Study On Preparation Of Metallic/Carbon Nanocomposite Structures And Application In Lithium Ion Batteries

Carbon-encapsulated metal nanoparticles?CEMNPs?is a new type of metal/carbon composite nanomaterial,which consist of amorphous carbon or graphite encapsulate metal nanoparticles to form a unique core/shell structure.This new type of composite material,which has both nanometal properties and carbon material properties,possesses unique electrical,optical,and magnetic properties,and shows great application prospects in the fields of new energy,biomedicine,and catalysts and so on.It's preparation,properties and application has been the focus of research in recent years.People have made improvements to commonly used preparation methods?such as arc discharge method,chemical vapor deposition method,pyrolysis method,etc.?and are constantly exploring new methods to obtain excellent performance?such as monodisperse,narrow particle size distribution,high graphite Degree of carbon shell,etc.?of CEMNPs.Although some breakthroughs have been made in some methods,there are also some deficiencies.In this context,this paper explores two ways to prepare CEMNPs by high energy growth and hydrothermal reaction.The plasma flame flow?high-energy growth pathway?method has failed to successfully prepare CEMNPs due to the limitation of equipment,but this method is relatively novel and has a guiding effect on the preparation of other composite structural materials.The carbon encapsulated iron nanoparticles?Fe@C?,carbon encapsulated cobalt nanoparticles?Co@C?,carbon encapsulated nickel nanoparticles?Ni@C?and carbon encapsulated copper nanoparticles?Cu@C?were successfully prepared by atomization reduction-water thermal carbonization method with glucose and metal nitrate as raw materials and by multiple adjustment process parameters.The phase,structure and morphology of the prepared samples were characterized by the test method of X-ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,and Raman spectroscopy?Raman?.The results show that all four CEMNPs have good nuclear shell structure and dispersibility,and the core is a metal monomer with a face-centered cubic structure,and the shell is a amorphous carbon with a low graphitization degree.The particle size distribution of Fe@C,Ni@C,and Cu@C is in the range of 20 to 50 nm,the diameter of Co@C is small in the range of 5 to 20 nm,and the thickness of carbon layer is in the range of 2 to 3 nm.The graphitization degree of carbon layer is low and the difference is not significant,which indicating that the metal nanoparticles have no effect on the graphitization of the carbon layer during the hydrothermal reaction.In this paper,four kinds of CEMNPs prepared as electrode active materials were assembled into button-type lithium ion half-cells,and the cyclic voltammetry performance and galvanostatic charge-discharge performance of the batteries were tested.When the current density of 100mAg^-1 was used for the galvanostatic charge and discharge tests,the first charge and discharge efficiencies of Fe@C,Co@C,Ni@C,and Cu@C as electrode materials were 70.39%,64.25%,55.44%,59.24%,first charge capacity 396 mAhg-1,354 mAhg-1,372 mAhg-1,186 mAhg-1,respectively.After 50cycles,the specific capacity of Fe@C,Co@C and Ni@C electrode materials decreased by8.4%,6.7%and 8.2%respectively compared with the third times.The result indicates that the structure of CEMNPs has good stability when used as an electrode material during charge and discharge cycles.After 10 cycles of current density of 0.1Ag-1,0.2Ag-1,0.5Ag-1,1Ag-1 and 0.1 Ag-1,the capacity holding rates of Fe@C,Co@C,Ni@C and Cu@C electrode materials are 96.4%,102.5%,93%,92%,respectively,which indicate the CEMNPs have good rate performance as electrode material.