Tracking Transient LixCo3O4 Intermediates during the Co3O4 Conversion Reaction by In situ XRD

Abstract Conversion-type anodes such as spinel Co3O4 are typically described by a two-step reduction pathway (Co3O4 → CoO → Co) accompanied by Li2O formation. However, transient crystalline states preceding full conversion are difficult to resolve because long-range order is rapidly lost during lithiation. In this study, in situ X-ray diffraction (XRD) was used to monitor the phase evolution of a Co3O4 electrode during lithiation/delithiation. During the initial discharge, new reflections emerged that were assigned to a LixCo3O4 intermediate, using Li1.47Co3O4 as the structural reference. The diffraction evolution indicates the formation of a lithiated LixCo3O4 intermediate derived from the pristine spinel Co3O4 framework prior to further conversion to nanoscale Co and Li2O. No distinct crystalline CoO reflections were resolved. The LixCo3O4-related reflections did not recover during subsequent charging, indicating structural irreversibility. These findings provide direct structural evidence for the formation of a LixCo3O4 intermediate during Co3O4 lithiation and clarify the irreversible structural evolution associated with conversion-type oxide anodes.