DOW-UAP-D147, AAWSAP DIRD, Ultracapacitors as Energy and Power Storage Devices, November 2010

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Ultracapacitors as Energy and Power Storage Devices for Commercial and Military Applications The Defense Intelligence Reference Document provides nonsubstantive but authoritative reference information related to intelli ence to ics or methodolo ies. Prepared by: Technology Warning Division (DW0-4) Defense Warning Office Directorate for Analysis Defense Intelligence Agency AAP Person 84, AAP Person 85 (U) COPYRIGHT WARNING: Further dissemination of the photographs in this publication is not authorized. This product is one of a series of advanced technology reports produced in FY 2010 under the Defense Intelligence Agency, Defense Warning Office's Advanced Aerospace Weapons System Applications (AAWSA) Program. Comments or questions pertaining to this document should be addressed to !MP Person 1 AAWSA Program Manager, Defense Intelligence Agency,

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Batteries and Ultracaps...................................................................................... 3 Electronics and Telecommunications................................................................ 13 Chapter 5: Future Developments......................................................................... 25 Figure 2. Operation of an Ultracapacitor................................................................3 Figure 4. Electrolytic Capacitor as Designed and Patented by SOHIO.....................5 Figure 5. Activated Carbon Porosity.....................................................................10 Figure 8. Transmission Electron Microscope Image of Graphene .........................19 Figure 9. Relationship Between Average Pore Size and Normalized Specific

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Figure 10. CDC Synthesis and Electrochemical Test Cell Preparation Schematic. 21 Figure 12. MCap Structure................................................................................... 22 Figure 13. Preliminary MCap Test Results........................................................... 23 Figure 14. Summary Chart of MCap Results to Date............................................ 23 Figure 15. Specific Energy and Estimated Costs vs. foMc ...................................... 24 Table 1: Contrasting Properties of Batteries and Ultracapacitors........................... 4 Table 2: Manufacturers of Ultracapacitors.............................................................. 7 Table 3: Properties of Various Electrolytes Used in Ultracapacitors....................... 8 Table 4: Properties of Various Materials used in Electrochemical Capacitor

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Ultracapacitors as Energy and Power Storage Devices for Commercial and Military Applications Ultracapacitors (ultracaps) are energy storage devices capable of extremely rapid charge and discharge rates with the ability to be cycled hundreds of thousands of times. These unique capabilities make ultracaps attractive for a number of applications. The advantages over lithium ion batteries are somewhat mitigated by the fact that they have less than 10% of the specific energy (Wh/kg) and require a power converter to regulate their voltage. The high capacitance is achieved by the enormously high surface area of the carbon electrodes compared to planar electrolytic capacitors. Ultracapacitors are commonly used to provide voltage stabilization of power converters and to supplement peak-power loading of electrical systems. Their application has expanded from electronics and telecommunications to industrial load leveling and transportation. Due to their durability, their use in aerospace has been for munitions fusing and missile power load leveling. Ultimately, application will be pulsed power storage and delivery for electric propulsion and directed­ energy weapons. Recent developments in ultracapacitors have focused on different active materials and electrode designs. By using advanced carbons, polymers, and metal oxides, increased power density and energy density can be achieved. Oxide-based thin-film ultracaps have demonstrated high-performance energy and power density, approaching theoretical limits. Carbon nanotubes and advanced carbons have been used as additives to and solely as electrode materials. Nanostructured materials and thin-film manufacturing process improvements will generate breakthroughs in mass production. Magnetic capacitors are a recent development, manufactured using semiconductor processes on silicon wafers. They possess a different storage mechanism and will transform energy storage and pulsed-power applications. Ultracapacitors are reaching widespread adoption and they are now available to support electronics through transportation. New advancements in materials will enable high-energy density devices with exceptional power capabilities.

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Chapter 1: Concept Ultracapacitors, also known as supercapacitors, hybrid capacitors, electrochemical capacitors, electrochemical double-layer capacitors, or ultracaps, are energy-storage platforms that offer energy storage capable of extremely rapid charge and discharge rates. Ultracapacitors also have the ability to be cycled hundreds of thousands of times. The phenomenal charge and discharge capabilities make them ideal for supporting volatile memory and computing applications, energy power applications. Ultracaps store their charge in the electrical double layer between the electrode and the electrolyte. Charge storage is a physical mechanism rather than a chemical phase change, so these are theoretically capable of cycling an infinite number of times. 2 One of the Figure 1. Ultracaps in Various Configurations.' disadvantages of ultracaps can be a high self-discharge rate.3 The charge and discharge voltage output for an ultracap is a sloping linear curve, which allows for straightforward and accurate state-of-charge monitoring.4 The real advantage of an ultracapacitor is the ability to deliver or accept bursts of power in a short time. Ultracaps were introduced in 1966 and found initial use 12 years later as backup power devices for volatile memory and clocks. Over the last 30 years, numerous advances have been made that have led to many uses of ultracaps, from transportation to portable electronics and more. Ultracaps are becoming more affordable as activated carbon electrodes and manufacturing improvements have driven costs down. Several companies now make ultracapacitors to fill a broad spectrum of applications. Figure 1 shows a number of ultracaps with various capacities to fill a range of functions. Transportation, microelectronics, and aerospace markets are some of the many areas where ultracaps have become enablers. Advanced materials and improved cell designs will lead to improvements in both power density and energy density. The improved performance is expected to make ultracaps important components for efficient power leveling and high-power receiving and delivery. The unique signature of ultracapacitors must be understood for aerospace and military applications. As an electrochemical capacitor, ultracapacitors store energy within the electric double layer formed at the interface between the electrode and electrolyte. In a conventional capacitor, the energy is stored by moving charge carriers from one plate to another, and the charge separation creates a potential. Voltage differentials in a conventional capacitor are dependent upon the dielectric material separating the plates. In the ultracap, the electrical double layer is the separation of charge in a vanishingly thin gap between two plates. Figure 2 depicts the components and basic design of the ultracap,

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showing the electrochemical double layer responsible for the characteristic performance.5 The basic principles of operation have not changed with improved technologies, only the materials and cell design. The two electrode plates are traditionally the same material, which is usually a