Innovative Sn-gradient sulfide solid electrolytes with superior air-stability for practical all-solid-state batteries

Abstract

Sulfide solid electrolytes (SSEs) with high ionic conductivity and mechanical flexibility are considered promising Li+ transport media for all-solid-state batteries (ASSBs). However, susceptibility to moisture originating from their crystal structures degrades their inherent superior properties. In this study, we synthesized core-shell structured SSEs by inducing the growth of compounds with moisture-stable SnS44- units on the surface of Li6PS5Cl (LPSC). This Li10SnP2S12 (LSPS)@LPSC showed > 30 times higher Li+ conductivity than LPSC after exposure to dry room environment for 2 h. Additionally, the hydrolysis reaction was effectively inhibited in LSPS@LPSC, resulting in not only significant reduction of hydrogen sulfide (H2S) gas release, but the onset of its generation was also more delayed than in LPSC. Also, in LSPS@LPSC, the inhibition of P-O bond formation after moisture exposure contributes to retention of mechanical properties, as demonstrated by nano-indentation measurements: hardness changes from 1.42 GPa to 1.50 GPa for LSPS@LPSC versus from 1.21 GPa to 1.62 GPa for LPSC (dew point of -7.5 degrees C, 5 min). Furthermore, the Li(Ni0.8Co0.1Mn0.1)O-2 cell with LSPS@LPSC exhibited excellent cycling stability comparable to that of LPSC under typical external pressure (30 MPa), and more remarkably, it showed superior cycle retention than LPSC cell under ultra-low external pressure (similar to 0.3 MPa).