High voltage Mg-doped Na0.67Ni0.3-xMgxMn0.7O2 (x = 0.05, 0.1) Na-ion cathodes with enhanced stability and rate capability
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Magnesium substituted P2-structure Na0.67Ni0.3Mn0.7O2 materials have been prepared by a facile solid-state method and investigated as cathodes in sodium-ion batteries. The Mg-doped materials described here were characterized by X-ray diffraction (XRD), 23Na solid-state nuclear magnetic resonance (SS-NMR), and scanning electron microscopy (SEM). The electrochemical performance of the samples was tested in half cells vs Na metal at room temperature. The Mg-doped materials operate at a high average voltage of ca. 3.3 V vs Na/Na+ delivering specific capacities of ∼120 mAh g-1, which remain stable up to 50 cycles. Mg doping suppresses the well-known P2-O2 phase transition observed in the undoped composition by stabilizing the reversible OP4 phase during charging (during Na removal). GITT measurements showed that the Na-ion mobility is improved by 2 orders of magnitude with respect to the parent P2-Na0.67Ni0.3Mn0.7O2 material. The fast Na-ion mobility may be the cause of the enhanced rate performance.
Singh , G , Tapia-Ruiz , N , Lopez Del Amo , J M , Maitra , U , Somerville , J W , Armstrong , A R , Martinez de Ilarduya , J , Rojo , T & Bruce , P G 2016 , ' High voltage Mg-doped Na 0.67 Ni 0.3-x Mg x Mn 0.7 O 2 (x = 0.05, 0.1) Na-ion cathodes with enhanced stability and rate capability ' Chemistry of Materials , vol 28 , no. 14 , pp. 5087-5094 . DOI: 10.1021/acs.chemmater.6b01935
Chemistry of Materials
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At CIC Energigune this work was financially supported by LINABATT project from Ministerio de Economía Competitividad (ENE2013-44330-R). P.G.B. (University of Oxford) is indebted to the Engineering and Physical Sciences Research Council, including the SUPERGEN program, for financial support.