Abstract
The emergence of magnesium and calcium batteries as potential beyond Li ion energy storage technologies has generated significant interest into the fundamental aspects of alkaline earth metal cation coordination in multivalent electrolytes and the impact of coordination on application-critical electrolyte properties such as solubility, transport, and electrochemical stability. Understanding these details in calcium electrolytes is of immediate importance due to recent, unprecedented demonstrations of reversible calcium metal electrodeposition in a limited number of ethereal solvent-based systems. In this work, we provide insight connecting Ca2+ coordination tendencies to important calcium battery electrolyte properties. Our results demonstrate a clear solvent:Ca2+ coordination strength trend across a series of cyclic ether and linear glyme solvents that controls the extent of ion association in solutions of "weakly"coordinating salts. We apply understanding gained from these results to rationalize relative anion:Ca2+ coordination tendencies and attendant Ca2+ coordination structures using two oxidatively stable anions of particular interest for current battery electrolytes. Armed with this understanding of solvent and anion interactions with Ca2+, we demonstrate and interpret differences in electrochemical calcium deposition behavior across several electrolyte exemplars with varying solvent and anion coordination strengths. Our findings demonstrate that solvents exhibiting especially strong coordination to Ca2+, such as triglyme, can inhibit reversible calcium deposition despite effective elimination of anion:Ca2+ coordination while solvents exhibiting more modest coordination strength, such as 1,2-dimethoxyethane, may enable deposition provided anion:Ca2+ coordination is substantially limited. These results reveal that the strength of coordination of both anion and solvent should be considered in the design of electrolytes for calcium batteries.
| Original language | English |
|---|---|
| Pages (from-to) | 8437-8447 |
| Number of pages | 11 |
| Journal | ACS Applied Energy Materials |
| Volume | 3 |
| Issue number | 9 |
| DOIs | |
| State | Published - Sep 28 2020 |
Funding
This work was supported by the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under Contract DE-NA0003525. This research used resources of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory and was supported by the U.S. DOE under Contract DE-AC02-06CH11357. The authors thank Changwook Lee for his help at APS 9-BM in the acquisition of the XAS data. The authors gratefully acknowledge the computing resources provided on Bebop, a high-performance computing cluster operated by the Laboratory Computing Resource Center at Argonne National Laboratory. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government.
Keywords
- Raman
- X-ray
- electrochemistry
- electrodeposition
- energy storage
- simulation
- spectroscopy