Composite Membrane of Poly(vinylidene fluoride) and 2D Ni(OH)₂ Nanosheets for High-Performance Lithium-Ion Battery

For the first time, we explored the possibility of utilizing 2D nickel hydroxide nanosheets (NHNs) to prepare NHN/poly­(vinylidene fluoride) composite membranes for battery separator applications. The effect of these ultrathin 2D nanosheets on the morphology, crystallization behaviors, porosity, electrolyte uptake ratio, ionic conductivity, and thermal stability of the composite membranes were systematically investigated. A low filler content of only 3 wt % NHNs into PVDF membranes not only promoted superior thermal stability (1.9% shrinkage at 130 °C for 0.5 h) but also led to a significant increase of β-phase content (85.0%), electrolyte affinity (327.6% uptake ratio), and ionic conductivity (1.5 mS cm^–1). Strong interfacial interactions between 2D NHNs and polymer molecular chains are responsible for significant α to β crystalline phase conversion, benefiting to high ionic conductivity and electrochemical performance of cells. Moreover, in order to gain more insights for battery applications, this membrane was assembled and evaluated in Li/LiFePO₄ half-cells, showing a good cycling performance and rate capability, with a capacity retention of 95.9% after 100 cycles at 2 C and a high specific capacity of 129.1 mAhg^–1 at 2 C. Thus, this NHN/PVDF composite membrane could be a promising separator for next generation lithium-ion batteries requiring high safety and ultrafast rechargeability.