Sustainable Terephthalic Acid Modified Polyimide Binder for Enhanced Li-Ion Storage in Silicon Nanoparticles

A simple, green and scalable in situ thermochemical method is reported for fabricating high-performance silicon-based lithium-ion battery (LIB) anodes using a novel terephthalic acid-modified polyimide (TM-PI) binder. TM-PI is synthesized via a condensation reaction between polyimide (PI) and terephthalic acid (TPA) during electrode fabrication, introducing new amide linkages and abundant functionalities. Due to the successful covalent incorporation of TPA into the PI backbone,  TM-PI exhibits enhanced molecular rigidity and crosslinking, which improve interfacial adhesion and structural stability when combined with silicon nanoparticles. The resulting electrode (Si@TM-PI) delivers a capacity of 2162 mAh g^{- 1} after 100 cycles at 200 mA g^{- 1} with a coulombic efficiency (CE) of 99.0%, along with excellent rate performance, and a significantly lower charge-transfer resistance (R_ct = 12.5 Ω) compared to the unmodified electrode(214.6 Ω). In full cell configuration with a LiFePO₄ cathode, the Si@TM-PI anode achieves an initial CE of 88.7% and a capacity of 81.3 mAh g^{- 1}, retaining 86.4% of the initial capacity after 400 cycles at 800 mA g^{- 1}, with a gravimetric energy density of 379.4 Wh kg^{- 1}based on the combined mass of the anode and cathode. TM-PI is established as a promising sustainable binder for next-generation high-capacity LIBs.