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Boron-doped porous carbon material derived from ZIF-11: Investigation of cotton fabric supercapacitor and Li-ion battery performances
(Wiley, 2022) Bugday, Nesrin; Altin, Serdar; Bulut, Fatih; Altin, Emine; Yasar, Sedat
Nitrogen-doped porous carbon (NPC@ZIF-11) and boron-NPC (BNPC@ZIF-11) materials were synthesized by pyrolysis methods, and structural characterization of the compounds was carried out by scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, Brunauer-Elmet-Teller technique, Raman spectroscopy, and inductively coupled plasma-mass spectrometry techniques. The ZIF-11 was converted to the NPC@ZIF11 by pyrolysis. BNPC@ZIF-11 was fabricated from NPC@ZIF-11 by pyrolysis in the presence of phenylboronic acid. The fabric supercapacitor, sandwich-type supercapacitor, and Li-ion battery performances of NPC@ZIF-11 and BNPC@ZIF-11 were investigated. The capacity of the Li-ion cell was found as 720 mAh g(-1) for the first cycle, and it was decreased to 250 mAh g(-1) after 100 cycles. The capacitance values of the cylindrical devices were 92 F g(-1) and 115.6 F g(-1), for C1 and C4000 in KOH electrolytes. The BNPC@ZIF-11 was used as an electrode material on cotton fabric, and the highest obtained capacitance was 72.8 mF for 0.1 mA, which is a promising result for wearable energy storage materials.
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, Serdar
This 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.
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, Messaoud
The 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.
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.
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.
High-performance electrodes for Li-ion cell: Heteroatom-doped porous carbon/CoS structure and investigation of their structural and electrochemical properties
(Wiley, 2022) Bugday, Nesrin; Altin, Emine; Altin, Serdar; Yasar, Sedat
As an essential class of anode materials, the synthesis and characterization of CoS@ZIF-12-C composite anode materials are reported. The two-step synthesis of CoS nanoparticles embedded in N-doped porous carbon by using a metal-organic framework (MOF) as the template. After structural characterization of CoS@ZIF-12-C composite materials, the main phase was found as CoS with symmetry of P63mmc. Benefiting from the CoS embedded in porous carbon structure, the half Li-ion battery cell tests of CoS@ZIF-12-C composite materials were performed by a 2-electrode method using CR2032 cells, and the capacities of the cells were measured for 200 cycles using 300 mAg(-1) and 500 cycles using 1000 mAg(-1). The first discharge capacities of the cells for 1000 mAg(-1) were found as 458, 1178, and 815 mAhg(-1) for CoS@ZIF-12-C-T, T = 700, 800, and 900 degrees C, respectively. An unexpected capacity increase was observed for the CoS@ZIF-12-C-700 and CoS@ZIF-12-C-900 half cells during the cycling. Ex-situ x-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and cyclic voltammetry (CV) analysis were performed after cycling of the cells for explanations of the capacity increase. Ex-situ XRD analysis of these cells showed phase transitions from crystalline to amorphous type structure, and ex-situ FTIR proves the preservation of the CoS phase during the cycling. A redox reaction mechanism was suggested to explain the cells' battery performance by ex-situ XRD analysis.
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.
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.
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.
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.
Investigation of electrochemical performance of Na-ion batteries by hard carbon anodes produced by biomass of Prunusarmeniaca seeds
(Springer, 2023) Oktay, Zeynep Melek; Onal, Yunus; Depci, Tolga; Altundag, Sebahat; Altin, Serdar; Yasar, Sedat; Altin, Emine
Hard carbon is successfully fabricated using biomass of Prunusarmeniaca seed shells, and its structural properties are examined by different spectroscopic techniques. For using as an anode electrode in Na-ion batteries, the material is subjected to further pyrolysis at varying temperatures for achieving the necessary levels of conductivity and surface area which are important features for electrode materials. Distinguish properties of the hard carbon in the XRD study appeared as broad peaks at 2 & theta; = 23 & DEG; and 43 & DEG;. The purity of produced hard carbons was approved by EDX to analyze that the purity of hard carbon is greater than 99.9%, making it suitable for industrial use. It was found that the CV curves of the cells created in this work utilizing hard carbon were quite comparable to the CV curves of commercially produced hard carbon cells. According to charge/discharge cycling measurements for constant current at rt, the highest capacity of 210.2 mAh/g using 0.1 A/g is obtained for the material pyrolyzed at 1200 & DEG;C and the capacity fade was found as 0.11. From these promising results, it is thought that the produced hard carbon can be easily used in the production of anode electrodes in commercial Na-ion batteries and technological applications. So it is summarized that P. armeniaca seed shells is one of the main sources for the production of the hard carbon and it can be used as an anode materials in battery cells.
Investigation of structural and electrochemical performance of Ru-substituted LiFePO4 cathode material: an improvement of the capacity and rate performance
(Springer, 2022) Yolun, Abdurrahman; Altin, Emine; Altundag, Sebahat; Arshad, Muhammad; Abbas, Syed Mustansar; Altin, Serdar
LiRuxFe1-xPO4 (where x = 0.01-0.12) samples are successfully fabricated by conventional solid-state reaction technique and the structural properties are analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and fourier transform infrared spectroscopy (FTIR) measurements. The XRD analysis shows that the minor impurity phases of RuO2 and LiRuO2 are observed for x >= 0.05 samples. Furthermore, the lattice volume is decreased with increasing Ru-content in the structure. The Ru-substituted battery cells exhibit similar cycling voltammetry (CV) data with the unsubstituted LiFePO4 battery cells. According to the charging/discharging cycles measurements for C/3-rate, the best capacity (147.58 mAh g(-1)) is obtained for LiFe0.93Ru0.07PO4 with a capacity fade of 0.0084 per cycle. It is found that Ru-substituted LiFePO4 has maximum C-rate when we analogize with the pristine LiFePO4 and the battery cycling performance is investigated for 4 C-rate up to 100 cycles and 3 and 4 C-rate up to 1000 cycles and it is found that Ru-substituted LiFePO4 exhibits excellent electrochemical performance such as 122, 84.5, and 53.1 mAh g(-1) for 1st, 500th, and 1000th cycles at 4 C-rate.
Investigation of Ti-substitution effects on structural and electrochemical properties of Na0.67Mn0.5Fe0.5O2batterycells
(Wiley-Hindawi, 2020) Altin, Serdar; Altundag, Sebahat; Altin, Emine; Oz, Erdinc; Harfouche, Messaoud; Bayri, Ali
Ti-substituted Na(0.67)Mn(0.5)Fe(0.5)O(2)powders were fabricated by quenching at high temperatures, and the structural properties were investigated by Fourier transform infrared (FTIR), Scanning Electron Microscope (SEM), X-ray powder diffraction (XRD), and X-ray absorption spectroscopy (XAS) measurements. According to XRD analysis, it was not observed any impurity phases and it was found that the lattice constants of the powders were slightly increased by Ti content. The change in the valence state of both Mn and Fe ions was investigated by X-ray absorption near edge structure (XANES), and it was found that Ti-substitution caused a decrease in the valance state of Fe in Na0.67Mn0.5Fe0.5O2. Fourier transform (FT) of XANES showed that the local structure around the metal ions changed with the addition of Ti ions. The cycling voltammetry (CV) graphs of Ti-substituted cells were almost the same as the pure sample, which may not change the cycling mechanism in the cells. According to galvanostatic cycling measurements at room temperature, the best performance was obtained with Ti-substitution of 0.06 to 0.09 in the structure. The effect of environmental temperature in the battery cells was investigated at 10 degrees C to 50 degrees C, and it was found that the battery performance depends on the environmental temperatures.
Investigations of the capacity fading mechanism of Na0.44MnO2via ex situ XAS and magnetization measurements
(Royal Soc Chemistry, 2018) Altin, Serdar; Oz, Erdinc; Altin, Emine; Demirel, Serkan; Bayri, Ali; Avci, Sevda
Na-ion batteries represent a promising complementary alternative to Li-ion batteries due to their high energy density and natural abundancy of Na. However, these batteries have short cycle life and extensive research activities on these batteries are required to understand the mechanism of such drawbacks. In this report, we investigate the capacity fading mechanism of Na(0.44)MnO(2)via ex situ X-ray diffraction, X-ray absorption spectroscopy, Fourier transform infrared spectroscopy and magnetization measurements. Our results show that the unit cell volume, the effective mass of Mn-O bonds, the number of Mn4+ ions and the effective magnetic moment decrease upon repeated cycling. We propose that some Mn4+ ions in the octahedral environment become Mn3+ ions in a square pyramidal environment, causing oxygen release upon cycling. Any free oxygen in the battery is expected to react with the electrolyte and cause capacity fade.
Magnetic and thermoelectric properties of B-substituted NaCoO2
(Springer Heidelberg, 2015) Altin, Emine; Oz, Erdinc; Demirel, Serkan; Bayri, Ali
We report the structural, electrical, thermal and magnetic properties of NaCo1-xBxO2 from 300 K down to 5 K. XRD analysis shows that B ions successfully incorporate in the crystal structure for x < 0.25. The resistivity of the samples increases with increasing B content and the transport mechanism change for x = 0.5. The highest thermopower value is obtained for x = 0.5 sample, and the thermoelectric behavior at low temperature is explained by Mott approximation. The experimentally obtained thermal conductivity data are analyzed by this model including the carrier thermal term, kappa(c), and the lattice thermal conductivity term, kappa(L). We found that phonon-phonon interaction and point defect contribution to kappa are affected by the B content and the temperature. The Co valance states are analyzed by Heike formula, and the effective magnetic moment is determined by these values. The chi-T curves of the samples are fitted by Curie-Weiss law, and the obtained mu(eff) values match well with the theoretically calculated values (0.9 mu(B)/Co). We observed a strong correlation between magnetic properties and thermopower.
Magnetic Properties and Environmental Temperature Effects on Battery Performance of Na0.67Mn0.5Fe0.5O2
(Wiley-V C H Verlag Gmbh, 2021) Altin, Serdar; Bayri, Ali; Altin, Emine; Oz, Erdinc; Yasar, Sedat; Altundag, Sebahat; Harfouche, Messaoud
Herein, a modified solid state synthesis of Na0.67Mn0.5Fe0.5O2 and the results of a detailed investigation of the structural and magnetic properties via Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) analysis are reported. The magnetic properties of Na0.67Mn0.5Fe0.5O2 do not fit the Curie-Weiss law and a model regarding the spin configuration of the Mn and Fe ions and a possible ferrimagnetic order is suggested. Electrochemical measurements and ex situ structural analysis of the cathode material confirm the reversible structural transitions for the cells charged up to 4.0 V. Environmental temperature-dependent electrochemical measurements reveal a strong temperature dependence of both, the initial capacity and the capacity retention. Ex situ SEM, FTIR, and XRD studies on the battery membrane verify the formation of a Na2CO3 phase on the membrane, which blocks the Na ion diffusion through membrane pores and is responsible for the capacity fade for this compound.
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.
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, Serdar
This 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.
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, Emine
In 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.
Production of Pb-doped LiFePO4 and analysis of their electrochemical performance
(Springer, 2023) Gultek, Ezgi; Altundag, Sebahat; Altin, Serdar; Altin, Emine
In this study, LiFe1-xPbxPO4 (x = 0-0.12) powders were successfully produced by solid-state technique. The XRD patterns of the samples exhibit that the main phase is LiFePO4 with minor impurity phases of PbO and Fe2O3 in the structure, in which the phase ratio of PbO increases with increasing doping content. Four probe electrical resistance measurements showed that resistance decreases from 111 kO to 37 kO when increasing Pb-content; however, CV measurement indicated that redox peak wideness increased for x = 0.09, unwanted behavior for the battery cells. The galvanostatic cycles at C/2-rate yielded the highest capacity value of 121.6 mAh/g at room conditions with 1.06% capacity fade over 100 cycles when using x = 0 0.06 sample-better than undoped cells-while C-rate tests confirmed promising results for LiFePO4 cells using same sample concentration level.

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