Method of manufacturing a porous separator membrane and separator membrane obtained therefrom

Abstract

A porous separator membrane (203) is manufactured by preparing a suspension comprising an organic solvent, a binder polymer, inorganic filler particles and an organic pore control additive having a molecular weight between 150 Da and 7500 Da, casting the suspension into a film (202), subjecting the film to phase separation and removing the organic pore control additive. Subjecting the film to phase separation comprises contacting the film with a first coagulation liquid (231) comprising 50% by weight or less non-solvents of the binder polymer without prior exposing the film to a non-solvent vapour phase. A ratio of the organic pore control additive to a total amount of the organic pore control additive and the binder polymer in the suspension is between 0.3 and 0.95 by weight, a ratio of the inorganic filler particles to a total amount of the inorganic filler particles and the binder polymer in the suspension is between 0.75 and 0.95 by weight, and a ratio of the binder polymer to a total amount of the solvent and the binder polymer in the suspension is between 0.15 and 0.30 by weight. An obtained porous separator membrane has a water permeability at between 150 l / h / m2 / bar and 900 l / h / m2 / bar and an ionic resistance between 0.02 Ωcm2 and 0.12 Ωcm2.

Description

METHOD OF MANUFACTURING A POROUS SEPARATOR MEMBRANE AND SEPARATOR MEMBRANE OBTAINED THEREFROMTechnical field

[0001] The present disclosure is related to methods of manufacturing porous separator membranes, also referred to as diaphragms, and to separator membranes obtained therefrom. In particular, the porous separator membranes comprise a polymeric binder phase and inorganic filler particles dispersed therein.Background art

[0002] There is an increasing demand for ‘green’ hydrogen that is made from sustainable materials and with renewable energy sources, without utilizing fossil fuels. One industrial process to produce such ‘green’ hydrogen is alkaline water electrolysis. In alkaline water electrolysis, an aqueous electrolyte solution, with typically KOH as the electrolyte, is provided between an anode compartment and a cathode compartment which are separated by an ion-permeable separator membrane, also referred to as diaphragm. Under the influence of an electric current, oxygen gas is produced at the anode and hydrogen gas is produced at the cathode. This process uses water as the raw material.

[0003] Apart from the electrodes, excellent separator membranes are an essential part of an alkaline water electrolyser because they determine to a very large extent the feasibility of the electrolysis process when operating at high rate (at high current densities), as they are responsible for more than 80% of total ionic resistance of the cell. Optimal separator membranes should have a low ionic resistance (preferably smaller than 0.1 Qcm2at 30°C in a 30 wt% KOH solution) allowing the cell potential to remain below its practical limit of 1.9 V at high to very high current densities (1 to 4A / cm2) at 80°C to up to 120°C operating temperature, hence keeping the efficiency of the electrolysis process at a high level. Such low ionic resistance can be mainly achieved through separator membranes having a high total porosity, reduced thickness and / or a high resistance to higher operating temperatures in concentrated alkaline electrolyte solutions. On the other hand, the separator membranes should have a low liquid permeability to keep the contamination by the gases produced at the other side of the separator membrane to a low and safe level (particularly hydrogen to oxygen (HTO) contamination in the anolyte). This would imply separator membranes having a more dense structure. A reduced liquid permeability to prevent diffusion of H2 gas towards the oxygen side is becoming increasingly important for alkaline water electrolysers in view of the higher operating temperatures and / or pressures of electrolytic cells. At higheroperating temperatures, the electrolyte has lower viscosity, facilitating permeability, whereas at higher operating pressures there is higher transport of dissolved gases due to the increased solubility of gases. In addition, the separator membranes should have sufficient mechanical strength to guarantee long service life. From these conflicting requirements, it follows that it is not straightforward to obtain optimal separator membranes for alkaline water electrolysis.

[0004] The separator membranes of the above kind typically have a material structure formed of a porous polymeric (synthetic) binder phase in which (hydrophilic) inorganic filler particles are dispersed. Materials of this kind are often referred to as mixed matrix materials and are obtained through a non-solvent induced phase separation process. In non-solvent induced phase separation, a membrane forming suspension comprising the binder polymer, a solvent and the inorganic filler particles is prepared and cast into a film, particularly by coating onto a reinforcement web. The film is solidified by subjecting it to phase separation, also referred to as phase inversion, in which the membrane forming suspension is contacted with a non-solvent composition which extracts the solvent from the film and coagulates the polymer binder into a porous structure.

[0005] EP 3272908, 24 January 2018, discloses a method for manufacturing a diaphragm for alkaline water electrolysis in which the coated film is exposed to a non-solvent vapour (vapour-induced phase separation or VIPS) prior to immersing the coated film in a coagulation bath comprising a poor solvent for the binder polymer (liquid-induced phase separation or LIPS). The vapour-induced phase separation creates surface pores which are sufficiently large to ensure that the subsequent liquid-induced phase separation proceeds rapidly and avoids formation of large internal pores. EP 3272908 additionally discloses adding an organic pore control additive to the membrane forming suspension, such as polyethylene glycol, polyvinylpyrrolidone or polyethylene oxide. The separator membranes obtained in EP 3270908 are reported to avoid detachment of the inorganic filler particles from the polymer binder phase in a variable power supply environment.

[0006] WO 2023 / 048006, 30 March 2023, discloses a method for producing a diaphragm for alkaline water electrolysis in which the formation of macrovoids is prevented. A compound of general formula R-X is added to the membrane forming suspension, with R being a hydrocarbon group with at least six carbon atoms and X being a hydrophilic functional group. The compound interacts with the binder polymer at the R-group whereas the X-group interacts with the inorganic filler particles. This interaction is alleged to suppress the formation of macrovoids. The process tomanufacture the separator membrane disclosed in WO 2023 / 048006 includes a step of liquid-induced phase separation, possibly preceded by a vapour-induced phase separation. In the liquid-induced phase separation the coated film is immersed in a coagulation bath. Thereafter, the obtained porous separator membrane is dried to remove the non-solvent.

[0007] US 4098930, 4 July 1978, discloses a method for producing a separator for an electrochemical cell, including dissolving a copolymer of acrylonitrile with a small amount of a comonomer into N,N-dimethyl formamide, applying the solution to a web or fabric and dipping the coated web in cold water, whereby the copolymer deposits on the web by coagulation. The cold water must be maintained at a temperature of 15°C or less, which results in a small maximum pore radius of the formed matrix, while the electric resistance is kept constant.

[0008] CN 117379999 A, 12 January 2024 discloses a method of preparing a sulfane polymer hollow fiber ultrafiltration membrane. The casting solution comprises, in parts by weight: 10-25 parts of sulfone polymer, 5-15 parts of pore-forming agent, 50- 90 parts of an organic solvent and 1-5 parts water. The pore-forming agent can be polyethylene glycol, polypropylene glycol or polyvinyl alcohol with number average molecular weight between 1500 and 5000. The cast hollow fiber is pre-treated under an air section of length 10-30 cm, temperature 20-40°C and humidity of not more than 20%. The pre-treated hollow fiber is pre-gelled by immersion in a first gel bath comprising a mixture of an organic solvent and water, in which the water content is 30%-60%, followed by immersion in a water bath for instantaneous phase separation. This document further discloses that the molecular weight of the pore-forming agent may not be too high as it will not be easy to clean out. The obtained membranes have fairly dense inner and outer surface layers and a bulk layer showing finger-like pores typical for filtration membranes. While these finger-like holes are beneficial to improve liquid permeability of filtration membranes, they are not beneficial for separator membranes as they typically lead to a too high permeability.Summary

[0009] Despite progress being made in the manufacturing processes of porous separator membranes, there is still a need in the art for obtaining improved porous separator membranes. It is therefore an aim of the present disclosure to provide methods of manufacturing porous separator membranes leading to improved properties of the obtained separator membranes. There is a need in the art to provide such methods that are economically feasible, allow for easy process control and / or are less complex.

[0010] There is a need in the art for porous separator membranes having at least equal or even improved performance compared to the separator membranes of the prior art, particularly in terms of reduced water permeability and / or reduced ionic resistance and / or improved mechanical strength at possibly equal or even reduced thickness. There is further a need in the art for porous separator membranes which are more economical and / or easier to manufacture.

[0011] According to a first aspect of the disclosure, there is therefore provided a method of manufacturing a porous separator membrane, as set out in the appended claims. Methods according to the present disclosure comprise a first operation of preparing a membrane forming suspension (also referred to as a dope or a slurry) comprising, or consisting of, a solvent, a binder polymer dissolved in the solvent, inorganic filler particles and an organic pore control additive dissolved in the solvent, a second operation of casting the suspension into a film and a third operation of subjecting the film to phase separation and removing the organic pore control additive, resulting in the porous separator membrane.

[0012] According to a first feature, subjecting the film to phase separation comprises contacting the film with a first coagulation liquid followed by contacting the film with a second coagulation liquid. The first coagulation liquid comprises one or more nonsolvents of the binder polymer in a first (total) concentration of 70% by weight or less, such as 50% by weight or less. The second coagulation liquid comprises one or more non-solvents of the binder polymer (same or different from the one or more non-solvents in the first coagulation liquid) in a second (total) concentration larger than the first (total) concentration. The total concentration refers to the concentration of all the non-solvents present in the respective coagulation liquid. Advantageously, the film is subjected to liquid-induced phase separation without prior subjecting the film to vapour-induced phase separation. The film is hence advantageously not substantially exposed to a nonsolvent vapour phase prior to contacting the film with the first coagulation liquid.

[0013] The lower concentration of the non-solvent in the first coagulation liquid advantageously prevents the pore control additive from being extracted from the film too rapidly. It is believed that this is due to a smaller concentration gradient of the non-solvent between the film and the first coagulation liquid, slowing down the phase separation process. As a result, pores at the surface of the film will not be too small. This is particularly relevant for pore control additives having smaller molecular weight. Furthermore, due to the absence of exposure to a non-solvent vapour, surface pores are advantageously created that are not too large. As a result, an optimal size of the surface pores can be created, enabling phase separation internal in the film to be performedunder optimal conditions, resulting in an isotropic pore structure in the bulk of the separator membrane. Macrovoids are advantageously avoided, improving mechanical strength and bonding to any optional reinforcement. In addition, present methods feature more degrees of freedom of the phase separation operations, particularly in terms of sequence of the various coagulation liquids and contact time of the film with the various coagulation liquids, compared to prior art methods. This advantageously allows for improved tailoring of the separator membrane properties.

[0014] According to a second feature, which can be provided independently of the first feature or in combination, the organic pore control additive has a weight average molecular weight between 150 Da and 7500 Da. These organic pore control additives can be polymers which are solid, liquid, or semi-solid (e.g., waxes or gels) at ambient conditions of temperature and pressure. Advantageously, the organic pore control additive is a polymer which is liquid at a temperature between 20°C and 60°C (at atmospheric pressure). Particularly, the organic pore control additive has a melting point at a temperature of 60°C or less, at atmospheric pressure.

[0015] An organic pore control additive of relatively low molecular weight being employed in the membrane forming suspension composition has twofold advantages. Firstly, it was observed that such low molecular weight pore control additives enable to improve the rheological properties of the membrane forming suspension. Without wishing to be bound by theory, such low molecular weight pore control additives advantageously act as dispersants for the inorganic filler particles, avoiding agglomeration and / or sedimentation. Additionally, it was found that such low molecular weight pore control additives readily dissolve both in the solvent(s) of the membrane forming suspension and in the non-solvent(s) of the coagulation liquids, even in high proportions. Such low molecular weight pore control additives can act as thinning agents or plasticizers, lowering the viscosity of the membrane forming suspension. As a result, the membrane forming suspension can be cast with greater ease, obtaining smooth surfaces without stripes. This further facilitates impregnation of the reinforcement web and complete filling of the meshes of the web by the membrane forming suspension. Secondly, it was observed that employing such low molecular weight pore control additives enables to obtain unique properties of the separator membrane. It was surprisingly found that such low molecular weight pore control additives assist in obtaining a fine pore structure without substantial reduction of total porosity values. As a result, separator membranes with both lower liquid permeability and smaller ionic resistance can be obtained. These properties are beneficial for keeping gas contamination at low levels, while maintaining high efficiency. In addition, the lowmolecular weight organic pore control additive can advantageously be readily extracted in the phase separation process, e.g. by dissolution in the non-solvent, resulting in separator membranes which have improved resistance against ageing in aggressive electrolyte environments. Optionally, such low molecular weight pore control additives advantageously enable to increase the amount of binder polymer in the membrane forming solution, resulting in stronger membranes, or allowing to reduce membrane thickness at equal strength.

[0016] Furthermore, the combination of the first and second features above advantageously allows to even further improve the properties of the porous separator membranes, particularly in terms of a unique porous microstructure which achieves both low water permeability and small values of ionic resistance, while at the same time ensuring a high stability of performance over time. Additionally, the combination of features advantageously allows for easier manufacturing.

[0017] Advantageously, the organic pore control additive is added to the suspension in a high amount relative to the amount of binder polymer. A ratio of amount of the organic pore control additive to a total amount of the organic pore control additive and the binder polymer in the suspension is advantageously between 0.3 and 0.95 by weight. Such high amounts enable to achieve high porosity and a unique isotropic structure with fine pores without macrovoids or finger-like pores. Additionally, since such low molecular weight pore control additives also act as plasticizers and dispersants, they enable to increase the loading of binder polymer and / or inorganic filler particles into the suspension.

[0018] A ratio of amount of the inorganic filler particles to a total amount of the inorganic filler particles and the binder polymer in the suspension is advantageously between 0.75 and 0.95 by weight. Such high amounts of inorganic filler particles lower the ionic resistance of the porous separator membranes on the one hand, and increase the tortuosity of the interconnected pores on the other hand, thereby lowering the water permeability of the porous separator membranes.

[0019] A ratio of amount of the binder polymer to a total amount of the solvent and the binder polymer in the suspension is advantageously between 0.15 and 0.30 by weight. Methods according to the present disclosure enable membrane forming solutions having a high binder polymer loading, resulting in stronger membranes. In addition, the high binder polymer loading in combination with a high loading of the organic pore control additive enables to obtain a fine pore structure without macrovoids or finger-like pores.

[0020] Advantageously, when contacting the film with the first coagulation liquid, the first coagulation liquid is at a temperature between 3°C and 25°C, preferably between 5°C and 15°C, which can assist both in creating smaller surface pores and in preventing non-solvent vapour being formed above the liquid level of the coagulation liquid.

[0021] According to a second aspect of the disclosure, there is provided a porous separator membrane, as set out in the appended claims. The porous separator membrane is advantageously obtained by methods according to the first aspect. The porous separator membrane is made of a material comprising, or substantially consisting of, a polymeric binder phase and inorganic filler particles dispersed in the binder phase. Advantageously the (solid) material of the porous separator membrane does not comprise any additive, such as the pore control additive utilized in the method of the first aspect. Advantageously, an amount of the inorganic filler particles in the composite material is between 75% and 95% by weight, optionally with the polymeric binder phase and the inorganic filler particles constituting 100% of the weight of the composite material.

[0022] The porous separator membrane comprises a first membrane face, a second membrane face opposite the first membrane face. The porous separator membrane can comprise a porous surface layer adjacent the first membrane face and an isotropic porous bulk layer. An average size of pores of the surface layer is smaller than an average size of pores of the bulk layer. The isotropic bulk layer with uniform porous structure can act as an appropriate backbone imparting strength, and if a reinforcement mesh is provided, the bulk layer can ensure appropriate bonding to the mesh by avoiding large voids around the mesh filaments.

[0023] The porous separator membrane has a water permeability at 30°C advantageously between 150 l / h / m2 / bar and 900 l / h / m2 / bar and / or has an ionic resistance, determined at 30°C in a 30% by weight KOH aqueous solution, advantageously between 0.02 Qcm2and 0.12 Qcm2, preferably between 0.025 Qcm2and 0.09 Qcm2. The above values of water permeability and ionic resistance are applicable to the virgin separator membrane, but are advantageously also applicable to separator membranes aged for two weeks in a 30% by weight KOH aqueous solution at 85°C.

[0024] According to a further aspect, there is provided a use of the porous separator membrane of the second aspect as a diaphragm in an electrolysis process, particularly in alkaline water electrolysis.

[0025] An electrolyser, particularly one configured for alkaline water electrolysis, comprising at least one electrolytic cell is described herein. The electrolytic cell comprises an anode compartment and a cathode compartment separated by a diaphragm. The diaphragm comprises or consists of the porous separator membrane according to the second aspect.

[0026] According to yet a further aspect, there is provided a use of an apparatus for manufacturing a porous separator membrane according to the second aspect of the present disclosure. The apparatus comprises a casting system for casting a membrane forming suspension into a film, a first coagulation bath, a second coagulation bath and possibly a third coagulation bath, and a conveyor system for transporting the film from the casting system sequentially through the first, second and optionally third coagulation baths. The apparatus is advantageously configured to execute methods according to the first aspect of the present disclosure.Brief description of the drawings

[0027] Aspects of the disclosure will now be described in more detail with reference to the appended drawings, wherein same reference numerals illustrate same features and wherein:

[0028] Figure 1 represents a flow diagram of a method of manufacturing a porous separator membrane according to the present disclosure;

[0029] Figure 2 represents a diagram of a plant for manufacturing a porous separator membrane according to the flow diagram of Fig. 1 ;

[0030] Figure 3 represents a flow diagram of another method of manufacturing a porous separator membrane according to the present disclosure;

[0031] Figure 4 represents a diagram of a plant for manufacturing a porous separator membrane according to the flow diagram of Fig. 3;

[0032] Figure 5 represents a cross section drawing of an asymmetric separator membrane according to the present disclosure;

[0033] Figure 6 represents a cross section drawing of a symmetric separator membrane according to the present disclosure;

[0034] Figure 7 represents a SEM image of a separator membrane obtained according to Comparative Example 1-1;

[0035] Figure 8 represents a SEM image of the surface layer of the separator membrane of Fig. 7 at larger magnification;

[0036] Figure 9 represents a SEM image of a separator membrane obtained according to Comparative Example 1-2;

[0037] Figure 10 represents a SEM image of the surface portion of the separator membrane of Fig. 9 at larger magnification;

[0038] Figure 11 represents a SEM image of a cross section of a separator membrane according to Example Ex2-1(a) at 250 magnification;

[0039] Figure 12 represents a SEM image of a portion of the cross section of Fig. 11 at 5000 magnification;

[0040] Figure 13 represents a SEM image of a cross section portion of a separator membrane according to Example Ex2-2 at 5000 magnification;

[0041] Figure 14 represents a diagram of an electrolyser for alkaline water electrolysis.Detailed description

[0042] Referring to Fig. 1 , a method 10 of manufacturing a porous separator membrane comprises an operation 11 of preparing a membrane forming suspension, an operation 12 of casting the membrane forming suspension into a film and an operation 13 of liquid-induced phase separation of the membrane forming suspension to obtain the porous separator membrane 15. The method 10 can comprise an optional post-processing operation 14.

[0043] In operation 11 , the ingredients to prepare the membrane forming suspension comprise or consist of: a binder polymer, a solvent, inorganic filler particles and an organic pore control additive. The membrane forming suspension advantageously does not comprise water or any non-solvent of the binder polymer. The membrane forming suspension is advantageously prepared by dissolving the binder polymer and the pore control additive in the solvent, typically until a clear or transparent solution is obtained. The binder polymer and the pore control additive can be dissolved consecutively in the solvent (in any order), or simultaneously. Next, the inorganic filler particles are mixed (dispersed) into the solution until a suspension is obtained.

[0044] The binder polymer is advantageously a high performance plastic compound, advantageously a thermoplastic compound. The binder polymer advantageously has a high temperature stability, e.g., it can have a glass transition temperature of at least 120°C, advantageously at least 150°C. The binder polymer advantageously features a high chemical resistance, such as being resistant to highly concentrated alkaline electrolyte solutions (e.g. 30 - 40 wt% KOH electrolyte solution) and / or to elevated temperatures (e.g. 110°C-130°C). The binder polymer is advantageously a sulfur-containing aromatic polymer compound, a fluoropolymer compound, a polyarylether compound, a polyketone compound or a combination of one or more of these. Specific examples of suitable binder polymers include: polysulfone(PSU), polyethersulfone (PESLI), polyarylethersulfone (PAES), polyphenylsulfone (PPSLI), polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), polyaryletherketone (PAEK), polyether ether ketone (PEEK), sulfonated polyether ether ketone (SPEEK), poly(oxa-p- phenylene-3,3- phtalido-p-phenylene-oxa-p-phenilene-oxy-phenylene) (PEEK-WC), sulfonated PEEK-WC (SPEEK-WC), polyethylene oxide (PEO), sulfonated polyether ether ketone (PEEK-WC), sulfonated PPS (SPPS or PPSS), polyetherimide (PEI), polyimide (PI), polyamide-imide (PAI), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polybenzimidazole (PBI), ethylene propylene diene monomer (EPDM), silicone rubber, poly[1-(trimethylsilyl)-1 -propyne] (PTMSP) and poly(4-methyl-2-pentyne) (PMP). The binder polymer can be a blend of one or more of the above polymers. The binder polymer can comprise one or more copolymers, which are advantageously independently selected from: poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and poly(vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE).

[0045] The binder polymer can be an ion-conducting polymer (e.g. a cation- and / or anion-conducting polymer). Ion-conducting polymers can assist in further reducing the ionic resistance of the separator membrane. Examples of cation-conducting polymers are PEEK-WC, SPEEK, SPEEK-WC and SPPS. Examples of anion- conducting polymers are polymers functionalized with a quaternary ammonium group.

[0046] The binder polymer is advantageously a sulfone-containing aromatic polymer compound, more particularly an aryl sulfone containing polymer compound, such as polysulfone (PSU), polyethersulfone (PESU), polyarylethersulfone (PAES) and polyphenylsulfone (PPSU). The electron withdrawing ability of the sulfone group allows these compounds to have a strong resonance structure. In addition, these polymer compounds advantageously have no ester or amide in their structure which is easily degradable, resulting in excellent chemical and temperature stability, particularly in highly concentrated alkaline solutions. Commercially available polysulfones are Ultrason® PSU, BASF, and Udel® PSU, Solvay / Syensqo. Specialty Polymers. A commercially available polyphenylsulfone is Radel® PPSU, Solvay Specialty Polymers.

[0047] The solvent is configured to dissolve the binder polymer in the membrane forming suspension. The solvent is advantageously an organic solvent, advantageously an aprotic solvent, which is advantageously miscible in water. The solvent is advantageously one or a blend of: dimethyl sulfoxide (DMSO), N-ethyl-2- pyrrolidone (NEP), N-methyl-2-pyrrolidone (NMP), N-butyl-2-pyrrolidone (NBP), dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), tetra hydrofuran (THF), 1 ,4- dioxane, triethyl phosphate (TEP), tetramethyl urea (TMU); N,N-dimethylacetamide(DMAC), acetonitrile, tetra oxaundecane (TOU), N,N-dimethyl lactamide (e.g. Agnique® AMD 3L), pentanoic acid, 5-(dimethylamino)-2-methyl-5-oxo-, methyl ester (e.g. Rhodiasolv® Polarclean) and cyrene. In addition or alternatively, the solvent can be a biosolvent blend (e.g. Astrobio™ NS or Astrobio™ NS3), a dimethyl ester based solvent blend (e.g. Sta-Sol® ESS I) and mixtures thereof. In the aforementioned list biosolvent blends, dimethyl ester based solvent blends, NBP (e.g. TamiSolve™ NxG); N,N-dimethyl lactamide and pentanoic acid, 5-(dimethylamino)-2-methyl-5-oxo-, methyl ester (e.g. Rhodiasolv® Polarclean) are advantageous since they are more environment-friendly and pose reduced health hazards.

[0048] Advantageously, a ratio of amount of the binder polymer (P) to a total amount of the solvent (S) and the binder polymer (P) in the membrane forming suspension, P / [P + S], is between 0.12 and 0.3 by weight, advantageously between 0.15 and 0.28 by weight, such as between 0.17 and 0.28 by weight, or between 0.15 and 0.27 by weight.

[0049] The inorganic filler particles advantageously have one or more of the following properties: they are hydrophilic, they are porous and they are insoluble in the solvent(s) utilized in the membrane forming suspension, in the non-solvent(s) such as water and in the electrolytic solution (e.g. KOH solution) at operating temperatures (e.g., between 80°C and 130°C). The inorganic filler particles can be oxides or hydroxides of one or more metal or metalloid elements, such as Mg, Ti, Zr, Hf, Al, Ce, Y and Si. Particularly advantageous are oxides and hydroxides (e.g., a hydroxy-oxide derivative) of one or more transition metals, particularly oxides and / or hydroxides of one or more elements of group 4 of the periodic table, more particular oxides or hydroxides of Ti, Zr and / or Hf, such as TiC>2, ZrC>2 and HfC>2. Other suitable inorganic filler particles are phosphates of elements of group 4 of the periodic table (such as Zra(PO4)4, barium sulfate (BaSO4), barium titanate (BaTiCh), carbides and nitrides of metals or metalloids, particularly carbides and nitrides of elements of group 4 of the periodic table, SiC, zeolites, metal-organic frameworks (MOFs), molecular sieves, silicates (e.g., clay minerals) and metal hydrides. Any suitable combination of the above listed inorganic filler particles may be made and utilized in preparing the membrane forming suspension.

[0050] The inorganic filler particles advantageously have a particle porosity(i.e., the porosity of the particles, disregarding voids between particles) between 20% and 80%, advantageously at least 40%, or at least 50%. The inorganic filler particles in the membrane forming suspension have a particle size distribution with a 50-percentile diameter (dso) advantageously between 0.1 pm and 2 pm, advantageously between 0.2 pm and 1 .5 pm, advantageously between 0.3 and 1.2 pm. The 90-percentile diameter(dgo) of the particle size distribution of the inorganic filler particles is advantageously 5 pm or less, advantageously 4 pm or less, advantageously 2.5 pm or less. The dso and dgo diameters can be measured based on a volumetric particle size distribution, e.g. as determined by laser diffraction.

[0051] Advantageously, a ratio of amount of the inorganic filler particles (F) to a total amount of the inorganic filler particles (F) and the binder polymer (P) in the membrane forming suspension, F / [F + P], is between 0.70 and 0.95 by weight, advantageously between 0.75 and 0.95 by weight, such as between 0.75 and 0.90 by weight.

[0052] According to an aspect, the membrane forming suspension comprises a pore control additive. The pore control additive is advantageously an organic compound or a combination (mixture) of organic compounds, which is advantageously soluble in the solvent and / or soluble in water or any non-solvent that is utilized as coagulation agent in the liquid-induced phase separation operation 13, as will be described further.

[0053] The membrane forming suspension can comprise additional ingredients, such as viscosity control additives and the like. Alternatively, the membrane forming suspension can consist of one or more binder polymers, one or more solvents of the binder polymer(s), one or more inorganic filler particles and one or more pore control additives only, without addition of further ingredients.

[0054] In operation 12, the membrane forming suspension is cast into a film, advantageously a continuous film. Referring to Fig. 2, in a membrane manufacturing plant 20, the casting operation 12 can comprise coating a porous web 201 with the membrane forming suspension 21 to obtain a film 202. Advantageously, operation 12 involves a continuous coating process. The membrane forming suspension 21 can be cast in a coating apparatus 22 by a single coating head, which is configured to provide membrane forming suspension at one or both sides of the porous web 201 . One example coating head that may be utilized for this purpose is disclosed in EP4023342. Alternatively, as illustrated in Fig. 2, the membrane forming suspension 21 can be cast by two coating heads 221 , 222 arranged at opposite sides of the porous web 201 for double-sided coating. Both coating heads 221 , 222 are configured to apply membrane forming suspension onto the respective side of the porous web 201 . Alternative coating techniques, such as drum coating or knife coating, can be applied instead of, or in combination with slot coating. It is beneficial to cast the membrane forming suspension at elevated temperature, such as between 40°C and 60°C, as this improves the suspension’s rheology and facilitates filling the meshes of the porous web 201.

[0055] The porous web 201 advantageously acts as a reinforcement of the separator membrane and can be any porous support suitable for the intended application. The porous web 201 can be a mesh or a woven or non-woven fabric made of monofilaments or multifilaments or any other suitable structure. The porous web 201 advantageously has a large open area (i.e. , face area of the meshes or through-openings relative to total face area), e.g. at least 50%, such as between 50% and 95%, advantageously at least 80%, so as not to significantly influence the properties of the porous separator membrane in terms of ion or liquid permeability. The porous web is advantageously made of a material that performs well in terms of temperature and chemical resistance. Advantageous materials for the porous web are polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polyoxymethylene (POM), polyethylene (PE), polypropylene (PP), a fluoropolymer, a polyketone compound, a polyaryletherketone compound (PAEK), polyimide (PI), and polyetherimide (PEI). The porous web 201 can be unwound from a roll 211 and guided to the coating apparatus 22 by a conveyor system 210.

[0056] The porous web 201 can be embedded in the film 202 either completely or partially (e.g., such as disclosed in EP3613495). The thickness of the porous web 201 is advantageously smaller than the thickness of the film 202. It is alternatively possible to manufacture non-reinforced separator membranes, i.e., with no embedded reinforcement. A non-reinforced separator membrane can be manufactured by casting the membrane forming suspension single-sided on a liner or a web with no substantial penetration of the suspension into the web, forming the separator membrane and separating the separator membrane from the liner or web, e.g. while the separator membrane is being formed or afterwards. In such cases, the web can be substantially dense.

[0057] With continued reference to Figs. 1 and 2, in operation 13, the film202 is subjected to liquid-induced phase separation (LIPS). Liquid-induced phase separation is a phase separation technique. The term phase separation, or phase inversion, refers to a number of known processes to coagulate the binder polymer from a solution, e.g. described in the handbook by M. Mulder, Basic Principles of Membrane Technology, Second Edition, Kluwer Academic Publishers, 1996. Phase separation is based on a transition between two phases, induced by a change of polymer solubility. Starting from an initial polymer solution, in which the polymer is completely dissolved, a change in composition induces demixing of the solution into a polymer rich and a polymer poor phase. Upon further separation, the solubility of the polymer is reduced and a solid phase with specific porous morphology will be formed. In liquid-induced phaseseparation, the change in composition of the membrane forming suspension, particularly a change in composition of the solution of binder polymer and solvent, is induced by contacting the coated membrane forming suspension (film) with a liquid compound that is a poor solvent for the binder polymer, referred to as a non-solvent. The non-solvent is advantageously miscible with the solvent utilized in the membrane forming suspension, and advantageously the affinity of the solvent for the non-solvent is higher than the affinity of the solvent for the binder polymer. As a result, a diffusion of the solvent from the membrane forming suspension towards the non-solvent liquid phase occurs, inducing demixing and eventual coagulation of the binder polymer in the film.

[0058] In the prior art often recourse is made to a combination of vapour- induced phase separation (VIPS) followed by liquid-induced phase separation, to obtain larger, open pores at the surface of the separator membrane by exposure of the film to a non-solvent vapour prior to exposure of the film to the non-solvent liquid. As a result, a faster penetration of the non-solvent liquid into the inside of the film is obtained during LIPS, resulting in a finer internal pore structure.

[0059] Conversely, according to the present disclosure, vapour-induced phase separation is not applied to the film. Instead, the film (membrane forming suspension) is contacted sequentially with multiple coagulation liquids, in which at least the coagulation liquid first contacting the film has a lower concentration of the non-solvent compared to the subsequent coagulation liquid(s). This slows down the initial liquid- induced phase separation process and creates pores at the surface of the film which are somewhat larger than with a 100% non-solvent coagulation liquid but still smaller than the surface pores obtained with VIPS. Surprisingly, it was observed that the process according to the present disclosure is beneficial to the pore structure of the internal bulk layer of the film as well, with fine pores and an isotropic pore structure advantageously free from macrovoids. As a result, not only the surface layer, but also the internal bulk layer contributes to defining liquid permeability and ionic resistance characteristics of the separator membrane.

[0060] Referring to Fig. 1 , the operation 13 comprises a first operation 131 of contacting the film with a first coagulation liquid. The first coagulation liquid comprises one or more non-solvents of the binder polymer and additionally comprises one or more solvents of the binder polymer and / or the one or more pore control additive(s). According to an aspect of the present disclosure, the concentration of the non-solvent (or mixture of non-solvents) of the binder polymer in the first coagulation liquid is smaller than or equal to 70% by weight, advantageously smaller than or equal to 50% by weight. The non-solvent concentration in the first coagulation liquid can e.g. be between 5% byweight and 50% by weight, advantageously between 10% by weight and 45% by weight, advantageously between 15% by weight and 40% by weight, and more particularly between 20% by weight and 35% by weight.

[0061] The first operation 131 is advantageously applied directly(immediately) following operation 12 of casting the membrane forming suspension into a film. This prevents the film to be exposed to any vapour of the non-solvent that emanates from the first coagulation liquid. Alternatively, or in addition, to prevent forming vapours of the non-solvents present in the first coagulation liquid, the temperature of the first coagulation liquid in operation 131 is advantageously 25°C (i.e. , room temperature) or less, such as between 3°C and 25°C, e.g. between 5°C and 15°C. Such low temperatures, in addition to preventing exposure to the non-solvent vapour advantageously further reduce the (surface) pore size of the separator membrane.

[0062] Operation 13 comprises a second operation 132 of contacting the film with a second coagulation liquid. Operation 132 is executed following operation 131. The second coagulation liquid comprises one or more non-solvents of the binder polymer in a concentration larger than the concentration of one or more non-solvents in the first coagulation liquid.

[0063] The concentration of the non-solvent (or mixture of non-solvents) in the second coagulation liquid is advantageously between 30% by weight and 100% by weight, advantageously at least 50% by weight, or at least 60% by weight, and advantageously 90% by weight or less, or 80% by weight or less or even 70% by weight or less.

[0064] Operation 13 can comprise an optional third operation 133 of contacting the film with a third coagulation liquid. Operation 133 is executed following operation 132. The third coagulation liquid comprises one or more non-solvents of the binder polymer in a concentration larger than the concentration of one or more nonsolvents in the first coagulation liquid, and larger than or equal to the concentration of the one or more non-solvents in the second coagulation liquid.

[0065] The concentration of the non-solvent (or mixture of non-solvents) in the third coagulation liquid is advantageously between 30% by weight and 100% by weight, advantageously at least 50% by weight, at least 60% by weight, or at least 70% by weight, and possibly 90% by weight or less.

[0066] Operation 13 can comprise even additional operations of contacting the film with one or more further coagulation liquids. One advantageous concept to the operations 131 , 132, optionally 133 and optionally further operations is that the film is sequentially contacted with coagulation liquids having increasing concentrations of oneor more non-solvents of the binder polymer. It will be appreciated that the non-solvents in the first, second, third and possibly further coagulation liquids can be different, but are advantageously the same.

[0067] In some examples, the concentration of the non-solvent (or mixture of non-solvents) is between 10% by weight and 50% by weight in the first coagulation liquid (operation 131), between 50% by weight and 100% by weight, advantageously between 55% and 95% by weight, in the second coagulation liquid (operation 132), and between 70% by weight and 100% by weight in the third coagulation liquid (operation 133).

[0068] The non-solvent utilized in any of the operations 13, is a solvent in which the binder polymer is substantially insoluble, particularly in which the binder polymer is completely insoluble. The non-solvent can be appropriately selected depending on the type of the binder polymer used. Specific examples of the non-solvent include, but are not limited to, water and lower alkyl alcohols (between 1 and 5, preferably between 1 and 4 carbon atoms), such as methanol, ethanol, propyl alcohol (1 -propanol), isopropyl alcohol and butyl alcohol (1 -butanol and 2-butanol). The non-solvent can be isobutyl alcohol. Of these, water and isopropyl alcohol are preferred.

[0069] The coagulation liquids having less than a 100% by weight nonsolvent concentration (e.g., the first coagulation liquid and possibly the second and even third coagulation liquid) advantageously comprise one or more solvents of the binder polymer, which may be the same as, or different from, the one or more solvents utilized in the membrane forming suspension. The concentration of the one or more solvents in the first coagulation liquid (operation 131) can be at least 30% by weight, advantageously at least 40% by weight, advantageously at least 50% by weight, e.g. 60% by weight or more, and can be 90% by weight or less, or 80% by weight or less. The concentration of the one or more solvents in the second coagulation liquid (operation 132) is advantageously 70% by weight or less, or 50% by weight or less, and is advantageously at least 10% by weight, or at least 20% by weight. It will be appreciated that the concentration of the one or more solvents in the second coagulation liquid is advantageously smaller than the concentration of the one or more solvents in the first coagulation liquid (in parts by weight).

[0070] The contact time (or exposure time) of the film with the coagulation liquids having smaller non-solvent concentration, such as the first coagulation liquid are appropriately selected to obtain a desired pore structure. Particularly, the contact time of the film with the first coagulation liquid is advantageously between 5 minutes and 1 hour, advantageously between 7 minutes and 45 minutes, such as between 8 minutes and30 minutes. A longer contact time advantageously results in a more uniform pore structure and possibly finer pores. However, a too long contact time may slow down the production rate and be economically unfeasible. The contact time of the film with the first coagulation liquid is advantageously not too long such that the phase separation process in the film is not yet completed when the film proceeds to operation 132. The contact time of the film with the second and further coagulation liquids can be smaller than, equal to or larger than the contact time with the first coagulation liquid, e.g. between 1 minute and 75 minutes, such as between 5 minutes and 60 minutes. The contact time obviously will depend on the thickness of the film.

[0071] The film is advantageously contacted with the various coagulation liquids by immersion in respective coagulation baths. Referring to Fig. 2, the manufacturing plant 20 can comprise multiple coagulation baths, and three coagulation baths 231 , 232 and 233 are shown by way of illustration. A film conveyor system 210 is configured to feed the film 202 through each coagulation bath and from one coagulation bath to the next one. The first coagulation bath 231 is filled with the first coagulation liquid, to execute operation 131.

[0072] The coating apparatus 22 is advantageously arranged above the first coagulation bath 231 . To prevent exposure of the film 202 to any non-solvent vapour, the gap between the outlet of the coating apparatus 22 and the liquid level of the first coagulation bath can be as small as possible. It may alternatively be possible to arrange the coating apparatus 22 such that its outlet is at or below the liquid level of the coagulation bath. In addition or alternatively, vapour-induced phase separation is prevented by keeping the first coagulation bath 231 at room temperature or below, as indicated above.

[0073] Between operation 12 and operation 131 , the film 202 may nevertheless be exposed to (ambient) air, particularly where the coating apparatus 22 is arranged somewhat remote from the first coagulation bath 231 containing the first coagulation liquid, e.g. with a clearance or gap in between. It will be appreciated that the air advantageously has a low relative humidity to prevent exposure to a non-solvent (water) vapour phase that may be formed above the coagulation bath. Exposure of the cast film to the non-solvent vapour can be expressed in terms of amount of vapour contact. The amount of vapour contact Pvc = pw. trrefers to the partial pressure pwof the non-solvent vapour in the ambient in which the film 202 travels between the outlet of the coating apparatus 22 and the first coagulation bath 231 , multiplied by the residence time trof the cast film in this ambient. When the non-solvent liquid is water, the amount of vapour contact can be expressed as: Pvc = RH . ps. tr, with RH the relative humidity ofthe air in the gap and psthe (saturation) vapour pressure of water at the temperature of the air in the gap. For continuous processes, trcan be determined by multiplication of the gap clearance and the conveyor speed. As an illustrative example, for air at 25°C (ps= 23.8 mm Hg), RH = 60% and a residence time tr= 3 s, Pvc = 42.84 mm Hg.s. Conversely, for air at 40°C (ps= 55.3 mm Hg), RH = 95% and tr= 3 s, Pvc = 157.60 mm Hg.s. Advantageously, substantial exposure of the cast film to non-solvent vapour is prevented when the amount of non-solvent vapour contact Pvc is 100 mm Hg.s or less, advantageously 80 mm Hg.s or less, advantageously 60 mm Hg.s or less, such as 50 mm Hg.s or less. Advantageously, the relative humidity of the air ambient contacting the film prior to immersion in the first coagulation liquid is 90% or less, advantageously 70% or less, advantageously 60% or less.

[0074] The film 202 is advantageously guided inside the first coagulation bath, e.g. by conveyor system 210, to define an appropriate residence time of the film 202 in the first coagulation bath 231 , corresponding to the contact time indicated above. Thereafter, the film 202 is guided to exit the first coagulation bath 231 and to enter the second coagulation bath 232. The second coagulation bath 232 is filled with the second coagulation liquid as indicated above, and is configured to execute operation 132. Thereafter, the film 202 is guided to exit the second coagulation bath 232 and possibly to enter a third coagulation bath 233, which is filled with the third coagulation liquid as indicated above, to execute operation 133. It will be appreciated that the second and third coagulation baths 232, 233 can be smaller than, of equal size as, or larger than the first coagulation bath 231 , depending on the residence time of the film 202.

[0075] At least the first coagulation bath 231 and possibly the further coagulation baths 232, 233, can comprise a temperature control system 239 configured to control a temperature of the coagulation liquid inside the respective coagulation bath.

[0076] It is alternatively possible to provide a single coagulation bath which is sequentially flushed with the first, second and third coagulation liquids, to thereby execute operations 131-133 in a single coagulation bath. Such a solution, while reducing the plant footprint may be technically more challenging in terms of flow control and production speed.

[0077] In an optional operation 14, one or more post-processing treatments may be executed on the separator membrane 203 obtained from operation 13. A possible post-processing treatment can be wetting of the separator membrane with an appropriate liquid to preserve the properties of the separator membrane during transport, e.g. a nonsolvent or a mixture of non-solvents, such as water and glycerol, possibly in combination with a fungicide to prevent biological growth. The pores of the separator membrane areadvantageously at least partially and advantageously completely filled with liquid (i.e., partial or complete saturation) at packaging. The separator membrane can be kept wet in a bath 240, e.g. at room temperature prior to being rolled up onto a roll 212. Roll 212 is advantageously at least partially immersed in a wetting bath 241 to keep the separator membrane wet.

[0078] In addition or alternative to the coagulation liquids having sequentially increasing concentrations of one or more non-solvents of the binder polymer, operations 132, 133, etc. can involve coagulation liquids at sequentially increasing temperatures. Referring to Fig. 3, operation 13 can comprise operations 131 , 132, 133 in which the film is sequentially contacted with coagulation liquids having sequentially increasing concentration of the one or more non-solvents. The coagulation liquids of operations 131 and 132 may be at a same or different temperature, which may be increasing from operation 131 to operation 132. Operation 13 can comprise further operations 133, 134 and 135 in which the film is sequentially contacted with further coagulation liquids. The coagulation liquids of operations 133, 134, 135 can have a same composition, e.g. consist 100% of the one or more non-solvents, preferably water, and these coagulation liquids can have a sequentially increasing temperature. In some examples, the temperature of the coagulation liquid evolves from a temperature Ti between 25°C and 50°C in operation 133 to a temperature T3 between 55°C and 95°C in operation 135. The temperature T2 of the coagulation liquid in operation 134 can be between 35°C and 75°C. Advantageously, T1 < T2 < T3. In some examples, the temperature of the coagulation liquid can be between 35°C and 55°C in operation 133, between 60°C and 75°C in operation 134 and between 80°C and 95°C in operation 135. Such elevated temperatures can assist in removing any additives, such as the pore control additives, as well as solvent remains from the separator membrane, and provide long-lasting stability to the separator membrane. Any of the operations 133-135, e.g. operation 135, can involve a longer contact time of the separator membrane with the respective coagulation liquid at elevated temperature, such as a longer immersion time in the coagulation bath 235, to ensure that any solvent still trapped in the pores of the separator membrane is washed out. This is illustrated in Fig. 4 with the dashed lines.

[0079] Referring to Fig. 4, the plant 20 can comprise coagulation baths231-235 arranged in sequence, with film conveyor system 210 configured to feed the film 202 from one coagulation bath to the next one. The three last coagulation baths 233, 234, 235 are configured to execute operations 133, 134, 135 respectively and can comprise respective temperature control systems 239 to control a temperature of therespective coagulation bath such that they are maintained at a sequentially increasing temperature.

[0080] It will be appreciated that it is possible to combine the operations131-132 and 133-135, e.g. to provide a sequence of operations in which the coagulation liquids have both sequentially increasing non-solvent concentrations and sequentially increasing temperatures. Advantageously, all of the operations 133-135, utilize a coagulation liquid consisting completely of the one or more non-solvents, i.e., in a concentration of substantially 100% by weight. It will be appreciated that operation 132 can be dispensed with and the film proceeds from operation 131 (coagulation bath 231) directly to one or more of operations 133-135 (coagulation baths 233-235). In addition, or alternatively, one or more of operations 133-135 can be dispensed with. In some examples, the operation 13 comprises a sequence of operations 131 , 133 and 135 and operations 132 and 134 are dispensed with. The concentration of the non-solvent (or mixture of non-solvents) can be between 10% by weight and 50% by weight in the first coagulation liquid (operation 131) and between 70% by weight and 100% by weight, possibly between 90% by weight and 100% by weight or even 100% by weight in operations 133 and 135. The temperature of the coagulation liquids can be between 5°C and 25°C in operation 131 , between 35°C and 55°C in operation 133 and between 80°C and 95°C in operation 135.

[0081] Operation 14 can comprise a washing bath 240, e.g. at 25°C (or room temperature), to cool down the hot separator membranes exiting the hot coagulation bath of operation 135 to keep the separator membranes at least partially wet. The washing bath may be filled with water or a mixture of water with any other nonsolvent such as glycerol.Pore control additive

[0082] According to aspects of the present disclosure, improved properties of the separator membranes are obtained when, in addition or alternatively to the particular sequence of operation 13 as described above, a pore control additive having a relatively low molecular weight is utilized in the membrane forming suspension. It has been surprisingly observed that such low molecular weight pore control additives, possibly along with the slower phase separation (coagulation) process as described above, result in improved pore structures of the obtained separator membranes, with finer internal pores and a more uniform pore structure, which furthermore has shown improved stability over time in aggressive alkaline environments. Without wishing to be bound by theory, such low molecular weight pore control additives are believed to act as dispersants, maintaining a proper dispersion of the inorganic filler particles and avoidingagglomeration of these filler particles. In addition, their smaller size allows the pore control additive to be easily and completely removed in the various operations 13. This reduces the need of possible further post-treatment processes 14. Weight average molecular weight of organic compounds can be determined by gel permeation chromatography (GPC).

[0083] Advantageously, the pore control additive has a weight average molecular weight of 7500 Da (g / mol) or less, advantageously 4000 Da or less, advantageously 2500 Da or less, advantageously 2000 Da or less, such as 1600 Da or less, or 1000 Da or less, and advantageously at least 100 Da, such as at least 150 Da, at least 350 Da, or at least 550 Da. In some examples, the pore control additive is a polymer which is liquid at atmospheric pressure and a temperature between 20°C and 60°C. Specifically, the pore control additive is a polymer which has a melting point of 60°C or less (at atmospheric pressure). Such pore control additives typically are liquids or waxes at ambient conditions of temperature and pressure. Specific examples of suitable pore control additives are polyols, advantageously polyether polyols, such as polyether glycol, particularly polyethylene glycol (PEG) and polypropylene glycol (PPG). Other examples are polyglycol and branched polyethyleneimines. Particularly preferred pore control additives are polyethylene glycol and polypropylene glycol with a weight average molecular weight between 180 Da and 1600 Da, as they are soluble in, and possibly miscible with, most of the solvents and most of the non-solvents, specifically water and lower alkyl alcohols such as isopropyl alcohol. Advantageously, the pore control additive is selected such that, even when added to the membrane forming suspension in relatively large proportions, it prevents inadvertent phase separation of the binder polymer induced by the pore control additive. In addition, the pore control additive is advantageously soluble in, and possibly even miscible with, the one or more solvents utilized to prepare the membrane forming suspension and soluble in the one or more non-solvents utilized in the coagulation liquids.

[0084] The pore control additive can refer to a mixture of pore control additive compounds, each of which may have different weight average molecular weights and each of these weight average molecular weights falling in the ranges as indicated above. Specific examples of such combinations are mixtures of PEG having different molecular weights. It will be appreciated that the membrane forming suspension advantageously does not comprise any pore control additive or possibly further organic compound (apart from the binder polymer) having a weight average molecular weight exceeding 7500 Da.

[0085] A particular advantage of such low molecular weight pore control additives is that they can act both as dispersant and / or stabilizer of the inorganic filler particles and as thinning agents of the membrane forming suspension, in contrast to high molecular weight pore control additives which have a secondary effect of thickening. Low molecular weight and possibly liquid pore control additives allow to increase the binder polymer content in the membrane forming suspension for a given viscosity. It can be beneficial when the pore control additive has a low molecular weight as indicated, and possibly a low melting point as indicated above (e.g., 60°C or less), as it may result in an improved pore structure and will facilitate removal of it from the separator membrane without requiring high temperatures of downstream coagulation baths. This results in separator membranes with improved mechanical properties. In addition, the low molecular weight additives are typically more economical than the high molecular weight additives utilized in the prior art, allowing to decrease manufacturing costs. Advantageously, a ratio of amount of the pore control additive (A) to a total amount of the pore control additive (A) and the binder polymer (P) in the membrane forming suspension, A / [A + P], is between 0.3 and 0.95 by weight, advantageously between 0.4 and 0.9 by weight, advantageously between 0.5 and 0.85 by weight. Higher amounts of the pore control additive advantageously result in separator membranes having higher porosity. Advantageously, a ratio of amount the binder polymer (P) to a total amount of the solvent (S), the pore control additive (A) and the binder polymer (P) in the membrane forming suspension, P / [S + A + P], is between 0.08 and 0.28 by weight, advantageously between 0.09 and 0.25 by weight, advantageously between 0.10 and 0.20 by weight, advantageously 0.17 by weight or less. Advantageously, a ratio of amount the binder polymer (P) to a total amount of the solvent (S) and the binder polymer (P) in the membrane forming suspension, P / [S + P], is between 0.15 and 0.30 by weight, advantageously between 0.17 and 0.29 by weight, advantageously between 0.21 and 0.28 by weight.

[0086] Alternatively, the pore control additive can be a polymer which is solid at atmospheric pressure and at a temperature between 20°C and 60°C, particularly at a temperature of 20°C, e.g. a powder or a particulate material. Specific examples of such pore control additives are polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), hydroxypropyl methylcellulose (HPMC), hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), polyether glycols such as polyethylene glycol (PEG) and polypropylene glycol (PPG), dextran or a combination thereof. Such pore control additives advantageously have a weight averagemolecular weight of at least 550 Da, advantageously at least 900 Da, advantageously at least 1200 Da, advantageously at least 2400 Da, and advantageously at least 4000 Da.

[0087] The one or more solvents can account for the remainder of the first coagulation liquid (in operation 131 and coagulation bath 231) and / or the second coagulation liquid (in operation 132 and coagulation bath 232) and / or further coagulation liquids, e.g. until achieving 100% by weight. It is alternatively possible to add one or more additives to the first and / or further coagulation liquids. It has particularly been observed that adding the pore control additive to at least the first coagulation liquid can assist in preventing early removal of the pore control additive before the separator membrane is properly solidified. This is particularly true where the removal of the pore control additive is diffusion controlled, which is particularly the case for pore control additives having a relatively low molecular weight. These pore control additives are particularly polymers that are soluble in, and / or miscible with, the non-solvent. Advantageously, the first coagulation liquid comprises at least 5% by weight of the pore control additive, such as between 10% by weight and 80% by weight, advantageously between 15% by weight and 70% by weight. Particularly for low molecular weight pore control additives, it is possible to dispense with the solvent in the first coagulation liquid, such that the first coagulation liquid consists of the non-solvent and the pore control additive alone.

[0088] It will be appreciated that, as the phase separation process proceeds, solvent from the membrane forming suspension diffuses into the coagulation liquid, and non-solvent diffuses from the coagulation liquid into the membrane forming suspension of the film. As a result, the composition of the coagulation bath tends to change. The plant 20 therefore advantageously comprises appropriate control systems to refresh and / or recycle the coagulation liquids in the various coagulation baths so as to keep the composition of the coagulation liquids substantially constant over time, within predetermined limits.Porous separator membranes

[0089] Methods according to the present disclosure advantageously allow obtaining porous separator membranes having unique properties. These separator membranes are made of a porous material, referred to as a mixed matrix material, that is formed of, and possibly consists of, a continuous polymer binder phase in which inorganic filler particles are dispersed. The mixed matrix material advantageously does not comprise any pore control additive, which is advantageously completely removed from the mixed matrix material in the manufacturing process as described above. The mixed matrix material advantageously has an open porosity with interconnected and possibly tortuous pores. Advantageously, the inorganic filler particles are accessible viathe interconnected pores. The porous separator membranes are advantageously flat or planar membranes and may be reinforced. Alternatively, the porous separator membranes may be tubular, such as having an internal diameter of at least 10 mm. Electrolytic cells utilizing tubular separator membranes are known from US 7510633 B2.

[0090] Referring to Figs. 5 and 6, the separator membrane 50 comprises a first membrane face 501 on one side and a second membrane face 502 on an opposite side. Separator membrane 50 can be symmetric (Fig. 6), with pore structure having substantial mirror symmetry with respect to a median plane 503 between the first and second membrane faces 501 , 502. This is typical when the phase separation operations 13 are executed (simultaneously) on both sides of the separator membrane. Alternatively, the separator membrane can have an asymmetric structure from the first membrane face 501 to the second membrane face 502 (Fig. 5). This can be obtained when the film 202 is coated on a substantially impermeable liner which is immersed in the first coagulation bath along with the film. The thickness of the separator membranes, i.e. the distance between the first and second membrane faces 501 , 502 depends on the application, and is advantageously between 80 pm and 500 pm, such as between 100 pm and 350 pm, particularly between 120 pm and 280 pm, or between 350 pm and 500 pm.

[0091] The separator membrane 50 advantageously comprises a surface layer 51 adjacent to the first membrane face 501 and a bulk layer 52 internal to the separator membrane. The symmetric separator membrane comprises a substantially identical surface layer 51 at the second membrane face 502. The surface layer 51 corresponds to those parts of the film that have coagulated first in the phase separation operations (in the first coagulation liquid). Typically, the surface layer 51 is characterised by a porous structure with fine pores which are somewhat finer than the pores of the bulk layer 52. The surface layer 51 is typically denser than the bulk layer 52. As a result, the average pore size of the surface layer pores is advantageously smaller than the average pore size of the bulk layer pores. The asymmetric separator membrane (Fig. 5) can have a surface layer 55 adjacent to the second membrane face 502 which is different from the surface layer 51 at the first membrane face. Particularly, surface layer 55 has a porous structure with pores having an average size which is larger than the average size of the pores of the surface layer 51 and possibly larger than the average size of the pores of the bulk layer 52. The surface layer can have a thickness between 1 pm and 50 pm and advantageously at least 5 pm. The thickness of the surface layer 51 is typically proportional to the exposure time in the first coagulation bath 231 and can further depend on the composition and possibly on the temperature of the first coagulation bath.

[0092] The bulk layer 52 of the separator membrane 50 advantageously has an isotropic porous structure. Surprisingly, macrovoids are absent in the bulk layer. This is ascribed to the specific phase separation operations 13, in which the film is first contacted with a coagulation liquid having a lower non-solvent concentration, without exposure to the non-solvent vapour phase. Any reinforcement mesh 54 is typically arranged in the bulk layer 52. The reinforcement mesh advantageously has an open area between 50% and 95%.

[0093] Advantageously, the separator membrane 50 can comprise an intermediate layer 53 between the surface layer 51 and the bulk layer 52. The intermediate layer 53 is characterised by a gradient in pore size and / or porosity with pore size and / or porosity increasing from the surface layer 51 towards the bulk layer 52. The thickness of the intermediate layer will typically depend on the composition of the coagulation liquid and the contact time, and can be between 5 pm and 80 pm, particularly between 10 pm and 50 pm. The thicknesses of the surface layer 51 and of the intermediate layer 53 can be tailored by selecting appropriate compositions of the coagulation baths and appropriate contact times in these coagulation baths. Typically, the thickness of the surface layer 51 will increase and the thickness of the intermediate layer 53 decrease with increasing contact time of the film with the first coagulation bath. It will be appreciated that an intermediate layer is absent between the surface layer 55 and the bulk layer 52.

[0094] Experiments have shown that the separator membranes obtained according to the present disclosure have outstanding performance. The water permeability at 30°C of the separator membranes, after ageing for two weeks in a 30% by weight aqueous KOH solution at 85°C, is advantageously between 150 l / h / m2 / bar (i.e., l / (h.m2.bar)) and 2500 l / h / m2 / bar, advantageously between 200 l / h / m2 / bar and 2000 l / h / m2 / bar, such as between 250 l / h / m2 / bar and 900 l / h / m2 / bar, advantageously between 100 l / h / m2 / bar and 900 l / h / m2 / bar, and advantageously 790 l / h / m2 / bar or less, advantageously 750 l / h / m2 / bar or less.

[0095] The ionic resistance of the separator membranes, after ageing for two weeks in a 30% by weight KOH aqueous solution at 85°C, is advantageously between 0.02 Qcm2and 0.12 Qcm2, advantageously between 0.025 Qcm2and 0.09 Qcm2, and advantageously 0.08 Qcm2or less, or 0.07 Qcm2or less. These values of the ionic resistance are determined in a 30% by weight KOH aqueous solution at 30°C.

[0096] The water permeability and the ionic resistance of separator membranes according to the present disclosure is surprisingly stable over time due to the low molecular weight pore control additive which can be completely removed duringmanufacture. Advantageously, the above values of water permeability and / or ionic resistance hence apply equally to separator membranes that are not aged (i.e., virgin membranes).

[0097] The total porosity of the separator membrane is advantageously between 40% and 70% by volume, such as between 45% and 70% by volume, or between 45% and 65% by volume. The pore size distribution of the separator membrane advantageously features a sharp maximum with steep decay. The (local) maximum of the pore size distribution of the separator membrane, also referred to as the pore mode size, is advantageously between 0.20 pm and 0.80 pm, advantageously between 0.30 pm and 0.65 pm, advantageously between 0.35 pm and 0.55 pm. The pore size distribution advantageously has a standard deviation with respect to the (local) maximum, i.e. the mode size, of 0.20 pm or less, advantageously 0.15 pm or less.

[0098] The open, connected pores of the porous separator membranes can be assessed using the Bubble Point Test method described in American Society for Testing and Materials Standard (ASTM) Method F316. This technique is based on the displacement of a wetting liquid embedded in the separator by applying an inert pressurised gas. The wetting liquid can be water. The minimum pressure required to force liquid out of the pores of the separator membrane is a measure of the largest pore size. The pressure at which a steady stream of bubbles at a flow rate of 100 ml / min appears in this test is the bubble point pressure. Typically, the bubble point pressure of the porous separator membranes is between 0.5 bar and 5 bar, advantageously between 1 bar and 5 bar, advantageously between 2 bar and 4.5 bar.

[0099] Separator membranes according to the disclosure can be utilized as diaphragm in various electrochemical applications such as electrolysers, batteries and fuel cells, particularly in alkaline water electrolysis, e.g. utilizing KOH or NaOH as the electrolyte, possibly in an aqueous solution at a concentration between 20% and 40% by weight and possibly at a temperature between 50°C and 130°C.

[0100] Referring to Fig. 14, an electrolyser 60 which can be configured for alkaline water electrolysis, comprises at least one electrolytic cell 600. The electrolytic cell 600 comprises a cathode compartment 61 and an anode compartment 62 separated by the porous separator membrane 50. Both the anode and the cathode compartment are filled with an aqueous electrolyte, such as an aqueous KOH solution. The anode and possibly the cathode can be arranged as so-called zero gap electrodes, with no gap between electrode and separator membrane 50. At the cathode 610, hydrogen gas and hydroxyl ions are produced through the equation:4e- + 4 H2O 2H2+ 4 OH'.At the anode 620, the hydroxyl ions are converted to oxygen gas through the equation: 4 OH’ O2+ 2 H2O + 4e- .The hydrogen and oxygen gas are separated from the electrolyte in respective gas separators 63 and 64.Experiments

[0101] Water permeability measurements were performed utilizing an inline stainless steel filter holder (Sartorius, Germany) for circular 25 mm diameter membrane samples. The filter holder allows to realize a net filtration area of 3 cm2. The membrane samples were punched from membrane sheets that were prepared from the examples listed below. These samples were left to soak in a 30% by weight KOH aqueous solution at 30°C for 24 h prior to testing. The inlet of the filter holder was connected to the outlet of a 1 litre pressure vessel filled with demineralized water at 20°C. The inlet of the pressure vessel was connected to pressurized air, the pressure of which was set via a control valve to realize a trans-membrane pressure of 1 bar. The permeate water from the filter holder was collected in a beaker that was placed on a precision balance (0.01 g). The permeate mass collected during a 1 minute timeframe was recorded. For each sample, three consecutive 1 minute measurements were performed. Furthermore, from each membrane sheet, three membrane samples were obtained and tested. It follows that each water permeability test results from the average of nine permeability tests as described above.

[0102] Ionic resistance measurements were performed utilizing a 4 electrode conductivity cell (TetraCon® 925, Xylem Analytics Germany) connected to a Multi 3630 IDS (Xylem Analytics Germany) precision meter. The conductivity cell was immersed in a 100 ml glass beaker filled with a 30% by weight KOH aqueous solution. The beaker was held in a water bath kept at 30°C. Rectangular 3 cm by 15 cm membrane ribbons were cut from the membrane sheets prepared from the experiments and left to soak in the 30% by weight KOH solution at 30°C for 24 h. These ribbons were then inserted in the conductivity cell and the measurements were obtained at three central positions of the rectangular ribbon spaced apart by 3 cm. In addition, conductivity measurements of the free electrolyte were obtained with the same conductivity cell. The ionic resistance of the membrane samples was obtained from the difference between the conductivity of the membrane samples and the conductivity of the free electrolyte.

[0103] Comparative Example 1-1 : A membrane forming suspension was prepared according to the ingredients listed in Table 1 . Firstly, the binder polymer PPSLI was dissolved in the NBP solvent by mixing until a clear (transparent) solution of the binder polymer was obtained. Next, the pore control additive PVP was added to thebinder polymer solution and mixed until again a clear (transparent) solution was obtained. The solution thus obtained and the inorganic filler were poured in a vacuum high energy mixer (Thinky Mixer type ARV-310P CE, Thinky Corporation) and mixed under 0.5 bar vacuum, first at 500 RPM (rotations per minute) for two minutes, next at 2000 RPM for five minutes to obtain a dope (membrane forming suspension). The inorganic filler ZrC>2 grade E101 (Luxfer Mel Technologies) had an average particle size of 0.8 pm. The PVP additive had a weight average molecular weight of 50 kDa. The weight ratio of binder polymer to the binder polymer and solvent (P / P + S) in the dope was 0.17. The weight ratio of binder polymer to the binder polymer, solvent and pore control additive (P / P + S + A) in the dope was 0.16. The amount of inorganic filler relative to the binder polymer was 85 parts by weight to 15 parts by weight.

[0104] The dope as obtained via the vacuum high energy mixer had a temperature of 60°C and was immediately cast on a pre-heated glass plate onto which a PEEK monofilament mesh reinforcing sheet was placed. The reinforcing sheet had a thickness of 105 pm and an open area of 62%. The dope was cast in a film such that the reinforcement sheet was completely embedded.

[0105] The cast film was immersed in a first coagulation bath filled with a first coagulation liquid consisting of 30% by weight deionized water and 70% by weight NBP (Eastman TamiSolve™ NxG) for 10 minutes. The first coagulation liquid was at a temperature of 10°C to avoid exposure to water vapour. Next, the cast film was immersed in a second coagulation bath filled with 100% deionized water at 50°C for 1 hour followed by immersion in a third bath filled with 100% deionized water at 90°C for 30 minutes to remove (wash out) any solvent trapped in the separator membrane.

[0106] The obtained separator membrane was detached from the glass plate. The final thickness was 170 pm. The structure of the membranes was investigated via scanning electron microscopy (SEM), and SEM images are illustrated in Fig. 7 and Fig. 8. The structure showed a surface layer 51 , an intermediate layer 53 with teardropshaped macropores 531 and an isotropic bulk layer 52.Table 1 : Membrane dope composition of Comparative Example 1-1 [P: binder polymer; F: inorganic filler; A: pore control additive; S: solvent]

[0107] The porosity of the separator membrane was investigated via mercury porosimetry. The total porosity was 49% with average pore size of 0.11 pm. The pore mode size was 0.417 pm.

[0108] The membrane was tested for water permeability at 30°C and ionic resistance in 30% by weight aqueous KOH solution at 30°C, both as virgin membrane and after ageing for two weeks in 30% by weight aqueous KOH solution at 85°C. The test results are shown in Table 2 as ‘CEx1-1’.

[0109] Comparative Example 1-2: The same procedure was followed as for Comparative Example 1-1 , except that the coagulation liquid in the first coagulation bath was 100% isopropyl alcohol (at a temperature of 10°C). The membrane structure is shown in the SEM images of Fig. 9 and Fig. 10. Comparing Figs. 9-10 with Figs. 7-8, it can be seen that the membrane of Comparative Example 1-2 has large macrovoids in the bulk layer (Fig. 9), which is hence not isotropic. Furthermore, the images do not show a surface layer distinct from the bulk layer (Fig. 10). Porosimetry measurements indicated a total porosity of 57% and a mode pore size of 0.205 pm, which is half as small as the mode pore size of Comparative Example 1-1.

[0110] Comparative Example 1-3: The same procedure was followed as for Comparative Example 1-1 , except that PVP Luvitec® K85 (BASF) was utilized as pore control additive (in same amounts as Table 1) instead of PVP K30 and the coagulation liquid in the first coagulation bath was 100% deionized water. PVP K85 had a weight average molecular weight of 1100 kDa. The permeability and ionic resistance results are indicated in Table 2 as ‘CEx1-3’.Table 2: Water permeability and ionic resistance measurements (Virgin: virgin membrane; Aged: ageing for two weeks in 30% by weight aqueous KOH solution at 85°C)

[0111] From Table 2 it can be seen that the water permeability values increase after ageing. Without wishing to be bound by theory, it is believed that the increase in the water permeability after ageing is due to disintegration of the high molecular weight pore control additive, leaving larger pores behind in the separator membrane.

[0112] Example 1 : A dope (membrane forming suspension) was prepared according to the ingredients listed in Table 3 and following the same procedure as Comparative Example 1-1. The inorganic filler ZrC>2 grade E101 (Luxfer Mel Technologies) had an average particle size of 0.8 pm. The PEG-200 (polyethylene glycol) pore control additive (CARBOWAX™ Polyethylene Glycol (PEG) 200, The Dow Chemical Company) was a liquid and had a weight average molecular weight between 190 and 210 Da. The molecular weight of the binder polymer Ultrason® S2010 was between 56000 Da and 59000 Da. The weight ratio of binder polymer P to the binder polymer P and solvent S in the dope, P / P + S = 0.21 . The weight ratio of binder polymer P to the binder polymer P, solvent S and pore control additive A in the dope, P / P + S + A = 0.17 and A / A + P = 0.53. The amount of inorganic filler relative to the binder polymer was 85 parts by weight to 15 parts by weight.

[0113] The dope was cast on a glass plate onto which a PEEK monofilament mesh reinforcing sheet was placed. The reinforcing sheet had a thickness of 105 pm and an open area of 62%. The dope was cast in films of two different thicknesses and such that the reinforcement sheet was completely embedded.

[0114] The glass plates with the cast films were immersed in a first coagulation bath filled with a first coagulation liquid consisting of 30% by weight deionized water and 70% by weight NBP (Eastman TamiSolve™ NxG) for 10 minutes. A time of about 5 seconds elapsed between casting the film and immersing the film in the first coagulation bath, during which the films were exposed to air at ambient conditions. The first coagulation liquid was at a temperature of 10°C to avoid creating a water vapour phase above the coagulation bath and hence avoid exposure of the film to a water vapour phase. Next, the cast films were immersed in a second coagulation bath filled with 100% deionized water at 50°C for 1 hour followed by immersion in a third coagulation bath filled with 100% deionized water at 90°C for 30 minutes to remove (wash out) any solvent trapped in the separator membrane.Table 3: Membrane dope composition of Example 1 [P: binder polymer; F: inorganic filler; A: pore control additive; S: solvent]

[0115] The obtained separator membranes were detached from the glass plates. The final thickness was 180 pm and 260 pm.

[0116] The membranes were tested for water permeability at 30°C and ionic resistance in 30% by weight aqueous KOH solution at 30°C, both as virgin membrane and after ageing for two weeks in 30% by weight aqueous KOH solution at 85°C. The test results are shown in Table 4 as ‘ExT.Table 4: Water permeability and ionic resistance measurements (Virgin: virgin membrane; Aged: ageing for two weeks in 30% by weight aqueous KOH solution at 85°C)

[0117] From Table 4 it can be seen that the Example 1 membranes show excellent stability of water permeability and ionic resistance values even after ageing. These values are furthermore optimal for use of the separator membranes for alkaline water electrolysis.

[0118] Example 2: Multiple dopes (membrane forming suspension) were prepared according to the recipe listed in Tables 5 and 6 and following the same procedure as Example 1. Particularly, the binder polymer PSU (type lldel® P3703 or lldel® P3500, Solvay Specialty Polymers) was dissolved in NBP (Eastman TamiSolve™ NxG) solvent by mixing until a clear (transparent) solution of the binder polymer was obtained. Next, the pore control additive PEG or PPG was added to the binder polymer solution and mixed until again a clear (transparent) solution was obtained. The solution thus obtained and the inorganic filler ZrO2 were poured in a vacuum high energy mixer (Thinky Mixer type ARV-31 OP CE, Thinky Corporation) and mixed under 0.5 bar vacuum, first at 500 RPM (rotations per minute) for two minutes, next at 2000 RPM for five minutes to obtain a dope (membrane forming suspension). The molecular weight of binder polymer PSU P3703 was between 55000 Da (g / mol) and 59000 Da. The molecular weight of PSU P3500 was between 77000 Da and 84000 Da. The inorganic filler was ZrO2 grade E101 (Luxfer Mel Technologies) and had an average particle size of 0.8 pm. The PEG-600 and PEG-1000 (polyethylene glycol) pore control additives (Dow Carbowax™) were waxes at room temperature with a weight average molecular weight between 570 and 630 Da and between 950 Da and 1050 Da, respectively. The PPG-600(propylene glycol) pore control additive (Carl Roth) was liquid at room temperature with a weight average molecular weight of about 600 Da.

[0119] Each of the dopes was cast on a glass plate onto which a PEEK monofilament mesh reinforcing sheet was placed. Two PEEK reinforcing sheets were utilized, according to Table 7. The reinforcing sheet 220 / 62 had a thickness of 105 pm, an open area of 62% and a mesh size of 220 pm. The reinforcing sheet 195 / 75 had a thickness of 75 pm, an open area of 75% and a mesh size of 195 pm. The dope was cast in films of different thicknesses and such that the reinforcement sheet was completely embedded.

[0120] The glass plates with the cast films were immersed in a first coagulation bath filled with a first coagulation liquid consisting of 30% by weight deionized water and 70% by weight NBP (Eastman TamiSolve™ NxG) for 10 minutes. The separator membranes detached from the glass plates in the first coagulation bath. In some experiments (Table 7), the first coagulation liquid was at a temperature of 8°C to avoid exposure to a water vapour phase. A short time of about 5 seconds elapsed between casting the films and immersing them in the first coagulation bath, during which the cast films were exposed to air at ambient conditions. The ambient temperature above the first coagulation bath varied between 16°C and 19°C and relative humidity varied between 39% and 50%. Experiment Ex2-1 was repeated with the first coagulation liquid brought to a temperature of 20°C (denoted Ex2-1(b) in Table 7). In the latter experiment, the ambient temperature above the first coagulation bath was 20°C and the relative humidity was 52%. It follows that in all experiments, the film is not exposed to any substantial water vapour phase and no substantial vapour induced phase separation (VIPS) occurs. Next, the cast films were immersed in a second coagulation bath filled with 100% deionized water at 50°C for 1 hour followed by immersion in a third coagulation bath filled with 100% deionized water at 90°C for 30 minutes to remove (wash out) any solvent trapped in the separator membrane.

[0121] With each dope composition, three to four separator membranes were made. The final thickness, as an average measurement of three film castings (three separator membranes) is indicated in Table 7. SEM images were obtained from cross sections of the separator membranes Ex2-1 (a) and Ex2-2 and these are shown in Figs. 11-12 for Ex2-1(a) at magnifications of 250 and 5000 respectively and in Fig. 13 for Ex2- 2 at magnification of 5000. It can be seen from the SEM images that the separator membranes comprise a surface layer 51 adjacent to the membrane face (top face in Figs. 11-12) and a bulk layer 52 internal to the separator membrane, the latter having an isotropic porous structure. Macro-voids are advantageously absent in the bulk layer. Inaddition, unlike the membranes of Comparative Example 1-1, the membranes of Example 2 have no intermediate layer between the surface layer and the bulk layer. It will be appreciated that due to the manufacturing process in which the dope is cast on a glass plate, the membranes of Example 2 are asymmetric and may not have a surface layer at the opposite membrane face (bottom face in Fig. 11). These membranes can however easily be made symmetric by adapting the casting method.

[0122] The membranes were tested for water permeability at 30°C and ionic resistance in 30% by weight aqueous KOH solution at 30°C, as virgin membrane. Table 7 gives the test results, from which it can be seen that the membranes according to the present disclosure have excellent water permeability and ionic resistance values. It will further be appreciated that the membranes of Example 2 are all asymmetrical membranes with a surface layer on one side only, as they were cast and immersed on a glass plate. The water permeability of the symmetrical variants of these membranes will be even lower. It follows that the performance of the separator membranes obtained according to the present disclosure can be tailored to make them optimal for use for alkaline water electrolysis. By analogy with Table 4 showing water permeability and ionic resistance measurements on virgin and aged membranes, it can be said that the water permeability and ionic resistance values of indicated in Table 7 also apply to aged versions of these membrane samples.Table 5: Membrane dope compositions of Example 2, by weight [P: binder polymer; F: inorganic filler; A: pore control additive; S: solvent]Table 6: Composition ratios of the dope compositions of Example 2, by weight [P: binder polymer; F: inorganic filler; A: pore control additive; S: solvent]Table 7: Reinforcement mesh type, temperature of first coagulation bath, dry thickness of separator membrane and results of water permeability and ionic resistance measurements of the virgin separator membranes of experiments of Example 2

[0123] Capillary flow porometer measurements were performed on the membranes of Ex2-1 , Ex2-2 and Ex2-6. Three samples of each were tested in a Porolux 500 capillary flow porometer utilizing a fluorinated hydrocarbon as wetting liquid (surface tension 16 dyn / cm) to determine bubble point pressure, smallest pore size and mean flow pore size. The Bubble point was determined as the size at a flow rate of 100 ml / min. The results are listed in Table 8. From these results it can be seen that the porosity of the various membranes obtained according to methods of the present disclosure are consistent.

[0124] Mercury intrusion porosimetry investigations were performed on membrane Ex2-6 on a Micromeritics AutoPore 9505 analyzer in the pressure range 0.002 - 220 MPa in accordance with ISO 15901-1 :2016. Two membrane samples were degassed in vacuum at room temperature for 16 hours prior to mercury intrusion testing. During mercury intrusion, the filling of voids internal to the membrane samples was observed to occur in a pressure range between about 1.5 MPa and 60 MPa. The pores in the membrane had a diameter between 0.02 pm and 1 pm, with a mode at 0.26 pm. The specific total pore volume was 0.67 cm3 / g and the total porosity was 67%. The specific intra-particle volume was 0.48 cm3 / g and the intra-particle porosity was 59%, both determined in a pressure range between 1 MPa and 220 MPa. The bulk density was 1.00 g / cm3and the apparent (skeletal) density was 3.07 g / cm3.Table 8: Capillary flow Porometer measurements on separator membranes of Example 2; indicated values are average of three measurements

[0125] Example 3: The same procedure was followed as for Example 2, except that the coagulation liquid in the first coagulation bath was a mixture of 30% NBP and 70% deionized water on weight basis. The dope composition was the same as for Example Ex2-3. The temperature of the first coagulation bath was 8°C, and relative humidity above the coagulation bath was 52% at 20°C. Hence, exposure to water vapour phase was avoided (no water vapour phase above first coagulation bath). Results are included in Table 9 as ‘Ex3’.

[0126] Comparative Example 2: The same procedure was followed as forExample 2, except that the coagulation liquid in the first coagulation bath was 100% deionized water at a temperature of 50°C. The first coagulation bath was furthermore covered with a dome-shaped lid to create a water vapour phase above the first coagulation bath. The temperature in the ambient above the first coagulation bath (under the lid) was measured to be 49.5°C with a relative humidity of 95.5%. The membrane dope composition of Ex2-1 and Ex2-2 were used to cast films on glass plates which were subsequently held for about 6 seconds below the dome shaped lid (i.e., in the water vapour phase) before immersing them in the first coagulation bath. On the obtained separator membranes, water permeability and ionic resistance measurements were performed, as listed in Table 9 (examples CEx2-1 and CEx2-2 respectively). It can be seen from Table 9 that the exposure of the cast film to a water vapour phase prior to immersion in the first coagulation bath significantly increases the water permeability of the separator membranes. Although water permeability could be reduced by increasing membrane thickness, this will in turn deteriorate the ionic resistance. Compared to these membranes, the separator membranes according to Example 2 hence show an improved performance, in particular for alkaline water electrolysis.Table 9: Reinforcement mesh type, temperature of first coagulation bath, thickness of separator membrane and results of water permeability and ionic resistance measurements of the virgin separator membranes of experiments of Example 3 and Comparative Example 2

[0127] Comparative Example 3: A dope composition was prepared according to the recipe of Ex2-4, except that PEG-10000 (Carl Roth Polyethylene glycol 10000) was used as pore control additive, with weight average molecular weight between 9000 Da and 11250 Da. A homogeneous dope mixture could however not be obtained due to demixing of the PEG pore control additive from the membrane forming suspension (at a temperature of 60°C).

[0128] Aspects of the present disclosure are set out in the following alphanumerically ordered clauses.A1. Method of manufacturing a porous separator membrane, the method comprising: preparing a suspension comprising an organic solvent, a binder polymer dissolved in the organic solvent, inorganic filler particles and an organic pore control additive, wherein the organic pore control additive has a weight average molecular weight of 200000 Da or less, casting the suspension into a film, subjecting the film to phase separation and removing the organic pore control additive, thereby forming the porous separator membrane.A2. Method of clause A1 , wherein subjecting the film to phase separation comprises: contacting the film with a first coagulation liquid, followed by contacting the film with a second coagulation liquid.A3. Method of clause A2, wherein the first coagulation liquid comprises one or more non-solvents of the binder polymer in a first total concentration of 50% by weight or less and the second coagulation liquid comprises one or more non-solvents of the binder polymer in a second total concentration larger than the first total concentration.A4. Method of clause A2 or A3, wherein the first coagulation liquid is at a first temperature and the second coagulation liquid is at a second temperature higher than the first temperature.A5. Method of any one of clause A2 to A4, wherein the film is not substantially exposed to a non-solvent vapour phase prior to contacting the film with the first coagulation liquid.A6. Method of any one of clauses A2 to A5, wherein an exposure time of contacting the film with the first coagulation liquid is at least 5 minutes.A7. Method of any one of the clauses A2 to A6, wherein the first coagulation liquid is at a temperature between 3°C and 25°C, preferably between 5°C and 15°C.A8. Method of any one of the clauses A2 to A7, wherein the second total concentration is between 30% by weight and 90% by weight.A9. Method of any one of the clauses A2 to 8, wherein the first coagulation liquid, and optionally the second coagulation liquid, comprises one or more organic solvents of the binder polymer in a total concentration of at least 30% by weight, preferably at least 50% by weight.A10. Method of any one of the clauses A2 to A9, wherein subjecting the film to phase separation comprises contacting the film with a third coagulation liquid following contacting the film with the second coagulation liquid, preferably wherein the third coagulation liquid comprises one or more non-solvents of the binder polymer in a third total concentration larger than the second total concentration, preferably wherein the third total concentration is between 60% by weight and 100% by weight.A11. Method of any one of the clauses A2 to A10, wherein the film is contacted with the first coagulation liquid in a first coagulation bath and the film is contacted with the second coagulation liquid in a second coagulation bath, optionally the film is contacted with the third coagulation liquid in a third coagulation bath.A12. Method of any one of the clauses A2 to A11 , wherein the organic pore control additive is a polymer which is soluble in the first coagulation liquid, such as being soluble in, and advantageously miscible with, the one or more non-solvents, and / or is soluble in, and advantageously miscible with, the solvent, preferably the organic pore control additive is a water-soluble polymer.A13. Method of clause A12, wherein the organic pore control additive is at least partially retained in the film between contacting the film with the first coagulation liquid and contacting the film with the second coagulation liquid.A14. Method of any one of the clauses A2 to A13, wherein the first coagulation liquid comprises at least 5% by weight of the organic pore control additive.A15. Method of any one of the clauses A1 to A14, wherein a ratio of amount of the binder polymer to a total amount of the solvent and the binder polymer in the suspension is between 0.15 and 0.3 by weight, preferably between 0.15 and 0.25 by weight.A16. Method of any one of the clauses A1 to A15, wherein a ratio of amount of the inorganic filler particles to a total amount of the inorganic filler particles and the binder polymer in the suspension is between 0.75 and 0.95 by weight.A17. Method of any one of the clauses A1 to A16, wherein casting the suspension into a film comprises casting the suspension on a porous reinforcement mesh to obtain the film.A18. Method of any one of the clauses A1 to A17, wherein the binder polymer is an aromatic hydrocarbon compound, preferably selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polybutylene naphthalate, polystyrene, polysulfone, polyethersulfone, polyphenylene sulfide, polyphenylsulfone, polyarylate, polyetherimide, polyimide, and polyamideimide.B1. Method of any one of the clauses A1 to A18, wherein the organic pore control additive has a weight average molecular weight of 7500 Da or less, preferably 4000 Da or less, preferably 2000 Da or less, preferably 1600 Da or less, and preferably at least 150 Da.B2. Method of clause B1 , wherein the organic pore control additive is a polyol, preferably a polyether polyol, most preferably one or a combination of polyethylene glycol and polypropylene glycol, or a branched polyethyleneimine.B3. Method of clause B1 or B2, wherein the organic pore control additive is a polymer which is liquid at a temperature between 20°C and 60°C and atmospheric pressure and / or which is liquid at a temperature of the first coagulation liquid and atmospheric pressure.B4. Method of any one of the clauses B1 to B3, wherein a ratio of amount of the organic pore control additive to a total amount of the organic pore control additive and the binder polymer in the suspension is between 0.3 and 0.95 by weight, preferably between 0.4 and 0.9 by weight.B5. Method of any one of the clauses B1 to B4, wherein a ratio of amount the binder polymer to a total amount of the organic solvent, the organic pore control additive and the binder polymer in the suspension is between 0.08 and 0.28 by weight, preferably between 0.09 and 0.25 by weight.C1. Porous separator membrane made of a material comprising or consisting of a polymeric binder phase and inorganic filler particles dispersed in the binder phase, wherein the porous separator membrane comprises a first membrane face, a second membrane face opposite the first membrane face, a porous surface layer adjacent the first membrane face and an isotropic porous bulk layer.C2. Porous separator membrane of clause C1 , wherein an average pore size of pores of the surface layer is smaller than an average size of pores of the bulk layer.C3. Porous separator membrane of clause C1 or C2, further comprising an intermediate layer between the surface layer and the bulk layer, wherein the intermediate layer comprises teardrop-shaped pores having pointed ends pointing towards the surface layer.C4. Porous separator membrane of any one of the clauses C1 to C3, having a water permeability at 30°C between 150 l / h / m2 / bar and 3000 l / h / m2 / bar after ageing for two weeks in a 30% by weight KOH aqueous solution at 85°C, preferably between 200 l / h / m2 / bar and 2000 l / h / m2 / bar.C5. Porous separator membrane of any one of clauses C1 to C4, having an ionic resistance, determined at 30°C in a 30% by weight KOH aqueous solution, between 0.02 Qcm2and 0.12 Qcm2after ageing of the porous separator membrane for two weeks in a 30% by weight KOH aqueous solution at 85°C, preferably between 0.025 Qcm2and 0.09 Qcm2.C6. Porous separator membrane of any one of the clauses C1 to C5, having a porosity between 40% and 70% by volume and preferably a pore size distribution with a local maximum between 0.20 pm and 0.80 pm, preferably between 0.30 pm and 0.65 pm, preferably between 0.35 pm and 0.55 pm as measured by mercury intrusion.C7. Porous separator membrane of clause C6, wherein the pore size distribution has a standard deviation with respect to the local maximum of 0.20 pm or less, preferably 0.15 pm or less.C8. Porous separator membrane of any one of the clauses C1 to C7, comprising a reinforcement mesh embedded between the first membrane face and the second membrane face.C9. Porous separator membrane of clause C8, wherein the reinforcement mesh has an open area between 50% and 95%.C10. Porous separator membrane of any one of the clauses C1 to C9, having a thickness from the first membrane face to the second membrane face between 80 pm and 500 pm.D1. Use of the porous separator membrane according to any one of the clauses C1 to C10 as a diaphragm in alkaline water electrolysis.D2. Use of an apparatus for manufacturing a porous separator membrane according to any one of the clauses C1 to C10, or for implementing the method according to any one of the clauses A1 to A18, or B1 to B5, the apparatus comprising: a casting system for casting a membrane forming suspension into a film, a first coagulation bath, a second coagulation bath, optionally a third coagulation bath, and a conveyor system for transporting the film from the casting system sequentially through the first, second and optionally third coagulation baths.

Claims

AMENDED CLAIMS received by the International Bureau on 14 October 2025 (14.10.2025)CLAIMS1. Method (10) of manufacturing a porous separator membrane (50), the method comprising: preparing (11) a suspension comprising an organic solvent, a binder polymer dissolved in the organic solvent, inorganic filler particles and an organic pore control additive dissolved in the organic solvent, casting (12) the suspension into a film (202), subjecting the film to phase separation (13) and removing the organic pore control additive, thereby forming the porous separator membrane, wherein subjecting the film to phase separation comprises contacting (131) the film with a first coagulation liquid, followed by contacting (132) the film with a second coagulation liquid, wherein the organic pore control additive has a weight average molecular weight between 150 Da and 7500 Da, wherein a ratio of amount of the organic pore control additive to a total amount of the organic pore control additive and the binder polymer in the suspension is between 0.3 and 0.95 by weight, wherein a ratio of amount of the inorganic filler particles to a total amount of the inorganic filler particles and the binder polymer in the suspension is between 0.75 and 0.95 by weight, and wherein a ratio of amount of the binder polymer to a total amount of the organic solvent and the binder polymer in the suspension is between 0.15 and 0.30 by weight, wherein the first coagulation liquid comprises one or more nonsolvents of the binder polymer in a first total concentration of 70% by weight or less and at least one of: an organic solvent of the binder polymer and the organic pore control additive, wherein the second coagulation liquid comprises one or more nonsolvents of the binder polymer in a second total concentration larger than the first total concentration, and wherein the film is not exposed to a non-solvent vapour phase prior to contacting the film with the first coagulation liquid.

2. Method of claim 1 , wherein the organic pore control additive is miscible with the one or more non-solvents.

3. Method of claim 1 or 2, wherein the organic pore control additive has a weight average molecular weight between 150 Da and 4000 Da.

4. Method of any one of the preceding claims, wherein the first coagulation liquid, and optionally the second coagulation liquid, comprises one or more organic solvents of the binder polymer in a total concentration of at least 30% by weight, preferably at least 50% by weight.

5. Method of any one of the preceding claims, wherein subjecting (13) the film (202) to phase separation comprises contacting (133) the film with a third coagulation liquid following contacting (132) the film with the second coagulation liquid, wherein the third coagulation liquid comprises one or more non-solvents of the binder polymer in a third total concentration larger than the first total concentration, wherein the film is contacted with the second coagulation liquid at a second temperature and the film is contacted with the third coagulation liquid at a third temperature higher than the second temperature.

6. Method of the preceding claim, wherein the third total concentration is between 90% by weight and 100% by weight and the third temperature is between 60°C and 95°C.

7. Method of any one of the preceding claims, wherein the first coagulation liquid comprises at least 5% by weight of the organic pore control additive.

8. Method of any one of the preceding claims, wherein the organic pore control additive is a polyol, preferably a polyether polyol.

9. Method of the preceding claim, wherein the organic pore control additive is one or a combination of polyethylene glycol and polypropylene glycol having a weight average molecular weight between 180 Da and 1600 Da.

10. Method of any one of the preceding claims, wherein the first coagulation liquid is at a temperature between 3°C and 25°C when contacting (131) the film with the first coagulation liquid.

11. Method of any one of the preceding claims, wherein the binder polymer is a sulfone-containing aromatic polymer compound.

12. Method of any one of the preceding claims, wherein a ratio of amount of the organic pore control additive to a total amount of the organic pore control additive and the binder polymer in the suspension is between 0.4 and 0.9 by weight, preferably between 0.5 and 0.85 by weight.

13. Method of any one of the preceding claims, wherein the one or more nonsolvents of the binder polymer in the first coagulation liquid are one or a combination of water and an alkyl alcohol having between 1 and 5 carbon atoms.

14. Method of any one of the preceding claims, wherein the porous separator membrane is a separator membrane for alkaline water electrolysis.

15. Porous separator membrane (50) obtainable by the method of any one of the preceding claims, wherein the porous separator membrane is made of a composite material consisting of a polymeric binder phase and inorganic filler particles dispersed in the polymeric binder phase, wherein an amount of the inorganic filler particles in the composite material is between 75% and 95% by weight, wherein the porous separator membrane has a water permeability at 30°C between 100 l / h / m2 / bar and 900 l / h / m2 / bar after ageing for two weeks in a 30% by weight KOH aqueous solution at 85°C and an ionic resistance, determined at 30°C in a 30% by weight KOH aqueous solution, between 0.02 Qcm2and 0.12 Qcm2after ageing of the porous separator membrane for two weeks in a 30% by weight KOH aqueous solution at 85°C.

16. Porous separator membrane of the preceding claim, wherein the porous separator membrane has a porosity between 40% and 70% by volume.

17. Porous separator membrane of claim 15 or 16, wherein the porous separator membrane comprises a first membrane face (501) and a second membrane face (502) opposite the first membrane face, a porous surface layer (51) adjacent the first membrane face (501) and a porous bulk layer (52) having anisotropic porous structure, wherein an average pore size of the porous surface layer (51) is smaller than an average pore size of the bulk layer.

18. Porous separator membrane of any one of the claims 15 to 17, further comprising a reinforcement mesh at least partially embedded in the composite material.

19. Porous separator membrane of any one of claims 15 to 18, wherein a thickness of the porous separator membrane is between 80 pm and 500 pm.

20. Use of the porous separator membrane according to any one of the claims 15 to 19 as a diaphragm in alkaline water electrolysis.

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