Yukio Chida

Relationship between cycle life of Li(Mn2−xLix)O4−δ and oxygen deficiency δ

We electrochemically and crystallographically investigated the quantitative details of relationship between cycle life of Li(Mn2−xLix)O4−δ (nominally x=0.02) spinel and oxygen deficiency δ which was precisely determined by chemical analysis. We found that capacity retention rate after the 100th cycle at 25°C is linearly decreased with increasing oxygen deficiency. The changes in lattice parameter before and after 500 times cycling test were compared with the changes in potential curves. The changes in lattice parameter at the end of discharged state after the 500th cycle depended on oxygen deficiency δ. They were in good accordance with the degradation in the low voltage region of potential curve, which was strongly affected by oxygen loss and rapidly saturated within about the 100th cycle. These results implied the influence of Jahn–Teller ion Mn3+ introduced with oxygen deficiency.

Potassium-graphite intercalation compounds from thin carbon films prepared between montmorillonite lamellae

An attempt was made to synthesize first stage potassium graphite intercalation compounds (K-GIC) from carbon films with thickness of only about 40 nm, which was prepared in the two-dimensional space between the lamellac of montmorillonite. For comparison, K-GIC from natural graphite flakes were also synthesized. The compounds thus obtained were characterized with X-ray diffractometer and their chemical stability was investigated. The process of potassium intercalation was discussed in relation to the change in average crystal size Lc, due to the intercalation.