Slurry coating device and method for manufacturing electrode

Abstract

This slurry coating device (20) applies a mixture slurry (12) to a belt-shaped electrode core (11) of an electrode of a battery. The slurry coating device (20) is provided with: a conveyance roll (9) that conveys the belt-shaped core (11); and a discharge port (22b) that faces the conveyance roll (9) at a gap from the conveyance roll (9) and discharges the mixture slurry to one side surface of the electrode core (11) conveyed by the conveyance roll (9). The conveyance roll (9) has a protrusion (9c) that protrudes outward in the radial direction.

Description

Slurry application device and electrode manufacturing method

[0001] The present disclosure relates to a slurry coating device that coats a material mixture slurry on a strip-shaped core of a battery electrode, and a method for manufacturing the electrode.

[0002] A conventional battery electrode manufacturing apparatus is described in Patent Document 1. This manufacturing apparatus includes a feed roll, a transport roll, a take-up roll, a slurry discharge unit, a drying furnace, and a cooling unit. The feed roll and the take-up roll are rotated in one direction by a motor, and the transport roll is disposed between the feed roll and the take-up roll. A strip-shaped electrode core made of metal foil is stretched over the feed roll, transport roll, and take-up roll. The feed roll, transport roll, and take-up roll apply a predetermined tension to the strip-shaped core, allowing it to stably travel from the feed roll to the take-up roll. The slurry discharge unit applies a mixture slurry containing an active material to the strip-shaped core guided by the transport roll to form a coating film. The drying furnace heats and dries the coating film disposed on the strip-shaped core. After the coating film on the strip-shaped core is dried in the drying furnace, it is naturally cooled and then wound up on the take-up roll.

[0003] Japanese Patent Application Publication No. 11-102696

[0004] There is a demand for varying the thickness of the mixture layer formed on a strip-shaped core in the longitudinal direction of the strip-shaped core. For example, if the thickness of the mixture layer at the winding start end of the electrode can be reduced, it becomes easier to efficiently and neatly wind the electrode when fabricating a wound electrode body, and it becomes easier to fabricate a wound electrode body with high roundness. In this context, by varying the discharge amount per unit time of the mixture slurry discharged onto the running strip-shaped core body, the mixture layer thickness can be varied in the longitudinal direction of the strip-shaped core body. However, methods that control the discharge amount of the mixture slurry do not easily produce the desired mixture layer with high reproducibility. Therefore, an object of the present disclosure is to provide a slurry coating device and an electrode manufacturing method that can easily and reproducibly fabricate electrodes including a mixture layer whose film thickness varies in the longitudinal direction.

[0005] In order to solve the above problems, the slurry coating device of the present disclosure is a slurry coating device that coats a composite slurry onto a strip-shaped core of a battery electrode, and is equipped with a transport roll that transports the strip-shaped core, and an ejection section that faces the transport roll via a gap and ejects the composite slurry onto one side of the strip-shaped core being transported by the transport roll, and the transport roll has a protrusion that protrudes radially outward.

[0006] In addition, the electrode manufacturing method according to the present disclosure includes a coating step in which, while a strip-shaped core of a battery electrode is being transported by a transport roll having protrusions protruding radially outward, a composite slurry is ejected onto one side of the strip-shaped core from an ejection section facing the transport roll via a gap, and a cutting step in which the strip-shaped core coated with the composite layer by the coating step is cut at a location where the thickness of the composite layer, which is coated on the strip-shaped core by the coating and whose thickness varies periodically in the longitudinal direction, reaches approximately a minimum value.

[0007] The transport roll may have one protrusion, or may have a plurality of protrusions spaced apart in the circumferential direction.

[0008] According to the slurry application device and electrode manufacturing method of the present disclosure, it is easy to reproducibly manufacture an electrode including a mixture layer whose film thickness varies in the longitudinal direction.

[0009] 1 is a schematic configuration diagram of an electrode manufacturing apparatus according to an embodiment of the present disclosure; FIG. 2 is a side view of a die head and a transport roll in a slurry coating apparatus when viewed from one axial side of the transport roll; FIG. 3 is a side view showing a state in which the distance between the discharge port and the transport roll is at its maximum; FIG. 4 is a side view corresponding to FIG. 2 of a slurry coating apparatus of a reference example; FIG. 5 is a diagram illustrating a problem when the film thickness of a mixture slurry is varied using the slurry coating apparatus of the reference example; FIG. 6 is a diagram illustrating an example of a film thickness variation of a mixture slurry when the discharge amount of the mixture slurry is kept constant in the slurry coating apparatus of the embodiment; FIG. 7 is a diagram illustrating an example of a film thickness variation of a mixture slurry when the discharge amount of the mixture slurry is periodically varied in the slurry coating apparatus of the embodiment, and the period is made to coincide with the rotation period of the transport roll; and FIG. 8 is a table showing the results of a test conducted by the present inventor.

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. It should be noted that, when multiple embodiments or variations are included below, it is assumed from the outset that new embodiments can be constructed by appropriately combining their characteristic features. In the following examples, the same components are denoted by the same reference numerals in the drawings, and redundant explanations will be omitted. The drawings include schematic diagrams, and the dimensional ratios of the length, width, height, etc. of each component between different drawings do not necessarily match.

[0011] The slurry applicator and electrode manufacturing method of the present disclosure can be used to manufacture electrodes (positive electrodes, negative electrodes) used in wound electrode bodies or stacked electrode bodies. The slurry applicator and electrode manufacturing method of the present disclosure may be used to manufacture a cylindrical battery having a bottomed cylindrical outer can, a prismatic battery having a prismatic outer can, or a pouch-type battery having an outer body composed of a laminate sheet including a metal layer and a resin layer.

[0012] The following describes an example in which electrodes (positive and negative electrodes) for a lithium-ion secondary battery are manufactured using the slurry applicator and electrode manufacturing method of the present disclosure. However, the slurry applicator and electrode manufacturing method of the present disclosure can be used to manufacture electrodes (positive and negative electrodes) for primary batteries, and can also be used to manufacture electrodes (positive and negative electrodes) for secondary batteries other than lithium-ion secondary batteries. Furthermore, among the components described below, components not recited in the independent claims representing the superordinate concepts are optional components and not essential components.

[0013] Fig. 1 is a schematic configuration diagram of an electrode manufacturing apparatus 1 according to an embodiment of the present disclosure. As shown in Fig. 1, the electrode manufacturing apparatus 1 includes a feed roll 2 that feeds out an electrode core 11, a slurry applicator 20 that applies a mixture slurry to one side of the traveling electrode core 11, a drying and cooling section 5 that heats, dries, and cools the mixture slurry applied to one side of the electrode core 11 by the slurry applicator 20, one or more first guide rolls 6 that are arranged between the slurry applicator 20 and the drying and cooling section 5 and guide the electrode core 11, one or more second guide rolls 7 that guide the electrode core 11 fed from the drying and cooling section 5, and a take-up roll 8 that winds up the core that has passed through the second guide rolls 7.

[0014] The slurry coating device 20 includes a kneader 21 that mixes, kneads, and crushes multiple materials, such as an active material, a conductive agent, and a binder, to produce a mixture slurry 12 in which the multiple materials are uniformly mixed, a discharge amount control unit 25 that adjusts the discharge amount of the mixture slurry 12 discharged from the die 22 by controlling the amount of the mixture slurry 12 supplied to the die 22, the die 22 that discharges the mixture slurry 12 supplied from the discharge amount control unit 25 onto one side of the electrode core 11, and a transport roll 9 that is disposed opposite the discharge opening of the die 22. The discharge opening of the die 22 constitutes the discharge unit. The transport roll 9 backs up the back side of the electrode core 11 around the coating location where the mixture slurry 12 discharged from the die 22 is to be coated, and transports the electrode core 11.

[0015] The discharge amount control unit 25 has a control device (not shown) that controls the aperture of a supply port (not shown) that supplies the composite slurry 12 to the die 22. By controlling the aperture of the supply port, the discharge amount per unit time of the composite slurry 12 that is discharged from the discharge port of the die 22 onto the electrode core 11 is controlled.

[0016] The electrode core 11 is stretched over a feed roll 2, a transport roll 9, one or more first guide rolls 6, one or more second guide rolls 7, and a take-up roll 8. By synchronously rotating the feed roll 2 and the take-up roll 8 by motors 2a and 8a, a predetermined tension is applied to the electrode core 11, and the electrode core 11 travels stably from the feed roll 2 toward the take-up roll 8. The transport roll 9 may be rotated synchronously with the feed roll 2 and the take-up roll 8 by a motor 9a, or may be rotatably supported on a stationary shaft via a bearing.

[0017] When the electrode is a positive electrode and the strip-shaped electrode core 11 is a positive electrode core, the positive electrode core is made of a foil of a metal stable in the potential range of the positive electrode, such as aluminum or an aluminum alloy, or a film with such a metal disposed on the surface layer. Furthermore, the positive electrode mixture layer obtained by removing the solvent from the positive electrode mixture slurry by drying contains a positive electrode active material, a conductive agent such as acetylene black, and a binder such as polyvinylidene fluoride (PVdF). For example, a lithium transition metal composite oxide containing Ni, Co, Mn, Al, or the like is used as the positive electrode active material.

[0018] When the electrode is a negative electrode and the strip-shaped electrode core 11 is a negative electrode core, the negative electrode core is made of a foil of a metal that is stable within the potential range of the negative electrode, such as copper or a copper alloy, or a film with such a metal disposed on the surface. The negative electrode mixture layer obtained by removing the solvent from the negative electrode mixture slurry by drying contains a negative electrode active material and a binder such as styrene-butadiene rubber (SBR) or PVdF. Examples of the negative electrode active material include graphite and silicon-containing compounds.

[0019] 2 is a side view of the die head 22a and the transport roll 9 in the slurry coating device 20 when viewed from one axial side of the transport roll 9. As shown in Fig. 2, the transport roll 9 has one protrusion 9c that protrudes radially outward from the cylindrical outer circumferential surface 9b. In this embodiment, the protrusion 9c is formed as a part of a cylinder, and the outer edge of the protrusion 9c has an arc shape that protrudes radially outward in the side view shown in Fig. 2.

[0020] The outer edge of the protrusion 9c does not have to have an arc shape in the side view. It is preferable that the outer edge of the protrusion 9c is configured as a curved line that protrudes radially outward in the side view. The transport roll 9 rotates in one circumferential direction as indicated by arrow A. The rotation center axis 9d of the transport roll 9 coincides with the center axis of the cylindrical outer circumferential surface 9b.

[0021] The die head 22a of the die 22 tapers toward the tip. The die head 22a is disposed on the transport roll 9 at a distance. A discharge port 22b provided at the tip of the die head 22a faces the discharge direction of the mixture slurry indicated by arrow B toward the rotation center axis 9d of the transport roll 9. The mixture slurry 12 is applied to the electrode core 11 at a location facing the discharge direction through the discharge port 22b.

[0022] Because the transport roll 9 has protrusions 9c protruding radially outward from the cylindrical outer peripheral surface 9b, the distance between the discharge port 22b and the transport roll 9 is maximum when the discharge port 22b faces the cylindrical outer peripheral surface 9b in the discharge direction as viewed from one axial side, as shown in Fig. 3. Furthermore, as shown in Fig. 4, the distance between the discharge port 22b and the transport roll 9 is minimum when the discharge port 22b faces the tip 9e of the protrusion 9c in the discharge direction as viewed from one axial side. When the transport roll 9 rotates in the circumferential direction, the distance between the discharge port 22b and the transport roll 9 varies from a maximum distance L1 to a minimum distance L2 at the position where the discharge port 22b faces the protrusion 9c in the discharge direction.

[0023] When the distance in the discharge direction between the discharge port 22b and the transport roll 9 is short, the discharge pressure of the mixture slurry 12 increases, so the application width of the region where the mixture slurry 12 is applied increases, and the application amount of the mixture slurry 12 per unit area of ​​the electrode core 11 decreases. On the other hand, when the distance in the discharge direction between the discharge port 22b and the transport roll 9 is long, the discharge pressure of the mixture slurry 12 decreases, so the application width of the region where the mixture slurry 12 is applied decreases, and the application amount of the mixture slurry 12 per unit area of ​​the electrode core 11 increases.

[0024] As a result, during one rotation of the conveying roll 9, the film thickness of the composite layer formed on the electrode core 11 gradually decreases from the maximum film thickness in the circumferential range in which the discharge port 22b faces the protrusion 9c in the above-mentioned discharge direction to the minimum film thickness, and then gradually increases to the maximum film thickness.

[0025] Next, the effects of the technology of the present disclosure will be described. Fig. 5 is a side view corresponding to Fig. 2 of a slurry coater 220 of a reference example. In the slurry coater 220, a transport roll 209 has a cylindrical outer peripheral surface 209b that contacts the electrode core 11 over the entire circumferential direction, and a rotation center axis 209d coincides with the central axis of the cylindrical outer peripheral surface 209b of the transport roll 209. Furthermore, the discharge port 22b of the die head 22a faces the rotation center axis 209c of the transport roll 209 in the discharge direction of the mixture slurry indicated by arrow C. The slurry coater 220 controls the discharge amount of the mixture slurry discharged from the discharge port 22b to vary the film thickness of the mixture layer in the longitudinal direction of the electrode.

[0026] Fig. 6 is a diagram illustrating a problem that occurs when the film thickness of the mixture slurry 212 is varied using the slurry applicator 220 of the reference example. Fig. 7 is a diagram illustrating an example of a film thickness variation of the mixture slurry 12 when the discharge rate of the mixture slurry 12 is constant in the slurry applicator 20 of this embodiment. Fig. 8 is a diagram illustrating an example of a film thickness variation of the mixture slurry 112 when the discharge rate of the mixture slurry 112 is periodically varied in the slurry applicator 20 of this embodiment and the period is made to coincide with the rotation period of the conveying roll 9.

[0027] In each of Figures 6 to 8, (a) is a graph showing the relationship between the amount of composite slurry discharged and time, (b) is a graph showing the relationship between the distance between the discharge port 22b and the conveying roll 9, 209 and time, and (c) is a graph showing the relationship between the thickness-wise cross section of the electrode core 11 to which the composite slurry 12, 112, 212 has been applied and time.

[0028] In the method of applying the composite slurry 212 onto the electrode core 11 using the slurry applicator 220 of the reference example, two-stage control was performed in which the amount of the composite slurry to be discharged was periodically switched between a first discharge amount and a second discharge amount smaller than the first discharge amount, as shown in Fig. 6(a). Furthermore, when a circular transport roll 209 was used as shown in Fig. 6(b), the distance between the discharge port 22b and the transport roll 209 was always constant even when the transport roll 209 rotated.

[0029] As shown schematically in Figure 6(c), in a method in which the composite slurry 112 is applied to the electrode core 11 using a circular conveying roll 209, it was confirmed that even when the discharge amount of the composite slurry is adjusted by simple two-stage control, in the longitudinal range of the electrode core 11 where the discharge amount is small, areas where the composite slurry 12 is applied and areas where the composite slurry 12 is not applied are likely to occur, and the composite slurry 12 is likely to be applied in a patchy manner.

[0030] 7, in which the slurry mix 12 is applied to the electrode core 11 using the slurry applicator 20 of the above embodiment, the amount of the slurry mix to be discharged is constant regardless of time, as shown in Fig. 7(a). Furthermore, as shown in Fig. 7(b), when a transport roll 9 having protrusions 9a is used, the distance between the discharge opening 22b and the transport roll 9 varies depending on the relative position of the protrusions 9c with respect to the discharge opening 22b as the transport roll 9 rotates.

[0031] 7(c), in the method of applying the mixture slurry 112 onto the electrode core 11 using the transport roll 9 having the protrusions 9c, even in the case of the simplest control of keeping the discharge amount of the mixture slurry 12 constant regardless of time, it was possible to vary the film thickness of the mixture slurry 12 with high precision into a complex shape corresponding to the shape of the protrusions 9c during the period when the discharge port 22b faces the protrusions 9c in the discharge direction. However, it was confirmed that there were cases, although very rare, where slight protrusions 28a, 28b were formed at both longitudinal ends of the depressions 28 where the film thickness of the mixture slurry 12 was small.

[0032] Next, in the method shown in FIG. 8 for applying the composite slurry 12 onto the electrode core 11 using the slurry applicator 20 of the above embodiment, as shown in FIG. 8( a), two-stage control was performed in which the amount of composite slurry to be discharged was periodically switched between a first discharge rate and a second discharge rate smaller than the first discharge rate. Furthermore, as shown in FIG. 8( b), when a transport roll 9 having protrusions 9 a is used, as the transport roll 9 rotates, the distance between the discharge opening 22 b and the transport roll 9 fluctuates based on the relative position of the protrusions 9 c with respect to the discharge opening 22 b. As shown in FIGS. 8( a) and 8(b), the first period of fluctuation in the discharge rate of the composite slurry 112 was set to coincide with the second period of fluctuation in the distance between the discharge opening 22 b and the transport roll 9. More specifically, the amount of the composite slurry ejected during the period when the ejection port 22b does not face the protrusion 9c in the ejection direction is controlled to a first ejection amount, and the amount of the composite slurry ejected during the period when the ejection port 22b faces the protrusion 9c in the ejection direction is controlled to a second ejection amount.

[0033] 8(c), in a method of applying the mixture slurry 112 onto the electrode core 11 using a transport roll 9 having protrusions 9c, when the discharge rate of the mixture slurry 12 was varied in accordance with the rotation cycle of the transport roll 9, the film thickness of the mixture slurry 12 could be varied with high precision into a complex shape corresponding to the shape of the protrusions 9c during the period when the discharge port 22b faced the protrusions 9c in the discharge direction. Furthermore, unlike the case shown in FIG. 7, no protrusions were formed at both longitudinal ends of the depressions 128 where the film thickness of the mixture slurry 12 was small.

[0034] The inventors of the present invention investigated the ratio of the minimum application weight of the composite slurry to the maximum application weight of the composite slurry in several test examples in which the roll protrusion height, the protrusion circumferential length, and whether or not control of the discharge fluctuation of the composite slurry was performed were changed.

[0035] Figure 9 is a graph showing the test results. According to the above test, it was confirmed that if the protrusion height is 4 μm, the minimum coating weight can be reduced by about 5% of the maximum coating weight. On the other hand, if the thickness of the thinnest part of the mixture layer is 5% or more smaller than the thickness of the thickest part of the mixture layer, a wound electrode body with high circularity is likely to be produced. Therefore, since it is easier to produce a wound electrode body with high circularity, it is preferable that the protrusion height be 4 μm or more.

[0036] Furthermore, if the distance in the discharge direction between the discharge port 22b and the cylindrical outer peripheral surface 9b becomes too large, the mixture slurry 12, 112 discharged from the discharge port 22b may have difficulty reaching the electrode core 11, and the mixture slurry 12, 112 may have difficulty being transferred to the electrode core 11. To achieve good transfer of the mixture slurry 12, 112 to the electrode core 11, it is preferable that the protrusion height be 50 μm or less.

[0037] The battery electrode may be produced by carrying out a coating step in which, while the strip-shaped electrode core 11 of the battery is being transported by a transport roll 9 having protrusions 9c protruding radially outward, a composite slurry 12, 112 is discharged onto one side of the electrode core 11 from a discharge port 22b facing the transport roll 9 via a gap, and a cutting step in which the electrode core coated with the composite layer in the coating step is cut at a location where the thickness of the composite layer, which has been coated on the electrode core 11 in the coating step and whose thickness varies periodically in the longitudinal direction, reaches approximately a minimum value.

[0038] That is, the electrode core 11 on which the mixture layer is disposed using the slurry coating device 20 may be cut at a location where the thickness of the mixture layer is approximately minimal to produce an electrode. In this case, the mixture layer of the electrode will have approximately minimum thickness at both longitudinal end portions. Therefore, when a wound electrode body is produced using this electrode, the mixture layer will have approximately minimum thickness at the end portion on the side where winding begins. This makes it easier to wind the electrode efficiently and neatly, making it easier to produce a wound electrode body with high roundness.

[0039] The present disclosure is not limited to the above-described embodiment and its modifications, and various improvements and modifications are possible within the scope of the claims of the present application and their equivalents.

[0040] For example, in the above embodiment, the transport roll 9 has one protrusion 9c. However, the transport roll may have multiple protrusions arranged at equal intervals in the circumferential direction, or multiple protrusions arranged at non-equidistant intervals in the circumferential direction. Furthermore, when the transport roll has multiple protrusions arranged at intervals, the multiple protrusions may include two or more different protrusions, for example, two or more protrusions of different sizes or two or more protrusions of different shapes.

[0041] REFERENCE SIGNS LIST 1 Electrode manufacturing device, 2 Feed roll, 2a, 8a, 9a Motor, 5 Drying and cooling section, 6 First guide roll, 7 Second guide roll, 8 Winding roll, 9 Conveying roll, 9b Cylinder outer peripheral surface, 9c Protrusion, 9d Rotation center axis, 9e Protrusion tip, 11 Electrode core, 12, 112 Mixed material slurry, 20 Slurry coating device, 21 Kneader, 22 Die, 22a Die head, 22b Discharge outlet, 25 Discharge amount control section, 28, 128 Depression, 28a, 28b Protrusion.

Claims

1. A slurry coating device for coating a composite slurry onto a strip-shaped core of a battery electrode, comprising: a transport roll for transporting the strip-shaped core; and an ejection section facing the transport roll across a gap and ejecting the composite slurry onto one side of the strip-shaped core being transported by the transport roll, wherein the transport roll has a protrusion protruding radially outward.

2. The slurry application device according to claim 1, wherein the height of the protrusions is from 4 μm to 50 μm.

3. A slurry coating device as described in claim 1 or 2, further comprising a discharge amount control unit which periodically changes the amount of the composite slurry discharged from the discharge unit, wherein when the transport roll rotates, the distance between the discharge unit and the transport roll periodically varies, and a first period of variation in the amount of the composite slurry discharged coincides with a second period of variation in the distance between the discharge unit and the transport roll.

4. A method for manufacturing an electrode, comprising: a coating step in which, while a strip-shaped core of a battery electrode is transported by a transport roll having protrusions protruding radially outward, a composite slurry is ejected onto one side of the strip-shaped core from an ejection section facing the transport roll via a gap; and a cutting step in which the strip-shaped core coated with the composite layer by the coating step is cut at a location where the thickness of the composite layer, which is coated on the strip-shaped core by the coating step and whose thickness periodically varies in the longitudinal direction, reaches an approximately minimum value.

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