Method for the fabrication of thick electrode films for secondary alkali ion energy storage devices

Abstract

The present invention relates to a method for producing a thick electrode film having a layer thickness of 100 μm or more and 600 μm or less for a secondary alkali ion energy storage device, the method comprising the steps of: a) preparing a dispersion comprising at least one solvent and solids, the dispersion having a total solids content of 40 wt. % or more and 80 wt. % or less, the solids comprising an active material, one or more conductive additives, and one or more binders, and mixing butanediol into the dispersion at a concentration of 2 wt. % or more and 10 wt. % or less, based on the total weight of the dispersion; b) coating the dispersion in a layer thickness of 200 μm or more and 1200 μm or less; and c) drying the coated dispersion to obtain an electrode film. The present invention also relates to the use of the method according to the present invention for producing an electrode film, and to an electrode film having a layer thickness of 100 μm or more and 600 μm or less, and having a specific composition.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a thick electrode film having a layer thickness of 100 μm or more and 600 μm or less for a secondary alkali ion energy storage device, the method comprising the steps of: a) preparing a dispersion comprising at least one solvent and solids, the dispersion having a total solids content of 40 wt. % or more and 80 wt. % or less, the solids comprising an active material, one or more conductive additives, and one or more binders, and mixing butanediol into the dispersion at a concentration of 2 wt. % or more and 10 wt. % or less, based on the total weight of the dispersion; b) coating the dispersion in a layer thickness of 200 μm or more and 1200 μm or less; and c) drying the coated dispersion to obtain an electrode film. The present invention also relates to the use of the method according to the present invention for producing an electrode film, and to an electrode film having a layer thickness of 100 μm or more and 600 μm or less, and having a specific composition. [Background technology]

[0002] Modern electrical storage devices must satisfy many different quality requirements for their marketability. In addition to manufacturing costs, these include, for example, structural safety, high self-discharge over time, recharge rate, general cell life, robust temperature behavior, and cycle stability. In addition to these peripheral requirements, the electrical conductivity of the energy storage device naturally plays an important role. One of the key factors for the electrical conductivity of alkali-ion energy storage devices considered here derives from the ratio between the amount of alkali stored in the electrodes of the battery structure and the weight of the electrodes to be used for that purpose. This quotient is one of the key measures of the maximum amount of electrical energy that can be stored in accumulators and capacitors and directly affects the required weight of the energy storage device to provide a specific amount of energy. Unfortunately, in the case of lithium-ion batteries, this parameter cannot be improved simply by providing a larger storage volume in the form of thicker electrode films or layers containing a larger amount of active material, potentially allowing for a larger amount of charge carriers to be stored. The difficulty in producing electrode films that are uniform and mechanically stable under charge and discharge conditions increases exponentially with increasing layer thickness; as a result, relatively thick layers are more likely to suffer from inherent defects, such as cracks and problems with adhesion of the layer to the current collector, which can lead to premature failure of the electrode structure under use conditions.

[0003] The patent literature also describes various approaches for the production of electrode films or electrodes for rechargeable alkali metal batteries.

[0004] For example, US2014178788A1 (Patent Document 1) describes the preparation of a catalyst slurry for a fuel cell, an electrode manufactured using the catalyst slurry, a membrane electrode assembly using the electrode, a fuel cell using the membrane electrode assembly, and a method for manufacturing the electrode. The catalyst slurry includes a catalyst material, an acid component, a binder, and a solvent component having a viscosity of at least about 20 cps at about 20°C.

[0005] KR101603657B1 (Patent Document 2) discloses a method for producing an active cathode material for a lithium secondary battery, and a lithium secondary battery including the active cathode material produced according to this method. In one embodiment of the method for producing an active cathode material for a lithium secondary battery according to the present invention, the mixing ratio of a first metal solution and a second metal solution to a complex ion-forming agent and the first metal solution is from 100:0 to 0:100 by volume, the mixed first solution is injected into a reactor while gradually stirring the second metal solution until the ratio of the second metal solution becomes 1%, and the first mixed solution and the precipitating agent are stirred in the reactor while injecting a precipitating agent into the reactor. When the reaction between the first metal solution and the second metal solution is completed, a first precipitate is formed, and a second mixed solution obtained by mixing a complex ion forming agent and a third metal solution is injected into the reactor to react with the precipitate, thereby forming a second precipitate on the surface of the first precipitate. The first and second precipitates are then washed and dried, and then heat-treated, during which the first metal solution, the second metal solution, and the third metal solution contain Ni, Co, and Mn, and the Ni concentration (mol %) in the metal solutions decreases in the order of the first metal solution, the second metal solution, and the third metal solution.

[0006] Furthermore, US2008089006A1 (Patent Document 3) discloses an energy storage device-electrode product. The product includes at least one current collector and at least one electrode film disposed adjacent to the at least one current collector. The at least one current collector includes a plurality of voids extending throughout the thickness of the current collector, allowing electrolyte to flow through the thickness of the current collector. The numerous voids extending throughout the current collector are formed without reducing the surface area of ​​the conductive material of the current collector adjacent to the electrode by more than approximately 15%. Methods for manufacturing electrode products and double layer capacitor products are also disclosed.

[0007] Such solutions known from the prior art may offer the potential for further improvement, in particular with regard to the production of homogeneous, crack-free and thick electrode layers. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] US2014178788A1 [Patent Document 2] KR101603657B1 [Patent Document 3] US2008089006A1 Summary of the Invention [Problem to be solved by the invention]

[0009] It is therefore an object of the present invention to at least partially overcome the drawbacks known from the prior art. It is particularly an object of the present invention to provide a method that allows the production of thick, crack-free electrode layers for use in alkali ion energy storage devices. It is also an object of the present invention to provide the inventive use of the method for producing an electrode film, as well as an electrode film that has a crack-free, uniform structure at thick layer thicknesses and improved adhesion of the electrode film to the current collector of the electrode.

[0010] This problem is solved by the features of the independent claims, which relate to the method according to the invention, the use of the method according to the invention, and the electrode membrane according to the invention. Preferred embodiments of the invention are set out in the dependent claims, the description and the drawings, whereby further features mentioned or suggested in the dependent claims, the description or the drawings may, individually or in any combination, constitute the subject matter of the invention, unless the context clearly indicates otherwise. [Means for solving the problem]

[0011] The present invention provides a method for producing a thick electrode film having a layer thickness of 100 μm or more and 600 μm or less for a secondary alkali ion energy storage device, comprising the steps of: a) a dispersion comprising at least one solvent and solids, the total solids content of the dispersion being equal to or greater than 40% by weight and equal to or less than 80% by weight, wherein the solids are: a proportion by weight of active material equal to or greater than 75% and equal to or less than 98%; - one or more conductive additives in a proportion of at least 0.5% and at most 5% by weight, and - one or more binders in a proportion of at least 1% and at most 10% by weight, wherein the weight percentages of solids in the dispersion total 100% by weight; preparing a dispersion, and mixing butanediol into the dispersion at a concentration of at least 2 wt. % and at most 10 wt. % based on the total weight of the dispersion; b) applying the dispersion in a layer thickness of ≧200 μm and ≦1200 μm; and c) drying the applied dispersion to obtain an electrode film; The method includes:

[0012] Surprisingly, it has been found that the above-described method makes it possible to obtain a dispersion having a specific composition that can be applied in the form of a thick layer and dried uniformly and crack-free to form a thick electrode film. The electrolyte film is particularly suitable as part of an electrode structure for use in an alkali-ion energy storage device. The electrodes are characterized by excellent electrical properties, and due to their thickness, more electrical charge carriers can be stored in the electrode. As a result, a larger amount of active material can provide a larger amount of power for a battery with approximately the same total weight. The electrode film is particularly crack-free after drying, which is one of the basic prerequisites for a high number of cycles. This behavior is particularly evident when compared with prior art methods using butanediol-free dispersions, which tend to develop strong cracks after drying when used in a relatively thick layer range. Surprisingly, this beneficial effect on crack formation is particularly pronounced when butanediol is added in a specified concentration range. These observed effects on the layer are significantly greater in the case of butanediol than those achievable by adding comparable or similar alcohols or diols. The macroscopic and microscopic effects of butanediol are significantly higher, or can be achieved at significantly lower concentrations. Without being bound by theory, butanediol appears to interact with the active material and binder during dispersion preparation and layer drying, resulting in improved adhesion between the active materials and / or improved interaction between the active materials and the binder. Alternatively or additionally, butanediol may result in a uniform application of the dispersion under shear and / or relatively gentle mechanical removal of all solvent during the drying process. The latter effect may be particularly pronounced when applying thick layers. In summary, the resulting dried electrode film exhibits significantly fewer cracks and improved adhesion of the electrode film to the electrode current collector.

[0013] The method of the present invention is for producing thick electrode films with layer thicknesses of 100 μm or more and 600 μm or less for secondary alkali ion energy storage devices. Secondary alkali ion energy storage devices are rechargeable electrical storage devices, unlike primary galvanic batteries. They store electrical energy in the form of chemical energy. Examples of such secondary energy storage devices are lithium-ion batteries or capacitors. These storage devices are used in mobile phones, electric vehicles, hybrid vehicles, laptop computers, and all electrical appliances that operate without a power cable. In everyday language, galvanic secondary elements are also called storage batteries or accumulators. Sodium, lithium, or potassium ions can be used as the alkali ion base. The main components of a battery cell usually form the two electrodes in the form of an anode and a cathode, a separator, an electrolyte, and a cell housing. The electrodes consist of electrode films or metal foils coated with current collectors. The electrode layers present on the current collectors are where alkali ions are stored or released during charge / discharge. In the method of the present invention, these layers have a certain minimum thickness in the dry state. These layers are at least 100 μm thick, preferably at least 150 μm thick, more preferably at least 200 μm thick, in the solvent-free state after drying, and the maximum thickness can preferably be in the range of not more than 500 μm, more preferably not more than 400 μm, more preferably not more than 350 μm.

[0014] The method includes a process step a) in which a dispersion is prepared from at least one solvent and multiple solids. The total solids content of the dispersion is 40% by weight or more and 80% by weight or less. In the first process step, a mixture of the different components of the dispersion is prepared. For this purpose, the dry components of the dispersion can be first homogenously premixed in a dry state, i.e., without adding a solvent, by inputting energy. However, it is also possible to first charge the solvent, then add the solids, and then homogenize, mix, and shear the dispersion with the input of energy. However, it is also possible to add or charge some of the solids in a portion of the solvent to another portion of the dry premix. The remaining solvent can then be added to the mixture containing the portion of the solvent. The dispersion can be prepared in a conventional mixer, mill, or dispersing device using more or less high shear forces. It is important that the solids content of the mixture of solids and solvent is within the above range. The solids content can be determined, for example, gravimetrically from the weight of the solvent-containing sample and the weight of the solvent-free sample after drying.

[0015] The dispersion contains solids, with the solids comprising an active material in a proportion of 75% by weight or more and 98% by weight or less. The active material of the electrode film is responsible for the reversible storage of chemically active species. Currently, different active materials are used for the anode and cathode. Examples of active materials for the cathode in lithium-ion batteries include olivine (LiMPO4, M = Fe, Mn, Co, Ni), layered metal oxides (LiMO2, M = Co, Ni, Mn), or spinel (LiMO2, M = Ni, Mn). Possible active materials are, for example, LiFePO4 (LFP), lithium-nickel-manganese-cobalt oxide (NMC), or lithium-nickel-cobalt-aluminum oxide (NCA). Graphite is primarily used as the anode active material. Various types of graphite are considered, including MCMB (mesocarbon microbeads), synthetic or natural graphite, or graphite in the form of nanotubes. In addition, lithium titanate (Li4Ti5O 12, LTO) or silicon-carbon composites can also be used. The proportion of active material relative to the total solid matter of the dispersion is in the weight ranges given above.

[0016] The dispersion contains one or more conductive additives in a proportion of 0.5% by weight or more and 5% by weight or less. The conductive additive generally serves to improve the conductivity of the active material or the entire electrode film. Carbon black is the most important conductive additive. The proportion of the conductive additive relative to the total solid matter of the dispersion is in the weight range mentioned above.

[0017] The dispersion contains one or more binders in a proportion of 1% by weight or more and 10% by weight or less, with the weight proportion of solids in the dispersion totaling 100% by weight. The binding agent or binder is used in the electrolyte to ensure good cohesion between the active material particles and sufficient adhesion of the entire electrode to the current collector. The binder enhances the mechanical strength of the electrode film. This can be achieved by the use of the binder alone. However, it may be necessary to first condition the binder by the use of shear forces to enable improved interaction between the individual binder molecules, for example, by forming a three-dimensional structure in the film. Synthetic or natural polymers such as Teflon, carboxymethylcellulose, gelatin, alginates, e.g., in the form of sodium alginate (SA), pectin, guar gum, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), or PVDF can be used. Mixtures of different binders can also be used. For example, in combination with an aqueous solvent, mixtures of CMC / PTFE, CMC / SA or their functionalized base skeletons, among others, can also be used.The proportion of said one or more binders relative to the total solid matter of the dispersion is in the weight ranges indicated above.

[0018] In this process step, butanediol is also mixed into the dispersion at a concentration of 2% by weight or more and 10% by weight or less, based on the total weight. During the preparation of the dispersion, butanediol is also added to the remaining components of the dispersion. This butanediol can be added to the dry premix of the solid components, together with the binder in the premix, together with the binder and part of the solvent in the premix, or to the premixed dry components before adding the solvent. Preferably, butanediol is added together with or shortly after adding the solvent to the premix. The proportion of butanediol, based on the total weight of the dispersion including the liquid and solid materials, is in the weight ranges stated above.

[0019] The method includes a process step b) in which the dispersion is applied in a layer thickness of 200 μm or more and 1200 μm or less. After the dispersion is prepared, the dispersion is applied in the form of a film. This can be done by casting, knife coating, extrusion, or roll coating. In this case, the application can be done under shear or without shear. The dispersion can be applied to a current collector, a coated current collector, or other material. In this case, the layer thickness of the applied film, which still contains the solvent, is in the above-mentioned range. Preferably, the layer thickness of the wet film can be 250 μm or more and 600 μm or less, more preferably 300 μm or more and 450 μm or less.

[0020] The method includes a process step c) of drying the applied dispersion to obtain an electrode film. The dispersion formed as a layer is dried with or without the supply of energy in the form of heat to obtain a dry, particularly solvent-free, film. This energy supply can be achieved by radiant heat or by contact drying on a hotter surface or in other ways. This drying can be carried out at normal pressure or under reduced pressure. Removing the solvent reduces the layer thickness and typically results in a thinner, solvent-free, or solvent-free layer. The solvent content after drying is preferably 1.5% by weight or less, more preferably 0.5% by weight or less, and even more preferably 0.005% by weight or less. During drying, it is also possible for the butanediol additive to be completely or partially removed from the electrode film. Preferably, the butanediol is almost completely removed from the electrode film by drying.

[0021] In one preferred embodiment of the method, the solvent can be water. It has been found that adding butanediol, particularly to the aqueous dispersion, is particularly advantageous for obtaining crack-free layers with very thick layer thicknesses. A thick and crack-free electrode layer can be obtained, which also has very similar electrical properties compared to layers produced without butanediol or with the addition of other alcohols. That is, the butanediol additive does not particularly lead to poor electrical properties of the electrode film, but significantly reduces the crack tendency and adhesion of the layer during drying. At a given layer thickness, a significantly higher yield of crack-free electrode films with very similar electrical properties can be obtained.

[0022] In yet another preferred embodiment of the method, the butanediol can be 1,3-butanediol. Among butanediol isomers, 1,3-butanediol (1,3-GB) has been found to be particularly suitable. A crack-free electrode film can be obtained using a relatively small amount of 1,3-BG added to the dispersion. Additionally, the addition of 1,3-BG improves the uniformity of the layer even when a relatively small mechanical force is applied to obtain the dispersion. This may enhance the uniformity of the film and contribute to protecting the binder framework.

[0023] In yet another preferred aspect of the method, butanediol can be added to the dispersion at a concentration of 2 wt. % or more and 6 wt. % or less. This amount of butanediol additive can produce a uniform, mechanically stable, crack-free, and well-adhered conductive electrode film. Additionally, the amount added results in only a minor change in the drying rate of the film compared to a dispersion without other additives. Preferably, the butanediol concentration can be 3.0 wt. % or more and 5.5 wt. % or less, more preferably 3.5 wt. % or more and 5.0 wt. % or less.

[0024] According to one preferred feature of the method, at least two different binders can be used, one of which is water-swellable and the other is not. It has proven particularly suitable to classify the binder materials used into two different classes according to their hydrophilicity and oleophilicity. This classification allows for highly uniform and mechanically stable layers, even at very thick dry film thicknesses. Without being bound by theory, it appears that 1,3-GB not only influences the interaction between the active material particles but also the interaction and swelling behavior of the binder materials in the solvent, resulting in improved interaction of different binder materials within the layer. A binder is considered water-swellable if, as a 1 wt. % solution, it absorbs more than 10 wt. % water at room temperature under equilibrium conditions. The amount of water can be determined by gravimetric analysis after separating and draining the swollen material. However, the basic water-swelling properties of different binder materials with respect to water are also described in the literature. Preferably, both of these different binders are used in substantial amounts, for example, the weight ratio of both binders to each other may preferably be 0.2 or more and 2 or less.

[0025] In yet another preferred embodiment of the method, carboxymethyl cellulose and styrene-butadiene rubber (SBR) can be used as binders. It has been found that the use of a water-swellable binder in combination with a non-water-swellable binder is particularly suitable for obtaining thick, crack-free electrode layers that are particularly mechanically stable. In particular, using water as the solvent and 1,3-BG results in high yields of crack-free electrode films, which, in addition, have electrical properties very similar to those of films without the 1,3-BG additive. Particularly preferably, the weight ratio of the two different binder materials can be 1:1. Preferably, the weight ratio can vary from a 1:1 distribution of both components by 15 wt. %, preferably 10 wt. %, in both directions.

[0026] In one preferred aspect of the method, in process step a), on a total solids basis: - the active material is present in a proportion of 90% by weight or more and 98% by weight or less, - the conductive additive in a proportion of at least 1% and at most 5% by weight, and - one or more binders in a proportion of at least 2% and at most 6% by weight, The weight percentages of solids in the dispersion can be present in the dispersion, and the weight percentages of solids in the dispersion total 100% by weight. Within the composition of the dispersion, electrode films can be obtained that are mechanically very stable, crack-free, and well-adhered. In addition, the films exhibit very similar electrical properties in direct comparison with electrode films obtained from dispersions without butanediol additives. Furthermore, the films exhibit a reduced tendency to crack in direct comparison with electrode films obtained from dispersions with other alcohol or dialcohol additives.

[0027] In a further preferred embodiment of the method, the dispersion in process step a) can have a total solids content of 40% by weight or more and 60% by weight or less. This total solids content in the dispersion has been found to be particularly advantageous for the gentlest possible processing of the dispersion and the most efficient possible drying step. A very thick, crack-free film layer is obtained, and its electrical properties are essentially insignificantly different from those of a dispersion not loaded with additives. Preferably, the solids content can be 42% by weight or more and 55% by weight or less, more preferably 45% by weight or more and 52.5% by weight or less. The solids content of the dispersion can be determined, for example, using a thermobalance.

[0028] In another embodiment of the method, in process step b), the mixture can be applied to a current collector. The composition of the dispersion, on the one hand, results in a self-supporting electrode film after drying, which is later fixed to the current collector of the battery structure, for example, by mechanical force. However, it is also possible to apply the dispersion directly to the current collector film. The dispersion is then dried on the current collector, and a solvent-free or solvent-low layer is obtained, which can then be later formed into an electrode body. This can particularly improve the mechanical adhesion of the electrode film to the current collector. The current collector can be made, for example, from copper, aluminum, or other metals.

[0029] In yet another preferred embodiment of the method, the current collector can be a coated current collector. The method according to the present invention, in which a predetermined amount of butanediol, e.g., 1,3-BG, is added to the dispersion, can contribute to improved adhesion of the electrode film, especially when applied directly to the coated electrode surface. Coatings of current collectors used in battery construction are known to those skilled in the art.

[0030] In one preferred embodiment of the method, butanediol can be added to the mixture in process step a) only at the end of mixing the remaining components.In order to obtain a dispersion that is as uniform as possible while preserving the structure of the added binder material, it has been found to be advantageous to add butanediol to the dispersion only after mixing the other components.In this order, the rate of shear force used can be kept low at the end of the mixing process.Despite the small amount of mixing energy introduced, butanediol disperses uniformly in solvents, especially water, and its advantageous effect in the form of reduced crack formation is exerted during drying.Compared to mixing methods in which butanediol is already charged at the beginning or butanediol is added and the dispersion is then subjected to shear or mechanical stress for a very long time, a significantly more mechanically robust film can be obtained.

[0031] In yet another preferred embodiment of the method, process step c) can be carried out at a temperature range of 50°C or higher and 200°C or lower. It has been found to be advantageous to dry the electrode film at a moderate temperature range in order to obtain a film as crack-free as possible. Drying can be carried out at very low temperatures, for example at room temperature, with or without vacuum. This process results in a crack-free film, but it takes a considerable amount of time. Furthermore, by using butanediol as an additive, higher drying temperatures can be used, and no crack formation in the film is observed, even at very thick layer thicknesses of 200 μm or more. This result cannot be obtained without the additive or by adding the equivalent alcohol. Preferably, the temperature can be 150°C or lower.

[0032] In yet another preferred aspect of the method, drying can be carried out at least partially under reduced pressure. Drying under negative pressure or in vacuum can result in an electrode film with improved mechanical strength. In addition, it has been unexpectedly shown that applying the dispersion directly onto a current collector and drying under vacuum can result in significantly improved adhesion of the electrode film to the current collector.

[0033] In yet another preferred aspect of the method, the viscosity of the dispersion is 50 s -1 At a shear rate of 0.5 Pa*s and room temperature, the viscosity can be greater than or equal to 0.5 Pa*s and less than or equal to 1.5 Pa*s. It has been found that the above viscosity range is particularly suitable for obtaining very thick wet film thicknesses that are as uniform as possible. Dispersions in this viscosity range and with a significant butanediol proportion can be applied by several different extrusion methods to very thick layers without significant anisotropy and exhibit no or very little crack formation after drying.

[0034] The present invention further relates to the use of the method according to the present invention for the production of an electrode film having a dry layer thickness of 100 μm or more and 600 μm or less for a secondary alkali ion energy storage device. Using the method according to the present invention, it is possible to produce an electrode film for an alkali ion energy storage device having, in particular, very good electrical properties and a high cycle number. Without being bound by theory, it appears that the cycle number is also favorably affected, particularly if the electrode film does not have discontinuities in the form of microscopic or macroscopic cracks. This can improve the reversibility of the storage and release of alkali species and prevent malfunctions due to mechanical failure of the electrode structure. Preferably, the alkali ion energy storage layer can be a Li-ion battery.

[0035] The present invention further provides an electrode film for a secondary alkali ion energy storage device, the electrode film having a layer thickness of 100 μm or more and 600 μm or less; a proportion by weight of active material equal to or greater than 90% and equal to or less than 98%; - conductive additives in a proportion of at least 1% and at most 5% by weight, - one or more binders in a proportion of at least 2% and at most 6% by weight, and - 1,3-butanediol in a proportion by weight equal to or greater than 0.001% and equal to or less than 0.1%; The electrode film according to the present invention comprises: (a) a 1,3-butylene glycol (BG)-containing polymer; (b) a 1,3-butylene glycol (BG)-containing polymer; (c) a 1,3-butylene glycol (BG)-containing polymer; and (d) a 1,3-butylene glycol (BG)-containing polymer. The electrode film according to the present invention exhibits electrical properties very similar to those of conventional electrode films, while exhibiting improved cycle stability due to the improved mechanical integrity of the electrode layer, free from microscopic and macroscopic cracks. In addition to improved yields during production, layer thicknesses that would otherwise be impossible to achieve using conventional methods due to cracking problems can be achieved. Preferably, the dry thickness of the layer can be 150 μm or more and 500 μm or less, more preferably 2000 μm or more and 500 μm or less, and even more preferably 250 μm or more and 450 μm or less. Further advantages of the electrode film according to the present invention for secondary alkali ion energy storage devices are as already described with respect to the advantageous properties of the product resulting from the method according to the present invention. In this regard, reference is expressly made to the advantages described herein for the electrode film. Preferably, the 1,3-butylene glycol (BG) content can be 0.05 wt. % or less, more preferably 0.01 wt. % or less. The content of 1,3-BG can be determined, for example, by HPLC measurement of the washed electrode film. [Example]

[0036] I) Comparison of various diol additives To compare the effects of various additives on anode fabrication, various alcohols and polyols were added to the base dispersion at a concentration of 4 wt. % based on the total mass of the dispersion. This control formulation consisted of 95 wt. % graphite, 2 wt. % CMC, 2 wt. % SBR, and 1 wt. % carbon black. The solids content of the aqueous dispersion was 40.5 wt. The dispersions were prepared in a vibratory mill. Films were applied to a carrier film using a film-forming apparatus at a wet layer thickness of approximately 300 μm and dried at 100°C. The dry film thickness was approximately 100 μm. In addition to a control without additives, samples were also prepared using glycerin, 1,2-propanediol, and 1,3-propanediol at concentrations of 4 wt. After drying, these various additives produced different patterns of crack formation. Glycerin had the least effect on crack formation, and the dried film showed the greatest number of cracks. With respect to crack formation, 1,3-butanediol is slightly better, and 1,2-propanediol is also slightly better. 1,3-butanediol gives by far the best results. The films show the fewest cracks and the most uniform appearance. This test demonstrates that for a relatively homogeneous subgroup of additives, i.e., the lower diols, there are significant differences with respect to crack formation in the production of electrode films.

[0037] II) Preparation of electrode membrane using 1,3-butanediol To further characterize the electrode films containing 1,3-BG, control electrode films were prepared from graphite active material, carbon black as a conductive additive, two different binders (CMC and SBR), and water as the solvent. For the preparation of electrode films according to the present invention, butanediol in the form of 1,3-butanediol was added as an additive component at a concentration of 3.2 wt. % based on the total weight of the control dispersion.

[0038] II.1) Preparation of the dispersion The following components were used to prepare the dispersion: graphite: SMG-A3 (Hitachi Chemicals), conductive carbon black: Super C65 (Imerys), SBR latex binder: TRD2001 (JSR Micro), CMC: CRT2000PA07, and solvent: deionized water.

[0039] CMC as a binder was prepared as a 2 wt% aqueous solution, and then graphite and conductive carbon black were added and processed to prepare a dispersion with the following weight composition: graphite:conductive carbon black:SBR:CMC=96:1.5:1.25:1.25. The dispersion was mixed in a Dissolver mixer (Dispermat, VMA Getzmann, Φ50 mm stirring disc). 1,3-BG was added after the remaining components were mixed. The additives were mixed at a low rotation speed. The dispersion was then degassed using negative pressure. The solids content of the dispersion without 1,3-BG was 52.3 wt%. The solids content of the dispersion with 1,3-BG was 50.7 wt%. The dispersion was then heated at 25°C and 50 s. -1 The viscosity at 1.6 Pas for the control sample without additive and 1.0 Pas for the sample with 1,3BG additive (rheometer, pair Physica MCR302, plate-plate geometry, 50 mm diameter).

[0040] II.2) Application of dispersion The electrode layers were formed using a roll-to-roll coating machine (Matisse, KTF-S) equipped with a doctor blade coating unit. The substrate was a 10 μm-thick copper foil. These dispersions were applied to a wet film thickness of approximately 300 to 340 μm.

[0041] II.3) Drying of the dispersion The layer applied as a film was dried in a drying tunnel at temperatures ranging from 30°C to 50°C.

[0042] III) Characterization of dispersions and electrode films After drying, the electrode film exhibited a thickness of 240 μm for the control and 230 μm for the sample with 1,3BG added. The slightly thinner layer thickness was due to the slightly lower solids content of the dispersion of the 1,3BG sample. The control sample exhibited obvious cracks in the electrode film after drying, whereas the electrode film from the dispersion with 1,3BG additive was crack-free.

[0043] To characterize the electrode film on the current collector, adhesion strength measurements were performed. These measurements were performed with a zwikiLine Z2.5 / TN (ZwickRoell) using a 10 N measuring cell. A 90° peel test (DIN EN 28510-1) was performed. For this, electrode strips measuring 80 mm x 17 mm were punched out and fixed with the coated side on a sample holder using double-sided adhesive tape. The metal foil was peeled off at a constant speed of 600 mm / min, and the adhesive strength in N / m was calculated from the force required for this.

[0044] The vacuum-dried sample, which was not mechanically post-treated (uncalendered), yielded an adhesion strength of 5.1±0.1 N / m for the control. The adhesion strength of the corresponding 1,3-BG sample was significantly higher, at 7.1±0.2 N / m. In particular, vacuum treatment or drying of the electrode film according to the invention can result in a significant improvement in the adhesion strength of the electrode film to the current collector. It is surprising that the 1,3-BG additive, in combination with the vacuum step, seems to contribute to improved adhesion of the electrode film, in addition to the absence of cracks in the layer.

[0045] Furthermore, these films were also tested for their electrical properties. Resistivity determinations were performed. This measurement was performed using a Hiki RM2610 electrode resistance measurement system. Six measurements were performed at different positions per electrode, and the average value and standard deviation were calculated. The resistivity of the uncalendered control layer was 73.5 ± 1.9 mΩ*cm. The resistivity of the calendered control film was 71.3 ± 2.3 mΩ*cm. The resistivity of the uncalendered 1,3BG layer was 74.1 ± 1.4 mΩ*cm. The resistivity of the calendered 1,3BG film was 69.3 ± 2.9 mΩ*cm. Therefore, the resistivity does not differ significantly between the control and the electrode films produced according to the present invention.

Claims

1. 1. A method for manufacturing a thick electrode film having a layer thickness of 100 μm or more and 600 μm or less for a secondary alkali ion energy storage device, comprising the steps of: a) a dispersion comprising at least one solvent and solids, the total solids content of the dispersion being equal to or greater than 40% by weight and equal to or less than 80% by weight, wherein the solids are: a proportion by weight of active material equal to or greater than 75% and equal to or less than 98%; - one or more conductive additives in a proportion of at least 0.5% and at most 5% by weight, and - one or more binders in a proportion of at least 1% and at most 10% by weight, wherein the weight percentages of solids in the dispersion total 100% by weight; preparing a dispersion, and mixing butanediol into the dispersion at a concentration of at least 2 wt. % and at most 10 wt. % based on the total weight of the dispersion; b) applying the dispersion in a layer thickness of ≧200 μm and ≦1200 μm; and c) drying the applied dispersion to obtain an electrode film; A method comprising:

2. The method of claim 1 wherein the solvent is water.

3. 3. The method of claim 1, wherein the butanediol is 1,3 butanediol.

4. 4. The method of claim 1, wherein the butanediol is added to the dispersion at a concentration of 2% by weight or more and 6% by weight or less.

5. 5. The method according to claim 1, wherein at least two different binders are used as binders, one of which is swellable in water and the other binder is not swellable in water.

6. 6. The method according to claim 5, wherein carboxymethyl cellulose and styrene-butadiene rubber (SBR) are used as binders.

7. 7. The method according to claim 1, wherein in process step a) on a total solids basis: the active material is present in a proportion of 90% by weight or more and 98% by weight or less, the conductive additive is present in a proportion of ≧1% and ≦5% by weight, and - the one or more binders are present in a proportion of at least 2% and at most 6% by weight, wherein said weight percentages of solids present in said dispersion and in said dispersion total 100% by weight.

8. 8. The method according to any one of claims 1 to 7, wherein the dispersion in process step a) has a total solids content of ≧40 wt. % and ≦60 wt. %.

9. The method according to any one of claims 1 to 8, wherein in process step b) the mixture is applied onto a current collector.

10. The method of claim 9 , wherein the current collector is a coated current collector.

11. 11. The method according to claim 1, wherein in process step a) the butanediol is added to the mixture only at the end of the mixing of the other constituents.

12. 12. The method according to any one of claims 1 to 11, wherein process step c) is carried out at a temperature range of ≧50°C and ≦200°C.

13. The method of claim 12 wherein the drying is performed at least in part under reduced pressure.

14. Use of the method according to any one of claims 1 to 13 for the production of an electrode film having a dry layer thickness of ≧100 μm and ≦600 μm for a secondary alkali ion energy storage device.

15. An electrode film for a secondary alkali ion energy storage device, the electrode film having a layer thickness of 100 μm or more and 600 μm or less; and a proportion by weight of active material equal to or greater than 90% and equal to or less than 98%; - a proportion by weight of conductive additives equal to or greater than 1% and equal to or less than 5%; - one or more binders in a proportion of at least 2% and at most 6% by weight, - 1,3-butanediol in a proportion of greater than or equal to 0.001% and less than or equal to 0.1% by weight, wherein the weight percentages total 100% by weight.

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