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.

Overcoming the Na-ion conductivity bottleneck for the cost-competitive chloride solid electrolytes

Chloride solid electrolytes possess multiple advantages for the construction of safe,energy-dense allsolid-state sodium batteries,but presently the chlorides with sufficiently high cost-competitiveness for commercialization almost all exhibit low Na-ion conductivities of around 10^(-5)S cm^(-1)or lower.Here,we report a chloride solid electrolyte,Na_(2.7)ZFCl_(5.3)O_(0.7),which reaches a Na-ion conductivity of 2.29×10^(-4)S cm^(-1)at 25℃without involving overly expensive raw materials such as rare-earth chlorides or Na_(2)S.In addition to the efficient ion transport,Na_(2.7)ZrCl_(5.3)O_(0.7)also shows an excellent deformability surpassing that of the widely studied Na_(3)PS_(4),Na_(3)SbS_(4),and Na_(2)ZrCl_(6)solid electrolytes.The combination of these advantages allows the all-solid-state cell based on Na_(2.7)ZrCl_(5.3)O_(0.7)and NaCrO_(2)to realize stable room-temperature cycling at a much higher specific current than those based on other non-viscoelastic chloride solid electrolytes in literature(120 mA g^(-1)vs.12-55 mA g^(-1));after 100 cycles at such a high rate,the Na_(2.7)ZFCl_(5.3)O_(0.7)-based cell can still deliver a discharge capacity of 80 mAh g^(-1)at25℃.

A critical review on composite solid electrolytes for lithium batteries:Design strategies and interface engineering

The rapid development of new energy vehicles and 5G communication technologies has led to higher demands for the safety,energy density,and cycle performance of lithium-ion batteries as power sources.However,the currently used liquid carbonate compounds in commercial lithium-ion battery electrolytes pose potential safety hazards such as leakage,swelling,corrosion,and flammability.Solid electrolytes can be used to mitigate these risks and create a safer lithium battery.Furthermore,high-energy density can be achieved by using solid electrolytes along with high-voltage cathode and metal lithium anode.Two types of solid electrolytes are generally used:inorganic solid electrolytes and polymer solid electrolytes.Inorganic solid electrolytes have high ionic conductivity,electrochemical stability window,and mechanical strength,but suffer from large solid/solid contact resistance between the electrode and electrolyte.Polymer solid electrolytes have good flexibility,processability,and contact interface properties,but low room temperature ionic conductivity,necessitating operation at elevated temperatures.Composite solid electrolytes(CSEs) are a promising alternative because they offer light weight and flexibility,like polymers,as well as the strength and stability of inorganic electrolytes.This paper presents a comprehensive review of recent advances in CSEs to help researchers optimize CSE composition and interactions for practical applications.It covers the development history of solid-state electrolytes,CSE properties with respect to nanofillers,morphology,and polymer types,and also discusses the lithium-ion transport mechanism of the composite electrolyte,and the methods of engineering interfaces with the positive and negative electrodes.Overall,the paper aims to provide an outlook on the potential applications of CSEs in solid-state lithium batteries,and to inspire further research aimed at the development of more systematic optimization strategies for CSEs.

How Does Stacking Pressure Affect the Performance of Solid Electrolytes and All-Solid-State Lithium Metal Batteries?

All-solid-state lithium metal batteries(ASSLMBs)with solid electrolytes(SEs)have emerged as a promising alternative to liquid electrolyte-based Li-ion batteries due to their higher energy density and safety.However,since ASSLMBs lack the wetting properties of liquid electrolytes,they require stacking pressure to prevent contact loss between electrodes and SEs.Though previous studies showed that stacking pressure could impact certain performance aspects,a comprehensive investigation into the effects of stacking pressure has not been conducted.To address this gap,we utilized the Li_(6)PS_(5)Cl solid electrolyte as a reference and investigated the effects of stacking pressures on the performance of SEs and ASSLMBs.We also developed models to explain the underlying origin of these effects and predict battery performance,such as ionic conductivity and critical current density.Our results demonstrated that an appropriate stacking pressure is necessary to achieve optimal performance,and each step of applying pressure requires a specific pressure value.These findings can help explain discrepancies in the literature and provide guidance to establish standardized testing conditions and reporting benchmarks for ASSLMBs.Overall,this study contributes to the understanding of the impact of stacking pressure on the performance of ASSLMBs and highlights the importance of careful pressure optimization for optimal battery performance.

In-situ polymerized PEO-based solid electrolytes contribute better Li metal batteries:Challenges,strategies,and perspectives

Polyethylene oxide(PEO)-based solid polymer electrolytes(SPEs)with good electrochemical stability and excellent Li salt solubility are considered as one of the most promising SPEs for solid-state lithium metal batteries(SSLMBs).However,PEO-based SPEs suffer from low ionic conductivity at room temperature and high interfacial resistance with the electrodes due to poor interfacial contact,seriously hindering their practical applications.As an emerging technology,in-situ polymerization process has been widely used in PEO-based SPEs because it can effectively increase Li-ion transport at the interface and improve the interfacial contact between the electrolyte and electrodes.Herein,we review recent advances in design and fabrication of in-situ polymerized PEO-based SPEs to realize enhanced performance in LMBs.The merits and current challenges of various SPEs,as well as their stabilizing strategies are presented.Furthermore,various in-situ polymerization methods(such as free radical polymerization,cationic polymerization,anionic polymerization)for the preparation of PEO-based SPEs are summarized.In addition,the application of in-situ polymerization technology in PEO-based SPEs for adjustment of the functional units and addition of different functional filler materials was systematically discussed to explore the design concepts,methods and working mechanisms.Finally,the challenges and future prospects of in-situ polymerized PEO-based SPEs for SSLMBs are also proposed.

All-solid-state lithium batteries with inorganic solid electrolytes:Review of fundamental science

The scientific basis of all-solid-state lithium batteries with inorganic solid electrolytes is reviewed briefly, touching upon solid electrolytes, electrode materials, electrolyte/electrode interface phenomena, fabrication, and evaluation. The challenges and prospects are outlined as well.

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/ceramicbased 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.

Progress of Solid Electrolytes and the Electrochemical Sensors

Four types of solid state electrochemical sensors and their general principles are introduced in the paper. The novel type-IV sensors developed in the last few years are emphasized to study hereafter. The ways to design new electrochemical sensors and the directions to develop new solid electrolytes for new electrochemical sensors are also discussed.

Nuclear magnetic resonance studies of organic-inorganic composite solid electrolytes

Solid electrolytes have received widespread attention due to their higher safety than liquid electrolytes in the past decades.In particular,organic-inorganic composite solid electro-lytes(CSEs)in which inorganic fllers dispersed in polymer solid electrolytes are consid-ered to be one of the most promising candidate electrolytes for high-performance solid-state lithium batteries.Understanding the local environments and the conduction pathway/dynamics of Lit is essential for the design of high-performance CSEs.Nuclear magnetic resonance(NMR)is a non-invasive quantitative technique that has unique ca-pabilities in providing molecular structure information,morphological evolution,and measuring the movement of ions at different time scales.Therefore,for battery re-searchers,an accurate and comprehensive under standing of the basic principles and experimental design of solid-state NMR(SSNMR)is of great significance for investigating the abundant molecular structure and dynamics information in CSEs.The specific appli-cations of the SSNMR technique in CSEs are briefly introduced in this present review.

Improving ionic conductivity of polymer-based solid electrolytes for lithium metal batteries

Because of its superior safety and excellent processability,solid polymer electrolytes(SPEs)have attracted widespread attention.In lithium based batteries,SPEs have great prospects in replacing leaky and flammable liquid electrolytes.However,the low ionic conductivity of SPEs cannot meet the requirements of high energy density systems,which is also an important obstacle to its practical application.In this respect,escalating charge carriers(i.e.Li^(+))and Li^(+)transport paths are two major aspects of improving the ionic conductivity of SPEs.This article reviews recent advances from the two perspectives,and the underlying mechanism of these proposed strategies is discussed,including increasing the Li^(+)number and optimizing the Li^(+)transport paths through increasing the types and shortening the distance of Li^(+)transport path.It is hoped that this article can enlighten profound thinking and open up new ways to improve the ionic conductivity of SPEs.

In situ Observation of Li Deposition-Induced Cracking in Garnet Solid Electrolytes

Lithium(Li)penetration through solid electrolytes(SEs)induces short circuits in Li solid-state batteries(SSBs),which is a critical issue that hinders the development of high energy density SSBs.While cracking in ceramic SEs has been often shown to accompany Li penetration,the interplay between Li deposition and cracking remains elusive.Here,we constructed a mesoscale SSB inside a focused ion beam-scanning electron microscope(FIB-SEM)for in situ observation of Li deposition-induced cracking in SEs at nanometer resolution.Our results revealed that Li propagated predominantly along transgranular cracks in a garnet Li_(6.4)La_(3)Zr_(1.4)Ta_(0.6)O_(12)(LLZTO).Cracks appeared to initiate from the interior of LLZTO beneath the electrode surface and then propagated by curving toward the LLZTO surface.The resulting bowl-shaped cracks resemble those from hydraulic fracture caused by high fluid pressure on the surface of internal cracks,suggesting that the Li deposition-induced pressure is the major driving force of crack initiation and propagation.The high pressure generated by Li deposition is further supported by in situ observation of the flow of filled Li between the crack flanks,causing crack widening and propagation.This work unveils the dynamic interplay between Li deposition and cracking in SEs and provides insight into the mitigation of Li dendrite penetration in SSBs.

A panoramic view of Li_(7)P_(3)S_(11) solid electrolytes synthesis, structural aspects and practical challenges for all-solid-state lithium batteries

The development of an inorganic electrochemical stable solid-state electrolyte is essentially responsible for future state-of-the-art all-solid-state lithium batteries(ASSLBs).Because of their advantages in safety,working temperature,high energy density,and packaging,ASSLBs can develop an ideal energy storage system for modern electric vehicles(EVs).A solid electrolyte(SE)model must have an economical synthesis approach,exhibit electrochemical and chemical stability,high ionic conductivity,and low interfacial resistance.Owing to its highest conductivity of 17 mS·cm^(-1),and deformability,the sulfide-based Li_(7)P_(3)S_(11) solid electrolyte is a promising contender for the high-performance bulk type of ASSLBs.Herein,we present a current glimpse of the progress of synthetic procedures,structural aspects,and ionic conductivity improvement strategies.Structural elucidation and mechanistic approaches have been extensively discussed by using various characterization techniques.The chemical stability of Li_(7)P_(3)S_(11) could be enhanced via oxide doping,and hard and soft acid/base(HSAB)concepts are also discussed.The issues to be undertaken for designing the ideal solid electrolytes,interfacial challenges,and high energy density have been discoursed.This review aims to provide a bird’s eye view of the recent development of Li_(7)P_(3)S_(11)-based solid-state electrolyte applications and explore the strategies for designing new solid electrolytes with a target-oriented approach to enhance the efficiency of high energy density allsolid-state lithium batteries.

Development of Doped Lanthanum Gallate Solid Electrolytes

Development of the doped lanthanum gallate solid electrolytes in the recent years was reviewed. The structure and oxygen ion transference mechanism were discussed. Effects of alkali earths, transition metals, and impurities on electrical conductivity of the doped lanthanum gallates were also discussed. The applications of doped lanthanum gallate were described. The current problems and corresponding strategies were explored.

Tuning hybrid liquid/solid electrolytes by lowering Li salt concentration for lithium batteries

Hybrid liquid/solid electrolytes（HLSEs） consisting of conventional organic liquid electrolyte（LE）, polyacrylonitrile（PAN）, and ceramic lithium ion conductor Li（1.5）Al（0.5）Ge（1.5）（PO4）3（LAGP） are proposed and investigated. The HLSE has a high ionic conductivity of over 2.25 × 10^（-3） S/cm at 25？C, and an extended electrochemical window of up to 4.8 V versus Li/Li＋. The Li｜HLSE｜Li symmetric cells and Li｜HLSE｜Li FePO4 cells exhibit small interfacial area specific resistances（ASRs） comparable to that of LE while much smaller than that of ceramic LAGP electrolyte, and excellent performance at room temperature. Bis（trifluoromethane sulfonimide） salt in HLSE significantly affects the properties and electrochemical behaviors. Side reactions can be effectively suppressed by lowering the concentration of Li salt. It is a feasible strategy for pursuing the high energy density batteries with higher safety.

Space Charge Layer Eff ect in Sulfide Solid Electrolytes in All-Solid-State Batteries: In-situ Characterization and Resolution

All-solid-state lithium batteries(ASSLBs)have advantages of safety and high energy density,and they are expected to become the next generation of energy storage devices.Sulfide-based solid-state electrolytes(SSEs)with high ionic conduc-tivity and low grain boundary resistance exhibit remarkable practical application.However,the space charge layer(SCL)eff ect and high interfacial resistance caused by a mismatch with the current commercial oxide cathodes restrict the develop-ment of sulfide SSEs and ASSLBs.This review summarizes the research progress on the SCL eff ect of sulfide SSEs and oxide cathodes,including the mechanism and direct evidence from high performance in-situ characterizations,as well as recent progress on the interfacial modification strategies to alleviate the SCL eff ect.This study provides future direction to stabilize the high performance sulfide-based solid electrolyte/oxide cathode interface for state-of-the-art ASSLBs and future all-SSE storage devices.

Synthesis and Conductivity Characterization of Anti-Perovskite Na3OX Solid Electrolytes for All Solid Na-Ion Batteries

Solid electrolytes for all solid sodium-ion batteries have been attracting much attention as an alternative energy storage system, which have the advantage of being extremely safe because it can be charged quickly and is nonflammable. We have synthesized anti-perovskite type Na3OX (X = Br, and I) electrolytes with high purity, by reactions of halogen mixtures with sodium oxides. After mixing, it was filled in an alumina crucible and heated for 6 hours at 330°C. It was confirmed that a large crystal strain was introduced by eutectication, which might reduce the activation energy of Na ion conduction and lead to an improvement of the conductivity. A relatively higher ionic conductivity of σ = 1.55 × 10-7 S/cm at 60°C has been obtained for Na3OBr0.6I0.4, which is about three orders higher than that in literature. A different ratio of X (X = Br, I) ions was added into sodium oxide to make the Na3OX crystal. The influence of strain introduction on optimizing the bottleneck and improving the conductivity was discussed.

Energy ceramic design for robust battery cathodes and solid electrolytes

Microstructural design and processing science of ceramics from materials to devices are critical to the present and future applications in various fields.They have profound effects on the mechanical and functional properties,as well as the reliability and lifetime of ceramics.The stability issue has been attracting more and more attentions,as many devices are pushed towards extreme service conditions to gain additional benefits such as energy density and efficiency.In this pespective article,we shall discuss on four selected topics of energy ceramic design,including the oxygen evolution issue of oxide battery cathodes under extreme charge voltages,the synthesis conundrum of single-crystalline battery cathodes,the metal/ceramic interface contact problem in all-solid-state lithium-metal batteries,and the nature of hole polarons in oxygen ion and protonic ceramic electrolytes.Our understanding and solutions to these challenging problems shall be discussed.The new fundamental insights and rationally optimized processing practices presented here could help to develop advanced interdisciplinary ceramics further,enabling exciting applications in the coming decades.

Enhancement of–OH content on mechanical properties of antiperovskite solid electrolytes

All-solid-state batteries,renowned for their enhanced safety and high energy density,have garnered broad interest.Oxide solid electrolytes are highly anticipated for their balanced performance.However,their high Young’s modulus and inadaptability to volume change during cycling lead to poor contact and eventual battery failure.In this work,Young’s modulus of Li_(1+x)(OH)_(x)Cl samples is lowered to a level comparable to that of sulfide by regulating the–OH content.As the–OH content increases,Young’s modulus of Li_(1+x)(OH)_(x)Cl samples decreases significantly.This may be due to the local aggregation of–OH groups,forming cavities similar to LiOH structure,which reduces the bonding of the structure.On the premise of high Li-ion conductivity and electrochemical stability,the lowered Young’s modulus improves the contact between the solid electrolyte and the electrodes,forming a strong and stable interfacial layer,thereby improving interfacial and cycling stability.The symmetrical lithium metal cell shows excellent cycle performance of 600 h,and the assembled LiFePO_(4)|Li_(2.4)(OH)1.4Cl|Li cell shows significantly enhanced cycling endurance with 80%capacity retention after 150 cycles.This work not only emphasizes the crucial importance of Young’s modulus in improving interface issues but also offers innovative approaches to advance the mechanical properties of solid electrolytes.

Structure designing,interface engineering,and application prospects for sodium-ion inorganic solid electrolytes

All-solid Na-ion batteries(ASNIBs)present significant potential for integration into large-scale energy storage systems,capitalizing on their abundant raw materials,exemplary safety,and high energy density.Among the pivotal components propelling the advancement of ASNIBs,inorganic solid electrolytes(ISEs)have garnered substantial attention in recent years due to their high ionic conductivity(σ),wide electrochemical stability window(ESW),and high shear modulus.Herein,this review systematically encapsulates the latest strides in Na-ion ISEs,furnishing a comprehensive panorama of various ISE systems along with their interface engineering strategies against the electrodes.The prime focus resides in accentuating key strategies for refining ion conduction properties and interfacial compatibility of ISEs through structure design and interface modification.Furthermore,the review explores the foremost challenges and prospects inherent to sodium-ion ISEs,striving to deepen our understanding of how to engineer more robust and efficient ISEs and interface stability,poised for the forthcoming era of advanced ASNIBs.

Sandwich-type composited solid polymer electrolytes to strengthen the interfacial ionic transportation and bulk conductivity for all-solid-state lithium batteries from room temperature to 120℃

The insurmountable charge transfer impedance at the Li metal/solid polymer electrolytes(SPEs)interface at room temperature as well as the ascending risk of short circuits at the operating temperature higher than the melting point,dominantly limits their applications in solid-state batteries(SSBs).Although the inorganic filler such as CeO_(2)nanoparticle content of composite solid polymer electrolytes(CSPEs)can significantly reduce the enormous charge transfer impedance at the Li metal/SPEs interface,we found that the required content of CeO_(2)nanoparticles in SPEs varies for achieving a decent interfacial charge transfer impedance and the bulk ionic conductivity in CSPEs.In this regard,a sandwich-type composited solid polymer electrolyte with a 10%CeO_(2)CSPEs interlayer sandwiched between two 50%CeO_(2)CSPEs thin layers(sandwiched CSPEs)is constructed to simultaneously achieve low charge transfer impedance and superior ionic conductivity at 30℃.The sandwiched CSPEs allow for stable cycling of Li plating and stripping for 1000 h with 129 mV polarized voltage at 0.1 mA cm^(-2)and 30℃.In addition,the LiFePO_(4)/Sandwiched CSPEs/Li cell also exhibits exceptional cycle performance at 30℃and even elevated120℃without short circuits.Constructing multi-layered CSPEs with optimized contents of the inorganic fillers can be an efficient method for developing all solid-state PEO-based batteries with high performance at a wide range of temperatures.