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Exploring cation–anion redox processes in one-dimensional linear chain vanadium tetrasulfide rechargeable magnesium ion cathodes

DOI: 10.1021/jacs.0c08222 DOI Help

Authors: Sunita Dey (University of Cambridge) , Jeongjae Lee (University of Cambridge) , Sylvia Britto (University of Cambridge; Diamond Light Source) , Joshua M. Stratford (University of Cambridge) , Evan N. Keyzer (University of Cambridge) , Matthew T. Dunstan (University of Cambridge) , Giannantonio Cibin (Diamond Light Source) , Simon J. Cassidy (University of Oxford) , Mahmoud Elgaml (University of Oxford) , Clare P. Grey (University of Cambridge)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of The American Chemical Society

State: Published (Approved)
Published: October 2020
Diamond Proposal Number(s): 22856 , 22930 , 24676

Open Access Open Access

Abstract: For magnesium ion batteries (MIBs) to be used commercially, new cathodes must be developed that show stable reversible Mg intercalation. VS4 is one such promising material, with vanadium and disulfide anions [S2]2– forming one-dimensional linear chains, with a large interchain spacing (5.83 Å) enabling reversible Mg insertion. However, little is known about the details of the redox processes and structural transformations that occur upon Mg intercalation and deintercalation. Here, employing a suite of local structure characterization methods including X-ray photoelectron spectroscopy (XPS), V and S X-ray absorption near-edge spectroscopy (XANES), and 51V Hahn echo and magic-angle turning with phase-adjusted sideband separation (MATPASS) NMR, we show that the reaction proceeds via internal electron transfer from V4+ to [S2]2–, resulting in the simultaneous and coupled oxidation of V4+ to V5+ and reduction of [S2]2– to S2–. We report the formation of a previously unknown intermediate in the Mg–V–S compositional space, Mg3V2S8, comprising [VS4]3– tetrahedral units, identified by using density functional theory coupled with an evolutionary structure-predicting algorithm. The structure is verified experimentally via X-ray pair distribution function analysis. The voltage associated with the competing conversion reaction to form MgS plus V metal directly is similar to that of intermediate formation, resulting in two competing reaction pathways. Partial reversibility is seen to re-form the V5+ and S2– containing intermediate on charging instead of VS4. This work showcases the possibility of developing a family of transition metal polychalcogenides functioning via coupled cationic–anionic redox processes as a potential way of achieving higher capacities for MIBs.

Journal Keywords: X-ray absorption near edge spectroscopy; Redox reactions; Ions; Chemical structure; Energy

Diamond Keywords: Batteries; Magnesium-ion

Subject Areas: Chemistry, Energy, Materials

Instruments: B18-Core EXAFS , I15-1-X-ray Pair Distribution Function (XPDF)

Added On: 02/11/2020 13:37

Discipline Tags:

Energy Storage Energy Physical Chemistry Energy Materials Chemistry Materials Science

Technical Tags:

Scattering Spectroscopy Pair Distribution Function (PDF) X-ray Absorption Spectroscopy (XAS)