Development of innovative process for producing metalic lithium by converting raw material

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The goal of present project is to establish the process for producing metallic lithium, which is important material as a negative electrode of high performance battery, with low cost by using Li_2CO_3 in stead of LiCl as a raw material. Li_2CO_3 has many advantages such as low price, no hygroscopicity and high purity compared with LiCl. Furthermore, the decomposition potential of Li_2CO_3 is about 1.5V lower than LiCl by reacting carbon anode. However, it was difficult to use Li2CO3 dissolved in the electrolyte directly because it reacts with metallic lithium deposited on the cathode.Therefore, the project was performed based on the idea that the electrolyte is divided with ceramic diaphragm into catholyte and anolyte. Lithium deposits on the cathode dipped in the catholyte which consists of just LiCl-KCl eutectic melt. On the other hand, Li_2CO_3 is fed into the anolyte and reacts with graphite anode to evolve CO_2 which is easy disposable compared with Cl_2.At first, the electrolysis … More was carried out at 400C^0 by using just LiCl-KCl eutectic melt to study the current efficiency of lithium deposition on the cathode! It was confirmed that high current efficiency higher than 90% was obtained. Next, anodic potential was studied to study the reaction of CO_3^<2-> by feeding Li_2CO_3 into the LiCl-KCl anolyte under 500C^0. As the result, reaction rate was very slow although the potential change was found.Based on above results, further experiments were performed at higher temperatures up to 800C^0. The anodic potential was found to decrease drastically by increasing temperature. Namely, the reaction to consume CO_3^<2-> has very strong temperature dependence. The mechanism of the reaction on the anode was clear as follows; first stage is CI_2 evolution and second stage is the reaction of CO_3^<2-> with graphite and Cl_2. First stage reaction occurs easily. However, second stage reaction has high activation energy. Therefore, second stage becomes the rate determining step. It was clear that the temperature higher than 650C^0 was effective to consume CO_3^<2-> sufficiently. It is considered that the knowledge obtained in this project is very useful to realize the process to use Li_2CO_3 as the raw material for producing lithium. Less