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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

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  • Gurpreet Singh
  • Nuria Tapia-Ruiz
  • Juan Miguel Lopez del Amo
  • Urmimala Maitra
  • James W. Somerville
  • A. Robert Armstrong
  • Jaione Martinez de Ilarduya
  • Teófilo Rojo
  • Peter G. Bruce
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<mark>Journal publication date</mark>26/07/2016
<mark>Journal</mark>Chemistry of Materials
Issue number14
Volume28
Number of pages8
Pages (from-to)5087-5094
Publication StatusPublished
Early online date27/06/16
<mark>Original language</mark>English

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.