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Journal ArticleDOI

Effects of fluorination on the structure, magnetic and electrochemical properties of the P2-type NaxCoO2 powder

05 Feb 2019-Journal of Alloys and Compounds (Elsevier)-Vol. 774, pp 30-37

AbstractThe main goal of this research has been to investigate for the first time the effects of fluorination on the crystal structure, magnetic, and electrochemical properties of the P2-type NaxCoO2 powder. Sodium cobalt oxide with a P2-type structure is synthesized by a modified solid-state reaction consisting of alternating processes of rapid heating up to 750 °C and rapid cooling to the room temperature. The obtained powder is fluorinated using a gas-solid reaction with NH4HF2 as fluorinating agent. Fluorination causes a decrease of sodium content in the parent phase with the concurrent formation of the minor phases of Na2CO3 and NaF. The structure of NaxCoO2 in both powders is refined in P63/mmc space group. The results of the Rietveld refinement combined with the findings from the XPS measurements confirm the Na0.76CoO2 and Na0.44CoO1.96F0.04 stoichiometries for the pristine and fluorinated powders, respectively, which indicates that 4 at.% of fluorine ions per formula unit are incorporated in the structure. Preliminary electrochemical investigations have revealed an improved charge/discharge performance. The influence of fluorination on morphology and magnetic properties has also been examined.

Topics: Rietveld refinement (55%), Fluorine (52%)

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Supplementary information for the article:
Jugović, D., Milović, M., Popović, M., Kusigerski, V., Škapin, S., Rakočević, Z.,
Mitrić, M., 2019. Effects of fluorination on the structure, magnetic and electrochemical
properties of the P2-type NaxCoO2 powder. Journal of Alloys and Compounds 774,
3037. https://doi.org/10.1016/j.jallcom.2018.09.372

Supplementary Information
Effects of fluorination on structure, magnetic and electrochemical properties of the P2-type
Na
x
CoO
2
powder
Dragana Jugović
a
, Miloš Milović
a
, Maja Popović
b
, Vladan Kusigerski
b
, Srečo Škapin
c
, Zlatko
Rakočević
b
, and Miodrag Mitrić
b*
a
Institute of Technical Sciences of SASA, Knez Mihailova 35/IV, 11 000 Belgrade, Serbia
b
Vinča Institute of Nuclear Sciences, University of Belgrade, P.O. Box 522, 11 001 Belgrade, Serbia
c
Jožef Štefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia
Figure S1. The evolution of FTIR spectra during the synthesis of pristine Na
x
CoO
2
.

Figure S2. X-ray diffractograms taken at different stages of a solid-state reaction between Na
2
CO
3
,
Co
3
O
4
, and NaF. The patterns at the bottom are taken from ICDD PDF database as reference patterns for
phase identification.
Citations
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Journal ArticleDOI
Abstract: We study the structural, magnetic, transport, and electronic properties of LaCoO3 with Sr/Nb cosubstitution, i.e., La(1–2x)Sr2xCo(1–x)NbxO3 using X-ray and neutron diffraction, dc- and ac-magnetiza...

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Journal ArticleDOI
Abstract: To optimize the Na0·74CoO2-based cathode materials for sodium-ion batteries, we fabricated a series of Na0·74CoO2/C/N-based composites by sintering the mixtures of ZIF-4(Co) (Co [H2C3N2]2) and Na2CO3, which possess various molar Na/Co ratios (X = 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2 and 2.0), at 800 °C for 6 h. By performing the electrochemical characterizations, we found that the composite with X = 0.7 (NC-0.7) exhibits the optimum sodium storage performance, i.e., excellent Na+ storage capacity (107.9 mA h g−1 at 0.1 C), and high cycling stability (74% of the discharge capacity retention after 500 cycles at 10 C). In addition, for this NC-0.7 composite, we discovered a large difference (48.1 mA h g−1) between the charging (59.8 mA h g−1) and discharging (107.9 mA h g−1) capacities for the first cycle. Using the X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and scanning transmission electron microscope, we clarified the atomic-scale origin of the large capacity difference, and revealed the role of the amorphous phase in the as-prepared Na0·74CoO2/C/N composite cathode.

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Journal ArticleDOI
Ruijuan Zhou1, Xiaoxu Guo1, Zihao Li1, Shijian Luo1, Min Luo1 
Abstract: Faradaic deionization (FDI) provides an effective solution to respond to the global water crisis. However, the ions intercalation/deintercalation process with multiple redox reactions leads to structural collapse and unstable cyclability. Here, we develop an asymmetrical FDI device assembled by Ca2+-decorated NaxCoO2 (x ≤ 0.71, y ≤ 0.05) as the Faradaic negative electrode and activated carbon as the positive electrode. Na0.27Ca0.03CoO2·0.6H2O was synthesized via a facile sol–gel and chemical oxidation method, which delivered a desalination capacity of 83.5 ± 2.4 mg g–1 and a charge efficiency close to 1, and an inappreciable capacity fading was observed after 50 cycles. It is found that the presence of Ca2+ residing in the face-sharing sites helps to maintain the layered structure and promotes efficient deintercalation of Na+ by anchoring the CoO2 slabs, which results in its unexpected desalination capacity and good cyclability. Moreover, electrochemical quartz-crystal microbalance (EQCM) was successfully...

7 citations


References
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"Effects of fluorination on the stru..." refers background in this paper

  • ...7 eV can be assigned to a defective oxide or hydrated oxide [44]....

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