Chain structure-dependent electrochemical performance of polyimide cathode materials for lithium-ion batteries

Organic polyimides have received an ever-growing interest in lithium-ion batteries based on the reversible anion stabilization mechanism of redox-active carbonyl groups due to their high theoretical capacities, resource sustainability, and diverse chain structures. Herein, four linear polyimides with different chain structures were synthesized by a facile and green hydrothermal method. The chain structure-electrochemical performance relationship was explored by regulating active anhydride units and diamine linkers. The incorporation of flexible linkers between redox-active anhydrides results in the facile movement of polyimide chains and the formation of porous networks with abundant active sites. In contrast, rigid aromatic linkers with strong π – π conjugation tend to assemble into the orderly-stacked sheets, enabling the efficient electron transfer. When used as the battery cathode, 1,4,5,8-naphthalenetetracarboxylic dianhydride-based polyimide with a relatively flexible linker delivers the largest specific capacity. Such a polyimide also demonstrates the high cycling stability with a capacity retention up to 52% over 10000 cycles. In contrast, pyromellitic dianhydride-based polyimide with a benzene-enriched linker exhibits the lowest capacity and poor rate capability due to its densely-stacked sheets and limited exposure of active groups. The chain structure-dependent performance relationship of polyimides would offer new insights into the rational design of high-performance organic electrodes for the next-generation batteries.