Mn(II) Deposition on Anodes and Its Effect on Capacity Fade in Spinel LiMn2O4-Carbon System

Dissolution and migration of manganese from cathode lead to severe capacity fading of Li₂MnO₄-carbon cells. Overcoming this major problem requires better understanding of the mechanism of manganese dissolution, migration, and deposition. Here, we apply a variety of advanced analytical methods to the study of LiMn₂O₄ cathodes cycled with different anodes. We provide solid evidence, for the first time, that oxidation state of manganese deposited on the anodes is +2, which differs from the results reported earlier. The results also indicates that a metathesis reaction between Mn(II) and some species on the solid-electrolyte interphase takes place during the deposition of Mn(II) on the anodes, rather than a reduction reaction that leads to the formation of metallic Mn otherwise, as speculated in earlier studies. The concentration of Mn deposited on the anode increases gradually with cycles; this trend is well correlated with anode’s rising impedance and capacity fading of the cell.