Method for producing a separator with an improved suction height

Abstract

The invention relates to a method for producing a separator for electrochemical elements, having the following steps A to F: A – providing an aqueous suspension comprising fibrillatable fibers of regenerated cellulose, B – fibrillating the fibrillatable fibers of regenerated cellulose in the aqueous suspension of step A by grinding to a freeness number of at least 80 °SR and at most 92 °SR, C – providing the aqueous suspension of step B in a headbox of a Fourdrinier machine, D – discharging the aqueous suspension of step C from the headbox onto a circulating screen of the Fourdrinier machine, the circulating speed of the screen being at least 0.0% and at most 4.0% greater than the speed at which the aqueous suspension flows from the headbox, E – dewatering the fiber web, and F – calendering the fiber web in a specially designed calender. The separator produced in this manner has a porosity-compensated EC / DMC suction height in the transverse direction (I) of at least 8.0 mm.

Description

[0001] delfortgroup AG H7O421WO

[0002] Method for manufacturing a separator with improved suction height

[0003] AREA OF INVENTION

[0004] The invention relates to a method for producing a separator for electrochemical elements, which is essentially formed from fibers of regenerated cellulose and to which a special fiber structure is imparted by the manufacturing process, such that it exhibits high permeability and a high absorption capacity in the transverse direction. The invention also relates to a separator and an electrochemical element incorporating this separator.

[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] There is interest in further optimizing the separator to improve the behavior of an electrochemical cell manufactured from it, without compromising the aforementioned key properties regarding volumetric energy density, chemical resistance, and thermal stability. SUMMARY OF THE INVENTION

[0011] The invention is therefore based on the objective of providing a method for producing an improved separator for electrochemical elements, which makes it possible to improve the properties of an electrochemical element produced therefrom without, however, impairing the aforementioned central properties with regard to volumetric energy density, chemical resistance, and thermal stability.

[0012] This problem is solved by a method for producing a separator for electrochemical elements according to claim i, a separator according to claim 26, and an electrochemical element comprising this separator according to claim 55. Advantageous embodiments are specified in the dependent claims.

[0013] The inventor has found that the uptake of the electrolyte by the separator in an electrochemical element plays a major role in several respects.

[0014] Firstly, in the production of an electrochemical cell, the space between the electrodes, which also contains the separator, is filled with an electrolyte. For an efficient manufacturing process, it is advantageous if the separator can absorb this electrolyte as quickly as possible, thus enabling a more efficient production process, and if the electrolyte is distributed evenly within the separator, ensuring good properties of the electrochemical cell. The inventor recognized that, in many electrochemical cells, such as cylindrical cells, the transverse transport of the electrolyte is of particular importance because, in the usual orientation of the electrochemical cell, it occurs against the direction of gravity.

[0015] The rapid absorption of the electrolyte by the separator is surprisingly also of practical importance during operation. This is because the electrodes of electrochemical cells deform during charging and discharging. For example, the porous anode of a lithium-ion battery expands during charging due to the incorporation of lithium ions and shrinks again during discharge. This effect is particularly pronounced in graphite anodes with a higher silicon content. Due to the typically quite rigid casing of an electrochemical cell, the internal pressure increases during charging. In particular, the electrodes exert high pressure on the separator, which in turn causes some of the electrolyte to be displaced from the separator and the space between the electrodes. During discharge, the pressure drops again, and the previously displaced electrolyte can be absorbed by the separator once more.According to the inventor's findings, it is important that the electrolyte is absorbed relatively quickly into the separator and is distributed evenly within the separator, because this improves the lifespan of the electrochemical element.

[0016] According to the inventor's findings, conventional separators generally do not allow for rapid electrolyte uptake. This is because, for the reasons mentioned above, the separator should be as thin as possible, particularly to provide short paths for the ions between the electrodes and to ensure an increased energy density. To achieve a sufficiently thin surface, separators are often calendered. However, this also increases the density, resulting in slower electrolyte uptake.

[0017] In fiber-based separators, the orientation of the fibers further complicates matters, as the electrolyte uptake occurs at different rates in different directions. Fiber-based separators typically have a machine direction, in which the separator moves through the machine during manufacturing, and a transverse direction, which lies orthogonal to the machine direction and in the plane of the separator. The fibers and the pores they form are generally oriented more towards the machine direction, resulting in uneven electrolyte uptake.

[0018] The inventor recognized the importance of the separator's ability to rapidly absorb an electrolyte. Furthermore, he determined that the inventive method allows the fiber structure of the separator to be influenced in such a way that even with thin, high-density separators, the electrolyte absorption behavior is improved, thus achieving further advantages in addition to the reduced thickness, particularly rapid transverse electrolyte absorption.

[0019] The inventive method for producing a separator for electrochemical elements comprises the following steps A to F.

[0020] A - Providing an aqueous suspension containing fibrillable fibers of regenerated cellulose

[0021] B - Fibrillation of the fibrillable fibers of regenerated cellulose in the aqueous suspension from step A by milling to a Schopper-Riegler grade according to ISO 5267-1:1999 of at least 80°SR and at most 92°SR,

[0022] C - Providing the aqueous suspension comprising the fibrillated fibers of regenerated cellulose from step B in a headbox of a Fourdrinier paper machine,

[0023] D - Emptying the aqueous suspension from step C from the headbox onto a rotating wire of the Fourdrinier paper machine to form a fiber web, wherein the rotational speed of the wire and the speed at which the aqueous suspension flows from the headbox are matched such that the rotational speed of the wire is at least 0.0% and at most 4.0% higher than the speed at which the aqueous suspension flows from the headbox.

[0024] E - Dewatering of the fiber web by mechanical pressure and the application of heat,

[0025] F - Calendering the fiber web in a calender, wherein the calender has at least 2 roll gaps, each formed by a pair of rolls, and each of the rolls comprises a roll body and a cover, and wherein the fiber web passes through at least 2 and at most 4 roll gaps, the temperature of the rolls forming the roll gaps is at least 105°C and at most 115°C, the line load in the roll gaps is at least 50 N / mm and at most 400 N / mm, and the covers of the rolls forming the roll gaps have a Shore hardness D, measured according to ISO 868:2003, of at least 88 and at most 92, and wherein at least 80% of the mass of the separator produced in steps A to F is formed by fibrillated fibers of regenerated cellulose, and wherein the separator produced in steps A to F has a mean thickness of a single sheet according to ISO 534:2011 of at most 22 pm and a density according to ISO 534:2011 of at least 0.60 g / cm³ 3and at most 1.10 g / cm² 3 exhibits and the separator produced in steps A to F has a machine direction and a transverse direction orthogonal to it in the plane of the separator and which is determined from the EC / DMC suction height h, in the transverse direction in mm and the density p in g / cm³ 3 Calculated porosity-compensated EC / DMC suction height in the transverse direction at least 8.0 mm, where the EC / DMC suction height h, in the transverse direction, is measured according to ISO 8787:1986, with the sole deviation that instead of the water specified in the standard ISO 8787:1986, a mass-based 1:1 mixture of ethylene carbonate and dimethyl carbonate is used.

[0026] The machine direction is the direction in which the fiber web runs through the machine in steps D, E, and F; the direction orthogonal to this, lying in the plane of the fiber web, is the transverse direction. The machine direction and the transverse direction apply analogously to the separator produced from the material in steps A to F.

[0027] According to the inventor's findings, the properties of a separator, particularly the transverse uptake rate of the electrolyte, can be favorably influenced by combining various features of the manufacturing process. A first feature is the specific fineness of the fibrillated fibers of regenerated cellulose from step B. In this range of fineness, the fibers are largely fibrillated, but a sufficient number of areas remain where the fiber bundles are not fibrillated. These thicker fiber portions facilitate the formation of a fiber web with isotropic properties and create a stable porous structure that is retained even after calendering in step F, thus accelerating electrolyte uptake.Another characteristic is the small difference between the speed at which the aqueous suspension flows from the stock feed of the Fourdrinier paper machine onto the rotating wire in step D and the speed of the rotating wire. The ratio of these speeds is known in the field as the wire-to-jet ratio and is usually displayed by the Fourdrinier paper machine's process control system. Speeds for determining the wire-to-jet ratio can also be measured, for example, with the pSpeed ​​laser encoder system from Elovis GmbH, Germany. This small speed difference results in the fibers being oriented less in the machine direction and more randomly. The thicker sections, where the fiber fibrils are still bonded together, are particularly prone to random orientation, carrying along the bonded fibrils.This effect is enhanced by the appropriately selected degree of refining and makes it possible to increase the suction height in the transverse direction. A third feature is the hardness of the calender roll coverings. According to the inventor, in addition to the number of roll gaps, the line load, and the temperature during calendering in step F, the Shore hardness D of the calender roll coverings is selected so favorably that the fiber structure formed in step D is strengthened but not destroyed. According to the inventor, the specific combination of all these features in the inventive process is crucial for achieving improved suction behavior in the transverse direction and an approximately isotropic suction height.

[0028] The inventor has found that fibrillated fibers of regenerated cellulose are particularly well suited for the separator according to the invention. In particular, lyocell fibers can be readily fibrillated for this purpose by milling according to step B, resulting in a fiber web that, despite its low thickness and high density, exhibits a high absorption height in the transverse direction.

[0029] The thickness of the separator produced in steps A to F is determined according to ISO 534:2011 as the mean thickness of a single sheet, and the density can be calculated according to ISO 534:2011 as the quotient of the basis weight and the mean thickness of a single sheet.

[0030] The suction head is determined according to a slightly modified version of ISO 8787:1986. This standard specifies that the measurement is to be carried out with water. However, the inventor's experiments have shown that cellulose fibers behave quite differently with respect to water than with respect to an electrolyte and the aprotic-polar solvents used therein. In particular, cellulose fibers swell in water and initially absorb water very rapidly, but this absorption also quickly ceases. In contrast, electrolytes based on aprotic-polar solvents are absorbed by the separator quite uniformly over time. To characterize the behavior of the separator in such a way that it is also meaningful for its properties in the electrochemical cell, the inventor found that a mass-based 1:1 mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) proved more effective.This solvent mixture is found in many electrolytes and is used in various standardized test procedures for separators. The suction head is therefore measured according to ISO 8787:1986, with the sole exception that a 1:1 mass-based mixture of ethylene carbonate and dimethyl carbonate is used instead of water. To clearly indicate this deviation from ISO 8787:1986, the suction head determined with this liquid is referred to as the EC / DMC suction head. The standard ISO 8787:1986 is incorporated into this disclosure by reference. It should be noted that, according to section 10(f), the standard ISO 8787:1986 permits deviations from the measurement procedure specified therein, provided that these deviations—as in this case, the use of the EC / DMC mixture as the test liquid instead of water—are reported in the measurement report.However, in all further details the measurement shall be carried out in accordance with ISO 8787:1986, including the measurement time of 10 minutes specified therein (see section 7 of ISO 8787:1986).

[0031] 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 dimensionless number. The porosity of the separator can be estimated from its density, measured according to ISO 534:2011, where the density p0 for fibers is 1.50 g / cm³. 3 is chosen. 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 density p is in g / cm³ 3 to be used. This will give the porosity a value between 0 and 1.

[0032] The inventor's experiments show that the suction head can be increased by increasing the separator's porosity; in particular, a direct proportionality to the square root of the porosity is observed. While a high porosity can easily be achieved through a greater thickness, the performance requirements of electrochemical elements necessitate keeping the thickness as low as possible. Furthermore, the thickness cannot always be arbitrarily varied but must be tailored to the specific type of electrochemical element for which the separator is intended. The parameter hh

[0033] According to the inventor, VLP 1.50 is an EC / DMC absorption height determined by the fiber structure of the separator, adjusted for the influence of porosity, and is therefore referred to as the "porosity-compensated EC / DMC absorption height." The porosity-compensated EC / DMC absorption height quantifies how far the EC / DMC absorption height, and thus the electrolyte uptake rate in the separator, could be increased beyond a mere change in porosity by adapting the fiber structure in the inventive process. It therefore characterizes the fiber structure and is a structural parameter of the separator.

[0034] The fibrillable fibers of regenerated cellulose in step A are preferably solvent-spun fibers. For example, lyocell fibers are particularly well suited for the process according to the invention.

[0035] The linear density of the fibrillable fibers of regenerated cellulose in step A is important for the fibrillation of the fibers in step B. Preferably, the mean linear density of the fibrillable fibers of regenerated cellulose in step A 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).

[0036] The length of the fibrillable fibers of regenerated cellulose 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 fibrillation in step B. Preferably, the average length of the fibrillable fibers of regenerated cellulose in step A is at least 2 mm and at most 8 mm, and particularly preferably at least 3 mm and at most 6 mm.

[0037] In step B, the fibrillable fibers of regenerated cellulose are fibrillated by milling. "Fibrillated" here means that the fibers have passed through at least one milling unit in step B that is capable of at least partially separating the fibrils bound together in a fiber bundle. It is not essential, nor is it within the scope of the invention, that all fibers are actually completely fibrillated, but only that they have passed through this milling unit and are fibrillated to the extent necessary to achieve the degree of refining according to the invention. Preferably, the degree of refining of the fibrillated fibers of regenerated cellulose in step B is at least 81°SR and at most 90°SR, and most preferably at least 82°SR and at most 88°SR.

[0038] In addition to the fibrillated fibers of regenerated cellulose, the suspension in step C can comprise further cellulose fibers, so that in a preferred embodiment of the process, providing the aqueous suspension in step C includes adding further cellulose fibers.

[0039] Preferably, the additional cellulose fibers in the suspension in step C can be formed entirely or partially by non-fibrillated fibers of regenerated cellulose.

[0040] 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.

[0041] Particularly preferred are the cellulose fibers, at least partially microfibrillated, nanofibrillated, or with a mean length-weighted length of no more than 0.20 mm, preferably no more than 0.15 mm. These types of cellulose fibers are especially well-suited for providing the separator with a small mean pore size. The mean length-weighted length of the cellulose fibers can be determined by optical analysis according to ISO 16065-2:2014.

[0042] In a preferred embodiment of the process, providing the aqueous suspension in step C includes adding nanofibrillated and / or microfibrillated cellulose fibers, such that the separator produced in steps A to F contains or consists of fibrillated fibers of regenerated cellulose and nanofibrillated and / or microfibrillated cellulose fibers.

[0043] In a particular embodiment of the process, providing the aqueous suspension in step C includes adding a mixture of cellulose fibers such that the separator produced in steps A to F 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 referring to the mass of the separator produced in steps A to F. Preferably, the speed of the circulating screen in step D is at least 0.5% and at most 3.5% higher, and particularly preferably at least 1.0% and at most 2.5% higher, than the speed at which the aqueous suspension flows from the headbox.

[0044] The dewatering of the fiber web in step E can be carried out according to the methods commonly used in papermaking and preferably includes dewatering in the press section and drying in the dryer section of a paper machine.

[0045] Calendering in step F is important to reduce the thickness of the separator and smooth the surface. The aim is to minimize the reduction in the separator's porosity and, above all, to avoid destroying the fiber structure created in step D.

[0046] Preferably, the fiber web passes through two or three roll gaps during calendering in step F.

[0047] Preferably, the temperature of the rollers forming the roller gap in step F is at least 108°C and at most 112°C.

[0048] Preferably, the line load in the roll gaps in step F is at least 70 N / mm and at most 350 N / mm, particularly preferably at least 100 N / mm and at most 300 N / mm.

[0049] Preferably, the Shore hardness D of the roller coverings in step F, measured according to ISO 868:2003, is at least 89 and at most 91.

[0050] The separator produced in steps A to F 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.

[0051] The separator produced in steps A to F preferably has a basis weight of at least 6 g / m². 2 and at most 22 g / m² 2 , particularly preferably of at least 7 g / m³ 2 and at most 21 g / m² 2 and especially preferably of at least 8 g / m² 2 and at most 20 g / m² 2 The basis weight can be determined according to ISO 536:2019.

[0052] Preferably, the porosity-compensated EC / DMC suction height in the transverse direction of the separator produced in steps A to F is at least 8.5 mm and at most 25.0 mm, particularly preferably at least 9.0 mm and at most 20.0 mm.

[0053] Preferably, the EC / DMC suction height in the transverse direction of the separator produced in steps A to F is at least 6.0 mm and at most 20.0 mm, particularly preferably at least 7.0 mm and at most 18.0 mm, and most preferably at least 8.0 mm and at most 15.0 mm. The EC / DMC suction height can also be determined in the machine direction in an analogous manner to the transverse direction, and a porosity-compensated EC / DMC suction height in the machine direction can be calculated from this.

[0054] Preferably, the porosity-compensated EC / DMC suction height in the machine direction of the separator produced in steps A to F is at least 10.0 mm and at most 30.0 mm, particularly preferably at least 10.5 mm and at most 25.0 mm and most preferably at least 11.0 mm and at most 25.0 mm.

[0055] Preferably, the EC / DMC suction height in the machine direction of the separator produced in steps A to F is at least 7 mm and at most 25 mm, particularly preferably at least 8 mm and at most 20 mm and most preferably at least 9 mm and at most 18 mm.

[0056] Furthermore, commercially available calendered separators exhibit highly anisotropic absorption behavior, meaning that the electrolyte distributes itself at different rates in the machine direction and transverse direction. This is disadvantageous, for example, when the electrochemical cell is a battery and the electrolyte needs to be absorbed uniformly in the separator during each charge and discharge cycle. For thin, high-density separators, especially calendered separators, this ratio can be significantly higher than 1.30.

[0057] The fiber structure of the separator produced in the inventive process allows for an almost isotropic suction behavior to be achieved even with separators of small thickness and high density. This behavior can be characterized by the ratio of the EC / DMC suction heights in the machine direction and transverse direction. For this purpose, the EC / DMC suction height of a sample of the separator is first measured in the machine direction, and then the EC / DMC suction height of another sample of the same separator is measured in the transverse direction. The ratio of these suction heights describes how isotropically the electrolyte will be distributed in the separator.

[0058] Preferably, the ratio of the EC / DMC suction heights of the separator produced in steps A to F in the machine direction and in the transverse direction is at least 0.90 and at most 1.35, particularly preferably at least 0.95 and at most 1.30, and most preferably at least 1.00 and at most 1.30.

[0059] Preferably, the mean thickness of a single sheet of the separator produced in steps A to F is at least 8 pm and at most 21 pm, particularly preferably at least 9 pm and at most 20 pm, and most preferably at least 10 pm and at most 19 pm. Preferably, the density of the separator produced in steps A to F is at least 0.65 g / cm³. 3 and at most 1.05 g / cm² 3 and especially preferably at least 0.70 g / cm² 3 and at most 1.00 g / cm² 3 .

[0060] Another aspect of the invention relates to a separator that can be obtained according to the inventive method. According to this aspect of the invention, the separator for an electrochemical element comprises, based on its mass, at least 80% fibrillated fibers of regenerated cellulose, and the mean thickness of a single sheet of the separator according to ISO 534:2011 is at most 22 pm and its density according to ISO 534:2011 is at least 0.60 g / cm³. 3 and at most 1.10 g / cm² 3 The separator according to the invention has a machine direction and a transverse direction orthogonal to it and lying in the plane of the separator, and it has a fiber structure such that the EC / DMC suction height h, in the transverse direction in mm and the density p in g / cm³ 3The calculated porosity-compensated EC / DMC suction height in the transverse direction hoo h _ P- 1.50 is at least 8.0 mm, where the EC / DMC suction height h«> in the transverse direction is measured according to ISO 8787:1986, with the only deviation being that instead of the water specified in the standard ISO 8787:1986, a mass-based 1:1 mixture of ethylene carbonate and dimethyl carbonate is used.

[0061] According to the inventor, the high porosity-compensated EC / DMC suction height in the transverse direction of the separator, as described in the invention, is crucial for giving an electrochemical element manufactured therefrom a longer service life and more favorable properties during production, charging, and discharging 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 porosity-compensated EC / DMC suction height in the transverse direction as described in the invention. However, according to this aspect of the invention, the separator is defined only by the aforementioned properties, in particular the high porosity-compensated EC / DMC suction height in the transverse direction as described in the invention, and not by the method of its manufacture.

[0062] Preferably, the porosity-compensated EC / DMC suction height of the separator in the transverse direction is at least 8.5 mm and at most 25.0 mm, particularly preferably at least 9.0 mm and at most 20.0 mm. More preferably, the EC / DMC suction height of the separator in the transverse direction is at least 6.0 mm and at most 20.0 mm, particularly preferably at least 7.0 mm and at most 18.0 mm, and most preferably at least 8.0 mm and at most 15.0 mm.

[0063] Preferably, the porosity-compensated EC / DMC suction height of the separator in the machine direction is at least 10.0 mm and at most 30.0 mm, particularly preferably at least 10.5 mm and at most 25.0 mm, and most preferably at least 11.0 mm and at most 25.0 mm.

[0064] Preferably, the EC / DMC suction height of the separator in the machine direction is at least 7 mm and at most 25 mm, particularly preferably at least 8 mm and at most 20 mm, and most preferably at least 9 mm and at most 18 mm.

[0065] Preferably, the ratio of the EC / DMC suction heights of the separator in the machine direction and in the transverse direction is at least 0.90 and at most 1.35, particularly preferably at least 0.95 and at most 1.30, and most particularly preferably at least 1.00 and at most 1.30.

[0066] Preferably, the mean thickness of a single sheet of the separator is at least 8 pm and at most 21 pm, particularly preferably at least 9 pm and at most 20 pm, and most preferably at least 10 pm and at most 19 pm.

[0067] Preferably, the density of the separator is at least 0.65 g / cm³. 3 and at most 1.05 g / cm² 3 and especially preferably at least 0.70 g / cm² 3 and at most 1.00 g / cm² 3 .

[0068] The separator 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 separator mass is formed by fibrillated fibers of regenerated cellulose. Preferably, the fineness of the fibrillated fibers of regenerated cellulose is at least 80°SR and at most 92°SR, particularly preferably at least 81°SR and at most 90°SR, and most preferably at least 82°SR and at most 88°SR.

[0069] The fibrillated fibers of regenerated cellulose are preferably fibers spun in a solvent.

[0070] In addition to the fibrillated fibers of regenerated cellulose, the separator according to the invention can also comprise further cellulose fibers.

[0071] Preferably, the additional cellulose fibers can be formed wholly or partly from non-fibrillated fibers of regenerated cellulose. Preferably, the additional cellulose fibers can be formed wholly or partly 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 for the production of the separator. Pulp fibers obtained from hardwoods, softwoods, or cotton are particularly preferred.

[0072] Particularly preferred are the cellulose fibers, at least partially, 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. These types of cellulose fibers are particularly well suited for equipping the separator with a small mean pore size.

[0073] 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.

[0074] 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 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 0.20 mm, preferably of at most 0.15 mm.

[0075] In a particularly preferred embodiment, the separator contains or consists of fibrillated fibers of regenerated cellulose and nanofibrillated and / or microfibrillated cellulose fibers.

[0076] 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.

[0077] 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 fibers made of polyolefins like polyethylene or polypropylene; of polyesters such as polyethylene terephthalate or polylactic acid; of polyarylates such as poly(4-hydroxybenzoic acid-co-6-hydroxy-2-naphthoic acid); of 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).

[0078] The separator according to the invention can preferably comprise, in addition to the fibrillated fibers of regenerated cellulose, a filler. 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.

[0079] The separator according to the invention can 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.

[0080] The separator according to the invention preferably has an basis weight of at least 6 g / m². 2 and at most 22 g / m² 2 , particularly preferably of at least 7 g / m³ 2 and at most 21 g / m² 2 and especially preferably of at least 8 g / m² 2 and at most 20 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.

[0081] 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 is taken from the separator for measurement. As explained in the context of EC / DMC suction head, a distinction is made between the machine direction and the transverse direction.

[0082] 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.

[0083] The tensile strength according to ISO 1924-2:2008 is preferably higher in the machine direction of the separator according to the invention 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.

[0084] 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%.

[0085] 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%. This means that the separator is first conditioned according to ISO 187:2022, and only then heated to 150°C for 3 hours in order to determine the shrinkage by comparing the dimensions immediately before and immediately after the 3-hour heating period.

[0086] The pore structure is of great importance for the properties of an electrochemical element manufactured from the separator according to the invention.

[0087] The pore structure can be characterized, in simplified terms, by the Gurley air permeability. Air permeability 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 70 s, particularly preferably at least 5 s and at most 55 s, and most preferably at least 10 s and at most 50 s, where a lower Gurley value indicates high air permeability.

[0088] The separator can be used in electrochemical cells. An electrochemical cell comprising the separator according to the invention is therefore a further aspect of the invention.

[0089] 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, and particularly preferably, the electrochemical element is a lithium-ion battery or a sodium-ion battery.

[0090] DESCRIPTION OF SOME PREFERRED EXECUTIONS AND COMPARISON WITH NON-INDUCTIVE EXECUTIONS

[0091] In the following, some preferred embodiments of the method and separators according to the invention, as well as separators not according to the invention, are described as a comparative example.

[0092] For the separators Si, S2, S3, ..., S9 and S10 according to the invention, lyocell fibers with a linear density of 1.25 g / 10000 m³ (1.25 dtex) to 1.7 g / 10000 m³ (1.7 dtex) and a length of 4 mm were used, and an aqueous suspension comprising these fibers was provided in step A. The fibers were fibrillated according to step B by milling them to a fineness between 80°SR and 92°SR. In some embodiments, nanofibrillated cellulose fibers were added to the aqueous suspension containing the fibrillated lyocell fibers in step C, so that the separators according to the invention consisted of 95% to 100% fibrillated lyocell fibers and 0% to 5% nanofibrillated cellulose fibers.

[0093] In step D, the aqueous suspension from step C flowed from the headbox of a Fourdrinier paper machine onto the rotating screen of the Fourdrinier paper machine, the speed of the rotating screen being about 1.3% higher than the speed of the suspension flowing from the headbox, and a fiber web formed on the screen.

[0094] According to step E, the fiber web was dewatered at the screen and by pressure in the press section of the paper machine and dried by contact with heated drying cylinders.

[0095] In step F, the fiber web was calendered in a calender with two or three roll nips at a temperature of no°C and a line load of 70 N / mm² to approximately 350 N / mm². The Shore hardness D of the calender roll coverings, measured according to ISO 868:2003, was 90.

[0096] The separators produced in steps A to F had basis weights of approximately 11.0 g / m². 2 up to approximately 17.0 g / m² 2on.

[0097] For comparison, non-inventive separators Zi, Z2, Z3, and Z4 were produced from the same lyocell fibers, but the features of the manufacturing process were partly chosen outside the ranges specified in the invention, and calendering in step F was partly omitted. Finally, a non-inventive, commercially available, fiber-based separator Z5 was also used for comparison, although its fiber composition was not analyzed. Due to its small thickness and high density, it was assumed to be a calendered separator.The separator data are summarized in Table 1, where "BW" is the basis weight according to ISO 536:2019, "TH" is the mean thickness of a single sheet according to ISO 534:2011, "DE" is the density according to ISO 534:2011, "LY" is the percentage of fibrillated lyocell fibers based on the mass of the separator, "NFC" is the percentage of nanofibrillated cellulose fibers based on the mass of the separator, "CR-MD" is the EC / DMC suction height in the machine direction, "CR-CD" is the EC / DMC suction height in the transverse direction, and "MD / CD" is the ratio of the EC / DMC suction height in the machine direction to the EC / DMC suction height in the transverse direction. The EC / DMC suction heights were determined according to the previously described procedure.

[0098] Table 1 - Data for separators according to the invention and those not according to the invention

[0099] Table 2 lists further data of the separators according to the invention and those not according to the invention, where the designation of the examples is identical to Table 1 and “PO” denotes the porosity calculated from the density, “CR-MD-PC” the porosity-compensated EC / DMC suction height in the machine direction and “CR-CD-PC” the porosity-compensated EC / DMC suction height in the transverse direction.

[0100] Table 2 - Further data on separators according to and not according to the invention The separators Si, S2, S3, S9, and S10 according to the invention demonstrate that fiber-based separators can be produced using the inventive method. Their porosity-compensated EC / DMC suction heights are comparatively high, and their ratio of EC / DMC suction heights in the machine direction and transverse direction is close to 1.0, indicating an almost isotropic suction behavior. The non-inventive separators Zi and Z2 show that EC / DMC suction heights of 20 mm to 35 mm can be easily achieved with a high thickness and thus high porosity. However, due to their high thickness, electrochemical elements produced from the non-inventive separators Zi and Z2 will not exhibit such good properties and, in particular, will not achieve such a high energy density as electrochemical elements with otherwise similar but thinner separators.

[0101] A comparison with the commercially available, fiber-based separator Z5 shows that calendered separators generally exhibit particularly low EC / DMC suction heights of 4 mm to 5 mm, and that the ratio of EC / DMC suction heights in the machine direction to the transverse direction is also particularly small. This would be a disadvantage, especially for cylindrical batteries, where the electrolyte is partially displaced from the separator during each charge and discharge cycle and then, due to the battery manufacturing process, must be reabsorbed, primarily in the machine direction. However, for this type of separator, the EC / DMC suction height in the machine direction is particularly low.

[0102] The separator Z3, which is not according to the invention, was manufactured using an identical process, with the exception that a temperature of 20°C was used in step F during calendering in three rolling gaps. This achieves a small thickness of only 13.3 pm and a high density of 0.94 g / cm³. 3 However, the EC / DMC suction heights of 5 mm in the machine direction and 4 mm in the transverse direction are practically no improvement compared to the non-inventive, commercially available separator Z5, and it does not achieve the favorable values ​​of the otherwise very similar inventive separator S9 with regard to the EC / DMC suction heights.

[0103] The non-inventive separator Z4 was manufactured using an identical process, with the exception that the fineness of the lyocell fibers was only 7°SR. This resulted in a higher density of thick fiber bundles compared to separators according to the invention. While this provides a favorable porous structure and high EC / DMC absorption heights, the separator cannot be calendered in such a way as to preserve this structure. The density achieved during calendering is 0.75 g / cm³. 3 and the thickness is 16.2 pm within the inventive interval, but due to the less intensive grinding in step B, the structure is coarser, has larger pores and thus achieves only low EC / DMC suction heights.

[0104] The tensile strength of the separators Si, S2, S3, ..., S9 and S10 according to the invention was measured in the machine direction according to ISO 1924-2:2008, and values ​​between 0.4 kN / m and 1.8 kN / m were obtained. Generally, a higher degree of refining of the lyocell fibers results in higher tensile strength. The tensile strength of the separators Si, S2, S3, ..., S9 and S10 according to the invention was also measured in the transverse direction according to ISO 1924-2:2008, and the ratio of the tensile strength in the machine direction to the tensile strength in the transverse direction was calculated; this ratio ranged between 1.08 and 2.49. The main influencing factor was the velocity difference between the rotating screen and the suspension flowing from the headbox in step D. A smaller velocity difference resulted in a smaller ratio of machine direction to transverse direction.

[0105] The elongation at break of the separators Si, S2, S3, ..., S9 and S10 according to the invention was measured in the machine direction according to ISO 1924-2:2008, and values ​​between 0.8% and 2.1% were obtained. More intensive calendering typically resulted in lower elongation at break. The shrinkage of the separators Si, S2, S3, S9 and S10 according to the invention was determined after conditioning according to ISO 187:2022 and subsequent heating to 150°C for 3 hours, and values ​​between 0.7% and 1.8% were obtained.

[0106] The Gurley air permeability of the separators Si, S2, S3, ..., S9 and S10 according to the invention was determined according to ISO 5636-5:2013 and values ​​between 11.0 s and 54.5 s were obtained.

[0107] The MacMullin number of the separators Si, S2, S3, ..., S9 and S10 according to the invention was also determined, and values ​​between 5.22 and 8.24 were obtained. The MacMullin 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 was measured according to the method described in "Application Note: Determination of MacMullin Numbers: The Stacking Method", 05.2021, rhd instruments GmbH & Co. KG. Indirectly, the MacMullin number 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.

[0108] The parameters of the separators Si, S2, S3, ..., S9 and S10 according to the invention show that they are very well suited for use in electrochemical cells. Furthermore, since they also exhibit a high EC / DMC suction head and an almost isotropic EC / DMC suction head, they can be incorporated particularly efficiently into electrochemical cells and can also contribute to increasing the service life of the electrochemical cells manufactured from them.

Claims

Claims i. Method for producing a separator for electrochemical elements, comprising the following steps Abis F: A - Providing an aqueous suspension containing fibrillable fibers of regenerated cellulose B - Fibrillation of the fibrillable fibers of regenerated cellulose in the aqueous suspension from step A by milling to a Schopper-Riegler grade according to ISO 5267-1:1999 of at least 80°SR and at most 92°SR, C - Providing the aqueous suspension comprising the fibrillated fibers of regenerated cellulose from step B in a headbox of a Fourdrinier paper machine, D - Emptying the aqueous suspension from step C from the headbox onto a rotating wire of the Fourdrinier paper machine to form a fiber web, wherein the rotational speed of the wire and the speed at which the aqueous suspension flows from the headbox are matched such that the rotational speed of the wire is at least 0.0% and at most 4.0% higher than the speed at which the aqueous suspension flows from the headbox. E - Dewatering of the fiber web by mechanical pressure and the application of heat, F - Calendering the fiber web in a calender, wherein the calender has at least 2 roll gaps, each formed by a pair of rolls, and each of the rolls comprises a roll body and a cover, wherein the fiber web passes through at least 2 and at most 4 roll gaps, the temperature of the rolls forming the roll gaps is at least 105°C and at most 115°C, the line load in the roll gaps is at least 50 N / mm and at most 400 N / mm, and the covers of the rolls forming the roll gaps have a Shore hardness D, measured according to ISO 868:2003, of at least 88 and at most 92, wherein at least 80% of the mass of the separator produced in steps A to F is formed by fibrillated fibers of regenerated cellulose, wherein the separator produced in steps A to F has a mean thickness of a single sheet according to ISO 534:2011 of at most 22 pm and a density according to ISO 534:2011 of at least 0.60 g / cm³ 3 and at most 1.10 g / cm²3 exhibits, and wherein the separator produced in steps A to F has a machine direction and a transverse direction orthogonal to it in the plane of the separator, and which is determined from the EC / DMC suction height h, in the transverse direction in mm and the density p in g / cm³ 3 calculated porosity-compensated EC / DMC suction height in the transverse direction hoo / 7TZ 1.50 is at least 8.0 mm, where the EC / DMC suction height h, in the transverse direction, is measured according to ISO 8787:1986, with the sole deviation being that instead of the water specified in the standard ISO 8787:1986, a mass-based 1:1 mixture of ethylene carbonate and dimethyl carbonate is used.

2. Method according to claim 1, wherein the fibrillable fibers of regenerated cellulose in step A are fibers spun in a solvent, in particular lyocell fibers.

3. Method according to claim 1 or 2, wherein the mean linear density of the fibrillable fibers of regenerated cellulose in step A is at least 0.6 g / 10000 m (0.6 dtex) and at most 3.0 g / 10000 m (3.0 dtex), preferably at least 0.8 g / 10000 m (0.8 dtex) and at most 1.8 g / 10000 m (1.8 dtex).

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

5. Method according to any of the preceding claims, wherein the degree of refining of the fibrillated fibers of regenerated cellulose in step B is at least 81°SR and at most 90°SR, preferably at least 82°SR and at most 88°SR.

6. Method according to one of the preceding claims, wherein the suspension in step C comprises, in addition to the fibrillated fibers of regenerated cellulose, further cellulose fibers.

7. The method of claim 6, wherein the further cellulose fibers in the suspension in step C are formed wholly or partly by non-fibrillated fibers of regenerated cellulose.

8. The method of claim 6, 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 derived 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 are obtained from recycled paper, or are a mixture of cellulose fibers from two or more different of the aforementioned sources.

9. Method according to claim 8, 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.

10. The method of claim 9, wherein the provision of the aqueous suspension in step C comprises the addition of nanofibrillated and / or microfibrillated cellulose fibers, such that the separator produced in steps A to F contains or consists of fibrillated fibers of regenerated cellulose and nanofibrillated and / or microfibrillated cellulose fibers.

11. The method of claim 6, wherein the provision of the aqueous suspension in step C comprises the addition of a mixture of cellulose fibers, such that the separator produced in steps A to F 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 in each case relating to the mass of the separator produced in steps A to F.

12. Method according to any of the preceding claims, wherein the speed of the circulating sieve in step D is at least 0.5% and at most 3.5%, preferably at least 1.0% and at most 2.5% higher than the speed at which the aqueous suspension flows out of the headbox.

13. Method according to one of the preceding claims, wherein the fiber web passes through two or three roll gaps during calendering in step F.

14. Method according to one of the preceding claims, wherein the temperature of the rolls forming the roll gap in step F is at least 108°C and at most 112°C.

15. Method according to one of the preceding claims, wherein the line load in the roll gaps in step F is at least 70 N / mm and at most 350 N / mm, preferably at least 100 N / mm and at most 300 N / mm.

16. Method according to any of the preceding claims, wherein the Shore hardness D of the coverings of the rollers in step F, measured according to ISO 868:2003, is at least 89 and at most 91.

17. A method according to any one of claims 1 to 5 or 12 to 16, 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 F is formed by fibrillated fibers of regenerated cellulose.

18. Method according to any of the preceding claims, wherein the separator produced in steps A to F has a basis weight of at least 6 g / m² 2 and at most 22 g / m² 2 , preferably of at least 7 g / m³ 2 and at most 21 g / m² 2 and especially preferably of at least 8 g / m² 2 and at most 20 g / m² 2 exhibits.

19. Method according to one of the preceding claims, wherein the porosity-compensated EC / DMC suction height in the transverse direction of the separator produced in steps Ab to F is at least 8.5 mm and at most 25.0 mm, preferably at least 9.0 mm and at most 20.0 mm.

20. Method according to one of the preceding claims, wherein the EC / DMC suction height in the transverse direction of the separator produced in steps A to F is at least 6.0 mm and at most 20.0 mm, preferably at least 7.0 mm and at most 18.0 mm and particularly preferably at least 8.0 mm and at most 15.0 mm.

21. Method according to one of the preceding claims, wherein the porosity-compensated EC / DMC suction height in the machine direction of the separator produced in steps A to F is at least 10.0 mm and at most 30.0 mm, preferably at least 10.5 mm and at most 25.0 mm and particularly preferably at least 11.0 mm and at most 25.0 mm.

22. Method according to one of the preceding claims, wherein the EC / DMC suction height in the machine direction of the separator produced in steps A to F is at least 7 mm and at most 25 mm, preferably at least 8 mm and at most 20 mm and particularly preferably at least 9 mm and at most 18 mm.

23. Method according to one of the preceding claims, wherein the ratio of the EC / DMC suction height of the separator produced in steps A to F in the machine direction to the EC / DMC suction height in the transverse direction is at least 0.90 and at most 1.35, preferably at least 0.95 and at most 1.30, and particularly preferably at least 1.00 and at most 1.

30. 24- Method according to one of the preceding claims, wherein the mean thickness of a The diameter of a single sheet of the separator produced in steps Ab to F is at least 8 pm and at most 21 pm, preferably at least 9 pm and at most 20 pm and particularly preferably at least 10 pm and at most 19 pm.

25. Method according to any of the preceding claims, wherein the density of the separator produced in steps A to F is at least 0.65 g / cm³ 3 and at most 1.05 g / cm² 3 , preferably at least 0.70 g / cm³ 3 and at most 1.00 g / cm² 3 amounts.

26. Separator for an electrochemical element, wherein the separator contains at least 80% fibrillated fibers of regenerated cellulose by mass, wherein the mean thickness of a single sheet of the separator according to ISO 534:2011 is not more than 22 pm, and wherein the separator has a density according to ISO 534:2011 of at least 0.60 g / cm³ 3 and at most 1.10 g / cm² 3 exhibits, wherein the separator has a machine direction and a transverse direction orthogonal to it, lying in the plane of the separator, and has such a fiber structure that the EC / DMC suction height h, in the transverse direction in mm and the density p in g / cm³ 3 calculated porosity-compensated EC / DMC suction height in the transverse direction hoo 1.50 at least 8.0 mm, where the EC / DMC suction height h«> is measured in the transverse direction, according to ISO 8787:1986, with the only deviation being that instead of the water specified in the standard ISO 8787:1986, a mass-based 1:1 mixture of ethylene carbonate and dimethyl carbonate is used.

27. Separator according to claim 26, wherein the porosity-compensated EC / DMC suction height in the transverse direction is at least 8.5 mm and at most 25.0 mm, preferably at least 9.0 mm and at most 20.0 mm.

28. Separator according to claim 26 or 27, wherein the EC / DMC suction height in the transverse direction is at least 6.0 mm and at most 20.0 mm, preferably at least 7.0 mm and at most 18.0 mm and particularly preferably at least 8.0 mm and at most 15.0 mm.

29. Separator according to one of claims 26 to 28, wherein the porosity-compensated EC / DMC suction height in the machine direction is at least 10.0 mm and at most 30.0 mm, preferably at least 10.5 mm and at most 25.0 mm and particularly preferably at least 11.0 mm and at most 25.0 mm.

30. Separator according to one of claims 26 to 29, wherein the EC / DMC suction height in the machine direction is at least 7 mm and at most 25 mm, preferably at least 8 mm and at most 20 mm and particularly preferably at least 9 mm and at most 18 mm.

31. Separator according to one of claims 26 to 30, wherein the ratio of the EC / DMC suction height of the separator in the machine direction to the EC / DMC suction height in the transverse direction is at least 0.90 and at most 1.35, preferably at least 0.95 and at most 1.30, and particularly preferably at least 1.00 and at most 1.

30.

32. Separator according to any one of claims 26 to 31, wherein the mean thickness of a single sheet of the separator is at least 8 pm and at most 21 pm, preferably at least 9 pm and at most 20 pm and particularly preferably at least 10 pm and at most 19 pm.

33. Separator according to one of claims 26 to 32, the density of which is at least 0.65 g / cm³ 3 and at most 1.05 g / cm² 3 , preferably at least 0.70 g / cm³ 3 and at most 1.00 g / cm² 3 amounts.

34. Separator according to any one of claims 26 to 33, 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.

35. Separator according to any one of claims 26 to 34, wherein the degree of refining of the fibrillated fibers of regenerated cellulose is at least 80°SR and at most 92°SR, preferably at least 81°SR and at most 90°SR and particularly preferably at least 82°SR and at most 88°SR.

36. Separator according to any one of claims 26 to 35, wherein the fibrillated fibers are regenerated cellulose spun fibers in a solvent.

37. Separator according to one of claims 26 to 33, 35 or 36, comprising, in addition to the fibrillated fibers of regenerated cellulose, further cellulose fibers.

38. Separator according to claim 37, wherein the further cellulose fibers are formed wholly or partly by non-fibrillated fibers of regenerated cellulose.

39. Separator according to claim 37 or 38, wherein the further cellulose fibers are formed wholly or partly by pulp fibers, the pulp fibers preferably being derived from coniferous trees, deciduous trees or other plants such as hemp, flax, - '2^ - Jute, ramie, kenaf, kapok, coconut, abaca, sisal, bamboo, cotton or esparto grass, or are derived from recycled paper, or are a mixture of cellulose fibers from two or more different sources mentioned.

40. Separator according to any one of claims 37 to 39, 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.

41. Separator according to any one of claims 37 to 40, 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.

42. Separator according to claim 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 0.20 mm, preferably of at most 0.15 mm.

43. Separator according to any one of claims 40 to 42, comprising or consisting of fibrillated fibers of regenerated cellulose and nanofibrillated and / or microfibrillated cellulose fibers.

44. Separator according to claim 37, comprising 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, each based on the mass of the separator.

45. Separator according to any one of claims 26 to 44, comprising further fibers selected from the group consisting of fibers made of cellulose derivatives, glass fibers, and plastic fibers.

46. ​​Separator according to claim 45, 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).

47. Separator according to any one of claims 26 to 46, 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.

48. Separator according to one of claims 26 to 47, having an basis weight of at least 6 g / m² 2 and at most 22 g / m² 2 , preferably of at least 7 g / m³ 2 and at most 21 g / m² 2 and especially preferably of at least 8 g / m² 2and at most 20 g / m² 2 exhibits.

49. Separator according to any one of claims 26 to 48, 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.

50. Separator according to one of claims 26 to 49, the tensile strength in the machine direction, based on the cross-sectional area, is at least 15 MPa and at most 75 MPa, preferably at least 25 MPa and at most 60 MPa.

51. Separator according to any one of claims 26 to 50, wherein the ratio of the tensile strength 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.

52. Separator according to any one of claims 26 to 51, 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%.

53. Separator according to any one of claims 26 to 52, 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%.

54. Separator according to any one of claims 26 to 53, the air permeability of which according to Gurley is at least 2 s and at most 70 s, preferably at least 5 s and at most 55 s and particularly preferably at least 10 s and at most 50 s. 55- Electrochemical element comprising at least two electrodes, an electrolyte and at least one separator according to any one of claims 26 to 54.

56. Electrochemical element according to claim 55, wherein the electrochemical element is a battery, preferably a lithium-ion battery or a sodium-ion battery.

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