Ethylene oxide–based polymer electrolytes with fluoroalkyl moieties for stable lithium metal batteries

In this study, we have developed a new ethylene oxide (EO)-based polymer electrolyte (PE) that contains fluoroalkyl moieties. The developed PE possesses high oxidative decomposition potential as well as adequate ionic conductivity (σ) and favorable mechanical properties for application to Li metal batteries. In particular, we designed a partially fluorinated copolymer, which is improved in conventional polyethylene oxide systems and could be used both as stable electrolyte matrix and electrode binder for high-voltage applications. The results indicated that the stabilization of the EO-based PE during the high-voltage operation of Li metal batteries was significantly improved by the introduction of a fluoroalkyl moiety via simple radical copolymerization. The synthesized copolymer exhibited satisfactory physical stability and unprecedented high oxidation decomposition voltage threshold, which exceeded 4.5 V. Moreover, the copolymer-based PEs presented moderate σ values (> 0.3 mS cm−1 at 60 °C) and retained the intrinsic properties of the EO-based PE.