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 NaNi 0.33 Co 0.67 PO 4 ·H 2 O 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 NaNi 0.33 Co 0.67 PO 4 ·H 2 O 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%.