| Lithium-ion batteries are emerging with high energy density and long life performance.However,with electric vehicles becoming the mainstream of vehicles and portable electronic devices widely used,people have higher and higher requirements for energy storage.Considering the uneven distribution of global lithium resources and cost,researchers began to shift their focus to the resource rich and low-cost sodium ion batteries.So far,sodium ion batteries have come into the field of vision of researchers,and the development of electrode materials for sodium ion batteries to meet the requirements of practical use has become the top priority in the research work.Iron based sulfide has become a hot electrode material with its environmentally friendly characteristics and high theoretical capacity(Fe S2/894 m Ah g-1,Fe S/609 m Ah g-1),Giving full play to the advantages of iron-based sulfide will make it have broad application prospects.In this paper,following the research frontier,sodium ion battery is the main research direction,and various and efficient operation methods are used to prepare special iron-based sulfide electrode materials.The specific research content is as follows:(1)Three dimensional tremella-like Fe S/C composite anode material was prepared by carbonizing the composite after high temperature heat treatment.Combined with this research direction,we applied it to sodium ion battery,prepared CR2025 button battery,and carried out the necessary electrochemical performance research.The final results showed the advantages of electrode materials.The reversible capacity of the first cycle is 621.9 m Ah g-1 and 539.2 m Ah g-1,and the long cycle stability is still excellent.After 100 cycles,it still has 410.5 m Ah g-1,even at 1000 m A g-1 current density it can maintain 394 m Ah g-1 after 130 cycles.It can be found that such a high degree of reversibility is closely related to its special structure.The lamellar structure can make the active material fully contact with the electrolyte,and the coating effect of carbon layer can make the active material keep stable structure during the charge discharge process.In addition,in order to further analyze the advantages of electrode materials,the dynamic analysis was carried out.The results show that the capacitive behavior occupies the main position of sodium ion storage in Fe S/C composite electrode materials,which is also one of the reasons for the remarkable performance of cycle stability and reversibility.(2)Fe S2/C composites were prepared by low-cost and environmentally friendly raw materials and mass production technology.Different proportions of iron and carbon sources were set up.The most appropriate carbon content was explored through comparative experiments.The discharge capacity and charge capacity of Fe S2/C-1 are1033.3 m Ah g-1 and 784.5 m Ah g-1,respectively.The coulomb efficiency of Fe S2/C-1is 75.9%.The loss of capacity is due to the formation of irreversible SEI film after the first charge and discharge.The capacity of Fe S2/C-0,Fe S2/C-2,and Fe S2/C-3composites with other carbon content is 377.3,487.8 and 346.1 m Ah g-1after 110 cycles of low rate cycling,which reflects that the composites with appropriate carbon content can not only improve the structure of the materials,but also improve the electrochemical performance.The results show that Fe S2/C-1 has a reversible capacity of 507.6 m Ah g-1 after 170 cycles,which is unmatched by other composites.The reversible capacities of Fe S2/C-0,Fe S2/C-2 and Fe S2/C-3 were 326.2,386.2 and 247m Ah g-1,after 150 cycles,110 cycles and 170 cycles,respectively.Therefore,the ratio of Fe S2/C-1 is the best to maintain the structure of the active material,and also can play the role of carbon layer conductivity to play the advantage of iron-based sulfide.(3)Fe S2/C composites with regular shape were designed and synthesized,and the structural advantages and carbon advantages explored in the first two chapters were integrated to achieve the best state.The results show that the carbon layer can fully cover the active material by selecting the appropriate carbon source,which not only enhances the conductivity but also relieves the volume expansion of Fe S2 during charging and discharging,and still maintains the original regular structure.Under this background,the electrochemical performance is slightly superior,with a reversible cycle capacity of 790.8 m Ah g-1 at the current density of 100 m A g-1.After 100 cycles of charging and discharging,the capacity can still be as high as 594.8 m Ah g-1,while the capacity of pure Fe S2 is as high as 544.8 m Ah g-1 under the condition of current density of 50 m A g-1,and only 352.5 m Ah g-1 after 100 cycles of charging and discharging.In this paper,there are 46 figures,2 tables and 134 reference articles. |
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