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Statistical approaches to powder preparation for Si/C anodes in Li-ion Batteries
Poster Exhibition
Active materials for Lithium-ion batteries

Increasing the lifetime and the capacity of Li-ion batteries by changing the production methods of the base materials, implementing or doping new elements into the active materials, is the main objective of researchers for a long time. Furthermore, properties of the active materials such as the composition ratio of the combined elements, microstructure and the amount of inactive phases, are quite effective on electrochemical performance. Besides that preparation of the slurry is another vital step to make the battery systems long-lasting and effective. To determine the optimal parameters for either powder and slurry preparation, using statistical methods is the key point to do low-cost experiments. The main aim of this study was to optimize the ball milling conditions and obtain contamination-free Si/C composite powders. After preparing powders, finding out the statistical model for suitable viscosity at different grain sizes and compositions is another part of the study. In the first step, 20:80 Si/Graphite powders were used as active material and 4factor-2level Full factorial design was used for plotting main effects and interactions. Contamination levels were investigated by using weight loss of milling balls. SEM analyses were carried out to check the microstructure of milled composite powders. Average composite grain sizes were calculated by using XRD data and D10-D90-Span was obtained with particle size distribution analysis. Regression equations were created with high R-sq(adj) values respectively %91, %82, %90 for contamination, grain size and span. Secondly, in order to prepare a well-defined slurry with precise viscosity, the regression model was generated in terms of the ratio of Si/C active material, average grain sizes of active materials and conductive agents, and the solid ratio of the slurry with %94 R-sq(adj) value. In addition, according to visual control, viscosity data was classified and the optimal interval was found at different shear rates for good cohesion. In the last step, three different powders from different ball milling conditions were chosen to compare the effect of powder characteristics on charging-discharging capacity at different current densities. Si/C anodes were prepared by coating N-Methyl pyrrolidone-based slurries on Cu foil and compositions were %60 active material, %30 carbon black, %10 PVDF as the binder. The coated Cu foil was punched in circular electrodes of 18mm radius, dried at 100°C under 150mBar in a vacuum furnace and, assembled in Argon filled glove box. Electrochemical tests were carried out between 0.05 and 1,5V vs. Li/Li+ potential window.

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Jaroslav Sedláček

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