| Flexible supercapacitors have been considered as one of most promising condition for wearable equipment due to their good mechanical flexibility,modest capacity performance,high power density,and long cycling stability.In fact,supercapacitors possess several key components,including electrodes and electrolyte.Therefore,preparing flexible electrodes and gel electrolytes is a valid way to fulfill the flexibility of supercapacitors.In addition,asymmetric supercapacitors with larger working potential can deliver a larger energy density,which is benefit for practical application.However,flexible supercapacitors suffer from low capacitance and cycling instabilityThis dissertation mainly focuses on improving the capacity and stability of assembled flexible devices by optimizing each parts of supercapacitor,including flexible electrodes and gel electrolytes.And the main contents are summarized briefly as below(1)The graphene flexible film made by vacuum filtrating method suffers restacked and aggregation problem.Therefore,a hard template method,which mixed ion-exchanging 3D graphene-like materials and graphene oxide sheets,was introduced.After vacuum filtrating and reducing process,the obtained graphene/3D graphene flexible film has a large layer space and abundant pore structure,resulting an enhancing electrochemical performance.The potassium persulfate was used as mild oxidant to functionalize 3D porous graphene.As a result,the functional 3D graphene can disperse in water and stabilize for over one year.The well-dispersed 3D graphene was able to be mixed with graphene oxide solution,and the composite film was prepared by filtrating and reducing the mixture.Consequently,the prepared graphene and 3D graphene composite film delivers a high specific capacitance of 142.9 F/g at the scan rate of 5 mV/s,and a capacitance of 97.1 F/g can be remained at the scan rate of 500 mV/s The assembled flexible supercapacitor possesses a good mechanical performance,and the electrochemical performance of the device is stable under various bending condition.In addition,the stability test shows that the device can remain 92%capacitance after 2000 charge/discharge process.As combined with 3D graphene-like materials,the composite flexible electrode has performance highly improved and can meet the need for practical application.(2)For the development of wearable electronic devices,it is crucial to develop energy storage components combining high-capacity and flexibility.Herein,an all-solid-state supercapacitor is prepared through an in-situ "growth and wrapping" method.The carbon woven fabric was used as substrate to deposit polyaniline nanosticks,and a facile immersing method was used to wrap the electrode with graphene layers.The hybrid electrode exhibits excellent mechanical and electrochemical performance.The optimized graphene wrapping layer provides for a conductive network,which effectively enhances the cycling stability as 88.9%of the starting capacitance is maintained after 5000 charge/discharge cycles.Furthermore,the assembled device delivers a high areal capacity(of 197.6 mF/cm2)at the current density of 1 mA/cm2,a high areal energy(28.21?Wh/cm2)at the power density of 0.12 mW/cm2 and shows no significant decrease in the performance with a bending angle of 180°.This unique flexible supercapacitor thus exhibits great potential for wearable electronics(3)The ability of self-healing for wearable electronic devices are critical,for their vulnerability and irreversible damages while practical applications.Herein,we report a ferric enhancing dual physical cross-linking polyelectrolyte for supercapacitors.The gel electrolyte is copolymerized by using acrylic acid as a hydrophilic monomer and stearyl methacrylate as a hydrophobic monomer in an aqueous ferric nitrate solution with cationic surfactant cetyltrimethylammonium bromide and subsequently immersed in the sulfuric acid solution.With the help of hydrogen bonding and ionic bonding,the prepared hydrogel containing 1 mol/L H2SO4 exhibits good mechanical performance(extensibility>2400%,and stress>230 kPa),excellent ionic conductive(>30 m S/cm),and good self-healing efficiency.Base on this poly electrolyte,we successfully assemble the self-healing supercapacitor by two identical electrodeposited nano-wire PANI electrodes.The self-healing device achieves an excellent energy density of 19.33 Wh/kg at power densities of 0.67 kW/kg,self-healable ability(about 86%capacitance retention after healing behavior),aging durability,and cycling stability.Our results provide a valid and straightforward strategy to design self-healing energy storage devices.(4)The development of pre-designed electrode with high performance received enormous attention for their potential application in energy storage field.In this work,we propose a facile method to synthesize NiCo2S4 nanoflake forests with in-situ deposited PPy shell on nickel foam.The well-design structure and polymer layers provide the electrode with a better kinetic behavior and prevent the active materials from peeling off.Therefore,the hybrid electrode possesses a specific capacitance of 1807 F/g at the current density of 1 A/g with 92%capacitance retention after 5000 charge/discharge cycles,and a capacity as high as 1289 F/g can be still remained at the current density of 20 A/g.By combining it with a N-doping graphene anode,the assembled asymmetric device operates at a voltage of 1.6 V,which is much higher than that of symmetric supercapacitors.As a result,the asymmetric supercapacitor delivers a maximum energy density of 73.54 Wh/kg at a power density of 836 W/kg,and an energy density of 40.2 Wh/kg can still be retained even at a high power density of 17.3 kW/kg.In addition,87%capacitance retention can be reached after 5000 cycling process,exhibiting an excellent stability.These results prove an efficient design method on high performance and stability asymmetric supercapacitors and can be extended to next-generation high-energy supercapacitors. |
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