GEL electrolyte, electrochemical cell and battery comprising said electrolyte, method of preparation and uses thereof

Abstract

The present invention relates to a gel electrolyte comprising: (i) at least one solvent selected from: a) a fluorinated ether of formula (I): wherein R1 is selected from -CHF2, -CF3, -CH2CHF2, -CH2CF3, -CF2CHF2, -CF2CF3, -CHFCHF2 and - CHFCF3; R3 is selected from -CHF2, -CF3, -CH2CHF2, -CH2CF3, -CF2CHF2, -CF2CF3, -CHFCHF2, - CHFCF3, -CH3, -CH2CH3 and (III); R2 is selected from -CH2-, -OCH2CH2-, -OCH2CH2CH2- and -OCH2CH2CH2CH2-; n is an integer from 0 to 10; b) a sulfonamide of formula (II): wherein R1 is selected from F, a linear or branched C1-C12 alkyl group which may be substituted with one or more fluorine atom(s), a linear or branched C2-C12 alkenyl group which may be substituted with one or more fluorine atom(s), a C3-C12 cycloalkyl group which may be substituted with one or more fluorine atom(s) and a C6-C12 aryl group which may be substituted with one or more fluorine atom(s), and R2 and R3 are independently selected from a linear or branched C1-C12 alkyl group which may be substituted with one or more fluorine atom(s), a linear or branched C2-C12 alkenyl group which may be substituted with one or more fluorine atom(s), a C6-C12 aryl group which may be substituted with one or more fluorine atom(s), and CH2CH2O-(CH2CH2O)n-R, wherein R is H 49 or a methyl group and n is an integer from 1 to 20; or R2 and R3 may be combined with each other to form a nitrogen-containing aliphatic ring; c) a combination of a) and b); (ii) at least one lithium salt; (iii) a cross-linked polymer obtainable by cross-linking a cross-linked polymer precursor formulation comprising: - a mixture of cross-linkable monomers, said mixture comprising: a) a mono(meth)acrylate and b) a di(meth)acrylate); and (iv) optionally, at least one co-solvent. The invention also relates to an electrochemical cell or battery comprising said gel electrolyte, as well as to a method for preparing the gel electrolyte of the invention and to a method for preparing the electrochemical cell or battery comprising the gel electrolyte of the invention.

Description

[0001] GEL ELECTROLYTE, ELECTROCHEMICAL CELL AND BATTERY COMPRISING SAID ELECTROLYTE, METHOD OF PREPARATION AND USES THEREOF

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the field of electrolytes for use in electrochemical cells or batteries. The present invention may find widespread application in energy storage and electronic devices.

[0004] BACKGROUND

[0005] Lithium metal batteries (LMBs) arguably represent an attractive technology for energy storage applications due to their high energy density and ultralow redox potential. Commercial batteries primarily use liquid electrolytes (LEs) as the ion-transport media owing to their high ionic conductivity and exceptional wettability with electrodes and separator. Typical liquid electrolytes are organic carbonates and ethers, such as ethylene carbonate (EC), ethyl methyl carbonate (EMC), 1,2-dimethoxy ethane (DME), etc. However, liquid electrolytes may be associated to potential safety concerns and performance degradation originating from dendrite growth and cathode electrochemistry. The organic solvents of liquid electrolytes are generally flammable solvents that may cause combustion (or even explosion) due to short-circuit and thermal runaway resulting from the growth of Li dendrites. These issues have so far hindered a practical use of LMBs.

[0006] Solid electrolytes, such as those made of polymers, ceramics or their hybrids, might solve the above problems related to the use of liquid electrolytes, however their conductivity is lower than that of established liquid electrolytes.

[0007] Polymers suitable for formulating polymer gel electrolytes are known in the art and include in their molecular formula heteroatoms, such as halogen, O, N and S, present on the side chain or the repeating unit(s) of the polymers. These can be able to form complexation with lithium ion thus promoting lithium ion transport through the segmental motions. Examples of such polymers include polyethylene oxide, polyacrylonitrile, polyacrylates, polyvinylidene fluoride, poly vinyl alcohol and polyurethanes.

[0008] Particularly, a way to address the low conductivity in polymer electrolytes is the introduction of an organic carbonate as liquid component or a plasticizer that can help dissociate the Li salt (or plasticize a polymeric component) to form gel polymer electrolyte (GPEs). While increasing the ionic conductivity and improving the charge / discharge capacity of an electrochemical cell, such organic carbonates might again affect the cell stability and safety. Thus, additional work is required for the design and fabrication of functional electrolytes that enable them to develop safe and durable LMBs.

[0009] In some work, thermal-stable polymers, such as fluorinated polymers, have been introduced to improve the thermal stability of GPEs (J.H. Baik, D.G. Kim, J.H. Lee, S. Kim, D.G. Hong, J.C. Lee, J. Ind. Eng. Chem. 2018, 64, 453-460).

[0010] Another effective improvement involves the use of fire-resistance additives, which can inhibit exothermic reactions via chemical reactions (e.g. SiCL, AI2O3, etc.). On the other hand, the fireresistance additives may be detrimental to ion-conducting pathways in GPEs, resulting in a decreased ionic conductivity. Several sulfonamides have been used as component of liquid electrolytes, however other organic carbonate are generally required to achieve stable electrochemical cycling.

[0011] Document EP3050872A1 relates to an electrolyte solution comprising a fluorinated sulfonamide according to the general formula R^SCL-bflGRs as part of a solvent system and an electrolyte salt, however this document teaches that flammable carbonate solvents are essential to solve the corresponding technical problem (e.g., aluminum current collector corrosion) while maintaining high electrolyte conductivity (figure 1).

[0012] Fluorinated ethers have also been described for their use in many applications, for example as a heat transfer fluid and as electrolyte solvent in lithium ion batteries. Zhiao et al. [Nature Energy, 2022, 7, 94-106] describes the combination of a partially fluorinated ether with lithium saltLiFSI. W02015 / 051131 discloses a method for preparing fluorinated ethers, as well as their use in electrolyte compositions. Application of fluoro-substituted ethers as a core solvent for non-aqueous electrolytes in lithium-sulfur batteries was presented in document US2018 / 0076485. Electrolyte composed of lithium salt, such as lithium bis ( trifluoromethanesulfonyl ) imide ( LiTFSI) and a fluoro - substituted ether solvent improves the capacity and coulombic efficiency when compared to conventional electrolytes for Li-S battery.

[0013] However, there is a need in art to develop new electrolyte systems which overcome the thermal stability issues of state-of-art liquid electrolytes and, at the same time, offer a viable electrochemical performance for widespread application.

[0014] BRIEF DESCRIPTION OF THE INVENTION

[0015] The present invention relates to a gel electrolyte comprising at least one solvent selected from a fluorinated ether, a sulfonamide and a combination thereof, at least one lithium salt and a cross-linked polymer obtainable by cross-linking a particular polymer precursor formulation. The inventors have found that such gel electrolyte impairs an improvement of the safety, durability and thermal resistance of the cell wherein it is included, while maintaining the discharge capacity and current efficiency after multiple charge / discharge cycles when compared to liquid electrolytes. Even discharge capacity and current efficiency is improved when compared to other gel electrolytes.

[0016] Thus, a first aspect of the invention refers to a gel electrolyte comprising: i. a solvent selected from: a) a fluorinated ether of formula (I): wherein

[0017] Ri is selected from -CHF2, -CF3, -CH2CHF2, -CH2CF3, -CF2CHF2, -CF2CF3, - CHFCHF2 and -CHFCF3;

[0018] R3is selected from

[0019] CHFCHF2, -CHFC R2is selected from -CH2-, -OCH2CH2-, -OCH2CH2CH2- and -OCH2CH2CH2CH2-; n is an integer from 0 to 10; b) a sulfonamide of formula (II): wherein:

[0020] Ri selected from F, a linear or branched Cl -Cl 2 alkyl group which may be substituted with one or more fluorine atom(s), a linear or branched C2-C12 alkenyl group which may be substituted with one or more fluorine atom(s), a C3- C12 cycloalkyl group which may be substituted with one or more fluorine atom(s) and a C6-C12 aryl group which may be substituted with one or more fluorine atom(s);

[0021] R2and R3 are independently selected from a linear or branched C1-C12 alkyl group which may be substituted with one or more fluorine atom(s), a linear or branched C2-Ci2alkenyl group which may be substituted with one or more fluorine atom(s), a Ce-Ci2aryl group which may be substituted with one or more fluorine atom(s), and -CH2CH2O-(CH2CH2O)n-R, wherein R is H or a methyl group and n is an integer from 1 to 20; or

[0022] R2and R3may be combined with each other to form a nitrogen-containing aliphatic ring; and c) a combination of a) and b); ii. at least one lithium salt, iii. at least one cross-linked polymer obtainable by cross-linking a cross-linked polymer precursor formulation, said cross-linked polymer precursor formulation comprising:

[0023] - a mixture of cross-linkable monomers, said mixture comprising: a) at least one monomer having one (meth)acrylate group; and b) at least one monomer having two (meth)acrylate groups; and iv. optionally, at least one co-solvent. The invention also refers to a method for preparing the gel electrolyte of the first aspect of the invention comprising the steps of:

[0024] (i) providing at least one lithium salt;

[0025] (ii) mixing at least one solvent selected from a fluorinated ether of formula (I), a sulphonamide of formula (II) and a combination thereof, as defined in the first aspect of the invention, with the lithium salt provided in step (i);

[0026] (iii) optionally, adding to the mixture obtained in step (ii) at least one co-solvent;

[0027] (iv) adding to the mixture obtained in step (ii) or step (iii) the cross-linked polymer precursor formulation as defined above; and a free radical initiator;

[0028] (v) cross-linking the polymer precursor formulation by free radical polymerization to form a gel electrolyte.

[0029] A third aspect of the invention refers to an electrolyte composition suitable for preparing the gel electrolyte of the first aspect of the invention, said electrolyte composition comprising: i) a solvent selected from a fluorinated ether of formula (I), a sulfonamide of formula (II) and a combination thereof, as defined in the first aspect; ii) at least one lithium salt: iii) a cross-linked polymer precursor formulation comprising:

[0030] - a mixture of cross-linkable monomers, said mixture comprising: a) at least one monomer having one (meth)acrylate group; and b) at least one monomer having two (meth)acrylate groups; and iv) optionally, at least one co-solvent.

[0031] A further aspect of the invention refers to an electrochemical cell or battery comprising the gel electrolyte of the first aspect of the invention as defined above. More preferably, the electrochemical cell or battery comprises the gel electrolyte, as well as a cathode, an anode, and, optionally, a porous separator.

[0032] Another aspect of the invention relates to a method for preparing an electrochemical cell or battery, said method comprising the steps of:

[0033] (i) providing a cathode for an electrochemical cell or a battery;

[0034] (ii) providing an anode for an electrochemical cell or a battery; (iii) providing the electrolyte composition of the third aspect of the invention which comprises the at least one solvent selected from a fluorinated ether of formula (I), a sulphonamide of formula (II) and a combination thereof, the at least one lithium salt, the cross-linked polymer precursor formulation; and a free radical initiator;

[0035] (iv) optionally, providing a porous separator;

[0036] (v) assembling the cathode and the anode provided in steps (i) and (ii) and, optionally the porous separator provided in step (iv), and injecting the electrolyte composition provided in step (iii) between the cathode and the anode or, when a separator is used, on both sides of the separator; and

[0037] (vi) cross-linking the polymer precursor formulation comprised in the electrolyte composition injected in step (v) by free radical polymerization to form a gel electrolyte.

[0038] According to this method, once the electrolyte composition is injected in the cell or battery, and once the polymer precursor formulation is cross-linked, a gel electrolyte is formed within the cell or battery.

[0039] A further aspect of the invention refers to the use of the electrochemical cell or battery of the fifth aspect of the invention in electric motors; electric cars, including electric vehicles (EV), hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), or the like; electric carts, including electric bikes (E-bikes) and electric scooters (E-scooters); electric golf carts; and electric power storage systems.

[0040] DESCRIPTION OF THE FIGURES

[0041] Figure 1 shows the capacity retention vs. cycle number for the Li°||LFP cells at 45 °C, comprising an electrolyte containing: a) a mixture of DF2EO solvent and LiFSI lithium salt at a molar concentration of 1.0 M with 10 vol% of a TMPTA / DDMA / TFEA polymer matrix (LFPE1P2); b) a mixture of FSA11 solvent and LiFSI lithium salt at a molar concentration of 1.0 M with 10 vol% of a TMPTA / DDMA / TFEA polymer matrix (LFPE2P2).

[0042] Figure 2 shows the discharge capacity and coulombic efficiency for cells comprising electrolytes NMCE1P2, NMCE1P3 and NMCE1P4. Figure 3 shows the capacity retention vs. cycle number for the Li°||NMC811 cells at 25 °C comprising an electrolyte containing a mixture of a) DF2EO solvent and LiFSI lithium salt at a molar concentration of 1.0 M with 10 vol% of a TMPTA / DDMA / TFEA polymer matrix (E1P2); b) DF2EO solvent and LiFSI lithium salt at a molar concentration of 1.0 M with 10 vol% of a EHA / HDA polymer matrix (E1P5)

[0043] Figure 4 shows the thermogravimetric analysis of a liquid electrolyte containing a mixture of DF2EO and LiFSI lithium salt and a gel electrolyte containing a mixture of DF2EO, LiFSI lithium salt and a polymer matrix (TMPTA:DDMA:TFEA). Temperature ramp of 10 K / min and an argon flow of 1 mL / min.

[0044] DETAILED DESCRIPTION OF THE INVENTION

[0045] All terms as used herein in this application, unless otherwise stated, shall be understood in their ordinary meaning as known in the art. Other more specific definitions for certain terms as used in the present application are as set forth below and are intended to apply uniformly throughout the specification and claims unless an otherwise expressly set out definition provides a broader definition.

[0046] 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 cases of “consist of’ and “consists essentially 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.

[0047] Throughout the description and claims, the terms “blend(s)” and “mixture(s)” will be used interchangeably.

[0048] For the purposes of the invention, any ranges given include both the lower and the upper endpoints of the range. Ranges or values given, such as temperatures, times, molar ratio, volume ratio and the like, should be considered approximate when they are defined by the term “about” (i.e. with a 5% margin of variation around indicated point).

[0049] As mentioned above, a first aspect of the invention refers to a gel electrolyte comprising: i. at least one solvent selected from: a) a fluorinated ether of formula (I) wherein

[0050] Ri is selected from -CHF2, -CF3, -CH2CHF2, -CH2CF3, -CF2CHF2, -CF2CF3, - CHFCHF2 and -CHFCF3;

[0051] R3is selected from

[0052] CHFCHF2, -CHFC

[0053] R2is selected from -CH2-, -OCH2CH2-, -OCH2CH2CH2- and -OCH2CH2CH2CH2-; n is an integer from 0 to 10; b) a sulfonamide of formula (II): wherein

[0054] R1is selected from F, a linear or branched C1-C12 alkyl group which may be substituted with one or more fluorine atom(s), a linear or branched C2-C12 alkenyl group which may be substituted with one or more fluorine atom(s), a C3- C12 cycloalkyl group which may be substituted with one or more fluorine atom(s) and a C6-C12 aryl group which may be substituted with one or more fluorine atom(s),

[0055] R2and R3are independently selected from a linear or branched C1-C12 alkyl group which may be substituted with one or more fluorine atom(s), a linear or branched C2-C12 alkenyl group which may be substituted with one or more fluorine atom(s), a C6-C12 aryl group which may be substituted with one or more fluorine atom(s), and CH2CH2O-(CH2CH2O)n-R, wherein R is H or a methyl group and n is an integer from 1 to 20; or R2and R3may be combined with each other to form a nitrogen-containing aliphatic ring; and c) a combination of a) and b); ii.at least one lithium salt, iii.at least one cross-linked polymer obtainable by cross-linking a cross-linked polymer precursor formulation comprising:

[0056] - a mixture of cross-linkable monomers, said mixture comprising: a) at least one monomer having one (meth)acrylate group; and b) at least one monomer having two (meth)acrylate groups; and iv. optionally, at least one co-solvent.

[0057] The inventors have surprisingly found that a gel electrolyte comprising at least one solvent of formula I and / or II, at least one lithium salt and a cross-linked polymer as defined above, is suitable for electrochemical applications (e.g. in lithium metal batteries) with the corresponding advantages of no flammability and thermal stability with lithium metal.

[0058] In a preferred embodiment, the gel electrolyte of the first aspect of the present invention further comprises at least one co-solvent, said at least one co-solvent being able to coordinate lithium salt and / or not able to coordinate lithium salt.

[0059] The gel electrolyte of the present invention is a polymer electrolyte in a gel form, i.e., it is a gel polymer electrolyte. In the context of the present invention, a gel polymer electrolyte is understood as a polymer network that is expanded or swelled throughout its whole volume by the presence of at least one fluorinated ether or sulfonamide solvent and, optionally, a cosolvent.

[0060] More embodiments regarding the first aspect of the invention will be given below.

[0061] Solvent

[0062] The gel electrolyte of the invention comprises at least one solvent selected from a fluorinated ether of formula (I), a sulfonamide of formula (II) and a combination thereof.

[0063] By the term “fluorinated ether” should be understood an ether or a glycol ether having at least one fluorine as substituent in the hydrocarbon chain, more particularly having at least one terminally fluorine in the hydrocarbon chain. The fluorinated ether may be symmetric or asymmetric.

[0064] Said fluorinated ether is represented by formula (I): wherein

[0065] Ri is selected from -CHF2, -CF3, -CH2CHF2, -CH2CF3, -CF2CHF2, -CF2CF3, - CHFCHF2 and -CHFCF3;

[0066] R3is selected from

[0067] CHFCHF2, -CHFC

[0068] R2is selected from -CH2-, -OCH2CH2-, -OCH2CH2CH2- and -OCH2CH2CH2CH2-; and n is an integer from 0 to 10.

[0069] In a preferred embodiment, integer n is an integer selected from 0, 1, 2, 3, 4 and 5. More preferably, integer n is selected from 0 and 1, even more preferably n is 1.

[0070] In another preferred embodiment, R2 is -OCH2CH2-.

[0071] In another preferred embodiment, Ri and R3 are independently selected from -CHF2, - CH2CHF2, -CHFCHF2 and -CF2CHF2. More preferably, at least one of Ri and R3 is -CH2CHF2, even more preferably Ri and R3 are both -CH2CHF2.

[0072] In a preferred embodiment, n is 0 or 1, R2is -OCH2CH2-, and Ri and R3 are independently selected from -CHF2, -CF3, -CH2CHF2, -CH2CF3, -CF2CHF2, -CF2CF3, -CHFCHF2 and - CHFCF3. In a more preferred embodiment, n is 1; R2 is -OCH2CH2; and Ri and R3 are independently selected from -CHF2, -CH2CHF2, -CHFCHF2 and -CF2CHF2. In an even more preferred embodiment, n is 1; R2 is -OCH2CH2; and at least one of Ri and R3 is -CH2CHF2.

[0073] Much more preferably, n is 1, R2 is -OCH2CH2- and Ri and R3 are both -CH2CHF2 and thus, the fluorinated ether of formula (I) is 1,2-bis (2,2-difluoroethoxy) ethane.

[0074] The sulfonamide is represented by general formula (II): wherein

[0075] R1is selected from F, a linear or branched C1-C12 alkyl group which may be substituted with one or more fluorine atom(s), a linear or branched C2-C12 alkenyl group which may be substituted with one or more fluorine atom(s), a C3-C12 cycloalkyl group which may be substituted with one or more fluorine atom(s) and a C6-C12 aryl group which may be substituted with one or more fluorine atom(s),

[0076] R2and R3are independently selected from a linear or branched C1-C12 alkyl group which may be substituted with one or more fluorine atom(s), a linear or branched C2-C12 alkenyl group which may be substituted with one or more fluorine atom(s), a C6-C12 aryl group which may be substituted with one or more fluorine atom(s), and CH2CH2O-(CH2CH2O)n-R, wherein R is H or a methyl group and n is an integer from 1 to 20; or R2and R3may be combined with each other to form a nitrogen-containing aliphatic ring.

[0077] A “C1-C12 alkyl” as used herein refers to a branched or linear aliphatic carbon chain consisting of 1 to 12 carbon atoms. Illustrative examples of C1-C12 alkyl groups include methyl, ethyl, n- propyl, i-propyl, n-butyl, i-butyl, t-butyl, pentyl, hexyl, heptyl, octyl, etc. In preferred embodiments, the aliphatic chain may comprise less carbon atoms, for example 6 or less (“Ci- Ce alkyl”) or 3 or less (“C1-C3 alkyl”) carbon atoms. The alkyl chain may be partially or completely fluorinated (“perfluorinated”), meaning that at least one but not all hydrogen atoms of any C-H bond is replaced by a fluorine atom or that all hydrogen atoms of any C-H bond is replaced by a fluorine atom, respectively.

[0078] A “C2-C12 alkenyl” as used herein refers to linear or branched aliphatic groups having from 2 to 12 carbon atoms and having at least 1 double C=C bond. Such alkenyl groups include ethenyl (-CH=CH2), n-2 -propenyl (allyl, -CH2CH=CH2) and the like. The alkenyl chain may be partially or completely fluorinated (“perfluorinated”), meaning that at least one but not all hydrogen atoms of any C-H bond is replaced by a fluorine atom or that all hydrogen atoms of any C-H bond is replaced by a fluorine atom. A “C3-C12 cycloalkyl” as used herein refers to mono-, bi- or tricyclic hydrocarbyl groups having 3 to 12 carbon atoms. Typical C3-C12 cycloalkyl include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclooctyl, cyclodecyl. The cycloalkyl may be partially or completely fluorinated (“perfluorinated”), meaning that at least one but not all hydrogen atoms of any C-H bond is replaced by a fluorine atom or that all hydrogen atoms of any C-H bond is replaced by a fluorine atom.

[0079] A “C6-C12 aryl” as used herein refers to aromatic hydrocarbon rings that contain 6 to 12 carbon atoms, also as two fused rings, optionally substituted with alkyl groups as already defined above, such as phenyl, a-naphthyl, P-naphthyl, m-methylphenyl, p-trifluoromethylphenyl and the like. The aryl may be partially or completely fluorinated (“perfluorinated”), meaning that at least one but not all hydrogen atoms of any C-H bond is replaced by a fluorine atom or that all hydrogen atoms of any C-H bond is replaced by a fluorine atom.

[0080] More particularly, Ri is selected from F, a linear or branched C1-C12 alkyl group which may be substituted with one or more fluorine atom(s), a linear or branched C2-C12 alkenyl group which may be substituted with one or more fluorine atom(s), and a C3-C12 cycloalkyl group which may be substituted with one or more fluorine atom(s).

[0081] Preferably, Ri is selected from F, a linear C1-C12 alkyl group which may be substituted with one or more fluorine atom(s), and a C3-C12 cycloalkyl group which may be substituted with one or more fluorine atom(s).

[0082] Even more preferably Ri is F or a linear C1-C12 alkyl group substituted with one or more fluorine atom(s), and even more preferably F or a linear C1-C4 alkyl group substituted with one or more fluorine atom(s). In the most preferred embodiment Ri is F.

[0083] More particularly, R2 and R3 are independently selected from a linear or branched C1-C12 alkyl group which may be substituted with one or more fluorine atom(s) and a linear or branched C2- C12 alkenyl group which may be substituted with one or more fluorine atom(s).

[0084] Preferably, R2 and R3 are independently selected from a linear C1-C12 alkyl group which may be substituted with one or more fluorine atom(s) and a linear C2-C12 alkenyl group which may be substituted with one or more fluorine atom(s). Even more preferably, R2 and R3 are independently selected from a linear C1-C10 alkyl group, and most preferably R2 and R3 are independently selected from a linear C1-C4 alkyl group. In an embodiment Ri and R2 are the same. In another embodiment, Ri and R2 are different. In the most preferred embodiment, Ri = R2 = CH3.

[0085] In a further embodiment, the at least one sulfonamide has the general formula (II) as shown above, wherein: - Ri is selected from F, a linear C1-C12 alkyl group which may be substituted with one or more fluorine atom(s), and a C3-C12 cycloalkyl group which may be substituted with one or more fluorine atom(s); and

[0086] - R2 and R3 are independently selected from a linear C1-C12 alkyl group which may be substituted with one or more fluorine atom(s) and a linear C2-C12 alkenyl group which may be substituted with one or more fluorine atom(s).

[0087] In a further embodiment, the at least one sulfonamide has the general formula (II) as shown above, wherein:

[0088] - Ri is selected from F and a linear C1-C4 alkyl group which may be substituted with one or more fluorine atom(s); and - R2 and R3 are linear C1-C4 alkyl groups which may be substituted with one or more fluorine atom(s).

[0089] In a further embodiment, the at least one sulfonamide is selected from at least one of the following structures:

[0090]

[0091] O O

[0092] N-S-(CH2)7CH3N-S-(CH2)11CH3

[0093] 6 6

[0094] In a preferred embodiment, the at least one sulfonamide is one wherein Ri is F and R2 = R3= CH3.

[0095] In a particular embodiment the at least one solvent represents from 30 to 92 wt.% with respect to the total weight of the electrolyte, preferably from 20 to 85 wt.% with respect to the total weight of the electrolyte, more preferably from 50 to 80 wt.% with respect to the total weight of the electrolyte; even more preferably, is about 75 wt.% with respect to the total weight of the electrolyte. Lithium salts

[0096] The gel electrolyte of the present invention comprises at least one lithium salt. The at least one lithium salt comprised in the electrolyte may be an organic lithium salt, an inorganic lithium salt, or a combination thereof.

[0097] In a particular embodiment, the inorganic lithium salt may include, but is not limited to, LiCICh, LiNO3, LiBF4, Li AsF6, LiPF6, LiBF3Cl, and LiF . In another particular embodiment, the organic lithium salt may include, but is not limited to, [LiN(SO2CF3)(SO2CF2H)], LiN(SO2CF3)2, LiN(SO2F)2, LiN(SO2CF3)(SO2F), LiN(C2F5SO2)(SO2F), LiB(C2O4)2, LiBF2(C2O4), LiC(SO2CF3)3, LiPF3(C2F5)3, and LiCF3SO3.

[0098] In an embodiment, the at least one a lithium salt is selected from LiC104, LiNO3, LiBF4, LiAsFe, LiPF6, LiBF3Cl, LiF, LiN(SO2CF3)2(LiTFSI), LiN(SO2F)2(LiFSI), LiN(SO2CF3)(SO2F), LiN(C2F5SO2)(SO2F) LiB(C2O4)2, LiBF2(C2O4), LiC(SO2CF3)3, LiPF3(C2F5)3, LiCF3SO3, and a combination thereof.

[0099] In another embodiment, the at least one lithium salt is selected from LiN(SO2CF3)2, LiN(SO2F)2, LiN(SO2CF3)(SO2F), LiB(C2O4)2, LiBF2(C2O4), LiC(SO2CF3)3, LiPF3(C2F5)3, LiCF3SO3, and LiNO3or a combination thereof.

[0100] In a preferred embodiment, the at least one lithium salt is an organic lithium salt, preferably selected from LiB(C2O4)2, LiBF2(C2O4), LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2CF3)(SO2F), or a combination thereof, more preferably the lithium salt is selected from LiN(SO2F)2, LiBF2(C2O4), or a combination thereof, even more preferably the lithium salt is LiN(SO2F)2.

[0101] The at least one lithium salt, comprised in the gel electrolyte, may vary from 0.1 to 50 wt.% with respect to the total weight of the gel electrolyte, preferably from 0.5 to 20 wt.%, even more preferably from 5 to 15 wt.% with respect to the total weight of the electrolyte.

[0102] Co-solvent

[0103] In a particular embodiment, the gel electrolyte of the first aspect of the invention further comprises at least one co-solvent. In the context of the invention, the term “co-solvent” refers to a substance suitable for dissolving the lithium salts in the electrolyte or if not able to dissolve lithium salts, it acts as filler in the electrolyte. Said co-solvent can also soften or swell a polymer when said polymer is present in the electrolyte formulation.

[0104] Examples of co-solvents able to dissolve salts are known in the art and include, among others, organic solvents and compounds such as dimethoxy ethane (DME), 1,2-di ethoxy ethane (DEE), 1,3-dioxolane (DOL), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (G3), tetraethylene glycol dimethyl ether (TEGDME), polyethylene glycol) dimethyl ether (PEGDME), tetrahydropyran (THP), y-butyrolactone, tetrahydrofuran (THF), 2- methyltetrahydrofuran, diethylether, methyl-tert-butylether, succinonitrile (SN), glutaronitrile (GN), adiponitrile (AN), Ethylene sulfite (ES), propylene sulfite (PS) di-ethylene sulfite (DES), di-methylsulfite (DMS), dimethyl 2,5-dioxahexanedioate (DMDOHD), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC) and any mixtures thereof.

[0105] Examples of co-solvents not dissolving the salts are known in the art and include, among others, organic solvents and compounds such as: fluorobenzene (FPh), tris(2,2,2-trifluoroethyl) orthoformate (TFEO), tetrafluoro 1 -(2,2,2, trifluoroetoxy) ethane (D2), bis(2,2,2-trifluoroethyl) ether (BTFE, l,l,2,2,teterafluoroethyl-2,2,3,3-tetrafluoropropyl-ether (TTE).

[0106] The quantity of co-solvents may be in range from 1% to 50% by weight of total mass of electrolyte. Preferably from 10 to 30 wt.% with respect to the total weight of the electrolyte.

[0107] Cross-linked Polymer

[0108] The gel electrolyte of the invention further comprises at least one cross-linked polymer obtainable by cross-linking a cross-linked polymer precursor formulation comprising at least one cross-linkable monomer and / or a mixture of cross-linkable monomers.

[0109] The cross-linked polymer is suitable for ions conduction, in particular lithium cations, via non- covalent interactions between the polymer chain and the ion. Suitable polymers for gel electrolytes are known in the art and typically comprise a heteroatom such as O, N, S or P in the repeating unit of the polymer chain that is suitable for interacting with a lithium cation through a lone pair of the heteroatom.

[0110] In the context of the present invention, the term “cross-linkable polymer precursor formulation” refers to a formulation comprising monomers containing one or more cross-linkable functional groups in their structures susceptible to form cross-linked polymers.

[0111] In the context of the present invention, cross-linkable monomers relate to those monomers having one or more cross-linkable functional groups which, upon polymerization reaction, they lead to a cross-linked polymer matrix.

[0112] In a preferred embodiment, the cross-linkable functional groups are (meth)acrylate groups. In the present invention, the cross-linked polymer results from the polymerization of a crosslinked polymer precursor formulation comprising a mixture of cross-linkable monomers comprising in its molecular formula at least one cross-linkable functional group. Namely, said mixture comprises a) at least one monomer having one (meth)acrylate group; and b) at least one monomer having two (meth)acrylate groups; such as a cross-linked polymer resulting from the free radical polymerization of a mixture of at least one monomer having one (meth)acrylate group with at least one monomer having two (meth)acrylate groups.

[0113] In a particular embodiment, the cross-linked polymer precursor formulation further comprises monomers having three or four cross-linkable functional groups, in particular tri- and / or tetra- (meth)acrylate groups.

[0114] In a particular embodiment, the monomers having (meth)acrylate groups are selected from alkyl mono-, di-, tri- or tetra-(meth) acrylates or any alkyl ester thereof; carbocyclic containing mono- (meth)acrylates; and mono- or di-alkyl siloxanes containing mono-, di- or tri-(meth)acrylate groups.

[0115] In this context, the term “alkyl” refers to a linear or branched aliphatic carbon chain consisting of 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms, which may be optionally substituted with halogen atoms, preferably fluorine atoms.

[0116] In a preferred embodiment, the polymer precursor formulation comprises a mixture of an alkyl mono-(meth) acrylate, or any alkyl ester thereof, with one or more di- (meth)acrylates.

[0117] In another preferred embodiment, the polymer precursor formulation comprises a mixture of: a) an alkyl mono-(meth) acrylate monomer, or any alkyl ester thereof, b) one or more di- (meth)acrylate monomers, and c) a tri- and / or tetra-(meth)acrylate monomers.

[0118] Examples of alkyl mono-(meth) acrylates, i.e. monomers having one cross-linkable functional group, include, but are not limited to, methyl acrylate (MA), methyl methacrylate (MMA), ethyl acrylate (EA), ethyl methacrylate (EMA), butyl acrylate (BA), butyl methacrylate (BMA), 2- ethylhexyl acrylate, trifluoroethyl acrylate (TFEA), ethylhexyl acrylate (EHA) and cyanoethyl acrylate (CEA). By the term di-, tri- or tetra- (meth)acrylates should be understood those monomers having two, three or four (meth)acrylate groups susceptible to form covalent bonds with other cross-linkable monomers or polymer chains.

[0119] Examples of di-(meth)acrylates, i.e. monomers having two cross-linkable functional group include, but are not limited to, hexanediol diacrylate (HD A) and dodecanediol dimethacrylate (DDMA).

[0120] In a particular embodiment, the tri-(meth)acrylate, i.e, a monomer having three cross-linkable functional groups, is trimethylolpropane triacrylate (TMPTA).

[0121] In another particular embodiment, the tetra-(meth)acrylate, i.e, a monomer having four crosslinkable functional groups is pentaerythritol tetraacrylate (PETA).

[0122] In a preferred embodiment, the monomers having one cross-linkable functional group are alkyl mono-(meth) acrylates, such as methyl acrylate (MA), ethyl acrylate (EA), trifluoroethyl acrylate (TFEA) and butyl acrylate (BA), more preferably is trifluoroethyl acrylate (TFEA).

[0123] In another preferred embodiment, di-(meth)acrylates are hexanediol diacrylate (HDA) or, dodecanediol dimethacrylate (DDMA).

[0124] In another preferred embodiment, tri- and tetra-(meth)acrylates include trimethylolpropane triacrylate (TMPTA) and pentaerythritol tetraacrylate (PETA).

[0125] Examples of carbocyclic containing mono- (meth)acrylates include, but are not limited to, benzyl acrylate or benzyl methacrylate.

[0126] Examples of mono- or di-alkyl siloxanes containing mono-, di- or tri-(meth)acrylate groups include, but are not limited to, dimethylsiloxane acrylate (DMSA) and dimethylsiloxane diacrylate (DMSDA).

[0127] In a particular embodiment, the cross-linked polymer precursor formulation comprises: a mixture of a) an alkyl mono-(meth)acrylates; of a carbocyclic containing mono- (meth)acrylates; or of any blend thereof, with b) with di-(meth) acrylates such as dodecanediol dimethacrylate (DDMA) and ethyl hexyl acrylate (EHA), and c) optionally with tri- or tetra-(meth)acrylates such as trimethylolpropane triacrylate (TMPTA) and pentaerythritol tetraacrylate (PETA) and / or. In a preferred embodiment, the cross-linked polymer precursor formulation comprises a mixture of a) an alkyl mono-(meth)acrylate, such as butyl acrylate (BA), ethyl acrylate (EA), cyanoethyl acrylate, 2-ethylhexyl acrylate, trifluoroethyl acrylate (TFEA); of a carbocyclic containing a mono- (meth)acrylate such as benzyl (meth)acrylate; or any blend thereof, with b) a di-(meth)acrylate such as butyl diacrylate (BDA), hexanediol diacrylate (HDA) and dodecanediol dimethacrylate (DDMA). Said polymer precursor formulation can optionally comprise trimethylolpropane triacrylate (TMPTA) and / or pentaerythritol tetraacrylate (PETA)

[0128] Preferably, the cross-linked polymer precursor comprises: a mixture of: o a) an alkyl mono-(meth)acrylate, such as butyl acrylate (BA), ethyl acrylate (EA), cyanoethyl acrylate, 2-ethylhexyl acrylate, trifluoroethyl acrylate (TFEA); or a carbocyclic containing mono-(meth)acrylate such as benzyl (meth)acrylate or any blend thereof, with o b) a di-(meth)acrylate such as butyl diacrylate (BDA), hexanediol diacrylate (HDA) and dodecanediol dimethacrylate (DDMA), and o c) optionally, trimethylolpropane triacrylate- (TMPTA) or pentaerythritol tetraacrylate (PETA.

[0129] More preferably, the cross-linked polymer precursor is selected from the group consisting of: a mixture of an alkyl (meth)acrylate with an alkyl di-(meth)acrylate, and optionally trimethylolpropane triacrylate (TMPTA) and / or pentaerythritol tetraacrylate (PETA); and a mixture of an alkyl (meth)acrylate and an alkyl di(meth)acrylate with trimethylolpropane triacrylate (TMPTA) and / or pentaerythritol tetraacrylate (PETA).

[0130] In a more preferred embodiment, the cross-linked polymer precursor formulation comprises a mixture of an alkyl mono-(meth)acrylate; an alkyl di(meth)acrylate; and optionally, trimethylolpropane triacrylate (TMPTA) and / or pentaerythritol tetraacrylate (PETA).

[0131] In another preferred embodiment, , the cross-linked polymer precursor formulation comprises a mixture of a) an alkyl mono-(meth)acrylate selected from trifluoroethyl acrylate (TFEA) and ethyl hexyl acrylate (EHA); b) an akyl di-(meth)acrylate selected from dodecanediol dimethacrylate (DDMA) and hexanediol diacrylate (HDA).

[0132] In a more preferred embodiment, the cross-linked polymer precursor formulation comprises a mixture of trifluoroethyl acrylate (TFEA), trimethylolpropane triacrylate (TMPTA) and dodecanediol dimethacrylate (DDMA); or a mixture ofethyl hexyl acrylate (EHA) and hexanediol di acrylate (HDA).

[0133] In another embodiment, when the cross-linked polymer precursor formulation is a mixture of trifluoroethyl acrylate (TFEA), dodecanediol dimethacrylate (DDMA) and trimethylolpropane triacrylate (TMPTA), the weight ratio of trifluoroethyl acrylate to dodecanediol dimethacrylate (DDMA) and trimethylolpropane triacrylate (TMPTA) is of between 50: 1 and 1 : 1; more preferably of between 10: 1 and 2: 1; even more preferably of about 3:1.

[0134] In another embodiment, when the cross-linked polymer precursor formulation is a mixture of ethyl hexyl acrylate (EHA) and hexanediol diacrylate (HDA), the weight ratio of ethyl hexyl acrylate (EHA) and hexanediol diacrylate (HDA) is of between 5: 1 and 1 : 1; more preferably of between 3: 1; even more preferably of about 2.5: 1.

[0135] Regardless of the chemical nature of the cross-linked polymer, its gravimetric content in the gel electrolyte may vary from 2 to 30 wt.% compared to the total weight of the gel electrolyte, preferably from 4 to 20 wt.%, even more preferably from 5 to 15% wt.%. In a most preferred embodiment, the gravimetric content of the cross-linked polymer is about 10 wt.% compared to the total weight of the gel electrolyte.

[0136] In another specific embodiment of the first aspect of the invention, the cross-linked polymer precursor formulation is a mixture of trifluoroethyl acrylate (TFEA), dodecanediol dimethacrylate (DDMA) and trimethylolpropane triacrylate (TMPTA), and:

[0137] - the mixture represents from 4% to 20% of the weight of the electrolyte; preferably, the mixture represents from 5% to 15% of the weight of the electrolyte; and / or

[0138] - the weight ratio of trifluoroethyl acrylate (TFEA) to DDMA and TMPTA is of between 50: 1 and 1 : 1; more preferably of between 10: 1 and 2: 1; even more preferably of about 3: 1. In another specific embodiment of the first aspect of the invention, the cross-linked polymer precursor formulation is a mixture of ethyl hexyl acrylate (EHA) and hexanediol diacrylate (HD A), and

[0139] - the mixture represents from 4% to 20% of the weight of the electrolyte; preferably, the mixture represents from 5% to 15% of the weight of the electrolyte; and / or

[0140] - the weight ratio of ethyl hexyl acrylate (EHA) and hexanediol diacrylate (HDA) is of between 5: 1 and 1 : 1; more preferably of between 3: 1; even more preferably of about 2.5: 1.

[0141] Further embodiments of the electrolyte

[0142] In an embodiment of the invention, the gel electrolyte consists of: i. at least one solvent selected from a fluorinated ether of formula (I), a sulfonamide of formula (II) and a combination thereof, as defined above; and ii. at least one lithium salt, iii. at least one cross-linked polymer obtainable by cross-linking a cross-linked polymer precursor formulation comprising:

[0143] - a mixture of cross-linkable monomers, said mixture comprising: a) at least one monomer having one (meth)acrylate group; and b) at least one monomer having two (meth)acrylate groups.

[0144] In a particular embodiment of the latter:

[0145] - the at least one solvent represents from 30 to 95 wt.% with respect to the total weight of the electrolyte, preferably from 40 to 85 wt.% with respect to the total weight of the electrolyte, more preferably from 50 to 80 wt.% with respect to the total weight of the electrolyte; even more preferably, is about 75 wt.% with respect to the total weight of the electrolyte; and / or

[0146] - the at least one lithium salt, amounts to from 1 to 95 wt.% with respect to the total weight of the electrolyte, preferably from 3 to 20 wt.%, even more preferably from 5 to 15 wt.%, even much more preferably from 10 to 15 wt.% of the composition; and / or - the cross-linked polymer amounts from 2 to 30 wt.% compared to the total weight of the electrolyte composition, preferably from 4 to 20 wt.%, even more preferably from 5 to 15% wt.%, even more preferably to about 10 wt.% with respect to the total weight of the gel electrolyte.

[0147] In an embodiment, the gel electrolyte of the invention comprises: i. at least one solvent selected from: a) fluorinated ether solvent of formula (I): wherein

[0148] Ri and R3 are independently selected from -CHF2, -CF3, -CH2CHF2, -CH2CF3, - CF2CHF2, -CF2CF3, -CHFCHF2 and -CHFCF3;

[0149] R2is -OCH2CH2-, -OCH2CH2CH2- or -OCH2CH2CH2CH2-; n is an integer from 0 to 10; b) a sulfonamide of formula (II): wherein

[0150] R1is selected from F, a linear or branched Ci-Ce alkyl group which may be substituted with one or more fluorine atom(s), a C3-C6 cycloalkyl group which may be substituted with one or more fluorine atom(s) and a C6-C12 aryl group which may be substituted with one or more fluorine atom(s),

[0151] R2and R3are independently selected from a linear or branched Ci-Ce alkyl group which may be substituted with one or more fluorine atom(s), a C6-C12 aryl group which may be substituted with one or more fluorine atom(s), and CH2CH2O- (CH2CH2O)n-R, wherein R is H or a methyl group and n is an integer from 1 to 20; or R2and R3may be combined with each other to form a nitrogen-containing aliphatic ring; and c) a combination of a) and b); ii. at least one lithium salt; and iii. a cross-linked polymer obtainable by cross-linking a cross-linked polymer precursor formulation comprising a mixture of at least one monomer having one (meth)acrylatel group and at least one monomer having two (meth)acrylate groups.

[0152] In another embodiment, the gel electrolyte of the invention comprises: i. at least one solvent selected from a fluorinated ether of formula (I), a sulfonamide of formula (II) and a combination thereof as defined above: ii. at least one lithium salt; iii. a cross-linked polymer obtainable by cross-linking a cross-linked polymer precursor formulation comprising a mixture of an alkyl mono-(meth)acrylate and one or more di(meth) acrylate; and iv. optionally, co-solvent.

[0153] In another embodiment, the gel electrolyte comprises: i. at least one fluorinated ether solvent of formula (I) wherein

[0154] Ri and R3 are independently selected from -CHF2, -CH2CHF2, -CHFCHF2 and - CF2CHF2;

[0155] R2is -OCH2CH2-; and n is an integer selected from 0, 1, 2, 3, 4, and 5, preferably form 0 and 1; or at least one sulfonamide of formula (II): wherein R1is selected from F, a linear or branched Ci-Ce alkyl group which may be substituted with one or more fluorine atom(s),

[0156] R2and R3are independently selected from a linear or branched Ci-Ce alkyl group which may be substituted with one or more fluorine atom(s; ii. at least one lithium salt; iii. at least one cross-linked polymer obtainable by cross-linking a cross-linked polymer precursor formulation comprising:

[0157] - a mixture of cross-linkable monomers, said mixture comprising: a) at least one monomer having one (meth)acrylate group; and b) at least one monomer having two (meth)acrylate groups; and iv. optionally a co-solvent.

[0158] In another embodiment, the gel electrolyte comprises: i. at least one fluorinated ether solvent of formula (I) wherein

[0159] Ri and R3 are independently selected from -CHF2, -CH2CHF2, -CHFCHF2 and - CF2CHF2;

[0160] R2is -OCH2CH2-; and n is an integer selected from 0, 1, 2, 3, 4, and 5, preferably form 0 and 1; or at least one sulfonamide of formula (II): tn) wherein

[0161] R1is selected from F, a linear or branched Ci-Ce alkyl group which may be substituted with one or more fluorine atom(s), R2and R3are independently selected from a linear or branched Ci-Ce alkyl group which may be substituted with one or more fluorine atom(s; ii. at least one lithium salt; iii. at least one cross-linked polymer obtainable by cross-linking a cross-linked polymer precursor formulation comprising a mixture of an alkyl mono-(meth)acrylate and one or more di-(meth) acrylates; and iv. optionally a co-solvent.

[0162] In another embodiment, the gel electrolyte comprises: i. at least one fluorinated ether solvent of formula (I) wherein

[0163] Ri and R3 are independently selected from -CHF2, -CH2CHF2, -CHFCHF2 and - CF2CHF2;

[0164] R2is -OCH2CH2-; and n is an integer selected from 0, 1, 2, 3, 4, and 5, preferably form 0 and 1; or at least one sulfonamide of formula (II): wherein

[0165] R1is selected from F, a linear or branched Ci-Ce alkyl group which may be substituted with one or more fluorine atom(s),

[0166] R2and R3are independently selected from a linear or branched Ci-Ce alkyl group which may be substituted with one or more fluorine atom(s); ii. at least one lithium salt; iii. at least one cross-linked polymer obtainable by cross-linking a cross-linked polymer precursor formulation comprising a mixture of: a) an alkyl mono-(meth)acrylate selected from methyl, ethyl, butyl acrylate, trifluoroethyl acrylate (TFEA), ethylhexyl acrylate (EHA), cyanoethyl acrylate (CEA), and one or more di-(meth) acrylate selected from hexanediol diacrylate (HD A) and dodecanediol dimethacrylate (DDMA); and iv. optionally a co-solvent.

[0167] In another embodiment, the gel electrolyte comprises: i. at least one fluorinated ether solvent of formula (I) wherein

[0168] Ri and R3 are independently selected from -CHF2, -CH2CHF2, -CHFCHF2 and - CF2CHF2;

[0169] R2is -OCH2CH2-; and n is an integer selected from 0, 1, 2, 3, 4, and 5, preferably form 0 and 1; or at least one sulfonamide of formula (II): wherein

[0170] R1is selected from F, a linear or branched Ci-Ce alkyl group which may be substituted with one or more fluorine atom(s),

[0171] R2and R3are independently selected from a linear or branched Ci-Ce alkyl group which may be substituted with one or more fluorine atom(s; ii. at least one lithium salt; iii. at least one cross-linked polymer obtainable by cross-linking a cross-linked polymer precursor formulation comprising a mixture of an alkyl mono-(meth)acrylate; with an alkyl di(meth)acrylate;; and iv. optionally a co-solvent. T1

[0172] In all the further embodiments above, the cross-linked polymer precursor formulation optionally comprises at least one monomer having tri- / or tetra-(meth)acrylates, such as trimethylolpropane triacrylate (TMPTA) and / or pentaerythritol tetraacrylate (PETA.

[0173] In another embodiment, the gel electrolyte comprises: i. at least one fluorinated ether solvent of formula (I) wherein

[0174] Ri and R3 are independently selected from -CHF2, -CH2CHF2, -CHFCHF2 and - CF2CHF2;

[0175] R2is -OCH2CH2-; and n is an integer selected from 0, 1, 2, 3, 4, and 5, preferably form 0 and 1; or at least one sulfonamide of formula (II): wherein

[0176] R1is selected from F, a linear or branched Ci-Ce alkyl group which may be substituted with one or more fluorine atom(s),

[0177] R2and R3are independently selected from a linear or branched Ci-Ce alkyl group which may be substituted with one or more fluorine atom(s; ii. at least one lithium salt; iii. at least one cross-linked polymer obtainable by cross-linking a cross-linked polymer precursor formulation comprising a mixture of trifluoroethyl acrylate (TFEA), trimethylolpropane triacrylate (TMPTA) and dodecanediol dimethacrylate (DDMA); or a mixture of ethyl hexyl acrylate (EHA) and hexanediol diacrylate (HDA)and iv. optionally a co-solvent. In another particular embodiment of any of the above, in the fluorinated ether of formula (I), Ri and R3 are -CH2CHF2, R2 is -OCH2CH2 and n is 1.

[0178] In another particular embodiment of any of the above, in the sulfonamide of formula (II), Ri is F, and R2 and R3 are C1-C3 alkyl, more preferably Ri and R2 are both CH .

[0179] In another particular embodiment of any of the above, the at least one lithium salt is selected from [LiN(SO2CF3)(SO2CF2H)], LiN(SO2CF3)2, LiN(SO2F)2, LiN(SO2CF3)(SO2F), LiN(C2F5SO2)(SO2F), LiB(C2O4)2, LiBF2(C2O4), LiC(SO2CF3)3, LiPF3(C2F5)3, and LiCF3SO3. Preferably, the at least one lithium salt is LiN(SO2F)2.

[0180] In any of the particular embodiments above:

[0181] - the at least one fluorinated ether or sulfonamide represents from 30 to 95 wt.% with respect to the total weight of the electrolyte, preferably from 40 to 85 wt.% with respect to the total weight of the electrolyte, more preferably from 50 to 80 wt.% with respect to the total weight of the electrolyte; even more preferably, is about 75 wt.% with respect to the total weight of the electrolyte; and / or

[0182] - the lithium salt amounts to from 1 to 95 wt.% with respect to the total weight of the electrolyte, preferably from 3 to 20 wt.%, even more preferably from 5 to 15 wt.%, even much more preferably from 10% to 15% wt.% of the composition,; and / or

[0183] - the cross-linked polymer amounts from 2 to 30 wt.% compared to the total weight of the electrolyte composition, preferably from 4 to 20 wt.%, even more preferably from 5 to 15% wt.%, even more preferably to about 10 wt.% with respect to the total weight of the gel electrolyte.

[0184] The gel electrolyte of the first aspect may be prepared by a method comprising:

[0185] (i) providing at least one lithium salt, as defined in the first aspect of the invention;

[0186] (ii) mixing at least one solvent selected from a fluorinated ether of formula (I), a sulfonamide of formula (II) and a combination thereof, as defined in the first aspect of the invention with the at least one lithium salt provided in step (i);

[0187] (iii) optionally, adding a to the mixture obtained in step (ii) at least one co-solvent; and / or (iv) adding to the mixture obtained in step (ii) or (iii) the cross-linked polymer precursor formulation; and a free radical initiator.

[0188] (v) cross-linking the cross-linked polymer precursor formulation by free radical polymerization to form a gel electrolyte.

[0189] All the steps of the method above may be performed by using the neat components of the electrolyte (e.g. as neat solid or liquid) or, alternatively, said components may be dissolved in a solvent prior to performing a given step.

[0190] In preferred embodiments, steps (i) and (ii) are carried out by using the neat components (lithium salts and fluorinated ether or sulfonamide).

[0191] In another embodiment, when step (iii) is carried out, firstly the co-solvent is added to the mixture obtained from step (ii).

[0192] In another embodiment, when step (iii) is carried out, firstly the co-solvent is added to the mixture obtained in step (ii) and then the polymer precursor formulation is added.

[0193] In another embodiment, step (iv) is carried out by adding the neat polymer precursors and the free radical initiator to the mixture obtained from step (ii) or (iii).

[0194] It is preferable that the mixture obtained from step (ii) or (iii), or from step (iv), is stirred for a certain time to ensure that a homogeneous solution is obtained (i.e. no suspended matter is present). The stirring is performed magnetically at 100 rpm, at 200 rpm, at 300 rpm, at 400 rpm, at 500 rpm, at 600 rpm, at 700 rpm, at 800 rpm, at 900 rpm, at 1000 rpm; preferably the stirring is performed in a range between 100 and 500 rpm, even more preferably at about 300 rpm. Additionally, the mixture from step (iv) is stirred for at least 5 min, at least 15 min, at least 30 min, at least 1 hour, at least 2 hours, at least 4 hours, at least 6 hours, at least 12 hours, at least 1 day; preferably, the mixture from step (iv) is stirred for 1 to 4 hours, more preferably for 2 hours.

[0195] All the steps of the method above are performed at a temperature comprised between 10 and 30 °C, preferably between 15 and 25 °C, even more preferably between 20 and 25 °C.

[0196] The cross-linked polymer precursor formulation comprises an initiator of free radical polymerization, such as azoisobutyronitrile (AIBN). Said initiator compound is preferably present in a weight amount corresponding to 0.1% to 1% of the weight of the electrolyte composition; more preferably in a weight amount of 0.3% of the weight of the electrolyte composition.

[0197] The free radical initiator can be any those widely known in the prior art allowing the initiation of the polymerization reaction of the monomers, such as azo compounds and peroxides, more preferably azobisisobutyronitrile (AIBN) or azobisdimethylvaleronitrile.

[0198] A third aspect of the invention refers to an electrolyte composition suitable for preparing the gel electrolyte of the first aspect of the invention, said electrolyte composition comprising: i) at least one solvent selected from a fluorinated ether of formula (I), a sulfonamide of formula (II) and a combination thereof, as defined in the first aspect; ii) at least one lithium salt: iii)a cross-linked polymer precursor formulation comprising:

[0199] - a mixture of cross-linkable monomers, said mixture comprising: a) at least one monomer having one (meth)acrylate group; and b) at least one monomer having two (meth)acrylate groups; and a free radical initiator; iv) optionally, at least one co-solvent.

[0200] All the particular and preferred embodiments related to the components of the gel electrolyte of the invention apply entirely for the electrolyte composition of the third aspect of the invention.

[0201] Electrochemical cell and battery

[0202] The gel electrolyte of the first aspect of the invention is particularly useful in electrochemical devices such as electrochemical cells or batteries, particularly secondary electrochemical cells or batteries wherein the cell reactions are reversible.

[0203] A fourth aspect of the invention thus relates to an electrochemical cell or a battery comprising the gel electrolyte according to the first aspect of the invention.

[0204] In a preferred embodiment, the fourth aspect of the invention relates to an electrochemical cell or a battery comprising the gel electrolyte according to any, preferred or particular, embodiment of the first aspect of the invention defined above. More preferably, the electrochemical cell or a battery comprising the gel electrolyte according to any, preferred or particular, embodiment of the first aspect of the invention defined above, as well as a cathode, an anode and, optionally a porous separator.

[0205] In a preferred embodiment, the fourth aspect of the invention relates to a lithium metal battery comprising the gel electrolyte according to any embodiment of the first aspect of the invention defined above. A lithium metal battery is a battery characterized in that it comprises an anode consisting essentially of metallic lithium.

[0206] In a further preferred embodiment, the fourth aspect of the invention relates to a lithium metal battery comprising a cathode wherein the cathode material is selected from the group consisting of lithium manganese oxide, lithium nickel oxide, lithium nickel manganese cobalt oxide, lithium nickel manganese oxide, lithium manganese cobalt oxide, lithium copper oxide, lithium copper sulphide, lithium iron phosphate, lithium iron sulphide, lithium manganese iron phosphate and lithium nickel cobalt aluminium oxide.

[0207] In a further preferred embodiment, the fourth aspect of the invention relates to a lithium metal battery comprising a cathode wherein the cathode material is lithium nickel manganese cobalt oxide, such as LiNi0.88Mn0.05Co0.07O2 (NMC9xx)); a lithium nickel cobalt aluminium oxide LiNixCoyAlzO2, wherein x+y+z=l (NCA), such as LiNi0.8Co0.15Al0.05O2; a lithium iron phosphate LiFePO4 (LFP) or a lithium manganese iron phosphate LiFexMni.xP04, wherein x<l (LMFP). Specifically, the lithium nickel cobalt aluminium oxide, the lithium nickel manganese cobalt oxide cathode, the lithium iron phosphate cathode or the lithium iron manganese phosphate cathode may additionally contain other additives. In a particular embodiment the cathode comprises NMC9xx or LFP, at least one conductive carbon, such as carbon black and / or CNT, and a polymeric binder.

[0208] In a preferred embodiment, the cathode consists of NMC9xx, carbon black as conductive carbon and polyvinylidene fluoride (PVdF) as a polymeric binder. It is preferred that the weight ratio between NMC9xx: conductive carbon: polymeric binder is 96:2:2.

[0209] In another preferred embodiment, the cathode consists of LiFePCU, carbon black and CNT as conductive carbon and polyvinylidene fluoride (PVdF) as a polymeric binder. It is preferred that the weight ratio between LiFePCU: conductive carbon: polymeric binder is 96.5: 1.5:2. In a further preferred embodiment, the fourth aspect of the invention relates to a lithium metal battery comprising a porous separator, such as a polyolefin separator, preferably microporous polypropylene or porous laminate having different layers of polyolefins, such as polypropylene / polyethylene / polypropylene, arranged between at least one electrode and the electrolyte in such a configuration that lithium cations can flow across said separator between the electrolyte and the surface of said at least one electrode. In specific embodiments, the separator has a thickness of between 1 and 50 pm, preferably of between 15 and 35 pm, more preferably of about 25 pm. The porosity of the separator may also vary between a certain range, particularly the average pore diameter is comprised between 0.001 and 0.100 pm, preferably between 0.020 and 0.080 pm, more preferably is about 0.064 pm.

[0210] In a preferred embodiment, in the electrochemical cell or battery of the invention:

[0211] - the cathode material comprises lithium nickel manganese cobalt oxide or lithium iron phosphate;

[0212] - the anode consists of metallic lithium; and

[0213] - the optional separator is a polypropylene separator.

[0214] In a further preferred embodiment, the fourth aspect of the invention relates to lithium metal battery having a charge retention capacity of at least 80%; preferably of at least 85%; and more preferably, of at least 90%, and much more preferably of at least 96% after 50 charging cycles. In a particular embodiment, the first cycle was applied at a current of C / 20, the 2 following cycles at a current of C / 10, and the remaining cycles at C / 5, at a temperature of 40 °C. In another embodiment, the voltage is comprised between 3 V and 4.2 V.

[0215] The electrochemical cell or battery of the invention may be applied to a variety of electronic devices which may include, but are not limited to: electric motors; electric cars, including electric vehicles (EV), hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), or the like; electric carts, including electric bikes (E-bikes) and electric scooters (E-scooters); electric golf carts; electric power storage systems; or the like.

[0216] Methods for preparing the electrochemical cell or battery comprising the gel electrolyte

[0217] A further aspect of the invention relates to a method for preparing an electrochemical cell or a battery, said method comprises the steps of: (i) providing a cathode for an electrochemical cell or a battery;

[0218] (ii) providing an anode for an electrochemical cell or a battery;

[0219] (iii) providing the electrolyte composition as defined in any preferred or particular embodiment of the third aspect of the invention, the electrolyte composition comprising the at least one solvent selected from a fluorinated ether of formula (I), a sulphonamide of formula (II) and a combination thereof, the at least one lithium salt, and the polymer precursor formulation;

[0220] (iv) optionally, providing a porous separator;

[0221] (v) assembling the cathode and the anode provided in steps (i) and (ii) and, optionally the separator provided in step (iv), and injecting the electrolyte composition provided in step (iii) between the cathode and the anode or, when a separator is used, on both sides of the separator; and

[0222] (vi) cross-linking the cross-linked polymer precursor formulation comprised in the electrolyte composition injected in step (v) by free radical polymerization to form a gel electrolyte.

[0223] Preferably such porous separator is a polymeric separator, more preferably the separator is made of a polyolefin, such as polypropylene.

[0224] In preferred embodiments, the cross-linking step (vi) is a free radical polymerization involving (meth)acrylate groups as cross-linkable functional groups present in the polymer precursor formulation such as those described herein above, preferably such functional groups are carboncarbon double bonds of (meth)acrylates.

[0225] Preferably, said (meth)acrylate groups are comprised in:

[0226] - a mixture of cross-linkable monomers selected from mono-, di-, tri- and tetra- (meth)acrylates, such as methyl, ethyl or butyl acrylate, trifluoroethyl acrylate (TFEA), ethylhexyl acrylate (EHA), cyanoethyl acrylate (CEA), methacryloxy propyltrimethoxysilane (MPTMS), hexanediol diacrylate (HDA), dodecanediol dimethacrylate (DDMA), trimethylolpropane triacrylate (TMPTA) and / or pentaerythritol tetraacrylate (PETA). The cross-linking is initiated by a radical polymerization initiator, such as AIBN, under conditions of temperature, pressure and for a reaction time easily deducible by a skilled person. In a preferred embodiment, the crosslinking step is performed at 50 °C, at 60°C, at 70 °C, at 80 °C, at 90 °C or at 100 °C, preferably in the range from 50 to 100 °C, more preferably at about 70 °C. The reaction time for the crosslinking step would be known to a skilled person depending on the group that undergoes crosslinking; this time would be at least 1 hour, at least 2 hours, at least 4 hours, at least 6 hours, at least 8 hours, at least 10 hours, at least 12 hours, at least 24 hours; preferably, the reaction time would be approximately 12 hours,

[0227] It is preferred that, after addition of AIBN, the so-obtained mixture is stirred to ensure homogeneity of the solution.

[0228] Preferred materials for the preparation of the electrochemical cell or battery are as defined in the preferred and particular embodiments of the second aspect of the invention.

[0229] EXAMPLES

[0230] The following examples are intended to illustrate but not to limit the disclosed embodiments.

[0231] List of abbreviations

[0232] DF2EO: l,2-bis(2,2-difluoroethoxy)ethane

[0233] FSA11 : N,N-Dimethylsulfamoylfluoride

[0234] LiFSL lithium bis(fluorosulfonyl)imide (LiN(SO2F)2

[0235] TFEA: 2,2,2-Trifluoroethyl acrylate

[0236] EHA: ethyl hexyl acrylate

[0237] BA: butyl acrylate

[0238] DDMA: 1,12-Dodecanediol Dimethacrylate

[0239] HDA: hexanediol diacrylate

[0240] TMPTA: Trimethylolpropane triacrylate

[0241] PETA: pentaerythritol tetraacrylate

[0242] AIBN: azobisisobutyronitrile rpm: rounds per minute RT : room temperature Reagents and starting materials

[0243] The following chemicals were purchased from Sigma-Aldrich, Chemfish, TCI and were dried under vacuum and / or with molecular sieves before use.

[0244] Example 1 : Preparation of electrolytes

[0245] Different electrolytes having the compositions (expressed in weight %) disclosed in Table below were prepared according to the following general procedure.

[0246] Electrolyte 1 (El) (comparative)

[0247] LiFSI was weighted in a vial and then DF2EO was added. The resulting mixture was left under stirring for approximately 2 h at 300 rpm and room temperature.

[0248] Electrolyte E1P2 (according to the invention)

[0249] In a first step, LiFSI was weighted in a vial and DF2EO was added. Then, TFEA, DDMA and TMPTA were added to the solution and the resulting mixture was left under stirring for approximately 2 h at 300 rpm and room temperature. After this time, the solution appeared homogeneous. Finally, AIBN (0.10 wt% of the total weight of the electrolyte) was then added to the solution and the resulting mixture was left stirring for another 10 min at 300 rpm.

[0250] Electrolyte EIP 3 (comparative)

[0251] In a first step, LiFSI was weighed in a vial and DF2EO was added. Then, BA and PETA were added to the solution and the resulting mixture was left under stirring for approximately 2 h at 300 rpm and room temperature. After this time, the solution appeared homogeneous. Finally, AIBN (0.10 wt% of the total weight of the electrolyte) was then added to the solution and the resulting mixture was left stirring for another 10 min at 300 rpm.

[0252] Electrolyte E1P4 (comparative)

[0253] In a first step, LiFSI was weighed in a vial and DF2EO was added. Then, TFEA and TMPTA were added to the solution and the resulting mixture was left under stirring for approximately 2 h at 300 rpm and room temperature. After this time, the solution appeared homogeneous. Finally, AIBN (0.10 wt% of the total weight of the electrolyte) was then added to the solution and the resulting mixture was left stirring for another 10 min at 300 rpm. Electrolyte ElP5(according to the invention)

[0254] In a first step, LiFSI was weighed in a vial and DF2E0 was added. Then, EHA and HD A were added to the solution and the resulting mixture was left under stirring for approximately 2 h at 300 rpm and room temperature. After this time, the solution appeared homogeneous. Finally, AIBN (0.10 wt% of the total weight of the electrolyte) was then added to the solution and the resulting mixture was left stirring for another 10 min at 300 rpm.

[0255] Electrolyte 2 (E2) (comparative)

[0256] LiFSI was weighted in a vial and FSA11 was added. The resulting mixture was left under stirring for approximately 2 h at 300 rpm and room temperature. Electrolyte E2P2 (according to the invention)

[0257] In a first step, LiFSI was weighted in a vial and FSA11 was added. Then, TFEA, DDMA and TMPTA were added to the solution and the resulting mixture was left under stirring for approximately 2 h at 300 rpm and room temperature. After this time, the solution appeared homogeneous. Finally, AIBN (0.10 wt.% of the total weight of the electrolyte) was then added to the solution and the resulting mixture was left stirring for another 10 min at 300 rpm.

[0258] The final electrolyte compositions were the following:

[0259] Electrolyte Electrolyte Electrolyte Electrolyte Electrolyte Electrolyte Electrolyte

[0260] ElE1P2E1P3 E1P4 E1P5 E2 E2P2

[0261] Compound(comparatlve)(invention) (comparative) (comparative) (invention)(comparatlve)(invention)

[0262] %wt%wt %wt %wt %wt%wt%wt

[0263] DF2EO 83.68 75.46 77.28 76.65 78.35

[0264] FSA11 86.46 77.78

[0265] LiFSI 16.32 14.72 14.23 14.11 14.43 13.54 13.66

[0266] TMPTA 0.6 2.24 0.48

[0267] DDMA 1.39 1.31

[0268] TFEA 7.74 6.88 6.66

[0269] PETA 2.26

[0270] BA 6.16

[0271] EHA 5.12

[0272] HDA 1.95

[0273] 5 Example 2: Preparation of electrochemical cell

[0274] 2.1. Lithium cells with electrolytes El (LFPE1), E1P2 (LFPE1P2), E2 (LFPE2) and E2P2 (LFPE2P2)

[0275] Lithium metal cells comprising electrolytes El, E1P2, E2 and E2P2 of Example 1 were prepared according to the following procedure:

[0276] 10 Cathode preparation: LiFePCU (LFP) cathode was composed of 96.5 wt.% of LFP, 1.5 wt.% of conductive carbon (carbon black and CNT), and 2 wt.% of polymeric binder (PVdF). The slurry was made using N-methyl-2 -pyrrolidone (NMP) as solvent and after homogenization of the dispersion it was cast on an aluminum current collector. Finally, it was dried overnight at 80-120 °C under vacuum, leading to an average loading of ca. 2.3 mAh cm'2.

[0277] 15 Anode provision'. Li metal foil (China Energy Lithium, 14 mm diameter and 50 pm thickness).

[0278] Cell assembly. Coin cells were assembled in an Argon filled glovebox using LFP (12 mm diameter) electrodes as cathode, Celgard 2500 as separator and Li metal disk (China Energy Lithium, 14 mm diameter and 50 pm thickness) as anode. The electrolytes prepared according to example 1 were injected between the cathode and the anode on both sides of the separator.

[0279] The cells with electrolyte El and E2 were left for wetting for 24h at RT, whereas the cells with electrolytes E1P2 and E2P2, apart from wetting for 24h at RT, were subjected crosslinking process by keeping them at 70°C for 12 hours.

[0280] 2.2. Lithium cells with electrolytes E1P2 (NMCE1P2), E1P3 (NMCE1P3), E1P4 (NMCE1P4) and E1P5 (NMCE1P5)

[0281] Lithium metal cells comprising electrolytes E1P2, E1P3, E1P4 and E1P5 of Example 1 were prepared according to the following procedure:

[0282] Cathode preparation'. LiNio.9MnxCoy02 (NMC9xx, purchased from Umicore) cathode was composed of 96 wt.% of NMC9xx, 2 wt. % of conductive carbon (Super C-65), and 2 wt.% of polymeric binder (PVdF). The slurry was made using N-methyl-2-pyrrolidone (NMP) as solvent and after homogenization of the dispersion it was cast on an aluminum current collector. Finally, it was dried at 80-120 °C leading to an average loading of ca. 3.0 mAh cm'2.

[0283] Anode provision'. Li metal foil (China Energy Lithium, 50 pm thickness).

[0284] Cell assembly. Coin cells were assembled in an Argon filled glovebox using NMC9XX (12 mm diameter) electrodes as cathode and prepared as defined above, Celgard 2500 as separator and Li metal disk (China Energy Lithium, 14 mm diameter and 50 pm thickness) as anode. Previously prepared electrolyte solution was cast on the separator and the cell was closed with a crimper. Then, after allowing 24 hours of wetting at RT, the crosslinking process was applied by keeping the cell at 70 °C for 12 hours.

[0285] Multilayer pouch cells with a total capacity of 0.5 Ah were assembled in a dry room with a dew point of -60 °C by stacking 3 double-side cathodes of NMC9xx, 2 single-side cathodes of NMC9xx, and 4 lithium metal anodes, isolated among them by Celgard 2500. After assembly, the pouch cell was then filled with the previously prepared electrolytes allowing 24 hours of wetting at RT, being subjected to crosslinking process by keeping them at 70°C for 12 hours. Example 3 : Electrochemical measurements

[0286] The cells LFPE1, LFPE1P2, LFPE2 and LFPE2P2 were cycled galvanostatically, between 2.8 V and 3.8 V vs. Li / Li+ using a Maccor Battery Tester (Series 4000). The applied protocol was based on 1 cycle at a current of C / 20, then 2 cycles at a current of C / 10, then constant cycling at either C / 5 -D / 2 at 45 °C.

[0287] Figure 1 shows the capacity retention vs. cycle number for the Li°||LFP cells at 45 °C, comprising an electrolyte containing a mixture of a) DF2EO of solvent and LiFSI lithium salt at a molar concentration of 1.0 M (El); b) DF2EO of solvent and LiFSI lithium salt at a molar concentration of 1.0 M with 10 vol% of a TMPTA / DDMA / TFEA polymer matrix (E1P2); c) FSA11 of solvent and LiFSI lithium salt at a molar concentration of 1.0 M (E2); d) FSA11 of solvent and LiFSI lithium salt at a molar concentration of 1.0 M with 10 vol% of a TMPTA / DDMA / TFEA polymer matrix (E2P2).

[0288] It is shown that the gel electrolytes E1P2 and E2P2 exhibit high capacity retention of 94.6% and 99.7% after 50 charging cycles, comparable to the capacity retention of liquid electrolytes used as a reference.

[0289] The cells NMCE1P2, NMCE1P3 and NMCE1P4 were cycled galvanostatically at 40 °C as follows:

[0290] Multilayer: 4.3 V - 3.0 V @40 °C C / 20-D / 20, C / 10-D / 10 x 2, [C / 10-D / 5xl, C / 5-D / 2x9] x oo

[0291] Coin cells: 4.3 V - 3.0 V @40 °C C / 20-D / 20, C / 10-D / 10 x 2, C / 10-D / 5 x oo and the charge retention capacity of said cells was tested.

[0292] Figure 2 shows the discharge capacity and coulombic efficiency of the cells, wherein it can be observed that the cell having a gel electrolyte comprising a cross-linked polymer obtained by cross-linking a mixture comprising a mono-acrylate and a dimethacrylate (NMCE1P2) exhibit much higher discharge capacity retention after more than 100 charging cycles, comparable to the discharge capacity of cells having a gel electrolyte comprising a cross-linked polymer obtained by cross-linking a mixture of a mono-acrylate with tri- or tetra-acrylates and without a di-(methacrylate) (NMCE1P3 and NMCE1P4). Figure 3 shows the capacity retention vs. cycle number for the Li°||NMC811 cells at 25 °C comprising an electrolyte containing a mixture of a) DF2E0 solvent and LiFSI lithium salt at a molar concentration of 1.0 M with 10 vol% of a TMPTA / DDMA / TFEA polymer matrix (E1P2); b) DF2EO solvent and LiFSI lithium salt at a molar concentration of 1.0 M with 10 vol% of a EHA / HDA polymer matrix (E1P5). It is shown that the polymer matrix of monoacrylate with di -(methacryl ate) (E1P5) results with nearly identical performance as the three- ingredient polymer matrix from electrolyte E1P2.

[0293] Example 4, Thermogravimetric measurements Cells LFPE1 and LFPE1P2 comprising electrolyte El and E1P2 were loaded in to open crucible in mass range 15 -20 mg and experiments were run with temperature ramp of 10 K / min starting from RT to 600 °C under an argon flow of 1 mL / min. The equipment used for analysis was Netzsch Thermogravimetric analysis TG 209 Fl Libra.

[0294] Figure 4 shows the thermogravimetric analysis of the liquid electrolyte containing a mixture of DF2EO and LiFSI lithium salt (El) and the gel electrolyte containing a mixture of DF2EO and

[0295] LiFSI lithium salt and a polymer matrix (TMPTA:DDMA:TFEA) (E1P2). As can be observed, the gel electrolyte of the invention provides a cell with an improved thermal resistance.

Claims

CLAIMS gel electrolyte comprising: i. at least one solvent selected from: a) a fluorinated ether of formula (I)R2is selected from -CH2-, -OCH2CH2-, -OCH2CH2CH2- and - OCH2CH2CH2CH2-; n is an integer from 0 to 10; b) a sulfonamide of formula (II):whereinR1is selected from F, a linear or branched C1-C12 alkyl group which may be substituted with one or more fluorine atom(s), a linear or branched C2-C12 alkenyl group which may be substituted with one or more fluorine atom(s), a C3- C12 cycloalkyl group which may be substituted with one or more fluorine atom(s) and a C6-C12 aryl group which may be substituted with one or more fluorine atom(s),R2and R3are independently selected from a linear or branched C1-C12 alkyl group which may be substituted with one or more fluorine atom(s), a linear or branched C2-C12 alkenyl group which may be substituted with one or more fluorine atom(s), a C6-C12 aryl group which may be substituted with one or more fluorine atom(s), and CH2CH2O-(CH2CH2O)n-R, wherein R is H or a methyl group and n is an integer from 1 to 20; or R2and R3may be combined with each other to form a nitrogen-containing aliphatic ring; and c) a combination of a) and b); ii. at least one lithium salt iii. a cross-linked polymer obtainable by cross-linking a cross-linked polymer precursor formulation comprising:- a mixture of cross-linkable monomers, said mixture comprising: a) at least one monomer having a one (meth)acrylate group; and b) at least one monomer having two (meth)acrylate groups, and iv. optionally, at least one co-solvent.2.- The gel electrolyte according to claim 1, wherein in the fluorinated ether Ri and R3 are independently selected from -CHF2, -CF3, -CH2CHF2, -CH2CF3, -CF2CHF2, -CF2CF3, - CHFCHF2 and -CHFCF3-CHF2,; R2 is -OCH2CH2-; and n is 0 or 1.

3. The gel electrolyte according to claim 1 or 2, wherein in the sulfonamide of formula (II), Ri is F and R2 and R3 are independently a C1-C3 alkyl group.4.- The gel electrolyte according to any one of claims 1 to 3, wherein the solvent is 1,2-bis (2,2- difluoroethoxy) ethane or N,N-dimethylsulfamoylfluoride.5.- The gel electrolyte according to any one of claims 1 to 4, wherein the at least one lithium salt is selected from LiN(SO2CF3)2, LiN(SO2F)2, LiN(SO2CF3)(SO2F), LiB(C2O4)2, LiBF2(C2O4), LiC(SO2CF3)3, LiPFTC^Fs)?, LiCFsSCh, and LiNO3and a combination thereof,preferably the at least one lithium salt is selected from LiN(SO2F)2, LiBF2(C2O4), and a combination thereof, more preferably the lithium salt is LiN(SO2F)2.

6. The gel electrolyte according to any one of the preceding claims, wherein the cross-linked polymer is obtainable by cross-linking a cross-linked polymer precursor formulation comprising a mixture of a) an alkyl mono-(meth)acrylate selected from methyl, ethyl, butyl acrylate, trifluoroethyl acrylate (TFEA), ethylhexyl acrylate (EHA), cyanoethyl acrylate (CEA), and b) one di -(meth) acrylate selected from hexanediol di acrylate (HD A) and dodecanediol dimethacrylate (DDMA).

7. The gel electrolyte according to any one of the preceding claims, wherein the cross-linked polymer precursor formulation further comprises trimethylolpropane triacrylate (TMPTA) and / or pentaerythritol tetraacrylate (PETA).

8. The gel electrolyte according to any one of the receding claims comprising: i. at least one fluorinated ether solvent of formula (I)whereinRi and R3 are independently selected from -CHF2, -CH2CHF2, -CHFCHF2 and - CF2CHF2;R2is -OCH2CH2-; and n is an integer selected from 0, 1, 2, 3, 4, and 5, preferably form 0 and 1; or at least one sulfonamide of formula (II):whereinR1is selected from F, a linear or branched Ci-Ce alkyl group which may be substituted with one or more fluorine atom(s),R2and R3are independently selected from a linear or branched Ci-Ce alkyl group which may be substituted with one or more fluorine atom(s; ii. at least one lithium salt; iii. at least one cross-linked polymer obtainable by cross-linking a cross-linked polymer precursor formulation comprising a mixture of an alkyl mono-(meth)acrylate and a di- (meth) acrylates and, optionally trimethylolpropane triacrylate (TMPTA) and / or pentaerythritol tetraacrylate (PETA); and iv. optionally a co-solvent.

9. The gel electrolyte according to any one of the preceding claims comprising: i. at least one fluorinated ether solvent of formula (I)whereinRi and R3 are independently selected from -CHF2, -CH2CHF2, -CHFCHF2 and - CF2CHF2;R2is -OCH2CH2-; and n is an integer selected from 0, 1, 2, 3, 4, and 5, preferably form 0 and 1; or at least one sulfonamide of formula (II):whereinR1is selected from F, a linear or branched Ci-Ce alkyl group which may be substituted with one or more fluorine atom(s),R2and R3are independently selected from a linear or branched Ci-Ce alkyl group which may be substituted with one or more fluorine atom(s; ii. at least one lithium salt; iii. at least one cross-linked polymer obtainable by cross-linking a cross-linked polymer precursor formulation comprising a mixture of an alkyl mono-(meth)acrylate with an alkyl di-(meth)acrylate; trimethylolpropane triacrylate (TMPTA) and / or pentaerythritol tetraacrylate (PET A); and iv. optionally a co-solvent.10.- The gel electrolyte according to any one of the preceding claims, comprising: i. at least one fluorinated ether solvent of formula (I):whereinRi and R3 are independently selected from -CHF2, -CH2CHF2, -CHFCHF2 and - CF2CHF2;R2is -OCH2CH2-; and n is an integer selected from 0, 1, 2, 3, 4, and 5, preferably form 0 and 1; or at least one sulfonamide of formula (II):whereinR1is selected from F, a linear or branched Ci-Ce alkyl group which may be substituted with one or more fluorine atom(s),R2and R3are independently selected from a linear or branched Ci-Ce alkyl group which may be substituted with one or more fluorine atoms; ii. at least one lithium salt which is LiN(SO2F)2;iii. at least one cross-linked polymer obtainable by cross-linking a cross-linked polymer precursor formulation comprising a mixture of a) a mono(methyl) acrylate selected from trifluoroethyl acrylate and ethyl hexyl acrylate and b) a di-(meth)acrylate selected from hexanediol diacrylate and dodecanediol dimethacrylate; and optionally trimethylolpropane triacrylate (TMPTA) and / or pentaerythritol tetraacrylate (PETA); and iv. optionally a co-solvent.

11. An electrolyte composition for preparing the gel electrolyte of any one of claims 1 to 10, said electrolyte composition comprising: i) a solvent selected from a fluorinated ether of formula (I) and a sulfonamide of formula (II) as defined in claim 1; ii) at least one lithium salt: iii) a cross-linked polymer precursor formulation comprising- a mixture of cross-linkable monomers, said mixture comprising: a) at least one monomer having one (meth)acrylate group; and b) at least one monomer having two (meth)acrylate groups; and optionally trimethylolpropane triacrylate (TMPTA) and / or pentaerythritol tetraacrylate (PETA); and- a free radical initiator; iv) optionally, at least one co-solvent.12.- An electrochemical cell or battery comprising the gel electrolyte according to any of claims 1 to 10, a cathode, an anode, and, optionally, a separator.13.- The electrochemical cell or battery according to claim 12 wherein:- the cathode material comprises a lithium nickel manganese cobalt oxide LiNixMnyCozCE wherein x+y+z=l; a lithium nickel cobalt aluminium oxide LiNixCoyAlzCE, wherein x+y+z=l; a lithium iron phosphate LiFePCE; or a lithium iron manganese phosphate LiFexMnx-iPO4, wherein x<l;;- the anode consists of metallic lithium; and- the optional separator is a polyolefin separator.14.- Use of the electrochemical cell or battery according to claims 12 or 13 in electric motors; electric cars, including electric vehicles (EV), hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), or the like; electric carts, including electric bikes (E-bikes) and electric scooters (E-scooters); electric golf carts; and electric power storage systems.15.- A method for preparing an electrochemical cell or a battery according to claim 12 or 13, said method comprising the steps of:(i) providing a cathode for an electrochemical cell or battery;(ii) providing an anode for an electrochemical cell or battery;(iii) providing an electrolyte composition as defined in claim 11 which comprises the at least one solvent selected from a fluorinated ether of formula (I), a sulphonamide of formula (II) and a combination thereof, the at least one lithium salt, and the cross-linked polymer precursor formulation;(iv)optionally, providing a porous separator;(v) assembling the cathode and the anode provided in steps (i) and (ii) and, optionally the separator provided in step (iv), and injecting the electrolyte provided in step (iii) between the cathode and the anode or, when a separator is used, on both sides of the separator ; and(vi) cross-linking the cross-linked polymer precursor formulation by free radical polymerization to form a gel electrolyte.

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