Ultrafast Laser Patterning of Silicon/Graphite Composite Electrodes to Boost Battery Performance

Abstract

The ever-increasing share of electric vehicles in the mobility sector urgently calls for an increase in the production capacity of high-power and high-energy lithium-ion batteries with low production costs. A gravimetric energy density of about 350 Wh/kg flanked by a volumetric energy densities of at least 750 Wh/L were defined as ambitious goals from the European Union to be achieved by 2025. For this purpose, novel, high-capacity anode materials containing significant silicon content should be utilized in next generation batteries. At room temperature, silicon has a theoretical specific capacity of 3579 mAh/g which is one order of magnitude higher compared to the state-of-the-art graphite anode material (372 mAh/g). The volume change which silicon undergoes during lithiation and delithiation and the thereby caused mechanical stresses inside the composite electrode, which lead to loss of electrical contact and delamination, are an obstacle for its implementation in industrial battery production. While many researchers focus on other promising approaches to facilitate the usage of silicon in electrodes, for example pre-lithiation, the usage of graphite-silicon composites, or carbon coating on the silicon particles, here, the implementation of additional porosity via laser patterning is pursued. A water-based silicon/graphite slurry concept for the large-scale electrode production is used. There, the silicon nanoparticles’ agglomerates are destroyed and the silicon is finely dispersed using a ball mill, while the slurry homogenization is finalized using a disk stirrer. This facilitates the production of electrode sheets on a roll-to-roll coater, delivering enough material for the high power, high repetition rate roll-to-roll laser patterning process, both of which exhibit a technology readiness level of 5 to 6. The slurry and electrode characterizations are performed using laser induced breakdown spectroscopy (LIBS) for both the binder and lithium spatial distribution, the cyclability and lifetime of the electrodes is assessed in pouch cells with NMC 622 as counter electrode, and the lithiation of the composite material is determined with cyclic voltammetry. Scanning electron, digital and light microscopy are used for the characterization of the laser patterning, while chemical analysis is used to assess the composition of the electrode and the silicon oxidation during water-based manufacturing.