Ultrathin hetero-nanosheets assembled hollow Ni-Co-P/C for hybrid supercapacitors with enhanced rate capability and cyclic stability.

Nanohybrid-type Ni-Co-phosphide/C (Ni-Co-P/C) hollow microflowers with ultrathin nanosheets (HUNs) are constructed through a modified ethylene glycol-mediated self-assembly process and further phosphating treatment. The peculiar structure can availably provide affluent mass transfer channels and active sites, meanwhile inhibit the aggregation of nanosheets. The synergistic effects of the produced Ni-Co-P/C are demonstrated systematically through regulating the initial Ni/Co ratio. A remarkable specific capacity of 205 mAh g can be achieved at 1 A g, and the optimized Ni-Co-P/C (referred to as NiCoP/CoP/C) still holds a superior rate capability with a capacity retention of 71% even at 50 A g. Notably, the electrode also reveals an attractive capacity of 133 mAh g with a high mass loading of 9.1 mg cm. A hybrid supercapacitor assembled with Ni-Co-P/C cathode and N-doped porous carbon anode demonstrates outstanding electrochemical performance, such as a high energy density (43 Wh kg at a power density of 818 W kg) and excellent stability (90% retention after 20,000 cycles at 12 A g). The facile fabrication process and attractive performance make Ni-Co-P/C HUNs promising in energy storage applications.