Preparation And Electrochemical Performance Of M_xO_y@C/rGO(M=Sn,Fe,Ni) Composites

As an energy storage device with high energy density and environmental friendliness,lithium ion battery has been widely used in electric vehicles and portable electronic products.However,as the anode of commercial batteries,graphite is difficult to meet the increasing development requirements because of its low specific capacity.Transition metal oxides Mx Oy?M=Sn,Fe,Ni?have higher theoretical capacities,but are subject to the problems of volume expansion during charging and discharging and the poor conductivity.As a common design strategy,particles in nano size have brought about new secondary problems,such as low efficiency of the first cycle,complex preparation methods and so on.In this paper,the structure of Mx Oy@C/rGO?M=Sn,Fe,Ni?composed of carbon coated ultra-small oxide and reduced graphene oxide?rGO?is proposed,and the preparation is completed by the method of rapid microwave heating after ion immersing into the metal organic framework,which effectively solve the above problems.The exploration SnO₂@C/rGO demonstrated that,using a metal-organic framework?MOF?,ZIF-8 as the infiltrating object,the choice of solute solvent system and subsequent microwave processing parameters has an important influence on the synthesis of materials.The infiltration system of SnCl₂-NMP was determined,and the fast treatment of microwave for 3 s with rGO as the microwave absorbing assistant was studied.Finally,the composite of 5 nm ultrafine SnO₂ particles coated with amorphous carbon and RGO was obtained.The size of micro-nano particles is about 0.5 ?m,and the mass ratio of SnO₂ is 22%.The combination of MOF adsorption and ultrafast microwave improves the complex and time-consuming preparation process in previous reports.SnO₂@C/rGO has an excellent electrochemical performance.The coulombic efficiency is is 68.4% in the first cycle at 0.1 A g-1.The specific discharge/charge capacity of is 590.7/586 m Ah g-1 after 200 cyles,and the capacity retention rate is 84.6%.Compared with the pure SnO₂ with particle size of 20 nm,SnO₂@C/rGO has a better performance,which is due to the three structural elements of ultra-small nanoparticles,carbon material coating and rGO.In addition,COMSOL is used to simulate the discharge process of a full cell with SnO₂@C/rGO as the anode.These results show that the materials obtained by the above simple process have effective morphological structure,and thus obtain better electrochemical characteristics.The process of SnO₂@C/rGO can be extended to a method of preparing carbon coated ultra-small oxide and graphene composite materials.First of all,by examining the calcination products of ZIF-8 with immersed ions,suitable iron and nickel immersed products were selected.Then,Fe₂O₃@C/rGO and NiO@C/rGO were prepared by microwave heating and impurity removal technology.Finally,the electrochemical reation potential of Fe₂O₃ and NiO was predicted by thermodynamic calculation.So far,the combination of MOF adsorption and ultrafast microwave treatment has become a widely applicable method to prepare metal oxide based nanocomposites.This new process and its composites of production provide a new strategy for the development and commercial application of the next generation anodes for lithium ion batteries.