Lithium ion batteries with carbonate electrolytes have been extensively used in portable energy due to their advantages of low cost, high energy density, high output power, and lack of memory effects. In most commercial lithium ion batteries, the electrolyte solvents are composed of the mixture of a linear and a cyclic carbonate, due to the synergistic effect between the high dielectric constant of the cyclic carbonate and the low viscosity of the linear carbonate. Numerous experimental and theoretical studies investigated the solvation structure and dynamics of lithium ion electrolytes. However, many of the studies provided contradictory molecular descriptions of the system. Consequently, a comprehensive theoretical study using the highest level of theory is required. In this work, ab initio molecular dynamics simulation and ab initio umbrella sampling were applied to study the lithium hexafluorophosphate in organic carbonate solutions. Specifically, the structure of the lithium solvation shell and the interaction potentials of ion pairing and solvent exchange as a function of the chemical nature of the organic carbonate were studied. Our results showed that molecular arrangement of the coordinated carbonates is not significantly altered by the chemical nature of the carbonate, but the speciation of ionic species is. Interestingly, differences are observed between carbonate with different structure in the dynamics and organization of the solvation shell as well as solvent exchange and ion pairing. Overall, our study provides a comprehensive picture of the solvent structure, energy, and dynamics of the molecular components in different carbonate-based lithium ion electrolytes.

Computational studies of solvation structure and dynamics of lithium salts in carbonate-based electrolytes

2019 Spring National Meeting

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