Correlating Calcium Electrodeposition with Solvation Structure: X-Ray Absorption Studies on Ethereal-Calcium Complexes in Solution

Ca-ion electrochemical systems have been on the forefront of multivalent energy storage due to their use of earth-abundant redox materials and their high theoretical specific capacities in relation to monovalent-charge carriers. However, significant pitfalls in cation plating and striping arise from electrolyte decomposition and can be related in-part to the coordination environment around Ca²⁺ with both the negatively charged anion and the organic–aprotic solvent. X-ray absorption fine structure (XAFS) studies of liquid electrolytes have been performed to identify the elemental and geometric coordination around the multivalent cation. Specifically, we can define the local geometry, coordination and electronic structure of Ca–ethereal complexes through the combined analysis of the X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) to provide clear indication of the extent of Ca²⁺–solvent interaction. Finally, we combined these characterization results with recent progress in Ca²⁺ electrochemistry and suggest important structural trends for reversible plating/stripping depending on the extent of solvent chelation. The submitted abstract has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory ("Argonne"). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.