Preparation Of MFe₂O₄?M=Zn,Co?/C Composites And Its Application In Lithium Ion Batteries

Spinel-type ferrite MFe2O4?M=Co,Zn,Ni,etc.?is considered as a potential high-performance lithium-ion battery anode materials due to its high specific capacity and abundant resources.However,the practical application of ferrite anode materials is limited by the problems of large volume change and low conductivity during Li⁺storage.In this regard,this paper takes common cobalt ferrite?CoFe₂O₄,CFO?and zinc ferrite?ZnFe2O4,ZFO?as research objects,and uses hydrothermal method,impregnation method and solvothermal method to prepare series of composites such as PVP-derived carbon-coated CFO?CFO@PC?,carbon fiber supported flower-shaped CFO?CFO/CCF?,and carbon-coated ZFO nanospheres/reduced graphene oxide?C/ZFO NSs/rGO?.Through the characterization of SEM,TEM,Raman spectroscopy,and electrochemical performance tests,the relationship between the structure,morphology,and electrical properties of composite materials was explored.The main contents are as follows:?1?CFO nanoparticles were synthesized by hydrothermal method,and then CFO nanoparticles were carbon-coated with PVP as a carbon source to obtain CFO@PC composite material.The test results show that the CFO particle size is approximately25-50 nm and is uniformly dispersed in the carbon material.This structure can alleviate the volume change of CFO during charge and discharge,promote charge transfer,and have a certain surface capacitance.Therefore,when the CFO@PC composite material is used as a lithium ion battery anode material,the reversible discharge/charge specific capacity is 775.6/768.6 mAh g^-1 after 380 cycles at 0.92 A g^-1,and the reversible discharge/charge specific capacity reaches 418.7/421.3 mAh g^-1 at a current density of4.58 A g^-1.Compared with the unmodified CFO?Bare-CFO?,it shows excellent cycle stability and rate performance.?2?A simple impregnation method was used to load CFO on the surface of carbon fiber?CCF?obtained by carbonizing absorbent cotton to obtain a CFO/CCF composite material.The structure and morphology test results show that flower-like CFO in CFO/CCF composites are dispersed on the CCF surface.Among them,carbon fiber can provide an effective electron transport channel,and flower-shaped CFO can increase the contact area with the electrolyte and reactive sites.This unique composite structure is also beneficial to alleviate the volume stress caused by lithium ion extraction/intercalation and shorten the lithium ion diffusion path.In addition,CFO/CCF composites also exhibit a certain surface/near-surface capacitance when used as anode material for lithium-ion batteries.Therefore,the CFO/CCF composite has a discharge/charge specific capacity of 1008.2/990.1 mAh g^-1 after 100 cycles at 0.3 Ag^-1,and exhibits excellent electrochemical performance.?3?Solvothermal method was used to load ZFO nanospheres?ZFO NSs?with a size of about 250 nm on the surface of reduced graphene oxide?rGO?.Then,a carbon film was coated on the surface of the ZFO nanospheres using the ionic liquid[HMIm]N?CN?₂as a carbon source to obtain a C/ZFO NSs/rGO composites with a sandwich structure.In this structure,ZFO nanospheres grow on the surface of rGO and are protected by both rGO and ionic liquid-derived carbon.Therefore,the electrochemical test results found that the C/ZFO NSs/rGO composite material has excellent electrochemical performance when used as a lithium ion battery anode material:it has a discharge/charge specific capacity of 963.5/952 mAh g^-1 after 60 cycles at a current density of 0.3 A g^-1;it maintains a reversible specific capacity of 183.3 mAh g^-1 after 2000 cycles at a current density of 8 A g^-1.The C/ZFO NSs/rGO after cycling is examined by SEM,and the results show that under the dual protection of rGO and the surface carbon film,the particles of ZFO NSs have no obvious damage and maintain a complete structure.In addition,the results of cyclic voltammetry analysis show that C/ZFO NSs/rGO composites have significant capacitive behavior when used as LIBs anode materials.