Ionic Liquid Based Zinc-ion Battery Electrolytes

Zinc metal anode,which is highly compatible with aqueous electrolytes,has the advantages of low redox potential and abundant reserves.Therefore,zinc-ion batteries based on zinc metal anode and aqueous electrolyte systems are considered to be one of the hot spots for next-generation safe and inexpensive energy storage technologies.Despite the fast ion transport and high conductivity of aqueous zinc-ion batteries,there are still problems such as low electrochemical window,severe electrode interface side reactions and growth of Zn dendrites.In order to solve these problems,organic electrolytes have been used in zinc-ion batteries in recent years.Although the electrochemical window is improved and the electrode interface side reactions are suppressed to some extent,the high safety and ion transfer efficiency inherent in aqueous electrolytes are sacrificed.Imidazolium ionic liquids,with high ionic conductivity,wide electrochemical window,good thermal stability and low volatility,can be used as additives to significantly improve the performance of electrolytes and compensate for the shortcomings of aqueous and organic electrolytes,which will open up the possibility of developing highly safe and stable zinc-ion batteries.Nevertheless,the development of ionic liquid-based zinc-ion electrolyte is slow and the mechanism of action in different types of electrolytes is still unclear.The performance of battery still needs to be improved.This paper develops ionic liquid-based aqueous electrolytes and solid electrolytes from the structure and advantages of imidazolium ionic liquids,and investigates in depth the effects of imidazolium ionic liquid addition,cation structure and hydrophobicity on zinc-ion batteries,in order to obtain highly stable zinc ion batteries.The details are as follows:（1）It is proposed to introduce imidazolium ionic liquids as additives into the aqueous electrolyte to change the water environment of electrolytes.BMIM（OTf）is selected and the ratio of water is adjusted to obtain a wide electrochemical window and a high ionic conductivity of electrolytes.The ionic liquids with different cation side chain lengths were compared to clarify the effect and mechanism of inhibiting Zn dendrites in aqueous electrolytes,to obtain dendrite-free zinc-ion batteries.It can be cycled for 2200 h at low current density.（2）The composite of imidazolium ionic liquids,zinc salts and PVDF-HFP polymer framework was used to prepare ionogel electrolytes for zinc-ion batteries to overcome the problem of easy leakage and volatilization of aqueous electrolytes.Three kinds of imidazolium ionic liquids（with different side chain lengths）were compared to clarify the mechanism of the imidazolium cation structure on Zn dendrites in ionogel electrolytes to obtain solid-state zinc-ion batteries with wide electrochemical windows and dendrite-free growth,of which cycle life can reach 2500 h.（3）It is proposed to introduce interfacial water and internal water into the ionogel electrolytes,to achieve the regulation of the distribution of interfacial water and internal water in the ionogel electrolyte,by changing the matrix and the type of ionic liquid.The fusion of water and ionic liquid in the interface and internal forms the rapid migration of Zn²⁺to improve the ionic conductivity in the solid-state system and the reaction kinetics of the cell to improve its interfacial stability,of which cycle life can reach 5500 h.