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Computational Investigation of Ionic Diffusion in Polymer Electrolytes for Lithium-Ion Batteries


Brooks, Daniel James (2018) Computational Investigation of Ionic Diffusion in Polymer Electrolytes for Lithium-Ion Batteries. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/ZE9T-V407.


Energy storage is a critical problem in the 21st century and improvements in battery technology are required for the next generation of electric cars and electronic devices. Solid polymer electrolytes show promise as a material for use in long-lifetime, high energy density lithium-ion batteries. Improvements in ionic conductivity, however, for the development of commercially viable materials, and, to this end, a series of computational studies of ionic diffusion were performed. First, pulsed charging is examined as a technique for inhibiting the growth of potentially dangerous lithium dendrites. The effective timescale for pulse lengths is determined as a function of cell geometry. Next, the atomistic diffusion mechanism in the leading polymer electrolyte, PEO-LiTFSI, is characterized as a function of temperature, molecular weight, and ionic concentration using molecular dynamics simulations. A novel model for describing coordination of lithium to the polymer structure is developed which describes two types of interchain motion "hops" and "shifts," the former of which is shown to contribute significantly to ionic diffusion. The methodology developed in this study is then applied to a new problem – the adsorption of CO2 at the surface of semi-permeable polymer membranes. Finally, a new method, PQEq, is developed, which provides an improved description of electrostatic interactions with the inclusion of explicit polarization, Gaussian shielding, and charge equilibration. The dipole interaction energies obtained from PQEq are shown to be in excellent agreement with QM and a preliminary application of PQEq to a polymer electrolyte suggest that it can provide an improved description of ionic diffusion. Taken as a whole, these techniques show promise as tools to explore and characterize novel materials for lithium-ion batteries.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Lithium-ion batteries, dendrite growth, polymer electrolytes, polarizable molecular dynamics
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Applied Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Goddard, William A., III
Thesis Committee:
  • Goddard, William A., III (chair)
  • Bernardi, Marco
  • Hoffmann, Michael R.
  • Wise, Mark B.
Defense Date:23 January 2018
Non-Caltech Author Email:daniel.brooks (AT)
Funding AgencyGrant Number
Bosch Energy Research Network (BERN)13.01.CC11
Bill and Melinda Gates Foundation OPP1069500
Bosch Energy Research Network (BERN)07.23.CS.15
Joint Center for Artificial Photosynthesis (JCAP)DE-SC0004993
Record Number:CaltechTHESIS:06012018-042437640
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:10995
Deposited By: Daniel Brooks
Deposited On:06 Jun 2018 19:05
Last Modified:25 May 2021 22:10

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