Controlled Synthesis And Lithium Storage Performance Of Schiff-base Polymers And Core-shell Nanostructured Composites With Carbon Nanotubes

At present,lithium-ion batteries are widely used in life,ranging from electronic cigarettes and mobile phones to electric vehicles and aerospace fields.Most of the electrode materials of commercial lithium-ion batteries are inorganic materials,these inorganic materials are non-renewable resources,and the mining process inevitably brings a series of environmental problems.At the same time,the leakage of these inorganic substances will cause serious security issues,which brings great troubles to the recycling and reuse of lithium-ion batteries.In contrast,green and renewable organic materials,with the advantages of adjustable structure,high theoretical capacity,and no environmental problems,are a kind of suitable electrode materials.However,organic electrode materials also have many defects,such as poor conductivity and solubility,which greatly limit the commercial application of organic electrode materials.Schiff base are usually formed by the condensation of amine and active carbonyl,mainly composed of C,H,O,N and other elements.The Schiff base have the advantages of simple synthesis method and no pollutive by-products(H2O).In addition,the characteristic group of C=N have low redox potential,are ideal electrode material.Based on the above research background,the main purpose of this work is to explore the lithium storage performance of Schiff base electrode materials.In this article,we mainly improve the electrochemical performance of Schiff bases by adjusting polymer segments and introducing carbon nanotubes.The specific research are as follows:(1)Based on the problems of capacity attenuation and poor rate performance of Schiff base electrode materials,most of the current researchers improve the performance through composite or carbonization,and seldom focus on the structural regulation of the polymer itself.In view of the above situation,the structural adjustment of the segment is used to improve the electrochemical properties of the materials.Here,six kinds of flexible polymer(P1,P2,P3,P4,P5,P6)with different chain sections are obtained by the reaction of p-benzaldehyde with phenylenediamine,ethylenediamine,butanediamine,hexanediamine,octanediamine and decanediamine respectively,and the electrochemical tests were carried out.It is found that P4 exhibits good electrochemical stability and rate performance.The capacity retention rate of P4 is 78.0% after 60 cycles at the current density of 0.1 A/g,and 77.1 m Ah/g at the current density of 5 A/g.In addition,P4 can reach 250 m Ah/g after 1000 cycles at a current density of 0.5 A/g.(2)Based on the work in the previous chapter,we find that P1 has the highest initial capacity,but there is a very serious capacity decay.In view of this situation,the carbon nanotubes compound(P1@CNTs)are obtained by in-situ complex method to improve the electrochemical performance of the electrode materials.Three kinds of composites with different morphologies are obtained by changing the solvents,and their electrochemical properties are also studied.The coating structure complex P1@CNTs(Et OH)are obtained by choosing the ethanol as the solvent.Imperfect “Nanohybrid shish-kebab”(NHSK)structure complex P1@CNTs(Ph Me)are obtained when toluene are selecte as the solvent.The perfect NHSK structure complex P1@CNTs(DMSO)are obtained when the solvent are dimethyl sulphoxide.The electrochemical test shows that P1@CNTs(DMSO)have the best electrochemical performance,with the capacity of 672.2 m Ah/g after 240 cycles at the current density of 0.1 A/g,and 336.9 m Ah/g after 500 cycles at the current density of 0.5 A/g.(3)The previous chapter explore the influence of the solvents on the NHSK structure,and researche of the superior electrochemical performance of the NHSK structure compound.Based on the above work,we explore the influence of carbon tube content and polymer segment flexibility on the NHSK structure.Here,NHSK structure compoisite P2@CNTs(DMSO)and P3@CNTs(DMSO)are obtained by in-situ composite,respectively.Electrochemical performance test results indicate that P1@CNTs(DMSO)with the highest benzene ring content in the polymer show the best electrochemical performance.(4)Unlike previous studies on linear Schiff bases and their complexes,we study the synthesis and electrochemical properties of hyperbranched conjugated Schiff bases in this chapter.2,4,6-tris(4-aminophenyl)-1,3,5-triazine,1,3,5-tris(4-aminophenyl)benzene are used to react with p-benzaldehyde to obtain the Schiff base polymers P8 and P9,respectively.Furthermore,P8@CNTs and P9@CNTs are also obtained by in-situ composite.The reversible capacity of P8@CNTs is 616.8 m Ah/g after 500 cycles at a current density of 0.5 A/g,suggesting an excellent cyclability.