Self-supported electrode constructed by hierarchical nickel-cobalt selenide nanosheet arrays for high-performance flexible supercapacitors

Flexible supercapacitors are a promising candidate as the energy storage device for wearable and portable electronics. Herein, nickel-cobalt selenide ((Ni,Co)Se2) nanosheet arrays with the hierarchical nanoparticle/nanosheet structure grown in-situ on acidified carbon cloth (CC) flexible substrate are prepared through simple hydrothermal and selenization process. The hierarchical (Ni,Co)Se2 nanosheet arrays with rough and porous surface enlarge the contact area between the electrode and electrolyte, and provide more abundant electrochemical active sites. While CC improves electrical conductivity, and renders a binder-free and flexible substrate with nanosheet arrays vertically anchored well on without aggregation. Consequently, the self-supported (Ni,Co)Se2/CC electrode displays an ultrahigh specific capacitance of 2054 F g−1 (285 mA h g−1) at 1 A g−1 and remarkable rate performance of 90.3 % retention at 10 A g−1. The all-solid-state flexible supercapacitor is assembled with (Ni,Co)Se2/CC as the positive electrode and activated carbon (AC/CC) as the negative electrode. The device exhibits a high energy density of 44.6 W h kg−1 at a power density of 976 W kg−1, as well as excellent cycling performance with 85.2 % capacitance retention after 5000 cycles and mechanical flexibility. The high-performance of (Ni,Co)Se2/CC self-supported electrode has a promising application in flexible energy storage devices.