Roller for pressing an electrode

Abstract

The present invention relates to a roller and calendaring machine for battery cell production. A roller for pressing an electrode sheet for a battery cell is disclosed. The roller comprises a body having a central portion and end portions, wherein the end portions have a diameter larger than that of the central portion. The body further comprises a tapered transition region between at least one of the end portions and the central portion. This arrangement may contribute to reducing wrinkles and edge deformation during pressing.

Description

[0001] ROLLER FOR PRESSING AN ELECTRODE

[0002] TECHNICAL FIELD

[0003] The present invention generally relates to battery manufacturing, and more particularly to a roller used for pressing an electrode for a battery cell, a calendaring machine comprising such a roller, and a method for pressing an electrode sheet.

[0004] BACKGROUND

[0005] The transition towards greener and more sustainable energy solutions has become a significant global focus in recent years. Central to this transition is the use of battery cells, particularly in the electric vehicle industry and for energy storage from renewable sources. Battery cells are vital components in promoting this shift away from fossil fuels, contributing to a more sustainable and environmentally-friendly future.

[0006] Manufacturing of battery cells is a complex, multi-step process. The process typically starts with the preparation of a slurry where active material, conductive agent, and binder are mixed together with a solvent. This slurry is coated onto a thin foil known as a current collector, forming an electrode sheet. Typically, copper foil is used for the anode electrode and aluminium foil for the cathode electrode, but different metals or other materials may be used depending on the battery cell design. After coating, the electrode is dried in an oven to remove the solvent, resulting in an electrode sheet with a layer of active material bound to the current collector foil. The coated electrode sheet then undergoes a process known as calendaring, where it is passed through a set of rollers in a calendaring machine to improve the active material density and electrical conductivity. By carefully controlling this process, an optimal structure of the electrode can be achieved, which is crucial for the electrochemical performance of the battery cell.

[0007] Notably, only the center region of the foil is typically coated with active material. The side regions of the foil are left uncoated, and are sometimes referred to as "tabs". These tabs are subsequently used for welding the electrode to the current collector of the cell. In a subsequent step, the foil is may be slit in two, such that each of the two parts becomes a separate electrode sheet. There is a need in the art to further improve the battery cell manufacturing process to ensure high quality for high-performance battery cells, which typically must fulfill tough performance requirements.

[0008] SUMMARY

[0009] During the calendaring process, wrinkling and deformation can occur, leading to poor electrode properties and reducing the overall performance of the battery cell. The inventors have found that this problem can be especially severe when manufacturing high-perfomance cells, which generally have a higher electrode density.

[0010] The present disclosure seeks to address these challenges by providing an improved roller for the calendaring process. The roller is designed to minimize imperfections such as wrinkles and deformations on the electrode material, including the tabs, thereby enhancing the quality of the calendared electrodes, the overall performance of the battery cells, the efficiency of the welding process, and the productivity of the battery cell production process.

[0011] In so doing, the invention contributes not only to advancements in battery technology but also to the broader goals of environmental sustainability and the green energy transition.

[0012] The present disclosure provides a roller 100 for pressing an electrode sheet for a battery cell. The roller 100 comprises a body 101 having a central portion 110 and end portions 120, 122. In some examples, the central portion 110 and the end portions 120, 122 may form a continuous body having a one-piece construction 101.

[0013] The end portions 120, 122 and the central portion 110 may be coaxial.

[0014] In some examples, the body 101 may be constructed from hard chromium.

[0015] The end portions 120, 122 have a diameter larger than that of the central portion 110. The body 101 further comprises a tapered transition region 130 between at least one of the end portions 120, 122 and the central portion 110. In some variants, such a tapered transition region 130 is formed between each one of the end portions 120, 122 and the central portion 110. The width of the transition region 130 may be 1-3 mm in some examples. Further, the transition region 130 may have a flat surface.

[0016] In some examples of the roller 100, the diameter of at least one of the end portions 120, 122 is 300-400 microns larger than the diameter of the central portion 110. In yet further examples, the diameter of at least one of the end portions 120, 122 is specifically 350-400 microns larger than the diameter of the central portion 110.

[0017] This disclosure further provides a calendaring machine 200 comprising a roller 100 as described above. The calendaring machine 200 further comprises a feeding mechanism 220 for feeding an electrode sheet for a battery cell to the roller 100.

[0018] In some variants, the calendaring machine further comprises a press roller 210. The calendaring machine 200 is then adapted to calendar the electrode sheet to a predefined active material density using the press roller 210. The roller 100 is arranged after the press roller 210 in the feeding direction in these variants.

[0019] Furthermore, the present disclosure provides a method 400 for pressing an electrode sheet 300 for a battery cell. The electrode sheet 300 to be pressed comprises a foil. A central region 310 of the foil is coated with an active material and an edge region 320, 322 of the foil is not coated with the active material. The edge region 320, 322 may alternatively be referred to as a tab or "uncoated region". The method comprises engaging 402 a roller 100, such as the roller 100 described above, with a surface of the electrode sheet. The roller is engaged with the electrode sheet such that the transition region 130 of the roller 100 overlaps an edge between the coated and uncoated regions of the foil 300. The positioning of the roller ensures that the tapered region will smoothen the active material edge as well as the bare foil. The method further comprises pressing 403 the electrode sheet using the roller 100.

[0020] In some examples, the width of the transition region 130 of the roller 100 is 10-20% of the width of the edge region 320, 322. The method 400 may further comprise calendaring 401 the electrode sheet to obtain a predefined density of the active material, where the thicknesses of end portions 120, 122 of the roller are adapted to the predefined density.

[0021] Additional favourable features and characteristics of the invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings.

[0022] BRIEF SUMMARY OF THE DRAWINGS

[0023] Figure 1 is a schematic illustration of a roller according to some embodiments.

[0024] Figure 2 is a schematic overview of a calendaring machine.

[0025] Figure 3 is a schematic illustration of an electrode sheet.

[0026] Figure 4 is a flow chart of a method for pressing an electrode sheet according to some embodiments.

[0027] DETAILED DESCRIPTION

[0028] The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description of the invention.

[0029] Reference Key:

[0030] 100 - Roller

[0031] 101 - Body

[0032] 110 - Central portion

[0033] 120, 122 - End portions 130 - Transition region

[0034] 200 - Calendaring machine

[0035] 206 - Guide roller

[0036] 210 - Press roller

[0037] 220 - Feeding mechanism

[0038] 300 - Electrode sheet

[0039] 310 - Central region

[0040] 320, 322 - Edge region (also referred to as tabs or "uncoated region" below).

[0041] Figure 2 shows an example calendaring machine 200 used in battery cell production. In this machine, several components work together to ensure the electrode sheet is processed to meet the required specifications. The electrode sheet is typically supplied from a large roll and processed by the calendaring machine as a continuous sheet. In subsequent processing steps (not further described in this disclosure), this sheet is cut into individual electrodes for assembly into battery cells using a stacking, folding or winding process.

[0042] The calendaring machine 200 comprises a feeding mechanism 220, responsible for accurately aligning and guiding the electrode sheet into the machine. The feeding mechanism needs to be finely tuned to ensure the sheet enters the processing area without displacement or misalignment.

[0043] After the feeding mechanism 220, the electrode sheet encounters a press roller 210. This roller calendars the electrode sheet by applying pressure onto the sheet as it passes through it. The press roller is for example operated by a pump 202 which is controlled by a control unit (not shown). The pressure of press roller 210 is determined by the width of the electrode sheet to be pressed, and the thickness to be achieved. The pressure and the gap between the roller 210 and the electrode sheet determine the final thickness of the electrode sheet. Uniform application of pressure is important for ensuring the sheet has consistent thickness throughout, enabling optimal performance in the battery cell. Therefore, in a conventional calendaring machine, the press roller 210 and the additional guide roller or rollers typically have a straight profile.

[0044] An additional roller 206 is positioned in the outfeeding section 204 of the machine, after the press roller 210. This roller, which may be referred to as a guide roller, further manipulates the electrode sheet before it exits the machine. The calendaring machine may comprise several such guide rollers, which guide the electrode and maintain the uniformity of tension across the width direction. The combination of the feeding mechanism 220 and the rollers 100 and 210 ensures the electrode sheets are treated correctly and made ready for the next stages of the battery cell production process.

[0045] The press roller 210 and additional roller 206 are typically made from highly durable materials like hardened or stainless steel coated with hard chromium. These materials enable application of sufficient calendaring pressure, and can withstand wear from continuous use. However, it should be understood that this disclosure is not limited to any particular material being used for the rollers.

[0046] It should further be noted that the calendaring machine 200 may comprise one or more additional guide rollers (not shown in Figure 2).

[0047] As mentioned above, the high pressure applied during calendaring can lead to wrinkles forming on the electrode tabs. The inventors have found that such wrinkle formation can lead to severe issues in the subsequent welding process. This applies especially when manufacturing high- performance cells, where the electrode density is high. In the context of this disclosure, a high electrode density is above 3.5 g / cc for the cathode, or above 1.5 g / cc for the anode, where g / cc denotes grams per cubic centimeter. A related problem is deformation of the edge between the active material layer and the foil, hereafter referred to simply as "edge deformation". In more detail, "edge deformation" refers to a process where the slurry gets lifted off the electrode foil due to application of high force, which may result in the formation of cracks or other defects. If not addressed, these issues may impact the cell's performance as well as the manufacturing yield, leading to increased production costs..

[0048] Referring now to Figures 1 and 3, an example roller 100 is illustrated which is particularly suitable for pressing an electrode sheet 300 without causing wrinkling of the tabs 320, 322 or edge deformation of the active material coated on the central region 310 of the electrode sheet. This roller may be implemented in the calendaring machine 200 shown in Figure 2, preferably as the additional roller 206. However, the example roller could alternatively be implemented as the press roller 210.

[0049] The roller 100 comprises a body 101 that includes a central portion 110 and end portions 120, 122. The end portions 120, 122 have a diameter 121 which is designed to be larger than that of the central portion 110.

[0050] Continuing with the configuration of the body 101, it includes a tapered transition region 130 situated between at least one of the end portions 120, 122 and the central portion 110.

[0051] The wider end portions 120, 122 ensure that the ends of the roll engage with the tabs 320, 322, where the sheet is thinner as a consequence of no active material being coated. The tapered transition regions further provide a gradual, smoothening effect in the direction from the center of the electrode toward the edges, which reduces the risk of wrinkles as well as prevents edge deformation. The transition region 130 should be configured to overlap the edge between the coated region 310 and the uncoated region 320, 322 and should cover about 10-20% of the uncoated region 320, 322 to provide optimal effect. Consequently, the transition region 130 may be configured to have a width 131 in the range of l-3mm. Preferably, the transition region 130 has a flat surface.

[0052] The difference in diameter between the central portion 110 and the end portions 120, 122 is advantageously in the range of 300-400 microns (i.e. micrometers). In some variants, the diameter difference is between 350-400 microns. More specifically, the difference in diameter should be adapted to the target electrode density in the calendared electrode. A diameter difference of about 300 microns has been found suitable for a cathode electrode density of about 3.5 g / cc, i.e. towards the lower end of a high-density electrode. For higher electrode densities a larger diameter difference should be applied. In a cell manufacturing facility, the calendaring machine 200 would typically be part of a manufacturing line configured to produce a specific type of cell. The dimensions of the roller would be adapted accordingly and potentially replaced with a different roller if the line needs to be reconfigured for another cell type.

[0053] Within the context of this disclosure, "electrode density" refers to the weight of active material per unit of volume of the active material.

[0054] Table 1 below shows the relationship between electrode density and diameter difference in more detail. The difference in diameter may also be referred to as the "step size".

[0055] Table 1

[0056] The roller 100 as a whole may constitute a continuous body 101 having a one-piece construction. This ensures robustness of the roller 100 during operation. The body 101 of the roller 100 is advantageously made from or coated with hard chrome for durability. The roller 100 is cylindrical.

[0057] It should be appreciated that although the example of Figure 2 shows both end portions 120, 122 of the roller 100 having tapered transition regions 130, a possible variant is that only one end portion has a wider thickness and thus only one tapered transition region 130 is arranged between the central portion 110 and the end portion with a wider thickness, whereas the other end of the roll has a straight profile. This variant could apply if only one side of the sheet has an uncoated region.

[0058] With reference now to Figure 4, a method 400 is provided for pressing an electrode sheet 300, such as the electrode sheet described above with reference to Figure 3. Hence, the electrode sheet 300 comprises a foil, wherein a central region 310 of the foil is coated with an active material and an edge region 320, 322 of the foil is not coated with the active material.

[0059] Before the method 400 is performed, electrode sheet 300 has been unwound from its roll and fed via the infeeding section 220, where it may also have been subjected to one or more preprocessing step (not shown).

[0060] In optional step 401, the electrode sheet 300 is first calendared to obtain a predefined density of the active material. The diameters of the end portions 120, 122 of the roller are adapted to the predefined density, as has been explained above with reference to Table 1.

[0061] In step 402, a roller 100 is engaged with a surface of the electrode sheet 300. The roller 100 may be the roller described above with reference to Figure 1. In other words, the roller 100 comprises a body 101 that includes a central portion 110 and end portions 120, 122. The end portions 120, 122 have a diameter 121 which is designed to be larger than that of the central portion 110. Further, the roller 100 includes a tapered transition region 130 between at least one of the end portions 120, 122 and the central portion 110. The roller 100 may further have any one or more of the features described above with reference to Figure 1.

[0062] In the engaging step 402, the transition region 130 of the roller 100 overlaps an edge between the coated and uncoated regions of the foil. This ensures that the tapered transition portion applies pressure to the active material edge and outwards toward the edge of the foil. Advantageously, the width of the transition region 130 of the roller 100 may be 10-20% of the width of a region 320, 322 of the foil which is not coated with the active material. In a further step 403, the electrode sheet is pressed using the roller 100. Optionally, the electrode sheet may be further post-processed in the outfeeding section 204 before being transferred to the next manufacturing step.

[0063] In conclusion, the present disclosure provides a roller, a calendaring machine and a method that solve some of the challenges currently faced in the battery cell manufacturing process, particularly in the calendaring process and in the production of high-performance battery cells. The novel design of the roller and its application, as described in the various embodiments above, provides an efficient means of reducing imperfections in an electrode sheet, thereby enhancing the quality and performance of the battery cells produced and contributing to overall manufacturing productivity.

Claims

CLAIMS1. A roller (100) for pressing an electrode sheet for a battery cell, the roller (100) comprising: a body (101) having a central portion (110) and end portions (120, 122), wherein the end portions (120, 122) have a diameter larger than that of the central portion (110); the body (101) further comprises a tapered transition region (130) between at least one of the end portions (120, 122) and the central portion (110).

2. The roller (100) according to claim 1, wherein the diameter of at least one of the end portions (120, 122) is 300-400 microns larger than the diameter of the central portion (110), preferably 350-400 microns larger than the diameter of the central portion (110).

3. The roller (100) according to any one of claims 1-2, wherein the width of the transition region (130) is 1-3 mm.

4. The roller (100) according to any one of claims 1-3, wherein the transition region (130) has a flat surface.

5. The roller (100) according to any preceding claim, wherein a tapered transition region (130) is formed between each one of the end portions (120, 122) and the central portion (110).

6. A calendaring machine (200) comprising a roller (100) as described in any of claims 1-5 and a feeding mechanism (220) for feeding an electrode sheet for a battery cell to the roller (100).

7. The calendaring machine (200) according to claim 6, further comprising a press roller (210), wherein the calendaring machine (200) is adapted to calendar the electrode sheet to a predefined active material density using the press roller (210), and wherein the roller (100) is arranged after the press roller (210) in the feeding direction.

8. A method (400) for pressing an electrode sheet (300) for a battery cell, the electrode sheet (300) comprising a foil, wherein a central region (310) of the foil is coated with an active material and an edge region (320, 322) of the foil is not coated with the active material, the method comprising:- engaging (402) a roller (100) according to any one of claims 1-9 with a surface of the electrode sheet, such that a transition region (130) of the roller (100) overlaps an edge between the coated and uncoated regions of the foil (300);- pressing (403) the electrode sheet using the roller (100).

9. The method (400) of claim 9, wherein the width of the transition region (130) of the roller (100) is 10-20% of the width of the edge region (320, 322).

10. The method (400) of claim 8 or 9, further comprising calendaring (401) the electrode sheet to obtain a predefined density of the active material, and wherein the thicknesses of end portions (120, 122) of the roller are adapted to the predefined density.

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