Preparation And Electrochemical Properties Of Perylene Imide Organic Electrode Materials

Sodium ion battery is a new type of ion battery which is expected and concerned.Sodium resource in the earth’s crust is richer than lithium,and the reduction potential is similar to lithium,which is an excellent alternative energy storage system with great development prospects.However,the radius of sodium ion is large,and the structure will produce irreversible deformation when it is embedded and removed in the electrode,resulting in poor electrochemical performance of electrode materials.Therefore,it is necessary to select electrode materials with high capacity,long service life and tolerance to Na⁺de/intercalation.Perylene imide conjugated carbonyl compounds have good structural flexibility,which can tolerate the de/intercalation of sodium ions with large particle the advantages of fast electron transfer,high structural schedulability and high theoretical specific capacity due to the existence of conjugated systems.They are ideal storage electrode materials for sodium ion batteries.However,the shortcomings of small molecule carbonyl compounds that are easy to dissolve in the electrolyte will lead to the rapid attenuation of battery capacity.In order to overcome this shortcoming,several perylene imide compounds were successfully synthesized in this paper.By changing the conjugation degree of materials,the position of groups,the number of groups and the ratio of composite conductive agent,the effects of compound structure on the battery and the effect of conductive agent on the battery performance were studied by charging and discharging,rate cycling and cyclic voltammetry..The specific research contents and conclusions are as follows:（1）By simple condensation reaction,three polyimide compounds B-PI,N-PI and P-PI with increasing degree of conjugation were synthesized by 2,6-diaminoanthraquinone and pyromellitic dianhydride,naphthalene dianhydride and perylene dianhydride,respectively,as electrode materials.By adjusting the proportion of conductive agent in B-PI and N-PI,four different proportions of electrodes were prepared,and their electrochemical performance was tested.It was found that the composite conductive agent(V_{active material}:V_KB:V_AB:V_PVDF=6:0.5:2:1.5 and 6:2:0.5:1.5)was beneficial to enhance the electrochemical performance of the material.Among them,the V_{active material}:V_KB:V_AB:V_PVDF=6:2:0.5:1.5 is more conducive to improving the electrochemical performance to a certain extent.Under this ratio,B-PI retains 110 mAh/g after 10 cycles at 20 mA/g,and N-PI retains 67.2 mAh/g after 10cycles at 100 mA/g.The P-PI sample has good cycle life and rate performance,and still has 210 mAh/g after 120 cycles at 60 mA/g.In the rate performance test,the specific capacities reached 132.2,120.7,102.4,93.9,88.8,76.3,55.7,97.0,106.5 and118.9 mAh/g,respectively,after five consecutive cycles at the current densities of 10,20,30,50,100,200,30,20 and 10 mA/g,indicating that the increase of conjugation degree can increase the electrochemical performance of the material to a certain extent.The discharge capacity of B-PI and N-PI samples was not ideal,the cycle time was short,and the reversibility was poor.Combined with cyclic voltammetry and scanning electron microscopy analysis,the main reasons for the poor electrochemical performance of B-PI and N-PI samples were related to the agglomeration of the material itself and the irreversible deformation of the structure in the electrode reaction process,which would lead to the failure to fully expose the active sites and the gradual decrease of the reversible active sites.（2）Four imine compounds were synthesized by perylenetetracarboxylic dianhydride with p-aminobenzoic acid,m-aminobenzoic acid,5-amino-m-phthalic acid and 2-amino-p-phthalic acid,respectively.The four imine carboxylates,PABA/Na-PI,MABA/Na-PI,AMPA/Na-PI and APPA/Na-PI,were synthesized by neutralization reaction with Na OH acid and base,respectively.The tests showed that the four sodium salts had excellent rate and cycle performance at low current density.After 100 cycles of 20 mA/g cycle at the ratio of V_{active material}:V_KB:V_AB:V_PVDF=6:0.5:2:1.5,the specific capacities were 78.6,74.8,80.4 and 97.6 mAh/g,respectively.By comparison,the electrochemical properties of AMPA/Na-PI and APPA/Na-PI were slightly better than those of PABA/Na-PI and MABA/Na-PI.The results show that increasing the number of groups can improve the electrochemical performance of the battery to a certain extent.（3）Through the comprehensive analysis of the electrochemical performance test results of B-PI、N-PI、P-PI,PABA Na-PI,MABA/Na-PI,AMPA/Na-PI and APPA/Na-PI,it is shown that the V_{active material}:V_KB:V_AB:V_PVDF=6:2:0.5:1.5 is good to improve the discharge capacity of the material.