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Issue 8, 2020
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Alkoxy-functionalized ionic liquid electrolytes: understanding ionic coordination of calcium ion speciation for the rational design of calcium electrolytes

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Abstract

There is growing interest in the rational design of electrolytes for multivalent-ion batteries by tuning the molecular-level interactions of solvate species present in the electrolytes. Herein, we report our effort to control Ca-ion speciation in ionic liquid (IL) based electrolytes through the design of alkoxy-functionalized cations. Quantitative analysis reveals that the alkoxy-functionalized ammonium cation (N07+), bearing seven ether oxygen atoms, can effectively displace the bis(trifluoromethanesulfonyl)imide anion (TFSI) from the Ca2+ ion coordination sphere, facilitating the reversible Ca deposition/stripping process. More importantly, post-analysis of Ca deposits surface chemistry and density functional theory calculations of Ca-ion speciation indicate the formation of an organic-rich, but inorganic-poor solid electrolyte interphase layer, which enables Ca2+ ion diffusion rather than passivating the Ca metal electrode. Finally, as a proof-of-concept, a prototype Ca/V2O5 cell using the optimized IL-based electrolyte ([Ca(BH4)2]0.05[N07TFSI]0.95) is demonstrated for the first time, exhibiting a remarkable initial discharge capacity of 332 mA h g−1 and reversible capacity of 244 mA h g−1.

Graphical abstract: Alkoxy-functionalized ionic liquid electrolytes: understanding ionic coordination of calcium ion speciation for the rational design of calcium electrolytes

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Supplementary files

Article information


Submitted
15 Mar 2020
Accepted
09 Jul 2020
First published
09 Jul 2020

This article is Open Access

Energy Environ. Sci., 2020,13, 2559-2569
Article type
Paper

Alkoxy-functionalized ionic liquid electrolytes: understanding ionic coordination of calcium ion speciation for the rational design of calcium electrolytes

X. Gao, X. Liu, A. Mariani, G. A. Elia, M. Lechner, C. Streb and S. Passerini, Energy Environ. Sci., 2020, 13, 2559
DOI: 10.1039/D0EE00831A

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