Synthesis And Modification Of Lithiun Ion Battery Anode Material MFe₂O₄

The development of modern society relies on finite fossil fuels and nonrenewable resources very much,which causes a series of serious environmental problems such as the greenhouse effect and pollution.Hence,it is urgent to find a sustainable way to meet our rigorous demand.Lithium-ion batteries?LIBs?can maintain long-term performance and high specific capacity,which have attracted significant attention in recent years as the most popular energy storage equipment.At present,LIBs have powered increasing applications from microchips to cars.However,existing LIBs cannot meet the desired demand for most products in the future.Graphite,the most commonly used commercial available anode material,has low volumetric specific capacity and potential safety issues.All of these problems stimulate researchers to look for novel anode materials with high energy density,low cost and longevity.MFe₂O₄ are a series of promising candidates for anode materials,owing to their high theoretical specific capacity,environment-friendliness.Among them,ZnFe₂O₄ and CoFe₂O₄ have attracted many researchers' attention due to its low cost and high theoretical capacity.Frustratingly,it is electrochemical inactive in bulk owing to its intrinsically poor electrical conductivity and large volume change during the charge/discharge process.In order to improve their performance,there are some explorations in this work.1.At first,the development and works of lithium-ion battery were introduced.Then the current situation and trend of every key compositions were elaborated.More important,all kinds of anodes matrials were analyzed in detail.Inaddation,the main synthetic and improved methods of MFe₂O₄ were analyzed.2.Micro-nano structure MFe₂O₄?M=Zn/Co?materials were synthesized directly by hydrothermal method.The structural and morphological properties were investigated by means of X-ray diffraction?XRD?and transmission electron microscopy?TEM?.The electrochemical performance of MFe₂O₄?M = Zn/Co?was examined by galvanostatic charge-discharge test and electrochemical AC impedance technique.Hollow Sphere CoFe₂O₄ and ZnFe₂O₄ have a reversible capacity of 1180 and 650 mA h g^-1 after 50 cycles,which are higher than that of solid sphere materials.At the same time,the formation mechanism of different morphology has been studied.3.Porous hierarchical and nitrogen-doped carbon coated ZnFe₂O₄?ZnFe₂O₄@NC?was obtained by combustion method and unique carbon coating technology.Gum Arabic was firstly introduced in the carbon coating process as an additive,which played an important role to control the uniformity of carbon coating layer.The nitrogen-doped carbon layer was obtained through the pyrolysis of glycine.The galvanostatic charge/discharge cycling was used to test the electrochemical performance of ZnFe₂O₄@NC and pure ZnFe₂O₄.The sub-micro size ZnFe₂O₄@NC with unique porous structure showed an excellent electrochemical performance as an anode material,which was higher than that of pure ZnFe₂O₄.ZnFe₂O₄@NC could maintain the specific discharge capacity of 1477 mAh g^-1 at 0.1 A g^-1 after 100 cycles and 705 mAh g^-1 at 1 A g^-1 after 1000 cycles,respectively.3.ZnFe₂O₄/C with a unique compound structure was in-situ synthesized using glycine as complexing agent and carbon source via a facile one-step route.ZnFe₂O₄ nanoparticles?less than 100 nm?are aggregated with carbon to form larger particles which are embedded in carbon matrix.ZnFe₂O₄/C shows specific capacity of 2055 mA h g^-1 at 1000 mA g^-1 and a capacity retention of 54% with the current density increased from 100 mA g^-1 to 5000 mA g^-1.The excellent performance is derived from the unique compound structure which can largely accommodate the mechanical stresses caused by the volume change of ZnFe₂O₄ during charge/discharge process,hence maintain their integrity and provide excellent properties.As well,the in-situ generated carbon not only facilitates the electronic conduction,but also inhibits the aggregation of ZnFe₂O₄ nanoparticles.This facile fabrication method is also effective for synthesizing other materials,such as CoFe₂O₄/C.