Microstructure Control And Lithium Storage Performance Of Iron-based Bimetallic Oxide Anode Materials

Up to now,lithium ion battery has become an essential energy storage device in industry production and people’s life.Exploring anode materials with low cost,high energy density and excellent cycle performance is an important direction for the development and progress of lithium ion batteries.As a promising anode material,iron-based bimetallic oxide has the advantages of low cost and high theoretical specific capacity.However,its further development is still seriously hindered by the problems of poor conductivity and large volume change in the charge and discharge process.Composite anode materials between iron-based bimetallic oxide and carbon material with good conductivity can usually acheive good electrochemical performance.In this paper,aiming to solve the problems of bimetallic oxide,iron-based bimetallic oxide MFe₂O₄（M=Ni,Zn）has been combinded with carbon materials.MFe₂O₄/C with hierarchical porous structure and MFe₂O₄/CNTs reinforced by carbon nanotubes have been constructed by adjusting the microstructure of the composite materials.When applied to the anode of lithium ion battery,the prepared materials show good electrochemical performance.（1）Porous structure can be produced by self-expansion of gelatin,which is employed as carbon source to successfully prepare MFe₂O₄/C materials with hierarchical porous structure by sol-gel method.The MFe₂O₄ nanoparticles are uniformly and dispersedly embedded in the hierarchical porous framework which is constructed by amorphous carbon.It is found that calcination temperature has significant influence on the structure,morphology and electrochemical properties of MFe₂O₄/C materials.Meantime,different bimetallic oxides have different requirements for calcination temperature.Electrochemical tests show that the prepared MFe₂O₄/C exhibits good cycle stability and rate performance.This may be because the graded porous carbon provides enough buffer space for MFe₂O₄ nanoparticles,maintains the structural stability of active particles,and effectively improves the electric conductivity of composite materials.The MFe₂O₄/C calcined at 350 ^oC and ZnFe2O4/C calcined at 450 ^oC have the best electrochemical performance.At a current density of 200 m A g^–1,their first specific discharge capacities are 1367.1 m Ah g^–1 and1385.8 m Ah g^–1,and the corresponding first Coulombic efficiencies are 72.49%and74.82%.After 200 cycles,the specific discharge capacities are 832 m Ah g^–1 and 861.1m Ah g^–1,and the capacity retentions are 60%and 63%.（2）The MFe₂O₄/CNTs composites derived from metal organic framework have been obtained by hydrothermal method and subsequent calcination oxidation using 2-methylimidazole as ligand skeleton,metal nitrate as metal ion ligands and carbon nanotubes（CNTs）as carbon source.CNTs are dispersed among spherical MFe₂O₄nanoparticles with uniformly distribution to form a three-dimensional network,which effectively improves the structural stability of MFe₂O₄ nanoparticles and the ability of MFe₂O₄ nanoparticles to bear stress.The volume expansion of MFe₂O₄ nanoparticles also can be buffered by the non-directional CNTs in different directions.Electrochemical performance tests show that the prepared NiFe2O4/CNTs and ZnFe2O4/CNTs materials exhibit the best electrochemical performance when the molar ratio of CNTs to MFe₂O₄ is 1.665:1.At a current density of 200 m A g^–1,the first specific discharge capacities are 1324.3 m Ah g^–1 and 1375.7 m Ah g^–1,and the corresponding first Coulombic efficiencies are 79.67%and 76.63%.After 100 cycles,the specific discharge capacities are 1324.3 m Ah g^–1 and 1375.7 m Ah g^–1,and the capacity retentions are 84.0%and 104%.