Electronic Thesis and Dissertation Repository

Degree

Master of Science

Program

Chemistry

Supervisor

Oleg Semenikhin

Abstract

This thesis focuses on the development of new poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) in order to enhance their ionic conductivity at ambient temperature and fabricate the prototypes of novel Li ion batteries using these SPEs. Different types of SPEs have been developed: (i) blends of high molecular weight PEO and low molecular weight poly(vinyl acetate) (PVAc); (ii) composites of high molecular weight PEO and titanium dioxide (TiO2)nanoparticles; and (iii) blend-based composite electrolytes consisting of PEO and PVAc with dispersed TiO2. The SPEs were characterized by scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC). The electrochemical performance of the battery prototypes were determined by galvanic cycles at various current densities.

The results revealed that the crystallization of PEO was easily suppressed by blending it with PVAc. The resistance of these blends were found to decrease with an increase in the PVAc content. TiO2 nanoparticles were found to be a compatible filler with the PEO matrix, as was proven by the lowered crystallinity, glass transition and melting temperatures of the matrix, as well as a significantly enhanced conductivity at ambient temperature.

A new type of SPE has been prepared by adding both PVAc and TiO2 to PEO-based electrolyte. The amorphous nature of the new electrolyte was confirmed by DSC. Several prototypes of a Li-ion battery, based on this blend-based composite electrolyte and utilizing LiFePO4 as cathode and Al as anode, were assembled and cycled at different current densities at room temperature, resulting in excellent performance. The best prototype so far showed more than 500 charge-discharge cycles with the coulombic efficiency approaching 100% and the resistance decreasing to 500 Ω.cm2.

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