Thermostable and nonflammable silica–polyetherimide–polyurethane nanofibrous separators for high power lithium ion batteries

Abstract

Safety remains a practical concern in lithium ion batteries (LIBs), which is closely associated with the internal shorting caused by the poor dimensional thermostability at elevated temperature and the flammability of separators. Here, we report a novel strategy to fabricate thermostable and nonflammable silica–polyetherimide–polyurethane (SiO₂–PEI–PU) nanofibrous membranes via an electrospinning process. Benefiting from the high porosity, interpenetrating network structure and synergetic effect of silica nanoparticles, PEI and PU, the as-prepared SiO₂–PEI–PU membranes exhibit uniform pore size distribution, high ionic conductivity (6.25 mS cm⁻¹) and good electrochemical stability up to 4.86 V. Notably, the hot oven and combustion tests reveal that the SiO₂–PEI–PU membranes possess improved thermostability displaying 2% dimensional change after exposure to 170 °C for 0.5 h and flame retardant properties, which could be beneficial for improving the safety of LIBs. Significantly, the SiO₂–PEI–PU membrane based Li/LiFePO₄ cell exhibits more excellent cyclability delivering a discharge capacity of 158.91 mA h g⁻¹ at the 90th cycle and better rate capability compared with the cell based on the Celgard membrane. Meanwhile, the SiO₂–PEI–PU membrane based Li/LiFePO₄ cell also shows more excellent cell performance even at an elevated temperature of 60 °C. The results clearly demonstrate that the SiO₂–PEI–PU membranes are promising separator candidates, which will also pave the way for further application of nanofibrous membranes in high power LIBs.