Flexible fibrous separator asymmetrically coated by silica and MXene for high performance lithium batteries with enhanced safety

Introducing inorganic particles into separator for lithium batteries has been proven to be a very effective and facile way to improve battery safety and performance. In this work, a composite separator (PBS-M-S) was developed via asymmetrically coating the conductive MXene particles and the nonconductive silica particles onto a biodegradable poly(butylene succinate) (PBS) fibrous membrane. Such a structure and material design was able to give the produced separator exceptional all-around properties. Specifically, the PBS-M-S separator displayed great flexibility with a 250% elongation at break, high temperature sensitivity with shutdown function at 120 °C, and thermal stability with flame retardancy. Moreover, the network constructed by PBS's micro/nano fibers and the electrolyte affinity of silica allowed the separator to maintain abundant electrolyte. This, combined with the incorporation of MXene, optimized the separator with high ionic conductivity (3.386 mS cm−1), lithium ion transference number (0.51) and lithium dendrite inhibition ability, which rendered the cell with outstanding cycling stability. Therefore, taking safety and battery performance into account, the as-prepared composite membrane could be a promising separator candidate for lithium ion batteries.