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    An investigation of the improvement in energy storage performance of Na2/3Mn1/2Fe1/2O2by systematic Al-substitution
    (Springer, 2020) Altin, S.; Altundag, S.; Altin, E.; Harfouche, M.; Bayri, A.
    We successfully fabricated Na2/3Mn1/2Fe1/2-xAlxO2, wherex = 0, 0.01, horizontal ellipsis 0.10, by a modified solid-state reaction technique. The structural properties of the Al-substituted samples were investigated by x-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy and x-ray absorption fine structure (XAFS) measurements. It was found that there were no impurity phases in the XRD patterns of the samples and they fit the P63/mmc symmetry. The Al substitution in Na(2/3)Mn(1/2)Fe(1/2)O(2)causes a decrease in the a-lattice parameter, but the c-parameter starts to increase after a certain substitution value of Al. We suggest that a certain proportion of Al in the samples triggers the change of the spin configuration of the Fe ions, and it may cause an increase in the lattice parameters. The size of the grains was found to be less than 0.9 mu m, from SEM images for all samples. The valence states of the substituted samples as well as the local structure around Fe and Mn were investigated by means of XAFS measurements. The highest capacity for the first cycle was obtained as 134.3 mAh/g forx = 0.07, and the best capacity fade was found to be 0.23 forx = 0.08 substitution. So, the highest performance of the Al-substituted cells was found when 0.08 >= x >= 0.06. The environmental temperature effects on the battery cells were determined at 10 oC, room temperature and 50 oC, and it was found that the temperature plays a crucial role in the Na-ion batteries.
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    LiNi0.8Co0.15Ti0.05O2: synthesis by solid state reaction and investigation of structural and electrochemical properties with enhanced battery performance
    (Springer, 2020) Bayri, A.; Gocer, E.; Altin, E.; Altundag, S.; Oz, E.; Harfouche, M.; Altin, S.
    Solid state synthesis is an essential technique for large-scale production of electrode active materials in battery industry. However, solid state synthesis of LiNi0.8Co0.15Al0.05O2(NCA), which is a well-known commercial cathode material for Li-ion batteries, provides electrochemically inactive compound. Here, we report the solid state synthesis of Li(x)Ni(0.8)Co(0.15)Ti(0.05)O(2)wherex = 1.03, 1.06, and 1.09, which is a modified version of conventional NCA. Our thorough studies consist of characterization of compounds by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and magnetization measurements. The results point out the significant effects of Li content on structural and magnetic properties of the samples. Battery performance tests show that Li(1.06)Ni(0.8)Co(0.15)Ti(0.05)O(2)exhibits better cycling properties than conventional NCA. X-ray absorption spectroscopy (XAS) technique is utilized to determine structural modifications upon cycling of this compound via ex-situ analysis. We conclude that substitution of Ti ions in Li(1.06)Ni(0.8)Co(0.15)Ti(0.05)O(2)improves the cycling capability of the cells by reducing the formation of NiO insulating layer which hinders the redox reactions. The capacity value ofx = 1.06 sample increases up to 150 mAh g(-1)at C/3 rate during cycling and the capacity fade is negative for the first 10 cycles. Possible mechanism for the negative capacity fade is also discussed.