Binder-Free TiO2-Coated Polypropylene Separators for Advanced Lithium-Ion Batteries

Modification with inorganic nanoparticles is a common method to enhance the thermal stability, electrolyte wettability, and overall functionality of commercial separators. However, the binders frequently used reduce the specific capacity of batteries and tend to swell in the electrolyte. Herein, a novel type of inorganic thin layer-coated separator that is easy to prepare and does not require a binder is designed. After treating by UV/O-3, a thin titania layer is uniformly deposited on the surface of a commercial polypropylene (PP) separator by a facile sol-gel coating method. The thin TiO2 layer considerably improves the thermal stability of the separator, and there is no obvious shrinkage when the separator is heated at 170 degrees C for 30 min. At the same time, the electrolyte wettability is greatly improved after modification, which increases the Li+ migration rate. A LiFePO4/Li battery with the PP@TiO2 separator shows superior rate capability and cycle performance at high currents; particularly, it demonstrates a high capacity of 92.6 mAh g(-1) at 15 C. The modified separator simultaneously improves the safety and electrochemical performance of the batteries, which will help to achieve the goal of preparing high-safety, high-capacity lithium-ion batteries (LIBs).