Binder composition for an electrochemical energy storage device

Abstract

The present invention relates to a binder composition for forming a binder of an electrode of an electrochemical energy storage device, the binder composition comprising a) a hydrogenated nitrile rubber, wherein the hydrogenated nitrile rubber has the following properties: - a Ra value against N-Methyl-2-pyrrolidone is at least 9 MPa1 / 2; and - a Ra value against a fluid blend of ethylene carbonate to linear carbonates, wherein ethylene carbonate is present in the range of ≥ 30 vol.-% to ≤ 33 vol.-% and linear carbonates are present in the range of ≥ 66 vol.-% to ≤ 70 vol.-%, each referring to the fluid blend, is at least 7 MPa1 / 2, and b) at least one amino-functional silane.

Description

[0001] Binder composition for an electrochemical energy storage device

[0002] The present invention relates to a binder composition for an electrode for an electrochemical energy storage device. The present invention further relates to an electrode material composition comprising such a binder composition as well as to an electrode, such as a cathode, being formed from said binder composition as well as to an electrochemical energy storage device comprising said electrode.

[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 Li B 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] All these materials are solid powders. Flexible polymer binders are thus needed to allow coating the binder composition 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, good dispersion of all particles in the binder must be ensured.

[0008] For binding of the particulate components of the LiB 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 the recent 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, or at least to a limited storage stability of the cathode slurry. Fluorinated binder materials require very high molecular weights for efficient bonding which will often exceed 1 million Dalton. When these polymers are dissolved in NMP, undesirably high viscosities occur which limit the achievable solid content. This means that high amounts of solvent are needed for coating and subsequently, much energy is needed for evaporation and drying and subsequent solvent recovery and purification. Recently, the manufacture of fluoropolymers faces the issue of the usage of PFAS (perfluorinated alkyl substances) which may eventually end up in the nature, either during the polymerization process or from traces that are contained in these polymers and subsequently in all articles made from them.

[0010] Further, the increasingly more important battery recycling is more complicated when there is the presence of fluorinated polymer in the cathode material. In case of dry pyrolytic recycling processes these polymers can be burnt to give HF gas which is very corrosive to all materials and need to be scrubbed out of flue gas which is difficult.

[0011] Hydrogenated nitrile rubber (HNBR) on the other side does not contain PFAS or fluorinated compounds in general and thus does not have these issues. Nitrile rubber, especially the more electrochemically stable hydrogenated version of nitrile rubber, HNBR, has been shown on the one hand 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. Therefore, polymers which support the dispersion of conductive carbon are needed. These polymers also prevent the conductive materials from reagglomeration. Hydrogenated nitrile rubber, HNBR, can thus take the role of a binder in the cathode slurry due to its excellent flexibility and binding power while being less sensitive to alkaline surfaces. However, swell of the binder in electrolyte is an important issue to take into account.

[0012] The role of HNBR as binder is exemplified in US2018 / 0183064, however this disclosure is silent on the effect of any electrolyte swell.

[0013] EP 3 240 069 A1 describes a binder with a swell in EC / EMC 3:7, 1M LiPF6in the range of 200 to 500% as weight ratio after swell I before swell while the binder needs to have a combined Ru and Rh content of 2 to 32 ppm according to the examples.

[0014] In EP 3 276 713 A1 , an HNBR binder is presented with a swell from 200 to 700% (ethylene carbonate (EC) / diethyl carbonate (DEC) I vinylene carbonate (VC) = 68.5 / 30 / 1.5, 1 M LiPFe, 72 h, 60°C, weight ratio after / before).

[0015] EP 3 220 461 A1 uses a main binder with a content of nitrile groups of at least 85% and acrylate units. Therefore, due to the very high polarity a very high swell in the equally highly polar electrolyte must be expected.

[0016] An important 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.

[0017] It is known in the industry that binder polymers will swell in the battery fluid to a certain degree. According to commercial literature, PVDF will have a swell between 30 and 50%. According to patent disclosures such as EP 3 240 069, a swell range between 100 and 500% is beneficial in the case of HNBR binder polymers. The swell can be measured by immersion of the binder polymer in a typical battery fluid under conditions such as 3d and 60°C. In the present invention the swell is determined as % weight gain relative to a polymer sample before immersion. The typical battery fluid is 1 M LiPFe dissolved in ethylene carbonate (EC) / diethylcarbonate (DEC) 3 / 7 by volume-%. The range of 100-500% is equivalent to 200-600% swell described in EP 3 240 069 where the mass% ratio after / before swell is used.

[0018] However, the inventors have found that such a high degree of swell in the battery fluid is detrimental to the battery performance. Without being bound to a theory it is believed that a too highly swollen polymer film inside a fluid filled electrode will give a larger polymer volume fraction within the electrode which has a high resistance against the diffusion of ions. This is because ion diffusion is hindered if the matrix viscosity is high. This negative effect is believed to be more pronounced if the polymer layer is more swollen and thus extends much into the free electrolyte filled space of the cathode. It may thus be preferred that the swell is reduced to an amount of 100 %, and / or to 50% of the solutions of the prior art.

[0019] A lower swell makes the volume of swollen binder smaller and thus the hindrance for the ion diffusion less. Another effect of polymer swell by the battery fluid is the volume change of the polymer film within the cathode. If one considers a density of compact LFP particles of 3.6 g / cm3, the true density of carbon black as 2.27 g / cm3and the polymer density as 0.98 g / cm3then for example the volume fraction of the polymer at a dosage of 1 ,6wt% would give a polymer volume fraction of 5.6%. If an assembled dry cathode film pack is filled with the battery fluid, then there will be volume expansion of the polymer film. A measured polymer swell in battery fluid from 50 to 500wt% would result into an increased weight between 2.4 and 8.9%. If one considers the volume fraction of the swollen polymer in the cathode, then one gets the range 7.7 to 23.5 vol% if one considers the battery fluid density to be 1.17 g / ml.

[0020] If the swollen polymer expands into all directions, then the isotropic linear swell factor would be between 1.11 and 1.61. However, considering that the polymer is constrained as a polymer film deposited roughly on the spherical active material particles, then the film can only expand in normal direction to the non-swellable active material so that the swell factor would be between 1 .38 and 4.2. If the polymer occupies the porosity of the cathode coating, it would take a considerable portion of this free volume. If one considers the dried cathode layers to fit into a defined packaging space, then the process of polymer swell will cause a considerable expansion pressure leading to deformation of even leakage of the cell pack. Object of the invention

[0021] It is thus an object of the present invention to overcome at least one disadvantage of the prior art at least in part. Specifically, it is an objective of the present invention to provide a binder for an electrode for an electrochemical energy storage device which has a low swell in typical organic carbonate-based battery fluids, and which has still good binding and adhesion performance. At the same time the polymer binder should preferably allow for a low viscosity of the cathode coating slurry and thus should allow the realization of high solid contents of the coating formulation. Thus, the inventive binder composition should be advantageous with regards to energy saving from less solvent drying and therefore contribute to the sustainability of the battery production. Further, the binder shall be free of halogenated compounds.

[0022] Means to solve the objective

[0023] The above-described objects are solved at least in part by a binder composition having the features of independent claim 1 . This object is further at least in part solved by a binder having the features of independent claim 9, by an electrode material composition having the features of independent claim 10, by an electrode having the features of independent claim 11 and by an electrochemical energy storage device having the features of independent claim 13. Advantageous embodiments are given in the dependent claims, in the further description as well as in the figures, wherein the described embodiments can, alone or in any combination of the respective embodiments, provide a feature of the present invention unless not clearly excluded. Further, features and advantages as described in respective embodiments can be transferred to further embodiments.

[0024] The present invention provides a binder composition for forming a binder of an electrode of an electrochemical energy storage device, the binder composition comprising a) a hydrogenated nitrile rubber, wherein the hydrogenated nitrile rubber has the following properties: a Ra value against N-Methyl-2-pyrrolidone (NMP) is < 9 MPa1 / 2; and a Ra value against a fluid blend of ethylene carbonate (EC) to linear carbonates (LC), wherein ethylene carbonate is present in the range of > 30 vol.-% to < 33 vol.-% and linear carbonates are present in the range of

[0025] > 66 vol.-% to < 70 vol.-%, each referring to the fluid blend, is at least 7 MPa1 / 2, and b) at least one amino-functional silane.

[0026] Such a binder composition allows significant advantages over solutions of the prior art and in particular allows polymer binder composites which are usable in electrodes for electrochemical energy storage devices, such as lithium-ion secondary batteries (Li B) and which is advantageous with regard to swell and adhesion and is further free of fluorinated compounds.

[0027] The binder composition as described is thus useful for forming a binder of an electrode of an electrochemical energy storage device.

[0028] The binder composition comprises two main components, namely a hydrogenated nitrile rubber (HNBR) and further an amino-functional silane.

[0029] The hydrogenated nitrile rubber is defined as component a). With regard to this component, this material is a flexible rubber-like material, and it allows to create softer cathode films and will in general give higher peel forces compared to PVDF, for example. However, generally, the swell of HNBR in the LiB electrolyte is higher than those of PVDF. This can give electrolyte swollen polymer layers in the cathode where the ion conductivity is slowed down. However, this problem is overcome effectively by the means of the present invention.

[0030] With this regard, it is provided that the hydrogenated nitrile rubber has the following properties: a Ra value against N-Methyl-2-pyrrolidone (NMP) is < 9 MPa1 / 2; and a Ra value against a fluid blend of ethylene carbonate (EC) to linear carbonates (LC), wherein ethylene carbonate is present in the range of > 30 vol.-% to < 33 vol.-% and linear carbonates are present in the range of

[0031] > 66 vol.-% to < 70 vol.-%, each referring to the fluid blend, is > 7 MPa1 / 2. It was found that especially these properties of the HNBR can solve issues of the prior art effectively.

[0032] To ensure a low swell in the typical battery fluids the Ra value between the used HNBR polymer and the defined battery fluid should be at least 7 MPa1 / 2, more preferable, at least 7.5 MPa1 / 2. With this regard, the Ra value is defined against a typical composition of battery fluids, which are commonly used as electrolytes in the electrochemical energy storage device, i.e. in the battery. Typically, such electrolytes contain carbonates from which around 1 / 3 is formed by cyclic carbonates such as EC and around 2 / 3 is formed by linear carbonates (LC). Thus, the defined values give a good parameter for battery fluids, or electrolyte, respectively, as such.

[0033] With regard to linear carbonates, suitable but non limiting examples comprise as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) for example.

[0034] To ensure complete and fast enough dissolution of the HNBR polymer, the Ra value of the polymer relative to NMP should be < 9 MPa1 / 2, more preferably < 8.5 MPa1 / 2and most preferably < 8 MPa1 / 2. With this regard, NMP or comparable compounds are common solvents which are used for adding to the binder composition in order to form a slurry. Thus, by reaching the values as defined, good properties with regard to common solvents are provided.

[0035] The Ra values as defined by the Hansen solubility parameters between the HNBR and the organic components of the battery electrolyte fluid are thus of importance and might essentially be sufficient to ensure a limited swell of the HNBR polymer in the battery fluid. It was found that a Ra value against NMP being < 9 MPa1 / 2; and a Ra value against a fluid blend of EC 30 to 33vol% and 70 to 66 vol% of linear carbonates being at least 7 MPa1 / 2is very beneficial for solving the object of the present invention.

[0036] With this regard, battery fluids according to the state of art contain blends of organic cyclic carbonates such as ethylene carbonate and linear carbonates such as methyl and ethyl carbonates and various combinations. These carbonates make up at least 90vol% of the fluid components of the battery fluid. Other important components are the electrolyte salts such as LiPF6, LiTFSI (bis-trifluoromethanesulfonimide lithium salt).

[0037] These salts are considered as not contributing to the polymer swell. Instead, dissolved electrolyte salts due to their very high polarity and ionic character will decrease the solvation power of the organic carbonate blends and will lower the swell of these fluids by a relatively constant factor in all battery fluids. The test fluids almost always contain 1 M LiPF6which gives roughly a 15% content by weight.

[0038] It was thus surprisingly found that realizing the Ra values as defined above can solve advantageously improves the swelling properties for conventional battery fluids.

[0039] With this regard, in EP 3276713 a correlation can be derived between acrylonitrile content of HNBR polymers and swell in battery fluid. However, the data were obtained from a battery fluid with the composition of EC / DEC / VC with the volume ratios of 68.5 I 30 / 1 / 5 which has a very high EC content which may not represent typical praxis in the industry. A too high content of EC renders the electrolyte too viscous, especially at lower temperatures which give a high Li-ion impedance.

[0040] HNBRs with acrylonitrile contents of 20 wt% and below have limited properties to be dissolved in NMP with acceptable solids content. For practical purposes the acceptable solution polymer content should be in the range from 5 to 12wt%, referring to the binder composition. Generally, it might be preferred that the HNBR has a content of acrylonitrile which is in the range of < 30 wt.-%. In particular, it might be preferred that the HNBR has a content of acrylonitrile which is in the range of > 20 wt.-% to < 30 wt.-%, preferably in the range of > 21 wt.-% to < 23 wt.-%.

[0041] HNBRs which are derived from the hydrogenation of nitrile rubber from the monomers acrylonitrile and butadiene are for simplicity considered as HNBR copolymers.

[0042] HNBRs which in addition contain further monomer units introduced in the parent nitrile rubber are considered as HNBR terpolymer regardless how many different monomer units there might be present.

[0043] However, both HNBR copolymers and HNBR terpolymers are generally comprised by the term HNBR.

[0044] The length of the HNBR binders support its bonding function and too short binders will not bond the particles of the cathode formulation strong enough together and on the current collector.

[0045] The chain length, here the contour length, is determined as the standard 0-0 length of 0.154 nm for sp3-hydridized carbon atoms. Monomer units from acrylonitrile or from acrylate units are counted with 2 C atoms, the same for hydrogenated 1 ,2-butadiene units while hydrogenated 1 ,4-butadiene units represent by 4 C atoms. The main chain is considered as saturated with a lowest energy bond angle of 109°. The contour length in L = N dCC* sin (109° / 2) where dCC is the standard C-C length and N the number of monomer units, calculated for each monomer type.

[0046] Regarding achieving a suitable swell range for the binder in typical battery fluids, a preferred HNBR structure includes nitrile units and alkylene units while the degree of remaining unsaturation is usually limited to an RDB value below 10% to ensure the electrochemical stability. The RDB is understood as the residual double bond content where 100% means that no hydrogenation has taken place while 0% means that all double bonds had been hydrogenated. With regard to the residual double-bond content (measured as RDB) of the hydrogenated nitrile rubber, it may be preferred that the RDB value is in the range of < 10 %, such as > 1 % to < 5 %, such as in the range of > 1.4 % to < 4.6 %, for example > 1 ,5 to < 4,5.

[0047] It may further be preferred that the hydrogenated nitrile rubber has a Mooney viscosity (ML(1+4 / 100 °C), especially according to DIN 53523) of < 200 MU, such as < 170 MU. This embodiment improves processing of the respective composition and further improves the adhesive strength of the binder formed from said composition.

[0048] The HNBR structure can also contain polar monomer units such as those provided by acrylate or methacrylate units. The monomer composition of the HNBR will influence its interaction with fluids such as the electrolyte fluid. In general, more polar monomer units will shift the Ra for the interaction of polymer-to-electrolyte to lower values which raises the swell, so that shifting Ra against NMP or against the blend of EC / LC may be realized.

[0049] With increasing nitrile content, the Ra against NMP decreases which facilitates polymer dissolution, but Ra against the electrolyte fluids at the same time decreases, so that the swell might become too high. Thus, there is a window where the dissolution is adbvantageous but the electrolyte swell is still low. An optimum might for example be found the HNBR has a content of acrylonitrile which is in the range of > 21 wt.-% to < 23 wt.-%. So, the teaching is, design a HNBR structure, calculate HSP and subsequently the Ra to find the best cobinder.

[0050] Regarding reducing the swell, it is preferred to have a limited interaction with the polar battery fluid. On the other hand, the typical processing solvents in battery manufacture are polar solvents such as NMP, thus the polymer need to be readily dissolved in those solvents.

[0051] The inventors thus surprisingly found that HNBR copolymers with a sufficiently low acrylonitrile content should have a lower swell in the carbonate components of the electrolyte fluid which will make the swell lower in the fully formulated electrolyte as well. This can be explained by the higher Ra values as shown in the figures as discussed below. Further, these copolymers will have an elevated level of crystallinity from uninterrupted ethylene sequences. Both factors may contribute to lower swell. In case of terpolymers the crystallinity is largely suppressed by the interruption of ethylene sequences and some polarity is retained even if the acrylonitrile content is lowered so that the HNBR grade do not give the necessary low electrolyte swell.

[0052] With regard to crystallinity, it was found that especially advantageous properties may be achieved when the HNBR has a degree of crystallinity of at least 10 J / g (DSC). This may be determined via DSC. The present invention thus preferably deals with semi-crystalline hydrogenated nitrile rubbers (HNBR) as binder in lithium-ion batteries (LiB).

[0053] The binder composition further comprises component b) and thus at least one aminofunctional silane. With this regard, it has been found that adhesion of HNBR binders to the current collector can be improved by using amino-functional silanes in the binder composition. This can be caused due to less stickiness from the higher degree of crystallinity or the lower polarity.

[0054] According to the present invention, it was found that additionally using amino-silanes in the binder composition surprisingly gives an improved level of adhesion. As the inventive HNBR copolymers are not reactive towards amino groups, no crosslinking of the binder occurs. Without being bound to the theory, the amino-silanes might work as primers for the metallic current collector. While the exact chemical mechanism is not clear, the examples as outlined below proving the effect of the present invention show that the amin-silanes preferably have a comparably high reactivity of the alkoxy-silyl group and of the amino group.

[0055] The structural variation of the silanes shows that primary amino-silanes give a high reactivity, possibly related to the availability of two amin-hydrogen atoms. Secondary amino-silanes are less reactive, unless they are bonded to the silyl group by way of an a-C bridge. These a-silanes are known to cause a higher reactivity of the alkoxy-silyl groups towards hydrolysis by nitrogen lone pair donation to the Si-atom. Per consequence, it is possible that these a-silanes bond to metallic surface faster and stronger compared to y-amino-silanes.

[0056] In order to allow the most preferred effect, it may thus be preferred that said aminofunctional silane comprises a primary amino group or that said amino-functional silane comprises one methylene carbon between the silicon atom and the nitrogen atom of the amino group or in other words that amino-groups which are connected to the silicon atom with an a-C bridge.

[0057] It may further or additionally be preferred that the silane contains a silicon atom carrying at least 2 alkoxy groups.

[0058] Functional silanes according to the prior art are generally known as coupling agents where in most cases, a hydrolysis must take place to activate the bonding mechanism. Company Gelest (in: Silane Coupling Agent: Connecting Across Boundaries, 2006 Gelest Inc.) explains a 4-step process involving the formation of silanol groups in the presence of water moisture. Under anhydrous conditions extended reaction times of 4- 12 hours and elevated temperatures (50-120 C) are useful for the alkoxysilanes to function; only methoxy-silanes are effective without catalysis according to Gelest (same source).

[0059] However, according to the present invention, moisture may be excluded by using carefully dried solvents and dried polymer binders. This might be important in order to avoid drying processes as moisture may be detrimental with regard to the cell chemistry.

[0060] It may generally be preferred that the binder composition has a water content of less than 0.3 wt.-%, relating to the binder composition. Advantageously, the binder composition may be free of water. The absence of water or at least the significantly reduced amount of water allows avoiding later drying processes as water, or moisture, respectively, should be avoided in a formed battery cell.

[0061] A preferred silane according to the present invention might be amino-propyl-triethoxy silane (APTES).

[0062] A binder composition as described above achieves significant advantages over solutions of the prior art. In detail, a binder which is formed from the binder composition as described allows suppressing the swelling in an electrolyte, very good bonding properties to the current collector and has further no need for the addition of fluorinated compounds.

[0063] Apart from that, the present invention is advantageous in that the respective binder composition is free of halogenated compounds. Like described above, this allows that the binder formed from the respective binder composition is superior to respective binders according to the prior art with respect to recycling properties. Especially recycling of the binder or the electrodes formed therefrom can be done much more effective.

[0064] Like stated above, the hydrogenated nitrile rubber has a Ra value against NMP is < 9 MPa1 / 2as this gives a good property for most used processing solvents. Thus, it might be preferred that the binder composition comprises N-Methyl-2-pyrrolidone (NMP) as solvent. Such a solvent is advantageously usable as a solvent in the electrode coating of battery manufacturing and especially for forming an active material composition. It is highly effective for dissolving for HNBR, for example, and thus further improves forming a stable electrode coating.

[0065] Reducing the swelling in electrolyte solvents may further avoid problems in the mass production of the battery cells and the long-term service life. For example, a limited swell of around 50% might be aimed at so that the deposited binder film still allows diffusion of lithium ions.

[0066] Thus, the binder composition as described provides a binder which has good adhesion properties and suppresses swelling effectively, thereby having no need of fluorinated products.

[0067] Consequently, also provided is a binder for an electrode of an electrochemical energy storage device, wherein the binder is formed from a binder composition as described above, the binder having the advantages as described.

[0068] With respect to further advantages and technical features of the binder composition and the binder, it is referred to the description of the electrode material composition, the electrode, the electrochemical energy storage device, the figures, the examples and vice versa.

[0069] Further described is an electrode material composition for an electrode of an electrochemical energy storage device, wherein the composition comprises a solvent, and the binder composition as described above or a binder formed from said binder composition, and wherein the electrode material composition further comprises an active material, conductive carbon material and optionally one or more further binders.

[0070] Such an electrode material composition is thus formed based on the binder composition as described above or the binder as described above. It thus comprises the binder composition, or the binder, respectively, as described. Additionally, it comprises respective components which may generally be used according to the prior art. With this regard, it should be noted that the binder composition as described does not show requirements being strict with regard to the further components. This allows that the binder composition, or the binder, respectively, may be used in known processes and in known systems without problems.

[0071] In addition to the binder composition, or the binder, respectively, the electrode material composition comprises a solvent, an electrode material which also might be called active material, conductive carbon material and optionally one or more further binders. These materials may generally be chosen according to the prior art.

[0072] With regard to the solvent, for example, N-Methyl-2-pyrrolidone (NMP) may be used. Like stated above, the hydrogenated nitrile rubber has a Ra value against NMP being < 9 MPa1 / 2as this gives a good property for most used processing solvents. Thus, it might be preferred that the active material composition comprises N-Methyl-2-pyrrolidone as solvent, if not already comprised in the binder composition. Such a solvent is advantageously usable as a solvent in the electrode coating of battery manufacturing. It is highly effective for dissolving for HNBR, for example and thus further improves forming a stable electrode coating.

[0073] As conductive carbon material, for example graphite, carbon nanotubes or further carbon materials, such as carbon black may be used.

[0074] Suitable active materials, especially cathode active materials, comprise inter alia Lithium Nickel Cobalt Manganese Oxide (LiNiCoMnO2, NCM), Lithium Iron Phosphate (LiFePO4 / C, LFP), Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAIO2, NCA), Lithium Manganese Oxide (LiMn2O4, LMO) or Lithium Cobalt Oxide (LiCoO2, LCO).

[0075] Additionally, a further binder different from the binder as described above, may be included, which may be chosen according to the desired need, if required.

[0076] The electrode material composition as described provides a solution which has good adhesion properties and suppresses swelling effectively, thereby having no need of fluorinated products.

[0077] With respect to further advantages and technical features of the electrode material composition, it is referred to the description of the binder composition, the binder, the electrode, the electrochemical energy storage device, the figures, the examples and vice versa.

[0078] Further described is an electrode for an electrochemical energy storage device, wherein the electrode comprises a current collector and an active material composition coated on the current collector, wherein the active material composition comprises a binder as described above.

[0079] In particular the electrode, such as the cathode, may comprise an electrode material composition as described above wherein, however, the solvent may be removed at least in part. The electrode particularly has the advantages as outlined above.

[0080] Correspondingly, further described is an electrochemical energy storage device, wherein the electrochemical energy storage device comprises an anode and a cathode, wherein at least one of the anode and the cathode is arranged like described above. In particular, the cathode is arranged as described before.

[0081] The electrochemical energy storage device may in particular be a lithium ion battery (LiB).

[0082] The electrochemical energy storage device further preferably comprises an electrolyte between the anode and the cathode in order to provide electrical contact between the anode and the cathode as described above. The electrolyte preferably comprises a fluid blend of ethylene carbonate to linear carbonates, wherein ethylene carbonate is present in the range of > 30 vol.-% to < 33 vol.-% and linear carbonates are present in the range of > 66 vol.-% to < 70 vol.-%, each referring to the fluid blend. To summarize, the electrochemical energy storage device as described provides a solution which has good adhesion properties and suppresses swelling effectively, thereby having no need of fluorinated products.

[0083] With respect to further advantages and technical features of the electrode and the electrochemical energy storage device, it is referred to the binder composition, the description of the binder, the electrode material composition, the figures, the examples and vice versa.

[0084] Examples and figures

[0085] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0086] In the figures:

[0087] Figure 1 shows a diagram of Ra values of HNBR polymers depending on the acrylonitrile content in relation to the fluid components of battery electrolyte fluids;

[0088] Figure 2 shows a diagram of Ra values of NMP polymers with regard to NMP depending on the acrylonitrile content;

[0089] Figure 3 shows flow curves of cathode slurry at different storage times;

[0090] Figure 4 shows Coin cell cycling tests;

[0091] Figure 5 shows a diagram relating to the cycle stability; and

[0092] Figure 6 shows a diagram showing the shear rate over the viscosity.

[0093] Materials used:

[0094] HNBR copolymer 1 : hydrogenated nitrile rubber, acrylonitrile content 27%, DSC Tg - 24.1 °C, melt enthalpy 21.7 J / g, Mw 346 kg / mol, contour length 2428 nm. The Ra value to NMP is 8.0 MPa1 / 2. The Ra value to 4 selected electrolyte solvent blends was found to be in the range from 7.8 to 8.9 MPa1 / 2. The RDB is below 0.9 % and the Mooney value (ML(1+4 / 100 °C) according to DIN 53523 lies at approximately 60 MU. HNBR copolymer 2, hydrogenated nitrile rubber, Mw 402 kg / mol, contour length 2821 nm, acrylonitrile content 27%, Tg (DSC, -24,4°C), melt enthalpy 16 J / g. The Ra values are the same is for copolymer 1 . The RDB is below 0.9 % and the Mooney value (ML(1+4 / 100 °C) according to DIN 53523 lies at 90 MU.

[0095] HNBR terpolymer 3, Mw 384 kg / mol, contour length 2609 nm, acrylonitrile content 21 %, DSC Tg -38.7°C, amorphous, no crystalline peak detected. It is s terpolymer of acrylonitrile (21 wt.-%), butadiene and acrylate monomer units. The Ra value to NMP is 7.3 MPa1 / 2. The Ra value to 4 selected electrolyte solvent blends was found to be in the range from 7.0 to 8.0 MPa1 / 2. The RDB is below 0.9 % and the Mooney value (ML(1+4 / 100 °C) according to DIN 53523 lies at 74.

[0096] HNBR terpolymer 4, DSC Tg -43.4°C, amorphous. It is s terpolymer of acrylonitrile (17 wt.-%), butadiene and acrylate monomer units The Ra value to NMP is 8.3 MPa1 / 2. The RDB is below 0.9 % and the Mooney value (ML(1+4 / 100 °C) according to DIN 53523 lies at 74 MU.

[0097] HNBR copolymer 5: hydrogenated nitrile rubber, acrylonitrile content 34%, molecular weight 210 kg / mol, contour length 1434 nm, DSC Tg -27.8°C, melt enthalpy 5.6 J / g, contour length 1434 nm. The Ra value to NMP is 6.4 MPa1 / 2. The Ra value to 4 selected electrolyte solvent blends was found to be in the range from 6.4 to 7.3 MPa1 / 2. The RDB is below 0.9 % and the Mooney value (ML(1+4 / 100 °C) according to DIN 53523 lies at 39 MU.

[0098] HNBR 6, hydrogenated nitrile rubber, acrylonitrile content 34%, DSC Tg -27.1°C, melt enthalpy 6.5 J / g, contour length 1911 nm. The Ra value to NMP is the same as copolymer 5. The RDB is below 0.9 % and the Mooney value (ML(1+4 / 100 °C) according to DIN 53523 lies at 70.

[0099] HNBR copolymer 7, hydrogenated nitrile rubber, acrylonitrile content 34%, DSC Tg - 27.1 °C, melt enthalpy 6.5 J / g. The Ra value to NMP is the same as copolymer 5. The RDB is below 0.9 % and the Mooney value (ML(1+4 / 100 °C) according to DIN 53523 lies at 90 MU.

[0100] HNBR copolymer 8, hydrogenated nitrile rubber, acrylonitrile content 34%, DSC Tg - 27.1 °C, melt enthalpy 6.5 J / g. The Ra value to NMP is the same as copolymer 5. The RDB is below 0.9 % and the Mooney value (ML(1+4 / 100 °C) according to DIN 53523 lies at 160 MU.

[0101] HNBR copolymer 9, hydrogenated nitrile rubber, acrylonitrile content 17%, DSC Tg - 26.4°C, melt peak at 30°C, melt enthalpy 41 J / g. The Ra value to NMP is 9.6 MPa1 / 2. The Ra value to 4 selected electrolyte solvent blends was found to be in the range from 9.6 to 10.9 MPa1 / 2. The RDB is below 0.9 % and the Mooney value (ML(1+4 / 100 °C) according to DIN 53523 lies at 90 MU.

[0102] HNBR copolymer 10, hydrogenated nitrile rubber, acrylonitrile content 39%, DSC Tg - 22.9°C, amorphous. The Ra value to NMP is 5.3 MPa1 / 2. The Ra value to 4 selected electrolyte solvent blends was found to be in the range from 5.8 to 6.6 MPa1 / 2. The RDB is below 0.9 % and the Mooney value (ML(1+4 / 100 °C) according to DIN 53523 lies at

[0103] 39 MU.

[0104] HNBR copolymer 11, hydrogenated nitrile rubber, acrylonitrile content 43%, DSC Tg - 17.6°C, amorphous. The Ra value to NMP is 4.5 MPa1 / 2. The Ra value to 4 selected electrolyte solvent blends was found to be in the range from 5.4 to 6.0 MPa1 / 2. The RDB is below 0.9 % and the Mooney value (ML(1+4 / 100 °C) according to DIN 53523 lies at

[0105] 40 MU.

[0106] HNBR 12, hydrogenated nitrile rubber, acrylonitrile content 34%, DSC Tg -28.0°C, melt enthalpy 6.4 J / g, contour length 2000 nm. The Ra value to NMP is the same as copolymer 5. The RDB is below 0.9 % and the Mooney value (ML(1+4 / 100 °C) according to DIN 53523 lies at 80.

[0107] PI: Polyimide from Shenzhen Yanyi New Materials, grade name PZ ONE12 S. The structure is not disclosed but may be inferred from WO2023232162 as a polyamic acid with some degree of imidization.

[0108] APTES: 3-aminopropyl-triethoxysilane (CAS no. 919-30-2), It is considered a primary y- aminosilane.

[0109]

[0110] Structure 1

[0111] N-(3-(trimethoxysilyl)propyl)cyclohexane amine, CAS 3068-78-8, it is considered secondary y-aminosilane.

[0112] Structure 2

[0113] N-(triethoxysilylmethyl)cyclohexanamine, CAS 26495-91-0, it is considered a secondary a-aminosilane.

[0114] Structure 3

[0115] With regard to the components present, all % are meant to mean wt.-% until clearly defined otherwise. DSC data were obtained with Netzsch DSC 204 F1 with 10 K / minute from -100 °C to 150 °C according to ISO 11357-3: 2018. Samples of 5 to 10 mg weighed into closed Al- pans. The melt endotherm was taken after a first run, holding for 2 minutes, fast quenching (20°C / minute to -100°C) and performing a second run. The analysis of the DSC scan was done by constructing a base line from initial to end temperature of the melting peak and calculating the endotherm as J / g.

[0116] HSP Method

[0117] The present invention uses Hansen solubility parameters (HSP) and the Flory-Huggins interaction parameter to predict the swell of HNBR binder in electrolyte fluids and the solubility in the process solvent for the manufacture of LiB. First, the HSP sets for HNBR polymers are determined. For that purpose, the equilibrium swell ratio of lightly crosslinked polymer samples solvent is determined in a series of solvents and used as input in the HSPiP program (ebook HSPiP, available from www.hansen-solubility.com). This software gives the HSP set after data fitting. This may be realized according to G. Lui et.al., Polymer Bulletin (Heidelberg) (2015), 72(8), 1961-1974. The vector distance of the HSP sets of the HNBR polymers and the known HSP of the organic solvent components of the battery electrolyte can be calculated as Ra=(4*(6DHNBR - 6D solvent )2+ (QP HNBR - 6p solvent )2+ (QD HNBR - 6D solvent )2)1 / 2where the 5 values are the HSP components for dispersion interaction (subscript D), polar interaction (subscript P) and hydrogen bonding interaction (subscript H), for HNBR and solvent, as indicated, Ra has the units MPa1 / 2. The same procedure also gives Ra values in relation to the process solvent, mostly NMP. Low Ra values indicate a high swell and even easy dissolution in the solvent, while high Ra values indicate lower swell and no or very little dissolution. From that it becomes clear that a balancing is needed to get low electrolyte swell and still sufficient dissolution in NMP, for example.

[0118] Another even easier way to obtain the HSP set for a given HNBR with a certain monomer composition uses group contribution methods in the above mentioned HSPiP software.

[0119] In the present invention, the HSP of polymeric dispersion aids, 5d, 5Pand 5hwere determined by the 3 groups contribution methods following the Hansen solubility parameter handbook and the HSPiP software package. First, the composition by weight% of the HNBR polymers was calculated into molar fractions for the acrylonitrile and hydrogenated butadiene units, assuming a random distribution. For HNBR grades below 34 wt.-% nitrile content, the complete composition is not strictly known from data sheets and the other monomer components and their mol fractions can be identified by 1 H-NMR. The structural information can then be used to calculate the HSP following C. M. Hansen, Hansen solubility parameters-A user’s handbook, Boca Raton, Florida, USA, CRC Press LLC, 2007. Table 1.1 in Page 10-11 , Table 3.111.1 and Table 3.III.2 in Page 70-73. Alternatively, the HSPiP software allows a structure input.

[0120] Then the method of Hoftyzer and Van Krevelen was used with the equations: bd= ( £FDI ) / V

[0121] 6P= ( £FPI2)1 / 2 / V bh= ( ZEHI / V)1 / 2and the factors in the respective tables for the respective groups.

[0122] Next, the system of equations for the Hoy method were taken. It contains four additive molar functions, a number of auxiliary equations and the final expressions for b(total) and for the components of 5. Ft is the molar attraction function, Fp is the polar component; V is the molar volume of the solvent molecule or the structural unit of the polymer. AT is the Lydersen correction for non-ideality, used in the auxiliary equations, see table 1.

[0123]

[0124] Table 1 Then method of Beerbower uses the calculation formula used is as follows:

[0125] Finally, the results for each HSP component were averaged to avoid a bias from an individual method. The data are collected in the table below including the HSP of electrolyte fluid which were taken from HSPiP software package. The HSP of the mixed electrolyte fluids were calculated as the volume weighed average from the individual components. In a general way, when x can be the D, P or H component of the HSP and <Pi are the volume fractions of fluid blend components, i=1 , 2, 3... Table 2 shows respective values for HNBR copolymers (copo), terpolymers (terpo) and electrolytes.

[0126] Table 2

[0127] Battery fluids according to the state of art contain blends of organic cyclic carbonates such as ethylene carbonate and linear carbonates such as methyl and ethyl carbonates and various combinations. These carbonates make up at least 90 vol% of the fluid components of the battery fluid. Other important components are the electrolyte salts such as LiPF6and LiTFSI (lithium bis(trifluoromethanesulfonyl)imide). These salts are considered as not contributing to the polymer swell. Instead, dissolved electrolyte salts due to their very high polarity and ion character will decrease the solvation power of the organic carbonate blends and will lower the swell of these fluids by a relatively constant factor in all battery fluids. The test fluids almost always contain 1 M LiPF6which gives roughly a 15% content by weight. Further additives such as vinyl-carbonate, fluorinated carbonate and nitrile compounds are present in small quantities and may not influence the polymer swell remarkably. As can be shown in the figures below where the Ra values for copolymers are only slightly shifted by the typical composition variations of battery test fluids. Therefore, a simulated battery fluid is taken as 30 / 70 vol% of ethylene carbonate (EC) and diethyl carbonate (DEC) as used to calculate the Ra values relative to the HNBR polymer. In other commercial battery electrolytes, the EC is used at 33 vol% and the remainder can be a combination of linear carbonates.

[0128] After having determined the HSP set of the HNBR used here by employing the preferred new group contribution method, the Ra values are determined against the solvent components of the electrolyte the volume averaged HSP components of these solvent are used.

[0129] Ra values of HNBR polymers in relation to the fluid components of battery electrolyte fluids are shown in figure 1 in which the X-axis shows the amount of acrylonitrile, and the Y-axis shows respective Ra values. Further, line 1 relates to a mixture of EC / EMC / DMC in a relation of 1 / 1 / 1 with regards to wt.-%, line 2 relates to a mixture of EC / EMC in a relation of 3 / 7 with regards to wt.-% and with 2 wt.-% VC added, line 3 relates to a mixture of EC / EMC in a relation of 3 / 7 with regards to wt.-%, and line 4 relates to a mixture of EC / DEC in a relation of 3 / 7 with regards to wt.-%. Copolymers as shown by solid lines in figure 1 are HNBR structures which contain acrylonitrile units and alkylidene units to make up at least 98% by weight of the polymers.

[0130] Terpolymers in figure 1as shown by dotted lines are HNBR structures which contain acrylonitrile units, alkylidene units and methacrylate or acrylate units where the latter are contained in an amount just enough, so that the crystallization of the alkylidene units is essentially suppressed by efficient interruption of crystallizable ethylene segments.

[0131] The process solvent chosen in the figure is NMP as being very representative for the manufacture of Lithium-ion batteries. It is understood that other solvents can also be chosen such as other organic amides, linear and cyclic ester with a suitable drying efficiency, high enough flash points to ensure safe processing and a favorable toxicologic profile for proper work hygiene and environmental protection. However, the binder polymer will need to be sufficiently soluble on those solvents.

[0132] Figure 2 in which the X-axis shows the amount of acrylonitrile and the Y-axis shows respective Ra values shows Ra values between NMP and HNBR, copolymers without acrylate units as solid line and terpolymers with acrylate units as dotted line.

[0133] Experiments

[0134] Swell of HNBR polymers in battery fluid The polymers were pressed into 1 mm thick sheets with an area of 1 to 3 cm2. They were weighed and placed on a Ni-mesh for support and immersed in the electrolyte fluid inside of a glass flask with a lightly closed lid to prevent pressure built-up and to avoid evaporation of fluid components. After passing the immersion time the flasks were removed from the conditioning chamber, cooled to RT. The swollen samples were carefully removed, slightly wiped with a tissue to remove free fluid from the sample surface and weighed. The swell is the weight gain expressed in wt% relative to the initial sample weight, see table 1.

[0135] Table 3 Swell in electrolyte fluid (1M LiPF6 in EC / EMC / DMC 1:1:1 by volume at 60°C and 80°C

[0136] HNBR copolymer 11 almost completely dissolved in the electrolyte fluid.

[0137] As can be seen in table 3, HNBR polymers with a medium to high nitrile content (HNBR 6, 12, 8, 7 and 11) and those which belong to the class of amorphous HNBR polymers (terpo 4 and 3) exhibit a swell in the test fluid of a range from around 100% to above 180% when a temperature of 60°C is chosen. Although these values are within the swell ranges of some patent disclosures of the prior art, they are considered as too high. The higher swell in the electrolyte fluid can be related to the Ra value against the solvent components of the electrolyte fluid. When the Ra is lower than 7 MPa1 / 2. Another influence factor for the swell is the crystallinity of the HNBR. The above mentioned HNBR are either completely amorphous or the melt endotherm is below 10 J / g which is not sufficient to induce enough swell resistance.

[0138] It becomes obvious that HNBR designated as copolymers with a nitrile content of 27% (HNBR 1 , HNBR 2) show swell values below 100%. Thus, HNBR copolymers with an acrylonitrile content below 30wt% are considered as sufficient swell resistant and can be used as long as they are soluble in the process solvent NMP or similar organic cyclic amides. The inventive HNBR polymers feature a melt endotherm above 10 J / g which contributes to a lower swell. The Ra values against the solvent components of the electrolyte is clearly higher than 7 MPa1 / 2and thus swell resistance is ensured. Thus, a surprisingly simple method has been found to predict the swell of HNBR binders in Li B electrolytes despite the complexity of the interactions of highly ion conductive salts loaded organic carbonate with HNBR structures.

[0139] Testing as binder in LiB cathodes including additives:

[0140] The active materials, conductive material and binder polymers were dried in an oven at 120°C for 2 hours. All preparation steps were carried out in a low humidity chamber with dew point <-50°C. The polymers were dissolved in dry NMP at RT in flasks on a shaker overnight to 8% solids. Binder solutions and additives were combined. Then the conductive material, the binder solution and 14 of the necessary NMP were first mixed in a Thinky mixer (Thinky Coporation, 12 minutes at 2000 rpm). Then the active material was added together with another 14 of the necessary amount of NMP to reach final solids content while mixing for 18 minutes at 2000 rpm. The mixing steps conducted in intervals of 6 minutes with intermediate cooling. Coating was carried out with a bar coater on carbon coated Al foil followed by drying (120°C 2 hours for mechanical testing; 120°C, 2 hours for electrochemical testing). Electrode testings were carried as indicated in the table with the testing devices also indicated. Table 4: Composition of examples 1 to 4

[0141] Copolymer binder HNBR copolymer 9 was tried but could not be dissolved in NMP. It is reasoned that the Ra value against NMP was too large. Binder compositions were designed based on a given HNBR polymer and additive selected from a polyimide resin and from an amino silane, see table 4. The binder compositions were made up into NMP solutions with solid content of 8% including a conductive carbon black Super P.

[0142] These solutions were then combined with a small particle size LFP under high shear mixing in a Thinky mixer to obtain an overall solids content of 65%.

[0143] The flow curves according to examples 1 to 4 taken immediately after preparation and after a storage of 7 d covered a range from 2.2 to 18 Pa s, see figure 3. Example 4 displayed an almost storage constant viscosity and low shear rate dependence.

[0144] Example 3 showed a viscosity increase from already high values while example 1 showed a decrease of viscosity.

[0145] The coated cathodes were flexible without cracks in the mandrel test (examples 1 and 4) while example 2 showed crack and example 3 a very few small cracks, see table 3. Importantly, the peel adhesion data were markedly improved in examples 2 to 4 over example 1 . The coating behavior of inventive examples 3 and 4 were considered to be best.

[0146] When examining the charge-discharge behavior of coin cells one can find cells with cathode 1 showed losses in cycling. This is explained by an insufficient bonding of the cathode material to the current collector so that cathode loses its electrical connection while in service.

[0147] Thus, although the HNBR copolymer 1 can provide flexible cathodes and rather low viscous cathode slurries it is still needed to improve the adhesion performance. While PI as binder polymer can provide better adhesion it will make the cathode more rigid so that crack can be formed upon flexing. The combined addition of PI resin and the amino silane further improves adhesion but tends to give a higher slurry viscosity upon storage. Therefore, the combination of the binder HNBR copolymer 1 and the amino silane give the most favorable property combination.

[0148] Figure 4 respectively shows Coin cell cycling tests in which the first number in the legend gives the trial number while the second number gives the coin cell number. With this regard, the discharging capacity retention was measured with charging rates of 0,5C / 0,5C, a capacity of 145mAh / g which is characteristic of LFP.

[0149] Table 5: Behavior of examples 1 to 4

[0150] In a further experiment series, the type of amino silane was varied, see table 5. All other experimental conditions were the same. The silanes had secondary amino groups with cyclohexyl substituents while the C spacer bridge to the silyl function was varied to be either propylene (C3), example 5 or methylene (C1), examples 6 to 8. Table 6 HNBR binder and amino silanes used for examples 5 to 8

[0151] Coin cells with the binder compositions 6 and 7 had the highest cycling stability while 5 and 8 were acceptable, see figure 5. Adhesion to the current collector was best with examples 6 and 7. Example 5 had decreased adhesion. With regard to figure 5, the discharging capacity retention was measured with charging rates of 0,5C / 0,5C, a capacity of 145mAh / g which is characteristic of LFP, and further 2.8 to 4.8 Volt versus Li / Li+.

[0152] Flexibility was best with examples 5 and 6 while trials 7 and 8 had some cracks. From these trials one can conclude that the secondary amino silanes alone did not give enough adhesion. However, when in addition the secondary amino group was connected to the silicon atom by one methylene carbon then adhesion was good. This may be explained by an a-silane effect which activates the alkoxy-silyl function and makes the secondary amino silanes as efficient as the primary amino silanes. In this regard the choice of ethoxy or methoxy silanes is not important. Therefore, amino alkoxy-silanes can be chosen which carry at least one of the features of primary amino groups or one methylene carbon between Si and nitrogen atom of an amino group.

[0153] Examples 5 to 8 provide good capacity retention in cycling. Example 7 gives cathode slurries with the best viscosity stability. Examples 6 and 7 give good peel adhesion while example 5 is too low. This is also visualized in figure 6, which shows a diagram showing the shear rate of a slurry over the viscosity at different storage times.

[0154] It can be concluded that the inventive binder composition preferably comprises a HNBR with a degree of crystallinity of at least 10 J / g and according to the invention further has a Ra value against N-Methyl-2-pyrrolidone is < 9 MPa1 / 2and a Ra value against a fluid blend of ethylene carbonate to linear carbonates, wherein ethylene carbonate is present in the range of > 30 vol.-% to < 33 vol.-% and linear carbonates are present in the range of > 66 vol.-% to < 70 vol.-%, each referring to the fluid blend, is at least 7 MPa1 / 2.

[0155] This criterion can best be realized with HNBR copolymers with an acrylonitrile content below 30% while acrylate groups can be present but preferably in a suitably low amount in order that the Ra values are dropping below the afore mentioned value or the crystallinity melt endotherm is becoming too small. The chain length of the HNBR binder need to be long enough to allow bonding of all particle components into a robust cathode layer. It is preferred to allow the chain length to be at least 1 ,500 nm, and more preferable at least 2,000 nm.

Claims

Claims1 . A binder composition for forming a binder of an electrode of an electrochemical energy storage device, the binder composition comprising a) a hydrogenated nitrile rubber, wherein the hydrogenated nitrile rubber has the following properties: a Ra value against N-Methyl-2-pyrrolidone is < 9 MPa1 / 2; and a Ra value against a fluid blend of ethylene carbonate to linear carbonates, wherein ethylene carbonate is present in the range of > 30 vol.-% to < 33 vol.-% and linear carbonates are present in the range of > 66 vol.-% to < 70 vol.-%, each referring to the fluid blend, is at least 7 MPa1 / 2, and b) at least one amino-functional silane.

2. The binder composition according to claim 1 , wherein said amino-functional silane comprises a primary amino group or wherein said amino-functional silane comprises one methylene carbon between the silicon atom and the nitrogen atom of the amino group.

3. The binder composition according to claim 1 or 2, wherein the silane contains a silicon atom carrying at least 2 alkoxy groups.

4. The binder composition according to any of claims 1 to 3, wherein the HNBR has a content of acrylonitrile which is in the range of < 30 wt.-%.

5. The binder composition according to any of claims 1 to 4, wherein the HNBR has a degree of crystallinity of at least 10 J / g.

6. The binder composition according to any of claims 1 to 5, wherein the binder composition comprises N-Methyl-2-pyrrolidone.

7. The binder composition according to any of claims 1 to 6, wherein the hydrogenated nitrile rubber has a degree of hydrogenation measured as RDB of < 10%.

8. The binder composition according to any of claims 1 to 7, wherein the binder composition is free of halogenated compounds.

9. A binder for an electrode of an electrochemical energy storage device, wherein the binder is formed from a binder composition according to any of claims 1 to 8.

10. An electrode material composition for an electrode of an electrochemical energy storage device, wherein the composition comprises a solvent, and the binder composition according to any of claims 1 to 8 or a binder according to claim 9, and wherein the electrode material composition further comprises an active material, conductive carbon material and optionally one or more further binders.11 . The electrode material composition according to claim 10, wherein the solvent comprises N-Methyl-2-pyrrolidone.

12. An electrode for an electrochemical energy storage device, wherein the electrode comprises a current collector and an active material composition coated on the currentcollector, wherein the active material composition comprises a binder being formed from a binder composition according to any of claims 1 to 8.

13. An electrochemical energy storage device, wherein the electrochemical energy storage device comprises an anode and a cathode, wherein at least one of the anode and the cathode is arranged according to claims 12.

14. The electrochemical energy storage device according to claim 13, wherein the electrochemical energy storage device further comprises an electrolyte between the anode and the cathode, wherein the electrolyte comprises a fluid blend of ethylene carbonate to linear carbonates, wherein ethylene carbonate is present in the range of > 30 vol.-% to < 33 vol.-% and linear carbonates are present in the range of > 66 vol.-% to < 70 vol.-%, each referring to the fluid blend.

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