Deterioration mechanisms of LiCoO2 electrode materials for lithium ion batteries remain unclear. Using electron energy-loss spectroscopy and transmission electron microscopy, this study investigated chemical states of LiCoO2 particles on first overcharging. We present a scheme for quantification of the Li/Co atomic ratio. Using quantitative Li mapping and comprehensive probing of Li–K, Co–M2,3, Co–L3, and O–K edges, we observed that overcharging causes the progression of Co3+/Co2+ reduction with oxygen extraction from the particle surface to the interior. A gradual change in the chemical composition at and around the particle surfaces after charging of 60% revealed the presence of Co3O4-like and CoO-like phases at surface regions. We also observed nanocracks with deficient Li ions. These results are key factors affecting degradation on overcharging.

Electrospinning enables fabrication of nanowires (NWs) of various materials from a polymer solution. Nevertheless, few reports have described single crystallization of oxide and polyanion NWs. Its mechanism remains unknown. This report presents transmission electron microscopy observations of conversion from electrospun amorphous NWs to single-crystalline olivine lithium phosphate NWs. After nucleation and grain growth, single crystallization is achieved by the attachment of adjacent crystal grains with common crystallographic orientations in an amorphous phase confined to self-forming carbon shells. The present NW axes have no specific orientation. These results imply that self-forming shells play a key role in achieving single-crystalline NWs in electrospinning.