Rate-limiting mechanism of all-solid-state battery unravelled by low-temperature test-analysis flow

All-solid-state batteries (ASSBs) with potentially improved energy density and safety have been recognized as the next-generation energy storage technology. However, their performances at subzero temperatures are rarely investigated, with rate-limiting process/mechanisms unidentified. Herein, the rate-limiting process/mechanisms for -40℃ ASSBs are accurately identified/analyzed by developing a standard test-analysis flow model. We reveal that the rate-limiting processes of LiCoO2 (LCO)+sulfide solid electrolyte (SE) composite cathode are the sluggish ion transport across unfavorable interfacial reaction layer and charge transfer at damaged LCO cathode surface. After inserting Li2ZrO3 (LZO) coating layer to suppress interfacial reactions, the rate-limiting process of LCO@LZO+sulfide SE composite cathode turns into the arduous ion transport across the interphase composed of the self-decomposition products of sulfide SE. Interestingly, by replacing sulfide SE with halide SE, LCO+halide SE composite cathode delivers fast charge transfer and the ion conduction through the thick SE separator becomes the rate-limiting process, thus enabling a superior capacity retention rate (41.4 %) at -40℃. Furthermore, the capacity retention of ASSB coupling LCO+halide SE composite cathode with Si anode can be boosted from 28.9 % to 38.6 % at -40℃ by employing superionic conductor with low activation energy. These successful identifications/modulations on rate-limiting process/mechanism and improvements on low-temperature performance demonstrate the significant role of this test-analysis flow in propelling the development of low-temperature ASSBs.