Study On Preparation And Energy Storage Of Iron Sulfide Carbon-based Composite Materials

Lithium ion batteries play a dominant role in the portable energy storage device market with their high energy density and wide output voltage.In recent years,with the continuous development of the electric vehicle industry,the lithium ion battery with graphite as the negative material can no longer meet the energy demand of the current market.Therefore,it is very important to find high-performance anode materials.Iron sulfides have attracted much attention due to their excellent mechanical stability,abundant natural resources and high theoretical lithium storage capacity,but it is difficult to be applied in practice due to its low conductivity and large volume expansion during charging and discharging as the negative material of lithium ion battery alone.To solve the above problems,FeS/pitch and Fe₇S₈/gelatin composite materials were prepared by two methods.On the one hand,the introduction of pitch-based carbon and gel-based carbon can improve the electrical conductivity of composite materials;on the other hand,it can effectively alleviate or eliminate the volume expansion during charging and discharging,ensure the stability of the main material structure,and significantly improve the lithium storage performance of FeS and Fe₇S₈.The main research contents are as follows:（1）Using ferrous sulfide and coal tar medium-temperature pitch as raw materials,the precursor of FeS/pitch-based composites were prepared by suspension method,and FeS/pitch-based composites were successfully prepared after non-melting and carbonization treatment.Taking FeS/pitch-based composite materials as the negative material of lithium ion battery,the results show that:under the test conditions of current density of 0.1 A/g and voltage range of 0.05-3V,when the amount of FeS added is 0.2g,the composite material has the highest reversible specific capacity.After 100 cycles,there is still 220.1 m Ah/g reversible specific capacity,which is greatly improved compared with the pure FeS.（2）Based on the above work,the preparation idea was applied to the preparation of Fe₇S₈/C composite materials.In this chapter,the one-step sol-gel method was used to successfully prepare the Fe₇S₈/gel-based composite materials,with gelatin as the carbon source,FeSO₄·7H₂O as the iron source and Na₂S·9H₂O as the sulfur source.In the synthesis process,Fe²⁺has a strong binding effect with the functional groups in the gelatin to form a viscous gel solution to achieve nano-level dispersion of the metal salt,and then combines with the sulfur source to form the Fe₇S₈/C precursor.After the high-temperature carbonization process,the gelatin will form a good conductive carbon network and coat on the surface of the nano-Fe₇S₈particles.The results show that the Fe₇S₈/C composite materials still have a highest reversible capacity of 657.3 m Ahg^-1 after 400 cycles under the current density of 0.1A/g,knowable lithium ion diffusion coefficient is much higher than that without carbon coating through GITT test.This indicates that the composites prepared by this method can effectively shorten the diffusion path of lithium ions,promote the transmission of lithium ions and electrons,significantly improve the electrochemical performance of the composite,and also provide experimental ideas for the preparation of other carbon composite materials.