Slurry application device and method for producing electrode

Abstract

A slurry application device (20) applies a mixture slurry (12) to a strip-shaped electrode core body (11) of an electrode of a battery. The slurry application device (20) comprises a conveyance roller (9) that conveys the electrode core body (11) and a discharge section (discharge port (22b)) that faces the conveyance roller (9) with a gap therebetween, and that discharges the mixture slurry (12) to one side surface of the electrode core body (11) which is being conveyed by the conveyance roller (9). In a side view seen from one side in the axial direction, the outer circumferential edge (9d) of the conveyance roller (9) is a smooth closed curve, and the distance between the outer circumferential edge (9d) and the rotational center axis (9c) of the conveyance roller (9) varies depending on the position in the circumferential direction of the outer circumferential edge (9d).

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 present disclosure provides a slurry coating device for coating a strip-shaped core of a battery electrode with a mixture slurry, the slurry coating device comprising: a transport roll for transporting the strip-shaped core; and a discharge unit facing the transport roll across a gap and discharging the mixture slurry onto one side of the strip-shaped core being transported by the transport roll, wherein in a side view of the transport roll as viewed from one axial side, the outer circumferential edge of the transport roll forms a smooth closed curved line in which the distance between the rotation center of the transport roll and the outer circumferential edge varies depending on the circumferential position of the outer circumferential edge. The smooth closed curved line is a closed curved line that does not have any sharp points that cannot be differentiated.

[0006] In addition, the electrode manufacturing method of the present disclosure includes a coating step in which a strip-shaped core of a battery electrode is transported by a transport roll having a shape in which the position where the distance between the center of rotation and the outer peripheral edge is maximum and the position where the distance between the center of rotation and the outer peripheral edge is minimum are repeated periodically and alternately multiple times in a side view when viewed from one side in the axial direction, and 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 on which the composite layer is arranged based on the coating in the coating step and whose thickness varies periodically in the longitudinal direction is cut at a location where the thickness of the composite layer is approximately minimum.

[0007] 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.

[0008] FIG. 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 coater 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 showing a state in which the distance between the discharge port and the transport roll is at its minimum. FIG. 5 is a side view corresponding to FIG. 2 of a slurry coater of a reference example. FIG. 6 is a diagram showing an example of a state in which the film thickness of a mixture layer arranged on an electrode core using a slurry coater electrode of a reference example varies. FIG. 7 is a diagram showing an example of a state in which the film thickness of a mixture layer arranged on an electrode core using a slurry coater electrode of the present disclosure varies. FIG. 8 is a side view of a transport roll of a first modified example when viewed from one axial side. FIG. 9 is a side view of a transport roll of a second modified example when viewed from one axial side.

[0009] 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.

[0010] 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.

[0011] 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 also 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.

[0012] 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 as a strip-shaped core, 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.

[0013] The slurry coating device 20 includes a kneader 21 that mixes, kneads, and crushes a plurality of materials, such as an active material, a conductive agent, and a binder, to produce a mixture slurry 12 in which the plurality of materials are uniformly mixed, a flow rate control unit 25 that controls the amount of the mixture slurry 12 supplied to a die 22, the die 22 that discharges the mixture slurry 12 supplied from the flow rate 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.

[0014] The flow rate control unit 25 has a control device (not shown) that controls the aperture of a supply hole (not shown) that supplies the composite slurry 12 to the die 22. By controlling the aperture of the supply hole, 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] FIG. 2 is a side view of the die head 22a and the conveying roll 9 in the slurry coating apparatus 20, as viewed from one axial side of the conveying roll 9. As shown in FIG. 2, in the side view from one axial side, the outer peripheral edge 9d of the conveying roll 9 is a smooth closed curved line in which the distance between the rotation center axis 9c of the conveying roll 9 and the outer peripheral edge 9d varies depending on the circumferential position of the outer peripheral edge 9d. A smooth closed curved line is a closed curved line that does not have any sharp points that cannot be differentiated. More specifically, in this embodiment, the conveying roll 9 has an outer peripheral surface 9b that is elliptical in side view from one axial side. The conveying roll 9 rotates in one circumferential direction indicated by arrow A. The rotation center axis 9c of the conveying roll 9 extends in the axial direction (perpendicular to the paper surface of FIG. 2) through the intersection of the major and minor axes of the ellipse in the side view.

[0019] The die head 22a of the die 22 tapers toward the tip. The die heads 22a are arranged at intervals on the outer peripheral surface 9b. A discharge port 22b provided at the tip of the die head 22a faces the rotation center shaft 9c of the transport roll 9 in the discharge direction of the mixture slurry indicated by arrow B. The mixture slurry 12 is applied to the electrode core 11 at a location facing the discharge direction through the discharge port 22b.

[0020] In a side view when viewed from one axial direction, the outer peripheral surface 9b of the transport roll 9 has an elliptical shape, and the rotation axis 9c extends axially through the center of the ellipse. Therefore, as shown in Fig. 3, the distance between the discharge port 22b and the transport roll 9 is maximum at a position where the minor axis J1 of the ellipse coincides with the discharge direction when viewed from one axial direction. Also, as shown in Fig. 4, the distance between the discharge port 22b and the transport roll 9 is minimum at a position where the major axis J2 of the ellipse coincides with the discharge direction when viewed from one axial direction. When the transport roll 9 rotates in the circumferential direction, the distance between the discharge port 22b and the transport roll 9 periodically varies between a maximum distance L1 and a minimum distance L2.

[0021] If the distance in the discharge direction between the discharge port 22b and the outer peripheral surface 9b is short, the discharge pressure of the mixture slurry 12 increases, so the application width of the region to which 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, if the distance in the discharge direction between the discharge port 22b and the outer peripheral surface 9b is long, the discharge pressure of the mixture slurry 12 decreases, so the application width of the region to which 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.

[0022] Therefore, the film thickness of the composite layer formed during one rotation of the conveying roll 9 from the position where the discharge direction distance between the discharge port 22b and the outer peripheral surface 9b is the minimum distance L2 repeats two fluctuations in which the film thickness gradually increases from the minimum film thickness to the maximum film thickness and then gradually decreases from the maximum film thickness to the minimum film thickness.

[0023] 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 coating device 320 of a reference example. In the slurry coating device 320, a transport roll 309 has a cylindrical outer peripheral surface 309b that contacts the electrode core 11, and a rotation center axis 309c of the transport roll 309 coincides with the central axis of the transport roll 309. The discharge port 22b of the die head 22a faces the rotation center axis 309c of the transport roll 309 in the discharge direction of the mixture slurry indicated by arrow C.

[0024] The slurry applicator 320 is configured to vary the film thickness of the mix layer in the longitudinal direction of the electrode by controlling the amount of mix slurry discharged from the discharge port 22 b to vary the film thickness of the mix layer. The present inventors have found through testing that when the film thickness of the mix layer is varied in the longitudinal direction of the electrode by controlling the amount of mix slurry discharged to vary the amount of mix slurry discharged, the film thickness of the mix layer 315 disposed on the electrode core 11 does not vary uniformly over different periods, as shown in Figure 6, and that it is not easy to vary the film thickness of the mix layer 315 periodically with good reproducibility.

[0025] In contrast, by using the slurry coating device 20 of the present disclosure, a constant amount of composite slurry is discharged from the discharge port 22b, and then the conveying roll 9 is simply rotated at a constant rotation speed, as shown in Figure 7, so that the fluctuation in the film thickness of the composite layer 15 can be made approximately the same at different periods, and the film thickness of the composite layer 15 can be varied periodically with good reproducibility.

[0026] The electrode core 11 on which the mixture layer 15 is disposed using the slurry coating device 20 is cut at a point K where the thickness of the mixture layer 15 is approximately minimal, thereby producing an electrode. As a result, the thickness of the mixture layer 15 at both longitudinal end portions of the electrode is approximately minimal. Therefore, when a wound electrode body is produced using this electrode, the thickness of the mixture layer 15 at the end portion on the side where the winding begins is approximately minimal. This makes it easier to wind the electrode efficiently and neatly, and therefore makes it easier to produce a wound electrode body with high roundness.

[0027] The present inventors experimentally investigated the relationship between the difference between the major axis length and the minor axis length of the ellipse constituting the outer peripheral surface 9b of the transport roll 9 in a side view when viewed from one side in the axial direction and the coating weight difference ratio, which is defined as the value obtained by dividing the weight of the mixture at the thinnest part by the weight of the mixture at the thickest part and multiplying the result by 100. Table 1 shows the test results.

[0028] According to the above test, it was confirmed that if the difference between the major axis length and the minor axis length (the difference between the maximum distance between the rotation center axis 9c and the outer peripheral edge 9d of the conveying roll 9 and the minimum distance between the rotation center axis 9c and the outer peripheral edge 9d in a side view when viewed from one side in the axial direction) is 3 μm, the weight of the mixture at the thinnest part can be reduced by about 5% relative to the weight of the mixture at the thickest part. 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 easily produced. Therefore, since it is easy to produce a wound electrode body with high circularity, it is preferable that the difference between the major axis length and the minor axis length is 3 μm or more.

[0029] Furthermore, if the distance in the discharge direction between the discharge port 22b and the outer peripheral surface 9b becomes too large, the mixture slurry 12 discharged from the discharge port 22b may have difficulty reaching the electrode core 11, and the mixture slurry 12 may have difficulty being transferred to the electrode core 11. To achieve good transfer of the mixture slurry 12 to the electrode core 11, it is preferable that the difference between the major axis length and the minor axis length be 50 μm or less.

[0030] The present disclosure is not limited to the above-described embodiments and their modifications, and various improvements and modifications are possible within the scope of the claims of the present application and their equivalents.

[0031] For example, in the above embodiment, the transport roll 9 has an elliptical shape in a side view when viewed from one axial side. However, the shape of the transport roll when viewed from one axial side may be changed as appropriate depending on the desired variation in film thickness of the mixture layer disposed on the electrode core. In the side view when viewed from one axial side, the outer circumferential edge of the transport roll may be a smoothly closed curved line in which the distance between the rotation center of the transport roll and the outer circumferential edge varies depending on the circumferential position of the outer circumferential edge.

[0032] For example, as shown in Fig. 8, in a side view when viewed from one axial side, the transport roll 109 may have a shape other than an ellipse. Furthermore, in the side view, the position (major axis position) where the distance R1 between the rotation center axis 109c and the outer peripheral edge 109d of the transport roll 109 is maximum and the position (minor axis position) where the distance R2 between the rotation center axis 109c and the outer peripheral edge 109d is minimum may be repeated every quarter of the circumference of the outer peripheral edge 109d. Even in this case, it is preferable that the difference between the major axis length (distance R1) and the minor axis length (distance R2) be 3 µm or more and 50 µm or less.

[0033] 9, in a side view seen from one axial side, the transport roll 209 may have a shape in which a position (major axis position) where the distance R3 between the rotation center axis 209c and the outer peripheral edge 209d is maximum and a position (minor axis position) where the distance R4 between the rotation center axis 209c and the outer peripheral edge 209d is minimum are periodically and alternately repeated three or more times. Even in this case, it is preferable that the difference between the major axis length (distance R3) and the minor axis length (distance R4) be 3 μm or more and 50 μm or less.

[0034] In addition, the case where a constant amount of the mixture slurry is discharged from the discharge port 22 b and the transport roll 9 is rotated at a constant rotation speed has been described. However, the transport roll 9 may be rotated at a constant rotation speed after periodically varying the amount of the mixture slurry discharged from the discharge port 22 b.

[0035] Furthermore, when performing such control, the timing when the amount of composite slurry ejected is greatest can be made to coincide with the timing when the distance in the ejection direction between the ejection port 22b and the outer peripheral surface 9b becomes the maximum distance L1, and the timing when the amount of composite slurry ejected is smallest can be made to coincide with the timing when the distance in the ejection direction between the ejection port 22b and the outer peripheral surface 9b becomes the minimum distance L2.

[0036] 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, 109, 209 Conveying roll, 9b Outer periphery, 9c, 109c, 209c Rotation center axis, 9d, 109d, 209d Outer periphery, 11 Electrode core, 12 Mixed material slurry, 15 Mixed material layer, 20 Slurry coating device, 21 Kneader, 22 Die, 22a Die head, 22b Discharge outlet, 25 Flow rate control section, L1 Maximum distance, L2 Minimum distance.

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 via a gap and ejecting the composite slurry onto one side of the strip-shaped core being transported by the transport roll, wherein in a side view of the transport roll viewed from one side in the axial direction, the outer peripheral edge of the transport roll forms a smooth closed curved line in which the distance between the center of rotation of the transport roll and the outer peripheral edge varies depending on the circumferential position of the outer peripheral edge.

2. A slurry coating device as described in claim 1, wherein the outer peripheral edge of the transport roll has a shape in which a position where the distance between the rotation center of the transport roll and the outer peripheral edge is maximum and a position where the distance between the rotation center of the transport roll and the outer peripheral edge is minimum are periodically and alternately repeated multiple times.

3. A slurry coating device as described in claim 2, wherein the position where the distance between the rotation center of the transport roll and the outer peripheral edge is maximum and the position where the distance between the rotation center of the transport roll and the outer peripheral edge is minimum are repeated every 1 / 4 of a revolution around the outer peripheral edge.

4. The slurry application device according to claim 3, wherein the outer peripheral edge of the transport roll is elliptical in shape.

5. A slurry application device described in any one of claims 1 to 4, wherein the difference between the maximum distance between the center of rotation of the transport roll and the outer peripheral edge and the minimum distance between the center of rotation of the transport roll and the outer peripheral edge is 3 μm or more and 50 μm or less.

6. A method for manufacturing an electrode, comprising: a coating step of ejecting a mixture slurry onto one side of a strip-shaped core of a battery electrode from an ejection section facing the transport roll via a gap, while the strip-shaped core is transported by a transport roll having a shape in which, in a side view when viewed from one side in the axial direction, the position where the distance between the center of rotation and the outer periphery is maximum and the position where the distance between the center of rotation and the outer periphery is minimum are repeated periodically and alternately multiple times; and a cutting step of cutting the strip-shaped core on which the mixture layer is arranged based on the coating in the coating step, at a location where the thickness of the mixture layer, which is arranged on the strip-shaped core and whose thickness varies periodically in the longitudinal direction, becomes approximately a minimum value.

Images