Interfacial defect engineering of S/O dual-doped carbon nanostructures for advanced sodium-ion hybrid capacitors

Porous carbon materials have important applications in energy storage and conversion due to sufficient raw materials, adjustable pore structure and specific surface area. However, developing porous carbons with both a simple preparation process and excellent performance remain a significant challenge. Herein, we propose synthesizing S/O co-doped porous carbon (SOPC-3) by regulating the S/O ratio and introducing abundant adsorption sites. According to electrochemical tests, SOPC-3 has a high Na⁺ storage capacity of 396.7 mAh g⁻¹ at 1 A g⁻¹. After 3500 cycles, it maintains 192.7 mAh g⁻¹ at a current density of 10 A g⁻¹. Combined with theoretical calculations and material characterization analysis, the excellent performance is attributed to the fact that the S/O co-doping promotes the reversible adsorption-desorption process of Na⁺, and the rich pore structure provides more ion diffusion paths. Meanwhile, the prepared by K₂CO₃-assisted KOH activated asphalt (KAC) maintains a reversible capacity of 69.0 mAh g⁻¹ over 2400 cycles at a current density of 0.5 A g⁻¹. Finally, at the power density of 140 W kg⁻¹, the assembled sodium-ion hybrid capacitor (SOPC-3//KAC) demonstrates a high energy density of 104.2 Wh kg⁻¹. This work provides important theoretical guidance for the design of high-performance carbon-based energy storage materials.