Ultrathin nickel-cobalt phosphate two-dimensional nanosheets for electrochemical energy storage unde

Two-dimensional materials have been an ideal material for constructing flexible electrochemical energy storage device, due to great advantages of flexibility, thinness and transparency. Here, a simple one-step hydrothermal process is proposed for the synthesis of nickel-cobalt phosphate two-dimensional nanosheets, and the structural influence on the pseudocapacitive performance of the obtained nickel-cobalt phosphate is investigated via electrochemical measurement. It is found that the ultrathin nickel-cobalt phosphate two-dimensional nanosheets with a Ni/Co ratio of 4:5 showed the best electrochemical performance for energy storage, and the maximum specific capacitance up to 1132.5 F g-1. More importantly, we have assembled aqueous and solid-state flexible electrochemical energy storage device. The aqueous device showed high energy density of 32.5 Wh Kg-1 at the power density of 0.6 KW Kg-1. The solid-state device showed high energy density of 35.8 Wh Kg-1 at the power density of 0.7 KW Kg-1. These excellent performances confirm that the nickel-cobalt phosphate two-dimensional nanosheets are promising materials for applications in electrochemical energy storage device.