3D NiCoP flowers assembled by 2D carbon-coated nanosheets as an efficient and stable positive electrode for supercapacitors†
Abstract
High rate performance and cycling stability are crucial factors in the construction of electrode materials for supercapacitors. Herein, we designed and synthesized flower-like NiCoP assembled with nanosheets stabilized by carbon layers (NiCoP/C) through a ‘hydrothermal assembly-phosphating’ route. Nanolayers with rich pore channels can provide transport for a large number of ions (providing transport pathways for ions in the electrolyte, effectively reducing resistance during ion transport within the electrode), improve the specific surface area of electrode materials (increasing the contact area between the electrode and electrolyte, and thereby promoting charge transfer between the electrode and electrolyte), and enhance the structural stability. The conductivity of the 3D assembly NiCoP/C is high, similar to that of phosphides with enhanced mass/charge transfer, and it possesses good ability from the carbon coating and 3D structure to buffer any volume variation. These characteristics are favourable for application as electrode materials in supercapacitors. Under optimized conditions, the capacitance of the prepared NiCoP/C-2 is high (1261 F g−1 at a current density of 1 A g−1, 799 F g−1 at a current density of 10 A g−1) in a three-electrode system. The asymmetric supercapacitor assembled with NiCoP/C-2 as the positive material and N-doped porous carbon as the negative material exhibited excellent stability. After 8000 cycles, the discharge capacitance remained at 88.5%, presenting a high energy density of 40.06 W h kg−1 at 640 W kg−1.