Balancing reactor for an electrochemical energy storage system

Abstract

Chemical balancing reactor (40) for an electrochemical energy storage system (21), the balancing reactor (40) comprising: - a first compartment (41) for circulating an electrolyte solution (24) containing permanganate ions, - a second compartment (42) for circulating a gaseous mixture containing at least dihydrogen, - a separator (43) extending between the first compartment (41) and the second compartment (42), the separator comprising a porous membrane, suitable for allowing contact between the gaseous mixture and the electrolyte solution (24), and for preventing the passage of the electrolyte solution (24) from the first compartment (41) into the second compartment (42). Figure to be published with the abbreviation: 2

Description

Title of the invention: Balancing reactor for an electrochemical energy storage system Technical field of the invention

[0001] The invention belongs to the field of electrochemical storage of electrical energy, in particular for stationary and / or long-term storage applications.

[0002] More specifically, the invention is part of the field of circulation batteries, and more specifically of zinc-permanganate circulation batteries.

[0003] The invention relates to a balancing reactor for an electro-chemical energy storage system, as well as an energy storage system comprising such a reactor. Prior art

[0004] Energy storage is essential for the stability of an electrical grid. Indeed, on an electrical grid, at any given time, every source of electricity generation injects electricity into the grid, which must be compensated by an equivalent consumption. Any imbalance between total production and total consumption has detrimental effects on all production and consumption resources connected to that grid.

[0005] A buffer in the form of reversible electricity storage is therefore essential to balance the grid and compensate for any difference between electricity production and consumption. This buffer or electricity storage becomes all the more essential when intermittent production methods, such as photovoltaic or wind power sources, are integrated into the grid. It can also be advantageous to store surplus electricity, for example at peak sunlight hours, on photovoltaic panels, for use when this photovoltaic source is no longer available, for example at night.

[0006] Centralized storage systems such as pumped storage hydroelectric plants (PSHPs) now exist, connected to the electrical grid. However, the possibilities for installing new PSHPs are limited by the geographical characteristics required for such an installation.

[0007] New decentralized electrochemical storage systems, using lithium-ion batteries for example, are beginning to be installed on the grid to supplement existing storage and stabilize the electricity grid. However, the high demand for batteries, particularly linked to the very rapid growth of electric vehicles, is creating supply constraints for the raw materials needed to manufacture these batteries.

[0008] New generation batteries, called circulation batteries, or "Redox Flow Batteries" in English, are beginning to be developed for such applications. Such a battery is characterized by storing the active material necessary for the electrochemical reaction of storing and releasing electrical energy in the form of a liquid electrolyte, generally in aqueous solution, in tanks placed away from the main reactor.

[0009] Circulation batteries offer a number of advantages over conventional batteries. For example, they can use a wider range of electrolytes, and the aqueous nature of the electrolytes, which makes them non-flammable, gives them superior safety.

[0010] Furthermore, their energy storage capacity can be increased without changing their rated power, simply by increasing the amount of electrolyte stored in the tanks, whereas conventional batteries require multiple tanks to increase capacity. The marginal cost of stored energy can therefore be significantly reduced, particularly for large installations, since such a modification only requires adding active material and increasing the size of the tanks. The operating principle of such a circulation battery is illustrated in [Fig. 1]. [Fig. 1] represents a hybrid circulation battery 1, in which part of the material storing energy in electrochemical form is contained in the main reactor.

[0011] The circulating battery 1 comprises a main reactor 2, a first reservoir 3 containing a first electrolyte solution 4 and a second reservoir 5 containing a second electrolyte solution 6.

[0012] The main reactor 2 comprises a first compartment 7 and a second compartment 8 separated by an ion exchange membrane 9, in which circulate respectively the first electrolyte solution 4 and the second electrolyte solution 6, brought by a first feed circuit 10 and a second feed circuit 11 equipped respectively with a first pump 12 and a second pump 13.

[0013] The main reactor 2 is represented in a simplified manner and thus comprises only one cell formed from the first compartment 7 and the second compartment 8 separated by the membrane 9, whereas in practice, the reactor comprises a plurality of such cells connected in series to each other and supplied by the first supply circuit 10 and the second supply circuit 11, the first reservoir 3 and the second reservoir 5 being common and shared by the plurality of cells.

[0014] Among hybrid circulation batteries, some use, for one of the electrolytes, an aqueous zinc-based solution, and an electrode containing zinc. Some Examples of zinc-based hybrid circulation batteries include zinc-bromine and zinc-iron batteries. The use of zinc as the active material at the negative electrode, the anode, has the advantage of being compatible with an aqueous electrolyte, using a metal that is much more abundant than the elements used in lithium-ion batteries, and being able to store a high charge in a relatively small amount of zinc with an interesting electrochemical potential.

[0015] The use of permanganate as an active material in alkaline solution at the positive electrode, the cathode, using the manganate / permanganate couple (MnO42 / MnO4 ), is particularly interesting because it allows the use of an abundant active material with a high electrochemical potential in aqueous medium.

[0016] A circulation battery combining these two electrochemical couples in an alkaline medium according to the following equation 1 then makes it possible to have an interesting voltage of 1.8 volts by using abundant components.

[0017] [Chem. 1]

[0018] 2 MnO4 + Zn 2 MnO? + Zn2+

[0019] During discharge, the zinc in the negative electrode is oxidized to produce zincate ions, and the permanganate ions are reduced to produce manganate ions. The reverse reactions occur during battery charging.

[0020] Such a circulation battery implementing these two couples is described for example in document CN 11053478 A.

[0021] However, these batteries do not give complete satisfaction.

[0022] Indeed, during charging, a parasitic reaction may take place at the negative electrode, according to the equation below.

[0023] [Chem. 2]

[0024] 2 H2O + 2e H2 + 2 OH

[0025] This side reaction has the effect of consuming manganate ions at the positive electrode to supply the electrons required for reaction 1, without depositing the equivalent amount of zinc metal at the negative electrode. Thus, during the next discharge, the amount of zinc metal available for discharge will be correspondingly reduced.

[0026] A second chemical, and not electrochemical, self-discharge reaction also occurs naturally in the battery, according to equation 3 below. This reaction also consumes metallic zinc without consuming the equivalent amount of permanganate ions.

[0027] [Chem. 3]

[0028] Zn + 2H2O + 2OH H2 + [Zn(OH)4]2

[0029] Reactions 2 and 3 result in an imbalance of charges between the negative and positive compartments. The negative compartment will gradually be depleted of metallic zinc at the end of charging, and the negative compartment will contain more and more of The permanganate is released at the end of the charge, at the expense of the manganate content. The storage capacity of the zinc / permanganate battery therefore gradually decreases with each charge cycle, due to this parasitic reaction, and over time due to self-discharge.

[0030] A known solution involves regenerating the positive compartment by draining the negative compartment and replacing it with a fresh permanganate solution. However, this solution is cumbersome and requires the installation to be shut down to allow for the replenishment, without providing electricity storage. Presentation of the invention

[0031] The invention aims to remedy these drawbacks by providing a circulation battery that allows the use of zinc and permanganate without progressive loss of capacity and does not require renewal of electrolytes.

[0032] To this end, the invention relates to a chemical balancing reactor for an electrochemical energy storage system, the balancing reactor comprising:

[0033] - a first circulation compartment of an electrolyte solution containing permanganate ions,

[0034] - a second circulation compartment for a gaseous mixture containing at least dihydrogen,

[0035] - a separator extending between the first compartment and the second compartment compartment, the separator comprising a porous membrane, suitable for allowing contact between the gas mixture and the electrolyte solution, while preventing the passage of the electrolyte solution from the first compartment into the second compartment.

[0036] Such a reactor is capable of continuously bringing the electrolyte solution and dihydrogen into contact to reduce permanganate ions into manganate ions, thus allowing the rebalancing of the electrolytes of the electrochemical energy storage system continuously and without external intervention.

[0037] The porous membrane may comprise a fabric on which a carbon powder and a hydrophobic binder, such as polytetrafluoroethylene, are deposited.

[0038] Such a characteristic allows the dihydrogen and the electrolyte solution to come into contact without migration of the solution into the second compartment.

[0039] The separator may include at least one catalyst for the oxidation reaction of dihydrogen and / or at least one catalyst for the reduction reaction of permanganate.

[0040] Such a characteristic makes it possible to facilitate the chemical reaction between dihydrogen and permanganate in the balancing reactor.

[0041] The separator may include a catalyst comprising platinum.

[0042] Such a characteristic allows the same catalyst to be used for both reactions.

[0043] The catalyst may comprise a metallic platinum powder dispersed on the porous membrane.

[0044] Such a characteristic makes it possible to obtain a good specific surface area and simplifies the placement of the catalyst on the separator.

[0045] The invention also relates to an electrochemical energy storage system comprising:

[0046] - a first reservoir containing a first electrolyte solution containing permanganate ions and manganate ions,

[0047] - a second reservoir containing a second electrolyte solution containing zincate ions,

[0048] - a main reactor adapted to allow the transfer of protons or anions hydroxyl, and electrons between the first electrolyte solution and the second electrolyte solution according to at least one redox reaction,

[0049] - a first circulation circuit of the first electrolyte solution between the first tank and main reactor,

[0050] - a second circulation circuit of the second electrolyte solution between the second tank and main reactor, and

[0051] - a balancing reactor as above, in which the first compartment is mounted in series in the first circulation circuit, and in which the second compartment is supplied with dihydrogen taken from the second tank.

[0052] Such an energy storage system makes it possible to benefit from the advantages obtained by the use of zinc / zincate and manganate / permanganate electrochemical couples, while compensating for the effects of parasitic and discharge reactions continuously and without external intervention.

[0053] The main reactor may include a negative electrode for the zinc / zincate couple.

[0054] The negative electrode can be a metal zinc plate or a zinc electrode made from a mixture of zinc oxide, calcium zincate, an electronically conductive additive and a binder.

[0055] The negative electrode may include a carbon felt disposed in the main reactor, and the second electrolyte solution may be an aqueous solution of potassium zincate or sodium zincate.

[0056] The first electrolyte solution can be an alkaline solution of sodium manganate or potassium manganate.

[0057] The balancing reactor can be configured to react the first electrolyte solution and the dihydrogen taken from the second reservoir continuously and automatically.

[0058] Such a characteristic makes it possible to chemically rebalance the solutions electrolyte is added as the energy storage system operates, to counteract the effects of parasitic reactions, without requiring external intervention. Brief description of the figures

[0059] [Fig. 1] is a schematic representation of the operation of a circulating battery,

[0060] [Fig.2] is a schematic view of a circulating battery according to the invention,

[0061] [Fig.3] is a schematic view of a battery rebalancing reactor of the [Fig.2] in a test setup, and

[0062] [Fig.4] is a graphical representation of the evolution of the absorbance spectrum of a electrolyte solution in the setup of [Fig.3]. Detailed description of the invention

[0063] A circulation battery 21 according to the invention is shown in [Fig.2]. The circulation battery 21 is an electrochemical energy storage system, designed to receive energy in electrical form for storage, and then release it in the form of electrical energy.

[0064] The circulating battery 21 comprises a main reactor 22, a first reservoir 23 containing a first electrolyte solution 24 and a second reservoir 25 containing a second electrolyte solution 26.

[0065] According to the invention, the circulating battery 21 also includes a balancing chemical reactor 40.

[0066] The first electrolyte solution 24 is an aqueous solution containing manganate MnO4 and permanganate MnO42 ions in a basic medium, contained in the first reservoir 23 and circulating in a first supply circuit 30 to the main reactor 22 at the positive electrode and then returning to the first reservoir 23 by a first return circuit 32.

[0067] The first electrolyte solution 24 is, for example, an alkaline solution of sodium manganate or potassium manganate.

[0068] The first electrolyte solution 24 fills at least partially the first reservoir 23, and, in the case of partial filling, a sky forms above solution 24.

[0069] The first supply circuit 30 takes the first electrolyte solution 24 from the first reservoir 23 and conveys it to an inlet of the main reactor 22.

[0070] The first return circuit 32 carries the first electrolyte solution 24 from an outlet of the main reactor 22, through the balancing reactor 40, to the first tank 23. The return circuit 32 opens into the first tank 23 and the first electrolyte solution 24 circulates in the return circuit 32 to the first reservoir 23 if necessary.

[0071] The first electrolyte solution 24 is driven through the first feed circuit 30, the main reactor 22, the balancing reactor 40 and the first return circuit 32 by the action of at least one first pump 35.

[0072] Each first pump 35 is mounted on the first supply circuit 30 or on the first return circuit 32. The first pump 35 is, for example, a circulation pump or a peristaltic pump.

[0073] The second electrolyte solution 26 is an aqueous solution containing zincate ions [Zn(OH)4]2 in a basic medium, contained in the second reservoir 25 and circulating in a second feed circuit 31 to the main reactor 22 at the negative electrode, then returning to the second reservoir 25 by a second return circuit 33.

[0074] The second electrolyte solution 26 is, for example, a solution of sodium zincate or potassium zincate.

[0075] The second electrolyte solution 26 partially fills the second reservoir 25, and forms in the second reservoir 25 a sky comprising in particular dihydrogen H2, produced by the parasitic reaction 2 and by the self-discharge reaction 3 previously described, and separated from the liquid phase by gravimetric separation.

[0076] The second supply circuit 31 takes the second electrolyte solution 26 from the second reservoir 25 and conveys it to an inlet of the main reactor 22.

[0077] The second return circuit 33 carries the second electrolyte solution 26 from an outlet of the main reactor 22 to the second tank 25, without passing through the balancing reactor 40. The second return circuit 33 opens into the second tank 25 and the second electrolyte solution 26 flows from the outlet of the second return circuit 33 into the second tank 25.

[0078] The second electrolyte solution 26 is driven through the second feed circuit 31, the main reactor 22 and the second return circuit 33 by the action of at least one second pump 36.

[0079] Each second pump 36 is mounted on the second supply circuit 31 or on the second return circuit 33. The second pump 36 is, for example, a circulation pump or a peristaltic pump.

[0080] The main reactor 22 comprises a first compartment 27 and a second compartment 28 separated by a cationic or anionic membrane 29.

[0081] As indicated above, the main reactor 22 is represented in a simplified manner and thus comprises only a single cell formed from the first compartment 27 and the second compartment 28 separated by the membrane 29, whereas in practice, the The main reactor 22 comprises a plurality of such cells connected in series to one another and supplied by the first supply circuit 30 and the second supply circuit 31, the first tank 23 and the second tank 25 being common and shared by the plurality of cells.

[0082] Moreover, the balancing reactor 40 is advantageously shared between a plurality of such cells, and preferably by all the cells of the main reactor 22.

[0083] The first compartment 27 receives the circulation of the manganate and permanganate ion solution and the positive electrode while the second compartment 28 receives the circulation of the zincate ion solution and the negative electrode.

[0084] The positive electrode consists of a carbon felt 34 through which the aqueous solution containing manganate and permanganate ions circulates.

[0085] The negative electrode for the Zn / Zn2+ couple can be a zinc metal plate or a zinc electrode made from a mixture of zinc oxide, calcium zincate, an electronically conductive additive and a binder, as described in document FR 3091042 AL

[0086] The negative electrode can also be made of the carbon felt 34 on which the reduction of a potassium zincate solution is carried out, as shown in [Fig.2]. In this case, the second electrolyte solution 26 is more specifically a saturated or supersaturated aqueous solution of potassium zincate or sodium zincate.

[0087] The carbon felt 34 constitutes a high-surface-area electrode in contact with the electrolyte solutions 24, 26 and offers good permeability for the flow of electrolytes. The membrane 29 allows ion exchange between the compartments while blocking electron flow. The membrane 29 is, for example, of the type marketed by Fumasep under the designation FKE-50 or of the type marketed by Chemours under the name Nafion 115 (registered trademark).

[0088] The balancing reactor 40 is adapted to regenerate the manganate ions consumed by the side reaction 2 and the self-discharge reaction 3, using the dihydrogen generated by these two reactions to reduce the excess permanganate ions in the first electrolyte solution. This regeneration is carried out according to the following equation:

[0089] [Chem. 4]

[0090] 2[MnO4] + H2 + 2OH -> 2[MnO4]2 + 2H2O

[0091] In this way, the imbalance between the quantity of manganate ions and the quantity of permanganate ions in the first electrolyte solution 24 caused by reactions 2 and 3 is automatically rebalanced by an amount of dihydrogen produced in stoichiometric proportions by the same reactions 2 and 3.

[0092] Manganate ions not resulting from the electrochemical discharge reaction, due to lack to have sufficient zinc metal, are then produced by chemical reaction 4 with parasitic dihydrogen.

[0093] The rebalancing reactor 40 comprises a first compartment 41 for circulating the first electrolyte solution containing permanganate ions, and a second compartment 42 for circulating a gaseous mixture containing at least dihydrogen, as well as a separator 43 extending between the first compartment 41 and the second compartment 42.

[0094] The separator 43 includes a porous membrane, designed to allow the passage of the gas mixture from the second compartment 42 and to prevent the passage of the first electrolyte solution 24 from the first compartment 4L

[0095] Thus, the porous membrane makes it possible to form an interface between a liquid phase and a gaseous phase without flooding the second compartment 42.

[0096] The porous membrane comprises, for example, a fabric on which a carbon powder and a hydrophobic binder, such as polytetrafluoroethylene, are deposited.

[0097] The hydrophobic properties of the binder prevent the liquid phase consisting of the first electrolyte solution 24 from passing through the porous membrane.

[0098] The separator 43 also advantageously comprises a catalyst for the oxidation reaction of dihydrogen and / or at least one catalyst for the reduction reaction of permanganate.

[0099] The catalyst includes, for example, platinum, in particular a metallic platinum powder dispersed on the membrane.

[0100] The first compartment 41 is placed in series in the first supply circuit 30 or in the first return circuit 32, the first electrolyte solution 24 comprising the permanganate ions entering at one end of the first compartment 41 and exiting at the other end.

[0101] The second compartment 42 is supplied with a gaseous mixture containing dihydrogen by a sampling circuit 44 arranged to sample the gaseous mixture from the top of the second tank 25, and circulate this gaseous mixture into the second compartment 42.

[0102] The quantity of hydrogen required to rebalance the first electrolyte solution 24 in the first compartment 41 is exactly the same as the quantity of hydrogen produced by the side reactions 2 and 3. The rebalancing reactor 40 therefore allows the first electrolyte solution 24 to be rebalanced automatically and continuously, without requiring any external intervention.

[0103] This effect was demonstrated by the applicant in an experiment monitoring the concentrations of manganate and permanganate ions in the aqueous electrolyte solution in the rebalancing reactor 40 as described above, in a assembly shown in [Fig.3].

[0104] The first compartment 41 has been placed in a circulation circuit 50 of a solution of manganate and permanganate ions 24, driven by a peristaltic pump 51. The second compartment 42 is supplied with dihydrogen by an external source 52.

[0105] The measurement of manganate and permanganate ion concentrations was carried out based on UV / visible spectrometry using Beer-Lambert's law.

[0106] Small amounts of the solution circulating in the rebalancing tank were taken from the circuit at different time intervals to perform a UV / visible spectrum of this solution and to monitor the progress of the reduction of permanganate by hydrogen.

[0107] Figure 4 shows the absorbance spectra A of the alkaline sodium permanganate solution as a function of wavelength X, over the UV / visible spectrum. The spectra are measured respectively before reduction (denoted t0), and after 20 minutes, 60 minutes, 100 minutes and 120 minutes of circulation in the rebalancing reactor 40.

[0108] These results show that the absorbance of the wavelength bands associated with permanganate decreases and that the absorbance of those associated with manganate increases with the circulation time through reactor 40 following reduction by hydrogen.

[0109] Thus, the efficiency of the rebalancing reactor 40 is established for the reduction of permanganate to manganate in the electrolyte solution 24.

Claims

Demands

1. Chemical balancing reactor (40) for an electrochemical energy storage system (21), the balancing reactor (40) comprising: - a first compartment (41) for circulating an electrolyte solution (24) containing permanganate ions, - a second compartment (42) for circulating a gaseous mixture containing at least dihydrogen, - a separator (43) extending between the first compartment (41) and the second compartment (42), the separator comprising a porous membrane, suitable for allowing contact between the gaseous mixture and the electrolyte solution (24), while preventing the passage of the electrolyte solution (24) from the first compartment (41) into the second compartment (42).

2. Balancing reactor (40) according to claim 1, wherein the porous membrane comprises a fabric on which are deposited a carbon powder and a hydrophobic binder, such as polytetrafluoroethylene.

3. Balancing reactor (40) according to claim 1 or 2, wherein the separator (43) comprises at least one catalyst for the oxidation reaction of dihydrogen and / or at least one catalyst for the reduction reaction of permanganate.

4. Balancing reactor (40) according to claim 3, wherein the separator comprises a catalyst comprising platinum.

5. Balancing reactor (40) according to claim 4, wherein the catalyst comprises a metallic platinum powder dispersed on the porous membrane.

6. An electrochemical energy storage system (21) comprising: - a first reservoir (23) containing a first electrolyte solution (24) containing permanganate and manganate ions, - a second reservoir (25) containing a second electrolyte solution (26) containing zincate ions, - a main reactor (22) adapted to allow the transfer of protons or hydroxyl anions and electrons between the first electrolyte solution (24) and the second electrolyte solution (26) according to at least one redox reaction, - a first circulation circuit (30, 32) for the first electrolyte solution (24) between the first reservoir (23) and the main reactor (22), - a second circulation circuit (31, 33) of the second electrolyte solution (26) between the second tank (25) and the main reactor (22), and - a balancing reactor (40) according to any one of the preceding claims, in which the first compartment (41) is mounted in series in the first circulation circuit (30, 32), and in which the second compartment (42) is supplied with dihydrogen taken from the second tank (25).

7. Electro-chemical energy storage system (21) according to claim 6, wherein the main reactor (22) comprises a negative electrode for the zinc / zincate couple.

8. Electro-chemical energy storage system (21) according to claim 7, wherein the negative electrode is a metal zinc plate or a zinc electrode made from a mixture of zinc oxide, calcium zincate, an electronically conductive additive and a binder.

9. Electrochemical energy storage system (21) according to claim 7, wherein the negative electrode comprises a carbon felt (34) disposed in the main reactor (22), and wherein the second electrolyte solution (26) is an aqueous solution of potassium zincate or sodium zincate.

10. Electrochemical energy storage system (21) according to any one of claims 6 to 9, wherein the first electrolyte solution (24) is an alkaline solution of sodium manganate or potassium manganate.

11. Electro-chemical energy storage system (21) according to any one of claims 6 to 10, wherein the balancing reactor (40) is configured to react the first electrolyte solution (24) and the dihydrogen taken from the second reservoir (25) continuously and automatically.

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