Insight into the electrolyte strategies for aqueous zinc ion batteries

Energy crisis caused by traditional energy utilization technology intensifies the demand for high energy density and environmentally friendly secondary batteries. As prospective alternative energy source with high capacity, rechargeable aqueous zinc ion batteries (AZIBs) have raised great concern. In AZIBs, electrolyte plays an important role in determining operating window, electrochemical performance, security, flexibility and cost. This review describes the insight into the electrolyte strategies for AZIBs. Firstly, diverse electrolytes consisting of organic, inorganic and hybrid zinc salts are classified and evaluated by chemical composition and property. Secondly, the choice of electrolyte concentration containing moderate and ultra-high concentration is discussed. Thirdly, flexible hydrogel electrolytes are introduced by different cross-linking types, including chemical cross-linking, physical cross-linking and uncross-linking. Fourthly, aqueous bio-electrolytes are prospected as good biocompatible or biodegradable candidate. Finally, the bottleneck and possible future development direction are put forward for the electrolytes of AZIBs.