Oxygen vacancies in polyimide carbon enable stable zinc‐ion storage

Abstract Aqueous zinc‐ion hybrid capacitors (ZIHCs) are promising electrochemical energy storage systems with advantages of high‐energy density, low cost, safety and environmental friendliness. However, application of carbon‐based cathodes is limited by their low‐energy density due to the lack of active sites. Herein, a chemisorption sites modulating strategy is proposed to construct nitrogen‐doped polyimide carbon nanoflowers with abundant oxygen vacancies and carbonyl functionalization via high‐temperature calcination and subsequent acid processing. The synergistic effect of oxygen vacancies, carbonyl groups, enhanced surface area and porous structure enables stable zinc‐ion storage with high capacity. Remarkably, the carbon materials can circulate 20,000 cycles stably at a current density of 2 A·g −1 . After 10,000 cycles at a high rate of 3 A·g −1 , a capacity retention rate of 64% can still be achieved. The as‐prepared ZIHCs provide an energy density of 65.61 Wh·kg −1 at the power density of 197.82 W·kg −1 . Current research shows that polyimide‐derived carbon material synthesized by acid activation provides a new idea for developing cathodes in aqueous ZIHCs.