Dual-Interface Engineering for Improved High-Voltage Performance in PEO-Based Solid-State Lithium-Metal Batteries

Poly(ethylene oxide) (PEO)-based solid electrolytes have attracted significant attention due to their high ionic conductivity, low expansion, and excellent compatibility with lithium-metal anodes. However, their oxidative stability is typically limited to below 3.9 V. This study addresses this limitation by forming a stable cathode–electrolyte interphase at the interface between the cathode and PEO-based composite polymer electrolyte (CPE), facilitated by the decomposition of the functional additive LiPO2F2 during cycling. Additionally, the incorporation of ethylene carbonate as a plasticizer significantly enhances the ionic conductivity. The parasitic reactions and lithium dendrite growth are effectively suppressed at the anode interface, allowing the Li/CPE/Li cell to achieve an outstanding lifespan of 2000 h at a current density of 0.1 mA cm–2. Moreover, the oxidation voltage of the CPE reaches up to 4.82 V. The LiNi0.33Co0.33Mn0.33O2/CPE/Li cell demonstrates a high discharge capacity of 138.1 mAh g–1 at a cutoff voltage of 4.2 V, maintaining an impressive capacity retention rate of 89.2% after 140 cycles.