Flexible energy storage devices based on carbon nanotube forests with built-in metal electrodes

Mechanically bendable energy storage devices have been demonstrated based on a lift-off and liquid densification process to construct carbon nanotube (CNT) forests with built-in bottom metal electrodes on top of a flexible substrate. The flexible CNT structure has been fabricated and tested as a supercapacitor electrode with the following salient features: (1) excellent transfer of charge from the aligned CNTs to the bottom contact metal layer, (2) a simple and straightforward fabrication process, and (3) easy integration with a variety of surfaces and topographies. Experimental results have shown that a 5 mm × 10 mm electrode with 40 μm-thick CNT forest and 50 nm-thick molybdenum bottom metal contact has been transferred from a silicon growth substrate onto a 200 μm-thick Al/Thermanox™ plastic substrate. The attached film survived the bending of as large as 180°. A measured specific capacitance of 7.0 mF/cm2 has been achieved. Repeated mechanical bending tests followed by CV cyclic measurements have shown good device stability. As such, flexible energy storage devices composed of CNT forests with built-in metal electrodes could have broad applications in modern systems that demand components with adaptable shapes to fit into small form factors and ergonomic designs.