Synthesis And Modification Of Transition Metal Oxide Iron-based Anode Materials

In recent years,iron-based transition metal oxides have been used as promising anode materials for lithium-ion batteries.With their low cost,non-toxicity,natural abundance,relatively high theoretical capacity(¹000mAh g^-1),and easy Large-scale manufacturing has attracted much attention.However,volume expansion during charging and discharging of iron-based transition metal oxides leads to poor cycle stability and poor conductivity,resulting in poor rate performance.In this dissertation,core-shell Fe₂O₃@TiO₂,porous Fe₂O₃/N-GO composites and core-shell NiFe₂O₄@SiO₂ were synthesized by clever design to improve the electrochemical performance of iron-based transition metal oxides.The research contents are summarized as follows:（1）Fe₂O₃ nanoparticles synthesized by co-precipitation method,and Fe₂O₃@TiO₂ core-shell nano-composites synthesized by hydrolysis of tetrabuty1 titanate.When used as lithium ion battery cathode material for charge and discharge test,at a current density of 0.1C,the reversible specific capacities of samples 1,2,3,and 4 after 100 cycles were maintained at292.6,497.3,427.5,and 352.3 mAh g^-1.Fe₂O₃@TiO₂ core-shell structures with different TiO₂ coatings all show better cycle stability and better rate performance.The improvement of electrochemical performance is attributed to the synergistic effect between Fe₂O₃ core and covering TiO₂ and the fact that TiO₂ can effectively alleviate the volume expansion of Fe₂O₃core.（2）A simple one-step hydrothermal method was used to prepare porous Fe₂O₃/N-GO composite with good crystallinity.Used as a negative electrode material for lithium-ion batteries,exhibits excellent lithium storage performance.At 0.1 C current density,after 100cycles,the specific capacity of Fe₂O₃/N-GO composite electrode can be stabilized at1080mAh g^-1,while the reversible capacity of pure Fe₂O₃ decreases to 805 mAh g^-1,and even after 250 cycles under the current density of 1 C,the specific capacity can still be maintained at 905.2 mAh g^-1.The excellent electrochemical performance is mainly attributed to the existence of the porous structure of Fe₂O₃.The N-GO of the surface layer improves the conductivity and alleviates the volume effect in the charging and discharging process of Fe₂O₃.（3）Through sol-gel self-propagating combustion method of spinel is octahedron NiFe₂O₄,and using the hydrolysis of ethyl orthosilicate（TEOS）cladding forming a core-shell structure NiFe₂O₄@SiO₂,when used in lithium ion battery anode materials showed excellent electrochemical performance,under the current density of 0.1 C,the specific capacity of NiFe₂O₄@SiO₂ electrode after 100 cycles is 1224.6 mAh g^-1,which is significantly higher than the reversible capacity of pure NiFe₂O₄ of 690.7 mAh g^-1.The improvement of cycle stability,rate performance and specific capacity can be attributed to the fact that SiO₂,as a coating material,provides a high additional capacity while forming an inert Li₄SiO₄ layer during charging and discharging,which can effectively avoid the direct contact between highly electrochemical active NiFe₂O₄ and the electrolyte and alleviate the volume expansion of NiFe₂O₄.