Mechanochemical Transformation From Zigzag-Type Layered/Phenakite to Disordered Rocksalt in Mn-Rich Cathodes for...

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Cation disorder in manganese-rich disordered rocksalt (DRX) systems is crucial for high-performance cathodes but its formation pathways, especially under mechanochemical activation, remain poorly understood.
• Existing DRX systems often involve complex redox mechanisms, limiting their stability and efficiency.

Purpose of the Study:

• To elucidate the transformation pathways leading to cation disorder in Mn-rich DRX systems activated by mechanochemistry.
• To investigate the role of molybdenum (Mo) and fluorine (F) co-doping in directing structural evolution and electrochemical properties.
• To establish a mechanistic framework for designing tunable, earth-abundant DRX cathodes.

Main Methods:

• Synthesis and characterization of Li_1.2Mn_(2+x)/3Mo_(0.4-x)/3O_2-xF_x (LMMOFx) materials with varying Mo and F content.
• Mechanochemical activation to induce cation disorder and structural transformation.
• Systematic structural analysis (e.g., XRD, TEM) and electrochemical testing (e.g., galvanostatic cycling) to correlate structure with performance.

Main Results:

• A novel transformation route was identified, driven by Mo and F co-doping, leading to a zigzag-type layered/phenakite-mixed structure.
• This phase transition promoted DRX formation and shifted the redox mechanism from a two-phase Mn/O process to a stable single-phase process.
• The optimized LMMOFx material achieved a high reversible capacity of 297.9 mAh g^-1, demonstrating improved electrochemical performance due to controlled disorder and phase mixing.

Conclusions:

• Mo and F co-doping effectively directs the formation of DRX structures via a unique layered/phenakite-mixed intermediate phase under mechanochemical activation.
• Controlled cation disorder and phase mixing are key to optimizing Li-ion transport and achieving high reversible capacity in Mn-rich DRX cathodes.
• The study provides a design principle for developing next-generation, earth-abundant DRX battery materials with tunable properties.