Method for manufacturing an electrode

Abstract

A method for producing an electrode, wherein an electrode slurry (13) comprising at least one electrode active material (16) is provided, wherein the electrode slurry (13) is applied as an electrode active material layer (8) to a current collector (7), wherein the electrode active material layer (8) is dried and provided with pores (12) such that an electrode (6) with a porous structure is obtained, wherein the electrode slurry (13) is enriched with gas (14) such that the gas (14) escapes from the electrode active material layer (8) during drying, forming the pores (12), wherein at least one further electrode active material layer is applied to the current collector (7), characterized in that the porosity of the electrode active material layer (8) differs from the porosity of the further electrode active material layer.

Description

[0001] The invention relates to a method for producing an electrode, wherein an electrode slurry comprising at least one electrode active material is provided, wherein the electrode slurry is applied as an electrode active material layer to a current collector, and wherein the electrode active material layer is dried and provided with pores in such a way that an electrode with a porous structure is obtained.

[0002] Furthermore, the invention relates to an electrode.

[0003] Furthermore, the invention relates to a lithium-ion cell.

[0004] Lithium-ion cells are considered a key technology, particularly in electromobility. Current developments aim to optimize lithium-ion cells with regard to aspects such as manufacturing costs, weight, energy density, lifespan, and charging speed.

[0005] A lithium-ion cell has a positive electrode, or cathode, and a negative electrode, or anode, as its electrodes. Each electrode typically has a current collector on which a layer of electrode active material, containing at least one electrode active material, is applied. The electrodes are often manufactured using wet coating processes, so-called slurry processes, low-solvent processes, or solvent-free processes. In a slurry process, an electrode slurry containing at least the electrode active material is first prepared. This electrode slurry is then applied to the current collector as an electrode active material layer to produce the electrode. The electrode active material layer applied to the current collector is then dried.To achieve high charging and discharging speeds in a lithium-ion cell, it is crucial that lithium ions can be rapidly incorporated into and extracted from the electrode active material across the entire thickness of the electrode active material layer. This can be achieved, for example, by using electrode active material layers with a thin layer thickness. However, to achieve high gravimetric and volumetric energy density, electrode active material layers with a greater thickness are advantageous because they improve the ratio of electrode active material to non-electrode active material. To overcome this apparent contradiction, it is known in the art to provide the electrode active material layer with pores, so that the electrode or the electrode active material layer then has a porous structure.The pores increase the contact area between the electrode active material layer and the electrolyte of the lithium-ion cell. A method of the type mentioned above is known, for example, from German patent application US 2021 / 0151764 A1. Various procedures are described for forming the pores in the electrode active material layer. For example, the pores can be formed using a laser or fine needles. A disadvantage of this method is that electrode active material is removed during pore formation, leading to a reduction in the electrode's energy density. German patent application DE 10 2018 209 955 A1 describes a method for manufacturing an electrode in which graphite and a blowing agent are mixed at a temperature and ambient pressure where the blowing agent is in a solid or liquid state.The resulting mixture is then rolled into a film. Finally, the ambient pressure is reduced and / or the film is heated, causing the blowing agent to transition into a gaseous state and escape from the film. This produces a porous graphite film.

[0006] The invention is based on the objective of improving a slurry process of the type mentioned above in such a way that an electrode with a high energy density is obtained. Furthermore, the inventive method allows for particularly precise control of the pore structure of the electrode active material layer.

[0007] The problem underlying the invention is solved by a method with the features of claim 1. This method has the advantage that no electrode active material is removed during pore formation. Accordingly, the gravimetric energy density of the electrode is not reduced by the formation of the pores. According to the invention, the electrode slurry is enriched with gas in such a way that the gas escapes from the electrode active material layer during drying and pore formation. Thus, a process step is carried out before the electrode slurry is applied to the current collector, in which the gas content of the electrode slurry is specifically increased. Because the electrode slurry is enriched with the gas and therefore contains the gas, the gas is also applied to the current collector as the electrode active material layer along with the other components of the electrode slurry.During the drying of the electrode active material layer, the gas escapes, leading to the formation of pores within the layer. The invention is based on the understanding that electrode slurries are fundamentally capable of stably absorbing a sufficiently large quantity of gas, such that the absorbed gas, during drying, can then create an electrode active material layer with sufficient porosity. According to the invention, the electrode slurry is enriched with gas. The gas is supplied to the electrode slurry in its natural state, i.e., at a temperature and ambient pressure at which the gas exists as such. For example, the escape of the gas from the electrode active material layer forms pores in the form of directed channels within the layer.Alternatively, the electrode active material layer is provided with spherically shaped pores, for example, by the escaping gas. The formation of pores by the escaping gas also has the advantage of achieving residue-free removal of the pore-forming agent, i.e., the gas. A current collector is a base body or substrate of the electrode. Preferably, a negative electrode is produced using this method. The electrode active material and the electrode active material layer are then a negative electrode active material or a negative electrode active material layer. Preferably, a negative electrode active material from the group consisting of graphite, silicon, silicon dioxide, lithium titanate, and mixtures thereof is used. When producing a negative electrode, a copper foil is preferably used as the current collector.According to a further embodiment, the method produces a positive electrode. The electrode active material and the electrode active material layer are then a positive electrode active material and a positive electrode active material layer, respectively. When producing a positive electrode, an aluminum foil is preferably used as the current collector. According to the invention, the electrode slurry is enriched with gas. The electrode slurry can optionally be enriched with only one gas or with several different gases or a gas mixture. Preferably, the electrode slurry comprises, in addition to the electrode active material, further materials, such as a binder and / or conductive carbon black. Preferably, the electrode slurry comprises at least one solvent. Preferably, the electrode slurry comprises only one solvent.Alternatively, the electrode slurry comprises a solvent mixture containing several solvents. Preferably, N-methyl-2-pyrrolidone (NMP), water, or a mixture of these solvents is used. Preferably, the electrode is an electrode for a lithium-ion cell. However, the process according to the invention can also be used to produce electrodes for other types of galvanic cells. Preferably, the electrode active material layer is subjected to calendering after drying.

[0008] According to a preferred embodiment, the electrode slurry is enriched with gas such that the gas is present in the slurry in the form of gas bubbles. This has the advantage that the pore size can be precisely controlled. If the gas is present in the electrode slurry in the form of gas bubbles, the size of the resulting pores corresponds at least substantially to the size of the gas bubbles present in the electrode slurry. Alternatively or additionally to the gas bubbles, the gas is dissolved in the electrode slurry or adsorbed onto a material suspended in the electrode slurry, in particular onto the electrode active material and / or the conductive carbon black. A layer of electrode active material with a porous structure can also be obtained during drying by means of dissolved and / or adsorbed gas.

[0009] According to a preferred embodiment, the electrode slurry is stirred in the presence of the gas to enrich it. Stirring the electrode slurry in the presence of the gas allows for effective enrichment. Furthermore, the extent of gas enrichment and the size of the absorbed gas bubbles can be precisely controlled by selecting the appropriate stirring speed.

[0010] Preferably, the gas is introduced into the electrode slurry. This involves a gas supply line leading into the electrode slurry, through which the gas is fed into the slurry. Introducing the gas into the electrode slurry results in a particularly effective enrichment of the slurry with the gas. Preferably, the temperature of the electrode slurry at the time of gas introduction is between -10 °C and 40 °C, and particularly preferably between 0 °C and 20 °C. At such temperatures, a particularly effective absorption of gas into the electrode slurry is achieved.

[0011] Preferably, air, nitrogen, argon, oxygen, carbon dioxide, or forming gas is used. The use of air, nitrogen, and oxygen offers the advantage of low cost. Furthermore, their inertness prevents chemical alteration of the other materials in the electrode slurry. Argon's high density allows for a particularly high gas concentration in the electrode slurry. If forming gas is used, the hydrogen content is preferably less than 5%.

[0012] Preferably, the viscosity of the electrode slurry is greater than 1800 mPa. * s at a shear rate of 10° * s -1 , greater than 1200 mPa * s at a shear rate of 101 * s -1 and / or greater than 600 mPa * s at a shear rate of 10 2 * s -1 . At such a viscosity, the gas or gas bubbles are reliably retained in the electrode slurry, so that the gas does not escape from the electrode slurry, or at most only to a small extent, before the electrode slurry is applied to the current collector.

[0013] According to a preferred embodiment, the mass fraction of solvent in the electrode slurry, based on the total mass of the electrode slurry, is at most 50%. This solvent fraction achieves an advantageous compromise between the viscosity of the electrode slurry and its processability in a slurry process. Preferably, the mass fraction of solvent is at most 35%, more preferably at most 25%. The mass fraction of solids in the electrode slurry, based on the total mass of the electrode slurry, is preferably 50% to 95%, more preferably 65% ​​to 95%, and more preferably 75% to 95%. The mass fraction of gas in the electrode slurry, based on the total mass of the electrode slurry, is preferably at least 1%, more preferably at least 2%, and more preferably at least 3%. This allows for an advantageous porosity to be achieved.

[0014] According to a preferred embodiment, the electrode active material layer is dried by heating it. Drying the electrode active material layer by heating is technically simple. For example, the current collector with the electrode active material layer applied to it is placed in an oven and heated there.

[0015] According to a preferred embodiment, the electrode active material layer is dried by reducing the ambient pressure.

[0016] This method has the advantage that the temperature stress on the electrode active material layer during drying is low. Preferably, the electrode active material layer is dried by simultaneously heating the electrode active material layer and reducing the ambient pressure.

[0017] According to a preferred embodiment, the electrode active material layer is subjected to a thermal shock treatment to increase its porosity. This thermal shock treatment can be performed at various times. For example, it can be carried out during the drying of the electrode active material layer. Alternatively, it can be performed only after calendering. Preferably, the thermal shock treatment is performed after the formation of the pores, i.e., after the gas has escaped from the electrode active material layer. The pores of the electrode active material layer can, in principle, be enlarged by a rapid change in the volume of the electrode active material layer, such as occurs during a thermal shock treatment.For example, the thermal shock treatment causes crack-like protrusions to form on the existing pores. Preferably, the electrode active material layer is moved successively through temperature zones with different temperatures for the thermal shock treatment. For example, the electrode active material layer is first moved through a temperature zone with a temperature between 50 °C and 300 °C, particularly between 100 °C and 120 °C, and then through a temperature zone with a temperature between -30 °C and 50 °C, particularly between -10 °C and 10 °C. Several of these temperature zones can be connected in series such that the electrode active material layer is heated and cooled multiple times during the thermal shock treatment. Preferably, the temperature difference between two immediately successive temperature zones is at least 30 °C, and particularly preferably at least 50 °C.

[0018] According to a preferred embodiment, at least one further electrode active material layer is applied to the current collector, and the porosity of the electrode active material layer differs from that of the further electrode active material layer. This approach is referred to as multilayer coating. By providing at least two electrode active material layers that differ from each other with respect to their porosity, the distribution of the electrolyte in the electrode active material layers can be adapted to the local current density requirement of the electrode. Preferably, the electrode active material layer is applied directly to the current collector, and the further electrode active material layer is applied directly to the electrode active material layer, i.e., indirectly to the current collector.Alternatively, the additional electrode active material layer is applied directly to the current collector, and the electrode active material layer is applied directly to the additional electrode active material layer, i.e., indirectly to the current collector. Preferably, the additional electrode active material layer is produced by a process that corresponds at least substantially to the process for producing the electrode active material layer. Thus, an additional electrode slurry is provided, which contains at least one electrode active material. The additional electrode slurry is then enriched with gas in such a way that the gas escapes from the additional electrode active material layer during drying, forming pores. Preferably, the different porosities are obtained by ensuring that the gas content of the electrode slurry differs from the gas content of the additional electrode slurry.

[0019] The electrode according to the invention is characterized by the features of claim 12 in that the electrode is manufactured using the method according to the invention. The advantages already mentioned also result from this. Further preferred features and combinations of features result from the foregoing and from the claims. Preferably, the pores of the electrode active material layer are channel-shaped. Channel-shaped pores allow the electrolyte to penetrate as deeply as possible into the electrode active material layer. Preferably, the channel-shaped pores extend at least substantially through the electrode active material layer in the direction of its thickness.

[0020] The lithium-ion cell according to the invention is characterized by the features of claim 13, namely the electrode according to the invention. The advantages already mentioned also result from this. Further preferred features and combinations of features result from the foregoing and from the claims.

[0021] The invention will be explained in more detail below with reference to the drawings. To this end, show Fig. 1. A lithium-ion cell in a schematic representation and Fig. 2 a method for manufacturing an electrode of the lithium-ion cell.

[0022] Fig. Figure 1 shows a simplified representation of a lithium-ion cell 1. The lithium-ion cell 1 has a housing 2. In this case, the housing 2 is pouch-shaped, or rather, designed as a flexible pouch 2. The lithium-ion cell 1 is therefore designed as a pouch-bag cell 1. The lithium-ion cell 1 has a positive electrode 3. The positive electrode 3 has a current collector 4, which in this case is an aluminum foil 4. A positive electrode active material layer 5 is formed on the current collector 4. The lithium-ion cell 1 also has a negative electrode 6. The negative electrode 6 has a current collector 7, which in this case is a copper foil 7. A negative electrode active material layer 8 is formed on the current collector 7. The negative electrode active material layer 8 has a negative electrode active material such as graphite or a graphite-silicon mixture.Preferably, the negative electrode active material layer 8 comprises, in addition to the negative electrode active material, further materials such as conductive carbon black and / or a binder. The current collector 4 and the current collector 7 protrude from the housing 2 for electrical contact with the positive electrode 3 and the negative electrode 6, respectively. The lithium-ion cell 1 also has a separator 9, which acts between the positive electrode 3 and the negative electrode 6. The separator 9 is arranged in the housing 2 such that it spatially and electrically separates the positive electrode 3 and the negative electrode 6 from each other. The lithium-ion cell 1 also has a liquid electrolyte 10, which is filled into the housing 2. In this case, the electrolyte 10 comprises lithium ions 11, which are in . Fig. 1 are shown greatly enlarged.

[0023] As from Fig. As can be seen in Figure 1, the negative electrode active material layer 8 has a porous structure, such that the negative electrode 6 is formed as a porous electrode 6. Thus, a multitude of pores 12 are present in the negative electrode active material layer 8. The pores 12 are in Fig. Figure 1 is shown greatly enlarged. The pores 12 increase the contact area between the electrode active material layer 8 and the electrolyte 10. This accelerates the incorporation of lithium ions 11 into the electrode active material layer 8 as well as the release of lithium ions 11 from the electrode active material layer 8. According to the Fig. In the embodiment shown in Figure 1, the pores 12 are designed as directed channels or are channel-shaped and extend through the electrode active material layer 8 in the layer thickness direction. However, the pores 12 can also have a different shape. For example, according to another embodiment, the pores 12 are spherical.

[0024] The following refers to Fig. 2 an advantageous method for producing the negative electrode 6 is described in more detail. Fig. Figure 2 illustrates the procedure using a flowchart.

[0025] In a first step S1, the current collector 7 is provided for the negative electrode 6.

[0026] In a second step S2, an electrode slurry 13 is provided, which comprises at least one negative electrode active material 16. For example, the electrode slurry 13 comprises graphite as the negative electrode active material 16. In addition to the negative electrode active material 16, the electrode slurry 13 also comprises at least one solvent. For example, the electrode slurry 13 comprises only one solvent or a solvent mixture of different solvents. The mass fraction of solvent in the electrode slurry 13 is preferably between 5% and 50%, based on the total mass of the electrode slurry 13. The negative electrode active material 16 is suspended in the solvent. Preferably, in addition to the at least one negative electrode active material 16, the electrode slurry 13 also comprises at least one further material, such as conductive carbon black and / or a binder.

[0027] In a third step S3, the electrode slurry 13 is enriched with gas 14. A supply line 18 is provided, leading into the electrode slurry 13, through which the gas 14 is introduced. During the introduction of the gas 14 into the electrode slurry 13, the slurry 13 is stirred by a stirring device 17. Stirring the electrode slurry 13 during the introduction of the gas 14 ensures effective enrichment of the electrode slurry 13 with the gas 14. In this case, stirring the electrode slurry 13 during the introduction of the gas 14 results in an electrode slurry 13 enriched with gas bubbles 15. However, the gas 14 can also dissolve in the electrode slurry 13 or adsorb onto materials suspended in the electrode slurry 13. Preferably, nitrogen, air, oxygen, carbon dioxide, argon or forming gas is used.

[0028] In a fourth step S4, the electrode slurry 13 enriched with gas 14 is applied to the current collector 7 as a negative electrode active material layer 8. Various methods are possible for applying the electrode slurry 13 to the current collector 7. For example, the electrode slurry 13 can be applied to the current collector 7 using a slot nozzle.

[0029] In a fifth step S5, the electrode active material layer 8 is dried. This involves removing the solvent or solvent mixture of the electrode slurry 13 from the electrode active material layer 8. For this purpose, the current collector 7 with the electrode active material layer 8 applied to it is placed in a heating device, and the electrode active material layer 8 is heated by the heating device. In addition to removing the solvent, heating the electrode active material layer 8 also causes the gas 14 or gas bubbles 15 to escape from the electrode active material layer 8. The volume previously occupied by the gas bubbles 15, as well as the path the gas bubbles 15 travel when escaping the electrode active material layer 8, then forms or defines the pores 12 of the electrode active material layer 8.

[0030] In an optional sixth step S6, the electrode active material layer 8 is calendered. Calendering compresses the electrode active material layer 8, thereby reducing its porosity, at least slightly.

[0031] In an optional seventh step S7, the electrode active material layer 8 is subjected to a temperature shock treatment. Preferably, the electrode active material layer 8 is moved successively through temperature zones with different temperatures for the temperature shock treatment. For example, the electrode active material layer 8 is first moved through a temperature zone with a temperature between 100 °C and 120 °C and then through a temperature zone with a temperature between -10 °C and 10 °C. This results in a rapid change in the volume of the electrode active material layer 8, which leads to mechanical stresses within the electrode active material layer 8. These stresses, in turn, cause crack-like extensions to form in the electrode active material layer 8, starting from the pores 12. The crack-like extensions are in Fig.1 not visible, but increase the porosity of the electrode active material layer 8. The temperature shock treatment thus increases the porosity of the electrode active material layer 8. In this case, the temperature shock treatment is performed as the seventh step S7 following calendering. However, the temperature shock treatment can also be performed during drying, i.e., in step S5, or between drying and calendering, i.e., in a step S5a not shown. In particular, several temperature shock treatments are performed, for example, a first temperature shock treatment during drying and a second temperature shock treatment after calendering.

[0032] According to a further embodiment, the electrode 6 has, in addition to the electrode active material layer 8, at least one further electrode active material layer, wherein the porosity of the electrode active material layer 8 differs from the porosity of the further electrode active material layer. By providing at least two electrode active material layers that differ from each other with respect to their porosity, the distribution of the electrolyte 10 in the electrode active material layers can be better adapted to the local current density requirement of the electrode 6.

[0033] The production of an electrode with a porous structure has been explained above using the negative electrode 6 as an example. However, the process can also be applied to the production of the positive electrode 3. According to a further embodiment, an electrode slurry is provided which contains at least one positive electrode active material. This electrode slurry is enriched with gas and applied as a positive electrode active material layer onto a current collector. Subsequently, the positive electrode active material layer is dried so that the gas escapes from the positive electrode active material layer, forming pores. Reference symbol list 1 lithium-ion cell 2 cases 3 positive electrode 4 current collectors 5 positive electrode active material layer 6 negative electrode 7 current collectors 8 negative electrode active material layer 9 Separator 10 Electrolyte 11 lithium ions 12 pores 13 Electrode slurry 14 Gas 15 gas bubbles 16 negative electrode active material 17 Stirring device 18 Supply line QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 2021 / 0151764 A1

[0005] DE 102018209955 A1

[0005]

Claims

[1] A method for producing an electrode, wherein an electrode slurry (13) comprising at least one electrode active material (16) is provided, wherein the electrode slurry (13) is applied as an electrode active material layer (8) to a current collector (7), and wherein the electrode active material layer (8) is dried and provided with pores (12) such that an electrode (6) with a porous structure is obtained, characterized by , that the electrode slurry (13) is enriched with gas (14) in such a way that the gas (14) escapes from the electrode active material layer (8) during the drying of the electrode active material layer (8) by forming the pores (12). [2] Method according to claim 1, characterized by , that the electrode slurry (13) is enriched with gas (14) in such a way that the gas (14) is present in the electrode slurry (8) in the form of gas bubbles (15). [3] Method according to any one of the preceding claims, characterized by, that the electrode slurry (13) is stirred in the presence of the gas (14) in order to enrich the electrode slurry (13) with the gas (14). [4] Method according to any one of the preceding claims, characterized by , that the gas (14) is introduced into the electrode slurry (13). [5] Method according to any one of the preceding claims, characterized by , that the gas (14) used is air, nitrogen, argon, oxygen, carbon dioxide or forming gas. [6] Method according to any one of the preceding claims, characterized by , that the viscosity of the electrode slurry (13) is greater than 1800 mPa * s at a shear rate of 10 0 * s -1 , greater than 1200 mPa * s at a shear rate of 10 1 * s -1 and / or greater than 600 mPa * s at a shear rate of 10 2 * s -1 is. [7] Method according to any one of the preceding claims, characterized by that the electrode slurry (13) contains at least one solvent, and that the mass fraction of solvent in the electrode slurry (13) is at most 50%, preferably at most 35%, and particularly preferably at most 25%. [8] Method according to any one of the preceding claims, characterized by , that the electrode active material layer (8) is dried by heating the electrode active material layer (8). [9] Method according to any one of the preceding claims, characterized by , that the electrode active material layer (8) is dried by reducing an ambient pressure. [10] Method according to any one of the preceding claims, characterized by , that the electrode active material layer (8) is subjected to a temperature shock treatment to increase the porosity of the electrode active material layer (8). [11] Method according to any one of the preceding claims, characterized by , that at least one further electrode active material layer is applied to the current collector (7), and that a porosity of the electrode active material layer (8) differs from a porosity of the further electrode active material layer. [12] Electrode produced by a method according to any one of the preceding claims. [13] Lithium-ion cell comprising an electrode (6) according to the preceding claim.

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