WO2017132357A1

WO2017132357A1 - Surfactants for improved bromine dispersion in electrolyte flow battery solutions

Info

Publication number: WO2017132357A1
Application number: PCT/US2017/015104
Authority: WO
Inventors: Peter Lex; Wu BI
Original assignee: Ensync, Inc.
Priority date: 2016-01-27
Filing date: 2017-01-26
Publication date: 2017-08-03

Abstract

A surfactant is provided that when combined with an aqueous solution containing bromine, such as in a zinc-bromine or hydrogen-bromine flow battery, enhances the dispersion of the bromine within the solution. The surfactants that can be employed to improve the dispersion of bromine within the electrolyte system include, but are not limited to, surfactants that include, but are not limited to, surfactants that possess a good stability in oxidative environment and a minimal foaming ability, such as the surfactant sodium cumene sulfonate. An appropriate amount may be within 0.01% to 3% by weight of the electrolyte solution.

Description

SURFACTANTS FOR IMPROVED BROMINE DISPERSION IN ELECTROLYTE

FLOW BATTERY SOLUTIONS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001 ] This application claims priority from US Provisional Patent Application Serial No. 62/287,526, filed on January 27, 2016, the entirety of which is expressly incorporated by reference herein for ail purposes.

FIELD OF THE INVENTION

[0002] The present invention relates generally to surfactants, and more specifically to surfactants for use in dispersing bromine in liquids, such as in an electrolyte system.

BACKGROUND OF THE INVENTION

[0003] in one example of the use of bromine in an electrolyte system, a bromide/bromine redox couple, with a standard electrochemical potential of 1.07V vs. or relative to the potential of the standard hydrogen electrode (SHE), is used as the active compound for positive electrodes in rechargeable flow batteries such as a zinc-bromine battery and/or a hydrogen-bromine battery, as the latter discussed in W.A. Braff. and et al, Nature Communications, v4 (2013) p. 2346.

[0004] When using the bromine/bromide redox couplet/combination in these batteries, during a charging step, the bromide ions are oxidized to form a heavy bromine liquid which is not readily soluble in the aqueous cathoiyte. Liquid bromine has a high saturation vapor pressure even at ambient temperature, so the bromine can be lost from the cathoiyte due to evaporation, thereby reducing the charging capacity of the battery. It is also a serious safety concern to minimize bromine vapor leakage out of these batteries or their electrolyte tanks. [0005] To address this evaporation issue, a eom lexing agent, typically a bromide salt Q-Br, is added to the electrolyte in order to bond with the bromine (Βΐτ) to form polybromide complexes to minimize its evaporation. One example of such a eomplexing agent is 1 -Ethyl- 1 - methylpyrrolidinium bromide (MEP-Br). The resulting polybromide-eomplex settles down out of the main aqueous cathoiyte, forming a distinctive heavy-and-oily phase commonly referred as the second phase. During discharge of the battery, this second brom ine phase may be pumped separately and mixed with the cathoiyte aqueous first phase prior to entering/re-entering the battesy stacks. The common electrolyte for the bromine/bromide redox reaction utilized in electrolyte flow batteries contains bromide salts including, but not limited to ZnBn, NaBr, KBr, HBr, N¾Br and any mixture thereof. The selected bromine complex agent Q-Br is oilers added, but not required, ^'with other additives to the electrolyte. [0006] The two phases present in the bromide bromine cathoiyte is a significant cause of inconsistent battery charge -discharge performance among charge-discharge cycles, due to nonuniform bromine distribution to positive electrodes in a battery stack. Non-uniform electrolyte distribution due to other factors including non-optimal stack channel design, gravity effects, and inappropriate electrolyte-pump speed, can also affect inconsistency ceil performance. In a metal-bromine flow battery such as zinc-bromine battery, this may also cause non-uniform metal plating-dissolution reactions due to distorted in-plane current distribution through the cathoiyte. Hence, this can result in a non-uniform metal distribution on the electrodes and a higher risk of the formation of dendrites on the electrode, which is undesirable, [0007] it has recently been reported that the surfactant polyoxyethyiene (20) sorbitan mono!aurate, commonly known as Tween 20, was found to increase zinc -bromine flow battery performance. See, Jung Hoon Yang, and et at, Journal of Power Sources, v275 (2015) p. 294. It is believed that the two-phase cathoiyte when mixed with this surfactant resulted in better two phase, i.e., the first or aqueous phase and the second or polybromide phase, mixing, hence a more uniform and higher flow rate of bromine distribution to the positive electrode for the reaction, resulting in better battery performance.

[0008] However, the foaming capability of a surfactant such as Tween 20 is generally not desirable for flow battery⁷ electrolyte applications. This is because a large volume of air bubbles in electrolyte will most likely result in non-uniform (time and spatial) and inefficient electrolyte pump-delivery to a flow battery cell or stack,

[0009] Thus, it is desirable to develo a surfactant that can be mixed with the bromide salt and any optional complexing agent to enhance the dispersion of bromine in a chemical system, such as within the electrolyte system utilized within an electrolyte battery.

SUMMARY OF THE INVENTION

[00010] Briefly described, according to one aspect of an exemplary embodiment of the invention, one or more other types of surfactants are combined with a bromide/bromine electrolyte system to improve or enhance the dispersion of the bromine within the electrolyte system, where the surfactants shall also have a minimal foaming ability, a good chemical compatibility with bromine, and a good electrochemical stability on the positive electrode. The surfactant acts to maintain the dispersion of the liquid bromine phase within the aqueous first phase for a longer time period, thus improving the performance of the electrolyte battery including the surfactant within the bromide/bromine electrolyte system.

[0001 1 ] Numerous other aspects, features, and advantages of the invention will be made apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[00012] The drawing figures illustrate the best, mode currently contemplated of practicing the invention.

[00013] in the drawings:

[00014] FIG. 3 is a schematic diagram of a stack of alternatively disposed zinc-bromine battery components, cooperating with electrolyte reservoirs according to an exemplary embodiment of the invention.

[00015] FIG. 2 is a perspective, exploded view of a stack of alternately disposed .zinc - bromine battery components according to an exemplary embodiment of the invention,

[00016] FIG. 3 is a schematic diagram of a zinc-bromine battery cell showing electrolyte flow to and from the reservoirs and through the battery according to an exemplary embodiment of the invention.

[00017] FIG. 4 are photographs illustrating liquid bromine dispersion in the standard electrolyte (left) and electrolyte mixed, with surfactant (right) (a) at 5 seconds after a vigorous mixing; (b) at 10 seconds after a vigorous mixing; (c) at 1 5 seconds after vigorous mixing; and (d) at 20 seconds after vigorous mixing.

DETAILED DESCRIPTION^' OF THE INVENTION

[00018] Referring more particularly to the drawings, one particular exemplary embodiment of an electrolyte flow battery including bromine complexes, as are known in the art, such as US Patent Nos. 4,049,886; 5,002,841 ; 5,1 88,91 5 and 5,650,239, and US Patent Application Publication No. 2012/0326672, each of which is expressly incorporated by reference herein for all purposes in its entirety, and. which each disclose a metal-bromine battery, is shown in an exploded view and is designated generally by the numeral 10 in FIG. 1 . The metal-bromine battery 10 includes a series of electrodes 1 1 and separators 12, welded together to form a stack 13 of electrochemical cells. Each battery 10 includes a predetermined number of electrodes U and separators 12 and, thus, a predetermined number of electrochemical cells. As best seen in FIG. 2, respective endblocks 14 are disposed at each end of the battery 10. The endblocks 14 each have a pair of openings 15 in which a pair of terminal studs 16 are positioned. The terminal studs 16 are electrically coupled to the battery's terminal electrodes 17 which may^¬ be mounted directly adjacent to the endblocks. The terminal studs provide a convenient means through which current may enter and leave the battery. Each terminal electrode is a current collector means capable of collecting current from, and distributing current to, the electrochemical ceils of the battery. Although not shown, it should be understood that terminal electrodes are mounted on, or are adjacent to, each end block. [0001 9] Referring back to FIG. 1 , aqueous, or optionally non-aqueous, electrolyte solution or catholyte is stored in a catholyte reservoir 20. A catholyte pump 22 pumps aqueous catholyte through a common catholyte manifold 24 into each cathodic half cell as indicated by the arrows labeled A in FIG. 1, and back to the catholyte reservoir 20 through a catholyte return manifold 26.

[00020] Similarly, aqueous, or optionally non-aqueous, electrolyte solution or anolyte is stored in an anolyte reservoir 30 and pumped through an anolyte inlet manifold 32 by an anolyte pump 34. The anolyte flows through each anodic half-cell, one of which is disposed between each cathodic half-cell, and back to the anolyte reservoir 30 through an anolyte return manifold 36, as indicated by the arrows labeled B in FIG. 1. Thus, the electrochemical cells of the battery 10 are coupled in fluid flowing relation to the reservoirs 20 and 30 through the manifolds 24, 26, 32, and 36.

[00021] Each electrode and separator includes a thin sheet of electrode or separator material, respectively. These sheets are individually mounted in a nonconductive flow frame 40. Preferably, the nonconductive flow frame is made from a polymeric material such as polyethylene. Long, winding electrolyte inlet and outlet channel patterns are incorporated into one or both sides of the separator frame, the electrode frame, or both. The geometry of the channels_., contributes to the electrical resistance required to reduce shunt currents which result in cell power losses. A leak-free internal sea! is maintained along the channels and about the common perimeter of adjacent separators and electrodes. [00022] As can be more readily seen by reference to the schematic representation of FIG. 3, during charge electron flow through the battery 10 results in metal/zinc being plated on an anode or zinc electrode 100 which is in an anodic haif-cell 1 10. During the same time bromine is evolved at a cathode or bromine electrode 120 which is in a cathodic half-cell 130. When the bromine is evolved it is immediaieiy complexed with a quaternary salt and is removed from the battery to the catholyte reservoir 30. The complexed bromine or dense second phase is separated by gravity from bromine in the reservoir. Normally, on discharge, the complexed bromine or second phase is returned to the battery stack were bromine is reduced to bromide ion and metal is oxidized to a metal ion, e.g., zinc ion. [00023] The electrolyte solution or system including the anoiyte and the catholyte in one exemplary embodiment is formed with a highly similar or identical electrolyte that is disposed on both sides of an ion-conducting membrane 12 within the electrolyte flow battery 10, such as a Nafion® membrane, a Solvay© membrane, among other suitabie ion exchange membranes, or a membrane/separator hybrid structure including one or more layers of an ion-conducting membrane with one or more layers of a porous non-ion-conducting separator, Non-ion- coiiducting porous separator(s) 12 includes, but not limited to Asahi® separator, Entek® separator, Daramic® separator, among other suitable separators.

[00024] In exemplary embodiments of the invention, a surfactant is added to the electrolyte system or solution to improve the dispersion of bromine with the electrolyte. While any suitable surfactants can be utilized, in one exemplary embodiment, of the invention, the surfactants that can be employed to improve the dispersion of bromine within the electrolyte system include, but are not limited to, surfactants that include, but are not limited to, surfactants that possess a good stability in oxidative environment and a minimal foaming ability. In another exemplary embodiment of the invention, the surfactant is not polyoxyethyiene (20) sorbitan monolaurate. A selected surfactant concentration for an electrolyte system depends on surfactant nature and electrolyte composition, but in one exemplary embodiment of the invention the concentration of the surfactant can be generally within the range of 0.01 %-3.0% by weight, or more specifically 0.5% w/w to 2.0% w/w of the overall chemical/electrolyte system w h or without any additional additives, such as eomplexing agents.

[00025] One example of a surfactant of this type is sodium cumene sulfonate (SCS). In 5 an exemplary embodiment, as shown in FIGS. 4(a)-(d), liquid bromine dispersion was formed with the formulation of 2,25 M zinc bromide, 0.5 M zinc chloride and 0.8 M N-ethyl-N- methylpyrrolidi urn brom ide. 10 grams of each solution was added to a separate vial, fol lowed by I ml bromine. To the solution in the vial illustrated on the right in FIG. 4, 1.0% w/w sodium cumene sulfonate (SCS) was added and mixed in a beaker with a magnetic stir bar. The vials it) were covered, shaken vigorously by hand an allowed to sit overnight. For the emulsion test, both solutions in the vials were hand shaken vigorously for 1 seconds, with images of the samples being taken at 5 seconds, J O seconds, 15 seconds and 20 seconds after agitation ceased,

[00026] As can be readily see in photographs of FIG. 4(a)-(d), in each set of 15 photographs, as substantia! amount of bromine remained dispersed in the electrolyte sampie including the surfactant as opposed to the control sample. Further, 20 seconds after vigorous mixing, as shown in FIG. 4(d), there is little bromine present in the top aqueous phase of the standard electrolyte sample without SCS surfactant, compared to a substantial amount of aqueous bromine in the eieetrolyte with SCS surfactant, Illustrated b the dark brown color at 0 the top of the surfactant-containing sample. In addition, as illustrated in each of the photographs of the surfactant-containing sample in FIGS. 4(a)-(d)_J the electrolyte with SCS surfactant did not generate an excess amount of foam or bubbles in the electrolyte sample after vigorous mixing of the sample, thus maintaining the uniform and efficient eieetrolyte pump-delivery of the electrolyte containing the surfactant to a flow battery cel l or stack.

5

[00027] In other exemplary embodiments of the invention, in addition to sodium cumene sulfonate (SCS), other useful surfactants include polyalkylene glycol, lauryl alcohol aikoxylate, tridecyl alcohol ethoxylate (PQYi-T), tallow amine ethoxylate (POE-2), quaternium-82, sodium toluene sulfonate, linear alcohol (Cjj-n) ethoxylate (POE-3), linear alcohol (Cu) ethoxylate 0 (PQE-3), linear alcohol (CVn) ethoxylate (POE-2.5), linear alcohol (Cts-is) ethoxylate (POE-3), alcohol ethoxylate, ammonium xylene sulfonate, sodium xylene sulfonate, polyalkoxyiate amide, alcohol phosphate, and any .mixtures of the above. In the above list, the number of moles of carbon atoms in the linear alcohol is indicated by the notation of C_ra" or "C_n" where m or n is the number of moles of carbon present in the surfactant, or the notation of "Cm-n" where m-n is a range of the number of moles of carbon present in the surfactant. The number of moles of ethylene oxide per mole of acid, amine, amide, or alcohol in each surface-active agent is indicated by the notation "POE-X", where X is the number of moles of ethylene oxide. 1000281 In still another exemplary embodiment of the invention, a small-scale zinc- bromine flow battery with an ion-conduction separator was charged with test solutions of 1% w/w of sodium cumene sulfonate added to both an aqueous anolyte of 3M ZnCb with 2M NaCl and an aqueous catholyte of 4M NaBr with 0.4M MEP-Br, The electrolyte was utilized in a 25- cra² zinc-bromine flow battery tested at 20 mA/cm² and 40 °C. This surfactant produced an excellent bromine dispersion i the aqueous catholyte as an average charge-discharge cycle energy efficiency of 80% was demonstrated over more than 10-20 charge-discharge cycles.

[00029] Further, the surfactants disclosed in this invention for bromine dispersion are not limited for zinc-bromine battery application, but are applicable for any chemical systems containing liquid bromine in aqueous, non-aqueous, or mixed multi-phase media.

[00030] Various other embodiments of the invention are contemplated as being within the scope of the filed claims particularly pointing out and distinctly claiming the subject matter regarded as the invention.

Claims

1. An electrolyte solution for use within an electrolyte flow battery; the solution comprising:

a) a solution including bromine; and

b) a surfactant for improving the dispersion of bromine within the solution, wherein the surfactant is not polyoxyethyiene (20) sorbitan monoiaurate.

2. The electrolyte solution of claim 1 wherein the solution is an aqueous solution.

3. The electrolyte solution of claim 1 wherein the surfactant is selected from the group consisting of; polyalkyletie glycol, lauryl alcohol alkoxylate, tridecyl alcohol ethoxylate (POE-3), tallow amine ethoxylate (POE-2), quaternium-82, sodium toluene sulfonate, sodium cumene sulfonate, linear alcohol (C12-13) ethoxylate (POE-3), linear alcohol (C 11) ethoxylate

(POE-3), linear alcohol (C9-11 ) ethoxylate (POE-2.5), linear alcohol (C)₂-i 5) ethoxylate (POE-3), alcohol ethoxylate, ammonium xylene sulfonate, sodium xylene sulfonate, poiyaikoxylate amide, alcohol phosphate, and any mixtures of the above.

4. The electrolyte solution of claim 1 wherein the surfactant is sodium cumene sulfonate.

5. The electrolyte solution of claim 1 wherein the surfactant is present in an amount of G.01%-3.0% by weight of the electrolyte solution.

6. The electrolyte solution of claim 1 wherein the surfactant is present in an amount of 0.5%-2.0% by weight of the electrolyte solution,

7. The electrolyte solution of claim 1 further .comprising a complexing agent,

8, A method of improving the dispersion of bromine in an electrolyte solution for a an electrolyte flow battery, the method comprising the steps of;

a) providing an electrolyte solution including bromine; and

b) adding an effective amount of a surfactant to the electrolyte solution, where the surfactant is not polyoxyethyiene (20) sorbitan monoiaurate.

9. The method of claim 8 wherein the step of adding the surfactant comprises adding a surfactant selected from the group consisting of: polyaikylene glycol, lauryl alcohol alkoxylate, tridecyl alcohol ethoxylate (POE-3), tallow amine ethoxyiate (POE-2), quaternium- 82, sodium tol uene sulfonate, of sodium cumene sulfonate, linear alcohol (€52- 13) ethoxylate (POE-3), linear alcohol (C 1 ethoxylate (POE-3), linear alcohol (C -1 1) ethoxyiate (POE-2.5), linear alcohol (Ci2-is) ethoxylate (POE-3), alcohol ethoxyiate, ammonium xylene sulfonate, sodium xylene sulfonate, polyalkoxylate amide, alcohol phosphate, and any mixtures of the above.

10. The method of claim 9 wherein the step of adding the surfactant comprises adding the surfactant in an amount o O.01 %-3.0% by weight of the electrolyte solution.

11. The method of claim 9 wherein the step of adding the surfactant comprises adding the surfactant in an amount of 0.5%-2.0% by weight of the electrolyte .solution.

12. The method of claim 9 further comprising the step of adding a eompiexing agent to the electrolvte solution.

13. An electrolyte flow battery including an electrolyte solution comprising:

a) a solution including bromine; and

b) a surfactant for improving the dispersion of bromine within the solution, wherein the surfactant is not polyoxyethylene (20) sorbitan monolaurate