Microstructures and electrochemical properties of Si-RE and Si-Fe anode materials for rechargeable Li-ion batteries

Abstract

The effects of iron and rare-earth (RE) elements on the microstructures and the electrochemical properties of rapidly solidified Si alloys were investigated. Rapidly solidified Si-Fe and Si-RE ribbons were prepared by using a melt-spinning process. The thicknesses of the obtained ribbons were 9 − 13 μm. The ribbons were fragmented by using a ball-milling process to produce powders. Each of the alloy powders was mixed with a conductive material and a binder and then dissolved in deionized water and SFG₆ to form electrodes. The electrolyte used was 1.5-M LiPF₆ dissolved in ethyl carbonate/dimethyl carbonate/fluoroethylene carbonate. The results showed that the microstructures of the ribbons consisted of Si particles, which were present in inactive phases composed of the intermetallic compound FeSi₂ or (Ce,La)Si₂. The diameters of the Si particles in the melt-spun Si-RE ribbons were 60 − 90 nm whereas those of the particles in the Si-Fe alloy were approximately 0.8 − 12 μm. The Si-RE alloy exhibited an initial irreversible capacity that was half that of the Si-Fe alloy. The higher Coulombic efficiency and capacity retention rate of the Si-RE alloy were attributable to its nanosized particles and the effects of the enthalpy of solution.