Method for producing and conditioning electrode mixtures and dry electrodes from the electrode mixtures

Abstract

The present invention relates to a method for producing and conditioning an electrode mixture which consists of active material, optionally additives, and a binder, the method comprising the steps of: 1) producing the electrode mixture in a mixing vessel of a mixer, wherein, during production, the mixture is heated to a temperature TH, where TH > 45°C; 2) removing the electrode mixture from the mixing vessel; 3) applying the electrode mixture to a sieve which separates the electrode mixture into an undersize fraction and an oversize fraction; and 4) using the undersize fraction as the conditioned electrode mixture.

Description

[0001] Maschinenfabrik Gustav Eirich GmbH & Co. KG

[0002] Our reference number: 240843WO

[0003] Methods for the production and conditioning of electrode mixtures and of dry electrodes from the electrode mixtures

[0004] The present invention relates to a method for producing and conditioning dry electrode mixtures. Furthermore, the present invention relates to a method for producing dry electrodes from these electrode mixtures.

[0005] In recent years, battery technology, and in particular lithium-ion technology, has moved into the spotlight, as it is essential for the functionality of, for example, fully electric vehicles, but also for stationary energy storage systems. A long-lasting, high-capacity battery that is cost-effective to manufacture is a prerequisite for the acceptance of fully electric vehicles.

[0006] Currently, lithium-ion batteries are predominantly used. Within this category, several specific cell chemistries dominate, with the following being the most widespread cathode materials:

[0007] • Nickel-manganese-cobalt (NMC) electrode mixture: These cells use a mixture of nickel, manganese, and cobalt. The nickel ensures high energy density, manganese provides thermal stability, and cobalt stabilizes the structure.

[0008] • Nickel-cobalt-aluminum (NCA) electrode mixture: This mixture contains nickel, cobalt, and aluminum in the cathode. The aluminum content stabilizes the structure and improves the lifespan, while nickel maximizes the energy density.

[0009] • Lithium iron phosphate (LFP) electrode mixture: In this cobalt-free cell chemistry, lithium iron phosphate is used as the cathode material, which is less energy-dense but offers a longer lifespan and better thermal stability.

[0010] The anodes are usually made of graphite or silicon-graphite mixtures. For all these types, electrode mixtures are produced using polymeric binders, sometimes with conductive additives, applied to conductive foils, and calendered during or after this process to optimize the structural integrity and density of the electrodes. Furthermore, there are developments that could play a significant role in the future. Besides more cost-effective but lower-performance, yet cobalt-free, sodium-ion cell chemistries, intensive research is also being conducted on all-solid-state batteries with solid electrolytes. This technology theoretically offers an even higher energy density than conventional lithium-ion batteries and, due to the solid electrolyte, even greater safety. The production of all these batteries is expected to continue requiring calendered electrodes, which present various calendering challenges.

[0011] In summary, the calendering of electrode mixtures will continue to play an important role in future battery technologies, as it optimizes the density, homogeneity, and mechanical properties of the electrodes. However, the specific materials that will be used will depend on advances in materials science and the requirements of electromobility.

[0012] A typical lithium-ion cell electrode consists of a copper foil acting as the anode and an aluminum foil acting as the cathode. The foils are usually coated on both sides with active material and, at least for the cathode, with additives.

[0013] The electrodes must meet high standards in order to produce a reliable, high-capacity lithium-ion battery.

[0014] The electrode layer must have a defined, constant thickness and a defined pore structure into which the electrolyte can penetrate to transport lithium ions to each particle of the active material. Ideally, the active material should be wetted by the electrolyte over as large an area as possible. Furthermore, the particles of the active material must be electrically connected to the metal foil—that is, in the described example, to the copper or aluminum foil—to ensure the transport of electrons to and from each particle of the active material.

[0015] Furthermore, the particles of the active material must be bound both to each other and to the metal foil, for which a binder material is used. Finally, the layer thickness should be as uniform as possible across the width and length.

[0016] To produce the layers for dry electrodes, the starting materials—that is, the active material, the binder, and any additives—must be mixed together and prepared into a so-called structured mixture. Electrode mixtures for dry electrodes are produced with either little or, more commonly, no solvent. However, more intensive preparation is required when mixing the components to convert the polymeric binders, which are no longer soluble in a solvent as usual, into a processable and bonding state. Especially when PTFE or PVDF is used as a binder, the mixture typically needs to be processed in successive steps at different temperatures. When using PTFE, the mixture is fibrillated by temperature activation and the application of shear energy at temperatures above 30°C.The nano- and microscale polymer fibers formed during fibrillation create a crumbly to plastic mass that is very difficult to remove from the mixer. Since the mixture then needs to be evenly metered into a calender gap to produce the desired electrode film, this crumbly to plastic mass is often unusable. The mass must first be converted into a readily meterable agglomerate, granules, or powder.

[0017] Based on the described prior art, it is therefore an object of the present invention to provide a method for producing dry electrode mixtures which provides a readily processable electrode mixture of high quality.

[0018] This task is solved by a process for the production and conditioning of an electrode mixture, which consists of active material and binder as well as, if necessary, additives, comprising the steps

[0019] 1) Producing the electrode mixture in a mixing vessel of a mixer, wherein during the production the mixture is heated to a temperature TH, where TH > 45°C,

[0020] 2) Removal of the electrode mixture from the mixing container,

[0021] 3) Applying the electrode mixture to a sieve which separates the electrode mixture into a sieve pass and a sieve overflow, and

[0022] 4) Using the sieve pass as a conditioned electrode mixture.

[0023] In this application, the term "mixer" means any device for producing a material mixture and / or for homogenizing, dispersing, kneading, plasticizing, or conveying a mixture, in which a relative movement is generated between the mixture and at least one boundary surface within a mixing chamber bounded by a wall. This relative movement can be effected by a mixing element arranged in the mixing chamber and / or by movement of the mixing vessel and / or by a gas flow; the movement can, in particular, include rotation or agitation. Operation can be continuous and / or discontinuous. Furthermore, the "mixer" can consist not only of a single machine but also of several machines connected in series, which provide the electrode mixture at the discharge of the last machine.Thus, the term "mixer" does not refer solely to machines that are marketed and offered as mixers, but also to machines for other basic process engineering operations such as mills, in which a mixing process is inextricably superimposed alongside the comminution or dispersing process when different raw materials are fed into the machine simultaneously or sequentially.

[0024] In this application, the term "mixing container" refers to the housing that defines the mixing or comminution space, regardless of its geometric design, including container-, trough-, pipe- or channel-shaped designs as well as linearly extended process spaces with inlet and outlet openings (in particular cylinders / housings of a screw machine, e.g. extruder cylinders).

[0025] The term "mixing element" encompasses dynamic and static elements that influence the flow or mixing, such as agitators, rotor / stator assemblies, and structures integrated into the wall. The mixing element can be a separate component or an integral part of the wall.

[0026] A twin-screw extruder, for example, is a mixer within the meaning of this application; its mixing chamber forms the process channel (extruder cylinder / housing), and the mixing elements are the two screws, co-rotating or counter-rotating, intermeshing or non-intermeshing. The mixing chamber itself can also produce the mixing action if its movement generates the relative motion, as in a V-mixer; a separate mixing element is then not required.

[0027] It has been shown that the quality of the electrode mixture can be significantly improved if the temperature of the mixture is considerably increased during the mixing process in the mixing vessel, i.e., raised to more than 45°C. This can be achieved, for example, by introducing high mechanical power using a stirrer to generate frictional heat. However, in the resulting plastic, elastic, and "sticky" state when using fibrillating binders such as PTFE, the electrode mixture is difficult to remove from the vessel. Furthermore, it has a consistency and particle size distribution that does not allow for uniform dosing into a calender gap. Therefore, according to the invention, the electrode mixture is placed on a sieve.

[0028] However, there are also reasons against using a sieving process when dealing with electrode mixtures.

[0029] 1. Particle size distribution: As a rule, dry-produced electrode mixtures exhibit a wide particle size distribution, ranging up to pieces several centimeters in size. There is a risk that the larger, especially stickier, elastic plastic particles will become trapped in the sieve and clog the sieve surface, leading to an interruption of the production process.

[0030] 2. Clumping of particles: In highly binding mixtures, clumping and compaction can occur due to the oscillating and rolling motion of the sieve against the mixture, making sieving difficult or even impossible. Such locally compacted clumps could lead to uneven layer thicknesses on the electrode.

[0031] 3. Heating during sieving: Mechanical processes such as sieving, especially with additional friction from rotors, can lead to a slight heating of the materials. With temperature-sensitive mixtures and those prone to fibrillation, this could result in an undesirable change in the bulk structure, negatively affecting the calendering process.

[0032] 4. Agglomeration or segregation: There is a risk that different materials in the mixture may segregate during the sieving process, especially if they have different densities or particle sizes. This could impair the homogeneity of the electrode mass.

[0033] Surprisingly, it has been shown that the described disadvantages of dry electrode mixtures are negligible, especially under optimal conditions such as low mixing temperatures and particularly when using special friction sieves and special sieve linings, for example made of plastic, and lead to significantly better dosing capability.

[0034] The sieve separates the electrode mixture into the sieve fraction and the sieve overflow, with the overflow containing components that have a diameter larger than the sieve mesh size. The sieve fraction, loosened and narrowed in particle size by the sieving process, can be dosed much more easily and uniformly, for example, into a calender gap. The sieve, preferably made of a mesh fabric, preferably has a mesh size of less than 10 mm, and particularly preferably less than 5 mm, and most preferably less than 2 mm.

[0035] In a further preferred embodiment, a friction screen or an eddy current screen is used, preferably in such a way that no screen overflow remains. By using a friction screen or an eddy current screen, a considerable force is exerted on the material, for example by a rotor, so that larger agglomerates are broken up and the screen overflow is significantly reduced. The forces and distances between the rotor and the screen are particularly preferably adjusted such that no screen overflow remains.

[0036] Without a screen overflow, all particles are crushed, regardless of their size. If, instead, the coarser film sections are fed in without being crushed, this can negatively affect the homogeneity of the mixture, as these already highly compacted larger particles are not present in the electrode mixture from the mixer. The electrode mixture from the mixer is significantly less compacted and therefore "fluffier." When these compacted particles are forced through the screen, the compacted portions are broken up at the screen mesh and mixed with less compacted material from the mixer passing through the screen in parallel, resulting in a uniform and homogeneous bulk material that can be passed through the screen to the subsequent dosing step.

[0037] Improved processability of the optimally blended electrode mixture in the mixer is achieved when it is cooled while simultaneously being agitated, for example, by a stirring or mixing tool. The plastic, cohesive mass then breaks down into a dosable bulk material. However, this is very time-consuming, as the container and its walls must be cooled, and heat dissipation through the cooled surface area of ​​the container walls is limited. Furthermore, the heat stored within the container itself must also be removed, which slows down the product cooling process. If the preparation takes place in a mixing vessel, the vessel must also be reheated after removal, as a high temperature is required for the subsequent production of the next batch.

[0038] Therefore, in a further preferred embodiment, it is provided that after step 1) 1a) the electrode mixture in the container is cooled by at least AT = 5°C and preferably to a temperature TMAX < 35°C, but not below a withdrawal temperature T. E > 24°C, and after step 2) the following steps follow

[0039] 2a) Feeding the electrode mixture to a cooling device,

[0040] 2b) Cooling the electrode mixture after step 2a) by at least 4°C, preferably to a temperature TK < 19°C using the cooling device.

[0041] According to this embodiment, the electrode mixture is conditioned in several steps. After heating the mixture, during which the added binder and / or solid electrolyte, along with the other mixture components, is brought into a segregation-free state, the mixture is cooled in the mixing vessel by at least AT = 5°C and preferably to a temperature T MAX < 35°C, but not below a withdrawal temperature TE > 24°C. This cooling, combined with slow agitation, transforms the mixture into a bulk material. The electrode mixture can then be more easily removed from the mixing vessel. Depending on the raw material formulation, it may not yet be completely storage-stable and thus can be easily discharged from buffer tanks or silos.Due to the presence of oversize material, it is not yet fully suitable for being fed with high accuracy into a calender gap only a few dozen micrometers wide.

[0042] For example, ethylene carbonate (EC) is used as a material in all-solid-state batteries (ASSBs). EC is used as a solid electrolyte. By heating it to over 45°C, the EC, which is solid at room temperature, transitions into a liquid state and can thus form an agglomerate or granules together with the other powdered raw materials. Cooling in step 2) to below 35°C causes the granules to solidify, making them easy to remove from the container. In principle, this production of melt granules is also possible with other meltable binders, electrolytes, or additives.

[0043] To ensure the electrode mixture is both stable during storage and easy to dose, it is removed from the mixing container and transferred to a cooling unit. This allows the electrode mixture to cool only slightly in the container before being removed while still warm. This has the advantage that the mixing container requires less cooling and therefore less heating for the next batch, thus reducing both energy consumption and cycle time. The removed electrode mixture is then cooled by at least 4°C, and preferably to a temperature (TK) < 19°C, using the cooling unit. Particularly when using PTFE as a binder, this stabilizes the electrode mixture during storage, transport, and dosing.Ideally, the PTFE contained in the mixture is first cooled to a temperature below 35°C (still in a pseudohexagonal, very disordered phase), at which point the mixture decomposes and can then be more easily pumped from the container. The tendency of PTFE to fibrill decreases with decreasing temperature due to changing crystal structures in two temperature ranges. Cooling preferably occurs below the transition temperature of PTFE, which is 30°C to the partially ordered hexagonal phase, or even better, below 19°C to the well-ordered triclinic phase.

[0044] Essentially, the cooling of the electrode mixture is carried out in two steps. In the first step, the mixture is cooled only to the point where it transitions into a structured bulk state, making it easier to remove from the mixing vessel. The further cooling required to bring the electrode mixture into a state that is as stable for storage and easy to dose as possible, so that it can be processed further in a calender, then takes place outside the mixing vessel. Because the mixing vessel no longer needs to be cooled as much, the cycle time can be significantly reduced.

[0045] The cooling system can, for example, consist of a second mixer arranged in a cascade configuration, a so-called cooling mixer, whose walls are preferably cooled. This increases the number of machines and thus initially the costs, but due to significantly reduced residence times in the heating and cooling mixers at high throughput rates, it can ultimately lead to fewer machines and lower operating costs. Furthermore, if the second mixer is arranged appropriately so that the mixture can be transferred as a whole from the mixing mixer producing the mixture directly into the second mixer, for example by gravity, step 1a) can even be carried out in the second mixer. Thus, in this case, steps 2) and 3) can be performed after step 2).

[0046] 2a1) Transferring the electrode mixture into a cooling mixer with a cooling vessel, the walls of which are preferably cooled,

[0047] 2a2) Cooling the electrode mixture in the cooling container by at least AT = 5°C to a withdrawal temperature TE, which is preferably < 35°C

[0048] 2a3) Removal of the electrode mixture from the cooling container is carried out. In a further preferred embodiment, a conveying line of a pneumatic conveying system for removing the electrode mixture from the mixing container is provided as a cooling device in steps 2a) and 2b), which is operated with a gas, preferably with a temperature TG < 19°C, wherein preferably in step 1a), between step 1a) and step 2b) and / or during step 2b), dry ice or liquefied gas is introduced into the mixing container, and the gas produced by sublimation or evaporation is directed into the conveying line.

[0049] Pneumatic conveying includes, among other things, a pneumatic conveying unit, which usually consists of a blower or compressor that generates the necessary airflow, as well as a feed device, conveying lines which may additionally be equipped with a double jacket for cooling and / or insulation, and a material separator.

[0050] The feed device is installed in the container, for example in the form of a suction pipe, or at the outlet of the mixing vessel and transfers the mixture into the conveying line. The actual conveying can be carried out using a vacuum suction system or a pressure chamber, which gently introduces the electrode mixture into the line. Vacuum conveying is preferred. A cooling effect can be achieved if the transport gas used for pneumatic conveying is cooled or mixed with the exhaust gas produced by sublimation or evaporation from the liquid gas added to cool the mixture.

[0051] In a preferred embodiment, liquefied gas, such as liquid nitrogen or liquid carbon dioxide, or even in solid form as dry ice, is introduced into the mixture for cooling. This significantly accelerates the cooling process within the container. For example, 100 kg of plastic, fibrillated mass was cooled from 90 °C to below 20 °C in less than 3 minutes by adding 10 kg of dry ice. If cooling is achieved solely via a double-walled container, the cooling process takes more than 30 minutes. The amount of liquefied gas or dry ice added is preferably calculated so that the target temperature, i.e., a cooling of at least 5 °C, is reached as quickly as possible through complete gasification or sublimation, while simultaneously ensuring that the mixture is not cooled below the minimum extraction temperature of 24 °C through gasification or sublimation.The faster the cooling process of the mixture, the less steel of the container is cooled by the limited heat transfer from the mixture to the container wall. This reduces the required amount of liquid gas and the cooling of the container to a minimum. If dry ice or liquid nitrogen is introduced into the container before extraction, the abrupt gas evolution during sublimation or evaporation leads to a pressure increase in the container, which can assist the feed system. Furthermore, the resulting gas has a very low temperature, so that when it flows into the conveying line and is in contact with the electrode mixture for an extended period, it further cools it. The described effect is particularly pronounced in dilute-phase conveying (also known as continuous flow conveying) due to the large mass and heat exchange surfaces between the electrode mixture and the gas.To prevent the temperature from dropping too low, warmer gas, such as ambient air, can be mixed with the gas produced by evaporation or sublimation. This also prevents condensation effects on cold pipes, for example.

[0052] At the end of the conveying line, the electrode material is separated from the gas in the material separator. A cyclone separator, a deflector separator, or a filter system can be used here to gently separate the material and transfer it, for example, to a buffer tank.

[0053] In a further preferred embodiment, the electrode mixture is transferred to a buffer tank after step 2) and before steps 3) and 4). The buffer tank is preferably temperature-controlled and used as a cooling device in steps 2a) and 2b). The buffer tank is preferably double-walled, with a cooling fluid flowing between the two walls, and / or the buffer tank has thermal insulation. The electrode mixture is particularly preferably moved within the buffer tank. Alternatively, if the electrode mixture is transferred directly from the mixing tank to the cooling tank, the buffer tank can be omitted, or the electrode mixture can be transferred from the cooling tank to the buffer tank.

[0054] This can be achieved by means of an agitator, gas aeration using nozzles, or in the form of a flowing or fluidized bed through a continuous flow of appropriately tempered pressurized gas.

[0055] The buffer tank can therefore itself be used as a cooling unit. A separate cooling unit, such as the described pneumatic conveying system with chilled transport gas, can be provided instead or in addition. To prevent the electrode mixture particles from sticking together, an agitator can be installed in the buffer tank to stir and loosen the mixture until it can be transferred to, for example, a calender.

[0056] The sieve can be located inside or after the buffer storage tank.

[0057] In a preferred embodiment, the screen overflow is directed into the container, the buffer tank, or the conveying line. Alternatively, the screen overflow can also be directed into a comminution device, e.g., a further mixer. This allows the screen overflow to be recycled. Preferably, it is returned to the buffer tank, or, if a pneumatic conveying line is provided for extracting the electrode mixture from the container, returned to this conveying line. Alternatively, the screen overflow can also be transferred to a feed tank or separator, which transfers the material as part of the electrode mixture into the container, so that it is heated together with fresh raw materials during the production of the electrode mixture to a temperature TH of > 45°C, producing a homogeneous electrode mixture of new and recycled raw materials.

[0058] If the sieve is used in such a way that there is no sieve overflow as described above, the return flow can then be omitted.

[0059] Finally, a dry electrode can be produced from the electrode mixture prepared according to the invention. For this purpose, the electrode mixture is fed, for example, to a calender and calendered into a web, whereby any protruding edge strips of the web are then removed, for example, by cutting them off, to ensure a uniform web width. The removed edge strips are fed into the container, the cooling container, the buffer container, the sieve, or the conveying line. If powder deposition processes are used to coat the electrode film before calendering, the excess powder can be returned to the process in the same form. The same applies to dusts that are stirred up and extracted by handling the electrode mixtures at the feed points of the coating unit.

[0060] The calendering process plays a crucial role in shaping and compacting the electrodes to achieve the desired electrochemical properties.

[0061] During calendering, the electrode mixture is rolled or compacted into a film by a pair or series of rollers and then pressed onto a current collector (usually copper for the anode or aluminum for the cathode) at the end or even during this process. This forms the mixture into a uniform, dense layer with a defined thickness and structure. This process directly influences the porosity, thickness, and adhesion of the electrode mixture to the collector. Depending on the cell type being manufactured, the sandwich structure (electrode mixture and current collector) can then be either wound or stacked. In winding, anode and cathode strips are wound together with a separator into a spiral structure (typical for cylindrical or prismatic cells). In stacking, the electrodes and separators are placed on top of each other in layers (typical for pouch cells).

[0062] By returning the edge strips or excess material, material can be recycled, thereby reducing production costs. If the excess material is not in bulk but in the form of a compressed film, a further preferred embodiment provides a shredding device that divides the separated edge strips into smaller strip sections. Ideally, the separated edge strips are shredded to such an extent that they constitute a fine bulk material with a particle size of < 2 mm.

[0063] The separated strip sections, usually in the form of an endless belt with varying width, could be continuously fed into the shredding device by means of a conveyor belt or a suction stream to make them available for reuse in the production process.

[0064] A batch mixer, for example, is suitable as a comminution device, in which both the screen overflow, if any, and the strip sections are collected or fed in batches. By briefly chopping the mixture, a conveyable, fine-grained product, such as an agglomerate or powder, can be produced, which has the same properties as the electrode mixture produced in the container.

[0065] This material can then preferably be pneumatically removed from the batch mixer and transferred to the buffer tank along with the fresh raw material. If sufficient height is available, as an alternative to pneumatic removal from the crushing mixer, the crushing mixer could be positioned above the buffer tank for pneumatic removal of the mixture from the main mixers and discharged directly into it by gravity via a bottom discharge device. Since both screen overflow and edge pieces accumulate continuously, a preferred embodiment provides for the use of a continuous crushing device, e.g., a continuously operated mixer or a mill, such as a pin mill or impact mill. The crushed end product can either fall directly into the buffer tank at the discharge or be pneumatically lifted into the buffer tank.

[0066] Alternatively, in a preferred embodiment, the edge strips can also be fed to the friction sieve, i.e., in one of the next batches in step 3).

[0067] Further advantages, features, and applications of the present invention will become clear with reference to the following description of preferred embodiments and the accompanying figures. These show:

[0068] Figure 1 shows an arrangement for carrying out a first embodiment of the method according to the invention.

[0069] Figure 2 shows an arrangement for carrying out a second embodiment of the method according to the invention and

[0070] Figure 3 shows an arrangement for carrying out a third embodiment of the method according to the invention.

[0071] Figure 1 shows a schematic view of an arrangement for carrying out a first embodiment of the method according to the invention.

[0072] In a container 1, the dry electrode mixture is produced preferably without the addition of solvents, such as low- or high-boiling solvents or water. However, it is also possible to add a small amount of low-boiling solvents to activate the binders superficially. The proportion of volatile, i.e., low-boiling, solvents in the mixture is less than 5%. In this embodiment, the container 1 is rotatable about the container axis 4, but can also be stationary. A mixing tool 2 is arranged inside the container 1 and is rotatable about the mixing tool axis. The container wall and bottom are double-walled, allowing a cooling or heating medium to be supplied between the two walls to heat or cool the container and thus the mixture contained within it.However, it is also possible that only the container wall or only the container bottom is double-walled and through which a cooling or heating medium flows. The mixing tool itself could also be double-walled and through which a heating or cooling medium flows. A suction lance 3 is also provided, which is connected to a first pneumatic conveying line 11, through which the electrode mixture produced in container 1 can be extracted by pneumatic conveying. A particle size sensor 8 is arranged in the first pneumatic conveying line, which provides feedback on the particle size within the first pneumatic conveying line. This information can be used to adjust the mixing process in container 1, for example, by changing the rotational speed or mixing time.

[0073] The electrode mixture is produced in container 1, which necessitates heating the mixture to a temperature greater than 45 °C. To facilitate the removal of the electrode mixture, a cooling medium is introduced between the walls of the double wall of container 1, cooling the mixture by at least AT = 5 °C, and in this example to a temperature of less than 35 °C. The mixture is then transferred into a conveyable bulk material by moving the mixing tool 2. For example, cooling to 30 °C can be achieved. The still warm but now conveyable electrode mixture is then transferred via the suction lance 3 into the first pneumatic conveying line and introduced into a buffer container 7. In this embodiment, the buffer container 7 has at least a section of a double jacket, which allows the introduction of a cooling medium between the two walls of the double jacket.The electrode mixture is therefore cooled in the buffer tank by at least 4 °C and preferably to a temperature below 19 °C. A vacuum pump 19 is provided above the buffer tank 7 to assist the pneumatic conveying. A gas-solid separator 38 is located in the upper part of the buffer tank.

[0074] To assist with cooling and / or material discharge, the illustrated embodiment includes a gas aeration unit 36, through which gas can be blown into the electrode mixture contained in the buffer tank 7. A friction screen 12 with a rotor is arranged at the outlet of the buffer tank 7, and this screen is fed with the electrode mixture by means of a screw conveyor.

[0075] In this embodiment, the friction screen is configured such that any oversize material present is broken up by mechanical force, preventing screen overflow. The material passing through the screen is then introduced via a transfer unit 22 into a feed device 21. Load cells 23 can be used to determine and control the weight of the introduced or discharged electrode mixture. Additionally, the buffer hopper 7 can also be equipped with load cells or other sensors for level control and metered material discharge. The discharge from the feed device 21 is directed onto a multi-roll calender 13, which forms the electrode mixture into a uniform web 14. Uneven strip sections at the edges of the web 14 are cut off by the cutting device 24, so that the strip sections 15 fall into a receiving device 16.The receiving device 16 is connected via a second pneumatic conveying line 10 to a separator 37, which is located above the mixer 1. To ensure pneumatic conveying, a conveying gas connection 25 is provided on the receiving device 16, and a vacuum pump or a correspondingly powerful blower is located above the separator 37. A Venturi nozzle 9 is provided in the second pneumatic conveying line 10. In the Venturi nozzle 9, an accelerated gas flow occurs due to a cross-sectional narrowing followed by a cross-sectional widening. This exerts high tensile forces on the strip sections 15, which are supplied as an endless belt, tearing this endless belt into smaller sections, ideally only a few centimeters in size. The Venturi nozzle 9 thus serves as a comminution device. The comminutioned edge strips 15 fall into the separator 37 and can be transferred to the container 1 via the metering device 6.The pieces of edge strips 15, temporarily stored in the separator 37, are preferably introduced into the mixer at the beginning of or during the fibrillation phase. This ensures that the edge strip sections are homogeneously incorporated into the electrode mixture. Particularly when the edge sections are added right at the beginning of the fibrillation phase, they act as inoculating nuclei, accelerating the fibrillation of the PTFE in the electrode mixture. For level monitoring and dosing control, the separator 37 can be equipped with load cells or level sensors. Additionally, a weighed buffer tank can be interposed between the dosing unit 6 and the mixing vessel 1 to allow for the weighing of a defined quantity of material for feeding into the mixing vessel.

[0076] Figure 2 shows a schematic representation of an arrangement with which a second embodiment of the method according to the invention can be carried out. Where possible, the same reference numerals as in Figure 1 have been used to denote identical or nearly identical elements. Therefore, in the following, Figure 2 essentially only illustrates the difference from the setup of Figure 1. In Figure 2, a liquid gas supply 18 is arranged above the container 1. At the end of the mixing process for producing the electrode mixture at temperatures above 45 °C, the liquid gas 18, which is then introduced into the interior of the container 1, causes an abrupt cooling of the electrode mixture by a temperature difference of AT = 5 °C, preferably to a temperature below 35 °C, which facilitates the removal of the electrode mixture from the container 1. As soon as the liquid gas comes into contact with the warm mixture, it evaporates.The resulting cold gas is then also transferred via the suction lance 3 into the first pneumatic conveying line 11 and assists the pneumatic conveying. Due to the low temperature of the gas produced by evaporation, the electrode mixture is further cooled in the first pneumatic conveying line 11 by direct heat exchange between the mixture and the conveying gas. To support the cooling process, the conveying line 11 can be provided with a double jacket through which a cooling medium flows and / or with insulation. Further cooling can take place in the buffer tank 7 in the manner already described, if this has not already occurred in the first pneumatic conveying line 11. The conditioning, sieving, and metering of the electrode mixture are carried out in the device shown in Figure 2 in the same way as shown in Figure 1 and described in this context.

[0077] In contrast to Figure 1, the second pneumatic conveying line 10 is not connected to a separator located above the container 1, but is instead returned to the buffer container 7 via a Venturi nozzle, which serves to shred the edge strips 15. Alternatively or additionally, a shredding device 17, which here consists of a blade rotor, further shreds the sections of the edge strip 15 before the shredded edge strips 15 are returned to the buffer container 7. The essential difference between the embodiments shown in Figure 1 and Figure 2 is therefore that, firstly, cooling in the container 1 is achieved by supplying liquid gas 18, and secondly, the return of the resulting edge strips 15 does not take place in the container 1, but in the buffer container 7.It is understood that in other equally preferred embodiments, only one of the two described modifications compared to the embodiment of Figure 1 could be implemented. Cooling in the container 1 can also be achieved by a combination of wall cooling via the double jacket and evaporative cooling using liquid gas. If only a liquid gas is used as the cooling medium, the double jacket in the mixer 1 can be omitted.

[0078] Figure 3 shows an arrangement with which a third embodiment of the method according to the invention can be implemented. The mixing vessel 1 is again visible, but here it serves only as a supply point 34 for the heating medium, for supplying the heating medium into the double wall of the vessel 1. The medium supply and discharge 34 is effected by means of immersion tubes at different heights in an open channel on the outer wall of the rotating mixing vessel. The heating medium is circulated by means of a pump via a heat exchanger. The electrode mixture is transferred via a bottom drain 26 and a connecting channel 27 into a cooling mixer 28 arranged in a cascade below the vessel 1. The cooling mixer 28 has a coolant supply and discharge 29, e.g., in the form of a rotary feedthrough, through which a cooling medium can be supplied to and discharged from the double wall of the cooling mixer 28.The still-warm electrode mixture is therefore first transferred to the cooling mixer 28 as a cooling device and then from the cooling mixer via the suction lance 3 into the first pneumatic conveying line 11 into the buffer tank 7. In addition to or even as an alternative to cooling via a double jacket, the mixture in the cooling mixer 28 can also be cooled by adding liquid gas or dry ice. In this embodiment, the buffer tank 7 has an agitator 35, which, via an agitator drive 30, can provide further movement and thus accelerate the cooling of the electrode mixture in combination with the double jacket cooling 20. A friction screen 12 is again located at the outlet of the buffer tank 7.In this embodiment with a flat screen, however, less force is exerted on the particles, resulting in screen overflow, which is transferred to a discontinuous mixer that acts as a comminution device. Here, too, at the end of the calender, the edge strips 15 are separated from the uniform sheet by means of a cutting device 24. The edge strips 15 are also transferred via a conveyor belt 33 to the discontinuous mixer, which has an agitator equipped with knives that chops both the oversize material and the edge strips 15 into small particles. These are then transferred via a suction lance into the second pneumatic conveying line 10, where a Venturi nozzle 9 can be used to assist with further comminution.

[0079] In the arrangement shown in Figure 3, a particle size measuring device 8 is arranged in both the first and the second pneumatic conveying lines 10, 11. Particle size measurement can be performed, for example, using an optical measuring method and serves to detect deviations from a reference size distribution of the electrode mixture or of the bulk material returned via the second pneumatic conveying line 10. Using this information, a control loop can be implemented that adjusts the size distribution of the electrode mixture directly in the container 1 by adapting the tool speed, the mixture temperature, or the comminution time. Alternatively, or in combination, the temperature in the buffer container or the operating parameters of the friction screen 12 can also be adjusted. For temperature monitoring of the electrode mixture in the buffer container, the container is equipped with contact or non-contact temperature sensors.

[0080] To regulate the temperature or quantity of the conveying gas, additional air 39 can be introduced into the conveying line 10. This air can be conditioned in terms of temperature and humidity via heat exchangers and / or absorbers. The inventive process significantly simplifies the production of electrode mixtures and the production of dry electrodes from these mixtures by reducing the cycle time and significantly improving quality. Furthermore, scrap is significantly reduced through the recycling of excess material.

[0081] Reference symbol list

[0082] 1 mixer with container

[0083] 2 Mixing tool

[0084] 3 suction lances

[0085] 4 Container rotation axis

[0086] 5 Mixing tool rotary axis

[0087] 6 Dosing unit

[0088] 7 buffer tanks

[0089] 8 Particle size measuring device

[0090] 9 Venturi nozzle

[0091] 10 second pneumatic conveying line

[0092] 11 first pneumatic conveying line

[0093] 12 grater sieve

[0094] 13 multi-roll calenders

[0095] 14 lane

[0096] 15 edge strips

[0097] 16 Receiving device for pneumatic conveying

[0098] 17. Shredding device

[0099] 18 Liquefied petroleum gas

[0100] 19 Vacuum pump

[0101] 20 double jacket

[0102] 21 Feed device

[0103] 22 Transition

[0104] 23 load cells

[0105] 24 cutting device

[0106] 25 Propellant gas

[0107] 26. Bottom emptying

[0108] 27 Transition

[0109] 28 cooling mixers

[0110] 29 Coolant supply and discharge

[0111] 30 agitator drive

[0112] 31 Sieve overflow for oversize

[0113] 32 Discontinuous Mixer

[0114] 33 Conveyor belt

[0115] 34 Heating medium supply and discharge

[0116] 35 Buffer storage agitator

[0117] 36 Gas loosening

[0118] 37 separators

[0119] 38 Gas-solid separators

[0120] 39 Additional air

Claims

Patent claims 1. Method for the preparation and conditioning of an electrode mixture consisting of active material and binder, and optionally additives, comprising the steps 1) Producing the electrode mixture in a mixing vessel of a mixer, wherein during the production the mixture is heated to a temperature TH, where TH > 45°C, 2) Removal of the electrode mixture from the mixing container, 3) Applying the electrode mixture to a sieve which separates the electrode mixture into a sieve pass and a sieve overflow, and 4) Using the sieve pass as a conditioned electrode mixture.

2. Method according to claim 1, characterized in that the sieve has a mesh size of less than 10 mm and particularly preferably less than 5 mm and preferably less than 2 mm.

3. Method according to claim 1 or 2, characterized in that a friction sieve or an eddy current sieve is used as the sieve.

4. Method according to one of the preceding claims, characterized in that the sieve is used in such a way that no sieve overflow remains.

5. Method according to one of the preceding claims, characterized in that after step 1) the following 1a) Cooling the electrode mixture in the container by at least AT = 5°C and preferably to a temperature TMAX < 35°C, but not below a withdrawal temperature TE > 24°C, and following step 2) the steps 2a) Feeding the electrode mixture to a cooling device, 2b) Cooling the electrode mixture after step 2a) by at least 4°C, preferably to a temperature TK < 19°C using the cooling device.

6. Method according to claim 5, characterized in that a conveying line of a pneumatic conveying system for removing the electrode mixture from the mixing vessel, which is operated with a gas, preferably with a temperature TG < 19°C, is provided as a cooling device in steps 2a) and 2b), wherein preferably in step 1a), between step 1a) and step 2b) and / or during step 2b) Dry ice or liquefied gas is introduced into the mixing container, and the gas produced by sublimation or evaporation is directed into the conveying line.

7. Method according to one of claims 1 to 4, characterized in that after step 2) and before step 3) the following occurs 2a1) Transferring the electrode mixture into a cooling mixer with a cooling vessel, the walls of which are preferably cooled, 2a2) Cooling the electrode mixture in the cooling container by at least AT = 5°C to a withdrawal temperature TE, which is preferably < 35°C 2a3) Removal of the electrode mixture from the cooling container.

8. Method according to claim 5, 6 or 7, characterized in that the electrode mixture is transferred to a buffer container after step 2) or, if present, after step 2a3) and before steps 3) and 4), wherein the buffer container is preferably temperature-controlled and is used as a cooling device in steps 2a) and 2b), wherein the buffer container is preferably double-walled, with a cooling fluid able to flow between the two walls, and / or the buffer container has thermal insulation, wherein the electrode mixture is particularly preferably moved in the buffer container.

9. A method for producing dry electrodes from electrode mixtures produced by a method according to one of the preceding claims, characterized in that the electrode mixture is fed to a calender and calendered into a web, wherein the edge strips of the web or excess material are then cut off to ensure a uniform width of the web, and the cut-off edge strips or excess material are fed into the container, the cooling container, the buffer container or into the conveying line.

10. Method according to claim 9, characterized in that a comminution device is provided which divides the separated edge strips into smaller strip sections or a fine bulk material.

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