WO2015074913A1

WO2015074913A1 - Cross-linked polymeric materials based on polyimides, production and use thereof

Info

Publication number: WO2015074913A1
Application number: PCT/EP2014/074242
Authority: WO
Inventors: Oliver Gronwald; Benedikt CRONE; Ingrid Haupt; Raimund Pietruschka; Anna MÜLLER-CRISTADORO
Original assignee: Basf Se
Priority date: 2013-11-21
Filing date: 2014-11-11
Publication date: 2015-05-28

Abstract

The present invention relates to a cross-linked polymeric material obtainable by reaction of (aa) a polymeric material obtainable by reaction of (a) at least one polyimide selected from condensation products of (a1) at least one polyisocyanate having on average at least two isocyanate groups per molecule and, (a2) at least one polycarboxylic acid having at least 3 COOH groups per molecule or anhydride thereof, with (b)at least one organic amine comprising at least one primary or secondary amino group, or a mixture of at least one organic amine comprising at least one primary or secondary amino group and at least one diol or triol,with (bb) at least one polyisocyanate having on average at least two isocyanate groups per molecule. In addition, the present invention relates to the production of a cross-linked polymeric material according to the invention. Furthermore, the present invention is directed towards a separator (D) comprising at least one cross-linked polymeric material according to the invention and towards an electrochemical cell comprising such a separator.

Description

CROSS-LINKED POLYMERIC MATERIALS BASED ON POLYIMIDES, PRODUCTION

AND USE THEREOF

Description The present invention relates to a cross-linked polymeric material obtainable by reaction of (aa) a polymeric material obtainable by reaction of

(a) at least one polyimide selected from condensation products of

(a1 ) at least one polyisocyanate having on average at least two isocyanate groups per molecule and,

(a2) at least one polycarboxylic acid having at least 3 COOH groups per molecule or anhydride thereof, with

(b) at least one organic amine comprising at least one primary or secondary amino

group, or a mixture of at least one organic amine comprising at least one primary or secondary amino group and at least one diol or triol, with

(bb) at least one polyisocyanate having on average at least two isocyanate groups per molecule.

In addition, the present invention relates to the production of a cross-linked polymeric material according to the invention. Furthermore, the present invention is directed towards a separator (D) comprising at least one cross-linked polymeric material according to the invention and towards an electrochemical cell comprising such a separator.

Batteries and electrochemical cells with non-aqueous electrolytes are currently of great interest. Many components are of significance, such as the electrodes and the electrolyte. However, par- ticular attention will be paid to the separator which physically separates the anode and the cathode, thereby preventing short circuits.

On one hand, the separator should allow lithium ions to pass. On the other hand, a separator should have the necessary mechanical properties to effectively separate anode and cathode from each other.

WO 2012/156903 describes an electrochemical cell comprising a separator that is manufactured from branched polyimides. The polymers known from the literature, which are suitable for the production of separators for lithium ion batteries, still have deficiencies in respect of one or more of the properties desired for such polymers, for example stability against the electrolyte solutions, good wettability with electrolytes, good ion conductivity, low thermal shrinkage, good mechanical properties and the potential to prepare thin layers of such polymers.

It was therefore an objective of the invention to provide polymeric materials for a separator of an electrochemical cell that has advantages in respect of one or more properties of a known poly- meric material for a separator of an electrochemical cell, in particular a material which displays improved ion conductivity, improved wettability with electrolytes or improved thermal stability like lower thermal shrinkage. Furthermore, it was an objective to provide batteries comprising a separator produced from a polymeric material, wherein the batteries do not suffer from short circuits after longer operation.

This object is achieved by a cross-linked polymeric material obtainable by reaction of

(aa) a polymeric material obtainable by reaction of

(a) at least one polyimide selected from condensation products of at least one polyisocyanate having on average at least two isocyanate groups per molecule and, at least one polycarboxylic acid having at least 3 COOH groups per molecule or anhydride thereof, with at least one organic amine comprising at least one primary or secondary amino group, or a mixture of at least one organic amine comprising at least one primary or secondary amino group and at least one diol or triol, with

(bb) at least one polyisocyanate having on average at least two isocyanate groups per molecule. The cross-linked polymeric material, which is obtainable by reacting a polymeric material, briefly referred to as polymeric material (aa), with at least one polyisocyanate, briefly referred to as polyisocyanate (bb), which has on average at least two isocyanate groups per molecule. The inventive cross-linked polymeric material is usually an insoluble material. In the context of the present invention the term cross-linked polymeric material means a polymer network wherein each of the initial macromolecules is connected chemically to more than two others.

Cross-linking between polymeric material (aa) and polyisocyanate (bb) takes place when at least one of the reactants comprises more than two, preferably at least three reactive functional groups per molecule. That means that either the polymeric material (aa) comprises more than two NH moieties or hydroxyl groups derived from alcohols, which are each able to react with an isocyanate group, or the polyisocyanate (bb) comprises more than two isocyanate groups per molecule. Polymeric material (aa), which is obtainable by reacting at least one polyimide, briefly referred to as polyimide (a), with at least one organic amine comprising at least one primary or secondary amino group, briefly referred to as organic amine (b), or a mixture of at least one organic amine (b) comprising at least one primary or secondary amino group and at least one diol or triol, is preferably a soluble polymer, which can be processed by solvent cast technology in order to form thin films during the production of separators, which are themselves insoluble in solvents, which are used in electrolytes of electrochemical cells.

Polyimide (a) is a condensation product of at least one polyisocyanate having on average at least two isocyanate groups per molecule, briefly referred to as polyisocyanate (a1 ), with at least one polycarboxylic acid having at least 3 COOH groups per molecule or anhydride thereof, briefly referred to as polycarboxylic acid (a2). Polyimide can be linear or branched and is usually soluble in polar solvents, in particular polar aprotic solvents such as amides like dimethyla- cetamide, dimethylformamide or N-methyl pyrrolidone, ethers like tetraglyme, diglyme, 1 ,2- dimethoxyethane, 1 ,3-dioxolane or THF, or carbonates like dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate ethylene carbonate, propylene carbonate or vinylene carbonate.

Polyimide (a) can have a molecular weight M_w in the range from 500 to 200,000 g/mol, preferably at least 1000 g/mol, in particular in the range from 2,000 to 20,000 g/mol.

In one embodiment of the present invention the cross-linked polymeric material is characterized in that the polyimide (a) is selected from those polyimides that have a molecular weight M_w of at least 1000 g/mol. Polyimide (a) can have at least two imide groups per molecule, preferably at least 3 imide groups per molecule.

In one embodiment of the present invention, polyimide (a) can have up to 1 ,000 imide groups per molecule, preferably up to 660 per molecule.

In one embodiment of the present invention, stating the isocyanate groups or the COOH groups per molecule in each case denotes the mean value (number-average).

Polyimide (a) can be composed of structurally and molecularly uniform molecules. However, preference is given to polyimide (a) being a mixture of molecularly and structurally differing molecules, for example, visible from the polydispersity M_w/M_n of at least 1.4, preferably M_w/M_n of 1.4 to 50, preferably 1.5 to 10. The polydispersity can be determined by known methods, in particular by gel permeation chromatography (GPC). A suitable standard is, for example, poly(methyl methacrylate) (PMMA).

In one embodiment of the present invention the cross-linked polymeric material is characterized in that the polyimide (a) has a polydispersity M_w/M_n of at least 1 .4. In one embodiment of the present invention, polyimide (a), in addition to imide groups which form the polymer backbone, comprises, terminally or in side chains, in addition at least three, preferably at least six, more preferably at least ten, terminal or side-chain functional groups. Functional groups in polyimide (a) are preferably anhydride or acid groups and/or free or capped NCO groups. Polyimide (a) preferably does not have more than 500 terminal or side- chain functional groups, preferably no more than 100.

AlkyI groups such as, for example, methyl groups are therefore not a branching of a molecule of polyimide (a).

Polyisocyanate (a1 ) can be selected from any polyisocyanates that have on average at least two isocyanate groups per molecule which can be present capped, or preferably free. Preferred polyisocyanates (a1 ) are diisocyanates, for example hexamethylene diisocyanate, tetrameth- ylene diisocyanate, isophorone diisocyanate, toluylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, and mixtures of at least two of the abovementioned polyisocyanates (a1 ). Preferred mixtures are mixtures of 4,4'-diphenylmethane diisocyanate and 2,4'-diphenylmethane diisocyanate and mixtures of 2,4-toluylene diisocyanate and 2,6- toluylene diisocyanate. In one embodiment of the present invention the cross-linked polymeric material is characterized in that polyisocyanate (a1 ) is selected from hexamethylene diisocyanate, tetramethylene diisocyanate, isophorone diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, toluylene diisocyanate and mixtures of at least two of the abovementioned polyisocyanates (a1 ).

In another embodiment of the present invention, polyisocyanate (1 a) is selected from oligomeric hexamethylene diisocyanate, oligomeric tetramethylene diisocyanate, oligomeric isophorone diisocyanate, oligomeric diphenylmethane diisocyanate, trimeric toluylene diisocyanate and mixtures of at least two of the abovementioned polyisocyanates (a1 ). For example, what is termed trimeric hexamethylene diisocyanate is in many cases not the pure trimeric diisocyanate, but the polyisocyanate having a mean functionality of 3.6 to 4 NCO groups per molecule. The same applies to oligomeric tetramethylene diisocyanate and oligomeric isophorone diisocyanate.

In one embodiment of the present invention the cross-linked polymeric material is characterized in that polyisocyanate (a1 ) is selected from oligomeric hexamethylene diisocyanate, oligomeric tetramethylene diisocyanate, oligomeric isophorone diisocyanate, oligomeric diphenylmethane diisocyanate, trimeric toluylene diisocyanate and mixtures of at least two of the abovementioned polyisocyanates (a1 ). In one embodiment of the present invention, polyisocyanate (a1 ) is a mixture of at least one diisocyanate and at least one triisocyanate or a polyisocyanate having at least 4 isocyanate groups per molecule. In one embodiment of the present invention, polyisocyanate (a1 ) has on average exactly 2.0 isocyanate groups per molecule. In another embodiment of the present invention, polyisocyanate (a1 ) has on average at least 2.2, preferably at least 2.5, particularly preferably at least 3.0, isocyanate groups per molecule.

In one embodiment of the present invention, polyisocyanate (a1 ) has on average up to 8, preferably up to 6, isocyanate groups per molecule.

In one embodiment of the present invention, polyisocyanate (a1 ) is selected from oligomeric hexamethylene diisocyanate, oligomeric isophorone diisocyanate, oligomeric diphenylmethane diisocyanate and mixtures of the abovementioned polyisocyanates.

Polyisocyanate (a1 ), in addition to urethane groups, can also have one or more other functional groups, for example urea, allophanate, biuret, carbodiimide, amide, ester, ether, uretonimine, uretdione, isocyanurate or oxazolidine groups.

As polycarboxylic acids (a2), aliphatic or preferably aromatic polycarboxylic acids are selected that have at least three COOH groups per molecule, or the respective anhydrides, preferably when they are in the low-molecular weight form, that is to say the non-polymer form. Those pol- ycarboxylic acids having 3 COOH groups in which two carboxylic acid groups are present as anhydride and the third as free carboxylic acid are also included.

In a preferred embodiment of the present invention, as polycarboxylic acid (a2), a polycarboxylic acid having at least 4 COOH groups per molecule is selected, or the respective anhydride.

In one embodiment of the present invention the cross-linked polymeric material is characterized in that as polycarboxylic acid (a2), a polycarboxylic acid having at least 4 COOH groups per molecule, or the respective anhydride, is selected. Examples of polycarboxylic acids (a2) and anhydrides thereof are 1 ,2,3-benzenetricarboxylic acid and 1 ,2,3-benzenetricarboxylic anhydride, 1 ,3,5-benzenetricarboxylic acid (trimesic acid), preferably 1 ,2,4-benzenetricarboxylic acid (trimellitic acid), trimellitic anhydride and, in particular, 1 ,2,4,5-benzenetetracarboxylic acid (pyromellitic acid) and 1 ,2,4,5-benzenetetracarboxylic di- anhydride (pyromellitic dianhydride), 3,3',4,4'-benzophenonetetracarboxylic acid, 3, 3', 4,4'- benzophenonetetracarboxylic dianhydride, in addition benzenehexacarboxylic acid (mellitic acid) and anhydrides of mellitic acid.

Other suitable polycarboxylic acids and anhydrides thereof are mellophanic acid and mello- phanic anhydride, 1 ,2,3,4-benzenetetracarboxylic acid and 1 ,2,3,4-benzenetetracarboxylic di- anhydride, 3,3,4,4-biphenyltetracarboxylic acid and 3,3,4,4-biphenyltetracarboxylic dianhydride, 2,2,3,3-biphenyltetracarboxylic acid and 2,2,3,3-biphenyltetracarboxylic dianhydride, 1 ,4,5,8- naphthalenetetracarboxylic acid and 1 ,4,5,8-naphthalenetetracarboxylic dianhydride, 1 ,2,4,5- naphthalenetetracarboxylic acid and 1 ,2,4,5-naphthalenetetracarboxylic dianhydride, 2,3,6,7- naphthalenetetracarboxylic acid and 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1 ,4,5,8- decahydronaphthalenetetracarboxylic acid and 1 ,4,5,8-decahydronaphthalenetetracarboxylic dianhydride, 4,8-dimethyl-1 ,2,3,5,6,7-hexahydronaphthalene-1 ,2,5,6-tetracarboxylic acid and 4,8-dimethyl-1 ,2,3,5,6,7-hexahydronaphthalene-1 ,2,5,6-tetracarboxylic dianhydride, 2,6- dichloronaphthalene-1 ,4,5,8-tetracarboxylic acid and 2,6-dichloronaphthalene-1 ,4,5,8- tetracarboxylic dianhydride, 2,7-dichloronaphthalene-1 ,4,5,8-tetracarboxylic acid and 2,7- dichloronaphthalene-1 ,4,5,8-tetracarboxylic dianhydride, 2,3,6,7-tetrachloronaphthalene- 1 ,4,5,8-tetracarboxylic acid and 2, 3, 6, 7-tetrachloronaphthalene-1 ,4,5,8-tetracarboxylic dianhy- dride, 1 ,3,9,10-phenanthrenetetracarboxylic acid and 1 ,3,9,10-phenanthrenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic acid and 3,4,9,10-perylenetetracarboxylic dianhydride, bis(2,3-dicarboxyphenyl)methane and bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane and bis(3,4-dicarboxyphenyl)methane dianhydride, 1 ,1 - bis(2,3-dicarboxyphenyl)ethane and 1 ,1 -bis(2,3-dicarboxyphenyl)ethane dianhydride, 1 ,1 - bis(3,4-dicarboxyphenyl)ethane and 1 ,1 -bis(3,4-dicarboxyphenyl)ethane dianhydride, 2,2- bis(2,3-dicarboxyphenyl)propane and 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, 2,3- bis(3,4-dicarboxyphenyl)propane and 2,3-bis(3,4-dicarboxyphenyl)propane dianhydride, bis(3,4- carboxyphenyl)sulfone and bis(3,4-carboxyphenyl)sulfone dianhydride, bis(3,4-carboxyphenyl) ether and bis(3,4-carboxyphenyl) ether dianhydride, ethylenetetracarboxylic acid and ethylene- tetracarboxylic dianhydride, 1 ,2,3,4-butanetetracarboxylic acid and 1 ,2,3,4- butanetetracarboxylic dianhydride, 1 ,2,3,4-cyclopentanetetracarboxylic acid and 1 ,2,3,4- cyclopentanetetracarboxylic dianhydride, 2,3,4,5-pyrrolidinetetracarboxylic acid and 2,3,4,5- pyrrolidinetetracarboxylic dianhydride, 2,3,5,6-pyrazinetetracarboxylic acid and 2,3,5,6- pyrazinetetracarboxylic dianhydride, 2,3,4,5-thiophenetetracarboxylic acid and 2,3,4,5- thiophenetetracarboxylic dianhydride.

In one embodiment of the present invention, anhydrides from US 2,155,687 or US 3,277,1 17 are used for the synthesis of polyimide (A). If polyisocyanate (a1 ) and polycarboxylic acid (a2) are condensed with one another - preferably in the presence of a catalyst - then an imide group is formed with elimination of CO2 and H2O. If, instead of polycarboxylic acid (a2), the corresponding anhydride is used, then an imide group is formed with elimination of CO2.

In this case R^* is the radical of polyisocyanate (a1 ) not specified further in the above reaction equation, and n is a number greater than or equal to 1 , for example 1 in the case of a tricarbox- ylic acid or 2 in the case of a tetracarboxylic acid, wherein (HOOC)_n can be replaced by an anhydride group of the formula C(=0)-0-C(=0).

In one embodiment of the present invention, polyisocyanate (a1 ) is used in a mixture with at least one diisocyanate, for example with toluylene diisocyanate, hexamethylene diisocyanate or with isophorone diisocyanate. In a particular variant, polyisocyanate (a1 ) is used in a mixture with the corresponding diisocyanate, for example trimeric HDI with hexamethylene diisocyanate, or trimeric isophorone diisocyanate with isophorone diisocyanate, or polymeric diphenylme- thane diisocyanate (polymer MDI) with diphenylmethane diisocyanate. In one embodiment of the present invention, polycarboxylic acid (a2) is used in a mixture with at least one dicarboxylic acid or with at least one dicarboxylic anhydride, for example with phthalic acid or phthalic anhydride.

In order to obtain polyimide (a) polyisocyanate (a1 ) and polycarboxylic acid (a2) or anhydride (a2) can be reacted in broad ratios. Preference is given to polyimides (a) wherein polyisocyanate (a1 ) and polycarboxylic acid (a2) or anhydride (a2) are used in a quantitative ratio such that the molar fraction of NCO groups to COOH groups is in the range from 1 : 3 to 3 : 1 , preferably 1 : 2 to 2 : 1 . In this case, one anhydride group of the formula CO-O-CO counts as two COOH groups.

In one embodiment of the present invention the cross-linked polymeric material is characterized in that polyisocyanate (a1 ) and polycarboxylic acid (a2) or anhydride (a2) are used in a quantitative ratio such that the molar fraction of NCO groups to COOH groups is in the range from 1 :2 to 2:1 , wherein one anhydride group of the formula CO-O-CO counts as two COOH groups. Organic amine (b) comprises at least one primary or secondary amino group. Preferably organic amine (b) is selected from amines comprising one, two or three, preferably one or two, in particular one, primary or secondary, in particular primary amino groups, wherein the molecular weight of the amines is in the range from 31 to 10000 g/mol, preferably in the range from 100 to 5000 g/mol.

Examples of organic monoamines are methylamine, octadecylamine, Jeffamine^® M 2070 (formula PEA a, Mw approximately 2000 g/mol, PO/EO mol ratio of 10/31 ), taurine, dibutylamine or di-n-tridecylamine. Examples of organic diamines are Jeffamin^® D 230 (formula PEA b, M_w ap- proximately 230 g/mol, x ~ 2.5), Jeffamin^® ED 600 (formula PEA c, M_w approximately 600 g/mol, PO/EO mol ratio of 1 .2/2.0), hexamethylenediamine, isophorone diamine, piperazine or N,N'-dimethylhexane-1 ,6-diamine. Examples of organic triamines are Jeffamin^® T-403 (formula PEA e, Mw approximately 440 g/mol, R = Ethyl, n = 1 , x+y+z = 5 to 6) , Jeffamin^® T-5000 (formula PEA e, Mw approximately 5000 g/mol, R = H, n = 0, x+y+z ~ 85) or N',N'-bis(2-aminoethyl)- ethane-1 ,2-diamine.

In one embodiment of the present invention the cross-linked polymeric material is characterized in that organic amine (b) is selected from amines comprising one, two or three, primary or secondary amino groups, wherein the molecular weight of the amines is in the range from 31 to 10000 g/mol.

As preferred organic amines (b), which comprise at least one primary or secondary amino group, may be mentioned aliphatic amines with a C& to C50, preferably C10 to C30, in particular CM to Ci8-alkyl group, polyetheramines containing one, two or three, preferably one or two pri- mary amino groups attached to the ends of a polyether backbone, wherein the polyether backbone is usually based on either propylene oxide (PO), ethylene oxide (EO) or mixed PO/EO, and organic acids comprising at least one primary or secondary, preferably primary amino group, like taurin. In one embodiment of the present invention the cross-linked polymeric material is characterized in that organic amine (b) is selected from polyetheramines, aliphatic amines with a with C10 to C3o-alkyl group and organic acids comprising at least one primary or secondary, in particular primary amino group. Preferred aliphatic amines are: methylamine, octadecylamine, dibutylamine, di-n-tridecylamine, hexamehylenediamine, isophorone diamine, piperazine, N,N'-dimethylhexane-1 ,6-diamine or N',N'-bis(2-aminoethyl)ethane-1 ,2-diamine, in particular octadecylamin.

A broad variety of different structural types of polyetheramines are commercially available, e.g. as JEFFAMINE^® from Huntsman. Preferred polyetheramines are monoamines of general formula PEA a, diamines of general formulae PEA b, PEA c and PEA d, and triamines of general formula PEA e., in particular monoamines of general formula PEA a.

40 PEAe Preferred organic acid comprising at least one primary group are 2-aminoethanesulfonic acid (taurine) or 2-aminopropanesulfonic acid (homotaurin), in particular taurine.

Diol or triol, which can be used in a mixture together with the organic amine (b), can be low- molecular-weight or high-molecular-weight. Examples of triols are glycerol and 1 ,1 ,1 - (trihydroxymethylene)methane, 1 ,1 ,1 -(trihydroxymethylene)ethane and 1 ,1 ,1 - (trihydroxymethylene)propane.

Diols are preferred.

As low-molecular-weight diols in the context of the present invention, those having a molecular weight up to 500 g/mol which may be mentioned by way of example are: 1 ,2-ethanediol, 1 ,2- propanediol, 1 ,3-propanediol, 1 ,2-butanediol, 1 ,3-butanediol, 1 ,4-butanediol, 1 ,4-but-2-enediol, 1 ,4-but-2-ynediol, 1 ,5-pentanediol and positional isomers thereof, 1 ,6-hexanediol, 1 ,8- octanediol, 1 ,4-bishydroxymethylcyclohexane, 2,2-bis-(4-hydroxycyclohexyl)propane, 2-methyl- 1 ,3-propanediol, diethylene glycol, triethylene glycol, tetraethylene glycol and, in particular, 2,2- dimethylpropane-1 ,3-diol (neopentyl glycol).

As polymeric diols, dihydric or polyhydric polyester polyols and polyether polyols may be men- tioned, with the dihydric being preferred. As polyether polyols, preferably polyether diols come into consideration as are obtainable, for example, by boron trifluoride-catalyzed linking of ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, styrene oxide or epichlorohydrin with itself or among one another or by addition of these compounds, individually or in a mixture, to starter components having reactive hydrogen atoms such as water, polyhydric alcohols, or amines such as 1 ,2-ethanediol, propane-(1 ,3)-diol, 1 ,2- or 2,2-bis-(4-hydroxyphenyl)propane or aniline. In addition, polyether-1 ,3-diols, for example trimethylol propane alkoxylated at an OH group, the alkylene oxide chain of which is closed with an alkyl radical comprising 1 to 18 carbon atoms, are preferably used polymeric diols. Preferred polymeric diols are: polyethylene glycol, polypropylene glycol and, in particular, poly- tetrahydrofuran (poly-THF).

Particularly preferably, polyether polyols are selected from: polyethylene glycol having an average molecular weight (M_n) in the range from 200 to 9000 g/mol, preferably in the range from 500 to 6000 g/mol, poly-1 ,2-propylene glycol or poly-1 ,3-propane diol having an average molecular weight (M_n) in the range from 250 to 6000, preferably 600 to 4000 g/mol, poly-THF having an average molecular weight (M_n) in the range from above 250 to 5000, preferably from 500 to 3000 g/mol, particularly preferably in the range from 750 to 2500 g/mol.

Other preferred polymeric diols are polyester polyols (polyester diols) and polycarbonate diols. As polycarbonate diols, in particular aliphatic polycarbonate diols may be mentioned, for example 1 ,4-butanediol polycarbonate and 1 ,6-hexanediol polycarbonate.

As polyester diols, those which may be mentioned are those which may be produced by poly- condensation of at least one primary diol, preferably at least one primary aliphatic diol, for example ethylene glycol, 1 ,4-butanediol, 1 ,6-hexanediol, neopentyl glycol or, particularly preferably, 1 ,4-dihydroxymethylcyclohexane (as mixture of isomers) or mixtures of at least two of the abovementioned diols on the one hand and at least one, preferably at least two, dicarboxylic acids or anhydrides thereof on the other. Preferred dicarboxylic acids are aliphatic dicarboxylic acids such as adipic acid, glutaric acid, succinic acid and aromatic dicarboxylic acids such as, for example, phthalic acid and, in particular, isophthalic acid.

In one embodiment of the present invention, polyester diols and polycarbonate diols are selected from those having an average molecular weight (M_n) in the range from 500 to 9000 g/mol, preferably in the range from 500 to 6000 g/mol.

Very particularly preferred diols are polytetrahydrofurans, for example having an average molecular weight M_n in the range from 250 to 2000 g/mol. In the mixture of at least one organic amine comprising at least one primary or secondary amino group and at least one diol or triol the molar ratio of the sum of all amino groups to the sum of all hydroxyl groups of the diol or triol can be varied in a wide range. Preferably the molar ratio of the sum of all amino groups to the sum of all hydroxyl groups of the diols and triols is in the range from 0.001 to 1000, more preferably in the range from 0,01 to 100, in particular 0,1 -10.

In one embodiment of the present invention, polyimide (a) and organic amine (b) or the mixture of organic amine (b) and at least one diol or triol are used in quantitative ratios such that the molar ratio of the sum of all amino groups and all hydroxyl groups to the sum of NCO groups and COOH groups of polyimide (a) is 1 :10 to 10:1 , preferably 1 :5 to 5:1 , particularly preferably 1 :3 to 3:1 .

In one embodiment of the present invention, polymeric material (aa), which is the reaction product from polyimide (a) and a mixture of at least one organic amine (b) and at least one diol or triol, has a hydroxyl number in the range from zero to 300 mg of KOH/g, determined as speci- fied in DIN 53240-2, preferably zero to 200 mg of KOH/g.

In one embodiment of the present invention, polymeric material (aa), which is the reaction product from polyimide (a) and at least one organic amine (b), has an acid value in the range from zero to 300 mg of KOH/g, determined as specified in DIN 53402, preferably zero to 200 mg of KOH/g. In one embodiment of the present invention the cross-linked polymeric material is characterized in that the polymeric material (aa) has an acid value in the range from 0 to 200 mg of KOH/g

In one embodiment of the present invention, polymeric material (aa), which is the reaction prod- uct from polyimide (a) and at least one organic amine (b), has a quotient M_w/M_n in the range from 1 .2 to 10, preferably 1 .5 to 5, particularly preferably 1 .8 to 4. In this case, M_w and M_n are preferably determined by gel-permeation chromatography.

The molecular weight M_w of polymeric material (aa) can be varied in a wide range depending on the molecular weight of polyimide (a) and the molecular weight of the organic amine (b). Preferably of polymeric material (aa) has a molecular weight M_w in the range from 500 to 200,000 g/mol, preferably at least 1000 g/mol, in particular in the range from 2,000 to 30,000 g/mol.

In one embodiment of the present invention the cross-linked polymeric material is characterized in that the polymeric material (aa) has a molecular weight M_w of at least 1000 g/mol.

Polyisocyanate (bb) can be selected from any polyisocyanates that have on average at least two isocyanate groups per molecule which can be present capped, or preferably free. Preferred polyisocyanates (bb) are diisocyanates, for example hexamethylene diisocyanate, isophorone diisocyanate, toluylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, and mixtures of at least two of the abovementioned polyisocyanates (a). Preferred mixtures are mixtures of 4,4'-diphenylmethane diisocyanate and 2,4'-diphenylmethane diisocyanate and mixtures of 2,4-toluylene diisocyanate and 2,6-toluylene diisocyanate. In another embodiment of the present invention, polyisocyanate (bb) is selected from oligomeric hexamethylene diisocyanate, oligomeric tetramethylene diisocyanate, oligomeric isophorone diisocyanate, oligomeric diphenylmethane diisocyanate, trimeric toluylene diisocyanate and mixtures of at least two of the abovementioned polyisocyanates (bb). For example, what is termed trimeric hexamethylene diisocyanate is in many cases not the pure trimeric diisocyanate, but the polyisocyanate having a mean functionality of 3.6 to 4 NCO groups per molecule. The same applies to oligomeric tetramethylene diisocyanate and oligomeric isophorone diisocyanate.

In one embodiment of the present invention, polyisocyanate (bb) is a mixture of at least one diisocyanate and at least one triisocyanate or a polyisocyanate having at least 4 isocyanate groups per molecule.

In one embodiment of the present invention, polyisocyanate (bb) has on average exactly 2.0 isocyanate groups per molecule.

In one embodiment of the present invention, polyisocyanate (bb has on average up to 8, preferably up to 6, isocyanate groups per molecule. In another embodiment of the present invention, polyisocyanate (bb) has on average at least 2.2, preferably at least 2.5, particularly preferably at least 3.0, isocyanate groups per molecule.

In one embodiment of the present invention, polyisocyanate (bb) is selected from oligomeric hexamethylene diisocyanate, oligomeric isophorone diisocyanate, oligomeric diphenylmethane diisocyanate and mixtures of the abovementioned polyisocyanates.

Polyisocyanate (bb), in addition to urethane groups, can also have one or more other functional groups, for example urea, allophanate, biuret, carbodiimide, amide, ester, ether, uretonimine, uretdione, isocyanurate or oxazolidine groups.

In one embodiment of the present invention, polyisocyanate (a1 ) and polyisocyanate (bb) of an inventive cross-linked polymeric material are equal. In an alternative embodiment, polyisocyanate (a1 ) and polyisocyanate (bb) of an inventive cross-linked polymeric material are different.

In one embodiment of the present invention the cross-linked polymeric material is characterized in that a) polyisocyanate (a1 ) is selected from hexamethylene diisocyanate, tetramethylene diisocyanate, isophorone diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'- diphenylmethane diisocyanate, toluylene diisocyanate and mixtures of at least two of the abovementioned polyisocyanates (a1 ), b) as polycarboxylic acid (a2), a polycarboxylic acid having at least 4, in particular exactly 4 COOH groups per molecule, or the respective anhydride, is selected, c) polyisocyanate (a1 ) and polycarboxylic acid (a2) or anhydride (a2) are used in a quantitative ratio such that the molar fraction of NCO groups to COOH groups is in the range from 1 :2 to 2:1 , wherein one anhydride group of the formula CO-O-CO counts as two COOH groups, and d) the organic amine (b) is selected from polyetheramines, in particular polyether- monoamines (formula PEA a), aliphatic amines with a Cio to C3o-alkyl group and organic acids comprising at least one primary or secondary, in particular a primary amino group. In one embodiment organic amine (b) is a mixture of a polyetheramine and taurine or a mixture of a poly- etheramine and an aliphatic amine like octadecylamine.

The present invention further also provides a method for producing a cross-linked polymeric material as described above, comprising the reaction steps of

(a) preparation of polyimide (a) by condensation of at least one polyisocyanate (a1 ) having on average at least two isocyanate groups per molecule with at least one polycarboxylic acid

(a2) having at least 3 COOH groups per molecule or anhydride (a2) thereof,

(β) preparation of polymeric material (aa) by reacting polyimide (a), which was prepared in reaction step (a), with at least one organic amine (b), which comprises at least one prima- ry or secondary amino group, or a mixture of at least one organic amine comprising at least one primary or secondary amino group and at least one diol or triol, (γ) cross-linking the polymeric material (aa), which was prepared in reaction step (β), by mixing it with at least one polyisocyanate (bb), which has on average at least two isocyanate groups per molecule. In this method for producing the inventive cross-linked polymeric material, also called production method according to the invention for short, polyisocyanate (a1 ), polycarboxylic acid (a2), polyimide (a), organic amine (b), diol, triol, polymeric material (aa) and polyisocyanate (bb) are each as defined above, especially also with regard to preferred embodiments thereof. The production method according to the invention is a three-step method. The product of reaction step (a), the polyimide (a), can be either isolated or it can be used directly without isolation in the following reaction step (β) in order to prepare polymeric material (aa). For the preparation of the inventive cross-linked polymeric material in reaction step (γ) the polymeric material (aa) can be either isolated or it can be used without isolation.

In one embodiment of the present invention reaction steps (a) and (β) are carried out as a one- pot method and the purification and isolation of polyimide (a) are omitted, but the polymeric material (aa) is isolated before it is reacted with polyisocyanate (bb) in reaction step (γ). The preparation of polyimide (a) according to reaction step (a) is in principle described in WO 2012/156903, page 15, line 15 to page 16, line 24. The condensation of at least one polyisocyanate (a1 ) having on average at least two isocyanate groups per molecule with at least one polycarboxylic acid (a2) in the form of its anhydride is preferably done without addition of a catalyst, wherein water is not considered as a catalyst.

In reaction step (a) polyisocyanate (a1 ) and polycarboxylic acid (a2) or anhydride (a2) can be used in a quantitative ratio such that the molar fraction of NCO groups to COOH groups is in the range from 1 : 3 to 3 : 1 , preferably 1 : 2 to 2 : 1. In this case, one anhydride group of the formula CO-O-CO counts as two COOH groups.

In an embodiment of the present invention, reaction step (a) for making polyimides (a) can be carried out at temperatures in the range from 25 to 200 °C, preferably 50 to 140 °C, particularly preferably 50 to 100 °C. In an embodiment of the present invention, reaction step (a) for making polyimides (a) can be carried out at atmospheric pressure. However, the synthesis is also possible under pressure, for example at pressures in the range from 1.1 to 10 bar.

In one embodiment of the present invention, reaction step (a) for making polyimides (a) can be carried out in the presence of a solvent or solvent mixture. Examples of suitable solvents are N- methylpyrrolidone, N-ethylpyrrolidone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dimethyl sulphones, xylene, phenol, cresol, cyclic ethers such as, for example, tetrahydrofu- rane or 1 ,4-dioxane, cyclic acetals such as 1 ,3-dioxolane or 1 ,3-dioxane, ketones such as, for example, acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), acetophenone, in addition mono- and dichlorobenzene, ethylene glycol monoethyl ether acetate and mixtures of two or more of the abovementioned mixtures. In this case, the solvent or solvents can be pre- sent during the entire synthesis time or only during part of the synthesis.

Reaction step (a) can be carried out, for example, for a time period of 10 minutes to 24 hours.

In a preferred embodiment of the present invention, reaction step (a) for making polyimides (a) is carried out under inert gas, for example under argon or under nitrogen.

The reaction conditions in reaction step (β) are similar to those of reaction step (a) with respect to solvents, temperature, pressure and reaction time. In one embodiment of the present invention polymeric material (aa) is isolated after finishing reaction step (β), in particular by removing used solvents.

The inventive cross-linked polymeric material is obtained in reaction step (γ) by reacting the polymeric material (aa), which was prepared in reaction step (β), preferably the isolated poly- meric material (aa), with at least one polyisocyanate (bb), which has been described above.

In one embodiment of the present invention, polyisocyanate (a1 ) and polyisocyanate (bb) of a specific cross-linked polymeric material are equal. In an alternative embodiment, polyisocyanate (a1 ) and polyisocyanate (bb) of a specific cross-linked polymeric material are different.

The reaction with polyisocyanate (bb) can be carried out without or with a solvent, such as NMP,THF, 1 ,3-dioxolane or 1 ,4-dioxane.

The reaction with polyisocyanate (bb) can be carried out without or with a catalyst, preferable it is carried out without.

The reaction with polyisocyanate (bb) can be carried out at a temperature in the range of from 10 to 90 °C, preferably 20 to 30 °C. In a preferred embodiment, the reaction with polyisocyanate (bb) is carried out at normal pressure.

Since the inventive cross-linked polymeric material is not soluble and the shape of the body of the formed cross-linked polymeric material can only be changed by mechanical means like cut- ting, milling or cold pressure welding, it is preferred to cast a mixture comprising polymeric material (aa) and polyisocyanate (bb) in a desired form, which is retained after the cross-linking reaction. In one embodiment of the present invention the inventive method for producing a cross-linked polymeric material is characterized in that a film of the cross-linked polymeric material is formed in reaction step (γ) by casting a thin film of a solution comprising polymeric material (aa) and polyisocyanate (bb).

The inventive cross-linked polymeric material can preferably be used for the production of thin films, like membranes for separation of matter, in particular for the preparation of separators for electrochemical cells. A further aspect of the present invention is a separator (D) comprising at least one cross-linked polymeric material as described above, which is obtainable by reaction of

(aa) a polymeric material obtainable by reaction of

(a) at least one polyimide selected from condensation products of

(b) at least one organic amine comprising at least one primary or secondary amino group, or a mixture of at least one organic amine comprising at least one primary or secondary amino group and at least one diol or triol, with

Cross-linked polymeric material, polyisocyanate (a1 ), polycarboxylic acid (a2), polyimide (a), organic amine (b), diol, triol, polymeric material (aa) and polyisocyanate (bb) are each as defined above, especially also with regard to preferred embodiments thereof.

Separator (D) can further comprise one or more inorganic particles (E). Inorganic particles can be selected, e. g., from oxides of Ti, Zr, Si or Al, non-stoichiometric or stoichiometric, preferred is Si0₂. In one embodiment of the present invention inventive separator (D) is characterized in that further comprising one or more inorganic particles (E).

The thickness of separator (D) can be varied in a wide range. Preferably separator (D) has a thickness in the range of from 1 μηη to 150 μηη, preferably 10 μηη to 35 μηη.

In one embodiment of the present invention inventive separator (D) is characterized in that having a thickness in the range of from 1 to 150 μηη. In one embodiment of the present invention, the specific ionic conductivity at room temperature of separator (D) in liquid electrolyte is in the range of from 10^-6 S/cm to 10^"3 S/cm, determined by impedance measurements of sandwich cells with separator/electrolyte combinations.

Separator (D) can in principle be prepared in the same way as films of the inventive cross-linked polymeric material as described above are prepared.

In one embodiment, one prepares a solution of at least one polymeric material (aa) as described above in a suitable solvent or mixture of solvents and then applies said solution to a flat surface, for example to a glass surface or to a metal foil, e. g., an aluminum foil, or to a plastics foil such as a polyethylene terephthalate film (PET foil). After partly or completely removing the solvent or solvents, the formed layer of polymeric material (aa) is treated with a solution of at least one polyisocyanate (bb) as described above in order to form the inventive separator comprising the inventive cross-linked polymeric material. Afterwards, the inventive separator can be dried and removed from the flat surface, for example mechanically. Alternatively a solution comprising at least one polymeric material (aa) and least one polyisocyanate (bb) is applied to a flat surface as described above before the cross-linked polymeric material is formed. Afterwards, the inventive separator can be dried and removed from the flat surface as described above. The cross-linking reaction between the amino groups of polymeric material (aa) and the isocyanate groups of polyisocyanate (bb) is preferably either thermally induced or it is catalyzed by tertiary amines like 1 ,4-Diazabicyclo[2.2.2]octane (DABCO) at a lower temperature.

Examples for suitable solvents are, e. g., cyclic or non-cyclic amides, ketones, acetals, and cyclic and non-cyclic ethers. Examples for cyclic amides are N-methylpyrrolidone (NMP) and N-ethylpyrrolidone (NEP). Examples for non-cyclic amides are Ν,Ν-dimethylformamide and Ν,Ν-dimethylacetamide. Examples for ketones are acetone, methylethylketone, methyl isobutyl ketone (MIBK), and cyclohex- anone. Examples for acetals are 1 ,2-dimethoxyethane and 1 ,3-dioxolane. Examples for ethers are di-n-butyl ether, tetrahydrofurane, 1 ,4-dioxolane and preferably anisole.

Solutions of at least one polyimide (a) can have a solids content in the range of from 5 to 50 % by weight, preferably 15 to 30 % by weight. Application of the solution to a flat surface can be performed by spraying, blade coating, spin coating, drop casting, or dip coating.

Removal of the solvent(s) can be achieved by evaporating the solvent(s) or allowing to evapo- rate, for example by heating, or via reduction of pressure, or via using a gas stream.

Removal of the separator from the flat surface can be achieved by mere mechanical means, or it can be supported by swelling. Inventive separators (D) are very well suitable for manufacturing inventive electrochemical cells. Another aspect of the present invention are thus electrochemical cells comprising at least one inventive separator (D).

An inventive electrochemical cell comprises

(A) at least one anode as component (A),

(B) at least one cathode as component (B), (C) at least one none-aqueous electrolyte as component (C), and (D) at least one separator (D) as described above.

Inventive cells can be selected from alkali metal containing cells. Preferably, inventive cells are selected from lithium-ion containing cells. In lithium-ion containing cells, the charge transport is effected by Li⁺ ions.

In the context with the present invention, the electrode where during discharging a net negative charge occurs is called the anode.

Anode (A) can be selected from anodes being based on various active materials. Suitable active materials are metallic lithium, carbon-containing materials such as graphite, graphene, charcoal, expanded graphite, furthermore lithium titanate (Li4Ti₅0i2), tin oxide (Sn02), and nanocrystalline silicon.

In a special embodiment of the present invention, anode (A) is selected from graphite anodes and lithium titanate anodes.

In one embodiment of the present invention the electrochemical cell is characterized in that anode (A) is selected from graphite anodes and lithium titanate anodes Anode (A) can further comprise a current collector. Suitable current collectors are, e.g., metal wires, metal grids, metal gaze and preferably metal foils such as copper foils.

Anode (A) can further comprise a binder. Suitable binders can be selected from organic (co)polymers. Suitable organic (co)polymers may be halogenated or halogen-free. Examples are polyethylene oxide (PEO), cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyethylene, polypropylene, polytetrafluoroethylene, polyacrylonitrile-methyl methacrylate, styrene- butadiene copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, vinylidene fluoride- hexafluoropropylene copolymers (PVdF-HFP), vinylidene fluoride-tetrafluoroethylene copoly- mers, perfluoroalkyl vinyl ether copolymers, ethylene-tetrafluoroethylene copolymers, vinylidene fluoride-chlorotrifluoroethylene copolymers, ethylene-chlorofluoroethylene copolymers, eth- ylene-acrylic acid copolymers, optionally at least partially neutralized with alkali metal salt or ammonia, ethylene-methacrylic acid copolymers, optionally at least partially neutralized with alkali metal salt or ammonia, ethylene-(meth)acrylic ester copolymers, polysulphones, polyi- mides and polyisobutene.

Suitable binders are especially polyvinyl alcohol and halogenated (co)polymers, for example polyvinyl chloride or polyvinylidene chloride, especially fluorinated (co)polymers such as polyvinyl fluoride and especially polyvinylidene fluoride and polytetrafluoroethylene.

The average molecular weight M_w of binder may be selected within wide limits, suitable examples being 20,000 g/mol to 1 ,000,000 g/mol.

In one embodiment of the present invention, anode (A) can have a thickness in the range of from 15 to 200 μηη, preferably from 30 to 100 μηη, determined without the current collector.

Inventive cells further comprise a cathode (B). Cathode (B) can be, e. g., air (or oxygen). In a preferred embodiment, however, cathode (B) contains a solid active material. Solid active materials for cathode (B) can be selected from phosphates with olivine structure such as lithium iron phosphates (LiFePC ) and lithium manganese phosphate (LiMnPC ) which can have a stoichiometric or non-stoichiometric composition and which can be doped or not doped. In one embodiment of the present invention, active material for cathode (B) can be selected from lithium containing transition metal spinels and lithium transition metal oxides with a layered crystal structure. In such cases, cathode (B) contains at least one material selected from lithium containing transition metal spinels and lithium transition metal oxides with a layered crystal structure, respectively. In one embodiment of the present invention the electrochemical cell is characterized in that cathode (B) contains at least one material selected from lithium containing transition metal spinels and lithium transition metal oxides with a layered crystal structure. In one embodiment of the present invention, lithium-containing metal spinels are selected from those of the general formula

the variables being defined as follows: 0.9 < a < 1 .3, preferably 0.95 < a < 1 .15, 0 < b < 0.6, for example 0.0 or 0.5, wherein, if M¹ = Ni, 0.4 < b < 0.55,

-0.1 < d < 0.4, preferably 0 < d < 0.1 , M¹ is selected from one or more out of Al, Mg, Ca, Na, B, Mo, W and transition metals of the first row of the transition metals in the periodic table of the elements. In a preferred embodiment, M¹ is selected from the group consisting of Ni, Co, Cr, Zn, and Al. Even more preferably, M¹ is defined to be Ni. In one embodiment of the present invention, lithium containing metal spinels are selected from LiNio,5Mni,₅04-d and LiM^C .

In one embodiment of the present invention, lithium transition metal oxides with a layered crystal structure are selected from compounds of general formula (II)

the variable being defined as follows: 0 < t≤0.3 und

M² selected from one or more elements from Al, Mg, B, Mo, W, Na, Ca and transition metals of the first row of the transition metals in the periodic table of the elements, at least one element being manganese.

In one embodiment of the present invention, at least 30 mole-% of M² are selected from manganese, preferably at least 35 mole-%, in each time with respect to the complete amount of M². In one embodiment of the present invention M² is selected from combinations of Ni, Co and Mn not containing significant amounts of additional elements.

In a different embodiment of the present invention M² is selected from combinations of Ni, Co and Mn containing significant amounts of at least one additional element, for example in the range of from 1 to 10 mole-% Al, Ca or Na.

In a particular embodiment of the present invention, lithium transition metal oxides with a lay- ered crystal structure are selected from compounds of general formula

Li₍i₊x)[NieCOfMn_gM³h](i-x)02 (I II) the variables being defined as follows: x a number in the range of from zero to 0.2, e a number in the range of from 0.2 to 0.6, f a number in the range of from 0.1 to 0.5, g a number in the range of from 0.2 to 0.6, h a number in the range of from zero to 0.1 , and: e + f + g + h = 1 , selected from Al, Mg, V, Fe, Cr, Zn, Cu, Ti and Mo. In one embodiment of the present invention, M² in formula (I I) is selected from Nio,33Coo,33Mno,33, Ni₀,5Coo,2Mn₀,3, Ni₀,4Coo,3Mn₀,4, Ni₀,4Coo,2Mn₀,4 und Ni₀,45Coo,ioMn₀,45.

Cathode (B) can further comprise a current collector. Suitable current collectors are, e.g., metal wires, metal grids, metal gaze and preferably metal foils such as aluminum foils.

Cathode (B) can further comprise a binder. Suitable binders can be selected from organic (co)polymers. Suitable organic (co)polymers may be halogenated or halogen-free. In general, the same binders used for anode (A) can also be employed for cathode (B). Preferred binders are especially polyvinyl alcohol and halogenated (co)polymers, for example polyvinyl chloride or polyvinylidene chloride, especially fluorinated (co)polymers such as polyvinyl fluoride and especially polyvinylidene fluoride and polytetrafluoroethylene. In one embodiment of the present invention, cathode (B) can have a thickness in the range of from 15 to 200 μηη, preferably from 30 to 100 μηη, determined without the current collector.

Cathode (B) can further comprise electrically conductive carbonaceous material.

Electrically conductive carbonaceous material can be selected, for example, from graphite, carbon black, carbon nanotubes, graphene or mixtures of at least two of the aforementioned substances. In the context of the present invention, electrically conductive, carbonaceous material can also be referred to as carbon for short.

In one embodiment of the present invention, electrically conductive carbonaceous material is carbon black. Carbon black may, for example, be selected from lamp black, furnace black, flame black, thermal black, acetylene black and industrial black. Carbon black may comprise impurities, for example hydrocarbons, especially aromatic hydrocarbons, or oxygen-containing compounds or oxygen-containing groups, for example OH groups. In addition, sulfur- or iron- containing impurities are possible in carbon black.

In one variant, electrically conductive carbonaceous material is partially oxidized carbon black. Inventive electrochemical cells further comprise at least one electrolyte (C). Electrolyte (C) in the context of the present invention can encompass at least one salt, preferably a lithium salt, and at least one non-aqueous solvent.

In one embodiment of the present invention, nonaqueous solvent may be liquid or solid at room temperature, preferably selected from polymers, cyclic or noncyclic ethers, cyclic and noncyclic acetals and cyclic or noncyclic organic carbonates.

Examples of suitable polymers are especially polyalkylene glycols, preferably poly-Ci-C4- alkylene glycols and especially polyethylene glycols. These polyethylene glycols may comprise up to 20 mol% of one or more Ci-C4-alkylene glycols in copolymerized form. The polyalkylene glycols are preferably polyalkylene glycols double-capped by methyl or ethyl.

The molecular weight M_w of suitable polyalkylene glycols and especially of suitable polyethylene glycols may be at least 400 g/mol. The molecular weight M_w of suitable polyalkylene glycols and especially of suitable polyethylene glycols may be up to 5,000,000 g/mol, preferably up to 2,000,000 g/mol.

Examples of suitable noncyclic ethers are, for example, diisopropyl ether, di-n-butyl ether, 1 ,2- dimethoxyethane, 1 ,2-diethoxyethane, preference being given to 1 ,2-dimethoxyethane.

Examples of suitable cyclic ethers are tetrahydrofuran and 1 ,4-dioxane. Examples of suitable noncyclic acetals are, for example, dimethoxymethane, diethoxymethane, 1 ,1 -dimethoxyethane and 1 ,1 -diethoxyethane.

Examples of suitable cyclic acetals are 1 ,3-dioxane and especially 1 ,3-dioxolane.

Examples of suitable noncyclic organic carbonates are dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate.

Examples of suitable cyclic organic carbonates are compounds of the general formulae (X) and (XI)

in which R¹, R² and R³ may be the same or different and are selected from hydrogen and C1-C4- alkyl, for example methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl, where R² and R³ are preferably not both tert-butyl.

In particularly preferred embodiments, R¹ is methyl and R² and R³ are each hydrogen, or R¹, R² and R³ are each hydrogen.

Another preferred cyclic organic carbonate is vinylene carbonate, formula (XII).

O

° ° <^x">

The solvent(s) is (are) preferably used in what is known as the anhydrous state, i.e. with a water content in the range from 1 ppm to 0.1 % by weight, determinable, for example, by Karl Fischer titration. Electrolyte further comprises one or more conductive salts. Suitable conductive salts are especially lithium salts. Examples of suitable lithium salts are Li PF6, LiBF₄, LiCI0₄, LiAsF6, UCF3SO3, LiC(C_nF2n+iS02)3, LiPFw(C_nF2n+i)6-w, lithium imides such as LiN(C_nF2n+iS02)2, where n is an integer in the range from 1 to 20, LiN(S02F)2, Li2SiF6, LiSbF6, LiAICU, and salts of the general for- mula (C_nF2n+iS02)mXLi, where m is defined as follows:

m = 1 when X is selected from oxygen and sulfur,

m = 2 when X is selected from nitrogen and phosphorus, and

m = 3 when X is selected from carbon and silicon. The integer w is a number in the range of from 1 to 6, preferably w = 3.

Preferred conductive salts are selected from LiC(CF₃S0₂)₃, LiN(CF₃S0₂)₂, LiPF₆, LiBF₄, LiCI0₄, and LiPF3(CF2CF3)3, particular preference being given to LiPF6, LiPF3(CF2CFs)3 and

In one embodiment of the present invention, the concentration of conductive salt in electrolyte is in the range of from 0.01 M to 5 M, preferably 0.5 M to 1 .5 M.

Inventive electrochemical cells further comprise at least one separator (D), said separator being positioned between anode (A) and cathode (B).

In one embodiment of the present invention, separator (D) is positioned between anode (A) and cathode (B) in a way that it is like a layer to either a major part of one surface of anode (A) or cathode (B).

In one embodiment of the present invention, separator (D) is positioned between anode (A) and cathode (B) in a way that it is like a layer to both a major part of one surface of anode (A) and cathode (B). In a preferred embodiment of the present invention, separator (D) is positioned between anode (A) and cathode (B) in a way that it is like a layer to one surface of anode (A) or of cathode (B).

In another preferred embodiment of the present invention, separator (D) is positioned between anode (A) and cathode (B) in a way that it is like a layer to one surface of both anode (A) and of cathode (B).

Inventive separators (D) have overall advantageous properties. They help to secure a long duration of electrochemical cells with very low loss of capacity, good cycling stability, and a reduced tendency towards short circuits after longer operation and/or repeated cycling. They can help batteries to have a long duration with very low loss of capacity, good cycling stability, and high temperature stability. In one embodiment of the present invention, inventive electrochemical cells can contain additives such as wetting agents, corrosion inhibitors, or protective agents such as agents to protect any of the electrodes or agents to protect the salt(s). In one embodiment of the present invention, inventive electrochemical cells can have a disc-like shape. In another embodiment, inventive electrochemical cells can have a prismatic shape.

In one embodiment of the present invention, inventive electrochemical cells can include a housing that can be from steel or aluminium.

In one embodiment of the present invention, inventive electrochemical cells are combined to stacks including electrodes that are laminated.

In one embodiment of the present invention, inventive electrochemical cells are selected from pouch cells.

Inventive electrochemical cells have overall advantageous properties. They have a long duration with very low loss of capacity, good cycling stability, and a reduced tendency towards short circuits after longer operation and/or repeated cycling.

A further aspect of the present invention refers to batteries, in particular alkali metal ion battery, comprising at least one inventive electrochemical cell, for example two or more. Inventive batteries have advantageous properties. They have a long duration with very low loss of capacity, good cycling stability, and high temperature stability. A further aspect of the present invention is the use of inventive electrochemical cells or inventive batteries according for making or operating cars, computers, personal digital assistants, mobile telephones, watches, camcorders, digital cameras, thermometers, calculators, laptop BIOS, communication equipment or remote car locks, and stationary applications such as energy storage devices for power plants. A further aspect of the present invention is a method of making or operating cars, computers, personal digital assistants, mobile telephones, watches, camcorders, digital cameras, thermometers, calculators, laptop BIOS, communication equipment, remote car locks, and stationary applications such as energy storage devices for power plants by employing at least one inventive battery or at least one inventive electrochemical cell. The present invention further provides a device comprising at least one inventive rechargeable electrochemical cell as described above.

A further aspect of the present invention refers to a polymeric material comprising urea moieties obtainable by reaction of

(a') at least one polyimide selected from condensation products of (a1 ') at least one polyisocyanate having two isocyanate groups per molecule and,

(a2') at least one polycarboxylic acid having 4 COOH groups per molecule or anhydride thereof, preferably having 2 anhydride groups, wherein polyisocyanate (aV) and polycarboxylic acid (a2') or anhydride (a2') are used in a quantitative ratio such that the molar fraction of NCO groups to COOH groups is in the range from 1 :2 to 2:1 , wherein one anhydride group of the formula CO-O-CO counts as two COOH groups, and wherein polyimide (a') comprises at least one terminal isocyanate group with

(b') at least one organic amine comprising at least one primary amino group.

The polymeric material comprising urea moieties, which is obtainable by reacting at least one polyimide, briefly referred to as polyimide (a'), with at least one organic amine comprising at least one primary amino group, briefly referred to as amine (b'), is preferably a soluble polymer, which can be processed together with a curing agent, such as above described polyisocyanate (bb) by solvent cast technology in order to form thin films during the production of separators, which are themselves insoluble in solvents, which are used in electrolytes of electrochemical cells.

Polyimide (a') is a condensation product of at least one polyisocyanate having on average at least two isocyanate groups per molecule, briefly referred to as polyisocyanate (a1 '), with at least one polycarboxylic acid having 4 COOH groups per molecule or anhydride thereof, briefly referred to as polycarboxylic acid (a2'), wherein polyisocyanate (a1 ') and polycarboxylic acid (a2') or anhydride (a2') are used in a quantitative ratio such that the molar fraction of NCO groups to COOH groups is in the range from 1 :2 to 2:1 , wherein one anhydride group of the formula CO-O-CO counts as two COOH groups, and wherein polyimide (a') comprises at least one terminal isocyanate group. Polyimide (a') is a linear molecule and is soluble in polar sol- vents.

Polyimide (a') can have a molecular weight M_w in the range from 500 to 200,000 g/mol, preferably at least 1000 g/mol, in particular in the range from 2,000 to 20,000 g/mol. Polyimide (a') can have at least two imide groups per molecule, preferably at least 3 imide groups per molecule.

Polyimide (a') can be composed of structurally and molecularly uniform molecules. However, preference is given to polyimide (a) being a mixture of molecularly and structurally differing mol- ecules, for example, visible from the polydispersity M_w/M_n of at least 1.4, preferably M_w/M_n is in the range from 1 .4 to 50, more preferably in the range from 1 .5 to 10, in particular in the range from 1.8 go 2.6. The polydispersity can be determined by known methods, in particular by gel permeation chromatography (GPC). A suitable standard is, for example, poly(methyl methacry- late) (PMMA).

Polyimide (a'), in addition to imide groups, which form the polymer backbone, preferably com- prises up to 4 terminal functional groups. A preferred polyimide (a') molecule contains either 4 COOH groups, 2 anhydride groups, 2 COOH groups and 1 anhydride group, 2 COOH groups and 1 NCO group, 1 anhydride group and 1 NCO group, or 2 NCO groups. A particularly preferred polyimide (a') molecule contains either 2 anhydride groups, 1 anhydride group and 1 NCO group, or 2 NCO groups.

Polyisocyanate (a1 ') is a diisocyanate as described above for polyisocyanate (a1 ). Preferred examples of diisocyanates are hexamethylene diisocyanate, tetramethylene diisocyanate, iso- phorone diisocyanate, toluylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'- diphenylmethane diisocyanate, and mixtures of at least two of the abovementioned diisocya- nates. Preferred mixtures are mixtures of 4,4'-diphenylmethane diisocyanate and 2,4'- diphenylmethane diisocyanate and mixtures of 2,4-toluylene diisocyanate and 2,6-toluylene diisocyanate.

Polycarboxylic acid (a2') is a tetracarboxylic acid or the corresponding anhydride. Preferred ex- amples of tetracarboxylic acids and anhydrides thereof are 1 ,2,4,5-benzenetetracarboxylic acid (pyromellitic acid), 1 ,2,4,5-benzenetetracarboxylic dianhydride (pyromellitic dianhydride), and 3,3',4,4'-benzophenonetetracarboxylic acid, 3,3',4,4'-benzophenonetetracarboxylic dianhydride.

Other suitable polycarboxylic acids and anhydrides thereof have been described above in con- nection with the description of polycarboxylic acid (a2).

Particularly preferred are the dianhydrides (a2').

Amine (b') is an organic amine comprising at least one primary amino group, preferably one or two, in particular one primary amino group. Examples of preferred amines (b') have been described above in connection with the description of organic amine (b). Examples are aliphatic amines with a C& to C50, preferably C10 to C30, in particular C14 to Cis-alkyl group, polyethera- mines containing one, two or three, preferably one or two primary amino groups attached to the ends of a polyether backbone, wherein the polyether backbone is usually based on either pro- pylene oxide (PO), ethylene oxide (EO) or mixed PO/EO, and organic acids comprising at least one primary amino group, like taurin.

The polymeric material comprising urea moieties can preferably be used as polymeric material (aa) for the preparation of the inventive cross-linked material, which can be used for the produc- tion of separators for electrochemical cells. In one embodiment of the present invention the cross-linked polymeric material is characterized in that the polymeric material (aa) is the polymeric material comprising urea moieties as described above. The invention is illustrated by the examples which follow but do not restrict the invention. Figures in percent are each based on % by weight, unless explicitly stated otherwise. I. Production of polyimides

Working examples General remarks: Polyisocyanate (a.1 ): polymeric 4,4'-diphenylmethane diisocyanate ("Polymer-MDI"), average of 2.7 isocyanate groups per molecule, dynamic viscosity: 195 mPa-s at 25 °C, commercially available as Lupranat^® M20W.

Polyisocyanate (a.2): isocyanurate from hexamethylendiisocyanate, average of 3,6 isocyanate groups per molecule.

Polyisocyanate (a.3): 4,4'-diphenylmethane diisocyanate, average of 2 isocyanate groups per molecule, dynamic viscosity: 5 mPa-s at 25 °C, commercially available as Lupranat^® MES.

Polycarboxylic acid (β.1 ): dianhydride of 1 ,2,4,5-benzene tetracarboxylic acid Diol (b.1 ): poly-THF having an average molecular weight M_n of 1000 g/mol

Diol (b.2): polypropylenglycol having an average molecular weight M_n of 1 100 g/mol

Diamine (b.3): polyetheramine derived from propylene capped polyethylenglycol having an average molecular weight M_n of 600 g/mol, commercially available as Jeffamin^® ED 600

Amin (b.4): mono functional polyetheramine derived from a methanol started propylene ox- ide/ethylene oxide (PO/EO) copolymer with a mol ratio of 10/31 , having an average molecular weight M_n of 2000 g/mol, commercially available as Jeffamin^® M 2070

Amine (b.5): octadecylamine

Amine (b.6): taurine "NCO": NCO content, determined by IR spectroscopy unless expressly mentioned otherwise, it is indicated in % by weight.

The molecular weights were determined by gel permeation chromatography (GPC using a re- fractometer as detector). The standard used was polymethyl methacrylate (PMMA). The sol- vents used were Ν,Ν-dimethylacetamide (DMAc), hexafluoroisopropanol (HFIP) or tetrahydrofu- rane (THF), if not stated otherwise. Percentages are % by weight unless expressly mentioned otherwise.

The syntheses were carried out under nitrogen, if not described otherwise. I. Production of polyimides

1.1 Synthesis of reaction product RP.1

An amount of 50 g (0.23 mol) of polycarboxylic acid (β.1 ) were dissolved in 700 ml of acetone which was not dried before the reaction and therefore comprised water and placed in a 4-I four- neck flask having a dropping funnel, reflux condenser, internal thermometer and Teflon agitator. Then, 58 g (0.23 mol) of polyisocyanate (a.3) were added dropwise at 20 °C. The mixture was heated with stirring to 55 °C. The mixture was stirred for a further five hours under reflux at 55 °C and 18 hours at room temperature. Thereafter a mixture of 135 g of diol (b.1 ) (0.135 mol) and 9 g of diamine (b.3) (0.015 mol) was added at room temperature. The temperature was increased to 55 °C and the reaction mixture was stirred for six hours. Then acetone was distilled off at atmospheric pressure in the course of 4 hours. Thereafter the pressure was decreased to 200 mbar. This produced reaction product RP.1 according to the invention as a solid red mass, which was then dissolved in 385 ml 1 ,3-dioxolane. Mn = 8,024 g/mol, M_w= 26,880 g/mol

OH number: 16 mg KOH/g

Acid value: 44 mg KOH/g

Amine value: < 1 mg KOH/g

1.2 Synthesis of reaction product RP.2

An amount of 50 g (0.23 mol) of polycarboxylic acid (β.1 ) were dissolved in 700 ml of acetone which was not dried before the reaction and therefore comprised water and placed in a 4-I four- neck flask having a dropping funnel, reflux condenser, internal thermometer and Teflon agitator. Then, 58 g (0.23 mol) of polyisocyanate (a.3) were added dropwise at 20 °C. The mixture was heated with stirring to 55 °C. The mixture was stirred for a further five hours under reflux at 55 °C and 18 hours at room temperature. Thereafter 310 g of amine (b.4) (0.15 mol) were added at room temperature. The temperature was increased to 55 °C and the reaction mixture was stirred for six hours. Then acetone was distilled off at atmospheric pressure in the course of 4 hours. Thereafter the pressure was decreased to 200 mbar. This produced reaction product RP.2 according to the invention as a solid red mass.

Mn = 5709 g/mol, M_w= 8593 g/mol

Acid value: 51 mg KOH/g

Amine value: 4 mg KOH/g 1.3 Synthesis of reaction product RP.3

An amount of 50 g (0.23 mol) of polycarboxylic acid (β.1 ) were dissolved in 700 ml of acetone which was not dried before the reaction and therefore comprised water and placed in a 4-I four- neck flask having a dropping funnel, reflux condenser, internal thermometer and Teflon agitator. Then, 58 g (0.23 mol) of polyisocyanate (a.3) were added dropwise at 20 °C. The mixture was heated with stirring to 55 °C. The mixture was stirred for a further five hours under reflux at 55 °C and 18 hours at room temperature. Thereafter a mixture of 33 g of diol (b.2) (0.030 mol) and 248 g of amine (b.4) (0.120 mol) was added at room temperature. The temperature was in- creased to 55 °C and the reaction mixture was stirred for five hours. Then acetone was distilled off at atmospheric pressure in the course of 4 hours. Thereafter the pressure was decreased to 200 mbar. This produced reaction product RP.3 according to the invention as a solid red mass.

Mn = 5479 g/mol, M_w= 8781 g/mol

OH number: 10 mg KOH/g

Acid value: 43 mg KOH/g

Amine value: 5 mg KOH/g 1.4 Synthesis of reaction product RP.4

An amount of 55 g (0.253 mol) of polycarboxylic acid (β.1 ) were dissolved in 750 ml of acetone which was not dried before the reaction and therefore comprised water and placed in a 4-I four- neck flask having a dropping funnel, reflux condenser, internal thermometer and Teflon agitator. Then, 63 g (0.253 mol) of polyisocyanate (a.3) were added dropwise at 20 °C. The mixture was heated with stirring to 55 °C. The mixture was stirred for a further five hours under reflux at 55 °C and 18 hours at room temperature. Thereafter a mixture of 10 g of amine (b.6) (0.082 mol), 170 g of amine (b.4) (0.082 mol) and 220 g NMP was added at room temperature. The temperature was increased to 55 °C and the reaction mixture was stirred for two hours. Then ace- tone was distilled off at atmospheric pressure in the course of 4 hours. This produced reaction product RP.4 according to the invention as a red solution in NMP (solid content 59%).

Mn = 2800 g/mol, M_w= 6170 g/mol

Acid value: 38 mg KOH/g

1.5 Synthesis of reaction product RP.5 An amount of 40 g (0.184 mol) of polycarboxylic acid (β.1 ) were dissolved in 520 ml of acetone which was not dried before the reaction and therefore comprised water and placed in a 4-I four- neck flask having a dropping funnel, reflux condenser, internal thermometer and Teflon agitator. Then, 46 g (0.184 mol) of polyisocyanate (a.3) were added dropwise at 20 °C. The mixture was heated with stirring to 55 °C. The mixture was stirred for a further five hours under reflux at 55 °C and 18 hours at room temperature. Thereafter a mixture of 3 g of amine (b.6) (0.024 mol), 198 g of amine (b.4) (0.095 mol) and 220 g NMP was added at room temperature. The tem- perature was increased to 55 °C and the reaction mixture was stirred for one hours. Then acetone was distilled off at atmospheric pressure in the course of 6 hours. This produced reaction product RP.5 according to the invention as a red solution in NMP (solid content 53%).

Mn = 2900 g/mol, M_w= 6390 g/mol

Acid value: 37 mg KOH/g

1.6 Synthesis of reaction product RP.6

An amount of 50 g (0.23 mol) of polycarboxylic acid (β.1 ) were dissolved in 700 ml of acetone which was not dried before the reaction and therefore comprised water and placed in a 4-I four- neck flask having a dropping funnel, reflux condenser, internal thermometer and Teflon agitator. Then, 58 g (0.23 mol) of polyisocyanate (a.3) were added dropwise at 20 °C. The mixture was heated with stirring to 55 °C. The mixture was stirred for a further five hours under reflux at 55 °C and 18 hours at room temperature. Thereafter a mixture of 3,8 g of amine (b.6) (0.03 mol), 248 g of amine (b.4) (0.12 mol), 350 g NMP and 150g water was added at room temperature. The temperature was increased to 55 °C and the reaction mixture was stirred for one hour. Then acetone was distilled off at atmospheric pressure in the course of 3 hours. Thereafter the temperature was increased to 85 °C and pressure decreased to 200 mbar to distill of the water. This produced reaction product RP.6 according to the invention as a red solution in NMP (solid content 54%).

Mn = 1 120 g/mol, M_w= 1940 g/mol

Acid value: 53 mg KOH/g

1.7 Synthesis of reaction product RP.7

An amount of 25 g (0.1 15 mol) of polycarboxylic acid (β.1 ) were dissolved in 300 ml of acetone which was not dried before the reaction and therefore comprised water and placed in a 4-I four- neck flask having a dropping funnel, reflux condenser, internal thermometer and Teflon agitator. Then, 29 g (0.1 15 mol) of polyisocyanate (a.3) were added dropwise at 20 °C. The mixture was heated with stirring to 55 °C. The mixture was stirred for a further five hours under reflux at 55 °C and 18 hours at room temperature. Thereafter a mixture of 10 g of amine (b.5) (0.0375 mol), 78 g of amine (b.4) (0.0375 mol) and 150 g toluene was added at room temperature. The tern- perature was increased to 55 °C and the reaction mixture was stirred for three hours. Then acetone and toluene were distilled off at 85 °C and a pressure of 200 mbar. This produced reaction product RP.7 according to the invention as a red solid. Mn = 13900 g/mol, M_w= 27700 g/mol

Acid value: 83 mg KOH/g 1.8 Synthesis of reaction product RP.8

An amount of 25 g (0.1 15 mol) of polycarboxylic acid (β.1 ) were dissolved in 300 ml of acetone which was not dried before the reaction and therefore comprised water and placed in a 4-I four- neck flask having a dropping funnel, reflux condenser, internal thermometer and Teflon agitator. Then, 29 g (0.1 15 mol) of polyisocyanate (a.3) were added dropwise at 20 °C. The mixture was heated with stirring to 55 °C. The mixture was stirred for a further five hours under reflux at 55 °C and 18 hours at room temperature. Thereafter a mixture of 4,6 g of amine (b.6) (0.0375 mol), 78 g of amine (b.4) (0.0375 mol), 150 g water and 3,7 g triethylamine (0,0366 mol) was added at room temperature. The temperature was increased to 55 °C and the reaction mixture was stirred for three hours. Then acetone and water were distilled off at 85 °C and a pressure of 200 mbar. This produced reaction product RP.8 according to the invention as a yellow solid.

Mn = 1550 g/mol, M_w= 3650 g/mol

Amine value: 7 mg KOH/g

Acid value: 61 mg KOH/g

1.9 Synthesis of reaction product RP.9

An amount of 25 g (0.1 15 mol) of polycarboxylic acid (β.1 ) were dissolved in 300 ml of acetone which was not dried before the reaction and therefore comprised water and placed in a 4-I four- neck flask having a dropping funnel, reflux condenser, internal thermometer and Teflon agitator. Then, 29 g (0.1 15 mol) of polyisocyanate (a.3) were added dropwise at 20 °C. The mixture was heated with stirring to 55 °C. The mixture was stirred for a further five hours under reflux at 55 °C and 18 hours at room temperature. Thereafter a mixture of 4,6 g of amine (b.6) (0.0375 mol), 78 g of amine (b.4) (0.0375 mol), 150 g water and 3,7 g triethylamine (0,0366 mol) was added at room temperature and the reaction mixture was stirred for one hour. Then acetone and water were distilled off at 85 °C and a pressure of 200 mbar. This produced reaction product RP.9 according to the invention as a yellow solid.

Mn = 12800 g/mol, M_w= 21200 g/mol (in HFIP) Amine value: 23 mg KOH/g

Acid value: 1 15 mg KOH/g II. Manufacture of inventive separators (D.1 ) to (D.5)

General procedure:

A solution of 30 g of RP.4 in N-methylpyrrolidone (NMP) was provided. The solids content was adjusted by addition of N-methylpyrrolidone, if necessary, and then warmed to 80 °C. Polyisocyanate (a.1 ) was added, and the solution so obtained was applied at 50 °C with a doctor blade method to a glass plate. The solvent-containing film so obtained had a thickness of 50 μηη. The N-methylpyrrolidone was allowed to evaporate for 120 minutes at 80 °C. The film was then - together with the glass plate - placed into a water bath having room temperature for 10 minutes. Then, a film was removed manually and dried over a period of 24 hours under vacuum at 80 °C. Inventive separator D.1 was so obtained.

Inventive separators (D.2) to (D.4) could be made accordingly. Details are summarized in table 1 .

As alternative procedure 30 wt% solution of RP.7 in N-methylpyrrolidone (NMP) was provided and 0.18 g 1 ,4-Diazabicyclo[2.2.2]octan (DABCO) added. Then 1 .97 g polyisocyanate (a.1 ) was added, and the solution so obtained was applied with a doctor blade method to a glass plate. The solvent-containing film so obtained had a thickness of 50 μηη. The N-methylpyrrolidone was allowed to evaporate for 120 minutes at 50 °C. The film was then - together with the glass plate - placed into a water bath having room temperature for 10 minutes. Then, a film was removed manually and dried over a period of 24 hours under vacuum at 80 °C. Inventive separator D.5 was obtained.

Table 1 : Manufacture of inventive separators

The specific electric conductivities of inventive separators (D.1 ) to (D.5) were determined in 1 M solutions of LiPF6 in a 1 :1 (by weight) mixture of ethylene carbonate/ethylmethyl carbonate (commercially available as LP 50 SelectiLyte™). The results are summarized in table 2. Table 2: Specific Electric Conductivities of inventive separators

III. Evaluation of thermal stability Circular samples of 3.6 cm diameter were punched out (do) and subjected to temperature treatment of 170 °C for 5 hours. Then the diameter (dwc) is evaluated again and the shrinkage calculated based on the formula (1 )

Table 3 summarizes the results obtained. As reference sample the polyolefine Celgard 2325 separator was subjected to the same procedure. As expected, all polyimide samples show excellent thermal stability and negligible shrinkage tendency (below 1 %). In contrast, the polyolefine separators are subject to significant shrinkage. Celgard 2325 as the trilayer separator (polypropylene /polyethylene /polypropylene) Celgard 2325 looses 58 % of its area. In summary, polyalkyleneoxide block polyimide separators show excellent high temperature stability.

Table 3: Shrinkage behaviour of polyalkyleneoxide block polyimide films

IV. Test of inventive separator (D.1 ) and (D.2) in a lithium ion battery An inventive electrochemical cell (E.1 ) and (E.2) according to figure 1 was assembled. The labels in figure 1 (Fig. 1 ) mean:

1 , 1 ' Dies

2, 2' Nuts

3, 3' Sealing ring - two in each case, the second sealing ring in each case, which is somewhat smaller, not being shown here

4 Coil spring

5 Nickel output conductor

6 Housing Anode: graphite on copper foil as current collector with a thickness of 36 to 38 μηη (Fa. Gaia, Nordhausen, Germany).

Cathode: LiNio.8Coo.15Alo.05O2, on aluminium foil as current collector (Fa. Gaia, Nordhausen, Germany). As cathode, a nickel manganese spinel electrode was used which had been manufactured as follows.

85% LiNio.8Coo.15Alo.05O2

6% PVdF, commercially available as Kynar Flex^® 2801 of Arkema Group,

6% carbon black, BET surface 62 m²/g, commercially available as„Super P Li" by Timcal, 3% graphite, commercially available as KS6 by Timcal,

were mixed in a container with a lid. Under stirring, an amount of NMP was added until a viscous lump-free paste was obtained. Stirring was performed over a time of 16 hours.

The paste so obtained was applied to an aluminium foil (thickness of the aluminium foil: 20 μηη) with a knife blade. Then, the aluminium foil so coated was dried in a drying cabinet at 120 °C under vacuum. The thickness of the dried coating was 30 μηη. Then round segments were punched out, diameter: 12 mm.

Round segments were punched out. Diameter: 12 mm.

1 M solution of LiPFe in a 1 :1 (by weight) mixture of ethylene carbonate/ ethylmethyl carbonate (commercially available as LP 50 SelectiLyte™). Inventive electrochemical cell (EC.1 ) and (E.2) was charged with a constant current to a voltage of 4.2 V followed by a final charging with constant voltage at 4.2 V. Then, inventive electrochemical cell (EC.1 ) and (E.2) was discharged at constant current to a voltage of 3 V. Three such cycles with 0.1 C and, thereafter, 20 and 100 cycles with 0.5 C were determined. The discharge capacity was determined to be 120 mA-g. Table 4: Discharge capacities of electrochemical cells with inventive separators

Separator Electrochemical Specific capacity Specific capacity cell [mA/g] [mA/g]

20^th 100^th

D.1 EC.1 1 19 120

D.2 EC.2 120 122

Claims

A cross-linked polymeric material obtainable by reaction of (aa) a polymeric material obtainable by reaction of

(a) at least one polyimide selected from condensation products of

(b) at least one organic amine comprising at least one primary or secondary amino group, or a mixture of at least one organic amine comprising at least one primary or secondary amino group and at least one diol or triol,

with

The cross-linked polymeric material according to claim 1 , wherein polyimide (a) is selected from those polyimides that have a molecular weight M_w of at least 1000 g/mol.

The cross-linked polymeric material according to claim 1 or 2, wherein polyimide (a) has a polydispersity M_w/M_n of at least 1 .4.

The cross-linked polymeric material according to any one of claims 1 to 3, wherein polyisocyanate (a1 ) is selected from hexamethylene diisocyanate, tetramethylene diisocyanate, isophorone diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, toluylene diisocyanate and mixtures of at least two of the abovementioned polyisocyanates (a1 ).

The cross-linked polymeric material according to any one of claims 1 to 4, wherein polyisocyanate (a1 ) is selected from oligomeric hexamethylene diisocyanate, oligomeric tetramethylene diisocyanate, oligomeric isophorone diisocyanate, oligomeric diphenylmethane diisocyanate, trimeric toluylene diisocyanate and mixtures of at least two of the above- mentioned polyisocyanates (a1 ). The cross-linked polymeric material according to any one of claims 1 to 5, wherein, as polycarboxylic acid (a2), a polycarboxylic acid having at least 4 COOH groups per molecule, or the respective anhydride, is selected.

The cross-linked polymeric material according to any one of claims 1 to 6, wherein poly- isocyanate (a1 ) and polycarboxylic acid (a2) or anhydride (a2) are used in a quantitative ratio such that the molar fraction of NCO groups to COOH groups is in the range from 1 :2 to 2:1 , wherein one anhydride group of the formula CO-O-CO counts as two COOH groups.

The cross-linked polymeric material according to any one of claims 1 to 7, wherein organic amine (b) is selected from amines comprising one, two or three, primary or secondary amino groups, wherein the molecular weight of the amines is in the range from 31 to 10000 g/mol.

The cross-linked polymeric material according to any one of claims 1 to 8, wherein the organic amine (b) is selected from polyetheramines, aliphatic amines with a with Cio to C3o-alkyl group and organic acids comprising at least one primary or secondary amino group.

0. The cross-linked polymeric material according to any one of claims 1 to 9, wherein the polymeric material (aa) has an acid value in the range from 0 to 200 mg of KOH/g.

1 . The cross-linked polymeric material according to any one of claims 1 to 10, wherein the polymeric material (aa) has a molecular weight M_w of at least 1000 g/mol.

2. A method for producing a cross-linked polymeric material according to any one of claims 1 to 1 1 , comprising the reaction steps of

(a) preparation of polyimide (a) by condensation of at least one polyisocyanate (a1 ) having on average at least two isocyanate groups per molecule with at least one polycarboxylic acid (a2) having at least 3 COOH groups per molecule or anhydride (a2) thereof,

(β) preparation of polymeric material (aa) by reacting polyimide (a), which was prepared in reaction step (a), with at least one organic amine (b), which comprises at least one primary or secondary amino group, or a mixture of at least one organic amine comprising at least one primary or secondary amino group and at least one diol or triol, (γ) cross-linking the polymeric material (aa), which was prepared in reaction step (β), by mixing it with at least one polyisocyanate (bb), which has on average at least two isocyanate groups per molecule. 13. The method according to claim 12, wherein a film of the cross-linked polymeric material is formed in reaction step (γ) by casting a thin film of a solution comprising polymeric material (aa) and polyisocyanate (bb).

14. A separator (D) comprising at least one cross-linked polymeric material according to any one of claims 1 to 1 1 .

15. Separator according to claim 14, further comprising one or more inorganic particles (E).

16. Separator according to claim 15 or 16 having a thickness in the range of from 1 to 150 μηη.

17. An electrochemical cell comprising

(A) at least one anode as component (A), at least one cathode as component (B), at least one none-aqueous electrolyte as component (C), and at least one separator according to any of claims 14 to 16.

18. Electrochemical cell according to claim 17, characterized in that it is a lithium-ion containing cell. 19. Electrochemical cell according to claim 17 or 18, characterized in that anode (A) is selected from graphite anodes and lithium titanate anodes.

20. Electrochemical cell according to any of claims 17 to 19, characterized in that cathode (B) contains at least one material selected from lithium containing transition metal spinels and lithium transition metal oxides with a layered crystal structure.

21 . Battery comprising at least one electrochemical cell according to any of claims 17 to 20.

22. A device comprising at least one electrochemical cell according to any of claims 17 to 21.

23. A polymeric material comprising urea moieties obtainable by reaction of

(a') at least one polyimide selected from condensation products of

(a1 ') at least one polyisocyanate having two isocyanate groups per molecule and,

(a2') at least one polycarboxylic acid having 4 COOH groups per molecule or anhydride thereof, wherein polyisocyanate (aV) and polycarboxylic acid (a2') or anhydride (a2') are used in a quantitative ratio such that the molar fraction of NCO groups to COOH groups is in the range from 1 :2 to 2:1 , wherein one anhydride group of the formula CO-O-CO counts as two COOH groups, and wherein polyimide (a') comprises at least one terminal isocyanate group with

(b') at least one organic amine comprising at least one primary amino group.