Engineering smart active interfacial layer-coated high-nickel ternary cathode materials for high-safety lithium ion batteries

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High‑nickel ternary cathode materials, specifically LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), are essential for the next generation of high-energy-density lithium-ion batteries. However, their practical application is severely limited by inherent thermal instability and safety concerns. In this study, we report a novel strategy to engineer a “Smart Active Interfacial Layer (SAIL)” on NCM811 cathode powders via the in-situ polymerization of bismaleimide (BMI) and barbituric acid (BTA). Morphological and chemical characterizations (SEM, TEM, and XPS) confirm the formation of a conformal, hyper-branched oligomeric nanolayer with a thickness of 3–12 nm. Thermal analysis (DSC/TGA) reveals that the SAIL coating significantly suppresses exothermic reactions without perturbing the R3m crystal structure. Electrochemical evaluations in 1.2 Ah pouch cells demonstrate that the SAIL-modified NCM811 (NCM811S) cell achieves a superior capacity retention of 90.1% after 500 cycles at 1C, compared to only 61.5% for the pristine counterpart. Most notably, the NCM811S cells successfully passed the rigorous drill penetration safety test without smoke, fire, or explosion, maintaining a maximum temperature of 104 °C, while pristine cells underwent catastrophic thermal runaway at 400 °C. This “smart” thermal-locking mechanism, which drastically increases local impedance during mechanical failure, provides a transformative pathway for developing high-safety, high‑nickel lithium-ion batteries for electric vehicle applications.