Design and Preparation of Soluble Polyimide Binder With Random Copolymerized Rigid‐Flexible Segments for Lithium Ion Batteries

Binders play a critical role in the preparation and operation of electrodes in lithium‐ion batteries (LIBs). Developing new binding materials with high affinity to Li ions and resistance to higher voltages was desirable for the practical applications of LIBs. In this work, soluble polyimide binder (PI) with random copolymerized rigid‐flexible segments were synthesized and evaluated as cathode binder for the typical lithium iron phosphate cathode material in terms of cycling performances, rate capability, and electrochemical impedance. By introducing the polar and soft ether segment into the rigid PI chains, the NMP‐soluble PI precursors were obtained. The rigid‐flexible segments in the PI binders work synergistically during the electrochemical process, in which the rigid segments of aromatic units with strong lithiophilic CO group provided the necessary mechanical support and affinity with electrolytes, while the flexible segments endow the high solubility and buffer effect to the volume change during the charge/discharge process. Moreover, the 3,5‐diaminobenzoic acid (DABA) working as the crosslinking unit was introduced during the synthesis and the addition ratios were optimized. The as‐optimized PI binders exhibited superior rate performances and comparable cycling stability when compared with the commercial PVDF binder, demonstrating the great potential for PI binder in the LIBs systems.