Synthesis And Electrochemical Properties Of Carbon Composite Iron-based Anode Material In Lithium-ion Batteries

With the development of industrialization,the countries of the world are faced with serious energy crisis and environmental deterioration,which makes people realize the limitation of traditional energy.While improving the utilization of traditional energy,they begin to study new materials with low price,abundant energy storage and environmental-friendly.Lithium-ion battery(LIBs)has become one of the hot spots of many researchers,because of its advantages of less self-discharge,long cycle life,high energy density and environmental friendliness.Graphite,which have been commercialized and widely used as anode materials for LIBs,has been limited due to low theoretical capacity and poor safety performance.How to select high performance lithium-ion battery anode materials to alleviate the energy crisis has become a topic of great concern.Transition-metal oxides and selenides with much higher theoretical specific capacity and suitable voltage platform than graphite,are ideal anode materials for LIBs.However,their poor structural stability and low intrinsic conductivity limit the practical production and application.Aiming at these defects,through some simple synthetic methods,a batch of anode electrode materials with high capacity and strong cycling performance were synthesized by several organic precursors.The main contents of this thesis can be summarized as follows:1.The organic precursor of ferrous tartrate was synthesized by hydrothermal method,then the Fe₃O₄@C composite was obtained by controlling the temperature of reaction and the time of annealing.The results of electrochemical performance test showed that the material showed good cyclic stability at the current density of 0.2 A·g^-1.The synthesis operation of the material is simple and can achieve expanded production.What's more,the synthetic method of the material is simple and can be expanded production.2.The tetragonal Fe₂O₃nanoparticles of nitrogen-doped carbon were obtained by one-step pyrolysis of the commercial ethylenediaminetetraacetic acid ferric sodium salt(C₁₀H₁₂Fe N₂Na O₈).We have studied the phase structure and lithium storage performance.The C₁₀H₁₂Fe N₂Na O₈can act as both iron source,carbon source,nitrogen source and oxygen source.The analysis of phase structure showed that no other impurities exist in the synthesized sample.The Fe₂O₃@C-N can reach a high specific capacity of 1060 m Ah·g^-1after cycling 210 cycles at a current density of 0.2 A·g^-1.The method of one-step pyrolysis to obtain nitrogen-doped carbon compounds provides a way for the synthesis of other materials.3.Iron acetylacetone,as an organic precursor,can provide carbon,oxygen and iron sources.The Fe₂O₃@C was obtained by one-step pyrolysis of the organic precursor,while Fe Se₂@C composite was collected through pyrolysis process of iron acetylacetone after mixing with selenium powder.And the application in the anode material of lithium-ion battery has been studied.Comparing Fe₂O₃@C with pure Fe₂O₃,Fe₂O₃@C exhibits excellent cycling stability and high reversible capacity.Capacity reaches to 733 m Ah·g^-1at the current density of 0.2 A·g^-1after 210 cycles.And at a high current density of 0.5 A·g^-1,although the capacity has declined,but reversible capacity can also be maintained to nearly600 m Ah·g^-1after 360 cycles.The Fe Se₂@C of the rod-like structure can also achieve a high reversible capacity of 852 m Ah·g^-1at the low current density of 0.1 A·g^-1.Carbon coated composites were obtained by direct pyrolysis of commercial organic metal salts.The synthetic method is simple,and no other impurities.The method can be applied to other anode materials in lithium-ion battery.