Nanostructure of the Interphase Layer between a Single Li Dendrite and Sulfide Electrolyte in All-Solid-State Li Batteries

A stable electrode–electrolyte interface is the key for the application of high-energy all-solid-state lithium metal batteries, but the nanoscale behavior of the interface remains mysterious. Herein, utilizing cryogenic transmission electron microscopy, we investigate the nanostructure of the interphase layer between a single Li dendrite and sulfide electrolyte (SE) at various temperatures. It is found that a single-crystal Li2S layer with ∼12 nm thickness is formed at 25 °C with good passivation on the interface, while at 60 °C, the interphase is composed of polycrystalline Li2S accompanied by a disorder–order phase transition. The increased grain boundaries and enlarged thickness of interphase at elevated temperature lead to ultra-high interface resistance. The temporal evolution of the atom-scale structure was further elucidated by reactive dynamics simulations to assist in understanding the kinetics. Our study provides new insight on the nanoscale interphase of the Li-SE interface and will offer valuable guidance for the future design and engineering of interfaces.