Rational design for the potential substitute of sulfide in halide-based all solid-state lithium metal batteries

Halide-type solid-state electrolytes (SEs) are regarded as promising candidates for the commercialization of all solid-state lithium metal batteries (ASLMBs). However, the poor reduction stability of their central structural metal cations complicates the direct contact with lithium metal, thus conventionally requiring a sulfide interlayer between the lithium metal anode and halide SE. Concerning this issue, we developed a systematic approach to identify the SE in the halide family with thermodynamic stability, cost-effectiveness, and ionic conductivity to substitute the sulfide buffer layer and support the operation of ASLMBs utilizing solely halide-type SEs. The initial screen results indicate that Li₃Y(BrCl)₃ (LYBC) is a promising candidate. Our theoretical calculations confirmed its lower reduction potential of 0.58 V. The lithium symmetrical cell using LYBC was able to cycle for over 1000 h at a current density of 0.255 mA cm^-2 and an areal capacity of 0.255mAh cm^-2. The performance of ASLMBs also notarized the feasibility of our strategy. In addition, according to our experiment, we deduce that the reduced LYBC can still conduct lithium-ion rapidly, which may be the key to supporting the normal operation of the electrochemical system. Combined with our cost analysis, LYBC is identified as one of the most suitable commercial materials for realizing the self-liberation of halide SEs. Our research proposes a novel pathway for the future development of halide SEs.