Morphology Controlled Synthesis Of Cobalt Nickel Phosphates Electrode Material And Their Electrochemical Properties

Supercapacitors, also commonly referred as electrochemical capacitors, have recently become a new energy storage device hotspot, because of their high power density, fast charge and discharge, long cycle life and little environmental pollution, etc. However, the low energy density has hampered its practical application. New electrode materials for electrochemical supercapacitors to improve the capacity and it will undoubtedly become a breakthrough to solve this problem.Firstly, through a mild hydrothermal method with a temperature of 120 ℃ and the reaction time of 4h, we synthesized cobalt-nickel hydroxide（mCo:mNi=1:1） precursor. By controlling the precursor of cobalt, nickel and phosphate source atomic mass ratio was1:0.5, 1:1 and 1:3 at the hydrothermal reaction temperature of 120 ℃ and reaction time of 24 h, respectively. We have successfully synthesized transition metal phosphate with three different morphologies（hexagonal porous, hybrid porous and rectangular sheet,rectangular sheet structure）. By studying the electrochemical properties of three types of electrode materials, we found that when the mass ratio of the precursor with a source of PO43- is 1:1, phosphate with the hybridized structure exhibits the best electrochemical performance. It present a high specific capacitance of 1128 F g^-1 at a current density of 0.5A g^-1. An asymmetric supercapacitor is fabricated using this hybridized material as positive electrode, and a hierarchical porous carbon derived from artemia cysts shell as negative electrode. The asymmetric supercapacitor exhibits good electrochemical performance, 95.6% capacitance retention after 5000 charge-discharge cycles.To study the properties of phosphate of the single structure, under the same condition of the precursor of cobalt, nickel and phosphate source atomic mass ratio of 1:3, by controlling the reaction time, we successfully synthesized phosphate with different morphologies. With the different reaction time（0.5h, 1h, 2h, 4h, 24h） at the temperature of120 ℃, the electrochemical performance exhibits best in the reaction time of 2 h. The electrode in KOH electrolyte at a current density of 0.5 A g^-1, specific capacitance up to1297 F g^-1. As an asymmetric supercapacitor electrode material, the asymmetric supercapacitor exhibits good electrochemical performance, 93.5 % capacitance retentionafter 10000 charge-discharge cycles.To study the electrochemical properties of composites, we synthesized cobalt and nickel phosphate with reducing graphene oxide composites through simple hydrothermal method. Firstly, we synthesized cobalt-nickel hydroxide and oxide graphene composites with the mass ratio of cobalt-nickel and oxide graphene of 1: 1under the temperature of120 ℃, reaction time of 4h. Then added PO43- source with the atomic mass ratio of cobalt-nickel of 1:1 under the temperature of 120 ℃, reaction time 12 h. Study on the electrochemical performance results show that at 0.5 A g^-1, the specific capacitance up to989 F g^-1. As an asymmetric supercapacitor electrode material, excellent electrochemical performance of energy density of 32 Wh kg^-1 at high power density of 14 kW kg^-1, and96 % capacitance retention after 10000 charge-discharge cycles.