Electron-Irradiated Montmorillonite/Polyethylene Composite Separator for High-Performance Lithium-Ion Battery

Abstract

Separators play a significant role in the safety and performance of lithium-ion batteries. In this study, composite separators were fabricated using montmorillonite (MMT) as a filler in a high-density polyethylene (HDPE) matrix, followed by electron irradiation to enhance the safety and performance of separator. Electron irradiation induces chemical bonds by crosslinking between HDPE chains, also between the MMT and HDPE. MMT features a two-dimensional layered structure with a high surface area, providing abundant crosslinking sites. MMT is treated with a silane coupling agent, which induces layer exfoliation. The exfoliation increases the surface area of MMT, thereby providing more crosslinking sites. Additionally, the surface modification of MMT enhances its affinity with HDPE, leading to better dispersion of MMT within the HDPE matrix. Simultaneously, electron irradiation in an air atmosphere generates polar functional groups, improving the electrolyte affinity of the separator. Consequently, the safety of the MMT composite separator was significantly enhanced, exhibiting a high puncture strength of 0.52 N μm⁻¹ and a thermal shrinkage rate of 21.4% at 135°C for 30 min. Li//LCO cells using the composite separator demonstrated superb cycle stability with a discharge retention of 98.7% and a coulombic efficiency of 99.6% after 200 cycles at 0.5 C, and exhibited rate capability maintaining 74.5% of the capacity at 20 C compared to 0.5 C.