Hybrid Liquid–Solid Composite Electrolytes for Sulfide-Based Solid-State Batteries: Advantages and Limitation

All-solid-state batteries (SSBs) represent one of the most promising avenues for surpassing the energy density limitations of conventional lithium-ion batteries. However, the unstable interfacial contact between the solid-state electrolyte and the electrode poses a critical challenge for practical applications. To tackle this issue, a hybrid system incorporating both liquid electrolytes (LEs) and sulfide solid-state electrolytes may serve as a viable alternative. In this hybrid system, the LE facilitates the in situ formation of a solid electrolyte interphase layer, thereby enhancing the physical interface contact. Consequently, the electrochemical lifetime of the hybrid all-SSBs is significantly improved, as evidenced by the stable lithium plating behavior observed through analytical techniques such as in situ X-ray imaging. Nonetheless, the hybrid system exhibits clear limitations, and several issues that need to be addressed for its practical implementation are identified. In conclusion, potential solutions that could be employed to overcome these challenges are proposed.     

Molecular-level Designed Polymer Electrolyte for High-Voltage Lithium–Metal Solid-State Batteries

In solid polymer electrolytes (SPEs) based Li–metal batteries, the inhomogeneous migration of dual-ion in the cell results in large concentration polarization and reduces interfacial stability during cycling. A special molecular-level designed polymer electrolyte (MDPE) is proposed by embedding a special functional group (4-vinylbenzotrifluoride) in the polycarbonate base. In MDPE, the polymer matrix obtained by copolymerization of vinylidene carbonate and 4-vinylbenzotrifluoride is coupled with the anion of lithium-salt by hydrogen bonding and the “σ-hole” effect of the C F bond. This intermolecular interaction limits the migration of the anion and increases the ionic transfer number of MDPE (t_Li⁺ = 0.76). The mechanisms of the enhanced t_Li⁺ of MDPE are profoundly understood by conducting first-principles density functional theory calculation. Furthermore, MDPE has an electrochemical stability window (4.9 V) and excellent electrochemical stability with Li–metal due to the CO group and trifluoromethylbenzene (ph-CF₃) of the polymer matrix. Benefited from these merits, LiNi_0.8Co_0.1Mn_0.1O₂-based solid-state cells with the MDPE as both the electrolyte host and electrode binder exhibit good rate and cycling performance. This study demonstrates that polymer electrolytes designed at the molecular level can provide a broader platform for the high-performance design needs of lithium batteries.     

Facile Li+ Transport in Interpenetrating O- and F-Containing Polymer Networks for Solid-State Lithium Batteries

Solid polymer electrolytes (SPEs) provide an intimate contact with electrodes and accommodate volume changes in the Li-anode, making them ideal for all-solid-state batteries (ASSBs); however, confined chain swing, poor ion-complex dissociation, and barricaded Li⁺-transport pathways limit the ionic conductivity of SPEs. This study develops an interpenetrating polymer network electrolyte (IPNE) comprising poly(ethylene oxide)- and poly(vinylidene fluoride)-based networked SPEs (O-NSPE and F-NSPE, respectively) and lithium bis(fluorosulfonyl) imide (LiFSI) to address these challenges. The  CF₂ / CF₃ segments of the F-NSPE segregate FSI⁻ to form connected Li⁺-diffusion domains, and  C O C segments of the O-NSPE dissociate the complexed ions to expedite Li⁺ transport. The synergy between O-NSPE and F-NSPE gives IPNE high ionic conductivity (≈1 mS cm⁻¹) and a high Li-transference number (≈0.7) at 30 °C. FSI⁻ aggregation prevents the formation of a space-charge zone on the Li-anode surface to enable uniform Li deposition. In Li||Li cells, the proposed IPNE exhibits an exchange current density exceeding that of liquid electrolytes (LEs). A Li|IPNE|LiFePO₄ ASSB achieves charge–discharge performance superior to that of LE-based batteries and delivers a high rate of 7 mA cm⁻². Exploiting the synergy between polymer networks to construct speedy Li⁺-transport pathways is a promising approach to the further development of SPEs.     

锂离子电池用聚合物电解质的最新进展II.含液聚合物电解质

由于干态聚合物电解质目前还不能满足聚合物锂离子电池的应用要求,人们致力于开发含液体增塑剂的聚合物电解质,包括凝胶型和微孔型两类体系。本文综述了含液聚合物电解质的最新进展,重点论述了各种新体系和新方法。     

Developing “Polymer-in-Salt” High Voltage Electrolyte Based on Composite Lithium Salts for Solid-State Li Metal Batteries

The stringent demands for lithium salts make the design of “polymer-in-salt” type solid electrolyte restricted since it was proposed in 1993. Herein, a novel polymer-in-salt solid electrolyte is developed via a supramolecular strategy based on poly(methyl vinyl ether-alt-maleic anhydride) (PME) and novel single-ion lithiated polyvinyl formal (LiPVFM)/lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) composite salts (Dual-Li). Hydroxyl of LiPVFM in Dual-Li forms a strong hydrogen bond with the carboxylic acid group generated by the partial ring-opening reaction of maleic anhydride in PME. Meanwhile, PME with abundant carbonyl enables the improved LiTFSI coordination in the polymer/salt composites. As a result, the greatly enhanced mutual solubility of PME and Dual-Li is of importance to build a “polymer-in-salt” solid electrolyte (PISE), which exhibits high ionic conductivity of 3.57 × 10^–4 S cm^–1, wide electrochemical window beyond 5 V, and superior lithium-ion transference number of 0.62 at 25 °C as well as excellent interfacial compatibility with electrodes. The as-assembled LiCoO₂||Li solid batteries present prominent high-voltage cyclability with 89.2% capacity retention in 225 cycles. Furthermore, LiNi_0.7Mn_0.2Co_0.1O₂||Li pouch cells exhibit remarkable safety even under harsh conditions. The study offers a promising strategy to address the high voltage compatibility and interfacial issues using PISE in solid-state batteries.     

Developing Single-Ion Conductive Polymer Electrolytes for High-Energy-Density Solid State Batteries

Single-ion conductive polymer electrolytes (SICPEs) with a cationic transference number (t_Li+) close to unity exhibit specific advantages in solid-state batteries (SSBs), including mitigating the ion concentration gradient and derived problems, suppressing the growth of lithium dendrites, and improving the utilization of cathode materials and the rate performance of SSBs. However, the application of SICPEs remains major challenges, i.e., the ionic conductivity is inferior at room temperature. Therefore, the recent accomplishments in improving the ambient ionic conductivity to be compatible SICPEs with a high transference number are discussed in this review. In particular, some strategies of delocalizing charges in polyanions, designing a highly conductive polymer matrix, and utilizing synergistic effects in SICPEs are focused to shed light on the further development of solid polymer electrolytes for SSBs. Finally, multifunctional species of SICPEs are discussed in view of the mechanical contact and/or charge transfer problems at the solid–solid interface in SSBs.     

Polyether-b-Amide Based Solid Electrolytes with Well-Adhered Interface and Fast Kinetics for Ultralow Temperature Solid-State Lithium Metal Batteries

Solid-state lithium metal batteries (SSLMBs) are highly desirable for energy storage because of the urgent need for higher energy density and safer batteries. However, it remains a critical challenge for stable cycling of SSLMBs at low temperature. Here, a highly viscoelastic polyether-b-amide (PEO-b-PA) based composite solid-state electrolyte is proposed through a one-pot melt processing without solvent to address this key process. By adjusting the molar ratio of PEO-b-PA to lithium bis(trifluoromethanesulphonyl)imide (ethylene oxide:Li = 6:1) and adding 20 wt.% succinonitrile, fast Li⁺ transport channel is conducted within the homogeneous polymer electrolyte, which enables its application at ultra-low temperature (−20 to 25 °C). The composite solid-state electrolyte utilizes dynamic hydrogen-bonding domains and ion-conducting domains to achieve a low interfacial charge transfer resistance (<600 Ω) at −20 °C and high ionic conductivity (25 °C, 3.7 × 10⁻⁴ S cm⁻¹). As a result, the LiFePO₄|Li battery based on composite electrolyte exhibits outstanding electrochemical performance with 81.5% capacity retention after 1200 cycles at −20 °C and high discharge specific capacities of 141.1 mAh g⁻¹ with high loading (16.1 mg cm⁻²) at 25 °C. Moreover, the solid-state SNCM811|Li cell achieves excellent safety performance under nail penetration test, showing great promise for practical application.     

Composition and Structure Design of Poly(vinylidene fluoride)-Based Solid Polymer Electrolytes for Lithium Batteries

Solid-state lithium batteries have become the focus of the next-generation high-safety lithium batteries due to their dimensional, thermal, and electrochemical stability. Thus, the progress of solid electrolytes with satisfactory comprehensive performances has become the key to promoting the development of solid batteries. Herein, poly(vinylidene fluoride) (PVDF) solid polymer electrolytes (SPEs) possess excellent flexibility, mechanical property, and high electrochemical and thermal stability, which show huge application potentiality in solid-state lithium batteries and obtain extensive research. But the PVDF SPEs have been suffering from low ionic conductivity, high crystallinity, and low reactive sites. The development of PVDF-based composite solid polymer electrolytes (CSPEs) has been confirmed to be a forceful strategy to optimize the performance of electrolytes. In this review, based on different design strategies, the recent progress of PVDF-based SPEs is introduced in detail, especially in the mechanism of ionic conductivity enhancement and interface regulation by modified fillers. Besides, the applications of PVDF-based SPEs in Li-S and Li-O₂ battery systems are also introduced. Finally, this review presents some insights for promoting the development of high-performance PVDF-based SPEs.     

Organoboron-Containing Polymer Electrolytes for High-Performance Lithium Batteries

Polymer electrolytes (PEs) have been deemed as a sought-after candidate for next-generation lithium batteries. Substantial effort has been dedicated to exploiting PEs with improved comprehensive performance. Organoboron compounds have aroused great interest in PEs due to their distinct characteristics such as high design diversity, excellent thermal stability, promoting lithium-ion transportation, and raising Li⁺ transference number. Organoboron compounds also have unique functions that facilitate the development of a stable solid electrolyte interface on the electrode surface. Their diversified structures and multiple functions are fundamentally associated with boron's hybridization form that determines the electronic structure of boron as a central atom. Here, recent advancement in organoboron-containing PEs is reviewed in the aspect of polymer matrixes with boron moieties and organoboron additives for PEs. This review aims to highlight the diverse roles and high application potentials of organoboron compounds utilized in PEs. It is anticipated to provide a clear perspective of organoboron-containing PEs and to spur more research interests for the exploration of safe and efficient lithium batteries.     

Recent Advances in Electrolytes for Potassium-Ion Batteries

Potassium-ion batteries (KIBs) are considered as the potential energy storage devices due to the abundant reserves and low cost of potassium. In the past decade, research on KIBs has generally focused on electrode materials. However, since electrolytes also play a key role in determining the cell performance, this review summarizes recent advances in KIB electrolytes and design strategies. Specifically, the review includes five parts. First, the organic liquid electrolyte is the most widely used type for KIBs. Its two major components, salts and solvents, have a huge impact on the formation of the solid electrolyte interphase and the performance of KIBs. Changes in salts/solvents, the introduction of additives, and the concentration increase all have a positive effect on organic liquid electrolytes. Second, the design of water-in-salt electrolytes can effectively widen the narrow electrochemical stability window of aqueous electrolytes. Third, despite the appealing properties, the ionic liquid electrolytes have not been widely applied due to its high cost. Fourth, the solid-state electrolytes have drawn much attention due to high safety, and current research has been working on improving their ionic conductivity at room temperature. Lastly, perspectives are provided to support the future development of suitable electrolytes for high-performance KIBs.     

High Performance Composite Polymer Electrolytes for Lithium-Ion Batteries

Today, there is an urgent demand to develop all solid-state lithium-ion batteries (LIBs) with a high energy density and a high degree of safety. The core technology in solid-state batteries is a solid-state electrolyte, which determines the performance of the battery. Among all the developed solid electrolytes, composite polymer electrolytes (CPEs) have been deemed as one of the most viable candidates because of their comprehensive performance. In this review, the limitations of traditional solid polymer electrolytes and the recent progress of CPEs are introduced. The effect and mechanism of inorganic fillers to the various properties of electrolytes are discussed in detail. Meanwhile, the factors affecting ionic conductivity are intensively reviewed. The recent representative CPEs with synthetic fillers and natural clay-based fillers are highlighted because of their great potential. Finally, the remaining challenges and promising prospects are outlined to provide strategies to develop novel CPEs for high-performance LIBs.     

Thin,Deformable, and Safety‐Reinforced Plastic Crystal Polymer Electrolytes for High‐Performance Flexible Lithium‐Ion Batteries

A new class of highly thin, deformable, and safety‐reinforced plastic crystal polymer electrolytes (N‐PCPEs) is demonstrated as an innovative solid electrolyte for potential use in high‐performance flexible lithium‐ion batteries with aesthetic versatility and robust safety. The unusual N‐PCPEs are fabricated by combining a plastic crystal polymer electrolyte with a porous polyethylene terephthalate (PET) nonwoven. Herein, the three‐dimensional reticulated plastic crystal polymer electrolyte matrix is formed directly inside the PET nonwoven skeleton via in‐situ UV‐crosslinking of ethoxylated trimethylolpropane triacrylate (ETPTA) monomer, under co‐presence of plastic crystal electrolyte. The PET nonwoven is incorporated as a compliant skeleton to enhance mechanical/dimensional strength of N‐PCPE. Owing to this structural uniqueness, the N‐PCPE shows significant improvements in the film thickness and deformability with maintaining advantageous features (such as high ionic conductivity and thermal stability) of the PCE. Based on structural/physicochemical characterization of N‐PCPE, its potential application as a solid electrolyte for flexible lithium‐ion batteries is explored by scrutinizing the electrochemical performance of cells. The high ionic conductance of N‐PCPE, along with its excellent deformability, plays a viable role in improving cell performance (particularly at high current densities and also mechanically deformed states). Notably, the cell assembled with N‐PCPE exhibits stable electrochemical performance even under a severely wrinkled state, without suffering from internal short‐circuit failures between electrodes.     

Flexible Stable Solid‐State Al‐Ion Batteries

Rechargeable aluminum‐ion batteries (AIBs) are regarded as promising candidates for post‐lithium energy storage systems (ESSs). For addressing the critical issues in the current liquid AIB systems, here a flexible solid‐state AIB is established using a gel‐polymer electrolyte for achieving robust electrode–electrolyte interfaces. Different from utilization of solid‐state systems for alleviating the safety issues and enhancing energy density in lithium‐ion batteries, employment of polymeric electrolytes mainly focuses on addressing the essential problems in the liquid AIBs, including unstable internal interfaces induced by mechanical deformation and production of gases as well as unfavorable separators. Particularly, such gel electrolyte enables the solid‐state AIBs to present an ultra‐fast charge capability within 10 s at current density of 600 mA g^?1. Meanwhile, an impressive specific capacity ≈120 mA h g^?1 is obtained at current density of 60 mA g^?1, approaching the theoretical limit of graphite‐based AIBs. In addition to the well‐retained electrochemical performance below the ice point, the solid‐state AIBs also hold great stability and safety under various critical conditions. The results suggest that such new prototype of solid‐state AIBs with robust electrode–electrolyte interfaces promises a novel strategy for fabricating stable and safe flexible ESSs.     

A Decade of Progress on Solid-State Electrolytes for Secondary Batteries: Advances and Contributions

Compared with conventional liquid batteries, all-solid-state batteries (ASSBs) show great promise for enabling higher safety in electric vehicles without compromising operational durability and range. As a key component of ASSBs, solid-state electrolytes (SSEs) need high ionic conductivity and favorable interfacial compatibility between electrodes and SSEs. In the recent decade, numerous efforts have been devoted to SSE advancement and fruitful achievements have been made, particularly regarding metal anode-oriented SSEs with high energy density. This review focuses on the historical process of SSEs employed in ASSBs. The new understanding and origins for the enhanced ionic conductivity and mechanical properties of SSEs are first summarized. As to the cathode/SSE interface, its decomposition mechanism and modification strategies are analyzed. As to the interfacial issues of SSEs with anodes, the mechanisms of dendrite formation and penetration into the SSEs are discussed in detail. Additionally, assisted by a library of big data sources, contributions are systematically highlighted from different countries, institutions, and corresponding authors to significantly advance SSE progress, and certain insights are provided into the underlying relationships between various items in a collective manner. Finally, current challenges and potential strategies are identified for the future development of SSEs in ASSBs.     

锂离子电池用聚合物电解质的最新进展I.干态聚合物电解质

聚合物锂离子电池的发展对聚合物电解质提出了更高的要求,促使人们开发性能优良的干态聚合物电解质。综述了近年来干态聚合物电解质的研究进展,包括:(1)以改性聚氧化乙烯-锂盐复合体系为代表的耦合体系;(2)导电机理完全不同的解耦合体系;(3)阴离子移动受限的单离子体系。其中,解耦合体系与单离子体系的研究得到了特别的关注。     

Advanced Electrolytes Enabling Safe and Stable Rechargeable Li-Metal Batteries: Progress and Prospects

Rechargeable Li-metal batteries (RLBs) can boost energy yet possess poor cycle stability and safety concerns when utilizing carbonate electrolytes. Countless effort has been invested in researching and developing electrolytes for RLBs to obtain stable and safe batteries. However, only few existing electrolytes meet the requirements for practical RLBs. In this perspective, the challenges of organic liquid electrolytes in the application in RLBs are summarized, and requirements for electrolytes for practical RLBs are proposed. This perspective briefly reviews the recent achievements of electrolytes (liquid- and solid-state) for RLBs and analyzes the corresponding drawbacks of each electrolyte. Further, possible solutions to the existing shortcomings of various electrolytes are proposed. In particular, this perspective outlines the development strategy of in situ gelation electrolytes, accompanied by a call for people using pouch cells to evaluate performance and paying more attention to battery safety research. This perspective aims to expound on the challenges and the possible research directions of RLBs electrolytes to promote practical RLBs better.     

Non-Flammable Liquid and Quasi-Solid Electrolytes toward Highly-Safe Alkali Metal-Based Batteries

Rechargeable alkali metal (i.e., lithium, sodium, potassium)-based batteries are considered as vital energy storage technologies in modern society. However, the traditional liquid electrolytes applied in alkali metal-based batteries mainly consist of thermally unstable salts and highly flammable organic solvents, which trigger numerous accidents related to fire, explosion, and leakage of toxic chemicals. Therefore, exploring non-flammable electrolytes is of paramount importance for achieving safe batteries. Although replacing traditional liquid electrolytes with all-solid-state electrolytes is the ultimate way to solve the above safety issues, developing non-flammable liquid electrolytes can more directly fulfill the current needs considering the low ionic conductivities and inferior interfacial properties of existing all-solid-state electrolytes. Moreover, the electrolyte leakage concern can be further resolved by gelling non-flammable liquid electrolytes to obtain quasi-solid electrolytes. Herein, a comprehensive review of the latest progress in emerging non-flammable liquid electrolytes, including non-flammable organic liquid electrolytes, aqueous electrolytes, and deep eutectic solvent-based electrolytes is provided, and systematically introduce their flame-retardant mechanisms and electrochemical behaviors in alkali metal-based batteries. Then, the gelation techniques for preparing quasi-solid electrolytes are also summarized. Finally, the remaining challenges and future perspectives are presented. It is anticipated that this review will promote a safety improvement of alkali metal-based batteries.     

3D Ion-Conducting,Scalable, and Mechanically Reinforced Ceramic Film for High Voltage Solid-State Batteries

Concerning the safety aspects of Li⁺ ion batteries, an epoxy-reinforced thin ceramic film (ERTCF) is prepared by firing and sintering a slurry-casted composite powder film. The ERTCF is composed of Li⁺ ion conduction channels and is made of high amounts of sintered ceramic Li_1+xTi_2-xAl_x(PO₄)₃ (LATP) and epoxy polymer with enhanced mechanical properties for solid-state batteries. The 2D and 3D characterizations are conducted not only for showing continuous Li⁺ ion channels thorough LATP ceramic channels with over 10⁻⁴ S cm⁻¹ of ionic conductivity but also to investigate small amounts of epoxy polymer with enhanced mechanical properties. Solid-state Li⁺ ion cells are fabricated using the ERTCF and they show initial charge–discharge capacities of 139/133 mAh g⁻¹. Furthermore, the scope of the ERTCF is expanded to high-voltage (>8 V) solid-state Li⁺ ion batteries through a bipolar stacked cell design. Hence, it is expected that the present investigation will significantly contribute in the preparation of the next generation reinforced thin ceramic film electrolytes for high-voltage solid-state batteries.     

Recent Progress in Solid Electrolytes for Energy Storage Devices

With the rapid advances in safe, flexible, and even stretchable electronic products, it is important to develop matching energy storage devices to more effectively power them. However, the use of conventional liquid electrolytes produces volatilization and leakage that are dangerous and requires strict packaging layers that are typically rigid. To this end, solid electrolytes that can overcome these problems have attracted increasing attention in recent decades. In this review article, three main types of solid electrolytes (i.e., inorganic, polymer, and composite electrolytes) are first described and compared in terms of their structures and properties. The advantages of solid electrolytes to make safe, flexible, stretchable, wearable, and self‐healing energy storage devices, including supercapacitors and batteries, are then discussed. The remaining challenges and possible directions are finally summarized to highlight future development in this field.