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Modeling Ion Solvation and Dynamics in Polymer Electrolytes via Molecular Dynamics Simulation

Fan, Mengdi
http://orcid.org/0000-0002-1626-2502
http://rave.ohiolink.edu/etdc/view?acc_num=osu1713497830142344

Abstract Details

2024, Doctor of Philosophy, Ohio State University, Chemical Engineering.
Polymers have gained attention for their use as solid electrolytes in lithium-ion batteries due to their high energy density and enhanced safety. To increase cation conductivity in solid-state polymer electrolytes, particularly at room temperature, a range of polymer systems have been explored extensively in recent years. Understanding the ion behavior in polymer systems at the molecular level is essential. Generic coarse-grained bead-spring models are widely used to describe polymeric systems in molecular dynamics simulations, which have demonstrated qualitative consistency with a variety of structural and dynamic results from experiments. When ions are present, additional model features are needed to account for their longer-ranged interactions with each other (typically through Coulomb interactions within a uniform dielectric constant background) and for their interactions with polarizable polymers. For example, using additional pairwise potentials or embedding the classic Drude oscillator to achieve polarizable modeling. One objective of this research is to study the ion behavior across various polymer systems by employing a pairwise solvation potential. Additionally, this study aims to develop the Drude oscillator integrated model in coarse-grained polymer simulations to study ion-containing polymer electrolytes. We first studied the single-ion block copolymers, which are gaining interest as potential electrolytes with high cation transference numbers. Because anions are tethered to the polymer chains, the cation transference number, which is the fractional contribution of cation conductivity to overall ion conductivity, is unity in the limit that transport of the polymer chains is negligible. Such a high transference number is of interest in reaching a high charging rate and avoiding concentration polarization that is possible in salt-doped systems. However, tethered anions may decrease polymer and cation dynamics and thus reduce cation conduction. To understand these effects, we simulated diblock copolymers with anions tethered at random locations on the conducting block (the block that more strongly solvates the ions), using an ion solvation potential proposed in our previous work. We studied a variety of ion concentrations and polymer dielectric constants, including salt-doped systems for comparison, and analyzed the ion clustering and dynamics. We found that single-ion block copolymers have higher cation conductivity than their analogous salt-doped block copolymers, especially at moderate ion concentrations. We also explored the tapered copolymers focusing on how the taper profile affects local segmental dynamics. We showed that monomer segmental dynamics correlate with their distributions. Monomers at the center of the conducting phase have higher segmental dynamics. Inverse-tapered systems show lower monomer segmental dynamics at the center of the conducting phase compared to non-tapered copolymer systems. We then investigated the integration of the Drude oscillator model with the Kremer-Grest bead-spring model for studying ion-containing polymer electrolytes. We developed a simulation framework and studied two parameters that can affect solvation energy, the simulation’s background dielectric constant and the charge downscaling parameter. Tuning these parameters enables the simulation of ion-containing systems at polymer dielectric constant of interest while maintaining reasonable computational costs. We compared the structural difference of monomer and ion by using the Solvation potential method and the Drude oscillator method.
Lisa Hall (Advisor)
Xiaoguang (William) Wang (Committee Member)
Isamu Kusaka (Committee Member)
143 p.
Chemical Engineering
Polymer electrolytes, Molecular dynamics simulations

Recommended Citations

Citations

  • Fan, M. (2024). Modeling Ion Solvation and Dynamics in Polymer Electrolytes via Molecular Dynamics Simulation [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1713497830142344

    APA Style (7th edition)

  • Fan, Mengdi. Modeling Ion Solvation and Dynamics in Polymer Electrolytes via Molecular Dynamics Simulation. 2024. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1713497830142344.

    MLA Style (8th edition)

  • Fan, Mengdi. "Modeling Ion Solvation and Dynamics in Polymer Electrolytes via Molecular Dynamics Simulation." Doctoral dissertation, Ohio State University, 2024. http://rave.ohiolink.edu/etdc/view?acc_num=osu1713497830142344

    Chicago Manual of Style (17th edition)

osu1713497830142344
© 2024, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.