(47e) Importance of Explicit Solvent Molecule Inclusion in Predicting Electrolyte Reduction Kinetics in Lithium Ion Batteries

Lithium ion batteries (LIBs) are the principal power source for consumer electronics. However, in order to extend their efficacy into applications such as electric vehicles and energy-storage systems coupled with renewable energy sources, there is an imminent need to expand the energy density, power density, and cycle life while retaining safety and cost at an affordable range. This represents a knowledge and materials challenge around interfacing high energy electrodes with stable, cyclable electrolytes to ensure a long-lasting battery. Many existing technologies to expand battery capacity, such as Si anode materials or high voltage metal oxide cathodes, have been extensively studied, but continue to face challenges with stability of the interfacial layer formed when the electrolyte is electrochemically reduced/oxidized. These passivating layers are commonly termed the solid electrolyte interphase (SEI). The composition and morphology of the SEI layers formed on graphite anodes derived from ethylene carbonate-based electrolytes still remains poorly described, despite having the best performance. This can be largely attributed to the SEI structure’s dependence on the kinetics of the electrochemical and chemical decomposition reactions, transport processes, and precipitation onto the electrode. Furthermore, the complex chemical environment, branching reaction pathways, and environmental sensitivity of the products makes characterization of different SEIs formed by different electrolytes difficult to study. In order to design electrolytes which can stabilize the electrochemical interfaces in next-generation LIBs, improved understanding of factors influencing reaction kinetics are required. Previous computational approaches rely on cluster-model density functional theory (DFT) and ab inito molecular dynamics simulations to study the chemical and electrochemical reactions associated with the SEI formation, but the former neglects the complexity of the chemical environment, while the latter does not provide a reliable means to compare relative rates of competing reactions. This work details an approach which accounts for explicit solvent systems in the calculation of the reaction energy barriers for electrolyte decomposition reactions of traditional electrolytes, as well as additives, in order to provide greater insight into which factors influence the competing reaction rates. In this talk we will present an outline of our methodology as well as some of the key findings studying the reaction pathway for the reductive decomposition of ethylene carbonate. The fundamental understanding of these reaction mechanisms may help inform simulations at other scales as well as experiments, while the computational approach could serve to improve the study of other chemical systems.