Control of side reactions using LiNbO3 mixed/doped solid electrolyte for enhanced sulfide-based all-solid-state batteries

Abstract

Control of side reactions is a critical issue for obtaining all-solid-state lithium batteries (ASSLBs) with comparable performance to lithium-ion batteries (LIBs). In particular, the interfacial reaction at the cathode/sulfide electrolyte interface and decomposition of the sulfide electrolyte lead to a significant deterioration in the electrochemical performance of ASSLBs. Surface-coated cathodes have been used in ASSLBs to mitigate these side reactions. However, the generally used LiNbO3 coating, a representative coating for ASSLBs, is expensive because of the high price of the source materials, and perfect coverage of the entire cathode surface by coating is practically very difficult. In this study, we introduced a LiNbO3 mixed/doped Li6PS5Cl solid electrolyte, instead of surface coating on the cathodes, to improve the resistance against side reactions concerning the sulfide electrolyte. The source material used for LiNbO3 mixing/doping is cheaper than that used for LiNbO3 coating. Partial doping of LiNbO3 was confirmed by laser Raman spectroscopy and field-emission scanning electron microscopy with energy dispersive X-ray spectroscopy (EDS) analysis. An optimum LiNbO3 mixed/doped electrolyte (4 mol.% of electrolyte) showed enhanced ionic conductivity than that of Li6PS5Cl solid electrolyte without LiNbO3. Moreover, the interfacial reaction at the cathode/electrolyte interface and the sulfide electrolyte decomposition were decreased owing to the LiNbO3 mixing/doping effect. The suppression of ion exchange between the cathode and electrolyte was also confirmed by the scanning transmission electron microscopy - energy dispersive X-ray spectroscopy (STEM-EDS) line profile. These results contributed to the increased discharge capacity and improved rate capability of the cell using 96LPSCl-4LNO (4 mol.% LiNbO3 mixing/doping), compared to those of the cell using pristine Li6PS5Cl.