EP3888174A2 - Aqueous electrolyte, redox flow battery and use thereof - Google Patents

Abstract

The invention relates to an aqueous electrolyte solution with a temperature of at least 30°C containing a compound having at least one redox-active moiety of formula I (X-C₅H₄) Fe (Y-C₅H₃-Z) (I), where X is a moiety of formula -(C_nH₂n)-FG or of formula -(C_nH₂n)-Sp-(C_nH_2n)-FG or of formula -(C_nH₂n)-Brgp-, Y is hydrogen or a moiety of formula -(C_nH₂n)-FG or of formula -(C_nH₂n)-Sp-(C_nH₂n)-FG, Z is hydrogen or a covalent bond linking the moiety of formula (I) to the remainder of the molecule, FG is a functional group selected from -OH, -NO₃, -NO₂, - CN, -OR₁, -(O-CH₂-CH₂)_o-OR₂, -(O-CH₂-CH₂)_o -NR₃R₄R₅ ⁺ (An^m-)_1/m, -COR₂, -COO" (Kat^m+)_1/m, - COOR₂, -SO₃- (Kat^m+)_1/m, -SO₃R₂, -S0₄ ^- (Kat^m+)_1/m, -SO₄R₂, -PO₄ ^2- (Kat^m+)_{2/ m}> -PO₄(R₂)₂, -PO₃ ^2- (Kat^m+)_2/m, -PO₃(R₂)2, -NR₃R₄R₅+ (An^m-)_1/m, -N⁺R₃R₄-C_tH_2t-S0₃- or — NR₂-SO₂-R₃, Brgp is a divalent bridging group linking the moiety of formula (I) to the remainder of the molecule, Sp is -O-, -S-, -SO- or -S0₂-, R₁ is C₁-C₄ alkyl, R₂ is hydrogen or C₁-C₄ alkyl, R₃, R₄ and R₅ are hydrogen or alkyl independently of one another, Kat is an m-valent cation, An is an m-valent anion, m is an integer between 1 and 4, n is an integer between 2 and 4, t is an integer between 2 and 5 and o is an integer from 1 to 50, preferably from 3 to 20. The electrolyte can be used in redox flow batteries and is distinguished by the high stability of the redox-active compounds at increased temperatures.

Description

description

Aqueous electrolyte, redox flow battery and their use

The invention relates to an aqueous electrolyte and a redox flow battery containing this aqueous electrolyte. Redox flow batteries, also known as redox flow batteries (hereinafter also referred to as “RFB”), are used to store electrical energy based on electrochemical redox reactions. A redox flow battery contains a chamber or two polarity-specific chambers (half cells) separated by a membrane, which are filled with a liquid and are fed by pumps from one or more separate tanks of any size. The respective liquid contains water in which redox-active substances and an inorganic or organic salt (lead additive) are dissolved. The main additive can itself be redox-active.

Due to their excellent scalability, RFBs are particularly suitable as stationary energy storage devices for various performance and capacities

requirements. For example, as buffer systems for renewable energies, both in the private (e.g. single or multi-family houses) and industrial sectors (e.g. wind and solar power plants). They therefore have great potential for ensuring the stability of the power grid and for decentralized energy supply. Mobile applications (electric cars, trucks or ships) are also conceivable.

Existing RFBs are electrochemical energy stores. The substances required for setting the potential on the electrodes are liquid, dissolved or also in

Redox-active species appearing in particle form, which during the charging or discharging process in an electrochemical reactor are converted into their respective other redox stages will. For this purpose, electrolyte solutions (catholyte, anolyte) are removed from a tank and actively pumped to the electrodes. Anode and cathode compartments are separated in the reactor by a semipermeable membrane, which usually shows a high selectivity for protons. As long as the electrolyte solution is being pumped, electricity can be drawn. The loading process is then simply the reverse of the

Process. The amount of energy that can be stored in an RFB is therefore directly proportional to the size of the storage tanks. The power that can be extracted is a function of the size of the electrochemical reactor.

RFBs have a ^· complex system technology that roughly corresponds to that of a fuel cell. Usual sizes of the individual reactors range from approximately 2 to 50 kW. The reactors can be combined very easily in a modular manner, and the tank size can be adjusted almost as desired.

A wide variety of redox-active chemical compounds have already been proposed for use in rechargeable batteries or batteries, such as RFB. An overview of the prior art can be found, for example, in an article by Feng Pan and Quing Wang, “Redox Species of Redox Flow Batteries: A Review” in Molecules 2015, 20, 20499-20517 or in an article by Winsberg et al. in Angew. Chem. 2017, 36, 686-711. According to this, RFBs are already known which contain ferrocene as the catholyte.

Ferrocene, bis (r | ⁵ -cyclopentadienyl) iron (ll), is a yellow-orange colored, easily in organic solvents, and hardly soluble in water

Connection. Ferrocene is the parent compound and one of the most important representatives of metallocenes. B. by reaction of iron (II) chloride with

Cyclopentadienyl sodium can be produced. Because of its aromatic

Characteristically, ferrocene is accessible to electrophilic substitutions and can thus be functionalized in many ways. For use in aqueous electrolytes, ferrocene must be functionalized by incorporating polar groups. The dissertation by A. Salmon entitled "Synthesis and Electrochemistry of Functional Ferrocenyl and Multiferrocenyl Compounds", Bielefeld (2001) provides an overview of the diverse possibilities of functionalizing ferrocene. RFB containing functionalized ferrocenes in the electrolyte are also known from WO 2018/032003 A1 and from US 2018/0072669 A1.

So far, RFBs have mainly been used in the literature at room temperature. There is little evidence in the scientific literature of investigations at elevated temperatures, e.g. from 40 to 50 ° C, as well as no systematic investigations on the behavior of aqueous electrolytes containing ferrocene (derivative) s at elevated temperatures. Commercial vanadium RFB (hereinafter also referred to as “V-RFB”) is known to be at temperatures above 40 ° C

Problems arise because the electrolytes fail irreversibly.

V-RFBs are therefore limited in their application temperature or complex cooling is required. Special applications, e.g. As a replacement for diesel generators on Indian cell phone masts, V-RFBs are prevented in this way. For V-RFB, special HCI-containing electrolytes were developed, which are more temperature-stable and therefore temperatures above 40 ° C, sometimes up to approx.

50 to 60 ° C enables (see also US 2012/0077067 A1). However, these electrolytes are extremely corrosive. Other RFB systems have not yet been described at these comparatively high temperatures.

In particular RFB containing organic redox-active compounds have so far not been used at these high temperatures. Here comes

to make matters worse, many electrolytes containing organic redox-active compounds are not stable at elevated temperatures. In this context it should also be noted that the stability of many organic redox active

Materials have been wrongly assessed even at room temperature (M - A. Goulet, M. J. Aziz, J. Electrochem. Soc. 2018, 165, A1466-A1477). Simple charge / discharge tests carried out to date do not provide any information about

Aging behavior of the electrolytes. The RFB containing A, A /, A / -2,2,6,6-heptamethylpiperidinyloxy-4-ammonium chloride (TEMPTMA), which has been described as the most stable so far, is also affected by these decomposition processes as an organic redox-active compound. At elevated temperatures Side reactions accelerated and lead to rapid

Loss of capacity of the RFB.

Functionalized ferrocene derivatives have now been found which surprisingly have high stability at elevated temperatures. These redox-active compounds allow the production of aqueous electrolyte solutions that are stable at elevated temperatures. In addition, these redox-active compounds allow the production of RFB that can be operated at elevated temperatures. Higher temperatures of the electrolyte can occur during operation of the RFB in environments with elevated temperatures, for example during operation in tropical or subtropical regions, and / or also during

Storage of electrolyte solutions at elevated temperatures and / or when throughput of high performance during the charging / discharging process in the

Electrode rooms.

It has been found that ferrocenes functionalized with solubilizing groups, which are attached to one via spacers having two to four carbon atoms

Cyclopentadienyl ring are attached, the desired combination of water solubility can be achieved with sufficient temperature stability. It has also been shown that ferrocenes with direct substitution of the cyclopentadienyl ring with solubilizing groups or with a C1 spacer do not show the desired stability.

The use of the electrolytes according to the invention makes RFBs with organic redox-active compounds accessible for “high-temperature” use. In this way, new fields of application for RFB can be opened up without the need for additional cooling.

The invention has for its object to provide an aqueous electrolyte containing redox-active ferrocene derivatives, which also with increased

Temperatures have sufficient stability for the operation of batteries or accumulators. Another object of the present invention is to provide a redox flow battery which can be operated at elevated temperatures without the electrolyte used experiencing any significant decomposition.

This object is achieved by the provision of the aqueous electrolyte solution described in claim 1.

The present invention relates to an aqueous electrolyte solution with a

Temperature of at least 30 ° C containing a compound with at least one redox-active radical of the formula (I)

(XC ₅ H ₄ ) Fe (YC ₅ H ₃ -Z) (I), where X is a radical of the formula - (C _n H2 _n ) -FG or of the formula - (C _n H2 _n ) -Sp- (C _n H _2n ) -FG or the formula - (C _n H2 _n ) -Brgp-,

Y is hydrogen or a radical of the formula - (C _n H _2n ) -FG or of the formula - (C _n H _2n ) -Sp- (C _n H _2n ) -FG,

Z is hydrogen or denotes a covalent bond which connects the rest of the formula (I) to the rest of the molecule,

FG is a functional group selected from -OH, -SH, -NO ₃ , -N0 ₂ , - CN, -OR ₁ ,

-SR, - (0-CH ₂ -CH ₂ ) _O -OR2, - (0-CH2-CH ₂ ) O-NR ₃ R4R5 ⁺ (An ^m ) i / _m , -COR ₂ , -COO

(Kat ^{m +} ) _{1 / m} , -COOR ₂ , -SO ₃ - (Kat ^{m +} ) i _{/ m} , -SO ₃ R ₂ , -SO ₄ - (Kat ^{m +} ) i _{/ m} , -SO4R2, -P0 ₄ ² ( Kat ^{m +} ) _{2 / m} , -P0 ₄ (R ₂ ) ₂ , -PO3 ² · (Kat ^{m +} ) _{2 / m} , -P0 ₃ (R ₂ ) 2, -NR ₃ R ₄ R5 ⁺ (An ^m -) _{1 / m}

-NR ₃ R ₄ -C _t H ₂ t-S0 ₃ or - NR ₂ -S0 ₂ -R ₃ ,

Brgp is a double-bonded bridging group which connects the rest of the formula (I) to the rest of the molecule,

Sp is -O-, -S-, -SO- or -S0 ₂ -,

R 1 is C ₁ -C ₄ alkyl, preferably methyl

R _{2 is} hydrogen or C ₁ -C ₄ alkyl, preferably hydrogen or methyl, and in particular hydrogen,

R ₃ , R ₄ and R ₅ independently of one another are hydrogen or alkyl,

preferably C ₁ -C ₄ alkyl, and in particular methyl, ethyl, propyl or butyl,

Kat is an m-valued inorganic or organic cation, An m-valued inorganic or organic anion means ,,

m represents an integer between 1 and 4,

n represents an integer between 2 and 4,

t is an integer between 2 and 5, and

o is an integer from 1 to 50, preferably from 3 to 20.

The redox-active compounds used in the electrolyte solution according to the invention can be low-molecular organic molecules

Act oligomers or polymers. These molecules can be found in the

Electrolyte solution must be dissolved or in the form of a dispersed or suspended particle, for example as dispersions, microgels or as nanogels. The redox-active compounds contain at least one radical of the formula (I) in which Z

Means hydrogen or which is connected to the rest of the molecule via the covalent bond Z.

The redox-active compounds containing the rest of the formula (I) used in the electrolyte solution according to the invention are preferably water-soluble. However, they can also be compounds which are dispersible in water.

In the context of this description, water solubility of a compound is understood to mean a solubility of at least 1 g of the compound in 1 l of water at 25 ° C.

Low molecular weight molecules are within the scope of this description

To understand compounds that are not derived from monomers

have recurring structural units and the at least one,

preferably contain one to six, particularly preferably one to four, in particular one to three and very particularly preferably one or two radicals of the formula (I).

In the context of this description, oligomeric molecules are understood to mean compounds which have two to ten recurring structural units derived from monomers, each of which carries a radical of the formula (I). The residues of formula (I) can also be attached to the oligomer structure via spacers. In the context of this description, polymeric molecules are to be understood as meaning compounds which have more than ten, preferably eleven to fifty, repeating structural units derived from monomers, each of which has a radical of the formula (I). The radicals of the formula (I) can also be attached to the

Polymer scaffold attached.

In a preferred embodiment, the electrolyte solution according to the invention contains a redox-active component with one to six, preferably one to four, in particular one to three and very particularly preferably one to two residues of the formula (I) in the molecule.

Examples of preferred low molecular weight, oligomeric and polymeric redox-active compounds are listed below.

The molecular weights of the redox-active compounds containing at least one radical of the formula (I) used in the electrolyte according to the invention can vary within wide ranges. Redox-active compounds containing radicals of the formula (I) are particularly preferably used, the molar masses of which are in the range from 150 to 80,000 g / mol, preferably in the range from 250 to 50,000 g / mol and very particularly preferably in the range from 500 to 20,000 g / mol move.

The viscosity of the electrolyte used according to the invention is typically in the range from 1 mPas to 10 ³ mPas, particularly preferably 1 to 10 ² mPas and very particularly preferably 1 to 20 mPas (measured at 25 ° C. with a rotary viscometer, plate / plate).

The redox-active compounds used according to the invention are characterized by the presence of at least one group X on at least one cyclopentadienyl ring. Group X consists of an alkylene group with two to four

Carbon atoms as spacers and a solubility-imparting group FG or from an alkylene oxide-alkylene group with two to four carbon atoms as spacers and a solubility-imparting group FG, or from an alkylene sulfide alkylene group with two to four carbon atoms as spacers and one the Solubility-imparting group FG or from an alkylene spacer with a double-bond bridging group Brgp which connects the rest of the formula (I) to the rest of the molecule. The bridging group Sp is oxygen, sulfur or -SO- or -S0 ₂ -, in particular 0

The alkylene spacer can be a radical of the formula -CH ₂ -CH (CH ₃ ) -, - (CH ₂ ) ₃ -, - (CH ₂ ) - or in particular - (CH ₂ ) ₂ -.

The alkylene oxide alkylene spacer can be a radical of the formula -CH ₂ - CH (CH ₃ ) -0-CH ₂ -CH (CH ₃ ) -, - (CH ₂ ) ₃ -0- (CH ₂ ) ₃ -, - (CH ₂ ) ₄ -0- (CH ₂ ) ₄ - or in particular - (CH ₂ ) ₂ -0- (CH ₂ ) ₂ -. The alkylene sulfide alkylene spacer can be a radical of the formula -CH ₂ - CH (CH ₃ ) -S-CH ₂ -CH (CH ₃ ) -, - (CH ₂ ) ₃ -S- (CH ₂ ) ₃ -, - (CH ₂ ) ₄ -S- (CH ₂ ) ₄ - or in particular - (CFI ₂ ) ₂ -S- (CH ₂ ) ₂ -.

The group FG was described in detail above.

The double-bonded bridging group Brgp can be any double-bonded residue which connects the residue of the formula (I) to the rest of the molecule, for example to a polymer backbone. Examples of bridging groups Brgp are alkylene, -O-, -S-, -SO-, -S0 ₂ -, -CO-, -CO-O-, -NR ₂ _, -CO-NR ₂ - and

-S0 ₂ NR ₂ -.

In addition to group X, the radicals of the formula (I) in the redox-active compounds used according to the invention can be a further radical of the formula

- (C _n H _2n ) -FG or the formula - (C _n H ₂ n) -Sp- (C _n H ₂ n) -FG (rest Y) on one

Have cyclopentadienyl ring. However, Y is preferably hydrogen.

The electrolyte solution according to the invention contains water or water and an organic solvent as well as the above-mentioned redox-active compound (s) and, if appropriate, further substances dissolved therein. These substances serve Charge balancing while charging or discharging the battery or have a positive impact on the stability or performance parameters of the battery.

Substances that are responsible for charge balance are called lead additives or salts, and substances that have a positive effect on stability or performance parameters are called auxiliary additives.

Examples of electrolyte solvents are water or mixtures of water with alcohols (e.g. ethanol), carbonic acid esters (e.g. propylene carbonate), nitriles (e.g. acetonitrile), amides (e.g. dimethylformamide, dimethylacetamide), sulfoxides (e.g. dimethyl sulfoxide), ketone (e.g. acetone), lactones (e.g. gamma-butyrolactone),

Lactams (e.g. / S / -Methyl-2-pyrrolidone), nitro compounds (e.g. nitromethane), ethers (e.g. tetrahydrofuran), chlorinated hydrocarbons (e.g. dichloromethane),

Carboxylic acids (e.g. formic acid, acetic acid), mineral acids (e.g. sulfuric acid, hydrogen halide or halogen acid). Water or mixtures of water with carbonic acid esters (e.g. propylene carbonate) or with nitriles (e.g. acetonitrile) are preferred. Water is particularly preferred.

The main additives are usually organic or inorganic salts. Examples of these are salts, the anions selected from the group

Halide ions (fluoride ion, chloride ion, bromide ion, iodide ion), hydroxide ions,

Anions of inorganic acids (eg., Phosphate ion, sulfate ion, nitrate ion, Hexafluorophosphationen, tetrafluoroborate, perchlorate ions, chlorate ions, Hexafluoroantimonationen, Hexafluoroarsenationen, cyanide ions) or anions of organic acids (eg acetate, formate, Trifluoroessigsäureionen, trifluoromethanesulfonate, Pentafluorethansulfonationen, Nonafluorbutansulfonat- ion, Butyrationen, Citrations, fumarations, glutarations, lactations,

Malations, malonations, oxalations, pyruvations, tartrations).

Chloride and fluoride ions, hydroxide ions, phosphate ions, sulfate ions, perchlorate ions, hexafluorophosphate ions and tetrafluoroborate ions are particularly preferred; as well as cations selected from the group of hydrogen ions (H ⁺ ), alkali or alkaline earth metal cations (e.g. lithium, sodium, potassium, magnesium, calcium), zinc, iron, and substituted or unsubstituted ammonium cations (e.g.

Tetrabutylammonium, tetramethylammonium, tetraethylammonium), the Substituents in general can be alkyl groups. Hydrogen ions,

Lithium ions, sodium ions, potassium ions, tetrabutylammonium ions and mixtures thereof are particularly preferred. In particular, the conductive salts: NaCI, KCl, LiPF ₆ , LiBF ₄ , NaBF ₄ , NaPF ₆ , NaCI0 ₄ , NaOH, KOH, Na ₃ P0 ₄ , K ₃ P0 ₄ , Na ₂ S0 ₄ , NaS0 ₃ CF ₃ , LiS0 ₃ CF ₃ , (CH ₃ ) ₄ NOH, n-Bu ₄ NOH, (CH ₃ ) ₄ NCI, n-Bu ₄ NCI, (CH ₃ ) ₄ NBr, n-Bu ₄ NBr, n-BU NPF ₆ , n-Bu ₄ NBF _, n-Bu ₄ NCI0 _4, NH ₄ CI and their mixtures, where n-Bu stands for the n-butyl group

Particularly preferred electrolyte solutions according to the invention contain a

Lead additive, the anions selected from the group of halide ions,

Contains hydroxide ions, phosphate ions, sulfate ions, perchlorate ions, hexafluorophosphate ions or tetrafluoroborate ions, in particular a lead additive made up of these anions and cations selected from the group of hydrogen ions, alkali metal or alkaline earth metal cations, and the substituted or unsubstituted ammonium cations.

Examples of auxiliary additives are surfactants, viscosity modifiers, pesticides, buffers, stabilizers, catalysts, lead additives, antifreeze, temperature

stabilizers and / or foam breakers.

Surfactants can be nonionic, anionic, cationic or amphoteric. Nonionic surfactants (e.g. polyalkylene glycol ethers, fatty alcohol propoxylates, alkyl glucosides, alkyl polyglucosides, octylphenol ethoxylates,

Nonylphenol ethoxylates, saponins, phospholipids).

Examples of buffers are carbonic acid bicarbonate buffer, carbonic acid silicate buffer, acetic acid acetate buffer, phosphate buffer, ammonia buffer, citric acid or citrate buffer, tris (hydroxymethyl) aminomethane, 4- (2-hydroxyethyl) -1 - piperazinethanesulfonic acid , 4- (2-hydroxyethyl) piperazin-1-propanesulfonic acid, 2- (N-morpholino) ethanesulfonic acid, barbital acetate buffer).

The electrolyte solutions according to the invention have an elevated temperature. These can occur when using the electrolyte solution in certain areas The battery or the accumulator occur, for example, only in the electrode chambers during charging and / or discharging processes and / or during storage of the electrolyte solution in external memories.

Aqueous electrolyte solutions with a temperature of 30 to 90 ° C., preferably 30 to 50 ° C. and in particular 40 to 50 ° C. are preferred.

Also preferred are aqueous electrolyte solutions that contain at least one

Leitsalz included.

Aqueous electrolyte solutions containing at least one conductive salt are particularly preferred, in particular those salts which are contained in highly concentrated salt solutions (sols).

The concentration of the conductive salts in the

aqueous electrolyte solutions according to the invention between 14% by weight up to the saturation limit. Saturated salt solutions are often used, with some of the salts being in a precipitated form.

Particularly preferred electrolyte solutions according to the invention have one

State of charge of less than 90%, in particular up to 80% and very particularly preferably from 70 to 80%. These electrolyte solutions are distinguished by a particularly good temperature stability of the redox-active compound containing at least one radical of the formula (I) in the electrolyte. Of course, electrolyte solutions with a charge level of 100% are also possible.

The state of charge (SOC) is a characteristic value for the state of charge of the electrolyte solution or a battery containing this electrolyte solution. The value for the state of charge indicates the still available capacity of an electrolyte solution or a battery in relation to the nominal value. The state of charge is given as a percentage of the fully charged state. The state of charge can be determined, for example, by the open circuit voltage (VOC). The open circuit voltage depends on the state of charge; this increases with increasing state of charge. The cell voltage is "open

Circuit ”measured, i.e. it is the cell voltage that results for a given state of charge without an external load.

Also preferred are aqueous electrolyte solutions containing a compound with at least one redox-active radical of the formula (I), in which Y is hydrogen and m is 1 or 2.

Also preferred are aqueous electrolyte solutions containing a compound with at least one redox-active radical of the formula (I), in which FG is a functional group selected from - (0-CH ₂ -CH ₂ ) ₀ -OR _2, -COR ₂ , -COO (Kat ^{m +} ) i _{/ m} , -S0 ₃ - (cat ^{m +} ) _{1 / m} , -SO4- (cat ^{m +} ) i _{/ m} , -R0 ₄ ² (cat ^{m +} ) _{2 / m} , -P0 ₃ ² (cat ^{m +} ) _{2 / m} or -NR ₃ R ₄ R5 ⁺ (An ^m ) i / m.

Preferred cations Kat are hydrogen cations, alkali metal cations, alkaline earth metal cations or ammonium cations, in particular hydrogen cations, sodium, potassium, magnesium or calcium cations, or quaternary ammonium cations.

Preferred anions An are selected from the group of halide ions, hydroxide ions, phosphate ions, sulfate ions, perchlorate ions, hexafluorophosphate ions or tetrafluoroborate ions.

Particularly preferred aqueous electrolyte solutions contain a compound having at least one redox-active radical of the formula (I), in which Z is a covalent bond which connects the rest of the formula (I) to a polymer backbone which is selected from the group of the polymethacrylates, polyacrylates, polystyrenes , Polyalkylene glycols, polyalkyleneimines or the polyvinyl ether, where the

Polymer backbone preferably has 5 to 100 groups of formula (I).

Very particularly preferred aqueous electrolyte solutions contain oligomers or polymers with recurring structural units of the formula (II) and, if appropriate with other comonomers derived from solubilizers

Structural units

dl),

wherein

ME a recurring derived from a polymerizable monomer

Structural unit is

BG is a covalent bond or a bridging group,

FC represents a radical of the formula (XC ₅ H4) Fe (YC ₅ H ₃ -Z),

X, Y and Z have the meanings defined above, and

r is an integer from 2 to 150, preferably from 2 to 80 and very particularly preferably from 8 to 40.

The repeating units ME and BG form the backbone of the oligomer or polymer, which contains several units of the redox-active unit of the formula (I) defined above.

Examples of classes of substances which can form the backbone of the oligomer or polymer are polymers derived from ethylenically unsaturated carboxylic acids or their esters or amides, such as polymethacrylate, polyacrylate, polymethacrylamide or polyacrylamide, polymers derived from ethylenically unsaturated aryl compounds, such as polystyrene, carboxylic acids saturated by vinyl esters derived polymers or their derivatives, such as polyvinyl acetate or polyvinyl alcohol, from

Polymers derived from olefins or bi- or polycyclic olefins, such as polyethylene, polypropylene or polynorbornene, polyimides derived from imide-forming tetracarboxylic acids and diamines, polymers derived from naturally occurring polymers and their chemically modified derivatives, such as cellulose or Cellulose ethers, as well as polyurethanes, polyvinyl ethers, polythiophenes, polyacetylene, polyalkylene glycols and their derivatives, such as their ethers, for example

Polyethylene glycol or polyethylene glycol methyl ether, poly-7-oxanorbornene, polysiloxanes, or polyalkyleneimines and their derivatives, such as their amines, for example polyethyleneimines or N, N, N ^' , N ^' -tetramethyl-polyethyleneimines.

Below are examples of combinations of the structural units ME and the bridge groups BG for some of the substance classes mentioned above. It refers to

Polymethacrylate BG = -COO-

Polyacrylate BG = -COO- ME = {-CH— CH—}

Polymethacrylamide BG = -CONH- ME =

Polyacrylamide BG = -CONH-.

Polystyrene BG = covalent ME =

C-C bond or

-CH ₂ - or -NH-

Polyvinyl acetate BG = covalent ME =

C-C bond

Polyethylene BG = covalent ME = {-CH— CH— -

C-C bond

Polypropylene BG = covalent ME =

CC binding Polyvinyl ether BG = -O- ME = - [-CH— CH—] -

Polyethyleneimine BG = covalent ME =

N-C bond

Substance classes which are particularly preferred and which form the backbone of the oligomer or polymer are polymethacrylates, polyacrylates, polymethacrylamides, polyacrylamides, polystyrene, polyethyleneimines and polyvinyl ethers.

The redox-active units of the formula (I) are covalently linked to the polymer backbone.

The polymers containing redox-active components can be in the form of linear polymers or they can be comb and star polymers, dendrimers, conductor polymers, ring-shaped polymers, polycatenanes and polyrotaxanes.

Comb and star polymers, dendrimers, ladder polymers, ring-shaped polymers, polycatenanes and polyrotaxanes are preferably used. These types are characterized by increased solubility and the viscosity of the solutions obtained is generally lower than that of corresponding linear polymers.

The solubility of the polymers containing redox-active components used according to the invention can furthermore be determined by co-polymerization or functionalization, e.g. be improved with ethylene glycol, methacrylic acid, acrylic acid or styrene sulfonate.

Preferred solubilizing comonomers are vinyl alcohol, vinyl acetate, methyl vinyl ether, methacrylic acid, acrylic acid, alkyl methacrylate,

Acrylic acid ethyl ester, methacrylic acid amide, acrylic acid amide, vinyl sulfonate,

Vinylphosphonic acid or styrene sulfonate. The redox-active compounds used according to the invention can be prepared by customary processes. Oligomers and polymers can be produced using the usual polymerization processes. Examples of this are polymerization in bulk, polymerization in solution or emulsion or suspension polymerization. These procedures are known to the person skilled in the art.

Low molecular weight compounds containing one or more radicals of the formula (I) typically have the following structure

(X-C5H4) Fe (YC ₅ H ₃ -) - R, where X and Y have the meanings defined above and R is hydrogen or a mono- or multi-bonded organic radical which may be further (X- C ₅ H ₄ ) Fe (YC ₅ H ₃ -) - may contain residues.

Very particularly preferred aqueous electrolyte solutions contain a compound of the formula (II) as redox-active compound

(X-C5H4) Fe (YC ₅ H ₄ ) (II), in which X and Y have the meaning defined above.

Further very particularly preferred aqueous electrolyte solutions contain a compound of the formula (III) as redox-active compound

[(X-C5H4) Fe (YC ₅ H3 -)] - R7 - [(- C ₅ H ₃ -Y) Fe (C ₅ H ₄ -X)] _P (III), where X and Y defined the above Have meaning

R _{7 is} a two- to four-bonded organic group, and

p represents an integer from 1 to 4. R as a two- to four-bonded organic group is to be understood as an organic radical which is connected to the rest of the molecule via two, three or four covalent bonds.

Examples of divalent organic radicals are alkylene, alkyleneoxy, poly (alkyleneoxy), alkylene sulfide, poly (alkylene sulfide), alkylene amino, poly (alkylene amino),

Cycloalkylene, arylene, aralkylene or heterocyclylene.

Alkylene groups can be either branched or unbranched. An alkylene group typically contains one to twenty carbon atoms, preferably two to four carbon atoms. Examples of alkylene groups are: methylene, ethylene, propylene and butylene. Alkylene groups can optionally be substituted, for example with carboxyl or sulfonic acid groups, with carboxyl ester or sulfonic acid ester groups, with carboxylamide or sulfonic acid amide groups, with hydroxyl or amino groups or with halogen atoms.

Alkyleneoxy and poly (alkyleneoxy) groups can contain both branched and unbranched alkylene groups. An alkylene group occurring in an alkyleneoxy or in a poly (alkyleneoxy) group typically contains two to four carbon atoms, preferably two or three carbon atoms. The number of repeating units in the poly (alkyleneoxy) groups can vary widely. Typical numbers of repeat units range from 2 to 50. Examples of alkyleneoxy groups are: ethyleneoxy, propyleneoxy and butyleneoxy. Examples of poly (alkyleneoxy) groups are: poly (ethyleneoxy),

Poly (propyleneoxy) and poly (butyleneoxy).

Alkylenamino and poly (alkylenamino) groups can contain both branched and unbranched alkylene groups. An alkylene group occurring in an alkylene amino or in a poly (alkylene amino) group typically contains two to four carbon atoms, preferably two or three carbon atoms. The number of repeating units in the poly (alkylenamino) groups can vary widely. Typical numbers of repeating units are in the range from 2 to 50. Examples of alkylene amino groups are: ethylene amino, propylene amino and butylene amino. Examples of poly (alkylene amino) groups are: poly (ethylene amino), poly (propylene amino) and poly (butylene amino).

Cycloalkylene groups typically contain five, six or seven ring carbon atoms, each of which can be independently substituted. Examples of substituents are alkyl groups or two alkyl groups which, together with the ring carbons to which they are attached, can form a further ring. An example of a cycloalkylene group is cyclohexylene. Cycloalkylene groups can optionally be substituted, for example with carboxyl or

Sulphonic acid groups, with carboxyl ester or sulphonic acid ester groups, with

Carboxylamide or sulfonamide groups, with hydroxyl or amino groups or with halogen atoms.

Arylene groups are typically cyclic aromatic groups containing five to fourteen carbon atoms, each independently

can be substituted. Examples of arylene groups are o-phenylene, m-phenylene, p-phenyl, o-biphenylyl, m-biphenylyl, p-biphenylyl, 1-naphthyl, 2-naphthyl, 1-anthryl, 2-anthryl, 9-anthryl, 1- Phenantolyl, 2-phenantolyl, 3-phenantolyl, 4-phenantolyl or 9-phenantolyl. Arylene groups can optionally be substituted, for example with carboxyl or sulfonic acid groups, with carboxyl ester or sulfonic acid ester groups, with carboxylamide or sulfonic acid amide groups, with hydroxyl or amino groups or with halogen atoms. Further examples of substituents are alkyl groups or two alkyl groups which, together with the ring carbon atoms to which they are attached, can form a further ring.

Heterocyclylene groups are typically cyclic groups with four to ten ring carbon atoms and at least one ring heteroatom, each

can be independently substituted. Examples of heteroatoms are oxygen, nitrogen, phosphorus, boron, selenium or sulfur. examples for

Heterocyclylene groups are furandiyl, thiophendiyl, pyrroldiyl or imidazole diyl. Heterocyclylene groups are preferably aromatic. Heterocyclyl groups can optionally be substituted, for example with carboxylic or sulfonic acid groups, with carboxyl ester or sulfonic acid ester groups, with carboxylamide or sulfonic acid amide groups, with hydroxyl or amino groups or with halogen atoms. Further examples of substituents are alkyl groups or two

Alkyl groups which together with the ring carbons to which they are attached can form a further ring.

Aralkylene groups are typically aryl groups to which one or two alkyl groups are covalently attached. Aralkyl groups can be covalently linked to the rest of the molecule via their aryl radical and their alkyl radical or via two alkyl radicals. The aralkylene group can, for example, on the aromatic ring

Alkyl groups or substituted with halogen atoms. Examples of aralkylene groups are benzylene or dimethylphenylene (xylylene).

Examples of R ₇ as a three-bonded organic radical are alkyltriyl, alkoxytriyl, tris-poly (alkyleneoxy), tris-poly (alkylenamino), cycloalkyltriyl, aryltriyl, aralkyltriyl or heterocyclyltriyl. These residues correspond to the double-bonded residues already described in detail above, with the difference that these are linked to the rest of the molecule by three covalent bonds instead of two covalent bonds.

Examples of R ₇ as a four-bonded organic radical are alkylquaternyl,

Alkoxyquaternyl, quaterpoly (alkyleneoxy), quaterpoly (alkylenamino), cycloalkylquaternyl, arylquaternyl, aralkylquatemyl or heterocyclylquaternyl. These residues correspond to the double-bonded residues already described in detail above, with the difference that these are connected to the rest of the molecule by four covalent bonds instead of two covalent bonds.

Aqueous electrolyte solutions containing a compound having at least one redox-active radical of the formula (I), in which n is 2, are very particularly preferred.

These compounds have a particularly favorable combination of water solubility and temperature stability. In addition, such compounds are particularly accessible synthetically by the cyclopentadienyl ring of Ferrocens treated with butyllithium and then reacted with ethylene oxide, or vinyl ferrocene reacted with thiol derivatives.

In a further embodiment, the invention relates to a first type of redox flow battery for storing electrical energy, comprising a reaction cell with two electrode chambers for catholyte and anolyte, each of which is connected to at least one liquid store, the electrode chambers being separated by a membrane, are equipped with electrodes and are each filled with electrolyte solutions that contain redox-active components in liquid form, dissolved or dispersed in an aqueous electrolyte solvent, and, if appropriate, conductive salts dissolved therein and possibly other additives. This redox flow battery is characterized in that the anolyte contains a water-soluble redox-active component and that the catholyte in the electrode chamber contains an aqueous electrolyte solution as defined above.

The electrolyte solutions in the electrode chambers can be coated with paraffin oil in order to minimize the diffusion of oxygen.

Preferred redox flow batteries of this first type also contain an aqueous electrolyte solution according to the definition given above in the liquid store (s).

Redox flow batteries of this first type are preferred, in which the anolyte contains a compound containing one or more bipyridiyl groups in the molecule

contains redox-active component.

These are typically compounds containing at least one redox-active radical of the formula (IV) or of the formula (V) in the molecule,

preferably one to six, in particular one to four, very particularly preferably one to three and extremely preferably one to two radicals of the formula (IV) or of the formula (V) in the molecule wherein

the lines extending from the nitrogen atoms in the structures of the formulas IV and V represent covalent bonds which connect the structures of the formulas IV and V to the rest of the molecule,

R ₈ and Rg independently of one another denote alkyl, alkoxy, haloalkyl, cycloalkyl, aryl, aralkyl, heterocyclyl, halogen, hydroxy, amino, nitro or cyano,

An m-valued inorganic or organic anion means

b and c are independently integers from 0 to 4, preferably 0, 1 or 2, in particular 0,

m is an integer from 1 to 4, and

a is a number with the value 2 / m.

The compounds containing one or more bipyridiyl groups in the molecule as a redox-active component can be low-molecular organic molecules, oligomers or polymers. These preferably contain

at least one radical of the formula (IV) or of the formula (V) which is linked to the rest of the molecule via the covalent bond. The redox-active compounds containing the radical of the formula (IV) or of the formula (V) are preferably water-soluble. However, they can also be compounds which are dispersible in water. Redox-active components preferably used in the anolyte are compounds of the formulas IVa or Va

wherein

R ₈ , Rg, An, a, b, c and m have the meaning defined above,

Rio and Rn independently of one another hydrogen, optionally with a carboxylic acid ester, carboxylic acid amide, carboxylic acid, sulfonic acid or

Amino group substituted alkyl, for example a 2-trialkylammonium ethyl group, optionally substituted with a carboxylic acid ester, carboxylic acid amide, carboxylic acid, sulfonic acid or amino group, cycloalkyl, optionally substituted with a carboxylic acid ester, carboxylic acid amide, carboxylic acid, sulfonic acid or amino group or aryl optionally with a carboxylic acid ester, carboxylic acid amide, carboxylic acid, sulfonic acid or

Aralkyl substituted amino group, in particular Ci-C6-alkyl, with a Ci-C _ö alkyl substituted with carboxylic acid ester, CrC6-alkyl substituted with a carboxylic acid amide group, Ci-C ₆ -alkyl substituted with a carboxylic acid group, CrC6-alkyl substituted with a sulfonic acid group, or Ci-C ₆ -alkyl substituted with an amino group, and whole particularly preferably propionate, isobutionate, ethyl or methyl, and

R- _I 2 and R13 independently of one another hydrogen, optionally substituted with a carboxylic acid ester, carboxylic acid amide, carboxylic acid, sulfonic acid or amino group, for example a 2-trialkylammonium ethyl group, optionally with a carboxylic acid ester, carboxylic acid amide, carboxylic acid, sulfonic acid - or amino group substituted cycloalkyl, aryl optionally substituted with a carboxylic acid ester, carboxylic acid amide, carboxylic acid, sulfonic acid or amino group or aralkyl optionally substituted with a carboxylic acid ester, carboxylic acid amide, carboxylic acid, sulfonic acid or amino group or two radicals R12 and R13 together form a Ci-C3-alkylene group, in particular CrC6-alkyl, Ci-C ₆ -alkyl substituted with a carboxylic acid ester group, Ci-C ₆ -alkyl substituted with a carboxamide group, CrC ₆ -alkyl substituted with a carboxylic acid group, Ci substituted with a sulfonic acid group -C _ö alkyl, or with an amino group subs substituted Ci-Ce-alkyl or together are ethylene, and very particularly preferably propionate, isobutionate, ethyl or methyl or together are ethylene.

Examples of particularly preferably used compounds are N, N ^' -Di-CrC ₄ - alkylbipyridyl cations with any anions for charge balancing, for example N, N ^' -Dimethylbipyridylhalogenide, such as N, N ^' -Di-methylbipyridylchloride.

Preferred redox flow batteries of the first type contain, as anolyte, an aqueous electrolyte solution with a temperature of at least 30 ° C., preferably from 30 to 90 ° C., and in particular from 30 to 50 ° C., which is redox-active

Compound containing at least one radical of formula (IV) or formula (V). In other preferred redox flow batteries of this first type, these are

Electrode chambers for catholyte and anolyte separated by a semipermeable membrane impermeable to the redox couple in the catholyte, and the anolyte contains zinc salt as a redox-active component.

In a further embodiment, the invention also relates to a second type of redox flow battery for storing electrical energy containing one

Reaction cell with an electrode chamber for an electrolyte solution, which is connected to at least one liquid store, the

Electrode chamber is equipped with a cathode and an anode, and is filled with electrolyte solution containing redox-active components in liquid form, dissolved or dispersed in an aqueous electrolyte solvent, and

if necessary, conductive salts dissolved therein and possibly further additives. This redox flow battery is characterized in that the electrolyte solution contains an aqueous electrolyte solution according to the definition given above and zinc salt as a further redox-active component.

Redox flow batteries of this second type are distinguished by the fact that they only have to have a liquid reservoir and that no membrane has to be used to separate the reaction cell in the anode and cathode compartments.

Preferred redox flow batteries of this second type also contain

Liquid storage is an aqueous electrolytic solution as defined above.

Redox flow batteries of this second type are preferred, in which a zinc solid anode with the redox pair zinc (II) / zinc (0) is used.

Examples of zinc salts for the redox flow batteries of the first and second type are zinc chloride, zinc fluoride, zinc bromide, zinc iodide, zinc nitrate, zinc nitrite, zinc hydrogen carbonate, zinc sulfate, zinc perchlorate, zinc tetrafluoroborate and zinc hexafluorophosphate. In addition to zinc salts with inorganic anions, Use zinc salts with organic anions, for example zinc acetate, zinc oxalate or zinc formate.

In the second type and in a preferred embodiment of the first type of the redox flow battery according to the invention, zinc is used as the redox-active anode material. The different ones are particularly noteworthy

Physical states that zinc can assume within the battery.

During the charging process, zinc (II) cations dissolved in the electrolyte on the anode surface are reduced to elemental zinc (O). This requires two

Electrons are absorbed. The active material zinc is found in the battery in both dissolved and solid form.

The zinc solid anode can be present permanently as a metallic electrode or can only be formed in situ during the charging process of the battery on an electrically conductive surface within the chamber by the reduction of zinc cations. The zinc cations can function mainly as an active material, but also secondarily as a lead additive or as part of a lead additive mixture.

During the charging process, zinc (II) cations dissolved in the electrolyte are reduced to elemental zinc (0) on the anode surface. The anode can consist of any electrically conductive material, preferably metal, in particular zinc or zinc alloys. By taking up two electrons, metallic zinc is deposited on the electrode surface. In the opposite case, metallic zinc passes from the electrode surface through the release of two electrons into zinc ions, which accumulate in the anolyte.

Particularly preferred redox flow batteries according to the invention have a zinc solid anode with the redox pair zinc (II) / zinc (0).

The advantage over the fully organic redox flow batteries described is the reduction in production costs. The zinc anode is to produce much more cost-effectively than known organic anodes. On the other hand, the redox couple zinc (II)) / zinc (0) is characterized by very good stability against external environmental influences, such as sensitivity to

Oxygen off. Conventional systems must be kept free of oxygen; this complicates the design of the battery considerably and increases the operating costs. If a zinc anode is used, this can be completely dispensed with.

Zinc also has a very high overvoltage in aqueous media and thus enables an extremely high potential window. The potential window is

To understand voltage (potential range), which can be reached due to the position of the redox pairs, in the area of the electrochemical voltage series, between cathode and anode, without unwanted side reactions or decomposition of the redox-active species, the main additive, the electrolyte, or any other component of the entire battery. Conventional aqueous flow batteries are limited to a potential window of approximately 1.2 volts. At the

Otherwise this would result in hydrogen gas. By using a zinc anode, the potential window can be expanded to more than 2 V. This leads to a considerable increase in the electrical power per cell. Zinc has a very high overvoltage compared to hydrogen, which is why, despite the high voltage of 2 V, there is no hydrogen at the anode and the battery can be operated safely.

The term “battery” is used in its broadest sense in the context of this description. This can be a single rechargeable electrochemical cell or a combination of several such electrochemical cells.

Particularly preferred redox flow batteries of the present invention have a charge state of the catholyte or of the catholyte and of the anolyte of less than 90%, in particular of up to 80% and very particularly preferably of 70 to 80%. These redox flow batteries are characterized by a particularly good temperature stability of the electrolyte and especially the redox-active ones

Compound containing at least one radical of formula (I) in the electrolyte. The state of charge is determined as described above. Of course, the state of charge of the catholyte or the catholyte and the

Anolytes in the RFB according to the invention are also 100%.

In addition to the components described above, the redox flow battery according to the invention can also contain further elements or components customary for such cells.

In the redox flow battery according to the invention, selected redox-active component residues are used in the chamber (s) which are present in the chamber (s) in dissolved, liquid or dispersed form.

The redox potential of the redox-active component can be, for example, by means of

Cyclic voltammetry can be determined. This method is known to the person skilled in the art (compare Allen J. Bard and Larry R. Faulkner, “Electrochemical Methods:

Fundamentals and Applications ”, 2001, 2nd edition, John Wiley &Sons; Richard G. Compton, Craig E. Banks, Understanding Voltammetry, 2010, 2nd Edition, Imperial College Press).

The first type of redox flow battery according to the invention contains a semi-permeable or microporous membrane. This fulfills the following functions

• Separation of anode and cathode compartments

• Retaining the redox-active component in the catholyte and in the

Anolytes, i.e. retention of the cathode and anode active material

• Permeability for the conductive salts of the electrolyte, which serve to balance the charge, that is to say for anions and / or cations of the conductive salt or for the charge carriers contained in the electrolyte in general.

The membrane may include a size exclusion membrane, e.g. B. a dialysis membrane, but also an ion-selective membrane.

The membrane prevents the redox-active ferrocene compound from penetrating into the anode compartment and the redox-active components of the anolyte from penetrating into the Cathode compartment. The passage of dissolved zinc (II) cations does not have to, but can also be inhibited by the membrane.

Depending on the application, the membrane materials can consist of plastics, ceramics, glasses, metals or textile fabrics. Examples of materials are organic polymers, such as cellulose or modified cellulose, for example cellulose ethers or cellulose esters, polyether sulfone, polysulfone, polyvinylidene fluoride, polyester, polyurethanes, polyamides, polypropylene,

Polyvinyl chloride, polyacrylonitrile, polystyrene, polyvinyl alcohol, polyphenylene oxide, polyimides, polytetrafluoroethylene and their derivatives, or also ceramics, glasses or felts. Also membranes made of several materials

(Composites) are possible.

The membranes and the resulting redox flow batteries can be used in various forms. Examples of this are

Flat membranes, pocket filter construction and wound modules. These

Embodiments are known to the person skilled in the art. To be favoured

Flat membranes used.

The thickness of the membrane used according to the invention can vary over a wide range. Typical thicknesses are in the range between 0.1 pm and 5 mm, particularly preferably between 10 pm and 200 pm.

In addition to the redox-active components, electrolytes and optionally membranes described above, the redox flow cell according to the invention preferably contains further components. It refers to

• Funding means, such as pumps, as well as tanks and pipes for the transport and storage of redox-active components

• Electrodes, preferably consisting of or containing graphite, graphite fleece, graphite paper, carbon nano-tube carpets, activated carbon, carbon black or graphene

• where appropriate, current arresters, such as those made of graphite or metals The negative electrode preferably contains zinc and may also contain the following materials, for example:

Stainless steel, Hastelloy or iron-chromium-nickel-containing alloys, graphite,

Graphite fleece, graphite paper, carbon nano tube carpets, activated carbon, carbon black or graphene.

The redox flow batteries according to the invention contain current collectors as a further optional but preferred component. These have the task of ensuring the best possible electrical contact between the electrode material and the external one

Establish current source or current sink.

In the redox flow batteries according to the invention, current conductors can be used

Aluminum, aluminum alloys, copper, stainless steel, hastelloy, iron-chromium-nickel alloys, titanium or tantalum coated with precious metals, in particular titanium, niobium, tantalum coated with platinum and / or iridium and / or ruthenium oxide,

Hafnium or zirconium can be used.

All components that allow the transmission of electrical current to the electrodes are referred to as current collectors. The redox reactions take place on the electrodes (cathode and anode), which are in direct contact with the electrolyte.

The redox flow batteries according to the invention can be used in a wide variety of fields. In the broadest sense, it can be the

Act storage of electrical energy for mobile and stationary applications. The invention also relates to the use of the redox flow batteries for these purposes.

Examples of applications include use as stationary storage for emergency power supply, peak load balancing, and for temporary storage

electrical energy from renewable energy sources, particularly in the sector photovoltaics, hydropower and wind power, from gas, coal, biomass, tidal, and marine power plants.

The redox flow batteries according to the invention can be connected to one another in a manner known per se in a serial or parallel manner.

The following examples illustrate the invention without pointing to it

limit.

Example 1: Synthesis of ferrocene-bis-sulfonic acid

The synthesis of the ferrocene-bis-sulfonic acid was carried out according to a modified one

Literature (K. Chanawanno, C. Holstrom, L.A. Crandall, H. Dodge, V.N. Nemykin, R.S. Herrick, C.J. Ziegler, Dalton Trans. 2016, 45, 14320) and is described below.

Ferrocene (8.00 g, 44 mmol) was dissolved in acetic anhydride (100 mL).

Chlorosulfonic acid (5.7 mL, 86 mmol) was slowly added. The reaction mixture was stirred in an argon atmosphere for 20 hours at room temperature. The suspension was then filtered in an argon atmosphere. The filtrate was washed with acetic anhydride. Then the product was dried. A portion (3.46 g, 8.5 mmol) of the dried product was dissolved in ethanol (10 mL). Then a 1 M NaOH solution (10 mL), which was freshly prepared from NaOH (4.0 g, 100 mmol) in ethanol (100 mL), was slowly added. The solution was stirred for 30 minutes at room temperature. The precipitate was collected on a filter and then washed with ethanol and then dried in vacuo. The sodium salt of ferrocene-bis-sulfonic acid was thus obtained as a yellow solid (2.1 g, 4.7 mmol). Example 2: Stability test of ferrocene-bis-sulfonic acid (comparison)

The ferrocene from Example 1 was oxidized using Oxone ^® and the stability of the “charged” molecule was examined. After storage at 60 ° C (even in the absence of air), the charged electrolytes show an irreversible precipitation after three days.

Example 3: Investigation of the temperature resistance of electrolyte solutions

Anolyte catholyte

Production of the electrolytes:

Catholyte: 400 mM solution of the ferrocene derivative (1, 77 g, 4 mmol) in deionized water (10 mL

Anolyte: 600 mM solution of the viologens (3.00 g, 6 mmol) in deionized water (10 mL)

Battery test: The electrolyte solutions were separated using a Fumasep FAA-3-50 anion exchange membrane with a surface area of 5 cm ² . Graphite plates with a graphite fleece were used as electrodes. A persistaltic pump pumped the electrolyte solutions through hoses in reservoirs, which were in a heatable sand bath, and through the half cell.

In the first three cycles, 101, 1, 100.3 and 100.1 mAh could be charged. Accordingly, 100.6, 100.5 and 100.4 mAh were discharged.

After about 12 days of constant cycling, 99.4, 99.3 and 99.3 mAh were charged and 99.6, 99.6 and 99.5 mAh discharged accordingly. The experiment was also carried out with a sand bath heated to 60 ° C, in which both storage tanks of the electrolytes stood. The solutions, which have been cycled for almost 19 days, were used for this purpose. 99.0 mAh could be charged and 98.5 mAh discharged after 24 hours.

Ferrocene from Example 3 can be purchased commercially, for example, from TCI Chemicals. The synthesis of this compound is in ACS Energy Lett. 2017, 2, 639-644. The synthesis of the viology derivative from Example 3 is also in ACS Energy Lett. 2017, 2, 639-644.

Example 4: Synthesis of a functionalized ferrocene

Vinyl ferrocene (100 mg, 0.47 mmol) was placed in a microwave glass (5 mL)

Tetrahydrofuran (2 mL) dissolved. Then 2,2-dimethoxy-2-phenylaceto-phenone (DMPA, 3 mg, 0.01 mmol) was added. After a stir fish was placed in the microwave glass, it was sealed with a teflon septum and argon was bubbled through the clear orange solution for 15 minutes.

Then 2-mercaptopropanoic acid (50 pL, 0.56 mmol) with a

Microsyringe added. This solution was then placed in a beaker on a stir plate in a UV chamber (365 nm) and irradiated for 20 minutes.

The solution was then allowed to cool for 10 minutes. A total of 120 minutes was irradiated. The solvent was removed and the crude product was dissolved in dichloromethane and purified by column chromatography (silica, EtOAc / hexane 2/8). After the solvents have been removed by distillation was, the crude product was dried in a high vacuum. The product was obtained as a highly viscous, orange oil.

Example 5: Synthesis of a ferrocene polymer

By means of a radical copolymerization of a ferrocene monomer and a sulfobetaine methacrylate, a copolymer containing ferrocene could be produced. The ferrocene monomer could be obtained by reacting the hydroxyethylferrocene with methacrylic acid chloride.

Example 6: Synthesis of Hydroxyethylferrocene

Hydroxyethylferrocene ferrocene was dissolved in methyl THF and reacted with tert-butyllithium.

Ethylene oxide was then added. The product could then be obtained after separation by column chromatography. Example 7: Synthesis of a ferrocene polymer

A copolymer of METAC ([2- (methacryloyloxy) ethyl] trimethylammonium chloride) and a ferrocene-containing methacrylamide with a composition of 10 to 30% of the ferrocene monomer can be produced with molecular weights of around 10,000 g / mol (M _n ) by means of free radical polymerization will. Aqueous electrolytes based on this polymer were temperature stable at 60 ° C and showed no degradation (ie decrease in capacity) over 100 cycles.

Claims

Claims 218fs02.wo

1. Aqueous electrolyte solution with a temperature of at least 30 ° C. containing a compound with at least one redox-active radical of the formula (I)

(X-C5H ₄ ) Fe (Y-C5H ₃ -Z) (I), where X is a radical of the formula - (C _n H _2n ) -FG or of the formula - (C _n H _2n ) -Sp- (C _n H _2n ) - FG or the formula - (C _n H _2n ) -Brgp-,

Y is hydrogen or a radical of the formula - (C _n H _2n ) -FG or of the formula - (C _n H _2n ) - Sp- (C _n H _2n ) -FG,

Z is hydrogen or denotes a covalent bond which connects the rest of the formula (I) to the rest of the molecule,

FG is a functional group selected from -OH, -SH, -NO ₃ , -N0 ₂ , - CN, -OR ₁ , -SR! , - (0-CH ₂ -CH ₂ ) ₀ -OR _2, - (0-CH ₂ -CH ₂ ) _O -NR ₃ R ₄ R5 ⁺ (An ^m ) i _{/ m} , -COR ₂ , -COO (Cat ^{m +} ) i _{/ m} , -COOR ₂ , -SO, (Kat ^{m +} ) _{1 / m} , -S0 ₃ R ₂ , -SO4 (Kat ^{m +} ) _{1 / m} , -SO4R2, -PO4 ^{2 ·} (Kat ^{m +} ) _{2 / m} , -P0 ₄ (R ₂ ) ₂ , -P0 ₃ ² (Kat ^{m +} ) _{2 / m} , -P0 ₃ (R ₂ ) ₂ , -NR ₃ R ₄ R ₅ ⁺ (An ^m -) _{1 / m} ,

-NR ₃ R ₄ -C _t H _2t -S0 ₃ or -NR ₂ -S0 ₂ -R ₃ ,

Brgp is a double-bonded bridging group which connects the rest of the formula (I) to the rest of the molecule,

Sp is -O-, -S-, -SO- or S0 ₂ -,

R 1 is C ₁ -C ₄ alkyl,

R _{2 is} hydrogen or C ₁ -C 4 alkyl,

R _{3, R.} and R independently of one another are hydrogen or alkyl, cat is an m-valent cation,

An m-valued anion is

m represents an integer between 1 and 4,

n represents an integer between 2 and 4,

t is an integer between 2 and 5, and

o is an integer from 1 to 50, preferably from 3 to 20.

2. Aqueous electrolyte solution according to claim 1, characterized in that

this has a temperature of 30 to 90 ° C, preferably 30 to 50 ° C.

3. Aqueous electrolyte solution according to at least one of claims 1 to 2, characterized in that it contains at least one conductive salt.

4. Aqueous electrolyte solution according to at least one of claims 1 to 3,

characterized in that their state of charge is less than 90%.

5. Aqueous electrolyte solution according to at least one of claims 1 to 4,

characterized in that Y is hydrogen and that m is 1 or 2.

6. Aqueous electrolyte solution according to at least one of claims 1 to 5,

characterized in that FG is a functional group selected from - (0-CH ₂ -CH ₂ ) _O -OR _2, -COR _2I -COO- (Kat ^{m +} ) i _{/ m} , -SO3 (Kat ^{m +} ) _{1 / m} , - SCV (Kat ^{m +} ) _{1 / m} , - PO4 ² - (Kat ^{m +} ) _{2 / m} , -PO3 ² - (Kat ^{m +} ) _{2 / m} or -NR ₃ R ₄ R5 ⁺ (An ^m -) i _{/ m} .

7. Aqueous electrolyte solution according to at least one of claims 1 to 6, characterized in that Kat is a hydrogen cation, a cation of a

Alkali metal, an alkaline earth metal or an ammonium cation is preferably a hydrogen cation, a sodium, potassium, magnesium or calcium cation, or a quaternary ammonium cation.

8. Aqueous electrolyte solution according to at least one of claims 1 to 7, characterized in that An is selected from the group of

Halide ions, hydroxide ions, phosphate ions, sulfate ions, perchlorate ions, hexafluorophosphate ions or tetrafluoroborate ions.

9. Aqueous electrolyte solution according to at least one of claims 1 to 8,

characterized in that Z is a covalent group which connects the rest of the formula (I) to a polymer backbone which is selected from the group of the polymethacrylates, polyacrylates, polystyrenes, polyalkylene glycols,

Polyalkylenimine or the polyvinyl ether, the polymer backbone

preferably has 5 to 100 groups of the formula (I).

10. Aqueous electrolyte solution according to at least one of claims 1 to 8, characterized in that these oligomers or polymers with

recurring structural units of the formula (II) and optionally derived from other solubilizing comonomers

Contains structural units

(ii).

wherein

ME is a recurring structural unit derived from a polymerizable monomer,

BG is a covalent bond or a bridging group,

FC represents a radical of the formula (X-C5H ₄ ) Fe (Y-C5H ₃ -Z),

X, Y and Z have the meanings defined in claim 1, and

r is an integer from 2 to 150.

11. Aqueous electrolyte solution according to at least one of claims 1 to 8,

characterized in that the redox-active compound is a compound of formula (II)

(X-C5H4) Fe (Y-C5H4) (II), wherein X and Y have the meaning defined in claim 1.

12. Aqueous electrolyte solution according to at least one of claims 1 to 8,

characterized in that the redox-active compound is a compound of formula (III) [(XC ₅ H ₄ ) Fe (YC ₅ H ₃ -)] - R ₇ - [(- C ₅ H ₃ -Y) Fe (C ₅ H ₄ -X)] _P (III), where X and Y are the have meaning as defined in claim 1,

R is a two- to four-bonded organic group, and

p represents an integer from 1 to 4.

13. Aqueous electrolyte solution according to at least one of claims 1 to 10, characterized in that n is 2.

14. Redox flow battery for storing electrical energy containing a

Reaction cell with two electrode chambers for catholyte and anolyte, each of which is connected to at least one liquid store, the electrode chambers being separated by a membrane, equipped with electrodes, and each filled with electrolyte solutions containing the redox-active components in liquid form, dissolved or dispersed contained in an aqueous electrolyte solvent, as well as any conductive salts and possibly other additives dissolved therein, characterized in that the anolyte contains a water-soluble redox-active component and that the catholyte in the electrode chamber contains an aqueous electrolyte solution according to at least one of Claims 1 to 13

15. Redox flow battery according to claim 14, characterized in that the anolyte contains a compound containing one or more bipyridiyl groups in the molecule as a redox-active component.

16. Redox flow battery according to claim 14, characterized in that the electrode chambers for catholyte and anolyte are separated by a semipermeable membrane impermeable to the redox couple in the catholyte, and that the anolyte contains zinc salt as the redox-active component.

17. Redox flow battery for storing electrical energy containing a

Reaction cell with an electrode chamber for an electrolyte solution, which is connected to at least one liquid store, the Electrode chamber is equipped with a cathode and an anode, and is filled with electrolyte solution containing redox-active components in liquid form, dissolved or dispersed in an aqueous electrolyte solvent, and, if appropriate, conductive salts and possibly other additives dissolved therein, characterized in that the electrolyte solution is an aqueous Contains electrolyte solution according to at least one of claims 1 to 13 and zinc salt as a further redox-active component.

18. Redox flow battery according to at least one of claims 14 to 17, characterized in that this is a zinc solid anode with the redox couple

Zinc (II) / Zinc (0).

19. Redox flow battery according to at least one of claims 14 to 18, characterized in that the state of charge of the catholyte or the catholyte and the anolyte is less than 90%.

20. Use of the redox flow battery according to one of claims 14 to 19 for storing electrical energy for stationary and mobile applications, in particular as a stationary memory for the emergency power supply

Peak load balancing, for the temporary storage of electrical energy from renewable energy sources, in particular in the photovoltaic, hydropower and wind power sector, or from gas, coal, biomass, tidal and marine power plants.