Effect of heteroatom doping and morphology tuning of CNT-derived material for potassium-ion hybrid capacitors

Carbon-based materials are all-around anodes for potassium-ion (K+) storage systems. To further boost the electrochemical performance, heteroatom doping ("HD") and morphology tuning ("MT") are two prominent ways. However, the detailed influence of "HD" and "MT" is still confused with each other, leading to a derived question that does the preparation sequence between "HD" and "MT" affect the ultimate performance? To reveal these questions, multi-wall carbon nanotube (CNT) is selected as a precursor, and further modulated to N/S dual doped carbon with hierarchical morphology and corresponding counterparts, respectively. By comprehensive comparisons, "MT" shows an advantage in introducing structural imperfection, making full use of surface absorption and capacitive contribution, while "HD" is good at expanding interlayer, facilitating the diffusion/ intercalation of K+. The revealed individual effects of "HD" and "MT" give a convenience to elucidate the role of preparation sequence played in the ultimate performance, subsequently guiding to synthesize N/S dual-doped carbon with hierarchical morphology derived from CNT. Such subtle structure design balances the capacity and capacitive contribution, and shows excellent performance in K-ion hybrid capacitor (a high power density of 21428.6 W kg(-1) and remarkable long cycle life of 14,000 times). This unique construction of superior universal anode with great performance provides a new avenue for next storage development and commercial application.