Preparation Of Carbon-encapsulated Transition Metal Oxides And Lithium Storage Properties

Cobalt oxide and ferric oxide have attracted great interest as anode materials for lithium-ion batteries,due to their high theoretical specific capacity,abundant sources and environmental friendly characteristics.However,the poor conductivity,low initial coulombic efficiency and poor cycle performance have limited its wide range of applications.Therefore,it is an effective way to solve the above defects by improving the conductivity of cobalt oxide and ferric oxide materials and inhibiting sever aggregation and large volume change during repeated charge/discharge reactions.In this paper,EDTA-2Na was used as the carbon and nitrogen sources to synthesize a composite anode of lithium ion battery,which exhibits high capacity,excellent cycling performance,and good rate capacity.The research contents of this paper are as follows:The carbon encapsulated ?-Fe2O3 nanoparticles(Fe2O3@NC)were prepared using EDTA-Fe(?)sodium complex as precursor.Its results illustrated that the composite have abundant mesopores,and highly crystalline ?-Fe2O3 nanoparticles with size about 23 nm were uniformly encapsulated in amorphous carbon matrix.Meanwhile,the electrochemical test results show that the Fe2O3@NC composite electrode material has a coulombic efficiency of 96%,a reversible specific capacity of 496 mAh/g and a capacity retention of 71%after 50 cycles at a current density of 100 mA/g.and an excellent rate capability of 100 mAh/g at 1600 mA/g.When the current density is restored to 50 mA/g,the discharge specific capacity can still be quickly restored to 585 mAh/g.The superior electrochemical performance can be ascribed to the mesoporous structure of the composite and the nitrogen-doped carbon material,which can improve the conductivity and structural stability of ?-Fe2O3 during repeated lithiation/delithiation processes.The carbon-coated cobalt/cobalt oxide ternary composites(CoOx@C)were prepared using EDTA-Co complex as precursor.The electrochemical results show that the composite electrode material has a coulombic efficiency of 99%,a reversible specific capacity of 407 mAh/g and a capacity retention of 86%after 50 cycles at a current density of 100 mA/g,and an excellent rate capability of 120 mAh/g at 1600 mA/g.When the current density is restored to 50 mA/g,the discharge specific capacitance can still be restored to 411 mAh/g.The superior electrochemical performance of CoOx@C nanocomposite electrode can be ascribed to the following characteristics.Firstly,the highly conductive metallic Co nanoparticles not only increase the electrical conductivity of the composite,but also function as effective catalysts to activate the reversible conversion of some SEI components,leading to outstanding rate capability.Secondly,the nitrogen-doped carbon material increases the conductivity of the composite and inhibits the agglomeration of the cobalt oxide nanoparticles,which contributes to the cycling performance of the composite.