The Preparation,doping Modification,and Cell Performance Of Sulfide Solid Electrolyte Li₆PS₅Cl

All-solid-state batteries have attracted much attention for their higher safety and energy density.Solid electrolytes are the key components of all-solid-state batteries,and their ionic conductivity,interfacial contact,and electrochemical stability affect the cycling performance of all-solid-state batteries directly.Compared to oxide solid electrolytes,sulfide solid electrolytes have slightly lower electrochemical stability,but their excellent ionic conductivity and good interfacial contact make them a hot research topic among inorganic solid electrolytes.Sulfide solid electrolytes are prepared in a variety of ways and with stringent preparation requirements,and their properties are closely related to the preparation method.The focus of this work is on argyrodite sulfide solid-state electrolytes.The preparing parameters of the typical argyrodite solid-state electrolyte Li₆PS₅Cl by solid-phase ball milling and inert atmosphere sintering were optimized,and the effect of Br^-doping on the properties of the halide-rich argyrodite solid-state electrolytes Li_6-xPS_5-xCl Br_x was investigated.The electrolytes were used to assemble all-solid-state batteries,and the effect of electrolyte property changes on the cycling performance in different battery systems were investigated.The main research contents and conclusions of this work are as follows.（1）The effects of the varying process parameters of solid-phase ball milling and inert atmosphere sintering processes on the properties of argyrodite solid-state electrolyte Li₆PS₅Cl were investigated.The longer ball milling time is beneficial to the amorphization and solid phase reaction of the raw materials.After ball milling at 300 r·min^-1 for 8 h,the precursors have reached the requirements for subsequent sintering.The purity of the Li₆PS₅Cl solid electrolyte increased with the increase of the sintering temperature,and the ionic conductivity gradually increased.However,overheating can damage the electrolyte structure.After sintering at 550℃for 8 h,the room temperature ionic conductivity of the Li₆PS₅Cl solid electrolyte reached its maximum value of 4.26×10^-3 S·cm^-1,while the activation energy was only 0.31 e V.（2）The effects of variations in the Br^-doping content on the properties of the halide-rich argyrodite electrolyte Li_6-xPS_5-xCl Br_x was investigated.With the increasing Br^-doping,the ionic conductivity of Li_6-xPS_5-xCl Br_x increased substantially,while the chemical stability of Li_6-xPS_5-xCl Br_x decreased and the impurity content in Li_6-xPS_5-xCl Br_xincreased.When Br^-doping was excessive,the structure of the electrolyte changed and ceased to be the typical argyrodite structure.After sintering at450℃for 8 h,the highest room temperature ionic conductivity of Li_5.25PS_4.25Cl Br_0.75 solid electrolyte was 12.23×10^-3 S·cm^-1,while the activation energy was only 0.18 e V.（3）The effects of the property changes of the solid electrolyte Li_6-xPS_5-xCl Br_x（Li₆PS₅Cl）on the cycling performance of all-solid-state batteries with In-Li metal anode or graphite（Gr）anode were investigated.The In-Li all-solid-state batteries achieved long and stable cycles with good rate performance after the Li⁺consumed during cycling was effectively replenished by applying a constant pressure.Among all the tests,the NCM811/Li₆PS₅Cl/In-Li battery with constant pressure had a discharge specific capacity of 181.7 m Ah·g^-1 at the first cycle and 130.5 m Ah·g^-1after 100 cycles,with a capacity retention rate of 84.1%.However,with the increase of Br^-doping,the stability of the electrolyte decreased and the cycle performance of the In-Li all-solid-state battery gradually deteriorated.In the cycle test of the Gr all-solid-state batteries,the Gr all-solid-state batteries attained long and stable cycles after improving the interface contact by applying constant pressure.As the ionic conductivity of the electrolyte increased with increasing Br^-doping,the cycling performance of the all-solid-state cell increased initially.The discharge specific capacity of the NCM811/Li_5.75PS_4.75Cl Br_0.25/Gr battery with constant pressure was174.3 m Ah·g^-1 in the first cycle and 127.7 m Ah·g^-1 after 100 cycles,with a capacity retention rate of 81.1%after 100 cycles.However,with increasing Br^-doping,the electrolyte electrochemical stability continued to decrease and the cycle performance of the Gr all-solid-state batteries gradually deteriorated.