Deterioration Factors of Electric Double-Layer Capacitors Obtained from Voltage Hold Test

A chemical analysis was carried out before and after a constant voltage hold test (applied at 2.5, 2.8, 3.0, and 3.2 V individually for 1 week) that was an acceleration deterioration examination to clarify the deterioration factors of electric double-layer capacitors. The results showed that the stress test slightly raised the internal resistances and decreased the capacitances. It was also confirmed that a range of fluorochemicals was formed on the electrode surface for approximately 10–13 nm in depth using electron spectroscopy for chemical analysis. From a chemical analysis of the electrolyte using an inductively coupling plasma-optical emission spectrometer (ICP-OES), it was confirmed that the electrolyte included Si, which is an ingredient element of an electrode, and that the increase in the holding voltage during the stress test decreased the Si density in the electrolyte

Effect of Ball Milling on the Electrochemical Performance of Activated Carbon with a Very High Specific Surface Area

Activated carbon (AC) with a very high specific surface area of >3000 m(2)g(-1) and a number of course particles (average size: 75 mu m) was pulverized by means of planetary ball milling under different conditions to find its greatest performances as the active material of an electric double-layer capacitor (EDLC) using a nonaqueous electrolyte. The variations in textural properties and particle morphology of the AC during the ball milling were investigated. The electrochemical performance (specific capacitance, rate and cyclic stabilities, and Ragone plot, both from gravimetric and volumetric viewpoints) was also evaluated for the ACs milled with different particle size distributions. A trade-off relation between the pulverization and the porosity maintenance of the AC was observed within the limited milling time. However, prolonged milling led to a degeneration of pores within the AC and a saturation of pulverization degree. The appropriate milling time provided the AC a high volumetric specific capacitance, as well as the greatest maintenance of both the gravimetric and volumetric specific capacitance. A high volumetric energy density of 6.6 Wh L-1 was attained at the high-power density of 1 kW L-1, which was a 35% increment compared with the nonmilled AC. The electrode densification (decreased interparticle gap) and the enhanced ion-transportation within the AC pores, which were attributed to the pulverization, were responsible for those excellent performances. It was also shown that excessive milling could degrade the EDLC performances because of the lowered micro- and meso-porosity and the excessive electrode densification to restrict the ion-transportation within the pores

Efect of Ball Milling on the Electrochemical Performance of Activated Carbon with a Very High Specific Surface Area

Activated carbon (AC) with a very high specific surface area of >3000 m2 g-1 and a number　of course particles (average size: 75 μm) was pulverized by means of planetary ball milling under　di erent conditions to find its greatest performances as the active material of an electric double-layer　capacitor (EDLC) using a nonaqueous electrolyte. The variations in textural properties and particle　morphology of the AC during the ball milling were investigated. The electrochemical performance　(specific capacitance, rate and cyclic stabilities, and Ragone plot, both from gravimetric and volumetric　viewpoints) was also evaluated for the ACs milled with di erent particle size distributions. A trade-o 　relation between the pulverization and the porosity maintenance of the AC was observed within the　limited milling time. However, prolonged milling led to a degeneration of pores within the AC and a　saturation of pulverization degree. The appropriate milling time provided the AC a high volumetric　specific capacitance, as well as the greatest maintenance of both the gravimetric and volumetric　specific capacitance. A high volumetric energy density of 6.6 Wh L-1 was attained at the high-power　density of 1 kW L-1, which was a 35% increment compared with the nonmilled AC. The electrode　densification (decreased interparticle gap) and the enhanced ion-transportation within the AC pores,　which were attributed to the pulverization, were responsible for those excellent performances. It was　also shown that excessive milling could degrade the EDLC performances because of the lowered　micro- and meso-porosity and the excessive electrode densification to restrict the ion-transportation　within the pores

子どもたちを加害者にも被害者にもしないインターネット安全教室の現状と対策 ～宮崎市内の小学校における情報モラル教育の調査～

パソコンやインターネットは近年急速な普及によって、私たちの生活をますます豊かにする可能性、いわゆるインターネットの光の部分を持っている。しかし、自動車のように、ルールとマナーを守って利用しなければ、自分や他人に危害を加える危険性も持っており、実際にコンピュータウィルス感染、詐欺行為、プライバシー侵害、情報漏えいなどの問題、いわゆるインターネットの影の部分が現実の社会問題になっている。また、青少年に対する有害な情報の氾濫も大きな社会問題となっている。本研究では、インターネット安全教室の現状、情報モラルに関する調査事例紹介、情報モラル出前授業、主に宮崎市内の5校の小学6年生を対象にした情報モラル出前授業の調査結果・分析を踏まえて、主に青少年の情報モラルの対策等について検討したので、以下に述べる

Modeling of Equivalent Circuit Analysis of Degraded Electric Double-Layer Capacitors

The demand for electric double-layer capacitors (EDLCs) has recently increased, especially for regenerative braking systems in electric or hybrid vehicles. However, using EDLCs under high temperature often enhances their degradation. Continuously monitoring EDLC degradation is important to prevent sudden malfunction and rapid drops in efficiency. Therefore, it is useful to diagnose the degradation at a lower frequency than that used in charge/discharge. Unused and degraded EDLCs were analyzed using the alternating current impedance method for measurements over a wide frequency range. Each result had a different spectrum up to 1 kHz. In addition, we show the basic inside condition of EDLCs with equivalent circuit analysis. This paper explores the possibility of degradation diagnosis at a high frequency and the basic physical mechanism

High-Temperature Degradation Tests on Electric Double-Layer Capacitors: The Effect of Residual Voltage on Degradation

The demand for electric double-layer capacitors, which have high capacity and are maintenance-free, for use in a variety of devices has increased. Nevertheless, it is important to know the degradation behavior of these capacitors at high temperatures because they are expected to be used in severe environments. Therefore, degradation tests at 25 °C and 80 °C were carried out in the current study to analyze the degradation behavior. Steam-activated carbon, Ketjen black, and PTFE were used as the electrodes, conductive material, and binder, respectively, and KOH was used as the electrolyte. The impedance and capacitance were calculated from the voltage and current in the device using the alternating current (AC) impedance method. The results showed that the impedance increased and the capacitance decreased over 14 days at 80 °C, which is the inverse of what we observed at 25 °C. Rapid degradation was also confirmed from the 80 °C degradation test. The residual voltage after measuring the current and voltage was a prominent factor influencing this rapid degradation

Influences of the pre-chamber orifices on the combustion behavior in a constant volume chamber simulating pre-chamber type medium-speed gas engines

The study aims to clarify the influence of pre-chamber (PC) configurations on the combustion process in the main chamber (MC) of medium-speed spark-ignition gas engines equipped with an active PC. A constant volume combustion chamber was prepared to simulate the chamber configurations of the gas engines. A high-speed shadowgraph was applied to visualize the torch flame development and the combustion process in the MC. Experiments were done by changing the charged gas in the MC, the number, and the diameter of the PC orifices. Combustion was most accelerated when the PC orifice configuration was set appropriately so that the adjacent torch flames would combine with each other. It was also found that the unburned mixture in the PC, which ejected prior to the torch flame, supported the penetration of the torch flame

Modeling of Equivalent Circuit Analysis of Degraded Electric Double-Layer Capacitors

The demand for electric double-layer capacitors (EDLCs) has recently increased, especially for regenerative braking systems in electric or hybrid vehicles. However, using EDLCs under high temperature often enhances their degradation. Continuously monitoring EDLC degradation is important to prevent sudden malfunction and rapid drops in efficiency. Therefore, it is useful to diagnose the degradation at a lower frequency than that used in charge/discharge. Unused and degraded EDLCs were analyzed using the alternating current impedance method for measurements over a wide frequency range. Each result had a different spectrum up to 1 kHz. In addition, we show the basic inside condition of EDLCs with equivalent circuit analysis. This paper explores the possibility of degradation diagnosis at a high frequency and the basic physical mechanism

Efect of Ball Milling on the Electrochemical Performance of Activated Carbon with a Very High Specific Surface Area

Activated carbon (AC) with a very high specific surface area of >3000 m2 g−1 and a number of course particles (average size: 75 µm) was pulverized by means of planetary ball milling under different conditions to find its greatest performances as the active material of an electric double-layer capacitor (EDLC) using a nonaqueous electrolyte. The variations in textural properties and particle morphology of the AC during the ball milling were investigated. The electrochemical performance (specific capacitance, rate and cyclic stabilities, and Ragone plot, both from gravimetric and volumetric viewpoints) was also evaluated for the ACs milled with different particle size distributions. A trade-off relation between the pulverization and the porosity maintenance of the AC was observed within the limited milling time. However, prolonged milling led to a degeneration of pores within the AC and a saturation of pulverization degree. The appropriate milling time provided the AC a high volumetric specific capacitance, as well as the greatest maintenance of both the gravimetric and volumetric specific capacitance. A high volumetric energy density of 6.6 Wh L−1 was attained at the high-power density of 1 kW L−1, which was a 35% increment compared with the nonmilled AC. The electrode densification (decreased interparticle gap) and the enhanced ion-transportation within the AC pores, which were attributed to the pulverization, were responsible for those excellent performances. It was also shown that excessive milling could degrade the EDLC performances because of the lowered micro- and meso-porosity and the excessive electrode densification to restrict the ion-transportation within the pores