Hisashi Satake

Study on High Power Electric Energy Storage Devices Using Polyacenic Semiconductor Material

Electric energy storage devices with higher energy density and higher power density are required for hybrid electric vehicle use. We have investigated the structure and property of polyacenic semiconductor materials (PAS) and polycyclic aromatic hydrocarbons (PAHs) materials and the power characteristics (the resistance and the rate capability) of devices using the PAS or PAHs materials as negative electrodes. We focused on the effect of the particle size and the Li predoping amount on the power characteristics. We found that submicrometer particles of polyacenic semiconductor materials (PAS) with the Li predoping over 600 mAh/g have an excellent rate capability with current density over 500C.

Evaluation of Li-Metal Electrode Resistance by "Current-Rest-Method" Using "Four-Electrode Cell"

Introduction Nowadays the lithium-ion batteries are known as the promising energy storage devices for HEV/PHEV. The devices are expected to put into practical use in several years. Lithium-ion capacitors and capacitors have been also remarkably developed. For power usage of these energy storage devices, the input-output power characteristics are critically important. S. Yata has proposed applying the advanced method of DC internal resistance measurement (S. Yata calls it the “CurrentRest-Method”), which is a useful evaluation method to link to input-output power characteristics. The Current-Interrupter-Method is also known as the DC internal resistance measurement used to determine values such as the ohmic resistance, the double layer capacitance and the diffusion coefficients by a current interruption of less than about 10 seconds. On the other hand, the C.R.M. resistance, which was obtained by the current rest of 10 to 10 seconds during the charge/discharge processes, can be used to calculate various C-rate charge/discharge curves around the region of the rest points using the time-dependence of the resistance . S. Yata has also proposed the use of a “four-electrode cell” 1,2,5) having two reference electrodes located close to a positive electrode and a negative electrode, which makes it possible to separate the internal resistance into three parts: the positive electrode resistance, the negative electrode resistance and the separator resistance (impregnated electrolyte). This method to separate the resistance significantly accelerates the studies in this field. We investigated the C.R.M. resistance of a lithium-ion battery (positive electrode: Co-based, negative electrode: graphitized MCMB) using the “four-electrode cell”, and we found that the C.R.M. resistance of the positive electrode strongly depended on the SOC, but that of the negative electrode did not. Moreover, we found that the C.R.M. resistance of the positive electrode (Co-based material) remarkably increased in a low voltage range during the 500-hour floating test.