Design And Electrochemical Capacitance Performance Of Wood Cellulose Nanofiber-based Flexible Electrode

Wood-cellulose nanofiber(CNF)inherenting flexibility,excellent film-forming ability,dispersibility and electrolyte absorption properties,are considered to be good potential framework/substrate materials for flexible storage electrode.It has aroused the interest of research workers.However,the poor structural stability and low energy density of CNF based flexible electrodes seriously restricted the efficient application in high-performance flexible supercapacitors.In view of the above problems,this thesis focuses on the optimization design of the structure and performance of the CNF based flexible electrode materials and its application in high-energy flexible supercapacitors.The main research contents include:1.A simple and effective method for improving the conductivity and structure stability of CNF/MWCNT(multi-walled carbon nanotube)hybrid aerogels(HAs)has been successfully developed.Here,on the one hand,carbon fiber(CF)effectively improves the conductivity of the electrode.Compared with CNF/MWCNT electrodes,the resistance charge transfer(Rct)of CF-CNF/MWCNT electrode significantly reduced from 8.5 to 3 92.On the other hand,three-dimensional porous structure of HAs also presents strong structural integrity,which provides a favorable platform for the subsequent introduction of high theoretical specific capacity(such as metal oxides,conductive polymers,etc).Used CF-CNF/MWCNT-HAs as a support,active substance MnO2 was in situ loaded via wet chemical reactions.It was found that the loading amount of MnO2 increased with the the extension of reaction time.The high loading(2.64 mg/cm2)MnO2 on the HAs was achieved when the reaction time was 3 h,and the composites electrode displayed the best electrochemical performance.Electrochemical results showed that the CF-CNF/MWCNT/MnO2 could deliever a high areal capacitance of 1744.5 mF/cm2 mA/cm2 and the capacity retention rate was 52.3%at 40 mA/cm2.In addition,this general strategy was extented to fabricate the carbon fiber-cellulose nanofiber/multi-walled CNT/activated carbon hybrid aerogels(CF-CNF/MWCNT/AC-HAs)as negative electrode matching the positive electrode,A flexible and high-performance all-solid-state CF-CNF/MWCNT/MnO2//CF-CNF/MWCNT/AC asymmetric supercapacitors(ASC)device has been constructed.This device operated at a 1.8 V voltage window was able to delivered a maximum volumetric energy density of 8.93 mWh/cm3.2.A "bottom-up" strategy was proposed to constructe three dimensional CNF/MWCNT/RGO hybrid aerogels,in which CNF act as dispersant to disperse 1-dimensiona MWCNT and 2-dimensiona graphene oxide(GO).CNF/MWCNT/RGO(reduction graphene oxide)was successfually prepared using a simple Freeze-drying and hydrazine hydrate steam reduction method.Four-point probe sheet resistance meter test results show that the resistance of CNF/MWCNT/RGO-HAs sheet was 5.4 Ω/sq.Then,the Fe3O4 nanoparticles was in situ embedded in CNF/MWCNT/RGO-HAs to develop flexible CNF/MWCNT/RGO/Fe3O4 electrode by the solvent thermal reaction.The effect of different Fe3+concentration on the final mass loading of Fe3O4 nanoparticles was studied.At the concentration of 0.02 mol/L to 0.10 mol/L,the mass loading was increased from 1.92 mg/cm2 to 5.93 mg/cm2.Fe3+ concentration is 0.08 mol/L(mass loading Fe3O4 nanoparticles was 4.93 mg/cm2),the preparation of CNF/MWCNT/RGO/Fe304 negative electrode under the current density of 1 mA/Cm2 shows high areal specific capacitance of 1193 mF/cm2,which is the highest level of among the reported Fe3O4 based-flexible electrode.Furthemore,CF reinforced CF-CNF/MWCNT/MnO2-HAs serve as positive electrode,a flexible and high-performance all-solid-state CF-CNF/MWCNT/Mn02//CNF/MWCNT/RGO/Fe3O4 ASC device has been assembled.This device operated at a 1.8V voltage window was able to delivered a maximum volumetric energy density of 2.35 mWh/cm3.The above studies provide us with a new strategy for the rational design and preparation of flexible asymmetric supercapacitors electrode materials with Wood-cellulose nanofiber,and it can be widely used in the field of portable and wearable electronics.