Heptazine-Based Polyimide with Dense Redox Sites and Large Conjugated Structure for Cathodic Lithium-Ion Storage

Abstract As organic cathode materials for lithium-ion batteries (LIBs), polyimides (PIs) have attracted widespread attention due to their abundant redox-active carbonyl sites, structural tunability, and environmental compatibility. However, the presence of electrochemically inactive structural units in conventional PIs limits their specific capacity. Herein, a novel heptazine-based polyimide (MePI) cathode for LIBs is prepared, which features dense redox sites and large conjugated structure, and its composites with multi-walled carbon nanotubes (MWCNTs) are prepared through an in situ solid-state thermal polymerization method. The composites exhibit improved electrochemical performance due to the enhanced conductivity and more accessible active sites provided by the carbon nanotubes. Among the prepared composites, MePI@MWCNT-50% achieves the highest specific capacity of 181 mAh g–1 at 0.1 A g–1 and maintains great cycling stability after 1000 cycles at 0.5 A g–1. Ex situ FT-IR and density functional theory calculations reveal that heptazine rings serve as reversible Li+ storage sites. This work provides a promising strategy for the development of advanced organic electrodes for next-generation LIBs.