Low-Temperature Imidized Polyimide Binder Enabling Structural and Electrochemical Stability of NCM811 Cathode for High-Safety and Long-Cycling Lithium-Ion Batteries

Abstract

Polyimide (PI) is a promising binder material for lithium-ion batteries due to its excellent mechanical strength, high thermal stability, and outstanding chemical inertness. However, the high-temperature imidization requirement (>300 °C) of traditional PI binders is incompatible with current electrode preparation processes, severely limiting their practical applications. In this study, a low-temperature-imidized polyimide (∼150 °C) was elaborately designed and utilized as NCM811 cathode binder, which works by covalently bonding 5-aminobenzimidazole (ABZ) to the ends of the flexible 4,4′-oxidiphthalic anhydride (ODPA)/4,4′-oxidiphenylamine (ODA) poly(amic acid) (PAA) chains to realize the self-catalysis at a low temperature, followed by the assistance of dual-functional N,N′-carbonyldiimidazole (CDI) as a catalyst and dehydrating agent to accelerate the condensation and low-temperature dehydration of amic acid, yielding the imidization of the PAA precursor to give PI at 150 °C. Compared to the conventional PVDF binder, the cathode utilizing this low-temperature imidized polyimide (LTPI) binder exhibited excellent capacity retention (84.9% vs 81.7%) after 100 cycles at 0.2C, and superior rate performance (119.3 mAh·g^–1 vs 95.7 mAh·g^–1 at 5.0C) under a 4.3 V cutoff voltage. The CV, SEM, XRD, and XPS results demonstrate that the designed LTPI binder effectively suppresses the hexagonal (H2) to hexagonal (H3) phase transition and transition metal dissolution, maintaining the cathode’s structural integrity during charge–discharge cycles, thereby ensuring excellent long-term cycle stability. Furthermore, the NCM811 cathode with LTPI binder exhibits significantly enhanced flame-retardant performance compared with the NCM811/PVDF cathode in the combustion experiments, demonstrating the superiority of LTPI binders in improving the safety of the cathode materials. The NCM811/LTPI cathode retains the excellent structural and electrochemical stability of traditional high-temperature-imidized PI binders, providing a practical pathway to develop high-performance binder materials for high-safety and long-cycling lithium-ion batteries.