Superior lithium-stable Li7P2S8I solid electrolyte for all-solid-state lithium batteries

High lithium ionic conductivity and stability against lithium metal of solid electrolytes are crucial to develop high energy density all-solid-state lithium batteries. Upon doping LiI in Li3PS4, the low temperature phase Li7P2S8I glass-ceramic electrolyte (LT-Li7P2S8I) can be synthesized by mechanical milling followed by heat treatment. Compared with Li3PS4, the obtained LT-Li7P2S8I shows a phase transition from low conductive thio-LISICON III analog to high conductive thio-LISICON II analog phase, exhibiting a favorable conductivity of 1.57 × 10−3 S cm−1 at room temperature. In addition, the as-prepared LT-Li7P2S8I possesses excellent dendrite suppression capability and compatibility with lithium metal. The Li/LT-Li7P2S8I/Li symmetric cell demonstrates long cycling stability for 2400 h at 0.2 mA cm−2. As a result, LiCoO2/LT-Li7P2S8I/Li all-solid-state battery delivers an initial discharge capacity of 115 mAh g−1 at 0.1 C and high capacity retention of 93% after 100 cycles at room temperature. Moreover, the obtained all-solid-state battery also shows improved rate capacity. This work provides a promising electrolyte with high ionic conductivity and stability against lithium for all-solid-state lithium batteries.