AmericanChemicalSociety.com

Polymer electrolyte batteries are expected to be key a component of future portable energy technology due to their high energy density, stability, and material properties.  A critical limitation, however, is low ionic conductivity, controlled by the complexation of ion by polymer.  The ionic motion is thought to occur by intrachain diffusion, polymer motion, and rare interchain hopping events.  This is a challenge for both theory, to capture local coordination, and simulation, due to the long timescale Marcus-like activated transport in large molecules.  This research program aims to overcome these difficulties in understanding ion transport in polymer electrolytes with a hybrid theory-simulation approach.  The strategy is to simulate only a few molecules explicitly, allowing faithful description of the local complexation, while the remaining molecules in the system are treated by statistical mechanical theory, saving computational expense.

In this first year of the project, we have focussed on developing the hybrid theory-simulation methodology capable of capturing both short-range interactions and many-body effects in a condensed polymer system.  We have preliminary results on polyethylene that validate this approach in pure polymers of a single (CH2) site-type, and have been working on extending these calculations to multiple site types.  This will be a key step to allow modeling of polymers with specific sites on the polymer backbone or side chains that can complex ions.  To attack this problem, we have developed flexible software to solve the integral equations of the statistical mechanical theory of liquids in Mathematica to allow rapid testing of novel analytical strategies underlying numerical solution methods as well as accuracy of closure approximations.  In parallel, we have also started developing atomistic molecular dynamics simulations of lithium ion dissolved in polymer-electrolytes to benchmark our hybrid theory-simulation methodology as it progresses.

The support provided by the Petroleum Research Fund is of significant benefit to the principal investigator as it has allowed for continuity in his long-term theoretical research on atomistic effects in polymer structure and interactions, and allows him to build on and extend from this expertise to attack fundamental problems relevant to battery technology.  The support for the first-year graduate research assistant is of significant educational benefit as it has allowed him to transition from experimental industrial work to building the theoretical skill set to attack this problem, including statistical mechanics of simple and complex fluids, numerical analysis and programming, and large-scale simulation.