Electrode mixture slurry coating device

Abstract

This electrode mixture slurry coating device comprises a transport roller for transporting a band-shaped base material, and a die head provided at a position facing the transport roller and serving to discharge and coat the electrode mixture slurry onto the base material being transported. The die head has a liquid accumulation part wherein the electrode mixture slurry accumulates, a discharge port for discharging the electrode mixture slurry, and a liquid passage wherethrough the liquid accumulation part and the discharge port communicate. Of the die head, at least the portion adjacent to the liquid passage is constituted from a first material whereof the linear expansion coefficient is 4.0 ppm / K or smaller. When x [ppm / K] represents the linear expansion coefficient of the first material, and y [mm] represents the length of the discharge port in the die head length direction, the relationship y < 2000 / √x is fulfilled.

Description

[Technical Field]

[0001] The present disclosure relates to an electrode mix slurry applicator used in a manufacturing process of an electrode for a secondary battery. [Background technology]

[0002] Conventionally, there is known a coating device equipped with a die head for applying a coating liquid to an object to be coated (for example, Patent Document 1). In the coating device of Patent Document 1, the main body of the die head is made of a first ceramic sintered body, and the tip of the die head is made of a second ceramic sintered body that has higher fracture toughness than the first ceramic sintered body. This results in a die head that is relatively light and reduces the inclusion of impurities in the coating liquid. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-042758 Summary of the Invention

[0004] A coating device equipped with a die head may be used to apply electrode mixture slurry for secondary battery electrodes. In such applications, it is required to make the coating thickness of the slurry as uniform as possible. This is because large variations in coating thickness result in reduced yields. In particular, in the field of high-capacity secondary batteries, where small manufacturing tolerances are required, suppressing variations in coating thickness is important. In this situation, the present disclosure improves yields in the manufacture of secondary batteries.

[0005] One aspect of the present disclosure relates to an electrode mixture slurry applicator, comprising: a conveying roller for conveying a strip-shaped substrate; and a die head disposed opposite the conveying roller and configured to dispense and apply electrode mixture slurry to the conveyed substrate, the die head having a reservoir for storing the electrode mixture slurry, a discharge port for discharging the electrode mixture slurry, and a liquid passage connecting the reservoir and the discharge port, wherein at least a portion of the die head adjacent to the liquid passage is made of a first material having a linear expansion coefficient of 4.0 ppm / K or less, where x [ppm / K] is the linear expansion coefficient of the first material, and y [mm] is the length of the discharge port in the longitudinal direction of the die head, and y<2000 / √x holds.

[0006] According to the present disclosure, it is possible to suppress variations in the coating thickness of electrode mixture slurry for secondary battery electrodes, and to improve the yield in the production of secondary batteries. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a cross-sectional view schematically illustrating an example of an electrode mixture slurry coating device according to the present disclosure. [Figure 2] FIG. 2 is a graph in which the horizontal axis represents the linear expansion coefficient of the constituent material of the die head and the vertical axis represents the coating width, and is used to explain the range in which the gap fluctuation width is equal to or less than the allowable value. DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment of an electrode mixture slurry applicator according to the present disclosure will be described below using examples. However, the present disclosure is not limited to the examples described below. While specific numerical values ​​and materials may be used in the following description, other numerical values ​​and materials may be used as long as the effects of the present disclosure are obtained.

[0009] (Electrode mixture slurry coating device) The electrode mixture slurry coating device (hereinafter also simply referred to as coating device) according to the present disclosure is a coating device that includes a conveying roller and a die head and is generally referred to as a die coater. Here, the conveying roller refers to a conveying roller that is arranged in a die coater so as to face the discharge opening of the die head, and is also referred to as a backup roller. The electrode mixture slurry is coated onto a strip-shaped substrate in the form of a film by the shear force generated between the discharge opening of the die head and the backup roller.

[0010] (Transport roller) The transport roller (backup roller) transports a strip-shaped substrate (such as a metal foil used as an electrode current collector) along its extension direction. The transport roller may be a columnar or cylindrical roller. The rotation axis of the transport roller may extend perpendicular to the extension direction of the substrate. The transport roller may rotate at a substantially constant rotational speed, in which case the substrate is transported at a substantially constant speed. The axial length of the transport roller may be longer than the longitudinal length of the die head.

[0011] (die head) The die head is disposed opposite the conveying roller and discharges and applies the electrode mixture slurry to the substrate being conveyed. The die head has a liquid reservoir, a discharge port, and a liquid passage. The liquid reservoir is a portion where the electrode mixture slurry is stored. The discharge port is a portion from which the electrode mixture slurry is discharged toward the substrate. The liquid passage is a passage that connects the liquid reservoir and the discharge port and through which the electrode mixture slurry flows.

[0012] The die head may have an inlet passage that is open to the outside and communicates with the liquid reservoir. The electrode mixture slurry may be supplied to the liquid reservoir from a slurry supply unit provided separately from the die head via the inlet passage.

[0013] The uniformity of the coating thickness of the electrode mixture slurry formed on the substrate surface significantly affects the production yield of secondary batteries. If the coating thickness of the electrode mixture slurry varies, it may become difficult to accommodate the produced electrode group in a battery case, or the required high capacity may not be achieved. As the capacity of secondary batteries increases, the allowable manufacturing tolerances become smaller, and it is becoming increasingly important to ensure the uniformity of the coating thickness of the electrode mixture slurry.

[0014] In response to this, it is possible to improve the uniformity of the coating thickness of the electrode mixture slurry by controlling the linear expansion coefficient of the constituent material of the die head. Specifically, at least the portion of the die head adjacent to the liquid passage is made of a first material with a linear expansion coefficient of 4.0 ppm / K or less. This prevents thermal expansion of the die head due to the heat of the electrode mixture slurry, and thus prevents fluctuations in the gap length between the die head outlet and the substrate (i.e., the coating thickness of the slurry). Because the coating thickness of the electrode mixture slurry is stable, the yield in the production of secondary batteries is improved.

[0015] Furthermore, where the linear expansion coefficient of the first material is x [ppm / K] and the length of the discharge port in the longitudinal direction of the die head is y [mm], y<2000 / √x holds. This allows for suppressing variations in the coating thickness of the electrode mixture slurry even when the discharge port is relatively long, thereby improving the yield in the production of secondary batteries. The discharge port length y may be 1000 mm or more, 1200 mm or more, or 1300 mm or more.

[0016] The temperature of the die head near its longitudinal center tends to be higher than the temperature near its longitudinal ends. If the longitudinal length of the die head is relatively short, the temperature can be homogenized by heat diffusion within the die head, but if the die head outlet is relatively long, a temperature difference is likely to occur between the longitudinal center and the longitudinal ends. Therefore, if the die head is made of a material with a large thermal expansion coefficient and a temperature difference occurs within the die head, the degree of deformation due to thermal expansion will differ between the longitudinal center and the longitudinal ends of the die head. Due to the large thermal expansion near the longitudinal center of the die head, the coating gap near the center will be smaller than the coating gap near the longitudinal ends, resulting in variation in the coating gap in the longitudinal direction of the die head.

[0017] In response to this, the inventors of the present application discovered that, even when the die head has a relatively long outlet, variation in the coating gap in the longitudinal direction of the die head can be suppressed by satisfying the relationship y<2000 / √x between the linear expansion coefficient x [ppm / K] of the first material and the length y [mm] of the outlet in the longitudinal direction of the die head. Here, a case where the die head has a relatively long outlet is, for example, a case where the length y of the outlet is 1000 mm or more, 1200 mm or more, or 1300 mm or more.

[0018] As described above, according to the present disclosure, it is possible to improve the yield in the manufacture of secondary batteries. Furthermore, according to the present disclosure, it is possible to improve the productivity of secondary batteries.

[0019] At least the portion of the die head adjacent to the discharge port may be coated with diamond-like carbon (DLC), which prevents the die head from wearing out near the discharge port and thereby extends the life of the die head.

[0020] The electrode mixture slurry applicator is preferably used as an applicator for a positive electrode mixture slurry containing a lithium-containing transition metal oxide. In this case, the presence of a lithium-containing transition metal oxide with high hardness makes the temperature of the die head more susceptible to fluctuations due to frictional heat. Furthermore, the positive electrode mixture slurry has a larger heat capacity than the negative electrode mixture slurry, and therefore has a greater impact on the temperature of the die head. In contrast, the die head of the present disclosure is less susceptible to thermal expansion due to temperature changes because at least the portion adjacent to the liquid passage is made of the first material. Therefore, a decrease in yield in the production of secondary batteries can be avoided. The difference in heat capacity between the positive electrode mixture slurry and the negative electrode mixture slurry is due to differences in the physical properties of the particulate materials, such as the active material, and the solvent contained in each slurry.

[0021] It is also possible for y to be 1000 or greater. Even when the discharge port is long in this way, according to the present disclosure, it is possible to avoid a decrease in yield in the manufacture of secondary batteries.

[0022] The portion of the die head adjacent to the portion made of the first material may be made of a second material having a Young's modulus of 170 GPa or more. Generally, materials with a small linear expansion coefficient also have a small Young's modulus. If the Young's modulus of the first material making up at least the portion of the die head adjacent to the liquid passage is too small, the first material may be deformed by the discharge pressure of the electrode mixture slurry passing through the liquid passage, resulting in variations in the coating gap. Therefore, it is preferable that the portion of the die head adjacent to at least the portion made of the first material adjacent to the liquid passage be made of a second material having a Young's modulus of 170 GPa or more. By sandwiching the portion made of the first material between the second materials, deformation of the first material due to the discharge pressure of the electrode mixture slurry passing through the liquid passage can be suppressed. Examples of the second material include stainless steels such as SUS304, SUS430, and S45C.

[0023] The die head may have a first part, a second part, and a shim sandwiched between the first part and the second part, and the shim may block a portion of the longitudinal center of the discharge port. With this configuration, the electrode mixture slurry is discharged only from the portion of the discharge port that is not blocked by the shim. Therefore, the electrode mixture slurry is applied in stripes to the coating target. The shim may block only one portion of the discharge port, or multiple portions. In this specification, the "longitudinal center of the discharge port" does not refer to a specific point (location) such as the center, but refers to the area excluding both longitudinal ends of the discharge port.

[0024] The shim may be made of a third material having a linear expansion coefficient of 4.0 ppm / K or less. The third material may be the same material as the first material, or may be a different material.

[0025] An example of an electrode mixture slurry coating device according to the present disclosure will be specifically described below with reference to the drawings. The components described above can be applied to the components of the coating device of the example described below. The components of the coating device of the example described below can be modified based on the above description. Furthermore, the matters described below may be applied to the above embodiment. Of the components of the coating device of the example described below, components that are not essential to the coating device according to the present disclosure may be omitted. Note that the diagrams shown below are schematic and do not accurately reflect the shapes and number of actual components.

[0026] As shown in FIG. 1, the electrode mixture slurry applicator 100 includes a conveying roller 110 and a die head 120.

[0027] The conveying roller 110 conveys the strip-shaped substrate B. The substrate B may be a current collector of a secondary battery. The conveying roller 110 may be a columnar or cylindrical roller. The rotation axis of the conveying roller 110 may extend perpendicular to the extension direction of the substrate B. The conveying roller 110 may rotate at a substantially constant rotation speed. The axial length of the conveying roller 110 (the length perpendicular to the plane of the paper in FIG. 1) may be longer than the longitudinal length of the die head 120 (the length perpendicular to the plane of the paper in FIG. 1).

[0028] The die head 120 is provided at a position facing the conveying roller 110, and discharges and applies the electrode mixture slurry to the conveyed substrate B. The die head 120 has a first part 121 that constitutes its upper half, a second part 122 that constitutes its lower half, and a shim 127 sandwiched between the first part 121 and the second part 122.

[0029] The electrode mixture slurry is prepared by mixing a dispersion medium and an electrode mixture. The electrode mixture contains an electrode active material as an essential component and may contain optional components such as a binder and a conductive material. The dispersion medium is a liquid component that disperses the electrode mixture.

[0030] An electrode active material is a material that exhibits electrochemical capacity; for example, the electrode active material of a lithium-ion secondary battery exhibits capacity through an oxidation-reduction reaction involving the insertion (absorption) and desorption (release) of lithium ions. When the electrode to be manufactured is a negative electrode, a carbon material or the like is used as the negative electrode active material. Examples of carbon materials that can be used include graphite, non-graphitizable carbon, and easily graphitizable carbon. When the electrode to be manufactured is a positive electrode, a lithium-containing transition metal oxide, olivine-type lithium phosphate, or the like is used as the positive electrode active material. Examples of lithium-containing transition metal oxides that can be used include, but are not limited to, rock salt-type oxides having a layered structure.

[0031] The electrode mixture slurry of this embodiment contains a lithium-containing transition metal oxide. Among lithium-containing transition metal oxides, materials containing nickel (Ni) as the main transition metal component are prone to fluctuating the temperature of the die head 120 due to frictional heat. Therefore, the coating device 100 is very useful as a coating device for electrode mixture slurry containing a lithium-containing transition metal oxide containing nickel (Ni) as the main transition metal component. Here, a lithium-containing transition metal oxide containing Ni as the main transition metal component refers to, for example, a lithium-containing transition metal oxide in which the content of Ni relative to all metals other than lithium is 50 mol % or more (or 70 mol % or more, or even 90 mol % or more).

[0032] The first component 121 is formed in the shape of a slightly flattened rectangular parallelepiped. At least a portion of the first component 121 adjacent to the liquid passage 125 is made of a first material having a linear expansion coefficient of 4.0 ppm / K or less (for example, an Invar material having a linear expansion coefficient of 0.5 to 1.5 ppm / K, preferably 0.5 to 0.6 ppm / K). The entire first component 121 of this embodiment is made of the first material. The lower surface of the first component 121 is substantially flat. A first protrusion 121a whose vertical length decreases toward the conveying roller 110 is formed in a portion of the first component 121 facing the conveying roller 110 (the lower left portion in FIG. 1). The tip of the first protrusion 121a may be coated with DLC.

[0033] The second component 122 is configured in the shape of a slightly flattened rectangular parallelepiped. At least the portion of the second component 122 adjacent to the liquid passage 125 is made of the first material. The entire second component 122 of this embodiment is made of the first material. The upper surface of the second component 122 is substantially flat except for the liquid reservoir 124. A second protrusion 122a whose vertical length decreases as it approaches the conveying roller 110 is formed in the portion of the second component 122 facing the conveying roller 110 (the upper left portion in FIG. 1). The tip of the second protrusion 122a may be coated with DLC.

[0034] A recess is formed in the upper part of the second part 122 as a liquid reservoir 124. The liquid reservoir 124 extends over substantially the entire longitudinal direction of the second part 122. An inlet channel 123 is formed in the longitudinal center of the second part 122, communicating with the liquid reservoir 124 from the outside. An electrode mixture slurry may be supplied to the inlet channel 123 from an external slurry supply unit.

[0035] A liquid passage 125 is formed between the first part 121 and the second part 122 in a region closer to the conveying roller 110 (to the left in FIG. 1 ) than the liquid reservoir 124. The liquid passage 125 is a passage through which the electrode mixture slurry flows. Both longitudinal ends of the liquid passage 125 are closed by shims 127. An outlet of the liquid passage 125 facing the conveying roller 110 is a discharge port 126. The electrode mixture slurry supplied to the die head 120 flows through the inlet channel 123, the liquid reservoir 124, the liquid passage 125, and the discharge port 126 in this order, and is then applied to the surface of the substrate B being conveyed by the conveying roller 110.

[0036] The shim 127 is a plate-shaped member also known as an inner deckle. The shim 127 is sandwiched between the first part 121 and the second part 122. The thickness of the shim 127 is substantially equal to the flow path width of the liquid passage 125. The longitudinal length of the shim 127 is substantially equal to the longitudinal length of the die head 120. The shim 127 has openings corresponding to the liquid passage 125 and the discharge port 126. The shim 127 closes both longitudinal ends of the liquid passage 125.

[0037] Since both longitudinal ends of the liquid passage 125 are closed by the shim 127, and the shim 127 has openings corresponding to the liquid passage 125 and the discharge port 126, it can be said that the discharge port 126 is an opening, and a non-opening portion closed by the shim 127 is located adjacent to this opening.

[0038] Here, a coating device used for stripe coating in which coated sections for coating the electrode mixture slurry and non-coated sections for not coating the electrode mixture slurry are alternately provided in the longitudinal direction of the belt-shaped substrate B can be realized, for example, by providing a shim 127 also in the longitudinal center of the discharge port 126. That is, in stripe coating, non-opening sections are provided not only at both longitudinal ends of the die head 120 adjacent to the discharge port 126 but also in the longitudinal center of the die head 120. The arrangement of the shim 127 for achieving stripe coating is not limited to one location.

[0039] Here, while the electrode mixture slurry is present in the openings, the electrode mixture slurry is absent in the non-openings due to the presence of the shim 127. Therefore, in stripe coating, a temperature gradient occurs even in the longitudinal center of the die head 120 due to the presence or absence of the electrode mixture slurry. When the die head 120 used in stripe coating is made of a material with a large thermal expansion coefficient and a temperature difference occurs inside the die head 120, the degree of deformation due to thermal expansion of the die head 120 varies depending on the presence or absence of the shim 127, even in the longitudinal center of the die head 120. Therefore, when the linear expansion coefficient of the first material constituting the die head 120 of the coating device 100 for performing such stripe coating is 4.0 ppm / K or less, and the linear expansion coefficient x [ppm / K] of the first material and the length y [mm] of the discharge port 126 in the longitudinal direction of the die head 120 satisfy the relationship y<2000 / √x, deformation of the die head 120 due to thermal expansion in the longitudinal center of the die head 120 can also be suppressed.

[0040] Furthermore, in order to suppress the influence of heat from the slurry on the shim 127 used to achieve stripe coating, it is preferable that the shim 127 is also made of a material with a thermal expansion coefficient of 4.0 ppm / K or less.

[0041] The length of the die head 120 (the length in the direction perpendicular to the paper surface in FIG. 1) may be 1300 to 1500 mm.

[0042] 2 is a graph in which the horizontal axis represents the linear expansion coefficient [ppm / K] of the constituent material of die head 120 (specifically, first part 121 and second part 122) and the vertical axis represents the coating width [mm] (in other words, the length of discharge port 126 in the longitudinal direction of die head 120). In this graph, the range in which the fluctuation of coating gap G (hereinafter simply referred to as gap G) between discharge port 126 and conveying roller 110 is equal to or less than the allowable value is hatched.

[0043] Here, the fluctuation range of the gap G refers to the difference between the minimum value of the gap G (typically, the value at the center of the die head 120 in the longitudinal direction) and the maximum value (typically, the value at both ends of the die head 120 in the longitudinal direction) when the die head 120 thermally expands. The allowable value refers to the maximum value of the fluctuation range of the gap G that is allowable when the coating device 100 is used to manufacture electrodes (typically, positive electrodes) of secondary batteries.

[0044] 2 was obtained by performing a numerical simulation under the conditions that the initial value of the gap G between the die head 120 and the conveying roller 110 is 150 μm, the temperature rise of the electrode mixture slurry (i.e., the temperature rise of the die head 120) is 7° C., and the tolerance for the fluctuation of the gap G is 2%. Note that a tolerance for the fluctuation of the gap G of 2% means that the minimum value of the gap G when the die head 120 thermally expands is 100 (reference), and the maximum value of the gap G is 102.

[0045] The curve shown in Figure 2 is given by y = 2000 / √x, where x [ppm / K] is the coefficient of linear expansion of the material constituting the die head 120 and y [mm] is the coating width. In the region below this curve (the hatched region), the fluctuation of the gap G can be kept below the allowable value. As can be seen from Figure 2, the absolute value of the slope of this curve increases sharply in the range below x = 4.0 ppm / K. In other words, by constructing the die head 120 using a material with a linear expansion coefficient of 4.0 ppm / K or less, it is possible to manufacture secondary battery electrodes with a wide coating width while keeping the fluctuation of the gap G below the allowable value. [Industrial Applicability]

[0046] The present disclosure can be used in an electrode mixture slurry coating device. [Explanation of symbols]

[0047] 100 Coating device 110 Conveyor roller 120 die head 121 First Part 121a 1st protrusion 122 2nd part 122a Second protrusion 123 Inflow channel 124 Liquid reservoir 125 Liquid passage 126 Discharge port 127 Sim B Base material G Coating gap

Claims

1. a conveying roller for conveying the strip-shaped base material; a die head provided at a position facing the conveying roller, which discharges and applies the electrode mixture slurry to the conveyed substrate; Equipped with the die head has a liquid reservoir in which the electrode mixture slurry is stored, a discharge port for discharging the electrode mixture slurry, and a liquid passage that connects the liquid reservoir with the discharge port; At least a portion of the die head adjacent to the liquid passage is made of a first material having a linear expansion coefficient of 4.0 ppm / K or less; The linear expansion coefficient of the first material is x [ppm / K], and the length of the discharge port in the longitudinal direction of the die head is y [mm]. The linear expansion coefficient x of the first material is 0.5 to 1.5 ppm / K; and An electrode mixture slurry coating device in which 1000≦y<2000 / √x holds.

2. 2. The electrode mixture slurry applicator according to claim 1, wherein at least a portion of the die head adjacent to the discharge port is coated with diamond-like carbon.

3. The electrode mixture slurry applicator according to claim 1 or 2, wherein the electrode mixture slurry contains a lithium-containing transition metal oxide.

4. The electrode mixture slurry coating device according to any one of claims 1 to 3, wherein a portion of the die head adjacent to the portion made of the first material is made of a second material having a Young's modulus of 170 GPa or more.

5. the die head has a first part, a second part, and a shim sandwiched between the first part and the second part; 5. The electrode mixture slurry applicator according to claim 1, wherein the shim closes a part of a central portion of the discharge port in a longitudinal direction.

6. 6. The electrode mixture slurry applicator according to claim 5, wherein the shim is made of a third material having a linear expansion coefficient of 4.0 ppm / K or less.

7. The electrode mixture slurry applicator according to claim 3 , wherein the lithium-containing transition metal oxide contains nickel as a main transition metal component.

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