Fabricating an Aqueous Symmetric Supercapacitor with a Stable High Working Voltage of 2 V by Using an Alkaline–Acidic Electrolyte

Aqueous symmetric carbon-based supercapacitors (CSCs) are always the research focus for energy storage devices because of the virtue of low cost, inherent safety, and encouraging electrochemical stability. As is well-known, so far most aqueous symmetric CSCs are subjected to low energy densities. Here, a symmetric supercapacitor comprising electrodes from biomass-derived activated carbon and alkaline–acidic electrolyte is reported. This aqueous symmetric CSC demonstrates exceptional electrochemical performance with high stable working voltage of 2 V and attractive cycling stability of no capacitance loss over 10 000 cycles. Impressively, it shows a remarkable energy density of 36.9 W h kg⁻¹ at 248 W kg⁻¹ based on the total mass of the active materials, which is much higher than traditional aqueous symmetric CSCs, and a power density of 4083 W kg⁻¹ with an energy density of 8.8 W h kg⁻¹. The use of stable alkaline–acidic electrolyte provides an innovative technique to enhance the energy density of aqueous supercapacitors.