A Thermodynamic Study of the Co-Li-Sn Ternary System

A growing demand on electrical energy for mobile systems (electrical cars) makes the development of devices for an efficient storage of electricity necessary, and one of the most promising technologies are the Lithium-Ion Batteries (LIBs) which are currently being further developed. Various intermetallic compounds have been discussed in the past as possible anode materials, including many compounds with Sn (for example, compounds in the systems Co-Sn, Cu-Sn, Ni-Sn, or Sb-Sn) for which it is hoped that Li can undergo a reversible reaction without drastic volume change that would destroy the anode and the LIB. In order to fully understand this reaction it is necessary to have a reliable knowledge of the corresponding ternary phase diagram. Thus the main goal of the proposed project is an experimental investigation of thermodynamic properties for the ternary Co-Li-Sn system (as one of the relevant systems) and to use these data for a corresponding thermodynamic modeling of this system by means of the CALPHAD method. The project is considered an additional support for a thermodynamic and kinetic database which is to be established within the Priority Programme 1473 "Materials with New Design for Improved Lithium Ion Batteries - WeNDeLIB" of the Deutsche Forschungsgemeinschaft. Research will focus on measuring the partial and integral enthalpy of mixing of liquid Co-Li-Sn alloys using calorimetric methods; the integral enthalpy of formation of solid compounds in the ternary Co-Li-Sn system using calorimetric methods; partial Gibbs energies of ternary Co-Li-Sn alloys using emf-measurements with liquid and/or solid electrolytes. If necessary we will also do experiments to understand the phase equilibria in the ternary Co-Li-Sn system which may be essential for a reliable evaluation of the thermodynamic measurements. For this the standard repertoire of experimental methods, i.e. X-ray diffraction, electron microprobe analysis, and thermal analysis, is available.