Browsing by Subject "Na0.67Mn0.5Fe0.5O2"

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    Investigation of Ti‐substitution effects on structural and electrochemical properties of Na0.67Mn0.5Fe0.5O2 battery cells
    (Wiley, 2020) Altın, S.; Altundağ, S.; Altın, E.; Öz, Erdinç; Harfouche, M.; Bayri, A.
    Ti‐substituted Na0.67Mn0.5Fe0.5O2 powders were fabricated by quenching at high temperatures, and the structural properties were investigated by Fourier transform infrared (FTIR), Scanning Electron Microscope (SEM), X‐ray powder diffraction (XRD), and X‐ray absorption spectroscopy (XAS) measurements. According to XRD analysis, it was not observed any impurity phases and it was found that the lattice constants of the powders were slightly increased by Ti content. The change in the valence state of both Mn and Fe ions was investigated by X‐ray absorption near edge structure (XANES), and it was found that Ti‐substitution caused a decrease in the valance state of Fe in Na0.67Mn0.5Fe0.5O2. Fourier transform (FT) of XANES showed that the local structure around the metal ions changed with the addition of Ti ions. The cycling voltammetry (CV) graphs of Ti‐substituted cells were almost the same as the pure sample, which may not change the cycling mechanism in the cells. According to galvanostatic cycling measurements at room temperature, the best performance was obtained with Ti‐substitution of 0.06 to 0.09 in the structure. The effect of environmental temperature in the battery cells was investigated at 10°C to 50°C, and it was found that the battery performance depends on the environmental temperatures.
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    Magnetic Properties and Environmental Temperature Effects on Battery Performance of Na0.67Mn0.5Fe0.5O2
    (Wiley-VCH Verlag GmbH & Co. KGaA, 2021-03-31) Altın, S.; Bayri, A.; Altın, E.; Öz, Erdinç; Yaşar, S.; Altundağ, S.; Harfouche, M.; Avcı, S.
    Herein, a modified solid state synthesis of Na0.67Mn0.5Fe0.5O2 and the results of a detailed investigation of the structural and magnetic properties via Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) analysis are reported. The magnetic properties of Na0.67Mn0.5Fe0.5O2 do not fit the Curie–Weiss law and a model regarding the spin configuration of the Mn and Fe ions and a possible ferrimagnetic order is suggested. Electrochemical measurements and ex situ structural analysis of the cathode material confirm the reversible structural transitions for the cells charged up to 4.0 V. Environmental temperature–dependent electrochemical measurements reveal a strong temperature dependence of both, the initial capacity and the capacity retention. Ex situ SEM, FTIR, and XRD studies on the battery membrane verify the formation of a Na2CO3 phase on the membrane, which blocks the Na ion diffusion through membrane pores and is responsible for the capacity fade for this compound.