The weight and volume of conventional energy storage technologies greatly limits their performance in mobile
platforms. Traditional research efforts target improvements in energy density to reduce device size and mass. Enabling a
device to perform additional functions, such as bearing mechanical load, is an alternative approach as long as the total
mass efficiency exceeds that of the individual materials it replaces. Our research focuses on structural composites that
function as batteries and supercapacitors. These multifunctional devices could be used to replace conventional structural
components, such as vehicle frame elements, to provide significant system-level weight reductions and extend mission
times. Our approach is to design structural properties directly into the electrolyte and electrode materials. Solid polymer
electrolyte materials bind the system and transfer load to the fibers while conducting ions between the electrodes. Carbon
fiber electrodes provide a route towards optimizing both energy storage and load-bearing capabilities, and may also
obviate the need for a separate current collector. The components are being integrated using scalable, cost-effective
composite processing techniques that are amenable to complex part shapes. Practical considerations of energy density
and rate behavior are described here as they relate to materials used. Our results highlight the viability as well as the
challenges of this multifunctional approach towards energy storage.
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