Studies on Preparation and Electric Energy Storage of Electrode Materials for Supercapacitors Applications

Author:Zhang Guo Xiong

Supervisor:chen yi gang


Degree Year:2019





In recent years,supercapacitors have attracted great attention of researchers and generate the research spree of electrode materials of supercapacitors due to their lots of advantages such as high energy density,high cycle life,wide operating temperature range and reliability.At present,the electrode materials of supercapacitors are mainly carbon materials and metal-oxides/metal sulfides,which electrochemical properties are determined by pore structure,conductivity,surface state and so on.With the continuous exhaustion of energy and deterioration of environment,people have put forward higher requirements for the sustainability of energy.As a new generation of energy storage devices,supercapacitors also need to meet the new era’s demand with the better electrochemical properties.This papers aims to study and synthetic new composited electrode materials in view of the shortage of current electrode materials from those aspects such as surface state,conductivity and microstructure,and explore the mechanism of these factors on electrochemical energy storage.The main research contents are as follows:1.Using two-steps method of carbonization and activation to prepare biomass activated carbon(ABC)with bamboo as carbon source,and we research the effects of different activation temperatures on pore structure,conductivity,surface state and electrochemical properties of biomass carbon.The results show that the pore structure and specific surface area have great changes with the activation temperatures ascension,and the ABC-900(BET:2221.2 m2g-1)exhibits the best electrochemical performance above all the biomass activated carbon samples.In the three-electrode system,the ABC-900 electrode material shows high capacitance of 293 F g-1 at a current density of 0.5 A g-1 and good cycle life.The ABC-900 electrode material also have been prepared to assemble symmetric supercapacitors device,which shows a high energy density of 10.9 Wh kg-1 at a power density of 63 W kg-1 and excellent capacitance retention rate(7.8 Wh kg-1 at a power density of 2500 W kg-1).2.By using a sample hydrothermal method,we have successfully synthesized ABC/NiCo2S4 composite electrode materials by combining the biomass activated carbon and NiCo2S4,and further study the effect of the amount of biomass activated carbon on the crystal,structure and electrochemical properties of the electrode materials.We also investigate the mechanism of biomass activated carbon on the composite electrode materials.The results show that the original agglomerated nanonetwork structure dispersed into nanowires structure.After the three-electrode system test,the ABC/NiCo2S4-4 composite electrode material shows the best electrochemical performance,and exhibits a high specific capacitance of 1948 F g-1 at a current density of 0.5 A g-1 and excellent capacitance retention rate and cycle life.3.For studying the effect of the amount of CMK-3(ordered mesoporous carbon)on conductivity,pore structure and microtopography of electrode materials,we prepared the CMK-3/Co3O4 and CMK-3/NiCo2S4 electrode materials respectively.The results show that CMK-3/Co3O4 samples reveal the coexistence of nanowires and nanosheets with the addition of the certain amount of CMK-3,which effectively improve the contact area between the electrode materials and electrolyte.The-C/Co3O4-6 sample shows the highest specific capacitance after the three-electrode system test.At a current density of 0.5 A g-1,the sample can reach a high capacitance of 1131.2 F g-1 and the capacitance can still have 82.6%retention rate even after 1000 cycle life tests.In the CMK-3/NiCo2S4 electrode materials,CMK-3 acts as a conductive agent and polymerization inhibitor.Conductivity of composite materials have been improved and the nanonetwork structure becomes the nanowire structure.The C/NiCo2S4-8 sample exhibits the highest specific capacitance(3293 F g-1 at 0.5 A g-1)and outstanding cycle life(94.2%retention rate after 2000 cycle life tests).Finally,the C/NiCo2S4-8 electrode material also have been prepared to assemble asymmetrie supercapacitors device,which shows a high energy density of 34.9 Wh kg-1 at a power density of 357 W kg-1.4.The core-shell nanowires Co3O4/Ni(OH)2 composite electrode materials are successfully synthesized by a new type of electrochemical deposition that the Ni(OH)2 was deposited on the Co3O4 nanowires.The results show that the content of deposited Ni(OH)2 is low and the crystallinity is poor.Different deposition cycles have great differences in the microstructure and electrochemical properties of electrode materials.The Co3O4/Ni(OH)2 sample shows the best electrochemical performance while the cycle times were two and named as Co3O4/Ni(OH)2-2.In the three-electrode system,the Co3O4/Ni(OH)2-2 electrode material shows high capacitance of 2055.1 F g-1 and outstanding cycle life.The Co3O4/Ni(OH)2-2 electrode material also have been prepared to assemble asymmetric supercapacitors device,which shows a high energy density of 48.6 Wh kg-1,and the capacitance can still have 72.7%retention rate even after 8000 cycle life tests.5.Using multi-step hydrothermal method to prepare Co3O4/NiCo2S4 composite electrode material which nanowires NiCo2S4 grafted onto Co3O4’s nansheets,and investigate the effect of morphology on electrochemical properties of composite electrode materials.The results show that this kind of structure can effectively increase the utilization rate of electrode materials and enrich the Faraday reaction.The unique pore structure is conducive to the rapid diffusion of electrolyte ions and overcome the limitation of kinetics,thus greatly improving the electrochemical properties.In 3 M KOH electrolyte,the specific capacitance is as high as 1774 F g-1 at the current density of 0.5 A g-1,with good multiplier characteristics.After 1000 cycle life tests,the specific capacitance retention rate still can achieve 88.7%,indicating the outstanding electrochemical performance.