Redox triphasic battery

Abstract

The present invention refers to a redox battery, to a method of storing electricity comprising the redox battery, to a method of delivering electricity comprising the redox battery, an energy storage and / or delivery system, and to the use of the redox battery or the energy system to store or deliver electricity.

Description

[0001] REDOX TRIPHASIC BATTERY

[0002] DESCRIPTION

[0003] TECHNICAL FIELD

[0004] The present invention relates to the field of batteries. More specifically, the present invention relates to the field of redox batteries.

[0005] BACKGROUND

[0006] Redox-batteries present unique advantages such as their flexible, modular design and fast response. The name ‘redox’ refers to electrochemical reduction and oxidation reactions through which energy is stored in electrolytes. A common redox battery configuration comprises a first and a second electrode in contact with a first and a second electrolyte comprising redox active species (named anolyte and catholyte). In this redox battery configuration, the anolyte and catholyte are usually separated by a separator such as an ion-selective membrane. The separator maintains electrical neutrality during operation and mitigates cross-over or cross-contamination of redox active species between catholyte and anolyte. However, a complete electrolyte separation is not guaranteed. In addition, separators cost about a 30-40% of the total cost of the battery and their durability is limited. Thus, separators need regular replacement increasing the maintenance costs of the batteries.

[0007] In order to eliminate the separator or membrane from the battery system and avoid the crossover phenomena, a membrane-free battery concept was proposed based on the use of two liquid redox electrolytes being immiscible between them. Thus, the two liquid electrolytes are separated by thermodynamics instead of by a membrane or separator. For example, ES2633601A1 describes a membrane-less redox battery comprising two immiscible electrolytes. No separator is needed in said redox battery and the two immiscible electrolytes are in contact with each other through an interphase. However, the battery described on ES2633601A1 cannot be completely charged, and has a low coulombic efficiency, low power density and a low energy density. In general, biphasic membrane-free batteries suffer from an inherent self-discharge phenomenon that consists on the recombination of charged species at the interphase of the two immiscible electrolytes which results in low coulombic efficiencies and low capacity utilization values. Chakraborty et al. (Chakraborty et al. ACS Appt. Energy Mater. 2023, 6, 605-610), disclosed a “split biphasic” model cell. Said cell replaces the direct anolyte-catholyte interphase that leads to self-discharge issues in existing biphasic cells by an electrolyte solution. Said electrolyte solution is immiscible with the anolyte and catholyte. However, this cell model shows a high internal cell resistance, and the proposed architecture of the phases (anolyte and catholyte are miscible between them) makes the cell not robust and stable enough.

[0008] Therefore, despite the above-mentioned systems, it is desirable to develop membrane- free battery alternatives with increased energy density, power density, energy efficiency and overall performance.

[0009] BRIEF DESCRIPTION OF THE INVENTION

[0010] The authors of the present invention have built a redox battery based on three liquid phases being immiscible between them: a catholyte, an anolyte and an intermediate liquid phase placed between the catholyte and the anolyte. The three phases are insoluble among each other (for example, when put in contact they form three immiscible phases). The use of the redox battery of the invention has the advantage of a reduced operative and fabrication cost compared to other redox batteries of the state of the art (i.e. no separator such as polymeric or ceramic membranes is needed and the battery can operate a temperatures below 200°C).

[0011] In addition, the presence of an intermediate liquid phase between the catholyte and the anolyte in the redox battery of the invention overcomes the self-discharge issues in existing biphasic membrane-free batteries.

[0012] Also, the composition of the three liquid phases being immiscible among each other of the redox battery of the invention makes it more stable over the time, robust and durable that the batteries of the art having an intermediate liquid phase between electrolytes but wherein those electrolytes are miscible between them. In addition, the battery of the present invention is able to work in dynamic state even at high flow rates. In addition, the battery architecture of the present invention reduces the internal cell resistance and allows reducing the distance between the electrodes over other batteries.

[0013] Thus, a first aspect of the invention is directed to a redox battery comprising: two electrodes; and - a catholyte and an anolyte; wherein the catholyte and the anolyte are liquid and comprise redox-active species; wherein the catholyte and the anolyte are in contact through an intermediate liquid phase placed between them; wherein the intermediate liquid phase, the catholyte and the anolyte are immiscible among each other; wherein the intermediate liquid phase is homogeneous and ionically conductive; and wherein the catholyte and / or the anolyte comprise at least a salt.

[0014] In a second aspect, the invention is directed to an energy storage and / or delivery system comprising at least one redox battery according to the present invention in any of its particular embodiments. In particular, the redox battery may act a secondary and / or rechargeable battery, i.e. the redox battery may be configured to be reversibly charged and discharged.

[0015] In a third aspect, the present invention is directed to a method of storing electricity comprising the steps of: a) providing a redox battery according to the invention; b) oxidizing the redox active species of the catholyte at one electrode to their corresponding oxidized state, while the redox active species of the anolyte are reduced to their corresponding reduced state at the other electrode of the two electrodes of the redox battery of (a).

[0016] In another aspect, the present invention is directed to method of delivering electricity comprising the steps of: a) providing a redox battery according to the invention; b) reducing the redox active species of the catholyte at one electrode to their reduced state while the redox active species of the anolyte are oxidized to their corresponding oxidized state at the other electrode of the two electrodes of the redox battery of (a).

[0017] Another aspect of the present invention is directed to the use of the redox battery of the present invention or the energy storage and / or delivery system, to store or deliver electricity. FIGURES

[0018] Figure 1 shows a scheme of a redox battery according to a particular embodiment of the present invention (battery A).

[0019] Figure 2 shows the voltage (V) results over time (h) for batteries (i) A and (ii) B.

[0020] Figure 3 shows the voltage (V) results over capacity for batteries (i) A and (ii) B.

[0021] Figure 4 shows the results of the coulombic efficiency over number of cycles for battery A.

[0022] Figure 5 shows a discharge polarization curve comparison between (i) battery A and (ii) battery B.

[0023] Figure 6 shows pictures of the stability over time of the three phases of battery A after being shaked (left picture).

[0024] Figure 7 shows the tilting test results for the three phases of battery A (a) in comparison with two organic electrolytes separated by an intermediate aqueous phase, namely system C (b).

[0025] Figure 8 shows pictures of the stability over time test of a three phase system D wherein the middle phase was formed by an emulsion of the top and bottom phases.

[0026] Figure 9 shows pictures of the stability after being shaked of a three phase system D wherein the middle phase was formed by an emulsion of the top and the bottom phases.

[0027] DETAILED DESCRIPTION OF THE INVENTION

[0028] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. The meaning and scope of the terms should be clear, however, in the event of any latent ambiguity, definitions provided herein take precedent over any dictionary or extrinsic definition.

[0029] As used herein, the singular forms “a” “an” and “the” include plural reference unless the context clearly dictates otherwise.

[0030] As used herein, the terms "about" or “around” means a slight variation of the value specified, preferably within 10 percent of the value specified. Further, to provide a more concise description, some of the quantitative expressions given herein are not qualified with the term “about". It is understood that whether the term “about" is used explicitly or not, every quantity given herein is meant to refer to the actual given value and it is also meant to refer to the approximation to such given value that would reasonably be inferred based on the ordinary skill in the art, including equivalents and approximation due to the experimental and / or measurement conditions for such given value.

[0031] In the context of the present invention, the term “redox” refers to electrochemical reduction and oxidation reactions which help to store energy in a battery during charge and deliver energy during discharge.

[0032] The redox battery of the invention is configured to act as an energy storage and delivery system. In particular, the redox-battery is a secondary or rechargeable battery, i.e. it is configured to be reversibly charged and discharged.

[0033] As defined above, a first aspect of the invention is directed to a redox battery comprising:

[0034] - two electrodes; and

[0035] - a catholyte and an anolyte; wherein the catholyte and the anolyte are liquid and comprise redox-active species; wherein the catholyte and the anolyte are in contact through an intermediate liquid phase placed between them; wherein the intermediate liquid phase, the catholyte and the anolyte are immiscible among each other; wherein the intermediate liquid phase is homogeneous and ionically conductive; and wherein the catholyte and / or the anolyte comprise at least a salt.

[0036] An alternative aspect of the invention is directed to a redox battery comprising:

[0037] - two electrodes; and

[0038] - a catholyte and an anolyte; wherein the catholyte and the anolyte are liquid and comprise redox-active species; wherein the catholyte and the anolyte are in contact through an intermediate liquid phase placed between them; wherein the intermediate liquid phase, the catholyte and the anolyte are immiscible among each other; wherein the intermediate liquid phase is homogeneous and ionically conductive, and wherein the intermediate liquid phase, the catholyte and / or the anolyte are aqueous solutions.

[0039] In an embodiment, the redox battery consist of:

[0040] - two electrodes; and

[0041] - a catholyte and an anolyte; wherein the catholyte and the anolyte are liquid and comprise redox-active species; wherein the catholyte and the anolyte are in contact through an intermediate liquid phase placed between them; wherein the intermediate liquid phase, the catholyte and the anolyte are immiscible among each other; wherein the intermediate liquid phase is homogeneous and ionically conductive; and wherein the catholyte and / or the anolyte comprise at least a salt.

[0042] In an alternative embodiment, the redox battery consist of:

[0043] - two electrodes; and

[0044] - a catholyte and an anolyte; wherein the catholyte and the anolyte are liquid and comprise redox-active species; wherein the catholyte and the anolyte are in contact through an intermediate liquid phase placed between them; wherein the intermediate liquid phase, the catholyte and the anolyte are immiscible among each other; wherein the intermediate liquid phase is homogeneous and ionically conductive; and wherein the intermediate liquid phase, the catholyte and / or the anolyte are aqueous solutions.

[0045] The redox battery of the invention is a three-liquid-phase redox battery comprising a catholyte liquid phase, an anolyte liquid phase and an intermediate liquid phase placed between them. In particular, the three-liquid-phase redox battery does not comprise a separator. Thus, the intermediate liquid phase, the catholyte and of the anolyte redox battery of the invention are liquid phases; and the catholyte and the anolyte are in contact with the intermediate liquid phase placed between them. An exemplary and non-limiting embodiment of the redox-battery of the invention is illustrated on Figure 1.

[0046] In an embodiment, the redox-battery of the invention may work in a dynamic or static mode; preferably in a dynamic mode, for example, wherein the intermediate liquid phase, the catholyte and / or the anolyte is in fluidic communication with an external reservoir container; preferably the catholyte and the anolyte are in fluidic communication with an external reservoir container.

[0047] In a particular embodiment, the redox-battery of the invention is a redox flow battery. In the context of the present invention, the term “flow battery” is intended to refer to a battery system in which the intermediate liquid phase, the catholyte and / or the anolyte are transported into and out of the battery, in particular, to one or more external reservoir containers.

[0048] The catholyte and the anolyte are in contact through an intermediate liquid phase placed between them, in particular, the intermediate liquid phase comprises two opposite sides and each of the catholyte and the anolyte is in physical contact with one side of the intermediate liquid phase placed between them; preferably in physical direct contact. In other words between each of the catholyte and the anolyte and the intermediate liquid phase there is only an interface; preferably an interface that consists of: (i) the catholyte or the anolyte, and (ii) the intermediate liquid phase; more preferably an interface that consists of (i) molecules from the catholyte or the anolyte and (ii) molecules from the intermediate liquid phase.

[0049] In a particular embodiment, the redox battery does not comprise a separator, particularly it does not comprise a physical separator as known in the art such as a membrane. In a more particular embodiment, the redox-battery of the invention is a membrane-less redox battery.

[0050] In a more particular embodiment, the redox battery of the present invention is able to work in transitional or turbulent flow conditions (i.e. not laminar flow conditions). Surprisingly, the authors of the present invention have observed that the battery of the present invention does not need laminar flow conditions to be able to work as a redox battery or as a redox flow battery. In the context of the present invention the expression “laminar flow conditions” is understood as conditions wherein a flow is characterized by fluid particles (i.e. liquid molecules) following smooth paths in layers, with each layer of fluid particles moving smoothly past the adjacent layers with little or no mixing.

[0051] The fact that the catholyte and the anolyte (electrolytes) are in contact through an intermediate liquid phase placed between them; means that the redox battery of the invention comprises three-liquid phases in the following order: (1) an electrolyte liquid phase (being a catholyte or an anolyte liquid phase), (2) an intermediate liquid phase and (3) another electrolyte liquid phase (being a catholyte or an anolyte liquid phase); thus, each of the electrolytes are in physical contact with the intermediate liquid phase; in other words one side of the intermediate liquid phase is in contact with the anolyte and the other side is in contact with the catholyte.

[0052] Miscibility

[0053] The intermediate liquid phase, the catholyte and the anolyte of the invention are immiscible among each other (i.e. they are insoluble in each other). Thus, when they are put in contact, the intermediate liquid phase, the catholyte and the anolyte of the battery of the invention form three immiscible phases (i.e. the intermediate liquid phase, the catholyte and the anolyte cannot form a homogeneous phase among each other); wherein the intermediate liquid phase is placed between the catholyte and the anolyte; in particular they form three thermodynamically immiscible phases. Then, the catholyte and the anolyte are in physical contact with the intermediate liquid phase. In particular, between the catholyte and the intermediate liquid phase there are an interphase and between the anolyte and the intermediate liquid phase there are another interphase; preferably wherein said interphases consist of (i) the catholyte or the anolyte and (ii) the intermediate liquid phase.

[0054] In an embodiment, the battery of the invention does not comprise separators in / on the interfaces between the each of the two electrolytes and the intermediate liquid phase.

[0055] In other words, the intermediate liquid phase and the catholyte of the battery of the invention are immiscible between them; the intermediate liquid phase and the anolyte are immiscible between them; and the catholyte and the anolyte are immiscible between them.

[0056] The term “intermediate” regarding the intermediate liquid phase of the battery of the invention is understood as indicating that said phase is placed between the catholyte and the anolyte. If the intermediate liquid phase, the catholyte and the anolyte of the invention are mixed, when the mixture is settled, spontaneous phase separation may occur, forming three immiscible phases: wherein the catholyte and the anolyte are separated by the intermediate liquid phase placed between them.

[0057] In addition, the intermediate liquid phase of the invention is ionically conductive. In the context of the present invention the term “ionic conductivity” is understood as known in the art, such as electrical conductivity due to the motion of ionic charge.

[0058] Density

[0059] In a particular embodiment, the intermediate liquid phase, the catholyte and the anolyte have different density values among them; preferably, the density value of the intermediate liquid phase is between the density value of the catholyte and the density value of the anolyte.

[0060] In a more particular embodiments, the intermediate liquid phase, the catholyte and the anolyte have different density values among them, wherein all of them are in the range from 0.5 to 2 g / ml; preferably from 0.6 to 1.5 g / ml; more preferably from 0.8 to 1.3 g / ml. In the context of the present invention, the density values of the intermediate liquid phase, the catholyte and the anolyte have been determined by any method known in the art, in particular they have been calculated from the average of a significant number of measurements done with a digital densimeter.

[0061] Without being bound to a particular theory, the authors of the present invention have observed that the fact that the intermediate liquid phase, the catholyte, and the anolyte are not miscible with each other and have different densities, makes the battery more robust and stable over time that other batteries of the art.

[0062] Homogeneous phases

[0063] The intermediate liquid phase is homogeneous; preferably is homogeneous at a molecular level. In particular, the intermediate liquid phase is not a heterogeneous phase such as an emulsion.

[0064] In an embodiment, the intermediate liquid phase, the catholyte and / or the anolyte of the invention are homogeneous; preferably are homogeneous liquid phases; more preferably are molecularly homogeneous liquid phases. In the context of the present invention the expression “molecularly homogenous liquid phase” is understood as referring to a liquid phase in which the molecular composition is uniform throughout. This means that the molecules are evenly distributed, and there are no regions with different molecular compositions within the phase. In such a phase, every small volume of the liquid has the same properties and composition as any other small volume, indicating complete miscibility and uniformity at the molecular level.

[0065] In an embodiment, the intermediate liquid phase, the catholyte and / or the anolyte of the invention are not heterogeneous; preferably are not heterogeneous liquid phases.

[0066] In an embodiment, the intermediate liquid phase, the catholyte and / or the anolyte of the invention are not emulsions.

[0067] In an embodiment, the intermediate liquid phase, the catholyte and / or the anolyte of the invention are not micro-emulsions.

[0068] Composition

[0069] In an embodiment, the catholyte and the anolyte comprise at least a salt; preferably, the al least a salt is in varying amounts between them.

[0070] In an embodiment, the intermediate liquid phase, the catholyte and / or the anolyte comprise at least a salt and an optional polymer; preferably, wherein the at least a salt is in varying amounts among them.

[0071] In another embodiment, the intermediate liquid phase, the catholyte and / or the anolyte comprise a polymer; preferably, wherein the polymer is in varying amounts among them.

[0072] In a more particular embodiment, the intermediate liquid phase, the catholyte and the anolyte have a different composition among them; preferably they comprise at least a salt and an optional polymer; wherein the at least a salt and the optional polymer are in different amounts among them.

[0073] In a particular embodiment, the intermediate liquid phase, the catholyte and the anolyte have different density values.

[0074] In a particular embodiment, the catholyte and the anolyte have different density values between them. In a particular embodiment, the catholyte and the anolyte have a different chemical composition between them. In an embodiment, the catholyte and the anolyte comprise: redox-active species, at least a salt, and an optional polymer.

[0075] In a more particular embodiment, the catholyte and the anolyte consist of: redox-active species; at least a salt; an optional polymer, and a solvent; preferably redox-active species; at least a salt, an optional polymer and water.

[0076] In another particular embodiment, the intermediate liquid phase consist of: at least a salt, a polymer and a solvent; preferably, at least a salt, a polymer and water.

[0077] In a particular embodiment, the at least a salt of the intermediate liquid phase, the catholyte and / or the anolyte is a phosphonium salt, an ammonium salt, or a mixture thereof; preferably is a mixture of phosphonium and ammonium salts.

[0078] In a particular embodiment, the phosphonium salt is an alkyl phosphonium salt; more preferably is an alkyl phosphonium chloride; even much more preferably tributyltetradecylphosphonium chloride.

[0079] In a particular embodiment, the ammonium salt is an ammonium sulfate salt.

[0080] In another particular embodiment, the polymer is a hydrophilic polymer such as acrylic polymers, epoxy resins, polyethylenes, polystyrenes, polyvinylchlorides, polytetrafluorethylenes, polydimethylsiloxanes, polyesters, polyurethanes and mixtures thereof.

[0081] In another particular embodiment, the polymer is a poly(ethylene glycol) (PEG) polymer. The poly(ethylene glycol) (PEG) polymers able to be used in the present invention may be prepared by polymerization of ethylene oxide. The PEG of the present invention may be commercially available over a wide range of molecular weights.

[0082] In a particular embodiment, the polymer has an average molecular weight of between 10 and 10000 g / mol; preferably an average molecular weight of between 100 and 8000; more preferably of between 500 and 6000; more preferably of between 600 and 4500 g / mol; more preferably of between 700 and 3000 g / mol; more preferably of between 1000 and 2500 g / mol; more preferably of between 1100 and 2000 g / mol; more preferably of between 1400 and 1600 g / mol; even much more preferably is around 1500 g / mol. In the context of the present invention, the “molecular weight” of the polymer may be calculated by any technique known in the art, for example as the z-average molecular weight as measured by high performance liquid chromatography (HPLC) as known in the art; preferably, as the z-average molecular weight calculated from the molecular weight distribution measured by high performance liquid chromatography (HPLC) in g / mol.

[0083] The term “alkyl” refers to a linear or branched hydrocarbon chain radical consisting of carbon and hydrogen atoms, containing no insaturation which is attached to the rest of the molecule by a single bond, including for example and in a non-limiting sense, methyl, ethyl, n-propyl, i-propyl, n-butyl, t-butyl, n-pentyl, etc. The aforementioned alkyl group can be unsubstituted or can be substituted at one or more available positions with the suitable groups disclosed in each case. In a particular embodiment, it can be substituted with one, two or three, preferably with one or two, more preferably with one said suitable groups.

[0084] In a particular embodiment, the solvent of the intermediate liquid phase, the catholyte and / or the anolyte is a polar solvent or solvent mixture such as water or alcohols (methanol, ethanol, isopropanol, n-propanol, t-butanol, benzyl alcohol, etc.); preferably water.

[0085] In a particular embodiment, the solvent of the intermediate liquid phase, the catholyte and the anolyte is the same. In another embodiment the electrolytes (catholyte and anolyte) comprise a different solvent or solvent mixture. In another particular embodiment one electrolyte comprises a polar solvent and the other electrolyte comprises a non-polar solvent.

[0086] In a particular embodiment, the intermediate liquid phase, the catholyte and the anolyte are aqueous solutions; preferably aqueous solutions further comprising at least a salt and an optional polymer.

[0087] In a more particular embodiments, the intermediate liquid phase, the catholyte and the anolyte are aqueous solutions having different water weight percentages; preferably wherein the intermediate liquid phase has a water weight percentage value between the water weight percentage value of the catholyte and of the anolyte. In a more particular embodiment, the water weight percentage of the intermediate liquid phase is between 35 and 65 %; preferably between 38 and 55 %.

[0088] In a particular embodiment, the intermediate liquid phase, the catholyte and the anolyte liquid phases are stacked on top of each other, preferably wherein the catholyte and the anolyte are positioned at the top or bottom positions, and the intermediate liquid phase is positioned between them.

[0089] In another particular embodiment, the intermediate liquid phase, the catholyte and the anolyte liquid phases are stratified; preferably wherein the catholyte and the anolyte are positioned at the top or bottom positions, and the intermediate liquid phase is positioned between them.

[0090] In an alternative embodiment, the intermediate liquid phase, the catholyte and the anolyte liquid phases form an H battery.

[0091] Electrolytes

[0092] In the context of the present invention, the term “electrolytes” is referred to both a catholyte and / or an anolyte. In addition, the term “electrolyte” refers to a catholyte or an anolyte.

[0093] The catholyte and the anolyte of the battery of the invention comprise redox-active species.

[0094] In the context of the present invention “redox active species” relates to redox species wherein one species (the reducing agent) undergoes oxidation (losing electrons) while the other species (the oxidizing agent) undergoes reduction (gains electrons). For example, redox active species can be redox couples or redox pairs as known by the Expert in the art.

[0095] In another particular embodiment, the catholyte and the anolyte comprise different, the same redox active species or a mixture of redox active species; preferably different redox active species.

[0096] In an embodiment, the redox active species are organic, metallic, and / or organometallic redox active species; preferably organic and / or organometallic redox active species comprising a group selected from alloxazines, diimides, quinones, viologens, quinoxalines, phenazines, nitroxides, pyridines, diols or a mixture thereof.

[0097] In a more particular embodiment, the metallic and / or organometallic redox active species of the present invention comprise at least one element selected from Li, Na, Al, Ca, Mg, Pb, Ru, Fe, II, V, Cr, Ni, Mn, Cu, Ti, Ce, Zn or Co; preferably selected from Mg, Ru, Fe, V, Cr, Ni, Mn, Cu, Zn or Co, more preferably selected from Mg, Fe, Cr, Cu, Zn or Co. In another alternative particular embodiment, the redox active species used in the present invention comprise metallic and / or organometallic redox active species comprising elements selected from V, Fe, Co, Cu, Ru, Ni, or Mn.

[0098] In a particular embodiment, the metallic and / or organometallic redox active species used in the present invention comprise a redox couple comprising Fe2+ / Fe3+; Cr27Cr3+, Ti2+ / Ti3+; U3+ / U4+; Ce3+ / Ce4+; V2+ / V3+; V4+ / V5+, Cu7Cu2+, Zn27Zn, Li+ / Li, Na+ / Na, AI3+ / AI, Ca2+ / Ca, Mg2+ / Mg, Sn2+ / Sn4+, ruthenium(lll) / ruthenium(ll), uranium(IV) / (V), uranium V(lll) / V(ll), chromium (lll) / chromium (IV), Mn(lll) / Mn(ll), Cu / Cu(ll) and / or Pb2+ / Pb; preferably a redox couple comprising Fe2+ / Fe3+; Cr27Cr3+, V2+ / V3+; V4+ / V5+or Cu+ / Cu2+.

[0099] In another particular embodiment, the redox active species used in the present invention comprise a redox couple comprising at least a group selected from quinones, viologens, quinoxalines, phenazines, nitroxides, pyridines, diols, flavines, phenothiazines, pyridinum derivates, benzene derivatives, phtalimides, antracene, thiadiazole, alloxacines, naphtoquines, perylene diimide, cyclopropenium, or p-phenylenediamine.

[0100] In another particular embodiment, the organic and / or oganometallic redox active species used in the present invention comprise a redox couple comprising a group selected from quinones, antraquinones, viologens, quinoxalines, phenazines, nitroxides, pyridines, diols, flavines, phenothiazines, pyridinum derivates, benzene derivatives, phtalimides, antracene, thiadiazole, alloxacines, naphtoquines, perylene diimide, cyclopropenium, p- phenylenediamine or a mixture thereof; preferably a redox couple comprising a group selected from quinones, viologens, quinoxalines, phenazines, nitroxides, pyrdines, diols, or a mixture thereof.

[0101] In a preferred embodiment, the redox active species of the redox battery of the present invention comprise a redox couple comprising a viologen group and another redox couple comprising Fe such as a ferrocene derivate; preferably they comprise a redox couple comprising methyl viologen (MV) and another redox couple comprising (Ferrocenylmethyl)trimethylammonium.

[0102] In a preferred embodiment, the redox active species of the redox battery of the present invention consist of a redox couple comprising a viologen group and another redox couple comprising Fe such as a ferrocene derivate; preferably they consist of a redox couple comprising methyl viologen (MV) and another redox couple comprising (Ferrocenylmethyl)trimethylammonium. In a particular embodiment, the anolyte and / or the catholyte of the redox battery of the present invention comprise at least 0.01 M of redox active species; preferably between 0.005 M and 5 M of redox active species; even more preferably between 0.01 M and 3 M of redox active species; even much more preferably between 0.05 and 1 M of redox active species.

[0103] In the context of the present invention, the term molar concentration also called molarity, expressed as M, is understood as mol / L.

[0104] In a more preferred embodiment, the anolyte comprises methylviologen dichloride (MV); and / or the catholyte comprises (Ferrocenylmethyl)trimethylammonium chloride (FcNCI); particularly the anolyte comprises at least 0.01 M of MV and / or the catholyte comprises at least 0.01 M of FcNCI; more particularly the anolyte comprises between 0.01 M and 3 M of MV and / or more particularly the catholyte comprises between 0.01 M and 3 M of FcNCI; even more particularly the anolyte comprises between 0.05 M and 1 M of MV and / or more particularly the catholyte comprises between 0.05 M and 1 M of FcNCI.

[0105] In a more preferred embodiment, the redox active species of the anolyte consist of methylviologen dichloride (MV); and / or the redox active species of the catholyte consist of (Ferrocenylmethyl)trimethylammonium chloride (FcNCI); preferably in an amount of at least 0.005M; more preferably between 0.005 M and 5 M; even more preferably between 0.01 M and 3 M; even much more preferably between 0.05 and 1 M.

[0106] The anolyte, the catholyte and the intermediate liquid phase of the invention form a three- phase immiscible system wherein the compounds of the redox active species have different solubility in each of the immiscible phases once the equilibrium between those phases has been reached. Particularly, for example, when MV and FcNCI are used as redox active species, then, FcNCI is mostly dissolved in the catholyte and MV is mostly dissolved in the anolyte.

[0107] In a more particular embodiment, the catholyte of the invention comprises:

[0108] - water;

[0109] - poly(ethylene glycol) (PEG); preferably in an amount of between 1 and 25 wt% of the total weight of the catholyte; preferably between 2 and 15 wt%; more preferably between 4 and 10 wt%;

[0110] - a mixture of phosphonium and ammonium salts; preferably in an amount of between 20 and 80 wt% of the total weight of the catholyte; preferably between 30 and 70 wt%; and

[0111] - redox active species; and / or the anolyte of the invention comprises:

[0112] - water;

[0113] - a mixture of phosphonium and ammonium salts; preferably in an amount of between 10 and 70 wt% of the total weight of the anolyte; preferably between 20 and 60 wt%; more preferably between 30 and 50 wt%; and

[0114] - redox active species; and / or the intermediate liquid phase of the invention comprises:

[0115] - water;

[0116] - poly(ethylene glycol) (PEG); preferably in an amount of between 10 and 80 wt% of the total weight of the intermediate liquid phase ; more preferably between 30 and 70 wt%; more preferably between 40 and 60 wt%;

[0117] - a mixture of phosphonium and ammonium salts; preferably in an amount of between 1 and 25 wt% of the total weight of the intermediate liquid phase; more preferably between 5 and 20 wt%.

[0118] In a more particular embodiment, the catholyte of the invention consist of:

[0119] - water;

[0120] - poly(ethylene glycol) (PEG); preferably in an amount of between 1 and 25 wt% of the total weight of the catholyte; preferably between 2 and 15 wt%; more preferably between 4 and 10 wt%;

[0121] - a mixture of phosphonium and ammonium salts; preferably in an amount of between 5 and 80 wt% of the total weight of the catholyte; preferably between 30 and 70 wt%; and

[0122] - redox active species; and / or the anolyte of the invention consist of:

[0123] - water;

[0124] - a mixture of phosphonium and ammonium salts; preferably in an amount of between 5 and 70 wt% of the total weight of the anolyte; preferably between 20 and 60 wt%; more preferably between 30 and 50 wt%; and

[0125] - redox active species; and / or the intermediate liquid phase of the invention consist of:

[0126] - water;

[0127] - poly(ethylene glycol) (PEG); preferably in an amount of between 10 and 80 wt% of the total weight of the intermediate liquid phase; preferably between 30 and 70 wt%; more preferably between 40 and 60 wt%;

[0128] - a mixture of phosphonium and ammonium salts; preferably in an amount of between 1 and 25 wt% of the total weight of the intermediate liquid phase; preferably between 5 and 20 wt%.

[0129] In an embodiment, the intermediate liquid phase, the catholyte and / or the anolyte are liquid at temperatures below 200°C; preferably below 150°C; more preferably below 100°C.

[0130] In another embodiment, the intermediate liquid phase, the catholyte and / or the anolyte are liquid at temperatures equal or between about -15 °C and about 200°C; preferably equal or between about -12 °C and about 150°C; more preferably equal or between about -10 °C and about 99°C, even much more preferably equal or between about 0 °C and about 99°C.

[0131] Electrodes

[0132] In the context of the present invention the term “electrodes” refers to the positive and negative electrodes. The electrodes are wherein the oxidation or reduction of redox active species of the electrolyte take place. The electrodes of the invention comprise, at least, a positive electrode and a negative electrode. Both electrodes may have connection terminals that may be electrically connected to each other by a connection wire through which electrons are able to travel.

[0133] In a particular embodiment, the positive electrode and the negative electrode are facing each other; preferably are parallel and face each other. In a particular embodiment, the positive electrode and the negative electrode are aligned. In another particular embodiment, the electrodes are perpendicular to each other. In another particular embodiment the positive electrode and the negative electrode form an angle between 1 and 89 degrees; preferably between 2 and 60 degrees.

[0134] In a particular embodiment, the positive and / or negative electrode of the battery of the present invention are porous; preferably the positive and / or negative electrodes of the battery have a porosity of between 30% and 97%; preferably of between 50 and 96%; more preferably of between 80 and 95%; even more preferably of about 90%. Porosity is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1 , or as a percentage between 0% and 100%.

[0135] In a particular embodiment, the electrodes of the redox battery are solid electrodes.

[0136] Non-limiting examples of suitable electrodes in the battery of the present invention are selected from a carbon matrix or a metallic matrix; particularly are selected from a porous carbon matrix or a porous metallic matrix; more preferably carbon paper, carbon felt, graphite felt, reticulated porous carbon, metallic mesh or metallic foam. In a preferred embodiment, the positive electrode and / or the negative electrode are made of a carbon based material, more preferably are carbon paper, carbon felt, graphite felt, or reticulated porous carbon; even much more preferably carbon felt.

[0137] In a more particular embodiment, the positive electrode and / or the negative electrode are made of a carbon based material that was pretreated at at least 100°C for between

[0138] 1 and 10 hours; preferably that was pretreated at between 200°C and 500°C for between

[0139] 2 and 8 hour; more preferably that was pretreated at about 400 °C for about 4 hours.

[0140] The authors of the present invention have observed that when the positive electrode and / or the negative electrodes are made of a pretreated carbon based material their hydrophilicity was enhanced, improving the performance of the battery.

[0141] In an embodiment, the positive and / or negative electrode of the battery of the present invention comprise a metallic matrix such as zinc, stainless steel, copper, nickel, lithium or sodium matrix or a carbon matrix such as graphite. In another particular embodiment, the matrix can be porous or non-porous; preferably the matrix is porous and can be selected from a mesh, paper or a felt.

[0142] In a particular embodiment, the battery of the invention further comprises at least one reservoir container, for example an anolyte, catholyte and / or an intermediate phase reservoir container; wherein reservoir container is connected in fluidic communication with the battery, for example with the anolyte, the catholyte and / or the intermediate phase.

[0143] Deformations, perturbations and / or distortions of the interfaces between the each of the two electrolytes and the intermediate liquid phase might occur if the battery is moved. Surprisingly, the authors of the present invention have found that due to the three phases being immiscible among each other, the battery is not significantly affected. For example, the three immiscible phases of the battery maintained their configuration after tilting. In addition, after being vigorously mixed, the original top, middle and bottom phases were formed after a few minutes / hours.

[0144] Power / source load

[0145] The battery of the present invention may comprise means for connecting a power / load source. The power / load source may be any external electrical device such as an electrical grid, an electric vehicle, a domestic appliance or a sensor, that draws / transfers energy from / to the battery. In general, the power / load source have controllable voltages and / or current supplies or uptakes.

[0146] Energy storage and / or delivery system

[0147] In another aspect, the invention is directed to an energy storage and / or delivery system comprising at least one redox battery according to the present invention in any of its particular embodiments; preferably at least two redox batteries according to the present invention in any of its particular embodiments. In particular, the redox battery may act a secondary and / or rechargeable battery, i.e. the redox battery may be configured to be reversibly charged and discharged.

[0148] Methods of operation of the battery

[0149] As mentioned before, the redox-battery of the present invention in any of its particular embodiments is configured to act as an energy storage and delivery system, i.e. it is configured to be reversibly charged and discharged.

[0150] Method of storing electricity

[0151] Another aspect of the present invention is directed to a method of storing electricity comprising the steps of: a) providing the battery of the invention in any of its particular embodiments; b) oxidizing the redox active species of the catholyte at one electrode to the corresponding oxidized state, while the redox active species of the anolyte are reduced to the corresponding reduced state at the other electrode.

[0152] An illustrative non-limiting example of an embodiment of the battery of the invention works as storage system (charging mode) is described as follows: during the charging process of an embodiment of the battery of the present invention, the redox active species of the catholyte are oxidized. Then, the electrons released on the positive electrode of the battery of the present invention move through an external circuit, i.e. the power / load source, to do useful work. At the same time, the redox active species of the anolyte are reduced (capture electrons) to the corresponding reduced state at the negative electrode. Catholyte and anolyte are separated by an intermediate liquid phase. The intermediate liquid phase, the catholyte and the anolyte of the battery are immiscible among each other. During the charging process, ions migrate from one electrolyte to the other crossing the intermediate liquid phase to keep electro-neutrality between them.

[0153] Method of delivering electricity

[0154] Therefore, another aspect of the present invention is directed to a method of delivering electricity comprising the steps of: a) providing the battery of the invention in any of its particular embodiments; b) reducing the redox active species of the catholyte at the one electrode to their reduced state while the redox active species of the anolyte are oxidized to the corresponding oxidized state at the other electrode.

[0155] An illustrative example on how the battery of the invention works as delivery system (discharging mode) is described as follows: During the discharging process of an embodiment of the battery of the present invention, the redox active species of the catholyte are reduced at one electrode. At the same time, the anolyte redox active species are oxidized to the corresponding oxidized state at the negative electrode. Catholyte and anolyte are separated by an intermediate liquid phase. The intermediate liquid phase, the catholyte and the anolyte of the battery are immiscible among each other. During the discharging process, ions migrate from one electrolyte to the other crossing the intermediate liquid phase to keep electro-neutrality between them.

[0156] Use

[0157] Additional aspects of the present invention are directed to the use of the redox-battery or the energy storage and / or delivery system as defined above in any of its particular embodiments, to store and / or deliver energy. To this end, the redox battery or the energy storage and / or delivery system of the present invention may be used individually, as modular redox-battery system, or in combination with other energy storage technologies (e.g., supercapacitors, etc.) and may be integrated into or with various systems and / or devices to improve efficiency, address energy demands, etc.

[0158] Furthermore, the redox battery or the energy storage and / or delivery system of the invention may be used in a variety of applications having different energy delivery and / or storage needs, including, but not limited to, very large scale applications (e.g., utilities, functioning as a green energy source for a smart grid, energy storage for use in combination with renewable energy resources such as wind and solar power, etc.) and smaller applications (e.g. backup power, residential power, electromobility sector, etc.).

[0159] Throughout the description and claims the word “comprises" and variations of the word, are not intended to exclude other technical features, additives, components or steps. Furthermore, the word “comprise” encompasses the case of “consisting of”. Additional objects, advantages and features of the invention will become apparent to those skilled in the art upon examination of the description or may be learned by practice of the invention.

[0160] In a particular embodiment, the redox battery of the invention is used to store and / or deliver electricity; preferably in stationary applications such as stationary power applications such as backup power systems or a grid-scale battery system, in large energy storage systems such as utility-scale battery farms, in residential energy storage (behind the meter), and / or in transportation or electro mobility such as in electric vehicles (EVs).

[0161] The present invention will be described in further detail with reference to the following examples. These examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0162] EXAMPLES

[0163] EXAMPLE 1 : Redox batteries performance.

[0164] The performance of a redox battery comprising two electrodes and three immiscible liquid phases (namely Battery A) was tested. In addition, the performance of Battery A was compared with the performance of a similar battery comprising only two immiscible phases (namely Battery B). Battery A and B were as follows:

[0165] Battery A was a redox battery comprising two electrodes and a main compartment containing three phases that are immiscible among them: a top phase, a middle phase and a bottom phase. The top and bottom phases are electrolytes of the battery and the middle phase was an intermediate liquid phase. In addition, Battery A did not have a separator such as a membrane.

[0166] The three phases system of the battery A (see Figure 1) were generated by dissolving three solutes in water in different amounts. The solutes were: polyethylene glycol with an average molecular weight of 1500 g / mol (PEG1500), Tributyltetradecylphosphonium chloride (P44414CI), and ammonium sulfate ((NH4)2SO4). Each of the three phases have a different amount of each of the three compounds. Therefore, each phase has a different density. The concentration of PEG1500 ranged from 0% to 55% by weight over the total weight of the liquid phase, while P44414CI ranged from 2% to 60% by weight, and (NH4)2SO4 ranged from 1% to 35% by weight.

[0167] The redox active species used in the top and bottom phase electrolytes of the three phases were (Ferrocenylmethyl)trimethylammonium chloride (FcNCI) and methylviologen dichloride (MV). FcNCI was present in a concentration of 0.1M in the top phase, serving as the catholyte, while MV was present in a concentration of 0.1 M in the bottom phase, acting as the anolyte.

[0168] For the battery A assembly, 1.5mL of the top and bottom phases were used, with 0.5mL of the middle phase positioned between them (being an intermediate liquid phase). As can be seen on Figure 1 , the three phases were vertically stacked.

[0169] Battery B was a redox battery comprising two electrodes and a pair of immiscible electrolytes. Battery B did not have a separator between the electrolytes.

[0170] In the case of battery B (included just for comparison) 1.5 mL of the top and bottom phases were used comprising redox active species as in the three phase's battery A. The redox active species used in the electrolytes were (Ferrocenylmethyl)trimethylammonium chloride (FcNCI) and methylviologen dichloride (MV). FcNCI was present in a concentration of 0.1 M in the top phase, serving as the catholyte, while MV was present in a concentration of 0.1 M in the bottom phase, acting as the anolyte. Each phase had a different amount of PEG1000 and (NH4)2SO4. The concentration of PEGwoo ranged from 0.010% to 70% by weight over the total weight of the liquid phase, while the concentration of (NH4)2SC>4 ranged from 1% to 60% by weight.

[0171] In both batteries, carbon felt electrodes were employed, measuring 4.6 mm in thickness and with a geometrical area of 1.7 cm2. One electrode was submerged in the top phase, while the other electrode was submerged in the bottom phase. Prior to usage, the carbon felt material underwent a pretreatment process at 400°C for 4 hours to enhance its hydrophilicity.

[0172] The A and B batteries, whose results are shown in Figures 2-5, were based on systems containing the same catholyte and anolyte species in all the cases. In none of them, a solid separator or layer was placed between the different liquid phases. The C-rate used in the experiments was determined based on the theoretical capacity of the battery at the determined state-of-charge (SOC). Thus, a C-rate of 1C corresponded to a current density of 4 mA. The coulombic efficiency (CE) of a battery is determined as the ratio between discharged capacity and charged capacity during a charge-discharge cycle.

[0173] Figure 2 shows the voltage (V) overtime (h) for batteries (i) A and (ii) B for an experiment that comprised recording of the open-circuit voltage (OCV) of the charged batteries at 20% SOC over time. The same redox active species were used in both batteries at 0.1 M concentration. Figure 2 shows that battery A comprising three phases being immiscible among them, had better values of self-discharge than battery B.

[0174] Figure 3 shows the voltage (V) results over capacity for batteries (i) A and (ii) B for their galvanostatic charge-discharge profile. In the corresponding experiment, both batteries were charged and discharged from 0 to 20% SOC at C / 2 with an upper and lower voltage cut-off of 1.5 and 0.4 V, respectively. Please notice that battery A comprising three phases has higher discharge capacity than battery B and therefore higher coulombic efficiency. Particularly, battery A had a 97% discharge capacity while battery B had 86%.

[0175] The rate performance of battery A was tested. Figure 4 shows the results of the coulombic efficiency (%) over number of cycles for battery A. For said experiment, battery A was consecutively galvanostatically charged-discharged from 0 to 20% SOC at different C-rates from C / 5 to 1C with upper and lower voltage cut-offs of 1.5 and 0.4 V, respectively. As can be seen on Figure 4, battery A show high % values of coulombic efficiency.

[0176] Figure 5 shows a discharge polarization curve comparison between (i) battery A and (ii) battery B. To obtain the discharge polarization curve of both batteries, a current scan was conducted in the range of 0 to 6 mA cm-2recording the voltage signal of the batteries. In addition, power density was calculated by applying the following equation:

[0177] Power density = Voltage ■ Current density.

[0178] In summary, battery A was able to operate at high current densities. Battery A also reached high states of charge (SOC). Moreover, Battery A comprising three phases being immiscible among them, had an improved performance over previous designs such as battery B. In particular, Battery A showed almost no self-discharge, in addition it had a greater coulombic efficiency than battery B, leading to greater energy density and power. Moreover, contrary to battery B, Battery A can be stored for long time once charged.

[0179] EXAMPLE 2: Three phases stability tests

[0180] The stability over time and after shanking of the three phases of battery A of example 1 was tested.

[0181] The three phases of battery A were shaked. After a few hours, the original top, middle and bottom phases were formed again (see figure 6). In addition, those three phases remained stable even after several months of storage. In addition, the three phases of battery A maintained their separated configuration after tilting (see figure 7a).

[0182] For comparative reasons a three phase system C was tested under tilting. System C consisted in two organic liquid electrolytes separated by an intermediate aqueous phase. In particular, the organic liquid electrolytes of system C comprised tetrabutylammonium perchlorate (TBACIO4), dimethylcarbonate (DMC) as solvent and 2, 2,6,6- Tetramethylpiperidin-1-yl)oxyl or (2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl (TEMPO) as redox specie. The intermediate aqueous phase of system C comprised water and 0.1 M of NaCI. Thus, the electrolytes were miscible between them but immiscible with the intermediate liquid phase. The tilting test of system C resulted in the mixing of said organic electrolytes (see figure 7b).

[0183] For additional comparative reasons the stability over time of an additional three phase system D was studied. The top phase of said system D was an aqueous phase and the bottom phase was an organic phase wherein the solvent was dichloromethane (DCM). The top and the bottom phases were electrolytes. In addition, the middle phase was formed by an emulsion of the top and bottom phases (i.e. the middle phase was a heterogeneous phase, in particular it was a bicontinuous phase). All the phases of system D further comprise surfactants and salts. Results showed that after just five hours of forming the three phase system, the volume of the middle phase had changed. Moreover, after less than 24 hours, the middle phase had disappeared (Figure 8). In addition, Figure 9 shows pictures of the two phases formed after the three phase system D was shaked.

Claims

CLAIMS1 . A redox battery comprising:- two electrodes; and- a catholyte and an anolyte; wherein the catholyte and the anolyte are liquid and comprise redox-active species; wherein the catholyte and the anolyte are in contact through an intermediate liquid phase placed between them; wherein the intermediate liquid phase, the catholyte and the anolyte are immiscible among each other; wherein the intermediate liquid phase is homogeneous and ionically conductive; and wherein the catholyte and / or the anolyte comprise at least a salt.

2. The redox battery according to claim 1 , wherein the intermediate liquid phase comprises at least a salt.

3. The redox battery according to claim 2, wherein the intermediate liquid phase, the catholyte and / or the anolyte comprise a polymer.

4. The redox battery according to claims 1 to 3, wherein the intermediate liquid phase, the catholyte and / or the anolyte are aqueous solutions.

5. The redox battery according to any one of claims 1 to 4, wherein the intermediate liquid phase, the catholyte and the anolyte have different density values among them.

6. The redox battery according to any one of claims 1 to 5, wherein the catholyte and the anolyte comprise different redox active species.

7. The redox battery according to claim 6, wherein the redox active species of the anolyte comprise a viologen group and the redox active species of the catholyte comprise Fe.

8. The redox battery according to any one of claims 1 to 7, wherein the battery does not comprise a separator.

9. The redox battery according to any one of claims 1 to 8, wherein the intermediate liquid phase, the catholyte and the anolyte are static.

10. The redox battery according to any one of the previous claims, wherein the intermediate liquid phase, the catholyte and the anolyte are stacked on top of each other.11 . The redox battery according to any one of the previous claims, wherein at least one of the intermediate liquid phase, the catholyte and / or the anolyte is in fluidic communication with an external reservoir container.

12. The redox battery according to any one of the previous claims, wherein the intermediate liquid phase, the catholyte and / or the anolyte are liquid at temperatures between about -10 and about 99°C.

13. An energy storage and / or delivery system comprising at least one redox battery according to any of claims 1 to 12.

14. A method of storing electricity comprising the steps of: a) providing a redox battery according to any of claims 1 to 12; b) oxidizing the redox active species of the catholyte at one electrode to the corresponding oxidized state, while the redox active species of the anolyte are reduced to the corresponding reduced state at the other electrode.

15. A method of delivering electricity comprising the steps of: a) providing a redox battery according to any of claims 1 to 12; b) reducing the redox active species of the catholyte at the one electrode to their reduced state while the redox active species of the anolyte are oxidized to the corresponding oxidized state at the other electrode.

16. Use of the redox battery (10) according to any of claims 1 to 12 or the energy storage and / or delivery system of claim 13 to store and / or deliver electricity.

17. The use according to claim 16 in stationary applications in large energy storage systems, in residential energy storage (behind the meter), and / or in transportation.

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