Dual‐Redox Active Sites Enable High Initial Coulombic Efficiency and Long Lifespan of Carbazole‐Based Cathodes for Lithium Dual‐Ion Batteries

Abstract Carbazole‐based compounds are a representative class of p‐type organic cathode materials featuring redox‐active nitrogen centers. However, the conventional single‐electron transfer mechanism of the carbazole molecule during redox reactions leads to electron delocalization across aromatic π‐conjugated systems, triggering destructive electropolymerization at para‐positions and thereby severely compromising both initial Coulombic efficiency (ICE) and cycling stability. To address these critical challenges, an innovative “dual‐redox active sites” strategy is proposed that enables the pairing of unpaired electrons through a two‐electron transfer mechanism, resulting in the formation of stable conjugated structures and effectively suppressing electropolymerization observed in conventional carbazole‐based cathodes. Two representative model materials, poly(9′′‐ethyl‐9H,9′′H‐3,3′:9′,3′′‐tercarbazole) (PETCZ) and poly(5‐(9‐ethyl‐9H‐carbazol‐3‐yl)‐5,11‐dihydroindolo[3,2‐b]carbazole) (PECDIC), are rationally designed and synthesized to validate this strategy. As expected, both compounds demonstrate high ICE exceeding 84% without any pretreatment for the electrode, setting a new benchmark among existing carbazole‐based organic cathode materials. Notably, PETCZ features a more developed porous architecture compared to PECDIC, which significantly increases the specific surface area and facilitates efficient ion transport kinetics. Li‐based dual‐ion full batteries (LDIBs) assembled using graphite anode and PETCZ cathode demonstrate a peak discharge capacity of 159 mAh g ⁻¹ with an energy density of 526 Wh kg ⁻¹ , maintaining stable cycling performance for over 4500 cycles.