Pseudocapacitive porous hard carbon anode with controllable pyridinic nitrogen and thiophene sulfur co-doping for high-power dual-carbon sodium ion hybrid capacitors

Abstract

Developing high-performance electrode materials for energy-storage devices with high energy-power densities, such as sodium ion hybrid capacitors (SIHCs), is of vital importance for applications in electric vehicles and portable electronics. Porous hard carbon is one of the most fascinating anode materials for SIHCs due to the rapid Na⁺ diffusion. Doping with heteroatoms, such as pyridinic N and thiophene S, may boost both the rate performance and specific capacity. However, it is still very challenging to modulate the content and configuration of N and S dopants efficiently. Furthermore, the trade-off for several storage mechanisms, which is vital for carbon anodes with rapid storage and release of sodium ions, is still scarce. Herein, a simple and efficient method is proposed to regulate the configuration of nitrogen dopants, increase the content of thiophene S, create micropores and adjust the structure of curved graphitic domains of hard carbon. Besides, the evolution mechanism of the structure and component is explored through ex situ XRD and XPS analysis. As-prepared NS-pHC-1.348 (N and S co-doped porous hard carbon with 1.348 g MgCl₂ precursor) delivers high reversible capacity (383.9 mA h g⁻¹ at 0.05 A g⁻¹), excellent rate ability (183.2 mA h g⁻¹ at 20 A g⁻¹) and fine cycle stability (287.2 mA h g⁻¹ at 1 A g⁻¹ after 1000 cycles). The ratio of pseudocapacitive behaviors in NS-pHC-1.348 reaches up to 70.19% at 0.2 mV s⁻¹, which could balance the electrochemical kinetics of the cathode and anode in SIHCs. Therefore, SIHCs, assembled from the presodiated NS-pHC-1.348 anode and NPC (N-doped porous carbon) cathode, showed superb power characteristics (92.03 kW kg⁻¹ at 5.98 W h kg⁻¹). This work will contribute to the design of high-performance anodes with tunable multi-active sites and the construction of high-power SIHCs.