The demand for optimized and affordable lithium-ion battery systems increases with the growing number of electrified vehicles. To this aim, 3D electrode architectures and new high energy density materials like silicon are in the focus of research. To implement silicon in the LIFT-process for fast prototype development, a silicon-rich paste was developed and optimized for the printing. The electrodes containing the silicon-rich paste showed a rather high specific capacity of 3029 mAh⋅g -1. To achieve an enhanced cyclability, a new electrode architecture was developed by using subtractive and additive laser processing in a process chain. For this purpose, a state-of-the-art coated graphite electrode was structured, and the cavities were subsequently partially filled with the silicon-rich paste. After reaching end-of-life, the coin cells were disassembled and analyzed using SEM and LIBS measurements regarding the failure mechanisms.
Graphite anodes with high areal loading of 3.6 mAh cm-2 were laser structured with various design patterns using an ultrashort pulsed laser system of high average power (⪆300 W). The upscaling potential of the most common pattern types in literature, namely the line, grid, and hexagonal hole pattern were evaluated and the influence of process parameters like laser fluence and repetition rate on the ablation characteristics were examined. The fast-charging capability of full-cells containing structured graphite anodes were studied with NMC622 cathodes. For each structure pattern the onset of lithium plating during fast-charging was determined by differential voltage analysis of the voltage relaxation.
The development of next-generation lithium-ion batteries with volumetric energy densities >750 Wh/L and gravimetric energy densities >400 Wh/kg is a key objective of the European Union’s Strategic Energy Technology Plan to be achieved by 2030. Both new materials and production strategies play an important role in the development of those batteries. Thick-film electrodes are advantageous to increase the volumetric and gravimetric energy densities alike since the amount of inactive material can be reduced. To facilitate higher C-rates during (dis-)charging in thick-film electrodes, laser generated structured are introduced, thus creating new lithium-ion diffusion pathways leading to a reduced cell polarization. Additionally, electrode wetting with liquid electrolyte is significantly improved, reducing the risk of dry spots in the electrode stack. Industry interest in implementing laser patterning of electrodes into existing or planned manufacturing lines has increased significantly in recent times. The strip speeds of electrode production are decisive for the required speeds to be realized in laser structuring. Various technical approaches can be applied to upscale the laser patterning process such as multibeam processing which can be realized by splitting a laser beam into several beamlets with a DOE. In this work, a large field scanner and a related optical lens system are combined with an ultrashort pulsed, high repetition rate, high power laser source. The ablation behavior of commercial graphite composite electrode material was investigated for upscaling using different laser patterning scenarios.
In the presented study, the use of an ultrashort pulsed laser system with high average laser power up to 300 W and repetition rate in the MHz regime in combination with multilayer coating was evaluated regarding the processing of multidimensional structured silicon/graphite anodes. Line patterned composite graphite anodes with grooves of different aspect ratios were generated by variation of laser and process parameters like laser fluence, pulse overlap, and repetition rate. The perspective of laser process upscaling is discussed, and it was shown that an increasing number of scans almost linearly increases the ablation depth, while the ablation width stays constant. The structured graphite anodes were handed over to a second coating step, in which a silicon containing slurry was coated to create an electrode architecture with spatial separation of graphite and silicon in the plane of the electrode. The quality of the multiple coated electrodes was studied to define a structure geometry in which defect-free filling is achieved in the second coating process. The filling of the electrode in the multilayer coating showed a dependence in blade gap during coating and laser-generated structure aspect ratio.
Possible laser processes in battery manufacturing are quite diverse regarding the control of electrochemical characteristics: LIPSS on current collector surfaces are used to adjust the adhesion of composite electrodes to current collectors, laser surface patterning turns ceramic-coated separator materials into superwicking with regard to electrolyte wetting properties, and laser structuring of composite thick film electrodes is applied to generate 3D electrode architectures with shortened lithium-ion diffusion pathways. In the field of cathode thick film development, secondary particles with nanoscaled primary particles are used and ultrafast laser ablation is applied to pattern the composite electrodes to optimize the lithiumion diffusion kinetics by enlarging the active material surface with a view to reducing cell polarization, which develops at high battery power. This enables high energy batteries to be upgraded for operation at high power. In the field of anode development for electromotive vehicles, efforts are being made to develop silicon anodes in order to significantly increase the energy density. In addition, the issue of fast charging, mainly influenced by the anode architecture, is a major topic in research and industrial development. Silicon nanoparticles are used and combined with graphite particles in a binder matrix. The large volume change as a result of the lithiation of silicon during battery operation requires laser structuring of the composite electrodes in order to counteract mechanical degradation. Analogous to cathode materials, the lithium diffusion kinetics for anodes are also significantly enhanced by the applied 3D battery concept. The impact of laser structuring and modification of battery materials on the electrochemical performance with respect to the nanoscale is of considerable relevance for future applications in battery manufacturing.
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