Electrochemical activation behaviors studied with graphitic carbon electrodes of different interlayer distance

A comparative study is made on the electrochemical activation behaviors for graphitic carbon electrodes having different interlayer distance: a pristine graphite (MCMB, mesocarbon microbead, 0.34 nm), an expanded graphite (e-MCMB, 0.41 nm), and a silica-pillared one (s-MCMB, 1.24 nm). The pristine MCMB does not show any electrochemical activation behavior. In the case of e- and s-MCMB, however, the electrochemical activation is indeed occurring but completed in the earlier period of the first charging with a substantial electrode swelling. Of the two, the electrochemical activation is easier for the s-MCMB electrode with a lower activation potential and less significant electrode expansion. Moreover, the s-MCMB electrode gives a better rate capability after the electrochemical activation. The impedance analysis based on the transmission-line model with pore size distribution (TLM-PSD) illustrates that the electrochemically activated s-MCMB has a more ion-accessible pore structure as compared with e-MCMB.