In English

Conductivity and Relaxation in Polymer Based Solid Electrolytes

Göteborg : Chalmers tekniska högskola, 2016. 58 s.
[Examensarbete på avancerad nivå]

Lithium ion batteries have received much attention as rechargeable batteries due to their high energy and power density. One way of satisfying the safety conditions required for Li-ion batteries is the use of solid polymer electrolytes (SPE) as opposed to the conventional liquid electrolytes. SPEs eliminate the shape limitation and overcome problems related to leakage and flammability. Different polymer electrolyte systems have been extensively studied. PEO- LiX, as used as the base polymer electrolyte in the present study, is one of these systems. In this study we have used lithium bis(trifluoromethanesulfone)imide (LiTFSI) as the salt, Al2O3 as the nanofiller and poly(ethylene oxide) (PEO) as the polymer. Samples of different molar ratios of PEO/ Li, 16:1 and 8:1 have been prepared. The obtained polymer electrolyte films have thicknesses of 100-150 μm. The major drawback of this PEO-Li system is its relatively low conductivity at room temperature. Since the ionic conductivity of the polymer electrolyte occurs in the amorphous phase of the polymer, the semicrystalline character of PEO below its melting point at 60 C is detrimental for the ionic conductivity. Various methods have been applied to suppress the crystallization, such as adding nanoparticles or ionic liquids. In this project we used 1-butyl-3 methylimidazolium bis(trifluoromethanesolfonyl)imide (BMITFSI) to enhance the ionic conductivity and reduce the crystallization. The ionic conductivity and relaxation processes of the system have been studied by dielectric spectroscopy (DS) and, furthermore, thermal properties, such as glass transition and melting temperature of the polymer, have been determined by differential scanning calorimetry (DSC). The results show that the introduction of the ionic liquid speeds up the segmental polymer dynamics, but only to concentrations of about 20 wt%, despite that the ionic conductivity increases further (to above 10−4 S/cm at 300 K) at higher concentrations of the ionic liquid. Thus, it is evident that the motion of the Li ions decouples from the segmental polymer dynamics at higher concentrations of the ionic liquid and instead becomes more dependent on the viscosity of the ionic liquid.

Nyckelord: Solid polymer electrolyte, PEO, ionic conductivity, ionic liquid.

Publikationen registrerades 2017-01-13. Den ändrades senast 2017-08-02

CPL ID: 246858

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