Recent Advancements in Polymer-Based Composite Electrolytes for Rechargeable Lithium 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).

An initiator loaded separator triggering in situ polymerization of a poly(1,3-dioxolane) quasi-solid electrolyte for lithium metal batteries

An in situ polymerization strategy is regarded as a promising approach to fabricate gel polymer electrolytes (GPEs) and improve interface contact between the electrolyte and electrodes, in which the initiator is initially dissolved in the precursor solution. Herein, aluminum trifluoromethanesulfonate (Al(OTf)3) is preloaded onto a separator sheet as the initiator to trigger the ring-opening reaction of 1,3-dioxolane (DOL). The polymer matrix near the separator has a higher crystallization degree than that far away from the separator. Fluoroethyl carbonate (FEC) is further introduced as a liquid plasticizer to produce an amorphous GPE for enhanced ionic conductivity and interfacial stability. As a result, the as-synthesized FEC based GPE exhibits a substantial ionic conductivity of 1.5 × 10-4 S cm-1 at room temperature, an expanded electrochemical window of 4.8 V, and a high Li+ transference number of 0.63. The symmetric Li|Li cell exhibits a stable lifespan for 650 h at 1 mA cm-2 and 1 mA h cm-2. Moreover, the LiFePO4 full cell exhibits stable cycling for 300 cycles at 1C with a capacity retention of 94.5%. This work provides a novel idea for the in situ synthesis of advanced GPEs toward practical application of solid-state lithium metal batteries.

Hybrid Solid Polymer Electrolytes Based on Epoxy Resins, Ionic Liquid, and Ceramic Nanoparticles for Structural Applications

Solid polymer electrolytes (SPE) and composite polymer electrolytes (CPE) serve as crucial components in all-solid-state energy storage devices. Structural batteries and supercapacitors present a promising alternative for electric vehicles, integrating structural functionality with energy storage capability. However, despite their potential, these applications are hampered by various challenges, particularly in the realm of developing new solid polymer electrolytes that require more investigation. In this study, novel solid polymer electrolytes and composite polymer electrolytes were synthesized using epoxy resin blends, ionic liquid, lithium salt, and alumina nanoparticles and subsequently characterized. Among the formulations tested, the optimal system, designated as L70P30ILE40Li1MAl2 and containing 40 wt.% of ionic liquid and 5.7 wt.% of lithium salt, exhibited exceptional mechanical properties. It displayed a remarkable storage modulus of 1.2 GPa and reached ionic conductivities of 0.085 mS/cm at 60 °C. Furthermore, a proof-of-concept supercapacitor was fabricated, demonstrating the practical application of the developed electrolyte system.

5.1 µm Ion-Regulated Rigid Quasi-Solid Electrolyte Constructed by Bridging Fast Li-Ion Transfer Channels for Lithium Metal Batteries

An ultra-thin quasi-solid electrolyte (QSE) with dendrite-inhibiting properties is a requirement for achieving high energy density quasi-solid lithium metal batteries (LMBs). Here, a 5.1 µm rigid QSE layer is directly designed on the cathode, in which Kevlar (poly(p-phenylene terephthalate)) nanofibers (KANFs) with negatively charged groups bridging metal-organic framework (MOF) particles are served as a rigid skeleton, and non-flammable deep eutectic solvent is selected to be encapsulated into the MOF channels, combined with in situ polymerization to complete safe electrolyte system with high rigidness and stability. The QSE with constructed topological network demonstrates high rigidity (5.4 GPa), high ionic conductivity (0.73 mS cm-1 at room temperature), good ion-regulated properties, and improved structural stability, contributing to homogenized Li-ion flux, excellent dendrite suppression, and prolonged cyclic performance for LMB. Additionally, ion regulation influences the Li deposition behavior, exhibiting a uniform morphology on the Li-metal surface after cycling. According to density-functional theory, KANFs bridging MOFs as hosts play a vital function in the free-state and fast diffusion dynamics of Li-ions. This work provides an effective strategy for constructing ultrathin robust electrolytes with a novel ionic conduction mode.

Review: Application of Bionic-Structured Materials in Solid-State Electrolytes for High-Performance Lithium Metal Batteries

Solid-state lithium metal batteries (SSLMBs) have gained significant attention in energy storage research due to their high energy density and significantly improved safety. But there are still certain problems with lithium dendrite growth, interface stability, and room-temperature practicality. Nature continually inspires human development and intricate design strategies to achieve optimal structural applications. Innovative solid-state electrolytes (SSEs), inspired by diverse natural species, have demonstrated exceptional physical, chemical, and mechanical properties. This review provides an overview of typical bionic-structured materials in SSEs, particularly those mimicking plant and animal structures, with a focus on their latest advancements in applications of solid-state lithium metal batteries. Commencing from plant structures encompassing roots, trunks, leaves, flowers, fruits, and cellular levels, the detailed influence of biomimetic strategies on SSE design and electrochemical performance are presented in this review. Subsequently, the recent progress of animal-inspired nanostructures in SSEs is summarized, including layered structures, surface morphologies, and interface compatibility in both two-dimensional (2D) and three-dimensional (3D) aspects. Finally, we also evaluate the current challenges and provide a concise outlook on future research directions. We anticipate that the review will provide useful information for future reference regarding the design of bionic-structured materials in SSEs.

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.

Solid Electrolyte Interphase on Lithium Metal Anodes

Lithium metal batteries (LMBs) represent the most promising next-generation high-energy density batteries. The solid electrolyte interphase (SEI) film on the lithium metal anode plays a crucial role in regulating lithium deposition and improving the cycling performance of LMBs. In this review, we comprehensively present the formation process of the SEI film, while elucidating the key properties such as electronic conductivity, ionic conductivity, and mechanical performance. Furthermore, various approaches for constructing the SEI film are discussed from both electrolyte regulation and artificial coating design perspectives. Lastly, future research directions along with development recommendations are also provided. This review aims to provide possible strategies for the further improvement of SEI film in LMBs and highlight their inspiration for future research directions.

Waste natural fibers for polymer toughening and biodegradability of epoxy-based polymer composite through toughness and thermal analysis

Polymeric materials are being increasingly used to replace many metallic components due to their beneficial properties such as higher strength-to-weight ratio and corrosion resistance. However, the widespread use of polymers poses a risk to the environment as they are not biodegradable. The addition of the waste jute fiber and sawdust fiber as reinforcement to the epoxy resin improved its toughness and induced the biodegradability of the polymer. To examine the effect of the jute fiber and sawdust fiber on biodegradability, the composites were then kept in the drainage system for one year, and the impact energy and fracture morphology of the as-cast and weathered samples were examined using a drop ball impact test and a Charpy impact test. During the weathering period, weight gain was initially observed due to the water absorption by the porous fibers, but after three months, the composites started to lose weight due to the degradation of the fiber by swelling and microbial attacks. Microorganisms in the drainage system used the fiber as their energy source, which resulted in the deterioration of the fiber and the production of CO2. The production of CO2 was identified by the FTIR analysis of the weathered composite samples. TGA analysis of the as-cast and weathered samples reveals the reduction of the onset thermal degradation temperature of the weathered composites due to the degradation of the composites. The fiber disintegrated through microbial attack and the fiber swelling caused by the absorption of water by jute fiber and sawdust fiber is identified through SEM imaging. The SEM image also reveals the formation of biofilms and the growth of microorganisms at the fibers. A higher growth rate of the microorganisms was observed in the jute fiber composite than in the sawdust fiber composite, as sawdust contains a high level of lignin that protects it from degradation. The results of this study suggest that both sawdust fiber and jute fiber composites induce biodegradability in the epoxy matrix, but jute fiber was more prominent in this regard. The discovery paves the way for using natural fibers in biodegradable polymer composites, reducing polymeric pollution in the environment.

Computational approach inspired advancements of solid-state electrolytes for lithium secondary batteries: from first-principles to machine learning

The increasing demand for high-security, high-performance, and low-cost energy storage systems (EESs) driven by the adoption of renewable energy is gradually surpassing the capabilities of commercial lithium-ion batteries (LIBs). Solid-state electrolytes (SSEs), including inorganics, polymers, and composites, have emerged as promising candidates for next-generation all-solid-state batteries (ASSBs). ASSBs offer higher theoretical energy densities, improved safety, and extended cyclic stability, making them increasingly popular in academia and industry. However, the commercialization of ASSBs still faces significant challenges, such as unsatisfactory interfacial resistance and rapid dendrite growth. To overcome these problems, a thorough understanding of the complex chemical-electrochemical-mechanical interactions of SSE materials is essential. Recently, computational methods have played a vital role in revealing the fundamental mechanisms associated with SSEs and accelerating their development, ranging from atomistic first-principles calculations, molecular dynamic simulations, multiphysics modeling, to machine learning approaches. These methods enable the prediction of intrinsic properties and interfacial stability, investigation of material degradation, and exploration of topological design, among other factors. In this comprehensive review, we provide an overview of different numerical methods used in SSE research. We discuss the current state of knowledge in numerical auxiliary approaches, with a particular focus on machine learning-enabled methods, for the understanding of multiphysics-couplings of SSEs at various spatial and time scales. Additionally, we highlight insights and prospects for SSE advancements. This review serves as a valuable resource for researchers and industry professionals working with energy storage systems and computational modeling and offers perspectives on the future directions of SSE development.

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.

Solvent-Tailored Reversible Self-Assembly: Unveiling Ionic Transport Nanochannels in Block Copolymer Composite Electrolytes

Block copolymer composite electrolytes have gained extensive attention for their promising performance in ionic conductivity and mechanical properties, making them valuable for future technologies. The control of the ionic conductivity through the self-assembly of block copolymers, however, remains a great challenge, especially in confined environments. In this study, we prepare block copolymer composite electrolytes using polystyrene-block-poly(ethylene oxide) (PS-b-PEO, SEO) as the polymer matrix and anodic aluminum oxide (AAO) templates as the ceramic skeleton. The self-assembly of SEO creates nanoscale ion transport pathways in the PEO regions through ionic interactions with lithium salts. The nanopores of the AAO templates provide a confined environment for complex phase separation of SEO controlled by selective solvent vapor annealing. Our findings demonstrate that transforming self-assembled SEO structures allows for precise control of ion transport pathways with cylindrical structures exhibiting 20 times higher ionic conductivities than those of helical structures. For AAO templates with pore diameters of 20 nm (SEO-LiTFSI@AAO-20), the ionic conductivities are approximately 410 times higher than those with pore diameters of 200 nm (SEO-LiTFSI@AAO-200), owing to the larger specific surface areas within the smaller nanopores. Utilizing the self-assembly of SEO not only enables the construction of vertically aligned ion transport channels on various scales but also offers a fascinating approach to tailor the conductive capabilities of composite electrolytes, enhancing the ion transport efficiency and allowing for the flexible design of block copolymer composite electrolytes.

In-situ construction of poly(tetraisopentyl acrylate) based gel polymer electrolytes with Lix La2-x TiO3 for high energy density lithium-metal batteries

As promising alternatives to liquid electrolytes, polymer electrolytes attract much research interest recently, but their widespread use is limited by the low ionic conductivity. In this study, we use electrostatic spinning to introduce particles of an ionic conductor into polyacrylonitrile (PAN) fibers to prepare a porous membrane as the host of gel polymer electrolytes (GPEs). The relevant in-situ produced GPE performs a high ionic conductivity of 6.0×10-3  S cm-1 , and a high lithium transfer number (tLi + ) of 0.85 at 30 °C, respectively. A symmetrical Li cell with this GPE can cycle stably for 550 h at a current density of 0.5 mA cm-2 . While the capacity retention of the NCM|GPE|Li cell is 79.84 % after 500 cycles at 2 C. Even with an increased cut-off voltage of 4.5 V, the 1st coulomb efficiency reaches 91.58 % with a specific discharge capacity of 213.4 mAh g-1 . This study provides a viable route for the practical application of high energy density lithium metal batteries.

Contributing to the Revolution of Electrolyte Systems via In Situ Polymerization at Different Scales: A Review

Solid-state batteries have become the most anticipated option for compatibility with high-energy density and safety. In situ polymerization, a novel strategy for the construction of solid-state systems, has extended its application from solid polymer electrolyte systems to other solid-state systems. This review summarizes the application of in situ polymerization strategies in solid-state batteries, which covers the construction of polymer, the formation of the electrolyte system, and the design of the full cell. For the polymer skeleton, multiple components and structures are being chosen. In the construction of solid polymer electrolyte systems, the choice of initiator for in situ polymerization is the focus of this review. New initiators, represented by lithium salts and additives, are the preferred choice because of their ability to play more diverse roles, while the coordination with other components can also improve the electrical properties of the system and introduce functionalities. In the construction of entire solid-state battery systems, the application of in situ polymerization to structure construction, interface construction, and the use of separators with multiplex functions has brought more possibilities for the development of various solid-state systems and even the perpetuation of liquid electrolytes.

One-Dimensional Oxide Nanostructures Possessing Reactive Surface Defects Enabled a Lithium-Rich Region and High-Voltage Stability for All-Solid-State Composite Electrolytes

The development of highly safe and low-cost solid polymer electrolytes for all-solid-state lithium batteries (ASSLBs) has been hindered by low ionic conductivity, poor stability under high-voltage conditions, and severe lithium-dendrite-induced short circuits. In this study, Li-doped MgO nanofibers bearing reactive surface defects of scaled-up production are introduced to the poly(ethylene oxide) (PEO)/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) system. The characterizations and density functional theory calculations reveal that TFSI- is strongly adsorbed on the nanofibers based on the electrostatic interactions of surface oxygen vacancies and the formation of Li-N and Li-O bonds derived from the exposed Li. Additionally, the introduced Li exposed near oxygen vacancies may be liberated from the lattice and engage in the formation of Li-rich domains. Therefore, a high ionic conductivity of 1.48 × 10-4 S cm-1 for the solid electrolyte at 30 °C and excellent cycling stability for the assembled battery, with a discharge capacity retention of 85.2% after 1500 cycles at 2C, can be achieved. Furthermore, the increased coordination of EO chains in the Li-rich region and chemical interactions with nanofibers substantially improve the antioxidant stability of the solid electrolyte, endowing the LiNi0.8Co0.1Mn0.1O2/Li battery with a long lifespan of more than 700 cycles. The results of this study suggest that the surface defects of 1D oxide nanostructures can substantially improve the Li+ diffusion kinetics. This study provides insight into the construction of Li-rich regions for high-voltage ASSLBs.

Recent Development in Topological Polymer Electrolytes for Rechargeable Lithium Batteries

Solid polymer electrolytes (SPEs) are still being considered as a candidate to replace liquid electrolytes for high-safety and flexible lithium batteries due to their superiorities including light-weight, good flexibility, and shape versatility. However, inefficient ion transportation of linear polymer electrolytes is still the biggest challenge. To improve ion transport capacity, developing novel polymer electrolytes are supposed to be an effective strategy. Nonlinear topological structures such as hyperbranched, star-shaped, comb-like, and brush-like types have highly branched features. Compared with linear polymer electrolytes, topological polymer electrolytes possess more functional groups, lower crystallization, glass transition temperature, and better solubility. Especially, a large number of functional groups are beneficial to dissociation of lithium salt for improving the ion conductivity. Furthermore, topological polymers have strong design ability to meet the requirements of comprehensive performances of SPEs. In this review, the recent development in topological polymer electrolytes is summarized and their design thought is analyzed. Outlooks are also provided for the development of future SPEs. It is expected that this review can raise a strong interest in the structural design of advanced polymer electrolyte, which can give inspirations for future research on novel SPEs and promote the development of next-generation high-safety flexible energy storage devices.

Current status on manufacturing routes to produce metal matrix composites: State-of-the-art

Owing to its excellent properties, Metal Matrix Composites (MMC) has gained popularity and finds application in aerospace, aircraft, shipbuilding, biomedical, biodegradable implant materials and many more. To serve the industrial needs, the manufactured MMC should have homogenous distribution along with minimum agglomeration of reinforcement particles, defect-free microstructure, superior mechanical, tribological and corrosive properties. The techniques implemented to manufacture MMC highly dominate the aforementioned characteristics. According to the physical state of the matrix, the techniques implemented for manufacturing MMC can be classified under two categories i.e. solid state processing and liquid state process. The present article attempts to review the current status of different manufacturing techniques covered under these two categories. The article elaborates on the working principles of state-of-the-art manufacturing techniques, the effect of dominating process parameters and the resulting characteristic of composites. Apart from this, the article does provide data regarding the range of dominating process parameters and resulting mechanical properties of different grades of manufactured MMC. Using this data along with the comparative study, various industries and academicians will be able to select the appropriate techniques for manufacturing MMC.

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.

Insight into the Key Factors in High Li+ Transference Number Composite Electrolytes for Solid Lithium Batteries

Solid lithium batteries (SLBs) have received much attention due to their potential to achieve secondary batteries with high energy density and high safety. The solid electrolyte (SE) is believed to be the essential material for SLBs. Among the recent SEs, composite electrolytes have good interfacial compatibility and customizability, which have been broadly investigated as promising contenders for commercial SLBs. The high Li⁺ transference number (t Li + ${{_{{\rm Li}{^{+}}}}}$ ) of composite electrolytes is critically important concerning the power/energy density and cycling life of SLBs, however, which is often overlooked. This Review presents a current opinion on the key factors in high t Li + ${{_{{\rm Li}{^{+}}}}}$ composite electrolytes, including polymers, Li-salts, inorganic fillers, and additives. Various strategies concerning providing a continuous pathway for Li-ions and immobilizing anions via component interaction are discussed. This Review highlights the major obstacles hindering the development of high t Li + ${{_{{\rm Li}{^{+}}}}}$ composite electrolytes and proposes future research directions for developing composite electrolytes with high t Li + ${{_{{\rm Li}{^{+}}}}}$ .

Unexpected Direct Synthesis of Tunable Redox-Active Benzil-Linked Polymers via the Benzoin Reaction

Strategies for the sustainable synthesis of redox-active organic polymers could lead to next-generation organic electrode materials for electrochemical energy storage, electrocatalysis, and electro-swing chemical separations. Among redox-active moieties, benzils or aromatic 1,2-diones are particularly attractive due to their high theoretical gravimetric capacities and fast charge/discharge rates. Herein, we demonstrate that the cyanide-catalyzed polymerization of simple dialdehyde monomers unexpectedly leads to insoluble redox-active benzil-linked polymers instead of the expected benzoin polymers, as supported by solid-state nuclear magnetic resonance spectroscopy and electrochemical characterization. Mechanistic studies suggest that cyanide-mediated benzoin oxidation occurs by hydride transfer to the solvent, and that the insolubility of the benzil-linked polymers protects them from subsequent cyanolysis. The thiophene-based polymer poly(BTDA) is an intriguing organic electrode material that demonstrates two reversible one-electron reductions with monovalent cations such as Li+ and Na+ but one two-electron reduction with divalent Mg2+. As such, the tandem benzoin-oxidation polymerization reported herein represents a sustainable method for the synthesis of highly tunable and redox-active organic materials.

Enhanced Electrochemical Performance of PEO-Based Composite Polymer Electrolyte with Single-Ion Conducting Polymer Grafted SiO2 Nanoparticles

In order to enhance the electrochemical performance and mechanical properties of poly(ethylene oxide) (PEO)-based solid polymer electrolytes, composite solid electrolytes (CSE) composed of single-ion conducting polymer-modified SiO₂, PEO and lithium salt were prepared and used in lithium-ion batteries in this work. The pyridyl disulfide terminated polymer (py-ss-PLiSSPSI) is synthesized through RAFT polymerization, then grafted onto SiO₂ via thiol-disulfide exchange reaction between SiO₂-SH and py-ss-PLiSSPSI. The chemical structure, surface morphology and elemental distribution of the as-prepared polymer and the PLiSSPSI-g-SiO₂ nanoparticles have been investigated. Moreover, CSEs containing 2, 6, and 10 wt% PLiSSPSI-g-SiO₂ nanoparticles (PLi-g-SiCSEs) are fabricated and characterized. The compatibility of the PLiSSPSI-g-SiO₂ nanoparticles and the PEO can be effectively improved owing to the excellent dispersibility of the functionalized nanoparticles in the polymer matrix, which promotes the comprehensive performances of PLi-g-SiCSEs. The PLi-g-SiCSE-6 exhibits the highest ionic conductivity (0.22 mS·cm^-1) at 60 °C, a large t_Li+ of 0.77, a wider electrochemical window of 5.6 V and a rather good lithium plating/stripping performance at 60 °C, as well as superior mechanical properties. Hence, the CSEs containing single-ion conducting polymer modified nanoparticles are promising candidates for all-solid-state lithium-ion batteries.

Insights into the use of polyepichlorohydrin polymer in lithium battery energy storage/conversion devices: review

Abstract

In this paper, the up-to-date state of polyepichlorohydrin-based electrolytes is reviewed. Research works are persistently ongoing to develop free-standing solid polymer electrolytes with exceptional performances and stabilities that can suit the needs of present and next-generation technologies. Polyepichlorohydrin (PECH), for example, is one of the polymer hosts under consideration due to its ether electron donor groups that deliver coordinating spots for cation transport as well as alkyl chloride groups for changing its surface character. Because of this structure, PECH has certain incredible characteristics including small glass transition temperature (Tg), tremendous flexibility, as well as the power to form complexation with diverse salts. Furthermore, the alkyl chloride groups serve as a location for surface modification of the polymer via nucleophilic substitution reactions, resulting in surface changes or bulk properties. As a result, the PECH in chemically modified or pristine form is an emerging option that has been researched and is being considered for use in energy storage devices. This paper reviews the latest studies on the improvements of PECH-based electrolytes for lithium-based battery storage systems. The synthesis methods of PECH polymer, types of lithium batteries, and opportunities and challenges of lithium batteries have been presented briefly. Findings on PECH-based electrolytes have been presented and discussed thoroughly. Lastly, the paper presents, battery performance needs, and cation transportation mechanisms as well as future prospects for the advancement of PECH electrolytes in the field of storage systems.

Article Highlights

Ultrathin Solid Polymer Electrolyte Design for High-Performance Li Metal Batteries: A Perspective of Synthetic Chemistry

Li metal batteries (LMBs) have attracted widespread attention in recent years because of their high energy densities. But traditional LMBs using liquid electrolyte have potential safety hazards, such as: leakage and flammability. Replacing liquid electrolyte with solid polymer electrolyte (SPE) can not only significantly improve the safety, but also improve the energy density of LMBs. However, till now, there is only limited success in improving the various physical and chemical properties of SPE, especially in thickness, posing great obstacles to further promoting its fundamental and applied studies. In this review, the authors mainly focus on evaluating the merits of ultrathin SPE and summarizing its existing challenges as well as fundamental requirements for designing and manufacturing advanced ultrathin SPE in the future. Meanwhile, the authors outline existing cases related to this field as much as possible and summarize them from the perspective of synthetic chemistry, hoping to provide a comprehensive understanding and serve as a strategic guidance for designing and fabricating high-performance ultrathin SPE. Challenges and opportunities regarding this burgeoning field are also critically evaluated at the end of this review.

Constructing an In Situ Polymer Electrolyte and a Na-Rich Artificial SEI Layer toward Practical Solid-State Na Metal Batteries

Sodium is one of the most promising anode candidates for the beyond-lithium-ion batteries. The development of Na metal batteries with a high energy density, high safety, and low cost is desirable to meet the requirements of both portable and stationary electrical energy storage. However, several problems caused by the unstable Na metal anode and the unsafe liquid electrolyte severely hinder their practical applications. Herein, we report a facile but effective methodology to construct an in situ polymer electrolyte and Na-rich artificial solid-electrolyte interface (SEI) layer concurrently. The obtained integrated Na metal batteries display long cycling life and admirable dynamic performance with total inhibition of dendrites, excellent contact of the cathode/polymer electrolyte, and reduction of side reactions during cycling. The modified Na metal electrode with the in situ polymer electrolyte is stable and dendrite-free in repeated plating/stripping processes with a life span of above 1000 h. Moreover, this method is compatible with different cathodes that demonstrate outstanding electrochemical performance in full cells. We believe that this approach provides a practical solution to solid-state Na metal batteries.

Effects of Molecular Weight on the Electrochemical Properties of Poly(vinylidene difluoride)-Based Polymer Electrolytes

Polymer-based electrolytes have attracted ever-increasing attention for solid-state batteries due to their excellent flexibility and processability. Among them, poly(vinylidene difluoride) (PVDF)-based electrolytes with high ionic conductivity, wide electrochemical stability window, and good mechanical properties show great potential and have been widely investigated by using different Li salts, solvents, and inorganic fillers. Here, we report the influence of the molecular weight of PVDF itself on the electrochemical properties of the electrolytes by using two kinds of common PVDF polymers, i.e., PVDF 761 and 5130. Our results demonstrate that the electrolyte with a larger molecular weight (PVDF 5130) has a denser structure and lower crystallinity, and thus much better electrochemical performance, than one with a smaller molecular weight (PVDF 761). With PVDF 5130, the LiFePO₄-based solid-state cells present a steady cycling performance with a capacity retention of 85% after 1000 cycles at 1 C and 30 °C. The cycle life of the LiCoO₂-based solid-state cells is also extended by using PVDF 5130.

Utilizing an Oxygen-Rich Interface by Hydroxyapatite to Regulate the Linear Diffusion for the Stable Solid-State Electrolytes

Improving dissociation and diffusion of lithium ions is the key to solving the practical application of polymer-based solid-state electrolytes (SSE). Here, a low-cost three-dimensional hydroxyapatite (HAP) nanowire is used in polyethene oxide to obtain an enhanced lithium-ion electrolyte. The oxygen-rich interface of HAP provides an integrated dissociation-diffusion platform for lithium salts. The TFSI- anions tend to coordinate with calcium ions, which makes it easier for lithium ions to escape and stay in a free state. The lateral nucleus in the HAP polyethene electrolyte regulates the diffusion from spherical diffusion into linear planar diffusion, which is confirmed by chronoamperometry curves and in situ observation. The stability of the electrolyte at high voltages is improved by inhibiting the superoxide radicals of polyethene oxide chains, which is demonstrated by nuclear magnetic resonance and electron paramagnetic resonance spectroscopy methods. The initial specific charge capacity of the Li/SPE/LiFePO4 cell with HAP-modified polyethene oxide at 2 C is 148.8 mA h/g, and its initial Coulombic efficiency is 95.17%. After 100 cycles, the specific discharge capacity is 125.5 mA h/g with 99.91% retention per cycle. This oxygen-rich interface strategy would guide the discovery of novel materials for polymer-based SSE.

New insights on the origin of chemical instabilities between poly(carbonate)-based polymer and Li-containing inorganic materials

Composites electrolytes, owing to their potential to combine both polymeric and ceramic properties, are promising candidates for Solid-State-Batteries (SSBs). Here, we assessed the effect of ceramic fillers (Li1+xAlxTi2-xP3O12, Li6.55Ga0.15La3Zr2O12, Al2O3) in a poly(ethylene oxide carbonate)-LiTFSI. First, the role of filler chemistry on thermal and electrochemical properties is evaluated: the polymer crystallinity is reduced, resulting in a gain of ionic conductivity at low temperatures; and the ionic conductivity at low temperature (<30 °C) is boosted for LLZO filler particles. This behaviour is commonly attributed to new conduction pathways generated within the fillers; however, here we demonstrate that a polymer degradation induced by the filler chemistry modifies the polymer chemistry in poly(ethylene glycol), initiated by LiOH that can be found on the LLZO surface. The electrolyte containing LATP or Al2O3 does not under any degradation. Hence, special attention must be paid to surface impurities, as instability/degradation may occur.

Organic-Inorganic Composite Electrolytes Optimized with Fluoroethylene Carbonate Additive for Quasi-Solid-State Lithium-Metal Batteries

Composite solid electrolytes (CSEs) are considered crucial materials for next-generation solid-state lithium batteries with high energy density and reliable safety, and they make full use of the advantages of both organic and inorganic solid-state electrolytes. However, few CSEs have sufficiently high ionic conductivity at room temperature for practical applications. Here, a traditional CSE consisting of poly(ethylene oxide) (PEO) matrix and Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) fillers was optimized by introducing a fluoroethylene carbonate (FEC) additive, resulting in an improved high ionic conductivity of 1.99 × 10^-4 S cm^-1 at 30 °C. The symmetric Li||Li cell assembled with the optimized CSE exhibited a low overpotential and a good cycling stability of more than 1500 h at room temperature. Moreover, the Li||LiFePO₄ battery with the optimized CSE delivered a discharge capacity of 132 mAh g^-1 at 0.2 C after 300 cycles at room temperature. Comparisons between the LATP-containing CSE and control electrolytes indicated that the enhanced ion conductivity of the former resulted from the synergistic effect of LATP and FEC. Comprehensive characterizations and DFT calculations suggest that with the presence of LATP, FEC additives in the precursor could transform into some other species in the preparation process of CSE. It is believed that these FEC-derived species improve the ion conductivity of the CSEs. The results reported here may open up new approaches to developing composite electrolytes with high ionic conductivity at room temperature by introducing organic additives in the precursor and converting them into species that facilitate ion conduction in the CSE preparation process.

Combining Organic Plastic Salts with a Bicontinuous Electrospun PVDF-HFP/Li7La3Zr2O12 Membrane: LiF-Rich Solid-Electrolyte Interphase Enabling Stable Solid-State Lithium Metal Batteries

Solid-state electrolytes can guarantee the safe operation of high-energy density lithium metal batteries (LMBs). However, major challenges still persist with LMBs due to the use of solid electrolytes, that is, poor ionic conductivity and poor compatibility at the electrolyte/electrode interface, which reduces the operational stability of solid-state LMBs. Herein, a novel fiber-network-reinforced composite polymer electrolyte (CPE) was designed by combining an organic plastic salt (OPS) with a bicontinuous electrospun polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP)/Li₇La₃Zr₂O₁₂ (LLZO) membrane. The presence of LLZO in the composite helps to promote the dissociation of FSI^- from OPSs. Subsequently, the dissociated FSI^- is then involved in the formation of a LiF-rich solid electrolyte interphase (SEI) layer on the lithium anode via a reductive decomposition reaction, which was affirmed by theoretical calculations and experimental results. Due to the LiF-rich SEI layer, the Li/Li symmetric cell was able to demonstrate a long cyclic life of over 2600 h at a current density of 0.1 mA cm^-2. More importantly, the as-prepared CPE achieved a high ionic conductivity of 2.8 × 10^-4 S cm^-1 at 25 °C, and the Li/LiFePO₄ cell based on the CPE exhibited a high discharge capacity and 83.3% capacity retention after 500 cycles at 1.0 C. Thus, the strategy proposed in this work can inspire the future development of highly conductive solid electrolytes and compatible interface designs toward high-energy density solid-state LMBs.

Ionic Liquid-Impregnated ZIF-8/Polypropylene Solid-like Electrolyte for Dendrite-free Lithium-Metal Batteries

Metal-organic framework (MOF)-based solid-like electrolytes have attracted more prospective due to the combined merits of solid-state electrolytes and liquid electrolytes. However, most MOF-based solid-like electrolytes using organic liquid electrolytes cannot fundamentally solve the safety issues of lithium-metal batteries, and the ionic conductivity and mechanical strength of the electrolytes should be further enhanced. Herein, the ionic liquid-impregnated polypropylene (PP) porous membrane with integrally distributed ZIF-8 nanoparticles is designed. The solid-like electrolyte possesses an increased ionic conductivity of 2.09 × 10^-4 S cm^-1 at 25 °C, lithium-ion transference number (0.45), mechanical strength, electrochemical window, and excellent nanowetted interfaces. Furthermore, the Li symmetrical cell shows excellent Li plating/stripping properties for 550 h at 0.1 mA cm^-2 and 0.1 mA h cm^-2. The LiFePO₄/Li full battery with the solid-like electrolyte demonstrates an excellent rate capability and cycling stability with the initial discharge capacity of 157.9 mA h g^-1 and a capacity retention ratio of 91.23% after 450 cycles at 0.2 C. The work offers a new avenue toward MOF-based solid-like electrolytes for high-safety lithium-metal batteries.

Metal–organic framework-based solid-state electrolytes for all solid-state lithium metal batteries: a review

This work systematically reviewed recent progress of MOF-based solid electrolytes in all solid-state metal batteries which has rarely been summarized.

Fast self-healing solid polymer electrolyte with high ionic conductivity for Lithium metal batteries

By introducing multiple molecule/intermolecular dynamic reversible hydrogen bonds into the polydimethylsiloxane elastomer system, the solid polymeric electrolyte with high ion conductivity (2.5×10-4 Scm-1) and stable electrochemical window (> 5 V)...

Ternary-Salt Solid Polymer Electrolyte for High-Rate and Long-Life Lithium Metal Batteries

Ternary-salt solid polymer electrolyte (TS-SPE) consisting of LiPF6-LiTFSI-LiFSI salts and poly(1,3-dioxolane) is created by in-situ polymerization. The TS-SPE possesses high ionic conductivity, high Li+ ion transference number, and stable SEI...

Emerging Two-Dimensional Covalent and Coordination Polymers for Stable Lithium Metal Batteries: From Liquid to Solid

Lithium metal anodes (LMAs) have attracted much attention in recent years because of their high theoretical capacity (3860 mAh g^-1) and low electrochemical potential (-3.040 V vs standard hydrogen electrode). Lithium metal can be coupled with various cathodes to construct high-energy-density lithium metal batteries (LMBs) which hold great promise for next-generation batteries. However, the unstable solid electrolyte interphases (SEIs) and the uncontrollable lithium dendrite growth severely hinder the commercial development of LMAs. The emerging 2D polymers (2DPs), which possess high mechanical flexibility, high specific surface area, abundant surface chemistry, and rich chemical modification characteristics, have shown great advantages in addressing the inherent issues of LMAs. Herein, the current progress of 2DPs for stable and dendrite-free LMAs in liquid- and solid-based batteries is comprehensively reviewed. Some perspectives for the application of 2DPs in LMBs are also discussed. It is believed that the emerging 2DPs will provide insights into developing high-energy-density LMBs and beyond.

Polybenzimidazole Ultrathin Anion Exchange Membrane with Comb-Shape Amphiphilic Microphase Networks for a High-Performance Fuel Cell

A comb-shape amphiphilic cationic side chain is proposed to well-balance the water sorption in anion exchange membranes (AEMs), in which the cationic group is in between of an ether-containing hydrophilic spacer and an alkyl hydrophobic spacer. By fully grafting the amphiphilic side chains onto polybenzimidazole (PBI), comb-shape amphiphilic microphase networks are well-developed in the AEMs, in which the alkyl hydrophobic network greatly restricts water swelling and the ether-containing hydrophilic network keeps the hydration of the cationic groups and enlarges the ion conductive channel. The as-prepared membranes achieve a high conductivity of about 91.2 mS cm^-1, an extremely low swelling ratio of about 8.1% at 80 °C, and good mechanical properties at a hydrated state (tensile strength and elongation at a break of about 14.6 MPa and 77.5%, respectively). Benefits from the balanced water sorption in AEMs, the H₂/O₂ fuel cell with a 10 μm ultrathin membrane could withstand 80 °C and 0.1 MPa back pressure and achieve a high open circuit voltage of about 1.0 V and a high peak power density of about 631.5 mW cm^-2. This work provides a new insight into the design of high-performance AEM.