(457d) In Operando Study of All-Solid-State Lithium Batteries Coupling Thioantimonate Superionic Conductors with Metal Sulfide

All Solid-state Lithium metal batteries (ASLBs) are considered as next generation energy storage devices to deliver high energy density and safety. The intrinsic nonflammability of solid-state electrolytes (SEs) can significantly improve the battery safety by reducing fire risk. Among various SEs candidates, sulfide SEs have ultrahigh ionic conductivity and low mechanical stiffness. However, sulfide SEs suffer from poor compatibility with the conventional transition metal oxide electrodes due to narrow electrochemical stability window and poor chemical stability. Therefore, it is crucial to pair sulfide electrolytes with the proper cathode in developing stable ASLBs.

In this work, we synthesized and systematically studied one type of thioantimonate ion conductor, Li_6+xGe_xSb_1-xS₅I, with different compositions, where Li_6.6Ge_0.6Sb_0.4S₅I exhibits highest ionic conductivity of 1.6 mS cm^-1 at room temperature. A metal sulfide FeS₂ cathode which owns high specific capacity and excellent chemical compatibility with sulfide electrolytes was chosen to couple with Li_6.6Ge_0.6Sb_0.4S₅I in ASLBs without additional interface engineering. For the first time, in situ energy dispersive X-ray diffraction (EDXRD) was applied in the study of ASLBs without disassembling the sealed cells or special cell designing to characterize the structural stability of the Li_6.6Ge_0.6Sb_0.4S₅I and FeS₂ during cycling. EDXRD in situ observed the decomposition of Li_6.6Ge_0.6Sb_0.4S₅I at low voltage which confirms the safe operation voltage range. The electrochemical stability was investigated, and a safe operating voltage window ranging from 0.7~2.4 V (vs. In-Li) was achieved. Compared with fast-decaying performance in liquid electrolyte batteries, the SEs can effectively confine Fe⁰ aggregation and polysulfide shuttle effect in the ASLBs. The ASLBs paring FeS₂ cathode and Li_6.6Ge_0.6Sb_0.4S₅I electrolyte delivers a high initial capacity of 715 mAh g^-1 at C/10 which keeps stable for 220 cycles with a high-capacity retention of 84.5%. As a result of excellent compatibility between FeS2 and Li_6.6Ge_0.6Sb_0.4S₅I, outstanding capacity and cycling stability are achieved at the same time.