Process for recycling aqueous posolyte from a redox flow battery

Abstract

Process for recycling aqueous posolyte from a redox flow battery. The present invention relates to a process for recycling an aqueous posolyte from a redox flow battery to be recycled, the aqueous posolyte comprising at least one electroactive compound and an aqueous solvent, the electroactive compound comprising at least one oxidized or reduced form of a redox couple, the reduced form of the redox couple being a water-soluble organometallic complex, characterized in that it comprises: - a precipitation step (300) of the electroactive compound, thereby obtaining a suspension, - a separation step (400) of the suspension, thereby obtaining a solid residue (52) and an effluent (54), and - a drying step (600) of the solid residue (52), comprising heating the solid residue (52) to a temperature less than or equal to 40°C, preferably less than or equal to 35°C, preferably less than or equal to at 30°C,more preferably less than or equal to 25°C, by which a recycled electroactive compound is obtained. Figure for the abbreviation: Figure 1,

Description

Title of the invention: Process for recycling aqueous posolyte from a redox flow battery

[0001] The present invention relates to a method for recycling an aqueous posolyte from a redox flow battery. State of the art

[0002] A redox flow battery is a system that uses liquids (called electrolytes) to store energy. Redox flow batteries store and generate electricity through redox reactions. They generally have two compartments separated by an ion-exchange membrane, in which current collectors (electrodes) are typically immersed.

[0003] One of the problems with current battery storage technologies in general is their use of minerals and metals whose extraction has a massive environmental impact. Furthermore, their complex design and the use of composite materials prevent simple, economical, and efficient recycling of critical materials. While they claim to resolve the environmental impact of energy production by storing renewable energy (and thus reduce CO2 emissions per kWh of electricity produced), these technologies have a very mixed life cycle analysis. They lead to resource depletion and significant pollution due to the waste represented by end-of-life batteries.

[0004] For existing technologies, recycling methods have been published in the literature, such as: - Li-ion battery (EP1269554B1): method for recycling and separating critical materials. Such a method is complex to implement and costly; - Lead-acid battery (CA2986001A1): electrochemical process for recovering lead for reuse in a closed loop; - Vanadium flow redox battery: recycling methods have already been proposed by mixing the two electrolytes, and must also be carried out continuously during cycling to counteract the cross-over of vanadium ions across the membrane (Zhang, Y., Liu, L., Xi, J., Wu, Z., & Qiu, X. (2017). The benefits and limitations of electrolyte mixing in vanadium flow batteries. Applied Energy, 204, 373-381); - Zn-Br flow redox battery: bromine recovery process by neutralization (CN103236570B).

[0005] Current recycling solutions do not exist for redox flow batteries which implement redox couples based on organic or organometallic compounds, particularly organometallic compounds, solubilized in aqueous medium.

[0006] KEMIWATT uses electrolytes based on organic and organometallic compounds, dissolved in an aqueous medium, to limit the environmental impact of this technology and resource depletion (use of critical metals / rare earth elements). However, to date, there is no recycling solution for such batteries. Objectives of the invention

[0007] The present invention aims to solve the technical problem of providing a recycling process for flow redox batteries implementing redox couples based on organic and / or organometallic compounds in aqueous solution.

[0008] The present invention aims in particular to solve the technical problem of providing a process for recycling aqueous posolyte for redox flow batteries.

[0009] The present invention aims in particular to solve the technical problem of providing a simple process for treating aqueous posolytes for end-of-life redox flow batteries in order to isolate the electroactive compound(s), to purify them, and in particular to use them as raw material for new posolytes.

[0010] In particular, the present invention aims to solve the technical problems stated above by limiting the impact on the environment and the depletion of natural resources, or by limiting the quantity of new organic / organometallic compounds used in electrolytes, particularly in the posolyte. Finally, the present invention aims to solve the technical problem of reducing the manufacturing costs of redox flow batteries. Detailed description of the invention

[0011] The present invention makes it possible to solve one, and preferably all, of the technical problems posed by the present invention.

[0012] To enhance the eco-compatibility and economic competitiveness of redox flow batteries using aqueous electrolytes comprising organic and / or organometallic compounds, the inventors have discovered and developed a process and system for recycling the electroactive compounds of the posolyte, in particular to reuse them in new redox flow batteries and thus create a circular economy around such a redox flow battery.

[0013] Advantageously, recycling according to the present invention includes isolating the electroactive compound(s) contained in the posolyte at the end of the battery's life, in order to then recover it / them, either directly by marketing it / them in Another application is preferably by reintroducing it(s) into a new redox flow battery as a new posolyte. A redox flow battery can advantageously be recycled once it has lost at least 20% of its initial capacity.

[0014] Thus, the present invention makes it possible to limit the quantity of newly introduced material for the production of redox flow batteries and / or to limit the consumption of raw materials, natural or synthesized.

[0015] Thus, the present invention relates to a method for recycling an aqueous posolyte from a redox flow battery to be recycled, the aqueous posolyte comprising at least one electroactive compound and an aqueous solvent, the electroactive compound comprising at least one oxidized or reduced form of a redox couple, the reduced form of the redox couple being a water-soluble organometallic complex, characterized in that it comprises:

[0016] - a precipitation step of the electroactive compound, by which a suspension is obtained,

[0017] - a suspension separation step, by which a solid residue and an effluent are obtained, and

[0018] - a step of drying the solid residue, comprising heating the solid residue to a temperature less than or equal to 40°C, preferably less than or equal to 35°C, preferably less than or equal to 30°C, more preferably less than or equal to 25°C, by which a recycled electroactive compound is obtained.

[0019] By electroactive compound, we mean an organic or organometallic compound that is part of a redox couple, and designates indifferently either the oxidant (the oxidized form) of the redox couple, or the reductant (the reduced form) of the redox couple, or the mixture of the oxidant and the reductant of the redox couple.

[0020] By aqueous electrolyte, we mean aqueous solutions comprising the electroactive compound(s) and arranged in the positive and negative compartments of a redox flow battery.

[0021] The term posolyte designates the electrolyte of the positive compartment of the redox flow battery, and the term negolyte designates the electrolyte of the negative compartment of the redox flow battery.

[0022] By water-soluble organometallic complex, we mean an organometallic complex having a solubility in water at 25°C greater than or equal to 0.1 mol / L, preferably greater than or equal to 0.3 mol / L, advantageously greater than or equal to 0.5 mol / L, that is to say that an aqueous solution comprising at least 0.1 mol / L, preferably at least 0.3 mol / L, advantageously at least 0.5 mol / L of this complex does not exhibit any precipitate or insoluble parts at 25°C.

[0023] Preferably, the metal of the organometallic complex is chosen from iron or the Copper. Preferably, the metal of the organometallic complex has, in its reduced form, an oxidation state between 0 and 2, preferably 0 if the metal is copper or 2 if the metal is iron. Preferably, the reduced form of the redox couple is an iron organometallic complex having an oxidation state of 2 in its reduced form, preferably chosen from ferrocene and the ferrocyanide ion, advantageously the ferrocyanide ion.

[0024] Preferably, the process comprises successively:

[0025] - a step of collecting an aqueous posolyte from a redox flow battery comprising at least one electroactive compound,

[0026] - a step of precipitation of the electroactive compound and obtaining a suspension,

[0027] - a step of separating the suspension and obtaining a solid residue and a effluent,

[0028] - optionally, a step of rinsing with water and triturating with water the residue solid obtained after the separation step, followed by a second separation step, and obtaining a rinsed solid residue, and

[0029] - a drying step of the solid residue or the rinsed solid residue to obtain a dried solid residue.

[0030] The steps of the process can be implemented by any technique known to a person skilled in the art.

[0031] The collection step is preferably carried out by pumping the posolyte from the redox flow battery to be recycled into a container, preferably directly at the battery's usage site. In one embodiment, the collection step further includes a step of transferring the posolyte from the container to a reactor.

[0032] The collection step is preferably carried out after a complete discharge step of the redox flow battery. In other words, the posolyte collected during the collection step is preferably a posolyte whose electroactive compound is in its reduced form.

[0033] The aqueous posolyte collected from the redox flow battery is a used aqueous posolyte since it has undergone at least one charge and / or discharge cycle. Preferably, the used aqueous posolyte is collected at the end of the battery's life cycle.

[0034] The separation step is preferably carried out by filtration, for example using a centrifugal decanter.

[0035] The solid residue obtained at the end of the separation step includes the precipitated electroactive compound(s).

[0036] The water rinsing and water trituration step improves the purity of the solid residue and, in particular, removes the precipitating agent used if it is weakly volatile. However, it increases the quantity of effluent to be treated.

[0037] The process according to the invention is preferably devoid of a step of rinsing the solid residue.

[0038] The drying step can be carried out by heating and / or by putting the solid residue under reduced pressure.

[0039] It has been surprisingly discovered that the drying temperature of the solid residue has a large influence on the electrochemical properties of the recycled electroactive compound obtained at the end of the recycling process: a drying temperature of the solid residue above 40°C leads to a significant drop in the performance of a battery comprising a recycled posolyte including such a recycled electroactive compound.

[0040] Preferably, the solid residue drying step includes heating the solid residue to a temperature between 15°C and 35°C, preferably between 20°C and 30°C, advantageously between 23°C and 27°C.

[0041] To improve the drying step, it may also be advantageous to carry it out under reduced pressure. Preferably, the drying step is carried out at an absolute pressure less than or equal to 1 bar, preferably less than or equal to 0.8 bar, advantageously less than 0.5 bar.

[0042] Preferably, the precipitation step includes the addition of an anti-solvent of the electroactive compound and / or the addition of an acid or a base and / or the addition of a salt to the aqueous posolyte.

[0043] Preferably, the step of adding an anti-solvent is carried out in a reactor tank, under agitation.

[0044] By anti-solvent, we mean an organic solvent in which the electroactive compound is less soluble than in water.

[0045] Preferably, the anti-solvent is chosen for its ability to lower the solubility of the electroactive compound in the initial aqueous medium, preferably chosen from among solvents in which the electroactive compound is 5 times less soluble than in water, more preferably 10 times less soluble, advantageously 100 times less soluble. In other words, the ratio of the solubility of the electroactive compound in water to the solubility of the electroactive compound in the anti-solvent is preferably greater than or equal to 5, more preferably greater than or equal to 10, advantageously greater than or equal to 100. The solubility of the electroactive compound in water or the anti-solvent is the maximum concentration, in g / mol at 25°C, at which the electroactive compound can dissolve in water or the anti-solvent, respectively, forming a homogeneous mixture, i.e., without the formation of a precipitate.

[0046] Preferably the anti-solvent is chosen from water-miscible aprotic and protic polar solvents comprising an alcohol function, a nitrile function or a ketone function.

[0047] Preferably, the anti-solvent is an organic solvent, preferably chosen from the group of water-miscible aprotic and protic polar solvents, more preferably Specifically chosen from among alcohols, preferably aliphatic alcohols, advantageously saturated aliphatic alcohols such as methanol, ethanol, or 1-propanol and isopropanol, and organic solvents comprising a nitrile function, such as acetonitrile, or a ketone function, such as acetone, or any mixture thereof. The use of a mixture of at least two antisolvents increases the amount of electroactive compound precipitated.

[0048] Preferably, the acid is a strong or weak acid. The strong acid may be selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, hydroiodic acid, hydrobromic acid, perchloric acid, permanganic acid, manganic acid, chloric acid, phosphoric acid, or any mixture thereof. The weak acid may include at least one carboxylic acid group, such as formic acid, acetic acid, benzoic acid, citric acid, lactic acid, oxalic acid, or maleic acid. Preferably, the acid is a strong acid. The use of a strong acid increases the amount of electroactive compound precipitated. Preferably, the acid is sulfuric acid or acetic acid, advantageously sulfuric acid.

[0049] Preferably, the quantity of acid added to the aqueous posolyte corresponds to the quantity of acid necessary to obtain a pH less than or equal to 10, preferably less than or equal to 8, preferably less than or equal to 7, more preferably less than or equal to 6. Even more preferably, the quantity of acid added to the aqueous posolyte corresponds to the quantity of acid necessary to obtain a pH less than or equal to 10 and greater than or equal to 1, preferably less than or equal to 8 and greater than or equal to 2, more preferably less than or equal to 6 and greater than or equal to 3.

[0050] Preferably, the acid is added under stirring.

[0051] Preferably, the base is an inorganic base. The base can be chosen from the group consisting of alkali hydroxides, such as NaOH or KOH, and alkali carbonates, such as Na2CO3 or K2CO3.

[0052] Preferably, the amount of base added to the aqueous posolyte corresponds to the amount of base necessary to obtain a pH greater than or equal to 7, preferably greater than or equal to 8, preferably greater than or equal to 10. Even more preferably, the amount of base added to the aqueous posolyte corresponds to the amount of base necessary to obtain a pH less than or equal to 14 and greater than or equal to 7, preferably less than or equal to 13 and greater than or equal to 10.

[0053] Preferably, the salt is an inorganic salt, preferably KCl or NaCl, or an organic salt, preferably sodium acetate or ammonium carbonate.

[0054] Preferably, the inorganic salt is chosen from among the inorganic salts whose cation corresponds to the cation or one of the cations included in the aqueous posolyte to be recycled.

[0055] The addition of an anti-solvent to the electroactive compound, the addition of an acid or a base and The addition of a salt to the aqueous posolyte can be combined two by two or implemented all together to optimize the precipitation of the electroactive compound, depending on its solubility.

[0056] Preferably, the precipitation step includes adding to the aqueous posolyte an anti-solvent of the electroactive compound, preferably an anti-solvent of the reducing agent of the redox couple included in the posolyte. The anti-solvent is as defined above.

[0057] Preferably, the volume of anti-solvent added represents between 1% and 70% of the volume of the aqueous solution to be treated, preferably between 20% and 40%, preferably between 25% and 35%. Preferably, the concentration of the electroactive compound is greater than or equal to 0.1 M, preferably greater than or equal to 0.2 M, preferably between 0.1 M and 10 M. Preferably, the concentration of the organometallic complex is greater than or equal to 0.1 M, preferably greater than or equal to 0.2 M, preferably between 0.1 M and 10 M.

[0058] Preferably, the anti-solvent added to the aqueous posolyte is at a temperature between 0 °C and 15 °C.

[0059] Preferably, the process according to the invention comprises a chemical reduction step prior to the precipitation step, including contacting the posolyte with a reducing agent capable of reducing the oxidized form of the redox couple. Preferably, the chemical reduction step is between the collection step and the precipitation step.

[0060] This step is preferably implemented when the posolyte has been collected from a flow redox battery that has not been completely discharged before the collection step.

[0061] Thus, preferably, the electroactive molecule to be precipitated is the reducing agent of the redox couple included in the posolyte.

[0062] By reducing agent capable of reducing the oxidant of the redox couple, we mean any compound belonging to a redox couple different from the redox couple included in the posolyte and whose standard redox potential is strictly less than the standard redox potential of the redox couple included in the posolyte.

[0063] Preferably, the step of contacting the polylyte with a reducing agent capable of reducing the oxidant of the redox couple includes adding a reducing agent to the aqueous electrolyte. Preferably, the addition of a reducing agent to the aqueous electrolyte is carried out while controlling the pH, which should preferably remain greater than or equal to 8.

[0064] Preferably, the reducing agent is chosen from the group consisting of H2O2, Na2SO3, Na2 S2O4, Na2S2O3, N2H4 (hydrazine), I2 (iodine) and organic reducing agents such as ascorbic acid, citric acid, and glucose derivatives.

[0065] Preferably, during the precipitation step, the aqueous electrolyte is at a temperature between 5°C and 40°C, preferably between 10°C and 35°C, advantageously between 15°C and 30°C.

[0066] According to one embodiment, the process according to the invention further comprises a step of formulation of the recycled electroactive compound comprising dissolving the recycled electroactive compound in an aqueous medium to obtain a recycled posolyte.

[0067] This formulation step may further include the addition of other constituents to the recycled posolyte, such as additives.

[0068] The choice of other constituents depends on the performance required for the recycled posolyte.

[0069] The process according to the invention may further include a step of introducing the recycled posolyte obtained in the formulation step (700) into the positive compartment of a redox flow battery.

[0070] According to one embodiment, the process according to the invention further comprises a step of treating the effluent obtained at the end of the separation step to obtain a treated effluent. The treated effluent can be reused in the precipitation step.

[0071] The process according to the invention may further include a step of verifying the purity of the solid residue, for example by chemical and / or electrochemical analysis.

[0072] According to one embodiment of the process of the invention, the aqueous posolyte to be recycled may comprise at least one additive. In this embodiment, depending on the solubility of the additive, the additive is either recycled with the electroactive compound, and is therefore included in the solid residue, or included in the effluent obtained at the end of the process.

[0073] By additive, we mean any compound capable of increasing certain physico-chemical properties of the posolyte.

[0074] The invention also relates to a recycling system for an aqueous posolyte from a redox flow battery comprising:

[0075] - a device for collecting an aqueous posolyte from a flow redox battery, the aqueous posolyte comprising at least one electroactive compound and an aqueous solvent,

[0076] - a device for precipitating the electroactive compound by adding an anti-solvent of the electroactive compound and / or addition of an acid or a base and / or addition of a salt, providing a suspension comprising a solid residue and an effluent, and

[0077] - a drying device allowing the solid residue to be dried at a temperature less than or equal to 40°C, preferably less than or equal to 35°C, preferably less than or equal to 30°C, more preferably less than or equal to 25°C.

[0078] The collection device preferably comprises a collection tank for the collected aqueous posolyte and a device capable of transferring the posolyte from the redox flow battery to be recycled to the collection tank. The collection tank is, for example, in fluidic connection with the positive reservoir of the redox flow battery to be recycled. The posolyte The aqueous solution collected from the redox flow battery is considered used aqueous solution since it has undergone at least one charge and / or discharge cycle. Preferably, the used aqueous solution is collected at the end of the battery's life cycle.

[0079] The device according to the invention may further comprise a first storage tank including an anti-solvent of the electroactive compound of the collected aqueous posolyte and / or an acid or a solution of a base and / or a solution of a salt as defined in the description of the process according to the invention, preferably a storage tank for an anti-solvent of the electroactive compound of the collected aqueous posolyte. The first storage tank is in fluidic connection with the precipitation device.

[0080] According to one embodiment, the recycling system according to the invention comprises a discharge device capable of reducing the oxidant of the redox couple of the posolyte. The discharge device is preferably fluidically connected to a second storage tank comprising a reducer capable of reducing the oxidant of the redox couple as defined above. The discharge device is preferably fluidically connected to the collection tank and the precipitation device.

[0081] Preferably, the recycling system according to the invention further comprises a separation device for separating the suspension from the precipitation device into a solid residue and an effluent. For example, the separation device may be a centrifugal decanter.

[0082] The solid residue obtained in the separation device comprises the precipitated electroactive compound(s).

[0083] The separation device is preferably in fluidic connection with the precipitation device and the drying or formulation device.

[0084] According to one embodiment of the invention, the separation device is capable of partially or completely drying the solid residue, optionally rinsed. In this embodiment, the drying device is included within the separation device.

[0085] Alternatively, the device according to the invention includes a separate drying device for the solid residue by heating and / or by putting the solid residue under reduced pressure, optionally rinsed.

[0086] According to one embodiment, the device of the invention further comprises a device for treating the effluent from the separation device to obtain treated effluent. The treatment device is in fluidic connection with the storage tank and / or with the precipitation device.

[0087] Preferably, the recycling system according to the invention further comprises a formulation device formulating the solid residue in the form of a recycled posolyte.

[0088] The device according to the invention may further include a formulation reservoir comprising an aqueous solution optionally including one or more additives, as defined above. The formulation tank is in fluidic connection with the formulation device.

[0089] At the outlet of the formulation device, the recycled posolyte can be introduced into the positive compartment of a new flow redox battery, preferably by a fluidic link.

[0090] Preferably the recycling system according to the invention is for the implementation of the process according to the invention. Advantage of the invention

[0091] It is particularly surprising that such electroactive compounds can be recycled by precipitation. The recycling process according to the invention is particularly easy to implement and therefore particularly innovative. This process makes it possible to obtain very good recycling yields of electroactive compounds.

[0092] Quite surprisingly, the electroactive compounds recycled by the process of the invention are reusable for further cycling in a new redox flow battery with very satisfactory performance, particularly in terms of capacity and / or ohmic resistance (< 2 Q.cm2) and stability during repeated operating cycles of the redox battery, which is substantially stable over several tens or hundreds of cycles. Such performance was not expected by those skilled in the art.

[0093] Another advantage of the process of the invention is that a small quantity (proportionally to the volume treated) of reagents is used. Furthermore, these reagents are readily available (and already used in many other applications) and inexpensive. For example, ethanol does not pose an environmental threat.

[0094] Furthermore, precipitation is rapid, and the process according to the invention does not generate pollution of the recycled electroactive compounds: the purification of the solid residue occurs solely through an evaporation step. Advantageously, the efficiency of the process according to the invention and its low cost allow for the industrialization of the process and the system according to the invention.

[0095] Unless explicitly stated otherwise, the expressions "from X to Y" and "between X and Y" denote intervals whose bounds X and Y are included. Figures

[0096] [Fig.1] The [Fig.1] is a schematic block diagram of a process according to the invention.

[0097] After the cycling 100 of a redox flow battery, an aqueous posolyte of the redox flow battery is collected during a collection step 200. The electroactive compound(s) included in the aqueous posolyte is / are optionally brought into contact with a reducing agent in order to be discharged during a chemical reduction step (250). The electroactive compound(s) in the aqueous posolyte is / are precipitated in a precipitation step 300, preferably by adding an antisolvent and / or an acid or base and / or a salt to the aqueous electrolyte of the electroactive compound in the aqueous posolyte. The suspension obtained at the end of the precipitation step 300 is then separated into a solid residue and an effluent in a separation step 400. A solid residue comprising the electroactive compound(s) and an effluent are obtained. The solid residue can be rinsed with water and triturized in a water rinsing and trituration step 500. The solid residue, rinsed or not, is then dried in a drying step 600 to reduce the amount of water and / or solvent present in the solid residue. The drying temperature must not exceed 40°C.The recycled electroactive compound obtained after the drying step can then be formulated in a formulation step 700 to obtain a recycled posolyte. The recycled posolyte can be used in a new redox flow battery, alone or mixed with a posolyte comprising one or more native electroactive compounds, i.e., compounds that have never been used in a charge and / or discharge cycle of a redox flow battery. In parallel, the effluent obtained after the separation step can be treated in a treatment step 800 to obtain a treated effluent suitable for reuse in the precipitation step 300 during a subsequent implementation of the process according to the invention.

[0098] [Fig.2] The [Fig.2] is a schematic representation of a recycling system 1 of an aqueous posolyte of a redox flux battery 10 according to the invention.

[0099] A posolyte 20 from a redox flux battery 10 is collected in a collection device 30, optionally conveyed to a discharge device 35, and then conveyed to a precipitation device 40. An anti-solvent and / or an acid or a base and / or a solution of a salt of the electroactive compound of the collected aqueous posolyte from a storage tank 45 is added to the posolyte 20 in the precipitation device 40 in order to precipitate the electroactive compound(s) of the posolyte 20. The resulting suspension is separated, preferably by filtration, in a separation device 50. A solid residue 52 comprising the electroactive compound(s) of the posolyte 20 and an effluent 54 are obtained. The effluent 54 is collected in an effluent collection device 80, and can be treated and then redirected to the storage tank 45.Optionally, the solid residue 52 is rinsed and triturated with water, then separated a second time to remove the wash water. The residue 52 (rinsed or not) is then dried or partially dried, either directly in the separation device or after being transferred to a drying device 60. The drying device heats the residue 52 under controlled temperature and / or reduces its pressure, thereby decreasing the amount of water and solvents present in the solid residue 52. The solid residue 52 is then conveyed to a formulation device. 70. An aqueous solution, possibly including additives, is also introduced into the formulation device 70 from a formulation reservoir 75 in order to prepare a recycled posolyte 78. The recycled posolyte 78 can then be introduced into the positive compartment of a new redox flow battery 90.

[0100] [Fig.3] Fig.3 is a graph representing accessible capacity in cycling battery (TRL 4) (as a percentage of the theoretical capacity of the electrolytes) of a battery comprising electrolytes with native electroactive compound and two batteries A and B comprising a negolyte with native electroactive compound and a posolyte with recycled electroactive compound, the recycled electroactive compound having been dried under different conditions for batteries A and B.

[0101] [Fig.4] The [Fig.4] is a graph representing the battery resistance (TRL 4) measured by polarization curve of a battery comprising electrolytes with native electroactive compound and two batteries A and B comprising a negolyte with native electroactive compound and a posolyte with recycled electroactive compound, the recycled electroactive compound having been dried under different conditions.

[0102] [Fig.5] Fig.5 is a graph representing the accessible cycling capacity battery (TRL 4) (as a percentage of the theoretical capacity of the electrolytes) of a battery comprising electrolytes with native electroactive compound and a battery comprising electrolytes with recycled electroactive compound on the posolyte side and the negolyte side.

[0103] [Fig.6] The [Fig.6] is a graph representing the battery resistance (TRL 4) measured by polarization curve of a battery comprising electrolytes with native electroactive compound and a battery comprising with recycled electroactive compound.

[0104] The present invention will now be described using non-limiting examples. Examples:

[0105] Example 1: Recycling of a posolyte comprising the ferrocyanide / iron-ricvanide redox couple - Effect of drying temperature

[0106] The recycling process was implemented on a posolyte used in batteries (> 500 cycles and 4 months of cycling).

[0107] At the end of the cycling process, the electroactive compound(s) of the ferrocyanide / ferricyanide redox couple in the posolyte are first chemically reduced, for example by adding H2O2, while controlling the pH (which should preferably remain above 8) and under stirring, in order to obtain an electrolyte comprising 100% ferrocyanide. The concentration of electroactive compounds in the negolyte is 0.2 M and the concentration of electroactive compounds in the posolyte is 0.7 M.

[0108] Precipitation is then carried out by adding a volume of 96% ethanol (in liquid form) to the electrolyte under magnetic stirring, the volume of ethanol cor corresponding to 30% of the volume of the posolyte; the quantity of ethanol must be controlled, because if it exceeds a certain volume, the effect is counterproductive and the ferrocyanide redissolves in the solvent mixture.

[0109] The solution is then filtered (for example through filter paper (5-10 µm)), and the resulting solid residue is dried by evaporating the residual traces of solvent (water + ethanol) at two temperatures: 20 °C and 45 °C.

[0110] The nature and quantity of solvent used in each case, as well as the yields and purities obtained, are presented in Table 1. [YES] [Table 1] AB Concentration of electroactive compounds in the 0.7 M electrolyte 0.7 M Proportion of solvent added (% of total volume of electrolyte to be recycled) and nature of solvent 30% 96% Ethanol at 5 °C 30% 96% Ethanol at 5 °C Drying temperature Drying at 20 °C Drying at 45 °C Recycling yield 76% 76% Purity of the electroactive compound after drying (UV analysis of the powder) 90% 93%

[0112] When the filtered powder is heated on a hot plate at 45 °C, it gradually releases moisture, forming a paste again; it must then be refiltered to obtain a powder, which is then dried in the open air without any special heating.

[0113] UV analysis of the 2 samples indicates satisfactory purities (greater than 90%), and an unchanged signature compared to the initial powder.

[0114] Each recycled electroactive compound A and B was then resolubilized in an aqueous medium to obtain two recycled posolytes A and B. Each posolyte was battery-tested in association with a non-recycled negolyte comprising (M3CH) as the electroactive compound:

[0115] [Chem.l] ïWCHj

[0116] Figures 3 and 4 show the performance obtained with a "native" battery comprising electrolytes with only native electroactive compounds (M3CH compound in the negolyte and ferrocyanide ion in the posolyte), and with the two batteries A and B comprising the same negolyte but the recycled posolyte A or B, respectively.

[0117] It is observed that the capacity ([Fig.3]) and the resistance in battery ([Fig.4]) are identical for the native battery and battery A (the visible difference between the two curves is included in the reproducibility error), but that the performance of battery B, which includes the recycled posolyte obtained after heating the ferrocyanide to 45 °C, is significantly lower than that of the native and A batteries, in terms of accessible capacity.

[0118] An excess of negolyte was added at the time of cycle 13 of battery B to ensure that the limitation was indeed due to the posolyte.

[0119] It is therefore observed that, unexpectedly, the drying temperature of the recycled ferrocyanide has a detrimental effect on its redox properties. This was entirely unforeseen since no degradation is visible by UV characterization, which is the indicated characterization method for the ferrocyanide compound.

[0120] Example 2: Battery recycling and testing of the ferrocyanide / ferricyanide redox couple (posolyte) and anthraquinone (M3CH) (negolyte)

[0121] The recycling process was implemented on electrolytes used in batteries (>350 cycles and 6 months of cycling). The results present both the characteristics of the recycling process and the performance of batteries containing the recycled electrolytes.

[0122] With regard to the negolyte, the electroactive molecule (M3CH) of the negolyte in its reduced form discharges (i.e., is oxidized) automatically to the air by the action of atmospheric oxygen. Then, the precipitation of the electroactive molecule occurs by The negolyte solution is acidified to a pH of 6 or lower. The process has been tested with several types of acid (strong acid, e.g., sulfuric acid; weak acid, e.g., acetic acid), yielding equivalent results. The amount of acid to add depends solely on the volume of negolyte to be treated and its initial pH. It is added while stirring. As soon as the pH reaches 6 or lower, precipitation is instantaneous. The effluent can be filtered through a coarse filter, as the resulting cake is very compact and forms a solid block. The precipitate should then be rinsed with water to remove traces of acid and spread out to facilitate drying and remove any residual solvent.

[0123] The nature and quantity of solvent used for each electrolyte, as well as the yields and purities obtained, are presented in Table 2. The required quantities of solvent are 10% and 30% by volume for the negolyte and posolyte, respectively. This addition tends to decrease for the posolyte as the concentration of the electroactive compound increases. The yields are greater than 65%, with further improvement expected through the implementation of an optimized industrial process. The purity of the recycled electroactive compound obtained after simple drying is estimated by quantitative proton NMR (qH NMR) with an internal standard. This purity is 92% and 93%, respectively, which demonstrates the ease of removal of the solvent used for precipitation. By comparison, the purity of these same native electroactive compounds is approximately 97% for anthraquinone and 96% for the ferrocyanide salt.

[0124] Quantitative NMR method: 1H NMR spectra were recorded on a BRUKER AC 300 P spectrometer (300 MHz). Maleic acid (Acros Organics) was used as an internal standard to assess the purity of the compounds.

[0125] [Tables2] Recycling of Electroactive Compounds Negolyte Posolyte Electroactive Compound Concentration 0.2 M 0.34 M Proportion of Solvent Added (% of total electrolyte volume to be recycled) and Solvent Nature 10% (99% pure CH3COOH) 30% (96% Ethanol) Recycling Yield 65% 72% Purity of Electroactive Compound After Drying (qNMR *H) 92% 93%

[0126] Figures 5 and 6 show the performance obtained with a battery comprising electrolytes with one or more native electroactive compounds and with a recycled battery, i.e. comprising a negolyte and a posolyte formulated from the recycled electroactive compound(s) according to the conditions of Table 2 above.

[0127] The accessible capacity ([Fig. 5]) is identical for both batteries (the visible difference between the two curves is included in the reproducibility error), which surprisingly proves that the recycling by precipitation of electroactive compounds has no impact on their electrochemical activity. The evolution of this capacity during cycling is stable.

[0128] The resistance measured in the battery ([Fig. 6]) is also equivalent for both batteries and remains constant throughout the cycling process. This result surprisingly confirms that the solvents used for precipitation have no impact on the system's performance.

[0129] Comparison of the two battery tests highlights that the active materials of an aqueous organic flux redox battery can be recycled by precipitation and reused in a new storage system without degradation of performance.

Claims

Demands

1. A process for recycling an aqueous posolyte from a redox flux battery to be recycled, the aqueous posolyte comprising at least one electroactive compound and an aqueous solvent, the electroactive compound comprising at least one oxidized or reduced form of a redox couple, the reduced form of the redox couple being an organometallic iron complex having an oxidation state of 2 and soluble in water, characterized in that it comprises: - a precipitation step (300) of the electroactive compound, thereby obtaining a suspension, - a separation step (400) of the suspension, thereby obtaining a solid residue (52) and an effluent (54), and - a drying step (600) of the solid residue (52), comprising heating the solid residue (52) to a temperature less than or equal to 40°C, preferably less than or equal to 35°C, preferably less than or equal to 30°C, more preferably less than or equal to 25°C,This is the process by which a recycled electroactive compound is obtained.

2. A process according to claim 1, wherein the precipitation step (300) comprises the addition of an anti-solvent of the electroactive compound and / or the addition of an acid or a base and / or the addition of a salt to the aqueous posolyte.

3. A method according to claim 1 or 2, wherein the precipitation step (400) comprises the addition to the aqueous posolyte of an antisolvent of the electroactive compound.

4. A method according to claim 3, wherein the volume of anti-solvent added represents between 1% and 70% of the volume of the aqueous posolyte to be treated, preferably between 20% and 40%, preferably between 25% and 35%.

5. A process according to claim 4, wherein the concentration of organometallic complex is greater than or equal to 0.1 M, preferably greater than or equal to 0.2 M.

6. A method according to any one of claims 3 to 5, wherein the anti-solvent added to the aqueous posolyte is at a temperature between 0 °C and 15 °C.

7. A method according to any one of claims 3 to 6, wherein the anti-solvent is selected from water-miscible aprotic and protic polar solvents comprising an alcohol function, a nitrile function or a ketone function.

8. A process according to any one of the preceding claims, further comprising a chemical reduction step (250) prior to the precipitation step (300), comprising bringing the posolyte into contact with a reducing agent capable of reducing the oxidized form of the redox couple.

9. A process according to any one of the preceding claims, wherein the reduced form of the redox couple is an organometallic iron complex having an oxidation state of 2 selected from ferrocene and the ferrocyanide ion, advantageously the ferrocyanide ion.

10. A process according to any one of the preceding claims, characterized in that it further comprises a formulation step (700) of the recycled electroactive compound comprising dissolving the recycled electroactive compound in an aqueous medium to obtain a recycled posolyte.

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