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

Gao, X.; Liu, X.; Mariani, A.; Elia, G. A.; Lechner, M.; Streb, C.; Passerini, S.

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 (N$_{07}$$^{+}$), bearing seven ether oxygen atoms, can effectively displace the bis(trifluoromethanesulfonyl)imide anion (TFSI$^{-}$) from the Ca$^{2+}$ 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 Ca$^{+2}$ ion diffusion rather than passivating the Ca metal electrode. Finally, as a proof-of-concept, a prototype Ca/V$_{2}$O$_{5}$ cell using the optimized IL-based electrolyte ([Ca(BH$_{4}$)$_{2}$]$_{0.05}$ [N$_{07}$TFSI]$_{0.95}$) 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$^{-1}$.

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Verlagsausgabe §
DOI: 10.5445/IR/1000123601
Veröffentlicht am 26.09.2020
Cover der Publikation
Zugehörige Institution(en) am KIT Helmholtz-Institut Ulm (HIU)
Publikationstyp Zeitschriftenaufsatz
Publikationsdatum 09.07.2020
Sprache Englisch
Identifikator ISSN: 1754-5692, 1754-5706
KITopen-ID: 1000123601
Erschienen in Energy & environmental science
Band 13
Heft 8
Seiten 2559-2569
Nachgewiesen in Scopus
Web of Science
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