Browsing by Author "Milović, M"

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    Fluorine doping of layered NaxCoO2 structure
    (Materials Research Society of Serbia, 2015-09-04) Jugović, D; Milović, M; Mitrić, M; Cvjetićanin, N; Avdeev, M; Jokić, BM; Uskoković, D
    The room temperature Na-ion secondary battery has been under focus lately due to its feasibility to compete against the already well-established Li-ion secondary battery. Transition metal oxides of general formula NaxMO2 have been investigated as potential cathode materials for sodium batteries. Layered NaxCoO2 is synthesized via solid-state method at 900 ºC in air atmosphere. Fluorine doping of the as-prepared powder is established by the use of ammonium hydrogen difluoride (NH4HF2) as a fluorinating agent. The fluorination takes place only at low temperature (200 ºC), while the treatment at higher temperatures (≥ 400 ºC) facilitates the formation of NaF. It is shown that various and controllable amounts of fluorine can be successfully incorporated into the structure. Finally, the effects of fluorine doping on both structural and electrochemical properties are examined.
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    Li2FeSiO4 cathode material: the structure and electrochemical performances
    (Materials Research Society of Serbia, 2014-09-01) Jugović, D; Milović, M; Mitrić, M; Ivanovski, VN; Avdeev, M; Jokić, B; Dominko, R; Uskoković, D
    Monoclinic Li2FeSiO4 that crystallizes in P21/n space group was investigated as a potential cathode material for lithium-ion batteries. A combined X-ray diffraction and Mössbauer spectroscopy study was used for the structural investigation. It was found that the crystal structure is prone to an “antisite” defect, the one in which the Fe ion and the Li ion exchange places. This finding was also confirmed by the Mössbauer spectroscopy. In order to obtain composites of Li2FeSiO4 and carbon, several synthesis techniques that use different carbon sources were involved. Electrochemical performances were investigated through galvanostatic charge/discharge tests. Discharge curve profile did not reflect a two-phase intercalation reaction (no obvious voltage plateau) due to the low conductivity at room temperature. © 2014 Materials Research Society of Serbia
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    Structural study of monoclinic Li2FeSiO4 by x-ray diffraction and Mössbauer spectroscopy
    (Elsevier, 2014-11-01) Jugović, D; Milović, M; Ivanovski, VN; Avdeev, M; Dominko, R; Jokić, B; Uskoković, D
    A composite powder Li2FeSiO4/C is synthesized through a solid state reaction at 750 °C. The Rietveld crystal structure refinement is done in the monoclinic P21/n space group. It is found that the crystal structure is prone to “antisite” defect where small part of iron ion occupies exclusively Li(2) crystallographic position, of two different lithium tetrahedral positions (Li(1) and Li(2)). This finding is also confirmed by Mössbauer spectroscopy study: the sextet evidenced in the Mössbauer spectrum is assigned to the iron ions positioned at the Li(2) sites. A bond-valence energy landscape calculation is used to predict the conduction pathways of lithium ions. The calculations suggest that Li conductivity is two-dimensional in the (101) plane. Upon galvanostatic cyclings the structure starts to rearrange to inverse βII polymorph. © 2014, Elsevier B.V.