Dual-salt coupled fluoroethylene carbonate synergistically regulated PVDF-HFP/phosphated Li6.4La3Zr1.4Ta0.6O12 composite polymer electrolytes enable Li metal batteries with stable dual interface

Composite polymer electrolytes (CPEs) based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)/Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) are regarded as promising electrolyte systems for developing high-energy-density solid-state lithium batteries. However, the combination of ceramic fillers and the polymer matrix often leads to poor lithium metal interface stability and limited ion transport. Here, we constructed phosphated LLZTO/PVDF-HFP CPEs synergistically regulated by a dual-salt (LiTFSI-LiBOB) and fluoroethylene carbonate (FEC). Surface phosphation of LLZTO reduces interfacial side reactions, LiBOB alleviates interfacial corrosion at the cathode/Al current collector, while FEC and dual-salt synergistically facilitate the formation of a robust SEI layer and suppress SN-induced nitrile polymerization side reactions. The electrolyte exhibits a wide electrochemical window (5.0 V), a low activation energy (0.285 eV), and an excellent Li + transference number (0.62). Besides, the assembled Li|PHL-DLi-FEC|Li cell exhibits the lifespan of over 1000 h at 0.2 mA cm −2 at both 25 °C and 60 °C. The assembled LiFePO 4 (LFP) |PHL-DLi-FEC|Li cell displays an initial capacity of 144.6 mAh g −1 , 91.9% capacity retention after 500 cycles under 0.5 C, and approaching 100% coulombic efficiency after 500 cycles at 1 C. This work offers new insights into composite polymer electrolytes with stable dual interfaces for solid-state batteries.