Preparation Of Graphene/Nickel Composite By In-situ Transformation And Its Properties

Supercapacitor is a new type of energy storage device between conventional capacitor and rechargeable battery,with a capacity of hundreds to thousands of Farad.Compared with traditional capacitors,supercapacitors are characterized by large specific capacitance,high energy density and power density,wide operating temperature range and long service life.Therefore,supercapacitors are widely used in the fields of solar energy system,wind power system,new energy vehicle development,intelligent distributed grid system and distributed energy storage system.Supercapacitors are novel devices that store energy through an interface layer formed between electrodes and electrolytes.As the electrode is the key component of the supercapacitor,the hotspot is how to develop a high-performance electrode material to improve the charging and discharging performance of the supercapacitor.The integrated electrode does not use adhesive or conductive agent,and the electrode material has high utilization efficiency and excellent mechanical properties.Therefore,the integrated electrode holds broad development prospects for supercapacitors.In this thesis,graphene/Ni?G/Ni?composites were prepared by two ways.On e was to prepare GOA/Ni composites by coating nickel powder with oleic acid?OA?and sintering by discharge plasma.The second one was to prepare GNF/Ni composite materials by discharge plasma sintering of composite powders decomposed by thermal decomposition of nickel formate?NF?.The characterization and performance analysis of the two G/Ni composites were carried out to study the morphology and properties of the two G/Ni composites.The results of X-ray diffraction?XRD?show that nickel in G/Ni composites is not oxidized.Scanning electron microscope?SEM?was performed after electrochemical corrosion of G/Ni composites with 3.5wt.%NaCl electrolyte for 2400 s at 1.5V),and layered structure was found on its surface.Using Raman characterization,both the G peak at 1580cm^-1 and the 2D peak near 2700 cm^-1 were found,indicating that the OA and NF were transformed into few-layer graphene during the sintering process.The hardness of G/Ni composites was analyzed,and the Vickers-hardness of G_OA/Ni composite sintered at 600?reached up to 176.5 HV,while that of G_NF/Ni composite prepared by thermal decomposition of nickel formate at 300?reached up to 244.1 HV.According to the analysis of compression strength of G/Ni composites,the maximum compression strength of GOA/Ni composite prepared by sintering at 600?reached 479.1 MPa,while that of G_NF/Ni composite prepared by thermal decomposition of nickel formate at 300?reached 1086.9 MPa.The corrosion resistance of G/Ni composites were tested and analyzed,and the electrolyte was 3.5 wt.%NaCl solution.The sintered GOA/Ni composite had the lowest corrosion current density?2.56E-05 A/cm²?and the most positive corrosion potential?-0.7259 V vs.Ag/AgCl?,suggesting the best corrosion resistance.The integrated electrode of G/Ni composite was prepared after electrochemical corrosion,and its capacitance performance was tested.The area capacitance of G_OA/Ni electrode sintering at 500?was the highest,reaching 4376 mF/cm² after electro-corrosion 600 s.XRD analysis suggested the presence of Ni,Ni?OH?2 and NaCl on the surface of G/Ni composite material after the electrochemical corrosion,indicating that Ni?OH?2 is the main source of pseudocapacitance.G/Ni composite material has high mechanical strength and excellent capacitance performance,laying a foundation for the preparation and application of the integrated electrode.