Method for producing an electrode of a battery cell

Abstract

Method for producing an electrode (1) of a battery cell (2); the method comprising at least the following steps: a) providing a carrier material (4) of an electrode (1) coated with an active material (3); b) applying a pore-forming fluid (5) to the coated carrier material (4) so that the fluid (5) is absorbed into the active material (3); c) heating the carrier material (4) impinged upon by the fluid (5) and at least partially expelling the fluid (5) from the active material (3) to form pores; wherein between steps b) and c) the active material (3) is compacted in a further step x); wherein step c) is carried out after step x).

Description

The invention relates to a method for producing an electrode of a battery cell. In particular, an active material which is arranged on a carrier material is to be admixed with a pore-forming agent. The carrier material comprises in particular a tape-shaped carrier material.Batteries, in particular lithium-ion batteries, are increasingly being used for driving motor vehicles. Batteries are usually assembled from cells, each cell having a stack of anode, cathode and separator sheets. At least some of the anode and cathode sheets are designed as current collectors for diverting the current provided by the cell to a load arranged outside the cell.In the production of a lithium-ion battery cell, a so-called carrier material, in particular a strip-shaped carrier material, for example a carrier film, is coated on both sides with a slurry via an application tool. The slurry consists of a plurality of components, including an active material, conductive carbon black, binder, solvents and optionally other additives. After the coating carried out on one side in each case, the coated carrier material is fed in each case to a drying process in order to evaporate the solvent present and to firmly bond the remaining constituents to the carrier film. The carrier film forms a current collector of the battery cell.The coating thus produced is porous. The porosity is reduced by calendering, since the coating is compacted here. Densification is required to increase specific capacity (by volume) and electrical conductivity.The active material is compressed by about 40% during calendering. The calendering operation is similar to the rolling operation. The active material is compressed in a small deformation zone with a high calendering force. The following problems occur during the calendering operation:First, due to the high calendering force, a porosity at the surface of the active material where the electrode is in contact with the calendering rolls decreases more. The anode consists in particular of graphite as active material; furthermore, the anode contains, for example, binder SBR, diluent CMS and conductive carbon. In particular, attempts are being made to achieve an active material density of 1.6 g / cm 3[ grams / cubic centimeter] in order to increase the volumetric energy density of the battery cell. A high density also increases the conductivity of the battery cell. The decrease in porosity close to the surface makes it difficult for lithium ions to be incorporated into the graphite layers. As a result, lithium plating occurs to an increased extent at the surface, i.e. the deposition of metallic lithium. However, the service life of the battery cell is thus drastically reduced. Since the deformation during calendering takes place in a very small area (depending on the diameter of the roll), there is a very high stress concentration in a small deformation area, which stress concentration causes cracks in the active material. In summary, high compression in calendering is desirable, but it is associated with the problem of lithium plating.Second, the change in pore structure for certain pore size ranges and the deformation of the active material have been identified as key factors that negatively affect the electrochemical performance of the battery cell. Surface roughness and open-surface pores, which definitely have an influence on the overall wetting behavior of the electrodes with an electrolyte, change with the compression ratio. Usually, during calendering, a porosity reduction of up to 30% takes place, but deformation of the active material particles can be observed at the surface even at a degree of compaction (i.e. a porosity reduction) of 20%. This means that the porosity is not uniformly distributed over the layer thickness of the active material. The porosity at the surface is then greatly reduced compared to the porosity in the vicinity of the carrier material.The particle deformation of the active material particles, which is exclusively limited to the particles arranged on the surface of the active material, has an influence on the electrochemical performance of the battery cell. The deformation of the particles at the surface, which was effected by the high calender compression, leads to a transport barrier for lithium ions during the electrochemical cycles, so that the long-term performance of these electrodes is drastically influenced, especially for relatively high C-rates. With high porosity reductions of about 20% to about 26%, for example, particularly large pores, with largest diameters between 2 μm [micrometers] and 5 μm, are closed by compression. The influence of these missing "large" pores, especially at the surface and the overall smaller total pore volume, on the electrochemical behavior is one of the main causes of lithium plating, which drastically reduces the service life of the battery cell.Both blocking and removing large pores and greatly reducing total pore volume results in a low amount of electrolyte / active material particle interfaces available for lithium ion transfer. The reduction of the electrolyte / active material particle interfaces may lead to a problem of electrolyte wetting. This also contributes to deterioration of the electrochemical performance.In order to solve the above problems, the following measures have been taken so far:• Adding graphite with higher porosity (porocarb) in higher proportion; however, porocarb is an expensive material;• Reducing the compression during calendering to less than 20%; however, this reduces the volumetric energy density of the battery cell and also the conductivity of the active material;• Addition of more conductive carbon of 2% to 5%, so that the spaces between the active material particles can be filled with conductive carbon and the conductivity is also achieved with lower calender compression.However, these measures have the following disadvantages:• Less compression during calendering means less volumetric energy density in the battery cell;• Less compression during calendering means less electrical conductivity in the active material, since conductive carbon is not capable of contacting active material particles;• More conductive carbon means a higher rebound after calendering; the calendering of the anode must then be done in two steps, the additional last step serving to compensate for rebound; this increases the space requirement and the cost of the machine;• With a higher proportion of conductive carbon, the viscosity of the slurry or of the slurry increases, which means a longer drying time and makes wet coating more difficult.As a possible alternative solution, for example, the active material can be applied in different layers with mutually different porosity. The top layer has a higher porosity to compensate for the reduction in porosity due to calender compaction. However, the coating process is very complicated as a result. Moreover, problems can arise with regard to the cohesion between two mutually adjacent coating layers.CN 111725479 A discloses an electrode of a lithium-ion battery cell and a production method for this electrode. The electrode is coated with an active material to which a pore-forming agent has already been added.US 2021 / 0 155 766 A1 provides compositions and methods for making and using electrode free-standing films for electrodes by methods that improve prior dry process techniques. Methods are provided for forming a first free-standing film.DE 10 2014 226 394 A1 relates to a method for producing a lithium-ion cell having a high energy density, specific energy and a long service life. This method is particularly suitable for the continuous production of lithium ion cells with processes running at high speed, such as, for example, winding methods.With the addition of a pore-forming agent to an active material already before the coating of the carrier material, at least the chemistry and the viscosity of the active material are influenced.The object of the present invention is to at least partially solve the problems mentioned with respect to the prior art. In particular, a method is to be proposed by means of which a porosity of an active material can be adjusted in an advantageous manner.To achieve these objects, a method with the features according to claim 1 contributes. Advantageous further developments are the subject of the dependent patent claims. The features individually listed in the patent claims can be combined with one another in a technically expedient manner and can be supplemented by explanatory facts from the description and / or details from the figures, wherein further embodiment variants of the invention are shown.A method for producing an electrode of a battery cell is proposed. The method comprises at least the following steps: a) providing an active material-coated carrier material of an electrode; b) applying a pore-forming fluid to the coated carrier material, such that the fluid is absorbed in the active material; c) heating the carrier material applied with the fluid and at least partially expelling the fluid from the active material, forming pores.The above (non-final) classification of the method steps in a) to c) is primarily intended only for differentiation purposes and does not force any sequence and / or dependency. The frequency of the method steps can also vary. It is likewise possible for method steps to overlap one another at least partially in terms of time. Preferably, steps a) to c) are carried out in the order given.The electrode to be produced is provided in particular for use in a lithium-ion battery cell. The electrode comprises in particular a carrier material, for example a copper or aluminum sequence. The carrier material used consists in particular of 10 to 12 μm thick copper for the anode and 12 to 15 μm thick aluminum for the cathode. The carrier material is coated with an active material at least on one largest side surface, optionally also on the opposing largest side surfaces.Specifically, the active material includes at least one of carbon black (NMC), lithium nickel cobalt manganese (as a lithium-storing active material), graphite (as a lithium-storing active material), carbon nanotubes (CNT), styrene-butadiene rubber (as a binder), carboxymethyl cellulose polymer (CMC), polyvinylidene fluoride (PVDF), and porous graphite. The components of the material that are not binding material are in particular added to the active material.According to step a), in particular a carrier material of an electrode coated with an active material is provided. The coated carrier material is provided in particular as a strip-shaped endless material. The strip-shaped endless material is conveyed in particular along a conveying direction, at least during steps b) and c). In particular, the active material is only applied to the carrier material and optionally smoothed or adjusted with respect to a thickness of the coating, but has not yet been calendered.During calendering, the coated carrier material is passed through a roll arrangement which is optionally tempered and can thus heat the coated carrier material.The coating is compacted via the rolls. An increase in a density (a reduction in the porosity) of the coating of at least 20% usually takes place.According to step b), in particular a pore-forming fluid is applied to the coated carrier material, so that the fluid is absorbed in the active material. The fluid is in particular in a liquid aggregate state. The fluid penetrates in particular into the porous active material. In particular, the total porosity present before step b) is filled by the fluid to an extent of at least 40%, preferably at least 60%, particularly preferably at least 80%.According to step c), in particular, the carrier material to which the fluid is applied is heated and the fluid is at least partially expelled from the active material, forming pores (first heating stage).In particular, the carrier material to which the fluid is applied is heated to at least a boiling temperature of the fluid, so that the fluid is driven out of the active material to form pores.Between steps b) and c), in a further step x), the active material is compacted, in particular by at least 15%, preferably by at least 20%, particularly preferably by at least 22%. In particular, a compaction takes place by at most 35%, preferably by at most 30%.In particular, the active material is compacted in step x) to a density of at least 1.5 g / cm 3[ grams / cubic centimeter], preferably of at least 1.6 g / cm 3.In particular, step x) comprises calendering and step c) is effected spaced apart from step x). In particular, calendering is carried out without heating device, i.e. without targeted increase of the temperature of the active material. The pores of the active material are additionally supported by the fluid absorbed in the active material, so that a compaction of the active material is equalized over the layer thickness. In particular, excessive compaction is thus prevented precisely at the surface of the coating. Calendering is carried out or compacting is carried out in particular at room temperature.The roll used in calendering can be excited in particular with an ultrasonic excitation. The fluid can thus be transferred into the pores of the coating of the carrier material.In particular, step c) takes place exclusively via heat convection or heat radiation, i.e. in particular just not via heat conduction. Thus, in particular, there is no contacting of the active material with heated rollers or (calendering) rollers. In particular, radiant heaters or heat gas streams are provided, via which heat is transported to the active material.In particular, the coated carrier material is processed as continuous material at least during steps a) to c) and, after step c), is separated into an electrode sheet, for example in a step d).In particular, step b) takes place in a dipping basin filled with the fluid, through which the coated carrier material is transported.In particular, the dipping basin is arranged in a housing. In particular, a pressure in the immersion tank is higher than an external pressure present outside the housing. In particular, a double housing is provided, so that no air from the environment can enter the inner housing or the immersion basin. An outer housing made of sheet steel about 10 mm [millimeters] in thickness can simultaneously be designed as a capsule for protection against liquid escape or explosion. An inner casing is made of stainless steel sheet in particular to resist corrosion. It consists in particular of a stainless steel sheet about 5 mm thick.Alternatively or additionally, the fluid is sprayed onto the active material in step b).In particular, the coated carrier material is guided in the context of step b) over a series of rollers or rollers, referred to below as pressure rollers, which are located, for example, in the dip tank or after optionally individual spraying devices, so that the surface of the active material can have maximum contact with the fluid. In particular, mechanical pressure is exerted on the surface of the active material by pressing rollers, so that the fluid penetrates into the active material and at least partially fills the pores.In particular, the coated carrier material is guided in the context of step b) over a series of rollers or rollers, referred to below as application rollers, which are acted upon by the fluid. In this case, the coated carrier material is in particular only acted upon by the fluid via the rollers and in particular is not transported through the fluid. The application rollers can be arranged, for example, partially in a dipping basin or can be acted upon with the fluid by a spraying device.If the coated carrier material is pressed to a thickness, in particular a final thickness, during compacting or calendering, it is possible that some fluid is pressed outwards from the pores, because fluid is in particular an incompressible medium. In order to prevent the extrusion of fluid, a carrier film, for example made of polyurethane material, can be arranged in particular on the upper and lower layers of the coated carrier material. The carrier film prevents in particular direct contact between the coated carrier material and the compaction roller or the calender or the calender roller. The carrier film transfers the compacting force or calendering force to the coated carrier material. The carrier film serves in particular as a sealing material in order to prevent fluid from being forced out of the pores to the outside. After compaction or calendering, the carrier film can be removed from the coated carrier material and optionally wound up.The application rollers can have in particular a structured surface, e.g. with concave indentations, e.g. with a depth of up to 20 μm and a largest width of 1 to 10 millimeters. This makes it possible to improve transfer of the fluid into the pores of the coating of the coated carrier material.In particular, the fluid has a boiling temperature of at most 105 degrees Celsius, preferably of below 100 degrees Celsius, particularly preferably of less than 95 degrees Celsius, under the ambient conditions of step d), for example at an ambient pressure of approximately 1 bar.In particular, the pore-forming fluid contains at least one of the following components or is made exclusively from this component or contains exclusively one or more of the following components:• Ether, e.g. tetrahydrofuran (THF); boiling temperature about 66 degrees Celsius;• methylene chloride; boiling temperature about 39 degrees Celsius;• light naphtha; at least comprising molecules having five to six carbon atoms; boiling temperature between 30 and 90 degrees Celsius;• Alcohol, e.g. methanol (boiling temperature about 65 degrees Celsius), ethanol (boiling temperature about 78 degrees Celsius) or 1-propanol (boiling temperature about 97 degrees Celsius);• Aldehyde, e.g. propanoic (boiling temperature about 46 degrees Celsius), butanal (boiling temperature about 75 degrees Celsius) or pentanal (boiling temperature about 102 degrees Celsius);• Ketone, e.g. 2-propanone (boiling temperature about 56 degrees Celsius), 2-butanone (boiling temperature about 80 degrees Celsius) or 2-pentanone (boiling temperature about 103 degrees Celsius);• Dimethyl carbonate (DMC - boiling temperature about 90 degrees Celsius).In particular, the fluid comprises exclusively constituents which are also constituents of an electrolyte used for the battery cell, with the result that a residual amount of fluid remaining in the active material is then not harmful to the operation of the battery cell.It is preferable to use a liquid that does not dissolve the binder in the active material, is not toxic, and is less combustible. In view of these requirements, tetrahydrofuran (THF) or dimethyl carbonate is particularly suitable.In particular, the coated carrier material can be subjected to a drawing process (skin drawing) before step b), such that a thickness of the electrode or of the active material coating is adjusted. During drawing (skin drawing), both sides of the coating or of the coated carrier material are compressed, while during strip drawing (strip drawing, leveling / smoothing), only one side of the coating is processed. However, the compression in drawing is at most 10%.In particular, after step c), in a further step d), the coated carrier material is cut. The cutting comprises, for example, separating the continuous material into individual electrode sheets and / or snapping out and / or dividing the continuous material into a plurality of strip materials of smaller width (so-called slitting).During the latching out, an (uncoated) collector region or arrester is formed on the carrier material.The cutting is effected in particular by mechanical slitting or punching, by laser, water jet or ultrasonic cutting.In particular, the coated carrier material is guided in the context of step b) and after the application of the fluid, in particular before step x), over a roller or roller, referred to below as a pressure roller, so that the penetration of the fluid into the pores of the active material is assisted. Preferably, the coated carrier material, which is wetted with the fluid having a low boiling temperature, is rubbed off with a (titanium) metal oxide, so that the fluid penetrates deeply into the pores.In particular, the coated carrier material is (immediately) then again guided over a roller, referred to below as a cleaning roller, by means of which excess fluid is removed from the surface of the active material. The cleaning roller is designed in particular with a rubber surface. This ensures that the fluid remains in the pores of the active material, but the excess fluid present on the surface of the active material is removed. Preferably, the cleaning roller can be excited with a vibration, so that excess fluid can be removed even better from the surface of the active material.Since the fluid with which the coated carrier material has been acted upon according to step b) can act as lubrication, it is provided in particular that the coated carrier material is pressed into the (calendering) rollers provided for compressing the active material. For this purpose, the coated carrier material is guided between steps b) and x), in particular via a roller or roller, referred to below as a friction roller (friction roller). With the friction roller, which in particular has a higher coefficient of friction on the surface contacting the coated carrier material, the coated carrier material can be pushed towards and through the (calendering) rollers.Step c) takes place (immediately) after step x), in which the compacted, coated carrier material is heated and dried by expelling the fluid from the active material. In particular, the active material is heated by a heat source, for example an infrared heater or a blower. In the case of a support material coated on one side, the active material is heated, in particular via the uncoated side of the support material, that is to say indirectly.The active material is heated in particular to a temperature of at most 100 to 110 degrees Celsius, so that the active material is not damaged. The binder in the active material coating may usually withstand temperatures of up to 120 degrees Celsius before it softens and melts.In particular, the active material is heated to a temperature which corresponds at least to the highest boiling temperature of a constituent of the fluid or exceeds it.As a result of the heating of the active material, the fluid incorporated in the active material evaporates. Gas bubbles emerge from the active material coating, in particular the compacted active material coating. As a result of the gas bubbles, new pores are formed in the active material and the existing pores are enlarged. These pores are used by the lithium ions for the intercalation process during the later operation of the battery cell. Lithium ions can thus easily penetrate into the active material, since the gas bubble ejection process provides sufficient pores on the surface of the active material. As a result, the lithium deposition, i.e. the deposition of metallic lithium (lithium plating), is also drastically reduced.In particular, in step c) it is provided to suck off the gaseous fluid and, if appropriate, to reuse it for step b). A suction device can be provided for this purpose.The heating of the active material or of the coated carrier material is carried out in particular in a (continuous) chamber through which the coated carrier material is conveyed.In particular, after step c), the coated carrier material is cooled, for example by guiding the coated carrier material over a roller or roller, referred to below as a cooling roller. The cooling is effected to a temperature of at most 40 degrees Celsius.In particular, after step c), or also after cooling, a surface check is carried out by a (optionally optical) measuring device. In this case, it is checked whether the surface of the active material possibly has damage.Moreover, after step c), the thickness of the coated carrier material is checked, in particular by means of a (optionally optical or tactile, etc.) Measuring device. If appropriate, the thickness can be corrected by changing step x).In particular, the coated carrier material is wound up or transported directly for further processing according to step d).In particular, the coated carrier material is heated before or after step d) for a period of two (2) to 15 hours, for example in an oven, in particular to temperatures of 100 to 110 degrees Celsius (second heating stage). In particular, residues of the fluid including any water particles present are thus also removed from the pores of the active material.In particular, the electrode provided as an anode has a greater problem with the closing or reduction of the pores with high calender compression or strong compaction. The proposed method steps can, however, also be carried out for electrodes provided as a cathode.The proposed method has the following advantages:• The closing of the pores due to the compaction (step x)) does not generate lithium plating here• The volume of the pores is increased after the compaction (step x)) by expelling the fluid from the active material;• The fluid absorption in the active material coating is controllable by mechanical pressure;• the fluid forms a lubricating film on the surface of the active material so that friction between rollers and coated support material is reduced; thereby reducing an elongation of the active material in the conveyance direction; thereby reducing wrinkles in the support material and also problems such as crack elongations on the surface of the active material;• The fluid enters the pores and generates a back pressure during the compaction according to step x); therefore the pores are not so easily closed; the pores are reduced during the compaction, but in particular they become not smaller than two μm; that is, not only does the porosity increase due to outgassing of the fluid, but also a useful pore size greater than two μm exists;• A high volumetric energy density of the electrode is achieved without reducing the pore volume;• The electrical conductivity of the active material is increased by the high density achieved after compaction;• Most of the proposed organic fluids are miscible with water; this means that all water particles remaining in the pores mix with the fluid and evaporate with the fluid and leave the pores during the first and second heating stages; in this way, the water content in the electrode can be drastically reduced, which has a positive effect on the performance of the battery cell.A battery cell is furthermore proposed, at least comprising a battery cell housing and arranged therein at least one electrode which is produced by the method described.The battery cell comprises in particular a battery cell housing enclosing a volume and arranged in the volume at least one first electrode foil of a first electrode type, a second electrode foil of a second electrode type and a separator material arranged therebetween, and a liquid electrolyte.The battery cell is in particular a pouch cell (with a deformable battery cell housing consisting of a pouch film) or a prismatic cell (with a dimensionally stable battery cell housing). A pouch film is a known deformable housing part which is used as a battery cell housing for so-called pouch cells. This is a composite material, for example comprising a plastic and aluminum.The battery cell is in particular a lithium-ion battery cell.The individual foils of the plurality of electrodes embodied as electrode foils are arranged one on top of the other and form in particular a stack. The electrode foils are each assigned to different electrode types, i.e. are designed as an anode or a cathode. Anodes and cathodes are arranged alternately and in each case separated from one another by the separator material.A battery cell is a current storage device which is used, for example, in a motor vehicle for storing electrical energy. In particular, a motor vehicle, for example, has an electric machine for driving the motor vehicle (a traction drive), wherein the electric machine can be driven by the electrical energy stored in the battery cell.A motor vehicle is furthermore proposed, at least comprising a traction drive and a battery having at least one of the described battery cells, wherein the traction drive can be supplied with energy by the at least one battery cell.In particular, at least one system for data processing is provided, which has means which are suitably equipped, configured or programmed for carrying out the method or which execute the method.The means comprise, for example, a processor and a memory in which instructions to be executed by the processor are stored, as well as data lines or transmission devices which enable a transmission of instructions, measured values, data or the like between the mentioned elements, for example the drive, the driven rollers / rollers, the spraying device, the suction device, etc.A computer program is also proposed, comprising instructions which, when the program is executed by a computer, cause the computer to execute the described method or the steps of the described method.A computer-readable storage medium is also proposed, comprising instructions which, when executed by a computer, cause the computer to execute the described method or the steps of the described method.The embodiments of the method can be transferred in particular to the battery cell, the motor vehicle, the system for data processing and / or the computer-implemented method (i.e. the computer program and the computer-readable storage medium) and vice versa.The use of indefinite articles ("a", "an", and "an"), in particular in the claims and the description reflecting them, is to be understood as such and not as a numerical word. Terms or components introduced therewith are thus to be understood such that they are present at least once and in particular can also be present multiple times.As a precautionary measure, it should be noted that the numerical words used here ("first", "second",... ) are primarily (only) used for distinguishing a plurality of articles, sizes or processes of the same type, that is to say in particular do not necessarily specify a dependence and / or sequence of these articles, sizes or processes with respect to one another. If a dependence and / or sequence is required, this is explicitly stated here or it is obvious to the person skilled in the art when studying the specifically described configuration. If a component can occur multiple times ("at least one"), the description of one of these components can apply equally to all or a part of the plurality of these components, but this is not obligatory.The invention and the technical field are explained in more detail below with reference to the attached figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments listed. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the facts explained in the figures and combine them with other constituent parts and findings from the present description. In particular, it should be pointed out that the figures and in particular the size relationships illustrated are only schematic. The following are shown: FIG. 1 : a first embodiment variant of a dipping basin in a side view in section; FIG. 2 : a second variant embodiment of a dipping basin in a side view in section; FIG. 3 : shows a spray device in a side view in section; FIG. 4 : the method subsequent to step b), in a side view in section; FIG. 5 : shows a third embodiment variant for step b) of the method; FIG. 6 : a fourth embodiment variant for step b) of the method; and FIG. 7 : a fifth embodiment variant for step b) of the method.FIG. 1 shows a first embodiment variant of a dipping basin 8 in a side view in section.According to step a), in particular a carrier material 4 coated with an active material 3 is provided to an electrode 1. The belt-shaped endless material 6 is conveyed along a conveying direction 14, at least during steps b) and c). The active material 3 is applied only to the carrier material 4 and optionally smoothed or adjusted with respect to a thickness of the coating, but has not yet been calendered.According to step b), a pore-forming fluid 5 is applied in particular to the coated carrier material 4, such that the fluid 5 is absorbed in the active material 4. The fluid 5 is in a liquid aggregate state. The fluid penetrates in particular into the porous active material 3.Step b) takes place in a dipping tank 8 filled with the fluid 5, through which the coated carrier material 4 is transported.The dipping basin 8 is arranged in a housing 12. A pressure in the dip tank 8 is higher than an external pressure present outside the housing 12. A double housing is provided, so that no air from the environment can enter the inner housing 12 or the immersion basin 8. A gas 11, for example nitrogen, is introduced into the housing 8 via an inlet 13. The immersion tank 8 and the fluid 5 are thus insulated from the environment via the gas 11. The housing 8 is sealed by seals 10.In the context of step b), the coated carrier material 4 is guided over a series of deflection rollers 9 which are located in the dip tank 8, so that the carrier material 4 is conveyed through the fluid 5 and the surface of the active material 4 can have maximum contact with the fluid 5. Mechanical pressure is also exerted on the surface of the active material 4 by the deflection rollers 9, so that the fluid 5 penetrates into the active material 4 and at least partially fills the pores.FIG. 2 shows a second embodiment variant of a dipping basin 8 in a side view in section. Reference is made to the explanations relating to FIG. 1.In contrast to FIG. 1, it is shown here that the coated carrier material 4 is unrolled from a roll and fed to the dipping basin 8. The roller is driven by a drive 16, so that the coated carrier material 4 is conveyed along a conveying direction 14. The coated carrier material 4 conveyed as endless material 6 is tensioned via tensioning rollers 17.In the context of step b), the coated carrier material 4 is guided over a multiplicity of deflection rollers 9 which are located in the dip tank 8, with the result that the carrier material 4 is conveyed through the fluid 5 and the surface of the active material 4 can have maximum contact with the fluid 5.The coated carrier material 4 is guided over pressure rollers 18 within the scope of step b) and still while being exposed to the fluid 5 and before step x), so that these support the penetration of the fluid 5 into the pores of the active material 3.The coated carrier material 4 is immediately thereafter and after step b) guided over cleaning rollers 20, by means of which excess fluid 5 is removed from the surface of the active material 4.Since the fluid 5 with which the coated carrier material 4 according to step b) has been acted upon can act as lubrication, it is provided that the coated carrier material 4 is pressed into the (calendering) rollers 21 provided for compressing the active material 3. For this purpose, the coated carrier material 4 is guided between steps b) and x) over friction rollers 19. With the friction roller 19 having a higher coefficient of friction on the surface contacting the coated carrier material 4, the coated carrier material 4 can be pushed towards and through the (calendering) rollers 21.FIG. 3 shows a spray device 15 in a side view in section. Reference is made to the explanations relating to FIG. 1.In contrast to FIG. 1, no dipping tank 8 is provided here, but instead the coated carrier material 4 is acted upon with fluid 5 via a plurality of spraying devices 15.FIG. 4 shows the method following step b), in a side view in section. Reference is made to the explanations relating to FIG. 2.In particular, the calendering rollers 21 shown here are arranged directly following the friction rollers 19.Between steps b) and c), in a further step x), the active material 3 is compacted or calendered. Step x) comprises calendering with calendering rollers 21. Calendering is carried out without heating apparatus, i.e. is carried out without targeted increase in the temperature of the active material 3. The pores of the active material 3 are additionally supported by the fluid 5 absorbed in the active material 3, so that a compaction of the active material 3 is equalized over the layer thickness. This thus prevents excessive compaction precisely on the surface of the coating. Calendering is carried out at room temperature.According to step c), the carrier material 4 to which the fluid 5 is applied is heated and the fluid 5 is at least partially expelled from the active material 3, forming pores (first heating stage).The carrier material 4 to which the fluid 5 is applied is heated to at least a boiling temperature of the fluid 5, so that the fluid 5 is expelled from the active material 3 to form pores.Step c) takes place exclusively via heat convection or heat radiation, i.e. in particular just not via heat conduction. Thus, there is no contact of the active material 3 with heated rollers or (calendering) rollers. In particular, radiant heaters or heat gas streams are provided, via which heat is transported to the active material.The active material 3 is heated by a heat source 24, for example an infrared heater or a blower. The active material 3 is heated, in the case of support material 4 coated on one side, via the uncoated side of the support material 4, that is to say indirectly.The coated carrier material 4 is processed as a continuous material 6 at least during steps a) to c) and is separated into an electrode sheet or an electrode 1 after step c), for example in a step d).After step c), in a further step d), the coated carrier material 3 is cut in a cutting device 27. the cutting comprises, for example, separating the continuous material 26 into individual electrode sheets 7 or electrodes 1 and / or snapping out and / or dividing the continuous material 26 into a plurality of band materials of smaller width (so-called slitting). The electrodes 1 can be arranged to form a stack and inserted into a battery cell 2.During the latching out, an (uncoated) collector region or arrester is formed on the carrier material 3.As a result of the heating of the active material 4, the fluid 5 incorporated in the active material 4 evaporates. gas bubbles emerge from the active material coating, in particular compressed active material coating. As a result of the gas bubbles, new pores are formed in the active material 4 and the existing pores are enlarged.In step c), provision is made for the gaseous fluid 5 to be suctioned off and, if appropriate, reused for step b). A suction device 22 can be provided for this purpose.The heating of the active material 4 or of the coated carrier material 3 is carried out in a (continuous) chamber 23, through which the coated carrier material 4 is conveyed.After step c), the coated carrier material 4 is cooled by guiding the coated carrier material 4 via cooling rollers 25.After step c) and also after cooling, the surface is checked by a (optionally optical) measuring device 26.In addition, after step c), the thickness of the coated carrier material 3 is checked by means of a (optionally optical or tactile, etc.) Measuring device 26. If necessary, the thickness can be corrected by changing step x).The coated carrier material 4 is transported for further processing according to step d).FIG. 5 shows a third embodiment variant for step b) of the method. Reference is made to the explanations relating to FIG. 2.In contrast to FIG. 2, it is shown here that the coated carrier material 4 is guided over application rollers 28 which are acted upon by the fluid 5 in the course of step b). In this case, the coated carrier material 4 is only acted upon by the fluid 5 via the application rollers 28 and is not transported through the fluid 5 itself. The application rollers 28 can be arranged, for example, partially in the dipping basin 8 or can be acted upon by the fluid 5 by a spraying device 15 or a transfer means 29, for example a sponge.The coated carrier material 4 is guided in the context of step b) over a multiplicity of deflection rollers 9, with the result that the carrier material 4 is conveyed through the application rollers 28 and the surface of the active material 4 can have contact with the fluid 5.The coated carrier material 4 is guided over pressure rollers 18 within the scope of step b) and still while being exposed to the fluid 5 and before step x), so that these support the penetration of the fluid 5 into the pores of the active material 3.The coated carrier material 4 is immediately thereafter and after step b) guided over cleaning rollers 20, by means of which excess fluid 5 is removed from the surface of the active material 4.FIG. 6 shows a fourth embodiment variant for step b) of the method. Reference is made to the explanations relating to FIG. 3.In contrast to FIG. 3, an application roller 28 is here acted upon by the fluid 5 by the spraying device 15. The spraying device 15 transfers the fluid 5 to a transfer means 29, here a sponge, which in turn contacts the application roller 28.FIG. 7 shows a fifth embodiment variant for step b) of the method. Reference is made to the explanations relating to FIG. 5.In contrast to FIG. 5, it is shown here that the coated carrier material 4 is guided over application rollers 28 which are acted upon by the fluid 5 in the course of step b). In this case, the coated carrier material 4 is only acted upon by the fluid 5 via the application rollers 28 and is not transported through the fluid 5 itself. The application rollers 28 are acted upon by the fluid 5 by a belt-shaped transfer means 29. The transfer means 29 is guided over deflection rollers 9 and in this case through a dipping basin 8. The fluid 5 is taken up by the transfer means 29 and transported towards the application roller 28. The application rollers 28 can be designed as calendering rollers 21, so that here a compaction of the active material 3 can already take place.List of reference characters1 Electrode 2 Battery cell 3 Active material 4 Carrier material 5 Fluid 6 Endless material 7 Electrode sheet 8 Dip basin 9 Deflection roller 10 Seal 11 Gas 12 Housing 13 Inlet 14 Conveying direction 15 Spraying device 16 Drive 17 Tension roller 18 Pressure roller 19 Friction roller 20 Cleaning roller 21 Calendering roller 22 Suction device 23 Chamber 24 Heat source 25 Cooling rollers 26 Measuring device 27 Cutting device 28 Application rollers 29 Transfer means

Claims

Method for producing an electrode (1) of a battery cell (2); wherein the method has at least the following steps: a) providing a carrier material (4) of an electrode (1) coated with an active material (3); b) subjecting the coated carrier material (4) to a pore-forming fluid (5) such that the fluid (5) is absorbed in the active material (3); c) heating the carrier material (4) subjected to the fluid (5) and at least partially expelling the fluid (5) from the active material (3) to form pores; wherein between steps b) and c) in a further step x) the active material (3) is compacted; wherein step c) is carried out after step x).Method according to claim 1, wherein the active material (3) is compressed by at least 15% in step x).The method according to any of the preceding claims, wherein step x) comprises calendering and step c) is spaced apart from step x).Method according to one of the preceding patent claims, wherein step c) takes place exclusively via heat convection or heat radiation.Method according to one of the preceding patent claims, wherein the coated carrier material (4) is processed as continuous material (6) at least during steps a) to c) and is separated into an electrode sheet (7) after step c).Method according to one of the preceding patent claims, wherein step b) takes place in a dipping tank (8) filled with the fluid (5), through which the coated carrier material (4) is transported.Method according to one of the preceding patent claims 1 to 5, wherein the fluid (5) in step b) is sprayed onto the active material (3) or applied to the active material (3) via application rollers (28).Method according to one of the preceding patent claims, wherein the (5) fluid has a boiling temperature of not more than 105 degrees Celsius under the ambient conditions of step d).The method according to any of the preceding claims, wherein the pore forming fluid (5) contains at least one of the following components: • ether, e.g. tetrahydrofuran (THF); • methylene chloride; • light naphtha; at least comprising molecules with five to six carbon atoms; • alcohol, e.g. methanol, ethanol or 1-propanol; • aldehyde, e.g. propanal, butanal or pentanal; • ketone, e.g. 2-propanone, 2-butanone or 2-pentanone; • dimethyl carbonate.

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