Microvoltammetric studies on single particle voltammetry of LiNiO₂ and LiCoO₂. In situ observation of particle splitting during Li-ion extraction/insertion

Microvoltammetry for oxide particles of micrometer sizes has been applied to investigate Li⁺ ion extraction/insertion processes of LiCoO₂ and LiNiO₂ prepared by a citrate complex method. We intended here high voltage cyclic voltammetry for Li⁺ extraction/insertion from/into the oxides up to the anodic potential of 5.2 V vs. Li/Li⁺ in organic solutions containing LiClO₄. With simultaneous measurements of voltammograms, in situ observation of the particle deformation during Li⁺ extraction/insertion was carried out using an optical microscope equipped with a CCD camera and a video recorder. In the case of LiNiC-4, particle splitting during the extraction/insertion was observed; most of the particles are split into several pieces about 4.5 V in the first anodic scanning , and in multi-potential cycling up to 5.0 V with a potential increment of 0.2 V, it takes at above 4.8 V in the anodic scan and at 4.0-4.1 V at the reversed cathodic scan.