Preparation And Electrochemical Properties Of Fe₂O₃/Graphene Composites

Transition metal oxides electrode as promising anode material have been widely studied in lithium-ion battery because of its high specific capacity.Among them,owing to high specific capacity(1007 mAh/g),low cost,rich resource,no pollution and other advantages,iron oxide attract a lot of attention.However,the large volume change of Fe2O3 during the processes of discharge/charge leads to poor cycle stability,which seriously limits its application in lithium-ion battery.The addition of graphene into Fe2O3 forming Fe2O3/Graphene can effectively improve electronic conductivity of anode material.On the other hand,graphene provides buffering space for the large volume change of Fe2O3 because of the large surface area.Firstly,Fe2O3/Graphene were prepared by oil bath method and hydrothermal method,and then annealed at 500? in Ar atmosphere for 3h.Two samples were characterized by XRD and XPS,The results show that a part of carbon were oxidized during the annealing process.Furthermore,in the sample prepared by oil bath method,graphene oxide was not fully reduced to graphene.After 50 cycles at a current density of 100 mA/g,the capacity remains 350 mAh/g.The lower capacity might be attributed to the high graphene content in the composite material.On the other hand,the impedance of sample prepared by hydrothermal method is better than sample prepared by oil bath method.Therefore,we will reduce the temperature during annealing and prepare the composites by hydrothermal method in the next experiment.Secondly,Fe2O3/Graphene were prepared by hydrothermal method with different ratio of Fe3(NO3)3 and graphene oxide,and then annealedat 350? in Ar atmosphere for 3h.The electrochemical properties were also investigated.The experimental results show that the electrochemical performance is improved after reducing the graphene content of the material.After 50 cycles at a current density of 100 mA/g,63.16%-Fe2O3/Graphene exhibited a good cycling stability,the capacity maintained at 612 mAh/g.In addition,63.16%-Fe2O3/Graphene also exhibited a good rate performance,and the specific capacity maintains at 490mAh/g at a current density of 1000 mA/g.Therefore,63.16%-Fe2O3/Graphene has best cycle and rate performances.Finally,Sn-doped Fe2O3/Graphene composites were prepared by hydrothemal method,and the different doping amounts were compared.The results show that Sn-Fe2O3/Graphene exhibited better cycling stability and rate performance than Fe2O3/G.Furthermore,15wt%Sn-Fe2O3/Graphene shows the best electrochemical properties.After 50 cycles at a current density of 100 mA/g,the capacity of 15wt%Sn-Fe2O3/Graphene was 811 mAh/g.These indicated that the synergistic effect between Sn and Fe2O3/G can effectively improve the electrochemical properties of composites.