Electrode sheet rolling device

Abstract

To provide an electrode sheet rolling device which does not generate contaminations easily even when a DLC coating of a roller is separated.SOLUTION: A rolling device is arranged in a conveyance path for conveying an electrode sheet of a power storage device and includes a pair of rollers 31. The pair of rollers 31 each includes: a base material 32; an underlying layer 33 formed in at least a rolling region for rolling the electrode sheet of an outer peripheral surface of the base material 32; and a diamond-like carbon (DLC) coating film 34 formed on the outer peripheral surface of the underlying layer 33. The underlying layer 33 is harder than the base material 32.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a rolling device for an electrode sheet. [Background technology]

[0002] For example, Patent Document 1 discloses a method for manufacturing an electrode material, which includes a step of pressing an electrode material in the thickness direction, the electrode material being formed by applying an active material slurry layer and a ceramic slurry layer to a strip-shaped metal foil. The ceramic slurry layer contains ceramic particles. In the method described in Patent Document 1, the electrode material is pressed by a press roll having an outer circumferential surface of a roll body covered with an abrasion-resistant layer of diamond-like carbon (DLC) while being conveyed. According to Patent Document 1, the abrasion-resistant layer prevents direct sliding contact between the roll body and the ceramic particles, suppressing wear of the roll body. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-190681 A Summary of the Invention [Problem to be solved by the invention]

[0004] As described in Patent Document 1, the wear resistance of the rolling roll can be improved by forming a DLC coating with high hardness on the surface of the rolling roll that rolls the electrode sheet of the electricity storage device. However, the DLC coating has low toughness and may peel off from the base material of the rolling roll. When the DLC coating peels off, the base material is rapidly worn. When the base material is rapidly worn, fine particles of the base material generated by the wear may become contaminants and may affect the quality of the electrode sheet.

[0005] Therefore, we propose a rolling device for electrode sheets that is less likely to cause contamination even if the DLC coating on the rolling roll peels off. [Means for solving the problem]

[0006] The electrode sheet rolling device disclosed herein is a rolling device arranged on a transport path along which an electrode sheet for an electricity storage device is transported, and includes a pair of rolling rolls. Each of the pair of rolling rolls includes a substrate, a base layer formed at least in a rolling region of the outer circumferential surface of the substrate where the electrode sheet is rolled, and a diamond-like carbon (DLC) coating formed on the outer circumferential surface of the base layer. The base layer is harder than the substrate.

[0007] According to the electrode sheet rolling device, a base layer harder than the substrate exists between the substrate and the DLC coating. Even if the DLC coating of the rolling roll peels off, the base layer prevents the substrate from touching the electrode sheet. Therefore, wear of the substrate is prevented. In addition, the base layer is harder than the substrate and is less likely to wear. As a result, contamination can be suppressed. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a schematic side view of a rolling device for an electrode sheet. [Diagram 2] FIG. 2 is a schematic plan view of a rolling device for an electrode sheet. [Diagram 3] FIG. 2 is a schematic cross-sectional view of a rolling roll. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, one embodiment of a rolling apparatus for electrode sheets of an electricity storage device will be described. Note that the embodiment described here is, of course, not intended to limit the present invention in particular. Also, each figure is a schematic diagram and does not necessarily faithfully reflect an actual product.

[0010] [Rolling equipment configuration] FIG. 1 is a schematic side view of an electrode sheet rolling apparatus 10 according to one embodiment. FIG. 2 is a schematic plan view of the electrode sheet rolling apparatus 10. The rolling apparatus 10 here rolls an electrode sheet 1 of a lithium-ion secondary battery. However, the electrode sheet 1 is not limited to an electrode sheet of a lithium-ion secondary battery, and may be an electrode sheet of various known electricity storage devices. The term electricity storage device refers to devices in general that can extract electric energy, and includes so-called storage batteries (chemical batteries) such as lithium-ion secondary batteries and nickel-metal hydride batteries, and capacitors (physical batteries) such as electric double layer capacitors.

[0011] The electrode sheet 1 includes a strip-shaped electrode foil 2 and an active material layer 3 formed on the electrode foil 2. The positive electrode sheet is a member in which a positive electrode active material layer 3 containing a positive electrode active material is formed on the surface of a strip-shaped electrode foil 2 (e.g., aluminum foil) having a predetermined width and thickness. The positive electrode active material is, for example, a material that can release lithium ions during charging and absorb lithium ions during discharging, such as a lithium transition metal composite material, in a lithium ion secondary battery. The negative electrode sheet is a member in which a negative electrode active material layer 3 containing a negative electrode active material is formed on the surface of a strip-shaped electrode foil 2 (e.g., copper foil) having a predetermined width and thickness. The negative electrode active material is, for example, a material that can absorb lithium ions during charging and release the absorbed lithium ions during discharging, such as natural graphite, in a lithium ion secondary battery. The positive electrode active material and the negative electrode active material are not particularly limited, and various materials other than those mentioned above have been proposed.

[0012] The positive electrode sheet further includes a protective layer 4 that protects the active material layer 3 and prevents a reaction with the electrolyte. Here, the protective layer 4 is a layer containing a passivation state of a metal oxide (ceramic). The protective layer 4 includes, for example, aluminum oxide (alumina). However, various materials other than the above-mentioned have been proposed for the protective layer 4, and the protective layer 4 is not particularly limited. The protective layer 4 is formed by being layered on the active material layer 3 of the positive electrode. In Figs. 1 and 2, a positive electrode sheet including a protective layer 4 is illustrated as the electrode sheet 1. In the following, unless otherwise specified, the electrode sheet 1 is described as having the protective layer 4.

[0013] The raw material of the active material layer 3 is made into a slurry and coated on the electrode foil 2. The raw material of the active material layer 3 may be coated on one side or both sides of the electrode foil 2. In the case of a positive electrode sheet, the material of the protective layer 4 is made into a slurry and coated on the active material layer 3. The electrode sheet 1 has a portion coated with the active material layer 3 and the protective layer 4, and an uncoated portion where neither the active material layer 3 nor the protective layer 4 is formed. The coated raw material of the active material layer 3 and the protective layer 4 in the slurry form is dried in a drying process. The rolling device 10 then continuously presses the electrode sheet 1 while conveying it in the longitudinal direction, adjusting the thickness of the active material layer 3 and the protective layer 4 to a thickness within a predetermined range, and densifying the active material in the active material layer 3.

[0014] As shown in FIG. 1, the rolling device 10 is disposed on a transport path along which the electrode sheet 1 of the electricity storage device is transported. As shown in FIG. 1, the rolling device 10 itself may also be equipped with a mechanism for transporting the electrode sheet 1. In this embodiment, the rolling device 10 includes an unwinding device 20, a pressing device 30, and a winding device 40. The electrode sheet 1 after the active material layer 3 and the protective layer 4 are dried is supplied to the unwinding device 20 on a roll. The winding device 40 winds up the electrode sheet 1 that has been unwound from the unwinding device 20 and rolled by the pressing device 30. However, the rolling device 10 may be provided on a transport path along which the electrode sheet 1 is transported by another transport device.

[0015] The rolling device 10 (more specifically, the press device 30) includes a pair of rolling rolls 31U and 31D. The upper rolling roll 31U and the lower rolling roll 31D face each other vertically with the transport path of the electrode sheet 1 in between. When rolling the electrode sheet 1, the upper rolling roll 31U is lowered by a driving device (not shown) and presses the electrode sheet 1 together with the lower rolling roll 31D. The thicknesses of the active material layer 3 and the protective layer 4 after rolling are measured by a film thickness sensor 35. The vertical position or pressing pressure of the upper rolling roll 31U is feedback-controlled in response to the thicknesses of the active material layer 3 and the protective layer 4 measured by the film thickness sensor 35. In the following, when there is no need to distinguish between the upper rolling roll 31U and the lower rolling roll 31D, the reference symbol 31 is used and they may be referred to as the rolling roll 31, a pair of rolling rolls 31, etc.

[0016] The pressing force of the rolling device 10 is not particularly limited, but may reach a linear pressure of 40000 N / cm. The length of the rolling rolls 31U and 31D in the width direction of the electrode sheet 1 may reach 100 cm. The conveying speed of the electrode sheet 1 during rolling is also not particularly limited, but may reach 100 m / min. Since the linear pressure of the rolling device 10 is high, the conveying speed of the electrode sheet 1 is fast, and the protective layer 4 is hard, a large frictional force is applied to the pair of rolling rolls 31U and 31D. The Vickers hardness of the ceramic part of the protective layer 4 is, for example, 1400 to 1800 HV. In addition, since the conveying speed of the electrode sheet 1 is fast, the wear amount of the rolling roll 31 per hour also becomes large.

[0017] FIG. 3 is a schematic cross-sectional view of a rolling roll 31. As shown in FIG. 3, the rolling roll 31 has a substrate 32, a base layer 33, and a diamond-like carbon (DLC) coating 34. The substrate 32 is a base body of the rolling roll 31 formed in a cylindrical shape. The substrate 32 is formed of, for example, a high carbon bearing steel material (SUJ material), preferably, for example, SUJ2, which has high versatility. However, the material of the substrate 32 is not limited to the SUJ material. The substrate 32 may be made of, for example, chromium steel, chromium molybdenum steel, stainless steel, etc. As the material of the substrate 32, a material that has a strength that can withstand the pressing pressure of the rolling roll 31 and is excellent in availability, processability, cost, etc. is preferable. In this embodiment, the hardness of the substrate 32 does not need to be so high. The Vickers hardness of a material preferable for the substrate 32 is, for example, 600HV or more and 900HV or less.

[0018] The underlayer 33 is a layer harder than the base material 32, and is formed on the surface of the base material 32. The underlayer 33 is formed at least in a rolling region 32a (see FIG. 2) of the outer peripheral surface of the base material 32 where the electrode sheet 1 is rolled. As shown in FIG. 2, the rolling region 32a is a region that contacts the electrode sheet 1 during rolling. The width of the rolling region 32a in the width direction of the electrode sheet 1 is equal to the width of the electrode sheet 1. The underlayer 33 may be formed in a portion of the outer peripheral surface of the base material 32 that includes the rolling region 32a and is wider than the rolling region 32a. For example, the underlayer 33 may be formed on the entire outer peripheral surface of the base material 32.

[0019] In this embodiment, the underlayer 33 is formed of a cemented carbide. More specifically, the underlayer 33 is formed of a thermal spray coating of a cemented carbide. A cemented carbide is a material in which tungsten carbide is sintered with a metal such as cobalt or nickel. In the cemented carbide, the metal that binds the tungsten carbide particles is not limited to cobalt or nickel. A thermal spray coating is a coating formed by spraying a material in a molten state or a state close to being molten onto a substrate. A thermal spray coating of a cemented carbide is formed, for example, by a high-velocity flame spraying method. However, the underlayer 33 may be a thermal spray coating of a material other than a cemented carbide, for example, a material containing a metal oxide (ceramic) and a metal (so-called cermet). Alternatively, the underlayer 33 may be formed by a method other than thermal spraying. For example, the underlayer 33 may be formed by hard chrome plating.

[0020] The underlayer 33 is formed of a material that is at least harder than the base material 32. The Vickers hardness of the underlayer 33 is preferably 900HV or more. It is more preferable that the Vickers hardness of the underlayer 33 is 1200HV or more. The Vickers hardness of the cemented carbide is about 1100HV to 1500HV. The Vickers hardness of the hard chrome plating is about 750HV to 1000HV.

[0021] The underlayer 33 is preferably formed thick. A suitable method for forming the underlayer 33 thick is thermal spraying. The underlayer 33 is preferably formed to have an average thickness of 50 μm or more. More preferably, the underlayer 33 is formed to have an average thickness of 100 μm or more.

[0022] As shown in FIG. 3, the DLC coating 34 is formed on the outer peripheral surface of the underlayer 33. The DLC coating 34 is a carbon coating having the carbon bond structure of both diamond and graphite. The DLC coating 34 is formed, for example, by a plasma CVD (chemical vapor deposition) method in which hydrogen carbonate gas is plasmatized and deposited, or by sputtering using graphite as a raw material. The Vickers hardness of the DLC coating 34 is, for example, 1600 HV or more and 2500 HV or less. The Vickers hardness of the DLC coating 34 is higher than that of the underlayer 33. The average thickness of the DLC coating 34 is, for example, 2 to 3 μm. The feasible thickness of the DLC coating 34 is several μm or less. The average thickness of the underlayer 33 is thicker than that of the DLC coating 34. The average thickness of the underlayer 33 is preferably 10 times or more the average thickness of the DLC coating 34.

[0023] [Effects of the embodiment] The following describes the effects that can be achieved by the rolling device 10 for the electrode sheet 1 according to this embodiment.

[0024] The rolling device 10 for the electrode sheet 1 according to this embodiment is a rolling device arranged on a transport path along which the electrode sheet 1 for an electricity storage device is transported, and includes a pair of rolling rolls 31. Each of the pair of rolling rolls 31 has a substrate 32, an underlayer 33 formed at least in a rolling region 32a of the outer circumferential surface of the substrate 32 where the electrode sheet 1 is rolled, and a DLC coating 34 formed on the outer circumferential surface of the underlayer 33. The underlayer 33 is harder than the substrate 32.

[0025] The DLC coating 34 has low toughness and may peel off from the substrate 32. For example, if the rolling roll 31 bites into a foreign object, the DLC coating 34 is likely to peel off. Conventionally, the rolling roll for rolling the electrode sheet 1 of the electricity storage device has a DLC coating formed on the outer peripheral surface of the substrate. Therefore, in the conventional rolling roll, when the DLC coating peels off, the substrate is rapidly worn. The electrode sheet 1, especially the protective layer 4, is very hard, and further, the pressing pressure is large and the conveying speed of the electrode sheet 1 is fast, so that the substrate is rapidly worn. When the substrate is rapidly worn, fine particles of the substrate generated by the wear may become contaminants and affect the quality of the electrode sheet 1.

[0026] In contrast, in the rolling device 10 according to this embodiment, an underlayer 33 harder than the substrate 32 is present between the substrate 32 and the DLC coating 34. Even if the DLC coating 34 of the rolling roll 31 peels off, the underlayer 33 prevents the substrate 32 from touching the electrode sheet 1. This prevents the substrate 32 from being worn down. Furthermore, the underlayer 33 is harder than the substrate 32 and is less susceptible to wear. As a result, contamination can be suppressed.

[0027] In addition, in conventional rolling rolls, when the DLC coating wears away after long-term use and is partially or completely worn away, the base material also wears away rapidly. Therefore, even after the DLC coating wears away or peels off, wear of the base material continues to progress between the time the DLC coating wears away or peels off and the time the rolling roll is replaced after it is discovered that the DLC coating has worn away or peeled off. This shortens the lifespan of the rolling roll. As long as the base material is still usable, the DLC coating can be formed again on the base material and it can be reused.

[0028] In contrast, in the rolling apparatus 10 according to this embodiment, it is the underlayer 33 that comes into contact with the electrode sheet 1 and wears after the DLC coating 34 has worn away or peeled off. The underlayer 33 is harder than the substrate 32, and wears less than the substrate 32. Therefore, the rolling roll 31 can be maintained in a reusable state for a longer period of time, and the DLC coating 34 can be re-formed more times than before. As a result, the life of the rolling roll 31 can be extended compared to before.

[0029] In this embodiment, the base layer 33 is made of a cemented carbide. With this configuration, the hardness of the base layer 33 made of a cemented carbide is high, so that the amount of wear of the reduction roll 31 can be reduced.

[0030] In this embodiment, the average thickness of the underlayer 33 is greater than the average thickness of the DLC coating 34. According to this configuration, since the underlayer 33 is thick, the life of the reduction roll 31 can be further extended.

[0031] In this embodiment, the average thickness of the underlayer 33 is 50 μm or more. With this configuration, the thickness of the underlayer 33 is large, so the life of the rolling roll 31 can be further extended. According to a prototype produced by the inventors of the present application, the life of the rolling roll 31 having the underlayer 33 with an average thickness of 50 μm or more is several times longer than that of a conventional rolling roll (the material of the base material is SUJ2) that forms a DLC coating on the surface of the base material.

[0032] In this embodiment, the base layer 33 is formed by a thermal spray coating. This configuration allows for a high degree of freedom in the material of the base layer 33. Thermal spraying has few limitations on the materials that can be used to form the coating. Furthermore, thermal spraying makes it easy to form a thick base layer 33.

[0033] [Other embodiments] An embodiment of the electrode sheet rolling device proposed herein has been described above. However, the above-mentioned embodiment is merely an example, and the present invention can be implemented in other aspects. For example, in the above-mentioned embodiment, the rolling roll 31 has a three-layer structure of the substrate 32, the underlayer 33, and the DLC coating 34, but is not limited to this. The rolling roll may have a layer structure of four or more layers in which the substrate is disposed at the innermost radial position, the DLC coating is disposed at the outermost radial position, and the underlayer is disposed between the substrate and the DLC coating.

[0034] In addition, the above-described embodiments do not limit the present invention unless otherwise specified. Furthermore, the technology disclosed herein can be modified in various ways, and the components and processes described herein can be omitted or combined as appropriate, provided that no particular problems arise.

[0035] This specification includes the disclosures set forth in the following sections:

[0036] Section 1: A rolling device disposed on a conveying path along which an electrode sheet of an electricity storage device is conveyed, A pair of rolling rolls is provided. The pair of rolling rolls each include A substrate; a base layer formed at least in a rolling region of the outer peripheral surface of the base material where the electrode sheet is rolled; A diamond-like carbon (DLC) coating is formed on the outer peripheral surface of the underlayer, The underlayer is harder than the substrate. Electrode sheet rolling equipment.

[0037] Section 2: The underlayer is formed of a cemented carbide. Item 1. A rolling device for an electrode sheet according to item 1.

[0038] Section 3: The average thickness of the underlayer is greater than the average thickness of the DLC coating. Item 3. A rolling apparatus for an electrode sheet according to item 1 or 2.

[0039] Section 4: The average thickness of the undercoat layer is 50 μm or more. Item 4. A rolling device for an electrode sheet according to any one of Items 1 to 3.

[0040] Section 5: The underlayer is formed of a thermal spray coating. Item 5. A rolling device for an electrode sheet according to any one of items 1 to 4. [Explanation of symbols]

[0041] 1 Electrode sheet 2 Electrode foil 3 Active material layer 4 protective layer 10. Rolling Equipment 20 Unwinding device 30 Press equipment 31 Rolling Mill 31D Lower Roll 31U Upper rolling roll 32 Base material 32a Rolling area 33 Base layer 34 DLC coating 35 Film Thickness Sensor 40 Winding device

Claims

1. A rolling device disposed on a conveying path along which an electrode sheet of an electricity storage device is conveyed, A pair of rolling rolls is provided. The pair of rolling rolls each include A substrate; a base layer formed at least in a rolling region of the outer peripheral surface of the base material where the electrode sheet is rolled; a diamond-like carbon (DLC) coating formed on an outer peripheral surface of the underlayer; The underlayer is harder than the substrate. Electrode sheet rolling equipment.

2. The underlayer is formed of a cemented carbide. The electrode sheet rolling device according to claim 1 .

3. The average thickness of the underlayer is greater than the average thickness of the DLC coating. The electrode sheet rolling device according to claim 1 .

4. The average thickness of the undercoat layer is 50 μm or more. The electrode sheet rolling device according to claim 1 .

5. The underlayer is formed of a thermal spray coating. The electrode sheet rolling device according to claim 1 .

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