Binder composite for electrochemical energy storage devices based on hydrogenated nitrile rubber and polycondensates

Abstract

The present invention relates to a binder composite for a binder of an electrode of an electrochemical energy storage device, the binder composite containing a) hydrogenated nitrile rubber; and b) a polycondensate selected from the group consisting of a polyamide having a melting point from 140 °C to 270 oC and a polyester having a melting point from 175 °C to 270 °C; wherein the polycondensate forms domains in the hydrogenated nitrile rubber, wherein the domains have a size D50% below 3 microns within the matrix of the hydrogenated nitrile rubber.

Description

[0001] Binder composite for electrochemical energy storage devices based on hydrogenated nitrile rubber and poiycondensates

[0002] The present invention relates to binder composites which are usable in electrodes for electrochemical energy storage devices, such as lithium-ion secondary batteries (LiB). The present invention further relates to electrodes, such as cathodes, comprising such composites as well as to electrochemical energy storage devices, which comprise the respective electrodes.

[0003] Lithium-ion secondary batteries have been widely used as power sources for portable devices since their inception around 1991 as small, lightweight, and large-capacity batteries. In recent year the demand has increased strongly due to the usage of batteries in electric vehicles.

[0004] The cathode of LiB mainly comprises a cathode active material making up more than 95 wt-% of all solid materials used in it.

[0005] The active material of the cathode of a lithium-ion battery allows reversible insertion and removal of lithium ions into and from this cathode while transition metal ion contained in the active material change their oxidation state. The higher the mass fraction of this active material in the cathode, the higher its capacity for charging and discharging and subsequently the energy density.

[0006] Further, conductive materials are used in cathodes and anodes which are basically various allotropes of high purity carbon, ranging from carbon black to carbon nanotubes to graphene.

[0007] As these materials are solid powders, flexible polymer binders are needed to allow coating on the current collector as a stable enough layer that can be further handled by cutting, slicing, and rolling together with the anode film to form the desired battery cell geometry. As the uniformity of the coating and the even distribution of all materials is of extreme importance for the battery performance the good dispersion of all particles must be ensured.

[0008] For binding of the particulate components of the LiB electrode such as cathode, fluorinated polymers have been used for a long time. The most common types of binder are based on polyvinylidene fluoride, PVDF which sometimes may contain a few other monomer units. Some PVDF grades have a very high molecular weight (Mw) to improve bonding efficiency. PVDF has a low swell in the battery electrolyte fluid which is believed to be important for the integrity of the binder film in battery service.

[0009] However, there are problems with the usage of PVDF as binder when active materials are chosen that possess highly active alkaline components on the surface. This can be case for nickel-rich active materials such as with nickel-cobalt-manganese oxides in their lithiated form and nickel-cobalt-aluminum oxides. Strongly basic surfaces can cause the dehydro-fluorination of PVDF which leads to the gelation of this polymer.

[0010] Nitrile rubber, especially the more electrochemically stable hydrogenated version of nitrile rubber, HNBR, has been shown to be a very suitable dispersion aid for all kind of carbon materials, this includes carbon coated active materials, such a lithium-iron-phosphate, LPF-C. Insufficient dispersion will result in gelling and agglomeration of conductive materials. Examples of the usage of various HNBR grades as dispersion aids can be found in EP 3319151 , EP 3348582, KR20150016852, EP3358651 , JP6933285, JP 2020194625, KR20150067049, EP 3355392. The conductive materials are used as an important component in the electrode to enable the conduction of electricity through the electrode. Hydrogenated nitrile rubber are very suitable polymeric dispersion aids to disperse nanosized carbon materials in organic solvents to create cathode slurries.

[0011] The role of HNBR as binder is exemplified in US2018 / 0183064, EP2660980, EP3240069, EP 3276713, W02020 / 206606, EP3220461 . HNBR can be used as sole binder or as cobinder together with PVDF.

[0012] KR102329520B1 suggested the addition of small amounts of organic diacids like oxalic acid to lessen the gelation effect while a certain portion of the PVDF is replaced by HNBR.

[0013] In case of LPF-C (carbon coated LFP) PVDF can be combined with HNBR to allow better dispersion of the carbon coated small sized LFP-C particles. Still gelation of PVDF can occur as it can split-off HF.

[0014] The main effect of HNBR as a binder or co-binder in the cathode slurry is the decrease of viscosity compared to PVDF as single binder which is important for the efficient coating step of the slurry on the current collector. A lower viscosity allows to raise the solids content of the slurry which lessens the amount of process solvent to be evaporated and therefore energy can be saved. The reason for the viscosity reduction is not fully understood, however, one aspect can be the lower molecular weight of HNBR compared to the battery grades of PVDF.

[0015] The viscosity of a cathode slurry depends on the selected formulation. The active material typically makes up more than 95% of all solid material. The particle size, shape and distribution can be very different. In case of NCM (based on oxides of Ni, Co and Mn) the particles are spherical with a rather large size up to 10 microns. Therefore, slurries with NCM can be used up to high solid content. In case of LFP (Li-iron-phosphate) the particles can be much smaller, below the micron range. They are mostly coated with a thin carbon layer so that the particles tend to agglomerate and therefore the typical solid contents are much lower. The conductive material can be carbon black of various particle size and structure, carbon nanotubes which can be single or multi-walled, bundled or entangled. The conductive material needs to be highly dispersed. It is assumed that HNBR contributes to the carbon material dispersion and prevents the re-agglomeration thereby lowering the viscosity. The binder polymer itself may contribute to the slurry viscosity with a disadvantage for the high molecular weight needed for PVDF.

[0016] Therefore, the solutions of the prior art still give room for improvements.

[0017] Object of the invention

[0018] It is an object of the present invention to provide a binder for an electrode which overcomes at least one problem of the prior art at least in part. It is in particular an object of the present invention to provide a binder for an electrode for an electrochemical energy storage device which has low viscosity and high solid contents and is advantageous with regard to sustainability.

[0019] Means to solve the objects

[0020] These objects are solved at least in part by a binder composite having the features of claim 1. This object is further solved by an electrode having the features of claim 12 as well as by an electrochemical energy storage device having the features of claim 13. Preferred embodiments of the invention are described in the dependent claims, in the description or in the figures, wherein further features described or shown in the dependent claims or in the description or in the figures may individually or in any combination constitute an object of the invention, unless the opposite clearly follows from the context.

[0021] Described is a binder composite for a binder of an electrode, preferably of a cathode, of an electrochemical energy storage device, the binder composite containing a) hydrogenated nitrile rubber (HNBR); and b) a polycondensate selected from the group consisting of a polyamide (PA) having a melting point from 140 °C to 270 °C and a polyester having a melting point from 175 °C to 270 °C; wherein the polycondensate forms domains in the hydrogenated nitrile rubber, wherein the domains have a size D50% below 3 microns (pm) within the HNBR matrix.

[0022] Such a composite shows significant advantages over solutions of the prior art when used as binder materials in electrodes, in particular in cathodes.

[0023] It was surprisingly found that binders comprising hydrogenated nitril rubber as polymeric matrix with domains formed from polyamide having defined size as outlined above may provide outstanding properties.

[0024] The usage of polycondensates such as a polyamide inside battery cells until now has been limited to PA nanofibers as part of the separator layer (M. Yanilmaz et.al., Electrochimica Acta (2014), 133, 501-508). Similarly, aramid nanofibers were used as separator membranes (B. Yang, J. Mat. Chem. A: Mat. Energy Sustain. (2021 ), 9(22) 12923-12946). Polyamide has been used as a carbon source for the conductive carbon coating on vanadate based active materials (J. Yan et.al., RSC Advances (2016), 6(114), 113228- 1 13228). Polyamides are further used in JP2011175841 as one of the layers on battery packaging metal foil. From that one can indirectly infer that polyamide might have sufficient electrochemical stability. However, there was no hint to using polyamide or further polycondensates in the sense of the present invention.

[0025] JP2015005391 A describes polyamic acids which are partially present as salts and soluble in NMP to serve as binders. However, these polymers may be too reactive with the highly alkaline active materials. In JP2007305574A an aromatic para-amide is prepared which is soluble in NMP, however the high modulus of such a resin may cause the electrodes to lack flexibility.

[0026] The composite according to the invention allows providing advantageous HNBR binders to give high solid cathode slurries with low viscosity. More specifically, it is possible by the present invention to modify HNBR by way of preparation of a composite to achieve the object of even higher solid contents and thus more energy savings in the cathode manufacturing process. It is believed that such a composite can potentially give bonding features which sole HNBR as a binder still lacks.

[0027] HNBR is a flexible rubber-like material, which allows to create softer and more flexible cathode films with similar forces compared to PVDF. According to the present invention, it is further possible to adjust the modulus of the HNBR-based binder, for example making the binder polymer stiffer. Thin cathodes may allow for stiffer polymer binders whereas thicker cathode may need softer binders. Thus, a very high degree of adaption becomes possible.

[0028] The binder composite allows even higher solid contents, which may give good adhesion to the current collector and good binding force within the electrode. Gelation issues are suppressed or at least reduced. In terms of dosage, the binder composite may allow the same or even higher efficiency at lower dosage compared to PVDF.

[0029] The addition of domains formed from polycondensates selected from a polyamide and a polyester like defined above allows acting as dispersion aid, as binder or as rheology modifiers in binders for batteries.

[0030] According to the present invention, it was further shown that providing domains formed from respective polycondensates does not require adding fluorinated binder polymers. It is thus a significant advantage of the present invention, that the use of fluorinated binders may be avoided.

[0031] The present invention finds a way to combine HNBR with suitable thermoplastic resin, i.e. polyamide or polyester, to create a new binder system. The resin can be chosen to provide a higher modulus of the binder film while maintaining its flexibility. The resin further allows to raise the adhesive performance of the binder. Another aspect of battery technology is becoming more urgent. This is the recycling of spent batteries. Several technologies have been suggested such as use pyrolytic or hydro- metallurgic methods to separate the current collectors from active materials and recycle them in some way via extraction of the valuable raw materials to manufacture new batteries. However, the content of polymers used as binders or modifiers, although small, make these processes more complicated. Especially the presence of polymers with organic bonded fluorine according to the prior art poses a great challenge as the removal requires the pyrolysis of the battery materials under high heat. Fluorinated polymers will be cracked forming HF. This gas needs to be scrubbed off the exhaust gas, however HF is very corrosive and will limit the lifetime of the equipment. Binder composites according to the present invention, however, which are free of fluorinated or even halogenated compounds, are easier to remove in battery recycling processes and have therefore found great technical attraction to solve these problems.

[0032] A binder composite according to the present invention thus also facilitates the recycling of batteries as no decomposition of organic fluorine materials is needed when retrieving the valuable metals, metal-oxides and carbon materials.

[0033] Generally, as known in the art, hydrogenated nitrile rubber is a copolymer formed from acrylonitrile and 1 ,3 butadiene in which the double bonds of the NBR units are hydrogenated at least to a high extent. In a preferred embodiment, the hydrogenated nitrile rubber contains acrylate unites, wherein the sum of remaining hydrocarbon-based monomer units is less than 70 wt.-%. In other words, the amount of acrylate units is in the range of at least 30 wt.-%, such as in the range of 30 to 50 wt.-%. This embodiment allows to tailor the properties of the binder composite, such as of the elasticity, to be especially well suited for an electrode binder.

[0034] Further and with regard to the degree of hydrogenation of the HNBR, it may be preferred that a degree of hydrogenation as measured as RDB is below 1%.

[0035] In particular, it is preferred that the hydrogenated nitrile rubber has a nitrile content of from 7 to 55 wt.-%, preferably of from 15 to 40 wt%, calculated as acrylonitrile, and a degree of hydrogenation as measured as RDB below 1%.

[0036] The preferred hydrogenated nitrile rubber can further contain polymerized monomer units selected from acrylates or methacrylate from 0 to 30 wt%. According to a further preferred embodiment, the content of polycondensate is in the range of 5 to 40 phr, wherein 100 phr refers to the hydrogenated nitrile rubber. It was shown that the advantages of the present invention are especially effective when the polyamide is present in an amount as defined in this embodiment.

[0037] Further, it may be preferred that the binder composite is present in an electrode coating dispersion containing an electrochemically active material and conductive carbon material dispersed in an organic solvent. According to this embodiment, additionally to the binder composite, the active material as well as the conductive material is present in a solvent, such as in NMP. This allows applying the binder composite as a dispersion in very simple manner. For example, the binder composite, or binder dispersion, respectively, may be applied to a current collector.

[0038] In a further preferred embodiment, the binder composite is present in an electrode coating dispersion containing a solid electrolyte, optionally an electrochemically active material, and optionally conductive carbon material dispersed in an organic solvent. It is thus also possible and may be preferred to use the binder composite in a dispersion having a solid electrolyte.

[0039] In order to produce respective composites, it was found that it is not possible to combine the HNBR with the defined polyamide or polyester by combining these different polymers in one solution. A solution blending step leads to the phase separation of the polymers within the solution which renders the binder solution as unusable. Therefore, it was necessary to find a way to combine the HNBR and the resin in a way that allows to create a stable solution of the binder system.

[0040] Thus, it has been found that the described polycondensate is generally not soluble in the process solvent which is mostly N-methyl pyrrolidone, NMP. Accordingly, the polycondensate resin cannot directly be used in the wet coating process of a cathode.

[0041] It was, however, shown that the formation of domains of the polycondensate in a matrix of HNBR can especially by realized by using a melt mix process. In detail and in a surprising manner, a melt mixing process of the HNBR and polycondensate turned out to be suitable to create soluble binder composites. The melt mixing can be carried out in any device which allows to apply shear and temperature in a controlled way to the mix. Twin-screw extruders or planetary extruders are very suitable and commonly available machines to carry out the melt mixing process. The type of melt mixer, however, may be changed in case the temperature can be well controlled along the process time and length, and shear can be applied by mechanical means for a defined time. Suitable melt mixing machines can also be planetary roller extruders, oscillating single shaft extruder such as available as Buss kneaders. However, it is believed that excessive temperatures or too long mixing times may lead to damage of the HNBR matrix.

[0042] The melt mixing refers to the melting behavior of the polycondensate which needs to be mixed when its melting temperature is reached or exceeded to some extent. In case of amorphous polycondensates, i.e. polyamides or polyesters, the melt mixing must be carried out high enough above the glass transition temperature so that the melt viscosity is low enough to allow good dispersion in the HNBR matrix.

[0043] The melt-mixing of HNBR with e.g. polyamides has been described in US2020392316A1 and in WO2019121157A1, however, the disclosures are silent on any possible use as dispersion aid, as binder or as rheology modifiers in batteries. There is no disclosure for melt mixed HNBR / polyconensate composites for use in batteries.

[0044] The melt mixing is understood as a process where during the mixing the resin needs to be converted into a melt stage to allow its dispersion into the rubber matrix. This means the melt temperature needs to be reached. The melt temperature of a resin can be determined by common analytical methods such as a DSC scan. A further optimization can be done by examining the viscosities of the molten resin and the HNBR at a certain temperature. The dispersion of the resin in the HNBR rubber is facilitated if the ratio of the viscosity of the rubber to the resin is between 1.3 and 5 (for reference see M. Hemstede, J. Dodevski, A. Kaiser, S. Lieber, 13thFall Rubber Colloquium, November 7, 2018).

[0045] It may thus be preferred that the ratio of the viscosity of the HNBR to the polycondensate is between 1.3 and 5.

[0046] With regard to further technical features and advantages of the composite, it is referred to the description of the electrode, the electrochemical energy storage device, the examples and the figures.

[0047] Further described is an electrode for an electrochemical energy storage device, wherein the electrode comprises a binder composite, the binder composite being arranged as described before. For example, the binder composite may be applied to a current collector of the electrode, such as to an Aluminum foil. In particular, the electrode may form a cathode.

[0048] Providing the binder composite in an electrode, such as in a cathode, particularly provides the advantages as described above with regard to the binder composite.

[0049] Another advantage is the secure bonding of the cathode materials to the current collector which typically is a thin aluminum foil. Insufficient bonding can cause the cathode to peel off when the cathode is bent in the core of a cylindrical cell. This can cause the loss of electrical contact therefore to battery failure. Another issue can arise from uneven electrode edges when materials is lost during slitting or cutting into size. This can even lead to short cut between cathode and anode current collector.

[0050] In another aspect of the present invention, very thin coatings of carbon materials are used to equip current collector foils with an electrically conductive layer before applying the electrode slurry. Such a thin coating can be based on carbon black, carbon nanotubes or graphene whereas a binder is needed for proper bonding to the metallic current collector. The polymer binder can be advantageously the HNBR composites due to its adhesion and strength.

[0051] It was shown that the defined polycondensate domains in the HNBR can assist in dispersing conductive carbon materials in an organic solvent. Therefore, the binder composite is especially preferred for forming a dispersion as described.

[0052] Correspondingly, the defined polycondensate domains in the HNBR can assist in dispersing solid electrolytes in an organic solvent and optionally other additives to be used in solid state batteries.

[0053] With regard to further technical features and advantages of the electrode, it is referred to the description of the composite, the electrochemical energy storage device, the examples and the figures.

[0054] Further described is an electrochemical energy storage device, wherein the electrochemical energy storage device comprises an anode and a cathode, the cathode being arranged as described before.

[0055] In particular, the electrochemical energy storage device is a secondary battery, such as a lithium-ion battery. It comprises in a manner known per se an anode, a cathode and a separator located between the anode and the cathode. The anode may be formed from graphite or other materials known in the art and the separator may comprise polymeric foils or ceramic structures as known for the person skilled in the art.

[0056] The cathode is arranged as described before which allows the respective advantages as described.

[0057] With regard to further technical features and advantages of the electrochemical energy storage device, it is referred to the description of the composite, the electrode, the examples and the figures.

[0058] In the following, the composite is described in more detail.

[0059] HNBR

[0060] First, the main binder HNBR is to be characterized. In the context of this application, “nitrile-diene copolymer” (nitrile-butadiene copolymer, nitrile rubber, also abbreviated to “NBR”) is understood to mean rubbers which are co-, ter- or quaterpolymers of at least one a,p-ethylenically unsaturated nitrile, at least one conjugated diene and optionally one or more additional copolymerizable monomers. The term thus also encompasses copolymers having two or more a,p-ethylenically unsaturated nitrile monomer units and two or more conjugated diene monomer units.

[0061] “Hydrogenated nitrile-diene copolymer” (“HNBR”) is understood to mean corresponding co-, ter- or quaterpolymers in which at least some of the C=C double bonds in the copolymerized diene units have been hydrogenated, preferably at least 50% of the C=C double bonds. For a sufficient electrochemical stability, it is preferred that the hydrogenated HNBR rubber is fully hydrogenated.

[0062] The term “fully hydrogenated” means that the degree of hydrogenation of the butadiene units in the hydrogenated nitrile-diene copolymer is 99.1% to 100%.

[0063] The term “copolymer” encompasses polymers having more than one monomer unit. a,p-ethylenically unsaturated nitrile

[0064] The a,p-ethylenically unsaturated nitrile used which forms the a,p-ethylenically unsaturated nitrile units may be any known a,p-ethylenically unsaturated nitrile. Preference is given to (C3 -C5 )-a,p-ethylenically unsaturated nitriles such as acrylonitrile, a-haloacrylonitrile, for example a-chloroacrylonitrile and a-bromoacrylonitrile, a- alkylacrylonitrile, for example methacrylonitrile, ethacrylonitrile or mixtures of two or more a,p-ethylenically unsaturated nitriles. Particular preference is given to acrylonitrile, methacrylonitrile, ethacrylonitrile or mixtures thereof. Very particular preference is given to acrylonitrile.

[0065] The amount of a,p-ethylenically unsaturated nitrile units is typically in the range from 10% to 60% by weight, preferably 15% to 50% by weight, more preferably from 17% to 44% by weight, based on the total amount of 100% by weight of all monomer units in the HNBR rubber.

[0066] Conjugated Diene

[0067] The conjugated diene which forms the conjugated diene units may any conjugated diene, especially conjugated C4 -C12 dienes. Preference is given to 1,3-butadiene, isoprene, 2,3-dimethylbutadiene, 1 ,3-pentadiene (piperylene), 2-chloro-1 ,3-butadiene or mixtures thereof. 1 ,3-Butadiene and isoprene or mixtures thereof are especially preferred. Very particular preference is given to 1,3-butadiene.

[0068] The amount of conjugated diene is typically in the range from 40% to 90% by weight, preferably 50% to 85% by weight and more preferably 56% to 83% by weight, based on the total amount of 100% by weight of all the monomer units in the HNBR rubber.

[0069] Further Comonomers a,p-Ethylenically Unsaturated Carboxylic Ester Units

[0070] In addition to the a,p-ethylenically unsaturated nitrile units and the conjugated diene units, the HNBR rubber may contain at least one a,p-ethylenically unsaturated carboxylic ester unit.

[0071] Typical a,p-ethylenically unsaturated carboxylic ester units are o alkyl (meth)acrylate, especially C4 -C18 -alkyl (meth)acrylate, preferably n- butyl, tert-butyl, n-pentyl or n-hexyl (meth)acrylate; alkoxyalkyl (meth)acrylate, especially C4 -C 18 -alkoxyalkyl (meth)acrylate, preferably C4 -C12 -alkoxyalkyl (meth)acrylate; hydroxyalkyl (meth)acrylate, especially C4 -C18 -hydroxyalkyl (meth)acrylate, preferably C4 -C12 -hydroxyalkyl (meth)acrylate; cycloalkyl (meth)acrylate, especially C5 -C18 -cycloalkyl (meth)acrylate, preferably C6 -C12 -cycloalkyl (meth)acrylate, more preferably cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate; alkylcycloalkyl (meth)acrylate, especially C6 -C12 -alkylcycloalkyl (meth)acrylate, preferably C7 -C10 -alkylcycloalkyl (meth)acrylate, more preferably methylcyclopentyl (meth)acrylate and ethylcyclohexyl (meth)acrylate; aryl monoesters, especially C6 -C14 -aryl monoesters, preferably phenyl (meth)acrylate or benzyl (meth)acrylate; amino-containing a,p-ethylenically unsaturated carboxylic esters, for example dimethylaminomethyl acrylate or diethylaminoethyl acrylate; a,p-ethylenically unsaturated monoalkyl dicarboxylates, preferably

[0072] ■ alkyl monoesters, especially C4 -C18 -alkyl monoesters, preferably n-butyl, tert-butyl, n-pentyl or n-hexyl monoesters, more preferably mono-n-butyl maleate, mono-n-butyl fumarate, mono-n-butyl citraconate, mono-n-butyl itaconate, most preferably mono-n-butyl maleate,

[0073] ■ alkoxyalkyl monoesters, especially C4 -C18 -alkoxyalkyl monoesters, preferably C4 -C12 -alkoxyalkyl monoesters,

[0074] ■ hydroxyalkyl monoesters, especially C4 -C18 -hydroxyalkyl monoesters, preferably C4 -C12 -hydroxyalkyl monoesters,

[0075] ■ cycloalkyl monoesters, especially C5 -C18 -cycloalkyl monoesters, preferably C6 -C12 -cycloalkyl monoesters, more preferably monocyclopentyl maleate, monocyclohexyl maleate, monocycloheptyl maleate, monocyclopentyl fumarate, monocyclohexyl fumarate, monocycloheptyl fumarate, monocyclopentyl citraconate, monocyclohexyl citraconate, monocycloheptyl citraconate, monocyclopentyl itaconate, monocyclohexyl itaconate and monocycloheptyl itaconate, ■ alkylcycloalkyl monoesters, especially C6 -C12 -alkylcycloalkyl monoesters, preferably C7 -C10 -alkylcycloalkyl monoesters, more preferably monomethylcyclopentyl maleate and monoethylcyclohexyl maleate, monomethylcyclopentyl fumarate and monoethylcyclohexyl fumarate, monomethylcyclopentyl citraconate and monoethylcyclohexyl citraconate; monomethylcyclopentyl itaconate and monoethylcyclohexyl itaconate;

[0076] ■ aryl monoesters, especially 06-014-aryl monoesters, preferably monoaryl maleates, monoaryl fumarates, monoaryl citraconates or monoaryl itaconates, particularly preferably monophenyl maleate or monobenzyl maleate, monophenyl fumarate or monobenzyl fumarate, monophenyl citraconate or monobenzyl citraconate, monophenyl itaconate or monobenzyl itaconate,

[0077] ■ unsaturated polyalkyl polycarboxylates, for example dimethyl maleate, dimethyl fumarate, dimethyl itaconate or diethyl itaconate; or mixtures thereof.

[0078] In a particularly preferred embodiment, the fully or partly hydrogenated HNBR rubber contains a (01-04)-alkyl methacrylate, most preferably butyl acrylate.

[0079] The amount of the optional a,p-ethylenically unsaturated carboxylic ester units in the HNBR rubbers according to the invention is typically in the range from 0% to 30% by weight, preferably 0.5% to 20% by weight and more preferably 1% to 10% by weight, based on the total amount of 100% by weight of all the monomer units.

[0080] The manufacture of such rubbers is well known in the industry and described for example in the Handbook of Synthetic Rubber, for rubbers in general in Chapter 5, pages 67 - 86 and specifically for HNBR Chapter 14, pages 295 - 314, ARLANXEO Deutschland GmbH, Germany, 2020.

[0081] The monomers used for the polymerization are typically obtained from fossil sources, for example by cracking from crude oil but monomers obtained from a sustainable source may be used as well. Using monomers from a sustainable source has the advantage of lowering the carbon dioxide footprint of the polymers and the articles produced from them. Monomers obtained from a sustainable source include monomers obtained from a biological source including plants fungi or bacteria. Such monomers are chemically identical to monomers obtained from fossil sources but have a higher content of the carbon 14 isotope, by which they can be identified. Monomers obtained from a sustainable source also includes monomers obtained from recycled waste materials, including recycled biological waste material (for example wood pulp), recycled rubber waste materials (for example obtained from the pyrolysis of tires) and recycled plastic waste materials. Monomers obtained from recycled materials also include ISCC+ certified monomers, which may be used, for example, in a so-called mass-balanced process to reduce the overall CC>2-content of the production chain (see for example, Pete Spanos et al, “Sustainable Keltan EPDM”, RUBBERWORLD.COM, April 2023, where the process is described for EPDM polymers but the principles set out there can be also applied to other polymers accordingly). Monomers from a sustainable source may or may not have to be purified differently than those obtained from fossil sources for providing monomers at the same degree of purity.

[0082] Polyamide

[0083] The polyamide in the binder composite according to the invention is preparable from a combination of diamine and dicarboxylic acid, from an o-amino carboxylic acid or the corresponding lactam. In principle, it is possible to use any aliphatic polyamide, preferably PA6, PA66, PA610, PA88, PA612, PA810, PA108, PA9, PA613, PA614, PA812, PA1010, PA10, PA814, PA148, PA1012, PA11 , PA1014, PA1212 or PA12. However, regarding the advantages achieved, polyamide 6 may be specially preferred.

[0084] Preference is given to nylon-6 (PA6) or nylon-6, 6 (PA66), very particular preference to using nylon-6.

[0085] Polyamides preferred in accordance with the invention are semicrystalline or amorphous polyamides that are preparable proceeding from diamines and dicarboxylic acids and / or lactams having at least 5 ring members or corresponding amino acids.

[0086] Useful reactants are preferably aliphatic and / or aromatic dicarboxylic acids, more preferably adipic acid, 2,2,4-trimethyladipic acid, 2,4,4-trimethyladipic acid, azelaic acid, sebacic acid, isophthalic acid, terephthalic acid, aliphatic and / or aromatic diamines, more preferably tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, nonane-1 ,9-diamine, 2,2,4- and 2,4,4-trimethylhexamethylenediamine, the isomeric diaminodicyclohexylmethanes, diaminodicyclohexylpropanes, bis(aminomethyl)cyclohexane, phenylenediamines, xylylenediamines, amino carboxylic acids, especially aminocaproic acid, or the corresponding lactams. Copolyamides of a plurality of the monomers mentioned are included.

[0087] Polyamide suitable in accordance with the invention is known, for example, by the Durethan® or Nylon® brand name. Most preferably, Durethan® B31 F PA 6 from LANXESS is used. It is of course also possible to use mixtures of these polyamides, where the mixing ratio is as desired. Proportions of recycled polyamide molding materials and / or fibre recyclates may also be present.

[0088] The polyamides preferably have a relative viscosity of 2.3 to 4.0, more preferably of 2.7 to 3.5, where the relative viscosity can be determined / measured on a 1% by weight solution in m-cresol at 25° C.

[0089] The preparation of the polyamides is prior art. Of course, it is alternatively possible to use copolyamides based on the abovementioned polyamides.

[0090] A multitude of procedures for preparation of polyamides has become known, with use, depending on the desired final product, of different monomer units and various chain transfer agents to establish a desired molecular weight or else monomers with reactive groups. The industrially relevant processes for preparing the polyamides for use in the substance mixture preferably proceed via polycondensation in the melt. In this context, the hydrolytic polymerization of lactams is also considered to be polycondensation. The preparation of polyamides by thermal polycondensation is known to those skilled in the art; see, inter alia, Nylon Plastics Handbook, Hanser-Verlag Munich 1995, pages 17-27, and Kunststoff-Handbuch [Plastics Handbook] 3 / 4, Polyamide [Polyamides], Carl Hanser Verlag, Munich 1998, pages 22-36.

[0091] Especially preferred are random, semicrystalline, aliphatic PA 6 / 66 copolyamides, polymerized from e-caprolactam and hexamethylenediamine adipate. e-Caprolactam (CAS number 105-60-2) is used with preference for preparation of polyamide inter alia. Cyclohexanone oxime is first prepared from cyclohexanone by reaction with the hydrogensulfate or the hydrochloride of hydroxylamine. This cyclohexanone oxime is converted to e-caprolactam by a Beckmann rearrangement.

[0092] Hexamethylenediamine adipate (CAS number 3323-53-3) is the reaction product of adipic acid and hexamethylenediamine. One of its uses is as an intermediate in the preparation of nylon-6, 6. The trivial name AH salt derives from the initial letters of the starting substances.

[0093] It is likewise also possible to use mixtures of different polyamides, provided that they are sufficiently compatible. Compatible combinations of polyamides are known to those skilled in the art. Polyamide combinations for use with preference are PA6 / PA66, PA12 / PA1012, PA12 / 1212, PA612 / PA12, PA613 / PA12, PA1014 / PA12 or PA610 / PA12 and corresponding combinations with PA11 , more preferably PA6 / PA66. In the case of doubt, compatible combinations can be ascertained by routine experiments.

[0094] Instead of aliphatic polyamides, it is advantageously also possible to use a semi-aromatic polyamide wherein the dicarboxylic acid component originates to an extent of 5 to 100 mol % from aromatic dicarboxylic acid having 8 to 22 carbon atoms and which preferably has a crystallite melting point Tm to ISO 11357-3 of at least 250° C., more preferably of at least 260° C. and especially preferably of at least 270° C. Polyamides of this kind are typically identified by the addition T (=semi-aromatic). They are preparable from a combination of diamine and dicarboxylic acid, optionally with addition of an o -amino carboxylic acid or a corresponding lactam. Suitable types are preferably PA66 / 6T, PA6 / 6T, PA6T / MPMDT (MPMD stands for 2-methylpentamethylenediamine), PA9T, PA10T, PA1 1T, PA12T, PA14T and copolycondensates of these latter types with an aliphatic diamine and an aliphatic dicarboxylic acid or with an w-amino carboxylic acid or a lactam. The semi-aromatic polyamide can also be used in the form of a blend with another, preferably aliphatic, polyamide, more preferably with PA6, PA66, PA11 or PA12.

[0095] Another suitable polyamide class is that of transparent polyamides; these are amorphous in most cases but may also be microcrystalline. They can be used either on their own or in a mixture with aliphatic and / or semi-aromatic polyamides, preferably PA6, PA66, PA1 1 or PA12. The glass transition point Tg, measured to ISO 1 1357-3, is at least 110° C., preferably at least 120° C., more preferably at least 130° C. and more preferably at least 140° C. Preferred transparent polyamides are the polyamide of dodecane-1 , 12-dioic acid and 4,4'-diaminodicyclohexylmethane (PAPACM12), especially proceeding from a 4,4'- diaminodicyclohexylmethane having a trans-trans isomer content of 35% to 65%, the polyamide of terephthalic acid and / or isophthalic acid and the isomer mixture of 2,2,4- and 2,4,4-trimethylhexamethylenediamine, the polyamide of isophthalic acid and hexamethylene-1 ,6-diamine, the copolyamide of a mixture of terephthalic acid / isophthalic acid and hexamethylene-1 ,6-diamine, optionally in a mixture with 4,4'- diaminodicyclohexylmethane, the copolyamide of terephthalic acid and / or isophthalic acid, 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane from laurolactam or caprolactam, the (co)polyamide of dodecane-1 , 12-dioic acid or sebacic acid, 3,3'-dimethyl-4,4'- diaminodicyclohexylmethane and optionally laurolactam or caprolactam, the copolyamide of isophthalic acid, 4,4'-diaminodicyclohexylmethane and laurolactam or caprolactam, the polyamide of dodecane-1 , 12-dioic acid and 4,4'-diaminodicyclohexylmethane (with low trans-trans isomer content), the copolyamide of terephthalic acid and / or isophthalic acid and an alkyl-substituted bis(4-aminocyclohexyl)methane homologue, optionally in a mixture with hexamethylenediamine, the copolyamide of bis(4-amino-3-methyl-5- ethylcyclohexyl)methane, optionally together with a further diamine, and isophthalic acid, optionally together with a further dicarboxylic acid, the copolyamide of a mixture of m- xylylenediamine and a further diamine, e.g. hexamethylenediamine, and isophthalic acid, optionally together with a further dicarboxylic acid, for example terephthalic acid and / or napthalene-2,6-dicarboxylic acid, the copolyamide of a mixture of bis(4- aminocyclohexyl)methane and bis-(4-amino-3-methyl-cyclohexyl)methane and aliphatic dicarboxylic acids having 8 to 14 carbon atoms, and polyamides or copolyamides formed from a mixture containing tetradecane-1 , 14-dioic acid and an aromatic, arylaliphatic or cycloaliphatic diamine.

[0096] These examples may be varied very substantially by addition of further components, preferably caprolactam, laurolactam or diamine / dicarboxylic acid combinations, or by partial or complete replacement of starting components with other components.

[0097] Lactams or uj-amino carboxylic acids that are used as polyamide-forming monomers contain 4 to 19 and especially 6 to 12 carbon atoms. Particular preference is given to using e-caprolactam, e-aminocaproic acid, caprylolactam, uj-aminocaprylic acid, laurolactam, OJ- amino dodecanoic acid and / or co-amino undecanoic acid. Combinations of diamine and dicarboxylic acid are, for example, hexamethylenediamine / adipic acid, hexamethylenediamine / dodecanedioic acid, octamethylenediamine / sebacic acid, decamethylenediamine / sebacic acid, decamethylenediamine / dodecanedioic acid, dodecamethylenediamine / dodecanedioic acid and dodecamethylenediamine / naphthalene-2,6-dicarboxylic acid. In addition, it is alternatively possible to use all other combinations, especially decamethylenediamine / dodecanedioic acid / terephthalic acid, hexamethylenediamine / adipic acid / terephthalic acid, hexamethylenediamine / adipic acid / caprolactam, decamethylenediamine / dodecanedioic acid / uj-amino undecanoic acid, decamethylenediamine / dodecanedioic acid / laurolactam, decamethylenediamine / terephthalic acid / laurolactam or dodecamethylenediamine / naphthalene-2,6-dicarboxylic acid / laurolactam.

[0098] The many straight chain aliphatic polyamides can be sorted according to the melting points. As the inventive composites are prepared by a melt blending processes the melting point of the polycondensate dictates the processing temperature. PA6, for example, has a melting point roughly in the range of 225°C. A suitable processing temperature is therefore around 230°C. In case of PA66 the melting point is around 270°C so that the melt processing should be carried out at that temperature or slightly above. This is deemed to be close to the upper limit of the processing temperature acceptable for the HNBR component so that PA66 is a less preferred resin for the inventive composites.

[0099] A simple guide for the choice of suitable polyamides is the amide frequency which is the 100 times the number of amide links divided by the total number of atoms along the chain (see K. Marchildon, Macromol. React. Eng. 2011 , 5, 22-54). A high amide frequency will give a higher melting point. PA66 is a AABB type polyamide, it has an amide frequency of 14.3. Therefore, in case of straight chain aliphatic AABB polyamides the amide frequency should not exceed 15, an amide frequency of 13 is more preferred.

[0100] Straight chain aliphatic AB polyamides provide a suitable processing temperature for the creation of the inventive composites. PA6 has an amide frequency of 14.3, PA1 1 has 8.3 and a melting point of 183°C, PA12 has an amide frequency of 7.7 and a melting point of 180°C. AB polyamides are also available as terpolymers (called terpo) with melting points in the range of 150 to 190°C and are therefore considered as very suitable. Aromatic polyamides can be used; however, these polyamides tend to have rather high melting points well above PA66. There are some structural variants of aromatic or semiaromatic polyamides with lower melting temperature which can then be used as components in the composites.

[0101] The amount of polyamide in the composite according to the invention is 5wt% and up to 50wt%. However, the polyamide should not exceed a content in the composite where the HNBR is not the continuous phase anymore. It is rather preferred that a sea-island morphology is realized with the polyamide forming small islands in the continuous HNBR matrix. If the amount of polyamide is too small, i.e. less than 5% then improvement in adhesion and viscosity reduction is not strong enough anymore.

[0102] If the amount of polyamide is too high, then the polyamide may form a continuous phase and the dissolution of the composite in an organic solvent such as NMP is incomplete or too difficult and may require too high dissolution temperatures.

[0103] With the correct amount of polyamide this resin will form small domains in the HNBR in the range of several hundreds of nanometers or a few microns. In the process of dissolution in NMP the HNBR phase will easily dissolve while the polyamide will form small partly swollen particles which form a stable dispersion within the HNBR solution.

[0104] Surprisingly, the obtained suspension of polyamide in a solution of HNBR in NMP is stable. Without being bound to a theory it is believed that the HNBR may have interacted to some extent with the PA particles to serve as a stabilizing layer. Otherwise, it is well known that binary blends of polymers in on solution will eventually separate, unless they have high enough negative enthalpy of mixing.

[0105] Polyester

[0106] The polyesters can be selected form thermoplastic polyesters and from thermoplastic polyester elastomers and blends of those. Preferred thermoplastic polyesters are polybutylene terephthalates (PBT) and polyethylene terephthalates (PET) and should contain at least 90 mol % of a terephthalic units based on the dicarboxylic acid unit content. They should contain diol components which are preferably ethylene glycol units or butylene glycol units. The thermoplastic polyesters are therefore mainly esters of aromatic diacids. Examples of the aromatic dicarboxylic acid or its derivative include dimethyl terephthalate, dimethyl isophthalate, terephthalic acid, isophthalic acid, and naphthalene-2,6- dicarboxylic acid. Examples of the aliphatic diol include butane diol and hexane diol.

[0107] The preferred polyethylene terephthalates and polybutylene terephthalates can comprise, in addition to terephthalic acid moieties, up to 20 mol % of moieties of other aromatic dicarboxylic acids having from 8 to 14 carbon atoms, or moieties of aliphatic dicarboxylic acids having from 4 to 12 carbon atoms, for example moieties of phthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, 4,4'-diphenyldicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, or cyclohexane-dicarboxylic acid and cyclohexanediacetic acid.

[0108] The preferred polyethylene terephthalates and polybutylene terephthalates can comprise, apart from ethylene glycol and 1 ,4-butanediol glycol moieties, respectively, up to 20 mol % of other aliphatic diols having from 3 to 12 carbon atoms or of cycloaliphatic diols having from 6 to 21 carbon atoms, preferably moieties of 1 ,3-propanediol, 2-ethyl-1 ,3- propanediol, neopentyl glycol, 1 ,5-pentanediol, 1 ,6-hexanediol, 2-methyl-2,4-pentanediol, 3-methyl-2,4-pentanediol, 2,2,4-trimethyl-1 ,3- or -1 ,6-pentanediol, 2-ethyl-1 ,3-hexanediol, 2,2-diethyl-1 ,3-propanediol, 2,5-hexanediol and 1 ,4-cyclohexane-dimethanol.

[0109] The thermoplastic polyester elastomers comprise thermoplastic polyesters as described above with added polymer segments of poly(alkylene-oxide), derived from the respective poly(alkylene-oxide) diols. These segments preferably have a molecular weight from 500 to 3,000 Da to provide a flexible, elastic chain components within the thermoplastic elastomer. The elastic segments are commonly referred to as soft blocks.

[0110] Preferred diol moieties are poly(butylene-glycol) diols and poly(ethylene-glycol) diols which can be also used in combinations. The amount of poly(alkylene-oxide) within the thermoplastic elastomer is in the range from 10 to 45 mol% diol units based on the diol fraction of the thermoplastic polyester segments. General properties and synthesis of thermoplastic elastomers can be found in Z. Roslaniec (Chapter 3 Polyester Thermoplastic Elastomers: Synthesis, properties, and some Applications, 2005 Wiley- VCH Handbook of Condensation Thermoplastic Elastomers, Weinheim ISBN 3-527- 30976-4). Solvents

[0111] The organic solvent allows for the dissolution of the binder or binder composite as a necessary step to create electrode slurries for coating. It further allows the dispersion of conductive materials such as carbon nanotubes. In that case the binder composite serves as a dispersion aid. Typical solvents are NMP, DMF, valero-lactones, butyrolactone, xylene and other aromatics, various esters and ethers and ether esters. Low polarity solvents are mainly used for solid state batteries where the process solvent needs to be compatible with the solid electrolyte.

[0112] The process solvent must be chosen to allow the dissolution of the HNBR while the solubility of a specific HNBR grade depends on its structure. However, the resin as part of the binder composite does not need to be soluble at all in the process solvents. Indeed, the benefit of the inventive composite is that non-soluble resins can be introduced into the wet electrode manufacturing process and therefore more choices of resins are possible regardless its solubility in the solvent.

[0113] The inventive composites based on HNBR and a polycondensate resin, i.e. polyamide or polyester as described, can be used in coating processes for the LiB cathode and in SSB as stable fine particle size dispersions in a polymer solution can be obtained. These solutions can be used as binders, as rheology modifiers and as polymeric dispersion aids for conductive carbon pastes, for example to prepare carbon nano-tube pastes.

[0114] The stability test for the composite solutions in battery process solvents a special test method of the Molau test. The Molau test is carried out by dissolving the composite in a solvent which is known to dissolve the polymer which forms the continuous matrix but not the dispersed polymer. If the dispersed polymer separates out as an upper or lower layer depending on the density the composites are considered as not compatibilized. If a turbid stable solution is obtained, then the dispersed phase is compatibilized. Conventionally, a third polymer needs to be introduced as compatibilizer such as described in Huahao Yang et.al. (Yang, H„ Cao, X., Ma, Y„ An, J., Ke, Y„ Liu, X., & Wang, F. (2011 ). Effect of maleic anhydride grafted polybutadiene on the compatibility of polyamide 66 / acrylonitrile- butadiene-styrene copolymer blend. Polymer Engineering & Science, 52(3), 481-488) for ABS dispersed in PA66. Similarly, stable opaque solution could only be obtained for PA6 with dispersed EPDM when maleic anhydride grafted EPDM was used as a compatibilizer, see Xu et.al. (M. Xu, W. Qiu, G. Qiu., Journal of Macromolecular Science, Part B: Physics, 52, 155-166,2013). The authors use the term Molau test to characterize stable solutions of compatibilized polymer blends. G. E. Molau described stable solution of immiscible polymers based on emulsification effects in the mid 60ies and beginning 1970 such as in G.E. Molau, J. Polym. Sci., Part A, General papers (1965), 3(4) 1267-1278.

[0115] Ethylene-propylene elastomer grafted maleic anhydride toughened polyamide-6 morphology and properties, J. Macromol. Science, Part B Physics, 52:155-166, 2013). Further, LDPE needed to be grafted with glycidyl methacrylate to allow melt blending with PA-6 and then passing the Molau test (Q. Wei et.al., Functionalization of LDPE by melt grafting with glycidyl methacrylate and reactive blending with polyamide-6, Macromol. Chem. Phys. (2003) 204(8), 1123-1 133).

[0116] It is also surprising that in the inventive composite’s based on melt mixed HNBR and the defined polycondensate, a high degree of compatibility was achieved without the usage of any third polymer as compatibilizer. Both polymers are considered as immiscible. No grafting reaction was carried out and the melt mixing was carried out avoiding excessive temperatures or to long mixing times.

[0117] Surprisingly, the Molau test which had been merely developed to assess polymer compatibility can now be used to design soluble composites in liquid form to be used as binders, rheology modifiers and dispersion aids for lithium-ion batteries.

[0118] Until now the Molau test has not been applied on composites based on nitrile rubber or HNBR in combination with a combination of a polycondensate, i.e. polyamide or polyester, as defined.

[0119] Examples

[0120] Materials used:

[0121] HNBR 1 : nitrile content of 34% (ISO 24698-1 ), Mooney viscosity of 63 MU (MI1 +4, 100°C) according to ISO 289 I ASTM D 1646, unsaturation <0.9% as residual double-bond content (RDB, IR spectroscopy) where the parent NBR would have an RDB of 100%. HNBR 2: nitrile content of 34% (ISO 24698-1 ), Mooney viscosity of 70 MU (MI1 +4, 100°C) according to ISO 289 / ASTM D 1646, unsaturation <0.9% as residual double-bond content (RDB, IR spectroscopy).

[0122] HNBR 3: nitrile content of 17% (ISO 24698-1 ), Mooney viscosity of 70 MU (MI1 +4, 100°C) according to ISO 289 / ASTM D 1646, unsaturation <0.9% as residual double-bond content (RDB, IR spectroscopy). The polymer contains acrylate monomer units and is amorphous (DSC temperature scan, Tg -43°C). The hydrocarbon-based monomer unit are below 65%.

[0123] HNBR 4: nitrile content of 34% (ISO 24698-1 ), Mooney viscosity of 40 MU (MI1 +4, 100°C) according to ISO 289 I ASTM D 1646, unsaturation <0.9% as residual double-bond content (RDB, IR spectroscopy).

[0124] HNBR 5: HNBR with a nitrile content of 27% (ISO 24698-1 ), unsaturation <0.9% (RDB, IR spectroscopy), Mooney viscosity of 70 MU (MI1 +4, 100°C) according to ISO 289 I ASTM D 1646, prepared by the hydrogenation of nitrile rubber with a nitrile content of 28% and a Mooney viscosity of 45 MU (MI1 +4, 100°C). The content of hydrocarbon-based monomer unit is 73%.

[0125] PA6, Durethan® B31 F: PA 6, provided by Lanxess AG, non-reinforced, for extrusion, low viscosity, no additives, melting point 222°C (ISO 1 1357-1 , -3 222)

[0126] Terpo PA ZN150 from Yixing Chemical Reagent Factory, China: mp. 150°C, copolymer from PA6, PA66 and PA1010 with weight ratios of 10% / 20% / 70%. The amide frequency was calculated to 10.7.

[0127] Terpo PA ZN 170 from Yixing Chemical Reagent Factory, China: mp. 165°C, copolymer from PA6, PA66 and PA1010, viscosity number 135±30 ml / L, melting point measured by DSC 167°C (2ndscan).

[0128] Terpo PA type A from Shanghai Sailuoluo: copolymer based on PA6, PA66 and PA1010 with weight ratios of 10% / 20% / 70%, mp. 145 to 155°C, several melt peaks (DSC first scan), mp 144°C (DSC second scan). DSC was taken with Netzsch DSC 204 F1 , 10 K / min. The amide frequency was calculated to 10.7.

[0129] PBT: Pocan® B 1000 from Lanxess AG, thermoplastic polyester with melt volume rate at 250°C, 2.16 kg 45 cm3 / 10 min, melt temperature 225°C. Skypel G140D: Thermoplastic polyester elastomer from SK Chemicals based on PBT and butylene glycol polyether soft block, hardness ShD 40 (max.), 37 (15 s), melt temperature 157°C, melt flow rate at 190°C (2.16 kg) 7 g / 10 min.

[0130] Skypel G155D: Thermoplastic polyester elastomer from SK Chemicals based on PBT and butylene glycol polyether soft block, hardness ShD 55, melt temperature 202°C, melt flow rate at 220°C (2.16 kg) 11 g / 10 min.

[0131] PVDF: Kynar® HSV 900, high molecular weight polyvinylidene fluoride homopolymer provided by Arkema, GPC shows a peak at Mw 93 kDa and at 1 ,37 kDa (Z. Chen et.al., Chem. Eng. J. 276 (2015) 174-184).

[0132] PVDF: Solef® 5130 from Solvay, PVDF modified with polar functional groups with a mol- weight of 1 .0 to 1.1 mio Dalton

[0133] Active material LFP: carbon coated nano-type LiFePO4, DY-1 1 from Shenzhen Dynanonic

[0134] Conductive carbon black: Super C® Li, from Timcal, BET 62 m2 / g, ash 0.010%

[0135] Conductive carbon black Super P, from Imerys.

[0136] Active material NCM: NCM (Ni-Co-Mn) type 523, from BASF China.

[0137] The content of all materials which is given in % should be defined as wt.-% unless otherwise specified.

[0138] General method for preparation of a blends of HNBR and polyamide or polyester in an internal mixer

[0139] Generally, the following methods which are described for using a polyamide are in a corresponding manner usable for polyesters.

[0140] Prior to use, the polyamide was stored at 80° C. for 16 h. The melting point of the polyamide was determined via DSC. The PA 6 polyamide was provided by Lanxess AG as Durethan® B31 F. At the start time, the internal mixer was charged with the polyamide. Prior to addition, the internal mixer was heated to 200° C. and, after addition, brought to at least the melting temperature of the polyamide, 230° C. in this case, by adjusting the rotor speed. After one minute, the HNBR rubber and the ageing stabilizer were added. The mixing was carried out under temperature control so that the mixture remained at a temperature in the range of at least 230° C. for 10 minutes. After one minute, the internal mixer was vented, and the shaft was cleaned. Thereafter, the internal mixer was emptied to obtain the mixture.

[0141] General method for preparation of a blends of HNBR and polyamide in a twin-screw extruder, I

[0142] A twin-screw extruder (Leistritz 27 Maxx, 48 D, screw diameter 28 mm) was fed with grinded HNBR and with PA6 pellets. The temperature profile was adjusted by the screw speed and the barrel temperature settings so that 240°C was reached. The throughput was 40 kg / h and the screw speed was 200 rpm.

[0143] The mix was extruded through a die and granulated under water, then quickly sieved-off and dried in air.

[0144] General method for preparation of a blend of HNBR and polyamide in a twin-screw mini extruder with internal cycling, II

[0145] HNBR, cut into small pieces, and polyamide resin (10wt%) were melt-blended with a conical vertically arranged micro twin-screw extruder, available from Explore as Micro compounder MC 15 HT with an internal volume of 15 ml. The materials are pushed in from a feed hopper with a piston, melt-mixed by internally cycling of the melt to simulate a continuous large scale twin-screw extruder operation. The PA was first introduced into the mixer and mixed for 1 minute, followed by the HNBR with further mixing of 5 minutes.

[0146] Composite preparation trials

[0147] Composite trial 1 : HNBR 1 (100 phr) and PA 6 (10 phr) were melt-blended with above twin-screw extruder method I to obtain composite 1 in the form of pellets. The melt peak of PA 6 was determined in the composite at 217°C (second heating, DSC). The melt peak of PA6 before compounding was determined at 221°C (DSC). The unit phr refers to 100 parts of rubber.

[0148] Composite trial 2: HNBR 1 (100 phr) and PA 6 (50 phr) were melt-blended with above twin-screw extruder method I to obtain composite 2 in the form of pellets.

[0149] Composite trial 3: HNBR 3 (90%) and terpo PA type ZN150 (10%) were melt-blended with the twin-screw extruder method II to obtain composite 3 in the form of pellets. The melt temperature was 180°C. The units % refer to 100% as the total amount of compound. Composite trial 4: HNBR 3 (90%) and terpo PA type A (10%) were melt-blended with the twin-screw extruder method II to obtain composite 4 in the form of pellets. The melt temperature was 180°C.

[0150] Composite trial 5: HNBR 3 (90%) and PA6 (10%) were melt-blended with the twin-screw extruder method II to obtain composite 5 in the form of pellets. The melt temperature was 230°C.

[0151] Composite trial 6: HNBR 4 (100 phr) and PA6 (10 phr) were melt-blended with twin-screw extruder method I to obtain composite 6 in the form of pellets.

[0152] Composite trial 7: HNBR 4 (100 phr) and PA6 (50 phr) were melt-blended with twin-screw extruder method I to obtain composite 7 in the form of pellets.

[0153] Compound trial 8: HNBR 4 (90wt%) and PA6 (10wt%) were melt-blended the twin-screw extruder method II. The melt temperature was varied in a series of individual trials from 230 to 220, 210, 200, 190°C where each mix was taken as a sample and evaluated for dissolution behavior in NMP. It was observed that the samples taken from the mixing machine were all homogeneous whereas those with higher temperatures tended to have a glossier surface. Surprisingly, all samples could be dissolved in NMP. However, for low solution viscosities a higher melt mixing temperature should be preferred. In case of PA6 as the modifying resins the temperature should not be below 21 CPC, or not lower than around 15°C below the DSC melt peak.

[0154] Composites 9 to 12: HNBR 5 was melt blended with PA 6 with the twin-screw extruder method II at 230°C, the PA 6 content was 10% and 30%. Then the trials were repeated by using terpo PA type A and a melt temperature of 180°C. In this way composites 9 and 10, and then 11 to 12 were obtained. The compounds appeared homogeneous.

[0155] The composites were tried to dissolve in NMP, however, after 7 days still undissolved pellets remained in the solution. It was concluded that the compatibility of this HNBR matrix with the PA resins was not sufficient to allow the formation of a stable dispersion in NMP.

[0156] Composite trial 13: HNBR 4 (90wt%) and PBT (dried 2h at 100°C) were melt-blended with the twin-screw extruder method II. The mixing temperature was 230°C. Extruded strands were homogeneous with a smooth surface. Composite trial 14: HNBR 4 (90wt%) and Skypel G140D (dried 2h at 100°C) were melt- blended with the twin-screw extruder method II. The mixing temperature was 165-167°C. Extruded strands were homogeneous with a smooth surface.

[0157] Composite trial 15: HNBR 4 (90wt%) and Skypel G155D (dried 2h at 100°C) were melt- blended with the twin-screw extruder method II. The mixing temperature was 213°C. Extruded strands were homogeneous with a smooth surface.

[0158] Mechanical properties of binder composites

[0159] Stress-strain curves were taken from pressed samples of composite trial 2 which show the increase of modulus at lower elongation for the composite of the invention against pure HNBR. Such curves are shown in Fig. 1 , wherein figure 1 in detail shows stress-strain curves of binder films of HNBR 1 and composite 2, wherein three respective samples are measured (HT 1 to HT 3).

[0160] Preparation of composite solutions in NMP

[0161] Polymer samples were cut into small pieces of around 1 cm, dried in a vacuum oven at 50°C overnight. These polymer crumbs were dissolved in dry NMP at RT with a shaker bed to obtain a homogeneous solution with a solid content of 8%. Composite samples were dried in the same way and dissolved. The solution viscosities (flow curves) were tested with a Brookfield rheometer with a shear sweep from 1 to 1000 s '1within 700 s and then back to 1 s1to check for any thixotropy. The particle size was tested with a Malvern ZetaSizer (laser correlation spectroscopy).

[0162] Composite 1 gave solution 1 , HNBR 1 gave solution 2. In case of PA6 no dissolution was observed, the granules remained unswollen.

[0163] Solution 1 was slightly opaque compared solution 2 based on pure HNBR which was clear. This gives an indication that the PA is dispersed in the HNBR matrix in very small domains.

[0164] Further, respective flow curves were provided as shown in figure 2. In detail, figure 2 shows flow curves, wherein composite trial 1 (composite with HNBR 1 fresh) and polymer HNBR1 , and a solution of composite trial 1 after 7 days of storage (composite with HNBR 1 after 7d) are shown. The flow curves as shown in figure 2 reveal that the added PA in the HNBR (composite trial 1 ) gives a lower viscosity over the complete shear range. The rheology did not change with storage of the solution which means that the polymers are stable in solution although PA is not miscible with HNBR. The solution is rated as stable as defined in the Molau test.

[0165] Further, the particle size distribution was observed, see figure 3. In detail, the particle size according to Malvern is around 550 nm. When examining the sample in atomic force microscopy (AFM, samples microtome cut at -190°C, analysis by phase contrast) one can see particle from 1 micron down to a few hundred nm. The arithmetic average was 240nm and the volume fraction above 1 micron was only 18.1 %. The largest particles found had a diameter of 1 .01 microns.

[0166] To allow for a stable dispersion of the resin when dissolving the composite into a processing solvent the particle size should not exceed 3 microns, more preferably it should be below 2 micron. This can be ensured if the measured volume fraction of particles above 1 micron does not exceed 50%, determined via phase contrast AFM. The analysis should be based on the evaluation of 40 and 10 pm2images.

[0167] Dissolution trials with composites 1 using MEK

[0168] Composite 1 : 12.2% insoluble in methylethylketone (MEK) according to DIN - ISO 17025, particle size via AFM D50% 423 nm, preparation details of composites: 20 kg / h throughput, 200 rpm.

[0169] Composite 1 : 1 1.1% insoluble, particle size via AFM D50% 409 nm, preparation details of composite: 40 kg / h throughput, 200 rpm.

[0170] Composite 1 : 12.5% insoluble, particle size via AFM D50% 412 nm, preparation details of composites: 60 kg / h throughput, 200 rpm.

[0171] HNBR 1 : 0.6%, for comparison

[0172] The dissolution trials show that the HNBR can be dissolved with a very small content of insoluble matter. However, the inventive composites have an insoluble content between 1 1.1 and 14.5%. The thermoplastic resin PA 6 is not soluble in MEK and was introduced in the composites with 10 phr, equivalent to 9.1 weight%. Therefore, a small but important excess of insoluble material can be assigned as HNBR rubber associated or bound to the thermoplastic resin. This may help to further stabilize the dispersion. Dissolution trials with composites 6 and 7 [effect of PA content]

[0173] Table 1

[0174] Composite 7 contains 50 phr PA6 (33%) and dissolved only partially in NMP. Dissolution was tried for 8% in NMP at RT on a shaker. After several days undissolved pellets remained in the mix. The mixture was sheared with an IKA lab mixer at 5,000 rpm which resulted in a thick white paste which remained inhomogeneous. From that it can be concluded that the amount of dispersed PA6 in the composite (50 phr, 33wt%) was too high. The analysis of composite 7 via AFM shows a particle fraction of 3 microns and more which are in closer proximity compared to the composites which contain only 10% PA6. This can explain why the dissolution at too high PA content is not good enough anymore.

[0175] The arithmetic average of the particle size distribution in AFM was 503 nm, the largest particle found in the analysis was 3.6 microns. The analysis was based on the evaluation of 40 and 10 pm2images. The volume fraction of particles above 1 micron was 74.3% which make the presence of significant numbers of larger particles more likely.

[0176] Figure 4 further shows flow curves of composite 6 and HNBR 4 dissolved in NMP. The flow curves of composite 6 compared to neat HNBR 4 showed a lower viscosity. This can be related to a lower HNBR content in the polymer composite or by a shear induced mol- weight degradation during the composite preparation or by both effects.

[0177] HNBR 4 and the derived composites can be used to prepare dispersion of conductive carbon materials such as CNT. It can be expected that the viscosity of CNT pastes with the inventive composites are lower compared to those with neat HNBR, such as HNBR 4.

[0178] Dissolution trials with composite 8 [variation of processing temperature]

[0179] Figure 5 shows flow curves after dissolution in NMP (8%) with trials 8, variation of mixing temperature. Figure 6 shows the respective curves after storage of 7 days. Mixing temperature at 230 and 220°C give flow curves with very little thixotropy while lower mixing temperatures give more thixotropy. The solutions show a moderate increase of viscosity with storage of 7 days. This indicates that mixing temperature should not be too much below the melting points of the PA resin. Figure 7 further shows the particle size of PA6 in composite 8 in the NMP solution over the melt processing temperature. According to the present invention, the discussed particle size corresponds to the domain size of the polycondensate within the matrix of the hydrogenated nitrile rubber, the latter this also being determined via AFM.

[0180] Dissolution trials with composites 9 to 12 [effect of nitrile content of HNBR]

[0181] Dissolution was tried for 8 wt.-% in NMP at RT on a shaker. After 7 days many undissolved pellets remained in the mix. It was concluded that the selected HNBR grade with an acrylonitrile content of 28% was not suitable for the manufacturing of NMP soluble composites. Therefore, in case of HNBR without further functional groups the nitrile content should not be much lower 34wt.-%, preferably not lower than 30wt.-%.

[0182] Dissolution trials with HNBR / polyester composites

[0183] The composites from compounding trials 13 to 15 were dissolved to a concentration of 8wt.-% in NMP. The composites dissolved completely and gave opaque solutions. As shown in figure 1 1 the composite 13 (with PBT) gave flow curves with lower viscosities compared to the uncompounded dissolved HNBR 4. Composite 15 (with Skypel G155D) gave flow curves very similar to the uncompounded HNBR 4. In both cases the viscosities remained stable after 7 d of storage. In case of composite 14 (with Skypel G140D) the flow curves were shifted to higher viscosities; a viscosity increase after storage of 7 d was observed. The viscosities follow the trend of polyester melt peak temperatures as shown in figure 12, in which the pair of entries with the lowest melt peak temperature corresponds to composite trial 14 (with Skypel G140D), the pair of entries having the medium melt peak temperature corresponds to composite trial 15 (with Skypel G155D) and in which the pair of entries having the highest melt peak temperature corresponds to composite trial 13 (with PBT). In order to limit the viscosities of the dissolved composites with polyesters the melting temperature should be at 175°C whereas an upper limit should be 270°C in order to avoid polymer degradation during melt mixing. According to figure 12, composites 13 to 15 are dissolved in NMP and the respective parameters are shown after mixing and after storage of 7 days.

[0184] Dissolution trials with composites 3, 4 and 5 in different battery process solvents, dissolution of the polyamide resins

[0185] Table 2

[0186] The trials show that none of the PA resins is soluble in xylene or NMP. However, opaque but homogeneous solutions were obtained with composites 4 and 5 in xylene. With composite 3 the opaque solution in xylene still had some gel particles. It is possible that a treatment with shear may have led to a full dispersion. The solutions don’t show thixotropy so that the shear history does not change the rheology which is good to coating applications.

[0187] Figure 8 shows flow curves of composites 4 to 5 in xylene with 10% solids content. In detail, solutions of composites 3 to 5 may be used as binder to disperse solid electrolyte to form freestanding sheets as an intermediate layer between cathode and anode in solid state batteries. The advantage of the inventive composites is that thermoplastic resins such as polyamide can be introduced together with HNBR to bond the solid electrolyte to sheets even though the resin is totally insoluble in the solvent. The coating solvents in solid state batteries need to be carefully selected for compatibility with solid electrolyte, especially the absence of undesired reactions with the latter. The inventive composites are melt-blended to create a dispersion in the soluble HNBR rubber matrix. Surprisingly, even with xylene as the solvent the thermoplastic resin form stable fine particle dispersion in the solvent together with the HNBR.

[0188] Preparation of cathode slurries with LFP

[0189] Active material LFP, DY 11 and conductive carbon black Super P was dried in an oven at 120°C for 2 hours. Binders HNBR and PVDF were dried in a vacuum oven at 120°C for 2 hours. All processing steps were carried out in a dry room with a dew point not exceeding -54°C. Binders were dissolved in dry NMP (shaker, RT) % of the total amount), Super P was added and then mixed with a Thinky mixer (planetary centrifugal mixer from Thinky Inc.) for 12 minutes at 2000 rpm. Then the LFP was added with the other % of the NMP and further mixed in the Thinky mixer for 18 minutes at 2000 rpm. Then, further NMP was added to achieve a viscosity of 8-10 Pa s at 10 s~1. All mixing steps were done in 6 minutes intervals, followed by cooling to RT. The cathode slurries were then coated on Al-foil and on PET film with a 150 pm gauge, dried with convection oven [120°C, 2hours] for physical testing, vacuum oven [120°C, 4 hours] for impedance testing and calendared with a 2-roll device to reduce the thickness by around 50%.

[0190] Table 3 Peel strength: The peel strength is determined by applying an adhesive tape from 3M (1500 Vinyl Electrical Tape) on the cathode and peeling off the tape so that a geometry of around 180° is realized, the median peel strength values are taken.

[0191] Flexibility: The coating flexibility was tested by winding of the coated electrode around a metal mandrel of 2 mm diameter and visual observation for any cracks. Detection of cracks is rated as bad; no detection of cracks is rated as good. The mandrel test simulates the winding of the combined electrodes for cylindrical and prismatic cells. The comparison trials 1 can only reach a cathode slurry solids content of 56% when taking a viscosity of 8 to 10 Pa s at 10 s1as a guide while in trial 2 with HNBR 1 the solids was already 66%. In trial 3 the composite 1 was used as binder and then a solid content of 68% could be reached. The peel strength values on Al-C were acceptable although somewhat lower for trial 3. In trials 4 and 5 the binder dosages were lowered to 1.6%. Then solids content could be further increased to 68 and 70%, respectively. The solids with the composite as binder surpass the those found with HNBR as binder alone which was a target of the invention.

[0192] Surprisingly the peel strength values even reached higher levels when either HNBR or the inventive composite are used at lower dosage levels.

[0193] When testing the flexibility of the cathode with the mandrel tester the cathode of comparative trial 1 with PVDF showed cracks and thus failed the flexibility test.

[0194] Figure 9 further relates to rheology curves from slurries as outlined n table 3 above.

[0195] Preparation of cathode slurries with NCM

[0196] Slurries were prepared using trials 6 to 8 in the same as with LFP, but as active material PVDF Solef 5130 was used.

[0197] Table 4

[0198] The overall solid contents were higher as NCM possesses larger particle size compared to LFP. The PVDF based slurries reach 72% solids while the HNBR based one achieves 78%. The slurry with the composite binder 1 gives even 80% solids which was a target of the invention. The peel strength values are higher for HNBR and for the composite binder compared to PVDF.

[0199] Figure 10 further relates to rheology flow curves from trials in table 4 with NCM cathode slurries.

Claims

Claims1. A binder composite for a binder of an electrode of an electrochemical energy storage device, the binder composite containing a) hydrogenated nitrile rubber; and b) a polycondensate selected from the group consisting of a polyamide having a melting point from 140 °C to 270 °C and a polyester having a melting point from 175 °C to 270 °C; wherein the polycondensate forms domains in the hydrogenated nitrile rubber, wherein the domains have a size D50% below 3 microns within the matrix of the hydrogenated nitrile rubber.

2. The binder composite according to claim 1 , wherein the hydrogenated nitrile rubber contains acrylate unites, wherein the sum of remaining hydrocarbon-based monomer units is less than 70 wt.-%.

3. The binder composite according to any of claims 1 or 2, wherein the hydrogenated nitrile rubber has a nitrile content of from 7 to 55 wt.-%, such as from 15 to 40 wt.-%, calculated as acrylonitrile, and a degree of hydrogenation measured as RDB below 1%.

4. The binder composite according to any of claims 1 to 3, wherein the content of polycondensate is in the range of 5 to 40 phr, wherein 100 phr refers to the hydrogenated nitrile rubber.

5. The binder composite according to any of claims 1 to 4, wherein the polyamide is polyamide 6.

6. The binder comoosite according to any of claims 1 to 5, wherein that the ratio of theJR to the polycondensate is between 1 .3 and 5.

7. The binder composite according to any of claims 1 to 6, wherein the binder composite is present in an electrode coating dispersion containing an electrochemically active material and conductive carbon material dispersed in an organic solvent.

8. The binder composite according to any of claims 1 to 6, wherein the binder composite is present in an electrode coating dispersion containing a solid electrolyte, optionally an electrochemically active material, and optionally conductive carbon material dispersed in an organic solvent.

9. The binder composite according to any of claims 1 to 8, wherein the composite is prepared by melt-mixing the polycondensate and the hydrogenated nitrile rubber.

10. The binder composite according to any of claims 1 to 9, wherein the binder composite is free of halogenated compounds.

11. The binder composite according to any of claims 1 to 10, wherein the binder composite passes the selective dissolution Molau test.

12. Electrode for an electrochemical energy storage device, wherein the electrode comprises a binder composite, the binder composite being arranged according to any of claims 1 to 11.

13. Electrochemical energy storage device, wherein the electrochemical energy storage device comprises an anode and a cathode, the cathode being arranged according to claim

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