High repetition ultrafast laser ablation of graphite and silicon/graphite composite electrodes for lithium-ion batteries

Abstract

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.