Preparation And Properties Of Nanocellulose-based Multifunctional Supercapacitor

At present,it is an important topic of energy storage through renewable materials.Among them,because of the advantages of long cycle life and high energy storage efficiency,supercapacitor(SC)has been widely focused by researchers.The introduction of intelligent functions into supercapacitors to broaden its application fields and promote its intelligent development,which has great practical value.Nanocellulose is a kind of biomass materials with high specific surface area and abundant hydroxyl groups,which shows great potential in manufacturing functional energy storage devices.Therefore,in this paper,cellulose nanofibers(CNF)with high aspect ratio were selected as the substrate,and different conductive media(polyaniline(PANI),reduced graphene oxide(rGO),MXene,Ni-MOF)were combined to prepare the composite electrodes,and their structures and properties were studied in detail.In addition,the composite materials were functionalized(polyvinyl alcohol(PVA)and glass-like polymer(Vitrimer)were introduced)and applied to the fields of energy storage,sensing,electromagnetic shielding and shape memory.Specific research conclusions are as follows:(1)PANI was synthesized by in-situ chemical polymerization based on CNF aerogel,and then coated with PVA-H2SO4 gel to prepare PANI@CNF/PVA-H2SO4 composite.The results show that the highest specific capacitance of PANI@CNF in the three-electrode system is 488.2 F g-1.After coating PVA-H2SO4,the PANI@CNF/PVA-H2SO4 composite material has a high specific capacitance of 502.2 F g-1 due to the energy storage capacity of PVA.The addition of PVA-H2SO4 can also significantly improve the cyclic stability of the electrode materials(the capacitance retention rate increased from 42.8%to 67.9%after 1000 cycles).When assembled into a symmetrical supercapacitor,it can still provide an energy density of 11.49 W h kg-1 at high power density of 413.55 W kg-1.In addition,PANI@CNF/PVA-H2SO4 composite has an electromagnetic shielding performance of 34.75 dB in X-band.PANI@CNF/PVA-H2SO4 composites can be further applied to stress sensors due to the excellent flexibility brought by PVA.(2)CNF/graphene oxide(GO)composite aerogels were prepared by freezedrying.Then through one-step hydrothermal reaction,GO was reduced and loaded with Ni-MOF,and Vitrimer(V)was further introduced to obtain MOF@CNF/rGOV composite.The results show that after reaction at 180℃ for 12 h,MOF@CNF/rGO not only has a specific capacitance of 189.9 F g-1,but also has an excellent cycle life(after 20000 cycles,the capacitance retention rate is up to 97.42%).The assembled symmetrical supercapacitor has an energy density of 6.51W h kg-1 at a power density of 117.8 W kg-1.In addition,after the introduction of Vitrimer,MOF@CNF/rGO-V composites not only have shape memory function,but also have good specific capacitance(the specific capacitance at different scanning rates is 80%-90%of MOF@CNF/rGO)and super cycle stability(after 20000 cycles,the capacitance retention rate is as high as 97.04%).(3)CNF/MXene composite aerogels were prepared by freeze-drying,PANI@CNF/MXene and MOF@CNF/MXene composites were obtained by insitu polymerization and hydrothermal reaction respectively.The results show that PANI@CNF/MXene composites can achieve a high specific capacitance of 704.78 F g-1 at 5 mV s-1.It was assembled into a symmetrical supercapacitor device with an energy density of 97.88 W h kg-1 and a power density of 1761.85 W kg-1,and a capacitance retention rate of 77.04%after 1000 cycles.MOF@CNF/MXene composites have a specific capacitance of 252.61 F g-1 at 5 mV s-1.It was assembled into a symmetrical supercapacitor device with an energy density of 12.63 W h kg-1 and a power density of 227.35 W kg-1,and excellent cycle stability of 95.23%after 20000 cycles.In addition,the electromagnetic shielding performance of CNF/MXene(the highest shielding performance is 60.08 dB)and the shape memory function combined with Vitrimer were studied respectively.In conclusion,this study provides a good theoretical basis for improving the energy storage characteristics of electrode materials and realizing their multifunctional applications.And further promotes the application of nanocellulose-based composites in the fields of energy storage,sensing,electromagnetic shielding and shape memory.