The Construction And Mechanism Investigation Of Wood-Derived Cellulose Nanofiber Based Multi-Dimensional Network In Energy Storage System

Wood-derived cellulose nanofiber(CNF)is a renewable natural polymer with high mechanical strength,a large aspect ratio,good dispersion,and hydrophilicity.Its cellulose chain is densely packed with oxygen-containing groups,and it is simple to construct a porous network structure with a high specific surface area.In addition,CNF is rich in carbon,and carbon fiber networks with high conductivity can be formed after carbonization.Because of these exceptional properties,CNF has a significant application value and future development potential in the field of green energy storage.The supercapacitor,a new energy storage device in the field of green energy storage,has the advantages of high power density,good safety,and good cycle stability.It has become one of the hotspots of energy storage and conversion research.Moreover,current supercapacitors continue to have issues,such as low energy density,poor rate performance,and short cycle life,which severely limit their practical application.In supercapacitors,electrodes and electrolytes are the core components,which have a decisive impact on their capacitive performance,stability,mechanical performance,and safety.Consequently,it is critical to creating new high-efficiency electrode materials and electrolytes that are both green and environmentally friendly.Given the aforementioned issues,this study,from the standpoint of structural design,uses the natural properties of CNF to compound with other active substances and develops a variety of CNF-based electrode materials and flexible and stretchable solid electrolyte materials,realizing the controllable preparation of the morphology and structure of the composites and the improvement of electrochemical properties.On this basis,the new electrode materials and electrolytes were integrated and assembled into a series of green,environment-friendly,and efficient supercapacitors.Simultaneously,the synergistic effect of CNF in energy storage materials is demonstrated through the analysis of characterization methods and electrochemical performance tests,and the high-efficiency energy storage mechanism is revealed,providing a new idea for the development of green energy storage materials and supercapacitors.The main research contents and results are as follows.(1)By freeze-drying and carbonization activation,a carbonized CNF aerogel(CCA)with a three-dimensional porous structure was formed.The lamellar thickness and microporous structure of CCA were effectively adjusted by adjusting the preparation conditions of the freeze-drying and high-temperature carbonization processes.Through the characterization of physicochemical properties and electrochemical tests,the effects of freeze-drying and carbonization activation on the micromorphology and electrochemical properties of CCA were analyzed and studied.The thickness and specific surface area of the CNF-formed lamellar structure increase with increasing CNF concentration.The micropore volume of CCA expands significantly as the carbonization temperature rises,and its specific surface area increases from 188.15 m2/g to 684.62 m2/g.The CCA electrode exhibits a high capacitance of 174 F/g at a current density of 0.625 A/g due to its high porosity structure and good conductivity.Furthermore,the CCA electrode has extremely high cycle stability.After 100000 long-time cycle tests,its capacitance retention can reach 97.22%.(2)Nickel-based nanomaterials were grown on CNF-derived carbon sheets by hydrothermal growth and high-temperature pyrolysis to prepare CNF supported nickel oxide(Ni-NiO/CC)electrode materials.By adjusting hydrothermal growth conditions,it was possible to achieve the controllable growth of nano-active substances on CNF-derived carbon sheets.The number of nanoparticles embedded in CNF carbon sheets gradually increased as the concentration of hexamethylenetetramine(HMTA)increased.Thanks to the fine nanostructure regulation and the dispersion and high conductivity of CNF,Ni-NiO/CC electrode has excellent capacitance and magnification performance.When the current density is 0.625 A/g,the specific capacitance can reach 1207.5 F/g;when the current density is increased from 0.625 A/g to 25 A/g,the specific capacitance of the Ni-NiO/CC-8 electrode maintains 45%of the initial specific capacitance.(3)Using the adsorption of oxygen-containing functional groups on the surface of CNF,iron oxide nanoparticles were deposited and grown on the surface of CNF,and CNF-derived carbon-supported iron oxide(CF)electrode material was further transformed under the action of heat treatment.The amount and morphology of iron oxide nanomaterials loaded on the surface of CNF-derived carbon was controlled by adjusting the NaOH content in the hydrothermal process and the calcination temperature in the high-temperature pyrolysis process.The existence of CNF effectively reduces the growth size of iron oxide nanoparticles,improves the active area of electrode materials,and greatly improves the capacitive performance of the electrode.When the acquired CF electrode material is 2.5 A/g,the specific capacitance can reach 541.11 F/g,whereas when the current density is increased to 25 A/g,the current density remains 388.89 F/g.(4)CNF enhanced polyacrylic acid(PAA)flexible gel electrolyte(CNF/PAA)with excellent tensile properties and high ionic conductivity was successfully prepared by in-situ polymerization.CNF and PAA polymer matrices form semi-interpenetrating network structures through physical entanglement and hydrogen bonding.CNF prevents the swelling of PAA gel electrolyte,increases alkaline content,aids in increasing ion transport rate,and effectively improves gel electrolyte ionic conductivity.The prepared CNF/PAA not only has good mechanical strength and ionic conductivity but also has good stretchability and elasticity.The tensile fracture length of the CNF/PAA gel electrolyte reached over 600%.The CNF/PAA gel electrolyte has an ionic conductivity of 0.31 S/cm.Furthermore,even after hundreds of stretch spring back cycles,the ionic conductivity of CNF/PAA gel electrolytes remains stable,indicating that they have a wide range of applications in the field of flexible electronics.(5)The prepared CCA electrode material,Ni-NiO/CC positive electrode material and CF negative electrode material were combined to form supercapacitors with various energy storage mechanisms,and their energy storage performance and energy storage behavior were thoroughly tested and evaluated in KOH electrolyte.In addition,the CNF/PAA gel electrolyte was substituted for the above KOH electrolyte and other electrode materials to form a series of solid supercapacitors and the electrochemical performance was tested.The test results demonstrate that the formed supercapacitor has good energy storage performance,the proper matching of positive and negative materials improves the device’s energy density,and the use of solid electrolytes improves the supercapacitor’s safety and mechanical properties.Herein,CNF aerogels with high specific surface area and porous network structure and CNF-derived carbon aerogel electrode materials were constructed by self-assembly characteristics of CNF.On this basis,electrode materials with hierarchical porous structures were created by combining the rich active sites of CNF with the active substances of iron oxide and nickel oxide,which rectified the problems of low capacitance and poor magnification performance caused by poor conductivity and easy agglomeration of electrode materials like iron oxide and nickel oxide.In addition,CNF was used as the reinforcing phase to prepare the extensible gel electrolyte with PAA,which solved the problem that the gel electrolyte was difficult to achieve high ionic conductivity and mechanical strength.The supercapacitor integrated and compiled with the aforementioned energy storage materials has excellent electrochemical performance and is expected to be used in wearable intelligent devices,portable electronic products,and other fields in the future.This research not only demonstrates the widespread and extensive use of CNF in energy storage devices but also improves the electrochemical performance of biomass-based electrode materials and the development of stretchable electrolyte materials.Simultaneously,it provides a research idea for the development of green and efficient energy storage materials through the use of sustainable biomass resources.