Mn(II) deposition on anodes and its effects on capacity fade in spinel lithium manganate-carbon systems.

Dissolution and migration of manganese from cathode lead to severe capacity fading of lithium manganate-carbon cells. Overcoming this major problem requires a better understanding of the mechanisms of manganese dissolution, migration and deposition. Here we apply a variety of advanced analytical methods to study lithium manganate cathodes that are cycled with different anodes. We show that the oxidation state of manganese deposited on the anodes is +2, which differs from the results reported earlier. Our results also indicate 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, as speculated in earlier studies. The concentration of Mn deposited on the anode gradually increases with cycles; this trend is well correlated with the anodes rising impedance and capacity fading of the cell.