A Highly Stable Separator from an Instantly Reformed Gel with Direct Post-Solidation for Long-Cycle High-Rate Lithium-Ion Batteries

Graphical A stable hierarchy : A hierarchical structure is constructed from a stable heterogeneous-phase gel by blending dissolved and undissolved polyvinylidene fluoride-hexafluoropropylene (PVDF–HFP) powders in acetone while adding N -methyl-2-pyrrolidone (NMP) to form a hierarchical inner-bound structure within the PVDF–HFP separator. LiFePO 4 /Li cells containing the solidified hierarchical structure exhibit a remarkable rate capacity of 95 mAh g −1 at 10 C and an excellent long-term cyclical stability with zero capacity fading after 1000 cycles. An efficient, scalable, and cost-effective approach was developed to synthesize a hierarchically constructed polyvinylidene fluoride-hexafluoropropylene (PVDF–HFP) separator from an instantly reformed solution. With partially dissolved PVDF–HFP as separator skeleton, the incorporation of warm PVDF–HFP solution in acetone led to a cross-linked structure before N -methyl-2-pyrrolidone (NMP) was added to solidify the hierarchical inner-bound structure of fresh PVDF–HFP. Owing to its hierarchical microporous structure, the separator exhibited remarkable wettability with a small contact angle of 18° and an electrolyte uptake of 114.81 %, leading to a high room-temperature ionic conductivity of 3.27×10 −3 S cm −1 . The hierarchical structure provided short pathways for efficient ion transfer with more electrolyte trapped inside and small intervals between adjacent nanopores. The separator outperformed commercial separators, showing high rate capacities of 104.8 mAh g −1 at 5 C and 95 mAh g −1 at 10 C as well as unparalleled perfect capacity retention at 10 C after 1000 cycles.