A big challenge with batteries for electrical vehicles is to combine a long driving range with fast charging – or, in in other words, to combine a high energy density with a high rate capability. Among others, the microstructure of the electrodes play a key role in this game. On the one hand side, one strives to increase the loading level and to reduce volume of the electrodes. On the other hand side, one has to ensure a good wettability of the electrodes with the ion conducting electrolyte as well as continuous pore paths for Li-ion diffusion. As published in earlier work [Zheng et al. (2012)] electrodes with a homogenous architecture are not well suitable to solve this conflict of goals. The thicker the electrodes get and the more they are densified, the more the diffusion of the Li-ion is hindered.
In this work, we investigated two different approaches to tailor the microstructure of electrodes in order to enhance their kinetic properties. First, the effect of a porosity gradient was studied for NCM based cathodes. To do so, we developed a double layer coating with higher porosity in the top and less porosity in the bottom layer by a sequential coating and densification process. Beside microstructural analysis of the electrodes we will present electrochemical data that show a slightly increased discharge performance of the double-layered cathodes in comparison to homogenous cathodes with a similar loading level and coating thickness.
The second approach was a laser based posttreatment of densified electrodes. As for today, we unfortunately cannot go into details about the laser processing because we finalize a patent application at the moment. But certainly we will be able to present detailed results at the time when the conference will be held. For the time being, we can report electrochemical data of the laser processed NCM based cathodes and graphite based anodes. In both cases, the laser processed electrodes achieve higher discharge performance of up to approx. 20 % compared to unmodified ones. Beside the electrochemical data, we will provide information about the laser processing itself as well as microstructural investigations that were conducted by SEM. The microstructural studies were indispensable to identify proper laser parameters in order to avoid undesired modifications of the electrode.