Manufacturing method of electrode sheet

Abstract

To provide a manufacturing method for an electrode sheet, in which the occurrence of a crack in a central part of an electrode paste layer in a width direction can be reduced.SOLUTION: Provided are a coating step of coating a surface 3b of a current collector foil 3 with an electrode paste 18, thereby forming an electrode paste layer 15 on the surface 3b of the current collector foil 3, and a drying step of drying the electrode paste layer 15, thereby forming an electrode material layer 5 on the surface 3b of the current collector foil 3. In the drying step, in a constant-rate drying period, a surface 15b of the electrode paste layer 15 is irradiated with an infrared ray IR and wind is supplied along the surface 15b of the electrode paste layer 15 irradiated with the infrared ray IR. The wind speed of the supplied wind is the highest at a central part in a width direction DB of the electrode paste layer 15 and made lower toward both end parts.SELECTED DRAWING: Figure 4

Description

[Technical field]

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

[0002] Patent Document 1 discloses a method for drying an electrode paste layer formed by applying an electrode paste containing an electrode material and a solvent onto a metal sheet. Specifically, in a first heating step, the electrode paste layer is heated by at least one of hot air and infrared heating. Furthermore, in a second heating step, heating of the electrode paste layer by electrical heating is started at a timing when at least a part of the electrode material is exposed on the surface of the electrode paste layer by the heating in the first heating step. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-18964 Summary of the Invention [Problem to be solved by the invention]

[0004] During the constant rate drying period of the drying period of the electrode paste layer, the solvent in the electrode paste layer evaporates rapidly, which may cause the electrode paste layer to shrink significantly. Furthermore, during this constant rate drying period, when the electrode paste layer is heated uniformly in the width direction, the center in the width direction tends to dry the slowest, and the layers tend to dry faster toward both ends in the width direction. Therefore, during the constant rate drying period, the electrode paste layer shrinks from both ends in the width direction toward the center, and cracks may occur in the center of the electrode paste layer in the width direction.

[0005] The present invention has been made in consideration of the above-mentioned current situation, and aims to provide a manufacturing method for an electrode sheet that can reduce the occurrence of cracks in the widthwise center of an electrode paste layer. [Means for solving the problem]

[0006] (1) One aspect of the present invention is a method for manufacturing an electrode sheet having a strip-shaped current collecting foil and an electrode material layer formed on a surface of the current collecting foil, the method comprising: a coating step of coating the surface of the current collecting foil with an electrode paste to form an electrode paste layer on the surface of the current collecting foil; and a drying step of drying the electrode paste layer to form the electrode material layer on the surface of the current collecting foil, wherein the drying step includes, during a constant-rate drying period, irradiating the surface of the electrode paste layer with infrared rays and blowing air along the surface of the electrode paste layer irradiated with the infrared rays, the air speed of the air being fastest in the center of the electrode paste layer in the width direction and slowing down toward both ends.

[0007] In the above-described manufacturing method, the drying step includes irradiating the surface of the electrode paste layer (e.g., the entirety of a part of the surface of the electrode paste layer in the longitudinal direction) with infrared rays during a constant-rate drying period of the drying period of the electrode paste layer, and blowing air along the surface of the electrode paste layer irradiated with infrared rays. By using such a constant-rate drying period, the electrode paste layer can be dried efficiently and quickly, as described below.

[0008] Specifically, when the electrode paste layer is dried at a fixed rate by only infrared irradiation, solvent vapor remains on the surface of the electrode paste layer, making it difficult for the electrode paste layer to dry. In contrast, by irradiating the surface of the electrode paste layer with infrared rays while blowing air along the surface of the electrode paste layer irradiated with infrared rays, the solvent vapor remaining on the surface of the electrode paste layer can be removed. This can promote the drying of the electrode paste layer.

[0009] As described above, when the electrode paste layer is dried by infrared irradiation and air blowing, it is possible to reduce the amount of electricity used compared to drying by hot air alone, and therefore it is possible to reduce the amount of CO2 emissions associated with electricity use. This is because heating by infrared irradiation has a higher heating efficiency for the electrode paste layer than heating by hot air.

[0010] Conventionally, when the electrode paste layer is heated uniformly in the width direction during the constant-rate drying period, the center of the electrode paste layer in the width direction tends to dry the slowest, and the closer to both ends in the width direction the faster the drying rate tends to be. For this reason, during the constant-rate drying period, the electrode paste layer shrinks from both ends in the width direction toward the center, and cracks may occur in the center of the electrode paste layer in the width direction.

[0011] In contrast, in the present manufacturing method, the wind speed of the blown air during the constant rate drying period of the drying period of the electrode paste layer is fastest in the center in the width direction of the electrode paste layer and slows toward both ends. That is, during the constant rate drying period, air having a wind speed distribution in which the wind speed is fastest in the center in the width direction of the electrode paste layer and slows toward both ends is blown along the surface of the electrode paste layer. For example, during the constant rate drying period, an airflow is formed that flows in the longitudinal direction perpendicular to the width direction along the surface of the electrode paste layer irradiated with infrared rays, and has a speed distribution in which the wind speed is fastest in the center in the width direction of the electrode paste layer and slows toward both ends.

[0012] In this way, during the constant rate drying period, the removal rate of the solvent vapor remaining on the surface of the electrode paste layer is fastest in the widthwise center and slows down toward both ends in the widthwise direction. As a result, during the constant rate drying period, the evaporation (release) of the solvent can be promoted in the widthwise center, which is the most difficult part of the electrode paste layer to dry, and the difference in the drying rate (constant rate drying rate) between the widthwise center and both ends of the electrode paste layer is reduced, thereby reducing the occurrence of cracks in the widthwise center.

[0013] (2) Furthermore, in the method for producing an electrode sheet according to (1), the electrode sheet has a coated section in which the electrode paste layer is formed on the front surface of the current collecting foil, and the drying step dries the electrode paste layer while transporting the electrode sheet by a transport roll that contacts a back surface of the coated section opposite to the front surface of the electrode paste layer, and during the fixed rate drying period, a heated transport roll is used as the transport roll, which contacts the entire back surface of the coated section in the width direction to heat the coated section, and the temperature of the outer circumferential surface of the heated transport roll is made highest in a portion that contacts a central portion of the back surface of the coated section in the width direction and is made lower in portions closer to both ends of the back surface of the coated section in the width direction.

[0014] In the above-mentioned manufacturing method, during the fixed rate drying period, a heated transport roll is used as the transport roll, which heats the coated portion by contacting the entire back surface of the coated portion in the width direction (for example, contacting the entire part of the back surface of the coated portion in the longitudinal direction). The coated portion is a portion of the electrode sheet where an electrode paste layer is formed on the surface of the current collecting foil. The surface of this coated portion is the surface of the electrode paste layer, and the opposite surface is the back surface of the coated portion. An example of an electrode sheet is an electrode sheet that includes a coated portion where an electrode paste layer is formed on the surface of the current collecting foil, and an uncoated portion that is adjacent to the coated portion in the width direction and where no electrode paste layer is formed on the surface of the current collecting foil.

[0015] By using a heated transport roll as the transport roll for transporting the electrode sheet during the fixed rate drying period, the electrode paste layer can be dried by not only infrared irradiation and air blowing from the front side of the electrode paste layer in the coating section, but also heating by the heated transport roll from the back side of the coating section, thereby allowing the electrode paste layer to be dried quickly.

[0016] Moreover, the temperature of the outer peripheral surface of the heated transport roll is highest at a portion that contacts the center of the back surface of the coated part in the width direction, and is lower in portions closer to both ends of the back surface of the coated part in the width direction. That is, the outer peripheral surface of the heated transport roll has a temperature distribution in which the temperature is highest at a portion that contacts the center of the back surface of the coated part in the width direction, and is lower in portions closer to both ends of the back surface of the coated part in the width direction.

[0017] By using such a heated transport roll during the constant rate drying period, it is possible to promote evaporation of the solvent in the width direction central portion of the electrode paste layer, which is the most difficult to dry, thereby reducing the difference in drying speed (constant rate drying speed) between the width direction central portion and both ends of the electrode paste layer, and reducing the occurrence of cracks in the width direction central portion. [Brief description of the drawings]

[0018] [Figure 1] FIG. 2 is a plan view of an electrode sheet according to an embodiment. [Diagram 2] FIG. 2 is a cross-sectional view of FIG. [Diagram 3] FIG. 2 is a cross-sectional view taken along CC in FIG. [Figure 4] FIG. 2 is a schematic diagram of an electrode sheet manufacturing apparatus according to an embodiment. [Diagram 5] FIG. 4 is a diagram illustrating a drying process according to the embodiment. [Figure 6] FIG. 2 is a diagram showing a structure of an air blowing nozzle of the drying device according to the embodiment. [Figure 7] FIG. 4 is another view showing the internal structure of the blower nozzle. [Figure 8] FIG. 4 is a diagram showing the outlet of the blower nozzle. [Figure 9] FIG. 2 is a diagram illustrating a heating and transporting roll of the drying device according to the embodiment. [Figure 10] FIG. 4 is a diagram illustrating a heating mechanism of the heating transport roll. [Figure 11] FIG. 11 is a cross-sectional view of an electrode sheet according to a modified embodiment. [Figure 12] FIG. 2 is another cross-sectional view of the electrode sheet. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] <Embodiment> Next, a method for manufacturing the electrode sheet 1 according to the embodiment will be described. As shown in Figs. 1 to 3, the electrode sheet 1 according to the embodiment has a strip-shaped current collector foil 3 extending in the longitudinal direction DA and an electrode material layer 5 formed on the surface 3b of the current collector foil 3. The electrode material layer 5 has, for example, active material particles and a binder. The electrode material layer 5 is not formed over the entire surface 3b of the current collector foil 3 in the width direction DB, but is formed on a portion of the surface 3b of the current collector foil 3 excluding both ends in the width direction DB. Specifically, the electrode sheet 1 includes a coated portion 6 in which the electrode material layer 5 is formed on the surface 3b of the current collector foil 3, and an uncoated portion 7 in which the electrode material layer 5 is not formed on the surface 3b of the current collector foil 3 and which is adjacent to both sides of the coated portion 6 in the width direction DB. The center of the electrode material layer 5 in the width direction DB coincides with the center of the width direction DB of the current collector foil 3. The width direction DB is a direction perpendicular to the longitudinal direction DA.

[0020] The manufacturing method of the electrode sheet of this embodiment will be described in detail below. In this embodiment, the electrode sheet 1 is manufactured using a manufacturing apparatus 300. Fig. 4 is a schematic diagram of the manufacturing apparatus 300. The manufacturing apparatus 300 includes a coating device 200, a drying device 100, and a press roll (not shown), which are arranged in this order in the conveying direction DL of the current collector foil 3 or the electrode sheet 1.

[0021] Specifically, first, in a coating step, the electrode paste 18 is applied to the surface 3b of the current collecting foil 3 using a coating device 200 to form an electrode paste layer 15 on the surface 3b of the current collecting foil 3. The coating device 200 is a known die coater, and includes a die 210 and a back roll 220 (see FIG. 4). The coating device 200 conveys the current collecting foil 3 in the conveying direction DL by the back roll 220, while applying the electrode paste 18 discharged from the die 210 to the surface 3b of the current collecting foil 3. The conveying direction DL coincides with the longitudinal direction DA. The electrode paste 18 is, for example, a paste-like mixture of negative electrode active material particles, CMC (carboxymethyl cellulose), SBR (styrene butadiene rubber), and water as a solvent.

[0022] In this embodiment, the electrode paste layer 15 is not formed over the entire surface 3b of the current collecting foil 3 in the width direction DB, but is formed on a portion of the surface 3b of the current collecting foil 3 excluding both end portions in the width direction DB (see FIGS. 1 and 5). Therefore, the electrode sheet 1 that is subjected to a subsequent drying step comprises a coated portion 16 where the electrode paste layer 15 is formed on the surface 3b of the current collecting foil 3, and an uncoated portion 17 that is adjacent to both sides of the coated portion 16 in the width direction DB and where the electrode paste layer 15 is not formed on the surface 3b of the current collecting foil 3.

[0023] Next, the process proceeds to a drying step, in which the electrode paste layer 15 on the surface 3b of the current collector foil 3 is dried using a drying device 100 to form an electrode material layer 5 on the surface 3b of the current collector foil 3. The electrode material layer 5 is obtained by evaporating the solvent from the electrode paste layer 15 in the drying step. As shown in FIG. 4, the drying device 100 includes a drying chamber 110, conveying rolls 120 and 180, a blower nozzle 130, an infrared ray irradiation device 140, a duct 150, and a gas supply device 160. The drying chamber 110 is box-shaped and separated from the outside by a wall 111. The drying chamber 110 is provided with an entrance 112 for carrying the electrode sheet 1 before drying that has been subjected to the coating step into the drying chamber 110 from the outside, and an exit 113 for carrying the electrode sheet 1 after drying out of the drying chamber 110.

[0024] A plurality of conveying rolls 120, 180 are arranged in the drying chamber 110. The conveying rolls 120, 180 are driven by a motor (not shown) and convey the electrode sheet 1 in a conveying direction DL (a direction from the left side to the right side in FIG. 4). More specifically, the conveying rolls 120, 180 are provided at intervals in the conveying direction DL along the longitudinal direction DA of the electrode sheet 1. The conveying rolls 120, 180 convey the electrode sheet 1 in the conveying direction DL in a manner that contacts the entire coated portion back surface 16c of the coated portion 16 on the opposite side to the front surface 15b of the electrode paste layer 15 in the width direction DB. In this embodiment, the conveying rolls 120, 180 convey the electrode sheet 1 in the conveying direction DL in a manner that contacts the entire sheet back surface 1c of the electrode sheet 1 on the opposite side to the front surface 15b of the electrode paste layer 15 in the width direction DB (see FIG. 9). The coated portion back surface 16c is a part of the sheet back surface 1c.

[0025] The gas supplying device 160 is disposed outside the drying chamber 110 and communicates with the duct 150 (see FIG. 4). The gas supplying device 160 has a heater and a blower fan (not shown), and sends out gas G heated by the heater to the duct 150 by the blower fan. The duct 150 is a connecting pipe that connects the gas supplying device 160 and the multiple blower nozzles 130. The gas G sent from the gas supplying device 160 into the duct 150 is supplied into the multiple blower nozzles 130 through the duct 150 (see FIG. 4).

[0026] A plurality of air blowing nozzles 130 are provided in the drying chamber 110. More specifically, the air blowing nozzles 130 are provided above the electrode sheet 1 transported by the transport rolls 120 (at positions facing the electrode paste layer 15) with gaps in between in the transport direction DL (see FIG. 4). There are two types of air blowing nozzles 130: a first air blowing nozzle 130A and a second air blowing nozzle 130B.

[0027] Among these, the second blowing nozzle 130B includes a nozzle body 131 that forms an internal space S of the second blowing nozzle 130B, and partition plates 133b, 133c, 133d, and 133e provided inside the nozzle body 131 (see Figs. 6 and 7). The internal space S is composed of a first space S1 and a second space S2 aligned in the conveying direction DL (see Figs. 6 and 7). The second space S2 is divided into five flow paths (a first flow path S21, a second flow path S22, a third flow path S23, a fourth flow path S24, and a fifth flow path S25) by partition plates 133b, 133c, 133d, and 133e aligned at intervals in the width direction DB (see Fig. 7). Note that Fig. 6 is a view of the second blowing nozzle 130B cut along the longitudinal direction DA at the center of the width direction DB. FIG. 7 is a diagram of the second blowing nozzle 130B cut along the width direction DB at the center in the up-down direction DC.

[0028] A communication hole 131b is formed in the wall of the nozzle body 131, which communicates the first space S1 of the nozzle body 131 with the internal space of the duct 150. The gas G flowing through the duct 150 is supplied to the inside of the first space S1 of the second blowing nozzle 130B through the communication hole 131b (see FIG. 6). In addition, a blowing port 135 is provided on the lower surface of the nozzle body 131, which blows out the gas G toward the surface 15b of the electrode paste layer 15. The blowing port 135 is an opening that connects to the second space S2. The blowing port 135 is also divided into five by partition plates 133b, 133c, 133d, and 133e. Therefore, the outlet 135 is divided into a first outlet 135b which forms an opening to the first flow path S21, a second outlet 135c which forms an opening to the second flow path S22, a third outlet 135d which forms an opening to the third flow path S23, a fourth outlet 135e which forms an opening to the fourth flow path S24, and a fifth outlet 135f which forms an opening to the fifth flow path S25 (see Figure 8).

[0029] In the second blower nozzle 130B, the gas G flowing through the duct 150 is supplied through the communication hole 131b into the first space S1 of the second blower nozzle 130B, and then into the five flow paths (the first flow path S21, the second flow path S22, the third flow path S23, the fourth flow path S24, and the fifth flow path S25) constituting the second space S2. The gas G is then blown out as an airflow GS from the blowout port 135 (the first blowout port 135b, the second blowout port 135c, the third blowout port 135d, the fourth blowout port 135e, and the fifth blowout port 135f) toward the surface 15b of the electrode paste layer 15. The airflow GS sent out from the air outlet 135 flows in the longitudinal direction DA (more specifically, in the direction opposite to the transport direction DL) along the surface 15b of the electrode paste layer 15 in a manner that brings the airflow GS into contact with the surface 15b of the electrode paste layer 15 (see Figures 4 to 8).

[0030] The first blowing nozzle 130A is different from the second blowing nozzle 130B only in that the partition plates 133b, 133c, 133d, and 133e are not provided inside the nozzle body 131, and the rest are the same. Therefore, in the first blowing nozzle 130A, the gas G flowing through the duct 150 is supplied to the inside of the first space S1 of the first blowing nozzle 130A through the communication hole 131b, and then supplied to the second space S2. Then, this gas G is blown out from the blowing outlet 135 toward the surface 15b of the electrode paste layer 15 as an airflow GS. The airflow GS blown out from the blowing outlet 135 flows in the longitudinal direction DA (more specifically, in the direction opposite to the conveying direction DL) along the surface 15b of the electrode paste layer 15 in a manner that contacts the surface 15b of the electrode paste layer 15 (see FIG. 4). The airflow GS is hot air (for example, hot air). When this airflow GS comes into contact with surface 15b of electrode paste layer 15, evaporation of the solvent contained in electrode paste layer 15 is promoted, and electrode paste layer 15 is dried.

[0031] The dimension of the blowing outlet 135 of the first blowing nozzle 130A and the second blowing nozzle 130B in the width direction DB is larger than the dimension of the width direction DB of the electrode paste layer 15. The center of the blowing outlet 135 in the width direction DB coincides with the center of the width direction DB of the electrode paste layer 15. Therefore, the airflow GS is blown out from the blowing outlet 135 to the surface 15b of the electrode paste layer 15 over the entirety of the width direction DB.

[0032] Incidentally, the drying period of the electrode paste layer 15 in the drying process is divided into a preheating period, a constant rate drying period, and a decreasing rate drying period. Therefore, as shown in FIG. 4, the drying device 100 (drying chamber 110) of this embodiment can be divided into a preheating region A which is the preheating period, a constant rate drying region B which is the constant rate drying period, and a decreasing rate drying region C which is the decreasing rate drying period. In the drying device 100 of this embodiment, two first air blowing nozzles 130A are arranged in the preheating region A in the conveying direction DL with a gap therebetween. In the constant rate drying region B, three second air blowing nozzles 130B are arranged in the conveying direction DL with a gap therebetween. In the decreasing rate drying region C, one second air blowing nozzle 130B and two first air blowing nozzles 130A are arranged in this order in the conveying direction DL with a gap therebetween.

[0033] In addition, the drying device 100 of this embodiment is provided with three infrared irradiation devices 140 in the constant rate drying region B. Specifically, in the constant rate drying region B, the infrared irradiation devices 140 and the second blowing nozzles 130B are arranged alternately in this order in the conveying direction DL. In addition, one infrared irradiation device 140 is also provided in the region of the falling rate drying region C closest to the constant rate drying region B. Therefore, in the region of the falling rate drying region C on the constant rate drying region B side, one infrared irradiation device 140 and one second blowing nozzle 130B are arranged side by side in this order in the conveying direction DL. This infrared irradiation device 140 irradiates the surface 15b of the electrode paste layer 15 with infrared rays IR to promote evaporation of the solvent contained in the electrode paste layer 15, thereby drying the electrode paste layer 15. The infrared rays IR are irradiated to the surface 15b of the electrode paste layer 15 over the entire width direction DB.

[0034] Therefore, in the drying step of this embodiment, during a constant-rate drying period of electrode paste layer 15, infrared rays IR are irradiated onto surface 15b of electrode paste layer 15 (specifically, the entirety of a part of surface 15b of electrode paste layer 15 in the longitudinal direction DA), and air is blown (airflow GS is caused to flow) along surface 15b of electrode paste layer 15 irradiated with infrared rays IR. By using such a constant-rate drying period, as will be described below, electrode paste layer 15 can be dried efficiently and quickly.

[0035] Specifically, when electrode paste layer 15 is dried at a fixed rate by only infrared irradiation, solvent vapor remains on surface 15b of electrode paste layer 15, making it difficult for drying of electrode paste layer 15 to proceed. In contrast, by irradiating surface 15b of electrode paste layer 15 with infrared rays IR while blowing air along surface 15b of electrode paste layer 15 irradiated with infrared rays IR, it is possible to remove the solvent vapor remaining on surface 15b of electrode paste layer 15. This can promote the drying of electrode paste layer 15.

[0036] In addition, when drying electrode paste layer 15 by infrared irradiation and airflow (airflow GS) as described above, it is possible to reduce the amount of power consumption compared to drying by hot air only, and therefore it is possible to reduce the amount of CO2 emissions associated with power consumption. This is because heating by infrared irradiation has a higher heating efficiency for electrode paste layer 15 than heating by hot air.

[0037] Conventionally, during the constant rate drying period, the solvent in the electrode paste layer evaporates rapidly, which can cause the electrode paste layer to shrink significantly. Furthermore, during this constant rate drying period, when the electrode paste layer is heated uniformly in the width direction, the center in the width direction tends to dry the slowest, and the closer to both ends in the width direction, the faster the drying tends to be. Therefore, during the constant rate drying period, the electrode paste layer shrinks from both ends in the width direction toward the center, and cracks may occur in the center of the electrode paste layer in the width direction.

[0038] In contrast, in this embodiment, the wind speed of the blown air (airflow GS) in the constant rate drying region B during the constant rate drying period is fastest in the center of the width direction DB of the electrode paste layer 15 and slows down toward both ends. That is, during the constant rate drying period, air (airflow GS) having a wind speed distribution in which the wind speed is fastest in the center of the electrode paste layer 15 in the width direction DB and slows down toward both ends is sent along the surface 15b of the electrode paste layer 15. More specifically, during the constant rate drying period, an airflow GS is formed that flows in the longitudinal direction DA perpendicular to the width direction DB along the surface 15b of the electrode paste layer 15 irradiated with infrared rays IR, and has a speed distribution in which the wind speed is fastest in the center of the electrode paste layer 15 in the width direction DB and slows down toward both ends (see FIG. 5).

[0039] In this way, during the constant rate drying period, the removal rate of the solvent vapor remaining on surface 15b of electrode paste layer 15 is fastest at the center in width direction DB, and the removal rate slows toward both ends in width direction DB. As a result, during the constant rate drying period, evaporation (release) of the solvent can be promoted in the center in width direction DB, which is the most difficult part of electrode paste layer 15 to dry, and the difference in drying rate (constant rate drying rate) between the center and both ends in width direction DB of electrode paste layer 15 becomes smaller, thereby reducing the occurrence of cracks in the center in width direction DB.

[0040] In this embodiment, the airflow GS is formed in such a manner that the airflow is fastest in the center of the electrode paste layer 15 in the width direction DB and the airflow is slower toward both ends as described below (see FIG. 5). Specifically, in the second blower nozzle 130B provided in the constant rate drying region B, the second space S2 is divided into five flow paths (specifically, the first flow path S21, the second flow path S22, the third flow path S23, the fourth flow path S24, and the fifth flow path S25) in the width direction DB as described above (see FIG. 7). Comparing the opening areas of the inlets of the five flow paths, the third flow path S23 located in the center of the width direction DB is the largest, the first flow path S21 and the fifth flow path S25 located at both ends of the width direction DB are the smallest, and the second flow path S22 and the fourth flow path S24 located therebetween are intermediate in size (see FIG. 7).

[0041] Therefore, when comparing the amounts of gas G supplied to the five flow paths, the amount supplied to the third flow path S23 located at the center in the width direction DB is the largest, the amount supplied to the first flow path S21 and the fifth flow path S25 located at both ends in the width direction DB is the smallest, and the amount supplied to the second flow path S22 and the fourth flow path S24 located therebetween is intermediate. Meanwhile, the opening areas of the first blowing outlet 135b, the second blowing outlet 135c, the third blowing outlet 135d, the fourth blowing outlet 135e, and the fifth blowing outlet 135f, which are the outlets of the five flow paths, are equal (see FIG. 8).

[0042] Therefore, when comparing the wind speeds of the airflow GS discharged from the five air outlets, the wind speed V3 of the airflow GS3 discharged from the third air outlet 135d located at the center in the width direction DB is the fastest, the wind speed V1 of the airflow GS1 and the wind speed V5 of the airflow GS5 discharged from the first air outlet 135b and the fifth air outlet 135f located at both ends in the width direction DB are the slowest, and the wind speed V2 of the airflow GS2 and the wind speed V4 of the airflow GS4 discharged from the second air outlet 135c and the third air outlet 135d located between them are intermediate speeds (see FIG. 5). As a result, during the constant rate drying period, the airflow GS that flows in the longitudinal direction DA perpendicular to the width direction DB along the surface 15b of the electrode paste layer 15 irradiated with infrared rays IR is formed to have a speed distribution that is fastest in the center of the electrode paste layer 15 in the width direction DB and slows down toward both ends.

[0043] As described above, the drying device 100 has a plurality of conveying rolls 120 and 180. Among them, the conveying roll 120 is a heated conveying roll 120 provided with a heating mechanism described later. Therefore, the temperature of the outer peripheral surface 121 of the heated conveying roll 120 becomes high. On the other hand, the conveying roll 180 is a conveying roll 180 without a heating mechanism. The drying device 100 of this embodiment is provided with three heated conveying rolls 120 in the constant rate drying region B, which is the constant rate drying period (see FIG. 4). In addition, one heated conveying roll 120 is also provided in the region of the falling rate drying region C that is closest to the constant rate drying region B. This heated conveying roll 120 contacts the entire back surface 16c of the coating part in the width direction DB (specifically, contacts the entire part of the back surface 16c of the coating part in the longitudinal direction DA) to heat the coating part 16 (see FIG. 9).

[0044] Therefore, in the drying step of this embodiment, during the fixed-rate drying period, in addition to drying by irradiation of infrared rays IR and airflow (airflow GS) from the front surface 15b side of the electrode paste layer 15 in the coating section 16, heating is also performed from the back surface 16c side of the coating section by the heating transport roll 120. This allows the electrode paste layer 15 to be dried efficiently and quickly.

[0045] In this embodiment, the temperature of the outer peripheral surface 121 of the heating transport roll 120 is highest at the portion contacting the center of the coating part back surface 16c in the width direction DB, and is lower in the portions closer to both ends of the coating part back surface 16c in the width direction DB. That is, the outer peripheral surface 121 of the heating transport roll 120 has a temperature distribution in which the portion contacting the center of the coating part back surface 16c in the width direction DB is highest, and the portions closer to both ends of the coating part back surface 16c in the width direction DB are lower. In this embodiment, the axial direction DX of the heating transport roll 120 coincides with the width direction DB. Furthermore, the center of the axial direction DX of the heating transport roll 120 coincides with the center of the coating part back surface 16c in the width direction DB. Therefore, the temperature of the outer peripheral surface 121 of the heating transport roll 120 is highest at the center of the axial direction DX, and is lower in the portions closer to both ends of the axial direction DX.

[0046] During the constant rate drying period, by using such heated transport rolls 120, it is possible to promote evaporation of the solvent in the center in the width direction DB, which is the most difficult part to dry, of the electrode paste layer 15. This reduces the difference in the drying speed (constant rate drying speed) between the center and both ends in the width direction DB of the electrode paste layer 15, thereby reducing the occurrence of cracks in the center in the width direction DB.

[0047] The heating transport roll 120 is provided with a heating mechanism as described below. Specifically, as shown in FIG. 10, the heating transport roll 120 is connected to a temperature adjustment unit 170 through flow pipes 174 and 176. A liquid heat medium HC is contained inside the temperature adjustment unit 170. The temperature adjustment unit 170 controls the temperature of the heat medium HC contained therein to a predetermined set temperature. A heat medium containing section 122 that contains the heat medium HC is formed in the center of the heating transport roll 120 in the axial direction DX.

[0048] The inlet 122b of the heat medium accommodating section 122 and the heat medium outlet 170b of the temperature adjustment unit 170 are connected by a flow pipe 174 having a pump 172. As a result, the heat medium HC adjusted to a predetermined set temperature by the temperature adjustment unit 170 is supplied into the heat medium accommodating section 122 of the heating transport roll 120 through the flow pipe 174, and the inside of the heat medium accommodating section 122 is filled with the heat medium HC. As a result, the center of the heating transport roll 120 in the axial direction DX is heated by the heat medium HC. Furthermore, this heat is transferred from the center of the heating transport roll 120 to both ends in the axial direction DX.

[0049] As a result, the temperature of the outer peripheral surface 121 of the heated transport roll 120 is highest at the center in the axial direction DX, and is lower in the areas closer to both ends in the axial direction DX. Therefore, the temperature of the outer peripheral surface 121 of the heated transport roll 120 is highest at the area contacting the center of the coating part back surface 16c in the width direction DB, and is lower in the areas closer to both ends of the coating part back surface 16c in the width direction DB. In other words, the outer peripheral surface 121 of the heated transport roll 120 has a temperature distribution in which the area contacting the center of the coating part back surface 16c in the width direction DB is highest, and the areas closer to both ends of the coating part back surface 16c in the width direction DB are lower.

[0050] The outlet 122c of the heat medium accommodating section 122 and the heat medium inlet 170c of the temperature adjustment unit 170 are connected by a circulation pipe 176. As a result, the heat medium HC that has heated the central portion of the heating transport roll 120 in the axial direction DX returns to the inside of the temperature adjustment unit 170 through the circulation pipe 176. In this way, the heat medium HC circulates between the temperature adjustment unit 170 and the heat medium accommodating section 122 of the heating transport roll 120. As a result, the temperature of the outer circumferential surface 121 of the heating transport roll 120 is kept in a state in which the central portion in the axial direction DX is made the highest temperature and the portions closer to both ends in the axial direction DX are made lower. The heating mechanism of the heating transport roll 120 is composed of the temperature adjustment unit 170, the circulation pipes 174 and 176, the pump 172, and the heat medium accommodating section 122 of the heating transport roll 120.

[0051] Next, the electrode sheet 1 that has completed the drying process is roll-pressed by a press roll (not shown) in a roll press process. As a result, the electrode sheet 1 becomes an electrode sheet 1 in which the electrode material layer 5 is densified. The electrode sheet 1 manufactured as described above becomes an electrode sheet in which the occurrence of cracks at the center of the electrode material layer 5 in the width direction DB is reduced. For example, the electrode sheet 1 is cut in the longitudinal direction DA at the center position of the width direction DB, and used as an electrode for a secondary battery. Specifically, an electrode body is formed by winding (or stacking) this electrode (e.g., a negative electrode), another electrode (e.g., a positive electrode), and a separator, and this electrode body is housed in a battery case to manufacture a secondary battery (e.g., a lithium-ion secondary battery).

[0052] <Transformation> In the embodiment, the electrode sheet 1 having the electrode material layer 5 on the front surface 3b of the current collecting foil 3 is manufactured. In contrast, in this modified embodiment, an electrode sheet 401 (see FIGS. 11 and 12) having the electrode material layer 5 not only on the front surface 3b of the current collecting foil 3 but also on the back surface 3c is manufactured. FIG. 11 is a view corresponding to the BB cross section of FIG. 1. FIG. 12 is a view corresponding to the CC cross section of FIG. 1. Specifically, after the electrode material layer 5 is formed on the front surface 3b of the current collecting foil 3 in the same manner as in the embodiment, the coating step and the drying step are similarly performed on the back surface 3c of the current collecting foil 3 using the manufacturing apparatus 300. This can reduce the occurrence of cracks in the center in the width direction DB for both the electrode paste layer 15 on the front surface 3b of the current collecting foil 3 and the electrode paste layer 15 on the back surface 3c.

[0053] While the present invention has been described above with reference to embodiments and modified forms, it goes without saying that the present invention is not limited to the above-described embodiments, and can be modified as appropriate without departing from the spirit of the present invention. [Explanation of symbols]

[0054] 1,401 Electrode sheets 3 Current collecting foil 5 Electrode material layer 6,16 Coating Section 7,17 Uncoated area 15 Electrode paste layer 16c Back side of coating section 18 Electrode Paste 100 Heating device 120 Heated transport roll (transport roll) 130 Blower nozzle 180 Transport roll 200 Coating device 300 Manufacturing equipment DA Longitudinal DB width direction DL conveying direction DX axis direction GS Airflow IR Infrared

Claims

1. A method for producing an electrode sheet having a strip-shaped current collecting foil and an electrode material layer formed on a surface of the current collecting foil, comprising: a coating step of coating the surface of the current collecting foil with an electrode paste to form an electrode paste layer on the surface of the current collecting foil; a drying step of drying the electrode paste layer to form the electrode material layer on the surface of the current collecting foil, The drying step includes, during a fixed rate drying period, irradiating a surface of the electrode paste layer with infrared rays and blowing air along the surface of the electrode paste layer irradiated with the infrared rays, The air speed is fastest at the center in the width direction of the electrode paste layer and is slower toward both ends. A method for manufacturing an electrode sheet.

2. A method for producing the electrode sheet according to claim 1, the electrode sheet has a coating portion in which the electrode paste layer is formed on the surface of the current collecting foil, the drying step includes drying the electrode paste layer while transporting the electrode sheet by a transport roll that contacts a back surface of the coating unit opposite to the front surface of the electrode paste layer, During the fixed rate drying period, a heated transport roll is used as the transport roll, which contacts the entire back surface of the coated portion in the width direction to heat the coated portion, The temperature of the outer circumferential surface of the heated transport roll is set to be the highest at a portion in contact with the center of the back surface of the coated part in the width direction, and is set to be lower at portions closer to both ends of the back surface of the coated part in the width direction. A method for manufacturing an electrode sheet.

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