Hermann Pauly

Li(Al 1– z Zn z ) alloys as anode materials for rechargeable Li-ion batteries

The cycling behavior of anode materials based on alloys from the Li(Al 1– z Zn z ) continuous solid solution has been studied. The performance of the most promising composition Li(Al 0.8 Zn 0.2 ) was tested in half-cells against metallic Li with three different electrolytes and in full Li-ion cells against a V 2 O 5 cathode. The underlying structure evolution during cycling and the most relevant fatigue mechanisms are elucidated by x-ray diffraction, nuclear magnetic resonance, and x-ray photoelectron spectroscopy, and reveal a loss of mobile Li due to the ongoing formation of solid electrolyte interfaces. An enhanced stability for Li(Al 1– z Zn z ) electrodes with z ˜0.2 results from a peculiar microstructure due to the decomposition of Al and Zn in the Li-poor state and their intermixing in the Li-rich state.

Li8Cu12+xAl6-x (x = 1.16): a new structure type related to Laves phases.

The new ternary lithium copper aluminide Li(8)Cu(12+x)Al(6-x) (x = 1.16) crystallizes in the P6(3)/mmc space group with six independent atom positions of site symmetries 3m. (Al/Cu mixture), 6m2 (Li atoms), 3m. (Al/Cu mixture and Li atoms) and .m. (Cu atoms). The compound is a derivative of the K(7)Cs(6) binary structure type and is related to the binary MgZn(2) Laves phase and the LiCuAl(2), MgCu(1.07)Al(0.93) and Mg(Cu(1-x)Al(x))(2) (x = 0.465) ternary Laves phases. The coordination polyhedra of the atoms in this structure are icosahedra (Cu atoms), slightly distorted icosahedra and bicapped hexagonal antiprisms (Al/Cu statistical mixture), and Frank-Kasper and distorted Frank-Kasper polyhedra (Li atoms). All interatomic distances indicate metallic type bonding.

Tetragonal low-temperature structure of LiAl

Abstract The cubic face-centered structure of LiAl ( Fd 3 m , a=6.35971(3) A at 290 K ) transforms into a tetragonal body-centered structure (I41/amd, a=4.47831(1) A , c=6.34435(2) A at 12 K ). This first-order phase transition at about 93(2) K during heating is probably the reason for the so-called “ 100 K anomalies” in some physical properties like specific heat, electrical resistivity and nuclear-spin lattice relaxation. This transition seems to be correlated with the composition Li:Al of the alloy and the amount of Li vacancies.

Li12Cu16+xAl26-x (x = 3.2): a new intermetallic structure type.

The new ternary lithium copper aluminide, Li(12)Cu(16+x)Al(26-x) (x = 3.2), dodecalithium nonadecacopper tricosaaluminide, crystallizes in a new structure type with space group P4/mbm. Among nine independent atomic positions, two Al (one of which is statistically disordered with Cu) and three Li atoms have point symmetry m.2m, two statistically disordered Al/Cu atoms are in m.. sites, one Al atom is in a 4/m.. site and one Cu atom occupies a general site. The framework of Li(12)Cu(16+x)Al(26-x) consists of pseudo-Frank-Kasper polyhedra enclosing channels of hexagonal prisms occupied by Li atoms. The crystallochemical peculiarity of this new structure type is discussed in relation to the derivatives from Laves phases (LiCuAl(2) and Li(8)Cu(12+x)Al(6-x)) and to the well known CaCu(5) structure.