Lithium insertion mechanism in CoSb3 analysed by 121Sb Mössbauer spectrometry, X-ray absorption spectroscopy and electronic structure calculations

Abstract

The lithium insertion mechanism into the skutterudite-type CoSb₃ compound has been studied using X-ray Absorption Near Edge Structure (XANES), ¹²¹Sb Mössbauer spectrometry and electronic structure calculations based on the Density Functional Theory (DFT) in the Linear Muffin Tin Orbital (LMTO) framework. ¹²¹Sb Mössbauer spectra are in agreement with a progressive restructuring which occurs during the second stage (voltage plateau at 0.6 V). The Mössbauer hyperfine parameters show the formation of Li₃Sb and of a ternary intermediate phase Li_xCoSb_y whose variable composition depends on the insertion conditions. XANES spectra at Sb L_{I, III} and Co K edges have been compared to calculated Projected Densities of States (PDOS) of reference compounds containing Co, Sb and Li. This analysis has allowed specification of the restructuring mechanism as a distortion of the CoSb₆ octahedral units and confirms the formation of Li₃Sb. The overall characterisations have been interpreted to suggest the first discharge mechanism of restructuring in accordance with the global reaction:CoSb₃ + (y + z) Li → (Li_xCo_1−mSb_y + m Co + Li₃Sb) ↔ Li_zCo + y Li₃Sb