First-Principles Modeling of Mn(II) Migration above and Dissolution from LixMn2O4 (001) Surfaces

Density functional theory and ab initio molecular dynamics simulations are applied to investigate the migration of Mn(II) ions to above-surface sites on spinel LixMn2O4 (001) surfaces, the subsequent Mn dissolution into the organic liquid electrolyte, and the detrimental effects on graphite anode solid electrolyte interphase (SEI) passivating films after Mn(II) ions diffuse through the separator. The dissolution mechanism proves complex; the much-quoted Hunter disproportionation of Mn(III) to form Mn(II) is far from sufficient. Key steps that facilitate Mn(II) loss include concerted liquid/solid-state motions; proton-induced weakening of Mn-O bonds forming mobile OH- surface groups; and chemical reactions of adsorbed decomposed organic fragments. Mn(II) lodged between the inorganic Li2CO3 and organic lithium ethylene dicarbonate (LEDC) anode SEI components facilitate electrochemical reduction and decomposition of LEDC. These findings help inform future design of protective coatings, electrolytes, additives, and interfaces.