Stable Thiophosphate-Based All-Solid-State Lithium Batteries through Conformally Interfacial Nanocoating.

All-solid-state lithium batteries (ASLBs) are promising for the next generation energy storage system with critical safety. Among various candidates, thiophosphate-based electrolytes have shown great promise because of their high ionic conductivity. However, the narrow operation voltage and poor compatibility with high voltage cathode materials impede their application in the development of high energy ASLBs. In this work, we studied the failure mechanism of Li ₆ PS ₅ Cl at high voltage through in situ Raman spectra and investigated the stability with high-voltage LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (NMC) cathode. With a facile wet chemical approach, we coated a thin layer of amorphous Li _0.35 La _0.5 Sr _0.05 TiO ₃ (LLSTO) with 15-20 nm at the interface between NMC and Li ₆ PS ₅ Cl. We studied different coating parameters and optimized the coating thickness of the interface layers. Meanwhile, we studied the effect of NMC dimension to the ASLBs performance. We further conducted the first-principles thermodynamic calculations to understand the electrochemical stability between Li ₆ PS ₅ Cl and carbon, NMC, LLSTO, NMC/LLSTO. Attributed to the high stability of Li ₆ PS ₅ Cl with NMC/LLSTO and outstanding ionic conductivity of the LLSTO and Li ₆ PS ₅ Cl, at room temperature, the ASLBs exhibit outstanding capacity of 107 mAh g ^-1 and keep stable for 850 cycles with a high capacity retention of 91.5% at C/3 and voltage window 2.5-4.0 V (vs Li-In).