Research On The Preparation And Electrochemical Performance Of Mesoporous Nickel/Cobalt Sulfides

Supercapacitor is a new energy storage and conversion device which possesses performances of high power density,fast charge and discharge rate and long-term cycling life.However,it still has low energy density,poor specific capacitance and other issues.Hence,exploring and improving the appropriate electrode material is an effective way to solve this problem.Sulfide is a kind of new electrode material due to its large theoretical capacitance value,simple preparation,low price,environmental pollution and other advantages.Sulfide has been attracted attentions to research this field.The main content of this thesis is to explore the optimal process to fabricate mesoporous sulfide nickel/cobalt as electrode materials by hydrolysis method using hot high-boiling solvent.Nickel,cobalt chloride hexahydrate and sodium sulfide nonahydrate were employed as raw materials,and silica as a template.The specific research contents are briefly described as follows:(1)Nickel sulfide electrode materials with different proportions were prepared by a high boiling solvent-thermal method: different Ni/S molar ratios of 1:1,1:2,1:3,1:4 weighed NiCl2·6H2O and Na2S·9H2O,which were used as raw materials,and dissolved into ethylene glycol to fabricate sulfide by refluxing,and obtain the optimum conditions of reaction.A series of structural and electrochemical performance of the prepared electrode materials were analyzed,and the comparative analysis of the measured data was to select the optimal reaction condition.The results showed that electrochemical performance gradually increased with the increase of S content.When the ratio is more than 1:3,the performance gradually stabilized so that Ni:S=1:3 is a preferable ratio.The capacity can still maintain more than 80% at 5 A g-1 after 20000 galvanostatic charge–discharge test cycles,indicating that the prepared sample has a good cycle stability.(2)The cobalt sulfide electrode material with different template dosage was obtained by high boiling solvent heat method: CoCl2·6H2O was weighed based on the Co/SiO2 in the mass ratio of 1:0.25,1:0.5,1:1,1:2 and 30% mass fraction of silica sol was dissolved in ethylene glycol organic solvent in order to explore the optimal dosage of template through the comparative analysis of the structural test and electrochemical performance test data.The results showed that four samples mainly concentrated on mesoporous with the increase of SiO2 dosage and the specific surface area was increased gradually.When the ratio is over 1:1,the specific surface area value and the performance of electrochemical are reduced.Hence,the optimum mass ratio of Co/SiO2 was considered to be 1:1,and its capacity can reach 469.36 F g-1.The specific capacity can still maintain 85% at 5 A g-1 after 20000 galvanostatic charge–discharge test cycles,indicating that the sample has a good cycle stability.(3)Based on the results of the previous two chapters,a better high-boiling solvent thermal process was obtained.With the development of exploration process,different proportions of Ni/Co are prepared.0.6g of CoCl2·6H2O and NiCl2·6H2O which Ni/Co in the molar ratio of 1:1,1:2,1:3,1:4 were dissolved in ethylene glycol organic solvent.The structural and electrochemical performances of as-prepared samples were tested.Compared with the previous single-component cobalt sulfide or nickel sulfide,the morphology and particle size of as-prepared nickel-cobalt sulfide composites tend to uniform and the agglomeration is significantly reduced.The large specific surface area is found and the pore size distribution of the prepared materials is mainly concentrated in the mesopores.Electrochemical performances,compared with the single-component cobalt sulfide or nickel sulfide,were obviously improved.When the molar ratio of Ni/Co was controlled to 1:2,the resulting sample had excellent electrochemical performance compared with the other ratios and the specific capacity can reach 817.02 F g-1.From the perspective of impedance,Faraday resistance and solution resistance were very small because NiCo2S4 material was a kind of conductor with good conductivity.The capacity can still maintain 93.7% at 5 A g-1 after 20000 galvanostatic charge–discharge test cycles,indicating that the sample has good cycle stability.Doping has a significant effect on improving the electrochemical performance of a single material hence,and the effect of appropriate proportion of the doping is much more pronounced.