Method and apparatus for thermal drying treatment of electrode-separator assembly by induction

Abstract

The present invention proposes a method and apparatus for thermal drying treatment of a plurality of electrode-separator composites (10). The composites each have at least one negative electrode and at least one positive electrode, each comprising a metal current collector coated with an electrode active material, specifically an anode current collector and a cathode current collector. All composites are dried simultaneously during thermal drying treatment. Drying is performed by a plurality of inductors (20), thereby inducing heating of the electrode-separator composites (10). In this method, the plurality of electrode-separator composites (10) are placed in a drying device within the operating area of ​​the inductor (20). For thermal drying treatment, a vacuum is applied and current is supplied to the inductor (20). In this method, each of the electrode-separator composites (10) to be dried in the drying device may be associated with exactly one inductor (20), or two or more electrode-separator composites (10) may be associated with one inductor (200) that generates an alternating magnetic field of an elongated range, so that two or more electrode-separator composites (10) may be arranged to be exposed to substantially the same magnetic field strength in an alternating field.

Description

Technology Field

[0001] The present invention relates to a method for thermal drying treatment of a plurality of electrode-separator assemblies and a drying apparatus for carrying out the method. Background Technology

[0002] Electrochemical energy storage elements can convert stored chemical energy into electrical energy through oxidation-reduction reactions. The simplest form of electrochemical energy storage is the electrochemical cell. It consists of a positive electrode and a negative electrode, which are separated from each other by a separator. During discharge, electrons are emitted from the negative electrode as a result of the oxidation process. This generates an electron current that can be drawn by an external electricity consumer, and the electrochemical cell acts as an energy source. Simultaneously, an ion current corresponding to the electrode reaction is generated within the cell. This ion current passes through the separator and is made possible by an ion-conductive electrolyte.

[0003] When the discharge of an electrochemical energy storage element is reversible—that is, when the conversion of chemical energy into electrical energy during discharge can be reversed to recharge the battery or element—it is called a secondary energy storage element. Generally, for a secondary energy storage element, designating the negative electrode as the anode and the positive electrode as the cathode indicates the discharge function of the electrochemical energy storage element.

[0004] In this specification, the term "electrochemical energy storage element" is understood to mean not only a single electrochemical cell but also a battery comprising a plurality of individual electrochemical cells.

[0005] Among known secondary electrochemical energy storage elements, relatively high energy densities are achieved particularly by lithium-ion batteries. In addition to using battery stacks composed of multiple individual cells, each having at least one positive electrode and at least one negative electrode, lithium-ion batteries equipped with a wound-shaped electrode-separator assembly are widely used. Such assemblies often have a sequence of "positive electrode / separator / negative electrode". Furthermore, these individual cells can be configured as so-called bi-cells having possible sequences of "negative electrode / separator / positive electrode / separator / negative electrode" or "positive electrode / separator / negative electrode / separator / positive electrode".

[0006] The electrodes of lithium-ion batteries typically include metallic current collectors in the form of foils, nets, grids, foams, fleeces, or felts. For the positive electrode, aluminum nets or foils (e.g., aluminum expandable metal or aluminum foil) are commonly used as current collectors. For the negative electrode, copper nets or foils are typically used as current collectors.

[0007] Generally, the lithium-ion batteries described are produced using a multi-stage method. In the first stage, it is common to produce electrodes and then combine them with one or more separators to form the aforementioned electrode-separator assembly. The electrodes and separators may be connected to each other in a stacked, wound, or lamination stage.

[0008] To produce electrodes for lithium-ion batteries, for example using a doctor blade or slot die, a thin electrode film is formed on a current collector from a composition, mainly paste-like, containing a suitable electrochemical active material (abbreviated as "active material"). The active material suitable for the electrodes of a lithium-ion battery must be able to absorb and release lithium ions moving from the negative electrode to the positive electrode (or vice versa) during charging and discharging.

[0009] Graphite-based or non-graphite-based carbon materials capable of intercalating lithium are particularly suitable active materials for the negative electrode of lithium-ion batteries. Metallic and semi-metallic materials capable of alloying with lithium may also be used. For example, elements such as tin, antimony, and silicon can form intermetallic phases with lithium. In particular, carbon-based active materials may be combined with metallic and / or semi-metallic materials.

[0010] Lithium cobalt oxide (LCO) with the chemical formula LiCoO2, chemical formula LiNi x Mn y Co z Lithium nickel manganese cobalt oxide (NMC) of O2, lithium manganese spinel (LMO) of the chemical formula LiMn2O4, lithium iron phosphate (LFP) of the chemical formula LiFePO4, or the chemical formula LiNi x Co y Al z Lithium nickel cobalt aluminum oxide (NCA) of O2 is particularly suitable for the cathode. Mixtures of these materials can also be used.

[0011] Typically, paste-like compositions contain, in addition to the active material, an electrode binder (abbreviated as "binder"), a conductivity enhancer, a solvent and / or suspending agent, and, if necessary, additives that affect processing characteristics. The electrode binder forms a matrix in which the active material and possibly the conductivity enhancer can be embedded. The matrix is ​​intended to ensure high structural stability during volume expansion and contraction caused by precipitation and precipitation removal. Possible solvents and / or suspending agents include water or organic solvents such as N-methyl-2-pyrrolidone (NMP) or N-ethyl-2-pyrrolidone (NEP). An example of an aqueous processable binder is sodium carboxymethyl cellulose (Na-CMC). An example of a binder that can be processed in an organic solvent is polyvinylidene difluoride (PVDF). For example, rheology aids may be added as additives. Conductivity enhancers are typically electrically conductive carbon-based materials, particularly conductive carbon black, conductive graphite, carbon fibers, or carbon nanotubes.

[0012] The solvent and / or suspension contained in the composition is typically found in the electrode film formed on the current collector and must be removed from it. The dried electrode film can then be compressed, for example, in a calendering process. The electrode thus formed can be assembled into the aforementioned battery.

[0013] Drying the electrode film formed on the current collector—that is, removing the solvent and / or suspension contained in the electrode film and subsequently eliminating residual moisture that may still be present in the electrode separator assembly—is a time- and energy-intensive process. Traditionally, electrode films can be dried using a tempered gas, specifically tempered air. The gas heats the electrode film, causing the solvent and / or suspension or any residual moisture contained within it to evaporate and escape. Heating initially occurs on the surface of the electrode film and gradually spreads into the interior. Consequently, drying proceeds slowly from the outside inward; while the outer layer of the electrode film may already be dry, the film still contains a significant amount of solvent and / or suspension in the layer adjacent to the current collector. This can be problematic in that film-like residues often remain when the solvent and / or suspension are removed. If these residues form on the outer layer of the electrode film, further drying of the electrode film can be significantly delayed because the solvent and / or suspension no longer protrude from the layer adjacent to the current collector without issue. In certain situations, air bubbles may form. In particular, attempts are being made to prevent this by using sufficiently long drying times. If dried slowly, only a slight drying gradient is observed. However, intentionally slowing down the drying process already takes a considerable amount of time.

[0014] As part of the manufacturing process for lithium-ion batteries, it is particularly important to remove residual moisture from the electrode-separator assembly before filling the battery with electrolyte. Traditionally, this is accomplished through an oven process, typically using a vacuum oven to dry the electrodes before the winding process or to dry the wound-shaped electrode-separator assembly directly in a housing cup before filling with electrolyte. For mass production, a batch typically consisting of hundreds of batteries is heated to about 100°C for several hours on a carrier (tray) to remove moisture. This process usually involves repeating vacuum and nitrogen purging several times to remove moisture from the oven chamber.

[0015] However, this procedure presents several difficulties. First, it is generally difficult to apply heat to such ovens because the drying medium cannot be circulated under a vacuum. Consequently, it is difficult to heat the cells uniformly and simultaneously. Uniform heating is only possible by adding nitrogen or other gases.

[0016] Furthermore, in these conventional oven processes, heating occurs through contact, such as by placing the battery on the oven's hot transport plate, which poses a problem. In a vacuum, heat transfer by convection does not occur, and since the vacuum also acts as an insulating layer, non-uniformity between the plate and the battery can hinder heat transfer. This can easily lead to uneven heating of the battery.

[0017] Furthermore, in the conventional oven process, it must be noted that the batteries should not be overheated, as excessive heating can cause damage to the batteries, particularly to the separator. This is difficult because using conventional heating plates results in heat and time loss, which can cause the temperature to rise excessively and lead to a degradation in the quality of the batteries to be dried.

[0018] In conventional oven processes, drying an electrode-separator assembly already contained within a battery cup or housing cup in an oven also presents a problem. In this case, the battery cup heats up first. Direct heat conduction to the electrode and current collector primarily occurs through the electrode's welding points or any existing metal contact plates. Consequently, heat transfer is not properly achieved. Furthermore, a small clearance between the inside of the can and the electrode-separator assembly often further hinders heat transfer.

[0019] Finally, in conventional oven processes, it is difficult to achieve uniform drying across the entire cell batch. Generally, cells at the outer edge of the batch reach a different temperature than the cells inside during the drying process. On the one hand, the temperature must not be too high during drying to prevent damage, particularly to the separator. On the other hand, the temperature must not be too low to allow moisture to evaporate safely. Overall, the temperature window that must be maintained is very small, and it is difficult to achieve the necessary temperature window for a sufficient amount of time for all cells in the batch.

[0020] It is already known that electrodes can be heated and dried using inductively generated eddy currents. For example, EP 3 439 079 B1 describes a method for heat-treating electrode films of metallic current collectors, in which the current collector is inductively heated by an induction device. However, the method described herein primarily provides a solution for drying electrode strips immediately after coating. When drying multiple already wound electrode-separator assemblies simultaneously, satisfactory results cannot be expected with this method.

[0021] Against this backdrop, the present invention sets as its objective an improved method and a corresponding apparatus capable of rapidly and uniformly drying a plurality of electrode-separator assemblies as part of a manufacturing process for lithium-ion energy storage elements, and in particular removing residual moisture. Furthermore, this method must be faster and more effective than existing processes, while simultaneously enabling energy savings.

[0022] This objective is achieved by the method according to claim 1. This objective is further addressed by a drying apparatus according to an additional independent claim. Preferred embodiments and embodiments of the method or drying apparatus are the subject of the dependent claims.

[0023] The method according to the present invention is used for the simultaneous thermal drying treatment of a plurality of electrode-separator assemblies. The plurality of electrode-separator assemblies can be dried simultaneously, particularly in a batch form.

[0024] The electrode-separator assemblies each comprise at least one anode, at least one cathode, and at least one separator. The electrodes themselves each comprise a metallic current collector coated with an electrode active material. In the case of the cathode, it is an anode current collector, and in the case of the anode, it is a cathode current collector. Thermal drying is performed by an inductor and is performed as non-contact as possible. It is preferable that the electrode-separator assembly be inductively heated simultaneously without direct contact with the inductor.

[0025] The method according to the present invention comprises the following steps:

[0026] a. The plurality of electrode-separator assemblies are positioned within the effective range of the inductor in a drying device,

[0027] b. Vacuum is applied for the above heat drying treatment,

[0028] c. Current is supplied to the above inductor.

[0029] The method according to the present invention is additionally characterized by the following:

[0030] d. Exactly one inductor is assigned to each of the electrode-separator assemblies to be dried in the above drying device.

[0031] or

[0032] e. Two or more electrode-separator assemblies are assigned to an inductor that generates an alternating magnetic field in an elongated range, and the two or more electrode-separator assemblies (10) may be arranged so as to be exposed to essentially the same magnetic field strength in the alternating magnetic field.

[0033] The method according to the present invention is based on the generation of an alternating magnetic field by an inductor, which can act on the metallic component of an electrode-separator assembly, particularly the current collector. The eddy current generated in the metallic component leads to heating, causing any moisture present in the electrode film deposited on the current collector to evaporate. Since heating is much more direct and faster than in conventional oven processes, the method according to the present invention can save a significant amount of time.

[0034] According to the induction principle of the method according to the present invention, an alternating current is supplied to an inductor. Depending on the frequency and / or amplitude of the alternating current, the temperature during the drying process can be set as desired.

[0035] In both the embodiment according to feature d and the embodiment according to feature e, the electrode-separator assembly to be dried is exposed to the same drying conditions so that drying can be performed uniformly and quickly.

[0036] Vacuum is applied in a manner known, for example, in conventional oven processes. In particular, vacuum pumps are used to create a vacuum, that is, a pressure lower than the ambient pressure. It is desirable to set a pressure of less than 300 mbar, for example, in the range of 20 mbar to 100 mbar.

[0037] Unlike conventional drying methods for electrodes on an inductive basis, the key to the method according to the present invention in the embodiment having the above feature d lies, above all, in the fact that each electrode-separator assembly to be dried is assigned to a single inductor to achieve highly targeted and directed heating of the electrode-separator assembly. In this way, any residual moisture present in the electrode-separator assembly can be removed safely, in a short time, particularly effectively, and at the same time energy-saving manner.

[0038] The key to the method according to the present invention in the embodiment having the above feature d is that the same effect is achieved, except that multiple electrode-separator assemblies are assigned to a single inductor and can be exposed to the same drying conditions. When using a magnetic field generated by a coil with a circular cross-section, it is difficult to arrange multiple coils to be exposed to nearly the same magnetic field strength. An elongated magnetic field that can be generated in an elongated inductor makes this possible.

[0039] These inductors can be manufactured with a length that allows for the uniform drying of 12 or more electrode-separator assemblies arranged in a row.

[0040] The drying device according to the present invention preferably includes one or more such elongated inductors capable of arranging a plurality of electrode-separator assemblies.

[0041] In an embodiment having the above feature d, the method according to the present invention can be individually controlled and / or regulated for individual electrode-separator assemblies if necessary so as not to cause harmful excessive temperatures in individual cells. Additionally, the method according to the present invention can achieve a high level of heating uniformity over the entire batch because mechanical and magnetic tolerances can be compensated by individual heating of individual electrode-separator assemblies through individual inductors. Since each electrode-separator assembly in the batch can be uniformly heated and dried, hotspots or other non-uniform heat distributions are not formed in the batch.

[0042] Compared to conventional drying ovens, the structure of this drying device is much lighter and requires less material. In particular, since it does not require conductive media such as oil or water, it can be used to heat oven drawers in conventional oven processes.

[0043] In addition, since the method according to the present invention can, in principle, operate individual inductors individually, different drying curves for different types of electrode-separator assemblies can be executed in a drying device, for example, a drying curve for one energy type and a different drying curve for one power type in an electrode-separator assembly.

[0044] Above all, the method according to the present invention enables significant energy savings compared to conventional methods. Compared to conventional oven processes, which generally require heating of the means of transporting the battery, such as pallets, energy savings in the range of 50% to 75% are possible.

[0045] To introduce and position the electrode-separator assemblies, individual assemblies can be pushed directly into a drying device and positioned within the effective range of each inductor, for example. Since it is not necessary to use transport pallets as in conventional processes, the steps of storing and transporting the electrode-separator assemblies in and out of the pallets are eliminated. Because the inductors deliver the energy required for non-contact drying, quality requirements, particularly the uniformity of the surface on which the electrode-separator assemblies are placed, may be relatively lower. Due to non-contact transport, conventional non-uniformity is not an issue. However, in the case of contact heat, the size of the contact surface is critical.

[0046] In another preferred embodiment, a product carrier, for example, a transport cup (puck) or a conveying means may be used. Conveniently, such a product carrier is made of an electrically non-conductive material (e.g., plastic) so that it does not interact with the induction heating process and is not heated, thus causing no energy loss.

[0047] In conventional oven processes, the use of transport pallets is also disadvantageous in terms of additional energy requirements during heating and cooling, as the transport pallets are inevitably heated along with the electrode-separator assembly to be processed. In the method according to the present invention, only the electrode-separator assembly can be heated in a targeted manner. Even when using a product carrier, if a material suitable for the product carrier is selected, heating of the product carrier does not occur, so the method according to the present invention saves significantly more time and energy than the conventional method.

[0048] When the electrode-separator assembly to be processed is introduced directly into a drying device or transported by an individual product carrier, the electrode-separator assembly is accumulated on a surface with an inductor, particularly on the transport plate of the drying device, so that each of the individual electrode-separator assemblies can be positioned on the inductor.

[0049] For example, after positioning the electrode-separator assembly to be processed, the vacuum hood can be lowered over the electrode-separator assembly to be processed, and the drying process can be started.

[0050] Once the heating process is complete, individual electrode-separator assemblies can be further transported and separated again, for example using a pusher. This offers significant advantages in the additional processing of electrode-separator assemblies compared to handling using transport pallets.

[0051] In a particularly preferred embodiment, this method features at least one of the following additional features:

[0052] a. The electrode-separator assembly is heated to a temperature greater than 99°C and below the melting point of the separator of the electrode-separator assembly,

[0053] b. The electrode-separator assembly is heated to a temperature in the range of 100°C to 110°C.

[0054] Preferably, the aforementioned features a and b are implemented in combination with each other.

[0055] For effective heating leading to the evaporation of any existing residual moisture, it is ideal to reach a temperature exceeding the boiling point of moisture or residual moisture during the drying process. Therefore, it is desirable to set the temperature above 100°C. It is convenient to select a desired temperature range to prevent damage to the electrode-separator assembly to be processed. The key component here is generally the separator, which can be made of, for example, microporous plastic or a nonwoven fabric made of glass fiber or polyethylene. The separator may also consist of, for example, a ceramic-coated nonwoven fabric. Therefore, to reliably prevent damage to the electrode-separator assembly, a temperature range of 100°C to 110°C is particularly suitable for the drying process.

[0056] Compared to conventional oven processes, the time required for drying treatment in the method according to the present invention can be significantly reduced, particularly by targeted and effective heating of the electrode.

[0057] In a particularly preferred embodiment, the method according to the present invention features at least one of the following additional features:

[0058] a. The electrode-separator assemblies are each formed as windings and have a cylindrical basic shape having two terminal end faces.

[0059] b. The electrode and each current collector are ribbon-shaped and are spirally wound within the electrode-separator assembly.

[0060] Preferably, the aforementioned features a and b are realized in combination with each other.

[0061] The method according to the present invention, based on inductive heat transfer, can be performed much more directly and rapidly than conventional methods and does not require contact heat as in conventional oven processes; therefore, the method according to the present invention can be used very flexibly in the manufacturing process of energy storage elements. In principle, the method according to the present invention can also be used for drying pure electrodes. However, the method according to the present invention is particularly preferred for drying already wound electrode-separator assemblies.

[0062] In a particularly preferred embodiment, the method according to the present invention is characterized by the following additional features:

[0063] a. The cathode and the anode are disposed within the electrode separator assembly such that the longitudinal edge of the anode current collector protrudes from one of the terminal end faces and the longitudinal edge of the cathode current collector protrudes from the other of the terminal end faces,

[0064] b. A contact element, in particular a contact plate, is attached to at least one of the end faces and covers at least 50% of each end face.

[0065] Preferably, the aforementioned features a and b are realized in combination with each other.

[0066] When the drying treatment according to the present invention is applied to an energy storage element known as itself, the so-called contact plate design according to the aforementioned features a and b provides a particular advantage because the contact element, for example, the contact plate, which is in direct contact with one of the current collectors, significantly promotes induction heating.

[0067] One such contact plate design can be found, for example, in WO 2017 / 215900 A1. This describes a cylindrical round battery equipped with a winding-shaped electrode-separator assembly. Electrodes of opposite polarity are offset from each other within the electrode-separator assembly, such that the longitudinal edge of the positive current collector protrudes from one end face and the longitudinal edge of the negative current collector protrudes from the other end face of the winding. For electrical contact of the current collectors, the battery has a contact plate on one end face of the winding and is assembled to the longitudinal edge of one of the current collectors, for example, by welding. This allows the current collector and the associated electrode to be electrically contacted along the entire length. This significantly reduces the resistance within the battery. Compared to conventional batteries, it can absorb large currents much better and dissipate heat from the winding more effectively.

[0068] The contact plate design of the electrode-separator assembly that can be dried according to the present invention may, for example, be designed such that the contact element is specifically designed as a contact plate or a metallic plate, and accordingly, the apertures of the plate may be provided such that only a specific proportion of each end face is covered by the contact element, for example, 50% or preferably more.

[0069] The contact element may be composed of, for example, nickel, copper, titanium, a nickel, copper, or titanium alloy, stainless steel, or nickel-plated copper. These materials are particularly preferred for the contact element assembled with the anode current collector. The contact element for connecting to the cathode current collector is preferably composed of aluminum or an aluminum alloy.

[0070] For example, the contact element may have a uniform thickness in the range of 50 μm to 600 μm, preferably 150 μm to 350 μm. Preferably, the contact element has the shape of a disk or a polygonal plate. It is desirable for the contact element to cover at least 60% of each end face and may have holes, particularly holes or slots, or multiple holes or slots if necessary.

[0071] The inventors were able to confirm that heating in an electrode-separator assembly equipped with a contact element in the method according to the present invention is much faster and more effective. This is likely because, among other things, the contact element provides more mass capable of absorbing magnetic field lines. Additionally, the contact element can be advantageously aligned with the magnetic field lines. Therefore, the method according to the present invention, combined with the contact element, can heat and dry the electrode-separator assembly particularly quickly, effectively, and directly.

[0072] With respect to positioning the electrode-separator assembly in a drying device, the method according to the present invention features at least one of the following additional features in a preferred embodiment:

[0073] a. When the electrode-separator assembly is positioned within the drying device, the electrode-separator assembly formed as a winding is aligned parallel to each other on a transport plate of the drying device, and one of the end faces of the winding faces the transport plate and the other of the end faces of the winding faces in a direction away from the transport plate.

[0074] b. The above inductor or the above inductors are placed within or below the above transport plate,

[0075] c. After the electrode-separator assembly is placed in the drying device, the inductor or the inductors are separated from the electrode-separator assembly by a dielectric.

[0076] Preferably, the aforementioned features a and b and, in a particularly preferred manner, the aforementioned features a, b and c are realized in combination with each other.

[0077] The transport plate of the drying device is preferably a bottom or base plate within the drying device, and the inductor or inductors for the electrode-separator assembly are generally placed within or beneath this bottom or base plate or transport plate.

[0078] According to feature c mentioned above, the dielectric, i.e., the insulator, is positioned between the electrode-separator assembly and the inductor after placement. For example, it may be a glass ceramic covering the inductor or the inductors on the carrier plate. According to the principle of induction heating, heat is transferred through electromagnetic field lines that induce heating only at any contact element of the metallic substrate, i.e., particularly the current collector and / or electrode-separator assembly. Therefore, in the method according to the present invention, the covering glass ceramic, etc., is not heated.

[0079] In a particularly preferred manner, the electrode-separator assembly is preferably positioned so that one end face of the electrode-separator assembly, on which a contact element is provided, is aligned on or faces the carrier plate. It is particularly preferred that the anode side of the electrode-separator assembly faces the carrier plate equipped with an inductor. However, in some embodiments, the cathode side of the electrode-separator assembly may also face the carrier plate equipped with an inductor.

[0080] Preferably, the anode-side contact element is placed on a transport plate. Preferably, the anode-side contact element is made of copper or nickel, and / or the anode current collector is made of copper. This enables particularly excellent induction heating.

[0081] In principle, the method according to the present invention is also suitable for heating a contact element on the cathode side, for example, made of aluminum.

[0082] In a further embodiment of the method according to the present invention, an electrode-separator assembly, with or without a contact element, may be provided to be dried together with a housing cup, e.g., a metallic housing cup. Accordingly, in a preferred embodiment, the method according to the present invention features at least one of the following additional features:

[0083] a. The electrode-separator assembly designed as a winding is inserted into a metallic housing cup that is cylindrical and has a cup base, and is inductively heated inside the housing cup.

[0084] b. To position the electrode-separator assembly, the electrode-separator assembly designed as a winding is disposed in the drying device together with the metallic housing cup, such that the housing bottom of the housing cup stands on the transport plate of the drying device.

[0085] Preferably, the aforementioned features a and b are realized in combination with each other.

[0086] In addition, by combining it with a housing cup, the drying process can be performed effectively. Since the heat inductively generated in the cup can be transferred to the electrode-separator assembly, the heating efficiency is further enhanced. By combining one or two contact elements with the electrode-separator assembly, the contact elements placed inside the cup or the contact elements themselves can also be inductively heated, generating heat within the cup and further increasing the heating effect. Because the energy supply is very direct due to the induction method, the drying process can be performed optimally with minimal power.

[0087] Drying only the electrode-separator assembly, or drying only the electrode-separator assembly having one or two contact elements, offers the particular advantage of not requiring energy consumption to heat the cup compared to heating the electrode-separator assembly inside the cup. This can be advantageous in certain situations. However, there may also be cases where drying the electrode-separator assembly inside the housing cup is advantageous for production-related reasons. Since the method according to the present invention is generally very efficient and saves energy and time, this method also offers advantages over conventional methods.

[0088] A particular advantage of the method according to the present invention is that highly targeted and individually adjustable heating of individual electrode-separator assemblies is possible through individual inductors each assigned to the electrode-separator assemblies to be processed. In a particularly preferred embodiment of the method according to the present invention, at least one of the following additional features is provided in this context:

[0089] a. Individual inductors operate in a controlled manner,

[0090] b. At least one performance value is measured in each individual inductor.

[0091] It is desirable that the previously mentioned features a and b be implemented in combination.

[0092] The controlled operation of individual inductors (in an embodiment of the invention according to feature d of claim 1) makes it possible to compensate for uneven heat supply that may occur due to the arrangement of the batch, for example, so as not to cause hot spots or other uneven heat distribution within the batch. However, in other embodiments, the adjustment may be omitted. It may also be possible to switch and / or control multiple inductors together. In particular, this is provided as such in an embodiment of the invention according to feature e of claim 1.

[0093] With conventional methods, it is not possible to guarantee that each individual electrode composite absorbs the same amount of heat within the batch. This may be due to non-uniformity or the fact that the introduced energy cannot reach all cells equally.

[0094] Performance measurements, such as current or temperature measurements, on individual inductors or possibly groups of inductors can be used to verify whether heating has been optimally performed in the intended manner on each assigned electrode-separator assembly or on each assigned electrode-separator assembly. Since quality control is possible through these performance measurements, sufficient and reliable heating and drying treatments can be guaranteed for all electrode-separator assemblies in the entire batch. Insufficient drying of individual electrode-separator assemblies can also be detected in this manner for quality control purposes, and the corresponding electrode-separator assemblies can be classified if necessary.

[0095] With respect to the inductor, the method according to the present invention features at least one of the following additional features:

[0096] a. The above inductor or the above inductors are induction coils,

[0097] b. The diameters of the inductors used according to feature d of claim 1, particularly the induction coils, and the diameters of the electrode-separator assemblies, particularly the electrode-separator assemblies formed as windings having a basic cylindrical shape, differ from each other by up to 20%.

[0098] In an embodiment having feature d of claim 1, it is preferable that the aforementioned features a and b be realized in combination with each other.

[0099] In principle, any device suitable for generating an alternating electric field capable of inducing eddy currents in a metallic substrate is suitable as an inductor. An inductor is preferably an induction coil, in particular a coil having multiple coil windings, or an induction device comprising at least one such coil. The induction coil is preferably wound in a flat, spiral shape and, in a preferred embodiment, is essentially composed of, for example, copper wire or coated copper wire.

[0100] Particularly effective energy utilization can be achieved by adjusting the diameter of the inductor, specifically the induction coil, to match the diameter of the electrode-separator assembly to be processed. However, since this method operates very efficiently overall, a certain deviation in the fit between the inductor and the electrode-separator assembly is also permitted. For example, even with a 20% deviation from the mentioned diameter, it is still suitable for performing drying processing in a very fast and energy-saving manner.

[0101] If necessary, larger variations between the diameters of the inductor and the electrode-separator assembly may be allowed. This enables the processing of electrode-separator assemblies of different dimensions using the same drying device.

[0102] The method according to the present invention is particularly suitable for a thermal drying treatment performed immediately before the electrolyte is impregnated into an electrode-separator assembly during the manufacturing process of an energy storage element. In particular, at this stage, that is, before the electrolyte is impregnated, any residual moisture must be removed from the electrode-separator assembly. The residual moisture that can be removed according to the present invention may have penetrated into the electrode-separator assembly, for example, during intermediate storage of the electrode-separator assembly during the manufacturing process. By using the method according to the present invention, the post-drying step can be performed in a manner that particularly saves time and energy.

[0103] The method according to the present invention is particularly suitable for round batteries because it can utilize an optimal round coil shape of an inductor corresponding to the round cross-section of the round battery.

[0104] The method according to the present invention is particularly suitable for use in the production process of lithium-ion batteries, preferably lithium-ion round batteries, and above all, can also be used for mass production. The energy and time saving potential of the method according to the present invention is particularly effective in mass production processes.

[0105] The present invention further comprises a drying apparatus for performing a thermal drying treatment according to the method described in particular. The drying apparatus is characterized by the following features:

[0106] a. The drying device comprises at least one vacuum chamber,

[0107] b. The drying device preferably comprises a plurality of inductors, particularly induction coils, in a regular arrangement, or at least one inductor that generates an alternating magnetic field of an elongated range, and the two or more electrode-separator assemblies may be arranged to be each exposed to essentially the same magnetic field strength in the alternating magnetic field.

[0108] c. The drying device comprises at least one device for supplying current to the inductor or inductors.

[0109] The vacuum chamber of the drying apparatus according to the present invention is preferably formed by a vacuum hood, preferably a lowerable vacuum hood, that surrounds one or more of the electrode-separator assemblies to be dried so that they or they may be subjected to a corresponding reduction in pressure. In many cases, it is preferable for a plurality of electrode-separator assemblies to be placed within the vacuum chamber, that is, to be surrounded by a vacuum hood. However, the apparatus according to the present invention may include a separate hood for each of the electrode-separator assemblies to be dried. In this case, each of the electrode-separator assemblies is placed in its own vacuum chamber.

[0110] With regard to additional details of this drying device, the method described above that can be performed with such a drying device is also referenced.

[0111] A device supplying current to the inductors preferably includes control devices for individual inductors or, if necessary, multiple inductors, so that the inductors can be operated individually or in groups at an appropriate AC frequency. Depending on the design of the drying device, it may also be possible to control all inductors at the same frequency and together.

[0112] In a particularly desirable manner, the drying device according to the present invention is characterized by the following additional features:

[0113] a. The above inductors or inductors are placed on the transport plate of the drying device, preferably cast into the transport plate or placed below the transport plate of the drying device.

[0114] As already explained above, the inductor is preferably an induction coil known in itself, placed on the carrying plate of the drying device, for example, the base plate. The coil may be covered by a plate or a layer of an electrically non-conductive material (e.g., glass ceramic). The inductor itself is preferably a parallel-wound induction coil made particularly of copper wire. If necessary, the induction coil may be equipped with a ferrite core to better concentrate the magnetic field lines on the electrode-separator assembly to be processed. In this particular case, it is not necessary to wind the induction coil flat.

[0115] With respect to the feeding and positioning of the electrode-separator assembly to be processed, the drying apparatus according to the present invention features at least one of the following additional features in a preferred embodiment:

[0116] a. The drying device includes a transfer means for introducing and / or removing the electrode-separator assembly to be processed into and / or from the drying device,

[0117] b. The drying device comprises means for positioning the electrode-separator assembly to be processed for an inductor or individual inductors,

[0118] c. The drying device includes a conveying means for holding the electrode-separator assembly to be processed.

[0119] Preferably, the aforementioned features a and b or a and c or b and c or a and b and c are realized in combination with each other.

[0120] The conveying means may be, for example, one or more pushers that push individual electrode-separator assemblies into the interior of the drying device. An inductor located inside or below the transport plate of the drying device may be positioned such that one inductor is assigned to each electrode-separator assembly when pushing the electrode-separator assemblies into their maximum packing, or so that the electrode-separator assembly is positioned directly above the inductor on the transport plate. This precise alignment of the electrode-separator assemblies may be supported, for example, by corresponding side bands or stops that simplify the correct positioning of the electrode-separator assemblies.

[0121] The correct positioning of the electrode-separator assembly on the transport plate of the drying device may also be supported by other means, such as using a gripper. The gripper may be used to grasp one or more electrode-separator assemblies and place them in the correct position on the transport plate.

[0122] Additionally, holding means, such as transfer cups or transfer pallets, may be provided to facilitate positioning and holding. The holding means may be designed as a single or multiple holder for multiple electrode-separator assemblies. Preferably, such holding means may be made of plastic or other non-metallic, and preferably non-heat conductive or low-heat conductive materials, so as not to interact with induction heating. For example, using such holding means, such as transfer cups, eliminates the need to directly touch sensitive electrode-separator assemblies during the drying process, whether or not contact elements are present, and can be particularly useful during the drying process of pure electrode-separator assemblies.

[0123] Preferably, each inductor can be switched individually or, where appropriate, as part of a group, preferably in a controlled manner.

[0124] In a particularly advantageous embodiment, the drying device includes an inductor or a device for measuring the performance of the inductors, and in an embodiment where the inductor is assigned to each electrode-separator assembly, it is desirable that the performance measurement be provided for each individual inductor or, where applicable, for a group of inductors. For example, absorbed current and / or temperature and / or time may be measured as performance values. For example, a temperature sensor may be integrated into each inductor. By measuring performance, the drying process can, in principle, be recorded for each individual electrode-separator assembly and traceable for quality control purposes. Since individual inductors can be operated in a controlled manner through such performance measurement, uniform and constant drying can be ensured, for example, across the entire batch.

[0125] Performance measurement can also be used to initially measure the amount of energy required for the electrode-separator assembly at a specific location within the batch or at a specific location on the transport plate of the drying device. Since the inductor can then be configured for the subsequent drying process, consistent drying quality is ensured without the need to record values ​​corresponding to each drying process.

[0126] In a more preferred embodiment of the drying device according to the present invention, a self-oscillating resonant converter may be associated with each inductor. For example, a self-oscillating Royer converter may be used. The resonant converter may be controlled internally or externally, and generally operates efficiently regardless of the control type and causes little EMC interference. In some embodiments, an externally controlled resonant converter is preferred because it is more controllable in terms of frequency.

[0127] Further features and advantages of the present invention are apparent from the description of the following embodiments associated with the drawings. Individual features may be implemented individually or in combination with one another. Brief explanation of the drawing

[0128] The drawing is as follows: FIG. 1 is a schematic diagram of a component related to a method according to the present invention; FIGS. 2A and 2B are cross-sectional views of inductors inserted into the transport plate of a drying device; FIG. 3 is a schematic diagram of the transport plate of the drying device; and FIG. 4 is a cross-sectional view of an inductor inserted into a transport plate of a drying device. Specific details for implementing the invention

[0129] FIG. 1 illustrates some components for carrying out a method according to the present invention, wherein a plurality of electrode-separator assemblies (10) are simultaneously subjected to thermal drying treatment based on induction heating. An important aspect of this method is that exactly one inductor (20) is assigned to each electrode-separator assembly (10) to be treated. The thermal drying treatment is performed under vacuum, and in the example illustrated herein, a vacuum hood (30) is lowered over the electrode-separator assembly (10) to be treated within the corresponding drying device to generate a vacuum.

[0130] The electrode-separator assembly (10) to be processed, illustrated herein, is formed from ribbon-shaped electrodes and a separator positioned between them in a known manner, as a winding having a cylindrical basic shape and two terminal end faces. Plate-shaped contact elements (11, 12) are located on each of the end faces of the electrode-separator assemblies (10) illustrated herein. The contact elements (11, 12) are each welded to the protruding longitudinal edges of the current collectors and connected to the electrodes. The contact element (11) on the lower end face of the electrode-separator assembly is connected to the anode current collector. The contact element (12) on the upper side of the electrode-separator assembly (10) is connected to the cathode current collector.

[0131] When positioning the electrode-separator assemblies (10) in relation to individual inductors (20), the anode-side contact element (11) is positioned within the effective range of each inductor (20) in this preferred embodiment. In this way, particularly excellent inductive heat transfer is achieved because the heating of the positive-side contact element (11) is transferred directly to the anode current collector. The anode current collector is preferably made of copper foil. Since copper has particularly excellent thermal conductivity, the heat drying treatment is particularly effective in this embodiment. The anode-side contact element (11) is also preferably made of copper or nickel.

[0132] In the example illustrated herein, induction heating is essentially performed from below. However, in principle, it is also possible to perform induction heating from above, or alternatively, from below and above.

[0133] FIG. 2 shows a cross-sectional view through which an inductor (20) in the form of an induction coil is inserted into a transport plate (40) of a drying device according to the present invention.

[0134] FIG. 2A illustrates a transport plate (40) with a plurality of induction coils (20) embedded therein. The induction coils (20) may be cast, for example, from glass ceramic. The electrode-separator assembly (10) to be processed is placed on the transport plate (40) equipped with the induction coils (20). In the example illustrated herein, the electrode-separator assembly (10) is placed in a cylindrical housing cup.

[0135] To simplify the handling of the electrode-separator assembly (10) during the drying process, two different means of transport (51, 52) for holding the electrode-separator assembly are illustrated in the example shown herein. The means of transport (51) is a product made particularly of plastic or a transport cup, which simplifies the handling and holding of the electrode-separator assembly (10). The means of transport (52) is a spacer that ensures an appropriate distance between individual electrode-separator assemblies (10) while inserting and removing the electrode-separator assembly (10) into and out of the drying process and drying device. In particular, this prevents the electrode-separator assemblies (10) from coming into contact with each other and potentially damaging each other.

[0136] With the help of holding means (51, 52), individual electrode-separator assemblies (10) can be held upright in a simple manner. Alternatively, for example, a holding device preferably made of plastic can be used for a plurality of electrode-separator assemblies (10) to be processed. Such a holding device can be opened toward the bottom, i.e., the inductor (20), for example, to enable optimal induction heating.

[0137] In particular, by using a suitable holder, the electrode-separator assemblies (10) can be positioned on the inductors (20) without contact, thereby preventing the electrode-separator assemblies (10) from being scratched onto the base plate and thus being damaged.

[0138] FIG. 2B illustrates a single induction coil (20) in detail, wherein individual windings (21) of the induction coil (20) and electrical connections (22) of the induction coil (20) are shown. The induction coil (20) can operate in an alternating current, preferably in a regulated form, through the electrical connections (22). For example, a ferrite core may be placed in the center of the windings (not shown).

[0139] Figure 3 illustrates a schematic top view of a transport plate (40) of a drying device in which indicated induction coils (20) are regularly arranged. To perform a thermal drying process according to the present invention, a corresponding number of electrode-separator assemblies (10) to be processed are positioned above these induction coils (20). For this purpose, for example, an elongated gripper element (60) having a semicircular concave portion is used, thereby allowing the electrode-separator assemblies (10) to be positioned correctly on the induction coils (20), so that the drying process can be performed by supplying alternating current of a frequency corresponding to the induction coils (10). As an alternative to the gripper system, for example, a conveyor belt system or a pusher may be used.

[0140] In a preferred embodiment, the induction coil (20) may have a ferrite core, for example, in the form of a shell core half. This allows the magnetic field lines to be better concentrated on the electrode-separator assembly (10) to be processed. In another embodiment, the coil core may also be open.

[0141] During the drying process, each induction coil (20) can preferably be individually controlled at an appropriate frequency, so that individual electrode-separator assemblies (10) can, in principle, be dried individually. This may be particularly advantageous when there is a different heat distribution within the batch for a larger quantity of electrode-separator assemblies (10) to be processed.

[0142] In principle, it is possible to control multiple inductors or induction coils (20) together. However, special possibilities arise from the individual control of individual inductors that can heat the electrode-separator assemblies individually. In this way, different requirements for heating different electrode-separator assemblies, which may be designed differently, can also be considered. This means that, for example, various battery variants can be optimally dried in a single batch.

[0143] FIG. 4 illustrates an embodiment of the present invention in which two or more electrode-separator assemblies (10) are associated with an inductor (20) that generates an alternating magnetic field in an elongated range, wherein the two or more electrode-separator assemblies (10) may be arranged so as to be exposed to substantially the same magnetic field strength in the alternating field.

[0144] To this end, the coil windings (21) are wound around an elongated ferrite core (25). This provides nearly identical alternating magnetic fields for several electrode-separator assemblies (10) arranged side by side (see Figure A).

[0145] FIG. 4B shows a cross-section passing through the arrangement shown in A in the area of ​​arresters (22).

[0146] FIG. 4C illustrates a schematic longitudinal cross-section passing through the arrangement.

Claims

Claim 1 A method for thermal drying of a plurality of electrode-separator assemblies (10) having at least one negative electrode and at least one positive electrode, each comprising a metallic current collector coated with an electrode active material, namely an anode current collector and a cathode current collector, wherein the electrode-separator assemblies (10) are subjected to thermal drying through an inductor (20) that is inductively heated, comprising the following steps: a. the plurality of electrode-separator assemblies (10) are positioned within the effective range of the inductor (20) in a drying device; b. a vacuum is applied for the thermal drying; c. current is supplied to the inductor (20); d. exactly one inductor (20) is assigned to each of the electrode-separator assemblies (10) to be dried in the drying device; or e. A thermal drying method characterized in that two or more electrode-separator assemblies (10) are assigned to an inductor that generates an alternating magnetic field of an elongated range, and the two or more electrode-separator assemblies (10) can be arranged so as to be exposed to essentially the same magnetic field strength in the alternating magnetic field. Claim 2 A heat drying method according to claim 1, having at least one of the following additional features: a. the electrode-separator assembly (10) is heated to a temperature greater than 99°C and below the melting point of the separator of the electrode-separator assembly, b. the electrode-separator assembly (10) is heated to a temperature in the range of 100°C to 110°C. Claim 3 A heat drying method according to claim 1, wherein the following additional features: a. the electrode-separator assembly (10) is formed as a winding and has a cylindrical base shape having two terminal end faces, b. the electrode and each current collector are ribbon-shaped and are spirally wound within the electrode-separator assembly (10). Claim 4 In paragraph 3, the following additional features: a. the cathode and the anode are disposed within the electrode separator assembly (10), such that the longitudinal edge of the anode current collector protrudes from one of the terminal end faces and the longitudinal edge of the cathode current collector protrudes from the other of the terminal end faces; b. a contact element (11, 12), wherein a contact plate is attached to at least one of the end faces and covers at least 50% of each end face, comprising a heat drying method. Claim 5 A thermal drying method having at least one of the following additional features in claim 3 or 4: a. when the electrode-separator assembly (10) is positioned in the drying device, the electrode-separator assembly (10), formed as a winding, is aligned parallel to each other on the transport plate (40) of the drying device, and one of the end faces of the winding faces the transport plate (40) and the other of the end faces of the winding faces in a direction away from the transport plate (40); b. the inductor (20) or the inductors (20) are positioned in the transport plate (40) or below the transport plate (40); c. after the electrode-separator assembly (10) is positioned in the drying device, the inductor (20) or the inductors (20) are separated from the electrode-separator assembly (10) by a dielectric. Claim 6 In claim 5, the following additional features: a. the electrode-separator assembly (10) formed as a winding is inserted into a metallic housing cup that is cylindrical and has a cup base, and is inductively heated inside the housing cup; b. at least one of the following, wherein the electrode-separator assembly (10) formed as a winding is positioned in the drying device together with the metallic housing cup, so that the housing bottom of the housing cup stands on the conveying plate (40) of the drying device. Claim 7 A heat drying method according to claim 1, having at least one of the following additional features: a. individual inductors (20) are operated in a controlled manner, b. at least one performance value is measured in individual inductors (20). Claim 8 A heat drying method according to claim 1, having at least one of the following additional features: a. the inductor or the inductors (20) are induction coils, b. the diameter of the inductors (20) and the diameter of the electrode-separator assembly (10) differ from each other by up to 20%. Claim 9 In claim 1, the following additional features: a. A heat drying method comprising performing the heat drying treatment immediately before impregnating the electrode-separator assembly (10) with an electrolyte. Claim 10 A drying device for performing a thermal drying process according to claim 1, having the following features: a. the drying device comprises at least one vacuum chamber; b. the drying device comprises a plurality of inductors (20) in a regular arrangement, induction coils, or at least one inductor that generates an alternating magnetic field of an elongated range, wherein two or more electrode-separator assemblies (10) may be arranged to be exposed to essentially the same magnetic field strength in the alternating magnetic field; c. the drying device comprises at least one device for supplying current to the inductors or inductors, wherein the inductors (20) or inductors (20) are placed on a carrying plate (40) of the drying device, cast on the carrying plate (40), or placed below the carrying plate (40) of the drying device. Claim 11 delete Claim 12 In claim 10, the following additional features: a. the drying device comprises means for transferring the electrode-separator assembly (10) to be processed into and / or removed from the drying device; b. the drying device comprises means for positioning the electrode-separator assembly (10) to be processed for individual inductors (20); c. the drying device comprises at least one of means for holding the electrode-separator assembly to be processed (51, 52). Claim 13 In paragraph 10, the following additional features: a. The drying device comprises a device for measuring the performance of the inductor (20) or the inductors (20). Claim 14 In paragraph 10, the following additional features: a. A drying device having a self-vibrating resonant converter assigned to the inductor (20) or each of the inductors (20).

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