Predictions of particle size and lattice diffusion pathway requirements for sodium-ion anodes using η-Cu6Sn5 thin films as a model system

Loïc Baggetto, Jean Claude Jumas, Joanna Górka, Craig A. Bridges, Gabriel M. Veith

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39 Scopus citations

Abstract

Geometrically well-defined Cu6Sn5 thin films were used as a model system to estimate the diffusion depth and diffusion pathway requirements of Na ions in alloy anodes. Cu6Sn5 anodes have an initial reversible capacity towards Li of 545 mA h g-1 (Li3.96Sn or 19.8 Li/Cu6Sn5), close to the theoretical 586 mA h g-1 (Li4.26Sn), and a very low initial irreversible capacity of 1.6 Li/Cu6Sn5 (Li 0.32Sn). In contrast, the reaction with Na is limited with a reversible capacity of 160 mA h g-1 compared to the expected 516 mA h g-1 (Na3.75Sn). X-ray diffraction and 119Sn-Mössbauer spectroscopy measurements show that this limited capacity likely results from the restricted diffusion of Na into the anode nanoparticles and not the formation of a low Na-content phase. Moreover, our results suggest that the η-Cu6Sn5 alloy should have optimized particle sizes of nearly 10 nm diameter to increase the Na capacity significantly. An alternative system consisting of a two-phase mixture of Cu6Sn5 and Sn of nominal composition 'Cu 6Sn10' has been studied and is able to deliver a larger initial reversible storage capacity of up to 400 mA h g-1. Finally, we have demonstrated that the presence of Cu in Cu6Sn5 and 'Cu6Sn10' suppresses the anomalous electrolyte decomposition normally observed for pure Sn.

Original languageEnglish
Pages (from-to)10885-10894
Number of pages10
JournalPhysical Chemistry Chemical Physics
Volume15
Issue number26
DOIs
StatePublished - Jul 14 2013

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