Lithium insertion mechanism in CoSb3 analysed by 121Sb Mössbauer spectrometry, X-ray: Absorption Spectroscopy and electronic structure calculations
Résumé
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 LixCoSby whose variable composition depends on the insertion conditions. XANES spectra at Sb LI, 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 → (LixCo1−mSby + m Co + Li3Sb) ↔ LizCo + y Li3Sb
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