Preparation Of Nanocellulose-based Conductive Composite Films And Their Application In Supercapacitor

With the global warming and resource shortage,clean,efficient and sustainable energy and environmentally friendly materials have attracted wide attention.At the same time,the development of stable,efficient and environmentally friendly energy storage devices has also become the hotspot of research.Nanocellulose,as a rich,environmentally friendly and sustainable biomass nanomaterial,can be utilized to manufacture stable electrochemical energy storage devices with high energy density and high power density.In this thesis,different nanocellulose/graphene conductive composite films were prepared,and the relationship between content of nanocellulose and performance of the composite films was revealed.Furthermore,nanocellulosebased supercapacitors were constructed,in which nanocellulose/graphene conductive composite films served as electrodes and cellulose nanofiber film acted as separator,and their electrochemical properties were studied.Reduced graphene oxide(RGO)/cellulose nanocrystal(CNC)composite films were prepared by mixing CNC suspension with graphene oxide(GO)suspension based on vacuum filtration and chemical reduction.The effect of CNC content on the structure and properties of RGO/CNC composite films was systematically studied.The results exhibited that when the content of CNC was low,CNC promoted the specific capacitance of RGO/CNC composite films.At the current density of 0.2 A/g,the specific capacitance of RGO film was 158.2 F/g,while the specific capacitance of RGO/CNC-0.5(the mass ratio of GO to CNC was 1:0.5)reached 169.5 F/g,which displayed an increase of 7.1%.Further research revealed that the specific capacitance of composite film was mainly related to the specific capacitance of RGO.In RGO film,the specific capacitance of RGO was 158.2 F/g,while in RGO/CNC-0.5,the specific capacitance of RGO touched 254.3 F/g,which displayed an increase of 60.7%.However,when the content of CNC was high,the content of electrochemically-active RGO in the composite films decreased,which leaded to the decrease of the specific capacitance of the composite films.At current density of 0.2 A/g,the specific capacitance of RGO/CNC-2.0(the mass ratio of GO to CNC was 1:2)was 72.0 F/g,which exhibited a decrease of 54.5%.Nanocellulose-based supercapacitor with RGO/CNC-0.5 as electrode and cellulose nanofiber(CNF)film as separator was constructed.At the current density of 0.2 A/g,the specific capacitance of the nanocellulose-based supercapacitor reached 145.8 F/g,with the energy density of 13.0m Wh/g and the power density of 0.08 W/g.After 10000 cycles,the capacitance retention of nanocellulose-based supercapacitor was 59.8%.In order to improve the flexibility of the composite films,CNF was introduced as the flexible skeleton of the composite films,and a preparation method of the flexible RGO/CNC/CNF composite films was developed.The influence of the addition amount of microcrystalline cellulose in the reaction process on the structure and properties of the composite film was systematically studied.In the process of composite film preparation,a portion of microcrystalline cellulose was hydrolyzed to produce CNC,while the residual microcrystalline cellulose could convert to CNF after high-pressure homogenization.CNC and CNF randomly distributed on the surface and inside of the RGO/CNC/CNF composite films,which eased the restacking of RGO during the film forming process and improved the mechanical and electrochemical properties of the composite films.The electrochemical analysis results demonstrated that at the current density of 0.5 A/g,the specific capacitance of RGO film was only 110.8 F/g,while the specific capacitance of RCC-1.0(the mass ratio of graphite to microcrystalline cellulose was 1:1)attained 168.0 F/g,which displayed an increase of 51.6%.The nanocellulosebased flexible supercapacitor with RCC-1.0 as electrodes and CNF film as separator was constructed,and its electrochemical performance was studied.The nanocellulosebased flexible supercapacitor possessed high specific capacitance(186.5 F/g at the current density of 0.2 A/g),high cycle stability(capacitance retention reached 71.1%after 10,000 charge-discharge cycles at current density of 1.0 A/g)and high energy density(16.4 m Wh/g).As a consequence,the above results supported the conclusion that the prepared supercapacitor exhibited excellent bendable properties,which might hold great promise in flexible electronic applications.