Lithium-ion batteries are widely used as energy storage devices due to their high energy density and versatile applicability. Key components of lithium-ion batteries are electrically isolated electrodes and a liquid electrolyte solution which enables ion transport between the electrodes. Laser structuring of electrodes is a promising approach to enhance the high-current capability of lithium-ion batteries by reducing cell internal resistances, as a larger contact area of the active material with the electrolyte solution is created. In the work described here, lithium-ion battery anodes were structured by locally ablating small fractions of the coating using femtosecond laser pulses with infrared wavelengths. A study on ablation characteristics depending on different process parameters such as laser fluence and repetition rate was performed. Special focus was on the ablation efficiency, enabling an optimized process design. The influence of the electrode composition was taken into account by studying the ablation behavior at a varying binder content. Evenly distributed micro holes were chosen in order to keep active material removal at a minimum. To evaluate the effect of structured graphite anodes on the electrochemical properties of lithium-ion batteries, test cells were manufactured and galvanostatically cycled at different current rates. Results show improvements in high-current performance which is expressed by an increased discharge capacity yield.

The simultaneous generation of nanostructures and redeposited nanoparticles on copper surfaces through their direct ablation in air by a high power and high repetition rate ps laser was demonstrated. Basic and detailed analysis on the formation and the size distribution of nanoparticles spreading over the nanostructured copper surfaces was performed. Lower scanning speed causes more laser pulse input onto the target surface, resulting in a more dense distribution of the nanoparticles with a nearly constant mean radius. The changes in the particle distribution render the copper surfaces to unique reflection spectra responses and surface colors, which are independent of the viewing angles. The present research can pave the way for the practical applications of ps laser in generating nanoparticles on metal surfaces and tailoring their optical properties.

A surface micro/nano structuring technique was demonstrated for colorizing metal surfaces with a picosecond laser. Sequential color change from black to pink was realized on copper surfaces by simply changing the ps laser scanning speeds. Systematic analyses on the spectral response and microstructure characteristics were reported. The spectrum shifting effect corresponding to color change was explained through the surface plasmon resonance mechanism. The current research shows that a high power and high repetition rate ps laser is capable of structuring metal surfaces with a speed up to several meters per second, presenting an efficient and affordable candidate for practical industrial applications.

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The energy sector has been changing in the past few years, driven by the transition toward renewable energy. This affects the technologies, as well as the structure of energy production by means of a decentralized and time-dependent energy generation. The resulting effects on the power grid require local storage systems to store the surplus energy and to limit the feed-in power. For these energy storage systems, the use of commercial 26650 LiFePO4 battery cells is highly promising. Since the capacity of these cells is comparatively low, a large quantity of cells is needed to match the storage requirements. For this reason, the interconnection between individual battery cells is the basic prerequisite for the production of energy storage systems. Recent research has shown that laser beam welding is suitable for the welding of small electrical contacts. However, the welding process of 26650 cells with contacts made of nickel plated steel is very complex. The requirements regarding the heat input during the joining process are high due to a low thickness of the case in the range of a few hundredth of a millimeter and a high temperature sensitivity of the battery materials. Within this work, experiments on laser beam welding of nickel-plated DC04 steel on copper, aluminum, and steel were carried out. The electrical and mechanical properties of the connection joints were evaluated within a comparative study. For the investigation of the heat input during the welding process, the change of temperature inside the battery case was measured. The results presented in this paper show that laser beam welding with continuous wave radiation is a suitable joining process for the electrical connection of 26650 battery cells, while avoiding a critical temperature change within the cells. Electrical joints with a low contact resistance and a high mechanical strength can be achieved. Furthermore, a clamping device for battery modules consisting of 24 battery cells is presented and the application of the welding process for a large scale production of energy storage systems is demonstrated.