Synthesis And Supercapacitive Properties Of Graphene-based Electrode Materials

Supercapacitor is a novel energy storage component for storing energy throughpolarized electrolyte. Supercapacitor has been paid more attention to in the recentresearch on electrochemical energy storage due to its good performances in high powerdensity, longevity and high energy exchange efficiency. However, the problem of lowenergy density has limited the development of supercapacitor. Graphene, initiallyoccurring in2004, with good electrochemical properties is deemed to a promisingadvanced material to enhance energy density of supercapacitor. Graphene was preparedby chemical oxidation-reduction method. XRD, SEM, Raman, cyclic voltammetry,galvanostatic charge discharge and alternating-current impedance were applied forinvestigating the structure and properties of graphene and graphene/MnO₂composites.1. Graphite oxide was prepared with the modified Hummer method. Graphene was,respectively, prepared with graphite oxide as the raw material by three different methodsas hydrazine hydrate reduction method, vacuum hot stripping reduction method andmicrowave stripping reduction method. Results exhibited that graphene generatedserious agglomeration based on hydrazine hydrate reduction method, residual oxygenfunctional group existed in the surface of graphene based on vacuum hot strippingreduction method, and however, graphene with low agglomeration could be completelyreduced based on microwave stripping reduction method.2. Graphene prepared by three different methods was respectively assembled asbutton cell supercapacitors to investigate electrochemical performances under organicor inorganic system. Results indicated graphene based on microwave strippingreduction method had best agreement with electrochemical properties under inorganicsystem or organic system. The assembling processes of supercapacitor with graphenebased on microwave stripping reduction was studied according to electrochemicaleffects of different current collectors, binding agent loading and electrode-formingpressure. Results exhibited that supercapacitor could perform best electrochemicalproperties with specific capacity up to147F/g and94%capacity retention after1000cycles in the condition of nickel foam as current collector, binding agent loading as 5%¹0%and electrode-forming pressure as5MPa.3. Graphene/MnO₂composites were synthetized via in-situ growth technology.Nanoscale birnessite-MnO₂as monoclinic with layered structure could well disperse inthe surface of graphene with lamellar structure. Graphene/MnO₂composites performeda maximum specific capacity with20%MnO₂. The single electrode specific capacity ofgraphene/MnO₂electrode is up to225F/g under scanning rate of10mV/s,53%higherthan that of pure graphene electrode （147F/g）. Graphene/MnO₂electrode also exhibited80%capacity retention after1000cycles.