Dynamical Ion Correlations in Polymer Electrolytes

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NONTECHNICAL SUMMARY Because batteries play an ever-increasing role as mobile energy storage devices, our society demands the design of more powerful and yet operationally safe batteries. One pathway toward this demand is the search for new types of battery materials, highly conductive and yet resistant to heat and other stress factors that can cause safety issues. An attractive emerging candidate are thin sheets of charged polymeric material—known as polymer electrolytes—with plastic-like properties and yet allowing for the passage of lithium and other ions. Unfortunately, currently available polymer electrolytes still lack the conductivity required for the fast charging and discharging needs of present-day batteries. A key missing ingredient for designing better batteries is a predictive understanding of how ions move in charged polymeric materials. This project will seek to develop such an understanding by using computer simulations that precisely account for the chemical details of a class of polymers pursued for lithium-ion batteries. Based on the findings of these simulations, new polymeric designs for faster charging and reduced safety concerns will be identified and communicated to experimental researchers. The outcomes of this work will also be useful for proposing polymer materials that facilitate water purification from contaminating salts and extract elements such as lithium, a scarce domestic resource, from waste streams. The computer simulations and findings of this project will be integrated into course work and communicated to the next generation scientists and leaders. Furthermore, the project will engage high school and undergraduate researchers by making research experiences a part of their education. TECHNICAL SUMMARY Recently, considerable interest has arisen in the use of polymer electrolytes as materials for use in energy storage and water purification, separation applications. In many of these applications, a key performance metric relates to the selective optimization of the transport of a specific ion relative to the other ions present. In such contexts, many of the materials recently explored involve concentrated solution of ions, in which novel physics arises from the influence of (i.e. correlations between) dynamics of one or more of the ions on the motion of a different ion. In this project, the PI proposes a hypothesis driven plan which builds on novel experimental results reported by other groups and the research team’s preliminary simulation results, to shed light on the microscopic origins and the influence of dynamical ion correlations in two broad classes of problems: (a) Counterion transport in polymeric ionic liquids; and (b) Lithium ion transport in salt-doped polymeric ionic liquids. The PI proposes to use a combination of atomistic and coarse-grained simulations to validate the hypotheses regarding the mechanistic origin of dynamical ion correlations in such materials. The research team will use newly gained understanding to identify physicochemical parameters which exploit the dynamical correlations between ions to enable higher conductivities and/or transference numbers.The project will impact the development of battery electrolytes based on polymeric materials. Such advances are of relevance for building sustainable energy sources and economic independence from depleting oil and gas resources. The PI’s computer simulations and fundamental advances will be integrated within new course materials and outreach modules for undergraduate and graduate students to illustrate the physics of dry and hydrated polymer electrolytes. The PI will also organize a special focus session at the APS March meeting which will bring together researchers working on different aspects of this diverse field. Further, the research project will be used as a means to recruit and train undergraduate and high school researchers, with a special focus towards enhancing the diversity among computational materials science researchers.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.