Preparation And Electrochemical Performance Of Several Noval Anode Materials For Lithium-ion Battery

Lithium-ion batteries possess advantages in high energy density,long cycle life,and environmental friendliness,which make them the most mainstream power source at present.At present,electrode materials of li-ion battery have attracted significant attentions because the energy density of commercially available Li Co O₂/graphite-based lithium-ion batteries is only 150 Wh/kg,which is difficult to meet the increasing demands of society.Transition metal oxides(Fe₂O₃,Fe₃O₄,MoO₂,etc.)have a theoretical capacity of 1000mAh/g,which is much higher than that of commercial graphite anode materials(372 mAh/g),making them promising as anode material.High-energy-density metal oxides have advantages in electric vehicle endurance.However,the poor conductivity of metal oxides and large volume changes during charge and discharge are the main obstacles for their practical application in lithium-ion batteries.The introduction of the base material to form composites can effectively alleviate the negative effect of the transition metal oxides as anode materials.MXenes,a family of graphene-like two-dimensional materials,show some unique properties,such as high metal conductivity and chemical compatibility,making them promising as substrate to effectively improve the defects of transition metal oxides as negative electrode in lithium-ion batteries.This thesis focuses on the research of Ti based MXene(Ti₃C₂T_x)as lithium-ion battery anodes.Firstly,The electrochemical properties of MXene prepared by two different methods were studied,Then,two kinds of lithium ion battery anode materials were designed and prepared by using heteroatom-doped MXene as the substrate and compounding with transition metal oxides.The electrochemical tests confirmed that these materials have excellent electrochemical performance.The main tasks are as follows:1)Two MXene materials,H-Ti₃C₂T_x and L-Ti₃C₂T_x,were successfully prepared by etching Ti₃AlC₂ of MAX phase ceramics by HF and HCl/Li F.Through experiments and various characterization tests,it was found that H-Ti₃C₂T_x had better chemical reactivity and L-Ti₃C₂T_x had better conductivity.After electrochemical analysis of the two materials,it was found that H-Ti₃C₂T_x exhibited more excellent constant current long-cycle performance(H-Ti₃C₂T_x maintains 140.0 mAh/g after 100 cycles at a current strength of 1 A/g,with a retention rate of 105%,and L-Ti₃C₂T_x maintains 113.6 mAh/g,with a retention rate of 88%);in the part of rate performance,L-Ti₃C₂T_x shows better performance.2)In this experiment,Ti₃C₂T_x was doped with nitrogen,and then the N-Ti₃C₂/Fe₂O₃@C nanocomposite was prepared by combining the high conductivity of nitrogen-doped MXene(N-Ti₃C₂)and the high lithium ion storage capacity of iron oxide nanoparticles,so that the composite showed better performance than the individual component.When the material is used as the anode of lithium ion battery,it shows high reversible capacity,fast charging/discharging capacity,excellent long cycle stability(after 400 cycles at 2 A/g current strength,it still maintains 549 mAh/g,with a retention rate of 126%)and good rate performance,which is very competitive in the application of lithium ion battery materials.3)In this experiment,N,P-Ti₃C₂/MoO₂@C nanocomposites were prepared by combining N-Ti₃C₂ and phosphomolybdic acid.Through this method,the materials are doped with N and P.The doping of double heteroatoms can not only exert the advantages of the two kinds of heteroatoms,but also cause the synergistic effect between them and further improve the material performance.The prepared material has the advantages of good rate performance,high capacity,and long cycle life(the capacity remains 374.9mAh/g after 240 cycles under a current strength of 1 A/g,with a retention rate of 116%),and has great potential as a lithium-ion battery material.