Stabilization of O-O bonds by d0 cations in Li4+xNi1-xWO6 (0 ≤ x ≤ 0.25) rocksalt oxides as the origin of large voltage hysteresis

DOI: 10.1021/jacs.8b13633

Authors: Zoe N. Taylor (University of Liverpool) , Arnaud J. Perez (University of Liverpool) , Jose A. Coca-Clemente (University of Liverpool) , Filipe Braga (University of Liverpool) , Nicholas E. Drewett (University of Liverpool) , Michael J. Pitcher (University of Liverpool) , William J. Thomas (University of Liverpool) , Matthew S. Dyer (University of Liverpool) , Christopher Collins (University of Liverpool) , Marco Zanella (University of Liverpool) , Timothy Johnson (University of Liverpool) , Sarah Day (Diamond Light Source) , Chiu Tang (Diamond Light Source) , Vinod R Dhanak (University of Liverpool) , John B. Claridge (University of Liverpool) , Laurence J. Hardwick (University of Liverpool) , Matthew J. Rosseinsky (University of Liverpool)
Co-authored by industrial partner: No

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

State: Published (Approved)
Published: April 2019

Abstract: Multinary lithium oxides with the rock salt structure are of technological importance as cathode materials in rechargeable lithium ion batteries. Current state of the art cathodes such as LiNi1/3Mn1/3Co1/3O2 rely on redox cycling of earth-abundant transition metal cations to provide charge capacity. Recently, the possibility of using the oxide anion as a redox center in Li-rich rock salt oxides has been established as a new paradigm in the design of cathode materials with enhanced capacities (> 200 mAh/g). To increase the lithium content and access electrons from oxygen-derived states, these materials typically require transition metals in high oxidation states, which can be easily achieved using d0 cations. However, Li-rich rocksalt oxides with high valent d0 cations such as Nb5+ and Mo6+ show strikingly high voltage hysteresis between charge and discharge, the origin of which is uninvestigated. In this work, we study a series of Li-rich compounds, Li4+xNi1-xWO6 (0 ≤ x ≤ 0.25), adopting two new and distinct cation-ordered variants of the rock salt structure. The phase Li4.15Ni0.85WO6 (x = 0.15) has a large reversible capacity of 200 mAh/g, without accessing the Ni3+/Ni4+ redox couple, implying that over two-thirds of the capacity is due to anionic redox, with good cyclability. The presence of the 5d0 W6+ cation affords extensive (> 2 V) voltage hysteresis associated with the anionic redox. We present experimental evidence for the formation of strongly stabilized localized O-O single bonds that explain the energy penalty required to reduce the material upon discharge. The high valent d0 cation associates localized anion-anion bonding with the anion redox capacity.

Journal Keywords: Redox reactions; Chemical structure; Oxygen; Cations; Materials

Diamond Keywords: Batteries; Lithium-ion

Subject Areas: Chemistry, Materials, Energy


Instruments: B18-Core EXAFS , I11-High Resolution Powder Diffraction

Added On: 15/04/2019 09:52

Discipline Tags:

Energy Storage Energy Physical Chemistry Energy Materials Chemistry Materials Science

Technical Tags:

Diffraction Spectroscopy X-ray Powder Diffraction X-ray Absorption Spectroscopy (XAS) X-ray Absorption Near Edge Structure (XANES)