First-Principles Modeling of the Initial Stages of Organic Solvent Decomposition on Li_<i>x</i>Mn₂O₄(100) Surfaces

Abstract

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 (100) surfaces, the subsequent Mn dissolution into the organic liquid electrolyte, and the detrimental effects on 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 necessary but far from sufficient. Key steps that facilitate Mn(II) ion migration 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 component facilitates electrochemical reduction and decomposition of LEDC. These findings help inform future design of protective coatings, electrolytes, additives, and interfaces.