Realizing high-voltage aqueous zinc-ion batteries with expanded electrolyte electrochemical stability window

Aqueous zinc-ion batteries(AZIBs) have aroused significant research interest around the world in the past decade. The use of low-cost aqueous electrolytes and a metallic Zn anode with a suitable redox potential and high energy density make AZIBs a potential alternative to commercial Li-ion batteries in the development of next-generation batteries. However, owing to the narrow electrochemical stability window(ESW) of aqueous electrolytes, the choice of cathode materials is limited, because of which AZIBs exhibit a relatively low operating voltage and energy density. Hence, expanding the ESW of aqueous electrolytes is important for the development of practical AZIBs. This paper systematically reviews the electrolyte engineering strategies being explored to broaden the ESW of AZIBs. An in-depth analysis of high-voltage AZIBs is also presented. We suggest that the realization of high-voltage AZIBs depends on the synergistic development of suitable electrolytes and cathode materials. In addition, the cost associated with their fabrication as well as the use of standardized electrochemical tests should be considered during the design of high-voltage AZIBs.

Trend of Developing Aqueous Liquid and Gel Electrolytes for Sustainable,Safe,and High‑Performance Li‑Ion Batteries

Current lithium-ion batteries(LIBs)rely on organic liquid electrolytes that pose significant risks due to their flammability and toxicity.The potential for environmental pollution and explosions resulting from battery damage or fracture is a critical concern.Water-based(aqueous)electrolytes have been receiving attention as an alternative to organic electrolytes.However,a narrow electrochemicalstability window,water decomposition,and the consequent low battery operating voltage and energy density hinder the practical use of aqueous electrolytes.Therefore,developing novel aqueous electrolytes for sustainable,safe,high-performance LIBs remains challenging.This Review first commences by summarizing the roles and requirements of electrolytes–separators and then delineates the progression of aqueous electrolytes for LIBs,encompassing aqueous liquid and gel electrolyte development trends along with detailed principles of the electrolytes.These aqueous electrolytes are progressed based on strategies using superconcentrated salts,concentrated diluents,polymer additives,polymer networks,and artificial passivation layers,which are used for suppressing water decomposition and widening the electrochemical stability window of water of the electrolytes.In addition,this Review discusses potential strategies for the implementation of aqueous Li-metal batteries with improved electrolyte–electrode interfaces.A comprehensive understanding of each strategy in the aqueous system will assist in the design of an aqueous electrolyte and the development of sustainable and safe high-performance batteries.

Asymmetric Electrolytes Design for Aqueous Multivalent Metal Ion Batteries

With the rapid development of portable electronics and electric road vehicles,high-energy-density batteries have been becoming front-burner issues.Traditionally,homogeneous electrolyte cannot simultaneously meet diametrically opposed demands of high-potential cathode and low-potential anode,which are essential for high-voltage batteries.Meanwhile,homogeneous electrolyte is difficult to achieve bi-or multi-functions to meet different requirements of electrodes.In comparison,the asymmetric electrolyte with bi-or multi-layer disparate components can satisfy distinct requirements by playing different roles of each electrolyte layer and meanwhile compensates weakness of individual electrolyte.Consequently,the asymmetric electrolyte can not only suppress by-product sedimentation and continuous electrolyte decomposition at the anode while preserving active substances at the cathode for high-voltage batteries with long cyclic lifespan.In this review,we comprehensively divide asymmetric electrolytes into three categories:decoupled liquid-state electrolytes,bi-phase solid/liquid electrolytes and decoupled asymmetric solid-state electrolytes.The design principles,reaction mechanism and mutual compatibility are also studied,respectively.Finally,we provide a comprehensive vision for the simplification of structure to reduce costs and increase device energy density,and the optimization of solvation structure at anolyte/catholyte interface to realize fast ion transport kinetics.

Challenges of polymer electrolyte with wide electrochemical window for high energy solid-state lithium batteries

With the rapid development of energy storage technology,solid-state lithium batteries with high energy density,power density,and safety are considered as the ideal choice for the next generation of energy storage devices.Solid electrolytes have attracted considerable attention as key components of solid-state batteries.Compared with inorganic solid electrolytes,solid polymer electrolytes have better flexibility,machinability,and more importantly,better contact with the electrode,and low interfacial impedance.However,its low ionic conductivity,narrow electrochemical stability window(ESW),and poor mechanical properties at room temperature limit its development and practical applications.In recent years,many studies have focused on improving the ionic conductivity of polymer electrolytes;however,few systematic studies and reviews have been conducted on their ESWs.A polymer electrolyte with wide electrochemical window will aid battery operation at a high voltage,which can effectively improve their energy density.Moreover,their stability toward lithium metal anode is also important.Therefore,this review summarizes the recent progress of solid polymer electrolytes on the ESW,discusses the factors affecting ESW of polymer electrolytes,and analyzes a strategy to broaden the window from the perspective of molecular interaction,polymer structural design,and interfacial tuning.The development trends of polymer electrolytes with wide electrochemical windows are also presented.

Reshaping Electrolyte Solvation Structure for High-Energy Aqueous Batteries

A highlight on reshaping aqueous electrolyte solvation structure for highenergy batteries is provided.Firstly,the recent key design routes for regulating solvation structure to widen electrochemical stability window(ESW)of aqueous electrolyte are briefly summarized.Then,the groundbreaking work of Wang et al.on reshaping electrolyte structure using urea as the diluent is elaborated.Finally,the significance of Wang's work is highlighted.

Electrochemically stable lithium-ion and electron insulators(LEIs)for solid-state batteries

Rechargeable solid-state Li metal batteries demand ordered flows of Li-ions and electrons in and out of solid structures,with repeated waxing and waning of Ubcc phase near contact interfaces which gives rise to various electro-chemo-mechanical challenges.There have been approaches that adopt three-dimensional(3D)nanoporous architectures consisting of mixed ion-electron conductors(MIECs)to combat these challenges.However,there has remained an issue of LiBcc nucleation at the interfaces between different solid components(e.g.,solid electrolyte/MlEC interface),which could undermine the interfacial bonding,thereby leading to the evolution of mechanical instability and the loss of ionic/electronic percolation.In this regard,the present work shows that the Li-ion and electron insulators(LEIs)that are thermodynamically stable against LiBcc could combat such challenges by blocking transportation of charge carriers on the interfaces,analogous to dielectric layers in transistors.We searched the ab initio database and have identified 48 crystalline compounds to be LEI candidates(46 experimentally reported compounds and 2 hypothetical compounds predicted to be stable)with a band gap greater than 3 eV and vanishing Li solubility.Among these compounds,those with good adhesion to solid electrolyte and mixed ion-electron conductor of interest,but are lithiophobic,are expected to be the most useful.We also extended the search to Na or K metal compatible alkali-ion and electron insulators,and identified some crystalline compounds with a property to resist corresponding alkali-ions and electrons.

Hydrogen isotope effects: A new path to high-energy aqueous rechargeable Li/Na-ion batteries

Aqueous rechargeable Li/Na-ion batteries have shown promise for sustainable large-scale energy storage due to their safety,low cost,and environmental benignity.However,practical applications of aqueous batteries are plagued by water's intrinsically narrow electrochemical stability window,which results in low energy density.In this perspective article,we review several strategies to broaden the electrochemical window of aqueous electrolytes and realize high-energy aqueous batteries.Specifically,we highlight our recent findings on stabilizing aqueous Li storage electrochemistry using a deuterium dioxide-based aqueous electrolyte,which shows significant hydrogen isotope effects that trigger a wider electrochemical window and inhibit detrimental parasitic processes.