Li-Ion-Batteries have shown a wide applicability for efficient energy storage, from small, portable devices to large systems for buffering of electrical grids. Also in the automotive sector, advanced battery systems are necessary to satisfy future demands. Every field of use has its own specific requirements and therefore needs appropriate battery systems. To create optimal energy storage devices, basic thermodynamic and phase equilibria information is required for new electrode materials. From experimental results concise phase diagrams can be obtained, which facilitate the modeling process using the CALPHAD method. The knowledge of basic thermodynamic data for Lithium based intermetallic electrodes is still weak and therefore further investigations are needed to design advanced battery materials for future applications.
A very powerful method to gain experimental thermodynamic data is the Coulometric Titration Technique (CT). This experimental setup allows the determination of thermodynamic activities, partial and integral molar Gibbs energies, enthalpies and entropies, through different electrochemical measurements. The open circuit voltage of the cell is measured in dependence of the composition of the electrodes and/or the cell temperature. This technique makes it also possible to examine narrow composition ranges and allows in situ sample preparation of partially intercalated electrode materials. Another advantage of this technique is the possibility to investigate a wide range of temperatures, which is basically limited by the type of electrolyte.
Various research groups have reported some hints for the existence of a new intermetallic phase in the Li-Sn system. Therefore measurements with the CT were performed at different temperature levels to verify the existence of this phase. Additionally, measurements in the ternary system Li-Cu-X (X = Sn, Sb) and their binary subsystems were performed. The thermodynamic data obtained can be used to calculate capacities, cell voltages and the heat, generated during the cycling of new electrodes. The results of these measurements will be shown with some aspects of a further improved experimental setup.