Improvement of High Rate Performance of a Lithium Ion Battery Composed of Laminated LiFePO4 Cathodes/ Graphite Anodes with Porous Electrode Structure Fabricated with a Pico-Second Pulsed Laser

Abstract

Development of lithium ion batteries (LIBs) helps promote the spread of electric vehicles (EVs) over the world. Everyone is expected that the next generation of eco-friendly and high-performance EVs that was driven with LIBs become very popular in our daily life in the future. However, it will take a long time before it becomes widespread because of two reasons; the performance of the electric vehicles cannot satisfy the demands of daily life, and LIBs are expensive. The achievement of charging and discharging with high current densities is one of the requirements for high performance LIBs in EVs, almost all of LIBs cannot satisfy the requirement specification (high rate performance) for the next generation of LIBs. When the present LIBs are charged and discharged with high current densities to shorten the charging time and to accelerate the EVs in shorter time, respectively, the charging and discharging capacities largely drop, and the rechargeable performance is seriously damaged. In order to improve the high rate performance of the present LIBs, selection of materials, optimization of cathode and anode particle sizes, composition of cathode and anode layers for active materials, binder and conductive additives, coating of the active material surfaces and design of cells and electrodes have been examined. Each examination has achieved some success in the point view of high rate performance. However, recently, improvement of the high rate performance in the present LIBs unfortunately reaches a deadlock. Therefore, in this study, we propose strongly one of the solutions for the improvement of high rate performance with our developed laser technology. In this study, we developed preparing a porous graphite anode and a lithium iron phosphate (LiFePO4, LFP) cathode with a pico-second pulsed laser, in which through-holes having 20 mm diameters and an opening rate of 0.5% were formed on the graphite layer/copper (Cu) anode and the LiFePO4 layer/aluminum (Al) cathode. The cells composed of porous cathodes and anodes exhibited improvement of the high rate discharging performance when compared with those of cells prepared with non-porous cathodes and anodes and with cells prepared with cathodes and anodes prepared with conventional porous current collectors. The formation of holes on the anodes and cathodes can be prepared simply and speedily with the pico-second pulsed laser to increase the accessibility of the anode and cathode materials to Li+, resulting in the enhancement of the rate performance of the electrodes. The mechanism of the improvement of the high rate discharging performance was discussed with the results of electrochemical impedance spectroscopy (EIS).