To improve the rate performance of graphite anodes and lithium iron phosphate (LiFePO4) cathodes, micrometer-sized through-holes were formed on the electrode surface with a picosecond pulsed laser. The through-holes with 20 m diameters were uniformly arranged with an opening rate of 1%. Compared with that of non-porous electrodes, the discharge capacities of the porous anode and cathode electrodes did not degrade even at a high current density at a 10 C rate. The formation of through-holes on the electrodes provides a remarkable improvement in the rate performance by enhancing the ability of Li + ions to reach the active material surfaces.
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.
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