Importance of Superstructure in Stabilizing Oxygen Redox in P3‐Na0.67Li0.2Mn0.8O2. Issue 3 (10th December 2021)

• Record Type: Journal Article
• Authors: Kim, Eun Jeong; Maughan, Philip A.; Bassey, Euan N.; Clément, Raphaële J.; Ma, Le Anh; Duda, Laurent C.; Sehrawat, Divya; Younesi, Reza; Sharma, Neeraj; Grey, Clare P.; Armstrong, A. Robert
• Is Part Of: Advanced energy materials. Volume 12:Issue 3(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-12-10
• Subjects: layered structures -- oxygen redox -- P3 structure -- sodium‐ion batteries -- superstructures; Energy harvesting -- Materials -- Periodicals; Energy conversion -- Materials -- Periodicals; Energy storage -- Materials -- Periodicals; Photovoltaics -- Periodicals; Fuel cells -- Periodicals; Thermoelectric materials -- Periodicals; 621.31
• DOI: 10.1002/aenm.202102325
• Languages: English
• ISSNs: 1614-6832

Abstract

Abstract: Activation of oxygen redox represents a promising strategy to enhance the energy density of positive electrode materials in both lithium and sodium‐ion batteries. However, the large voltage hysteresis associated with oxidation of oxygen anions during the first charge represents a significant challenge. Here, P3‐type Na0.67 Li0.2 Mn0.8 O2 is reinvestigated and a ribbon superlattice is identified for the first time in P3‐type materials. The ribbon superstructure is maintained over cycling with very minor unit cell volume changes in the bulk while Li ions migrate reversibly between the transition metal and Na layers at the atomic scale. In addition, a range of spectroscopic techniques reveal that a strongly hybridized Mn 3d–O 2p favors ligand‐to‐metal charge transfer, also described as a reductive coupling mechanism, to stabilize reversible oxygen redox. By preparing materials under three different synthetic conditions, the degree of ordering between Li and Mn is varied. The sample with the maximum cation ordering delivers the largest capacity regardless of the voltage windows applied. These findings highlight the importance of cationic ordering in the transition metal layers, which can be tuned by synthetic control to enhance anionic redox and hence energy density in rechargeable batteries. Abstract : A higher degree of cationic ordering in P3‐type Na0.67 Li0.2 Mn0.8 O2 adopting a ribbon superstructure helps deliver stable oxygen redox. Bulk and local structure investigations reveal that the absence of voltage hysteresis originates from the well‐maintained P3 structure and reversible migration of Li + . These influence the hybridized Mn–O band, inducing a reductive coupling mechanism to stabilize oxidized oxygen.