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Thesis-Camilo Piedrahita-30Aug.pdf (4.75 MB)

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Study of highly conductive, flexible polymer electrolyte membranes and their novel flexoelectric effect

Rendon Piedrahita, Camilo
http://orcid.org/0000-0001-7267-2808
http://rave.ohiolink.edu/etdc/view?acc_num=akron1541440496157425

Abstract Details

2018, Doctor of Philosophy, University of Akron, Polymer Engineering.
Present dissertation outlines a study of the basic important physicochemical properties of photo-cured polymer electrolyte membranes (PEM) that can be enhanced and optimized in order to be implemented as electrolyte in solid-state Li-ion batteries. The studied properties include mechanical integrity, ionic conductivity, thermal and electrochemical stability, etc. This dissertation also introduces and characterizes a novel application of PEMs as energy harvesting materials, due to their capability to transform mechanical stimuli into an electrical signal and vice versa. Chapter I provides a brief overview of the general content of the dissertation. Chapter II presents the material that was taken as the basis for the study. It contains essential information related to the battery principles, operation, development and applications. In addition, it encompasses the description of electroactive polymers, which are in principle, equivalent to the discovered flexoelectric PEMs that are as well introduced in this work. Chapter III illustrates the materials, methods and calculations utilized to perform and analyze the data collected for the purpose of the study. Chapter IV describes an incorporation of mercaptopropyl methyl siloxane homopolymer (thiosiloxane) as a co-component to the matrix of the PEM, which in result enables enhancement of the polymer segmental motion and hence, the ionic conductivity. UV irradiation was applied to various thiosiloxane and poly(ethylene glycol) diacrylate (PEGDA) mixtures to get the `thio-ene’ reaction between the thiol functionality and the double bonds of the PEGDA precursor, which formed a complete amorphous self-standing PEM. The thiosiloxane modified PEM film exhibits higher extension-at-break in comparison to the PEM containing only PEGDA such as PEGDA700/SCN/LiTFSI 20/40/40, FTIR and Raman spectroscopy techniques were employed to detect the thiol (SH) groups consumed after performing the so-called thiol-ene reaction. It was found that there is a direct relationship between the level of the thiosiloxane content and the resulting ionic conductivity of the PEM. Discovered PEMs were also analyzed via thermal and electrochemical techniques in order to determine their implementation as electrolyte in solid-state Li-ion batteries. Chapter V presents the implementation of different PEG-based macromolecules with different chemical architectures. Different chemical architectures increase the mechanical strength of the PEMs without affecting drastically the ionic conductivity. PEMs are fabricated by exposing the mixtures of PEGnA/SCN/LiTFSI 20/40/40 to UV irradiation. Following the photo-curing process, FITR spectroscopy was utilized to detect the consumption of acrylate groups. It is believed that succinonitrile (SCN) increases the diffusion of the solutions and therefore improves the probability of acrylate groups to react. PEG4A, PEG3A and PEG2A PEMs were analyzed with the stress-strain curve test in order to determine the influence of different architectures on the mechanical properties and their relationship with the glass transition temperature (Tg) Other important properties, such as thermal stability and optimal electrochemical window were also studied. Chapter VI introduces an innovative way to create electrical potential as a consequence of ionic polarization. Generated electrical potential can be used to design sensors and energy harvesting devices. This section presents the application of passive and active ion transports found in neuron cells to the solid-state PEM (PEGnA/SC/LiTFSI 20/40/40) system. The application of passive ion transport was studied by fabricating a bilayer PEM system where ion diffusion was induced along the concentration gradient. The study didn’t provide proper results for further investigation. For the application of active ion transport, an external stimulus was utilized, such as pressure and temperature gradient, to a single layer PEM system. This application revealed mechanoelectric and pyroelectric properties in PEM. In other words, when pressure gradient (bending deformation) is applied to a PEM, ionic polarization takes place within the PEM, resulting in an electrical output in a form of voltage or current. These properties indicate that PEMs are “smart” materials that can sense and harvest energy via mechano and pyroelectricity. Chapter VII presents the flexoelectric effect on ion conductive PEMs composed of poly(ethylene glycol) diacrylate (PEGDA) - thiosiloxane (TS) copolymer and Ionic liquid (IL). These flexoelectric PEMs operate based on the principle of ion polarization of dissociated ions to transform input deformation into electrical output. Electrical outputs are collected by monitoring voltage (VOC) and current (ISC) signals while the sample is deformed (square wave mode) by utilizing a Solartron Galvanostat/Potentiostat. The voltage is directly related to the modulus of the PEM, whereas the current is directly correlated with the ionic conductivity of the PEM. Flexoelectric coefficients were calculated for all the composition in correlation to the above-mentioned properties. The magnitude of the calculated flexoelectric coefficients outperforms those reported in the literature for other materials such as some ceramics, PVDF and bent-core liquid crystals. Similarly, Chapter VIII complements the previous work of flexoelectric PEMs. In this case, the deformation of the sample was performed via sinusoidal wave at different amplitudes. The efficiency of the samples has been studied by calculating flexoelectric coefficients. These were found to be of much lower magnitude compared with those from square wave input. The reason lies in the lack of charge relaxation when the sample is being deformed. The effect of frequency on the amplitude of the current, voltage and magnitude of flexoelectric coefficients is also analyzed. Due to the rubber-like nature of these types of PEMs, they can be potentially applied in rubber based materials as sensors or energy harvesting devices from dynamic deformations
Thein Kyu, Dr (Advisor)
Mark Soucek , Dr (Committee Member)
Younjin Min, Dr (Committee Chair)
Steven Chuang, Dr (Committee Member)
Siamak Farhad, Dr (Committee Member)
203 p.
Chemistry; Energy; Plastics; Polymer Chemistry; Polymers; Solid State Physics
Polymer electrolyte membranes; Ionic conductivity; Flexoelectricity; Ion polarization; Li-ion batteries

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Citations

  • Rendon Piedrahita, C. (2018). Study of highly conductive, flexible polymer electrolyte membranes and their novel flexoelectric effect [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1541440496157425

    APA Style (7th edition)

  • Rendon Piedrahita, Camilo. Study of highly conductive, flexible polymer electrolyte membranes and their novel flexoelectric effect . 2018. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1541440496157425.

    MLA Style (8th edition)

  • Rendon Piedrahita, Camilo. "Study of highly conductive, flexible polymer electrolyte membranes and their novel flexoelectric effect ." Doctoral dissertation, University of Akron, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1541440496157425

    Chicago Manual of Style (17th edition)

akron1541440496157425
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This open access ETD is published by University of Akron and OhioLINK.