Liquid electrolyte for metal / oxygen batteries

Abstract

Liquid Electrolyte for Metal / Oxygen Battery. The present invention relates to a liquid electrolyte for a metal / oxygen battery, comprising: - at least one alkali or alkaline earth metal salt, in particular a lithium salt; - at least one fluorocarbon solvent having an oxygen solubility of at least 30% v / v; - at least one fluorinated solubilizing agent, distinct from said fluorocarbon solvent(s), selected from mono-, poly-, or per-fluorocarbon compounds, saturated, unsaturated, and / or aromatic, linear, branched, and / or cyclic, having from 4 to 18 carbon atoms, the carbon chain of which bears at least one polar terminal unit; and - at least one ether-type solvent. It also relates to a metal / oxygen battery, in particular a lithium / oxygen battery, comprising such a liquid electrolyte, as well as a portable device comprising such a battery.

Description

Description Title of the invention: Liquid electrolyte for metal / oxygen batteries technical field

[0001] — The present invention relates to the field of metal / oxygen batteries, such as Lithium / oxygen batteries, it relates more specifically to a new liquid electrolyte that can be used in such metal / oxygen batteries. Previous technique

[0002] — Metal-oxygen batteries, also called metal-air batteries, are a category of electrochemical generators, in which oxygen, from the ambient environment, is reduced in the surface area of ​​the cathode. The reduction of oxygen forms an oxide or peroxide ion which reacts with a metallic species ca- tionic.

[0003] — The best-known metal / air batteries, which are the subject of much research These include zinc / oxygen, magnesium / oxygen, and aluminum / oxygen batteries. or lithium / oxygen.

[0004] — Generally speaking, in these batteries, oxygen is the active material of the positive electrode. It is a powerful, lightweight oxidant and readily available. "free of charge." Furthermore, depending on the system's design, it may not be possible to... initially stored in the battery. Oxygen can then be drawn directly. in the atmosphere via the use of an air cathode employing a membrane filtering, for selective oxygen supply. These systems therefore theoretically possess- likely a high mass energy density.

[0005] — In order to retain the advantages associated with the use of oxygen, the material of The negative electrode of a metal / air battery must possess several characteristics. Its molar mass must be low and the charge carried by its oxidized species (cations) must be large to offer maximum capacity density (per unit of weight or volume). It must be a powerful reducer to provide a significant voltage to battery terminals and thus a high energy density. Finally, it must be abundant and low-cost for obvious economic reasons. The elements Materials meeting these requirements include lithium, aluminum, and magnesium. calcium, iron and zinc, with lithium appearing to be the best choice for the development of electrochemical systems with high mass energy density.

[0006] For obvious reasons, the optimization of the performance of metal / oxygen, and in particular lithium / oxygen batteries, is a permanent objective.

[0007] — The formulation of the electrolyte used in metal / oxygen batteries, in particular lithium / oxygen, therefore, plays a crucial role in influencing performance of the electrochemical system. This electrolyte must of course have good ionic conductivity to ensure the mobility of ions between the positive and negative electrodes, but also be able to solubilize a large quantity of oxygen. Other parameters also influence the choice of electrolyte used. The liquid electrolyte must exhibit good electrochemical stability within the electrochemical system; it must also maintain low viscosity and remain liquid over a wide temperature range. Generally speaking, no single solvent can meet all of these requirements. Research has therefore focused on formulating liquid electrolytes that combine several solvents. As electrolytic solvents usually chosen for this purpose, aprotic polar solvents, such as carbonate solvents, for example ethylene carbonate, propylene carbonate, dimethyl carbonate, dipropyl carbonate and ethylmethyl carbonate, can be particularly cited. US patent application 2010 / 0266907 also reported the ability of perfluorocarbon solvents to dissolve oxygen and their potential as electrolytes for the positive electrode in a metal-ion battery, to increase the cathode potential. Unfortunately, this type of solvent is not compatible with the simultaneous dissolution of lithium salts. This is particularly true for LiCoPO4F, LiNiO4Mn, LiCoPO4, or LiCoPO4, which are especially advantageous because they allow access to higher potentials, on the order of 4.3 to 4.4 V, without requiring the use of additives. We can also cite document WO 2017 / 050672, which proposes formulating a liquid electrolyte for metal-oxygen batteries, combining fluorocarbon solvents with lithium salts and carbonate solvents. As illustrated in the examples section, these liquid electrolytes, however, have the drawback of resulting in low discharge capacity for lithium-air batteries, due to significant secondary reactions between the electrolyte and the lithium metal. We can also cite document CN 103996892, which describes electrolytes for lithium / air batteries, composed of ether(s) and a lithium salt, providing good stability and a capacity of 1000 mAh / g to 100 mAh / g in rechargeable form. Summary of the invention The present invention aims to provide a new liquid electrolyte exhibiting improved electrochemical stability, enabling access to a metal / oxygen battery, in particular a lithium / oxygen battery, having improved electrochemical performance, in particular exhibiting a high capacity, recovered in discharge. Thus, the invention relates, according to a first aspect, to a liquid electrolyte for a metal / oxygen battery, comprising: - at least one alkali or alkaline earth metal salt, in particular a lithium salt; - at least one fluorocarbon solvent having a solubility for oxygen of at least 30% v / v; - at least one fluorinated solubilizing agent, distinct from said fluorocarbon solvent(s), selected from mono-, poly- or per-fluorinated hydrocarbon compounds, saturated, unsaturated and / or aromatic, linear, branched and / or cyclic, having from 4 to 18 carbon atoms, the carbon chain of which bears at least one polar terminal motif, and possibly interrupted by one or more heteroatoms, in particular selected from oxygen and sulfur atoms and the radicals -N(R!)-, -B(R!)- and -P(R'R?)-, with R! and R, identical or different, representing a hydrogen atom or an alkyl radical in C, to C;, ; and - at least one ether-type solvent. The invention also relates to the use of a liquid electrolyte according to the invention, as defined above, in a metal / oxygen battery, and more particularly in a lithium / oxygen battery. It also relates to a metal / oxygen battery, in particular a lithium / oxygen battery, using a liquid electrolyte according to the invention. A metal / oxygen battery according to the invention can be integrated into a portable object such as a complex smart card. This battery can optionally enable additional functions by powering components embedded in the object, such as, for example: a microprocessor, a real-time clock, a keyboard, a display, a buzzer, a Bluetooth interface, one or more biometric sensors, a light source, the emission of a radio signal (various frequencies), etc. Thus, the invention also relates, according to another of its aspects, to a portable object comprising a metal / oxygen battery according to the invention. The wearable device can be in the form of a smart card or a wearable object such as a bracelet, a clip, a pendant, a ring, glasses for example. As illustrated in the examples that follow, the inventors have shown that the implementation of an ether solvent, in combination with a fluorocarbon solvent and a fluorinated solubilizing agent as defined above, to form the solvent medium of a liquid electrolyte, makes it possible to achieve particularly advantageous properties. In particular, the liquid electrolyte according to the invention, implemented as the electrolyte of a metal / oxygen battery, in particular a lithium / oxygen battery, makes it possible to achieve a capacity, recovered during discharge of the metal / oxygen battery, high, and in particular significantly improved compared to liquid electrolytes as described in application WO2017 / 050672, using carbonated solvents. The liquid electrolyte according to the invention thus exhibits improved electrochemical stability. In particular, it exhibits better chemical stability, meaning it generates fewer secondary reactions during calendar aging, and therefore a less significant self-discharge of the battery incorporating such a liquid electrolyte. A liquid electrolyte according to the invention makes it possible, for example, to access a lithium / oxygen battery with a capacity greater than 5 mAh / cm². Also, the liquid electrolyte according to the invention meets the requirements, discussed previously, required for its implementation in a metal / oxygen battery, in particular lithium / oxygen. In particular, a liquid electrolyte according to the invention fully ensures the dual function of solubilizing the alkali or alkaline-earth metal salt, also called the "support salt", and solubilizing oxygen. The ability to solubilize the supporting salt, for example lithium salt, is reflected in particular by the fact that the liquid electrolyte is monophasic. For the purposes of the invention, a "monophasic" medium is one in which microscopic examination does not reveal more than one phase. In other words, the supporting salt is present as a solute in the electrolyte medium of the invention. As such, the electrolyte medium according to the invention is distinct from a dispersion, in which the supporting salt is present, in whole or in part, in particulate form. The solubility of the supporting salt in the solvent medium of the liquid electrolyte according to the invention may have been previously achieved by heating the electrolyte. However, this state of solubilization, reached under heating, persists when the electrolyte is cooled to room temperature. "Room temperature" is defined as a temperature of 20°C ± 2°C. Similarly, the fluorinated solubilizing agent, the fluorocarbon solvent, and the ether-type solvent, used together to form the solvent medium of the liquid electrolyte according to the invention, advantageously exhibit an affinity for one another in the presence of the supporting salt. The liquid electrolyte according to the invention is advantageously not subject to a demixing phenomenon that could separate the fluorinated solvent, the solubilizing agent, and / or the ether-type solvent from the rest of the formulation. Furthermore, the liquid electrolyte according to the invention is advantageously a non-aqueous electrolyte. By "non-aqueous," we mean that the liquid electrolyte incorporates less than 100 ppm by mass of water, or is even completely water-free. This advantageously eliminates the problems associated with protecting lithium in aqueous environments, particularly when used in lithium-oxygen batteries. Also, the liquid electrolyte according to the invention exhibits excellent performance in terms of ionic conductivity. It advantageously exhibits an ionic conductivity, measured at 25 °C, greater than 105 S.cm-1, in particular greater than or equal to 5.105 S.cm-1, or even greater than 104 S.cm-1. It advantageously exhibits good electrochemical performance over a wide potential window, particularly exceeding 4 V vs. Li+ / Li. Advantageously, the reaction rate within the metal / oxygen battery according to the invention is increased, because the reaction site no longer takes place at the triple point (reaction between three phases), but at the double point (reaction between two phases). Furthermore, the liquid electrolyte according to the invention allows for the storage of oxygen in solution. This capability constitutes a major advantage: in fact, if, for any reason, the battery loses contact with the outside air, it can continue to function thanks to the oxygen dissolved in the electrolyte. Other characteristics, variants and advantages of liquid electrolytes and their implementation in metal / oxygen batteries according to the invention will become clearer from reading the description, examples and figures which follow, given by way of illustration and not limitation of the invention. In the following text, the expressions "between … and …", "ranging from … to …" and "varying from … to …" are equivalent and are meant to mean that the boundaries are included, unless otherwise stated. Brief description of the drawings [Fig.1] presents the curves of evolution of the potential (V) as a function of the capacity (mAh) in discharge regime of each of the cells prepared in example 1, respectively implementing a liquid electrolyte 1 according to the invention and a non-conforming electrolyte 3; [Fig.2] presents the curves of evolution of the potential (V) as a function of the capacity (mAh) in discharge regime of each of the cells prepared in example 2, respectively implementing a liquid electrolyte 1 according to the invention and a non-conforming electrolyte 3. Detailed description LIQUID ELECTROLYTE SOLVENT MEDIUM As previously stated, the solvent medium of a liquid electrolyte according to the invention combines at least three distinct compounds: - at least one fluorocarbon solvent; - at least one fluorinated solubilizing agent; and - at least one ether-type solvent. In the context of the invention, the following definitions apply: - «C7» Where t and z are integers, a carbon chain can have from t to Zz carbon atoms; for example C,, a carbon chain that can have from 1 to 4 carbon atoms, also called a C carbon chain, to C;, ; - "alkyl", a saturated aliphatic group, linear or branched; for example a C,.,-alkyl group represents a carbon chain of 1 to 4 carbon atoms, linear or branched, more particularly a methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl. - "alkylene" is a saturated divalent group, linear or branched, with the molecular formula -C,H 2n-, where m is an integer, obtained by removing two hydrogen atoms from an alkane. Examples include methylene (-CH>-), ethylene (-CH; CH,-), propylene (-CH,CH,CH,-), and butylene (-CH,CH,CH.CH,-). The alkylene group may more specifically have the formula -(CH2),,-, where M represents an integer. - "cyclic", a monocyclic or polycyclic group. A "polycyclic" group is a group having two or more nuclei (rings), condensed (ortho-condensed or ortho- and peri-condensed) to each other, that is to say having, two by two, at least two carbons in common. - a radical or a "perfluorocarbon" chain, a group composed of carbon and fluorine atoms. For example, it could be a perfluoroalkyl group, such as a perfluorooctyl group, or, when the chain is divalent, that is, positioned between two other groups, a perfluoroalkylene group. Fluorocarbon solvent As previously stated, a liquid electrolyte according to the invention comprises one or more fluorocarbon solvents, also called "fluorocarbons". In the following text, "fluorocarbon solvent" refers to a single fluorocarbon solvent or a mixture of at least two fluorocarbon solvents. For the purposes of the invention, a fluorocarbon solvent means a compound that is fluid at room temperature and atmospheric pressure, and whose carbon skeleton comprises at least one, preferably several, fluorine atoms, or is advantageously perfluorinated. Advantageously, the fluorocarbon solvent(s) considered according to the invention are excellent solvents for oxygen. In particular, the solubility of oxygen in a fluorocarbon solvent according to the invention is at least 30% by volume (30% v / v). This solubility is assessed at room temperature and atmospheric pressure. It can notably be evaluated using the Winkler method, which involves saturating a liquid medium with oxygen and measuring the difference in volume of the liquid medium. In the context of the invention, a fluorocarbon solvent may comprise atoms of hydrogen, oxygen, sulfur, nitrogen and / or phosphorus. In a particular embodiment, the fluorocarbon solvent is devoid of oxygen, sulfur, nitrogen and phosphorus atoms. The fluorocarbon compound used to form a liquid electrolyte according to the invention can be formed solely from carbon, hydrogen and fluorine atoms. According to a particular embodiment, the fluorocarbon compound according to the invention comprises a hydrocarbon skeleton, saturated, unsaturated and / or aromatic, linear, branched and / or cyclic, having from 4 to 18 carbon atoms, substituted by one or more, preferably several fluorine atoms. Examples of fluorocarbon solvents include decafluoropentane (C,H,F;p), 1H-perfluorohexane (CsHF;), nonafluorohexane (CsH;F;), pentafluorohexane (C;HsF;), heptafluorocyclopentane (CH;F;), perfluorohexane (CeF,4), perfluoroheptane (C;F;6), perfluorooctane (C;F;s), 1H-perfluorooctane (C;HF,7), perfluorononane (CyFz), perfluorodecalin (C,0F18). According to a particular embodiment, the fluorocarbon solvent is perfluorinated; in other words, it is composed solely of carbon and fluorine atoms. In particular, the fluorocarbon solvents used to form a liquid electrolyte according to the invention can be chosen from perfluorocarbon compounds, saturated, unsaturated and / or aromatic, linear, branched and / or cyclic, having from 4 to 18 carbon atoms. The fluorocarbon compound(s) used according to the invention can thus have the following empirical formula (1): CF, (M with a representing an integer between 4 and 18, and b being an integer > a. In particular, the fluorocarbon compound may be of the aforementioned formula (I) in which a is between 6 and 12, in particular a is 10. According to a particular embodiment, the fluorocarbon solvent(s) are chosen from saturated perfluorocarbon compounds, also called perfluoroalkanes, linear or cyclic, in particular in C4 to C,>. According to a particular embodiment, a liquid electrolyte according to the invention may comprise at least one perfluoroalkane, linear or cyclic, in particular cyclic, in particular in C; to C,>. In particular, the [fluorocarbon solvent used in a liquid electrolyte according to the invention can be a cyclic perfluoroalkane, in particular in C1 to C1. In one particular embodiment, the fluorocarbon solvent is perfluoro-decalin. According to a particular embodiment, the fluorocarbon solvent(s), in particular perfluorocarbon solvents, especially of the perfluoroalkane type, for example perfluoro- rodecaline, may represent from 20 to 90% by volume, in particular from 50 to 90% by volume, in particular from 60 to 90% by volume, and in particular from 60 to 70% by volume, of the total volume of the liquid electrolyte according to the invention. In particular, the fluorocarbon solvent(s) may be present in the liquid electrolyte according to the invention in a fluorocarbon solvent / salt carrier molar ratio of between 1 and 5, in particular between 2 and 3. Fluorinated solubilizing agent As previously stated, a liquid electrolyte according to the invention combines the fluorocarbon solvent(s), as described above, with at least one fluorinated solubilizing agent. In the following text, "solubilizing agent" means a single fluorinated solubilizing agent or a mixture of at least two fluorinated solubilizing agents. The solubilizing agent implemented according to the invention makes it possible in particular to solubilize the support salt, and to guarantee its presence in the electrolytic medium in the state of solute, even in the presence of said fluorocarbon solvent(s). Furthermore, it is important that the solubilizing agent does not affect the electrochemical stability, nor the solubilizing capacity with respect to oxygen, of the electrolytic medium. The solubilizing agent considered according to the invention is a fluorinated compound, distinct from the fluorocarbon solvent(s) jointly used in the liquid electrolyte according to the invention, has a character that can be described as amphiphilic, like surfactants in particular, and has a polarity greater than that of the fluorocarbon solvent(s). The solubilizing agent considered according to the invention is more particularly a mono-, poly- or per-fluorinated hydrocarbon compound, saturated, unsaturated and / or aromatic, linear, branched and / or cyclic having from 4 to 18 carbon atoms, the carbon chain of which bears at least one polar terminal motif, and optionally interrupted by one or more heteroatoms, in particular selected from oxygen and sulfur atoms and the radicals -N(R!)-, -B(R!)- and -P(R'R?)- with R! and R, identical or different, re- presenting a hydrogen atom or an alkyl group at C, to C4, For the purposes of the invention, a polar terminal motif means a functional group at the free end on the carbon skeleton of the solubilizing agent, that is to say at the terminal end of the main carbon chain or at the end of a carbon radical constituting a branch of this chain if present, this motif being of such a nature as to confer on the solubilizing agent an affinity for the alkali or alkaline-earth metal salt with which it is associated at the level of the formulation of the liquid electrolyte. According to a particular embodiment, the solubilizing agent corresponds to the following general formula (II): [Chem.2] Z-{(CeF26)-(Xn i-(CeHze)pY (M in which: - CF. represents a saturated perfluorocarbon group, linear or branched, with c representing an integer from 4 to 18; - X is chosen from among the oxygen and sulfur atoms, and the radicals -N(R!)-, -B(R!)- and -P(R'R?)-, with R! and R?, identical or different, representing a hydrogen atom or an alkyl radical in C, to C4, -nestégal à 0 ou 1, - q is equal to zero or is an integer ranging from 1 to 15, it being understood that, when q is greater than or equal to 2, X, c and n can be identical or different in each of the units -[(C.F2e)-(X),]- ; preferably q is different from zero; - CH represents a saturated hydrocarbon radical, linear or branched, with e re- representing an integer from 1 to 12; - pestégalà 0 or 1, - Z represents a hydrogen atom, a fluorine atom, or a hydroxyl group, and Y represents a group -OH, -OR3, -OM, -NH, -NHR3, -N(R3), -N(R3);+, -COOH, -COOM, -COOR3, -OCORS, -CN, -SO;H, -SO;M, with R° being a C, to C alkyl radical; and M a metal ion, in particular an alkali or alkaline earth metal cation, for example lithium; or Z and ŸY are linked to each other to form a polar motif of the oxo, ether or ester type. Advantageously, this solubilizing agent has a polar part, particularly with regard to the presence of the polar group Y as defined above. Advantageously, the solubilizing agent, particularly due to the presence of such a polar motif, exhibits an affinity for the alkali or alkaline earth salt(s) with which it is associated within the liquid electrolyte according to the invention. Furthermore, the presence of the fluorocarbon skeleton provides the solubilizing agent according to the invention with an affinity for the fluorocarbon solvent(s) as described above, with which it is jointly used in the liquid electrolyte according to the invention. Preferably, q, in the aforementioned formula (IT), can be equal to 1. Preferably, n, in the aforementioned formula (IT), can be equal to 0. Preferably, p, in the aforementioned formula (IT), can be equal to 1. Preferably, c, in the aforementioned formula (IT), can be between 4 and 8. Preferably, e, in the aforementioned formula (ID), can be between 1 and 4, in particular e is 1. According to a particular embodiment, the solubilizing agent is a compound of formula (ID), saturated, in particular in C, to C,. In particular, the solubilizing agent may be a compound of formula (IT), linear and saturated, especially in C, to Cys. According to a particular embodiment, the solubilizing agent is a compound of formula (II) in which q is equal to 1, n is equal to 0 and p is equal to 1. In particular, the solubilizing agent can be of formula (II) in which c is between 4 and 8, and e is between 1 and 4, in particular equals 1. According to a particular embodiment, Y, in the aforementioned formula (ID), is chosen from the groups -OH, -OR!, -OM, -COOM, -COOR! and -OCOR|, with M and R! being as defined above. Preferably, Y is an -OH group. According to a particular embodiment, Z is a fluorine atom. It is understood that the various embodiments mentioned above can be combined, as far as possible, to define compounds of formula (II) more particularly considered according to the invention. Thus, according to a particular embodiment, the fluorinated solubilizing agent used in a liquid electrolyte according to the invention corresponds to the following formula (I'): [Chem.3] F-(CeFze)-(CeHre)p-ŸY ar) in which Y, c, € and p are such as defined above. In the aforementioned formula (Il'), c can more specifically be between 4 and 8. In the aforementioned formula (Il), € can more specifically be between 1 and 4, in particular is worth 1. In formula (IT), Y can more particularly be an -OH group or a -COOR* group, with R! being as defined previously; in particular Y is an -OH group. According to a particular embodiment, the solubilizing agent is of the aforementioned formula (IT), in which p equals 1. According to another particular embodiment, the solubilizing agent has formula (IT) in which p equals 0. In other words, the solubilizing agent implemented according to the invention can correspond to the following formula (IT): [Chem.4] grouping -COOR}, with R! being as defined previously; in particular Y is a grouping -OH. In the aforementioned (IT) formula, € can be more specifically between 4 and 8, in particular worth 8. Thus, in a particular embodiment, the solubilizing agent used to form a liquid electrolyte according to the invention can be chosen from perfluoroalkanols and alkyl perfluoroesters, in particular in C1 to C1s. According to a particular embodiment, the solubilizing agent is chosen from among the per-fluoroalkanols, in particular the acyclic perfluoroalkanols, especially in C, to C5. As an example, the solubilizing agent could be perfluorooctanol. The fluorinated solubilizing agent(s), in particular of the perfluoroalkanol type, for example perfluorooctanol, may represent from 5 to 60% by volume, in particular from 10 to 40%, notably from 10 to 25% by volume, of the total volume of the liquid electrolyte according to the invention. In particular, the fluorinated solubilizing agent(s), for example of the per-fluoroalkanol type, may be present in the liquid electrolyte according to the invention in a solubilizing agent(s) / supporting salt molar ratio of between 1 and 5, in particular between 1.5 and 2.5. According to a particular embodiment, a liquid electrolyte according to the invention may comprise said fluorocarbon solvent(s) and said fluorinated solubilizing agent(s), in particular as defined above, in a fluorocarbon solvent(s) / solubilizing agent(s) volume ratio of between 10 / 1 and 3 / 2, in particular between 6 / 1 and 2 / 1, in particular between 5 / 1 and 3 / 1 and more particularly about 4 / 1. Advantageously, the fluorinated solubilizing agent(s) and the fluorocarbon solvent(s) are chosen so as to exhibit excellent compatibility. For example, the fluorinated solubilizing agent(s) and the fluorocarbon solvent(s) respectively have a saturated carbon skeleton, acyclic or cyclic, preferably perfluorinated. For example, the fluorocarbon solvent may be a C2-Ce perfluoroalkane, such as perfluorodecalin; and the solubilizing agent may advantageously be of the acyclic perfluoroalkanol type. Preferably, the respective carbon numbers of the fluorocarbon solvent and the fluorinated solubilizing agent differ by less than five carbon atoms, and in particular by less than three carbon atoms. Perfluorodecalin / perfluorooctanol is an example of a fluorocarbon solvent / fluorinated solubilizing agent pair. The liquid electrolyte according to the invention can thus implement at least the per- fluorodecalin as a fluorocarbon solvent in association with at least per-fluorooctanol as a fluorinated solubilizing agent. Ether solvent As previously stated, a liquid electrolyte according to the invention further comprises at least one ether-type solvent, more simply referred to in the remainder of the text as "ether solvent". The term "ether solvent" refers to a solvent containing at least one ether function. A liquid electrolyte according to the invention may comprise a single ether-type solvent or a mixture of at least two ether-type solvents. These ether-type solvents can be designated as dissociating solvents; they advantageously increase the ionic conductivity of the electrolytic medium containing them, given their high dielectric constant. The ether solvents considered according to the invention can thus exhibit a dielectric constant e, measured at 25 °C, greater than or equal to 7.5. Moreover, surprisingly, as illustrated in the examples that follow, the inventors have shown that the implementation of ether solvents, unlike carbonate solvents, makes it possible to access a liquid electrolyte exhibiting improved electrochemical stability, and making it possible to significantly increase the capacity recovered during discharge of the metal / oxygen battery in which this electrolyte is implemented. The ether solvents used according to the invention can more particularly correspond to the following formula (III): [Chem.5] R*-O-(QO)yR° (I) in which: q is 0 or q is an integer between | and 10, in particular between l and 6; Q is an alkylene group, linear or branched, from C to C4, in particular from C to C4, it being extended that, when q is greater than or equal to 2, the Q groups may be identical or different, preferably identical; R* and RS, identical or different, represent alkyl groups at C, to C,2, or R* and R5 are linked to form a C,-C;-alkylene group. Preferably, R* and R° in the aforementioned (IIT) formula are chosen from methyl and ethyl groups, in particular methyl. Preferably, q in the aforementioned formula (III) is between 1 and 6, in particular between 1 and 5 and more particularly between 1 and 4. Preferably, Q in the aforementioned formula (III) represents an alkylene group linear, in particular in C, to C4, notably a group -CH,CH-. According to a particular embodiment, the ether solvent used to formulate a liquid electrolyte according to the invention is chosen from 1,3-dioxolane (symbolized by the abbreviation DIOX), tetrahydrofuran (symbolized by the abbreviation THF), ethers of general formula CH,0-[CH,CH,0],-CH;, with q being an integer between 1 and 10, in particular between 1 and 6, especially between 1 and 5 and more particularly between 1 and 4, such as 1,2-dimethoxyethane (DME, also known as monoglyme), di(2-methoxyethyl)ether (or diglyme), triethylene glycol dimethyl ether (or triglyme); tetraethylene glycol dimethyl ether (symbolized by the abbreviation TEGDME, also known as tetraglyme); and mixtures thereof. According to a particular embodiment, the ether solvent is chosen from DME, TEGDME and their mixtures. Preferably, the ether solvent is DME. The said ether-type solvent(s), in particular as defined above, in particular of the aforementioned formula (IIT'), may represent from 2 to 30% by volume, in particular from 3 to 20% by volume, in particular from 5 to 15% by volume and more particularly from 5 to 10% by volume, of the total volume of the liquid electrolyte according to the invention. In particular, the ether-type solvent(s) may be present, at the level of the liquid electrolyte according to the invention, in a molar ratio of ether solvent(s) / support salt(s) of between 0.10 and 4.00, in particular between 0.30 and 0.80. It is understood that the various embodiments mentioned above, in particular in terms of the nature and content of the fluorocarbon solvent(s), the fluorinated solubilizing agent(s) and the ether-type solvent(s), may be combined as far as possible. Thus, in a particular embodiment, a liquid electrolyte according to the invention may comprise: - one or more fluorocarbon solvents as defined above, in particular perfluorocarbons, especially of the perfluoroalkane type, such as perfluorodecalin; - one or more fluorinated solubilizing agents as defined above, in particular of the aforementioned formula (IT), in particular of the perfluoroalkanol type, such as perfluorooctanol; - one or more ether solvents, as defined above, in particular of formula CH;O-[CH,CH,O],-CH; as defined above, for example TEGDME and / or DME. Advantageously, the fluorocarbon solvent(s) and the agent(s) fluorinated solubilizers and the ether-type solvent(s), in particular as defined above, represent more than 90% by volume, in particular more than 95% by volume, and more particularly more than 98% by volume, of the total volume of the liquid electrolyte according to the invention. According to one embodiment, the liquid electrolyte according to the invention may further comprise one or more auxiliary solvent(s), distinct from the aforementioned solvents, such as, for example, a carbonate solvent. Examples of carbonate solvents include ethylene carbonate, propylene carbonate, diethyl carbonate, ethylmethyl carbonate, dimethyl carbonate, and mixtures thereof. Preferably, the said auxiliary solvent(s), in particular of the carbonate type, represent less than 10% by volume of the total volume of the liquid electrolyte according to the invention, in particular less than 5% by volume and more particularly less than 1% by volume, of the total volume of the liquid electrolyte. According to another particularly preferred embodiment, the liquid electrolyte according to the invention does not comprise any solvent other than said fluorocarbon solvent(s), said fluorinated solubilizing agent(s) and said ether-type solvent(s) as described above. In particular, the liquid electrolyte according to the invention can be free of carbonate solvent. According to a particular embodiment, the solvent medium of a liquid electrolyte according to the invention comprises, or is formed from: - 20 to 90% by volume, in particular 50 to 90% by volume, of one or more fluorocarbon solvents, in particular as defined above, in particular perfluorocarbons, in particular of the perfluoroalkane type, such as perfluorodecalin; - 5 to 60% by volume, in particular 10 to 25% by volume, of one or more fluorinated solubilizing agents, in particular as defined above, especially of the aforementioned formula (ID), (IT) or (IT), in particular of the perfluoroalkanol type, such as perfluorooctanol; and - 2 to 30% by volume, in particular 5 to 15% by volume, of one or more ether solvents, in particular as defined above, especially of formula CH,0-[CH,CH,0],-CH; as defined above, for example TEGDME and / or DME; the volume percentages given relative to the total volume of the liquid electrolyte. According to a particular embodiment, the liquid electrolyte according to the invention is formed: - of a solvent medium, in particular as defined above, consisting of: one or more fluorocarbon solvents, in particular as defined above, in particular perfluorocarbons, especially of the perfluoroalkane type, such as per-fluorodecalin; one or more fluorinated solubilizing agents, in particular as defined above, including of formula (II), (I) or (ID) above, including of the per-fluoroalkanol type, such as perfluorooctanol; one or more ether solvents, in particular as defined above, notably of formula CH0-[CH,CH2O],-CH; as defined above, for example TEGDME and / or DME; and - of one or more alkali or alkaline-earth metal salts, in particular a lithium salt. According to a particular embodiment, a liquid electrolyte according to the invention comprises, or is formed from: from 1 to 5 mol.L"!, in particular from 2 to 3 mol.L"!, of one or more fluorocarbon solvent(s), in particular such as described above, for example perfluoro-decalin; from 1 to 5 mol.L"', in particular from 1.5 to 2.5 mol.L", of one or more fluorinated solubilizing agent(s), in particular as defined above, for example per-fluorooctanol; from 0.10 to 4.0 mol.L!, in particular from 0.3 to 0.8 mol.L"', of one or more ether solvent(s), in particular as defined above, for example of TEGDME and / or DME; the molar proportions being given for 1 mol.L"! of support salt, in particular lithium salt. ALKALINE OR ALKALINE-EARTH METAL SALT As previously stated, the liquid electrolyte according to the invention comprises at least one alkali or alkaline-earth metal salt, called the "support salt", to ensure the conduction of ions. In the context of the invention, the following definitions apply: - "Alkali metals", the chemical elements in the first column of the periodic table of elements, and more particularly chosen from lithium, sodium, potassium, rubidium, cesium. Preferably, the alkali metal is lithium, sodium or potassium, and more preferably lithium; - "Alkaline earth metals", the chemical elements of the second column of the periodic table of elements, and more particularly chosen from among beryllium, magnesium, calcium, strontium, barium, radium. Preferably, the alkaline earth metal is magnesium or calcium. The salt of an alkali metal can be, for example, a lithium salt, sodium salt, or potassium; the salt of an alkaline earth metal can be, for example, a magnesium salt. In particular, the salt used is a lithium salt. Examples of lithium salts include LiPFg, LICIO, LiBF4, LiAsFe, LiCF;SO, LIN(C:F;SO), lithium bis(trifluoromethylsulfonyl)imide LIN[SO,CF; ], (known by the abbreviation LITFSI), lithium bis(fluorosulfonyl)amide (known by the abbreviation LiFSI) LIN[SO-F], lithium 4,5-dicyano-2-(trifluoromethyl)imidazole (known by the abbreviation LITDI), lithium bispentafluoroethylsulfonylimide (known by the abbreviation LiBETI), lithium bis(oxalato)borate (known by the abbreviation LiBOB) and lithium difluoro(oxalato)borate (known by the abbreviation LiIFOB) and mixtures thereof. Preferably, the electrolyte comprises, as lithium salt, LITFSI, LITDI or LiFSI, preferably LITFSI or LiFSI and more preferably LITFSI. It is the responsibility of a person skilled in the art to adjust the quantity of alkali or alkaline earth metal salts to optimize the ionic conductivity of the electrolyte. This quantity is likely to vary depending on the chemical nature of the salt in question. Generally speaking, the aforementioned alkali or alkaline-earth metal salt(s), particularly lithium salts, are used in a content ranging from 0.1 to 5 mol.L" (M), in particular about 1 mol.L", in the liquid electrolyte according to the invention. Examples of liquid electrolytes according to the invention include those comprising at least: - perfluorodecalin as a fluorocarbon solvent, - perfluorooctanol as a fluorinated solubilizing agent, - TEGDME or DME as an ether solvent, and - LIiTFSI as a supporting salt, particularly at a molar concentration of 1 mol.L*. According to a particular embodiment, the liquid electrolyte of the invention can be formulated within a polymer matrix to form a gelled electrolyte. The polymer matrix must allow for maximum liquid incorporation while maintaining mechanical properties to ensure physical separation between the positive and negative electrodes of the electrochemical cell. A polymer matrix can, for example, be formed from polymers selected from polyethers, polyacrylamides, polycarbonates, polyethersulfones, and their copolymers. Alternatively, the liquid electrolyte according to the invention can be made to impregnate a separator element disposed between the negative electrode and the positive electrode of the electrochemical cell. This separator can be made of a porous material, such as a polymeric material, suitable for accommodating the liquid electrolyte within its porosity. ELECTROCHEMICAL SYSTEM The invention also relates to an electrochemical system comprising at least one liquid electrolyte according to the invention. In particular, as mentioned previously, due to its ability to solubilize both an alkali or alkaline-earth metal salt and a large quantity of oxygen, a liquid electrolyte according to the invention finds a particularly advantageous application as an electrolyte for metal / oxygen batteries. For example, it can be implemented for a lithium / oxygen, aluminum / oxygen, zinc / oxygen battery. According to a particular embodiment, the liquid electrolyte according to the invention is used for a lithium / oxygen battery. The rest of the battery can be formed using conventional methods. In a conventional manner, a metal / oxygen battery (or accumulator) is formed of at least one electrochemical cell comprising a separator impregnated by the liquid electrolyte according to the invention, or alternatively a gelled electrolyte obtained from a liquid electrolyte according to the invention, between a positive electrode and a negative electrode, a current collector connected to the cathode and a current collector connected to the anode. A metal-oxygen battery according to the invention may more particularly comprise a metallic negative electrode and an oxygen-reducing positive electrode. The active material of the negative electrode can be lithium, aluminum or metallic zinc, for example metallic lithium in the context of a lithium / oxygen battery. The positive oxygen-reducing electrode may include a carbon material, for example carbon fibers, and one or more catalysts for the redox reaction of alkali or alkaline earth ions, for example Li* ions, and oxygen, such as platinum, manganese or manganese oxide (MnO). The current collector connected to the positive electrode is usually made of aluminum. The current collector connected to the negative electrode is usually made of copper. Due to their wide electrochemical stability window, chemical inertness, and low toxicity, the liquid electrolytes according to the invention can find particularly advantageous applications in cation-ion batteries, for example, lithium-ion, sodium-ion, potassium-ion, and magnesium-ion batteries. In a particular embodiment, a liquid electrolyte according to the invention can be used in a lithium-ion battery. The invention will now be described by means of the following examples and figures, given of course by way of illustration and not limitation of the invention. Examples In the following examples, the liquid electrolytes have the compositions shown in Table 1 below. The quantities are given as molar concentration mol / L (or M). They are obtained by dissolving lithium salt in a mixture of different solvents. [Table 1] Electralyte 1 Electroivte 2 Electroyte 3 Compounds (invention) (invention) (excluding invention) Perfluorodecalin 2.55 M 2.5M 2.55 M Perfluorooctanol UM 2M 2M Tetraethylene glycol 0.45M dimethyl ether (TEGDME) 1,2-dimethoxyethane (DME) 0.45 M Propylene carbonate 0.45 M LiITFSI hthium salt 1 M 1 M 1M Example 1 In this example, pouch cells without oxygen inlet, with packaging dimensions of 7 x 7 cm and active surface area of ​​3 x 3.5 cm, are used. They are composed of lithium metal, a Celgard® 2320 separator impregnated with the liquid electrolyte and a cathode consisting of a sheet of Freudenberg® H2315 covered with an ink containing MnO. The first cell contains the electrolyte 3 indicated above, in accordance with patent WO 2017050672; the second cell contains the electrolyte 1 in accordance with the invention, using tetraethylene glycol dimethyl ether (TEGDME). The cells are discharged under 20°C and 50 pA. Figure [Fig.1] represents the evolution of the potential (V) as a function of the capacity (mAh) in discharge regime of each of the cells implementing respectively the liquid electrolyte 1 and the comparative electrolyte 3. It can be observed that the discharged capacity is multiplied by 5 when using the liquid electrolyte 1 according to the invention, comprising TEGDME, compared to electrolyte 3, comprising propylene carbonate. Thus, the electrochemical stability of the electrolyte according to the invention makes it possible to utilize the excess capacity provided by the MnO catalyst. Example 2 In this example, El-Cell® cells under a flow of 0.6 mL / min of pure oxygen were used. They are composed of the same elements as those mentioned in example 1. These cells are discharged at 20°C and 10 u A. Fig. 2 represents the evolution of the potential (V) as a function of the capacity (mAh) in discharge regime of El-Cell® cells using electrolytes 1 (with TEGDME) and 3 (with propylene carbonate). The results show a strong improvement in discharge capacity for the cell implementing a liquid electrolyte according to the invention comprising TEGDME, compared to that implementing the liquid electrolyte 3 not according to the invention comprising propylene carbonate. Example 3 The ionic conductivities of the different liquid electrolytes 1 to 3 described previously were measured at room temperature according to the following protocol. The conductivity measurements were carried out under an argon atmosphere using a thermostatically controlled conductivity meter. The measuring cell was immersed in the electrolyte at 25°C. The results are summarized in the following table 2. [Tables 2] Electrolyte Conductivity (mS / cm) Electrolyte 1 15.0.102 (invention) Electrolyte 2 13,1,107 (invention) Electrolyte 3 11.3.102 (excluding invention) All the electrolytes exhibit good performance in terms of ionic conductivity.

Claims

Demands

1. Liquid electrolyte for a metal / oxygen battery, comprising: - at least one salt of an alkali or alkaline earth metal, in particular a lithium salt; - at least one fluorocarbon solvent with solubility for oxygen of at least 30% v / v; - at least one fluorinated solubilizing agent, separate from the aforementioned solvent(s) fluorocarbons, chosen from mono-, poly- hydrocarbon compounds or per-fluorinated, saturated, unsaturated and / or aromatic, linear, branched and / or cyclic compounds having from 4 to 18 carbon atoms, including the chain carbonaceous carries at least one polar terminal motif, and even- temporarily interrupted by one or more heteroatoms, notably chosen from among the oxygen and sulfur atoms and the -N(R!)- radicals, -B(R!)- and -P(RIR?)-, with R! and R?, identical or different, representing a hydrogen atom or an alkyl radical at C, C4, ; and - at least one ether-type solvent.

2. Liquid electrolyte according to the preceding claim, wherein the or said fluorocarbon solvents are chosen from perfluo- compounds carbonaceous, saturated, unsaturated and / or aromatic, linear, branched and / or cyclic, having from 4 to 18 carbon atoms, particularly among the perfluoroalkanes, linear or cyclic, in C5 to C1, said fluoro- solvent carbonaceous, being more particularly perfluorodecalin.

3. Liquid electrolyte according to any one of the preceding claims preceding, in which the said fluorinated solubilizing agent(s) respond to the following general formula (IT): Z-[(CF2e)-nJa-(CeHze)p- Y UD in which: - CF represents a saturated, linear or perfluorocarbon group branched, with c representing an integer from 4 to 18; - X is chosen from among the oxygen and sulfur atoms, and the radicals - N(R!)-, -B(R!)- and -P(RIR?)- with R! and R?, identical or different, re- featuring a hydrogen atom or an alkyl radical at C, to C4, - nest equal to 0 or 1, - q is equal to zero or is an integer ranging from 1 to 15, it being understood that when q is greater than or equal to 2, X, c and n can be identical or different in each of the units -[(CF,.)-(X)p]-, - C,H>, represents a saturated hydrocarbon radical, linear or branched, with e representing an integer from 1 to 12; - pest equal to O or 1, - Z represents a hydrogen atom, a fluorine atom, or a group hydroxyl, and Y represents a group -OH, -OR3, -OM, -NH, -NHR3, -N(R3), -N(R*),+, -COOH, -COOM, -COOR3, -OCOR3, -CN, -SO,H, -SO4M, with R° being an alkyl radical at C, at C4 and M a metal ion, in par- tactile an alkali or alkaline earth metal cation, for example lithium: or Z and ŸY are linked to each other to form a polar pattern of type oxo, ether or ester.

4. Liquid electrolyte according to any one of the preceding claims preceding, in which the said fluorinated solubilizing agent(s) are chosen from among perfluoroalkanols and alkyl perfluoroesters, particularly in C; to C,s, in particular acyclic perfluoroalkanols; preferably said fluorinated solubilizing agent is perfluorooctanol.

5. Liquid electrolyte according to any one of the preceding claims- preceding, in which the said fluorocarbon solvent(s) and the or said fluorinated solubilizing agents, in particular as defined in re- recommendations 2 to 4, are present in a solvent volume ratio(s) fluorocarbon(s) / solubilizing agent(s), between 10 / 1 and 3 / 2, in particularly between 6 / 1 and 2 / 1, especially between 5 / 1 and 3 / 1 and more particularly- approximately 4 / 1.

6. Liquid electrolyte according to any one of the preceding claims preceding, said electrolyte comprising at least perfluorodecalin fluorocarbon solvent titer in association with at least perfluo- rooctanol as a fluorinated solubilizing agent.

7. Liquid electrolyte according to any one of the preceding claims preceding, in which the said ether solvent(s) are chosen from among the 1,3-dioxolane, tetrahydrofuran, ethers of general formula CH; O-[CH,CH,0],-CH;3, with q being an integer between | and 10, in particularly between 1 and 6, especially between 1 and 5, and more specifically between 1 and 4, such as 1,2-dimethoxyethane, the di(2-methoxyethyl)ether, triethylene glycol dimethyl ether; di- tetraethylene glycol methyl ether; and mixtures thereof; in part- in particular the said ether solvent(s) are chosen from among the 1,2-Dimethoxyethane, tetraethylene glycol dimethyl ether and their mixtures.

8. Liquid electrolyte according to any one of the preceding claims preceding, said electrolyte comprising: - from 20 to 90% by volume, in particular from 50 to 90% by volume, of a or several fluorocarbon solvents, in particular as defined in claim 2, in particular perfluorodecalin; - from 5 to 60% by volume, in particular from 10 to 25% by volume, of a or several fluorinated solubilizing agents, in particular as defined in claim 3 or A4, such as perfluorooctanol; and - from 2 to 30% by volume, in particular from 5 to 15% by volume, of one or several ether solvents, in particular as defined in claim '7, for example the TEGDME and / or DME; the volume percentages given relative to the total volume of the liquid electrolyte.

9. Liquid electrolyte according to any one of the preceding claims previous, in which the alkali or alkaline-earth metal salt is a lithium salt, specifically chosen from LiTFSI, LiTDI or LiFSI, of preference for LiTFSI or LiFSI and more preferably for LiTFSI.

10. Use of a liquid electrolyte as defined according to any claims 1 to 9 in a metal / oxygen battery, in particular a lithium / oxygen battery.

11. Metal / oxygen battery comprising a liquid electrolyte as defined according to any one of claims 1 to 9, said battery being including a lithium / oxygen battery.

12. Metal / oxygen battery according to the preceding claim, said battery comprising a metallic negative electrode and a positive electrode oxygen reducing agent.

13. Portable article comprising a metal / oxygen battery as defined according to claim 11 or 12.

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