The Research Of Lithium-Ion Supercapacitors Based On Graphene-Carbon Aerogels

Lithium-ion supercapacitor, as a novel high performance energy storage device, has attracted considerable attention due to possess higher energy density than the supercapacitor, higher power density and long cycle life than the lithium-ion battery. In general, electrode materials for the electrochemical performance of energy storage devices play a vital role. So the development of outstanding electrode materials is still the biggest challenge to achieve the high performance energy storage devices. Studies of the new electrode materials or modifying existing electrode material have been become a research hotspot. Graphene-carbon aerogels has the advantages of three-dimensional interconnecting network structure, well-developed porosity, and excellent electrical and thermal performance. Owing to these advantages, Graphene-carbon aerogels has attracted significant attention for use as electrode materials for supercapacitor. Consequently, in this article, on the basis of porous carbon cathode materials lithium-ion capacitor, we prepared several kinds of high surface area graphene-carbon aerogels by activation or nitrogen doped. Moreover, we use it as a cathode active material for fabricate lithium-ion hybrid supercapacitor with anode active material Li4Ti5O12.1. Synthesis of graphene-carbon aerogels (GA) by a sol-gel polymerization, and KOH activation used to increase the specific surface area and optimizing the porous structure of GA. The results showed that KOH activation effectively modified the porous structure of GA and improved its specific surface area to achieve better porosity. With the increasing proportion of KOH, the specific surface area of GA is gradually increased. It exhibited the optimal electrochemical performance while setting ratio of KOH/GA as 4, and the specific capacity could reach to 51.8mAh g-1, while the pristine only has 21.7mAh g-1. Moreover, the assembled a-GA-4/LTO lithium-ion supercapacitor provides a maximum energy density of 55.8Wh kg-1.2. Nitrogen-doped graphene-carbon aerogel (NGA) were prepared by a sol-gel polymerization, and then KOH activation was introduced to increase the specific surface area and optimizing the porous structure of GA. The results indicated that nitrogen-doped plays an important role in the KOH activation process and eventually results in improved performance. Compared with the half-cells of a-GA-4 and a-NGA, although they have close specific surface area, the specific capacity of a-NGA (76mAh g-1) is greater than that of a-GA (51.8mAh g-1), which resulted in increased mesoporosity. More significantly, the assembled a-NGA/LTO lithium-ion supercapacitor delivers a maximum energy density of 70.2 Wh kg-1 with the power density of 200 W kg-1 in a voltage of 1-3 V.3. CO2 activation was introduced to modify the surface morphology and porous structure of GA to increase the specific surface area and achieve better porosity. The influence of flowing rate of CO2 on electrochemical performance of GA had been studied. The results indicated that the important role of CO2 flowing rate at the activation process in increasing micro and small mesopores, and eventually leading to a high surface area. The specific capacity of CO2-0.5GA-120 half-cells is 69.6 mAh g-1, and the assembled CO2-0.5GA-120/LTO lithium-ion supercapacitor delivers a maximum energy density of 66.8 Wh kg-1 with the power density of 200 W kg-1 in a voltage of 1-3 V.