(Invited) Understanding Ion-Ion Correlations: From Liquid Electrolytes to Polymer Electrolytes

Mass transport in electrolytes is one of the most important design focuses of electrochemical devices such as batteries, fuel cells, and supercapacitors. Compared to the infinitely dilute solution, ion-ion correlations play a central role in determining the structure-property relationships in the concentrated solution. Therefore, disentangling ion-ion correlations and establishing their impact on transport coefficients is a fundamental and pressing issue in the field of electrolyte materials. In this talk, I will present the recent works of my group and collaborators on using molecular dynamics simulations to understand ion-ion correlations. In particular, we looked into this issue by exploring the synergy between liquid electrolytes and polymer electrolytes following the physical chemistry route started by Onsager. This has led to a number of interesting results on the relationship between the ion-pairing and the deviation from the Nernst-Einstein relation [1-3], and shed light on resolving the controversy of the negative transference number found in polymer electrolytes [4]. References: [1] Y. Shao, M. Hellström, A. Yllö, J. Mindemark, K. Hermansson, J. Behler, and C. Zhang, “Temperature effects on the ionic conductivity in concentrated alkaline electrolyte solutions”, Phys. Chem. Chem. Phys . 2020 , 22: 10426. [2] Y. Shao, K. Shigenobu, M. Watanabe, and C. Zhang, “Role of viscosity in deviations from the Nernst–Einstein relation”, J. Phys. Chem. B , 2020 , 124: 4774. [3] H. Gudla, Y. Shao, S. Phunnarungsi, D. Brandell, and C. Zhang, “Importance of the ion-pair lifetime in polymer electrolytes”, J. Phys. Chem. Lett., 2021 , 12: 8460. [4] Y. Shao, H. Gudla, D. Brandell, and C. Zhang, “Transference number in polymer electrolytes: mind the reference-frame gap”, J. Am. Chem. Soc., 2022 , 144: 7583.