Thermal processes in the systems with Li-battery cathode materials and LiPF6 -based organic solutions

Thermodynamic instability of positive electrodes (cathodes) in Li-ion batteries in humid air and battery solutions results in capacity fading and batteries degradation, especially at elevated temperatures. In this work, we studied thermal interactions between cathode materials Li₂MnO₃, xLi₂MnO₃ ^.(1???x)Li(MnNiCo)O₂,LiNi_0.33Mn_0.33Co_0.33O₂, LiNi_0.4Mn_0.4Co_0.2O₂, LiNi_0.8Co_0.15Al_0.05O₂ LiMn_1.5Ni_0.5O₄, LiMn(or Fe)PO₄, and battery solutions containing ethylene carbonate (EC) or propylene carbonate (PC), dimethyl carbonate (DMC) or ethylmethyl carbonate (EMC) and LiPF₆ salt in the temperature range of 40–400 °C. It was found that these materials are stable chemically and well performing in LiPF₆-based solutions up to 60 °C. The thermal decomposition of the electrolyte solutions starts >180 °C. The macro-structural transformations of cathode materials upon exothermic reactions were studied by transmission electron microscopy (TEM), X-ray difraction (XRD) and Raman spectroscopy. Differential scanning calorimetry (DSC) studies have shown that the exothermic reactions in the temperature range of 60–140 °C lead to partial decomposition of both the cathode material and electrolyte solution. The systems thus formed consisted of partially decomposed solutions and partially chemically delithiated cathode materials covered by reactions products. Thermal reactions terminate and this system reaches equilibrium at about 120 °C. It remains stable up to the beginning of the solution decomposition at about 180 °C. The increased content of surface Li₂CO₃ is found to significantly affect the thermal processes at high temperature range due to extensive exothermic decomposition at low temperatures.     

The refractive index correction to the radiative rate constant in fluorescence lifetime measurements

The dependence of fluorescence decay times upon the refractive index of the solvent has been measured in two types of system: (a) in a single solvent at different temperatures, (b) in different solvents. The results are consistent with an n² dependence of the radiative rate constant, as has been predicted theoretically.     

Bücherbesprechungen

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Photon counting distributions for interacting laser modes

The photon courting distributions obtained from the beta-distribution for the intensity of interacting waves are proposed to describe the intensity fluctuations in a single laser mode which is intensity-coupled to other equivalent modes of a multimode laser. Numerical results are given for a five-mode laser including dead-time corrections for extremely small counting-interval-dead-time ratios.     

Electron-spectroscopic investigations of Ba and Ba compounds

Electron spectroscopic investigations of barium, barium compounds and barium thin film structures are reported. It is found that the barium 3d photoelectrons from BaO are at lower binding energies than for the case of pure barium metal. This effect is ascribed to relaxation processes. In some cases the compounds studied exhibited charging. In these cases plots of the Auger—Photoelectron energy separations are measured which were found to provide a using means of identifying the chemical environment of the barium atoms. Finally, measurements of the ionization loss spectra, principally the barium 4d lines, and changes in the plasmon energies for this series of barium compounds are reported.     

Untersuchung der niedrigliegenden Niveaus des54Fe durch die (p,p′γγ)-Reaktion

The low-lying levels of⁵⁴Fe were studied. The method ofγ γ-triple-correlations was used. Angular distributions were also measured. The levels at 2.5 MeV were found to be a doublett, withI=0(⁺) for the 2563 keV-level andI=4(⁺ or 2(⁺) for the lower level at 2539 keV. The experimental level scheme is compared with calculations according to nuclear models.     

A model of dispenser cathode activity

A semiquantitative model of dispenser cathode activity based on recent work on the co-adsorption of Ba and O onto W surfaces is presented. The co-adsorption studies have determined the shape of a three-dimensional surface of work function as a function of θ_O and θ_Ba, the surface coverages of O and Ba, respectively. Compositions of a variety of pedigreed dispenser cathodes were fitted to this surface and their composition changes during lifetime were modeled. Changes of surface composition with temperature and of workfunction, φ, with temperature were also found to fit these curves. The concept of a patchy surface implied by the co-adsorption measurements was used to explain earlier results on the shape of the X-ray excited Ba MNN Auger feature. Finally, SIMS measurements under UHV conditions was found to provide an extremely sensitive measurement of surface composition in the region of surface coverages of interest in the study of cathode phenomena. Extensions of this work to other types of cathodes such as M-types, and rhenium substrate cathodes is also discussed.     

Die Bedeutung der Kapillaranalyse für die physikalische Therapie

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Chemiluminescence simulation method for the evaluation of the termination rate constant for 2-cyanopropyl peroxy and α-phenyl-ethyl peroxy radicals

An iterative method has been devised for the simulation of chemiluminescence data during the oxidative decomposition of αα′ azobisisobutyronitrile in the presence of ethylbenzene. From this simulation the cross termination rate constant of the two types of peroxy radicals present has been estimated.