Electrochemical-Based Purification of Electrolyte Solutions, and Related Systems and Methods

Abstract

Methods and systems for removing impurities from electrolyte solutions having three or more valence states. In some embodiments, a method includes electrochemically reducing an electrolyte solution to lower its valence state to a level that causes impurities to precipitate out of the electrolyte solution and then filtering the precipitate(s) out of the electrolyte solution. In embodiments in which the electrolyte solution is desired to be at a valence state higher than the precipitation valence state, a method of the disclosure includes oxidizing the purified electrolyte solution to the target valence.

What is claimed is: 
     
         1 . A method of making a purified electrolyte solution, the method comprising:
 providing an electrolyte solution having a precipitation valence and containing at least one impurity that precipitates out of the electrolyte solution when the valence of the electrolyte solution is at or below the precipitation valence;   reducing the electrolyte solution to a valence below the precipitation valence so as to cause the at least one impurity to precipitate out of the electrolyte solution as a precipitate; and   removing a desired portion of the precipitate from the electrolyte solution so as to make the purified electrolyte solution.   
     
     
         2 . The method according to  claim 1 , wherein the electrolyte solution comprises a vanadium-based electrolyte solution, and the reducing of the electrolyte solution includes reducing the vanadium-based electrolyte solution to a valence of less than 3.0. 
     
     
         3 . The method according to  claim 2 , wherein the reducing of the vanadium-based electrolyte solution to a valence of less than 3.0 includes reducing the vanadium-based electrolyte solution to a valence of less than 2.5. 
     
     
         4 . The method according to  claim 2 , wherein the reducing of the vanadium-based electrolyte solution to a valence of less than 3.0 includes reducing the vanadium-based electrolyte solution to a valence of substantially 2.0. 
     
     
         5 . The method according to  claim 1 , wherein the reducing of the electrolyte solution is performed using a hybrid electrochemical cell. 
     
     
         6 . The method according to  claim 5 , wherein the reducing of the electrolyte solution utilizes hydrogen gas as a reductant. 
     
     
         7 . The method according to  claim 1 , further comprising oxidizing the purified electrolyte solution to a desired valence. 
     
     
         8 . The method according to  claim 7 , wherein the purified electrolyte solution comprises a purified vanadium-based electrolyte solution and the oxidizing of the purified electrolyte solution includes oxidizing the purified vanadium-based electrolyte to the desired valence. 
     
     
         9 . The method according to  claim 8 , wherein the desired valence is substantially 3.5. 
     
     
         10 . The method according to  claim 8 , wherein the desired valence is substantially 4.5. 
     
     
         11 . The method according to  claim 8 , wherein the desired valence is substantially 2.5. 
     
     
         12 . The method according to  claim 1 , further comprising oxidizing the purified electrolyte solution to each of two valences so as to create a plurality of purified valence-adjusted electrolyte solutions of differing valence. 
     
     
         13 . The method according to  claim 12 , wherein the purified electrolyte solution comprises a purified vanadium-based electrolyte solution and the oxidizing of the purified electrolyte solution to each of two valences includes oxidizing a first portion of the purified vanadium-based electrolyte solution to a valence of greater than 3.5 and oxidizing a second portion of the purified vanadium-based electrolyte solution to a valence of less than 2.5. 
     
     
         14 . The method according to  claim 13 , wherein the oxidizing of a first portion of the purified vanadium-based electrolyte solution to a valence of greater than 3.5 includes oxidizing the first portion to a valence of about 4.5 and oxidizing a second portion of the purified vanadium-based electrolyte solution to a valence of less than 2.5 includes oxidizing the second portion to a valence of about 2.5. 
     
     
         15 . The method according to  claim 12 , wherein the oxidizing of the purified electrolyte solution is performed using a hybrid electrochemical reduction cell. 
     
     
         16 . The method according to  claim 15 , wherein the oxidizing of the purified electrolyte solution utilizes the formation of hydrogen gas from protons. 
     
     
         17 . The method according to  claim 16 , wherein the reducing of the electrolyte solution is performed using a hybrid electrochemical reduction cell. 
     
     
         18 . The method according to  claim 17 , wherein the reducing of the electrolyte solution utilizes hydrogen gas output from the hybrid electrochemical oxidation cell. 
     
     
         19 . The method according to  claim 12 , wherein the reducing of the electrolyte solution and the oxidizing of the purified electrolyte solution are performed using an electrolyte-only electrochemical cell having a reduction side and an oxidation side with the electrolyte solution on the reduction side and the purified electrolyte solution on the oxidation side. 
     
     
         20 . The method according to  claim 19 , wherein each of the electrolyte solution and purified electrolyte solution comprises a vanadium-based electrolyte solution. 
     
     
         21 . The method according to  claim 1 , wherein the providing of an electrolyte solution comprises providing a vanadium-based electrolyte solution. 
     
     
         22 . The method according to  claim 21 , wherein all vanadium in the vanadium-based electrolyte solution comes substantially only from mixing V 2 O 5  with at least one strong acid. 
     
     
         23 . The method according to  claim 22 , wherein all the vanadium in the vanadium based electrolyte solution comes substantially from V 2 O 5  and V 2 O 3 , each mixed with at least one strong acid. 
     
     
         24 . The method according to  claim 1 , wherein the electrolyte solution has a lowest possible valence and the reducing of the electrolyte solution includes reducing the electrolyte solution to about the lowest possible valence. 
     
     
         25 . The method according to  claim 1 , wherein the precipitate is in the form of particles having different sizes, and removing a desired portion of the precipitate includes removing particles having sizes larger than a predetermined size. 
     
     
         26 . The method according to  claim 1 , further comprising, prior to providing the electrolyte solution, identifying that the electrolyte solution contains the at least one impurity that the method removes to make the purified electrolyte solution. 
     
     
         27 . The method according to  claim 1 , further comprising measuring valence of the electrolyte solution to determine whether or not the valence is at or below the precipitation valence so as to ensure the precipitation of the at least one impurity. 
     
     
         28 . The method according to  claim 1 , wherein:
 the purified electrolyte solution will be used in a redox flow battery; and   the method is performed prior to the purified electrolyte solution being installed into the redox flow battery.   
     
     
         29 . The method according to  claim 1 , wherein:
 the purified electrolyte solution is installed in a redox flow battery prior to performing the method; and   the method is performed using the redox flow battery prior to placing the redox flow battery into service.   
     
     
         30 . The method according to  claim 1 , wherein removing a desired portion of the precipitate includes mechanically or passively separating the desired portion from the electrolyte solution.