(Invited) Tuning Electrochemical Performance of Lithium-Ion Cells By Introducing Laser-Generated Electrode Architectures

Abstract

Laser technology in lithium-ion battery (LIB) manufacturing could enable rapid manufacturing, high reliability, and a reduction of production costs. Laser cutting and welding processes for batteries already reached a high industrial readiness level. A new approach which is assigned to laser micro-structuring of battery materials has a huge impact on battery performance and operational lifetime of lithium-ion cells and an up-scaling for industrial production is currently investigated. So far, different types of laser structuring were used on metallic current collectors, separators, and thin or thick film composite electrodes. For thin metallic current collector foils, at anode and cathode sides, self-organized structuring by laser-induced periodical surface structures were successfully applied for improving electrode film adhesion. Direct laser ablation was applied for the generation of capillary structures, which was found to be most powerful in order to transform electrode and separator surfaces to superwicking. Thick film composite electrodes in lithium-ion cells are complex multi-material systems with defined material components, grain sizes, porosities, and pore size distributions in the micrometer and sub-micron range. The development of laser generated electrode architectures became a promising approach to overcome limitations in lithium-ion diffusion kinetics, high inter-electrode ohmic resistances, and mechanical stresses due to high volume changes during battery operation. It was shown, that structure sizes down to 10-30 µm and high aspect ratios enable advanced electrode architectures with huge benefits regarding capacity retention and cell life-time for high power operations during charging/discharging. For laser structured electrodes, the overall impedance was reduced and the diffusion kinetics could be enhanced which was proven by galvanostatic intermittent titration technique, cyclic voltammetry, and electrochemical impedance spectroscopy. Furthermore, the new electrode architecture provides new lithium-ion diffusion pathways, which could be indirectly proven by post-mortem analysis of entire electrodes by laser-induced breakdown spectroscopy (LIBS). It is evident that the increased active surface area provided by laser generated electrode architectures act as an attractor for lithium-ions which finally is responsible for the boost in battery performances. By increasing the cathode film thickness to values significantly larger than 150 μm an increase of the specific capacity or energy density at cell level was achieved. While the energy per area increases with the cathode layer thickness, the power density will in general decrease due to an increasing diffusion overpotential. In addition, the mechanical integrity of the films will decrease with increasing layer thickness and the migration of binders to the electrode surface will occur through altered drying conditions. The mechanical degradation of the cells due to the volume change inherent in the battery process in the electrodes will become more important as the layer thickness increases. Laser structuring of the electrodes can counteract these processes and will also improve the high current capability. Finally, LIBs with high-energy and high-power density can be realized by introducing laser generated electrode architectures (3D battery concept), i.e., at the same time, improved electrolyte transfer in thick film electrodes and improved lithium ion transport kinetics are achieved. For developing next generation batteries including the 3D battery concept for large footprint areas, high energy materials such as nickel-enriched Lithium-Nickel-Manganese-Cobalt-Oxide (NMC) for cathodes and silicon-based anodes are introduced.