Abuse‐Tolerant Separator Enabled by Surface Charge Modulation and Structural Reinforcement for High‐Safety Lithium‐Ion Batteries

ABSTRACT The growing demand for high‐energy lithium‐ion batteries for electric vehicles has highlighted battery safety as a critical challenge. While polyimide (PI) separators provide superior thermal stability and electrolyte wettability compared to conventional polyolefin separators, their practical application is limited by insufficient mechanical robustness. Herein, an abuse‐tolerant separator (ATS) is fabricated by integrating PI with surface‐oxidized carbon nanotubes (s‐CNTs) via non‐solvent induced phase separation while maintaining the s‐CNT content below the percolation threshold to prevent conductive network formation. The tensile strength of the resulting ATS is increased by ∼92%, enabling a thinner separator without compromised safety. Partial surface oxidation of the CNTs introduces negative surface charges, thereby increasing the Li‐ion transference number from 0.39 to 0.47, promoting uniform ion transport, and suppressing dendrite growth. Consequently, ATS‐based Li||Cu and Li||Li cells exhibit substantially improved cycling stability, retaining a CE of 69.6% after 200 cycles and maintaining lower polarization throughout long‐term cycling, respectively. Moreover, NCM||Graphite full cells with an inverted N/P ratio further verify the efficacy of the ATS in promoting safer and more reliable practical battery performance. This approach provides an effective strategy for protecting the battery from internal and external stresses while improving its practical energy density via reduced separator volume.