Hierarchical nickel hydroxide hydrate assembled by ultrathin nanosheets for high-performance hybrid supercapacitors

Due to its unique nature, nickel hydroxide is an attractive cathode material for hybrid supercapacitors (HSCs). A facile solvothermal strategy was proposed to synthesize hierarchical nickel hydroxide hydrate (HNHH) assem-bled by ultrathin nanosheets. The reaction temperature (T) has a dramatic effect on the morphology and specific surface area (SSA). The prepared HNHH-T could offer large SSAs from 175.3 to 287.2 m2g- 1 with rich mesopores at 3.3-4.3 nm, which are favorable for boosting the electrochemical activity. Among diverse HNHH-T electrodes, HNHH-120 delivered a maximum specific capacity of 718.0 C g-1 at 0.5 A g-1. Furthermore, the assembled HNHH-120//activated carbon (AC) HSC could acquire 95.0 F g-1 at 0.5 A g-1. Strikingly, this HSC could deliver 35.9 Wh kg-1 at 412.5 W kg-1 with robust cycle durability (82.6% after 15,000 cycles at 3 A g-1). Moreover, an HNHH-120//AC device can operate a micro-fan for 54 s, demonstrating its real application prospect. The dazzling energy storage capability of HNHH-120 is mainly thanks to its large SSA and rich mesopores.