| Wearable technology guides the rapid development of the electronics industry,and flexible energy storage devices have also become the focus of academic and industrial circles.Flexible supercapacitors have the advantages of fast charge/discharge rate,high power density,long cycle life,safety and environmental protection,etc.,which are favored by scientific researchers.As an important part of flexible devices,electrode materials with high specific surface area,good electrical conductivity,excellent mechanical properties,high mass loading and stable electrochemical properties are expected to assemble high-performance energy storage devices.Reduced graphene oxide(RGO)film is an ideal electrode material because of its various characteristics that meet the requirements of flexible electrode preparation,so it has received more and more attention.However,the problems such as the easy agglomeration and stacking of RGO nanosheets and the weakening of electron transport performance by oxygen-containing functional groups result in mediocre capacitance performance of the RGO film.Based on these,this dissertation mainly focuses on RGO and its intermediate product graphene oxide(GO),carried out a series of work around the design and preparation of flexible electrode materials,and studied its electrochemical performance in the supercapacitor system.The specific research conclusions are as follows:(1)According to the formation mechanism of the bilayer bubble film,the RGO film with a controllable thickness is prepared for use as a flexible supercapacitor electrode material.GO films with different thicknesses are obtained by changing the amount of surfactant added,and then the reduction of the GO film is achieved by two reduction methods of hydroiodic acid/glacial acetic acid in the gas phase and the liquid phase.Studies have shown that vapor phase reduced RGO(VRGO)film exhibits an uneven reduction effect,VRGO based devices have poor rate performance and capacitance performance,while liquid phase reduced RGO(LRGO)film exhibits high conductivity(17200 S m-1)and excellent electrochemical performance,its gravimetric and areal specific capacitance can reach 111 F g-1 and 112 m F cm-2,respectively.Besides,flexible supercapacitors based on LRGO films exhibit excellent structure and electrochemical stability in various bending states.(2)The iodine doped RGO(I-RGO)film is developed using the iodine vapor doping strategy.This method ensures that a certain amount of oxygen-containing functional groups are evenly distributed on the RGO film through low-temperature heat treatment.At the same time,charge transfer occurs between the doped iodine atoms and the RGO sheet,which effectively improves the conductivity of the I-RGO film,thereby obtaining high performance electrode material.Studies have shown that,within the mass loading range of 1.5?6.7 mg cm-2,the gravimetric specific capacitance of the I-RGO film remains almost unchanged,that is,at 0.4 A g-1,its value is about 150 F g-1.with the increase of the mass loading,the areal specific capacitance of the I-RGO film always maintains a quasi-linear increase in the range of 1?30 m A cm-2,and its maximum value can reach1048 m F cm-2(1 m A cm-2)while the mass loading is 6.7 mg cm-2.In addition,the I-RGO film based flexible device not only has a good cycle life,but also has a capacity retention rate of 94%after being bent at 180°continuously for 600 times.(3)A new folding strategy is used to prepare the RGO film with like“folded paper”structure.This method can not only realize the double growth of the mass loading,but also can use the excellent in-plane electron transport characteristics of the RGO film to complete its longitudinal electron transmission,thereby improving the problem of poor longitudinal electron transport performance of the RGO film.Studies have shown that the prepared high mass loading folded RGO(F-RGO)film exhibits excellent capacitance behavior.By increasing the number of fold,the F-RGO film exhibits capacitance retention behavior with like“relay”,that is,in the range of 2?9 mg cm-2,the gravimetric specific capacitance can always be maintained at about 180 F g-1.While the volumetric specific capacitance also shows an increasing trend.At 11.3 mg cm-2,its value can reach232 F cm-3.At the same time,the areal specific capacitance of the F-RGO film also exhibits capacitance growth behavior with like“relay”,and its value is as high as 3400m F cm-2 at 17 mg cm-2.(4)The swelling strategy of GO film is used to prepare a self-supporting RGO hydrogel(GH)film with a controllable structure.By changing the microscopic forces between the GO nanosheets,such as van der Waals force,hydrogen bonding and electrostatic repulsion,the expansion of the GO film can be controlled,thereby obtaining a highly ordered GH film with a porous structure.Studies have shown that gravimetric and areal specific capacitance of the GH film can reach 237.6 F g-1 and 608 m F cm-2,respectively.Zinc-ion hybrid supercapacitors based on GH film also show excellent energy storage capacity of 99.3 m A h g-1 and high energy density of 76.2 Wh kg-1.At the same time,after 10,000 charge/discharge cycles,it still has a capacitance retention rate of90%,demonstrating an excellent cycle life of the device.(5)A flexible graphene-based integrated supercapacitor was fabricated using capillary contractility and non-volatile solvent intercalation strategies.The device uses GO film as the separator and hydroquinone(HQ)molecule modified RGO(HQ-RGO)film as the electrode material,showing excellent electrochemical performance.Studies have shown that the dense structure of the HQ-RGO film has excellent charge transport properties,which can achieve high specific capacities of 333 F g-1 and 804.6 m F cm-2.In addition,energy density of the device can reach 109.5?Wh cm-2(1400?W cm-2).When the power density is 21060?W cm-2,its energy density can still reach 60?Wh cm-2,which proves that this type of device has very good energy storage performance.Moreover,after800 times of continuous bending at a bending angle of 180°,the device capacity can still retain 92%of the initial value,indicating that the device has good structural stability. |
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