Hierarchical core-shell Ag@Ni(OH)2@PPy nanowire electrode for ultrahigh energy density asymmetric supercapacitor

Pseudocapacitive transition-metal oxides/hydroxides, due to their high theoretical capacity, are increasingly promising for supercapacitor electrodes. While, the most critical predicament involved is the inferior electrical conductivity that has lowered specific capacitance and further undermined the practical applications. To this end, we design a conductivity dual-enhanced structure, i.e. coaxial hierarchical AgNW@Ni(OH)(2)@PPy that the electrochemical active Ni(OH)(2) is grown on highly conductive Ag nanowires (AgNW) and further wrapped by a highly conductive polypyrrole layer (PPy). The designed AgNW@Ni(OH)(2)@PPy electrode demonstrates an outstanding specific capacitance (3103.5 F g(-1) at 2.6 A g(-1)) that can be retained in 92.2% after 20,000 charging/discharging cycles. The all-solid-state asymmetric supercapacitor (ASC) based on AgNW@Ni(OH)(2)@PPy is further fabricated and exhibits an ultrahigh energy density of about 121 Wh kg(-1) and excellent cyclic stability with 97.4% capacitance retention after 10,000 cycles. Finally, three ASCs in series that can achieve a high output voltage of 4.5 V, after charging for only 10 s, light up a LED light (0.03 W) over 2.5 h. The high performance is attributed to the coaxial hierarchical design with innermost and outermost dual-electric channels that not only ensure good conductivity and rapid charge transport, but also significantly improve the utilization efficiency of Ni(OH)(2).