Issue 2, 2022

Concentration-dependent ion correlations impact the electrochemical behavior of calcium battery electrolytes

Abstract

Ion interactions strongly determine the solvation environments of multivalent electrolytes even at concentrations below that required for practical battery-based energy storage. This statement is particularly true of electrolytes utilizing ethereal solvents due to their low dielectric constants. These solvents are among the most commonly used for multivalent batteries based on reactive metals (Mg, Ca) due to their reductive stability. Recent developments in multivalent electrolyte design have produced a variety of new salts for Mg2+ and Ca2+ that test the limits of weak coordination strength and oxidative stability. Such electrolytes have great potential for enabling full-cell cycling of batteries based on these working ions. However, the ion interactions in these electrolytes exhibit significant and non-intuitive concentration relationships. In this work, we investigate a promising exemplar, calcium tetrakis(hexafluoroisopropoxy)borate (Ca(BHFIP)2), in the ethereal solvents 1,2-dimethoxyethane (DME) and tetrahydrofuran (THF) across a concentration range of several orders of magnitude. Surprisingly, we find that effective salt dissociation is lower at relatively dilute concentrations (e.g. 0.01 M) than at higher concentrations (e.g. 0.2 M). Combined experimental and computational dielectric and X-ray spectroscopic analyses of the changes occurring in the Ca2+ solvation environment across these concentration regimes reveals a progressive transition from well-defined solvent-separated ion pairs to de-correlated free ions. This transition in ion correlation results in improvements in both conductivity and calcium cycling stability with increased salt concentration. Comparison with previous findings involving more strongly associating salts highlights the generality of this phenomenon, leading to important insight into controlling ion interactions in ether-based multivalent battery electrolytes.

Graphical abstract: Concentration-dependent ion correlations impact the electrochemical behavior of calcium battery electrolytes

Supplementary files

Article information

Article type
Paper
Submitted
23 Sep. 2021
Accepted
25 Nov. 2021
First published
15 Des. 2021

Phys. Chem. Chem. Phys., 2022,24, 674-686

Author version available

Concentration-dependent ion correlations impact the electrochemical behavior of calcium battery electrolytes

N. T. Hahn, J. Self, D. M. Driscoll, N. Dandu, K. S. Han, V. Murugesan, K. T. Mueller, L. A. Curtiss, M. Balasubramanian, K. A. Persson and K. R. Zavadil, Phys. Chem. Chem. Phys., 2022, 24, 674 DOI: 10.1039/D1CP04370F

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements