Cross-linked solid electrolyte for lithium-ion batteries

Abstract

The present invention relates to a crosslinkable electrolyte formulation comprising at least: - hydrocarbon molecules containing 3 to 6, preferably 4, thiol functional groups; - bifunctional chain extenders in the form of hydrocarbon chains with two C=C double bonds; Monofunctional single-ion end-cappers containing a -C=C double bond and containing a mobile lithium; -monofunctional polyethylene glycol end-capping agent; - nucleophilic base catalysts, Here, the [C=C double bond] / [thiol] molar ratio is 1. The present invention also relates to the preparation and use of crosslinked solid electrolytes.

Description

[Technical Field]

[0001] The present invention relates to the preparation of crosslinked solid electrolytes for lithium ion batteries based on the thiol-ene reaction. [Background technology]

[0002] The thiol-ene reaction has applications in many areas, including batteries.

[0003] The thiol-ene (also known as alkene hydrothiolation) reaction is the reaction of thiols with alkenes to form thioethers. This reaction was first reported in 1905, but gained importance in the late 1990s and early 2000s due to its feasibility and wide range of applications, especially as an electrolyte.

[0004] Thiols are converted to thiolate anions (RS - ) and is an excellent nucleophile through the formation of a thiyl radical (RS * ), one of the most studied reactions involving thiols is the hydrothiolation of the (C=C) double bond. Depending on the nature of the double bond substituent (i.e., electron donor or electron acceptor) and the type of catalyst used, the thiol-C=C reaction can occur according to either a radical or nucleophilic mechanism.

[0005] In the case of the nucleophilic mechanism, the reaction used is a Michael polyaddition (also called nucleophilic thiol-ene polyaddition) to a double bond substituted with an electron-withdrawing group, such as a (meth)acrylate (a monomer containing an activated double bond), using a nucleophilic base as a catalyst.

[0006] The Michael polyaddition reaction has applications in many fields.

[0007] Li et al., ACS Energy Letters, 2018, vol. 3, pp. 20-27. DOI: 10.1021 / acsenergylett.7b00999, propose a single-ionic polymer solid electrolyte synthesized from the photoinduced click chemistry reaction of azides and alkynes. It has PEO (poly(ethylene oxide)) repeating units and TFSI (bis{(trifluoromethyl)sulfonyl}imide) counteranions attached to the polymer chain. Because no crosslinker is used, a viscous liquid polymer is obtained, not a network (hence, the mechanical and physicochemical properties are quite different). Although the transference number is close to 1, the reported conductivity value at 90 °C is 2 × 10 -5 It is on the order of S / cm.

[0008] Shen et al., ChemElectroChem, 2019, vol. 6, 4483-4490. DOI: 10.1002 / celc.201901045, proposed a quasi-solid electrolyte in the form of a semi-interpenetrating network formed by a polyacrylate-based single-ion crosslinked polymer and a PEO matrix, and thus is independent of thiol-ene reactions. The counter anion here is sulfonate. At 60 °C, the solubility of 1.34 × 10 -5 The conductivity of 0.25 S / cm is observed because 5 μL of plasticizer (EC:PC = 1:1 (volume ratio)) was added to the cathode-electrolyte interface during assembly of the button cell. The transference number is 0.77.

[0009] Du et al., ACS Appl. Energy Mater., 2020, vol. 3, pp. 1128-1138. DOI: 10.1021 / acsaem.9b02180, propose a quasi-solid single-ion electrolyte obtained from the solvent-phase coating of a mixture of PVDF and a single-ion polyimide. Although the counteranion is TFSI, the resulting electrolyte is a physical network rather than a chemical one, and furthermore, the synthesis does not involve a thiol-ene reaction. Due to prior immersion in carbonate solvent during electrochemical characterization, this electrolyte exhibited a 1.6 × 10 ionic strength at 25 °C. -4 They have a very good conductivity of 0.93 S / cm. However, the presence of solvents is an obstacle to the industrial development of this type of material, since the aim is to use solid electrolytes properly in batteries to avoid the thermal problems associated with solvents (evaporation, pressure buildup, risk of combustion). The transference number is 0.93.

[0010] Zhang et al., Energy Storage Material, 2020, vol. 24, pp. 579-587. DOI: 10.1016 / j.ensm.2019.06.029, propose a quasi-solid single-ion electrolyte formed by a photoinduced thiol-ene reaction from a mixture of four monomers dissolved in acetonitrile, which is deposited on a polypropylene nonwoven fabric. The counteranion is TFSI, and the thiol crosslinker is pentaerythritol tetrakis(3-mercaptopropionate). The authors use a solvent in the starting mixture and a support. Note that the resulting membrane is immersed in a mixture of ethylene carbonate and dimethylene carbonate before characterization. Thus, at 25 °C, the solubility of 8.4 × 10 -4 The excellent conductivity of 500 S / cm is not inherent to this material. Furthermore, the presented network does not contain PEO segments that would facilitate ionic conduction in the absence of significant amounts of solvent.

[0011] Patent applications US2016 / 0315348A1, J.R. Long, J. Van Humbeck, R.P.A. Meloot, Polymer network single-ion conductors, and US2018 / 0166744A1, R. Long, J. Van Humbeck, J.C.A. Xelson, Polymer network single-ion conductors with flexible linkers, contain borate anion (C6F4)4B - A single-ionic polymer network based on cis-2-butene-1,4-diol has been described. The nodes are formed by tetrafluorophenylborate anions, and the neutral crosslinker provides greater or less mechanical flexibility depending on its chemical structure. Therefore, the most advantageous crosslinker, which also functions as a spacer, is cis-2-butene-1,4-diol, which allows for excellent structural flexibility. The network formation reaction is carried out in two steps: deprotonation of cis-2-butene-1,4-diol with n-butyllithium; and nucleophilic substitution between methyl chloride (derived from the lithium chloromethyl tetrafluorophenylborate precursor) and the deprotonated cis-2-butene-1,4-diol. The final film is obtained by coating using the solvents N,N-dimethylformamide and 2,2'-azobis(2-methylpropionitrile). The Young's modulus (E = 0.27 GPa) and ionic conductivity (σ = 8.5 × 10 at 40 °C) are excellent. -5 It should be noted that the values ​​(S / cm) are given for films containing 30% by weight of plasticizer, and therefore the examples in these patents relate only to gels containing very high amounts of propylene carbonate. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] US Patent Application Publication No. 2016 / 0315348 [Patent Document 2] US Patent Application Publication No. 2018 / 0166744 Summary of the Invention

[0013] The present applicant has surprisingly found that crosslinking improves the mechanical properties of networks in non-aqueous solid electrolyte formulations compared to those obtained using homopolymers. The applicant has also found that the use of hydrocarbon molecules containing 3 to 6 thiol functional groups in combination with hydrocarbon molecules containing two C=C double bonds in the presence of a nucleophilic base catalyst can enhance the resistance of the network to chemical degradation, provided that the [alkene] / [thiol] molar ratio in the formulation is substantially stoichiometric. The [alkene] / [thiol] molar ratio is understood to mean the molar ratio of all C=C double bonds to all thiol bonds in the formulation.

[0014] The electrolyte formulations according to the invention are particularly advantageous in that they are superior to the conductivity (10 -5 ~10 -7 The crosslinkable electrolyte formulations of the present invention can be synthesized in one step by a thiol-ene reaction, making it possible to obtain self-supported chemical networks with transference numbers of 1, without necessarily requiring solvents.

[0015] The present invention relates to a crosslinkable electrolyte formulation comprising at least: - hydrocarbon molecules containing 3 to 6, preferably 4, thiol functional groups; - bifunctional chain extenders in the form of hydrocarbon chains with two C=C double bonds; Monofunctional single-ionic chain terminators containing a -C=C double bond and containing a mobile lithium; -monofunctional polyethylene glycol end-capping agent; - nucleophilic base catalysts, Here, the [C=C double bond] / [thiol] molar ratio is 1.

[0016] The formulation may comprise a soluble lithium salt or a mixture of soluble lithium salts in the formulation; the amount of lithium salt(s) may represent 2% to 30% by weight relative to the total weight of the formulation, preferably 5% to 15% by weight relative to the total weight of the formulation.

[0017] The catalyst may be selected from 1,8-diazabicyclo[5.4.0]undec-7-ene, dimethylphenylphosphine, triphenylphosphine or triethylamine, pyridine and dimethylaminopyridine, preferably 1,8-diazabicyclo[5.4.0]undec-7-ene, dimethylphenylphosphine, triphenylphosphine or triethylamine, and very preferably the catalyst is triethylamine.

[0018] The hydrocarbon molecule containing 3 to 6 thiol functional groups can be selected from pentaerythritol tetrakis(3-mercaptopropionate), trimethylolpropane tris(3-mercaptopropionate), poly[(mercaptopropyl)methylsiloxane] or (mercaptopropyl)methylsiloxane-co-dimethylsiloxane copolymers having an average functionality of 3 or more, preferably pentaerythritol tetrakis(3-mercaptopropionate).

[0019] The difunctional chain extender can be selected from any oligoethylene glycol unit having two C=C double bonds, or any norbornene, vinyl ether, allyl ether, acrylate, methacrylate, or alkene unit.

[0020] The difunctional chain extender may be selected from poly(ethylene glycol) dimethacrylate, PEG diacrylate, PEG diallyl, PEG divinyl.

[0021] The monofunctional single ion end-stopper is preferably lithium 3-[(trifluoromethane)sulfonamidosulfonyl]propyl methacrylate.

[0022] The polyethylene glycol terminator can be selected from poly(ethylene glycol) methyl ether acrylate, poly(ethylene glycol) allyl methyl ether, poly(ethylene glycol) vinyl methyl ether, or poly(ethylene glycol) maleimide methyl ether.

[0023] The catalyst may be present in an amount such that the molar ratio of thiol functional groups to catalyst is 200-600.

[0024] The formulation may also contain a second chain extender of the dithiol family, preferably selected from polydimethylsiloxane (PDMS) or polyethylene glycol (PEG) polymers terminated at both ends with mercaptoethyl or mercaptopropyl functional groups.

[0025] The formulation may comprise a plasticizer selected from the following compounds: oligoethylene glycol, carbonate ester, succinonitrile, polar aprotic solvent, or aprotic ionic liquid, said plasticizer representing from 2% to 30% by weight, preferably from 5% to 15% by weight, relative to the total weight of the formulation.

[0026] The present invention also relates to a process for preparing a crosslinked solid electrolyte, comprising: a) crosslinking a crosslinkable electrolyte formulation according to any one of the preceding variations, optionally in the presence of a non-aqueous solvent, by a catalyst present in the formulation and by thermal activation to form a polymer that conducts lithium ions; b) Evaporating any solvent present in the polymer to obtain a cross-linked solid electrolyte.

[0027] Heat activation can be carried out by heating the formulation at a temperature between 50° C. and 80° C. for a period of 1 hour to 24 hours, preferentially 6 hours to 12 hours.

[0028] The present invention also relates to the preparation of a crosslinked solid electrolyte in the form of an electrode, in which in step a) a crosslinkable electrolyte formulation is impregnated into a porous electrode by coating or spraying, and the coated or sprayed formulation is then crosslinked, or in step a) an active material and an electronic percolant are added to the crosslinkable electrolyte formulation to prepare an electrode ink, which is then coated and crosslinked to obtain a solid electrode.

[0029] The invention finally relates to the use of a crosslinked electrolyte obtained by crosslinking a formulation according to any one of the preceding variants or obtained by a process according to any one of the preceding variants as a solid electrolyte in an all-solid-state lithium-ion battery or as a component of the positive electrode (posolyte or catholyte) or of the negative electrode (negolyte or anolyte) of an electrochemical system. [Brief explanation of the drawings]

[0030] [Figure 1] FIG. 1 shows the conductivity (S / cm) as a function of the reciprocal of temperature (1000 / T, where T is in K) for a temperature cycle (cooling-hot-hot-cooling) between 20°C and 80°C for formulation ABC (according to the present invention) in the example. DETAILED DESCRIPTION OF THE INVENTION

[0031] Detailed Description of the Invention The present invention relates to an electrolyte formulation crosslinkable by a thiol-ene reaction, in which at least one of the monomers contains an anion with a covalently bonded delocalized charge, such as the TFSI ion, and optionally a lithium salt to ensure good transport of lithium ions in the electrolyte and catholyte. This formulation allows for the production of crosslinked electrolytes for use as solid electrolytes in all-solid-state lithium batteries or as a component of the positive electrode (potholyte or catholyte).

[0032] The novelty of the present invention lies in the development of an in situ polymerized and crosslinked single-ion electrolyte, which is initially liquid and forms a chemical network in one step via a thiol-ene reaction, and has the advantage of exhibiting advantageous lithium ion transport properties for applications without the need for a solvent. The crosslinkable formulation of the present invention is particularly advantageous for preparing electrodes for all-solid-state batteries. Specifically, an electrode prepared according to a conventional method can be immersed in a precursor of the formulation of the present invention, which allows the in situ formation of an ionic percolation network with a good interface with the active material.

[0033] For clarity, in this specification, a "single ionic" polymer refers to a polymer with self-doping blocks or a polymer with unipolar conduction.

[0034] The starting ingredients, all liquid, are as follows: - molecules containing 3 to 6, preferably 4, thiol functions acting as crosslinkers: tetrafunctional molecules (A4) may in particular be pentaerythritol tetrakis(3-mercaptopropionate) (preferentially), but also trivalent thiols (A3) such as trimethylolpropane tris(3-mercaptopropionate) may be used, or alternatively poly[(mercaptopropyl)methylsiloxane] or (mercaptopropyl)methylsiloxane-dimethylsiloxane copolymers with an average functionality of 3 or more; - a difunctional chain extender (B2) which can be selected from any oligo- or poly(ethylene glycol) chain having two C=C double bonds: the difunctional chain extender can therefore be a methacrylate, which is often more stable than an acrylate, and in particular (preferentially) a poly(ethylene glycol) dimethacrylate.More generally, the difunctional chain extender can be an oligo- or poly(ethylene glycol) chain having two C=C double bonds selected from the following compounds: PEG diacrylate, PEG dimethacrylate, PEG diallyl, PEG divinyl, or any norbornene, vinyl ether, allyl ether, acrylate, methacrylate, maleimide, or alkene unit; - a monofunctional monoionic end-stopper (B'1) containing a C=C double bond providing a mobile lithium and a counter anion anchored to the chain, which may in particular be lithium 3-[(trifluoromethane)sulfonamidosulfonyl]propyl methacrylate; - monofunctional polyethylene glycol end-stoppers (B''1), which may be selected from poly(ethylene glycol) methyl ether methacrylate, poly(ethylene glycol) methyl ether acrylate, poly(ethylene glycol) allyl methyl ether, poly(ethylene glycol) vinyl methyl ether, or poly(ethylene glycol) methyl ether maleimide, etc.

[0035] The chemical functionality of the bifunctional chain extender (B2) and the monofunctional PEG terminator (B1'') need not be the same.

[0036] In the crosslinkable electrolyte formulations according to the present invention, it is preferable to emphasize the molar equivalence of thiol and alkene functional groups (stoichiometry of 1). The novelty of the formulations according to the present invention lies in the fact that, due to the presence of the PEG end-capping agent (B"1), the crosslink density of the network and its mechanical and physicochemical properties are independent of the amount of the single-ion end-capping agent (B'1). Therefore, the ionic conductivity of the network can be easily adjusted according to the B1' / B1" molar ratio, without changing the mechanical properties of the electrolyte.

[0037] In one embodiment, a second chain extender of the dithiol family (eg, a PDMS or PEG polymer terminated at both ends with mercaptoethyl or mercaptopropyl functional groups) can be added.

[0038] The crosslinking reaction is initiated by a nucleophilic base-type catalyst (also called an initiator), commonly used in Michael polyaddition reactions. The catalyst can be selected from 1,8-diazabicyclo[5.4.0]undec-7-ene, dimethylphenylphosphine, triphenylphosphine, triethylamine, pyridine, or other dimethylaminopyridines. Preferably, the catalyst is 1,8-diazabicyclo[5.4.0]undec-7-ene, dimethylphenylphosphine, triphenylphosphine, or triethylamine. Even more preferably, the catalyst is triethylamine. The molar ratio of thiol functional groups to catalyst is advantageously 200-600, which corresponds to a molar ratio of tetrafunctional crosslinker to catalyst of about 50-150, especially when the thiol-containing molecule is tetrafunctional (four thiol functional groups).

[0039] Thus, the crosslinkable electrolyte formulation according to the present invention comprises at least the following components: molecules with 3 to 6 thiol functional groups, for example 4 thiol functional groups (in the example pentaerythritol tetrakis(3-mercaptopropionate)), or 3 or 6 thiol functional groups if this changes the flexibility of the final material; chain extenders with two C═C double bonds (in the example, poly(ethylene glycol) dimethacrylate): said chain extenders are advantageously chosen from any oligo-ethylene glycol unit with two C═C double bonds, or any norbornene, vinyl ether, allyl ether, acrylate, methacrylate, maleimide or alkene unit; - monofunctional single-ion end-stoppers with one C=C double bond, which provide mobile lithium and a counter-anion fixed to the chain, i.e. covalently bound, making it possible to generate pendant chains and thus mechanical flexibility (in the example lithium 3-[(trifluoromethane)sulfonamidosulfonyl]propyl methacrylate); -monofunctional polyethylene glycol end-capping agent; - a nucleophilic base catalyst (triethylamine in the example), The amount of catalyst used is advantageously of the order of 0.04 molar equivalents, the choice of the exact amount being adjustable by those skilled in the art.

[0040] In one embodiment of the present invention, the crosslinkable electrolyte formulation comprises: - Pentaerythritol tetrakis(3-mercaptopropionate) (A4); - Poly(ethylene glycol) dimethacrylate (B2); -lithium 3-[(trifluoromethane)sulfonamidosulfonyl]propyl methacrylate (B'1); - poly(ethylene glycol) methyl ether methacrylate (B''1); triethylamine as a catalyst, preferably with a molar ratio of tetrafunctional crosslinker (A4) to catalyst of 50-150;

[0041] Optionally, a lithium salt or a mixture of several salts soluble in the starting formulation can be added. The lithium salt(s) soluble in the starting formulation are preferably selected from LiTFSI, LiPF6, LiFSI, LiClO4, LiTDI, and very preferably, the soluble lithium salt is LiTFSI or any mixture of several lithium salts soluble in the starting formulation. The exact amount of soluble lithium salt can be 2% to 30% by weight of the starting formulation, preferentially 5% to 15% by weight.

[0042] It is also possible to add a plasticizer chosen from the following compounds: oligoethylene glycols, alkyl carbonates, succinonitrile, polar aprotic solvents of low volatility or aprotic ionic liquids. The amount of plasticizer may be between 2% and 30% by weight of the starting formulation, preferentially between 5% and 15% by weight.

[0043] The crosslinkable liquid formulations of the present invention can be cast between two plates or onto a substrate by spreading or spraying, followed by heating at 50°C to 80°C for 1 to 24 hours, preferably 6 to 12 hours, to crosslink the resulting network. Catholytes or anolytes can be formed by impregnating (spraying or spraying) a porous electrode with the liquid formulation or by mixing the liquid formulation with an active material to form an ink, optionally in the presence of a solvent that evaporates after crosslinking.

[0044] When the solid electrolyte is in contact with the positive electrode, the liquid crosslinking formulation according to the present invention can be applied or sprayed onto the positive electrode prepared according to the protocols of those skilled in the art, allowing the liquid formulation to wet the porosity of the electrode. Crosslinking is finally achieved after a thermal initiation reaction. Preferably, the formulation is applied or sprayed and then crosslinked before the electrode is calendered.

[0045] For example, the formulations of the present invention can be used to prepare positive electrode (cathode) inks, particularly by adding active materials (e.g., lithiated nickel-manganese-cobalt mixed oxide or lithiated iron phosphate) and electronic percolants to the formulation, which can be coated and dried to form a solid positive electrode.

[0046] [Characteristics evaluation technology] The ionic conductivity of an electrolyte is measured in S / cm and indicates the ability of the electrolyte to transport ions.

[0047] The ionic conductivity of the electrolyte is measured by electrochemical impedance spectroscopy in a Biologic® CESH cell. Measurements are performed at several temperatures using a thermostatically controlled Biologic® ITS chamber. Impedance spectra are acquired using a Biologic® MTZ 35 potentiostat at frequencies between 30 MHz and 0.1 Hz with an amplitude of ±10 mV around 0 V. The conductivity value can be determined by fitting the curve using an equivalent circuit of the type (R1 + R2 / / CPE1 + CPE2) or visually by using the value of the real part of the impedance, Re(Z), at the minimum value reached by the curve between the semicircle and semilinear line corresponding to the capacitive part on the Nyquist diagram.

[0048] The cation transference number (t+), which corresponds to the fraction of total conductivity related to charge transport by cations, is characterized by impedance spectroscopy using a Biologic VMP3 potentiostat, mounting the sample between two non-blocking electrodes (made of lithium metal), at 60 °C, between 1 MHz and 0.1 MHz, with an amplitude of 10 mV near 0 V. The transference number is obtained by adjusting the equivalent circuit (R1 + R2 / / CPE2 + R3 / / CPE3 + Wd1) and applying the following equation: t+ = R2 / (R Wd1 +R2). This measurement method corresponds to the "Watanabe" method (Solid State Ionics, Vol. 28-30, (1988), 911-917).

[0049] Solvent swelling tests and calculation of the soluble fraction are conventional methods for characterizing polymer networks to indirectly evaluate the crosslink density and chemical stability of the polymer network. Approximately 300 mg of a polymer network sample is immersed in a large excess of chloroform (CHCl3) at ambient temperature for 72 hours, after which the weight of the swollen sample is measured and then vacuum dried.

[0050] The soluble fraction (ws) is calculated by the following formula: ws=1-w d / w0 where w0 is the initial weight of the sample swollen with the solvent (estimated by linear regression of the weight curve measured at regular intervals of 0.5 to 5 minutes after the sample was removed from the solvent), and w d is the weight of the sample after the soluble fraction has been extracted and dried.

[0051] The swelling index (1 / q2) corresponds to the volume increase of the network after immersion in the solvent and is calculated by the following formula: 1 / q2=ρ p (q1-1) / ρ s where q1 is the ratio of the weight of the swollen sample to the weight of the dry sample, and ρ s is the density of the solvent (ρs = 1.492 g / cm for CHCl3). 3 ) and ρ p is the density of the polymer network.

[0052] A variety of techniques can characterize the thermomechanical properties of single ionic polymer networks.

[0053] Differential scanning calorimetry (DSC) is a technique for characterizing thermochemical processes involving phase transitions and changes of state. Here, the glass transition temperature (T g ) is used to measure

[0054] Differential scanning calorimetry (DSC) experiments were performed using a DSC Q200 (TA Instruments) instrument calibrated with an indium standard. Samples (5–10 mg) were prepared in hermetically sealed capsules and measured in a helium flow of 25 mL / min. The samples were first heated to 120°C at a heating rate of 10°C / min and held at this temperature for 2 minutes. They were then cooled to -80°C at a cooling rate of 10°C / min, and after 2 minutes of isotherm, they were heated again to 200°C at a heating rate of 10°C / min. The glass transition temperature (T g ) was measured at half-height of the transition occurring during the second heating using TA Thermal Analysis software.

[0055] Thermogravimetric analysis is a technique that allows the characterization of the weight loss profile of a sample subjected to temperature changes. It characterizes the chemical changes in a material, such as evaporation and chemical degradation, as a function of temperature.

[0056] Thermogravimetric analysis (TGA) experiments were performed using a TGA Q500 (TA Instruments) instrument. To avoid weight loss due to the presence of water, the temperature was increased at 20 °C / min, followed by an isothermal period at 110 °C for 8 min. Approximately 8 mg of sample was then heated from 20 °C to 600 °C at a rate of 10 °C / min under a continuous helium flow of 60 mL / min.

[0057] [Advantages of the present invention] The crosslinkable electrolyte formulations according to the invention have the advantage, in particular compared to prepolymerized polymers, of being liquid at the start, which allows for easy filling of the porosity of the material and thus good cohesion at the interface with the electrode. The single ion character (t+=1) is due to the presence of Li in the material. + This results in a uniform distribution of ions, which makes it possible to eliminate the concentration gradient of ions in the material under an electric field (during charging and discharging of the battery). + The overvoltage associated with ion diffusion is significantly reduced.

[0058] The use of controlled cross-linking in specific monomer mixtures and specific morphologies of the three-dimensional network further enhances chain mobility and, as a result, ionic conduction. The performance characteristics of the solid electrolytes of the present invention are based in particular on the specific selection of specific monomers that are very flexible and good solvents for lithium ions, and on the controlled cross-linking.

[0059] The rheological behavior obtained for samples of crosslinked electrolyte according to the invention advantageously corresponds to that of a crosslinked polymer. [Example]

[0060] material and method For ease of notation, the products that make up the network are referred to as follows: - Pentaerythritol tetrakis(3-mercaptopropionate): A4 -Poly(ethylene glycol) dimethacrylate: B2 -Lithium 3-[(trifluoromethane)sulfonamidosulfonyl]propyl methacrylate B'1 -Poly(ethylene glycol) methyl ether methacrylate: B''1 -Triethylamine: Et3N

[0061] The molar equivalent of the functional groups is 2A4 = 2B2 + 2(B'1 + B''1).

[0062] The starting liquid mixture is deposited between two glass plates covered with Teflon tape and separated by a 200 μm thick PTFE film for ionic conductivity and transport number measurements, and a 2 mm thick PTFE film for thermomechanical property measurements. The device is placed in an oven at 60 °C for 12 h. The resulting solid sample is dried in a Buchi oven before characterization.

[0063] Solvent swelling tests and calculation of the soluble fraction are conventional methods for characterizing polymer networks to indirectly estimate their crosslink density and, therefore, their chemical stability. These measurements are performed after immersing approximately 300 mg of the network in a large excess of chloroform (CHCl3) at room temperature for 72 hours. The swollen network is weighed and then dried under vacuum. The insoluble content is calculated using the following formula: Ci=(w d / w0)×100 where w0 is the initial weight of the sample and w d is the weight of the sample after the soluble fraction has been extracted and dried.

[0064] The swelling degree (1 / q2) is calculated by the following formula: 1 / q2=ρ p (q1-1) / ρ s where q1 is the ratio of the weight of the swollen sample to the weight of the dry sample, and ρ s is the density of the solvent (ρ s =1.492g / cm 3 ) and ρ p is the density of the polymer network (ρ p ≒1).

[0065] The thermomechanical properties of the single ionic polymer network were determined by DSC, TGA, and DMA, revealing the glass transition value T g , decomposition temperature T at 10% weight loss d10 The value of the storage modulus E' in the rubbery plateau and the α-transition temperature T α were evaluated to determine

[0066] Differential scanning calorimetry (DSC) experiments were performed using a DSC Q200 (TA Instruments) instrument calibrated with an indium standard. Samples (5–10 mg) were prepared in sealed capsules and measured in a helium flow of 25 mL / min. The samples were first heated to 120°C at a heating rate of 10°C / min and held at this temperature for 2 minutes. Next, the temperature was reduced to -80°C at a cooling rate of 10°C / min, and after 2 minutes of isothermal incubation, they were heated again to 200°C at a heating rate of 10°C / min. The glass transition temperature (T g ) was measured at half the height of the transition occurring during the second heating using TA Thermal Analysis software.

[0067] Thermogravimetric analysis (TGA) experiments were performed using a TGA Q500 (TA Instruments) instrument. To avoid weight loss due to the presence of water, a 20 °C / min heating rate was used, followed by an 8-min isothermal period at 110 °C. Approximately 8 mg of sample was then heated from 20 °C to 600 °C at a rate of 10 °C / min under a continuous helium flow of 60 mL / min.

[0068] The ionic conductivity of the electrolyte is measured by impedance spectroscopy in a Biologic® CESH cell. Measurements are performed at several temperatures using a thermostatically controlled Biologic® ITS chamber. Impedance spectra are acquired at 10 mV amplitude between 30 MHz and 0.1 Hz near 0 V using a Biologic® MTZ 35 potentiostat.

[0069] The transference numbers of the samples are measured by impedance spectroscopy. The electrolyte is placed between two lithium metal electrodes and characterized at 60 °C. Impedance spectra are acquired with a Biologic® VMP3 potentiostat at 0 V between 1 MHz and 0.1 MHz with an amplitude of 10 mV. The impedance spectra are fitted with an equivalent circuit to extract the electrolyte resistance and the diffusion resistance. The transference numbers are calculated from these resistances.

[0070] Three formulations were tested to vary the molar ratios of the four starting components, specifically the amount of lithium in the resulting monoionic network (proportional to the weight percent of B'1), and to test the effect of adding a lithium salt (here, LiTFSI) and a plasticizer (here, succinonitrile). The catalyst (a nucleophilic base-type initiator) was added last, and its molar equivalent was kept constant (0.04). Table 1 shows the compositions (molar equivalents) of Samples A–C, along with the weight percent of the lithiated endcapper and plasticizer in the starting formulations.

[0071] [Table 1]

[0072] Table 2 shows the results obtained after immersion of the networks in chloroform at room temperature (insoluble matter content Ci and swelling index S for networks A to C). The insoluble matter content is all above 85%, indicating that the three formulations are materials with good chemical stability. The swelling index values ​​are low (all below 5), indicating very good cross-linking of the networks.

[0073] [Table 2]

[0074] Table 3 (glass transition temperatures T g and the decomposition temperature T at 10% of the initial weight d10 ) shows the results obtained by DSC and TGA analysis. The low glass transition temperatures (not exceeding -15°C) indicate sufficient segmental mobility for lithium transport over the battery's operating temperature range. The three formulations tested have decomposition temperatures above 280°C at 10% of their initial weight, which is fully compatible with the intended field of application.

[0075] [Table 3]

[0076] Figure 1 shows the measured conductivity of the networks obtained from the three tested formulations A, B, and C. It can be seen that as the weight fraction of the single-ion endcapper increases from 26% to 32%, the conductivity of the final network also increases (6.7 × 10 at 60 °C) due to the provision of mobile lithium ions to the system. -6 vs 9.5 x 10 -6 Furthermore, adding small amounts of lithium salt and plasticizer to the starting compound further increases the conductivity (1.4 × 10 at 60 °C). -5 S / cm).

[0077] The transference numbers obtained for formulations A and B are equal to 1, which is characteristic of single ionic systems. The transference number for network C is less than 1 due to the presence of lithium salts.

Claims

1. A crosslinkable electrolyte formulation comprising at least: - hydrocarbon molecules containing 3 to 6, preferably 4, thiol functions; - a difunctional chain extender in the form of a hydrocarbon chain having two C=C double bonds; a monofunctional single ionic end-capper containing a -C=C double bond and containing a mobile lithium; - monofunctional polyethylene glycol end-capping agents; - nucleophilic base catalysts, Here, the [C═C double bond] / [thiol] molar ratio is 1.

2. 2. A crosslinkable electrolyte formulation according to claim 1, comprising a soluble lithium salt or a mixture of soluble lithium salts in the formulation, the amount of lithium salt representing from 2% to 30% by weight relative to the total weight of the formulation, preferably from 5% to 15% by weight relative to the total weight of the formulation.

3. 3. A crosslinkable electrolyte formulation according to claim 1 or 2, wherein the catalyst is selected from 1,8-diazabicyclo[5.4.0]undec-7-ene, dimethylphenylphosphine, triphenylphosphine or triethylamine, pyridine and dimethylaminopyridine, preferably selected from 1,8-diazabicyclo[5.4.0]undec-7-ene, dimethylphenylphosphine, triphenylphosphine or triethylamine, very preferably triethylamine.

4. 4. A crosslinkable electrolyte formulation according to any one of claims 1 to 3, wherein the hydrocarbon molecules containing 3 to 6 thiol functional groups are selected from pentaerythritol tetrakis(3-mercaptopropionate), trimethylolpropane tris(3-mercaptopropionate), poly[(mercaptopropyl)methylsiloxane] or (mercaptopropyl)methylsiloxane-co-dimethylsiloxane copolymers having an average functionality of 3 or greater, preferably pentaerythritol tetrakis(3-mercaptopropionate).

5. 5. The crosslinkable electrolyte formulation of claim 1, wherein the difunctional chain extender is selected from any oligoethylene glycol unit having two C═C double bonds, or any norbornene, vinyl ether, allyl ether, acrylate, methacrylate, or alkene unit.

6. 6. The crosslinkable electrolyte formulation of claim 5, wherein the difunctional chain extender is selected from poly(ethylene glycol) dimethacrylate, PEG diacrylate, PEG diallyl, PEG divinyl.

7. 7. The crosslinkable electrolyte formulation of any one of claims 1 to 6, wherein the monofunctional single-ion end-capper is lithium 3-[(trifluoromethane)sulfonamidosulfonyl]propyl methacrylate.

8. 8. The crosslinkable electrolyte formulation of claim 1, wherein the polyethylene glycol end-capper is selected from poly(ethylene glycol) methyl ether acrylate, poly(ethylene glycol) allyl methyl ether, poly(ethylene glycol) vinyl methyl ether, or poly(ethylene glycol) maleimide methyl ether.

9. 9. The crosslinkable electrolyte formulation of claim 1, wherein the catalyst is present in an amount such that the molar ratio of thiol functional groups to catalyst is between 200 and 600.

10. 10. A crosslinkable electrolyte formulation according to any one of claims 1 to 9, comprising a second chain extender of the dithiol family, preferably selected from polydimethylsiloxane (PDMS) polymers or polyethylene glycol (PEG) polymers terminated at both ends with mercaptoethyl or mercaptopropyl functional groups.

11. 11. A crosslinkable electrolyte formulation according to any one of claims 1 to 10, comprising a plasticizer selected from the following compounds: oligoethylene glycol, carbonate ester, succinonitrile, polar aprotic solvent, or aprotic ionic liquid, said plasticizer representing from 2 to 30% by weight, preferably from 5 to 15% by weight, relative to the total weight of the formulation.

12. 1. A process for preparing a crosslinked solid electrolyte, comprising: a) crosslinking the crosslinkable electrolyte formulation of any one of claims 1 to 11, optionally in the presence of a non-aqueous solvent, by a catalyst present in the formulation and by thermal activation to form a polymer that conducts lithium ions; b) evaporating any solvent present in the polymer to obtain a crosslinked solid electrolyte; process.

13. 13. The process for preparing a crosslinked solid electrolyte according to claim 12, wherein the thermal activation is carried out by heating the formulation at a temperature between 50°C and 80°C for a period of time between 1 hour and 24 hours, preferentially between 6 hours and 12 hours.

14. 14. The process for preparing a crosslinked solid electrolyte in the form of an electrode according to claim 12 or 13, wherein in step a) the crosslinkable electrolyte formulation is impregnated into a porous electrode by coating or spraying, and then the coated or sprayed formulation is crosslinked; or in step a) an active material and an electron percolant are added to the crosslinkable electrolyte formulation to prepare an electrode ink, which is coated and then crosslinked to obtain a solid electrode.

15. Use of a crosslinked electrolyte obtained by crosslinking a formulation according to any one of claims 1 to 11 or obtained by the process according to any one of claims 12 to 14 as a solid electrolyte in an all-solid-state lithium-ion battery or as a component of the positive electrode (posolite or catholyte) or of the negative electrode (negolite or anolyte) of an electrochemical system.

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