Alkoxy-functionalized ionic liquid electrolytes: understanding ionic coordination of calcium ion speciation for the rational design of calcium electrolytes. Issue 8 (15th July 2020)

• Record Type: Journal Article
• Authors: Gao, Xinpei; Liu, Xu; Mariani, Alessandro; Elia, Giuseppe Antonio; Lechner, Manuel; Streb, Carsten; Passerini, Stefano
• Is Part Of: Energy & environmental science. Volume 13:Issue 8(2020)
• Page Start: 2559
• Page End: 2569
• Publication Date: 2020-07-15
• Subjects: Energy conversion -- Periodicals; Fuel switching -- Periodicals; Environmental sciences -- Periodicals; Environmental chemistry -- Periodicals; 333.79
• DOI: 10.1039/d0ee00831a
• Languages: English
• ISSNs: 1754-5692

Abstract

Abstract : The proof-of-concept demonstration of a rechargeable Ca/V2 O5 cell is given, taking advantage of an alkoxy-functionalized ionic liquid-based electrolyte enabling the displacement of the anions from the coordination of the Ca 2+ cations. 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 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/V2 O5 cell using the optimized IL-based electrolyte ([Ca(BH4 )2 ]0.05 [N07 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 .