A facile approach to form an artificial CEI layer induced by residual Li compounds on LiNi_0.9Co_0.05Mn_0.05O₂ and Li₆PS₅Cl for all-solid-state batteries

All-solid-state batteries (ASSBs) are attracting significant attention as alternatives to conventional lithium-ion batteries due to their safety and higher energy density. However, electrochemical reactions between the solid electrolytes and active materials result in the degradation of electrochemical cell performances. A conventional approach is to employ protective layers onto the active materials, but this approach could have the drawback of being costly and time-consuming. The artificial cathode electrolyte interphase (CEI) layer generated by reactions between components within the electrode could provide a solution to these challenges. However, this approach can cause component degradation due to its intrinsically degradative nature of the forming process. In this study, we demonstrate the ASSBs with enhanced electrochemical performances by introducing lithium oxy-thiophosphate species (P-Ox-Sy-...Li+, LPOS) and LiCl artificial CEI layer, which could be spontaneously formed during heat treatment by chemical reactions between the solid electrolytes and residual Li compounds on the LiNi0.9Co0.05Mn0.05O2 (NCM) without the degradation. The LPOS-LiCl layer effectively suppresses the side reactions between solid electrolytes and NCM during the repeated electrochemical cyclings. As a result, the NCM full-cell (3.7 mAh cm-2) with the LPOS-LiCl artificial CEI layer exhibits 80.0 % cycle retention after 300 cycles at 0.2 C rate and room temperature. Moreover, it demonstrates 58 % higher Li-ion mobility and 36 % lower internal resistance after cycling compared to the NCM full-cell without the LPOS-LiCl artificial CEI layer.