Anti-NASICON Fe2(MoO4)3 is a potential candidate for intercalation electrode materials in both rechargeable lithium and sodium ion batteries, owing to the open three dimensional framework, and the earth abundant nature of iron. Fe2(MoO4)3 crystallizes into a monoclinic (P21/c) structure, which consists of FeO6 octahedra and MoO4 tetrahedra interconnected through corner sharing oxygen atoms. Moreover, Fe2(MoO4)3 exhibits highly reversible lithium and sodium storage with reasonable capacity. In this presentation, the key underlying difference between Li+ and Na+ intercalation into monoclinic anti-NASICON Fe2(MoO4)3 is demonstrated using a combination of in-situ X-ray diffraction and electrochemical cycling along with neutron diffraction measurements. A two-phase structural change occurs during Li+-intercalation that is driven by a concerted rotation of rigid polyhedral subunits, as verified by symmetry mode-analysis. In contrast, Na+-intercalation proceeds through two different solid solution regions that are related to the filling of two different sites for Na+ in NaxFe2(MoO4)3 as reflected by a continuous expansion in the unit cell along two different crystallographic directions. The effect of the intercalation processes on the local structure of Fe2(MoO4)3, characterized by neutron total scattering measurements, implies that these correlated rotational distortions are much less coherent in the case of Na+ insertion than Li+ insertion.

Effect of rotational polyhedra distortions on guest ion intercalation in anti-NASICON Fe2(MoO4)3

251st National Meeting (2016)

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