US-12626946-B2 - Protective layer for an electrolyte in a flow battery

Abstract

A protective layer for an electrolyte in a flow battery and an electrolyte tank having a protective layer. The protective layer includes a light oil that includes hydrophobic hydrocarbons. The light oil having a density lower than a density of the electrolyte, the hydrophobic hydrocarbons being non-reactive to the electrolyte. The protective layer may be a liquid layer or may include a substrate impregnated with the light oil. An inert gas may also be utilized in the electrolyte tank.

Inventors

• Jinfeng Wu
• Stuart R. Miller

Assignees

• UOP LLC

Dates

Publication Date

20260512

Application Date

20220817

Claims (13)

1. 1 . A flow battery comprising: an electrolyte; and a protective layer disposed on the electrolyte, the protective layer comprising: a substrate impregnated with a light oil comprising hydrophobic hydrocarbons, wherein the light oil having a density lower than a density of the electrolyte, the hydrophobic hydrocarbons being non-reactive to the electrolyte.
2. 2 . The flow battery of claim 1 , wherein the substrate comprises an oil absorbing material.
3. 3 . The flow battery of claim 2 , wherein the oil absorbing material is selected from a group consisting of: natural fabrics, synthetic fabrics, inorganic material, and biomass materials.
4. 4 . The flow battery of claim 1 , wherein the substrate has a thickness between 0.1 to 100 cm.
5. 5 . The flow battery of claim 1 , wherein the light oil is selected from a group consisting of: silicone oil, mineral oils, vegetable oils, or combinations thereof.
6. 6 . An electrolyte tank for a flow battery, the electrolyte tank comprising: a closed vessel having an inlet and an outlet, a liquid electrolyte in the closed vessel, and a protective layer on top of the liquid electrolyte, wherein the protective layer comprises a substrate impregnated with a light oil comprising hydrophobic hydrocarbons, the light oil having a density lower than a density of the liquid electrolyte, the hydrophobic hydrocarbons being non-reactive to the liquid electrolyte.
7. 7 . The electrolyte tank of claim 6 , wherein the substrate comprises an oil absorbing material.
8. 8 . The electrolyte tank of claim 7 , wherein the oil absorbing material is selected from a group consisting of: natural fabrics, synthetic fabrics, inorganic material, and biomass materials.
9. 9 . The electrolyte tank of claim 6 , wherein the substrate has a thickness between 0.1 to 100 cm.
10. 10 . The electrolyte tank of claim 6 , wherein the light oil is selected from a group consisting of: silicone oil, mineral oils, vegetable oils, or combinations thereof.
11. 11 . The electrolyte tank of claim 6 , further comprising: an inert gas disposed between the liquid protective layer and the vessel.
12. 12 . The electrolyte tank of claim 11 , wherein the inert gas comprises nitrogen or argon.
13. 13 . The electrolyte tank of claim 6 , wherein the liquid electrolyte comprises a catholyte electrolyte, an anolyte electrolyte, a fresh electrolyte, or combinations thereof.

Description

RELATED APPLICATIONS This application claims priority to U.S. Patent Application Ser. No. 63/283,015 filed on Nov. 24, 2021, the entirety of which is incorporated herein by reference. FIELD OF THE INVENTION This invention relates generally to flow batteries, and more particularly to a protective layer for use in the electrolyte tanks to protect the electrolyte from oxidization and/or evaporation. BACKGROUND OF THE INVENTION The large-scale integration of renewable energy derived from solar or wind sources into the electric grid requires robust energy storage systems to improve its reliability, power quality, and economy. Among various energy storage technologies that having been considered and explored, redox flow batteries (RFB) are unique because they can convert electrical energy into chemical potential energy by means of a reversible electrochemical reaction between two aqueous electrolyte solutions. The redox electroactive species can be stored in external tanks and introduced into the batteries when needed. RFBs generally comprise flow cell stack with multiple separation membranes, two circulation pumps, and two external storage tanks filled with active materials containing metal ions that may be in different valance states. Therefore, the power and energy capacity can be independent, indicating that the storage capacity is determined by the quantity of electrolyte used and the rating power is decided by the active area as well as the cell number of the battery stacks. Compared with the other redox flow battery technologies, such as all-vanadium redox flow battery, zinc-bromine redox flow battery, or iron-chromium redox flow battery, all iron redox flow batteries (IFB) are particularly attractive for grid scale storage applications because of its advantages such as low chemical toxicity and very low material cost by utilizing abundantly available iron, salt, and water as the electrolyte. IFBs have iron in different valence states as both the positive and negative electrolytes for the positive and negative electrodes, respectively. The iron-based positive and negative electrolyte solutions stored in the external storage tanks flow through the stacks of the batteries. In the positive side, half-cell reaction involves Fe2+ losing electrons to form Fe3+ during charge and Fe3+ gaining electrons to form Fe2+ during discharge, and the positive reaction is given by Equation 1. For the negative side, half-cell reaction involves the plating and stripping of iron in the form of a solid plate, and the reaction is represented by Equation 2. The overall IFB reaction is shown in Equation 3. Positive electrode: 2Fe2+↔Fe3++2e− E0=−0.77V  Eq. (1) Negative electrode: Fe2++2e−↔Fe0 E0=−0.44V  Eq. (2) Total: 3Fe2+↔Fe0+2Fe3+ E0=1.21V  Eq. (3) The Equations 1 and 2 indicate that the standard potentials of both positive and negative redox couples in an IFB battery are lower than that of the oxygen reduction reaction, as shown below in Equation 4, below. O2+4H++4e−=2H2O, E0=1.229 V  Eq. (4) Consequently, both catholyte and anolyte electrolytes in IFB are prone to be oxidized by air. During IFB operating, the ideal pHs of catholyte and anolyte electrolytes are in the range of 0-1 and 4-5, respectively. The oxidation of Fe2+ to Fe3+ in catholyte side can cause catholyte and anolyte electrolytes imbalance, shift in electrolyte average oxidation state (AOS), as well as redox flow battery system capacity decay, as displayed in Equation 5. 4Fe2++O2+4H+=4Fe3++2H2O  Eq. (5) 12Fe2++3O2+6H2O=8Fe3++4Fe(OH)3  Eq. (6) For anolyte side, the air oxidation of anolyte electrolyte will bring even worse consequences because of the higher pH of anolyte electrolyte. As shown in the Equation 6, the oxidation of Fe2+ to Fe3+ and the subsequent precipitation of particulate forms of Fe3+ like ferric hydroxide Fe(OH)3 can not only cause the electrolyte AOS increase and severe capacity loss, but also block the flow channel, increase the flow resistance and IFB area specific resistance (ASR), and eventually lead to irreversible damage to IFB stack. Therefore, it is desirable to avoid oxygen containing the electrolyte. Current solutions to minimize or avoid air ingress, and the electrolyte oxidation, is to fill, purge, or pressurize the positive and negative electrolyte tanks constantly or periodically with inert gas, such as argon (Ar) or nitrogen (N2), during IFB operating. The addition of an inert gas generator or inert gas cylinders to energy storage plants significantly increases the complexity of the system, the battery product capital, and maintenance costs. Further such a protection scheme is not very stable and this makes it difficult and costly for the transport and/or the long-term storage of electrolyte. Accordingly, it would be desirable to have more effective and efficient designs to protect the electrolytes in such a flow battery from exposure to oxygen. SUMMARY OF THE INVENTION One or more protective layers have been invented for pro