Lithium-ion batteries commonly used in personal electronics (cell phones and laptops) rely on liquid carbonate solvents to facilitate charging and discharging. Cyclic carbonates, such as ethylene carbonate (EC) and propylene carbonate (PC), are ubiquitous to the electrolytes present in these devices and are responsible for shuttling lithium ions between the electrodes. While simple electrolytes composed of only EC or PC have been extensively studied, little is known about mixtures of these particular carbonates. It is possible that electrolytes could be improved by mixing these compounds to harness the advantages of EC and PC. Predictions of electrolyte properties for these mixtures can be made by simulating the molecular interactions between EC, PC, and lithium salts using molecular dynamics. Earlier work by von Wald Cresce, Borodin, and Xu [1] concluded a strong preference for PC binding of lithium ions over EC. However, the impact of molecular environment on co-solvent preference was not extensively considered. In particular, we present in this work the impact of different types of interfaces on EC/PC preference including the air interface and an ideal conductor interface. Both of these interface simulations are compared with results from bulk studies using a charge-scaling approach to correct our previous pair-wise potentials. We report the impact of charge-scaling on simulations of EC+1M LiPF6 and PC+1M LiPF6 electrolytes as well as mixtures of both EC and PC with 1M LiPF6. We do not see significant preference for PC over EC in bulk electrolyte or at the electrode interface, however the air interface does favor PC. The general propensity for PC at the air interface is reflected in the solvation shells for lithium ions at the surface, indicating a slight preference for PC. Our work indicates that the nature of the interface can alter co-solvent preferences and could have important implications for studying battery chemistry in other binary electrolyte systems containing cyclic and linear carbonates.

Lithium electrolyte co-solvent preference: Impact of interfaces on EC and PC ion solvation

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.