Insulator for battery cells

Abstract

The present invention relates to an insulating layer suitable for use in battery cells, to the use of such layer for insulating adjacent battery cells, and to battery cells stacks comprising the same, wherein said battery cells are preferably pouch cells.

Description

DescriptionInsulator for battery cellsCross-reference to related patent application

[0001] This application claims priority filed on 2024-06-06 in Europe with Nr. 24180560.5, the whole content of this application being incorporated herein by reference for all purposes.Technical Field

[0002] The present invention relates to an insulating layer suitable for use in battery cells, to the use of such layer for insulating adjacent battery cells and to battery cells stacks comprising the same, wherein said battery cells are preferably pouch cells.Background Art

[0003] Nowadays, electric vehicles are spreading and lithium batteries having increased and faster charging capacity are required by car manufacturers. More in detail, in the automotive industry, pouch cells are used due to their high energy density and lightweight design. In addition, pouch cells are also widespread in the consumer electronics industry, in particular for use in smartphones, tablets and laptops.

[0004] At the same time, the safety of lithium batteries is more than ever a need.

[0005] Indeed, when a battery is charged with a known amount of energy, the exact same energy is not being delivered during discharge in the form of electrical energy. There are always losses, in which the energy is released into the environment in the form of heat.

[0006] To prevent the enormous heat transfer between a failed cell to its neighbouring cell or other modules, insulator materials need to be installed, which might be difficult in view of the little space available in the battery stack.

[0007] The issue of thermal runaway has been known for a long time and has been addressed in different ways. Polyurethane foams have been used for a long time, and more recently silicon-based foams have been introduced.

[0008] For example, US 2012 / 0003508 (in the name of SAFT) discloses the use of a rigid, flame-retardant foam formed of an electrically insulating material filling the space between the inner wall of a casein and the free surface of the case wall. Such foam consists of a material chosen from polyurethane, epoxy, polyethylene, melamine, polyester, formophenol, polystyrene, silicone or a mixture thereof.

[0009] Thermally insulating sheets have been disclosed for example in US 2021 / 257690 and US 2024 / 0088483 (both in the name of Rogers Corporation). The latter discloses a multilayer sheet for preventing thermal runaway includes a nonporous elastomeric barrier layer having a first and a second opposed surface, a flexible foam layer disposed on the first surface of the barrier layer and a flame retardant component isdistributed within the flexible foam layer, contacts a surface of the flexible foam layer, or both.

[0010] Also, WO 2022 / 192213 (in the name of Rogers Corporation) discloses a composite thermal management sheet for a battery, including a silicone foam layer and a reactive filler composition disposed within the silicone foam layer.

[0011] Fluoroelastomer compositions are known in the art.

[0012] For example, WO 2017 / 046379 (in the name of Solvay Specialty Polymers Italy S.p.A.) discloses a fluoroelastomer composition comprising:(a) a vinylidene fluoride-based fluoroelastomer comprising recurring units derived from vinylidene fluoride (VDF) and recurring units derived from at least one additional (per)fluorinated monomer; said fluoroelastomer being characterised by a certain polydispersity index (IMWD), by the amount of polar end groups and by the type of its chain end groups,(b) at least one polyhydroxylated curing agent;(c) at least one accelerant; and(d) at least one metal oxide selected from the group consisting of divalent metal oxides.Optionally, such fluoroelastomer comprises at least one metal hydroxide, which - when present - is in an amount below 3 phr, based on 100 weight parts of fluoroelastomer.Such fluoroelastomer composition is said to be useful for manufacturing cured articles, such as pipes, joint, O-rings , hoses and the like.

[0013] US 5883197 (in the name of Ausimont Spa) discloses compositions based one elastomeric polymers of VDF, HFP and optionally TFE, suitable for providing microcellular foamed vulcanized articles by extrusion or compression moulding. The composition disclosed in this document is very specific and comprises the copolymer, bisphenol AF, a quaternary phosphonium of aminophosphonium salt, azodicarbonamide, MgO, Ca(OH)2, zinc stearate and a plasticizer, each of the components being contained in an exactly defined proportion.This document teaches specific compositions. However, it does not disclose the use of barium sulphate and does not suggest its use. Furthermore, this document does not teach to select a proper thickness of the microcellular foamed article, not its use in pouch cells.Summary of invention

[0014] In this frame, the Applicant perceived that as lithium batteries are becoming more efficient, the requirements for insulators and insulating materials are increasing.

[0015] Hence, the Applicant faced the problem of providing an insulating material that is suitable for use in pouch cells stacks, easy to manufacture at industrial scale and which provides outstanding thermal insulation.

[0016] More in particular, the Applicant surprisingly found (per)fluoroelastomers can be used to manufacture foam sheets having a thickness below 5 mm, which are able to prevent or delay the thermal runaway in battery stacks without the need of adding flame retardants or other additives.

[0017] In addition, the Applicant surprisingly found that such foam sheets are compressible, thus allowing the volume changes of pouch cells during charge and discharge cycles.Brief description of drawings

[0018] Fig. 1 is a side view of an exemplary battery system.Description of embodiments

[0019] In the present application and in the following claims:- any description, even though described in relation to a specific embodiment, is applicable to and interchangeable with other embodiments of the present invention;- any recitation herein of numerical ranges by endpoints includes all numbers subsumed within the recited ranges as well as the endpoints of the range and equivalents;- the term “foam” is intended to indicate a material having a flexible and cellular structure, for example characterised by a density lower that 900 kg / m3(as measured according to ASTM D3574), and / or a void volume content greater than 15%, preferably greater than 25% based on the total volume of the foam;- the term “fluoroelastomer” is intended to indicate a fluoropolymer resin serving as a base constituent for obtaining a true elastomer, said fluoropolymer resin comprising more than 10 % wt, preferably more than 30 % wt, of recurring units derived from at least one ethylenically unsaturated monomer comprising at least one fluorine atom (hereafter, (per)fluorinated monomer) and, optionally, recurring units derived from at least one ethylenically unsaturated monomer free from fluorine atom (hereafter, hydrogenated monomer). True elastomers are defined by the ASTM, Special Technical Bulletin, No. 184 standard as materials capable of being stretched, at room temperature, to twice their intrinsic length and which, once they have been released after holding them under tension for 5 minutes, return to within 10 % of their initial length in the same time. Fluoroelastomers are in general amorphous products or products having a low degree of crystallinity (crystalline phase less than 20 % by volume) and a glass transition temperature (Tg) below room temperature. In most cases, the fluoroelastomer (A) has advantageously a Tg below 10° C, preferably below 5°C, more preferably 0°C, even more preferably below - 5°C.- the term “alkyl”, as well as derivative terms such as “alkoxy”, “acyl” and “alkylthio” include straight chain, branched chain and cyclic moieties. Examples of alkyl groups are methyl, ethyl, 1 -methylethyl, propyl, 1 ,1 dimethylethyl, and cyclo-propyl. Unless specifically stated otherwise, each alkyl and aryl group may be unsubstituted or substituted with one or more substituents selected from but not limited to halogen, hydroxy, sulfo, Ci-Ce alkoxy, Ci-Ce alkylthio, Ci-Ce acyl, formyl, cyano, Ce-Cis aryloxy or Ce-Cis aryl, provided that the substituents are sterically compatible and the rules of chemical bonding and strain energy are satisfied;- the term “halogen” or “halo” includes fluorine, chlorine, bromine and iodine, with fluorine being preferred;- the term “aryl” refers to a phenyl, indanyl or naphthyl group. The aryl group may comprise one or more alkyl groups, and are called sometimes in this case “alkylaryl”; for example may be composed of an aromatic group and two Ci-Ce groups (e.g. methyl or ethyl). The aryl group may also comprise one or more heteroatoms, e.g. N, 0 or S, and are sometimes called ” heteroaryl” group; these heteroaromatic rings may be fused to other aromatic systems. Such heteroaromatic rings include, but are not limited to furanyl, thienyl, pyrrolyl, pyrazolyl, imidazolyl, triazolyl, isoxazolyl, oxazolyl, thiazolyl, isothiazolyl, pyridyl, pyridazyl, pyrimidyl, pyrazinyl and triazinyl ring structures. The aryl or heteroaryl substituents may be unsubstituted or substituted with one or more substituents selected from but not limited to halogen, hydroxy, Ci-Ce alkoxy, sulfo, Ci-Ce alkylthio, Ci- Ce acyl, formyl, cyano, C6-C15 aryloxy or C6-C15 aryl, provided that the substituents are sterically compatible and the rules of chemical bonding and strain energy are satisfied;- “mol %” of each recurring unit is relative to the total number of moles of recurring units in the polymer, unless explicitly indicated otherwise;- the expression “(per)fluorinated monomer” is intended to indicate a partially or fully fluorinated monomer; and- the expression “derived from” refers to the recurring unit formed from the reaction of the recited monomer.

[0020] Thus, in a first aspect the present invention relates to a foam sheet [sheet (P)] having a thickness lower than 5.0 mm, preferably from about 0.9 mm to about 4.9 mm, and comprising:(i) a fluoroelastomer composition comprising:(a) at least a vinylidene-based fluoroelastomer [fluoroelastomer (A)] comprising recurring units derived from vinylidene fluoride and at least one other (per)fluorinated monomer [monomer (F)];(b) at least one polyhydroxylated curing agent;(c) at least one accelerant; and(ii) at least two mineral fillers, wherein at least one mineral filler is barium sulphate in an amount of at least 0.1 phr and of at most 9.0 phr based on 100 weight parts (phr) of said fluoroelastomer composition (i).

[0021] Preferably, said fluoroelastomer (A) comprises at least 15 % moles, preferably at least 20 % moles, more preferably at least 35 % moles of recurring units derived from VDF, with respect to all recurring units of the fluoroelastomer.

[0022] Preferably, fluoroelastomer (A) comprises at most 85 % moles, preferably at most 80 % moles, more preferably at most 78 % moles of recurring units derived from VDF, with respect to all recurring units of the fluoroelastomer.

[0023] Preferably, said monomer (F) is selected from:(a) C2-C8 perfluoroolefins, such as tetrafluoroethylene (TFE) and hexafluoropropylene (HFP);(b) hydrogen-containing C2-C8 olefins different from VDF, such as vinyl fluoride (VF), trifluoroethylene (TrFE), perfluoroalkyl ethylenes of formula CH2 = CH-Rf, wherein Rf is a Ci-Ce perfluoroalkyl group;(c) C2-C8 chloro and / or bromo and / or iodo-fluoroolefins such aschlorotrifluoroethylene (CTFE);(d) (per)fluoroalkylvinylethers (PAVE) of formula CF2=CFORf, wherein Rf is a Ci-Ce (per)fluoroalkyl group, e.g. CF3, C2F5, C3F7;(e) (per)fluoro-oxy-alkylvinylethers of formula CF2 = CFOX, wherein X is a C1-C12 ((per)fluoro)-oxyalkyl comprising catenary oxygen atoms, e.g. the perfluoro-2-propoxypropyl group;(f) (per)fluorodioxoles having formula :wherein Rf3, Rf4, Rfs, Rf6, equal or different from each other, are independently selected among fluorine atoms and Ci-Ce (per)fluoroalkyl groups, optionally comprising one or more than one oxygen atom, such as notably -CF3, -C2F5, -C3F7, -OCF3, -OCF2CF2OCF3; preferably, perfluorodioxoles;(g) (per)fluoro-methoxy-vinylethers (MOVE, hereinafter) having formula: CFX2= CX2OCF2OR"f wherein R"f is selected among Ci-Ce (per)fluoroalkyls, linear or branched; Cs-Ce cyclic (per)fluoroalkyls; and C2-C6 (per)fluorooxyalkyls, linear or branched, comprising from 1 to 3 catenary oxygen atoms, and X2 = F, H; preferably X2is F and R"f is -CF2CF3 (M0VE1 ); -CF2CF2OCF3 (M0VE2); or -CF3(M0VE3).

[0024] It is generally preferred for the fluoroelastomer (A) to comprise, in addition to recurring units derived from VDF, recurring units derived from HFP.

[0025] In this case, fluoroelastomer (A) typically comprises at least 10 % moles, preferably at least 12 % moles, more preferably at least 15 % moles of recurring units derived from HFP, with respect to all recurring units of the fluoroelastomer.

[0026] Still, fluoroelastomer (A) typically comprises at most 45 % moles, preferably at most 40 % moles, more preferably at most 35 % moles and even more preferably at most 25 % moles of recurring units derived from HFP, with respect to all recurring units of the fluoroelastomer.

[0027] Said fluoroelastomers (A) may comprise, in addition to recurring units derived from VDF and HFP, one or more of the followings:- recurring units derived from at least one bis-olefin [bis-olefin (OF)] having general formula : wl or different from each other, are H, a halogen, or a C1-C5 optionally halogenated group, optionallycomprising one or more oxygen group; Z is a linear or branched C1-C18 optionally halogenated alkylene or cycloalkylene radical, optionally containing oxygen atoms, or a (per)fluoropolyoxyalkylene radical;- recurring units derived from at least one (per)fluorinated monomer different from VDF and HFP; and- recurring units derived from at least one hydrogenated monomer.

[0028] Examples of hydrogenated monomers are notably non-fluorinated alphaolefins, including ethylene, propylene, 1 -butene, diene monomers, styrene monomers, alpha-olefins being typically used. C2-C8 non-fluorinated alphaolefins (Ol), and more particularly ethylene and propylene, will be selected for achieving increased resistance to bases.

[0029] The bis-olefin (OF) is preferably selected from the group consisting of those complying with formulae (OF-1 ), (OF-2) and (OF-3) :(OF-1 )wherein j is an integer between 2 and 10, preferably between 4 and 8, and R1 , R2, R3, R4, equal or different from each other, are H, F or C1-5 alkyl or (per)fluoroalkyl group;(OF-2)wherein each of A, equal or different from each other and at each occurrence, is independently selected from F, Cl, and H; each of B, equal or different from each other and at each occurrence, is independently selected from F, Cl, H and ORB, wherein RB is a branched or straight chain alkyl radical which can be partially, substantially or completely fluorinated or chlorinated; E is a divalent group having 2 to 10 carbon atom, optionally fluorinated, which may be inserted with ether linkages; preferably E is a - (CF2)m- group, with m being an integer from 3 to 5; a preferred bis-olefin of (OF-2) type is F2C=CF-O-(CF2)5-O-CF=CF2.(OF-3)wherein E, A and B have the same meaning as above defined; R5, R6, R7, equal or different from each other, are H, F or C1-5 alkyl or (per)fluoroalkyl group.

[0030] Most preferred fluoroelastomers (A) are those having the following compositions (in mol %) :(i) vinylidene fluoride (VDF) 45-85%; hexafluoropropene (HFP) 15- 45 %; tetrafluoroethylene (TFE) 0-30 %;(ii) vinylidene fluoride (VDF) 20-30%; hexafluoropropene (HFP) 18-27 %; C2-C8 non-fluorinated olefins (Ol) 5-30 %; perfluoroalkyl vinyl ethers (PAVE) 0-35 %; bis-olefin (OF) 0-5 %;(iii) vinylidene fluoride (VDF) 60-75 %; hexafluoropropene (HFP) 10- 25%; tetrafluoroethylene (TFE) 0-20 %; perfluoroalkyl vinyl ethers (PAVE) 1 -15 %.

[0031] Preferably, said fluoroelastomer (A) comprises an amount of polar end groups of at least 5 mmol / kg and at most 12 mmol / kg.

[0032] The amount of polar end groups of formula -CF2CH2OH is determined by NMR, following the methodology which is notably described in PIANCA, Maurizio, et al. End groups in fluoropolymers. Journal of Fluorine Chemistry. 1999, vol.95, p.71-84.

[0033] Said fluoroelastomer composition comprises (b) at least one polyhydroxylated curing agent.

[0034] Aromatic or aliphatic polyhydroxylated compounds, or derivatives thereof, may be used as polyhydroxylated curing agents; examples thereof are described, notably, in EP 335705 (MINNESOTA MINING) and US 4233427 (RHONE POULENC IND).

[0035] Among these, mention will be made in particular of dihydroxy, trihydroxy and tetrahydroxy benzenes, naphthalenes or anthracenes; bisphenols of formula (B):wherein:- Z' is selected from the group consisting of bivalent C1-C13 alkyl or alkylidene group, C4-C13 cycloaliphatic, C6-C13 aromatic or arylalkylenic groups, optionally substituted with at least one chlorine or fluorine atom; a thio (-S-), oxy (-O-), carbonyl (-C(O)-), sulphinyl (-S(O)-) and sulphonyl group (-SO2-);- x is 0 or 1 ;- u, equal to or different from each other, is independently at each occurrence an integer of at least 1 , preferably 1 or 2;- and wherein the phenyl rings can be optionally substituted by one or more substituents selected from the group consisting of chlorine, fluorine, bromine; -CHO, Ci-Cs alkoxy groups, -COOR10 groups, wherein R10 is H or Ci-Cs alkyl, C6-C14 aryl, C4-C12 cycloalkyl.

[0036] When Z' is a C1-C13 divalent alkyl group, it can be for example methylene, ethylene, chloroethylene, fluoroethylene, difluoroethylene, 1 ,3-propylene, tetramethylene, chlorotetramethylene, fluorotetramethylene, trifluorotetramethylene, 2-methyl-1 ,3-propylene, 2-methyl-1 ,2-propylene, pentamethylene, hexamethylene.When Z' is a C1-C13 divalent alkylidene group, it can be for example ethylidene, dichloroethylidene, difluoroethylidene, propylidene,isopropylidene, trifluoroisopropylidene, hexafluoroisopropylidene, butylidene, heptachlorobutylidene, heptafluorobutylidene, pentylidene, hexylidene, 1 ,1 -cyclohexylidene.When Z' is C4-C13 cycloaliphatic group, it can be for example 1 ,4- cyclohexylene, 2-chloro-1 ,4-cyclohexylene, 2-fluoro-1 ,4-cyclohexylene, 1 ,3-cyclohexylene, cyclopentylene, chlorocyclopentylene, fluorocyclopentylene, and cycloheptylene.When Z' is a C6-C13 aromatic or arylalkylenic group, it can be for example m-phenylene, p-phenylene, 2-chloro-1 ,4-phenylene, 2-fluoro-1 ,4- phenylene, o-phenylene, methyl phenylene, dimethylphenylene, trimethylphenylene, tetramethyl phenylene, 1 ,4-naphthylene, 3-fluoro-1 ,4- naphthylene, 5-chloro-1 ,4-naphthylene, 1 ,5-naphtylene and 2,6- naphthylene.

[0037] Among the polyhydroxylated curing agents of formula (B), hexafluoroisopropylidene bis (4-hydroxybenzene), known as bisphenol AF, 4,4'-dihydroxydiphenyl sulfone and isopropylidene bis (4-hydroxybenzene), known as bisphenol A, are preferred, with Bisphenol AF being particularly preferred.

[0038] Other polyhydroxylic curing agents are dihydroxy benzenes selected from the group consisting of catechol, resorcinol, 2-methyl resorcinol, 5-methyl resorcinol, hydroquinone, 2-methyl hydroquinone, 2,5-dimethyl hydroquinone, 2-t-butyl hydroquinone, and dihydroxy naphthalenes, in particular 1 ,5-dehydroxynaphthalene.

[0039] It is also understood that derivatives of aforementioned aromatic or aliphatic polyhydroxylated compounds can be used; mention can be notably made of metal salts formed by the anion of said aromatic or aliphatic polyhydroxylated compounds wherein one or more of the hydroxyl group has been deprotonated, with one or more than one cation (as required for reaching neutrality) of a metal, typically of an alkaline or alkaline earth metal; examples thereof are notably the dipotassium salt of bisphenol AF and the monosodic monopotassium salt of bisphenol AF.

[0040] In addition, -onium hydroxylates, i.e. salts formed by the anion of said aromatic or aliphatic polyhydroxylated compounds wherein one or more of the hydroxyl group has been deprotonated, with one or more -onium cation can also be used. As cations, all the cations corresponding to the above - onium organic derivatives accelerant component c) can be used.

[0041] The amount of the polyhydroxylated curing agent is generally of at least 0.5 phr, preferably at least 1 phr, and / or generally at most 15 phr, preferably at most 10 phr, with respect to the weight of fluoroelastomer (A).

[0042] Said fluoroelastomer composition comprises (c) at least one accelerant.

[0043] Accelerants for ionic curing of VDF-based fluoroelastomers are well known in the art.

[0044] Said at least one accelerant is generally selected in the group consisting of organic onium compounds, amino-phosphonium derivatives, phosphoranes, imine compounds.

[0045] Preferably, amino-phosphonium derivatives comply with formula (AP-1 ) or (AP-2):{[P(NR6R7)nR84-n]+}qYq- (AP-1 ){[R83-r(NR6R7)rP-E-P(NR6R7)rR83-r]2+}{Yq-}2 / q (AP-2)wherein:- each of R6, R7and R8, equal to or different from each other, is independently selected from the group consisting of:C1-C18 alkyl group (preferably C1-C12 alkyl group); C4-C7 cycloalkyl group;C6-C18 aryl group (preferably C6-C12 aryl group); Ce-C arylalkyl group (preferably C6-C12 arylalkyl group);C1-C18 oxyalkyl group comprising one or more than one hydroxyl or oxygen ethereal group; and wherein R6, R7and R8can optionally contain halogens, CN, OH, carbalkoxy groups; wherein R6and R7can form with the nitrogen atom an heterocyclic ring;- E is a Ci-Ce divalent alkylenic, oxyalkylenic or C6-C12 arylenic radical;- n is an integer from 1 to 4;- r is an integer from 1 to 3;- q is the valence of the anion Y, and is preferably an integer from 1 to 2;- Y is an organic or inorganic anion having valence q; Y can be selected from halides, perchlorate, nitrate, tetrafluoroborate, hexafluorophosphate, oxalate, acetate, stearate, haloacetate, para-toluensulphonate, phenate, bisphenate, hydroxide; Y can also be a complex anion for example ZnCl42-, CdCI42-, NiBr42-, Hgh-.

[0046] Preferably, phosphoranes comply with formula (P):wherein:- each of Ar’, equal to or different from each other, is a optionally substituted aryl group, preferably an optionally substituted phenyl group or an optionally substituted naphthyl group;- each of R10and R11, equal to or different from each other, is independently selected from the group consisting of -H, -CN, Ci-Cs alkyl, - O-C(O)-R12group, -C(O)-R12group, -NR13-C(O)-R12 group, with R12 being a Ci-Ce (cyclo)alkyl group, and R13 being H or a Ci-Ce (cyclo)alkyl group, R10and R11possibly forming together with the carbon atom of the P=C bond a cyclic group.

[0047] Preferably, imine compounds comply with formula (I) :[(Rl4)3p=N =p(R14)3 }zXz-(|) wherein:- R14, equal to or different from each other at each occurrence, is selected from the group consisting of C1-C12 hydrocarbon groups, optionally comprising one or more than one group including a heteroatom selected from the group consisting of 0, N, S, halogen;- X is an anion of valence z, with z being an integer, generally 1 or 2.

[0048] The amount of the accelerant is generally of at least 0.05 phr, preferably at least 0.1 phr, and / or generally at most 10.0 phr, preferably at most 5.0 phr, with respect to the weight of fluoroelastomer (A).

[0049] Preferably, the at least one other mineral filler is selected from the group comprising: metal oxide, metal hydroxide, metal sulphates and silicates.

[0050] Preferably, said metal oxides are selected in the group comprising: ZnO, MgO, PbO, TiCh.ZrCh, and mixtures thereof.

[0051] Preferably, said metal hydroxides are selected from Ca(OH)2, Sr(OH)2, Ba(OH)2 and mixtures thereof.

[0052] Preferably, said metal sulphate is selected from barium sulphate.

[0053] Preferably, said silicate is selected from wollastonite, vermiculite, zeolite, silica, barite, mica, and mixtures thereof.

[0054] Preferably, the amount of the metal oxide is of at least 0.5 phr, more preferably at least 1 .0 phr and even more preferably at least 1 .5 phr, and / or at most 8.0 phr, preferably at most 7.0 phr, more preferably at most 5.0 phr, based on 100 weight parts (phr) of said fluoroelastomer composition.

[0055] More preferably, the amount of metal oxide is from 0.5 phr to 8.0 phr, even more preferably from 1 .5 phr to 6.0 phr based on 100 weight parts (phr) of said fluoroelastomer composition.

[0056] Preferably, the amount of metal hydroxide is at least 0.1 phr, more preferably at least 0.7 phr, and / or at most 8.0 phr, preferably at most 5.0 phr based on 100 weight parts (phr) of said fluoroelastomer composition.

[0057] Preferably, the amount of said metal sulphate is at least 0.1 phr, more preferably at least 0.5 phr, and / or at most 9.0 phr, more preferably at most 5.0 phr based on 100 weight parts (phr) of said fluoroelastomer composition.

[0058] Preferably, the amount of said silicate is at least 0.1 phr, more preferably at least 0.5 phr, and / or at most 9.0 phr, more preferably at most 5.0 phr based on 100 weight parts (phr) of said fluoroelastomer composition.

[0059] According to a preferred embodiment, sheet (P) comprises at least three mineral fillers, as defined above.

[0060] Without being bound by any theory, the mineral fillers can be advantageously selected based on their inherent properties, for example based on their inherent hardness and / or thermal resistance.

[0061] According to a preferred embodiment, sheet (P) comprises a first mineral filler having a Mohs’ hardness higher than 5, for example higher than 5.5 and more preferably between 5.5 and 7.5, and at least one other mineral filler having a Mohs’ hardness equal to or lower than 5.

[0062] The ‘Mohs’ hardness’, also referred to as ‘Mohs’ scale’ or ‘Mohs’ scale of mineral hardness’, is one measure of hardness used in materials science, which provides an index of the relative measure of mineral hardness in terms of resistance to abrasion. The scale characterises mineral harness from 1 to 10, based on a harder mineral’s ability to scratch a softer mineral. Exemplary materials are talc for Mohs’ hardness equal to 1 and diamond for Mohs’ hardness equal to 10.

[0063] Preferably, said first mineral filler having a Mohs’ hardness higher than 5 is selected from MgO, TiO2, ZrO2 and mixtures thereof.

[0064] Preferably, the amount of said mineral filler having a Mohs’ hardness higher than 5 is from 1.0 phr to 9.0 phr, based on 100 phr of said fluoroelastomer composition.

[0065] Preferably, said at least one other mineral filler having a Mohs’ hardness equal to or lower than 5 is barium sulphate.

[0066] Preferably, at least one other mineral filler having a Mohs’ hardness equal to or lower than 5 is present in the foam sheet. Preferably, said at leastone other mineral filler having a Mohs’ hardness equal to or lower than 5 is selected from Ca(0H)2, wollastonite, vermiculite, zeolite, silica, barite, mica, and mixtures thereof.

[0067] Preferably, the amount of said at least one other mineral filler having a Mohs’ hardness equal to or lower than 5 is from 0.1 phr to 15.0 phr, more preferably from 0.5 phr to 12.0 phr and even more preferably from 1 .0 phr to 9.0 phr, based on 100 phr of said fluoroelastomer composition.

[0068] According to a preferred embodiment, the total amount of mineral fillers in sheet (P) is below 20.0 phr, more preferably below 18.0 phr, even more preferably below 15.0 phr, and still more preferably below 12.0 phr based on 100 phr of the fluoroelastomer composition.

[0069] An advantage of the composition of the present invention is provided by the limited amount of mineral fillers that is added to the composition, as described herein above.

[0070] Indeed, while the mineral fillers are required to reinforce the elastomer composition, their presence can negatively affect the density or the mechanical properties of the final foamed article as well as the curing process of the same (for example, curing time, scorch time and aging properties). As a consequence, finding a balance between the need for reinforcement provided by the mineral fillers and their limited amount in the composition is of high interest.

[0071] Furthermore, a limited amount of mineral fillers allows to reduce the overall environmental impact of the composition and its overall cost.

[0072] According to certain preferred embodiments, sheet (P) is substantially free from fluorinated surfactants, which means that either said fluorinated surfactants are absent, or are comprised in an amount of not exceeding 100 ppm, preferably not exceeding 50 ppm, more preferably not exceeding 10 ppm, with respect to the weight of the fluoroelastomer composition.

[0073] According to these preferred embodiments, fluoroelastomer (A) is obtained from emulsion polymerization in the absence of added fluorinated surfactant.

[0074] According to a preferred aspect, sheet (P) according to the present invention is obtained from a composition [composition (C)] comprising:(i) a fluoroelastomer composition comprising:(a) a vinylidene-based fluoroelastomer [fluoroelastomer (A)] comprising recurring units derived from vinylidene fluoride and at least one other (per)fluorinated monomer [monomer (F)],(b) at least one polyhydroxylated curing agent, and(c) at least one accelerant;(ii) at least one mineral filler; and(iii) at least one blowing agent.

[0075] Such fluoroelastomer composition, fluoroelastomer (A), polyhydroxylated curing agent, accelerant and mineral filler are as described above.

[0076] Preferably, said at least one blowing agent is selected from chemically- acting blowing agents and physically-acting blowing agents.

[0077] Preferably, said chemically-acting blowing agent is selected from microspheres, azodicarbonamide and benzenesulphonohydrazide.

[0078] Preferably, said physically-acting blowing agent is selected from liquefied gas or supercritical.

[0079] According to a preferred embodiment, said blowing agent has a decomposition temperature below 220°C, preferably below 200 °C and more preferably below 170 °C.

[0080] According to a preferred embodiment, composition (C) is substantially free from fluorinated surfactants, which means that either said fluorinated surfactants are absent, or are comprised in an amount of not exceeding 100 ppm, preferably not exceeding 50 ppm, more preferably not exceeding 10 ppm, with respect to the weight of the fluoroelastomer composition.

[0081] According to this preferred embodiment, fluoroelastomer (A) is obtained from emulsion polymerization in the absence of added fluorinated surfactant.

[0082] Composition (C) is preferably manufactured via methods known in the art. For example, as described in WO 2017 / 046379 (in the name of Solvay Specialty Polymers Italy S.p.A.).

[0083] The method for manufacturing the foam sheet (P) according to the present invention is not limited.

[0084] For example, a composition [composition (C1 )] comprising the fluoroelastomer composition and the at least one mineral filler as defined above is blended with at least one blowing agent.

[0085] When microspheres are used, such microspheres can be contacted with composition (C1) as defined above, via any suitable method, for example by injection moulding.

[0086] When a physically-acting blowing agent is used, composition (C1 ) can be physically foamed with a supercritical fluid, preferably with supercritical CO2.

[0087] Accordingly, composition (C) according to the present invention is then used to manufacture foam pads.

[0088] The method for manufacturing the foam pads according to the present invention is not limited.

[0089] Suitable methods comprise for example compression moulding, injection moulding and the like.

[0090] In a further aspect, and in particular by reference to Figure 1 , the present invention relates to a battery system 1 comprising:- a battery block comprising at least two stacked battery cells 2;- fastening components 3 that hold said at least two battery cells, comprising (i) a pair of endplates 4, each disposed at one end of said at least two battery cells, and (ii) metal bands 5 disposed at the battery block side-walls extending in the stacking direction of the battery cells and connected at both ends to the endplates 4; wherein at least one sheet (P) 6 as above defined is interposed between said at least two battery cells.

[0091] According to a preferred embodiment, said at least two battery cells are pouch cells.

[0092] Advantageously, sheet (P) according to the present invention provides for an insulating layer capable of withstanding very high temperatures, notably from 200 to 600 °C or even higher, for 30-60 minutes, thus allowing to delay or even prevent the thermal runaway from the failed cell to its neighbouring cell or other modules, while, at the same time, said sheet (P) is capable of being compressed if the pouch cells swell during the chargingcycles and returns to its previous thickness when the pouch cells shrink during the discharging cycles.

[0093] In a further aspect, the present invention relates to the use of said sheet (P) as above defined, for the manufacture of a battery system comprising at least two battery cells, wherein said at least one sheet (P) is interposed between said at least two battery cells of said battery system.

[0094] According to a preferred embodiment, said at least two battery cells are pouch cells.

[0095] Advantageously, said sheet (P) has a thickness of from about 1 .0 to 4.7 mm, preferably from 1 .1 to 4.5 mm and more preferably from 1 .2 to 4.2 mm. Even more preferably, sheet (P) has a thickness from 1 .5 to 4.0 mm.

[0096] Without being bound by any theory, the thickness of the sheet (P) is of particular importance when the sheet (P) is used in a battery stack wherein the batteries are pouch cells. Indeed, a thickness below 0.9 or 1 .0 mm, such as for example in the range of micrometres as disclosed in certain prior art documents, could be not sufficient to provide the required mechanical strength to the sheet (P) of the invention.

[0097] Sheet (P) according to the present invention is not restricted in use within a specific battery system. However, it is advantageously used in a battery system comprising pouch cells.

[0098] Fig. 1 shows an exemplary battery system comprising sheet (P) according to the present invention, wherein the shape, dimension and thickness of the different parts are not scaled to each other.

[0099] Referring to Fig. 1 , the battery system comprises a battery block 1 having a plurality of stacked battery cells 2 and fastening components 3 that hold the battery cells 2 of the battery block 1 . Preferably, the battery cells 2 are lithium ion batteries. However, other types of batteries can be used depending on the circumstances. Preferably, the battery cells 2 are pouch cells. In Fig. 1 , said battery cells 2 are represented as rectangular batteries. However, batteries having other shapes and disposed in different configurations can be provided. The battery cells 2 are held in a fixed position by the fastening components 3, which comprise a pair of endplates 4 disposed at the end of the stacked battery cells 2 and metal bands 5 connected to said end plates 4 to hold the battery stack in a compressed state.

[0100] Optionally, a pair of side plates (not represented in Fig. 1 ) can be disposed at the side-walls of the battery block 1 , extending in the stacking direction of the battery cells 2 and connected with said end plates 4 or said metal bands 5.

[0101] As represented in Fig. 1 , the endplates 4 have a rectangular shape that is the same shape of the battery cells 2. It is preferred that the endplates 4 are of the same shape and dimension of the battery cells 2 (or slightly larger) so that the endplates 4 connected by the metal bands 5 do not distort and can hence prevent the expansion at the centre region of the battery cells 2. However, the endplates 4 can be provided of any shape and dimension, depending on the shape and dimension of the battery cells 2 and on the final use for which the battery system 1 is intended.

[0102] Preferably, the endplates 4 are made of metal, such as aluminium or an alloy of aluminium, or from a plastic resin, more preferably a thermoplastic resin.

[0103] As represented in Fig. 1 , the sheet (P) 6 according to the present invention has the same shape and dimension of the battery cells 2.

[0104] However, said sheet (P) 6 can be provided of any shape and dimension, depending on the final shape and dimensions of the battery cells 2, the end plates 4 and the battery system 1 .

[0105] Preferably, sheet (P) 6 is interposed between at least two battery cells 2. For example, an adhesive layer (not shown in the figure 1 ) can be used to keep said sheet (P) 6 in the position between said at least two battery cells 2, such as a pressure-sensitive adhesive.

[0106] Alternatively, sheet (P) 6 can be laminated onto the endplates 4 and hence sheet (P) 6 is interposed between at least one battery cell 2 and the endplate 4.

[0107] Embodiments wherein more than one sheet (P) 6 is used along a battery stack are also encompassed by the present invention. For example, at least two sheets (P) 6 are interposed between non consecutive battery cells 2 in the battery block 1. Also, at least three sheets (P) 6 are interposed between non consecutive battery cells 2 in block 1 .

[0108] As disclosed above, advantageously said battery cells 2 are pouch cells.

[0109] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[0110] The present invention will be further described with reference to the following examples.Experimental Section

[0111] Materials

[0112] [Comp 1] Fluoroelastomer composition comprising copolymer VDF-HFP (ratio 79:21 ), curing agent and accelerant was obtained from Solvay Specialty Polymers Italy S.p.A.

[0113] Fillers were purchased and used as received: magnesium oxide (MgO - Mohs hardness = 5.8), calcium hydroxide (Ca(OH)2 - Mohs hardness < 2) barium sulphate (BaSCU - Mohs hardness = 3-3.5).

[0114] [BA1] Blowing agent was purchased and used as received: azodicarbonamide.

[0115] The compositions having the ingredients detailed in Table 1 below were prepared:Table 1(*) of comparison

[0116] Foam pad sheet specimens having the dimensions specified below were prepared using such fluoroelastomer composition.

[0117] Test 1 - Shore hardness 00 type (for expanded rubbers, sponge rubbers and cellular rubbers)

[0118] Shore Hardness was evaluated according to ASTM D2240 onto a specimen of size 45 x 50 mm and 6 mm thick. 5 runs were performed. Acceptable result was considered if the average value calculated on the 5 runs was lower than 90.

[0119] The results (calculated as the average value of the 5 runs) were as follows:- composition 1 C = 91- composition 2 = 79

[0120] Composition 2 according to the present invention provided acceptable results, while comparative composition 1 C provided a result considered non acceptable.

[0121] Test 2 - Compression strength

[0122] Compression strength was evaluated on Composition 2 according to the invention, according to ASTM C165 onto a specimen measuring 47 x 73 mm and 2.6 mm thick.

[0123] The results obtained are reported in Table 2.Table 2he results were considered positive.

Claims

Claims1 . A foam sheet [sheet (P)] having a thickness lower than 5.0 mm, preferably from 0.9 mm to 4.9 mm, and comprising:(i) a fluoroelastomer composition comprising:(a) at least a vinylidene-based fluoroelastomer [fluoroelastomer (A)] comprising recurring units derived from vinylidene fluoride and at least one other (per)fluorinated monomer [monomer (F)];(b) at least one polyhydroxylated curing agent;(c) at least one accelerant; and(ii) at least two mineral fillers, wherein at least one mineral filler is barium sulphate in an amount of at least 0.1 phr and of at most 9.0 phr based on 100 weight parts (phr) of said (i) fluoroelastomer composition.

2. Sheet (P) according to Claim 1 , wherein said fluoroelastomer (A) comprises at least 15 % moles, preferably at least 20 % moles, more preferably at least 35 % moles of recurring units derived from VDF, with respect to all recurring units of the fluoroelastomer (A); and / or at most 85 % moles, preferably at most 80 % moles, more preferably at most 78 % moles of recurring units derived from VDF, with respect to all recurring units of the fluoroelastomer (A).

3. Sheet (P) according to Claim 1 or 2, wherein said monomer (F) is selected from:(a) C2-C8 perfluoroolefins;(b) hydrogen-containing C2-C8 olefins different from VDF;(c) C2-C8 chloro and / or bromo and / or iodo-fluoroolefins;(d) (per)fluoroalkylvinylethers (PAVE) of formula CF2=CFORf, wherein Rf is a Ci-Ce (per)fluoroalkyl group;(e) (per)fluoro-oxy-alkylvinylethers of formula CF2 = CFOX, wherein X is a C1-C12 ((per)fluoro)-oxyalkyl comprising catenary oxygen atoms;(f) (per)fluorodioxoles having formula:wherein Rf3, Rf4, Rfs, Rf6, equal or different from each other, are independently selected among fluorine atoms and Ci-Ce (per)fluoroalkyl groups, optionally comprising one or more than one oxygen atom;(g) (per)fluoro-methoxy-vinylethers (MOVE, hereinafter) having formula: CFX2= CX2OCF2OR"f wherein R"f is selected among Ci-Ce (per)fluoroalkyls, linear or branched; Cs-Ce cyclic (per)fluoroalkyls; and C2-C6 (per)fluorooxyalkyls, linear orbranched, comprising from 1 to 3 catenary oxygen atoms, and X2= F, H; preferably X2is F and R"f is -CF2CF3 (M0VE1 ); -CF2CF2OCF3 (M0VE2); or -CF3(M0VE3).

4. Sheet (P) according to any one of Claims 1 to 3, wherein said fluoroelastomer (A) further comprises one or more of the followings:- recurring units derived from at least one bis-olefin [bis-olefin (OF)] having general formula :whereinR1 , R2, R3, R4, Rs and Re, equal or different from each other, are H, a halogen, or a C1-C5 optionally halogenated group, optionally comprising one or more oxygen group;Z is a linear or branched C1-C18 optionally halogenated alkylene or cycloalkylene radical, optionally containing oxygen atoms, or a (per)fluoropolyoxyalkylene radical;- recurring units derived from at least one (per)fluorinated monomer different from VDF and HFP; and- recurring units derived from at least one hydrogenated monomer.

5. Sheet (P) according to any one of Claims 1 to 4, wherein said at least one polyhydroxylated curing agent is selected from aromatic or aliphatic polyhydroxylated compounds, preferably from dihydroxy, trihydroxy and tetrahydroxy benzenes, naphthalenes or anthracenes; bisphenols of formula (B):wherein:- Z' is selected from the group consisting of bivalent C1-C13 alkyl or alkylidene group, C4-C13 cycloaliphatic, C6-C13 aromatic or arylalkylenic groups, optionally substituted with at least one chlorine or fluorine atom; a thio (-S-), oxy (-O-), carbonyl (-C(O)-), sulphinyl (-S(O)-) and sulphonyl group (-SO2-);- x is 0 or 1 ;- u, equal to or different from each other, is independently at each occurrence an integer of at least 1 , preferably 1 or 2;- and wherein the phenyl rings can be optionally substituted by one or more substituents selected from the group consisting of chlorine, fluorine, bromine; -CHO, Ci-Cs alkoxy groups, -COOR10 groups, wherein R10 is H or Ci-Cs alkyl, C6-C14 aryl, C4-C12 cycloalkyl.

6. Sheet (P) according to any one of Claims 1 to 5, wherein said at least one accelerant is selected from organic onium compounds, amino-phosphoniumderivatives, phosphoranes, imine compounds.

7. Sheet (P) according to any one of Claims 1 to 6, wherein at least one other mineral filler is selected from the group comprising: metal oxides, metal hydroxides, metal sulphates and silicates.

8. Sheet (P) according to Claim 7, wherein:- said metal oxide is selected in the group comprising ZnO, MgO, PbO, and mixtures thereof; and / or- said metal hydroxides are selected from Ca(0H)2, Sr(OH)2, Ba(OH)2 and mixtures thereof; and / or- said silicate is selected from wollastonite, vermiculite, zeolite, silica, mica, and mixtures thereof.

9. Sheet (P) according to Claims 7 or 8, wherein:- the amount of said metal oxide is of at least 0.5 phr and / or at most 8 phr based on 100 weight parts (phr) of said fluoroelastomer composition; and / or- the amount of said metal hydroxide is at least 0.1 phr and / or at most 8 phr based on 100 weight parts (phr) of said fluoroelastomer composition; and / or- the amount of said silicate is at least 0.1 phr and / or at most 9 phr based on 100 weight parts (phr) of said fluoroelastomer composition.

10. Sheet (P) according to any one of Claims 1 to 9, wherein the total amount of mineral fillers in sheet (P) is below 20.0 phr, preferably below 18.0 phr based on 100 phr of said (i) fluoroelastomer composition.11 . Sheet (P) according to Claim 10, wherein said sheet (P) comprises a first mineral filler having a Mohs’ hardness higher than 5, and at least one other mineral filler having a Mohs’ hardness equal to or lower than 5.

12. Sheet (P) according to any one of Claims 1 to 11 , wherein sheet (P) comprises no fluorinated surfactants.

13. Sheet (P) according to any one of Claims 1 to 12, wherein said sheet (P) has a thickness from 1 .0 to 4.7 mm.

14. Sheet (P) according to any one of Claims 1 to 13, which is obtained from a composition [composition (C)] comprising:(i) a fluoroelastomer composition comprising: (a) a vinylidene-based fluoroelastomer [fluoroelastomer (A)] comprising recurring units derived from vinylidene fluoride and at least one other (per)fluorinated monomer [monomer (F)]; (b) at least one polyhydroxylated curing agent; and (c) at least one accelerant;(ii) at least one mineral filler; and(iii) at least one blowing agent.

15. A battery system (1 ) comprising:- a battery block comprising at least two stacked battery cells (2);- fastening components (3) that hold said at least two battery cells, comprising(i) a pair of endplates (4), each disposed at one end of said at least two battery cells, and(ii) metal bands (5) disposed at the battery block side-walls extending in the stacking direction of the battery cells and connected at both ends to the endplates (4); wherein at least one sheet (P) (6) according to any one of Claims 1 to 13 is interposed between said at least two stacked battery cells (2).

16. The battery system according to Claim 15, wherein each of said at least two stacked battery cells (2) is a pouch cell.

17. Use of at least one sheet (P) according to any one of Claims 1 to 13 for the manufacture of a battery system comprising at least two battery cells, preferably each of said battery cell being a pouch cell, wherein said at least one sheet (P) is interposed between said at least two battery cells of said battery system.

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