| The exploitation on the wearable and compatible power apparatus has become the hotspot in the field of intelligent textiles with the high development of lightweight,flexible and portable electronic devices correspondingly.As a highly promising green power,supercapacitors have drawn wide scientific attention mainly due to their high charge/discharge efficiency,long durability and environmental friendliness.However,the presently available supercapacitors have some disadvantages of low capacity,heavy weight and strong rigidity,which limit their development in the field of wearable energy storage with high-performance.In this paper,the controllable preparation of fiber-based carbon skeletons with different morphologies and structures were developed by“electrospinning”and“electrostatic flocking”technology,respectively,followed by electroactive materials recombination to prepare multi-stage complex electrode based on the demand of composite materials with low cost,satisfactory energy density and high flexiblility for wearable supercapacitors.At the same time,the technical bottleneck of the brittle mechanical property of carbon nanofiber electrode based on electrospinning was conducted and the rapid,high efficient construction on the flexible multistage nano-array electrodes by“electrostatic flocking”was applied to fill gaps.The structure-function relationship of composite composition,preparation method and condition,morphological structure and electrochemical performance were investigated.The electrochemical performances and capacitive coupling mechanisms produced by flexible multistage nano-array electrodes and the assembled supercapacitor in various states were analyzed.The main contents and achievements were summarized as follows:Preparation and designation of polyacrylonitrile/modified carbon nanotube-based carbon nanofiber and its assembled supercapacitor.Highly flexible polyacrylonitrile(PAN)-based carbon nanofibers with hierarchical nanostructure,which provided an excellent distribution of differently functionalized-carbon nanotubes and terephthalic acid(PTA),were prepared cost-effectively by electrospinning.The influence of different modified carbon nanotubes(acid-modified carbon nanotubes as AC-MWNTs and amino-modified carbon nanotubes as AM-MWNTs)on the construction and performance of carbon nanofibers were analyzed combined with peroxidation,carbonization and activation process.The results indicated that,the high content of AM-MWNTs-based carbon nanofibers which was defined as PCNFs/2.0 wt%AM-MWNTs had more excellent hybrid structure,conductivity and electrochemical properties.The flexibility mechanism of terephthalic acid acted on the carbon nanofibers was inverstigated and the overall capacity performance of the nanomembrane was improved by controlling the multistage aperture structure,micro morphology and doping methods of carbon nanofibers.Symmetric solid-state supercapacitors(SCs)based on PCNFs/2.0 wt%AM-MWNTs electrode with high performance and PVA/Li Cl gel-electrolyte were then fabricated and could be operated reversibly in the voltage range of 0?1.8 V.The expansion mechanism of voltage window and its flexible capacitive performances were explored.Furthermore,internal series-connected supercapacitors(ISSCs)based on the prepared porous carbon nanofibers were designed and fabricated.Such supercapacitors were found to be flexible enough to be rolled up or twisted with excellent capacitive performance and electrochemical cycleability at a high working voltage of up to 3.6 V and exhibited a 38.9%increase in energy density based on the whole mass of assembled supercapacitors(ISSCs)than that of the single-cell supercapacitors(SCs).The composite construction of carbon/Mn O2 nanofiber and its application for supercapacitor.Highly flexible polyacrylonitrile(PAN)-based carbon nanofibers were prepared by adding high content of amino-modified carbon nanotubes(AM-MWNTs)and terephthalic acid(PTA)in electrospinning,followed by in-situ redox reaction with different concentrations of KMn O4 to fabricate carbon/Mn O2nanocomposite fibers with different morphologies.The structure-function relationship of composite composition,preparation method and condition,morphological structure and electrochemical performance were investigated.Hedgehog-like carbon/Mn O2 nanofibers(TP-CNF/Mn O2-2)with coaxial configuration could be realized with remarkable electrochemical properties without using polymer substrates.Wearable symmetric solid-state supercapacitors(SCs)were further assembled using PVA/Li Cl gel electrolyte,which exhibited excellent capacitive performance and time-stability over the high working voltage of 0?1.8 V.The assembled SCs retained about 88.6%capacitance over 3000 charge/discharge cycles at a current density of 0.5A/g,and the decay of the specific capacitance was mainly due to the water evaporation of PVA/Li Cl gel electrolyte and the nonstructural deformation of TP-CNF/Mn O2-2 during the long-term cycling measurements.The as-fabricated symmetrical supercapacitor exhibited maximum energy density of 44.57 Wh/kg(at a power density of 337.1 W/kg)and power density of 13330 W/kg(at an energy density of 19.64 Wh/kg)with a working voltage as high as 1.8 V.Due to the combination of several favorable traits such as flexibility,high energy density,and excellent electrochemical cycleability,the presently developed wearable supercapacitors with wide potential window are expected to be useful for the wearable intelligent textiles.Preparation and electrochemical performances of the free-standing C/Zn O/Mn O2composites with multi-stage nanoarrays structure.Carbon nanofiber/Zn O nanoarrays with different morphologies were built based on electrospinning and hydrothermal growth process.Polyacrylonitrile was applied as carbon substrate,acid-treated carbon nanotubes were added to enhance the whole conductivity and specific surface area.Zinc acetate was selected as a precursor for Zn O nanocrystals,terephthalic acid(PTA)was explored as the sublimating agent to generate macropores inside electrospun carbon nanofibers during carbonization resulting in self-sustained carbon film.The multi-level connected C/Zn O/Mn O2nanoarray electrodes were fabricated by galvanostatic electrodeposition of nano-Mn O2shell.The dual-acting mechanism of zinc salt in electrospun solution and orientated growth mechanism of Zn O nanoarrays inclined to fiber matrix were investigated,which indicated that the crystallinity,orientation degree and electrochemical performance of flexible carbon nanofiber/Zn O nanorods were enhanced accordingly with the prolongation of hydrothermal growth time.The flexible ZTP-CNFs/Zn O-2 nanofibers prepared at95oC for 5h possessed more excellent capacitive properties,which exhibited maximum energy density of 21.30 Wh/kg at a power density of 480.0 W/kg.Furthermore,the pseudocapacitance mechanism of Zn O nano-arrays and Mn O2 nano-layers were combined with electric double layer energy storage mechanism of carbon nanofibers with high flexibility and large specific surface area,from which the constructed C/Zn O/Mn O2 electrode with multi-level nanoarray structure was calculated to be 709 F/g at a low current density of 1 A/g,and the electrode showed over 90%capacitance retention after 3000 cycles at a current density of 5 A/g.Preparation and electrochemical performances of the stretchable fabric electrodes with multi-stage arrays structure.The stretchable cotton/spandex with multi-pore structure and high ability of water-absorbing was applied as the flexible supported base,and the conductive fabric was prepared by depositing the acid-treated carbon nanotubes(AC-MWNTs)on the surface of cationic cotton/spandex.Then the carbon fibers were erected on the surface of the conductive fabric by“electrostatic flocking”,followed by deposition of thin layered nano-Mn O2 to fabricate3D stretchable electrodes with multi-stage arrays structure.The formation mechanisms of multistage array architecture,complex methods and the relationships between interface effects and ion/electron transportations were discussed,the composition effect and capacitive coupling mechanism of nanocomposite electrode under different conditions were analyzed.The results indicated that,the cationic cotton/spandex had stronger interaction with AC-MWNTs compared with the one before cationization,and the capacity of AC-MWNTs and its conductivity were improved through repeated“dipping-drying”process.The high-loading,strong conductivity and excellent pseudocapacitive behaviors of electroactive material could be realized through simple,rapid and easily large-scale“electrostatic flocking”technology by establishing“branch”structure on the surface of two-dimensional conductive fabric.The Mn O2@C-MC/S1-2 composite electrode with multistage arrays had favourable electrochemical performance by further optimizating the heat treatment concentration of KMn O4as 4 m M,the capacitance of which was calculated to be252 F/g at a scan rate of 5 m V/s,and the electrode showed 88.2%capacitance retention after 3000cycles at a current density of 2 A/g.Moreover,the Mn O2@C-MC/S1-2 electrode had excellent conductivity and capacitive performance under different drawing conditions,and showed 96.3%capacitance retention after stretching 100 repetitions with the draw ratio of 50%,which confirmed its ideal electrochemical reversibility,charge transfer property and cycling stability. |
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