Synthesis And Electrochemical Performance Of Lithium-Rich Li₃OCl And Li₃InCl₆ Solid Electrolytes

With the global energy shortage and increasingly serious environmental pollution, it has become a global consensus to seek sustainable and degradable new environmentally friendly energy.In recent years,lithium-ion batteries have been widely used in electronic products,energy storage,electric vehicles and other fields.However,the commercial lithium batteries have safety problems due to the use of organic liquid electrolyte.Recently,all-solid-state lithium batteries have attracted much attention due to their reliable safety.The core material of all solid-state lithium batteries is solid-state electrolyte,which is one of the important factors affecting the performance of all solid-state lithium batteries.Among the numerous solid electrolytes,Li₃OCl and Li₃In Cl₆ solid electrolytes are considered to be the most attractive candidates.Anti-perovskite Li₃OCl solid electrolyte has a wide electrochemical stability window and it is very stable for lithium metal anode.However,due to its low ionic conductivity at room temperature,it is difficult to meet the requirements of all-solid-state lithium batteries for solid electrolyte ionic conductivity.The solid electrolyte of halide Li₃In Cl₆ has attracted much attention due to its high ionic conductivity at room temperature and good compatibility with the cathode,but it is not compatible with lithium metal anodes.In this paper,lithium-rich Li₃OCl solid electrolyties were synthesized by changing the initial composition to improve the ionic conductivity of Li₃OCl.By constructing Li₃OCl/Li₃In Cl₆ double-layer solid electrolyte to improve the incompatibility of Li₃In Cl₆ and lithium metal anode,compared with the single Li₃OCl,the ionic conductivity is improved,the main experimental process is as follows:（1）In this paper,lithium-rich Li₃OCl solid electrolyties was prepared by changing the molar ratio of the starting material Li₂O and Li Cl,producing Li₂O or Li Cl Schottky defects,thus improving the ionic conductivity of solid electrolyte.X-ray powder diffraction test results showed that the prepared lithium-rich Li₃OCl solid electrolyties are very pure,and the main structure is cubic crystal system.The results of AC impedance test show that the Li₃OCl+0.5 Li Cl synthesized from Li₂O:Li Cl=1:1.5 has the best performance,and its ionic conductivity is 8.04×10^-7 S/cm at 25℃.The ionic conductivity is 3.06×10^-4 S/cm at 130℃,and the activation energy is 0.589 e V at 25～210℃.The results of cyclic voltammetry test show that the five lithium-rich Li₃OCl solid electrolyties have wide electrochemical stability windows at 130℃.The Li-Li constant-current charge-discharge cycle test shows that the five lithium-rich Li₃OCl solid electrolyties can maintain stable polarization voltages at the current density of 0.025、0.05 and 0.1 m A/cm² at 130℃,and the polarization voltage of Li₃OCl+0.5Li Cl material is the lowest at the current density of0.025 m A/cm²,it is 5.2 m V.The electrochemical performance test proved that the initial material Li₂O:Li Cl=1:1.5 is the best synthesis ratio.（2）In this paper,Li₃In Cl₆ solid electrolyte was synthesized by aqueous solvent method,which has the advantages of short synthesis period,high yield and simple operation.According to the results of AC impedance test,the ionic conductivity is 1.68×10^-4 S/cm at 25℃.The ionic conductivity is 2.88×10^-3S/cm at 130℃,and the activation energy is 0.314 e V at 25～130℃.However,the cycle voltammetry test and Li-Li constant current charge-discharge cycle test indicate that the Li₃In Cl₆ solid electrolyte is not compatible with lithium metal.Then,the electrochemical performance of Li₃OCl/Li₃In Cl₆double-layer solid electrolyte was tested.The results showed that Li₃OCl/Li₃In Cl₆ double-layer solid electrolyte had good chemical and electrochemical stability and wide electrochemical stability window for lithium metal.The ionic conductivity of the Li₃OCl/Li₃In Cl₆ double-layer solid electrolyte was improved compared to the Li₃OCl solid electrolyte.（3）Because Li₃OCl solid state electrolysis is very stable to lithium metal;Li₃In Cl₆solid electrolyte has good cathode compatibility and high ionic conductivity.Therefore,Li₃OCl/Li₃In Cl₆ double-layer solid electrolyte was constructed to assemble all-solid lithium metal battery,and the application of double-layer solid electrolyte in all-solid lithium battery was initially explored.The application of lithium anode improves the energy density of all-solid-state lithium battery.The initial discharge capacity of Li Co O₂cathode is 103.1 m Ah/g.The capacity of all-solid-state lithium battery decreases seriously due to the increase of internal resistance during the cycle.Therefore,the assembly process of all-solid-state lithium batteries still need to be further optimized.