Electrochemical activation and capacitance enhancement of expanded mesocarbon microbeads for high-voltage, symmetric supercapacitors

Abstract

To increase the specific energy of supercapacitors (SCs), the expanded mesocarbon microbead (EMCMB) is electrochemically activated in 1 M tetraethylammonium tetrafluoroborate in propylene carbonate (TEABF4/PC) to construct a high-voltage but symmetric SC. The EMCMB is successfully made from MCMB through the oxidation in a solution containing concentrated H2SO4, HNO3 and KMnO4 followed by a thermo-expansion treatment at 800°C. This carbon with a specific surface area of only 93.2 m2 g−1 shows excellent capacitive performance after the electrochemical activation process in the highly positive or very negative potential regions in 1 M TEABF4/PC, especially when an aqueous-based binder, KOH-partially-neutralized polyurethane-polyacrylic acid (denoted as PUPAH6K4) was employed. These electrochemically activated EMCMB-PUPAH6K4 electrodes are able to be charged and discharged reversibly in a wide potential range between −2.6 V and 1.4 V (vs. Ag/AgNO3). Consequently, a 4V SC consisting of two identical EMCMB-coated electrodes, i.e., symmetric, with good capacitive performances in 1 M TEABF4/PC has been successfully demonstrated, showing the great application potential in the advanced high-voltage SCs.