First-Principles Modeling of Mn(II) Migration above and Dissolution from Li_xMn₂O₄ (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 Li_xMn₂O₄ (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.