AAWSAP DIRD, Ultracapacitors as Energy and Power Storage Devices, November 2010

This Defense Intelligence Reference Document was prepared by the Defense Intelligence Agency's Defense Warning Office and dated 1 November 2010. It is one of a series of advanced technology reports produced under the Advanced Aerospace Weapons System Applications Program. The report reviews how ultracapacitors work, how they compare with batteries, their history and materials, and their commercial, military and aerospace uses. It concludes that new materials and cell designs will raise energy density and that the U.S. government must understand the devices' spectral signatures.

From the source:Release of 2026-09-18 Incident: 11/1/10, Las Vegas, Nevada. Released with redactions. This document is a Defense Intelligence Reference Document (DIRD), a technical reference format used by the Defense Intelligence Agency (DIA) to capture baseline knowledge on a specific topic for later analytic use. DIRDs are best understood as reference and synthesis products rather than as original research. It is one of 38 DIRDs produced under the Advanced Aerospace Weapon System Applications Program (AAWSAP) between 2009 and 2011. Because AAWSAP’s scope permitted a broad range of supporting topics, not every DIRD in the series directly concerns aerospace systems or future threat assessment. The following summary reflects the DIRD’s scope and framing at the time of writing and should not be read as implying current validation of the concepts discussed. This DIRD surveys ultracapacitors as high-power energy-storage devices and argues that their main value lies in extremely rapid charge and discharge, very long cycle life, and usefulness in systems that need short bursts of power rather than sustained energy delivery. The report explains how ultracapacitors differ from batteries, reviews the materials and cell designs that determine their performance, and emphasizes that they are especially useful for power stabilization, backup power, load leveling, regenerative braking, and other applications where fast energy transfer matters more than total stored energy. It also notes their drawbacks, including lower energy density, self-discharge, and voltage-management requirements that limit their usefulness as stand-alone replacements for batteries in many applications. The document presents ultracapacitors as a maturing and increasingly important technology whose most credible aerospace and military uses lie in pulsed-power, missile and munitions systems, electric propulsion support, and other hybrid power architectures rather than in long-duration primary energy storage.

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Figure 9. Relationship Between Average Pore Size and Normalized Specific Capacitance. As the average
pore size decreases below 1 nm, the specific capacitance increases due to distorted electrolyte Ion salvation .
THIN FILMS
CNT films have been used in 2D thin-film ultracapacitors having respectable gravimetric
and volumetric capacitance. Activated carbon powders have a better performance in
terms of energy per unit area, 35 but they need to be processed into films before use,
and th is limits their choice for microdevice fabrication, which allows mass production of
capacitors on semiconductor wafers. Carbide-derived carbo n (CDC) is a class of carbon
materials produced by selectively etching metals from meta l carbides using chlorine at
elevated temperatures in a process similar to current dry-etching techniques used in
MEMS and microchip fabrication. CDC has been shown to have excellent performance as
the active material in traditionally processed ultracaps36 since it can have its
microstructure precisely tuned by ta iloring the synthesis conditions for a particular
electrolyte. 37
For microfabricated supercapacitors, CDC is attractive for several reasons. The
precursor carbides are conductive and can be deposited in uniform t hin and th ick films
by well-known chemical and physical vapor deposition (CVD and PVD) techniques. 38 I n
addition, the chlorination process can be performed at tempe ratures at least as low as
200°C, 39 and the resulting coatings are well-adhered with an atomically perfect
interface,40 which minimizes device impedance. This technology can be used to produce
the microfabricated ultracaps on the same chip as the integrated circuits, which they
are powering (shown in Figure 10).41 Chlorine-containing plasma etching of materials in
semiconductor manufacturing is a well-established technique and is similar to the
chlorination procedure in CDC manufacturing. Continuous porous carbon films cannot
be produced by conventional CVD, PVD, or other techniques, and the high-temperature
activation needed to produce the microstructures necessary for ultracapacitor
performance in CVD carbons would destroy the devices they were intended to power.
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