Synthesis Of Nano-sized One Dimensional Hard Carbon Materials And Their Sodium Storage Performance

Sodium-ion batteries(SIBs) have attracted wide attention in the field of large-scale energy storage for the abundance of Na resources and high security performance. However, the commercial graphite anode widely used in lithium-ion batteries(LIBs) has been confirmed not suitable for SIBs due to bad sodium storage performance. Recently, the research of carbon anode materials of sodium ion battery focus on hard carbon materials, which have large interlayer distance and disordered structure. The sodium storage properties of carbon materials can be improved effectively by increasing the graphite interlayer distance or preparation of nanostructure. In this paper, we designed nano-sized 1D hard carbon materials such as nitrogen-doped carbon nanotubes and carbon nanofibers, and researched their electrochemical performance.Firstly, the nitrogen-doped carbon nanotubes were synthesized by carbonization of hollow PPy nanotubes and used as anode materials for sodium-ion battery. The obtained N-CNTs have disordered carbon structure, high N doping level and N-, O-functional groups in the surface. And the effects of sodium polyacrylate(PAA- Na) and poly(vinylidene difluoride)(PVDF) binders on electrochemical performance are comparatively investigated. The results demonstrated that the electrochemical performance of N-CNTs electrode strongly depends on the binder used. When using Na-PAA as the binder, the N-CNTs electrode exhibits high initial coulombic efficiency, excellent cycling stability and rate performance. The N-CNTs electrode with Na-PAA binder exhibits an initial coulombic efficiency of 61.2%, delivers a reversible capacity of 175.5 mAh/g after 300 cycles at 200 mA/g and maintains a capacity up to 127.7 mAh/g when the current increase to 5 A/g. Compared with the traditional PVDF binder, the water soluble Na-PAA binder shows higher electrochemical activity, better viscosity and coatability, can coat particle surface much more uniformly to form a better ionic conductive film on the surface of active materials.With this ion conductive film, a stable and homogeneous SEI layer can be formed. Further investigations show that the binding capability of Na-PAA is closely related to the molecular weight. The Na-PAA with moderate molecular weight is more suitable for the binder of sodium-ion batteries.Secondly, the carbon nanofibers with one dimensional(1D) nanostructure were prepared using a simple electrospinning process followed by thermal treatment. The obtained CFs have disordered structure, large interlayer distance, and interconnect with each other to form a network structure, which favour the storage and transport of sodium ion. As the anode material of sodium ion battery, the CFs electrode shows good cycling stability and rate performance, delivers a reversible capacity of 152.1m Ah/g after 100 cycles at 200 mA/g and maintains a capacity of 61.1 mAh/g at a high current density of 2 A/g. The good performance dues to its unique 1D fibrous nanostructure.Nano-sized 1D hard carbon materials,which have disordered structure and large interlayer distance, meanwhile can decrease the diffusion distance of sodium ion and increase the contact area of active materials and electrolyte, is a promising anode material of sodium ion battery.