Study Of Preparation,modification And Electrochemical Performance Of Fe₂O₃@Ti₃C₂T_x Composites

With the continuous development of the energy storage market,the lithium-ion batteries（LIBs）with high energy density and long service life are increasingly demanding,and the anode and cathode electrode materials of LIBs are the key to their energy density and service life.Transition metal oxides（TMOs）are considered as promising anode materials for LIBs due to the advantages of high theoretical specific capacity,abundant resources and non-toxicity.However,the development of transition metal oxide anode electrode is severely limited by its poor conductivity and large volume variation during charging and discharging.It is an effective strategy to solve their defects that rational design of TMOs compounded with carbon materials.MXenes are a new type of two-dimensional material with good electronic conductivity and structural stability,and the terminal is rich in functional groups that can be easily compounded with other materials,compared with carbon materials is a more ideal conductive substrate material.In this paper,Fe₂O₃@Ti₃C₂T_x composite was synthesized by combining Fe₂O₃ with Ti₃C₂T_x to alleviate the volume expansion of Fe₂O₃ and thus improved the electrochemical properties.To further improve the overall electrochemical performance,we introduced carbon,Si nanoparticles or another metal oxide on the basis of Fe₂O₃@Ti₃C₂T_x（1）Firstly,monolayer or few-layer Ti₃C₂T_x was prepared by using HCl/Li F in situ etching with ultrasonic assistance.Then,Fe₂O₃@Ti₃C₂T_xcomposites was successfully synthesized by using dopamine to grow Fe₂O₃particles in situ on the Ti₃C₂T_x surface in combination with the chemical modification method of Mussel mimicry.Fe₂O₃@Ti₃C₂T_x has a specific capacity of 505 m Ah g^-1 at 0.1 A/g after 100 cycles and maintains a specific capacity of 500 m Ah g^-1 at 0.5 A/g after 400 cycles,which is a great improvement in electrochemical performance compared with pure Ti₃C₂T_x(230m Ah g^-1 at 0.1 A/g after 70 cycles).This main reason is that Ti₃C₂T_x in the composite can provide access for Li⁺transportation and mitigate the volume expansion of Fe₂O₃,and the polydopamine-derived carbon at high temperatures can further stabilize the structure of the material.（2）According to the preparation method of Fe₂O₃@Ti₃C₂T_x composites,the content of dopamine was adjusted,and it was found that the Fe₂O₃@Ti₃C₂Tx-I composite prepared by adding 0.2 g of dopamine improved both the specific capacity and cycling stability,with a specific capacity of 740 m Ah g^-1 at 0.1 A/g after 100 cycles and a remaining specific capacity of 430 m Ah g^-1 at 2 A/g after 500 cycles.（3）According to the preparation method of Fe₂O₃@Ti₃C₂T_x composite,the Si-Fe₂O₃@Ti₃C₂T_x composite was successfully synthesized by introducing a small amount of Si nanoparticles during the in situ growth of Fe₂O₃.Compared with Fe₂O₃@Ti₃C₂T_x,the specific capacity of Si-Fe₂O₃@Ti₃C₂T_x anode material is significantly improved,and the discharge specific capacity is stabilized at 740 m Ah g^-1at 0.1 A/g after 100 cycles and up to 559 m Ah g^-1 at 0.5 A/g after 300 cycles.The increased specific capacity of Si-Fe₂O₃@Ti₃C₂T_x composites comes from that Fe₂O₃@Ti₃C₂T_x provides a stable structure for Si nanoparticles,bringing out the capacity advantage of Si（4）Compared with monometallic oxides,bimetallic oxides have a more complex chemical composition,and the interaction between the elements is conducive to improving the electrochemical properties and lithium storage properties of the material and the activation energy of charge transfer between different cations is lower than the activation energy of charge transfer between the same cation,which is conducive to improving the electrical conductivity of the material.A ZnFe₂O₄@Ti₃C₂T_x composite with bimetallic oxide（ZnFe₂O₄）grown on the surface of Ti₃C₂T_x was prepared on the basis of Fe₂O₃@Ti₃C₂T_xcomposite.This material mainly improves the cycling stability relative to Fe₂O₃@Ti₃C₂T_x,with a stable capacity of 584.9 m Ah g^-1 at 0.1 A/g after 100cycles and up to 508.1 m Ah g^-1at 1 A/g after 300 cycles.