The initial capacity irreversibility caused by film formation on a mesophase pitch-based carbon fibre (MPCF) electrode surface is studied with the goal of improving the performance of a lithium-ion battery. The addition of Li2CO3 to a solution of 1 M LiPF6/EC:DFC (1:1, v/v) results in a decrease in the initial irreversible capacity caused by solvent decomposition and the passivation film on the MPCF electrode surface. Suppression of the initial irreversible capacity at the anode electrode by the introduction of Li2CO3 is investigated by means of chronopotentiometry, cyclic voltammetry, ac impedance spectroscopy, FTIR, scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) analysis. It is concluded that the suppression is caused mainly by prevention of solvent decomposition and by structural change in the passivation film on the anode electrode.