Intermetallic Li-Anode Alloys Based on Cu, Sb and Sn

Intermetallic alloys are promising candidates for new anode materials for lithium ion batteries (LIBs) in high energy applications because of the significantly increased theoretic capacities when compared to conventionally used graphite. However, the drastic volume changes during lithiation of pure metals such as Si or Sn lead to degradation of the electrode material resulting in very high capacity fading and low cycling stability. One of the various concepts to solve this problem is to use intermetallic alloys instead of pure metals. For example, Cu 6 Sn 5 , Cu 3 Sn and Cu 2 Sb are promising anode materials because Cu does not form intermetallic compounds with Li. A (Cu)-alloy matrix which precipitates during lithiation would act to buffer the strain induced by volume changes and simultaneously ensures electrical contact between lithiated phases. A similar effect can be observed using SbSn as anode material. In this case Sn acts as a buffer because Li-Sb alloys are preferably formed by lithiation. Advanced materials design and engineering based on computational methods rely significantly on experimentally determined thermodynamic and phase diagram data of the material systems. These data are used as inputs to model the Gibbs free energies of all phases, thereby generating self-consistent thermodynamic descriptions of the multi-component systems. These can in turn be used to predict lithiation pathways and simulate the electrochemical behaviour of half cells with different active material compositions. Furthermore, knowledge of phases and their crystal structures is crucial for kinetic studies of lithiation processes. From our comprehensive experimental data, including powder X-ray diffraction, single crystal X-ray diffraction, thermal analysis, and coulometric titration, we obtained self-consistent CALPHAD descriptions.This presentation will give an overview of our experimental procedures and the results of our work on the materials systems Cu-Li-Sn, Cu-Li-Sb and Li-Sb-Sn. This work has been funded by the FWF under the project I559-N19 and by the DFG under the projects FL-730/1-2 and CU 203/ 1-2, all within the DFG priority project SPP 1473 “WeNDeLIB”.