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    Copper-Induced Phase Transitions in NaMn1-xCuxO2: Structural Insights from Operando XAS, DFT Calculations, and Electrochemical Evaluation Using Laurus Nobilis-Derived Hard Carbon
    (Wiley-V C H Verlag Gmbh, 2026) Whba, Rawdah; Dogan, Ebru; Harfouche, Messaoud; Ozturk, Zeynep Reyhan; Farhan, Ahlam; Ipek, Semran; Corut, Sumeyye
    This study investigates the effect of Cu2+ doping on NaMn1- xCuxO2 layered cathodes. It also explores their integration with Laurus nobilis-derived hard carbon (HC) anodes for sodium-ion batteries (SIBs). Cu doping, particularly at x = 0.20, stabilizes the beta-NaMnO2 phase, suppresses Jahn-Teller distortions, and improves the structural stability of the MnO2 framework. In situ X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations confirm that Cu improved Na+ diffusion kinetics and reduces charge-transfer resistance, despite its electrochemical inactivity. X-ray Difraction (XRD), Raman, and Fourier transform infrared spectroscopy (FTIR) analyses reveal phase destabilization and segregation at higher Cu concentrations, while XPS indicates shifts in the Mn/Cu oxidation states, consistent with improved electronic conductivity and multivalent redox behavior. The scanning electron microscope (SEM and transmission electron microscopy (TEM) images demonstrate Cu-induced morphological transitions toward denser, more crystalline structures. Brunauer-Emmett-Teller (BET) measurements reveal that the L. nobilis-derived hard carbon (HC) anode possesses a high surface area and hierarchical porosity, which facilitated efficient Na + storage and rapid ion transport. Full-cell tests demonstrate high reversible capacity (approximate to 126 mAh g-1), excellent rate capability, and 56% capacity retention over 250 cycles. This work demonstrates that Cu doping and porous HC anodes synergistically enhance the structural and electrochemical performance of SIBs, thereby providing a sustainable strategy for advanced energy storage.
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    Influence of iron doping on α-NaMnO2 lattice symmetry: Insight from operando X-ray absorption, ex-situ structural analysis, and electrochemical performance using chestnut shell-derived hard carbon
    (Elsevier, 2026) Dogan, Ebru; Maiga, Abdulhadi; Whba, Rawdah; Harfouche, Messaoud; Ozturk, Zeynep Reyhan; Farhan, Ahlam; Altin, Emine
    The structural instability and moderate electrochemical performance of NaMnO2 cathodes limit the use of sodium-ion batteries (SIBs). This limitation is primarily due to lattice distortions and valence variations that occur during the cycling process. To address this limitation, NaMn(1-x)FexO(2) (0.00 <= x <= 0.50) powders were synthesized using a conventional solid-state method. Their structural and electrochemical properties were systematically investigated through a combination of structural characterization, in situ X-ray absorption spectroscopy, and computational modeling. X-ray diffraction and Rietveld refinement reveal a contraction of the beta-angle from 112 degrees to 105 degrees, indicative of a phase transition from alpha to alpha', with the x = 0.5 composition stabilizing as a single-phase alpha' structure. Fe incorporation reduces the average Mn valence from 3.23+ to 3.18+, thereby enhancing structural stability, as corroborated by electron diffraction and density functional theory (DFT) calculations. At the same time, hard carbon (HC) derived from chestnut shells was developed as a sustainable anode material, exhibiting a disordered framework favorable for Na+ storage. Electrochemical evaluation demonstrates that the x = 0.5 cathode delivers an initial half-cell capacity of 130.2 mAh/g, which declines to 77.1 mAh/g upon cycling. In contrast, the optimized electrode configuration affords improved stability. The HC anode attains a high reversible capacity of 317.3 mAh/g. Full-cell assemblies incorporating pre-sodiated HC anodes exhibit promising performance, underscoring the potential of this dual-material approach for developing high-performance, sustainable SIBs.