In this work, the sulfonic acid group was introduced into the resorcinol–formaldehyde (RF) microspheres by the addition of p-phenolsulfonic acid during the polycondensation process of RF. The hydrophilicity of the sulfonated RF allowed KOH to infiltrate inside the microspheres, which enhanced the formation of mesopores in the carbon microspheres during the activation process by KOH. SEM and TEM observations and N2 adsorption measurements verified the formation of abundant mesopores in the porous carbon microspheres. The BET surface area of these mesoporous carbons exceeded 2000 m2/ g. In 17 m NaClO4 “water-in-salt” (WIS) electrolyte-based supercapacitor, the synthesized mesoporous carbon exhibited high specific capacitance of 170 F/g at current density of 0.5 A/g, comparable to those in regular KOH electrolyte. When graphite was used as current collectors, the symmetric cell could operate at 2.5 V, and the mesoporous carbon exhibited an energy density of 43 Wh/kg at power density of 0.25 kW/kg, and 25 Wh/kg at power density of 6.25 kW/kg, respectively, which were superior to those using Pt or stainless steel as current collectors. The mesoporous carbon/graphite was an excellent electrode in new-generation “WIS” electrolyte-based high-voltage supercapacitor due to their high energy and power density.

    Abstract
    1 Introduction
    2 Experimental
        2.1 Synthesis of porous carbon microspheres
        2.2 Characterization and electrochemical measurement
    3 Results and discussion
        3.1 Morphology and microstructures of porous carbon microspheres
        3.2 Electrochemical properties
    4 Conclusions
    Acknowledgements 
    References

• Sangho Yu(Division of Chemistry and Materials Engineering, Graduate School of Engineering, Nagasaki University)
• Hideaki Sano(Division of Chemistry and Materials Engineering, Graduate School of Engineering, Nagasaki University)
• Guobin Zheng(Division of Chemistry and Materials Engineering, Graduate School of Engineering, Nagasaki University)