类化学气相沉积法制备缺陷可控的三维石墨烯泡沫及其复合电极电化学性能

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

三维石墨烯为开发高能量密度的电极提供了有效的途径.与二维石墨烯相比,三维石墨烯具有三维导电网络,极大地改善锂离子和电子传输的能力,同时能够承受电极循环期间的结构和体积变化.本文发展了低压封闭化学气相沉积法(CVD),以泡沫镍为模板,采用聚甲基丙烯酸甲酯为固态碳源来制备缺陷可控的三维石墨烯泡沫.分别研究了碳源添加量、反应时间及氢气含量对三维石墨烯泡沫形貌及结构的影响,发展了一种新型的三维石墨烯泡沫制备工艺,所制备的三维石墨烯泡沫具有缺陷密度可控,质量轻及化学性能稳定的特点.以三维石墨烯泡沫为导电框架和活性物载体来制备ZnO/石墨烯泡沫(ZnO/GF)复合电极并作为锂离子电池负极,循环200圈后仍能保持851.5 mA·h·g^-1的高比容量,ZnO/三维石墨烯电极表现出较高的可逆容量以及优异的循环性能.

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℃,500μL 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.