Modification And Electrochemical Properties Of Low-Temperature Exfoliated Graphene

Graphene, which is characterized by high surface area and good conductivity, is a kind of flexible two-dimensional carbon material that has potential applications in the area of solar cells, supercapacitors and lithium-ion battery (LIB). In this study, transmittance tunable graphene oxide membrane is prepared by a liquid-air interface self-assembly method and electrochemical properties of low-temperature exfoliated graphene are investigated with the focus on potential applications as supercapacitor electrode materials, conductive additives for LIB and negative electrode materials for LIB.Graphene oxide (GO) membrane whose transmittance can be tuned precisely is prepared by a liquid-air interface self-assembly method. The transmittance of the GO suspension and the resulting membrane both decrease with the increase of the pH value (pH: 2~13) of the parent suspension. The comparison results show higher and lower transmittances can be obtained for the resulting membranes when the pH values are 2.0 and 11.0 respectively.The electrochemical properties of supercapacitors based on graphene that is treated under different temperature are amazingly different. With the increase of the heat-treatment temperature, the capacitance of graphene-based supercapacitors with aqueous electrolytes shows a declined trend with an exceptional case where the heat-treatment temperature is 300℃. The capacitances of original graphene(GN) and graphene that treated at 900℃(GN(900)) are 250 and 25 F/g respectively with the current density of 50 mA/g. Graphene treated at 300℃(GN(300)) shows the largest capacitance which is up to 302 F/g at the same current density. With the organic electrolytes, the graphene based capacitances show a monotonously increasing trend with the increase of the heat-treatment temperature.Graphene shows excellent performance as the conductive additive of LIB. The battery shows higher performance when the content of graphene is low (2 wt%) and the graphenes after heat-treatment show higher performance. As compared to the battery with Super-P (20 wt%) as additives, the graphene-introduced battery (2 wt%) that treated at 500℃shows much better performance.Graphene as the negative electrode material of LIB reveals high capacity that is up to 905 mAh/g in the first cycle but no charge/discharge platform appears. When graphene/Al composite is employed as the negative electrode material, the battery shows very high capacity (up to 1134 at first cycle), low/smooth platform (0.42V) and good cycling performance.