WO2004049480A2 - Separator having a low water content for an electrochemical cell - Google Patents

Abstract

The invention relates to a method for producing a separator having a low water content for an electrochemical cell, comprising the following steps: (a) preparing a mixture consisting of (a-1) a lithium compound having a radical that volatizes easily when heated, of (a-2) a solvent and/or dispersant, and of (a-3) optional additional mixture constituents; (b) producing a separator intermediate product with the mixture during which the lithium compound is, at least in part, exposed on the surface of the separator intermediate product; (c) heating the separator intermediate product to a temperature ranging from 50 to 350 °C for a predetermined time in order to remove the radical of the lithium compound, optionally pyrolytically, at least partially from the surface of the separator intermediate product and to create a separator having a low water content.

Description

Low water separator for an electrochemical cell

The present invention relates to a method for producing a separator with a low water content for an electrochemical cell, a separator which can be produced by this method, and an electrochemical cell which comprises such a separator with a low water content.

In this description, electrochemical cell or battery means batteries and accumulators (secondary batteries) of any kind, in particular alkali, such as Lithium, lithium ion, lithium polymer, and alkaline earth batteries and accumulators, including in the form of high-energy or high-performance systems.

Electrochemical cells comprise electrodes with opposite poles, which are separated from one another by a separator while maintaining ion conductivity.

Conventionally, a separator is a thin, porous, electrically insulating material with high ion permeability, good mechanical strength and long-term stability against those in the system, e.g. B. in the electrolyte of the electrochemical cell, chemicals and solvents used. It is intended to completely electronically isolate the cathode from the anode in electrochemical cells. He must also be permanently elastic and the movements in the system, for. B. in the electrode package when loading and unloading, follow.

The separator largely determines the life of the arrangement in which it is used, e.g. B. that of an electrochemical cell. The development of rechargeable electrochemical cells or batteries is therefore influenced by the development of suitable separator materials. General information about electrical separators and batteries can e.g. B. at J.O. Besenhard can be read in "Handbook of Battery Materials" (VCH Verlag, Weinheim 1999).

High-energy batteries are used in various applications where it is important to have the largest possible amount of electrical energy available. This is the case, for example, with traction batteries, but also with emergency power supply with batteries (Auxillary Power Systems) the case. The energy density is often given in weight [Wh / kg] or volume-related [Wh / L] sizes. Energy densities of 350 to 400 Wh / L and 150 to 200 Wh / kg are currently being achieved in high-energy batteries. The requested performance with such batteries is not so large, so that one can make compromises with regard to the internal resistance. This means that the conductivity of the electrolyte-filled separator, for example, does not have to be as great as that of high-performance batteries, so that other separator concepts are also possible.

For example, polymer electrolytes can be used in high-energy systems, which have a very low conductivity of 0.1 to 2 mS / cm. Such polymer electrolyte cells cannot be used as high-performance batteries.

Separator materials for use in high-performance battery systems must have the following properties: They must be as thin as possible to ensure a small specific space requirement and to keep the internal resistance low. To ensure these low internal resistances, it is important that the separator also has a large porosity. They must also be light in order to achieve a low specific weight. In addition, the wettability must be high, otherwise dead zones that are not wetted will arise.

In many, especially mobile applications, very large amounts of energy are required (e.g. in traction batteries). The batteries in these applications therefore store large amounts of energy when fully charged. The separator must be safe for this, since very large specific amounts of electrical energy are transported in these batteries. These energies must not be released in an uncontrolled manner in the event of a malfunction of the battery or in an accident, since this would inevitably lead to an explosion of the cell under fire.

Currently used separators consist mainly of porous organic polymer films or inorganic nonwovens such as. B. fleeces of glass or

Ceramic materials or ceramic papers. These are made by different companies. Important producers are: Celgard, Tonen, Übe, Asahi, Binzer, Mitsubishi, Daramic and others.

The separators made of inorganic nonwovens or ceramic paper are mechanically unstable and break easily. This leads to short circuits. Because the electrodes can easily come into contact due to broken points.

A typical organic separator is e.g. B. made of polypropylene or a polypropylene / polyethylene / polypropylene composite. A major disadvantage of these organic polyolefin separators is their relatively low thermal load capacity of below 150 ° C. A short-lasting reaching of the melting point of these polymers leads to a large melting of the separator and to a short circuit in the electrochemical cell which uses such a separator. The use of such separators is therefore generally not very safe. Because when higher temperatures are reached, especially at least 150 ° C or even at least 180 ° C, these separators are destroyed.

In addition to this instability at high temperatures, the polymer-based separators have other serious disadvantages in terms of chemical resistance. The polymers in the electrochemical cells are slowly but steadily attacked by contact with the electrodes, even at normal operating and storage temperatures such as room temperature. In particular, problems arise when such separators are used in electrochemical cells which use lithium. The polymer is slowly attacked on the contact surface of the separator with the lithium or with the lithiated graphite. Furthermore, the polymer separators are also attacked inside the separator by the substances formed during the operation of an electrical cell. As a result, these separators can no longer reliably protect the electrodes from a short circuit. The service life is reduced. In addition, the capacity of an electrochemical cell that uses such separators decreases over time.

In order to overcome these disadvantages, there were first attempts to use inorganic composite materials as separators. In DE 198 38 800 Cl an electrical separator with a

Composite structure proposed, which comprises a flat, provided with a plurality of openings, flexible substrate with a coating thereon. The The material of the substrate is selected from metals, alloys, plastics, glass and carbon fiber or a combination of such materials, and the coating is a continuous, porous, electrically non-conductive ceramic coating. The use of the ceramic coating promises thermal and chemical resistance. However, the separators, which have a carrier or a substrate made of electrically conductive material (as indicated in the example), have proven unsuitable for lithium-ion cells, since the coating of the thickness described cannot be produced without defects over a large area. Short circuits are therefore very easy. In addition, metal meshes as thin as are required for very thin separators are not commercially available.

In previous work (DE 101 42 622) it was shown that with a material comprising a flat, flexible substrate provided with a plurality of openings with a coating on and in this substrate, the material of the substrate being selected from woven or non-woven, non-electrically conductive fibers of glass or ceramic or a combination of such materials and the coating is a porous, electrically insulating, ceramic coating, and the resulting separator has a very small thickness of less than 100 μm and is bendable, a separator can be produced, which has a sufficiently low resistance in connection with the electrolyte and nevertheless has a sufficiently large long-term resistance.

Although the separator described in DE 101 42 622 has a very high conductivity, the separator described there still does not meet the requirements for a separator that can be used technically in terms of thickness and weight, as well as safety. With the small thickness of the separator of less than 100 μm, problems arise such that the growth of dendrites is facilitated with the relatively large pores with a uniform distribution which ensure good ion conductivity. Therefore, short circuits often occur in practice if the thickness of the separators is very small.

In the not yet published application DE 102 08 277, the weight and the thickness of the separator were reduced by using a polymer fleece, but the embodiments of a separator described there also do not yet meet all requirements to a separator for a lithium high-energy battery, in particular because special emphasis was placed on the largest possible pores of the separator in this application. However, with the particles up to 5 μm in size described there, it is not possible to produce very thin, for example only 10 - 20 μm thick, separators, since only a few particles would lie on top of one another here. As a result, the separator would inevitably have a high density of defects and defects (e.g. holes, cracks, ...). However, the large pores allow dendrites to grow, which can easily form in the large pores. This means that short circuits often occur with these separators in practice. In addition, the large particles in this document consist of Al ₂ O ₃ and ZrO ₂ . Due to the high density of these ceramics, these separators also have a large basis weight, which reduces the mass-specific specific energy density (in Wh / g).

However, all of these separators with an inorganic composite structure were found to contain water, especially if they are stored in high humidity. The water in such a separator is available in two forms: first, in the very small pores of the separator, where it is liquid due to the pore condensation; on the other hand in the form of partially hydrolyzed ceramic material, e.g. Silicon dioxide that is present on the surface of the pores of the inorganic composite structure. If such a moist separator is used to produce electrochemical cells, only the water in the pores can be removed in a drying step in the manufacture of the electrochemical cells. However, the water, which is in the form of partially hydrolyzed ceramic material, cannot be removed in this way. This leads to problems in charged electrochemical cells, in particular in cells in which alkali or alkaline earth ions are used. Because the reaction of battery components with this water leads to exothermic battery-damaging reactions. This makes the cell very hot overall, which consumes a lot of energy in the first charge cycle. This leads to a significantly deteriorated long-term stability. In addition, very high overheating occurs locally. As a result, the cell can be damaged so badly during production that it can no longer be used.

The object of the present invention was therefore to provide a method for producing an almost water-free separator for an electrochemical cell, one Separator, which can be produced by this method, and an improved electrochemical cell, which comprises such a separator.

This object is achieved with a method for producing a separator with a low water content for an electrochemical cell, which comprises the following steps:

(a) providing a mixture that

(a-1) a lithium compound with a readily volatilizing when heated

Balance, (a-2) a solvent and / or dispersant and (a-3) optionally further mixture components;

(b) producing a separator intermediate with the mixture, the lithium compound being at least partially exposed on the surface of the separator intermediate;

(c) heating the separator intermediate to a temperature of 50 to 350 ° C for a predetermined time to at least partially remove the rest of the lithium compound, optionally pyrolytically, from the surface of the separator intermediate and

To create a separator with a low water content.

In one embodiment of the invention, step (b) comprises contacting a porous carrier having an inorganic coating with the mixture from step (a), the mixture preferably being a solution of the lithium compound in a solvent around the inner and / or outer surface to treat the porous carrier with the mixture and to create the separator intermediate.

The porous support having an inorganic coating preferably comprises a flat, flexible substrate provided with a plurality of openings, on and in which the inorganic coating is located.

The contacting and treatment of inner and / or outer surfaces of a porous carrier having an inorganic coating with a mixture can, for. B. be carried out so that the porous carrier having an inorganic coating is rolled off a roll at a speed of 1 m / h to 2 m / s, preferably at a speed of 0.5 m / min to 20 m / min and most preferably with one Speed from 1 m / min to 5 m / min through at least one apparatus which brings the mixture onto and into the carrier, such as e.g. B. a roller, and at least one other apparatus which enables the heating of the separator intermediate, such. B. an electrically heated oven, and the product thus produced is rolled up on a second roll. In this way it is possible to create a separator according to the invention in a continuous process. The pre-treatment steps can also be carried out in a continuous process while maintaining the parameters mentioned.

It has proven to be particularly advantageous if the method is carried out such that the porous support having an inorganic coating has a maximum longitudinal tension of 10 N / cm, preferably 3 N / cm, during the treatment process. Treatment processes are understood to mean all process steps in which a material is brought onto and into a carrier. The carrier is preferably stretched during the treatment process with a maximum force of 0.01 N / cm. It can be particularly preferred if the carrier is guided untensioned in the longitudinal direction during the treatment process.

By checking the tensile stress during the treatment, it can be avoided that a deformation (also elastic) of the carrier material takes place. Due to a possible deformation (elongation) when the tensile stress is too high, the ceramic coating cannot follow the carrier material or substrate material, which leads to the coating becoming detached from the substrate over the entire surface. The resulting product cannot then be used as intended.

The porous carrier having an inorganic coating can be, for example, a separator with an inorganic composite structure, which is already known from the prior art. Thus, a separator which is improved in terms of water content can advantageously be created by subsequent treatment.

In a particularly preferred embodiment, only after the free OH groups in the porous support have been determined, in relation to the number of these free OH groups, 0.5 to 1.5 times, preferably 0.7 to 1.0 times times the stoichiometric amount Lithium compound used. This is to prevent Li ₂ O from forming in excessive amounts. With an excess of the lithium compound of more than 1.5 times the molar excess in relation to the number of OH groups in the support, Li ₂ O can form in larger amounts. Because of the hygroscopic nature of Li ₂ O, larger amounts of Li ₂ O should be preferably avoided but, otherwise, the water content of the separator may be adversely increased. It is therefore particularly preferred to use an equimolar amount of lithium compound in relation to the OH groups or even a deficit in the lithium compound. However, the deficit should preferably be used not less than 0.5 times, particularly preferably not less than 0.7 times the stoichiometric amount of lithium compound in relation to the amount of OH groups.

The OH groups are determined using the following procedure:

A sample dried in a vacuum at 120 ° C. (only water but no OH groups being removed) is placed in a two-necked flask with a dropping funnel and a side outlet for gases. A solution of 1 mol / L lithium aluminum hydride in tetrahydrofuran is then slowly added dropwise to this sample. When the lithium aluminum hydride is reacted with OH groups, hydrogen is produced (in a stoichiometry of 1 mol of escaping hydrogen per 1 mol of OH groups in the sample). The hydrogen produced is measured volumetrically. The amount of hydrogen produced can thus be converted into the number of OH groups.

The reduction in the water content in a separator treated according to the process described above can be explained as follows. By treating a separator which has bound water in the form of partially hydrolyzed ceramic material, such as silicon dioxide, groups with the structure -MOH are converted into groups with the structure -MO-Li, where M stands for an element which is a ceramic Material forms. M is preferably an element from group 3A, 4A, 3B or 4B of the periodic table of the elements, usually one of the elements silicon, aluminum and zirconium. This means that a structure is created in which one of the elements M is bonded to oxygen atoms via oxygen bridges. Even if water gets to this structure due to adverse circumstances, this does not cause any major problems. It can a slight hydrolysis of the structure -MO-Li takes place again to re-form a group with the structure -MOH. This regressed -MOH structure is now isolated. There is no other -MOH group in their neighborhood with which they release free water that damages the components of the electrochemical cell.

Another advantage of the invention is an increase in the conductivity of a separator filled with an electrolyte achieved by the method according to the invention. In a separator according to the invention, which is filled with an electrolyte, the surface positions of the lithium ion are available for the charge transport over the surface. This leads to an increased conductivity through the separator. Since this rapid charge transport takes place exclusively via lithium ions, there is an advantageous increase in the number of transfers for cations. As a result, the sensitivity of an electrochemical cell equipped with such a separator to high discharge currents can advantageously be reduced. In this way, the polarization in such an electrochemical cell is advantageously reduced. This has the additional advantage that the load capacity of the separators produced by the method according to the invention is increased. The electrochemical cells can thus advantageously be discharged with larger currents.

However, it is also possible to create an improved separator during the manufacture of the same according to the following embodiment. In this further embodiment of the invention, the mixture in step (a) is preferably a dispersion which is used as further mixture components

(a-3.1) an oxide sol, in particular a silica sol, (a-3.2) ceramic particles and

(a-3.3) optionally fine particles, wherein step (b) comprises the following steps:

(b-1) providing a flat, multi-aperture flexible substrate, (b-2) applying the dispersion in a thin layer on and into the substrate, thereby creating the separator precursor, and wherein in step (c ) by heating the separator intermediate to 50 to 350 ° C Separator is created with a porous carrier having an inorganic coating.

This embodiment has the advantage that fewer steps are required overall to create a separator with a low water content.

The substrate can consist of a nonwoven made of non-woven, non-electrically conductive polymer fibers, ceramic fibers or glass fibers.

The fine particles can have an average primary particle size in the range from 1 to 200 nm, preferably 2 to 100 nm, very particularly preferably 3 to 50 nm. As a result, the service life and life of the separator can be improved in an advantageous manner. In a preferred embodiment, the fine particles contain a pyrogenic oxide of the elements silicon, zirconium and / or aluminum, such as. B. silica, in particular Aerosil or aluminum oxide.

The dispersion preferably has oxide particles as ceramic particles

Elements Si and optionally AI, and or Zr with an average particle size of 0.1 to

10 μm, preferably 0.5 to 5 μm.

The lithium compound to be used in step (a) is preferably selected from lithium nitrate, lithium chloride, lithium carbonate, lithium acetate, lithium formate, lithium azide, lithium metal hydrides, such as e.g. LiAlH, lithium alcoholates or organolithium compounds.

The solvent or dispersant in step (a) can be aqueous or non-aqueous, e.g. Water, an alcohol, ketone, ether, saturated and or unsaturated hydrocarbon or a mixture thereof.

In a preferred embodiment of the method according to the invention, the carrier is a flexible nonwoven with a porous inorganic coating on and in this nonwoven, the material of the nonwoven being made of nonwoven, not electrically conductive Polymer fibers can be selected. However, it can also be a nonwoven or woven fabric made of ceramic or glass fibers.

Such a fleece preferably has a thickness of at most 30 μm, very particularly preferably a thickness of 5 to 30 μm.

In a preferred embodiment of the present invention, the porous support having an inorganic coating or the planar, flexible substrate having a plurality of openings comprises fibers, preferably selected from fibers of polyamide, polyacrylonitrile, polyester, such as e.g. Polyethylene terephthalate (PET) and / or polyolefin, e.g. Polyethylene (PE) or polypropylene (PP), glass fibers or ceramic fibers. If the carrier or the flexible substrate comprises polymer fibers, polymer fibers other than those mentioned above can be used, provided that they both have the temperature stability required for the production of the separators and are stable under the operating conditions in a lithium battery. In a preferred embodiment, the separator according to the invention has polymer fibers which have a softening temperature of greater than 100 ° C. and a melting temperature of greater than 110 ° C.

The carrier or the substrate can comprise fibers and or filaments with a diameter of 1 to 150 μm, preferably 1 to 20 μm, and / or threads with a diameter of 3 to 150 μm, preferably 10 to 70 μm.

In a further embodiment of the invention, the substrate is a fleece with a pore size of 5 to 500 μm, preferably 10 to 200 μm.

The flexible nonwoven preferably has a weight per unit area of less than 20 g / m.

It is further preferred that the flexible nonwoven has a porosity of more than 50%.

In a preferred embodiment, the porous inorganic coating on and in the fleece has ceramic oxide particles of the elements Si and optionally Al, and / or Zr with an average particle size of 0.1 to 10 μm, preferably 0.5 to 5 μm.

The porous inorganic coating located on and in the fleece very particularly preferably has aluminum oxide particles with an average particle size of 0.5 to 5 μm, which are bonded to an oxide of the elements Zr or Si.

The carrier preferably has a porosity of 30 to 90%.

Advantageously, the separator obtained according to the invention will have a tensile strength of more than 1 N / cm.

In addition, due to its composite structure, the separator or the separator intermediate product can preferably be bent to a radius down to 100 mm, preferably up to 1 mm, without damage.

In a preferred embodiment, the thickness of the separator is at most 35 μm.

The contact in step (b) or the application of the thin layer in step (b-2) is preferably carried out by printing, pressing, pressing, rolling, knife coating, spreading, dipping, spraying or pouring on the mixture or the dispersion.

Furthermore, the object of the invention is achieved by a separator for an electrochemical cell, which can be obtained by one of the methods described above.

Lithium atoms are preferably present on inner and / or outer surfaces of the separator according to the invention via an oxygen bridge on atoms of a group 3A, 4A, 3B or 4B element in the periodic table of the elements, preferably selected from one of the elements silicon, aluminum and zirconium. Such structures can be detected by Raman spectroscopy.

In a particularly advantageous embodiment of the invention, the separator also has a low water content has a water content of less than 1000 ppm, preferably less than 500 ppm, very particularly preferably less than 200 ppm.

The separator of the present invention is outstandingly suitable for electrochemical cells with high capacity and high energy density due to its configuration according to the invention. In particular, the separator according to the invention is suitable for electrochemical cells which are based on the transfer of alkali and / or alkaline earth metal ions, such as e.g. Lithium metal and lithium ion batteries. It is therefore advantageous if these separators also show the protective measures specific to these applications, such as the interruption property and short-circuit property with a high short-circuit temperature. Interrupting property or "shut-down" is to be understood as a measure in which easily separable substances, such as, for example, thermoplastic plastics, can be incorporated into the separator for specific operating temperatures. If the operating temperature rises due to faults such as overloading, external or internal short circuits, such easily melting substances can melt and clog the pores of the separator. The ion flow through the separator is thus partially or completely blocked and a further rise in temperature is prevented. Short-circuit property or melt-down means that the separator melts completely at a short-circuit temperature. A contact and a short circuit can then occur between large areas of the electrodes of an electrochemical cell. For a safe operation of an electrochemical cell with a high capacity and energy density, the highest possible short-circuit temperature is desirable. The separator according to the invention has a significant advantage. This is because the ceramic material which adheres to the perforated support in the separator of the present invention has a melting point which is far above the safety-relevant temperature range for electrochemical cells. The separator of the present invention therefore has superior safety. It is namely stable in a preferred safe embodiment under operating conditions of at least 50 ° C. Even more preferably, it is stable at at least 100 ° C, 150 ° C, and most preferably at least 180 ° C.

Polymer separators, for example, bring the currently required for lithium batteries Safety by preventing any current transport through the electrolyte above a certain temperature (the shutdown temperature, which is around 120 ° C). This happens because the pore structure of the separator collapses at this temperature and all pores are closed. Because no more ions can be transported, the dangerous reaction that can lead to the explosion comes to a standstill. If the cell is heated further due to external circumstances, the breakdown temperature is exceeded at approx. 150 to 180 ° C. From this temperature, the separator melts and contracts. At many points in the battery cell there is now a direct contact between the two electrodes and thus a large internal short circuit. This leads to an uncontrolled reaction, which ends with an explosion of the cell, or the pressure that is created is often reduced by fire through a pressure relief valve (a rupture disc).

In a particularly preferred embodiment of the invention, the carrier of the separator comprises polymer fibers. This hybrid separator, which has inorganic components and polymeric carrier material, is shutdown when the high temperature causes the polymer structure of the carrier material to melt and penetrate into the pores of the inorganic material, thereby closing it. In contrast, there is no so-called meltdown (breakdown) in the separator of the invention. The separator according to the invention thus meets the requirements for a safety shutdown required by various battery manufacturers due to the shutdown in the battery cells. The inorganic particles ensure that there can never be a meltdown. This ensures that there are no operating states in which a large-scale short circuit can occur.

It can be advantageous if the separator has an additional non-inherent shutdown mechanism. This can e.g. B. can be realized in that a very thin wax or polymer particle layer of so-called shutdown particles, which melt at a desired shutdown temperature, is present on or in the separator. Particularly preferred materials from which the shutdown particles can consist are, for example, natural or artificial waxes, low-melting polymers, such as. B. polyolefins, wherein the material of the shutdown particles is selected so that the particles at the desired Melt the cut-off temperature and close the pores of the separator so that further ion flow is prevented.

The shutdown particles preferably have an average particle size (D _w ) which is greater than or equal to the average pore size (d _s ) of the pores of the porous inorganic layer of the separator. This is particularly advantageous because such penetration and closure of the

Pores of the separator layer, which reduces the pore volume and thus the

Conductivity of the separator and also the performance of the battery would be prevented. The thickness of the cut-off particle layer is only critical if an excessively thick layer would unnecessarily increase the resistance in the battery system. To be safe

To achieve shutdown, the shutdown particle layer should have a thickness (z _w ) that is approximately equal to the average particle size of the shutdown particles (D _w ) up to 10 D _w , preferably from 2 D _w to D _w . A separator equipped in this way has a primary one

Security feature on. In contrast to the purely organic separator materials, this separator cannot melt completely and therefore there can be no meltdown. These security features are due to the very large amounts of energy

High-energy batteries are very important and are therefore often required.

Even in the event of an internal short circuit, e.g. B. was caused by an accident, the separator according to the invention is very safe. Would z. Depending on the separator, the following happens, for example, when drilling a nail through a battery: The polymer separator would melt and contract at the point of penetration (a short-circuit current flows over the nail and heats it up). As a result, the short circuit point becomes larger and the reaction gets out of control. In the embodiment with the hybrid separator according to the invention, at most the polymeric substrate material melts, but not the inorganic separator material. The reaction inside the battery cell after such an accident is much more moderate. This battery is therefore significantly safer than one with a polymer separator. This is particularly important in the mobile area.

The method for applying a dispersion as a thin layer on and into a substrate for producing a separator or separator intermediate, and the production of a porous carrier having an inorganic coating, which preferably has a flat surface comprising a plurality of openings provided, flexible substrate is known in principle from WO 99/15262. However, not all parameters or input materials can be used.

A dispersion can e.g. B. by printing, pressing, pressing, rolling, knife coating, spreading, dipping, spraying or pouring onto and into the flexible substrate provided with a plurality of openings.

The flexible substrate provided for application and introduction into the plurality of openings can have a sol of the elements Al, Zr and / or Si, and is preferably produced by dispersing ceramic particles and optionally fine particles in one of these brines. The sols can be obtained by hydrolyzing at least one compound, with water or an acid, or a combination of these compounds. It may be advantageous to add the compound to be hydrolyzed to alcohol or an acid or a combination of these liquids before the hydrolysis. As the compound to be hydrolyzed, at least one nitrate, a chloride, a carbonate, an alcoholate or an element-organic compound of the elements Al, Zr and / or Si is preferably hydrolyzed. The hydrolysis is preferably carried out in the presence of water, steam, ice or an acid or a combination of these compounds.

In an embodiment variant of the method according to the invention, particulate sols are produced by hydrolysis of the compounds to be hydrolyzed. These particulate sols are characterized by the fact that the compounds formed in the sol by hydrolysis are present in particulate form. The particulate sols can be prepared as described above or as described in WO 99/15262. These brines usually have a very high water content, which is preferably greater than 50% by weight. It may be advantageous to add the compound to be hydrolyzed to alcohol or an acid or a combination of these liquids before the hydrolysis. For peptizing, the hydrolyzed compound can be treated with at least one organic or inorganic acid, preferably with a 10 to 60% organic or inorganic acid, particularly preferably with a mineral acid selected from sulfuric acid, hydrochloric acid, perchloric acid, phosphoric acid and nitric acid or a mixture of these acids become. The particulate sols thus produced can then be used to prepare dispersions, the production of dispersions for application to nonwovens pretreated with polymer sol being preferred.

In a further embodiment of the process according to the invention, polymeric sols are produced by hydrolysis of the compounds to be hydrolyzed. In this preferred embodiment of the method according to the invention, the sol has a water and / or acid content of less than 50% by weight. These polymeric sols are distinguished by the fact that the compounds formed in the sol by hydrolysis are polymeric (ie chain-like crosslinked over a larger space). The polymeric sols usually have less than 50% by weight, preferably very much less than 20% by weight, of water and / or aqueous acid. In order to arrive at the preferred proportion of water and / or aqueous acid, the hydrolysis is preferably carried out in such a way that the compound to be hydrolyzed with the 0.5 to 10 times molar ratio and preferably with half the molar ratio of water, steam or ice, based on the hydrolyzable group, the hydrolyzable compound, is hydrolyzed. Up to 10 times the amount of water can be used with very slow hydrolyzing compounds such. B. be used in tetraethoxysilane. Very rapidly hydrolyzing compounds such as zirconium tetraethylate can already form particulate sols under these conditions, which is why 0.5 times the amount of water is preferably used for the hydrolysis of such compounds. Hydrolysis with less than the preferred amount of water, water vapor, or ice also gives good results. Falling below the preferred amount of half a molar ratio by more than 50% is possible but not very useful, since if this value is not reached the hydrolysis is no longer complete and coatings based on such brine are not very stable. For the production of sols with a desired very low proportion of water and / or acid in the sol, it can be advantageous if the compound to be hydrolyzed is in an organic solvent, in particular ethanol, isopropanol, butanol, amyl alcohol, hexane, cyclohexane, ethyl acetate and or mixtures of these compounds is dissolved before the actual hydrolysis is carried out. A sol produced in this way can be used to produce the separators according to the invention.

Both particulate brine (high water content, low solvent content) and polymer Sols (low water content, large solvent content) can be used as sol in the process according to the invention for producing a dispersion. In addition to the brines that are available as just described, commercially available brines such as e.g. B. zirconium nitrate sol or silica sol can be used. The process for creating separator precursors by applying and solidifying a suspension on a substrate is known per se from DE 101 42 622 and in a similar form from WO 99/15262, but not all parameters or feedstocks can be referred to the production of the Separator intermediate and separators transferred. The process described in WO 99/15262, in this form, is in particular not transferable to polymeric nonwoven materials without compromises, since the very water-containing sol systems described there often do not allow continuous wetting of the usually hydrophobic polymeric nonwovens in depth, since the very water-containing ones Sol systems do not, or only poorly, wet most polymer nonwovens. It was found that even the smallest unwetted areas in the nonwoven material can result in separators being obtained which have defects and are therefore unusable.

It has been found that a sol system or a dispersion which has been adapted to the polymers in terms of wetting behavior completely impregnates nonwoven materials and thus flawless coatings are obtainable. The method therefore preferably adjusts the wetting behavior of the sol or the dispersion. This adjustment is preferably carried out by the production of sols or dispersions, these sols one or more alcohols, such as. B. methanol, ethanol or propanol or mixtures thereof, and / or have aliphatic hydrocarbons. However, other solvent mixtures are also conceivable which can be added to the sol or the dispersion in order to adapt them to the fleece used in terms of wetting behavior.

The mass fraction of the suspended or dispersed component (ceramic particles) in the dispersion is preferably 1 to 100 times, particularly preferably 1 to 50 times and very particularly preferably 1 to 10 times the sol used. Oxide particles, such as aluminum oxide particles, which preferably have an average particle size of 0.1 to 10 μm, in particular 0.5 to 5 μm, are particularly preferably used to produce the dispersion as ceramic particles. Alumina particles in the area of preferred particle sizes are for example from the company Martinswerke under the designations MDS 6; DN 206, MZS 3 and MZS 1 and offered by Alcoa with the designations CL3000 SG, CT800 SG and HVA SG.

It has been found that the use of commercially available oxide particles or ceramic particles may lead to unsatisfactory results, since there is often a very large particle size distribution. Ceramic particles are therefore preferably used, which by a conventional method such. B. Air classification, centrifuging and hydroclassification were classified. Fractions in which the coarse grain fraction, which makes up up to 10% of the total amount, have been separated off by wet sieving are preferably used as ceramic particles. This disruptive coarse grain fraction, which cannot be broken up or only with great difficulty by the processes typical in the production of the slurries, such as grinding (ball mill, attritor mill, mortar mill), dispersing (Ultra-Turrax, ultrasound), grinding or chopping, B. consist of aggregates, hard agglomerates, grinding ball abrasion. The aforementioned measures ensure that the inorganic porous layer has a very uniform pore size distribution. This is achieved in particular by using ceramic particles which have a maximum particle size of preferably 1/3 to 1/5 and particularly preferably less than or equal to 1/10 of the thickness of the nonwoven used.

The following Table 1 gives an overview of how the choice of different aluminum oxides affects the porosity and the resulting pore size of the respective porous inorganic coating. To determine this data, the corresponding slurries (suspensions or dispersions) were produced and dried and solidified as pure moldings at 200 ° C.

Table 1: Typical data of ceramics depending on the type of powder used

To improve the adhesion of the inorganic components to polymer fibers as a substrate, it may be advantageous to add adhesion promoters, such as e.g. B. add organofunctional silanes. In particular, compounds selected from the octylsilanes, the vinylsilanes, the amine-functionalized silanes and / or the glycidyl-functionalized silanes, such as, for. B. the Dynasilane from Degussa can be used. Particularly preferred adhesion promoters for polymer fibers, such as polyethylene (PE) and polypropylene (PP), are vinyl, methyl and octylsilanes, the exclusive use of methylsilanes not being optimal; for polyamides and polyamines, it is amine-functional silanes, for polyacrylates and polyesters Glycidyl-functionalized silanes and for polyacrylonitrile it is also possible to use glycidyl-functionalized silanes. Other adhesion promoters can also be used, but these have to be matched to the respective polymers. The adhesion promoters are advantageously selected such that the solidification temperature is below the melting or softening point of the polymer used as the substrate and below its decomposition temperature. Dispersions according to the invention preferably have very much less than 25% by weight, preferably less than 10% by weight, of compounds which can act as adhesion promoters. An optimal proportion of adhesion promoter results from the coating of the fibers and / or particles with a monomolecular layer of the adhesion promoter. The amount of adhesion promoter required in grams can be obtained by multiplying the amount of oxides or fibers used (in g) by the specific surface area of the materials (in m ² g ^" ') and then dividing by the specific space requirement of the adhesion promoter (in m ² g ^"1 ) are obtained, 1 • where the specific space requirement is often in the order of 300 to 400 mg ^" .

Table 2 below contains an exemplary overview of usable adhesion promoters based on organofunctional Si compounds for typical polymers used as nonwoven material. Table 2

With:

AMEO = 3-aminopropyltriethoxysilane

DAMO = 2-aminoethyl-3-aminopropyltrimethoxysilane GLYMO = 3-glycidyloxytrimethoxysilane

MEMO = 3-methacryloxypropyltrimethoxysilane

Silfin = vinylsilane + initiator + catalyst

VTEO = vinyl triethoxysilane

VTMO = vinyltrimethoxysilane VTMOEO = vinyltris (2-methoxyethoxy) silane

In a particular embodiment, the abovementioned adhesion promoters are applied in a preceding step to a flat, flexible substrate, such as a polymer fleece, which is provided with a multiplicity of openings. For this purpose, the adhesion promoter in a suitable solvent, such as. B. dissolved ethanol. This solution can also contain a small amount of water, preferably 0.5 to 10 times the amount based on the molar amount of the hydrolyzable group, and small amounts of an acid, such as. B. HCl or HNO, as a catalyst for the hydrolysis and condensation of the Si-OR groups. By the known techniques such. B. spraying, printing, pressing, pressing, rolling, knife coating, spreading, dipping, spraying or pouring, this solution is applied to the carrier or the substrate and the adhesion promoter is fixed by a temperature treatment at 50 to a maximum of 350 ° C. on the carrier or substrate. In this embodiment variant, the method only takes place after the adhesion promoter has been applied the application and solidification of the dispersion.

By applying an adhesion promoter before the actual application of the dispersion, the adhesive behavior of the flexible carriers or substrates can be improved, in particular with respect to aqueous, particulate sols, which is why carriers or substrates with suspensions or dispersions based on commercially available sols such as, B. zirconium nitrate sol or silica sol can be coated. However, this procedure of applying an adhesion promoter also means that the manufacturing process of the separators according to the invention must be expanded by an intermediate or pretreatment step. This is feasible, however, also more complex than the use of adapted brines to which adhesion promoters have been added, but also has the advantage that better results are achieved even when dispersions based on commercially available brines are used.

The coatings according to the invention are brought into and onto the substrate by solidifying the dispersion. According to the invention, the dispersion present on and in the substrate can be solidified by heating to 50 to 350 ° C. Since the maximum temperature is determined by the polymer fleece when using polymeric substrate materials, this must be adjusted accordingly. Depending on the variant of the method according to the invention, the dispersion present on and in a substrate is solidified by heating to 100 to 350 ° C. and very particularly preferably by heating to 110 to 280 ° C. It can be advantageous if the heating is carried out for 1 second to 60 minutes at a temperature of 100 to 350 ° C. The dispersion is particularly preferably heated for solidification to a temperature of 110 to 300 ° C., very particularly preferably at a temperature of 110 to 280 ° C. and preferably for 0.5 to 10 min.

The composite can be heated by means of heated air, hot air, infrared radiation or by other heating methods according to the prior art.

The method for applying a thin layer on and in the substrate or contacting a porous carrier having an inorganic coating with a mixture can, for. B. be carried out such that the flexible substrate, for example a polymer fleece, or the porous carrier having an inorganic coating is unrolled from a roll at a speed of 1 m / h to 2 m / s, preferably at a speed of 0.5 m / min. up to 20 m / min and very particularly preferably at a speed of 1 m / min to 5 m / min through at least one apparatus which brings the dispersion or the mixture onto and into the substrate or the carrier, such as, for. B. a roller, and at least one other apparatus which enables the dispersion to solidify on and in the carrier by heating, such as. B. passes through an electrically heated oven and the product so produced is rolled up on a second roll. In this way it is possible to create a separator intermediate according to the invention or a separator in a continuous process. The pre-treatment steps can also be carried out in a continuous process while maintaining the parameters mentioned.

It has proven to be particularly advantageous if the method is carried out in such a way that the flat, flexible substrate having a plurality of openings, in particular a polymer fleece, has a maximum longitudinal tension of 10 N / cm, preferably 3 N, during the coating process / cm. The coating process is understood to mean all process steps in which a material is brought onto and into a flexible substrate and is subjected to a heat treatment there, that is to say also the application of the adhesion promoter. The substrate is preferably stretched during the coating process with a maximum force of 0.01 N / cm. It can be particularly preferred if the substrate is guided in the longitudinal direction without tension during the treatment process or the coating process.

By checking the tensile stress during the coating, it can be avoided that the substrate material is deformed (also elastic). The ceramic coating cannot follow the substrate material due to possible deformation (elongation) when the tensile stress is too high, which leads to the coating becoming detached from the substrate over the entire surface. The resulting product cannot then be used as intended.

If the separator according to the invention is to be equipped with an additional automatic shutdown mechanism, this can be done e.g. B. happen that after after solidifying the dispersion applied to the substrate, a layer of particles which melt at a desired temperature and close the pores of the separator, so-called shutdown particles, is applied to the separator to produce a shutdown mechanism and fixed. The layer of shutdown particles can e.g. B. by applying a suspension of wax particles with an average particle size larger than the average pore size of the separator in a sol, water, solvent or solvent mixture.

The suspension for applying the particles preferably contains from 1 to 50% by weight, preferably from 5 to 40% by weight and very particularly preferably from 10 to 30% by weight of shutdown particles, in particular wax particles, in the suspension.

Since the inorganic coating of the separator often has a very hydrophilic character, it has proven to be advantageous if the coating of the separator was produced using a silane in a polymeric sol as an adhesion promoter and was thus rendered hydrophobic. In order to achieve good adhesion and uniform distribution of the shutdown particles in the shutdown layer even on hydrophilic porous inorganic separator layers, several variants are possible.

In an embodiment variant of the method according to the invention, it has proven to be advantageous to hydrophobicize the porous inorganic layer of the separator before the shutdown particles are applied. The production of hydrophobic membranes, which works on the same principle, is described for example in WO 99/62624. The porous inorganic coating is preferably treated by treatment with alkyl, aryl or fluoroalkylsilanes, as described, for. B. are sold under the name Dynasilan by Degussa, hydrophobized. It can z. B. the known methods of hydrophobization, which are used, inter alia, for textiles (D. Knittel; E. Schollmeyer; Melliand Textilber. (1998) 79 (5), 362-363), with a slight change in the recipes, also for the porous ones Coatings of the separator are applied. For this purpose, the coating or the separator is treated with a solution which has at least one hydrophobic substance. It can be advantageous if the solution is water, which is preferably mixed with an acid, preferably acetic acid or Hydrochloric acid, has been adjusted to a pH of 1 to 3, and / or an alcohol, preferably ethanol. The proportion of water treated with acid or of alcohol in the solvent can in each case be from 0 to 100% by volume. The proportion of water in the solvent is preferably from 0 to 60% by volume and the proportion of alcohol from 40 to 100% by volume. To prepare the solution, 0.1 to 30% by weight, preferably 1 to 10% by weight, of a hydrophobic substance are added to the solvent. As hydrophobic substances such. B. the silanes listed above can be used. Surprisingly, good hydrophobization takes place not only with strongly hydrophobic compounds, such as, for example, with triethoxy (3,3,4,4,5,5,6,6,7,7,8,8-tridecafluorooctyl) silane, but also one Treatment with methyltriethoxysilane or i-butyltriethoxysilane is completely sufficient to achieve the desired effect. The solutions are stirred at room temperature for uniform distribution of the hydrophobic substances in the solution and then applied to the inorganic coating of the separator and dried. Drying can be accelerated by treatment at temperatures from 25 to 100 ° C.

In a further embodiment variant of the method according to the invention, the porous inorganic coating can also be treated with other adhesion promoters before the shutdown particles are applied. Treatment with one of the adhesion promoters mentioned below can then also be carried out as described above, i. H. that the porous inorganic layer is treated with a polymeric sol which has a silane as an adhesion promoter.

The layer of shutdown particles is preferably applied by applying a suspension of shutdown particles in a suspension medium selected from a sol, water or solvent, such as. B. alcohol, ether or ketones, or a solvent mixture on the inorganic coating of the separator and subsequent drying. In principle, the particle size of the shutdown particles present in the suspension is arbitrary. However, it is advantageous if shutdown particles with an average particle size (D _w ) greater than or equal to, preferably greater than the average pore size of the pores of the porous inorganic layer (d _s ) are present in the suspension, since this ensures that the pores of the inorganic layer in the manufacture of the separator according to the invention are not blocked by shutdown particles. The shutdown particles used preferably have a average particle size (D _w ) which is greater than the average pore diameter (d _s ) and less than 5 d _s , particularly preferably less than 2 d _s .

If it is desired to use shutdown particles that have a particle size smaller than the pore size of the pores of the porous inorganic layer, it must be avoided that the particles penetrate into the pores of the porous inorganic separator layer.

Reasons for the use of such particles can e.g. B. in large price differences but also in the availability of such particles. One way of penetrating the

Preventing cut-off particles into the pores of the porous inorganic layer consists in adjusting the viscosity of the suspension in such a way that, in the absence of external shear forces, the suspension does not penetrate into the pores of the inorganic layer of the separator.

Such a high viscosity of the suspension can e.g. can be achieved by the

Suspension auxiliaries that influence the flow behavior, e.g. Silicas (Aerosil,

Degussa) can be added. When using auxiliary materials such as Aerosil 200 is often a proportion of 0.1 to 50% by weight, preferably 0.5 to 10% by weight, of silica, based on the suspension, sufficient to achieve a sufficiently high viscosity of the suspension. The proportion of auxiliary substances can be determined by simple preliminary tests.

It can be advantageous if the suspension used has shut-off particles with adhesion promoters. Such an adhesion promoter suspension can be applied directly to an inorganic layer of the separator, even if this is not before

Application was made hydrophobic. Of course, a suspension having an adhesion promoter can also be applied to a hydrophobized layer or to a separator layer during its manufacture

Adhesion promoter was used to be applied. Silanes which are preferably used as adhesion promoters in the suspension having shutdown particles

Have amino, vinyl or methacrylic side groups. Such adhesion promoters are e.g. B.

AMEO (3-aminopropyltriethoxysilane), MEMO (3-methacryloxypropyltrimethoxysilane),

Silfin (vinylsilane + initiator + catalyst), VTEO (vinyltriethoxysilane) or VTMO

(Vinyltrimethoxysilane). Such silanes are e.g. B. from Degussa also available in aqueous solution under the name Dynasilan 2926, 2907 or 2781. A maximum share

10% by weight of adhesion promoter has been found to be sufficient to ensure sufficient adhesion of the shutdown particles to the porous inorganic layer. Suspensions containing switch-off particles preferably contain adhesion promoters from 0.1 to 10% by weight, preferably from 1 to 7.5% by weight and very particularly preferably from 2.5 to 5% by weight, based on the suspension, of adhesion promoters ,

All particles that have a defined melting point can be used as shutdown particles. The material of the particles is selected according to the desired switch-off temperature. Since relatively low switch-off temperatures are desired for most batteries, it is advantageous to use switch-off particles which are selected from particles of polymers, polymer mixtures, natural and or artificial waxes. Particles made of polypropylene or polyethylene wax are particularly preferably used as shutdown particles.

The suspension containing the shutdown particles can be applied to the porous inorganic layer of the separator by printing, pressing on, pressing in, rolling up, knife coating, spreading on, dipping, spraying or pouring on. The switch-off layer is preferably obtained by drying the applied suspension at a temperature from room temperature to 100 ° C., preferably from 40 to 60 ° C.

It may be advantageous if, after being applied to the porous inorganic layer, the cut-off particles are fixed by heating at least once to a temperature above the glass temperature, so that the particles melt without changing the actual shape. In this way it can be achieved that the shutdown particles adhere particularly well to the porous inorganic separator layer.

The suspension containing the cut-off particles can be applied with subsequent drying and any heating above the glass transition temperature can be carried out continuously or quasi-continuously. If a flexible separator is used as the starting material, this can in turn be unwound from a roll, passed through a coating, drying and optionally heating apparatus and then rolled up again.

In another aspect of the invention, an electrochemical cell, in particular a lithium battery, lithium ion battery or a lithium polymer battery, provided, the cell comprising one of the separators described above with a low water content.

The electrolyte which is used in such an electrochemical cell can be any conventional electrolyte which can be used in electrochemical cells. Solutions of a soluble lithium salt in one or more organic solvents, such as, for example, ethylene carbonate and dimethyl carbonate (EC-DMC) can be mentioned as examples. Other suitable non-aqueous solvents include, for example, γ-butyrolactone, tetrahydrofuran, 1,2-dimethoxyethane, propylene carbonate, diethyl carbonate, methyl ethyl carbonate, diethoxyethane, dioxolane and methyl formate. Suitable soluble lithium salts are those commonly used. Examples include LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiClO, LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₃ and LiN (C ₂ F ₅ SO) ₃ , LiPF _{6 being} particularly preferred. Furthermore, the use of one of the above-described separators with a low water content for producing an electrochemical cell, in particular a lithium battery, lithium ion battery or a lithium polymer battery, is provided, in each case preferably for high-current or high-performance applications.

The electrochemical cell is preferably rechargeable.

The porosity is to be understood as the porosity that can be determined using the known mercury porosimetry method with a Porosimeter 4000 from Carlo Erba Instruments. Mercury porosimetry is based on the Washburn equation (EW Washburn, "Note on a Method of Determining the Distribution of Pore Sizes in a Porous Material", Proc. Natl. Acad. Sei., 7, 115-16 (1921) ).

The determination of the water content of the separators is carried out in the following way: A precisely balanced sample from a separator is heated to 180 ° C. in a tightly closed sample vessel. The amount of water released is continuously transferred over a period of more than 2 hours with a dry nitrogen stream into a (previously) anhydrous solution and there according to the method of Karl Fischer (see E. Eberius: water determination with Karl Fischer Solution, 3rd edition, Verlag Chemie, Weinheim 1968).

The present invention will now be described below with reference to examples, test and reference examples.

Examples, test and reference examples

Reference example 1: Production of an S450PET separator

30 g of a 5% strength by weight aqueous HNO ₃ solution, 10 g of tetraethoxysilane, 2.5 g of methyltriethoxysilane and 7.5 g of Dynasilane GLYMO are first added to 130 g of water and 15 g of ethanol. 125 g of the aluminum oxides Martoxid MZS-1 and Martoxid MZS-3 are then suspended in this sol, which was initially stirred for a few hours. This slip (suspension or dispersion) is homogenized for at least a further 24 h using a magnetic stirrer, the stirring vessel having to be covered so that there is no loss of solvent.

A 56 cm wide PET fleece with a thickness of approx. 13 μm and a basis weight of approx. 6 g / m ² is then coated with the above slip in a continuous rolling process (belt speed approx. 30 m / h, T = 210 ° C.) , At the end, a separator with an average pore size of 450 nm was obtained, which had very good adhesive strength and a thickness of approx. 30 μm. The water content in the separator is about 0.28% by weight.

Reference example 2: Production of an S800PET separator

30 g of a 5% strength by weight aqueous HO solution, 10 g of tetraethoxysilane, 2.5 g of methyltriethoxysilane and 7.5 g of Dynasilane GLYMO are first added to 130 g of water and 15 g of ethanol. 280 g of the aluminum oxide AICoA CT800 SG are then suspended in this sol, which was initially stirred for a few hours. This slip (suspension or dispersion) is homogenized for at least a further 24 h using a magnetic stirrer, the stirring vessel having to be covered so that there is no loss of solvent. A 56 cm wide PET fleece with a thickness of approx. 35 m and a weight per unit area of approx. 18 g / m ² is thus made using the continuous rolling method known from reference example 1 (belt speed approx. 30 m / h, T = 200 ° C.) Coated above slip. In this way, a separator with an average pore size of 800 nm is obtained, which has a very good adhesive strength and a thickness of approx. 55 μm. The water content in the separator is about 0.34% by weight.

Test example 2: Lithium battery with S450PET separator from reference example 1

The S450PET separator produced in reference example 1 is placed in a Li-ion cell consisting of a positive mass made of LiCoO ₂ , a negative mass consisting of graphite and an electrolyte made of LiPF _6. In ethylene carbonate / dimethyl carbonate (EC / DMC), built-in [LiCoO ₂ // S450PET, EC / DMC 1: 1, IM LiPF ₆ // graphite]. The charging behavior of this battery was checked. After more than 250 cycles, the battery shows only a slight decrease in capacity by a few percentage points. An increase in the charging voltage from 4.1 to 4.2 volts in the 200th charging cycle does not harm the battery.

During the first cycle, the battery heats up excessively and consumes significantly more electricity than its nominal capacity. No special features can be observed from the 5th cycle. However, this separator is not suitable for use in a battery due to the heating.

Test example 2: Lithium battery with S800PET separator from reference example 2

The S800PET separator produced in reference example 2 is placed in a Li-ion cell consisting of a positive mass as LiCoO ₂ , a negative mass consisting of graphite and an electrolyte made of LiPF ₆ in ethylene carbonate / dimethyl carbonate (EC / DMC) , built-in [LiCoO ₂ // S800PET, EC / DMC 1: 1, IM LiPF ₆ // graphite]. The charging behavior of this battery is checked. After more than 250 cycles, the battery shows only a slight decrease in capacity by a few percentage points. An increase in the charging voltage from 4.1 to 4.2 volts in the 200th charging cycle does not harm the battery. During the first cycle, the battery heats up excessively and consumes significantly more electricity than its nominal capacity. No special features can be observed from the 5th cycle. However, this separator is not suitable for use in a battery due to the heating.

Manufacture of separators according to the invention

Example 1: Production of an S100PET separator with low water content

30 g of a 5% by weight aqueous HCl solution, 1.5 g of LiNO ₃ , 10 g of tetraethoxysilane, 2.5 g of methyltriethoxysilane and 7.5 g of Dynasilane GLYMO are first added to 145 g of water. 140 g of the aluminum oxide AICoA CT3000 are then suspended in this sol, which was initially stirred for a few hours. This slurry (suspension or dispersion) is homogenized for at least another 72 h with a magnetic stirrer, whereby the Ruhr vessel must be covered so that there is no loss of solvent.

A 56 cm wide PET fleece with a thickness of approx. 13 μm and a weight per unit area of approx. 6 g / m ² is then coated with the above slip in a continuous rolling process (belt speed approx. 30 m / h, 1 = 200 ° C.) , At the end, a separator with an average pore size of 80 nm is obtained, which has a very good adhesive strength and a thickness of approx. 24 μm. The water content in the separator is less than 200 ppm.

Example 2: Preparation of a S240PET separator with low water content

30 g of a 5% strength by weight aqueous HCl solution, 2.8 g of L1NO _3, 10 g of tetraethoxysilane, 2.5 g of methyltriethoxysilane and 7.5 g of Dynasilane GLYMO are first added to 140 g of water and 10 g of ethanol. This sol, which was initially stirred for a few hours, is then used to suspend 265 g of the aluminum oxide AICOA CT1200 SG. This slip (suspension or dispersion) is homogenized for at least a further 24 h using a magnetic stirrer, the stirring vessel having to be covered so that there is no loss of solvent. A 56 cm wide PET fleece with a thickness of approx. 13 μm and a weight per unit area of approx. 6 g / m ² is then coated with the above slip in a continuous rolling process (belt speed approx. 30 m / h, T = 200 ° C.) , A separator with an average pore size of 240 nm is obtained in this way, which has a very good adhesive strength and a thickness of approx. 27 μm. The water content in the separator is less than 200 ppm.

Example 3: Preparation of a S450PET separator with low water content

A water-containing S450PET separator (0.28% by weight water content) produced according to reference example 1 is treated in a continuous impregnation process (belt speed approx. 30 m / h) with a 1% solution of LiNO ₃ in water and then at 200 ° C dried in vacuo. After that, the water content in the separator is less than 200 ppm.

Example 4: Preparation of an S800PET separator with low water content

A water-containing S800PET separator (0.34% by weight water content) produced according to reference example 2 is treated in a continuous impregnation process (belt speed approx. 30 m / h) with a solution of 0.1 mol lithium ethylate in one liter of ethanol and then at 200 ° C dried in vacuo. After that, the water content in the separator is less than 200 ppm.

Test Example 3: Lithium battery with the S450PET separator according to the invention with a low water content from Example 3

The S450PET separator produced in Example 3 is placed in a Li-ion cell consisting of a positive mass of LiCoO ₂ , a negative mass of graphite and an electrolyte of LiPF ₆ in ethylene carbonate / dimethyl carbonate (EC / DMC), built-in [LiCoO ₂ // S450PET, EC / DMC 1: 1, IM LiPF ₆ // graphite]. The charging behavior of this battery is checked. After more than 500 cycles, the battery shows only a slight decrease in capacity by a few percentage points. Even an increase in the charging voltage from 4.1 to 4.2 volts in the 450th charging cycle does not harm the battery. In contrast to test examples 1 and 2, the battery does not overheat during the first cycle. The power consumption in the first cycle largely corresponds to the nominal capacity of the cell. This separator is ideal for use in a battery.

Claims

claims A method of manufacturing a low water separator for an electrochemical cell, comprising the steps of: (a) providing a mixture comprising: (a-1) a lithium compound with a readily volatilized residue on heating, (a-2) a solvent and / or dispersant and (a-3) optionally further mixture components; (b) Preparation of a separator intermediate with the mixture, wherein on the Surface of the separator intermediate is at least partially exposed to the lithium compound; (c) heating the separator intermediate to a temperature of 50 to 350 ° C for a predetermined time to at least partially remove the rest of the lithium compound, optionally pyrolytically, from the surface of the separator intermediate and to provide the separator with a low water content. 2. The method of claim 1, wherein step (b) comprises contacting a porous carrier having an inorganic coating with the mixture from step (a), which is a solution of the lithium compound in a solvent, to the inner and / or outer Treat the surface of the porous support with the mixture and create the separator intermediate. 3. The method according to claim 2, wherein after a determination of the free OH groups in the porous carrier, in relation to the number of these free OH groups the 0.5 to 1.5 times, preferably 0.7 to 1.0 times the stoichiometric amount of lithium compound is used. 4. The method of claim 1, wherein the mixture in step (a) is a dispersion, which as further mixture components (a-3.1) an oxide sol, (a-3.2) ceramic particles and (a-3.3) optionally fine particles, wherein step (b) comprises the following steps: (b-1) providing a flat, multi-aperture flexible substrate, (b-2) applying the dispersion in a thin layer on and in the Substrate, wherein the separator precursor is created, and wherein in step (c) a separator with a porous carrier having an inorganic coating is created by heating the separator precursor to 50 to 350 ° C. 5. The method of claim 4, wherein the substrate consists of a nonwoven web of non-electrically conductive polymer fibers. 6. The method according to claim 4 or 5, wherein the fine particles have an average primary particle size in the range of 1 to 200 nm, preferably 2 to 100 nm, very particularly preferably 3 to 50 nm. 7. The method according to any one of claims 4 to 6, wherein the fine particles contain a pyrogenic oxide of the elements silicon, zirconium and / or aluminum. 8. The method according to any one of claims 4 to 7, wherein the dispersion as ceramic particles oxide particles of the elements Si and optionally AI, and / or Zr with an average particle size of 0.1 to 10 microns, preferably 0.5 to 5 microns , having 9. The method according to any one of the preceding claims, wherein in step (a) the lithium compound is selected from lithium nitrate, lithium chloride, lithium carbonate, lithium acetate, lithium formate, lithium azide, lithium metal hydrides, lithium alcoholates or organolithium compounds. 10. The method according to any one of the preceding claims, wherein the solvent or dispersant in step (a) is aqueous or non-aqueous. 11. The method according to any one of the preceding claims, wherein the carrier is a flexible nonwoven with a porous inorganic coating located on and in this fleece, and wherein the material of the fleece is selected from non-woven, non-electrically conductive polymer fibers. 12. The method according to any one of the preceding claims, wherein the fleece has a thickness of at most 30 microns. 13. The method according to any one of the preceding claims, wherein the polymer fibers are selected from fibers of polyacrylonitrile, polyester, polyamide and / or polyolefin. 14. The method according to any one of the preceding claims, wherein the flexible nonwoven has a basis weight of less than 20 g / m. 15. The method according to any one of the preceding claims, wherein the flexible nonwoven has a porosity of more than 50%. 16. The method according to any one of the preceding claims, wherein the fleece has a thickness of 5 to 30 microns. 17. The method according to any one of the preceding claims, wherein the porous inorganic coating on and in the fleece ceramic oxide particles of the elements Si and optionally Al, and / or Zr with an average particle size of 0.1 to 10 microns, preferably 0, 5 to 5 μm. 18. The method according to any one of the preceding claims, wherein the porous inorganic coating on and in the fleece has aluminum oxide particles with an average particle size of 0.5 to 5 microns, which are bonded to an oxide of the elements Zr or Si. 19. The method according to any one of the preceding claims, wherein the carrier has a porosity of 30 to 90%. 20. The method according to any one of the preceding claims, wherein the separator has a tensile strength of more than 1 N / cm. 21. The method according to any one of the preceding claims, wherein the separator is bendable to a radius down to 100 mm, preferably up to 1 mm, without damage. 22. The method according to any one of the preceding claims, wherein the thickness of the separator is at most 35 microns. 23. The method according to any one of claims 2 to 22, wherein the contacting in step (b) or the application of the thin layer in step (b-2) by printing, pressing, pressing, rolling, knife coating, brushing, dipping, spraying or Pouring the mixture or the dispersion takes place. 24. Separator for an electrochemical cell, which is obtainable by a process of claims 1 to 23. 25. Separator according to claim 24, characterized in that on inner and / or outer surfaces via an oxygen bridge on atoms of an element of the group 3A, 4A, 3B or 4B of the periodic table of the elements, preferably selected from one of the elements silicon, aluminum and zirconium, there are bound lithium atoms. 26. Separator according to claim 24 or 25, which has a water content of less than 1000 ppm, preferably less than 500 ppm, very particularly preferably less than 200 ppm. 27. Electrochemical cell, in particular a lithium battery, lithium ion battery or a lithium polymer battery, the cell being a separator according to one of the Claims 24 to 26 comprises. 28. Use of a separator according to one of claims 24 to 26 for producing a electrochemical cell, in particular a lithium battery, lithium ion battery or a lithium polymer battery, in each case preferably for high-current or high-performance applications.