Self-healing polymer electrolytes with dynamic-covalent borate for solid-state lithium metal batteries

Developing a solid polymer electrolyte (SPE) combining superior interface stability with high ionic conductivity is still a challenge in the energy storage field. Herein, a series of novel self-healing solid polymer electrolytes were prepared by free radical photopolymerization with poly(ethylene glycol) methyl ether methacrylate and monomers containing borate. The reversible reaction induced by interesterification of borate ester endows the polymer electrolytes with excellent self-healing ability. The comb-like structure based on flexible poly(ethylene glycol) provides an amorphous state, which is conducive to lithium-ion transport. Further benefiting from the strong interaction between electron capture groups and anions of electrolyte salts, the borate-containing combshaped solid polymer electrolytes (PPBSPE) films display optimal ionic conductivity of 0.272 mS cm-1 at 60 degrees C, satisfactory transfer number for lithium ion, wide working voltage window, and remarkable stability towards lithium metal. The initial discharge capacities of the cell based on PPBSPE reach 156.2 mAh g-1 at a current rate of 0.1C, and high Coulombic efficiency (CE) of 99.4 %. This enhancement is due to the introduction of borate to the comb-shaped polymer, which is beneficial to form a more suitable electrolyte that can stabilize and improve the performance of lithium metal batteries.