Progress of the conversion reaction of Mn3O4 particles as a function of the depth of discharge

Abstract

A comprehensive investigation of the morphological and interfacial changes of Mn₃O₄ particles at different lithiation stages was performed in order to improve our understanding of the mechanism of the irreversible conversion reaction of Mn₃O₄. The micronization of Mn₃O₄ into a Mn–Li₂O nanocomposite microstructure and the formation of a solid electrolyte interphase (SEI) on the Mn₃O₄ surface were carefully observed and characterized by combining high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and in situ X-ray absorption fine structure (XAFS) measurements. Accumulation of a thin SEI film of 2–5 nm thickness on the surfaces of the Mn₃O₄ particles due to their catalytic decomposition was observed at a depth of discharge (DOD) of 0%. As the DOD increases from 25% to 75%, the SEI layer composed of Li₂CO₃ and LiF continues to grow to 20–30 nm, and Li₂O nanoparticles are clearly observed. At 100% DOD, the Mn–Li₂O particles with diameters of 2–5 nm become totally encapsulated within a huge organic–inorganic coating structure, while the overall starting shape of the particles remains.