Study of Sn30(Co1-xFex)30C40 Alloy Negative Electrode Materials Prepared by Mechanical Attriting

A vertical axis attritor was used to prepare several compositions of Sn-30(Co1-xFex)(30)C-40 for 0 <= x <= 1. The attrited materials were studied using X-ray diffraction (XRD), Mossbauer effect spectroscopy (Fe-57 and Sn-119), and electrochemical methods. XRD and Mossbauer studies showed evidence of a nanostructured phase, most prominent near x=0, and nanocrystalline FeSn2, most prominent near x=1. The nanostructured phase is thought to be nanoscopic grains of amorphous Co1-xFexSn in a carbon matrix. Fe-57 Mossbauer effect spectroscopy showed an increase in the amount of nanoscopic Fe3C as the Fe content increased, consistent with the formation of FeSn2 in the same material due to the removal of Fe from Co1-xFexSn when x is near 1. Electrochemical testing was performed for the x=0, 0.5, and 1 samples. Both the x=0 and x=0.5 samples showed excellent capacity retention with a specific capacity of 450 mAh/g for at least 100 cycles. The irreversible capacity of these samples was about 85 mAh/g. The x=1 sample showed the highest reversible capacity of about 500 mAh/g but its capacity retention was poor. Sn-30(Co0.5Fe0.5)(30)C-40 may be a good compromise, allowing cost reduction by eliminating 50% of the Co while maintaining capacity retention.