METHOD AND DEVICE FOR THE THERMAL DRYING TREATMENT OF ELECTRODE-SEPARATOR COMPLEXES BY MEANS OF INDUCTION

Description

[0001] The present invention relates to a method for the thermal drying treatment of a plurality of electrode-separator assemblies and to a drying device for carrying out the method. SCOPE OF APPLICATION AND STATE OF THE ART

[0002] Electrochemical energy storage devices are capable of converting stored chemical energy into electrical energy through a redox reaction. The simplest form of an electrochemical energy storage device is the electrochemical cell. It comprises a positive electrode and a negative electrode, separated by a separator. During discharge, electrons are released at the negative electrode through an oxidation process. This results in an electron current that can be drawn from an external electrical device, for which the electrochemical cell serves as an energy source. Simultaneously, an ion current corresponding to the electrode reaction occurs within the cell. This ion current passes through the separator and is facilitated by an ion-conducting electrolyte.

[0003] If the discharge of the electrochemical energy storage element is reversible, meaning that the conversion of chemical energy into electrical energy during discharge can be reversed and the cell or element recharged, it is referred to as a secondary energy storage element. The common designation of the negative electrode as the anode and the positive electrode as the cathode for secondary energy storage elements refers to the discharge function of the electrochemical energy storage element.

[0004] In the present context, the term "electrochemical energy storage element" refers not only to a single electrochemical cell, but also to a battery comprising a plurality of individual electrochemical cells.

[0005] Among known secondary electrochemical energy storage devices, comparatively high energy densities are achieved, particularly by lithium-ion cells. Besides the use of cell stacks consisting of several individual cells, each with at least one positive and at least one negative electrode, lithium-ion cells with a coiled electrode-separator assembly are widespread. Such an assembly often exhibits the sequence "positive electrode / separator / negative electrode". Furthermore, such individual cells can be configured as so-called bicells with the possible sequences "negative electrode / separator / positive electrode / separator / negative electrode" or "positive electrode / separator / negative electrode / separator / positive electrode".

[0006] The electrodes of lithium-ion cells typically consist of metallic current collectors, usually in the form of foils, meshes, grids, foams, fleeces, or felts. For the positive electrode, current collectors are usually made of aluminum, for example, expanded aluminum metal or aluminum foil. For the negative electrode, current collectors are usually made of copper.

[0007] The described cells for lithium-ion energy storage elements are typically produced in a multi-stage process. Usually, the electrodes are manufactured in a first step and then combined with one or more separators to form the aforementioned electrode-separator assemblies. Electrodes and separators can be loosely stacked or wound, or bonded together in a lamination step.

[0008] To manufacture the electrodes for lithium-ion cells, thin electrode films are formed on the current collectors from mostly paste-like compositions containing a suitable electrochemically active material (or "active material" for short). This is done, for example, using a doctor blade or a slot die. Active materials suitable for the electrodes of a lithium-ion cell must be able to absorb and release lithium ions, which migrate from the negative to the positive electrode (and vice versa) during charging and discharging.

[0009] Suitable active materials for the negative electrodes of lithium-ion cells include, in particular, graphitic carbon or non-graphitic carbon materials capable of lithium intercalation. Furthermore, metallic and semi-metallic materials that can be alloyed with lithium can also be used. For example, the elements tin, antimony, and silicon are able to form intermetallic phases with lithium. In particular, the carbon-based active materials can also be combined with the metallic and / or semi-metallic materials.

[0010] For positive electrodes, lithium cobalt oxide (LCO) with the molecular formula LiCoO₂, lithium nickel manganese cobalt oxide (NMC) with the molecular formula LiNi x Mn y Co z O₂, lithium manganese spinel (LMO) with the molecular formula LiMn ₂O₄, lithium iron phosphate (LFP) with the molecular formula LiFePO₄, or lithium nickel cobalt aluminum oxide with the molecular formula LiNi x Co y Al z O₂ (NCA) are particularly suitable. Mixtures of the aforementioned materials can also be used.

[0011] In addition to the active materials, these mostly paste-like compositions typically contain an electrode binder (or simply "binder"), a conductivity enhancer, a solvent and / or suspension agent, and possibly additives, for example, to influence their processing properties. An electrode binder forms a matrix in which the active material and, if applicable, the conductivity enhancer can be embedded. The matrix is ​​intended to provide increased structural stability during the volume expansions and contractions caused by lithiation and delithiation. Suitable solvents and / or suspension agents include, for example, water or organic solvents such as N-methyl-2-pyrrolidone (NMP) or N-ethyl-2-pyrrolidone (NEP). Sodium carboxymethylcellulose (Na-CMC) is an example of a binder that can be processed in aqueous solutions. Polyvinylidene fluoride (PVDF) is an example of a binder that can be processed in organic solvents.Rheology aids, for example, can be added as additives. The conductivity improver is usually an electrically conductive, carbon-based material, in particular conductive carbon black, conductive graphite, carbon fibers, or carbon nanotubes.

[0012] Solvents and / or suspending agents contained in the compositions are typically found in the electrode films formed on the current collectors and must be removed. The dry electrode films can then be compacted, for example, in a calendering process. The electrodes thus formed can be used to create the cells mentioned earlier.

[0013] Drying electrode films formed on current collectors, i.e., removing the solvent and / or suspension agent contained in the electrode films, as well as removing any residual moisture that may remain in the electrode-separator assemblies, is time-consuming and energy-intensive. Conventionally, the electrode films can be dried using a temperature-controlled gas, particularly temperature-controlled air. The gas heats the electrode film, causing any solvent and / or suspension agent, or any residual moisture, to evaporate and escape. This heating process initially occurs at the surface of the electrode film and then gradually spreads into the interior of the film.Accordingly, drying also progresses gradually from the outside in; an outer layer of the electrode film may already be dry, while the electrode film in a layer adjacent to the current collector still contains significant amounts of solvent and / or suspension agent. This can be problematic because a film-like residue often remains when the solvent and / or suspension agent is removed. If this residue forms in an outer layer of the electrode film, it can significantly delay further drying, as the solvent and / or suspension agent can no longer easily escape from the layer adjacent to the current collector. In some cases, bubbles may even form. Attempts are made to counteract this, in particular, by using sufficiently long drying times. With slow drying, the observed drying gradient occurs only to a small extent.However, deliberately slowing down the drying process increases the already considerable time required.

[0014] As part of the manufacturing process for lithium-ion cells, it is particularly important to remove any residual moisture from the electrode-separator assemblies before filling the cell with electrolyte. This is conventionally done via an oven process, usually using vacuum ovens, in which either the electrodes are dried before the winding process or the coiled electrode-separator assemblies are dried in a housing cup immediately before electrolyte filling. For mass production, a batch, typically consisting of several hundred cells, is usually placed in a carrier ( tray The furnace chamber is heated to approximately 100 °C for several hours to remove any remaining moisture. This process typically involves multiple cycles of vacuum and nitrogen purging to extract the moisture from the furnace chamber.

[0015] However, this approach presents several challenges. First, introducing heat into such an oven is generally difficult, as direct circulation of the drying medium is not possible in a vacuum. Simultaneous and homogeneous heating of the cells is therefore challenging. Uniform heating is only achievable with the addition of nitrogen or another gas.

[0016] Furthermore, it is problematic that in such a conventional furnace process, heating occurs via contact heat, for example, by placing the cells on a hot support plate of the furnace. In a vacuum, unevenness between the plate and the cells can disrupt heat transfer, since no heat transport by convection occurs in a vacuum, and the vacuum even acts as insulation. This easily leads to uneven heating of the cells.

[0017] Furthermore, in a conventional oven process, it is important to ensure that the cells are not overheated, as this can damage the cells, particularly the separator. This is difficult when heating with a conventional hot plate due to the heat and time losses involved, which can sometimes lead to temperature overshoot and thus to a loss of quality in the cells being dried.

[0018] In a conventional oven process, it remains problematic when an electrode-separator assembly is to be dried in the oven if it is already housed in a cell or casing. In this case, the cell itself is primarily heated. Direct heat conduction to the electrodes and current collectors occurs mainly via the electrode weld points or any existing metallic contact plates. Heat transfer is therefore poor. Furthermore, a small gap often exists between the inside of the casing and the electrode-separator assembly, which further impedes heat transfer.

[0019] Finally, achieving homogeneity of the drying treatment across the entire batch of cells is difficult with a conventional oven process. Generally, outer cells of a batch reach a different temperature than inner cells during the drying process. During the drying treatment, the temperature must not be too high to avoid damaging components, particularly the separator. Conversely, the temperature must not be too low to ensure that the moisture evaporates completely. Overall, the required temperature range is very narrow, and maintaining it for a sufficient duration across all cells of the batch is challenging.

[0020] It is already known to dry electrodes by heating them using inductively generated eddy currents. For example, EP 3 439 079 B1 describes a method for the thermal treatment of electrode films on a metallic current collector, in which the current collector is inductively heated by means of an induction device. However, the method described there primarily offers a solution for drying electrode strips immediately after their coating. Satisfactory results cannot be expected with this method for the simultaneous drying of a large number of already wound electrode-separator assemblies.

[0021] From JP 4292453 B2, a method and a drying device for the thermal drying treatment of an electrode-separator assembly are known, wherein the thermal drying treatment is carried out by means of two inductors with which the assembly is inductively heated.

[0022] From US 2004 / 208222 A1, a vacuum chamber for the induction heating and / or melting of a metal is known in which a significant part of the magnetic field generated in the vacuum induction heating and / or melting process comes into contact with the wall of the chamber without the chamber wall being overheated by the induction heating. TASK AND SOLUTION

[0023] Against this background, the invention aims to provide an improved method and a corresponding device for drying electrode-separator assemblies, enabling the rapid and uniform drying of a large number of electrode-separator assemblies and, in particular, the removal of residual moisture during the manufacturing process of lithium-ion energy storage elements. Furthermore, the method is intended to be faster and more efficient compared to conventional processes, while simultaneously enabling energy savings.

[0024] This problem is solved by a method as defined in claim 1. Furthermore, this problem is solved by a drying device according to the further independent claim. Preferred embodiments and configurations of the method and the drying device are the subject of the dependent claims.

[0025] The method according to the invention serves 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 the form of a batch.

[0026] The electrode-separator assemblies each comprise at least one positive and at least one negative electrode, as well as at least one separator. The electrodes themselves each comprise a metallic current collector coated with electrode active material. In the case of the negative electrode, this is an anode current collector, and in the case of the positive electrode, it is a cathode current collector. The thermal drying treatment is preferably carried out contactlessly using inductors. In this process, the electrode-separator assemblies are preferably heated inductively without direct contact with the inductors.

[0027] The method according to the invention comprises the following steps: a. The majority of electrode-separator assemblies are placed in a drying device within the effective range of the inductors, b. a vacuum is applied for thermal drying treatment, and c. the inductors are energized.

[0028] The method according to the invention is further characterized in that d. each of the electrode-separator assemblies to be dried is assigned to exactly one inductor in the drying device, or e. more than two electrode-separator assemblies are assigned to one inductor which generates an alternating magnetic field of elongated extent in which the more than two electrode-separator assemblies (10) can be arranged so that they are each exposed to a substantially equal magnetic field strength in the alternating field, f. wherein the electrode-separator assemblies (10) are heated to a temperature above 99 °C and below the melting temperature of the separator of the electrode-separator assemblies.

[0029] The inventive method is based on the generation of an alternating magnetic field by the inductor, which can act on the metallic components of the electrode-separator assemblies, in particular on the current collectors. The eddy currents generated in the metallic components thereby lead to heating, which in turn causes any moisture present in electrode films deposited on the current collectors to evaporate. Compared to conventional furnace processes, the heating occurs much more directly and quickly, so that a considerable time saving is possible with the inventive method.

[0030] According to the inductive principle of the method according to the invention, the inductors are supplied with an alternating current. Depending on the frequency and / or amplitude of the alternating current, the temperature during the drying treatment can be adjusted accordingly.

[0031] Both the embodiment according to the preceding feature d. and the embodiment according to the preceding feature e. ensure that the electrode-separator assemblies to be dried are exposed to identical drying conditions, so that drying can take place uniformly and quickly.

[0032] The application of a vacuum is carried out in a manner known per se, as is also known, for example, from conventional furnace processes. In particular, a vacuum pump is used for this purpose, which generates a negative pressure, i.e., a pressure that is lower than the ambient pressure. Preferably, a pressure below 300 mbar is set, for example, a pressure in the range between 20 mbar and 100 mbar.

[0033] In contrast to conventional electrode drying methods that already operate on an inductive basis, the core of the inventive method according to the embodiment with the aforementioned feature d. lies primarily in the fact that each electrode-separator assembly to be dried is assigned to an inductor in order to achieve highly targeted and directional heating of the electrode-separator assembly. This allows any residual moisture present in the electrode-separator assembly to be removed safely and quickly in a particularly effective and simultaneously energy-saving manner.

[0034] The core of the inventive method according to the embodiment with the preceding feature d. achieves the same effect, except that here several electrode-separator assemblies can be assigned to one inductor and are thereby exposed to identical drying conditions. With a magnetic field generated by a coil with an annular cross-section, it is difficult to position several coils in such a way that they are exposed to nearly identical magnetic field forces. An elongated magnetic field, such as that which can be generated by an equally elongated inductor, makes this possible.

[0035] It is possible to build such inductors in a length that allows for the uniform drying of a dozen or more electrode-separator assemblies arranged in a row.

[0036] A drying device according to the invention preferably comprises more than one such elongated inductor, on which several electrode-separator assemblies can be arranged.

[0037] The inventive method according to the embodiment with the preceding feature d. can optionally be individually controlled and / or regulated for individual electrode-separator assemblies, so that no damaging overtemperatures occur in individual cells. Furthermore, the inventive method achieves a high degree of heating homogeneity across an entire batch, since mechanical and magnetic tolerances can be compensated for by individually heating the individual electrode-separator assemblies via individual inductors. Each electrode-separator assembly in the batch can be heated and dried uniformly, so that hotspots or other uneven heat distributions do not form in the batch.

[0038] The construction of a suitable drying device is also significantly easier and requires less material compared to conventional drying ovens. In particular, no conductive medium, such as oil or water, is necessary, which is used to heat the oven drawers in conventional oven processes.

[0039] Furthermore, the inventive method allows, in principle, different drying curves for different types of electrode-separator assemblies to be operated in a drying device, for example, drying curves for one energy type and other drying curves for one power type in the electrode-separator assemblies, since the individual inductors can be operated individually.

[0040] Above all, the inventive method allows for significant energy savings compared to conventional methods. Compared to a conventional furnace process, in which support materials for the cells, e.g., pallets, also have to be heated, energy savings in the range of 50% to 75% are possible.

[0041] For the insertion and placement of the electrode-separator assemblies, the individual assemblies can, for example, be pushed directly into the drying unit and positioned within the effective range of the respective inductor. The use of a carrier pallet, as in conventional processes, is not strictly necessary, thus eliminating the step of storing and repositioning the electrode-separator assemblies in and out of the carrier pallets. Since the inductor transfers the energy required for drying without contact, the quality requirements, particularly the flatness of the surface on which the electrode-separator assemblies are arranged, can be relatively low. Due to the contactless transfer, any unevenness present is irrelevant. In the case of contact heat, however, the size of the contact area is crucial.

[0042] In other preferred embodiments, product carriers, for example transport cups, can be used. (Pucks) or other carrier materials. These product carriers are advantageously made of electrically non-conductive material, e.g., plastic, so that they do not interact with the inductive heating process and are not heated along with it, and therefore do not cause any energy losses.

[0043] In conventional furnace processes, the use of carrier pallets is disadvantageous due to the associated additional energy consumption during heating and cooling, as the carrier pallets are inevitably heated along with the electrode-separator assemblies being treated. In the process according to the invention, only the electrode-separator assemblies can be heated selectively. Even when product carriers are used, the carriers themselves do not heat up if the material is selected appropriately, making the process according to the invention significantly more time- and energy-efficient compared to conventional processes.

[0044] If the electrode-separator assemblies to be treated are inserted directly or supported by individual product carriers into the drying device, the electrode-separator assemblies can be piled up on a surface with the inductors, in particular a carrier plate of the drying device, in such a way that the individual electrode-separator assemblies are each placed above an inductor.

[0045] After the electrode-separator assemblies to be treated have been placed, a vacuum hood can be lowered over them, for example, and the drying process can be started.

[0046] After the heating process is complete, the individual electrode-separator assemblies can be conveyed further, for example using a slide, and separated again. Compared to handling with a carrier pallet, this offers significant advantages for the further processing of the electrode-separator assemblies.

[0047] In particularly preferred embodiments, the method is characterized by the following additional feature: a. The electrode-separator assemblies are heated to a temperature in the range of 100 °C to 110 °C.

[0048] For effective heating that leads to the evaporation of any residual moisture, it is ideal to reach a temperature above the boiling point of the moisture or the residual moisture during the drying process. A temperature of 100 °C or higher is therefore preferably set. The target temperature range is expediently selected to prevent damage to the electrode-separator assemblies being treated. The critical component is generally the separator, which can be made, for example, of microporous plastics or nonwovens of glass fiber or polyethylene. The separator can also consist of nonwovens with a ceramic coating. To reliably prevent damage to the electrode-separator assemblies, a temperature range of 100 °C to 110 °C is particularly suitable for the drying process.

[0049] Compared to conventional oven processes, the drying time in the inventive method can be significantly reduced by the particularly targeted and effective heating of the electrodes.

[0050] In particularly preferred embodiments, the method according to the invention is characterized by at least one of the following additional features: a. The electrode-separator assemblies are each formed as coils and have a cylindrical shape with two end faces. b. The electrodes and their respective current collectors are ribbon-shaped and are spirally wound within the electrode-separator assemblies.

[0051] Preferably, the aforementioned features a. and b. are realized in combination with each other.

[0052] Since the inventive method, based on inductive heat transfer, can be carried out much more directly and quickly than conventional methods and does not require contact heat as in conventional furnace processes, the inventive method is very flexible in the manufacturing process of energy storage elements. In principle, the inventive method can also be used for pure electrode drying. However, it is particularly preferred that the inventive method be used to dry pre-wound electrode-separator assemblies.

[0053] In a particularly preferred embodiment, the method according to the invention is characterized by the following additional features: a. The negative electrode and the positive electrode are arranged within the electrode-separator assemblies such that a longitudinal edge of the anode current collector emerges from one of the terminal end faces and a longitudinal edge of the cathode current collector emerges from the other terminal end face. b. A contact element, in particular a contact plate, is attached to at least one of the end faces, covering at least 50% of the respective end face.

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

[0055] The application of the drying treatment according to the invention for energy storage elements in the known per se, so-called contact plate design according to the aforementioned features a. and b. offers particular advantages, since the contact element, for example a contact plate, which is in direct contact with one of the current collectors, significantly promotes inductive heating.

[0056] Such a contact plate design is described, for example, in WO 2017 / 215900 A1. This document describes cylindrical cells with a coiled electrode-separator assembly. The oppositely polarized electrodes are arranged offset from each other within the electrode-separator assembly, so that longitudinal edges of the current collectors of the positive electrodes protrude from one end face and longitudinal edges of the current collectors of the negative electrodes protrude from the other end face of the coil. For electrical contact of the current collectors, the cell has a contact plate that sits on one end face of the coil and is connected to a longitudinal edge of one of the current collectors, for example, by welding. This makes it possible to electrically contact the current collector, and thus also the associated electrode, along its entire length. This significantly reduces the internal resistance within the cell.Compared to conventional cells, the occurrence of large currents can be absorbed much better, and heat can also be dissipated more effectively from the winding.

[0057] The contact plate design of the electrode-separator assemblies, which can be dried according to the invention, can for example be designed such that the contact element is designed in particular as a contact sheet or as a metallic plate, wherein openings in the plate can also be provided so that only a certain proportion of the respective end face is covered with the contact element, for example 50% or preferably more.

[0058] The contact element can be made, for example, of nickel, copper, titanium, a nickel, copper, or titanium alloy, stainless steel, or nickel-plated copper. These materials are particularly preferred for a contact element connected to the anode current collector. A contact element intended for connection to the cathode current collector is preferably made of aluminum or an aluminum alloy.

[0059] The contact element can, for example, 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 form of a disk or a polygonal plate. The contact element preferably covers 60% or more of the respective end face and can have an opening, in particular a hole or a slot, or optionally several holes or slots.

[0060] The inventors were able to determine that, in the inventive method, heating of an electrode-separator assembly with a contact element occurs significantly faster and more effectively. This is presumably due, among other things, to the fact that the contact element provides more mass to absorb the magnetic field lines. Furthermore, the contact element can be oriented favorably with respect to the field lines. In combination with a contact element, the inventive method therefore allows for particularly fast, effective, and directed heating and thus drying of the electrode-separator assembly.

[0061] With regard to the placement of the electrode-separator assemblies in the drying device, the method according to the invention is characterized in preferred embodiments by at least one of the following additional features: a. When placing the electrode-separator assemblies in the drying device, the coiled electrode-separator assemblies are aligned parallel to each other on a carrier plate of the drying device, with one end face of the coil facing the carrier plate and the other end face away from the carrier plate. b. The inductor(s) are arranged in or under the carrier plate. c. After the electrode-separator assemblies are placed in the drying device, the inductor(s) are separated from the electrode-separator assemblies by a dielectric.

[0062] Preferably, the aforementioned features a. and b. are realized, and in a particularly preferred manner, the aforementioned features a., b. and c. are realized in combination with one another.

[0063] The support plate of the drying device is preferably a base or base plate within the drying device, wherein the inductor or inductors for the electrode-separator assemblies are arranged in or under this base or base plate or, more generally, the support plate.

[0064] According to the aforementioned feature c., a dielectric, i.e., a non-conductor, is located between the electrode-separator assemblies and the inductors after placement. This can, for example, be a glass-ceramic that covers the inductor(s) in the carrier plate. According to the principle of inductive heating, heat transfer occurs via electromagnetic field lines, which only induce heating in a metallic substrate, i.e., in particular in the current collectors and / or the contact elements of the electrode-separator assemblies, if present. Therefore, a covering glass-ceramic or similar material will not be heated within the scope of the method according to the invention.

[0065] In a particularly preferred embodiment, the electrode-separator assemblies are positioned such that an end face of the electrode-separator assemblies, which may preferably be provided with a contact element, is aligned with or faces the carrier plate. It is especially preferred that the anodic side of the electrode-separator assemblies faces the carrier plate with the inductors. In some embodiments, however, the cathodic side of the electrode-separator assemblies may also face the carrier plate with the inductors.

[0066] Preferably, the anode-side contact element is placed on the carrier plate. Preferably, the anode-side contact element is made of copper or nickel and / or the anode current collector is made of copper. This allows for particularly good inductive heating.

[0067] In principle, the method according to the invention is also suitable for heating a cathode-side contact element, which is made of aluminium, for example.

[0068] In further embodiments, the electrode-separator assembly, with or without contact elements, can be dried together with a housing cup, for example a metallic housing cup, according to the inventive method. In preferred embodiments, the inventive method is therefore characterized by at least one of the following additional features: a. The electrode-separator assemblies, designed as coils, are inserted into a cylindrical metallic housing cup with a cup bottom and are inductively heated inside the housing cup. b. To position the electrode-separator assemblies, the coiled electrode-separator assemblies, together with the metallic housing cup, are placed in the drying device so that the base of the housing cup rests on the support plate of the drying device.

[0069] Preferably, the aforementioned features a. and b. are realized in combination with each other.

[0070] Drying treatment can also be effectively carried out in conjunction with a housing cup. Inductively generated heating of the cup can also be transferred to the electrode-separator assembly, further increasing the heating efficiency. In combination with one or two contact elements in the electrode-separator assembly, the heating efficiency can be increased even further, since in this case, the contact elements located inside the cup, or the contact element itself, are also inductively heated, thus generating heat within the cup as well. The energy supply is very direct due to the inductive process, so only minimal electrical power is required to optimally perform the drying process.

[0071] A drying treatment performed solely on the electrode-separator assembly, or solely on the electrode-separator assembly with one or two contact elements, offers a particular advantage over heating the electrode-separator assembly within a cup: no energy is required to heat the cup. This can be advantageous in certain circumstances. However, there are also cases where, for production reasons, it is more beneficial to subject the electrode-separator assembly to the drying treatment within the housing cup. Since the inventive method is generally very efficient and saves both energy and time, this approach also offers advantages compared to conventional methods.

[0072] A particular advantage of the method according to the invention is that highly targeted and individually adjustable heating of the individual electrode-separator assemblies is possible via the individual inductors, each of which is assigned to the electrode-separator assemblies to be treated. In particularly preferred embodiments of the method according to the invention, at least one of the following additional features is provided in this context: a. The individual inductors are operated in a controlled manner. b. At least one power parameter in each inductor is measured.

[0073] Preferably, the aforementioned features a. and b. are realized in combination with each other.

[0074] By controlling the operation of the individual inductors (in an embodiment of the invention according to feature d. of claim 1), it is possible to compensate for the uneven heat input that may occur due to the arrangement in the batch, so that, for example, hotspots or other uneven heat distributions do not develop within the batch. In other embodiments, however, control may be omitted. It may also be provided that several inductors are switched and / or controlled together. This is provided for in particular in an embodiment of the invention according to feature e. of claim 1.

[0075] With conventional methods, it cannot be guaranteed that every single electrode array within a batch absorbs the same amount of heat. This can be due to unevenness or, more generally, to the fact that the applied energy cannot reach all cells equally.

[0076] By measuring performance, such as current or temperature, in individual inductors or, if necessary, in a group of inductors, it can be verified whether the heating in the respective assigned electrode-separator assembly(s) has actually been carried out optimally as intended. Such performance measurement thus enables quality control, ensuring sufficient and reliable heating and drying for all electrode-separator assemblies in the entire batch. Insufficient drying of individual electrode-separator assemblies can also be identified in this way as part of quality control, and the corresponding electrode-separator assemblies can be rejected if necessary.

[0077] With regard to the inductors, the method according to the invention is characterized by at least one of the following additional features: a. The inductor or inductors are induction coils. b. The diameter of the inductors used according to feature d. of claim 1, in particular the induction coils, and the diameter of the electrode-separator assemblies, in particular the electrode-separator assemblies designed as windings with a cylindrical basic shape, differ from each other by a maximum of 20%.

[0078] In embodiments with feature d. of claim 1, the aforementioned features a. and b. are preferably implemented in combination with each other.

[0079] In principle, any device capable of generating an alternating electric field that can induce an eddy current in a metallic substrate can serve as an inductor. Particularly preferred are induction coils, especially coils with multiple turns, or induction devices comprising at least one such coil. The induction coils are preferably wound in a flat, spiral shape and, in preferred embodiments, consist essentially of, for example, copper wire or coated copper wire.

[0080] By matching the diameter of the inductors, especially the induction coils, to the diameter of the electrode-separator assemblies being treated, particularly efficient energy utilization can be achieved. However, since the process is generally very efficient, certain deviations in the fit between the inductors and the electrode-separator assemblies are acceptable. For example, a 20% variance in the aforementioned diameters is still sufficient to perform the drying treatment in a very energy-efficient and rapid manner.

[0081] In some cases, larger deviations between the diameters of the inductors and the electrode-separator assemblies may be acceptable. This makes it possible to treat electrode-separator assemblies of different dimensions with the same drying device.

[0082] The method according to the invention is particularly suitable for a thermal drying treatment carried out immediately before the electrode-separator assemblies are impregnated with an electrolyte during the manufacturing process of the energy storage elements. In particular, at this step, i.e., before impregnation with an electrolyte, any residual moisture should be removed from the electrode-separator assemblies. The residual moisture that can be removed according to the invention may, for example, have entered the electrode-separator assemblies during intermediate storage during the manufacturing process. The method according to the invention allows the post-drying step to be carried out in a particularly time- and energy-efficient manner.

[0083] The method according to the invention is particularly suitable for cylindrical cells, since it allows for the use of an optimal round coil shape for the inductors, which corresponds to the round cross-section of a cylindrical cell.

[0084] The inventive method is particularly suitable for use in the production process of lithium-ion cells, preferably cylindrical lithium-ion cells, and can especially be used in mass production. The energy and time-saving potential of the inventive method is particularly evident in mass production processes.

[0085] The invention further comprises a drying device for carrying out a thermal drying treatment, in particular according to the described method. This drying device is characterized by the following features: a. The drying device comprises at least one vacuum chamber. b. The drying device comprises a plurality of inductors, in particular induction coils, preferably in a regular arrangement, or it comprises at least one inductor that generates an elongated alternating magnetic field in which the more than two electrode-separator assemblies can be arranged so that they are each exposed to a substantially equal magnetic field strength in the alternating field. c. The drying device comprises at least one device for supplying current to the inductor or inductors. d. The inductor or inductors are arranged in or beneath a support plate of the drying device.

[0086] A vacuum chamber of a drying device according to the invention is preferably defined by a vacuum hood, preferably a retractable vacuum hood, which can enclose one or more of the electrode-separator assemblies to be dried so that they can be exposed to a corresponding negative pressure. In many cases, it is preferred that a plurality of electrode-separator assemblies are arranged together in a vacuum chamber, i.e., enclosed by a vacuum hood. However, the device according to the invention can also include a separate hood for each of the electrode-separator assemblies to be dried. In this case, each of the electrode-separator assemblies is arranged in its own vacuum chamber.

[0087] For further details of this drying device, reference is also made to the procedure described above, which can be carried out with such a drying device.

[0088] The device for supplying current to the inductors preferably comprises a control device for the individual inductors or, optionally, for a plurality of inductors, so that the inductors can be operated individually or in groups at a suitable alternating current frequency. Depending on the design of the drying device, it is also possible to control all inductors together at the same frequency.

[0089] The drying device according to the invention is particularly preferably characterized by the following additional feature: a. The inductor or inductors are cast into the carrier plate.

[0090] As explained above, the inductors are preferably known induction coils arranged in the support plate, for example, a base plate, of the drying device. The coils can be covered by a plate or a layer of electrically non-conductive material, such as a glass ceramic. The inductors themselves are preferably flat-wound induction coils, particularly made of copper wire. Optionally, the induction coil can be equipped with a ferrite core to further focus the magnetic field lines onto the electrode-separator assemblies to be treated. In this case, a flat winding of the induction coils is not necessary.

[0091] With regard to the loading and placement of the electrode-separator assemblies to be treated, the drying device according to the invention is characterized in preferred embodiments by at least one of the following additional features: a. The drying device comprises means for introducing and / or removing the electrode-separator assemblies to be treated into and / or from the drying device, b. the drying device comprises means for placing the electrode-separator assemblies to be treated in relation to the inductor or individual inductors, c. the drying device comprises support means for holding the electrode-separator assemblies to be treated.

[0092] 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.

[0093] The transport means can be, for example, one or more slides with which the individual electrode-separator assemblies are inserted into the interior of the drying device. The inductors in or under the carrier plate of the drying device can be arranged such that, when the electrode-separator assemblies are inserted at maximum packing capacity, each assembly is assigned one inductor, or that the electrode-separator assembly is placed directly above an inductor on the carrier plate. This precise alignment of the electrode-separator assemblies can be supported, for example, by appropriate lateral bands or stops, which simplify correct placement of the electrode-separator assemblies.

[0094] Correct placement of the electrode-separator assemblies on the drying device's carrier plate can also be facilitated by other means, such as a gripper. A gripper can be used to grasp one or more electrode-separator assemblies at a time and place them in the correct position on the carrier plate.

[0095] Furthermore, support means can be provided for holding the electrodes, for example, transport cups or pallets, or similar items, which facilitate placement and holding. These support means can be designed as single or multiple holders for several electrode-separator assemblies. Preferably, such support means can be made of plastic or other non-metallic materials, and preferably of materials with non-conductive or low thermal conductivity, so that they do not interact with the inductive heating. The use of such support means, for example, transport cups, can be particularly helpful during the drying treatment of the pure electrode-separator assemblies, with or without contact elements, as this avoids the need for direct contact with the sensitive electrode-separator assemblies during the drying process.

[0096] Preferably, each inductor can be switched individually or, if necessary, as a group, and preferably controlled.

[0097] In particularly advantageous embodiments, the drying device comprises a power measurement device for the inductor or inductors. Particularly in embodiments where each electrode-separator assembly is assigned an inductor, power measurement can preferably be provided for each individual inductor or, optionally, for a group of inductors. The power measurement can be, for example, the current drawn and / or the temperature and / or the time. A temperature sensor can, for example, be integrated into each inductor. By means of power measurement, the progress of the drying treatment can, in principle, be recorded for each individual electrode-separator assembly and also traced for quality control purposes.Furthermore, such power measurement allows for controlled operation of the individual inductors, ensuring, for example, a homogeneous and uniform drying treatment over an entire batch.

[0098] Power measurement can also be used to initially determine the energy required for an electrode-separator assembly at a specific position within the batch or at a specific position on the drying device's carrier plate. The inductor can then be adjusted accordingly for subsequent drying processes, ensuring consistent drying quality without having to record the relevant values ​​for each drying cycle.

[0099] In further preferred embodiments of the drying device according to the invention, each inductor can be assigned a self-oscillating resonant converter. For example, a self-oscillating Royer converter can be used. The resonant converter can be self- or externally controlled; regardless of the type of control, it generally operates efficiently and causes only minimal EMC interference. In some embodiments, the externally controlled resonant converter is preferred because it offers better frequency control.

[0100] Further features and advantages of the invention will become apparent from the following description of exemplary embodiments in conjunction with the drawings. The individual features can be implemented individually or in combination with one another. BRIEF DESCRIPTION OF THE DRAWINGS

[0101] The drawings show: Fig. 1 schematic representation of components involved in the method according to the invention; Fig. 2A, B sectional views of the inductors inserted into a carrier plate of a drying device; Fig. 3 schematic top view of the carrier plate of a drying device; and Fig. 4 sectional views of an inductor inserted into a carrier plate of a drying device. DETAILED DESCRIPTION OF THE EXECUTION EXAMPLES

[0102] Out of Fig. 1 Several components for carrying out the method according to the invention are described, wherein a plurality of electrode-separator assemblies 10 are simultaneously subjected to a thermal drying treatment based on inductive heating. An important aspect of the method is that exactly one inductor 20 is assigned to each electrode-separator assembly 10 to be treated. The thermal drying treatment is carried out in a vacuum, wherein, in the embodiment shown here, a vacuum hood 30 is lowered over the electrode-separator assemblies 10 to be treated within a corresponding drying device to generate the vacuum.

[0103] The electrode-separator assemblies 10 shown here, which are to be discussed, are coils with a cylindrical base shape and two end faces, formed from ribbon-shaped electrodes and an intermediate separator in a manner known per se. A plate-shaped contact element 11, 12 is located on each end face of the electrode-separator assemblies 10 shown here. The contact elements 11 and 12 are each welded to projecting longitudinal edges of the current collectors and thus 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.

[0104] In this preferred embodiment, when positioning the electrode-separator assemblies 10 in relation to the individual inductors 20, the anode-side contact element 11 is placed within the effective range of the respective inductor 20. This achieves particularly good inductive heat transfer, as the heating of the anode-side contact element 11 is transferred directly to the anode current collector. The anode current collector is preferably made of copper foil. Copper exhibits particularly good thermal conductivity properties, making the thermal drying treatment especially effective in this embodiment. The anode-side contact element 11 is also preferably made of copper or nickel.

[0105] In the embodiment shown here, inductive heating occurs primarily from below. However, it is also possible in principle to perform inductive heating from above, or alternatively from both below and above.

[0106] Fig. 2 shows cross-sectional views through the carrier plate 40 of a drying device according to the invention with inductors 20 in the form of induction coils inserted therein.

[0107] Fig. 2A Figure 40 shows the carrier plate with several induction coils 20 embedded in it. The induction coils 20 can, for example, be cast into a glass ceramic. Above the carrier plate 40 with the induction coils 20, the electrode-separator assemblies 10 to be treated are positioned. In the embodiment shown here, the electrode-separator assemblies 10 are each located in a cylindrical housing cup.

[0108] To simplify the handling of the electrode-separator assemblies 10 during the drying process, two different support means 51, 52 for holding the electrode-separator assemblies are shown in the exemplary embodiment presented here. The support means 51 is a product or transport cup, particularly made of plastic, which simplifies the handling and holding of the electrode-separator assemblies 10. The support means 52 is a spacer that ensures a suitable distance between the individual electrode-separator assemblies 10 during the drying process and when inserting and removing the electrode-separator assemblies 10 into and out of the drying device. This prevents, in particular, the electrode-separator assemblies 10 from touching and potentially damaging each other.

[0109] The individual electrode-separator assemblies 10 can be easily held upright by means of the holding means 51, 52. Alternatively, a holding device, preferably made of plastic, can be used for a plurality of electrode-separator assemblies 10 to be treated. Such a holding device can, for example, be open at the bottom, i.e., in the direction of the inductors 20, to enable optimal inductive heating.

[0110] The use of suitable holders allows, in particular, contactless positioning of the electrode-separator assemblies 10 above the inductors 20. This prevents the electrode-separator assemblies from scraping against the base plate and thus causing damage to the electrode-separator assemblies 10.

[0111] Fig. 2B Figure 1 shows a single induction coil 20 in detail, illustrating the individual windings 21 of the induction coil 20 and the electrical connection 22 of the induction coil 20. The induction coil 20 can be operated with an alternating current, preferably in a regulated form, via the electrical connection 22. A ferrite core, for example, can be arranged in the center of the windings (not shown).

[0112] Fig. 3 Figure 1 shows a schematic top view of the carrier plate 40 of a drying device with a regular arrangement of the indicated induction coils 20. To carry out the thermal drying treatment according to the invention, a corresponding number of electrode-separator assemblies 10 to be treated are placed above these induction coils 20. For this purpose, for example, an elongated gripper element 60 with semicircular recesses is used, with which the electrode-separator assemblies 10 can be placed on the induction coils 20 in the correct position, so that the drying treatment can then be carried out by applying an alternating current of the appropriate frequency to the induction coils 10. Alternatively, a conveyor belt system or a slide gate can also be used, for example, instead of a gripper system.

[0113] In preferred embodiments, the induction coils 20 can have a ferrite core, for example in the form of a cup core half. This allows the magnetic field lines to be focused even more effectively on the electrode-separator assembly 10 to be treated. In other embodiments, the coil core can also be open.

[0114] During the drying process, each induction coil 20 can preferably be controlled separately at a suitable frequency, so that the individual electrode-separator assemblies 10 can, in principle, be dried individually. This can be particularly advantageous when there is a different heat distribution within the batch when dealing with a larger quantity of electrode-separator assemblies 10 to be treated.

[0115] In principle, it is possible to control several inductors or induction coils 20 together. However, individual control of each inductor offers particular advantages, allowing for individual heating of the electrode-separator assemblies. This makes it possible, for example, to accommodate the different heating requirements of various electrode-separator assemblies, which may have different configurations. Thus, different cell variants within a single batch can each be dried optimally.

[0116] Fig. 4 Figure 1 illustrates an embodiment of the invention in which more than two electrode-separator assemblies 10 are associated with an inductor 20 which generates an alternating magnetic field of elongated extent in which the more than two electrode-separator assemblies 10 can be arranged so that they are each exposed to a substantially equal magnetic field strength in the alternating field.

[0117] For this purpose, the turns 21 of a coil are wound around an elongated ferrite core 25. This provides an alternating magnetic field that is almost identical for several adjacent electrode-separator assemblies 10 (see A).

[0118] In Fig. 2B Figure A shows a cross-section through the arrangement shown in A in the area of ​​the arresters 22.

[0119] Fig. 2C schematically shows a longitudinal section through the arrangement.

Claims

1. Method for the thermal drying treatment of a plurality of electrode-separator assemblies (10) each having at least one negative electrode and at least one positive electrode, each comprising a metallic current collector coated with electrode active material, namely an electrode current collector and a cathode current collector, the thermal drying treatment being carried out by means of inductors (20) with which the electrode-separator assemblies (10) are inductively heated, comprising the following steps: a. The plurality of electrode-separator assemblies (10) is positioned in a drying device in the effective range of the inductors (20), b. a vacuum is applied for the thermal drying treatment, c. a current is supplied to the inductors (20), characterized in that d. exactly one inductor (20) is assigned to each of the electrode-separator assemblies (10) to be dried in the drying device or e. more than two electrode-separator assemblies (10) are assigned to an inductor which generates an alternating magnetic field of elongate extension, in which the more than two electrode-separator assemblies (10) can be arranged so that they are each exposed to essentially the same magnetic field strength in the alternating field, f. wherein the electrode-separator assemblies (10) are heated to a temperature above 99 °C and below the melting temperature of the separator of the electrode-separator assemblies.

2. The method according to claim 1 having the following additional feature: a. The electrode-separator assemblies (10) are heated to a temperature in a range from 100 °C to 110 °C.

3. The method according to claim 1 or claim 2, having at least one of the following additional features: a. The electrode-separator assemblies (10) are formed as a winding and have a cylindrical basic shape with two terminal end faces, b. the electrodes and their respective current collectors are ribbon-shaped and are spirally wound within the electrode-separator assemblies (10).

4. The method according to claim 3 with the following additional features: a. The negative electrode and the positive electrode are arranged within the electrode-separator assemblies (10) such that a longitudinal edge of the anode current collector protrudes from one of the terminal end faces and a longitudinal edge of the cathode current collector protrudes from the other of the terminal end faces, b. a contact element (11, 12), in particular a contact plate, is attached to at least one of the end faces, which covers at least 50% of the respective end face.

5. The method according to claim 3 or claim 4, having at least one of the following additional features: a. When positioning the electrode-separator assemblies (10) in the drying device, the electrode-separator assemblies (10) which are formed as windings are aligned parallel to one another on a carrier plate (40) of the drying device, with one of the end faces of the winding facing the carrier plate (40) and the other of the end faces of the winding facing away from the carrier plate (40), b. the inductor (20) or the inductors (20) are arranged in the carrier plate (40) or under the carrier plate (40), c. after the electrode-separator assemblies (10) have been positioned in the drying device, the inductor (20) or the inductors (20) are separated from the electrode-separator assemblies (10) by a dielectric.

6. The method according to claim 5, comprising at least one of the following additional features: a. The electrode-separator assemblies (10), that are formed as a winding, are inserted into a metallic housing cup, which is cylindrical and has a cup base, and are inductively heated inside the housing cup, b. to position the electrode-separator assemblies (10), the electrode-separator assemblies that are formed as a winding are, together with the metal housing cup, placed in the drying device, such that the housing bottom of the housing cup stands on the carrier plate (40) of the drying device.

7. The method according to any one of the preceding claims, having at least one of the following additional features: a. The individual inductors (20) are operated in a controlled manner, b. At least one performance value in the individual inductors (20) is measured.

8. The method according to any one of the preceding claims, having at least one of the following additional features: a. The inductor or inductors (20) are induction coils; b. The diameter of the inductors (20) and the diameter of the electrode-separator assemblies (10) deviate from each other by a maximum of 20 %.

9. Method according to any one of the preceding claims with the following additional feature: a. The thermal drying treatment is carried out directly before the electrode-separator assemblies (10) are impregnated with an electrolyte.

10. Drying device for carrying out a thermal drying treatment according to the method according to any one of claims 1 to 9, 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 particular induction coils, preferably in a regular arrangement, or it comprises at least one inductor which generates an alternating magnetic field of elongate extension, in which the more than two electrode-separator assemblies (10) can be arranged so that they are each exposed to essentially the same magnetic field strength in the alternating field. c. The drying device comprises at least one device for supplying a current to the inductor or inductors. d. The inductor or inductors (20) are arranged in a carrier plate (40) of the drying device or under a carrier plate (40) of the drying device.

11. The drying device according to claim 10 with the following additional feature: a. The inductor or inductors (20) are cast into the carrier plate (40).

12. The drying device according to claim 10 or claim 11, comprising at least one of the following additional features: a. The drying device comprises transport means for introducing and / or removing the electrode-separator assemblies (10) to be treated into and / or from the drying device, b. the drying device comprises means for positioning the electrode-separator assemblies (10) to be treated relative to the individual inductors (20), c. the drying device comprises carrier means (51, 52) for holding the electrode-separator assemblies to be treated.

13. The drying device according to any one of claims 10 to 12, with the following additional feature: a. The drying device comprises a device for measuring the performance of the inductor (20) or inductors (20).

14. The drying device according to any one of claims 10 to 13, with the following additional feature: a. A self-oscillating resonant converter is assigned to the inductor (20) or to each of the inductors (20).