Solid electrolytes and method for manufacturing the same

Abstract

The technology of the present invention generally relates to the field of power storage devices, and more specifically to a solid electrolyte composition and a method for producing said solid electrolyte composition. In an aspect of the invention, the method comprises the steps of: mixing a silicon precursor comprising at least one alkoxysilane and an ionic liquid electrolyte comprising an ionically conductive compound, a solvent, and a metal salt to form a liquid mixture; wherein the solvent comprises an amount of water sufficient for hydrolyzing at least a portion of the silicon precursor; adding a halogen-containing organosilicon compound to the liquid mixture; hydrolyzing at least a portion of the silicon precursor by contacting the halogen-containing organosilicon compound and the silicon precursor; reacting the halogen-containing organosilicon compound and the hydrolyzed portion of the silicon precursor, thereby forming a gel mixture; and, curing, drying and / or ageing the formed gel mixture, thereby forming the solid electrolyte composition.

Description

[0001] SOLID ELECTROLYTES AND METHOD FOR MANUFACTURING THE SAME

[0002] FIELD OF THE INVENTION

[0003] The technology of the present invention generally relates to the field of power storage devices, and more specifically to solid electrolytes and solid electrolyte compositions comprising a porous silica matrix, which is at least partially modified by a halogen-containing organosilicon compound and comprises an ionic liquid electrolyte, and a method for producing the same.

[0004] BACKGROUND

[0005] Electrochemical energy storage devices find widespread use in various transport applications, from automotive to aviation, marine to space. To improve these devices, ionogels, comprising ionic liquid electrolytes (ILEs) and solid supporting matrices, are proposed for use. However, although ionogels with high ILE content (> 90 vol.%) exhibit fast ion conduction, their mechanical properties are generally poor, leading to electrical shorts and ILE leakage under external pressure.

[0006] Solid-composite electrolytes (SCEs) offer key advantages over conventional ionogels. SCEs are prepared through a one-pot aqueous sol-gel process. General advantages of sol-gel reactions include easy fabrication, cost-effectiveness, versatility, preparation under mild conditions (low temperature and ambient atmosphere), and the possibility of large-area coating on substrates of any size. Development of solid-state batteries with a solid electrolyte is increasingly important due to high energy demand, safety, and stability requirements.

[0007] For example, EP 4280 335 Al describes a solution for forming a solid electrolyte comprising: a plurality of silicon oxide particles dissolved in a liquid medium, the silicon oxide particles being functionalized with organic moieties comprising: at least four non-hydrogen atoms, of which one atom is covalently bonded to a silicon atom of the silicon oxide particles, and a linkable functional group capable, after activation by a radical species, of forming a covalent bond by reaction with another identical linkable functional group, wherein the organic moiety comprises at least two atoms, not part of the linkable functional group, that are bonded by a n bond to each other, wherein a ratio of the number of said organic moieties to the number of silicon atoms comprised in the plurality of silicon oxide particles is at least 0.3, and an electrolyte compound

[0008] However, a major challenge in SCE development is achieving both fast ion conduction and good mechanical stability. For instance, increasing the content of the solid network in SCEs improves elasticity and mechanical integrity, but results in stiff materials that induce stress cracking and poor ion conductivity. In contrast, increasing the content of ILE improves resilience and ion conductivity, but results in poor mechanical stability. Therefore, a wide variety of additives are commonly introduced to overcome the aforementioned disadvantages, which can negatively affect the (electro-) chemical stability of the final electrolyte.

[0009] Thus, there is a need to address the limitations of current battery technology by providing an improved solid electrolyte with enhanced mechanical properties, while maintaining or even improving its ionic conductance without the need for detrimental additives. This is crucial for the development of commercially relevant solid-state batteries.

[0010] SUMMARY OF THE INVENTION

[0011] As described above, there is a need to address the limitations of battery technology. Therefore, this present disclosure describes a solid electrolyte, a solid electrolyte composition and methods to produce the aforementioned, with enhanced mechanical properties capable of maintaining or even improving its ionic conductance without the need for further additives. The solid electrolyte and the solid electrolyte composition described in the present disclosure can be utilized in the field of energy storage devices, and more specifically in the production of energy storage devices such as batteries, supercapacitors, or fuel cells.

[0012] The herein disclosed method relates to a sol-gel process, wherein a silicon precursor and halogencontaining organosilicon (OS) compound are converted into a cross-linked silica network and the ionic liquid electrolyte (ILE) is embedded in said network. Advantageously, it was found that the halogencontaining organosilicon compound can act as both a catalyst and a co-reactant in the sol-gel process. Without wishing to be bound by theory, it is believed that halogen-containing organosilicon compounds as disclosed herein participate in the hydrolysis of the silicon precursor and subsequent polycondensation to form a hybrid organic-inorganic polymer network. By in-situ functionalising or reacting the silica network or silica matrix with the halogen-containing organosilicon compound it was found that the mechanical integrity of the solid electrolyte can be improved without compromising its high ion conductivity, or necessitating the inclusion of leachable or chemically unstable additives. Hence, by incorporating or linking the halogen-containing organosilicon compound into the network structure during the curing process, the present invention is able to overcome several drawbacks of conventional solid electrolytes.

[0013] Furthermore, it was found that the herein disclosed method provides solid electrolytes with reduced stress cracking and increased porosity and / or smaller pores even at low concentrations of halogen- containing organosilicon compound, resulting in a mesoporous material. Said mesoporous structure has the advantage that it mat increase the ionic conductivity of the solid electrolyte and improve the retention of the ILE.

[0014] Another advantage of using a halogen-containing organosilicon compound in the sol-gel process as disclosed herein is that the self-condensation of hydrolyzed silicon precursors and / or the reaction between the portion of hydrolyzed silicon precursors and the halogen-containing organosilicon compound can be triggered or accelerated without the need of additional catalysts or initiators. Hence, avoiding additional compounds that may alter the (electro-) chemical stability of the solid electrolyte. Furthermore, such an acceleration of the sol-gel process may enable an improved control over the curing process which may lead to a high batch-to-batch reproducibility.

[0015] An overview of various other aspects of the technology of the present invention is given hereinbelow, after which specific embodiments will be described in more detail. This overview is meant to aid the reader in understanding the technological concepts more quickly, but it is not meant to identify the most important or essential features thereof, nor is it meant to limit the scope of the present invention, which is limited only by the claims. The invention is defined by the independent patent claims. The dependent claims define advantageous embodiments of the invention.

[0016] An aspect of the present invention relates method for producing a solid electrolyte composition, the method comprising the steps of: mixing a silicon precursor comprising at least one alkoxysilane, a solvent, and an ionic liquid electrolyte comprising an ionically conductive compound and a metal salt to form a liquid mixture; adding an organosilicon compound to the liquid mixture to form a modified organosilicon compound; modifying the reactivity of at least a portion of the silicon precursor through interactions between the modified organosilicon compound and the silicon precursor to form an activated silicon precursor; reacting the activated silicon precursor in the presence of the modified organosilicon compound, thereby forming a hybrid organic-inorganic gel mixture; and, drying and / or ageing the formed gel mixture, thereby forming the solid electrolyte composition.

[0017] Another aspect of the present invention relates to a method for producing a solid electrolyte composition, the method comprising the steps of: mixing a silicon precursor comprising at least one alkoxysilane, a solvent, and an ionic liquid electrolyte comprising an ionically conductive compound and a metal salt to form a liquid mixture; adding a halogen-containing organosilicon compound to the liquid mixture to form a modified halogen-containing organosilicon compound; modifying the reactivity of at least a portion of the silicon precursor through interactions between the modified halogen-containing organosilicon compound and the silicon precursor to form an activated silicon precursor; reacting the activated silicon precursor in the presence of the modified halogen-containing organosilicon compound, thereby forming a hybrid organic-inorganic gel mixture; and, drying and / or ageing the formed gel mixture, thereby forming the solid electrolyte composition.

[0018] Another aspect of the present invention relates to a method for producing a solid electrolyte composition, the method comprising the steps of: mixing a silicon precursor comprising at least one alkoxysilane, a solvent, and an ionic liquid electrolyte comprising an ionically conductive compound and a metal salt to form a liquid mixture; adding a halogen-containing organosilicon compound to the liquid mixture; hydrolyzing at least a portion of the silicon precursor by contacting the halogen-containing organosilicon compound and the silicon precursor; reacting the halogen-containing organosilicon compound and the hydrolyzed portion of the silicon precursor, thereby forming a gel mixture; and, drying and / or ageing the formed gel mixture, thereby forming the solid electrolyte composition.

[0019] Another aspect of the present invention relates to a method for producing a solid electrolyte composition, the method comprising the steps of: mixing a silicon precursor comprising at least one alkoxysilane, a solvent, and an ionic liquid electrolyte comprising an ionically conductive compound and a metal salt to form a liquid mixture; adding a halogen-containing organosilicon compound to the liquid mixture; hydrolyzing at least a portion of the silicon precursor by contacting the halogen-containing organosilicon compound and the silicon precursor; reacting the halogen-containing organosilicon compound and the hydrolyzed portion of the silicon precursor, thereby forming a gel mixture; and, drying and / or ageing the formed gel mixture, thereby forming the solid electrolyte composition.

[0020] In a particular embodiment, the molar ratio between the organosilicon compound, preferably the halogen-containing organosilicon compound and the silicon precursor is between at least 0.01 and at most 0.50, preferably between at least 0.01 and at most 0.45 or between at least 0.01 and at most 0.40, more preferably between at least 0.01 and at most 0.35 or between at least 0.01 and at most 0.30, more preferably still between at least 0.01 and at most 0.25 or between at least 0.01 and at most 0.20, for example about 0.10 or 0.15, or between at least 0.01 and at most 0.10, for example about 0.05. In a particular embodiment, the molar ratio between the organosilicon compound, preferably halogencontaining organosilicon compound and the silicon precursor is between at least 0.05 and at most 0.50, between at least 0.07 and at most 0.25, more preferably between at least 0.10 and at most 0.15, more preferably still about 0.13.

[0021] In a particular embodiment, the method as disclosed herein provides that the organosilicon compound, preferably the halogen-containing organosilicon compound is represented by the general formula (I), wherein R1, R2, and R3are each independently selected from the group consisting of halogen, alkyl, alkenyl, alkoxy, and aminoalkyl; wherein X is selected from the group consisting of halogen, aminoalkyl, and cyanoalkyl; optionally or additionally comprising a terminal cyano (-CN), cyanate (-OCN), isocyanate (-NCO), thiocyanate (-SCN), isothiocyanate (-NCS), amine, imine, thiol, halide, epoxy, hydroxy, carbonate, carboxylate, acrylate, or vinyl group; and wherein at least one of R1, R2, and R3is halogen, preferably fluoro.

[0022] In a particular embodiment, the method as disclosed herein provides that the halogen-containing organosilicon compound is represented by the general formula (I), wherein R1, R2, and R3are each independently selected from the group consisting of hydrogen, halogen, alkyl, alkenyl, alkoxy, and aminoalkyl; preferably wherein R1, R2, and R3are each independently selected from the group consisting of halogen, alkyl, alkenyl, alkoxy, and aminoalkyl; wherein X is selected from the group consisting of hydrogen, halogen, alkyl, alkenyl, alkoxy, aminoalkyl, and cyanoalkyl; preferably wherein X is selected from the group consisting of halogen, aminoalkyl, and cyanoalkyl; and wherein at least one of R1, R2, and R3is halogen, preferably fluoro.

[0023] In a particular embodiment, the method as disclosed herein provides that the organosilicon compound, preferably the halogen-containing organosilicon compound is represented by general formula (II), wherein X is a halogen selected from the group consisting of fluoride, chloride, bromide, and iodide; and wherein R1and R2, are each independently selected from the group consisting of halogen, alkyl, alkenyl, phenyl, and alkoxy; and wherein Y is selected from the group consisting of alkyl, alkenyl, phenyl; optionally or additionally comprising a terminal cyano (-CN), cyanate (-OCN), isocyanate (-NCO), thiocyanate (-SCN), isothiocyanate (-NCS), amine, imine, thiol, halide, epoxy, hydroxy, carbonate, carboxylate, acrylate, or vinyl group.

[0024] In a particular embodiment, the solvent comprises an amount of water sufficient modifying the reactivity of at least a portion of the silicon precursor, preferably by hydrolyzing at least a portion of the silicon precursor; preferably the solvent comprises an aqueous solvent.

[0025] In a particular embodiment, the method as disclosed herein further provides that the solid electrolyte composition is substantially free of a catalyst and / or initiator.

[0026] A further aspect of the invention relates to an electrode comprising: a solid electrolyte composition, prepared according to the method of an aspect of the invention, and an electrode active material.

[0027] A further aspect of the invention relates to a solid electrolyte composition for an electrochemical energy storage device, preferably obtained or obtainable by a method according to an aspect of the present invention or (preferred) embodiments thereof, comprising a porous silica matrix comprising an ionic liquid electrolyte which comprises an ionically conductive compound and a metal salt; wherein the porous silica matrix is at least partially modified by an organosilicon compound, preferably a halogen-containing organosilicon compound; and wherein the total wt.% of silica in the solid electrolyte composition is at least 5.0 wt.% and at most 30.0 wt.%, and the total wt.% of the organosilicon compound, preferably the halogen-containing organosilicon compound in the solid electrolyte composition is between at least 0.01 wt.% and at most 25.0 wt.%, preferably at least 0.03 wt.% and at most 20.0 wt.%.

[0028] A further aspect of the invention relates to an electrochemical energy storage device, comprising a positive electrode, a negative electrode; and the solid electrolyte composition according to an aspect of the invention; preferably wherein the energy storage device is an alkali metal battery, more preferably still a lithium and / or a sodium battery. Aspects of the invention are detailed in the accompanying independent and dependent claims. Features in the dependent claims may be freely combined with those of the independent claims, as well as with features from other dependent claims, where appropriate, and not solely in the explicit combinations set forth in the claims. Specifically, any embodiments of the method for producing a solid electrolyte composition, as described herein, also serve as embodiments of the solid electrolyte composition, for instance, for use in an electrochemical energy storage device, and vice versa. These considerations similarly apply to other aspects of the present invention.

[0029] BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The following description of the figures relates to specific embodiments of the disclosure which are merely exemplary in nature and not intended to limit the present teachings, their application or uses. In the different figures, the same reference signs refer to the same or analogous elements.

[0031] FIG 1. shows a transparent solid electrolyte as obtained in Example 1.

[0032] FIG 2. shows a graph of pressure vs ionic conductivity (i.e., piezoelectric conductivity) of the solid electrolyte composition obtained in Example 1 measured at 20 °C on a sample of about 400 pm thickness.

[0033] FIG 3. shows a series of scanning electron microscopy (SEM) images of Example 1 (including an OS compound) and Comparative Example 2 (without an OS compound).

[0034] FIG 4. shows a graph illustrating the electrochemical properties of Example 1, Example 4, Example 5, Comparative Example 2, Comparative Example 3, and Comparative Example 4 as a function of the molar ratio of I LE:silicon precursor ( I LE:TEOS).

[0035] FIG 5. shows a graph illustrating the voltage profile of the lithium battery of Example 6.

[0036] FIG 6. shows a graph illustrating the anodic stability of the lithium battery of Example 6.

[0037] DETAILED DESCRIPTION

[0038] It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this disclosure. This description is meant to aid the reader in understanding the technological concepts more easily, but it is not meant to limit the scope of the present disclosure, which is limited only by the claims. As outlined above, the present invention generally relates to technology for production of a solid electrolyte composition suitable for the manufacturing of an electrochemical energy storage device such as a (solid-state) battery.

[0039] An aspect of the present invention relates to a method for producing a solid electrolyte composition, the method may comprise the steps of: mixing a silicon precursor comprising at least one alkoxysilane, a solvent, and an ionic liquid electrolyte comprising an ionically conductive compound and a metal salt to form a liquid mixture; adding a halogen-containing organosilicon (OS) compound to the liquid mixture to form a modified halogen-containing organosilicon compound; modifying the reactivity of at least a portion of the silicon precursor through interactions between the modified halogen-containing organosilicon compound and the silicon precursor to form an activated silicon precursor; reacting the activated silicon precursor in the presence of the modified halogen-containing organosilicon compound, thereby forming a hybrid organic-inorganic gel mixture; curing, preferably by drying and / or ageing, the formed gel mixture, thereby forming the solid electrolyte composition.

[0040] Another aspect of the present invention relates to a method for producing a solid electrolyte composition, the method may comprise the steps of: mixing a silicon precursor comprising one or more alkoxysilane, a solvent, and an ionic liquid electrolyte comprising one or more ionically conductive compound and one or more metal salt to form a liquid mixture; adding a halogen-containing organosilicon (OS) compound to the liquid mixture; hydrolyzing at least a portion of the silicon precursor by contacting the halogen-containing organosilicon compound and the silicon precursor; reacting the halogen-containing organosilicon compound and the hydrolyzed portion of the silicon precursor, thereby forming a gel mixture; curing, preferably by drying and / or ageing, the formed gel mixture, thereby forming the solid electrolyte composition.

[0041] The term "silicon precursor" has a well-established meaning within the art and is used herein as such. In particular, a silicon precursor may generally refer to a compound that contains silicon and is used as a starting material in the synthesis of silicon-containing structures (e.g., silica). Silicon precursors as described herein comprise one or more alkoxysilane group, such as one alkoxysilane group, two alkoxysilane groups, three alkoxysilane groups, or four alkoxysilane groups. Hence, said compounds are composed of silicon atoms bonded to one or more alkoxide groups (e.g., methoxy groups for tetramethoxysilane).

[0042] The term "halogen-containing organosilicon compound" as used herein generally refers to compounds comprising both organic groups and one or more halogen atoms (e.g., fluorine, chlorine, bromine, or iodine) directly bonded to silicon.

[0043] In some embodiments, the molar ratio between the halogen-containing organosilicon compound and the silicon precursor is between at least 0.01 and at most 0.50, preferably between at least 0.01 and at most 0.45 or between at least 0.01 and at most 0.40; more preferably still between at least 0.01 and at most 0.35 or between at least 0.01 and at most 0.30; more preferably still between at least 0.01 and at most 0.25 or between at least 0.01 and at most 0.20; for example about 0.05, 0.10 or 0.15.

[0044] In some other embodiments, the molar ratio between the halogen-containing organosilicon compound and the silicon precursor is between at least 0.01 and at most 0.85, or at least 0.01 and at most 0.80, or at least 0.01 and at most 0.70, or at least 0.01 and at most 0.60, preferably between at least 0.05 and at most 0.60, or at least 0.05 and at most 0.50, preferably between at least 0.05 and at most 0.40, or between at least 0.05 and at most 0.30, preferably between at least 0.05 and at most 0.25, for example, 0.10, or 0.15, or 0.20.

[0045] An "electrolyte" as referred to herein involves a medium that contains ions and is electrically conductive through the movement of said ions, but does not conduct electrons. When an electric field is applied to said electrolyte, cations and anions are drawn to opposite charged electrodes, where electrons are provided / removed from the electrolyte. Specifically, a negative charge cloud develops in the electrolyte around the cathode, and a positive charge cloud develops in the electrolyte around the anode. Hence, when cations and anions are drawn to said opposite charged electrodes, formed charges at the interface are neutralized and the electrons continue to flow through said electrodes, which creates an electric current. The term "solid" as used herein refers to being in a substantially solid state as a whole system at room temperature. Partial inclusion of a liquid is therefore not excluded. Gels, for example, are considered "solid" within the present disclosure. Hence, the "solid electrolyte" as disclosed herein refers to the electrolyte being in solid state at room temperature so that it is suitable for fast ion conduction. For example, the solid electrolyte is applied to prepare a solid-state battery. However, unless noted otherwise, the invention is not necessarily limited to such solid-state battery applications. Alternatively or in combination, the electrolyte can be referred to as a "composite electrolyte" based on the combination of constituent materials, more specifically, a combination of the hybrid organic-inorganic matrix and the ionic liquid-based electrolyte.

[0046] Hence, the herein disclosed method refers to a gelation or sol-gel method to prepare a conductive medium that can be solidified at room temperature, for example within a temperature range of about 20 °C to 25 °C at normal atmosphere. A "sol-gel process" as referred to herein involves the conversion of reactive inorganic precursor compounds into a colloidal suspension (sol), which acts as a precursor for an integrated network (gel). In particular, the herein disclosed sol-gel process is a wet-crosslinking technique that may be initiated by hydrolysis and / or alcoholysis of a silicon precursor, optionally in the presence of an organic solvent that can be included, for example, as a second solvent.

[0047] Therefore, in particular embodiments, the liquid mixture used to prepare the solid electrolyte composition as disclosed herein may further comprise a solvent. Preferably said solvent comprises water in an amount sufficient for modifying the reactivity of at least a portion of the silicon precursor, preferably by hydrolyzing at least a portion of the silicon precursor. The solvent may aid in the mixing and dispersion of the silicon precursor, the ionic liquid electrolyte (ILE), and the halogen-containing organosilicon compound. Moreover, the solvent may alter the viscosity of the gel mixture and thereby provide easier handling and processing of the gel mixture to form the solid electrolyte composition. Preferably, the solvent comprises an aqueous solvent.

[0048] The hydrolysis and / or alcoholysis products comprised in the liquid mixture may condense and cross-link to form dispersed particles in said liquid mixture. Further condensation or curing results in the formation of a three-dimensional network or gel mixture. Subsequently, the wet gel can be dried or aged to form a dry organic-inorganic network, which is preferably free of solvent. When an ILE is embedded in said three- dimensional organic-inorganic network, a solid electrolyte is obtained.

[0049] Advantageously, the method as disclosed herein provides that the halogen-containing organosilicon compound is integrated in the silica matrix, which results in an improved mechanical strength without compromising the high ion conductivity. This is in contrast to additives that are not incorporated in the inorganic network, which may result in issues such as phase separation, chemical stability, and reduced ionic conductivity. Therefore, the method as disclosed herein can provide solid electrolyte compositions and solid electrolytes with improved mechanical stability and high overall performance.

[0050] It should be noted that partial hydrolysis of the silicon precursor(s) may be initiated immediately after formation of the liquid mixture (i.e., before addition of the halogen-containing organosilicon compound to the liquid mixture). However, in the absence of a catalyst or initiator hydrolysis and / or alcoholysis of the silicon precursor is typically slow and inefficient. In the method as disclosed herein, significant hydrolysis of at least a portion of the silicon precursor may be initiated, resulting in the formation of reactive silicon species, such as silanol groups. Subsequently, said reactive silicon species may condense to form a cross-linked silica network. Hence, another advantage of the present invention, is that the halogen-containing organosilicon compound may act as a catalyst to promote the formation of reactive silicon species and accelerate cross-linking reactions, which decreases the necessary gelation time.

[0051] The term "liquid mixture" is therefore used to identify a liquid medium (e.g., a solution) comprising the silicon precursor, the ILE, and optionally a solvent, which can gradually evolve to a gel-like network. Specifically, the silicon precursor may comprise at least one alkoxysilane functional group (i.e., -SiOR), which undergoes hydrolysis to a silanol functional group (i.e., -SiOH). The hydrolyzed silicon precursor comprising silanol functional groups can subsequently participate in polycondensation reactions to form discrete colloid particles to continuous chain-like polymer networks. The optional solvent may preferably comprise a protic solvent, which can increase the hydrolysis rate of the silicon precursor. In some embodiments, a solvent mixture can be used to obtain a miscible liquid mixture.

[0052] For example, and in an embodiment, the liquid mixture may be formed by placing the silicon precursor and the ILE into a container and subsequently mixing the components at a low temperature such as between 20 °C and 70 °C, or 30 °C and 60 °C, or 30 °C and 40 °C. The liquid mixture is stirred until all components are fully dissolved, for example, by using a magnetic stirrer.

[0053] Optionally, the ILE may be dissolved in a solvent first such as a water-alcohol mixture comprising ethanol, isopropanol, and / or l-methoxy-2-propanol to improve the solubility of the components comprised in the liquid mixture. In some embodiments, the solvent may comprise de-ionized water and an alcohol-based co-solvent, preferably propylene glycol methyl ether (PGME). Relevant alcohol-based co-solvents include methanol, ethanol, propan-l-ol, butan-l-ol, pentan-l-ol, hexan-l-ol, heptan-l-ol, octan-l-ol, and mixtures thereof. Preferably, the alcohol-based co-solvent is a glycol ether selected from the group consisting of: ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-butyl ether, dipropyleneglycol methyl ether, propylene glycol methyl ether, or mixtures thereof. Most preferably, the alcohol co-solvent is propylene glycol methyl ether. The concentration of the optional solvent will depend on the nature and amount of the silicon precursor and / or ionic liquid electrolyte. The skilled person understands how this selection can be made and knows how to obtain a miscible liquid mixture. Hence, an important step of the sol-gel process as disclosed herein is the hydrolysis of one or more of the functional groups of the silicon precursor. In particular, hydrolysis of at least one alkoxysilane to silanol.

[0054] In particular embodiments, the silicon precursor can be selected from the group consisting of tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS), methyltriethoxysilane (MTES), tetraisopropyl orthosilicate (TIOS), tetrapropyl orthosilicate (TPOS), tetrabutyl orthosilicate (TBOS), substitutions thereof, and / or a combination thereof. It may be appreciated that in principle any alkoxysilane could be comprised in the silica precursor in the mixture. The substitution of ethoxy / methoxy groups in alkoxysilane can lead to a change in the morphology / propriety of silica obtained, hence allowing some degree of adjustment in the properties of the composite matrix. The skilled person understands how this selection can be made. It will be further understood that the herein disclosed method may comprise the addition of one or more silicon precursors.

[0055] After hydrolysis and condensation of at least some of the silicon precursor(s), the liquid mixture gels to form a "gel mixture". The gelation reaction as disclosed herein is characterized in that the halogencontaining organosilicon compound reacts with at least a part of the hydrolyzed silicon precursor. In particular, reactive functional groups of the halogen-containing organosilicon compound reacts with the formed silanol functional groups.

[0056] It has been observed that the addition of a halogen-containing organosilicon compound to the liquid (curing) mixture in a molar ratio between the halogen-containing organosilicon compound and the silicon precursor of at least 0.01 and at most 0.85, or at least 0.01 and at most 0.80, or at least 0.01 and at most 0.70, or at least 0.01 and at most 0.60, preferably between at least 0.05 and at most 0.60, or at least 0.05 and at most 0.50, preferably between at least 0.05 and at most 0.40, or between at least 0.05 and at most 0.30, preferably between at least 0.05 and at most 0.25 more preferably still about 0.13; can accelerate and / or trigger gelation without affecting, or even improving, the mechanical integrity and conductivity of the solid electrolyte composition.

[0057] In general, the disclosed halogen-containing organosilicon compound according to formula (I) can be considered to consist of: a silicon head group (R1RzR3Si-), and a functional tail group X.

[0058] In particular embodiments, the method as disclosed herein provides that the halogen-containing organosilicon compound is represented by general formula (I), wherein R1, R2, and R3are each independently selected from the group consisting of hydrogen, halogen, alkyl, alkenyl, alkoxy, and aminoalkyl; wherein X is selected from the group consisting of hydrogen, halogen, alkyl, alkenyl, alkoxy, aminoalkyl, and cyanoalkyl, and wherein at least one of R1, R2, and R3is halogen, preferably fluoro.

[0059] In preferred embodiments, the method as disclosed herein provides that at least one of R1, R2, and R3is halogen.

[0060] In preferred embodiments, the method as disclosed herein provides that X is an electron-withdrawing group (EWG). In other words, X can be a functional group that is able to reduce the electron density around the silicon atom. Without wishing to be bound by theory, it is rationalized that when an EWG is attached to a silicon atom that is also bonded to at least one halogen (e.g., fluorine, chlorine, bromine, or iodine), it can polarize the silicon-halogen bond thereby changing its reactivity.

[0061] For example, in an exemplary embodiment involving a fluorinated organosilicon nitrile solvent with a hydrolyzable Si-F bond, the hydrolysis of the Si-F bond in the presence of water can lead to the release of F' ions. This displacement reaction at the silicon atom cam produce a more electrophilic silicon species. The modified silicon species can react more readily with Si-OH groups, resulting in the acceleration of polycondensation reactions, wherein the F' ions can essentially act as a catalyst. The same examples can be considered for the other halogen groups as disclosed herein.

[0062] In preferred embodiments, the method as disclosed herein provides that the halogen-containing organosilicon compound is represented by general formula (I), wherein R1, R2, and R3are each independently selected from the group consisting of halogen, alkyl, alkenyl, and alkoxy; wherein X is selected from the group consisting of halogen, alkyl, alkenyl, aminoalkyl, and cyanoalkyl, and wherein at least one of R1, R2, and R3is halogen, preferably fluoro. In preferred embodiments, the method as disclosed herein provides that the halogen-containing organosilicon compound is represented by general formula (I), wherein R1, R2, and R3are each independently selected from the group consisting of halogen, alkyl, and alkoxy; wherein X is selected from the group consisting of halogen, aminoalkyl, and cyanoalkyl, and wherein at least one of R1, R2, and R3is halogen, preferably fluoro.

[0063] In general, the disclosed halogen-containing organosilicon compound according to formula (II) can be considered to consist of: a silicon head group (R1RzSi-), a halogen X, and a functional tail group Y.

[0064] In particular embodiments, the method as disclosed herein provides that the halogen-containing organosilicon compound is represented by general formula (II), wherein X is a halogen selected from the group consisting of fluoride, chloride, bromide, and iodide;

[0065] R1and R2, are each independently selected from the group consisting of halogen, alkyl, alkenyl, phenyl, and alkoxy; and wherein Y is selected from the group consisting of alkyl, alkenyl, phenyl; optionally or additionally comprising a terminal cyano (-CN), cyanate (-OCN), isocyanate (-NCO), thiocyanate (-SCN), isothiocyanate (-NCS), amine, imine, thiol, halide, epoxy, hydroxy, carbonate, carboxylate, acrylate, or vinyl group.

[0066] The term "halo" or "halogen" as a group or part of a group is generic for fluoro, chloro, bromo, iodo.

[0067] The term "alkyl" as a group or part of a group, refers to a hydrocarbyl group of formula CnH2n+i wherein n is a number greater than or equal to 1. Alkyl groups may be linear or branched and may be substituted as indicated herein. Generally, alkyl groups of this invention comprise from 1 to 20 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 8 carbon atoms, preferably from 1 to 6 carbon atoms, more preferably from 1 to 4 carbon atoms. When a subscript is used herein following a carbon atom, the subscript refers to the number of carbon atoms that the named group may contain. For example, the term "Ci-2oalkyl", as a group or part of a group, refers to a hydrocarbyl group of formula -CnH2n+i wherein n is a number ranging from 1 to 20. Thus, for example, "Ci-8alkyl" includes all linear or branched alkyl groups with between 1 and 8 carbon atoms, and thus includes methyl, ethyl, n-propyl, i-propyl, butyl and its isomers (e.g. n-butyl, i-butyl and t-butyl); pentyl and its isomers, hexyl and its isomers, etc. A "substituted alkyl" refers to an alkyl group substituted with one or more substituent(s) (for example 1 to 3 substituent(s), for example 1, 2, or 3 substituent(s)) at any available point of attachment.

[0068] When the suffix "ene" is used in conjunction with an alkyl group, i.e. "alkylene", this is intended to mean the alkyl group as defined herein having two single bonds as points of attachment to other groups. As used herein, the term "alkylene" also referred as "alkanediyl", by itself or as part of another substituent, refers to alkyl groups that are divalent, i.e., with two single bonds for attachment to two other groups. Alkylene groups may be linear or branched and may be substituted as indicated herein. Non-limiting examples of alkylene groups include methylene (-CH2-), ethylene (-CH2-CH2-), methylmethylene (-CH (CH3)- ), 1-methyl-ethylene (-CH(CH3)-CH2-), n-propylene (-CH2-CH2-CH2-), 2-methylpropylene (-CH2-CH(CH3)- CH2-), 3-methylpropylene (-CH2-CH2-CH(CH3)-), n-butylene (-CH2-CH2-CH2-CH2-), 2-methylbutylene (-CH2- CH(CH3)-CH2-CH2-), 4-methylbutylene (-CH2-CH2-CH2-CH(CH3)-), pentylene and its chain isomers, hexylene and its chain isomers.

[0069] The term "alkenyl" as a group or part of a group, refers to an unsaturated hydrocarbyl group, which may be linear, or branched, comprising one or more carbon-carbon double bonds. Generally, alkenyl groups of this invention comprise from 3 to 20 carbon atoms, preferably from 3 to 10 carbon atoms, preferably from 3 to 8 carbon atoms. When a subscript is used herein following a carbon atom, the subscript refers to the number of carbon atoms that the named group may contain. Examples of C3.20alkenyl groups are ethenyl, 2-propenyl, 2-butenyl, 3-butenyl, 2-pentenyl and its isomers, 2-hexenyl and its isomers, 2,4- pentadienyl, and the like.

[0070] The term "alkoxy" or "alkyloxy", as a group or part of a group, refers to a group having the formula -ORbwherein Rbis alkyl as defined herein above. Non-limiting examples of suitable alkoxy include methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, tert-butoxy, pentyloxy and hexyloxy.

[0071] The term "aminoalkyl" as a group or part of a group, refers to the group -Rc-NRdRewherein Rcis alkylene as defined herein, Rdis hydrogen or alkyl as defined herein, and Reis hydrogen or alkyl as defined herein. The term "cyanoalkyl" as a group or part of a group, refers to the group -RJ-CN wherein RJis alkylene or heteroalkylene as defined herein.

[0072] In some embodiments, R1, R2, and R3are each independently selected from the group consisting of hydrogen, halogen, Ci-20alkyl, C2.2oalkenyl, Ci-20alkoxy, and aminoCi-20alkyl; and X is selected from the group consisting of hydrogen, halogen, Ci-20alkyl, C2.2oalkenyl, Ci.2oalkoxy, aminoCi.20alkyl, and cyanoCi.2oalkyl.

[0073] In some embodiments, R1, R2, and R3are each independently selected from the group consisting of hydrogen, halogen, Ci-8alkyl, C2.8alkenyl, Ci-8alkoxy, and aminoCi.8alkyl; and

[0074] X is selected from the group consisting of hydrogen, halogen, Ci-8alkyl, C2.8alkenyl, Ci.8alkoxy, aminoCi.8a Ikyl, and cyanoCi.8alkyl.

[0075] In some embodiments, R1, R2, and R3are each independently selected from the group consisting of - hydrogen, halogen, Ci-4alkyl, C2.4alkenyl, Ci-4alkoxy, and aminoCi.4alkyl; and

[0076] X is selected from the group consisting of hydrogen, halogen, Ci-4alkyl, C2.4alkenyl, Ci.4alkoxy, aminoCi.4a Ikyl, and cyanoCi.4alkyl.

[0077] In some exemplary embodiments, R1, R2, and R3are each independently Cialkyl, C2a Ikyl, C3alkyl, or C4alkyl. In some exemplary embodiments, R1, R2, and R3are each independently fluoro, chloro, bromo, or iodo. In some exemplary embodiments, X is cyanoCialkyl, cyanoC2alkyl, cyanoC3alkyl, or cyanoC4alkyl.

[0078] In some exemplary embodiments, X is fluoro, chloro, bromo, or iodo.

[0079] In some particular embodiments, the halogen-containing organosilicon compound may be selected from the group consisting of: 4-[fluoro(dimethyl)silyl]butanenitrile, 4-[fluoro(diethyl)silyl]butanenitrile, 4- [fluoro(di-n-propyl)silyl] butanenitrile, 4-[fluoro(d i-i-propyl)silyl] butanenitrile, 4-[fluoro(di-n- butyl)silyl] butanenitrile, 4-[fluoro(d i-t-butyl)silyl] butanenitrile, 4-[difluoro(methyl)silyl]butanenitrile, 4- [difluoro(ethyl)silyl]butanenitrile, 4-[d ifluoro(n-propyl)silyl] buta nenitrile, 4-[difluoro(i- propyl)silyl] buta nenitrile, 4-[difluoro(n-butyl)silyl] buta nenitrile, 4-[difluoro(t-butyl)silyl] buta nenitrile, 4- [trifluorosilyl] butanenitrile, 4-[chloro(dimethyl)silyl] buta nenitrile, 4-[chloro(diethyl)silyl] butanenitrile, 4- [chloro(di-n-propyl)silyl] buta nenitrile, 4-[chloro(di-i-propyl)silyl] buta nenitrile, 4-[chloro(di-n- butyl)silyl] buta nenitrile, 4-[chloro(di-t-butyl)silyl] buta nenitrile, 4-[dichloro(methyl)silyl] buta nenitrile, 4- [dichloro(ethyl)silyl] buta nenitrile, 4-[dichloro(n-propyl)silyl] buta nenitrile, 4-[dichloro(i- propyl)silyl] buta nenitrile, 4-[dichloro(n-butyl)silyl] butanenitrile, 4-[dichloro(t-butyl)silyl] buta nenitrile, 4- [trichlorosilyl] buta nenitrile, 4-[bromo(dimethyl)silyl] buta nenitrile, 4-[bromo(diethyl)silyl] buta nenitrile, 4-[bromo(di-n-propyl)silyl] butanenitrile, 4-[bromo(di-i-propyl)silyl] buta nenitrile, 4-[bromo(di-n- butyl)silyl] buta nenitrile, 4-[bromo(di-t-butyl)silyl] buta nenitrile, 4-[bromo(methyl)silyl] buta nenitrile, 4- [dibromo(ethyl)silyl] buta nenitrile, 4-[dibromo(n-propyl)silyl] buta nenitrile, 4-[dibromo(i- propyl)silyl] buta nenitrile, 4-[d ibromo(n-butyl)silyl] butanenitrile, 4-[d ibromo(t-butyl)silyl] buta nenitrile, 4- [tribromosilyl] buta nenitrile. Y1

[0080] As opposed to traditional sol-gel methods using additives, catalysts and / or fillers, the herein disclosed method comprising the halogen-containing organosilicon compound provides the advantage that this compound may be covalently integrated in the growing polymer network. It has been found that by adding the halogen-containing organosilicon compound in the molar ratio as disclosed herein, it will not interfere (or interfere less) with the diffusion of ions in the formed solid electrolyte, which is necessary for a highly conductive solid electrolyte.

[0081] Another advantage of the halogen-containing organosilicon compound used in the molar ratio as disclosed herein, is the provision of a solid electrolyte composition with improved mechanical strength. Furthermore, compared to methods for forming solid electrolyte compositions disclosed in the art, the method described herein may offer a significant reduction in the number or reagents and purification steps required for the formation of solid electrolyte compositions.

[0082] In some embodiments, the halogen-containing organosilicon compound may act as a catalyst, and is supported by the silica matrix (i.e., grafted to or embedded in said silica matrix). It will be understood that the herein disclosed method may comprise the addition of one or more halogen-containing organosilicon compounds. For instance, a mixture of at least two halogen-containing organosilicon compounds may be used to stimulate an improved performance of the solid electrolyte composition.

[0083] In some embodiments, the liquid mixture may further comprise a catalyst and / or polymerization precursor. Suitable catalysts comprise alkyl carboxylic acid, aryl carboxylic acid, cycloalkyl carboxylic acid, HF, HCI, HBr, HI, metal ions such as Na+, Mg2+, and K+, and wherein alkyl, aryl, and cycloalkyl have the meaning as defined herein above. Suitable polymerization precursors comprise a polymerizable functional group such as an alcohol, a polyolefin, an acrylate, a methacrylate, an acrylamide, and a methacrylamide. It should be understood that other catalysts and / or polymerization precursors may be used. The additional catalyst has the effect that the resulting curing mixture can gel faster. The additional polymerization precursor can be advantageously selected so as to self-polymerize and / or react with terminal functional groups from the halogen-containing organosilicon compound in order to stimulate an improved mechanical stability of the solid electrolyte composition.

[0084] In some embodiments, gelation can be performed by storage in a storage room. For example, a container containing the liquid mixture can be sealed and stored at room temperature (25 °C, ambient temperature) for several days, during which the liquid mixture turns into a wet gel mixture.

[0085] The time required for the gelation can be controlled by the amount of water added, amount of the solvent and / or organic solvent added, and storage temperature. In some embodiments, the gelation can be performed at a temperature of at most 70 °C to at least 30 °C, preferably at most 60 °C to at least 40 °C, more preferably at most 55 °C to at least 45 °C, more preferably still about 50 °C. The listed temperatures can decrease the time needed for gelation to occur, although lower temperatures can be considered still. In some particular embodiments, the method as disclosed herein provides that the formation of the gel mixture can occur in at least 1 minute and at most 300 minutes, or at least 5 minutes and at most 300 minutes, or at least 5 minutes and at most 240 minutes, or at least 5 minutes and at most 120 minutes, preferably in at least 5 minutes and at most 60 minutes.

[0086] After gelation, the solid electrolyte composition can be formed by drying of the wet gel mixture. The drying can be performed by a classic drying and / or ageing process. For example, the gel mixture can be dried, for example, using a vacuum dryer under the conditions of a pressure of 0.01 to 100 Pa and a temperature of 15 to 120 °C. Optionally, a pre-drying process may be carried out before the vacuum drying step to slowly remove the solvent throughout the final curing stages. This additional step may avoid uncontrolled changes in the textural properties of the gel, and prevent the formations of cracks in the solid pellets which can be caused by fast solvent removal. In the pre-drying process, the gel mixture is kept for about 24 h under dry room conditions (e.g., between 20 and 25 °C when the dew point ranges from - 50 to -42 °C). Most of the water from the solvent, and optionally the organic solvent, contained in the gel mixture can be evaporated by the pre-drying process.

[0087] The terms "ionic liquid" (IL) and "ionically conductive compound" are used herein interchangeably and refers to a salt that has a melting temperature of 100 °C or less, such as 60 °C or less, preferably 40 °C or less. It should be understood that the terms ionic liquid and ionically conductive compound may refer to ionic liquid mixtures comprising one or more ionic liquid.

[0088] The term "ionic liquid electrolyte" refers to a composite or mixture comprising one or more ionic liquid or ionically conductive compound and one or more metal salt. ILEs as described herein are characterized by a low flammability and high dielectric constant, which ensures strong dissociation of the metal salts leading to a highly conductive solid electrolyte. For example, the solid electrolyte as disclosed herein may comprise l-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIFSI) and lithium salt in accordance with a preferred embodiment of the electrolyte. A solid-state alkali metal battery using said solid electrolyte can ensure a long-term cycle life, improved rate capability, and an enhanced low-temperature performance. Nonetheless, other combinations of ILs and metal salts may be considered, as described below.

[0089] In some embodiments, the metal salt can comprise Li+, Na+, Mg2+, Ca2+, Al3+, and / or a combination thereof. Preferably the metal salt comprises Li+and / or Na+, which are industry standard for the manufacturing of a high energy solid-state battery. In some embodiments, the molar ratio of the ionically conductive compound to the silicon precursor is between at least 0.10 and at most 10.0, or between at least 0.10 and at most 9.0, or between at least 0.20 and at most 8.0, or between at least 0.20 and at most 7.0, or between at least 0.20 and at most 6.0, or between at least 0.20 and at most 5.0, or between at least 0.30 and at most 5.0, or between at least 0.40 and at most 5.0, or between at least 0.50 and at most 5.0, or between at least 0.50 and at most 4.0, or between at least 0.50 and at most 3.0, or between at least 0.50 and at most 2.5, preferably between at least between 0.50 and at most 2.0, more preferably between at least 0.50 and at most 1.85, or between at least 0.50 and at most 1.50. The latter ranges are advantageous for the manufacturing of a solid-state battery having improved mechanical properties and satisfactory ionic conductivity.

[0090] In some embodiment, the amount of dissolved metal salt concentration may be at least 1 mol / Lto at most 2 mol / L. Preferably, the amount of dissolved LiFSI may be at least 1 mol / L to at most 2 mol / L. Preferably, the amount of dissolved LiTFSI may be at least 1 mol / L to at most 2 mol / L. Preferably, the amount of dissolved NaFSI may be at least 1 mol / L to at most 2 mol / L. Preferably, the amount of dissolved NaTFSI may be at least 1 mol / L to at most 2 mol / L. The listed amounts are advantageous for the manufacturing of a solid-state battery having improved ionic conduction properties.

[0091] Alternatively or in combination, the lithium salt may comprise one or more other anions, such as Lithium bis(trifluoromethanesulfonyl)imide (LiFSI), Lithium bis(trifluoromethane)sulfonimide (LiTFSI), Lithium hexafluorophosphate (LiPFs), Lithium tetrafluoroborate (LiBF4), Lithium bis(oxalato)borate (LiBOB), Lithium nitrate (LiNO3), any substitutions known in the art, and / or a combination thereof. Nonetheless, LiTFSI is preferred because it is more chemically stable in an organic solvent. Additionally, a plurality of different metal salts may be used, for example, LiFSI and LiTFSI.

[0092] Alternatively or in combination, the sodium salt may comprise one or more other anions, such as Sodium bis(trifluoromethanesulfonyl)imide (NaFSI), Sodium bis(trifluoromethane)sulfonimide (NaTFSI), Sodium hexafluorophosphate (NaPFs), Sodium tetrafluoroborate (NaBF ), Sodium bis(oxalato)borate (NaBOB), Sodium nitrate (NaNO3), any substitutions known in the art, and / or a combination thereof. Nonetheless, NaTFSI is preferred because it is more chemically stable in an organic solvent. Additionally, a plurality of different metal salts may be used, for example, NaFSI and NaTFSI.

[0093] In particular embodiments, the ionically conductive compound is selected from the group consisting of: l-Ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIFSI), l-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI), l-Ethyl-3-methylimidazolium fluorosulfonyl (trifluoromethanesulfonyl)imide (EMIFTFSI), l-Ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIOTf), Butyltrimethylammonium bis(trifluoromethylsulfonyl)imide (BMATFSI), l-Ethyl-3- methylimidazolium bis(pentafluoroethylsulfonyl)imide (EMIBeti), l-Ethyl-3-methylimidazolium dicyanamide (EMIDCA), l-Ethyl-3-methylimidazolium diethylphosphate (EMIDEP), l-Butyl-3- methylimidazolium bis(fluorosulfonyl)imide (BMIFSI), l-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMITFSI), l-Butyl-3-methylimidazolium fluorosulfonyl (trifluoromethanesulfonyl)imide (BMIFTFSI) l-Butyl-3-methylirnidazoliurn trifluoromethanesulfonate (BMIOTf), l-Butyl-3-methylimidazolium bis(pentafluoroethylsulfonyl)imide (BMIBeti), 1-Butyl-l- methylpyrrolidinium bis(fluorosulfonyl)imide (BMPFSI), 1-Butyl-l-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPTFSI), 1-Butyl-l-methylpyrrolidinium fluorosulfonyl (trifluoromethanesulfonyl)imide (BMPFTFSI), 1-Butyl-l-methylpyrrolidinium trifluoromethanesulfonate (BMPOTf), 1-Butyl-l-methylpyrrolidinium bis(pentafluoroethylsulfonyl)imide (BMPBeti), 1-Methyl-l- pentylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PyrlSTFSI), 1-Methyl-l-pentylpyrrolidinium fluorosulfonyl (trifluoromethanesulfonyl)imide (PyrlSFTFSI), 1-Methyl-l-pentylpyrrolidinium trifluoromethanesulfonate (Pyrl5OTf), 1-Methyl-l-pentylpyrrolidinium bis(pentafluoroethylsulfonyl)imide (Pyrl5 Beti), triethylsulfonium bis(trifluoromethanesulfonyl)imide (TESTFSI), tetrabutylammonium bis(trifluoromethane)sulfonylimide (TBATFSI), and mixtures thereof.

[0094] In some embodiments, the ionically conductive compound is selected from the group consisting of: 1- Ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIFSI), l-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (EMITFSI), Butyltrimethylammonium bis(trifluoromethylsulfonyl)imide (BMATFSI), l-Butyl-3-methylimidazolium bis(fluorosulfonyl)imide (BMIFSI), l-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (BMITFSI), 1-Butyl-l-methylpyrrolidinium bis(fluorosulfonyl)imide (BMPFSI), 1-Butyl-l-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPTFSI), 1-Butyl-l- methylpyrrolidinium fluorosulfonyl (trifluoromethanesulfonyl)imide (BMPFTFSI), 1-Methyl-l- pentylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PyrlSTFSI), triethylsulfonium bis(trifluoromethanesulfonyl)imide (TESTFSI), tetra butylammonium bis(trifluoromethane)sulfonylimide (TBATFSI), and mixtures thereof.

[0095] In some embodiments, the ionically conductive compound is selected from the group consisting of: 1- Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI), Butyltrimethylammonium bis(trifluoromethylsulfonyl) imide (BMATFSI), l-Butyl-3-methylimidazolium bis(fluorosulfonyl)imide (BMIFSI), l-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMITFSI), 1-Butyl-l- methylpyrrolidinium bis(fluorosulfonyl)imide (BMPFSI), 1-Methyl-l-pentylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PyrlSTFSI), and mixtures thereof. In another aspect, the present invention relates to a composite electrode comprising: a solid electrolyte composition prepared according to any of the above embodiments, and an electrode. In some embodiments, the solid electrolyte composition may cover and / or coat a surface of the electrode as a covering / coating layer, as will be described below. Preferably, the solid electrolyte composition may impregnate the porosity of the electrode as described below.

[0096] The electrode can be, for example, produced by applying a slurry containing active material particles, a binder and conductive agent particles onto a current collector. The slurry can be applied by using a coating technique known in the art, for example, drop casting, blade coating, slot die coating, spray coating, and so on. The slurry can be dried to obtain an electrode film on top of the current collector.

[0097] Subsequently, the electrode can be impregnated, for example, by applying a solid electrolyte composition precursor solution and / or or pre-gelated electrolyte solution onto said electrode. In this way, a composite electrode comprising the solid electrolyte can be obtained, with or without an overfill. The impregnation with a solid electrolyte composition precursor and / or pre-gelated electrolyte solution can be performed by using a coating technique known in the art, for example, drop casting, blade coating, slot die coating, spray coating, dip coating and the like. The amount of solid electrolyte composition precursor and / or pre- gelated electrolyte solution can be adapted, for example, to form or not form an overfill on top of the electrode. The skilled person understands that the exemplary embodiment can be adapted based on the relevant assembly process strategy.

[0098] It may be, moreover, appreciated that, because of the improved properties of the herein disclosed solid electrolyte obtained by the method according to any of the above embodiments, there exists the possibility to adapt the production process, for example, to produce a self-standing film, which was previously difficult with other types of solid electrolytes, such as pure porous silica.

[0099] Accordingly, in some embodiments the electrode can be impregnated to form a composite electrode by pressing the electrode onto a self-standing solid electrolyte film and / or pellet produced in accordance with any of the above methods, in the cell. This latter approach does not involve the abovementioned coating techniques known in the art. Nonetheless, the solid electrolyte can also be produced using classic production techniques, as described above, allowing for great adaptability based on the relevant assembly process strategy.

[0100] As described above, the solid electrolyte composition obtained by the method of the present invention can demonstrate a suitable ionic conductivity for an application in alkali metal batteries; therefore, an electrode comprising said solid electrolyte composition can demonstrate improved ionic conduction properties also. Similarly, the electrode can have improved mechanical properties due to the improved elasticity of the solid electrolyte composition. It is understood that any of the above embodiments related to the solid electrolyte composition form embodiments of the electrode.

[0101] The term "covering" or "coating" is used to refer to a point or position where the electrode comes in contact with the solid electrolyte according to any of the above embodiments and results in the formation of a layer that covers and / or coats the electrode active material, more specifically on one or more surfaces thereof. Advantageously, the layer completely covers at least one surface of the electrode.

[0102] In some embodiments, the solid electrolyte composition may be a uniform covering / coating layer on the electrode active material. The term "uniform" as used herein referring to the composite layer means that said layer does not contain segregated areas of amorphous and / or crystalline content that can be easily discerned using the analytical techniques described herein.

[0103] In some embodiments, the solid electrolyte composition may be a homogeneous covering / coating layer on the electrode active material. The term "homogeneous" as used herein referring to the composite layer means that the components of said layer, more specifically the ILE and the hybrid organic-inorganic silica network that incorporate silica and halogen-containing organosilicon compounds in accordance with any of the herein described embodiments, are homogeneously mixed and said layer and / or a surface thereof therefore does not contain areas wherein the components can be easily discerned using the analytical techniques described herein.

[0104] In some embodiments the covering layer may have a dried thickness, before compression, lower than about 200 pm, preferably lower than about 150 pm; more preferably lower than about 100 pm; more preferably still lower than about 60 pm, for example 50 pm, 40 pm or 30 pm.

[0105] In some embodiments the thickness of the covering layer, preferably as excess overfill solid electrolyte, may be between 0 pm and 1000 pm, preferably between 0 pm and 300 pm, more preferably between 0 pm and 100 pm, more preferably still between 0 pm and 30 pm. The thickness of the covering layer can impact the electrical properties of the battery, and the skilled person understands that the thickness of the herein described exemplary embodiments can be adapted based on the relevant assembly process strategy.

[0106] As used herein, a "thick" film refers to an electrolyte film that, after drying has a layer thickness greater than about 50 pm, and a "thin" film refers to an electrolyte film that, after drying has a layer thickness lower than about 50 pm. Advantageously, the solid electrolyte thickness, after compression, is produced to be as thin as possible while maintaining its mechanical functionality (no cracking) to separate positive and negative electrodes from each other such that the maximum Wh / L can be realised at device and stack level. Nonetheless, it should be appreciated that the herein disclosed composite electrolyte has the advantage of allowing the production of th ick / thin films of varying thickness and diameter due to its improved mechanical properties as discussed earlier, making the fabrication of large and / or thick selfstanding films possible, or obtaining a crack-free film of few pm (for example, in a range of >20 pm & < 150 pm on top of the electrode).

[0107] In preferred embodiments, the produced solid electrolyte film may have an average thickness of between 100 pm and 1000 pm, or between 100 pm and 900 pm, or between 100 pm and 800 pm, or between 100 pm and 700 pm, preferably between 100 pm and 600 pm, or between 200 pm and 600 pm, or between 300 pm and 600 pm, or between 400 pm and 600 pm, more preferably between 400 pm and 500 pm, for example about 450 pm. Alternatively or in combination with any of the above embodiments, the solid electrolyte composition may be a self-standing film. Preferably the solid electrolyte composition is a homogeneous / uniform self-standing film. Due to the improved mechanical properties of the solid electrolyte, it is possible to cast a film that can be placed onto an electrode, and preferably between two opposite electrodes. The self-standing film can be produced by being deposited on a substrate that is removed after solidification of the solid electrolyte.

[0108] In some embodiments an electrode active material used in the electrode can be a positive electrode active material. Examples of the positive electrode active material may include a lithium-containing transition metal oxide, vanadium oxide, chromium oxide, and lithium-containing transition metal sulfide. Examples of the lithium-containing transition metal oxide include LiCoO2, Li NiO2, LiMnO2, LiMn2O4, LiNiCoMnO2(referred as NMC family with various compositions NMXxyz, where x, y z, refers to the relative amounts of Ni, Mn and Co present in the cathode active material, for example, NMC 111 corresponding to a material composed of Ni 33.33%; Mn 33.3% and Co3.33%; or NMC 532, NMC 622, NMC 721, NMC 811, NMC 90.50.5 and any other composition of NMC or combination thereof), LiNiCoO2, LiCoMnO2, LiNiMnO2, LiNiCoMnO4, LiMnNiO4, LiMnCoO4, LiNiCoAIO2, LiNiPO4, LiCoPO4, LiMnPO4, LiFePO4, LiMnFePO4, Li2NiSiO4, Li2CoSiO4, Li2MnSiO4, Li2FeSiO4, LiNiBO3, LiCoBO3, LiMnBO3, and LiFeBO3. Examples of the lithium- containing transition metal sulfide include LiTiS2, Li2TiS3, and Li3NbS4. One positive electrode active material or two or more positive electrode active materials selected from these positive electrode active materials can be used.

[0109] In some embodiments an electrode active material used in the electrode can be a negative electrode active material. Examples of the negative electrode active material may include a metal, semimetal, oxide, nitride, and carbon. Examples of the metal and semimetal include lithium, silicon, amorphous silicon, aluminium, silver, tin, antimony, and their alloys. Examples of the oxide can include Li4Ti50i2, Li2SrTi60i4, TiO2, Nb2O5, SnO2, Ta2O5, WO2, WO3, Fe2O3, CoO, MoO2, SiO, SnBPOs, and their mixtures. Examples of the nitride can include LiCoN, Li3FeN2, LiyMnIX , and their mixtures. Examples of the carbon include graphite, graphene, hard carbon, carbon nanotube, and their mixtures. One negative electrode active material or two or more negative electrode active materials selected from these negative electrode active materials can be used.

[0110] In some embodiments, the electrode may comprise a binder. The binder may fix particles of the electrode active material to each other. When the particles of the electrode active material are fixed to each other, the occurrence of a gap due to expansion and shrinkage of the particles of the electrode active material is reduced. This reduces a decrease in the discharged capacity of a battery including the electrode. The binder may, for example, comprise carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF) and the like.

[0111] In another aspect of the invention, the present invention relates to a solid electrolyte composition for use in the manufacturing of an electrochemical energy storage device and is preferably obtained or obtainable by means of the method according to an aspect of the present invention or (preferred) embodiments thereof.

[0112] In a particular embodiment, the solid electrolyte composition comprises a porous silica matrix, preferably a mesoporous silica matrix, comprising an ionic liquid electrolyte which comprises an ionically conductive compound and a metal salt; wherein the porous silica matrix is at least partially modified by a halogen-containing organosilicon compound; and preferably wherein the total wt.% of silica in the solid electrolyte composition is at least 5.0 and at most 30.0 wt.%, and the total wt.% of the halogen-containing organosilicon compound in the solid electrolyte composition is between at least 0.3 wt.% and at most 25.0 wt.%.

[0113] In some embodiments, the total wt.% of silica in the solid electrolyte composition may be at least 5.0 and at most 50.0 wt.%, or at least 5.0 and at most 45.0 wt.%, or at least 5.0 and at most 40.0 wt.%, or at least 5.0 and at most 35.0 wt.%, preferably at least 5.0 and at most 30.0 wt.%, for example, 10.0 wt.%, 15.0 wt.%, 20.0 wt.%, or 25.0 wt.%.

[0114] In some embodiments, the total wt.% of the halogen-containing organosilicon compound in the solid electrolyte composition may be between at least 0.1 wt.% and at most 40.0 wt.%, or between at least 0.1 wt.% and at most 35.0 wt.%, or between at least 0.3 wt.% and at most 35.0 wt.%, or between at least 0.3 wt.% and at most 30.0 wt.%, preferably between at least 0.3 wt.% and at most 25.0 wt.%, for example, 1.0 wt.%, 5.0 wt.%, 10.0 wt.%, or 20.0 wt.%.

[0115] In particular embodiments, the porous silica matrix is a condensation product of a silicon precursor, and the halogen-containing organosilicon compound represented general formula (I),

[0116] R1, R2, and R3are each independently selected from the group consisting of hydrogen, halogen, alkyl, alkenyl, alkoxy, and aminoalkyl;

[0117] X is selected from the group consisting of hydrogen, halogen, alkyl, alkenyl, alkoxy, aminoalkyl, cyanoalkyl; and wherein at least one of R1, R2, and R3is halogen.

[0118] In preferred embodiments, at least one of R1, R2, and R3is fluoro.

[0119] In preferred embodiments, the composition as disclosed herein provides thatX is an electron-withdrawing group (EWG). In other words, X can be a functional group that is able to reduce the electron density around the silicon atom. Without wishing to be bound by theory, it is rationalized that when an EWG is attached to a silicon atom that is also bonded to at least one halogen (e.g., fluorine, chlorine, bromine, or iodine), it can polarize the silicon-halogen bond and change its reactivity.

[0120] In preferred embodiments, the composition as disclosed herein provides that the halogen-containing organosilicon compound is represented by general formula (I), wherein R1, R2, and R3are each independently selected from the group consisting of halogen, alkyl, alkenyl, and alkoxy; wherein X is selected from the group consisting of halogen, alkyl, alkenyl, aminoalkyl, and cyanoalkyl, and wherein at least one of R1, R2, and R3is halogen, preferably fluoro.

[0121] In preferred embodiments, the composition as disclosed herein provides that the halogen-containing organosilicon compound is represented by general formula (I), wherein R1, R2, and R3are each independently selected from the group consisting of halogen, alkyl, and alkoxy; wherein X is selected from the group consisting of halogen, aminoalkyl, and cyanoalkyl, and wherein at least one of R1, R2, and R3is halogen, preferably fluoro.

[0122] In particular embodiments, the porous silica matrix is a condensation product of a silicon precursor, and the halogen-containing organosilicon compound represented general formula (II),

[0123] (ID wherein X is a halogen selected from the group consisting of fluoride, chloride, bromide, and iodide; and wherein R1and R2, are each independently selected from the group consisting of halogen, alkyl, alkenyl, phenyl, and alkoxy; and wherein Y is selected from the group consisting of alkyl, alkenyl, phenyl; optionally or additionally comprising a terminal cyano (-CN), cyanate (-OCN), isocyanate (-NCO), thiocyanate (-SCN), isothiocyanate (-NCS), amine, imine, thiol, halide, epoxy, hydroxy, carbonate, carboxylate, acrylate, or vinyl group.

[0124] It should be clear that the exemplary embodiments of the halogen-containing organosilicon compound listed above for the method as disclosed herein, are interchangeable with the halogen-containing organosilicon compound comprised in the solid electrolyte composition as disclosed herein. Advantageously, even at low amounts of halogen-containing organosilicon compound, the mechanical properties of the solid electrolyte composition can be improved (e.g. improved resilience and flexibility). Alternatively or in combination, the electrical properties of the solid electrolyte composition can be preserved or improved (e.g. improving ionic conductivity). Alternatively or in combination, the thermal properties of the solid electrolyte composition can be preserved or improved (e.g. reduced thermal degradation).

[0125] In some embodiments, the solid electrolyte composition can have an anodic limiting current of between 0.1 mA cm'2and 5.0 mA cm'2, or between 0.1 mA cm'2and 4.0 mA cm'2, or between 0.1 mA cm'2and 3.0 mA cm'2, or between 0.1 mA cm'2and 2.0 mA cm'2, or between 0.1 mA cm'2and 1.5 mA cm'2, or between 0.2 mA cm'2and 1.5 mA cm'2, or between 0.3 mA cm'2and 1.5 mA cm'2, or between 0.4 mA cm'2and 1.5 mA cm'2, or preferably between 0.5 mA cm'2and 1.5 mA cm'2, or between 0.5 mA cm'2and 1.0 mA cm'2. The anodic current limit can be measured by chronoamperometry at 20 °C. In some embodiments, the solid electrolyte composition can have an ionic conductivity at 20 °C between 10-6S cm-1and 10 S cm-1, or between 10-5S cm-1and 1 S cm-1, or between 10-4S cm-1and 101S cm-1, preferably between 10-4S cm-1and 10-2S cm-1. The ionic conductivity can be calculated using methods of the art suitable for analysis of an impedance plot.

[0126] In some embodiments, the solid electrolyte composition can have an anodic stability of at most 5.0 V vs. SHE, or at most 4.0 V vs. SHE, or at most 3.5 V vs. SHE, or at most 3.0 V vs. SHE, or at most 2.5 V vs. SHE, or at most 2.0 V vs. SHE, preferably at most 1.7 V vs. SHE.

[0127] In some embodiments, the solid electrolyte composition can have a mesoporous silica matrix material with some macropores, preferably up to 10 wt.% macropores, or up to 20 wt.% macropores, or up to 30 wt.% macropores, or up to 40 wt.% macropores, or up to 50 wt.% macropores, or up to 60 wt.% macropores, or up to 70 wt.% macropores, or up to 80 wt.% macropores, or up to 90 wt.% macropores, or up to 99 wt.% macropores.

[0128] In a particular embodiment, said solid electrolyte composition for use in the manufacturing of an electrochemical energy storage device is preferably produced according to the method for producing a solid electrolyte composition as disclosed herein.

[0129] In another aspect of the invention, the present invention relates to an electrochemical energy storage device, such as a battery or cell, comprising a positive electrode, a negative electrode; and the solid electrolyte composition as disclosed herein. It is understood that an electrochemical energy storage device may comprise various combinations of electrode, for example, a plurality of negative and positive electrodes that are advantageously stacked on top of each other. Techniques for producing an electrochemical energy storage device from a solid electrolyte composition are known in the art.

[0130] As used herein, an "electrochemical energy storage device" refers to a device capable of either generating electrical energy from chemical reactions or using electrical energy to cause chemical reactions. The technology of the present invention can be regarded as general-purpose technology in the sense that it can be readily adapted for a variety of different electrochemical energy storage devices, including for example, solid-state electrochemistry which may be implemented in various battery applications, such as automotive, aviation, marine, space, but not limited thereto.

[0131] Advantageously, the electrochemical energy storage device comprising the solid electrolyte composition as disclosed herein may provide increased thermal stability for longer lifetime of e.g., a battery, increased voltage stability, and reduced failure of said device. In some embodiments, the electrochemical energy storage device may comprise the solid electrolyte as a self-standing film that is arranged on at least one electrode, preferably between two opposite electrodes.

[0132] As described above, because the solid electrolyte composition of the present invention can demonstrate high ionic conductivity; therefore, a power storage device comprising an electrode with said solid electrolyte composition can demonstrate improved ionic conduction properties also. Similarly, the power storage device can have improved mechanical properties due to the improved flexibility of the solid electrolyte composition comprised in the electrode. It is understood that any of the above embodiments of the solid electrolyte composition form embodiments of the power storage device.

[0133] In particular embodiments, the present invention provides that the energy storage device is an alkali metal battery, preferably a lithium and / or a sodium battery.

[0134] It is understood that although specific embodiments, constructions, configurations, and materials for devices according to the present invention have been discussed herein, various changes or modifications in form and detail may be made without departing from the scope of this invention. For example, any drawings provided are merely representative of possible procedures. Functionality may be added to or removed from block diagrams, and operations may be interchanged among functional blocks. Steps may also be added or omitted in the methods described within the scope of the present invention.

[0135] Additionally, while certain embodiments, constructions, and configurations are described as providing an "improvement," it should be understood that any such improvement represents a benefit based on a comparison to similar devices, structures, systems, or methods in the art, depending on the context. The degree of improved performance may vary between disclosed embodiments, and no uniformity in the amount, degree, or realization of improved performance should be assumed to apply universally across all embodiments.

[0136] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment.

[0137] As used herein, the terms "comprising", "comprises" and "comprised of" as used herein are synonymous with "including", "includes" or "containing", "contains", and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. The terms "comprising", "comprises" and "comprised of" when referring to recited members, elements or method steps also include embodiments which "consist of" said recited members, elements or method steps. The singular forms "a", "an", and "the" include both singular and plural referents unless the context clearly dictates otherwise.

[0138] As used herein, relative terms, such as "left," "right," "front," "back," "top," "bottom," "over," "under," etc., are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that such terms are interchangeable under appropriate circumstances and that the embodiment as described herein are capable of operation in other orientations than those illustrated or described herein unless the context clearly dictates otherwise.

[0139] Objects described herein as being "adjacent" to each other reflect a functional relationship between the described objects, that is, the term indicates the described objects must be adjacent in a way to perform a designated function which may be a direct ( / .e. physical) or indirect ( / .e. close to or near) contact, as appropriate for the context in which the phrase is used.

[0140] Objects described herein as being "connected" or "coupled" reflect a functional relationship between the described objects, that is, the terms indicate the described objects must be connected in a way to perform a designated function which may be a direct or indirect connection in an electrical or nonelectrical ( / .e. physical) manner, as appropriate for the context in which the term is used.

[0141] As used herein, the term "substantially" refers to the complete or nearly complete extent or degree of an action, characteristic, property, state, structure, item, or result. For example, an object that is "substantially" enclosed would mean that the object is either completely enclosed or nearly completely enclosed. The exact allowable degree of deviation from absolute completeness may in some cases depend on the specific context. However, generally speaking the nearness of completion will be so as to have the same overall result as if absolute and total completion were obtained. The use of "substantially" is equally applicable when used in a negative connotation to refer to the complete or near complete lack of an action, characteristic, property, state, structure, item, or result.

[0142] As used herein, the term "about" is used to provide flexibility to a numerical value or range endpoint by providing that a given value may be "a little above" or "a little below" said value or endpoint, depending on the specific context. Unless otherwise stated, use of the term "about" in accordance with a specific number or numerical range should also be understood to provide support for such numerical terms or range without the term "about". For example, the recitation of "about 30" should be construed as not only providing support for values a little above and a little below 30, but also for the actual numerical value of 30 as well. The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within the respective ranges, as well as the recited endpoints. Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order, unless specified. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the disclosure described herein are capable of operation in other sequences than described or illustrated herein.

[0143] Reference throughout this specification to substituents is meant to indicate that one or more hydrogen atoms on the atom indicated in the expression using "substituted" is replaced with a selection from an indicated group as detailed below, provided that the indicated atom's normal valence is not exceeded, and that the substitution results in a chemically stable compound, i.e., a compound that is sufficiently robust to survive isolation from a reaction mixture.

[0144] EXAMPLES

[0145] Examples of the implementation of the technology according to the present invention are given hereinbelow. The provision of examples is meant to aid the reader in understanding the technological concepts more easily, but it is not meant to identify the most important or essential features thereof, nor is it meant to limit the scope of the present invention.

[0146] To demonstrate the improved mechanical properties of the herein disclosed solid electrolyte, a number of solid electrolyte films are produced using drop casting of an electrolyte solution prepared through a sol-gel process based on the following process parameters.

[0147] Example 1

[0148] First, 10.71 g of l-Ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIFSI) and 2.64 g of Lithium bis(trifluoromethane)sulfonimide (LiTFSI) were mixed in a glass bottle container equipped with a magnetic stirring bar placed in a glovebox in a molar ratio of EM I FSI : LiTFSI 4.0:1.0 to obtain an ionic liquid electrolyte (ILE). Next, 7.66 g of tetraethyl orthosilicate (TEOS), 8.20 g of de-ionized water and 15.10 g of PGME were added to the formed ILE in the container to obtain a liquid mixture. The molar mixing ratio of ILE:TEOS was 1.0:1.0. To the formed liquid mixture, 693 mg of 4-[fluoro(dimethyl)silyl]buta nenitrile (OS, purchased from Silatronix) was added in a molar ratio of OS:TEOS of 0.13:1.0.

[0149] Once a homogeneous, clear solution was obtained, the container was sealed and stored at 25 °C for 10 minutes. Then, the reaction mixture was kept in the closed container for 1 hour at 35 °C and subsequently quenched at -18 °C for 15 minutes. The obtained solution was drop-cast in an aluminium CR2025 coin cell cap used as a mold. Around 400 mg of the sol was used per mold. The drop cast sol was kept at ambient temperature (40-60% relative humidity and 20.5-22.5°C) for 1 to 2 days to obtain a gel mixture.

[0150] The obtained gel mixture was then stored in a dry atmosphere (dew point of -48 to -38 °C and temperature of 21.5-23.5°C) for 1 day. Subsequently, the wet samples were demolded and dried at 60 °C under vacuum (< 10'2mbar) for 3 days to obtain a solid electrolyte composition in the form of solid pellets. The selfstanding solid pellets of 400 pm thickness were sealed under vacuum (< 10'2mbar) and kept in a dry room atmosphere prior to use.

[0151] Example 2

[0152] A solid electrolyte composition was prepared in the same manner as for Example 1, but wherein the molar ratio of OS:TEOS was 0.01:1.0 and the reaction mixture was kept in the closed container for 2 hours at 35 °C before quenching at - 18 °C for 15 minutes.

[0153] Example 3

[0154] A solid electrolyte composition was prepared in the same manner as for Example 1, but wherein the molar mixing ratio of ILE:TEOS was 1.5:1.0.

[0155] Example 4

[0156] A solid electrolyte composition was prepared in the same manner as for Example 1, but wherein the molar mixing ratio of ILE:TEOS was 1.85:1.0.

[0157] Comparative Example 1

[0158] A solid electrolyte composition was prepared in the same manner as for Example 1, but wherein the molar ratio of OS:TEOS was 0.90:1.0 and the reaction mixture was kept in the closed container for 21 hours at 35 °C before quenching at - 18 °C for 15 minutes.

[0159] Comparative Example 2

[0160] First, 10.87 g of l-Ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIFSI) and 2.68 g of Lithium bis(trifluoromethane)sulfonimide (LiTFSI) were mixed in a container placed in a glovebox in a molar ratio of EM I FSI : LiTFSI 4.0:1.0 to obtain an ionic liquid electrolyte (ILE). Next, 7.78 g of tetraethyl orthosilicate (TEOS), 8.33 g of de-ionized water and 15.34 g of PGME were added to the formed ILE in the container to obtain a liquid mixture. The molar mixing ratio of ILE:TEOS was 1.0:1.0.

[0161] Once a homogeneous, clear solution was obtained, the container was sealed and stored at 25 °C for 10 minutes. Then, the reaction mixture was kept in the closed container for 60 hours at 35 °C. The obtained solution was drop-cast either inside empty molds or on glass microfiber support structures to prepare two different sets of samples. • Free standing pellets were prepared for Comparative Examples 2, 3, and 4, as well as for Examples 1, 3, and 4. The pellets were drop-cast in an aluminium CR2025 coin cell cap used as a mold. Approximately 400 mg of the sol was used per mold. The drop cast sol was left at ambient temperature (40-60% relative humidity and 20.5-22.5°C) for 1 to 2 days to obtain a gel mixture.

[0162] • Solid electrolyte incorporated GF / A disks were prepared for Comparative Examples 2, 3, and 4. The support structures included glass microfiber filters GF / A (Whatman) with a diameter of 19 mm, and Teflon molds with a diameter of 20 mm. Approximately 800 mg of the sol per filter was incorporated by drop-casting. The support structures allowed the production of free-standing cell separators. The obtained gel mixture was then stored in a dry atmosphere (dew point of -48 to -38 °C and temperature of 21.5-23.5°C) for 1 day.

[0163] The above wet samples were dried at 60 °C under vacuum (< 10'2mbar) for 3 days. The drop-cast samples were dried inside the aluminium CR2025 coin cell caps, while the GF / A incorporated samples were demolded before drying. The solid pellets were sealed under vacuum (< 10'2mbar) and kept in a dry room atmosphere prior to use.

[0164] Comparative Example 3

[0165] A solid electrolyte composition was prepared in the same manner as for Comparative Example 1, but wherein the molar mixing ratio of ILE:TEOS was 1.5:1.0.

[0166] Comparative Example 4

[0167] A solid electrolyte composition was prepared in the same manner as for Comparative Example 1, but wherein the molar mixing ratio of ILE:TEOS was 1.85:1.0.

[0168] FIG 1. depicts the pellet structure of the solid electrolyte composition obtained in Example 1. The transparent nature of the solid electrolyte composition confirms the absence of (macro)phase separation of the porous silica matrix and the halogen-containing organosilicon compound. Hence, this demonstrates that the method of the present invention provides solid electrolyte compositions with improved structural homogeneity. It should be noted that the pattern visible on the rear of pellet results from the use of the aluminium CR2025 coin cell caps as mold.

[0169] FIG 2. shows the ionic conductivity of the solid electrolyte composition obtained in Example 1 measured at 20 °C on a sample of about 400 pm thickness during a compression experiment. Before compression, at 100% of the original thickness, the ionic conductivity is significantly lower. However, the trace depicted in FIG 2. demonstrates that the solid electrolyte compositions described herein show an increase in conductivity (in mS.crrT2) when compressed (i.e. lower than 100% of the original thickness), which may provide faster charge and discharge cycles when applied in, for instance, solid-state batteries. Example 4

[0170] The impact of the molar ratio of halogen-containing organosilicon compound to the silicon precursor on the curing rate was assessed by comparing the gelation time of Example 1, Example 2, Comparative Example 1, and Comparative Example 2. As shown in Table 1, addition of a large amount of the halogencontaining organosilicon compound (cfr. Comparative Example 1) ensured only a three-fold decrease of the gelation time compared to the solid electrolyte composition without a halogen-containing organosilicon compound (cfr. Comparative Example 2). In contrast, the introduction of lower amounts of halogen-containing organosilicon compound in the reaction mixture ensured faster gelation with a thirtyfold decrease for a molar ratio of OS:TEOS of 0.01:1.0, and a sixty-fold decrease for a molar ratio of OS:TEOS of 0.13:1.0.

[0171] Table 1. Comparison of the curing rate of solid electrolyte compositions with a different molar ratio of halogencontaining organosilicon compound to silicon precursor measured at 35 °C.

[0172] FIG 3. illustrates scanning electron microscopy (SEM) images of Example 1 (including a halogen-containing organosilicon compound) and Comparative Example 2 (without a halogen-containing organosilicon compound). The respective images demonstrate the impact of the halogen-containing organosilicon compound on the mechanical integrity and morphology of the porous silica matrix comprised in the solid electrolyte compositions of Example 1 (c-d) and Comparative Example 2 (a-b). To obtain the SEM images, the ILE was first removed from the porous silica matrix. The SEM images show that the porous silica matrix of Example 1 mainly comprises a mesoporous structure, while the porous silica matrix of Comparative Example 2 mainly comprises macropores. Advantageously, the mesoporous structure of the solid electrolyte compositions of the invention provides a higher surface area which may allow an improved interface with electrodes in an energy storage device, may increase the number of sites for ion transport, and may improve ionic conductivity.

[0173] Scanning electron microscopy (SEM) images of the solid electrolyte composition obtained according to a method of the invention, preferably as a free-standing film, may be taken with a Nova microscope with an operating voltage between 3 and 5 kV, a working distance between 5 and 6 mm, and image acquisition in secondary electron mode. Example 5

[0174] The impact of the molar ratio of the ILE to the silicon precursor on the electrochemical properties of the solid electrolyte composition both with and without the addition of a halogen-containing organosilicon compound was assessed by comparing the ion conductivity (o) and anodic current limit (ACL) of Example 1, Example 3, Example 4, Comparative Example 2, Comparative Example 3, and Comparative Example 4. As shown in Table 2, the addition of the halogen-containing organosilicon compound did not affect the conductivity of the solid electrolyte composition.

[0175] Table 2. Comparison of the ionic conductivity and anodic current limit of solid electrolyte compositions with a different molar ratio of ionic liquid electrolyte to silicon precursor.

[0176] FIG 4. illustrates the electrochemical properties of Example 1, Example 4, Example 5, Comparative Example 2, Comparative Example 3, and Comparative Example 4. It follows from the data presented in FIG 4. that the molar ratio of the ILE to the silicon precursor has an important impact on the ionic conductivity and the anodic current limit of the respective solid electrolyte compositions. A similar trend could be observed for the solid electrolyte compositions with a halogen-containing organosilicon compound and without a halogen-containing organosilicon compound. Hence, it could be demonstrated that the halogen-containing organosilicon compound does not significantly affect the electrochemical properties of the solid electrolyte composition. A summary of the results can be found in Table 2.

[0177] To measure the ionic conductivity of each solid electrolyte composition, each respective composition was sandwiched between stainless steel electrodes to form electrolytic cell 1. Next, an alternating potential is applied to the electrolytic cell with an amplitude of 10 mV within a frequency range of 10 kHz to 500 kHz. The resulting alternating current flowing through the cell is measured via electrical impedance spectroscopy (EIS) and converted to conductivity values.

[0178] To measure the anodic current limit, each respective composition was sandwiched between Li electrodes to form electrolytic cell 2. Next, voltammetry experiments were conducted by measuring the current as a function of potential using chronoamperometry at 1 V. The maximum current observed is the anodic current limit.

[0179] Electrical impedance spectroscopy (EIS) may be used to determine the electromechanical properties of the solid electrolyte composition obtained according to a method of the invention, preferably as an electrolytic cell comprising said composition, by applying an alternating potential with an amplitude of 10 mV and within a frequency range of 10 kHz to 500 kHz. A suitable device includes a VMP-3 BioLogic instrument.

[0180] Example 6

[0181] A lithium battery coin cell was constructed by sandwiching the solid electrolyte composition of Example 1 of 400 pm thickness between a Li electrode and a LiNi0.6Mn0.2Co0.2O2 electrode. To determine the performance characteristics of the obtained lithium battery, voltage changes during discharge were measured.

[0182] FIG 5. Illustrates the electrochemical properties of the lithium battery of Example 6. The discharge curve in FIG. 5 was obtained by cycling the lithium battery at a constant current of C / 10 (1C = 165 mA g"1as referred to the mass of cathode active material). FIG.6. Illustrates the anodic stability of the lithium battery coin cell of Example 6. It follows from the data presented in FIG 6. that the lithium battery remains electrochemically stable up to 1.7 V.

[0183] From FIG 5. and FIG 6. it is concluded that the lithium battery coin cell can outperform cells using conventional solid state electrolytes - such as inorganic (e.g., sulphides, oxides) and polymeric (e.g., PEO) - in terms of both rate capability and operating temperature. Moreover, the working voltage is higher than that typically reported for solid polymer electrolytes (e.g., PEO) and comparable to the one enabled by the use of inorganic electrolytes (e.g., sulphides, oxides).

Claims

CLAIMS1. A method for producing a solid electrolyte composition, the method comprising the steps of: mixing a silicon precursor comprising at least one alkoxysilane and an ionic liquid electrolyte comprising an ionically conductive compound, a solvent, and a metal salt to form a liquid mixture; wherein the solvent comprises an amount of water sufficient for hydrolyzing at least a portion of the silicon precursor; adding a halogen-containing organosilicon compound to the liquid mixture; hydrolyzing at least a portion of the silicon precursor by contacting the halogen-containing organosilicon compound and the silicon precursor; reacting the halogen-containing organosilicon compound and the hydrolyzed portion of the silicon precursor, thereby forming a gel mixture; and, curing, drying and / or ageing the formed gel mixture, thereby forming the solid electrolyte composition; wherein the molar ratio between the halogen-containing organosilicon compound and the silicon precursor is between at least 0.01 and at most 0.50.

2. The method according to claim 1, wherein the halogen-containing organosilicon compound is represented by general formula (I),wherein R1, R2, and R3are each independently selected from the group consisting of halogen, alkyl, alkenyl, alkoxy, and aminoalkyl;X is selected from the group consisting of halogen, aminoalkyl, cyanoalkyl; and wherein at least one of R1, R2, and R3is halogen, preferably fluoro.

3. The method according to claim 2, whereinR1, R2, and R3are each independently selected from the group consisting of halogen, Ci-8alkyl, C2- 8alkenyl, and Ci.8alkoxy; and,X is selected from the group consisting of halogen, aminoCi.8alkyl, cyanoCi.8alkyl.

4. The method according to any one of the preceding claims, wherein the halogen-containing organosilicon compound is selected from the group consisting of: 4-[fluoro(dimethyl)silyl]butanenitrile, 4-[fluoro(diethyl)silyl] butanenitrile, 4-[fluoro(di-n- propyl)silyl] butanenitrile, 4-[fluoro(di-i-propyl)silyl] butanenitrile, 4-[fluoro(di-n- butyl)silyl] butanenitrile, 4-[fluoro(d i-t-butyl)silyl] butanenitrile, 4-[difluoro(methyl)silyl] butanenitrile, 4-[difluoro(ethyl)silyl]butanenitrile, 4-[difluoro(n- propyl)silyl] butanenitrile, 4-[d ifluoro(i-propyl)silyl] butanenitrile, 4-[difluoro(n- butyl) silyl] butanenitrile, 4-[difluoro(t-butyl)silyl] butanenitrile, 4-[trifluorosilyl] butanenitrile, 4-[chloro(dimethyl)silyl]butanenitrile, 4-[chloro(diethyl)silyl] butanenitrile, 4-[chloro(di-n- propyl)silyl] butanenitrile, 4-[chloro(di-i-propyl)silyl] butanenitrile, 4-[chloro(di-n- butyl)silyl] butanenitrile, 4-[chloro(di-t-butyl)silyl] butanenitrile, 4-[dichloro(methyl)silyl] butanenitrile, 4-[dichloro(ethyl)silyl] butanenitrile, 4-[dichloro(n- propyl)silyl] butanenitrile, 4-[dichloro(i-propyl)silyl] butanenitrile, 4-[dichloro(n- butyl)silyl] butanenitrile, 4-[dichloro(t-butyl)silyl] butanenitrile, 4-[trichlorosilyl] butanenitrile, 4- [bromo(dimethyl)silyl]butanenitrile, 4-[bromo(diethyl)silyl]butanenitrile, 4-[bromo(di-n- propyl)silyl] butanenitrile, 4-[bromo(d i-i-propyl)silyl] butanenitrile, 4-[bromo(di-n- butyl)silyl] butanenitrile, 4-[bromo(di-t-butyl)silyl]butanenitrile, 4-[bromo(methyl)silyl] butanenitrile, 4-[dibromo(ethyl)silyl] butanenitrile, 4-[dibromo(n- propyl)silyl] butanenitrile, 4-[dibromo(i-propyl)silyl] butanenitrile, 4-[dibromo(n- butyl)silyl] butanenitrile, 4-[dibromo(t-butyl)silyl]butanenitrile, 4-[tribromosilyl]butanenitrile.

5. The method according to any one of the preceding claims, wherein the molar ratio between the halogen-containing organosilicon compound and the silicon precursor is between at least 0.01 and at most 0.45 or between at least 0.01 and at most 0.40, preferably between at least 0.01 and at most 0.35 or between at least 0.01 and at most 0.30; more preferably between at least 0.01 and at most 0.25 or between at least 0.01 and at most 0.20; for example about 0.13.

6. The method according to any one of the preceding claims, wherein the molar ratio of the ionically conductive compound to the silicon precursor is between at least 0.50 and at most 2.5, preferably between at least between 0.50 and at most 2.0, more preferably between at least 0.50 and at most 1.85.

7. The method according to any one of the preceding claims, wherein the silicon precursor is selected from the group consisting of tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS), methyltriethoxysilane (MTES), tetraisopropyl orthosilicate (TIOS), tetrapropyl orthosilicate (TPOS), tetrabutyl orthosilicate (TBOS), substitutions thereof, and / or a combination thereof.

8. The method according to any one of the preceding claims, wherein the ionically conductive compound is selected from the group consisting of: l-Ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIFSI), l-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide(EMITFSI), l-Ethyl-3-methylimidazolium fluorosulfonyl (trifluoromethanesulfonyl)imide(EMIFTFSI), l-Ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIOTf),Butyltrimethylammonium bis(trifluoromethylsulfonyl)imide (BMATFSI), l-Ethyl-3- methylimidazolium bis(pentafluoroethylsulfonyl)imide (EMIBeti), l-Ethyl-3-methylimidazolium dicyanamide (EMIDCA), l-Ethyl-3-methylimidazolium diethylphosphate (EMIDEP), l-Butyl-3- methylimidazolium bis(fluorosulfonyl)imide (BMIFSI), l-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMITFSI), l-Butyl-3-methylimidazolium fluorosulfonyl(trifluoromethanesulfonyl)imide (BMIFTFSI) l-Butyl-3-methylimidazolium trifluoromethanesulfonate (BMIOTf), l-Butyl-3-methylimidazolium bis(pentafluoroethylsulfonyl)imide (BMIBeti), 1-Butyl-l-methylpyrrolidinium bis(fluorosulfonyl)imide (BMPFSI), 1-Butyl-l-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPTFSI), 1-Butyl-l-methylpyrrolidinium fluorosulfonyl(trifluoromethanesulfonyl)imide (BMPFTFSI), 1-Butyl-l-methylpyrrolidinium trifluoromethanesulfonate (BMPOTf), 1-Butyl-l-methylpyrrolidinium bis(pentafluoroethylsulfonyl)imide (BMPBeti), 1-Methyl-l-pentylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PyrlSTFSI), 1-Methyl-l-pentylpyrrolidinium fluorosulfonyl(trifluoromethanesulfonyl)imide (PyrlSFTFSI), 1-Methyl-l-pentylpyrrolidinium trifluoromethanesulfonate (Pyrl5OTf), 1-Methyl-l-pentylpyrrolidinium bis(pentafluoroethylsulfonyl)imide (PyrlS Beti), triethylsulfonium bis(trifluoromethanesulfonyl)imide (TESTFSI), tetra butylammonium bis(trifluoromethane)sulfonylimide (TBATFSI), and mixtures thereof.

9. The method according to any one of the preceding claims, wherein the gelation time of the liquid mixture at a temperature of 20 °C to 45 °C is at least 5 min and at most 240 min after adding the halogen-containing organosilicon compound.

10. The method according to any one of the preceding claims, wherein the solid electrolyte composition is substantially free of a catalyst and / or initiator.

11. A composite electrode comprising a solid electrolyte composition, prepared according to the method of any one of the preceding claims, and an electrode.

12. A solid electrolyte composition for an electrochemical energy storage device, obtained or obtainable by a method according to any one of claims 1 to 11, comprising: a porous silica matrix comprising an ionic liquid electrolyte which comprises an ionically conductive compound and a metal salt; wherein the porous silica matrix is at least partially modified by a halogen-containing organosilicon compound; wherein the total wt.% of silica in the solid electrolyte composition is at least 5.0 wt.% and at most 30.0 wt.%; and, wherein the total wt.% of the halogen-containing organosilicon compound in the solid electrolyte composition is between at least 0.03 wt.% and at most 25.0 wt.%.

13. The solid electrolyte composition according to claim 12, wherein the porous silica matrix is a condensation product of a silicon precursor, and the halogen-containing organosilicon compound is represented by general formula (I),wherein R1, R2, and R3are each independently selected from the group consisting of halogen, alkyl, alkenyl, alkoxy, and aminoalkyl; wherein X is selected from the group consisting of halogen, aminoalkyl, cyanoalkyl; and wherein at least one of R1, R2, and R3is halogen, preferably fluoro.

14. The solid electrolyte composition according to claim 12 or 13, wherein the solid electrolyte composition is characterized by at least one of the following: an ionic conductivity at 20 °C between 104S cm1and 102S cm-1; an anodic stability of at most 1.7 V vs. SHE; an anode current limit of between 0.1 mA cm'2and 2.0 mA cm'2; a thickness of between 300 pm and 600 pm; and / or, a mesoporous silica matrix material with some macropores.

15. An electrochemical energy storage device, comprising a positive electrode, a negative electrode; and the solid electrolyte composition according to any one of claims 12 to 14; preferably wherein the energy storage device is an alkali metal battery, more preferably still a lithium and / or a sodium battery.

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