Abstract

The production of halloysite-derived silicon (HDS) is investigated as a potential anode material in lithium-ion batteries (LIBs). Other researchers have found HDS to be electrochemically active in small test cells. To test larger electrochemical cells, the production process needs to be scaled up and optimized. HDS is produced through magnesiothermic reduction of acid-etched halloysite. The reduction process is very exothermic and requires special consideration while being scaled up. A reactor and pressure release system were designed and fabricated to perform the reduction process in a safe manner. Various steps of the process were tested to determine their influence on the purity of the HDS and the stability of the reaction. The concentration of aluminum chloride was determined to be critical in preventing excessive thermal spikes during the reaction. We also found that there was no benefit to increasing the amount of the reducing agent, as it can lead to undesired side reactions. We also determined that proper mixing and sufficient temperature are some of the most important influences on the purity of HDS product. The HDS produced in our process performed well electrochemically. Si electrodes had up to 2284 mAh/g of discharge capacity after initial formation cycle. The Coulombic efficiency was as high as 95% for a given Si-G electrode. Detailed analyses using differential scanning calorimetry (DSC) revealed multiple side reactions involving magnesium, aluminum chloride, and silica. Magnesium reacts with aluminum chloride to produce magnesium chloride. This would mean that aluminum metal would react with silica, instead of magnesium. The combination of those two reactions releases 90% more heat than would magnesiothermic reduction of silica, increasing the possibility of unwanted thermal events. The newly formed magnesium chloride then reacts with the remaining aluminum chloride to form a hybrid salt, MgAl2Cl8.

Degree

College and Department

Ira A. Fulton College of Engineering; Chemical Engineering

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