Enhancing the rate capability of highly densified Li-ion battery cathodes by selective laser ablation

摘要

Lithium-ion batteries applied for example in electric driven vehicles aim towards increased energydensity at high active mass loading per unit area. Therefore, calendering processes are used to densifythe electrodes. However, a low porosity, especially in top layer of the material compound, leads ingeneral to a low rate (dis-) charging capability due to hindered lithium-ion diffusion.This work proposes a laser surface treatment method of highly densified cathodes to reduce theapparent process limitation of ion diffusion. The surface treatment is done with a short pulsed infraredlaser in the nanosecond regime. Depending on the provided energy density in the laser spot theelectrochemical inactive matrix of the cathode can be ablated partially and most of the pores below thetop layer get reopened. Cathodes with different high densities after calendering are laser treated andelectrochemically analyzed. Highly densified cathodes with a porosity of 20% exhibit a distinctimprovement of rate capability at C-rates higher than 2C in relation to cathodes without lasertreatment. Explicitly, at high current rates of 5C the electrodes of 20% porosity show an improvedcapacity of more than 20%. In addition, at low current rates the results show no negative impact of thelaser treatment. The results lead to the interpretation, that selective laser ablation enables an improvedaccess of Li-ions into the active mass of the cathode.