A Thermally Stable, Combustion‐Resistant, and Highly Ion‐Conductive Separator for Lithium‐Ion Batteries Based on Electrospun Fiber Mats of Crosslinked Polybenzoxazine

Porous and thermally stable membranes are attractive materials as separators in lithium‐ion batteries. This work reports a new class of high‐performance separators for Li‐ion batteries based on a crosslinked polybenzoxazine electrospun fiber mat (CR‐PBz‐FbM). The CR‐PBz‐FbM separator shows a high ion conductivity of 2.92 mS cm−1 (5.2 times the value recorded for Celgard 2300), a low MacMullin number of 3.35, ultrahigh electrolyte uptake (≈825 %), and near‐zero shrinkage at 150 °C. Consequently, the CR‐PBz‐FbM separator shows a high C‐rate capacity and good cycle retention in the half‐cell test. At a C‐rate of 2.0, the CR‐PBz‐FbM‐based Li‐ion cell only exhibits a capacity loss of 16 % compared to a 40 % capacity loss found with the cell based on Celgard 2300. The results demonstrate that CR‐PBz‐FbM is an inexpensive, non‐shutdown‐type, thermally stable, and highly ion‐conductive separator for Li‐ion batteries.