Decoding the Oxygen Activity with Iron through Ligand-to-Metal Charge Transfer in Li-Rich Layered Cathodes

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Lithium-rich iron-based oxides are crucial for high-energy-density, cost-effective cathode materials.
• Iron's Fe³⁺ ions offer unique potential in regulating oxygen redox activity via ligand-to-metal charge transfer (LMCT).

Purpose of the Study:

• To investigate the mechanism of enhanced Fe-O redox activity through LMCT in Li-rich layered oxides.
• To understand the relationship between local structure distortion and redox processes.
• To provide insights into designing advanced iron-based cathode materials.

Main Methods:

• Operando ⁵⁷Fe Mössbauer spectroscopy.
• Synchrotron X-ray techniques.
• Density functional theory (DFT) calculations.

Main Results:

• Identified enhanced Fe-O redox activity driven by LMCT, facilitated by metastable Fe⁴⁺ intermediates.
• Observed suppression of Jahn-Teller distortion and dominance of Fe-O redox over Fe³⁺/Fe⁴⁺ redox.
• Achieved improved initial Coulombic efficiency and 95% capacity retention over 200 cycles at 4.4 V.

Conclusions:

• Demonstrated iron's role in regulating oxygen redox via LMCT in Li-rich layered systems.
• Highlighted challenges including cation migration and voltage fade at low potentials, requiring mitigation.
• Provided fundamental insights for developing high-performance, cost-effective iron-based cathode materials.