Singh, Gurpreet and Tapia-Ruiz, Nuria and Lopez del Amo, Juan Miguel and Maitra, Urmimala and Somerville, James W. and Armstrong, A. Robert and Martinez de Ilarduya, Jaione and Rojo, Teófilo and Bruce, Peter 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, 28 (14). pp. 5087-5094. ISSN 0897-4756
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Abstract
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.