Coulometric titration in the system Cu-Li-Sb: Thermodynamic, structural and kinetic aspects.
A. Beutl, H. Flandorfer
University of Vienna, Department of Inorganic Chemistry – functional materials
Währingerstraße 42, 1090 Wien, Austria
The experimental investigation of lithium containing systems is a fundamental contribution to the development of new generation lithium ion batteries. As the well established electrode materials are meeting their limits in regard of energy density and cycle lives, alternative materials are demanded. One potential group of materials, the so called alloying type electrodes, might be able to increase the energy density of LIBs by manifold. However, the structural changes upon lithiation of these materials are tremendous and therefore the cycle lives are petty. A promising technique to buffer volume changes is the combimation of alloying and conversion in intermetallic anodes. Cu2Sb is one of the more feasible conversion type alloying electrode materials, as it provides large volumetric capacities combined with good cycling performances. In order to fully understand the mechanisms, which occur upon lithium incorporation, the respective phase diagrams are of utmost importance.
However not much is known about the thermodynamic background of the underlying system Cu-Li-Sb. Therefore experimental investigations of phase equilibria in this system were conducted. Different samples were prepared and analyzed by XRD. An isothermal section and several new ternary compounds could be established. The position of the phase boundaries, however, could only be estimated, as conventional techniques like SEM-EDX are not accessible in lithium containing systems.
To accurately determine the position of phase boundaries, the coulometric titration method was applied. By electrochemical lithiation along concentrational sections of the ternary system and measuring the emf it was possible to accurately determine the position of the phase boundaries. Apart from this thermodynamic information, insights into the kinetics of the lithiation processes could be gained.
This work has been funded by the DFG under the project No. FL-730/1-2 within the priority project SPP 1473 “WeNDeLIB”.