Copper hydroxide-embedded PVDF composite membranes with asymmetric ion-conducting pathways for high performance lithium metal batteries

High safety and prolonged cycling stability are vital for the widespread commercialization of lithium (Li) metal batteries. In this study, we report a copper hydroxide (Cu(OH)₂)-embedded polyvinylidene difluoride (PVDF) composite membrane with asymmetric porous structure for gel polymer electrolytes. Our experimental results combined with molecular dynamics simulations reveal that incorporating a low doping content of 3 wt% Cu(OH)₂ into PVDF membrane (PVDF-CH-3) significantly enhance the ion transport properties of gel polymer electrolyte, delivering an ionic conductivity of 1.35 mS cm⁻¹, elevated transference number of 0.69, low interfacial impedance with Li, and uniform Li deposition. These improvements are primarily attributed to the enriched β-phase PVDF crystallinity (61 %) within the membrane. Additionally, long cycle lifespan of PVDF-CH-3 gel polymer electrolytes in Li||Li (>500 cycles), Li||Cu (>100 cycles), and Li||LFP (>200 cycles) cells are achieved with high coulombic efficiency (>97 %). Moreover, the porous PVDF-CH-3 membranes are applied as a scaffold to host the in-situ polymerization of 1,3-dioxolane and obtain quasi-solid-state electrolytes, that exhibit outstanding battery performance at high rate of 10 C under room temperature. In sum, this work presents a novel route for the design of composite membranes for the development of gel-type and quasi-solid-state Li metal batteries with high capacity and stability.