Single ion conducting GEL electrolyte

Abstract

The present invention relates to a gel electrolyte comprising: i. at least one cross-linked polymeric matrix obtainable by cross-linking a polymer precursor formulation, said polymer precursor formulation comprising: - a) at least one monomer lithium salt comprising a vinyl group or an acrylate or a methacrylate group, and at least one sulfonimide or sulfonate group; and - b) a mixture of monomers, said mixture comprising: a) at least one monomer having one acrylate or methacrylate group; and b) at least one cross-linkable monomer having two or more cross-linkable acrylate or methacrylate groups; and ii. at least one lithium salt, other than the monomer lithium salt; iii.at least one solvent selected from a fluorinated ether, a sulfonamide and a combination thereof; and iv. optionally, at least one co-solvent and / or a lithophilic salt.

Description

[0001] SINGLE ION CONDUCTING GEL ELECTROLYTE

[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, despite outstanding energy density, still suffer with the safety aspect. From numerous methods of improvement, the safety force the change in the character of the electrolyte. One significant improvement can be achieved by incorporating a gel electrolyte composed of polymer matrix plasticized by different solvents and containing Li salt. Nevertheless, this usually reduces thermal cycling performance and C-rate capability of the cells. To overcome this problem, single ion polymer gel electrolytes are considered as a solution. The interest of gel systems is proved by numerous publications. In the work of Xiang Guan et. al. [In-situ crosslinked single ion gel polymer electrolyte with superior performances for lithium metal batteries. Chemical Engineering Journal, 2020, 382, 122935], solid state gel single ion electrolytes are prepared by in-situ polymerization of lithium (4- styrenesulfonyl)(trifluorom ethanesulfonyl) imide - STFSILi with polyethylene glycol dimethacrylate - PEGDMA and latter impregnated by liquid electrolyte composed of 1.0 M LiTFSI, 0.1 m LiNCh, DME:DOL = 1 : 1 %Vol. In this solution self-standing membranes were obtained and latter applied in the cell as electrolyte, thus improving C-rate capability and Li transference number. Different approach is in the work of Changxing Hanat et al [Recent progress in gel polymer electrolyte for lithium metal batteries. Giant, 2024, 20, 100337] where membrane of polymer matrix is obtained by electrospinning technique of modified Li-SPEEK, latter immersed in IM LiPFe EC / DMC. This modification improves the thermal durability.

[0006] Improvement of single ion polymer matrix was presented in solvent free polymer electrolytes presented by Maria Martinez et al [Unprecedented Improvement of Single Li-Ion Conductive Solid Polymer Electrolyte Through Salt Additive. Advanced Functional Materials, 2020, 30(16), 2000455] in a system composed of ((trifluoromethane)sulfonimide lithium styrene - poly(ethylene oxide) - lithium bis(fluorosulfonyl)imide) (PSTFSILi+PEO+LiFSI). Blended polymer matrix includes binary salt improving interfacial stability and ionic conductivity. Similar conclusion to Maria Martinez et al. were presented in work of Pedram Ghorbanzade et al. [Plasticized and salt-doped single-ion conducting polymer electrolytes for lithium batteries. RSC Adv., 2022,12, 18164-18167], System composed of ((trifhroromethane)sulfonimide lithium styrene - polypropylene oxide) - lithium bis(trifluoromethanesulfonyl)imide) (PSTFSILi+PPO+LiTFSI) has also been investigated. Similar improvements can be found in patent number US, 10,461,317 B2. However, this patent describes homopolymer gel electrolyte based on carbonates containing liquid electrolyte. Patent application US2007 / 0224502 Al concerns multilayer anode protective layer. However, submission does not explain in details of any structure neither performance just claiming that protective layer is comprising a protective layer positioned between the electrode and an electrolyte used within the cell. The submission claims the protective layer is a single-ion, electronically conductive material. Additionally, the method of single-ion protective layer preparation is not matching the preparation method of proposed invention. Similar approach of monolayer single-ion conducting layer is present in patent US 10,367,201 B2, wherein it is described a copolymer with perfluorinated aliphatic chain prepared as a self-standing membrane and placed in the cell soaked in liquid electrolyte. Another patent application US2017 / 0162862 Al describes application of single-ion conducting polymer matrices where some are obtained using AIBN as a reaction initiator. These matrices can be impregnated by different electrolyte creating a gel. Authors are not presenting data from electrochemical performance neither detailed composition of the gel electrolyte. Another general description can be found in patent US 10,347,904 B2 describing multilayer anode protection including single-ion layer.

[0007] The current submission concerns gel type polymer electrolyte created in-situ by polymerization of a mixture of monomers including monomer salt. The mixture is dissolved in desired liquid electrolyte thus forming a homogenous gel after polymerization. This modification improves cationic current and lowers the high concentration gradient of anions while polarization. The consequences of these properties are higher cell durability and better C-Rate capability compared to standard gel systems. Additionally liquid plasticizer improves transporting properties of the gel electrolyte. BRIEF DESCRIPTION OF THE INVENTION

[0008] The present invention relates to a single ion conducting gel electrolyte comprising a polymer matrix obtainable by cross-linking a polymer precursor formulation which includes, among other, a monomer lithium salt; a mixture of cross-linkable (meth)acrylate-bearing monomers, at least one solvent selected from a fluorinated ether and a sulfonamide, and at least one lithium salt, other than the monomer salt. The inventors have found that, in contrast to other gel electrolytes lacking the monomer lithium salt or having obtained by using cross-linked homopolymers, such gel electrolyte impairs higher cationic current and allows the elimination of high concentration gradient in the cell under polarization, thus reducing dendrites grow. As a consequence of these features, the cells show higher C-rate capability and better cyclability compared to other gel electrolytes. Furthermore, it impairs a higher discharge capacity and current efficiency after multiple charge / discharge cycles when compared also to other gel electrolytes.

[0009] Thus, a first aspect of the invention refers to a single ion-conducting gel electrolyte comprising: i. at least one cross-linked polymeric matrix obtainable by cross-linking a polymer precursor formulation, said polymer precursor formulation comprising:

[0010] - a) at least one monomer lithium salt comprising a vinyl group or an acrylate or a methacrylate group, and at least one sulfonimide or sulfonate group; and

[0011] - b) a mixture of monomers, said mixture comprising: a) at least one monomer having one acrylate or methacrylate group; and b) at least one cross-linkable monomer having two or more cross-linkable acrylate or methacrylate groups; and ii. at least one lithium salt, other than the monomer lithium salt; iii. at least one solvent selected from: a) a fluorinated ether of formula (II):

[0012] Rl (R2) 0 ^3

[0013] (II) wherein

[0014] Ri is selected from -CHF2, -CF3, -CH2CHF2, -CH2CF3, -CF2CHF2, -CF2CF3, - CHFCHF2 and -CHFCF3; R3is selected from

[0015] CHFCHF2, -CHFC

[0016] R2is selected from -CH2-, -OCH2CH2-, -OCH2CH2CH2- and -OCH2CH2CH2CH2-; n is an integer from 0 to 10; b) a sulfonamide of formula (III): wherein:

[0017] 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);

[0018] R2 and 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

[0019] R2and R3may be combined with each other to form a nitrogen-containing aliphatic ring; and c) a combination of a) and b); iv. optionally, at least one co-solvent and / or a lithophilic salt.

[0020] The invention also refers to a method for preparing the gel electrolyte of the first aspect of the invention comprising the steps of:

[0021] (i) providing at least one lithium salt; (ii) mixing at least one solvent selected from a fluorinated ether of formula (II), a sulphonamide of formula (III) and a combination thereof, as defined in the first aspect of the invention, with the lithium salt provided in step (i);

[0022] (iii) optionally, adding to the mixture obtained in step (ii) at least one co-solvent;

[0023] (iv) adding to the mixture obtained in step (ii) or step (iii) the polymer precursor formulation as defined above; and a free radical initiator;

[0024] (v) cross-linking the polymer precursor formulation by free radical polymerization to form a gel electrolyte.

[0025] 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 polymer precursor formulation comprising: a) at least one monomer lithium salt comprising a vinyl group or an acrylate or a methacrylate group; and at least one sulfonimide or sulfonate group; and b) a mixture of monomers, said mixture comprising: a) at least one monomer having one acrylate or methacrylate group; and b) at least one cross-linkable monomer having two or more cross-linkable acrylate or methacrylate groups; ii) at least one solvent selected from a fluorinated ether of formula (II), a sulfonamide of formula (III) and a combination thereof, as defined in the first aspect; iii) at least one lithium salt, other than the monomer lithium salt: iv) a free radical initiator; and v) optionally, at least one co-solvent and / or a lithophilic salt.

[0026] 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.

[0027] Another aspect of the invention relates to a method for preparing an electrochemical cell or battery, said method comprising the steps of:

[0028] (i) providing a cathode for an electrochemical cell or a battery;

[0029] (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 polymer precursor formulation; at least one solvent selected from a fluorinated ether of formula (II), a sulphonamide of formula (III) and a combination thereof; the at least one lithium salt; the free radical initiator; and optionally, the at least one co-solvent and / or the lithophilic salt;

[0030] (iv) optionally, providing a porous separator;

[0031] (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

[0032] (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.

[0033] 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.

[0034] 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.

[0035] DESCRIPTION OF THE FIGURES

[0036] 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) DF2E0 / TEGDME in 50 / 50 vol.% ratio 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); b) DF2EO / TEGDME in 50 / 50 vol.% ratio of solvent and LiFSI / LiMTFSI lithium salts at a molar concentration of 0.8 M and 0.2 M, respectively, with 10 vol% of a TMPTA / DDMA / TFEA polymer matrix (E2P2). Figure 2 shows the specific discharge capacity vs. cycle number for the Li°||LFP cells at 45 °C and at different charge rates, comprising an electrolyte containing a mixture of a) DF2E0 / TEGDME in 50 / 50 vol.% ratio 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); b) DF2EO / TEGDME in 50 / 50 vol.% ratio of solvent and LiFSI / LiMTFSI lithium salts at a molar concentration of 0.8 M and 0.2 M, respectively, with 10 vol% of a TMPTA / DDMA / TFEA polymer matrix (E2P2).

[0037] Figure 3 shows the specific discharge capacity vs. cycle number for the Li°||LFP cells at 45 °C comprising an electrolyte containing a mixture of a) DF2EO / TEGDME in 50 / 50 vol.% ratio of solvent and LiFSI / LiMTFSI lithium salts at a molar concentration of 0.8 M and 0.2 M, respectively, with 10 vol% of a TMPTA / DDMA / TFEA polymer matrix (E2P2); b) DF2EO / TEGDME in 50 / 50 vol.% ratio of solvent and LiFSI / LiMTFSI lithium salts at a molar concentration of 0.8 M and 0.2 M, respectively, with 10 vol% of a PEGDA polymer matrix (E3P2).

[0038] DETAILED DESCRIPTION OF THE INVENTION

[0039] 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.

[0040] 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.

[0041] Throughout the description and claims, the terms “combination”, “blend(s)” and “mixture(s)” will be used interchangeably. 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).

[0042] As mentioned above, a first aspect of the invention refers to a single ion conducting gel electrolyte comprising: i. at least one cross-linked polymeric matrix obtainable by cross-linking a polymer precursor formulation, said polymer precursor formulation comprising:

[0043] - a) at least one monomer lithium salt comprising a vinyl or an acrylate or a methacrylate group, and at least one sulfonimide or sulfonate group; and

[0044] - b) a mixture of monomers, said mixture comprising: a) at least one monomer having one acrylate or methacrylate group; and b) at least one cross-linkable monomer having two or more cross-linkable acrylate or methacrylate groups; and ii. at least one lithium salt, other than the monomer lithium salt, iii. at least one solvent selected from: a) a fluorinated ether of formula (II):

[0045] Rl (R2) 0 ^3

[0046] (II) wherein

[0047] Ri is selected from -CHF2, -CF3, -CH2CHF2, -CH2CF3, -CF2CHF2, -CF2CF3, - CHFCHF2 and -CHFCF3;

[0048] R3is selected from

[0049] CHFCHF2, -CHFC

[0050] R2is selected from -CH2-, -OCH2CH2-, -OCH2CH2CH2- and -OCH2CH2CH2CH2-; n is an integer from 0 to 10; b) a sulfonamide of formula (III): wherein:

[0051] 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);

[0052] 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 or a methyl group and n is an integer from 1 to 20; or

[0053] R2and R3may be combined with each other to form a nitrogen-containing aliphatic ring; and c) a combination of a) and b); iv. optionally, at least one co-solvent and / or a lithophilic salt.

[0054] The inventors have surprisingly found that a single ion conducting gel electrolyte comprising a cross-linked polymeric matrix having acrylate or methacrylate lithium salt monomeric units, in combination with a solvent of formula II and / or III and at least one lithium salt as defined above, is suitable for electrochemical applications (e.g. in lithium metal batteries) with the corresponding advantages of impairing a higher cation current and reducing dendrites grow.

[0055] 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. 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.

[0056] More embodiments regarding the first aspect of the invention will be given below.

[0057] Cross-linked polymer

[0058] The gel electrolyte of the invention comprises a cross-linked polymer matrix obtainable by cross-linking a polymer precursor formulation comprising:

[0059] - at least a monomer lithium salt having a vinyl group or an acrylate or methacrylate group, and a sulfonimide or sulfonate group, and

[0060] - a mixture of cross-linkable monomers comprising: a) at least one monomer having one acrylate or methacrylate group; and b) at least one cross-linkable monomer having two or more cross-linkable acrylate or methacrylate groups.

[0061] The cross-linked polymer matrix is suitable for ions conduction, in particular lithium cations, via non-covalent interactions between the polymer chain and the ion.

[0062] In the context of the present invention, the term “polymer precursor formulation” refers to a formulation comprising monomers containing one or more cross-linkable functional groups, namely acrylate or methacrylate groups, in their structures susceptible to form cross-linked polymers.

[0063] In a particular embodiment, the at least one monomer lithium salt comprised in the polymer precursor formulation has formula (I): wherein:

[0064] Ri is H or CH3;

[0065] R2 is phenylene, -C(0)0- or -0(CH2)n-, wherein n is an integer from 1 to 10;

[0066] X is a single bond or a group selected from -(CH2)n-, -(CFhCFhC n-, -(CF2CF2O)n- and - (SiO(CH3)2)n-(*), wherein n is an integer from 1 to 20;

[0067] Y is -O or -NSO2R3, wherein R3 is selected from F, CF3, CHF2, CH2F and phenyl, provided that: when R2 is phenylene, X is a single bond and when R2 is -C(O)O or -O(CH2)n-, then X is not a single bond.

[0068] By the term phenylene is understood a group , whereas phenyl refers to terminal group

[0069] In a preferred embodiment, R2 is phenylene or -C(O)O-.

[0070] In a more particular embodiment, the lithium salt is selected from the following formulas:

[0071] 1(c) wherein

[0072] Ri is H or CH3; X is group selected from -(CH2)n-, -(CH2CH2O)n, -(CF2CF2O)nand -(SiO(CH3)2)n(*), wherein n is an integer from 1 to 20; and

[0073] R3 is selected from F, CF3, CHF2, CH2F and phenyl.

[0074] In another preferred embodiment, the monomer lithium salt is selected from formula (la) and 1(b), more preferably is a salt of formula 1(a).

[0075] In a preferred embodiment, X is selected from -(CH2)n-, -(CH2CH2O)nand -(CF2CF2O)n, wherein n range from 1 to 3; more preferably X is -(CH2)n-, wherein n ranges from 1 to 3, even more preferably n is 3.

[0076] In another preferred embodiment, R3 is selected from F, CF3, CHF2, CFfcF, more preferably is CF3.

[0077] Even more preferably, the monomer lithium salt is the one of formula 1(a) wherein R1 is CEE, X is -(CH2)3- and R3is CF3.

[0078] In addition to the monomer lithium salt, the polymer precursor formulation also comprises a mixture of monomers, said mixture comprising one or more cross-linkable monomers.

[0079] Particularly, the polymer precursor formulation comprises, in addition to the monomer lithium salt:

[0080] - a mixture of monomers, said mixture comprising: a) at least one monomer having one acrylate or methacrylate group; and b) at least one cross-linkable monomer having two or more cross-linkable acrylate or methacrylate groups.

[0081] Cross-linkable monomers relate to those monomers having two or more cross-linkable acrylate or methacrylate groups which, upon polymerization reaction, they lead to a cross-linked polymer matrix. Monomers having two or more cross-linkable acrylate or methacrylate groups can also react with monomers having one acrylate or methacrylate group also leading to a crosslinked polymer matrix.

[0082] In a particular embodiment, the monomers having one, two or more acrylate or methacrylate groups are selected from alkyl mono-, di-, tri-, tetra or penta-(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. 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.

[0083] Examples of monomers having one acrylate or methacrylate 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), hexyl acrylate (HA), 2-ethylhexyl acrylate, dodecyl acrylate (DA), trifluoroethyl acrylate (TFEA), ethylhexyl acrylate (EHA) and cyanoethyl acrylate (CEA), benzyl acrylate (BzA), ethylene glycol methyl ether acrylate (EGMEA), di(ethylene glycol) ethyl ether acrylate (DEGMA).

[0084] In a preferred embodiment, monomers having one acrylate or methacrylate group are alkyl mono(meth) acrylates, i.e., monomers having an alkyl and one (meth) acrylate group. These are preferably selected from methyl acrylate (MA), ethyl acrylate (EA), trifluoroethyl acrylate (TFEA) and butyl acrylate (BA), more preferably is trifluoroethyl acrylate (TFEA).

[0085] By the term di-, tri-, tetra- or penta-(meth)acrylates should be understood those monomers having two, three, four or five cross-linkable (meth)acrylate groups susceptible to form covalent bonds with other monomers or cross-linkable monomers.

[0086] Examples of di-(meth)acrylates, i.e. monomers having two cross-linkable acrylate or methacrylate groups include, but are not limited to, 1,4-butanediol diacrylate (BDA), 1,6- hexanediol diacrylate (HDA), dodecanediol dimethacrylate (DDMA), neopentyl glycol diacrylate (NPDA), cyclohexane dimethanol diacrylate (CHDA), ethoxylated (n) Bisphenol A dimethacrylate (EBADMA) n = 1-10.

[0087] In a preferred embodiment, monomers having two cross-linkable acrylate or methacrylate groups are alkyl di-(meth)acrylates, i.e., monomers having an alkyl and two (meth) acrylate groups. These are preferably selected from hexanediol diacrylate (HDA) and dodecanediol dimethacrylate (DDMA).

[0088] In a particular embodiment, the tri-(meth)acrylate, i.e, a monomer having three cross-linkable acrylate or methacrylate groups, include trimethylolpropane triacrylate (TMPTA), tris (2- hydroxy ethyl) isocyanurate triacrylate (THEICTA), ethoxylated trimethylolpropane triacrylate (TMP(nEO)TA), ethoxylated trimethylolpropane triacrylate TMP(nEO)TA, more preferably is trimethylolpropane triacrylate (TMPTA).

[0089] In another particular embodiment, the tetra-(meth)acrylate, i.e, a monomer having four crosslinkable functional groups is pentaerythritol tetraacrylate (PETA).

[0090] In another particular embodiment, the penta-(meth)acrylate, i.e, a monomer having five crosslinkable functional groups is dipentaerythritol pentaacrylate (DiPEPA).

[0091] Examples of carbocyclic containing mono- (meth)acrylates include, but are not limited to, benzyl acrylate or benzyl methacrylate.

[0092] 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).

[0093] In a preferred embodiment of the first aspect of the invention, the crosslinked polymer matrix results from the polymerization of a polymer precursor formulation comprising:

[0094] - at least a monomer lithium salt having a vinyl group or an acrylate or methacrylate group, and a sulfonimide or sulfonate group, and

[0095] - a mixture of monomers, said mixture comprising: a) at least one monomer having one acrylate or methacrylate group; and b) at least one cross-linkable monomer having two or more cross-linkable acrylate or methacrylate groups; so that a cross-linked polymer resulting from the free radical polymerization of the at least one monomer lithium salt with the mixture of monomers is obtained.

[0096] In a particular embodiment, the cross-linked polymer precursor formulation comprises:

[0097] - at least a monomer lithium salt having a vinyl group or an acrylate or methacrylate group, and a sulfonimide or sulfonate group, and

[0098] - a mixture of a) an alkyl mono-(meth)acrylate; a carbocyclic containing mono- (meth)acrylates; or of any blend thereof, with b) with di-, tri-, tetra-and / or penta-(meth) acrylates, such as trimethylolpropane triacrylate (TMPTA), pentaerythritol tetraacrylate (PETA), dodecanediol dimethacrylate (DDMA) or any combination thereof. In a preferred embodiment, the cross-linked polymer precursor formulation comprises:

[0099] - at least a monomer lithium salt having a vinyl group or an acrylate or methacrylate group, and a sulfonimide or sulfonate group, and

[0100] - a mixture of an alkyl mono-(meth)acrylate, selected from butyl acrylate (BA) and trifluoroethyl acrylate (TFEA); with butanediol diacrylate (BDA), hexanediol diacrylate (HDA), trimethylolpropane triacrylate (TMPTA), pentaerythritol tetraacrylate (PETA) dodecanediol dimethacrylate (DDMA) or any combination thereof.

[0101] Preferably, the cross-linked polymer precursor formulation comprises:

[0102] - at least a monomer lithium salt having an acrylate or methacrylate group, and a sulfonimide or sulfonate group, and

[0103] - a mixture of an alkyl mono-(meth)acrylate selected from butyl acrylate (BA) and trifluoroethyl acrylate (TFEA); with butanediol diacrylate (BDA), hexanediol diacrylate (HAD), trimethylolpropane triacrylate (TMPTA), pentaerythritol tetraacrylate (PETA), dodecanediol dimethacrylate (DDMA) or any combination thereof.

[0104] More preferably, the cross-linked polymer precursor formulation comprises:

[0105] - at least a monomer lithium salt of formula 1(a), 1(b), 1(c) or 1(d), and

[0106] - a mixture of a) an alkyl mono-(meth)acrylate; with b) di-, tri- and / or tetra-(meth) acrylates.

[0107] Even more preferably, the cross-linked polymer precursor formulation comprises:

[0108] - at least a monomer lithium salt of formula (1(a), 1(b), 1(c) or 1(d), and

[0109] - a mixture of an alkyl mono-(meth)acrylate, selected from butyl acrylate (BA) and trifluoroethyl acrylate (TFEA); with trimethylolpropane triacrylate (TMPTA), pentaerythritol tetraacrylate (PETA), dodecanediol dimethacrylate (DDMA) or any combination thereof.

[0110] Most preferably, the cross-linked polymer precursor formulation comprises:

[0111] - at least a monomer lithium salt of formula 1(a), and - a mixture of an alkyl mono-(meth)acrylate, such as butyl acrylate (BA), trifluoroethyl acrylate (TFEA); with trimethylolpropane triacrylate (TMPTA), pentaerythritol tetraacrylate (PETA), dodecanediol dimethacrylate (DDMA) or any combination thereof.

[0112] Even most preferably, the cross-linked polymer precursor formulation comprises:

[0113] - at least a monomer lithium salt of formula 1(a), wherein Ri is CH3, X is -(CEh)3- and R3 is CF3; and

[0114] - a mixture of an alkyl mono-(meth)acrylate, which is trifluoroethyl acrylate (TFEA); dodecanediol dimethacrylate (DDMA) and trimethylolpropane triacrylate (TMPTA).

[0115] In another embodiment, the volume% of the mixture of monomers with respect to monomer lithium salt ranges from 1 to 50 vol%.

[0116] Regarding the mixture of monomers, the alkyl mono-(meth)acrylate is present in a volume proportion between 1 to 99 vol% with respect to the total volume of the mixture of monomers. The di-, tri-, tetra- and / or penta-(meth) acrylate(s) ranges also between 1 to 99 vol% with respect to the mixture of monomers.

[0117] Preferably, the volume ratio between the alkyl mono-(meth)acrylate and the di-, tri-, tetra- and / or penta-(meth) acrylates preferably ranges from 60:40 to 80:20, more preferably is 75:25.

[0118] Regardless of the chemical nature of the resulting 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 resulting cross-linked polymer is about 10 wt.% compared to the total weight of the gel electrolyte.

[0119] In a specific embodiment of the first aspect of the invention, the cross-linked polymer precursor formulation is a mixture of:

[0120] - at least a monomer lithium salt of formula 1(a), wherein Ri is CH3, X is -(CH2)s- and R3 is CF3; and

[0121] - a mixture of an alkyl mono-(meth)acrylate, which is trifluoroethyl acrylate (TFEA); dodecanediol dimethacrylate (DDMA) and trimethylolpropane triacrylate (TMPTA), and - 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

[0122] - the weight ratio of trifluoroethyl acrylate (TFEA) : dodecanediol dimethacrylate (DDMA) and trimethylolpropane triacrylate (TMPTA) is of between 60:40 to 80:20; more preferably of 75:25.

[0123] 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:

[0124] Solvent

[0125] The gel electrolyte of the invention comprises at least one solvent selected from a fluorinated ether of formula (II), a sulfonamide of formula (III) and a combination thereof.

[0126] These solvents are suitable for dissolving the lithium salts present in the electrolyte, but not the lithium salt monomer.

[0127] 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.

[0128] Said fluorinated ether is represented by formula (II):

[0129] Rl (R2) 0 ^3

[0130] (II) wherein

[0131] Ri is selected from -CHF2, -CF3, -CH2CHF2, -CH2CF3, -CF2CHF2, -CF2CF3, - CHFCHF2 and -CHFCF3;

[0132] R3is selected from

[0133] CHFCHF2, -CHFC

[0134] R2is selected from -CH2-, -OCH2CH2-, -OCH2CH2CH2- and -OCH2CH2CH2CH2-; and n is an integer from 0 to 10.

[0135] 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.

[0136] In another preferred embodiment, R2 is -OCH2CH2-.

[0137] 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.

[0138] In a preferred embodiment, n is 0 or 1, R2 is -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.

[0139] 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.

[0140] The sulfonamide is represented by general formula (III): wherein

[0141] 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),

[0142] 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.

[0143] 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.

[0144] 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.

[0145] 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.

[0146] 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. 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).

[0147] 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).

[0148] 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.

[0149] 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).

[0150] 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.

[0151] In an embodiment Ri and R2 are the same. In another embodiment, Ri and R2 are different. In the most preferred embodiment, Ri = R2 = CEE.

[0152] In a further embodiment, the at least one sulfonamide has the general formula (II) as shown above, wherein:

[0153] - 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

[0154] - 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).

[0155] In a further embodiment, the at least one sulfonamide has the general formula (II) as shown above, wherein: - Ri is selected from F and a linear C1-C4 alkyl group which may be substituted with one or more fluorine atom(s); and

[0156] - R2 and R3 are linear C1-C4 alkyl groups which may be substituted with one or more fluorine atom(s).

[0157] In a further embodiment, the at least one sulfonamide is selected from at least one of the following structures:

[0158] In a preferred embodiment, the at least one sulfonamide is one wherein Ri is F and R2 = R3 = CH3.

[0159] 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.

[0160] Lithium salts The gel electrolyte of the present invention comprises at least one lithium salt, other than the monomer 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.

[0161] In a particular embodiment, the inorganic lithium salt may include, but is not limited to, LiCICh, LiNO3, LiBF4, LiAsF6, LiPF6, LiBF3Cl, and LiF.

[0162] 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(SO2CHF2)(SO2F), LiN(C2F5SO2)(SO2F), LiB(C2O4)2, LiBF2(C2O4), LiC(SO2CF3)3, LiPF3(C2F5)3, and LiCF3SO3.

[0163] 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(SO2CHF2)(SO2F), LiN(C2F5SO2)(SO2F), LiB(C2O4)2, LiBF2(C2O4), LiC(SO2CF3)3, LiPF3(C2Fs)3, LiCF3SO3, and a combination thereof.

[0164] In another embodiment, the at least one lithium salt is selected from LiN(SO2CF3)2, LiN(SO2F)2, LiN(SO2CHF2)(SO2F), LiN(SO2CF3)(SO2F), LiB(C2O4)2, LiBF2(C2O4), LiC(SO2CF3)3, LiPF3(C2Fs)3, LiCF3SO3, and LiNO3or a combination thereof.

[0165] 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(SO2CHF2)(SO2F), 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.

[0166] 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.

[0167] Lithophilic salt

[0168] The gel electrolyte of the present invention may contain a lithophilic salt. In a particular embodiment, the lithophilic salt has formula M(X)z, where M is a metal cation Mz+selected from Bi, Sn, Cu, Al, As, Ca, Si, Ag, Au, Zn, Mg, In, K, Na, and Cs; X is an anion selected from Cl’, C1O4’, NO3’, BF4’, ASF6‘, PF6‘, BF3Cf, (Oct)2‘, F, N(SO2CF3)2-, N(SO2F)2-, N(SO2CF3)(SO2F)-, N(C2F5SO2)(SO2F)-, B(C2O4)2-, BF2(C2O4)-, C(SO2CF3)3’, PF3(C2F5)3- , CFsSCh', ionic liquid; and z is the cation valence. The lithophilic salt, comprised in the gel electrolyte, may vary from 0.005 to 5 wt.% with respect to the total weight of the gel electrolyte, preferably from 0.08 to 2 wt.%, even more preferably from 0.05 to 0. lwt.% with respect to the total weight of the electrolyte.

[0169] Co-solvent

[0170] 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 and salt monomer 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 the polymer matrix.

[0171] 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, methyl-tert-butylether, succinonitrile (SN), glutaronitrile (GN), adiponitrile (AN), ethylene sulfitde (ES), propylene sulfitde (PS) di-ethylene sulfitde (DES), di-methylsulfitde (DMS), dimethyl 2,5-dioxahexanedioate (DMDOHD), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), difluoroethyl acetate (DFEA), methyl difluoroacetate (MDFA), trimethyl silyl acetate (TMSA), trimethylsilyl-2,2-difluoro-2-(fluorosulfonyl)acetate (TMSDFA), 2-(2,2,2-trifluoroethoxy)ethyl methyl ether (TEME), 2-methoxyethoxy 2,2 difluroethylether (MDFE), triethyl phosphate (TEP), trimethyl phosphate (TMP), tripropyl phosphate (TPP), methyl formate (MF), methyl acetate (MA), methyl butyrate (MB), ethyl acetate (EA), ethyl propionate (EP), trimethyl silylpropane sulfonate (TMSP), acetamide of chemical structure RICONR2R3 where Ri can be F, CF3, CF2H or CFH2, and R2and R3 can be independently H, -(CH2)nCH3, -(CH2)nCF3, -(CH2)nF, or -(CH2)nCH2F or -(CH2)nCHF2where n = 1-10; and polyoxyethylene alkyl ethers of formula CnEm, wherein Cnrefers to al alkyl chain with n methylene groups and Emrefers to a hydrophilic part having m oxy ethylene units.

[0172] The quantity of co-solvents may be in range from 0% to 50% by volume with respect to the total volume of the solvent and co-solvent. Preferably from 30 to 50 wt.% with respect to the total volume of the solvent and co-solvent.

[0173] Further additives

[0174] In a particular embodiment, the gel electrolyte of the first aspect of the invention further comprises additives which do not dissolve the salts. Examples of such additives are known in the art and include, among others, organic solvents and compounds such as: fluorobenzene (FPh), 1,2-difluoro benzene, 1,3 -difluoro benzene, 1,4-difhiorobenzene, anisole, fluoroanisole, 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).

[0175] Further embodiments of the gel electrolyte

[0176] In an embodiment of the invention, the gel electrolyte consists of: i. at least one cross-linked polymeric matrix obtainable by cross-linking a polymer precursor formulation, said polymer precursor formulation comprising:

[0177] - a) at least one monomer lithium salt comprising a vinyl group or an acrylate or a methacrylate group; and at least one sulfonimide or sulfonate group; and

[0178] - b) a mixture of monomers, said mixture comprising: a) at least one monomer having one acrylate or methacrylate group; and b) at least one cross-linkable monomer having two or more cross-linkable acrylate or methacrylate groups; and ii. at least one lithium salt, other than the monomer lithium salt, iii. at least one solvent selected from a fluorinated ether of formula (II), a sulfonamide of formula (III) and a combination thereof, as defined above; and iv. optionally, at least one co-solvent and / or a lithophilic salt.

[0179] In a particular embodiment of the latter:

[0180] - 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

[0181] - 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

[0182] - 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.

[0183] In an embodiment, the gel electrolyte of the invention comprises: i. at least one cross-linked polymeric matrix obtainable by cross-linking a polymer precursor formulation, said polymer precursor formulation comprising:

[0184] - at least one monomer lithium salt comprising a vinyl group or an acrylate or a methacrylate group; and at least one sulfonimide or sulfonate group; and

[0185] - a mixture of monomers, said mixture comprising: a) at least one monomer having one acrylate or methacrylate group; and b) at least one cross-linkable monomer having two or more cross-linkable acrylate or methacrylate groups; and ii. at least one lithium salt, other than the monomer lithium salt, iii. a solvent selected from a fluorinated ether of formula (II), a sulfonamide of formula (III) and a combination thereof, as defined above; and iv. optionally, a co-solvent and / or a lithophilic salt.

[0186] In a particular embodiment, the gel electrolyte of the invention comprises: i. at least one cross-linked polymeric matrix obtainable by cross-linking a polymer precursor formulation, said polymer precursor formulation comprising: - at least one monomer lithium salt comprising a vinyl group or an acrylate or a methacrylate group; and at least one sulfonimide or sulfonate group; and

[0187] - a mixture of a) an alkyl mono-(meth)acrylate; a carbocyclic containing mono- (meth)acrylates; or of any blend thereof, with b) di-, tri-, tetra-and / or penta- (meth) acrylates, such as trimethylolpropane triacrylate (TMPTA), pentaerythritol tetraacrylate (PETA), dodecanediol dimethacrylate (DDMA) or any combination thereof; ii. at least one lithium salt selected from LiC104, LiNCh, LiBF4, LiAsFe, LiPFe, LiBF3Cl, LiF, LiN(SO2CF3)2 (LiTFSI), LiN(SO2F)2(LiFSI), LiN(SO2CF3)(SO2F), LiN(SO2CHF2)(SO2F), LiN(C2F5SO2)(SO2F), LiB(C2O4)2, LiBF2(C2O4), LiC(SO2CF3)3, LiPF3(C2Fs)3, LiCF3SO3, and a combination thereof; iii. a solvent selected from a fluorinated ether of formula (II), a sulfonamide of formula (III) and a combination thereof, as defined above; and iv. optionally, a co-solvent and / or a lithophilic salt.

[0188] In a preferred embodiment, the gel electrolyte of the invention comprises: i. at least one cross-linked polymeric matrix obtainable by cross-linking a polymer precursor formulation, said polymer precursor formulation comprising:

[0189] - at least a monomer lithium salt having a vinyl group or an acrylate or methacrylate group, and a sulfonimide or sulfonate group, and

[0190] - a mixture of an alkyl mono-(meth)acrylate selected from butyl acrylate (BA) and trifluoroethyl acrylate (TFEA); with trimethylolpropane triacrylate (TMPTA), pentaerythritol tetraacrylate (PETA) dodecanediol dimethacrylate (DDMA) or any combination thereof; ii. at least one lithium salt, selected from LiC104, LiNO3, LiBF4, LiAsFe, LiPFe, LiBF3Cl, LiF, LiN(SO2CF3)2(LiTFSI), LiN(SO2F)2(LiFSI), LiN(SO2CF3)(SO2F), LiN(SO2CHF2)(SO2F), LiN(C2F5SO2)(SO2F), LiB(C2O4)2, LiBF2(C2O4), LiC(SO2CF3)3, LiPF3(C2Fs)3, LiCF3SO3, and a combination thereof; iii. a solvent which is a fluorinated ether of formula (II), a sulfonamide of formula (III) and a combination thereof, as defined above as defined above; and iv. optionally, a co-solvent and / or a lithophilic salt. Preferably, the gel electrolyte of the invention comprises: i. at least one cross-linked polymeric matrix obtainable by cross-linking a polymer precursor formulation, said polymer precursor formulation comprising:

[0191] - at least a monomer lithium salt having an acrylate or methacrylate group, and a sulfonimide or sulfonate group, and

[0192] - a mixture of an alkyl mono-(meth)acrylate selected from butyl acrylate (BA) and trifluoroethyl acrylate (TFEA); with trimethylolpropane triacrylate (TMPTA), pentaerythritol tetraacrylate (PETA), dodecanediol dimethacrylate (DDMA) or any combination thereof; ii. at least one lithium salt, selected from LiC104, LiNCh, LiBF4, LiAsFe, LiPFe, LiBF3Cl, LiF, LiN(SO2CF3)2 (LiTFSI), LiN(SO2F)2(LiFSI), LiN(SO2CF3)(SO2F), LiN(SO2CHF2)(SO2F), LiN(C2F5SO2)(SO2F), LiB(C2O4)2, LiBF2(C2O4), LiC(SO2CF3)3, LiPF3(C2Fs)3, LiCF3SO3, and a combination thereof; iii. a solvent which is a fluorinated ether of formula (II), a sulfonamide of formula (III) and a combination thereof, as defined above as defined above; and iv. optionally, a co-solvent and / or a lithophilic salt.

[0193] More preferably, the gel electrolyte of the invention comprises: i. at least one cross-linked polymeric matrix obtainable by cross-linking a polymer precursor formulation, said polymer precursor formulation comprising:

[0194] - at least a monomer lithium salt of formula 1(a), 1(b), 1(c) or 1(d) as de fined above, and

[0195] - a mixture of a) an alkyl mono-(meth)acrylate; with b) di-, tri- or tetra-(meth) acrylate(s); ii. at least one lithium salt, selected from LiC104, LiNO3, LiBF4, LiAsFe, LiPFe, LiBF3Cl, LiF, LiN(SO2CF3)2(LiTFSI), LiN(SO2F)2(LiFSI), LiN(SO2CF3)(SO2F), LiN(SO2CHF2)(SO2F), LiN(C2F5SO2)(SO2F), LiB(C2O4)2, LiBF2(C2O4), LiC(SO2CF3)3, LiPF3(C2Fs)3, LiCF3SO3, and a combination thereof; iii. a solvent which is a fluorinated ether of formula (II) as defined above; and iv. optionally, a co-solvent and / or a lithophilic salt.

[0196] Even more preferably, the gel electrolyte of the invention comprises: i. at least one cross-linked polymeric matrix obtainable by cross-linking a polymer precursor formulation, said polymer precursor formulation comprising:

[0197] - at least a monomer lithium salt of formula (1(a), 1(b), 1(c) or 1(d), and

[0198] - a mixture of an alkyl mono-(meth)acrylate selected from butyl acrylate (BA) and trifluoroethyl acrylate (TFEA); with trimethylolpropane triacrylate (TMPTA), pentaerythritol tetraacrylate (PETA), dodecanediol dimethacrylate (DDMA) or any combination thereof. ii. at least one lithium salt, selected from LiC104, LiNCh, LiBF4, LiAsFe, LiPFe, LiBF3Cl, LiF, LiN(SO2CF3)2 (LiTFSI), LiN(SO2F)2(LiFSI), LiN(SO2CF3)(SO2F), LiN(SO2CHF2)(SO2F), LiN(C2F5SO2)(SO2F), LiB(C2O4)2, LiBF2(C2O4), LiC(SO2CF3)3, LiPF3(C2Fs)3, LiCF3SO3, and a combination thereof; iii. a solvent which is a fluorinated ether of formula (II) as defined above; and iv. optionally, a co-solvent and / or a lithophilic salt.

[0199] Most preferably, the gel electrolyte of the invention comprises: i. at least one cross-linked polymeric matrix obtainable by cross-linking a polymer precursor formulation, said polymer precursor formulation comprising:

[0200] - at least a monomer lithium salt of formula 1(a), and

[0201] - a mixture of an alkyl mono-(meth)acrylate selected from butyl acrylate (BA) and trifluoroethyl acrylate (TFEA); with trimethylolpropane triacrylate (TMPTA), pentaerythritol tetraacrylate (PETA), dodecanediol dimethacrylate (DDMA) or any combination thereof; ii. at least one lithium salt, selected from LiC104, LiNO3, LiBF4, LiAsFe, LiPFe, LiBF3Cl, LiF, LiN(SO2CF3)2(LiTFSI), LiN(SO2F)2(LiFSI), LiN(SO2CF3)(SO2F), LiN(SO2CHF2)(SO2F), LiN(C2F5SO2)(SO2F), LiB(C2O4)2, LiBF2(C2O4), LiC(SO2CF3)3, LiPF3(C2Fs)3, LiCF3SO3, and a combination thereof; iii. a solvent which is a fluorinated ether of formula (II) as defined above; and iv. optionally, a co-solvent and / or a lithophilic salt.

[0202] Even most preferably, the gel electrolyte of the invention comprises: i. at least one cross-linked polymeric matrix obtainable by cross-linking a polymer precursor formulation, said polymer precursor formulation comprising: - at least a monomer lithium salt of formula 1(a), wherein Ri is CH3, X is - (CH2)3- and R3 is CF3; and

[0203] - a mixture of an alkyl mono-(meth)acrylate, which is trifluoroethyl acrylate (TFEA); dodecanediol dimethacrylate (DDMA) and trimethylolpropane tri acrylate (TMPTA); ii. at least one lithium salt, selected from LiC104, LiNCh, LiBF4, LiAsFe, LiPFe, LiBF3Cl, LiF, LiN(SO2CF3)2 (LiTFSI), LiN(SO2F)2(LiFSI), LiN(SO2CF3)(SO2F), LiN(SO2CHF2)(SO2F), LiN(C2F5SO2)(SO2F), LiB(C2O4)2, LiBF2(C2O4), LiC(SO2CF3)3, LiPF3(C2Fs)3, LiCFsSCL, and a combination thereof; iii. a solvent which is a fluorinated ether of formula (II) as defined above; and iv. optionally, a co-solvent and / or a lithophilic salt.

[0204] In a particular embodiment of any of the preferred embodiments above, the fluorinated ether of formula (II) is such that Ri and R3 are independently selected from -CHF2, -CH2CHF2, - CHFCHF2and -CF2CHF2; R2is -OCH2CH2-; and n is an integer selected from 0, 1, 2, 3, 4, and 5, preferably form 0 and 1.

[0205] In another particular embodiment of the preferred embodiments, the at least one lithium salt is selected from LiN(SO2CF3)2(LiTFSI), LiN(SO2F)2(LiFSI), LiN(SO2CF3)(SO2F), LiN(SO2CHF2)(SO2F), LiN(C2FsSO2)(SO2F), and any combination thereof, preferably is LiFSI.

[0206] In any of the particular embodiments above:

[0207] - 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; and / or

[0208] - 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 - 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.

[0209] Method for preparing the gel electrolyte

[0210] The gel electrolyte of the first aspect may be prepared by a method comprising:

[0211] (i) providing at least one lithium salt, and optionally a lithophilic salt, as defined in the first aspect of the invention;

[0212] (ii) mixing at least one solvent selected from a fluorinated ether of formula (II), a sulfonamide of formula (III) and a combination thereof, as defined in the first aspect of the invention, with the at least one lithium salt provided in step (i), and optionally the lithophilic salt;

[0213] (iii) optionally, adding to the mixture obtained in step (ii) at least one co-solvent; and / or

[0214] (iv) adding to the mixture obtained in step (ii) or (iii) the polymer precursor formulation as defined above; and a free radical initiator.

[0215] (v) cross-linking the polymer precursor formulation by free radical polymerization to form a gel electrolyte.

[0216] 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.

[0217] In preferred embodiments, steps (i) and (ii) are carried out by using the neat components (lithium salts and fluorinated ether or sulfonamide).

[0218] In another embodiment, when step (iii) is carried out, firstly the co-solvent is added to the mixture obtained from step (ii).

[0219] 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.

[0220] 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). 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.

[0221] 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.

[0222] 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 0.01% 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.

[0223] 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.

[0224] 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 cross-linked polymeric matrix obtainable by cross-linking a polymer precursor formulation, said polymer precursor formulation comprising:

[0225] - a) at least one monomer lithium salt comprising a vinyl group or an acrylate or a methacrylate group; and at least one sulfonimide or sulfonate group; and

[0226] - b) a mixture of monomers and / or polymers, said mixture comprising: a) at least one monomer having one acrylate or methacrylate group; and b) at least one cross-linkable monomer having two or more cross-linkable acrylate or methacrylate groups; ii) at least one solvent selected from a fluorinated ether of formula (II), a sulfonamide of formula (III) and a combination thereof, as defined in the first aspect; iii)at least one lithium salt, other than the monomer lithium salt of i); iv)a free radical initiator; and v) optionally, at least one co-solvent and / or a lithophilic salt.

[0227] 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.

[0228] Electrochemical cell and battery

[0229] 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.

[0230] 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.

[0231] 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.

[0232] 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.

[0233] 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.

[0234] 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 (also known as NMC cathodes), such as LiNi0.88Mn0.05Co0.07O2 (NMC9xx) and LiNio.83Mno o4Coo.13O2 (NMC811); a lithium nickel cobalt aluminium oxide LiNixCoyAlzO2, wherein x+y+z=l (also known as NCA cathodes), such as LiNio.8Coo.15Alo.05O2; a lithium iron phosphate LiFePO4 (also known as LFP cathodes) or a lithium manganese iron phosphate LiFexMni.xP04, wherein x<l (also known as LMFP cathodes). 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, NMC811 or LFP, at least one conductive carbon, such as carbon black and / or CNT, and a polymeric binder.

[0235] In a preferred embodiment, the cathode consists of NMC9xx or NMC811, carbon black as conductive carbon and polyvinylidene fluoride (PVdF) as a polymeric binder. It is preferred that the weight ratio between NMC9xx or NMC811: conductive carbon: polymeric binder is 96:2:2.

[0236] 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.

[0237] 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 or any type of polyolefin separator coated by ceramic phase, 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. If the separator is coated by a ceramic phase, said phase has a thickness between 0.5 and 5 microns.

[0238] In a preferred embodiment, in the electrochemical cell or battery of the invention:

[0239] - the cathode material comprises lithium nickel manganese cobalt oxide or lithium iron phosphate;

[0240] - the anode consists of metallic lithium; and

[0241] - the optional separator is a polypropylene separator.

[0242] 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.

[0243] 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.

[0244] Methods for preparing the electrochemical cell or battery comprising the gel electrolyte

[0245] A further aspect of the invention relates to a method for preparing an electrochemical cell or a battery, said method comprises the steps of:

[0246] (i) providing a cathode for an electrochemical cell or a battery;

[0247] (ii) providing an anode for an electrochemical cell or a battery;

[0248] (iii) providing the electrolyte composition as defined in the third aspect of the invention, the electrolyte composition comprising the polymer precursor formulation; the at least one solvent selected from a fluorinated ether of formula (II), a sulphonamide of formula (III) and a combination thereof, the at least one lithium salt, and the free radical initiator; (iv) optionally, providing a porous separator;

[0249] (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

[0250] (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.

[0251] Preferably such porous separator is a polymeric separator, more preferably the separator is made of a polyolefin, such as polypropylene.

[0252] 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.

[0253] 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,

[0254] It is preferred that, after addition of AIBN, the so-obtained mixture is stirred to ensure homogeneity of the solution.

[0255] 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.

[0256] EXAMPLES

[0257] The following examples are intended to illustrate but not to limit the disclosed embodiments. List of abbreviations

[0258] DF2E0: l,2-bis(2,2-difluoroethoxy)ethane

[0259] TEGDME: Tetraethylene glycol dimethyl ether

[0260] LiFSL lithium bis(fluorosulfonyl)imide (LiN(SO2F)2

[0261] LiMTFSL Lithium 3-[(trifluoromethane)sulfonamidosulfonyl]propyl methacrylate

[0262] TMPTA: Trimethylolpropane triacrylate

[0263] DDMA: 1,12-Dodecanediol Dimethacrylate

[0264] TFEA: 2,2,2-Trifluoroethyl acrylate

[0265] PEGDA: polyethylene glycol diacrylate

[0266] AIBN: azobisisobutyronitrile rpm: rounds per minute

[0267] RT : room temperature

[0268] Reagents and starting materials

[0269] The following chemicals were purchased from Sigma-Aldrich, Chemfish, TCI, Specific polymers, and were dried under dynamic vacuum and / or with molecular sieves before use.

[0270] Example 1 : Preparation of electrolytes

[0271] Different electrolytes having the compositions (expressed in weight %) disclosed in Table below were prepared according to the following general procedure.

[0272] Electrolyte E1P2 (comparative)

[0273] In a first step, LiFSI was weighted in a vial and then DF2EO and TEGDME were added. Subsequently, 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.

[0274] Electrolyte E2P 2 (according to the invention) In a first step, LiMTFSI was weighted in a vial and the corresponding amount of TEGDME was added and left stirring during 10 minutes at 300 rpm and room temperature. Next, LiFSI was weighted and DF2EO was added. The solution was left stirring during 10 minutes at 300 rpm and room temperature. Subsequently, 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.

[0275] Electrolyte E3P2 (comparative)

[0276] In a first step, LiMTFSI was weighted in a vial and the corresponding amount of TEGDME was added and left stirring during 10 minutes at 300 rpm and room temperature. Next, LiFSI was weighted and DF2EO was added. The solution was left stirring during 10 minutes at 300 rpm and room temperature. Subsequently, PEGDA was 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.

[0277] The final electrolyte compositions were the following:

[0278] Electrolyte El P2 Electrolyte E2P2 Electrolyte E3P2

[0279] Compound (%wt) (%wt) (%wt)

[0280] (comparative) (invention) (comparative)

[0281] DF2EO 40.79 39.67 39.77

[0282] TEGDME 35.30 34.33 34.42

[0283] LiFSI 14.23 11.25 11.28

[0284] LiMTFSI 5.19 5.20

[0285] TMPTA 0.58 0.57

[0286] DDMA 1.51 1.49 TFEA 7.49 7.40

[0287] PEGDA

[0288] AIBN 0.10 0.10

[0289] Example 2: Preparation of electrochemical cell

[0290] Lithium metal batteries comprising the electrolytes of Example 1 were prepared according to the following procedure:

[0291] Cathode preparation for cyclability: LiFePCU cathode was composed of 96.5 wt.% of LFP (Y7 from Hunan Yuneng), 1.5 wt. % of conductive carbon (comprised of 1.0% Super P Carbon and 0.5% of Carbon Nanotubes), and 2 wt.% of polymeric binder (PVdF). A slurry was made using N-methyl-2 -pyrrolidone (NMP) as solvent and after homogenization of the dispersion it was cast on a 12 um thick aluminum current collector. Finally, it was dried overnight at 80-120 °C under vacuum, leading to an average loading of ca. 3.8 mAh cm2.

[0292] Cathode preparation for C-rate capability: LiFePCU cathode was composed of 96.5 wt.% of LFP(Y7 from Hunan Yuneng), 1.5 wt. % of conductive carbon (comprised of 1.0% Super P Carbon and 0.5% of Carbon Nanotubes), and 2 wt.% of polymeric binder (PVdF). A slurry was made using N-methyl-2-pyrrolidone (NMP) as solvent and after homogenization of the dispersion it was cast on a 12 um thick aluminum current collector. Finally, it was dried overnight at 80-120 °C under vacuum, leading to an average loading of ca. 2.3 mAh cm2.

[0293] Anode provision'. Li metal foil (China Energy Lithium, 14 mm diameter and 50 pm thickness).

[0294] Cell assembly for cyclability '. 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.

[0295] Cell assembly for C-rate capability. Coin cells were assembled in an Argon filled glovebox using LFP (12 mm diameter) electrodes as cathode, Celgard H2010 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.

[0296] Lithium symmetric cell assembly for cationic current analysis'. Coin cells were assembled in an Argon filled glovebox, Celgard H2010 as separator and two Li metal disk (China Energy Lithium, 14 mm diameter and 50 pm thickness) as electrodes. The electrolytes prepared according to example 1 were injected between two lithium metal electrodes on both sides of the separator.

[0297] The cells with electrolyte E1P2, E2P2, E3P2 were left for wetting for 24 h at RT, and then crosslinked by keeping them at 70°C for 12 hours.

[0298] Example 3 : Electrochemical measurements

[0299] The cells were cycled galvanostatically, between 2.8 V and 3.8 V vs. Li / Li+ using a Neware Battery Tester. 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 C / 5-D / 2 at 45 °C.

[0300] 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 / TEGDME in 50 / 50 vol.% ratio 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); b) DF2EO / TEGDME in 50 / 50 vol.% ratio of solvent and LiFSI / LiMTFSI lithium salts at a molar concentration of 0.8 M and 0.2 M, respectively, with 10 vol% of a TMPTA / DDMA / TFEA polymer matrix (E2P2).

[0301] It is shown that the gel electrolyte E2P2 having a monomer lithium salt exhibits better capacity retention and longer cycle life, when compared to the capacity retention of the gel electrolyte E1P2 lacking said monomer lithium salt, used as a reference. E1P2 and E2P2 are reaching a capacity retention of 80 % after 108 and 150 cycles, respectively.

[0302] Example 4: Electrochemical measurements

[0303] The cells were cycled galvanostatically, between 2.8 V and 3.8 V vs. Li / Li+ using a Neware Battery Tester. The applied protocol was based on 1 cycle at a current of C / 10, then the applied protocol for rate capability was based on 3 cycles at different charge rates: C / 3-D / 10, C / 2-D / 10, 1C-C / 10, 2C-C / 10 at 45 °C. A recovery cycle between the different charge rates at C / 10 was included.

[0304] Figure 2 shows the specific discharge capacity vs. cycle number for the Li°||LFP cells at 45 °C and at different charge rates, comprising an electrolyte containing a mixture of a) DF2E0 / TEGDME in 50 / 50 vol.% ratio 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); b) DF2EO / TEGDME in 50 / 50 vol.% ratio of solvent and LiFSI / LiMTFSI lithium salts at a molar concentration of 0.8 M and 0.2 M, respectively, with 10 vol% of a TMPTA / DDMA / TFEA polymer matrix (E2P2).

[0305] It is shown that the gel electrolytes E2P2 can sustain higher current densities compared to E1P2 without any sign of overcharging, equivalent to 2C and providing a discharge capacity of 153 mAh g ' . Besides, the first side reactions of E1P2 start at C / 3.

[0306] Example 5: Electrochemical measurements

[0307] The lithium symmetric cells were subjected to potentiostatic polarization for 10 min at 45 °C using the Biologic VMP3 potentiostat in which the cation current was recorded.

[0308] Table 1 shows the registered cationic current at 45 °C for electrolytes containing a mixture of a) DF2EO / TEGDME in 50 / 50 vol.% ratio 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); b) DF2EO / TEGDME in 50 / 50 vol.% ratio of solvent and LiFSI / LiMTFSI lithium salts at a molar concentration of 0.8 M and 0.2 M, respectively, with 10 vol% of a TMPTA / DDMA / TFEA polymer matrix (E2P2).

[0309] As tabulated in Table 1, E2P2 delivers higher cationic current than E1P2.

[0310] Table 1. Example 6: Electrochemical measurements

[0311] The cells were cycled galvanostatically, between 2.8 V and 3.8 V vs. Li / Li+ using a Neware Battery Tester. 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 C / 5-D / 2 at 45 °C. Figure 3 shows the specific discharge capacity vs. cycle number for the Li°||LFP cells at 45 °C comprising an electrolyte containing a mixture of a) DF2E0 / TEGDME in 50 / 50 vol.% ratio of solvent and LiFSI / LiMTFSI lithium salts at a molar concentration of 0.8 M and 0.2 M, respectively, with 10 vol% of a TMPTA / DDMA / TFEA polymer matrix (E2P2); b) DF2EO / TEGDME in 50 / 50 vol.% ratio of solvent and LiFSI / LiMTFSI lithium salts at a molar concentration of 0.8 M and 0.2 M, respectively, with 10 vol% of a PEGDA polymer matrix (E3P2).

[0312] It is shown that the gel electrolyte E2P2 of the invention (prepared from a polymer precursor formulation comprising a mixture of monomers) provides a discharge capacity of almost 150 mAh g1compared to E3P2, which barely reaches 100 mAh g-1, dropping dramatically after 14 cycles.

Claims

42CLAIMS ngle ion-conducting gel electrolyte comprising: i. at least one cross-linked polymeric matrix obtainable by cross-linking a polymer precursor formulation, said polymer precursor formulation comprising:- a) at least one monomer lithium salt comprising a vinyl group or an acrylate or a methacrylate group, and at least one sulfonimide or sulfonate group; and- b) a mixture of monomers, said mixture comprising: a) at least one monomer having one acrylate or methacrylate group; and b) at least one cross-linkable monomer having two or more cross-linkable acrylate or methacrylate groups; and ii. at least one lithium salt, other than the monomer lithium salt; iii. at least one solvent selected from: a) a fluorinated ether of formula (II):Rl (R2) 0 ^3(II) whereinRi is selected from -CHF2, -CF3, -CH2CHF2, -CH2CF3, -CF2CHF2, -CF2CF3, - CHFCHF2 and -CHFCF3;R3is selected fromCHFCHF2, -CHFCR2is selected from -CH2-, -OCH2CH2-, -OCH2CH2CH2- and -OCH2CH2CH2CH2-; n is an integer from 0 to 10; b) a sulfonamide of formula (III):43 wherein: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);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 or a methyl group and n is an integer from 1 to 20; orR2and R3may be combined with each other to form a nitrogen-containing aliphatic ring; and c) a combination of a) and b); iv. optionally, at least one co-solvent and / or a lithophilic salt.2.- The gel electrolyte according to claim 1, wherein the at least one monomer lithium salt is a compound of formula (I):wherein:Ri is H or CH3;44R.2 is phenylene, -C(0)0- or -0(CH2)n-, wherein n is an integer from 1 to 10;X is a single bond or a group selected from -(CH2)n-, -(CH2CH2O)n-, -(CF2CF2O)n- and -(SiO(CH3)2)n-, wherein n is an integer from 1 to 20;Y is -O or -NSO2R3, wherein R3 is selected from F, CF3, CHF2, CH2F and phenyl, provided that: when R2 is phenylene, X is a single bond and when R2 is -C(O)O- or -O(CH2)n-, then X is not a single bond.3.- The gel electrolyte according to claim 2, wherein the compound of formula (I) is selected from one or more of:1(c) whereinRi is H or CH3;X is a group selected from -(CH2)n-, -(CH2CH2O)n, -(CF2CF2O)nand -(SiO(CH3)2)n, wherein n is an integer from 1 to 20; andR3 is selected from F, CF3, CHF2, CH2F and phenyl.4.- The gel electrolyte according to claim 3, wherein the monomer lithium salt is the one formula 1(a), wherein Ri is H or CH3; X is a group selected from -(CH2)n-, -(CH2CH2O)nand -(CF2CF2O)n, wherein n is an integer from 1 to 3; and R3 is selected from F, CF3, CHF2 and CH2F.5.- The gel electrolyte according to any one of the preceding claims, wherein the cross-linked polymer matrix is obtainable by cross-linking a polymer precursor formulation comprising: at least a monomer lithium salt having a vinyl group or an acrylate or methacrylate group, and a sulfonimide or sulfonate group, and a mixture of monomers, said mixture comprising: a) at least one monomer having at least one acrylate or methacrylate group; and b) at least one cross-linkable monomer having two or more cross-linkable acrylate or methacrylate groups.6.- The gel electrolyte according to claim 5, wherein the cross-linked polymer matrix is obtainable by cross-linking a polymer precursor formulation comprising: at least a monomer lithium salt of formula 1(a), 1(b), 1(c) or 1(d), and a mixture of a) an alkyl mono-(meth)acrylate; with b) di-, tri- and / or tetra-(meth) acrylates.7.- The gel electrolyte according to any one of the preceding claims, wherein the solvent is a fluorinated ether of formula (II), wherein Ri and R3 are independently selected from -CHF2, - CH2CHF2, -CHFCHF2 and -CF2CHF2; R2 is -OCH2CH2-; and n is an integer selected from 0, 1, 2, 3, 4, and 5, preferably from 0 and 1.8.- The gel electrolyte according to any one of the preceding claims, wherein the at least one lithium salt, other than the monomer lithium salt, is selected from LiCICU, LiNCh, LiBF4, LiAsF6, LiPF6, LiBF3Cl, LiF, LiN(SO2CF3)2 (LiTFSI), LiN(SO2F)2(LiFSI), LiN(SO2CF3)(SO2F), LiN(SO2CHF2)(SO2F), LiN(C2F5SO2)(SO2F), LiB(C2O4)2, LiBF2(C2O4), LiC(SO2CF3)3, LiPF3(C2Fs)3, LiCFsSCh, and any combination thereof.9.- The gel electrolyte according to any one of the preceding claims, further comprising a cosolvent selected from dimethoxy ethane (DME), 1,2-di ethoxy ethane (DEE), 1,3 -di oxolane(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, methyl-tert-butylether, succinonitrile (SN), glutaronitrile (GN), adiponitrile (AN), ethylene sulfitde (ES), propylene sulfitde (PS) di-ethylene sulfitde (DES), di-methylsulfitde (DMS), dimethyl 2,5-dioxahexanedioate (DMDOHD), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), difluoroethyl acetate (DFEA), methyl difluoroacetate (MDFA), trimethylsilyl acetate (TMSA), 2-(2,2,2-trifluoroethoxy)ethyl methyl ether (TEME), 2-methoxyethoxy 2,2 difluroethylether (MDFE), triethyl phosphate (TEP), trimethyl phosphate (TMP), tripropyl phosphate (TPP), methyl formate (MF), methyl acetate (MA), methyl butyrate (MB), ethyl acetate (EA), ethyl propionate (EP), trimethyl silylpropane sulfonate (TMSP), acetamide of chemical structure R1CONR2R3 where Ri can be F, CF3, CF2H or CFH2, and R2 and R3 can be independently H, -(CE^nCEE, -(CH2)nCF3, -(CH2)nF, or -(CE^nCEEF or - (CH2)nCHF2where n = 1-10; and polyoxyethylene alkyl ethers of formula CnEm, wherein Cnrefers to al alkyl chain with n methylene groups and Emrefers to a hydrophilic part having m oxyethylene units.

10. The gel electrolyte according to any one of the preceding claims, which comprises a lithophilic salt, said lithophilic salt has formula M(X)Z, where M is a metal cation Mz+selected from Bi, Sn, Cu, Al, As, Ca, Si, Ag, Au, Zn, Mg, In, K, Na, and Cs; X is an anion selected from Cl’, C1O4’, NO3’, BF4’, ASF6‘, PF6’, BF3CI; (Oct)2; F; N(SO2CF3)2’, N(SO2F)2-, N(SO2CF3)(SO2F)-, N(C2F5SO2)(SO2F)-, B(C2O4)2, BF2(C2O4)-, C(SO2CF3)3’, PF3(C2F5)3- , CFsSCE', and ionic liquid; and z is the cation valence.

11. The gel electrolyte according to any one of the preceding claims, which further comprises an additive selected from fluorobenzene (FPh), 1,2-difluoro benzene, 1,3-difluoro benzene, 1,4- difluorobenzene, anisole, fluoroanisole, tris(2,2,2-trifluoroethyl) orthoformate (TFEO), tetrafluoro 1 -(2,2,2, trifluoroetoxy) ethane (D2), bis(2,2,2-trifluoroethyl) ether (BTFE), and 1, l,2,2,teterafluoroethyl-2,2,3,3-tetrafluoropropyl-ether (TTE).4712. An electrolyte composition for preparing the gel electrolyte of any one of claims 1 to 11, said electrolyte composition comprising: i) a polymer precursor formulation comprising: a) at least one monomer lithium salt comprising a vinyl group or an acrylate or a methacrylate group; and at least one sulfonimide or sulfonate group; and b) a mixture of monomers, said mixture comprising: a) at least one monomer having one acrylate or methacrylate group; and b) at least one cross-linkable monomer having two or more cross-linkable acrylate or methacrylate groups; ii) at least one solvent selected from a fluorinated ether of formula (II), a sulfonamide of formula (III) and a combination thereof, as defined in the first aspect; iii)at least one lithium salt, other than the monomer lithium salt: iv)a free radical initiator; and v) optionally, at least one co-solvent and / or lithophilic salt.13.- An electrochemical cell or battery comprising the gel electrolyte according to any of claims1 to 11, a cathode, an anode, and, optionally, a separator.14.- The electrochemical cell or battery according to claim 13 wherein:- the cathode material comprises a lithium nickel manganese cobalt oxide LiNixMnyCozCh wherein x+y+z=l; a lithium nickel cobalt aluminium oxide LiNixCoyAlzCh, wherein x+y+z=l; a lithium iron phosphate LiFePCU; or a lithium iron manganese phosphate LiFexMnx-iP04, wherein x<l;;- the anode consists of metallic lithium; and- the optional separator is a polyolefin separator.15.- A method for preparing an electrochemical cell or a battery according to claim 13 or 14, 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;48(iii) providing an electrolyte composition as defined in claim 12;(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 comprised in the electrolyte composition injected in step (v) by free radical polymerization to form a gel electrolyte.

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