Characterization Of Modified Poly (Vinylidene Fluoride) For Lithium-ion Battery

Separator is an important factor for the discharge capacity and the circulation service life in lithium-ion battery. Poly(vinylidene fluoride)(PVDF) is a kind of suitable material to be used as a separator due to its excellent thermal stability, mechanical properties,chemical and electrochemical stability.But the high crystallinity of PVDF limits its use as a separator in lithium-ion battery. PVDF has some shortages such as the easy leakage of electrolyte, the low porosity and so on. On account of its disadvantages, our experiment used PVDF modified by a kind of polymer to get a lacunose battery separator. At the same time, the separator can act as a electrolyte in lithium-ion battery.Polymer (Poly(AN-co-PEGDMA)) is prepared by using the dispersion polymerization methods. AN and PEGDMA were polymerized with ABIN as an initiator. IR spectroscopy was used to detect the surface features of PVDF separator. Result shows that the polymerization of two monomers was successful. PEGDMA is a macromolecule which can act as a good stabilizer. The factors of reaction time, reaction temperature, initiator and monomer concentration were discussed in this research.The change of dispersion during the polymerization is relevant to free radical reaction mechanism as well as the diffusion movement of monomer. For this dispersion polymerization system, the optimum time is 10h, the suitable temperature is 75℃, the concentration of monomer is 25% and a appropriate used amount of the initiator is 0.5% of the monomer mass. The separator was prepared by Ploy (AN-co-PEGDMA) and PVDF in a N,N-diethyl-formatted (DMF) solvent. Microprobes membranes were prepared by the Tape Casting Method. The thermal properties and structures of separator were characterized through the thermal analysis (TGA), X-ray diffraction (XRD) analysis curves, differential scanning calorimetry quantity analysis (DSC) and scanning electron microscopy (SEM).The performance of alloying separator will be tested. We investigated the effect of fluid amount absorbing from the different dosage of modified polymer Poly (AN-PEGDMA) and PVDF as well as the soaking time. Only to find that when the ratio of Poly (AN - co -PEGDMA) and PVDF is 3:7 and the soaking time is 30min, absorbing fluid amount of the diaphragm is the largest. In the best ratio, the conversion rate of blending diaphragm also reaches the maximum. On investigating of the effect on time and temperature of the diaphragm conductivity, the diaphragm conductivity decreased with the extension of time, but not too much. And the rise of temperature can make conductivity increased, the relation change of lgσand 1/T accords with VTF ionic conduction mechanism.