Structural Design And Interfacial Modification Of Lithium-zirconium-chlorine Halide Solid Electrolytes

All solid-state lithium-ion batteries,with their excellent safety,high potential energy density,and low self-discharge,have become one of the most promising choices for the next generation of lithium-ion batteries.As an important component of solid-state lithium-ion batteries,solid electrolytes have attracted attention.Li₂Zr Cl₆（LZC）halide solid electrolyte is considered as one of the candidate solid electrolyte materials for solid-state lithium-ion batteries due to its low preparation cost,good high-voltage cathode compatibility,and wide electrochemical window.However,LZC has low ionic conductivity and poor stability with lithium metal,which limits its application prospects.To address these issues,this paper proposes a lithium-rich strategy to improve the ionic conductivity of LZC and improve its stability with lithium metal by introducing interface layers,guided by theoretical computational results.Simulation and analysis were performed using first-principles molecular dynamics（AIMD）and density functional theory（DFT）methods to verify the simulation results.The main research contents of this paper include:（1）A Li-richening strategy was proposed to improve the ion conductivity of the LZC halide solid electrolyte.By doping LZC with Mg,Li⁺was introduced into the LZC lattice in an appropriate amount,which increased the Li⁺concentration and thus improved the Li⁺conductivity.The crystal models of LZC and Mg-doped LZC(Li_2+2xZr_1-xMg_xCl₆,Mg-LZC)were established using Visualization for Electronic and Structural Analysis（VEST）.The Li⁺conductivity and activation energy were calculated by AIMD,and Mg5-LZC,which was LZC doped with an appropriate amount of Mg by ball milling,was prepared.The ion conductivity of Mg5-LZC reaches 0.62 m S cm^-1,higher than that of undoped LZC solid electrolyte(approximately 0.3 m S cm^-1).Finally,we used the prepared Mg5-LZC electrolyte for full solid-state lithium-ion battery experiments,which demonstrate high initial coulombic efficiency of 96.6%,as well as excellent long-term cycling stability and rate performance.These results indicate that the lithium-rich strategy is an effective method to improve the ion conductivity of halide solid electrolytes,thereby enhancing the performance of all solid-state lithium-ion batteries.（2）Through introducing a Li₆PS₅Cl（LPSC）interfacial layer between LZC and Li metal,the side reactions at the interface between LZC and Li metal were suppressed.First,a Li-LPSC interface model was established to verify that there would be no violent side reactions between Li and LPSC.Based on this result,LPSC was added to the surface of LZC to obtain a composite solid electrolyte.Subsequently,the morphology,structure,and electrochemical properties of the composite solid electrolyte were tested and systematically analyzed.Finally,Li symmetrical cells and all-solid-state batteries were assembled for testing.The experimental results show that the composite solid electrolyte could significantly improve the stability of Li.The Li/LPSC-LZC-LPSC/Li symmetrical cell can cycle steadily for more than 1000 h at a current density of 0.3 m A cm^-2 and 25℃,and the critical current density value is as high as 2.1 m A cm^-2.In addition,the all-solid-state battery based on the composite solid electrolyte has extremely high initial coulomb efficiency,good cycling performance,and excellent rate performance.（3）The interface impedance between LZC and Li metal is reduced by introducing a halide interface layer（Li I）.First,a Li-I₂ interface model was established to verify that significant reaction occurs between I₂ and Li metal to generate Li I.Based on this,LZC with I₂ coating（I₂@LZC）was prepared by physical vapor deposition,and was then subjected to morphology,structure and electrochemical testing and analysis.The results show that a Li I interface layer is formed between I₂@LZC and Li metal upon contact,effectively reducing the interface impedance between LZC and Li metal.A Li symmetric cell（Li/I₂@LZC@I₂/Li）was assembled and tested.The cell can stably cycle for more than 2000 h at 0.1 m A cm^-2and 25℃.The introduction of a halide interface layer can effectively improve the interface stability between LZC and Li metal.