Unravelling redox phenomenon and electrochemical stability of Li_1.6Al_0.5Ge_1.5P_2.9Si_0.1O₁₂ solid electrolyte against Li metal and silicon anodes for advanced solid-state batteries

In the pursuit of advanced solid-state batteries (SSBs) with higher energy density, improved safety, and reduced costs, the negative electrode's role is paramount. Lithium metal is propitious for ceramic-type SSBs but faces challenges due to interfacial reactions. Silicon has emerged as a compelling alternative to lithium, though it contends with issues like structural and mechanical deformation accompanied by uncontrolled solid electrolyte interphase formation. This work reports the synthesis of Li_1.6Al_0.5Ge_1.5P_2.9Si_0.1O₁₂ (LAGPS) solid electrolyte and the systematic study of its chemical and electrochemical degradation against lithium by experimental and theoretical investigations. Initially, interphase formation accelerates during discharge, but irreversible processes trigger cracks and premature cell failure upon the first charge. To inhibit the formation of undesired interphase between LAGPS and Li, an artificial lithium fluoride (LiF) and lithium nitride (Li₃N)-rich layer was prepared, which enabled a significantly enhanced lithium stripping-plating cycling lifetime (1,000 h) and critical current density (5 mA/cm²). Silicon anode modified by carbon coating exhibited superior stability with LAGPS and delivered a high specific capacity of 2,077 mAh/g at 0.8 A/g with modified Li. Furthermore, LiNi_0.8Mn_0.1Co_0.1O₂|modified Li full cell demonstrated 97% capacity retention after 50 cycles, bringing practical and efficient applications of SSBs closer to reality.