Siegfried Fürtauer

The tin-rich copper lithium stannides: Li3Cu6Sn4 and Li2CuSn2

Abstract The Sn rich ternary intermetallic compounds Li3Cu6Sn4 (CSD-427097) and Li2CuSn2 (CSD-427098) were synthesized from the pure elements by induction melting and annealing at 400°C. Structural investigations were performed by powder- and single-crystal XRD. Li3Cu6Sn4 crystallizes in space group P6/mmm; it is structurally related to but not isotypic with MgFe6Ge6 (a = 5.095(2) Å, c = 9.524(3) Å; wR2 = 0.059; 239 unique F2-values, 17 free variables). Li3Cu6Sn4 is characterized by two sites with a mixed Cu:Sn occupation. In contrast to all other Cu-Li-Sn compounds known so far, any mixed occupation was found for Cu-Li pairs only. In addition, one Li site is only half occupied. The second Sn rich phase is Li2CuSn2 (space group I41/amd, a = 4.4281(15) Å, c = 19.416(4) Å; wR2 = 0.033; 213 unique F2-values, 12 atom free variables); it is the only phase in the Cu-Li-Sn system which is noted for full ordering. Both crystal structures exhibit 3D-networks which host Li atoms in channels. They are important for understanding the lithiation mechanism in Cu-Sn electrodes for Li-ion batteries.

Enthalpy of mixing of liquid systems for lead free soldering: Ni–Sb–Sn system

Highlights ► First paper providing enthalpy of mixing determined by calorimetry for Ni–Sb. ► First paper providing enthalpy of mixing determined by calorimetry for Ni–Sb–Sn. ► Full report of measured values for readers own evaluation. ► Isoenthalpy plot and detailed discussion of possible ternary interactions.

New intermetallic phases in the Cu–Li–Sn system: the lithium-rich phases Li3CuSn and Li6Cu2Sn3

Abstract The Li-rich ternary intermetallic compounds with the idealized end-member compositions Li3CuSn (CSD-427099) and Li6Cu2Sn3 (CSD-427100) were synthesized from the pure elements by induction melting in Ta crucibles and annealing at 400°C. Both powder and single-crystal XRD investigations were performed. Li3CuSn crystallizes in space group P6/mmm [a=4.5769(2), c=8.461(2) Å; wR2=0.073 for 180 unique F2-values and 25 free variables]. All atoms are located along [00z], [1/3 2/3 z] and [2/3 1/3 z]; individual sites are arranged in layers parallel to (00.1). One site is fully, one partially occupied by Sn atoms. Fully but mixed occupation with Cu and Li atoms was found for one site. The remaining electron-density distribution resulting from the strong anisotropic displacement parallel to the c axis is considered in four further sites, which are mixed occupied with (Li, Cu, □), but modelled solely by Li atoms. The crystal structure exhibits analogies with that of Li2CuSn (F4̅3m); comparable layers occur parallel to {111} but the stacking sequence and packing density differs adopting cubic symmetry. In Li6Cu2Sn3 [space group R3̅2/m, a=4.5900(2), c=30.910(6) Å; wR2=0.039 for 253 unique F2-values for 25 free variables] all atoms are arranged again at (00z), (1/3 2/3 z) and (2/3 1/3 z). Three sites are fully occupied (two by Sn atoms, a further one by Li atoms). Three additional positions are mixed occupied by Cu and Li atoms. The crystal structure is closely related to that of the binary phases Li13Sn5 and Li5Sn2; the substitution of Li by Cu atoms and vice versa is evident. The structural relationship to Li13Ag5Si6, which is permeable for Li ions, makes the title compound interesting as anode material in Li-ion batteries.

Liquid Co–Sn alloys at high temperatures: structure and physical properties

ABSTRACT The Co–Sn system is an important subsystem for Sn-based anode materials of lithium-ion batteries. Experimental results on the physical–chemical properties of this system in the liquid state, however, are rather sparse. In this work, the atomic structure and structure-sensitive thermophysical properties (viscosity, electrical resistivity, and thermoelectric power) of liquid Co–Sn alloys were investigated in a wide temperature range with special attention to the melting-solidification region. The obtained experimental results were combined with differential thermal analysis (DTA) data in order to verify the liquidus curve in the Sn-rich part of the Co–Sn phase diagram.

The Cu-Li-Sn Phase Diagram: Isopleths, Liquidus Projection and Reaction Scheme

The Cu-Li-Sn phase diagram was constructed based on XRD and DTA data of 60 different alloy compositions. Eight ternary phases and 14 binary solid phases form 44 invariant ternary reactions, which are illustrated by a Scheil-Schulz reaction scheme and a liquidus projection. Phase equilibria as a function of concentration and temperature are shown along nine isopleths. This report together with an earlier publication of our group provides for the first time comprehensive investigations of phase equilibria and respective phase diagrams. Most of the phase equilibria could be established based on our experimental results. Only in the Li-rich part where many binary and ternary compounds are present estimations had to be done which are all indicated by dashed lines. A stable ternary miscibility gap could be found which was predicted by modelling the liquid ternary phase in a recent work. The phase diagrams are a crucial input for material databases and thermodynamic optimizations regarding new anode materials for high-power Li-ion batteries.

Phase diagram, thermodynamic investigations, and modelling of systems relevant to lithium-ion batteries

Abstract This article reports on two consecutive joint projects titled “Experimental Thermodynamics and Phase Relations of New Electrode Materials for Lithium-Ion Batteries”, which were performed in the framework of the WenDeLIB 1473 priority program “Materials with new Design for Lithium Ion Batteries”. Hundreds of samples were synthesized using experimental techniques specifically developed to deal with highly reactive lithium and lithium-containing compounds to generate electrochemical, phase diagram and crystal structure data in the Cu–Li, Li–Sn, Li–Sb, Cu–Li–Sn, Cu–Li–Sb and selected oxide systems. The thermochemical and phase diagram data were subsequently used to develop self-consistent thermodynamic descriptions of several binary systems. In the present contribution, the experimental techniques, working procedures, results and their relevance to the development of new electrode materials for lithium ion batteries are discussed and summarized. The collaboration between the three groups has resulted in more than fifteen (15) published articles during the six-year funding period.