Interface and mechanical degradation mechanisms of the silicon anode in sulfide-based solid-state batteries at high temperatures

Silicon (Si) is a competitive anode material owing to its high theoretical capacity and low electrochemical potential. Recently, the prospect of Si anodes in solid-state batteries (SSBs) has been proposed due to less solid electrolyte interphase (SEI) formation and particle pulverization. However, major challenges arise for Si anodes in SSBs at elevated temperatures. In this work, the failure mechanisms of Si-Li₆PS₅Cl (LPSC) composite anodes above 80 °C are thoroughly investigated from the perspectives of interface stability and (electro)chemo-mechanical effect. The chemistry and growth kinetics of Li_xSi|LPSC interphase are demonstrated by combining electrochemical, chemical and computational characterizations. Si and/or Si–P compound formed at Li_xSi|LPSC interface prove to be detrimental to interface stability at high temperatures. On the other hand, excessive volume expansion and local stress caused by Si lithiation at high temperatures damage the mechanical structure of Si-LPSC composite anodes. This work elucidates the behavior and failure mechanisms of Si-based anodes in SSBs at high temperatures and provides insights into upgrading Si-based anodes for application in SSBs.