DE10255123A1 - Low water separator for an electrochemical cell - Google Patents

Abstract

A method of making a low water separator for an electrochemical cell, comprising the steps of: (a) providing a mixture comprising (a-1) a lithium compound with a residue that volatilizes on heating, (a-2) a solvent, and / or dispersant and (a-3) optionally further mixture components; (b) production of 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 in order to at least partially remove the rest of the lithium compound, optionally pyrolytically, from the surface of the separator intermediate and to create the separator with a low water content.

Description

The present invention relates to a method of manufacturing a separator with a low water content for one electrochemical cell, a separator made by this method is producible, as well as an electrochemical cell, such Low water separator included.

Under electrochemical cell or In this description, batteries are batteries and accumulators (secondary batteries) any kind of understanding, especially alkali, e.g. Lithium-, Lithium ion, lithium polymer, and alkaline earth batteries and accumulators in the form of high-energy or high-performance systems.

Include electrochemical cells antipolar electrodes maintained by a separator of ion conductivity, are separated from each other.

Traditionally, a separator 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. In electrochemical cells, it is supposed to electronically separate the cathode from the anode completely isolate. Moreover it must be permanently elastic and the movements in the system, e.g. B. in the electrode pack when loading and unloading.

The separator is decisive the life of the arrangement in which it is used, e.g. B. the an electrochemical cell. The development of rechargeable electrochemical cells or batteries will therefore be developed suitable separator materials. General information about electrical Separators and batteries can z. B. at J.O. Besenhard in “Handbook of Battery Materials "(VCH publishing house, Weinheim 1999) can be read.

High energy batteries are used in different Applications where it matters where possible size Amount of electrical energy available. For example, this is with traction batteries but also with the emergency power supply Batteries (Auxillary Power Systems) the case. The energy density is common specified in weight [Wh / kg] or volume-related [Wh / L] sizes. Energy densities of 350 to 400 Wh / L and from 150 to 200 Wh / kg reached. The queried Power on such batteries is not that great, so you have to compromise of internal resistance. That is, the conductivity of the electrolyte filled Separators, for example, do not have to be as big as high-performance batteries, so that other separator concepts are also possible.

So with high energy systems polymer electrolytes are also used, with 0.1 to 2 mS / cm quite a low conductivity have. Such polymer electrolyte cells cannot be used as high-performance batteries be used.

Separator materials for use in high-performance battery systems must have the following properties:
They have to 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 become very big Amounts of energy needed (e.g. in traction batteries). Save the batteries in these applications Large amounts of energy when fully charged. For this, the Separator be safe because very large specific in these batteries electrical energy quantities are transported. These energies are allowed to malfunction of the battery or in an accident not uncontrolled to be released as this inevitably causes the cell to explode under fire would.

Separators currently in use exist predominantly from porous organic polymer films or from inorganic nonwovens, such as z. B. nonwovens made of glass or ceramic materials or ceramic papers. These are made by different companies. Major producers are here: Celgard, Tonen, Ube, Asahi, Binzer, Mitsubishi, Daramic and other.

The separators from inorganic Nonwovens or ceramic paper are mechanically unstable and break easily. this leads to to short circuits. Because the electrodes can easily come into contact through broken areas.

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 that 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 with regard to chemical resistance. The polymers namely in the electrochemical cells through contact with the electrodes even at normal operating and storage temperatures like room temperature slowly but steadily attacked. In particular happens when such separators are used in electrochemical cells, using lithium, problems. At the contact surface of the Separator with the lithium or with the lithiated graphite the polymer slowly attacked. Furthermore, the polymer separators also by the while of the operation of an electrical cell Attacked inside the separator. This allows these separators Protect electrodes from a short circuit no longer secured. The Tool life is reduced. In addition, the capacity takes one electrochemical cell using such separators with the Time off.

In order to overcome these disadvantages, there were first attempts to use inorganic composite materials as separators. So in DE 198 38 800 C1 proposed an electrical separator with a composite structure, which comprises a flat, provided with a plurality of openings, flexible substrate with a coating thereon. 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 flat, 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 ) has been shown that with a material comprising a flat, multi-hole flexible substrate 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 wherein the resulting separator has a very small thickness of less than 100 microns and is bendable, a separator can be produced in conjunction with the Electrolyte has a sufficiently low resistance and nevertheless has a sufficiently large long-term resistance.

The in DE 101 42 622 Although the separator described has a very high conductivity, the separator described there still does not meet the requirements for a separator which can be used industrially with regard to the thickness and weight and also the 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 was reduced by using a polymer fleece, but the embodiments of a separator described there also do not yet meet all the requirements for a separator for a lithium high-energy battery, in particular because in this application special emphasis was placed on if possible large pores of the separator. 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, such as silicon dioxide, which 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 results in charged electrochemical cells, in particular problems with 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 present invention was therefore the task is based on a method for producing an almost anhydrous separator for to provide an electrochemical cell, a separator that can be produced by this method, and an improved electrochemical Cell that includes such a separator.

• (a) Bereitstellung eines Gemisches, das (a-1) eine Lithiumverbindung mit einem sich bei Erwärmung leicht verflüchtigenden Rest, (a-2) ein Löse- und/oder Dispergiermittel und (a-3) gegebenenfalls weitere Gemischkomponenten umfasst;
• (b) Herstellung eines Separatorvorprodukts mit dem Gemisch, wobei auf der Oberfläche des Separatorvorprodukts zumindest teilweise die Lithiumverbindung exponiert vorliegt;
• (c) Erhitzen des Separatorvorprodukts auf eine Temperatur von 50 bis 350°C für eine vorbestimmte Zeit, um den Rest der Lithiumverbindung, gegebenenfalls pyrolytisch, zumindest teilweise von der Oberfläche des Separatorvorprodukts zu entfernen und den Separator mit niedrigem Wassergehalt zu schaffen.

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 which comprises (a-1) a lithium compound with a residue which is readily volatilized on heating, (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 provide the separator with a low water content.

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

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

Contacting and treatment inner and / or outer surfaces of a porous a carrier having an inorganic coating with a mixture z. B. done so be that the porous a carrier having an inorganic coating is unrolled from a roll is preferably at a speed of 1 m / h to 2 m / s at a speed of 0.5 m / min to 20 m / min and very special preferably at a speed of 1 m / min to 5 m / min at least one apparatus which brings the mixture onto and into the carrier, such as B. a roller, and at least one other apparatus, which heating the separator precursor enables such. B. an electric heated oven, goes through and the product thus produced is rolled up on a second roll. In this way it is possible a separator according to the invention in a continuous process. Even the pre-treatment steps can in Continuous process can be carried out while maintaining the parameters mentioned.

It has proven to be particularly beneficial proved if the process is carried out so that the porous one carriers having an inorganic coating during the treatment process a maximum tension in the longitudinal direction of 10 N / cm, preferably of 3 N / cm. Be among treatment processes understood all process steps in which a material on and in a carrier brought. The carrier is preferably used during the treatment process tensioned with a maximum force of 0.01 N / cm. Particularly preferred it can be if the carrier while of the treatment process in the longitudinal direction led relaxed becomes.

By checking the tension while Treatment can prevent deformation (also elastic) of the carrier material takes place. Due to a possible deformation (elongation) with too high The ceramic coating can tension the carrier material or substrate material does not follow, which leads to the fact that the coating itself over the entire area detaches from the substrate. The resulting product cannot then be used as intended become.

The porous is an inorganic coating having carriers can for example a separator with an inorganic composite structure be that is already known from the prior art. So can advantageous through a subsequent Treatment an improved separator in terms of water content be created.

In a particularly preferred embodiment, only after a determination of the free OH groups in the porous carrier, in relation to the number of these free OH groups, is the 0.5 to 1.5 times che, preferably 0.7 to 1.0 times the stoichiometric amount of 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 carrier, 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 water content in a separator treated according to the method described above let yourself explain as follows. By treating a separator, the bound water is in the form of partially hydrolyzed ceramic material, e.g. silica has groups with the structure -M-O-H in groups with transferred to the structure -M-O-Li, where M for one Element stands that forms a ceramic material. M is there 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. That it creates a structure in which oxygen bonds Atoms of one of the elements M are bound lithium atoms. Self if by adverse circumstances Water getting to this structure does not cause any major problems. Although a minor Hydrolysis of the structure -M-O-Li again to re-form a group with of the structure -M-O-H take place. This diminished -M-O-H structure but is now isolated. There are no others in their neighborhood -M-O-H group more with which it releases free water, that damages the components of the electrochemical cell.

Another advantage of the invention is one by the inventive method achieved increase in conductivity one filled with an electrolyte separator according to the invention. In a separator according to the invention, which is filled with an electrolyte is the surface positions of the lithium ion for the charge transport over the surface to disposal. this leads to to an elevated conductivity through the separator. Because this rapid charge transport is carried out exclusively via lithium ions takes place, there is an advantageous increase in the number of transfers for cations. As a result, the sensitivity of one with a such a separator equipped electrochemical cell against high discharging be reduced. In this way, polarization becomes advantageous reduced in such an electrochemical cell. This has the additional Advantage that the resilience of the process according to the invention manufactured separators increased is. So you can the electrochemical cells are advantageously 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, comprises,
step (b) comprising the following steps:
(b-1) providing a flat flexible substrate provided with a plurality of openings,
(b-2) applying the dispersion in a thin layer on and into the substrate, thereby creating the separator intermediate,
and wherein in step (c) a separator with a porous carrier having an inorganic coating is created by heating the separator intermediate to 50 to 350 ° C.

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

The substrate can be made from 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 service 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 as ceramic particles 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, on.

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 LiAlH ₄ , lithium alcoholates or organolithium compounds.

The solvent or dispersant in Step (a) can be aqueous or not watery be such as Water, an alcohol, ketone, ether, saturated and / or unsaturated Hydrocarbon or a mixture thereof.

The carrier is one preferred embodiment of the method according to the invention a flexible fleece with one on and in this fleece porous inorganic coating, the material of the fleece made of non-woven, not electrically conductive Polymer fibers selected can be. But it can also be a fleece or woven ceramic or be glass fibers.

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

The porous is an inorganic coating having carriers or the flat, a variety of openings comprising, flexible substrate comprises in a preferred embodiment fibers of the present invention, preferably selected from Fibers of polyamide, polyacrylonitrile, polyester, 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 Includes polymer fibers polymer fibers other than those mentioned above are used, provided they both the for the manufacture of the separators have the required temperature stability as well as under the operating conditions in a lithium battery are stable. In a preferred embodiment, the separator according to the invention Polymer fibers that have a softening temperature of greater than 100 ° C and a Have a melting temperature of greater than 110 ° C.

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

In a further embodiment According to the invention, the substrate is a nonwoven 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 ² .

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

In a preferred embodiment has 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 μm, preferably 0.5 to 5 μm, on.

Very particularly preferably, the porous inorganic coating on and in the fleece Alumina particles with an average particle size of 0.5 up to 5 μm which are bonded with an oxide of the elements Zr or Si.

The carrier preferably has one porosity from 30 to 90%.

The separator can advantageously who received according to the invention, becomes a tear resistance of more than 1 N / cm.

In addition, the separator or the pre-separator is preferred due to its composite structure without damage to a radius down to 100 mm, preferably up to 1 mm, bendable.

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

The contacting in step (b) or the application of the thin Layer in step (b-2) is preferably carried out by printing, pressing, Pressing in, rolling up, knife application, spreading, dipping, spraying or infusion of the mixture or the dispersion.

Furthermore, the object of the invention through a separator for solved an electrochemical cell that is obtainable by one of the methods described above.

Preferably lie on inner and / or outer surfaces of the separator according to the invention via a oxygen bridge on atoms of an element from group 3A, 4A, 3B or 4B of the periodic table of the Elements, preferably selected bonded from one of the elements silicon, aluminum and zirconium Lithium atoms. The detection of such structures is by Raman spectroscopy possible.

With a particularly advantageous embodiment According to the invention, the separator has a low water content 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, for example, lithium metal and lithium ion batteries. Therefore, it is 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 carrier 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.

For example, polymer separators the for Lithium batteries currently require security by starting from one certain temperature (the shutdown temperature, which is around 120 ° C) prevent any current transport through the electrolyte. This happens because at this temperature the pore structure of the separator collapses and all pores are closed. As a result of that dangerous ions can no longer be transported Reaction leading to the explosion can, to succumb. If the cell is heated further due to external circumstances, then becomes at approx. 150 to 180 ° C the breakdown temperature was exceeded. From this temperature, the separator melts, whereby this contracts. In many places in the battery cell there is now a direct contact between the two electrodes and thus to a large interior Short circuit. This leads to the uncontrolled reaction with an explosion of the cell ends, or the pressure generated is through a pressure relief valve (a rupture disc) often degraded under fire.

In a particularly preferred embodiment of the invention comprises the carrier of the separator polymer fibers. With this hybrid separator, the has inorganic components and polymeric carrier material comes it to shutdown if the high temperature Polymer structure of the support material melts and penetrates into the pores of the inorganic material and thereby closes it. The separator according to the invention, on the other hand, leads to so-called meltdown Not. The separator according to the invention Fulfills so the requirements for one of different battery manufacturers required safety shutdown by the shutdown in the battery cells. The inorganic particles ensure that it never becomes one Melt-down can come. This ensures that there are no operating states, in which a large-scale short circuit can arise.

It can be advantageous if the Separator an additional not inherent Shut-down mechanism. This can e.g. B. realized thereby that there is a very thin wax on or in the separator or polymer particle layer of so-called shutdown particles, which at a desired one Melt shutdown temperature, is present. Particularly preferred Materials from which the shutdown particles can be made 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 one you want Melt the switch-off temperature and close the pores of the separator, see above 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 it prevents the pores of the separator layer from penetrating and closing, which would result in a reduction in the pore volume and thus in the conductivity of the separator and also in the performance of the battery. 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. In order to achieve a safe 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 safety feature. In contrast to the purely organic separator materials, this separator cannot melt completely and therefore there can be no meltdown. These safety features are very important due to the very large amounts of energy for high-energy batteries 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. B. drill a nail through a battery, depending on the Se parator the following: The polymer separator would melt and contract at the penetration point (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 procedure for applying a Dispersion as a thin Layer on and in a substrate for the production of a separator or separator precursor, and the manufacture of a porous one inorganic coating carrier, preferably a sheetlike with a variety of openings provided, flexible substrate is principally from WO 99/15262 known. However, not all parameters or input materials can be deploy.

A dispersion can e.g. B. by Printing, pressing, pressing, rolling up, knife application, spreading, Dipping, spraying or pouring on and into the flexible substrate provided with a plurality of openings to be brought.

The to apply and bring into the with a variety of openings provided, flexible substrate can be a sol of the elements Al, Zr and / or Si, and is preferably by dispersing ceramic particles and optionally made of fine particles in one of these brines. The brine can by hydrolyzing at least one compound, with water or an acid or a combination of these compounds. It can be advantageous, the compound to be hydrolyzed before hydrolysis in alcohol or an acid or a combination of these liquids to give. The compound to be hydrolyzed is preferably at least a nitrate, a chloride, a carbonate, an alcoholate or an element-organic Connection of the elements Al, Zr and / or Si 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 become particulate sols by hydrolysis of the compounds to be hydrolyzed manufactured. These particular ones Brines are characterized in that those in the sol by hydrolysis the resulting compounds are particulate. The particulate brine can be like above or as described in WO 99/15262. This Sols usually have one very high water content, which is preferably greater than 50 wt .-%. It can be advantageous, the compound to be hydrolyzed before hydrolysis in alcohol or an acid or a combination of these liquids to give. The hydrolyzed compound can be peptized with at least one organic or inorganic acid, preferably with one 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 be treated. The particulate sols thus produced can then be used for Production of dispersions are used, the production of Dispersions for application to polymer sol pretreated Nonwoven is preferred.

In a further variant of the method according to the invention are polymerized by hydrolysis of the compounds to be hydrolyzed Brine made. In this preferred embodiment variant 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 characterized in that the in the Sol compounds formed by hydrolysis polymer (i.e. chain-like over a larger space networked). The polymeric sols usually have less than 50 % By weight, preferably very much less than 20% by weight, of water and / or aqueous Acid on. To the preferred proportion of water and / or water Acid to come the hydrolysis is preferably carried out so that the hydrolysed Compound with the 0.5 to 10 times the molar ratio and preferably with the half molar ratio Water, steam or ice, based on the hydrolyzable group, the hydrolyzable compound is hydrolyzed. One up to 10 times the amount of water can with very slow hydrolyzing compounds such as B. be used in tetraethoxysilane. Very fast Hydrolyzing compounds such as zirconium tetraethylate can be found under These conditions already form particulate brine, which is why Hydrolysis of such compounds prefers 0.5 times the amount of water is used. Hydrolysis with less than the preferred one Amount of water, water vapor, or ice also gives good results. Falling below the preferred amount by half a mole ratio more than 50% is possible but not very useful, because if the value falls below this, the Hydrolysis is no longer complete and coatings based on such brine are not very stable are.

For the production of brines with a desired very small amount of water and / or acid in the sol it can be advantageous be when the compound to be hydrolyzed in an organic Solvents in particular ethanol, isopropanol, butanol, amyl alcohol, hexane, Cyclohexane, ethyl acetate and or mixtures of these compounds, solved before the actual hydrolysis is carried out. A so made Sol can be used to produce the separators according to the invention become.

Both particulate brine (large water content, low solvent content) and polymeric brine (ge 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, which 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 in and of itself DE 101 42 622 and known in a similar form from WO 99/15262, but not all parameters or feedstocks can be transferred to the manufacture of the separator intermediate and separator. 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 spots in the nonwoven material can lead to separators being obtained which have defects and are therefore unusable.

It was found that a sol system or a dispersion which or which in wetting behavior adapted to the polymers, soaked with nonwoven materials and thus flawless coatings are available. Preferably done in the process, therefore, an adjustment of the wetting behavior of the sol or the dispersion. This adjustment is preferably done by the production of brines or dispersions, these brines one or more alcohols, such as. B. methanol, ethanol or propanol or mixtures thereof, and / or aliphatic hydrocarbons have include. However, other solvent mixtures are also conceivable that can be added to the sol or the dispersion in order to improve the wetting behavior adapt to the fleece used.

The mass fraction of the suspended is preferably or dispersed component (ceramic particles) on the dispersion 1 to 100 times, particularly preferably 1 to 50 times and whole particularly preferably 1 to 10 times the sol used. Especially are preferred for producing the dispersion as ceramic particles Oxide particles, e.g. Alumina particles used, which are preferred an average particle size of 0.1 up to 10 μm, in particular 0.5 to 5 μm exhibit. Alumina particles are in the range of preferred particle sizes for example from the company Martinswerke under the designation MDS 6; DN 206, MZS 3 and MZS 1 and from Alcoa with the designation CL3000 SG, CT800 SG and NVA SG offered.

It has been found that the use of commercially available Under certain circumstances, oxide particles or ceramic particles leads to unsatisfactory results, because often a very big one Particle size distribution is present. Ceramic particles are therefore preferably used, by a conventional one Methods such as B. Air classification, centrifuging and hydroclassification were classified. Such ceramic particles are preferred Fractions are used in which the coarse grain fraction, which up accounts for 10% of the total amount, was separated by wet sieving. This annoying Coarse grain, which is also due to the production of the slip typical processes such as milling (ball mill, attritor mill, mortar mill), dispersing (Ultra-Turrax, ultrasound), not grating or chopping or can be crushed only with great difficulty, e.g. B. consist of Aggregates, hard agglomerates, grinding ball wear. By the aforementioned activities it is achieved that the inorganic porous layer has a very uniform pore size distribution having. This is achieved in particular in that ceramic Particles are used which preferably have a maximum particle size 1/3 to 1/5 and particularly preferably less than or equal to 1/10 of Have thickness of the fleece used.

The following table 1 gives an overview, how the choice of different aluminum oxides depends on the porosity and the resulting pore size of the respective porous inorganic coating. To determine this data the corresponding slips (suspensions or dispersions) manufactured and as a pure molded body at 200 ° C dried and solidified.

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 glycidyl-functionalized silanes can also be used for polyacrylonitrile. 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 ^–1 ) and then dividing by the specific space requirement of the adhesion promoter (in m ² g ^-1 ) are obtained, the specific space requirement often being in the order of 300 to 400 m ² g ^-1 .

Table 2 below contains one exemplary overview of usable Adhesion promoter 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 = vinyl trimethoxysilane
VTMOEO = vinyl tris (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 ₃ , 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 dispersion is applied and solidified only after the adhesion promoter has been applied.

By applying an adhesion promoter before the actual application of the dispersion, the adhesion behavior the flexible carrier or substrates in particular with respect to aqueous, particulate sols be improved, which is why so pretreated carriers or Substrates with suspensions or dispersions based on commercially available Soles such as B. zirconium nitrate sol or silica sol can be coated. This How to apply an adhesion promoter means also that the manufacturing process of the separators according to the invention must be expanded by an intermediate or pre-treatment step. This is feasible, however, more complex than using adapted sols to which adhesion promoters have been added, however also the advantage that even when using dispersions based on of commercially available Should better results be achieved.

The coatings according to the invention are made by Solidifying the dispersion brought in and on the substrate. According to the dispersion on and in the substrate by heating on 50 to 350 ° C be solidified. Because when using polymeric substrate materials the maximum temperature is determined by the polymer fleece, it must be adjusted accordingly. Depending on the design variant of the method according to the invention the dispersion present on and in a substrate by heating up 100 to 350 ° C and very particularly preferably solidified by heating to 110 to 280 ° C. It can be beneficial if heating for 1 second to 60 minutes at a temperature of 100 to 350 ° C. Particularly preferred the heating takes place the dispersion for solidification to a temperature of 110 to 300 ° C, very special 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 state the technology.

The procedure for applying a thin Layer on and in the substrate or the contacting of a porous one can have inorganic coating carrier with a mixture z. B. done so that the flexible substrate, e.g. a polymer fleece, or the porous a carrier having an inorganic coating is unrolled from a roll is preferably at a speed of 1 m / h to 2 m / s at a speed of 0.5 m / min. up to 20 m / min and very special preferably at a speed of 1 m / min to 5 m / min at least one apparatus, which the dispersion or the mixture brings on and in the substrate or the carrier, such as. Legs Roller, and at least one other apparatus that solidifies the dispersion on and in the carrier by heating allows such as B. passes through an electrically heated oven and the so produced Product is rolled up on a second roll. In this way Is it possible, a separator intermediate according to the invention or to create a separator in a continuous process. Also the Pretreatment steps can in a continuous process while maintaining the parameters mentioned carried out become.

It has proven to be particularly beneficial proven if the method is carried out so that the flat, one Variety of openings having, flexible substrate, in particular a polymer fleece, during the Coating process a maximum tension in the longitudinal direction of 10 N / cm, preferably of 3 N / cm. Under coating process all process steps are understood in which a material is brought on and into a flexible substrate and there a heat treatment is subject, so also the application of the adhesion promoter. Preferably the substrate is used during Coating process with a maximum force of 0.01 N / cm. It can be particularly preferred if the substrate during the Treatment process or the coating process in the longitudinal direction is carried out untensioned.

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

Should the separator according to the invention with an additional automatic shutdown mechanism can be equipped, so this can e.g. B. happen in that after solidifying the applied to the substrate Dispersion a layer of particles at a desired Melt temperature and close the pores of the separator, see above called shutdown particles to generate a shutdown mechanism is applied to the separator and fixed. The layer out 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 be generated.

The suspension for applying the Contains particles preferably 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, especially wax particles in the suspension.

Because the inorganic coating of the separator often has a very hydrophilic character, it has proven to be advantageous proven when using the coating of the separator a silane in a polymeric sol as an adhesion promoter were and thus were made hydrophobic. To have good liability and even distribution the shutdown particle in the shutdown layer also on hydrophilic porous There are several ways to achieve inorganic separator layers possible.

In an embodiment variant of the method according to the invention it has proven advantageous to use the porous inorganic layer of the Separator to hydrophobize before applying the shutdown. The Production of hydrophobic membrane that works on the same principle is described for example in WO 99/62624. Preferably the porous inorganic coating by treatment with alkyl, aryl or Fluoroalkylsilanes such as z. B. under the name brand name Dynasilan distributed by Degussa, hydrophobic. You can do it z. B. the known methods of waterproofing, among others for textiles can be applied (D. Knittel; E. Schollmeyer; Melliand Textilber. (1998) 79 (5), 362-363), with minor change of the recipes, also for the porous Coatings of the separator are applied. To this end the coating or the separator is treated with a solution which has at least one hydrophobic substance. It can be beneficial be when the solution as a solvent 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 one Alcohol, preferably ethanol. The proportion of acid treated Water or alcohol on the solvent can be from 0 to 100% by volume. The proportion is preferably of water on the solvent from 0 to 60 vol .-% and the proportion of alcohol from 40 to 100 vol .-%. In the solvent are going to build the solution 0.1 to 30 wt .-%, preferably 1 to 10 wt .-% of a hydrophobic Be given. As hydrophobic substances such. B. the silanes listed above be used. Surprisingly finds good hydrophobization not only with highly hydrophobic Compounds, such as with the triethoxy (3,3,4,4,5,5,6,6,7,7,8,8-tridecafluorooctyl) silane instead, but a treatment with methyltriethoxysilane or i-butyltriethoxysilane is completely sufficient to achieve the desired effect. The solutions for even distribution the hydrophobic substances in the solution, stirred at room temperature and subsequently applied to the inorganic coating of the separator and dried. Drying can be done by treatment at temperatures from 25 to 100 ° C be accelerated.

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

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 an 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 to prevent the cut-off particles from penetrating into the pores of the porous inorganic layer is to adjust the viscosity of the suspension so that in the absence of external shear forces there is no on penetration of the suspension into the pores of the inorganic layer of the separator takes place. Such a high viscosity of the suspension can be achieved, for example, by adding auxiliaries which influence the flow behavior, such as, for example, silicas (Aerosil, Degussa) to the suspension. When auxiliaries such as Aerosil 200 are used, a proportion of 0.1 to 50% by weight, preferably 0.5 to 10% by weight, of silica, based on the suspension, is often sufficient to ensure a sufficiently high viscosity of the suspension achieve. The proportion of auxiliary substances can be determined by simple preliminary tests.

It can be beneficial if the Has used suspension particles containing adhesion promoter. Such a suspension having an adhesion promoter can be applied directly an inorganic layer of the separator can be applied, too if it has not been made hydrophobic before application. Of course you can an adhesion promoter suspension also on a hydrophobized Layer or on a separator layer in the manufacture of a Adhesion promoter was used to be applied. As an adhesion promoter in of the suspension having shutdown particles are preferred Silanes used, the amino, vinyl or methacrylic side groups exhibit. Such adhesion promoters are e.g. B. AMEO (3-aminopropyltriethoxysilane), MEMO (3-methacryloxypropyl trimethoxysilane), silfin (vinylsilane + initiator + Catalyst), VTEO (vinyltriethoxysilane) or VTMO (vinyltrimethoxysilane). Such silanes are e.g. B. from Degussa also in aqueous Solution under the designation Dynasilan 2926, 2907 or 2781 available. A maximum of 10% by weight of adhesion promoter has proven to be enough for ensuring a sufficient huge Adhesion of the switch-off particles to the porous inorganic layer is highlighted. Adhesion promoters preferably have suspensions of Switch-off particles 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 of adhesion promoter based on the suspension.

All can be used as shutdown particles Particles are used that have a defined melting point. The material of the particles will be the desired one Switch-off temperature selected. There relatively low cut-off temperatures for most batteries required it is advantageous to use such shutdown particles the selected are made of particles of polymers, polymer mixtures, natural and / or artificial To grow. Particles are particularly preferred as shutdown particles made of polypropylene or polyethylene wax.

The application of the shutdown particles having suspension can by printing, pressing, pressing, Roll up, knife, spread, dip, spray or pour on the porous inorganic layer of the separator. The shutdown layer is preferably obtained in that the applied suspension dried at a temperature from room temperature to 100 ° C, preferably from 40 to 60 ° C becomes.

It can be beneficial if the Switch-off particles after application to the porous inorganic layer heating at least once to a temperature above the glass temperature so that it melts the particle with no change the actual shape is achieved, fixed. That way achieved that the shutdown particles particularly well on the porous inorganic separator layer stick.

The application of the shutdown particles having suspension with subsequent drying and a possible Warming over the Glass transition temperature can be carried out continuously or quasi continuously. If a flexible separator is used as the starting material, then can in turn be unwound from a roll by a coating, Drying and possibly heating apparatus performed and subsequently be rolled up again.

From another point of view The invention is an electrochemical cell, in particular a Lithium battery, lithium ion battery or a lithium polymer battery, provided, the cell being one of the separators described above with 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 ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₃ and LiN (C ₂ F ₅ SO ₂ ) ₃ , with LiPF _{6 being} particularly preferred.

Furthermore, the use according to the invention one of the separators with low water content described above for the production of an electrochemical cell, in particular one Lithium battery, lithium ion battery or a lithium polymer battery, provided, each preferred for high current or high performance applications.

It is preferably electrochemical Cell 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 Determi ning the Distribution of Pore Sizes in a Porous Material ", Proc. Natl. Acad. Sci., 7, 115-16 (1921)).

The determination of the water content The separators are carried out in the following way: A precisely balanced one Sample from a separator is heated to 180 ° C in a tightly closed sample vessel. The released amount of water is continuously over a Period of more than 2 hours with a dry stream of nitrogen transferred to 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 described below using examples, test and reference examples.

Examples, test and reference examples

Reference Example 1: Manufacturing 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: Manufacturing an S800PET separator

To 130 g of water and 15 g of ethanol be first 30 g of a 5 wt .-%, aqueous HCl solution, 10 g tetraethoxysilane, 2.5 g methyltriethoxysilane and 7.5 g dynasilane Given GLYMO. In this sol, which was initially stirred for a few hours, 280 g of the aluminum oxide AlCoA CT800 SG are then suspended. This slip (suspension or dispersion) is used for at least another 24 h with a magnetic stirrer homogenized, covering the mixing vessel must be avoided 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. This gives a separator with an average pore size of 800 nm, which has 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, 1 M 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.

While of the first cycle warmed the battery becomes excessively strong and consumes significantly more electricity than its nominal capacity. No special features can be observed from the 5th cycle. For one use in a battery this separator is eliminated 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) , installed [LiCoO ₂ // S800PET, EC / DMC 1: 1, 1 M 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.

While of the first cycle warmed the battery becomes excessively strong and consumes significantly more electricity than its nominal capacity. No special features can be observed from the 5th cycle. For one use in a battery this separator is eliminated due to the heating.

Manufacture of separators according to the invention

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

30 g of a 5% strength 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 AlCoA CT3000 are then suspended in this sol, which was initially stirred for a further 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, l = 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: Production of a S240PET separator with low water content

30 g of a 5% strength by weight aqueous HCl solution, 2.8 g of LiNO _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 is obtained in this way with an average pore size of 240 nm, which has a very good adhesive strength and a thickness of approx. 27 μm having. The water content in the separator is less than 200 ppm.

Example 3: Production an 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: Production a S800PET separator with low water content

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

Test Example 3: Lithium Battery with the low S450PET separator according to the invention Water content from example 3

The S450PET separator produced in Example 3 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, 1 M 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. Also an increase in the charging voltage from 4.1 to 4.2 Volt in the 450th charging cycle does not harm the battery.

In contrast to the test examples 1 and 2 it occurs during of the first cycle does not cause excessive heating of the battery. The electricity consumption in the first cycle largely corresponds to the nominal capacity of the cell. For one This separator is excellent for use in a battery suitable.

Claims (28)

Process for producing a separator with low water content for an electrochemical cell, which comprises the following steps: (A) Providing a mixture that (a-1) a lithium compound with one when heated easily volatilizing Rest, (a-2) a release and / or dispersants and (a-3) optionally further Mixture components includes; (b) Preparation of a separator intermediate with the mixture, being on the surface of the separator intermediate the lithium compound is at least partially exposed; (C) Heating the separator intermediate to a temperature of 50 to 350 ° C for a predetermined Time to the rest of the lithium compound, optionally pyrolytic, at least partially from the surface of the separator intermediate to remove and create the separator with low water content. The method of claim 1, wherein step (b) the contacting of a porous an inorganic coating carrier with the mixture from step (a) that's a solution the lithium compound in a solvent is included to treat the inner and / or outer surface of the porous support with the mixture and to create the separator intermediate. The method of claim 2, wherein after a determination the free OH groups in the porous Carrier, in relation to to the number of these free OH groups 0.5 to 1.5 times, preferably 0.7 to 1.0 times stoichiometric Amount of lithium compound is used. The method of claim 1, wherein the mixture in step (a) is a dispersion that is used as additional mixture components (A-3.1) an oxide sol, (a-3.2) ceramic particles and (A-3.3) optionally fine particles, where step (b) includes the following steps: (b-1) provision of a flat, with a variety of openings provided, flexible substrate, (b-2) applying the dispersion in a thin Layer on and in the substrate, creating the separator intermediate becomes, and wherein in step (c) by heating the Separator intermediate at 50 to 350 ° C a separator with a porous one inorganic coating carrier is created. The method of claim 4, wherein the substrate is made of a fleece made of non-woven, non-electrically conductive polymer fibers consists. A method according to claim 4 or 5, wherein the fine Particles have an average primary particle size in the range from 1 to 200 nm, preferably 2 to 100 nm, very particularly preferred 3 to 50 nm. Method according to one of claims 4 to 6, wherein the fine Particles a fumed oxide of the elements silicon, zirconium and / or Aluminum included. Method according to one of claims 4 to 7, wherein the dispersion as ceramic particles 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, having Method according to 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 Links. Method according to one of the preceding claims, wherein the release or dispersant in step (a) is aqueous or non-aqueous. Method according to one of the preceding claims, wherein the carrier a flexible fleece with one on and in this fleece porous is inorganic coating, and wherein the material of the nonwoven is selected made of non-woven, non-electrically conductive polymer fibers. Method according to one of the preceding claims, wherein the fleece has a thickness of at most 30 μm. Method according to one of the preceding claims, wherein the polymer fibers selected are made of fibers of polyacrylonitrile, polyester, polyamide and / or Polyolefin. Method according to one of the preceding claims, wherein the flexible nonwoven has a basis weight of less than 20 g / m ² . Method according to one of the preceding claims, wherein the flexible fleece has a porosity of more than 50%. Method according to one of the preceding claims, wherein the fleece has a thickness of 5 to 30 μm. Method according to 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 up to 10 μm, preferably 0.5 to 5 μm, having. Method according to one of the preceding claims, wherein the porous inorganic coating on and in the fleece Alumina particles with an average particle size of 0.5 up to 5 μm has, which are glued with an oxide of the elements Zr or Si. Method according to one of the preceding claims, wherein the carrier a porosity from 30 to 90%. Method according to one of the preceding claims, wherein the separator has a tear resistance of more than 1 N / cm. Method according to one of the preceding claims, wherein the separator without damage to a radius down to 100 mm, preferably up to 1 mm, is bendable. Method according to one of the preceding claims, wherein the thickness of the separator at most Is 35 μm. Method according to 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 on, pressing on, pressing in, rolling on, knife coating, Spreading, dipping, spraying or pouring the mixture or the dispersion he follows. Separator for an electrochemical cell that is available by a process of claims 1 to 23. Separator according to claim 24, characterized in that on inner and / or outer surfaces via a oxygen bridge on atoms of a group 3A, 4A, 3B or 4B element of the periodic table of the elements, preferably selected from one of the elements Silicon, aluminum and zirconium, bound lithium atoms are present. A separator according to claim 24 or 25, which has a water content less than 1000 ppm, preferably less than 500 ppm, whole particularly preferably has less than 200 ppm. 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 includes. Use of a separator according to one of claims 24 to 26 for producing an electrochemical cell, in particular a lithium battery, lithium ion battery or a lithium polymer battery rie, each preferred for high-current or high-performance applications.