Yasunori Ozawa

Self-discharge study of LiCoO2 cathode materials

Abstract The time dependence of the open-circuit voltage (OCV) and the capacity loss in Li/Li 1− y CoO 2 half-cells during high temperature aging were measured experimentally, and tentatively simulated with simple kinetics equations involving Li-ion diffusion and a phase transition, respectively. The respective activation energies were determined. The capacity loss was found to have a reversible and irreversible component. The latter is discussed in contest of recent observation of an irreversible hexagonal-to-spine phase transition.

An XRD Study of Chemical Self-Discharge in Delithiated Cobalt Oxide

Changes in samples of Li1–xCoO2 were measured by X-ray diffractometry (XRD) after thermal aging treatments that cause capacity losses in electrochemical cells. Changes in lattice parameters were used to identify lithium re-intercalation into Li1–xCoO2 when it was aged in the presence of LiClO4, LiPF6, and LiAsF6 in propylene carbonate (PC). Li+ re-intercalation could account for the reversible capacity loss. Thermal aging at 75°C in pure PC or pure argon gas resulted in other changes that are attributed to the formation of spinel phase. The rate of the lithium re-intercalation increases in the following sequence: LiPF6

The Kinetics of Sub-Fluorinated Carbon Fluoride Cathodes for Lithium Batteries

Sub-fluorinated carbon materials (CFx, x<1) were prepared by direct fluorination of synthetic graphite (Timcal KS15) and multi-walled carbon nanotubes (MWNT, MER). The fluorination parameters (temperature, fluorine partial pressure, fluorine flow rate and time) were set to achieve a target composition ’x’ in CFx, according to the starting carbonaceous material. The fluorine composition was determined by weight uptake and SEM/XEDX cross analyses.