Unlocking High-Energy Metal Fluoride Cathodes through Modulated Interfacial Kinetics

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Conversion-type cathodes offer high energy density for lithium-ion batteries.
• Sluggish nanoscale kinetics and complex phase transformations hinder their performance.
• Copper fluoride (CuF2) cathodes historically suffer from irreversibility issues.

Purpose of the Study:

• To reconcile the electrochemical reversibility of isostructural FeF2 and CuF2 cathodes.
• To overcome the irreversibility limitations of CuF2 cathodes for improved lithium-ion battery performance.
• To elucidate the role of interfacial kinetics in conversion reactions.

Main Methods:

• Infiltration of liquid gallium (Ga) into a CuF2/carbon matrix to form a percolation network (pGa-CuF2/C).
• Mechanistic studies to investigate the effect of Ga on fluorine mobility and phase transformations.
• Fabrication of an optimized pGa-CuF2/C@TiO2 core-shell structure.

Main Results:

• The Ga interlayer enabled reversible two-electron transfer via a displacement-reaction pathway in CuF2.
• Ga retarded fluorine mobility, promoting the Li2CuF4 intermediate phase.
• Ga minimized lattice mismatch and interfacial energy, facilitating homogeneous nucleation and a bicontinuous copper network.
• The optimized core-shell structure achieved ~300 mAh/g at 2.8 V after 20 cycles.

Conclusions:

• Interfacial kinetics are critical in determining the pathway and reversibility of conversion reactions.
• Modulating interfacial energy and lattice mismatch is key to unlocking the potential of conversion cathodes.
• Gallium infiltration presents a viable strategy to enhance the performance of fluoride-based conversion cathodes.