Construction of high safety and stability polymer solid electrolytes for lithium metal batteries via a multifunctional group synergistic mechanism

Abstract Polymer electrolytes based on poly (ethylene oxide) (PEO) show significant potential for use in all solid‐state lithium metal batteries. Improving the ionic conductivity, broaden the electrochemical stability window and flame retardant property of solid polymer electrolytes (SPEs) is vital for developing safer, higher‐energy–density batteries. This paper introduces an innovative flame retardant strategy based on the unique chemical structure of phosphonitrile fluoride, by incorporating ethoxy pentafluorocyclotriphosphonitrile (PFPN) as a functional additive, the strategy not only reduces PEO crystallinity and improves electrochemical performance at quasi‐room temperature but also enhances oxidation resistance and widens the electrochemical window. Additionally, PFPN confers flame retardant properties to PEO, thereby enhancing battery safety and facilitating the creation of a high‐performance polymer solid electrolyte. The optimized solid‐state electrolyte exhibited an ionic conductivity of 8.2 × 10 –4 S cm −1 at 60 °C. The electrochemical window was expanded to 5.1 V, and the LiNi 0.8 Co 0.1 Mn 0.1 O 2 /FNOP‐10/Li cell maintained a capacity of 123 mAh g −1 after 100 cycles at 0.2C at 60 °C. And the Li/FNOP‐10/Li cell was able to cycle stably for more than 1400 h at a current density of 0.1 mA cm −2 , and no short‐circuiting caused by lithium dendrites was observed. These results demonstrate that the proposed method significantly enhances the overall performance of the electrolyte.