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

To increase the specific energy of supercapacitors (SCs), the expanded mesocarbon microbead (EMCMB) is electrochemically activated in 1 M tetraethylammonium tetrafluoroborate in propylene carbonate (TEABF 4 /PC) to construct a high-voltage but symmetric SC. The EMCMB is successfully made from MCMB through the oxidation in a solution containing concentrated H 2 SO 4 , HNO 3 and KMnO 4 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 TEABF 4 /PC, especially when an aqueous-based binder, KOH-partially-neutralized polyurethane-polyacrylic acid (denoted as PUPAH 6 K 4) was employed. These electrochemically activated EMCMB-PUPAH 6 K 4 electrodes are able to be charged and discharged reversibly in a wide potential range between −2.6 V and 1.4 V (vs. Ag/AgNO 3). Consequently, a 4V SC consisting of two identical EMCMB-coated electrodes, i.e., symmetric, with good capacitive performances in 1 M TEABF 4 /PC has been successfully demonstrated, showing the great application potential in the advanced high-voltage SCs. [ABSTRACT FROM AUTHOR]