High-wettability composite separator with barium sulfate nanoparticle coating and electrolyte synergistic flame retardation for high performance sodium ion batteries

The conventional polyethylene (PE) separators used in sodium-ion batteries (SIBs) have demonstrated poor compatibility with the polar solvents, and the flammability of the separator and the electrolyte solvents also pose safety risks for SIBs. To address these challenges, a composite separator (PE@BSO) with a barium sulfate (BSO) nano-coating, prepared using a colloid of ultrafine BSO nanoparticles, has been developed to synergistically enhance the flame retardancy with a designed electrolyte. The designed electrolyte consists of high boiling point and high flash point solvents with only 5 % trimethyl phosphate (TMP). When combined with the designed electrolyte, the PE@BSO composite separator shows excellent flame retardancy due to the high compatibility and synergy between the BSO nano-coatings and the high flash point electrolyte. Additionally, the PE@BSO separator has improved ionic conductivity (0.52 mS cm−1) and Na+ transfer number (0.65). The Na3V2(PO4)3 half-cell assembled with PE@BSO shows an enhanced discharge capacity of 109.2 mAh g−1 at 0.5C with 97.9 % capacity retention after 300 cycles and a C-rate capacity of 95.4 mAh g−1 at 5C. These results demonstrate that the as-prepared separator has promising potential for the application in SIBs.