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Effects of Ball-Milling on the Morphologies and Capacitive Performances of Graphene Nanosheets

Author: ZhaoShengNa
Tutor: SongHuaiHe
School: Beijing University of Chemical Technology
Course: Materials Science and Engineering
Keywords: Expanded graphite Graphene nanosheets Supercapacitor Ball milling method
CLC: TB383.1
Type: Master's thesis
Year: 2010
Downloads: 516
Quote: 1
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Abstract


Supercapacitor Following another new lithium-ion battery energy storage element, and in recent years has gradually become the hot new energy research. The porous carbon material has a high specific surface area and the stability of chemical properties and is widely used as a super-capacitor electrode material, but due to its poor conductivity, pore structure complex limits its extensive application in supercapacitors. Two-dimensional layer of carbon atoms as a single layer graphene, due to the simple structure, good electrical conductivity, large specific surface area and become the best choice for one of the electrode materials for supercapacitor natural flake graphite and artificial graphite as raw material, through oxidation - prepared by a method of thermal expansion of the expanded graphite, and on this basis to milling method to obtain graphene nanosheet graphene nanosheet as the performance of the electrode materials for supercapacitor. The morphology of the samples, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, nitrogen adsorption BET, Fourier transform infrared spectroscopy and Raman spectroscopy. Concentration of 30% aqueous KOH solution electrochemical charge-discharge tests, cyclic voltammetry and AC impedance test. The studies show that the different raw material preparation of the expanded graphite having a worm-like porous structure, inflating the volume expansion coefficient of the artificial graphite is much less than the expanded natural graphite, but its specific surface area is higher than the latter, respectively 524m2 · g-1 and 358m2 · g-1. Under the same charging and discharging conditions, the expansion ratio of the artificial graphite electrode capacitance compared expanded natural graphite electrode, and a current density of 100mA · g-1 respectively 196F · g-1 and 157F · g--1, but with the current density gradually increases to 2000mA · g-1, the capacity retention ratio of the former than the latter. Vermicular expanded graphite structure destroyed after milling, the formation of lamellar structure the container stacking of carbon atoms is decreased and then increased with the milling time, milling 3h sample stacking least electron micrograph shows its structure for graphene nano-sheet stacked on top of each other. Milling, and with the milling time, the sample than the capacitance first increases and then decreases, milling 3h when specific capacitance reaches its maximum current density of 100mA · g-1 211F · g-1, 4h and 6h samples capacity lower than 170F · g-1 and 167F · g-1, respectively, but still significantly higher than the expanded graphite electrode. Analysis of the specific reason can be provided from the simple structure of the graphene nanosheet easy diffusion of the electrolyte, a surface defect generated in the milling process is conducive to the accumulation of charge. With increasing current density, the graphene nanosheet electrode showed a good capacity retention rate.

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