Master of Science, University of Akron, 2020, Polymer Engineering

The present thesis focuses on elucidation on the role of ionic liquid in polymer electrolyte membranes for energy harvesting and storage. Recently, research interest on ionic liquid-in-salt has gained considerably due to its high thermal stability and ionic conductivity, which has potential as a replacement for the facile organic solvent electrolyte in lithium ion battery. The status of emerging lithium ion batteries has been reviewed in Chapter I, followed by Materials and Methods including physical and electrochemical characterizations in Chapter II and Chapter III. In Chapter IV, the polymer electrolyte membrane (PEM) containing liquid polyether sulfide (PES, Thiokol) was fabricated via thiol-ene click reaction with poly (ethylene glycol) diacrylate (PEGDA) with the aid of a photo-initiator under UV light for photocuring. The so-called solid polymer electrolyte membrane thus formed is an isotropic, completely amorphous, transparent, and flexible solid-state membrane. The ionic conductivity of (PES-co-PEGDA/HMIMTFSI) was determined by AC impedance as a function of thiol (SH) content which served as flexible side chains. The ionic liquid (HMIMTFSI) can dissociate Li ions from its salt and also plasticize the PEM network. As a result, the increasing amount of Thiokol and HMIMTFSI can both sevred as the ionizers to enhance the ionic conductivity. The flexoelectric coefficients (μ) of various PEMs-(TK-co-PEGDA/HMITFSI) were determined under intermittent square wave and dynamic oscillatory bending modes by using Dynamic Mechanical Analyzer (DMA) combined with Solartron Potentiostat/Galvanostat. The present PEM (TK-co-PEGDA/HMIMTFSI) exhibited larger flexoelectric coefficient than those of conventional insulating materials such as ferroelectric ceramics and bent-core nematic liquid crystals. Last not least, the efficiency of mechano-electrical energy conversion the PEM (TK-co-PEGDA/HMITFSI) is discussed. Chapter V addresses the mutual solubility of ionic liquid (IL) (open full item for complete abstract)

Committee: Thein Kyu (Advisor); Xing Gong (Committee Member); Kevin Cavicchi (Committee Member) Subjects: Energy; Engineering; Polymer Chemistry; Polymers

Master of Science, University of Akron, 2014, Polymer Engineering

Binary and ternary phase diagram of poly(ethylene glycol) dimethacrylate (PEGDMA), bis(trifluoromethane)sulfonimide (LiTFSI), and succinonitrile (SCN) blends have been established by means of differential scanning calorimetry and polarized optical microscopy. The binary phase diagram of PEGDMA/SCN mixture is of typical eutectic type, whereas the binary phase diagram of PEGDMA/LiTFSI mixture exhibits a wide single-phase region at the intermediate compositions. The ternary phase diagram of PEGDMA/SCN/LiTFSI mixture shows a wide isotropic region. The polymer electrolyte membrane (PEM), which is formed by ternary blends in this region after UV-crosslinking, remains in the isotropic phase and performs. The room temperature ion conductivity as evidenced in AC impedance measurement, was found to be extremely high (i.e., 10-3 S/cm). This ionic conductivity increases to 10-2 S/cm at 60 °C that continues to improve further up to 135 °C investigated. More importantly, the high ionic conductivity behavior is reproducible in repeated heating/cooling cycles. Those PEM are solid-state, stretchable, nonflammable, and light weight, which may be applicable to lithium ion battery as a replacement of commercial liquid electrolyte. SCN in ternary blends affords not only dissociation of the lithium salt, but also plasticization to the cross-linked PEGDMA network. Last not least, thermal and electrochemical stability of these membranes were examined for further application probability.

Committee: Thein Kyu Dr. (Advisor); Nicole Zacharia Dr. (Committee Member); Xiong Gong Dr. (Committee Member) Subjects: Energy; Engineering; Polymer Chemistry; Polymers

Doctor of Philosophy (PhD), Ohio University, 2001, Chemistry (Arts and Sciences)

The stability of uncoated copper (Cu) foils and graphite-coated copper (Cu-C) foils in lithium-ion battery electrolytes were extensively studied in this dissertation. At first, the electrochemical behavior and stability of the Cu foils and Cu-C foils were studied. Cyclic voltammetry was used to study the redox behavior of the foils in the electrolyte solutions. The reduction of electrolyte and its effect on the oxidation of copper was also studied. Bulk electrolysis was used to quantitatively study the dissolution of the foils in dry electrolytes and in electrolytes doped with impurities of H2O or HF. It was found that the graphite coating greatly influenced the redox behavior of the copper substrate and provided some protection to the copper from oxidation. Impurities increased the oxidation tendency of both Cu foils and Cu-C foils and may influence the integrity of the Cu-C foil electrode. During these studies, the open-circuit voltage (OCV) of Cu foil and Cu-C foil electrodes in Li-ion battery electrolytes was found to be a variable value over time. A detailed study showed that the OCV first rapidly decreased until reaching a minimum, and then gradually increased until reaching a meta-steady or steady state. These results were compared with OCV studies of Al foil, Pt wire, glassy carbon and Cu disk and wire electrodes. The OCV variation appeared to correlate to a surface change on the electrode after being immersed into the electrolyte solutions. The influence of aging of the reference electrode, the surface condition and edge effect of the copper foil, and solution impurities on the stability of the OCV was also studied. Atomic absorption spectroscopy (AAS) was used to quantitatively evaluate the stability of Cu and Cu-C foils in lithium-ion battery electrolytes at open-circuit. Results showed that the stability of Cu and Cu-C foils was different in “fresh” electrolytes whereas it was similar in “aged” electrolytes. For Cu foils, in the “fresh” electrolyte, the (open full item for complete abstract)

Committee: Howard Dewald (Advisor) Subjects: Chemistry, Analytical