To withstand the demanding operation of electric arc furnaces, high-quality electrodes made from graphite are required. The electrodes will erode due to the combination of factors, such as Joule heat and arc heat. Regular electrode replacement is required to maintain the continuity of production. For every ton produced of steel, up to 3kg of graphite is consumed.
The electrodes are fabricated from industrially available carbon materials such as expanded graphite felt (GF) or carbon felt (CF). The CF materials are bonded together with epoxy resins or phenolic inhibitors to form the electrode. Dielectric fluids or powder supplies can be used to enhance the electrode's performance. But despite all these efforts, graphite electrodes are susceptible to shorting electrically during use. Also, the electrodes lack strength in tension.
In order to overcome these issues, researchers are investigating various methods for improving the tensile characteristics of graphite electrodes. To achieve this, researchers have been using the freeze-casting method to shape graphite with crystals of ice to create low-tortuosity structural forms. It can also be slow and expensive to use the freeze-casting process. The use of a heating system based on plasma is an alternative. This technology can be applied to the tundish of a double-strand slab caster, which is a highly efficient solution.
The influx of Li electrons and ions from the current collector and separator causes local reactions in the electrode during lithiation. They are driven by diffusion of ions and are affected by material's resistance to charged particle motion, resulting in heterogeneous reaction amounts. The lithium-ion battery is especially susceptible to this phenomenon. The heterogeneity reduces battery capacity and increases cell level voltage to the point of thermal runaway.
Using real-time monitoring, we studied the effects of rate in the development of heterogeneity reaction of multilayer graphite electrodes. We observed that the theoretical capacity of the first layer increases with rate, but does not reach its full potential, while the capacities of the remaining layers remain below their theoretical values. This counter-intuitive behavior is due to the fact that the gradient of ion concentration in the multilayer electrolyte becomes stronger with increasing rate.
The findings suggest that the lithiation process in graphite electrodes is affected by the rate of increase in the number of oxygen vacancies and by the concentration of lithium on the graphite surface. It leads to an increase in the amount of solid electrolyte phase (SEI), occupying pore spaces and reducing the capability of the electrode. It has been shown that the SEI can reduce lithium-ion battery cycling. The SEI may also exert pressure on the separation and interact with the graphite lithium coating. This could result in by-product reactions that increase battery swelling, and cause safety concerns. Understanding the evolution and occurrence of heterogeneity in reaction extent is therefore crucial for improving battery performance.
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