Mechanical energy storage usually is operated on a macroscopic scale, such as water reservoirs or flywheels, and the energy density is not very high. With the rapid development of nano- and micro-electromechanical systems, nanoscale mechanical energy storage is highly required.

Fei Wie and co-workers, Tsinghua University, China, have grown defect-free carbon nanotubes (CNTs) that are over 10 cm long. The CNTs simultaneously exhibited high strength, high Young’s modulus, and large breaking strain. They could store mechanical energy with a density as high as 1125 Wh kg^–1 and a power density of 144 MW kg^–1 (see picture). The CNTs could withstand a continuously repeated mechanical strain-release test over 1.8 × 10⁸ times. This indicates these CNTs are a promising medium for the storage of mechanical energy that might be used in areas such as flexible devices, actuators and antenna.

_{Images: (c) Wiley-VCH}

• Superstrong Ultralong Carbon Nanotubes for Mechanical Energy Storage
  Rufan Zhang, Qian Wen, Weizhong Qian, Dang Sheng Su, Qiang Zhang and Fei Wei
  Adv. Mater. 2011.
  DOI: 10.1002/adma.201100344