Boehmite/Polyacrylonitrile Composite Nanofiber Separator with Enhanced Ionic Conductivity and Thermal Stability for Lithium-Ion Batteries

Polyethylene (PE) and polypropylene (PP) are widely used in commercial lithium-ion battery (LIB) separators owing to their high mechanical strength and chemical stability. However, both polymers suffer from poor high-temperature tolerance, low porosity, and inadequate electrolyte wettability, making it difficult to reconcile electrochemical performance with safety under thermal stress. Developing advanced lithium-ion battery separators is therefore crucial for achieving high efficiency, safe LIBs. This study presents a boehmite/polyacrylonitrile (BM/PAN) composite nanofiber separator fabricated by electrospinning and systematically examines how BM loading affects separator microstructure and electrochemical behavior. Compared with commercial PP separators, the BM/PAN composites exhibit a unique three-dimensional interconnected fiber network, together with markedly improved wettability, thermal stability and electrochemical properties. The optimal formulation contains 4 wt% BM (denoted PAN-BM-4) exhibited an outstanding wettability with electrolyte uptake of 692.5% with the porosity of 80.7% and electrolyte contact angle of 25.5°, ensuring rapid electrolyte infiltration and efficient ion transport. it also displayed a higher mechanical property with tensile strength of 7.9 MPa and elongation at break of 27% (cf. 6.5 MPa and about 45% for pure PAN), indicating enhanced structural integrity. Meanwhile, such PAN-BM-4 separator demonstrates an excellent thermal stability with negligible shrinkage at 200 °C and a residual mass of 57.6% at 800 °C, effectively mitigating the thermal-runaway risk of conventional separators. Moreover, as to the electrochemical performance, this unique PAN-BM-4 separator showed an ionic conductivity of 3.31 mS/cm, more than six times that of commercial PP, and the electrochemical stability window exceeding 5.5 V (versus Li + /Li) and a Li + transference number ( t Li +) of 0.42, substantially higher than PP (0.28) and pure PAN (0.34), reflecting enhanced selective Li+ transport. Besides, in half-cell testing, the PAN-BM-4 separator delivers an initial discharge capacity of 140.6 mAh/g at 0.5 C with 88.3% capacity retention after 100 cycles. in summary, this work establishes a viable materials-design strategy and experimental framework for next-generation LiB separators that simultaneously achieve high ionic conductivity, superior thermal stability and favorable interfacial compatibility.