Hydrate/moisture co-assisted synthesis enables humid-air stability of halide solid-state electrolytes

Halide solid-state electrolytes (HSSEs) combine high ionic conductivity with wide electrochemical stability windows, making them promising candidates for all-solid-state lithium batteries (ASSLBs). However, their poor humid-air stability demands ultra-dry processing environments, severely limiting industrial scalability. Here, we report a water-assisted synthesis strategy to construct a zirconium-based core-shell structured HSSE, Li₂Zr_1.5OCl₆@Li₂CO₃ (LZOC-H), under industrially viable dry-room conditions (dew point <-40 °C). By exploiting trace ambient H₂O and CO₂ during synthesis, a self-derived Li₂CO₃-rich layer is formed in situ, significantly enhancing air stability. The resulting LZOC-H electrolyte achieves a relatively high room-temperature ionic conductivity of 1.12 mS cm^-1 and excellent moisture resistance. Full cell (Ni89|LZOC-H|LPSC|Li-In) shows an initial capacity of 200.4 mAh g^-1 and retains 93.5% capacity over 1000 cycles at 1 C. Moreover, a pouch cell with a silicon anode fabricated in a dry room demonstrates stable cycling (85.1% retention over 300 cycles). This work offers a scalable and rare-earth-metal-free pathway for producing moisture-resistant HSSEs, addressing key challenges in ASSLBs' commercialization.