Search

• Chemical storage material for concentrating solar power technology. • Synthesis and characterization of an innovative chemical storage system based on an aluminium manganese spinel. • Very simple, cost effective and readily employable spinel preparation route for larger scale application. • Synthetized spinel characterization against its thermophysical, stability and structural properties. • Reaction enthalpy and temperatures for an innovative chemical storage material. Chemical storage systems are a promising innovative route to overcome the issue of the solar irradiation storage, resulting as cost effective and with high energy density. A main problem with these kinds of materials is to design a synthesis method for preparing stable reactive structures, presenting at the same time a high volumetric charging/discharging enthalpy. At this purpose, a size controlled spinel was produced, characterized and investigated regarding its thermophysical and kinetics properties. The obtained powder presents an average diameter between 100 and 200 µm and an energy density of 133 J/g and an experimental test was carried out to verify the spinel morphology stability under thermal cycles. The specific heat is similar to other structured chemical storage system and makes the spinel feasible to be used also as sensible accumulation medium. Despite the relatively high particles size, and the expected small exposed reactive area, the charging, and especially discharging reaction rates resulted particularly favourable and comparable with the reported behaviour of micrometric powders. The particularly simple preparation method plus the cost effectiveness of the precursors leads to a quite convenient expected cost for the storage material, absolutely similar to commercially available accumulation systems. [ABSTRACT FROM AUTHOR]

In this work, a detailed characterization of LixMn2O4 spinel oxides is shown to demonstrate the correlation between the anomalous thermoelectric properties of this cathode material and its crystal and electronic structure. The analysis of structural and transport in LixMn2O4 cathode materials obtained by solid-state reaction and sol-gel method allows formulating a conclusion that the performance of manganese spinel-based cathode depends on the occurrence of anomalous electron effects. The recorded maxima in absolute values of thermoelectric power correspond to high diffusivity of electrons at the Fermi level. A correlation between the occurrence of thermoelectric peaks and effectiveness of deintercalation/intercalation of lithium has been shown. The obtained results indicate a beneficial effect of phase transition on electrochemical properties of lithium-manganese spinel cathode material. [ABSTRACT FROM AUTHOR]

Spinel-structured lithium manganese oxide (LiMn2O4) has been successfully used as a cathode material for various lithium batteries. To improve the capacity and increase the discharge potential of the battery, transition metals are commonly added to the spinel as dopants or as a substitute for manganese. This can also confer stability on the structure of the cathode material. In this work, the production and performance of spinel LiMn2O4 (LMO) and LiN i0.5Mn1.5O4 (LNMO) by solid-state and sol-gel synthesis methods were studied. Synthetized (LMO) and (LNMO) materials were characterized by Raman spectroscopy and X-ray diffraction (XRD) to verify the formation of a spinel-like structure. It was corroborated that both synthesis methods can produce an adequate spinel structure. SEM analyses showed that in general, spinel take an octahedral form. The particle size changes according to the synthesis method used. Lower particle sizes were obtained by sol-gel. The electrochemical characterization demonstrates that solid-state synthesis generates compounds with greater purity and crystallinity, which induces a greater capacity of lithium ion intercalation. The addition of nickel to the spinel increases the discharge potential of the cathode by 0.5V.

Spinel-structured lithium manganese oxide (LiMn2O4) has been successfully used as a cathode material for various lithium batteries. To improve the capacity and increase the discharge potential of the battery, transition metals are commonly added to the spinel as dopants or as a substitute for manganese. This can also confer stability on the structure of the cathode material. In this work, the production and performance of spinel LiMn2O4 (LMO) and LiNi0:5Mn1:5O4 (LNMO) by solid-state and sol-gel synthesis methods were studied. Synthetized (LMO) and (LNMO) materials were characterized by Raman spectroscopy and X-ray diffraction (XRD) to verify the formation of a spinel-like structure. It was corroborated that both synthesis methods can produce an adequate spinel structure. SEM analyses showed that in general, spinel take an octahedral form. The particle size changes according to the synthesis method used. Lower particle sizes were obtained by sol-gel. The electrochemical characterization demonstrates that solid-state synthesis generates compounds with greater purity and crystallinity, which induces a greater capacity of lithium ion intercalation. The addition of nickel to the spinel increases the discharge potential of the cathode by 0.5V. [ABSTRACT FROM AUTHOR]

In-situ diagnostic tools have become established to as a means to understanding the aging processes that occur during charge/discharge cycles in Li-ion batteries (LIBs). One electrochemical thermodynamic technique that can be applied to this problem is known as entropy profiling. Entropy profiles are obtained by monitoring the variation in the open circuit potential as a function of temperature. The peaks in these profiles are related to phase transitions, such as order/disorder transitions, in the lattice. In battery aging studies of cathode materials, the peaks become suppressed but the mechanism by which this occurs is currently poorly understood. One suggested mechanism is the formation of point defects. Intentional modifications of LIB electrodes may also lead to the introduction of point defects. To gain quantitative understanding of the entropy profile changes that could be caused by point defects, we have performed Monte Carlo simulations on lattices of variable defect content. As a model cathode, we have chosen manganese spinel, which has a well-described order-disorder transition when it is half filled with Li. We assume, in the case of trivalent defect substitution (M = Cr,Co) that each defect M permanently pins one Li atom. This assumption is supported by Density Functional Theory (DFT) calculations. Assuming that the distribution of the pinned Li sites is completely random, we observe the same trend in the change in partial molar entropy with defect content as observed in experiment: the peak amplitudes become increasing suppressed as the defect fraction is increased. We also examine changes in the configurational entropy itself, rather than the entropy change, as a function of the defect fraction and analyse these results with respect to the ones expected for an ideal solid solution. We discuss the implications of the quantitative differences between some of the results obtained from the model and the experimentally observed ones. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes catalytic investigations into soot oxidation over KOH, K2CO3, KNO3, CH3COOK and K2SO4 doped iron and manganese spinels. For Fe3O4 it was found that alkali doping (0.5 monolayer) is confined to the surface and results in the substantial enhancement of its catalytic activity (ΔT 50% ≈80°C for K2CO3), depending on the precursor nature. For Mn3O4 K-doping at low loading (0.5 ML) has a negative effect, whereas at high loading (9 ML) leads to the formation of a birnessite shell on the Mn3O4 core catalyst with a spectacular increase of the soot oxidation rate (ΔT 50% ≈150°C). [Copyright &y& Elsevier]

Abstract: Homogeneous substitution of Cu(II), Al(III) and Ti(IV) for Mn in the spinel Li[Mn2]O4 is synthesized by lactic-acid assisted Pechini method. Galvanostatic charge–discharge between 3.5 and 4.3V (versus Li+/Li) at C/2 rate shows that the multi-cations doped spinel exhibits initial discharge capacity of 134mAhg−1 with a 97% capacity retention after 400 cycles at room temperature. When cycling at 55°C, the doped sample shows 91% capacity retention after 50 cycles compared to 70% retention for the undoped sample. As the charge–discharge rate increases to 12C, the doped sample delivers capacity of 111mAhg−1, which is much higher than that of the undoped sample of only 84mAhg−1. Moreover, as the charge–discharge rate returns from 12C to C/2, the discharge capacity of the doped electrode recovers nearly completely while the undoped sample lost more than 7% of its capacity. [Copyright &y& Elsevier]

Abstract: We have been developing lithium-ion batteries for electric power storage and have chosen cell chemistries having a high energy density and long life. The cell chemistry consisted of a positive electrode containing a lithium–manganese spinel or a mixture of it with a layered-manganese-based material, and a negative electrode containing a hard carbon. The 8Ah-class cells consisting of these cell chemistries showed that their extrapolated lives were long enough to withstand a cycling load for 10 years of use. A comparison of the cycle life data with the storage life data suggested the possibility to separate the capacity fading caused only by the storage and that only by the cycling, which is expected to be the basis of a prediction method for the calendar life. However, much work still needs to be done to achieve it. We also manufactured two types of 100Ah-class cells as an experiment based on the results for the 8Ah-class cells. They showed specific energies of 100Whkg−1 and 106Whkg−1. [Copyright &y& Elsevier]

Abstract: Li1.05Mn2O4 cathodes with different amounts of sulfate were synthesized by sol–gel process. X-ray diffraction (XRD) patterns indicated the pristine Li1.05Mn2O4 has a single phase of cubic spinel structure. Mn2O3 impurity was observed in the XRD patterns of Li1.05Mn2O4 spinels with SO4 2− anions, and the content of the Mn2O3 impurity rose with increasing SO4 2− amount. The sulfate ions coming from source materials existed as Li2SO4 in the Li1.05Mn2O4 spinels. As the molar ratio of SO4 2− to Mn increased from 0 to 0.03, the initial discharge capacity of the Li1.05Mn2O4 cathodes decreased from 119.4 to 97.9mAhg−1, and the storage performance decreased dramatically. Cyclic voltammetry (CV) and AC impedance studies revealed that the reversibility of the cathodes decreased and the electrochemical impedance rose with the increase of SO4 2− amount. [ABSTRACT FROM AUTHOR]

Abstract: The heat generation of LiMn2O4, Li1.156Mn1.844O4, and Li1.06Mn1.89Al0.05O4 spinel cathode materials in a half-cell system was investigated by isothermal micro-calorimetry (IMC). The heat variations of the Li/LiMn2O4 cell during charging were attributed to the LiMn2O4 phase transition and order/disorder changes. This heat variation was largely suppressed when the stoichiometric spinel was doped with excess lithium or lithium and aluminum. The calculated entropy change (dE/dT) from the IMC confirmed that the order/disorder change of LiMn2O4, which occurs in the middle of the charge, was largely suppressed with lithium or lithium and aluminum doping. The dE/dT values obtained did not agree between the charge and the discharge at room temperature (25°C), which was attributed to cell self-discharge. This discrepancy was not observed at low temperature (10°C). Differential scanning calorimeter (DSC) results showed that the fully charged spinel with lithium doping has better thermal stability. [Copyright &y& Elsevier]

Abstract: Electrical conductivity and thermoelectric power (TEP) measurements accompanied by differential scanning calorimetry (DSC) and XRD studies of series of manganese spinel samples with manganese substituted with 3d metals LiMxMn2−xO4 (M=Cr, Fe, Co, Ni, and Cu; x=0–0.5) are presented. Charge curves of Li/Li+/LiyMxMn2−xO4 type cells and therein determined chemical diffusion coefficients of lithium are shown. In the charge curves of Li/Li+/LiyMxMn2−xO4 cells, two visible plateaux separated with distinct potential jump (0.5–0.7 V) were observed. The lower plateau is related to the Mn3+→Mn4+ oxidation, while the next of higher voltage, of the Mm+ dopant oxidation. Substitution of manganese causes disappearance of the phase transition characteristic of a stoichiometric spinel. The schematic diagrams of relative Mn–M electronic levels alignment are proposed. It was shown that substitution of manganese with copper and iron improves both electrical conductivity and chemical diffusion coefficient of lithium in the cathode materials. [Copyright &y& Elsevier]

These studies are devoted to electrical and electrochemical investigations of cobalt-doped manganese spinel. The studies of electrical conductivity and thermoelectric power in the wide temperature range (220–1090 K) in relation to oxygen nonstoichiometry together with the behaviour of the material in Li/Li+/LixCoyMn2−yO4 cell enable to determine electronic defect structure of the LiCoyMn2−yO4 cathode material. [Copyright &y& Elsevier]

The Li1+δMn2−δO4 samples (0.00≤δ≤0.20) were obtained by a sol–gel method and characterized using: chemical analyses, XRD, SEM, TGA, DSC, electric conductivity and thermoelectric power. The obtained results were discussed in relation to the calcination temperature, and to the results obtained on commercial LiMn2O4. The samples calcined at 300 °C (S-samples) consisting small excess of Li (δ≤0.04) showed no phase transition at 285 K and no disturbance in electric conductivity and thermoelectric power, as observed for the related samples calcined at 800 °C (H-samples). Partial thermal decomposition of the S-samples or oxygen uptake by the H-samples were observed during TGA experiments above 350 °C. The beginning of the thermal decomposition of the H-samples started at higher temperatures, depending on Li-contents. At about 920 °C, the rapid acceleration took place independently on type of the samples. The thermal decomposition up to 800 °C seems to be reversible, owing to the samples reoxidation. [Copyright &y& Elsevier]

This work presents results of measurements of electrical conductivity, thermoelectric power and thermal properties of manganese spinel samples deintercalated in two different ways—an electrochemical and chemical one. It was shown that different methods of lithium extraction lead to striking differences in electrical properties of the obtained LixMn2O4 samples what agrees with the observed differences in their structure as seen by XRD. [Copyright &y& Elsevier]