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.

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Polyvinylidene fluoride-based separators for secondary battery have attracted enormous attention both in academia and in industries during the last decade. In this study, a facile, cost-effective, and environmentally friendly melt extrusion-stretching (MES) process was applied to prepare high performance PVDF microporous membranes for separator applications. In order to achieve a balance between the formation of row-nucleated lamellar structure and sufficient lamellae separation during stretching, a blend of high-and low-molecular-weight PVDF grades was chosen as raw material. Meanwhile, the effects of annealing time on physical and mechanical properties of PVDF cast films and membranes were systematically investigated, demonstrating that 6 h @145 C annealing treatment can lead to a preferable crystalline structure for the following stretching process. Therefore, PVDF membrane with high porosity, high electrolyte uptake ratio, and superior tensile strength was obtained by this MES process. Interestingly, the increase of β phase content by stretching was not significant for this PVDF membrane, revealing that the formation of micropores/ microfibrils in the stretching process would lead to stress relaxation and less crystalline structure conversion.

Thermal runaway and dendrite growth in lithium-ion batteries (LIBs) always induce serious safety hazards and impede their further applications. Although extensive advances have been attained in terms of LIBs safety,...