Flexible Nitrogen-doped Carbon Material With Interconnected Network Structure:Preparation,Mechanical And Electrochemical Performance

With the rapid development of wearable,thin and flexible electronic products,major research and development efforts have been devoted to design advanced flexible energy storage devices with high power and energy density.Unfortunately,currently electrodes were prepared by adding conductive additives,polymeric binders and metallic current collectors.The conductive additives and binders are electrochemically inactive and do not contribute to energy storage,thus greatly reduce the specific capacity of energy storage devices.Further,the use of metallic current collectors seriously reduces the overall energy density and flexible of devices.Therefore,it is of great importance to design and develop high-capacity,lightweight and self-standing flexible electrode materials for flexible energy storage devices.At present,studies on flexible electrode materials have the following two drawbacks: Firstly,the complex preparation processes and high manufacturing cost impede their wide application;Secondly,the electrochemical performance of flexible electrode materials is still not up to the level of conventional electrodes and has been unable to meet practical needs.To address these issues,in this paper,we designed and prepared two kinds of flexible nitrogen-doped carbon materials with 3D network,then studied their applications in the fields of fuel cells and flexible lithium ions batteries electrode materials.The details of this dissertation are as follows:1.A nitrogen-doped carbon foam?NCF?with porous structure was fabricated by a two-step pyrolysis process.The effects of oxidizing process and temperature on the structure and performance were investigated.The results show that NCF not only possessed hierarchical porosity with high specific surface area of 980 m2 g^-1,but also displayed excellent resilience.It could recover to its original shape without leaving any residual?plastic?deformation even under compressive strain of 80%.When used as self-supported ORR catalyst,NCF showed excellent electro-catalytic activity and durability for oxygen reduction,which is very close to Pt/C catalyst due to the unique hierarchical porous and graphitic carbon structure.2.Porous nitrogen-doped carbon paper?NCP?with both highly-dense 3D cellular structure and bending flexibility was fabricated by pyrolyzing melamine foam under compression.The effects of pressure during pyrolysis process on the structure and performance were investigated.When directly used as anode materials of LIB,the NCP-600 k exhibits initial reversible capacity of 480 mA h g^-1 at 0.05 A g^-1 and a stable capacity of 329.8 mA h g^-1 at a current density of 0.5 A g^-1 after 200 cycles.Even at a high current density of 8.0 A g^-1,a steady capacity of 126.5 mA h g^-1 was maintained after 500 cycles with high retention of up to 98.8%.Such outstanding electrochemical performance of NCP-600 k can be ascribed to the 3D highly-dense interconnected carbon network,which can facilitate efficient electron transfer and also provide short transportation paths for lithium ions;and the cooperation of hierarchical porous structure and nitrogen doping,which can provide abundant anchoring sites for Li-ions,thus improve the lithium storage capacity.