| Over the past few decades,lithium-ion batteries have made significant advances in both commercial value and academic research.As a successful energy storage device,lithium-ion batteries play a vital role in many applications such as electronics,electric vehicles,and aerospace products.However,limited lithium resources lead to high production costs,and lithium dendrites pose safety issues.Compared with lithium-ion batteries,rechargeable magnesium-ion batteries have the advantages of sufficient storage capacity,low cost,good safety and high volumetric energy density,and are receiving more and more attention as next-generation battery systems.However,the development of cathode materials has been hindering the development of magnesium ion batteries.Magnesium can provide two electrons in the redox process,providing a high theoretical capacity,but it also leads to the polarization of Mg2+,which makes the ion diffusion difficult.Therefore,it is necessary to find high-performance cathode materials for magnesium ion batteries.In this paper,Fe S2 with different morphologies were synthesized by solvothermal method,and the magnesium storage properties of solid Fe S2microspheres and hollow flower-shaped Fe S2 microspheres were studied.Then,in order to further improve the electrochemical performance of Fe S2 material,carbon-nitrogen doped Fe S2/CN-10 was synthesized by gel method.And the magnesium storage properties of Fe S2/CN-10 were investigated using a series of characterization and electrochemical tests.The details of the study are as follows:（1）Solid Fe S2 microspheres with a thin sheet structure were synthesized by a solvothermal method.The phase of Fe S2 was characterized by XRD,XPS,SEM and EDS,and the electrochemical performance of solid Fe S2 microspheres when used as positive electrode of magnesium ion batteries was investigated.Due to the excellent characteristics of Fe S2 itself and the structural features of Fe S2 microspheres,the Fe S2 electrode can provide a discharge specific capacity of 269 m Ah g-1 at a current density of 0.05 A g-1.（2）Based on the above work,Fe S2 with different morphologies were synthesized by solvothermal method,and the effects of urea content and the ratio of N,N-dimethylformamide（DMF）to ethylene glycol in solvents on the morphology of Fe S2 were investigated.Without the addition of urea,the surface of Fe S2 particles was relatively rough,and with the increase of urea content,flakes gradually appeared on the surface of the particles,and the thickness of the flakes also became thinner.It indicates that the amount of urea addition has a certain influence on the morphology of Fe S2.When the urea content is certain and the solvent only contains ethylene glycol without DMF,the Fe S2 particles resemble stone shape,and after gradually increasing the ratio of DMF to ethylene glycol,the surface of the particles gradually appear flake structure and change from solid to hollow structure,and finally when the solvent only contains DMF without ethylene glycol,the particles become fragmented,indicating that the increase of the ratio of DMF to ethylene glycol helps to generate flake structure and decreasing the ratio helps to generate stone structure.Finally,hollow flower-like Fe S2 with the solvent ratio of DMF to ethylene glycol of 12.5:2.5 was selected as the cathode material for the magnesium ion battery for the study.Since the hollow flower-like Fe S2 consists of a large number of thin flakes,it has a large specific surface area,which increases the contact area between the electrolyte and the active material.The discharge capacity of Fe S2 electrode can reach 294 m Ah g-1 at a current density of 0.05 A g-1.（3）To further improve the electrochemical properties of Fe S2 materials,nitrogen-doped amorphous carbon-loaded Fe S2 nanoparticles（Fe S2/CN-10）were synthesized by the gel method and used as cathode materials for magnesium ion batteries.On the one hand,the doping of carbon and nitrogen elements improves the electrical conductivity of the material,and on the other hand,Fe S2/CN-10 has a unique pore structure and layered structure.This structure promotes the penetration of electrolyte,increases the specific surface area of the material,provides a large number of active sites,shortens the ion transport path,and helps the embedding and de-embedding of Mg2+,thus accelerating the reaction process.Compared with solid Fe S2microspheres and hollow flower-like Fe S2 microspheres,the Fe S2/CN-10 composites provided higher Mg storage capacity,and the highest discharge capacity of Fe S2/CN-10 electrode reached413 m Ah g-1 at a current density of 0.05 A g-1. |
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