Surface Reactivity of Li₂MnO₃: First-Principles and Experimental Study.

Area of Science:

• Materials Science
• Electrochemistry
• Surface Chemistry

Background:

• Layered lithium oxides are critical cathode materials for lithium-ion batteries.
• Understanding surface reactivity is key to mitigating parasitic reactions causing battery aging.
• Li$_{2}$MnO$_{3}$ serves as a model compound for studying tetravalent manganese in these oxides.

Purpose of the Study:

• To investigate the surface reactivity of (001)-oriented Li$_{2}$MnO$_{3}$ crystals.
• To elucidate the role of tetravalent manganese in surface interactions.
• To understand mechanisms behind early battery aging and poor storage.

Main Methods:

• Multitechnique approach: material synthesis, X-ray photoemission spectroscopy (XPS), scanning electron microscopy, Auger electron spectroscopy.
• First-principles calculations using a slab model of the Li$_{2}$MnO$_{3}$ surface.
• SO$_{2}$ gas adsorption experiments on large Li$_{2}$MnO$_{3}$ crystals.

Main Results:

• SO$_{2}$ adsorption was found to be homogeneous at micro- and nanoscale.
• XPS and chemical mapping indicated manganese reduction upon SO$_{2}$ adsorption.
• Calculations confirmed sulfate formation with charge transfer, involving Mn reduction.

Conclusions:

• Surface reactivity of Li$_{2}$MnO$_{3}$ involves Mn reduction upon SO$_{2}$ exposure.
• Sulfate species formation is the energetically favorable outcome.
• This study provides insights into degradation mechanisms affecting lithium-ion battery performance.