Laser modification and characterization of Li-Mn-O thin film cathodes for lithium-ion batteries

The development of future battery systems is mainly focused on powerful rechargeable lithium-ion batteries. To satisfy this demand, current studies are focused on cathodes based on nano-composite materials which lead to an increase in power density of the LIB primarily due to large electrochemically active surface areas. Electrode materials made of lithium manganese oxides (Li-Mn-O) are assumed to replace commonly used cathode materials like LiCoO2 due to less toxicity and lower costs. Thin films in the Li-Mn-O system were synthesized by non-reactive r.f. magnetron sputtering of a LiMn2O4 target on silicon and stainless steel substrates. In order to enhance power density and cycle stability of the cathode material, direct laser structuring methods were investigated using a laser system operating at a wavelength of 248 nm. Therefore, high aspect ratio micro-structures were formed on the thin films. Laser annealing processes were investigated in order to achieve an appropriate crystalline phase for unstructured and structured thin films as well as for an increase in energy density and control of grain size. Laser annealing was realized via a high power diode laser system. The effects of post-thermal treatment on the thin films were studied with Raman spectroscopy, X-ray diffraction and scanning electron microscopy. The formation of electrochemically active and inactive phases was discussed. Surface chemistry was investigated via X-ray photoelectron spectroscopy. Interaction between UV-laser radiation and the thin film material was analyzed through ablation experiments. Finally, to investigate the electrochemical properties, the manufactured thin film cathodes were cycled against a lithium anode. The formation of a solid electrolyte interphase on the cathode side was discussed.