A 4 V-electrochemical capacitor using electrode and electrolyte materials free of metals

• MCMBs as electrodes for 4 V electrochemical capacitors using metal-free electrolytes.
• Electrochemical activation has big influence on activated MCMB negative electrode.
• Both energy and power densities of a capacitor are elevated remarkably.

A 4 V asymmetric capacitor has been assembled using non-porous activated mesophase carbon microbeads (AMCMB) as the negative electrode, a graphitized carbon (GMCMB) as the positive electrode and quaternary alkyl ammonium based organic electrolyte. AMCMB has been heated under the reduction atmosphere of hydrogen/nitrogen after a chemical activation. It has small specific surface area (24.48 m2 g−1), but delivers a large capacitance value due to the irreversible “electrochemical activation” in the initial galvanostatic charge–discharge process. The storage charge behavior of AMCMB has also been investigated by ex situ XRD, Raman spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy. In terms of specific capacity, energy density, power density and cycle ability, the AMCMB/GMCMB capacitor is superior the other capacitors like AC/graphite, AC/AC.