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Issue 30, 2019
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Exploring the high-voltage Mg2+/Na+ co-intercalation reaction of Na3VCr(PO4)3 in Mg-ion batteries

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Abstract

Na3VCr(PO4)3 has attracted great attention due to its high energy density and stable structure. The substitution of vanadium with chromium led to an increase in the redox potential from 3.4 to 4.2 V (vs. Na+/Na). In this work, the electrochemical performance of Na3VCr(PO4)3 (NVCP) in Mg cells is successfully investigated. Reversible multielectron Mg2+/Na+ extraction/insertion is observed. Upon charging, NVCP exhibits two plateaus at 1.75 V and 2.3 V vs. Mg2+/Mg0 achieving a maximum reversible capacity of 85 mA h g−1 (a 1.45 electron reaction) enabling oxidation to VV as determined by 51V NMR and XPS, and accompanied by extraction of sodium from Na2 sites according to 23Na NMR. During the subsequent cycles Mg2+/Na+ ions react at 2.3 and 1.7 V, and an additional peak of Mg2+ at 1.2 V is observed. Alternatively, electrochemical cells were also assembled with activated carbon in a 0.1 M Mg(TFSI)2 electrolyte, leading to similar profiles and capacity even at higher current density. Finally, the chemical desodiation of NVCP using I2, Cl2 and NO2BF4 is performed to avoid mobile sodium ions. XRD, XPS and 51V NMR confirmed the contraction of the cell and the oxidation to VIV and VV. Iodine was not capable of full sodium extraction. Despite this fact, the ability of this sample to retain 65 mA h g−1 during a few cycles evidences the reversibility of magnesium insertion. The use of stronger oxidants such as Cl2 or NO2BF4 allowed the increase of the initial OCV and resulted in a plateau at 4 V. The chemical desodiation was also accompanied by an enhanced capacity decrease which could be correlated with the structural degradation.

Graphical abstract: Exploring the high-voltage Mg2+/Na+ co-intercalation reaction of Na3VCr(PO4)3 in Mg-ion batteries

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Supplementary files

Article information


Submitted
27 May 2019
Accepted
01 Jul 2019
First published
02 Jul 2019

J. Mater. Chem. A, 2019,7, 18081-18091
Article type
Paper

Exploring the high-voltage Mg2+/Na+ co-intercalation reaction of Na3VCr(PO4)3 in Mg-ion batteries

S. Rubio, R. Liu, X. Liu, P. Lavela, J. L. Tirado, Q. Li, Z. Liang, G. F. Ortiz and Y. Yang, J. Mater. Chem. A, 2019, 7, 18081
DOI: 10.1039/C9TA05608D

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