Sulfonic acid-based electrolyte compositions containing phosphorus additives - Patents.com

Abstract

The present invention relates to an aqueous electrolyte composition comprising a sulfonic acid, optionally sulfuric acid, a redox metal ion, and at least one inorganic additive (A) comprising at least one phosphorus atom having an oxidation degree of less than or equal to +5. The present invention also relates to an electrochemical cell comprising said electrolyte composition and a redox battery (also called a redox battery) comprising such a cell.

Description

[Technical field]

[0001] The present invention relates to an aqueous electrolyte composition comprising a sulfonic acid, optionally sulfuric acid, a redox metal ion, and at least one inorganic additive (A) comprising at least one phosphorus atom having an oxidation degree of less than or equal to +5. The present invention also relates to an electrochemical cell comprising said electrolyte composition and a redox battery (also called redox battery) comprising such a cell. [Background technology]

[0002] The development of renewable energies such as solar and wind energy is an important issue on a global scale. However, one of the main drawbacks of these energy sources is that they are dependent on meteorological phenomena and are therefore intermittent. Therefore, to ensure a reliable supply of energy from these new sources, appropriate storage means are necessary.

[0003] Among the solutions considered, redox batteries are a promising storage option: these rechargeable batteries use metals in different oxidation states (in the form of metal ions in an electrolyte) to store energy in chemical form and restore it in electrical form through reversible redox reactions.

[0004] Vanadium redox flow batteries (or VRFBs) are of particular interest because they can be deeply discharged (100%), have life spans of tens of thousands of cycles, and can store virtually unlimited amounts of energy simply by increasing the size of the electrolyte storage tank.

[0005] However, the performance of redox batteries, especially their energy density, is generally limited by metal ion precipitation phenomena: for example, in the case of vanadium batteries, V(V) ions (vanadium with an oxidation degree of +5) precipitate at temperatures above about 40° C., while V(II) and V(III) ions precipitate at temperatures below about 10° C. These precipitation phenomena strongly limit the use of these batteries, since they require strict temperature control within a relatively limited range, for example by means of air conditioning and / or ventilation systems.

[0006] In fact, the useful energy density of these batteries is directly proportional to the concentration of metal ions undergoing redox reactions in the electrolyte composition, and is therefore limited by the maximum solubility of the metal salts or oxides (salts or oxides that, when dissolved, are found in the form of metal ions) in the electrolyte composition.

[0007] As a result, if the precipitation of metal ions in the electrolyte composition is prevented, reduced, retarded, or slowed down, the maximum energy density of the redox battery is increased, and the battery can still be used under more extreme conditions, particularly at temperatures below 10° C. and / or above 40° C. Summary of the Invention [Problem to be solved by the invention]

[0008] There is therefore a need for electrolyte compositions that make it possible to prevent, reduce, slow down or retard the precipitation of metal ions and to improve their solubility, and also for electrolyte compositions that make it possible to improve the performance of redox batteries.

[0009] Therefore, one of the objects of the present invention is to provide an electrolyte composition that makes it possible to prevent, reduce, slow down and / or retard the deposition of metal ions that undergo redox reactions.

[0010] Another object of the present invention is to provide an electrolyte composition which makes it possible to improve the solubility of redox metal ions and / or to improve the performance, in particular the energy density, of redox batteries.

[0011] It is also an object of the present invention to provide an electrolyte composition that is stable at temperatures between about 0°C and about 60°C. [Means for solving the problem]

[0012] The inventors have surprisingly found that the use of sulfonic acid bound to the phosphorus additive of the present invention makes it possible to prevent, reduce, slow down and / or retard the precipitation of redox metal ions, particularly vanadium ions, in the electrolyte composition.

[0013] Thus, the inventors have found that the combination of the sulfonic acid and phosphorus additive of the present invention makes it possible to improve the solubility of redox metal ions in the electrolyte composition. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Thus, the present invention provides with a sulfonic acid of formula R-SO3H, where R is (C1-C4) alkyl or (C6-C 14 ) aryl; Optionally, sulfuric acid, A redox metal ion; At least one inorganic additive (A) containing at least one phosphorus atom having an oxidation degree of +5 or less; and water.

[0015] The electrolyte composition of the invention makes it possible in particular to obtain more efficient batteries having in particular increased energy density.

[0016] In one embodiment, the energy density of the battery of the present invention is between 30 and 50 Wh / L.

[0017] The battery of the present invention can be particularly used at temperatures between about 0°C and about 60°C, preferably between about 5°C and about 50°C.

[0018] The term "redox battery" specifically refers to any battery that stores energy in chemical form and restores it in electrical form through oxidation-reduction reactions. These oxidation-reduction reactions involve an oxidation-reduction pair or "redox couple," specifically in the form of metal ions.

[0019] More specifically, in a redox flow battery, the electrochemical couple can be stored outside the battery, two tanks contain electrolyte in a liquid state, and a pump circulates the electrolyte through an ion-exchange cell whose two compartments are separated by a solid-state membrane.

[0020] These batteries are widely known and are described, for example, in Electrochemical Energy Storage for Renewable Sources and Grid Balancing, 2015 Elsevier BV Chapter 17, “Redox Flow Batteries”, G. Tomazic et al., 2015, pages 309-336.

[0021] These batteries may in particular be vanadium batteries as described in WO 1996 / 035239, titanium-manganese batteries as described in US Pat. No. 9,118,064, iron as described in US Pat. App. Pub. No. 2018 / 0013164, or zinc hybrid batteries.

[0022] The term "energy density" of a battery refers to the amount of energy stored per unit mass or volume, typically expressed in Wh / kg or Wh / L.

[0023] The term "inorganic additive" specifically refers to compounds that do not contain carbon atoms.

[0024] The term "(C1-C4) alkyl" means a saturated aliphatic hydrocarbon that can be straight-chained or branched and contains from 1 to 4 carbon atoms. The term "branched" means that the alkyl groups are substituted on the main alkyl chain.

[0025] "(C6-C 14 The term "aryl" refers to monocyclic, bicyclic, or tricyclic aromatic hydrocarbon compounds, especially phenyl.

[0026] electrolyte composition In the present invention, unless otherwise specified, the terms "electrolyte composition" and "electrolytic composition" are used interchangeably.

[0027] Thus, the present invention provides with a sulfonic acid of formula R-SO3H, where R is (C1-C4) alkyl or (C6-C 14 ) aryl; Optionally, sulfuric acid, A redox metal ion; At least one inorganic additive (A) containing at least one phosphorus atom having an oxidation state of +5 or less; and water.

[0028] electrolyte The electrolyte composition is in particular in the form of a solution, preferably in the form of an aqueous solution, more preferentially in the form of an acidic aqueous solution.

[0029] The electrolyte composition is preferably liquid and / or stable at a temperature between 0°C and 60°C, preferably between 5°C and 50°C.

[0030] In particular, the sulfonic acid is present in said composition in a molar concentration between 0.08M and 8M, preferably between 0.1M and 4M.

[0031] In particular, sulfuric acid is present in said composition in a molar concentration between 0.08M and 8M, preferably between 0.1M and 4M.

[0032] Thus, the sulfonic acid and optionally the sulfuric acid are preferentially diluted with the amount of water necessary to obtain the targeted molar concentration in the electrolyte composition, particularly in the form of an aqueous solution.

[0033] In particular, the sulfonic acid is selected from the group consisting of methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, 1-naphthalenesulfonic acid, 2-naphthalenesulfonic acid, and p-toluenesulfonic acid, preferably methanesulfonic acid.

[0034] Preferably, the electrolyte composition of the present invention comprises sulfuric acid. A mixture of methanesulfonic acid and sulfuric acid is particularly preferred. The sulfonic acid can be supplied, for example, in the formulation sold by Arkema under the trade name MSA LC®.

[0035] In said composition, the molar ratio of sulfonic acid / sulfuric acid may be between 1 / 99 and 99 / 1, preferably between 1 / 99 and 50 / 50, more preferably between 5 / 95 and 15 / 85, for example 8 / 92. This ratio range makes it possible to obtain a battery with particularly optimized characteristics, in particular having a higher energy density than a battery containing only sulfuric acid.

[0036] The mass ratio of methanesulfonic acid / sulfuric acid may be between 1 / 99 and 50 / 50, preferably between 5 / 95 and 15 / 85, for example 8 / 92.

[0037] Inorganic additives (A) The electrolyte composition of the present invention comprises at least one, preferably one or two inorganic additives (A) (also called mineral additives (A)) containing at least one phosphorus atom with an oxidation degree of +5 or less.

[0038] For example, the inorganic additive (A) contains 1, 2, 3 or 6 phosphorus atoms, preferably only 1 phosphorus atom. The inorganic additive (A) may in particular be in the form of a polymer, for example a polyphosphate, in particular a polymetaphosphate.

[0039] The degree of oxidation of the phosphorus atom may be +I, +III, +IV or +V. Preferably, the inorganic additive (A) is an oxoacid of phosphorus.

[0040] In particular, said additive (A) does not contain an NP bond (nitrogen-phosphorus bond). In particular, said additive (A) is not an ammonia derivative of phosphorous acid.

[0041] The salts of the inorganic additive (A) may be chosen from sodium salts, potassium salts and ammonium salts.

[0042] The inorganic additive (A) may be selected from the group consisting of hypophosphorous acid (+I), phosphorous acids (+III), hypophosphoric acid (+IV), phosphoric acids (+V), polyphosphoric acids (+V), salts thereof, and mixtures thereof.

[0043] More specifically, the inorganic additive (A) is selected from the group consisting of hypophosphorous acid (+I), metaphosphorous acid (+III), pyrophosphorous acid (+III), orthophosphorous acid (+III), hypophosphoric acid (+IV), metaphosphoric acid (+V), pyrophosphoric acid (+V), orthophosphoric acid (+V), triphosphoric acid (+V), salts thereof, sodium hexametaphosphate (+V), and mixtures thereof.

[0044] The inorganic additive (A) may be selected from the group consisting of hypophosphorous acid (+I), hypophosphoric acid (+IV), metaphosphoric acid (+V), pyrophosphoric acid (+V), orthophosphoric acid (+V), triphosphoric acid (+V), their sodium, potassium and ammonium salts, and sodium hexametaphosphate (+V).

[0045] Preferably, said inorganic additive (A) is selected from the group consisting of hypophosphorous acid (+I), orthophosphorous acid (+III), metaphosphoric acid (+V), pyrophosphoric acid (+V), orthophosphoric acid (+V), sodium hexametaphosphate and sodium triphosphate (+V), tripotassium phosphate (+V), mono- and diammonium phosphate (+V), and mixtures thereof.

[0046] Particularly preferably, said inorganic additive (A) is selected from sodium hexametaphosphate and sodium triphosphate (+V), tripotassium phosphate (+V) and mono- and diammonium phosphate (+V).

[0047] The amount of the inorganic additive (A) may be 5% by weight or less, preferably strictly between 0% by weight and 5% by weight, for example between 0.5% by weight and 5% by weight, based on the total weight of the electrolyte composition. Preferably, the amount of the inorganic additive (A) is between 0.5% by weight and 3% by weight, based on the total weight of the electrolyte composition.

[0048] Redox metal ions The electrolyte composition comprises metal ions, which in particular are obtained from salts or metal oxides dissolved in said electrolyte composition. The metal ions used in particular form redox couples in the electrolyte composition. In the present invention, the terms "metal ion", "redox ion" and "redox metal ion" are interchangeable and in particular correspond to metal ions that undergo redox reactions that allow the implementation of electrochemical cells and / or batteries as defined below.

[0049] The molar concentration of the redox metal ion in the electrolyte composition may be between 0.1 mol / L and 15 mol / L, preferably between 1 mol / L and 10 mol / L, and preferentially between 1.6 mol / L and 5 mol / L. For example, the molar concentration of the redox metal ion in the electrolyte composition is about 3 mol / L, about 4 mol / L, or about 5 mol / L. The electrolyte composition of the present invention may be a composition supersaturated with the redox metal ion.

[0050] The redox metal ions are in particular the following ions: Mn 2+ , Mn 3+ , Ti 3+ , TiO 2+ , Fe 2+ , Fe 3+ , V 2+ , V 3+ , V.O. 2+ , VO2+ , Zn 2+ , Ce 3+ , Ce 4+ and mixtures thereof.

[0051] Redox couples that may be included in the electrolyte composition are as follows: Mn 2+ / Mn 3+ , Ti 3+ / TiO 2+ , Fe 2+ / Fe, Fe 2+ / Fe 3+ , V 2+ / V 3+ , V.O. 2+ / VO2 + , Zn 2+ / Zn and Ce 3+ / Ce 4+ .

[0052] Most particularly preferably, the metal ion is a vanadium ion, preferentially V 2+ , V 3+ , V.O. 2+ , VO2 + and mixtures thereof.

[0053] In one embodiment, the electrolyte composition in which the anode is located is V 2+ and V 3+ The electrolyte composition containing ions and in which the cathode is located is VO 2+ and VO2 + Contains ions.

[0054] In one embodiment, the electrolyte composition in which the anode is located comprises Ti 3+ and TiO 2+ The electrolyte composition in which the cathode is located contains Mn ions. 2+ and Mn 3+ Contains ions.

[0055] In one embodiment, the electrolyte composition in which the anode is located comprises Fe 2+ The electrolyte composition containing the ions and in which the cathode is located is Fe 2+and Fe 3+ ions (iron batteries are hybrid redox batteries with iron deposits in the anode).

[0056] In one embodiment, the electrolyte composition in which the anode is located is Zn 2+ The electrolyte composition in which the cathode is located contains Ce ions. 3+ and Ce 4+ ions (the battery is a hybrid redox battery with a deposit of zinc on the anode).

[0057] The redox metal ions can be obtained after dissolution of the salts and / or the corresponding metal oxides in an aqueous solution of sulfonic acid, optionally in the presence of sulfuric acid.

[0058] Among the vanadium salts or oxides which can thus be dissolved, in particular ammonium metavanadate (NH4VO3); (NH4V(SO4)2); barium pyrovanadate (Ba2V2O7); bismuth vanadate (Bi2O3V2O5); (VCs(SO4)212H2O); iron metavanadate (Fe(VO2)3); lead vanadate (Pb(VO5)2); potassium metavanadate (KVO3); (KVSO4); Rubidium vanadium sulfate (RbV(SO4)2);Sodium metavanadate (NaVO3);Vanadic acid (HVO3);Sodium metavanadate (Na3VO4);Potassium orthovanadate (K3VO4);Ammonium orthovanadate;Sodium pyrovanadate (Na4V2O7);Potassium pyrovanadate (K4V2O7);Ammonium pyrovanadate;Sodium hexavanadate (Na4V6O 17 ); Potassium hexavanadate (K4V6O 17 ); ammonium hexavanadate; thallium pyrovanadate (Tl4V2O7); thallium metavanadate (TIVO3); thallium pyrovanadate (TlV2O76H2O); vanadium pentoxide (V2O5); vanadium sulfate (V(SO4)2); vanadium oxide VO; magnesium calcium vanadate; and VOCl3.

[0059] Preferably, vanadium pentoxide or vanadium sulfate is used, more preferentially vanadium sulfate.

[0060] It is also possible to obtain an electrolyte containing vanadium ions from vanadyl halides such as vanadyl trichloride VOCl3.

[0061] Corrosion Inhibitors The electrolyte composition of the present invention may further comprise a corrosion inhibitor. The term "corrosion inhibitor" means in particular a compound capable of limiting or even preventing the corrosion of metals by the sulfonic acids of the present invention. Such inhibitors are in particular described in patent application WO 2019 / 043340.

[0062] Specifically, the corrosion inhibitor is selected from compounds of the following general formula (1) or (2): NO2X (1) or NO3X (2) wherein X is selected from Na, K, NH4, and H; When the corrosion inhibitor is a compound of formula (1), X further represents a linear or branched alkyl group R' containing 1 to 6 carbon atoms; an aryl group Ar, which may be substituted, in particular by at least one alkyl group R', -SO2-G groups, where G is H, OH, R', OR', OM, Ar, OAr, NH2, NHR', and NR'R'', where R' and Ar are as defined above, R'' is a linear or branched alkyl group containing 1 to 6 carbon atoms, and M is a monovalent or divalent metal cation, preferably an alkali metal or alkaline earth metal cation, a -CO-G group, where G is as defined above, may be selected from:

[0063] When X is a hydrogen atom, the compound of formula (1) is nitrous acid. In a preferred embodiment of the invention, the inhibitor is such that X represents -SO2-G, more preferably -G is -OH (in this case the corrosion inhibitor is nitrosylsulfuric acid (SHN; CAS No. 7782-78-7)), Or, an alkyl group R', preferably a methyl group (in this case the corrosion inhibitor (CAS No. 117933-98-9) is the product of the reaction of methanesulfonic acid (or its chloride) with nitrous acid); wherein -SO2-G is either

[0064] Preferably, the corrosion inhibitor is selected from nitrites and nitrates of sodium, potassium, and ammonium.

[0065] The electrolyte composition may be prepared by dissolving metal salts and / or oxides in an acidic aqueous solution in appropriate proportions, preferably with stirring and / or ultrasound.

[0066] For example, the electrolyte composition of the present invention may be prepared by the following method: a) preparing an aqueous solution of a sulfonic acid as defined above; b) optionally mixing said aqueous solution obtained in step a) with sulfuric acid; said sulfuric acid is optionally prepared beforehand in the form of an aqueous solution; c) adding and dissolving an inorganic additive (A) in the aqueous solution obtained in step a) or step b); and d) adding and dissolving redox metal salts and / or oxides;

[0067] Electrochemical Cells and Batteries The invention also relates to an electrochemical cell comprising an anode, a cathode and, in particular between said anode and said cathode, an electrolyte composition as described above. The electrochemical cell may further comprise a proton exchange membrane impermeable to redox metal ions, preferably impermeable to vanadium ions. Such membranes are known in particular under the trade name Nafion® (for example Nafion® N115, N117) and are based on fluorinated copolymers based on sulfonated tetrafluoroethylene.

[0068] The electrolyte compositions of the present invention can be catholytes (compositions in which the cathode is immersed) and / or anolytes (compositions in which the anode is immersed). They are generally stored in external tanks and injected into the cathode or anode compartments in which the cathode and anode of the cell are immersed, respectively. Electrochemical cells comprising the electrolyte compositions of the present invention are particularly those commonly used in the context of redox batteries, preferably redox flow batteries, more particularly vanadium redox flow batteries.

[0069] For the purposes of the present invention, the term "negative electrode" or "anode" refers to an electrode that allows for the oxidation of reduced species upon discharge.

[0070] In the present invention, the term "positive electrode" or "cathode" refers to the electrode that ensures the reduction of oxidizable species during discharge.

[0071] The structure of a redox battery cell includes, among others, a metal frame, a current collector, a bipolar plate, a seal with an electrode, a proton conducting membrane, a seal with an electrode, a bipolar plate, a current collector, and a metal frame. Needless to say, the cell is assembled in such a way as to ensure the voltage and current flow.

[0072] The present invention also relates to a redox battery, preferably a redox flow battery, comprising at least one electrochemical cell as described above. When the battery comprises a plurality of electrochemical cells of the present invention, said cells can be assembled in series and / or in parallel.

[0073] Particularly preferably, the battery of the present invention is a vanadium redox flow battery.

[0074] use The present invention also relates to the use of said inorganic additive (A) for increasing the concentration of redox metal ions and / or for preventing or reducing and / or slowing down or retarding the precipitation of redox metal ions in said electrolyte compositions, in particular for electrolyte compositions not containing inorganic additive (A).

[0075] The present invention also relates to the use of the aforementioned inorganic additive (A) for stabilizing the aforementioned electrolyte composition at temperatures between 0°C and 60°C, preferably between 5°C and 50°C.

[0076] The present invention also relates to the use of the inorganic additive (A) as defined above for preventing or reducing and / or retarding or slowing down the precipitation of redox metal ions, in particular vanadium ions, in the electrolyte composition as defined above at temperatures between 0°C and 60°C, preferably between 5°C and 50°C.

[0077] The invention also relates to a battery according to the invention for storing and recovering renewable energy, in particular solar and wind energy.

[0078] In these uses, the electrolyte composition and its components are as defined above for said compositions, said electrochemical cells, and said batteries.

[0079] In the present invention, the terms "between x and y" or "between x and y" refer to an interval that includes boundary values ​​x and y. EXAMPLES

[0080] Example 1: High and / or low temperature stability of aqueous electrolytes for vanadium redox flow batteries containing methanesulfonic acid (MSA) and one or more phosphorus additives

[0081] The thermal stability of the vanadium redox flow battery electrolyte containing the H2SO4 / MSA / inorganic phosphorus additive mixture was compared to that of conventional vanadium redox flow battery electrolytes, such as those commercially available, for example, those sold by Oxkem (https: / / www.oxkem.com / _html / product_pages / vanadium_sulfate_electrolyte.html) or GfE (https: / / www.gfe.com / en / products-and-solutions / vanadium-chemicals / product-overview), where: The concentration of vanadium in oxidation state +4 (V+4) is generally about 1.55-1.75 M (mol / l), The concentration of sulfuric acid (H2SO4) is generally about 2-3M, and The concentration of the stabilizing additive, usually phosphoric acid, is about 0.05M.

[0082] Alfa Aesar 99.9% Vanadyl Sulfate VOSO4, H2O 4.8 A series of electrolytes were prepared from (V4+), 95% sulfuric acid (H2SO4) from Carl-Roth, 99.5% methanesulfonic acid from Arkema, and 85% phosphoric acid (H3PO4) in water from VWR (Ph.Eur pa) (see Table 1 below).

[0083] For this, the desired appropriate amount of VOSO4 is weighed and added to about 10 ml of water previously acidified with the desired amount of acid (sulfuric acid and / or methanesulfonic and / or phosphoric acid) calculated to a final volume of 15 ml. The resulting mixture is heated to 60 ° C in a water bath to dissolve the vanadyl sulfate. After dissolution is complete, add the amount of water required to obtain 15 ml of electrolyte at 60 ° C and cool to 20-23 ° C.

[0084] After stabilization for at least two days, the vanadium +4 and +5 concentrations are determined by cerimetric titration (see Table 1 below).

[0085] [Table 1]

[0086] Next, the three electrolytes prepared above were electrolyzed in an electrochemical cell according to a conventional method to obtain electrolytes V+5 and V+3 for thermal stability testing.

[0087] After this electrolysis was completed, two other additives were added to electrolytes V+3 and V+5 containing MSA (but not phosphoric acid): Diammonium phosphate: 99.9% (NH4)2PO4 from Sigma-Aldrich; Sigma-Aldrich 99.9% potassium phosphate K3PO4 and 96% sodium hexametaphosphate (NaPO3) n A 50 / 50% mass mixture of.

[0088] Finally, 1 ml of each electrolyte was placed in a small plastic tube, and the samples were placed in an oven at 49-51 °C and visually inspected daily until the appearance of the first solid particles or the onset of a color change, which is a sign of electrolyte degradation. This allows the determination of the "induction time", i.e. the time for the electrolyte to stabilize at the investigated temperature. The vanadium concentration in the supernatant is then measured to quantitatively assess the proportion of vanadium that has precipitated.

[0089] The compositions and induction times of the various electrolytes subjected to the thermal stability test are given in Table 2 below.

[0090] [Table 2]

[0091] The results in Table 2 clearly show that, firstly, the electrolyte according to the present invention, unlike the reference electrolyte, has a total vanadium concentration after the thermal test that is not significantly different or equal to the initial concentration (1.7M) before the test, making it possible to significantly improve the stability of vanadium-based electrolytes.

[0092] Secondly, the first signs of electrolyte degradation appear later than the reference electrolyte, 13 days longer for electrolyte 2 of the invention.

[0093] Furthermore, the composition H2SO4 / MSA / additive of the present invention also allows good stability at low temperatures. It is known that V+3 and V+2 electrolytes are the most sensitive to low temperatures. However, none of the V+3 electrolyte solutions obtained after electrolysis of the V+4 solutions showed any signs of degradation (change in color or appearance of solid particles) after 8 days at 5°C.

[0094] From the above, the electrolyte composition of the present invention exhibits excellent thermal stability, particularly with respect to vanadium redox flow batteries. The present invention includes the following aspects. <1> Formula R-SO 3 H sulfonic acid, where R is (C 1 -C 4 ) alkyl or (C 1 -C 4 ) optionally substituted with alkyl (C 6 -C 14 ) aryl; Optionally, sulfuric acid, A redox metal ion; At least one inorganic additive (A) containing at least one phosphorus atom having an oxidation state of +5 or less; and water. <2> The sulfonic acid is selected from the group consisting of methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, 1-naphthalenesulfonic acid, 2-naphthalenesulfonic acid, and p-toluenesulfonic acid, preferably methanesulfonic acid; <1> The composition described in <3> Sulfuric acid, preferably a mixture of methanesulfonic acid and sulfuric acid; <1> or <2> The composition described in <4> The inorganic additive (A) is selected from the group consisting of hypophosphorous acid, phosphorous acids, hypophosphoric acid, phosphoric acids, polyphosphoric acids, salts thereof, and mixtures thereof; <1> ~ <3> The composition according to any one of the preceding claims. <5> The inorganic additive (A) is selected from the group consisting of hypophosphorous acid, metaphosphorous acid, pyrophosphorous acid, orthophosphorous acid, hypophosphoric acid, metaphosphoric acid, pyrophosphoric acid, orthophosphoric acid, triphosphoric acid, salts thereof, sodium hexametaphosphate, and mixtures thereof; <1> ~ <4> The composition according to any one of the preceding claims. <6> The amount of the inorganic additive (A) is 5% by weight or less, preferably between 0.5% by weight and 3% by weight, based on the total weight of the electrolyte composition; <1> ~ <5> The composition according to any one of the preceding claims. <7> The redox metal ion is a vanadium ion, preferably V 2+ 、V 3+ , V.O. 2+ , V.O. 2 + and mixtures thereof; <1> ~ <6> The composition according to any one of the preceding claims. <8> Further comprising a corrosion inhibitor, <1> ~ <7> The composition according to any one of the preceding claims. <9> The corrosion inhibitor is selected from compounds represented by the following general formula (1) or (2): <8> The composition described in NO 2 X (1) or NO 3 X (2) [Wherein, X is Na, K, NH 4 and H; When the corrosion inhibitor is a compound of formula (1), X further represents a linear or branched alkyl group R' containing 1 to 6 carbon atoms; an aryl group Ar, which may be substituted, in particular by at least one alkyl group R', -SO 2 -G groups (where G is H, OH, R', OR', OM, Ar, OAr, NH 2 , NHR', and NR'R'', where R' and Ar are as defined above, R'' is a linear or branched alkyl group containing 1 to 6 carbon atoms, and M is a monovalent or divalent metal cation, preferably an alkali metal or alkaline earth metal cation; a -CO-G group, where G is as defined above, may be selected from <10> A negative electrode, a positive electrode, <1> ~ <9> and an electrolyte composition according to any one of claims 1 to 5. <11> <10> 2. A redox battery comprising at least one electrochemical cell according to claim 1, preferably a vanadium redox flow battery. <12> To increase the concentration of redox metal ions; and / or <1> ~ <9> In order to prevent, reduce and / or slow down or delay the precipitation of redox metal ions in the electrolyte composition according to any one of the preceding claims, <1> , <4> , <5> , and <6> 2. Use of the inorganic additive (A) according to any one of claims 1 to 11. <13> At a temperature between 0°C and 60°C, preferably between 5°C and 50°C, <1> ~ <9> In order to stabilize the electrolyte composition according to any one of the above, <1> , <4> , <5> , and <6> 2. Use of the inorganic additive (A) according to any one of claims 1 to 11.

Claims

1. A compound of the formula R-SO having a molecular weight of 0.08M to 8M. ３ H sulfonic acid, where R is (C １ -C ４ ) alkyl or (C １ -C ４ ) optionally substituted with alkyl (C ６ -C １４ ) aryl; 0.1 mol / l to 15 mol / l of a redox metal ion; 0.5% to 5% by weight of at least one inorganic additive (A) containing at least one phosphorus atom having an oxidation state of +5 or less; and water.

2. 2. The composition of claim 1, wherein the sulfonic acid is selected from the group consisting of methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, 1-naphthalenesulfonic acid, 2-naphthalenesulfonic acid, and p-toluenesulfonic acid.

3. 3. The composition of claim 1 or claim 2, further comprising sulfuric acid.

4. The composition of any one of claims 1 to 3, further comprising a mixture of methanesulfonic acid and sulfuric acid.

5. The composition according to any one of claims 1 to 4, wherein the inorganic additive (A) is selected from the group consisting of hypophosphorous acid, phosphorous acids, hypophosphoric acid, phosphoric acids, polyphosphoric acids, salts thereof, and mixtures thereof.

6. The composition according to any one of claims 1 to 5, wherein the inorganic additive (A) is selected from the group consisting of hypophosphorous acid, metaphosphorous acid, pyrophosphorous acid, orthophosphorous acid, hypophosphoric acid, metaphosphoric acid, pyrophosphoric acid, orthophosphoric acid, triphosphoric acid, salts thereof, sodium hexametaphosphate, and mixtures thereof.

7. The composition according to any one of claims 1 to 6, wherein the redox metal ion is a vanadium ion.

8. The composition of any one of claims 1 to 7, further comprising a corrosion inhibitor.

9. 9. The composition according to claim 8, wherein the corrosion inhibitor is selected from compounds of the following general formula (1) or (2): NO ２ X (1) or NO ３ X (2) [Wherein, X is Na, K, NH ４ , and H; and When the corrosion inhibitor is a compound of formula (1), X further represents a linear or branched alkyl group R' containing 1 to 6 carbon atoms; an optionally substituted aryl group Ar; -SO ２ -G group (wherein G is H, OH, R', OR', OM, Ar, OAr, NH ２ , NHR', and NR'R'', where R' and Ar are as defined above, R'' is a linear or branched alkyl group containing 1 to 6 carbon atoms, and M is a monovalent or divalent metal cation); a -CO-G group, where G is as defined above; may be selected from

10. An electrochemical cell comprising a negative electrode, a positive electrode, and the electrolyte composition according to any one of claims 1 to 9.

11. A redox battery comprising at least one electrochemical cell according to claim 10.

12. Use of the inorganic additive (A) according to any one of claims 1, 5 and 6 in a redox battery for inhibiting a decrease in the total molar concentration of redox metal ions and / or for preventing, reducing and / or slowing down or delaying the precipitation of redox metal ions in the electrolyte composition according to any one of claims 1 to 9.

13. 13. Use of the inorganic additive (A) according to claim 12 in a redox battery for preventing, reducing, slowing down and / or retarding the precipitation of the redox metal ions in the electrolyte composition at temperatures between 0°C and 60°C.

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