Method and apparatus for manufacturing electrodes of battery cells

Abstract

In a method for manufacturing the electrodes (40) of a battery cell, first, an electrode paste (22, 32) is applied to a metal foil (20) as a coating layer. Then, the coating layer is dried in a dryer (42; 142) with adjustable drying conditions. According to the present invention, for in-line process monitoring, at least one characteristic of the coating layer is measured non-contact by measuring instruments (48a, 48b). The measuring instruments may include, for example, one or more chromatic confocal distance sensors or laser photothermal sensors. If the value measured by the measuring instruments is outside the range of reference values, the temperature in the dryer (42; 142) or other process conditions are changed. The measuring instruments can recognize the transitions between each stage of the drying process, for example, by adjusting the drying rate as the drying process progresses.

Description

[Technical Field]

[0001] This invention relates to a method and apparatus for manufacturing electrodes for battery cells. The electrodes consist of a thin metal foil with electrode paste applied to both sides. This invention relates, in particular, to drying the applied electrode paste. [Background technology]

[0002] The electrodes of a lithium-ion battery cell include a metal foil coated on both sides with electrode paste. When the electrode is the cathode, the metal foil is made of aluminum, and the electrode paste consists of a mixture of a chemical active material (e.g., lithium metal oxide), conductive carbon black, an adhesive, and a solvent. In the case of the anode, the metal foil is made of copper, and the electrode paste is typically a mixture of graphite, silicon, conductive carbon black, an adhesive, and a solvent.

[0003] The thickness of the metal foil ranges from 8 μm to 20 μm, and the thickness of the coating layer on each side is approximately 70 μm to 1500 μm, with the anode thickness often being much larger than the cathode.

[0004] First, a wet electrode paste (slurry) is applied to a metal foil by a process called slot-die coating. The metal foil, on a roller, is guided through a slot die that extends across the entire width of the foil. The electrode paste, with a solvent content of approximately 40-60% by weight, is discharged from the slot die under pressure and pressed onto the metal foil, adhering to one side of the foil. The wet electrode paste is then dried in a dryer to remove the solvent. During drying, the residue of the electrode paste forms a porous solid network.

[0005] After drying, the coated layer is compressed and cut using a calender.

[0006] The simplest approach involves coating one side of the metal foil, drying it, then coating and drying the other side. However, achieving a continuous process requires two dryers, each up to 80 meters long. A more efficient, but technically more demanding, method involves coating both sides of the metal foil and then drying them. In this way, a continuous process can be achieved with just one dryer.

[0007] Drying the electrode paste is not only energy-intensive, but also a critical process step for the subsequent function of the battery cell. Optimal results have been shown only when process conditions are modified during the drying process. For example, drying at a continuously high heating rate can negatively affect the adhesion of the electrode paste to the metal foil, leading to delamination. This, in turn, reduces and eventually eliminates the battery cell's capacity.

[0008] Typically, an impact jet dryer is used as the dryer, which has multiple nozzles that direct hot air onto the coated layer. The nozzles are positioned on opposite sides of the strip electrode along the conveyor line, and the temperature and flow rate of the discharged hot air can be individually adjusted for each nozzle. In this way, process conditions can be changed during the drying period. Alternatively, the strip electrode may be guided to pass through multiple independent dryers with different process conditions.

[0009] Currently, during the drying period, sensors monitor process conditions in different zones of the dryer (or multiple independent dryers). Measured quantities include the temperature, humidity, and flow rate of the hot air directed towards the corresponding coating layer.

[0010] Numerous tests employing different time flows of process conditions are conducted in advance to define the process conditions for zone or independent dryers. The optimal sequence of process conditions is then determined by studying the electrodes of the final product. Mechanical measuring instruments such as dial gauges and micrometer screws, or optical measuring instruments using laser trigonometry or chromatic confocal imaging, are used to inspect the total thickness. More detailed information about the porous network generated by drying can be measured by X-ray methods or micro-Raman spectroscopy (MRS), see, for example, the paper by J. Kaise et al., Prozess - und Produktentwicklung von Elektroden fuer Li-Ionen-Zellen (Process and Product Development of Electrodes for Lithium-Ion Battery Cells), (2014), Chemie Ingenieur Technik. 86. 10.1002 / cite.201300085. These known methods have investigated the adhesive / solvent system at the fractured edges of the electrodes in the final product.

[0011] Even with the optimal process conditions established and the drying process monitored by sensors, defects in the electrodes repeatedly occur after drying. In particular, if these defects are only discovered during subsequent testing of the battery cells, the economic losses due to defective products become substantial. [Overview of the project]

[0012] The object of the present invention is to provide a method and apparatus for manufacturing battery cell electrodes that can avoid or at least significantly reduce defective products caused by such defects.

[0013] The solution for achieving the objective of the present invention is: a) A step of applying electrode paste as a coating layer to a metal foil to obtain a coated metal foil, b) A step of drying the coating applied to the metal foil in a dryer in which the drying conditions can be changed, c) For inline process monitoring, a step of non - contact measurement of at least one property of the coating layer by a measuring device; d) When the value of the at least one property measured by the measuring device is outside the range of the reference value, a step of changing at least one of the process conditions in the dryer, a method for manufacturing an electrode of a battery cell.

[0014] The present invention is based on the view that defective products due to defects can be avoided only by inline process monitoring, that is, during the drying process, by non - contact measurement of at least one property of the coating layer by a measuring device. Non - contact measurement is necessary because the coating layer can be deformed until drying is complete, and contact may cause undesirable deformation that cannot be excluded.

[0015] Inline process monitoring is a method of monitoring an ongoing process or facility in real time. The concept of "inline" means monitoring without taking out a sample. By inline process monitoring, deviations from desirable operating parameters can be quickly recognized. This is a prerequisite for avoiding mass defects and defective products caused thereby.

[0016] The at least one measured property of the coating layer may be, for example, the thickness of the coating layer. However, the drying conditions cannot be accurately set by only the thickness. Therefore, since the dryness of the coating layer is a more important quantity for the optimal setting of the drying conditions, it is preferably determined by the at least one measured property.

[0017] At least one other property of the coating layer may particularly be the specular reflectance and / or diffuse reflectance of the coating layer, the roughness of the surface of the coating layer, or the thermal conductivity of the coating layer. The roughness can be easily derived from the spatial distribution of the measured thickness. Preferably, at least two of these properties of the coating layer are non - contact measured by the measuring device.

[0018] The degree of drying of the coating layer during the drying process is usually specified qualitatively rather than quantitatively. The drying process can be divided into five stages: stage (a) where a wet film of the coating layer is formed; stage (b) where a capillary network completely filled with the coating layer is formed; stage (c) where a capillary network partially filled with the coating layer is formed; stage (d) where only individual separated liquid residues are present in the coating layer; stage (e) where a film containing no liquid is formed by the coating layer. It has been proven effective to divide it into these five stages.

[0019] The transitions between stage (b) and (c), and between stage (c) and (d) are particularly important. It is necessary to decelerate drying only at stage (c). For this purpose, it is necessary to derive the timing of the occurrence of the transition between stage (b) and (c) during coating based on the measured values. When the transition between stage (c) and (d) is recognized, drying can be accelerated again.

[0020] The deceleration or acceleration of drying is usually accompanied by a decrease or increase in temperature. Additionally or alternatively, the speed of the hot air directed at the coating layer can be decreased or increased.

[0021] When the surface roughness or a quantity derived therefrom (e.g., the time derivative of the average roughness value R

[0022] , <00,00109>, , , a ,

[0023] , exceeds a threshold value, the transition between stage (b) and stage (c) can be estimated with a high degree of reliability. The decrease in the filling degree of the capillary network appears as a significant increase in the surface roughness. Also, the decrease in the specular reflectance during this transition can be easily measured with an appropriate measuring instrument. The roughness can be indicated by one or more of the usual quantities for quantifying roughness, such as the average roughness value Ra, the root mean square roughness Rq, or the average roughness depth Rz.

[0022] When the at least one characteristic is the surface reflectance, this characteristic can be derived from the amplitude of the response of the coating layer to thermal excitation.

[0023] If the at least one property is the thermal conductivity of the coating layer, this property can be derived from the phase shift of the coating layer's response to thermal excitation.

[0024] By determining the thermal conductivity of the coating layer, the transition between stages (b) and (c) can be estimated. This transition can be identified by the phase shift curve of the coating layer's response to thermal excitation, or by the fact that the resulting quantity is minimized. As the mass fractions of water, carbon, and air in the coating layer change during the drying process, and because the thermal conductivity of these components is clearly different, conclusions can be drawn about water impregnation.

[0025] Furthermore, if the diffuse reflectance of the surface decreases and then continues to increase until it reaches its final value, the transition between stage (c) and stage (d) can be estimated. Part of the reason for this remarkable observation is that the surface of an undried coated layer is initially smooth and wet, and therefore has high specular reflectance. When the capillary network is emptied in stage (c), the diffuse reflectance of the incident light increases at this time, causing the specular reflectance to decrease. Surprisingly, if emptiness continues, the diffuse reflectance increases again. Therefore, the above transition between stage (c) and stage (d) can be recognized by a sensor that measures diffuse reflectance (and sometimes specular reflectance).

[0026] Surface roughness and reflectivity have been shown to depend only slightly on the layer thickness. In other words, in many cases, it is not possible to reliably determine whether a transition has occurred between steps (b) and (c) or between steps (c) and (d) due to changes in layer thickness.

[0027] The roughness threshold and the final value of diffuse reflectance are preferably determined experimentally by preliminary tests, where a transition between stage (b) and stage (c) is recognized when the threshold is exceeded, and a transition between stage (c) and stage (d) is recognized when the final value is reached. The same applies to thermal conductivity.

[0028] For optimal in-line process monitoring, the measuring instrument should measure at least one of the properties of the coating layer quasi-continuously during the drying process; however, measurements may be taken intermittently at predetermined time intervals.

[0029] Preferably, the measuring instrument is a measuring element of a control circuit that adjusts the process conditions in the dryer according to the measured at least one characteristic. The performing element of the control circuit may be, for example, a heating device that can change the temperature in the dryer or dryer zone, and / or a blower that can change the velocity of the hot air in the dryer.

[0030] However, the adjustment is not mandatory, because measurements may be taken at large intervals, for example, and these measurements may trigger different pre-set control operations, which cannot be strictly called adjustments.

[0031] The present invention further relates to an apparatus for manufacturing electrodes for battery cells. The apparatus comprises a coating device configured to apply an electrode paste as a coating layer to a metal foil to obtain a coated metal foil. The apparatus further comprises a dryer having a plurality of separate dryer units or a dryer zone provided in a common housing. Different process conditions can be generated within the dryer units or dryer zones. According to the present invention, the apparatus comprises a measuring instrument configured to non-contactively measure at least one characteristic of the coating layer during the drying period. A control or adjustment device is configured to change at least one of the process conditions in the dryer if the value of the at least one characteristic measured by the measuring instrument is outside a range of reference values ​​for inline process monitoring.

[0032] The measuring instrument preferably comprises a plurality of distance sensors, which may be chromatic confocal distance sensors or laser photothermal sensors configured to determine phase shift and amplitude from the response to thermal excitation.

[0033] The present invention further relates to the application of a chromatic confocal distance sensor, or to its application for measuring the thickness, roughness, and reflectance of a coated layer in a method according to the present invention. It has been shown that all three quantities can be measured with such a sensor. Since the measuring beam is perpendicular to the coated layer, the total reflectance, consisting of specular reflectance and diffuse reflectance, can be estimated from the midpoint of the intensity. If two such distance sensors are placed on opposite sides of an electrode, the total thickness of the electrode can be estimated by subtraction. Since the thickness of the metal foil is known or can be easily measured in advance, the total thickness of these two coated layers can be derived. The measurement accuracy of such a sensor is sufficient for non-contact measurement of roughness.

[0034] The present invention further relates to the application of a laser photothermal sensor to the above method. [Brief explanation of the drawing]

[0035] The embodiments of the present invention will be described in detail below with reference to the drawings. [Figure 1] This is a schematic side view, not to scale, of the apparatus of the present invention according to the first embodiment. [Figure 2] This is a longitudinal cross-sectional view of an impact jet dryer, and according to the present invention, multiple sensors detect the degree of dryness of the coated layer in the impact jet dryer. [Figures 3a-3d] This is a schematic diagram of the five drying stages. [Figure 4] This chart shows the changes over time in the roughness R and total thickness of the coated layer during the drying period. [Figure 5] This chart shows the changes over time in intensity I, measured by a chromatic confocal distance sensor during the drying period, and the total thickness of the coated layer. [Figure 6] This is a schematic plan view of a fixed measuring unit having electrodes and multiple distance sensors. [Figure 7] This schematic plan view is similar to Figure 6, except that a vertically movable measuring unit is shown. [Figure 8]This schematic plan view is similar to Figure 6, except that two fixed measuring units are shown. [Figure 9] This is a dryer according to another embodiment, having multiple separate dryer units. [Figure 10] This chart shows the time-dependent change in the phase shift of the thermal excitation response during the drying period. [Figure 11] This chart shows the time-dependent change in the amplitude of the thermal excitation response during the drying period. [Figure 12] This chart shows the time-dependent changes in the phase shift of the thermal excitation response during multiple drying operations. [Modes for carrying out the invention]

[0036] 1. First Embodiment Figure 1 shows a schematic side view of a first embodiment of the components of the apparatus of the present invention for manufacturing electrodes of a battery cell, represented as 10 as a whole. The apparatus 10 comprises a slot die coating apparatus 11 having a first slot die 12, the nozzle opening 14 of the slot die positioned at a precisely defined distance from the surface of a roller 16. During coating, the roller 16 rotates in the rotational direction indicated by arrow 18, and a thickness d is fed out from a storage roll (not shown). F The metal foil 20 is supplied to the first slot die 12.

[0037] The first slot die 12 is connected via a pump (not shown) to a storage container (not shown) for a first electrode paste 22 having a wet, granular viscosity. Possible compositions of the electrode paste have been described above in relation to the prior art and also apply to the electrode paste 22. The same applies to the metal foil 20.

[0038] The pump pumps the first electrode paste 22 from the storage container and delivers it to the nozzle opening 14 under uniform pressure. The nozzle opening 14 is slit-shaped and extends perpendicular to the paper surface across the entire width of the metal foil 20.

[0039] The pump applies and adheres the first electrode paste 22 to the metal foil 20 by pressurizing it from the nozzle opening 14. When the rotation speed of the roller 16 and the mass flow of the first electrode paste 22 are precisely matched, a layer of the first electrode paste 22 with a uniform thickness d1 is formed on the surface 24 of the metal foil 20. The thickness d1 is defined by the distance between the nozzle opening 14 and the metal foil 20, and the positions of the nozzle opening and the metal foil are precisely defined by the stationary roller 16. However, this does not mean that the thickness d1 does not change. Depending on the properties of the electrode paste 22, it may shrink or expand after application.

[0040] A second slot die 30 is positioned behind the first slot die 12 in the transport direction, and coats the back surface of the metal foil 20 with the second electrode paste 32. A pump that supplies the second electrode paste 32 to the second slot die 30 transports the second electrode paste from a storage container (not shown) to the nozzle opening 36 of the second slot die 30. Here, the mass flow of the second electrode paste 32 and the transport speed of the metal foil 20 are matched to uniformly coat the back surface 38 of the metal foil 20 with the second electrode paste 32. However, because the metal foil 20 is not supported by rollers or a similar stationary structure during the coating of the back surface 38, the variation in the thickness d2 of the electrode paste 32 on the back surface 38 is much greater than the thickness d1 of the first electrode paste 22.

[0041] The metal foil, coated on both sides and hereafter referred to as electrode 40, is transported to the dryer 42 by a transport member (not shown as it is known) for the next process step. Since the electrode pastes 22 and 32 are soft before drying, contact with the electrode paste by drive wheels or the like should be avoided. For example, if the metal foil 20 has uncoated longitudinal stripes, the drive wheels or skids may engage with them.

[0042] The dryer 42 includes a housing 44 equipped with a controllable heating device 46, a thermometer 47, and two distance sensors 48a and 48b, which have very high measurement accuracy at a sampling rate of approximately 35 kHz based on the chromatic confocal measurement principle. For details of such sensors, see, for example, DE 10 2006 017 400 A1. The distance sensors 48a and 48b measure the total thickness d of the coating layer during the drying period of the electrode 40. G The distance between the two distance sensors 48a and 48b and the thickness d of the metal foil 20 are measured quasi-continuously. F Since this is known, the total thickness d of these two coating layers G =d1+d2 is the distance value measured from the aforementioned distance and the thickness d of the metal foil 20. F The value is obtained by subtracting [a certain value]. To improve measurement accuracy, calibration using a thickness standard can be performed. The components inside the housing 44 are connected to a regulator 50 located outside the housing 44 in the shown embodiment. The sensing parts of the distance sensors 48a and 48b can also be located outside the housing 44 so as not to be exposed to the high temperature inside the dryer 42. As a distance sensor based on the chromatic confocal measurement principle, for example, only a measuring head (which may be water-cooled) including one lens is located inside the dryer 42, but a spectrometer including electronic analysis equipment may be located outside the housing 44 and connected to the measuring head via an optical fiber.

[0043] In the illustrated embodiment, the drying rate of the coating layer depends primarily on the temperature inside the dryer 42, as measured by the thermometer 47. The degree of drying of the coating layer can be roughly estimated based on the total thickness of the coating layer, as measured by distance sensors 48a and 48b. If the coating layer dries too quickly or too slowly, it may adversely affect the properties of the electrode 40.

[0044] Therefore, the controller 50 adjusts the temperature T inside the dryer 42 so that the thickness of the coated layer is within the standard range. Distance sensors 48a and 48b are measuring elements, and the heating device 46 is the executing element of the adjustment circuit. The adjustment reduces the possibility that the coated layer will not adhere properly to the metal foil 20 due to drying too slowly or too quickly, which could later cause delamination and even functional failure.

[0045] After drying, electrodes 40 with a maximum length of 2000m and a width of 1m are compressed by calendering using a known method, and then further processed by longitudinal cutting.

[0046] 2. Second Example To ensure that the electrode pastes 22 and 32 of the final product electrode 40 have an optimal structure and adhere tightly to the metal foil 20, it is advantageous to temporarily slow down the drying process. For this reason, it is necessary to reduce the drying rate in the dryer 42 by an appropriate amount at the right time. Drying at a consistently low drying rate would result in a longer drying time, which is disadvantageous from a process economic standpoint.

[0047] Figure 2 schematically shows an impact jet dryer 142, which allows for flexible changes in the drying speed during the drying period. The impact jet dryer 142 includes a housing 44 through which an electrode 40 is guided to pass. Each side of the electrode 40 is provided with a plurality of hot air nozzles 52, from which hot air 54 is discharged and directed towards the passing strip electrode 40. In the shown embodiment, both the temperature T and the speed of the hot air 54 can be adjusted individually for each hot air nozzle 52, as is not shown in detail. By appropriately changing the temperature T and / or the speed of the discharged hot air 54, different drying speeds can be achieved in different zones of the impact jet dryer 142.

[0048] Figures 3a to 3e show different degrees of dryness or stages during the drying period, taking the anode electrode paste as an example. In these drawings, large white grains 56 are graphite particles, small circles 58 are SBR particles (where SBR represents Styrene-Butadiene Rubber), thin lines 60 are carboxymethyl cellulose (CMC), and the remaining grains 62 are carbon black particles.

[0049] It has been proven effective and is accepted in the art to divide the drying process into the following five stages.

[0050] Figure 3a - Stage (a): The coating layer forms a wet film.

[0051] Figure 3b - Stage (b): The coating layer forms a completely filled capillary network.

[0052] Figure 3c - Stage (c): The coating layer forms a partially filled capillary network.

[0053] Figure 3d - Stage (d): Only isolated liquid residues are present in the coating layer.

[0054] Figure 3e - Stage (e): The coating layer forms a film without liquid.

[0055] During stage (c), the drying should be decelerated. For this, it is necessary to reliably recognize the transitions between stages (b) and (c), and between stages (c) and (d). The total thickness d measured by the distance sensors 48a, 48b G cannot reliably measure the time points of these transitions. The total thickness d G continuously decreases as the degree of dryness increases. However, the total thickness d at the time when the transitions between the above-described stages occur G mainly and unpredictably depends on the thicknesses d1 and d2 of the newly applied electrode pastes 22, 32.

[0056] Therefore, the distance values measured by the distance sensors 48a, 48b (or the total thickness d derived therefrom)G In addition to the above, the controller 50 is provided with additional information to determine the degree of dryness and to recognize the above transitions between stages (b) and (c) and between (c) and (d).

[0057] To recognize the transition between stages (b) and (c), the roughness of the corresponding opposing surfaces is determined from the measured distance values. When using fixed distance sensors 48a and 48b, the fact that electrode 40 passes through distance sensors 48a and 48b 20 times consecutively at a constant speed is utilized. In this way, a large number of adjacent measurement points are obtained, and from these measurement points, the measurement variable for roughness can be derived. By comparing Figure 3b and Figure 3c, it can be seen that the surface roughness increases sharply in the transition between stages (b) and (c).

[0058] Figure 4 illustrates this using a chart, which shows the total thickness d during the drying period. G (Dashed line) and the average roughness value R a The (solid line) schematically shows the change over time t of the measurement variable indicating roughness. Thickness d G The continuous decrease described above is observed. Although the decrease in thickness is not constant, for the reasons stated above, the change in gradient is not a reliable indicator of the transition between stages (b) and (c).

[0059] The average roughness value R shown in Figures 3b and 3c a The increase can be well determined quantitatively using the diagram in Figure 4. For example, the transition timing between stages (b) and (c) is determined by the average roughness value R a The time point t at which the increase (i.e., the first time derivative) of is at its maximum value. bc (See vertical dashed line) This can be defined as time t. bc Therefore, the heating rate can be reduced, for example, by lowering the temperature and / or velocity of the exhausted hot air.

[0060] During stage (c), and in the subsequent stages (d) and (e), the roughness increases slightly. As can be seen from Figures 3c and 3d, the transition between stages (c) and (d) is not clearly discernible by the increase in roughness.

[0061] To reliably recognize this transition, distance sensors 48a and 48b detect the intensity of the measurement light that is incident perpendicularly on the surface of the coated layer and is also partially reflected from the surface. Because the light is incident perpendicularly, distance sensors 48a and 48b measure both the specular and diffuse reflection portions of the reflected light.

[0062] Figure 5, similar to Figure 4, shows the change in intensity I (or more precisely, its intermediate value) measured by distance sensors 48a and 48b during the drying period. During stages (a) and (b), the liquid component in the electrode pastes 22 and 32 smooths the surface, causing a relatively large amount of measurement light to be specularly reflected, resulting in a high and slight decrease in intensity. During stage (c), the surface becomes rougher, significantly reducing the amount of measurement light specularly reflected, which is represented by a significant decrease in the measured intensity I. Surprisingly, however, just before the end of stage (c), the measured intensity I rises again due to increased reflection on the surface. This increase ends at the transition between stages (c) and (d). In other words, if intensity I continues to rise from a decrease to its final value, the point at which this final value is reached (or the increase ends) is the point at which the transition between stages (c) and (d) occurs. cd This can be considered as such. cd Therefore, drying can be accelerated again, for example, to the original values ​​in steps (a) and (b).

[0063] Therefore, in the shown embodiment, the total thickness d is determined solely by the distance sensors 48a and 48b. G This allows for the determination of surface roughness and reflectivity, and thereby the degree of dryness. In particular, it enables the determination of the timing of transitions between stages (b) and (c), and between stages (c) and (d), which are important for process control.

[0064] In Figure 2, multiple pairs of distance sensors 48a and 48b are sequentially installed in the impact jet dryer 142 in the transport direction. The desired number of distance sensors 48a and 48b, and their ideal arrangement in the transport path, depend on various parameters of each individual case. Usually, it is sufficient to install only one pair of distance sensors 48a and 48b laterally to the electrode (i.e., perpendicular to the plane of the paper in Figure 2), for example, in the center of the electrode 40. However, depending on the number and arrangement of the hot air nozzles 52, the degree of drying in the lateral direction may vary. In these cases, it is preferable to install multiple pairs of distance sensors 48a and 48b at different positions in the lateral direction, as shown in Figure 6. It can be seen that the coating layer facing upwards towards the observer does not completely cover the metal foil 20, and that uncoated vertical stripes 72 and horizontal stripes 74 remain.

[0065] 76 represents a measurement station containing a total of six distance sensors 48a distributed laterally across the coated section of the electrode 40.

[0066] To monitor drying at a specific point on the electrode 40, the measurement station 76 can be moved in sync with the electrode 40, as shown in Figure 7. The common transport direction is indicated by arrow 78.

[0067] Alternatively, as shown in Figure 8, multiple measurement stations 76a, 76b may be provided, each associated with a specific point on the electrode where the measurement result corresponds. At the subsequent position of the electrode 40, indicated by the dashed line, the point measured by the first measurement station 76a is directly below the second measurement station 76b.

[0068] In the metal foil 20, which is coated on both sides, the total thickness of the coating layer is d. G To measure the total thickness d, two distance sensors 48a and 48b must be installed at each measurement point. However, the transitions between stages (b) and (c), and between stages (c) and (d) can only be recognized by the roughness or measured intensity. G Understanding this can improve the certainty of recognition, but it has been shown not to be essential. Total thickness dG If it is not necessary, the measurement can be performed with one distance sensor 48a or 48b. This is because the measurement of the distance value is the average value of roughness R a And it is merely for determining intensity I.

[0069] In equipment where the second coating layer is applied after the first coating layer has dried, two dryers are required, each drying only one coating layer. Even in these cases, it is sufficient to perform measurements using only one distance sensor 48a or 48b.

[0070] 3. Third Example The descriptions of Figures 2 and 3a to 3e also apply to the third embodiment.

[0071] In this embodiment, a laser photothermal sensor is used instead of a chromatic confocal distance sensor to provide the controller 50 with information for determining the degree of dryness and for recognizing the transitions between stages (b) and (c) and between stages (c) and (d).

[0072] EP 3 017 274 A1 discloses, for example, the operating principle of such a laser photothermal sensor. A laser thermally excites the surface of a material, and a near-infrared photodiode records the temperature response of the material. The excitation is modulated. Therefore, the temperature response is also modulated. Two important parameters of the temperature response related to the excitation, the amplitude and phase shift of the modulation, can be evaluated.

[0073] Figure 10 shows a schematic diagram illustrating a typical curve of the phase shift P during the drying process. During stages a and b, the moisture content in the coating layer decreases, increasing the mass percentage of graphite. Because graphite has better thermal conductivity than water, the thermal conductivity of the coating layer improves, which reduces the phase shift.

[0074] At stage c, the capillary network begins to empty, and the moisture is replaced by air. Since air has significantly worse thermal conductivity than water, the overall thermal conductivity of the coated layer decreases again, which causes the phase shift P to increase. bc In this stage, the phase shift is minimized during the transition between stages (b) and (c), at which point the amount of water required to completely fill the capillary network is minimized, and no air is present. Therefore, this transition can be easily recognized by determining the minimum value of the phase shift P curve. Just before the end of stage (d), where only very scattered and spaced-out liquid residue exists, and in the completely dry stage (e), the thermal conductivity stabilizes, and the phase shift P remains constant. f It is stable.

[0075] Therefore, the phase shift is essentially a measure of the thermal conductivity of the coating layer. Thermal conductivity largely depends on the mass fraction of water in the coating layer.

[0076] This value P f It has been shown that this is largely independent of other sensory sensitive factors such as the dilution of the coating layer at the start of the process and the total thickness.

[0077] Figure 11 shows schematic curves of the phase shift P in several drying processes with different dilution levels, thicknesses, and drying processes. These curves change over time, but all end at the same final plateau. Therefore, the value P is... f This may be used as a reliable indicator of the completion of the drying process.

[0078] Figure 12 shows a schematic diagram illustrating a typical curve of the amplitude A of the temperature response during the drying process. Similar to the intensity measured by the chromatic confocal sensor in Example 2, the amplitude A is primarily dependent on reflectance. Therefore, the curve is similar to the curve in Figure 4, and is more sensitive to the drying process at deeper locations within the coating layer because the thermal response also includes a component from reflection from below the surface.

[0079] During stages (a) and (b), drying / evaporation mainly leads to a decrease in layer thickness, but the surface and pores remain moist. Therefore, the reflectance decreases very slowly, and the amplitude A increases slowly. In the laser photothermal method, high surface reflectance means low absorptance and also a small temperature response (low amplitude). Once the thickness stabilizes in stage (c), drying begins due to evaporation, especially near the surface, and the surface reflectance decreases rapidly at this stage. Therefore, at time t bc A sharp rise can be seen from this point.

[0080] However, in stage (d), the surface is almost dry, and evaporation mainly occurs from within. In other words, the surface reflectivity stabilizes, which stabilizes the amplitude A of the temperature response. This stabilization allows us to recognize the transition between stages (c) and (d).

[0081] Therefore, amplitude is essentially a measure of the reflectance of the coated layer.

[0082] It was found that the effect at different depths of the coating layer significantly contributes to the temperature response depending on the excitation modulation frequency. When measuring the curves shown in Figures 10 to 12, excitation frequencies of 2000 to 4000 Hz are used, so information about the surface drying state of the coating layer is mainly obtained. However, when excitation is performed at frequencies of 20 to 400 Hz, information about the interior of the material can be obtained. In this way, the drying state of both the surface of the coating layer (laser modulation between 2000 and 4000 Hz) and the interior of the coating layer (laser excitation between 20 and 400 Hz) can be clearly determined.

[0083] To implement the method described here, the impact jet dryer 142 shown in Figure 2 may be equipped with a laser photothermal sensor instead of a distance sensor, similar to the second embodiment described above. In this case, adjustments are made based on the values ​​of the phase shift P and amplitude A.

[0084] 4. Examples Figure 9 shows a fourth embodiment combining elements of the first and second embodiments or the first and third embodiments. In this embodiment, the dryer 42 includes three dryer units 42a, 42b, and 42c, each configured similarly to the dryer shown in Figure 2. The regulator 50 controls all three dryer units 42a, 42b, and 42c. Different drying conditions can be set for the dryer units 42a, 42b, and 42c. This allows for a temporary reduction in drying speed, particularly in stage (c), as in the second embodiment.

[0085] The dryer having multiple dryer units 42a, 42b, and 42c as shown in Figure 9 is particularly advantageous when it is necessary to avoid exposing the coated layer to strong air movement, as in the case of the impact jet dryer 142. The hot air remains in the drying units 42a, 42b, and 42c, and the drying rate can be set only by the temperature T in the corresponding unit.

[0086] 5. Examples It is also preferable to combine the distance sensor described in the second embodiment and the laser photothermal sensor described in the third embodiment into a single device. In this case, the determination and adjustment of the step transition can be carried out by any combination of quantities such as thickness, reflectance, roughness, phase shift of the temperature response, and amplitude of the temperature response.

Claims

1. a) A step of applying electrode paste (22, 32) as a coating layer to a metal foil (20) to obtain a coated metal foil, b) A step of drying the coating layer applied to the metal foil (20) in a dryer (42; 142) in which the drying conditions can be changed, A method for manufacturing an electrode (40) of a battery cell, including A method characterized by measuring at least one characteristic of the coating layer non-contact using measuring instruments (48a, 48b) for inline process monitoring, and changing at least one of the process conditions in the dryer (42; 142) if the value of the at least one characteristic measured by the measuring instruments is outside the range of a reference value.

2. The method according to claim 1, characterized in that the degree of dryness of the coating layer is determined from the at least one measured characteristic.

3. The dryness of the coating layer during the drying process can be described in five stages that progress sequentially during the drying process: (a) a stage in which the coating layer forms a moist film; (b) a stage in which the coating layer forms a completely filled capillary network; (c) a stage in which the coating layer forms a partially filled capillary network; (d) a stage in which only individual, spaced-out liquid residues exist in the coating layer; and (e) a stage in which the coating layer forms a film that does not contain liquid. The method according to claim 2, wherein the timing of the transition between stages (b) and (c) and / or between stages (c) and (d) during the coating process can be derived from the measured values.

4. The at least one of the above characteristics is the thickness (d) of the coating layer. Ｇ The method according to any one of claims 1 to 3, characterized in that it is selected from the group consisting of the reflectance of the coating layer, the surface roughness of the coating layer, and the thermal conductivity of the coating layer.

5. Measuring instruments (48a, 48b) are used to non-contact measure at least two properties of the coating layer, and these two properties are defined as the thickness (d) of the coating layer. Ｇ The method according to any one of claims 1 to 4, characterized in that it is selected from the group consisting of the reflectance of the coating layer, the surface roughness of the coating layer, and the thermal conductivity of the coating layer.

6. The method according to 4 or 5, characterized in that the surface roughness of the coating layer is derived from the spatial distribution of the measured thickness.

7. The method according to any one of claims 4 to 6, referencing claim 3, characterized in that when the roughness of the surface or the amount derived thereby exceeds a threshold, the transition between step (b) and step (c) is estimated.

8. The method according to 4 or 5, characterized in that the reflectance of the surface is derived from the amplitude of the response of the coating layer to thermal excitation, and / or the thermal conductivity of the surface is derived from the phase shift of the response of the coating layer to thermal excitation.

9. The method according to claim 4, 5, or 8, relating to claim 3, characterized in that when the phase shift curve of the response of the coated layer to thermal excitation or the amount derived thereby becomes the minimum value, the transition between step (b) and step (c) is estimated.

10. The method according to 6 or 9, characterized in that if the transition between step (b) and step (c) is estimated, the drying is slowed down.

11. The method according to any one of claims 4 to 10, relating to claim 3, characterized in that, if the diffuse reflectance of the surface decreases and then continues to increase until it reaches a final value, the transition between step (c) and step (d) is estimated.

12. The method according to 11, characterized in that if the transition between step (c) and step (d) is estimated, the drying is accelerated.

13. The method according to any one of claims 1 to 12, characterized in that the measuring instruments (48a, 48b) are measuring elements of a control circuit that adjusts the process conditions in the dryer (42; 142) according to at least one measured characteristic.

14. A coating device (11) is configured to apply electrode paste (22, 32) as a coating layer to a metal foil (20) to obtain a coated metal foil, A dryer having multiple separate dryer units (42a, 42b, 42c) or dryer zones provided in a common housing (44), wherein the dryer (42; 142) is capable of generating different process conditions within the dryer units or the dryer zones, An apparatus (10) for manufacturing electrodes (40) of a battery cell, comprising: The measuring instruments (48a, 48b) are configured to non-contact measure at least one characteristic of the coating layer during the drying period. The apparatus is characterized in that the control or adjustment device (50) is configured to change at least one of the process conditions in the dryer if the value of at least one characteristic measured by the measuring device is outside the range of a reference value for inline process monitoring.

15. The apparatus according to claim 14, characterized in that the measuring instrument comprises a plurality of chromatic confocal distance sensors (48a, 48b) configured to determine the surface roughness of the coating layer from the measured distance.

16. Application of a chromatic confocal distance sensor (48a, 48b) to the method according to any one of claims 1 to 13.

17. The apparatus according to claim 14, characterized in that the measuring instrument comprises a plurality of laser photothermal sensors configured to determine the phase shift and amplitude from the response to thermal excitation.

18. Application of a laser photothermal sensor to the method according to any one of claims 1 to 13.

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