Theoretical insights into the catalytic mechanisms of LiNi1/3Co1/3Mn1/3O2 cathode surfaces in diverse ethylene carbonate decomposition reactions

Abstract

The surface structural degradation of the cathode commonly results from the decomposition of electrolytes at the cathode material surfaces of lithium-ion batteries, which are closely related to the cathode electrolyte interphase (CEI) formation and gas evolution issues. This work systematically reveals the catalytic mechanisms of LiNi_1/3Co_1/3Mn_1/3O₂ (LiNCMO) cathode surfaces in diverse EC decomposition reactions through comprehensive first-principles calculations, involving the adsorption, direct ring-opening reactions, intramolecular H-transfer-assisted ring-opening reactions, F-assisted ring-opening reactions, direct dehydrogenation reactions, F-assisted dehydrogenation reactions, CO₂ release reactions, and polymerization reactions of EC on Li_xNCMO cathode (104) surfaces, as well as the role of PF₆⁻. The catalytic behaviors of multiple active sites involving Ni, Co, Mn, and O centers have been examined. Our computational results reveal Li-state-dependent reaction pathways on Li_xNCMO surfaces, with direct dehydrogenation preferentially occurring on Li_1/3NCMO and F-assisted ring-opening dominating on LiNCMO. EC demonstrates preferential adsorption at Mn sites across both lithiation states. The ring-opening reaction activity is closely related to electronic stability. The direct ring-opening of the EC molecule is extremely unlikely to occur, as the methylene carbon atom of EC cannot satisfy the octet rule in the ring-opened state. The intramolecular H-transfer-assisted ring-opening reactions of EC molecules enable the ring-opened EC molecule to achieve a thermodynamically stable state. The coupling reaction between EC and PF₆⁻ highlights the crucial role of PF₆⁻ in the EC ring-opening reaction. The polymerization termination proceeds through intramolecular H-transfer-assisted and F-assisted ring-opening reactions of the terminal EC molecule in the oligomer chain. The CO₂ release reactions yielding CO₂ and CH₃CHO are subject to kinetic limitations. Overall, this work provides atomic-level insights into the structure–activity relationships of degradation mechanisms of EC molecules at the layered cathode materials.