PEO/Li1.25Al0.25Zr1.75(PO4)3 composite solid electrolytes for high-rate and ultra-stable all-solid-state lithium metal batteries with impregnated cathode modification

Abstract

All-solid-state lithium metal batteries (ASSLMBs) are considered the most competitive next-generation energy storage batteries due to their high energy density and high safety. Polyethylene oxide (PEO) is an ideal solid-state electrolyte due to its high chain flexibility, high dielectric constant, and strong dissociation ability towards lithium salts. However, the application of PEO is severely hindered by drawbacks such as low ion conductivity at room temperature and low electrochemical window. In this work, we constructed a Li_1.25Al_0.25Zr_1.75(PO₄)₃ (LAZP)/PEO composite solid-state electrolyte (CSSE) with improved ion conductivity, enlarged electrochemical window, and stable charge–discharge cycle performance. The CSSE leads to an obvious LiF layer and Li₂CO₃ formation at the interface of lithium metal. Meanwhile, the addition of LAZP reduces the side reaction between PEO and the lithium metal significantly and suppresses the deterioration of ion conductivity. In addition, we modified LiFePO₄ (M-LFP), the cathode sheet of the ASSLMBs, by adding an appropriate proportion of multi-walled carbon nanotubes (MWCNTs), PEO and lithium bis(trifluoromethane sulfonimide) (LiTFSI) to improve the ionic and electronic conductivity inside the cathode of the ASSLMBs. The Li/CSSE/M-LFP full cell exhibits a specific discharge capacity of 152 mA h g⁻¹ at 60 °C and 2 C rate and a capacity retention rate of 93.5% after 200 cycles at 1 C. This work demonstrates an effective strategy for increasing the specific capacity, rate ability and long-cycle performance of ASSLMBs.