Preparation Of PVDF-based Porous Polymer Electrolyte And Its Application In Lithium-ion Batteries

In the era of rapid development of information technology, more and more attention has been taken on the storage, conversion and re-use of energy, polymer electrolyte has been developed rapidly due to better safety performance and flexible design, and becomes one of the most promising materials in lithium ion batteries. Compared with solid polymer electrolyte, porous polymer electrolyte(PPE) has good membrane stability and higher ionic conductivity. But the electrolyte leakage problem in pure porous polymer electrolyte, which makes the coulomb efficiency and cycle stability decreased during the use of lithium ion batteries, seriously hindered the development for PPE, In order to solve this problem, optimal experiments have been carried out to improve the electrochemical properties for PPE membrane thus promote its rapid development and application.Firstly, star polymer with several PEO chain arms were prepared by atom transfer radical polymerization(ATRP), and the PPE membranes containing star polymer were obtained by phase inversion technique through mixing the star polymer with polyvinylidene fluoride(PVDF). The characteristics such as surface morphology, uptake and leakage rate, and ionic conductivity of PPE membranes with different content of star polymer had been studied. The results showed that the PPE-3 with 30wt% of the PEO based star polymer with molecular weight of 2000 showed the highest porosity of the PPE, also the uptake of electrolyte was the highest while the leakage rate decreased remarkably. It is worthy note that the ionic conductivity was about 0.5 orders of magnitude higher than that of pure PPE, the electrochemical stability window was 5.0V(vs. Li/ Li+) and the coulomb efficiency kept over 90% after 70 cycles.To further improve the electrochemical properties of PPE, a serial of organogelators(MDBS) were added into the pores of PPE-3 membranes, cooled down to room temperature and subjected to gel to yield the GPPEs. The influence of organogelator content on leakage rate of electrolyte, ionic conductivity, electrochemical stability had been investigated. The results showed that 3wt% addition of organogelator exhibited the best performance in all GPPEs. Ionic conductivity at room temperature reached up to 1.18× 10-4 Scm-1, with the leakage rate decreased significantly and obtained an electrochemical stability window of above 4.8V(vs. Li/ Li+).