Ionic conductivity enhancement of polymer electrolytes with ceramic nanowire fillers

In Situ Alloying Enabled by Active Liquid Metal Filler for Self-Healing Composite Polymer Electrolytes

Solid inorganics, known for kinetically inhibiting polymer crystallization and enhancing ionic conductivity, have attracted significant attention in solid polymer electrolytes. However, current composite polymer electrolytes (CPEs) are still facing challenges in Li metal batteries, falling short of inhibiting severe dendritic growth and resulting in very limited cycling life. This study introduces Ga62.5In21.5Sn16 (Galinstan) liquid metal (LM) as an active liquid alternative to conventional passive solid fillers, aiming at realizing self-healing protection against dendrite problems. Compared to solid inorganics, for example silica, LM droplets could more significantly reduce polymer crystallinity and enhance Li-ion conductivity due to their liquid nature, especially at temperatures below the polymer melting point. More importantly, LMs are unraveled as dynamic chemical traps, which are capable of blocking and consuming lithium dendrites upon contact via in situ alloying during battery operation and further inhibiting dendritic growth due to the lower deposition energy barrier of the formed Li-LM alloy. As a proof of concept, by strategically designing an asymmetric CPE with the active LM filling, a solid-state Li/LiFePO4 battery achieves promising full-cell functionality with notable rate performance and stable cycle life. This active filler-mediated self-healing approach could bring new insights into the battery design in versatile solid-state systems.

Highly Conductive and Stable Composite Polymer Electrolyte with Boron Nitride Nanotubes for All-Solid-State Lithium Metal Batteries

All-solid-state lithium metal batteries (ASSLMBs) have emerged as the most promising next-generation energy storage devices. However, the unsatisfactory ionic conductivity of solid electrolytes at room temperature has impeded the advancement of solid-state batteries. In this work, a multifunctional composite solid electrolyte (CSE) is developed by incorporating boron nitride nanotubes (BNNTs) into polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP). BNNTs, with a high aspect ratio, trigger the dissociation of Li salts, thus generating a greater population of mobile Li+, and establishing long-distance Li+ transport pathways. PVDF-HFP/BNNT exhibits a high ionic conductivity of 8.0 × 10-4 S cm-1 at room temperature and a Li+ transference number of 0.60. Moreover, a Li//Li symmetric cell based on PVDF-HFP/BNNT demonstrates robust cyclic performance for 3400 h at a current density of 0.2 mA cm-2. The ASSLMB formed from the assembly of PVDF-HFP/BNNT with LiFePO4 and Li exhibits a capacity retention of 93.2% after 850 cycles at 0.5C and 25 °C. The high-voltage all-solid-state LiCoO2/Li cell based on PVDF-HFP/BNNT also exhibits excellent cyclic performance, maintaining a capacity retention of 96.4% after 400 cycles at 1C and 25 °C. Furthermore, the introduction of BNNTs is shown to enhance the thermal conductivity and flame retardancy of the CSE.

Thin, Uniform, and Highly Packed Multifunctional Structural Carbon Fiber Composite Battery Lamina Informed by Solid Polymer Electrolyte Cure Kinetics

Multifunctional structural batteries promise advancements in structural energy storage technologies by seamlessly integrating load-bearing and energy-storage functions within a single material, reducing weight, and enhancing safety. Yet, commercialization faces challenges in materials processing, assembly, and design optimization. Here, we report a systematic approach to develop a carbon fiber (CF)-based structural battery impregnated with epoxy-based solid polymer electrolyte (SPE) via robust vacuum-assisted compression molding (VACM). Informed by cure kinetics, SPE processing enhances the multifunctional performance with no fillers or additives. The thin flexible CF-based laminae impregnated under high pressure achieved a substantial enhancement of ∼160% in the fiber volume fraction (FVF) as although thin and strip-shaped, the fibers were optimally packed with low void. A CF/SPE-based battery was fabricated, with a hybrid layered ionic liquid (IL)/ carbonate electrolyte (CE) showing enhanced safety and multifunctional performance. Enhanced by thin, uniform, and stiff CF-based composites, this study propels the development of advanced multifunctional structures, thereby expediting sustainable commercialization.

In Situ Constructing Robust Interface by Deep Eutectic Polymeric Electrolyte Enables High Performance Lithium Metal Batteries with High-Loading Cathode

The low Li+ transport and poor interface have consistently been two major impediments to practical applications of Polyacrylonitrile (PAN)-based composite solid-state electrolytes (PCPE). In this work, a polymerizable deep eutectic electrolyte is meticulously designed with high fluidity which consists of Poly (Ethylene Glycol) Diacrylate (PEGDA), Fluoroethylene Carbonate (FEC), Succinonitrile (SN) and dual salts (LiTFSI/LiDFOB) to promote Li+ transport and ameliorate the interface of PCPE. Inclusion of PEGDA monomers and FEC alters the crystallinity of SN, enhancing the wettability of thick electrode, and formation of polymeric 3D network from polymerization of PEGDA can anchor SN and suppress the side reactions between SN and lithium metal. Consequently, the modified PCPE exhibit an enhanced conductivity of 4.47 × 10-4 S cm-1 with Li-ion transference number of 0.60, and show an excellent lithium stability. LiCoO2(LCO)/SP-PCPE/Li batteries with higher loading (3-4.4 V, 6 mg cm-2) can work for over 300 cycles at 0.5 C. Even with an ultra-high loading of 16 mg cm-2, LCO/SP-PCPE/Li batteries achieve an excellent cycling performance. This work provides new insights into how to construct a robust interface for solid-state batteries with high-loading cathode.

Unveiling the potential of emergent nanoscale composite polymer electrolytes for safe and efficient all solid-state lithium-ion batteries

Solid-state polymer electrolytes (SSPEs) are promising materials for Li-ion batteries due to their enhanced safety features, which are crucial for preventing short circuits and explosions, replacing traditional liquid electrolytes with solid electrolytes are increasingly important to improve battery reliability and lifespan. There are essentially three-types of solid-state electrolytes such as solid polymer electrolyte, composite based polymer electrolyte and gel-based polymer electrolyte are largely used in battery applications. Additionally, battery separators must have high ionic conductivity and porosity to boost safety and performance. Durable solid composites electrolytes with excellent thermal and mechanical properties are key to reducing the risk of lithium dendrite growth, thereby improving overall battery efficiency. Despite their potential, challenges like scalability, cost and real-world performance optimizations still need to be addressed.

Advancements and Challenges in Organic-Inorganic Composite Solid Electrolytes for All-Solid-State Lithium Batteries

To address the limitations of contemporary lithium-ion batteries, particularly their low energy density and safety concerns, all-solid-state lithium batteries equipped with solid-state electrolytes have been identified as an up-and-coming alternative. Among the various SEs, organic-inorganic composite solid electrolytes (OICSEs) that combine the advantages of both polymer and inorganic materials demonstrate promising potential for large-scale applications. However, OICSEs still face many challenges in practical applications, such as low ionic conductivity and poor interfacial stability, which severely limit their applications. This review provides a comprehensive overview of recent research advancements in OICSEs. Specifically, the influence of inorganic fillers on the main functional parameters of OICSEs, including ionic conductivity, Li+ transfer number, mechanical strength, electrochemical stability, electronic conductivity, and thermal stability are systematically discussed. The lithium-ion conduction mechanism of OICSE is thoroughly analyzed and concluded from the microscopic perspective. Besides, the classic inorganic filler types, including both inert and active fillers, are categorized with special emphasis on the relationship between inorganic filler structure design and the electrochemical performance of OICSEs. Finally, the advanced characterization techniques relevant to OICSEs are summarized, and the challenges and perspectives on the future development of OICSEs are also highlighted for constructing superior ASSLBs.

Highly Ionic Conductive, Self-Healing, Li10GeP2S12-Filled Composite Solid Electrolytes Based on Reversibly Interlocked Macromolecule Networks for Lithium Metal Batteries with Improved Cycling Stability

Ceramic-polymer composite solid electrolytes (CSEs) have attracted great attention by combining the advantages of polymer electrolytes and inorganic ceramic electrolytes. Herein, Li10GeP2S12 (LGPS) particles are incorporated into poly(ethylene oxide) (PEO)-based reversibly interlocked polymer networks (RILNs) derived from the topological rearrangement of two PEO networks cross-linked by reversible imine bonds and disulfide linkages. A series of highly ionic conductive, self-healing CSEs are obtained accordingly. The interlocking architecture successfully inhibits PEO crystallization, increasing the amorphous phase for Li ion transportation, and stabilizes the conductive pathways of LGPS particles by its unique confinement effect. Meanwhile, the LGPS particles cooperate with the RILN matrix, forming a filler-polymer interfacial phase for additional Li ion transportation and strengthening and toughening the resultant CSEs via the strong intermolecular Li+-O2- interactions. Furthermore, the dynamic characteristics of the included reversible bonds ensure a multiple intrinsic self-healing capability. Consequently, the CSEs containing 15 wt % LGPS deliver a high ionic conductivity (1.06 × 10-3 S cm-1) and high Li ion transference number (∼0.6) at 25 °C, a wide electrochemical stability window (>4.9 V), good mechanical properties (0.63 MPa, 377%), and a stable CSE/Li anode interface. The integrated Li/CSE/LiFePO4 battery exhibits a specific discharge capacity of 110.8 mAh g-1 at 1 C (25 °C) and a capacity retention of 76.9% after 200 cycles. Thanks to the healability, the damaged CSEs can regain the structural integrity, ion conductive capability, and cycling performance of the assembled cells. The present work provides an effective strategy to fabricate CSEs for lithium metal batteries that are workable at ambient temperature.

A-LLTO Nanoparticles Embedded Composite Solid Polymer Electrolyte for Room Temperature Operational Li-metal Batteries

Solid-state batteries (SSBs) have the potential to revolutionize the current energy storage sector. A significant portion of the current development of electric vehicles and the electrification of various appliances relies on Lithium (Li)-ion batteries. However, future energy demands will require the development of stronger and more reliable batteries. This report presents a novel solid state electrolyte (SSE) composed of a self-healing composite solid polymer electrolyte (CSPE) matrix and aluminum-doped (Li0.33La0.56)1.005Ti0.99Al0.01O3 (A-LLTO) nanofillers. The CSPE contains Jeffamine ED-2003 monomer, Benzene-1,3,5-tricarbaldehyde (BTC) crosslinker dissolved in a 1:1 ratio of Dimethylformamide (DMF) to LiPF6, and a certain amount (x) of A-LLTO nanofillers (x = 5, 7.5, 10, 12.5%). A CSPE containing x-amount of A-LLTO fillers (referred to as CAL-x%) demonstrates excellent ion-conducting properties and stable battery performance. The CAL-10% demonstrates 1.1 × 10-3 S cm-1 of ionic conductivity at room temperature (RT). A-LLTO nanofillers dispersed uniformly within the polymer matrix form a percolation network, which is believed to improve ionic conductivity and the diffusion of Li+ ions. The CR-2032 cell, consisting of LiFePO4 (LFP)║CAL-10%║Li, at RT offers an initial discharge capacity of ≈165 mAh g-1 at 0.1C rate for 120 cycles with 98.85% coulombic efficiency (C.E.).

Accelerating the Development of LLZO in Solid-State Batteries Toward Commercialization: A Comprehensive Review

Solid-state batteries (SSBs) are under development as high-priority technologies for safe and energy-dense next-generation electrochemical energy storage systems operating over a wide temperature range. Solid-state electrolytes (SSEs) exhibit high thermal stability and, in some cases, the ability to prevent dendrite growth through a physical barrier, and compatibility with the "holy grail" metallic lithium. These unique advantages of SSEs have spurred significant research interests during the last decade. Garnet-type SSEs, that is, Li7La3Zr2O12 (LLZO), are intensively investigated due to their high Li-ion conductivity and exceptional chemical and electrochemical stability against lithium metal anodes. However, poor interfacial contact with cathode materials, undesirable lithium plating along grain boundaries, and moisture-induced chemical degradation greatly hinder the practical implementation of LLZO-based SSEs for SSBs. In this review, the recent advances in synthesis methods, modification strategies, corresponding mechanisms, and applications of garnet-based SSEs in SSBs are critically summarized. Furthermore, a comprehensive evaluation of the challenges and development trends of LLZO-based electrolytes in practical applications is presented to accelerate their development for high-performance SSBs.

Small Additives Make Big Differences: A Review on Advanced Additives for High-Performance Solid-State Li Metal Batteries

Solid-state lithium (Li) metal batteries, represent a significant advancement in energy storage technology, offering higher energy densities and enhanced safety over traditional Li-ion batteries. However, solid-state electrolytes (SSEs) face critical challenges such as lower ionic conductivity, poor stability at the electrode-electrolyte interface, and dendrite formation, potentially leading to short circuits and battery failure. The introduction of additives into SSEs has emerged as a transformative approach to address these challenges. A small amount of additives, encompassing a range from inorganic and organic materials to nanostructures, effectively improve ionic conductivity, drawing it nearer to that of their liquid counterparts, and strengthen mechanical properties to prevent cracking of SSEs and maintain stable interfaces. Importantly, they also play a critical role in inhibiting the growth of dendritic Li, thereby enhancing the safety and extending the lifespan of the batteries. In this review, the wide variety of additives that have been investigated, is comprehensively explored, emphasizing how they can be effectively incorporated into SSEs. By dissecting the operational mechanisms of these additives, the review hopes to provide valuable insights that can help researchers in developing more effective SSEs, leading to the creation of more efficient and reliable solid-state Li metal batteries.

Electrolytes for Sodium Ion Batteries: The Current Transition from Liquid to Solid and Hybrid systems

Sodium-ion batteries (NIBs) have recently garnered significant interest in being employed alongside conventional lithium-ion batteries, particularly in applications where cost and sustainability are particularly relevant. The rapid progress in NIBs will undoubtedly expedite the commercialization process. In this regard, tailoring and designing electrolyte formulation is a top priority, as they profoundly influence the overall electrochemical performance and thermal, mechanical, and dimensional stability. Moreover, electrolytes play a critical role in determining the system's safety level and overall lifespan. This review delves into recent electrolyte advancements from liquid (organic and ionic liquid) to solid and quasi-solid electrolyte (dry, hybrid, and single ion conducting electrolyte) for NIBs, encompassing comprehensive strategies for electrolyte design across various materials, systems, and their functional applications. The objective is to offer strategic direction for the systematic production of safe electrolytes and to investigate the potential applications of these designs in real-world scenarios while thoroughly assessing the current obstacles and forthcoming prospects within this rapidly evolving field.

Progress of Polymer Electrolytes Worked in Solid-State Lithium Batteries for Wide-Temperature Application

Solid-state Li-ion batteries have emerged as the most promising next-generation energy storage systems, offering theoretical advantages such as superior safety and higher energy density. However, polymer-based solid-state Li-ion batteries face challenges across wide temperature ranges. The primary issue lies in the fact that most polymer electrolytes exhibit relatively low ionic conductivity at or below room temperature. This sensitivity to temperature variations poses challenges in operating solid-state lithium batteries at sub-zero temperatures. Moreover, elevated working temperatures lead to polymer shrinkage and deformation, ultimately resulting in battery failure. To address this challenge of polymer-based solid-state batteries, this review presents an overview of various promising polymer electrolyte systems. The review provides insights into the temperature-dependent physical and electrochemical properties of polymers, aiming to expand the temperature range of operation. The review also further summarizes modification strategies for polymer electrolytes suited to diverse temperatures. The final section summarizes the performance of various polymer-based solid-state batteries at different temperatures. Valuable insights and potential future research directions for designing wide-temperature polymer electrolytes are presented based on the differences in battery performance. This information is intended to inspire practical applications of wide-temperature polymer-based solid-state batteries.

Research Progress on the Composite Methods of Composite Electrolytes for Solid-State Lithium Batteries

In the current challenging energy storage and conversion landscape, solid-state lithium metal batteries with high energy conversion efficiency, high energy density, and high safety stand out. Due to the limitations of material properties, it is difficult to achieve the ideal requirements of solid electrolytes with a single-phase electrolyte. A composite solid electrolyte is composed of two or more different materials. Composite electrolytes can simultaneously offer the advantages of multiple materials. Through different composite methods, the merits of various materials can be incorporated into the most essential part of the battery in a specific form. Currently, more and more researchers are focusing on composite methods for combining components in composite electrolytes. The ion transport capacity, interface stability, machinability, and safety of electrolytes can be significantly improved by selecting appropriate composite methods. This review summarizes the composite methods used for the components of composite electrolytes, such as filler blending, embedded framework, and multilayer bonding. It also discusses the future development trends of all-solid-state lithium batteries (ASSLBs).

Solvent-Mediated Synthesis and Characterization of Li3InCl6 Electrolytes for All-Solid-State Li-Ion Battery Applications

Superionic halides have attracted widespread attention as solid electrolytes due to their excellent ionic conductivity, soft texture, and stability toward high-voltage electrode materials. Among them, Li3InCl6 has aroused interest since it can be easily synthesized in water or ethanol. However, investigations into the influence of solvents on both the crystal structure and properties remain unexplored. In this work, Li3InCl6 is synthesized by three different solvents: water, ethanol, and water-ethanol mixture, and the difference in properties has been studied. The results show that the product obtained by the ethanol solvent demonstrates the largest unit cell parameters with more vacancies, which tend to crystallize on the (131) plane and provide the 3D isotropic network migration for lithium-ions. Thus, it exhibits the highest ionic conductivity (1.06 mS cm-1) at room temperature and the lowest binding energy (0.272 eV). The assembled all-solid-state lithium metal batteries (ASSLMBs) employing Li3InCl6 electrolytes demonstrate a high initial discharge capacity of 153.9 mA h g-1 at 0.1 C (1 C = 170 mA h g-1) and the reversible capacity retention rate can reach 82.83% after 50 cycles. This work studies the difference in ionic conductivity between Li3InCl6 electrolytes synthesized by different solvents, which can provide a reference for the future synthesis of halide electrolytes and enable their practical application in halide-based ASSLMBs with a high energy density.

Composition regulation of polyacrylonitrile-based polymer electrolytes enabling dual-interfacially stable solid-state lithium batteries

The polyacrylonitrile (PAN) is an attractive matrix of polymer electrolytes owing to its wide electrochemical window and strong coordination with Li salts. However, the PAN-based electrolytes undergo severe interfacial problems from both cathode and anode sides, including uneven ionic transfer induced by high rigidity of dry PAN-based polymer, as well as inferior stability against Li-metal anode. Herein, the composition regulation of PAN-based electrolytes is proposed by introducing succinonitrile (SN) plastic crystal and LiNO3 salt for the construction of interfacially stable solid-state lithium batteries. The plastic nature of SN enables the rapid ionic transfer in electrolytes, along with the establishment of conformally interfacial contacts. Meanwhile, a stable solid-electrolyte-interface (SEI) layer consisting of Li3N and LiNO2 is in-situ formed at Li/electrolyte interface, contributing to the inhibition of uncontrol reactions between PAN and Li-metal. Consequently, the resultant Li symmetric cell delivers an extended critical current density of 1.7 mA cm-2 and an outstanding cycling lifespan of 700 h at 0.1 mA cm-2. Moreover, the corresponding solid-state LiNi0.6Co0.2Mn0.2O2/Li full cell shows an initial discharge capacity of 161 mAh/g followed by an outstanding capacity retention of 88.7 % after 100 cycles at 0.1C. This work paves the way for application of PAN-based electrolytes in the field of solid-state batteries by facile composition regulation.

PVDF-HFP Based, Quasi-Solid Nanocomposite Electrolytes for Lithium Metal Batteries

Composite polymer electrolytes are systems of choice for future solid-state lithium metal batteries (LMBs). Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) is among the most interesting matrices to develop new generation quasi-solid electrolytes (QSEs). Here it is reported on nanocomposites made of PVDF-HFP and pegylated SiO2 nanoparticles. Silica-based hybrid nanofillers are obtained by grafting chains of poly(ethylene glycol) methyl ether (PEG) with different molecular weight on the surface of silica nanoparticles. The functionalized nanofiller improves the mechanical, transport and electrochemical properties of the QSEs, which show good ionic conductivity values and high resistance against dendrite penetration, ensuring boosted long and safe device operation. The most promising result is obtained by dispersing 5 wt% of SiO2 functionalized with short PEG chains (PEG750, Mw = 750 g mol-1) in the PVDF-HFP matrix with an ease solvent-casting procedure. It shows ionic conductivity of 0.1 mS cm-1 at 25 °C, more than 250 h resistance to stripping/plating, and impressive results during cycling tests in LMB with LiFePO4 cathode.

High-Entropy Polymer Electrolytes Derived from Multivalent Polymeric Ligands for Solid-State Lithium Metal Batteries with Accelerated Li+ Transport

Solid-state polymer-based electrolytes (SSPEs) exhibit great possibilities in realizing high-energy-density solid-state lithium metal batteries (SSLMBs). However, current SSPEs suffer from low ionic conductivity and unsatisfactory interfacial compatibility with metallic Li because of the high crystallinity of polymers and sluggish Li+ movement in SSPEs. Herein, differing from common strategies of copolymerization, a new strategy of constructing a high-entropy SSPE from multivariant polymeric ligands is proposed. As a protocol, poly(vinylidene fluoride-co-hexafluoropropylene) (PH) chains are grafted to the demoed polyethylene imine (PEI) with abundant -NH2 groups via a click-like reaction (HE-PEIgPHE). Compared to a PH-based SSPE, our HE-PEIgPHE shows a higher modulus (6.75 vs 5.18 MPa), a higher ionic conductivity (2.14 × 10-4 vs 1.03 × 10-4 S cm-1), and a higher Li+ transference number (0.55 vs 0.42). A Li|HE-PEIgPHE|Li cell exhibits a long lifetime (1500 h), and a Li|HE-PEIgPHE|LiFePO4 cell delivers an initial capacity of 160 mAh g-1 and a capacity retention of 98.7%, demonstrating the potential of our HE-PEIgPHE for the SSLMBs.

Interface-Targeting Carrier-Catalytic Integrated Design Contributing to Lithium Dihalide-Rich SEI toward High Interface Stability for Long-Life Solid-State Lithium-Metal Batteries

The generation of solid electrolyte interphase (SEI) largely determines the comprehensive performance of all-solid-state batteries. Herein, a novel "carrier-catalytic" integrated design is strategically exploited to in situ construct a stable LiF-LiBr rich SEI by improving the electron transfer kinetics to accelerate the bond-breaking dynamics. Specifically, the high electron transport capacity of Br-TPOM skeleton increases the polarity of C-Br, thus promoting the generation of LiBr. Then, the enhancement of electron transfer kinetics further promotes the fracture of C-F from TFSI- to form LiF. Finally, the stable and homogeneous artificial-SEI with enriched lithium dihalide is constructed through the in situ co-growth mechanism of LiF and LiBr, which facilitatse the Li-ion transport kinetics and regulates the lithium deposition behavior. Impressively, the PEO-Br-TPOM paired with LiFePO4 delivers ultra-long cycling stability over 1000 cycles with 81 % capacity retention at 1 C while the pouch cells possess 88 % superior capacity retention after 550 cycles with initial discharge capacity of 145 mAh g-1at 0.2 C in the absence of external pressure. Even under stringent conditions, the practical pouch cells possess the practical capacity with stable electric quantities plateau in 30 cycles demonstrates its application potential in energy storage field.

Surface-enhanced Raman scattering spectroscopy monitoring and degradation of organic pollutants using a novel nanowire

A multifunctional Ag/AlOOH nanowires (ANW) composite substrate was constructed, which not only accomplishes highly sensitive detection of organic dye molecules, but also has excellent performance in the degradation of pollutants. The ANW in the Ag/ANW substrate possesses a high aspect ratio, which extends the distribution area of Ag and enables a large number of hot spots on the active substrate. Additionally, due to the abundant OH groups on the ANW, there is an increased number of anchor sites for adsorbed metal ions in the Ag/ANW compound, thus contributing to the enhancement and degradation of molecules. Moreover, the constructed multifunctional Ag/ANW nanocomplexes also show great promise for practical applications, providing a reference for the detection and degradation of contaminants.

Enabling High-Performance Hybrid Solid-State Batteries by Improving the Microstructure of Free-Standing LATP/LFP Composite Cathodes

The phosphate lithium-ion conductor Li1.5Al0.5Ti1.5(PO4)3 (LATP) is an economically attractive solid electrolyte for the fabrication of safe and robust solid-state batteries, but high sintering temperatures pose a material engineering challenge for the fabrication of cell components. In particular, the high surface roughness of composite cathodes resulting from enhanced crystal growth is detrimental to their integration into cells with practical energy density. In this work, we demonstrate that efficient free-standing ceramic cathodes of LATP and LiFePO4 (LFP) can be produced by using a scalable tape casting process. This is achieved by adding 5 wt % of Li2WO4 (LWO) to the casting slurry and optimizing the fabrication process. LWO lowers the sintering temperature without affecting the phase composition of the materials, resulting in mechanically stable, electronically conductive, and free-standing cathodes with a smooth, homogeneous surface. The optimized cathode microstructure enables the deposition of a thin polymer separator attached to the Li metal anode to produce a cell with good volumetric and gravimetric energy densities of 289 Wh dm-3 and 180 Wh kg-1, respectively, on the cell level and Coulombic efficiency above 99% after 30 cycles at 30 °C.

An Advanced Gel Polymer Electrolyte for Solid-State Lithium Metal Batteries

All-solid-state lithium metal batteries (LMBs) are regarded as one of the most viable energy storage devices and their comprehensive properties are mainly controlled by solid electrolytes and interface compatibility. This work proposes an advanced poly(vinylidene fluoride-hexafluoropropylene) based gel polymer electrolyte (AP-GPEs) via functional superposition strategy, which involves incorporating butyl acrylate and polyethylene glycol diacrylate as elastic optimization framework, triethyl phosphate and fluoroethylene carbonate as flameproof liquid plasticizers, and Li7La3Zr2O12 nanowires (LLZO-w) as ion-conductive fillers, endowing the designed AP-GPEs/LLZO-w membrane with high mechanical strength, excellent flexibility, low flammability, low activation energy (0.137 eV), and improved ionic conductivity (0.42 × 10-3 S cm-1 at 20 °C) due to continuous ionic transport pathways. Additionally, the AP-GPEs/LLZO-w membrane shows good safety and chemical/electrochemical compatibility with the lithium anode, owing to the synergistic effect of LLZO-w filler, flexible frameworks, and flame retardants. Consequently, the LiFePO4/Li batteries assembled with AP-GPEs/LLZO-w electrolyte exhibit enhanced cycling performance (87.3% capacity retention after 600 cycles at 1 C) and notable high-rate capacity (93.3 mAh g-1 at 5 C). This work proposes a novel functional superposition strategy for the synthesis of high-performance comprehensive GPEs for LMBs.

Design advanced lithium metal anode materials in high energy density lithium batteries

Nowadays, the ongoing electrical vehicles and energy storage devices give a great demand of high-energy-density lithium battery. The commercial graphite anode has been reached the limit of the theoretical capacity. Herein, we introduce lithium metal anode to demonstrate the promising anode which can replace graphite. Lithium metal has a high theoretical capacity and the lowest electrochemical potential. Hence, using lithium metal as the anode material of lithium batteries can reach the limit of energy and power density of lithium batteries. However, lithium metal has huge flaw such as unstable SEI layer, volume change and dendrites formation. Therefore, we give a review of the lithium metal anode on its issues and introduce the existing research to overcome these. Besides, we give the perspective that the engineering problems also restrict the commercial use of lithium metal. This review provides the reasonable method to enhance the lithium metal performance and give the development direction for the subsequent research.

Synthesis and Properties of Polyvinylidene Fluoride-Hexafluoropropylene Copolymer/Li6PS5Cl Gel Composite Electrolyte for Lithium Solid-State Batteries

Gel electrolytes for lithium-ion batteries continue to replace the organic liquid electrolytes in conventional batteries due to their advantages of being less prone to leakage and non-explosive and possessing a high modulus of elasticity. However, the development of gel electrolytes has been hindered by their generally low ionic conductivity at room temperature and high interfacial impedance with electrodes. In this paper, a poly (vinylidene fluoride)-hexafluoropropylene copolymer (PVdF-HFP) with a flexible structure, Li6PS5Cl (LPSCl) powder of the sulfur-silver-germanium ore type, and lithium perchlorate salt (LiClO4) were prepared into sulfide gel composite electrolyte films (GCEs) via a thermosetting process. The experimental results showed that the gel composite electrolyte with 1% LPSCl in the PVdF-HFP matrix exhibited an ionic conductivity as high as 1.27 × 10-3 S·cm-1 at 25 °C and a lithium ion transference number of 0.63. The assembled LiFePO4||GCEs||Li batteries have excellent rate (130 mAh·g-1 at 1 C and 54 mAh·g-1 at 5 C) and cycling (capacity retention was 93% after 100 cycles at 0.1 C and 80% after 150 cycles at 0.2 C) performance. This work provides new methods and strategies for the design and fabrication of solid-state batteries with high ionic conductivity and high specific energy.

All-Perfluorosulfonated-Ionomer Composite Membranes Containing Blow-Spun Fibers: Effect of a Thin Fiber Framework on Proton Conductivity and Mechanical Properties

In this study, thin fiber composite polymer electrolyte membranes (PEMs) were prepared using short side-chain perfluorosulfonic acid (PFSA) ionomers, Aquivion, to create composite PEMs with improved proton conductivity and improved mechanical properties. PFSA thin fiber webs prepared by blow spinning and successive hot pressing were used as the porous substrate. Herein, PFSA ionomers were used for both the substrate and the matrix of the composite PEMs, and their structures, properties, and fuel cell performance were characterized. By adding the PFSA thin fiber webs to the matrix, the proton conductivity was enhanced and the mechanical properties were slightly improved. The prepared PFSA thin fiber composite PEM showed better FC performance than that of the pristine PFSA one for the high-temperature low-humidity condition in addition to the low-temperature high-humidity one. To the best of our knowledge, this is the first report on the all PFSA composite membranes containing a PFSA thin fiber framework.

Solid-State Electrolytes and Electrode/Electrolyte Interfaces in Rechargeable Batteries

Solid-state batteries (SSBs) are considered to be one of the most promising candidates for next-generation energy storage systems due to the high safety, high energy density and wide operating temperature range of solid-state electrolytes (SSEs) they use. Unfortunately, the practical application of SSEs has rarely been successful, which is largely attributed to the low chemical stability and ionic conductivity, ineluctable solid-solid interface issues including limited ion transport channels, high energy barriers, and poor interface contact. A comprehensive understanding of ion transport mechanisms of various SSEs, interactions between fillers and polymer matrixes and the role of the interface in SSBs are indispensable for rational design and performance optimization of novel electrolytes. The categories, research advances and ion transport mechanism of inorganic glass/ceramic electrolytes, polymer-based electrolytes and corresponding composite electrolytes are detailly summarized and discussed. Moreover, interface contact and compatibility between electrolyte and cathode/anode are also briefly discussed. Furthermore, the electrochemical characterization methods of SSEs used in different types of SSBs are also introduced. On this basis, the principles and prospects of novel SSEs and interface design are curtly proposed according to the development requirements of SSBs. Moreover, the advanced characterizations for real-time monitoring of interface changes are also brought forward to promote the development of SSBs.

Dielectric Filler-Induced Hybrid Interphase Enabling Robust Solid-State Li Metal Batteries at High Areal Capacity

The fillers in composite solid-state electrolyte are mainly responsible for the enhancement of the conduction of Li ions but barely regulate the formation of solid electrolyte interphase (SEI). Herein, a unique filler of dielectric NaNbO3 for the poly(vinylidene fluoride) (PVDF)-based polymer electrolyte, which is subjected to the exchange of Li+ and Na+ during cycling, is reported and the substituted Na+ is engaged in the construction of a fluorinated Li/Na hybrid SEI with high Young's modulus, facilitating the fast transport of Li+ at the interface at a high areal capacity and suppressing the Li dendrite growth. The dielectric NaNbO3 also induces the generation of high-dielectric β phase of PVDF to promote the dissociation of Li salt. The Li/Li symmetrical cell exhibits a long-term dendrite-free cycling over 600 h at a high areal capacity of 3 mA h cm-2 . The LiNi0.8 Mn0.1 Co0.1 O2 /Li solid-state cells with NaNbO3 stably cycle 2200 times at 2 C and that paired with high-loading cathode (10 mg cm-2 ) can stably cycle for 150 times and exhibit excellent performances at -20 °C. This work provides a novel design principle of fillers undertaking interfacial engineering in composite solid-state electrolytes for developing the safe and stable solid-state lithium metal battery.

Reliable lateral Zn deposition along (002) plane by oxidized PAN separator for zinc-ion batteries

Aqueous zinc ion batteries (AZIBs) are the promising candidate for energy storage where safety and low cost are the major concerns. However, the uneven and random electrodeposition of Zn has become a serious impediment to the deep recharging of AZIBs. Conventional modifications on zinc substrate can promote homogenous zinc deposition initially, but not sustainably. Here, an oxidized polyacrylonitrile (OPAN) membrane with a conjugated planar structure is proposed as a zinc ion battery separator. This separator can continuously regulate the growth of Zn with (002) texture to inhibit dendrites. In addition, the separator has a fast Zn2+ ion transfer, which can spontaneously repel SO42- and relieve side reactions. As a result, the Zn-symmetric batteries show cycle lifetime of more than 1300 hours at 1 mA cm-2 and 1 mA h cm-2, and kept stable for more than 160 hours even at 65% high discharge of depth (DOD). The MnO2//Zn full celled assembled with an OPAN separator had very little decay for 5000 cycles at 2 A g-1. This work provides a new method for realizing the continuous and uniform deposition of Zn metals, which also provides a new route for batteries with metallic anodes.

Monodispersed Sub-1 nm Inorganic Cluster Chains in Polymers for Solid Electrolytes with Enhanced Li-Ion Transport

The organic-inorganic interfaces can enhance Li+ transport in composite solid-state electrolytes (CSEs) due to the strong interface interactions. However, Li+ non-conductive areas in CSEs with inert fillers will hinder the construction of efficient Li+ transport channels. Herein, CSEs with fully active Li+ conductive networks are proposed to improve Li+ transport by composing sub-1 nm inorganic cluster chains and organic polymer chains. The inorganic cluster chains are monodispersed in polymer matrix by a brief mixed-solvent strategy, their sub-1 nm diameter and ultrafine dispersion state eliminate Li+ non-conductive areas in the interior of inert fillers and filler-agglomeration, respectively, providing rich surface areas for interface interactions. Therefore, the 3D networks connected by the monodispersed cluster chains finally construct homogeneous, large-scale, continuous Li+ fast transport channels. Furthermore, a conjecture about 1D oriented distribution of organic polymer chains along the inorganic cluster chains is proposed to optimize Li+ pathways. Consequently, the as-obtained CSEs possess high ionic conductivity at room temperature (0.52 mS cm-1 ), high Li+ transference number (0.62), and more mobile Li+ (50.7%). The assembled LiFePO4 /Li cell delivers excellent stability of 1000 cycles at 0.5 C and 700 cycles at 1 C. This research provides a new strategy for enhancing Li+ transport by efficient interfaces.

Dry-Processable Polymer Electrolytes for Solid Manufactured Batteries

Designing a solid-state electrolyte that satisfies the operating requirements of solid-state batteries is key to solid-state battery applications. The consensus is that solid-state electrolytes need to allow fast ion transport, while providing better interfacial compatibility and mechanical tolerance. Herein, a simple but effective strategy is proposed, combining hard and soft component polymer systems, to exploit a solid polymer electrolyte (SPE) with a 3D network via an in situ graft polymerization. The 3D structure is constructed by a hard cellulose nanocrystal (CNC) as the skeleton and a soft polyacrylonitrile (PAN) as the filler through a dry-processing method. The reported systems have several advantages, including ease of processing, only requiring using an exceedingly small amount of solvent, light weight (ρ = 1.2 g cm-3), excellent mechanical stability (tensile strength of 9.5 MPa), and high ionic conductivity (3.9 × 10-4 S cm-1, 18 °C) and migration number (tLi+ = 0.8). In particular, the high conductivity is enabled: the efficient Li+ transportation path constructed between CNC-PAN powders and abundant sulfonate radicals and hydroxyl groups on the CNC surface acts as the bridge of Li+ transition. When the CNCs are grafted onto the PAN polymer, the dipole-dipole interaction between the nitrile groups of the PAN and the hydroxyl groups of the CNCs can help to improve the mechanical stability and ionic conductivity of the SPE. Moreover, a tightly formed interface between SPE and LiFePO4 (LFP)/carbon black/SPE cathode can be achieved in an assembled solid-state battery by hot pressing, thus further enhancing the battery's performance.

An LLTO-containing heterogeneous composite electrolyte with a stable interface for solid-state lithium metal batteries

The interaction between Li0.33La0.56TiO3 (LLTO) and metallic lithium leads to severe interfacial instability of LLTO-containing solid-state electrolytes with a lithium metal anode. To improve the interfacial stability, a heterogeneous composite electrolyte PVDF-HFP@LLTO/PEO (PLTP) is designed and fabricated with a PEO electrolyte layer adhered to the PVDF-HFP@LLTO (PLT) electrolyte membrane. The PLTP heterogeneous composite electrolyte exhibits a superior ionic conductivity of 3.23 × 10-4 S cm-1 at 60 °C and a highly stable electrochemical window of up to 4.7 V (vs. Li/Li+). Remarkably, taking advantage of the effective protection of the PEO electrolyte layer, the chemical stability at the electrolyte/lithium metal anode interface is significantly enhanced. As a result, solid-state Li||LiFePO4 and Li||LiNi0.6Co0.2Mn0.2O2 batteries with the heterogeneous electrolyte exhibit an impressive electrochemical performance with high Coulombic efficiency and stable cycling capability. The strengthened interfacial stability enables the heterogeneous electrolyte to be a promising alternative for the further development of solid-state lithium metal batteries.

Advancements in Performance Optimization of Electrospun Polyethylene Oxide-Based Solid-State Electrolytes for Lithium-Ion Batteries

Polyethylene oxide (PEO)-based solid-state electrolytes for lithium-ion batteries have garnered significant interest due to their enhanced potential window, high energy density, and improved safety features. However, the issues such as low ionic conductivity at ambient temperature, substantial ionic conductivity fluctuations with temperature changes, and inadequate electrolyte interfacial compatibility hinder their widespread applications. Electrospinning is a popular approach for fabricating solid-state electrolytes owing to its superior advantages of adjustable component constitution and the unique internal fiber structure of the resultant electrolytes. Thus, this technique has been extensively adopted in related studies. This review provides an overview of recent advancements in optimizing the performance of PEO solid-state electrolytes via electrospinning technology. Initially, the impacts of different lithium salts and their concentrations on the performance of electrospun PEO-based solid-state electrolytes were compared. Subsequently, research pertaining to the effects of various additives on these electrolytes was reviewed. Furthermore, investigations concerning the enhancement of electrospun solid-state electrolytes via modifications of PEO molecular chains are herein detailed, and lastly, the prevalent challenges and future directions of PEO-based solid-state electrolytes for lithium-ion batteries are summarized.

Dendritic Solid Polymer Electrolytes: A New Paradigm for High-Performance Lithium-Based Batteries

Li-ions battery is widely used and recognized, but its energy density based on organic electrolytes has approached the theoretical upper limit, while the use of organic electrolytes also brings some safety hazards (leakage and flammability). Polymer electrolytes (PEs) are expected to fundamentally solve the safety problem and improve energy density. Therefore, Li-ions battery based on solid PE has become a research hotspot in recent years. However, low ionic conductivity and poor mechanical properties, as well as a narrow electrochemical window limit its further development. Dendritic PEs with unique topology structure has low crystallinity, high segmental mobility, and reduced chain entanglement, providing a new avenue for designing high-performance PEs. In this review, the basic concept and synthetic chemistry of dendritic polymers are first introduced. Then, this story will turn to how to balance the mechanical properties, ionic conductivity, and electrochemical stability of dendritic PEs from synthetic chemistry. In addition, accomplishments on dendritic PEs based on different synthesis strategies and recent advances in battery applications are summarized and discussed. Subsequently, the ionic transport mechanism and interfacial interaction are deeply analyzed. In the end, the challenges and prospects are outlined to promote further development in this booming field.

A reflection on polymer electrolytes for solid-state lithium metal batteries

Before the debut of lithium-ion batteries (LIBs) in the commodity market, solid-state lithium metal batteries (SSLMBs) were considered promising high-energy electrochemical energy storage systems before being almost abandoned in the late 1980s because of safety concerns. However, after three decades of development, LIB technologies are now approaching their energy content and safety limits imposed by the rocking chair chemistry. These aspects are prompting the revival of research activities in SSLMB technologies at both academic and industrial levels. In this perspective article, we present a personal reflection on solid polymer electrolytes (SPEs), spanning from early development to their implementation in SSLMBs, highlighting key milestones. In particular, we discuss the SPEs' characteristics taking into account the concept of coupled and decoupled SPEs proposed by C. Austen Angell in the early 1990s. Possible remedies to improve the physicochemical and electrochemical properties of SPEs are also examined. With this article, we also aim to highlight the missing blocks in building ideal SSLMBs and stimulate research towards innovative electrolyte materials for future rechargeable high-energy batteries.

Dual-Coordination-Induced Poly(vinylidene fluoride)/Li6.4Ga0.2La3Zr2O12/Succinonitrile Composite Solid Electrolytes Toward Enhanced Rate Performance in All-Solid-State Lithium Batteries

Pursuing high energy and power density in all-solid-state lithium batteries (ASSLBs) has been the focus of attention. However, due to their inferior ion transport, their rate performance is limited compared to traditional lithium-ion batteries. Herein, a dual-coordination mechanism is first proposed to construct a high-performance poly(vinylidene fluoride)/Li6.4Ga0.2La3Zr2O12/succinonitrile (PVDF/LLZO/SN) composite solid electrolyte. The dual-coordination interactions of SN with both LLZO and Li+ in lithium salts allow SN to act like a branched chain of PVDF, realizing an increase in the free volume of the composite electrolyte. Meanwhile, SN molecules are immobilized within the electrolyte membrane by coordinating with LLZO, ensuring good interfacial stability. Profiting from the dual-coordination mechanism, the PVDF/LLZO/SN composite solid electrolyte combines enhanced electrochemical performance and interfacial compatibility. When applied to ASSLBs, the composite solid electrolyte enables the battery to operate at rates up to 6 C. The LiFePO4/Li batteries operated at 4 C can still deliver a high capacity retention rate of 96.4% after 50 cycles. Notably, these batteries also exhibit good long-cycle stability. After 500 cycles at 0.5 C, the discharge capacity was maintained at 145.9 mAh g-1.

Cycling of block copolymer composites with lithium-conducting ceramic nanoparticles

Solid polymer and perovskite-type ceramic electrolytes have both shown promise in advancing solid-state lithium metal batteries. Despite their favorable interfacial stability against lithium metal, polymer electrolytes face issues due to their low ionic conductivity and poor mechanical strength. Highly conductive and mechanically robust ceramics, on the other hand, cannot physically remain in contact with redox-active particles that expand and contract during charge-discharge cycles unless excessive pressures are used. To overcome the disadvantages of each material, polymer-ceramic composites can be formed; however, depletion interactions will always lead to aggregation of the ceramic particles if a homopolymer above its melting temperature is used. In this study, we incorporate Li_0.33La_0.56TiO₃ (LLTO) nanoparticles into a block copolymer, polystyrene-b-poly (ethylene oxide) (SEO), to develop a polymer-composite electrolyte (SEO-LLTO). TEMs of the same nanoparticles in polyethylene oxide (PEO) show highly aggregated particles whereas a significant fraction of the nanoparticles are dispersed within the PEO-rich lamellae of the SEO-LLTO electrolyte. We use synchrotron hard x-ray microtomography to study the cell failure and interfacial stability of SEO-LLTO in cycled lithium-lithium symmetric cells. Three-dimensional tomograms reveal the formation of large globular lithium structures in the vicinity of the LLTO aggregates. Encasing the SEO-LLTO between layers of SEO to form a "sandwich" electrolyte, we prevent direct contact of LLTO with lithium metal, which allows for the passage of seven-fold higher current densities without signatures of lithium deposition around LLTO. We posit that eliminating particle clustering and direct contact of LLTO and lithium metal through dry processing techniques is crucial to enabling composite electrolytes.

Recent advances and interfacial challenges in solid-state electrolytes for rechargeable Li-air batteries

Among the promising batteries for electric vehicles, rechargeable Li-air (O2) batteries (LABs) have risen keen interest due to their high energy density. However, safety issues of conventional nonaqueous electrolytes remain the bottleneck of practical implementation of LABs. Solid-state electrolytes (SSEs) with non-flammable and eco-friendly properties are expected to alleviate their safety concerns, which have become a research focus in the research field of LABs. Herein, we present a systematic review on the progress of SSEs for rechargeable LABs, mainly focusing on the interfacial issues existing between the SSEs and electrodes. The discussion highlights the challenges and feasible strategies for designing suitable SSEs for LABs.

A Flexible Lithium-Ion-Conducting Membrane with Highly Loaded Titanium Oxide Nanoparticles to Promote Charge Transfer for Lithium-Air Battery

In this research, we aim to investigate a flexible composite lithium-ion-conducting membrane (FC-LICM) consisting of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and titanium dioxide (TiO2) nanoparticles with a TiO2-rich configuration. PVDF-HFP was selected as the host polymer owing to its chemically compatible nature with lithium metal. TiO2 (40-60 wt%) was incorporated into the polymer matrix, and the FC-LICM charge transfer resistance values (Rct) were reduced by two-thirds (from 1609 Ω to 420 Ω) at the 50 wt% TiO2 loading compared with the pristine PVDF-HFP. This improvement may be attributed to the electron transport properties enabled by the incorporation of semiconductive TiO2. After being immersed in an electrolyte, the FC-LICM also exhibited a Rct that was lower by 45% (from 141 to 76 Ω), suggesting enhanced ionic transfer upon the addition of TiO2. The TiO2 nanoparticles in the FC-LICM facilitated charge transfers for both electron transfer and ionic transport. The FC-LICM incorporated at an optimal load of 50 wt% TiO2 was assembled into a hybrid electrolyte Li-air battery (HELAB). This battery was operated for 70 h with a cut-off capacity of 500 mAh g-1 in a passive air-breathing mode under an atmosphere with high humidity. A 33% reduction in the overpotential of the HELAB was observed in comparison with using the bare polymer. The present work provides a simple FC-LICM approach for use in HELABs.

Advanced Composite Solid Electrolytes for Lithium Batteries: Filler Dimensional Design and Ion Path Optimization

Composite solid electrolytes are considered to be the crucial components of all-solid-state lithium batteries, which are viewed as the next-generation energy storage devices for high energy density and long working life. Numerous studies have shown that fillers in composite solid electrolytes can effectively improve the ion-transport behavior, the essence of which lies in the optimization of the ion-transport path in the electrolyte. The performance is closely related to the structure of the fillers and the interaction between fillers and other electrolyte components including polymer matrices and lithium salts. In this review, the dimensional design of fillers in advanced composite solid electrolytes involving 0D-2D nanofillers, and 3D continuous frameworks are focused on. The ion-transport mechanism and the interaction between fillers and other electrolyte components are highlighted. In addition, sandwich-structured composite solid electrolytes with fillers are also discussed. Strategies for the design of composite solid electrolytes with high room temperature ionic conductivity are summarized, aiming to assist target-oriented research for high-performance composite solid electrolytes.

LiNO3-Assisted Succinonitrile-Based Solid-State Electrolyte for Long Cycle Life toward a Li-Metal Anode via an In Situ Thermal Polymerization Method

Succinonitrile (SN)-based electrolytes have a great potential for the practical application of all-solid-state lithium-metal batteries (ASSLMBs) due to their high room-temperature ionic conductivity, broad electrochemical window, and favorable thermal stability. Nevertheless, the poor mechanical strength and low stability toward Li metal hinder the further application of SN-based electrolytes to ASSLMBs. In this work, the LiNO₃-assisted SN-based electrolytes are synthesized via an in situ thermal polymerization method. With this method, the mechanical problem is negligible, and the stability of the electrolyte enhances tremendously toward Li metal due to the addition of LiNO₃. The LiNO₃-assisted electrolytes exhibit a high ionic conductivity of 1.4 mS cm^-1 at 25 °C, a wide electrochemical window (0-4.5 V vs Li⁺/Li), and excellent interfacial compatibility with Li (stable for over 2000 h at a current density of 0.1 mA cm^-1). The LiFePO₄/Li cells with the LiNO₃-assisted electrolytes present significantly enhanced rate capability and cycling performance compared to the control group. NCM622/Li batteries also exhibit good cycling and rate performances with a voltage range of 3.0 to 4.4 V. Furthermore, ex situ SEM and XPS are employed. A compact interface is observed on Li anode after cycling, and the polymerization of SN is found to be suppressed. This paper will promote the development of practical application of SN-based ASSLMBs.

Ionic Conduction in Polymer-Based Solid Electrolytes

Good safety, high interfacial compatibility, low cost, and facile processability make polymer-based solid electrolytes promising materials for next-generation batteries. Key issues related to polymer-based solid electrolytes, such as synthesis methods, ionic conductivity, and battery architecture, are investigated in past decades. However, mechanistic understanding of the ionic conduction is still lacking, which impedes the design and optimization of polymer-based solid electrolytes. In this review, the ionic conduction mechanisms and optimization strategies of polymer-based solid electrolytes, including solvent-free polymer electrolytes, composite polymer electrolytes, and quasi-solid/gel polymer electrolytes, are summarized and evaluated. Challenges and strategies for enhancing the ionic conductivity are elaborated, while the ion-pair dissociation, ion mobility, polymer relaxation, and interactions at polymer/filler interfaces are highlighted. This comprehensive review is especially pertinent for the targeted enhancement of the Li-ion conductivity of polymer-based solid electrolytes.

Rational Design of High-Performance PEO/Ceramic Composite Solid Electrolytes for Lithium Metal Batteries

Composite solid electrolytes (CSEs) with poly(ethylene oxide) (PEO) have become fairly prevalent for fabricating high-performance solid-state lithium metal batteries due to their high Li+ solvating capability, flexible processability and low cost. However, unsatisfactory room-temperature ionic conductivity, weak interfacial compatibility and uncontrollable Li dendrite growth seriously hinder their progress. Enormous efforts have been devoted to combining PEO with ceramics either as fillers or major matrix with the rational design of two-phase architecture, spatial distribution and content, which is anticipated to hold the key to increasing ionic conductivity and resolving interfacial compatibility within CSEs and between CSEs/electrodes. Unfortunately, a comprehensive review exclusively discussing the design, preparation and application of PEO/ceramic-based CSEs is largely lacking, in spite of tremendous reviews dealing with a broad spectrum of polymers and ceramics. Consequently, this review targets recent advances in PEO/ceramic-based CSEs, starting with a brief introduction, followed by their ionic conduction mechanism, preparation methods, and then an emphasis on resolving ionic conductivity and interfacial compatibility. Afterward, their applications in solid-state lithium metal batteries with transition metal oxides and sulfur cathodes are summarized. Finally, a summary and outlook on existing challenges and future research directions are proposed.

Suppression of Dehydrofluorination Reactions of a Li0.33La0.557TiO3-Nanofiber-Dispersed Poly(vinylidene fluoride-co-hexafluoropropylene) Electrolyte for Quasi-Solid-State Lithium-Metal Batteries by a Fluorine-Rich Succinonitrile Interlayer

Solid-state lithium-metal batteries have great potential to simultaneously achieve high safety and high energy density for energy storage. However, the low ionic conductivity of the solid electrolyte and large electrode/electrolyte interfacial impedance are bottlenecks. A composite solid electrolyte (CSE) that integrates electrospun Li_0.33La_0.557TiO₃ (LLTO) nanofibers, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is fabricated in this work. The effects of the LLTO filler fraction and morphology (spherical vs fibrous) on CSE conductivity are examined. Additionally, a fluorine-rich interlayer based on succinonitrile, fluoroethylene carbonate, and LiTFSI, denoted as succinonitrile interlayer (SNI), is developed to reduce the large interfacial impedance. The use of SNI rather than a conventional ester-based interlayer (EBI) effectively decreases the Li//CSE interfacial resistance and suppresses unfavorable interfacial side reactions. The LiF- and CF_x-rich solid electrolyte interphase (SEI), derived from SNI, on the Li metal electrode, mitigates the accumulation of dead Li and excessive SEI. Importantly, dehydrofluorination reactions of PVDF-HFP are significantly reduced by the introduction of SNI. A symmetric Li//CSE//Li cell with SNI exhibits a much longer cycle life than that of an EBI counterpart. A Li//CSE@SNI//LiFePO₄ cell shows specific capacities of 150 and 112 mAh g^-1 at 0.1 and 2 C (based on LiFePO₄), respectively. After 100 charge-discharge cycles, 98% of the initial capacity is retained.

The Critical Role of Fillers in Composite Polymer Electrolytes for Lithium Battery

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.

A Brief Review of Gel Polymer Electrolytes Using In Situ Polymerization for Lithium-ion Polymer Batteries

Polymer electrolytes (PEs) have been thoroughly investigated due to their advantages that can prevent severe problems of Li-ion batteries, such as electrolyte leakage, flammability, and lithium dendrite growth to enhance thermal and electrochemical stabilities. Gel polymer electrolytes (GPEs) using in situ polymerization are typically prepared by thermal or UV curing methods by initially impregnating liquid precursors inside the electrode. The in situ method can resolve insufficient interfacial problems between electrode and electrolyte compared with the ex situ method, which could led to a poor cycle performance due to high interfacial resistance. In addition to the abovementioned advantage, it can enhance the form factor of bare cells since the precursor can be injected before polymerization prior to the solidification of the desired shapes. These suggest that gel polymer electrolytes prepared by in situ polymerization are a promising material for lithium-ion batteries.

Directional Ion Transport Enabled by Self-Luminous Framework for High-Performance Quasi-Solid-State Lithium Metal Batteries

Composite gel polymer electrolyte (CGPE), derived from ceramic fillers has emerged as one of the most promising candidates to improve the safety and cycling stability of lithium metal batteries. However, the poor interface compatibility between the ceramic phase and polymer phase in CGPE severely deteriorates lithium-ion pathways and cell performances. In this work, a fluorescent ceramic nanowire network that can palliate the energy barrier of photoinitiators and contribute to preferential nucleation and growth of polymer monomers is developed, thus inducing polymer segment orderly arrangement and tightly combination. A proof-of-concept study lies on fabrications of poly(ethylene oxide) closely coating on the ceramic nanowires, thus dividing the matrix into mesh units that contribute to directional lithium-ion flux and dendrite-free deposition on the metallic anode. The CGPE, based on the state-of-the-art self-luminous framework, facilitates high-performance quasi-solid-state Li||LiFePO₄ cell, registering a high capacity of 143.3 mAh g^-1 after 120 cycles at a mass loading of 12 mg cm^-2 . X-ray computed tomography provides an insight into the relationship between directional lithium-ion diffusion and lithium deposition behavior over the electrochemical processes. The results open a door to improve the electrochemical performances of composite electrolytes in various applications.

Pendant Length-Dependent Electrochemical Performances for Conjugated Organic Polymers as Solid-State Polymer Electrolytes in Lithium Metal Batteries

The development of solid-state polymer electrolytes (SPEs) has been plagued by poor ionic conductivity, low ionic transference number, and limited electrochemical potential window. The exploitation of ionized SPEs is a feasible avenue to solve this problem. Herein, conjugated organic polymers (COPs) with excellent designability and rich pore structures have been selected as platforms for exploration. Three cationic COPs with different chain lengths of quaternary ammonium salts (CbzT@C_x, x = 4, 6, 9) are designed and applied to SPEs for the first time. Meanwhile, the effects of chain lengths on their electrochemical performances are compared. Especially, CbzT@C₉ shows the most attractive electrochemical performance due to its high specific surface area of 212.3 m² g^-1. The larger specific surface area allows more exposure of the long-chain quaternary ammonium cation groups, which is more favorable for the dissociation of lithium salts. Moreover, the flexible long-chain structure increases the compatibility with poly(ethylene oxide) (PEO) and reduces the crystallinity of PEO to some extent. The richer pore structure can accommodate more PEO, further disrupting the crystallinity of PEO and creating more channels for the ether-oxygen chain to transport lithium ions. At 60 °C, the SPE (CbzTM@C₉) presents an excellent ionic conductivity (σ) of 8.00 × 10^-4 S cm^-1. CbzTM@C₉ has a lithium-ion transference number (t_Li+) of 0.48. Thus, the assembled Li/CbzTM@C₉/LiFePO₄ battery provides a good discharge capacity of 158.8 mAh g^-1 at 0.1C. After 70 cycles, the capacity retention rate is 93.8% with a Coulombic efficiency of 98%. The excellent flexibility brings stable power supply capability under various bending angles to the assembled Li/CbzTM@C₉/LiFePO₄ soft-packed battery. The project uses conjugated organic polymers in SPEs and creates an avenue to develop flexible energy storage equipment.

Tailoring Practically Accessible Polymer/Inorganic Composite Electrolytes for All-Solid-State Lithium Metal Batteries: A Review

Highlights

The current issues and recent advances in polymer/inorganic composite electrolytes are reviewed. The molecular interaction between different components in the composite environment is highlighted for designing high-performance polymer/inorganic composite electrolytes. Inorganic filler properties that affect polymer/inorganic composite electrolyte performance are pointed out. Future research directions for polymer/inorganic composite electrolytes compatible with high-voltage lithium metal batteries are outlined.

Abstract

Solid-state electrolytes (SSEs) are widely considered the essential components for upcoming rechargeable lithium-ion batteries owing to the potential for great safety and energy density. Among them, polymer solid-state electrolytes (PSEs) are competitive candidates for replacing commercial liquid electrolytes due to their flexibility, shape versatility and easy machinability. Despite the rapid development of PSEs, their practical application still faces obstacles including poor ionic conductivity, narrow electrochemical stable window and inferior mechanical strength. Polymer/inorganic composite electrolytes (PIEs) formed by adding ceramic fillers in PSEs merge the benefits of PSEs and inorganic solid-state electrolytes (ISEs), exhibiting appreciable comprehensive properties due to the abundant interfaces with unique characteristics. Some PIEs are highly compatible with high-voltage cathode and lithium metal anode, which offer desirable access to obtaining lithium metal batteries with high energy density. This review elucidates the current issues and recent advances in PIEs. The performance of PIEs was remarkably influenced by the characteristics of the fillers including type, content, morphology, arrangement and surface groups. We focus on the molecular interaction between different components in the composite environment for designing high-performance PIEs. Finally, the obstacles and opportunities for creating high-performance PIEs are outlined. This review aims to provide some theoretical guidance and direction for the development of PIEs.

Contiguous High-Mobility Interphase Surrounding Nano-Precipitates in Polymer Matrix Solid Electrolyte

We establish that an interfacial region develops around amorphous Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) nanoparticles in a poly(ethylene oxide) (PEO), which exhibits a 30 times higher Li⁺ mobility than the polymer matrix. To take advantage of this gain throughout the material, nanoparticles must be uniformly dispersed across the matrix, so that the interphase formation is minimally blocked by LATP particle agglomeration. This is achieved using a water-based in situ precipitation method, carefully controlling the temperature schedule during processing. A maximum conductivity of 3.80 × 10^-4 S cm^-1 at 20 °C for an ethylene oxide to Li ratio of 10 is observed at 25 wt % (12.5 vol %) particle loading, as predicted by our tri-phase model. Comparative infrared spectroscopy reveals softening and broadening of the C-O-C stretching modes, reflecting increased disorder in the polymer backbone that is consistent with opening passageways for cation migration. A transition state theory-based approach for analyzing the temperature dependence of the ionic conductivity reveals that thermally activated processes within the interphase benefit more from higher activation entropy than from the decrease in activation enthalpy. The lithium infusion from LATP particles is small, and the charge carriers tend to concentrate in a space-charge configuration near the particle/polymer interface.