Organic–Organic Composite Electrolyte Enables Ultralong Cycle Life in Solid-State Lithium Metal Batteries

Ionic conducting polymer electrolytes for solid-state lithium-ion batteries have attracted ever-increasing attention because of their decent ionic conductivity, flexibility, no liquid leakage, and good processability. Poly(vinylidene fluoride) (PVDF)-based polymer electrolytes have recently stood out among the polymer electrolytes due to their high room temperature ionic conductivity. However, the interface between PVDF-based polymer electrolytes and lithium metal decays over time until the batteries break down. Here, we introduce a small amount of poly(acrylic acid) (PAA) into a PVDF-based polymer electrolyte and synthesize an organic–organic composite electrolyte that alleviates the interfacial reaction with lithium metal, which shows great superiority over other modification methods such as coating. The cycle life of lithium symmetric cells is prolonged from 130 to 850 h at 0.44 mA cm–2 due to the effective suppression of interfacial reaction. The much more stable interface also enables excellent cycle performance in a solid-state LiCoO2||Li cell at 30 °C with a capacity decay of 0.03% per cycle for 1000 cycles, which is much lower than that of a cell without blending PAA (0.13% per cycle for only 450 cycles). The results would shed light on the applications of PVDF-based polymer electrolytes in solid-state lithium metal batteries.