Adsorbed Water on Nano-Silicon Powder and Its Effects on Charge and Discharge Characteristics as Anode in Lithium-Ion Batteries

Abstract

The amounts of adsorbed water on several kinds of carbon and silicon materials including Si nano-flake powder (Si LeafPowder, Si-LP) were determined at 250°C. It was found that nano-sized Si materials adsorb a large amount of water even after being dried at 120°C because of the hydrophilicity of the surface and the high specific surface area. The adsorbed water on Si-LP can be removed, but not completely, after drying at a 180°C. The charge and discharge characteristics of Si-LP, especially the initial irreversible capacity and the coulombic efficiencies upon repeated cycling, were significantly improved by removal of the adsorbed water at 180°C. The 180°C-dried sample also suppressed gas evolution during the initial charging and discharging cycle. From the results of gas analysis, it was found that gases evolved from the Si-LP electrodes were mainly H2 and CO2. From the results of charge and discharge tests and gas analysis, the effect of the adsorbed water on the irreversible decomposition of the electrolyte solution was discussed.