Solid polymer electrolyte materials comprising an anionic thermoplastic rubber matrix

Abstract

The present invention relates to a solid polymer electrolyte material comprising an alkali metal salt and a thermoplastic rubber matrix, wherein the thermoplastic rubber matrix comprises a mixture of at least one crosslinked elastomer phase and at least one thermoplastic polymer phase, said crosslinked elastomer phase comprising elastomer polymer chains bearing one or more anionic groups.

Description

[0001] DESCRIPTION

[0002] TITLE: Solid polymer electrolyte materials comprising an anionic thermoplastic rubber matrix

[0003] The present invention relates to the field of energy storage, and more particularly to solid-state batteries.

[0004] The present invention particularly relates to a solid polymer electrolyte material comprising an alkali metal salt and an anionic thermoplastic rubber matrix.

[0005] Lithium-ion (Li-ion) batteries offer exceptional energy density and are widely used, for example, in portable devices and electric and hybrid vehicles. They are based on the reversible exchange of lithium ions between positive and negative electrodes, separated by an ionically conductive liquid electrolyte. These liquid electrolytes are essential to enable good mobility of Li cations. +in the battery cell. However, they are based on organic solvents that are flammable, which can lead to potential thermal drifts in the event of an incident.

[0006] In this context, polymer electrolytes have been developed as ion-conducting solid electrolytes for solid-state batteries, particularly to promote system safety and potentially increase stored energy. However, most of these batteries suffer from lithium dendrite growth during charge / discharge cycles, related to the use of a metallic lithium electrode, which can affect their morphological integrity and potentially lead to internal short circuits.

[0007] Dendrite growth is influenced by different parameters, including the quality of the interface between lithium and the solid electrolyte, as a poor interface can generate electric field heterogeneity at the interface and thus dendrite formation. In particular, Chazalviel et al. suggested that anion depletion near the Li electrode could lead to large electric fields, which in turn cause dendrite growth (J.-N. Chazalviel, Phys. Rev. A 42 (1990) 7355). The other model proposed by Monroe and Newman suggests that lithium dendrite growth can be mechanically blocked if the shear modulus of electrolytes is about twice that of lithium metal (C. Monroe, J. Newman, J. Electrochem. Soc. 152 (2005) 396-404).

[0008] In order to optimize solid-state batteries, ionically conductive solid electrolytes must therefore have excellent ionic conductivity (to be able to operate in a power range comparable to that of Li-ion) as well as high mechanical properties (to promote the integrity of the battery cells), while minimizing, or even eliminating, the formation of dendrites.

[0009] A recently published application by the inventors (WO 2023083801) describes solid polymer electrolytes comprising an alkali metal salt and a thermoplastic rubber matrix comprising a mixture of at least one crosslinked elastomer phase and at least one thermoplastic polymer phase. These solid polymer electrolytes have improved properties compared to conventional polymer electrolytes, including better electrochemical stability than polyethylene oxide, high mechanical properties and high resistance under pressure (including at room temperature and elevated temperature), which makes them particularly suitable for gel systems. They also have:

[0010] - good stability with high potential electrodes (e.g. LMFP);

[0011] - low flammability (a non-flammable solvent such as TEP can be used);

[0012] - good cyclability at high temperature; and

[0013] - good cyclability at high cycling rates.

[0014] This document also mentions good resistance to dendritic growth of alkali metals, such as dendritic growth of lithium, but this aspect still needs to be improved.

[0015] The aim of the invention is therefore to propose a solid polymer electrolyte material making it possible to obtain solid polymer electrolytes having excellent ionic conductivity combined with high mechanical properties, while minimizing, or even eliminating, the formation of dendrites.

[0016] The present invention therefore relates to a solid polymer electrolyte material comprising an alkali metal salt and a thermoplastic rubber matrix, wherein the thermoplastic rubber matrix comprises a mixture of at least one crosslinked elastomeric phase and at least one thermoplastic polymer phase, said crosslinked elastomeric phase comprising elastomeric polymer chains carrying one or more anionic groups.

[0017] Indeed, the inventors have discovered that the presence of anionic groups in the crosslinked elastomer phase makes it possible to maintain the excellent mechanical and electrochemical properties of solid polymer electrolytes comprising an alkali metal salt and a thermoplastic rubber matrix of the prior art, while solving the problem of dendrite formation. Without wishing to be bound by any theory, the inventors believe that the specific microstructure of the anionic thermoplastic rubber matrix, as detailed in the description below, makes it possible to stabilize the Li-metal interface and thus very effectively prevent the formation of dendrites.

[0018] A thermoplastic rubber matrix is ​​usually known by the acronym TPV, for ThermoPlastic Vulcanized.

[0019] Advantageously, the crosslinked elastomer phase is in the form of nodules dispersed in the thermoplastic polymer phase.

[0020] The crosslinked elastomer phase is therefore advantageously a phase homogeneously dispersed in the thermoplastic polymer phase.

[0021] Preferably, the crosslinked elastomeric phase nodules are substantially spherical.

[0022] Preferably, the crosslinked elastomeric phase nodules have a diameter less than or equal to 5 pm, preferably less than or equal to 2 pm, preferably less than or equal to 1 pm, preferably less than or equal to 0.5 pm, preferably between 10 nm and 5 pm.

[0023] The nodules are therefore relatively small in size, which is related to the process of preparation, preferably by dry method, of the solid polymer electrolyte material. Such small sizes are advantageous in that it improves the properties of each phase of the thermoplastic rubber matrix. The smaller the nodules, the more visible the properties of each polymer are. In particular, the elastomeric properties of the crosslinked elastomeric phase are very efficiently transmitted (visible) to the anionic thermoplastic rubber matrix, which significantly improves the mechanical properties of the solid polymer electrolyte material, and thus in particular of the solid polymer electrolyte comprising it (or consisting of it).In addition, the smaller the size of the nodules, the greater the density of accessible anionic groups (on the surface of the nodules), which makes it possible to maximize their effectiveness and / or reduce their content for a given effectiveness.

[0024] Preferably, the anionic group(s) are grafted, preferably indirectly, to the elastomeric polymer chains of the crosslinked elastomeric phase.

[0025] Formulated differently, each anionic group is grafted, preferably indirectly, to an elastomeric polymer chain of the crosslinked elastomeric phase.

[0026] By "indirectly grafted" is meant that the atom of the anionic group(s) carrying the anionic charge is not directly bonded to an atom of the elastomeric polymer chains, but is separated from the atoms of the main chain of the elastomeric polymer by at least one atom.

[0027] According to one embodiment, the anionic group(s) are carried by one or more pendant groups which are grafted to the (main) elastomeric polymer chains. Formulated differently, each anionic group is carried by a pendant group which is grafted to a (main) elastomeric polymer chain.

[0028] This makes it possible to move the anionic groups away from the (main) elastomeric polymer chains, and advantageously makes it possible to maximize the density of anionic groups on the surface of the crosslinked elastomeric phase nodules, and therefore to increase the effect linked to their presence.

[0029] In summary, each of the above characteristics defining the particular microstructure of the thermoplastic rubber matrix (in particular the presence of anionic groups in the elastomer phase, the arrangement of the anionic groups, the presence of nodules, and the shape and size of the nodules) contributes to ensuring that the electric fields at the electrolyte layer comprising the electrolyte material according to the invention are homogeneous and to avoiding anion depletion at the Li metal / electrolyte interface, which blocks the formation of dendrites.

[0030] In addition, the particular microstructure of the thermoplastic rubber matrix provides a uniform distribution of Li ions + . In addition to the advantages mentioned above, this microstructure also acts as a redistributor of Li ions. +, as reported by Chen-Zi Zhao et al. (Science Advances, 4 (2018), eaat3446) for composite polypropylene separators comprising LLZTO ceramic particles to prevent dendrite formation. In the present invention, the same Li ion distribution effect is observed + , but using phase separation in the thermoplastic rubber matrix, the crosslinked elastomer phase (dispersed in the form of nodules) instead of the heavy and expensive LLZTO ceramic particles. "Alkali metal" means a chemical element such as lithium (Li), sodium (Na), and potassium (K). The alkali metal is in particular lithium.

[0031] The alkali metal salt is preferably a lithium salt.

[0032] The alkali metal salt, preferably the lithium salt, may be selected from a variety of lithium ion-conducting electrolyte salts (lithium salts) typically used for lithium batteries.

[0033] Various types of lithium salts used to conduct Li ions + in electrolyte solutions for rechargeable lithium batteries are described in particular in Xu et al. Formulation of Blended-Lithium-Salt Electrolytes for Lithium Batteries Angew. Chem. Int. Ed. 2020, 59, 3400, and Auger et al. Materials Science and Engineering: R: Reports 2018, 134, 1-21.

[0034] Lithium hexafluorophosphate (LiPFe) is the primary lithium salt used in commercial rechargeable lithium-ion batteries. Other examples of lithium salts suitable as alkali metal salts are lithium bis(trifluoromethanesulfonyl)imidate (LiTFSI), lithium bis(fluorosulfonyl)imidate (LiFSI), lithium hexafluoroarsenate (LiAsFe), lithium perchlorate (LiCICL), lithium hexafluorophosphate (LiPFe), lithium tetrafluoroborate (UBF4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(oxalato)borate (LiBOB), and lithium difluoro(oxalato)borate (LiBODFB).

[0035] The alkali metal salt may generally be present in dissociated form, either in one or more polymer phases or in one or more optional additives possibly present in the solid polymer electrolyte material.

[0036] The alkali metal salt is preferably present in the thermoplastic polymer phase, preferably in dissociated form. It thus makes it possible to confer ionic conductivity properties on the thermoplastic polymer phase. The alkali metal salt may, however, also be present, in smaller quantities, in the crosslinked elastomer phase.

[0037] Preferably, the anionic group(s) are chosen from carboxylate (-COOj), sulfonate (-SCh), sulfonylimidates, borates, phosphates, phosphonates and phosphinates.

[0038] Preferably, the sulfonylimidate groups are of the following formula (I): in which

[0039] - R 1is a halogen (preferably fluorine), a C1-C10 alkyl group or an aryl group, the alkyl and aryl groups being optionally substituted by one or more halogens, preferably by one or more fluorine atoms, preferably R 1 is chosen from F, CF3, Ph and CeFs,

[0040] - X is an oxygen atom or a -NS(O)(O)-R group 1 , with R 1 as defined above, preferably is an oxygen atom, and

[0041] - R 2 is -S(O)(O)- or -C(O)- , preferably is -S(O)(O)-.

[0042] Advantageously, the sulfonylimidate group has the following formula:

[0043] Preferably, the borate groups are chosen from the oxalate borate group and the tetraphenyl borate groups, the phenyl groups being optionally substituted by one or more fluorine atoms, preferably the borate groups are chosen from an oxalate borate group of the following formula: a tetraphenyl borate group of the following formula: and a tetra(pentafluorophenyl) borate group of the following formula:

[0044] The phosphate groups have the following formula (II): in which X' = OH, OR or OR being chosen from a linear or branched C1-C10 alkyl group, a linear or branched C2-C10 alkylene group, and a phenyl group.

[0045] The phosphonate groups have the following formula (III): in which X' = OH, OR or OR being chosen from a linear or branched C10-C10 alkyl group, a linear or branched C2-C10 alkylene group, and a phenyl group.

[0046] Advantageously, the anionic group(s) are COO' groups.

[0047] Preferably, the COO' groups are independently linked to the elastomeric polymer (main) chains via a linear or branched C1-C18 alkyl or C2-C18 alkylene group, preferably a linear or branched C1-C18 alkyl group, preferably C1-C12, more preferably C1-C7. The alkyl or alkylene groups may optionally be further substituted by an anionic group as defined above, preferably carrying at least a second coo- group.

[0048] In other words, the (main) elastomeric polymer chains therefore carry one or more, preferably several, grafts of formula -CH(Ra)(Rb), with, independently for each graft:

[0049] - either Ra = H and Rb is a linear or branched C1-C18 alkyl or C2-C18 alkylene group, preferably a linear or branched C1-C18 alkyl group, preferably C1-C12, more preferably C1-C7, substituted by a COO group preferably substituted at the end of the chain,

[0050] - either Ra = COO; and Rb is a linear or branched C1-C18 alkyl or C2-C18 alkylene group, preferably a linear or branched C1-C18 alkyl group, preferably C1-C12, more preferably C1-C7, optionally substituted by a COO group; preferably at the end of the chain,

[0051] - either Ra and Rb are each independently a linear or branched C1-C18 alkyl or C2-C18 alkylene group, preferably a linear or branched C1-C18 alkyl group, preferably C1-C12, more preferably C1-C7, with the condition that at least one of Ra and Rb, preferably both Ra and Rb, is / are substituted by a COO group; preferably substituted at the end of the chain.

[0052] “End-substituted” means that preferably, Rb (and Ra if applicable) is of the formula -Rb'-COO' (and Ra is of the formula -Ra'-COO; if applicable), with Rb' (and Ra', if applicable) being a linear or branched C1-C18 alkyl or C2-C18 alkylene group, preferably a linear or branched C1-C18 alkyl group, preferably C1-C12, more preferably C1-C7.

[0053] Preferably, the counter-cation of the anionic group(s) is an alkali metal, preferably Li + .

[0054] "Elastomeric phase" means a polymer phase that is homogeneous in chemical composition and / or texture, consisting of a polymer that exhibits rubber-like elasticity, as defined by IUPAC.

[0055] This phase is called "crosslinked" or vulcanized because it has been subjected to a crosslinking reaction under the action of one or more crosslinking agents. The elastomer is crosslinked in the sense that it comprises covalent bonds or relatively short sequences of chemical bonds to connect two elastomeric polymer chains together, which have been formed by the crosslinking reaction. Suitable crosslinking agents generally depend on the elastomeric polymer in question. These agents can be chosen from organic peroxides, including dialkyl peroxides, such as Luperox® peroxides, such as Luperox® DI marketed by Arkema.

[0056] Preferably, the elastomer is a crosslinkable polymer, typically selected from cis-1,4-polyisoprene (NR) and trans-1,4-polyisoprene, synthetic polyisoprene, polybutadiene, chloroprene rubber (CR), polychloroprene, neoprene, Baypren, butyl rubber (HR), halogenated butyl rubbers such as chlorobutyl rubber (CIIR) and bromobutyl rubber (BIIR), styrene-butadiene rubber (SBR), styrene-butadiene-styrene polymers (SBS), styrene-ethylene-butadiene-styrene polymers (SEBS), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), ethylene-propylene rubber (EPM), ethylene-propylene-diene rubber (EPDM), epichlorohydrin rubber (ECO), polyacrylic rubber (ACM, ABR), silicone rubber (SI, Q, VMQ), fluorosilicone rubber (FVMQ), fluoroelastomers (FKM for fluorocarbon-based fluoroelastomer materials defined by international standard ASTM D1418,and FEPM), perfluoroelastomers (FFKM), polyether block amides (PEBA), chlorosulfonated polyethylene (CSM), and ethylene vinyl acetate (EVA).,

[0057] Preferably, the elastomer is chosen from unsaturated or saturated rubbers, preferably the elastomer is a styrene-ethylene-butadiene-styrene polymer.

[0058] The term "thermoplastic polymer phase" means a polymer phase consisting of a plastic polymer that becomes soft or malleable at a certain elevated temperature and solidifies upon cooling.

[0059] Preferably, the thermoplastic polymer is selected from polyacrylates, acrylonitrile butadiene styrene (ABS), nylon, polylactic acid (PLA), polybenzimidazole, polycarbonate, polyether sulfone, polyoxymethylene, polyether ether ketone, polyetherimide, polyethylene, polyphenylene oxide, poly(phenylene sulfide), polypropylene, polystyrene, poly(vinyl chloride), poly(vinylidene fluoride), polytetrafluoroethylene (Teflon), poly(ethylene oxide) (PEO) and polycaprolactone (PCL).

[0060] Preferably, the thermoplastic polymer is poly(ethylene oxide) (PEO) or polycaprolactone (PCL), advantageously polycaprolactone (PCL).

[0061] Preferably, the thermoplastic polymer has a multimodal molecular weight distribution, in particular has a bimodal or trimodal molecular weight distribution, advantageously has a trimodal molecular weight distribution.

[0062] A molecular mass distribution is said to be multimodal when it includes several (at least two) groups of polymer chains with different average molecular masses. This characteristic is visible in particular in gel permeation chromatography, the curves obtained in GPC for such polymers can have several (at least two) maxima. A polymer containing two groups of molecules with different average molecular masses is said to be bimodal ("bimodal" polymer). A polymer containing three groups of molecules with different average molecular masses is said to be trimodal ("trimodal" polymer).

[0063] This advantageously allows the mixture to be plasticized and softened during the preparation of the electrolyte material according to the invention, which allows, among other things, better fluidity during processing as well as better adhesion and a better interface during calendering with other elements of the battery such as, for example, Li-metal or other anodes and cathodes. In addition, during use in cycling, better flexibility of the thermoplastic phase is obtained, thus facilitating the transport of the Li + as well as plating and removal on Li metal.

[0064] Advantageously, the thermoplastic polymer phase is ionically conductive, preferably due to the presence of the alkali metal salt as defined above. The thermoplastic polymer phase therefore preferably comprises the alkali metal salt.

[0065] The solid polymer electrolyte material according to the invention may further comprise one or more additional ingredients, such as dopants and / or additives such as those usually used in solid polymer electrolytes.

[0066] According to one embodiment, the thermoplastic rubber matrix of the electrolyte material according to the invention may further comprise one or more dopants, generally to improve ionic conductivity. This dopant may be an organic molecule chosen from trimethylphosphate (TMP), triethylphosphate (TEP), fluoroethylene carbonate (FEC), vinylene carbonate (VC).

[0067] According to one embodiment, the thermoplastic rubber matrix of the electrolyte material according to the invention may also comprise one or more additives, such as solvents, plasticizers, lithium ceramic, inorganic fillers and radical scavengers. The solvents may be chosen from organic liquids, water, ionic liquids. They may be, for example, trimethylphosphate (TMP), triethylphosphate (TEP), fluoroethylene carbonate (FEC), vinylene carbonate (VC).

[0068] Solvents can be selected from a variety of lithium-ion conductive liquids typically used for lithium batteries. Different types of solvents used for rechargeable lithium batteries are presented in Chem. Rev. 2004, 104, 4303-4417 and Chem. Rev. 2014, 114, 11503-1161.

[0069] Plasticizers can be selected from the variety of plasticizers known to the polymer melt processing industry, but can also be any oligomer that helps reduce the viscosity of the overall formulation. Plasticizers can be compounds such as synthetic or natural oils or polymer oligomers such as glyme molecules, for example.

[0070] Lithium ceramics can be in the form of lithium-aluminium-titanium phosphate (LATP, Lii.3Alo.3Tii.7(P04)3), lithium-lanthanum-zirconium oxide (LLZO, Li?La3Zr20i2).

[0071] Radical scavengers can be used to extend compounding times by controlling the rate of the crosslinking reaction. Radical scavengers include 2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl (TEMPO), another example is presented by Bertin et al. Kinetic subtleties of nitroxide mediated polymerization. Chemical Society Reviews 2011, 40 (5), 2189-2198.

[0072] Inorganic fillers can be used to further strengthen the polymer phases. They can be added to the elastomer phase with the crosslinking agent (during step a) or a') of the processes described below) to ensure that they remain in this phase during crosslinking. Inorganic fillers are, for example, ceramic fillers such as TiO2 or SiO2.

[0073] According to one embodiment, in the thermoplastic rubber matrix of the electrolyte material according to the invention:

[0074] - the ratio between the volume of the crosslinked elastomer phase and the volume of the thermoplastic rubber matrix is ​​between 40% and 60% (by volume); and / or

[0075] - the ratio of the thermoplastic polymer phase to the volume of the thermoplastic rubber matrix is ​​between 40% and 60% (by volume).

[0076] Generally, the crosslinked elastomer phase and the thermoplastic polymer phase may be present in the thermoplastic rubber matrix in a volumetric ratio ranging from 40 / 60 to 60 / 40, advantageously around 50 / 50. Their respective weight generally depends on their respective density.

[0077] According to one embodiment, the solid polymer electrolyte material may comprise, relative to the total weight of the solid polymer electrolyte material:

[0078] - 10 to 70% by weight of crosslinked elastomer phase;

[0079] - 10 to 70% by weight of thermoplastic polymer;

[0080] - 10 to 45% by weight of alkali metal salt;

[0081] - 0 to 70% by weight of dopant; and

[0082] - 0 to 20% by weight of additives.

[0083] Another objective of the invention is to provide a solid-state battery that can be easily produced on an industrial scale.

[0084] The invention also relates, according to a first alternative, to a method for preparing a solid polymer electrolyte material according to the invention, comprising the following steps: a) mixing an elastomeric polymer, a crosslinking agent, a compound carrying at least one anionic or anionizable group, and optionally a base capable of anionizing said anionizable group, at a temperature T1, where T1 is between the melting temperature of the elastomeric polymer and the activation temperature of the crosslinking agent, b) adding an alkali metal salt and a thermoplastic polymer to the mixture obtained in step a), and c) mixing the mixture obtained in step b) at a temperature T2, where T2 is higher than the activation temperature of the crosslinking agent.

[0085] Preferably, the mixture obtained in step a) comprises a base capable of anionizing said anionizable group if it further comprises a compound carrying at least one anionizable group.

[0086] During step a), the elastomeric polymer, the crosslinking agent, the compound bearing at least one anionic or anionizable group, and the optional base capable of anionizing said anionizable group may be added simultaneously or sequentially. According to a preferred embodiment, the compound bearing at least one anionic or anionizable group, and the optional base capable of anionizing said anionizable group are first mixed with the elastomeric polymer, then the crosslinking agent is added, and mixed. During step b), the alkali metal salt and the thermoplastic polymer may be introduced simultaneously or sequentially to the mixture obtained in step a). According to a preferred embodiment, the thermoplastic polymer is added to the mixture obtained in step a) first, then the alkali metal salt is then added and mixed.

[0087] Step b) may be carried out at the temperature T1 of step a) or at a different temperature, preferably higher than the temperature T1, provided that it is lower than the activation temperature of the crosslinking agent. The temperature during step b) may be fixed or variable. Thus, according to this first alternative, the alkali metal salt is added before crosslinking.

[0088] According to a second alternative, the solid polymer electrolyte material according to the invention can be prepared according to a preparation method comprising the following steps: a') mixing an elastomeric polymer, a crosslinking agent, a compound carrying at least one anionic or anionizable group, and optionally a base capable of anionizing said anionizable group, at a temperature T1, where T1 is between the melting temperature of the elastomeric polymer and the activation temperature of the crosslinking agent, b') adding a thermoplastic polymer to the mixture obtained in step a'), c') mixing the mixture obtained in step b') at a temperature T2, where T2 is higher than the activation temperature of the crosslinking agent, and d') adding an alkali metal salt to the mixture obtained in step c').

[0089] During step a'), the elastomeric polymer, the crosslinking agent, the compound carrying at least one anionic or anionizable group, and the optional base capable of anionizing said anionizable group can be added simultaneously or sequentially. According to a preferred embodiment, the compound carrying at least one anionic or anionizable group, and the optional base capable of anionizing said anionizable group are first mixed with the elastomeric polymer, then the crosslinking agent is added, and mixed.

[0090] Step b') may be carried out at the temperature T1 of step a) or at a different temperature, preferably higher than the temperature T1, provided that it is lower than the activation temperature of the crosslinking agent. The temperature during step b') may be fixed or variable.

[0091] According to this second alternative, the alkali metal salt is added after initiation of crosslinking of the elastomeric polymer. According to these first and second alternatives, step c) (and c'), respectively) allows crosslinking of the elastomeric polymer, and the anionic group (possibly obtained by anionization of the anionizable group under the effect of the base) is grafted to the main chains of the elastomeric polymer during crosslinking (therefore during step c) or c')).

[0092] These first or second alternatives are preferred for preparing the solid polymer electrolyte material according to the invention, in particular using a compound carrying at least one anionizable group and a base capable of anionizing said anionizable group during step a) (or a'), respectively).

[0093] According to a third alternative, the solid polymer electrolyte material according to the invention can be prepared according to a preparation method comprising the following steps: a”) mixing an elastomeric polymer comprising at least one monomeric unit carrying an anionic or anionizable group, a crosslinking agent and optionally a base capable of anionizing said anionizable group, at a temperature T1, where T1 is between the melting temperature of the elastomeric polymer and the activation temperature of the crosslinking agent, b”) adding a thermoplastic polymer, and optionally an alkali metal salt to the mixture obtained in step a”), c”) mixing the mixture obtained in step b”) at a temperature T2, where T2 is higher than the activation temperature of the crosslinking agent, and d”) if and only if an alkali metal salt has not been added during step b”), adding an alkali metal salt to the mixture obtained in step c”).

[0094] The alkali metal salt is therefore added either during step b”) or during step d”).

[0095] Preferably, the mixture obtained in step a”) comprises a base capable of anionizing said anionizable group if the elastomeric polymer comprises one or more anionizable groups.

[0096] Alternatively, the base capable of anionizing said anionizable group is introduced during step b”) of the process according to the second alternative, if the elastomeric polymer comprises one or more anionizable groups. The alternative according to which the base capable of anionizing said anionizable group is introduced during step a”) is however preferred. Whether the base capable of anionizing said anionizable group is introduced during step a”) or b”), it implies that the elastomeric polymer comprises one or more anionizable groups and that these anionizable groups are anionized during step(s) a”) and / or b”) and / or c”).

[0097] According to another possibility, the method according to the second alternative may further comprise a step a1”) prior to step a”) and comprising the provision of an elastomeric polymer comprising at least one monomeric unit carrying an anionizable group, and the anionization of said anionizable group, preferably by mixing the elastomeric polymer with a base capable of anionizing the anionizable group, to obtain an elastomeric polymer comprising at least one monomeric unit carrying an anionic group. In this case, preferably, neither step a”) nor step b”) comprises the addition of a base capable of anionizing the anionizable group, since the anionization was carried out during step a1”).

[0098] According to one embodiment, the method according to the second alternative may further comprise a step a0”) prior to step a”) and optionally prior to step a1”) if present, comprising the provision of an elastomeric polymer and the grafting of an anionic or anionizable group onto said elastomeric polymer, preferably onto the (main) chains of elastomeric polymer.

[0099] According to another embodiment, the method according to the second alternative may further comprise a step a0'”) prior to step a”) and optionally prior to step a1”) if present, comprising the provision of an elastomeric polymer by polymerization of at least one monomer carrying an anionic or anionizable group.

[0100] For the processes according to the first, second, and third alternatives:

[0101] - the elastomeric and thermoplastic polymers are as defined above for the solid polymer electrolyte material;

[0102] - the alkali metal salt is as defined above for the solid polymer electrolyte material;

[0103] - the anionic groups are as defined above for the solid polymer electrolyte material;

[0104] - by anionizable group, we mean a group of atoms capable of becoming anionic, by loss of at least one atom constituting it, preferably a hydrogen atom, for example under the action of a base. Anionizable groups are for example:

[0105] - the COOH group,

[0106] - the SO3H group, - the sulfonimide groups of formula (I') with R 1 , R 2 and X as defined above for formula (I), bound with phosphoric acid of formula (II'), v' with R' being chosen from H, a linear or branched C1-C10 alkyl group, a linear or branched C2-C10 alkylene group, and a phenyl group, and

[0107] - groups derived from phosphonic acid of formula (III'):

[0108] O

[0109] HO—P™

[0110] GOLD

[0111] / iiin

[0112] ' with R' being chosen from H, a linear or branched C1-C10 alkyl group, a linear or branched C2-C10 alkylene group, and a phenyl group.

[0113] Advantageously, the anionizable group is COOH.

[0114] Preferably, the compound carrying at least one anionic or anionizable group is a compound carrying at least one COO' or COOH group. Preferably, it is a compound carrying at least one COOH group, in particular a compound of formula Rc-COOH or of formula Rc-COO Rc being a linear or branched C1-C36 alkyl or C2-C36 alkylene group.

[0115] Preferably, Rc comprises at least one unsaturation. The presence of this unsaturation facilitates the grafting of the compound onto the main chains of the elastomeric polymer.

[0116] Preferably, Rc is C2-C24, preferably C4-C18, more preferably C4-C12. Rc may further be substituted by an anionic group as defined above, preferably carrying at least a second COOH or COO group, preferably at the end of the chain.

[0117] Advantageously, the compound bearing at least one anionic or anionizable group is of formula A-Rc'-A, with A being independently COOH or COO, preferably COOH, and Rc' is a linear or branched C1-C36 alkyl or C2-C36 alkylene group. Preferably, Rc' comprises at least one unsaturation. Preferably, Rc' is C2-C24, preferably C4-C18, more preferably C4-C12. An example of a compound bearing at least one anionic or anionizable group is sebacic acid or the corresponding lithium sebacate dianion, or adipic acid or the corresponding lithium adipate dianion.

[0118] Preferably, for each process, the optional base capable of anionizing the anionizable group is added in a molar quantity substantially equivalent (stoichiometric relative) to the molar quantity of anionizable group(s).

[0119] By "anionizing" we mean removing an atom, for example a hydrogen, from a group of atoms so that this group of atoms becomes anionic.

[0120] The base capable of anionizing the anionizable group is preferably a lithium salt, organic or inorganic. It may be organolithiums, such as MeLi or nBuLi of lithium alkoxides, especially C1-C2, or LiOH. LiOH is particularly preferred in that the by-product of the anionization reaction is water.

[0121] The melting temperature of the elastomeric polymer is defined as the temperature of its melting point, at which the polymer changes from solid to molten form.

[0122] The crosslinking agent is as defined above. Its activation temperature is defined as the temperature triggering the crosslinking reaction.

[0123] T1 and T2 depend on the nature of the elastomeric polymer and the crosslinking agent.

[0124] Optional additional ingredients as defined above may be added during step a) or a') or a”) and / or step b) or b') or b”), as appropriate.

[0125] Typically, dopants can be added in step a) or b), or a') or b') or a”) or b”).

[0126] Generally, additives may be added at step a) or b), or a') or b'), or or a”) or b”).

[0127] The methods of the invention may be carried out by extrusion. As a general rule, the mixing steps a) and b), or a') and b'), or or a”) or b”), may be carried out in one or more heated extruders or in one or more internal mixers.

[0128] Steps c) and c'), d') and the optional step d”) may also be carried out in one or more heated extruders or in one or more internal mixers.

[0129] Suitable extruders can be of the twin screw type.

[0130] Preferably, the solid polymer electrolyte material is therefore obtained at the end of step c), d'), and c”) or d”) in the form of extrudates or filaments.

[0131] After step c), d'), and c”) or d”), the solid polymer electrolyte material obtained may be shaped according to a step e) to give it the desired shape, in particular to give it the shape of a solid polymer electrolyte, typically a film. The shaping step e) is typically carried out by calendering extrusion.

[0132] Alternatively, step e) may comprise additive printing of a solid polymer electrolyte layer using the solid polymer electrolyte material of the invention as a raw material.

[0133] Another subject of the present invention therefore relates to a solid polymer electrolyte comprising a solid polymer electrolyte material according to the invention. As mentioned above, this solid polymer electrolyte is preferably in the form of a film. It may also be in the form of a three-dimensional layer obtained by additive printing.

[0134] The present invention relates more broadly to an electrochemical element, preferably an all-solid-state battery, comprising a solid polymer electrolyte material according to the invention.

[0135] In this document, a solid-state battery cell is understood to mean a cell comprising a positive electrode / electrolyte / negative electrode assembly configured to store electrical energy produced by a chemical reaction and release it in the form of an electric current.

[0136] The present invention therefore also relates to an electrochemical element, preferably an all-solid-state battery, comprising a solid polymer electrolyte as defined above, the electrochemical element further comprising a positive electrode and a negative electrode.

[0137] Typically, the battery element of the invention is a Li-ion cell.

[0138] The positive electrode comprises a current collector, at least one of whose faces is coated with a layer of a composition of positive active materials. "Composition of active materials" means a composition comprising one or more active materials and optionally one or more binders and one or more electronically conductive materials.

[0139] The positive current collector is a solid or perforated metal strip which may be made of aluminum or an aluminum alloy or steel or stainless steel. Its thickness may be in the range of 6 to 30 μm or 5 to 20 μm or 10 to 15 μm, preferably 10 to 15 μm.

[0140] The positive active material may be any positive active material known in lithium cell technology. It may be a lithium oxide of at least one transition metal, an LVPF type active material, or a lithium phosphate of at least one transition metal.

[0141] The lithiated oxide of at least one transition metal may be chosen from: i) a lithiated oxide of nickel, manganese and cobalt of formula Liw(NixMn yCOzMt)O2 (NMC) where 0.9 <w<1 ,1 ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci ; ii) un oxyde lithié de nickel, cobalt et aluminium de formule Li w (NixCOyAl z Mt)O2 (NCA) where 0.9 <w<1 ,1 ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci ; iii) un composé de formule Lii +x Mi-xO2-yFy of cubic crystal structure where 0 <x<0,5 et 0<y<1 et M représente un élément choisi dans le groupe constitué de Na, K, Mg, Ca, B, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Y, Zr, Nb, Mo, Ru, Ag, Sn, Sb, Ta, W, Bi, La, Pr, Eu, Nd et Sm et des mélanges de ceux-ci ; iv) un oxyde lithié de nickel et de manganèse (NMX) de formule Lia(Nii-x-y-zMn xCOyMz)O2 with 0.9 <a<1 ,1 ; 0,60<1-x-y-z<0,80 ; 0<x ; 0<y<0,02 ; 0<z ; et M étant choisi dans le groupe consistant en Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ga, Ta, Nd, Pr, La et des mélanges de ceux-ci ; v) un oxyde lithié de nickel et de manganèse de formule Liw(Ni x Mn y CozMt)O2 where 1,1 <w<1 ,6 ; 0<x ; 0,50<y<0,80 ; 0<z<0,02 ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci. vi) un oxyde lithié de nickel et de manganèse de formule LixMn2.y.zM'yM"zO4-5où M' et M" sont choisis dans le groupe consistant en B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb et Mo;. M' et M" étant différents l’un de l’autre, et 1<x<1 ,4 ; 0<y<0,6 ; 0<z<0,2 ; 0<5<1 , et des mélanges de différents composés des catégories i) à vi).

[0142] LVPF type active ingredients have the formula Lii+xVi.yMyPCLFz with 0 <x<0,15, 0<y<0,5, 0.8<z<1 ,2, et M est choisi parmi le groupe consistant en Ti, Al, Mg, Mn, Fe, Co, Y, Cr, Cu, Ni et Zr.

[0143] The lithium phosphate of at least one transition metal may be chosen from: a) a lithium iron phosphate of formula Li x Fei-yM y PO4 (LFP), where 0.8 <x<1 ,2 ; 0<y<0,6 et M est choisi dans le groupe consistant en Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Mn, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S et des mélanges de ceux-ci ; b) un phosphate lithié de manganèse de formule Li x Mni-yM y PO4 (LMP), where 0.8 <x<1 ,2 ; 0<y<0,6 et M est choisi dans le groupe consistant en Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Fe, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S et des mélanges de ceux-ci ; c) un phosphate lithié de manganèse et de fer de formule : Li x Mni-y-zFe yMzPO4 (LMFP) where 0.8 <x<1 ,2 ; 0,5<1-y-z<1 ; 0<y+z<0,5 ; 0<y<0,50 et 0<z<0,2 et M est choisi dans le groupe constitué de Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S et des mélanges de ceux-ci ; d) et des mélanges de différents composés des catégories a) à c).

[0144] The term "positive electrode" refers to the electrode functioning as a cathode when the battery is discharging, and the electrode functioning as an anode when the battery is charging.

[0145] The negative electrode comprises a current collector at least one of whose faces is coated with a layer of a negative active material composition. The current collector is prepared in a conventional manner. The negative electrode active material is not particularly limited. It can be selected from the following groups and mixtures thereof:

[0146] - Metallic lithium or a metallic lithium alloy

[0147] - Graphite

[0148] - Silicon

[0149] - Anode-free type

[0150] - a titanium and niobium oxide of the TNO type

[0151] - a lithiated titanium oxide or a titanium oxide capable of being lithiated, of the LTO type.

[0152] Examples of lithiated titanium oxides are spinel Li4TisOi2, Li2TiOs, ramsdellite Li2TiaO7, LiTi2O4, Li x Ti2C>4, with 0 <x<2 et Li2Na2TieOi4. Un composé LTO préféré a pour formule Li^aMaTis-bM’bCU, par exemple Li4Ti50i2 qui s’écrit encore Li^sTis / sC

[0153] The term "negative electrode" refers to the electrode functioning as an anode when the battery is discharging, and the electrode functioning as a cathode when the battery is charging.

[0154] According to another object, the present invention also relates to an electrochemical module comprising the stack of at least two electrochemical elements according to the invention, each element being electrically connected to one or more other element(s).

[0155] The term "module" therefore designates the set of several electrochemical elements, this set being able to be in series and / or in parallel.

[0156] According to another object, the invention also relates to a battery or "accumulator" comprising one or more modules according to the invention. The term "battery" therefore designates the set of one or more modules according to the invention.

[0157] Example of a process for preparing electrolyte materials according to the invention

[0158] The electrolyte material according to the invention can be prepared according to the following protocol:

[0159] Step a /

[0160] The elastomeric polymer (for example, a hydrogenated nitrile rubber HNBR), a compound carrying at least one anionizable group (for example, adipic acid or sebacic acid), a base capable of anionizing these anionizable groups (such as LiOH) and an elastomer crosslinking agent (for example, the compound sold under the name Luperox® Di) are mixed. The amount of base used is substantially stoichiometric with the amount of anionizable groups: for example, for 0.53 g of adipic acid, 0.174 g of LiOH is used. The amount of crosslinking agent is adjusted according to the knowledge of a person skilled in the art. The amount of compound carrying at least one anionizable group may be, for example, 5% by mass relative to the mass of elastomeric polymer.

[0161] These ingredients can be mixed in an extruder or mixer, for example of the Xplore® brand. The mixing is carried out at a temperature T 1 located between the melting temperature of the elastomer and the activation temperature of the crosslinking agent (for example 80 °C with HNBR and Luperox® Di). Preferably, these ingredients are mixed sequentially, first mixing the elastomer, the base and the compound carrying the anionizable groups until a homogeneous mixture is obtained, then adding the crosslinking agent.

[0162] Step b /

[0163] To the mixture obtained in step a / is added a thermoplastic polymer (for example a polycaprolactone having a molecular mass of approximately 80,000 g / mol). This addition can be carried out by heating, to facilitate mixing, but always at a temperature lower than the activation temperature of the crosslinking agent (for example up to 120°C). The mass quantity of thermoplastic polymer can be, for example, substantially equivalent to the mass quantity of the mixture obtained in step a.

[0164] Step c /

[0165] The mixture obtained in step b is heated to a temperature T2 higher than the activation temperature of the crosslinking agent (e.g. 170°C), while being continuously mixed. The elastomeric polymer crosslinks.

[0166] Step d /

[0167] After crosslinking the elastomeric polymer, an alkali metal salt (e.g. LiTFSI) is added to the mixture obtained in step c, still at temperature T2. Mixing continues until homogenization. The amount of alkali metal salt is approximately 30% by mass of the mass of the mixture obtained in step c.

[0168] The resulting electrolyte material typically comprises about 35% by mass of elastomeric phase, about 40% by mass of thermoplastic polymer and about 25% by mass of alkali metal salt.

[0169] More specifically, a material according to the invention MI1 was prepared according to the following protocol:

[0170] Step 1: Elastomeric phase mixing - preparation of mixture 1

[0171] - Mixture of 0.53 g of sebacic acid and 0.126 g of LiOH (stoichiometric acid-base ratio) with 10 g of HN BR (hydrogenated butadiene-acrylonitrile copolymer) on a cylinder mixer at 60°C,

[0172] - Heating of the extruder (Xplore) to 80°C, rotation of the screws at 80rpm,

[0173] - Addition of the HNBR / sebacic acid / LiOH mixture and homogenization for 5 min,

[0174] - Addition of 0.25g of Luperox and homogenization for 5 min,

[0175] - Extrusion of the mixture.

[0176] Step 2: Preparation of the final material

[0177] - Heating the extruder to 80°C, rotating the screws at 30rpm, - Adding 5.22g of mixture 1 and homogenizing by gradually increasing the speed to 80rpm in 5min,

[0178] - Change of temperature setpoint to 170°C,

[0179] - Addition of 5.6g of polycaprolactone and increase of speed to 150rpm,

[0180] - Addition of 3.41g of LiTFSI,

[0181] - Once the temperature of 170°C is reached, homogenize for 20 minutes,

[0182] - Extrusion of the mixture.

[0183] Two other comparative materials MC1 and MC2 were also prepared, MC1 having been obtained following the same protocol as described above but without the addition of sebacic acid or LiOH, and MC2 having been obtained following the same protocol as described above but without the addition of LiOH.

[0184] MI1 is therefore a material according to the invention in which the crosslinked elastomer phase comprises elastomer polymer chains carrying COO' groups. The material MC1 does not comprise an anionic group, and the material MC2 is a material in which the crosslinked elastomer phase comprises elastomer polymer chains carrying COOH groups in protonated, therefore non-anionic, form.

[0185] Cells comprising each of these three materials were prepared according to the following protocol: films from MI1, MC1 and MC2 of respectively 160pm, 170pm and 160pm were obtained by calendering. These were then laminated between two sheets of Li metal and then integrated into a button cell.

[0186] Dendritic growth resistance was assessed by cycling each cell successively at 300, 400, 500 and 600pA / cm2 for 30min per cycle for 50 cycles at each current density at 80°C. Dendritic growth resistance was measured by determining the cycle at which the cut-off potential (4.5 V) was first reached. Table 1 below shows the results obtained for the three cells.

[0187] Table 1 These results clearly illustrate that the presence of anionic groups on the elastomeric polymer chains makes it possible to obtain a solid polymer electrolyte material for solid polymer electrolytes with excellent ionic conductivity combined with high mechanical properties, while minimizing the formation of dendrites.

Claims

CLAIMS 1. A solid polymer electrolyte material comprising an alkali metal salt and a thermoplastic rubber matrix, wherein the thermoplastic rubber matrix comprises a mixture of at least one crosslinked elastomeric phase and at least one thermoplastic polymer phase, said crosslinked elastomeric phase comprising elastomeric polymer chains carrying one or more anionic groups.

2. A solid polymer electrolyte material according to claim 1, wherein the crosslinked elastomeric phase is in the form of nodules dispersed in the thermoplastic polymer phase.

3. Solid polymer electrolyte material according to claim 2, wherein the crosslinked elastomeric phase nodules have a diameter less than or equal to 5 pm, preferably less than or equal to 2 pm, preferably less than or equal to 1 pm, preferably less than or equal to 0.5 pm, preferably between 10 nm and 5 pm.

4. Solid polymer electrolyte material according to any one of the preceding claims, in which the anionic group(s) are grafted, preferably indirectly, to the elastomeric polymer chains of the crosslinked elastomeric phase.

5. Solid polymer electrolyte material according to any one of the preceding claims, wherein the anionic group(s) are chosen from carboxylate, sulfonate, sulfonylimidate, borate, phosphate, phosphonate and phosphinate groups.

6. A solid polymer electrolyte material according to any preceding claim, wherein the alkali metal salt is a lithium salt.

7. Solid polymer electrolyte material according to any one of the preceding claims, wherein the elastomer is selected from unsaturated or saturated rubbers, preferably the elastomer is a styrene-ethylene-butadiene-styrene polymer.

8. A solid polymer electrolyte material according to any preceding claim, wherein the thermoplastic polymer is polycaprolactone.

9. A solid polymer electrolyte material according to any preceding claim, wherein the thermoplastic polymer has a multimodal molecular weight distribution, in particular has a trimodal molecular weight distribution.

10. A solid polymer electrolyte material according to any preceding claim, wherein the thermoplastic rubber matrix further comprises a dopant, preferably selected from trimethylphosphate, triethylphosphate, fluoroethylene carbonate and vinylene carbonate.

11. A solid polymer electrolyte material according to any preceding claim, comprising: - 10 to 70% by weight of crosslinked elastomer phase; - 10 to 70% by weight of thermoplastic polymer; - 10 to 45% by weight of alkali metal salt; - 0 to 70% by weight of dopant; and - 0 to 20% by weight of additives.

12. A method for preparing a solid polymer electrolyte material according to any one of the preceding claims, comprising the following steps: a) mixing an elastomeric polymer, a crosslinking agent, a compound carrying at least one anionic or anionizable group, and optionally a base capable of anionizing said anionizable group, at a temperature T1, where T1 is between the melting temperature of the elastomeric polymer and the activation temperature of the crosslinking agent, b) adding an alkali metal salt and a thermoplastic polymer to the mixture obtained in step a), and c) mixing the mixture obtained in step b) at a temperature T2, where T2 is higher than the activation temperature of the crosslinking agent.

13. A method of preparing a solid polymer electrolyte material according to any one of claims 1 to 11, comprising the following steps: a') mixing an elastomeric polymer, a crosslinking agent, a compound carrying at least one anionic or anionizable group, and optionally a base capable of anionizing said anionizable group, at a temperature T1, where T1 is between the melting temperature of the elastomeric polymer and the activation temperature of the crosslinking agent, b') adding a thermoplastic polymer to the mixture obtained in step a'), c') mixing the mixture obtained in step b') at a temperature T2, where T2 is higher than the activation temperature of the crosslinking agent, and d') adding an alkali metal salt to the mixture obtained in step c').

14. A solid polymer electrolyte comprising a solid polymer electrolyte material according to any one of claims 1 to 11.

15. Electrochemical element comprising an electrolyte according to claim 14, further comprising a positive electrode and a negative electrode.

16. Battery comprising one or more modules, each module comprising the stack of at least two electrochemical elements according to claim 15.

Images