Surface micro-structuring of intercalation cathode materials for lithium-ion batteries - a study of laser-assisted cone formation

摘要

Strong efforts are currently undertaken in order to further improve the electrochemical performance of high energy lithium-ion batteries containing thick composite electrode materials. The properties of these electrode materials such as active surface area, film thickness, and film porosity strongly impact the cell life-time and cycling stability. A rather new approach is to generate hierarchical architectures into cathode materials by laser direct ablation as well as by laser-assisted formation of self-organized structures. It could be shown that appropriate surface structures can lead to a significant improvement of lithium-ion diffusion kinetics leading to higher specific capacities at high charging and discharging currents. In this paper, the formation of self-organized conical structures in intercalation materials such as LiCoO_2 and LiNi_(1/3)Mn_(1/3)Co_(1/3)O_2 is investigated in detail. For this purpose, the cathode materials are exposed to excimer laser radiation with wavelengths of 248 nm and 193 nm leading to cone structures with outer dimensions in the micrometer range. The process of cone formation is investigated using laser ablation inductively coupled plasma mass spectrometry and laser-induced breakdown spectroscopy (LIBS). Cone formation can be initiated for laser fluences up to 3 J/cm~2 while selective removal of lithium was observed to be one of the key issues for starting the cone formation process. It could be shown that material re-deposition supports the cone-growth process leading to a low loss of active material. Besides the cone formation process, laser-induced chemical surface modification will be analysed by LIBS.