A facile one-pot solvothermal method has been developed to synthesize nickel phosphide (NiP) nanoparticles which were further assembled into new asymmetric and symmetric supercapacitor cells. The electrochemical properties of these assembled supercapacitor cells were investigated in 3.0 mol L-1 KOH electrolyte. Results show that the asymmetric supercapacitor cells based on Ni2P nanoparticles and activated carbon exhibited excellent electrochemical properties, i.e.: a stable electrochemical window of 0-1.5 V, higher energy density of 64.6 Wh kg(-1) at a power density of 1029W kg(-1) and excellent cycling stability (95.1% capacitance retention). But the symmetric supercapacitor cells with Ni2P nanoparticles as positive/negative electrodes show narrower voltage window, lower specific capacitance and the resulted lower energy density which largely restricted the real application. Additionally, two asymmetric supercapacitor cells linked in series can be charged and then discharged to light a red light-emitting diode and drive a rotating motor. All these results demonstrate the asymmetric supercapacitor cells based on Ni2P nanoparticles and activated carbon have the promising potential application in the field of high-performance energy storage. (C) 2015 Elsevier B.V. All rights reserved.