LiCaFeF6 A zero strain cathode material for use in Li ion batteries

A new zero strain LiCaFeF6 cathode material for reversible insertion and extraction of lithium ions is presented. LiCaFeF6 is synthesized by a solid state reaction and processed to a conductive electrode composite via high energy ball milling. In the first cycle, a discharge capacity of 112 mAh g amp; 8315; is achieved in the voltage range from 2.0 V to 4.5 V. The electrochemically active redox couple is Fe3 amp; 8314; Fe2 amp; 8314; as confirmed by Mössbauer spectroscopy and X ray absorption spectroscopy. The compound has a trigonal colquiriite type crystal structure space group . By means of in situ and ex situ XRD as well as X ray absorption fine structure spectroscopy a reversible response to Li uptake release is found. For an uptake of 0.8 mol Li per formula unit only minimal changes occur in the lattice parameters causing a total change in unit cell volume of less than 0.5 . The spatial distribution of cations in the crystal structure as well as the linkage between their corresponding fluorine octahedra is responsible for this very small structural response. With its zero strain behaviour this material is expected to exhibit only negligible mechanical degradation. It may be used as a cathode material in future lithium ion batteries with strongly improved safety and cycle lif

Unravelling ultraslow lithium-ion diffusion in γ-LiAlO2 : experiments with tracers, neutrons, and charge carriers

Lithium aluminum oxide (γ-LiAlO2) has been discussed and used for various applications, e.g., as electrode coating, membrane, or tritium breeder material. Although lithium-ion diffusion in this solid is essential for these purposes, it is still not sufficiently understood on the microscopic scale. Herein, we not only summarize and assess the available studies on diffusion in different crystalline forms of γ-LiAlO2, but also complement them with tracer-diffusion experiments on (001)- and conductivity spectroscopy on (100)-oriented single crystals, yielding activation energies of 1.20(5) and 1.12(1) eV, respectively. Scrutinous crystal-chemical considerations, Voronoi–Dirichlet partitioning, and Hirshfeld surface analysis are employed to identify possible diffusion pathways. The one-particle potential, as derived from high-temperature powder neutron diffraction data presented as well, reveals the major path to be strongly curved and to run between adjacent lithium positions with a migration barrier of 0.72(5) eV. This finding is substantiated by comparison with recently published computational results. For the first time, a complete model for lithium-ion diffusion in γ-LiAlO2, consistent with all available data, is presented.DFG, FOR 1277, Mobilität von Lithiumionen in Festkörpern (molife

Nonequilibrium structure of Zn 2SnO 4 spinel nanoparticles

Zinc stannate (Zn 2SnO 4) nanoparticles with an average size of about 26 nm are synthesized via single-step mechanochemical processing of binary oxide precursors (ZnO and SnO 2) at ambient temperature, without the need for the subsequent calcination, thus making the synthesis route very simple and cost-effective. The mechanically induced phase evolution of the 2ZnO + SnO 2 mixture is followed by XRD and by a variety of spectroscopic techniques including 119Sn MAS NMR, Raman spectroscopy, 119Sn Mössbauer spectroscopy, and XPS. High-resolution TEM studies reveal a non-uniform structure of mechanosynthesized Zn 2SnO 4 nanoparticles consisting of a crystalline core surrounded by a structurally disordered surface shell. Due to the ability of the applied solid-state spectroscopies to probe the local environment of Sn cations, valuable complementary insight into the nature of the local structural disorder of mechanosynthesized Zn 2SnO 4 is obtained. The findings hint at a highly nonequilibrium state of the as-prepared stannate characterized by its partly inverse spinel structure and the presence of deformed polyhedra in the surface shell of nanoparticles. © 2012 The Royal Society of Chemistry

Mechanochemical synthesis of amorphous and crystalline Na₂P₂S₆-elucidation of local structural changes by X-ray total scattering and NMR

The development of all-solid-state sodium-ion batteries as an alternative energy storage system to lithium based techniques demands for sodium conducting solid electrolytes and an understanding of the sodium conduction mechanism governed by the local structure of these glass-ceramic materials. Na2P2S6 was synthesized in an amorphous state with subsequent crystallization. The change of the local structure before and after crystallization was analyzed in detail regarding the presence of structural building blocks such as [P2S6]2−, [P2S6]4−, [P2S7]4−, and [PS4]3−. The structure of the crystalline phase differs markedly compared to the corresponding amorphous phase

Crystallite size dependent cation distribution in nanostructured spinels studied by nmr, mössbauer spectroscopy and XPS

Owing to the structural flexibility of spinels, providing a wide range of physical and chemical behavior, these materials have been considered as a convenient model system for the investigation of the size dependent properties of complex ionic systems. In this work, quantitative formation is obtained on the crystallite size dependent ionic configuration in nanosized spinel oxides prepared by mechanochemical processing of the corresponding bulk materials. Experimentally determined values of the crystallite size and of the mean degree of inversion of nanostructured spinels are used to calculate the volume fraction of interfaces/surfaces and their thickness in the nanomaterials