Chemical Double Layer Research Articles

Alternate Direct-Drive Option for Electric Propulsion

The goal of this research is to power a 1.5-kW Hall thruster with a power source based on chemical double layer capacitor technology and to access performance characteristics of this power/propulsion system. The thruster was operatedinalong-pulsemodewithdecayingpowerinputandexhibitedsimilarperformancecharacteristicstobeing operatedundersteady-stateconditions.Overthetestedpowerrangeof450–1750W,thethrustergeneratedthrustof 30–100 mN at an efficiency of 30–55% and a specific impulse of 900–1950 s. These results formed the basis for a mission analysis considering extremes with regard to shading and atmospheric density. A near-Earth orbiting spacecraft served as an analysis platform to compare the mission performance of direct-drive electric propulsion options and a state-of-the-art hydrazine monopropellant system. Regardless of orbit conditions, electric propulsion options outperformed the conventional chemical system in terms of wet mass decrease (41–59%) and net mass increase (14–47%), while capacitor-powered electric propulsion options substantially reduced the onboard power requirement (66–91%).

Capacitors

Over the last decade, significant increases in capacitor performance, especially in reliability and energy/power densities, have been achieved for energy discharge applications in plasma science and fusion research applications through a combination of advanced manufacturing techniques, new materials, and diagnostic methodologies to provide requisite lifecycle performance for high energy pulse applications. Recent innovations in analysis of aging are introduced for predicting component performance and fault tolerance, especially relevant for very high energy storage applications necessary for next generation simulators, electrically energized fusion research machines, and advanced high power electronics for commercial, industrial, and military applications. Included in this study will be developments in capacitor technologies for electronics filtering and resonant energy transfer applications, as well as multisecond energy reservoir applications for uninterruptible power sources and the like. Next generation power electronics, driven by advances in solid state switching technologies, will require reduced capacitor dissipation factor by 1/3 to 1/10 at the same cost, particularly for AC applications. In addition, higher power electronics will require robust high frequency mica capacitor technology for >300/spl deg/C operation, up to 5 kV. The increasing expansion of the motor drive and industrial switched mode power supply (SMPS) market will be driven in cost by the availability of electrolytic capacitors of 750-850 Vdc ratings, at 450 Vdc cost and size. New formation processes and electrolytes are anticipated to be needed to achieve these extended performance levels. At higher frequencies, advanced power electronics drives the need for lower equivalent series resistance (ESR)/spl Lt/0.1% to 100 MHz, multimicrofarad value solid tantalum capacitors, having fail-safe surface mount configurations. Emerging power electronics applications in the millisecond and longer time are projected to have a broad application need for electrochemical chemical double layer capacitors, especially for compact sizes as this technology has the potential of achieving energy densities of many 20 kJ/kg for discharge times of tens of seconds. The prismatic power conditioning system, designed to be compliant with the available volume and surfaces into which it is to be placed, is described in some detail. It permits flexibility for the design engineer to optimize the design without having to allocate a specific space for the power conditioning system or subcomponents. Such prismatic geometry power and power conditioning systems are becoming commercially feasible In the low power consumer and industrial regime because of dramatic advances in multichip module switching, energy storage, and planarized interconnections. This work builds on assessing the applicability of these technologies to the megawatt-class average power, power electronics regime. Higher power density prismatic power electronics enables abroad range of applications in the commercial arena in areas such as motor drives, inverters, power quality systems, and mobile power systems.

Chemical double-layer capacitor power source for electromechanical thrust vector control actuator

Power sources for electrical actuation systems need to be made as compact as possible for many potential applications. Size and weight constraints require that the energy and power densities of the source be as large as possible. While, in general, it is not possible to optimize both these parameters simultaneously, chemical double-layer (CDL) capacitor technology offers an excellent combination of the desirable energy and power density characteristics required in a source for these applications. The work presented here focuses on the design, testing, and evaluation of the CDL capacitor technology in combination with batteries as a unique power source for electrical actuation systems. In this research effort CDL capacitor technology was applied in the design and development of a power source for thrust vector control electromechanical actuators currently being developed for use on the Space Shuttle's solid rocket boosters. CDL capacitors have many properties that make them well suited for actuator applications. Among them are that they have the highest demonstrated energy density for capacitive storage (about a factor of 5-10 less than NiCd batteries), have power densities up to 50 times greater than NiCd batteries, are capable of 500,000 charge-discharge cycles, can be charged at extremely high rates, and have nonexplosive failure modes. Thus, CDL capacitors exhibit a combination of desirable battery and capacitor characteristics.

Limiting factors for carbon-based chemical double-layer capacitors

The chemical double-layer (CDL) capacitor improves the energy storage density dramatically when compared with conventional electrolytic capacitors. When compared to batteries, the CDL capacitor is much less energy dense, however the power density is orders of magnitude better. As a result, CDL-battery combinations present an interesting pulse power system with many potential applications. Due to the nature of the CDL, it is inherently a low voltage device. The applications of the CDL can be tailored to auxiliary energy and burst mode storages which require fast charge/discharge cycles. Typical of the applications envisioned are power system backup, directed energy weapons concepts, electric automobiles, and electric actuators. In this paper, we will discuss some of the general characteristics of carbon-based CDL technology, describing the structure, performance parameters, and methods of construction. Further, analytical and experimental results which define the state-of-the-art are presented and described in terms of impact on applications.

Effect of nuclear radiation on the electrical properties of chemical double layer capacitors

The effects of nuclear radiation on the electrical properties of chemical double-layer capacitors are determined. The capacitors were irradiated in a 2-MW nuclear reactor to different fluence levels. The exposure rate was 2.2*10/sup 10/ n/cm/sup 2/-s for thermal neutrons, 9.52*10/sup 8/ n/cm/sup 2/-s for fast neutrons (>3 MeV), and 1.47*10/sup 6/ rad/h for gamma radiation. The properties measured during and after irradiation included the capacitance, equivalent series resistance, and open-circuit voltage. The postirradiation effect on the leakage current was also determined. It was found that, while the capacitance increased during irradiation, the equivalent series resistance and the open-circuit voltage decreased slightly during irradiation. Changes in these properties, however, were not permanent, as was evident from postirradiation measurements. The leakage current did not show any significant change with radiation. The results indicate that chemical double-layer capacitors can be suitably used as a backup power source in electronic equipment operating in a radiation environment with total fluences up to 4.05*10/sup 14/ n/cm/sup 2/. >