TiO2 modified para-aramid nanofiber composite separator for thermal runaway prevention and shuttle effect mitigation of lithium-sulfur batteries

The polyolefin separators commonly used in lithium-sulfur (Li-S) batteries are not able to withstand high temperatures and easily lead to thermal runaway and cause safety problems. In addition, the pore size of the polyolefin separator is too large to inhibit the shuttle effect of polysulfide. Herein, TiO2 modified para-aramid nanofiber (TiO2/ANFs) composite separator for thermal runaway prevention and shuttle effect mitigation of lithium-sulfur batteries was designed and obtained. The TiO2/ANFs composite separators remained intact at 200 °C and showed excellent self-quenching characteristic. In addition, the TiO2/ANFs composite separators could inhibit the growth of lithium dendrites to a certain extent. Therefore, the TiO2/ANFs composite separators could prevent thermal runaway and had excellent safety. And TiO2 could anchor the polysulfide, which could inhibit the shuttle effect. In addition, ionic conductivity had been greatly improved due to the addition of TiO2, which was conducive to high-flux lithium-ion transfer. In particular, 2-TiO2/ANFs composite separators had an average discharge specific capacity of 889.7mAhg−1 at 0.2C. Through density functional theory (DFT) calculation, the effective chemisorption mechanism of active sulfur and TiO2 was deeply carried out. The result showed that TiO2 could ensure the effective chemisorption of active sulfur, resulting in the long-term cycling stability.