Synthesis And Electrochemical Performance Of Iron-Based Oxide Negative Materials For Lithium-ion Batteries

The problems of energy shortage and ecological damage caused by the wanton development and unreasonable use of conventional energy based on combustion technology are becoming more and more prominent,so renewable green new energy sources such as wind,solar and tidal energy have emerged.In view of the intermittent shortcomings of these new energy sources,lithium-ion batteries（LIBs）have attracted much attention because of excellent energy storage and conversion performance.With the progress of science and technology,especially the continuous development of new industries such as hybrid electric vehicles,higher requirements are put forward for the performance of LIBs.At present,the anode material of commercial LIBs is graphite.Although it has the characteristics of low working voltage and stable structure,it limits the wide use of LIBs because of low specific capacity(372 mAh g^-1).Therefore,researchers are trying to find anode materials that can replace graphite and provide higher capacity and safety.In recent years,iron-based oxides have attracted the attention of many enterprises and researchers because of abundant reserves in nature,green,pollution-free,safe,reliable and high theoretical specific capacity.However,iron-based materials still have many defects that have not been overcome,such as structural damage caused by volume changes during cycling and poor conductivity of the materials themselves,which make the electrochemical performance of the battery poor,thus limiting its further development and application.A large number of research results indicate that methods such as nano-crystallization,doping carbon materials,and compounding multiple metal oxides can effectively improve the performance of the materials.If we can combine several methods and learn from each other,it is expected to further improve the properties of the materials.Based on the above considerations,this paper takes Fe₂O₃(theoretical capacity is 1006 mAh g^-1)as the research object and uses two modification methods to modify Fe₂O₃.The specific studies are as follows:（1）The pure rice granule Fe₂O₃ was prepared by a hydrothermal method.SiO₂ and resorcinol-formaldehyde resin were coated with Fe₂O₃ as the core,and then the yolk shell structure Fe₂O₃@C was formed by carbonization and etching.A layer of Mn₃O₄lamellar structure was introduced into the carbon layer to prepare Fe₂O₃@C@Mn₃O₄with three-layer core-shell structure.The composition,structure and morphology of the composite were physically characterized by XRD,XPS,TGA,SEM and TEM.The electrochemical properties of the composite were characterized by CV,charge-discharge and rate performance curves.The special core-shell structure of the composite ensures the structural stability of the material.Fe₂O₃ with high lithium storage capacity provides support.On the one hand,the carbon layer provides good conductivity,on the other hand,the synergistic effect of Mn₃O₄ and Fe₂O₃ makes the electrochemical performance of the material better.As for Fe₂O₃@C@Mn₃O₄,the discharge specific capacity can be maintained at 1062 mAh g^-1 after 100 cycles at a small current density of 200 mA g^-1,which is much higher than that of pure phase Fe₂O₃ and Fe₂O₃@C.At a high current density of 1000 mA g^-1,the discharge specific capacity of Fe₂O₃@C@Mn₃O₄ can be maintained at 853 mAh g^-1 after 450 cycles.（2）Fe₂O₃/MoS₂/rGO composite was synthesized by two-step hydrothermal method and subsequent heat treatment.The composition,structure and morphology of the composite were physically characterized by XRD,XPS,SEM and TEM.The electrochemical properties of the composite were characterized by CV,charge-discharge and rate performance curves.In the composite,MoS₂ is lamellar,Fe₂O₃ is rice granule and adheres to MoS₂,and rGO forms a three-dimensional network structure to connect the whole composite.Fe₂O₃ provides high specific capacity for the composite,and rGO enhances the electronic conductivity of the material.The synergistic effect of three components makes Fe₂O₃/MoS₂/rGO composite has better electrochemical properties than pure Fe₂O₃.The test results show that the discharge specific capacity of Fe₂O₃/MoS₂/rGO composite is 906 mAh g^-1 after 100 cycles at a current density of 200mA g^-1.Even at a high current density of 1000 mA g^-1,the discharge specific capacity can be maintained at 711 mAh g^-1 after 500 cycles.