Analysis of the temperature dependence of the high-frequency EMR spectra of Mn ions in the lithium-ion battery material LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript>

This paper deals with the analysis of the temperature dependence of high-frequency EMR (HF-EMR) spectra due to Mn³⁺ and Mn⁴⁺ ions in the lithium manganese spinel LiMn₂O₄. A range of powder samples obtained by the sol-gel method with calcinations in several temperature ranges were prepared for this study. Based on the initial characterization carried out by a number of techniques, the physicochemical and structural properties of the samples were earlier determined. Independently, temperature magnetization and HF-EMR measurements were carried out. The EMR spectra vary strongly between samples, indicating possible structural or chemical changes. Quantitative analysis of the temperature dependence of the HF-EMR spectra due to Mn³⁺ and Mn⁴⁺ ions in LiMn₂O₄ is presented in this paper. The spectral analysis concerns the line shape, linewidth, intensity and g-factors. Fittings using the Lorentzian spectral shape and, to a certain extent, the Gaussian spectral shape have been carried out in order to parameterize the temperature dependence of the HF-EMR spectra. This parameterization of the HF-EMR experimental data enables a deeper characterization of the samples. Subsequently, a better insight into the role of the Mn³⁺ and Mn⁴⁺ ions in accounting for the characteristics most suitable for application of LiMn₂O₄ as a cathode material may be gained.     

Leak testing of carbon–tin nanocomposites by thermal analysis methods

Electrode materials consisted of tin nanograins encapsulated in different origin carbon buffer matrix (starch or water soluble polymer) were obtained in a simple and inexpensive process. The tin precursor was synthesized using modified reverse nanoemulsion technique (w/o) and then coated by a source of carbon. The composites precursors were pyrolysed, affording formation of C/Sn anode materials. The resulting samples were investigated by powder X-ray diffraction studies in order to verify the structure and calculate crystallites sizes. The morphology of the nanocomposites was characterized by low-temperature nitrogen adsorption method (N₂-BET). Thermal analysis measurements (EGA-TG/DTG/DTA and DSC) allowed determining optimal conditions of preparation process and estimating carbon content in the obtained anode materials. Thermogravimetric studies also proved to be highly useful in establishing the leak behaviour of C/Sn nanocomposites. The electrochemical performance of the nanopowders was examined by charge–discharge tests in R2032-type coin cell. The thermal analysis results as well as low-temperature nitrogen adsorption data indicated that the origin of carbon precursor has major impact on morphology and leak behaviour of the obtained carbon buffer matrix. The electrochemical tests showed that better tightness of carbon–tin nanocomposites resulted in higher gravimetric capacity and better cell performance.     

Transport and Electrochemical Properties of Bi2Sr2CaCu2O8 Superconductors

Abstract

Electrical conductivity and thermoelectric power measurements (77–300K) of both the pure and electrochemically doped with lithium Bi₂Sr₂CaCu₂O₈ system, are presented. Clear correlation between transport and electrochemical properties of Li_xBi₂Sr₂CaCu₂O₈ was shown.     

Changes in local structure of lithium manganese spinels (Li:Mn=1:2) characterised by XRD, DSC, TGA, IR, and Raman spectroscopy

A series of LiMn₂O₄ spinels, obtained by the sol-gel method maintaining constant Li:Mn ratio, were calcined at different temperatures (300-900 °C) to create crystal lattice defects. The structure and electronic properties of the samples were studied by complementary experimental techniques (XRD with Rietveld analysis, BET-N₂, DSC, MS-TG/SDTA, electrical conductivity, laser Raman and IR spectroscopy with 2D correlation analysis). The oxygen-spinel equilibrium shifts caused by various calcination in the air and in oxygen free atmosphere modulate the type and concentration of the anionic or cationic defects. The relationship between the local symmetry of MnO₆ octahedrons, manifested in symmetric and asymmetric vibrations, seemed to determine the phase transition at around the room temperature. Removing of the degeneration of t_2g and e_g orbitals, due to Jahn-Teller effect, evolves stabilization energy causing increase of activation energy of electron migration. Distortion of the local symmetry makes impossible the Jahn-Teller effect and in consequence stops the phase transition around room temperature.     

固体氧化物燃料电池——材料与前瞻(英文)

本文依据固体氧化物燃料电池(SOFC)于运作条件下的基本性能,诸如化学稳定性、电迁移、催化和热机械性能等评述SOFC组成部分(电极材料和电解质)的基本性质.示明由氧偏离化学计量比引起的电极材料结构缺陷与其电子性质及催化活性之间的相互关系,提出单室燃料电池概念.     

Applicability of Gd-doped BaZrO3, SrZrO3, BaCeO3 and SrCeO3 proton conducting perovskites as electrolytes for solid oxide fuel cells

Four proton conducting oxides of perovskite structure: BaZrO₃, SrZrO₃, BaCeO₃ and SrCeO₃ doped with 5 mol.% of gadolinium are compared in terms of crystal structure, microstructure, sinterability, water sorption ability, ionic transference number, electrical conductivity and stability towards CO₂. Relations between proton conductivity, structural and chemical parameters: pseudo-cubic unit cell volume, lattice free volume, tolerance factor, crystal symmetry and electronegativity are discussed. The grain boundary resistance is shown to be the limiting factor of total proton-conductivity for the materials examined. The highest proton conductivity was observed for BaCeO₃, however, it turned out to be prone to degradation in CO₂-containing atmosphere and reduction at high temperatures. On the other hand, Ba and Sr zirconates are found to be more chemically stable, but exhibit low electrical conductivity. Electrical conductivity relaxation upon hydration is used to calculate proton diffusion coefficient. Selected materials were tested as electrolytes in solid oxide fuel cells.      

On Applicability of a Direct Shear Test for Strength Estimation of Cereal Grain

Investigations were performed to verify the applicability of a direct shear method as recommended by Eurocode 1 for testing the strength of cereal grains [2]. Tests on rye without preconsolidation have shown that stress‐strain characteristics depend on the method of sample deposition. However, consolidation of the sample by twisting the top plate, as recommended by the code, neutralizes the influence of the grain packing structure on values of the angle of internal friction. Determination of the strength parameters for grain of six genera, under normal reference pressure of 100 kPa, and five levels of moisture content in a range from 10% to 20%, confirmed the applicability of the test. The only necessary modification of Eurocode procedure was elongation of the shear path up to the 0.1 ΔL/D level of the sample diameter. Values for the angle of internal friction were found to range from 22.1°–35.5° and were dependent on the grain genus and moisture content. The majority of dry grain samples showed low cohesion (below 4 kPa), and thus, should be treated as free flowing material. The increase in moisture content resulted in an increase of cohesion up to the highest observed value of 12 kPa. Triaxial compression tests were performed on wheat of five levels of moisture content, and gave results that were in close agreement with the results of the direct shear test.     

Thermally activated and non-activated charge transport processes in the oxides NaxMo2

The electrical properties of Na_xM_1+yO₂ (M=Mn,Co) were measured as a function of temperature under conditions of thermodynamic equilibrium for a quenched defect structure. The results of electrochemical studies of Na_xM_1+yO₂ are also presented. A correlation is demonstrated between the structures of the ionic and electronic defects in these materials and the potential changes of the cathode in Na/Na⁺/Na_xM_1+yO₂.The author is grateful to Prof. S. Mrowec and Dr. A. Stoklosa for helpful discussions.     

Structural, transport and electrochemical properties of LiNi1 − yCoyMn0.1O2 and Al, Mg and Cu-substituted LiNi0.65Co0.25Mn0.1O2 oxides

LiNi_{1 - y − z}Co_yMn_zO₂ (y = 0.25, 0.35, 0.5, 0.6; z = 0.1, 0.2), LiNi_0.63Cu_0.02Co_0.25Mn_0.1O₂, LiNi_0.65Co_0.25Mn_0.08Al_0.02O₂, LiNi_0.65Co_0.25Mn_0.08Mg_0.02O₂ and LiNi_0.65Co_0.25Mn_0.08Al_0.01Mg_0.01O₂ cathode materials were synthesized by a soft chemistry EDTA-based method. Structural and transport properties of pristine and delithiated materials (Li_xNi_0.65Co_0.25Mn_0.1O₂, Li_xNi_0.55Co_0.35Mn_0.1O₂ and LiNi_0.63Cu_0.02Co_0.25Mn_0.1O₂ oxides) are presented. In the considered group of oxides there is no correlation between electrical conductivity and the a parameter (M-M distance in the octahedra layers). The results of electrochemical performance of cathode materials are presented. The best stability during first 10 cycles was obtained for Li/Li_xNi_0.63Cu_0.02Co_0.25Mn_0.1O₂ cell due to enhanced kinetics of intercalation process.