Development of solid-state hybrid capacitor using carbon nanotube film as current collector

Structural energy-storage devices are receiving considerable attention because they can simultaneously store electrical energy and provide structural support, thereby offering high volumetric and gravimetric capacities. Although carbon fiber–based materials have been the most popular choice for current collectors, their conductivity and specific surface area are relatively low; this limits the ability to load other active materials on to the current collector. Carbon nanotube (CNT) fiber is a promising alternative for lightweight structural materials because it has a density of less than 1 g cm−3 as well as high strength and electrical conductivity. In this study, we produced a light, strong, and porous CNT film (CNTF) via direct spinning for use as a current collector. The CNTF exhibited a high specific strength compared with Al foil. We also created an activated carbon–lithium titanium oxide hybrid capacitor with the CNTF current collector, which achieved a capacity similar to that of a capacitor having an Al current collector. Furthermore, a planar pouch cell created using a solid polymer electrolyte achieved a capacity of 74.1 mAh g−1, which is comparable to that of coin cells. Thus, our findings highlight the feasibility of CNTF as a material for current collectors and provide a foundation to develop manufacturing processes for structural batteries.