Controlled Synthesis Of Nickel-based And Carbon-based Supercapacitor Electrode Materials And The Electrochemical Performance Study

Supercapacitor,as one kind of the most important electrochemical charge storage devices,has been widely applied in the field of energy storage and conversion,like renewable energy storage system,new energy vehicles domain,portable electronics and smart grid system,because of its remarkable power density,long-term cycling ability and high safety.In this dissertation,we aim at the fabrication of high-performance supercapacitors with excellent power and energy density,based on the controlled synthesis of nickel-,cobalt-and molybdenum-based electrode materials and biomass-derived electrode materials with great electrochemical performance.Through the regulation of the structure,composition and crystalline structure of the electrode materials,we have proposed creative ideas about the preparation of electrode materials and realized the designed synthesis of positive and negative electrode materials with high specific capacitance,rate performance and cycling stability,and have consequently assembled high-performance hybrid and symmetric supercapacitors.We have clearly illustrated the designed synthesis idea of the electrode materials,and systematically analyzed the material synthetic mechanism,performance improvement mechanism and the application potential,based on the characterization and electrochemical test results.The research results are summarized briefly as follows:(1)In order to overcome the poor cycling stability of transition metal compound and the lower electrochemical activity of the monocomponent electrode materials,we have prepared Ni3S4/Ni(OH)2/Mo,Oy composite with microsphere structure,through partially sulfidation treatment of the precursor and rational regulation of the reaction parameters.In this study,we have systematically analyzed the effects of reaction conditions,material composition and structure on the electrochemical performance of the electrode materials,which are utilized to optimize the material synthesis process and regulate the charge storage performance of the materials.On one hand,the main composition of the composite is nickel oxide and sulfide,which could effectively improve the electric conductivity and charge storage ability of the material,and the loading of minor molybdenum oxide could also remarkably enhance the electrochemical reaction activity of the electrode material,fully utilizing the synergetic and complementary effect of different components to improve the electrochemical performance.On the other hand,the robust microsphere structure of the material is beneficial for the improvement of the cycling stability.At the current density of 1 A·g-1,the specific capacitance is up to 2177.5 F·g-1,and after 5000 cycles,the specific capacitance could retain 86.25%.The as-assembled hybrid supercapacitor possesses high energy density and cycling stability,at the power density of 850 W·kg-1,the energy density is 50.61 Wh·kg-1,and after cycling for 10000 times,the specific capacitance could retain 93.38%.(2)In order to deal with the problem of complex preparation process,high cost and low yield of the bimetal or multi-metal compound electrode materials,we have proposed the material synthesis idea by using metal oxalate as the precursor to synthesize electrode materials with specific composition,morphology,structure and high electrochemical performance,and have consequently realized the fabrication of solid-state hybrid supercapacitor with high energy density and power density.The metal oxalate is firstly prepared by chemical precipitation,and used as precursor to synthesize bimetal and ternary metal compound electrode materials via a simple anion exchange reaction.The products are of excellent cycling stability and electrochemical activity,due to the stable nanostructure and the synergetic and complementary effect of the materials.At the current density of 1 A·g-1,the specific capacitances of CoNi2S4 and Cu(Ni,Co)2S4 are 1836.6 and 2168.5 F·g-1,and after 10000 cycles,the specific capacitances could retain 76.7%and 85.1%.In addition,the electrochemical performance of the CoNi2S4 and the as-fabricated hybrid supercapacitor is studied at 0,25 and 50?,however,their charge storage performance almost remain the same,which demonstrates that the electrode material and the charge storage device exhibit excellent electrochemical performance in a wide range of applied temperature.Besides,biomass-derived carbon material is utilized as the negative electrode to assemble solid-state hybrid supercapacitor with higher energy and power density.(3)In order to solve the problem of the complex synthesis process and high energy consumption,we have prepared biomass-derived multi-heteroatom doped carbon materials with excellent cycling property and electrochemical activity,using laver and soybean milk as the carbon source,to further improve the cycling performance,energy density and power density of the supercapacitor.During the material synthesis process,in order to retain the multi-elements composition and the stable structure of the biomass,we have not applied any other physical or chemical treatments to activate the materials.Besides,we have taken advantage of the negatively charged nature of the protein in the liquid state soybean milk to react with positively charged Ag+,and prepared silver nanoparticle loaded biomass-derived carbon material by one-step annealing treatment.The silver doping is favorable for the regulation of the structure and improvement of the electric conductivity of the materials,facilitating the charge transfer and ion diffusion process.The as-fabricated solid-state symmetric supercapacitors were of great energy density and excellent cycling stability,which are better than the electrochemical performance of the commercial carbon material-based supercapacitor,and after cycling for 50000 times,the retentions of the specific capacitances are more than 100%.The electrode material synthesis idea proposed in this study has high application potential for the preparation of other heteroatom-doped biomass-derived carbon materials.(4)Based on the biomass-derived carbon material synthesis idea proposed in this study,we have synthesized heteroatom doped carbon materials utilizing orange peel and egg white as the biomass carbon source,and consequently fabricated solid-state hybrid supercapacitor with high energy density and power density using batter-type electrode material as positive electrode.Because of the simple preparation process,the products could retain more heteroatoms and more robust structure.The doped heteroatoms could efficiently improve the electrochemical activity,wettability and electronic structure of the materials,and the robust structure is beneficial for the superior long-term cycling stability.In addition,we have also utilized the negatively charged nature of the protein in the egg white,introduced Ag+ based on the charge neutralization reaction,and prepared silver nanoparticle doped biomass-derived carbon material.The carbon materials are employed to fabricate solid-state hybrid supercapacitors with core-shell structure C/N-CoO@CoO/NiO as the positive electrode,and the supercapacitors possess excellent electrochemical performance.At the power density of about 850 W·kg-1,the energy densities are 33.1,30.1 and 35.6 Wh·kg-1,and after cycling for 50000 times,the specific capacitances could retain 145.9%,139.2%and 140.0%.