Structural originations of irreversible capacity loss from highly lithiated copper oxides

We use electrochemistry, high-energy X-ray diffraction (XRD) with pair-distribution function analysis (PDF), and density functional theory (DFT) to study the instabilities of Li2CuO2 at varying state of charge. Rietveld refinement of XRD patterns revealed phase evolution from pure Li2CuO2 body-centered orthorhombic (Immm) space group to multiphase compositions after cycling. The PDF showed CuO4 square chains with varying packing during electrochemical cycling. Peaks in the G(r) at the Cu–O distance for delithiated, LiCuO2, showed CuO4 square chains with reduced ionic radius for Cu in the 3+ state. At full depth of discharge to 1.5 V, CuO was observed in fractions greater than the initial impurity level which strongly affects the reversibility of the lithiation reactions contributing to capacity loss. DFT calculations showed electron removal from Cu and O during delithiation of Li2CuO2.

Graphical abstractStructural transformation from Li2CuO2 to delithiated LiCuO2.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► We use experimental techniques and theoretical calculation to study the instabilities of Li2CuO2. ► After initial charge multiphase material persists through charge–discharge cycle. ► Precipitation of CuO strongly affects electrode reversibility contributing to capacity loss. ► Structural disorganization in Li2CuO2 after cycling is the result of CuO4 square chain packing. ► DFT calculations show electron removal from both Cu and O during delithiation of Li2CuO2.