Design, synthesis, and characterization of polymeric materials for uses in energy storage applications
Open Access
- Author:
- Welna, Daniel Thomas
- Graduate Program:
- Chemistry
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 09, 2006
- Committee Members:
- Harry R Allcock, Committee Chair/Co-Chair
Karl Todd Mueller, Committee Member
Alan James Benesi, Committee Member
James Patrick Runt, Committee Member - Keywords:
- polyphosphazene
lithium battery
polymer electrolyte
ionic conductivity - Abstract:
- The work described in this thesis focuses on the design, synthesis, and characterization of polymeric materials for energy storage applications, which include small molecule electrolyte additives, solid polymer electrolyte, and gel polymer electrolyte systems. In addition, non-woven nanofiberous mats of a pre-ceramic polymer were examined for high-strength and temperature material applications. Chapter 2 of this thesis describes the synthesis of novel polyphosphazene single ion conductors for use in secondary lithium ion batteries. Chapters 3 and 4 details work towards the synthesis and evaluation of highly selective membranes for use in lithium-seawater batteries. The fifth chapter deals with the synthesis and characterization of a polyphosphazene-silicate solid polymer electrolyte networks for secondary lithium batteries. Chapter 6 describes the fabrications and evaluation a gel polymer electrolyte system which utilizes a phosphate-based small molecule electrolyte additive. The appendix details the electrostatic spinning of a polymeric ceramic precursor to produce a nanofiberous mat, which upon pyrolysis yield boron carbide nanofibers. Chapter 2 describes the synthesis and characterization of novel single ion conductive polymer electrolytes developed by covalently linking an arylsulfonimide substituent to the polyphosphazene backbone. An immobilized sulfonimide lithium salt is the source of lithium cations, while a cation-solvating cosubstituent, 2-(2-methoxyethoxy)ethoxy, was used to increase free volume and assist cation transport. The ionic conductivities showed a dependence on the percentage of lithiated sulfonimide substituent present. Increasing amounts of the lithium sulfonimide component increased the charge carrier concentration but decreased the ionic conductivity due to decreased macromolecular motion and possible increased shielding of the nitrogen atoms in the polyphosphazene backbone. The ion conduction process was investigated through model polymers that contained the non-immobilized sulfonimide – systems that had higher conductivities than their single ion counterparts. Chapter 3 details the synthesis of novel polyoctenamers with pendent functionalized-cyclotriphosphazenes as amphiphilic lithium-ion conductive membranes. Cyclotriphosphazene monomers were functionalized with one cycloocteneoxy substituent per ring. Two different types of monomer units, one with oligoethyleneoxy cation-coordination side groups and the other with hydrophobic fluoroalkoxy side groups, were then prepared. The syntheses of these monomers, their ring-opening metathesis copolymerization, and the characteristics of the resultant polymers are discussed, with an emphasis on the dependence of ionic conductivity and hydrophobicity on polymer composition. Chapter 4 focuses the design of novel amphiphilic single-ion conductive polynorbornenes with pendent cyclotriphosphazenes as candidates for lithium-ion conductive membranes for lithium-seawater batteries. The cyclotriphosphazene components were linked to a 5-norbornene-2-methoxy substituent to provide a polymerizable unit. 2-(2-Phenoxyethoxy)ethoxy co-substituents on the cyclotriphosphazene unit of the first co-monomer were utilized to simultaneously facilitate lithium cation transport and introduce hydrophobicity into the polymer electrolyte. 4-(Lithium carboxalato)phenoxy side groups were linked to the rings of a second co-monomer to provide tethered anions with mobile lithium cations and to increase the dimensional stability of the final polymers. The synthesis of norbornenemethoxy-based cyclotriphosphazene monomers, their ring-opening metathesis polymerization, deprotection and lithiation of the 4-(propylcarboxalato)phenoxy side groups, and the characterization of the polymers are discussed to illustrate the dependence of ion transport and hydrophobic properties on the polymer composition. Chapter 5 is an analysis of the ionic conduction characteristics of silicate sol-gel poly[bis(methoxyethoxyethoxy)phosphazene] hybrid networks synthesized by hydrolysis and condensation reactions. Conversion of the precursor polymers to covalently interconnected hybrid networks with controlled morphologies and physical properties was achieved. Thermal analyses showed no melting transitions for the networks and low glass transition temperatures that ranged from approximately -38 °C to -67 °C. Solid solutions with lithium bis(trifluoromethanesulfonyl)amide in the network showed a maximum ionic conductivity value of 7.69 × 10-5 S/cm, making these materials interesting candidates for dimensionally stable solid polymer electrolytes. Chapter 6 investigates the influence of an organophosphate electrolyte additive on poly(ethylene oxide) lithium bis(trifluoromethylsulfonyl)imide-based gel polymer electrolytes for secondary lithium battery applications. Tris(2-(2-methoxyethoxy)ethyl)phosphate, is compared to the well known gel-battery component, propylene carbonate, through a study of complex impedance analysis, differential scanning calorimetry, and limiting oxygen index combustion analysis. The conductivities of the gels at low concentrations of tris(2-(2-methoxyethoxy)ethyl)phosphate (1.9 - 4.2 mol %) are higher to those of propylene carbonate based systems with the same concentration. Despite micro-phase separation at high concentrations of tris(2-(2-methoxyethoxy)ethyl)phosphate (7.0 – 14.9 mol %), the conductivities remain comparable to systems that use propylene carbonate. The addition of tris(2-(2-methoxyethoxy)ethyl)phosphate to poly(ethylene oxide) gives increased fire retardancy, while the addition of propylene carbonate to poly(ethylene oxide) results in increased flammability. The appendix is a pyrolysis study of electrostatically spun poly(norbornenyldecaborane), a polymeric boron carbide precursor. Electrostatic spinning techniques provided an efficient and large scale route to non-woven mats of boron-carbide/carbon nanoscale ceramic fibers with narrow size distributions. Scanning electron microscopy, x-ray diffraction analysis and diffuse reflectance infrared Fourier transform spectroscopy were used to characterize the polymer and ceramic fibers. The results suggest that electrostatic spinning followed by pyrolysis can be used as a general route to a wide variety of single-phase and hybrid non-oxide ceramic fibers.