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What triggers oxygen loss in oxygen redox cathode materials?

DOI: 10.1021/acs.chemmater.9b00227 DOI Help

Authors: Robert A. House (University of Oxford) , Urmimala Maitra (University of Oxford) , Liyu Jin (University of Oxford) , Juan G. Lozano (University of Oxford) , James W. Somerville (University of Oxford) , Nicholas H. Rees (University of Oxford) , Andrew J. Naylor (Uppsala University) , Laurent C. Duda (Uppsala University) , Felix Massel (Uppsala University) , Alan V. Chadwick (University of Kent at Canterbury) , Silvia Ramos (Uppsala University) , David M. Pickup (University of Kent) , Daniel E. Mcnally (Swiss Light Source) , Xingye Lu (Swiss Light Source) , Thorsten Schmitt (Swiss Light Source) , Matthew R. Roberts (University of Oxford) , Peter G. Bruce (University of Oxford; The Faraday Institution)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Chemistry Of Materials

State: Published (Approved)
Published: April 2019
Diamond Proposal Number(s): 14239 , 20870

Abstract: It is possible to increase the charge capacity of transition metal oxide cathodes in alkali-ion batteries by invoking redox reactions on the oxygen. However, oxygen loss often occurs. To explore what affects oxygen loss in oxygen redox materials, we have compared two analogous Na-ion cathodes, P2-Na0.67Mg0.28Mn0.72O2 and P2-Na0.78Li0.25Mn0.75O2. On charging to 4.5 V, >0.4 e- are removed from the oxide ions of these materials, but neither compound exhibits oxygen loss. Li is retained in P2-Na0.78Li0.25Mn0.75O2 but displaced from the transition metal to the alkali metal layers, showing that vacancies in the transition metal layers, which also occur in other oxygen redox compounds that exhibit oxygen loss such as Li[Li0.2Ni0.2Mn0.6]O2, is not a trigger for oxygen loss. On charging at 5 V, P2-Na0.78Li0.25Mn0.75O2 exhibits oxygen loss whereas P2-Na0.67Mg0.28Mn0.72O2 does not. Under these conditions both Na+ and Li+ are removed from P2-Na0.78Li0.25Mn0.75O2 resulting in underbonded oxygen (fewer than 3 cations coordinating oxygen) and surface localised O loss. In contrast, for P2-Na0.67Mg0.28Mn0.72O2, oxygen remains coordinated by at least 2 Mn4+ and 1 Mg2+ ions, stabilising the oxygen and avoiding oxygen loss.

Subject Areas: Materials, Chemistry

Beamlines: B18-Core EXAFS , I09-Surface and Interface Structural Analysis

Other Synchrotrons: Swiss Light Source