Balancing reactor for an electro-chemical energy storage system

Abstract

The invention relates to a chemical balancing reactor (40) for an electro-chemical 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 gas mixture containing at least dihydrogen; and - a separator (43) which extends between the first compartment (41) and the second compartment (42), the separator comprising a porous membrane which is suitable for allowing contact between the gas mixture and the electrolyte solution (24) and for preventing the electrolyte solution (24) from passing from the first compartment (41) into the second compartment (42).

Description

[0001] DESCRIPTION

[0002] TITLE: Balancing reactor for an electrochemical energy storage system

[0003] Technical field of the invention

[0004] The invention belongs to the field of electrochemical storage of electrical energy, in particular for stationary and / or long-term storage applications.

[0005] More specifically, the invention falls within the field of flow batteries, and more specifically zinc-permanganate flow batteries.

[0006] The invention relates to a balancing reactor for an electrochemical energy storage system, as well as to an energy storage system comprising such a reactor.

[0007] State of the prior art

[0008] Energy storage is a critical component of a stable electricity grid. On an electricity grid, at any given time, every source of electricity production injects electricity into the grid, which must be offset by equivalent consumption. Any imbalance between total production and total consumption has adverse effects on all means of production and consumption connected to the grid.

[0009] A buffer in the form of reversible electricity storage is therefore essential to balance the network and compensate for any difference between electricity production and consumption. This buffer or electricity storage becomes even more essential when intermittent production means, such as photovoltaic or wind energy sources, are integrated into the network. It can also be interesting to store electricity when it is produced in surplus, for example at peak sunshine, on photovoltaic panels, to use it when this photovoltaic source is no longer available, during the night for example.

[0010] Centralized storage systems such as pumped storage stations (PSTs) are currently available and are connected to the electricity grid. However, the possibilities for installing new PSTs are limited by the geographical characteristics required for such an installation.

[0011] New decentralized electrochemical storage systems, using batteries such as lithium-ion batteries, are beginning to be installed on the grid to supplement existing storage and stabilize the electricity network. However, the high demand for batteries, particularly linked to the very rapid growth of electric vehicles, brings constraints to the supply of raw materials needed to manufacture these batteries. New generation batteries, called circulation batteries, or "Redox Flow Batteries" in English, are beginning to be developed for such applications. Such a battery has the particularity of storing the active material necessary for the electrochemical reaction of storage and restitution of electrical energy in the form of liquid electrolyte, generally in aqueous solution, in tanks placed away from the main reactor.

[0012] Flow batteries have several 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, makes them safer.

[0013] Furthermore, their energy storage capacity can be increased without changing the nominal power, simply by increasing the amount of electrolyte stored in the tanks, whereas conventional batteries must be multiplied to increase capacity. The marginal cost of stored energy can therefore be made much lower, particularly for large installations, since such a modification only requires adding active material and increasing the size of the tanks.

[0014] The principle of operation of such a flow battery is illustrated in Figure 1. Figure 1 represents a flow battery 1 of the hybrid flow type, in which part of the material storing energy in electrochemical form is contained in the main reactor.

[0015] The circulation battery 1 comprises a main reactor 2, a first tank 3 containing a first electrolyte solution 4 and a second tank 5 containing a second electrolyte solution 6.

[0016] The main reactor 2 comprises a first compartment 7 and a second compartment 8 separated by an ion exchange membrane 9, in which the first electrolyte solution 4 and the second electrolyte solution 6 circulate respectively, supplied by a first supply circuit 10 and a second supply circuit 11 provided respectively with a first pump 12 and a second pump 13.

[0017] The main reactor 2 is represented in a simplified manner and thus comprises only a single cell formed of 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.

[0018] Among hybrid flow batteries, some use an aqueous zinc-based solution as one of the electrolytes, and an electrode containing zinc. Some examples of zinc-based hybrid flow batteries are zinc-bromine batteries or 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, of using a metal that is much more abundant than the elements used for lithium-ion batteries, and of being able to store a high charge in a relatively small amount of zinc with an interesting electrochemical potential.

[0019] The use of permanganate as an active material in alkaline solution at the positive electrode, the cathode, using the manganate / permanganate couple (MnC / MnC ), is particularly interesting because it allows the use of an abundant active material with a high electrochemical potential in an aqueous medium.

[0020] 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.

[0021] [Chem. 1]

[0022] 2 MnC ' + Zn «-> 2 MnC 2- + Zn 2+

[0023] 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.

[0024] Such a circulation battery using these two pairs is for example described in document CN 1 1053478 A.

[0025] However, these batteries do not give complete satisfaction.

[0026] Indeed, during charging, a parasitic reaction can take place at the negative electrode, according to the equation below.

[0027] [Chem. 2]

[0028] 2 H2O + 2e - H2+ 2 OH-

[0029] This parasitic reaction has the effect of consuming manganate ions at the positive electrode to provide the electrons needed 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 reduced accordingly.

[0030] A second chemical, not electrochemical, self-discharge reaction also occurs naturally in the battery, according to equation 3 below. This reaction also consumes zinc metal without consuming the equivalent of permanganate ions.

[0031] [Chem. 3]

[0032] Zn + 2H2O + 2OH- H2+ [Zn(OH)4] 2 '

[0033] Reactions 2 and 3 have the effect of unbalancing the charges between the negative and positive compartments. The negative compartment will gradually be devoid of zinc metal at the end of the charge and the negative compartment will contain more and more permanganate at the end of the charge, to the detriment of the quantity of manganate. The storage capacity of the zinc / permanganate battery therefore gradually decreases with each charge cycle, due to the parasitic reaction and over time with self-discharge.

[0034] A known solution is to regenerate the positive compartment by draining the negative compartment and replacing it with a fresh permanganate solution. However, this solution is restrictive and requires the installation to be shut down to ensure renewal, without being able to ensure electricity storage.

[0035] Presentation of the invention

[0036] The invention aims to overcome these drawbacks by providing a circulation battery allowing the use of zinc and permanganate without progressive loss of capacity and not requiring renewal of the electrolytes.

[0037] To this end, the invention relates to a chemical balancing reactor for an electrochemical energy storage system, the balancing reactor comprising:

[0038] - a first compartment for circulating an electrolyte solution containing permanganate ions,

[0039] - a second compartment for circulating a gas mixture containing at least dihydrogen,

[0040] - a separator extending between the first compartment and the second compartment, the separator comprising a porous membrane, capable of 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.

[0041] Such a reactor is capable of continuously bringing the electrolyte solution and dihydrogen into contact to reduce the permanganate ions to manganate ions, thus allowing the rebalancing of the electrolytes of the electrochemical energy storage system continuously and without external intervention.

[0042] The porous membrane may comprise a fabric on which a carbon powder and a hydrophobic binder, such as polytetrafluoroethylene, are deposited.

[0043] Such a feature allows for contact between the dihydrogen and the electrolyte solution without migration of the solution into the second compartment.

[0044] The separator may comprise at least one catalyst for the hydrogen oxidation reaction and / or at least one catalyst for the permanganate reduction reaction.

[0045] Such a feature helps facilitate the chemical reaction between dihydrogen and permanganate in the balancing reactor.

[0046] The separator may comprise a catalyst comprising platinum.

[0047] Such a feature allows the use of the same catalyst for both reactions. The catalyst may comprise a platinum metal powder dispersed on the porous membrane.

[0048] Such a characteristic allows to obtain a good specific surface and simplifies the installation of the catalyst on the separator.

[0049] The invention also relates to an electrochemical energy storage system comprising:

[0050] - a first reservoir containing a first electrolyte solution containing permanganate ions and manganate ions,

[0051] - a second reservoir containing a second electrolyte solution containing zincate ions,

[0052] - a main reactor adapted to allow a transfer of protons or hydroxyl anions, and electrons between the first electrolyte solution and the second electrolyte solution according to at least one oxidation-reduction reaction,

[0053] - a first circuit for circulating the first electrolyte solution between the first tank and the main reactor,

[0054] - a second circuit for circulating the second electrolyte solution between the second tank and the main reactor, and

[0055] - a balancing reactor according to one of the preceding claims, in which the first compartment is connected in series in the first circulation circuit, and in which the second compartment is supplied with dihydrogen taken from the second tank.

[0056] Such an energy storage system allows 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.

[0057] The main reactor may include a negative electrode for the zinc / zincate couple.

[0058] The negative electrode 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.

[0059] The negative electrode may comprise a carbon felt disposed in the main reactor, and the second electrolyte solution may be an aqueous solution of potassium zincate or sodium zincate.

[0060] The first electrolyte solution can be an alkaline solution of sodium manganate or potassium manganate.

[0061] The balancing reactor can be configured to react the first electrolyte solution and the hydrogen taken from the second tank continuously and automatically. Such a feature allows the electrolyte solutions to be chemically rebalanced as the energy storage system operates, to counteract the effects of parasitic reactions, without requiring external intervention.

[0062] Brief description of the figures

[0063] [Fig. 1] is a schematic representation of the operation of a flow battery, [Fig. 2] is a schematic view of a flow battery according to the invention,

[0064] [Fig. 3] is a schematic view of a battery rebalancing reactor of Figure 2 in a test setup, and

[0065] [Fig. 4] is a graphical representation of the evolution of the absorbance spectrum of an electrolyte solution in the setup of Figure 3.

[0066] Detailed description of the invention

[0067] A flow battery 21 according to the invention is shown in Figure 2. The flow battery 21 is an electrochemical energy storage system, capable of receiving energy in electrical form to store it, then restoring it in the form of electrical energy.

[0068] The flow 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.

[0069] According to the invention, the circulation battery 21 also comprises a chemical balancing reactor 40.

[0070] The first electrolyte solution 24 is an aqueous solution containing manganate ions MnC - and permanganate MnC 2- in 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 then returning to the first reservoir 23 by a first return circuit 32.

[0071] The first electrolyte solution 24 is for example an alkaline solution of sodium manganate or potassium manganate.

[0072] The first electrolyte solution 24 at least partially fills the first reservoir 23, and, in the case of partial filling, a cloud forms above the solution 24.

[0073] 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.

[0074] 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 reservoir 23. The return circuit 32 opens into the first reservoir 23 and the first electrolyte solution 24 circulates in the return circuit 32 to the first reservoir 23 if applicable. The first electrolyte solution 24 is driven through the first feed circuit

[0075] 30, the main reactor 22, the balancing reactor 40 and the first return circuit 32 by the action of at least a first pump 35.

[0076] 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.

[0077] The second electrolyte solution 26 is an aqueous solution containing zincate ions [Zn(OH)4] 2- in basic medium, contained in the second tank 25 and circulating in a second supply circuit 31 to the main reactor 22 at the negative electrode, then returning to the second tank 25 by a second return circuit 33.

[0078] The second electrolyte solution 26 is for example a sodium zincate or potassium zincate solution.

[0079] The second electrolyte solution 26 partially fills the second reservoir 25, and forms in the second reservoir 25 a canopy 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.

[0080] The second feed circuit 31 takes the second electrolyte solution 26 from the second tank 25 and conveys it to an inlet of the main reactor 22.

[0081] The second return circuit 33 conveys the second electrolyte solution 26 from an outlet of the main reactor 22 to the second reservoir 25, without passing through the balancing reactor 40. The second return circuit 33 opens into the second reservoir 25 and the second electrolyte solution 26 flows at the outlet of the second return circuit 33 into the second reservoir 25.

[0082] The second electrolyte solution 26 is driven through the second feed circuit

[0083] 31, the main reactor 22 and the second return circuit 33 by the action of at least one second pump 36.

[0084] 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.

[0085] The main reactor 22 comprises a first compartment 27 and a second compartment 28 separated by a cationic or anionic membrane 29.

[0086] As indicated above, the main reactor 22 is represented in a simplified manner and thus comprises only a single cell formed of the first compartment 27 and the second compartment 28 separated by the membrane 29, whereas in practice, the main reactor 22 comprises a plurality of such cells connected in series to each other and supplied by the first supply circuit 30 and the second supply circuit 31, the first reservoir 23 and the second reservoir 25 being common and shared by the plurality of cells. In addition, the balancing reactor 40 is advantageously shared between a plurality of such cells, and preferably by all the cells of the main reactor 22.

[0087] 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.

[0088] The positive electrode consists of a carbon 34 felt in which the aqueous solution containing manganate and permanganate ions circulates.

[0089] The negative electrode for the Zn / Zn couple 2+ may 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 A1. The negative electrode may also be made of the carbon felt 34 on which the reduction of a potassium zincate solution takes place, as shown in Figure 2. In this case, the second electrolyte solution 26 is more specifically a saturated or supersaturated aqueous solution of potassium zincate or sodium zincate.

[0090] The carbon felt 34 constitutes an electrode with a high contact surface with the electrolyte solutions 24, 26 and offers good permeability for the circulation of electrolyte flows. The membrane 29 allows the exchange of ions between the compartments while blocking the flow of electrons. The membrane 29 is for example of the type marketed by the company Fumasep under the acronym FKE-50 or of the type marketed by the company Chemours under the name Nation 115 (registered trademark).

[0091] The balancing reactor 40 is adapted to regenerate the manganate ions consumed by the parasitic reaction 2 and the self-discharge reaction 3, by using the dihydrogen generated by these two reactions to reduce the excess permanganate ions in the first electrolyte solution. This regeneration is done according to the following equation: [Chem. 4] 2[MnO4]' + H2+ 2OH- 2[MnO4] 2 ' + 2H2O

[0092] In this way, the imbalance between the amount of manganate ions and the amount 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.

[0093] Manganate ions not produced by the electrochemical discharge reaction, due to a lack of zinc metal, are then produced by chemical reaction 4 with the parasitic dihydrogen.

[0094] 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 gas mixture containing at least dihydrogen, as well as a separator 43 extending between the first compartment 41 and the second compartment 42.

[0095] The separator 43 comprises a porous membrane, capable of allowing the passage of the gas mixture from the second compartment 42 and of preventing the passage of the first electrolyte solution 24 from the first compartment 41.

[0096] 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.

[0097] The porous membrane comprises, for example, a fabric on which a carbon powder and a hydrophobic binder, such as polytetrafluoroethylene, are deposited.

[0098] The hydrophobic properties of the binder make it possible to prevent the liquid phase constituted by the first electrolyte solution 24 from passing through the porous membrane.

[0099] The separator 43 also advantageously comprises a catalyst for the hydrogen oxidation reaction and / or at least one catalyst for the permanganate reduction reaction.

[0100] The catalyst comprises, for example, platinum, in particular a platinum metal powder dispersed on the membrane.

[0101] 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 leaving at the other end.

[0102] The second compartment 42 is supplied with a gas mixture containing dihydrogen by a sampling circuit 44 arranged to sample the gas mixture from the top of the second tank 25, and circulate this gas mixture in the second compartment 42.

[0103] 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 parasitic reactions 2 and 3. The rebalancing reactor 40 therefore makes it possible to rebalance the first electrolyte solution 24 automatically and continuously, without requiring external intervention.

[0104] 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 setup shown in Figure 3.

[0105] The first compartment 41 was 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. The measurement of the concentrations of manganate and permanganate ions was carried out based on UV / visible spectrometry using the Beer-Lambert law.

[0106] Small quantities of the solution circulating in the rebalancing tank were sampled from the circuit at different time intervals to perform a UV / visible spectrum of this solution and 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 the wavelength λ, on the UV / visible spectrum. The spectra are measured respectively before the reduction (denoted tO), and after 20 minutes, 60 minutes, 100 minutes and 120 minutes of circulation in the re-equilibration reactor 40. 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 the reactor 40 following the reduction by hydrogen.

[0108] Thus, the efficiency of the rebalancing reactor 40 is established for the reduction of permanganate to manganate in the electrolyte solution 24.

Claims

CLAIMS 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 gas 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, capable of allowing contact between the gas 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, in which the porous membrane comprises a fabric on which are deposited a carbon powder and a hydrophobic binder, such as for example polytetrafluoroethylene.

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

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

5. The balancing reactor (40) of claim 4, wherein the catalyst comprises a platinum metal powder dispersed on the porous membrane.

6. Electrochemical energy storage system (21) comprising: - a first reservoir (23) containing a first electrolyte solution (24) containing permanganate ions and manganate ions, - a second reservoir (25) containing a second electrolyte solution (26) containing zincate ions, - a main reactor (22) adapted to allow a 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 oxidation-reduction reaction, - a first circulation circuit (30, 32) of 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 one of the preceding claims, in which the first compartment (41) is connected 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. Electrochemical energy storage system (21) according to claim 6, wherein the main reactor (22) comprises at least one negative electrode for the zinc / zincate couple.

8. An electrochemical energy storage system (21) according to claim 7, wherein the negative electrode is a zinc metal 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 one of claims 6 to 9, wherein the first electrolyte solution (24) is an alkaline solution of sodium manganate or potassium manganate.

11. Electrochemical energy storage system (21) according to one of claims 6 to 10, in which the balancing reactor (40) is configured to react the first electrolyte solution (24) and the dihydrogen taken from the second tank (25) continuously and automatically.

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