Issue 34, 2020

Phase transformation, charge transfer, and ionic diffusion of Na4MnV(PO4)3 in sodium-ion batteries: a combined first-principles and experimental study

Abstract

NASICON-structured Na4MnV(PO4)3 has been recognized as a potential positive electrode material for sodium-ion batteries, but its electrochemical mechanism during de(sodiation) has not been well understood. In this work, the structural transformation, charge transfer, and ionic diffusion properties of Na4MnV(PO4)3 were comprehensively studied by first-principles calculations combined with experimental studies. The results revealed two independent Na sites, Na(1) and Na(2), in the structure of Na4MnV(PO4)3, but only Na(2) can be extracted between 2.5 and 3.8 V. Extraction of the first Na+ caused charge transfer on V3+ and was associated with a solid-solution reaction. In addition, Na+ migrated along the 3D channels in the NASICON structure with low energy barriers of <0.4 eV. With extraction of the second Na+, the charge transfer process occurred on Mn2+. The material underwent a biphasic transition with the Na(1) atom auto-migrating to a nearby interstitial site, Na(3). During this process, Na+ migrated in a 1D channel with a relatively higher diffusion barrier of 0.52 eV. In line with the structural evolution, the Na+ diffusion coefficients remained at 2.0 × 10−12 cm2 s−1 during the first Na+ extraction, and then decreased to 9.7 × 10−14 cm2 s−1 with the extraction of the second Na+.

Graphical abstract: Phase transformation, charge transfer, and ionic diffusion of Na4MnV(PO4)3 in sodium-ion batteries: a combined first-principles and experimental study

Supplementary files

Article information

Article type
Paper
Submitted
15 Jun 2020
Accepted
27 Jul 2020
First published
28 Jul 2020

J. Mater. Chem. A, 2020,8, 17477-17486

Phase transformation, charge transfer, and ionic diffusion of Na4MnV(PO4)3 in sodium-ion batteries: a combined first-principles and experimental study

X. Gao, R. Lian, L. He, Q. Fu, S. Indris, B. Schwarz, X. Wang, G. Chen, H. Ehrenberg and Y. Wei, J. Mater. Chem. A, 2020, 8, 17477 DOI: 10.1039/D0TA05929C

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