Kohji Yuasa

Assessment of lithium ion doping into low crystallized carbonaceous materials using molecular orbital calculations

Using molecular orbital calculation, the Li doping reaction in low crystallized carbonaceous material was investigated. As the Li doping reaction occurs on the surface of the graphite layer, the influence on the electric charge of the graphite layer was examined with graphitic models attached with functional groups (-OH, -CHO). As a result, it is suggested that Li was doped at the different parts of the graphite layer after the typical intercalation reaction into the stacking structure. Furthermore, the structure doped with lithium became more stable when Li was doped on the negatively charged-carbon atom. It was concluded that the localization of charge densities of the structure of carbon conjugated-material effected strongly the Li induced adsorption at different parts of the graphite layer.

Improvement of basic performances of a nickel–metal hydride battery

To develop a sealed-type nickel-metal hydride battery for use in portable equipment or in electric vehicles, investigations were conducted on negative electrodes using AB5-type hydrogen storage alloy and positive electrodes. For the cycle life performance of the battery, alkaline treatment of the alloy and the substitution of more than 50% to the alloy with Co were effective. For the positive electrode, zinc as a solid solution in the nickel positive electrode obviously prevented γ-NiOOH from being formed in the charging process of β-Ni(OH)2 and suppressed the migration of the electrolyte solution in the separator to the active material of the positive electrode. Also, hydrophobic treatment of the surface of the alloy was effective to prevent the elevation of the battery internal pressure of the battery in high rate charge.