Previous studies have found that high entropy oxides can be used as electrode materials for supercapacitors. However, there is still the problem of their low energy density. We tried to increase the energy density while increasing the specific capacitance of high entropy oxides from the potential window. Transition metal elements Fe, Co, Cr, Mn and Ni were selected for their electrochemical activity, and high entropy oxides were prepared by a sol-gel method under different calcination temperatures. The calcination temperature affects the structural morphology and crystallinity of the high entropy oxides and thus also affects the electrochemical performance. The spinel-phase (FeCoCrMnNi)3O4 with a high specific surface area of 63.1 m2 g-1 was prepared at a low calcination temperature of 450 °C. The specific capacitance is 332.2 F g-1 at a current density of 0.3 A g-1 in 1 M KOH electrolyte with a wide potential window of (-1, 0.6). An improved energy density of 103.8 W h kg-1 is reached via the designed microstructure of the high entropy oxide electrode.