RII Track-4: Deciphering the Role of Polarization on Ion Transport in Ionic Liquid Batteries

Oklahoma State University, Stillwater OK

Investigators

Abstract

Safe and reliable operation of Li-ion batteries depends critically on the type of electrolytes used. Ionic liquids, novel solvents composed entirely of ions much like common salt but existing as liquids at the temperatures of battery operation, present exciting opportunities as electrolytes due to low volatility and nonflammability. Potentially a million ionic liquids and roughly a billion ionic liquid-ionic liquid mixtures can be designed providing a materials platform for developing next generation of Li-ion batteries. Despite these significant advantages, the progress in ionic liquid-based Li-ion batteries has been limited due to slow Li-ion transport, which increases the time for charging. The objective of the current project is, therefore, to understand ionic liquid-Li interactions to enable the design of novel ionic liquids for fast Li-ion transport. By partnering with researchers from the Pacific Northwest National Laboratory (PNNL), the PI will develop the capability to study ionic liquid-Li interactions using state-of-the-art modeling techniques and DOE's Leadership Computing Facilities. The expertise developed will be shared with undergraduate and graduate students at Oklahoma State University and researchers in the jurisdiction. It is expected that the collaboration resulting from this fellowship will foster engagement of researchers at OSU with those at PNNL and lead to development of new ideas accelerating discoveries in multiple science and engineering disciplines. Li-ion batteries present a promising technological solution for sustainable transportation. One of the major components of Li-ion batteries is the electrolyte through which an efficient transport of Li ions is critical for reliable operation. Room temperature ionic liquids easily fulfill the required electrolyte properties such as electrochemical stability, nonvolatility, nonflammability, and high conductivity over a wide range of temperatures. Despite significant advantages, application of ionic liquids as electrolytes is hampered because the high viscosity of many ionic liquids hinders transport of Li ions causing slow charging and discharging times. Mixing two ionic liquids offers a simple yet powerful strategy to overcome this challenge. However, currently there is a lack of fundamental understanding regarding which ionic liquid combinations are likely to yield promising electrolytes. Further, accurate modeling of such mixtures necessitates capturing the composition-dependent changes in electronic distributions around ions, highlighting the need for polarization. First principles molecular dynamics (FPMD) based on density functional theory approach naturally incorporates this crucial aspect in modeling ionic liquids. The PI will develop this capability in his research group by partnering with researchers from the Pacific Northwest National Laboratory. FPMD simulations will be performed on DOE's Leadership Computing Facilities for ionic liquid mixtures, Li+-ionic liquid mixtures, ionic liquids at electrode interfaces and in the presence of electric field. The newly developed expertise will be shared with researchers at the host institution increasing its research capacity. The proposed fellowship will lead to the training of a graduate student and integration of FPMD simulations in the PI's 'Molecular Modeling and Simulation' course. 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.