Solid anionic conduction electrolyte

Abstract

The invention relates to a crosslinkable anionic electrolyte precursor comprising: - a first hydrocarbon monomer having two thiol groups and a second hydrocarbon monomer having two C=C double bonds, - a charge carrier comprising a hydrocarbon compound having at least one or two C=C double bonds and an organic cation, said cation being associated in particular with an anion, - a crosslinking agent comprising a hydrocarbon compound having at least three C=C double bonds. Figure 1 to be published

Description

Title of the invention: Anionic conduction solid electrolyte technical field

[0001] The invention relates to the preparation of solid polymeric electrolytes with anionic conduction, particularly for applications in the field of anion shuttle batteries. Previous technique

[0002] The invention, for preparing this type of electrolyte, uses the so-called thiol-ene reaction:

[0003] The thiol-ene reaction (also called alkene hydrothiolation) is a reaction between a thiol and an alkene to form a thioether. This reaction, first reported in 1905, gained importance in the late 1990s and early 2000s due to its feasibility and its wide range of applications, particularly for electrolytes.

[0004] Thiols are excellent nucleophiles through the formation of thiolate anions (RS) and are also electrophiles via thiyl radicals (RS). One of the most studied reactions involving thiols is the hydrothiolation of double bonds (C=C). Depending on the nature of the substituents of the double bond, namely electron donors or acceptors, and the type of catalyst used, the reaction of the thiol group with the C=C double bond can occur via a radical or nucleophilic mechanism.

[0005] In the case of a nucleophilic mechanism, the reaction is the Michael addition on a double bond substituted by an electron-withdrawing group, such as (meth)acrylates (monomers containing an active double bond), and a nucleophilic base is used as a catalyst.

[0006] In the case of a radical mechanism, electron-withdrawing substituents (monomers containing an active double bond) are avoided in order to prevent the polymerization of unsaturated species and uncontrolled side reactions. Preferably, non-activated monomers such as allyl or vinyl ethers are used. Hydrothiolation can then be initiated thermally or photochemically.

[0007] Anion exchange membranes based on ionic polybenzimidazoles crosslinked by thiol-ene reaction are known from the publication "Anion exchange membranes based on ionic polybenzimidazoles crosslinked by thiol-ene reaction" by Zelalem Gudeta Abdi and Al. Reactive and Functional Polymers 156 (2020) 104719, DOI10.1016 / j.reactfunctpolym.2020.104719 of anion-conducting polymer networks made by thiol-ene chemistry, these polymers bearing cations crosslinked by a thiol-ene type reaction.

[0008] US patent 5,593,795 also discloses a polymer electrolyte composition obtained also by a thiol-ene type reaction, for use in lithium-ion batteries.

[0009] The invention aims at developing an improved anionically conductive polymer-type electrolyte in solid form, synthesized via a thiol-ene reaction. It also aims at developing a process for its synthesis from precursor(s) and the development of said precursor(s). Summary of the invention

[0010] The invention relates firstly to a crosslinkable anionic unipolar conduction electrolyte precursor comprising: - a first hydrocarbon monomer containing two thiol groups, called di-thiol, - a second hydrocarbon monomer containing two C=C double bonds, called divalent alkene or divinyl, - a charge carrier comprising a hydrocarbon compound having at least one or two C=C double bond(s) and an organic cation, said cation being notably associated with an anion, for example chosen from compounds of fluorine or chlorine or boron, or being dicyanoamidide, - a crosslinking agent comprising a hydrocarbon compound having at least three C=C double bonds, called a multivalent alkene.

[0011] In the present invention, "precursor of crosslinkable anionic unipolar conduction electrolyte" means a mixture of compounds, including the four types of compounds listed above, which, after crosslinking, makes it possible to obtain an anionic unipolar conduction electrolyte, in particular of the solid type.

[0012] In the present invention, "solid" material means a material that is not liquid, and which can therefore include a solid material in the strict sense or a gel-type material.

[0013] In the present invention, "comprising two thiol functions" means that the first monomer comprises only two thiol functions.

[0014] In the present invention, "comprising two C=C double bonds" means that the second monomer preferably comprises only two C=C double bonds.

[0015] In the present invention, "cation being notably associated with an anion" means that - in the precursor, the cation is found attached to the hydrocarbon component of the charge carrier

[0016] - in the final cross-linked electrolyte, the cation is also found fixed / grafted onto the polymer of the final electrolyte, - in both cases, the anion is associated with the cation but is, itself, free, that is to say not fixed on one of the components of the precursor or on the final polymer of the electrolyte.

[0017] This precursor formulation therefore contains different components, each having a function / contribution in the final solid polymer (after crosslinking):

[0018] The first monomer and the second monomer are intended to react together according to a click chemistry thiol-ene reaction to form a polymeric structure. The crosslinking agent is intended to play its role within the polymer structure, to create crosslinking nodes and a three-dimensional polymer network. The charge carrier will enable the desired anionic conduction within the electrolyte. In fact, the cations of the charge carrier will be "immobilized" in the polymer network; this is referred to as unipolar conduction.

[0019] The association of these two divalent monomers, namely di-thiol and divalent alkene, has proven to be very relevant for creating polymer chains, and the crosslinker in the form of a multivalent alkene has also proven to be very effective in obtaining the desired level of crosslinking, and thus obtaining an electrolyte with the desired conductivity and mechanical / rheological properties.

[0020] The fact that the cation is grafted to the polymer network during its formation prevents it from diffusing and creates a unipolar conducting network (also called a "single-ion" network). Unipolar conduction limits / prevents the formation of concentration gradients in species during the passage of ions through the electrolyte, thus avoiding a problematic phenomenon in electrochemical systems such as batteries. Indeed, if the ion concentration gradient is too steep, the concentration of the transported species (here, anions) can become zero near one of the electrodes, and the electrolyte becomes blocking, meaning that locally the electrolyte is no longer conductive, with the charge carrier concentration approaching zero. In this case, the resistance of the electrolyte in a battery can increase sharply and prevent the system from supplying more current.

[0021] Preferably, the stoichiometry (expressed in moles) between the number of thiol functions of the first monomer and the number of C=C double bonds of the second monomer, the crosslinker and the charge carrier can be between 0.9 and 1.1, and is preferably equal to 1. It is desirable to limit any excess of thiol functions relative to the C=C double bond functions. Indeed, in a thiol-ene type reaction carried out in the invention, it is possible to react several C=C double bonds with the same thiol, but the reverse is not True, and an (excessive) amount of thiol could cause a problem in the way crosslinking occurs.

[0022] Preferably, the amount of the charge carrier may be between 10 and 25% by mass of said precursor. Note that this proportion is found in the electrolyte once crosslinked (excluding any solvent).

[0023] Preferably, a first part of the crosslinker can be provided to compensate for the termination of the polymer chains of the charge carrier, which is a function of the number of C=C double bonds carried by the charge carrier and by the crosslinker.

[0024] Preferably, a second part of the crosslinking agent may be provided to crosslink the precursor, the quantity of this second part preferably being between 1% and 5% mass of said precursor.

[0025] Indeed, the quantity of crosslinking agent to be added to the precursor according to the invention can be defined as follows:

[0026] The first part of the crosslinking agent mentioned above is intended to compensate for the termination of polymer chains by the (monovalent) charge carrier. This quantity of crosslinking agent is calculated based on the functionality of the chosen molecule (for example, 3 for a trivinyl cyclohexane type crosslinking agent, 4 for a tetramethyltetravinyl cyclo-tetrasiloxane type crosslinking agent). For x moles of charge carriers, y moles of crosslinking agent with functionality F must be added, where F is the number of C=C double bond functions, in order to comply with the formula:

[0027] (F-ÿxy-x

[0028] The second part of the crosslinking agent mentioned above is intended to crosslink the network; it is given as a mass percentage of the precursor formulation and is also referred to in the context of the present invention as the "effective crosslinking agent." It is preferably chosen to be between 0.5% and 10% by mass, and more preferably between 1% and 5% by mass of the crosslinkable precursor, as indicated above.

[0029] Preferably, the first monomer can be chosen from at least the following di-thiols: 2,2'-(ethylenedioxy)diethanethiol, which is the preferred di-thiol, but also 1,4-butane dithiol and 1,2-ethane dithiol.

[0030] Preferably, the second monomer can be chosen from at least one of the following divalent alkenes: triethylene glycol divinyl ether, which is the preferred compound, but also an oligo- or poly-(ethylene glycol) divinyl ether, diallyl ether, or 1,5-hexadiene.

[0031] This second monomer is in particular intended to modulate the chain lengths in the polymer obtained by reaction between the two monomers, after crosslinking, by varying its stoichiometry relative to that of the crosslinking agent.

[0032] Preferably, the crosslinking agent can be chosen from poly-(methyl-vinyl) siloxanes, in particular from 2,4,6,8-tetramethyl-2,4,6,8-tetravinyl-cyclotetrasiloxane or hexavinyldisiloxane, in particular 2,4,6,8-tetramethyl-2,4,6,8-tetravinyl-cyclotetrasiloxane, tetramethylvinylcyclo-siloxane, poly-methylvinyl-siloxane, trivinyl cyclohexane.

[0033] This component has the role of connecting the different polymer chains together to form a three-dimensional polymer network, and not a linear polymer.

[0034] Preferably, the charge carrier may include at least one cation belonging to the following types of cations: a tetra-alkyl ammonium, a pyrrolidinium, a pyridinium, a piperidinium, a triazolium, an imidazolium, the latter being a preferred charge carrier. The charge carrier is covalently bound to the polymer network after crosslinking of the precursor.

[0035] Preferably, the charge carrier comprising a hydrocarbon compound having one or two C=C double bond(s) comprises a vinyl allyl acrylate or a methyl acrylate.

[0036] Preferably, the charge carrier is chosen from allyl-methyl imidazolium, trimethylammonium propylacrylate, diallyl-dimethyl-ammonium, diallyl-imidazolium, 4-vinyl-1,2,3-triazolium.

[0037] Preferably, the anion associated with the charge carrier can be an anion belonging to at least one of the following types of anions: - a fluorine compound, in particular selected from a fluoride ion, tetrafluoroborate, hexafluorophosphate, difluoro(oxalato)borate, bis(fluorosulfonyl)amide, bis(trifluorosulfonyl)amide - or a chlorine compound, in particular a chloride ion or a perchlorate, - or a boron compound, in particular bis(oxalato)borate, - or dicyanoamidide (nitrogen compound).

[0038] The charge carrier associated with its anion can be allyl-methyl imidazolium chloride or tetrafluoroborate (preferably), or diallyl-dimethyl-ammonium chloride.

[0039] The invention also relates to a precursor of an anionic unipolar conductive crosslinkable electrolyte which is additized, and which comprises - the precursor described above - and at least one additive chosen from at least one of the following additives:

[0040] - at least one sacrificial solvent, in particular selected from ethanol, methanol and the N-methylpyrrolidone (the term "sacrificial" will be explained later)

[0041] - at least one activator or catalyst, in particular selected from among the activators or thiol-ene reaction catalysts

[0042] - at least one plasticizer, in particular selected from at least one of the following types of The following plasticizers: glymes, including tri- and tetraethylene glycol dimethyl ether, succinonitrile, amides, lactams, azoles, sulfonamides, including acetanilide, benzamide, 2-pyrrolidone, 2-piperidinone or acetanilide.

[0043] The optional sacrificial solvent can be added during the precursor formulation to make all the constituent compounds of the precursor (more) miscible with each other. However, it is designated as "sacrificial" because it is intended to be removed, notably by evaporation, before the final use of the material. It no longer forms part of the final composition of the crosslinked electrolyte. It is preferably chosen to be sufficiently volatile and capable of (completely) solubilizing the precursor compounds.

[0044] The amount of sacrificial solvent can be up to 75% by mass of the formulation. Preferably, between 10% and 75% by mass of sacrificial solvent is used in the formulation, more preferably between 25% and 50% by mass of sacrificial solvent. The use of a sacrificial solvent does not significantly change the conductivity properties of the materials once the solvent has evaporated.

[0045] The activator or catalyst functions to initiate the reaction between the monomers with thiol groups (first monomer) and the other components with C=C double bonds, a thiol-ene type reaction. An activator requires an additional specific condition (UV radiation, thermal activation, or others) for the reaction to start, whereas a catalyst can act immediately upon its addition to the precursor formulation.

[0046] The plasticizer serves to improve the ionic conductivity of the electrolyte obtained after crosslinking, by promoting the mobility of the polymer chains and, possibly, by coordinating the transported anion. Molecules such as glymes (tri- and tetraethylene glycol dimethyl ether) or succinonitrile can be used. Preferably, a plasticizer capable of providing a hydrogen bond can also be chosen: this hydrogen bond allows for better affinity with the anion and can facilitate its solvation and transport. This hydrogen bond donor preferably has a high pKa (for example, at least 18), which can prevent its deprotonation and thus avoid the occurrence of side reactions linked to the free proton.The plasticizers useful for the invention can be selected from amides, lactams, azoles, sulfonamides, preferably acetanilide, benzamide, 2-pyrrolidone, 2-piperidinone, preferably acetanilide.

[0047] Preferably, the plasticizer can represent at most 30% by mass of the crosslinkable precursor (the precursor here is without additives, it is not the additive-containing precursor), in particular at most 25% by mass, very preferably at most 20% by mass, even more preferably in the vicinity of 15% by mass.

[0048] The plasticizer is advantageously chosen to be less volatile than the sacrificial solvent when both a sacrificial solvent and a plasticizer are used in the additive version of the precursor.

[0049] The invention also relates to the process of preparing an electrolyte in the form of a crosslinked anionic unipolar conductive solid polymer, in which: - the precursor of an additized crosslinkable anionic unipolar conductive electrolyte comprising the first and second monomers and at least one activator or catalyst as described above is formed, in particular by coating onto a support or by impregnation into the porosity of an electrode or by confinement between two support plates, with possible premixing with an electrode material before coating or confinement; - said formulation is activated as needed to ensure the polymerization of the two monomers, in particular by thermal activation or by exposure to radiation, in particular ultraviolet radiation, or by so-called redox activation; - the sacrificial solvent, when present, is removed, in particular by evaporation (this last step being therefore optional).depending on whether or not a sacrificial solvent is used).

[0050] According to a particular embodiment of this preparation process, said preparation with polymerization / crosslinking of the electrolyte precursor can be carried out sequentially: the addition of activator / catalyst activation is then done in several steps, and at each additional step after the first, a certain quantity of activator / catalyst is added, and a certain quantity of all or part of the components of the additivated crosslinkable anionic electrolyte precursor.

[0051] Indeed, multi-step polymerization can be advantageous for limiting the volatility of certain monomers when the process for preparing the crosslinked electrolyte involves a vacuum treatment step, particularly when the electrolyte is intended to impregnate a porous electrode material. In this case, the addition of an initiator at each step, in addition to the extra monomers, is necessary.

[0052] When using an activator that requires activation, this activation can occur through a radical or anionic mechanism. It can be achieved by irradiation with UV radiation, by thermal activation, or by redox activation (using a peroxide / amine couple). UV radical activation is preferred. The quantity of activator required should be determined by a person skilled in the art.

[0053] Preferably, a mass percentage of activator (or catalyst) is provided to be between 1% and 5% by mass of the precursor (the precursor is considered to be unadditized).

[0054] The "activation" step can thus correspond to: - a defined temperature setting (depending on the activator) for thermal activation - exposure to UV radiation with a defined intensity and wavelength in the case of UV activation - a waiting time to be chosen appropriately in the case of redox activation, where cross-linking starts at the moment of mixing two activators (generally a peroxide and an amine), this can be controlled in particular by the choice of the molar ratio of these two constituents and possibly by the presence of an inhibitor.

[0055] Activation by exposure to radiation, also called photo-induced, can be carried out with a UV lamp or stereolithography.

[0056] Redox activation can be carried out as follows: the reaction can be initiated using a peroxide (most preferably benzoyl peroxide, BPO) and an amine (preferably N,N-dimethyl-p-toluidine or p-tolyldiethanolamine). An inhibitor can be added to slow down radical generation (preferably 4-methoxyphenol or 4-hydroxy-2,2,6,6-tetramethylpiperidine-l-oxyl / TEMPOL). Radicals are generated immediately upon mixing the first two components, which must be added just before the electrolyte is formed. The amounts of peroxide, amine, and inhibitor are chosen by those skilled in the art.

[0057] It is also noted that when several additives are added to the precursor, they are not necessarily added simultaneously. Thus, it is possible to add the plasticizer and / or the sacrificial solvent first, and then add the activator later, for example when preparing the electrolyte, for example during its shaping.

[0058] The invention also relates to an electrolyte in the form of a solid polymer with unipolar anionic conduction, and obtained by crosslinking the precursor (in particular additized) described above or obtained by the preparation process described above.

[0059] The invention also relates to a solid electrolyte comprising a crosslinked polymer with unipolar anionic conduction in a non-aqueous medium and an organic cation grafted by covalent bond to said crosslinked polymer. The said organic cation can in particular be chosen from among a tetra-alkyl ammonium, an imidazolium, a pyrrolidinium, a pyridinium, a piperidinium, a triazolium (The same cation, in particular, as that described above for the precursor). The said organic cation can notably be associated with an anion chosen from - a fluorine compound, in particular selected from a fluoride ion, tetrafluoroborate, hexafluorophosphate, difluoro(oxalato)borate, bis(fluorosulfonyl)amide, bis(trifluorosulfonyl)amide - or a chlorine compound, in particular a chloride ion or a perchlorate, - or a boron compound, in particular bis(oxalato)borate - or dicyanoamidide (nitrogen compound) (The same anion, in particular, as that described above for the precursor).

[0060] This type of electrolyte can in particular be obtained from the precursors described above.

[0061] This type of electrolyte can notably be prepared by thiol-ene click chemistry, in particular from a first hydrocarbon monomer having two thiol groups and a second hydrocarbon monomer having two C=C double bonds, a charge carrier comprising a hydrocarbon compound having one or two C=C double bond(s) and an organic cation, said cation being notably intended to be associated with an anion selected from fluorine or chlorine or boron compounds or to be dicyanoamidide - a crosslinking agent comprising a hydrocarbon compound having at least three C=C double bonds (preferably the same anions and cations as those described above).

[0062] The invention also relates to any electrochemical system, particularly a battery-type system, comprising at least one electrode containing the electrolyte as described above or obtained by crosslinking the precursor as described above or obtained by the preparation process described above. The solid electrolyte according to the invention can thus be a component of at least one of the electrodes, namely the negative electrode (negolyte or anolyte) and / or the positive electrode (posolyte or catholyte) of an electrochemical system.

[0063] This refers in particular to battery-type electrochemical systems equipping vehicles (two, three or four wheels) with electric motors, but also to any electrochemical / battery system for stationary electrical energy storage or any portable electrical application. List of figures

[0064] Figures 1 to 4 illustrate the invention by way of non-limiting example.

[0065] [Fig.1]

[0066] Fig. 1 is a graph representing the ionic conductivity (S / cm) as a function of temperature (1000 / T with T in K) of electrolytes according to the invention with different quantities of charge carrier.

[0067] [Fig.2]

[0068] Fig. 2 is a graph representing the ionic conductivity (S / cm) as a function of temperature (1000 / T with T in K) of electrolytes according to the invention with different plasticizers.

[0069] [Fig.3]

[0070] Fig. 3 is a graph representing the ionic conductivity (S / cm) as a function of temperature (1000 / T with T in K) of electrolytes according to the invention with plasticizers with and without hydrogen bonding.

[0071] [Fig.4]

[0072] Fig. 4 is a graph representing the ionic conductivity (S / cm) as a function of temperature (1000 / T with T in K) of electrolytes according to the invention with a charge carrier associated with two different anions. Description of the implementation methods

[0073] The invention will be described below with the aid of four non-limiting sets of examples illustrated by figures 1 to 4.

[0074] The invention therefore relates to a crosslinkable anionic unipolar conduction electrolyte precursor comprising: - a first hydrocarbon monomer containing two thiol groups, called di-thiol - a second hydrocarbon monomer containing two C=C double bonds, called a divalent alkene - a charge carrier comprising a hydrocarbon compound having a C=C double bond and an organic cation, said cation being associated with an anion chosen from compounds of fluorine or chlorine or boron or possibly being a dicyanoamide - a crosslinking agent comprising a hydrocarbon compound having at least three C=C double bonds, called a multivalent alkene,

[0075] - to which one or more additives are added before shaping and crosslinking to obtain an anionic unipolar conductive polymeric material.

[0076] The crosslinkable electrolyte formulation according to the invention may contain a radical initiator or anionic activator to subsequently initiate the polymerization / crosslinking reaction. In one embodiment, this activator may be added to the formulation according to the invention during the polymerization / crosslinking reaction.

[0077] The resulting formulation can be crosslinked by any technique known to a person skilled in the art.

[0078] In the electrolyte formulation according to the invention, the stoichiometry between the number of thiol functions of the first monomer and the number of C=C double bonds of the second monomer, the crosslinker and the charge carrier is advantageously between 0.9 and 1.1, and is preferably equal to 1, in order to obtain a crosslinkable formulation having the rheological properties allowing good implementation. This formulation makes it possible to obtain an electrolyte with both increased ionic conductivity and resistance to chemical degradation.

[0079] In particular, according to a preferred embodiment, the invention can implement the association of three organic molecules: 2,2'-(ethylenedioxy)diethanethiol, triethylene glycol divinyl ether and polymethylvinylsiloxane as a crosslinker, in the presence of a charge carrier which is allyl-methyl-imidazolium chloride or allyl-methyl-imidazolium tetrafluoroborate.

[0080] The anionic unipolar conduction electrolyte obtained by crosslinking can be used as a solid battery electrolyte, as a component of the negative electrode (negolyte or anolyte) or positive electrode (posolyte or catholyte).

[0081] In one embodiment, a chain terminator compound may optionally also be added to the crosslinkable electrolyte formulation according to the invention to create dangling chains during crosslinking: it may be any molecule bearing a single C=C double bond, but the presence of ether or poly(ethylene glycol) functions is desirable.

[0082] At the end of the reaction, an anionic conducting polymer is formed, this polymer may contain a so-called sacrificial solvent trapped if a solvent is present, which can then be removed / evaporated in order to obtain a solid material.

[0083] In electrolyte formulations according to the invention, the thiol / double bond ratio is generally stoichiometric or in a slight excess of C=C double bonds; on the other hand, an excess of thiol is not desirable.

[0084] The composition of the formulation can be modified, adapted, in particular by varying the quantity of crosslinker and charge carrier.

[0085] The quantity of charge carrier as well as activator (radical or anionic initiator in particular) can also be modified and a plasticizer can be added.

[0086] The crosslinking agent may be selected from compounds bearing at least one Si-O-Si siloxane motif and at least three vinyl functionalities (C=C double bonds), advantageously at a concentration of between 0.5% and 20% by mass relative to the total mass of the formulation, most preferably between 1% and 15% by mass, and even more preferably between 1% and 5% by mass. The crosslinking agent is preferably a polymethylvinylsiloxane. In the following description, the term vinylsiloxane crosslinking agent refers to linear or cyclic oligomethylvinylsiloxanes or any crosslinking agent comprising at least three vinyl functionalities and at least one Si-O-Si bond.

[0087] In the crosslinkable electrolyte formulation according to the invention, the ratios between the different components are chosen according to appropriate criteria to obtain the rheological properties of the formulation to ensure good implementation, and good conductivity of the crosslinked electrolyte (once the sacrificial solvent has evaporated if there is one) and optimized mechanical properties of the crosslinked electrolyte.

[0088] The root or anionic initiator, preferably radical (AIBN and TPO in the following non-limiting examples), allows the crosslinking reaction to begin.

[0089] The initiator can be activated thermally (for example, a diazo compound or peroxide) or by UV radiation or by redox activation. Any initiator known to those skilled in the art, in particular any commercial initiator, can be chosen.

[0090] The quantity of initiator to be used advantageously represents between 0.01 and 0.05 times the mass of the mixture of crosslinkable reagents (i.e. the mass of the formulation of the unadditized precursor), the choice of the exact quantity is adjusted by the person skilled in the art.

[0091] For redox activation, the reaction can be initiated using a peroxide (most preferably benzoyl peroxide, BPO) and an amine (preferably N,N-dimethyl-p-toluidine or p-tolyldiethanolamine). An inhibitor can be added to slow down radical generation (preferably 4-methoxyphenol or 4-hydroxy-2,2,6,6-tetramethylpiperidine-l-oxyl / TEMPOL). Radicals are generated immediately upon mixing the first two components, which must be added just before shaping the electrolyte. The amounts of peroxide, amine, and inhibitor are chosen by those skilled in the art.

[0092] Preferably, the crosslinking agent is 2,4,6,8-tetramethyl-2,4,6,8-tetravinyl-cyclotetrasiloxane. This molecule has the particular advantage of being commercially available and does not contain easily hydrolyzable functions (ester, amide, etc.) that could potentially weaken the network.

[0093] In the case of a poly-methylvinylsiloxane useful for the invention, the chain length is not important as long as it is greater than or equal to 4 monomers (which gives a linear polymer of viscosity 3-7 cSt), i.e. the average functionality of the monomer is greater than or equal to 4.

[0094] The use of a crosslinker according to the invention makes it possible to obtain a greater number of vinyl functions on the crosslinker and therefore to obtain networks with better mechanical strength for the same quantity of crosslinker used.

[0095] Another advantage of this family of crosslinking agents is that crosslinking via click chemistry is more efficient and the reagents are relatively inexpensive.

[0096] Furthermore, the use of a vinylsiloxane crosslinking agent also improves the ionic conductivity of the electrolyte (shown in the examples), probably due to increased mobility of the polymer chains within the network. Without being bound by any particular theory, this enhanced mobility of the vinylsiloxane chains is partly explained by the high angle of the Si-O-Si bond (145°).

[0097] Advantageously, a crosslinking agent based on a polysiloxane bearing at least three vinyl functions and preferably having a viscosity greater than or equal to 3 cSt can be used, preferably cyclo-tetravinyl siloxane or a poly-(methyl- vinylsiloxane) [p-MVS] of variable molar mass. In practice, poly-(methyl-vinyl siloxane) is generally marketed according to its viscosity (expressed in centistokes or cSt). Two different polymers, 3-5 cSt and 7-15 cSt, are shown in the examples, but in practice any poly-(methyl-vinyl siloxane) can be suitable. Viscosity is a function of the polymer's molar mass, that is, the number of monomer units.

[0098] For example, polymethylvinylsiloxane 7-15 cSt is immiscible with other reagents and requires a sacrificial solvent, for example acetone, for its preparation. The sacrificial solvent is then removed by evaporation to obtain an all-solid electrolyte. If another product used as a plasticizer is added, it is preferably chosen to be less volatile than the sacrificial solvent so as not to evaporate along with the sacrificial solvent.

[0099] The sacrificial solvent may be, without limitation, selected from at least one of the following compounds: N-methylpyrrolidone (NMP), acetone, methylethyl ketone, toluene, anisole, acetonitrile, chloroform, dichloromethane, diethyl ether, methyl tert-butyl ether, 2-methyltetrahydrofuran (2-MeTHF), dioxane, 1,2-dimethoxyethane (DME), THF, methoxycyclopentane, dimethyl carbonate, methylisobutyl ketone, alone or in mixture, hexane (in mixture), heptane (in mixture).

[0100] Solvent mixtures are also possible. In practice, any solvent that makes all the reactants miscible can be used. Acetone is particularly preferred for solubilizing the p-MVS 7-15 cSt crosslinker.

[0101] Activation of the crosslinking can be achieved after the addition of the radical or anionic initiator, or by implementing the radical or anionic initiator already present in the formulation by photo-induction or by thermal activation or by redox activation.

[0102] Photo-induction can be achieved using a UV lamp or stereolithographic techniques, including lasers, LCD screens, and 3D printing (also known as additive manufacturing). The invention can be applied, in particular, to the 3D printing of batteries, especially vehicle batteries.

[0103] The crosslinkable precursor according to the invention can be coated in liquid form onto an electrode already prepared according to protocols known to those skilled in the art so that the liquid formulation wets the porosity of the electrode. Crosslinking is then obtained after thermal or photo-initiation (UV).

[0104] In one embodiment of the invention, the formulations according to the invention can be used to formulate an electrode ink. This ink, once coated and dried, can constitute a solid electrode. Characterization technique

[0105] The ionic conductivity of an electrolyte is measured in S / cm and characterizes the electrolyte's ability to transport ions.

[0106] The ionic conductivity of the electrolyte is measured by electrochemical impedance spectroscopy in a Biologie® CESH cell. The measurement is performed at several temperatures using a Biologie® ITS temperature-controlled chamber. The impedance spectrum is acquired using a Biologie® MTZ 35 potentiostat between 30 MHz and 0.1 Hz around 0 V and with an amplitude of 10 mV. The conductivity value can be determined by fitting the curve with an equivalent circuit of the type (RI + R2 / / CPE1 + CPE2) or visually by taking the value of the real part of the impedance Re(Z) at the minimum reached by the curve between the semicircle and the half-line corresponding to the capacitive part on the Nyquist diagram. Advantages of the invention

[0107] The crosslinkable anionic unipolar conductive electrolyte formulation according to the invention has the advantage, in particular compared to already polymerized polymers, of being liquid at the start, which allows good cohesion to be obtained at the interfaces with the electrodes, in particular due to an facilitated filling of the porosity of the materials constituting the electrodes.

[0108] The rheological behavior obtained for the crosslinked electrolyte examples according to the invention advantageously corresponds to that of a crosslinked polymer. Examples

[0109] In all the following examples, the samples are designated and prepared in the following manner:

[0110] All electrolytes are prepared using

[0111] as a charge carrier with its following counter-ion: - either allyl-methyl-imidazolium chloride - either allyl-methyl-imidazolium tetrafluoroborate

[0112] and as a crosslinking agent methyl-vinyl-tetracyclosiloxane.

[0113] The first monomer with two thiol functions is 2,2'-(ethylenedioxy)diethanethiol.

[0114] The second monomer with two C=C double bonds is triethylene glycol. divinyl ether.

[0115] The effective crosslinker is present at a level of 5% by mass of the network (which here corresponds to the quantities of di-thiol, divalent alkene and trivalent alkene of the precursor mixture before addition of additives, therefore to the quantity of the two monomers and the crosslinker).

[0116] The reactants, corresponding here to the crosslinkable precursor to which a plasticizer is added, are mixed in the presence of a sacrificial solvent (35 wt. methanol for the examples with allyl-methylimidazolium chloride and 17 wt. for examples with allyl-methyl-imidazolium tetrafluoroborate) until a homogeneous sample is obtained.

[0117] The UV activator is the commercial reference product Irgacure 2959, marketed by the company MERCK and corresponding to 2-Hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, for tests with allyl-methyl-imidazolium chloride.

[0118] The UV activator is TPO, which is diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, for tests with allyl-methylimidazolium tetrafluoroborate).

[0119] In both cases, it is added to the precursor which has been additively mixed with the plasticizer, and then the latter is placed between a glass plate and another glass plate covered with Teflon® tape. The two plates are separated by a 0.5 mm steel spacer.

[0120] The sample is crosslinked by irradiation at 365 nm at 1800 W / m2 for 10 seconds using a Delolux 20 lamp.

[0121] The electrolyte sample is separated from the two glass plates, dried under vacuum at room temperature (approximately 20°C) overnight, and its ionic conductivity is measured by electrochemical impedance spectroscopy in a CESH cell manufactured by Biologie® with an MTZ-35 impedance meter, the temperature is controlled by an ITS peltier system also manufactured by Biologie®.

[0122] Samples not containing plasticizer are named according to the mass percentage of charge carrier present (for example: 15% imidazolium)

[0123] A sample containing plasticizer is named according to the total mass of plasticizer in the sample, after evaporation of the sacrificial solvent if present (for example: 10% acetanilide)

[0124] When, in an example, samples containing plasticizer and samples not containing plasticizer are present, the quantity of charge carrier present in the crosslinkable mixture is always the same, and given by the unplasticized sample which serves as a reference. Examples: la, lb, lc, ld

[0125] This series of examples aims to measure the impact of the amount of charge carrier on the ionic conductivity of the electrolyte according to the invention. This example specifically aims to study the effect of the amount of charge carrier, rimidazolium, present in the polymeric network of the electrolyte on its ionic conductivity.

[0126] For this purpose, four electrolytes containing different amounts of charge carrier and an identical amount of effective crosslinker are compared. Example 1a corresponds to a content of 10% mass of imidazolium (curve 1 on the graph in [Fig. 1])

[0127] Example 1b corresponds to a content of 15% mass of imidazolium (curve 2 on the graph of [Fig.1]).

[0128] The example corresponds to a content of 20% mass in imidazolium (curve 3 on the graph of [Fig.1]).

[0129] Example Id corresponds to a content of 25% mass of imidazolium (curve 4 on the graph of [Fig.1]).

[0130] The results are grouped in the graph of [Fig.1]: it can be observed that the quantity of charge carrier present does not very significantly change the value of the ionic conductivity, however a larger quantity improves the conductivity at 80°C, with the best performance obtained with example Id (curve 4) which is the one which contains the most charge carrier.

[0131] For the following examples, the value of 15% mass for the load carrier was chosen to compare the plasticizers with each other.

[0132] Examples 2a,2b,2c, 2d,2e,2f,2g,2h

[0133] This series of examples aims to study the influence of a plasticizer on the ionic conductivity of electrolytes according to the invention.

[0134] These examples are intended to show the influence of different plasticizers on the ionic conductivity of a material with an identical crosslinkable mixture composition (containing 15% by mass of allylmethylimidazolium chloride). The plasticizers tested are

[0135] - no plasticizer: example 2a (curve 1 in the graph of [Fig.2])

[0136] - tetraethylene glycol dimethyl ether (TEGDME): example 2b at 10% by mass, example 2c at 20% mass and example 2d at 30% mass of plasticizer (respectively curves 2, 3 and 4 on the graph of [Fig.2])

[0137] - succinonitrile: example 2e at 10% mass of plasticizer (curve 8 on the graph of [Fig. 2])

[0138] - acetanilide: example 2f at 10% mass of plasticizer, example 2g at 20% mass of plasticizer and example 2h at 30% mass of plasticizer (respectively curves 5, 6 and 7 of the graph in [Fig.2])

[0139] The quantities of plasticizer tested therefore represent between 10% mass and 30% mass of the total mixture, except for example 2a which does not contain any.

[0140] The results are presented in [Fig.2]: from this graph, it can be observed that the plasticizers having the most notable influence on the ionic conductivity of the electrolyte are succinonitrile (curve 8) and acetanilide (curves 5 to 7), and it appears that the presence of TEGDME (curves 2 to 4) does not significantly change the ionic conductivity of the electrolyte.

[0141] It can be noted that the addition of plasticizer can tend to decrease the concentration of chloride ions in the total electrolyte, due to a dilution effect. The plasticizing effect of TEGDME would therefore be real, but it would not be sufficient to compensate for the loss of conductivity linked to the decrease in the number of charge carriers present. Other plasticizers succeed in increasing ionic conductivity, the resulting gain in polymer chain mobility allowing this dilution effect to be overcome.

[0142] The best performance is provided by acetanilide (examples 2f, 2g, 2h); part of this good performance could be attributed to its ability to provide hydrogen bonds to chloride ions transported by the electrolyte. This hypothesis is investigated in the following series of examples. Examples 3a, 3b, 3c

[0143] This series of examples is intended to evaluate the importance of hydrogen bonds in plasticizers.

[0144] It aims to demonstrate the influence of a hydrogen bond-donating plasticizer on the ionic conductivity of the electrolyte. To this end, a plasticizer capable of providing a hydrogen bond (acetanilide) is compared to a plasticizer incapable of providing a hydrogen bond but of similar structure (methylacetanilide).

[0145] Example 3a is identical to example 2a: no plasticizer (curve 1 on the graph in [Fig.3]).

[0146] Example 3b contains 10% mass of acetanilide plasticizer (curve 2 on the graph in [Fig.3]).

[0147] Example 3c contains 10% mass of methylacetanilide (curve 3 on the graph in [Fig.3]).

[0148] The results of the ionic conductivity measurements carried out on these three electrolytes are grouped in the graph in [Fig.3].

[0149] An observation of these curves shows a clear effect of the plasticizer capable of providing a hydrogen bond, namely the acetanilide of example 3b (curve 2), with an improvement in ionic conductivity by a factor of 4, whereas the effect of the methylacetanilide of example 3c on ionic conductivity exists but is clearly less notable.

[0150] The invention thus makes it possible to highlight the beneficial effect of choosing a hydrogen bonded plasticizer, whose ability to coordinate anions thus seems, surprisingly, to be more important than its ability to promote the mobility of polymer chains in the electrolyte.

[0151] Examples 4a,4b This series of examples studies the effect of two different anions associated with the same charge carrier, '-methylimidazolium, on the ionic conductivity of the electrolyte

[0152] . For this, we study allyl-methylimidazolium tetrafluoroborate (anion: BF4) and allyl-methylimidazolium chloride (anion: Cl), with in both cases 15% mass of imidazolium.

[0153] The results of ionic conductivity at several measurement temperatures between 80 and 20°C are presented in the graph of [Fig.4] (curve 1): curve 1 corresponds to the ionic conductivity of the electrolyte with the tetrafluoroborate anion, and curve 2 corresponds to the ionic conductivity of the electrolyte with the chloride anion.

[0154] It appears from the comparison of the two curves that the electrolyte with the BF4 anion is more conductive than that with the Cl anion.

[0155] In any event, the ionic conductivity of the electrolyte with this charge carrier, and with either of the anions, is high, especially when compared with similar materials with a lithium salt in the literature.

[0156] In conclusion, the solid anionic unipolar conductive electrolytes obtained according to the invention have a high ionic conductivity, sufficient for the battery-type electrochemical system applications envisaged, particularly in non-aqueous media. They can be obtained by thiol-ene click chemistry, with organic cations grafted onto a polymeric backbone.

Claims

Demands

1. Anionic unipolar conductive crosslinkable electrolyte precursor comprising: - a first hydrocarbon monomer having two thiol functions and a second hydrocarbon monomer having two C=C double bonds, - a charge carrier comprising a hydrocarbon compound having one or two C=C double bond(s) and an organic cation, said cation being associated with an anion, - a crosslinker comprising a hydrocarbon compound having at least three C=C double bonds.

2. Anionic unipolar conductive electrolyte precursor crosslinkable according to the preceding claim, characterized in that the stoichiometry between the number of thiol functions of the first monomer and the number of C=C double bonds of the second monomer, the crosslinker and the charge carrier is between 0.9 and 1.1, and is preferably equal to 1.

3. Anionic unipolar conductive crosslinkable electrolyte precursor according to any one of the preceding claims, characterized in that the amount of charge carrier is between 10 and 25% mass of said precursor.

4. Anionic unipolar conductive electrolyte precursor crosslinkable according to any one of the preceding claims, characterized in that a first part of the crosslinker compensates for the termination of the polymer chains of the charge carrier, which is a function of the number of C=C double bonds carried by the charge carrier and by the crosslinker.

5. Anionic unipolar conductive electrolyte precursor crosslinkable according to any one of the preceding claims, characterized in that a second part of the crosslinker crosslinks the precursor, the amount of this second part preferably being between 1% and 5% mass of said precursor.

6. Anionic unipolar conductive crosslinkable electrolyte precursor according to any one of the preceding claims, characterized in that the first monomer is selected from at least the following dithiols: 2,2'-(ethylenedioxy)diethanethiol, 1,4-butane dithiol, 1,2-ethane dithiol.

7. Anionic unipolar conductive crosslinkable electrolyte precursor according to any one of the preceding claims, characterized in that the second monomer is selected from at least one of the following divalent alkenes: triethylene glycol divinyl ether, an oligo- or poly-(ethylene glycol) divinyl ether, diallyl ether, 1,5-hexadiene.

8. Anionic unipolar conductive crosslinkable electrolyte precursor according to any one of the preceding claims, characterized in that the crosslinking agent is selected from poly-methyl-vinyl siloxanes, in particular from 2,4,6,8-tetramethyl-2,4,6,8-tetravinyl-cyclotetrasiloxane or hexavinyldisiloxane, in particular 2,4,6,8-tetramethyl-2,4,6,8-tetravinyl-cyclotetrasiloxane, tetramethylvinylcyclo-siloxane, poly-methylvinyl-siloxane, trivinyl cyclohexane.

9. Anionic unipolar conductive crosslinkable electrolyte precursor according to any one of the preceding claims, characterized in that the charge carrier comprises at least one cation belonging to the following cation types: a tetra-alkyl ammonium, an imidazolium, a pyrrolidinium, a pyridinium, a piperidinium, a triazolium.

10. Anionic unipolar conductive crosslinkable electrolyte precursor according to any one of the preceding claims, characterized in that the charge carrier comprising a hydrocarbon compound having one or two C=C double bond(s) comprises a vinyl allyl acrylate or a methyl acrylate.

11. Anionic unipolar conductive crosslinkable electrolyte precursor according to any one of the preceding claims, characterized in that the charge carrier is selected from allyl-methyl imidazolium, trimethylammonium propylacrylate, diallyl-dimethyl-ammonium, diallyl-imidazolium, 4-vinyl-1,2,3-triazolium.

12. A precursor of a crosslinkable anionic unipolar conducting electrolyte according to any one of the preceding claims, characterized in that the anion associated with the charge carrier is an anion belonging to at least one of the following types of anions: - a fluorine compound, in particular selected from a fluoride ion, tetrafluoroborate, hexafluorophosphate, difluoro(oxalato)borate, bis(fluorosulfonyl)amide, bis(trifluorosulfonyl)amide - or a chlorine compound, in particular a chloride ion or a perchlorate, - or a boron compound, in particular bis(oxalato)borate - or dicyanoamidide.

13. An additivated anionic unipolar conductive electrolyte precursor, characterized in that it comprises the anionic crosslinkable electrolyte precursor according to any one of the preceding claims and at least one additive selected from at least one of the following additives: - at least one sacrificial solvent, in particular selected from ethanol, methanol and N-methylpyrrolidone, - at least one activator or catalyst, in particular selected from thiol-ene reaction activators or catalysts, - at least one plasticizer, in particular selected from at least one of the following types of plasticizers: glymes, in particular tri- and tetraethylene glycol dimethyl ethers, succinonitrile, amides, lactams, azoles, sulfonamides, in particular acetanilide, benzamide, 2-pyrrolidone, 2-piperidinone or acetanilide.

14. A method for preparing an electrolyte in the form of a crosslinked anionic unipolar conductive solid polymer, wherein - the crosslinkable anionic unipolar conductive electrolyte precursor according to the preceding claim is formed, comprising the first and second monomers, and at least one activator, in particular by coating on a support or by impregnation in the porosity of an electrode or by confinement between two support plates, with possible premixing with an electrode material before coating or confinement, - said formulation is activated as needed to ensure polymerization of the two monomers, in particular by thermal activation or by exposure to radiation, in particular ultraviolet, or by so-called redox activation, - the sacrificial solvent, if present, is removed, in particular by evaporation.

15. A method for preparing an electrolyte in the form of a crosslinked anionic unipolar conductive solid polymer according to the preceding claim, characterized in that said preparation is carried out sequentially.

16. Electrolyte in the form of a solid anionic unipolar conductive polymer, and obtained by crosslinking the precursor according to any one of claims 1 to 13 or obtained by the preparation process according to any one of claims 14 or 15.

17. Electrolyte according to claim 16, comprising a crosslinked polymer with unipolar anionic conduction in non-aqueous medium and an organic cation covalently grafted to said crosslinked polymer, said organic cation being in particular selected from a tetra-alkyl ammonium, an imidazolium, a pyrrolidinium, a pyridinium, a piperidinium, a triazolium.

18. Solid electrolyte according to the preceding claim, characterized in that the organic cation is associated with an anion selected from - a fluorine compound, in particular selected from a fluoride ion, tetrafluoroborate, hexafluorophosphate, difluoro(oxalato)borate, bis(fluorosulfonyl)amide, bis(trifluorosulfonyl)amide - or a chlorine compound, in particular a chloride ion or a perchlorate, - or a boron compound, in particular bis(oxalato)borate - or dicyanoamidide.

19. Solid electrolyte according to claim 17 or 18, characterized in that it is prepared by thiol-ene click chemistry, in particular from a first hydrocarbon monomer comprising two thiol functions and a second hydrocarbon monomer comprising two C=C double bonds, a charge carrier comprising a hydrocarbon compound comprising one or two C=C double bonds and an organic cation, said cation being in particular associated with an anion, and a crosslinker comprising a hydrocarbon compound comprising at least three C=C double bonds.

20. Electrochemical system comprising at least one electrode comprising an electrolyte according to any one of claims 16 to 19 or obtained by crosslinking the precursor according to any one of claims 1 to 13 or obtained by the preparation process according to any one of claims 14 or 15.

Images