Electrochimica Acta, Vol.289, 168-174, 2018
NASICON-type NaMo2(PO4)(3): Electrochemical activity of the Mo+4 polyanion compound in Na-cell
Vital need to reduce battery cost inspired intensive research in the field of sodium-storage systems, which required extending the range of perspective electrode materials. Herein, we present a new member of the electrochemically active NASICON material family, rhombohedral NaMo2(PO4)(3), which demonstrates both Mo+4/Mo+5 and Mo+4/Mo+3 redox activities towards sodium (de)intercalation. Desodiation of the initial NaMo2(PO4)(3) material with subsequent discharge within the 1.2-4.0 V range leads to a multi-electron redox transition with reversible capacity of 130 mAh g(-1). However, the single Mo+4/Mo+3 redox transition at 2.45 V (vs. Na/Na+) with capacity of 95 mAh g(-1) was found to be more stable during cycling, and operando X-ray diffraction confirmed its two-phase mechanism. Sodiation of the initial phase results in Na2.5Mo2(PO4)(3), which maintains the parent NASICON structure (R-3c, a = 8.90532(7) angstrom, c = 22.2379(3) angstrom, V = 1527.30(3) angstrom(3)), with two Na-positions being almost equal in occupancy and energy. (C) 2018 Elsevier Ltd. All rights reserved.
Keywords:Na-ion battery;NASICON-type materials;Freeze drying;Multi-electron redox transitions;Reversible sodium (de)intercalation