Safety and performance enhanced boehmite-coupled polyethylene nanocomposite separator for lithium-ion batteries by synergetic effects of silane treatment and electron irradiation

Abstract

Separators are among the key components affecting both the safety and performance of batteries. Herein, boehmite-coupled high-density polyethylene (HDPE) nanocomposite separators with enhanced safety and performance are prepared via silane treatments and electron irradiation. The silane treatment of boehmite nanoparticles (BNPs) leads to the homogeneous dispersion of the BNPs in HDPE owing to the spacer alkyl groups in silane. Electron irradiation induces chemical coupling between the silane-treated BNPs and HDPE, as well as the crosslinking of HDPE. Electron irradiation also oxidizes HDPE, improving the electrolyte affinity of the separators. Consequently, the safety and performance of the separators are significantly improved, and the degree of improvement depends on the type of silane. A nanocomposite separator comprising octadecyl-functionalized BNPs exhibits superior dimensional stability (puncture strength of 0.74 N μm$^{−1}$ and thermal shrinkage of 3.2% at 140 °C for 30 min). In addition, a nanocomposite separator comprising aminopropyl-functionalized BNPs demonstrates excellent ionic conductivity (1.61 mS cm$^{−1}$). A lithium-ion cell assembled with the nanocomposite separator has an exceptional rate capability (discharge capacity at 20 C maintains 72.9% of the capacity at 0.5 C) and cyclic stability (discharge capacity retention of 96.2% with a Coulombic efficiency of 99.5% after 100 charge/discharge cycles at 0.5 C).