Fire-retardant and thermally conductive polyacrylonitrile-based separators enabling the safety of lithium-ion batteries

Lithium-ion batteries (LIBs) have broad application prospects in many fields because of their high energy density. However, the poor heat resistance of polyolefin membranes and uneven lithium deposition result in battery failure and even infamous thermal runaway behavior. To improve the intrinsic safety of batteries, fire-retardant, thermally conductive, electrospinning strategies are employed to acquire a functional polyacrylonitrile (PAN) nanofiber separator (PAN@FBN/TPP) containing modified boron nitride (FBN) and triphenyl phosphate (TPP). Compared with those of the Celgard separator, the porosity, contact angle, and electrolyte uptake of the Celgard separator are greatly improved. Moreover, the designed separator shows excellent thermal stability without shrinkage when heated at 220 °C. The char residue at 800 °C is 43.7 wt%, which is much greater than that of the Celgard separator (∼0.26 wt%). The maximal peak heat release rate (PHRR_max) is only 30 % that of the Celgard separator. The improvement in heat resistance laid a solid foundation for the preparation of high-safety LIBs. The advantages of a uniform pore size distribution and extremely high porosity provide abundant active sites and convenient channels for Li⁺ migration. The cell with the PAN@FBN/TPP separator shows excellent cycle stability and rate performance. Owing to the high heat resistance of PAN and the excellent flame-retardant capability of FBN, the LIBs presented the highest self-heating temperature (T₀) and thermal runaway temperature (T₁) and the smallest maximum temperature (T_max) and heat release rate (HRR_max) in the safety performance test; compared with those of commercial separator batteries, the above thermal safety parameters increased by 16.9 %, 6.5 %, 21.8 % and 81.5 %, respectively. Overall, this work may provide an effective way to fabricate LIBs with high thermal safety.