Considerably enhanced electrochemical and thermomechanical performance of lithium battery (LIB) separators of PVDF/vermiculite nanosheets (VNs) composites via constructing well-defined hierarchical microstructure

Abstract

In this study, polyvinylidene difluoride (PVDF) lithium battery (LIB) separators were prepared by nonsolvent- induced phase separation (NIPS) technique, and effect of vermiculite nano-sheets (VNs) on the performance of PVDF separator was studied by altering the proportions of VNs added. The microscopic morphologies of PVDF films were observed by scanning electron microscope (SEM), and it was found that the incorporation of two-dimensional VNs greatly improved the thermodynamic instability of PVDF/N, N-dimethylacetamide (DMAc) solution, which further induced the formation of long finger-like pore structure, leading to improved porosity and electrolyte uptake rate of the prepared separators. Meanwhile, differential scanning calorimeter (DSC) analysis showed that the presence of VNs decreased PVDF's crystallinity and greatly improved the thermal stability of the separators primarily owing to VNs’ two-dimensional structure as well as excellent thermal stability. When the VNs content reached 7.0 wt%, the ionic conductivity of the separator increased from 0.300 mS⋅cm−1 to 1.679 mS⋅cm−1, coupled with significant improvement in both mechanical properties and battery performance. The present study provides a facile method for preparing LIB separators with high safety and superior performance.