Low-cost flow battery and application thereof

Abstract

The invention provides a low-cost flow battery and an application thereof, a redox active substance of a positive electrode electrolyte of the low-cost flow battery contains a hydroxylamine cyclic structure group with hindered amine, and the hydroxylamine cyclic structure group with hindered amine is preferably selected from 1-hydroxy-2, 2, 6, 7, 8-tetramethyl-1, 3, 5-tetramethyl-1, 3, 5-tetramethyl-1, 3, 5-tetramethyl-1, 3, 5-tetramethyl-1, 3, 5-tetramethyl-1, 3, 5-tetramethyl-1, 3, 5-tetramethyl-1, one or more of a 1-oxo-2, 2, 6, 6-tetrasubstituted piperidine group, a 1-oxo-2, 2, 6, 6-tetrasubstituted piperidine group, a 1-oxo-2, 2, 6, 6-tetrasubstituted piperidine group, and a 1-oxo-2, 2, 6, 6-tetrasubstituted piperidinium group; a redox active substance of the negative electrode electrolyte contains one or more of a titanium element, a vanadium element, a chromium element, an iron element and a zinc element. The low-cost flow battery has the advantages of high output voltage, high energy density, environment friendliness and low cost, and has good application prospects and large-scale popularization potential in the field of energy storage.

Description

Technical Field

[0001] The present invention relates to organic flow battery technology, and particularly to a low-cost flow battery and its applications. Background Art

[0002] A redox flow battery (RFB) is a storage device for converting electrical energy and chemical energy, mainly applicable to fixed energy storage applications, such as a buffer battery for a wind power plant and a solar power plant, or a power and regulation reserve for load distribution in a power grid, and as a mobile energy storage device, or for operating electric vehicles and electronic devices. During the charging or discharging process of the battery, the active substances in the positive electrolyte and the negative electrolyte will transform into their respective redox states; the positive and negative electrolytes are transferred from their respective tanks and pumped into their respective reaction chambers. The positive and negative chambers in the stack are separated by an ion-selective membrane, which usually has high selectivity for the corresponding ions (such as Nafion membrane). In addition, there are size-selective membranes (such as dialysis membranes or ultrafiltration membranes) that allow anions or cations to pass through.

[0003] With the continuous expansion of the scale of renewable energy power generation such as solar energy and wind energy, the problems of intermittency and instability have become increasingly prominent. As a large-scale energy storage technology, redox flow batteries can store electrical energy when the power generation of renewable energy is excessive and release electrical energy when the power generation is insufficient, playing a role in smoothing the output and stabilizing the power grid. However, traditional redox flow batteries have a low energy density, making it difficult to meet the large-scale energy storage requirements, and the low voltage limits their overall performance. Therefore, in order to adapt to the continuous expansion of the scale of renewable energy power generation, it is urgent to develop a new type of redox flow battery with high voltage and high energy density. Summary of the Invention

[0004] The object of the present invention is to propose a low-cost flow battery aiming at the above problems. The flow battery has the advantages of high output voltage, high energy density, environmental friendliness and low cost, and has good application prospects and large-scale popularization potential in the energy storage field.

[0005] It should be noted that in the present invention, unless otherwise specified, the specific meaning of "including" related to composition limitation and description includes both the open "including", "containing" and their similar meanings, and also the closed "consisting of", "composed of" and their similar meanings.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a low-cost flow battery, in which the redox active substance of the positive electrolyte contains a hydroxylamine cyclic structure group with a hindered amine.

[0007] Furthermore, one or more of titanium, vanadium, chromium, iron, and zinc are included in the redox active substances of the negative electrolyte.

[0008] Another object of the present invention also discloses an application of a low-cost flow battery in the fields of mobile and stationary energy storage devices.

[0009] The low-cost flow battery and its application of the present invention have the following advantages compared with the prior art:

[0010] 1) The open-circuit voltage of a single-stack low-cost flow battery exceeds 1.35 V, which is significantly higher than that of traditional iron-chromium flow batteries. A higher open-circuit voltage means that under the same current conditions, the battery can provide a greater output power, which is particularly important for application scenarios requiring high power output. In addition, the high-voltage design can also reduce the number of battery strings, thus simplifying the structural design of the battery system and subsequent maintenance work.

[0011] 2) The low-cost flow battery of the present invention has significant environmental friendly characteristics. This battery system avoids the use of highly toxic chemicals, meeting the current urgent needs for green energy and environmental protection technologies.

[0012] 3) Energy density is one of the important indicators for measuring battery performance. Usually, TEMPO-based flow batteries only utilize their single-electron characteristics. The redox active substance in the positive electrolyte of the present invention can charge and discharge 2 electrons per molecule, greatly improving the energy density, up to 30 - 300 Wh / L.

[0013] 4) The low-cost flow battery of the present invention has significant cost advantages. Since it does not rely on rare metals, it effectively reduces the production cost of the battery and enhances the market competitiveness. This innovation not only helps to promote the wide application in the field of large-scale energy storage, but also provides an economically viable solution for sustainable energy storage.

[0014] 5) Part of the pairing of the low-cost flow battery of the present invention is a dual-flow battery, which is a non-depositing battery, and the power and capacity are completely decoupled. The electrolytes of the positive and negative electrodes of the dual-flow battery are stored in different liquid storage tanks respectively, and the electrolytes are driven by pumps to react in the battery stack. This design helps to improve the flexibility and scalability of the battery system; the power and capacity can be designed independently to meet the requirements of different application scenarios. Specifically, in high-power output scenarios, the power can be increased by increasing the number of battery stacks; while in long-term energy storage scenarios, a larger energy storage capacity can be achieved by increasing the electrolyte capacity. This modular design concept enables the battery system to be flexibly configured according to actual needs, having significant application advantages.

[0015] In summary, the low-cost flow battery of the present invention can operate safely, economically, and effectively, showing significant advantages in aspects such as voltage output, environmental friendliness, energy density, cost, and system flexibility, and having good application prospects and large-scale popularization potential in the energy storage field. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a diagram of the test device;

[0017] Figure 2 Charge and discharge curves of the battery in Example 1 over time;

[0018] Figure 3 Charge and discharge curves of the battery in Example 2 over time;

[0019] Figure 4 Charge and discharge efficiency curve of the battery in Example 2

[0020] Figure 5 Energy efficiency curve of the battery in Example 2;

[0021] Figure 6 Discharge capacity curve of the battery in Example 2;

[0022] Figure 7 Charge and discharge curves of the battery in Example 3 over time;

[0023] Figure 8 Charge and discharge efficiency curve of the battery in Example 3

[0024] Figure 9 Energy efficiency curve of the battery in Example 3;

[0025] Figure 10 Discharge capacity curve of the battery in Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention relates to a flow battery - redox flow battery (also known as redox battery pack or redox flow battery pack) that stores electrical energy through the oxidation and reduction of chemical media. The core structure of the system consists of an electrostack, which contains multiple groups of reaction sheets configured in series or parallel. Each group of reaction sheets is provided with a positive electrode chamber (cathode) and a negative electrode chamber (anode), and the two chambers are physically isolated by an ion exchange membrane or a diaphragm. The positive electrode chamber is defined as the area extending from the positive electrode to the diaphragm facing the positive electrode, and the negative electrode chamber extends from the negative electrode to the diaphragm facing the negative electrode. Each chamber is connected to the corresponding liquid storage tank through an independent circulation loop: the positive electrode chamber forms a closed-loop system with the positive electrode liquid storage tank, and the negative electrode chamber forms another independent closed-loop system with the negative electrode liquid storage tank. The two systems achieve ion conduction through the diaphragm but are physically isolated from the electrolyte.

[0027] The electrolyte containing redox-active substances is stored in the chambers and the liquid storage tank. The active substances exist in the electrolyte solvent in a dissolved or dispersed form. At the same time, conductive salts and other functional additives can be selectively added to optimize the electrochemical performance. During the charge and discharge processes, reversible reactions occur in the corresponding chambers for the positive and negative electrode electrolytes respectively: during charging, the positive electrode active substance undergoes an oxidation reaction in the positive electrode chamber, and the negative electrode active substance undergoes a reduction reaction in the negative electrode chamber; during discharging, the reaction direction is reversed, the positive electrode active substance is reduced, and the negative electrode active substance is oxidized. During this process, ions migrate directionally through the diaphragm to maintain charge balance, while the redox reaction of the active substances on the electrode surface realizes the storage and release of electrical energy through the external circuit.

[0028] The energy storage capacity of the system is determined by the total amount of active substances in the positive and negative electrode electrolytes, while the output power depends on the effective reaction area formed by stacking multiple groups of reaction sheets in the stack. This decoupled design of energy and power enables the flow battery to flexibly adapt to the requirements of different application scenarios by independently adjusting the volume of the liquid storage tank (controlling the capacity) and the scale of the stack (controlling the power).

[0029] The low-cost flow battery of the present invention has a structure in formula Y in the redox-active substance of the positive electrode electrolyte:

[0030]

[0031] Formula Y is a hydroxylamine cyclic structure group with a hindered amine, and the cyclic structure is a 3-membered ring, 4-membered ring, 5-membered ring, 6-membered ring, 7-membered ring or 8-membered ring;

[0032] The cyclic structure contains one or more of carbon-carbon single bonds, carbon-carbon double bonds and carbon-carbon triple bonds;

[0033] R1, R2, R3 and R4 are each independently selected from alkyl, cycloalkyl, aryl and aralkyl.

[0034] Furthermore, the cyclic structure can be connected to the remaining molecular structure through an extended covalent bond, and one or more groups such as methyl, propyl and phenyl can also be attached to the ring, and the number of attached groups is not limited.

[0035] The hydroxylamine cyclic structure group with a hindered amine can undergo a highly reversible redox reaction of formula Ya. This reversible conversion between hydroxylamine, nitroxide radical and nitronium salt is one of the cores disclosed and protected by the present invention. In this way, a single hydroxylamine cyclic structure group with a hindered amine can charge and discharge 2 electrons.

[0036] Further, the hydroxylamine cyclic structural group of the hindered amine is one or more of a 1-hydroxy-2,2,6,6-tetrasubstituted piperidine group, a 1-hydroxy-2,2,5,5-tetrasubstituted pyrrole group, and a 1-hydroxy-2,2,5,5-tetrasubstituted pyrroline group; these groups can all undergo a reversible redox reaction as shown in Formula Ya and have a 2-electron charge-discharge characteristic.

[0037] Further, the most preferred hydroxylamine cyclic structural group of the hindered amine is a 1-hydroxy-2,2,6,6-tetrasubstituted piperidine group, which has the lowest cost.

[0038]

[0039] Further, the redox active substance in the described positive electrolyte contains one or more of a 1-hydroxy-2,2,6,6-tetrasubstituted piperidine group, a 1-oxyl-2,2,6,6-tetrasubstituted piperidine group, and a 1-oxo-2,2,6,6-tetrasubstituted piperidinium group; the redox active substance in its negative electrolyte contains one or more of titanium, vanadium, chromium, iron, and zinc elements.

[0040] The reaction that occurs at the positive electrode during the charge and discharge process of the low-cost flow battery of the present invention is as follows:

[0041]

[0042] The 1-hydroxy-2,2,6,6-tetrasubstituted piperidine group unit loses a proton and an electron during the charging process and is transformed into a 1-oxyl-2,2,6,6-tetrasubstituted piperidine group unit; when charging continues, the 1-oxyl-2,2,6,6-tetrasubstituted piperidine group unit loses an electron and is oxidized into a 1-oxo-2,2,6,6-tetrasubstituted piperidinium group unit. During the discharging process, the 1-oxo-2,2,6,6-tetrasubstituted piperidinium group unit is successively reduced to a 1-oxyl-2,2,6,6-tetrasubstituted piperidine group unit and a 1-hydroxy-2,2,6,6-tetrasubstituted piperidine group unit. The above formula shows the redox balance among the 1-hydroxy-2,2,6,6-tetrasubstituted piperidine group unit, the 1-oxyl-2,2,6,6-tetrasubstituted piperidine group unit, and the 1-oxo-2,2,6,6-tetrasubstituted piperidinium group unit during the charging process / discharging process.

[0043] The reaction formula that occurs at the negative electrode during the charge and discharge process of the low-cost flow battery of the present invention is as follows:

[0044]

[0045] During the charging process, metal cations in the negative electrolyte are reduced to corresponding lower-valence metal cations or metallic elements on the surface of the negative electrode; during the discharging process, the reduced metal cations or metallic elements are oxidized to higher-valence metal cations. The above equation shows the oxidation-reduction equilibrium of metal cations or metallic elements during the charging / discharging process. When the negative active material is titanium cations, during charging, titanium(IV) cations are successively reduced to titanium(III) cations and titanium(II) cations on the surface of the negative electrode; during discharging, titanium(III) cations and titanium(II) cations are successively oxidized to titanium(IV) cations on the surface of the negative electrode, and titanium cations can be used as a two-electron active material. When the negative active material is vanadium cations, during charging, vanadium(IV) cations are successively reduced to vanadium(III) cations and vanadium(II) cations on the surface of the negative electrode; during discharging, vanadium(III) cations and vanadium(II) cations are successively oxidized to vanadium(IV) cations on the surface of the negative electrode, and vanadium cations can be used as a two-electron active material. When the negative active material is chromium cations, during charging, chromium(III) cations are reduced to chromium(II) cations on the surface of the negative electrode; during discharging, chromium(II) cations are oxidized to chromium(III) cations on the surface of the negative electrode. When the negative active material is iron(II) cations, during charging, iron(II) cations are reduced to elemental iron(0) on the surface of the negative electrode; during discharging, elemental iron(0) is oxidized to iron(II) cations on the surface of the negative electrode, and iron cations can be used as a two-electron active material. When the negative active material is zinc(II) cations, during charging, zinc(II) cations are reduced to elemental zinc(0) on the surface of the negative electrode; during discharging, elemental zinc(0) is oxidized to zinc(II) cations on the surface of the negative electrode, and zinc cations can be used as a two-electron active material. Of course, the negative electrode can also be a mixture of titanium ions, vanadium ions, chromium ions, iron ions, iron elements, zinc ions, and zinc elements; of course, these metal cations or metallic elements can act as a conductivity additive or part of a conductivity additive. When elemental iron and elemental zinc are involved, the solid negative electrodes of elemental iron and elemental zinc can exist permanently as metal electrodes, but they can also be formed in situ on the conductive surface in the chamber only during the charging process of the battery pack by reducing iron cations and zinc cations.

[0046] Although the 1-hydroxy-2,2,6,6-tetrasubstituted piperidine group, the 1-oxyl-2,2,6,6-tetrasubstituted piperidine group, and the 1-oxo-2,2,6,6-tetrasubstituted piperidinium group are different substances, there is a high charge-discharge reversibility between these three groups. For the convenience of writing and description below, only the 1-hydroxy-2,2,6,6-tetrasubstituted piperidine group is used as the starting substance for description below. Of course, the 1-oxyl-2,2,6,6-tetrasubstituted piperidine group, the 1-oxo-2,2,6,6-tetrasubstituted piperidinium group, and any combination of the three are also included in the present invention.

[0047] The redox active substance of the positive electrode electrolyte is a 1-hydroxy-2,2,6,6-tetrasubstituted piperidine group. Its preferred representative is the 1-hydroxy-2,2,6,6-tetramethylpiperidine group. The 1-hydroxy-2,2,6,6-tetrasubstituted piperidine group can be both a component of a low molecular weight compound or an oligomeric compound (also known as an oligomer), and a part of a high molecular weight compound (also known as a polymer). In the latter case, the 1-hydroxy-2,2,6,6-tetrasubstituted piperidine group unit is located in the side chain of the polymer. The macromolecule itself can additionally carry, in addition to the side chain having the redox active unit, other side chains that improve solubility in the electrolyte, for example. In addition to the 2,2,6,6-tetrasubstitution, the hydroxypiperidine unit can also be modified by additional substituents.

[0048] The positive electrode electrolyte can contain, in dissolved form in an aqueous or water-organic electrolyte and as a dispersion, molecules having a 1-hydroxy-2,2,6,6-tetrasubstituted piperidine group unit. Additionally, the molecule having a 1-hydroxy-2,2,6,6-tetrasubstituted piperidine group unit can also be a liquid compound.

[0049] The positive electrode electrolyte uses a compound containing at least one group of formula I as a redox active component:

[0050]

[0051] The leaving line at the 4-position in the structure of formula I represents a covalent bond, and the structure of formula I is connected to the rest of the compound molecule through the covalent bond at the 4-position. R1, R2, R3, and R4 are each independently selected from alkyl, cycloalkyl, aryl, and aralkyl. As described above, the group of formula I can be a part of a low molecular weight compound, an oligomeric compound, or a high molecular weight compound. The 1-position above is the position of the nitrogen atom. Counting clockwise, R1 and R2 are distributed at the 2-position, the 4-position corresponds to the 4th carbon atom on the ring, and R3 and R4 are distributed at the 6-position.

[0052] "Low molecular weight compound" is understood in the context of this specification as a compound that does not have repeating structural units derived from monomers, and it contains at least 1, preferably 1 to 6, particularly preferably 1 to 4, especially 1 to 3, and very particularly preferably 1 or 2 groups of formula I.

[0053] "Oligomeric compound" is understood in the context of this specification as a compound having 2 to 10 repeating structural units derived from monomers, and each of the structural units carries 1 group of formula I.

[0054] "High molecular weight compound" is understood in the context of this specification as a compound having more than 10, preferably 11 to 15 repeating structural units derived from monomers, each of said structural units carrying one group of formula I.

[0055] The positive electrode electrolyte uses a compound having 1 to 6, preferably 1 to 4, especially 1 to 3, and very particularly preferably 1 to 2 groups of formula I in the molecule as the redox active component.

[0056] The positive electrode electrolyte uses a compound containing one or more of formula Ia, Ib, Ic, Id, Ie and If as the redox active component:

[0057]

[0058]

[0059] In formula Ia, Ib, Ic, Id, Ie and If, R1, R2, R3 and R4 have the meanings defined in formula I, X represents a q-valent inorganic or organic anion or a mixture of anions of this type, q is an integer from 1 to 3, o is an integer from 1 to 4, u is an integer from 1 to 4, R8 is a divalent to tetravalent organic bridging group, R5 is hydrogen, alkyl, alkoxy, haloalkyl, cycloalkyl, aryl, aralkyl, heterocyclic group, halogen, hydroxy, amino, nitro or cyano, and R6 is a monovalent organic group carrying o times, preferably once, a positive charge, especially a quaternary ammonium group, a quaternary phosphonium group, a tertiary sulfonium group, or a monovalent heterocyclic group carrying o times, preferably once, a positive charge, R9 is a divalent to tetravalent organic group carrying m times a positive charge, especially a divalent to tetravalent quaternary ammonium group, a divalent to tetravalent quaternary phosphonium group, a divalent to trivalent tertiary sulfonium group, or a divalent to tetravalent heterocyclic group carrying m times a positive charge, R7 is a monovalent group carrying u times, preferably once, a negative charge, especially a carboxyl group or a sulfonic acid group, or a monovalent heterocyclic group carrying u times, preferably once, a negative charge, R 10 is a divalent to tetravalent organic group carrying m times a negative charge, especially an alkylene group substituted by 1 or 2 carboxyl groups or sulfonic acid groups, or a phenylene group substituted by 1 or 2 carboxyl groups or sulfonic acid groups, or a divalent heterocyclic group substituted by 1 or 2 carboxyl groups or sulfonic acid groups, Z is a q-valent inorganic or organic cation or a mixture of cations of this type, f is an integer from 1 to 3, l is a number having the value o / q or u / q, m is an integer from 1 to 4, and n represents a number having the value m / q.

[0060] The redox active component is an oligomer or polymer having a backbone containing a plurality of redox active units of formula I as defined above.

[0061] The redox active component is an oligomer or polymer having a backbone containing a plurality of redox active units of one or more of the formulas Ia, Ib, Ic, Id, Ie and If as defined above.

[0062] The positive electrode electrolyte contains a compound of formula II as the redox active component, and the compound of formula II is an oligomer or polymer having a plurality of redox active units of formula I;

[0063]

[0064] In formula II, R1, R2, R3 and R4 have the meanings defined in formula I, ME is a repeating structural unit derived from a polymerizable monomer, BG is a covalent bond or a bridging group, r is an integer from 2 to 150, preferably an integer from 2 to 80, and very particularly preferably an integer from 8 to 40.

[0065] The repeating units ME and BG form the backbone of an oligomer or polymer containing a plurality of units of the redox active unit of formula I defined above.

[0066] Examples of substance classes that can form the backbone of an oligomer or polymer are polymers derived from ethylenically unsaturated carboxylic acids or their esters or amides, such as polymethacrylates, polyacrylates, polymethacrylamides or polyacrylamides, polymers derived from ethylenically unsaturated aryl compounds, such as polystyrene, polymers or their derivatives derived from vinyl esters of saturated carboxylic acids, such as polyvinyl acetate or polyvinyl alcohol, polymers derived from olefins or bicyclic or polycyclic olefins, such as polyethylene, polypropylene or polynorbornene, polyimides derived from tetracarboxylic acids and diamines forming imides, polymers derived from naturally occurring polymers and their chemically modified derivatives, such as cellulose or cellulose ethers, and polyurethanes, polyvinyl ethers, polythiophenes, polyacetylenes, polyalkylene glycols, poly-7-oxanorbornenes, polysiloxanes, polyethylene glycols, and their derivatives, such as their ethers.

[0067] Examples of combinations of the structural unit ME and the bridging group BG of some of the substance classes mentioned above are given below. Here are:

[0068]

[0069]

[0070] Particularly preferably used substance classes for forming oligomeric or copolymeric backbones are polymethacrylates, polyacrylates, polystyrenes, and polyvinyl ethers. The redox-active units of formula I are covalently bonded to the polymer backbone. The polymer-containing redox-active components can be present as linear polymers or they are comb-shaped and star polymers, dendrimers, ladder polymers, cyclic polymers, polycatenanes, and polyrotaxanes.

[0071] Comb-shaped and star polymers, dendrimers, ladder polymers, cyclic polymers, polycatenanes, and polyrotaxanes are used. These types are characterized by increased solubility and the viscosity of the solutions obtained is generally lower than that of the corresponding linear polymers.

[0072] The solubility of the polymers containing redox-active components used according to the invention can be additionally improved by copolymerization or functionalization, for example with polyethylene glycol, polymethacrylic acid, polyacrylic acid, or polystyrene sulfonate / salt.

[0073] The preparation of the redox-active oligomeric or polymeric components used according to the invention can be carried out by conventional polymerization methods. Examples thereof are polymerization per se, polymerization in solution, or emulsion polymerization or suspension polymerization. These procedures are known to the person skilled in the art.

[0074] Examples of preferably used oligomeric or polymeric redox-active components are oligomers or polymers derived from 1-hydroxy-2,2,6,6-tetramethylpiperidinyl-methacrylate and / or 1-hydroxy-2,2,6,6-tetramethylpiperidinyl-acrylate, in particular copolymeric oligomers or copolymers derived from 1-hydroxy-2,2,6,6-tetramethylpiperidinyl-methacrylate and / or 1-hydroxy-2,2,6,6-tetramethylpiperidinyl-acrylate, which are copolymerized with [2-(methacryloyloxy)ethyl]amine or an ammonium salt derived therefrom, such as trimethylammonium chloride, and / or with [2-(acryloyloxy)ethyl]amine or an ammonium salt derived therefrom, such as trimethylammonium chloride, in order to improve solubility.

[0075] When one of the groups R1, R2, R3, R4, and / or R5 represents an alkyl group, the alkyl group can be either branched or unbranched. The alkyl group typically contains 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms. Examples of the alkyl group are: methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, n-hexyl, n-heptyl, 2-ethylhexyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, n-nonadecyl, or eicosyl. Particularly preferred is an alkyl group having 1 to 6 carbon atoms. The alkyl group can be optionally substituted, for example, by a carboxyl or sulfonic acid group, by a carboxylic acid ester or sulfonic acid ester group, by a carboxylic acid amide or sulfonic acid amide group, by a hydroxyl or amino group, or by a halogen atom.

[0076] When the group R5 is an alkoxy group, the alkoxy group can be composed of alkyl units that can be either branched or unbranched. The alkoxy group typically contains 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms. Examples of the alkoxy group are: methoxy, ethoxy, isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, pentyloxy, n-hexyloxy, n-heptyloxy, 2-ethylhexyloxy, n-octyloxy, n-nonyloxy, n-decyloxy, n-tridecyloxy, n-tetradecyloxy, n-pentadecyloxy, n-hexadecyloxy, n-octadecyloxy, or eicosyloxy. Particularly preferred is an alkoxy group having 1 to 6 carbon atoms.

[0077] When the group R5 represents a haloalkyl group, the haloalkyl group can be either branched or unbranched. The haloalkyl group typically contains 1 to 20 carbon atoms, and the carbon atoms are independently substituted by one or more halogen atoms, preferably 1 to 10 carbon atoms. Examples of the halogen atom are fluorine, chlorine, bromine, or iodine. Preferred are fluorine and chlorine. Examples of the haloalkyl group are: trifluoromethyl, difluoromethyl, fluoromethyl, bromodifluoromethyl, 2-chloroethyl, 2-bromoethyl, 1,1-difluoroethyl, 2,2,2-trifluoroethyl, 1,1,2,2-tetrafluoroethyl, 2-chloro-1,1,2-trifluoroethyl, pentafluoroethyl, 3-bromopropyl, 2,2,3,3-tetrafluoropropyl, 1,1,2,3,3,3-hexafluoropropyl, 1,1,1,3,3,3-hexafluoropropyl, 3-bromo-2-methylpropyl, 4-bromobutyl, perfluoropentyl.

[0078] When one of the groups R1, R2, R3, R4 and / or R5 represents a cycloalkyl group, the cycloalkyl group is typically a cyclic group containing 3 to 8, preferably 5, 6 or 7 ring carbon atoms, which may each be independently substituted. Examples of substituents are alkyl groups or two alkyl groups which together with the ring carbon atom to which they are attached form another ring. Examples of cycloalkyl groups are cyclopropyl, cyclopentyl or cyclohexyl. The cycloalkyl group may optionally be substituted, for example by a carboxyl or sulfonic acid group, by a carboxylic acid ester or sulfonic acid ester group, by a carboxylic acid amide or sulfonic acid amide group, by a hydroxyl or amino group or by a halogen atom.

[0079] When the group R5 represents a heterocyclic group, the heterocyclic group is typically a cyclic group having 4 to 10 ring carbon atoms and at least one ring heteroatom, which may each be independently substituted. Examples of substituents are alkyl groups or two alkyl groups which together with the ring carbon atom to which they are attached form another ring. Examples of heteroatoms are oxygen, nitrogen, phosphorus, boron, selenium or sulfur. Examples of heterocyclic groups are furyl, thienyl, pyrrolyl or imidazolyl. The heterocyclic group is preferably aromatic. The heterocyclic group may optionally be substituted, for example by a carboxyl or sulfonic acid group, by a carboxylic acid ester or sulfonic acid ester group, by a carboxylic acid amide or sulfonic acid amide group, by a hydroxyl or amino group or by a halogen atom.

[0080] When one of the groups R1, R2, R3, R4 and / or R5 represents an aralkyl group, the aralkyl group is typically an aryl group as defined above which is covalently bonded to an alkyl group. The aralkyl group may be substituted on the aromatic ring, for example by an alkyl group or by a halogen atom. An example of an aralkyl group is benzyl. The aralkyl group may optionally be substituted, for example by a carboxyl or sulfonic acid group, by a carboxylic acid ester or sulfonic acid ester group, by a carboxylic acid amide or sulfonic acid amide group, by a hydroxyl or amino group or by a halogen atom.

[0081] When the group R5 represents an amino group, the amino group may be unsubstituted or carry 1 or 2 or 3 substituents, preferably alkyl and / or aryl groups. The alkyl substituents may be branched or unbranched. Monoalkylamino or dialkylamino typically contain 1 or 2 alkyl groups having 1 to 20 carbon atoms, preferably 1 to 6 carbon atoms. Examples of monoalkylamino are: methylamino, ethylamino, propylamino or butylamino. Examples of dialkylamino are: diethylamino, dipropylamino or dibutylamino. Examples of trialkylamino are: triethylamino, tripropylamino or tributylamino.

[0082] When the group R5 represents a halogen, this is understood to mean a covalently bonded fluorine atom, chlorine atom, bromine atom or iodine atom. Fluorine or chlorine is preferred.

[0083] When R8 represents a divalent to tetravalent organic bridging group, this is understood to be an organic group bonded to the remainder of the molecule by 2, 3 or 4 covalent bonds.

[0084] Examples of divalent organic groups are alkylene, alkyleneoxy, poly(alkyleneoxy), alkyleneamino, poly(alkyleneamino), cycloalkylene, arylene, arylalkylene or heterocyclylene. These groups have been described in more detail above.

[0085] The alkylene can be either branched or unbranched. The alkylene typically contains 1 to 20 carbon atoms, preferably 2 to 4 carbon atoms. Examples of alkylene are: methylene, ethylene, propylene and butylene. The alkylene can be optionally substituted, for example by a carboxyl or sulfonic acid group, by a carboxylate or sulfonate group, by a carboxamide or sulfonamide group, by a hydroxyl or amino group or by a halogen atom.

[0086] The alkyleneoxy and poly(alkyleneoxy) can contain either branched or unbranched alkylene. The alkylene occurring in the alkyleneoxy or poly(alkyleneoxy) typically contains 2 to 4 carbon atoms, preferably 2 or 3 carbon atoms. The number of repeating units in the poly(alkyleneoxy) can vary within a wide range. The typical number of repeating units varies within the range of 2 to 50. Examples of alkyleneoxy are: ethoxy, propoxy and butoxy. Examples of poly(alkyleneoxy) are: poly(ethoxy), poly(propoxy) and poly(butoxy).

[0087] The alkyleneamino and poly(alkyleneamino) can contain either branched or unbranched alkylene. The alkylene occurring in the alkyleneamino or poly(alkyleneamino) typically contains 2 to 4 carbon atoms, preferably 2 or 3 carbon atoms. The number of repeating units in the poly(alkyleneamino) can vary within a wide range. The typical number of repeating units varies within the range of 2 to 50. Examples of alkyleneamino are ethylamino, propylamino and butylamino. Examples of poly(alkyleneamino) are: poly(ethylamino), poly(propylamino) and poly(butylamino).

[0088] The cycloalkylene typically contains 5, 6 or 7 ring carbon atoms which can each be independently substituted. Examples of substituents are alkyl or two alkyls which can together with the ring carbon atom to which they are attached form another ring. An example of cycloalkylene is cyclohexylene. The cycloalkylene can be optionally substituted, for example by a carboxyl or sulfonic acid group, by a carboxylate or sulfonate group, by a carboxamide or sulfonamide group, by a hydroxyl or amino group or by a halogen atom.

[0089] An arylene is typically a cyclic aromatic group containing 5 to 14 carbon atoms which may each be independently substituted. Examples of arylene are o-phenylene, m-phenylene, p-phenylene, o-biphenylene, m-biphenylene, p-biphenylene, 1-anthryl, 2-anthryl, 9-anthryl, 1-phenanthryl, 2-phenanthryl, 3-phenanthryl, 4-phenanthryl or 9-phenanthryl. The arylene may be optionally substituted, for example by a carboxyl or sulfonic acid group, by a carboxylic acid ester or sulfonic acid ester group, by a carboxylic acid amide or sulfonic acid amide group, by a hydroxyl or amino group or by a halogen atom. Further examples of substituents are alkyl groups or two alkyl groups which together with the ring carbon atom to which they are attached may form another ring.

[0090] A heteroarylene is typically a cyclic group containing 4 to 10 ring carbon atoms and at least one ring heteroatom which may each be independently substituted. Examples of heteroatoms are oxygen, nitrogen, phosphorus, boron, selenium or sulfur. Examples of heteroarylene are furandiyl, thiophenediyl, pyrrolediyl or imidazoldiyl. The heteroarylene is preferably aromatic. The heteroarylene may be optionally substituted, for example by a carboxyl or sulfonic acid group, by a carboxylic acid ester or sulfonic acid ester group, by a carboxylic acid amide or sulfonic acid amide group, by a hydroxyl or amino group or by a halogen atom. Further examples of substituents are alkyl groups or two alkyl groups which together with the ring carbon atom to which they are attached may form another ring.

[0091] An arylalkyl is typically an aryl group to which 1 or 2 alkyl groups are bonded. The arylalkyl may be covalently bonded to the rest of the molecule through its aryl group and its alkyl group or through two alkyl groups. The arylalkyl may be substituted on the aromatic ring, for example by an alkyl group or by a halogen atom. Examples of arylalkyl are benzylidene or dimethylphenylene (dimethylyphenyl).

[0092] Examples of the trivalent organic group R8 are alkyltriyl, alkoxytriyl, tri(alkyleneoxy), tri(alkylamino), cycloalkyltriyl, aryltriyl, arylalkyltriyl or heteroaryl triyl. These groups correspond to the divalent groups which have been described in detail above, with the difference that they are bonded to the rest of the molecule by three covalent bonds instead of two.

[0093] Examples of the tetravalent organic group R8 are alkyltetrayl, alkoxytetrayl, tetra(alkyleneoxy), tetra(alkylamino), cycloalkyltetrayl, aryltetrayl, arylalkyltetrayl or heteroaryl tetrayl. These groups correspond to the divalent groups which have been described in detail above, with the difference that they are bonded to the rest of the molecule by four covalent bonds instead of two.

[0094] R6 is a monovalent organic group with o-fold positive charge, preferably a single positive charge. In this case, it is usually an alkyl group, an alkoxy group, a haloalkyl group, a cycloalkyl group, an aryl group, an aralkyl group or a heterocyclic group, which contains 1 to 4 positively charged groups, especially a quaternary ammonium group, a quaternary phosphonium group, a tertiary sulfonium group or a monovalent heterocyclic group with 1 to 4-fold charge. The charge balance is carried out by one or more anions X q- . The connection of the group with o-fold positive charge to the piperidine-1-oxy group is preferably carried out through the heteroatom of the group with o-fold positive charge. Particularly preferred examples of the group R6 are the groups -N + R 11 R 12 R 13 , -P + R 11 R 12 R 13 , -S + R 11 R 12 or –Het + , where R 11 , R 12 and R 13 are independently of one another hydrogen, an alkyl group, a cycloalkyl group, an aryl group, an aralkyl group or a heterocyclic group, especially a C1-C6-alkyl group, a cyclohexyl group, a phenyl group or a benzyl group, and Het is a monovalent and singly positively charged heterocyclic group having 1 to 3 ring nitrogen atoms or 1 ring nitrogen atom and 1 to 2 ring oxygen atoms or ring sulfur atoms, particularly preferably a monovalent imidazolium, pyridinium, guanidinium, ureas, thioureas, piperidinium or morpholinium group.

[0095] R9 is a divalent to tetravalent organic group with m-fold positive charge. In this case, it is an organic group having a group with m positive charges and bonded to the rest of the molecule by 2, 3 or 4 covalent bonds. Examples of R9 correspond to the examples shown above for R8, with the difference that these groups are additionally substituted by a group with m positive charges or have a group with m positive charges in the molecular backbone. Thus, R9 can represent an alkylene group, an alkyleneoxy group, poly(alkyleneoxy), an alkyleneamino group, poly(alkyleneamino), a cycloalkylene group, an arylene group, an aralkylene group or a heterocyclylene group, which is substituted by m singly positively charged groups. Examples of the positively charged groups are quaternary ammonium, quaternary phosphonium, tertiary sulfonium or divalent to tetravalent heterocyclic groups with m-fold charge. The connection of the group R9 with m-fold positive charge to the piperidine-1-oxy group is preferably carried out through the heteroatom of the group with m-fold positive charge. Particularly preferred examples of the group R9 are the groups -N + R 14 R 15 -R 16 -[N + R 14 R 15 f ​-, -P + R 14 R 15 -R 16 -[P + R 14 R 15 f -, -S + R 14 -R 15 -[S + R 14 f - or -[Het m+ f -, where R 14 and R 15 are, independently of one another, alkyl, cycloalkyl, aryl, aralkyl or heterocyclic group, especially C1-C6-alkyl, cyclohexyl, phenyl or benzyl, f has the meaning defined above, R 16 represents an f+1-valent organic group and Het represents a divalent to tetravalent and m-fold positively charged heterocyclic group having 1 to 3 ring nitrogen atoms or 1 ring nitrogen atom and 1 to 2 ring oxygen atoms or ring sulfur atoms, particularly preferably a divalent to tetravalent imidazolium, pyridinium, guanidinium, ureas, thioureas, piperidinium or morpholinium group. Examples of R 16 correspond to the examples of R8.

[0096] Examples of the divalent organic group R 16 are alkylene, cycloalkylene, arylene, aralkylene or heterocyclylene. These groups have been described in detail above.

[0097] Examples of the trivalent organic group R 16 are alkyltriyl, cycloalkyltriyl, aryltriyl, aralkyltriyl or heterocyclic triyl. These groups correspond to the divalent groups described in detail above, except that they are bonded to the rest of the molecule by three covalent bonds instead of two.

[0098] Examples of the tetravalent organic group R 16 are alkyltetrayl, cycloalkyltetrayl, aryltetrayl, aralkyltetrayl or heterocyclic tetrayl. These groups correspond to the divalent groups described in detail above, except that they are bonded to the rest of the molecule by four covalent bonds instead of two.

[0099] ​​​R7 is a monovalent organic group with u-fold negative charge, preferably a single-fold negative charge. In this case, it is usually an alkyl group, an alkoxy group, a haloalkyl group, a cycloalkyl group, an aryl group, an aralkyl group or a heterocyclic group, which contains 1 to 4 groups with a single-fold negative charge, especially 1 to 4 carboxylic acid groups or 1 to 4 sulfonic acid groups or a monovalent heterocyclic group substituted by 1 to 4 carboxylic acid groups or by 1 to 4 sulfonic acid groups. Charge balance is achieved by one or more cations Z q+ is carried out. The connection of the group with u-fold negative charge to the piperidine-1-oxy group is preferably carried out through the carbon atom of the group with a single-fold negative charge.

[0100] R 10 is a divalent to tetravalent organic group with m-fold negative charge, preferably with a single or double-fold negative charge. In this case, it is an organic group having m groups with a single-fold negative charge and connected to the rest of the molecule by 2, 3 or 4 covalent bonds. Examples of R 10 correspond to the examples shown above for R8, except that these groups are additionally substituted by m groups with a single-fold negative charge or have m negatively charged groups in the molecular backbone. Thus, R 26 can represent an alkylene group, an alkyleneoxy group, poly(alkyleneoxy), an alkyleneamino group, poly(alkyleneamino), a cycloalkylene group, an arylene group, an aralkyl group or a heterocyclylene group, which is substituted by m groups with a single-fold negative charge. Examples of the group with a single-fold negative charge are a carboxylic acid group or a sulfonic acid group or a monovalent heterocyclic group substituted by 1 to 4 carboxylic acid groups or by 1 to 4 sulfonic acid groups. Charge balance is achieved by one or more cations Z q+ is carried out. The connection of the group with m-fold negative charge to the piperidine-1-oxy group is preferably carried out through the carbon atom of the group with m-fold negative charge.

[0101] The redox-active components of formula Ib and Ie used according to the invention contain counterions X q- . By them, the positive charges present in the remaining molecule are balanced. The counterion X q- can be an inorganic or an organic q-valent anion.

[0102] Examples of inorganic anions X q- are halide ions, such as fluoride ion, chloride ion, bromide ion or iodide ion, or hydroxide ion or anions of inorganic acids, such as phosphate, hydrogen phosphate, sulfate, hydrogen sulfate, nitrate, hexafluorophosphate, tetrafluoroborate, perchlorate, chlorate, hexafluoroantimonate, hexafluoroarsenate, cyanide ion and mixtures thereof.

[0103] Examples of organic anions X q-Examples are anions of mono- or polycarboxylic acids or mono- or polysulfonic acids, where these acids can be saturated or unsaturated. Examples of anions of organic acids are acetate, formate, trifluoroacetate, trifluoromethanesulfonate, pentafluoroethanesulfonate, nonafluorobutanesulfonate, butyrate, citrate, fumarate, glutarate, lactate, malate, malonate, oxalate, pyruvate or tartrate and mixtures thereof.

[0104] The redox-active components of formulae Ic and If used according to the invention have a counterion Z q+ . By means of them, the negative charges present in the remaining molecule are balanced. The counterion Z q+ can be an inorganic or an organic q-valent cation.

[0105] Examples of inorganic cations Z q+ are hydrogen ions or mono- or polyvalent metal ions. Preference is given to using hydrogen ions or mono- or divalent metal ions, in particular alkali metal cations or alkaline earth metal cations.

[0106] Examples of organic cations Z q+ are ammonium, imidazolium, pyridinium, guanidinium, uronium, thiouronium, piperidinium, morpholinium or phosphonium.

[0107] The index q is preferably 1 or 2 and in particular 1. The index f is preferably 1 or 2 and in particular 1. The index l is preferably 1 / 2 or 1 and in particular 1. The index m is preferably 1 or 2 and in particular 1. The index n is preferably 1 / 2, 1 or 2 and in particular 1 / 2 or 1. The index o is preferably 1 or 2 and in particular 1. The index u is preferably 1 or 2, in particular 1. Particular preference is given to using the positive electrolyte in a redox flow battery according to the invention, said positive electrolyte comprising a compound of formula Ia and / or Id as defined above as the redox-active component.

[0108] Also particularly preferred is the use of a positive electrolyte in a redox flow battery according to the invention, said positive electrolyte comprising a compound of formula Ib and / or Ie or of formula Ic and / or If as defined above as the redox-active component, where X is selected from halide ions, hydroxide ions, phosphate ions, sulfate ions, perchlorate ions, hexafluorophosphate ions or tetrafluoroborate ions, and where Z is selected from hydrogen ions, alkali metal cations or alkaline earth metal cations and substituted or unsubstituted ammonium cations.

[0109] Also particularly preferred is the use of a positive electrolyte in a redox flow battery according to the invention, said positive electrolyte comprising a compound of formula I, Ia, Ib, Ic, Id, Ie or If as defined above and mixtures thereof as the redox-active component, where R1, R2, R3 and R4 represent C1-C6-alkyl and are preferably ethyl or methyl.

[0110] It is very particularly preferred to use a positive electrolyte in a redox flow battery according to the invention, said positive electrolyte comprising a compound of formula Ia as defined above as a redox-active component, where R5 is hydrogen, C1-C6-alkyl, C1-C6-alkoxy, C1-C6-partially fluorinated alkyl or C1-C6-perfluoroalkyl, C1-C6-partially chlorinated alkyl or C1-C6-perchloroalkyl, C1-C6-fluorochloroalkyl, phenyl, benzyl, fluorine, chlorine, hydroxyl, amino or nitro.

[0111] It is likewise very particularly preferred to use a positive electrolyte in a redox flow battery according to the invention, said positive electrolyte comprising a compound of formula Id as defined above as a redox-active component, where R8 is alkylene, alkyltriyl, alkyltetrayl, alkoxydiyl, alkoxytriyl, alkoxytetrayl, arylene, aryltriyl, aryltetrayl, heterocyclylene, heterocyclyltriyl or heterocyclyltetrayl, very particularly preferably C2-C6-alkylene such as ethylene or propylene, or C2-C6-alkoxydiyl, such as 1,2-dioxoethylene or 1,3-dioxopropylene, or C3-C6-alkoxytriyl, such as 1,2,3-propanetriol residue or trimethylolpropane residue, or C4-C6-alkoxytetrayl such as pentaerythritol residue, or phenylene, phenyltriyl or phenyltetrayl.

[0112] Since titanium(IV) cations, vanadium(IV) cations, chromium(III) cations, iron(II) cations, zinc(II) cations and mixtures thereof are highly reversible with their respective corresponding lower-valent titanium(III) cations, titanium(II) cations, vanadium(III) cations, vanadium(II) cations, chromium(II) cations, elemental iron(0), elemental zinc(0) and mixtures thereof, for the sake of convenience in the following writing and description, only titanium(IV) cations, vanadium(IV) cations, chromium(III) cations, iron(II) cations, zinc(II) cations and mixtures thereof will be described below as starting materials. Of course, all forms of existence of titanium(III) cations, titanium(II) cations, vanadium(III) cations, vanadium(II) cations, chromium(II) cations, elemental iron(0), elemental zinc(0) and mixtures thereof are also included in the present invention.

[0113] The metal salts used as the negative electrode liquid in the redox flow battery pack according to the present invention include the following metal cations: titanium (IV) cation, vanadium (IV) cation, chromium (III) cation, iron (II) cation, zinc (II) cation, and mixtures thereof. The metal cations in the negative electrode liquid can mainly act as active materials, but also secondarily act as a conductivity additive or a part of the conductivity additive. The titanium (IV) cation, vanadium (IV) cation, chromium (III) cation, iron (II) cation, zinc (II) cation, and mixtures thereof used according to the present invention are preferably water-soluble. The titanium (IV) cation, vanadium (IV) cation, chromium (III) cation, iron (II) cation, zinc (II) cation, and mixtures thereof can have any inorganic or organic anions, such as fluoride ion, chloride ion, bromide ion, or iodide ion, or hydroxide ion or anions of inorganic acids, such as phosphate, hydrogen phosphate, sulfate, hydrogen sulfate, nitrate, hexafluorophosphate, tetrafluoroborate, perchlorate, chlorate, hexafluoroantimonate, hexafluoroarsenate, cyanide ion, acetate, formate, trifluoroacetate, trifluoromethanesulfonate, pentafluoroethanesulfonate, nonafluorobutanesulfonate, butyrate, citrate, fumarate, glutarate, lactate, malate, malonate, oxalate, pyruvate, or tartrate, and mixtures thereof.

[0114] "Water-soluble" is understood within the scope of this specification as the solubility of at least 1 g of the compound in 1 L of water at 25 °C.

[0115] Examples of the titanium salts are titanium chloride, titanium fluoride, titanium bromide, titanium iodide, titanium nitrate, titanium nitrite, titanium carbonate, titanium hydrogencarbonate, titanium sulfate, titanium hydrogen sulfate, titanium oxysulfate, titanium phosphate, monohydrogen titanium phosphate, dihydrogen titanium phosphate, titanium perchlorate, titanium thiocyanate salts, titanium hexacyanide salts, titanium tetrafluoroborate, titanium hexafluorophosphate, titanium fluorides, titanium oxide. In addition to the titanium salts having inorganic anions, titanium salts having organic anions, such as titanium acetate, titanium oxalate, or titanium formate, can also be used.

[0116] Examples of the vanadium salts are vanadium chloride, vanadium fluoride, vanadium bromide, vanadium iodide, vanadium nitrate, vanadium nitrite, vanadium carbonate, vanadium hydrogencarbonate, vanadium sulfate, vanadium hydrogen sulfate, vanadium oxysulfate, vanadium phosphate, monohydrogen vanadium phosphate, dihydrogen vanadium phosphate, vanadium perchlorate, vanadium thiocyanate salts, vanadium hexacyanide salts, vanadium tetrafluoroborate, vanadium hexafluorophosphate, vanadium fluorides, vanadium oxide. In addition to the vanadium salts having inorganic anions, vanadium salts having organic anions, such as vanadium acetate, vanadium oxalate, or vanadium formate, can also be used.

[0117] Examples of the chromium salts are chromium chloride, chromium fluoride, chromium bromide, chromium iodide, chromium nitrate, chromium nitrite, chromium hydrogencarbonate, chromium carbonate, chromium sulfate, chromium hydrogensulfate, chromium phosphate, chromium hydrogenphosphate, chromium dihydrogenphosphate, chromium perchlorate, chromium thiocyanate salts, chromium hexacyanide salts, chromium tetrafluoroborate, chromium hexafluorophosphate, chromium fluorochromate, chromium oxide. In addition to chromium salts having inorganic anions, chromium salts having organic anions such as chromium acetate, chromium oxalate or chromium formate can also be used.

[0118] Examples of the iron salts are iron chloride, iron fluoride, iron bromide, iron iodide, iron nitrate, iron nitrite, iron carbonate, iron hydrogencarbonate, iron sulfate, iron hydrogensulfate, iron phosphate, iron hydrogenphosphate, iron dihydrogenphosphate, iron perchlorate, iron thiocyanate salts, iron hexacyanide salts, iron tetrafluoroborate, iron hexafluorophosphate, iron fluorochromate, iron oxide. In addition to iron salts having inorganic anions, vanadium salts having organic anions such as iron acetate, iron oxalate or iron formate can also be used.

[0119] Examples of the zinc salts are zinc chloride, zinc fluoride, zinc bromide, zinc iodide, zinc nitrate, zinc nitrite, zinc carbonate, zinc hydrogencarbonate, zinc sulfate, zinc hydrogensulfate, zinc phosphate, zinc hydrogenphosphate, zinc dihydrogenphosphate, zinc perchlorate, zinc thiocyanate salts, zinc hexacyanide salts, zinc tetrafluoroborate, zinc hexafluorophosphate, zinc fluorochromate, zinc oxide. In addition to zinc salts having inorganic anions, zinc salts having organic anions such as zinc acetate, iron oxalate or zinc formate can also be used.

[0120] A particularly preferred redox flow battery pack according to the present invention has a positive electrode based on 1-hydroxy-2,2,6,6-tetramethylpiperidine groups, which has a redox pair of 1-hydroxy-2,2,6,6-tetramethylpiperidine groups / 1-oxyl-2,2,6,6-tetrasubstituted piperidine groups / 1-oxo-2,2,6,6-tetrasubstituted piperidinium groups.

[0121] A particularly preferred redox flow battery pack according to the present invention has a negative electrode of one or a mixture of titanium ions, vanadium ions, chromium ions, iron ions, zinc ions, and the negative electrode has a redox pair of titanium(IV) / titanium(III) / titanium(II), vanadium(IV) / vanadium(III) / vanadium(II), chromium(III) / chromium(II), iron(II) / elemental iron(0), zinc(II) / elemental zinc(0) or a mixed pair thereof.

[0122] The redox active components are preferably used in a dissolved form. However, dispersions of the redox active components or liquid redox active components can also be used.

[0123] The molar mass of the redox-active component containing the group of formula I used in the positive electrolyte according to the invention can vary within a wide range. It is particularly preferred to use a redox-active component containing the group of formula I, the molar mass of the redox-active substance of the positive electrolyte fluctuating within the range of 150 to 20,000 g / mol, preferably within the range of 150 to 2,000 g / mol and very particularly preferably within the range of 150 to 800 g / mol.

[0124] The molar mass of the redox-active substance of the negative electrolyte fluctuates within the range of 45 to 2,000 g / mol, preferably within the range of 47 to 500 g / mol and very particularly preferably within the range of 115 to 300 g / mol.

[0125] In the redox flow battery according to the invention, selected redox-active components are used in two chambers, which are separated from each other by a semipermeable membrane and are present in dissolved form, liquid form or in dispersed form in the chambers.

[0126] The positive and negative electrode electrolytes consist of water or a mixture of water and an organic solvent, in which additional substances are dissolved. They are used for charge balancing during the charging and discharging of the battery pack or have a positive impact on the stability and performance parameters of the battery pack. Substances responsible for charge balancing are called conductive additives and substances having a positive impact on stability and performance parameters are called auxiliary additives. Conductive additives are usually organic or inorganic salts. In addition, in the case of electrolytes, a positive electrode electrolyte and a negative electrode electrolyte are distinguished. The positive electrode electrolyte contains, in addition to the solvent and / or conductive additive / auxiliary additive, redox-active positive electrode materials such as 1-hydroxy-2,2,6,6-tetrasubstituted piperidine groups, 1-oxyl-2,2,6,6-tetrasubstituted piperidine groups, 1-oxo-2,2,6,6-tetrasubstituted piperidinium groups and mixtures thereof, in particular 1-hydroxy-2,2,6,6-tetramethylpiperidine groups, 1-oxyl-2,2,6,6-tetramethylpiperidine groups (TEMPO), 1-oxo-2,2,6,6-tetramethylpiperidinium groups and mixtures thereof. The negative electrode electrolyte contains, in addition to the solvent and conductive additive / auxiliary additive, one or a mixture of redox-active negative electrode materials such as titanium(IV) / titanium(III) / titanium(II), vanadium(IV) / vanadium(III) / vanadium(II), chromium(III) / chromium(II), iron(II) / elemental iron(0), zinc(II) / elemental zinc(0); likewise, these metal cations or elemental substances can also be part of the additive. Therefore, the redox-active positive electrode materials such as 1-hydroxy-2,2,6,6-tetrasubstituted piperidine groups, 1-oxyl-2,2,6,6-tetrasubstituted piperidine groups, 1-oxo-2,2,6,6-tetrasubstituted piperidinium groups and mixtures thereof and one or a mixture of the negative electrode materials such as titanium(IV) / titanium(III) / titanium(II), vanadium(IV) / vanadium(III) / vanadium(II), chromium(III) / chromium(II), iron(II) / elemental iron(0), zinc(II) / elemental zinc(0) can also be included in the positive electrode electrolyte and the negative electrode electrolyte to form a symmetric battery that is impervious to penetration.

[0127] Examples of positive and negative electrode electrolyte solvents are water, alcohols (such as ethanol), carbonates (such as propylene carbonate), nitriles (such as acetonitrile), amides (such as dimethylformamide, dimethylacetamide), sulfoxides (such as dimethyl sulfoxide), ketones (such as acetone), lactones (such as γ-butyrolactone), lactams (such as N-methyl-2-pyrrolidone), nitro compounds (such as nitromethane), ethers (such as tetrahydrofuran), chlorinated hydrocarbons (such as dichloromethane), carboxylic acids (such as formic acid, acetic acid) and inorganic acids (such as sulfuric acid, hydrogen halide or hydrohalic acid), or a mixture of one or more thereof. Preferred is a mixture of one or more of water, carbonates (such as propylene carbonate) and nitriles (such as acetonitrile). Particularly preferred is water.

[0128] Examples of the conductive additive for the positive and negative electrode electrolytes are one or more of salts, acids, and bases, and the anions thereof are selected from halide ions (fluoride ion, chloride ion, bromide ion, iodide ion), hydroxide ion, anions of inorganic acids (such as phosphate ion, sulfate ion, nitrate ion, hexafluorophosphate ion, tetrafluoroborate ion, perchlorate ion, chlorate ion, hexafluoroantimonate ion, hexafluoroarsenate ion, cyanide ion) or anions of organic acids (such as acetate ion, formate ion, methanesulfonate ion, trifluoroacetate ion, trifluoromethanesulfonate ion, pentafluoroethanesulfonate ion, nonafluorobutanesulfonate ion, butyrate ion, citrate ion, fumarate ion, glutarate ion, lactate ion, malate ion, malonate ion, oxalate ion, pyruvate ion, tartrate ion). Particularly preferred are chloride ion and fluoride ion, hydroxide ion, phosphate ion, sulfate ion, perchlorate ion, hexafluorophosphate ion, and tetrafluoroborate ion; and cations selected from the following: hydrogen ion (H + +), alkali metal cations or alkaline earth metal cations (such as lithium, sodium, potassium, magnesium, calcium), zinc, iron, and substituted or unsubstituted ammonium cations (such as tetrabutylammonium, tetramethylammonium, tetraethylammonium), where the substituent can generally be an alkyl group. Hydrogen ion, lithium ion, sodium ion, potassium ion, tetrabutylammonium ion, and mixtures thereof are particularly preferred. In particular, conductive salts, acids, bases: HCl, H2SO4, HNO3, NaCl, KCl, LiPF6, LiBF4, NaBF4, NaPF6, NaClO4, NaOH, KOH, Na3PO4, K3PO4, Na2SO4, NaSO3CF3, LiSO3CF3, (CH3)4NOH, n-Bu4NOH, (CH3)4NCl, n-Bu4NCl, (CH3)4NBr, n-Bu4NBr, n-Bu4NPF6, n-Bu4NBF4, n-Bu4NClO4, and mixtures thereof, where n-Bu represents n-butyl.

[0129] Particularly preferred redox flow battery packs according to the present invention contain a conductive additive in the electrolyte, which contains an anion selected from halide ions, hydroxide ion, phosphate ion, sulfate ion, perchlorate ion, hexafluorophosphate ion, or tetrafluoroborate ion. In particular, the conductive additive is composed of these anions and cations selected from hydrogen ion, alkali metal cations or alkaline earth metal cations, and substituted or unsubstituted ammonium cations.

[0130] The auxiliary additive can be a mixture of one or more of a complexing agent, a surfactant, a viscosity modifier, a pesticide, a buffer, a stabilizer, a catalyst, a conductive additive, an antifreeze, a temperature stabilizer, and a defoaming agent.

[0131] The complexing agent can be ethylenediamine, urea, sulfamic acid, sulfonamide, EDTA, DPTA, acetylacetone, biuret, N,N-dimethylformamide, hydantoin, sodium dehydroacetate, sulfoxydiamide, oxalic acid, citric acid, malic acid, formic acid, acetic acid, and mixtures thereof.

[0132] The surfactant can be nonionic, anionic, cationic, or amphoteric. Particularly preferred are nonionic surfactants (such as polyalkylene glycol ethers, fatty alcohol propoxylates, alkyl glucosides, alkyl polyglucosides, octylphenol ethoxylates, nonylphenol ethoxylates, saponins, phospholipids) and mixtures thereof.

[0133] The buffer can be a carbonate-bicarbonate buffer, a carbonate-silicate buffer, an acetic acid-acetate buffer, a phosphate buffer, an ammonia buffer, a citric acid buffer or citrate buffer, tris(hydroxymethyl)-aminomethane, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, 4-(2-hydroxyethyl)-piperazine-1-propanesulfonic acid, 2-(N-morpholino)ethanesulfonic acid, a barbiturate-acetate buffer), and mixtures thereof.

[0134] The stabilizer can be silicate, cyclohexylamine, dodecylamine, hexamethylenediamine, ethylenediamine, thiourea and its derivatives, imidazolines, benzotriazole (BTA), phytic acid, amino acids (such as glutamic acid, histidine), dodecyl sulfates, and mixtures thereof

[0135] The catalyst can be a bismuth salt, a lead salt, an indium salt, boric acid and borate salts, a titanium salt, a platinum salt, a gold salt, or a mixture of these substances.

[0136] The redox flow battery pack according to the present invention includes a semipermeable membrane. This membrane serves the following functions: 1) separating the negative electrode chamber and the positive electrode chamber; 2) retaining the redox active components in the positive and negative electrode liquids respectively, thus retaining the positive and negative electrode active materials; 3) the permeability of the conductive salt of the electrolyte, which is used for charge balance, that is, for the anions and / or cations of the conductive salt or for the charge carriers contained in the electrolyte.

[0137] The membrane can be, in particular, a size exclusion membrane, such as a dialysis membrane, but also an ion-selective membrane. The membrane prevents the interpenetration of compounds of redox active 1-hydroxy-2,2,6,6-tetrasubstituted piperidine groups, 1-oxyl-2,2,6,6-tetrasubstituted piperidine groups, 1-oxo-2,2,6,6-tetrasubstituted piperidinium groups, and mixtures thereof, and titanium cations, vanadium cations, chromium cations, iron cations, elemental iron, zinc cations, and elemental zinc.

[0138] The separator used according to the present invention, for example, an ion-permeable separator or dialysis membrane for conductive additives, separates the redox-active components in two chambers.

[0139] The material of the separator can consist of plastics, ceramics, glass, metals, or fabric webs depending on the application. Examples of materials are organic polymers such as cellulose or modified cellulose, such as cellulose ethers or cellulose esters, polyethersulfone, polysulfone, polyvinylidene fluoride, polyester, polyurethane, polyamide, polypropylene, polyvinyl chloride, polyacrylonitrile, polystyrene, polyvinyl alcohol, polyphenylene ether, polyimide, polytetrafluoroethylene and its derivatives, or also ceramics, glass, or felts. Separators (composites) consisting of multiple materials are also possible. It can also be an ion-exchange membrane, and both cation-exchange membranes and anion-exchange membranes are possible.

[0140] The thickness of the separator used according to the present invention can vary within a wide range. Typical thicknesses are in the range between 0.1 μm and 5 mm, particularly preferably in the range between 10 μm and 200 μm.

[0141] In addition to the redox-active components, electrolytes, and separators described above, the redox flow battery according to the present invention preferably contains additional components. In this case: 1) conveying devices such as pumps, as well as tanks and pipes for transporting and storing the redox-active components; 2) electrodes, preferably consisting of or containing: graphite, graphite fiber mesh, graphite paper, carbon nanotube blanket, activated carbon, carbon black, or graphene, carbon felt, and the electrode surface can be loaded with elements such as titanium, lead, boron, nitrogen, etc.; 3) optionally, current collectors, such as using aluminum, aluminum alloy, copper, stainless steel, Hastelloy, ferronickel alloy, titanium or tantalum coated with noble metals, especially titanium coated with platinum and / or iridium and / or ruthenium oxide, niobium, tantalum, hafnium, or zirconium.

[0142] The low-cost flow battery of the present invention can be widely used in the fields of mobile and stationary energy storage: (1) as a stationary energy storage device, suitable for grid-level backup power systems, peak-valley load regulation systems, and power caching units for renewable energy generation (especially photovoltaic and wind power generation) and traditional energy (gas / coal / biomass / tidal / offshore power plants) synergy systems; (2) as a mobile energy storage device integrated into the power systems of electric vehicles, including land-based vehicles, aircraft, and ships.

[0143] Redox flow battery packs containing the low-cost flow battery of the present invention show significant advantages in miniaturized application scenarios, especially suitable for home energy storage systems and mobile device fields. Because they ensure high electric power and capacity, low self-power consumption, low toxicity, uncomplicated structure, and low operating costs with a smaller volume compared to conventional redox flow battery packs.

[0144] The present invention will be further described below in conjunction with embodiments.

[0145] Embodiment 1:

[0146] This embodiment discloses a low-cost flow battery. The positive electrolyte uses (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) trimethylammonium chloride as the positive active material, which is dissolved in water with a concentration of 1.5 mol / L; chromium trichloride is used as the negative active material, which is dissolved in water with a concentration of 2.0 mol / L; the ion membrane is an anion membrane, and the electrode material is carbon felt. The test device is as Figure 1 shown.

[0147] Positive electrode charge and discharge reaction formula:

[0148]

[0149] Negative electrode charge and discharge reaction formula:

[0150]

[0151] The charge and discharge curve of the low-cost flow battery is as Figure 2 shown. It can be seen that (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) trimethylammonium chloride and chromium trichloride are paired together, having the ability of charge and discharge, avoiding the use of rare metals, and reducing the initial installation cost of the flow battery.

[0152] Embodiment 2:

[0153] This embodiment discloses a low-cost flow battery. The positive electrolyte uses (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) trimethylammonium chloride as the positive active material, which is dissolved in water with a concentration of 1.5 mol / L, and 2.0 mol / L HCl is further added to the positive electrolyte, with a total of 50 ml; chromium trichloride is used as the negative active material, which is dissolved in water with a concentration of 2.0 mol / L, and 2.0 mol / L HCl and 0.005 mol / L PbCl2 are further added to the negative electrolyte, with a total of 50 ml; the ion membrane is an anion membrane, and the electrode material is carbon felt. Figures 3 - 6 For the charge and discharge curve, Coulomb efficiency, energy efficiency, and discharge capacity of the low-cost flow battery, it can be seen that by adding the supporting electrolyte HCl and the catalyst lead chloride, the stability is significantly increased compared with Embodiment 1, the energy efficiency is stable above 80%, and the capacity utilization rate is about 74.6%.

[0154] Embodiment 3:

[0155] This embodiment discloses a low-cost flow battery. The positive electrolyte uses (1-hydroxy-2,2,6,6-tetramethylpiperidin-4-yl) trimethylammonium chloride as the positive active material, which is dissolved in water with a concentration of 1.5 mol / L. Then, 2.0 mol / L HCl is added to the positive electrolyte, with a total volume of 50 ml. Chromium trichloride is used as the negative active material, which is dissolved in water with a concentration of 2.0 mol / L. Then, 2.0 mol / L HCl and 0.005 mol / L PbCl2 are added to the negative electrolyte, with a total volume of 90 ml. The ion membrane is an anion membrane, and the electrode material is carbon felt.

[0156] Positive electrode charge-discharge reaction formula:

[0157]

[0158] Negative electrode charge-discharge reaction formula:

[0159]

[0160] Figures 7 - 10 For the charge-discharge curves, Coulomb efficiency, energy efficiency, and discharge capacity of the low-cost flow battery, it can be seen that when using two electrons, there is no obvious second-order plateau, indicating that this system will not significantly reduce the battery energy efficiency when using two electrons. With the same positive electrolyte and concentration, the discharged capacity is twice that of Example 2, and the capacity utilization rate of two electrons is more than 75%, which proves the feasibility of using two electrons in this system and also proves the superior energy density and cost advantages of this system.

Claims

1. A low-cost flow battery, characterized in that, The redox active substance of its positive electrolyte contains a hydroxylamine cyclic structure group with a hindered amine.

2. The low-cost flow battery according to claim 1, wherein The redox active substance of its positive electrolyte contains the structure in Formula Y: In Formula Y, the cyclic structure is a 3-membered ring, 4-membered ring, 5-membered ring, 6-membered ring, 7-membered ring or 8-membered ring; the cyclic structure contains one or more of carbon-carbon single bonds, carbon-carbon double bonds and carbon-carbon triple bonds; R1, R2, R3 and R4 are each independently selected from alkyl, cycloalkyl, aryl and aralkyl.

3. The low-cost flow battery according to claim 1, wherein The redox active substance of its positive electrolyte contains one or more of 1-hydroxy-2,2,6,6-tetrasubstituted piperidine groups, 1-hydroxy-2,2,5,5-tetrasubstituted pyrrole groups and 1-hydroxy-2,2,5,5-tetrasubstituted pyrroline groups.

4. The low-cost flow battery according to claim 1, wherein The redox active substance of its positive electrolyte contains one or more of 1-hydroxy-2,2,6,6-tetrasubstituted piperidine groups, 1-oxyl-2,2,6,6-tetrasubstituted piperidine groups and 1-oxo-2,2,6,6-tetrasubstituted piperidinium groups.

5. The low-cost flow battery according to claim 1, wherein The positive electrolyte uses a compound containing at least one Formula I group as the redox active component: Wherein, the line leaving from the 4-position in the Formula I structure represents a covalent bond, and the structure of Formula I is connected to the rest of the compound molecule through the covalent bond at the 4-position, and R1, R2, R3 and R4 are each independently selected from alkyl, cycloalkyl, aryl and aralkyl.

6. The low-cost flow battery according to claim 1 or 2, characterized in that, The positive electrolyte uses a compound containing one or more of Formula Ia, Ib, Ic, Id, Ie and If as the redox active component: In formulas Ia, Ib, Ic, Id, Ie and If, R1, R2, R3 and R4 are each independently selected from alkyl, cycloalkyl, aryl and aralkyl; X represents a q-valent inorganic or organic anion or a mixture of anions of this type, q is an integer from 1 to 3, o is an integer from 1 to 4, u is an integer from 1 to 4, R8 is a divalent to tetravalent organic bridging group, R5 is hydrogen, alkyl, alkoxy, haloalkyl, cycloalkyl, aryl, aralkyl, heterocyclic group, halogen, hydroxy, amino, nitro or cyano, and R6 is a monovalent organic group with o-fold, preferably single-fold positive charge, especially a quaternary ammonium group, a quaternary phosphonium group, a tertiary sulfonium group, or a monovalent heterocyclic group with o-fold, preferably single-fold positive charge, R9 is a divalent to tetravalent organic group with m-fold positive charge, especially a divalent to tetravalent quaternary ammonium group, a divalent to tetravalent quaternary phosphonium group, a divalent to trivalent tertiary sulfonium group, or a divalent to tetravalent heterocyclic group with m-fold positive charge, R7 is a monovalent group with u-fold, preferably single-fold negative charge, especially a carboxyl or sulfonic acid group, or a monovalent heterocyclic group with u-fold, preferably single-fold negative charge, R 10 is a divalent to tetravalent organic group with m-fold negative charge, especially an alkylene group substituted by 1 or 2 carboxyl or sulfonic acid groups, or a phenylene group substituted by 1 or 2 carboxyl or sulfonic acid groups, or a divalent heterocyclic group substituted by 1 or 2 carboxyl or sulfonic acid groups, Z is a q-valent inorganic or organic cation or a mixture of cations of this type, f is an integer from 1 to 3, l is a number with a value of o / q or u / q, m is an integer from 1 to 4, and n represents a number with a value of m / q.

7. The low-cost flow battery according to claim 1, wherein The positive electrolyte uses a compound containing Formula II as the redox active component: In Formula II, R1, R2, R3 and R4 are each independently selected from alkyl, cycloalkyl, aryl and aralkyl, ME is a repeating structural unit derived from a polymerizable monomer, BG is a covalent bond or a bridging group, and r is an integer from 2 to 150.

8. The low-cost flow battery according to claim 1, wherein The redox active substance of its negative electrolyte contains one or more of titanium element, vanadium element, chromium element, iron element and zinc element.

9. The low-cost flow battery according to claim 8, wherein The molar mass of the redox active substance of the positive electrolyte is 150 to 20000 g / mol; And / or, the molar mass of the redox active substance of the negative electrolyte is 45 to 2000 g / mol.

10. Application of the low-cost flow battery according to any one of claims 1-9 in the fields of mobile and stationary energy storage devices.

Images