High-performance asymmetric supercapacitor based on flowery nickel-zinc phosphate microspheres with carbon dots

Abstract Despite of high theoretical capacity, transition metal phosphates always suffer from obvious volume expansion and poor conductivity in electrochemical reaction, thus resulting in rapid capacity fade and restricted comprehensive performance. In this work, we used a simple hydrothermal route to graft carbon dots on the binary mulberry-like Ni-Zn phosphates (CDs/NZP). Introducing carbon dots could not only raise the 50.9% specific capacitance at 1 A g −1 than bare Ni-Zn phosphates, but also enhance long-term cycling duration. The enhanced capacitance performance of CDs/NZP greatly contribute to synergistic effect, wherein mulberry-like CDs/NZP-10 structure achieve high-performance energy conversion, while CDs could provide a mechanical protector for mulberry-like structure and simulate fast charge transport. Furthermore, an asymmetric supercapacitor was prepared, utilizing positive CDs/NZP-10 and negative activated carbon (AC), respectively. The asymmetric device displays a high specific capacitance of 89.2 F g −1 (at 1 A g −1 ) and suitable energy density of 33.7 Wh kg −1 (at 824.9 W kg −1 ). The low cost, easy preparation and suitable electrochemical performance endow CDs/NZP-10 with voltage application in supercapacitor industry.