Browsing by Author "Mariyappan, S"

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    Mastering the synthesis of high Na-content, moisture-stable layered oxide cathode for Na-ion batteries
    (Elsevier, 2024-09) Grépin, E; Jacquet, Q; Moiseev, IA; Iadecola, A; Rousse, G; Avdeev, M; Abakumov, AM; Tarascon, JM; Mariyappan, S
    Sodium layered oxides NaxMO2 (x ≤ 1 and M = transition metal) are of great interest for sodium-ion batteries due to their high energy density and cost-effectiveness. However, these materials, whether they are stoichiometric (Na/M ≈ 1 as in O3 NaMO2) or not (Na/M ≈ 0.7 as in P3/P2 NaxMO2), have certain disadvantages, namely sensitivity to humidity or inadequate capacity, respectively. Herein, we propose an intermediate composition Na0.85Ni0.38Zn0.04Mn0.48Ti0.1O2 that we succeed to stabilize in either O3 or a nanoscale mixture of O3–P3 or O3–P2 phases as proven by X-ray diffraction and transmission electron microscopy, through complex synthesis approaches including quenching, slow cooling and annealing in different atmospheres (Ar, air, O2 etc). We rationalize the stabilization of different phases and microstructure as a function of synthesis conditions and show how it influences the electrochemical performance. Through this study we identified a single phase O3 Na0.85Ni0.38Zn0.04Mn0.48Ti0.1O2 synthesized at 1000 °C in air, which exhibits a high capacity of ∼170 mAh/g and good moisture stability. Furthermore, thanks to the synthesis-structure- electrochemical performance relationship identified here, we believe that this study will provide a reliable basis for optimizing the synthesis for best performing sodium layered oxides for commercialization. © 2024 Elsevier B.V.
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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.