The electrolyte filling process of battery cells is one of the time-critical bottlenecks in cell production. Wetting is of particular importance here, since only completely wetted electrode sections are working. In order to accelerate and facilitate this process, the authors of this study developed a method to significantly increase the wettability of graphite-based anodes by a laser surface modification using low energy nanosecond laser pulses. The anode surface microstructure was evaluated by means of white-light interferometry and scanning electron microscopy. The assessment of wettability was done by drop test and capillary rise test of the liquid electrolyte. The results show that there is a predominantly selective ablation process for laser energy inputs below 2 J/m by which the graphite active material remains unaffected and the binder material is decomposed. The observed increase in surface roughness correlates with the increasing wettability. Investigations using Raman spectroscopy showed that laser treatment leads to a damage on the crystalline structure of the graphite particle surface. However, treating an entire anode including 6 wt% binder and conductive carbon black has shown that the overall amorphous content of the anodes surface can be reduced by 32% through treating the surface with a laser energy of 1.29 J/m. Up to that point, which is the resulting parameter range for the selective process, it is possible to ablate the amorphous binder and carbon black phase coevally exposing graphite particles while keeping their crystalline structure. Exceeding that range, ablation of the whole anode composite dominates and amorphization of the graphite surface occurs. The electrode’s capacity was tested on half-cells in coin cell format. For the whole laser parameter range investigated, the anodes capacity matches the mass loss caused by laser ablation. No additional capacity loss was observed due to amorphization of the exterior graphite particle’s surface.

The microstructural optimization of lithium-ion battery (LiB) electrodes has recently gained a lot of interest. Versatile approaches to enhance fast charging abilities of LiB electrodes are the subject of current research. One of these approaches is the laser based photothermic removal of superficial inactive electrode components in order to improve the accessibility of the active material particles for the lithium-ions. In this work, we established a thermophysical model to describe the temperature fields within the electrode resulting from laser material processing. The model delivers satisfying results regarding the prediction of the removal of the top surface electrode layer that mainly consists of a binder and conductive additives. Lining up a simple approach of estimating the average depth in which the inactive binder-additive compound is selectively removed from the electrode's active mass layer led to a good agreement between the calculated and experimental results. Additionally, a potential negative thermal impact on the active material particles themselves due to the laser processing is evaluated. The established model can be used to optimize laser parameters in order to simultaneously maximize the selectively ablated inactive material and to minimize the thermal impact on the active material particles. Moreover, the model is capable of being transferred to laser processing of other types of composite materials such as LiB-anodes or carbon fiber reinforced polymers.

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