Study On A Star Network Polymer Electrolytes And Its Applications

In recent years, the study of polymer electrolytes have been attracting much interest in macromolecule material field, because of its outstanding advantages such as mass light, flexible, good film processing, electrochemical and thermal stability, and many potentially applications in lithium-ion batteries, electrochromic devices, supercapacitors and sensors. The crystallinity of polymer electrolytes currently was very high, their ionic conductivity was too low to be satisfied for practical applications at room temperature. In order to improve ionic conductivity of polymer electrolytes, Much efforts have been done, such as using copolymer, cross-linking network polymer, blends with other polymers, adding plasticizers and inorganic filling. However, the ionic conductivity and mechanical properties were mutual inconsistent, We are trying to find a optimal balance point for the contradiction between ionic conductivity and mechanical properties.In this work, a star network polymer with a pentaerythritol core linking four PEG-block polymeric arms was synthesized from the poly (ethylene glycol), pentaerythritol, and dichloromethane in the presence of potassium hydroxide powder. The polymer host was characterized and confirmed to be star network and amorphous structure by FTIR, ¹H-NMR and XRD studies. The polymer host held well mechanical properties and thermal stability for pentaerythritol cross-linking, TG curve of the polymer host showed that the thermal stability was up to at least 260℃. All solid polymer electrolytes based on star network polymer and LiClO₄ were prepared and characterized by AC impedance spectroscopy , the results showed ionic conductivity reached 1.03×10^-4S·cm^-1 at room temperature.The gel polymer electrolytes based on star network polymer, LiClO₄ and EC/PC were prepared and characterized by AC impedance spectroscopy, the results showed: when W_(LiClO4)=12% and W_(EC/PC)=80% , the maximum ionic conductivity of gel polymer electrolytes reached 8.83×10^-4S·cm^-1 at room temperature and good mechanical properties. The gel polymer electrolytes were characterized by transmittance spectral and TG curve, the result showed good transmittance properties and good thermal stability (up to at least 150℃). The gel polymer electrolytes were applied in electrochromic devices and reveals excellent colorization performance , fast response time (less than 50 ms) and high cyclic times (above 10⁷ times).The gel composite polymer electrolytes based on star network polymer blending with PVDF were prepared. The effects of the amounts of LiClO₄, EC/PC ,SiO₂ and the mass ratio of star network polymer and PVDF were investigated and the result showed: when m_{(star network polymer)}: m((PVDF))=7:3, W((LiClO₄))=16%, W((EC/PC))=200%, W((SiO2))=10% , the maximum ionic conductivity of gel polymer electrolytes reached 2.12×10^-3 S·cm^-1 at room temperature and good mechanical properties. The gel composite polymer electrolytes were applied in polymer lithium ion battery, and the big current discharge and circle performance of experiment lithium batteries were tested , the result showed that the work voltage and capacity of experiment lithium batteries all descended at big current than small current, and circle performance need be improved and more researching.