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    Öğe
    Assessment on the stable and high capacity Na-Se batteries with carbonate electrolytes
    (Wiley, 2022) Erdöl, Zeynep; Ata, Ali; Çakan, Rezan Demir
    Factors affecting proper functioning of Na-Se system are investigated focusing on the polyselenide formation in ether- and carbonate-based electrolytes. To do so, Se cathode is prepared by ball milling with commercial carbon and selenium powders. It is revealed that the soluble polyselenide species form in ether while no signature in carbonates proven by the in-situ cyclic voltammetry and ex-situ ultraviolet-visible spectroscopy measurements as well as monitoring self-discharge behaviours. Different Se discharge mechanism is also highlighted by staircase potentio electrochemical impedance spectroscopy (SPEIS) that is an impedance measurement applied to each potential step. Volume expansion is targeted using different types of binders in which carboxyl methylcellulose-styrene butadiene rubber (CMC-SBR) delivers the highest reversible capacity and the best rate performance resulting from its high adhesion strength. To further improve the performances, fluoroethylene carbonate (FEC) is used as a film forming additive that preserves Na metal integrity proven by the Na-Na symmetric cells and voltage relaxation upon cycling. As a whole, binders and electrolyte compositions are found to be the two crucial factors to obtain stable and high-capacity Na-Se cells. This study underlines that much effort needs to be put on the strategies to overcome volume expansion than that of Se confinement into porous cathode.
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    Öğe
    Sodium-Selenium Batteries with Outstanding Rate Capability by Introducing Cubic Mn2O3 Electrocatalyst
    (Wiley-V C H Verlag Gmbh, 2024) Erdol, Zeynep; Ata, Ali; Demir-Cakan, Rezan
    With their high volumetric capacity and electronic conductivity, sodium-selenium (Na-Se) batteries have attracted attention for advanced battery systems. However, the irreversible deposition of sodium selenide (Na2Se) results in rapid capacity degradation and poor Coulombic efficiency. To address these issues, cubic alpha-Mn2O3 is introduced herein as an electrocatalyst to effectively catalyze Na2Se conversion and improve the utilization of active materials. The results show that the addition of 10 wt% Mn2O3 in the selenium/Ketjen black (Se/KB) composite enhances the conversion from Na2Se to Se by lowering activation energy barrier and leads to fast sodium-ion kinetics and low internal resistance. Consequently, the Mn2O3-based composite delivers a high specific capacity of 635 mAh & sdot; g(-1) at 675 mA & sdot; g(-1) after 250 cycles as well as excellent cycling stability for 800 cycles with a high specific capacity of 317 mAh & sdot; g(-1) even at the high current density of 3375 mA & sdot; g(-1). Due to the cubic Mn2O3 electrocatalyst, the performance of the composites is superior to existing state-of-the-art Na-Se batteries reported in the literature.
  • [ X ]
    Öğe
    Tetraiodo nickel phthalocyanine electrocatalyst enables superior Na-Se battery performances by enhancing the utilization of Na2Se
    (Elsevier, 2023) Erdol, Zeynep; Yuzer, Celil; Kilic, Nazmiye; Ince, Mine; Ata, Ali; Demir-Cakan, Rezan
    Sodium: -Selenium (Na-Se) batteries are regarded as one of the most promising alternative energy storage de-vices compared to their room-temperature sodium-sulfur battery counterparts. Since Selenium cathodes operate well in carbonate-based electrolytes, the solubility issue of polyselenides is no longer an issue. However, the main obstacles of Na-Se batteries remain the precipitation and reoxidation of sodium selenide (Na2Se) owing to the high energy barrier of these reactions and passivation of the electrode during cycling. Herein, we propose a tetraiodo nickel phthalocyanine (NiPc) electrocatalyst to improve the electrochemical performance of Na-Se batteries. It is demonstrated that the presence of even a small amount of NiPc improves the electrocatalytic conversion of Na2Se by lowering the decomposition energy barrier of Na2Se. The improved cell performances are verified by the decrease in reaction polarization, Tafel slope values, and the measured internal resistance of Na-Se cells in addition to the density functional theory (DFT) calculations. Consequently, the Na-Se cell with the NiPc electrocatalyst exhibited outstanding rate capability (405 mAh & BULL;g- 1 after 250 cycles at 3375 mA g-1 and superior long-term cyclic stability (563 mAh & BULL;g- 1 after 250 cycles at 675 mA g-1), which are among the most promising rate performance characteristics demonstrated in the literature.