Solid electrolyte separators 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 electrodes, electrode assemblies, solid electrolyte separators, and methods for producing the same. An aspect of the invention relates to a method for producing a solid electrolyte separator, comprising the steps of: providing a porous non-metallic, preferably polymer or fibrous, substrate having a plurality of pores, wherein an initial porosity of the porous non-metallic substrate is between 10.0% and 90.0%; preparing a liquid mixture comprising a silica precursor or an alumina precursor, an ionically conductive compound, a metal salt, and a solvent; contacting the porous non-metallic substrate with the liquid mixture, thereby impregnating the pores of the porous non-metallic substrate with the liquid mixture; and, curing the liquid mixture to form a solid electrolyte network within the pores of the porous non-metallic substrate, thereby obtaining a solid electrolyte separator with a post-curing porosity lower than the initial porosity of the porous non-metallic substrate.

Description

[0001] SOLID ELECTROLYTE SEPARATORS 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 electrodes, electrode assemblies, and solid electrolyte separators comprising a porous substrate having a plurality of pores embedded with a solid electrolyte, and methods for producing the same.

[0004] BACKGROUND

[0005] Alkali metal batteries have emerged as a groundbreaking technology with profound implications across a wide range of industries, especially in the electric vehicle sector and consumer electronics market. Their high energy density and good rechargeability have enabled the development of compact and lightweight electronics with high potential. For instance, the electrochemical cells of a lithium-ion battery usually include an anode, a liquid electrolyte prepared by dissolving a lithium salt in an organic solvent, and a cathode.

[0006] Moreover, to physically and electronically separate the anode and the cathode, an electrically insulating separator can be used that allows for the passage of ions essential for charging and discharging the electrochemical cell. Importantly, the thickness of the separator can greatly influence the overall performance and safety of the battery. For instance, conventional separators often require a balance between the (thermo)mechanical stability, the rate capability, and the high energy density of the battery. In addition, depending on the choice of electrode material, the separator may be susceptible to piercing during operation, resulting in short circuits and safety concerns such as battery fire.

[0007] US 2016 / 013463 Al and WO 2015 / 157339 Al are exemplary documents relating to ionically conductive composite membranes, which include a solid-state ionically conducting material, and may be used in electrochemical cells. Therefore, there is a need to address the limitations of current battery technology by providing an improved separator with enhanced thermomechanical properties behavior and a reduced thickness, while improving the overall performance and safety of the battery. This advancement is relevant for the development of commercially relevant alkali metal batteries.

[0008] SUMMARY OF THE INVENTION

[0009] As described above, a need exists to address the limitations of battery manufacturing and design. It has been found that these objective(s) can be attained either individually or in any combination by using a solid electrolyte separator and methods of manufacturing a solid electrolyte separator as described herein. As a result, components suitable for use in alkali metal batteries can be obtained with enhanced thermomechanical properties and reduced thickness, which can increase the overall battery performance and safety. Hence, the solid electrolyte separator and corresponding electrode assembly described in the present invention can be utilized in the field of energy storage devices, and more specifically in the production of various solid-state batteries.

[0010] In accordance with the present subject matter, the herein disclosed solid electrolyte separator comprises a porous substrate (which, in certain embodiments, may include a plastic material, a ceramic material, and / or a glass material) that has a plurality of pores embedded with a solid electrolyte. In contrast to conventional organic liquid electrolytes, the solid electrolyte in this disclosure comprises a solidified silica and / or alumina matrix functionalized with an electrolyte comprising an ionically conductive compound and a metal salt.

[0011] A distinguishing feature is that the solid electrolyte forms a matrix 'in-situ' within an inner space of the pores of the substrate, thereby impregnating these pores and reducing the overall porosity and available pore size of the separator. This sets it apart from, for instance, a coating layer applied inside or onto the inner surface of the pores. As a result, the present invention can overcome several of the drawbacks of the state of the art.

[0012] An advantage of the present invention is that the present separator can be manufactured at a reduced thickness (e.g., lower than 200 micron), while still providing improved thermomechanical stability and good ion conductivity (e.g., higher than 0.066 mS cm1), by filling, impregnating, and encasing the pores of the substrate with the solid electrolyte material. In this way, the embedded solid electrolyte may provide several additional advantages. For instance, the improved mechanical strength, provided by the in situ formed nano-porous silica and / or alumina matrix filling in the pores of the pristine substrate, may increase the resistance against externally applied stresses during manufacturing and / or operation. Furthermore, it was found that the present solid electrolyte separator can sustain a high mechanical integrity even at elevated temperatures and very low thickness (e.g., lower than 100 micron).

[0013] Another advantage of the present invention is that when applying the solid electrolyte separator to produce electrochemical cells for an energy storage device, high-rate performance during chargedischarge cycling can be achieved even at a relatively high water content (e.g., lower than 3000 ppm). Consequently, an electrochemical cell incorporating the solid electrolyte separator of this disclosure may maintain relatively high moisture content while retaining good charging and discharging behavior.

[0014] Yet another advantage of the present invention is that, when applying the solid electrolyte separator to produce one or more electrochemical cells for an energy storage device, an improved electrode / electrolyte interface can be achieved. This improved interface can enhance the electrochemical performance of the cell, which is particularly beneficial when connecting the solid electrolyte separator to an active electrode material comprising a porous electrode. Such porous electrode materials are commonly characterized by an inhomogeneous surface, leading to poor interface quality. Therefore, the separator may facilitate improved adaptability to accommodate various types of electrodes with variable surface roughness.

[0015] An overview of various other aspects of the technology of the present invention is given herein below, 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 to a solid electrolyte separator for an electrochemical energy storage device, comprising: a porous substrate having a plurality of pores embedded with a solid electrolyte; wherein the porosity of the porous substrate is between at least 10.0% and at most 90.0%; wherein the solid electrolyte comprises a silica matrix and / or alumina matrix incorporating an electrolyte; wherein the electrolyte comprises an ionically conductive compound and a metal salt; and wherein the solid electrolyte, preferably the silica matrix and / or alumina matrix, is positioned within an inner space of the pores such that the porosity of the solid electrolyte separator is lower than the porosity of the porous substrate.

[0017] Another aspect of the present invention relates to a solid electrolyte separator for an electrochemical energy storage device, preferably obtained or obtainable by a method for producing a solid electrolyte separator according to an aspect of the present invention or (preferred) embodiments thereof, the solid electrolyte separator comprising: a porous non-metallic, preferably polymer or fibrous, substrate having a plurality of pores embedded with a solid electrolyte network; wherein an initial porosity of the porous non-metallic, preferably polymer or fibrous, substrate is between at least 10.0 % and at most 90.0%; wherein the solid electrolyte network comprises a silica or alumina matrix and an electrolyte, confined within the silica or alumina matrix; wherein the electrolyte comprises an ionically conductive compound and a metal salt; and wherein the solid electrolyte network fills at least a portion of the inner space of the pores of the porous non-metallic, preferably polymer or fibrous, substrate, such that the porosity of the solid electrolyte separator is lower than the initial porosity of the porous non-metallic, preferably polymer or fibrous, substrate. In other words, the separator is distinguished in that at least a portion of the free or empty space of the porous non-metallic, preferably polymer or fibrous, substrate is filled with solid electrolyte material, which reinforces the porous structure and results in an improved separator. Advantageously, said separator provides improved mechanical integrity, while maintaining or even improving ionic conductivity.

[0018] In a particular embodiment, the porosity of the solid electrolyte separator is between 0.1% and 10.0%, preferably between 0.1% and 9.5% or between 0.1% and 9.0%, more preferably between 0.1% and 8.5% or between 0.1% and 8.0%, more preferably still between 0.1% and 7.5% or between 0.1% and 7.0%, more preferably still 0.1% and 6.5% or between 0.1% and 6.0%, more preferably still between 0.1% and 5.5% or between 0.1% and 5.0%, more preferably still between 0.1% and 4.5% or between 0.1% and 4.0%, more preferably still between 0.1% and 3.0% or between 0.1% and 3.5%, more preferably still between 0.1% and 2.5% or between 0.1% and 2.0%, more preferably still between 0.1% and 1.5% or between 0.1% and 1.0%.

[0019] In a particular embodiment, the porous non-metallic substrate comprises and preferably is a porous polymer substrate; preferably comprising a polymer material selected from the group consisting of polyethylene, polypropylene, polystyrene, Nylon 6, Nylon 6,6, polyether sulfone, polyether ether ketone, cellulose acetate, cellulose triacetate, cellulose, polyimide, polyvinylidene fluoride, and mixtures thereof. In a particular embodiment, the porous non-metallic substrate comprises and preferably is a porous fibrous substrate; preferably comprising fibrous material selected from the group consisting of glass fibers, carbon fibers, and combinations thereof.

[0020] In a particular embodiment, the thickness of the solid electrolyte separator is between 1.0 pm and 250.0 pm, preferably between 1.0 pm and 100.0 pm, more preferably still between 1.0 pm and 50.0 pm.

[0021] In a particular embodiment, the solid electrolyte separator has a water content of less than 3000 ppm, preferably less than 2000 ppm, more preferably less than 1000 ppm.

[0022] In a particular embodiment, the solid electrolyte further comprises a solid electrolyte layer positioned on at least one side of the porous non-metallic, preferably polymer or fibrous, substrate, wherein the solid electrolyte layer is configured for ionically contacting an active electrode material.

[0023] In a particular embodiment, the solid electrolyte further comprises at least two solid electrolyte layers positioned on at least two opposite sides of the porous non-metallic, preferably polymer or fibrous, substrate, wherein the solid electrolyte layers are configured for ionically contacting oppositely arranged active electrode materials.

[0024] In a particular embodiment, the solid electrolyte layer has an average thickness of between 0.01 pm and 100.0 pm, preferably between 0.01 pm and 50.0 pm, more preferably between 0.1 pm and 25.0 pm more preferably still between 1.0 pm and 10.0 pm. In a particular embodiment, the solid electrolyte layer has a water content of less than 3000 ppm, preferably less than 2000 ppm, more preferably less than 1000 ppm.

[0025] Another aspect of the invention relates to an electrode assembly comprising an active electrode material and a solid electrolyte separator, preferably the solid electrolyte as described herein and / or preferably obtainable or obtained according to the method as described herein; wherein the electrolyte separator is configured for ionically connecting to the active electrode material.

[0026] In a particular embodiment, the active electrode material comprises a porous material and a plurality of active material particles, optionally wherein the active electrode material has an uneven or rough electrode surface.

[0027] Another aspect of the invention relates to a method for producing a solid electrolyte separator comprising the steps of: a) providing a porous substrate having a plurality of pores with a porosity between 10.0% and 90.0%; b) preparing a liquid mixture by mixing a silica precursor and / or an alumina precursor, an ionically conductive compound, a metal salt, and a solvent; c) contacting the porous substrate with the liquid mixture, thereby impregnating the pores of the porous substrate with the liquid mixture; d) curing the liquid mixture to form a solid electrolyte within the pores of the porous substrate, thereby obtaining a solid electrolyte separator with a porosity lower than the porosity of the microporous substrate; e) optionally, drying and / or aging the solid electrolyte separator.

[0028] Another aspect of the present invention relates to a method for producing a solid electrolyte separator, preferably a solid electrolyte separator according to an aspect of the present invention or (preferred) embodiments thereof, the method comprising the steps of: a) providing a porous non-metallic, preferably polymer or fibrous, substrate having a plurality of pores, wherein an initial porosity of the porous non-metallic, preferably polymer or fibrous, substrate is between 10.0% and 90.0%; b) preparing a liquid mixture comprising a silica precursor or an alumina precursor, an ionically conductive compound, a metal salt, and a solvent; c) contacting the porous non-metallic, preferably polymer or fibrous, substrate with the liquid mixture, thereby impregnating (filling) the pores of the porous non-metallic, preferably polymer or fibrous, substrate with the liquid mixture; d) curing the liquid mixture to form a solid electrolyte network within the pores of the porous non- metallic, preferably polymer or fibrous, substrate, thereby obtaining a solid electrolyte separator with a post-curing porosity lower than the initial porosity of the porous non-metallic, preferably polymer or fibrous, substrate, and; e) optionally, drying and / or aging the solid electrolyte separator.

[0029] In a particular embodiment, the method further comprises the steps of contacting the porous non- metallic, preferably polymer or fibrous, substrate with an excess amount of liquid mixture, surpassing the capacity of the pores of the porous non-metallic, preferably polymer or fibrous, substrate, thereby forming at least one liquid mixture layer positioned on at least one side of the porous non-metallic, preferably polymer or fibrous, substrate; and curing the at least one liquid mixture layer to obtain at least solid electrolyte layer; and optionally, drying and / or aging the solid electrolyte layer.

[0030] In a particular embodiment, the solid electrolyte layer after curing, and optionally drying and / or aging, has an average thickness of between 0.01 pm and 50.0 pm.

[0031] Another aspect of the invention relates to a method for producing an electrode assembly, preferably the electrode assembly as disclosed herein, comprising the steps of: providing a porous substrate having a plurality of pores with a porosity between 10.0% and 90.0%; providing an active electrode material; positioning the porous substrate on the active electrode material; applying pressure onto the microporous substrate, thereby pressing the porous substrate against the active electrode material; and producing a solid electrolyte separator according to the method of an aspect of the present invention or (preferred) embodiments thereof, thereby obtaining the electrode assembly

[0032] Another aspect of the present invention relates to a method for producing an electrode assembly, preferably the electrode assembly as disclosed herein, comprising the steps of: i) providing a porous non-metallic, preferably polymer or fibrous, substrate having a plurality of pores, wherein an initial porosity of the porous non-metallic, preferably polymer or fibrous, substrate is between 10.0% and 90.0%; ii) providing an active electrode material, preferably wherein the active electrode material comprises a porous material and a plurality of active material particles; iii) positioning the porous non-metallic, preferably polymer or fibrous, substrate on the active electrode material; iv) applying a pressure onto the porous non-metallic, preferably polymer or fibrous, substrate, thereby pressing the porous non-metallic, preferably polymer or fibrous, substrate against the active electrode material; v) producing a solid electrolyte separator according to the method of an aspect of the present invention or (preferred) embodiments thereof, thereby obtaining the electrode assembly; and, vi) optionally, wherein the method further comprises repeating the preceding steps for one or more further solid electrolyte separators, thereby obtaining an electrode assembly comprising a stack of solid electrolyte separators.

[0033] Another aspect of the invention relates to a method for producing an electrode assembly, preferably the electrode assembly as disclosed herein, comprising the steps of: producing a solid electrolyte separator according to the method of an aspect of the present invention or (preferred) embodiments thereof; providing an active electrode material, preferably wherein the active electrode material comprises a porous material and a plurality of active material particles; positioning the solid electrolyte separator on the active electrode material; and applying pressure onto the solid electrolyte separator, thereby pressing the porous substrate against the active electrode material, thereby obtaining the electrode assembly

[0034] Another aspect of the present invention relates to a method for producing an electrode assembly, preferably the electrode assembly as disclosed herein, comprising the steps of: i) producing a solid electrolyte separator according to the method of an aspect of the present invention or (preferred) embodiments thereof; ii) providing an active electrode material, preferably wherein the active electrode material comprises a porous material and a plurality of active material particles; iii) positioning the solid electrolyte separator on the active electrode material; iv) applying a pressure onto the solid electrolyte separator, thereby pressing the porous non- metallic, preferably polymer or fibrous, substrate against the active electrode material, thereby obtaining the electrode assembly; and, v) optionally, wherein the method further comprises repeating the preceding steps for one or more further solid electrolyte separators, thereby obtaining an electrode assembly comprising a stack of solid electrolyte separators.

[0035] In a particular embodiment, the method further comprises repeating the preceding steps for one or more solid electrolyte separators, thereby obtaining an electrode assembly comprising a stack of solid electrolyte separators.

[0036] In a particular embodiment, the applied pressure is between 0.1 MPa and 10.0 MPa, preferably between 0.1 MPa and 7.5 MPa, more preferably between 0.1 MPa and 5.0 MPa, more preferably still between 0.1 MPa and 2.5 MPa, more preferably still between 0.1 MPa and 1.0 MPa. In a particular embodiment, the active electrode material comprises a porous electrode material and a plurality of active material particles, wherein producing the solid electrolyte separator comprises the step of applying the solid electrolyte into or onto the porous electrode material.

[0037] In a particular embodiment, the active electrode material comprises a porous electrode material and a plurality of active material particles, resulting in a rough or uneven electrode surface, and pressing the porous substrate against the active electrode material such that the electrode surface matches the solid electrolyte of the solid electrolyte separator, preferably a layer solid electrolyte of the solid electrolyte separator.

[0038] Another aspect of the invention relates to an electrochemical energy storage device comprising one or more unit cells, wherein each cell comprises: a solid electrolyte separator, preferably the solid electrolyte as described herein and / or preferably obtainable or obtained according to the method as described herein; and a positive electrode and a negative electrode; wherein the solid electrolyte separator is arranged between the positive electrode and the negative electrode.

[0039] BRIEF DESCRIPTION OF THE DRAWINGS

[0040] 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. It should be appreciated that certain drawings are a schematic representation of the claimed invention with enlarged proportions of components for easier understanding.

[0041] FIG 1. schematically illustrates an exemplary embodiment of a solid electrolyte separator (100) as disclosed herein comprising a solid electrolyte layer positioned at one side of a porous substrate embedded with a solid electrolyte.

[0042] FIG 2. schematically illustrates another exemplary embodiment of a solid electrolyte separator (200) as disclosed herein further comprising two layers positioned on opposite sides of the porous substrate.

[0043] FIG 3. schematically illustrates another exemplary embodiment of a solid electrolyte separator (300) as disclosed herein comprising two layers of different thicknesses positioned on opposite sides of the porous substrate.

[0044] FIG 4. schematically illustrates an exemplary embodiment of a method (400) for producing a solid electrolyte separator, preferably a solid electrolyte separator as disclosed herein.

[0045] FIG 5. schematically illustrates an exemplary embodiment of an electrode assembly (500) as disclosed herein. FIG 6. schematically illustrates an exemplary embodiment of a method (600) for producing an electrode assembly as disclosed herein.

[0046] FIG 7. schematically illustrates another exemplary embodiment of a method (700) for producing an electrode assembly as disclosed herein.

[0047] FIG 8. schematically illustrates an exemplary embodiment of an electrochemical energy storage device (800) as disclosed herein comprising one unit cell.

[0048] FIG 9. schematically illustrates another exemplary embodiment of an electrochemical energy storage device (900) as disclosed herein comprising two unit cells.

[0049] FIG 10. shows the electrochemical performance for a single electrochemical cell comprising a solid electrolyte separator of 950 pm thickness, which comprises a glass fiber (GFA) substrate embedded with a solid electrolyte (experiment 1).

[0050] FIG 11. shows the electrochemical performance for a single electrochemical cell comprising a solid electrolyte separator of 35 pm thickness, which comprises a trilayer porous substrate consisting of a polypropylene-polyethylene-polypropylene structure embedded with a solid electrolyte (experiment 5).

[0051] FIG 12. shows the electrochemical performance for a single electrochemical cell comprising a lithium electrode of 100 pm thickness pressed on a solid electrolyte separator of 35 pm thickness, which comprises a trilayer porous substrate consisting of a polypropylene-polyethylene-polypropylene structure embedded with a solid electrolyte (experiment 6).

[0052] FIG 13. shows the electrochemical performance for a four-layer multistack electrochemical cell comprising four solid electrolyte separators of 35 pm thickness, which comprises a trilayer porous substrate consisting of a polypropylene-polyethylene-polypropylene structure embedded with a solid electrolyte (experiment 5).

[0053] FIG 14. Shows the thermomechanical behavior of a solid electrolyte separator as disclosed herein by heating at 120 °C for 1 h under air.

[0054] FIG 15. Shows the thermomechanical behavior of a pristine porous substrate by heating at 120 °C for 1 h under air.

[0055] FIG 16. Shows an SEM image of a solid electrolyte separator with two oppositely arranged solid electrolyte layers of a similar thickness, resulting in a symmetric structure.

[0056] FIG 17. Shows an SEM image of a solid electrolyte separator with two oppositely arranged solid electrolyte layers of a different thickness, resulting in an asymmetric structure.

[0057] DETAILED DESCRIPTION

[0058] In the following detailed description, the technology underlying the present invention will be described by means of different aspects thereof. It will be readily understood that the aspects of the present invention, 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 invention. 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 invention, which is limited only by the claims. When describing the invention, the terms used are to be construed in accordance with the following definitions, unless the context dictates otherwise.

[0059] The present description generally relates to electrochemical energy storage devices, electrode assemblies comprising solid electrolyte separators, and the manufacturing thereof.

[0060] An aspect of the invention relates to a solid electrolyte separator for an electrochemical energy storage device, comprising: a porous substrate having a plurality of pores embedded with a solid electrolyte; wherein the porosity of the porous substrate is between at least 10.0% and at most 90.0%; wherein the solid electrolyte comprises a silica and / or alumina matrix incorporating an electrolyte; wherein the electrolyte comprises an ionically conductive compound and a metal salt; and wherein the solid electrolyte is positioned within an inner space of the pores such that the porosity of the solid electrolyte separator is lower than the porosity of the porous substrate.

[0061] In particular embodiments, the solid electrolyte separator comprises

[0062] - a porous non-metallic, preferably polymer or fibrous, substrate having a plurality of pores embedded with a solid electrolyte network; wherein an initial porosity of the porous non-metallic, preferably polymer or fibrous, substrate is between at least 10.0 % and at most 90.0%;

[0063] - wherein the solid electrolyte network comprises a silica or alumina matrix and an electrolyte, confined within the silica or alumina matrix;

[0064] - wherein the electrolyte comprises an ionically conductive compound and a dissolved metal salt;

[0065] - wherein the solid electrolyte network fills at least a portion of the inner space of the pores of the porous non-metallic, preferably polymer or fibrous, substrate, such that the porosity of the solid electrolyte separator is lower than the initial porosity of the porous non-metallic, preferably polymer or fibrous, substrate.

[0066] The present solid electrolyte separator is characterized in that a specific solid electrolyte network is embedded within the pores of a porous, non-metallic substrate. The solid electrolyte network is designed to contain the electrolyte within the silica or alumina matrix. This can be accomplished herein because the electrolyte is comprised in the liquid mixture prior to curing the polymer network. Advantageously, the electrolyte creates a conductive network inside the silica or alumina matrix, mechanically supporting both the electrolyte material and the non-metallic substrate. The solid electrolyte separator as disclosed herein is suitable for use in an electrochemical energy storage device, such as an electrochemical cell or a battery, that may be configured to physically separate a positive electrode (i.e., cathode) and the negative electrode (i.e., anode), while allowing the passage of ions for charging and discharging of the storage device. The "electrolyte" comprised in the solid electrolyte separator provides a medium that allows the movement of said ions, but is electrically insulating and therefore does not conduct electrons. This ensures that the electrical energy of an energy storage device is stored and released through an external circuit.

[0067] The physical properties of the separator are considered to have an influence on ionic conductivity and resistance against externally applied stresses and penetration (e.g., leading to short circuits). In contrast to conventional separators requiring a highly porous structure with a large plurality of pores to facilitate the transport of the ions from one electrode to another electrode through a liquid medium, the present invention provides that the movement of ions is facilitated and / or stimulated by the solid electrolyte embedded and formed 'in-situ' within the pores of the porous non-metallic, preferably polymer or fibrous, substrate. Moreover, it has been found that by embedding the solid electrolyte in the pores of the substrate, the present solid electrolyte separator can provide a stronger physical barrier with improved protection against short circuiting, even at reduced thickness.

[0068] Moreover, the dense solid electrolyte structure may provide a separator with improved mechanical stability and / or ionic conductivity. In particular, and in some embodiments, alkali metal solid-state batteries that use a solid electrolyte separator as disclosed herein, may provide additional protection against the dendrite growth of a lithium anode during battery operation.

[0069] Another advantage of the present solid electrolyte separator is that the cost of materials and complexity of the manufacturing of electrochemical energy storage devices may be significantly reduced.

[0070] In particular embodiments, the solid electrolyte separator as disclosed herein provides that the postcured porosity of the separator may be between 0.1% and 10.0%, or between 0.1% and 7.5%, or between 0.1% and 5.0%, or between 0.1% and 2.5%, or between 0.1% and 1.0%. The porosity of the solid electrolyte separator can be determined with the Brunauer-Emmett-Teller (BET) theory that describes the amount of gas adsorbed on a silica surface as a function of pressure. This method involves first outgassing the separator for 4 h at 40 °C under a 1 mbar vacuum, and measuring the Nitrogen physisorption isotherms at T = -196 °C, for example using an Autosorb 3 analyzer. The surface area can then be calculated from the adsorption isotherm with the Barret-Joyner-Halenda (BJH) method.

[0071] The above listed porosity of the solid electrolyte separator has been found to improve the infiltrated porous structure of the substrate by decreasing the free volume or empty space of the pores, which can provide a separator with improved mechanical strength and durability. In some embodiments, the solid electrolyte separator is substantially free of void spaces. In particular, the solid electrolyte separator may be devoid of accessible void space.

[0072] The term "porosity" as used herein has a well-established meaning within the art and is used herein as such. In particular, it may refer to the amount of a material or component that corresponds to pores, such as apertures, channels, voids, etc. Porosity may be expressed as the percentage of the volume of a material, structure, or device component and can be measured by means of the BJH method described above.

[0073] In the context of the present invention, a distinction is made between the initial porosity of the substrate (i.e., prior to embedding a solid electrolyte network in the pores) and the final, post-cured porosity of the solid electrolyte separator, which is lower than the initial porosity of the substrate.

[0074] In some embodiments, the porous non-metallic, preferably polymer or fibrous, substrate may form a continuous medium with the solid electrolyte (network). Alternatively, and in some embodiments, the porous non-metallic, preferably polymer or fibrous, substrate and the solid electrolyte may form two interpenetrating structures that are interlaced at a microscopic level but not covalently bound. Preferably, the solid electrolyte described herein forms a continuous network.

[0075] In particular embodiments, the solid electrolyte separator may have a thickness between 1.0 pm and 250.0 pm, preferably between 1.0 pm and 200.0 pm, or between 1.0 pm and 150.0 pm, or between 1.0 pm and 100.0 pm, or more preferably between 1.0 pm and 50.0 pm, or between 1.0 pm and 25.0 pm. Preferably, the solid electrolyte separator may have a thickness between 5.0 pm and 50.0 pm, or between 5.0 pm and 45.0 pm, or between 5.0 pm and 40.0 pm, or between 5.0 pm and 35.0 pm, or between 5.0 pm and 30.0 pm, preferably between 10.0 pm and 30.0pm, for example, 15.0 pm or 25.0 pm, more preferably still around 20.0 pm. The thickness of the solid electrolyte separator can be measured using techniques known in the art, such as SEM with a digital micrometer screw or AFM.

[0076] The above listed thickness of the solid electrolyte separator has been found to provide an improved balance between conductivity and mechanical strength of the solid electrolyte separator and can be advantageous for the manufacturing of a commercially relevant solid-state battery. In particular, this can allow a solid-state battery to operate safely with good power output characteristics at room temperature, and preferably even at elevated temperatures (e.g., between -20 °C and 120 °C). It can be appreciated that the listed separator thickness is well below the experimentally viable thickness of a self-standing solid electrolyte film, such as one composed of a silica and / or alumina matrix. Therefore, the reduced separator thickness may facilitate an improvement in the thermomechanical stability, the rate capability, and the high energy density when integrated into an electrochemical cell. In particular embodiments, the solid electrolyte loading of the porous non-metallic, preferably polymer or fibrous, the substrate may be between 1.0 mg / cm2and 50.0 mg / cm2, or between 1.0 mg / cm2and 45.0 mg / cm2, or between 1.0 mg / cm2 and 40.0 mg / cm2, or between 1.0 mg / cm2and 35.0 mg / cm2, or between 1.0 mg / cm2and 30.0 mg / cm2, or between 1.0 mg / cm2and 25.0 mg / cm2, or between 1.0 mg / cm2and 20.0 mg / cm2, or between 1.0 mg / cm2and 15.0 mg / cm2, or between 1.0 mg / cm2and 10.0 mg / cm2, preferably between 3.0 mg / cm2and 10.0 mg / cm2. The solid electrolyte loading can be determined by measuring the weight and volume of the separator.

[0077] As used herein the term "porous substrate" can refer to any underlying material or materials that has a plurality of pores and can be used to form a solid electrolyte separator. The pore size distribution structure may be uniform resulting in a homogenous porous material (i.e., the pore size is consistently distributed throughout the substrate) or non-uniform resulting in a heterogenous porous substrate (i.e., the pore varies in size throughout the substrate). Accordingly, the term "porous polymer substrate" can refer to any underlying polymeric material or materials that have a plurality of pores and can be used to form a solid electrolyte separator. Preferably, the present porous polymer substrate is a non-metallic material.

[0078] In particular embodiments, the porosity of the porous non-metallic, preferably polymer or fibrous, substrate may be between at least 10.0% and at most 95.0%, or between at least 10.0% and at most 90.0%, or between at least 15.0% and at most 90.0%, or between at least 20.0% and at most 90.0%, or between at least 25.0% and at most 90.0%, or between at least 30.0% and at most 90.0%, or between at least 30.0% and at most 85.0%, preferably between at least 30.0% and at most 80.0%, or between at least 30.0% and at most 75.0%, more preferably between at least 30.0% and at most 70.0%, or between at least 30.0% and at most 60.0%, even more preferably between 40.0% and 60.0%.

[0079] In particular embodiments, the pore size or average diameter of the pores of the porous non-metallic, preferably polymer or fibrous, substrate may be between at least 0.01 pm and at most 2.0 pm, or between at least 0.01 pm and at most 1.5 pm, or between at least 0.01 pm and at most 1.25 pm, or between at least 0.01 pm and at most 1.0 pm, preferably between at least 0.01 pm and at most 0.75 pm, or between at least 0.01 pm and at most 0.5 pm, or between at least 0.05 pm and at most 0.5 pm, or between at least 0.1 pm and at most 0.5 pm. The porosity of the substrate can be determined using the BET method as described earlier.

[0080] In a particular embodiment, the thickness of the porous non-metallic, preferably polymer or fibrous, substrate may be between 0.5 pm and 200.0 pm, or between 1.0 pm and 200.0 pm, or between 5.0 pm and 200.0 pm, or between 10.0 pm and 200.0 pm, or between 10.0 pm and 100.0 pm, or between 15.0 pm and 100.0 pm, or between 15.0 pm and 75.0 pm, preferably between 15.0 pm and 50.0 pm. The listed substrate properties above may provide a number of desirable properties such as good thermomechanical stability, good impregnability of the solid electrolyte, and ease of processability. According to the embodiment, the porous non-metallic, preferably polymer or fibrous, substrate can be a microporous substrate. The porous non-metallic, preferably polymer or fibrous, substrate may refer to a membrane, a nonwoven fabric, a woven fabric, a continuous sheet, or a film that has desirable thermomechanical properties. Any organic material or inorganic material having sufficient electrical insulation properties (i.e., to block the transfer of electrons between the anode and cathode) may be used as a material to form the porous non- metallic, preferably polymer or fibrous, substrate.

[0081] In particular embodiments, the porous non-metallic, preferably polymer or fibrous, substrate may comprise a polymer material and / or a fibrous material. Non-limiting examples of a fibrous material include glass fibers and / or carbon fibers.

[0082] In a particular embodiment, the porous non-metallic, preferably polymer or fibrous, substrate may comprise a polymer material selected from the group consisting of polyolefins, such as polyethylene and polypropylene, polyamide; such as Nylon 6 and Nylon 6,6; polyacrylonitrile; polyether sulfone; sulfonated polyether sulfone; polysulfone; sulfonated polysulfone; polyether ether ketone; sulfonated polyether ether ketone, polyester, cellulose acetate, cellulose triacetate, polybenzimidazole, polyimide, polyvinylidene fluoride, polycarbonate, cellulose, or mixtures and / or combinations thereof.

[0083] In particular embodiments, the porous non-metallic, preferably polymer or fibrous, substrate may comprise a multilayer polymer. Preferably, the porous non-metallic, preferably polymer or fibrous, substrate comprises a plurality of polymer layers, preferably at least three polymer layers, for example a trilayer polymer, or more layers, such as four polymer layers, five polymer layers, or more. Advantageously, the substrate may be a multilayer polymer. The advantage of having three or more layers is that the one or more inner layers may provide for a thermal shutdown function to avoid thermal runaway of the electrochemical cell or battery.

[0084] In particular embodiments, the porous non-metallic, preferably polymer or fibrous, substrate may comprise a polymer selected from the group consisting of polyethylene, polypropylene, polystyrene, Nylon 6, Nylon 6,6, polyether sulfone, polyether ether ketone, cellulose acetate, cellulose triacetate, cellulose, polyimide, polyvinylidene fluoride, and mixtures thereof.

[0085] In particular embodiments, the porous non-metallic, preferably polymer or fibrous, substrate can be configured to be substantially hydrophobic, preferably by substantially inhibiting the absorption, wetting, or dissolution by water or a water-containing liquid such as a solvent. Preferably, the porous non-metallic, preferably polymer or fibrous, substrate may comprise a hydrophobic material or be primarily composed of a hydrophobic material. The selection of a hydrophobic material may be based on any of the above embodiments preferably including one or more hydrophobic polymers. Alternatively, or in combination, a hydrophobic coating or layer may be applied to the porous non-metallic, preferably polymer or fibrous, substrate, for example, using conventional coating techniques known to the person skilled in the art. An advantage of a hydrophobic porous non-metallic, preferably polymer or fibrous, substrate can be the reduction of moisture content within the solid electrolyte separator, which may provide an advantageous effect for solid-state batteries by reducing the occurrence of side-reactions during charging and discharging cycles.

[0086] The solid electrolyte as disclosed herein comprises a silica and / or alumina matrix. In the present invention, the matrix may advantageously be obtained from a silica and / or alumina precursor sol. The silica and / or alumina precursor sol as used herein refers to a solution containing one or more compounds that can be used to produce the silica and / or alumina matrix. For example, the silica and / or alumina matrix may be formed by a sol-gel process using the silica precursor sol.

[0087] In particular embodiments, the silica precursor may be selected from the group consisting of tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), tetraisopropyl orthosilicate (TIOS), tetrapropyl orthosilicate (TPOS), tetrabutyl orthosilicate (TBOS), triethylvinylorthosilcate (VTEOS), and mixtures thereof. The silica precursor sol may be obtained by mixing the silica precursor with a solvent or a solvent mixture.

[0088] In particular embodiments, the alumina precursor may be selected from the group consisting of aluminum triethoxide (AI(OEt)3). The alumina precursor sol may be obtained by mixing the alumina precursor with a solvent or a solvent mixture.

[0089] In preferred embodiments, the solvent comprises water. The solvent may further comprise an alkane, alkyl alcohol, alkyl ether, and mixtures thereof.

[0090] The solvent may comprise a Ci.g alcohol; including all linear or branched alkyl groups with between 1 and 6 carbon atoms, and thus includes methanol, ethanol, n-propanol, i-propanol, n-butanol and its isomers. The solvent may comprise a C2-10 ether; including all linear or branched alkyl groups with between 2 and 10 carbon atoms, and thus includes dimethyl ether, diethyl ether, di-n-propyl ether, di-i-propyl ether, di- n-butyl ether and its isomers. Preferably, the solvent comprises propylene glycol methyl ether (PGME).

[0091] The hydrolysis and polycondensation of the silica and / or alumina precursor may be accelerated by adding an acidic aqueous solution. The silica and / or alumina matrix obtained after gelation of the silica and / or alumina precursor sol and drying of the wet three-dimensional network may be partially chemically bonded with the porous non-metallic, preferably polymer or fibrous, substrate.

[0092] The present invention further provides that the silica and / or alumina and / or alumina matrix is functionalized with an electrolyte comprising an ionically conductive compound in which a metal salt is dissolved that functions as an ion-conducting component. Preferably, the ionically conductive compound is adsorbed into the silica and / or alumina matrix. It should be noted that the electrolyte is, preferably, added to the silica and / or alumina precursor sol to homogeneously distribute the electrolyte in the inner space of the pores of the porous non-metallic, preferably polymer or fibrous, substrate. The terms "ionic liquid" (IL) and "ionically conductive compound" are used herein interchangeably and refer 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 liquids.

[0093] The term "electrolyte" as used herein refers to a composite or mixture comprising one or more ionic liquid or ionically conductive compound and one or more metal salt. Electrolytes as described herein may be 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. 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 silica and / or alumina matrix and the electrolyte.

[0094] In particular embodiments, the metal salt is selected from the list of Li+, Na+, Mg2+, Ca2+, Al3+, and / or a combination thereof. Preferably the metal salt comprises Li+and / or Na+, which are industry standards for the manufacturing of a high energy solid-state battery.

[0095] 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 (LiPFg), Lithium tetrafluoroborate (LiBF4), Lithium bis(oxalato)borate (LiBOB), Lithium nitrate (LiNOa), 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.

[0096] 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 (NaPFg), Sodium tetrafluoroborate (NaBF4), Sodium bis(oxalato)borate (NaBOB), Sodium nitrate (NaNOs), 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.

[0097] 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

[0098] (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 (Pyrl5TFSI), 1-Methyl-l-pentylpyrrolidinium fluorosulfonyl (trifluoromethanesulfonyl)imide (Pyrl5FTFSI), 1-Methyl-l-pentylpyrrolidinium trifluoromethanesulfonate (Pyrl50Tf), 1-Methyl-l-pentylpyrrolidinium bis(pentafluoroethylsulfonyl)imide (Pyrl5Beti), triethylsulfonium bis(trifluoromethanesulfonyl)imide (TESTFSI), tetrabutylammonium bis(trifluoromethane)sulfonylimide (TBATFSI), and mixtures thereof.

[0099] 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 (Pyrl5TFSI), triethylsulfonium bis(trifluoromethanesulfonyl)imide (TESTFSI), tetrabutylammonium bis(trifluoromethane)sulfonylimide (TBATFSI), and mixtures thereof.

[0100] 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 (Pyrl5TFSI), and mixtures thereof.

[0101] In particular embodiments, the solid electrolyte separator may further comprise a layer of a solid electrolyte positioned on at least one side of the porous non-metallic, preferably polymer or fibrous, substrate, wherein the layer is configured for ionically contacting an active electrode material. Advantageously, the layer may fill in any voids or surface inconsistencies on the porous non-metallic, preferably polymer or fibrous, substrate, resulting in a more homogenous and uniform surface of the solid electrolyte separator.

[0102] The layer(s) can be any material or underlying material that is suitable for ionically contacting an active electrode material. The layer(s) may be a continuous or non-continuous structure and can include a two- dimensional or three-dimensional material, nanoparticles or partial or full films. Hence, the solid electrolyte may simultaneously provide reinforcement to the substrate (i.e., through the embedded material) and adherence to other components (i.e., through the one or more layers), such as components of an electrochemical energy storage device. Preferably, the layer may comprise the same solid electrolyte material as embedded within porous non-metallic, preferably polymer or fibrous, substrate.

[0103] In particular embodiments, the solid electrolyte layer may comprise or form a self-standing film configured for an ionically conductive connection with the solid electrolyte embedded within the porous non-metallic, preferably polymer or fibrous, substrate. It should, therefore, be noted that the solid electrolyte embedded in the pores of the porous non-metallic, preferably polymer or fibrous, substrate and the layer(s) can form a continuous (integrated) structure.

[0104] In particular embodiments, the solid electrolyte layer can be obtained by adding an excess amount of solid electrolyte material to the porous non-metallic, preferably polymer or fibrous, substrate, sufficient for overfilling of the pores of the porous non-metallic, preferably polymer or fibrous, substrate with the solid electrolyte material, thereby forming an overfill layer on a side of the porous non-metallic, preferably polymer or fibrous, substrate. The thickness of the layer can be controlled by managing the excess amount of solid electrolyte material added to the porous non-metallic, preferably polymer or fibrous, substrate. Alternatively or in combination, the thickness of the layer can be reduced after solidification. For example, chemical etching can be used to remove a portion of the layer, or the layer's surface can be mechanically removed through grinding or cutting.

[0105] Fig. 1 illustrates an exemplary embodiment of the solid electrolyte separator (100) of the disclosure comprising a layer positioned at one side of the porous non-metallic, preferably polymer or fibrous, substrate. In the illustrated example, the solid electrolyte separator (100) comprises a layer (111) positioned on the porous non-metallic, preferably polymer or fibrous, substrate (112). A solid electrolyte is embedded within (at least a part of) the pores of the porous non-metallic, preferably polymer or fibrous, substrate (112). Moreover, the layer (111) is formed from the same solid electrolyte material.

[0106] The provision of at least one solid electrolyte layer on the solid electrolyte separator can further enhance the interface for ionic contact with the surface of an electrode by adaptively conforming to the electrode surface shape, preferably filling or matching any inhomogeneities. A high-quality electrode / electrolyte interface is advantageous for the electrochemical performance of the electrochemical cell (e.g., capacity, C-rate, cycling). Additionally, the layer can enhance the adaptability of the separator to accommodate electrodes with variable surface roughness or with an inhomogeneous surface quality, for example, when the electrode surface is e rough or uneven). This is particularly advantageous when implementing the solid electrolyte separator onto an active electrode material comprising a porous matrix.

[0107] In particular embodiments, the solid electrolyte separator may further comprise at least two layers of a solid electrolyte positioned on at least two opposite sides of the porous non-metallic, preferably polymer or fibrous, substrate, wherein the layers are configured for ionically contacting oppositely arranged active electrode materials. Preferably, at least one layer and advantageously both layers may comprise the same solid electrolyte material as embedded within the porous non-metallic, preferably polymer or fibrous, substrate. In addition to the advantageous electrode / electrolyte interface properties described above, the inclusion of at least two oppositely arranged layers on the solid electrolyte separator can enhance the deformability of the solid electrolyte. This improvement may allow for better integration into an electrochemical cell and can permit a stronger pressure to be applied to the separator without the risk of deformation.

[0108] Fig. 2 illustrates another exemplary embodiment of the solid electrolyte separator (200) of the disclosure comprising two layers positioned on opposite sides of the porous non-metallic, preferably polymer or fibrous, substrate. In the illustrated example, the solid electrolyte separator (200) comprises a first layer (211) positioned on one end of the substrate (212) and a second layer (213) positioned on the other end of the substrate (212). The first and the second layer have a substantially similar thickness, resulting in a symmetric structure. A solid electrolyte is embedded within at least a part of the pores of the porous non- metallic, preferably polymer or fibrous, substrate (112). Moreover, the first layer (211) and second layer (213) are formed from the same solid electrolyte material.

[0109] A solid electrolyte separator comprising two oppositely arranged layers with a symmetric structure can be produced by applying similar coating processes on both sides of the porous non-metallic, preferably polymer or fibrous, substrate, adjusting the properties of the porous non-metallic, preferably polymer or fibrous, substrates (e.g., porosity, roughness, thickness, surface functionalization of the substrate), and / or by adjusting the thickness of one layer after impregnation to match that of the other layer.

[0110] Fig. 3 illustrates another exemplary embodiment of the solid electrolyte separator (300) of the disclosure comprising two layers having a different thickness positioned on opposite sides of the porous non- metallic, preferably polymer or fibrous, substrate. In the illustrated example, the solid electrolyte separator (300) comprises a first layer (311) positioned on one end of the substrate (312) and a second layer (313) positioned on the other end of the substrate (312). The first layer (311) is thinner compared to the second layer (313), resulting in an asymmetric structure. A solid electrolyte is embedded within at least a part of the pores of the porous non-metallic, preferably polymer or fibrous, substrate (312). Moreover, the first layer (311) and / or second layer (313) are formed from the same solid electrolyte material.

[0111] A solid electrolyte separator comprising two oppositely arranged layers with an asymmetric structure can be produced by applying different coating processes on both sides of the porous non-metallic, preferably polymer or fibrous, substrate (e.g., blade and / or bar coating), adjusting the properties of the porous non- metallic, preferably polymer or fibrous, substrates (e.g., porosity, roughness, thickness, surface functionalization of the substrate), and / or modifying one layer after impregnation to have a different thickness than the other layer.

[0112] In a particular embodiment, the solid electrolyte separator may be created with two oppositely arranged layers, and at least one layer can be subsequently removed, resulting in a separator comprising a single layer. Although this method involves more processing steps, it offers the advantage of allowing the solid electrolyte to fill any voids or surface inconsistencies present on the porous non-metallic, preferably polymer or fibrous, substrate. This results in a more homogeneous and uniform surface of the solid electrolyte separator compared to the single-layer embodiment depicted in Fig. 1.

[0113] The solid electrolyte may be configured to enable a flow of ions between physically separated components of an electrochemical energy storage device, which can play a crucial role in completing electrical circuits. The solid electrolyte layer referred to herein may have an average thickness of between 0.01 pm and 50.0 pm, or between 0.05 pm and 50.0 pm, or preferably between 0.1 pm and 50.0 pm, or between 0.25 pm and 50.0 pm, or between 0.5 pm and 50.0 pm, or between 1.0 pm and 50.0 pm, or between 2.0 pm and 50.0 pm. Advantageously, and in some embodiments, the solid electrolyte may simultaneously reinforce the porous non-metallic, preferably polymer or fibrous, substrate, adhere to an active electrode material, and provide a good conductive medium within the substrate and between the substrate and active electrode material.

[0114] In any of the above embodiments, the solid electrolyte layer positioned on at least one side of the porous non-metallic, preferably polymer or fibrous, substrate may be configured to absorb and advantageously trap hydrophilic contaminants that may be present in the porous non-metallic, preferably polymer or fibrous, substrate. When applied to an electrochemical cell structure, this has the advantage that the hydrophilic contaminants are not "free" to induce parasitic reactions with cell components such as anodes and cathodes. Non-limiting examples of hydrophilic contaminants include water, methanol, ethanol, n- propanol, i-propanol, butanol and its isomers; and / or propylene glycol methyl ether (PGME). This configuration may advantageously reduce the water content within the porous non-metallic, preferably polymer or fibrous, substrate. Notably, the advantageous effect can be enhanced when two or more solid electrolyte layers with the aforementioned configuration are provided on opposite sides of the porous non-metallic, preferably polymer or fibrous, substrate, enabling the concurrent absorption of hydrophilic contaminants from different sides of the porous non-metallic, preferably polymer or fibrous, substrate. Without wishing to be bound by theory, it is considered that the core of the solid electrolyte separator may be dried by one or more layer(s) due to the hygroscopic nature of the solid electrolyte material. Hence, the solid electrolyte layer(s) may act as a desiccant to promote or sustain a state of dryness by chemically bonding the hydrophilic contaminants of the porous non-metallic, preferably polymer or fibrous, substrate. Hence, the present solid electrolyte separator may require less severe external drying after manufacturing and / or before use. This has the advantage that expensive and time-consuming drying steps can be avoided when assembling, for instance, an electrochemical cell.

[0115] In particular embodiments, the solid electrolyte separator can have a water content of less than 3000 ppm, or less than 2500 ppm, or less than 2000 ppm, preferably less than 1500 ppm, or less than 1000 ppm. The water content of the separator can be measured with a moisture analyzer, for example a Vapor Pro® XL moisture analyzer operating at 150 °C under N2 FLOW.

[0116] Advantageously, the solid electrolyte separator may provide that the majority of the water content is chemically bound to the solid electrolyte (i.e., electrochemically inactive). Therefore, in contrast with solid-state batteries comprised in the art, batteries incorporating the solid electrolyte separator of the present disclosure may have a relatively high moisture content, while retaining good charging and discharging behavior.

[0117] As described above, the solid electrolyte separator of the present invention can demonstrate a suitable ionic conductivity for application in alkali metal batteries. In some embodiments, the separator can have an ionic conductivity between 0.01 and 20.0 mS cm-1, preferably 0.1 and 10.0 mS cm-1, or between 0.2 and 10.0 mS cm-1, more preferably between 0.3 and 10.0 mS cm-1, or between 0.4 and 10.0 mS cm-1, or between 0.5 and 10.0 mS cm-1, or more preferably still between 1.0 and 10.0 mS cm-1, or between 2.5 and 10.0 mS cm-1, or between 3.0 and 10.0 mS cm-1, or between 5.0 and 10.0 mS cm-1as measured by electrochemical impedance spectroscopy (EIS) at 20 °C. The ionic conductivity can be calculated using methods of the art suitable for analysis of an impedance plot.

[0118] In particular embodiments, the separator is further configured to act as an electrical insulator during operation (i.e., only allows the flow of ions and not electrons) and has an electronic conductivity of at most 1 nS cm-1, or at most 0.9 nS cm-1, or at most 0.8 nS cm-1, or at most 0.7 nS cm-1, or at most 0.6 nS cm-1, or at most 0.5 nS cm-1, or at most at most 0.4 nS cm-1, or at most at most 0.4 nS cm-1, or at most at most 0.3 nS cm-1, or at most at most 0.2 nS cm-1, more preferably at most 0.1 nS S cm-1, more preferably still at most at most 0.05 nS cm-1. The electronic conductivity can be measured by chronoamperometry tests by applying a 0.1V DC voltage on the separator at 20 °C. In particular embodiments, the separator can have an anodic limiting current of at least 0.1 mA cm'2, or at least 0.2 mA cm'2, or at least 0.3 mA cm'2, or at least 0.4 mA cm'2, or at least 0.5 mA cm'2, preferably at least 1.0 mA cm'2. The anodic limiting current can be measured by chronoamperometry at 20 °C.

[0119] In particular embodiments solid electrolyte separator may be characterized by the following mechanical properties: transverse direction tensile strength (typical / min) of 150 / 80 Kg / cm2, machine direction transverse direction tensile strength (typical / min) 1900 / 1000 Kg / cm2, and / or puncture strength (typical / min) 450 / 380 grams force (gf). The skilled person understands that the thermomechanical properties of the separator vary depending on the properties of the porous non-metallic, preferably polymer or fibrous, substrate. Therefore, the separator may exhibit the same or improved properties as the porous non-metallic, preferably polymer or fibrous, substrate due to the solid electrolyte strengthening the porous non-metallic, preferably polymer or fibrous, substrate, even though the latter can result in a reduction in elasticity. Advantageously, the separator can better retain its mechanical properties at increased temperatures, for example, above 100 °C or above 120 °C.

[0120] Another aspect of the invention relates to a method for producing a solid electrolyte separator, preferably a solid electrolyte separator as disclosed herein, comprising the steps of: a) providing a porous substrate having a plurality of pores with a porosity between 10.0% and 90.0%; b) preparing a liquid mixture by mixing a silica precursor, an ionically conductive compound, a metal salt, and a solvent; c) contacting the porous substrate with the liquid mixture, thereby impregnating the pores of the porous substrate with the liquid mixture; d) curing the liquid mixture to form a solid electrolyte within the pores of the porous substrate, thereby obtaining a solid electrolyte separator with a porosity lower than the porosity of the porous substrate; and e) optionally, applying a pressure on the porous substrate, preferably after the curing process.

[0121] In particular embodiments, the present method comprises the steps of: a) providing a porous non-metallic, preferably polymer or fibrous, substrate having a plurality of pores, wherein an initial porosity of the porous non-metallic, preferably polymer or fibrous, substrate is between 10.0% and 90.0%; b) preparing a liquid mixture comprising a silica precursor or an alumina precursor, an ionically conductive compound, a metal salt, and a solvent; c) contacting the porous non-metallic, preferably polymer or fibrous, substrate with the liquid mixture, thereby filling the pores of the porous non-metallic, preferably polymer or fibrous, substrate with the liquid mixture; d) curing the liquid mixture to form a solid electrolyte network within the pores of the porous non- metallic, preferably polymer or fibrous, substrate, thereby obtaining a solid electrolyte separator with a post-curing porosity lower than the initial porosity of the porous non-metallic, preferably polymer or fibrous, substrate, and; e) optionally, drying and / or aging the solid electrolyte separator.

[0122] Fig. 4 describes an exemplary embodiment of the method (400) as described herein for producing a solid electrolyte separator, preferably a solid electrolyte separator as disclosed herein. In the illustrated example, the method (400) includes providing a porous non-metallic, preferably polymer or fibrous, substrate to a vessel (411), which may include, for example, a chamber, a container or a mixer, and preparing a liquid mixture (412), optionally partially gelling the mixture (413), contacting the porous non- metallic, preferably polymer or fibrous, substrate with the mixture (414), optionally overfilling the pores of the substrate (415), curing the liquid mixture to form a solid electrolyte within the pores of the substrate (416) to obtain a solid electrolyte separator, and optionally drying the separator (417). The vessel (411) may be any suitable vessel configured to receive and hold the porous non-metallic, preferably polymer or fibrous, substrate. In preferred embodiments, the porous non-metallic, preferably polymer or fibrous, substrate is the same substrate as defined herein above.

[0123] In general, the method (400) as disclosed herein refers to a gelation or sol-gel method to prepare a highly ionically conductive medium that is solid at a temperature of about 20 to 25 °C. A "sol-gel process" as referred to herein involves the conversion of monomers or reactive compounds (i.e., a silica precursor) into a colloidal solution (sol) that acts as a precursor for an integrated network (gel). The sol may be a suspension in which solid nanostructures are dispersed in a continuous liquid phase. For instance, the solid nanostructures may comprise nanoparticles, nanotubes, nanoplatelets, oligomers, and / or polymer aggregates.

[0124] In particular, the herein disclosed sol-gel process is a wet-crosslinking technique that is initiated by hydrolysis and / or alcoholysis of a silicon alkoxide, in the presence of a solvent. Partial hydrolysis and / or alcoholysis of the silica and / or alumina precursor(s) may be initiated immediately after the formation of the liquid mixture (412) (i.e., mixing of the silica and / or alumina precursor, the ionically conductive compound, the metal salt, and the solvent). However, the rate of hydrolysis / alcoholysis may depend on the concentration of water / moisture and / or alcohols in the liquid mixture and the addition of optional catalysts or initiators.

[0125] In certain embodiments, the provision of an alcohol-based solvent may impact the hydrolysis and condensation mechanisms. However, the hydrolysis of the silicon alkoxide precursor is the pivotal step in the formation of siloxane bonds (i.e., Si-O-Si). Conversely, alcoholysis of Si-O-Si bonds can be responsible for the continuous restructuring of the forming polymeric network. Alternatively, alcohols can play a role in the formation of metal oxides through non-hydrolytic sol-gel routes. For instance, alcohols can react with Si chloride to form Si-O-Si bonds (alkyl halide elimination). In these routes, the oxygen donor differs from water.

[0126] The hydrolyzed silicon alkoxide may subsequently condense to form silica and / or alumina oligomers and / or nanoparticles. Condensation reactions typically comprise the reaction of reactive silanol groups to form siloxane bonds. The formed aggregates or oligomers may grow by further aggregation or polymerization, respectively. The degree of aggregation and / or polymerization determines the viscosity of the liquid mixture. Suitable viscosities for contacting the liquid mixture and the porous non-metallic, preferably polymer or fibrous, the substrate as disclosed herein may depend on the wettability of the substrate and / or flowability of the liquid mixture.

[0127] The viscosity of the liquid mixture may be optimized by the nature and / or the amount of the solvent comprised in said mixture. The solvent preferably comprises at least one protic substance or compound to initiate and / or promote hydrolysis of a silicon alkoxide. In preferred embodiments, the solvent comprises water. The solvent may further comprise an alkane, alkyl alcohol, alkyl ether, and mixtures thereof.

[0128] The solvent may comprise a Ci.g alcohol; including all linear or branched alkyl groups with between 1 and 6 carbon atoms, and thus includes methanol, ethanol, n-propanol, i-propanol, n-butanol and its isomers. The solvent may comprise a C2-10 ether; including all linear or branched alkyl groups with between 2 and 10 carbon atoms, and thus includes dimethyl ether, diethyl ether, di-n-propyl ether, di-i-propyl ether, di- n-butyl ether and its isomers. Preferably, the solvent comprises propylene glycol methyl ether (PGME).

[0129] In particular embodiments, the solvent may comprise an acidic aqueous solution to increase the rate of hydrolysis. Hence, the present method provides that the amount of reactive silicon species, such as silanol groups, may be tuned and adjusted depending on the desired viscosity for impregnation of the porous non-metallic, preferably polymer or fibrous, substrate.

[0130] The term "liquid mixture" may therefore refer to a liquid medium comprising suspended solid structures of varying size. In particular, the liquid mixture may gradually evolve into a gel-like network.

[0131] For example, and in an embodiment, the liquid mixture may be formed by placing the silica precursor, the ionically conductive compound, the metal salt, and the solvent 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. Optionally, the ionically conductive compound and the metal salt may be dissolved in a solvent first such as a water-alcohol mixture (e.g., water-methanol, water-ethanol, water-isopropanol) to improve the solubility of the components comprised in the liquid mixture. The skilled person understands how this selection can be made and knows how to obtain a miscible liquid mixture. In particular embodiments, the method as disclosed herein provides that the liquid mixture may be partially gelled before contacting with the porous non-metallic, preferably polymer or fibrous, substrate

[0132] (413). Partial gelation may provide the formation of larger aggregates and / or continuous clusters, resulting in a partial gel mixture with a viscosity higher than the viscosity of the liquid mixture. This has the advantage that the partially gelled mixture may provide easier handling and application to impregnate the porous non-metallic, preferably polymer or fibrous, substrate. Moreover, the curing time may be significantly reduced using a partially gelled mixture.

[0133] The viscosity of the partial gel mixture is advantageously adjusted for impregnating the substrate via a selected coating method (e.g., dip coating, blade coating). It is understood by those skilled in the art that each coating method may have a different optimal viscosity range, and the invention is not limited thereto. Furthermore, the optimal viscosity may be influenced by the porosity and surface properties of the substrate, with temperature playing an additional role. As a non-limiting example, a suitable viscosity value for impregnating might fall within the range of 20 to 50 mPa.s. In an alternative embodiment the liquid mixture may be kept liquid to avoid the partial gelation.

[0134] In some embodiments, partial gelation can be performed by storage of the liquid mixture 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 partial gel mixture.

[0135] Upon contacting the porous non-metallic, preferably polymer or fibrous, substrate with the liquid mixture

[0136] (414) the pores of the substrate are infiltrated with the viscous mixture. The pores may be filled until saturation of the pore volume or inner space of the pore. Hence, the free volume of the pores may be completely filled with liquid mixture. Filling of the free volume of the pores of the substrate results in a significant decrease of the porosity (i.e., inner space). Hence, the solid electrolyte separator is characterized by a lower porosity compared to the porous non-metallic, preferably polymer or fibrous, substrate.

[0137] In some embodiments, filling of the pores of the porous non-metallic, preferably polymer or fibrous, substrate may comprise dipping the substrate in the liquid mixture, or alternatively dropping the liquid mixture onto the substrate. The liquid mixture will subsequently penetrate into the pores of the substrate, thereby impregnating the porous non-metallic, preferably polymer or fibrous, substrate.

[0138] In some embodiments, contacting the substrate with the liquid mixture can be performed using a coating method known in the art. Suitable methods may include drop casting, blade coating, slot die coating, spray coating, and alternative methods, but the method is limited to these. The skilled person understands that certain coatings methods are more suitable for experimental sample preparation while other methods are more suitable for commercial production. Accordingly, in a preferred embodiment the method for contacting the substrate with a liquid mixture includes sheet-to-sheet, roll-to-roll, or alternative in-line methods allowing for continuous and high-throughput production. In the latter embodiments, the solid electrolyte may be poured on an assembly line and moved for further processing such as drying or cutting.

[0139] In some embodiments, the drying of the separator after contacting the substrate with the liquid mixture can be performed in a drying chamber such as an oven. The skilled person understands that certain drying methods are more suitable for experimental sample preparation while other methods are more suitable for commercial production. Accordingly, in a preferred embodiment the drying method includes placing the substrate impregnated with the liquid mixture in an oven attached to an in-line method, such as a sheet-to-sheet line or a roll-to-roll line. In the latter embodiments, the solid electrolyte may be dried on top or along an assembly line and moved for further processing such as cutting.

[0140] In particular embodiments, the method as disclosed herein provides that the porosity of the separator may be between 0.1% and 10.0%, or between 0.1% and 7.5%, or between 0.1% and 5.0%, or between 0.1% and 2.5%, or between 0.1% and 1.0%.

[0141] Optionally, impregnation of the pores of the porous non-metallic, preferably polymer or fibrous, substrate with the liquid mixture may reach a point where the pores become saturated and filled beyond their usual capacity, resulting in an overfill of the pores. The liquid mixture flowing from the saturated pores may subsequently form a solid electrolyte layer according to any of the previously described embodiments on at least one side of the porous non-metallic, preferably polymer or fibrous, substrate. The method may include a step of manipulating the porous non-metallic, preferably polymer or fibrous, substrate to provide sufficient space for the formation of at least two layers on two opposite sides of the porous non- metallic, preferably polymer or fibrous, substrate.

[0142] In particular embodiments, the method as disclosed herein further comprises the steps of contacting the porous non-metallic, preferably polymer or fibrous, substrate with an excess amount of liquid mixture (415), surpassing a capacity of the porous non-metallic, preferably polymer or fibrous, substrate, thereby forming at least one liquid mixture layer positioned on at least one side of the porous non-metallic, preferably polymer or fibrous, substrate; and curing the at least one liquid mixture layer to obtain a solid electrolyte layer. The thickness of the formed layer may depend on the amount of the liquid mixture and porosity of the porous non-metallic, preferably polymer or fibrous, substrate.

[0143] In particular embodiments, the formed solid electrolyte layer has an average thickness of between 0.01 pm and 50.0 pm, or between 0.05 pm and 50.0 pm, or preferably between 0.1 pm and 50.0 pm, or between 0.25 pm and 50.0 pm, or between 0.5 pm and 50.0 pm, or between 1.0 pm and 50.0 pm, or between 2.0 pm and 50.0 pm. The formed solid electrolyte layer(s) may be a continuous or non-continuous structure and can include a two-dimensional or three-dimensional material, nanoparticles or partial or full films. Said layer(s) may have a heterogeneous morphology and can be homogenized by trimming, thinning, or annealing said layer. Additional solid electrolyte material may be added and / or positioned on at least one side of the substrate to form at least one homogeneous layer.

[0144] In particular embodiments, the method as disclosed herein further comprises the step of thinning the solid electrolyte separator by selectively removing at least part of the layer.

[0145] After filling the pores of the porous non-metallic, preferably polymer or fibrous, substrate with the liquid mixture, the mixture is cured to yield a solid electrolyte gel (416). In particular, the aggregates and / or oligomers comprised in the liquid mixture may bond with each other to form a continuous cluster or network that spans the liquid phase. Formation of a continuous cluster may occur via polycondensation, resulting in a wet gel structure.

[0146] The time required for the gelation can be controlled by the amount of solvent added, and in particular the water content of the solvent, and storage temperature of the liquid mixture. 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.

[0147] In some particular embodiments, the method as disclosed herein provides that the formation of the (partial) 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.

[0148] In some embodiments, polycondensation may still take place after the formation of the gel structure. For example, the gel may be allowed to sit, which may be referred to herein as "ageing". Ageing may take place at a temperature in the range from 20.0 °C to 60.0 °C, such as 20.0 °C to 50.0 °C.

[0149] The formed wet gel structure may subsequently be dried to obtain a solid electrolyte separator (417), preferably a solid electrolyte separator as disclosed herein. After curing of the liquid mixture, the solid electrolyte separator may still comprise a high solvent content, which is undesirable for solid-state battery applications. To remove the excess solvent, the separator may be dried using a conventional drying and / or ageing process. For example, the separator 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 silica and / or alumina matrix, and prevent the formation of cracks in the solid matrix which can be caused by fast solvent removal. In the pre-drying process, the separator 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 solvent may be evaporated / removed in the pre-drying process. Depending on the threshold solvent content, additional drying steps may be required. The skilled person understands how to obtain a separator with a desired maximal solvent content.

[0150] In particular embodiments, the method as disclosed herein further comprises the step of drying the separator until reaching a water content of less than a water content of less than 3000 ppm, or less than 2500 ppm, or less than 2000 ppm, preferably less than 1500 ppm, or less than 1000 ppm. Advantageously, the present method may provide less stringent drying conditions of the separator, resulting in a more cost-effective and efficient manufacturing process.

[0151] From the process steps described above it should be clear that, in contrast with applying a solid electrolyte coating at the inner surface of the pores, the present method provides that the inner volume of the pores is filled with solid electrolyte material.

[0152] The conductivity of the obtained solid electrolyte separator may depend on the relative amount of the ionically conductive compound and the silica and / or alumina precursor comprised in the liquid mixture. In some embodiments, the molar ratio of the ionically conductive compound to the silica and / or alumina precursor in the liquid mixture 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 thermomechanical properties and good ionic conductivity.

[0153] Another aspect of the invention relates to an electrode assembly comprising an active electrode material and a solid electrolyte separator, preferably the solid electrolyte as described herein and / or preferably obtainable or obtained according to the method as described herein; wherein the electrolyte separator is configured for ionically connecting to the active electrode material.

[0154] In some embodiments, the electrode assembly comprises: a solid electrolyte separator comprising a porous non-metallic, preferably polymer or fibrous, substrate having a plurality of pores embedded with a solid electrolyte; and an active electrode material configured for ionically contacting at least one side of the solid electrolyte separator; wherein the porosity of the porous non-metallic, preferably polymer or fibrous, the substrate is between at least 10.0% and at most 90.0%; wherein the solid electrolyte comprises a silica and / or alumina matrix incorporating an electrolyte; wherein the electrolyte comprises an ionically conductive compound and a metal salt; and wherein the solid electrolyte is positioned within an inner space of the pores such that the porosity of the solid electrolyte separator is lower than the porosity of the porous non-metallic, preferably polymer or fibrous, substrate.

[0155] In a particular embodiment, the active electrode material may comprise a porous material and a plurality of active material particles. It is common for the active electrode material to have an inhomogeneous surface (i.e., the electrode surface may be rough or uneven), leading to a poor interface between the solid electrolyte and the electrode. However, the solid electrolyte separator can enhance the interface for ionic contact with the surface of an electrode by adaptively conforming to the electrode surface shape, preferably filling, or matching any inhomogeneities. This results in an improved electrode / electrolyte interface, providing advantages for the electrochemical performance of the cell. Additionally, the provision of a solid electrolyte layer can further enhance the electrode / electrolyte interface quality. Therefore, the solid electrolyte separator may comprise one or more solid electrolyte layers, as described herein, to provide and promote contact with one or more active electrode materials.

[0156] FIG 5. schematically illustrates an exemplary embodiment of an electrode assembly (500) as disclosed herein. In the illustrated example, the electrode assembly (500) includes a stack of a solid electrolyte separator and an active electrode material (514). The solid electrolyte separator comprises a first solid electrolyte layer (511), a second solid electrolyte layer (513) and a porous non-metallic, preferably polymer or fibrous, substrate (512) having a plurality of pores embedded with a solid electrolyte arranged between the first layer (511) and the second layer (513).

[0157] It should be appreciated that the configuration of the electrode assembly may be adapted to any of the embodiments of the solid electrolyte separator and the optional solid electrolyte layers as described above, such as the embodiments of FIGs 1-3. These combinations of embodiments are therefore explicitly disclosed herein.

[0158] As further shown, the separator is positioned on or adjacent to the active electrode material (514). In particular, the second layer (513) of the separator is adhered to the active electrode material (514) and may provide for ionic contact allowing the transfer of ions from the separator to the electrode and vice versa.

[0159] The active material used in the active electrode material may vary depending on the type of battery and electrode. For example, common anode materials may include graphite and various forms of lithium- containing materials in lithium-ion batteries, while common cathode material may include materials like lithium cobalt oxide (LiCoO2) in lithium-ion batteries. Any type of electrode known in the art can, therefore, be considered as the active electrode material. Preferably, the active electrode material may comprise a 'supportive' electrode material combined with an active material, optionally forming a composite electrode.

[0160] As further shown, the assembly (500) optionally includes a current collector (515) in electrical contact with the active electrode material (514). The current collector may be configured to provide mechanical support to the active electrode material and / or conduct the flow of electrons between said material and external battery terminals. The active electrode material (514) can be, for example, produced by applying a slurry containing active material particles, a binder and conductive agent particles onto a current collector (515).

[0161] 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 a current collector. Optionally, the current collector may include a coating of a protective layer positioned between the contact surfaces of the current collector and any adjacent surface, for example, a surface of the solid electrolyte separator or a surface of the electrode active material (514).

[0162] In particular embodiments, the active electrode material is a porous material having a porosity of between at least 10.0 % to at most 90.0 %, or between or between at least 15.0% and at most 90.0%, or between at least 20.0% and at most 90.0%, or between at least 25.0% and at most 90.0%, or between at least 30.0% and at most 90.0%, or between at least 30.0% and at most 85.0%, preferably between at least 30.0% and at most 80.0%, or between at least 30.0% and at most 75.0%, more preferably between at least 30.0% and at most 70.0%, or between at least 30.0% and at most 60.0%, even more preferably between 30.0% and 55.0%. The skilled person understands that the porosity is advantageously adapted to the desired amount of solid electrolyte impregnation, which can depend on the intended implementation and application of the separator.

[0163] In particular embodiments, the pore size or average diameter of the pores of the active electrode material may be between at least 0.01 pm and at most 2.0 pm, or between at least 0.01 pm and at most 1.5 pm, or between at least 0.01 pm and at most 1.25 pm, or between at least 0.01 pm and at most 1.0 pm, preferably between at least 0.01 pm and at most 0.75 pm, or between at least 0.01 pm and at most 0.5 pm, or between at least 0.05 pm and at most 0.5 pm, or between at least 0.1 pm and at most 0.5 pm. The skilled person understands that the pore size is advantageously adapted to the desired amount of solid electrolyte impregnation, which can depend on the intended implementation and application of the separator.

[0164] In some embodiments, the active electrode material may be covered and / or coated with the solid electrolyte as described herein. In further embodiments, the active electrode material may comprise a porous active electrode material having pores that are covered and / or coated with the solid electrolyte as described herein. Advantageously, it has been found that infiltrating the porous structure of a porous active electrode material with a solid electrolyte decreases the porous structure and significantly improves the mechanical strength while retaining or even improving the ionic conductivity of the electrode assembly.

[0165] As described above, the solid electrolyte separator described herein can demonstrate a suitable ionic conductivity for an application in alkali metal batteries; therefore, an electrode assembly comprising said solid electrolyte separator can demonstrate improved ionic conduction properties also. Similarly, the electrode assembly can have improved mechanical properties due to the improved elasticity of the solid electrolyte separator. It is understood that any of the above embodiments relating to the solid electrolyte separator form embodiments of the electrode assembly.

[0166] In some embodiments, an active electrode material used in the electrode assembly can be a positive active electrode material. Examples of the positive active electrode material may include a lithium- containing transition metal oxide, vanadium oxide, chromium oxide, and lithium-containing transition metal. Examples of the lithium-containing transition metal oxide include LiCoC , LiN iOz, LiMnC , LiMnjC , LiNiCoMnC (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), LiNiCoC , LiCoMnC , LiNiMnOj, LiNiCoMnO4, LiMnNiO4, LiMnCoO4, LiNiCoAIC , LiNiPO4, LiCoPO4, LiMnPO4, LiFePO4, LiMnFePO4, Li2NiSiO4, LizCoSiC , LizMnSiC , LizFeSiC , LiNiBOa, LiCoBOa, LiMnBOa, and LiFeBOa. Examples of the lithium-containing transition metal sulfide include LiTiSz, LizTiSa, and LiaNbS4. One positive active electrode material or two or more positive active electrode materials selected from these positive active electrode materials can be used.

[0167] In some embodiments, an active electrode material used in the electrode assembly can be a negative active electrode material. Examples of the negative active electrode 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 Li4Ti50iz, Li2SrTigOi4, TiC , Nb2O5, SnC>2, Ta2O5, WO2, WO3, Fe2O3, CoO, MOO2, SiO, SnBPOg, and their mixtures. Examples of the nitride can include LiCoN, LisFe^, Li7MnN4, and their mixtures. Examples of carbon include graphite, graphene, hard carbon, carbon nanotube, and their mixtures. One negative active electrode material or two or more negative active electrode materials selected from these negative active electrode materials can be used.

[0168] In some embodiments, the electrode active material may comprise a binder. The binder may fix particles of the active electrode material to each other. When the particles of the active electrode material are fixed to each other, the occurrence of a gap due to expansion and shrinkage of the particles of the active electrode 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 styrenebutadiene rubber (SBR), polyvinylidene fluoride (PVDF) and the like.

[0169] In particular embodiments, a method for producing an electrode assembly as described herein may comprise the steps of: producing a solid electrolyte separator by: o providing a porous non-metallic, preferably polymer or fibrous, substrate having a plurality of pores with an initial porosity between 10.0% and 90.0%; o preparing a liquid mixture by mixing a silica and / or alumina precursor, an ionically conductive compound, a metal salt, and a solvent; o contacting the porous non-metallic, preferably polymer or fibrous, substrate with the liquid mixture, thereby impregnating the pores of the porous non-metallic, preferably polymer or fibrous, substrate with the liquid mixture; o curing the liquid mixture to form a solid electrolyte within the pores of the porous non-metallic, preferably polymer or fibrous, substrate, thereby obtaining a solid electrolyte separator with a post-curing porosity lower than the initial porosity of the porous non-metallic, preferably polymer or fibrous, substrate; providing an active electrode material, optionally arranged on an electrode; positioning the solid electrolyte separator on the active electrode material; and applying a pressure onto the solid electrolyte separator, thereby pressing the solid electrolyte separator into the active electrode material to obtain the electrode assembly.

[0170] Fig. 6 schematically shows an example of a method (600) that may be used to produce an electrode assembly in accordance with embodiments of the present invention, wherein a solid electrolyte separator and an active electrode material are compressed together using low to moderate pressure (e.g. 0.1 MPa) to form the electrode assembly. Optionally, the active electrode material can be impregnated with the solid electrolyte.

[0171] According to this method (600), first a solid electrolyte separator is prepared by impregnating a porous non-metallic, preferably polymer or fibrous, substrate with a liquid mixture comprising a silica and / or alumina precursor, an ionically conductive compound, a metal salt, and a solvent. To impregnate the substrate, the porous non-metallic, preferably polymer or fibrous, substrate is provided to a vessel (611) that is configured to receive and hold the substrate in a desired position. For example, the vessel (611) can be a container, chamber or mixer. Optionally, the vessel can include means for an in-line process such as an assembly line. Next, the liquid mixture is prepared (612) by mixing a silica and / or alumina precursor, an ionically conductive compound, a metal salt, and a solvent until a homogeneous and miscible solution is obtained. Optionally, the liquid mixture may be partially gelled (613) to initiate gel formation and increase the viscosity of the solution. Then, the porous non-metallic, preferably polymer or fibrous, substrate is contacted with the (at least partially gelled) liquid mixture (614) to impregnate the pores of the substrate with the liquid mixture. Optionally, an excess amount of the (at least partially gelled) liquid mixture can be used to intentionally overfill the pores of the substrate (615) and obtain a liquid mixture layer on at least one side of the substrate. After filling the pores of the substrate with the (at least partially gelled) liquid mixture, said mixture is cured (616) to form a solid electrolyte within the pores of the substrate and obtain a solid electrolyte separator. Advantageously, the formed solid electrolyte separator is dried (617) to remove any (excess) remaining solvent. Optionally, the liquid mixture layer can be cured to form a solid electrolyte layer on at least one side of the substrate.

[0172] After preparing the solid electrolyte separator, an active electrode material, optionally arranged on an electrode, is provided to the vessel (618). The solid electrolyte separator is subsequently positioned on the active electrode material (619) to pre-assemble the different components. The pre-assembly is subsequently compressed (620) by applying pressure onto the solid electrolyte separator, resulting in an electrode assembly according to embodiments of the present invention.

[0173] Optionally, the method can further comprise the step of contacting the active electrode material having a plurality of pores with the liquid mixture as described herein; thereby impregnating the pores of the active electrode material; and curing the liquid mixture to form a solid electrolyte within the pores of the active electrode material, which reduces the porosity of the active electrode material. By providing a continuous solid electrolyte material across the separator and the active electrode material, advantageously a continuous path for ionic conduction exists between said components. This advantageously results in an improved adhesion between both components and / or an improved conductivity as compared to electrode assemblies comprised in the state of the art.

[0174] In some embodiments, the active electrode material can be impregnated, for example, by applying a liquid mixture as described herein onto said active electrode material. In this way, a composite electrode comprising the solid electrolyte can be obtained. An excess amount of the liquid mixture may be used to overfill the pores of the active electrode material, which may result in the formation of a solid electrolyte layer on at least one side of the active electrode material. Alternatively, the active electrode material can be provided with the active material already formed, for example, as a layer deposited on the electrode material.

[0175] In particular embodiments, the solid electrolyte separator after pressing may have a thickness between 1.0 pm and 250.0 pm, preferably between 1.0 pm and 200.0 pm, or between 1.0 pm and 150.0 pm, or between 1.0 pm and 100.0 pm, or more preferably between 1.0 pm and 50.0 pm, or between 1.0 pm and 25.0 pm. Preferably, the solid electrolyte separator may have a thickness between 5.0 pm and 50.0 pm, or between 5.0 pm and 45.0 pm, or between 5.0 pm and 40.0 pm, or between 5.0 pm and 35.0 pm, or between 5.0 pm and 30.0 pm, preferably between 10.0 pm and 30.0pm, for example, 15.0 pm or 25.0 pm, more preferably still around 20.0 pm. It is understood that the thickness of the separator may be reduced after pressing compared to its thickness during initial production.

[0176] The impregnation with the liquid mixture 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 the liquid mixture can be adapted, for example, to 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.

[0177] In some preferred embodiments, the method may further comprise the step of providing a second active electrode material, positioning the second active electrode material on the solid electrolyte separator, such that the solid electrolyte separator is arranged between the first and the active electrode materials, and applying a pressure onto at least the first and / or the second active electrode materials.

[0178] In particular embodiments, a method for producing an electrode assembly as described herein may comprise the steps of: providing a porous non-metallic, preferably polymer or fibrous, substrate having a plurality of pores with an initial porosity between 10.0% and 90.0%; providing an active electrode material, optionally arranged on an electrode; positioning the porous non-metallic, preferably polymer or fibrous, substrate on the active electrode material; and applying a pressure onto the porous non-metallic, preferably polymer or fibrous, substrate, thereby pressing the porous non-metallic, preferably polymer or fibrous, substrate into the active electrode material; and producing a solid electrolyte separator by: o preparing a liquid mixture by mixing a silica and / or alumina precursor, an ionically conductive compound, a metal salt, and optionally a solvent; o contacting the porous non-metallic, preferably polymer or fibrous, substrate positioned on the active electrode material with the liquid mixture, thereby impregnating the pores of the porous non-metallic, preferably polymer or fibrous, substrate, and optionally the pores of the active electrode material, with the liquid mixture; o curing the liquid mixture to form a solid electrolyte within the pores of the porous non-metallic, preferably polymer or fibrous, substrate, and optionally the pores of the active electrode material, thereby obtaining a solid electrolyte separator with a post-curing porosity lower than the initial porosity of the porous non-metallic, preferably polymer or fibrous, substrate.

[0179] Fig. 7 schematically shows another example of a method (700) that may be used to produce an electrode assembly in accordance with embodiments of the present invention, wherein a porous non-metallic, preferably polymer or fibrous, substrate and an active electrode material are compressed together using low to moderate pressure (e.g. 0.1 MPa) to form an assembly and subsequently impregnating the pores of the porous non-metallic, preferably polymer or fibrous, substrate with a solid electrolyte material to form the electrode assembly.

[0180] According to this method, first a pre-assembly is prepared by positioning a porous non-metallic, preferably polymer or fibrous, substrate on an active electrode material and compressing said structure to form an assembly. To form the pre-assembly, a porous non-metallic, preferably polymer or fibrous, substrate is provided to a vessel (711). For example, the vessel (711) can be a container, chamber or mixer. Then, an active electrode material, optionally arranged on an electrode, is provided to said vessel (712). Next, the porous non-metallic, preferably polymer or fibrous, substrate is positioned on the active electrode material (713) to pre-assemble the different components. The pre-assembly is subsequently compressed (714) by applying pressure onto the porous non-metallic, preferably polymer or fibrous, substrate, resulting in an assembly.

[0181] After preparing the assembly, a liquid mixture is prepared (715) by mixing a silica and / or alumina precursor, an ionically conductive compound, a metal salt, and a solvent until a homogeneous and miscible solution is obtained. Optionally, the liquid mixture may be partially gelled (716) to initiate gel formation and increase the viscosity of the solution. Then, the porous non-metallic, preferably polymer or fibrous, substrate is contacted with the (at least partially gelled) liquid mixture (717) to impregnate the pores of the substrate with the liquid mixture. Optionally, an excess amount of the (at least partially gelled) liquid mixture is used to intentionally overfill the pores of the substrate (718) and obtain a liquid mixture layer on at least one side of the substrate. After filling the pores of the substrate with the (at least partially gelled) liquid mixture, said mixture is cured (719) to form a solid electrolyte within the pores of the substrate and obtain a solid electrolyte separator. Optionally, the formed solid electrolyte separator is dried (720) to remove any (excess) remaining solvent. The resulting assembly is an electrode assembly according to embodiments of the present invention.

[0182] In particular embodiments, an excess amount of liquid mixture may be used to impregnate the pores of the porous non-metallic, preferably polymer or fibrous, substrate and the active electrode material. In other words, a continuous solid electrolyte material may be formed that can advantageously cover the entire structure of the electrode assembly. This has the advantage that both structures are entangled with and / or chemically bound to the same solid electrolyte material, resulting in an improved adhesion between both components and / or an improved conductivity as compared to electrode assemblies comprised in the state of the art.

[0183] In some preferred embodiments, the method as disclosed herein may further comprise the step of providing a second active electrode material, positioning the second active electrode material on the solid electrolyte separator, such that the solid electrolyte separator is arranged between the first and the active electrode materials, and applying a pressure onto at least the first and / or the second active electrode materials.

[0184] In particular embodiments, the pressure applied according to any one of the methods as disclosed herein to form an electrode assembly may be between 0.1 MPa and 10.0 MPa, or between 0.1 MPa and 7.5 MPa, or between 0.1 MPa and 5.0 MPa, or between 0.1 MPa and 2.5 MPa, preferably between 0.1 MPa and 1.0 MPa, or between 0.1 MPa and 0.75 MPa, or between 0.1 MPa and 0.5 MPa.

[0185] It should be noted that the present invention provides high flexibility in electrode assembly design and production. Moreover, another advantage is that the porous non-metallic, preferably polymer or fibrous, substrate and the active electrode material may be impregnated with the same solid electrolyte, resulting in a homogeneous and continuous conductive medium.

[0186] Another aspect of the present invention relates to an electrochemical energy storage device comprising one or more unit cells, wherein each cell comprises: a solid electrolyte separator as described herein; and at least two active electrode materials, wherein a first active electrode material is configured as a positive electrode and a second active electrode material is configured as a negative electrode; wherein the solid electrolyte separator is arranged between the positive electrode and the negative electrode. Preferably, solid electrolyte separator is configured for ionically contacting the positive and the negative electrodes.

[0187] 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 chemical reactions in the cell may involve the solid electrolyte separator, the electrodes, or an external substance. 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.

[0188] As described above, because the solid electrolyte separator of the present invention can demonstrate high ionic conductivity; therefore, a power storage device comprising an electrochemical cell that comprises a solid electrolyte separator arranged between and in electrical contact with a positive and negative electrode can demonstrate improved ionic conduction properties also. Similarly, the power storage device can have improved mechanical properties due to the reinforced solid electrolyte separator as described herein. It is understood that any of the above embodiments of the solid electrolyte separator forms embodiments of the power storage device.

[0189] A particular advantage is that the present solid electrolyte separator may be manufactured at a significantly reduced thickness (i.e., below 200.0 pm, preferably below 100.0 pm) compared to free standing solid electrolyte film, resulting in smaller and more compact unit cells. This advantageously may result in power storage devices comprising more stacks and / or a higher stack density. A further advantage is that the thickness of the solid electrolyte separator can be reduced further still based on the selection of porous non-metallic, preferably polymer or fibrous, substrate.

[0190] In some embodiments, the electrochemical energy storage device may comprise one or more unit cells, wherein each cell comprises a solid electrolyte separator comprising a porous non-metallic, preferably polymer or fibrous, substrate having a plurality of pores embedded with a solid electrolyte; and a positive electrode and a negative electrode; wherein the porosity of the porous non-metallic, preferably polymer or fibrous, substrate is between at least 10.0% and at most 90.0%; wherein the solid electrolyte comprises a silica and / or alumina matrix incorporating an electrolyte; wherein the electrolyte comprises an ionically conductive compound and a metal salt; and wherein the solid electrolyte is positioned within an inner space of the pores such that the porosity of the solid electrolyte separator is lower than the porosity of the porous non-metallic, preferably polymer or fibrous, substrate.

[0191] In particular embodiments, the electrochemical energy storage device provides that the one or more unit cells are enclosed in a container, preferably a flexible container in the form of a pouch bag.

[0192] In a rechargeable power storage device, the electrode that is the negative electrode in discharge (i.e., battery operation) becomes the positive electrode when charging the battery. Herein further with anode material and cathode material are meant the materials that are the anode (negative electrode) and, respectively, the cathode (positive electrode) during battery operation or discharge.

[0193] FIG 8. schematically illustrates an exemplary embodiment of an electrochemical energy storage device (800) as disclosed herein. The storage device (800) comprises a stack of a first electrode, e.g. an anode (812), a solid electrolyte separator (818), and a second electrode, e.g. a cathode (816); forming a unit cell. The storage device (800) further comprises a first current collector (811) in electrical contact with the anode (812), and a second current collector (817) in electrical contact with the cathode (816). The solid electrolyte separator (818) comprises a porous non-metallic, preferably polymer or fibrous, substrate (814) embedded with a solid electrolyte, and a first solid electrolyte layer (813) and a second solid electrolyte layer (815) positioned on opposite sides of the substrate (814). The layers (813, 815) are configured for adhering to the electrodes (812, 816) and forming an electrical contact with said electrodes (812, 816). The solid electrolyte material comprises a silica and / or alumina matrix and an electrolyte as described herein. Optionally, the unit cell is enclosed in a pouch bag (819).

[0194] In particular embodiments, the electrochemical energy storage device may comprise a plurality of unit cells arranged sequentially in a stack, preferably vertically aligned. For example, the storage device may comprise two unit cells, or three unit cells, or four unit cells, or five unit cells, or ten unit cells.

[0195] FIG 9. schematically illustrates another exemplary embodiment of an electrochemical energy storage device (900) as disclosed herein. The storage device (900) comprises a stack of two unit cells ionically connected by a bridging current collector (917). The first unit cell comprises a stack of a first electrode, e.g., an anode (912), a first solid electrolyte separator (924), and a second electrode, e.g., a cathode (916). The first unit cell further comprises a first current collector (911) in electrical contact with the anode (912). The second unit cell comprises a stack of a third electrode, e.g., a cathode (918), a second solid electrolyte separator (925), and a fourth electrode, e.g., an anode (922). The second unit cell further comprises a second current collector (923) in electrical contact with the anode (912). The bridging current collector (917) is configured to physically separate the second electrode, e.g., the cathode (916) and the third electrode, e.g., the cathode (918). Optionally, the stack of the two unit cells is enclosed in a pouch bag (926).

[0196] It should be appreciated that the configuration of the electrochemical energy storage device may be adapted to any of the embodiments of the solid electrolyte separator and the optional solid electrolyte layers as described above, such as the embodiments of FIGs 1-3. Further, the configuration and interface formed between the solid electrolyte separator and any of the active electrode materials can adapted to any of the embodiments described above, such as the embodiment of FIG 5. These combinations of embodiments are therefore explicitly disclosed herein.

[0197] Advantageously, the electrochemical energy storage device comprising one or more unit cells, wherein each cell comprises the solid electrolyte separator 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 preferred embodiments, the present invention provides that the electrochemical energy storage device is an alkali metal battery, preferably a lithium and / or a sodium battery.

[0198] 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 invention. 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.

[0199] 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.

[0200] 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 include a direct or indirect connection in an electrical or nonelectrical (i.e. physical) manner, as appropriate for the context in which the term is used.

[0201] The recitation of numerical ranges by endpoints includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g., 1 to 5 can include 1, 2, 3, 4 when referring to, for example, a number of elements, and can also include 1.5, 2, 2.75 and 3.80, when referring to, for example, measurements). The recitation of end points also includes the end point values themselves (e.g., from 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein. 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 invention described herein are capable of operation in other sequences than described or illustrated herein.

[0202] 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.

[0203] 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. Reference in this specification may be made to devices, structures, systems, or methods that provide "improved" performance (e.g. increased or decreased results, depending on the context). It is to be understood that unless otherwise stated, such "improvement" is a measure of a benefit obtained based on a comparison to devices, structures, systems or methods in the prior art. Furthermore, it is to be understood that the degree of improved performance may vary between disclosed embodiments and that no equality or consistency in the amount, degree, or realization of improved performance is to be assumed as universally applicable.

[0204] 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.

[0205] EXAMPLES

[0206] Examples of various implementations of the technology in accordance with aspects of the present disclosure are given below. Providing these examples is intended to aid the reader in understanding the technological concepts more easily, but it is not meant to identify the most important or essential features, nor is it meant to limit the scope of the present invention. The provided examples form preferred embodiments that can be combined with any of the above-discussed embodiments unless otherwise specified.

[0207] Example 1 - Electrochemical storage device comprising a glass fiber substrate

[0208] Example 1 illustrates single unit cells comprising a solid electrolyte separator, which comprises a glass fiber (GF / A) substrate embedded with a solid electrolyte, and the effects thereof on electrochemical performance.

[0209] Impregnation of a GF / A substrate

[0210] First, a GFA spacer (Whatman) with a thickness of 260 pm, 53 g m“2areal density, a porosity of about 64%, and a pore size of 1.6 pm was placed in a container. Then, a liquid mixture was prepared by mixing 2.75 g of tetraethyl orthosilicate (TEOS), 7.12 g of l-Ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIFSI), 1.75 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 5.43 g of propylene glycol methyl ether (PGME), and 2.95 g of water in a glass bottle container equipped with a magnetic stirring bar placed in a glovebox. The molar ratio of TEOS:EM IFSI:LiTFSI was 1.0:1.85:0.46.

[0211] Once a homogeneous, clear solution was obtained, the liquid mixture was heated at 35 °C for 19 to 35 hours in a convection oven to initiate gelation and increase the viscosity of the mixture. After obtaining a desirable viscosity, the mixture was applied to the porous substrate via a dip-coating technique. In particular, the GFA substrate was fully submerged in the liquid mixture. After remaining immersed in the liquid mixture for around 30 seconds, the liquid mixture was impregnated in the pores of the GFA substrate and excess liquid mixture was removed from the surface of the substrate.

[0212] The impregnated substrate was subsequently subjected to an ageing step at room temperature for 2 days in a fume hood and an additional day in a dry room at about 22°C (dew point of -45 °C). The obtained solid electrolyte separator was subsequently dried at 60 °C for 3 days under vacuum of 1 to 10 Pa. The dried solid electrolyte separator was characterized by a thickness of about 950 pm, and two solid electrolyte layers that each have a thickness of about 350 pm and are positioned on opposite sides of the substrate. Formation of the electrochemical energy storage device

[0213] An electrochemical energy storage device comprising one unit cell was assembled under dry room conditions at about 22 °C with a dew point below -45 °C.

[0214] A stack was prepared by pressing a composite cathode comprising an active material loading of 2mAh / cm2on a single-layer cathode footprint measuring 3x4.5 cm2(or 13.5 cm2) onto the formed solid electrolyte separator by applying a pressure of 150 kPa. Then, a lithium metal electrode with a thickness of 100 pm was pressed onto the opposite side of the solid electrolyte separator by applying a pressure of 150 kPa to form the unit cell. The thickness of the composite cathode and Al foil is about 90pm.

[0215] The resulting stack was positioned between two pouch foils, each measuring 8 x 5 cm2, and the pouch foil was sealed using a vacuum sealing device. The resulting unit cell was characterized by a moisture content of 2000 ppm as measured by an automated moisture analyzer after nitrogen purging of the cell at 15 °C. Electrochemical performance

[0216] The electrochemical characterization of the obtained energy storage device was conducted in a Cell Test System at a controlled temperature of 25.0 ± 0.5 °C. Testing was performed at different C-rates, including C / 20 for the formation cycle and C / 10 for normal cycling tests. Additionally, the cycle life of the pouch cells was evaluated through continuous charge-discharge cycles within a voltage window of 3.0-4.2 V. As shown in FIG. 10, the discharge capacity remained around 110 mA h / g for up to 40 cycles.

[0217] Example 2 - Electrochemical storage device comprising a trilayer PP-PE-PP substrate

[0218] Example 2 illustrates single unit cells comprising a solid electrolyte separator, which comprises a trilayer porous substrate consisting of a polypropylene-polyethylene-polypropylene structure embedded with a solid electrolyte, and the effects thereof on electrochemical performance.

[0219] Impregnation of the trilayer PP-PE-PP substrate

[0220] First, a trilayer porous substrate consisting of a polypropylene-polyethylene-polypropylene structure with a thickness of 25 pm, a porosity of 55%, and a pore size of 0.027 pm was placed in a container. Then, a liquid mixture was prepared by mixing 0.47 g of tetraethyl orthosilicate (TEOS), 1.21 g of l-Ethyl-3- methylimidazolium bis(fluorosulfonyl)imide (EMIFSI), 0.30 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 0.92 g of propylene glycol methyl ether (PGME), and 0.5 g of water in a glass bottle container equipped with a magnetic stirring bar placed in a glovebox. The molar ratio of TEOS: EM I FSI :LiTFSI was 1.0:1.85:0.46.

[0221] Once a homogeneous, clear solution was obtained, the liquid mixture was heated at 35 °C for 19 to 35 hours in a convection oven to initiate gelation and increase the viscosity of the mixture. After obtaining a desirable viscosity, the mixture was applied to the porous substrate via a dip-coating technique. In particular, the porous substrate was fully submerged in the liquid mixture. After remaining immersed in the liquid mixture for 30 seconds, the liquid mixture was impregnated in the pores of the porous substrate and excess liquid mixture was removed from the surface of the substrate.

[0222] The impregnated substrate was subsequently subjected to an ageing step at room temperature for 2 days in a fume hood and an additional day in a dry room at about 22 °C (dew point of -45 °C). The obtained solid electrolyte separator was subsequently dried at 60 °C for 3 days under vacuum of 1 to 10 Pa. The dried solid electrolyte separator was characterized by a thickness of 35 pm, and two solid electrolyte layers that each have a thickness of 5 pm and are positioned on opposite sides of the substrate.

[0223] Formation of the electrochemical energy storage

[0224] An electrochemical energy storage device comprising one unit cell was assembled under dry room conditions at about 22 °C with a dew point below -45 °C.

[0225] A stack was prepared by pressing a composite cathode comprising an active material loading of 2mAh / cm2on a single-layer cathode footprint measuring 3x4.5 cm2(or 13.5 cm2) onto the formed solid electrolyte separator by applying a pressure of 500 kPa. Then, a lithium metal electrode with a thickness of 30 pm was pressed onto the opposite side of the solid electrolyte separator by applying a pressure of 500 kPa to form the unit cell. The resulting stack was positioned between two pouch foils, each measuring 8 x 5 cm2, and the pouch foil was sealed using a vacuum sealing device.

[0226] The resulting unit cell was characterized by a moisture content of 2950 ppm as measured by an automated moisture analyzer after nitrogen purging of the cell at 15 °C.

[0227] Electrochemical performance

[0228] The electrochemical characterization of the obtained energy storage device was conducted in a Cell Test System at a controlled temperature of 25.0 ± 0.59C. Testing was performed at different C-rates, including C / 20 for the formation cycle and C / 10 for normal cycling tests. Additionally, the cycle life of the pouch cells was evaluated through continuous charge-discharge cycles within a voltage window of 3.0-4.2 V.

[0229] As shown in FIG. 11, the discharge capacity remained around 130 mAh / g for up to 80 cycles at 500 kPa.

[0230] Impact of thickness The same experiment (experiment 5) as described above was repeated by pressing a lithium metal electrode with a thickness of 100 pm was pressed onto the opposite side of the solid electrolyte separator by applying an external pressure of 900 kPa to form another unit cell. The resulting cell is herein identified as experiment 6.

[0231] The electrochemical characterization of the obtained energy storage device was conducted in a Cell Test System at a controlled temperature of 25.0 ± 0.59C. Testing was performed at different C-rates, including C / 20 for the formation cycle and C / 10 for normal cycling tests, with a pressure of 900 kPa applied in addition to vacuum sealing.

[0232] Additionally, the cycle life of the pouch cells was evaluated through continuous charge-discharge cycles within a voltage window of 3.0-4.2 V.

[0233] As shown in FIG. 12, the discharge capacity remained around 130 mAh / g for up to 100 cycles at 900 kPa and gradually decreased to 100 mAh / g from 100-200 cycles at 900 kPa.

[0234] Example 3 - Solid electrolyte separator having a different molar ratio of components

[0235] Example 3 illustrates the impact of producing a solid electrolyte separator using a different molar ratio of compounds by using the synthesis protocol described in Example 2. Each sample was left immersed in the liquid mixture for 2 to 5 minutes. The subsequent curing step lasted approximately 24 hours. Finally, the drying step took about 3 days at 60 °C under a vacuum 1 mbar.

[0236] The procedure of Example 2 was repeated, resulting in solid electrolyte separator 1.

[0237] The procedure of Example 2 was repeated, but the molar ratio of TEOS: E M I FSI : LiTFSI was 1.0:0.50:0.17, resulting in solid electrolyte separator 2.

[0238] The procedure of Example 2 was repeated, but the molar ratio of TEOS: EM IFSI: LiTFSI was 1.0:1.0:0.33, resulting in solid electrolyte separator 3.

[0239] The procedure of Example 2 was repeated, but the molar ratio of TEOS: EM I FSI: LiTFSI was 1.0:1.5:0.50, resulting in solid electrolyte separator 4.

[0240] The procedure of Example 2 was repeated, but the molar ratio of TEOS: EM I FSI :LiTFSI was 1.0:3.5:1.16, resulting in solid electrolyte separator 5.

[0241] Example 4 - Electrochemical energy storage device comprising multiple cells

[0242] An electrochemical energy storage device comprising four unit cells was assembled under dry room conditions with a dew point below -45 °C. The electrochemical energy storage device is characterized by four composite cathodes, four lithium metal anodes, and four solid electrolyte separators according to the invention, configured to separate a cathode from an anode. The synthesis procedure started with preparing four solid electrolyte separators by following the procedure of Example 2. Four separate stacks were prepared by placing a composite cathode comprising an active material loading of 2mAh / cm2into contact with a single layer cathode footprint measuring 13.5 cm2onto a formed solid electrolyte separator, and subsequently placing a lithium metal anode onto the opposite side of said solid electrolyte separator.

[0243] To assemble the four separate stacks into a four-layer multi-stack configuration, an ultrasonic welder was used to attach tabs made of conductive materials to each of the individual stacks. A Ni / Cu tab was welded to the copper current collector, while an Al tab was welded to the aluminum current collector using an ultrasonic welding device.

[0244] The resulting four-layer multi-stack was positioned on a pouch foil measuring 8 x 5 cm2, which was sealed using a vacuum sealing device. This configuration resulted in a nominal cell capacity of 27 x 4 layers = 108 mAh for the entire multi-stack.

[0245] The electrochemical characterization of these pouch cells was conducted in a Cell Test System at a controlled temperature of 25.0 ± 0.59C. Testing was performed at different C-rates, including C / 20 for the formation cycle and C / 10 for normal cycling tests at varying applied pressures. Initially, a pressure of 500 kPa in addition to vacuum sealing is applied during cycles 1 to 17, and from cycle 18 onwards, the pressure is increased to 900 kPa in addition to vacuum sealing until the end of cell cycling.

[0246] Additionally, the cycle life of the pouch cells was evaluated through continuous charge-discharge cycles within a voltage window of 3.0-4.2 V.

[0247] As shown in FIG. 13, the discharge capacity remained around 120 mAh / g from cycle 1-17 at 500 kPa and from cycle 18-30 at 900 kPa.

[0248] Example 5 - Thermomechanical behavior of a solid electrolyte separator

[0249] First, a solid electrolyte separator was prepared by following the procedure of Example 2 described above. Then, said separator was cut into a thin membrane of about 35 pm thickness and 19.0 mm diameter. The sample was subjected to a heat treatment at 120 °C for 1 h under air.

[0250] The same heat treatment at 120 °C for 1 h under air was repeated on a pristine trilayer porous substrate consisting of a polypropylene-polyethylene-polypropylene structure with a thickness of 25 pm, a porosity of 55%, and a pore size of 0.027 pm.

[0251] The results for the solid electrolyte separator are shown FIG. 14 and the pristine reference porous substrate in FIG. 15. It is clearly observed that the solid electrolyte separator (FIG. 14) displayed reduced shrinkage with a diameter of 18.0 mm versus 14.0 mm for the pristine sample (FIG. 15). Example 6 - Characterization of a solid electrolyte separator

[0252] In the present example, a solid electrolyte separator was prepared by following the procedure of Example 2 described above. Further, during the impregnation step an excess amount of liquid mixture is used that is sufficient to overfill the pores of the porous substrate with the solid electrolyte material, thereby forming an overfill layer on the selected sides of the substrate. The overfill layer is cured using the same drying steps as described above to form a solid electrolyte film on the sides of the porous substrate.

[0253] In the first experiment, the amount of material for overfilling the pores is kept the same for both sides of the substrate, resulting in the formation of a solid electrolyte separator with two oppositely arranged solid electrolyte layers of similar thickness. As demonstrated in FIG. 16, the SEM image shows that the top solid electrolyte layer has a thickness of 25.26 pm, the porous membrane has a thickness of 25.85 pm, and the bottom solid electrolyte layer has a thickness of 34.13 pm as determined by a standard measurement tool from SEM software. This results in a solid electrolyte separator with a symmetric structure.

[0254] In a different experiment, the amount for overfilling the pores is adjusted to ensure that a layer is formed on one side of the solid electrolyte separator only. As demonstrated in FIG. 17, the SEM image shows that the top solid electrolyte layer has a thickness of 14.55 pm, and the porous membrane has a thickness of 26.85 pm as determined by a standard measurement tool from SEM software. This results in a solid electrolyte separator with an asymmetric structure.

[0255] Compared to a solid electrolyte separator without overfill layers, the one and / or two overfill layers of solid electrolyte material are configured to provide a better interface and contact between an electrode and the separator, which advantageously results in good or even improved electrochemical performance. Moreover, said overfill layer(s) enables to accommodate variations in solid electrolyte separator roughness and / or when using electrodes with an irregular surface.

Claims

CLAIMSA method for producing a solid electrolyte separator, comprising the steps of: providing a porous non-metallic, preferably polymer or fibrous, substrate having a plurality of pores, wherein an initial porosity of the porous non-metallic substrate is between 10.0% and 90.0%; preparing a liquid mixture comprising a silica precursor or an alumina precursor, an ionically conductive compound, a metal salt, and a solvent; contacting the porous non-metallic substrate with the liquid mixture, thereby impregnating the pores of the porous non-metallic substrate with the liquid mixture; curing the liquid mixture to form a solid electrolyte network within the pores of the porous non-metallic substrate, thereby obtaining a solid electrolyte separator with a post-curing porosity lower than the initial porosity of the porous non-metallic substrate; and, optionally, drying and / or aging the solid electrolyte separator.

2. The method according to claim 1, wherein the silica precursor is selected from the group consisting of tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), tetraisopropyl orthosilicate (TIOS), tetrapropyl orthosilicate (TPOS), tetrabutyl orthosilicate (TBOS), triethylvinylorthosilcate (VTEOS), and mixtures thereof; or wherein the alumina precursor is selected from the group consisting of aluminum triethoxide(AI(OEt)3).

3. The method according to any one of claims 1 or 2, wherein the metal salt is selected from the group consisting of Li+, Na+, Mg2+, Ca2+, Al3+, and mixtures thereof; and / or 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-methylimidazoliumtrifluoromethanesulfonate (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 (Pyrl5TFSI), 1-Methyl-l-pentylpyrrolidinium fluorosulfonyl(trifluoromethanesulfonyl)imide (Pyrl5FTFSI), 1-Methyl-l-pentylpyrrolidinium trifluoromethanesulfonate (Pyrl5OTf), 1-Methyl-l-pentylpyrrolidinium bis(pentafluoroethylsulfonyl)imide (Pyrl5Beti), triethylsulfonium bis(trifluoromethanesulfonyl)imide (TESTFSI), tetrabutylammonium bis(trifluoromethane)sulfonylimide (TBATFSI), and mixtures thereof.

4. The method according to one of claims 1 to 3, further comprising the steps of contacting the porous non-metallic substrate with an excess amount of liquid mixture, surpassing a capacity of the pores of the porous non-metallic substrate, thereby forming at least one liquid mixture layer positioned on at least one side of the porous non-metallic substrate; and curing the at least one liquid mixture layer to obtain at least solid electrolyte layer; preferably wherein the solid electrolyte layer after curing, and optionally drying and / or aging, has an average thickness of between 0.01 pm and 50.0 pm.

5. The method according to one of claims 1 to 4, wherein the porous substrate is a porous polymer substrate comprising a polymer selected from the group consisting of polyethylene, polypropylene, polystyrene, Nylon 6, Nylon 6,6, polyether sulfone, polyether ether ketone, cellulose acetate, cellulose triacetate, cellulose, polyimide, polyvinylidene fluoride, and mixtures thereof; more preferably wherein the porous polymer substrate comprises a plurality of polymer layers, preferably at least three polymer layers.

6. A solid electrolyte separator for an electrochemical energy storage device, comprising:- a porous non-metallic, preferably polymer or fibrous, substrate having a plurality of pores embedded with a solid electrolyte network; wherein an initial porosity of the porous non- metallic substrate is between at least 10.0 % and at most 90.0%;- wherein the solid electrolyte network comprises a silica or alumina matrix and an electrolyte, confined within the silica or alumina matrix;- wherein said electrolyte comprises an ionically conductive compound and a metal salt; and,- wherein the solid electrolyte network fills at least a portion of the inner space of the pores of the porous non-metallic substrate such that a post-curing porosity of the solid electrolyte separator is lower than the initial porosity of the porous non-metallic substrate.

7. The solid electrolyte separator according to claim 6, wherein the porosity of the solid electrolyte separator is between 0.1% and 9.0%, preferably between 0.1% and 7.5%, more preferably between 0.1% and 5.0%, more preferably still between 0.1% and 2.5%, more preferably still between 0.1% and 1.0%.

8. The solid electrolyte separator according to any one of claims 6 or 7, wherein the solid electrolyte separator has a thickness between 1.0 pm and 250.0 pm, preferably between 1.0 pm and 100.0 pm, more preferably still between 1.0 pm and 50.0 pm.

9. The solid electrolyte separator according to any one of claims 6 to 8, wherein the porous substrate is a porous polymer substrate comprising a polymer selected from the group consisting of polyethylene, polypropylene, polystyrene, Nylon 6, Nylon 6,6, polyether sulfone, polyether ether ketone, cellulose acetate, cellulose triacetate, cellulose, polyimide, polyvinylidene fluoride, and mixtures thereof; more preferably wherein the porous polymer substrate comprises a plurality of polymer layers, preferably at least three polymer layers.

10. The solid electrolyte separator according to any one of claims 6 to 9, further comprising a layer of the solid electrolyte network positioned on at least one side of the porous non-metallic substrate, preferably at least two layers of the solid electrolyte network positioned on at least two opposite sides of the porous non-metallic substrate, wherein the layer is configured for ionically connecting to an active electrode material.

11. The solid electrolyte separator according to claim 10, wherein the solid electrolyte network layer has an average thickness of between 0.01 pm and 50.0 pm.

12. The solid electrolyte separator according to any one of claims 6 to 11, wherein the solid electrolyte separator, optionally comprising one or more solid electrolyte network layers, has a water content of less than 3000 ppm, preferably less than 2000 ppm, more preferably less than 1000 ppm.

13. An electrode assembly comprising an electrode material and one or more solid electrolyte separators according to any one of claims 6 to 12, preferably obtainable or obtained according to the method of any one of the claims 1 to 5; wherein the electrolyte separator is configured for ionically connecting to the active electrode material.

14. The electrode assembly according to claim 13, wherein the active electrode material comprises a porous electrode material and a plurality of active material particles.

15. A method for producing an electrode assembly according to claim 14, comprising the steps of: providing a porous non-metallic, preferably polymer or fibrous, substrate having a plurality of pores, wherein an initial porosity of the porous non-metallic substrate is between 10.0% and 90.0%; providing an active electrode material, preferably wherein the active electrode material comprises a porous material and a plurality of active material particles; positioning the porous non-metallic substrate on the active electrode material; applying a pressure onto the porous non-metallic substrate, thereby pressing the porous non-metallic substrate against the active electrode material; producing a solid electrolyte separator according to the method of any one of claims 1 to 5, thereby obtaining the electrode assembly; and, optionally, wherein the method further comprises repeating the preceding steps for one or more further solid electrolyte separators, thereby obtaining an electrode assembly comprising a stack of solid electrolyte separators.

16. A method for producing an electrode assembly according to claim 14, comprising the steps of: producing a solid electrolyte separator according to the method of any one of claims 1 to 5; providing an active electrode material, preferably wherein the active electrode material comprises a porous material and a plurality of active material particles; positioning the solid electrolyte separator on the active electrode material; applying a pressure onto the solid electrolyte separator, thereby pressing the porous non- metallic substrate against the active electrode material, thereby obtaining the electrode assembly; and, optionally, wherein the method further comprises repeating the preceding steps for one or more further solid electrolyte separators, thereby obtaining an electrode assembly comprising a stack of solid electrolyte separators.

17. The methods according to any one of claims 15 or 16, wherein the porous substrate is porous polymer substrate comprising a polymer selected from the group consisting of polyethylene, polypropylene, polystyrene, Nylon 6, Nylon 6,6, polyether sulfone, polyether ether ketone, cellulose acetate, cellulose triacetate, cellulose, polyimide, polyvinylidene fluoride, and mixturesthereof; more preferably wherein the porous polymer substrate comprises a plurality of polymer layers, preferably at least three polymer layers.

18. The methods according to any one of claims 15 to 17, wherein the applied pressure is between 0.1 MPa and 10.0 MPa, preferably between 0.1 MPa and 7.5 MPa, more preferably between 0.1 MPa and 5.0 MPa, more preferably still between 0.1 MPa and 2.5 MPa, more preferably still between 0.1 MPa and 1.0 MPa.

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