(346bs) Structure/Dynamics of Electrolyte at Various Graphitic Electrode Interfaces

Commercial electrolytes for lithium ion batteries consist of ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and lithium salt (LiPF₆); some contain low concentrations of additives such as fluoroethylene carbonate (FEC), propylene carbonate (PC), and vinylene carbonate (VC). Solvents and additives have been shown to strongly influence the performance of electrodes by altering the SEI layer composition, thickness, and conductivity.¹ The addition of additives has consistently been demonstrated as advantages, sometimes necessary for better performance. However, still much needed to be understood, cause certain surface chemistry/binder pairing shown to be removing the positive effects of FEC additives completely.²

Due to complexity of chemical and electrochemical reactions involved, as well as lack of experimental tools for the direct measurement, it is still difficult for current experimental methods to characterize the SEI (beyond chemical composition). This leads to a deficit in the understanding of the thermodynamic and kinetic phenomena associated with the process. Molecular simulations, however, grant a level of detail that is not afforded to experimentalists. Understanding the structure and dynamics of electrolyte at the electrolyte-electrode interface is essential in understanding reaction mechanisms for SEI formation. Here, we investigate the interplay between surface characteristics and interfacial structure and dynamics for concentrated electrolytes with lithium salt over four different interfaces (hydroxyl-, hydrogen-, carbonyl-, and carboxyl-terminated) using classical force fields with molecular dynamic simulations.

1. Zhang, S. S. A review on electrolyte additives for lithium-ion batteries. Journal of Power Sources 162, 1379–1394 (2006).
2. Pandres, E. P., Olson, J. Z., Schlenker, C. W. & Holmberg, V. C. Germanium Nanowire Battery Electrodes with Engineered Surface-Binder Interactions Exhibit Improved Cycle Life and High Energy Density without Fluorinated Additives. ACS Appl. Energy Mater. 2, 6200–6208 (2019).