Study Of The Triphenylamine-based Polymer As Cathode Materials For Lithium-ion Battery

In order to improve the energy density of lithium ion batteries,we focused on improving the potential plateaus of lithium ion batteries,and studied the triphenylamine-based polymer as cathode materials for lithium ion batteries in this work.Triphenylamine?TPA?was modified by introducing of a series of groups with different electronic effect,exploring the relationship between the electronic effect of the groups and the potential plateaus of lithium ion batteries.A series of triphenylamine derivatives with different electronic effect were synthesized,including4-?diphenylamino?benzonitrile?TPA-CN?,4-methyltriphenylamine?TPA-CH₃?,4-methox ytriphenylamine?TPA-OCH₃?,4,4',4''-?1,3,5-triazine-2,4,6-triyl?tris?N,N-diphenylaniline??TTPATZ?and N,N-diphenylpyridin-4-amine?DPN?.The corresponding homopolymers of triphenylamine derivatives were prepared by chemical oxidation polymerization method.The electrochemical properties of cathode materials and charge-discharge performance of lithium ion batteries were recored.The chemical structure of the monomer and polymers were confirmed by 1H NMR,FT-IR,UV-vis,MS and SEM.The electrochemical properties of the polymers as the cathode material were further tested by lithium ion half-cell method.The introduction of-CN group as the electron with-drawing group into polytriphenyamine backbone obviously increased the redox potential of the polymers,which significantly improved the potential plateaus of lithium ion batteries.The voltage platform increased from 3.6V?PTPAn?to 3.8V?PTPA-CN?.The discharge capacity of the PTPA-CN electrode decreased from 96.4 mAh·g^-1 to 85.4 mAh·g^-1 after 50 cycles,the discharge capacity loss rate of PTPA-CN was 11.4%.The voltage platform of poly-2,4,6-triphenylamine-1,3,5-triazine?PTTPATZ?electrode was improved with respect to the polytriphenylamine?PTPAn?.At the rate of20 mA·g^-1,The voltage platform of PTTPATZ reached 3.8V,higher than 3.6V to the PTPAn.In addition,the discharge capacity loss rate of PTTPATZ was only 7.8%after50 cycles,which maintained a good discharge platform at the same time.In addition,the specific surface area of the polymer reached 931.04 m²·g^-1,its large specific surface area could provide a sufficiently large contact area for the polymer electrode reaction.These outstanding battery performance was due to the strong electron-withdrawing effect of the triazine and the large specific surface area of the polymer.Comparing with polytriphenylamine?PTPAn?electrode,the potential plateaus of the poly-N,N--diphenyl-4-amine electrode?PDPN?was improved in some degree.At the rate of 20 mA·g^-1,the initial discharge capacity of the PDPN electrode reached 92.3mAh·g^-1.The discharge capacity of the PDPN electrode decreased from 92.3 mAh·g^-1 to78.2 mAh·g^-1 after 50 cycles,the discharge capacity loss rate of PDPN was 15.1%,...