Synthesis Of Cobalt-based Metal Organic Framework And Its Application In Lithium-ion Batteries

With the depletion of fossil energy and the deterioration of the environment,electric vehicles have developed vigorously.New-type lithium-ion batteries have received extensive attention and research as a new generation of green power sources with excellent performance.Lithium ion battery is mainly composed of three parts:positive electrode material,negative electrode material and electrolyte.Graphite electrode,as the negative electrode material of traditional commercial lithium-ion batteries,cannot meet the energy density and service life requirements of the new generation of batteries due to its relatively low theoretical capacity(372 mAh g^-1).Therefore,researchers are working to develop new types of composite materials with high energy and long service life.For example,metal oxide composites containing carbon layer are obtained by calcining metal organic frameworks.This composite material not only has a unique frame structure,but also combines the advantages of metal oxides and carbon materials.This not only improves the stability of the composite material during charging and discharging,but also helps to improve the overall conductivity of the material.Get better electrochemical performance.The related work of this paper mainly focuses on the preparation of composite materials of cobalt-based metal organic frameworks?MOFs?for the anode materials of lithium ion batteries.The specific research content mainly includes the following three tasks:?1?The nano-level Si@ZIF-67-600 composite material was synthesized by co-precipitation method,and its electrochemical performance was compared as a lithium ion battery anode material with pure ZIF-67-600 frame material and Si nanomaterial.The results show that after 100 cycles at a current density of 500 mA g^-1,the Si@ZIF-67-600 material still maintains the reversible specific capacity of 1200 mAh g^-1,while ZIF-67-600 and Si nanomaterials only are 650 mAh g^-11 and 500 mAh g^-1.The excellent electrochemical performance of Si@ZIF-67-600 composite material shows that encapsulating Si nanoparticles in the frame structure of ZIF-67 can effectively alleviate the severe volume expansion of Si material.After high temperature calcination,the carbon layer obtained on the surface of the material can improve the overall conductivity of the material.Therefore,the successfully synthesized Si@ZIF-67 composite material not only solves the volume effect of Si,but also is a high lithium storage material itself.The simple and easy preparation method provides reference value for large-scale production.?2?Titanium dioxide is produced by hydrolysis of butyl titanate,which is compounded with Si@ZIF-67-600 composite material to form Si@ZIF-67/TiO₂ composite material.The prepared Si@ZIF-67/TiO₂ composite material exhibits excellent lithium storage performance when used as a negative electrode for lithium batteries,and exhibits an excellent capacity of681 mAh g^-11 after 400 cycles at a current density of 4 A g^-1.After compounding with TiO₂,the outer surface of Si@ZIF-67-600 material forms a heterojunction structure with TiO₂material with semiconductor properties,which greatly improves the overall conductivity of the material,making Si@ZIF-67-600 material become a very promising anode material.?3?While synthesizing ZIF-67 material,replace some cobalt ions with other metal(Ni²⁺,Mg²⁺)salt particles to synthesize bimetallic organic framework materials.The bimetallic material after high-temperature calcination has obtained the corresponding transition metal oxide?AB₂O₄?.This spinel-type transition metal oxide has a higher electronic conductivity,a larger specific capacity and a higher electricity chemical activity.When the prepared bimetallic MOF materials are used as a negative electrode material for lithium batteries,Mg-Co MOF and Ni-Co MOF materials still have 1195 mAh g^-11 and 891 mAh g^-11 after circulating 200 cycles at a current density of 500 mA g^-1.In addition,the bimetallic MOF material also exhibits extremely excellent rate performance.After rapid charge and discharge,the capacity of the material is not only maintained but also improved.Therefore,this bimetallic MOF material is a lithium ion anode material with potential application value.