Boron nitride nanosheet-reinforced glass-fiber separator for safe and high-performance aluminum-ion batteries

High-performance separators are crucial for the development of aluminum-ion batteries (AIBs). In this work, boron nitride nanosheets (BNNSs) are prepared via a low-cost, environmentally benign, and scalable method developed in our laboratory, yielding few-layer nanosheets with enlarged interlayer spacing, suppressed restacking, and oxygen-containing surface functionalities. The BNNSs are uniformly deposited onto commercial glass-fiber (GF) separators through vacuum-assisted filtration, forming BNNSs@GF composite membranes with improved electrolyte wettability, enhanced mechanical robustness, and intrinsic flame-retardant characteristics. Electrochemical evaluations demonstrate that BNNSs@GF separators effectively regulate ion transport and homogenize interfacial ion flux, thereby stabilizing aluminum deposition behavior and enhancing interfacial stability. When applied in Al||graphite full cells, the BNNSs@GF separator enables a high discharge capacity of about 130 mAh·g −1 at 1000 mA g −1 , which is more than 2.5 times higher than that of cells using pristine GF separators. It exhibits excellent rate reversibility (≈89 % capacity recovery) and outstanding cycling stability, retaining about 40 mAh·g −1 after 2000 cycles at 2000 mA g −1 (≈80 % capacity retention). This work demonstrates a robust separator-engineering strategy based on two-dimensional BNNSs for developing high-performance, durable, and safer aluminum-ion batteries.