Improvement of High-Rate Discharging Performance of LiFePO4 Cathodes By Forming Micrometer-Sized through-Holed Electrode Structures with a Pico-Second Pulsed Laser

Abstract

Holing of lithium iron phosphate (LiFePO4, LFP) cathodes with a pico-second pulsed laser, whose the average diameter and opening rate were 20-30 mm and 1-2%, respectively, could retain the high-rate discharge performance even in the LFP cathodes having the thickness of LFP layer over 40 mm on an aluminum current collector. The conventional thick and flat LFP cathode electrodes exhibited the degradation of discharge retention at the high-rate discharge because of the low utilization of LFP materials in the case of the thick cathode layer. On the other hand, in through-holed and non-through-holed LFP cathodes, Li+ ions can do more efficient insertion/deinsertion to/from the LFP materials through the holes formed in the LFP layer, resulting in retaining the high-rate charge-discharge performance even in thick LFP cathodes. The electrochemical impedance spectroscopy analysis confirmed that the formation of through-holes in the thick LFP layer is significantly effective to improve the high-rate discharging performance as a result of the decreased charge-transfer resistance of the LFP discharge process. The decrease in the charge-transfer resistance was brought from the increase in the area for the LFP discharge process based on the fact that the sidewalls of the holes are also available for the process. Fig. １ Schematic description of the cell arrangement of the cells used. (A) Non-holed, (B) through-holed and (C) non-through-holed LFP/LFP cathodes.Two Li metal were used as anodes. Figure 1