Synthesis And Electrochemical Performance Of Transition Metal Oxide And Nitride/Carbon Anode Materials

The application of lithium ion batteries in electric vehicles is an important part for solving the energy crisis.As a critical component of lithium ion battery,commercial graphene anode has low theoretical energy density and power density,hardly meeting the application requirements of electric vehicles.Transition metal oxides and nitrides show high energy density and power density and attract great interest from scientists,being considered as one of the best alternatives to replace graphite-based anode.However,as anode materials of lithium ion batteries,the transition metal oxides and nitrides have severe volume change during the charging and discharging process,which leads to the rapid decay of capacity.A large number of studies have shown that combining transition metal oxide or nitride nanoparticles with carbon to form composite can solve the above problems and achieve excellent electrochemical properties.Nevertheless,the synthesis procedures of transition metal oxide and nitride nanoparticles/carbon composites are generally complex,which seriously limit their development and application.Therefore,it is of great significance to develop and design simple methods to synthesize transition metal oxide and nitride nanoparticles/carbon composites and achieve excellent electrochemical performance.This thesis deeply analyzes the present research situation of transition metal oxide and nitride nanoparticles/carbon composite materials in our country and abroad.On this basis,a series of simple methods are smartly design to synthesize several transition metal oxide and nitride nanoparticles/carbon composite materials with special structure.After detailed electrochemical study for these materials,the main research achievements are obtained as follows:1.Using cheap and non-toxic NaCl as template,V₂O₃ nanoparticle/porous nitrogen doped 3D carbon nanosheet framework composite?V₂O₃/PNCNF?was prepared through simple freeze drying and calcination strategies.The characterization results showed that V₂O₃ nanoparticles are grown in the porous nitrogen doped 3D carbon nanosheet framework,and there is a strong chemical interaction between them.When used as anode material for lithium ion battery,V₂O₃/PNCNF achieves high reversible capacity,excellent cycling performance and rate performance.A high discharge capacity of 436 mA h g^-1 is retained at 500 mA g^-1 after 200 cycles.Even at2000 mA g^-1,a capacity of 344 mA h g^-1 is achieved.2.Utilizing the reaction between potassium permanganate and carbon,Mn₃O₄nanoparticle/hollow carbon nanofiber composite?HCF/Mn₃O₄?was synthesized in situ by simple stirring and low-temperature reduction.Measurement results showed that Mn₃O₄ nanoparticles with small size are grown on hollow carbon nanofiber,and there is a strong chemical interaction between them.These features can significantly alleviate the volume change during charging and discharging process,accelerate the transfer of electrons and lithium ions,and improve the reversible electrochemical reaction from MnO to Mn₃O₄.When HCF/Mn₃O₄ is used as anode material for lithium ion battery,it shows excellent electrochemical performance.The composite delivers a high discharge capacity of 835 mA h g^-1 after 100 cycles at 200 mA g^-1,and652 mA h g^-1 after 240 cycles at 1000 mA g^-1.Even at 2000 mA g^-1,it still shows a high capacity of 528 mA h g^-1.3.A fast and simple method of hydrothermally assisted strategy was developed to prepare Co_1.8V_1.2O₄ nanoparticle/reduced graphene oxide?CoVO/rGO?composite.TEM tests showed that ultrasmall Co_1.8V_1.2O₄ nanoparticles?with an average particle size of 8.4nm?are grown on reduced graphene oxide nanosheet.The XPS and XANES tests further show that there is a strong chemical interaction between the two components.These characteristics significantly improve the electron and lithium ion transfer and effectively alleviate the volume change in the charging and discharging process.When used as the anode material for lithium ion battery,CoVO/rGO achieves excellent rate performance and cycling performance.It delivered high discharge capacities of 789 mA h g^-1 at 100 mA g^-1 and 628 mA h g^-1 at 2000 mA g^-1.Even after 300 cycles at 2000 mA g^-1,it still shows a high capacity of 683 mA h g^-1.4.A novel Mn_2.1V_0.9O₄ nanoparticle/reduced graphene oxide composite?MnVO/rGO?was successfully prepared by a simple method.TEM tests showed that Mn_2.1V_0.9O₄ nanoparticles with small size?20-50 nm?are grown on reduced graphene oxide composite nanosheet.The XPS and XANES tests demonstrate that there is a strong chemical interaction between MnVO and rGO.These features significantly accelerate the transfer of electrons and lithium ions and effectively improve the volume change during charging and discharging.When MnVO/rGO is used as the anode material for lithium ion battery,it achieves high reversible capacity and excellent rate performance.A high discharge capacity of 981 mA h g^-1 is retained after80 cycles at 100 mA g^-1.Even at 2000 mA g^-1,a high capacity of 748 mA h g^-1 is achieved.5.Fe₄N/Fe₂O₃/Fe nanoparticle/porous nitrogen doped carbon nanosheet composite?Fe₄N/Fe₂O₃/Fe/PNCN?was synthesized by simple stirring and calcining under a non-ammonia atmosphere.The characterization results show that the Fe₄N/Fe₂O₃/Fe nanoparticles with small size are grown in the porous nitrogen doped carbon nanosheet,which effectively solves the problem of volume change during charging and discharging process.Fe₄N/Fe₂O₃/Fe/PNCN shows excellent electrochemical properties when it is used as the anode material for lithium ion battery.A high discharge capacity of 554 mA h g^-1 after 100 cycles at 100 mA g^-1 is obtained,and 389 mA h g^-1 after 300 cycles at 1000 mA g^-1 is retained.Even at 2000mA g^-1,a high capacity of 330 mA h g^-1 can be achieved.