Study On Preparation Of Polypyrole (Polyaniline)-based Conducting Composites And Its Properties As Cathode Of Lithium Secondary Batteries

Polypyrrole(PPy) and polyaniline(PAn) can be used as cathode electroactive materials in secondary battery because they possess good conductivity and electrochemical redox property, high electric charge reserve ability and good stability in air or water. In this paper, polymer/inorganic nanoparticles conducting composites such as polypyrrole/silica (PPy/SiO₂), polypyrrole/carbon black (PPy/C), polyaniline/carbon black(PAn/C) were prepared by adsorption chemical polymerization. As a result, compactness and particles interaction force were improved. Composites showed higher conductivity and bulk density, better granularity and adapt more to make cathode film than PPy. Accordingly, Li/PPy secondary battery showed good properties.For PPy-based composites, preparation conditions were optimized firstly. The influences of reaction temperature, reaction time, the kinds and amount of doping agent , the amount of coupling agent and inorganic nanoparticles(SiO₂, C) on the conductivity were investigated. Through analysis by XPS, TEM, SEM, TGA and four-probe messurement, it was indicated that the distribution of SiO₂ nanoparticles was meliorated after modified by coupling agent MPS, and thereby the resulted PPy/MPS-SiO₂ composites which showed "raspberry" shape exhibited PPy-rich surface compared to PPy/SiO₂, and they have higher PPy content and resulted in higher conductivity increased from 19.23 S/cm to 31.25 S/cm. Also, PPy/C composites synthesized by carbon black adsorption polymerization showed more moderate particle size, morphology and higher conductivity. At the same time, the bulk density and film molding property were also improved. Button-type lithium secondary batteries were assembled with PPy-based composites synthesized above as cathode, lithium film as anode and lmol/1 LiPF₆/EC+DMC+EMC(l:l:l) as electrolyte. In order to study the properties of these batteries, electrochemical techniques, elemental analysis and SEM measurements were applied. It was found that PPy-based composites used as cathode were through doping and de-doping to realize charge and discharge. They showed relative stability and no side-reaction occurred accompanying when batteries were cycled between 2V and 3.8V at less than 1mA electric current. The most discharge capacity is 85.02mAh/g. The cyclability is good with which the reversibility of the cathode reaction was possible since the capacity decreased no more than 6.8% and coulombic efficiency was yet over98% after 30 cycles. In sum, PPy-based composites were perfect electroactive materials used as cathode in lithium secondary battery. It was also indicated that component and conductivity of these composite and cathode film' s bulk density had distinctly influence on the properties of these batteries. The thiner of separators, the better properties of these batteries when they ensured insulation and mechanical intensity. Aluminum foil was better than aluminum net when used as collector.As for PAn-based composites, the influences of the kinds of oxidant, the amount of hydrochloric acid and barbon black on conductivity were investigated, Li/PAn button-type secondary batteries were assembled with PAn-based composites which were synthesized by chemical oxidative polymerization and used as cathode, the influences of the kinds of oxidant, synthesized technics, conducting carbon black added mode and PAn/metal oxide composites used as cathode on the properties of these batteries were studied. It was indicated that PAn-based composites used as electrode materials in lithium secondary battery were inferior to PPy-based composites, but they were also perfect electroactive materials considered all-around.