Free-standing 3D composite of CoO nanocrystals anchored on carbon nanotubes as high-power anodes in Li-Ion hybrid supercapacitors

Abstract An effective strategy for constructing free-standing films of CoO nanocrystals and highly conductive carbon nanotubes as binder-free anodes for Li-ion hybrid supercapacitors is reported. Microstructure analysis reveals that the CoO nanocrystals with an average diameter about 20 nm are discretely and intimately anchored onto the surface of interconnected carbon nanotubes without agglomeration, thereby leading to approximately the entire surface of each CoO nanocrystal being available for electrochemical reactions. The unique free-standing nanocomposite not only provides a conductive network to increase conductivity and a protective buffer to accommodate volume variation, but also has large specific surface area and abundant active sites to result in an enhanced capacitive-controlled Li-storage behavior. In a half cell, the free-standing nanocomposite as an anode exhibits ultrahigh capacity and excellent cycling stability at temperatures of 0 °C, 25 °C, and 55 °C. Furthermore, a Li-ion hybrid supercapacitor is assembled using the free-standing nanocomposite as an anode and active carbon as the cathode and shows high-energy density (91 W h kg−1), high-power density (13.9 kW kg−1) and excellent capacity retention about 74% after 10000 cycles. Our results suggest great potential of the developed free-standing CoO-based composite in high-performance Li-ion hybrid supercapacitors.