Yazar "Harfouche, Messaoud" seçeneğine göre listele

Listeleniyor 1 - 6 / 6
  • [ X ]
    Öğe
    Boron activity in the inactive Li2MnO3 cathode material
    (Elsevier, 2019) Ozkendir, O. Murat; Harfouche, Messaoud; Ulfat, Intikhab; Kaya, Cigdem; Celik, Gultekin; Ates, Sule; Aktas, Sevda
    Boron substituted Li2MnO3 cathode materials have frequently been studied and found to be inactive. In this reseach, crystal and electronic properties of the Li-ion cathode material with boron substitution having general formula; Li(2)Mn(1-x)BxO(3) (where x has values of 0.00, 0.05, 0.10, 0.15 and 0.20, respectively) were studied. The study revealed that, with the substitution of boron atoms in the manganese coordinates in the Li2MnO3 cathode materials, boron atoms acted as a landmark for the parent oxides by forming LiBO2 crystal domains. In the studied samples, boron atoms were determined as the key to construct new crystals and to restrict the excess of oxygen in the materials. Beyond the boron coordinations, the manganese atoms formed a cubic LiMn2O4 crystal structure which was reported to have good electrochemical properties. With the formation of the LiMn2O4 crystal, the substituted samples became a polycrystalline material with Li2MnO3- LiBO2- LiMn2O4 crystals. The obtained structure in the cathode materials have similarity with the general formula xLi(2)MnO(3)center dot(1-x)LiMn2O4 which had been reported to have good intercalation and electrochemical properties.
  • [ X ]
    Öğe
    Electronic and crystal structure analyses of boron doped LiFeO2 cathode material by the XAFS spectroscopy
    (Elsevier, 2022) Gunaydin, Selen; Harfouche, Messaoud; Ozkendir, O. Murat
    The influence of boron substitution in LiFeO2 (LFO) material on crystal and electronic structure properties has been investigated by x-ray absorption fine structure (XAFS) spectroscopy with the general formula LiFe1_xBxO2 where x has values of 0.00, 0.05, and 0.10. The study revealed that boron has a key role in oxide materials due to its high effect on the oxygen regions and provides better performance values by reducing the excess oxygen in the material. The electronic structure properties were investigated by x-ray absorption near-edge spectroscopy (XANES). In this study, a new analysis method has also been applied for crystal properties determination like the Rietveld method for the first time and named Inverse EXAFS Fitting . For the crystal structure study, extended XAFS (EXAFS) analyses were processed in reverse mode to determine the crystal lattice properties as an alter-native way to the x-ray diffraction pattern (XRD) study and also to find out the atomic distances from the source Fe atoms. Due to the smaller ionic radii of B3+ cations than the Fe3+ cations, EXAFS data analysis has revealed that boron atoms did not sit in iron coordination, but formed the LiBO2 crystals and caused minor perturbations around iron atoms by loosening the Fe-O bonds.
  • [ X ]
    Öğe
    Electronic structure and electrochemical analysis of the Li2Mn1-xSexO3 materials
    (Elsevier, 2020) Ozkendir, O. Murat; Celik, Gultekin; Ates, Sule; Aktas, Sevda; Gunaydin, Selen; Harfouche, Messaoud; Bondino, Federica
    With the aim of probing the influence of the highly oxidizable selenium in the electrochemically inactive cathode Li2MnO3 material, samples were prepared with selenium substitution in the manganese coordination according to the general formula of Li2Mn1-xSexO3. In Li-ion batteries, oxygen instabilities are one of the major problems confronted that effect the performances of the cathode materials. The crystal and electronic structure properties of the materials were studied with x-ray absorption techniques. Selenium atoms were determined to build Li2SeO4 crystal and due to the oxygen removal during sample preparation mechanisms were determined to cause lower ionic conductivity than the parent Li2MnO3 oxide. The atomic distances in the materials were determined by the fits performed by the commercial code FEFF 8.2. Li2SeO4 crystal was determined as stacked between manganese and lithium atoms and isolated with each other.
  • Küçük Resim
    Öğe
    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.
  • [ X ]
    Öğe
    Study on crystallographic and electronic structure of micrometre-scale ZnO and ZnO:B rods via X-ray absorption fine-structure spectroscopy
    (Int Union Crystallography, 2021) Erat, Selma; Ozkendir, Osman Murat; Yildirimcan, Saadet; Gunaydin, Selen; Harfouche, Messaoud; Demir, Bunyamin; Braun, Artur
    X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) spectra were recorded to investigate the electronic structure and local crystal structure of ZnO and ZnO:B powders produced via hydrothermal synthesis. ZnO and ZnO:B grow as micrometre-scale rods with hexagonal shape, as confirmed by scanning electron microscopy micrographs. The number of broken ZnO:B rods increases with increasing B concentration, as observed in the images, due to B atoms locating in between the Zn and O atoms which weakens and/or breaks the Zn-O bonds. However, no disorder within the crystallographic structure of ZnO upon B doping is observed from X-ray diffraction results, which were supported by EXAFS results. To determine the atomic locations of boron atoms in the crystal structure and their influence on the zinc atoms, EXAFS data were fitted with calculated spectra using the crystal structure parameters obtained from the crystallographic analysis of the samples. EXAFS data fitting and complementary k-weight analysis revealed the positions of the B atoms - their positions were determined to be in between the Zn and O atoms.
  • [ X ]
    Öğe
    The Effect of CrFe2O4 Addition on the Ionic Conductivity Properties of Manganese-Substituted LiFeO2 Material
    (Springer, 2024) Gunaydin, Selen; Miyazaki, Hidetoshi; Saran, Sevda; Baveghar, Hadi; Celik, Gultekin; Harfouche, Messaoud; Abdellatief, Mahmoud
    The influence of Mn substitution on the iron lattice sites in LiFeO2 material was investigated with respect to the electronic, crystalline, and electrochemical properties of the material, using the LiFe1-xMnxO2 (x = 0.0, 0.05, and 0.10) series. The electronic structure study was conducted with the acquisition of x-ray absorption fine structure spectroscopy data, while the crystal structure properties of the studied materials were investigated using x-ray diffraction patterns. The data collected for the ionic conductivity properties of the samples by electrochemical impedance spectroscopy under increasing temperature conditions around and above room temperature aided the crystal and electronic structure studies on cathode materials. Furthermore, studies were conducted with the addition of CrFe2O4 material in varying molar concentrations into LiFeO2 material, as CrFe2O4 is known to have thermoelectric properties well above the room temperature of 400 K (127 degrees C). Encouraging results for next-generation battery cathodes were obtained.