Based On Graphene Nanosheets Modified Materials As The Anode For Sodium Ion Batteries

Lithium ion batteries are considered to be excellent energy storage systems for its high voltage,high energy density,and cycle stability.However,the lithium resources in the earth's crust is very limited.The lithium resources will become the bottleneck to restrict the further development of the energy storage systems.Sodium ion batteries are regarded as the next generation batteries for its abundant resources,low cost,and similar physicochemical properties and storage mechanism with lithium.However,the sodium ions are more difficult to insert/extraction from the materials due to the lager relative atomic mass and ionic radius.Therefore,it is of great significance to study the high performance sodium storage electrode materials.In this paper,we prepared the high performance anode materials for sodium ion batteries,improving the capacity,cycle performance and rate performance,so that it can be used in practice.The main contents are included as the following aspects:1.The thin layer of nitrogen doped graphene nanosheets were prepared by sol-gel method.By changing the sintering temperature,the graphene sheets with suitable nitrogen content and excellent morphology were obtained?750 ??.This method greatly optimize the preparation process of graphene.The electrochemical properties of the materials were prepared.The results show that the material has a relatively good cycle stability and rate perfprmance the sample obtained at 750 ?can provide a reversible capacity of 225 mAh g^-1 at 0.1 A g^-1 and it can remin 150 mA h g^-1 after 2000 cycles at 1 A g^-1.2.?1?In order to suppress the stacking of graphene nanosheets and improve the capacity of graphene,we integrated functional graphene nanosheets?FGNs?and cobalt sulfide(Co_1-xS)nanoparticles into the same synthesis procedure by a improved facile sol-gel method to prepare the Co_1-xS/FGNs nanocomposites.Consequently,the Co_1-xS/FGNs composites delivered a higher reversible capacity of 466 mA h g^-1 at 100 mA g^-1,211 mA h g^-1 capacity retained at 10 A g^-1 campared to nitrogen doped graphene nanosheets,and noticeably cycle performance with 251 mA h g^-1 capacity after 200 cycles.?2?To highlight the advantages of Co_1-xS/FGNs nanocomposites in structural design and,we compared the differences of the electrochemical properties of Co_1-xS/FGNs nanocomposites with pure Col-xS and FGNs.The FGNs delivered only 275 mA h g^-1 at 0.1 A g^-1,and the capacity of Co_1-xS dropped to-50 mA h g^-1 at 1 A g^-1 after 130 cycles.The good electrochemical properties of Co_1-xS/FGNs could be ascribed to the following reasons.The small particles of Co_1-xS and thin graphene nanosheets reduced the sodium ion diffusion distance.The FGNs dopping with N and S provide more active sites for sodium ions and effectively improve the stability of the material,rate performance and cycle stability.