Preparation of ionic conductive polyimide binder and its application in cathode of lithium-ion batteries
Lithium-ion batteries(LIBs)are widely used in emerging energy applications due to their advantages such as high energy density and output power,as well as long service life.Polymer binders used in the cathode play a crucial role in LIBs as they provide adhesion between active material particles and the electrode current collector,thereby facilitating the diffusion of Li+ions and improving the cycle performance of batteries.Commercial polyvinylidene fluoride(PVDF)is the main binder used in cathode materials at present,but it still has the problems of low bonding performance and poor ion conductivity.Polyimide(PI),on the other hand,offers excellent mechanical properties,adhesive strength,and favorable design flexibility,making it an attractive alternative binder.Therefore,we designed and synthesized a sulfonimide lithium structure-based diamine monomer(BAPSI-Li),taking the advantage of excellent mechanical properties and structural tunability of PI.The BAPSI-Li monomer was copolymerized with 3,3',4,4'-Biphenyltetracarboxylic dianhydride(s-BPDA)and 4,4'-oxydianiline(ODA)to form an ion-conductive PI binder.The adhesive performance of PI binder was found to be improved compared to PVDF.The LFP electrodes prepared with this ion-conductive PI binder exhibited outstanding electrochemical performance,with a discharge specific capacity of 158.19 mA·h·g-1 after 250 cycles at a current density of 0.2 C.Compared with commercial PVDF binder,the ion-conductive PI binder demonstrated superior cycling stability.This was due to the excellent adhesive performance of PI,which enabled the electrode to maintain structural integrity during long cycling processes.Meanwhile,the introduction of the ion-conductive diamine monomer was beneficial for promoting the transport of lithium ions within the electrode.
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