Discrete Li-occupation versus pseudo-continuous Na-occupation and their relationship with structural change behaviors in Fe2(MoO4)3

TL;DR

This study compares Li and Na intercalation in Fe2(MoO4)3, revealing distinct occupation paths and their effects on phase behavior, supported by atomic-scale observations and theoretical analysis, advancing understanding of battery electrode mechanisms.

Contribution

It uncovers the different atomic occupation modes of Li and Na in Fe2(MoO4)3 and links these to phase change behaviors, providing new insights into intercalation mechanisms.

Findings

Discreet Li occupation correlates with single-phase behavior.

Pseudo-continuous Na occupation correlates with two-phase behavior.

Atomic-scale imaging reveals biphasic domains and occupation modes.

Abstract

The key factors governing the single-phase or multi-phase structural change behaviors during the intercalation/deintercalation of guest ions have not been well studied and understood yet. Through systematic studies of orthorhombic Fe2(MoO4)3 electrode, two distinct guest ion occupation paths, namely discrete one for Li and pseudo-continuous one for Na, as well as their relationship with single-phase and two-phase modes for Na1 and Li1, respectively during the intercalation/deintercalation process have been demonstrated. For the first time, the direct atomic-scale observation of biphasic domains (discrete occupation) in partially lithiated Fe2(MoO4)3 and the one by one Na occupation (pseudo-continuous occupation) at 8d sites in partially sodiated Fe2(MoO4)3 are obtained during the discharge processes of Li/Fe2(MoO4)3 and Na/Fe2(MoO4)3 cells respectively. Our combined experimental and theoretical studies bring the new insights for the research and development of intercalation compounds as electrode materials for secondary batteries.