Insertion of SnF₂–C Layer between Current Collector and Li₃PS₄–LiI Glass Electrolytes for Improving Li Deposition Behavior

抄録

Li metal has a high theoretical capacity (3860 mAh g⁻¹) and the lowest electrochemical potential (−3.04 V vs. the standard hydrogen electrode). Li deposition/dissolution at the interface between the current collector (CC)/sulfide solid electrolyte (SSE), with Li⁺ ion supply from the positive electrode, is important for fabricating all-solid-state cells with high energy density. However, repeated inhomogeneous Li deposition/dissolution at the CC/SSE interface leads to short-circuiting of the cells.

In this study, to promote homogeneous Li deposition, all-solid-state cells with a composite of SnF₂ and acetylene black (SnF₂–AB) at the interface between the CC and SSE were fabricated, and the Li deposition behavior was investigated. Li₃PS₄ (LPS) and 54Li₃PS₄·46LiI (LPSI) glasses were used as SSE. During Li deposition, the cell without the SnF₂–AB layer short-circuited immediately because of inhomogeneous Li deposition. In contrast, in the cell with the SnF₂–AB layer, SnF₂ reacted with Li to form Li₁₇Sn₄ and LiF, which mainly remained within the SnF₂–AB layer, promoting homogeneous Li deposition at the CC/SnF₂–AB interface and suppressing short-circuiting of the cell. The use of LPSI instead of LPS in a cell with a SnF₂–AB layer suppressed the formation of Li₂S during reductive decomposition of the solid electrolyte, resulting in improved Li deposition capacity. The insertion of the SnF₂–AB layer effectively promotes homogeneous Li deposition and is useful for applications in anode-free all-solid-state batteries.