Sn2fe-TiOx Composite Prepared By High Energy Ball Milling As an Anode Material for Li-Ion Batteries

Abstract

Recently, as portable electronic devices and electric vehicles have been developed, the market needs for energy storage systems are rapidly increasing. Rechargeable Li-ion batteries (LIBs) are representative energy storage devices due to its long cycle life, high energy density, and reasonable cost. To meet the demand for long-lasting batteries, the energy density, which is determined by operating voltage and electrode capacities, should be increased. Therefore, many researchers have been developing high-capacity electrode materials. Currently, carbon-based materials are the most widely used anode materials because of their low operating voltage, moderate capacity, and excellent cycle performance. But, its relatively low capacity (372 mAh g–1 for LiC6 phase after full lithiation) is a limiting factor to meet current energy demands. In order to solve this problem, many researchers have investigated replacements and Li-alloy based materials such Si, Sn and Ge have attracted great attention because of their high theoretical capacity. Among them, Sn-based materials (theoretical capacity: 993 mAh g–1 for Li4.4Sn phase) are one of the most attractive anode materials for high-capacity LIBs. However, commercialization of alloying materials with Li is limited due to the poor cycle performance. When Li is inserted and extracted into/from the electrode materials during charging/discharging, they suffer from rapid capacity fading because of volume change and pulverization of the active materials. In 2007, a Japanese company showed the possibility for solving this problem. SONY released the Nexelion battery which consisted of Sn-Co-C anode materials. This revealed that Sn-based materials have still a potential for widespread commercialization. In this study, we designed and synthesized Sn2Fe@TiOx composites as high-capacity anode materials by high energy mechanical milling. First, tin oxide (SnO), titanium (Ti) and iron (Fe) powders were ball-milled together. During the milling process, SnO was reduced to Sn by Ti and remaining Sn was combined with Fe. As a result, a Sn2Fe-TiOx composite was synthesized. To improve cycling stability, heat treatment and carbon incorporation were employed. Materials and electrochemical characterization were performed to analyze the synthesized materials for LIB anodes.