Study On Preparation And Performance Of Polypyrrole And Polypyrrole/Vanadium Pentoxide As Anodes Of Lithium Secondary Batteries

Polypyrrole(PPy) is one of the typical conducting polymers. It can be used as anode of lithium secondary battery because of its high conductivity and electrical redox property, high electric charge reserve ability and good stability in air or water. In this study, PPy, PPy/ Vanadium pentoxide(V₂O₅) and PPy/V₂O₅ xerogel(VXG)were synthesized by oxidatively chemical polymerization.As for PPy, polymerization conditions such as reaction temperature, reaction time, the amount of oxidant, the kind and amount of sulfonic dopants were optimized. The highest conductivity of PPy achieved 58.8S/cm. It was shown that the micro-morphology of PPy doped with B-NSNa was fiber, which was identical to that of PPy doped with other sulfonic dopants. The constitutions, structures and morphologies of these materials were studied and characterized by FT-IR, TGA, ICP and TEM. The conductivities of these materials were measured by four-probe instrument. The button-type battery was fabricated with PPy as anode, lithium sheet as cathode and 1mol/1 LiPF6/EC+DMC+EMC(1:1:1) as electrolyte. Properties of the batteries were investigated and characterized by SEM, IC, ICP, galvanostatic charge-discharge test, cyclic voltammetry and a.c.impedance spectroscopy. It was found that the charging-discharging of PPy anode were realized by doping-undoping of anions. The effects of electric current, separator, cold-molded pressure of anode pellet and conductivity of PPy on the properties of batteries were discussed in detail. It showed that microporous PP/PE/PP compositive separator, cold-molded pressure of 20MPa and high conductivity of PPy would make the battery performance good. The highest discharge capacity of Li/PPy secondary battery achieved 95.2mAh/g.The composites of PPy and V₂O₅ were synthesized by oxidatively chemical polymerization in water medium. The effects of the amount and adding method of oxidant, the amount of V₂O₅ and reaction time on the conductivities of composites were researched. VXG was prepared by sol-gel method and the preparation, structure and property of VXG were studied. The composites of PPy and VXG were prepared. The constitutions, structures and morphologies of PPy/V₂O₅ and PPy/VXG were studied and characterized by SEM, TGA and XRD. The conductivities of these materials were measured by four-probe instrument. In order to study the electrochemical performances of these materials, button-type lithium secondary batteries were fabricated with the composites as anodes. The results showed that the electrochemical performances of composites were superior to PPy. The cyclability and capacity of batteries were elevated. The charging-discharging of PPy/V₂O₅ and PPy/VXG anodes were realized by doping-undoping of anions and lithium ions. The electrochemical performances of PPy/V₂O₅ and PPy/VXG were compared. The capacity of PPy/VXG was lower than that of PPy/V₂O₂, but the cyclability and out-circuit stability of PPy/VXG were higher than that of PPy/V₂O₂. The highest discharge capacity of PPy/V₂O₅ achieved 230mAh/g.