Mössbauer effect studies of sputter-deposited tin–cobalt and tin–cobalt–carbon alloys

Sn–Co–C alloys are now used as negative electrodes in the latest generation of Li-ion batteries, although not much is known about the phases present in the materials, their micro or nanostructure nor their physical properties. Here, sputtered combinatorial libraries of Sn1−xCox (0 < x < 0.6) and [Sn0.63Co0.37]1−yCy (0.1 < y < 0.5) were studied by 119Sn Mössbauer effect spectroscopy and X-ray diffraction to learn their phase content and micro or nanostructure. The sputtered Sn1−xCox films showed the presence of crystalline β-Sn, a new metastable cubic Sn–Co phase, an amorphous Sn1−xCox (0.26 < x < 0.45) phase and Co3Sn2 as x, or the Co content, increased. The sputtered [Sn0.63Co0.37]1−yCy (0.1 < y < 0.5) materials consist of amorphous grains of Sn0.63Co0.37 separated by a carbon matrix. The impact of this nanostructure on the utility of these materials as negative electrodes in Li-ion batteries is discussed.