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    Long-life (Co, Al, Mg)-doped LiMn1.5Ni0.5O4 cathodes prepared by co-precipitation method
    (Springer Science and Business Media Deutschland GmbH, 2024) Kunduracı, Muharrem; Boyacı, Hilmi; Görmez, Özkan; Çağlayan, Uğur; Çirmi, Doğan; Özkendir, Osman Murat; Harfouche, Messaoud; Gözmen, Belgin
    The spinel cathode LiMn1.5Ni0.5O4 (LMN) is garnering significant interest in the realm of lithium-ion batteries owing to its economical nature, elevated operating voltage, high theoretical energy density, and commendable thermal stability at a charged state. Various doping elements have been suggested to enhance the discharge capacity and prolong the lifetime of the LMN cathode. In this study, three doping elements (cobalt, aluminum, and magnesium) are investigated and compared using different characterization techniques. All three elements proved to be effective in extending the cycle life. Among all three elements, cobalt exhibits the highest threshold for dopant concentration beyond which performance degradation initiates. The cathode material with the highest performance, LiMn1.5Ni0.4Co0.1O4, is projected to have a cycle life of 900 cycles, contrasting with the 500 cycles of the undoped sample.
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    Significance of surface roughness in the supercapacitor activity of nickel-based electrodes
    (Springer, 2021) Kunduracı, Muharrem; Çirmi, Doğan; Doğan Çalhan, Selda; Çağlayan, Uğur
    Nickel-based thin film electrodes were electrodeposited onto copper substrate using a deep eutectic solvent. The supercapacitor performance of these electrodes in alkaline KOH solution was greatly enhanced by altering surface roughness of coatings. In order to create a rougher surface, two paths were followed. In the first path, Ni-only coatings were prepared at different deposition potentials and smooth-to-rough transition in surface morphology took place at higher potentials due to increasing emission of hydrogen bubbles. In the second path, Ni-Zn binary coatings with varying zinc concentration were electrodeposited and surface roughness was formed by dealloying zinc element from the electrodes as corroborated by Scanning Electron Microscopy and Atomic Force Microscopy results. In both paths, noticeable improvements in the capacitance of nickel electrodes were observed upon the apperance of rougher surface. A linear relationship was discovered between cathodic peak currents and polarization values in the cyclic voltammetry scans of electrodes, possibly for the first time here in literature. The increase in polarization was explained by the decrease in electrode conductivity proved by dwindling of metallic nickel peaks in X-ray diffraction upon electrochemical testing.