Oxygen vacancies in polyimide carbon enable stable zinc-ion storage

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.

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