Design And Synthesis Of Transition Metal Oxide Hollow Structure And Its Application In Anode Materials Of Lithium Ion Batteries

After decades of development,lithium-ion batteries have been successfully applied in various fields,ranging from mobile phones,computers,smart watches and other portable electronic devices to balance vehicles,military equipment,electric vehicles and so on.In order to further meet the market demand,researchers mainly focus on the pursuit of higher capacity,higher power density and lower cost of lithium-ion batteries.In the structure system of lithium-ion batteries,the capacity,rate and cycle life of batteries are generally determined by the properties of positive and negative materials.Transition metal oxides(TMOs)have become a research hotspot due to their high theoretical lithium storage capacity,abundant reserves and easy industrial synthesis.They are considered as a potential anode material to substitute carbon materials.However,the low electronic conductivity of these materials and the obvious volume effect seriously affect the cycle performance and rate performance of batteries during charge/discharge process.In order to alleviate these problems,many studies have designed different micro/nano-structures,in which hollow structure is an effective way to improve the performance of materials.In this paper,a simple self-template method is used to design a hollow structure to optimize its cycle and rate performance.The phase structure,morphology and electrochemical properties were analyzed by X-ray diffraction,scanning electron microscopy,transmission electron microscopy and electrochemical measurements.Multishelled hollow structure Co3O4 nanopheres were synthesized by solvothermal synthesis of spherical cobalt Metal organic frameworks(MOFs)as precursor,followed by simple annealing in air.The hollow structure alleviated the volume expansion problem during the charge/discharge process of Co3O4,and the residual carbon after annealing could improve the electonic conductivity of materials,aiming at improving the problems of TMO materials through structural design.After 70 cycles at 100 mA/g current density,the specific capacity reached 1300 mA·h·g-1,and after 100 cycles at 500 mA/g current density,the lithium storage capacity remained 1300 mA·h·g-1.At 10 A/g current density,the lithium storage capacity still remained 720 mA·h·g-1,showing extremely high capacity and excellent rate performance.In the past few decades,many conventional methods of synthesizing multishelled hollow structures are complex,high-cost and low-efficient template methods.Therefore,in this paper,we further studied the synthesis method of this kind of multishelled hollow metal oxides,and extend this simple self-template method to synthesize multishelled hollow structures with different compositions.In order to ensure the universality of the method,we kept the metal organic ligands and reaction solvents,only changed the metal salts of the reaction,synthesized a variety of precursors MOF:Zn-Co,Ni-Co,Mn-Co,Ni-Mn,Ni-Co-Mn,Ni-Co-Zn,Zn-Co-Mn,and then annealed them under the same conditions to form a variety of bimetallic oxides and ternary metal oxides.The multishelled hollow structure of these materials was proved by various morphological characterizations.Among them,ZnCo2O4 was selected to test its electrochemical performance.A high specific capacity of 1200 mA-h-g"’ can be achieved for the multishelled ZnCo2O4 electrode after 200 cycles at 100 mA/g.Simultaneously,a high reversible capacity of 730 mA·h·g-1 could be achieved at a high current density of 5 A/g.