(247t) Reaxff Reactive Molecular Dynamics Simulations with Explicit Electrons and Applications to Battery Interfaces

Authors: 
Islam, M. M. - Presenter, The Pennsylvania State Univerisity
Kolesov, G. - Presenter, Harvard University
Kaxiras, E. - Presenter, Harvard University
van Duin, A. C. T. - Presenter, The Pennsylvania State University

Interfacial chemistry at the electrode-electrolyte interfaces are crucial for Li-based rechargeable battery performance. In typical Lithium ion batteries (LIBs) with the most prevalent carbonate type electrolytes, anode-electrolyte interface undergoes reduction reaction, while oxidation occurs at the cathode-electrolyte interface. The formation of the cathode/electrolyte and anode/electrolyte interface and the stability and diffusion properties of this interface layer are of crucial importance for life-cycle, power density, and safety of LiBs. This interfacial chemistry involves explicit electron flow and redox reactions. Any theoretical method to elucidate this intricate chemistry requires the capability of describing electron flow, and associated redox reactions. However, at this moment, no single computational method contains the capability to fully simulate the electron flow/chemistry coupling. Quantum mechanics based methods (QM) have the ability to simulate explicit electrons, but the requirement of extremely high length and time scale limits their usage to couple the complex chemistry at the cathode/anode interfaces to the electron flow. On the other hand, parameterization of the most of the force field methods are aimed to coarse grained, therefore, access to the electronic structures are usually absent. In the genre of reactive force fields, current version of ReaxFF method also possesses limitations in studying redox reactions. Therefore, an effective way for investigating interfacial chemistry is to extend the capability of the ReaxFF method to incorporate explicit electron- or hole-description for studying reduction and oxidation reactions, respectively. The extension of the ReaxFF method towards explicit electron- or hole-particle concept requires introducing new energy terms as well as redefinition of some of the current energy functional. In this study, we employed this newly developed electron version of ReaxFF (eReaxFF) for training our force field to capture electron affinities and ionization potential of various species. We are studying electron dynamics on different molecules and validating our findings against Ehrenfest dynamics results. We also apply this method to describe ionic liquid systems. The basic concepts of explicit electron treatment in eReaxFF, results from force field fitting and MD simulations will be presented.