Functional Group Regulated Polyimide Binders for Silicon-Based Anodes in Lithium-Ion Batteries

Binders play a critical role in mitigating the severe volume variation of silicon anodes during charge/discharge and maintaining electrode integrity. In this work, a series of polyimide (PI) binders with different functional groups are prepared to systematically investigate the structure-property relationship. The PI-DABA binder containing amide groups can effectively resist electrolyte swelling and possess strong interfacial interactions toward Si materials. In contrast, the PI-APAB binder, which contains ester groups, shows severely degraded mechanical properties upon electrolyte swelling and excessively strong coordination with Li⁺. The PI-PDA binder, which contains no additional polar groups, resists electrolyte swelling but shows weak interfacial interaction with Si particles. As a result, the PI-DABA-based silicon anode exhibits the best performance at 1 A g^–1, retaining over 70% of its initial capacity after 300 cycles with a specific capacity of about 2300 mAh g^–1. It forms a stable solid electrolyte interphase (SEI) featuring an organic-rich outer layer and a LiF-rich inner layer, while PI-APAB or PI-PDA-based SEIs consist of mixed organic and inorganic species. This study uncovers the significant impact of polymer binder structures on their electrolyte swelling behaviors and interfacial interactions and provides practical designing principles toward high-performance polymer binders for silicon anodes in lithium-ion batteries.