Journal Publications

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Browsing Journal Publications by Author "Abakumov, AM"

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    Monoclinic α-Na2FePO4F with strong antisite disorder and enhanced Na+ diffusion
    (American Chemical Society, 2020-11-02) Kirsanova, MA; Akmaev, AS; Aksyonov, DA; Ryazantsev, SV; Nikitina, VA; Filimonov, DS; Avdeev, M; Abakumov, AM
    A new monoclinic α-polymorph of the Na2FePO4F fluoride-phosphate has been directly synthesized via a hydrothermal method for application in metal-ion batteries. The crystal structure of the as-prepared α-Na2FePO4F studied with powder X-ray and neutron diffraction (P21/c, a = 13.6753(10) Å, b = 5.2503(2) Å, c = 13.7202(8) Å, β = 120.230(4)°) demonstrates strong antisite disorder between the Na and Fe atoms. As revealed with DFT-based calculations, α-Na2FePO4F has low migration barriers for Na+ along the main pathway parallel to the b axis, and an additional diffusion bypass allowing the Na+ cations to go around the Na/Fe antisite defects. These results corroborate with the extremely high experimental Na-ion diffusion coefficient of (1–5)·10–11 cm2·s–1, which is 2 orders of magnitude higher than that for the orthorhombic β-polymorph ((5–10)·10–13 cm2·s–1). Being tested as a cathode material in Na- and Li-ion battery cells, monoclinic α-Na2FePO4F exhibits a reversible specific capacity of 90 and 80 mAh g–1, respectively. © 2020 American Chemical Society
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    Unlocking anionic redox activity in O3-type sodium 3d layered oxides via Li substitution
    (Springer Nature, 2021-01-11) lorem, Ipsum; Wang, Q; Mariyappan, S; Rousse, G; Morozov, AV; Porcheron, B; Dedryvère, R; Wu, JP; Yang, WL; Zhang, LT; Chakir, M; Avdeev, M; Deschamps, M; Yu, YS; Cabana, J; Doublet, ML; Abakumov, AM; Tarascon, JM
    Sodium ion batteries, because of their sustainability attributes, could be an attractive alternative to Li-ion technology for specific applications. However, it remains challenging to design high energy density and moisture stable Na-based positive electrodes. Here, we report an O3-type NaLi1/3Mn2/3O2 phase showing anionic redox activity, obtained through a ceramic process by carefully adjusting synthesis conditions and stoichiometry. This phase shows a sustained reversible capacity of 190 mAh g−1 that is rooted in cumulative oxygen and manganese redox processes as deduced by combined spectroscopy techniques. Unlike many other anionic redox layered oxides so far reported, O3-NaLi1/3Mn2/3O2 electrodes do not show discernible voltage fade on cycling. This finding, rationalized by density functional theory, sheds light on the role of inter- versus intralayer 3d cationic migration in ruling voltage fade in anionic redox electrodes. Another practical asset of this material stems from its moisture stability, hence facilitating its handling and electrode processing. Overall, this work offers future directions towards designing highly performing sodium electrodes for advanced Na-ion batteries. © 2021, The Author(s), under exclusive licence to Springer Nature Limited.