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Öğe Elucidating the optimized P2 type Na0.67Mn1-xCuxO2 cathode active material via operando XAS(Elsevier Science Sa, 2023) Altin, S.; Altundag, S.; Altin, E.; Vanpoucke, D. E. P.; Avci, S.; Ates, M. N.Here we report on the structural and electrochemical properties of P2-type Na0.67Mn1-xCuxO2 (where x = 0.20-0.50) via various techniques. X-ray diffraction (XRD) reveals a reduction of the unit cell volume upon substitution of Cu elucidated through detailed Rietveld analysis. The cyclic voltammetry (CV) behavior is also affected by the Cu substitution indicating new redox reactions stemming from Cu substitution. Galvanostatic cycling measurements at room temperature show that when x = 0.35 in a P2-type Na0.67Mn1-xCuxO2 cathode active material, the best electrochemical performance is obtained. The Na-ion diffusion rate is found to be strongly dependent upon the environmental temperature. Changes in the valence state and the local structures of P2-type Na0.67Mn1-xCuxO2 during the charge/discharge are in-vestigated through the operando X-ray absorption spectroscopy (XAS) technique. (c) 2022 Elsevier B.V. All rights reserved.Öğe Fabrication of Cr doped Na0.67Fe0.5Mn0.5O2 compounds and investigation of their structural, electrical, magnetic and electrochemical properties(Springer, 2019) Altin, E.; Altundag, S.; Altin, S.; Bayri, A.The main purpose of the study is to investigate the battery properties behind the electrical and magnetic properties. The first part of the study is about the fabrication of Cr-doped Na0.67Fe0.5Mn0.5O2 and the structural properties of the powders, which were investigated by XRD, EXAFS, FTIR and Raman Spectroscopy. Temperature-dependent resistivity measurements showed that room temperature resistivity values increased with Cr-ion content and all samples show an exponential decrease with increasing temperature. The magnetic properties of the Cr-doped samples were investigated, and it was found that the Cr ions strongly affected the magnetic structure of the samples. The second part of the study is about battery performance using the samples as cathode materials. Hence, CR2032 coin cells were fabricated by using the Cr-doped samples and the CV measurements showed that a high level doping of Cr ions in the structure prevented Na diffusion in the cells. The obtained CV graphs were discussed from the viewpoint of lattice dynamics. The EIS and cycling properties showed that Cr-ions in Na0.67Fe0.5Mn0.5O2 decrease of the capacity fade of the cells.Öğe Improved battery performance of silicon modified Na0.67Fe0.5Mn0.5O2 and its structural and electrochemical properties: An investigation of infrared thermal imaging(Elsevier, 2021) Altin, S.; Altundag, E.; Altin, E.; Altundag, S.Here, we present a systematically Si-doping strategy to improve the structural stability and battery performances of P2-type Na0.67Mn0.5Fe0.5O2 samples. Through Si4+ doping intended to settlement of the interstitial region in the crystal structure and investigate the effect on the electrical conductivity of the Na0.67Mn0.5Fe0.5O2. The structural properties were examined by x-ray absorption near-edge structure (XANES), x-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) measurements. The XANES spectra showed that the valence of both Manganese and iron ions was unchanged by Si. According to charge/discharge cycling measurements for constant current at room temperature, the lowest capacity fade was obtained for Na0.67Mn0.5Fe0.48Si0.02O2. The cycling measurements were also investigated at 50 degrees C, and it was observed that the electrochemical properties were changed with temperature. It was developed an experimental setup for the measurements of the internal temperature of the battery cells during the charging/discharging process of CR2032 coin cells using an infrared thermal camera. The ohmic heat was calculated from chronoamperometry measurements using a developed setup, and the heat generation was explained by a quadratic equation in the system.Öğe Improved performance of the NaFePO4/Hardcarbon sodium-ion full cell(Pergamon-Elsevier Science Ltd, 2023) Altundag, S.; Altin, S.; Yasar, S.; Altin, E.Chronoamperometry and galvanostatic procedures were applied in the LiFePO4-based ion exchange approach for the production of NaFePO4 cathodes. The materials obtained by various processes were employed as the cathode electrode in Na-ion half cells, and their structural and electrochemical properties were investigated. According to XRD patterns for both processes, it is seen that the Na-ions were successfully replaced with Li-ions. In addition of this, XPS and EDX-dot mapping analyses were supports the ion exchange procedure. The electrochemical properties of the cathode were investigated using CR2032 cells, and the diffusion coefficient and diffusion activation energy were calculated using the CV graphs at various scan rates and environmental temperatures. It was found that the Na-diffusion rate in the cell is faster at higher temperatures than at lower temperatures. The galvanostatic cycling tests were performed for C/10 and 1C rates at room temperature, 10 degrees C, and 50 degrees C and determined that the first capacities for C/10 and 1C at room temperature were 140mAh/g and 60mAh/g, respectively, with good stability. The full cells of NaFePO4/hard carbon were fabricated by pre-sodiation tech-nique and the battery performance tests revealed that the cells have a 74 mAh/g for C/10-rate with a voltage window of 2-4 V.Öğe Improving of the battery performance of Dy-substituted LiCoO2 and investigating the mechanism of the cells(Springer, 2019) Altin, S.; Altundag, S.; Altin, E.; Bayri, A.In this study, we successfully fabricated LiCo1-xDyxO2 (where x = 0.0-0.5) samples and investigated the structural and electrochemical properties. The Dy-substituted LiCoO2 samples were characterized by X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), Fourier-transform infrared (FTIR), and Raman measurements before and after cycling. The lattice volume and effective magnetic moment were increased by the substitution of the Dy ions in the structure. The capacity fading mechanism of Dy-substituted LiCoO2 via ex situ X-ray diffraction, XAS, Raman and FTIR spectroscopy were investigated. According to the electrochemical performance of the batteries, the x = 0.04 electrode had better cycling properties up to 400 cycles, which are better than that of the pure LiCoO2. We suggested that the critical number of Dy in LiCoO2 facilitates the Li-diffusion by increasing lattice volume. According to the battery performance temperature dependence analysis from 10 to 50 degrees C, the electrolyte just below degradation temperature shows better cycling since the ions are more mobile in this case.Öğe 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.Öğe Li1+xFePO4 (x=0-0.5) production from Fe3+ sources by glass-ceramic technique with different carbon sources and investigation of structural, thermal and electrochemical performance(Elsevier, 2022) Altin, E.; Altundag, S.; Gultek, E.; Altin, S.Li1+xFePO4 (x=0 - 0.5) samples were successfully fabricated by the glass-ceramics technique with quenching from high temperatures. Thermal properties were analyzed by DTA, TG and the glass transition temperature, crystallization activation energy and Avrami parameters were calculated as 3.99 indicating that three dimensions of growth and one representing a constant nucleation rate. The XRD analysis shows that there are two-phase of LiFePO4 and Li3Fe2P3O12 which compete with each other according to increasing heat treatment temperatures. Glucose and ascorbic acid were used as the carbon source for increasing the conductivity of the powders during to crystallization process with different heating and cooling rates and it was found that the heating/cooling rates are effective for battery performance. The battery cells exhibit similar cycling voltammetry (CV) data with the undoped LiFePO4 battery cells. The charging/discharging cycles measurements for C/5- rate and C/20- rate for different environmental temperatures were made and it was found that the best capacity values for different carbon sources were obtained as 165.8 mAh/g and 169.9 mAh/g for using ascorbic acid and glucose addition, respectively. The environmental effect on the battery performance was investigated and the Li-diffusion rate depending on the temperature was calculated and it was found that the diffusion rate obtained from CV curves for 50 degrees C, room temperature, and 10 degrees C and the diffusion activation energy were found as 2.93 and 8.03 meV for glucose and ascorbic acid respectively.Öğe 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.Öğe Na0.67Mn0.33Ni0.33Co0.33O2: Effect of synthesis technique on competing P3 and P2 phases br(Elsevier, 2023) Ecer, S.; Altundag, S.; Altin, S.; Avci, S.In layered NaxTMO2 (TM = transition metal) common understanding attributes the emergence of P2 and P3 phases to the synthesis temperature. In this work, we show that the synthesis technique is the main responsible for these phases. We synthesize Na0.67Mn0.33Ni0.33Co0.33O2 with two techniques, solid-state and electrospinning, using two temperatures, 700 degrees C and 900 degrees C. Both electrospun samples sintered at 900 degrees C and 700 degrees C show single phase P2 and P3, respectively. Both solid-state synthesized samples at 900 degrees C and 700 degrees C show mixture of P2/P3. Electrochemical properties of the sample with only P3 phase has the highest initial capacity of 130 mAhg(-1) at C/ 3 rate. The sample with only P2 phase has very stable cycle performance with 87 % capacity retention over 100 cycles consistent with its large interlayer separation. Our results show that the synthesis technique plays a crucial role in the crystal structure and the electrochemical performance of the layered cathode materials for Na-ion batteries.Öğe Production of Eu-doped LiFePO4 by glass-ceramic technique and investigation of their thermal, structural, electrochemical performances(Springer, 2022) Altin, S.; Coban, M.; Altundag, S.; Altin, E.LiFe1-xEuxPO4 (x = 0-0.1) samples were successfully fabricated by glass-ceramics technique quenching from high temperature. Thermal properties were analyzed by DTA analysis. Crystallization activation energy and Avrami parameters were calculated depending on the Eu content and heating rates. The XRD analysis shows that there are two-phases of LiFePO4 and Li3Fe2P3O12 which compete with Eu-doping in the samples and it is found that the x = 0.02 sample has the lowest impurity phases. The battery cells exhibit similar cycling voltammetry (CV) data with the undoped LiFePO4 battery cells. The charging/discharging cycles measurements were done for C/2-rate at room conditions and the best capacity value for C/2-rate was obtained as 149.4 mAh/g for x = 0.02 Eu-doped sample. Although the best capacity was obtained for x = 0.02, the best capacity fade was obtained for x = 0.03 Eu-doped sample. C-rate measurements provided that x = 0.02 cells have the promising results for the battery applications.
