Core-shell nanofiber separator incorporated with PDA-PEI co-modified Li0.33La0.57TiO3 nanowires prepared by co-axial electrospinning for dendrite-free lithium metal batteries

Abstract

The core-shell nanofibers containing PDA-PEI co-modified Li0.33La0.57TiO3 (LLTO) perovskite nanowires in the shell layer were fabricated by co-axial electrospinning technique to apply as separator in dendrite-free lithium metal batteries. The PVDF-HFP with good mechanical properties and polar C–F bonds was used as the core material, and polyacrylonitrile (PAN) with high thermal stability was employed as the shell layer in nanofibers. The PDA-PEI co-modified Li0.33La0.57TiO3 nanowires, reacting with PF6− anions in LiPF6 salt can not only capture free anions but also provide a lithium-ion migration pathway. Moreover, the core-shell structured nanofibers exhibited high mechanical strength (9.2 N/mm2), robust thermal stability (>0% at 200 °C for 1 h), and favorable electrolyte affinity (electrolyte uptake of 732%). Gelation of PVDF-HFP in liquid electrolyte leads to high-ionic conductivity (3.52 mS/cm), Li+ transference number (tLi+ = 0.68), uniform Li+ flux, and smooth Li deposition. The Li plating/stripping test consisting of Li–Li cells (with CS/LLTO-PDA-PEI) carried out at 0.4 mA/cm2 was conducted for 1000 h without a short circuit. NCM-Li and NCM-Gr coin cells using the CS (core-shell)/LLTO-PDA-PEI separator retained long-term cycle stability and good Coulombic efficiency (CE).