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

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Chapter 6: Conclusions
Ultracapacitors are becoming increasingly important in applications ranging from
portable electronics to cargo transport cranes. Their introduction in electronic circuits
for conversion and storage assistance will become the next major milestone. The
virtually unlimited cycle life combined with high power capabilities has made them an
integral component to many energy-management schemes. Early adoption of ultracaps
by the military was an important differentiator for vehicle performance and a
technology driver. Improvements to activated carbons and manufacturing techniques
have brought costs down. The ultracapacitor is relatively young and is expanding
rapidly as ultracaps are reaching a more widespread audience. Increased adoption has
led to recognition of the benefits, and the attention has allowed researchers to develop
a better understanding of the power-storage mechanisms.
New materials and cell designs will produce increased capacitance and higher voltages,
which will in turn give ultracapacitors better energy density. Advanced carbons show
great promise to generate a carbon electrode with much higher capacitance than the
activated carbons in use today. These include porous carbons, carbon nanotubes, and
graphene. Capacitance increases by the carbon electrode alone could double the energy
density. Additional advantages in conductivity and the ability to functionalize these
materials will generate improvements in power density as well as energy density.
Hybrid systems utilizing a battery-like electrode are beginning to gain acceptance.
These pseudocapacitive systems maintain the high power density of a symmetric
ultracap and also have substantially higher energy density. While these systems
sacrifice some cycle-life capability, it appears as though they will survive tens of
thousands of cycles.
Ultracapacitors are a solution for generating or absorbing high pulse power. They also
are excellent devices for backup power and stabilization of fluctuating power
requirements. Increased power densities and energy densities will open up new
applications for ultracaps, replacing fuel and batteries in some cases, supplementing
them in others. Power management and generation for military systems will see
increasing uses for ultracaps. Their unique capabilities will enable future designs. Their
specific performance capabilities must be optimally utilized and we must have a keen
understanding and awareness of the unique spectral signatures these devices generate
when storing high power and in charge or discharge modes. Development of these
advanced ultracaps must be performed, understood, and adopted by the U.S.
government and those who are developing the systems to be used by the government.
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