Carbon-based asymmetric capacitor for high-performance energy storage devices

Carbon-based materials are widely used in energy storage research, as attractive materials with high conductivity, low cost, and high availability. However, a relatively low performance (e.g., energy and power densities) compared with metal oxides is an obstacle to use for commercial applications. Herein, we report on high-performance metal oxide-free asymmetric capacitors (ASCs) using n-type and p-type graphene films which are doped by nitrogen and boron atoms, respectively, exhibiting high energy and power densities with excellent stability. The enhanced performances of the ASCs arises from the synergistic effect of the non-faradaic capacitance and pseudocapacitance, which are confirmed with new analysis using cyclic voltammetry and electrochemical impedance spectroscopy for a pseudocapacitance effect of intercalation/deintercalation and galvanostatic charge-discharge profiles for and non-faradaic capacitance. The new ASC in an ionic liquid electrolyte (e.g., pure EMIMBF₄) shows the high energy density of 77.41 Wh kg⁻¹ in 3.0 V of the operating potential window with the excellent retention stability of ∼87% after 10,000 cycles. The carbon-based asymmetric capacitor of semiconducting graphene electrodes can offer the promise of exploiting both non-faradaic capacitance and intercalation/deintercalation pseudocapacitance to obtain a high-performance energy storage device.