Cobalt-Doped Nickel Phosphite for High Performance of Electrochemical Energy Storage

Compared to single metallic Ni or Co phosphides, bimetallic Ni-Co phosphides own ameliorative properties, such as high electrical conductivity, remarkable rate capability, upper specific capacity, and excellent cycle performance. Here, a simple one-step solvothermal process is proposed for the synthesis of bouquet-like cobalt-doped nickel phosphite (Ni₁₁ (HPO₃ )₈ (OH)₆ ), and the effect of the structure on the pseudocapacitive performance is investigated via a series of electrochemical measurements. It is found that when the cobalt content is low, the glycol/deionized water ratio is 1, and the reaction is under 200 °C for 20 h, the morphology of the sample is uniform and has the highest specific surface area. The cobalt-doped Ni₁₁ (HPO₃ )₈ (OH)₆ electrode presents a maximum specific capacitance of 714.8 F g^-1 . More significantly, aqueous and solid-state flexible electrochemical energy storage devices are successfully assembled. The aqueous device shows a high energy density of 15.48 mWh cm^-2 at the power density of 0.6 KW cm^-2 . The solid-state device shows a high energy density of 14.72 mWh cm^-2 at the power density of 0.6 KW cm^-2 . These excellent performances confirm that the cobalt-doped Ni₁₁ (HPO₃ )₈ (OH)₆ are promising materials for applications in electrochemical energy storage devices.