Method for producing dry electrodes from electrode mixtures

Abstract

The present invention relates to a method for producing dry electrodes from electrode mixtures produced in a mixing and / or conditioning process, in which the electrode mixtures are 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, characterized in that the cut-off edge strips or the excess material are fed to a comminution device which divides the cut-off edge strips into smaller strip sections which are fed to the mixing and / or conditioning process to produce a further electrode mixture.

Description

[0001] The present invention relates to a method for producing dry electrodes from electrode mixtures produced in a mixing and / or conditioning process, in which the electrode mixtures are 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.

[0002] A calender for manufacturing electrodes from a dry electrode mixture typically consists of several coordinated components that enable precise compaction and shaping of the electrode mixture. The basic structure of such a calender usually includes the following main components: 1. Roller pair: The core of the calender consists of two parallel rollers rotating in opposite directions at the same or different speeds. The rollers are made of high-strength material and can often be heated to improve the processing properties of the electrode compound. The roller surfaces can be smooth or textured to achieve the desired electrode surface structure. 2. Roll gap: The distance between the two rolls, the so-called calender or roll gap, is precisely adjustable and determines the thickness of the resulting electrode. Accurate control of this gap is crucial to ensure the required homogeneity and thickness of the electrodes. 3. Feed unit: The electrode mixture is continuously introduced into the roller gap via a feed unit. This unit may include conveying systems such as belts or hoppers to ensure a uniform and controlled material feed. 4. Receiving unit: After calendering, the finished electrode is transported further via a receiving unit. This can be, for example, a conveyor belt or another rotating roller that transfers the electrode to the next process step. 5. Edge cutter: To trim the edges of the electrode film to an exact width, the calender can be equipped with an edge cutter that removes material laterally, thus adjusting the electrode geometry. 6. Laminating unit: The formed electrode film must then be laminated onto the conductive foil. For this purpose, the electrode film and the conductive foil are guided between a rotating pair of rollers, and the electrode film is pressed onto the conductive foil. In some processes for manufacturing dry electrodes, the film formation and lamination onto the conductive foil takes place directly in the first roller gap below the feeding unit.

[0003] By precisely controlling pressure, temperature and gap width, the calender produces a homogeneous electrode film with a defined thickness and smooth surface, suitable for further processing in battery cells.

[0004] 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.

[0005] Currently, lithium-ion batteries are predominantly used. Within this category, several specific cell chemistries dominate, with the following being the most widespread cathode materials: • 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. • 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. • 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.

[0006] The anodes usually consist of graphite or silicon-graphite mixtures. For all these types, electrode mixtures are produced using polymeric binders, sometimes also with conductive additives, applied to conductive foils, and calendered during or after this process to optimize the structural integrity and density of the electrodes.

[0007] Furthermore, there are developments that could play a significant role in the future. Besides more cost-effective, but lower-performing, 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 will likely continue to require calendered electrodes, which present various calendering challenges.

[0008] 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.

[0009] 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.

[0010] The electrodes must meet high standards in order to produce a reliable, high-capacity lithium-ion battery.

[0011] 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.

[0012] 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.

[0013] To produce the layers for dry electrodes, the starting materials, i.e. the active material, the binder and, if applicable, the additives, must be mixed together and prepared into a so-called structured mixture.

[0014] Electrode mixtures for dry electrodes are produced with either little or, more commonly, no solvent. However, this necessitates more intensive preparation during the mixing process to convert the polymeric binders, which no longer dissolve in a solvent as usual, into a processable and bondable state. Particularly when PTFE or PVDF is used as a binder, the mixture typically requires processing 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 dosed into a calender gap to produce the desired electrode film, the crumbly to plastic mass is often unusable. The mass must first be converted into a readily dosable agglomerate, granules, or powder.

[0015] The edge strips that are cut off during the calendering process, or that are separated after calendering, are usually treated as offcut material and discarded.

[0016] Based on the described prior art, it is therefore an object of the present invention to provide a method for producing dry electrodes from dry electrode mixtures produced in a mixing and / or conditioning process, which is very efficient and provides a high-quality, easily processable electrode mixture.

[0017] This problem is solved by feeding the separated edge strips or excess material into a shredding unit, which divides the separated edge strips into smaller strip sections. These smaller sections are then fed into the mixing and / or conditioning process to produce a further electrode mixture. Surprisingly, it has been found that the edge strips, once divided into smaller strip sections in a shredding unit, can be fed back into the mixing and / or conditioning process without any further processing.

[0018] A Venturi nozzle, a discontinuous crushing mixer, a continuous crushing mixer, a granulator, a mill, a friction or eddy current sieve or a knife rotor is preferably suitable as a comminution device.

[0019] In a Venturi nozzle, an accelerated gas flow occurs due to a cross-sectional narrowing and subsequent cross-sectional widening, which exerts high tensile forces on the strip sections, which are present as an endless strip, tearing this endless strip into smaller sections, ideally only a few centimeters in size.

[0020] A batch-operated comminution mixer is a mixing system that operates in batches. In this system, material is subjected to mechanical forces in a closed working container to crush and homogeneously mix it. The system processes a specific quantity of material at a time, which is removed after the crushing and mixing process is complete before a new batch is fed in. The mixing process is carried out by rotating tools or kneading elements, which primarily reduce the material to a powder or agglomerate.

[0021] A continuous shredding mixer is a mixing device that continuously feeds material and simultaneously subjects it to mechanical forces for shredding and homogenization. The material is transported through the mixing system in a continuous flow and processed by rotating tools or mixing shafts. This continuous feed and discharge ensures uniform shredding of the material over extended periods of operation.

[0022] A granulator is a device for the mechanical comminution of solids into defined particle sizes, whereby the material is processed by rotating cutting tools, such as rotor blades, in combination with stationary counter blades. The material is reduced in size by a combination of shear, impact, and cutting forces.

[0023] A mill is a comminution unit that reduces material into finer particles through mechanical processing. This comminution process typically occurs through shear, impact, or frictional forces generated by rotating rollers, grinding elements, or impact mechanisms.

[0024] A knife rotor is a rotating shredding tool equipped with multiple cutting blades, designed to shred material using shear forces. The knife rotor rotates, for example, in close proximity to stationary counter blades, thereby cutting the material into small particles.

[0025] By briefly chopping the mixture, a conveyable, fine-grained product, e.g. an agglomerate or powder, can be produced which has the same properties as the electrode mixture produced in the mixing container.

[0026] Furthermore, it is advantageous if the electrode mixtures are produced in a mixing vessel, whereby the mixture is kept at a temperature T during production. H is heated, whereby T H > 45°C.

[0027] It has been shown that the quality of the electrode mixture can be significantly improved if the temperature of the electrode mixture is significantly increased during the mixing and / or conditioning process, 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.

[0028] In its resulting plastic, elastic, and "sticky" state, the electrode mixture is difficult to remove from the mixing container. Furthermore, its consistency makes uniform dosing into a calender gap challenging.

[0029] The mixing and conditioning process according to step 1) is therefore particularly preferred and includes the following steps: 2) Cooling the electrode mixture in the mixing container by at least ΔT = 5°C and preferably to a temperature T MAX < 35°C, but not below a withdrawal temperature T E > 24°C, 3) Extraction of the electrode mixture at the extraction temperature and feeding of the electrode mixture to a cooling device, 4) Cooling the electrode mixture after step 2) by at least 4°C, preferably to a temperature T K < 19°C using the cooling device.

[0030] Improved processability of the optimally blended electrode mixture 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 mixing vessel and its walls must be cooled, and heat dissipation through the cooled surface area of ​​the mixing vessel walls is limited. Furthermore, the heat stored within the mixing vessel 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.

[0031] Therefore, the electrode mixture is preferably conditioned in several steps. After heating the mixture, during which the added binder and / or solid electrolyte, together with the other mixture components, is brought into a segregation-free state, the mixture is then cooled in the mixing vessel by at least ΔT = 5°C and preferably to a temperature T. MAX < 35°C, but not below a withdrawal temperature T EThe mixture is cooled to > 24°C. This cooling, combined with slow agitation, transforms the mixture into a bulk material. This makes it easier to remove the electrode mixture from the mixing vessel. Depending on the raw material formulation, it may not yet be completely stable for storage and cannot be easily discharged from buffer tanks or silos. Furthermore, due to the presence of oversize particles, it is not yet fully suitable for precise feeding into a calender gap only a few dozen micrometers wide.

[0032] 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 mixing container. In principle, this production of melt granules is also possible with other meltable binders, electrolytes, or additives.

[0033] To ensure the electrode mixture is both stable for storage and easy to dose, it is removed from the mixing container and transferred to a cooling unit. This means the electrode mixture is only slightly cooled in the mixing container and 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.

[0034] The extracted electrode mixture is then cooled by at least 4°C and preferably to a temperature T KThe mixture is cooled to < 19°C using the cooling device. 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 < 35°C (still in a pseudohexagonal, very disordered phase), causing the mixture to decompose and thus allowing it to be more easily pumped from the mixing container. The tendency of PTFE to fibrillate decreases with decreasing temperature due to changing crystal structures in two temperature ranges. Cooling preferably occurs below the transition temperature of PTFE of 30°C to the partially ordered hexagonal phase, or even better, below 19°C to the well-ordered triclinic phase.

[0035] Essentially, the cooling of the electrode mixture is preferably carried out in two steps. In the first step, cooling occurs only to the point where the electrode mixture transitions into a structured bulk state, making it easier to remove from the mixer. 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 further processed 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.

[0036] The cooling system can, for example, consist of a second mixer arranged in a cascade configuration, the walls of which are cooled. While this increases the number of machines and thus initially the costs, significantly shorter residence times in the heating and cooling mixers can lead to fewer machines overall and lower operating costs at high throughput rates. Furthermore, with a suitable arrangement of the second mixer such 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 2) can even be carried out in the second mixer.

[0037] In a preferred embodiment, a conveying line of a pneumatic conveying system for extracting the electrode mixture from the mixing vessel of a mixer is provided as a cooling device in steps 3) and 4), which is supplied with a gas preferably at a temperature TG < 19°C, wherein preferably in step 2), between steps 2) and 3) and / or during step 3) dry ice or a liquefied gas, e.g. liquid nitrogen, is introduced into the mixing vessel, wherein the gas produced by sublimation or evaporation is directed into the conveying line.

[0038] Pneumatic conveying for the removal of an electrode mixture from a mixing container ensures that the mixture can be removed efficiently, cleanly and without segregation or significant change in the bulk properties or damage to the particles.

[0039] 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.

[0040] The feed device is installed in the mixing vessel, 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.

[0041] 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 in the mixing vessel. 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 mixing vessel, the cooling process takes more than 30 minutes. The amount of liquefied gas or dry ice added is preferably measured so that the target temperature, i.e., a cooling of at least ΔT = 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 is carried out, the less steel of the mixing vessel is cooled by the limited heat transfer from the mixture to the vessel wall. This reduces the required amount of liquefied gas and the cooling of the mixing vessel to a minimum.

[0042] If dry ice or liquid nitrogen is introduced into the mixing vessel before extraction, the abrupt gas evolution during sublimation or evaporation leads to a pressure increase within the vessel, 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 remains in contact with the electrode mixture for an extended period, it further cools the mixture. This effect is particularly pronounced in low-flow 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 added to the gas produced by evaporation or sublimation. This also prevents condensation effects on cold pipes.

[0043] 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.

[0044] In a further preferred embodiment, the electrode mixture according to step 2) is transferred to a buffer tank, wherein the buffer tank is preferably temperature-controlled and used as a cooling device in steps 3) and 4), wherein the buffer tank is preferably double-walled, with a cooling fluid able to flow between the two walls, and / or the buffer tank has thermal insulation, and wherein the electrode mixture is particularly preferably moved within the buffer tank. This can be achieved by an agitator, gas aeration via nozzles, or in the form of a fluidized bed or fluidized bed by means of a continuously flowing, appropriately temperature-controlled pressurized gas.

[0045] The buffer tank can thus be used as a cooling device itself. A separate cooling device, 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 present in the buffer tank, which stirs and loosens the mixture until it can be transferred to, for example, a calender. However, it is also possible to provide the buffer tank in addition to the cooling device, so that the transfer of the electrode mixture takes place after step 2) but only after step 4).

[0046] In a preferred embodiment, the electrode mixture is applied to a sieve after step 1), and preferably after step 3), or even more preferably after step 4), and only the sieve-passed material is used as the conditioned electrode mixture for electrode production. The sieve can be located within or after the buffer storage tank. The sieve separates the electrode mixture into the sieve-passed material and the sieve overflow, with the overflow collecting components that have a diameter larger than the sieve mesh size. The sieve-loosened material can be dosed much more easily and uniformly, for example, into a calender gap.

[0047] The sieve preferably has a mesh size of less than 10 mm, and particularly preferably less than 5 mm, and most particularly preferably less than 2 mm.

[0048] In a preferred embodiment, the screen overflow is directed into the mixing vessel, the cooling mixer, the buffer tank, the comminution unit, or the conveying line. This allows the screen overflow to be recycled. Returning it to the buffer tank is preferred, or, if a pneumatic conveying line is provided for extracting the electrode mixture from the mixing vessel, returning it 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 mixing vessel, so that it is brought to a temperature T together with fresh raw materials during the production of the electrode mixture. H heated to > 45°C and producing a homogeneous electrode mixture of new and recycled raw materials.

[0049] 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 are particularly preferably adjusted so that no screen overflow remains that would need to be recycled. Recycling can then be omitted.

[0050] A dry electrode is then produced from the electrode mixture prepared in this way. For this purpose, the electrode mixture is fed into the calender and calendered into a sheet. Any excess edge strips of the sheet are then removed, for example, by cutting them off, to ensure a uniform sheet width. The removed edge strips are, if necessary, conveyed via a shredding device into the mixing vessel, the cooling mixer, the buffer tank, or the conveying line. If powder application methods are used to coat the electrode foil before calendering, the excess powder can be returned to the process in the same form. The same applies to dust that is stirred up and extracted during the handling of the electrode mixtures at the feed points of the coating unit.

[0051] The calendering process plays a crucial role in shaping and compacting the electrodes to achieve the desired electrochemical properties.

[0052] 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).

[0053] 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.

[0054] 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.

[0055] This material can then preferably be pneumatically removed from the comminution unit, i.e., for example, a batch crushing mixer, and transferred to the buffer tank together with the fresh raw material. If sufficient headroom 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 the main mixer by gravity via a bottom discharge device.

[0056] Since both screen overflow and edge sections can accumulate continuously, a preferred embodiment provides for the use of a continuous comminution device, e.g., a continuously operated mixer or mill, such as a pin mill or impact mill. The comminutioned end product can either fall directly into the buffer container at the discharge or be pneumatically lifted into the buffer container.

[0057] Alternatively, the edge strips can also be fed directly to the grinding sieve as a shredding device.

[0058] 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: Fig. 1 an arrangement for carrying out a first embodiment of the method according to the invention, Fig. 2 an arrangement for carrying out a second embodiment of the method according to the invention and Fig. 3 an arrangement for carrying out a third embodiment of the method according to the invention.

[0059] In Fig. Figure 1 shows a schematic view of an arrangement for carrying out a first embodiment of the method according to the invention.

[0060] In a mixing vessel 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 mixing vessel 1 is rotatable about the mixing vessel axis 4, but it can also be stationary. A mixing tool 2 is arranged inside the mixing vessel 1 and is rotatable about the mixing tool axis. The mixing vessel wall and bottom are double-walled, allowing a cooling or heating medium to be supplied between the two walls to heat or cool the mixing vessel and thus also the mixture contained within it.However, it is also possible that only the mixing vessel wall or only the mixing vessel 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.

[0061] A suction lance 3 is also provided, which is connected to a first pneumatic conveying line 11, through which the electrode mixture produced in the mixing vessel 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 the mixing vessel 1, for example, by changing the rotational speed or mixing time.

[0062] The electrode mixture is produced in mixing vessel 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 mixing vessel 1. This cools the mixture by at least ΔT = 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 vessel 7. In this embodiment, the buffer vessel 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.

[0063] To assist with cooling and / or material discharge, the illustrated embodiment includes a gas aeration system 36, through which gas can be injected 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.

[0064] 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. Using load cells 23, the weight of the introduced or discharged electrode mixture can be determined and controlled accordingly. Additionally, the buffer tank 7 can also be equipped with load cells or other sensors for level control and metered material discharge.

[0065] 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 present as an endless strip, tearing this endless strip 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 mixing vessel 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. In particular, if the edge sections are added right at the beginning of the fibrillation phase, they act as inoculation 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 installed between the dosing unit 6 and the mixing tank 1 to allow for the weighing of a defined quantity of material for feeding into the mixing tank.

[0066] In Fig. 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 2 have been used. Fig. 1 is used to denote identical or nearly identical elements. In the following, Fig. 2. Therefore, the difference is essentially only to the structure of Fig. 1 shown. Fig. 2 A liquid gas supply 18 is arranged above the mixing vessel 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 mixing vessel 1, causes an abrupt cooling of the electrode mixture by a temperature difference of ΔT = 5 °C, preferably to a temperature below 35 °C, which facilitates the removal of the electrode mixture from the mixing vessel 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 dosing of the electrode mixture takes place in the [unit / section]. Fig. 2 device shown, just as in Fig. 1 is shown and described in this context.

[0067] The second pneumatic conveying line 10 is now, in contrast to Fig. 1, however, is not connected to a separator located above the mixing vessel 1, but is returned to the buffer vessel 7 via a Venturi nozzle, which serves to shred the edge strips 15. Alternatively or additionally to the Venturi nozzle, a shredding device 17, which here consists of a knife rotor, further shreds the sections of the edge strip 15 before the shredded edge strips 15 are returned to the buffer vessel 7. The essential difference between the in Fig. 1 and Fig. The embodiments shown in 2 therefore consist in the fact that, firstly, cooling in the mixing container 1 is effected by supplying liquid gas 18, and secondly, the return of the resulting edge strips 15 is not to the mixing container 1, but to the buffer container 7. It is understood that in other equally preferred embodiments, only one of the two described modifications compared to the embodiment shown may be necessary. Fig. 1 could be implemented. Cooling in the mixing vessel 1 can also be achieved through a combination of wall cooling via the double jacket and evaporative cooling using liquid gas. If only liquid gas is used as the cooling medium, the double jacket in mixer 1 can be omitted.

[0068] In Fig. 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 mixing 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 here via a bottom drain 26 and a connecting channel 27 into a cooling mixer 28 arranged in a cascade below the mixing 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 mixing vessel 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.

[0069] In the Fig.In the arrangement shown in Figure 3, a particle size measuring device 8 is arranged in both the first and second pneumatic conveying lines 10 and 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 mixing vessel 1 by adapting the tool speed, the mixture temperature, or the comminution time. Alternatively or in combination, the temperature in the buffer vessel or the operating parameters of the friction screen 12 can also be adjusted. For temperature monitoring of the electrode mixture in the buffer vessel, the vessel is equipped with contact or non-contact temperature sensors.

[0070] To regulate the delivery gas temperature or delivery gas quantity, additional air 39 can be introduced into the delivery line 10. This air can be conditioned in terms of temperature and humidity via heat exchangers and / or absorbers.

[0071] The inventive process significantly simplifies the production of dry electrodes from these mixtures by reducing the cycle time and considerably improving quality. Furthermore, waste is significantly reduced through the recycling of excess material. Reference symbol list 1 mixer with mixing container 2 Mixing tool 3 suction lances 4 Container rotation axis 5 Mixing tool rotary axis 6 Dosing unit 7 buffer tanks 8 Particle size measuring device 9 Venturi nozzle 10 second pneumatic conveying line 11 first pneumatic conveying line 12 grater sieve 13 multi-roll calenders 14 lane 15 edge strips 16 Receiving device for pneumatic conveying 17. Shredding device 18 Liquefied petroleum gas 19 Vacuum pump 20 double jacket 21 Feed device 22 Transition 23 load cells 24 cutting device 25 Propellant gas 26. Bottom emptying 27 Transition 28 cooling mixers 29 Coolant supply and discharge 30 agitator drive 31 Sieve overflow for oversize 32 Discontinuous Mixer 33 Conveyor belt 34 Heating medium supply and discharge 35 Buffer storage agitator 36 Gas loosening 37 separators 38 Gas-solid separators 39 Additional air

Claims

Method for producing dry electrodes from electrode mixtures produced in a mixing and / or conditioning process, in which the electrode mixtures are fed to a calender and calendered into a web, wherein the edge strips of the web or excess material are then separated to ensure a uniform width of the web, characterized in that the separated edge strips or excess material are fed to a comminution device which divides the separated edge strips into smaller strip sections which are fed to the mixing and / or conditioning process to produce a further electrode mixture. Method according to claim 1, characterized in that a Venturi nozzle, a discontinuous crushing mixer, a continuous crushing mixer, a granulator, a mill or a knife rotor is used as the crushing device. Method according to claim 1 or 2, characterized in that for the production and conditioning of the electrode mixtures, which consist of active material, optionally additives and binder, a method is used comprising step 1) producing the electrode mixture in a mixing vessel, wherein during production the mixture is heated to a temperature TH, where TH > 45°C. The method according to claim 3, characterized in that the manufacturing and conditioning method according to step 1) comprises the following steps: 2) Cooling the electrode mixture in the mixing vessel by at least ΔT = 5°C and preferably to a temperature TMAX < 35°C, but not below a withdrawal temperature TE > 24°C, 3) Withdrawing the electrode mixture at the withdrawal temperature and feeding the electrode mixture to a cooling device, 4) Cooling the electrode mixture according to step 2) by at least 4°C, preferably to a temperature TK < 19°C by means of the cooling device. The method according to claim 4, characterized in that a conveying line of a pneumatic conveying system for removing the electrode mixture from the mixing container, which is operated with a gas, preferably with a temperature TG< 19°C, is provided as a cooling device in steps 3) and 4), wherein preferably in step 2), between steps 2) and 3) and / or during step 3) 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. Method according to claim 4 or 5, characterized in that the electrode mixture according to step 2) is transferred into a buffer container, wherein the buffer container is preferably temperature-controlled and is used as a cooling device in steps 3) and 4), wherein the buffer container is preferably double-walled, wherein a cooling fluid can 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. Method according to one of claims 3 to 6, characterized in that the electrode mixture according to step 1) and preferably according to step 3) is applied to a sieve and only sieve passage is used as conditioned electrode mixture, wherein preferably the sieve has a mesh size of less than 10 mm and particularly preferably of less than 5 mm and best of less than 2 mm. Method according to claim 7, characterized in that the sieve overflow is directed into the mixing container, the cooling mixer, the buffer container, a comminution device or into the conveying line. Method according to claim 7, characterized in that a friction sieve or, more preferably, an eddy current sieve is used as the sieve, wherein the use is preferably carried out in such a way that no sieve overflow remains. Method according to one of the preceding claims, characterized in that the separated edge strips or the excess material are fed into the mixing container, the cooling mixer, the buffer container or into the conveying line.

Images