Owing to their unique electronic properties and capability to host diverse functional groups on the surface, carbon dots (CDs) have attracted increasing attention in energy storage field. Herein, ultrathin nitrogen-doped carbon dots (NCDs) decorated nickel hydroxide (Ni(OH)(2)) nanosheets were fabricated by a facile hydrothermal approach, where NCDs play an important role as a structure-directing agent in tuning the size and thickness of the Ni(OH)(2). With the merits of the battery-type faradaic behavior of Ni(OH)(2) and high electronic properties of NCDs, the achieved Ni(OH)(2)/NCDs ultrathin nanosheets show a specific capacitance of about 1711.2 F g(-1) at a current density of 1 A g(-1), which is twice more than that of pristine Ni(OH)(2). A hybrid supercapacitor device was constructed using Ni(OH)(2)/NCDs ultrathin nanosheets as the positive electrode and three-dimensional graphene (3DGE) as the negative electrode, respectively, which presents high energy density of 23.8-34.6 Wh kg(-1) at power density of 700-7000 W kg(-1). The enhanced electrochemical properties of Ni(OH)(2)/NCDs nanocomposite hold potential for future high-performance energy storage applications. (C) 2019 Elsevier Inc. All rights reserved.