X-ray absorption spectroscopy and resonant inelastic scattering study of the first lithiation cycle of the Li-ion battery cathode Li2−xMnSiO4

Abstract

We employ soft X-ray absorption spectroscopy and resonant inelastic X-ray scattering spectroscopy to study the redox behavior in the first lithiation/delithiation cycle of Li_2−xMnSiO₄ (4.0–4.6 V). For extraction of lithium ions up to an end potential of 4.1 V, we do not detect any change in the oxidation state for the expected redox-active Mn atom, instead the electronic structure of the Si–O network is affected. Above 4.1 V, there is an abrupt change in the oxidation state of the Mn-ions, from 2+ to 4+, which is accompanied by a complete loss of long range order in the material, as detected by X-ray diffraction. Further lithium extraction leads to progressive loss of crystallinity of Li_2−xMnSiO₄, rather than formation of a new structure, explaining the measured first-cycle capacity loss of this material. Our results suggest that future improvement of the crystalline stability of the material, particularly with respect to the SiO₄ network, is required to harness the full charge capacity of Li_2−xMnSiO₄.