Interface modification of hierarchical Co9S8@NiCo layered dihydroxide nanotube arrays using polypyrrole as charge transfer layer in flexible all-solid asymmetric supercapacitors

In this article, we design a flexible binder-free supercapacitor cathode of Co9S8@PPy@NiCo layered dihydroxide nanotube arrays (Co9S8@PPy@NiCo-LDH NTAs) with excellent electrochemical energy storage performance. The conductive charge transfer layer of polypyrrole (PPy) constructed between Co9S8 nanotubes and NiCo-LDH nanosheets is effectively improved the charge transfer rate, capacity rate and electrochemical stability. Benefiting from the synergistic effect of hollow structure, high electron mobility and abundant active sites, the prepared Co9S8@PPy@NiCo-LDH NTAs electrode presents ideal electrochemical properties for supercapacitors with area specific capacity of 2.65 F cm-2 at 1 mA cm-2, which is clearly much higher than Co9S8@NiCo-LDH NTAs (1.28 F cm-2). With the activated carbon (AC) as anode, the all-solid asymmetric supercapacitor (AAS) device is assembled, and an area specific capacity of 0.371 F cm-2 at 1 mA cm-2, an energy density of 0.132 mW h cm-2 at power density of 0.8 mW cm-2 is achieved. For specially, the AAS maintains good cycle stability (92.74% capacity retention after 10,000 cycles at 10 mA cm-2) and it can illuminate 11 blue lamp beads for about 15 min when 6 devices (one about 1 cm2) connected in series.