Efficient Fabrication of PVDF Separators with Excellent Thermal Stability and High Ionic Conductivity by Melt Blending for Lithium Metal Batteries

Abstract

Lithium (Li) metal batteries represent a transformative candidate for high-end energy storage due to their ultra-high energy density. However, commercial polyolefin separators suffer from poor thermal stability and insufficient electrolyte wettability, resulting in high interfacial resistance and inferior compatibility that severely restrict their practical applications. To address these issues, we report the fabrication of LMB separators using polyvinylidene fluoride (PVDF) as the matrix and dibutyl phthalate (DBP) as the diluent via melt blending. The PD46 separator, fabricated with an optimized PVDF/DBP mass ratio of 4:6, exhibits a three-dimensional interconnected porous structure. It demonstrates excellent thermal stability with a shrinkage of merely 4.5% at 150 °C. Furthermore, the PD46 separator delivers high ionic conductivity of 1.23 mS cm–1 and satisfactory Li+ transference number of 0.73, showing its potential as a high-performance separator for LMBs. More importantly, the PD46 separator effectively suppresses Li dendrite growth, enabling stable Li||PD46||Li symmetric cells cycling for over 1500 h at 0.5 mA cm–2. Li||PD46||LiFePO4 cells deliver excellent cycling stability, retaining over 95% capacity after 1350 cycles at 1C. This work offers a novel strategy for designing separators with high safety and excellent electrochemical performance for LMBs, contributing to the advancement of next-generation energy storage systems.