The Study Of Carbon-iron Disulfide Composites As Cathode Materials For Lithium-ion Batteries

The iron disulfide?FeS₂?/lithium ion batteries with the property of high charge/discharge capacity,stable voltage plateau and good compatibility for 1.5V batteries used in the daily life,have attracted great attention from industry.However,there are some problems faced by FeS₂ secondary batteries,including the great volume fluctuation during cycling process,the formation of soluble lithium polysulfide,and poor conductivity of Li₂S.The author adopts the modification methods of FeS₂ compositing with carbon materials to improve the electrochemical cyclic stability of FeS₂ secondary batteries.The main results are as follows:?1?Hierarchical porous carbon?HPC?is synthesized through the evaporation method induced by self-assembly strategy,and its structure with microporous and macroporous shows great advantages.The carbon capsules working as reaction sites inhibit the growth of the FeS₂ crystals and result in smaller FeS₂ nanocrystals,which benefit the quick and thorough electrochemical reaction of the active materials.Microporous structure provides buffer space for volume change,releases stress and prevents the particles pulverizing at the same time.The porous structure as fast ion transport channel allows better electrolyte accessibility.HPC encapsulated FeS₂ can reduce the side reaction between active materials and electrolyte,and can inhibit the solution of polysulfide.The carbon skeleton provides electronic transport channel for improving the conductivity of the material.The results show that problems faced by FeS₂ secondary battery can be greatly mitigated at once by compositing with HPC.The composites exhibit excellent electrochemical performance with specific capacity of 720 mAh g^-1 after 100 cycles at the rate of 1C.?2?Biomass carbon@FeS₂ composite is prepared using green and cheap auricularia as raw material after the process of carbonization and sulfuration at high temperature.The auricularia has strong swelling characteristics to absorb solution which can effectively absorb Fe ions into its body.FeS₂ homogeneously distributing in biomass carbon matrix performs high electrical conductivity.The initial specific capacity of the composite materials is up to 783 mAh g^-1 and remains 703 mAh g^-1after 80 cycles.Biomass carbon@FeS₂ composite materials exhibit high rate capacity and high specific capacity(600 mAh g^-1)at the rate of 5C.The work in this thesis applied a simple method to form composite of HPC with FeS₂,which greatly improved the electrochemical performance of FeS₂ battery.The way of using auricularia as raw material of carbon composite inspires more ideas about the application of cheap biomass materials for lithium ion battery.