Redox flow battery

Abstract

The present invention relates to a redox flow battery, an energy storage system comprising the redox flow battery, and a method of delivering and / or storing power by the redox flow battery.

Description

Technical Field

[0001] The present invention relates to a redox flow battery, an energy storage system comprising the redox flow battery, and a method of transmitting and / or storing electricity via the redox flow battery. Background Art

[0002] Global energy demand doubles every 15 years and is expected to continue to grow in the future, with the urgent need for high-energy resources also growing. However, more than 60% of global electricity is generated by coal and natural gas, with the associated large amounts of CO 2 Emissions, CO 2 It is considered to be the main factor causing the greenhouse effect and global warming.

[0003] Due to this harmful environmental impact, it has become necessary to replace fossil fuels with renewable energy sources, mainly wind and solar. The most relevant problem is that they are intermittent and do not guarantee a constant flow of energy. As our reliance on renewable energy sources needs to increase, there is a growing need to store renewable energy sources when they cannot be collected.

[0004] Among the possible alternatives, electrochemical storage and conversion play a key role. Researchers are working hard to find new materials to improve performance: environmental sustainability is essential given the urgent need for large-scale production and diffusion.

[0005] Redox flow batteries (RFBs) offer the unique advantage of energy and power independence. RFBs consist of an electrolyte tank that stores chemical energy and an electrochemical cell that reversibly converts the chemical energy into electrical energy.

[0006] So far, various types of RFBs have been developed, which can be divided into two types according to the electrolyte: aqueous RFB and non-aqueous RFB. Aqueous RFB offers advantages over non-aqueous RFB in terms of safety, toxicity, and cost.

[0007] Although energy storage systems using aqueous RFBs are the subject of considerable and growing interest due to their potential, Applicants have discovered to date that significant technical and functional limitations remain in this area.

[0008] Among various redox-active species of RFBs, manganese-based RFBs have attracted attention due to the very interesting properties of manganese as a redox-active species, via the following one-electron mechanism (Eq. 1):

[0009]

[0010] Manganese-based RFBs have a high redox potential of 1.51 V (vs. SHE) and also allow high energy density to be achieved due to their high solubility.

[0011] However, the main disadvantage of Mn-based RFBs is the formation of solid MnO in the electrolyte. 2 , which is achieved through Mn 3+ Disproportionation or electrochemical spontaneous generation. Solid MnO 2 The precipitates can reduce the active species in the redox reaction and adversely affect the operation of the RFB (clogging, deposition on the electrode surface), which leads to a loss of efficiency of the RFB over time.

[0012] So far, several inhibitors of MnO in batteries are known. 2 The most common strategy is to use additives to suppress the 3+ Disproportionation to form MnO 2 , as well as limiting the charging process to 90% SOC.

[0013] Another strategy found in the literature describes the use of MnO in a controlled manner. 2 To this end, the electrolyte formulation and electrode properties were designed to promote the formation of MnO 2 In other words, according to the two-electron mechanism (Equation 2), MnO 2 Electrochemically deposited on the electrode during charging and electrochemically dissolved during discharge:

[0014]

[0015] However, plating / stripping is the limiting mechanism of redox flow batteries in terms of power and energy decoupling. Typically, redox flow batteries have a power to energy ratio that can be adjusted by varying the size of the electrolyte volume (energy) and varying the size of the cell stack (power). This flexibility is not available for systems that perform plating. In isolating plating compounds such as MnO 2 ) system, the energy will be limited by the electrode surface area, because when the electrode surface is completely covered, the electrochemical reaction will be blocked. This greatly limits the use of MnO in redox flow batteries. 2 Possibility of plating / stripping system.

[0016] Applicants have noted that these strategies have several technical and functional limitations and surprisingly discovered that a completely different mechanism can be exploited for the operation of RFBs in manganese-based electrolytes. Summary of the invention

[0017] Therefore, a first object of the present invention is to provide a manganese-based redox flow battery capable of overcoming the technical limitations of the prior art.

[0018] According to the present invention, the applicant has surprisingly found that a specific manganese-based cathode electrolyte releases a reversible two-electron redox mechanism (Formula 2):

[0019]

[0020] A stable suspension of a manganese (IV) species is produced in the electrolyte. The manganese (IV) species comprises MnO 2 Or by MnO 2 composition, advantageously in the form of a particle suspension.

[0021] The electrochemical exploitation of this reversible two-electron redox mechanism, which avoids the adverse effects of precipitation, has attracted high attention because it offers twice the energy density and other benefits compared to the single-electron mechanism (Equation 1) with the same electrolyte cost and shows distinct advantages over MnO 2 Decoupled power / energy performance of the plating / stripping mechanism.

[0022] Thus, in a first aspect, the present invention relates to a redox flow battery in which a positive electrode electrolyte and a negative electrode electrolyte are supplied to a battery cell comprising a positive electrode, a negative electrode, a membrane interposed between the electrodes, to charge and discharge the battery, wherein:

[0023] - the positive electrolyte comprises at least one manganese ion and at least one complexing agent, wherein the at least one complexing agent is selected from the group consisting of titanium ions, tin ions, chromium ions, aluminum ions, vanadium ions, cerium ions or mixtures thereof;

[0024] - the negative electrolyte comprises at least one active redox species coupled to the manganese ions of the positive electrolyte; and

[0025] - The positive electrode is a thermally activated carbon-based electrode.

[0026] The working principle of the redox flow battery according to the present invention is based on the manganese redox mechanism. The applicant surprisingly found that it is possible to avoid the presence of MnO in the electrolyte. 2 The adverse effects of precipitation and MnO 2 The limited positive electrode surface area of ​​the plating / stripping mechanism, while, during the operation of the RFB, a relatively stable manganese (IV) species can be advantageously generated and maintained in the electrolyte by using a complexing agent selected from the group consisting of titanium ions, tin ions, chromium ions, aluminum ions, vanadium ions, cerium ions or mixtures thereof, wherein the positive electrode is a thermally activated carbon-based electrode. Such conditions do allow the release and utilization of a reversible two-electron redox mechanism (Equation 2), which provides twice the energy density compared to a single-electron redox mechanism (Equation 1) with the same amount of manganese species, while avoiding the interaction with MnO 2The energy capacity limitations associated with the plating / stripping mechanism are reduced, thereby improving the efficiency and cost-effectiveness of RFB.

[0027] In another aspect, the present invention also relates to an energy storage or delivery system comprising at least one redox flow battery according to the first aspect of the present invention and at least one connection device that facilitates connecting the at least one redox flow battery to an external power source or load.

[0028] The advantages of the energy storage or delivery system according to this further aspect have already been outlined with reference to the above-described redox flow battery according to the first aspect of the invention and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In the attached picture:

[0030] Figure 1 Schematically shows a redox flow battery used in the experiments according to Examples 1-11;

[0031] Figure 2 shows the first charge / discharge cycle obtained according to the experiment of Example 1;

[0032] Figure 3 shows the visual appearance of the manganese-based positive electrolyte during charging and discharging according to the experiment of Example 1;

[0033] Figure 4 shows the first 7 charge / discharge cycles obtained according to the experiment of Example 2;

[0034] Figure 5 shows the first 7 charge / discharge cycles obtained according to the experiment of Example 3;

[0035] Figure 6 shows the first 7 charge / discharge cycles obtained according to the experiment of Example 4;

[0036] Figure 7 A performance comparison of an RFB according to the present invention (Example 2) and a reference system (Examples 3 and 4 - Reference Examples) is shown;

[0037] Figure 8 FE-SEM micrographs of the electrodes of the batteries of Examples 2, 3 and 4 after charging are shown;

[0038] Fig. 9 shows the charge / discharge cycles obtained from the experiments of Example 6 (9a), Example 7 (9b) and Example 8 (9c);

[0039] Fig.10 shows the charge / discharge cycle obtained according to the experiment of Example 9;

[0040] Fig.11 The charge / discharge cycles obtained according to the experiments of Example 10 and Reference Example 11 are shown. DETAILED DESCRIPTION

[0041] In a first aspect, the present invention relates to a redox flow battery invention, wherein a positive electrode electrolyte and a negative electrode electrolyte are supplied to a battery cell comprising a positive electrode, a negative electrode, and a membrane interposed between the electrodes to charge and discharge the battery, wherein:

[0042] - the positive electrolyte comprises at least one manganese ion and at least one complexing agent, wherein the at least one complexing agent is selected from the group consisting of titanium ions, tin ions, chromium ions, aluminum ions, vanadium ions, cerium ions or mixtures thereof;

[0043] - the negative electrolyte comprises at least one active redox species coupled to the manganese ions of the positive electrolyte; and

[0044] - The positive electrode is a thermally activated carbon-based electrode.

[0045] The working principle of the redox flow battery according to the present invention is based on the manganese redox mechanism. The applicant surprisingly found that it is possible to avoid the presence of MnO in the electrolyte. 2 The adverse effects of precipitation and MnO 2 The limited positive electrode surface area of ​​the plating / stripping mechanism can advantageously generate and maintain relatively stable manganese (IV) species in the electrolyte during operation of the RFB according to the present invention. This allows the release and utilization of a reversible two-electron redox mechanism (Equation 2) that provides twice the energy density compared to the one-electron redox mechanism (Equation 1) for the same amount of manganese species, while avoiding the 2 The energy capacity limitations associated with the plating / stripping mechanism are reduced, thereby improving the efficiency and cost-effectiveness of RFB.

[0046] Within the framework of the present description and in the claims that follow, unless otherwise indicated, all numerical entities expressing quantities, parameters, percentages and the like are to be understood as being preceded in all cases by the term "about". Furthermore, all ranges of numerical entities include all possible combinations of maximum and minimum values ​​and include all possible intermediate ranges, except those specifically indicated below.

[0047] The present invention may have one or more of the features disclosed below in one or more of the above aspects.

[0048] In the redox flow battery of the present invention, the positive electrode electrolyte and the negative electrode electrolyte are supplied to the battery cell.

[0049] Preferably, the positive electrode electrolyte and the negative electrode electrolyte are aqueous electrolytes.

[0050] The positive electrolyte includes at least one manganese ion.

[0051] Preferably, the cathode electrolyte comprises the at least one manganese ion in a concentration of 0.1M to 4.2M, more preferably in a concentration of 1M to 3.5M, even more preferably in a concentration of 1.5M to 3M.

[0052] Advantageously, in the cathode electrolyte, the redox reaction of the at least one manganese ion is

[0053]

[0054] Thus, manganese (IV)-containing species are generated during battery charging and are depleted during battery discharge.

[0055] Preferably, the positive electrode electrolyte comprises a manganese (IV)-containing substance. Preferably, the manganese (IV)-containing substance is MnO 2 .

[0056] Depending on the state of charge of the redox flow battery according to the invention, the manganese (IV) containing substance forms a particle suspension.

[0057] Preferably, the cathode electrolyte comprises the at least one complexing agent in a concentration of 0.1M to 8M, more preferably in a concentration of 0.25M to 6M, even more preferably in a concentration of 0.5M to 5M.

[0058] Preferably, the molar ratio between the at least one manganese ion and the at least one complexing agent is from 0.1 to 2, more preferably from 0.25 to 1.5.

[0059] The positive electrode electrolyte further includes at least one complexing agent, wherein the at least one complexing agent is selected from the group consisting of titanium ions, tin ions, chromium ions, aluminum ions, vanadium ions, cerium ions, or mixtures thereof.

[0060] Preferably, the at least one complexing agent comprises titanium ions or tin ions.

[0061] Preferably, the at least one titanium ion is selected from the group consisting of trivalent titanium ions (Ti 3+ ) and tetravalent titanium ions (Ti 4+ or TiO 2+ ).

[0062] Preferably, the titanium ion is a tetravalent titanium ion (Ti 4+ or TiO 2+ ).

[0063] Preferably, the at least one tin ion is selected from the group consisting of divalent tin ions (Sn 2+ ) and tetravalent tin ions (Sn 4+ ).

[0064] The tetravalent tin ions may advantageously be added to the electrolyte or prepared in situ by adding divalent tin ions to the electrolyte and oxidizing them to tetravalent tin (also known as "tin (IV)") using chemical oxidation, electrochemical oxidation or any alternative process known to the skilled person.

[0065] The electrolyte may also advantageously contain at least one solvating agent, such as acetonitrile.

[0066] Thus, in a preferred embodiment, the present invention is directed to a redox flow battery wherein the cathode electrolyte comprises at least one manganese ion and at least one tetravalent tin ion.

[0067] Therefore, in another preferred embodiment, the present invention also relates to a redox flow battery, wherein the cathode electrolyte comprises at least one manganese ion and at least one tin ion selected from divalent tin ions and tetravalent tin ions and at least one solvating agent, preferably acetonitrile.

[0068] Preferably, in the redox flow battery according to the present invention, the pH of the cathode electrolyte is 0 to 2.

[0069] Preferably, the cathode electrolyte comprises at least one acid at a concentration equal to or lower than 4M, more preferably at a concentration equal to or lower than 3.5M, even more preferably at a concentration equal to or lower than 3M.

[0070] Preferably, the at least one acid is selected from the group consisting of sulfuric acid, hydrochloric acid, phosphoric acid, diphosphoric acid and nitric acid. More preferably, the at least one acid is sulfuric acid (H 2 SO 4 ).

[0071] The positive electrolyte of the RFB according to the present invention advantageously further comprises at least one anion in an amount sufficient to maintain the charge balance of the electrolyte. The anion is preferably selected from SO 4 2- , Cl - Br - ,PO 4 2- , P 2 O 7 4- and NO 3 - Composed of groups.

[0072] The cathode electrolyte of the RFB according to the present invention may also include other ingredients such as suspension stabilizers, co-solvents, organic solvents, surfactants, wetting agents and dispersants. The anode electrolyte of the redox flow battery according to the present invention includes at least one active redox species coupled to the manganese ions of the cathode electrolyte.

[0073] As known to those skilled in the art, in order to ensure high energy density, the redox potential difference between the negative electrode electrolyte and the positive electrode electrolyte should advantageously be as high as possible.

[0074] Preferably, at least one active redox species of the negative electrode electrolyte is selected from the group consisting of: protons, nickel ions, cobalt ions, iron ions, lead ions, copper ions, sulfur ions, sulfide ions, zinc ions, titanium ions, vanadium ions, tin ions, cerium ions, chromium ions, iron ions, their quinone derivatives, anthraquinone or its derivatives, viologens or its derivatives, indigo or its derivatives, naphtalenediimide or its derivatives, diazaanthracenedione or its derivatives.

[0075] Preferably, the E° of at least one active redox species of the negative electrolyte is at least 0.6 V lower than the E° of the reaction:

[0076]

[0077] Preferably, at least one active redox species of the negative electrode electrolyte is a proton, and the redox reaction of the proton in the negative electrode electrolyte is

[0078]

[0079] As known to those skilled in the art, the basic building block of a redox flow battery is a battery cell comprising a positive electrode, a negative electrode, and a membrane interposed between the electrodes. The components have characteristics and can be assembled according to common practices well known in the relevant art to perform its charge / discharge operation.

[0080] In the redox flow battery according to the present invention, the positive electrode is a thermally activated carbon-based electrode.

[0081] The applicants have indeed surprisingly found that the thermally activated carbon-based electrodes act synergistically with the complexing agents according to the present invention, allowing the release and utilization of a reversible two-electron redox mechanism (Equation 2) that provides twice the energy density compared to the one-electron redox mechanism (Equation 1) with the same amount of manganese species, while avoiding the 2 The energy capacity limitations associated with the plating / stripping mechanism are reduced, thereby improving the efficiency and cost-effectiveness of RFB.

[0082] Without wishing to be bound by any particular theory, the applicant believes that thermal activation imparts physicochemical and surface properties to the carbon-based electrode that are capable of synergistically interacting with the complexing agent to produce and maintain stable manganese (IV) species in the electrolyte during RFB operation. The applicant also believes that the same synergistic effect can be obtained using other activation techniques (e.g., physicochemical activation) as long as such physicochemical and surface properties are imparted to the carbon-based electrode.

[0083] Preferably, the thermally activated carbon-based electrode is selected from the group consisting of graphite felt, carbon felt, graphite cloth, graphite nanoparticles, graphite nanofibers, carbon cloth, carbon nanotubes, carbon nanoparticles or carbon nanofiber thermally activated electrodes.

[0084] In a preferred embodiment, the thermally activated carbon electrode is a graphite felt thermally activated electrode.

[0085] Preferably, the positive electrode is coupled to at least one flow-by type flow field.

[0086] Preferably, the side-flow type flow field comprises a channel design, and the channel design is selected from the group consisting of: a single serpentine channel design, a multi-serpentine channel design and a parallel channel design.

[0087] In another aspect, the present invention also relates to an energy storage or delivery system comprising at least one redox flow battery according to the first aspect of the present invention and at least one connection device facilitating connection of the at least one redox flow battery to an external power source or load.

[0088] The advantages of the energy storage or delivery system according to this further aspect have already been outlined with reference to the above-described redox flow battery according to the first aspect of the invention and will not be repeated here.

[0089] In other aspects, the present invention also relates to a method for storing electricity by means of a redox flow battery according to the present invention, and a method for delivering electricity by means of a redox flow battery according to the present invention.

[0090] In particular, the present invention also relates to a method for storing electricity, comprising the following steps:

[0091] a) providing a redox flow battery according to the present invention;

[0092] b) electrically connecting the redox flow battery to a power source;

[0093] and a method of transmitting electric power, comprising the steps of:

[0094] a) providing a redox flow battery according to the present invention;

[0095] b) electrically connecting the redox flow battery to a load.

[0096] The advantages of the methods according to these other aspects have already been outlined with reference to the above-described redox flow battery according to the first aspect of the invention and will not be repeated here.

[0097] In another aspect, the present invention also relates to a thermally activated carbon-based electrode in combination with at least one complexing agent for inhibiting the oxidation of MnO in an electrolyte comprising at least one manganese ion during operation of a redox flow battery. 2 The invention relates to a method for preparing a precipitate of manganese ions, wherein at least one complexing agent is selected from the group consisting of titanium ions, tin ions, chromium ions, aluminum ions, vanadium ions, cerium ions or mixtures thereof, wherein the redox reaction of the manganese ions in the electrolyte is

[0098]

[0099] The advantages of the use according to this further aspect have already been outlined with reference to the above-described redox flow battery according to the first aspect of the invention and will not be repeated here.

[0100] Preferably, in the use, the thermally activated carbon-based electrode is selected from the group consisting of: graphite felt, carbon felt, graphite cloth, graphite nanoparticles, graphite nanofibers, carbon cloth, carbon nanotubes, carbon nanoparticles or carbon nanofiber thermally activated electrodes. More preferably, in the use, the thermally activated carbon-based electrode is a graphite felt thermally activated electrode.

[0101] Preferably, in the use, the complexing agent comprises titanium ions or tin ions.

[0102] Preferably, the at least one titanium ion is selected from the group consisting of trivalent titanium ions (Ti 3+ ) and tetravalent titanium ions (Ti 4+ or TiO 2+ ).

[0103] Preferably, the titanium ion is a tetravalent titanium ion (Ti 4+ or TiO 2+ ).

[0104] Preferably, the at least one tin ion is selected from the group consisting of divalent tin ions (Sn 2+ ) and tetravalent tin ions (Sn 4+ ).

[0105] Preferably, the tin ions are tetravalent tin ions.

[0106] Preferably, in said use, said electrolyte comprises said at least one complexing agent in a concentration of 0.25M to 6M, more preferably in a concentration of 0.5M to 5M.

[0107] Preferably, in said use, the molar ratio between said at least one manganese ion and said at least one complexing agent is from 0.1 to 2, more preferably from 0.25 to 1.5.

[0108] The features and advantages of the present invention will also appear more clearly from the following non-limiting examples.

[0109] Experimental Section

[0110] The following electrochemical experiments according to Examples 1-11 were carried out at H 2 -Mn redox flow battery. In the redox flow battery used for the experiment, hydrogen was used as a proton source in the negative electrode electrolyte to carry out the redox reaction:

[0111]

[0112] Thus, during charging, H 2 Produced in electrochemical cells. Bubbles indicate the presence of H during charging. 2 During the discharge period, H 2 The pressure flows into the cell at 1.5 bar.

[0113] MnSO in the range of 0.3-1.5 M with a Mn:Ti molar ratio of 1:1.5 4 ·H 2 O (Sigma-Aldrich; ≥99.0%) and TiOSO 4 (Sigma-Ardrich; Ti(as TiO 2 ) ≥ 29%, industrial grade) to prepare the positive electrode electrolyte. In Examples 1-7, 3M H 2 SO 4 (Fisher scientific, 96%), while in Example 8, 2M MnSO 4 ·H 2 O, 1M TiOSO 4 and 2M H 2 SO 4 In Example 9, it is 0.3M MnSO 4 ·H 2 O and 0.45 M SnCl 4 ·5H 2 O (Fischer; 98%) and 3M H 2 SO 4 In the experiments, 20 mL of aqueous electrolyte was used and pumped at a rate of 100 mL / min.

[0114] In Example 10, Sn(IV) was prepared as follows: 23 mL of 0.5 M MnSO 4 20% V / V Acetonitrile deionized water at 22 mA / cm 2 Charge to 225 mAh to generate Mn 3+ Then add 0.125M SnSO 4 (Fisher Scientific, 95%), by Mn 3+ and Sn 2+ The reaction between 2+ and Sn 4+ The Sn(IV) electrolyte contains 0.5 M MnSO 4 ·H 2 O, 0.125 M Sn(IV), 3 M H 2 SO 4 20% V / V Acetonitrile / deionized water. 23 mL of this electrolyte has been tested at 43 mA / cm 2 The current density was 100 mL / min and the flow rate was 100 mL / min.

[0115] The electrolyte in Example 11 (reference example) is called Sn-free electrolyte, which consists of 0.5 M MnSO 4 、3M's H 2 SO 4 and 20% V / V 20 mL of this electrolyte has been used at a flow rate of 100 mL / min at 0.43 mA / cm 2 current density cycle.

[0116] The nominal capacity calculated from the reversible two-electron redox mechanism (Equation 2) is used as a reference in each case:

[0117]

[0118] The redox flow battery used in the experiment Figure 1 The system is schematically depicted in FIG. 1 and consists of the following components denoted by the following reference numerals:

[0119] 1- positive electrode electrolyte tank (positive electrode electrolyte tank);

[0120] 2- negative electrode electrolyte tank (hydrogen tank);

[0121] 3-Battery;

[0122] 4-current collector;

[0123] 5-current collector;

[0124] 6-Isolation board;

[0125] 7-Isolation board;

[0126] 8-end plate;

[0127] 9-end plate;

[0128] 10- Pump;

[0129] 11-membrane;

[0130] 12- catalyst;

[0131] 13-bipolar plate-flow field;

[0132] 14-bipolar plate-flow field;

[0133] 15-Liquid diffusion electrode;

[0134] 16-gas diffusion electrode;

[0135] In Examples 1-7, 20 mL of Mn-cathode electrolyte was pumped into the cell at room temperature at a flow rate of 50 mL / min, while in Example 8 it was pumped into the cell at a flow rate of 150 mL / min. The hydrogen flow was supplied at a pressure of 1.5 bar only during discharge. The electrochemical cell consisted of two end plates, between which the remaining components were sandwiched: two polypropylene separators, two copper current collectors, bipolar plate flow field (double serpentine for the positive side and staggered for the negative side). A 5x5 cm 2 The active area was a 2.5 mm thick heat-activated commercial graphite felt (SGL-GFD 2.5EA heat-activated) positive electrode. Finally, a 0.5 mg / cm 2 Pt catalyst 5x5cm 2 The active area gas diffusion layer electrode was used as the negative electrode (Quintech-BC-H100-05S).

[0136] The charge-discharge process was carried out at 2 C relative to the nominal capacity of the cathode electrolyte, or as specified in each case. The lower and upper potential limits were 0.6 V and 1.75 V, respectively.

[0137] The cathodes to be analyzed were cleaned by immersion in deionized water and dried in air for at least 72 h after charging. Morphological and chemical characterizations were performed in FE-SEM, EDS (SEM JEOL IT300).

[0138] Example 1

[0139] In this experiment, a Mn 2+ and 534mAh nominal capacity H 2 -Mn battery. Use a MnSO with 0.5M4 , 0.75M TiOSO 4 and 3M's H 2 SO 4 20 mL of aqueous solution was used as the positive electrode electrolyte.

[0140] Figure 2 The first cycle obtained is shown. 2 The current density discharge delivered a capacity of 523 mAh, which is 97.6% relative to the nominal capacity calculated considering Equation 2 (reversible two-electron redox mechanism). The coulombic efficiency obtained was 99.7%, indicating good reversibility of the system.

[0141] Figure 3 The visual appearance of the Mn-based cathode electrolyte during the charge and discharge process is shown. It is worth noting that Figure 3 a depicts the visual appearance of the electrolyte from the beginning of the charging process (Photo 1, SoC>0%) to 100% SoC (Photo 5). The 100% SoC electrolyte appearance is visually homogeneous and opaque, consistent with the characteristics of a solid suspension. Figure 3 b depicts the visual appearance of the electrolyte during the discharge process from Photo A (100% SoC) to Photo E (0% SoC). At 0% SoC (Photo E) there is no solid, which is the reversible MnO 2 - Visual evidence of a suspension mechanism process (no irreversible precipitation of charge products).

[0142] Example 2

[0143] Example 1 was repeated, but using 0.3 M MnSO 4 , 0.45M TiOSO 4 and 3M's H 2 SO 4 20 mL of aqueous solution was used as the positive electrode electrolyte.

[0144] Figure 4 It shows that at 2C (25mA / cm 2 ) for the first 7 cycles obtained under .

[0145] Table 1 summarizes the different performance parameters for each cycle.

[0146] Table 1

[0147] Loop 1 Loop 2 Loop 3 Loop 4 Loop 5 Loop 6 Loop 7 capacity 228mAh 223mAh 224mAh 222mAh 226mAh 225mAh 226mAh C retention rate - 100 100 100 101 101 101 Q efficiency (%) 96.9 99.1 99.2 99.3 99.2 99.0 99.3 Efficiency (%) 78.0 80.9 81.2 81.3 81.2 80.8 81.3

[0148] Excluding the first cycle, which is not representative due to its initial stabilization of the battery, the remaining cycles show an average discharge capacity of 224 mAh with negligible variations. No capacity drop was found. In addition, Coulombic efficiency values ​​above 99.1% indicate good reversibility of the system. Finally, an energy efficiency average of 81% was recorded.

[0149] Example 3 (reference)

[0150] Example 2 was repeated, but using a non-heat-activated graphite felt positive electrode (unactivated SGL-GFD 2.5EA).

[0151] Figure 5 It shows that at 2C (25mA / cm 2 ) for the first 7 cycles obtained under .

[0152] Table 2 summarizes the different performance parameters for each cycle.

[0153] Table 2

[0154] Loop 1 Loop 2 Loop 3 Loop 4 Loop 5 Loop 6 Loop 7 capacity 206mAh 205mAh 204mAh 203mAh 197mAh 194mAh 194mAh C retention rate - 100 99.5 99.0 96.1 94.6 94.6 Q efficiency (%) 97.5 99.1 99.2 99.2 99.2 99.2 85.1 Efficiency (%) 73.0 76.5 76.8 76.5 75.9 77.2 66.8

[0155] Excluding the first cycle, which is not representative due to its initial stabilization of the battery, the remaining cycles show that the discharge capacity decreases with the cycle, which means that the capacity retention rate at the 7th cycle is 94.6%. This result is consistent with the prior art (e.g. WO2017103578A1) on MnO 2 The statements made for production and precipitation are very consistent. Furthermore, with respect to the system according to Example 2, the average energy efficiency reaches a lower value of 75%.

[0156] Example 4 (reference)

[0157] Example 2 was repeated, but using 0.3 M MnSO 4 and 3M's H 2 SO 4 20 mL of aqueous solution was used as the positive electrode electrolyte. In other words, the positive electrode electrolyte does not contain TiOSO 4 .

[0158] Figure 6 It shows that at 2C (25mA / cm 2 ) for the first 7 cycles of the battery obtained under . Table 3 summarizes the performance parameters.

[0159] Table 3

[0160]

[0161]

[0162] Excluding the first cycle, which is not representative due to the initial stabilization of the battery, the remaining cycles show highly variable performance and rapid capacity loss starting from the second cycle, as well as a capacity retention rate of 71.8% at the 7th cycle. The voltage overpotential between the charge and discharge curves resulted in an energy efficiency value of 75.4%, which is significantly lower than the result of Example 2. This result is consistent with the prior art (e.g., Javier Rubio Garcia et al. Hydrogen / manganese hybrid redox flow battery. J. Phys.: Energy, Vol 1 (2019) 015006) on the absence of Ti in the electrolyte. 4+ The statements made about the instability of the system are very consistent.

[0163] Example 5 - Comparison between systems

[0164] In order to evaluate the different performances of the RFB according to the invention (Example 2) and the reference system (Example 3 and Example 4 - Reference Example), a comparison was performed at the 7th charge / discharge cycle.

[0165] Figure 7 To summarize the comparison: Figure 7 The 7th charge / discharge of the system is reported. The RFB according to Example 2 is denoted as "TA-GF+Ti(IV)", the RFB according to Example 3 is denoted as GF+Ti(IV), and the RFB according to Example 4 is denoted as "TA-GF".

[0166] Table 4 summarizes the different parameters determined.

[0167] Table 4

[0168]

[0169] It may be noted that the RFB according to Example 2 (TA-GF + Ti(IV)) delivered higher capacity values ​​and capacity retention, which confirms that when MnO is promoted 2 - In the suspension mechanism, the electrolyte charging is not blocked by sediment.

[0170] Figure 8 FE-SEM micrographs of the electrodes in Examples 2, 3 and 4 at different reinforcements after battery charging are shown. The electrodes of Reference Examples 3 and 4 show a relevant number of particles attached to the positive electrode fibers, which are not present in the combination of thermally activated graphite felt and Ti in the electrolyte. 4+EDS analysis further confirmed the presence of Mn species on the electrodes of Example 3 (6.6%) and Example 4 (42.7%), while the Mn content on the electrode of Example 2 was significantly lower (0.9%).

[0171] Table 5 summarizes the different parameters determined.

[0172] Table 5

[0173]

[0174]

[0175] These results demonstrate that MnO 2 Electroplated systems (TA-GF and GF+Ti(IV)) and unplated MnO 2 system (TA-GF+Ti(Ⅳ)).

[0176] Examples 6, 7 and 8

[0177] In Example 6, Example 2 was repeated, but using MnSO 4 , 1.5M TiOSO 4 and 3M's H 2 SO 4 20 mL of aqueous solution was used as the positive electrode electrolyte.

[0178] In Example 7, Example 2 was repeated, but using a 1.5 M MnSO 4 , 2M TiOSO 4 and 3M's H 2 SO 4 20 mL of aqueous solution was used as the positive electrode electrolyte.

[0179] In Example 8, Example 2 was repeated, but using MnSO with 2M 4 , 1M TiOSO 4 and 2M H 2 SO 4 20mL of aqueous solution was used as the positive electrolyte with a flow rate of 150mL / min.

[0180] Fig. 9 The charge / discharge cycles of the obtained batteries are depicted. Fig. 9 a shows that Example 6 is at 1C (43 mA / cm 2 ) cycles obtained under 1M Mn 2+ The energy density is 51.4Wh / L, which is comparable to the existing technology 1e - Exchange H 2Compared to the 33Wh / L claimed in the -Mn system (Formula 1 - Javier Rubio Garcia et al, 2019 J. Phys. Energy 1 015006), the energy density is 55% higher.

[0181] Fig. 9 b shows the temperature of Example 7 at 0.67C (43 mA / cm 2 ) cycles obtained under . The battery delivered an energy density of 91Wh / L with reversibility of 99.2% coulombic efficiency and 80.1% energy efficiency, respectively.

[0182] Fig. 9 c shows the temperature of Example 8 at 0.25C (22 mA / cm 2 ) cycles obtained under . The battery delivered an energy density of 125Wh / L with a reversibility of 98.9% Coulombic efficiency and 81.8% energy efficiency, respectively. These results demonstrate the great potential of this mechanism.

[0183] All the results show that MnO 2 -The suspension mechanism is feasible in concentrated electrolytes, where competitive performance can be achieved.

[0184] Example 9

[0185] In Example 9, Example 2 was repeated, but using a 0.3 M MnSO 4 , 0.45M SnCl 4 and 3M's H 2 SO 4 20 mL of aqueous solution was used as the positive electrode electrolyte.

[0186] Fig.10 Depicted at 1C (43mA / cm 2 ) under the charge / discharge cycle of the battery obtained. The battery showed a capacity utilization of 84.4% of the nominal capacity for the two-electron redox reaction (271 mAh / 321 mAh), which indicates that Sn 4+ Effective as complexing agent according to the present invention.

[0187] Examples 10 to 11

[0188] In Examples 10 to 11, the performance of cells containing the following electrolytes was compared: In Example 11, the electrolyte was named Sn-free (Example 11), and 0.5 M MnSO 4 and H containing 3M 2 SO 4 In Example 10, designated as Sn(IV) (Example 10), a 20% acetonitrile aqueous solution containing 0.5 M MnSO4 , 0.125 M Sn(IV) and 3 M H 2 SO 4 The electrolyte is 20% acetonitrile aqueous solution.

[0189] Fig.11 The electrochemical behavior of two cells is compared. The first depicts the behavior of the Sn-free (Example 11) electrolyte containing acetonitrile in the absence of Sn(IV). In this case, the electrochemical reaction shows limited performance, with the charging process reaching a cutoff limit of 196 mAh (32% of the nominal capacity), most likely blocked by large amounts of solids deposited on the system tubes and electrolyte tanks, which are caused by uncontrolled Mn 3+ Disproportionation to MnO 2 Solids are produced and further adversely affected. The discharge capacity reached 173 mAh (28% of the nominal capacity). The electrolyte named Sn(IV)-Cycle 1 to 4 (Example 10) containing Sn ions and acetonitrile showed a reversible charge-discharge curve reaching 583 mAh capacity (95% of the nominal capacity). These results demonstrate that Sn ions act as a complexing agent to utilize the di-electron MnO 2 The role of suspension mechanisms.

Claims

1. A redox flow battery, wherein: A positive electrode electrolyte and a negative electrode electrolyte are supplied to a battery cell including a positive electrode, a negative electrode, and a membrane interposed between the electrodes to charge and discharge the battery, wherein: - the positive electrolyte comprises at least one manganese ion and at least one complexing agent, wherein the at least one complexing agent is selected from the group consisting of titanium ions, tin ions, chromium ions, aluminum ions, vanadium ions, cerium ions or mixtures thereof; - the negative electrolyte comprises at least one active redox species coupled to the manganese ions of the positive electrolyte; and - The positive electrode is a thermally activated carbon-based electrode.

2. The redox flow battery according to claim 1, wherein: The positive electrolyte includes the at least one manganese ion at a concentration of 0.1M to 4.2M.

3. The redox flow battery according to claim 2, wherein: The positive electrolyte includes the at least one manganese ion at a concentration of 1M to 3.5M.

4. The redox flow battery according to claim 3, wherein: The positive electrolyte includes the at least one manganese ion at a concentration of 1.5M to 3M.

5. The redox flow battery according to any one of claims 1 to 4, wherein: The redox reaction of the at least one manganese ion in the positive electrolyte is 6. The redox flow battery according to any one of claims 1 to 5, wherein: The positive electrolyte includes a manganese (IV)-containing substance.

7. The redox flow battery according to claim 6, wherein: The manganese (IV)-containing substance is MnO2.

8. The redox flow battery according to any one of claims 1 to 7, wherein: The cathode electrolyte includes the at least one complexing agent at a concentration of 0.1M to 8M.

9. The redox flow battery according to claim 8, wherein: The cathode electrolyte includes the at least one complexing agent at a concentration of 0.25M to 6M.

10. The redox flow battery according to claim 9, wherein: The cathode electrolyte includes the at least one complexing agent at a concentration of 0.5M to 5M.

11. The redox flow battery according to any one of claims 1 to 10, wherein: The molar ratio between the at least one manganese ion and the at least one complexing agent is from 0.1 to 2.

12. The redox flow battery according to claim 11, wherein: The molar ratio between the at least one manganese ion and the at least one complexing agent is from 0.25 to 1.

5.

13. The redox flow battery according to any one of claims 1 to 12, wherein: The at least one complexing agent includes titanium ions or tin ions.

14. The redox flow battery according to any one of claims 1 to 13, wherein: The titanium ion is selected from the group consisting of: trivalent titanium ion (Ti 3+ ) and tetravalent titanium ions (Ti 4+ or TiO 2+ ).

15. The redox flow battery according to any one of claims 1 to 14, wherein: The tin ions are selected from the group consisting of divalent tin ions (Sn 2+ ) and tetravalent tin ions (Sn 4+ ).

16. The redox flow battery according to any one of claims 1 to 15, wherein: The tin ions are selected from the group consisting of divalent tin ions (Sn 2+ ) and tetravalent tin ions (Sn 4+ ), and the positive electrode electrolyte includes at least one solvating agent, preferably acetonitrile.

17. The redox flow battery according to any one of claims 1 to 16, wherein: The pH of the positive electrode electrolyte is 0 to 2.

18. The redox flow battery according to any one of claims 1 to 17, wherein: The positive electrolyte includes at least one acid at a concentration equal to or lower than 4M.

19. The redox flow battery according to claim 18, wherein: The positive electrolyte includes at least one acid at a concentration equal to or lower than 3.5M.

20. The redox flow battery according to claim 19, wherein: The positive electrolyte includes at least one acid at a concentration equal to or lower than 3M.

21. The redox flow battery according to any one of claims 18 to 20, wherein: The at least one acid is selected from the group consisting of sulfuric acid, hydrochloric acid, phosphoric acid, diphosphoric acid and nitric acid.

22. The redox flow battery according to claim 21, wherein: The at least one acid is sulfuric acid.

23. The redox flow battery according to any one of claims 1 to 22, wherein: The positive electrolyte includes at least one anion selected from SO4 2- , Cl - Br - PO4 2- 、P2O7 4- and NO3 - The group composed of.

24. The redox flow battery according to any one of claims 1 to 23, wherein: The at least one active redox species of the negative electrode electrolyte is selected from the group consisting of: protons, nickel ions, cobalt ions, iron ions, lead ions, copper ions, sulfur ions, sulfide ions, zinc ions, titanium ions, vanadium ions, tin ions, cerium ions, iron ions, their quinone derivatives, anthraquinone or its derivatives, viologen or its derivatives, indigo or its derivatives, naphthalene diimide or its derivatives, diazaanthraquinone or its derivatives.

25. The redox flow battery according to any one of claims 1 to 24, wherein: The E° of the at least one active redox species of the negative electrolyte is at least 0.6 V lower than the E° of the reaction:

26. The redox flow battery according to any one of claims 1 to 25, wherein: The at least one active redox species of the negative electrode electrolyte is a proton, and the redox reaction of the proton in the negative electrode electrolyte is 27. The redox flow battery according to any one of claims 1 to 26, wherein: The thermally activated carbon-based electrode is selected from the group consisting of graphite felt, carbon felt, graphite cloth, graphite nanoparticles, graphite nanofibers, carbon cloth, carbon nanotubes, carbon nanoparticles or carbon nanofiber thermally activated electrodes.

28. The redox flow battery according to any one of claims 1 to 27, wherein: The thermally activated carbon-based electrode is a graphite felt thermally activated electrode.

29. The redox flow battery according to any one of claims 1 to 28, wherein: The positive electrode is coupled to at least one side-flow type flow field.

30. The redox flow battery according to claim 29, wherein: The side-stream type flow field comprises a channel design selected from the group consisting of a single serpentine channel design, a multi-serpentine channel design and a parallel channel design.

31. A method for storing electricity, comprising the steps of: a) providing a redox flow battery according to any one of claims 1 to 30; b) electrically connecting the redox flow battery to a power source.

32. A method of transmitting electric power, comprising the steps of: a) providing a redox flow battery according to any one of claims 1 to 30; b) electrically connecting the redox flow battery to a load.

33. Use of a thermally activated carbon-based electrode in combination with at least one complexing agent for inhibiting the precipitation of MnO2 in an electrolyte comprising at least one manganese ion during operation of a redox flow battery, wherein the at least one complexing agent is selected from the group consisting of titanium ions, tin ions, chromium ions, aluminum ions, vanadium ions, cerium ions, or mixtures thereof, wherein the redox reaction of the manganese ion in the electrolyte is 34. The use according to claim 33, wherein The thermally activated carbon-based electrode is selected from the group consisting of graphite felt, carbon felt, graphite cloth, graphite nanoparticles, graphite nanofibers, carbon cloth, carbon nanotubes, carbon nanoparticles or carbon nanofiber thermally activated electrodes.

35. The use according to claim 33 or 34, wherein The thermally activated carbon-based electrode is a graphite felt thermally activated electrode.

36. The use according to any one of claims 33 to 35, wherein The complexing agent includes titanium ions or tin ions.

37. The use according to any one of claims 33 to 36, wherein The electrolyte includes the at least one complexing agent at a concentration of 0.1M to 8M.

38. The use according to claim 37, wherein The electrolyte comprises the at least one complexing agent at a concentration of 0.25M to 6M.

39. The use according to claim 37, wherein The electrolyte comprises the at least one complexing agent at a concentration of 0.5M to 5M.

40. The use according to any one of claims 33 to 39, wherein The molar ratio between the at least one manganese ion and the at least one complexing agent is from 0.1 to 2.

41. The use according to claim 40, wherein The molar ratio between the at least one manganese ion and the at least one complexing agent is from 0.25 to 1.5.

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