Mossbauer 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-y)C-y (0.1 < y < 0.5) were studied by Sn-119 Mossbauer 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 beta-Sn, anew metastable cubic Sn-Cophase, 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-y)C-y (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. (c) 2007 Elsevier B.V All rights reserved.