Flame-retardant single-ion conducting polymer electrolytes based on anion acceptors for high-safety lithium metal batteries

Solid-state lithium metal batteries (LMBs) assembled with polymer electrolytes (PEs) and lithium metal anodes are promising batteries owing to their enhanced safeties and ultrahigh theoretical energy densities. Nevertheless, polymer electrolytes (PE) suffer from low ionic conductivities, low lithium-ion transference numbers (LITNs) and high flammability. To address these issues, a novel nonflammable single-ion conducting polymer electrolyte (SIC-PE) with ultrahigh ionic conductivity, unity LITN, excellent flame retardance and high flexibility has been developed. The nonflammable SIC-PE (AEP) is prepared via thiol-ene click reaction. Allylboronic acid pinacol ester (AAPE) is incorporated into the 3D cross-linking network of AEP to act as anion acceptor and trap the anions, improving LITN to 0.79. AEP possesses ultrahigh ionic conductivity of 2.52 mS cm−1 at 25 °C. AEP can not be ignited by the flame. AEP can construct robust LiF-rich SEIs on Li metal anode and effectively suppress dendrite growth. LiFePO4 cells assembled with AEP demonstrates excellent rate capacity (specific capacity of 112.4 mAh g−1 at 5 C rate) and long-term cycle stability (93.2% capacity retention after 500 cycles). This work provides a promising approach to prepare new PEs for high-safety, high-stability and high-energy LMBs.