Advanced calender measurement and control for battery electrode fabrication

Abstract

The invention relates to advanced calender measurement and control for battery electrode fabrication. A calender measurement and control system for manufacturing an electrode sheet of a lithium ion battery onto an apparatus includes: a dual rotating roller through which a sheet material travels; a heating element (induction coil) positioned along the length of one or both of the rotating rollers; and means for controlling the heating intensity in the rotating roller along the length of the rotating roller to which the heating is applied. The diameter of the heated rotating roller expands in response to heat, thereby adjusting the thickness of the electrode. The controller input includes operating point data including an electrode material composition, an electrode coating weight, a maximum electrode coating density, an initial electrode coating thickness, a temperature of one or both of the rotating rollers containing the heating element, and a line load. The controller may be tuned whereby a process gain from the line load to the final thickness is automatically calculated at a specified operating point defined by the operating point data.

Description

Technical Field

[0001] The present invention relates generally to the manufacture of electrochemical cells and, more particularly, to automated calender control in the production of continuous electrode sheets exhibiting improved uniform thickness. Background Art

[0002] Lithium-ion batteries are a type of secondary battery and contain four main components: a positive electrode (cathode), a negative electrode (anode), a separator placed between the electrodes to prevent contact and short circuits, and an electrolyte. Examples of cathode active materials may include, but are not limited to, mixed metal oxides, metal phosphates, or related materials. Examples of anode materials may include, but are not limited to, graphite, silicon, or a composite thereof. The electrolyte provides the transport of ions and may be a liquid such as LiPF6 or a solid. Battery manufacturing begins with the manufacture of large sheets of double-sided coated anode copper substrates and double-sided coated cathode aluminum substrates. The electrodes are manufactured using a continuous roll-to-roll process in which premixed anode or cathode materials are coated onto a metal substrate sheet used as a current collector. The electrodes are calendered or pressed before the electrode sheets are cut into double-sided coated metal substrates of appropriate size to assemble into batteries.

[0003] In order to achieve and maintain the quality of continuous roll-to-roll production of electrodes, continuous online measurement of quality factors that are closely related to battery performance must be performed. Weight is most directly related to the amount of active particles, so uniform weight per unit area (area weight) is a basic requirement for high-quality electrodes. Similarly, the thickness of the coating must be uniformly maintained at the target value to ensure good electrochemical performance of the finished battery and to ensure that the layered electrode fits into the battery container. Currently, calender control is usually performed manually or by simply adjusting the roll gap based on endpoint measurements. These thickness adjustment methods have various disadvantages and do not take into account many factors that contribute to electrode uniformity and performance.

[0004] With current control technology, the calender rolls do not compress the entire electrode sheet uniformly. The effects of short-term and long-term springback on the electrode material are not considered. Sheet temperature can vary and can affect measurement and coating compressibility. Electrode composition can change and require different parameters. Finally, compression without considering the effects on the structural properties of the electrode material can produce defective electrodes. These problems will become more prevalent as sheet width increases. In addition, as facilities become larger and include more assembly lines, it becomes more difficult to maintain a large number of non-automated pressing stations. Summary of the invention

[0005] The invention is based in part on the development of a measurement and control system for a calender used to make electrode sheets for lithium-ion batteries. The system produces anode and cathode electrodes with more uniform properties, allowing the coating to be compressed to increase energy density while maintaining sufficient porosity to maintain good ionic conductivity. At the same time, compression provides an improved path for electronic conductivity. Using the invention, electrode manufacturers can optimize production by getting closer to specification targets.

[0006] In one aspect, the invention relates to a device for controlling the thickness of a layer of electrode material on a moving electrode sheet, the moving electrode sheet comprising a metal substrate coated on at least one side with a layer of electrode material, the device comprising:

[0007] means for passing the electrode sheet moving in the machine direction (MD) through a gap formed by a first rotating roller and a second rotating roller;

[0008] means for heating the first rotating roller at selected locations along the length of the first rotating roller, wherein a plurality of first heating elements are positioned along the length of the first rotating roller; and

[0009] Means for controlling the intensity of the heat in the first rotating roller and the location along the length of the first rotating roller where the heat is applied.

[0010] In a preferred embodiment, the heating element comprises an induction coil.The diameter of the heated rotating roller expands in response to the heat, thereby adjusting the thickness of the electrode.

[0011] In another aspect, the invention relates to a controller for controlling the thickness of a layer of electrode material on a moving electrode sheet, the moving electrode sheet comprising a metal substrate coated on at least one side with a layer of electrode material, the layer of electrode material exiting a calender having a first rotating roller and a second rotating roller defining a gap through which the electrode sheet passes, wherein at least one of the first rotating roller or the second rotating roller has a heating element positioned along its length, the controller comprising:

[0012] (a) processor;

[0013] (b) means for measuring the temperature of at least one of the first rotating roller or the second rotating roller having a heating element;

[0014] (c) means for determining the linear load applied by the calender;

[0015] (d) means for applying heat at selected locations along the length of at least one of the first rotating roller or the second rotating roller to heat at the first rotating roller or the second rotating roller to adjust its diameter;

[0016] (e) a memory device coupled to the processor and including a readable program,

[0017] The readable program is executed by the processor to:

[0018] (i) receiving an input including a thickness of a layer of electrode material exiting the calender;

[0019] (ii) receiving an input including a temperature of at least one of the first rotating roller or the second rotating roller having a heating element;

[0020] (iii) receiving an input comprising the line load applied by the calender;

[0021] (iv) processing a model of the calender; and

[0022] (v) providing an output coupled to control the application of heat along the length of at least one of the first rotating roller or the second rotating roller having the heating element.

[0023] In a preferred embodiment, the controller input also includes operating point data, which includes electrode material composition, electrode coating weight, maximum electrode coating density, initial electrode coating thickness, temperature of at least one of the first rotating roller or the second rotating roller having a heating element, and line load.

[0024] The controller may be tuned whereby the process gain from line load to final thickness is automatically calculated at a specified operating point defined by the operating point data.

[0025] Plasticity is the ability of a material to permanently change shape when subjected to force. During battery electrode calendering, the magnitude of the force applied to compress the electrode will result in some permanent coating compression. That is, the thickness of the coating after pressing is less than the thickness of the coating before pressing. In this case, it is useful to quantify the deformation resistance rather than the plasticity itself by a temperature-dependent compaction factor, which is a key parameter in the equation that controls the relationship between load and final thickness in the pressing of coated electrodes. Using the present invention, the relationship between line load and final thickness is used to automatically adjust the controller tuning when the pressing conditions change. In particular, the gain from line load to final coating thickness can be calculated from measured process operating variables. This gain is used to update the controller tuning and maintain good control of the pressing operation. Thus, time-consuming tuning experiments and losses due to poor operation are avoided.

[0026] The invention is particularly suitable for quality control in the manufacture of electrodes for lithium-ion batteries, where metal aluminum or copper foils from metal rolls are continuously coated with cathode active materials or anode active materials, respectively. The present technology provides manufacturers with quality measurement data at an early stage of the production process, which provides better control of process conditions and reduces scrap rates. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The battery electrode calendering process is shown;

[0028] Figure 2 It is a plan view of the calendering rollers and heating system;

[0029] Figure 3 depicts a roll-to-roll sheet production system for continuously coating a metal substrate with an anodic or cathodic material; and

[0030] Figure 4 A calendering system is shown. DETAILED DESCRIPTION

[0031] Figure 1 A calender device 132 is shown including an upper metal roller 126 and a lower metal roller 128, which defines a roller gap or a controlled gap through which a continuous electrode material sheet 122 passes. The length and diameter of the two vertically mounted rollers are preferably the same. The electrode material includes an anode or cathode material that may contain a solvent. The electrode sheet 122 travels through the roller gap in the longitudinal direction (MD) to roll the electrode sheet 122 into a compressed electrode sheet 124 of a predetermined thickness. The transverse direction (CD) of the moving electrode sheet 122 is perpendicular to the MD. The scanning sensor 130 measures one or more characteristics along the CD of the compressed electrode sheet 124. The measured characteristics may include, for example, sheet thickness and temperature. The scanning sensor 130 generates a transverse measurement curve. An inlet scanning sensor (not shown) may also be positioned to measure one or more characteristics along the CD of the electrode sheet 122 before the sheet enters the roller gap between rollers 126 and 128.

[0032] The present invention is characterized in that the outer surface temperature of the roller 126 along its CD can be controlled so that the temperature T r (x) can vary along the length of roller 126, and heating causes roller 126 to expand, so the thickness of the cylinder increases with temperature. The temperature increase required to obtain a small change in roller thickness is very small. For example, if the desired actuation Δt is 1 micron and if the roller is a 60 cm diameter stainless steel roller, and for simplicity, the coefficient of linear expansion CTE is assumed to be 10×10 -6 m / m·℃ (this is at the lower end of possible values). Assuming CTE = Δt / R / ΔT, this means that the temperature change is only 0.3 degrees. This small number also highlights the requirement for roller temperature measurement and control. The lower roller 128 can also be heated to control its outer surface temperature.

[0033] Figure 2 A technique for producing a temperature distribution along the length of a roll is shown, which employs induction heating. A continuous roll 154 made of stainless steel or other conductive material is divided into a plurality of sections, zones or regions 170, 172, 174, 176 and 178 along its length. Induction coils 140, 142, 144, 146 and 148 are placed adjacent to zones 170, 172, 174, 176 and 178, respectively. A controller 152 regulates a power supply 150 so that the alternating current driving each coil can be regulated. A multi-zone induction heating system is described in U.S. Pat. No. 8,415,595 to Chirico, U.S. Pat. No. 9,756,686 to Dohmeier et al., and U.S. Pat. No. 5,059,762 to Simcock, which are incorporated herein by reference. The outer diameter of each zone along the length of the roll can be controlled by induction heating to produce a curve of the calender roll diameter. Roller 154 may also be heated with heated fluid from a heating fluid source 160 that circulates through channels 162 in the roller.

[0034] In one embodiment of the invention, roller induction heating is used to control the electrode sheet thickness profile. Simultaneously, thermal fluid roller heating controls the average roller or sheet temperature to a specific target. Since both induction heating and thermal fluid heating affect the roller diameter, the nominal gap can be controlled by an electro-hydraulic or other gap control device.

[0035] Figure 3 A process for coating a metal web or sheet used to make electrodes for lithium ion electrochemical cells and batteries is shown. To make an anode, the electrode coating comprises an anode active material such as graphite, and to make a cathode, the electrode coating comprises a cathode active material such as lithium metal oxide. The electrode comprises a current collector metal foil coated with an electrode slurry on both sides of the foil, which may also include carbon black, a binder, and a solvent. After the electrode slurry is applied to one side of the foil, the wet-coated foil is heated in a dryer to extract the solvent, leaving a solid layer of the electrode material adhered to the metal foil. Copper foil is a preferred anode current collector material, and aluminum foil is a preferred cathode current collector material.

[0036] like Figure 3 As shown, a roll 2 is unwound from an unwinder and supplies a continuous metal web or sheet 30, which is coated with a layer of electrode slurry on the top surface by a coater 6. The basis weight, thickness and other characteristics of the metal web or sheet 30 from the roll 2 are generally known; the basis weight and / or thickness are measured using scanning beta meters 4 and 8, respectively, before and after the electrode slurry is applied by the coater 6.

[0037] The coater 6 (such as a slot die coater) includes an actuator that controls the slot die / knife to adjust the amount of slurry extruded onto the sheet 30. The dryer 10 removes excess solvent and solidifies the slurry on the moving coated sheet 32 ​​to form an electrode layer on the sheet. The imaging devices 58 and 78 capture images of the surface of the coated sheet 32 ​​before and after the dryer 10. Each imaging device typically includes a camera and a light source that illuminates the surface of the coated sheet 32. The imaging device can be fixed or scanning. For a fixed device, the camera captures a digital image of the surface of the coated sheet 32 ​​across the entire width. The camera generates a series of images that can be superimposed to form a continuous image of the entire coated sheet 32.

[0038] The scanning beta meter 12 measures the basis weight and / or thickness of the moving coated sheet 32 ​​exiting the dryer 10 after the calender 54. The rolling supports 34, 36 then reverse the orientation of the moving sheet 38 so that the uncoated side is at the top, whereupon the coater 14 applies a layer of electrode slurry to the top uncoated surface of the moving sheet 38. The scanning beta meter 16 then measures the basis weight and / or thickness of the double-sided coated sheet 40 before entering the dryer 18. The imaging devices 70 and 72 capture images of the top and bottom surfaces of the sheet before the dryer 18, while the imaging devices 74 and 76 capture images of the top and bottom surfaces of the sheet after exiting the dryer 18.

[0039] Further downstream, a beta meter housed in the scanning device 24 together with an infrared temperature sensor measures the basis weight and / or thickness and temperature of the double-side coated sheet 42 as the scanning device 24 moves back and forth over the double-side coated sheet 42. A rewinder rolls the double-side coated sheet 42 into a roll 44. Surface defects on the top and bottom coatings are monitored by imaging devices 26, 28.

[0040] Figure 4 The calendaring process is shown, whereby the double coated electrode layer 106 from the electrode roll 80 passes through the calendar system 84, which trims and smoothes the electrode layer 108. The calendar system includes an upper calendar roll 96, an upper calendar roll 92, a lower calendar roll 94, and a lower calendar roll 98. The two calendar rolls define a gap through which the electrode layer 106 passes. The calendar rolls 92 and 94 are each divided into a plurality of zones along their length, and each zone is heated by a multi-zone induction heating mechanism 102 and 104, respectively. Each calendar roll may also be heated with a hot fluid.

[0041] A gap positioning system including an upper pressure roller 96 and a lower pressure roller 98 can change the gap between the calender rollers. A pair of press-down mechanism motors or hydraulic cylinders (each equipped with a press-down mechanism or screw that clamps the opposite ends of the pressure rollers 96, 98, respectively) applies roller force (pressure) to the calender rollers 92, 94. An infrared thermal sensor 110 measures the temperature of the heated calender roller 92, which provides an estimate of the surface temperature of the top electrode coating in the gap during compression. Since the radiation and convection heat losses from the calender rollers will be relatively small, infrared temperature measurements of the calender rollers should provide a good estimate of the electrode coating temperature. Alternatively, similar temperature measurements can be made on the sheet as it leaves the calender rollers. A similar infrared thermal sensor associated with the calender roller 94 provides an estimate of the surface temperature of the lower electrode coating during compression.

[0042] Scanner sensors 98 and 88 measure various properties of the double-sided coated sheet before and after calendering. These properties include, for example, the basis weight of the sheet, the basis weight of each coating, the thickness of the sheet, the thickness of each coating. Scanning callipers operating according to optical and magnetic measurement principles can be used. The finished electrode layer 108 is collected in the finished electrode roll 82.

[0043] A quality control system including an automatic calender controller 100, which includes a computer with memory and a processor, receives signals from the various sensors, thereby generating and comparing cross-directional sheet property curves of the double-sided coated sheet before and after calendering. A calender control strategy can be implemented that allows cross-directional control of material properties, as well as better control of average material properties by utilizing roll or sheet temperature measurements.

[0044] For example, the thickness profile of the upper and lower anodic or cathodic coatings may be determined. The multi-zone induction heating mechanism 102 and / or 104 is then activated to adjust the temperature and diameter of the various zones in the calender rolls 92 and / or 94 along their lengths to form a compressed sheet having a uniform thickness in the transverse direction. When roller induction heating is used to control the thickness profile, at the same time, e.g. Figure 2 The hot fluid shown can be circulated through the calendar rolls to control the average roll or sheet temperature to a specific target. The nominal gap target is selected to control the average (also called machine direction) coating thickness. The average roll temperature set point will be selected to provide the best preservation of the material structure, as determined by off-line experiments and modeling or by feedback control based on conductivity or other available measurements.

[0045] Data from the sensors also enables the controller 100 to determine the plasticity of the compressed sheet for use in managing and controlling the calendaring operation. Equation (1) characterizes how the electrode (positive or negative) coating is permanently compressed for a given amount of force applied during the calendaring process.

[0046]

[0047] Here ρC is the coating density after calendering, ρ C,0 is the coating density before calendering, PM is the maximum possible density of the coating, q L is the applied calender load, and γ C is the resistance of the coating to compaction. C is the inverse of the plastic deformability coefficient. In addition, the coating density is the mass load (area weight) M C and thickness δ.

[0048]

[0049] Substituting (2) into (1) and rearranging it yields:

[0050]

[0051] Resistance to compaction (the inverse of plasticity) is a function of both mass loading and temperature and takes the following form:

[0052] γ C =(μ 0℃ -ξT R )×M C (4)

[0053] Here, μ 0℃ is the anti-compaction mass load factor at a temperature of 0 °C, ξ is the slope of the temperature-dependent mass load factor, and T R is the roller temperature in degrees Celsius. Thus, with a small amount of data, the operator can fit the parameters in the coating compression model as a function of mass load, temperature, and line load. Once these parameters are obtained, the operator has a steady-state model for the coating thickness after compression as a function of mass load, initial thickness, line load, and roller temperature. Combining the above four equations and rearranging them yields the following equation (5).

[0054]

[0055] In tuning model-based controllers such as model predictive control (MPC) or internal model control (IMC), and in model-based tuning methods for controllers (such as IMC-based tuning for proportional-integral-derivative (PID) controllers), it is necessary to have a model of the process behavior that includes the process gain. The process gain is the change in the value of the controlled variable that occurs for a unit change in the value of the manipulated variable. In the case of controlling thickness by manipulating line load, the process gain k qδ for:

[0056]

[0057] The gain can be calculated by differentiation using equation (5):

[0058]

[0059] The derivative formula is used to obtain an exact expression from equation (5), or numerical techniques can be used. In either case, for a given coating weight Mc, the maximum coating density ρ M , initial thickness δ C,0 、Mass load factor μ of anti-compaction at 0℃ 0℃ , the slope of the temperature-dependent mass load factor ξ, the roller temperature (℃) T R , gain from line loading to coating thickness.

[0060] In addition to μ 0℃ All of these values, except for ξ, can be measured directly or obtained from known material properties. However, by obtaining pressing data at at least two different temperatures, the two constants μ 0℃ The values ​​of and ξ can be derived from equations (3) and (4). Once these values ​​are determined, they can be used in equation (5) for all future operations involving the same type of coating (i.e., coatings with the same composition). This allows calculation of the C , M , δ C,0 , T R and q L The set of describes the process gain kqδ at any operating point.

[0061] Being able to calculate this process gain at any operating point simplifies controller commissioning and maintenance. This information can be calculated from equation (5) rather than having to perform plant experiments to determine the process model gains and re-tune the controller for different grades (thicknesses) of electrodes.

[0062] Similarly, for a set grade of electrode, if the process operation changes (e.g., desired final thickness or preferred pressing temperature), the load to thickness gain and controller tuning can be automatically updated based on equation (5).

[0063] Thus, using the present invention, a controller can be programmed to adjust the thickness of a continuous electrode sheet in a calender apparatus having dual rotating rollers, at least one of which has a heating element positioned along its length. A memory device is coupled to a processor, the memory device having a readable program that is executed by the processor to: (i) receive an input of the thickness of the electrode material layer leaving the calender; (ii) receive an input of the temperature of at least one of the first rotating roller or the second rotating roller having the heating element; (iii) receive an input of the line load applied by the calender; (iv) process a model of the calender; and (v) provide an output that is coupled to control the application of heat along the length of at least one of the first rotating roller or the second rotating roller having the heating element.

[0064] A feature of the invention is that the controller can use model-based control and / or model-based controller tuning, where the gain from line load to final thickness can be automatically calculated at any given operating point defined by electrode composition, coating weight, maximum coating density, initial thickness, roller temperature, and line load.

[0065] By automating the controller tuning process, commissioning time can be reduced and quality can be maintained at a high level, thereby avoiding losses due to poor quality by ensuring that the control continues to operate well even when process operations change.

[0066] The algorithms to achieve this control include:

[0067] 1. Obtain process data of at least two different roller temperatures δ C 、M C , M , δ C,0 、T R and q L ,as well as

[0068] 2. Apply equations (3) and (4) to calculate the anti-compaction parameter μ 0℃ and Once these parameters are calculated,

[0069] The gain can be calculated automatically.

[0070] Automatic gain calculation and controller tuning including:

[0071] 1. Determine the new process data set M C , M , δ C,0 , and T R ,

[0072] 2. Use the process data set plus the previously determined parameters μ 0℃ and The process gain is calculated from the derivative of equation (5), and

[0073] 3. Update the process model used in model-based control or for model-based controller tuning.

[0074] The controller continues to be well tuned for different process operations, ensuring good electrode product quality.

[0075] The foregoing describes the principles, preferred embodiments and modes of operation of the present invention. However, the present invention should not be construed as being limited to the specific embodiments discussed. Therefore, the above embodiments should be considered as exemplary rather than restrictive, and it should be understood that variations may be made in these embodiments by those skilled in the art without departing from the scope of the present invention as defined by the following claims.

Claims

1. A device for controlling the thickness of an electrode material layer on a moving electrode sheet, the moving electrode sheet comprising a metal substrate coated with an electrode material layer on at least one side, the device comprising: means for passing the electrode sheet moving in the machine direction (MD) through a gap formed by a first rotating roller and a second rotating roller; means for heating the first rotating roller at selected locations along the length of the first rotating roller, wherein a plurality of first heating elements are positioned along the length of the first rotating roller; and Means for controlling the intensity of said heat in said first rotating roller and said location along the length of said first rotating roller at which said heat is applied.

2. The apparatus of claim 1, wherein the means for heating the first rotating roller produces electrical induction heating.

3. The device according to claim 1, further comprising: means for heating the second rotating roller at selected locations along the length of the second rotating roller, wherein a plurality of second heating elements are positioned along the length of the second rotating roller; and Means for controlling the intensity of said heat in said second rotating roller and said location along the length of said second rotating roller at which said heat is applied.

4. The device of claim 3, wherein the metal substrate is coated with a layer of a first electrode material on a first side and with a second electrode material on a second side.

5. A method of controlling the thickness of a continuous electrode sheet moving in a machine direction (MD), wherein the electrode sheet comprises a metal substrate coated on at least one side with an electrode material, the method comprising: advancing the electrode sheet through a gap defined by a first rotating roller and a second rotating roller, wherein a plurality of first heating elements are positioned along a length of the first rotating roller; as well as Heat is applied at selected locations along the length of the first rotating roller to heat the first rotating roller to adjust its diameter.

6. The method of claim 5, further comprising applying heat at selected locations along the length of the second rotating roller to heat the second rotating roller to adjust its diameter. 7 . The method of claim 6 , wherein the metal substrate is coated with a layer of a first electrode material on a first side and with a second electrode material on a second side.

8. A controller for controlling the thickness of a layer of electrode material on a moving electrode sheet, the moving electrode sheet comprising a metal substrate coated on at least one side with a layer of electrode material, the layer of electrode material exiting a calender, the calender having a first rotating roller and a second rotating roller defining a gap through which the electrode sheet passes, wherein at least one of the first rotating roller or the second rotating roller has a heating element positioned along its length, the controller comprising: (a) processor; (b) means for measuring the temperature of at least one of the first rotating roller or the second rotating roller having a heating element; (c) means for determining the linear load applied by the calender; (d) means for applying heat at selected locations along the length of at least one of the first rotating roller or the second rotating roller to heat at the first rotating roller or the second rotating roller to adjust its diameter; (e) a memory device coupled to the processor and comprising a readable program executable by the processor to: (i) receiving an input comprising a thickness of a layer of electrode material exiting said calender; (ii) receiving an input including a temperature of at least one of the first rotating roller or the second rotating roller having a heating element; (iii) receiving an input comprising said line load applied by said calender; (iv) treating a model of the calender; as well as (v) providing an output coupled to control the application of heat along the length of at least one of the first rotating roller or the second rotating roller having a heating element.

9. The controller of claim 8, wherein the input further comprises operating point data, the operating point data comprising electrode material composition, electrode coating weight, maximum electrode coating density, initial electrode coating thickness, temperature of at least one of the first rotating roller or the second rotating roller having a heating element, and line load.

10. The controller of claim 8, wherein the controller is tuned whereby a process gain from line load to final thickness is automatically calculated at a specified operating point defined by the operating point data.

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