Synergistic bulk and interfacial engineering of PEO-based electrolyte via LiFePO4 and LiPO2F2 for robust solid-state lithium metal batteries

Solid polymer electrolytes (SPEs) are promising candidates for next-generation safe solid-state lithium metal batteries (SSLMBs) due to their high flexibility and ease of processing. However, their widespread application is hindered by intrinsic limitations such as high crystallinity, inadequate mechanical strength, and interfacial instability against the lithium anode. To address these issues and construct a stable solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI), this study introduces a solid polymer electrolyte (SPE) design. The design incorporates commercial LiFePO 4 (LFP, 30 wt%) particles as an inorganic filler into a polyethylene oxide (PEO) matrix, along with LiPO 2 F 2 (LDP, 5 wt%) as a film-forming additive. The optimized SPE enables a Li||Li symmetric cell to cycle stably for over 1360 h at a current density of 0.2 mA cm −2 . Furthermore, the LFP||Li cell demonstrates remarkable durability, sustaining 800 cycles at 1 C (1 C = 170 mA g −1 ) with a high-capacity retention of 81.1%. The NCM811||Li cell further validates this robustness, retaining 87.4% of its capacity after 300 cycles at 1 C (1 C = 180 mA g −1 ). This work presents a simple and cost-effective strategy for fabricating high-performance SPEs and provides new insight into selecting composite fillers for durable solid-state lithium-metal batteries (SSLMBs).