Takanobu Kawai

Particle-size effect of carbon powders on the discharge capacity of lithium ion batteries

To improve the performance of the negative electrodes for lithium-ion batteries, a study has been made of the particle-size effect of carbon powder on discharge capacity and the optimum mixing ratio between large (average diameter: 25.8 μm) and small (average diameter: 4.2 μm) powder particle size has been found. The largest capacity is obtained when the large particle size fraction is about 70 wt.%. The smaller the particle size ratio, the larger the capacity, where the particle size ratio is the ratio of the average diameter of the smaller component to that of the larger one. These results indicate that discharge capacity is closely related to carbon powder packing, which is controlled by the mixing weight and particle-size ratios.

Characteristics of coke carbon modified with mesophase-pitch as a negative electrode for lithium ion batteries

Abstract To increase the charge–discharge capacity of carbon electrodes for lithium ion secondary batteries, coke carbon, a relatively cheap material, was modified with mesophase-pitch carbon by a heat treatment. While coke carbon powder, mesophase-pitch, and a mixture thereof (4:1 by weight) supplied between 0 and 1.5 V vs. Li/Li+ an initial discharge capacity of about 295 mAh/g, 310 mAh/g, and 310 mAh/g, respectively, the modified coke deintercalated 400 mA h/g of lithium with a high degree of reversibility. The difference in capacity between the modified carbon and mixture are discussed based on the shape of their current–potential curves and their galvanostatic charge–discharge curves.