Slurry coating device and method for manufacturing electrode

Abstract

A slurry coating device (20) coats a belt-form electrode core body (11) of an electrode of a battery with a mixture slurry (12). The slurry coating device (20) comprises a conveyance roller (9) that conveys the electrode core body (11), and a discharge part (discharge port (22b)) that faces the conveyance roller (9) with a gap therebetween and discharges the mixture slurry (12) onto one side surface of the electrode core body (11) being conveyed by the conveyance roller (9). The rotational central axis (9c) of the conveyance roller (9) is eccentric with respect to the central axis (9d) of the conveyance roller (9).

Description

Slurry application device and electrode manufacturing method

[0001] The present disclosure relates to a slurry application device that applies a mixture slurry to 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 central axis of rotation of the transport roll is eccentric with respect to the central axis of the transport roll.

[0006] In addition, the electrode manufacturing method according to the present disclosure includes a coating step in which a strip-shaped core of a battery electrode is transported by a transport roll whose central axis of rotation is eccentric with respect to the central axis, and a composite slurry is ejected onto one side of the strip-shaped core from an ejection section facing the transport roll through 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 is cut at a location where the thickness of the composite layer, which is arranged on the strip-shaped core and whose thickness varies periodically in the longitudinal direction, reaches approximately a minimum value.

[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 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 showing an example of a state in which the film thickness of a mixture layer arranged on an electrode core using a slurry coating apparatus electrode of a reference example varies. 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 coating apparatus electrode of the present disclosure varies.

[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 fixed to 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 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 a cylindrical outer peripheral surface 9b that contacts the strip-shaped electrode core 11. The transport roll 9 rotates to one side in the circumferential direction indicated by arrow A. The rotation center axis 9c of the transport roll 9 is eccentric with respect to the center axis 9d of the transport roll 9. The center axis 9d of the transport roll 9 coincides with the center axis of the cylindrical outer peripheral surface 9b.

[0019] The die head 22a of the die 22 tapers toward the tip. The die head 22a is arranged at intervals on the cylindrical outer circumferential 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] Because the rotation central axis 9c is eccentric with respect to the central axis 9d of the transport roll 9, the distance between the discharge port 22b and the transport roll 9 is maximum when the rotation central axis 9c is located between the central axis 9d and the discharge port 22b, as shown in Fig. 3. Furthermore, the distance between the discharge port 22b and the transport roll 9 is minimum when the central axis 9d is located between the rotation central axis 9c and the discharge port 22b, as shown in Fig. 4. 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 cylindrical 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 cylindrical 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 outlet 22b and the cylindrical outer peripheral surface 9b is the minimum distance L2 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 applicator 120 of a reference example. In the slurry applicator 120, a transport roll 109 has a cylindrical outer peripheral surface 109b that contacts the electrode core 11, and a rotation center axis 109c of the transport roll 109 coincides with a central axis 109d. The discharge port 22b of the die head 22a faces the rotation center axis 109c of the transport roll 109 in the discharge direction of the mixture slurry indicated by arrow C.

[0024] The slurry applicator 120 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 115 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 115 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 eccentricity of the rotational center axis 9c with respect to the center axis 9d of the transport roll 9 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 eccentricity is 2 μm, the weight of the mixture at the thinnest portion can be reduced by about 5% compared to the weight of the mixture at the thickest portion. On the other hand, if the thickness of the thinnest portion of the mixture layer is 5% or more smaller than the thickness of the thickest portion 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 eccentricity of the rotation center axis 9c with respect to the center axis 9d is 2 μm or more.

[0029] 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 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 eccentricity of the rotation center axis 9c with respect to the center axis 9d be 25 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, a case has been described in which a constant amount of slurry mixture is discharged from the discharge port 22 b and the transport roll 9 is rotated at a constant rotation speed. However, the amount of slurry mixture discharged from the discharge port 22 b may be periodically varied, and the transport roll 9, whose rotation central axis 9 c is eccentric with respect to the central axis 9 d, may be rotated at a constant rotation speed.

[0032] 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 cylindrical outer peripheral surface 9b is 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 cylindrical outer peripheral surface 9b is the minimum distance L2.

[0033] 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 circumferential surface, 9c Rotation central axis, 9d Central axis, 11 Electrode core, 12 Mixture slurry, 15 Mixture 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 the central axis of rotation of the transport roll is eccentric with respect to the central axis of the transport roll.

2. A slurry coating device as set forth in claim 1, wherein the amount of eccentricity of said rotational axis with respect to said central axis is 2 μm or more and 25 μm or less.

3. 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 whose central axis of rotation is eccentric with respect to the central axis, 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 disposed is cut at a location where the thickness of the composite layer, which is disposed on the strip-shaped core based on the coating in the coating step and whose thickness periodically varies in the longitudinal direction, becomes approximately a minimum value.

Images