Daisuke Tashima

Plasma Surface Treatment of Carbonaceous Materials for Application in Electric Double Layer Capacitors

In this work, carbonaceous materials were modified in order to improve capacitance and charge density in electric double layer capacitors (EDLCs). Optimal conditions for plasma surface treatment of activated carbon have been examined for times from 1 to 10 h at 150 °C. The plasma is a high-frequency glow discharge in N2. The pressure of the gas is 13.3 Pa. The electrode is set up so that the EDLC sample is covered with the glow discharge. Specific capacitance and charge density can be improved by plasma surface treatment of carbon materials.

Influence of reflection wave on measurement of space charge in electric double layer capacitor

In this study, the electrolyte was injected to Electric Double Layer Capacitor (EDLC) after degas treatment in vacuum and directly in air and the internal charge distribution in the EDLC was examined by Pulsed Electro Acoustic(PEA) method. However, those results do not take the reflected wave into consideration. Here, the reflected wave was examined, and discussed the internal charge distribution of EDLC. As a result, the reflected wave component included in the measurement result of PEA technique is little, and it was understood to hardly influence to calculate the electrostatic capacity. Those results are described in this paper.

Measurement of internal charge distribution of electric double layer capacitor by PEA method

In this study, electrolyte was injected into an electric double layer capacitor (EDLC) after degas treatment in vacuum and directly in air, respectively, and the internal charge distribution in the EDLC was examined by the pulsed electro acoustic (PEA) method. It was found that volume charge density in the case of injection of electrolyte after degas treatment in vacuum is about seven times compared with that injected directly in air. It was thought that sufficient electrolyte can be injected into the polarized microporous electrode by degas in vacuum and more electric charge can be saved. Moreover, the sound velocity in the material is examined. It has been understood that electrostatic capacity gradually increases with the rise of applied voltage. The electrostatic capacity was estimated by the PEA method and the energy conversion method, respectively. The results from two methods are in good agreement.

Evaluation of quantity of stored charge in electric double layer capacitor by pulsed electro acoustic method

In this research, the space charge distribution in electric double layer capacitor (EDLC) for energy storage has been examined by a pulsed electro-acoustic (PEA) method. However, the measurement result has a reflection wave component generated by reflection and penetration of the acoustic wave, because the EDLC with five layer structures consists of three kind of materials (aluminum, cellulose, and activated carbon). Then, it is calculated from the acoustic impedance and relative permittivity of the material of EDLC, and examined the influence of reflected wave components on signal voltage. In this research, charge density influenced by reflection wave component from signal voltage was investigated. As a result, the correlation between signal voltage and charge density was understood, and the influence on charge distribution was examined.

Roles of pore structure and type of electrolyte on the capacitive performance of activated carbons used in electrical double-layer capacitors

Capacitive performances of the microporous activated carbon (AC) and the mesoporous AC, having a comparable BET specific surface area, were evaluated for the use in the electrodes of electrical double-layer capacitors (EDLCs). The propylene carbonate-based organic electrolytes and the ionic liquid electrolyte were used in the EDLC cells. The gravimetric specific capacitance of the microporous AC was higher than that of the mesoporous AC when the organic electrolyte was used, while the difference between those ACs diminished when the ionic liquid was used. The results obtained revealed that the capacitive performances of ACs were influenced by the affinity between the pore structure and the electrolyte, and the applied voltage.

Temperature dependence of capacitance in electrochemical super capacitor

In this study, ketjen black was used for polarized electrodes instead of conventionally used acetylene black in order to improve the capacitance of activated carbon-based electric double layer capacitor (EDLC). Usually, ketjen black exhibits higher electronic conductivity compared to acetylene black, so that ketjen black could be considered as conducting filler. Moreover, N2 adsorption-desorption isotherm as well as TEM observation revealed that ketjen black used in this study has different type of pore structures compared to acetylene black. The capacitances of prepared EDLC were evaluated from discharge characteristics. It was found that the ketjen black containing EDLC showed fairly high capacitance compared to acetylene black containing one. In addition, in a temperature characteristic of EDLC which made ketjen black and acetylene black with quantity of same combination, we understood that ketjen black was superior to acetylene black. This experiment was done 50degC from 0degC in a temperature range. Ketjen black was superior to acetylene black in all temperature. It is understood that capacitance of EDLC was increased by using ketjen black.

Effect of Nitrogen Atom Doping for Electric Double Layer Capacitors Application

In this research, we measured spatio-temporal profiles of positive and negative charges in Electric Double Layer Capacitors (EDLCs) consist of activated carbon exposed to plasma discharge. The state of plasma is a high frequency glow discharge and sample of activated carbon is set on the center of glow discharge. Optimal conditions for plasma surface treatment of activated carbon have been examined with a time of 1~10 h at 150degC in N2. As the result, nitrogen atom is doped in the surface layer of the activated carbon, and capacitance of EDLCs has a peak in case of 1 h of plasma surface treatment. It is reported that capacitance increases with the nitrogen dope. Capacitance of EDLCs increased until 1 h of treatment time, but capacitance was decreasing in case of over 1 h of treatment time

Relation between Space Charge and Pore Size of Nano Porous Electrode for Super Capacitor

The space charge distribution in electric double layer capacitor (EDLC) for energy storage has been examined by pulsed electro-acoustic (PEA) method since 2002. It is found that the measuremental result can be influenced by the reflection and penetration of the sound wave when the space charge distribution of EDLC is measured by PEA method, because the EDLC has a five layer structure consisting of three materials (aluminum, cellulose, and activated carbon). Then, we calculated reflection wave components that influence on charge density from the acoustic impedance and relative permittivity of the materials. As a result, it has been understood that the changes in the space charge distribution of EDLC and the charge characteristic of the EDLC are almost corresponding. The use of the PEA method can be expected as a method of evaluating the accumulation charge of EDLC by measuring the space charge distribution of it. In this paper, a polarized electrode is made to develop EDLC and a ratio of surface area and average pore diameter of polarized electrode is measured by nitrogen adsorption method at 77K. Also, relation between a ratio of surface area and average pore diameter and space charge distributions of EDLC are discussed.

Basic characteristics of a heat and electricity combined generation system using biomass fuel

In this paper, we propose a unique co-generation system including a biomass boiler-using a thermoelectric generator (TEG). The boiler burned biomass fuel derived from a cow dung. In this system, warm water is generated through heat exchange in the boiler, and electricity is generated through the TEG that uses the high temperature of an exhaust gas from the boiler. In this study, the co-generation system was not well optimized, with the result that both the heat exchange efficiency of the biomass boiler and hence, - the amount of electric power generated were very low. However, the study demonstrated that the co-generation system that using the biomass as a heat source, and a TEG as an electric power generator can provide an effective energy source.

Maximum Output Power Control Using Short-Circuit Current and Open-Circuit Voltage of a Solar Panel

A control method to optimize the output power of a solar cell is necessary because the output of a solar cell strongly depends on solar radiation. We here proposed two output power control methods using the short-circuit current and open-circuit voltage of a solar panel. One of them used a current ratio and a voltage ratio (αβ control), and the other used a current ratio and a short-circuit current–electric power characteristic coefficient (αγ control). The usefulness of the αβ and the αγ control methods was evaluated. The results showed that the output power controlled by our proposed methods was close to the maximum output power of a solar panel.