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Öğe Cobalt-substituted P2-Na0.67MnO2 and purple basil-derived hard carbon for high-performance sodium-ion battery full cells: insight to ex situ structural analysis(Springer Heidelberg, 2025) Whba, Rawdah; Dogan, Ebru; Altin, Emine; Benzaid, Abdelali; Arshad, Muhammad; Altin, SerdarThis study explores two energy storage materials: cobalt-doped P2-type Na0.67MnO2 (Na0.67Mn0.9Co0.1O2, NMCO) and hard carbon derived from purple basil (Ocimum basilicum L., HC-based PB) biomass. NMCO was synthesized via a solid-state method involving high-temperature quenching in liquid nitrogen (LN2). Analytical techniques confirmed a pure P2-type layered structure with reduced lattice volume due to Co3+ substitution. FTIR identified Na-O, Mn-O, and Co-O bonds, while XPS revealed reduced Mn3+ content, enhancing structural stability by mitigating the Jahn-Teller effect. Electrochemical tests of NMCO showed charge/discharge capacities of 184 mAhg(-1) and 185 mAhg(-1) with a coulombic efficiency of 99.5%. HC-based PB, exhibiting disordered graphitic structures, demonstrated higher charge and discharge capacities of 231 and 349 mAhg(-)(1), respectively, despite a relatively low efficiency of 66%. Long-term cycling demonstrated capacity fading for both materials after 100 cycles. Ex situ XRD confirmed NMCO's structural integrity, while HC's amorphous structure contributed to its stability. These findings provide valuable insights into these materials' electrochemical performance and durability for energy storage applications.Öğe 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, SumeyyeThis 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.Öğe Cost-effective sodium-ion batteries using a Na0.67Mn0.9Ni0.1O2 cathode and lavender-flower-waste-derived hard carbon with a comparative presodiation approach(Elsevier, 2026) Dogan, Ebru; Moeez, Iqra; Whba, Rawdah; Ozcan, Sibel; Akkoc, Mitat; Altin, Emine; Harfouche, MessaoudThe development of cost-effective, high-performance sodium-ion batteries (SIBs) is essential for large-scale energy storage systems. In this study, low-cost SIBs are fabricated using P2-type Na0.67Mn0.9Ni0.1O2 as the cathode and hard carbon (HC) derived from lavender flower waste as the anode. The synthesis of both electrode materials from widely accessible precursors ensures scalability and environmental sustainability. To address the sodium deficiency of HC, three different presodiation strategies-electrochemical, chemical, and direct contact-are systematically investigated, and the electrochemical performances of the full cells are compared. This evaluation reveals significant variations in the initial capacity, capacity retention, Coulombic efficiency, and rate performance. Although the direct-contact method delivers the highest initial capacity, electrochemical presodiation delivers superior long-term cycling stability and enhanced energy density. This comprehensive comparison of the electrochemical performance emphasizes the vital role of presodiation in enhancing the full-cell efficiency, while highlighting the potential methods for developing cost-effective and sustainable SIBs.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, EmineIn 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.Öğe 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, EmineThe 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.Öğe Influence of precursor selection on the structural integrity and electrochemical performance of α-NaMnO2 cathode(Wiley, 2025) Dogan, Ebru; Whba, Rawdah; Canbay, Canan Aksu; Arshad, Muhammad; Sahinbay, Sevda; Altin, SerdarIn this study, the alpha-NaMnO2 phase was successfully synthesized using three different combinations of starting materials: Na2O2/Mn2O3, Na2O2/MnO2, and Na2CO3/Mn2O3. A one-step heat treatment at 900 degrees C for 5 h under air with quenching was applied. X-ray diffraction analysis confirmed the formation of pure alpha-NaMnO2 phase in all three samples, with only slight variations in lattice parameters. Elemental and oxidation state analyses were conducted using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy with energy-dispersive X-ray spectroscopy, and inductively coupled plasma measurements. XPS results revealed noticeable differences in Mn ion valence states, suggesting variations in oxygen stoichiometry and the presence of oxygen-excess structures. Electrochemical evaluations were performed in both half-cell and full-cell configurations. The samples exhibited distinct performance characteristics, with capacity fade over 100 cycles at C/3 between 1.5 and 4.3 V measured at 83.6%, 73.9%, and 83.1%, respectively. These differences correlated with the average oxidation state of Mn and O content. Full-cells, paired with presodiated commercial hard carbon anodes, showed the highest capacity for the Na2O2/MnO2 system and the best retention for the Na2CO3/Mn2O3 sample. Overall, this work demonstrates how even small variations in starting materials can significantly influence the structural and electrochemical behavior of alpha-NaMnO2.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, MesutThis 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.Öğe Interfacial Evaluation in ZnO-Coated NaxMn0.5Fe0.5O2 Cathodes and Hard Carbon Anodes Induced by Sodium Azide: Operando EIS and Structural Insights(Wiley-V C H Verlag Gmbh, 2025) Whba, Rawdah; Dogan, Ebru; Duygulu, Ozgur; Alanazi, Abdullah K.; Arshad, Muhammad; Stoyanova, Radostina; Koleva, VioletaThis article explores the synthesis and electrochemical properties of NaxMn0.5Fe0.5O2 powders, prepared via a conventional solid-state reaction. Subsequently, the powders are functionalized with a ZnO protective coating through a wet-chemical approach employing zinc acetate in ethanol. Structural characterization confirmed that the ZnO layer maintained the P2-type (P6 3 /mmc) structure, while energy-dispersive X-ray spectrometry mapping verified the successful coating. Electrochemical analyses, including electrochemical impedance spectroscopy (EIS) and cyclic voltammetry, revealed that although the redox reaction mechanism remained unchanged, the charge-transfer resistance (R ct) depended on the coating thickness. ZnO-coated NMFO electrodes exhibited initial discharge capacities of 159.3, 153.6, and 124.8 mAh g- 1 with respective capacity retentions of 48.9%, 41.9%, and 52.0% after 100 cycles for ZnO contents of 0.2, 0.4, and 0.6 wt.%. The galvanostatic intermittent titration technique results indicated that the diffusion coefficients varied with the coating conditions. Operando EIS from 1.5 to 4.3 V showed stable bulk resistance (R b) but voltage-dependent variations in solid electrolyte interface resistance (R SEI) and R ct. Additionally, sodium azide is used to presodiate the hard carbon (HC) anode to enhance the full-cell performance. The ZnO-coated cathode paired with NaN3 presodiated HC delivered a capacity of over 120 mAh g- 1 at C/10. Ex situ analysis after 500 cycles confirmed structural stability, demonstrating that ZnO coating and NaN3 presodiation collectively improve sodium-ion battery performance.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, VioletaWe 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.Öğe 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, SerdarThis 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.Öğe Production of high entropy (FeNiMnCrV)3O4 oxide by mechanical alloying process and electrochemical performance analysis for Li-ion cells(Academic Press Inc Elsevier Science, 2024) Dogan, Ebru; Altin, Serdar; Guler, Seval Hale; Guler, Omer; Altin, EmineIn this study, a high entropy oxide material was fabricated from its alloy using mechanical alloying technique in the form of (FeNiMnCrV)(3)O-4 with a symmetry of Fd-3m, and their structural properties were investigated by XRD, SEM-EDS dot mapping, and XPS analyses. The EDS analysis results of oxide and alloy show that Fe, Ni, Mn, Cr, and V have similar ratios for both samples. The elemental ratios were also measured by ICP-MS and the results support the EDS and XPS data. The alloy and oxide powders were used for the production of the anode materials for the half-cell configuration of the battery. The CV analysis of both cells showed that they have similar characteristic redox reactions and the main difference between the two electrodes is the current density values in the peaks. The initial capacity value of the (FeNiMnCrV)(3)O-4 for 10 mA/g was found as 1070 mAh/g for the first cycle which is promising results as an anode material for Li-ion cells.Öğe 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, EmineThe 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.Öğe Sodium-induced phase shift in α-NaMnO2 and electrochemical properties of the full cells using hard carbon anodes derived from regional olive leaves(Springer Japan Kk, 2025) Dogan, Ebru; Ozcan, Sibel; Canbay, Canan Aksu; Karta, Mesut; Depci, Tolga; Altin, SerdarIn this study, we investigated the effect of excess sodium (Na) in a NaMnO2 structure using one-step heat treatment at 900 degrees C followed by quenching in liquid nitrogen (N-2). According to the X-ray diffraction (XRD) analysis, there was a competition between the monoclinic and orthorhombic phases, and we found that there were two monoclinic phases with similar structural properties. Therefore, we focused on revealing the formation of two isostructures of the monoclinic phase triggered by Na ions. We found that the lattice parameters and beta angle changed from 113 degrees to 105 degrees in the samples with increasing Na content. Structural analysis of the powders using the XRD data was conducted using Rietveld refinement, and the phase ratios for all samples were calculated. The sample with x = 1.3 showed a 95% alpha-phase. To understand the formation of the two isostructures, we performed Density functional theory (DFT) calculations to examine their band structure, stability, and formation energy. A structural analysis of the excess Na-doped samples was performed using common techniques, and it was found that excess Na caused the formation of a coating on the grains in the form of sodium oxide. To validate this prediction, we conducted inductively coupled plasma mass spectrometry (ICP-MS), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy coupled with energy dispersive X-ray (SEM-EDX) analyses using the basic properties of these techniques and their interactions with materials. In the second part of the study, we produced HC from locally sourced olive leaves and investigated their structural properties. The electrochemical properties of the electrode materials were examined using a half-cell configuration as electrodes with Na metal and a full-cell configuration using x = 1.3 cathode and HC anode. A direct-contact pre-sodiation strategy was used as the anode in the full-cell measurements. It was found that the full cells had initial capacity values of 150 mAh/g for the voltage range 1.5-4.3 V and 120 mAh/g for the voltage range 1.5-3.5 V.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 NurullahThis 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.Öğe The ion-exchange study by LiMn2O4 for Na-ion cathodes: an investigation of structural and electrochemical performance(Springer, 2025) Dogan, Ebru; Arshad, Muhammad; Altin, Emine; Altundag, Sebahat; Altin, SerdarThe sodium manganese oxide phase was synthesized by an ion-exchange process in the glovebox using LiMn2O4 electrodes. For this process, LiMn2O4 cathodes were discharged at specific voltage values that correspond to the redox reaction values in cycling voltammetry measurements and then the cell was disassembled, and the cathode was used for Na-ion cell by Na metal. The newly assembled cell was discharged to 1.5 V for the ion-exchange process. To understand the mechanism during the ion-exchange process, the cells were disassembled in each redox voltage during the charging and discharging of the cell for structural analysis. The XRD patterns of each electrode were analyzed by Rietveld refinement and the possible reaction mechanism for the ion-exchange process was investigated. It was found that there are lambda-MnO2, Li2MnO3, and NaMn2O4 phases in the electrodes which formed at different cut of voltages. According to Fourier Transform Infrared Spectroscopy measurements, the presence of Na-O bands was confirmed the successful ion-exchange within the materials. Structural properties were further examined using Scanning Electron Microscopy combined with Energy Dispersive X-ray analysis dot mapping and X-ray photoelectron spectroscopy analysis, supported by X-ray diffraction experimental results. The electrochemical performance of the ion-exchanged electrodes was investigated by cyclic voltammetry, electrochemical impedance spectroscopy, galvanostatic cycling, and C-rate measurements. The results showed that there was a significant change in the redox reaction mechanism by the ion-exchange process. According to galvanostatic measurements, the ion-exchanged electrodes showed better performance up to 50 cycles, but a phase change in the electrodes during the cycling caused a sharp decrease in capacity. Ex-situ XRD analysis after 100 cycles revealed the formation of the Na2Mn3O7 phase which is electrochemically inactive, and it has Mn4+ ions in the structure. The results suggest that the ion-exchange mechanism is a successful method, but the crystal structure has a crucial role in the cycling process of the cells.
