Microwave synthesis of sodium nickel-cobalt phosphates as high-performance electrode materials for supercapacitors

Abstract

The abundant and low-cost transition metal phosphates are considered to be promising supercapacitor electrode materials. In this study, sodium nickel-cobalt phosphates were fabricated via a facile microwave synthesis method and used as a high-magnification electrode material for asymmetric supercapacitors. The effect of the ratio of Co and Ni was investigated, and the palmary electrochemical performance was found in NaNi0.33Co0.67PO4·H2O with the specific capacitance of 828 F g−1 at 1 A g−1. When the discharge current density is 10 A g−1, the capacitance retention rate is 88.7% and the cycle stability is good with remaining 81.3% after 3000 cycles at 5 A g−1. Furthermore, an asymmetric supercapacitors (ASCs) with graphene as negative electrode material and NaNi0.33Co0.67PO4·H2O as positive electrode material was also successfully constructed, when the power density is 374.95 W kg−1, the energy density is as high as 29.85 Wh kg−1. Even at a power density of 7500 W kg−1, the energy density can reach 24.375 Wh kg−1, and the high capacitance retention after 10,000 cycles is 76.9%.