MetILs3: A Strategy for High Density Energy Storage Using Redox‐Active Ionic Liquids. (26th July 2017)

• Record Type: Journal Article
• Authors: Small, Leo J.; Pratt, Harry D.; Staiger, Chad L.; Anderson, Travis M.
• Is Part Of: Advanced sustainable systems. Volume 1:Number 9(2017)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2017-07-26
• Subjects: electrochemistry -- flow batteries -- grid scale storage -- ionic liquids -- redox; Sustainable living -- Periodicals; Sustainability -- Periodicals; Green technology -- Periodicals; Periodicals; 628
• DOI: 10.1002/adsu.201700066
• Languages: English
• ISSNs: 2366-7486

Abstract

Abstract : A systematic approach is presented for increasing the concentration of redox‐active species in electrolytes for nonaqueous redox flow batteries (RFBs). Starting with an ionic liquid consisting of a metal coordination cation (MetIL), ferrocene‐containing ligands and iodide anions are substituted incrementally into the structure. While chemical structures can be drawn for molecules with 10m redox‐active electrons (RAE), practical limitations such as melting point and phase stability constrain the structures to 4.2m RAE, a 2.3× improvement over the original MetIL. Dubbed "MetILs 3, " these ionic liquids possess redox activity in the cation core, ligands, and anions. Throughout all compositions, infrared spectroscopy shows the ethanolamine‐based ligands primarily coordinate to the Fe 2+ core via hydroxyl groups. Calorimetry conveys a profound change in thermophysical properties, not only in melting temperature but also in suppression of a cold crystallization only observed in the original MetIL. Square wave voltammetry reveals redox processes characteristic of each molecular location. Testing a laboratory‐scale RFB demonstrates Coulombic efficiencies >95% and increased voltage efficiencies due to more facile redox kinetics, effectively increasing capacity 4×. Application of this strategy to other chemistries, optimizing melting point and conductivity, can yield >10m RAE, making nonaqueous RFB a viable technology for grid scale storage. Abstract : Nonaqueous redox flow batteries (RFBs) hold the potential for high energy density grid scale storage, though they are often limited by the solubility of the redox‐active species in their electrolytes. Here, a systematic approach is presented for increasing the concentration of redox‐active species in electrolytes for nonaqueous RFBs, starting from a metal coordination cation‐based ionic liquid.