Significantly enhanced capacitance of symmetrical supercapacitor based on Cu-CuxS@S-C electrode by thiourea electrolyte additive

Abstract Metal sulfides have been considered to be excellent electrode materials for supercapacitors (SCs) due to their high conductivity and electrochemical activity. Meanwhile, the addition of redox additives to the electrolyte can increase the pseudocapacitance of SCs. Herein, the composite (Cu-CuxS@S-C) of Cu nanocrystals and CuxS embedded in S-doped carbon matrix was prepared through impregnation method followed by high-temperature pyrolysis. The optimal Cu-CuxS@S-C-600 has an extremely high capacitance of 9607 mF cm−2 at 5 mA cm−2 in the alkaline electrolyte with thiourea (TU), which is due to the good conductivity of Cu and CuxS, large crystal plane spacing of CuxS, and the redox reaction caused by the addition of TU. The symmetrical SC based on Cu-CuxS@S-C-600 electrode was fabricated, its pseudocapacitance (960 mF cm−2) in the electrolyte with TU is 4.6 times that (208 mF cm−2) in the electrolyte without TU. The energy density (E) of SC reaches 261 µ Wh cm−2, and the power density (P) is 2800 µW cm−2 at 4 mA cm−2 in the gel electrolyte with TU.