Study On The Preparation And Electrochemical Properties Of Iron Based Composite Anode Electrode Materials For Lithium Ion Batteries

With the development of society and the progress of technology,portable electronic products and electric vehicles have been widely used in our daily life.These applications are inextricably linked with the rapid development of lithium-ion battery technology.The anode material of lithium ion battery is the focus of research.At present,as commercialized lithium ion battery anode material,the theoretical capacity of graphite is about 372 m Ah g-1.This can not meet the requirement for late-modle and high energy storage batteries evidently.The transition metal oxides?Mx Oy,M = Fe,Co,Mn?have high theoretical specific capacity as anode materials for lithium ion batteries and have no pollution to the environment.However,poor conductivity,and large volumetric expansion during charge-discharge cycles that severely impact the cycle stability and cycle life of the battery.The reasonable modification is an important way to make the transition metal oxides become the anode electrode material of the commercial lithium ion battery.The research shows that multi-walled carbon nanotubes?MWNTs?have unique hollow tubular structure and light weight,high conductivity,high mechanical strength and other excellent properties,but it possess low capacity as anode materials for lithium ion batteries.Therefore,in this paper the MWNTs were choosed as skeleton to composite with transition metal oxides.The composites with a reinforced concrete structure possessed excellent electrochemical performance.The MWNTs composites were used as support framework to make full use of the high conductivity and support to improve the cyclic stability of transition metal oxides.The ternary of bimetallic oxide-MWNTs had been prepared,using the synergistic action of different metal oxides further improving.The main contents of this paper are as follows:?1?Fe₂O₃-MWNTs composites were successfully synthesized by sol-gel calcination method.The morphology,structure and composition of the composites were characterized by SEM,TEM,XRD,XPS and BET.CV and EIS were used to characterize the electrochemical reaction mechanism and conductivity of the composites.The test results showed that when the molar ratio of ferric nitrate and citric acid was 1:1,the Fe₂O₃-MWNTs composite exhibited the best electrochemical cycling performance.Its reversible specific capacity remained at896.3 m Ah g-1after 100 cycles at a current density of 100 m A g-1.The reversible specific capacities of the Fe₂O₃-MWNTs composites were 864,842,728,631,551 and 870 m Ah g-1respectively,after 10 cycles at current densities of 100,200,500,1000,2000 and 100 m A g-1.The coulombic efficiency for the 1st cycle reached 75.5%.?2?Heterostructured Fe₂O₃-Mn₃O₄-MWNTs composites were successfully synthesized by the sol-gel calcination route.The morphology,structure and composition of the composites were characterized by SEM,TEM,XRD,XPS and BET.CV and EIS were used to characterize the electrochemical reaction mechanism and conductivity of the composites.The cyclic test results showed that when the molar ratio of ferric nitrate and manganese acetate was 3:2,the Fe₂O₃-Mn₃O₄-MWNTs composites exhibited the best electrochemical cycling performance: The reversible capacity still possessed 956 m Ah g-1 when cycled for 100 cycles at a current density of 100 m A g-1 with no significant capacity decay,its reversible specific capacity could also be maintained at 475 m Ah g-1when cycled for 300 cycles at a current density of 500 m A g-1.The reversible specific capacities of the Fe₂O₃-Mn₃O₄-MWNTs composites were 951,810,743,632,470,303 and 944 m Ah g-1 after 10 cycles respectively at current densities of 100,200,500,1000,2000 and 100 m A g-1.?3?The ternary Co Fe₂O₄-MWNTs composites were successfully synthesized by a similar synthetic route.The morphology,structure and composition of the composites were characterized by SEM,TEM,XRD,XPS and BET.CV and EIS were used to characterize the electrochemical reaction mechanism and conductivity of the composites.The cyclic test results showed that Co Fe₂O₄-MWNTs composites exhibited excellent large-rate cycling stability as anode material for lithium-ion batteries.Co Fe₂O₄-MWNTs as anode material for lithium-ion batteries was cycled for 1000 cycles at a current density of 1000 m A g-1 with no significant attenuation and the reversible specific capacity remained at 371 m Ah g-1.The reversible specific capacities of Co Fe₂O₄-MWNTs composites was 934,899,798,722,644,581 and 1014 m Ah g-1 respectively after 10 cycles respectively at current densities of 100,200,500,1000,2000,3000 and 100 m A g-1.In summary,this paper designed single metal iron oxide/MWNTs composites,bimetallic iron manganese heterostructured oxide/MWNTs composites and ternary bimetallic Cobalt ferrite/MWNTs composites synthesized by sol-gel calcination,all possessed better rateperformance and cycle stability.The excellent electrochemical properties of the materials could be attributed to the following two aspects:?1?Based on the structural analysis of the material,MWNTs-based reinforced-concrete-structure enhanced the conductivity of the material and accelerated the ion transport rate,the mechanical strength of the material was greatly strengthening.?2?Based on the composition analysis of materials,the synergistic effect of different metal oxides alleviated the problem of material shedding caused by huge volume expansion during charging and discharging,and enhanced the cycling stability of materials.