Performances of high voltage electrochemical capacitor using ball-milled graphite/Mn3O4 composite electrodes

► Ball-milled graphite/Mn3O4 composite is prepared by direct reaction between graphite and KMnO4. ► Ball-milled graphite/Mn3O4 composite shows a stable potential window of 1.9 V in 1 M Na2SO4. ► Ball-milled graphite/Mn3O4 supercapacitor could operate reversibly during 8000 cycles up to 1.8 V.