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    P2-type Na0.67Mn0.5-xVxFe0.43Ti0.07O2 powders for Na-ion cathodes: Ex-situ structural analysis and full-cell study
    (Pergamon-Elsevier Science Ltd, 2024) Dogan, Ebru; Altundag, Sebahat; Altin, Emine; Oz, Erdinc; Altin, Serdar
    This study used a modified solid-state synthesis technique to synthesize Na0.67Mn0.5-xVxFe0.43Ti0.07O2 (x = 0.02 0.1) cathode materials. The XRD pattern shows that there are no impurity phases in the samples for x <= 0.06. The granular grain formation was observed in each sample and the largest surface area was obtained for x = 0.06 Vdoped composition. According to XPS analysis of the x = 0.06 sample, the V and Ti ions have three different valence states in the structure and the ratio of V3+/V4+/V5+ ions in the powders was calculated as 13 %/36 %/51 % and the spin splitting binding energy gaps were found as 7.1 eV for each V-ions and they affected by cycling process. The redox mechanism of the half cells was investigated at 10 degrees C and room temperature. The diffusion coefficient values of Na+ were calculated by cycling voltammetry (CV) and GITT techniques for the x = 0.06. Although the highest capacity of the half cells for the V-substituted samples was found to be 188.3 mAh/g for x = 0.02 V-doping in the cells for C/3-rate, the best capacity fade among the cells was obtained for x = 0.06 as 36.9 %. The ex-situ analysis of the electrodes after 100 cycles at the environmental temperatures of 10 degrees C, 50 degrees C, and 60 degrees C was investigated and it was found that the valence state of the elements changed by the cycling process. The artificial solid electrolyte interface (SEI) formation on the anode surface was performed by presodiation technique and the full cells were assembled using Na0.67Mn0.44V0.06Fe0.43Ti0.07O2/hard carbon architecture and the obtained first capacity values for C/3-rate were 90.1 mAh/g and 66.6 mAh/g, respectively, and the capacity value decreased with the cycling process up to 60 cycles and then gave a plateau with increasing cycle numbers up to 500 cycles.
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    Production of V-Doped P2-type Na0.67Mn0.5Fe0.43Al0.07O2 Cathodes and Investigation of Na-Ion Full Cells Performance
    (Wiley-V C H Verlag Gmbh, 2024) Dogan, Ebru; Altundag, Sebahat; Altin, Serdar; Arshad, Muhammad; Balci, Esra; Altin, Emine
    The Na0.67Mn0.5Fe0.43Al0.07O2(x = 0-0.1) samples are successfully produced and their structural properties are investigated by common techniques. The highest surface area is found as 4.94 m(2) g(-1) for x = 0.04 V by the Brunauer-Elmet-Teller analysis. According to X-ray photoelectron spectroscopy of x = 0.04 V-doped sample,V4+, and V5+ ions are formed in the structure. The main phase is observed as P63/mmc symmetry with an impurity phase of V6O13 for x >= 0.06 . According to the CV analysis, while the redox voltage decreases for the Mn3+/Mn4+ , the intensity of the peaks of Fe2+/Fe3+ redox reaction decreases. While the best capacity value of the half cells at C/3-rate is obtained as 171 mAh g(-1) for x = 0.04, the lowest capacity fade is found for x = 0.08 . It is mentioned the V6O13 may contribute to the electrochemical process . The galvanostatic tests are investigated for the voltage windows of 3.5-1.5, 4-1.5, 4-2.5, 4-2, and 4-2.5 V and it is seen that the battery cells for 3.5-1.5 V have the best capacity fade (6%) among the others. The Na0.67Mn0.5Fe0.43Al0.07O2/ hard carbon is used for the full cells with presodiated anode and the first capacity value of the full cell is obtained as 80.2 mAh g(-1) for C/2-rate.