A bacterial cellulose composite separator with high thermal stability and flame retardancy for high-performance lithium ion batteries

Separators play a crucial role in enhancing the safety of lithium-ion batteries (LIBs); however, commercial polyolefin separators exhibit poor thermal stability and are flammable. This study investigates the use of green, environmentally friendly, and renewable bacterial cellulose as a substrate for developing a composite separator (BHM/5). The BHM/5 separator, comprising bacterial cellulose, an inorganic mineral nano-hydroxyapatite (HAP) and flame-retardant melamine polyphosphate (MPP), is fabricated via freeze drying and high-temperature pressing. The developed composite separator demonstrates superior thermal stability and excellent flame retardancy compared with commercial polyolefin separators while maintaining structural integrity at 200 °C and exhibiting self-extinguishing properties after ignition. Furthermore, the BHM/5 separator exhibits a high porosity of 74 % and a substantial electrolyte uptake of 459 %, achieving an ion conductivity of 1.44 mS/cm. As a result, the cell of the LiFePO₄-Li system assembled demonstrates an initial discharge capacity of 131.35 mAh·g^-1 at a current density of 1C and a capacity retention of 95.4 % after 150 cycles.