| Wearable electronics have been received increasing attention in our life,especially those can monitor the daily activities of the human body or physical condition,as well as the functions in terms of remote communication and interactive features which can be realized by the smart wristband or smart watch.The combination of electronictechnology and traditional textile technology has gradually become a direction of the development of wearable electronics in the future.Intelligent textile,also called smart textile,is the product of these two technologies and has been widely used in the field of biological and health,sports monitoring,entertainment and military,etc.The growth projections for smart garments are based around seamless and invisible integration of the electronic functionality into the garment,but with aesthetic appeal and comfort continuing to be priorities.Strategies to achieve this objective do not yet exist and represent challenges for materials researchers to produce fibers and fabrics with the desired electronic functionality compromising strength,comfort and aesthetic appeal.In addition,the integrated sensors,actuators and other electronics in smart textiles should be drived by the energy devices which also need to meet the properties of highly integrated,flexible,portable,stretchable and so on.Developing a flexible and stretchable supercapacitor with a fiber or fabric structure can be easily integrated into textiles or garment to transfer and strore the energy harvested by other forms,thus to achieve the sustainable enegy supply of smart textiles.Although there are many supercapacitor electrode materials developed based on existing fibers or fabrics,the electrochemical and mechanical properties still can not satisfy the practical applications.In that case,some new types of fabrication have been developed to obatain fiber-based supercapacitors with high-performance as well as extraordinary flexibility or stretchablity to be further applied as the energy storage devices for smart textiles.Here we describe a noval method to combine carbon nanotube(CNT)with other elecchemical active materials by using conventional wet spinning technology to explore its feasibility as a supercapacitor electrode material.A linear asymmetric supercapacitor with high integrationhas also been fabricated by coaxial spinning method.The electrochemical performances and practical applications of the prepared fiber-based supercapacitors have been investigated with following results.(1)Chlorosulfonic acid(CSA),as the only solvent that can dissolve carbon nanotubes,has been utilized to dissolve commercial single-walled carbon nanotubes to prepare a liquid-crystal like spinning dope.The liquid crystalline state of the dispersion greatly enhances the spinnability of the fibers,as well as the mechanical properties.The traditional wet spinning technology has been carried out to prepare carbon nanotube fibers by using a selection coagulation bath of acetone.The obtained none post-treatment fibers express an excellent mechanical property with a tensile strength of 225 MPa,a modulus of 23 GPa aswell as a conductivity of 450 S cm-1,which demonstrate a potential for ideal supercapacitor electrode materials in smarte textiles.With the problem of over-stacking in the cross-section of carbon nanotube fibers,graphene sheets have been exfoliated by the huge heat generated by the reaction of CSA and H2O2.The mixed graphene flakes and single-walled carbon nanotubes are used as the spinning dispersion to obtain the composite fibers with three-dimensional porous structure.The morphological,electrical and electrochemical properties of carbon nanotubes/graphene composite fibers have been investigated.The electrochemical specific capacitance of the fiber can be reached as high as 49.7 F g-1 when the content of graphene reaches at 33.3%,which is about 38.8% higher than that of pure carbon nanotube fiber.But the conductivity of the composite fiberis reduced with the increase of graphene content.(2)The prepared carbon nanotube fiber has been chosen as the current collector and substrate for the electode of supercapacitor.The manganese dioxide/carbon nanotube composite fiber electrode is fabricated by electrochemical depositing manganese dioxide nanoparticles on the surface of the fiber.The morphological characteristics of the surface and cross-section of the fiber have been observed to discuss the change of the thickness of the manganese dioxide layer on the fiber surface.It is found that the thickness of Mn O2 increases from about 110 nm to 9.9 ?m.By using the method of four-probe,the conductivity of fibe shows a decreasing trend with the increasing deposition time.The highest specific capacitance is obtained when the deposition time is 20 min with a value of 94.9 F g-1 at a scan rate of 20 m V s-1.In two-electrode system,the cyclic voltammetric performances and the charge-discharge properties of flexible fiber-based supercapacitor have been investigated.For the manganese dioxide/carbon nanotube fiber supercapacitors with different deposition time,the highest specific capacitance of the fiber-based supercapacitor can reach 152.4 F g-1 with a scan rate of 5 m V s-1 when the deposition time is 20 min.But the supercapacitor suffers poor rate property and stability.Cycling measurements have been carried out using a current density of 1 A g-1.There is almost no obvious drop of the specific capacitance after 10000 cycles,but showing a 16% increase after 3500 cycles,which points to an extraordinary long-life cycling structure of the composite electrode.However,the supercapacitors with 3 min and 10 min deposition time both showing a decrease after 5000 cycles.The average energy density and power density of the supercapacitor are greatly improved compared with other fiber supercapacitors,which are 11.7 m Wh cm-3 and 167.7 m W cm-3,respectively.In addition,the electrochemical properties of the prepared supercapacitor at different bending angles from 0 to 180°do not change much even at the maximum bending angle.Multipleunits of supercapacitors can also be assembled to match the practical applicationsin the future.(3)Polyaniline/carbon nanotube/graphene composite fiber electrode has been prepared by using high performance carbon nanotube/graphene composite fiber as substrate and electrochemical polymerizing polyaniline(PANI)on the surface.The electrochemical performance of the composite fibers with different deposition time has been investigated.The highest specific capacitance of PANI/CNT/Graphene fiber can be achieved at 225.4 F g-1 at a scan rate of 10 m V s-1,the electrodeposition time is 5 min.The prepared two fiber electrodes are assembled in the form of twisted supercapacitor,and on this basis,the features of the stretchable fiber structure and the stretchable material are combined.In another word,the coiled fiber supercapacitor is combined with the SEBS rubber to form a super-elastic fiber supercapacitor.For the stretchable fiber-based supercapacitor,the shapes of CV curves change slightly with an increasing strain,which carry out a specific capacitance of 137.5 F g-1 at a current density of 1 A g-1 with an 800% strain.To investigate the stability of the superelastic fiber-based supercapacitor,a cyclic charge-discharge characterization is carried out at a current density of 1 A g-1,and the specific capacitances are maintained by 106.3 F g-1 after 5,000 cycles with 800% strain.It also shows the dependence of specific capacitance on stretched number with increasing strains from 100% to 500%,and the capacitance has almost no change after stretching for 5,000 cycles in total.In addition,the capacitance has been maintained by 78% and the superecapacitor also presents a 75% elongation after 96 h long-time strain.(4)With the utilization of wet spinning technology,a coaxial structured linear asymmetric supercapacitor has been developed.Firstly,the rheological properties of the spinning dopes of each materialare explored,and the concentrations of them are determined according to the respective viscosity and the changes under different shear rates.The conductivities of the alginate and chitosan hydrogel electrolytes are invetigated.It is found that the alginate solution with a content of 1% sodium chloride has a conductivity of 22.7 m S cm-1,which can be used as an electrolyte.The multi-layered structure fiber is obtained by using the coaxial spinning technology with a following chemical vapor deposition of polypyrrole(PPy)on the surface of fiber.The distribution of each component has been discussed by observing the cross-section of fiber and energy spectrum analysising.The tensile strength and Young's modulus of the as-spun fiber can be achieved at 64.8 MPa and 2.2 GPa respectively,and the elongation at break is 3.5%.The electrochemical performances of PEDOT: PSS doped carbon nanotube and polypyrrole electrodes are illustrated to determine the maximum operating voltage of asymmetric supercapacitor.It can be shown that the stable potential windows of the two electrode materials are-1 to 0 V and 0 to 0.6 V respectively,so the operating voltage of the entire device is 1.6V.The maximum specific capacitance is 10.4 F g-1 at a scan rate of 50 m V s-1.For the galvanostatic charge-discharge test,it can be found that the supercapacitor has a specific capacitance of 25.1 F g-1 at a current density of 0.5 A g-1.In addition,the supercapacitor has an energy density of 8.9 Wh kg-1 at a power density of 1606.4 W kg-1 and enjoys an 86.2% capacity retention after 2000 cycles of charge-discharge,showing an excellent electrochemical performance. |
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