FIELD OF THE INVENTION

The present invention is related to purification and production of electrolyte solutions. More particularly, the present invention is directed to electrochemical-based purification of electrolyte solutions, and related systems and methods.

BACKGROUND

Electrolytes for batteries and other uses generally need to be free of impurities that are detrimental to those uses. For example, in the context of a redox flow battery, each electrolyte used needs to be free of impurities that foul components of the battery. In a particular example, a vanadium redox flow battery (VRFB) is a system that converts electrical energy into chemical energy and then releases that chemical energy as electricity when there is demand. This type of battery is often paired with a solar and/or wind farm to help smooth out the power production intermittency associated with these renewable energy sources.

A VRFB comprises an electrochemical cell that performs the conversion between chemical and electrical energy. The electrochemical cell includes a negative electrode, an electrolyte separator (often a proton exchange membrane), and a negative electrode. Two separate vanadium solutions are stored in individual tanks—one tank contains a negative electrolyte solution that is fed to the negative electrode, and the other tank contains a positive electrolyte solution that is fed to the positive electrode. During normal operation, the negative electrolyte solution contains vanadium (II) and (III) ions, and the positive electrolyte solution contains vanadium (IV) and (V) ions. During charge, vanadium (III) ions are reduced to vanadium (II) ions in the negative electrolyte solution at the negative electrode, and vanadium (IV) ions are oxidized to vanadium (V) ions in the positive electrolyte solution at the positive electrode; the opposite happens during discharge.

When commissioning a new VRFB, a balanced electrolyte solution of average valence of roughly 3.5, i.e., an electrolyte solution of equal concentration of vanadium (III) and vanadium (IV) ions, is transferred into both the negative and positive electrolyte tanks. The battery is slowly charged until the negative and positive electrolyte solutions are at the desired ratio of vanadium (II)/(III) and vanadium (IV)/(V) ions, respectively. After this initial charge, some impurities present in the negative electrolyte solution will typically precipitate out as a solid metal phase precipitate. These impurities include, but are not limited to, As and Ge. These precipitates are detrimental to the electrochemical cell, because they clog the negative electrode and negatively impact battery performance.

The majority of conventional methods for making a vanadium-based electrolyte solution involve one of two methods:Method 1: Mixing V2O3and V2O5in a 3:1 molar ratio in excess acid to produce a solution of a 3.5 average valence.Method 2: Using a VRFB electrochemical cell in which the negative electrode is used to reduce a vanadium-based electrolyte solution to a 3.5 valence and the positive electrode is oxidizing a vanadium-based electrolyte solution that is periodically or continually reduced using a chemical reducing agent. This type of approach is needed because most organic reducing agents are only able to reduce vanadium (V) ions to vanadium (IV) ions (i.e. most organic reductants can't chemically reduce vanadium (IV) ions to a lower valence).

Neither of these conventional methods adequately remove impurities that often foul the electrochemical cell of a VRFB. Rather, both methods require that the vanadium feedstocks have low impurity content of select impurities for proper function and inhibiting fouling in a VRFB system. Consequently, many purification methods focus on the purification of the vanadium feedstock. While many of these methods are effective, they consume many chemicals and the final product commands a high cost premium.

SUMMARY OF THE DISCLOSURE

In one implementation, the present disclosure is directed to a method of commissioning a redox flow battery having a positive side and a negative side. The method includes providing an electrolyte solution having an initial valence and at least four available oxidation states comprising a set of higher oxidation states and a set of lower oxidation states; reducing the electrolyte solution to a valence below the initial valence to make a reduced electrolyte solution having a valence within the set of lower oxidation states; oxidizing a first portion of the reduced electrolyte solution to make a positive-side electrolyte solution having a valence within the set of higher oxidation states; providing, for the commissioning, the positive-side electrolyte solution for the positive side of the redox flow battery; and providing, for the negative side of the redox flow battery for the commissioning, a second portion of the reduced electrolyte solution as a negative-side electrolyte solution having a valence within the set of lower oxidation states.

In another implementation, the present disclosure is directed to a system for making a purified electrolyte solution from an electrolyte solution containing at least one impurity that precipitates out of the electrolyte solution at or below a precipitation valence. The system includes a reduction system that includes: an electrochemical reduction cell designed and configured to electrochemically reduce the electrolyte solution based on a reductant; a recirculation loop designed and configured to recirculate at least a portion of the electrolyte solution to the electrochemical reduction cell; a reduction-process control system in operative communication with the reduction system so as to control the valence of the electrolyte solution in the reduction system to a desired value at or below the precipitation value so as to cause the at least one impurity to precipitate out of the electrolyte solution as a precipitate; and a solid/liquid mechanical separation system designed and configured to remove at least a portion of the precipitate out of the electrolyte solution to make the purified electrolyte solution.

In yet another implementation, the present disclosure is directed to a system for making a valence-adjusted electrolyte solution from an electrolyte solution having at least four oxidation states. The system includes a reduction system that includes: an electrochemical reduction cell designed and configured to electrochemically reduce the electrolyte solution based on a reductant; a recirculation loop designed and configured to recirculate at least a portion of the electrolyte solution to the electrochemical reduction cell; a reduction-process control system in operative communication with the reduction system so as to control the valence of the electrolyte solution in the reduction system to a desired value; and an output designed, configured, and located to output the electrolyte solution as previously reduced electrolyte solution at about the desired value; and an oxidation system that includes: an electrochemical oxidation cell designed and configured to electrochemically oxidize the previously reduced electrolyte solution based on an oxidant; a recirculation loop designed and configured to recirculate at least a portion of the previously reduced electrolyte solution to the electrochemical oxidation cell; an oxidation-process control system in operative communication with the oxidation system so as to control the valence of the previously reduced electrolyte solution in the oxidation system to a desired final value; and an output designed, configured, and located to output the previously reduced electrolyte solution at about the desired final value.

