Relationship between Hole Design on Anode Electrode, the Reaction Temperature and the Rate of Li⁺ Ion Pre-doping Reaction to Porous Laminated Graphite Anodes

Abstract

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.

Review of the structure and performance of through-holed anodes and cathodes prepared with a picosecond pulsed laser for lithium-ion batteries

“…In conclusion, the smaller the hole size is at a hole opening rate of 1%, the faster the prelithiation progress. In addition, it could be confirmed that an increase in temperature during prelithiation remarkably improves the speed of the prelithiation in the cell designed in this study [34]. As the anodes and cathode for prelithiation in laminated cells, the employment of not only through-holed anodes and cathodes but also anodes and cathodes formed on through-holed current collectors can be considered.…”

“…To chemically analyze the anode and cathode materials that were exposed to laser irradiation, the chemical states of the anode and cathode materials were determined by Raman spectroscopy and x-ray photoelectron spectroscopy (XPS). The G-, D-and 2D bands of graphite (b) before and (a) after laser treatment of graphite anodes and (c) graphite powder before preparation of the graphite anode were compared (figure 9) [34]. In the through-holed graphite anode, the hole diameter was not 20 µm, which was mentioned above, but rather 50 µm because a larger area in the edge part of a through-hole formed by the laser beam can be analyzed with a laser Raman microscopy system (the Raman laser beam diameter is 50 µm).…”

“…In addition, after the laser treatment, the through-holed anode did not show a new Raman peak. The chemical state of carbon 1s in graphite deposited in the through-holed and nonholed layers was then measured with XPS (figure 10) [34]. In the case of both through-holed and nonholed graphite layers, the main peaks can be thought to be from C-C and C=O bonds [36].…”

“…However, the transportation speed of Li + on the anodes and cathodes formed on the holed current collector is much lower than that on the anodes and cathodes having through-holes. The speed of prelithiation in the case of a through-holed structure is 3-7 times greater as that in the case of through-holed current collectors [34]. During the prelithiation with the laminated cell composed of through-holed anodes and cathodes, the status of cathodes was checked with the electrode potential and capacity before and after the prelithiation.…”

Application of a Holed Cathode and Anode Prepared with a Picosecond Pulsed Laser to Lithium Ion Battery (2) ~ Analysis of the Structure of Holed Cathode Layers ~

“…Thermal decomposition of chemical compounds in the anodes and cathodes at the entry points is assumed. In our past paper, we showed the result that the graphite in a holed anode was not damaged by laser irradiation based on X-ray photoelectron spectroscopy (XPS) and laser Raman spectroscopy 12 . In this study, the LFP layer after laser irradiation was chemically analyzed with laser Raman spectroscopy.…”