Design And Performance Study Of Flexible Electrode Based On Cellulose Nanofibrils

With the rapid consumption of fossil energy such as global oil and the aggravation of environmental pollution,the development of green renewable energy and efficient energy storage technology has become an urgent problem.Super capacitors have attracted much attention in the field of energy storage due to their high capacity,portability and stability,and have been widely used in wearable electronic devices.However,high-performance flexible super capacitors require their electrodes to have good mechanical and electrochemical properties.Nano cellulose has good biodegradability,mechanical properties and chemical reaction activity,and is often used as the substrate of electronic devices.Graphene with high conductivity and stability is also considered to be very suitable for making electrode materials,while polypyrrole(PPy)has attracted much attention because of its high pseudo capacitance,easy preparation and stability.However,nano cellulose is not suitable for single assembly of high-performance electronic devices due to its lack of conductivity,serious aggregation between graphene sheets and poor flexibility and cycle stability of PPy.Therefore,in this study,bamboo cellulose is used as raw material to prepare cellulose nanofibrils(CNFs)which are suitable for flexible electrode materials.After the CNFs are combined with graphene oxide(go)and PPy,the flexible film electrodes with excellent mechanical and electrochemical properties are prepared to meet the requirements of modern society for high-performance energy storage materials.The specific research and results are as follows:(1)After the lignin and hemicellulose in bamboo powder were removed by acid-base treatment,the dispersion of CNFs was prepared by tempo oxidation and ultrasonic treatment.Compared with cellulose,the chemical components and functional groups of CNFs have no obvious change.The I crystal structure of CNFs has not been damaged by tempo and ultrasonic treatment,and the diameter of CNFs is mainly distributed between 14-24 nm,with an average diameter of 18±3.6 nm.The two dispersions of CNFs dispersions were obtained by direct filtration and membrane filtration.The two CNFs films prepared by these two methods had excellent optical and mechanical properties.The transmittance reached 98.2%and 95.7%respectively,and the tensile strength reached 157.3 MPa and 141.9 MPa,respectively.(2)The transparent and flexible CNFs/RGO_(n)film electrode was prepared by layer by layer self-assembly after the CNFs dispersion was directly filtered into CNFs thin film.The test and analysis show that the go attached to the surface of the CNFs film is effectively reduced to RGO,and the CNFs/RGO₍₁₈₎film prepared by self-assembly times of 18 shows high transmittance,tensile strength and conductivity,reaching 86.7%,128 MPa and 2.015 S/cm respectively,and the area specific capacitance(C_A)reaches 2.25 m F cm^-2when the current density is 0.01 m A cm^-2in the three electrode system,After 1500 charge discharge cycles,the capacitance is still 97.3%.(3)By dispersing CNFs dispersions of different mass ratios and GO aqueous dispersions evenly,CNFs/GO dispersions were obtained and then filtered to gel,then dried and reduced to obtain a flexible CNFs/RGO film electrode.The test and analysis show that the method of preparing film electrode after filtration to gel and then drying makes CNFs/RGO film electrode have layered and rich pore structure,thereby obtaining good mechanical properties and good electrochemical performance.When the mass ratio of CNFs and GO is 1:2,the comprehensive properties of CNFs/RGO12 film electrode are the best,its tensile strength,elongation at break and conductivity are 85.4 MPa,5.4%and 202.94 S/m,respectively,and when the current density is 5 m A cm^-2in the three electrode system,its C_Avalue is as high as 146 m F cm^-2.In addition,after 200 bends with a bending radius of 4 mm,the capacitance is almost unchanged,and after2000 charge discharge cycles,CNFs/RGO12 still has a high capacitance retention rate.(4)In order to prepare flexible film electrodes with higher capacitance,the CNFs/RGO/PPy films with sandwich structure were prepared by in-situ polymerization and water phase oil boundary method,and the effect of deposition times of Py on the properties of the films was investigated.After 4 times of deposition,the surface of CNFs/RGO12 film obtained a complete and continuous PPy layer and a complete sandwich structure,and the CNFs/RGO/PPy4 film showed the best comprehensive properties.Its tensile strength and strain reached 72.8 MPa and4.79%,respectively,and its conductivity reached 536.31S/m.These are attributed to the formation of complete and continuous PPy layer network structure on the surface of core material by 4 times of deposition of PPy,and the good interaction among CNFs,RGO and PPy.In addition,the addition of PPy and the synergistic effect among CNFs,RGO and PPy greatly improve the electrochemical performance of the film.In the three electrode system,when the current density is 5 m A cm^-2,the C_Aof CNFs/RGO/PPy4 film increases to 387.1 m F cm^-2,and after 2000 cycles of charging and discharging and 200 times of bending with a bending radius of4mm,the capacitance retention of the film reaches 96.6%and 98.4%,respectively.