Yazar "Chung, Kyung Yoon" seçeneğine göre listele

Listeleniyor 1 - 6 / 6
  • Küçük Resim Yok
    Öğe
    Evaluation of the Effect of Precursor NMC622@TiO2 Core-Shell Powders Using a Prelithiated Anode from Figure Seeds: Spotlight on Li-ion Full-Cell Performance
    (Amer Chemical Soc, 2024) Whba, Rawdah; Dogan, Ebru; Moeez, Iqra; Bhatti, Ali Hussain Umar; Akbar, Muhammad; Chung, Kyung Yoon; Altin, Emine
    In this study, innovative electrode materials for lithium-ion batteries (LIBs) were developed and characterized, demonstrating significant performance enhancements. Initially, NMC622@TiO2 was synthesized using a wet-chemical method with titanium(IV) ethoxide as the Ti source. Advanced structural investigations confirmed the successful formation of a core@shell structure with negligible cation mixing (Li+/Ni2+) at the NMC622 surface, contributing to enhanced electrochemical performance. Subsequently, carbon-based anode materials were produced from biomass, specifically figure seeds, and subjected to high-temperature heat treatment. The resulting powders exhibited dominant graphitic properties, evidenced by a Raman I D/I G ratio of 0.5. Electrochemical evaluations of both electrode materials were conducted using half-cell configurations. The optimization of the TiO2 coating process was assessed through half-cell performance metrics and diffusion rates calculated from galvanostatic intermittent titration technique (GITT) experiments. The final phase focused on full-cell design, employing a prelithiation strategy for anodes using a direct contact technique. Optimization of the prelithiation process led to the assembly of full cells combining NMC622/prelithiated figure-seed anodes and NMC622@TiO2/prelithiated figure-seed anodes. The results revealed that TiO2-coated NMC622, paired with prelithiated carbon anodes derived from figure seeds, delivered superior performance compared to uncoated NMC622 full cells. This study underscores the potential of biomass-derived carbon anodes and TiO2 coatings in enhancing the efficiency and performance of LIBs.
  • Küçük Resim Yok
    Öğe
    High-Performance Ag-Doped Na0.67MnO2 Cathode: Operando XRD Study and Full-Cell Performance Analysis with Presodiated Anode
    (Amer Chemical Soc, 2023) Kalyoncuoglu, Burcu; Ozgul, Metin; Altundag, Sebahat; Altin, Emine; Moeez, Iqra; Chung, Kyung Yoon; Arshad, Muhammad
    The key challenges of Na-ion batteries are to design structurally stable electrodes and reach high-enough capacities with full-cells. In this study, we report the positive effects of Ag substitution/addition to Na0.67MnO2. We determined that some of the intended Ag was incorporated into the structure, while the rest remained in metallic form. Ag substitution/addition increases the capacity (208 mA h/g at C/3 rate) and improves the cycle life of Na0.67MnO2 (42% capacity fade with 100 cycles) in half-cells. We attribute these results to an enlarged interlayer spacing due to the large ionic radius of Ag, a suppressed Jahn-Teller effect due to the reduced number of Mn3+ ions, and an increased electrical conductivity due to the presence of metallic Ag. We also produced full-cells with an electrochemically presodiated hard carbon anode. We reached a very high initial capacity of 190 mA h/g at the C/3 rate, showing that Ag substituted/added Na0.67MnO2 is a promising candidate for commercialization of Na-ion batteries.
  • Küçük Resim Yok
    Öğe
    Interface-Engineered P2-Type Cathode and Biomass-Derived Anode for Stable Sodium-Ion Full Cells
    (Wiley-V C H Verlag Gmbh, 2025) Dogan, Ebru; Moeez, Iqra; Chung, Kyung Yoon; Whba, Rawdah; Altin, Emine; Harfouche, Messaoud; Karta, Mesut
    This work presents a sustainable and high-performance sodium-ion full-cell architecture by combining a core@shell Na0.67Mn0.5Fe0.5O2@Al2O3 cathode with a hard carbon anode derived from cherry seed biowaste. The P2-type cathode material is synthesized via a conventional solid-state method and coated with Al2O3 using a scalable wet-chemical route. Structural and surface analyses confirmed the formation of a uniform Al2O3 shell, which enhanced the cathode's electrochemical stability by mitigating Mn3(+)-induced distortion and suppressing electrolyte side reactions. In parallel, the hard carbon anode is produced from cherry seeds-a low-cost and abundant byproduct-through high-temperature pyrolysis, delivering high capacity and excellent cycling performance. Electrochemical evaluation of both electrodes in half-cell and full-cell configurations revealed favorable sodium-ion diffusion, robust structural integrity, and improved interfacial properties. The half-cell, assembled with Na0.67Mn0.5Fe0.5O2@Al2O3 cathode, demonstrated remarkable cycling stability and rate capability within a practical 1.5-3.5 V window, retaining 94.5% capacity after 100 cycles. In situ XRD studies further elucidated the phase transitions and stability of the cathode during cycling. This study demonstrates a sustainable and scalable pathway for sodium-ion battery development by integrating surface-engineered cathodes and biomass-derived anodes.
  • Küçük Resim Yok
    Öğe
    Optimized performance of Na0.67Mn0.5Fe0.5O2@TiO2 and presodiated hard carbon (Pre-SHC) full-cells using direct contact method
    (Elsevier, 2025) Dogan, Ebru; Whba, Rawdah; Altin, Emine; Moeez, Iqra; Chung, Kyung Yoon; Stoyanova, Radostina; Koleva, Violeta
    We report the synthesis and electrochemical performance of an optimized core-shell structure composed of P2type Na0.67Mn0.5Fe0.5O2 coated with TiO2. The structural properties are characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM), which confirm the successful formation of the core-shell structure. Electrochemical performance is evaluated through tests on halfcells and full-cells. Na0.67Mn0.5Fe0.5O2@TiO2 as cathode and sodium metal as anode are used in half-cells, while in full-cells, presodiated hard carbon (Pre-SHC) anodes are prepared via a direct-contact method. Cyclic voltammetry (CV) tests show similar redox behavior for uncoated and TiO2-coated Na0.67Mn0.5Fe0.5O2. Galvanostatic cycling tests are performed using two different voltage windows of 1.5-3.5 V and 1.5-4.3 V and capacity retention values are compared. Performance analysis of the full-cells reveals the best conditions for the presodiation process for the hard carbon (HC) anode. The first charge and discharge capacity values are used to determine the optimized presodiation conditions. Long-term cycling tests for both uncoated and TiO2-coated Na0.67Mn0.5Fe0.5O2 cathodes show significantly improved capacity retention and stability for the Na0.67Mn.0.5Fe0.5O2 @TiO2 cathode over 500 cycles at 0.5 and 1.0C rates. This study highlights the effectiveness of the TiO2 coating in enhancing the electrochemical performance and stability of Na0.67Mn0.5Fe0.5O2 cathode material.
  • Küçük Resim Yok
    Öğe
    Revealing the Role of Ruthenium on the Performance of P2-Type Na0.67Mn1-xRuxO2 Cathodes for Na-Ion Full-Cells
    (Wiley-V C H Verlag Gmbh, 2024) Altin, Emine; Moeez, Iqra; Kwon, Eunji; Bhatti, Ali Hussain Umar; Yu, Seungho; Chung, Kyung Yoon; Arshad, Muhammad
    Herein, P2-type layered manganese and ruthenium oxide is synthesized as an outstanding intercalation cathode material for high-energy density Na-ion batteries (NIBs). P2-type sodium deficient transition metal oxide structure, Na0.67Mn1-xRuxO2 cathodes where x varied between 0.05 and 0.5 are fabricated. The partially substituted main phase where x = 0.4 exhibits the best electrochemical performance with a discharge capacity of approximate to 170 mAh g(-1). The in situ X-ray Absorption Spectroscopy (XAS) and time-resolved X-ray Diffraction (TR-XRD) measurements are performed to elucidate the neighborhood of the local structure and lattice parameters during cycling. X-ray photoelectron spectroscopy (XPS) revealed the oxygen-rich structure when Ru is introduced. Density of States (DOS) calculations revealed the Fermi-Level bandgap increases when Ru is doped, which enhances the electronic conductivity of the cathode. Furthermore, magnetization calculations revealed the presence of stronger Ru & horbar;O bonds and the stabilizing effect of Ru-doping on MnO6 octahedra. The results of Time-of-flight secondary-ion mass spectroscopy (TOF-SIMS) revealed that the Ru-doped sample has more sodium and oxygenated-based species on the surface, while the inner layers mainly contain Ru-O and Mn-O species. The full cell study demonstrated the outstanding capacity retention where the cell maintained 70% of its initial capacity at 1 C-rate after 500 cycles.
  • Küçük Resim Yok
    Öğe
    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.