| As a typical conductive polymer, polypyrrole not only has the electrical properties and excellent electrochemical performance, but also has the advantages of simple preparation, green environmental protection and higher environmental stability. Particularly, compared with other members in the family of the conductive polymer, the sensitive ability to capture information and relatively high doping degree make polypyrrole more suitable for electrode materials.Due to its high theoretical energy density(2600 Wh/kg), lithium sulfur batteries have attracted much attention. Especially, the positive electrode active material of elemental sulfur has high theoretical specific capacity(1675 mAh/g). What’s more, element sulfur is abundant in nature, low cost, and environmental friendly. Therefore, the lithium sulfur battery is considered as one of the most development potential of the battery systems. However, the energy density of lithium sulfur battery that can realize application is much lower than its theoretical value, mainly presenting as the short cycle life、fast fading and other issues. The reasons are shown as follows: firstly, the insulation of sulfur makes it has to composite with electronic conductor that can’t participate in the electrode reaction, so that reduce the discharge capacity of the cathode; secondly, the intermediate product polysulfide lithium is easy to dissolve in the electrolyte, which leads to the shuttle effect, resulting in the low utilization rate of active material, poor cycle performance and other negative effects. Based on a large number of documents, this paper used conducting polypyrrole with active surface area and porous flower shap that synthesized by electrochemical method as skeleton and composited with elemental sulfur as the cathode,material. Finally, the electrochemical properties of cathode materials were also characterized. The main research results of this paper are as follows:(1) With the technology of cyclic voltammetry, the metal tantalum, stainless steel and saturated calomel electrode worked as working electrode, auxiliary electrode and reference electrode, respectively. The flower like morphology of PPy was synthesized on the surface of aqueous solution with the P?toluene sulfonic acid and dodecyl benzene sulfonic acid sodium as dopants, The flower like morphology of PPy not only has a large specific surface area, good thermal stability, but also has soft elasticity.(2) Optimized the synthesis conditions of PPy. Designed different synthesis rates and achieved the flower shaped PPy. With the PPy as cathode and lithium as anode, We compared the open circuit voltage and the first discharge capacity of the batteries, and got the optimum synthesis rate 0.1 V/s of the flower like PPy.(3) Under the temperature of 120 ℃, we composited elemental sulfur with PPy synthesized In 0.1 V/s scan rate and received the PPy/S composite cathode materials. Next we characterized its electrochemical properties. Results presented that the soft elastic flower shaped PPy has good inhibition to the collapse failure of cathode structure and the dissolution of the intermediate product in the electrolyte, showing that the circulation reversible of the battery was very good and the average coulombic efficiency reached 93% after charging and discharging many times in the current rate of 0.5 C.In summary, the flower like polypyrrole, synthesized by electrochemical method, has good electrochemical activity and physical adsorption to polysulfide lithium, which greatly improves the utilization rate of active materials, the capacity retention ratio and cycling stability of the battery, and finally provides a reference to the design of cathode materials of lithium sulfur battery. |
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