WO2025098832A1

WO2025098832A1 - Potting material for stabilization of battery cells in a battery module

Info

Publication number: WO2025098832A1
Application number: PCT/EP2024/080577
Authority: WO
Inventors: Niklas VOIGT; Philipp KROEMER; Nabarun Roy; Martin Linnenbrink; Alexandre Felix CARVALHO; Bert Neuhaus
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2023-11-09
Filing date: 2024-10-29
Publication date: 2025-05-15
Anticipated expiration: 2026-05-09

Abstract

The present invention relates to a battery module wherein the electric cells are potted into a potting material and the potting material is obtained by mixing (a) one or more organic polyiso- cyanates, (b) one or more compounds having at least two isocyanate-reactive hydrogen atoms, (c) one or more catalysts, (d) optionally fillers and/or polyurethane additives to give a reaction mixture and allow the reaction mixture to cure, wherein the compounds having at least two iso- cyanate-reactive hydrogen atoms comprise at least one polyetherpolyol having a functionality of 1.8 to 3 and a hydroxyl number of less than 140 mg KOH/g (b1), at least one polyetherpolyol having a functionality of more than 3 to 6 and having a hydroxyl number of more than 180 mg KOH/g (b2) and optionally at least one polyether polyol (b3) having a functionality of 1.8 to 3 having a hydroxyl number of more than 200 mg KOH/g and optionally at least one chain ex- tender (b4) and wherein the components to obtain the reaction mixture are mixed at an isocya- nate index of 100 to 200. The present invention is further directed to a method of producing a battery module wherein the electric cells are potted into a potting material and the potting mate- rial is obtained by inserting a reaction mixture according to the invention into the spaces be- tween the adjacent electric cells of a battery case having the electric cells arranged within and allowing the reaction mixture to cure.

Description

Potting material for stabilization of battery cells in a battery module

Description

The present invention relates to a battery module wherein the electric cells are potted into a potting material and the potting material is obtained by mixing (a) one or more organic polyisocyanates, (b) one or more compounds having at least two isocyanate-reactive hydrogen atoms, (c) one or more catalysts, (d) optionally fillers and/or polyurethane additives to give a reaction mixture and allow the reaction mixture to cure, wherein the compounds having at least two iso- cyanate-reactive hydrogen atoms comprise at least one polyetherpolyol (b1) having a functionality of 1.8 to 3 and a hydroxyl number of less than 140 mg KOH/g, at least one polyetherpolyol (b2) having a functionality of more than 3 to 6 and having a hydroxyl number of more than 180 mg KOH/g and optionally at least one polyether polyol (b3) having a functionality of 1.8 to 3 having a hydroxyl number of more than 200 mg KOH/g and optionally at least one chain extender (b4) and wherein the components to obtain the reaction mixture are mixed at an isocyanate index of 100 to 200. The present invention is further directed to a method of producing a battery module wherein the electric cells are potted into a potting material and the potting material is obtained by inserting a reaction mixture according to the invention into the spaces between the adjacent electric cells of a battery case having the electric cells arranged within and allowing the reaction mixture to cure.

There is a very fast transition in the automotive industry to go from combustion engines to electrified vehicles. The design of the batteries can be very different and is usually based on three types of battery cells: prismatic, pouch or cylindrical cells. Especially for the cell-to-pack design of cylindrical cells but not limited to that there is a filling material described in the literature that fills the cavities between the cells. The main goals of filling material is to stabilize the battery mechanically by stiffening the battery for example against mechanical stress resulting from temperature change, vibrations during driving and mechanical impact in traffic accidents and keeping the cells in contact with a cooling device.

A gap filling material must provide a given stiffness over a broad temperature of less than -30°C in winter to more than 70°C in summer but nonetheless keep a certain level of flexibility to prevent crack formation.

EP 3753056 discloses a battery module comprising a polyurethane-based potting compound that reacts to a foam with a density below 0.5 g/cm³ and which contains liquid flame retardants and additives such as chain extenders. The electric cells embedded into the foam are described as cylinders. After being fully cured, the potting compound may have a certain degree of elastic- ity, thereby buffering shock or vibrations imparted to the battery module. The encapsulation of the battery cells ensures a suitable level of protection, such as a suitable amount of structural stability and/or a suitable amount of flame retardant to help to reduce the likelihood of an uncontrolled fire from the battery module. Nevertheless, it turned out that mechanical stability provided by a foam is often not sufficient.

On the other hand, thermally conductive adhesives are known. These materials improve heat transfer from the battery cell to a cooling plate.

PCT/EP2023/074553 and CN111607351 disclose a thermal conductive adhesive for battery modules comprising organic polyisocyanates, polyether polyol, chain extender, flame retardant catalyst and thermoconductive filler.

Thermoconductive adhesives comprise a high amount of inorganic filler and do not show excellent mechanical properties as stiffness and elasticity over a broad temperature range.

It was object of the present invention to provide a battery module battery module wherein the electric cells are potted into a potting material and the potting material with improved mechanical properties as elasticity and stiffness over a temperature range of -35°C to 60°C.

The object of the present invention has been solved by a battery module wherein the electric cells are potted into a potting material and the potting material is obtained by mixing (a) one or more organic polyisocyanates, (b) one or more compounds having at least two isocyanatereactive hydrogen atoms, (c) one or more catalysts, (d) optionally fillers and/or polyurethane additives to give a reaction mixture and allow the reaction mixture to cure, wherein the compounds having at least two isocyanate-reactive hydrogen atoms comprise at least one polyetherpolyol (b1) having a functionality of 1.8 to 3 and a hydroxyl number of less than

140 mg KOH/g, at least one polyetherpolyol (b2) having a functionality of more than 3 to 6 and having a hydroxyl number of more than 180 mg KOH/g and optionally at least one polyether polyol (b3) having a functionality of 1.8 to 3 having a hydroxyl number of more than 200 mg KOH/g and optionally at least one chain extender (b4) and wherein the components to obtain the reaction mixture are mixed at an isocyanate index of 100 to 200.

A battery module according to the present invention can be obtained by a method wherein the electric cells are potted into a potting material and the potting material is obtained by inserting a reaction mixture according to the invention into the spaces between the adjacent electric cells of a battery case having the electric cells arranged within and allowing the reaction mixture to cure. A battery module, according to the present invention, comprises several electric cells. In a preferred method the cells are of cylindric shape. In a preferred embodiment the outer surface of the cells is a metal, preferably steel and especially preferred Hilumin®-steel. Such battery modules can be applied for a series of mobile devices and are especially suited for electric vehicles such as electric cars. The cells of the battery module according to the present invention are positioned in a potting material. In a preferred embodiment, the central part of the cells may be inserted into a foam, for example a polyurethane foam.

The battery case may be configured to provide protection from moisture, heat, cold, or any other potential factors that may cause damage to the electric cells. In a preferred embodiment the case comprises a bottom part, a top part and a wall, extending between the bottom and the top. The bottom may be a positive terminal or may be a negative terminal of the electric cell, depending on the desired orientation. Preferably, the bottom of the electric cell is positioned in the potting compound. The potting compound occupies a portion of the internal volume of the battery case and extends a substantially equal distance at various points along the wall from the bottom of the battery case toward the top. Typically, the top of the potting compound is lower than the top of the electric cells. Alternatively, the top of the electric cells may be lower than the top of the potting compound. The spaces can be filled completely or partial, for example in the lower part, as for example up to 50% of the height of a battery cell, or in the upper part and the lower part, for example up to 30% of the height of a battery cell and from 70% to 100% of the height of the battery cell. Preferably the level of filling between the battery cells is consistent across the entire battery module. In case that the cells are partially inserted into a foam the potting material according to the invention is able to flow around the foam and to adhere to the foam.

The size of the gap between adjacent electric cells and/or the battery case can be selected based on several variables, including but not limited to the size and/or weight of each electric cell, the operating temperature of each electric cell, the dimensions of each electric cell and the intended use of the battery module. In some examples, the size of the space between adjacent electric cells may be from greater than 0 mm, about 0.25 mm, about 0.50 mm, about 0.75 mm, to about 1.0 mm, about 1.5 mm, or about 2.0 mm, or a length between any pair of the foregoing values.

The battery module according to the present invention may be used to power any number of applications, such as but not limited to a household appliance, outdoor electrical equipment, or a vehicle such as a car or a boat.

In a preferred embodiment according to the present invention, the cured potting material has a tensile strength of more than 15 MPa over a temperature range of -35°C to +60°C, an elonga- tion at break of more than 5% at a temperature range of -35°C to +25°C- and at least 10% at 65°C and an E-Modulus of more than 1500 MPa at -35 °C and more than 500 MPa, preferably more than 600 and more preferred more than 750 MPa at +25°C and +60°C each. All measurements are performed according to ISO 527-3.

The potting material according to the present invention is obtained by mixing (a) one or more organic polyisocyanates, (b) one or more compounds having at least two isocyanate-reactive hydrogen atoms, (c) one or more catalysts, (d) optionally fillers and/or polyurethane additives to give a reaction mixture and allow the reaction mixture to cure. The reaction mixture can flow through the gap between adjacent electric cells and settle at a level height around the electric cells and in the gap or spaces defined between the electric cells. For example, the reaction mixture may be poured into the battery case having the electric cells arranged within. The liquid reaction mixture has sufficient flowability before curing to permit the liquid potting composition to flow through the spaces defined by the gap between the adjacent electric cells and/or between an electric cell and the battery case and to settle at a substantially level height before its viscosity increases significantly due to the hardening process.

According to the present invention, the polyisocyanate components (a) used for the production of the polyurethanes of the invention comprise any of the polyisocyanates known for the production of polyurethanes. These comprise the aliphatic, cycloaliphatic, and aromatic difunctional or polyfunctional isocyanates known from the prior art, and also any desired mixtures thereof. Examples are diphenylmethane 2, 2’-, 2,4’-, and 4,4’-diisocyanate, the mixtures of monomeric diphenylmethane diisocyanates with diphenylmethane diisocyanate homologs having a larger number of rings (polymer MDI), isophorone diisocyanate (IPDI) and its oligomers, tolylene 2,4- and 2,6-diisocyanate (TDI), and mixtures of these, tetramethylene diisocyanate and its oligomers, hexamethylene diisocyanate (H DI) and its oligomers, pentane diisocyanate and its oligomers, naphthylene diisocyanate (N DI), and mixtures thereof.

It is preferably to use tolylene 2,4- and/or 2,6-diisocynate (TDI) or a mixture thereof, monomeric diphenylmethane diisocyanates, and/or diphenylmethane diisocyanate homologs (polymer MDI), and mixtures of these. Other possible isocyanates are mentioned by way of example in "Polyurethanes Handbook”, Carl Hanser Verlag, 2^nd edition 1994, chapter 3.2 and 3.3.2.

In an especially preferred embodiment, the polyisocyanates (a) comprise at least one Isocyanate selected from the group consisting of monomeric MDI, polymeric MDI, or modified MDI as MDI based prepolymers or carbodiimide modified MDI or mixtures of at least two of these. At least 80%, preferably at least 90%, and more preferred 100% by weight of the isocyanates (a) consist of monomeric MDI, polymeric MDI, or modified MDI or mixtures of at least two of these. Even more preferred, the polyisocyanate (a) does not comprise polymeric MDI.

Polyisocyanate component (a) used can be used in form of polyisocyanate prepolymers. These polyisocyanates prepolymers are obtainable by reacting the polyisocyanates described above (constituent (a-1)) in excess, for example at temperatures of from 30°C to 100°C, preferably at about 80°C, with compounds (b) (constituent (a-2)), having groups reactive toward isocyanates, to give the isocyanate prepolymer.

Compounds having groups reactive toward isocyanates (b) are known to the person skilled in the art and are described by way of example in "Polyurethanes Handbook", Carl Hanser Verlag, 2^nd edition 1994, chapter 3.1. It is preferred to use, as polymeric compounds (a-2) having groups reactive toward isocyanates, the polymeric compounds described under (b) having groups reactive toward isocyanates.

It is possible to use, compounds having groups reactive toward isocyanates (b), any of the known compounds having at least two hydrogen atoms reactive toward isocyanates, for example those with functionality from 2 to 8 and with number-average molar mass from 62 to 15.000 g/mol. By way of example, it is possible to use compounds selected from the group of the polyether polyols, fatty acid based polyols, polybutadiene based polyols, polyester polyols, and mixtures thereof as well as chain extenders and crosslinking agents as compounds with at least two hydrogen atoms reactive towards isocyanate.

Polyetherols are by way of example produced from alkylene oxides, for example, propylene oxide and/or ethylene oxide, or from tetrahydrofuran, with starter compounds exhibiting hydro- gen-activity containing 1 to 8, preferably 2 to 6 and more preferably 2 to 4 reactive hydrogen atoms bound, or a starter molecule mixture which contains 1.5 to 8, preferably 1.8 to 6 and more preferably 1.9 to 3.5 reactive hydrogen atoms bound in the presence of catalysts. As starter molecules for example aliphatic alcohols, phenols, amines, carboxylic acids, water, or compounds based on natural substances, for example sucrose, saccharose, sorbitol or mannitol can be applied. If mixtures of starter molecules with different functionalities are used, fractional functionalities can be obtained. Influences on the functionality, for example through side reactions, are not considered in the nominal functionality. Examples for suitable catalysts are basic catalysts and double-metal cyanide catalysts, as described by way of example in PCT/EP2005/010124, EP90444, or W005/090440.

Polyesterols are by way of example produced from aliphatic or aromatic dicarboxylic acids and polyhydric alcohols, polythioether polyols, polyesteramides, hydroxylated polyacetals, and/or hydroxylated aliphatic polycarbonates, preferably in the presence of an esterification catalyst. Other possible polyols are mentioned by way of example in " Polyurethane Handbook, 2^nd edition 1993, editor Guether Oertel, Carl Hanser Verlag Munich, Chapter chapter 3.1.

In a particularly preferred embodiment of the present invention, component (b) comprises polyetherols, and more preferably comprises no polyesterols.

According to the invention, the compounds having at least two isocyanate-reactive hydrogen atoms (b) comprise at least one polyetherpolyol (b1) having a functionality of 1.8 to 3, preferably 2 or 3 and especially preferred 2, and a hydroxyl number of less than 140 mg KOH/g, preferably 20 to 100 mg KOH/g and especially 25 to 50 mg KOH/g. Preferred starter molecules are selected from the group consisting of monoethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerol and trimethylolpropane. Especially preferred as starter molecules are glycerol and/or propylene glycol and most preferred propylene glycol. As alkylene oxides preferably ethylene glycol and or propylene glycol are used. Preferably, the polyether (b1) comprises at least 50%, more preferred at least 60% and especially preferred at least 70% by weight of propylene oxide, based on the total amount of alkylenoxide used for the production of polyether (b1).

According to the invention, the compounds having at least two isocyanate-reactive hydrogen atoms (b) comprise at least one polyetherpolyol (b2) having a functionality of more than 3 to 6, preferably 3.0 to 5 and especially preferred 3.0 to 4.5, having a hydroxyl number of more than 180 mg KOH/g, preferably 200 to 800, more preferred 300 to 700 and especially preferred 400 to 600 mg KOH/g. Preferred starter molecules are selected from the group, consisting of glycerol, pentane diol, diethylene glycol, trimethylene propane, sugar molecules as sucrose, saccharose, sorbitol or mannitol, and fatty acid methyl esters, known as biodiesel. Preferably at least one of the polyetherols (b2) is produced from a mixture of starter molecules as glycerol, biodiesel and saccharose. Examples of suitable alkylene oxides are tetra hydrofuran, propylene 1 ,3-oxide, butylene 1 ,2- or 2,3-oxide and preferably ethylene oxide and propylene 1 ,2-oxide. Preferably, the polyether (b2) comprises at least 50%, more preferred at least 60% and especially preferred at least 70% by weight of propylene oxide, based on the total amount of alkylenoxide used for the production of polyether (b1).

The polyetherol (b3) according to the present invention has a functionality of 1.8 to 3, preferably of 2, and a hydroxyl number of more than 200 mg KOH/g, preferably 210 to 500 mg KOH/g, more preferred 220 to 400 mg KOH/g. Preferred starter molecules are selected from the group consisting of water, monoethylene glycol, diethylene glycol, propylene glycol, dipropylene gly- col, glycerol and trimethylolpropane. Especially preferred as starter molecules are glycerol and ore propylene glycol and most preferred propylene glycol. As alkylene oxides preferably ethylene glycol and or propylene glycol are used. Preferably, the polyether (b1) comprises at least 50%, more preferred at least 60% and especially preferred at least 70% by weight of propylene oxide, based on the total amount of alkylenoxide used for the production of polyether (b1).

Chain extenders (b4) used here are compounds of molar mass less than 200 g/mol, preferably less than 150 g/mol and more preferred 62 to 150 g/mol, which have two groups reactive toward isocyanates as for example -SH or NH2-groups and preferably OH-groups. According to the present invention, if chain extenders (b4) are used, they are preferably used in an amount of 0.1 to 20 wt.-%, more preferred 1-10 and especially preferred 1 to 5 wt.-%, each based on the total weight of components (b). As chain extenders (b4), use may be made of the chain extenders known in the production of polyurethanes. These are preferably low-molecular-weight compounds having two functional groups reactive toward isocyanates, for example monoethylene glycol, diethylene glycol, 1 ,2-propane diol, 1 ,3 propane diol, 1 ,4 butane diol, 1 ,3 butane diol, 1 ,5 pentane diol, 1 ,6-hexane diol, neopentyl glycol, tetraethylene glycol, dipropylene glycol, cyclohexane diol and aliphatic or aromatic amine based chain extenders as aliphatic or aromatic diamines like ethylene diamine, triethylene diamine and/or diethyl toluene diamine (DETDA). Other possible low-molecular-weight chain extenders are mentioned by way of example in "Polyurethane Handbook”, Carl Hanser Verlag, 2^nd edition 1994, chapter 3.2 and 3.3.2. In a preferred embodiment the chain extender (b4) is selected from the group, consisting of monoethylene glycol, diethylene glycol, dipropylene glycol, 1 ,2-propane diol, 1 ,3 propane diol, 1 ,4 butane diol, 1 ,6 hexane diol or mixtures thereof.

In addition, crosslinking agents may be added to the mixture. As crosslinking agents used in the invention are compounds of molar mass less than 200 g/mol preferably less than 150 g/mol which have at least three groups reactive toward isocyanates. Examples for crosslinking agents are glycerine, trimethylolpropane, pentaerythritol and triethanolamine, in a preferred embodiment glycerine is used as crosslinking agent. Other possible low-molecular-weight crosslinking agents are mentioned by way of example in "Polyurethane Handbook”, Carl Hanser Verlag, 2^nd edition 1994, chapter 3.2 and 3.3.2. According to the present invention, if chain extenders and /or crosslinking agents are used, they are used in an amount of 0.1 to 10 wt.-%, preferably 0.5- 10 and especially preferred ably 1 to 5 wt.-%, each based on the total weight of component (b).

In a preferred embodiment the amount of polyetherol (b1) is 15 to 60%, preferably 20% to 50% by weight and more preferred 25% to 40% by weight, of polyetherol (b2) is 35% to 80%, preferably 50% to 75% by weight, of polyetherpolyol (b3) is 0% to 25%, preferably 0% to 20% by weight, of chain extender (b4) is 0 to 20 wt.-%, more preferred 1-10 and especially preferred 1 to 5 wt.-%, each based on the total weight of compound (b). For the calculation of the ratio of compounds (b) it is irrelevant if a compound is pre-reacted with isocyanate to form a prepolymer or the compound is directly added to the reaction mixture.

In a preferred embodiment at least part of polyetherol (b3) and/or chain extender (b4) are prereacted with isocyanate to form an isocyanate prepolymer. Preferably, the isocyanate content of the isocyanate prepolymer is 15% to 30% by weight, more preferred 20% to 25% by weight.

In a preferred embodiment, the polyetherol (b1), the polyetherol (b2) and, if present, the polyetherpolyol (b3) comprise more than 70%, preferably more than 80% and especially preferred more than 90% by weight of propylene glycol units, based on the total amount of alkylene oxide units in polyetherols (b1), (b2) and (b3). It is further preferred that the polyetherpolyols (b1), (b2) and, if present polyetherpolyol (b3) and chain extender (b4), comprise at least 50%, preferably at least 80% and especially preferred more than 95% of secondary alcohol groups.

In a preferred embodiment of the present invention, in addition to compounds (b1), (b2) (b3) and (b4), less than 20%, preferably less than 10% and especially preferred less than 5% by weight of compounds having at least two isocyanate-reactive hydrogen atoms, based on the total amount of compounds having at least two isocyanate-reactive hydrogen atoms (b) are added.

In particular, compounds are used as catalysts (c) for the production of the polyurethanes according to the invention, which strongly accelerate the reaction of the reactive hydrogen atoms, in particular hydroxyl groups, containing compounds of component (b) with the polyisocyanates (a).

Catalysts comprise nitrogen based catalysts. Examples include amidines such as 2,3-dimethyl- 3,4,5,6-tetrahydropyrimidine, tertiary amines such as triethylamine, tributylamine, dimethylbenzylamine, N-methyl-, N-ethyl-, N-cyclohexylmorpholine, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetramethylbutanediamine, N,N,N',N'-tetramethylhexanediamine, pentamethyldiethylenetriamine, tetramethyldiaminoethyl ether, bis(dimethylaminopropyl)urea, dimethylpiperazine, 1 ,2-dimethylimidazole, 1-azabicyclo[3.3.0]octane and preferably 1,4-diazabicyclo[2.2.2]octane, and alkanolamine compounds such as triethanolamine, triisopropanolamine, N-methyl- and N- ethyldiethanolamine and dimethylethanolamine. In a preferred embodiment, the nitrogen based catalysts comprise are reactive towards isocyanates. Preferred reactive catalysts are amine catalysts with an -OH, -NH or -NH2 function, such as ethylenediamine, triethanolamine, di- ephanomine, ethanolamine and dimethylethanolamine. Such reactive catalysts or “built-in cataysts” can be considered as compounds of both component (b) and component (c). and can be used to replace non-reactive amine catalysts if emissions are to be reduced.

Likewise useful are organic transition metal compounds, preferably organic tin compounds, such as tin(ll) salts of organic carboxylic acids, e.g. tin(ll) acetate, tin(ll) octoate, tin(ll) ethylhexoate and tin(ll) laurate, and the dialkyltin(IV) salts of organic carboxylic acids, for example dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate and dioctyltin diacetate, and also bismuth carboxylates such as bismuth(lll) neodecanoate, bismuth 2-ethylhexanoate and bismuth octanoate or mixtures thereof. The organic transition metal compounds can be used alone or preferably in combination with strongly basic amines.

In a preferred embodiment, catalysts (c) comprise catalysts that catalyze the trimerization of isocyanates by forming isocyanurate structures, also referred to as isocyanurate catalysts or trimerization catalysts. The following catalysts may be considered as catalysts for the trimerization reaction of the excess -NCO groups among each other: Catalysts forming isocyanurate groups are for example ammonium or alkali metal salts, especially ammonium or alkali metal carboxylates., in particular selected from the group consisting of potassium formiate, potassium acetate, potassium-2-ethylhexanoate, potassium octoate, potassium neodecanoate, potassium pivalate, potassium hexanoate and potassium sorbate.

In a preferred embodiment, the catalyst (c) contains at least one amine catalyst, for example triethylene diamine, and at least one organic transition metal catalyst, for example zinc neodecanoate and/or bismuth neodecanoate. Preferably, the catalyst (c) comprises in addition to the amine catalyst and the organic transition metal catalyst a trimerization catalyst, for example potassium acetate.

If catalysts (c) are used, these can by way of example be used at a concentration of from 0.001% to 5% by weight, in particular from 0.01 % to 1 % by weight, as catalyst or, respectively, catalyst combination, based on the weight of component (b).

Optionally, fillers and/or polyurethane additives (d) may be added to the mixture of components (a) to (c). It is possible to use any of the fillers and additives known for the production of polyurethanes. Examples here include surface-active substances, dyes, pigments, reinforcing fillers, liquid and solid flame retardants, water scavengers, hydrolysis stabilizers and oxidation stabilizers. Such compounds are well known in the art and disclosed for example in "Polyurethanes Handbook”, Carl Hanser Verlag, 2^nd edition 1994, chapter 3.4.4 and 3.4.6 to 3.4.11. In a preferred embodiment, the potting material according to the invention contains less than 30% by weight, more preferred less than 20% by weight, even more preferred less than 10% by weight and especially preferred less than 5% by weight, each based on the total weight of the potting material, of filler.

In addition, it is possible to add blowing agents known from the prior art as additives (d). However, it is preferable that no blowing agent is used, and more particularly that no water is added. Thus, components (a) and (b) more preferably do not comprise any blowing agent apart from residual water present in industrially produced polyols. In a preferred embodiment, components (b) and (c) comprise less than 0.2%, more preferred less than 0.1 % and especially preferred less than 0.05%, each based on the total weight of compounds (b) and (c), of water.

It is especially preferable when the residual water content is reduced by addition of water scavengers. Suitable water scavengers are, for example, zeolites. These water scavengers are used, for example, in an amount of 0.1 to 10% by weight, based on the total weight of the compounds having at least two isocyanate-reactive hydrogen atoms (b) (b).

If, as described above, no blowing agents are used, compact polyurethanes and not polyurethane foams are obtained as the inventive product. In a preferred embodiment the potting material according to the present invention comprises less than 5% by volume, preferably less than 3% by volume and especially preferred less than 1 % by volume of entrapped gas bubbles. This results in a preferred density of at least 900 g/cm³, more preferred 950 to 1200 g/cm³.

The starting components are typically mixed and reacted at a temperature of 0°C to 100°C, preferably 15°C to 60°C. The mixing can be effected with the customary PUR processing machines. In a preferred embodiment, the mixing is effected by low-pressure machines or high- pressure machines. Preferably the mixing is performed at an isocyanate index of 100 to 200, more preferred 103 to 200, even more preferred at 105 to 160, and even more preferred at 105 to 140 and especially preferred 115 to 140. The isocyanate index is defined as ratio of NCO groups of the isocyanate to the sum total of the reactive hydrogen atoms, an Isocyanate index of 100 relates to a ratio of NCO groups of the isocyanate to the sum total of the reactive hydrogen atoms of 1 :1.

In a preferred embodiment the two component process is used wherein all of the starting materials (a) to (d) are present either in the isocyanate component (A) or in the polyol component (B). It is preferable here that all of the substances that can react with isocyanate are added to the polyol component (B), while starting materials not reactive toward isocyanates can be added either to the isocyanate component (A) or to the polyol component (B). Isocyanate component (A) and polyol component (B) are mixed to form the reaction mixture. In a preferred embodiment isocyanate component (A) comprising polyisocyanates (a), and a polyol component (B) com- prising compounds (b) having at least two hydrogen atoms reactive toward isocyanate groups, catalyst (c) and fillers and/or polyurethane additives (d) are produced, and then isocyanate component (A) and polyol component (B), are mixed to give the reaction mixture.

For the production of the battery module according to the present invention the reaction mixture according to the present invention can flow through the gap between adjacent electric cells and settle at a level height around the electric cells and in the gap or spaces defined between the electric cells. For example, the potting composition may be poured into the battery case having the electric cells arranged within. Preferably, the liquid potting composition has sufficient flowability before curing to permit the liquid potting composition to flow through the spaces defined by the gap between the adjacent electric cells and/or between an electric cell and the battery case. In a preferred embodiment the liquid reaction mixture has sufficient flowability to settle at a substantially level height before curing to form the potting material. In an especially preferred embodiment, the theoretical viscosity of the reaction mixture at 40°C is less than 1000 mPas, more preferred less than 500 mPas and especially preferred less than 260 mPas. According to the invention, the theoretical viscosity r|(mix) of the reaction mixture is calculated from the viscosity r|(B) of the polyol component (B) comprising components (b) to (d) and the viscosity r|(A) of the isocyanate component (A) comprising component (a) according to the following formula: ln(r|(mix))=ln(r|(A)*parts(A)/(parts(A) + parts(B)) + ln(r|(B)*parts(B)/(parts(A) + parts(B)), wherein parts (A) stand for parts by weight of polyisocyanate component (A) and parts (B) stands for parts by weight of polyol component (B). The viscosity of the polyisocyanate component (A) and the polyol component (B) are each measured at a shear rate of 50s^-1 and 40°C with a cone and plate geometry.

In a preferred embodiment the electric cells are cleaned before brought into contact with the reaction mixture according to the present invention, for example by laser cleaning or plasma treatment. Furthermore, known adhesion promotors or known techniques to improve adhesion can be used.

The potting material according to the present invention shows superior mechanical properties as stiffness and elasticity over a broad temperature range. This can for example be observed in passing the climate change test for more than 10 cycles between -40°C and +80°C as disclosed in the examples section.

The invention will be illustrated below with reference to examples. Examples:

Raw materials:

Polyol 1 : polyalkylene glycol obtained by propoxylation and ethoxylation of glycerin having an OH-Number of 26 mgKOH/g and a propylene oxide content of 80 to 90% by weight based on the total weight of the alkylene oxide.

Polyol 2: polyalkylene glycol obtained by propoxylation of glycerin having an OH-

Number of 42 mgKOH/g

Polyol 3: polyalkylene glycol obtained by propoxylation of glycerin having an OH-

Number of 400 mgKOH/g

Polyol 4: polyalkylene glycol obtained by propoxylation of glycerin having an OH-

Number of 805 mgKOH/g

Polyol 5: polyalkylene glycol obtained by propoxylation of a mixture of biodiesel, glycerin and saccharose having an OH-Number of 420 mgKOH/g

Additive 1 : Water scavenger, K-Ca-Na-Zeolite in castor oil (50% by weight each)

Additive 2: Antifoaming agent polydimethylsiloxane

Catalyst 1: triethylene diamine (33% by weight) in dipropylene glycol (67% by weight) catalyst 2: transition metal catalyst based on bismuth and zinc

Catalyst 3: potassium acetate (40% by weight) in ethylene glycol (60% by weight)

Isocyanate 1 : MDI based prepolymer obtained by reaction of MDI and polypropylene glycol having an NCO content of 23% by weight.

Production of the samples

Test specimens were obtained by mixing the components according to table 1 at room temperature and pouring the reaction mixture in a mold. All data are given in parts by weight unless specified otherwise.

Table 1

Tensile strength, elongation at break and E-Modulus were determined according to ISO 527-3. The cyclic climate change test was performed as follows:

A fiberglass reinforced plastic (GFK) tube (75 mm internal diameter, 110 mm height; degreased with isopropanol) is sealed on one side. A cylindrical battery cell (Hilumin®-steel, 45 mm diameter, 100 mm height; degreased with isopropanol) is placed in the middle of the GFK tube on the sealed side. The mixed reaction mixture (speed mixer, 1600 rpm under vacuum (<300 bar), 60 seconds; components at room temperature) is poured into the gap between the battery cell and the inner wall of the GFK tube, achieving a fill height of exactly 90 mm. The composite is cured for at least 24 hours at atmospheric conditions. The test specimen is tested according to the following protocol in the climatic change test for about 14 days, with no cracks in the material or detachment from the battery cell allowed:

1) The test specimen is cooled at a rate of 2 K/min from room temperature to -40°C.

2) (C1) The material is held at -40°C for 10 hours. 3) (C2) Then, the material is heated at a rate of 2 K/min to +80°C over the period of one hour.

4) (C3) The material is held at +80°C for 10 hours.

5) (C4) The material is cooled at a rate of 2 K/min to -40°C over the period of one hour.

6) Steps C1-C4 are repeated for 14 cycles. In a 15th cycle, the material is cooled at a rate of 2 K/min from 80°C to room temperature. Then, the climatic change test is completed and the test specimen is visually inspected for damages. The sealed bottom side is also opened for this purpose.

It can be observed, that potting materials according to example 1 and 2 have good mechanical properties as tensile strength and elongation at break in a broad temperature interval from - 35°C to 60°C. In addition, the material according Example 1 passes the cyclic climate change test.

Claims

1. Battery module wherein the electric cells are potted into a potting material and the potting material is obtained by mixing a) one or more organic polyisocyanates, b) one or more compounds having at least two isocyanate-reactive hydrogen atoms c) one or more catalysts, d) optionally fillers and/or polyurethane additives to give a reaction mixture and allow the reaction mixture to cure wherein the compounds having at least two isocyanate-reactive hydrogen atoms comprise at least one polyetherpolyol (b1) having a functionality of 1.8 to 3 and a hydroxyl number of less than 140 mg KOH/g, at least one polyetherpolyol (b2) having a functionality of more than 3 to 6 and having a hydroxyl number of more than 180 mg KOH/g and optionally at least one polyether polyol (b3) having a functionality of 1.8 to 3 having a hydroxyl number of more than 200 mg KOH/g and optionally at least one chain extender (b4), wherein in addition to compounds (b1), (b2), (b3) and (b4) less than 20% by weight of compounds having at least two isocyanate-reactive hydrogen atoms, based on the total amount of compounds having at least two isocyanate-reactive hydrogen atoms (b) are added, in case that a filler is added, the amount of a filler material is less than 20 % by weight, based on the total weight of the potting material and wherein the components to obtain the reaction mixture are mixed at an isocyanate index of 100 to 200.

2. Battery module according to claim 1 wherein the polyetherol (b1), the polyetherol (b2) and, if present, the polyetherpolyol (b3) comprise more than 70% by weight of propylene glycol units, based on the total amount of alkylene oxide units in polyetherols (b1), (b2) and (b3).

3. Battery module according to claim 1 or 2, wherein the amount of polyetherol (b1) is 15% to 60% by weight, of polyetherol (b2) is 35% to 80% by weight, of polyetherpolyol (b3) is 0% to 25% by weight and of chain extender (b4) is 0% to 20% by weight, each based on the total weight of compound (b).

4. Battery module according to any of claims 1 to 3, wherein the density of the potting material is at least 900 g/cm³ (900 kg/m³)

5. Battery module according to any of claims 1 to 4 wherein the components to obtain the reaction mixture are mixed at an isocyanate index of 105 to 160.

6. Battery module according to any of claims 1 to 5 wherein the catalyst (c) comprises an amine based catalyst and a metal based catalyst.

7. Battery module according to claim 6 wherein the catalyst (c) comprises a trimerization catalyst.

8. Battery module according to any of claims 1 to 7 wherein the isocyanate (a) comprises methylene diphenylene diisocyanate (MDI) or its prepolymers.

9. Battery module according to any of claims 1 to 8 wherein the potting material has a E- Modulus at -35°C of more than 1500 MPa and a E-Modulus at 60°C of at least

500 MPa, an elongation at break at -35°C of at least 5% and at 60°C of at least 10% and a tensile strength at -35°C of at least 15 MPa and at 60°C of at least 15 MPa.

10. Method of producing a battery module wherein the electric cells are potted into a potting material comprising the steps of providing battery case having the electric cells arranged within defining spaces between the adjacent electric cells, obtaining a reaction mixture as defined in any of claims 1 to 9, puring the reaction mixture into the battery and allowing the reaction mixture to cure.