Preparation Of Graphene-based Composites And Applications For Supercapacitors

As a new type of energy storage device,supercapacitor has become a hot topic in academic circles due to its advantages,such as high power density,good cycle performance and fast charging speed.Generally,supercapacitors can be divided into electric double layer capacitors and Faraday tantalum capacitors according to the energy storage mechanism.As the core component of supercapacitors,electrode materials have been paid much attention.As a kind of typical carbon material,graphene has excellent advantages such as excellent electrical conductivity,stable cycle performance and environmental protection.It is an ideal material for supercapacitors.However,due to its own structural problems,it is easy to agglomerate between layers,thereby reducing the specific surface and affecting the performance of the capacitor.Moreover,graphene is expensive and not conducive to industrial production.So,this paper optimized the structure of graphene by freeze-drying,and simultaneously combines with high theoretical specific capacitance(conductive polymer,metal oxide/hydroxide)to prepare high performance composite materials for supercapacitors electrode material.Moreover,the unresolved cost problem is to replace the graphene and manganese oxide with a relatively low cost graphene sheet to prepare a low-cost and high-quality composite material.The main research contents are summarized as follows:1.PANI-PGR composite was successfully prepared by cyclic voltammetry.The microstructure of PANI-PGR composite was characterized by field emission scanning electron microscopy.The electrochemical properties of the composites were tested by cyclic voltammetry(CV),constant current charge-discharge(GCD)in 0.1 M H2SO4.The effects of precursor concentration,polymerization number and PGR concentration on the electrochemical properties of the composites were investigated.The results showed that the specific capacitance of the composites reached 1209 F·g-1 at a current density of 0.2 A·g-1.The retention ratio of the specific capacitance still maintained at 92%after 1000 cycles of discharge at a current density of 1 A·g-1.2.Ni(OH)2 particles were synthesized on the surface of PGR by constant piezoelectric deposition.The microstructure and crystal structure of the composites were characterized by scanning electron microscopy.The effect of deposition time,the precursor concentration and deposition voltage on the capacitive performance of composite were investigated.The results showed that the composite exhibited the best specific capacitance of 1474 F·g-1 when the deposition voltage was-1.0 V and the deposition time was 400 s.3.MnO2-GRS1,MnO2-GRS2 composites were successfully prepared using the impregnation method with 0.1 M KMnO4-K2SO4 as precursor.Raman,scanning electron microscope and X-ray diffraction analysis was used to characterize the microstructure and crystal structure of the composite.The thickness of the graphene sheet,the immersion time and the amount of activated carbon were investigated by CV and GCD in 0.1 M KOH solution.The effect of the capacitance on the composite material showed that MnO2 adhered to the surface of the graphene sheet in the form of particles.For the MnO2-GRS1,when the immersion time was 3 h and the activated carbon addition amount was 2:1.The composite exhibited the best specific capacitance.For the MnO2-GRS2 composite,when the immersion time is 5 h,the composite exhibited the best specific capacitance performance without activated carbon.The maximum specific capacitance was 640F·g-1(10 mV·s-1).