Advances of designing effective and functional electrolyte system for high-stability aqueous Zn ion battery

Aqueous Zn ions battery (ZIBs) is regarded as the most promising alternative energy storage system, which is powered by the aqueous electrolyte. However, uncontrolled water interactions often generate a series of thorny problems to jeopardize the cycle stability of the ZIBs, such as the dissolution of cathode material, the occurrence of hydrogen evolution reaction, and uncontrollable growth of dendrites in the Zn anode. Compared with a great deal of effort on the cathode materials for ZIBs, inadequate attention is received concerning the design of electrolytes aimed at addressing the above-mentioned problems. Although there are review articles about Zn ion electrolytes, a review of electrolyte design strategies for highly stable ZIBs and the key problems they can address is still lacking. Therefore, in this review, the comprehensive introduction to the strategies based on electrolyte engineering is elaborated, containing the type of Zn salt, the concentration of salt, the choice of functional additives, and the design of gel electrolyte and solid electrolyte. In fact, the hydration of Zn2+ ions is one of the main causing of undesired side reactions. And this review also provides an in-depth and fundamental understanding of the effects, mechanisms and strategies of electrolyte modification on Zn2+ solvation shells, which can provide guidelines for the accurate evaluation and analysis of ZIBs in the future. Moreover, several designed strategies for electrolytes are proposed in this review for the further exploration of high performance aqueous rechargeable ZIBs.