Core-shell Structure Design And Sodium Storage Performance Of Metal Sulfide

At present,the main problem of sodium ion battery is to find a suitable anode material.Graphite,the traditional anode material of lithium ion battery,can not be directly used in sodium ion battery.Among the widely studied anode materials,the multi-electron-transfer conversion reaction materials is considered to be ideal anodes for sodium ion battery because of its high specific capacity.However,due to the large volume expansion of the electrode material caused by the conversion reaction itself,the original crystal structure of the material will be destroyed in the long cycle process,and the strian caused by the volume change will make the structure of material crumble.In order to solve the above problems,nano-size design and compounded with carbon materials were considered,which will alleviate the adverse effects of volume changes on materials to a certain extent.However,the traditional preparation method of composite with carbon material is tedious and the composite quality is not high,and the cost of excellent graphene matrix is very high.It is of great significance to obtain high quality composite electrode materials for sodium ion battery anode materials trough a simple method.In this paper,a variety of conversion reactive anode materials compounded with carbon materials were prepared.the main contents of this thesis are as follows:1.Metal nitride @ nitrogen-doped graphene-like,metal phosphide @nitrogen-phosphorus co-doped graphene,and metal sulfides @ nitrogen-sulfur co-doped were prepared by simple one-pot sol-gel method and the electrochemical performance was tested.The effects of different formulations of electrolytes on the electrochemical sodium storage performance of sulfides,such as carbonate electrolytes and ether electrolytes,were studied.2.In the first part of the study of conversion reactive materials,it is found that metal sulfides have a good electrochemical performance in sodium ion batteries.However,the composite electrode materials of metal sulphides and graphene-like materials are faced with the problems of poor cycle life and low Coulomb efficiency in the first cycle.The simple core-shell structure is difficult to inhibit the structural collapse of sulfides during the cycle process.Carbon nanotubes have good electrical conductivity,and the unique tubular structure can provide strong protection for sulfides.The previous preparation methods are tedious and the quality of the composite of sulfides and carbon nanotubes is not high.Carbon nanotubes are prepared by chemical vapor deposition,and then the sulfides with core-shell structure are obtained by additional vulcanization,and the cost is also high.The one-step sol-gel method can achieve the direct in-situ coating of sulphide particles in carbon nanotubes during the growth process,and the carbon nanotube-limited sulfide nanoparticles can be obtained.Not only the ultra-long carbon nanotubes are obtained,but also there are abundant nitrogen and sulfur doping sites on the tube wall,which directly overcomes the shortcomings of carbon nanotubes.this structure directly determines that the nickel sulfide @ nitrogen-sulfur co-doped carbon nanotubes have excellent long cycle performance.