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, 2011

"... Energy storage in mechanical springs made of carbon nanotubes is a promising new technology. Springs made of dense, ordered arrays of carbon nanotubes have the potential to surpass both the energy density of electrochemical batteries and the power density of capacitors due to the effective Young&apo ..."

Abstract
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Energy storage in mechanical springs made of carbon nanotubes is a promising new technology. Springs made of dense, ordered arrays of carbon nanotubes have the potential to surpass both the energy density of electrochemical batteries and the power density of capacitors due to the effective Young's modulus of carbon nanotubes of 1 TPa and their high elastic strain limit of up to 20%. The energy density of springs made of carbon nanotubes is predicted to be more than three orders of magnitudes higher than the energy density of conventional springs made of steel. The present work studies the mechanical properties and energy storage capabilities of two types of carbon nanotube arrays: fibers made of continuous, millimeter-long carbon nanotubes prepared from forests, and spun yarn made of carbon nanotubes. The highest recorded strength and stiffness of the fibers are 2 N/tex and 68 N/tex, respectively, and the fibers have demonstrated reversible energy storage of 670 kJ/m 3 or 6.9 kJ/kg. The spun yarn has a specific strength of 0.8 N/tex, a specific stiffness of 48 N/tex, a maximum energy density of 7720 kJ/m 3 or 6.7 kJ/kg, and a maximum demonstrated power density of 190 MW/m 3 or 170 kW/kg. The