Preparation Of Zn-based Transition Bimetal Oxides And Their Potential Applications As Anode For Lithium Ion Batteries

As a competitive anode material of lithium ion batteries?LIBs?,the Zn-based transition bimetal oxides are getting increasing interests because of it relatively higher electrochemical activity,high theoretical capacity,low cost,and environmental friendliness.When used as an anode material in the LIBs,however,the Zn-based transition bimetal oxides still face the problem of large volumetric change during repeated charge/discharge cycles,which severely decreases their cycle stability and limits its practical application.Moreover,to meet the requirement for high power density application,the electrical conductivity of the Zn-based transition bimetal oxides need to be further improved.To address these problems,we took the following approaches to improve to the performance of ZnCo₂O₄ and ZnFe₂O₄ in this thesis:?1?developing ZnCo₂O₄ microparallelepipeds with a porous structure;?2?fabricating ZnFe₂O₄@C composites from a metal-organic framework?MOF?.?1?ZnCo₂O₄ microparallelepipeds with a porous structure: The ZnCo₂O₄ microparallelepipeds were obtained through the calcination of Zn_1/3Co₂/3CO3 prepared by a simple hydrothermal.The microparallelepiped morphology of ZnCo₂O₄ could be clearly observed by SEM,which shows the maintenance of the morphology of Zn_1/3Co₂/3CO3 during the calcination.Careful observation demonstrates a porous structure of the ZnCo₂O₄ microparallelepipeds.The performance tests show that the porous ZnCo₂O₄ microparallelepipeds could deliver initial discharge and charge capacities of 1184 mAh g^-1 and 908 mAh g^-1 at the current density of 0.1 C,respectively.After 100 discharged/charged cycles,the porous ZnCo₂O₄ microparallelepipeds could still give the reversible capacity of 860 mAh g^-1.These results strongly suggest the good electrochemical performance of the porous ZnCo₂O₄ microparallelepipeds.?2?ZnFe₂O₄@C composites from the metal-organic framework?MOF?: The ZnFe₂O₄@C nanocomposite material were developed from a metal-organic framework?MOF?consisting of Zn and Fe.The SEM and TEM images show that the obtained ZnFe₂O₄@C composites have a spindle structure with a size of ³00 nm.These ZnFe₂O₄@C composites are composed of the carbon coated ZnFe₂O₄ with a diameter of 10-20 nm.The weight percentage of carbon in the composite estimated by the thermogravimetric analysis was 28 %.When used as the anode for LIBs,these Zn Fe₂O₄@C composites could deliver an initial capacity of 808 mAh g^-1 at the current density of 1 C.After 400 discharged/charged cycles,the Zn Fe₂O₄@C composites still show a reversible capacity of 630 mAh g^-1,suggesting a good cycling stability.A reversible capacity up to 380 mAh g^-1 was observed when the ZnFe₂O₄@C composites were discharged/charged at the current density of 6.4 C.These results demonstrate the great promise of using the ZnFe₂O₄@C composites as the anode for LIBs.