Study On The Preparation And Electrochemical Performance Of Polyhedron Co-based Oxide

Co3O4 has been extensively investigated owing to the high theoretical capacity and abundant raw materials.However,several hurdles such as poor conductivity and volumetric expansion need to be overcome for them to be commercially viable.A great deal of efforts approache to resolve these problems has been designed and fabricated special structured materials and hybrid materials,which can increase the conductivity and buffer the volume changes.But,there are cumbersome process,preparation problems and other issues,which is not conducive to the development of commercialization.Based on the Co3O4 material,the anode materials of lithium ion batteries with different structure and morphology are designed to study the electrochemical properties.The main results and new findings in this work are summarized as follows:(1)Preparation and research of single crystal Co3O4 Cubes anode material:via cobalt nitrate as precursors,the single crystal Co3O4 cubes were obtained by hydrothermal reaction.In three-dimensional space,the single crystal material is arranged regularly and periodically,so the highly ordered and complete single crystal structure reduces the surface defects of the material,which can alleviate the corrosion of the electrolyte on the surface of the material.In addition,the single crystal material with a high degree of crystallinity can inhibit the crystal structure irreversible phase transition,which effectively alleviate the volume expansion during the charge and discharge process.The lattice of single crystal material is continuous,without grain boundary,which provides smooth channels to promote Li+ and electrons diffusion.It delivers a high capacity of 877 mAh g-1 at current density of 200 mA g-1 after 110 cycles,as well as good capacity retention of 98%.Even at a high rate of 2000 mAg-1,the reversible capacity could be still retained at 576 mAh g"1.Considering of the facile of preparation process and excellent electrochemical performance,this single crystal Co3O4 cubes electrode material will serve as a greatly promising candidate for the application to the future development.(2)Preparation and research of PDA@Co3O4 anode material:via the dopamine monomer as the precursor,it is found that a thin layer of amorphous PDA is uniformly coated on the surface of the single crystal Co3O4 cubes.Polydopamine(PDA),a conducting polymer with polar groups,has been considered as an effective coating layer to effectively promote the immersion of the electrolyte and shorten the electrode material Li+ diffusion path.Co3O4 anode material with the coating layer can improve mechanical strength and maintain stable structure,which can improve cycling stability at the high current density.The tests display that the initial capacitance of the PDA@Co3O4-2 electrode material with the best electrochemical performance is low.As the number of cycles increasing,it delivers a high capacity of 460 mAh g-1 after 90 cycles,and the discharge capacity almost keeps constant after the next cycle.The single crystal Co3O4 cubes with a uniform protective layer can effectively alleviate the volume expansion during the charge and discharge process,which ensure cycle stability at high current density.(3)Preparation and research of MnCo2O4 micro/nano-octahedrons anode material:in this paper,alternative element(Mn)partially replace the cobalt element in Co3O4 to form binary transition metal oxides-MnCo2O4.The uniform micro/nano-octahedrons composed of many densely compact nanoparticles with diameters ranging from 30 to 40 nm bonded to each other lead to an improved mechanical strength,which can ease the volume change during prolonged cycles.When used as anode for lithium ion batteries,the MnCo2O4 micro/nano-octahedrons anode material obtained by hydrothermal reaction for 15 h exhibits an excellent electrochemical performance of capacity of 720.4 mAh g-1 at a current density of 300 mA g-1 after 200 cycles with remarkable capacity retention of 88%.