Amphiphilic complexing agents for improved membrane compatibility and stability of redox species

Abstract

Amphiphilic complexing agents for electrolyte solutions are provided. The complexing agent includes at least one soft ionic group covalently bonded to at least one hard ionic group or polyether chain. The soft ionic groups are coupled to the soft, oppositely charged ionic redox species in the electrolyte solution, and the hard ionic groups or polyethylene chains make complexes formed from the complexing agent and the ionic redox species soluble in the electrolyte solution. The size of the complex formed by coupling the amphiphilic complexing agent to the soft ionic redox species is significantly greater than the size of the soft ionic redox species alone, as a result, the electrochemical cell comprising the amphiphilic complexing agent in the electrolyte solution has less membrane permeation than a similar electrochemical cell not comprising the amphiphilic complexing agent.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 396,759, filed on August 10, 2022, the entire contents of which are incorporated herein by reference. Background Art

[0003] One approach to grid energy storage is to use redox flow batteries (RFBs), which have decoupled energy and power scaling because capacity can be expanded by simply expanding the size of the storage tank. This decoupling of capacity and power allows for simplified design of devices with long storage durations by increasing the amount of active energy storage material without the need to simultaneously increase the size of the electrodes. Despite this practical advantage, RFBs have only been commercially implemented in a few experimental grid applications. This is in part due to unwanted electrolyte crossovers through the ion-permeable membrane that separates the solutions of the anode electrolyte and cathode electrolyte. This problem is caused by the relatively large ion-conducting channels in the prior art ion exchange membranes and the relatively small size differences between the electrolyte species and the charge-balancing ions in the electrolyte solution. This undesirable crossover causes electrochemical cells to have rapid capacity decay, low energy efficiency, and operating heat.

[0004] One approach that has been used to address the electrolyte penetration problem is to use charged complexing agents in the electrolyte solution (e.g., in bromide flow batteries). These complexing agents capture charged redox species based on the thermodynamic equilibrium of the system. Due to their large size, the complex formed by the complexing agent and the charged redox species (e.g., polybromide) is less sensitive to membrane penetration. However, significant membrane penetration of the complexing agent / electrolyte complex remains a problem, and phase separation of the complexing agent / electrolyte complex often occurs. As a result, in addition to kinetic and flow problems, electrochemical cells, particularly RFBs including known complexing agents, still have the disadvantages of rapid capacity decay and low energy efficiency. These challenges have severely limited the commercial success of RFBs. Summary of the invention

[0005] An amphiphilic complexing agent for an electrolyte solution and an electrochemical cell using the electrolyte solution as a catholyte solution or an anolyte solution is provided.

[0006] One embodiment of the electrolyte solution includes: a solvent; a soft ionic redox species dissolved in the solvent, which can be cationic or anionic (the phrase "cation or anion" is abbreviated herein as "cation / anion", and the phrase "anion or cation" is abbreviated herein as "anion / cation"); a charge balancing counterion dissolved in the solvent; and an amphiphilic complexing agent dissolved in the solvent. The amphiphilic complexing agent has a soft ionic group covalently bonded to a hard ionic group, a polyethylene glycol chain, or a combination thereof. The soft ionic group and the soft ionic redox species are oppositely charged, and the soft ionic group and the hard ionic group of the amphiphilic complexing agent can have opposite charges (e.g., cation and anion or anion and cation) or can have the same charge type (e.g., both are anions or both are cations).

[0007] One embodiment of the electrochemical device includes: an anode in an anolyte solution; a cathode in a catholyte solution; and an ion-permeable membrane separating the anolyte solution from the catholyte solution. In the electrochemical device, one or both of the anolyte solution and the catholyte solution comprise an electrolyte solution as described herein.

[0008] Other principal features and advantages of the present invention will become apparent to those skilled in the art after reviewing the following drawings, detailed description and appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Illustrative embodiments of the present invention will now be described with reference to the drawings, wherein like reference numerals refer to like elements.

[0010] Figure 1A Schematic diagram of the complexation of an amphiphilic complexing agent with a soft anionic redox species and its charge balancing hard cation.

[0011] Figure 1B Schematic diagram of the complexation of an amphiphilic complexing agent with a hard anionic redox species and its charge-balancing soft cation.

[0012] Figure 2 The structures of various soft quaternary ammonium, protonated secondary and tertiary ammonium, heteroaromatic, heterocyclic, phosphonium, and sulfonium cations are shown.

[0013] Figure 3A-3B The general structure of various amphiphilic complexing agents including soft quaternary ammonium or soft nitrogen-containing heteroaryl groups is shown. "NG" in the figure represents an anionic group.

[0014] Figures 4A-4F The structures of specific examples of amphiphilic complexing agents including soft quaternary ammonium or soft nitrogen-containing heteroaryl groups are shown. Figure 4C The top structure in ( ) is an example of a redox-active complexing agent.

[0015] Figure 5 The structures of various soft redox-active metal-ligand coordination complexes are shown.

[0016] Figure 6 Shown are structures of specific examples of redox-active amphiphilic complexing agents that include a soft metal-ligand coordination complex as a soft cationic group.

[0017] Figure 7 Shown are structures of specific examples of redox-active amphiphilic complexing agents that include a redox-active soft cationic group.

[0018] Figure 8 The structures of some polymeric amphiphilic complexing agents are shown.

[0019] Fig.9A A reaction scheme for the synthesis of amphiphilic complexing agents is shown.

[0020] Fig. 9B An alternative reaction scheme for the synthesis of amphiphilic complexing agents is shown.

[0021] Fig.10 Another reaction scheme for the synthesis of amphiphilic complexing agents is shown.

[0022] Figures 11A-11H Various reactants that can be used to synthesize amphiphilic complexing agents are shown.

[0023] Fig.12 Shown is the complexation of anionic catholyte with an amphiphilic complexing agent in the catholyte solution.

[0024] Fig.13 is a schematic diagram of an aqueous organic redox flow battery.

[0025] Fig.14A and 14B Shown are the structures of 13 amphiphilic complexing agents that can be used with the soft cationic redox species synthesized according to the methods described in the Examples, as well as their experimentally measured permeabilities.

[0026] Fig.15A and 15B The performance of redox flow batteries using amphiphilic complexing agents is demonstrated, as described in the Examples. DETAILED DESCRIPTION

[0027] An amphiphilic complexing agent for an electrolyte solution is provided. Also provided is an electrolyte solution containing the amphiphilic complexing agent and an electrochemical unit using the electrolyte solution as a cathode electrolyte solution or an anode electrolyte solution.

[0028] The complexing agent is a molecule including at least one soft ion group, which is covalently bonded to at least one hard ion group and / or to a polyether chain by covalent bonding. The soft ion group of the complexing agent couples with the soft ion redox species in the electrolyte solution due to the thermodynamic equilibrium in the solution, while the strongly hydrophilic hard ion group and / or polyethylene chain couples with the hard counter ion in the solution to prevent the complex from phase separation from the aqueous solution.

[0029] The size of the complex formed by coupling the amphiphilic complexing agent to the soft redox species is significantly larger than the size of the redox species alone, and as a result, the electrochemical cell comprising the amphiphilic complexing agent in the electrolyte solution has much less membrane penetration than a similar electrochemical cell not comprising the amphiphilic complexing agent. As a result, the electrochemical cell comprising the amphiphilic complexing agent in the electrolyte solution is characterized by improved cycle stability, higher coulombic efficiency and higher utilization capacity.

[0030] Figure 1A Schematically shown are the amphiphilic complexing agent, the soft anionic redox species and their hard countercomplexation to form a large water-soluble complex. Figure 1B Schematically shows the complexation of an amphiphilic complexing agent, a soft cationic redox species and its hard counterion to form a large water-soluble complex. It should be noted that although Figure 1A and 1B The soft and hard ionic groups of the meso-complexing agent have opposite charges, but amphiphilic complexing agents in which the soft and hard ionic groups have the same charge can also be used, provided that the soft redox species also has the same charge type (cationic or anionic).

[0031] Typically, "soft" ionic groups and ions have a smaller charge-to-size ratio than "hard" ionic groups and ions. Although the "soft" or "hard" nature of ionic groups cannot be quantified per se, soft and hard ionic groups can be identified based on how these groups interact with ions in aqueous solution. For purposes of this disclosure, hard ionic (anionic or cationic) groups on complexing agents are characterized in that the ionic groups preferably interact (i.e., are more strongly attracted) with counterions (e.g., charge-balancing cations or anions) of ionic redox species rather than with soft ionic groups of the complexing agent. Thus, ionic redox species and other ionic groups of the complexing agent are classified as "soft" because they are left to coordinate with each other. As an illustration, in the case of an amphiphilic complexing agent having soft cationic groups and hard anionic groups, the cationic groups of the complexing agent can be considered "soft" as long as the interaction between the charge-balancing countercations of the anionic redox species and the anionic groups of the complexing agent is stronger than the interaction between the cationic groups of the complexing agent and the anionic groups of the complexing agent. Due to their relatively large size and relatively low charge density, the organic cationic groups of the complexing agents are relatively + will be soft. Due to their relatively small size and relatively high charge density, counter anions such as Cl - Br - 、CO3 2- 、SO4 2- OH - 、NO3 - 、CH3SO3 - CF3SO3 - etc., are characterized as hard anions.

[0032] The hard anionic groups of the amphiphilic complexing agent include anionic sulfate, phosphate and carboxylate groups. As described in more detail herein, these hard anionic groups can be connected to the soft anionic groups through organic linkers, so that the soft anionic groups are functionalized with sulfonate groups, phosphonate groups and carboxylate groups. These sulfonate groups, phosphonate groups and carboxylate groups can be generally represented as R-SO3 - 、R-PO3 2- and R-COO - , where R contains -SO3 - 、-PO3 2- and -COO - The group is covalently attached to the alkyl group of the soft ionic group of the amphiphilic complexing agent. The alkyl group typically has 1 to 6 carbon atoms. However, longer alkyl groups can be used.

[0033] In some embodiments of the amphiphilic complexing agent, the soft cationic group includes aliphatic quaternary ammonium groups, alicyclic quaternary ammonium groups and cationic nitrogen-containing heteroaromatic rings, wherein the term "quaternary ammonium group" includes protonated quaternary ammonium groups. The soft cationic group can be monovalent (having one positively charged atom), divalent (having two positively charged atoms) or can have a higher valence (having three or more positively charged atoms). Aliphatic quaternary ammonium groups include alkyl quaternary ammonium groups, such as trimethyl quaternary ammonium groups and triethyl quaternary ammonium groups. Examples of the alicyclic quaternary ammonium group and the cationic nitrogen-containing heteroaryl group include an imidazolium group, a benzimidazolium group, a pyridinium group, a bipyridinium group, a 1,4-diazabicyclo[2.2.2]octane-1,4-diol group, an aziridinium group, an azetidinium group, a pyrrolidinium group, a piperidinium group, a morpholinium group, a piperazinium group, and an imidazolidinium group.

[0034] In some embodiments of amphiphilic complexing agents, the soft cationic group is a phosphonium cation, while in some embodiments of complexing agents, the soft cationic group is a sulfonium cation.

[0035] The structures of some soft aliphatic and alicyclic quaternary ammonium cations, cationic nitrogen-containing heteroaromatic cations, phosphonium cations and sulfonium cations are shown in Figure 2 In, wherein R1-R5 independently represents a hydrogen atom, an alkyl group, an alkyl alcohol and / or a polyether chain, for example a polyethylene glycol chain. The alkyl groups in the soft cationic groups may be identical or different. When these soft cations are introduced into an amphiphilic complexing agent comprising a hard anionic group, at least one R group on a positively charged nitrogen atom, a sulphur atom and / or a phosphorus atom will form a covalent connection with the hard anionic group. Alkyl groups are typically low alkyl groups containing 1 to 6 carbon atoms. However, larger alkyl groups may be used.

[0036] The general structures of some illustrative amphiphilic complexing agents are shown in Figure 3A-3B In these structures, R1-R3 are independently hydrogen atoms, alkyl groups, alkyl alcohol groups or polyether groups, l, m, n and q are independently integer values ​​of 1 or greater, including but not limited to integers from 1 to 6, "NG" represents a hard ion group, and M represents a general charge-balancing cation, such as a metal cation (such as a transition metal cation). In some embodiments, NG is a hard anion group, such as -SO3 - 、-PO3 2- or -COO - Examples of charge-balancing cations include H + , metal cations (such as Li + 、Na + , K + ) or NH4 + . Figures 4A-4FSome specific amphiphilic complexing agents with soft cationic groups and hard anionic groups are shown. Figures 4A-4D The structures of various amphiphilic complexing agents are shown, in which the soft cationic group is a monovalent ( Figure 4A and 4B ) or bivalent ( Figure 4C and 4D ) a cationic nitrogen-containing heteroaromatic ring having a cationic charge. Figure 4E and 4F The structures of various amphiphilic complexing agents are shown, in which the soft cationic group is a monovalent cationic aliphatic or alicyclic quaternary ammonium group ( Figure 4E ) or a divalent cationic aliphatic or alicyclic quaternary ammonium group ( Figure 4F ).exist Figures 4A-4F In the above, M represents a counter cation for balancing the charge, R1-R5 are as defined above, and R is a hydrogen atom or an alkyl group, such as a C1-C6 alkyl group.

[0037] Organic borate groups are examples of soft anionic groups. Figure 4G-4I It shows that the soft anionic groups and hard cationic groups ( Figure 4G ), soft anionic groups and hard anionic groups ( Figure 4H and Fig. 4I ) is an example of an amphiphilic complexing agent, wherein Figure 4G and 4H R1 and R2 in are alkyl, alkyl alcohol, aryl, alkyl aryl and / or polyalkylene glycol (e.g. polyethylene glycol) groups. These and other amphiphilic complexing agents containing soft anionic groups are capable of complexing with soft cationic redox species such as cationic-organic complexes. Cationic metal-organic complexes include ferrocenium and metal-organic complexes with cyclopentadienyl or 2,2-bipyridyl ligands, while hydrophilic hard ion groups provide complexes with high water solubility.

[0038] In some embodiments of amphiphilic complexing agents, the soft cationic group is a coordination complex comprising a central positively charged atom (usually a metal cation) surrounded by an array of molecules called ligands. In redox-active embodiments of these complexing agents, the hard anionic group is covalently bonded to the ligands of the coordination complex. The structures of some coordination complexes (which are soft cationic) are as follows Figure 5 Some examples of amphiphilic complexing agents whose soft cationic groups are metal ligand coordination complexes are Figure 6 shown.

[0039] In some embodiments of amphipathic complexing agents, the soft cationic group itself is redox active. Examples of redox active groups with soft cationic states include nitroxyl radicals, such as substituted or unsubstituted piperidinyl radicals, pyrrolidinyl radicals and imidazolidinyl radicals, which are converted into soft cationic groups when oxidized. Specific examples of nitroxyl radical groups that are converted into soft cationic groups when oxidized include 2,2,6,6-tetramethylpiperidin-1-oxygen (TEMPO) groups and 2,2,5,5-tetramethyl-1-pyrrolidinyloxy (PROXYL). Although these amphipathic complexing agents themselves are redox active, they can be combined with other anionic redox species in the electrolyte solution to reduce the membrane penetration of smaller redox species and increase the unit capacity. Figure 7 The structures of some exemplary redox-active amphiphilic complexing agents are shown.

[0040] The polymeric amphiphilic complexing agent incorporates multiple soft ion groups and multiple hard ion groups along the polymer backbone. The soft ion groups and hard ion groups can be separate pendant groups along the polymer backbone, or the polymer backbone can have multiple pendant groups, each pendant group comprising at least one soft ion group and at least one hard ion group. The structures of some exemplary polymeric amphiphilic complexing agents are shown in Figure 8 In which R1-R3 are independently hydrogen atoms, alkyl groups, alkyl alcohol groups or polyether groups, and n is an integer value of 1 or greater. As an illustration, n can be in the range of 1-20, including in the range of 2-10. However, groups with n values ​​outside this range can be used.

[0041] Amphiphilic complexing agents having soft nitrogen-containing cationic groups and hard anionic groups can be prepared by reacting a cyclic or linear tertiary amine reactant, a reactant having a tertiary nitrogen-containing heterocyclic ring, or a reactant having a nitrogen-containing heteroaromatic ring with a cyclic sulfate, cyclic phosphate, and / or cyclic carboxylate to form an amphiphilic complexing agent comprising a positively charged nitrogen atom and a sulfonate, phosphonate, or carboxylate group (on the nitrogen atom). This type of synthetic reaction is shown in Fig.9A Various alternative cyclic anion-forming reactants that can be used in this reaction scheme are also shown in the figure (bottom). Fig. 9B Other synthetic schemes are shown in which a cationic nitrogen-containing heteroaromatic or heterocyclic ring having a hydroxyl (-OH) substituent on the nitrogen atom is reacted with sulfuric acid or phosphoric acid to convert the hydroxyl group to a sulfate or phosphate group.

[0042] Alternatively, with hard anionic groups such as -SO3 - 、-PO3 2- or -COO - Organic molecules with halogen atoms, mesylate (OM) groups or tosylate (OT) groups can be removed by S NThe 2-substituted amine reacts with the nitrogen atom of the tertiary amine to form an amphiphilic complexing agent containing a positively charged nitrogen atom and a sulfonate, phosphonate or carbonate group (on the nitrogen atom). Fig.10 This type of synthesis reaction is shown. Examples of other organic molecules that can be used as reactants are shown at the bottom of the figure, where X represents a typical leaving group, M represents a typical charge balancing cation, R represents an alkyl group, and n is an integer equal to or greater than 1.

[0043] It should be noted that Fig.9A , 9B The tertiary amines and nitrogen-containing heterocyclic and heteroaromatic reactants shown in and 10 are for illustrative purposes only. Many different tertiary amines, heterocyclic and heteroaromatic reactants can be used, including many that are commercially available. For illustrative purposes, various commercially available reactants that can be used are shown in Fig.11A –11h.

[0044] Fig.11A 1-ethylpiperidine, N,N-dimethylcyclohexylamine, 1-methylpiperidine, 1-methyl-4-[3-(1-methylpiperidin-4-yl)propyl]piperidine, N'-[2-(dimethylamino)ethyl]-N,N,N'-trimethylethane-1,2-diamine, N',N'-bis[2-(dimethylamino)ethyl]-N,N-dimethylethane-1,2-diamine, N'-[2-(dimethylamino)ethyl]- The structures of: [(2-(dimethylamino)ethoxy]ethanol, [(2-(dimethylamino)ethoxy]ethanol, and [(2-(dimethylamino)ethoxy]ethanol], [(2-(dimethylamino)ethoxy]ethanol], [(2-(dimethylamino)ethoxy]ethanol], [(2-(dimethylamino)ethoxy]ethanol], [(2-(dimethylamino)ethoxy]ethanol], and ...

[0045] Fig. 11B The structures of (1-methylpiperidin-4-yl)methanol, 1-methylpyrrolidine, 1-azabicyclo[2.2.2]octane, 2,3,4,6,7,8,9,10-octahydropyrimido[1,2-a]azepine, 2-[2-(dimethylamino)ethoxy]-N,N-dimethylethylamine, N,N,N',N'-tetraethylpropane-1,3-diamine, N-cyclohexyl-N-methylcyclohexylamine and N,N,N',N'-tetramethylhexane-1,6-diamine are shown.

[0046] Fig. 11C4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane, 4,7,13,16,21-pentaoxa-1,10-diazabicyclo[8.8.5]tricosane, 2-(2-methoxyethoxy) -N,N-bis[2-(2-methoxyethoxy)ethyl]ethylamine, 4-[2-(2-morpholin-4-ylethoxy)ethyl]morpholine, 1-[bis(2-hydroxypropyl)amino]propan-2-ol, 1-[2-[bis(2-hydroxypropyl)amino]ethyl-(2-hydroxypropyl)amino]propan-2-ol, 2-[4-(2-hydroxyethyl)piperazin-1-yl]ethanol, 2-[2-[bis(2-hydroxyethyl)amino]ethyl-(2-hydroxyethyl)amino]ethanol, 2-[2-hydroxyethyl(methyl)amino]ethanol, 2-[bis(2-hydroxyethyl)amino]ethanol and 1-(dimethylamino)propan-2-ol.

[0047] Fig.11D The structures of 3-butylpyridine, 4-ethylpyridine, 4-tert-butylpyridine, 4-methylpyridine, pyridin-2-ylmethanol, pyridin-4-ylmethanol, pyridine-3-ol, pyridine-3,5-dicarboxylic acid, 2,6-lutidine, 2,4,6-trimethylpyridine, 2,4,6-tri-tert-butylpyridine, and 3,4-lutidine are shown.

[0048] Fig.11E The structures of 2-methylpyridine, 3-methylpyridine, 2-methoxypyridine, 4-methoxypyridine, 3-methoxypyridine, pyridine-2,6-dicarboxylic acid, 4-oxo-1H-pyridine-2,6-dicarboxylic acid, 1-pyridin-4-ylethanone, 1-pyridin-2-ylethanone, 1-pyridin-3-ylethanone, 2,5-lutidine, 3,5-lutidine, 2-(4-pyridyl)ethanesulfonic acid, pyridine-2-sulfonic acid, and 3-pyridinesulfonic acid are shown.

[0049] Fig.11F The structures of 4-methoxy-2-(4-methoxypyridin-2-yl)pyridine, 4-tert-butyl-2-(4-tert-butylpyridin-2-yl)pyridine, 4-methyl-2-(4-methylpyridin-2-yl)pyridine, 4-pyridin-4-ylpyridine, dipyridin-4-yl-diazene, 4-[(E)-2-pyridin-4-ylvinyl]pyridine, 5-methyl-2-(5-methylpyridin-2-yl)pyridine, 1,10-phenanthroline-5,6-dione and 3,13-diazatricyclo[7.4.0.02,7]tridecane-1(9), 2(7), 3,5,10,12-hexaen-8-one are shown.

[0050] Fig.11GThe structures of 2-pyridin-2-ylpyridine, 1,10-phenanthroline, 2-(4-carboxypyridin-2-yl)pyridine-4-carboxylic acid, 2-[(E)-2-pyridin-2-ylvinyl]pyridine, 4-(2-pyridin-4-ylethyl)pyridine, 4-(3-pyridin-4-ylpropyl)pyridine, 1,10-dihydro-1,10-phenanthroline-4,7-dione, 4,7-dimethoxy-1,10-phenanthroline and 2-(3-hydroxypyridin-2-yl)pyridine-3-ol are shown.

[0051] Fig.11H The structures of 2,6-bis(4-methoxycarbonylpyridin-2-yl)pyridine-4-carboxylate, 4-tert-butyl-2,6-bis(4-tert-butylpyridin-2-yl)pyridine, 4-[4-(2,6-bipyridin-2-ylpyridin-4-yl)phenyl]-2,6-bipyridin-2-ylpyridine, 2-methylimidazole, 1-methylimidazole, 4-methylimidazole, 1-butylimidazole, 1,2-dimethylimidazole, 1-methylimidazole-4-carboxylic acid, 1-methylimidazole-2-carboxylic acid, and benzimidazole, 1-methylbenzimidazole are shown.

[0052] As used herein, the term redox species generally refers to a chemical species that undergoes electron transfer during operation of an electrochemical cell. A variety of soft anionic or cationic redox species can be used in combination with an amphiphilic complexing agent. Soft anionic redox species include, but are not limited to, polyhalides, polysulfides, and thiolates. The polyhalide cathode electrolyte can be composed of the structure [X p ] - , wherein X represents a halogen atom, such as Br, I or Cl, p is an integer value of 3-29, and the X atoms constituting the polyhalide may be the same or different. Some polyhalide cathode electrolytes have the structure [X1X2X3] - , wherein X1, X2 and X3 are independently selected from halogen atoms, such as Br, I and Cl. Specific examples of soft anion trihalide cathode electrolytes include Br3 - 、I3 - 、Cl3 - Br2I - ,I2Br - Br2Cl - BrCl2 - 、I2Cl - ICl2 - and BrICl - Soft polysulfide anolytes have the structure [S p ] 2- , where p is an integer value in the range of 1 to 4. Polyhalides and polysulfides can react with charge-balancing cations such as H + or metal cations (such as Li + 、Na+ , K + ) or NH4 + Combination. Amphiphilic complexing agents are particularly useful when combined with anionic cathode electrolytes such as polyhalides, which are susceptible to conversion to gases or reactive species, because complexation of the polyhalide with the amphiphilic complexing agent prevents such conversion. The anionic redox species can also be an anionic metal-organic complex, such as an anionic metal-complex with cyano, carboxylate, polycarboxylate or polyaminocarboxylate ligands.

[0053] Fig.12 The complexation of anionic redox species and amphiphilic complexing agents having soft cationic groups and hard anionic groups in a cathode electrolyte solution is illustrated. As shown in the figure, when a redox species in a soft anionic state, such as a polyhalide, is combined in a solution with an amphiphilic complexing agent having soft cationic groups and hard anionic groups and / or a polyether chain, the soft anionic redox species couples with the soft cationic groups of the complexing agent to form a size-enlarged complex that is soluble in the solution (right figure). Although polyhalide cathode electrolytes (e.g., Br3 - ) is used as the cathode electrolyte, and a bifunctional molecule including an imidazolium group (soft cationic group) and a sulfonate group (hard anionic group) is used as Fig.12 Although the amphiphilic complexing agent in the invention is not disclosed, other anionic redox species and / or amphiphilic complexing agents, including those described herein, may be used in the complexing scheme.

[0054] Amphiphilic complexing agents have applications in a variety of different devices where an electrolyte solution is in contact with an ion-permeable membrane. These applications include electrochemical and non-electrochemical ion separation devices. The basic components of an electrochemical device include an anode, an anolyte solution in contact with the anode, a cathode, a catholyte solution in contact with the cathode, an ion-permeable membrane separating the anolyte solution and the catholyte solution, and an external wire or circuit connecting the anode to the cathode. At least one electrolyte solution includes one or more redox substances having a soft anionic state and one or more amphiphilic complexing agents of the type described herein. When the redox substances are in a soft anionic state, they couple with the soft cationic groups of the amphiphilic complexing agent through electrostatic balance, thereby reducing the redox substances from penetrating the ion-permeable membrane. The anolyte solution and the catholyte solution can be aqueous or non-aqueous. However, amphiphilic complexing agents are particularly useful for use in aqueous electrolyte solutions because hard anionic groups can make the complex soluble in water. The electrochemical unit into which the amphiphilic complexing agent described herein is introduced is characterized by a long life with low capacity decay and high energy efficiency.

[0055] Aqueous organic redox flow batteries (AORFBs) are examples of electrochemical cells in which amphiphilic complexing agents can be used. Fig.13One embodiment of an AORFB including an ion selective membrane is schematically shown. In the AORFB, redox active chemicals are dissolved in a supporting electrolyte aqueous solution in which they serve as anode and cathode electrolytes. These anode and cathode electrolytes (which are referred to as anolyte and cathode electrolyte, respectively) can be housed in an anode cell compartment 1302 and a cathode cell compartment 1304. For simplicity, Fig.13 In the figure, the anode electrolyte is generally represented by "A", the cathode electrolyte is generally represented by "C", the charges of the anode electrolyte in its oxidized and reduced states are represented by n- and (nx)-, respectively, and the charges of the cathode electrolyte in its oxidized and reduced states are represented by m- and (my)-, respectively. The ion-conducting membrane 1306 separates the anode unit compartment 1302 from the cathode unit compartment 1304.

[0056] During the charge-discharge process, the redox-active anolyte and cathode electrolyte are stored in the anolyte storage 1308 and cathode electrolyte storage 1310, respectively. The storages 1308 and 1310 are in fluid communication with their respective unit compartments 1302 and 1304 so that the anolyte and cathode electrolyte can be circulated through the unit compartments. This circulation can be accomplished using, for example, a pump 1311. During the charging process, a bias voltage is applied across the anode 1312 in the anode unit compartment 1302 and the cathode 1314 in the cathode unit compartment 1304. Fig.13 As shown, the anode current collector 1315 and the cathode current collector 1317 can be used to provide electrical conduction between the electrodes and the external circuit. During the charging process, when the anode electrolyte passes through the anode 1312, the anode electrolyte molecules undergo an electrochemical reduction reaction, and the cathode electrolyte molecules passing through the cathode 1314 undergo an electrochemical oxidation reaction. During the discharge process, the anode electrolyte molecules undergo an electrochemical oxidation reaction, and the cathode electrolyte molecules passing through the cathode 1314 undergo an electrochemical reduction reaction, thereby providing power to the load across the anode 1312 and the cathode 1314.

[0057] Ion permeable membranes that can be used with the electrolyte solutions described herein include, but are not limited to, positively charged membranes ("cationic membranes"), since the electrostatic repulsion between the hard anionic groups of the amphiphilic complexing agent and the positively charged membrane further reduces unwanted membrane penetration.

[0058] A variety of redox species can be used as counter-anolyte or catholyte, including inorganic redox pairs (e.g., sulfide / polysulfide, Zn / ZnX2 (X = I, Br, Cl), Cr 2+ / Cr 3+, iron / ferrocyanide) and organic redox pairs (e.g., viologen, anthraquinone, phenazine, thiolate), viologen derivatives, such as bis(3-trimethylammonio)propyl viologen tetrachloride, and other pyridyl derivatives, such as those described in U.S. Patent Application Serial No. 17 / 734,377 and Lv, Xiu-Liang et al., ACS Energy Letters 7(2022):2428-2434, are examples of anolytes that can be used in electrochemical cells, including AORFB. However, other anolytes may be used.

[0059] In the electrolyte solution, the non-redox active amphiphilic complexing agent can serve as a supporting electrolyte. As used herein, the term "non-redox active" refers to an amphiphilic complexing agent that does not undergo a reversible redox reaction when the electrochemical cell is in operation. Optionally, one or more additional supporting electrolytes may be included. A supporting electrolyte is a chemical substance (e.g., a salt) that is not electroactive within the applied potential range of the electrochemical cell but has a high ionic strength and therefore contributes to the conductivity of the solution.

[0060] Example

[0061] This embodiment describes Fig.14A and 14B Synthesis, ion permeability, and battery cycling of the 13 amphiphilic complexing agents shown.

[0062] synthesis

[0063] for Fig.14A Eight monomeric amphiphilic complexing agents: 0.5 mol of 4-methylmorpholine, 2-morpholinoethane-1-ol, 1-methyl-1H-imidazole, 1,2-dimethyl-1H-imidazole, pyridine, triethylamine, tripropylamine or tributylamine and 0.5 mol of 1,3-propanesultone were dissolved in 200 mL of acetone and placed in a 500 mL round-bottom flask. The resulting mixture was stirred at 50°C for 48 hours. After cooling to room temperature, the product was obtained by filtration, washed with acetone (100 mL *3), and dried in an oven at 50°C overnight. The yield was 92-98%.

[0064] for Fig. 14BFive dimeric amphiphilic complexing agents: 0.2 mol of N1, N1, N2, N2-tetramethylethane-1,2-diamine, N1, N1, N3, N3-tetramethylpropane-1,3-diamine, 1,3-bis(2-methyl-1H-imidazol-1-yl)propane, dimorpholine diethyl ether or MOPS-Na and 0.5 mol of 1,3-propane sultone were dissolved in 200 mL of methanol and placed in a 500 mL round-bottom flask. The resulting mixture was refluxed at 75°C for 72 hours. After cooling to room temperature, the solvent was evaporated by a rotary evaporator. The solid product was washed with acetone (100 mL * 3) and dried in an oven at 50°C overnight. The yield was 92%.

[0065] Ion Permeability:

[0066] Fig.14A and 14B The table in Fig.14A and 14B Permeability of potassium triiodide across a CMVN cation exchange membrane in the presence of representative amphiphilic complexing agents. Measurements were performed using a standard H-cell setup and the concentration on the receiving side was monitored using UV-Vis. All complexing agents showed an order of magnitude reduction in potassium triiodide penetration, since in the absence of complexing agents the permeability of potassium triiodide across the CMVN membrane was in the range of 10 -5 cm 2 / s.

[0067] Battery Cycle:

[0068] The amphiphilic complexing agent concept was demonstrated in a redox flow battery with an anionic halide catholyte. Fig.15A Results are shown for continuous cycling of 10 mL of 4.5 M KI with 4.5 M 3-(triethylammonium)-propyl sulfonate catholyte and excess (45 mL) of 1 M bis(propyl sulfonate) viologen with 4.5 M KI anolyte. Fig. 15B Results are shown for sequential cycling of 10 mL 3M KBr with 3M 3-(triethylammonium)-propylsulfonate cathode electrolyte and excess (30 mL) 1M bis(propylsulfonate) viologen with 3M KBr anode electrolyte. Both experiments fully charged the halide to the trihalide state (2 / 3 of full capacity), exhibited no capacity fade, had nearly 100% coulombic efficiency, and remained uniform during cycling with minimal observed vaporization.

[0069] The word "illustrative" is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as "illustrative" is not necessarily to be construed as preferred or advantageous over other aspects or designs. In addition, for purposes of this disclosure and unless otherwise specified, "a" or "an" (many not translated in the text) may mean only one or may mean "one or more."

[0070] For the purpose of illustration and description, the above description of illustrative embodiments of the present invention has been given. It is not exhaustive, nor is it intended to limit the present invention to the precise form disclosed, and modifications and variations may be made in accordance with the above teachings, or modifications and variations may be obtained from the practice of the present invention. The embodiments are selected and described in order to explain the principles of the present invention, and as a practical application of the present invention, so that those skilled in the art can utilize the present invention in various embodiments, and with various modifications suitable for the specific use contemplated. The scope of the present invention is defined by the appended claims and their equivalents.

[0071] If not already included, all numerical values ​​for parameters in this disclosure are preceded by the term "about," which means approximately. This includes those variations that are inherent in the measurement of the relevant parameter as understood by one of ordinary skill in the art. This also includes the exact value of the disclosed value and values ​​rounded to the disclosed value.

Claims

1. A redox flow unit comprising: an anode cell compartment containing an anode in an anolyte solution; an anolyte reservoir in fluid communication with the anode cell compartment; a cathode cell compartment containing a cathode in a catholyte solution; a cathode electrolyte storage portion in fluid communication with the cathode cell compartment; and an ion-permeable membrane separating the anolyte solution from the catholyte solution, wherein one or both of the anolyte solution and the catholyte solution comprises: Solvents; an ionic redox species dissolved in the solvent; charge-balancing counterions dissolved in the solvent; and An amphiphilic complexing agent is dissolved in the solvent, wherein the amphiphilic complexing agent comprises an anionic group connected to a cationic group through an organic linking chain.

2. The redox flow cell of claim 1, wherein the anionic groups are sulfate groups, phosphate groups or carboxylate groups.

3. The redox flow cell of claim 1, wherein the cationic group is a cationic aliphatic quaternary ammonium group, a protonated secondary or tertiary ammonium group, a cyclic quaternary ammonium group, or a nitrogen-containing heteroaromatic ring.

4. The redox flow cell of claim 3, wherein the cationic group comprises an alkyl substituent, an alkyl alcohol substituent, a polyether substituent, or a combination of two or more thereof.

5. The redox flow cell of claim 3, wherein the cationic group is an imidazolium group, a benzimidazolium group, a pyridinium group, a bipyridinium group, a 1,4-diazabicyclo[2.2.2]octane-1,4-diol group, an aziridinium group, an azetidinium group, a pyrrolidinium group, a piperidinium group, a morpholinium group, a piperazinium group, or an imidazolidinium group.

6. The redox flow cell of claim 1, wherein the cationic group is a sulfonium cation or a phosphonium cation.

7. The redox flow cell of claim 1, wherein said amphiphilic complexing agent comprises at least two of said anionic groups.

8. The redox flow cell of claim 1, wherein said amphiphilic complexing agent comprises at least two of said cationic groups.

9. The redox flow cell of claim 1, wherein said amphiphilic complexing agent is a polymeric amphiphilic complexing agent comprising a plurality of said anionic groups and a plurality of said cationic groups along a polymer backbone.

10. The redox flow cell of claim 1, wherein the amphiphilic complexing agent is non-redox active.

11. The redox flow cell of claim 1, wherein the ionic redox species is an anionic redox species and the charge balancing counterion is a cation.

12. The redox flow cell of claim 11, wherein the ionic redox species comprises a polyhalide, a polysulfide, or a thiolate.

13. The redox flow cell of claim 12, wherein the charge balancing counterions comprise H + , metal cations or NH4 + .

14. The redox flow cell of claim 1, wherein the ionic redox species is a cationic redox species and the charge balancing counterion is an anion.

15. The redox flow cell of claim 14, wherein the ionic redox species comprises a cationic metal-organic complex.

16. The redox flow cell of claim 15, wherein the charge balancing counterions include halide ions, sulfate ions, hydroxide ions, nitrate ions, phosphate ions, borate ions, and chlorate ions.

17. The redox flow cell of claim 1, wherein the solvent comprises water.

18. The redox flow cell of claim 1, wherein the ion permeable membrane is an ion exchange membrane or a size exclusion membrane.

19. An electrolyte solution comprising: Solvents; an ionic redox species dissolved in the solvent; charge-balancing counterions dissolved in the solvent; and An amphiphilic complexing agent is dissolved in the solvent, wherein the amphiphilic complexing agent comprises an anionic group connected to a cationic group via an organic linking chain.

20. The electrolyte solution of claim 19, wherein the anionic group is a sulfate group, a phosphate group or a carboxylate group, and the cationic group is an aliphatic quaternary ammonium group, a protonated secondary or tertiary ammonium group, a cyclic quaternary ammonium group, a nitrogen-containing heteroaromatic ring, a sulfonium cation or a phosphonium cation.

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