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Structure and electrochemical properties of holographically polymerized polymer electrolyte membranes for lithium batteries
Dissertation   Open access

Structure and electrochemical properties of holographically polymerized polymer electrolyte membranes for lithium batteries

Derrick M. Smith
Doctor of Philosophy (Ph.D.), Drexel University
Jul 2016
DOI:
https://doi.org/10.17918/etd-7600
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Abstract

Power resources Electric batteries Electrochemistry Materials Science
With the increasing demand for mobile technology, the next generation of power storage devices must be realized. The insertion-type electrodes typically used in commercially available secondary batteries have low capacitances; for instance, a graphitic anode has a theoretical specific capacitance of 372 mAhg-1. The most promising route to increasing the energy density is by switching the anode to Li metal, which has a specific capacitance of 3860 mAhg-1, and using stabilizing additives for the latter. However, Li metal experiences unacceptable Li dendritic failure at consumer operating conditions. Polymer electrolyte membranes (PEMs) have been explored over the past four decades to address this; however, a suitable material has not yet been found to address this failure mechanism prohibiting commercialization. In this dissertation, we demonstrate using holographic polymerization induced phase separation as a facile top-down technique to nanostructure the PEM and exploit the long-range phase separation offered by this technique to decouple the mechanical and ion transport properties. Isotropically floodlit samples were used as a baseline to examine the nanostructuring effect. For example, with 30% electrolyte, the baseline isotropic samples showed a room temperature conductivity and tensile modulus of 1.5 x 10-6 S/cm and 156 MPa, where the 1D lamellar patterned PEMs boasted an impressive improvement to both properties, 2.0 x 10-5 S/cm and 618 MPa. The nanostructuring and mechanical enhancemet effects regarding Li metal and dendritic growth were also observed using galvanostatic polarization. It was found that there was a tradeoff between certain nanostructure geometries that increased the current density and the mechanical enhancement provided by said nanostructures. Two nanostructures exhibited a 100-150 fold increase in cell lifetime before dendritic failure over the predicted lifetime based on Chazalviez's model. This top-down nanostructuring technique also uniquely offers a new exciting platform for exploring other structure-property relationships in electrochemical membranes.

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