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, in which the average hole diameter and hole opening rate were 20–30 μm and 1–2%, respectively, enabled to retain the high-rate discharging performance even in the LFP cathodes composed of the having the LFP layer with the thickness of over 40 μm on an aluminum current collector. The conventional and flat LFP cathode 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 the case of “through-holed” and “non-through-holed” LFP cathodes, there can be a more efficient insertion/de-insertion of Li+ ions to/from the LFP materials through the holes formed in the LFP layer, resulting in retaining the high-rate charging/discharging 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 results from the increase in the area available in the LFP discharge process because the sidewalls of the holes can also take part in the Li+ ion transfer during the discharge process.