Method and device for producing an electrode for a lithium-ion battery cell, electrode and lithium-ion battery

Abstract

The invention relates to a method for producing an electrode, in particular an anode, for a lithium-ion battery cell, wherein a coated electrode film (8) is introduced into a plating bath (14), wherein the electrolyte (18) of the plating bath (14) comprises a lithium salt (22) and at least one solvent (20), wherein the electrode film (8) impregnated with the electrolyte (18) and coated is subsequently calendered, wherein the coated electrode film (8) is subsequently heated so that the solvent (20) contained in the coating partially evaporates or so that one of the solvents (20) at least partially evaporates. The invention also relates to a device (2) for producing an electrode for a lithium-ion battery cell, an electrode and a corresponding lithium-ion battery.

Description

Technical Field

[0001] The invention relates to a method and a device for producing an electrode for a lithium-ion battery cell, wherein a coated electrode film is introduced into a plating bath. Background Art

[0002] A lithium-ion battery cell (hereinafter referred to as a battery cell) comprises at least one anode and at least one cathode, wherein a separator is arranged between the anode and the cathode.

[0003] To produce such an anode or such a cathode, a foil-like or strip-like substrate is usually provided with a coating of active material. The coating is then compacted by at least one pair of rollers of a calender. To form the anode or cathode, the coated substrate is then shortened and / or cut.

[0004] By calendering, in particular in the case of high densification rates (height reduction) of the coating, for example at densification rates of more than 20%, the porosity of the coating is reduced more strongly in the region of its outer surface, i.e. on its surface facing away from the substrate, than in the region of the substrate. The porosity after calendering is therefore not uniform (homogeneous). Typically, at such compaction rates, relatively large pores with a size of between 2 and 5 μm at the outer surface of the coating are substantially closed.

[0005] The reduction of the pore size and / or the closing of the pores leads to a reduction in the (contact) area between the electrolyte and the coating material. On the one hand, this makes the transfer of lithium ions between the electrolyte and the material difficult. On the other hand, this may disadvantageously favor so-called lithium plating, i.e., for depositing metallic lithium on the anode.

[0006] Another disadvantage of conventional production methods arises during the formation of the battery cell, i.e. during the first charge and discharge cycle. Here, a boundary layer, the so-called SEI ("solid electrolyte interphase"), forms on the surface of the anode, in which lithium ions and degradation products of the electrolyte react on the surface of the anode. As a result, the lithium consumed to form the SEI is no longer available for charge transport. As a result, the capacity of the battery cell is disadvantageously and irreversibly reduced. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a particularly suitable method for producing an electrode for a lithium-ion battery cell. In particular, the capacity loss due to the formation of SEI and / or the risk of lithium plating should be avoided or at least reduced by the production method. In addition, a particularly suitable device for producing an electrode for a lithium-ion battery cell is provided, as well as such an electrode and such a lithium-ion battery cell are provided.

[0008] According to the invention, the technical problem is solved in terms of the method by a method for producing an electrode, in particular an anode, for a lithium-ion battery cell. In terms of the device, the technical problem is solved by a device for producing an electrode for a lithium-ion battery cell, in particular a device for producing an electrode according to the above method, and in terms of the electrode by an electrode, in particular an electrode produced according to the above method and / or device, and in terms of the lithium-ion battery cell by a lithium-ion battery, in particular a lithium-ion battery cell having the above electrode. In this case, the embodiments associated with the method also apply expediently to the device, the electrode and the lithium-ion battery cell, and vice versa.

[0009] In the method, a coated electrode film is first provided. In other words, the electrode film, also referred to as the substrate, is provided with a coating. Preferably, the substrate is provided with the coating on both sides. In other words, the substrate is arranged between two layers forming the coating. The coating comprises an active material, such as graphite, graphene, so-called hard carbon nanotubes or soft carbon nanotubes or titanium oxide, into which lithium ions can be embedded or deintercalated. In addition, the active material can contain silicon. The coating also expediently comprises a binder and a conductive agent, such as graphite or conductive carbon black.

[0010] The electrode film is preferably in the form of a strip, so that it can be unwound from a roll and conveyed in the system, in particular in the manner of a calender, by means of rolls. The electrodes are therefore preferably produced using a roll-to-roll method. However, as an alternative to this, it is also possible to first remove the individual electrode sheets from the electrode film, in particular to cut them out, and then - similarly to the following embodiments - to process these electrode sheets.

[0011] If the electrode is an anode, the electrode film is, for example, a metal film, in particular a copper foil.

[0012] According to the method, the coated electrode film is introduced into a (first) electroplating tank. Preferably, the electrode film is conveyed through the electroplating tank, for example by means of rollers and / or rolls. During this process, the electrolyte penetrates into the coating. In other words, the electrolyte from the electroplating tank is absorbed in the coating, in particular in the pores of the coating.

[0013] In this case, the coating is particularly preferably not compacted, i.e. not compressed. In particular, the electrode film is not compacted by means of a calender after the coating is applied and before it is introduced into the electroplating tank, or at least not compacted for this purpose. However, a reduction in the layer thickness of the coating can be achieved when the electrode film is transported by means of a calender, for example by means of its transport rollers, deflection rollers or friction rollers, or a reduction in the layer thickness of the coating can be achieved when the electrode film is wound or unwound. However, this reduction is relatively small and cannot therefore be understood as "compression based on a calender". Here, i.e. when the electrode film is transported, the reduction in the layer thickness of the coating is in particular less than 5%, preferably less than 2%, and / or the linear load acting on the coating is less than 1000 N / mm, in particular less than 500 N / mm, preferably less than 200 N / mm.

[0014] Therefore, the pores of the coating are not closed and / or the porosity of the coating is relatively large.

[0015] Advantageously, it is easier to get the electrolyte in the electroplating bath into the coating in this way. Thus, in the electroplating bath, a relatively large amount of electrolyte is absorbed in the coating and / or the time required for this is reduced.

[0016] For example, the duration of the coated electrode film in the plating tank, or the duration of the corresponding section of the coated electrode film in the plating tank in the roller-to-roll process, is between 0.5 minutes and 10 minutes, in particular between 1 minute and 5 minutes, and suitably between 2 minutes and 3 minutes.

[0017] Furthermore, the electrolyte of the electrolyte salt has a lithium salt and at least one solvent, ie a single solvent or more than one solvent. In other words, the electrolyte is formed by a solvent or solution, ie a mixture of more than one solvent, in which or in which the lithium salt is dissolved.

[0018] According to the method, the electrode film impregnated with electrolyte and coated is subsequently calendered, i.e. compacted by means of a pair of rollers. For this purpose, the coated electrode film is preferably first conveyed out of the electroplating tank. In other words, the coated electrode film is subjected to a linear load, which causes a reduction in the layer thickness of the coating, for example by between 15% and 35%, in particular by between 20% and 30%. For this purpose, the linear load is, for example, between 1000 N / mm and 2500 N / mm, in particular between 1300 N / mm and 2000 N / mm.

[0019] If the electrolyte does not fully penetrate into the substrate in the electroplating bath, i.e. if the electrolyte is only contained in the region of the (outer) surface of the coating, which faces away from the substrate, the electrolyte is advantageously pressed into deeper regions of the coating during deposition, i.e. into regions near the substrate. The electrolyte and the lithium salt dissolved therein are thus also in contact with regions of the coating close to the substrate. Furthermore, advantageously, during calendering, a relatively uniform pressure distribution in the coating is achieved due to the electrolyte in the coating, and thus a relatively uniform deformation and compression of the coating. Thus, a relatively uniform, i.e. uniform porosity of the coating is advantageously achieved.

[0020] The lithium is dissolved in the electrolyte, ie not present in its metallic form. Therefore, the rolling does not have to be carried out in a drying chamber.

[0021] For the calendering (calendering process), a film is advantageously introduced between the rollers and the impregnated coating. The film prevents or at least reduces the outflow and / or outflow of electrolyte from the coating.

[0022] According to the method, the coated electrode film is then heated, i.e. heated for a period of time until curing, so that the solvent absorbed in the coating partially evaporates. If a solution of more than one solvent is used for the electrolyte, the coated electrode film is then heated so that only one of the solvents partially or completely evaporates. In other words, in this case, substantially only one of the solvents evaporates.

[0023] The evaporation of the solvent absorbed in the pores of the coating results in at least a slight increase in the pore size due to the volume increase of the solvent and / or the opening of pores that were closed during calendering. In other words, the porosity is advantageously increased by partial evaporation of the solvent or by at least partial evaporation of one of the solvents.

[0024] In contrast to the electrolyte used in the finished battery cell, no additives are required and preferably no additives are present in the electrolyte of the electroplating bath, since this electrolyte escapes from the coating to some extent by evaporation anyway.

[0025] In summary, the method is used to produce an electrode for a lithium-ion battery cell. Here, it is enriched with lithium, in particular with lithium ions. In other words, a pre-lithiation of the electrode is carried out.

[0026] In this case, a portion of the solvent and / or one of the solvents remains. During the production of a battery cell with electrodes, wetting with the electrolyte which is provided in the battery cell is advantageously carried out more quickly.

[0027] During the formation of a lithium-ion battery cell with an electrode, in particular an anode, produced in this way, the lithium introduced into the electrode by means of the electroplating bath or the lithium ions embedded therein are essentially used for forming the SEI. Thus, no lithium or active material from the cathode or lithium or lithium ions from the electrolyte are used for this purpose, or only relatively little lithium or lithium ions are used. As a result, a reduction in the capacity of the lithium-ion battery cell due to the formation of the SEI is particularly advantageously avoided or at least reduced.

[0028] The electrode is expediently the anode, on the one hand because the SEI forms at the anode and on the other hand because the lithium is already present in the cathode in the form of compounds. However, the method can in principle also be used for cathodes.

[0029] According to an advantageous refinement of the method, subsequently, that is, after partial evaporation of the solvent or after at least partial evaporation of one of the solvents of the electrolyte, a voltage is applied to the coated electrode film. In other words, the coated electrode film is electrically connected to a voltage source, preferably a DC voltage source. In the case of an electrode film coated on both sides, one of the coatings is, for example, in electrical contact with one of the poles, and the other coating is in electrical contact with the other pole of the voltage source. The voltage is suitably between 0.1 V and 2.0 V, in particular between 0.2 V and 1.5 V, preferably between 0.4 and 0.9 V.

[0030] In summary, the lithium salt is selected in such a way that, in particular in the coating, its anions form a gas when the electrode membrane is subjected to a voltage. As a result, the anions of the lithium salt escape from the coating due to the formation of gas. This is also referred to here and below as the electrolysis of the lithium salt.

[0031] For this purpose, lithium chloride (LiCl), lithium carbonate (Li 2 CO 3 ) or preferably lithium nitride (Li 3 N) are suitably used as lithium salts, from which chlorine, carbon dioxide or the inert gas nitrogen are formed.

[0032] The generation of nitrogen and lithium from lithium nitride occurs in several stages:

[0033] (1) Li3N+H2→Li2NH+LiH

[0034] (2) 2LiNH2→Li2NH+NH3

[0035] (3) LiH+NH3→LiNH2+H2

[0036] (4)2Li2NH→4Li+H2+N2

[0037] For example, a mixture of lithium nitride and lithium chloride is used, wherein chloride ions assist the dissociation of lithium nitride.

[0038] Such lithium salts are usually unsuitable for use in battery cells due to the gas generation. However, in this method, the porosity is advantageously further increased by gas generation, wherein the anions of the lithium salt are also removed from the electrode.

[0039] According to an advantageous embodiment, the electrolyte has at least two solvents. Ethylene carbonate (EC) is one of the solvents, since the lithium salt has a relatively high solubility in ethylene carbonate.

[0040] Here, the proportion of ethylene carbonate is suitably 15 to 45% by volume, in particular 20 to 40% by volume, preferably 25 to 35% by volume, based on the total volume of all solvents of the electrolyte. The melting point of ethylene carbonate is 45° C. Although ethylene carbonate can be used as the only solvent for the electrolyte, the temperature must be kept above 45° C. during the production of the electrode. Therefore, it is preferred to use a second solvent for the electrolyte so that the melting point of the electrolyte is reduced.

[0041] The second solvent is particularly preferably selected such that its boiling point is less than 150° C., preferably less than 100° C., so that substantially only the second solvent evaporates when the coated electrode film is heated.

[0042] For example, a linear carbonate or a chain carbonate, preferably dimethyl carbonate (DMC) is used as the second solvent.

[0043] According to an advantageous design, the coated electrode film is heated after heating to evaporate the solvent or part of the solvent. In order to at least partially evaporate one of the solvents, processing is performed using a stretching tool. Here, the stretching tool has a gap that tapers in the conveying direction of the coated electrode film, i.e., becomes smaller in this direction. The gap is preferably continuously tapered here. For this purpose, the stretching tool has two jaws (or jaws) that are opposite to each other, wherein the opposite surfaces of the jaws are opposite to each other or opposite to each other. Figure 1 The middle plane between the two jaws according to the invention is shown in FIG. Here, the coated electrode film rests against the two jaws during its transport through the gap. The stretching process is carried out in particular in the manner of strip stretching (English "strip drawing"). Advantageously, the surface of the coating is flattened with the aid of a strip stretching tool.

[0044] Preferably, the coated electrode film is additionally loaded with voltage by means of a stretching tool for forming a gas from the anions of the lithium salt. For example, each jaw is connected to one of the poles of a DC voltage source. The stretching tool is not provided for compressing the coating. Therefore, no compression or only slight compression is performed. More precisely, a large contact surface is provided by means of the stretching tool, on which the coated electrode film is loaded with voltage. Therefore, compared with loading the coated electrode film with voltage by means of rollers, the area of ​​the coating is in contact with the stretching tool for a relatively long duration, and thus a relatively long duration of gas formation from the anions of the lithium salt is given. For this purpose, the inclination of the jaws relative to the middle plane is between 0.1° and 2°, and / or the length of the jaws in the conveying direction is between 1m and 5m.

[0045] According to an advantageous refinement of the method, in order to form the (SEI) solid electrolyte interphase, after heating, in particular after applying a voltage, the coated electrode film is placed in another electroplating tank. This electroplating tank is referred to below as the second electroplating tank. The coated electrode film is preferably conveyed through the second electroplating tank.

[0046] Electrodes are arranged in the second electroplating tank, wherein a voltage is applied between the coated electrode film and the (additional) electrode. Here, the coated electrode film is connected to the positive pole of a DC voltage source and the electrode is connected to the negative pole of the DC voltage source. The voltage provides a voltage between 0.5 V and 5.0 V. Here, lithium ions absorbed in the coating, in particular embedded in the coating, are used to form a solid electrolyte interphase. Therefore, advantageously, it is not necessary for the (additional) electrode to have lithium for the formation of the SEI. In other words, the additional electrode can be lithium-free.

[0047] Preferably, the coated electrode film is conveyed through the electrolyte of the second electroplating tank more than once, in particular twice or three times. For example, different C rates (C factors) or charging rates and / or different current intensities are used here. For example, a C rate of 0.5 C is selected for the first pass and a C rate of 1 C is selected for the second and / or third pass.

[0048] For example, the electrolyte of the second plating tank is temperature-adjusted to 50° C. to promote the formation of SEI.

[0049] Due to this voltage, the SEI forms on the coating. Advantageously, therefore, it is no longer necessary to form a battery cell with an electrode (suitably an anode) produced in this way in order to form the SEI. Furthermore, no additives for the electrolyte (for forming the SEI) need to be provided in the electrolyte (provided for the battery cell).

[0050] According to an advantageous design, a pair of rollers for introducing the electrolyte into the coating is arranged in the first electroplating tank. In other words, the pair of rollers is arranged in the electrolyte. Here, the coated electrode film is guided through the gap between the rollers of the pair of rollers. The rollers of the pair of rollers are used here for conveying, i.e. accelerating the absorption of the electrolyte into the coating on the electrode film. Therefore, this pair of rollers is referred to here and below as an impregnation roller pair. For this purpose, the two rollers vibrate. For example, the axes of the individual rollers are movable, wherein the axes of the rollers are moved by means of a piezoelectric actuator and vibrate, i.e. tremble. Preferably, the first roller and the second roller vibrate in antiphase. Thus, the two rollers move towards or away from each other.

[0051] For example, the amplitude of the vibration is between 5 μm and 50 μm, in particular between 10 μm and 15 μm. The frequency of the vibration is, for example, 5 kHz.

[0052] On the one hand, the electrolyte is pressed into the coating in the electrolyte bath by a pair of dipping rollers. On the other hand, due to the vibrations, any bands (composed of the coating's binder) arranged on the outer surface of the coating are loosened or broken, so that the electrolyte can be more easily absorbed into the coating.

[0053] Preferably, the roller, which is made of titanium, for example, has a coating made of Teflon, ie, polytetrafluoroethylene, on the circumference. Adhesion of the coating material to the roller is thus avoided, or the risk of such adhesion is at least reduced.

[0054] According to an advantageous embodiment, a recess is formed in the coating of the electrode film in the electroplating bath, preferably by means of a dipping roller pair. For example, the depth of the recess, i.e. the spatial dimension in the direction perpendicular to the substrate, in other words in the direction of the layer thickness, is between 5 μm and 50 μm, in particular between 10 μm and 30 μm. The length of the recess, i.e. the dimension parallel to the surface extending through the substrate, is, for example, between 0.1 mm and 10 mm, in particular between 1 mm and 5 mm.

[0055] For example, the rollers of the impregnation roller pair are provided with raised structures on their surface. Advantageously, the electrolyte in the electroplating tank is absorbed and retained in these recesses. The recesses thus form a kind of reservoir for the electrolyte. The friction during the calendering process is advantageously reduced by means of the electrolyte in these recesses. In addition, at least a portion of the electrolyte can be pressed from the recesses into the coating during calendering.

[0056] Another aspect of the invention relates to a device for producing electrodes for lithium-ion battery cells. In particular, the device is configured and set up to carry out the method according to one of the above-mentioned variants.

[0057] The device comprises an impregnation device having an electroplating tank and a conveying unit for conveying the electrode film provided with the coating through the electroplating tank. The electrolyte in the electroplating tank again comprises at least one solvent, preferably a solution consisting of two solvents, and a lithium salt. The conveying device expediently comprises a plurality of rollers and / or rolls, by means of which the coated electrode film can be conveyed through the electroplating tank, in particular through the electrolyte.

[0058] The impregnation device preferably additionally comprises an impregnation roller pair. In particular, the rollers of the impregnation roller pair each have a structure by means of which they can be introduced deeper into the coating.

[0059] The device also includes a calender roller pair for compacting the coating. The calender roller pair is connected downstream of the impregnation device with reference to the conveying direction of the coated electrode film. The calender roller pair is always outside the electrolyte bath.

[0060] Furthermore, the apparatus has a heating device which is arranged and configured to evaporate a portion of the solvent or at least a portion of one of the solvents of the electrolyte (if a solution of more than one solvent is used) contained in the calendered coating of the electrode film. The heating device is therefore connected downstream of the calender roller pair with respect to the conveying direction of the coated electrode film.

[0061] Preferably, the device further comprises a stretching tool, by means of which a voltage can be applied to the coated electrode film.

[0062] For example, the device additionally has a second electroplating tank and a second conveying device for conveying the coated electrode film through the second electroplating tank. In this case, the negative pole of the DC voltage source is connected to an electrode, in particular a lithium-free electrode, which is arranged in the electrolyte of the second electroplating tank, i.e. immersed therein. The positive pole of the DC voltage source is connected to the coated electrode film, for example by means of grinding contact or rolling contact, so that a voltage exists between the electrode film and the electrode.

[0063] A further aspect of the invention relates to an electrode, in particular an anode, which is produced according to the method in one of the above variants and / or by means of the device in one of the above variants.

[0064] Thus, lithium ions are accommodated in the electrode, which is preferably configured as an anode. In particular, the lithium ions are incorporated into the active material of the coating. According to an embodiment of the method, for example, a solvent, in particular (only) ethylene carbonate, is also absorbed in the pores of the active material.

[0065] Furthermore, the porosity, especially on the surface facing away from the substrate, is increased compared to conventionally produced electrodes, even at relatively high compaction rates of more than 20%, suitably between 20% and 30%. In addition, relatively many pores are open on this surface.

[0066] For example, the porosity in the region of the outer surface of the coating is greater than 0.03 cm 3 / g, for example between 0.03 and 0.07, especially at 0.05 cm 3 / g to 0.07cm 3 / g, especially for pore sizes between 0.2μm and 5μm.

[0067] Another aspect of the invention relates to a lithium-ion battery having such an electrode. Such a lithium-ion battery comprises a number of, i.e. a single, lithium-ion battery cell or more than one lithium-ion battery cell, which in turn comprises at least one anode and at least one cathode. According to the invention, the battery cell or at least one of the battery cells comprises at least one electrode, in particular an anode, which is produced according to the method of the above variant and / or by means of the device of the above variant.

[0068] Such lithium-ion batteries can be used, for example, in notebook computers, in mobile phones. In particular, lithium-ion batteries are provided for traction batteries of electrically driven or electrically drivable motor vehicles, which provide electrical energy for driving the motor vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. In the accompanying drawings:

[0070] Figure 1 A first section of a plant for producing an electrode is schematically shown, comprising an impregnation device with an electroplating tank, a conveying unit for conveying the coated electrode film through the electroplating tank, and an impregnation roller pair,

[0071] Figure 2 A dip roller pair is schematically shown in cross section, wherein the shafts of the dip roller pair are each coupled to a piezoelectric actuator,

[0072] Figure 3 Schematically showing a side view of an impregnation roller pair,

[0073] Figure 4 Schematic representation of a detail of the surface of one of the rollers of an impregnation roller pair, wherein the roller has a raised structure for introducing depressions into the coating,

[0074] Figure 5 The second section of the apparatus is shown, which has a calendering roller pair for laminating the impregnated and coated electrode film and a heating device for heating the calendered coated electrode film,

[0075] Figure 6A third section of the device is shown, wherein the section of the device has a stretching tool having two jaws with a tapered gap formed between the two jaws, wherein the jaws are connected to a DC voltage source,

[0076] Figure 7 A fourth section of the device is shown, wherein the section of the device comprises a second electroplating tank, wherein a lithium-free electrode is introduced into the electroplating tank, the lithium-free electrode is connected to the negative pole of a DC voltage source, and wherein the coated electrode film can be conveyed through the electroplating tank and can come into contact with the positive pole of the electroplating tank, and

[0077] Figure 8 The method sequence for producing an electrode is illustrated with the aid of a flow chart, wherein an electrode film provided with an uncompressed coating is conveyed through a plating bath and subsequently calendered. DETAILED DESCRIPTION

[0078] Parts and dimensions that correspond to one another are always provided with the same reference symbols in all the figures.

[0079] exist Figures 1 to 7 2 shows a device 2 which is arranged and configured for producing electrodes, here anodes. The device 2 has a plurality of modules or sections 2a, 2b, 2c and 2d, wherein for better recognition, these sections are each shown in one figure. The device 2 is designed in the manner of a calendering device. Therefore, the roll-to-roll method is used to produce the electrodes.

[0080] exist Figure 1 2 shows a first section 2a of the device 2. In this case, a strip-shaped electrode film 4 is provided, which is provided with a coating 6 on both sides, which has an active material, a binder and a conductive agent, see also Figure 7 The electrode film 4 is, for example, a metal film, in particular a metal film made of copper for producing anodes, or a plastic film coated with metal. In this case, the coating 6 is initially uncompacted, i.e. uncompressed. This is to be understood in particular to mean that the coating has not yet been processed for compression using a calender or the like. This is therefore not to be understood as a possible but comparable compression during the transport, delivery, storage or winding / unwinding of the coated electrode film.

[0081] The coated electrode film is generally provided with the reference numeral 8. The coated electrode film 8 is unwound from a supply roll 9 by means of an unwinding device (not shown in any more detail).

[0082] Optionally, the coated electrode film is divided in the longitudinal direction of the strip by means of a cutting device 10 to form so-called sub-coils (English: "slitting", "cutting"). The following embodiments are then applied in a similar manner to each sub-coil. For example, contact sections, which are called discharge pads, are also formed on the sides of the electrode film or the corresponding sub-coil by cutting, punching, etc.

[0083] The coated electrode film 8 is guided through a first electroplating tank 14 by means of a deflection roller (deflection roller) or a stretching roller (stretching roller) 12 and is transported through the electroplating tank 14 by means of a friction roller 56 as a conveying device. The electroplating tank 14 comprises a tank 16 filled with an electrolyte 18. Here, the coated electrode film 8 is transported through the electrolyte and thus immersed in the electrolyte 18 in the electroplating tank. In general, the apparatus comprises an immersion device 19 having an electroplating tank 14 and a conveying device.

[0084] The conveying direction of the coated electrode film 8 is indicated here by means of arrows which are provided with the reference symbol F.

[0085] The duration of the respective section of the coated electrode film in the electrolyte 18 of the electroplating bath 14 is between 0.5 min and 10 min, in particular between 1 min and 5 min, and suitably between 2 min and 3 min.

[0086] The electrolyte 18 is formed here by a solvent 20 or, alternatively, by a solution, ie, a mixture, of more than one solvent 20 in which a lithium salt 22 is dissolved. Figure 1 The electrolyte 18 shown in comprises, for example, 30% by volume of ethylene carbonate and 70% by volume of dimethyl carbonate, based on the total volume of all solvents 20 of the electrolyte 18. Lithium chloride (LiCl), lithium carbonate (Li2CO3) or preferably lithium nitride (Li3N) is dissolved as a lithium salt 22 in the solution.

[0087] The lithium salt 22 has a relatively high solubility in ethylene carbonate. However, ethylene carbonate is solid at room temperature, so ethylene carbonate is mixed with dimethyl carbonate. Thus, an electrolyte that is liquid even at room temperature is formed.

[0088] The electrolyte 18 penetrates into the pores of the coating 6 in the electroplating tank 14. Since the coating 6 is not compressed, the absorption of the electrolyte 18 in the pores is easier. In order to improve the absorption of the electrolyte into the coating 6, a dip roller pair 24 is arranged in the electroplating tank 14. Here, the roller 26 of the dip roller pair 24 is immersed in the electrolyte 18, in other words, the roller 26 is arranged in the electrolyte 18.

[0089] exist Figures 2 to 4 The impregnation roller pair 24 and its working principle are shown in more detail in FIG.

[0090] The rollers 26 of the impregnation roller pair 24 each have an axis 28. The axis 28 of one roller can be moved towards and away from the other roller 26 and vice versa. In this case, the axes of the two rollers 26 are each coupled to a piezoelectric actuator 30 and can be caused to vibrate. For this purpose, the piezoelectric actuator 30 is each supplied with energy by means of a voltage source 32. In this case, the rollers 26 preferably vibrate in antiphase. Thus, the two rollers 26 move towards or away from each other. The antiphase movement of the two rollers 26, which are fixedly coupled to their axes, can be particularly effective in Figure 3 There, the arrows provided with the reference symbol V indicate the anti-phase movement of the vibrations relative to one another.

[0091] The amplitude of the vibration is, for example, between 5 μm and 50 μm, in particular between 10 μm and 15 μm. The frequency of the vibration is, for example, 5 kHz.

[0092] The rollers 26, which are formed of titanium, for example, are coated with Teflon to prevent the coating from sticking. In addition, a structure is vertically erected on the surface of each roller. In other words, the structure protrudes beyond the cylindrical circumference 29 of the corresponding roller 26 in the radial direction about the axis 28. Figure 4 , a possible design of a structure as an elliptical protrusion 34 is shown by way of example. The height of the protrusion 34, i.e. the extension of the structure in the radial direction with respect to the axis 28, ranges between 5 μm and 50 μm, in particular between 10 μm and 30 μm. The extension of the corresponding protrusion 34 in a direction perpendicular thereto is, for example, between 0.1 mm and 10 mm, in particular between 1 mm and 5 mm. The corresponding recess is introduced into the coating 6 by means of the structure.

[0093] In summary, the impregnation roller pair 24 fulfills several functions: On the one hand, the electrolyte 18 is pressed into the pores of the coating 6 by means of the rollers 26. On the other hand, a reservoir is formed by means of the recesses, in which the electrolyte 18 is retained. In addition, any existing bands of adhesive on the (outer) surface of the coating 6 facing the rollers 26 are loosened or broken by means of the rollers 26 and in particular by means of the projections 34.

[0094] Optionally, with respect to the conveying direction F of the coated electrode film 8, a pair of cleaning rollers is arranged in the tank 16, suitably above the electrolyte 18. Its rollers or rolls 36 are made of an elastic rubber-like material. They are used to remove excess electrolyte 18 from the surface of the coated electrode film 8. The removed electrolyte 18 falls back into the electrolyte bath 14.

[0095] For this purpose, the roller 36 is vibrated, for example, in a similar manner to the roller 26 of the impregnation roller pair. Here, the amplitude and / or frequency can be selected to be smaller than the two rollers 26 of the impregnation roller pair 24.

[0096] exist Figure 52 shows the second section 2b of the device 2. This includes a first calendering roller pair 38 and an optional second calendering roller pair 40. The electrode film 8 impregnated and coated with the electrolyte 18 is supplied to the first calendering roller pair 38 and optionally subsequently to the second calendering roller pair 40. The second calendering roller pair 40 is preferably provided to compensate for the elastic rebound, also known as rebound (English "Springback"), after calendering by the first calendering roller pair 38. With the aid of the calendering roller pair 38 or with the aid of the calendering roller pairs 38 and 40, the coating 6 is compacted, that is, compressed. Here, the coating 6 is compacted, for example, to a degree between 20% and 30%, in particular between 23% and 27%.

[0097] In other words, the coating 6 is squeezed and its layer thickness is reduced by a corresponding amount. For this purpose, the impregnated and coated electrode film 8 is loaded with a linear load of between 1000 N / mm and 2500 N / mm, in particular between 1300 N / mm and 2000 N / mm, for example, by means of the first calendering roller pair 38. The device 2 also includes a device 41 for detecting the thickness of the coated electrode film 8. Here, the device includes an ultrasonic sensor, a light sensor or a laser sensor for this purpose. Preferably, the gap width and / or the linear load of the first calendering roller pair 38 and / or the linear load based on the second calendering roller pair 40 can be adjusted or regulated according to the thickness detected by the device 41.

[0098] The device 2 further comprises a heating device 42, which is connected to the calender roller pair 38 and, if necessary, to the calender roller pair 38. A second calender roller pair 40 is connected downstream with respect to the provided conveying direction F of the coated electrode film 8. The heating device 42 is hereby suitably designed as a dry dryer. The heating device 42 is provided and configured to evaporate a portion of the solvent 20 or - as long as the electrolyte 18 contained in the coating 6, i.e. the electrolyte 18 of the electroplating bath 14, has a solution of at least two solvents 20 - to evaporate at least a portion of the solvents 20 of the electrolyte 18. If the electrolyte 18 is, as in Figure 1 As shown by way of example in FIG. 1 , with a solution of ethylene carbonate and dimethyl carbonate, the coated electrode film 8 and the electrolyte 18 contained in the coating 6 are heated to about 100° C. This temperature is greater than the boiling point of dimethyl carbonate and significantly less than the boiling point of ethylene carbonate. As a result, the dimethyl carbonate essentially evaporates.

[0099] Due to evaporation, the pores increase and at least a portion of the closed pores are opened during calendering. Thus, the porosity is advantageously increased by evaporation, in particular in the region of the outer surface of the coating 6 in contact with the calendering rolls.

[0100] As in Figure 5As shown in , the heating device 42 is arranged in a (furnace) housing 44, through which the coated electrode film 8 is conveyed. The electrolyte 18 thus evaporates in the housing 44, so that the electrolyte can be collected, for example, by means of a suction device 46 for reuse.

[0101] According to an alternative not shown in further detail, the heating device 42 has one or more heating rollers, wherein the impregnated and coated electrode film 8 is in contact with these heating rollers, in particular is guided over these heating rollers. In this case, the heating rollers are heated, so that the solvent 20 is heated and evaporated by means of the heating rollers. The heating rollers are expediently introduced into a (oven) housing, which is provided in a similar manner with a suction device 46 for the evaporated solvent 20.

[0102] With reference to the conveying direction F, a cooling drum or roller 48 is connected downstream between the heating device 42 and the device 41 for detecting the thickness, in order to cool the coated electrode film 8 to room temperature, for example.

[0103] In summary, after heating, a portion of the solvent 20 or one of the solvents 20 of the electrolyte 18 and the lithium salt 22 remain in the coating. Figure 1 In the embodiment of the electrolyte 18, the dimethyl carbonate evaporates and the ethylene carbonate remains in the coating. This is fixed after cooling by means of a cooled roller or rollers 48.

[0104] Furthermore, the device 2 comprises an inspection unit 50 which is designed, for example, as a camera and is used to inspect the applied electrode film 8 for defects.

[0105] The device 2 comprises a flattening roller 52, in particular a wide roller, which has a structure for generating a transverse tensile stress, i.e. a tensile stress, which is perpendicular to the conveying direction F and extends in the plane unfolded by the electrode film onto the coated electrode film 8. The transverse tensile stress advantageously reduces or even removes the corrugations of the electrode film 8 and / or the wrinkles in the electrode film 8, which may be present in particular during the first calendering. As a result, the coated electrode film 8 is flattened.

[0106] The device 2 comprises a winding device (not shown in further detail) for winding onto a supply roll 54 .

[0107] Figure 6 The third section 2c of the device 2 is shown. It comprises an unwinding device (not shown in detail) by means of which the coated electrode film 8, whose coating contains the lithium salt 22 and the solvent 20 remaining after heating, is unwound from a storage roll 54. The coated electrode film 8 is stretched by means of a friction roller 56 through a stretching tool 58.

[0108] A further (second) heating device 42 is arranged upstream of the stretching tool 58, ie between the supply roller 54 and the stretching tool 58, with reference to the conveying direction F, and is provided and configured to liquefy the electrolyte 18 (here ethylene carbonate) contained in the coating. For this purpose, the coated electrode film 8 is heated to 40° C. to 45° C., for example.

[0109] The stretching tool 58 has two jaws 60 which are opposite to each other, wherein the opposite surfaces of the jaws are inclined relative to the conveying direction F, forming a gap which tapers continuously in the conveying direction F. In this case, the gap has an extension which is initially greater than the thickness of the electrode film, i.e., greater than its extension perpendicular to the surface along which the electrode film is extended. The size of the gap decreases continuously, wherein the extension of the gap with reference to the conveying direction F is smaller at the end than the thickness of the coated electrode film 8 before processing by the stretching tool 58. As a result, the coated electrode film 8 rests against the two jaws during its conveyance through the gap.

[0110] The jaws 60 of the stretching tool 58 are connected to a DC voltage source 62. In this case, one of the jaws 60 is electrically connected to the positive pole of the DC voltage source 62, and the other of the two jaws is electrically connected to the negative pole of the DC voltage source 62. The voltage is suitably between 0.1V and 2.0V, in particular between 0.2V and 1.5V, preferably between 0.4 and 0.9V.

[0111] The inclination of the mutually facing surfaces of the jaws 60 is between 0.1° and 2° and / or the length of the jaws 60 in the conveying direction F is between 1 m and 5 m. A slight reduction in the layer thickness of the coating 6 is thus achieved by means of the stretching tool 58. However, the purpose of the stretching tool is in particular to achieve a contact surface that is as large as possible and / or uniform with the jaws 60 connected to the DC voltage source 62. For this purpose, the jaws have a section 64 arranged at the end in the conveying direction F, wherein the mutually facing surfaces of the jaws are arranged parallel to each other.

[0112] In this way, the coated electrode film 8 and the electrolyte accompanying it are subjected to voltage for a relatively long period of time when conveyed through the stretching tool 58. The lithium salt 22 is selected (especially in the coating 6) so that its anions form a gas G. In other words, the gas G is formed from the anions of the lithium salt 22 due to the voltage. This gas G escapes from the coating 6. This is also referred to here and below as the electrolysis of the lithium salt.

[0113] If lithium chloride (LiCl), lithium carbonate (Li2CO3) or lithium nitride (Li3N) is used as the lithium salt, for example, chlorine, carbon dioxide or nitrogen forms as gas G. This escapes from the coating 6 via the channel 65 introduced into the jaws 60 and can be sucked off.

[0114] In summary, the anions of the lithium salt 22 are removed from the coating 6. Furthermore, the lithium ions—if this has not already occurred—are inserted into the active material of the coating 6, wherein the solvent 20, here ethylene carbonate, remains further in the coating 6. The gas molecules formed from the anions of the electrolyte 18 are relatively large, so that the porosity is further increased due to this gas formation.

[0115] In a manner not shown in further detail, the jaws 60 are temperature-controlled so that overheating due to ohmic losses is avoided.

[0116] When the gas G escapes during the evaporation of the solvent and during processing with the stretching tool, unevenness is generated on the surface of the coating 6. The device 2 comprises a second stretching tool 66, for example made of titanium. The second stretching tool 66 is connected downstream of the first stretching tool 58 with reference to the conveying direction F. This helps to compensate for these unevennesses. Figure 2 For better visibility, the reduction in layer thickness by means of the stretching tool 58 and the second stretching tool 66 is shown in an exaggerated manner. The two stretching tools 58 and 66 are not used to compact the coating 6, but rather to provide the largest possible contact surface or to compensate for unevenness.

[0117] Optionally, the third section 2c of the device 2 comprises a further device 41 for detecting the thickness of the coated electrode film. In a similar manner to the second section 2b of the device, the third section 2c comprises a leveling roller 52 for generating transverse tensile stresses on the coated electrode film 8 and a second supply roller 54 onto which the coated electrode film 8 is wound.

[0118] Individual electrodes for battery cells are cut out from the coated electrode film 8 by means of a cutting device (not shown in detail). As an alternative to this, the coated electrode film 8 is previously cut according to Figure 7 Processing is carried out with the aid of the fourth section 2d.

[0119] exist Figure 7 2 shows an optional fourth section 2d of the device 2. The housing comprises an outer housing 68, which is made of steel, for example. The wall thickness of the housing is, for example, 5 mm to 10 mm, so that adequate safety measures are taken even in the event of an explosion. The outer housing 68 has an inlet 69, through which nitrogen can be pumped into the outer housing 68 as an inert gas. Preferably, the nitrogen is fed into the housing 68 at a pressure between 1.0 bar and 1.5 bar, in particular at 1.15 bar.

[0120] A second electroplating tank 70 is arranged in the housing 69. For example, it includes a through hole for nitrogen, which is not further shown, preferably on the cover side. The electrolyte 18' is filled in the tank 16 of the second electroplating tank 70, which is composed of stainless steel, for example. For example, the electrolyte 18' includes ethylene carbonate and dimethyl carbonate as solvents 20' and lithium salts 22'. For example, lithium hexafluorophosphate (LiPF6) is used as lithium salt 22'. Preferably, the electrolyte 18' of the second electroplating tank 70 additionally includes additives, such as vinylene carbonate (VC), which promote the formation of SEI. Advantageously, such additives can then be saved in the electrolyte poured into the battery cell, or only a smaller amount of these additives is required.

[0121] The coated electrode strip 18 processed by the stretching tool 58 is guided through the housing 68 of the second electroplating tank 70 and the opening of the tank 16 into the electroplating tank 70 and is fed through the electrolyte 18 ′. The opening has a silicone seal 72 .

[0122] In the second electroplating tank 70, a lithium-free electrode 74 is arranged in the electrolyte 18'. Figure 7 As shown only schematically in FIG. 1 , the electrode 74 is connected to the negative pole of a DC voltage source 76. The positive pole of the DC voltage source 76 is in electrical contact with the coated electrode film 8, for example by means of a grinding contact or rolling contact (not shown in detail), so that a voltage exists between the electrode film and the electrode. The voltage is between 0.5V and 5.0V.

[0123] Based on this, SEI is formed on the coated electrode film 8. In this case, lithium ions present in the coating and / or lithium ions of the electrolyte 18' are advantageously used to form SEI. If the coated electrode film processed in this way enters a battery cell as an anode, then advantageously, a formation process for forming SEI is not necessary or only lasts relatively short.

[0124] exist Figure 8 In summary, a method flow for producing an electrode, in particular an anode, is shown with the aid of a flow chart. In particular, the method uses a method according to Figures 1 to 6 and, if necessary, according to Figure 7 Device 2.

[0125] In a first step I, the coated electrode foil 8 without compacted coating is introduced into the electroplating bath 14 and conveyed through it. In this case, the electrolyte 18 of the electroplating bath is taken up into the coating by means of a dip roller pair 24, for example.

[0126] In a subsequent second step II, the coated electrode film 8 is calendered, in particular by means of a calendering roller pair 38. The coating 6 is thus compacted.

[0127] The calendered coated electrode film 18 is then heated in a third step III so that the solvent 20 of the electrolyte 18 partially evaporates, or if the electrolyte 18 has a solution of more than one solvent 20, at least one of the solvents 20 is evaporated partially, in particular by means of a heating device 42, so that the porosity of the coating 6 is increased.

[0128] In the subsequent fourth step IV, the coated electrode film 18 is processed by means of a stretching tool 58, wherein the coated electrode film 18 is subjected to a voltage by means of the stretching tool 58. Thus, gas is formed by means of the anions of the lithium salt 22 of the electrolyte 18, in particular. In summary, the anions of the lithium salt 22 are thus removed from the coating, wherein the porosity is further increased. For example, the surface of the coating is then leveled by means of a second stretching tool 66.

[0129] In an optional fifth step V, which follows the fourth step in time, the coated electrode film is conveyed through a second electroplating tank 70, wherein an electrode 74 is arranged in the second electroplating tank and is connected to the negative pole of a DC voltage source 76. The coated electrode film is connected to the positive pole of the DC voltage source 76.

[0130] Due to the electrical potential between the electrode 74 and the coated electrode film 8 fed through the second electroplating bath 70 , an SEI forms on the electrode film, wherein the SEI is formed in particular by means of lithium ions contained in the coating 6 .

[0131] The coated electrode film 8 is trimmed and / or cut after the fourth step, or if the fifth step is performed, after the fifth step, so that the electrode or electrode sheet has a shape suitable for the battery cell (step VI).

[0132] The electrode produced in this way is in particular an anode. The electrode is provided for a lithium-ion battery, in particular for a battery cell of a lithium-ion battery. The lithium-ion battery is, for example, a traction battery of an electrically driven motor vehicle.

[0133] The present invention is not limited to the above-mentioned embodiments. More specifically, those skilled in the art may also derive other variants of the present invention therefrom without departing from the technical solution of the present invention. In addition, in particular, all individual features described in conjunction with the embodiments may also be combined with each other in other ways without departing from the technical solution of the present invention.

[0134] Reference numerals list

[0135] 2 Equipment

[0136] 2a The first section of the device

[0137] 2b Second segment of the device

[0138] 2c The third section of the device

[0139] 2d Device's fourth section

[0140] 4 Substrate / Film

[0141] 6 Coating

[0142] 8 Coated electrode membrane

[0143] 9 Reserve rollers

[0144] 10 Cutting device

[0145] 12 Guide roller or stretching roller

[0146] 14 Electrolyte bath

[0147] 16 cans

[0148] 18, 18' Electrolyte

[0149] 19 Impregnation device

[0150] 20, 20' Solvent

[0151] 22,22' Lithium salt

[0152] 24 (Impregnated) roller pairs

[0153] 26 Rollers of the impregnation roller pair

[0154] 28 Roller shaft

[0155] 29 Side

[0156] 30 Piezoelectric Actuator

[0157] 32 Voltage Source

[0158] 34 protrusion

[0159] 36 Roller

[0160] 38 calender roller pairs

[0161] 40 Second calender roller pair

[0162] 41. Device for detecting the thickness of a coated electrode film

[0163] 42 Heating device

[0164] 44 Shell

[0165] 46 Suction device

[0166] 48 Cooling drum or roller

[0167] 50 Inspection Unit

[0168] 52 Leveling roller

[0169] 54 Reserve Roller

[0170] 56 Friction roller / conveying unit

[0171] 58 Stretch Tool

[0172] 60 Jaws of the stretching tool

[0173] 62 Voltage Source

[0174] 64 jaws segment

[0175] 65 channels

[0176] 66 Second Stretch Tool

[0177] 68 outer shell

[0178] 60 Entrance

[0179] 70 Another / Second Electrolytic Cell

[0180] 72 Silicone seal

[0181] 74 Electrodes

[0182] 76 DC voltage source

[0183] F Conveying direction

[0184] G Gas

[0185] V Vibration

[0186] I Introducing the coated electrode membrane into the electrolyte bath

[0187] II Calendered coated electrode membrane

[0188] III Heating the coated electrode membrane

[0189] IV Processing of coated electrode membrane using stretching tool

[0190] V SEI formation

[0191] VI cutting of coated electrode membrane.

Claims

1. A method for producing an electrode for a lithium-ion battery cell, - wherein the coated electrode film (8) is introduced into a plating tank (14), wherein The electrolyte (18) of the electroplating bath (14) comprises a lithium salt (22) and at least one solvent (20), wherein the electrode film (8) impregnated with the electrolyte (18) and coated is subsequently calendered, and - wherein the coated electrode membrane (8) is subsequently heated so that the solvent (20) contained in the coating of the electrode membrane (8) partially evaporates, or so that one of the solvents (20) at least partially evaporates, wherein, after the partial evaporation of the solvent (20) or after the at least partial evaporation of one of the solvents (20) of the electrolyte (18), a voltage is applied to the coated electrode membrane (8), wherein a gas (G) is formed from the anions of the lithium salt (22) by means of the voltage.

2. The method according to claim 1, characterized in that: The electrode is an anode.

3. The method according to claim 1, characterized in that The electrolyte (18) comprises at least two solvents (20), wherein one of the solvents (20) is ethylene carbonate and / or wherein the proportion of ethylene carbonate is 15 to 45 volume percent based on the total volume of all solvents (20) of the electrolyte (18).

4. The method according to claim 3, characterized in that: The proportion of ethylene carbonate is 20 to 40 volume percent based on the total volume of all solvents (20) of the electrolyte (18).

5. The method according to claim 3, characterized in that: The proportion of ethylene carbonate is 25 to 35 volume percent based on the total volume of all solvents (20) of the electrolyte (18).

6. The method according to claim 1, characterized in that The coated electrode film (8) is processed using a stretching tool (58), wherein the stretching tool (58) has a gap that tapers gradually along a conveying direction (F) of the coated electrode film (8), and / or wherein a voltage is applied to the coated electrode film (8) by means of the stretching tool (58).

7. The method according to claim 1, characterized in that In order to form a solid electrolyte interphase, after heating, the coated electrode film (8) is placed in a second electroplating tank (70), wherein an electrode (74) is arranged in the second electroplating tank (70), and wherein the coated electrode film (8) is connected to the positive pole of a DC voltage source (76), and the electrode (74) is connected to the negative pole of the DC voltage source (76).

8. The method according to claim 7, characterized in that In order to form a solid electrolyte interphase, after applying voltage, the coated electrode film (8) is placed in a second electroplating tank (70), wherein an electrode (74) is arranged in the second electroplating tank (70), and wherein the coated electrode film (8) is connected to the positive pole of a DC voltage source (76), and the electrode (74) is connected to the negative pole of the DC voltage source (76).

9. The method according to claim 7 or 8, characterized in that: The electrode (74) arranged in the second electroplating tank (70) is a lithium-free electrode.

10. The method according to claim 1, characterized in that A dip roller pair (24) is arranged in the electroplating tank (14), and the rollers (26) of the dip roller pair vibrate to promote absorption of electrolyte into the coating of the electrode membrane (8).

11. The method according to claim 10, characterized in that In the electroplating bath (14), recesses are introduced into the coating of the electrode film (8).

12. The method according to claim 11, characterized in that In the electroplating bath (14), recesses are introduced into the coating of the electrode film (8) by means of the dip roller pair (24).

13. A device (2) for producing an electrode for a lithium-ion battery cell according to a method according to any one of claims 1 to 12, comprising: - an impregnation device (19) comprising an electroplating tank (14) having an electrolyte (18), a lithium salt (22) and at least one solvent (20), and a conveying unit (56) for conveying the coated electrode film (8) through the electroplating tank (14), at least one calendering roller pair (38) for calendering the impregnated and coated electrode membrane (8), a heating device (42) arranged and configured to evaporate a portion of the solvent (20) or at least a portion of one of the solvents (20) of the electrolyte (18), the solvent (20) being contained in the calendered coating of the electrode film (8), and A voltage source for applying a voltage to the coated electrode membrane (8) after a certain period of time of partial evaporation of the solvent (20) or after a certain period of time of at least partial evaporation of one of the solvents (20) of the electrolyte (18).

14. An electrode produced according to the method of any one of claims 1 to 12 and / or produced by means of the device (2) according to claim 13. 15 . A lithium ion battery comprising the electrode according to claim 14 .

16. The lithium ion battery according to claim 15, characterized in that: The lithium-ion battery is suitable for use as a traction battery for an electrically driven motor vehicle.

Images