Micro/mesopore carbon spheres derived from sucrose for use in high performance supercapacitors

Micro/mesopore carbon spheres for supercapacitor application were prepared by hydrothermal carbonization followed by KOH/NaOH activation using sucrose as the carbon precursor. The effects of the KOH and NaOH activation parameters on the specific surface area, pore size distribution and electrochemical performance of the carbon spheres were investigated. Results indicate that the use of NaOH leads to the development of mesopores while the use of KOH increases the specific surface area and micropore volume. The pore size distribution of carbon spheres could be adjusted by varying the relative amounts of the reagents during the activation. Using a NaOH/KOH mass ratio of 2:1 and a reagent/carbon sphere mass ratio of 3:1, good capacitance and rate performance of the supercapacitor electrode in both 6 mol L-1 KOH aqueous electrolyte and 1 mol L-1 MeEt3NBF4/propylene carbonate electrolyte were achieved. The prepared activated carbon shows a high capacitance of 235 F g-1 at 0.1 A g-1 and a capacitance retention of 81.5% at 20 A g-1 in the 6 mol L-1 KOH aqueous electrolyte, the symmetric device assembled by 1 mol L-1 MeEt3NBF4/propylene carbonate electrolyte delivers the maximum energy density of 30.4 Wh kg-1 and the highest power output of 18.5 kW kg-1, respectively.