Preparation Of One-dimensional Polypyrrole Nanotubes And Their Application In Lithium Air Batteries

Among the available energy storage systems,a lithium-air battery(LAB)is considered as a potential solution to the insufficient voyage course for the electric vehicles and even a paramount important strategy to solve the crisis for the energy and environment,due to highest theoretical capacity(10 times higher than that of the advanced lithium-ion battery).However,it is urgent to settle some crucial problems(such as undesirable power density,short life span and lower depth of discharge/charge)before this promising device is industrialized.Most efforts were focused on the exploitation of the electrode materials or catalyst with excellent electrochemical performance and the development of the electrolyte with better comprehensive properties.Previously,carbon-based materials have been intensively investigated on the basis of the attractive features of cheap,rich pore structure,high conductivity and better chemical stability.Surely,the electrochemical behavior of the lithium-air cell was dramatically enhanced by the design of the micro-architecture and hierarchy pores.However,the in-depth investigations found that the utilization ratio of the available pores was not as high as expected and the chemical stability was not satisfying.As a result,it is meaningful to find out an alternative electrode material with cheap,high active and excellent stability.Based on the characteristics of the tunable conductivity,adjustable micromorphology and excellent electrochemical activity,polypyrrole(PPy)was selected as a candidate for the lithium-air cell.Therefore,it is significative to investigate the electrochemical responses of PPy in the lithium-air battery.In this thesis,one-dimensional nanostructured PPy was synthesized by soft-templated method using MO as template.The related formation mechanism was systematically investigated by adjusting the template concentration,the usage of the oxidants and Py monomer.The electrochemical behavior of PPys with typical micromorphologies were further characterized.(1)Influence of the concentration of the methyl orange on the micromorphology and conductivity of PPy was investigated thoroughly.It was found that the morphology of PPychanged from granular to rod upon the concentration of methyl orange.With the increase in the concentration,the diameter of the PPy nanorobs(NRs)was gradually reduced,the polymerization behavior tended to ?-? linkage and further the conductivity was greatly increased.When the concentration of MO is as high as 5 mM,the sample exhibits a highest conductivity of about 16.67 S/cm,one order of magnitude higher than that of the granular PPy.(2)Influence of the amount of the oxidant on the micromorphology and conductivity of PPy was investigated thoroughly.The morphology of PPy grew from incomplete tubular-type structure to the complete rod-type structure upon increasing amount of oxident(herein FeCl3).Correspondingly,the conjugate degree and the conductivity of PPy NRs first rise then fall.It was found that the sample indicates the highest conjugate degree of PPy when the oxidant(FeCl3)to monomer(Pyrrole)ratio is 3:2,the sample exhibits the highest conductivity of about 49.7 S/cm.(3)Influence of the amount of reactant Py monomer on the micromorphology of PPy was investigated thoroughly.The morphology of PPy changed from flake-type to tubular-type structure upon varying concentration of monomer pyrrole.In this case,it seems that the diameter of PPy NRs is almost invariably,indicating the oriented growth of Py assisted by MO template.(4)One-dimensional polypyrrole nanowires with two different morphologies(tubular and rod-shaped)were synthesized and the corresponding electrochemical responses were investigated.The results indicated that:under the current density of 100 mA /g,the discharge capacity of the polypyrrole nanotube based air electrode with an open structure is as high as2300 m Ah /g,and the capacity loss is only about 5% at the current density of 300 m A/g.PPy nanotube-based electrode with opening structure exhibited the highest discharge specific capacity and the rate capability performance.However,the cycling stability is to be greatly enhanced.