Predicting the Properties of Ionic Liquids from a Polarizable Force Field in Molecular Dynamics Simulations

Oleg Borodin at the Army Research Laboratory has developed and validated a polarizable force field for a wide class of ionic liquids (ILs), which are being explored as additives to lithium-battery electrolytes for improved stability. The developed force field for a wide range of anions shown in Figure 1 will serve as a starting point for molecular dynamics simulations (MD) of liquid electrolytes doped with variety of conventional and novel lithium salts.  This force field, when used in MD simulations, is a tool for predicting thermodynamic and transport properties of conceptual ILs and IL-solvent mixtures and may shed light on structure-property relationships. Using predictions of promising properties to direct materials design can accelerate the development of ILs suitable for battery applications.

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Designing Better Electrolyte Components for Lithium-Ion Batteries 

Researchers at North Carolina State University are cooking up next-generation electrolytes for lithium-ion batteries, and their recipe calls for more salt. The Ionic Liquids and Electrolytes for Energy Technologies (ILEET) Laboratory, run by Professor Wesley Henderson, creates and characterizes new lithium salts and ionic liquids to formulate electrolytes with a wider range of operating temperatures and voltages. Electrolytes in current Li-ion batteries are limited by poor low temperature performance (< -10°C) and decompose at elevated temperatures (>55°C), potentially causing a fire hazard. To circumvent these issues, Henderson is developing new electrolyte components based on organoborates related to bis(oxalato)borate (BOB^–) and cyanocarbanions. These anions are first synthesized as lithium salts, and then scaled up to form ionic liquids, which are salts that remain liquid even at room temperature or below and have low volatility. 

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A Reactive Molecular Dynamics Simulation Study of Single-Electron Reduction Pathways

The Smith Group, at the University of Utah, has identified reaction products of the single-electron reduction of ethylene carbonate (EC), an important component in lithium-ion battery electrolytes.  Reactive force field (ReaxFF) simulations were used to discover the fate of EC, which provides insight into the structure of the solid electrolyte interphase (SEI) – a thin film covering carbon anodes that limits the charge/discharge rate.  Reactive force fields allow for the making/breaking of chemical bonds during classical molecular dynamics simulations.  Because electronic degrees of freedom are treated in a simplified manner, these reactive molecular dynamics (RMD) simulations allow for the study of chemical reactions in much larger collections of molecules over much longer times than can be studied using ab initio methods.

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