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The electrochemical performance of a graphite electrode for rechargeable lithium-ion batteries was successfully enhanced by pretreatment of graphite powders with NaCl and Na 2 CO 3 aqueous solutions. The procedure of the pretreatment is simple and easy, that is, graphite powders are dispersed in the aqueous solutions, and then filtered and dried. Since the surface of the graphite powder was modified with a sodium salt coating, the irreversible capacity at the initial cycle was suppressed by the pretreatment which is capable of modifying the solid electrolyte interface layer formed on the graphite electrode. Further, reversible discharge capacities at 175 mA g −1 ͑C/2 rate when 350 mAh g −1 ͒ increased with better capacity retention in a 1 mol dm −3 LiClO 4 ethylene carbonate-diethyl carbonate electrolyte solution.Among various carbon materials which possess high electrochemical activity in a lithium cell, graphite is favored for battery applications because it exhibits a high specific capacity, low working potential close to that of lithium metal, and superior cycling behavior as the negative electrode. 1-4 When graphite powders are employed as the negative electrode, the graphite shows a large irreversible capacity at the first cycle since reductive decomposition of an electrolyte solution occurred at the graphite surface during the first charge, including the formation of solid electrolyte interface ͑SEI͒. The existence of an SEI layer plays an important role in reversible lithium intercalation into the interspace between graphene slabs; therefore, the chemical modification of a graphite surface including an SEI film has attracted wide attention for improving battery performances.Electrolyte additives exhibited a significant effect on modifying the SEI formation during the first charge ͑electroreduction͒ process. With the aim of enhancing the negative electrode performance in lithium-based rechargeable batteries, various organic/inorganic additives dissolved into an electrolyte solution are known to be effective; e.g., CO 2 , 5,6 HF, 7,8 HI, 9 AlI 3 , and MgI 2 10,11 for metallic lithium, and ethylene sulfite, 12 vinylene carbonate, 13-15 cobalt ion, 16 lithium carbonate, 17,18 and sodium ion 19 for carbon anodes. These additives successfully suppress the initial irreversibility and improve their cycle performance. We recently found several particular additives for LiMn 2 O 4 /C batteries, vinyl-pyridine, 20 LiI, LiBr, and NH 4 I. 21 On the other hand, the electrochemical lithiation properties of the carbon anode were improved by its surface treatment with metal oxides 22,23 and lithium carbonate. 24 Recently, our group has been emphasizing the key role of inorganic ingredients at the graphite surface, such as lithium, sodium, potassium, 25 and fluorine. 26 Moreover, we described that the impact of Na + ions as an electrolyte additive on the enhancement of battery performance was attributed to the entrapment of Na + ions in the SEI layer. 19 In the present study, we found that Na 2 CO 3 -and NaClcoating improve...

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A new process for solar grade silicon production by molten salt electrolysis has been proposed and its feasibility discussed. This process consists of an electrolysis step of SiO 2 dissolved in a fluoride melt using an aluminum-silicon liquid alloy cathode and a precipitation step of silicon from the liquid alloy. According to the calculation based on literature data, the proposed process has the possibility to produce solar grade silicon in combination with directional solidification, even if the electrolysis step has no purification effect. A preliminary electrolysis using aluminum cathode and carbon anode in a NaF-AlF 3 -SiO 2 melt at 1273 K revealed that silicon was formed by the electrolysis and that sub-reactions, such as the reduction of SiO 2 by aluminum and metal fog formation, also took place. Especially, SiO 2 reduction by aluminum was found to be fast compared to the reduction by the electrolysis, which made it difficult to evaluate the current efficiency. Thus, these sub-reactions were further investigated in order to measure the reaction rates, and their potential dependence. Based on the obtained data, the cathodic current efficiency during the preliminary electrolysis was evaluated to be greater than 46%.

Battery performance of a graphite electrode for negative electrodes of lithium-ion batteries was successfully enhanced by pretreatment of graphite powders with lithium, sodium, and potassium chloride aqueous solutions. In the process of the pretreatment, graphite powders were simply dispersed in the aqueous solutions and dried to coat the graphite powder with alkali chloride solid after filtration. When the optimum concentrations of each chloride, 0.1wt% LiCl, 0.1wt% NaCl, and 0.5wt% KCl, were adopted for the pretreatment, the irreversible electroreduction capacity at the initial cycle was reduced by the chloride coating which was capable of modifying the solid electrolyte interphase formed on the graphite electrode surface, furthermore, the reversible capacity at a relatively high rate was improved by the coating from ≊ ∼320to340–350mAhnormalg−1 during successive cycles in a 1moldm−3 LiClnormalO4 ethylene carbonate:diethyl carbonate electrolyte solution. The origins of the improvement were discussed from surface and electrochemical analyses.