Preparation And Electrochemical Properties Of Anode Materials For Fe 2 O 3 Based Lithium Ion Batteries

Lithium-ion batteries are widely used in our daily life because of their high open circuit voltage,large energy density,long service life and so on.As a widely commercial anode material,the theoretical specific capacity?372 mA h g-1?of graphite is lower,which is impossible to meet the requirements of a new type of lithium ion battery with high performance.Fe₂O₃ have a high theoretical specific capacity?1006 mA h g-1?,which attracts great attention.However,Fe₂O₃ face enormous volume expansion in charge and discharge which leads to capacity loss,and the conductivity of Fe₂O₃ is poor,which is unfavorable to the transmission of electrons and ions.In order to solve these problems,on the one hand,researchers prepared Fe₂O₃ materials with different morphologies and structures,such as nanoparticles,rod-like structures,hollow structures,etc.,which shows better cycle performance.On the other hand,researchers prepared Fe₂O₃/carbon composites and Fe₂O₃/conductive polymer composites,the electrochemical properties have been greatly improved.In this paper,Fe₂O₃ anode electrode materials were prepared and their electrochemical properties were investigated.Then Fe₂O₃/PPy and Fe₂O₃/rGO composite were prepared and the electrochemical properties of composite materials were investigated.The main research contents are as follows:?1?Fe₂O₃ nanosheets were synthesized by hydrothermal method using FeCl₂· 4H₂0 as Fe source,and then electrochemical properties of the nanosheets were investigated.A reversible capacity of 172.6 mA h g-1 is delivered at a current density of 200 mA g-1 after 100 cycles,the materials have large capacity decay and poor cycle stability.This is mainly attributed to large specific volume change and severe particles aggregation during lithiation/delithiation processes.?2?The Fe₂O₃/PPy composites with different PPy contents were synthesized by in situ polymerization at room temperature.The effect of PPy content on the properties of Fe₂O₃/PPy composites were investigated.The results show that the cyclic performance of Fe₂O₃/PPy composites with different PPy content were higher than that of pure Fe₂O₃,which indicates that PPy improves the performance of Fe₂O₃.This is mainly attributed to the PPy layer as a protective layer,on the one hand,can buffer expansion and agglomeration of Fe₂O₃ during the insertion/extraction processes of lithium-ion.On the other hand,it can prevent the direct contact of Fe₂O₃ with the electrolyte,so the integrity of Fe₂O₃ particles was protected.Fe₂O₃/5.0wt%PPy has a better cyclic performance and the specific capacity is 487.4 mA h g-1 after 100 cycles at a current density of 200 mA g-1.?3?Fe₂O₃/rGO composites were prepared by hydrothermal method.The influence of hydrothermal time and rGO content on the properties of the material was investigated.The results show Fe₂O₃/rGO?4-25?with reaction time of 4h and rGO content of 25%has a better cyclic performance.A specific capacity reaches up to 783.7 mA h g-1 at a current density of 200 mA g-1 after 100 cycles.It is higher than other conditions for the preparation of Fe₂O₃/rGO composites and Fe₂O₃.When the current density is increased to 1 A g-1,it still shows a better cycle performance.A specific capacity reaches up to 352.3 mA h g-1 at a current density of 1 A g-1 after 500 cycles.The good cyclic performance of composites is attributed to the addition of graphene.which effectively inhibits the volume change and agglomeration of Fe₂O₃ in the process of insertion/extraction of lithium-ion as well as enhancing the conductivity of Fe₂O₃.