ALBERT

Description: Lithium-ion batteries have become the most promising energy storage devices in recent years. However, the simultaneous increase of energy density and power density is still a huge challenge. Ultrafast laser structuring of electrodes is feasible to increase power density of lithium-ion batteries by improving the lithium-ion diffusion kinetics. The influences of laser processing pattern and film thickness on the rate capability and energy density were investigated using Li(Ni0.6Mn0.2Co0.2)O2 (NMC 622) as cathode material. NMC 622 electrodes with thicknesses from 91 µm to 250 µm were prepared, while line patterns with pitch distances varying from 200 µm to 600 µm were applied. The NMC 622 cathodes were assembled opposing lithium using coin cell design. Cells with structured, 91 µm thick film cathodes showed lesser capacity losses with C-rates 3C compared to cells with unstructured cathode. Cells with 250 µm thick film cathode showed higher discharge capacity with low C-rates of up to C/5, and the structured cathodes showed higher discharge capacity, with C-rates of up to 1C. However, the discharge capacity deteriorated with higher C-rate. An appropriate choice of laser generated patterns and electrode thickness depends on the requested battery application scenario; i.e., charge/discharge rate and specific/volumetric energy density.

Description: Laser powder bed fusion (LPBF) is one of the additive manufacturing methods used to build metallic parts. To achieve the design requirements, the LPBF process chain can become long and complex. This work aimed to use different laser techniques as alternatives to traditional post-processes, in order to add value and new perspectives on applications, while also simplifying the process chain. Laser polishing (LP) with a continuous wave laser was used for improving the surface quality of the parts, and an ultrashort pulse laser was applied to functionalize it. Each technique, individually and combined, was performed following distinct stages of the process chain. In addition to removing asperities, the samples after LP had contact angles within the hydrophilic range. In contrast, all functionalized surfaces presented hydrophobicity. Oxides were predominant on these samples, while prior to the second laser processing step, the presence of TiN and TiC was also observed. The cell growth viability study indicated that any post-process applied did not negatively affect the biocompatibility of the parts. The presented approach was considered a suitable post-process option for achieving different functionalities in localized areas of the parts, for replacing certain steps of the process chain, or a combination of both.

Description: For the development of thick film graphite electrodes, a 3D battery concept is applied, which significantly improves lithium-ion diffusion kinetics, high-rate capability, and cell lifetime and reduces mechanical tensions. Our current research indicates that 3D architectures of anode materials can prevent cells from capacity fading at high C-rates and improve cell lifespan. For the further research and development of 3D battery concepts, it is important to scientifically understand the influence of laser-generated 3D anode architectures on lithium distribution during charging and discharging at elevated C-rates. Laser-induced breakdown spectroscopy (LIBS) is applied post-mortem for quantitatively studying the lithium concentration profiles within the entire structured and unstructured graphite electrodes. Space-resolved LIBS measurements revealed that less lithium-ion content could be detected in structured electrodes at delithiated state in comparison to unstructured electrodes. This result indicates that 3D architectures established on anode electrodes can accelerate the lithium-ion extraction process and reduce the formation of inactive materials during electrochemical cycling. Furthermore, LIBS measurements showed that at high C-rates, lithium-ion concentration is increased along the contour of laser-generated structures indicating enhanced lithium-ion diffusion kinetics for 3D anode materials. This result is correlated with significantly increased capacity retention. Moreover, the lithium-ion distribution profiles provide meaningful information about optimizing the electrode architecture with respect to film thickness, pitch distance, and battery usage scenario.

Description: Over the last decade, the demand for safer batteries with excellent performance and lower costs has been intensively increasing. The abundantly available precursors and environmental friendliness are generating more and more interest in sodium ion batteries (SIBs), especially because of the lower material costs compared to Li-ion batteries. Therefore, significant efforts are being dedicated to investigating new cathode materials for SIBs. Since the thermal characterization of cathode materials is one of the key factors for designing safe batteries, the thermophysical properties of a commercial layered P2 type structure Na0.53MnO2 cathode material in powder form were measured in the temperature range between −20 and 1200 °C by differential scanning calorimetry (DSC), laser flash analysis (LFA), and thermogravimetry (TG). The thermogravimetry (TG) was combined with mass spectrometry (MS) to study the thermal decomposition of the cathode material with respect to the evolved gas analysis (EGA) and was performed from room temperature up to 1200 °C. The specific heat (Cp) and the thermal diffusivity (α) were measured up to 400 °C because beyond this temperature, the cathode material starts to decompose. The thermal conductivity (λ) as a function of temperature was calculated from the thermal diffusivity, the specific heat capacity, and the density. Such thermophysical data are highly relevant and important for thermal simulation studies, thermal management, and the mitigation of thermal runaway.