Yazar "Ates, Mehmet Nurullah" seçeneğine göre listele

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    High-Performance Full Sodium Cells Based on MgO-Treated P2-Type Na0.67(Mn0.5Fe0.5)1-xCoxO2 Cathodes
    (Mdpi, 2023) Taskiran, Nermin; Altundag, Sebahat; Koleva, Violeta; Altin, Emine; Arshad, Muhammad; Avci, Sevda; Ates, Mehmet Nurullah
    Herein, we design a cathode material based on layered Na-2/3(Mn1/2Fe1/2)O-2 for practical application by combining the Co substitution and MgO treatment strategies. The oxides are prepared via solid-state reactions at 900 degrees C. The structure, morphology, and oxidation state of transition metal ions for Co-substituted and MgO-treated oxides are carefully examined via X-ray diffraction, IR and Raman spectroscopies, FESEM with EDX, specific surface area measurement, and XPS spectroscopy. The ability of oxides to store sodium reversibly is analyzed within a temperature range of 10 to 50 degrees C via CV experiments, galvanostatic measurements, and EIS, using half and full sodium ion cells. The changes in the local structure and oxidation state of transition metal ions during Na+ intercalation are monitored via operando XAS experiments. It is found that the Co substituents have a positive impact on the rate capability of layered oxides, while Mg additives lead to a strong increase in the capacity and an enhancement of the cycling stability. Thus, the highest capacity is obtained for 2 at.%-MgO-treated Na-2/3(Mn1/2Fe1/2)(0.9)Co0.1O2 (175 mAh/g, with a capacity fade of 28% after 100 cycles). In comparison with Co substituents, the Mg treatment has a crucial role in the improvement of the lattice stability during the cycling process. The best electrode materials, with a chemical formula of 2 at.%-MgO treated Na-2/3(Mn1/2Fe1/2)(0.9)Co0.1O2, were also used for the full cells design, with hard carbon as an anode. In the voltage window of 2-4 V, the capacity of the cells was obtained as 78 mAh/g and 51 mAh/g for applied current densities of 12 mA/g and 60 mA/g, respectively.
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    High-performance P2-Na0.67Mn0.85Cu0.15O2/Hard carbon full cell Na-ion battery: Pre-Sodiation of anode, p/n ratio optimizations, and Operando XAS studies
    (Pergamon-Elsevier Science Ltd, 2023) Altundag, Sebahat; Altin, Emine; Altin, Serdar; Ates, Mehmet Nurullah; Ji, Xiaobo; Sahinbay, Sevda
    Na-ion batteries have gained significant attention as a cost-effective and efficient energy storage option for large scale applications, serving as an alternative to the Li-ion batteries. However, commercialization of these batteries is still many steps away since most cathode materials suffer from significant capacity loss and more full-cell studies are required. In this work, we report the electrochemical properties of half-and full-cells of P2-type Na0.67Mn0.85Cu0.15O2 synthesized by solid state technique. X-ray diffraction, FT-IR, and Raman spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy techniques are used to determine the structural properties. Surface properties are studied by X-ray photoelectron spectroscopy and Bru-nauer-Emmett-Teller techniques. Half cells and full cells were constructed with Na-metal and hard carbon, respectively. Na-ion diffusion kinetics at 10 degrees C, room temperature, and 50 degrees C were determined experimentally. Galvanostatic cycling tests on half-cells show capacity values of 165/124 mAh/g for the 1./100. cycles with 24.8 % capacity fade. Operando x-ray absorption spectroscopy measurements were utilized to study local structural modification around transition metal ions during charge/discharge. In the full-cell studies, electrode mass ratio (p/n) and parameters for presodiation of hard carbon were optimized. Using 30 mA/g current density, the un-processed and the pre-sodiated full-cells reach capacity values of 48 mAh/g (p/n = 2.5) and 150 mAh/g (p/n = 0.75 and 1.15), respectively.
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    Mechanistic insights into cathode-driven capacity degradation of NMC111/ graphite pouch cells under long-term cycling
    (Pergamon-Elsevier Science Ltd, 2025) Ates, Mehmet Nurullah; Zengin, Feyza; Whba, Rawdah; Tunaboylu, Bahadir; Aydemir, Umut; Peighambardoust, Naeimeh Sadat; Karslioglu, Nergiz Gurbuz
    To investigate long-term degradation, 2000 mAh NMC111/graphite (Gr) pouch cells were cycled 5500 times at a 1C rate. After cycling, the resulting degradation mechanisms were systematically analyzed. Structurally, X-ray diffraction (XRD) peak shifts (003, 108, 110) revealed Jahn-Teller (JT) distortion, evidenced by an increase in the c-lattice parameter. This led to the rise in internal resistance, consistent with scanning electron microscopy (SEM) images that revealed pronounced grain deformation on the cathode. Chemically, ex-situ X-ray absorption near-edge structure (XANES) spectroscopy revealed an increase in the valence states of Mn, Ni, and Co ions, indicating significant bulk changes that could potentially destabilize the oxygen lattice. X-ray absorption fine structure (XAFS) analysis further underscored the key role of weakening transition metal-oxygen (TM-O) bonds in driving this structural deformation. At the surface, X-ray photoelectron spectroscopy (XPS) confirmed the formation of a cathode-electrolyte interphase (CEI) comprising lithium fluoride (LiF), LixPFy, and organic carbonates. The progression of these surface reactions is a key contributor to impedance growth and capacity fade over long-term cycling.
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    Synergistic interface design of Al2O3-coated NMC811 and graphitic-based pre-lithiated anodes for enhanced full-cell performance
    (Royal Soc Chemistry, 2026) Dogan, Ebru; Whba, Rawdah; Moeez, Iqra; Chung, Kyung Yoon; Yilmaz, Ece Unur; Altin, Emine; Ates, Mehmet Nurullah
    This study investigated aluminum oxide (Al2O3) surface coatings on lithium nickel manganese cobalt oxide (NMC811) cathodes using a wet chemical process based on ethanol-dissolved aluminum ethoxide (Al(OEt)3). Three coating concentrations, 1, 2, and 3 wt% Al precursor relative to the NMC811 mass, were synthesized and referred to as NMC811@AlO-1, NMC811@AlO-2, and NMC811@AlO-3, respectively. The workflow encompassed structural and surface characterizations of the coated samples, followed by electrochemical evaluation in half- and full-cell configurations. FTIR confirmed Al-O bond formation, while XRD and Raman spectroscopy verified that the NMC811 lattice structure remained unchanged after coating. Furthermore, transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (TEM-EDX) confirmed the successful deposition of the Al2O3 layer. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis revealed Al3+ ion diffusion into the grain interiors, indicating a potential impact on the electrochemical performance of the electrodes. Electrochemical tests showed that all the coated samples exhibited improved stability, with NMC811@AlO-3 (3 wt% coating) achieving the best capacity retention in half cells. In the second phase, full cells were formed using pre-lithiated graphite, graphene, and graphene oxide (GO) anodes, for which pre-lithiation conditions were optimized. Among all combinations, the NMC811@AlO-3/GO full cell demonstrated the highest initial discharge capacity (183 mAh g-1) and the best cycling retention (80.1% after 250 cycles at C/2). These results suggest that a 3 wt% Al2O3 coating, combined with a GO anode, provides the most promising pathway toward high-performance full-cell systems.
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    ZIF-12-derived N-doped Fe/Co/S/@C nanoparticles as high-performance composite anode electrode materials for lithium-ion batteries
    (Elsevier Science Sa, 2022) Bugday, Nesrin; Ates, Mehmet Nurullah; Duygulu, Ozgur; Deng, Wentao; Ji, Xiaobo; Altin, Serdar; Yasar, Sedat
    Different sulfide species of both iron and cobalt metals (FeS2, FeS, CoS, and FeCoS2) are composed together in N-doped porous carbon (NPC) for the synthesis of composite anode materials (labeled as Fe/Co/S@NPC-T hereafter, T = 700, 800, 900) by sulfurization and pyrolysis of Fe/Co-based zeolitic imidazolate framework (ZIF-12). Their structural properties are investigated by XRD, FTIR, SEM, TEM, BET and XPS analysis, and Fe/ Co/S@NPC-T composite materials, heat treated at different temperatures, are used as anode materials in rechargeable lithium-ion batteries. According to XRD results, the heat treatment of the Fe/Co@ZIF-12/S heat treated at 900 ? leads to the formation of the FeCoS2 phase (66 %) along with CoS (33 %) phase impurity. The heat treatment of the Fe/Co@ZIF-12/S heat treated at 800 ? causes the formation of the main phase of FeCoS2 with minor impurity phases of CoS and FeS2. However, pyrolysis of the Fe/Co@ZIF-12/S heat treated at 700 & DEG;C leads to the formation of the FeCoS2, CoS, FeS, and FeS2 phases. Among the samples, the highest BET surface area is 53.4 m2/g for the Fe/Co/S@NPC-90 0 sample. The CV analysis of the battery cell shows anodic and cathodic redox peaks, which belong to the redox reaction of CoS, FeS2, and FeS. The first dis-charge capacities of the cells for Fe/Co/S@NPC-70 0, Fe/Co/S@NPC-80 0 and Fe/Co/S@NPC-90 0 are 395, 963, 574 mA h/g at 300 mA/g, and 229, 835 and 1024 mA h/g at 1000 mA/g, respectively. (c) 2022 Elsevier B.V. All rights reserved.