Method of producing a separator with high surface energy

Abstract

The invention relates to a method of producing a separator for electrochemical elements, comprising the following steps A to E: A - providing an aqueous suspension comprising fibrillatable fibres of regenerated cellulose, B - treating the fibrillatable fibres of regenerated cellulose in the aqueous suspension from step A in a colloid mill with a grinding gap of at least 1.0 mm and at most 3.0 mm, an edge speed of at least 30 m / s and at most 50 m / s, and a discharge pressure of at least 0.4 MPa and at most 1.5 MPa, C - providing the aqueous suspension from step B in a headbox, D - dewatering the aqueous suspension from step C from the headbox at a revolving screen, in order to obtain a fibre web, and E - drying the fibre web by mechanical pressure and supply of heat, wherein at least 80% of the mass of the separator produced in steps A to E is formed by fibrillated fibers of regenerated cellulose, and the separator produced in steps A to E has a surface energy, determined by inverse gas chromatography, of at least 80 mJ / g, which is formed by the sum total of disperse and specific surface energy, and wherein the polarity of the separator is at least 0.06 and at most 0.20, wherein the polarity is the proportion of the specific surface energy in mJ / g of the surface energy in mJ / g.

Description

[0001] delfortgroup AG H7O458WO

[0002] Method for producing a high surface energy separator

[0003] AREA OF INVENTION

[0004] The invention relates to a method for producing a separator for electrochemical elements, wherein the separator is essentially formed by fibers of regenerated cellulose and is given a particularly high surface energy and, in particular, a high dispersed fraction of the surface energy by the manufacturing process, so that an electrochemical element made from the separator has an increased cycle lifetime.

[0005] BACKGROUND AND STATE OF THE ART

[0006] An electrochemical cell typically comprises at least one positive electrode, one negative electrode, an electrolyte, a separator, a casing, and current collectors. The separator is saturated with the electrolyte and serves to electrically separate the two electrodes. At the same time, it should allow as unimpeded a flow of ions as possible between the electrodes and from the electrolyte to the electrodes, so that the electrochemical cell has favorable properties, in particular rapid charging and the ability to draw high currents.

[0007] These requirements for the separator mean that it should be as thin as possible so that the path of the ions from one electrode to the other through the separator's pores is short, resulting in a high volumetric energy density of the electrochemical element, and that it should possess high porosity. The pore volume absorbs the electrolyte, which is why a large pore volume is advantageous for rapid ion transport. Furthermore, it is beneficial if the pores in the separator are formed by a multitude of small pores.

[0008] The separator must be chemically resistant to the electrolyte, as electrochemical elements can be recharged multiple times and are typically in use for several years. Therefore, the separator must also be resistant to oxidative and reductive environments.

[0009] For safety reasons, the separator should have good thermal stability in order to limit the risk of fire in case of damage to the electrochemical element.

[0010] In electrochemical cells, especially batteries, the capacity gradually decreases with each charge and discharge cycle. After a certain number of charge cycles, the capacity eventually becomes so low that the electrochemical cell is no longer usable for its intended application. Since replacing such cells is complex and expensive, and in some cases even impossible, there is an interest in minimizing the capacity decrease over many charge cycles, thus maximizing the cycle life.

[0011] It is known to manufacture separators from regenerated cellulose fibers. This typically involves the use of methods and equipment familiar from papermaking. These manufacturing processes still offer potential for improvement in order to maximize the cycle life of an electrochemical element produced from this separator without compromising other essential properties of the electrochemical element. There is an interest in industry in exploiting this potential for improvement.

[0012] SUMMARY OF THE INVENTION

[0013] The invention is therefore based on the objective of providing a method for manufacturing a separator for electrochemical elements that gives the separator such properties that the electrochemical element manufactured therefrom has a high cycle life.

[0014] This problem is solved by a method for producing a separator for electrochemical elements according to claim i, a separator according to claim 29, and an electrochemical element comprising this separator according to claim 60. Advantageous embodiments are specified in the dependent claims.

[0015] The inventor has found that the separator in an electrochemical cell can make a significant contribution to the cycle life. The inventor's reasoning is based on the understanding that, especially for non-aqueous electrolytes in combination with a separator formed primarily from regenerated cellulose fibers, a high surface energy and a high dispersed surface energy fraction are advantageous. This ensures that the electrolyte wets the separator as effectively as possible, that the mobility of the ions through the electrolyte and the separator is high, and that undesirable side reactions are avoided. However, achieving a high surface energy and a high dispersed surface energy fraction of the separator is not straightforward if the separator is formed primarily from regenerated cellulose fibers.The inventor further recognized that the surface energy of regenerated cellulose fibers is generally too low, and especially that of their dispersed fraction, to achieve the desired effect, but that it can be increased through a special treatment of the fibers. In the production of regenerated cellulose fibers, the cellulose is dissolved and spun into fibers. The spinning process causes the outer layer of the fibers to exhibit different properties, particularly an undesirably low surface energy. With a special treatment of the regenerated cellulose fibers, which is explained in detail below, this outer layer can be removed without significantly cutting or crushing the fibers. After the removal of this outer layer, the fibers exhibit a considerably higher surface energy than is otherwise achievable for regenerated cellulose fibers.The dispersed component of the surface energy can also be favorably influenced in this way, so that a separator made from it gives the electrochemical element a high cycle life.

[0016] The inventive method for producing a separator for electrochemical elements comprises the following steps A to E.

[0017] A - Providing an aqueous suspension containing fibrillable fibers of regenerated cellulose

[0018] B - Treating the fibrillable fibers of regenerated cellulose in the aqueous suspension from step A in a colloid mill with a grinding gap of at least 1.0 mm and at most 3.0 mm, an edge velocity of at least 30 m / s and at most 50 m / s and an outlet pressure of at least 0.4 MPa and at most 1.5 MPa

[0019] C - Providing the aqueous suspension comprising the fibrillated fibers of regenerated cellulose from step B in a headbox,

[0020] D - Dewatering the aqueous suspension from step C from the headbox onto a circulating screen to obtain a fiber web,

[0021] E - Drying the fiber web by mechanical pressure and the application of heat, wherein at least 80% of the mass of the separator produced in steps A to E is formed by fibrillated fibers of regenerated cellulose, and the separator produced in steps A to E has a surface energy of at least 80 mJ / g as determined by inverse gas chromatography, which is formed by the sum of dispersed and specific surface energy, and wherein the polarity of the separator is at least 0.06 and at most 0.20, where the polarity is the proportion of the specific surface energy in mJ / g to the surface energy in mJ / g.

[0022] According to the inventor's findings, the surface energy of the separator can be increased by treating the fibers in a modified colloid mill. A colloid mill is not typically used for fibrillating fibers and producing paper, but rather for producing spherical colloids, i.e., for dispersing solids or liquids in a fine suspension or emulsion. Surprisingly, the inventor discovered that a colloid mill with suitable modifications can be used to treat the fibrillable fibers of regenerated cellulose.

[0023] When using a colloid mill for this purpose, it is important according to the invention that the grinding gap and edge velocity are appropriately adjusted. This results in the removal of the fiber surface without significantly cutting or crushing the fibers. Generally, this requires a grinding gap between 1.0 mm and 3.0 mm and a comparatively high edge velocity of 30 m / s to 50 m / s. According to the invention, these colloid mill settings are to be combined with a high outlet pressure to increase the residence time of the fibers in the colloid mill. This cannot be achieved with conventional colloid mills but requires a modification of the colloid mill by providing a separate means for throttling the suspension flow at the outlet of the colloid mill. This reduces the flow rate and the outlet pressure inside the colloid mill to the value of 0.4 MPa according to the invention.

[0024] Increased by 1.5 MPa.

[0025] The effect of the treatment in the colloid mill manifests itself in a higher surface energy of the separator and a high proportion of the dispersed surface energy.

[0026] Surface energy can be measured using inverse gas chromatography and is additively composed of the dispersed surface energy, which contains, for example, the interaction energy of the van der Waals forces, and the specific surface energy, sometimes also referred to as polar surface energy, which contains the energy of polar interactions and acid-base interactions.

[0027] The measurement can be performed, for example, using an inverse gas chromatography-side analysis (iGC-SEA) instrument from Surface Measurement Systems. Experimental conditions are set to a temperature of 303.15 K, a relative humidity of 0%, and a nitrogen flow rate of 10 ml / min. The column and the sample prepared for measurement are conditioned under these conditions for one hour to dry the sample. The nonpolar eluents used are n-decane, n-nonane, n-octane, and n-heptane, and the polar eluents are acetone, acetonitrile, chloroform, dichloromethane, ethanol, ethyl acetate, and toluene. A flame ionization detector (FID) is used for detection. The method used to calculate the surface energy and the dispersed component of the surface energy is directly implemented in the instrument (iGC-SEA) and is based on the method described by Dorris, G.M., and Gray, D.G.(1980) Adsorption of normal-alkanes at zero surface coverage on cellulose paper and wood fibers.

[0028] J. Colloid & Interface Sector, 77(2), pp. 353-362 and Della Volpe, C. and Siboni, S. (1997) Some reflections on acid-base solid surface free energy theories. J. Colloid Interface Sector, 195, pp. 2i-136. The total surface energy of the separator is the additive composition of the dispersed and specific surface energies, and the polarity is the proportion of the specific surface energy in mJ / g to the total surface energy in mJ / g.

[0029] Surface energy is usually calculated from inverse gas chromatography in mJ / m². 2obtained, i.e., with respect to the surface area of ​​the pore structure of the separator. However, since the effectiveness of the separator in the electrochemical element also depends on a sufficiently large pore area being available for interaction with the electrolyte, it is essential, according to the inventor's findings, that the surface energy, relative to the mass—and not the specific surface area—of the separator, exceeds the lower limit according to the invention.

[0030] The specific surface area in m² 2The surface area per gram of the separator can be determined using the BET method according to ISO 9277:2022. The specific surface area can also be measured using an inverse gas chromatography (iGC-SEA) instrument from Surface Measurement Systems. For this, experimental conditions of 303.15 K, 0% relative humidity, and a nitrogen flow of 10 ml / min are used, and the column and sample are conditioned under these conditions for one hour. The surface energy per unit mass of the separator in mJ / g is then obtained by subtracting the surface energy from the iGC analysis in mJ / m². 2 with the specific surface area of ​​the separator in m² 2 multiplied by / g.

[0031] Preferably, the surface energy of the separator produced in steps A to E is at least 90 mJ / g and at most 300 mJ / g, and particularly preferably at least 100 mJ / g and at most 200 mJ / g.

[0032] Preferably, the polarity of the separator produced in steps A to E is at least 0.07 and at most 0.18, and particularly preferably at least 0.075 and at most 0.15.

[0033] In a preferred embodiment of the process according to the invention, the surface energy of the separator produced in steps A to E is at least 80 mJ / g and the polarity is at least 0.07 and at most 0.18 and particularly preferably at least 0.075 and at most 0.15.

[0034] In a preferred embodiment of the process according to the invention, the surface energy of the separator produced in steps A to E is at least 90 mJ / g and at most 300 mJ / g, and the polarity is at least 0.06 and at most 0.20, particularly preferably at least 0.07 and at most 0.18, and most preferably at least 0.075 and at most 0.15. In a preferred embodiment of the process according to the invention, the surface energy of the separator produced in steps Ab to E is at least 100 mJ / g and at most 200 mJ / g, and the polarity is at least 0.06 and at most 0.20, particularly preferably at least 0.07 and at most 0.18, and most preferably at least 0.075 and at most 0.15.

[0035] The fibrillable fibers of regenerated cellulose in the suspension in step A are preferably solvent-spun fibers. For example, lyocell fibers are particularly well suited for the separator according to the invention.

[0036] The linear density of the fibrillable fibers of regenerated cellulose in the suspension in step A is important for the treatment of the fibers in step B. Preferably, the mean linear density of the fibrillable fibers of regenerated cellulose is at least 0.6 g / 10000 m (0.6 dtex) and at most 3.0 g / 10000 m (3.0 dtex), and particularly preferably at least 0.8 g / 10000 m (0.8 dtex) and at most 1.8 g / 10000 m (1.8 dtex).

[0037] The length of the fibrillable fibers of regenerated cellulose in the suspension in step A is particularly important for the strength of the separator, with longer fibers leading to higher strength but also requiring more energy for treatment in step B. Preferably, the average length of the fibrillable fibers of regenerated cellulose is at least 2 mm and at most 8 mm, and particularly preferably at least 3 mm and at most 6 mm.

[0038] Preferably, the solids content of the aqueous suspension in step A is at least 0.5% and at most 3.0%, and particularly preferably at least 1.0% and at most 2.5%, in each case based on the mass of the aqueous suspension.

[0039] The treatment of the fibrillable fibers of regenerated cellulose in the suspension from step A is carried out in step B in a colloid mill according to the invention.

[0040] Preferably, the grinding gap when treating the fibers in the colloid mill in step B is at least 1.0 mm and at most 2.5 mm.

[0041] Preferably, the edge velocity during the treatment of the fibers in the colloid mill in step B is at least 30 m / s and at most 45 m / s, particularly preferably at least 30 m / s and at most 40 m / s.

[0042] Preferably, the outlet pressure of the colloid mill in step B is at least 0.4 MPa and at most 1.2 MPa.

[0043] The colloid mill itself, with the settings and modifications according to the invention in step B, can achieve sufficient fibrillation of the fibers. In a preferred embodiment of the process, however, step B additionally comprises fibrillating the fibers in a different grinding unit than the colloid mill.

[0044] In this context, "fibrillation" or "fibrillated" means that the fibers have passed through the colloid mill and optionally at least one grinding unit capable of at least partially separating the fibrils bound together in a fiber bundle. It is neither necessary nor within the scope of the invention that all fibers be completely fibrillated, but only that the fibers are fibrillated to the extent required to achieve a specific degree of grinding.

[0045] The fibers should not be completely fibrillated because, for removing the outer layer of the fibers and thus increasing the surface energy, it has proven advantageous if the refining is not too intensive. The degree of fibrillation can be determined by the degree of refining according to ISO 5267-1:1999 and expressed in degrees Schopper-Riegler (°SR). Preferably, the degree of refining of the fibrillated fibers of regenerated cellulose directly after step B is at least 75°SR and at most 95°SR, particularly preferably at least 78°SR and at most 92°SR, and most preferably at least 80°SR and at most 90°SR.

[0046] In addition to the fibrillated fibers of regenerated cellulose, the aqueous suspension in step C can also contain further cellulose fibers. Preferably, providing the aqueous suspension in step C further comprises adding additional cellulose fibers to the suspension in step C.

[0047] Preferably, the additional cellulose fibers in the suspension in step C can be formed entirely or partially by non-fibrillated fibers of regenerated cellulose.

[0048] Preferably, the additional cellulose fibers in the suspension in step C can be formed entirely or partially from pulp fibers, wherein the pulp fibers are preferably obtained from softwoods, hardwoods, or other plants such as hemp, flax, jute, ramie, kenaf, kapok, coconut, abaca, sisal, bamboo, cotton, or esparto grass, or from recycled paper pulp. Mixtures of pulp fibers from different sources can also be used in the suspension in step C. Pulp fibers obtained from hardwoods, softwoods, or cotton are particularly preferred. The use of hemp for the production of pulp fibers from the bast of this plant and their use in paper or textiles has long been known and is unrelated to the psychoactive substances such as tetrahydrocannabinol (THC) that may be contained in other parts of this plant. Pulp fibers from hemp do not contain THC.

[0049] Particularly preferred are the cellulose fibers in the suspension in step C, at least partially being microfibrillated cellulose fibers, nanofibrillated cellulose fibers, or cellulose fibers with a mean length-weighted length of at most 0.2 mm, preferably at most 0.15 mm. These types of cellulose fibers are particularly well suited for equipping the separator with a small mean pore size.

[0050] The mean length-weighted length of cellulose fibers can be determined by optical analysis according to ISO 16065-2:2014.

[0051] The dewatering of the suspension in step D can be carried out according to the methods commonly used in papermaking and preferably includes dewatering by means of vacuum boxes or suitably shaped vanes that create a vacuum.

[0052] The drying of the fiber web in step E can be carried out according to the methods commonly used in papermaking and preferably includes drying in the press section of a paper machine by mechanical pressure and drying in the dryer section of a paper machine by the supply of heat.

[0053] Preferably, in step E, the separator undergoes a further partial calendering step. This partial calendering step is particularly preferably carried out by compressing the fiber web in the thickness direction in at least one and at most four roll gaps, wherein the temperature of the rolls forming the roll gaps is at least 90°C and at most 150°C and the line load of the roll gaps is at least 20 N / mm and at most 380 N / mm.

[0054] The separator produced according to the invention in steps A to E comprises fibrillated fibers of regenerated cellulose, wherein at least 80%, preferably at least 90%, particularly preferably at least 95% and most preferably at least 99% of the mass of the separator is formed by fibrillated fibers of regenerated cellulose.

[0055] Preferably, the proportion of additional cellulose fibers in the separator produced in steps A to E is at least 1% and at most 10%, particularly preferably at least 2% and at most 10%, and most preferably at least 3% and at most 7%, in each case based on the mass of the separator.

[0056] In a preferred embodiment of the separator produced in steps A to E, at least 1% and at most 10%, particularly preferably at least 2% and at most 10%, and most preferably at least 3% and at most 7% of the separator's mass is formed by nanofibrillated cellulose fibers, microfibrillated cellulose fibers, or cellulose fibers with a mean length-weighted length of at most 0.2 mm, preferably at most 0.15 mm. These percentages refer to the total amount of these three cellulose fiber types if more than one of these types is present. In a particularly preferred embodiment, the separator produced in steps A to E contains or consists of fibrillated fibers of regenerated cellulose and nanofibrillated and / or microfibrillated cellulose fibers.

[0057] In a particular embodiment of the separator produced in steps A to E, the separator comprises at least 80% and at most 90% fibrillated fibers of regenerated cellulose, at least 10% and at most 20% cellulose fibers from cotton and at most 5% nanofibrillated cellulose fibers, the percentages in each case relating to the mass of the separator.

[0058] The separator produced in steps A to E preferably has an basis weight of at least 6 g / m². 2 and at most 30 g / m² 2 , particularly preferably at least 7 g / m³ 2 and at most 28 g / m² 2 and especially preferably at least 8 g / m² 2 and at most 25 g / m² 2 The basis weight can be determined according to ISO 536:2019.

[0059] The separator produced in steps A to E preferably has a mean thickness of a single sheet, according to ISO 534:2011, of at least 8 pm and at most 75 pm, preferably at least 10 pm and at most 60 pm, and particularly preferably at least 12 pm and at most 50 pm.

[0060] Further preferred properties of the separator produced in steps A to E correspond to those disclosed below in connection with the preferred embodiments of a separator according to a further aspect of the invention, in particular with regard to composition, density, tensile strength, elongation at break, shrinkage, porosity, pore structure, air permeability according to Gurley and MacMullin number.

[0061] This further aspect of the invention relates to a separator that can be manufactured according to the inventive method. This separator exhibits the high surface energy resulting from the manufacturing process and a polarity according to the invention.

[0062] According to the inventor, the high surface energy and polarity of the separator according to the invention are crucial for the separator to give an electrochemical element manufactured therefrom a longer cycle life than is possible with conventional separators. Such a separator is particularly obtainable by manufacturing it using a process according to one of the embodiments described above, which allows the production of a separator with the high surface energy and polarity according to the invention. However, according to this aspect of the invention, the separator is defined only by the aforementioned properties, in particular the high surface energy and polarity according to the invention, and not by the method of its manufacture.The separator according to the invention for an electrochemical element comprises, based on its mass, at least 80% fibrillated fibers of regenerated cellulose and has a surface energy of at least 80 mJ / g determined by inverse gas chromatography, which is formed by the sum of dispersed and specific surface energy, and the polarity of the separator is at least 0.06 and at most 0.20, wherein the polarity is the proportion of the specific surface energy in mJ / g to the surface energy in mJ / g.

[0063] Preferably the surface energy of the separator is at least 90 mJ / g and at most 300 mJ / g, and particularly preferably at least 100 mJ / g and at most 200 mJ / g.

[0064] Preferably the polarity of the separator is at least 0.07 and at most 0.18, and particularly preferably at least 0.075 and at most 0.15.

[0065] In a preferred embodiment of the separator, the surface energy is at least 80 mJ / g and the polarity is at least 0.07 and at most 0.18, and particularly preferably at least 0.075 and at most 0.15.

[0066] In a preferred embodiment of the separator, the surface energy is at least 90 mJ / g and at most 300 mJ / g, and the polarity is at least 0.06 and at most 0.20, particularly preferably at least 0.07 and at most 0.18, and most preferably at least 0.075 and at most 0.15.

[0067] In a preferred embodiment of the separator, the surface energy is at least 100 mJ / g and at most 200 mJ / g, and the polarity is at least 0.06 and at most 0.20, particularly preferably at least 0.07 and at most 0.18, and most preferably at least 0.075 and at most 0.15.

[0068] The separator according to the invention comprises fibrillated fibers of regenerated cellulose, wherein at least 80%, preferably at least 90%, particularly preferably at least 95% and most preferably at least 99% of the mass of the separator is formed by fibrillated fibers of regenerated cellulose.

[0069] Preferably, the fineness of the fibrillated fibers of regenerated cellulose in the separator is at least 75°SR and at most 95°SR, particularly preferably at least 78°SR and at most 92°SR and most preferably at least 80°SR and at most 90°SR.

[0070] The fibrillated fibers of regenerated cellulose are preferably fibers spun in a solvent.

[0071] In addition to the fibrillated fibers of regenerated cellulose, the separator according to the invention can comprise further cellulose fibers. Preferably, the further cellulose fibers can be formed entirely or partially by non-fibrillated fibers of regenerated cellulose.

[0072] Preferably, the additional cellulose fibers can be formed wholly or partially from pulp fibers, wherein the pulp fibers are preferably obtained from softwoods, hardwoods, or other plants such as hemp, flax, jute, ramie, kenaf, kapok, coconut, abaca, sisal, bamboo, cotton, or esparto grass, or from recycled paper pulp. The separator can also comprise mixtures of pulp fibers from various of these plants. Pulp fibers obtained from hardwoods, softwoods, or cotton are particularly preferred.

[0073] Particularly preferred are the cellulose fibers being at least partially microfibrillated cellulose fibers, nanofibrillated cellulose fibers or cellulose fibers with a mean length-weighted length of at most 0.2 mm, preferably at most 0.15 mm.

[0074] Preferably, the proportion of additional cellulose fibers is at least 1% and at most 10%, particularly preferably at least 2% and at most 10%, and most preferably at least 3% and at most 7%, in each case based on the mass of the separator.

[0075] In a preferred embodiment of the separator, at least 1% and at most 10%, particularly preferably at least 2% and at most 10%, and most preferably at least 3% and at most 7% of the separator's mass are formed by nanofibrillated cellulose fibers, microfibrillated cellulose fibers, or cellulose fibers with a mean length-weighted length of at most 0.2 mm, preferably at most 0.15 mm. These percentages refer to the total amount of these three cellulose fiber types if more than one of these types is present.

[0076] In a particularly preferred embodiment, the separator contains or consists of fibrillated fibers of regenerated cellulose and nanofibrillated and / or microfibrillated cellulose fibers.

[0077] In a particular embodiment of the separator, the separator comprises at least 80% and at most 90% fibrillated fibers of regenerated cellulose, at least 10% and at most 20% cellulose fibers from cotton and at most 5% nanofibrillated cellulose fibers, the percentages relating to the mass of the separator.

[0078] The separator according to the invention can contain, in addition to the fibrillated fibers of regenerated cellulose and other optional cellulose fibers, other fibers as well. These preferably include fibers made of cellulose derivatives, glass fibers, plastic fibers such as polyolefins like polyethylene or polypropylene; polyesters such as polyethylene terephthalate or polylactic acid; polyarylates such as poly(4-hydroxybenzoic acid-co-6-hydroxy-2-naphthoic acid); polyethers, polysulfones, polyurethanes, polyamides, aromatic polyamides such as poly(p-phenylene terephthalamide); polyimides, polyvinyl alcohol, polyacrylates such as polyacrylonitrile or poly(acrylonitrile-co-methyl acrylate); polyphenylene sulfide, or poly(ethylene-co-vinyl acetate). However, these fibers can only be used with the restriction that the surface energy and polarity of the separator lie within the intervals specified in the invention or the preferred intervals.

[0079] The separator according to the invention can preferably comprise filler in addition to the fibrillated fibers of regenerated cellulose. The filler is particularly preferably selected from the group consisting of kaolin, titanium dioxide (TiO2), silicon dioxide (SiO2), aluminum oxide (Al2O3), zirconium dioxide (ZrO2), calcium carbonate (CaCO3), and zinc oxide (ZnO), or a mixture thereof, wherein the filler constitutes at least 1% and at most 10%, and particularly preferably at least 1% and at most 7%, of the mass of the separator.

[0080] The separator according to the invention may contain further components which the person skilled in the art can select according to their experience to suit the manufacturing process, including, for example, polyvinyl alcohol, polyethylene glycol, polyvinylidene fluoride, guarana, starch, carboxymethylcellulose, methylcellulose or dialdehydes such as glyoxal, sizing agents such as alkyl ketene dimer (AKD) and alkenylsuccinic anhydride (ASA), or wet-strength agents such as polyamide-polyamine-epichlorohydrin resin.

[0081] The separator according to the invention preferably has an basis weight of at least 6 g / m². 2 and at most 30 g / m² 2 , particularly preferably of at least 7 g / m³ 2 and at most 28 g / m² 2 and especially preferably of at least 8 g / m² 2 and at most 25 g / m² 2The basis weight can be determined according to ISO 536:2019. The basis weight influences the separator's thickness, strength, and material requirements. Due to its thickness, the basis weight significantly impacts the performance parameters of an electrochemical cell manufactured from the separator, and therefore, it is generally desirable to keep the basis weight as low as possible. The specified preferred ranges allow for a favorable balance between these requirements.

[0082] The separator according to the invention preferably has a mean thickness of a single sheet, according to ISO 534:2011, of at least 8 pm and at most 75 pm, preferably at least 10 pm and at most 60 pm, and particularly preferably at least 12 pm and at most 50 pm. The thickness should be as small as possible, but is limited from below by the requirements regarding reliable electrical separation of the electrodes and strength, and from above by the expected performance parameters of the electrochemical cell manufactured therefrom. The specified preferred intervals allow for a favorable balance between these requirements.

[0083] Preferably, the separator is calendered. This allows the separator thickness to be reduced. The effect of calendering can be characterized by the separator's density, which is calculated as the ratio of the basis weight according to ISO 536:2019 to the mean thickness of a single sheet according to ISO 534:2011. Preferably, the density is at least 300 kg / m². 3 and at most 1000 kg / m² 3 , preferably at least 350 kg / m² 3 and at most 900 kg / m² 3 and especially preferably at least 400 kg / m² 3 and at most 850 kg / m² 3 .

[0084] For the processing of the separator into an electrochemical element, the separator's mechanical properties are important. These include, for example, tensile strength and elongation at break. The mechanical properties depend on the direction in which a sample was taken from the separator. A distinction is usually made between the machine direction, which is the direction in which the separator moves through the machine during manufacturing, and the transverse direction, which is the direction orthogonal to the machine direction and lies in the plane of the separator.

[0085] The tensile strength according to ISO 1924-2:2008 in the machine direction of the separator according to the invention is, based on the width, preferably at least 0.3 kN / m and at most 2.0 kN / m, particularly preferably at least 0.4 kN / m and at most 1.5 kN / m. Based on the cross-sectional area, calculated from the width of the test strip and the mean thickness of a single sheet according to ISO 534:2011, the tensile strength in the machine direction of the separator according to the invention is preferably at least 15 MPa and at most 75 MPa, particularly preferably at least 25 MPa and at most 60 MPa.

[0086] The tensile strength according to ISO 1924-2:2008 in the machine direction of the separator according to the invention is preferably higher than the tensile strength in the transverse direction. Preferably, the ratio of the tensile strength in the machine direction to that in the transverse direction is at least 1.0 and at most 3.0, particularly preferably at least 1.2 and at most 2.2, and most preferably at least 1.5 and at most 1.8.

[0087] The elongation at break according to ISO 1924-2:2008 in the machine direction of the separator according to the invention is preferably at least 0.5% and at most 5.0%, particularly preferably at least 1.0% and at most 4.0%.

[0088] A feature important for the safety of the electrochemical element manufactured from the separator according to the invention is the shrinkage of the separator at elevated temperatures. Preferably, the shrinkage of the separator according to the invention, conditioned according to ISO 187:2022, after heating to 150°C for 3 hours, is at least 0.5% and at most 2.0%, more preferably at least 0.5% and at most 1.5%.

[0089] The pore structure is of great importance for the properties of an electrochemical element manufactured from the separator according to the invention. The pore structure can be characterized by the overall porosity as well as by the pore size distribution.

[0090] The porosity of a separator is the ratio of the pore volume to the total volume of the separator and is usually expressed as a percentage. The porosity of the separator can be estimated from the mean thickness of a single sheet, measured according to ISO 534:2011, the basis weight, measured according to ISO 536:2019, the moisture content of the separator, measured according to ISO 287:2017, and the density of the fibers, where the density p0 for the fibers is 1500 kg / m³. 3 can be chosen, and p denotes the dry density of the separator. Under these assumptions, the porosity p can be approximated as the ratio of the pore volume to the total volume of the separator by to be calculated, where the basis weight m in g / m² is used in the above equation. 2The mean thickness of a single sheet, d, in pm, and the moisture content, c, of the separator, in %, are to be used. This yields the porosity as a value between 0 and 1, which can be converted into a percentage by multiplying by 100. The porosity should be as high as possible, but is primarily limited by the required mechanical strength and the requirement that the pores should be as small as possible. Preferably, the porosity is at least 35% and at most 75%, more preferably at least 40% and at most 70%.

[0091] The pore structure can be characterized, in simplified terms, by the Gurley air permeability. The air permeability, in combination with the high surface energy and polarity according to the invention, is also a good measure of how quickly the separator can absorb the electrolyte. A high absorption rate is advantageous for productivity in the production of electrochemical cells. The Gurley air permeability can be determined according to ISO 5636-5:2013 and is preferably at least 2 s and at most 60 s, more preferably at least 4 s and at most 50 s, and most preferably at least 5 s and at most 40 s, where a lower Gurley value indicates high air permeability.

[0092] The pore structure of the separator according to the invention is an essential feature that influences the transport of ions through the separator. Those skilled in the art typically assess the pore structure of a separator using the MacMullin number. This number is the ratio of the specific electrical conductivity of the pure electrolyte to the specific electrical conductivity of the electrolyte-impregnated separator in the thickness direction. The MacMullin number can be measured according to the method described in "Application Note: Determination of MacMullin Numbers: The Stacking-Method", 05.2021, rhd instruments GmbH & Co. KG. The MacMullin number thus indirectly provides information about the porosity and tortuosity of the pores. High porosity and low tortuosity result in a low MacMullin number, which is generally desirable for separators.Preferably, the MacMullin number is at least 2 and at most 14, particularly preferably at least 2.5 and at most 12, and most preferably at least 3 and at most 10. The MacMullin number is practically independent of the specific choice of electrolyte used for measurement and is thus a property of the separator itself. To determine the MacMullin number for a specific separator, it is advantageous to use the same electrolyte as is used in an electrochemical cell in which the separator is to be used. Within the scope of the present disclosure, an electrolyte consisting of 1 mol / L lithium hexafluorophosphate (LiPF₆) can be used. (l ) in a volumetric 1:1:1 mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate.

[0093] The separator can be used in electrochemical elements.

[0094] An electrochemical element according to the invention comprises two electrodes, an electrolyte, and a separator according to one of the embodiments described above. Preferably, the electrochemical element is a battery, an electrochemical capacitor, a double-layer capacitor, or a supercapacitor, and particularly preferably, the electrochemical element is a lithium-ion battery. It is especially preferred that the electrochemical element is a battery and the electrolyte is a non-aqueous electrolyte.

[0095] BRIEF DESCRIPTION OF THE FIGURES

[0096] Figure 1 shows in a diagram the course of the capacity of accumulator cells over a multitude of charge and discharge cycles with a separator according to the invention and one not according to the invention.

[0097] DESCRIPTION OF SOME PREFERRED EMBODYWORKS AND COMPARISON WITH NON-INVENTIONAL EMBODYWORKS In the following, some preferred embodiments of the inventive method, some inventive separators, and non-inventive separators are described as a comparative example.

[0098] For the separators Si, S2, and S3 according to the invention, lyocell fibers with a linear density of 1.7 g / 10,000 m³ (1.7 dtex) and a length of 4 mm were provided in an aqueous suspension according to step A of the process according to the invention. According to step B of the process according to the invention, the fibers were treated in a colloid mill with a grinding gap of 1.5 mm and an edge velocity of 35 m / s. An additional valve at the outlet of the colloid mill reduced the flow rate to 25% of the nominal flow rate, resulting in an outlet pressure of approximately 0.6 MPa. With these settings, fibrillation was achieved in addition to the removal of the outer layer of the fibers, so that the degree of refining after treatment was between 81°SR and 86°SR. Therefore, grinding the fibers in a separate grinding unit was unnecessary.

[0099] For separator S3, an additional fibrillated long fiber pulp was used, which was added to the suspension from step C.

[0100] The suspension from step C was dewatered on the wire of a paper machine, step D, and passed through the press section and the drying section of the paper machine, step E.

[0101] Separator S2 was calendered in a 4-roll nip calender at a temperature of no°C and a line load of 150 N / mm to approximately 400 N / mm according to an optional sub-step of step E.

[0102] The separators Si, S2 and S3 according to the invention had basis weights of approximately 12.5 g / m². 2 up to approximately 15.8 g / m² 2 on.

[0103] For comparison, non-inventive separators Zi, Z2, and Z3 were produced from the same lyocell fibers and cellulose fibers, and additionally from polyvinyl alcohol fibers, but step B was omitted, and a conventional milling unit was used to fibrillate the fibers to a specific degree of refining. The degree of refining was in the same range as that of the inventive separators Si, S2, and S3. The non-inventive separator Zi was calendered in the same manner as the inventive separator S3.

[0104] The separator data are summarized in Table 1, where “BW” is the basis weight according to ISO 536:2019, “TH” is the thickness according to ISO 534:2011, “DE” is the density calculated from basis weight and thickness, “LY” is the percentage of fibrillated lyocell fibers based on the mass of the separator, “PU” is the percentage of cellulose fibers based on the mass of the separator, and “PVOH” is the percentage of polyvinyl alcohol fibers based on the mass of the separator.

[0105] Table 1 - Data for separators according to the invention and those not according to the invention The surface energy and specific surface energy of the separators according to and not according to the invention were determined by inverse gas chromatography-separation analysis (iGC-SEA) under the conditions described above, and the polarity was calculated from these values. Likewise, the specific surface area was determined by the BET method according to ISO 9277:2022 in order to express the surface energy in mJ / g. The results are summarized in Table 2, where the designation of the separators is identical to that in Table 1. "SE" denotes the surface energy as the sum of the dispersed and specific surface energy, in mJ / m². 2 and mJ / g, “SSE” the specific surface energy and “POL” the polarity as the ratio of the specific surface energy in mJ / g to the surface energy in mJ / g. Table 2 - Further data of separators according to the invention and those not according to the invention. The separators Si, S2, and S3 according to the invention demonstrate that the surface energy in mJ / g can be significantly increased by the special treatment in a modified colloid mill in step B, reaching between 127.9 mJ / g and 239.3 mJ / g, whereas without this treatment, the surface energy does not exceed 60 mJ / g, as shown by the non-inventive separators Zi, Z2, and Z3. The polarity of the separators Si, S2, and S3 according to the invention is also favorable, whereas, for example, the non-inventive separator Z2, which, like the separators Si and S2 according to the invention, consists of 100% lyocell fibers, achieves a significantly higher polarity.

[0106] Lithium-ion batteries with a nominal capacity of 100 mAh at 23°C and 0.5c were produced from the separator Si according to the invention and the separator Z2 not according to the invention, both made of 100% lyocell fibers. An NMC811 cathode with an area capacity of approximately 3.2 mAh / cm² was used. 2 and a graphite anode was used. The electrolyte was a mass-based 1:2 mixture of ethylene carbonate and ethyl methyl carbonate with 1 mol / L lithium hexafluorophosphate (LiPF₆). (l ) and 2 wt% vinylene carbonate were used. The batteries were repeatedly charged and discharged at 45°C with a constant C-rate of 0.5 between 2.8 V and 4.2 V, corresponding to 100% depth of discharge (DoD). The battery capacity was determined in each charge-discharge cycle. Three batteries were produced for each separator, and the average of the results was calculated.

[0107] Figure 1 shows a diagram illustrating the capacity over charge-discharge cycles. The x-axis 101 represents the number of charge-discharge cycles, and the y-axis 102 represents the discharge capacity of the batteries in mAh as an average over three batteries. Curve 103 shows the average discharge capacity for the batteries manufactured from the separator Si according to the invention, while curve 104 shows the average discharge capacity for the batteries manufactured from the separator Z2 not according to the invention.

[0108] It can be seen that the discharge capacity of the accumulators with the separator Si according to the invention, curve 103, decreases significantly more slowly than the discharge capacity of the accumulators with the non-inventive separator Z2, curve 104, which is, however, also suitable as a separator in principle. The inventor attributes this favorable effect to the fact that the electrolyte, due to its high surface energy and favorable polarity, better wets the separator according to the invention, improves the mobility of the ions, and prevents undesirable side reactions, so that the discharge capacity does not decrease as rapidly. The accumulators with the separators according to the invention therefore have a longer cycle life and, with comparable usage, need to be replaced less frequently.

Claims

Claims 1. Method for manufacturing a separator for electrochemical elements, comprising the following steps A to E. A - Providing an aqueous suspension comprising fibrillable fibers of regenerated cellulose, B - Treating the fibrillable fibers of regenerated cellulose in the aqueous suspension from step A in a colloid mill with a grinding gap of at least 1.0 mm and at most 3.0 mm, an edge velocity of at least 30 m / s and at most 50 m / s and an outlet pressure of at least 0.4 MPa and at most 1.5 MPa, C - Providing the aqueous suspension comprising the fibrillated fibers of regenerated cellulose from step B in a headbox, D - Dewatering the aqueous suspension from step C from the headbox onto a circulating screen to obtain a fiber web, E - Drying of the fiber web by mechanical pressure and application of heat, wherein at least 80% of the mass of the separator produced in steps A to E is formed by fibrillated fibers of regenerated cellulose and the separator produced in steps A to E has a surface energy of at least 80 mJ / g determined by inverse gas chromatography, which is formed by the sum of dispersed and specific surface energy, and wherein the polarity of the separator is at least 0.06 and at most 0.20, where the polarity is the fraction of the specific surface energy in mJ / g to the surface energy in mJ / g.

2. The method according to claim 1, wherein the surface energy of the separator produced in steps A to E is at least 90 mJ / g and at most 300 mJ / g, preferably at least 100 mJ / g and at most 200 mJ / g.

3. Method according to claim 1 or 2, wherein the polarity of the separator produced in steps A to E is at least 0.07 and at most 0.18, preferably at least 0.075 and at most 0.

15. 4- Method according to claim 1, wherein the surface energy of the separator produced in steps A to E is at least 80 mJ / g and the polarity is at least 0.07 and at most 0.18, preferably at least 0.075 and at most 0.

15.

5. The method of claim 1, wherein the surface energy of the separator produced in steps A to E is at least 90 mJ / g and at most 300 mJ / g and the polarity is at least 0.06 and at most 0.20, preferably at least 0.07 and at most 0.18 and particularly preferably at least 0.075 and at most 0.

15.

6. The method of claim 1, wherein the surface energy of the separator produced in steps A to E is at least 100 mJ / g and at most 200 mJ / g and the polarity is at least 0.06 and at most 0.20, preferably at least 0.07 and at most 0.18 and particularly preferably at least 0.075 and at most 0.

15.

7. Method according to one of the preceding claims, wherein the fibrillable fibers of regenerated cellulose in the suspension in step A are fibers spun in a solvent, in particular lyocell fibers.

8. A method according to any of the preceding claims, wherein the mean linear density of the fibrillable fibers of regenerated cellulose is at least 0.6 g / 10000 m (0.6 dtex) and at most 3.0 g / 10000 m (3.0 dtex) and preferably at least 0.8 g / 10000 m (0.8 dtex) and at most 1.8 g / 10000 m (1.8 dtex).

9. Method according to any of the preceding claims, wherein the mean length of the fibrillable fibers of regenerated cellulose is at least 2 mm and at most 8 mm and particularly preferably at least 3 mm and at most 6 mm.

10. Method according to any of the preceding claims, wherein the solids content of the aqueous suspension in step A is at least 0.5% and at most 3.0%, preferably at least 1.0% and at most 2.5%, in each case based on the mass of the aqueous suspension.

11. Method according to one of the preceding claims, wherein the grinding gap during the treatment of the fibers in the colloid mill in step B is at least 1.0 mm and at most 2.5 mm.

12. Method according to one of the preceding claims, wherein the edge velocity during the treatment of the fibers in the colloid mill in step B is at least 30 m / s and at most 45 m / s, preferably at least 30 m / s and at most 40 m / s. 13- Method according to one of the preceding claims, wherein the outlet pressure of the colloid mill in step B is at least 0.4 MPa and at most 1.2 MPa.

14. Method according to any of the preceding claims, wherein the method in step B additionally comprises fibrillating the fibers in a grinding unit other than the colloid mill.

15. Method according to any of the preceding claims, wherein the degree of refining of the fibrillated fibers of regenerated cellulose directly after step B is at least 75°SR and at most 95°SR, preferably at least 78°SR and at most 92°SR and particularly preferably at least 80°SR and at most 90°SR.

16. Method according to any of the preceding claims, wherein the provision of the aqueous suspension in step C further comprises the addition of further cellulose fibers to the suspension in step C.

17. The method of claim 16, wherein the further cellulose fibers in the suspension in step C are formed wholly or partly by non-fibrillated fibers of regenerated cellulose.

18. The method of claim 16, wherein the further cellulose fibers in the suspension in step C are formed wholly or partly by pulp fibers, wherein the pulp fibers are preferably obtained from coniferous trees, deciduous trees or other plants, in particular hemp, flax, jute, ramie, kenaf, kapok, coconut, abaca, sisal, bamboo, cotton or esparto grass, or from recycled paper pulp, or are a mixture of pulp fibers of two or more different sources mentioned.

19. Method according to claim 18, wherein the cellulose fibers are at least partly microfibrillated cellulose fibers, nanofibrillated cellulose fibers or cellulose fibers with a mean length-weighted length of at most 0.20 mm, preferably at most 0.15 mm.

20. Method according to one of the preceding claims, wherein the separator undergoes a further partial step of calendering in step E.

21. Method according to claim 20, wherein the said partial step of calendering is carried out by compressing the fiber web in the thickness direction in at least one and at most four roll gaps, wherein the temperature of the rolls forming the roll gaps is at least 90°C and at most 150°C and the line load of the roll gaps is at least 20 N / mm and at most 380 N / mm.

22. Method according to any of the preceding claims, wherein at least 90%, preferably at least 95% and particularly preferably at least 99% of the mass of the separator produced in steps A to E is formed by fibrillated fibers of regenerated cellulose.

23. A method according to any one of claims 16 to 22, wherein the proportion of further cellulose fibers in the separator produced in steps A to E is at least 1% and at most 10%, particularly preferably at least 2% and at most 10% and most preferably at least 3% and at most 7%, in each case based on the mass of the separator.

24. A method according to any one of claims 18 to 23, wherein at least 1% and at most 10%, preferably at least 2% and at most 10% and particularly preferably at least 3% and at most 7% of the mass of the separator produced in steps A to E are formed by nanofibrillated cellulose fibers or microfibrillated cellulose fibers or cellulose fibers with a mean length-weighted length of at most 0.20 mm, preferably of at most 0.15 mm.

25. The method of claim 16, wherein the separator produced in steps A to E contains or consists of fibrillated fibers of regenerated cellulose and nanofibrillated and / or microfibrillated cellulose fibers.

26. The method of claim 16, wherein the separator produced in steps A to E comprises at least 80% and at most 90% fibrillated fibers of regenerated cellulose, at least 10% and at most 20% cotton pulp fibers and at most 5% nanofibrillated pulp fibers, the percentages relating in each case to the mass of the separator produced in steps A to E.

27. Method according to one of the preceding claims, wherein the separator produced in steps A to E has an basis weight of at least 6 g / m². 2 and at most 30 g / m² 2 , preferably at least 7 g / m² 2 and at most 28 g / m² 2 and especially preferably at least 8 g / m² 2 and at most 25 g / m² 2 exhibits.

28. Method according to any of the preceding claims, wherein the separator produced in steps A to E has a mean thickness of a single sheet, according to ISO 534:2011, of at least 8 pm and at most 75 pm, preferably at least 10 pm and at most 60 pm, and particularly preferably at least 12 pm and at most 50 pm.

29. Separator for an electrochemical element comprising at least 80% fibrillated fibers of regenerated cellulose by mass, and which has a surface energy of at least 80 mJ / g determined by inverse gas chromatography, which is formed by the sum of dispersed and specific surface energy, wherein the polarity of the separator is at least 0.06 and at most 0.20, where the polarity is the proportion of the specific surface energy in mJ / g to the surface energy in mJ / g.

30. Separator according to claim 29, wherein the surface energy of the separator is at least 90 mJ / g and at most 300 mJ / g, preferably at least 100 mJ / g and at most 200 mJ / g.

31. Separator according to claim 29 or 30, wherein the polarity of the separator is at least 0.07 and at most 0.18, preferably at least 0.075 and at most 0.

15.

32. Separator according to claim 29, wherein the surface energy of the separator is at least 80 mJ / g and the polarity is at least 0.07 and at most 0.18, preferably at least 0.075 and at most 0.

15.

33. Separator according to claim 29, wherein the surface energy is at least 90 mJ / g and at most 300 mJ / g and the polarity is at least 0.06 and at most 0.20, preferably at least 0.07 and at most 0.18 and particularly preferably at least 0.075 and at most 0.

15.

34. Separator according to claim 29, wherein the surface energy of the separator is at least 100 mJ / g and at most 200 mJ / g and the polarity is at least 0.06 and at most 0.20, preferably at least 0.07 and at most 0.18 and particularly preferably at least 0.075 and at most 0.

15.

35. Separator according to any one of claims 29 to 34, wherein at least 90%, preferably at least 95% and particularly preferably at least 99% of the mass of the separator is formed by fibrillated fibers of regenerated cellulose.

36. Separator according to any one of claims 29 to 35, wherein the degree of refining of the fibrillated fibers of regenerated cellulose in the separator is at least 75°SR and at most 95°SR, preferably at least 78°SR and at most 92°SR and particularly preferably at least 80°SR and at most 90°SR.

37. Separator according to any one of claims 29 to 36, wherein the fibrillated fibers are regenerated cellulose spun in a solvent, in particular lyocell fibers.

38. Separator according to one of claims 29 to 37, comprising, in addition to the fibrillated fibers of regenerated cellulose, further cellulose fibers.

39. Separator according to claim 38, wherein the further cellulose fibers are formed wholly or partly by non-fibrillated fibers of regenerated cellulose.

40. Separator according to claim 38, wherein the further cellulose fibers are formed wholly or partly by pulp fibers, wherein the pulp fibers are preferably obtained from coniferous trees, deciduous trees or other plants, in particular hemp, flax, jute, ramie, kenaf, kapok, coconut, abaca, sisal, bamboo, cotton or esparto grass, or from recycled paper pulp, or are a mixture of pulp fibers of two or more different sources mentioned.

41. Separator according to claim 40, wherein the cellulose fibers are at least partly microfibrillated cellulose fibers, nanofibrillated cellulose fibers or cellulose fibers with a mean length-weighted length of at most 0.2 mm, preferably at most 0.15 mm.

42. Separator according to any one of claims 38 to 41, wherein the proportion of further cellulose fibers is at least 1% and at most 10%, preferably at least 2% and at most 10% and particularly preferably at least 3% and at most 7%, in each case based on the mass of the separator.

43. Separator according to one of claims 40 or 41, wherein at least 1% and at most 10%, preferably at least 2% and at most 10% and particularly preferably at least 3% and at most 7% of the mass of the separator are formed by nanofibrillated cellulose fibers or microfibrillated cellulose fibers or cellulose fibers with a mean length-weighted length of at most 0.2 mm, preferably of at most 0.15 mm.

44. Separator according to any one of claims 40 to 43, wherein the separator consists of fibrillated fibers of regenerated cellulose and nanofibrillated and / or microfibrillated cellulose fibers.

45. Separator according to claim 38, wherein the separator comprises at least 80% and at most 90% fibrillated fibers of regenerated cellulose, at least 10% and at most 20% cellulose fibers from cotton and at most 5% nanofibrillated cellulose fibers, the percentages relating to the mass of the separator.

46. ​​Separator according to any one of claims 29 to 45, comprising further fibers selected from the group consisting of fibers made of cellulose derivatives, glass fibers, and plastic fibers. 47- Separator according to claim 46, wherein the plastic fibers are selected from the group consisting of fibers made of polyol olefins, in particular polyethylene or polypropylene; polyesters, in particular polyethylene terephthalate or polylactic acids; polyarylates, in particular poly-(4-hydroxybenzoic acid-co-6-hydroxy-2-naphthoic acid); polyethers; polysulfones; polyurethanes; polyamides; aromatic polyamides, in particular poly-(p-phenylene terephthalamide); polyimides; polyvinyl alcohol; polyacrylates, in particular polyacrylonitrile or poly-(acrylonitrile-co-methyl acrylate); polyphenylene sulfide; and poly-(ethylene-co-vinyl acetate).

48. Separator according to any one of claims 29 to 47, wherein the separator comprises filler, wherein the filler is preferably selected from the group consisting of kaolin, titanium dioxide (TiO2), silicon dioxide (SiO2), aluminum oxide (Al2O3), zirconium dioxide (ZrO2), calcium carbonate (CaCO3) and zinc oxide (ZnO), or is formed by a mixture of two or more of these fillers, wherein the filler constitutes at least 1% and at most 10%, preferably at least 1% and at most 7% of the mass of the separator.

49. Separator according to one of claims 29 to 48, having a basis weight of at least 6 g / m² 2 and at most 30 g / m² 2 , preferably of at least 7 g / m³ 2 and at most 28 g / m² 2 and especially preferably of at least 8 g / m² 2 and at most 25 g / m² 2 .

50. Separator according to any one of claims 29 to 49, having a mean thickness of a single sheet, according to ISO 534:2011, of at least 8 pm and at most 75 pm, preferably at least 10 pm and at most 60 pm, and particularly preferably at least 12 pm and at most 50 pm.

51. Separator according to one of claims 29 to 50, the density of which is at least 300 kg / m³ 3 and at most 1000 kg / m² 3 , preferably at least 350 kg / m² 3 and at most 900 kg / m² 3 and especially preferably at least 400 kg / m² 3 and at most 850 kg / m² 3 amounts.

52. Separator according to any one of claims 29 to 51, the tensile strength of which, according to ISO 1924-2:2008 in the machine direction, based on the width, is at least 0.3 kN / m and at most 2.0 kN / m, preferably at least 0.4 kN / m and at most 1.5 kN / m.

53. Separator according to any one of claims 29 to 52, the tensile strength in the machine direction, based on the cross-sectional area, being at least 15 MPa and at most 75 MPa, preferably at least 25 MPa and at most 60 MPa.

54. Separator according to any one of claims 29 to 53, wherein the ratio of the tensile strength according to ISO 1924-2:2008 in the machine direction to that in the transverse direction is at least 1.0 and at most 3.0, preferably at least 1.2 and at most 2.2 and particularly preferably at least 1.5 and at most 1.

8.

55. Separator according to any one of claims 29 to 54, the elongation at break of which, according to ISO 1924-2:2008 in the machine direction, is at least 0.5% and at most 5.0%, preferably at least 1.0% and at most 4.0%.

56. Separator according to any one of claims 29 to 55, the shrinkage of which, conditioned according to ISO 187:2022, after heating to 150°C for 3 hours, is at least 0.5% and at most 2.0%, preferably at least 0.5% and at most 1.5%.

57. Separator according to any one of claims 29 to 56, the porosity p of which is at least 35% and at most 75%, preferably at least 40% and at most 70%, wherein the porosity p is to be calculated as follows: where the basis weight m in g / m² is used in the above equation 2 , the mean thickness of a single sheet d in pm and the moisture content c of the separator in % are to be used.

58. Separator according to any one of claims 29 to 57, the air permeability of which according to Gurley is at least 2 s and at most 60 s, preferably at least 4 s and at most 50 s and particularly preferably at least 5 s and at most 40 s.

59. Separator according to any one of claims 29 to 58, wherein the MacMullin number is at least 2 and at most 14, preferably at least 2.5 and at most 12 and particularly preferably at least 3 and at most 10.

60. Electrochemical element comprising at least two electrodes, an electrolyte and at least one separator according to any one of claims 29 to 59.

61. Electrochemical element according to claim 60, wherein the electrochemical element is a battery, preferably a lithium-ion battery, wherein the electrolyte is preferably a non-aqueous electrolyte.

62. Electrochemical element according to claim 60, wherein the electrochemical element is a double-layer capacitor or a supercapacitor.

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