Nickel cobalt sulfides and carbon nanotube intercalated graphene film electrodes for high-performance flexible all-solid-state asymmetric supercapacitors

Graphene-based flexible self-supporting supercapacitors hold great promise for wearable and portable electronic devices due to high electrical conductivity, large theoretical ion-accessible surface area, excellent mechanical strength, and flexibility. However, the self-stacking of graphene sheets caused by the interlayer interaction forces restrains the available active site exposure, make it difficult to achieve high specific capacitance. Herein, nickel cobalt sulfides/exfoliated graphene/carbon nanotubes (NCS/EG/CNTs-H) hybrid films were prepared by vacuum filtration and hydrothermal treatment. Specifically, exfoliated graphene sheets were used as the substrate, and nickel cobalt sulfides (NiCo2S4) 2 S 4 ) and carbon nanotubes (CNTs) were introduced between graphene layers to alleviate the self-stacking. NiCo2S4 2 S 4 increases the active surface sites and provides pseudocapacitance. CNTs connects NiCo2S4 2 S 4 and graphene layers as a medium for electronic transmission. The optimal flexible selfsupporting electrode NCS/EG/CNTs-H delivers high specific capacitance of 2.34 F cm- 2 at the current density of 0.2 mA cm-- 2 . The assembled flexible all-solid-state asymmetric supercapacitor exhibits an energy density of 72.8 mu W h cm- 2 at a power density of 0.8 mW cm-- 2 . In addition, the flexible supercapacitor device can maintain its capacitance and electrochemical stability under cyclic operation and mechanical bending, demonstrating great promise in the application of wearable electronics.