| Along with the advancement of economy,energy shortage and environmental pollution has aroused widespread concern in the society.How to realize the utilization and efficient and stable storage of renewable energy are the key issues and waiting to be solved.As an electrochemical energy storage device,supercapacitors have attracted extensive attention due to their fast charge-discharge rate,high power density,and long cyclic duration.However,the lack of energy density is a major shortcoming of electrochemical capacitors,so it cannot be applied on a large scale.As we all know,the performance of supercapacitors is closely related to the composition of electrode materials.Therefore,in this article,we took nickel-cobalt-based materials as the precursor,doped them with P/S/Se elements,and simultaneously manipulated their surface morphology and lattice defects.The introduction of defects contributed to the formation of porous transitional metal structure,with rich grain boundaries,improving the energy storage performance of electrode materials.The main contents are as follows:(1)Design and synthesis of grain-boundary-rich Ni-Co-Se electrode materials.First,a nano-flower nickel-cobalt carbonate was prepared through one-step hydrothermal reaction.This was followed by heat treatment to generate uniform nanowire with rich particle composition.Compared to the precursor,nickel cobaltate exhibited excellent rate capability.Finally,Se doping is carried out,and the different grain boundary densities of Ni-Co-Se were achieved by changing the doping time.It has excellent specific capacity and cycle stability.The specific capacitance is as high as 242.6?Ah cm-2 at 30 m A cm-2.When assembled with AC to form asymmetric electrode material(ASC),the specific capacitance reached 329.2?Ah cm-2 at current density of 3 m A cm-2,and after 8000 cycles of testing,the specific capacitance can still maintain 73.33%.Furthermore,the composite showed a power density of 342.94 W kg-1 and 3441.33 Wh kg-1 at energy density of 37.62 Wh kg-1 and 25.81 Wh kg-1.(2)Design and synthesis of grain-boundary-rich NiCo2O4/NiCo2S4 electrode materials.To further enhance the charge storage capacity of NiCo-based array electrodes,binder-free self-supporting transition metal sulfide array electrodes were fabricated.Its rich grain boundary provided more active sites for energy storage,and the addition of S further improved the electrical conductivity of the material.In this work,the control of grain boundaries densities was achieved by exposing NiCo2O4 nanowire arrays to a sulfur atmosphere at 300°C for different exposure times.The results showed that the highest capacitance of the NiCo2S4 reached 400?Ah cm-2 at 30 m A cm-2,and the current retention rate is 58.6%.The assembled NiCo2O4/NiCo2S4//activated carbon electrodes exhibited capacitances of 299.2?Ah cm-2 and 241.7?Ah cm-2at current densities of 3m A cm-2 and 30 m A cm-2,respectively.Cyclic measurement showed a good current retention rate of 88.1%after 8000 cycles.Furthermore,the NiCo2O4/NiCo2S4composite exhibited a power density of 4773.66 W kg-1 at energy density of 38.67 Wh kg-1,indicating the potential for practical applications.(3)Design and synthesis of grain-boundary-rich NiCoP/NiCoP4O12 electrode materials.The composition of the composite precursors was slightly tuned by firstly constructing a porous structure in the primitives of NiCoP electrode array nanorods based on the principle of Kirkendall effect,and then attaching the phosphate particles generated through the in situ oxidation to the surface.The effect of phase composition on the energy storage performance of capacitors was systematically investigated,concluding that the electronic structure was regulated after in situ oxidation process.In the three-electrode system,the specific capacity increased to 0.9583 m Ah cm-2 at current density of 2 m A cm-2.When combined with alternating current to form an asymmetric supercapacitor cell(ASC),the specific capacitance reached 338?Ah cm-2,and then decreased to 280?Ah cm-2 as current density increases from 2 m A cm-2 to 30 m A cm-2,with the capacitance retention rate as 82.84%.The excellent cycle stability is reflected in only 13.21%loss after 8000 GCDs.Furthermore,when the energy density was equal to 42.25 Wh kg-1,the power densities of this composite were as high as 250 W kg-1. |
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