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Title: MetILs 3: A Strategy for High Density Energy Storage Using Redox-Active Ionic Liquids

We present a systematic approach 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 10 m redox-active electrons (RAE), practical limitations such as melting point and phase stability constrain the structures to 4.2 m 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 >10 m RAE, making nonaqueous RFB a viable technology for gridmore » scale storage.« less
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  1. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Publication Date:
Report Number(s):
Journal ID: ISSN 2366-7486; 657059
Grant/Contract Number:
AC04-94AL85000; NA0003525
Accepted Manuscript
Journal Name:
Advanced Sustainable Systems
Additional Journal Information:
Journal Volume: 1; Journal Issue: 9; Journal ID: ISSN 2366-7486
Research Org:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA); USDOE Office of Electricity Delivery and Energy Reliability (OE)
Country of Publication:
United States
25 ENERGY STORAGE; 36 MATERIALS SCIENCE; electrochemistry; flow batteries; grid scale storage; ionic liquids; redox
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1378388