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Preparation Of Nickel-cobalt Sulfides And Their Applications In Supercapacitor

Posted on:2020-01-08Degree:MasterType:Thesis
Country:ChinaCandidate:D D WuFull Text:PDF
GTID:2392330590996963Subject:Physical Chemistry
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With the development of economy,there is an increasing demand for efficient,safe,and sustainable energy storage devices for electronic devices.Supercapacitors are considered to be one of the most promising energy storage candidates in urban and electric vehicles because of their high power density,excellent electrochemical reversibility and extremely long cycle stability.However,the energy storage density and power density of supercapacitors still need to be improved.Therefore,the development of electrode materials with high energy density and high power density has become an important way to further improve the performance of capacitors.In this thesis,we focus on nickel-cobalt sulfide as its low cost,environmental friendliness and good conductivity.By changing the composition and morphology of nickel-cobalt sulfide during the experiment,double-shell nanomaterials with high energy density and long cycle life were prepared.The specific research contents are as follows:After preparation of NiCo alkoxide precursor by solvothermal synthesis,the sulfide was prepared by sulfidation by ion exchange reaction using the NiCo precursor as a self-template.In the experiment,thioacetamide?TAA?,thiourea?TU?,sulfur powder?S?and sodium sulfide?Na2S?were used as sulfur sources.Among them,TAA and TU are used as sulfur source to form NiCo2S4 double-shell structure.NiCo2S4-TU has secondary particle accumulation phenomenon compared with NiCo2S4-TAA;S-powder is used as sulfur source to form small balls which adhere to each other;Na2S as sulfur source can form an irregular flower-like structure.Further analysis of the electrochemical properties of NiCo2S4 shows that NiCo2S4-TAA exhibits better electrochemical performance than NiCo2S4-TU.The specific capacitance is 2064 F g-1 at a current density of 0.5 A g-1 and 1291 F g-1 at a high current density of 20 A g-1.The capacity retention rate was 57.8%after 2000 charge and discharge cycles of 10 A g-1.It can be seen from the experimental analysis that NiCo2S4 synthesized by TAA is composed of smaller particles,which is beneficial to the diffusion of electrolyte ions in the electrochemical process.Since its good electrical conductivity and ion diffusion rate,NiCo2S4-TAA exhibits excellent electrochemical performance.The dynamic mechanism analysis shows that the NiCo2S4-TAA surface controlled capacitance and diffusion controlled capacitance are improved compared with NiCo2S4-TU.Therefore,in this experimental condition,TAA is the best sulfur source for the preparation of NiCo2S4 electrode materials.Based on the excellent capacitance properties of hollow structure sulfide prepared by TAA as sulfur source,the double-shell NixCo3-xS4 sphere was prepared by atomic structure substitution doping engineering.After Ni substitute Co atom,the inner shell structure of NixCo3-xS4 gradually becomes thinner as the Ni substitution amount increases.The XRD analysis results show that the Ni atom successfully substitute the Co atom in the Co3S4 spinel structure without causing a crystal change.Electrochemical performance tests show that Ni1.5Co1.5S4 exhibits excellent electrochemical performance compared to other Ni-substituted sulfides.The specific capacitance is 2210 F g-1 at a current density of 0.5 A g-1,and 1154 F g-1 at a higher current density of 20 A g-1.After 3000 cycles at a current density of 5 A g-1,the capacitance retention rate was 87.0%.The excellent electrochemical performance of Ni1.5Co1.5S4 can be attributed to the optimized Ni substitution amount,which improved the conductivity of the electrode material and accelerated the diffusion rate of OH-.Comparing to the energy storage kinetics and capacitance contribution of Ni-substituted NixCo3-xS4 and Co3S4 electrodes,the surface-controlled capacitance and diffusion-controlled capacitance of Ni-doped NixCo3-x-x S4 electrode materials are both improved compared with Co3S4,indicating that Ni atom substitution doping can simultaneously evaluate surface-controlled capacitance and diffusion-controlled capacitance.The Ni1.5Co1.5S4//AC asymmetric capacitor with Ni1.5Co1.5S4 as positive electrode and activated carbon as negative electrode exhibits an energy density of 36.94 Wh kg-1 at power density of 0.15 kW kg-1,18.13 Wh kg-1 at the power density of 7.5 kW kg-1 and a blue LED small light can be illuminated.
Keywords/Search Tags:Nickel-cobalt sulfide, different sulfur sources, Ni atom substitution doping, double shell structure, supercapacitor
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