Construction Of High Energy Density Energy Storage Device Based On Three-dimensional Dense Graphene Material And The Study Of Electrochemical Performance

Carbon-based electrode materials have been widely used in supercapacitors due to large specific surface area,excellent conductivity,and high specific capacity.In spite of many merits of supercapacitors with carbon-based materials,the relatively low volumetric energy density severely restricts it to be applied to miniaturized setups,rendering development of carbon-based supercapacitors with excellent volumetric performance?volumetric energy density and power density?has become an urgently unsolved question.On the basis of structure of carbon-based electrode materials,it is an effective strategy to exploit a three-dimensional?abbreviated as 3D?and densely porous-network structure,which is able to boost the volumetric performance of devices.Meanwhile,in consideration of certain correlation between pore structure and ion transport,density of materials has some apparent influence on volumetric performance of electrode materials.Accordingly,with porous carbon electrode established to optimize electrode structure,holding a good balance both pore structure and density of the carbon material similarly becomes a high-efficiency way to enhance volumetric performance of equipment.Based on the above,the regulation of pore structure of graphene is attached to importance in this thesis,in which,high density porous graphene hydrogel?abbreviated as HDGH?as electrode materials,depending on evaporation-induced drying,are used in two distinct energy-storage devices with greatly volumetric performance;Furthermore,with chemical activation method of Zinc chloride?ZnCl₂?applied,structure-activity relationship?SAR?between pore structure and capacitance behavior for activated carbon is comprehensively inspected,which unfolds the mechanism of ions transmission in porous activated carbon electrode.According to the construction of porous carbon structure,the pore size distribution with optimal property of volume is successful.The primary contents of the paper are as follows:1.In order to prepare HDGH,evaporation-induced drying?herein vacuum drying at room temperature?is used for the removal of water from the graphene-based hydrogel,afterwards its oxygen-containing functional group is altered by annealing,to promote electrical conductivity.The obtained material wins varieties of virtues with high density of 1.27 g cm^-3,large specific surface area?SSA?of 538.77 m² g^-1and high conductivity of 0.356 S cm^-1.Using 17 m NaClO₄ aqueous solution of high concentration as electrolyte and HDGH as electrode material,symmetric supercapacitor is assembled,which has many merits consisting of high security,wide voltage window of 0².1 V,a high volumetric energy density of 22.3 Wh L^-1(at a volumetric power density of 35.0 kW L^-1)and ultra-long cycle life up to 10,000 circle with about 93.6%capacitance retention at 1 A g^-1.2.For the first time,using HDGH as cathode and zinc foil as anode,zinc ion hybrid supercapacitor is constructed,showing high volumetric energy density of118.42 Wh L^-11 at a volumetric power density of 24.00 kW L^-11 and excellent cyclic stability,that is,retaining about 80%capacity of the initial capacity after 30,000cycles at 10 A g^-1.Counting on ex-situ XRD spectrum and SEM analysis at certain working states,its working mechanism is understood in depth,i.e.,the rapid adsorption/de-adsorption of anions onto positive electrode as cathode reaction and the reversible deposition/dissolution of Zn²⁺on Zn foil as anode reaction,simultaneously.3.Activated carbon of different pore size is successfully synthesized via chemical activation method of ZnCl₂.The evolution of pore structure and capacitance for electrode material is roundly investigated in electrolyte of high concentration,suggesting that,with the pore size being 1 nm or so,its normalized specific capacitance meets maximum;Additionally,with the proportion of mesopores growing,the normalized specific capacity decreases and tends to be stable finally.These illustrates that there are a great number of solvated ions in the micropore with diameter of 1 nm approximately,on the surface of which the solvent molecules are dissolved,shortening scope from center of ionic charge to electrode surface and resulting in remarkable growth of specific capacitance.Moreover,mesopores lead to ion transport channels,achieving efficient ion transport in porous materials.The optimal pore distribution is received likewise,by virtue of establishing porous carbon and analyzing contribution of specific capacity of pore volume in both mesopore and micropore,respectively.