Influence of Electrolytes (TEABF₄ and TEMABF₄) on Electrochemical Performance of Graphite Oxide Derived from Needle Coke

The structure of needle coke was changed to graphite oxide structure after oxidation treatment with 70 wt.% of nitric acid and sodium chlorate (NaClO₃), and the inter-layer distance of the oxidized needle coke was expanded to 6.9 Å. The first charge profile of the oxidized needle coke-cell with 1.2 M TEMABF₄/acetonitrile solution displayed that the intercalation of electrolyte ions into the interlayer occurred at 1.0 V, which value is lower than 1.3 V of the oxidized needle coke-cell with 1.2 M TEABF₄/acetonitrile solution. After first charge/discharge, the cell using TEMABF₄ electrolyte exhibited smaller electrode resistance of 0.05 Ω, and larger specific volume capacitance of 25.5 F/ml at the two-electrode system in the potential range 0∼2.5 V than those of the cell using TEABF₄ electrolyte. Compared to the TEABF₄ electrolyte, better electrochemical performance of the TEMABF₄ electrolyte in the oxidized needle coke may be caused by the smaller cation (TEMA⁺) size and better ion mobility in the nanopores between inter-layers.