Electrolytes with improved stability and transport properties have the potential to transform the current state-of-the-art Li-ion architectures and enable future technologies such as multivalent systems (e.g., Mg²⁺, Ca²⁺ and Zn²⁺), as well as Li-S and Li-O₂ conversion systems. To address the need for novel and optimized electrolytes, in this work, we apply our high-throughput computational infrastructure¹ to a range of systems – spanning both multivalent as well as monovalent charge carriers- and present our insights, highlighting the role of careful speciation for rational design of future, improved energy storage concepts.

To improve our understanding of structural and dynamical properties of highly concentrated LIB electrolytes, we use classical molecular dynamics simulations with enhanced sampling techniques to allow for correct statistics in these more viscous systems. We describe the modes of charge transport in LiPF₆ /propylene carbonate electrolyte in concentrated to superconcentrated regimes and elucidate the minority as well as majority species solvation structures and corresponding atomistic transport motifs. For multivalent systems, we find that the existence of multimeric species, such as contact-ion pairs are vitally important to account for the anodic stability of the electrolyte.^2-4 The plating process inherently requires the solvated divalent ion to undergo a transient, partially charged valence state; e.g. Mg⁺ or Ca⁺, which is identified as the fundamental descriptor for electrolyte stability. We find most solvent molecules as well as ion-paired anion molecules to be highly susceptible to rapid decomposition when in close contact with the reactive partially charged cation, thereby precluding stable, reversible plating behavior. This insight provides a ready explanation why so few classes of solvents and salts have demonstrated reversible Mg and Ca metal plating as well as enabling a path forward for rapid, in silico rational design and testing of novel, highly functional electrolyte molecules. ⁵

References:

¹ X. Qu, A. Jain, N.N. Rajput, L. Cheng, Y. Zhang, S.P. Ong, M. Brafman, E. Maginn, L. a. Curtiss, and K. a. Persson, Comput. Mater. Sci. 103, 56–67 (2015).

² N.N. Rajput, X. Qu, N. Sa, A.K. Burrell, and K.A. Persson, J. Am. Chem. Soc. (2015).

³ S.-D. Han, N.N. Rajput, X. Qu, B. Pan, M. He, M.S. Ferrandon, C. Liao, K.A. Persson, and A.K. Burrell, ACS Appl. Mater. Interfaces 8, (2016).

⁴ N.N. Rajput, T.J. Seguin, B.M. Wood, X. Qu, and K.A. Persson, Elucidating Solvation Structures for Rational Design of Multivalent Electrolytes—A Review (Springer International Publishing, 2018).

⁵ N.T. Hahn, T.J. Seguin, K.C. Lau, C. Liao, B.J. Ingram, K.A. Persson, and K.R. Zavadil, J. Am. Chem. Soc. 140, 11076–11084 (2018).