An In Situ Study of the Electrochemical Reaction of Li with Nanostructured Sn[sub 30]Co[sub 30]C[sub 40]

The reaction of lithium with nanostructured alloy prepared by mechanical attrition was studied using in situ X-ray diffraction (XRD) and in situ Mössbauer effect spectroscopy. During the first discharge (insertion of Li into the alloy) of cells, similarities between the structures of fully lithiated and lithiated Sn were observed by XRD. Both XRD patterns showed evidence for the Sn tetrahedra, with neighboring Li atoms, as found in . This implies that fully lithiated is composed of nanoscale regions of , nanoscale Co, and lithiated disordered carbon. In situ Mössbauer spectroscopy results were consistent with this interpretation and showed the presence of unlithiated Sn atoms at the bottom of the discharge. This observation agrees well with the fact that attrited samples only reach about two-thirds of the theoretical capacity. During the first recharge, in situ results from both techniques show that Co is rebonded to the Sn atoms in the CoSn grains as Li is removed. Overall, the insertion of lithium in nanostructured is believed to proceed via the following reaction where only the fully charged (left) and fully discharged (right) states are indicated: , where .