Optimal Design Of Electrolyte Additive For High-Performance Aqueous Zinc-Ion Battery And Study On The Reversibility Of Zinc Anode

Compared with lithium-ion batteries on the market,aqueous zinc-ion batteries have attracted extensive attention from researchers because of their high safety,low cost,low pollution and high theoretical specific capacity(mass specific capacity 820 m Ah g^-1,volume capacity 5855 m Ah cm^-3).However,aqueous zinc-ion batteries also face many challenges in the development process;For example,the growth of zinc dendrites,corrosion of zinc anodes,hydrogen evolution and other problems will greatly shorten the cycle life of aqueous zinc-ion batteries.At present,researchers have done a lot of work to solve these problems:for example:the construction of a protective layer on the surface of zinc anodes,the development of ultra-concentrated salt electrolytes,solid electrolytes,and gel electrolytes;These works have made certain breakthroughs in solving many problems faced by zinc anodes,but these solutions also have shortcomings,they either have more stringent requirements in the process or require higher costs.Here we start with the electrolyte,and introduce additives in the electrolyte to inhibit the growth of zinc dendrites and the corrosion of zinc anodes,which is due to the simple and easy operation of the process of introducing additives to prepare electrolytes,and the cost of additives used is low.Therefore,we designed three electrolyte additives to inhibit the growth of zinc dendrites and the corrosion of zinc anodes to improve the cycling performance of aqueous zinc-ion batteries.The main studies are as follows:（1）we selected trimethyl phosphate（TMP）as an electrolyte additive to study its effect on the electrochemical performance of zinc anodes in aqueous zinc-ion batteries.Studies have shown that the cycle life of Zn//Zn symmetrical batteries operating under the electrolyte of trimethyl phosphate as an additive has been greatly improved.Moreover,under the condition of current density of 1 m A cm^-2 and area capacity of 0.5 m A h cm^-2,the Zn//Cu half-cell can run smoothly after 800 cycles of smooth operation.This shows that the introduction of trimethyl phosphate additives makes the battery system stable.After a full battery assembled with V₂O₅,the specific capacity reaches 60 m A h g^-1 after 1000 cycles at a current density of1 A g^-1.This is because the electron cloud density of oxygen atoms in trimethyl phosphate is higher the that of oxygen atoms in water,which is used to destroy the network structure of water,the solvation structure of zinc and reduce the activity of water,while inhibiting the formation of zinc dendrites and the occurrence of side reactions,inhibiting the formation of zinc dendrites,which can improve the stability of the electrolyte.We proved that trimethyl phosphate additives have an inhibitory effect on the formation of zinc dendrites by dissecting the battery and observing the zinc anode by scanning electron microscopy.（2）we selected dimethyl sulfoxide as an electrolyte additive to study its effect on the electrochemical performance of zinc anode in aqueous zinc-ion batteries.By introducing dimethyl sulfoxide（DMSO）into the electrolyte,the diffusion behavior of zinc ions changed,where two-dimensional（2D）diffusion time of zinc ions is shortened.Meanwhile,zinc ions quickly enter the 3D diffusion stage,which shortens the"tip effect"time of zinc ions and effectively inhibits the growth of zinc dendrites during the cycle.Since the number of Goodman donors in DMSO is higher than that of H₂O,it can replace the water in the zinc ion solvation sheath,and a stable hydrogen bond can be formed between DMSO and H₂O to reduce the activity of water,inhibit the hydrogen evolution reaction and the corrosion of the zinc anode,and then greatly improve the reversibility of the zinc anode.In the electrolyte with 20%DMSO,the Zn//Zn symmetric battery can be stably cycled for 3000 h at a current density of 1 m A cm^-2,and the Zn//Cu half-cell can work stably for 2100 cycles.After the Zn//Mn O₂ full cell work for 800 times at a current density of 2 C,the capacity of electrolyte with DMSO additives is still as high as 100 m A h g^-1.This work provides a new strategy for developing high-performance aqueous zinc-ion batteries.（3）Ethylene glycol monomethyl ether（MOE）with medium ligand field was selected as the electrolyte additive,and MOE molecules were used to replace H₂O molecules in the Zn²⁺solvation sheath to form a stable water-deficient solvation sheath,which can achieve rapid zinc nucleation/dissolution kinetics and significantly inhibit hydrogen evolution reaction（HER）.At the same time,through electrochemical performance test and physical characterization,it was found that the deposition/stripping reversibility of zinc ions,the cycle life of Zn//Zn symmetrical battery and Zn//Cu half-cell,and the capacity retention rate of Zn//V₂O₅ full-cell were significantly improved.The Zn//Zn symmetrical battery can be stably cycled for 4300 hours at a current density of 1 m A cm^-2,the Zn//Cu half-cell can be stably cycled for 2000 cycles,and the capacity of the Zn//V₂O₅ full-cell is still as high as 100 m Ah g^-1 after 1000 cycles at a current density of 5 A g^-1.It shows that the introduction of MOE improves the overall performance of zinc ion batteries.This work provides a new idea for the design of the solvation sheath of aqueous zinc ion batteries.