Effect of annealing on nanostructured Sn_(30)Co_(30)C_(40) prepared by mechanical attrition

摘要

Sn_(30)Co_(30)C_(40) prepared by mechanical attriting is nanostructured with grains of amorphous CoSn dispersed in a disordered carbon matrix. The effects of annealing on the structure of the material were examined using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and Mossbauer effect spectroscopy. XRD experiments show that the X-ray amorphous diffraction pattern is basically unchanged up to 300 deg C and that crystallization of the amorphous CoSn grains occurs between 350 and 400 deg C. DSC experiments show a sharp exothermic feature near 360 deg C associated with this crystallization as well as a broad exothermic signal between 100 and 360 deg C thought to be caused by changes in short-range order in the amorphous CoSn grains, prior to crystallization. Mossbauer effect spectroscopy shows evidence for the changes in short-range order (SRO) below the crystallization temperature. The Mossbauer effect spectrum above the crystallization temperature changes with temperature as the Co and Sn site occupations approach the expected values in crystalline Co-Sn, which are reached near 600 deg C. A study of the impact of these structural changes on the performance of nanostructured Sn_(30)Co_(30)C_(40) negative electrodes for Li-ion batteries is underway.