Competitive Polymerization Pathways of Barbituric Acid With Bismaleimide for Enhanced Thermal Stability and Electrochemical Performance of Cathode Material

To meet the rising demand for safe and high‐energy lithium‐ion batteries, it bears advanced methods that prevent thermal runaway while maintaining electrochemical performance. In this study, LiNi 0.6 CO 0.2 MnO 2 O 2 (NMC) cathode surface was treated with novel polymers (Polymer A and Polymer B), which were designed through distinct structural mechanisms. The as‐synthesized polymers were probed using surface plasmon resonance (SPR), soft x‐ray absorption spectroscopy (XAS), electrochemical and thermal characterization tools. SPR analysis revealed that the hyperbranched Polymer B amplifies electronic oscillations at the sensor interface, resulting in a higher resonance angle. Elevated temperatures consistently increased the binding constant of Polymer B from 2.7 × 10 4 to 4.8 × 10 4 M −1 s −1 . Correspondingly, this polymer impedes Li + transport, leading to a higher irreversible capacity of 14.4%, compared to 11.9% for bare LiNi 0.6 CO 0.2 MnO 2 O 2 (NMC). In contrast, Polymer A undergoes electrochemical and thermal self‐polymerization through its unreacted NH groups in the first cycle. Soft XAS confirmed that these functional groups drive spectral evolution upon full delithiation, facilitating the formation of a secondary protective layer. Thus, Polymer A reduced the total heat released during thermal decomposition from 319 to 110 J g −1 while maintaining cycle stability. These findings establish a structural relationship of Polymer A excelling interfacial stabilization and heat absorption through reactive self‐termination and Polymer B provides mechanical robustness and gas suppression. By leveraging the NH reactivity of Polymer A and the highly cross‐linked nature of Polymer B, optimal operating conditions can be achieved that simultaneously enhance thermal stability and electrochemical performance, offering promising pathway toward next‐generation lithium‐ion batteries.