Synthesis,Modification And Electrochemical Properties Of Zn Fe₂O₄ Electrode Materials

With the development of the global economy,the problems such as environment pollution,fossil fuel consumption and global warming have become far more serious.Thus,energy storage devices for renewable sources are in urgent need.Lithium ion batteries?LIBs?are considered to be the most promising energy storage devices because of their high energy density,light weight,and long-term cycling life.The traditional commercial LIBs usually use graphite as an anode material,but graphite's theoretical capacity is very low?only 372 mAh g-1?,which cannot meet the requirements of newer battery applications,such as higher specific capacity and safety.Therefore,many efforts have been made to explore alternative anode materials that can provide higher capacity and safety.In recent years,binary transition metal oxides have been more and more widely applied as anode materials for LIBs because they can enhance the electrochemical performance beyond that of single transition metal oxides.ZnFe₂O₄ emerges from these transition metal oxides on account of its large theoretical capacity?1000.5 mAh g–1?,but the poor electrical conductivity,rapid capacity attenuation and large volume variation during charge-discharge process restrict its practical use.To overcome these disadvantages of ZnFe₂O₄,we made many efforts to improve the electrochemical properties of ZnFe₂O₄.The main research contents and results in this paper are as follows:?1?A traditional hydrothermal method was adopted to fabricate Ni-doped ZnFe₂O₄,the synthesized compounds are Nix Zn1-x Fe₂O₄?x = 0,0.25,0.5,0.75,1?.Regulating the proportion of Ni and Zn and utilizing the synergistic effect of Ni,Zn and Fe make the Ni-doped ZnFe₂O₄ compound exhibit excellent electrochemical performance.The crystal structures of the samples were characterized by XRD,SEM,TEM,XPS and Raman spectroscopy.The electrochemical properties were evaluated by CV,cycling performance,charge-discharge performance and rate performance.The results indicate that Ni0.25Zn0.75Fe₂O₄ possesses the best electrochemical properties with a high discharge capacity of 855.9 mAh g–1 after 100 cycles at a current density of 100 mA g-1.The Ni0.25Zn0.75Fe₂O₄ also shows the best rate performance with a high discharge capacity of 480.8 mAh g–1 even at a high current density of 750 mA g–1.?2?First,we fabricated ZnFe₂O₄ via a hydrothermal method with further heattreatment,then the as-prepared Zn Fe₂O₄ was mixed with the MWCNTs?5 wt%?under ultrasonic.The MWCNTs was acidized by concentrated HNO3?68%?.The performance of the samples was characterized by various structural characterization methods and electrochemical performance tests.The results demonstrate ZnFe₂O₄-MWCNTs exhibits the excellent electrochemical performance with high discharge capacity of 907.5 mAh–1 after 100 cycles at current density of 100 mA g–1,while the discharge capacity of the Zn Fe₂O₄ is only 523.3 mAh g–1.The electrochemical performance of ZnFe₂O₄ have been improved a lot after added the MWCNTs.?3?We adopted a simple solvothermal method to prepare the ZnFe₂O₄ and ZnFe₂O₄/MWCNTs-?15,30,50?composite to study the doping effect of MWCNTs on the electrochemical performance of ZnFe₂O₄ as an anode material for LIBs.The MWCNTs was acidified by concentrated HNO3?68%?and oxidized by H2O2.The results of electrochemical measurements demonstrate Zn Fe₂O₄/MWCNTs-30 composite shows the best electrochemical properties with a high discharge capacity of 1278.5 mAh g–1 after 200 cycles at a current density of 200 m A g-1,When the current density was increased to 500 mA g–1,the discharge capacity of ZnFe₂O₄/MWCNTs-30 still can reach 943.9 mAh g–1 after 400 cycles.The electrochemical performance of ZnFe₂O₄ have been improved a lot after added the MWCNTs.The improved electrochemical properties can be attributed to the good electrical conductivity and the tubular structure of the MWCNTs.