| Supercapacitors not only has the characteristics of fast charging and discharging of capacitors,but also has the energy storage characteristics of batteries,and both high power density and excellent cycle stability.It is widely used in various fields.Nickel-based sulfides have high theoretical capacity and are widely studied.However,the single-phase nickel-based sulfide structure occurs collapses during the charging and discharging process,making the nickel-based sulfide electrode poor cycle stability.Another disadvantage is relatively low the operating voltage window（limited to 0.3-0.7 V）,which limits the energy density and power density of this type material.Therefore,while devoting to the development of nickel-based sulfide composite materials,it is of great significance to introduce hetero-elements to widen the voltage window of the material,thereby improving the stability and energy density of the material.Therefore,this article takes this as the starting point and nickel-based sulfide as the research object.Through in-situ introduction of hetero-elements,vacancies and non-catalytically active porous materials,the morphology and structure of nickel-based sulfide composite materials are adjusted.Study the influence on the electrochemical performance of different morphology and structure nickel-based sulfide composite electrodes,combined with theoretical calculations and molecular dynamics simulations,illustrates the effects of hetero-elements on the voltage window and charge storage of composite materials in alkaline electrolyte.1.Using traditional solvothermal theory,p-diphenylboronic acid and Ni（NO3）2·6H2O as raw materials,ping-pong chrysanthemum-like hierarchical structureα-Ni（OH）2（Ni-MOF）is obtained by solvothermal synthesis in a mixture of N,N-dimethylformamide（DMF）and water in an alkali-free environment.In order to improve the conductivity of the material,dopamine polymerization coating and vulcanization heat treatment are used to obtain a nitrogen-containing carbon-coated nickel-based sulfide composite material Ni S2@NC.The composite material coated with nitrogen-containing carbon has a porous structure,and its specific surface area is increased to 21.38 m2 g-1,which is more conducive to the wetting of the electrolyte and effectively improves the electrochemical performance.The existence of the porous structure is more conducive to electrolyte ions transmission.At the same time,the electrochemical performance of the material was evaluated,and the influence of different structures on the electrochemical performance is explained.The results showed that the material Ni S2@NC showed better capacitance performance,and the coating of nitrogen-containing carbon and the introduction of hetero-elements accelerated the migration of electrons,effectively improve the conductivity of the composite material.In this work,a water-based asymmetric supercapacitor was successfully assembled,and a working voltage window of 1.7 V was obtained.Among them,the Ni S2@NC//activated carbon YP80F（YP-80）device showed the best electrochemical performance at power density of 594.9 W kg-1,a high energy density of 47.1 Wh kg-1 is obtained,and it exhibits high cycle stability.2.The structure of the electrode material was adjusted by directly introducing mesoporous silica spherical nanoparticles,sulfur source and nitrogen source.A two-step method was used successfully synthesized to obtain functional porous m Si O2@BN/Ni3S2/Ni S2 composite materials with different structures,and the mechanism of formation was explained in detail.Using synchrotron radiation characterization methods,combined with EPR and XPS analysis methods,the doping of hetero-elements and the formation of sulfur vacancies are described.The introduction of hetero-elements and sulfur vacancies increases electrochemically active sites and conductivity,and enhances the electrochemical performance of a single nickel-based sulfide material.The optimal rod-spherical structure composite material obtained a high specific potential of 1.8 V in a 6M KOH electrolyte,and showed a reversible capacity of 449.7 F g-1,and obtained a maximum energy density of 202.5 Wh kg-1.After 8000 cycles,it has an appreciable capacity retention rate of 200%,indicating that the introduction of mesoporous silica improves the cycle stability of the material.The water-based asymmetric supercapacitor device assembled with YP-80 has a working voltage window of 1.8 V.When the power density is 1800 W kg-1,the energy density reaches 56 Wh kg-1.In order to deeply study the mechanism of widening the high voltage window and the mechanism of charge enhancement,reveal the influence mechanism of the hetero-elements-doped on the operating voltage window and charge storage of nickel-based sulfides in alkaline electrolytes.The first principles of density functional theory（DFT）were used to calculate the adsorption and water decomposition kinetics of different structural models of hetero-elements doped composite materials on electrolyte ions and molecules.The formation of sulfur vacancies and the doping of B and N not only inhibited the decomposition of water,but also increased the adsorption sites of OH-and enhanced charge storage.At the same time,molecular dynamics simulation（MDS）was used to calculate the charge storage kinetics of micro-mesopores.The results show that while micro-mesopores coexist,the time required for the maximum charge accumulation is the least.At the same time,the existence of the mesoporous structure provides more storage space for the electrolyte,and accelerates the transfer of OH-,enhancing the electrochemical performance of m Si O2@BN/Ni3S2/Ni S2.3.The construction of the supercapacitor was optimized,activated carbon YP-80 and self-made N and O doped carbon materials were used as anodes.The influence of different carbon-based anode materials on the electrochemical performance of m Si O2@BN/Ni3S2/Ni S2 composites was described.Using the sol-gel method to prepare porous silica nanosheets with surface protrusions as a template,the N/O co-doped ultra-thin folded carbon nanosheet anode material with surface protrusions and mesoporous structure was prepared.The structural advantages of 2D and 3D materials are improved.N doping can improve the conductivity of the material and increase the electrochemical active sites with high pseudocapacitance.O doping can not only improve the surface wettability of the electrode material,reduce the resistance between the electrolyte and the electrode surface,but also improve the electrochemical performance.The optimal structure of the electrode material shows a huge specific surface area and hierarchical distribution of micro-mesoporous structure,and the folded structure provides more edge active sites and enhances electrochemical performance.The electrode material exhibits a wide operating voltage window（-0.9-0.6 V.vs.SCE;-1.2-0.3 V.vs.Hg O）and ultra-high specific capacity in alkaline electrolyte.The NCP-700//NCP-700 symmetrical water-based supercapacitor exhibits an ultra-high energy density of 27.9 Wh kg-1 at a power density of 749.55 W kg-1.After 10,000 cycles,it maintains a capacity retention rate of 84.6%and good cycle stability,satisfied the requirement as a negative electrode material.The asymmetric all-solid-state supercapacitor device m Si O2@BN/Ni3S2/Ni S2//NCP-700 was assembled to obtain a high-voltage window of 2.2 V,showing a maximum energy density of 76.39 Wh kg-1.After 4500 cycles at current density 6 A g-1,it has an excellent capacity retention rate of≈98%.The all-solid-state asymmetric device assembled with YP-80 has a working voltage window of 2 V,and the device only exhibits a maximum energy density of 49.72 Wh kg-1.A single m Si O2@BN/Ni3S2/Ni S2//NCP-700 device can light a yellow light-emitting diode for 120 s and light up a red light-emitting diode for 300 s.For the preparation of high-energy and high-power density wide voltage window nickel-based sulfide supercapacitor device provides design ideas... |
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