Cation-Disordered Lithium-Excess Li-Fe-Ti Oxide Cathode Materials for Enhanced Li-Ion Storage

Area of Science:

• Materials Science
• Electrochemistry
• Solid-state Chemistry

Background:

• Cation-disordered Li-excess lithium-transition metal (Li-TM) oxides are promising cathode materials for Li-ion batteries.
• Percolation theory guides the design of these high-performance materials.
• Understanding the role of Li excess is crucial for optimizing electrochemical properties.

Purpose of the Study:

• To investigate the effect of Li excess on the electrochemical Li-ion storage properties of cation-disordered rocksalt-type Li-Fe-Ti oxides.
• To correlate Li-to-transition metal ratios with structural and electrochemical performance.
• To elucidate the mechanisms responsible for enhanced Li-ion storage.

Main Methods:

• Synthesis of Li-Fe-Ti oxides with varying Li-to-transition metal (Li/TM) ratios (1, 1.49, 1.63).
• Electrochemical characterization including capacity and rate capability measurements.
• Spectroscopic analysis (57Fe Mössbauer, XPS, soft X-ray absorption) to study redox reactions and local structure.

Main Results:

• Li excess induces local structural fluctuations, creating 0-TM diffusion channels for rapid Li-ion migration.
• Li-excess cathodes (Li/TM = 1.49 and 1.63) exhibit reversible capacities over 220 mAh g⁻¹, significantly higher than the Li/TM = 1 electrode (165 mAh g⁻¹).
• Improved rate capability observed in Li-excess compositions.

Conclusions:

• Li excess in cation-disordered rocksalt-type Li-Fe-Ti oxides enhances electrochemical performance.
• The enhanced properties are attributed to improved Li-ion diffusion pathways and redox activity.
• Redox reactions involving Fe and O species are key contributors to the high capacity in Li-excess cathodes.