Laser structuring can be applied to composite electrodes of lithium-ion cells to enhance wetting and to facilitate the usage of thick-film electrodes by reducing the lithium-ion diffusion overpotential and the tortuosity of the electrodes or the usage of electrodes containing silicon, where additional porosity is required to compensate the volume expansion during lithium de-/insertion. To integrate the additional laser processing step in the well-established electrode manufacturing route, the laser processing speed must be significantly increased to match with the belt speed, which is dependent on the electrode thickness and the type of manufacturing route. Upscaling can be realized by increasing the average laser power, laser intensity, and/or laser repetition rate. Here, an ultrashort pulsed laser source with an average power of 300 W and a pulse duration of 600 fs was applied. For the first time, the presented research provides detailed laser ablation processing data for thick-film composite anodes associated with high repetition rates ranging from 4.9 to 48.8 MHz. The patterning results are compared depending on the widths, depths, aspect ratios, the total appearance regarding debris and cracks, and the volume ablation rate. In high repetition rate laser patterning, the subsequent laser pulses interact with the material vapor plasma generated by the previous laser pulses, resulting in lower ablation depths and higher ablation widths. The increase in laser peak intensity leads to higher achievable ablation depths. Processing strategies are identified for two different ablation scenarios focusing on the pouch cells of a Volkswagen ID.3 and the Tesla 4680 cell.

Direct Laser Interference Patterning (DLIP) is used to texture current collector foils in a roll-to-roll process using a high-power picosecond pulsed laser system operating at either fundamental wavelength of 1064 nm or 2nd harmonic of 532 nm. The raw beam having a diameter of 3 mm @ 1/e ² is shaped into an elongated top-hat intensity profile using a diffractive so-called FBS®-L element and cylindrical telescopes. The shaped beam is split into its diffraction orders, where the two first orders are parallelized and guided into a galvanometer scanner. The deflected beams inside the scan head are recombined with an F-theta objective on the working position generating the interference pattern. The DLIP spot has a line-like interference pattern with about 15 μm spatial period. Laser fluences of up to 8 J cm⁻² were achieved using a maximum pulse energy of 0.6 mJ. Furthermore, an in-house built roll-to-roll machine was developed. Using this setup, aluminum and copper foil of 20 μm and 9 μm thickness, respectively, could be processed. Subsequently to current collector structuring coating of composite electrode material took place. In case of lithium nickel manganese cobalt oxide (NMC 622) cathode deposited onto textured aluminum current collector, an increased specific discharge capacity could be achieved at a C-rate of 1 °C. For the silicon/graphite anode material deposited onto textured copper current collector, an improved rate capability at all C-rates between C/10 and 5 °C was achieved. The rate capability was increased up to 100% compared to reference material. At C-rates between C/2 and 2 °C, the specific discharge capacity was increased to 200 mAh g⁻¹, while the reference electrodes with untextured current collector foils provided a specific discharge capacity of 100 mAh g⁻¹, showing the potential of the DLIP technology for cost-effective production of battery cells with increased cycle lifetime.

To increase the specific capacity of anodes for lithium-ion cells, advanced active materials, such as silicon, can be utilized. Silicon has an order of magnitude higher specific capacity compared to the state-of-the-art anode material graphite; therefore, it is a promising candidate to achieve this target. In this study, different types of silicon nanopowders were introduced as active material for the manufacturing of composite silicon/graphite electrodes. The materials were selected from different suppliers providing different grades of purity and different grain sizes. The slurry preparation, including binder, additives, and active material, was established using a ball milling device and coating was performed via tape casting on a thin copper current collector foil. Composite electrodes with an areal capacity of approximately 1.70 mAh/cm² were deposited. Reference electrodes without silicon were prepared in the same manner, and they showed slightly lower areal capacities. High repetition rate, ultrafast laser ablation was applied to these high-power electrodes in order to introduce line structures with a periodicity of 200 µm. The electrochemical performance of the anodes was evaluated as rate capability and operational lifetime measurements including pouch cells with NMC 622 as counter electrodes. For the silicon/graphite composite electrodes with the best performance, up to 200 full cycles at a C-rate of 1C were achieved until end of life was reached at 80% relative capacity. Additionally, electrochemical impedance spectroscopies were conducted as a function of state of health to correlate the used silicon grade with solid electrolyte interface (SEI) formation and charge transfer resistance values.

For the first time, the laser structuring of large-footprint electrodes with a loading of 4 mAh cm⁻² has been validated in a relevant environment, including subsequent multi-layer stack cell assembly and electrochemical characterization of the resulting high-capacity lithium-ion pouch cell prototypes, i.e., a technological readiness level of 6 has been achieved for the 3D battery concept. The structuring was performed using a high-power ultrashort-pulsed laser, resulting in well-defined line structures in electrodes without damaging the current collector, and without melting or altering the battery active materials. For cells containing structured electrodes, higher charge and discharge capacities were measured for C-rates >1C compared to reference cells based on unstructured electrodes. In addition, cells with structured electrodes showed a three-fold increase in cycle lifetime at a C-rate of 1C compared to those with reference electrodes.

This presentation was recorded for SPIE Photonics West LASE 2021.