Flow batteries incorporating a nitroxide compound within an aqueous electrolyte solution

Abstract

Flow batteries can include a first half-cell containing a first aqueous electrolyte solution. a second half-cell containing a second aqueous electrolyte solution, and a separator disposed between the first half-cell and the second half-cell, The first aqueous electrolyte solution contains a first redox-active material, and the second aqueous electrolyte solution contains a second redox-active material. At least one of the first redox-active material and the second redox-active material is a nitroxide compound or a salt thereof. Particular nitroxide compounds can include a doubly bonded oxygen contained in a ring bearing the nitroxide group, a doubly bonded oxygen appended to a ring bearing the nitroxide group, sulfate or phosphate groups appended to a ring bearing the nitroxide group, various heterocyclic rings bearing the nitroxide group, or acyclic nitroxide compounds.

What is claimed is: 
     
         1 . A flow battery comprising:
 a positive half-cell containing a positive, aqueous electrolyte solution;   a negative half-cell containing an aqueous electrolyte solution comprising a titanium coordination compound; and   a separator disposed between the positive half-cell and the negative half-cell;   wherein the positive, aqueous electrolyte solution comprises a nitroxide compound having a structure of:   
       
         
           
           
               
               
           
         
         or a salt form thereof; 
         wherein:
 R 1 -R 4  are, independently, optionally substituted C 1 -C 10  straight chain or branched alkyl; 
 each R 5  is, independently, H; optionally substituted alkyl, alkenyl, alkynyl, aryl, aralkyl, heterocyclyl, or heteroaryl; C 2 -C 6  polyol; C(═O)R 6 ; C(═O)OR 6 ; C(═O)NR 6 R 6 ; OR 6 ; O(C═O)R 6 ; SR 6 ; S(═O)R 6 ; S(═O) 2 R 6 ; NR 6 R 6 ; NR 6 (C═O)R 6 ; NR 6 (C═O)NR 6 R 6 ; (CH 2 ) 1-10 CO 2 H; (CH 2 ) 1-10 (CHOH)CO 2 H; CH 2 (OCH 2 CH 2 ) x OCH 3 ; CH(OH)CH 2 OH; halogen; cyano; sulfonyl; or perfluoroalkyl; 
 each R 6  is, independently, H; optionally substituted alkyl, alkenyl, alkynyl, aryl, aralkyl, heterocyclyl, or heteroaryl; perfluoroalkyl; (CH 2 ) 1-10 CO 2 H; (CH 2 ) 1-10 (CHOH)CO 2 H; (CH 2 CH 2 O) x CH 3 ; CH 2 (OCH 2 CH 2 ) x OCH 3 ; CH(OH)CH 2 OH; or C 2 -C 6  polyol; 
 optional double bonds are present; 
 a and b are, independently, 1 or 2; 
 x is an integer in a range between 0 and about 100; 
 A 1  is C(═O), S(═O), S(═O) 2 , P(═O)R 7 , or P(═O)OR 7 ; and 
 R 7  is an optionally substituted alkyl or aryl group. 
 
       
     
     
         2 . The flow battery of  claim 1 , wherein each R 5  is H. 
     
     
         3 . The flow battery of  claim 2 , wherein R 1 -R 4  are methyl. 
     
     
         4 . The flow battery of  claim 1 , wherein R 1 -R 4  are methyl. 
     
     
         5 . The flow battery of  claim 1 , wherein A 1  is S(═O), S(═O) 2 , P(═O)R 7 , or P(═O)OR 7 . 
     
     
         6 . The flow battery of  claim 5 , wherein A 1  is S(═O). 
     
     
         7 . The flow battery of  claim 1 , wherein the nitroxide compound is present in only the positive, aqueous electrolyte solution. 
     
     
         8 . The flow battery of  claim 1 , wherein the coordination compound has a formula of:
   D g M(L 1 )(L 2 )(L 3 )   wherein:
 M is Ti; 
 D is ammonium, tetraalkylammonium, an alkali metal ion, or any combination thereof; 
 g is an integer in a range between 0 and 6; and 
 L 1 , L 2  and L 3  are ligands. 
   
     
     
         9 . The flow battery of  claim 8 , wherein at least one of L 1 , L 2  and L 3  is a catecholate ligand. 
     
     
         10 . The flow battery of  claim 8 , wherein at least one of L 1 , L 2  and L 3  is a substituted catecholate ligand. 
     
     
         11 . The flow battery of  claim 1 , wherein the salt form is an alkali metal salt form, a combination of alkali metal salt forms, an ammonium salt form, a tetraalkylammonium salt form, or any combination thereof. 
     
     
         12 . A flow battery comprising:
 a first half-cell containing a first aqueous electrolyte solution;   a second half-cell containing a second aqueous electrolyte solution; and   a separator disposed between the first half-cell and the second half-cell;   wherein at least one of the first redox-active material and the second redox-active material comprises a nitroxide compound or a salt thereof having a heterocyclic ring framework that is pyrroline, pyrrolidine, imidazoline, imidazolidine, oxazoline, oxazolidine, thiazoline, thioazolidine, or a benzo-fused analogue thereof; indoline, isoindoline, or azabicycloheptane.   
     
     
         13 . A flow battery comprising:
 a first half-cell containing a first aqueous electrolyte solution;   a second half-cell containing a second aqueous electrolyte solution; and   a separator disposed between the first half-cell and the second half-cell;   wherein at least one of the first redox-active material and the second redox-active material comprises an acyclic nitroxide compound or a salt thereof.   
     
     
         14 . The flow battery of  claim 13 , wherein the nitroxide compound is [2,2,6,6-tetramethyl-4-(sulfooxy)piperidin-1-yl]oxidanyl or a salt thereof. 
     
     
         15 . The flow battery of  claim 14 , wherein the nitroxide compound is an alkali metal, ammonium, or tetraalkylammonium salt of [2,2,6,6-tetramethyl-4-(sulfooxy)piperidin-1-yl]oxidanyl.