(Sub)surface-Promoted Disproportionation and Absolute Band Alignment in High-Power LiMn₂O₄ Cathodes

Abstract

We present an isotropic ( U eff ) and anisotropic ( U – J ) Hubbard and van der Waals (vdW)-corrected density functional theory study of bulk and low-index surfaces of lithium manganese oxide LiMn 2 O 4 (LMO), a promising cathode material for high-power Li-ion batteries. Use of anisotropic ( U – J ) corrections in the simulation of bulk LMO leads to improved agreement with available experimental data, whereas vdW corrections do not affect the results. Carefully converged relaxation of slab geometries indicates that when vdW corrections are included the spinel-reconstructed Li-terminated (111) surface is always energetically favored for both U eff and ( U – J ) methods regardless of the LMO phase. In contrast, neglect of vdW corrections leads to the (001) surface in orthorhombic phase being favored when applying ( U – J ) corrections. Independent of the simulation protocol and crystalline phase, (111) truncation, reconstructed or not, promotes LMO disproportionation and appearance of Mn 2+ cations without the need of any chemical or electrochemical surface treatment. Absolute band alignment of the considered surfaces reveals increased reductive propensity for the (111) terminations. Finally, our computational findings are discussed with respect to available data on the observed surface dependence of Mn disproportionation and electrochemical passivation of LMO substrates.