Nonaqueous Redox Flow Battery Electrolyte Comprising an Ionic Liquid with a Metal Cation Coordinated to Redox-Active Ligands

Abstract

Nonaqueous redox flow batteries (RFB) hold the potential for high energy density grid scale storage, though are often limited by the solubility of the redox-active species in their electrolytes. A systematic approach enables an increase the concentration of redox-active species in electrolytes for nonaqueous RFB, starting from a metal-coordination-cation-based ionic liquid. As an example, starting with an ionic liquid consisting of a metal coordination cation (MetIL), ferrocene-containing ligands and iodide anions can be substituted into the original MetIL structure, enabling a nearly 4× increase in capacity compared to original MetIL structure. Application of this strategy to other chemistries, optimizing electrolyte melting point and conductivity could yield >10 M redox-active electrons.

We claim: 
     
         1 . A nonaqueous redox flow battery electrolyte, comprising an ionic liquid comprising a redox-active metal cation coordinated to a plurality of aminoalcohol or dialcoholamine ligands and at least one redox-active ligand, and at least one redox-active anion, wherein the metal cation comprises a transition metal ion. 
     
     
         2 . The electrolyte of  claim 1 , wherein the transition metal ion comprises iron, copper, or manganese. 
     
     
         3 . The electrolyte of  claim 1 , wherein the aminoalcohol ligand comprises ethanolamine, butanolamine, or hexanolamine. 
     
     
         4 . The electrolyte of  claim 1 , wherein the at least one redox-active ligand comprises a metallocene. 
     
     
         5 . The electrolyte of  claim 4 , wherein the metallocene comprises ferrocene. 
     
     
         6 . The electrolyte of  claim 1 , wherein the at least one redox-active ligand comprises a transition metal coordinated to a bipyridine group. 
     
     
         7 . The electrolyte of  claim 6 , wherein the at least one redox-active ligand comprises tris(2,2′-bipyridine)nickel(II) or tris(2,2′-bipyridine)iron(II). 
     
     
         8 . The electrolyte of  claim 1 , wherein the at least one redox-active ligand comprises a quinone, (2,2,6,6-tetramethyl-piperidin-1-yl)oxyl, aniline, or methylviologen. 
     
     
         9 . The electrolyte of  claim 1 , wherein the at least one redox-active anion comprises iodide, ferricyanide, polyoxometallate, or peroxosulfate.