Bulk O2 formation and Mg displacement explain O-redox in Na0.67Mn0.72Mg0.28O2

DOI: 10.1016/j.joule.2021.04.006

Authors: Edouard Boivin (University of Oxford; Henry Royce Institute) , Robert A. House (University of Oxford; Faraday Institution; Henry Royce Institute) , Miguel A. Pérez-Osorio (University of Oxford; Faraday Institution; Henry Royce Institute) , John-Joseph Marie (University of Oxford; Faraday Institution; Henry Royce Institute) , Urmimala Maitra (University of Oxford) , Gregory J. Rees (University of Oxford; Faraday Institution; Henry Royce Institute) , Peter G. Bruce (University of Oxford; Faraday Institution; Henry Royce Institute)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Joule , VOL 5 , PAGES 1267 - 1280

State: Published (Approved)
Published: May 2021

Abstract: O-redox in compounds with Li on the transition-metal layers (TML) has recently been attributed to the formation of molecular O2 on charge, trapped in the lattice. Here, we show that a similar process occurs for P2-Na0.67[Mn0.72Mg0.28]O2, which contains Mg2+ on the TML. The molecular O2 is identified by high-resolution RIXS and quantified by magnetometry, showing that it equates to the charge passed. This O2 is trapped in voids that are formed by Mg2+ out-of-plane displacement and Mn4+ in-plane disordering and is then reduced on discharge associated with a large voltage hysteresis. In contrast to compounds containing Li+ in the TML, in which the honeycomb ordering and the high-voltage plateau are irreversibly lost after the first cycle, in P2-Na0.67[Mn0.72Mg0.28]O2, the plateau reappears partially on the second charge due to the partial reversibility of Mn in-plane and Mg out-of-plane migration and the local reformation of the honeycomb ordering.

Journal Keywords: Na-ion batteries; cathode material; oxygen redox; molecular oxygen; hr-RIXS spectroscopy

Diamond Keywords: Batteries; Sodium-ion

Subject Areas: Materials, Chemistry


Instruments: B18-Core EXAFS

Other Facilities: BL27SU at Spring8; ADRESS at SLS; POLARIS at ISIS

Added On: 25/05/2021 11:00

Discipline Tags:

Energy Storage Energy Physical Chemistry Energy Materials Chemistry Materials Science

Technical Tags:

Spectroscopy X-ray Absorption Spectroscopy (XAS) Extended X-ray Absorption Fine Structure (EXAFS)