Preparation of three-dimensional graphene foam with controllable defects by closed-environment chemical vapor deposition method and composite electrode electrochemical performance

Three-dimensional graphene provides a promising approach to developing high-energy-density electrodes. Compared with two-dimensional (2D) graphene, three-dimensional (3D) graphene has a three-dimensional conductive network, which greatly improves the ability of lithium ions and electron to transport and can tolerate the changes of structural and volume in the cycling process. In this paper, 3D graphene with controllable defects is prepared by using an innovative low-pressure closed chemical vapor deposition method, through using nickel foam as the template and polymethyl methacrylate as a solid carbon source. The effects of the amount of carbon source addition, reaction time and hydrogen content on the morphology and structure of graphene foam are analyzed. The experimental results indicate that the amount of carbon source added, the reaction time, and the hydrogen content have significant effects on the morphology and structure of graphene. The defect density and the number of layers of as-prepared graphene are directly proportional to the amount of carbon source added. There is a threshold for the reaction time. After reaching a certain reaction time, graphene with good structure and morphology can be formed. The optimal reaction time is about 20 min. The hydrogen content promotes the high-temperature pyrolysis of solid carbon source. The sample has a highest defect density at 0.5 kPa hydrogen content. In summary, the low-pressure closed CVD method has strong safety and can synthesize 3D graphene with excellent controllable structure and defects. The 3D graphene foam with a complete structure of 2–5 layers can be prepared under the conditions of 1000 ℃, 500 μL carbon source addition, 20 min reaction time and 0.5 kPa hydrogen content, displaying the best physical chemistry performance. The graphene foam prepared in this experiment has the characteristics of convenient and controllable defect density, light weight and stable chemical properties. When ZnO/GF electrode prepared with 3D GF as a conductive frame and active carrier is used as an anode, the lithium ion battery has a high specific capacity of 851.5 mA·h·g –1 after 200 cycles, which exhibites high reversible capacity and good cycling performance. Although ZnO/GF electrode displays excellent lithium storage performance, the GF prepared based on the 3D Ni foam has a low spatial structure density and the surface loading of the ZnO/GF composite electrode is still low, resulting in a low energy density. Therefore, the following researchers should focus on the structural design of 3D graphene host/current collector to obtain a 3D graphene frame with high conductivity and high loading capacity.