A dilatometric and small-angle X-ray scattering study of the electrochemical activation of mesophase pitch-derived carbon in non-aqueous electrolyte solution

The electrochemical activation of certain pitch-derived carbons has been proposed as a promising route towards obtaining high-capacitance electrodes for electrochemical double-layer capacitors. In the present work, the mechanism of electrochemical activation of a graphitizable carbon after calcination and KOH-activation was studied by nitrogen adsorption, electrochemical dilatometry and in situ small-angle X-ray scattering (SAXS). During electrochemical activation, a large capacitance gain from 1 to 121 F/g (at 0 V in a 1 mol/L solution of Et4NBF4 in propylene carbonate) was accompanied by a significant irreversible swelling of the electrode by 24% (6%) for activation in the negative (positive) potential range, respectively. In situ SAXS provided clear evidence for the insertion of ions into the latent microporosity of the carbon during electrochemical activation. Thus, the mechanism of electrochemical activation of weakly activated graphitizable carbon is not strictly due to ion intercalation between parallel graphene sheets.