Dual-Function Polyimide Binders Containing Benzimidazole/Benzoxazole Moieties for High-Performance SiO_<i>x</i>/C Anodes in Lithium-Ion Batteries

N-Heteroaromatic moieties in polymer binders are found to be beneficial to enhance battery performance, although the mechanism remains unclear. Here, a series of polyimide (PI) binders with benzimidazole or benzoxazole moieties were prepared and evaluated for application in SiOx/C anodes. The specific capacity retention rates of the batteries using the PI-BIDA binder (based on 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 4,4′-oxidianiline (ODA), and 2-(4-aminophenyl)-5-aminobenzimidazole (BIDA)) exceeded 90% at 0.2C after 150 cycles, achieving specific capacities of about 1350 mAh g–1 and 3.5 mAh cm–2. By contrast, the batteries using the PI-ODA (based on BPDA and ODA) and PI-BOA (based on BPDA, ODA, and 2-(4-amino-phenyl)-5-aminobenzoxazole (BOA)) binders retained only 84 and 71% of their original specific capacity after 150 cycles, respectively. This was attributed to their difference in lithium-ion affinity and solid electrolyte interphase (SEI) formation, as revealed by the simulation and spectroscopic results. The PI-BIDA binder displayed higher lithium-ion affinity, and the resulting batteries contained stable and high content of LiF in their SEIs during long-term cycling. This work provides meaningful insights into the structure design of polymer binders for lithium-ion batteries.