[0001] The present invention is related to semi-permeable membranes, which comprise an integral support to which the same permeable membranes are bonded. In particular, the semi-permeable membrane is obtained by phase separation of a polymer compound from its solution.

[0002] In membranes of the above kind, the support is either embedded in the semi-permeable membrane layer (in particular in case of woven and nonwoven supports), or the membrane layer is cast on top of the support. In both cases, the semi-permeable membrane layer spreads over a surface of the support and the resulting thickness of the composite sheet is the sum of the support thickness and the membrane layer thickness on top of the support.

[0003] In a number of applications, such as electrochemical cells, reduction of total thickness of the composite sheet is an important design consideration. However, there are limitations in the reduction of the support thickness due to handling capability and mechanical strength. In other cases, in which the support is at least partially embedded in the membrane layer, the thickness of the membrane layer must be sufficient, on the one hand to impregnate the support, e.g. to ensure effective mechanical anchoring, and on the other to completely cover the support surface, e.g. preventing protrusion of errant fibres.

[0004] Aspects of the present invention aim at overcoming the above drawbacks. It is an object of aspects of the present invention to provide composite (supported) semi-permeable membrane sheets which allow for further reducing total sheet thickness and/or the thickness of the active membrane layer and possibly reducing material usage.

[0005] It is known from WO 93/23153, EP 0521304 and US 5143616 to produce supported semi-permeable membrane sheets by casting a polymeric membrane forming solution on top of a support which comprises a polymer that is dissolved by the solvent used in the membrane forming solution. The solvent softens or dissolves a superficial layer of the support, causing molecular interaction between the membrane polymer and the support polymer to occur. The support with membrane forming solution cast on it is then immersed in a formation bath containing a nonsolvent of the polymer which will cause precipitation/phase separation of the polymer from its solution, thereby forming the semi-permeable membrane. Also the softened/dissolved superficial layer of the support will be subjected to precipitation/phase separation, causing bonding of the semi-permeable membrane layer to the support by chemical and/or physical interlinking. This way of bonding a semi-permeable membrane layer to a support is used in the present invention for making novel composite membrane sheets as indicated below.

[0006] According to a first aspect of the invention, there is therefore provided a

(composite) membrane sheet as set out in the appended claims. The membrane sheet comprises a support layer having opposed surfaces and comprising through holes extending from one of the opposed surfaces to the other one. The membrane sheet further comprises a plurality of membrane patches made of a semi-permeable membrane material. Each of the plurality of membrane patches extends in or over a respective one of the through holes, and each closes the respective through hole. In other words, each membrane patch forms a complete covering of the respective through hole. The support layer and the membrane patches jointly form a composite layer, comprising support layer material extending between opposed surfaces at first locations, and semi permeable membrane material at second locations, possibly though not necessarily extending between the opposed surfaces as well. No semi permeable material is present at the first locations, and no support layer material is present at the second locations. Advantageously, each of the second locations is completely enclosed by the first locations, the second locations hence forming islands of semi permeable membrane material totally enclosed by support layer material, which is advantageously dense.

[0007] The semi-permeable membrane material comprises a first polymer compound and the support layer comprises a second polymer compound. Each of the plurality of membrane patches is obtained by applying a membrane forming solution comprising the first polymer compound onto or into the respective through hole to close the through hole. The second polymer compound is at least partially softened and/or dissolved at an interface with the membrane forming solution, possibly by a solvent comprised in the membrane forming solution. By so doing, molecules of the first polymer compound are made to interact with molecules of the second polymer compound. Thereafter, the semi-permeable membrane material is formed, which comprises phase separation of the first polymer compound from the solution and which consolidates the molecular interaction between the first and the second polymer compounds. As a result, each of the plurality of membrane patches is bonded to the support layer at the interface. Such a type of bonding is referred to as solvent bonding and advantageously does not require any extraneous material or additional process step.

[0008] It has been observed that the solvent assisted bonding at the interface between membrane patch and support layer as described above enables forming a composite layer as described above, wherein the support material and the semi permeable membrane material are integral. There is a strong bond between the semi-permeable membrane material and the support layer at the interface between the two, without requiring additional reinforcement or bonding for the patch. Furthermore, a seal between the membrane patches and the support layer is naturally obtained at the interface. This interface is advantageously porous. As a result, by freeing the support layerfrom unnecessary semi-permeable membrane material, it is obtained that there is no direct interrelationship any more between the total thickness of the composite sheet and the thickness of each of its constituents, viz. the support layer and the membrane patches. By so doing, on the one hand, the useful (active) membrane thickness can be reduced as desired, reducing the resistance across the membrane, such as electrolytic resistance, leading to improved performance of electrochemical cells. Moreover, less amount of membrane material is used, making membrane sheets according to the invention more economical. On the other hand, the thickness of the support layer can be tailored as desired (e.g. thicker for improving handling and mechanical strength, or thinner for reducing total thickness). Moreover, the free/uncovered spots on the support layer allow for providing additional functionalities on the membrane sheet. By way of example, these free spots may be used as attachment spots for bonding the membrane/composite sheet to any other structure, without interfering with the membrane material/membrane layer.

[0009] According to a second aspect of the invention, there is provided an electrochemical cell as set out in the appended claims. The electrochemical cell comprises one or more membrane sheets according to the first aspect of the invention.

[0010] According to a third aspect of the invention, there is provided a method of manufacturing a membrane sheet according to the first aspect of the invention. In a first step, the method provides preparing a membrane forming solution comprising a first polymer compound and a solvent of the first polymer compound. A support layer comprising through holes is provided, which support layer comprises or consists of a second polymer compound. In a second step, the membrane forming solution is applied onto or into the through holes. The support layer is free from covering by the membrane forming solution at locations between the through holes, in particular between adjacent through holes. The support layer can be kept free from covering by the membrane forming solution when the solution is applied, or alternatively, membrane forming solution may be removed from the support layer to free or expose the support layer at locations intermediate the through holes. In a third step, semipermeable membrane material is formed by subjecting the membrane forming solution to a phase separation or phase precipitation of the first polymer compound. By so doing, a plurality of membrane patches extending in or over the through holes are obtained. According to the method, the second polymer compound is brought in a swollen or at least partially solvated state at an edge of the through holes. This way, molecular interactions between the first polymer compound and the second polymer compound are made to occur at the edge, which solvent bond each of the plurality of membrane patches to the support layer when the semipermeable membrane material is formed. [0011] Aspects of the invention will now be described in more detail with reference to the appended drawings, wherein same reference numerals illustrate same features and wherein:

[0012] Figure 1 represents a plan view of a membrane sheet according to aspects of the invention;

[0013] Figure 2 represents a cross sectional view of the membrane sheet of figure 1 along section line A-A;

[0014] Figure 3 represents a detail of a cross sectional view of a membrane sheet according to another aspect of the invention, having the same support layer as in figure 1 but with thinner membrane patches;

[0015] Figure 4 represents a plan view of a membrane sheet according to yet another aspect of the invention, wherein membrane patches are arranged in arrays and the membrane patches within each array are linked to one another through membrane material;

[0016] Figure 5 represents a cross sectional view of the membrane sheet of figure 4 along section line B-B;

[0017] Figure 6 represents a cross sectional view of part of a membrane sheet according to yet another aspect of the invention, wherein there is no substantial penetration of a membrane patch into the through hole of the support layer;

[0018] Figure 7 represents a scanning electron microscope (SEM) image of a bare support layer cross section traversing a through hole, prior to making the membrane patches;

[0019] Figures 8 A-B represent SEM images of a cross section of a composite sheet as in figure 1 , with a same support layer as in figure 7. Figure 8B is a magnification of figure 8A at the interface between support layer and membrane patch.

[0020] Referring to Figs. 1 and 2, shown is a membrane sheet 10 comprising a support layer 1 1 and a plurality of membrane patches 12 extending in and/or upon through holes (perforations) 1 1 1 of the support layer 1 1 . The support layer 1 1 is advantageously formed of a dense sheet or film. The support layer comprises a first surface 1 12 (top face) and an opposed second surface 1 13 (bottom face), which are spaced apart by the thickness Ts of the support layer 1 1. The support layer further comprises an arrangement of through holes 1 1 1 which traverse the thickness Ts, from the first surface 1 12 to the second surface 1 13. These through holes 1 1 1 are advantageously isolated from one another by material constituting the support layer 1 1 . Alternatively, the through holes 1 1 1 may be interconnected within the support layer 1 1 (but not at one or both the opposed surfaces 1 12, 1 13). The material of the support layer 1 1 may have any one of the following properties: dense, nonporous and liquid (or gas) impermeable. The term dense may refer to a material being free from pores which are interconnected from one surface to the opposite surface, advantageously a material being free from porosity at all. The term impermeable may refer to zero (water) permeability at 1 bar differential pressure. The support layer 1 1 may for example comprise or consist of a polymeric film which is perforated to provide for the through holes. The film can suitably be made by extrusion, rolling or other processes as known in the art. Injection moulding may be used for small area films. The support layer is advantageously flexible, but can alternatively be rigid.

[0021] The membrane patches 12 are made of an advantageously polymeric semi-permeable membrane material. The semi-permeable membrane material as referred to in the present description refers to a solid, continuous and possibly porous material having a structure allowing one or more compounds to be selectively transported through the membrane material (while retaining others). The term compound should be broadly interpreted and can refer to monovalent ions (e.g. protons). The semi-permeable membrane material as used in the present description can hence be configured as a material for separator membranes, such as battery separator membranes, e.g. allowing transport of monovalent ions (e.g. protons) through it while retaining other (multivalent) ions. The semi-permeable membrane material as used in the present description may be a filtration medium, enabling to separate the one or more compounds from a feed, which can be liquid or gaseous, and to transport them through the membrane material, e.g. to a place where they can be collected.

[0022] The semi-permeable membrane material can feature a determined permeability for the one or more compounds which are selectively transported through it. The permselectivity can be determined by all kinds of separation mechanisms, such as but not limited to a characteristic pore size of the membrane material (e.g. microporous or nanoporous filtration membranes), or by a characteristic attraction of specific charge types (e.g. an ion exchange membrane).

[0023] Each of the membrane patches 12 extends in or over a corresponding through hole 1 1 1 and closes the corresponding through hole. The membrane patches are advantageously spaced apart from one another, meaning that the semi-permeable membrane material is not continuous from one membrane patch to an adjacent one, with support layer material separating the membrane patches. In between adjacent membrane patches 12, the support layer is exposed and hence not covered by semi-permeable membrane material at both surfaces 1 12 and 1 13.

[0024] Referring to figures 1 and 2, each membrane patch 12 advantageously extends on an area substantially coinciding with the area of the corresponding through hole 1 1 1 . In the present example, the membrane patch 12 is bonded to the support layer 1 1 at the edge 1 14 of the through hole. As will be described later, it is an aspect of the invention that an interfacial zone 122 extends between the edge 1 14 of the support layer and the membrane patch 12. This interfacial zone 122 forms an edge of the patch 12 and seals the patch 12 to the support layer 1 1 .

[0025] As can be seen in figure 2, the membrane patches 12 may have a thickness TM which is equal to the thickness Ts of the support layer 1 1. This is however not a requirement and the thickness of a membrane patch 12 may be larger, or smaller than the thickness of the support layer 1 1. Referring to figure 3, the case is shown wherein the membrane patch 22 has a thickness TM smaller than the support layer 1 1 . The thickness TM of the membrane patch 22, defined as the smallest thickness of a membrane patch, can be at least 10% smaller than the thickness Ts of the support layer 1 1 (i.e., TM ≤ 0.9Ts), advantageously at least 20% smaller, advantageously at least 30% smaller, advantageously at least 50% smaller, advantageously at least 70% smaller. The patch thickness TM can be as small as 5% or 10% of the support layer thickness Ts.

[0026] It will be clear from the cross sections of figures 2 and 3 that composite sheets 10 according to aspects of the invention feature a support material and a semi permeable membrane material within a same (composite) layer. That is, the composite sheet comprises a layer which comprises an advantageously dense support material at first locations within the layer, and patches of semi permeable membrane material at second locations within the layer. The second locations are isolated from one another by interposition of the first locations, which fully enclose or surround each of the second locations. Since, as will be described further below, there is a seal between the patches and the support material, it is obtained that no stacking of additional layers of semi-permeable membrane or reinforcement is required. Furthermore, the second locations of the membrane patches are also free from support layer material.

[0027] Referring to figures 4 and 5, a membrane sheet 30 is shown wherein membrane patch 32 is interconnected with membrane patches 32', 32" to form a group 42 of interconnected membrane patches, in which the semi-permeable membrane material is continuous between the patches within the group 42. Similarly, membrane patches 33, 33', 33", 33"' form another group 43 of interconnected membrane patches, and patches 34, 34', 34" are interconnected to form yet another group 44. The different groups 42, 43, 44 are isolated and spaced apart from one another, with semi-permeable membrane material not being continuous between different groups. The patches within each group 42-44 are interconnected with one another through a band 333 of semi-permeable membrane material arranged on the top surface 1 12 of the support layer 1 1 in correspondence of the patches of the respective group. The band 333 forms a continuous bridge linking the bulk semipermeable membrane material 332 of adjacent patches 32, 32', 32" within a group. However, the bands of the different groups 42-44 are spaced apart from one another. The support layer 1 1 is exposed at both top and bottom surfaces 1 12, 1 13, i.e. not covered with semi-permeable membrane material, in between bands 333 of adjacent groups. Possibly, the different groups 42, 43, 44 are formed of different semi-permeable membrane materials. It will be convenient to note that in the case of figures 4 and 5, the bands 333 extend over the top surface 1 12 of the support layer, so that there is partial overlap between the material of support layer 1 1 and the semi-permeable membrane material of the groups 42-44 of membrane patches.

[0028] In the previous examples, it has been described that the membrane patches 12, 22, 32 extend within a through hole 1 1 1 . It will be convenient to note that this is no requirement for aspects of the present invention. Referring to figure 6, a membrane patch 52 may extend over or upon a through hole 1 1 1 to close the through hole, and there may or may not be substantial penetration of semi-permeable membrane material of patch 52 into through hole 1 1 1. In such case, there may be an edge 521 of membrane patch 52 which encloses or circumscribes an edge 1 14 of through hole 1 1 1.

[0029] It is an important aspect of the present invention that there is a seal between the membrane patches 12, 22, 32, 52 and the support layer 1 1. Since each membrane patch extends so as to close its corresponding through hole and is sealed to the support layer around the through hole, there is no way for compounds to pass through the membrane sheet 10, 30 other than through the semi-permeable material of the membrane patches, in particular when the support layer 1 1 is dense or impermeable between the through holes 1 1 1 . The patched membrane sheets 10, 30 according to aspects of the invention can therefore be used as replacement of traditional membrane sheets.

[0030] Advantageously, this seal is formed by an interfacial layer 122 between the support layer 1 1 and the membrane patch where molecules of the support layer material and molecules of the semi-permeable membrane material of the patch are interlinked or interact to form chemical and/or physical bonds. The interfacial layer hence not only provides a seal between the membrane patch and the support layer, but also forms a point of attachment of the membrane patch to the support layer. It will be appreciated that the membrane patch is advantageously unsupported within the through holes 1 1 1 , and is bonded to the support layer 1 1 along the interfacial layer 122 only. The interfacial layer is typically enclosed between the edge 1 14 (or inner wall) of a through hole 1 1 1 and the edge 121 of the membrane patch 12. The interfacial layer will typically be porous.

[0031] Advantageously, the seal is such that it does not alter the permselectivity of the membrane patches, e.g. because a skin of the membrane patch extends up to the support layer 1 1 at the edge 121 , 521 of the membrane patch, or because the interfacial layer may have a pore size characteristic identical or similar to the pore size characteristic of the semi-permeable membrane material. The skin of a membrane patch refers to an outer surface of the membrane patch and typically comprises pores of (pre-)determined size which determine the permselectivity of the entire semi-permeable membrane material. The pores of the skin may be smaller than pores in the bulk semi-permeable membrane material. It will be convenient to note that the semi-permeable membrane material of membrane patches according to aspects of the invention may be skinned or skinless.

[0032] The interfacial layer which seals and bonds the membrane patch is advantageously obtained according to aspects of the invention by direct application of the membrane patch as a polymeric solution on the support layer and obtaining solvent bonding to the support layer upon precipitation of the polymer from the solution as described below.

[0033] The membrane patches 12, as referred to in the present description, are

(small area) membranes obtained by subjecting a membrane forming solution, comprising a polymer dissolved in the solution, to a phase separation process. Phase separation, which is also referred to as phase inversion, is a well-known process wherein demixing between the polymer and the solvent is induced. As a result of demixing, the polymer precipitates, thereby forming a membrane lattice with a desired structure (pore size, pore structure, etc.). Further process steps can be carried out in order to remove the solvent completely (e.g., washing in a possibly hot water bath) and to obtain a final pore structure (e.g., removing pore formers by washing in a bleach solution). The final material obtained after the phase separation process is the semi-permeable membrane material as referred to above. Demixing can be induced based on several techniques. One possibility is thermally induced phase separation (TIPS), wherein demixing is induced by a temperature change at the interface of the polymer solution. Another possibility is to induce a chemical reaction in the polymer solution, causing demixing. This is referred to as reaction induced phase separation (RIPS). However, in the vast majority of cases, demixing is induced by phase diffusion. The polymer solution is contacted with another phase, being a liquid (liquid induced phase separation or LIPS), or a gas (vapour, referred to as vapour induced phase separation or VIPS), which is a non-solvent of the polymer but which is miscible with the solvent. The liquid or vapour will diffuse through the membrane forming solution and cause a local change in the membrane forming solution composition, inducing demixing. As a result, the polymer precipitates from the solution. LIPS is also referred to as immersion precipitation. It will be convenient to note that any phase separation process can be applied to prepare the membrane patches as described herein.

[0034] To this end, the semi-permeable membrane material of patch 12-52 comprises or consists of an advantageously thermoplastic polymer compound, which will be referred to hereinafter as the first polymer compound. The first polymer compound is advantageously the principal or primary polymeric compound used for preparing the membrane forming solution, e.g. the polymer compound present in largest amount in the membrane forming solution.

[0035] In order to obtain a sealing and bonding interfacial layer between the membrane patch and the support layer, the support layer 1 1 advantageously comprises or consists of a thermoplastic polymer compound, which will be referred to hereinafter as the second polymer compound. The second polymer compound is such, that it has some degree of affinity (e.g. compatibility) with the first polymer compound to allow for molecular interaction, such as molecular interpenetration, molecular entanglement, molecular interdiffusion, or molecular adhesion between polymer chains of the membrane material (i.e. of the first polymer compound) and polymer chains of the support layer (i.e. of the second polymer compound). Such molecular interactions can be physical interactions between molecules, chemical interactions, or a combination of both.

[0036] The strong molecular interactions between the first polymer compound and the second polymer compound are made possible by the use of one or more solvents to at least partially soften and/or dissolve the material of the support layer, in particular the second polymer compound, at least at a superficial layer in contact with the membrane forming solution. The one or more solvents advantageously refer to one or more solvents used in the membrane forming solution, such that the support layer is at least superficially softened and/or dissolved upon applying the membrane forming solution on it. Therefore, the material of the support layer is advantageously one which can be softened and/or dissolved by a solvent used in the membrane forming solution. Advantageously the first polymer compound and the second polymer compound can be dissolved by a same solvent which is used in the membrane forming solution. Possibly, different solvents can be used for distinctively dissolving the first and the second polymer compounds, or even a mixture of solvents. In such case, it will be advantageous that the different solvents be miscible in a proportion of at least 90/10 or higher (e.g. 70/30, 50/50, 30/70 or 90/10) by weight, wherein the first numbers of the fractions (e.g. '90' in '90/30') refer to the solvent of the first polymer compound. The solvents are advantageously miscible in all proportions. As a result, the first polymer compound is dissolved and the second polymer compound is softened (swells) or (at least partially) dissolved at an interface in contact with the first polymer compound, hence allowing for molecular mobility, which causes interactions between molecules of the polymers leading to bonding of the membrane patch to the support layer.

[0037] In order to obtain sufficiently strong interactions yielding suitable bonding between membrane patch and support, the first polymer compound and the second polymer compound are advantageously compatible. In general, compatibility refers to the first and the second polymers being able to forming a miscible, homogeneous blend being usually caused by sufficiently strong interactions between the polymers. In general, miscibility refers to the ability of the first and the second polymer to forming a blend that is a single phase structure. Advantageously, the first and second polymer compounds are miscible in all proportions. The concepts of compatible and miscible polymers are defined by "W.J. Work, K. Horie, M. Hess and F. T. Stepto in International Union of Pure and Applied Chemistry - Definitions of terms related to Polymer Blends, Composites and Multiphase Polymeric Materials - Pure & Applied Chemistry, Vol. 76, No. 11, page 1987 (miscible) and page 1993 (compatible) ".

[0038] It will be convenient to note that the first and second polymer compounds can be identical compounds (e.g. identical chemical species or homopolymers).

[0039] The first polymer compound can be polysulfone (PSU), polyethersulfone

(PESU), a grafted variant of them, or a copolymer of either one of the polymers. The first polymer compound can be polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), a grafted variant of them, or a copolymer of either one of the polymers. The first polymer compound can be polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), a grafted variant of them, or a copolymer of either one of the polymers. The first polymer compound can be a polymer of the polyaryletherketone (PAEK) family, such as polyether ether ketone (PEEK), a grafted variant of any of these polymers, such as sulfonated polyether ether ketone (PEEK-WC), or a copolymer of any one of these polymers. The first polymer compound can be polychlorotrifluoroethene (PCTFE), polyether imide (PEI), polyimide (PI), polyamide imide (PAI), polyacrylonitrile (PAN), polyurethane (PUR), in particular a thermoplastic polyurethane (PUR), a grafted variant of any of these polymers, or a copolymer of any one of these polymers. The first polymer compound can be polyphenylene sulphide (PPS), cellulose acetate (CA), cellulose triacetate (CTA), a grafted variant of any of these polymers, or a copolymer of any of these polymers. The copolymers as indicated above can be suitable copolymers of the indicated polymer with any one of polyvinyl chloride (PVC), polymethyl methacrylate (PMMA), polycarbonate (PC), cyanoacrylate, cellulose triacetate (CTA), polyphenylene sulphide (PPS), polystyrene (PS), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), and polyamides (PA) such as polycaprolactam (nylon 6) and nylon-6,6. The first polymer compound can be a suitable blend of two or more of the above listed polymers.

[0040] The semi-permeable membrane material as referred to in the present invention advantageously is a high polymer content membrane material, which refers to a membrane material obtained through phase separation using a membrane forming solution with a ratio of polymer content to solvent content of at least 0.15 by weight, advantageously at least 0.20 by weight, advantageously at least 0.25 by weight and advantageously not exceeding 0.50 by weight. The above values are to be determined just prior to the moment of inducing phase separation. [0041] The amount of first polymer compound in the (dry) (final) semi-permeable membrane material is advantageously at least 5% by weight, advantageously at least 10% by weight, advantageously at least 25% by weight, advantageously at least 35% by weight, advantageously at least 50% by weight.

[0042] The first polymer compound can be an organic binder forming a matrix or lattice of the semi-permeable membrane material, in which a possibly hydrophilic filler material is optionally dispersed. The filler material may be organic and is advantageously one or a combination of: hydroxypropylcellulose (HPC), carboxymethylcellulose (CMC), polyvinyl pyrrolidone (PVP), cross-linked polyvinyl pyrrolidone (PVPP), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polyethylene oxide (PEO), polyethylene glycol (PEG), and glycerol. Such filler materials can be provided as pore formers and can be removed in a post treatment step, such as by washing in a bleach solution (e.g. for PVP). Other filler materials, which remain in the final semi-permeable membrane material are listed below. The filler material can be an amine, such as but not limited to one or a combination of: monoethanolamine (MEA), diethanolamine (DEA), polyethylenimine, aminopropyl-trimethoxysilane and polyethylenimine-trimethoxysilane. The filler material can be an amide or amine containing polymer, such as but not limited to one or a combination of: polyamide (PA), polyurethane (PUR), polyvinylamine (PVArm) and melamine. The filler material may be inorganic, such as one or a combination of T1O2, HfC>2, AI2O3, ZrC>2, Zr3(P0 ₄ ) ₄ , Y2O3, S1O2, carbon, possibly on Pt, Ru or Rh support, BaS0 ₄ , BaTiC , perovskite oxide powder materials, zeolites, metal- organic frameworks (MOF) and silicon carbides. Functionalized variants of the filler materials (such as aminated, quaternary ammonium groups, sulfonated, acrylated) can be used. Combinations of the above organic and inorganic materials can be used as well as filler material. The membrane forming solution can comprise suitable fillers as described above and other ingredients as known in the art, such as thickeners (viscosity increasing agents).

[0043] The second polymer compound can be polysulfone (PSU), polyethersulfone (PESU), a grafted variant of them, or a copolymer of either one of the polymers. The second polymer compound can be polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), a grafted variant of them, or a copolymer of either one of the polymers. The second polymer compound can be polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), a grafted variant of them, or a copolymer of either one of the polymers. The second polymer compound can be a polymer of the polyaryletherketone (PAEK) family, such as polyether ether ketone (PEEK), a grafted variant of any of these polymers, such as sulfonated polyether ether ketone (PEEK-WC), or a copolymer of any one of these polymers. The second polymer compound can be polychlorotrifluoroethene (PCTFE), polyether imide (PEI), polyimide (PI), polyamide imide, polyacrylonitrile (PAN), polyurethane (PUR), in particular a thermoplastic polyurethane, a grafted variant of any of these polymers, or a copolymer of any one of these polymers. The second polymer compound can be polyphenylene sulphide (PPS), cellulose acetate (CA), cellulose triacetate (CTA), a grafted variant of any of these polymers, or a copolymer of any of these polymers. The second polymer compound can be: polycarbonate (PC), poly(methyl methacrylate) (PMMA), polyamide (e.g., nylon), polystyrene (PS), acrylonitrile-butadiene-styrene (ABS), polychlorotrifluoroethylene (PCTFE), polybutyrene terephthalate (PBT) and polyphenylene sulphide (PPS), a grafted variant of any of these polymers (such as aminated sulfonated, or acrylated), or a copolymer of any of these polymers. The second polymer compound can be polyethylene (PE), polypropylene (PP), poly(ethylene terephthalate) (PET), possibly modified by copolymerization such as PET-G (Glycol-modified), amorphous PET (PET-A), or PET-GAG (a multilayer PET-G foil with A-PET core). Combinations of the above indicated compounds can be used as well for making the support layer.

[0044] The support layer can comprise reinforcement or filler materials, such as glass fibres, basalt fibres, metal fibres, carbon nanotubes, and glass beads.

[0045] The support layer can be an axially oriented film, e.g. stretched along one or two perpendicular directions, such as a uniaxially or biaxially oriented film. Such films have greater strength.

[0046] The amount of second polymer compound in the support layer is advantageously at least 5% by weight, advantageously at least 10% by weight, advantageously at least 25% by weight, advantageously at least 35% by weight, advantageously at least 50% by weight.

[0047] Suitable solvents for carrying out aspects of the invention are advantageously aprotic solvents and are advantageously one or more of: dimethylformamide (DMF), dimethylsulfoxide (DMSO), dimethylacetate (DMAc), N-methyl-2-pyrrolidone (NMP), and N-ethyl-2-pyrrolidone (NEP), since these allowfor being easily removed from a membrane forming solution by phase separation. Additional suitable solvents, possibly for use in a solvent:co-solvent system in the membrane forming solution are: tetrahydrofuran (THF), tetramethyl urea (TMU), Ν,Ν-dimethylpropylene urea (DMPU), trimethyl phosphate (TMP), triethyl phosphate (TEP), tri-n-butyl phosphate (TBP), tricresyl phosphate (TCP), acetone, aniline. Ketones, such as methyl ethyl ketone (MEK) can be suitable solvents as well. Chlorinated hydrocarbons, such as methylene chloride, dichloromethane, and trichloroethylene can be suitable solvents as well. Tamisolve® NxG solvent (Taminco bvba, Belgium) can be suitable as well. It will be convenient to note that those skilled in the art can select a suitable solvent for a predetermined combination of first and second polymer compounds based on readily available solubility data. [0048] Other possibly suitable solvents, which can be used in combination with the above indicated solvents, in particular for softening or dissolving polymer compounds of the support layer, are aromatic fluids, such as Solvesso™ (Exxon Mobil Corp.) solvents, and chloroform.

[0049] The amount of solvent (or mixture of solvents) in the membrane forming solution is advantageously at least 25% by weight, advantageously at least 35% by weight, advantageously at least 45% by weight based on the total amount of solvents and polymers in solution.

[0050] Possible combinations of first polymer compound for the semi-permeable membrane material and second polymer compound for the support layer are:

polyvinylidene fluoride (PVDF), polysulfone (PSU) or polyethersulfone (PESU) as first polymer compound, polycarbonate (PC) as second polymer compound and N-ethyl-2- pyrrolidone (NEP) or N-methyl-2-pyrrolidone (NMP) as solvent, providing good bonding strength;

- polyethersulfone (PESU) or polysulfone (PSU) as first polymer compound, polyether imide (PEI) as second polymer compound and NEP or dimethylformamide (DMF) as solvent, providing good bonding strength;

PVDF, possibly with copolymer and/or with filler (ZrC>2), as first polymer compound and

PSU as the second polymer compound with NEP as solvent;

- PVDF, PEI or PC as both the first polymer compound and the second polymer compound, with NEP as solvent, providing excellent bonding strength.

[0051] The thickness Ts of the support layer 1 1 is not particularly limited.

Advantageously, the support layer has a thickness smaller than or equal to 5 mm, advantageously smaller than or equal to 2 mm, advantageously smaller than or equal to 1000 μηη, advantageously smaller than or equal to 600 μηη, advantageously smaller than or equal to 500 μηη, advantageously smaller than or equal to 200 μηη, advantageously smaller than or equal to 150 μηη, advantageously small than or equal to 100 μηη, advantageously smaller than or equal to 50 μηη. The thickness of the film can be as small as 2.5 μηη or less, or 1 μηη or less, e.g. 0.5 μηι.

[0052] The dimensions of the through holes are not particularly limited and suitable dimensions depend on the application. The through holes may have a size smaller than or equal to 10 mm, or smaller than or equal to 5 mm, or smaller than or equal to 2 mm, possibly smaller than or equal to 1 .5 mm, possibly smaller than or equal to 1 .2 mm, possibly smaller than or equal to 1 .0 mm, possibly smaller than or equal to 0.8 mm. When the holes are too large, the membrane patch may become too weak. The through holes advantageously have a size of at least 20 μηη, advantageously at least 50 μηη, advantageously at least 100 μηι. When holes are too small, they can be closed under attack by the solvent. The size of the through-holes refers to a dimension along a straight line passing from side to side of the through-hole, through its centre, i.e. diameter.

[0053] There is no restriction on the cross-sectional shape of the through holes 1 1 1 , i.e. they may be circular, square, polygonal, such as hexagonal, star-shaped or slit- shaped holes, or holes of any other suitable shape. Circular or polygonal through holes are preferred, and the perforations advantageously have substantially cylindrical or prismatic shape with axes advantageously perpendicular to the top/bottom surfaces 1 12, 1 13.

[0054] The through holes can be made through the support layer by laser or by mechanical perforation techniques, e.g. punching such as advantageously hot needle punching, piercing, micro drilling, etc., to provide perforations, advantageously arranged in a regular pattern, and advantageously uniformly distributed throughout the support layer.

[0055] The support layer advantageously exhibits an open area (porosity due to the through holes) of at least 2%, advantageously at least 5%, advantageously at least 10%, advantageously at least 15%, advantageously at least 20%, advantageously at least 25%, advantageously at least 30%, advantageously at least 35%. The open area can be 90% or smaller and is advantageously at most 80%, advantageously at most 70%, advantageously at most 60%, advantageously at most 55%, advantageously at most 50%. The open area refers to the area of the perforations per unit total area of the film (including the perforations), expressed in percentage values.

[0056] Membrane patches as referred to in the present description are advantageously thin. They advantageously have a thickness TM smaller than or equal to 2000 μηη, advantageously smaller than or equal to 1000 μηη, advantageously smaller than or equal to 500 μηη, advantageously smaller than or equal to 350 μηη, advantageously smaller than or equal to 250 μηη, advantageously smaller than or equal to 200 μηη, advantageously smaller than or equal to 150 μηη, advantageously smaller than or equal to 100 μηη, advantageously smaller than or equal to 80 μηη, advantageously smaller than or equal to 60 μηη, advantageously smaller than or equal to 50 μηη, advantageously smaller than or equal to 30 μηη, advantageously smaller than or equal to 20 μηη. The thickness of the membrane patch is advantageously at least 1 μηι, advantageously at least 5 μηι, and can be about or at least 10μηι.

[0057] In the following, possible processes are described for producing or obtaining membrane sheets according to aspects of the invention. It will be apparent that the processes can be readily adapted to work with other types of supports as long as polymer materials as described herein are used. [0058] Membrane sheets 10 as shown in figures 1 and 2 can be obtained by first selecting a first polymer compound for the semi-permeable membrane material and possibly a solvent of the first polymer compound for preparing the membrane forming solution providing a suitable match with the second polymer compound of the support layer. The support layer 1 1 , provided with through holes 1 1 1 , is placed on a dense or nonporous coating support, such as a glass plate. The coating support will prevent that membrane forming solution will flow past the bottom surface 1 13 of the support layer 1 1. Next, a membrane forming solution is directly spread on the top surface 1 12 of support layer 1 1 according to known techniques, such as with a slot coater or other casting technique. Appropriate control of coating conditions will ensure that membrane forming solution penetrates into the through holes 1 1 1. Subsequently, the membrane forming solution present on the top surface 1 12 is completely scraped off, such as with a doctor blade. By so doing, the top surface 1 12 is exposed again, whereas the through holes 1 1 1 are or remain filled with membrane forming solution.

[0059] In case the solvent of the membrane forming solution is able to at least partially dissolve the second polymer compound of the support layer, it will be advantageous to allow a contact time between membrane forming solution and support layer at this stage of the manufacturing process. By so doing, the second polymer compound along the edges of the through holes (i.e. at the interface with the membrane forming solution) is allowed to at least partially dissolve or soften. Due to molecular mobility and the interaction between first and second polymer compounds, advantageously, the polymer chains of the first polymer compound penetrate into and/or entangle and/or link with the polymer chains of the second polymer compound at the interface between membrane patch and support layer.

[0060] The support layer with through holes filled with membrane forming solution is now immersed in a precipitation bath to induce phase separation of the first polymer compound from the solution. Since the phase separation process is carried out after softening/dissolving of the second polymer compound, it is advantageously obtained that also the softened/dissolved second polymer compound in the interfacial layer is subjected to the phase separation process, in addition to the membrane forming solution. As a result, a possible porous interface layer in which the first and second polymer compounds interact on a molecular level is advantageously formed. The phase separation process will consolidate the process of molecular interaction between the first polymer compound and the second polymer compound and make it permanent. Further process steps, which are known in the field of phase separation, can be applied as required, such as washing in a hot demineralised water bath.

[0061] It is known that phase separation induces some amount of shrinkage, depending e.g. on the phase separation process conditions, and the composition of the membrane forming solution. Based on the amount of shrinkage occurring, membrane patches 22 as shown in figure 3 instead of those shown in figures 1 and 2 can be obtained with the above process.

[0062] The pattern of membrane patches as shown in figures 4 and 5 can be obtained by using a grooved or comb-like doctor blade with grooves corresponding to the positions of the groups 42 to 44 of membrane patches. In this case, membrane forming solution is completely scraped off only in between the groups 42 to 44 of membrane patches to isolate them from one another. It is possible to coat the different groups 42 to 44 with different membrane forming solutions, e.g. using different slot coaters for each row.

[0063] In case the membrane forming solution(s) is/are correctly premetered, the need for a doctor blade can be obviated in all or some of the above processes.

[0064] The membrane patches as shown in figure 6 can be obtained by use of an array of injection nozzles or syringes, which inject suitable amounts of membrane forming solution in correspondence of the through holes 1 1 1 . By using an array of injection nozzles, a complete row of through holes can be covered with membrane forming solution at a time.

[0065] All of the above processes can be performed either in batch or continuously. A continuous process is particularly suited for continuous films as support layers. In such case the coating head for coating/casting the membrane forming solution and/or the doctor blade could be arranged oppositely a drum over which the continuous film is made to move.

[0066] It will be convenient to note that depending on the combination of first and second polymer compounds, and solvent used in the membrane forming solution, it may be required to use a second solvent for softening or at least partially dissolving the second polymer compound in the support layer prior to coating/casting the membrane forming solution. In such case, the support layer will hence be pre-treated with a suitable solvent, which can be the same or a different solvent as used in the membrane forming solution. Alternatively, or in addition, it is possible to use a solvent:co-solvent system in the membrane forming solution, with the solvent able to dissolve the membrane polymer and the co-solvent able to attack the second polymer compound of the support layer, with the solvent and the co- solvent being miscible. Advantageously, both solvents are removed in one or more solvent removal steps.

[0067] Advantageously, the support is pre-heated to a temperature substantially equal or close to the temperature of the membrane forming solution upon coating, such as a temperature within 10°C, possibly within 5°C of the temperature of the membrane forming solution. [0068] By careful adjustment of the contact time between the membrane forming solution and the support layer before membrane formation (i.e. before phase separation), a suitable degree of molecular interaction can take place at the interface between membrane solution and support layer, while the softening of the second polymer compound can be limited to a superficial thickness of the support layer, e.g. at the edges 140 of the through holes 1 1 1 .

[0069] Suitable contact times between membrane forming solution and support

(before membrane formation) can differ between various combination of materials used, and generally depend on the degree of solubility of the second polymer compound in the solvent and on the degree of interaction between the first and the second compounds. Suitable contact times can be as low as 1 s, possibly at least 5 s, possibly at least 10 s. From an industrial process point of view, contact times are advantageously smaller than or equal to 5 min. The contact time can also be limited by the maximal time period in which the membrane dope can be in contact with ambient before membrane formation, which can influence characteristic pore size.

[0070] What is also possible and advantageous is to manufacture membrane sheets wherein the first and second polymer compounds are the same, i.e. they are homopolymers, being polymers consisting of identical repeating units. This leads to the membrane patches and the support layer having same/similar chemical and/or thermal resistance. Having membrane patches and support layer made of a same polymer compound also avoids differential thermal dilatation, so that mechanical integrity can be preserved easily in membranes sheets of the present invention. Furthermore, same polymer compounds are intrinsically compatible towards solvent bonding, and a same solvent can be used, which eases manufacturing processing.

[0071] It is advantageous to use a high viscosity membrane forming solution (dope) in methods according to the present invention. Such a dope advantageously has a viscosity of at least 10 Pa.s, advantageously at least 20 Pa.s, advantageously at least 100 Pa.s at 35°C. Viscosity can be measured with a HAAKE MARS rotational rheometer (Thermo Electron, Germany) using two titanium discs of 35 mm diameter. In addition to enabling coating of the through-holes, such a high-viscosity dope also allows to obtain membranes with high cohesive strength, and hence high-resistant membranes. This is not possible with low- viscosity dopes as they are generally used in the prior art.

[0072] An advantage of membrane sheets according to aspects of the invention over the prior art, is that a seal between membrane patches and support layer is automatically created along the edges of the membrane. There is hence no need of providing additional process steps or structures with which to secure the membrane patches to the support layer. [0073] Example 1

An Ajedium™ plastic film (Solvay Plastics, US) made from Udel® polysulfone type P1700 NT- 1 1 (= second polymer compound) having a thickness of 50 μηη (2 mil) was perforated with 2 mm diameter holes to obtain an open area of about 70%. The number of holes per m ² of film to achieve this open area was around 318300. A SEM image of the cross section of the support layer 1 1 at the occurrence of a through hole 1 1 1 is shown in figure 7.

[0074] The film was placed horizontally onto a glass plate. The film was tensioned on the glass plate to ensure intimate contact between the bottom face of the film and the glass plate. A membrane forming solution was applied on the top surface of this perforated PSU film and scraped off using a doctor blade to leave membrane forming solution only in the perforations. A Zirfon® membrane forming solution was used, which comprised 85 wt.% Zr0 ₂ and 15 wt.% Udel® polysulfone type P1800 NT-1 1 (= first polymer compound). NEP was used as solvent. After a contact time of about 30 s, the coated film was immersed in demineralised water to induce liquid induced phase separation (LIPS). The membrane sheet was removed from the water bath after 15 minutes of residence time. It was subsequently washed for one hour in a demineralised water bath at a temperature of 70°C.

[0075] The membrane patches thus formed had edges corresponding to the edges of the perforations, where a very good bonding between Z PSU membrane material and the PSU film was observed. SEM images of the cross section of the membrane patch 12 thus obtained at the interface with the support film 1 1 are shown in figures 8 A-B. The membrane patch had a thickness TM = 9.2 μηι, whereas the support film measured Ts = 52 μηι. The interfacial layer 122 which bonds the patch 12 to the support 1 1 is clearly visible in the images. The interface 122 is clearly porous and the difference in colour (due to absence of ZrC>2) makes it distinct from the bulk semi permeable membrane material of the patch 12. Comparison of figure 8 B with figure 7 clearly shows the edge 1 14 of the through hole 1 1 1 having been dissolved to merge with the interface 122.

[0076] Membrane sheets according to aspects of the present invention can find use in a variety of applications, in particular requiring extremely thin membranes, including, but not limited to, the following uses:

use as membranes for any one of the following batteries:

"Metal-ion" batteries: Lithium-ion; Potassium-ion, Aluminium-ion;

"Metal-Air" batteries: Aluminium-air, Zinc-air, Silicon-air and Lithium-air;

Lithium-ion batteries: Lithium-ion manganese, Lithium-ion polymer, Lithium-iron phosphate; Lithium-sulfur, Lithium-Titanate;

- Nickel-Hydrogen batteries;

Nickel-Metal Hydride- Zinc Systems: Silver-Zinc, Nickel-Zinc, Zinc-Bromine; Silver oxide, Silver Zinc batteries;

Flow batteries: Vanadium redox , Zinc-bromine and Zinc-cerium;

Nickel-Cadmium;

Alkaline batteries;

- Fuel-cell batteries;

use as semi-permeable membranes for any one of the following applications:

immuno assays;

Elisa tests

diffusive air samplers;

- diffusive water samplers;

use as ion-exchange membranes in any one of the following fields:

Electrodialysis;

Reverse electrodialysis;

Diffusion dialysis;

- Donnan dialysis;

Capacitive deionization;

Electrolysis (hb, C and lye production);

use as filtration membranes in any one of the following fields:

Micro-, ultra, nanofiltration;

- Reverse osmosis;

Forward osmosis;

Pressure retarded osmosis;

Membrane bioreactors;

Pervaporation;

- Membrane distillation;

Supported liquid membranes;

Pertraction;

Membrane absorbers;

Enzyme reactors;

- Other membrane contractors.

[0077] The membrane sheets as referred to in the present description are advantageously configured for electrochemically driven selective transport of compounds, such as alkaline water electrolysis and chlor-alkali electrolysis.