Long-stable lithium metal batteries with a high-performance dual-salt solid polymer electrolyte

Abstract

Lithium metal batteries (LMBs) are gaining recognition as promising high-energy-density batteries due to the high theoretical specific capacity of lithium anodes and their lowest redox potential. However, conventional liquid electrolytes are unsuitable for LMBs as they can cause the formation of lithium dendrites during charge/discharge cycles, posing risks such as internal short circuits and thermal instability. Consequently, solid polymer electrolytes (SPEs) have become the favored choice, providing improved safety and performance for the practical application of LMBs. In this study, an all-solid-state, dual-salt SPE with a semi-interpenetrating polymer network structure was synthesized through the in situ copolymerization of neopentyl glycol diacrylate (NPGDA) and vinyl ethylene carbonate (VEC), and the incorporation of dual lithium salts—lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(oxalato)borate (LiBOB)—within a porous poly(vinylidene fluoride–hexafluoropropylene) (PVDF–HFP) nanofiber matrix. The prepared dual-salt SPE demonstrated excellent lithium ion conductivity at room temperature (0.264 mS cm⁻¹), high oxidation resistance (5.0 V), and robust mechanical properties. Notably, the inclusion of dual lithium salts facilitated the formation of stable solid-state electrolyte interphase (SEI) layers enriched with B–F and B–O inorganic groups on both cathode and anode interfaces. These layers promoted rapid Li⁺ transport, facilitated uniform lithium stripping/deposition, and effectively suppressed lithium dendrite growth. Furthermore, the presence of LiBOB significantly mitigated aluminum foil corrosion during cycling, fostering the development of durable and high-performance Li|SPE|LiFePO₄ batteries.