3D morphological evolution of Li-ion battery negative electrode LiVO ₂ during oxidation using X-ray nano-tomography

Lithium vanadium oxide (LiVO ₂ ¹) holds the potential promise to replace graphite as an anode material in commercial Li-ion batteries as it doubles the volumetric energy density compared to graphite but can still operate at low voltage (~ 0.1 V vs. Li/Li ⁺). Its degradation mechanism was investigated using a synchrotron X-ray nano-tomography technique to image the LiVO ₂ in three dimensions (3D). In particular an oxidation effect is discussed by a direct visualization and quantification of the 3D microstructure of the LiVO ₂ before and after being exposed to the air, which results in the oxidation of the LiVO ₂. After being exposed to air, an oxidation layer with thickness ~ 120-240 nm was observed at the interface of the LiVO ₂ particles and the binders/pores. While the total volume of LiVO ₂ remains relatively constant before and after oxidation, the particle size reduces, which is consistent with crack growth possibly due to the local exothermal oxidation reactions, accompanied by phase transition at an elevated temperature. The findings confirm the air-sensitivity of LiVO ₂ observed indirectly in the literature.