Design Of Organic Electrolytes And Study On Solvation Structure Of Zinc Ion Batteries

Among the many alternatives to lithium ion batteries,zinc ion batteries have become one of the most promising new-generation electrochemical energy storage devices due to their high energy densities(820 m Ah g^-1 and 5855 m Ah cm^-3),abundant reserves,low cost and environmental friendliness.However,there are still many challenges of zinc ion batteries.The development of zinc ion batteries is severely restricted by the uncontrolled growth of zinc dendrites,by-products generation,corrosion and hydrogen evolution reaction（HER）caused by free water molecules in traditional aqueous electrolytes.Among them,uncontrolled dendrite growth will lead to the reduction of coulombic efficiency of the battery,and even breakdown of the diaphragm to make the battery short circuit.The formation of by-products will lead to low utilization rate of zinc anode and unstable internal electrochemical system.As a bridge connecting cathode and anode,the electrolyte provides a necessary working environment of the battery.In order to alleviate dendrite growth and side reactions,two organic electrolytes are designed from the point of view of electrolyte modification.The electrochemical performances and solvation structure of zinc ion batteries with different electrolytes are studied.The improved battery performances further prove the feasibility of these two organic electrolytes.The main research contents of this paper are as follows:（1）Design and properties of glutaronitrile-based electrolyte.A new electrolyte based on glutaronitrile is formed by adding Zn（Cl O₄）₂·6H₂O to glutaronitrile solvent.Raman spectroscopy and molecular dynamics simulations show that the strong coordination between Zn²⁺and GN can effectively regulate the solvation structure of Zn²⁺.Moreover,most H₂O molecules in the electrolyte exist in a bound state rather than a free state.Owing to the unique solvation structure of Zn²⁺,Zn||Zn symmetrical cells can be stable cycle more than 800 hours,and the coulombic efficiency of Zn||Cu half cells can reach 99%.XRD and XPS show that the Zn O-rich solid electrolyte interface（SEI）formed on the zinc electrode surface of the battery using GN-based electrolyte can effectively inhibit dendrite growth and side reactions,and improve the stability of the battery.In addition,Zn||NH₄V₄O₁₀ full cells using GN-based electrolyte can maintain2500 cycles and obtain 239 m Ah g^-1 high specific capacity.In addition,the full cell can still maintain more than 100 cycles even at the low temperature of-13℃.Finally,the differences in the electrochemical reaction mechanism of NH₄V₄O₁₀ cathode in different electrolytes are revealed by ex-situ XRD.（2）Design and properties of trimethyl phosphate-based non-flammable electrolyte.In order to solve the problems of dendrite growth and side reactions of zinc electrode,and avoid the risk of flammable organic electrolyte,a non-flammable organic electrolyte composed of Zn（Cl O₄）₂·6H₂O and TMP is designed.Molecular dynamics simulations show that the coordination between TMP and Zn²⁺in the TMP-based electrolyte weaken the binding affinity between Zn²⁺with H₂O and Cl O₄^-in the solvated shell,leading to an increase in atomic distance.Zn||Zn symmetric cells using TMP electrolye can be stable more than 2000 hours.At the same time,the long cycle performance and rate performance of the full cells are obviously better than that of the aqueous electrolyte.Through XRD and XPS analysis,it can also be found that a layer of SEI rich in zinc phosphate will form on the surface of the zinc electrode using TMP electrolyte during the cycle.This layer of SEI inhibits the formation of side reactions and guides uniform zinc deposition.In addition,by analyzing the pseudocapacitance,it can be found that the excellent electrochemical performance of the TMP electrolyte is related to its high capacitance contribution rate.