The Preparation And Electrochemical Performance Of Graphene Hydrogel

Graphene Hydrogel (GH) is a new kind of graphene self-assembled materials, connected by Hydrogen bond, force of functional groups and π-bond. GH still possesses the merits of graphene, such as the large specific surface area, low density, good conductivity and toughness, and it has great application prospect in many fields. As a kind of macroscopic material, GH has many advantages when it is used as electrode material for energy-storage device. It does not need solvent, conductive agent and addictive agent, and can be directly used as a whole to put between two current collectors. What’s more, GH has abundant pore structure, which is useful for electrolyte migration.This paper firstly synthesis GH through one step hydrothermal method, then we treated it with drying processing and investigated the capacitance for supercapacitor. The test results are that the capacitance of GH annealed respectively at300,600and1000℃are220F/g,100F/g and20F/g at the current density of0.5A/g. While the specific surface area are3,<3,<3m2/g. Then we compared the capacitance of samples dried by conventional drying method and freeze drying method, they are both about240F/g, while the specific surface area are1.6m2/g and26m2/g. The factors influencing the capacitance of supercapacitor include specific surface area, content of functional groups, defect sites and edge sites. In the first chapter we find the content of functional groups is the determining factor, while the others factors have little influence for capacitance by controlling the content of functional groups, specific surface area and defect sites, and comparing the corresponding capacitance. We also put forward a supercapacitor model, this model is for explaining the cooperation of functional groups and defect sites.For improving the mechanical properties and electrical conductivity, we disperse carbon fiber into GO solution to get graphene/carbon fiber composite hydrogel (CF-GH). Carbon fiber could disperse into this macroscopic material uniformly and could combine with graphene very well. The results show that the carbon fiber could improve the mechanical properties and electrical conductivity. We use a weight of100g to compress the columns, the pressure on CF-GH is3100Pa, releasing and compressing for20times, there is no deformantion. In order to get the capacitance performance of CF-GH in the field of practical application, we used two-elextrode testing system to get the capacitance. The testing result of10wt%CF GH was about185F/g, it did not decay almost after1000cycles.In addition, this article not only explores GH capacitive property, but also takes the GH as a carrier material and combines with inorganic sulfur to get three-dimensional macroscopic material for the lithium sulfur battery. By controlling pH of the solution, we can achieve homogeneous sulfur modified GO (S-GO) with different morphologies, and then we can get graphene/sulfur composite hydrogel (S-GH) by self-assembly. This material can makes up the innate defect of the lithium sulfur battery, the sulfur particles can be dispersed in the conductive carrier material uniformly, when sulfurs particles becomes polysulfide they are still kept in the inter space of reduced graphene oxide (rGO). The inter-connected structure is helpful for charging and discharging rapidly. The testing result showed that the effect of limiting sulfur is very good, the first cycle charging capacitance is1475mAh/g and the first discharging capacitance is1390mAh/g, it did not decay after50cycles. But the defect of this material is the content of sulfur is a little low, it showed a capacity of1300mAh/g.