<i>In Situ</i> Transmission Electron Microscopy Study of Electrochemical Lithiation and Delithiation Cycling of the Conversion Anode RuO₂

Abstract

Conversion-type electrodes represent a broad class of materials with a new Li⁺ reactivity concept. Of these materials, RuO₂ can be considered a model material due to its metallic-like conductivity and its high theoretical capacity of 806 mAh/g. In this paper, we use <i>in situ</i> transmission electron microscopy to study the reaction between single-crystal RuO₂ nanowires and Li⁺. We show that a large volume expansion of 95% occurs after lithiation, 26% of which is irreversible after delithiation. Significant surface roughening and lithium embrittlement are also present. Furthermore, we show that the initial reaction from crystalline RuO₂ to the fully lithiated mixed phase of Ru/Li₂O is not fully reversible, passing through an intermediate phase of Li_<i>x</i>RuO₂. In subsequent cycles, the phase transitions are between amorphous RuO₂ in the delithiated state and a nanostructured network of Ru/Li₂O in the fully lithiated phase