Li 2 ZrO 3 -coated LiFePO 4 (LFP@C/LZO) was prepared by hydrothermal synthesis and ex-situ coating for the first time. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and charge-discharge tests were used to characterize lithium iron phosphate and the influences of different coating amounts on the material were systematically studied. The results show that when Li 2 ZrO 3 is 2 wt%, LFP@C/LZO-2 exhibits excellent electrochemical performance where the initial discharge capacities are 156.7 mAh/g and 111 mAh/g at 0.1 C and 1 C, respectively. And after 200 cycles at 1 C, the capacity can retain 81.62% of the initial value. Electrochemical impedance spectroscopy (EIS) shows that the introduction of Li 2 ZrO 3 can decrease the charge transfer resistance and improve the lithium-ion diffusion rate. The study reveals a moderate amount of Li 2 ZrO 3 can helpfully enhance the electrochemical properties of LFP and broadens options for surface coating of LFP and other electrode materials.
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 LiCoO 2 (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 Li 2 ZrO 3 (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.
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