Electrolyte additive engineering for aqueous Zn ion batteries

Aqueous Zn ion batteries (AZIBs) are one of the most promising new-generation electrochemical energy storage devices with high specific capacity, good security, and economic benefits. The electrolyte acts as a bridge connecting cathode and anode, providing a realistic working environment. However, using aqueous electrolytes presents many challenges for cathode (dissolution, electrostatic interaction, by-products) and anode (Zn dendrite, side reactions). As an innovative and maneuverable technology, additive engineering has effectively solved electrodes' critical problems. Therefore, it is essential to systematically summarize additive engineering and explore new perspectives in response to the existing issues. Based on the challenges of electrolytes for electrodes, the review focuses on an overview of the effects of additive engineering on cathode and anode, respectively. Additive engineering can improve the problems existing in the cathode, such as relieving dissolution, adjusting electrostatic interaction, and reducing by-products. The effects on anode are summarized in aspects of inhibiting Zn dendrites and reducing side reactions. In addition, the effects of different additives on the charge storage mechanism as well as the kinetic characteristics of AZIBs are described separately. Finally, the potential directions and development prospects for further improvement of additive engineering in AZIBs are proposed. In this review, we retrospect the challenges faced by the cathode and anode of AZIBs during the use of aqueous electrolytes. As an innovative and maneuverable technology, additive engineering can be used to effectively solve most of the critical problems of cathode and anode. Thus, a comprehensive overview of additive engineering strategies is presented from a new perspective of function and mechanism. Finally, potential directions and development prospects for further improvement of additive engineering in AZIBs are presented based on the authors’ best knowledge.