Interface Engineering Of High Energy Density FeS₂ Cathode Materials

In the past 30 years,lithium-ion batteries have entered thousands of households as high-efficiency energy storage devices and are widely used in various products such as electric vehicles and portable electronic devices.However,the growing demand for higher cruising range and affordability has put traditional lithium-ion battery materials in an awkward position.In order to achieve the goal of higher energy density,people have been working hard to find the next generation of electrode materials.It is well known that the energy density and capacity of lithium-ion batteries are mainly determined by the cathode material.Compared with traditional intercalation cathode materials,much attention has been paid to conversion cathode materials because of their higher energy density and capacity.FeS₂is recognized as one of the most potential next generation of high energy density cathode materials due to its ability to undergo a four-electron transfer reaction with a theoretical energy density of 1671 Wh/kg and a theoretical specific capacity of 893.5 m Ah/g.However,the commercialization of FeS₂in the field of rechargeable batteries has been prevented due to the"shuttle effect"of polysulfide during the cycle,the huge volume expansion of active substances and the pulverization of active substances.In the face of the above challenges,this paper took a research on the effect of particle size on the electrochemical performance of FeS₂material,and carried out the elastic coating modification research,the specific content is as follows:The particle size of the active material undoubtedly has a great impact on its electrochemical performance.In this thesis,the effect of the particle size of the FeS₂material on its electrochemical performance was first studied,and a total of five FeS₂materials were prepared with particle sizes of 300 nm,2μm FeS₂,5μm FeS₂,10μm FeS₂and 20μm FeS₂.By comparing the cycle performance,rate performance,and electrochemical reaction kinetics,the 10μm FeS₂with the best electrochemical performance was selected.At a particle size of about 10μm,the side reaction between the active substances and the electrolyte is weakened,and the impedance is small,the reaction kinetics are good.At 0.5C,the discharge specific capacity of 10μm FeS₂was702.51 m Ah/g at the first cycle,and capacity retention rate was 40.60%after 100cycles.Although the electrochemical performance of 10μm FeS₂was better than that of FeS₂of other particle sizes,the capacity and cycling performance were still unsatisfactory.The electrically elastic core-shell FeS₂@PDMS/CNTs composite was prepared by in-situ coating of 10μm FeS₂,and the optimal amount of carbon nanotubes and the coating ratio of PDMS were explored.PDMS elastic coating can effectively inhibit the huge volume expansion during the cycle and reduce the dissolution of polysulfide,alleviating the"shuttle effect".Meanwhile,the three-dimensional conductive network formed by CNTs in the PDMS coating enhances the electronic conductance of the composite.The electrochemical performance of FeS₂was significantly improved by the synergistic effect of PDMS and CNTs.At 0.5C,the volume expansion rate decreased from 124%to 49%after 100 cycles.The specific discharge capacity of FeS₂@PDMS/CNTs reached 814.21 m Ah/g in the initial cycle,and capacity retention rate was 68.67%after 100 cycles.