Towards high performance polyimide cathode materials for lithium–organic batteries by regulating active-site density, accessibility, and reactivity

Organic carbonyl electrode materials offer promising prospects for future energy storage systems due to their high theoretical capacity, resource sustainability, and structural diversity. Although much progress has been made in the research of high-performance carbonyl electrode materials, systematic and in-depth studies on the underlying factors affecting their electrochemical properties are rather limited. Herein, five polyimides containing different types of diamine linkers are designed and synthesized as cathode materials for Li-ion batteries. First, the incorporation of carbonyl groups increases the active-site density in both conjugated and non-conjugated systems. Second, increased molecular rigidity can improve the accessibility of the active sites. Third, the introduction of the conjugated structure between two carbonyl groups can increase the reactivity of the active sites. Consequently, the incorporation of carbonyl structures and conjugated structures increases the capacity of polyimides. PTN, PAN, PMN, PSN, and PBN exhibit 212, 198, 199, 151, and 115 mAh g−1 at 50 mA g−1, respectively. In addition, the introduction of a carbonyl structure and a conjugated structure is also beneficial for improving cycling stability and rate performance. This work can deepen the understanding of the structure−function relationship for the rational design of polyimide electrode materials and can be extended to the molecular design of other organic cathode materials.