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    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.
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    High-performance Na-ion full-cells with P2-type Na0.67Mn0.5-xNixFe0.43Al0.07O2 cathodes: Cost analysis for stationary battery storage systems
    (Elsevier, 2024) Kalyoncuoglu, Burcu; Ozgul, Metin; Altundag, Sebahat; Bulut, Fatih; Oz, Erdinc; Sahinbay, Sevda; Altin, Serdar
    Na -ion batteries are viable alternatives to Li-ion batteries especially for stationary applications. Developing suitable electrode materials, half-cell and full-cell studies and cost analysis are major steps and challenges for their commercialization. In this study, we report the synthesis of a promising cathode material, Na0.67Mn0.5- xNixFe0.43Al0.07O2 (x = 0.02-0.10 with Delta x = 0.02), using a modified solid-state synthesis technique. The materials were heated at high temperature for 6 h in air and quenched in liquid N-2. We determined the solubility limit of Ni in Na0.67Mn0.5Fe0.43Al0.07O2 as x <= 0.06. The interlayer separation increases with increasing Ni content due to the ionic radii difference between Mn and Ni. X-ray photoelectron spectroscopy (XPS) measurements evidence the valance state of Ni in the x = 0.06 sample as 2+ and 3+. Cyclic voltammetry (CV) analysis of the half-cells were performed at 10 C-degrees, room temperature, and 50 degrees C to observe the effect of environmental temperature on redox mechanism. The highest half-cell capacity of the cells was determined as 181 mAh/g for x = 0.06 at C/3-rate. Artificial solid electrolyte interface (SEI) formation was performed on the hard carbon anode by presodiation technique and the full-cells of Na0.67Mn0.44Ni0.06- Fe0.43Al0.07O2/hard carbon were assembled in CR2032 coin cells. The capacity values of the cells at C/2, C, and 2C-rate were determined as 131.4 mAh/g, 116 mAh/g and 100.8 mAh/g for the 1 cycle and 33 mAh/g, 40.6 mAh/g and 49.9 mAh/g for the 500th cycle, respectively. The cost analysis for the commercial package for stationary energy storage system was performed by BatPac program and results are discussed.
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    Unveiling the outstanding full-cell performance of P2-type Na0.67(Mn0.44Ni0.06Fe0.43Ti0.07)O2 cathode active material for Na-ion batteries
    (Elsevier, 2024) Kalyoncuoglu, Burcu; Ozgul, Metin; Altundag, Sebahat; Harfouche, Messaoud; Oz, Erdinc; Avci, Sevda; Ji, Xiaobo
    In this study, we unravel the effect of Ni doping on the half-cell and full-cell performances of the Na0.67Mn0.5-xNixFe0.43Ti0.07O2 cathode materials where x varies between 0.02 and 0.1. The cyclic voltammetry (CV) analysis of the half-cells is performed at 10 degrees C, room temperature (RT), and 50 degrees C to elucidate the redox reaction mechanisms at different temperatures. Among the studied cathodes, the highest specific capacity is obtained fox = 0.06 which delivered a specific capacity of 186 mAh g-1 at C/3-rate. The full cell of Na0.67Mn0.44Ni0.06-Fe0.43Ti0.07O2/hard carbon couple is assembled in coin cell format and the specific capacity of the cell at C/2, 1C, and 2C rates are found as 153 mAh g- 1, 125 mAh g-1 and 120 mAh g-1, respectively. At the C/2-rate, the excellent capacity retention of the full cell is around 70% after 500 cycles delivering a specific capacity of 103 mAh g- 1. Along with the conventional physicochemical characterization methods such as X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Raman and Fourier-transform Infrared Spectroscopies (FTIR), we also utilize X-ray photoelectron spectroscopy (XPS) to bridge the nexus between the performance and the structure properties of the studied materials. Furthermore, we also employ synchrotron-based X-ray Absorption (XAS) to understand the local geometry of the optimized cathode materials in operando.