Study On Polyimide Active Materials And Binders For Lithium Ion Batteries

Polyimide is a polymer material with excellent thermal stability and mechanical properties,which is widely used in storage materials,covalent organic skeleton,hydrogen storage and optical materials.The structural diversity,green sustainability and potential high specific capacity of this polymer make it effectively solve the problems of traditional inorganic active materials of lithium ion batteries in short of natural reserves and low theoretical capacity,as well as the problems existing in the application of commercial polyvinylidene fluoride binder in electrodes.Based on this,a variety of polyimide materials with different structures were prepared,and their effects on the electrochemical performance of lithium ion batteries as positive active materials and binders were discussed in detail.The main research contents are as follows:Firstly,DDS-PMDA,DABP-PMDA and ODA-PMDA powders were prepared by one-step method with 4,4’-diaminodiphenyl sulfone（DDS）,4,4’-diaminodiphenyl ketone（DABP）,4,4’-diaminodiphenyl ether（ODA）and pyromellitic dianhydride（PMDA）,respectively.The structure and thermal stability of these powders were studied.The effect of groups in polyimide powder on the morphology,structure and electrochemical performance of the electrodes was investigated.DDS-PMDA electrodes have smaller impedance values and polarization phenomena,the platforms of the electrodes are obvious during charging and discharging,and the capacity retention rate is 75.47%after 100 cycles at 40 mA g^-1 current density.DDS-PMDA electrodes have relatively good cycle stability and relatively excellent rate performance.Secondly,6FAPB-BTDA and 6FAPB/DDS-BTDA polymers were prepared by one-step method using 4,4’-diaminodiphenyl sulfone（DDS）,1,4-bis（4-amino-2-trifluoromethylphenoxy）benzene（6FAPB）and 3,3’,4,4’-benzophenone tetracarboxylic anhydride（BTDA）as monomers.The structure and thermal stability of the prepared polyimide were analyzed,and the structure and morphology of the lithium iron phosphate electrode with polyimid binders were characterized.Finally,the effect of the binders on the electrochemical performance of the electrodes were explored.The two kinds of polyimides did not break the crystalline form of the active materials in the lithium iron phosphate electrode and formed a good conductive network.The electrodes with polyimide binders have smaller impedance value and polarization phenomenon.Polyimide binders enhance the compatibility with the electrolyte,and make the electrolyte easier to immerse into the electrode structure,in addition they can improve the overcharge safety of the assembled lithium ion battery.The discharge specific capacity of the electrode prepared with 6FAPB/DDS-BTDA binder was 134.1 mAh g^-1 after100 cycles at the current density of 0.5 C.,and the capacity retention rate was 94.11%.At the same time,the rate performance of lithium iron phosphate electrode was improved.