Synthesis And Properties Of Novel Anode Materials For High Capacity Li-Ion Batteries

In recent years,with the intensification of energy consumption and environmental pollution,the development of sustainable energy and electrochemical energy storage technology has become the focus of people's attention.Among many energy storage devices,lithium-ion batteries have currently dominated the portable electronic products market and expanded the territory into electric vehicles in nearly 30 years due to their high operating voltage,large specific energy,good performance in harsh temperature,safety and long working life.However,the constant upgrading of electronic device and the popularity of electric vehicles have put high demands on the performance of lithium-ion batteries,especially in terms of energy density.The traditional graphite anode material hinders the further improvement of the energy density for lithium ion batteries owing to the limited theoretical capacity.In terms of inorganic materials,the conversion and alloying anode with high theoretical capacity attract much attention,but serious volume expansion and poor cyclic performance during charge-discharge process hinder their development.In terms of organic materials,conjugated carbonyl compounds have rapid reaction kinetics and high theoretical capacity.Unfortunately,organic materials are readily soluble in the polar electrolytes,resulting in substantial loss of active materials.In view of the issues of different materials,this paper designs and optimizes the material structure to prepare the novel anode materials with high capacity and long cycle for lithium ion battery.The specific contents mainly include the following parts:First,the conversion materials have attracted much attention in the new anode research.As a conversion anode material,Fe₃O₄has the advantages of high theoretical capacity,abundant resources and environmental friendliness.However,the volume expansion and poor conductivity of Fe₃O₄-based materials restrict the development and commercial application.In order to solve the pivotal issues,cornlike N-doped carbon coated hollow Fe₃O₄ materials?OH-Fe₃O₄@NC?are prepared for the first time by hydrothermal synthesis and magnetic self-assembly.This unique structure has several beneficial characteristics:?1?the hollow structure could alleviate the volume expansion during cycling;?2?the nitrogen-doped carbon layer could fastly transfer electrons,reduce the polarization and improve rate capability;?3?the successive carbon shell could strengthen the structural stability and prevent the nanoparticle from collapsing over long cycles.Benefiting from such a unique structure,the cornlike structure delivers an excellent rate capacity of 725,551 and 361 mAhg^-1 at 1,4,10 A g^-1,and a stable capacity retention of 1316 mAhg^-1 at 0.1 A g^-1 after 50 cycles for lithium ion storage.Subsequently,the volume change during electrochemical process is discussed in detail through ex-situ SEM and HRTEM,which shows that the unique structure design can significantly alleviate volume expansion.Second,quinone compounds contain multiple redox-active sites,and undergo multi-electron reversible reactions in the electrochemical process,which endow the electrode with high specific capacity.Tetrahydroxybenzoquinone,a commonly used quinone compound,has attracted much attention from researchers.However,quinone compounds inclusive of tetrahydroxybenzoquinone inevitably suffer the following difficult problems:?1?high solubility in organic electrolytes,resulting in substantial loss of active materials in the circulation;?2?the poor electrical conductivity seriously reduces the rate capability of the material.To solve these problems,we firstly synthesize tetrahydroxybenzoquinone grafted graphene material?THBQ-GO?and verify the existence of the graft process by different analytical techniques including FT-IR,Raman and XPS.The THBQ-GO material has several beneficial characteristics:?1?the existence of ester linkage would effectively inhibit the dissolution of organic active materials in the polar electrolytes;?2?the graphene sheets would serve as a continuous electron transport pathway to improve the overall conductivity of the material;?3?we found that the ester group attached to graphene sheets make valuable contribution to the electrochemical capacity.When applied to the anode of lithium ion battery,the material delivers an ultrahigh capacity,excellent cycling stability and rate capability.The capacity of the electrode material is as high as 1075.9mAhg^-1 at 0.05 A g^-1,and retained 88.9%over 100 cycles.When the current density is increased to 1,4 and 10 A g^-1,the THBQ-GO electrode can still exhibit the high capacity of525.9,284.7 and 163.7 mAhg^-1.Then,electrochemical reaction mechanism for THBQ-GO electrode are discussed in detail through ex-situ FT-IR and XPS analyses.Third,organic carbonyl compounds have attracted wide attention due to their high capacity,rapid reaction kinetics,abundant sources and environmental friendliness.Inspired by the second part of the paper,we still adopte grafting method to inhibit the dissolution and improve conductivity of carbonyl compounds.The chelidamic acid grafted graphene material?CA-GO?is synthesized for the first time,and the graft process is confirmed by different analytical techniques including FT-IR and Raman.As the anode of lithium ion battery,this material has the following advantages:?1?highly conductive graphene improves the electron and ion transport capability;?2?the covalent linkage on the graphene sheets can effectively prevent the dissolution of the active material in organic electrolyte.Benefitting from the advantages mentioned above,this electrode material exhibits excellent rate capability and stable cycling performance.It delivers a high capacity of 1589.2 mAhg^-1 at 0.05 A g^-1 and the capacity retention of 94.2%after 50 cycles.When the current density is increased to 1,2,4 and 10 A g^-1,the CA-GO electrode can still exhibit the high capacity of 794.7,661.9,490.4 and 268.3 mAhg^-1.Fourth,among many anode materials,Zn₂Ge O₄ materials with high theoretical capacity,low working voltage and environmental friendliness,are considered as the promising candidate for high-capacity anode material.We prepare Zn₂Ge O₄-C ultrasmall size nanoparticle composites by hydrothermal synthesis with particle size of about 20 nm and good dispersion.In this structure,the small particle size can shorten the diffusion distance of lithium ions and electrons,and alleviate the volume expansion during cycling.In addition,the amorphous carbon in this material improves the overall conductivity.When applied to the anode of lithium ion battery,Zn₂Ge O₄-C material exhibits excellent reversible capacity and cyclic stability.At the current density of 0.1 A g^-1,it delivers a high capacity of 1098.6 mAhg^-1 after 30 cycles and the capacity retention of 91.4%.Furthermore,under the large current density of 1.0 A g^-1,it can still exhibit the high lithium storage capacity of 340.9 mAhg^-1 after 800 cycles.