Studies On The Preparation And Lithium Storage Performance Of Metal Sulfides

Recently,the application of lithium-ion batteries have changed from small equipment to large-scale equipment such as hybrid electric vehicles and aerospace devices.However,the energy density is more and more difficult to meet the demand of social development.Therefore,it is urgent to improve the energy density.Developing high-capacity anode materials is an important method to improve the energy density of lithium-ion batteries.Compared with the current commercial carbon materials,the metal sulfide anodes have higher lithium storage capacities,thus becoming attractive in recent years.However,there still exist some problems in their synthesis,such as higher energy consumption,unable to achieve equal stoichiometric reaction and waste of the raw material of sulfur.Besides,using a solvothermal method will introduce organic solvents in the product,which has an adverse effect on the electrochemical performance.Currently,the most metal sulfide anodes are transition metal sulfides,which has lower lithium storage capacity compared with light metal sulfides.Hence,this work discusses the effects of the low-temperature molten salt method on the morphology and performance of Fe S₂@C.Moreover,Al₂S₃/C samples with different crystal types are prepared by mechanical milling.And,we compare the performance of different Al₂S₃/C samples.The main contents of this thesis are summarized as follows:Spherical Fe S₂@C with porous structure is synthesized at different temperatures with different molten salts and Fe@C by low temperature molten salt method.The uniform dispersion of sulfur to the atomic level can increase its reactivity,thus this method can efficiently reduce the reaction temperature.Besides,this method can realize the stoichiometric ratio synthesis of iron and sulfur without waste of raw materials.It is an environmentally friendly synthetic method benefit to mass production.The first reversible capacity of Fe S₂@C is 963.5 m Ah/g,witch is possesses outstanding rate capability.The reaction kinetics is jointly controlled by the lithium process and pseudocapacitive charge result of the porous structure of Fe S₂@C.Therefore,Fe S₂@C has the advantages of high lithium storage capacity,rapid charging and discharging ability.Simultaneously,the porous structure provides space for the intercalation/deintercalation of lithium ions,which shows an excellent cyclic stability.At a high current of 1.0 A/g,the capacity retention rate can reach 82.7%after 900 cycles.In addition,the paper studies the conversion reaction during Li⁺intercalation/deintercalation process.Al₂S₃/C is synthesized with sublimated sulfur（sulfur elemental solid）,metal aluminum powder and carbon by mechanical milling.Changing the content of carbon,speed and time of mechanical milling etc.,we control the preparation of hexagonal and cubic Al₂S₃.Comparing the lithium storage performance of them,the hexagonal crystal Al₂S₃ has better cycle stability and rate capability.Furthermore,it has the lower discharge voltage platform,which is beneficial to be used as a high capacity anode material.