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A formal FeIII/V redox couple in an intercalation electrode
Hari Ramachandran1, Edward W Mu2, Eder G Lomeli1,3
1Department of Materials Science & Engineering, Stanford University, Stanford, CA, USA.
Nature Materials
|October 15, 2025
Summary
Researchers discovered a high-valent iron redox couple (FeIII/V) in Li4FeSbO6 for advanced lithium-ion batteries. This FeIII/V couple enables higher energy densities and stable, high-voltage cathodes.
Area of Science:
- Materials Science
- Electrochemistry
- Solid-State Chemistry
Background:
- Iron redox cycling (FeII/III) is vital in nature and batteries.
- High-valent iron redox couples offer potential for higher battery energy densities.
- Instability of high-valent iron electrodes hinders their application in intercalation systems.
Purpose of the Study:
- To explore and characterize a formal FeIII/V redox couple in Li4FeSbO6.
- To understand the charge compensation mechanism during (de)lithiation in Li4FeSbO6.
- To assess the potential of the FeIII/V couple for high-voltage battery applications.
Main Methods:
- Valence-sensitive experimental and computational core-level spectroscopy.
- Analysis of cation ordering and its effect on phase transitions.
- Electrochemical characterization of Li4FeSbO6 for battery performance.
Main Results:
- A direct transition from FeIII to a negative-charge-transfer FeV ground state was observed during delithiation.
- Cation ordering in Li4FeSbO6 stabilizes the FeV species and drives a templated phase transition.
- Disrupting cation ordering was shown to suppress the FeIII/V redox couple.
Conclusions:
- The FeIII/V redox couple in Li4FeSbO6 is stabilized by cation ordering.
- This system demonstrates resistance to calendar aging, high operating potential, and low voltage hysteresis.
- Li4FeSbO6 provides a framework for developing sustainable, Fe-based intercalation cathodes for high-voltage applications.
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