JP2020087856A - Electrode for lithium ion secondary battery and manufacturing installation of electrode for lithium ion secondary battery - Google Patents

Abstract

To restrain wrinkling of a metal foil.SOLUTION: An electrode sheet 10 includes a coating part 21 where an active material layer 12 is provided on a long-sized metal foil 11, and an uncoated part 22 where the metal foil 11 is exposed. The active material layer 12 includes a high density region 13, and a low density region 14. The high density region 13 is composed of a first active material layer 15. The low density region 14 is composed of a layer where a second active material layer 16, having a density lower than that of the first active material layer 15, is superposed on the first active material layer 15. The low density region 14 is located between the high density region 13 and the uncoated part 22.SELECTED DRAWING: Figure 2

Description

The present invention relates to an electrode for a lithium ion secondary battery and an apparatus for manufacturing an electrode for a lithium ion secondary battery.

The lithium ion secondary battery includes positive and negative electrodes. The electrode is obtained by cutting an electrode sheet which is a raw material of the electrode. The electrode sheet includes a coated portion where the strip-shaped metal foil and the active material layer overlap with each other, and an uncoated portion where the strip-shaped metal foil and the active material layer do not overlap with each other. Patent Document 1 describes a manufacturing apparatus for manufacturing an electrode sheet. The electrode sheet is manufactured by providing an active material layer on a strip-shaped metal foil and pressing the active material layer. The manufacturing apparatus described in Patent Document 1 presses the active material layer with a pair of press rolls.

JP, 2016-139582, A

By the way, by being pressed by the press roll, the strip-shaped metal foil of the coated portion is rolled through the active material layer. On the other hand, the uncoated portion where the active material layer is not provided is hardly pressed by the press roll. There is a difference in the lengthwise direction between the strip-shaped metal foil of the coated part and the uncoated part, and wrinkles may occur at the boundary between the uncoated part and the coated part due to this difference. is there. The wrinkles also remain on the electrode obtained from the electrode sheet, which causes the active material layer to peel off from the metal foil.

An object of the present invention is to provide an electrode for a lithium ion secondary battery and an apparatus for manufacturing an electrode for a lithium ion secondary battery, which is capable of suppressing wrinkles on a metal foil.

An electrode for a lithium-ion secondary battery that solves the above-mentioned problems includes a coated portion in which an active material layer is provided on a metal foil, and an uncoated portion where the metal foil is exposed, and the active material layer is The high-density region composed only of the first active material layer and the layer in which the second active material layer having a lower density than the first active material layer is laminated on the first active material layer, A low-density region located between the density region and the uncoated portion.

The force applied to the metal foil when the active material layer is pressed is greater in the portion of the metal foil that is in contact with the active material layer having a higher density. Therefore, when manufacturing an electrode for a lithium ion secondary battery, the amount of extension of the metal foil generated by applying pressure to the active material layer is in contact with the low-density region as compared with the part in contact with the high-density region. There are less parts. Since the uncoated area is adjacent to the low-density area, the occurrence of wrinkles due to rolling of the metal foil due to pressure is suppressed compared to when the uncoated area and the high-density area are adjacent. it can.

In the electrode for the lithium-ion secondary battery, the low-density region may have a density that gradually decreases from the high-density region toward the uncoated portion.
The portion of the metal foil in contact with the low-density region has a smaller amount of extension due to pressure as it approaches the uncoated portion. Therefore, it is possible to suppress the concentration of stress generated at the boundary between the uncoated portion and the coated portion.

An apparatus for manufacturing an electrode for a lithium-ion secondary battery that solves the above-mentioned problems includes a carrier device that conveys a long metal foil and a first active material mixture layer that becomes a first active material layer by drying. A first coating device for forming on the metal foil, a first drying device for drying the first active material mixture layer, and both edges of the first active material mixture layer and the metal foil in the lateral direction. And a portion where the metal foil is exposed is an uncoated portion, both end portions of the first active material mixture layer along the uncoated portion are located at the center of the first active material mixture layer. After molding by the molding part, a molding part that is thinner than the first part and a second active material mixture layer that becomes a second active material layer having a lower density than the first active material layer by drying are molded. Second coating device for coating the both ends of the, a second drying device for drying the second active material mixture layer, and a pressurization for pressurizing the first active material layer and the second active material layer And a device.

The second active material layer has a lower density than the first active material layer. Therefore, the portion where the first active material layer and the second active material layer are stacked has a lower density than the portion where only the first active material layer is formed. The amount of extension of the metal foil when pressed by the pressing device is such that the first active material layer and the second active material layer are overlapped with each other compared to the portion in contact with the portion where only the first active material layer is provided. There are fewer parts that touch the open parts. Since the portion where the first active material layer and the second active material layer overlap each other is provided along the uncoated portion, it is possible to suppress the generation of wrinkles due to the rolling of the metal foil due to pressure.

According to the present invention, it is possible to prevent wrinkles from being generated on the metal foil.

The top view of an electrode sheet. FIG. 2 is a sectional view taken along line 2-2 of FIG. 1, showing an electrode sheet. The schematic block diagram which shows the manufacturing apparatus of the electrode for lithium ion secondary batteries. The perspective view which shows the scraper arrange|positioned in the drying device. The perspective view of a 2nd coating device.

Hereinafter, an embodiment of an electrode for a lithium ion secondary battery and an apparatus for manufacturing an electrode for a lithium ion secondary battery will be described.
As shown in FIGS. 1 and 2, the electrode sheet 10 has an elongated shape. The electrode sheet 10 includes a coated portion 21 in which an active material layer 12 is provided on a long metal foil 11 and an uncoated portion 22 from which the metal foil 11 is exposed. The electrode sheet 10 is a raw material of the electrode 30. The lithium ion secondary battery is an electrode assembly in which individual electrodes 30 cut out from the electrode sheet 10 are stacked via a separator, and the electrode assembly is housed in a case.

When the electrode sheet 10 is a raw material for a positive electrode of a lithium ion secondary battery, the metal foil 11 is an aluminum foil. When the electrode sheet 10 is a raw material of the negative electrode of the lithium ion secondary battery, the metal foil 11 is a copper foil. The active material layer 12 contains an active material, a conductive agent, and a binder depending on the polarity.

The active material layer 12 is provided over the entire length of the metal foil 11. The active material layer 12 is provided with a constant width in the center of the metal foil 11 in the lateral direction. The uncoated portions 22 are provided on both sides in the lateral direction of the metal foil 11 with the coated portion 21 interposed therebetween. The uncoated portion 22 is provided over the entire length of the metal foil 11 in the longitudinal direction.

The active material layer 12 includes a high density region 13 and a low density region 14. The high-density region 13 is provided at the center of the active material layer 12 in the width direction. The low density regions 14 are provided at both ends of the active material layer 12 in the width direction with the high density region 13 interposed therebetween. The width of the low density region 14 is shorter than the width of the high density region 13. The low density region 14 is located between the high density region 13 and the uncoated portion 22 in the direction along the surface of the metal foil 11. Although the surface of the active material layer 12 has fine irregularities due to the material forming the active material layer 12, such as the active material, the thickness of the active material layer 12 is substantially uniform. The difference between the thickness of the high-density region 13 and the thickness of the low-density region 14 is within the range of tolerance that can occur during manufacturing.

The high-density region 13 is composed of only the first active material layer 15. The low-density region 14 is composed of a layer in which a second active material layer 16 having a lower density than the first active material layer 15 is stacked on the first active material layer 15. The first active material layer 15 in the low-density region 14 gradually becomes thinner as it moves away from the first active material layer 15 in the high-density region 13 in the width direction of the active material layer 12. In other words, the first active material layer 15 in the low density region 14 is gradually thinned toward the uncoated portion 22 closest to the first active material layer 15. The second active material layer 16 becomes thicker as the first active material layer 15 becomes thinner. Therefore, the density of the low density region 14 gradually decreases from the high density region 13 toward the uncoated portion 22.

The first active material layer 15 and the second active material layer 16 have the same type of active material, conductive agent, and binder, but the porosity of the second active material layer 16 is the same as that of the first active material layer 15. Higher than the rate. As a result, the second active material layer 16 has a lower density than the first active material layer 15. The density of the second active material layer 16 is, for example, 30% to 70% of the density of the first active material layer 15.

The electrode sheet 10 includes a coated portion 21 and an uncoated portion 22, and the active material layer 12 includes a high density region 13 and a low density region 14. Therefore, the electrode sheet 10 can be regarded as an electrode for a lithium ion secondary battery. Further, as can be understood from FIG. 1, the individual electrode 30 cut out from the electrode sheet 10 is also cut out from the electrode sheet 10 in a state where the electrode 30 is provided with the coated portion 21 and the uncoated portion 22. Therefore, the individual electrode 30 can be regarded as an electrode for a lithium ion secondary battery. That is, the electrode for the lithium ion secondary battery may be configured so that the low-density region 14 and the uncoated portion 22 are adjacent to each other, and the electrode sheet 10 before cutting out the individual electrode 30 is made of lithium. It can be regarded as an electrode for an ion secondary battery, or the individual electrode 30 cut out from the electrode sheet 10 can be regarded as an electrode for a lithium ion secondary battery.

Next, an apparatus for manufacturing an electrode for a lithium ion secondary battery (hereinafter referred to as a manufacturing apparatus) will be described. The manufacturing apparatus of this embodiment is an apparatus for manufacturing the electrode sheet 10. The manufacturing apparatus of the present embodiment may be provided with a cutting device that cuts out the individual electrodes 30 from the electrode sheet 10, so that the manufacturing apparatus may be a device that manufactures the electrodes 30. That is, the manufacturing apparatus may be an apparatus for manufacturing the electrode sheet 10 or an apparatus for manufacturing the individual electrode 30 as the electrode for the lithium ion secondary battery.

As shown in FIGS. 3 and 4, the manufacturing apparatus 41 includes a carrying device 50 for carrying the metal foil 11, a first coating device 60 for applying the first active material mixture 42 to the metal foil 11, and a first coating device 60. A first drying device 80 for drying the active material mixture 42, and a molding unit 91 arranged in the first drying device 80 are provided. The manufacturing apparatus 41 includes a second coating device 94 for applying the second active material mixture 44 to the metal foil 11, a second drying device 95 for drying the second active material mixture 44, and a pressurizing device 81. Equipped with.

The transport device 50 includes a supply device 51 that supplies the metal foil 11 and a winding device 55 that winds the manufactured electrode sheet 10. The supply device 51 includes a supply reel 52 around which the metal foil 11 is wound, and a first shaft 53 on which the supply reel 52 is installed. The supply reel 52 is rotatably supported by the first shaft 53. The metal foil 11 pulled out from the supply reel 52 is in a state where the longitudinal direction extends in the circumferential direction of the supply reel 52. Although illustration is omitted, in the present embodiment, it is assumed that the metal foil 11 having the active material layer 12 already formed on one of the both surfaces is wound around the supply reel 52.

The winding device 55 includes a winding reel 56 that winds the electrode sheet 10, and a second shaft 57 on which the winding reel 56 is installed. The take-up reel 56 is rotatably supported by the second shaft 57. The electrode sheet 10 is wound around the take-up reel 56 with the longitudinal direction extending in the circumferential direction of the take-up reel 56. The supply reel 52 and the take-up reel 56 rotate by rotating both the first shaft 53 and the second shaft 57, or the second shaft 57 by a drive source such as a motor (not shown). Thereby, the metal foil 11 is conveyed.

The first coating device 60 is located downstream of the supply device 51 in the transport direction of the metal foil 11. The first coating device 60 includes a die head 62 and a backup roll 61 arranged apart from the die head 62. The die head 62 has a manifold 63 in which the first active material mixture 42 is stored, a discharge port 64 of the first active material mixture 42, and a slot 65 for discharging the first active material mixture 42 from the discharge port 64. With. The die head 62 is arranged so that the ejection port 64 faces the metal foil 11. The slot 65 connects the manifold 63 and the discharge port 64. The first active material mixture 42 is a paste in which an active material, a conductive agent, a binder and a solvent are mixed. The first coating device 60 applies the first active material mixture 42 with a constant width to the center of the metal foil 11 in the lateral direction. As a result, the first active material mixture layer 43, which is a layer of the first active material mixture 42, is formed on the metal foil 11. The first active material mixture layer 43 becomes the first active material layer 15 by drying. Both ends 43A and 43B in the width direction of the first active material mixture layer 43 are uncoated located between the first active material mixture layer 43 and both edges E1 and E2 in the lateral direction of the metal foil 11. Along the section 22.

The first drying device 80 is located downstream of the first coating device 60 in the transport direction of the metal foil 11. The first drying device 80 is a device that accelerates the drying of the first active material mixture layer 43, for example, by raising the atmospheric temperature in the furnace by a heating unit.

As shown in FIG. 4, the molding unit 91 includes two scrapers 92 and 93 arranged in the first drying device 80. The scrapers 92 and 93 scrape off a part of the first active material mixture layer 43 during drying, so that both widthwise end portions 43A and 43B of the first active material mixture layer 43 become thinner than the central portion 43C. Mold as follows. In the present embodiment, molding is performed so that both end portions 43A and 43B gradually become thinner toward the uncoated portion 22. In the scrapers 92 and 93, the solvent contained in the first active material mixture layer 43 is smaller than that immediately after coating, and the solvent contained in the first active material mixture 42 is larger than that after passing through the first drying device 80. The first active material mixture layer 43 is arranged so that a part of the first active material mixture layer 43 can be scraped off at a position where the state is achieved.

The scrapers 92 and 93 are arranged so as to obliquely enter both end portions 43A and 43B of the first active material layer 15 from the center side of the metal foil 11 in the lateral direction toward both edges E1 and E2 in the lateral direction. ing. As a result, when the first active material mixture layer 43 is transported together with the metal foil 11, both end portions 43A, 43B of the first active material mixture layer 43 are scraped off by the scrapers 92, 93.

The first active material mixture layer 43 becomes the first active material layer 15 by being dried by the first drying device 80 after the both end portions 43A and 43B are made thinner than the central portion 43C by the scrapers 92 and 93. ..

As shown in FIG. 3, the second coating device 94 is located downstream of the first drying device 80 in the transport direction of the metal foil 11. As the second coating device 94, for example, the same device as the first coating device 60 is used.

As shown in FIG. 5, the second coating device 94 coats the second active material mixture 44 on the metal foil 11. The second coating device 94 coats the second active material mixture 44 on both end portions 43A, 43B formed by the scrapers 92, 93 to be thinner than the central portion 43C. More specifically, in the second coating device 94, a part of the first active material mixture layer 43 is scraped off by the scrapers 92, 93, and the second active material mixture is formed in a portion thinner than the central portion 43C. Apply 44 to coat. As a result, the second active material mixture layer 45 is formed on the metal foil 11. The second active material mixture layer 45 becomes the second active material layer 16 by drying.

The second active material mixture 44 is a paste in which an active material, a conductive agent, a binder and a solvent are mixed. The second active material mixture 44 is a mixture having a lower density than the first active material layer 15 when it becomes the second active material layer 16 by drying. The second active material mixture 44, for example, is such that the density of the second active material layer 16 before being pressed is 30% to 70% of the density of the first active material layer 15 before being pressed. It is a good combination. Specifically, a plurality of active materials having different particle diameters are used as the active materials included in the first active material mixture 42 and the second active material mixture 44, and the first active material mixture 42 and the second active material are used. The ratio of the active material is changed with the material mixture 44. For example, the ratio of the active material having a particle size of 100 [μm] and the active material having a particle size of 10 [μm] is 70:30 in the first active material mixture 42, while the ratio of the second active material mixture 44 is set to 70:30. Then set it to 100:10. The larger the particle size of the active material, the larger the voids in the active material layers 15 and 16. Therefore, the larger the proportion of the active material having the larger particle size, the higher the void ratio. Further, the ratio of the solvent of the first active material mixture 42 may be lower than the ratio of the solvent of the second active material mixture 44 without changing the ratio of the active materials having different particle sizes. Since the solvent volatilizes, the larger the amount of the solvent, the higher the porosity of the active material layer. Further, the ratio of the binder of the first active material mixture 42 may be higher than the ratio of the binder of the second active material mixture 44.

The second drying device 95 is located downstream of the second coating device 94 in the transport direction of the metal foil 11. The second drying device 95 is a device that accelerates the drying of the second active material mixture layer 45, for example, by raising the atmospheric temperature in the furnace by a heating unit. The second active material mixture layer 45 becomes the second active material layer 16 by being dried by the second drying device 95. By forming the second active material layer 16, the active material layer 12 including the first active material layer 15 and the second active material layer 16 is formed on the metal foil 11.

The pressure device 81 is located downstream of the second drying device 95 in the transport direction of the metal foil 11. The pressure device 81 includes a pair of press rolls 82 arranged with the active material layer 12 sandwiched therebetween. Each press roll 82 of the present embodiment has a structure in which a heat medium can flow inside. Therefore, the peripheral surface of the press roll 82 is heated by the heat medium.

By passing between the pair of press rolls 82, the active material layer 12 is pressed and thereby densified. Further, the active material layer 12 is pressed while being heated, so that the active material layer 12 is further densified. The electrode sheet 10 is manufactured by pressing the active material layer 12 by the pressing device 81. A portion of the active material layer 12 where only the first active material layer 15 is provided becomes a high-density region 13, and a portion where the first active material layer 15 and the second active material layer 16 overlap is a low-density region 14. Becomes

The operation of this embodiment will be described.
When manufacturing the electrode sheet 10, the active material layer 12 is pressed by the pressing device 81. The force applied to the metal foil 11 when the active material layer 12 is pressed becomes greater in a portion (high-density region 13) in contact with the active material layer 12 having a higher density. The portion where the first active material layer 15 and the second active material layer 16 are overlapped (low density region 14) has a lower density than the portion where only the first active material layer 15 is. The amount of extension of the metal foil 11 when pressed by the pressing device 81 is larger than that of the portion in contact with the portion where only the first active material layer 15 is provided. The number of portions that are in contact with the overlapping portion of 16 and 16 is smaller. Since the portion where the first active material layer 15 and the second active material layer 16 overlap is provided along the uncoated portion 22, the amount of extension of the portion along the uncoated portion 22 is small.

The effects of this embodiment will be described.
(1) The amount of extension of the metal foil 11 caused by applying pressure to the active material layer 12 when manufacturing the electrode sheet 10 is in contact with the low-density region 14 as compared with the part in contact with the high-density region 13. There are less parts. Since the uncoated part 22 is adjacent to the low-density region 14, the rolling of the metal foil 11 due to pressure is caused as compared with the case where the uncoated part 22 and the high-density region 13 are adjacent to each other. Wrinkles can be suppressed.

In particular, when the coating portion 21 is pressed by the press roll 82 whose peripheral surface is heated as in the present embodiment, the metal foil 11 is easily softened and deformed by the heat of the press roll 82, and the metal foil 11 is wrinkled. Is likely to occur. Specifically, heating the metal foil 11 lowers the yield point, and wrinkles are likely to occur on the metal foil 11 due to the lowering of the yield point. Therefore, when the electrode sheet 10 is manufactured using the press roll 82 whose peripheral surface is heated, a remarkable effect is obtained.

(2) In order to suppress wrinkles generated in the metal foil 11, both ends of the first active material layer 15 are made thinner than the central part, and compared with the case where the second active material layer 16 is not provided at both ends. It is possible to suppress a decrease in the battery capacity of the lithium-ion secondary battery.

(3) The density of the low-density region 14 gradually decreases from the high-density region 13 toward the uncoated portion 22. The portion of the metal foil 11 in contact with the low-density region 14 has a smaller amount of extension due to pressure as it approaches the uncoated portion 22. As compared with the case where the low-density region 14 has a constant density, it is possible to suppress the concentration of stress generated at the boundary between the coated portion 21 and the uncoated portion 22.

(4) In the manufacturing apparatus 41, both end portions 43A and 43B of the first active material mixture layer 43 are formed thinner than the central portion 43C, and the second active material mixture layer 45 is applied to both end portions 43A and 43B. is doing. Thereby, the 1st active material layer 15 and the 2nd active material layer 16 can be provided with the part which overlaps, and the electrode sheet 10 which can suppress generation of wrinkles can be manufactured.

The embodiment can be modified and implemented as follows. The embodiment and the following modifications can be implemented in combination with each other within a technically consistent range.
The low-density region 14 only needs to be provided by stacking the first active material layer 15 and the second active material layer 16, and the density is constant between the high-density region 13 and the uncoated portion 22. May be. For example, the thickness of the first active material layer 15 and the thickness of the second active material layer 16 in the low density region 14 may be the same.

A device that blows air to the first active material mixture layer 43 may be used as the molding unit 91. In this case, air is blown toward both ends 43A, 43B of the first active material mixture layer 43, and both ends 43A, 43B are formed thinner than the central part 43C by wind pressure.

The molding unit 91 may be provided between the first coating device 60 and the first drying device 80.
The first coating device 60 and the second coating device 94 may be a comma coater, a lip coater or the like as long as the active material mixture can be applied.

The peripheral surface of the press roll 82 may not be heated. Further, the peripheral surface of the press roll 82 may be cooled.
The electrode sheet 10 may have the active material layer 12 provided on only one surface of the metal foil 11.

E1, E2... Both edges, 10... Electrode sheet (electrode for lithium ion secondary battery), 11... Metal foil, 12... Active material layer, 13... High density area, 14... Low density area, 15... First activity Material layer, 16... Second active material layer, 21... Coated part, 22... Uncoated part, 30... Electrode (electrode for lithium ion secondary battery), 41... Manufacture of electrode for lithium ion secondary battery Device, 43... First active material mixture layer, 43A, 43B... Both ends, 43C... Central part, 45... Second active material mixture layer, 50... Conveying device, 60... First coating device, 80... DESCRIPTION OF SYMBOLS 1 Drying device, 81... Pressurizing device, 91... Molding part, 94... Second coating device, 95... Second drying device.

Claims (3)

A coating part in which an active material layer is provided on a metal foil,
An uncoated part where the metal foil is exposed,
The active material layer is
A high-density region composed only of the first active material layer,
The first active material layer is formed of a layer in which a second active material layer having a lower density than that of the first active material layer is stacked, and a low layer located between the high density region and the uncoated portion. An electrode for a lithium ion secondary battery, comprising: a density region; The electrode for a lithium ion secondary battery according to claim 1, wherein the low-density region has a density that gradually decreases from the high-density region toward the uncoated portion. A transport device for transporting a long metal foil,
A first coating device for forming a first active material mixture layer on the metal foil by drying to form a first active material layer;
A first drying device for drying the first active material mixture layer;
When the portion that is located between the first active material mixture layer and both edges of the metal foil in the lateral direction and that the metal foil is exposed is an uncoated portion, the first along the uncoated portion 1. A molding portion for molding both end portions of the active material mixture layer to be thinner than the central portion of the first active material mixture layer,
A second active material mixture layer, which becomes a second active material layer having a density lower than that of the first active material layer by drying, is applied to the both ends after the molding by the molding part is performed. A coating device,
A second drying device for drying the second active material mixture layer;
An apparatus for manufacturing an electrode for a lithium ion secondary battery, comprising: a pressurizing device that pressurizes the first active material layer and the second active material layer.