Research On Design And Synthesis Of Organic Polymers And Their Electrochemical Performance

Lithium-ion batteries（LIBs）,as widely commercialized electrochemical energy storage device,have many advantages compared to other energy storage devices,such as high energy density,low self-discharge rate,long service life,and fast charging speed.Up to now,LIBs have been successfully applied in daily life fields such as portable electronic devices,new energy vehicles,and State Grid,and have achieved remarkable results.As an important component of LIBs,anode materials play an extremely important role in the performance of LIBs.The current research on LIBs anode materials by researchers mainly includes inorganic metallic and non-metallic materials such as embedded,alloy,and conversion types.But with the continuous improvement of people’s requirements for quality of life,as well as the increasing awareness of resource conservation and environmental protection,traditional inorganic negative electrode materials have gradually become difficult to meet the needs of society.Compared to inorganic materials,organic materials have advantages such as abundant raw materials,flexible design,and adjustable structure,and are currently receiving increasing attention and research from researchers.In the work of this paper,we designed and synthesized various organic polymer materials.Firstly,we used chemical analysis methods such as Fourier transform infrared spectroscopy（FT-IR）,elemental analysis（EA）,powder X-ray diffraction（PXRD）,thermogravimetric analysis（TGA）,field emission scanning electron microscopy（FESEM）,nitrogen adsorption desorption specific surface area testing（BET）,and nuclear magnetic resonance（NMR）to test the structure and characterize the morphology of these compounds;Then,these materials are made into electrode plates,with lithium metal plates as reference electrodes and counter electrodes,the electrode plates made are used as test electrodes,and they are assembled together into a coin cell for electrochemical testing.In electrochemical testing,we used a battery testing system to conduct constant current charging and discharging tests,rate charging and discharging tests,cycling stability tests under extremely high current density,and lithium storage performance tests in extreme high and low temperature environments on coin cells to understand their electrochemical performance;In addition,we also conducted cyclic voltammetry（CV）and alternating current impedance（EIS）tests on the assembled batteries using an electrochemical workstation to understand the electrochemical behavior and reaction kinetics of the synthesized materials.The specific work mainly includes the following five aspects:（1）Three conjugated Schiff base materials,GO-PDA,TTD-PDA,and DFBP-PDA,were successfully synthesized using glyoxal（GO）,1,4-phthalaldehyde（TTD）,4,4’-biphenyldicarboxaldehyde（DFBP）,and p-phenylenediamine（PDA）as raw materials based on the principle of aldimine condensation reaction.We characterized their structure and morphology using a series of chemical analysis methods such as FT-IR,PXRD,EA,and FESEM;TGA curves indicate that these three materials have high thermal stability.In the electrochemical test,the constant current charge-discharge data show that the three Schiff base materials have satisfactory lithium storage performance,which is shown as follows:when GO-PDA,TTD-PDA,DFBP-PDA are cycling 200times under the current density of 100 m A g^-1,the specific charging capacities are 445m Ah g^-1,772 m Ah g^-1,578 m Ah g^-1,respectively.When cycled 5,000 times at a super high current density of 5 A g^-1,their charging capacities can reach:206 m Ah g^-1,174m Ah g^-1and 222 m Ah g^-1.In addition,GO-PDA,TTD-PDA,and DFBP-PDA have specific capacities close to 1000 m Ah g^-1 or even higher when tested at a current density of 100 m A g^-1 in 50°C environment,exhibiting much higher specific capacity values than those under room temperature conditions.Furthermore they can also operate stably and have good reversible performance when operating in extreme low temperature environments of﹣15°C.Through these test results,it can be proven that these three Schiff base materials with conjugated structures have excellent electrochemical performance and are suitable as anode materials for LIBs.（2）In order to investigate the electrochemical activity of non-conjugated organic polymers as anode materials for LIBs,we synthesized three non-conjugated Schiff base materials,TTD-EDA,DFBP-EDA,and GA-PDA,by using 1,4-phthalaldehyde（TTD）,4,4’-biphenyldicarboxaldehyde（DFBP）,Glutaraldehyde（GA）,ethylenediamine（EDA）,and p-phenylenediamine（PDA）as raw materials through aldimine condensation reaction.In electrochemical testing,constant current charge discharge test data indicated that when cycled 200 times at a current density of 100 m A g^-1,the charging specific capacities of TTD-EDA,DFBP-EDA,and GA-PDA were 341 m Ah g^-1,735m Ah g^-1,and 473 m Ah g^-1,respectively.At the super current density of 5 A g^-1 cycling5,000 times,the charging specific capacities of TTD-EDA,DFBP-EDA,GA-PDA are318 m Ah g^-1,355 m Ah g^-1,227 m Ah g^-1.The impressive lithium storage performance is sufficient to demonstrate that these three non-conjugated Schiff bases clearly have electrochemical activity.In addition,when tested at a current density of 100 m A g^-1 in a high temperature environment of 50°C,the charging specific capacities of these three materials are approximately 700 m Ah g^-1.Similar to the test results of conjugated Schiff bases,these three non-conjugated Schiff base materials also exhibit better electrochemical performance at high temperatures than at room temperature.When tested in a low-temperature environment of﹣15°C,their charge transfer capabilities were not suppressed due to their non-conjugated structures.Instead,they exhibited reversible capacities exceeding 100 m Ah g^-1 and were able to operate stably.According to the above experimental data,it can be concluded that non-conjugated organic polymers can exhibit electrochemical activity when used as anode materials for LIBs.Moreover,in terms of Schiff base materials,non-conjugated Schiff bases are not inferior to conjugated Schiff bases in aspects of lithium storage performance,cycling stability,and working at extreme temperatures.（3）Two kinds of organic polymer polyimides（PD-PDA and ND-PDA）containing carbonyl structures were synthesized by using dianhydride[pyromellitic dianhydride（PD）,1,8,4,5-naphthalenetetracarboxylic dianhydride（ND）]and diamine[p-phenylenediamine（PDA）]as reaction monomers through condensation polymerization.BET and TGA test results show that they are materials with high thermal stability and small specific surface area.In electrochemical testing,PD-PDA and ND-PDA exhibited charging specific capacities of 534 m Ah g^-1 and 731 m Ah g^-1,respectively,after 200cycles at a current density of 100 m A g^-1.At a super high current density of 5 A g^-1 for5000 cycles,the two polyimides exhibited charging specific capacities of 218 m Ah g^-1and 130 m Ah g^-1,respectively.By comparison,ND-PDA has slightly higher lithium storage performance compared to PD-PDA when operating at low current density,while its lithium storage performance is weaker when operating at high current density.This may be due to the fact that the theoretical number of charges that ND-PDA with a naphthalene ring structure can accommodate is greater than that of PD-PDA with a benzene ring structure.However,the pore size and specific surface area of ND-PDA are smaller,which may result in kinetic inhibition of ion diffusion when working at high current densities,and the electrochemical performance of the material cannot be fully utilized.Therefore,under 5 A g^-1 conditions,the capacity of ND-PDA is actually lower than that of PD-PDA.Testing in extreme high and low temperature environments can also fully demonstrate this point.At 50°C,the capacity value and capacity retention ability of ND-PDA are much stronger than PD-PDA.However,at﹣15°C,the electrochemical performance of ND-PDA sharply decreases,and the reversible capacity is even worse than PD-PDA.（4）Covalent organic frameworks（COFs）are currently a very popular type of organic materials,which have a regular and ordered pore structure and a large specific surface area.In this part of the work,we prepared two types of COF materials:TAB-BTT and TAT-BTT,using 1,3,5-tris（4-aminophenyl）benzene（TAB）,2,4,6-tris（4-aminophenyl）-1,3,5-triazine（TAT）,and benzo[1,2-b:3,4-b’:5,6-b’’]trithiophene-2,5,8-tricarbaldehyde（BTT）as raw materials through ketoamine condensation reaction mechanism.In chemical analysis techniques,PXRD testing and simulation results indicate that they have a very regular crystal structure,BET testing results show that they have a large specific surface area,and TGA curves indicate that they have excellent thermal stability.The electrochemical test results show that TAB-BTT and TAT-BTT have excellent lithium storage capacity and rate performance,and can operate stably in extremely high current density and extreme temperature environments,demonstrating satisfactory electrochemical properties.It is worth mentioning that by comparing the CV,EIS,GCD and other test results of the two materials,it can be seen that the triazine ring containing N heteroatoms has a larger specific capacity and higher group activation efficiency compared to the benzene ring without heteroatoms.（5）By using organic synthesis methods,silicon atoms are integrated into the aromatic framework of the benzene ring to produce three-dimensional porous materials based on organic silicon.The specific experimental steps are as follows:using silicon tetrachloride,1,4-dibromobenzene,4,4’-dibromobiphenyl,and n-butyllithium as raw materials,two organosilicon based materials,polytetraphenylsilane（p TPS）and polytetrakis（4-phenylphenyl）silane（pTPPS）,were prepared using the principle of lithium halide exchange reaction.According to TGA and BET data,they have high thermal stability and a large specific surface area.In electrochemical performance testing,they demonstrate strong lithium storage capacity,excellent rate performance,good cycling stability,and operational ability in extremely high current density and extreme temperature environment.Moreover,by comparing the FESEM images before and after cycling,it can be seen that the organic silicon carbon materials p TPS and pTPPS we synthesized did not experience the serious volume expansion phenomenon similar to traditional inorganic silicon materials after repeated charging and discharging processes.This indicates that our designed experimental plan is successful.