Enhanced supercapacitor performance of ultrathin NiCoMn(OH) nanosheets over NiCo2O4 nanoarray on Ni foam

Abstract

A novel hierarchical 3D core-shell material [NF@NiCo2O4 @NiCoMn(OH)] were fabricated for supercapacitors, in which the ultrathin NiCoMn(OH) nanosheets were coated on the NiCo2O4 nanoarray supported on Ni foam. At the optimal Co-doping (Co/Ni molar ratio = 1: 5 at (Co+Ni)/Mn molar ratio of 4.0), the NiCoMn(OH)1/5 had better rate capability and higher specific capacitance than the NiMn(OH) precursor, which improved the electrochemical properties. To further enhance the electrochemical performance, the NF@NiCo2O4 @NiCoMn(OH) core-shell material was designed and prepared, which exhibited a much higher specific capacitance of 2300 F·g−1 than the NiCoMn(OH)1/5 (1417 F·g−1) at 1 A∙g−1 and 87.7% retention at 5 A∙g−1 for 2 000 cycles. The excellent capacitive properties were ascribed to the unique 3D hierarchical structure and strong synergistic effect between the ultrathin NiCoMn(OH) nanosheets shell and NF@NiCo2O4 nanoarray core. As a result of the asymmetric supercapacitor, the NiCo2O4 @NiCoMn(OH)//AC device showed a remarkably high energy density (61.3 Wh∙kg−1) at a power density of 850 W∙kg−1. The strategy can be extended to other core-shell electrode material toward energy storage applications.