(Digital Presentation) On the Origin of High Resistance at the Interface between Lithium Metal and Sulfide Solid Electrolytes

Abstract

Sulfide materials have been extensively studied as solid-state electrolytes (SSEs) for all-solid-state lithium metal batteries (ASSLMBs) because of their high ionic conductivity, wide electrochemical window, and appropriate mechanical properties. However, they suffer from the high interfacial resistance with Li metal anode, besides poor stability when exposed to air, hindering the application of sulfide-based SSEs in ASSLMBs. Sulfide materials are well known to undergo reaction with Li metal, leading to solid-electrolyte interphase layer formation at the SSE/Li metal interface. The side reactions could be primarily responsible for the high resistance at the interface between SSE and Li metal anode, but the underlying mechanisms still remain unclear. To better understand the structure and property changes of the sulfide SSE due to the reaction with Li metal, we took β-Li3PS4 (LPS) as a model system and systematically analyzed the structural, electronic, transport, and mechanical properties of lithiated LPS with varying Li contents using first-principles methods. Moreover, we examined the compositional and structural evolution at the LPS/Li metal interface using ab initio molecular dynamics (AIMD) simulations. Our results unequivocally show that Li incorporation leads to decomposition of PS4 3- to Li2S and Li3P when fully lithiated. With lithiation, Li-ion conductivity is predicted to remain in the same order of magnitude despite the significant structural and compositional changes. Both the band gap and density of the lithiated LPS becomes smaller than those of the unlithiated LPS. More importantly, we found the formation of voids at the LPS/Li metal interface. In this talk, based on our results we will discuss the mechanisms responsible for the high interfacial impedance as often observed in previous experimental studies.