Solid Polymer Electrolytes for Lithium Secondary Batteries

Student thesis: Master's Thesis

Abstract

Solid polymer electrolytes (SPEs) are of great importance in electrochemical devices such as lithium ion batteries and dye sensitized solar cells as they are safer and eliminate the need for extensive sealing issues. Polyethylene oxide (PEO) is a wellknown solid electrolyte for Li ion batteries; however, its mechanical strength starts deteriorating at temperatures greater than about 60 oC. In this work we have developed PEO and novel cellulosic materials based SPEs with enhanced thermal and mechanical properties. Solution cast PEO was reinforced with Networked Cellulose (NC) having a networked structure. Cellulose is not ionically conductive, so, a networked structure of cellulose with entrapped PEO didn't degrade the conductivity to any significant value and provided structural stability and high strength to the SPE up to 200 oC. With an addition of 15wt% NC in SPE there was about five-time increase in both tensile as well as storage modulus measured via tensile testing and Dynamic mechanical analysis (DMA) respectively. Electrochemical impedance spectroscopy (EIS) of SPEs with LiClO4 showed that the reduction in ionic conductivity due to NC addition was not significant for NC content equal and below 15wt%. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) studies validated that the electrochemical stability window of PEO+15wt%NC with salt is correspondent to that of neat PEO with salt. For electrospun PEO SPEs a novel cellulose based material (GELPEO) was used. And the SPEs were electrospun by blending different amounts of GELPEO with PEO. The reinforced SPE fiber mats show a two-fold increase in the tensile strength and up to five times increase in the young's modulus with no diminution in electrochemical properties. In the course of developing and characterizing composite SPEs, we introduced a technique to identify the structural and thermal properties of polymer composites and blends in a single step. We presented a non-destructive method local thermal analysis (LTA), based on a heated AFM cantilever, for the in-situ characterization of structural and thermal properties of polymer composites. The technique allows measurement of the local melting point, the dehydration temperature and the thermal expansion. The LTA technique coupled with Transmission electron microscopy (TEM) allows obtaining a more precise description of the nanostructure of the developed GELPEO material.
Date of Award2012
Original languageAmerican English
SupervisorRaed Hashaikeh (Supervisor)

Keywords

  • Lithium-Spectra
  • Lithium Cells
  • Lithium Titanate-Metallography

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