Structural Transformations in Lithiated ηʹ-Cu6Sn5 Electrodes Probed by In Situ Mossbauer Spectroscopy and X-Ray Diffraction

The electrochemical reaction of lithium with hereafter generally referred to as has been investigated. Two complementary techniques, which provide a consistent picture of the structural changes that occur during discharge and charge, have been used in this study: in situ Mössbauer spectroscopy and X-ray diffraction (XRD). The data confirm earlier reports that initially undergoes a phase transition on lithiation to form a -type structure, and that further lithiation results in copper extrusion and, ultimately, the formation of a compound resembling The Mössbauer and XRD data provide strong evidence for solid-solution behavior in the Li-Cu-Sn system. The reversibility of the reaction to regenerate the structure is compromised by an inability of the extruded copper to be completely reincorporated during charge, particularly when cells are deeply discharged to 0 V vs. lithium metal, or if nickel rather than copper is used as the current collector. Part of the capacity loss observed on the initial cycle is attributed to irreversible reactions with tin oxides in the electrode and to reactions of the lithiated electrode with the electrolyte. © 2002 The Electrochemical Society. All rights reserved.