Research On Preparation Of Nickel Territe-Based Composite Materials And Its Properties In Lithium-Ion Batteries

In this paper,the yolk-shell NiFe₂O₄ and solid NiFe₂O₄ nanospheres were prepared by a simple self-template solvothermal method combined with an annealing process.NiFe₂O₄ nanospheres with different morphologies were combined with carbon(C)materials and reduced graphene oxide(rGO)to obtain yolk-shell NiFe₂O₄@C and NiFe₂O₄/rGO nanocomposites,and applied them in lithium-ion batteries(LIBs).(1)The nickel-iron precursor is obtained by a simple self-template solvothermal method,and NiFe₂O₄ nanospheres with different morphologies are obtained by controlling the heating rate during the annealing process.Specifically,the yolk-shell NiFe₂O₄ is obtained at a heating rate of 1?min^-1,and the solid NiFe₂O₄ is obtained at2?min^-1.NiFe₂O₄ was coated with phenolic resin as a carbon source.After calcination,the yolk-shell NiFe₂O₄ with carbon-coated(NFO-YS@C)and solid NiFe₂O₄ with carbon-coated(NFO-S@C)were obtained.Among them,NFO-YS@C nanospheres have obvious yolk-shell shell structure.The core-shell spacing is about 60nm,the thickness of the NiFe₂O₄ shell is about 15 nm,and the thickness of the carbon shell is about 30 nm.The yolk-shell structure can alleviate volume changes and shorten the ion/electron diffusion path,while carbon materials can improve conductivity.Therefore,NFO-YS@C nanospheres as the anode materials of LIBs show a high initial capacity of 1087.1 m A h g^-1 at 100 m A g^-1,and the capacity of NFO-YS@C nanospheres impressively remains at 1023.5 m A h g^-1 after 200 cycles at 200 m A g^-1.The electrochemical performance of NFO-YS@C is significantly better than that of NFO-S@C,which proves that the carbon coating and yolk-shell structure have good stability and excellent electron transport ability.(2)The prepared solid NiFe₂O₄ nanospheres and graphene oxide(GO)are self-assembled by a one-step hydrothermal method to form a three-dimensional(3D)NiFe₂O₄/rGO composite hydrogel,then the NiFe₂O₄/rGO composite aerogel is obtained after freeze-drying.NiFe₂O₄ nanospheres are solid spheres of uniform size with a diameter of about 650 nm,and the hybrid structure improves the number of active material sites accessible to the electrolyte.The synthesized NiFe₂O₄/rGO composite material has a 3D network structure,abundant pores and large pores.The sample material is used as the LIBs anode material for electrochemical testing.The NiFe₂O₄/rGO composite aerogel exhibits a high initial discharge capacity of 1654.6 m A h g^-1 when the current density is 100 m A g^-1,even at a high current density(1000 m A g^-1),after 300 cycles,the reversible capacity of the electrode remains at 452.5 m A h g^-1.The excellent Li⁺migration kinetics is mainly due to the introduction of rGO.The 3D structure of rGO enables the electrolyte to contact the active sites faster and more,and provides a 3D conductive network for rapid electron transfer.More importantly,the synergistic effect between NiFe₂O₄ and rGO can enhance the transport of Li⁺and electrons.This improves the structural stability of the negative electrode,thereby improving electrochemical performance.