Fluorinated polymer electrolyte via dual-salt coupling for solid-state lithium metal batteries

Abstract

The development of lithium (Li) metal batteries (LMBs) has been significantly impeded by the inherent safety risks of flammable and leaky organic liquid electrolytes. Solid electrolytes offer a promising solution to mitigate these risks and improve overall battery safety. In this study, a novel fluorinated polymer solid-state electrolyte was designed through a targeted material coupling strategy, resulting in functional decoupling within the electrolyte system. A highly electronegative fluorinated polymer backbone was constructed to primarily regulate interfacial reactions, broadening the electrochemical window, and promote Li salt dissociation. Concurrently, a dual-salt system with differentiated coordination capabilities (e.g., LiTFSI and LiBOB) was employed to synergistically ensure Li⁺ conduction in the bulk phase and stabilize the electrolyte/electrode interphase. Consequently, the resulting 3D interconnected fluorinated ether-based polymer network (D-PFPS) with dual-salt coupling exhibits an extended electrochemical window up to 4.9 V. The Li/Li symmetric cells demonstrate exceptional cycling stability exceeding 1400 h. The LiFePO₄/D-PFPS/Li full cell shows a capacity retention of 80% for over 1000 cycles at 60 °C and the NCM811/D-PFPS/Li full cell exhibits stable cycling for over 100 cycles, representing excellent cycling performance. This strategy provides a promising pathway towards realizing stable and safe high-energy-density LMBs.