Aqueous supercapacitors represent an extremely attractive candidate for next-generation energy storage devices, attributed to their excellent high-power density, low cost, nonflammability and environmental friendliness. Nonetheless, compared with their nonaqueous counterparts, the main challenge of aqueous supercapacitors lies in their narrow operating cell voltages and lower energy densities. Here we demonstrate that such issues can be overcome via optimizing the electrolyte and electrode materials by using high concentration “water-in-salt” electrolyte and low electrocatalytic activity all-pseudocapacitive metal-oxide electrodes, respectively. The high operating voltage of 2.2 V can be achieved for hybrid supercapacitor with MnO2 and Fe3O4 as positive and negative electrode, combining with a “water-in-salt” electrolyte. This hybrid supercapacitor exhibits a maximum specific energy of 35.5 Wh kg total − 1 at a specific power of 151.9 W kg total − 1 based on the mass of total activate materials. In addition, the hybrid system retains 87% of its initial specific energy even after 3000 charge/discharge cycles.