 制备了 ZIF-67-PEO CPE。与 PEO-LiTFSI 相比（- 37.6 °C），ZIF-67-PEO CPE 的 Tg 显著降低（- 40.0 °C）。

Inorganic fillers are advantageous for reducing the Tg of CPEs mainly for the following reasons:
无机填料在降低氯化聚乙烯的 Tg 方面具有优势，主要原因如下：

• (1) The polar groups in the polymer molecule may lead to the high rigidity of the molecular chain segments. However, the interaction between inorganic fillers and polymer chain segments can lower the intermolecular forces and enhance the motion of the polymer chains.
  聚合物分子中的极性基团可能会导致分子链段的高刚性。然而，无机填料与聚合物链段之间的相互作用可降低分子间作用力，增强聚合物链的运动。

• (2) Inorganic filler, as a small molecule plasticizer, can increase the flexibility of polymer molecular chains.
  无机填料作为一种小分子增塑剂，可以增加聚合物分子链的柔韧性。

3.2.2 Degree of Crystallinity Xc
3.2.2结晶度 Xc

It is widely believed that ionic conduction happens mostly in the amorphous. The crystallization process of polymers involves two processes: nucleation and crystal growth. Nuclei are formed in the nanoregions of polymer chain segments and then further separated or grown. Xc is the degree of long-range ordering of the polymer chains. In CPEs, inorganic fillers act as a solid plasticizer to disrupt the orderly arrangement of polymer chains, thereby reducing the crystallinity of the polymer.
人们普遍认为，离子传导主要发生在非晶态中。聚合物的结晶过程包括两个过程：成核和晶体生长。晶核在聚合物链段的纳米区域形成，然后进一步分离或生长。Xc 是聚合物链的长程有序度。在氯化聚乙烯中，无机填料起着固体增塑剂的作用，会破坏聚合物链的有序排列，从而降低聚合物的结晶度。

As shown in Fig. 12a, fillers decrease Xc by disrupting the ordered structure of the polymer. A systematic study of the relation between the crystallinity and ionic conductivity of PEO was conducted by Bo et al. [149]. As shown in Fig. 12b, the Xc of PEO first decreased with increasing LLZTO. The crystallinity of LLZTO-PEO CPEs reached the minimum value when the addition of LLZTO was 50 wt%. Unexpectedly, after continuing to increase LLZTO, the Xc was increased. The consequence may be associated with the spatial distribution of LLZTO particles in the PEO substrates. Moreover, with the increase in LLZTO, a maximum ionic conductivity of LLZTO- PEO CPEs was obtained with 50 wt% LLZTO, then it started to decrease, as shown in Fig. 12c. The ionic conductivity of LLZTO-PEO CPEs showed a completely opposite trend to that of the crystallinity. This work suggests a possible relationship between the Xc and the ionic conductivity of CPEs. Yang et al. [150] introduced nickel–iron-based layered hydroxide (NILDH) into the polymer matrix to reduce the crystallinity of NILDH-PEO CPEs (Fig. 12d). It can be observed that the intensity of the characteristic diffraction peak of PEO gradually decreases with the increase in NILDH (Fig. 12e). The NILDH particles disrupt the normal organization of PEO chains and prevent the crystallization. As illustrated in Fig. 12f, Guan et al. [151] used the hydrogen bonding effect between nickel phosphate (VSB-5) nanorods and PEO to disorder polymer chains in VSB-5-PEO CPEs. Wang et al. [152] doped phenolic resin nanospheres (RFS) fillers into PEO-LiClO₄ to investigate the effect of RFS on Xc, as shown in Fig. 12g. The surface groups (-OH) of RFS interacted with the PEO through hydrogen bonding. As shown in Fig. 12h, PEO showed distinct C–O–C stretching vibrations at 1103, 1147 and 1061 cm⁻¹. When the RFS filler was doped, the C–O–C in the amorphous region was shifted from 1096 to 1099 cm⁻¹, as illustrated in Fig. 12i. That is, the addition of filler changed the conformation of PEO to increase the amorphous region.
如图 12a 所示，填料会破坏聚合物的有序结构，从而降低 Xc。Bo 等人[149]对 PEO 的结晶度和离子电导率之间的关系进行了系统研究。如图 12b 所示，随着 LLZTO 的增加，PEO 的 Xc 首先下降。当 LLZTO 的添加量为 50 wt% 时，LLZTO-PEO CPE 的结晶度达到最小值。出乎意料的是，继续增加 LLZTO 后，Xc 反而增加了。这可能与 LLZTO 颗粒在 PEO 基底中的空间分布有关。此外，如图12c所示，随着 LLZTO 的增加，LLZTO-PEO CPE 的离子电导率在 50 wt% LLZTO 时达到最大值，随后开始下降。LLZTO-PEO CPE 的离子电导率与结晶度的变化趋势完全相反。这项研究表明，Xc 与 CPE 的离子电导率之间可能存在某种关系。Yang 等人[150]在聚合物基体中引入了镍铁基层状氢氧化物（NILDH），以降低 NILDH-PEO CPE 的结晶度（图12d）。可以观察到，随着 NILDH 的增加，PEO 特征衍射峰的强度逐渐降低（图12e）。NILDH 颗粒破坏了 PEO 链的正常组织，阻碍了结晶。如图12f所示，Guan等人[151]利用磷酸镍（VSB-5）纳米棒和 PEO 之间的氢键效应使VSB-5-PEO CPE中的聚合物链发生紊乱。Wang 等人 [152] 掺杂酚醛树脂纳米球（RFS）填料到 PEO-LiClO₄ 中，研究 RFS 对 Xc 的影响，如图 12g 所示。RFS 的表面基团（-OH）通过氢键与 PEO 相互作用。如图12h所示，PEO在1103、1147和1061 cm^-1处显示出明显的C-O-C伸缩振动。如图 12i 所示，当掺入 RFS 填料时，无定形区的 C-O-C 从 1096 cm^-1 移动到 1099 cm^-1。也就是说，添加填料改变了 PEO 的构象，增加了无定形区。

Fig. 12 图 12

a Schematic illustration of the lithium-ion transfer across crystalline polymer and crystalline polymer with nanofillers; b Xc of PEO on LLZTO contents; c the dependence of ionic conductivity on LLZTO contents. Adapted with permission from Ref. [149]. d Structure sketch of NILDH-PEO CPEs improving the ionic conductivity; e XRD patterns of NILDH and NILDH-PEO CPEs. Adapted with permission from Ref. [150]. f VSB-5-enhanced SPEs for lithium battery. Adapted with permission from Ref. [151]. g Schematic diagram of RFS effect the lithium-ion conduction; h-i Attenuated total reflection infrared spectra of PEO and PEO16-RFS. Adapted with permission from Ref. [152]
a 晶体聚合物和含有纳米填料的晶体聚合物之间的锂离子转移示意图；b PEO 的 Xc 与 LLZTO 含量的关系；c 离子电导率与 LLZTO 含量的关系。经授权改编自参考文献。[149]。d 提高离子电导率的 NILDH-PEO CPE 结构简图；e NILDH 和 NILDH-PEO CPE 的 XRD 图。经允许改编自参考文献。[150]。f 用于锂电池的 VSB-5 增强 SPE。经授权改编自参考文献。[151]。g RFS 对锂离子传导的影响示意图；h-i PEO 和 PEO16-RFS 的衰减全反射红外光谱。经允许改编自参考文献。[152] 改编自参考文献。

Semicrystalline polymers usually present a low ionic conductivity (10^–8–10^–6 S cm⁻¹) due to the high Xc of the polymer matrix. Therefore, in addition to inorganic fillers reducing Xc, there are two common methods:
由于聚合物基体的 Xc 较高，半结晶聚合物通常具有较低的离子电导率（10^-8-10^-6 S cm^-1 ）。因此，除了使用无机填料降低 Xc 外，还有两种常用的方法：

• (1) Modifying the polymer by grafting to reduce the degree of regularity of the molecular chains.
  通过接枝改变聚合物，降低分子链的规整度。

• (2) Adding organic plasticizers into the polymer decreases the intermolecular interactions and increase the flexibility of the molecular chains.
  在聚合物中加入有机增塑剂可减少分子间的相互作用，增加分子链的柔韧性。

Although the above two approaches can effectively reduce the crystallinity of CPEs, it would sacrifice the mechanical strength. Accordingly, it is necessary to achieve a compromise between Xc and mechanical strength in the following work.
虽然上述两种方法可以有效降低氯化聚乙烯的结晶度，但会牺牲机械强度。因此，在接下来的工作中，有必要在 Xc 和机械强度之间实现折中。

3.2.3 Effective of Spherulites for Polymers
3.2.3球化剂对聚合物的影响

Crystalline polymers mainly show many spherulites. Spherulite is spherical in shape and varies in size from micrometers to a few millimeters. Figure 13a [153] shows a transport schematic of lithium ions in PEO. Large spherulites stacked with one another that makes the diffusion of lithium ions difficult. When the spherulites become small, the amorphous area increases, and the diffusion of lithium ions is accelerated. Marzantowicz [154] reported that the morphology of spherulites varied with different EO/Li ratios (Fig. 13b). When the concentration of lithium salt was low (EO/Li = 50), the crystalline phase of PEO mainly dominated. When EO/Li = 6, the spherulites became small. The crystalline region was clearly distinguished from the amorphous region. However, high concentrations of salt led to severe phase separation.
结晶聚合物主要表现为许多球粒。球粒呈球形，大小从微米到几毫米不等。图 13a [153] 显示了锂离子在 PEO 中的传输示意图。大的球粒相互堆叠，使锂离子难以扩散。当球粒变小时，无定形面积增加，锂离子的扩散就会加快。Marzantowicz [154]报告说，不同的环氧乙烷/锂比率会使球粒的形态发生变化（图13b）。当锂盐浓度较低时（EO/Li = 50），主要以 PEO 结晶相为主。当 EO/Li = 6 时，球晶变得很小。结晶区与无定形区明显区分开来。然而，高浓度的盐会导致严重的相分离。

Fig. 13 图 13

a Illustration of the transport of lithium ions in PEO spherites. Adapted with permission from Ref. [153]. b The results for PEO/LiTFSI electrolytes of different content salt. Adapted with permission from Ref. [154]. c–f POM pictures of PEO with neat SiO₂, M–SiO₂, C-SiO₂ and A-SiO₂; g Log plot of the spherites growth rate of SiO2-PEO composites versus the crystallization temperature of as a function of SiO₂ content. Adapted with permission from Ref. [156]. h DSC plots of PEO10-LiClO₄/10%ZSM-5. Adapted with permission from Ref. [157]
a 锂离子在 PEO 球体内的传输示意图。经授权改编自参考文献[153[153]。b 不同含量盐的 PEO/LiTFSI 电解质的结果。经授权改编自参考文献。[154]。c-f PEO 与纯 SiO₂, M-SiO₂, C-SiO₂ 和 A-SiO₂ 的 POM 照片；g SiO2-PEO 复合材料的球粒生长率与 SiO₂ 含量的结晶温度的对数图。经授权改编自参考文献。[156]。h PEO10-LiClO₄/10%ZSM-5 的 DSC 图。经授权改编自参考文献。[157] 改编自参考文献。

Choi et al. [155] found that different sizes of Fe₃O₄ nanoparticles had completely different effects on the aggregated state of PEO. The small size of Fe₃O₄ (0.023 µm, 10 wt%) produced more nucleation sites, which led to smaller spherulites, resulting in a decrease in crystallinity. However, Fe₃O₄ (5 µm, 10 wt%) produced significantly larger spherulites due to fewer nucleation sites, and the Xc was higher than that of Fe₃O₄ (0.023 µm, 10 wt%). Jang et al. [156] analyzed the effect of different surface modifications of SiO₂ nanofillers on spherulites, including SiO₂ (Fig. 13c), methoxy-treated SiO₂ (M–SiO₂, Fig. 13d), carboxylate-treated SiO₂ (C-SiO₂, Fig. 13e) and amine-treated SiO₂ (A-SiO₂, Fig. 13f). The high nucleation densities of C-SiO₂ and A-SiO₂ led to a smaller spherulite size. This may be attributed to the electrostatic force between the strong polar groups (on the SiO₂ surface) and the PEO segments. This interaction affects the migration of the polymer chains to the crystalline surface, which results in a lower crystallinity. Furthermore, the interaction between the M-SiO₂ and PEO segments was relatively weak, thus resulting in a higher Xc growth rate (Fig. 13g). Qiu et al. [157] compared the influence of Al₂O₃ and ZSM-5 on Xc. The number of PEO spherulites further increased with the incorporation of Al₂O₃ and ZSM-5. And the radius of spherulites decreased to about 20 μ m on average. The melt enthalpy (∆Hm) and Xc were both affected, as shown in Fig. 13h. The ionic conductivity increased from 1.5 × 10^–7 S cm⁻¹ (PEO10-LiClO₄) to 1.4 × 10^–5 S cm⁻¹ (PEO10-LiClO₄/10%ZSM-5).
Choi 等人[155]发现，不同尺寸的 Fe₃O₄ 纳米粒子对 PEO 的聚集状态具有完全不同的影响。小尺寸的 Fe₃O₄ (0.023 µm, 10 wt%)会产生更多的成核点，从而形成更小的球粒，导致结晶度下降。然而，Fe₃O₄ (5 µm, 10 wt%)由于成核位点较少，产生的球晶明显较大，Xc 也高于 Fe₃O₄ (0.023 µm, 10 wt%)。Jang 等人[156]分析了不同表面修饰的 SiO₂ 纳米填料对球泡石的影响，包括 SiO₂ （图 2）。13c), 甲氧基处理的 SiO₂ (M-SiO₂, Fig.13d）、羧酸处理的 SiO2（C-SiO2，图。13e) 和胺处理的 SiO₂ (A-SiO₂, 图 13f) 。C-SiO₂ 和 A-SiO₂ 的成核密度较高，导致球晶尺寸较小。这可能是由于强极性基团（在 SiO₂ 表面）和 PEO 段之间的静电力所致。这种相互作用会影响聚合物链向结晶表面迁移，从而导致结晶度降低。 此外，M-SiO₂ 和 PEO 段之间的相互作用相对较弱，因此 Xc 生长率较高（图13g）。Qiu 等人[157]比较了 Al₂O₃ 和 ZSM-5 对 Xc 的影响。随着 Al₂O₃ 和 ZSM-5 的加入，PEO 球形颗粒的数量进一步增加。球状云母的半径平均减小到约 20 μ m。如图13h所示，熔体焓（ΔHm）和 Xc 都受到了影响。离子导电率从 1.5 × 10^-7 S cm^-1 (PEO10-LiClO₄) 增加到 1.4 × 10^-5 S cm^-1 (PEO10-LiClO₄/10%ZSM-5).

The ionic conductivity of CPEs is complicated by the presence of both crystalline and noncrystalline phases below the Tm. The morphology and number of spherulites are related to Xc. In general, the large number of nucleation sites formed by inorganic fillers in polymers increases the number of spherulites significantly. However, the size of spherulites decreases rapidly. In this procedure, the amorphous region increases, which accelerates the conduction of lithium ions.
氯化聚乙烯的离子导电性因其在 Tm 以下同时存在结晶相和非晶相而变得复杂。球晶的形态和数量与 Xc 有关。一般来说，聚合物中无机填料形成的大量成核点会显著增加球晶的数量。但是，球粒的尺寸会迅速减小。在此过程中，无定形区域增加，从而加速了锂离子的传导。

From the above analysis, it is clear that the interactions among the inorganic filler, lithium salt and polymer matrix have important effects on the electrochemical properties of CPEs. At present, it is widely assumed that the addition of inorganic fillers can enhance the electrochemical properties of CPEs, which is mainly reflected by an increased ionic conductivity and t_Li⁺. However, this process involves several factors, including carrier concentration, ion migration rate, Tg and Xc. Despite inorganic fillers enhancing the electrochemical and mechanical characteristics of CPEs, aggregation in the polymer matrix and compatibility with the electrode are still major obstacles to practical applications.
从以上分析可以看出，无机填料、锂盐和聚合物基体之间的相互作用对 CPE 的电化学性能有重要影响。目前，人们普遍认为添加无机填料可以增强 CPE 的电化学性能，这主要体现在离子电导率和 t_Li⁺ 的增加上。不过，这一过程涉及多个因素，包括载流子浓度、离子迁移率、Tg 和 Xc。尽管无机填料增强了 CPE 的电化学和机械特性，但聚合物基体中的聚集以及与电极的兼容性仍然是实际应用的主要障碍。

4 Interface Between CPEs and Electrodes
4 CPE 与电极之间的接口

Although the migration of lithium ions in the bulk of CPEs has been addressed, lithium-ion conduction should not be neglected at the electrode–electrolyte interface. The ion conduction at the electrode interface is quite different from that in the bulk phase of CPEs. In addition, the stability of the interface between electrolyte and electrode remains a bottleneck of SSLBs. The interfacial stability is determined by poor electrolyte–electrode contact, lithium dendrite growth and high-pressure decomposition [27]. To solve these problems, CPEs with the advantages of two components (organic and inorganic) become popular in recent years [158, 159].
虽然锂离子在 CPE 体积中的迁移问题已经得到解决，但不应忽视电极-电解质界面上的锂离子传导。电极界面的离子传导与 CPE 体相的离子传导截然不同。此外，电解质和电极之间界面的稳定性仍然是 SSLB 的瓶颈。界面稳定性取决于电解质-电极接触不良、锂枝晶生长和高压分解 [27]。为了解决这些问题，具有两种成分（有机和无机）优点的 CPE 近年来开始流行[158, 159] 。

In this section, we will discuss the improvement in the interfacial stability between CPEs and electrodes in terms of CPEs stabilizing the cathode and CPEs stabilizing the anode. The relationship between CPEs and anode and cathode is depicted in Fig. 14.
在本节中，我们将从 CPE 稳定阴极和 CPE 稳定阳极的角度来讨论 CPE 与电极之间界面稳定性的改善。CPE 与阳极和阴极之间的关系如图 14 所示。

Fig. 14 图 14

Relationship between composite polymer electrolytes and anode and cathode
复合聚合物电解质与阳极和阴极的关系

4.1 Modifications of the CPE/Cathode Interface
4.1 CPE/阴极接口的修改

Under an electric field, electrolytes generate many polarization domains due to intermolecular forces, resulting in the deterioration of electrochemical properties (Fig. 15a) [160]. Thermodynamically, high-voltage compatibility of the electrolyte indicates the ability to resist oxidative decomposition. The highest occupied molecular orbital (HOMO) of all components in the electrolyte (polymers, lithium salts, additives, etc.) must be lower than that of the cathode. Inorganic fillers improve the electrochemical stability of CPEs through Lewis acid–base interactions (hydrogen bonding, vacancy and dipole–dipole interactions) with polymers and lithium salts (Fig. 15b) [36].
在电场作用下，电解质会因分子间作用力而产生许多极化域，导致电化学特性恶化（图15a）[160]。从热力学角度看，电解质的高电压兼容性表明其具有抗氧化分解的能力。电解液中所有成分（聚合物、锂盐、添加剂等）的最高占位分子轨道（HOMO）必须低于阴极的最高占位分子轨道。无机填料通过与聚合物和锂盐的路易斯酸碱相互作用（氢键、空位和偶极-偶极相互作用）提高了 CPE 的电化学稳定性（图15b）[36]。

Fig. 15 图 15

a Schematic for the electrochemical attenuation with the electric field. Adapted with permission from Ref. [160]. b Lewis acid–base interactions between inorganic additives and polymers. Adapted with permission from Ref. [36]. c Schematic diagram of preparing the PVEC-SiO₂ CPEs; d Intermolecular interaction in PVEC-SiO₂ CPEs by DFT; e electrochemical stability window of PVEC-SiO₂ CPEs; f cycling stability of PVEC-SiO₂ CPEs. Adapted with permission from Ref. [161]. g Diagram of lithium-ion conductive pathways without and with LiF additive; h Comparison of LSV results of LLZTO-PEO/PVDF CSEs with different additives. Adapted with permission from Ref. [162]. i Schematic illustration of the preparation of the HNTs-PCL CPEs. Adapted with permission from Ref. [163]
a 电场电化学衰减示意图。经授权改编自参考文献[160] 。[160]。b 无机添加剂与聚合物之间的路易斯酸碱相互作用。经授权改编自参考文献。[36]。c 通过 DFT 制备 PVEC-SiO₂ CPEs 的示意图；d PVEC-SiO₂ CPEs 中的分子间相互作用；e PVEC-SiO₂ CPE 的电化学稳定性窗口；f PVEC-SiO₂ CPE 的循环稳定性。经授权改编自参考文献。[161]。g 不含和含 LiF 添加剂的锂离子传导路径图；h 含不同添加剂的 LLZTO-PEO/PVDF CSE 的 LSV 结果比较。经授权改编自参考文献。[162]。i HNTs-PCL CPE 的制备示意图。经授权改编自参考文献。[163] 。

Wang et al. [161] prepared CPEs with a wide electrochemical stability window and high ionic conductivity by admixing SiO₂ nanoparticles into polyvinyl ethylene carbonate (PVEC) (Fig. 15c). Theoretical calculations and experimental results confirmed that the enhancement of the antioxidant capacity of SiO₂-PVEC CPEs was mainly attributed to hydrogen bonds. As shown in Fig. 15d, the H atoms on the surface of SiO₂ and the O atoms (C=O and O=S=O) in PVEC and TFSI⁻ formed hydrogen bonds. The local intermolecular interaction increased the antioxidant capacity of the SiO₂-PVEC CPEs. As a result, the electrochemical window was up to 5.0 V, as in Fig. 15e. LCO|SiO₂-PVEC CPEs|Li cells provide favorable cycle stability with about 94% capacity retention at a cutoff voltage of 4.5 V (Fig. 15f). In the work of Li et al. [162], LiF as a synergistic additive was added to LLZTO-PEO CPEs to improve the electrochemical stability at a high cutoff voltage (Fig. 15g). Due to the dipole–dipole interactions between LiF and PEO, the electron-hopping energy level of PEO changed to increase the oxidative decomposition potential of PEO. As depicted in Fig. 15h, the oxidative decomposition potential of the LLZTO-PEO/PVDF CPEs increased to 4.8 V. Xu et al. [163] prepared high-voltage compatible CPEs consisting of HNTs and PCL by an in situ technique (Fig. 15i). The external surface of the HNTs was negatively charged, while the internal surface was positively charged. The Lewis acid–base interactions between the HNTs and polymers induced changes in the electron-hopping energy levels of the polymer, thereby enhancing the high voltage resistance of the HNTs-PCL CPEs. These HNTs-PCL CPEs exhibited a potential window of 5.1 V.
Wang 等人[161]将 SiO₂ 纳米粒子掺入聚乙烯醇碳酸酯 (PVEC) 中，制备了具有宽电化学稳定性窗口和高离子电导率的 CPE（图15c）。理论计算和实验结果证实，SiO₂-PVEC CPE 抗氧化能力的增强主要归功于氢键。如图 15d 所示，SiO₂ 表面的 H 原子与 PVEC 和 TFSI^- 中的 O 原子（C=O 和 O=S=O）形成氢键。分子间的局部相互作用提高了 SiO₂-PVEC CPE 的抗氧化能力。因此，如图15e所示，电化学窗口可达 5.0 V。LCO|SiO₂-PVEC CPEs|Li 电池具有良好的循环稳定性，在截止电压为 4.5 V 时，容量保持率约为 94%（图15f）。在 Li 等人的研究中[162]，LiF 作为一种增效添加剂被添加到 LLZTO-PEO CPE 中，以提高高截止电压下的电化学稳定性（图15g）。由于 LiF 和 PEO 之间的偶极-偶极相互作用，PEO 的电子跳跃能级发生了变化，从而提高了 PEO 的氧化分解电位。如图15h 所示，LLZTO-PEO/PVDF CPE 的氧化分解电位升高到 4.8 V。Xu 等人[163] 采用原位技术制备了由 HNT 和 PCL 组成的高压兼容 CPE（图15i）。 HNT 外表面带负电，而内表面带正电。HNTs 和聚合物之间的路易斯酸碱相互作用引起了聚合物电子跳跃能级的变化，从而增强了 HNTs-PCL CPEs 的耐高压能力。这些 HNTs-PCL CPE 的电位窗口为 5.1 V。

In addition, a number of inorganic fillers with oxygen vacancies were effective in enhancing the high-voltage stability of CPEs. Kang et al. [164] introduced Gd–CeO₂ nanowire into PEO to prepare Gd–CeO₂-PEO CPEs. Benefiting from the abundant oxygen vacancies on the surface of Gd–CeO₂, the electrochemical window of Gd–CeO₂-PEO CPEs was increased to 5.0 V (vs. PEO-LITFSI at 4 V), and the ionic conductivity was increased 5 × 10^–4 S cm⁻¹. NCATP (Ce-NASICO) was synthesized by Huang et al. [165]. NCATP enabled the electrolyte to exhibit an excellent antioxidant capacity (5 V) by influencing the electron-hopping energy level of PVDF-HFP. MoO₃-PEO CPEs were prepared by Wang et al. [166]. The abundant lattice oxygen on the surface of MoO₃ showed a certain adsorption effect on the PEO segments, which stabilized the PEO chain structure and inhibited the decomposition of PEO chains under high voltage.
此外，一些含有氧空位的无机填料也能有效增强 CPE 的高压稳定性。Kang 等人 [164] 将 Gd-CeO₂ 纳米线引入 PEO 中，制备了 Gd-CeO₂-PEO CPE。得益于 Gd-CeO₂ 表面丰富的氧空位，Gd-CeO₂-PEO CPEs 的电化学窗口提高到 5.0 V（相对于 4 V 下的 PEO-LITFSI），离子导电率提高了 5 × 10^-4 S cm^-1 。Huang等人合成了NCATP（Ce-NASICO）[165]。NCATP 通过影响 PVDF-HFP 的电子跳跃能级，使电解质表现出卓越的抗氧化能力（5 V）。Wang 等人制备了 MoO₃-PEO CPE [166] 。MoO₃ 表面丰富的晶格氧对 PEO 段有一定的吸附作用，从而稳定了 PEO 链结构，抑制了 PEO 链在高电压下的分解。

Inorganic fillers can improve the antioxidant capacity of CPEs. This is mainly reflected in the effect on the electron-hopping energy levels of the polymer. On the one hand, inorganic fillers are enriched with polar groups (–OH, –COOH, etc.) by grafting which can stabilize the polymer matrix. On the other hand, the elemental doping of inorganic fillers increases surface defects. These defects can stabilize the lithium salt from which the electrochemical stability of the electrolyte is enhanced.
无机填料可以提高氯化聚乙烯的抗氧化能力。这主要体现在对聚合物电子跳跃能级的影响上。一方面，无机填料通过接枝富含极性基团（-OH、-COOH 等），可以稳定聚合物基体。另一方面，无机填料的元素掺杂会增加表面缺陷。这些缺陷可以稳定锂盐，从而提高电解质的电化学稳定性。

4.2 Modifications of the CPE/Anode Interface
4.2 CPE/节点接口的修改

As the “holy grail” of high-performance solid-state cells, lithium metal is one of the most promising anodes. However, interface problems between lithium metal and CPEs still remain. The problems of lithium metal are mainly related to two aspects:
作为高性能固态电池的 "圣杯"，金属锂是最有前途的阳极之一。然而，金属锂与 CPE 之间的界面问题依然存在。金属锂的问题主要涉及两个方面：

• (1) During the periodic cycling of the battery, the expansion and shrinkage of the lithium metal lead to a poor contact.
  在电池的周期性循环过程中，锂金属的膨胀和收缩会导致接触不良。

• (2) Unstable ion transport behavior leads to uneven lithium deposition and thus to the formation of lithium dendrites [167, 168].
  不稳定的离子传输行为会导致锂沉积不均匀，从而形成锂枝晶[167、168]。

The growth of lithium dendrites may puncture the electrolyte, resulting in contact between cathodes and anodes. Recent work has demonstrated that the compatibility of the solid-state electrolyte with the anode can also be improved effectively by the incorporation of inorganic fillers. The roles played by inorganic fillers in alleviating the interface problems are as follows: first, the inorganic filler can homogenize the lithium flux by regulating the ion transport behavior in the electrolyte bulk phase. Thus, the lithium dendrite generation can be controlled at the origin. Second, the inorganic filler can significantly reinforce the mechanical strength of CPEs to suppress the growth of lithium dendrites.
锂枝晶的生长可能会刺穿电解质，导致阴极和阳极接触。最近的研究表明，加入无机填料也能有效改善固态电解质与阳极的相容性。无机填料在缓解界面问题方面的作用如下：首先，无机填料可以通过调节电解质体相中的离子传输行为来均匀锂通量。因此，锂枝晶的生成可以在源头得到控制。其次，无机填料可显著增强 CPE 的机械强度，从而抑制锂枝晶的生长。

4.2.1 Regulation of Lithium-Ion Deposition
4.2.1 锂离子沉积监管

Thermodynamically, lithium dendrites originate from the nucleation of lithium dendrites due to uneven local current densities. Therefore, the structural design of CPEs is beneficial for reducing the effective current density. In particular, some 3D inorganic fillers can accelerate ion transport and reduce the space charge density to slow down the formation of lithium dendrites [11].
从热力学角度来看，锂枝晶源于局部电流密度不均匀导致的锂枝晶成核。因此，CPE 的结构设计有利于降低有效电流密度。特别是一些三维无机填料可以加速离子传输，降低空间电荷密度，从而减缓锂枝晶的形成[11]。

An anion-immobilized LLZTO-PEO CPE was proposed by Zhang et al. [169]. Compared with conventional liquid electrolytes, LLZTO-PEO CPEs can bundle anions to induce a uniform distribution of lithium ions. Sun et al. [170] proposed a self-healing electrostatic shielding strategy to achieve uniform lithium-ion deposition in PEO-based electrolytes. As shown in Fig. 16a, homogeneous lithium-ion deposition was accomplished by introducing CsClO₄ (0.05 M). Interestingly, Cs⁺ showed a lower reduction potential than lithium ions (1.7 mol L⁻¹). Different from the conventional CPEs, Cs⁺ initially formed a positively charged electrostatic shield coating around the lithium tip during lithium deposition. This forced the lithium ions to be deposited preferentially in the neighboring region of Cs⁺. Finally, a smooth deposition layer and a dendrite-free lithium anode surface were obtained. After 100 h of cycling, a large amount of mossy lithium was observed on the anode when coupled with PEO SPEs (Fig. 16b1, b2). In addition, some large lithium dendrites in 10–20 μm were also observed on the surface of PEO SPEs in (Fig. 16b3, b4). However, for CsClO₄-PEO CPEs, no lithium dendrites or mossy lithium were observed on the anode (Fig. 16b5, b6). Moreover, the original morphology of CsClO₄-PEO CPEs was maintained. Thus, the CsClO₄-PEO CPEs benefitted from the low potential to achieve uniform lithium deposition. The Li|CsClO₄-PEO CPEs|Li battery realized stable plating/exfoliation performance for 500 h at 0.2 mA cm⁻² (Fig. 16c). Cai et al. [171] exploited a network of interconnected 3D-UIO-66-PAN/PEO CPEs to homogenize lithium-ion fluxes. As shown in Fig. 16d, the uniform distribution of UIO-66 on nanofibers favored the creation of a continuous ion transport pathway, which facilitated lithium-ion transport. Moreover, UIO-66 with a moderate pore size and strong cationic sites allowed a uniform lithium flux distribution by limiting anion transport. In Fig. 16e, the COMSOL result reveals that 3D-UIO-66-PAN/PEO CPEs with a small concentration gradient for lithium ions and TFSI⁻ ions during lithium deposition, which suggests a homogeneous lithium-ion flux. Moreover, the potential field was smaller than that of the UIO-66-PAN/PEO CPEs. Notably, due to the uniform lithium-ion flux and the fast lithium-ion transport of 3D-UIO-66-PAN/PPEO, the Li|3D-UIO-66/PAN/PEO CPEs|Li cells did not suffer from short-circuiting even after 700 h of cycling (Fig. 16f). Fan et al. [172] designed NCN-CPEs composed of corrugated 3D nanowire bulk-ceramic-nanowires (NCN) (Fig. 16g). This special NCN backbone alleviated the polarization concentration at the electrode/electrolyte interface and provided a uniform interfacial lithium-ion flux to the anode. In Fig. 16h, finite element simulation results show that the electrolyte composed of LLZTO ceramic sheets (NET-PEO CPEs) and LLZTO nanowires (PCP-PEO CPEs) suffered from a high diffusion potential barrier for lithium-ion transport due to the higher local space charge. This resulted in a nonuniform lithium-ion flux at the electrode. However, the special sandwich structure of the NCN-PEO CPEs provided a definite advantage. Notably, the NCN-PEO CPEs exhibited an excellent t_Li⁺ of 0.9 (Fig. 16i). The Li|NCN-PEO CPEs|Li cell showed a flat voltage profile with no short-circuiting (0.1 mA cm⁻²) for 600 h (Fig. 16j). LLZO-PEO CPEs with vertical/horizontal anisotropy were prepared by Guo et al. [173]. As shown in Fig. 16k, the LLZO ultrafine fibers rapidly transferred lithium ions and reduced the uneven distribution of the electric field, thus achieving excellent electrochemical performance. Wu et al. [174] adjusted the interfacial potential distribution between the electrolyte and the anode in situ generating Li₃P on the surface of SPEs, allowing the homogenous plating and stripping of lithium ions.
Zhang 等人提出了阴离子固定化 LLZTO-PEO CPE [169]。与传统的液态电解质相比，LLZTO-PEO CPE 可以捆绑阴离子，诱导锂离子均匀分布。Sun 等人[170]提出了一种自修复静电屏蔽策略，以实现锂离子在 PEO 基电解质中的均匀沉积。如图 16a 所示，通过引入 CsClO₄ (0.05 M) 实现了均匀的锂离子沉积。有趣的是，铯⁺的还原电位低于锂离子（1.7 mol L^-1）。与传统的 CPE 不同，在锂沉积过程中，Cs⁺ 最初会在锂尖端周围形成一层带正电荷的静电屏蔽层。这迫使锂离子优先沉积在 Cs⁺ 的邻近区域。最后，获得了光滑的沉积层和无枝晶的锂阳极表面。经过 100 小时的循环后，与 PEO SPE 相结合的阳极上出现了大量苔藓状锂（图16b1、b2）。此外，在 PEO SPE 表面还观察到一些 10-20 μm 的大型锂枝晶（图16b3、b4）。然而，对于 CsClO₄-PEO CPE，阳极上没有观察到锂枝晶或苔藓状锂（图 16b5, b6）。此外，CsClO₄-PEO CPE 的原始形态得以保持。因此，CsClO₄-PEO CPE 从低电位实现均匀锂沉积中受益匪浅。 Li|CsClO₄-PEO CPEs|Li 电池在 0.2 mA cm^-2 的条件下实现了 500 h 稳定的电镀/剥离性能（图16c）。Cai 等人[171]利用相互连接的 3D-UIO-66-PAN/PEO CPE 网络来均匀锂离子通量。如图16d所示，UIO-66在纳米纤维上的均匀分布有利于建立连续的离子传输通道，从而促进锂离子传输。此外，具有中等孔径和强阳离子位点的 UIO-66 还能通过限制阴离子传输实现均匀的锂通量分布。在图 16e 中，COMSOL 结果显示，在锂沉积过程中，3D-UIO-66-PAN/PEO CPE 的锂离子和 TFSI^- 离子浓度梯度较小，这表明锂离子通量是均匀的。此外，电位场小于 UIO-66-PAN/PEO CPE。值得注意的是，由于 3D-UIO-66-PAN/PPEO 具有均匀的锂离子通量和快速的锂离子传输，即使在循环 700 小时后，锂|3D-UIO-66/PAN/PEO CPEs|Li 电池也没有出现短路现象（图 16f）。Fan 等人[172]设计了由波纹状三维纳米线体陶瓷纳米线（NCN）组成的 NCN-CPE（图16g）。这种特殊的 NCN 骨架减轻了电极/电解质界面的极化浓度，并为阳极提供了均匀的界面锂离子通量。图16h，有限元模拟结果表明，由 LLZTO 陶瓷片（NET-PEO CPEs）和 LLZTO 纳米线（PCP-PEO CPEs）组成的电解质由于局部空间电荷较高，在锂离子传输过程中存在较高的扩散势垒。这导致电极上的锂离子通量不均匀。然而，NCN-PEO CPE 的特殊夹层结构却带来了明显的优势。值得注意的是，NCN-PEO CPE 的 t_Li⁺ 值为 0.9（图 16i ）。Li|NCN-PEO CPEs|Li 电池在 600 小时内显示出平坦的电压曲线，没有短路现象（0.1 mA cm^-2）（图16j）。Guo 等人[173]制备了具有垂直/水平各向异性的 LLZO-PEO CPE。如图16k所示，LLZO超细纤维能快速转移锂离子，减少电场的不均匀分布，从而获得优异的电化学性能。Wu 等人[174]调整了电解液与阳极之间的界面电位分布，在固相萃取器表面生成了锂₃P，实现了锂离子的均匀电镀和剥离。

Fig. 16 图 16

a Illustration of the Li deposition process for PEO-Cs⁺ and conventional PEO electrolyte; b SEM images of (b1–b4) PEO SPEs after 100 h; SEM images of (b5–b8) CsClO₄-PEO CPEs after 100 h; c cycling stability of the Li||Li symmetrical cells assembled with CsClO₄-PEO CPEs and PEO SPEs. Adapted with permission from Ref. [170]. d Schematic diagram of the growth of Li dendrites in PEO and 3D-MOF/PAN/PEO; e the COMSOL simulation for Li⁺, TFSI⁻ and potential distribution of UIO-66/PEO and 3D-UIO-66/PAN/PEO; f long-term cycle reliability of symmetric Li|3D-UIO-66/PAN/PEO CPEs|Li cells. Adapted with permission from Ref. [171]. g Schematic diagram of lithium-ion transport NCN-PEO CPEs and the side view and top view of NCN-PEO CPEs; h FEM simulations of electric potential distribution in NET-PEO CPEs, PCP-PEO CPEs and NCN-PEO CPE; i lithium-ion transference number of NCN-PEO CPEs; j Li plating/stripping test with a constant current density of 0.1 mA cm.⁻². Adapted with permission from Ref. [172]. k Schematic illustration of LLZO-PEO CPEs works in solid-state Li metal batteries. Adapted with permission from Ref. [173]
a PEO-Cs⁺ 和传统 PEO 电解质的锂沉积过程示意图； b 100 小时后 (b1-b4) PEO SPE 的 SEM 图像；(b5-b8) CsClO₄-PEO CPEs 100 h 后的 SEM 图像；c 使用 CsClO₄-PEO CPEs 和 PEO SPEs 装配的 Li||Li 对称电池的循环稳定性。经授权改编自参考文献。[170]。 d 锂枝晶在 PEO 和 3D-MOF/PAN/PEO 中的生长示意图；e COMSOL 模拟 Li⁺, TFSI^- 以及 UIO-66/PEO 和 3D-UIO-66/PAN/PEO 的电位分布；f 对称锂|3D-UIO-66/PAN/PEO CPEs|锂电池的长期循环可靠性。经授权改编自参考文献。[171]。g 锂离子传输 NCN-PEO CPE 的示意图以及 NCN-PEO CPE 的侧视图和俯视图；h NET-PEO、PCP-PEO CPE 和 NCN-PEO CPE 中电动势分布的有限元模拟；i NCN-PEO CPE 的锂离子转移数量；j 恒定电流密度为 0.1 mA cm.-2。经授权改编自参考文献。[172]。k LLZO-PEO CPEs 在固态锂金属电池中的工作原理图。经授权改编自参考文献。[173].

The incorporation of electronegative (vs. Li⁺) elements in the electrolyte to prevent the formation of lithium cores and the addition of porous inorganic fillers to realize a uniform lithium-ion flux are effective strategies for promoting homogeneous lithium-ion deposition and inhibiting the formation of lithium dendrites. In addition, strategies for modifying lithium metal can also achieve the same purposes.
在电解液中加入电负性（相对于锂⁺）元素以防止形成锂核，以及添加多孔无机填料以实现均匀的锂离子通量，是促进锂离子均匀沉积和抑制锂枝晶形成的有效策略。此外，对金属锂进行改性的策略也能达到同样的目的。

4.2.2 Inhibition of Lithium Dendrites
4.2.2抑制锂树突

ISEs have a superior shear modulus, which can strongly restrain the growth of lithium dendrites. However, ISEs suffer from high interfacial resistance. Therefore, it is difficult to balance interfacial compatibility and ionic conductivity. SPEs have excellent interface contact. But lithium dendrites can still penetrate the electrolyte and cause short-circuiting inside the cells. Therefore, enhancing the mechanical strength of SPEs is another important strategy to restrain lithium dendrites.
ISE 具有优异的剪切模量，可有效抑制锂枝晶的生长。然而，ISE 存在较高的界面电阻。因此，很难在界面兼容性和离子导电性之间取得平衡。SPE 具有良好的界面接触性。但锂枝晶仍可渗透电解质，导致电池内部短路。因此，提高 SPE 的机械强度是抑制锂枝晶的另一个重要策略。

To balance the mechanical and electrochemical properties of CPEs, LLZTO-PEO CPEs with a sandwich structure were designed by Huo et al. [175]. Figure 17a shows these sandwich-structured LLZTO-PEO CPEs. The external layer consisted of 20%-LLZTO (200 nm) and PEO, which resulted in good interfacial contact. The intermediate layer consisted of 80%-LLZTO (5 µm) and PEO, which effectively inhibited lithium dendrites. Figure 17b shows the SEM images of the LLZTO-PEO CPEs with a hierarchical structure. With this rigid-flexible design, the Li|LLZTO-PEO CPEs|Li cell was stably maintained for 400 h at 0.2 mA cm⁻². Jiang et al. [176] reported BNNF-PAN-BNNF CPEs, as presented in Fig. 17c. The BNNF-PAN-BNNF CPEs with a bilayer structure are shown in Fig. 17d. For these CPEs, the BNNFs endowed it with an excellent tensile strength (16.0 MPa) and Young's modulus (563.7 MPa), as shown in Fig. 17e. Due to the above advantages, the Li|BNNF-PAN- BNNF CPEs|Li cell had a small overpotential, while the lithium metal hardly changed after 400 h of cycling (Fig. 17f). Fan et al. [177] adopted a new strategy for inhibiting lithium dendrites, as illustrated in Fig. 17g. The excellent mechanical strength of the flexible network of LATP-PAN (tensile strength of 10.72 MPa in Fig. 17h) enhanced stress tolerance. Thus, LATP-PAN/PEO CPEs suppressed the development of lithium dendrites through the fiber network. Moreover, the Coulombic efficiency of the Li|LATP-PAN/PEO CPEs|LiFePO₄ battery was maintained at 99% after 100 cycles, which indicated the excellent interfacial stability between the electrolyte and anode during the cycles (Fig. 17i). Hu et al. [178] prepared LLZO-PEO CPEs by filling a 3D conductive lithium framework (LLZO) with PEO in Fig. 17j. The LLZO-PEO CPEs not only provided a high ionic conductivity (8 × 10^–4 S cm⁻¹), but the rigid backbone structure hindered the growth of dendrites. As indicated in Fig. 17k, the Li|LLZO-PEO CPEs|Li cell did not short circuit even after 500 h cycles at 0.2 and 0.5 mA cm⁻². Moreover, the LiFePO₄|LLZO-PEO CPEs|Li cell maintained nearly 100% capacity in 50 cycles, as shown in Fig. 17l.
为了平衡 CPE 的机械性能和电化学性能，Huo 等人设计了具有夹层结构的 LLZTO-PEO CPE [175]。图17a 显示了这些夹层结构的 LLZTO-PEO CPE。外层由 20% 的 LLZTO（200 nm）和 PEO 组成，从而实现了良好的界面接触。中间层由 80%-LLZTO (5 µm) 和 PEO 组成，可有效抑制锂枝晶。图 17b 显示了具有分层结构的 LLZTO-PEO CPE 的 SEM 图像。在这种刚柔相济的设计下，锂|LLZTO-PEO CPEs|锂电池在 0.2 mA cm^-2 的条件下稳定地维持了 400 小时。Jiang 等人[176]报道了 BNNF-PAN-BNNF CPEs，如图17c 所示。具有双层结构的 BNNF-PAN-BNNF CPE 如图17d 所示。如图17e所示，BNNF赋予了这些 CPE 极佳的拉伸强度（16.0 兆帕）和杨氏模量（563.7 兆帕）。由于上述优点，Li|BBNNF-PAN- BNNF CPEs|Li 电池的过电位很小，而锂金属在循环 400 小时后几乎没有变化（图 17f）。Fan 等人[177]采用了一种抑制锂枝晶的新策略，如图17g 所示。LATP-PAN 柔性网络出色的机械强度（图 17h 中的拉伸强度为 10.72 兆帕）增强了应力耐受性。因此，LATP-PAN/PEO CPE 通过纤维网络抑制了锂枝晶的发展。 此外，Li|LATP-PAN/PEO CPEs|LiFePO₄ 电池的库仑效率在 100 次循环后保持在 99%，这表明在循环过程中电解质和负极之间具有良好的界面稳定性（图17i）。Hu 等人[178]通过在三维导电锂框架（LLZO）中填充 PEO 制备了 LLZO-PEO CPE，如图17j。LLZO-PEO CPE 不仅具有很高的离子电导率（8 × 10^-4 S cm^-1 ），而且刚性骨架结构阻碍了树枝状突起的生长。如图17k所示，即使在 0.2 和 0.5 mA cm^-2条件下循环 500 h，锂|LLZO-PEO CPEs|Li 电池也不会短路。此外，如图17l所示，LiFePO₄|LLZO-PEO CPEs|Li 电池在 50 个循环中保持了近 100% 的容量。

Fig. 17 图 17

a Description of the PIC-5 µm, CIP-200 nm, and hierarchical CPEs; b cross-sectional SEM pictures of LLZTO-PEO CPEs with hierarchical structure. Adapted with permission from Ref. [175]. c Schematic of the BNNF-PAN-LiClO₄-BNNF; d cross-sectional SEM image of the BNNF-PAN-LiClO₄-BNNF; e stress–strain curves of the PAN-LiClO₄ and BNNF-PAN-LiClO₄-BNNF CPEs; f BNNF-PAN-LiClO₄-BNNF CPEs and lithium metal anodes after cycles. Adapted with permission from Ref. [176]. g Schematic Illustration for the preparation of the LATP-PAN-PEO CPEs; h stress–strain curves of LATP-PAN-PEO CPEs and PEO8–LiTFSI; i cycling stability of Li|LATP-PAN-PEO CPEs|LiFePO₄ batteries at 0.2C. Adapted with permission from Ref. [177]. j Schematic illustration for the preparation of the LLZO-PEO CPEs. k Cycles of Li|LLZO-PEO CPEs|Li 0.1 and 0.2 mA cm⁻.²; l Cycling performance of LiFePO₄|LLZO-PEO CPEs|Li at 0.2C. Adapted with permission from Ref. [178]
a PIC-5 µm、CIP-200 nm 和分层 CPE 的描述；b 具有分层结构的 LLZTO-PEO CPE 的截面 SEM 照片。经授权改编自参考文献。[175]。c BNNF-PAN-LiClO₄-BNNF 的示意图；d BNNF-PAN-LiClO₄-BNNF 的截面 SEM 图像；e PAN-LiClO₄ 和 BNNF-PAN-LiClO₄-BNNF CPE 的应力-应变曲线； f BNNF-PAN-LiClO₄-BNNF CPE 和锂金属阳极循环后。经授权改编自参考文献。[176]。g LATP-PAN-PEO CPE 的制备示意图；h LATP-PAN-PEO CPE 和 PEO8-LiTFSI 的应力-应变曲线；i Li|LATP-PAN-PEO CPEs|LiFePO₄ 电池在 0.2C.经允许改编自参考文献。[177]. j LLZO-PEO CPE 的制备示意图。k Li|LLZO-PEO CPEs|Li 0.1 和 0.2 mA cm 的循环^-.²; l LiFePO₄|LLZO-PEO CPEs|Li 在 0.2C 下的循环性能。经授权改编自参考文献。[178].

5 Conclusion
5 结论

The solid-state electrolyte plays a significant role in SSLBs. Currently, CPEs are regarded as a prospective solid-state electrolyte because they inherit the advantages of ISEs and SPEs. However, CPEs still need to overcome some drawbacks, for example, a low ionic conductivity and undesirable interfaces. Therefore, this review explores the contribution of inorganic fillers in improving the electrochemical performance as well as the interfacial compatibility of CPEs.
固态电解质在 SSLB 中发挥着重要作用。目前，CPE 因继承了 ISE 和 SPE 的优点而被视为一种前景广阔的固态电解质。然而，CPE 仍需克服一些缺点，例如离子电导率低和不理想的界面。因此，本综述探讨了无机填料在改善 CPE 的电化学性能和界面兼容性方面的贡献。

According to the transport method of lithium ions in CPEs, it is known that the important role of inorganic fillers is to increase the amorphous region of the polymer matrix and, in this way, to increase the number of movable polymer chain segments. At the macroscopic level, the changes in the polymer aggregated state structure are an important reason for the changes in the amorphous regions. Spherites are the main crystalline structure of polymers. spherites, including size and quantities. Once the aggregated structure of CPEs is changed, Xc as well as Tg will also be changed.
根据锂离子在氯化聚乙烯中的传输方法可知，无机填料的重要作用是增加聚合物基体的无定形区，从而增加可移动聚合物链段的数量。在宏观层面上，聚合物聚集态结构的变化是非晶区发生变化的重要原因。球晶是聚合物的主要结晶结构，包括尺寸和数量。一旦氯化聚乙烯的聚集结构发生变化，Xc 和 Tg 也会随之改变。

And at the microscopic level, the inorganic filler will induce a change in the ion transport behavior. This is due to the fact that a new interfacial phase, the polymer–filler interface, is created in CPEs. New ion transport channels will be formed at this interface. This interfacial effect can be attributed to the Lewis acid–base interaction among lithium salt–filler–polymer. The intensity of Lewis acid–base interactions is related to the species, morphology, concentration and surface properties of the inorganic filler. Besides, the special structures of inorganic fillers, such as nanowires, 3D network structures, and vertically aligned structures, can increase the u. Next, functionalized inorganic fillers, such as Lewis acid or base sites on the surface, can accelerate the dissociation of lithium salts and promote the coordination of the polymer with lithium ions. Also, Lewis acid–base interactions can increase the n in the CPEs systems. They both contribute to the ionic conductivity of the CPEs. In addition, the special characteristics of the fillers, such as the surface with positive charges, -HSO₃, -NH₂, -COOH, generally interact with the lithium salt in two ways: increasing the mobility of the lithium ion or limiting the motility of the anion. Those interactions all contribute to t_Li⁺.
在微观层面上，无机填料会导致离子传输行为发生变化。这是由于在 CPE 中产生了一种新的界面相，即聚合物-填料界面。新的离子传输通道将在该界面上形成。这种界面效应可归因于锂盐-填料-聚合物之间的路易斯酸碱相互作用。路易斯酸碱相互作用的强度与无机填料的种类、形态、浓度和表面特性有关。此外，无机填料的特殊结构，如纳米线、三维网络结构和垂直排列结构，可以增加u。此外，路易斯酸和碱的相互作用也能增加 CPEs 系统中的 n。它们都有助于提高 CPE 的离子导电性。此外，填料的特殊特性，如表面带正电荷、-HSO₃、-NH₂、-COOH，通常以两种方式与锂盐相互作用：增加锂离子的移动性或限制阴离子的移动性。这些相互作用都会对 t_Li⁺ 起作用。

Therefore, based on the above analysis, we speculate that:
因此，根据上述分析，我们推测

When T < Tm, the ionic conductivity of the electrolyte is significantly different for fillers doped or not. As shown in Fig. 18, the ionic conductivity of CPEs is significantly higher than that of SPEs. Even the curve changes relatively slowly. For this, we speculate that the ionic conductivity of CPEs is mainly controlled by the crystallization of the polymer in the low-temperature region. When the filler is doped, the crystalline structure of the polymer is disrupted allowing an additional region for ion conductivity.
当 T < Tm 时，电解质的离子电导率与是否掺入填料有显著不同。如图 18 所示，CPE 的离子电导率明显高于 SPE。即使是曲线变化也相对缓慢。因此，我们推测 CPE 的离子电导率主要受低温区聚合物结晶的控制。掺入填料后，聚合物的结晶结构会被破坏，从而为离子导电提供了额外的区域。

Fig. 18 图 18

Temperature dependence of ionic conductivity
离子导电率的温度依赖性

Notably, Lewis acid–base interactions at the filler–polymer interface are also present. At this point, the lithium-ion transport behavior is quite complex and governed by several factors. Therefore, ∆σ₁ is a combination of the inhibition of polymer crystallization by the filler and the Lewis acid–base interactions. When T > Tm, we roughly assume that the polymer is completely in the amorphous state. At this moment, the thermal motility of the polymer chains is consistent under the same temperature conditions. When the filler is incorporated, we find that the ionic conductivity of the CPEs is elevated compared to that of the SPEs. It can be approximated that ∆σ₂ is the contribution of Lewis acid–base interactions at the filler–polymer interface.
值得注意的是，填料-聚合物界面上还存在路易斯酸碱相互作用。在这一点上，锂离子传输行为相当复杂，受多种因素制约。因此，Δσ₁ 是填料对聚合物结晶的抑制和路易斯酸碱相互作用的综合结果。当 T > Tm 时，我们大致认为聚合物完全处于无定形状态。此时，聚合物链的热运动在相同温度条件下是一致的。加入填料后，我们发现与 SPE 相比，CPE 的离子导电率有所提高。可以近似认为 ∆σ₂ 是填料-聚合物界面上路易斯酸碱相互作用的贡献。

However, we found that current research regarding Lewis acid–base interactions is generalized. We need to clarify the types of Lewis acid–base interactions, such as electrostatic interactions, van der Waals forces, hydrogen bonds, π-π interactions, etc. Even in CPEs, it should be fully understood which components are the Lewis acids or Lewis bases. In addition, the effects of the same type of inert filler (Al₂O₃, SiO₂, TiO₂, Ba₂TiO₃, etc.) or active filler (LLZTO, LLZO, LATP) on the ionic conductivity, t_Li⁺, etc., of CPEs still need to be further investigated. This kind of research is important for finding the best-performance inorganic fillers for the application of CPEs.
然而，我们发现，目前有关路易斯酸碱相互作用的研究都是泛泛而谈。我们需要明确路易斯酸碱相互作用的类型，如静电相互作用、范德华力、氢键、π-π 相互作用等。即使在 CPE 中，也应充分了解哪些成分是路易斯酸或路易斯碱。此外，同类惰性填料（Al₂O₃、SiO₂, TiO₂, Ba₂TiO₃ 等。此外，还需要研究活性填料（LLZTO、LLZO、LATP）或活性填料（LLZTO、LLZO、LATP）对离子电导率 t_Li⁺ 等的影响、CPEs的研究还有待进一步深入。这类研究对于为 CPE 的应用找到性能最佳的无机填料非常重要。

Furthermore, the impact of the interface compatibility needs to be considered. In recent years, many bulk phase problems, such as the ionic conductivity and t_Li⁺, have been greatly improved with the increasing research works on CPEs. However, in general, the diffusion of ions at the electrode–electrolyte interface depends on the interfacial contact. Thus, the electrode–electrolyte interface needs to be focused on. On the anode side, the cell is prone to uneven lithium deposition and dendrite growth during lithium embedding and delithiation at high current densities. The ability to resist high voltage on the cathode is the key for the electrolyte to be applied in high energy density batteries. Thus, the chemical, electrochemical, mechanical and thermal stability of the electrode–electrolyte interface becomes another bottleneck in the development of SSLBs. For the electrode–electrolyte interface, CPEs need to possess the following properties:
此外，还需要考虑界面兼容性的影响。近年来，随着对 CPE 研究的不断深入，许多体相问题，如离子电导率和 t_Li⁺ 都得到了很大改善。然而，一般来说，离子在电极-电解质界面的扩散取决于界面接触。因此，需要重点关注电极-电解质界面。在阳极一侧，电池在高电流密度下进行锂嵌入和脱锂时，容易出现锂沉积不均匀和枝晶生长的现象。阴极的耐高压能力是电解液应用于高能量密度电池的关键。因此，电极-电解质界面的化学、电化学、机械和热稳定性成为开发 SSLB 的另一个瓶颈。对于电极-电解质界面，CPE 需要具备以下特性：

• (1) Adhesion. To minimize the interfacial resistance caused by physical contact, the solid-state electrolyte must have good adhesion to the electrode. This may be accomplished by adding some additives, such as plasticizers or liquid electrolytes. However, the amount of plasticizer must be strictly controlled. Otherwise, the mechanical strength of the solid-state electrolyte will be reduced, which can be fatal to the long cycle life of the battery.
  附着力。为了尽量减少物理接触造成的界面电阻，固态电解质必须与电极有良好的粘附性。这可以通过添加增塑剂或液态电解质等添加剂来实现。但必须严格控制增塑剂的用量。否则，固态电解液的机械强度会降低，这对电池的长循环寿命是致命的。

• (2) Efficient and uniform ion transport channels. The uneven deposition of lithium ions on the anode can lead to lithium dendrites, which can threaten the safety of the battery. On the one hand, the space for dendrite growth is reduced by decreasing the physical spaces between the lithium metal and the electrolyte. On the other hand, the uniform deposition of lithium ions is induced by regulating the electrolyte bulk phase. There are two approaches: one is to establish fast and uniform ion transport pathways in the electrolyte to accelerate ion transport and reduce the inhomogeneous charge distribution at the anode. Some ceramic components with different morphologies, such as 3D frameworks, nanowires and nanosheets, can accelerate ions transport. Among them, 3D frameworks and nanowires are of interest because of their long-range continuous ion conduction channels. Second, doping the electrolyte with some low-potential elements is another effective method for inducing uniform lithium deposition.
  高效均匀的离子传输通道。锂离子在负极上的不均匀沉积会导致锂枝晶，从而威胁电池的安全。一方面，通过减少锂金属和电解液之间的物理空间，可以减少枝晶生长的空间。另一方面，通过调节电解质的体相，促使锂离子均匀沉积。方法有两种：一种是在电解质中建立快速、均匀的离子传输通道，以加速离子传输，减少阳极电荷分布的不均匀性。一些具有不同形态的陶瓷成分，如三维框架、纳米线和纳米片，可以加速离子传输。其中，三维框架和纳米线因其长程连续离子传导通道而备受关注。其次，在电解质中掺入一些低电位元素是诱导锂均匀沉积的另一种有效方法。

• (3) High-pressure compatibility. Most solid-state electrolytes easily decompose when in contact with electrode materials. The interfacial stability of the cathode can be enhanced by changing the HOMO of the polymer through Lewis acid–base interactions. Some inorganic fillers (Al₂O₃, etc.) with small molecule plasticizers (SN, etc.) are suitable candidates.
  高压兼容性。大多数固态电解质在与电极材料接触时很容易分解。通过路易斯酸碱相互作用改变聚合物的 HOMO，可增强阴极的界面稳定性。一些无机填料（Al₂O₃ 等）和小分子增塑剂（SN 等）是合适的候选材料。