Effects of 3D electrode design on high-energy silicon-graphite anode materials

Graphite-based anode materials have dominated the lithium-ion batteries (LIBs) for almost three decades due to its outstanding electrochemical cycle stability, moderate specific capacity, and low production costs. However, it could not meet the application requirements of LIBs regarding fast charging, and high energy and power density operations, especially for electrical vehicles. Silicon due to its high theoretic capacity (4200mAh/g) has been regarded as a promising anode material for next-generation LIBs. At KIT, the silicon-graphite (Si-C) composite anode material is being developed assisted by ultrafast laser processing. Commercial composite graphite anodes are doped with nano-sized silicon particles (10-20 wt.%). This approach is expected to meet the demand of high energy density by adding silicon as active material and to maintain the cycle stability and battery lifetime using graphite as basic material. In addition, ultrafast laser processing is applied for generation of three-dimensional (3D) cell architectures on silicon-graphite electrodes. 3D electrode architectures can enhance the interfacial area between the active material and the free liquid electrolyte. ... mehrThereby the lithium-ion transport kinetic can be significantly improved. Furthermore, the laser-generated free-standing channels within the electrode provide sufficient free spaces for volume charging during alloying and de-alloying with silicon while reducing mechanical stress. Coin cells with structured and unstructured electrodes were assembled for subsequent electrochemical analytics. The impact of 3D electrode architectures on battery performances was systematically investigated and demonstrated by means of cyclic voltammetry, galvanostatic measurements, and electrochemical impedance spectroscopy. Cells with structured electrodes revealed a significant improvement in rate capability, cycle stability, and lifetimes. Furthermore, in-situ scanning electron microscopy enabled to observe a real-time morphological and structural evolution of 3D Si-C electrodes compared with the unstructured electrodes. Finally, laser-induced breakdown spectroscopy (LIBS) was applied for evaluation of lithium diffusion length and quantitative lithium distribution along the electrode as function of cycling conditions. On base of these data, the degradation mechanisms in Si-C electrodes will be discussed.