Composite membranes for flow batteries

Abstract

A composite membrane for use in flow batteries is contemplated. The membrane comprises a hydrogel, such as poly(vinyl alcohol), applied to a polymeric microporous film substrate. This composite is interposed between two half cells of a flow battery. The resulting membrane and system, as well as corresponding methods for making the membrane and making and operating the system itself, provide unexpectedly good performance at a significant cost advantage over currently known systems.

1 . A flow battery system comprising:
 a positive electrolyte flowing through a positive reaction chamber;   a negative electrolyte flowing through a negative reaction chamber;   a non-ionomeric membrane comprising a hydrogel physically separating the positive reaction chamber from the negative reaction chamber; and   wherein the membrane is ionically conductive but resistant to hydraulic crossover and wherein at least one of the positive and negative electrolytes comprises an aqueous solution.   
     
     
         2 . A flow battery according to  claim 1 , wherein the hydrogel comprises poly(vinyl alcohol). 
     
     
         3 . (canceled) 
     
     
         4 . A flow battery according to  claim 1 , wherein at least one of the positive and negative electrolytes comprise a multi-valent ionic species. 
     
     
         5 . A flow battery according to  claim 1 , wherein the hydrogel is selected from: poly(vinyl alcohol), poly(acrylic acid), poly(ethylene glycol), and combinations thereof. 
     
     
         6 . A flow battery according to  claim 5 , wherein the hydrogel effectively blocks all pores of a polymeric substrate so as to prevent any flow of fluid through the pores. 
     
     
         7 . A flow battery according to  claim 1 , wherein the polymeric substrate is microporous. 
     
     
         8 . A flow battery according to  claim 7 , wherein the polymeric substrate consists of polyethylene, polypropylene, and combinations thereof. 
     
     
         9 . A flow battery according to  claim 1 , wherein the polymeric substrate has a void volume between 30% and 80%. 
     
     
         10 . A flow battery according to  claim 1 , wherein the polymeric substrate has a void volume exceeding 80%. 
     
     
         11 . A flow battery according to  claim 1 , wherein the membrane consists of hydrogel. 
     
     
         12 . A flow battery according to  claim 1 , wherein the pH of the positive and negative electrolytes is less than 3.0. 
     
     
         13 . A flow battery according to  claim 1 , wherein the hydrogel is at least one of: hydrolyzed, crystalline, semi-crystalline, and crosslinked. 
     
     
         14 . A method of making a composite membrane that is ionically conductive and resistant to hydraulic crossover, the method comprising:
 providing a substrate having a plurality of pores forming a void volume;   impregnating the pores with a hydrogel;   treating the hydrogel to create a non-ionomeric membrane; and   wherein the hydrogel is selected from: poly(vinyl alcohol), poly(acrylic acid), poly(ethylene glycol), and combinations thereof.   
     
     
         15 . The method according to  claim 14 , wherein the treating the hydrogel includes at least one of thermal crosslinking, chemical crosslinking, photochemical crosslinking, and hydrolyzing the hydrogel. 
     
     
         16 . The method according to  claim 14 , wherein the impregnating the pores comprises at least one of film casting, roll-to-roll casting, infiltration, and dip coating. 
     
     
         17 . The method according to  claim 14 , wherein the impregnating the pores results in a layer of hydrogel deposited on at least one side of the substrate at a thickness of 0.1 to 25 micrometers. 
     
     
         18 . The method according to any preceding method  claim 17 , further comprising, prior to the impregnating the pores, at least one of: cleaning the pores and removing air from the pores. 
     
     
         19 . The method according to  claim 14 , further comprising submerging the substrate in alcohol. 
     
     
         20 . The method according to any preceding method  claim 14 , wherein the hydrogel comprises poly(vinyl alcohol) selected to have a purity of at least 99 wt. %. 
     
     
         21 . The method according to  claim 14 , wherein at least 95 wt. % of the hydrogel is hydrolyzed. 
     
     
         22 . The method according to any preceding method  claim 14 , wherein a plurality of layers of hydrogel are successively impregnated on the substrate. 
     
     
         23 . A flow battery according to  claim 4 , wherein the multi-valent species include at least one of: vanadium (2 + ) ions, vanadium (3 + ) ions, vanadium (4 + ) ions, vanadium (5 + ) ions, cuprous ions, cupric ions, ferric ions, and ferrous ions.