Sulfur modulated oxygen-rich porous carbon exhibiting high-capacity as cathode for sodium ion hybrid capacitors

Abstract

Sodium-ion hybrid capacitors (SIHCs) offer significant potential for energy storage applications, owing to their high energy density, excellent power density, and the abundance of sodium resources. However, the specific capacity of carbon-based cathodes is considerably lower than that of battery-type anodes, creating a capacity imbalance that limits the overall energy density of SIHCs. Therefore, developing high-performance carbon cathodes is crucial for enhancing their energy storage capabilities. Herein, we report the successful synthesis of sulfur- and oxygen-doped porous carbon (SOPC). The resulting material features an interconnected, honeycomb-like pore structure with an exceptionally high specific surface area of 1219 m² g⁻¹. Its hierarchical pore structure significantly improves ion transport and accelerates adsorption/desorption processes. Additionally, the SOPC contains 6.96 % sulfur and 9.84 % oxygen. The introduction of sulfur enhances the pseudocapacitive behavior of the oxygen-rich porous carbon, achieving a high specific capacity of 135.2 mAh g⁻¹ at 0.05 A g⁻¹ and 63.8 mAh g⁻¹ at 10 A g⁻¹. Consequently, SOPC-based SIHCs exhibit an impressive energy density of 105.6 Wh kg⁻¹ and excellent capacity retention of 83.5 % after 4000 cycles at 10 A g⁻¹. These results highlight the considerable potential of sulfur-modulated, oxygen-rich porous carbon materials for high-performance energy storage applications.