| Supercapacitor,a new type of electrochemical energy storage device,has attracted the attention of researchers because of its high power density and long cycle life.As a core component,electrode material determines the electrochemical performance of the supercapacitor device.In addition,the volumetric performance has attracted more and more attention and gradually become an important parameter for evaluating supercapacitor performance due to the rapid development of miniaturized portable electronic devices in recent years.Therefore,developing an electrode material with high volumetric performance is crucial to the implementation of supercapacitors.Currently,mostly studied electrode materials consists of carbon materials,metal compounds,conductive polymers and other categories.Graphene film,a macro paper-like material,has quickly become a hot spot in the field of supercapacitor electrode materials development due to its unique free-standing structure,high conductivity and high flexibility.However,problems such as?-?stacking between graphene sheets and the electric double layer energy storage mechanism greatly limit the electrochemical performance of graphene films,including the gravimetric capacitance and volumetric capacitance.In order to solve these problems,this thesis adopted electrochemical oxidation and organic molecular grafting to modify graphene films to improve electrochemical performance.The specific research work and conclusions are as follows:(1)Room temperature ultrafast synthesis of N-and O-rich graphene films for high volumetric capacitance supercapacitors.The electrochemical oxidation method is used to modify the graphene film reduced by hydroiodic acid.It is worth emphasizing that the electrochemical oxidation process can be completed within 60 seconds at room temperature,which is beneficial for large-scale applications.In addition,the following two goals can be achieved at the same time during the electrochemical oxidation process:1.The expansion of the interlayer distance caused by the bubble effect,which will lead to more active surface area exposure;2.The introduction of N-doped sites and oxygen-containing functional groups,which can not only improve the hydrophilicity,but also provide additional pseudocapacitance.Benefiting from the above advantages,the of F-RGO-60 film displays a gravimetric capacitance of 217.3 F g-1 at 1 A g-1 under the three-electrode system,which is much larger than the RGO film(60 F g-1).Based on the density of the F-RGO-60 film(1.47 g cm-3),the corresponding volumetric capacitance was calculated to be 319.4 F cm-3.When assembled into a symmetrical supercapacitor,the volumetric energy density of the F-RGO-60 film is as high as 9.14 Wh L-1,and also dilivers excellent cycle life(the specific capacitance retention rate after 6000 cycles is91%).(2)Dopamine modified graphene film is used for ultra-high volume performance supercapacitor.The"outer and inner dual space utilizing"strategy was adopted to solve the problem of low space utilization of graphene film electrode materials,and the prepared polydopamine-coated reduced graphene oxide/dopamine composite film(DA/rGO@PDA)was used as electrode material for electrochemical performance test:In the three-electrode system,the gravimetric specific capacitance of DA/rGO@PDA film is still as high as 449.3 F g-1 under high density(1.72 g cm-3),and the corresponding volume specific capacitance is 772.8 F cm-3.In addition,the two-electrode coin-liked symmetric supercapacitor displays a specific capacitance of 277 F g-1 or 476.4 F cm-3at 0.5 A g-1,which corresponds to a volumetric energy density of 16.3 Wh L-1.The excellent electrochemical performance of the DA/rGO@PDA film is mainly due to:DA molecules are not only used as redox active spacers to expand the interlayer distance and provide additional pseudocapacitance,which ensures the internal space of the graphene composite film use efficiently.The polydopamine layer is uniformly grown on the macro surface of the graphene composite film to provide pseudocapacitance,which realizes the effective utilization of the outer surface of the graphene composite film.In this paper,two different methods are proposed to modify the graphene film,which provides new ideas for improving its electrochemical performance. |
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