In our previous paper (Electrochemistry, 85(4) 186 (2017)), we have reported that the porous current collector could be produced with a pico-second pulse laser system and that graphite electrodes prepared with porous Cu current collectors improved the rate of Li⁺-pre-doping reaction in the laminated graphite electrodes. In this study, in order to speed up the rate of the pre-doping reaction more, the porous graphite electrodes were prepared by directly opening the holes on the surface of graphite electrodes with a pico-second laser. In the cell composed of laminated graphite electrodes and a lithium metal, the Li⁺-doping reaction proceeded much faster than in the cells of the graphite electrodes prepared with porous current collectors and a Li metal. In addition, the results of electrochemical impedance spectroscopy suggested that the transfer of Li⁺ ions though the holes on the graphite electrodes was a rate determining step of the doping reaction of Li⁺ to laminated graphite electrodes and that the decrease in the hole diameter at the constant of opening rate of holes on the graphite electrodes cased the reduction of resistance for Li⁺ ions, resulting in shortening the time for completing the doping reaction of Li⁺ ions.

Fig. 1 SEM images (1: low magnification, 2: high magnification) of prepared porous graphite electrodes in a view from the plane of the incident laser. The opening rate of hole on the electrode: 1%. The average hole sizes were (A) 50, (B) 20 and (C) 10 mm.