Electrolyte Regulation By Adding Organic Additives Toward Stable Zinc Anode For Zinc Ion Batteries

Aqueous zinc-ion batteries are energy storage devices in which water is employed as electrolyte solvent.They are more suitable for large-scale energy storage applications compared to traditional lithium-ion batteries due to their high theoretical specific capacity(820 m Ah g^-1),suitable oxidation-reduction potential（-0.76 V vs SHE）,low cost,safety,and environmental friendliness.However,aqueous zinc ion batteries also face some challenges,including the growth of zinc dendrites,side reactions,and limitations in energy density.These issues would deteriorate the cycle life,safety,and efficiency of aqueous zinc ion batteries.To address these issues,researchers have conducted numerous strategies,such as modification of cathode materials,design of zinc anode surfaces,and optimization of electrolytes.Among them,electrolytes play an important role in aqueous zinc-ion batteries which facilitate the transportation of zinc ions and exert a significant influence on the zinc anode.Therefore,electrolyte regulation is considered as one of the most efficient methods to solve the problem of aqueous zinc-ion batteries.Compared with other electrolyte regulation strategies that require a large number of zinc salts and organic compounds,such as“water in salt”,deep eutectic solvents,and water-in-gel electrolytes,electrolyte additives are a simple and economical method.Therefore,this thesis designed two organic electrolyte additives（trimethyl phosphate and sulfolane）for aqueous zinc ion batteries.Organic compounds can preferentially adsorb on the surface of the Znanode electrode,thereby guiding the deposition of Zn²⁺along the（002）plane direction of the zinc anode.Compared with other crystal planes,the（002）plane has a stronger effect of corrosion resistance and inhibition of hydrogen evolution reaction,which can prolong the life of the zinc anode.The main contents are as follows:（1）Trimethyl phosphate（TMP）was used as an additive in ZnSO₄ electrolyte to guide the deposition of Zn²⁺on the（002）plane of the Znanode electrode,thereby inhibiting dendrite growth and side reactions.The experimental results show that TMP molecules participate in the solvation structure of zinc ions,preventing water molecules from contacting the Znanode electrode,and weakening hydrogen evolution and side reactions.At the same time,TMP molecules preferentially adsorbed on the surface of the Znanode electrode,guiding Zn²⁺to deposit uniformly along the（002）plane direction.Therefore,the battery could cycle for 1400 h at a current density of 1 m A cm^-2 in 2 M ZnSO₄+5%TMP electrolyte.The average coulombic efficiency of the Zn||Cu half-cell cycled at a current density of 1 m A cm^-2 for 800 cycles was as high as 99.5%.The Zn||V₂O₅ cell maintains a high capacity retention after 500 cycles at a current density of 1 A g^-1.（2）Using economical ZnSO₄ as the zinc salt and sulfolane as an additive effectively suppress dendrite growth and side reactions on the zinc anode.XRD and SEM characterization revealed that after adding 2%volume ratio of sulfolane,dendrite growth and electrochemical corrosion on the zinc anode were significantly alleviated.In addition,sulfolane molecules preferentially adsorbed on the surface of the zinc anode,guiding Zn²⁺to deposit along the（002）plane direction,thereby suppressing zinc dendrite growth and improving the stability of the Znanode electrode.At the same time,sulfolane can prevent water molecules from contacting the zinc anode electrode,and avoid a large number of water molecules decomposing on the zinc anode electrode to produce H₂,thereby suppressing the occurrence of hydrogen evolution reaction and improving the coulombic efficiency of the battery.The suppression of dendrite growth and formation of by-products were also more evident in the Zn||V₂O₃ cell cycling,with higher capacity after 500 cycles at a current density of 2 A g^-1.