Cu-Sb alloys have recently gained much attention as promising electrode materials for lithium ion batteries. Sb, as the active agent, has a theoretical capacity of 660 mAhg^-1, forming Li₃Sb in the fully lithiated state. Cu on the other hand does not react with lithium and can precipitate upon lithiation of Cu-Sb alloys. The Cu matrix is mandatory, as the change in volume between pure Sb and Li₃Sb is about 200% and therefore the structural integrity of the electrode material is compromised by the mechanical stress built up upon cycling of the cell.

Although much information is already available on the cycling performance of Cu-Sb electrodes, almost no data on the thermodynamics behavior exists. This is surprising as many thermodynamic parameters have a direct correlation to the electrochemical performance as well as kinetics of a material system. Therefore an extensive experimental investigation was conducted in the system Cu-Li-Sb, applying thermochemical as well as electrochemical methods.

Our investigations started with the development of fundamental property diagrams like isothermal sections and isopleths in the system Cu-Li-Sb. Thereby yet unknown ternary compounds were found and structurally characterized. On the basis of this data, reaction paths for the lithiation of different Cu-Sb alloys were proposed and further validated by electrochemical investigations, i.e. coulometric titrations. Reasons for the good cyclability of Cu-Sb alloys were found to be deeply rooted in the structural relations of the ternary compounds formed upon lithiation and their corresponding binary counterparts β-Cu₃Sb and Li₃Sb.

This work has been funded by the DFG under project FL-730/1-2 within the priority program SPP 1473 “WeNDeLIB”.