Construction And Properties Of Flexible Electrode Materials Based On Cotton Fibers

With the rapidly development of wearable electronic devices,traditional energy storage devices cannot meet people’s needs.It’s due to their rigid structures and low energy storage efficiency.The design and development of flexible supercapacitors is imperative.In this study,cotton fibers are used as flexible substrates,layered double hydroxides(LDHs),silver nanowires(AgNWs)and polypyrrole(PPy)with different morphologies are functionalized on cotton fibers.The three-dimensional network structure,hierarchical structure,and "sandwich" structure flexible electrode materials are constructed,and applied them to the preparation of supercapacitors.AgNWs with a aspect ratio of about 400 were synthesized by polyol method,and they were impregnated onto cotton fibers to obtain silver nanowires/cotton fibers(AgNWs/Cotton)with a square resistance of 0.096 Ω.In situ growth of cobalt based metal organic frameworks(ZIF-67)as templates for LDHs growth,resulting in cobalt based metal organic frameworks/silver nanowires/cotton fibers(ZIF-67/AgNWs/Cotton).Furthermore,Ni2+ was introduced to obtain three-dimensional network NiCo layered bimetallic hydroxide/silver nanowire/cotton fiber(NiCo-LDH/AgNWs/Cotton)electrode materials by hydrothermal method.The results of SEM,TEM,and EDS indicate that NiCo-LDH nanosheets uniformly grow on AgNWs/Cotton,forming a "coral like" three-dimensional network structure.The results of XRD,FT-IR,XPS indicate the successful preparation of NiCo-LDH/AgNWs/Cotton electrode materials.The porosity results indicate that the derivative of ZIF-67 into NiCo LDH significantly improves the porosity of the electrode material.The electrochemical results shows that when ZIF-67 is grown twice,the mass ratio of Ni2+ to ZIF-67/AgNWs/Cotton is 8:1,and the solvent moisture content is 60%,the NiCo-LDH/AgNWs/Cotton electrode material has the best specific capacitance(823.90 mF cm-2,1 mA cm-2)and cycling stability(1000 cycles,77.70%).The NiCo-LDH/AgNWs/Cotton supercapacitor achieve maximum energy density of 8.63 Wh cm-2 at a power density of 0.23 mW cm-2.Dense ZIF-67 is grown on cotton fiber by in-situ method,and then Ni2+,Al3+are introduced to transform ZIF-67 into nickel cobalt aluminum layered metal hydroxide(NiCoAl-LDH)array by hydrothermal method.Subsequently,pyrrole(Py)and FeCl3·6H2O are introduced to form a PPy conductive layer on the array through chemical oxidation polymerization.Polypyrrole/nickel cobalt aluminum layered metal hydroxide/cotton fiber(PPy/NiCoAl-LDH/Cotton)electrode material with layered array structure is obtained.The results of SEM,TEM,and EDS indicate that NiCoAl-LDH nanosheets form a uniform array structure on cotton fibers,and PPy particles form a continuous and dense film layer on the array.The results of XRD,FT-IR,XPS indicate the successful preparation of NiCo-LDH/AgNWs/Cotton electrode material.The porosity results indicate that the introduction of NiCoAl-LDH into PPy/Cotton can significantly improve the porosity of electrode materials.The electrochemical results indicate that when ZIF-67 undergoes 4 cycles of growth,the molar ratio of Ni2+to Al3+is 3:1,the molar ratio of FeCl3·6H2O to Py is 4:1,and the Py polymerization time is 120 minutes,the specific capacitance(754.72 mF cm-2,5 mA cm-2)and cycling stability of PPy/NiCoAl-LDH/Cotton electrode material are the best(1000 cycles,80.95%).The PPy/NiCoAl-LDH/Cotton supercapacitor achieve maximum energy density of 20.83 Wh cm-2 at a power density of 0.26 mW cm-2.Introducing AgNWs,NiCoAl-LDH,and PPy into cotton fibers and regulating the morphology of PPy further enhances the electrochemical performance of electrode materials.Ni2+and Al3+are introduced into ZIF-67/AgNWs/Cotton to convert them into nickel cobalt aluminum layered metal hydroxide/silver nanowire/cotton fiber(NiCoAl-LDH/AgNWs/Cotton).Then,the polypyrrole nanowire/nickel cobalt aluminum layered metal hydroxide/cotton fiber(PPy-NW/NiCoAl-LDH/AgNWs/Cotton)electrode material is obtained by chemical oxidation polymerization using methyl orange(MO)as template and introducing Py,FeCl3·6H2O.The results of SEM and EDS indicate that PPy-NW is clustered and uniformly coated on NiCoAl-LDH/AgNWs/Cotton.The results of FT-IR and XPS indicate that the successful preparation of PPy-NW/NiCoAl-LDH/AgNWs/Cotton electrode material and MO can promote the polymerization of PPy-NW.The porosity results indicate that PPy NW further enhances the porosity of the electrode material.The electrochemical results show that when the MO concentration is 0.9 mM and the Py polymerization time is 24 hours,the specific capacitance(1207.58 mF cm-2,5 mA cm-2)and cycling stability(2000 cycles,87.5%)of PPy-NW/NiCoAl-LDH/AgNWs/Cotton electrode material are the best.This electrode material has excellent flexibility and wearability.The PPy-NW/NiCoAl-LDH/AgNWs/Cotton supercapacitor achieve maximum energy density of 36.28 Wh cm-2 at a power density of 0.31 mW cm-2.Compare the performance of three electrode materials and assembled supercapacitors.The results show that PPy-NW/NiCoAl-LDH/AgNWs/Cotton electrode material has the best specific capacitance and cycling stability,and the assembled supercapacitor has the best power density and energy density.The PPy/NiCoAl-LDH/Cotton electrode material has the best bending stability,and friction stability.