| With the development of society and the improvement of people's living standards,people have more and more demands for various kinds of energy,and the application of energy storage materials is increasingly concerned.Supercapacitors are widely used in instrumentation,solar energy,wind energy and electric vehicles because of their high power density,long cycle life,and high charging and discharging efficiency.However,low energy density and poor cycle stability hinder its promotion and application.Therefore,the research and development of high-performance supercapacitor electrode materials is imminent and has gradually attracted people's attention.In this project,metal sulfide with high theoretical specific capacitance value was selected as the pseudo capacitor materials,and carbon fiber was used as the substrate with good conductivity and certain electric double layer performance.The electrode material of metal sulfide composite carbon fiber with corresponding microstructure was obtained by hydrothermal synthesis method and proper control of the molar ratio of each component,which shows an excellent performance.The following is the main research content of the thesis:(1)Nickel acetate(Ni(CH3COO)2)and ammonium fluoride(NH4F)were used as a precursor to synthesize nickel hydroxide(Ni(OH)2)by hydrothermal method,and the molar ratio of Ni to S was 1:1,1:2 and 1:3.The Ni(OH)2,sodium sulfide(Na2S·9H2O)was placed in a high-temperature reaction kettle with pre-treated carbon fiber(CFS).The NiS/CFs composite electrode material was prepared again using the hydrothermal method.NiS nanosheets with excellent pseudocapacitance properties are more evenly distributed on CFs with electric double layer characteristics.The electrochemical test shows that the 2-NiS/CFs composite electrode material has a more obvious redox peak,and its impedance value is smaller.The specific capacitance is 213.9 F·g-1at a current density of 1 A·g-1.After 2000times of charging and discharging,the capacity retention rate is about 86%.When the power density is 252 W·kg-1,its energy density can reach 18.7 Wh·kg-1.(2)Cobalt hydroxide(Co(OH)2)was prepared by mixing with cobalt acetate(Co(CH3COO)2)and NH4F and by hydrothermal method.Co(OH)2and Na2S·9H2O were proporfied with the ratio of Co and S at the molar ratio of 1:1,1:2 and 1:3.The composite electrode material of CoS2/CFs were synthesized by the hydrothermal method with the pretreated CFs.The results show that electrochemical tests show The distribution of flower-like CoS2on the CFs is relatively uniform.Throughelectrochemical tests,it is found that the 2-CoS2/CFs composite material has a lower impedance value and more obvious pseudocapacitance properties.When the current density is 1 A·g-1,the specific capacitance is as high as 1701.7 F·g-1,and the capacity retention rate is 88%after 2000 cycles of charge and discharge.The energy density is 38.1 Wh·kg-1at the power density of 366.2 W·kg-1.(3)The ratio of Ni(CH3COO)2,Co(CH3COO)2,NH4F and Na2S·9H2O was 1:1:2,1:1:3 and 1:1:4 according to molar ratio of Ni,Co,S.Further,the pretreated CFs and solution was added to a high temperature reactor together.The electrode materials of prepared cobalt nickel sulfide(NiCo2S4)composite carbon fiber were prepared by hydrothermal method.The experimental results show that 2-NiCo2S4/CFs has a more uniform structure distribution and better electrochemical performance.When the current density is 1 A·g-1,the specific capacitance of 2-NiCo2S4/CFs is 334.38 F·g-1;The capacity retention rate is about 90%after 2000 cycles of charging and discharging,The energy density is 42.8 Wh·kg-1and the power density is 400 W·kg-1. |
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