Research Of Organic Cathode Of Lithium Batteries Based On Organic Free Radical Polymers

In this work,pyrrole and triphenylamine were modified by introducing of electro-active groups(2,2,6,6-tetramethylpiperidin-1-yloxy and triphenylamine).A series of novel pyrrole and triphenylamine derivatives were synthesized successfully,4-(3-(Pyrrol-1-yl)butyryloxy)-2,2,6,6-tetramethylpiperidin-1-yloxy(Py-B-TEMPO),4-(3-(Pyrrol-1-yl)hexanoyloxy)-2,2,6,6-tetramethylpiperidin-1-yloxy(Py-C-TEMPO),triphenylamine-2,2,6,6-tetramethylpiperidin-1-yloxy derivative(TPA-TEMPO)and N,N,N,N-tetraphenylphenylenediamine(DDP).And the corresponding homopolymers(PPy-B-TEMPO,PPy-C-TEMPO,PTPA-TEMPO,PDDP)of these pyrrole and triphenylamine derivatives were prepared by chemical oxidative polymerization.The electrochemical properties and charge/discharge performances of the as-prepared Li-ion battery cathode materials have been studied.The homopolymers of two 2,2,6,6-tetramethylpiperidin-1-yloxy(TEMPO)contained polypyrrole(PPy)derivatives with the different side-chain electrodes displayed a high discharge capacity compared with polypyrrole electrodes.At 20 mA·g-1,PPy-B-TEMPO and PPy-C-TEMPO electrodes delivered a high discharge capacity of 86.5 mAh-g-1 and 115 mAh·g-1 in the first cycle and showed a reversible two-electron redox reaction process at voltage plateaus of 2.7 V and 3.6 V vs Li/Li+,respectively.Moreover,PPy-B-TEMPO and PPy-C-TEMPO electrodes still exhibited their flat voltage plateausafter 50 cycles.These excellent electrochemical performances were ascribed to the flexible linking side-chain and electro-catalysis of the introduced PPy backbone,which benefited the improvement of charge carrier transportation in the aggregated polymer bulkand the stable redox-active couples of the TEMPO.Poly(triphenylamine-TEMPO)derivative(PTPA-TEMPO)electrode had a high discharge capacity of 140 mAh-g-1 at 20 mA·g-1 with two well-defined plateaus at discharge voltages of 3.8 and 2.7 V vs Li/Li+.In addition,PTPA-TEMPO electrode maintained a discharge capacity about125 mAh·g-1 with only 11%loss of capacity after 50 cycles.These high battery performances could be attributed to the electro-catalysis of the introduced PTPA backbone and theintroduction of TEMPO as aterminating group to the triphenylamine moieties,which benefited the charge carriertransportation in the molecular polymerand the improvement of particles microstructure.The poly(N,N,N,N-tetraphenylphenylenediamine)electrode exhibited two well-defined plateaus at two discharge voltages of 3.8 and 3.3 V vs Li/Li+with a high capacity of 129 mAh·g-1.Moreover,the discharge capacity of PDDPretained over 110.6 mAh·g-1 after 50 cycles which was still higher with 14%loss of capacity.The excellent electrochemical performancesof PDDPelectrode were due to its high free radical density structure,the improvement of polymer particles microstructurewhich enhanced the utilization of active material and the stability of charge transport network.