Composition, microstructure and performance of cobalt nickel phosphate as advanced battery-type capacitive material

A series of cobalt nickel phosphates are prepared via a mild chemical precipitation method followed by calcination at a low temperature. With variation of Co/Ni molar ratio, the compositions and microstructures of the as-prepared samples are modulated and their electrochemical performances as battery-type materials are optimized. Electrochemical measurements by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) technique and electrochemical impedance spectroscopy (EIS) reveal that the flower-like CoNi2(PO4)2 with the molar ratio of Co/Ni = 1:2 exhibits a high specific capacity of 630.4 C g−1 at the current density of 1 A g−1, and an excellent cycling stability of 84.3% capacity retention after 1000 cycles. Furthermore, a hybrid supercapacitor, fabricated with the CoNi2(PO4)2 as positive and graphene as negative electrode material, exhibits a high specific capacitance of 103 F g−1 at the current density of 1 A g−1, along with a high energy density of 32.2 Wh kg−1 at the power density of 377.6 W kg−1, and even 21.7 Wh kg−1 at 4.9 kW kg−1. These figures demonstrate that cobalt nickel phosphates as electrode materials with the optimized composition and microstructure may hold promising application in energy storage devices. •Cobalt nickel phosphates are prepared.•The composition and microstructure are modulated with variation of Co/Ni ratio.•The electrode properties as battery-type material are optimized.•The flower-like CoNi2(PO4)2 shows high-performance hybrid capacitor application.