Synthesis Of O-Diamine Based Covalent Organic Frameworks And Their Applications As Anode Materials For Lithium Ion Batteries

Along with the green and sustainable development,there is an ever-increasing demand for high-performance lithium ion batteries with high energy and power density,good stability and environmental compatibility for electronic devices and electric vehicles.In addition,it has also become the focus of attention to synthesize the electrode materials for the next generation lithium ion batteries that possessing the balance between high electrochemical performance and low in cost.Covalent organic frameworks materials are connected by the strong covalent bonds with the advantages such like designable structure,high specific surface area and more.Up till now,they have been used as applications in many fields.Among them,o-diamine based covalent organic frameworks contain nitrogen-rich conjugated structure as redox sites.It could make highly concerned in the electrochemical field.In this paper,new o-diamine based covalent organic frameworks are synthesized and applied as anode materials for lithium ion batteries.From the perspective of molecular design level,these novel covalent organic framework materials are designed and synthesized.Besides,from the perspective of material modification level,we also improve them and make the high performance anode materials for lithium ion batteries.The first chapter introduces the design and synthesis methods of covalent organic framework materials.The o-diamine based covalent organic frameworks and their advantages are also introduced.At last,the development of covalent organic frameworks as electrodes for lithium ion batteries are introduced as well.In the second chapter,novel benzoquinone and pyrazine based double-site conjugated microporous polymer named Ben-CMP is designed and synthesized through o-diamine reactant.As comparison,non-benzoquinone sites phenazine based conjugated microporous polymer named Phe-CMP is also synthesized.The successful preparation of the two CMPs materials is proved by a variety of characterization methods.As anode materials for lithium ion batteries,Ben-CMP shows higher specific capacity,excellent rate performance and good cycle stability.At a current density of 1 A g^-1,after 500 cycles the reversible specific capacity of Ben-CMP is more than 493.7 m Ah g^-1.But the Phe-CMP material shows only a reversible specific capacity of 401.6 m Ah g^-1 under the same conditions.These two CMPs have the similar framework structures.From the perspective of molecular design,these CMPs use the phenazine groups as the linker and Ben-CMP contains the benzoquinone groups.Therefore,Ben-CMP has a benzoquinone pyrazine double sites.The introduction of more heteroatoms could provide more lithium storage sites when it is used as lithium ion batteries anode materials which exhibiting higher reversible specific capacities.These could provide new ideas for new organic porous materials as anode materials for lithium ion batteries.In the third chapter,a conjugated microporous polymer named NGA-CMP with fused-ring aromatic and nitrogen-rich site is synthesized through the condensation of o-diamine and o-diketone.A variety of experiments show that the material is successfully synthesized and there are unreacted edging groups as well.The NGA-CMP-400 without unreacted edging groups is prepared and used as anode materials for lithium ion batteries for the first time.It shows a higher specific capacity and excellent rate performance.NGA-CMP-400 material showing a reversible specific capacity of 701.2 m Ah g^-1can still be maintained at a testing current density of 1 A g^-1 after 500 cycles.In addition,the non-heat treated NGA-CMP,the incompletely NGA-CMP-300 and over the appropriate temperature NGA-CMP-600materials are tested under the same conditions.The results shows that they are not as good as the NGA-CMP-400 based anode materials.This kind of synthetic method through reasonable design and modification of materials provides important guiding significance for the synthesis and development of electrode materials in the future.In the fourth chapter,from the perspective of molecular design,pyromellitic acid is used as a substitute reactant to condense with o-diamine to synthesize the undiscovered MPBI in the poly-benzimidazole family.Various test methods have been used to prove that the catalytic system of polyphosphoric acid can successfully prepare MPBI materials with high crystallinity.In addition,the remaining unreacted edging-groups are removed by heat treatment.And it is used as anode material for lithium ion batteries.It showed a high specific capacity,good cycle performance and rate performance.Among them,MPBI-550 under a current density of 1 A g^-1after 500 cycles could still have an ultra-high reversible specific capacity of 740.3 m Ah g^-1.This experiment is the very first time that PBIs materials have been applied to electrode materials for lithium ion batteries.The preparation strategy of this new type of anode material provides a new demonstration for the development of functional materials and can be used as a favorable candidate material for the next generation of lithium ion battery anode materials.The last chapter is a summary and outlook of these three research systems in this paper.