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- Title
Controlling Iron Versus Oxygen Redox in the Layered Cathode Na<sub>0.67</sub>Fe<sub>0.5</sub>Mn<sub>0.5</sub>O<sub>2</sub>: Mitigating Voltage and Capacity Fade by Mg Substitution.
- Authors
Boivin, Edouard; House, Robert A.; Marie, John‐Joseph; Bruce, Peter G.
- Abstract
Layered oxides for Na‐ion batteries containing Fe have attracted strong interest mainly due to their low cost. However, full oxidation of Fe3+ to Fe4+ is rarely seen before O‐redox sets in and is typically accompanied by voltage and capacity fade on cycling. On charging P2‐Na0.67[Fe0.5Mn0.5]O2, Fe3+ is oxidized to only ≈Fe3.3+ before the onset of O‐redox. O‐redox occurs when the Na content is sufficiently low (Na ≈0.3) to permit the transition from P‐type to O‐type stacking, thus enabling Fe3+ migration to the Na layer. Fe3+ migration generates cation vacancies in the transition metal layer, forming □‐O‐□ configurations, which trigger the onset of O‐redox. In contrast, doping this material with Mg2+ to form P2‐Na0.67[Fe0.25Mn0.6Mg0.15]O2 allows full oxidation of Fe3+ to Fe4+ before the Na content is low enough to favor O‐type stacking. During O‐redox, Mg2+ is displaced into the Na layers instead of Fe. Mg substitution enables greater reversibility of the Fe3+/Fe4+ redox couple and significantly suppresses Fe migration, which is responsible for the voltage and capacity fade observed for P2‐Na0.67Fe0.5Mn0.5O2.
- Subjects
OXIDATION-reduction reaction; CATHODES; VOLTAGE; TRANSITION metals; IRON; OXYGEN; IRON-nickel alloys
- Publication
Advanced Energy Materials, 2022, Vol 12, Issue 30, p1
- ISSN
1614-6832
- Publication type
Article
- DOI
10.1002/aenm.202200702