Two-dimensional porous (Co, Ni)-based monometallic hydroxides and bimetallic layered double hydroxides thin sheets with honeycomb-like nanostructure as positive electrode for high-performance hybrid supercapacitors.

CoNi layered double hydroxides (LDH) and related monometallic hydroxides (Ni(OH)2 and Co(OH)2) were synthesized by a facile, simple and inexpensive method under mild condition (50 °C). The resulting products displayed a unique honeycomb-like nanoflakes array assembled two-dimensional (2D) thin sheets structure. Among them, CoNi-LDH thin sheets delivered higher specific capacity (394.5 C g-1 at 1 A g-1) with superior cyclic performance (92.3% capacity retention over 10,000 cycles) than Co/Ni monometallic hydroxides owing to the synergistic effect of cobalt and nickel. Afterward, hybrid supercapacitors (HSC) devices were fabricated using the as-obtained products (CoNi-LDH, Co(OH)2 and Ni(OH)2 thin sheets) and activated carbon (AC) as the positive and negative electrode, respectively. The operating voltage of the devices can be extended to 1.6 V. What's more, the assembled CoNi-LDH HSC device exhibited a maximum energy density of 20.38 Wh kg-1 at the power density of 800 W kg-1. Consequently, these outstanding electrochemical performances of the CoNi-LDH thin sheet endow it with great potential to be implemented in HSCs or other energy storage systems.