Method and device for thermal drying treatment of electrode-separator assemblies by induction

Abstract

A method and device are proposed for the thermal drying treatment of a number of electrode-separator assemblies (10). The assemblies 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, i.e. an anode current collector and a cathode current collector, respectively. During the thermal drying treatment, all assemblies are dried simultaneously. Drying is performed by a number of inductors (20) in which the electrode-separator assemblies (10) are inductively heated. In the method, several electrode-separator assemblies (10) are positioned in a drying device in the effective range of the inductors (20). For the thermal drying treatment, a vacuum is applied and a current is supplied to the inductors (20). The method is further characterized in that exactly one inductor (20) is assigned to each electrode-separator assembly (10) to be dried in the drying device, or three or more electrode-separator assemblies (10) are assigned to one inductor (200) generating an elongated alternating magnetic field, in which three or more electrode-separator assemblies (10) can be arranged such that they are each exposed to essentially the same magnetic field strength in the alternating field.

Description

[Technical field]

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

[0002] Electrochemical energy storage elements can convert stored chemical energy into electrical energy through the power of redox reactions. The simplest form of an electrochemical energy storage element is an electrochemical cell. It includes a positive electrode and a negative electrode separated from each other by a separator. During discharge, electrons are released at the negative electrode as a result of an oxidation process. This results in an electron flow that can be extracted by an external electrical consumer, for which the electrochemical cell serves as an energy source. At the same time, an ionic current corresponding to the electrode reactions is generated in the cell. This ionic current crosses the separator and is made possible by an ion-conducting electrolyte.

[0003] If the discharge of an electrochemical energy storage element is reversible, i.e. it is possible to reverse the conversion of chemical energy to electrical energy during discharge and charge the cell or element again, it is said to be a secondary energy storage element. For secondary energy storage elements, the common designation of the negative electrode as the anode and the positive electrode as the cathode refers to the discharge function of the electrochemical energy storage element.

[0004] In this case, 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 the known secondary electrochemical energy storage elements, lithium-ion cells in particular achieve relatively high energy densities. In addition to using cell stacks made up of a number of individual cells, each having at least one positive electrode and at least one negative electrode, lithium-ion cells with wound electrode-separator assemblies are widely used. Such assemblies often have a "positive electrode / separator / negative electrode" sequence. Furthermore, such individual cells can be constructed 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 usually comprise a metal current collector, which is usually in the form of a foil, mesh, grid, foam, fleece or felt. For the positive electrode, a mesh or foil made of aluminum, such as aluminum expanded metal or aluminum foil, is usually used as the current collector. For the negative electrode side, a mesh or foil made of copper is usually used as the current collector.

[0007] Generally, the cells described for lithium-ion cells are produced in a multi-step process. The electrodes are generally produced in a first step, and then the electrodes are combined with one or more separators to form the electrode-separator assembly described above. The electrodes and separators may be loosely stacked or wound, or may be connected together in a lamination step.

[0008] To produce electrodes for lithium-ion cells, thin-film electrodes are formed on current collectors from a generally paste-like composition containing suitable electrochemically active materials (abbreviated "active materials"), for example using a doctor blade or slot die. Active materials suitable for electrodes in lithium-ion cells must be capable of absorbing and releasing lithium ions, which migrate from the negative electrode to the positive electrode (and vice versa) during charge and discharge.

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

[0010] Lithium cobalt oxide (LCO), with the formula LiCoO2, with the formula LiNi x Mn y Co z Lithium Nickel Manganese Cobalt Oxide (NMC) with formula O2, Lithium Manganese Spinel (LMO) with formula LiMn2O4, Lithium Iron Phosphate (LFP) with formula LiFePO4 or LiNi x Co y Al z Lithium nickel cobalt aluminum oxide (NCA) with O2 is particularly suitable for the cathode. Mixtures of these materials can also be used.

[0011] In addition to the active material, the paste-like compositions generally also contain an electrode binder ("binder" for short), a conductivity enhancer, a solvent and / or a suspending agent and optionally additives, for example to affect their processing properties. The electrode binder forms a matrix in which the active material and possibly the conductivity enhancer can be incorporated. The matrix is ​​intended to ensure improved structural stability during the volume expansion and contraction caused by lithiation and delithiation. 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 a water-soluble processable binder is sodium carboxymethylcellulose (Na-CMC). An example of a binder that can be processed in an organic solvent is polyvinylidene fluoride (PVDF). For example, it is possible to add rheology aids as additives. The conductivity enhancer is usually a conductive carbon-based material, in particular conductive carbon black, conductive graphite, carbon fibers or carbon nanotubes.

[0012] The solvent and / or suspending agent contained in the composition is usually found in the electrode film formed on the current collector and needs to be removed therefrom. The dry electrode film can then be compressed in a calendaring process. The electrode thus formed can be assembled into the cell described above.

[0013] Drying of the electrode film formed on the current collector, i.e. removing the solvent and / or suspending agent contained therein, is time-consuming and energy-intensive, as is the removal of any residual moisture that may still be present in the electrode-separator assembly afterwards. Conventionally, the electrode film can be dried using an enhanced gas, in particular preheated air. The gas heats the electrode film, which causes any solvent and / or suspending agent or any residual moisture contained therein to evaporate and escape. Heating is first performed on the surface of the electrode film and then gradually spreads to the interior of the film. Thus, drying also proceeds gradually from the outside to the inside, and the outer layer of the electrode film may already be dry, while the electrode film still contains a significant amount of solvent and / or suspending agent in the layer adjacent to the current collector. This can often be problematic in that a film-like residue remains when the solvent and / or suspending agent are removed. If this residue forms on the outer layer of the electrode film, the drying of the electrode film can be further significantly delayed, since the solvent and / or suspending agent can no longer leave the adjacent layer of the current collector without any problem. In some circumstances, bubbles may also form. In particular, attempts have been made to combat this by significantly lengthening the drying time. With slow drying, the observed drying gradient occurs only slightly. However, deliberately slowing down the drying process increases the time required, which is already considerable.

[0014] As part of the manufacturing process for lithium-ion cells, it is particularly important to remove any residual moisture from the electrode-separator assembly before filling the cell with electrolyte. Traditionally, this is done by an oven process, typically using a vacuum oven, where the electrodes are dried before the winding process, or the wound electrode-separator assembly is dried in a housing cup just prior to filling with electrolyte. For mass production, a batch, typically consisting of several hundred cells, is typically heated in a carrier (tray) to about 100° C. for several hours, thereby removing any moisture present. This is typically accompanied by several cycles of vacuum and nitrogen purging to remove moisture from the oven chamber.

[0015] However, this procedure is associated with various challenges. First, it is generally difficult to get heat into such ovens, since the drying medium cannot be circulated in a vacuum. Therefore, simultaneous and homogeneous heating of the cells is difficult. Uniform heating is possible only if nitrogen or another gas is added.

[0016] Another problem with such conventional oven processes is that the heating is done by contact heating, for example by placing the cell on a hot carrier plate of the oven. In a vacuum, there is no heat transfer by convection in the vacuum, and the vacuum also has an insulating effect, so unevenness between the plate and the cell can interfere with the heat transfer. This can easily lead to uneven heating of the cell.

[0017] It should also be noted that in conventional oven processes, the cells must not be overheated, as this can cause damage to the cells, especially to the separators, which is difficult when heating using conventional heating plates, due to the heat and time losses that occur, which can cause the temperature to overshoot, which can be associated with quality losses in the cells being dried.

[0018] A problem also exists in the conventional oven process when the electrode-separator assembly already in the cell cup or housing cup is dried in the oven. In this case, the cell cup is heated first. Direct heat transfer to the electrode and current collector occurs mainly through the welds on the electrode or any metal contact plates present. This results in poor heat transfer. In addition, there is often a small free space between the inside of the can and the electrode-separator assembly, which further inhibits heat transfer.

[0019] Finally, with conventional oven processes, it is difficult to achieve homogeneity of the drying process across an entire batch of cells. Generally, the outer cells of the batch reach a different temperature during the drying process than the inner cells. On the one hand, the temperature must not be too high during the drying process, in order to avoid damage, especially to the separator. On the other hand, the temperature must not be too low so that the moisture can safely evaporate. Overall, the temperature window to be maintained is very small, and it is difficult to achieve the required temperature window for a sufficient period of time for all cells in the batch.

[0020] It is already known that electrodes can be dried by heating them using inductively generated eddy currents. For example, EP 3439079 B1 describes a method for the heat treatment of an electrode film on a metal current collector, in which the current collector is inductively heated by an induction device. However, the method described therein mainly provides a solution for drying electrode strips immediately after they have been coated. If several already wound electrode-separator assemblies are to be dried simultaneously, satisfactory results cannot be expected with this method. Summary of the Invention [Problem to be solved by the invention]

[0021] Against this background, the present invention aims at providing an improved method and corresponding device for drying electrode-separator assemblies, whereby a rapid and uniform drying of a large number of electrode-separator assemblies, and in particular the removal of residual moisture, can be carried out as part of the manufacturing process of lithium-ion energy storage elements. In addition, the method should be faster and more efficient compared to conventional processes, while at the same time allowing energy savings. [Means for solving the problem]

[0022] This object is achieved by a method according to claim 1. This object is further solved by a drying device according to the further independent claims. Preferred embodiments and embodiments of the method or drying device are subject matter of the dependent claims.

[0023] The method according to the invention is used for the simultaneous thermal drying treatment of several electrode-separator assemblies, which may be dried simultaneously, in particular in the form of batches.

[0024] The electrode-separator assemblies each include at least one positive electrode and at least one negative electrode and at least one separator. The electrodes themselves each include a metal current collector coated with an electrode active material. In the case of the negative electrode, this is the anode current collector, and in the case of the positive electrode, it is the cathode current collector. The thermal drying treatment is preferably carried out contactlessly by an inductor. The electrode-separator assemblies are preferably inductively heated simultaneously without direct contact with the inductor.

[0025] The method according to the invention comprises the steps of: a. a plurality of electrode-separator assemblies are positioned within a dryer device at an effective area of ​​an inductor; b. a vacuum is applied for a thermal drying process; c. A step in which current is supplied to the inductor; Includes.

[0026] The method according to the invention comprises the steps of: d. Exactly one inductor is assigned to each electrode-separator assembly to be dried in the drying device; or e. More than two electrode-separator assemblies are assigned to an inductor that generates an elongated alternating magnetic field, and in the inductor, the three or more electrode-separator assemblies (10) can be arranged such that they are each exposed to substantially the same magnetic field strength within the alternating field. The present invention is further characterized by the following.

[0027] The method according to the invention is based on the generation of an alternating magnetic field by an inductor, which can act on the metal components of the electrode-separator assembly, in particular the current collector. The eddy currents generated in the metal components lead to heating and thus evaporation of any moisture present in the electrode film deposited on the current collector. Compared to conventional oven processes, the heating is more direct and faster, so that the method according to the invention saves a considerable amount of time.

[0028] According to the induction principle of the method according to the 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 required.

[0029] Both the embodiment according to feature d. above and the embodiment according to feature e. above ensure that the electrode-separator assembly to be dried is exposed to the same drying conditions, so that drying can be performed uniformly and quickly.

[0030] The vacuum is applied in a known manner, for example also known from conventional oven processes. In particular, a vacuum pump is used for this purpose, which generates the vacuum, i.e. a pressure lower than the ambient pressure. Preferably, a pressure of less than 300 mbar is set, for example in the range of 20 mbar to 100 mbar.

[0031] In contrast to conventional induction-based electrode drying methods, the essence of the method according to the invention in its embodiment with feature d. above lies inter alia in the fact that each electrode-separator assembly to be dried is assigned an inductor in order to realize a very targeted heating of the electrode-separator assembly. In this way, any residual moisture present in the electrode-separator assembly can be removed safely and in a short time in a particularly effective and at the same time energy-saving manner.

[0032] By the core of the method according to the invention in an embodiment having the above feature d., the same effect is achieved, except that now several electrode-separator assemblies can be assigned to one inductor and are exposed to the same drying conditions. With the magnetic field generated by a coil with a circular cross section, it is difficult to position several coils so that they are subjected to approximately the same magnetic field force. With an elongated magnetic field, which can also be generated by an elongated inductor, this becomes possible.

[0033] It is possible to construct such an inductor with a length that allows for even drying of a dozen or more electrode-separator assemblies arranged in a row.

[0034] A desiccant device according to the invention preferably comprises two or more such elongated inductors, on which several electrode-separator assemblies may be arranged.

[0035] The method according to the invention in an embodiment having feature d. above can be individually controlled and / or adjusted for each electrode-separator assembly as necessary, so that harmful excessive temperatures do not occur in individual cells. Furthermore, because mechanical and magnetic tolerances can be compensated for by individual heating of each electrode-separator assembly via individual inductors, the method according to the invention achieves a high degree of heating homogeneity across the batch. Each electrode-separator assembly in the batch can be heated and dried evenly, so that hot spots or other uneven heat distributions do not form within the batch.

[0036] Compared to conventional drying ovens, the construction of the corresponding drying device is also much lighter and requires less material, in particular no conductive medium such as oil or water that may be used to heat the oven drawer in conventional oven processes is required.

[0037] Furthermore, the method according to the invention means that since the individual inductors can be operated independently, it is in principle possible that different drying curves for different kinds of electrode-separator assemblies can be implemented in the drying device, e.g. a drying curve for one energy type and another drying curve for one power type in the electrode-separator assemblies.

[0038] Above all, the method according to the invention allows significant energy savings compared to conventional methods: typically, energy savings in the range of 50% to 75% are possible compared to conventional oven processes in which the carrier means of the cells, e.g. the pallet, must also be heated.

[0039] To introduce and position the electrode-separator assemblies, the individual electrode-separator assemblies can, for example, be pushed directly into the drying device and positioned in the effective range of the respective inductor. The use of a carrier pallet as in conventional processes is not required at all, thereby eliminating the steps of storing and transporting the electrode-separator assemblies in and out of the carrier pallet. Since the inductors transfer the energy required for non-contact drying, the quality requirements, in particular the uniformity of the surface on which the electrode-separator assemblies are placed, can be relatively low. Due to the non-contact transfer, any existing non-uniformities are irrelevant. However, in the case of contact heating, the size of the contact surface is decisive.

[0040] In other preferred embodiments, product carriers, such as shipping cups (pucks) or other carrier means may be used. Conveniently, these product carriers are made of a non-conductive material, such as plastic, so that they do not interact with the induction heating process, become heated, and therefore do not cause any energy loss.

[0041] The use of a carrier pallet is also disadvantageous with regard to the associated additional energy requirements during heating and cooling, since in conventional oven processes the carrier pallet is necessarily heated together with the electrode-separator assemblies being processed. In the method according to the invention, only the electrode-separator assemblies can be heated in a targeted manner. Even if a product carrier is used, no heating of the product carrier occurs if an appropriate material is selected for the product carrier, thereby making the method according to the invention significantly more time- and energy-saving than conventional methods.

[0042] If the electrode-separator assemblies to be processed are introduced directly into the drying device or are transported by individual product carriers, the electrode-separator assemblies may be accumulated on a surface carrying the inductor, in particular on a carrier plate of the drying device, so that each individual electrode-separator assembly is positioned above the inductor.

[0043] After positioning the electrode-separator assembly to be treated, a vacuum hood may be lowered over the electrode-separator assembly to be treated, for example, and a drying process may be initiated.

[0044] Once the heating process is complete, the individual electrode-separator assemblies can be further transported, for example using a pusher, and separated again. Compared to handling carrier pallets, this offers considerable advantages for further processing of the electrode-separator assemblies.

[0045] In a particularly preferred embodiment, the method comprises the following additional features: a. the electrode-separator assembly is heated to a temperature above 99° C. and below the melting temperature of the separator of the electrode-separator assembly; b. The electrode-separator assembly is heated to a temperature in the range of 100°C to 110°C. Preferably, the above-mentioned features a. and b. are implemented in combination with each other.

[0046] Effective heating leads to the evaporation of any residual moisture present, and it is ideal to achieve a temperature above the boiling point of water vapor or residual moisture during the drying process. It is therefore preferable to set a temperature of 100°C or higher. It is expedient to select the desired temperature range so that the electrode-separator assembly to be treated is not damaged. The key component here is generally the separator, which can be made of microporous plastic or nonwoven fabric, for example made of glass fiber or polyethylene. The separator can also be composed of a ceramic-coated nonwoven material, for example. The temperature range of 100°C to 110°C is therefore particularly suitable for the drying process in order to reliably prevent damage to the electrode-separator assembly.

[0047] Compared to conventional oven processes, the time required for the drying treatment in the method according to the invention can be significantly reduced by specifically targeted and efficient heating of the electrodes.

[0048] In a particularly preferred embodiment, the method comprises the following additional features: a. the electrode-separator assemblies are each 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 spirally wound within the electrode-separator assembly; Preferably, the above-mentioned features a. and b. are implemented in combination with each other.

[0049] The method according to the invention, which is based on inductive heat transfer, can be carried out much more directly and quickly than conventional methods and does not require contact heating, as in conventional oven processes, so that the method according to the invention can be used very flexibly in the manufacturing process of energy storage elements. In principle, the method according to the invention can also be used for pure electrode drying. However, it is particularly preferred to use the method according to the invention for drying already wound electrode-separator assemblies.

[0050] In a particularly preferred embodiment, the method according to the invention comprises the following additional features: a. the negative and positive electrodes are disposed within the electrode-separator assembly 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, in particular a contact plate, is attached to at least one of the end faces and covers at least 50% of the respective end face; Preferably, the above-mentioned features a. and b. are implemented in combination with each other.

[0051] The application of the drying treatment according to the invention to energy storage elements in a so-called contact plate design according to the aforementioned features a. and b., which is known per se, offers particular advantages, since the contact element, e.g. the contact plate, is in direct contact with one of the current collectors and significantly promotes inductive heating.

[0052] One such contact plate design can be found, for example, in WO 2017 / 215900 A1. A cylindrical cell with a winding-shaped electrode-separator assembly is described here. The electrodes of opposite polarity are arranged offset from each other in the electrode-separator assembly, so 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 cell has a contact plate at one end face of the winding, which is assembled, for example by welding, with one longitudinal edge of the current collector. This allows electrical contact of the current collector and therefore also of the associated electrode over its entire length. This can significantly reduce the internal resistance in the cell. Compared to conventional cells, large current generation can be absorbed very well and heat can also be better dissipated from the winding.

[0053] The contact plate design of the electrode-separator assembly which can be dried according to the invention can, for example, be designed such that the contact elements are specifically designed as contact plates or metal plates, whereby openings are also provided in the plate, whereby a certain proportion of the respective end face, for example 50% or preferably more than 50%, is covered with the contact elements.

[0054] The contact elements may be made of, for example, nickel, copper, titanium, or nickel, copper, or titanium alloys, or stainless steel or nickel-plated copper. These materials are particularly suitable for contact elements that are to be assembled with the anode current collector. Contact elements intended for connection to the cathode current collector are preferably made of aluminum or an aluminum alloy.

[0055] The contact elements may have a uniform thickness, for example, in the range of 50 μm to 600 μm, preferably 150 μm to 350 μm. Preferably, the contact elements have the shape of a disk or a polygonal plate. The contact elements preferably cover more than 60% of the respective end faces and may have an opening, in particular a hole or slot or, if desired, several holes or slots.

[0056] The inventors have been able to determine that in the method according to the invention, heating is faster and more effective with electrode-separator assemblies having contact elements. This is probably due in particular to the fact that the contact elements provide more mass that can absorb the magnetic field lines. In addition, the contact elements can be properly aligned with the magnetic field lines. In combination with the contact elements, the method according to the invention therefore allows a particularly fast, effective and directed heating and thus drying of the electrode-separator assemblies.

[0057] With regard to the positioning of the electrode-separator assembly in the drying device, the method according to the invention may, in a preferred embodiment, have the following additional features: a. when positioning the electrode-separator assemblies in the drying device, the electrode-separator assemblies formed as windings are aligned parallel to one another on a carrier plate of the drying device, with one end surface of the windings facing the carrier plate and the other end surface of the windings facing away from the carrier plate; b. one or more inductors are disposed on or beneath the carrier plate; c. After the electrode-separator assembly is positioned within the drying device, the one or more inductors are spaced from the electrode-separator assembly by an inductor. Preferably, the above-mentioned features a. and b. and in a particularly preferred manner the above-mentioned features a., b. and c. are realised in combination with one another.

[0058] The carrier plate of the drying device is preferably the bottom or bottom plate within the drying device, and the inductor or inductors for the electrode-separator assembly are generally located at or below this bottom or bottom plate or carrier plate.

[0059] According to the above feature c., an insulator, i.e. a non-conductor, is located between the electrode-separator assembly and the inductor after positioning. This can be a glass ceramic, for example, which covers the inductor or inductors of the carrier plate. According to the principle of induction heating, heat is transferred via electromagnetic field lines which only induce heating of the metal substrate, i.e. in particular the current collector and / or any contact elements of the electrode-separator assembly. The covering glass ceramic or the like is therefore not heated in the method according to the invention.

[0060] In a particularly preferred manner, the electrode-separator assembly is preferably positioned such that one end face of the electrode-separator assembly provided with the contact element is aligned on or faces the carrier plate. It is particularly preferred if the anode side of the electrode-separator assembly faces the carrier plate with the inductor. However, in some embodiments, the cathode side of the electrode-separator assembly may also face the carrier plate with the inductor.

[0061] Preferably, the anode-side contact element is placed on a carrier plate. Preferably, the anode-side contact element is made of copper or nickel and / or the anode current collector is made of copper, which allows a particularly good inductive heating.

[0062] In principle, the method according to the invention is also suitable for heating the contact elements on the cathode side, which consist, for example, of aluminum.

[0063] In a further embodiment of the method according to the invention, it can be provided that the electrode-separator assembly is dried together with a housing cup, for example a metal housing cup, with or without contact elements. In a preferred embodiment, the method according to the invention therefore comprises the following additional features: a. the electrode-separator assembly, designed as a winding, is inserted into a metal housing cup, which is cylindrical and has a cup base, and is inductively heated inside the housing cup; b. To position the electrode-separator assembly, the electrode-separator assembly designed as a winding is positioned in the drying device together with the metal housing cup so that the housing bottom of the housing cup stands on the carrier plate of the drying device. Preferably, the above-mentioned features a. and b. are implemented in combination with each other.

[0064] Also in combination with a housing cup, the drying process can be carried out effectively. The heat inductively generated in the cup can also be transferred to the electrode-separator assembly, which further improves the effectiveness of the heating. In combination with one or two contact elements of the electrode-separator assembly, the effectiveness of the heating can be further improved, since in this case the contact element or contact elements arranged inside the cup are also inductively heated, so that heat is also generated inside the cup. The energy supply is very direct by the inductive method, so that only a minimum power is needed to optimally carry out the drying process.

[0065] Drying only for electrode-separator assemblies or electrode-separator assemblies with one or two contact elements has certain advantages over heating the electrode-separator assemblies in a cup, since no energy has to be consumed for heating the cup, which may be advantageous under certain circumstances. However, it may also be advantageous for production-related reasons to dry the electrode-separator assemblies in the housing cup. The method according to the invention also offers advantages over conventional methods, since it is generally very efficient and saves energy and time.

[0066] A particular advantage of the method according to the invention is that a very targeted and individually adjustable heating of the individual electrode-separator assemblies is possible by means of individual inductors, each of which is assigned to an electrode-separator assembly to be treated. In particularly preferred embodiments of the method according to the invention, the following additional features are present: a. individual inductors are operated in a controlled manner; b. At least one performance value of each inductor is measured. At least one of the following is provided in this regard: Preferably, the above-mentioned features a. and b. are realised in combination with each other.

[0067] The controlled operation of the individual inductors (in an embodiment of the invention according to feature d. of claim 1) makes it possible to compensate for non-uniform heat supply that may occur due to the configuration within the batch, so that e.g. hot spots or non-uniform heat distribution over the batch are not developed inside the batch. However, in other embodiments, no adjustment may be necessary either. It may also be possible for several inductors to be switched and / or controlled together. In particular, this is so provided in an embodiment of the invention according to feature e. of claim 1.

[0068] Conventional methods cannot guarantee that each individual electrode composite absorbs the same amount of heat within a batch, which can be due to non-uniformity or the fact that the delivered energy cannot reach all cells equally.

[0069] Performance measurements, e.g. current or temperature measurements, on individual inductors or possibly groups of inductors can be used to check whether the heating in the respective assigned electrode-separator assembly or assemblies is in fact optimally performed in the intended manner. Quality control is therefore possible by means of such performance measurements, whereby an adequate and reliable heating and drying process can be guaranteed for all electrode-separator assemblies of the entire batch. Insufficient drying process of individual electrode-separator assemblies can thus also be detected for quality control purposes, making it possible to classify the corresponding electrode-separator assemblies if necessary.

[0070] With regard to the inductor, the method according to the invention has the following additional features: a. the one or more inductors are induction coils; b. The diameter of the inductor, in particular the induction coil, used according to feature d. of claim 1 and the diameter of the electrode-separator assembly, in particular the electrode-separator assembly formed as a winding having a basic cylindrical shape, deviates from each other by a maximum of 20%. In an embodiment having feature d. of claim 1, features a. and b. above are preferably realised in combination with each other.

[0071] In principle, all devices suitable for generating an alternating electric field capable of inducing eddy currents in a metal substrate are suitable as inductors. The inductor is preferably an induction coil, in particular a coil having multiple coil windings or an induction device comprising at least one such coil, respectively. The induction coil is preferably wound in a flat spiral shape and in a preferred embodiment essentially consists of, for example, a copper wire or a coated copper wire.

[0072] By adapting the diameter of the inductor, in particular the induction coil, to the diameter of the electrode-separator assembly to be treated, a particularly efficient energy utilization can be achieved. However, certain deviations in the adaptation between the inductor and the electrode-separator assembly are also tolerated, since the method works overall very efficiently without it. For example, the mentioned 20% diameter difference is still adequate to carry out the drying process in a very rapid and energy-saving manner.

[0073] If necessary, a larger difference in diameter between the inductor and the electrode-separator assembly can be tolerated, allowing electrode-separator assemblies with different dimensions to be processed in the same drying device.

[0074] The method according to the invention is particularly suitable for a thermal drying treatment that is carried out immediately before the electrode-separator assembly is impregnated with an electrolyte during the manufacturing process of the energy storage element. In particular, any residual moisture should be removed from the electrode-separator assembly before this step, i.e. before the impregnation with the electrolyte. Residual moisture that can be removed according to the invention can penetrate into the electrode-separator assembly, for example, during intermediate storage of the electrode-separator assembly during the manufacturing process. Using the method according to the invention, the post-drying steps can be carried out in a particularly time- and energy-saving manner.

[0075] The method according to the invention is particularly suitable for circular cells since an optimal circular coil shape of the inductor corresponding to the circular cross section of the circular cell can be utilized.

[0076] The method according to the invention is suitable for use in the production process of lithium ion cells, preferably lithium ion circular cells, and can be used in particular for mass production. The energy and time saving capabilities of the method according to the invention are particularly useful in mass production processes.

[0077] The invention further comprises a drying device for carrying out the thermal drying treatment according to the method specifically described, said drying device having the following characteristics: a. the drying device includes at least one vacuum chamber; b. the drying device comprises a plurality of inductors, in particular induction coils, preferably in a regular arrangement, or the drying device comprises at least one inductor generating an elongated alternating magnetic field, in which three or more electrode-separator assemblies may be arranged such that they are each exposed to essentially the same magnetic field strength within the alternating field; c. the drying device includes at least one device for supplying current to one or more inductors. It is characterized by:

[0078] The vacuum chamber of the drying device according to the invention is preferably defined by a vacuum hood, preferably a descendable vacuum hood, which can surround one or more of the electrode-separator assemblies to be dried, so that this or these can be subjected to a corresponding reduced pressure. In many cases, it is preferred that a plurality of electrode-separator assemblies are arranged in the vacuum chamber, i.e. surrounded by a vacuum hood. However, the device according to the invention can also include a separate hood for each electrode-separator assembly to be dried. In this case, each electrode-separator assembly is arranged in its own vacuum chamber.

[0079] For further details of this drying device, reference is also made to the above mentioned methods, which can be carried out using such a drying device.

[0080] The device for supplying the current to the inductors preferably comprises a control device for each inductor or, if necessary, for multiple inductors, whereby the inductors can be operated individually or in groups at a suitable AC frequency. Depending on the design of the drying device, it may also be possible to control all inductors together at the same frequency. In a particularly preferred manner, the drying device according to the invention has the following additional features: a. one or more inductors are disposed on the carrier plate of the drying device, preferably cast into the carrier plate or disposed below the carrier plate of the drying device; It is characterized by:

[0081] As already explained above, the inductor is preferably an induction coil known per se and is arranged on a carrier plate, for example the bottom plate, of the drying device. The coil may be covered by a plate or layer of non-conductive material, for example glass ceramic. The inductor itself is preferably a flat-wound induction coil, in particular made of copper wire. If necessary, the induction coil may be equipped with a ferrite core in order to better concentrate the magnetic field lines on the electrode-separator assembly to be treated. In this case, in particular, a flat winding of the induction coil is not mandatory.

[0082] With regard to the feeding and positioning of the electrode-separator assemblies to be treated, the drying device according to the invention may, in a preferred embodiment, have the following additional features: a. the drying device includes a transport means for introducing and / or removing the electrode-separator assembly to be treated into and from the drying device; b. the drying device includes a means for positioning the electrode-separator assembly to be treated relative to the inductor or individual inductors; c. the drying device includes a carrier means for holding the electrode-separator assembly being processed; Preferably, the above-mentioned features a. and b., or a. and c., or b. and c., or a., b., and c. are realized in combination with each other.

[0083] The transport means can be, for example, one or more pushers with which the individual electrode-separator assemblies are pushed into the interior of the drying device. The inductors in or below the carrier plate of the drying device can be arranged such that, when the electrode-separator assemblies are pushed in with maximum packing of the electrode-separator assemblies, one inductor is assigned to each electrode-separator assembly or the electrode-separator assembly is located directly above the inductor on the carrier plate. This precise alignment of the electrode-separator assemblies can be supported, for example, by corresponding lateral bands or stops, which simplifies the correct positioning of the electrode-separator assemblies.

[0084] Correct positioning of the electrode-separator assemblies on the carrier plate of the drying device may also be supported by other means, for example using a gripper that may be used to grip and place one or more electrode-separator assemblies in the correct position on the carrier plate.

[0085] Furthermore, carrier means may be provided for holding, for example, a transport cup or a transport pallet, which facilitates positioning and holding. The carrier means may be designed as a single or multiple holder for multiple electrode-separator assemblies. Preferably, such carrier means may be made of plastic or other non-metallic and preferably non- or low-thermal conductive material so as not to interact with the induction heating. The use of such carrier means, for example a transport cup, with or without contact elements, may be particularly useful during the drying process of pure electrode-separator assemblies, since it means that there is no need to directly contact the delicate electrode-separator assemblies during the drying process.

[0086] Preferably, each inductor may be switched individually, or as part of a group as required, preferably in a controlled manner.

[0087] In a particularly advantageous embodiment, the drying device comprises a device for measuring the performance of one or more inductors; in particular in the embodiment in which an inductor is assigned to each electrode-separator assembly, a performance measurement can preferably be provided for each individual inductor or, if necessary, for groups of inductors. For example, the absorbed current and / or the temperature and / or the time can be measured as performance values. For example, a sensor for measuring the temperature can be integrated into each inductor. By measuring the performance, the course of the drying process can be recorded for each individual electrode-separator assembly and can also be tracked in terms of quality control. Such a performance measurement also makes it possible for the individual inductors to be operated in a controlled manner, so that, for example, a homogeneous and uniform drying process can be ensured over the entire batch.

[0088] The performance measurements can also be used to initially measure the amount of energy required for the electrode-separator assembly at a particular position in the batch or on the carrier plate of the drying device, after which the inductor can be set accordingly for subsequent drying processes, thereby ensuring consistent drying quality without having to record the corresponding values ​​for each drying process.

[0089] In further preferred embodiments of the drying device according to the 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 self-controlled or externally controlled and generally operates effectively regardless of the type of control and causes little EMC interference. In some embodiments, an externally controlled resonant converter is preferred as it is more controllable in terms of frequency.

[0090] Further features and advantages of the invention become apparent from the following description of examples in conjunction with the drawings, in which: The individual features can be realized separately or in combination with one another. [Brief description of the drawings]

[0091] [Figure 1]FIG. 2 is a schematic diagram of the components involved in the method according to the invention. [Figure 2A-B] FIG. 13 is a cross-sectional view of an inductor inserted into a carrier plate of a drying device. [Diagram 3] FIG. 1 is a schematic diagram of a drying device on a carrier plate. [Figure 4] FIG. 13 is a cross-sectional view of an inductor inserted into a carrier plate of a drying device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0092] 1 shows some components for carrying out the method according to the invention, where several electrode-separator assemblies 10 are simultaneously subjected to a thermal drying treatment based on induction 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 with a vacuum, and in the example shown here a vacuum hood 30 is lowered in a corresponding drying device over the electrode-separator assemblies 10 to be treated to generate a vacuum.

[0093] The electrode-separator assembly 10 shown here to be processed is a winding with a cylindrical basic shape and two terminal end faces, which are formed from ribbon-shaped electrodes and a separator located between them in a manner known per se. Plate-shaped contact elements 11, 12 are located on each of the end faces of the electrode-separator assembly 10 shown here. The contact elements 11 and 12 are respectively welded to the protruding longitudinal edges of the current collectors and are thereby 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.

[0094] When positioning the electrode-separator assembly 10 relative to the individual inductors 20, the anode-side contact element 11 is in this preferred embodiment positioned in the effective range of the respective inductor 20. In this way, particularly good inductive heat transfer is achieved, since 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 has particularly good heat conducting properties, which makes the thermal drying treatment particularly effective in this embodiment. The anode-side contact element 11 is preferably made of copper or even nickel.

[0095] In the example shown here, the induction heating is essentially carried out from below, however, it is also possible in principle to carry out the induction heating from above or alternatively from below and above.

[0096] FIG. 2 shows a cross-section through a carrier plate 40 of a drying device according to the invention, having an inductor 20 in the form of an induction coil inserted in the drying device.

[0097] 2A shows a carrier plate 40 with several induction coils 20 embedded therein. The induction coils 20 can be, for example, castings of glass ceramic. The electrode-separator assemblies 10 to be processed are located above the carrier plate 40 with the induction coils 20. In the example shown here, the electrode-separator assemblies 10 are each located in a cylindrical housing cup.

[0098] In order to simplify the handling of the electrode-separator assemblies 10 during the drying process, two different carrier means 51, 52 for holding the electrode-separator assemblies are shown in the examples shown herein. The carrier means 51 is a product or transport cup, in particular made of plastic, which simplifies the handling and holding of the electrode-separator assemblies 10. The carrier means 52 is a spacer that ensures a suitable distance between the individual electrode-separator assemblies 10 during the drying process as well as the insertion and removal of the electrode-separator assemblies 10 into and from the drying device. In particular, it prevents the electrode-separator assemblies 10 from contacting each other and possibly damaging each other.

[0099] By means of the holding means 51, 52, individual electrode-separator assemblies 10 can be held upright in a simple manner. Alternatively, for example, a holding device can be used for multiple electrode-separator assemblies 10, preferably made of plastic and processed. Such a holding device can be open, for example, at the bottom, i.e. towards the inductor 20, to allow optimal induction heating.

[0100] In particular, the use of a suitable holder allows the electrode-separator assembly 10 to be positioned above the inductor 20 without contact, thereby preventing the electrode-separator assembly from interfering with the bottom plate and causing damage to the electrode-separator assembly 10.

[0101] 2B shows a single induction coil 20 in detail, thereby showing the individual windings 21 of the coil 20 and the electrical connections 22 of the induction coil 20. The electrical connections 22 allow the induction coil 20 to be operated with alternating current, preferably in a regulated manner. For example, a ferrite core may be placed in the center of the windings (not shown).

[0102] 3 shows a schematic top view of a carrier plate 40 of a drying device with a regular arrangement of the induction coils 20 shown. To perform 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, e.g. elongated gripper elements 60 with semicircular recesses are used, by means of which the electrode-separator assemblies 10 can be placed in the correct position on the induction coils 20. Thereby, the drying treatment can then be performed by supplying the induction coils 10 with an alternating current having the corresponding frequency. As an alternative to a gripper system, e.g. a conveyor belt system or a pusher can also be used.

[0103] In a preferred embodiment, the induction coil 20 may have a ferrite core, for example in the form of a shell-core half, which allows the magnetic field lines to be better concentrated on the electrode-separator assembly 10 being treated. In other embodiments, the coil core may also be open.

[0104] During the drying process, each induction coil 20 can preferably be controlled separately at an appropriate frequency, so that each individual electrode-separator assembly 10 can in principle be dried separately. This can be particularly advantageous when there are different heat distributions within the batch, due to the higher quality of the electrode-separator assemblies 10 being processed.

[0105] In principle, it is also possible for several inductors or induction coils 20 to be controlled together. However, certain possibilities arise from the individual control of the individual inductors, which allows for individual heating of the electrode-separator assemblies. In this way, different requirements for heating different electrode-separator assemblies, which can for example be designed differently, can also be taken into account. This means, for example, that different cell variants can be optimally dried in one batch.

[0106] FIG. 4 shows an embodiment of the invention in which three or more electrode-separator assemblies 10 are associated with an inductor 20 that generates an elongated alternating magnetic field, and each of the three or more electrode-separator assemblies 10 may be positioned such that they are exposed to substantially the same magnetic field strength within the alternating field.

[0107] For this purpose, the windings 21 of the coil are wound around an elongated ferrite core 25. This provides approximately the same alternating magnetic field for several electrode-separator assemblies 10 arranged next to each other (see A).

[0108] FIG. 2B shows a cross section through the configuration shown at A in the region of arrestor 22.

[0109] FIG. 2C shows a schematic longitudinal section through the configuration.

Claims

1. A method for heat-drying a plurality of electrode-separator assemblies (10) having at least one negative electrode and at least one positive electrode, each including a metal current collector coated with an electrode active material, i.e., an anode current collector and a cathode current collector, wherein the heat-drying is performed by an inductor (20) that inductively heats the electrode-separator assemblies (10), and the method is as follows: a. The step of positioning the plurality of electrode-separator assemblies (10) within the effective range of the inductor (20) within the drying device, b. Steps in which a vacuum is applied for the heat drying treatment, c. The step in which current is supplied to the inductor (20) In a method including, d. Each of the electrode-separator assemblies (10) that are dried in the drying device is assigned to exactly one inductor (20), or e. Three or more electrode-separator assemblies (10) are assigned to an inductor that generates an elongated alternating magnetic field, and in the inductor, the three or more electrode-separator assemblies (10) may be arranged such that they are each exposed to essentially the same magnetic field strength within the alternating field. A method characterized by the following features f to i. f. When positioning the electrode-separator assembly (10) within the drying device, the electrode-separator assembly (10), which is formed as a winding, is aligned parallel to each other on the carrier plate (40) of the drying device, with one end face of the winding facing the carrier plate (40) and the other end face of the winding facing away from the carrier plate (40). g. The one or more inductors (20) are arranged on or below the carrier plate (40), h. After the electrode-separator assembly (10) is positioned within the drying device, a dielectric material is positioned between the one or more inductors (20) and the electrode-separator assembly (10). i. Heating is induced by eddy currents generated in the metal components of the electrode-separator assembly (10).

2. The following additional features: a. The electrode-separator assembly (10) is heated to a temperature higher than 99°C and below the melting temperature 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. The method according to claim 1, comprising at least one of the following.

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

4. The following additional features: a. The negative electrode and the positive electrode are arranged 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. The contact elements (11, 12) are attached to at least one of the end faces and cover at least 50% of each end face. The method according to claim 3, having the following characteristics.

5. The following additional features: a. The electrode-separator assembly (10), which is formed as a winding, is cylindrical, inserted into a metal housing cup having a cup base, and is induction heated inside the housing cup, and the metal components include the metal housing cup. b. In order to position the electrode-separator assembly (10), the electrode-separator assembly, which is formed as a winding, is placed inside the drying device together with the metal housing cup such that the housing bottom of the housing cup stands on the carrier plate (40) of the drying device. The method according to claim 1, comprising at least one of the following.

6. The following additional features: a. Each of the inductors (20) is operated in a controlled manner. b. At least one performance value of each of the individual inductors (20) is measured. The method according to claim 1, comprising at least one of the following.

7. The following additional features: a. The one or more inductors (20) are induction coils. b. The diameter of the inductor (20) and the diameter of the electrode-separator assembly (10) differ from each other by a maximum of 20%. The method according to claim 1, comprising at least one of the following.

8. The following additional features: a. The heat drying treatment is performed immediately before the electrode-separator assembly (10) is impregnated with the electrolyte. The method according to claim 1, comprising:

9. A drying device for performing a heat drying treatment by the method described in any one of claims 1 to 8, the device having the following features: a. The drying device includes at least one vacuum chamber. b. The drying device includes a plurality of inductors (20), or the drying device includes at least one inductor that generates an elongated alternating magnetic field, wherein in the at least one inductor, the three or more electrode-separator assemblies (10) may be arranged such that they are each exposed to essentially the same magnetic field strength in the alternating field, and the plurality of inductors (20) or the at least one inductor is located on or below the carrier plate (40) of the drying device. c. The drying device includes at least one device for supplying current to the one or more inductors. A drying device having

10. The following additional features: a. The one or more inductors (20) are cast within the carrier plate (40). A drying device according to claim 9, having the following features.

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

12. The following additional features: a. The drying device includes a device for measuring the performance of the one or more inductors (20). A drying device according to claim 9, having the following features.

13. The following additional features: a. The self-oscillating resonant converter is assigned to one inductor (20) or to each of the multiple inductors (20). A drying device according to claim 9, having the following features.

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