JP2021051881A - Electrode assembly and method for manufacturing the same - Google Patents

Abstract

To provide an electrode assembly capable of suppressing cracking of a second active material layer and a method for manufacturing the same.SOLUTION: In an electrode assembly 12, a first electrode 20 is would so that a first surface 22a having a first active material layer 24 existing thereon is located on an inner peripheral side, and a second surface 22b having a second active material layer 25 existing thereon is located on an outer peripheral side. The electrode assembly 12 includes a central laminate portion 12a in which the first electrode 20 is laminated flatly, and a first end side laminate portion 12b and a second end side laminate portion 12c in which the first electrode 20 is laminated in a curved state. The thickness of the second active material layer 25 of the first electrode 20 is constant in a longitudinal direction of a first main body portion 22. The second active material layer 25 alternately has high-density portions 25a and low-density portions 25b in the longitudinal direction of the first main body portion 22, the low-density portions 25b having a lower active material density in the second active material layer 25 than the high-density portion 25a. The high-density portion 25a constitutes the central laminated portion 12a, and the low-density portion 25b constitutes the first end side laminated portion 12b or the second end side laminated portion 12c.SELECTED DRAWING: Figure 2

Description

The present invention relates to an electrode assembly in which long sheet-shaped electrodes are wound and a method for manufacturing the electrode assembly.

Patent Document 1 discloses an electrode assembly in which a long sheet-shaped positive electrode and a long sheet-shaped negative electrode are wound in a layered manner via a long sheet-shaped separator. .. The electrodes of the positive electrode and the negative electrode are a long sheet-shaped current collector, a first active material layer extending in the longitudinal direction of the current collector on the first surface of the current collector, and a first surface of the current collector. Has a second active material layer extending in the longitudinal direction of the current collector on the opposite second surface. The electrodes of the positive electrode and the negative electrode are wound so that the first surface is located on the inner peripheral side and the second surface is located on the outer peripheral side. The electrode assembly has a first laminated portion in which the electrodes are laminated flat, and a second laminated portion in which the electrodes are laminated in a curved state.

Japanese Unexamined Patent Publication No. 2013-149388

In such an electrode assembly, a pulling force acts on a portion of the second active material layer that constitutes the second laminated portion so as to spread in the longitudinal direction of the current collector, so that the second active material layer is cracked. May occur.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an electrode assembly and a method for manufacturing the electrode assembly, which can suppress cracking of the second active material layer.

The electrode assembly for solving the above problems includes a long sheet-shaped current collector, a first active material layer extending in the longitudinal direction of the current collector on the first surface of the current collector, and the like. An electrode having a second active material layer extending in the longitudinal direction of the current collector on a second surface opposite to the first surface of the current collector is located such that the first surface is on the inner peripheral side. It has a first laminated portion in which the second surface is wound so as to be located on the outer peripheral side and the electrodes are laminated in a flat manner, and a second laminated portion in which the electrodes are laminated in a curved state. In the electrode assembly, the thickness of the second active material layer is constant in the longitudinal direction of the current collector, and the second active material layer has a high-density portion and the second active material layer rather than the high-density portion. The two low-density portions having a low active material density in the active material layer are alternately provided in the longitudinal direction of the current collector, the high-density portion constitutes the first laminated portion, and the low-density portion constitutes the first laminated portion. The gist is to constitute the second laminated portion.

According to this, the hardness of the second active material layer is lower in the portion constituting the second laminated portion than in the portion constituting the first laminated portion, so that the second laminated portion of the second active material layer is formed. The ductility in the part to be improved is improved. Therefore, cracking of the second active material layer can be suppressed.

Further, regarding the electrode assembly, the active material density in the low density portion is lower in the low density portion located on the inner peripheral side of the winding and higher in the low density portion located on the outer peripheral side of the winding. preferable.

Since the R shape of the portion of the electrode that constitutes the second laminated portion is tighter toward the inner peripheral side of the winding and gentler toward the outer peripheral side of the winding, the second active material layer Cracks are more likely to occur in the portion of the portion constituting the second laminated portion, which is located on the inner peripheral side of the winding. Therefore, by lowering the density of the active material in the low-density portion toward the lower density portion located on the inner peripheral side, cracking of the second active material layer can be suppressed. Further, the capacity of the electrode assembly can be increased by increasing the density of the active material in the low-density portion in the low-density portion located on the outer peripheral side where cracks are less likely to occur as compared with the inner peripheral side.

Further, with respect to the electrode assembly, it is preferable that the electrode has a groove portion extending in the lateral direction of the current collector in a portion constituting the second laminated portion in the first active material layer.
According to this, since the groove portion makes it easy to bend the electrode, the formation of the second laminated portion becomes easy. Further, a compressive force acts on the portion of the first active material layer that constitutes the second laminated portion in the longitudinal direction of the current collector, but a part of the compressive force is absorbed by the groove portion. Therefore, it is possible to suppress the detachment of the first active material layer that may occur due to the action of the compressive force on the first active material layer.

Further, in the electrode assembly, the electrode has the electrode of the positive electrode and the electrode of the negative electrode, and at least for the electrode of the positive electrode, the thickness of the second active material layer is the longitudinal direction of the current collector. The second active material layer has the high-density portion and the low-density portion, the high-density portion constitutes the first laminated portion, and the low-density portion is the same. It is preferable to form the second laminated portion.

Generally, the active material used for the positive electrode has a higher hardness than the active material used for the negative electrode, so that the hardness of the second active material layer in the positive electrode is the same as that of the second active material layer in the negative electrode. It will be higher than the hardness. Therefore, cracking of the second active material layer is more likely to occur in the positive electrode than in the negative electrode. Based on this, at least for the positive electrode, the low density portion constitutes the second laminated portion, so that cracking of the second active material layer in the positive electrode can be suppressed.

A method for manufacturing an electrode assembly for solving the above problems is a method of manufacturing a long sheet-shaped current collector and a first active material extending in the longitudinal direction of the current collector on the first surface of the current collector. An electrode manufacturing step of manufacturing an electrode having a layer and a second active material layer extending in the longitudinal direction of the current collector on a second surface opposite to the first surface of the current collector, and the above-mentioned. The electrodes are wound so that the first surface is located on the inner peripheral side and the second surface is located on the outer peripheral side, and the first laminated portion in which the electrodes are laminated flat and the electrodes are curved. The electrode manufacturing step includes a winding step of forming a second laminated portion laminated in the above-mentioned state, and the electrode manufacturing step applies an active material mixture to the first surface and the second surface of the current collector. By pressing the coating step to be applied and the current collector coated with the active material mixture, the first active material layer is formed from the active material mixture coated on the first surface. A method for manufacturing an electrode assembly having a press step of forming the second active material layer from the active material mixture coated on the second surface, and the collection in the coating step. On the second surface of the electric body, a portion coated with the active material mixture having a first coating thickness and a portion coated with a second coating thickness thinner than the first coating thickness are formed. The thickness of the second active material layer is increased by pressing the active material mixture with a pair of press rolls that are alternately formed in the longitudinal direction of the current collector and are set at regular intervals. The active material is made constant in the longitudinal direction of the current collector, and a high-density portion is formed from the active material mixture coated with the first coating thickness, and the active material coated with the second coating thickness. A low-density portion having a lower active material density than the high-density portion is formed from the material mixture, and in the winding step, the high-density portion constitutes the first laminated portion, and the low-density portion forms the second laminated portion. The gist is to wind the electrodes so as to form a laminated portion.

According to this, the hardness of the second active material layer is lower in the portion constituting the second laminated portion than in the portion constituting the first laminated portion, so that the second laminated portion of the second active material layer is formed. The ductility in the part to be improved is improved. Therefore, cracking of the second active material layer can be suppressed.

Regarding the method for manufacturing the electrode assembly, in the coating step, the second coating thickness is the second coating of the active material mixture coated near one end in the longitudinal direction of the current collector. The coating thickness is set to be thicker, and the coating thickness is set to be thinner than the second coating thickness of the active material mixture to be coated near the other end in the longitudinal direction of the current collector. The portions are formed so that the active material density is lower toward the low density portion closest to one end in the longitudinal direction of the current collector and higher at the lower density portion closest to the other end in the longitudinal direction of the current collector. In the winding step, it is preferable to wind the electrode so that one end of the current collector in the longitudinal direction is the winding start side and the other end of the current collector in the longitudinal direction is the winding end side.

Since the R shape of the portion of the electrode that constitutes the second laminated portion is tighter toward the inner peripheral side of the winding and gentler toward the outer peripheral side, cracking of the second active material layer is caused. Of the portions constituting the second laminated portion, the portion located on the inner peripheral side of the winding is more likely to occur. Therefore, by lowering the density of the active material in the low-density portion toward the lower density portion located on the inner peripheral side, cracking of the second active material layer can be suppressed. Further, the capacity of the electrode assembly can be increased by increasing the density of the active material in the low-density portion in the low-density portion located on the outer peripheral side where cracks are less likely to occur as compared with the inner peripheral side.

According to the present invention, cracking of the second active material layer can be suppressed.

An exploded perspective view of the secondary battery. The plan view of the electrode assembly of 1st Embodiment. (A) and (b) are plan views of the first electrode before winding. (A) is a cross-sectional view of the first electrode before winding, (b) is a diagram showing the thickness of the first active material layer, (c) is a diagram showing the active material density in the first active material layer, (d). Is a diagram showing the thickness of the second active material layer, and (e) is a diagram showing the active material density in the second active material layer. Sectional view of electrode material. (A) and (b) are plan views of the metal foil material. (A) and (b) are cross-sectional views showing a pressing process. The plan view which shows typically the winding process. The plan view of the electrode assembly of 2nd Embodiment. (A) is a cross-sectional view of another example of the first electrode, (b) is a diagram showing the thickness of the second active material layer, and (c) is a diagram showing the active material density in the second active material layer. The cross-sectional view which shows the manufacturing method of the 1st electrode of another example.

(First Embodiment)
Hereinafter, a first embodiment embodying the electrode assembly and the method for manufacturing the electrode assembly will be described with reference to FIGS. 1 to 8.

As shown in FIG. 1, the secondary battery 10 as a power storage device includes a rectangular parallelepiped case 11, an electrode assembly 12 housed in the case 11, and an electrolytic solution (not shown) housed in the case 11. The case 11 has a bottomed tubular case body 13 and a plate-shaped lid 14 that closes the opening 13a of the case body 13. The case body 13 and the lid 14 are made of metal such as aluminum. The case body 13 was erected from a rectangular bottom wall 13b, a pair of long side walls 13c erected from a pair of long side edges of the bottom wall 13b, and a pair of short side edges of the bottom wall 13b. It has a pair of short side walls 13d. The lid 14 has a rectangular shape. Therefore, the secondary battery 10 of the present embodiment is a square battery having a square appearance. Further, the secondary battery 10 of the present embodiment is a lithium ion secondary battery.

As shown in FIG. 2, in the electrode assembly 12, a long sheet-shaped first electrode 20, a long sheet-shaped second electrode 30, and two long sheet-shaped separators 40 are wound around. Is formed. In the present embodiment, the first electrode 20 is a positive electrode and the second electrode 30 is a negative electrode.

The first electrode 20 has a first metal foil 21 as a long sheet-shaped current collector, a first active material layer 24, and a second active material layer 25.
3 (a), 3 (b), and 4 (a) show the first electrode 20 before being wound as the electrode assembly 12. As shown in FIGS. 3 (a) and 3 (b), the first metal leaf 21 protrudes from the rectangular first main body portion 22 and the one edge portion 221 along the longitudinal direction of the first main body portion 22. It has a plurality of first tabs 23. The longitudinal direction of the first main body 22 corresponds to the longitudinal direction of the first electrode 20, and the lateral direction of the first main body 22 corresponds to the lateral direction of the first electrode 20. The first metal foil 21 of the present embodiment is an aluminum foil having a thickness of 12 μm.

As shown in FIG. 4A, the first active material layer 24 extends over the entire longitudinal direction of the first main body 22 on the first surface 22a of the first main body 22. The second active material layer 25 extends over the entire longitudinal direction of the first main body portion 22 on the second surface 22b, which is the surface of the first main body portion 22 opposite to the first surface 22a. The first active material layer 24 and the second active material layer 25 include an active material, a binder, and a conductive auxiliary agent. In the present embodiment, the active material contained in the first active material layer 24 and the second active material layer 25, that is, the positive electrode active material is a composite oxide containing lithium.

As shown in FIG. 4B, the thickness of the first active material layer 24 is constant in the entire longitudinal direction of the first main body portion 22, except for the groove portion 28 described later. Further, the thickness of the first active material layer 24 is constant in the entire lateral direction of the first main body portion 22. In addition, "the thickness of the first active material layer 24 is constant" includes a state in which the thickness of the first active material layer 24 varies within an allowable range. The permissible range is a range that is permissible in the design of the first electrode 20, and is a so-called manufacturing tolerance.

As shown in FIG. 4C, the active material density in the first active material layer 24 is constant in the entire longitudinal direction of the first main body portion 22. Further, the density of the active material in the first active material layer 24 is constant in the entire lateral direction of the first main body portion 22. In addition, "the active material density in the first active material layer 24 is constant" includes a state in which the active material density varies within an allowable range.

As shown in FIG. 4D, the thickness of the second active material layer 25 is constant in the entire longitudinal direction of the first main body portion 22. Further, the thickness of the second active material layer 25 is constant in the entire lateral direction of the first main body portion 22. In addition, "the thickness of the second active material layer 25 is constant" includes a state in which the thickness of the second active material layer 25 varies within an allowable range.

As shown in FIGS. 4A and 4E, the second active material layer 25 has a plurality of high-density portions 25a, and the active material density in the second active material layer 25 is lower than that in the high-density portion 25a. It has a plurality of low-density portions 25b. In FIGS. 2, 3 (b), and 4 (a), the high-density portion 25a is shown by dark dot hatching, and the low-density portion 25b is shown by light dot hatching. The high-density portion 25a and the low-density portion 25b are alternately present in the longitudinal direction of the first main body portion 22. As described above, since the thickness of the second active material layer 25 is constant in the entire longitudinal direction of the first main body portion 22, the thickness of the high-density portion 25a and the thickness of the low-density portion 25b are the same.

As shown in FIG. 4 (e), the active material density in each high-density portion 25a is constant in the entire longitudinal direction of the first main body portion 22. Further, the density of the active material in each high-density portion 25a is constant in the entire lateral direction of the first main body portion 22. In addition, "the active material density in the high density portion 25a is constant" includes a state in which the active material density varies within an allowable range. In the present embodiment, the active material density in the high density portion 25a is 3.42 [mg / cm ³ ].

On the other hand, the active material density in the low density portion 25b gradually decreases from both ends of the low density portion 25b close to the high density portion 25a toward the center of the low density portion 25b in the longitudinal direction of the first main body portion 22. In the present embodiment, the active material density in the vicinity of the center where the active material density is the lowest among the low density portions 25b is 2.23 [mg / cm ³ ]. The active material density in each low-density portion 25b is constant in the entire lateral direction of the first main body portion 22.

As shown in FIG. 3B, the longitudinal direction of the high-density portion 25a coincides with the longitudinal direction of the first main body portion 22, and the lateral direction of the high-density portion 25a is the lateral direction of the first main body portion 22. Is consistent with. The dimensions of the high-density portion 25a in the longitudinal direction are substantially the same for all the high-density portions 25a. The dimension of the high-density portion 25a in the longitudinal direction is larger than the dimension of the low-density portion 25b in the longitudinal direction of the first main body portion 22. The dimension of the low-density portion 25b in the longitudinal direction of the first main body portion 22 is as small as the low-density portion 25b closest to the first end 20a in the longitudinal direction of the first electrode 20, and the second end in the longitudinal direction of the first electrode 20. The lower density portion 25b, which is the closest to 20b, is larger. That is, the dimension of the low-density portion 25b in the longitudinal direction of the first main body portion 22 from the low-density portion 25b closest to the first end 20a of the first electrode 20 to the low-density portion 25b closest to the second end 20b is It is getting bigger and bigger.

As shown in FIGS. 3A and 4A, the first electrode 20 has a short portion of the first main body 22 at a portion of the first active material layer 24 located on the opposite side of the low density portion 25b. It has a groove 28 extending along the hand direction. The groove portion 28 is located in the center of the portion of the first active material layer 24 that is located on the opposite side of the low density portion 25b in the longitudinal direction of the first main body portion 22. The groove 28 of the present embodiment is a V-shaped groove in which the width of the first main body 22 in the longitudinal direction gradually decreases from the surface of the first active material layer 24 toward the first surface 22a of the first main body 22. is there.

The first electrode 20 has a high-density portion 25a of the second active material layer 25, a portion of the first active material layer 24 located on the opposite side of the high-density portion 25a, and a high-density portion of the first main body portion 22. It has a plurality of first high-density coating portions 26 including a portion sandwiched between the 25a and the first active material layer 24. Further, the first electrode 20 has a low density portion 25b of the second active material layer 25, a portion of the first active material layer 24 located on the opposite side of the low density portion 25b, and a low density portion 22 of the first main body portion 22. It has a plurality of first low-density coating portions 27 including a portion sandwiched between the density portion 25b and the first active material layer 24. The first high-density coating portion 26 and the first low-density coating portion 27 are alternately present in the longitudinal direction of the first electrode 20.

The dimensions of the high-density portion 25a in the longitudinal direction of the first main body portion 22 match the dimensions of the first high-density coated portion 26 in the longitudinal direction of the first electrode 20, and the low density in the longitudinal direction of the first main body portion 22. The dimensions of the portion 25b match the dimensions of the first low-density coated portion 27 in the longitudinal direction of the first electrode 20. That is, the dimensions of the first high-density coating portion 26 in the longitudinal direction of the first electrode 20 are substantially the same in all the first high-density coating portions 26. On the other hand, the dimension of the first low-density coated portion 27 in the longitudinal direction of the first electrode 20 is smaller than that of the first low-density coated portion 27 closest to the first end 20a of the first electrode 20, and the first electrode 20 The size of the first low-density coating portion 27 closest to the second end 20b is larger. In the present embodiment, the first electrode 20 has six first high-density coating portions 26 and five first low-density coating portions 27.

Each first tab 23 is a portion where the first active material layer 24 and the second active material layer 25 do not exist and the first metal foil 21 is exposed. The shape of the first tab 23 is the same for all the first tabs 23, and is rectangular in the present embodiment. Each first tab 23 protrudes from one edge portion 221 of the portion of the first main body portion 22 that constitutes the first high-density coating portion 26. That is, each first tab 23 is arranged at a position corresponding to the first high-density coating portion 26 in the longitudinal direction of the first main body portion 22. Further, each of the first tabs 23 has a first tab 23 located closer to one end of the first high-density coating portion 26 in the longitudinal direction of the first main body portion 22 and a first height in the longitudinal direction of the first main body portion 22. The first tab 23 located near the other end of the density coating portion 26 is arranged so as to be alternately present in the longitudinal direction of the first main body portion 22.

As shown in FIG. 2, the second electrode 30 has a second metal foil 31 as a long sheet-shaped current collector, a first active material layer 34, and a second active material layer 35.
The second metal foil 31 has a rectangular second main body portion 32 and a plurality of second tabs 33 protruding from one edge portion 321 along the longitudinal direction of the second main body portion 32. The longitudinal direction of the second main body 32 corresponds to the longitudinal direction of the second electrode 30, and the lateral direction of the second main body 32 corresponds to the lateral direction of the second electrode 30. The second metal foil 31 of the present embodiment is a copper foil having a thickness of 12 μm. Further, in the present embodiment, the longitudinal dimension of the second main body 32 is longer than the longitudinal dimension of the first main body 22, and the lateral dimension of the second main body 32 is also the first main body. It is longer than the lateral dimension of 22.

The first active material layer 34 extends over the entire longitudinal direction of the second main body 32 on the first surface 32a of the second main body 32. The second active material layer 35 extends over the entire longitudinal direction of the second main body 32 on the second surface 32b, which is the surface of the second main body 32 opposite to the first surface 32a. The first active material layer 34 and the second active material layer 35 include an active material, a binder, and a conductive auxiliary agent. The active material contained in the first active material layer 34 and the second active material layer 35 of the present embodiment, that is, the negative electrode active material is carbon.

The thickness of the first active material layer 34 is constant in the entire longitudinal direction of the second main body portion 32. Further, the thickness of the first active material layer 34 is constant in the entire lateral direction of the second main body portion 32. In addition, "the thickness of the first active material layer 34 is constant" includes a state in which the thickness of the first active material layer 34 varies within an allowable range. The permissible range is a range that is permissible in the design of the second electrode 30, and is a so-called manufacturing tolerance. The active material density in the first active material layer 34 is constant in the entire longitudinal direction of the second main body portion 32. Further, the density of the active material in the first active material layer 34 is constant in the entire lateral direction of the second main body portion 32. In addition, "the density of the active material in the first active material layer 34 is constant" includes a state in which the density of the active material varies within an allowable range.

The thickness of the second active material layer 35 is constant in the entire longitudinal direction of the second main body portion 32. Further, the thickness of the second active material layer 35 is constant in the entire lateral direction of the second main body portion 32. In addition, "the thickness of the second active material layer 35 is constant" includes a state in which the thickness of the second active material layer 35 varies within an allowable range. The active material density in the second active material layer 35 is constant in the entire longitudinal direction of the second main body portion 32. Further, the density of the active material in the second active material layer 35 is constant in the entire lateral direction of the second main body portion 32. In addition, "the active material density in the second active material layer 35 is constant" includes a state in which the active material density varies within an allowable range.

The second electrode 30 has a second coating portion 36 including a second main body portion 32, a first active material layer 34, and a second active material layer 35. The second coating portion 36 exists from the first end 30a to the second end 30b in the longitudinal direction of the second electrode 30 over the entire longitudinal direction of the second electrode 30.

Each second tab 33 is a portion where the first active material layer 34 and the second active material layer 35 do not exist and the second metal foil 31 is exposed. The shape of the second tab 33 is the same for all the second tabs 33, and is rectangular in this embodiment. Each of the second tabs 33 is arranged at a predetermined position in the longitudinal direction of the second main body portion 32. Here, the predetermined position refers to a position set so that a plurality of second tabs 33 are lined up in a row when the second electrode 30 is wound.

Each separator 40 is interposed between the first electrode 20 and the second electrode 30. Each separator 40 is a porous membrane through which lithium ions can pass. In the present embodiment, the longitudinal dimension of each separator 40 is longer than the longitudinal dimension of the second main body 32, and the lateral dimension of each separator 40 is the lateral dimension of the second main body 32. It is almost the same as the dimensions.

In the electrode assembly 12, one of the first electrode 20 and the two separators 40, the second electrode 30, and the other of the two separators 40 are laminated in this order to form the winding shaft L. It is formed by being spirally wound as an axis. The winding direction of the first electrode 20, the second electrode 30, and each separator 40 coincides with the longitudinal direction of the first electrode 20, the second electrode 30, and each separator 40. The electrode assembly 12 has a layered structure in which the first electrode 20 and the second electrode 30 are laminated via the separator 40.

The first electrode 20 is wound so that the first end 20a is located on the winding start side and the second end 20b is located on the winding end side. In other words, the first end 20a of the first electrode 20 is located on the innermost circumference of the electrode assembly 12, and the second end 20b of the first electrode 20 is located on the outermost circumference of the electrode assembly 12. Therefore, among the plurality of first high-density coating portions 26 and first low-density coating portions 27, the first high-density coating portion 26 and the first low-density coating portion 26 closest to the first end 20a of the first electrode 20. The coating unit 27 is a first high-density coating unit 26 and a first low-density coating unit 27 located on the innermost circumference. Of the plurality of first high-density coating portions 26 and first low-density coating portions 27, the first high-density coating portion 26 and the first low-density coating portion closest to the second end 20b of the first electrode 20. Reference numeral 27 denotes a first high-density coating portion 26 and a first low-density coating portion 27 located on the outermost periphery.

Further, the second electrode 30 is wound so that the first end 30a is located on the winding start side and the second end 30b is located on the winding end side. The separator 40 is also wound so that the first end 40a is located on the winding start side and the second end 40b is located on the winding end side. In other words, the first ends 30a and 40a of the second electrode 30 and the separator 40 are located on the innermost circumference of the electrode assembly 12, and the second electrodes 30 and the second ends 30b and 40b of the separator 40 are the electrode assembly. It is located on the outermost circumference of 12.

The second end 20b of the first electrode 20, the second end 30b of the second electrode 30, and 2 so that the first electrode 20, the second electrode 30, and each separator 40 do not separate from the wound state. The second end 40b of the sheet separator 40 is fixed to the electrode assembly 12 by a tape (not shown).

The first electrode 20 is wound so that the first surface 22a of the first main body 22 is the inner peripheral surface and the second surface 22b of the first main body 22 is the outer peripheral surface. Therefore, the first active material layer 24 is located on the inner peripheral side of the winding, and the second active material layer 25 is located on the outer peripheral side of the winding. Similarly, the second electrode 30 is wound so that the first surface 32a of the second main body 32 becomes the inner peripheral surface and the second surface 32b of the second main body 32 becomes the outer peripheral surface. Therefore, the first active material layer 34 is located on the inner peripheral side of the winding, and the second active material layer 35 is located on the outer peripheral side of the winding.

The electrode assembly 12 has a central laminated portion 12a as a first laminated portion in which a first high-density coating portion 26 and a part of a second coating portion 36 are alternately laminated via a separator 40. The direction in which the first high-density coating portion 26 and a part of the second coating portion 36 are laminated is defined as the lamination direction. In the central laminated portion 12a, in a part of the first high-density coating portion 26 and the second coating portion 36 adjacent to each other in the lamination direction, the first active material layer 24 is interposed via the second active material layer 35 and the separator 40. Face each other. Further, in a part of the first high-density coating portion 26 and the second coating portion 36 adjacent to each other in the stacking direction, the high-density portion 25a of the second active material layer 25 has the first active material layer 34 and the separator 40. Face each other through. In the central laminated portion 12a, a part of the first high-density coating portion 26 and the second coating portion 36 is laminated flat.

In the present embodiment, the second coating portions 36 are present at both ends of the electrode assembly 12 in the stacking direction. Therefore, the first end surface 121 of the electrode assembly 12 in the stacking direction is composed of a portion of the second coating portion 36 located at one end in the stacking direction, and the second end surface 122 of the electrode assembly 12 in the stacking direction is , The second coating portion 36 is composed of a portion located at the other end in the stacking direction. The first end surface 121 and the second end surface 122 are surfaces facing the long side wall 13c of the case body 13.

In the first electrode 20, the first high-density coating portion 26 located on one end side in the stacking direction with respect to the winding shaft L and the first high-density coating portion 26 located on the other end side in the stacking direction with respect to the winding shaft L. The work portions 26 are alternately present in the longitudinal direction of the first electrode 20. In other words, of the two first high-density coating portions 26 adjacent to each other with the first low-density coating portion 27 in the longitudinal direction of the first electrode 20, one of the first high-density coating portions 26 is wound. When it is located on one end side in the stacking direction with respect to the shaft L, the other first high-density coating portion 26 is located on the other end side in the stacking direction with respect to the winding shaft L.

In the electrode assembly 12, the first tab 23 is arranged in a row in the stacking direction, and the second tab 33 is arranged in a row in the stacking direction at a position different from the position where the first tab 23 is arranged in a row. In the present embodiment, the first tab 23 is arranged in a row in the stacking direction on one end side in the longitudinal direction of the high-density portion 25a, and the second tab 33 is arranged in the stacking direction on the other end side in the longitudinal direction of the high-density portion 25a. Line up in a row. As shown in FIG. 1, the electrode assembly 12 includes a first tab group 15 in which a plurality of first tabs 23 arranged in a row are stacked, and a plurality of second tabs arranged in a row at positions different from those of the first tab 23. It has a second tab group 16 in which 33 are laminated.

The electrode assembly 12 has a first end-side laminated portion 12b as a second laminated portion located on one end side of the central laminated portion 12a in the longitudinal direction of the high-density portion 25a and a central laminated portion 12b in the longitudinal direction of the high-density portion 25a. It has a second end-side laminated portion 12c as a second laminated portion located on the other end side of the portion 12a.

The first end-side laminated portion 12b and the second end-side laminated portion 12c are portions in which the first low-density coated portion 27 and a part of the second coated portion 36 are alternately laminated via the separator 40. .. The first end side laminated portion 12b and the second end side laminated portion 12c face the long side wall 13c and the short side wall 13d of the case body 13. In the first end-side laminated portion 12b and the second end-side laminated portion 12c, a part of the first low-density coated portion 27 and the second coated portion 36 is convex in a direction away from the central laminated portion 12a. Stacked in a curved state.

In the first electrode 20, the first low-density coated portion 27 constituting the first end-side laminated portion 12b and the first low-density coated portion 27 forming the second end-side laminated portion 12c are the first electrodes. It exists alternately in the longitudinal direction of 20. In other words, of the two first low-density coating portions 27 adjacent to each other with the first high-density coating portion 26 in the longitudinal direction of the first electrode 20, one of the first low-density coating portions 27 is the first. When the end-side laminated portion 12b is formed, the other first low-density coating portion 27 constitutes the second end-side laminated portion 12c. Further, as described above, the first electrode 20 is wound so that the first end 20a is on the winding start side. Therefore, the dimensions of the first low-density coating portion 27 in the longitudinal direction of the first main body portion 22 are the first low-density coating located on the outer peripheral side of the first end-side laminated portion 12b or the second end-side laminated portion 12c. It is as long as the engineering department 27.

As shown in FIG. 1, the secondary battery 10 includes a first terminal structure 17 and a second terminal structure 18 for extracting electricity from the electrode assembly 12. The first terminal structure 17 has a plate-shaped first conductive member 17a joined to the first tab group 15, and a rod-shaped first terminal 17b protruding from the first conductive member 17a. The second terminal structure 18 has a plate-shaped second conductive member 18a joined to the second tab group 16 and a rod-shaped second terminal 18b protruding from the second conductive member 18a. The first terminal 17b and the second terminal 18b penetrate the lid 14 and project to the outside of the case 11 to connect the inside and outside of the case 11. A bus bar (not shown) that electrically connects the secondary batteries 10 to each other can be fixed to the first terminal 17b and the second terminal 18b. The secondary battery 10 includes an insulating ring 19 for insulating the lid 14 from the first terminal 17b or the second terminal 18b.

Next, among the methods for manufacturing the electrode assembly 12, an electrode manufacturing step for manufacturing the first electrode 20 and a winding step for winding the first electrode 20, the second electrode 30, and the separator 40 will be described.

As shown in FIG. 5, the electrode manufacturing process includes a coating process of applying the active material mixture 220 to the long sheet-shaped metal leaf material 210. The metal foil material 210 of the present embodiment is an aluminum foil having a thickness of 12 μm, and the active material mixture 220 is a kneaded mixture of a positive electrode active material, a binder, a conductive auxiliary agent, and a solvent. The coating steps include a first coating step of applying the active material mixture 220 to the first surface 210a of the metal leaf material 210 and a coating of the active material mixture 220 to the second surface 210b of the metal foil material 210. It has a second coating process.

The coating step of the present embodiment is performed by applying the active material mixture 220 to the metal foil material 210 transported in the longitudinal direction by a transport device (not shown) by a die coating device (not shown). The die coating device is connected to a tank (not shown) in which the active material mixture 220 is stored, and the active material mixture 220 is pumped from the tank to the die coating device by a pump (not shown).

As shown in FIG. 6A, the first coating area A1 on which the active material mixture 220 is applied and the first coating area A1 on which the active material mixture 220 is not applied are not coated on the first surface 210a of the metal foil material 210. 1 Uncoated area B1 is preset. The first coating area A1 is set over the entire longitudinal direction of the metal foil material 210. In the present embodiment, the dimension of the first coating area A1 in the lateral direction of the metal leaf material 210 is set to be substantially the same as the dimension of the first main body portion 22 in the lateral direction. The first uncoated area B1 is set at one end of the metal leaf material 210 in the lateral direction over the entire longitudinal direction of the metal leaf material 210.

As shown in FIG. 6B, the second surface 210b of the metal foil material 210 is coated with the active material mixture 220 in the second coating area A2 and the active material mixture 220 is not coated. 2 Uncoated area B2 is preset. The second coating area A2 is set over the entire longitudinal direction of the metal leaf material 210. In the present embodiment, the dimension of the second coating area A2 in the lateral direction of the metal foil material 210 is set to be substantially the same as the dimension of the first main body portion 22 in the lateral direction. The second uncoated region B2 exists at one end of the metal foil material 210 in the lateral direction where the first uncoated region B1 exists, over the entire longitudinal direction of the metal foil material 210.

The second coating area A2 has a plurality of thick coating areas A2a and a plurality of thin coating areas A2b. The thick coating region A2a and the thin coating region A2b are alternately present in the longitudinal direction of the metal leaf material 210. In the present embodiment, the dimensions of the thick coating region A2a in the longitudinal direction of the metal foil material 210 are set to substantially the same dimensions in all the thick coating regions A2a. On the other hand, the dimension of the thin coating region A2b in the longitudinal direction of the metal foil material 210 is as large as the thin coating region A2b located at one end of the metal foil material 210 in the longitudinal direction, and is located at the other end of the metal foil material 210 in the longitudinal direction. It is set to be smaller as the light coating area A2b is located.

As shown in FIG. 5, the active material mixture 220 is coated with a thickness H1 on the first coating region A1 of the first surface 210a of the metal foil material 210 by the first coating step. By the second coating step, the active material mixture 220 is coated on the thick coating region A2a of the second surface 210b of the metal foil material 210 with the thickness H2a as the first coating thickness, and the metal foil material 210 is coated. The active material mixture 220 is coated on the thin coating region A2b of the second surface 210b with the second coating thickness. The second coating thickness is thinner than the thickness H2a. In this embodiment, the thickness H1 is set to 152 μm and the thickness H2a is set to 87 μm. In the first coating step and the second coating step, the first uncoated region B1 of the first surface 210a of the metal foil material 210 and the second uncoated region B2 of the second surface 210b of the metal foil material 210 The active material mixture 220 is not coated.

In the coating process of the present embodiment, the thickness of the active material mixture 220 to be coated on the metal foil material 210 is controlled by controlling the opening and closing of a valve (not shown) provided between the tank and the die coating device. To adjust. Specifically, when the valve is opened, the active material mixture 220 is supplied to the die coating device, so that the active material mixture 220 is coated on the metal foil material 210. On the other hand, when the valve is closed, the active material mixture 220 is not supplied to the die coating device, so that the active material mixture 220 is not coated on the metal foil material 210. Further, when the valve is changed from the open state to the closed state, the supply amount of the active material mixture 220 to the die coating device is reduced, so that the thickness of the active material mixture 220 coated on the metal foil material 210 is reduced. Gradually becomes thinner. On the contrary, when the valve is changed from the closed state to the open state, the supply amount of the active material mixture 220 to the die coating device increases, so that the active material mixture 220 coated on the metal foil material 210 The thickness gradually increases.

When the active material mixture 220 is applied to the first coating area A1 of the metal leaf material 210, the valve is always open. As a result, the active material mixture 220 is coated on the first coating area A1 of the metal foil material 210 with a constant thickness H1.

On the other hand, when the active material mixture 220 is applied to the second coating area A2 of the metal foil material 210, the valve is opened and closed. Specifically, when the active material mixture 220 is applied to the thick coating area A2a of the metal leaf material 210, the valve is opened and the active material mixture 220 is applied to the thin coating area A2b of the metal leaf material 210. When painting, the valve is changed from the open state to the closed state, and when it is closed, it is returned to the open state. As a result, the active material mixture 220 is coated on the thick coating region A2a of the metal foil material 210 with a constant thickness H2a. Further, the thin coating region A2b of the metal foil material 210 has a thickness increasing from both ends of the thin coating region A2b close to the thick coating region A2a in the longitudinal direction of the metal foil material 210 toward the center of the thin coating region A2b. The active material mixture 220 is applied so as to gradually become thinner. In the present embodiment, the thickness H2b of the thinnest portion of the active material mixture 220 coated on the thin coating region A2b of the metal foil material 210 is 87 μm.

The electrode manufacturing process is a drying process in which the active material mixture 220 is dried by removing the solvent from the active material mixture 220 coated on the first surface 210a and the second surface 210b of the metal foil material 210 in the coating process. Has a process.

The electrode material 200 is formed through a coating process and a drying process. The electrode material 200 has a first coating portion precursor 230 composed of the metal foil material 210 and the active material mixture 220 in the thick coating region A2a of the metal foil material 210. Further, the electrode material 200 has a second coating portion precursor 240 composed of the metal foil material 210 and the active material mixture 220 in the thin coating region A2b of the metal foil material 210. The thickness H230 of the first coated portion precursor 230 is thicker than the thickness of the second coated portion precursor 240. In the present embodiment, the thickness H230 of the first coated portion precursor 230 is 152 μm, and the thickness H240 of the thinnest portion of the second coated portion precursor 240 is 68 μm.

Although not shown, in the electrode material 200, the active material mixture 220 is not coated on both sides of the metal foil material 210 in the first uncoated region B1 and the second uncoated region B2 of the metal foil material 210, and the metal The foil material 210 has an exposed uncoated portion.

As shown in FIGS. 7 (a) and 7 (b), the electrode manufacturing process includes a pressing process of pressing the electrode material 200.
The pressing process is performed by the pressing apparatus 50. The press device 50 includes a pair of press rolls 51 and 52 arranged on both sides in the vertical direction with the electrode material 200 interposed therebetween. Each press roll 51, 52 is made of metal. The press rolls 51 and 52 are rotatably supported by a rotating shaft (not shown). Each of the press rolls 51 and 52 is integrally rotated with the rotating shaft by a driving device (not shown) connected to the rotating shaft. The distance W between the end portion 51a of the outer peripheral surface of the first press roll 51 closest to the second press roll 52 and the end portion 52a of the outer peripheral surface of the second press roll 52 closest to the first press roll 51 is constant. Is set to. In the present embodiment, the distance W between the press rolls 51 and 52 is set to be smaller than the thickness H240 of the thinnest portion of the second coating portion precursor 240.

The electrode material 200 is conveyed in the longitudinal direction of the metal foil material 210 by a transfer device (not shown) so as to pass between the pair of rotating press rolls 51 and 52. The first coating part precursor 230 and the second coating part precursor 240 are pressed by a pair of press rolls 51 and 52. As a result, the active material density in the active material mixture 220 increases, so that the active material mixture 220 coated on the first surface 210a of the metal foil material 210 becomes the first active material layer 24. Further, the active material mixture 220 coated on the second surface 210b of the metal foil material 210 becomes the second active material layer 25.

As described above, the thickness H230 of the first coated portion precursor 230 is thicker than the thickness of the second coated portion precursor 240. On the other hand, the intervals W of the press rolls 51 and 52 are set to constant intervals. Therefore, in the pressing step, the pressing force applied to the first coating portion precursor 230 is larger than the pressing force applied to the second coating portion precursor 240. As a result, of the active material mixture 220 coated on the second coating region A2 of the metal foil material 210, the portion coated on the thick coating region A2a becomes the high-density portion 25a, and the thin coating region A2b The portion coated on is a low density portion 25b. In the present embodiment, the active material density in the high density portion 25a is 3.48 [mg / cm ³ ], and the compressibility is 34.8%.

Further, as described above, the thickness of each second coated portion precursor 240 becomes thinner from both ends of the second coated portion precursor 240 in the longitudinal direction of the metal leaf material 210 toward the center. Therefore, the pressing force applied to the second coating portion precursor 240 decreases from both ends in the longitudinal direction of the metal foil material 210 toward the center. In the present embodiment, the vicinity of the center of the second coating portion precursor 240 in the longitudinal direction of the metal foil material 210 is not pressurized. As a result, the low density portion 25b is formed so that the active material density decreases from both ends in the longitudinal direction of the metal foil material 210 toward the center. In the present embodiment, the active material density near the center where the active material density is the lowest among the low density portions 25b is 21.3 [mg / cm ³ ], and the compressibility is 10.4%.

Further, in the pressing step, the first coated portion precursor 230 and the second coated portion precursor 240 are compressed so that the thickness after pressing is the same as the interval W of the press rolls 51 and 52, respectively. Therefore, the thickness of the first active material layer 24 becomes a constant thickness in the longitudinal direction of the metal foil material 210, and the thickness of the second active material layer 25 becomes a constant thickness in the longitudinal direction of the metal foil material 210. .. By the pressing process, the first coating part precursor 230 becomes the first high-density coating part 26, and the second coating part precursor 240 becomes the first low-density coating part 27.

The electrode manufacturing step includes a groove forming step of forming a groove 28 in a portion of the first active material layer 24 located on the opposite side of the low density portion 25b. In the longitudinal direction of the metal foil material 210, the groove portion 28 is located at the center of the portion of the first active material layer 24 opposite to the low density portion 25b, along the lateral direction of the metal foil material 210. It is formed by scraping.

The electrode manufacturing process includes a cutting step of cutting the electrode material 200. In the cutting step, the electrode material 200 is punched along the cutting line CL set to have the same shape as the outer shape of the first electrode 20 shown in FIG. As a result, a plurality of first tabs 23 are formed from the uncoated portion of the metal foil material 210. The portion punched out from the electrode material 200 becomes the first electrode 20.

In the winding step, the electrode assembly 12 is formed by winding the first electrode 20, the second electrode 30, and the two separators 40.
As shown in FIG. 8, the first electrode 20 and the second electrode 30 before being wound as the electrode assembly 12 are respectively wound around the first supply roll 61. Further, the two separators 40 before being wound as the electrode assembly 12 are wound one by one on the second supply roll 62. In the state where the first electrode 20 is wound around the first supply roll 61, the first electrodes 20 and the first ends 20a and 30a of the second electrode 30 are located on the outer peripheral side of the first supply roll 61. The second ends 20b and 30b of the first electrode 20 and the second electrode 30 are located on the inner peripheral side of the first supply roll 61.

In the electrode manufacturing process, the rotary table 63 and the first core material 64a and the second core material 64b attached to the rotary table 63 are used. The first core material 64a and the second core material 64b are arranged side by side so that the midpoint between the first core material 64a and the second core material 64b coincides with the rotation axis O of the rotary table 63. Further, the distance between the first core material 64a and the second core material 64b is set so as to be substantially the same as the dimension in the longitudinal direction of the high-density portion 25a. The first core material 64a has a first curved surface 64c that is convex in the direction away from the second core material 64b, and the second core material 64b has a second curvature that is convex in the direction away from the first core material 64a. It has a surface 64d.

In the present embodiment, the first end 20a of the first electrode 20 drawn out from the first supply roll 61 is fixed to the first core material 64a. The first end 30a of the second electrode 30 unwound from the first supply roll 61 and the first end 40a of each separator 40 unwound from each of the second supply rolls 62 are fixed to the second core material 64b. ing.

When the rotary table 63 is rotated in this state, the first electrode 20 and the second electrode 30 are wound around the first core material 64a and the second core material 64b while being unwound from the first supply roll 61. Further, the separator 40 is also wound around the first core material 64a and the second core material 64b while being unwound from the second supply roll 62. As a result, the first electrode 20, the second electrode 30, and each separator 40 are wound so that the first electrode 20 and the second electrode 30 form a layered structure via the separator 40.

Between the first core material 64a and the second core material 64b, the first high-density coating portion 26 of the first electrode 20 and a part of the second coating portion 36 of the second electrode 30 are laminated in a flat manner. By doing so, the central laminated portion 12a is formed. On both sides of the first core material 64a and the second core material 64b, a part of the first low-density coated portion 27 of the first electrode 20 and the second coated portion 36 of the second electrode 30 is a first curved surface. The first end side laminated portion 12b and the second end side laminated portion 12c are formed by laminating in a curved state along the 64c or the second curved surface 64d.

Then, the first electrode 20 and the second electrode 30 wound around the first supply roll 61 and the separator 40 wound around the second supply roll 62 are all the first core material 64a and When wound around the second core material 64b, the second end 20b of the first electrode 20, the second end 30b of the second electrode 30, and the second end 40b of each separator 40 are wound electrode sets. It is fixed to the solid 12 by a tape (not shown). After that, the electrode assembly 12 is removed from the first core material 64a and the second core material 64b. As a result, the electrode assembly 12 is completed.

The operation of the first embodiment will be described.
In the present embodiment, if the active material density in the second active material layer 25 is 2.51 [mg / cm ³ ] or less, the second active material layer 25 is cracked regardless of the degree of curvature of the first electrode 20. It is experimentally known that it does not occur.

The thickness of the second active material layer 25 of the present embodiment is constant in the entire longitudinal direction of the first main body portion 22. On the other hand, the active material density in the second active material layer 25 differs in the longitudinal direction of the first main body portion 22. The second active material layer 25 alternately has a high-density portion 25a and a low-density portion 25b having a lower active material density than the high-density portion 25a in the longitudinal direction of the first main body portion 22. The active material density in the high-density portion 25a is 1.55 [mg / cm ³ ], and the active material density in the low-density portion 25b where the active material density is the lowest is 1.36 [mg / cm ^3]. ]. The high-density portion 25a constitutes the central laminated portion 12a, and the low-density portion 25b constitutes the first end-side laminated portion 12b or the second end-side laminated portion 12c.

As a result, the hardness of the second active material layer 25 is lower in the portion constituting the first end side laminated portion 12b or the second end side laminated portion 12c than in the portion constituting the central laminated portion 12a. Therefore, the ductility of the portion of the second active material layer 25 that constitutes the first end-side laminated portion 12b or the second end-side laminated portion 12c is improved. Therefore, cracking of the second active material layer 25 can be suppressed.

The effect of the first embodiment will be described.
(1-1) The hardness of the second active material layer 25 is lower in the portion constituting the first end side laminated portion 12b or the second end side laminated portion 12c than in the portion constituting the central laminated portion 12a. Therefore, the ductility of the portion of the second active material layer 25 that constitutes the first end-side laminated portion 12b or the second end-side laminated portion 12c is improved. Therefore, cracking of the second active material layer 25 can be suppressed.

(1-2) The lithium-containing composite oxide used as the positive electrode active material has a higher hardness than the carbon used as the negative electrode active material. Therefore, the hardness of the second active material layer 25 of the first electrode 20 is higher than the hardness of the second active material layer 35 of the second electrode 30. Therefore, the cracks in the portion constituting the first end side laminated portion 12b or the second end side laminated portion 12c are more cracked in the second active material layer of the first electrode 20 than in the second active material layer 35 of the second electrode 30. It tends to occur at 25. Based on this, with respect to the first electrode 20, the low density portion 25b constitutes the first end side laminated portion 12b or the second end side laminated portion 12c, so that the first electrode 20, that is, the second active material in the positive electrode electrode. Cracking of the layer 25 can be suppressed.

(1-3) The first electrode 20 has a groove 28 in a portion of each of the first active material layers 24 that constitutes the first end-side laminated portion 12b or the second end-side laminated portion 12c. Since the groove portion 28 makes it easy to bend the first electrode 20, the formation of the first end side laminated portion 12b and the second end side laminated portion 12c becomes easy. Further, a compressive force acts on the portion of the first active material layer 24 that constitutes the first end-side laminated portion 12b or the second end-side laminated portion 12c in the longitudinal direction of the first main body portion 22, but the compressive force is applied. Is partially absorbed by the groove 28. Therefore, it is possible to suppress the detachment of the first active material layer 24 that may occur due to the action of the compressive force on the first active material layer 24.

(1-4) In the coating step, the coating thickness of the active material mixture 220 on the thick coating area A2a of the metal foil material 210 and the coating thickness of the active material mixture 220 on the thin coating area A2b are changed. I'm letting you. Therefore, in the pressing step, the second active material layer having the high-density portion 25a and the low-density portion 25b is simply pressed by pressing the electrode material 200 while maintaining the interval W of the pair of press rolls 51 and 52 at a constant interval. 25 can be formed.

(Second Embodiment)
Hereinafter, a second embodiment in which the electrode assembly is embodied will be described. In the second embodiment, the configuration different from that of the first embodiment will be mainly described, and the description of the same configuration as that of the first embodiment will be omitted.

In the second embodiment, the negative electrode active material is a silicon-based material containing Si. Therefore, the hardness of the active material layer of the negative electrode of the second embodiment is higher than the hardness of the active material layer of the negative electrode of the first embodiment, and the brittleness of the active material layer of the negative electrode of the second embodiment is the first embodiment. It is lower than the brittleness of the active material layer of the negative electrode of the form. Therefore, there is a possibility that cracks may occur in the portions constituting the first end side laminated portion 12b and the second end side laminated portion 12c in the active material layer of the negative electrode.

As shown in FIG. 9, in the second embodiment, the electrode assembly 12 is formed by winding two first electrodes 20 and two separators 40. That is, the electrode assembly 12 does not have the second electrode 30. Of the two first electrodes 20, one is a positive electrode and the other is a negative electrode.

The longitudinal dimension of the first main body 22 of the negative electrode is longer than the longitudinal dimension of the first main body 22 of the positive electrode, and the lateral dimension of the first main body 22 of the negative electrode is the first main body of the positive electrode. It is longer than the lateral dimension of the portion 22. Further, the first electrode 20 of the positive electrode has six first high-density coating portions 26 and five first low-density coating portions 27, and the first electrode 20 of the negative electrode has seven first highs. It has a density coating unit 26 and six first low density coating units 27.

The longitudinal dimension X251 of each high-density portion 25a of the negative electrode is longer than the longitudinal dimension X252 of each high-density portion 25a of the positive electrode. In the central laminated portion 12a, the pair of ends 251 located at both ends of the high-density portion 25a of the negative electrode in the longitudinal direction are located outside the pair of ends 252 located at both ends of the high-density portion 25a of the positive electrode in the longitudinal direction. .. Further, although not shown, the dimension of each high-density portion 25a of the negative electrode in the lateral direction is longer than the dimension of each high-density portion 25a of the positive electrode in the lateral direction. In the central laminated portion 12a, the pair of ends located at both ends of the high-density portion 25a of the negative electrode in the lateral direction are located outside the pair of ends located at both ends of the high-density portion 25a of the positive electrode in the lateral direction. ..

In the second embodiment, in addition to the effects similar to the effects (1-1) to (1-4) of the first embodiment, the following effects can be obtained.
(2-1) When a silicon-based material containing Si is used as the negative electrode active material, there is a possibility that cracks may occur in the portion constituting the first end side laminated portion 12b or the second end side laminated portion 12c in the negative electrode active material layer. There is. Based on this, also in the electrode of the negative electrode, the high density portion 25a and the low density portion 25b are formed on the second active material layer 25, and the low density portion 25b forms the first end side laminated portion 12b or the second end side laminated portion 12c. By configuring the above, it is possible to suppress cracking of the second active material layer 25 in the electrode of the negative electrode.

The above embodiment can be modified and implemented as follows. The above-described embodiments and modifications can be implemented in combination with each other within a technically consistent range.
○ The active material density in each low-density portion 25b may be constant in the longitudinal direction of the first main body portion 22.

○ The gradient of the active material density in each low-density portion 25b does not have to be the same in all low-density portions 25b. That is, the gradient of the active material density in each low-density portion 25b may be different for each low-density portion 25b.

As shown in FIGS. 10A and 10B, in the first electrode 20, the thickness of the second active material layer 25 is constant in the longitudinal direction of the first main body 22. Therefore, the thickness of each high-density portion 25a and the thickness of each low-density portion 25b are the same.

As shown in FIG. 10 (c), the active material density of the portion having the lowest active material density in the low density portion 25b is as low as the low density portion 25b closest to the first end 20a of the first electrode 20, and the first electrode The lower density portion 25b closest to the second end 20b of 20 is higher. Further, as described above, the dimension of the low density portion 25b in the longitudinal direction of the first main body portion 22 is smaller as the low density portion 25b closest to the first end 20a in the longitudinal direction of the first electrode 20, and the first electrode 20 The lower density portion 25b closest to the second end 20b in the longitudinal direction of the is larger. Therefore, the gradient of the active material density in the low density portion 25b is steeper toward the low density portion 25b closest to the first end 20a of the first electrode 20, and is closest to the second end 20b of the first electrode 20. The high-density portion 25b is looser.

Next, the method for manufacturing the first electrode 20 described above will be described.
As shown in FIG. 11, the active material mixture 220 is applied from both ends of the thin coating region A2b in the longitudinal direction of the metal foil material 210 to the center of the thin coating region A2b with respect to the thin coating region A2b of the metal foil material 210. It is coated so that the thickness gradually decreases as it goes toward it. Since the coating of the active material mixture 220 on the first coating region A1 of the first surface 210a of the metal leaf material 210 and the thick coating region A2a of the second surface 210b is the same as that of the first embodiment. The explanation is omitted.

At this time, the thickness of the active material mixture 220 when it is applied to the thinnest in each thin coating area A2b is as thin as the thin coating area A2b located on one end side in the longitudinal direction of the metal foil material 210, and is a metal. The foil material 210 is formed so as to be thicker as the thin coating region A2b located on the other end side in the longitudinal direction. Therefore, the thickness H240 of the thinnest portion of the second coating portion precursor 240 is also as thin as the second coating portion precursor 240 located on one end side in the longitudinal direction of the metal foil material 210, and the metal foil material 210. The thickness of the second coating portion precursor 240 located on the other end side in the longitudinal direction of the above is increased.

In the pressing step, the thickness of the first coated portion precursor 230 and the second coated portion precursor 240 after being pressed is made constant in the longitudinal direction of the metal foil material 210 by the above-mentioned press rolls 51 and 52. Be pressed. Therefore, the pressing force applied to the second coating portion precursor 240 is as small as that of the second coating portion precursor 240 located on one end side in the longitudinal direction of the metal foil material 210, and is other than that in the longitudinal direction of the metal foil material 210. The size is as large as the second coating part precursor 240 located on the end side. As a result, the active material density of the portion having the lowest active material density in the low density portion 25b is lower as the low density portion 25b closest to the first end 20a of the first electrode 20 and becomes the second end 20b of the first electrode 20. The closest high-density portion 25b forms a higher first electrode 20.

As described in the first embodiment, the electrode assembly 12 is wound so that the first end 20a of the first electrode 20 is the winding start side and the second end 20b is the winding end side. Therefore, the active material density in the low-density portion 25b is lower as the low-density portion 25b located on the inner peripheral side of the winding and higher as the low-density portion 25b located on the outer peripheral side of the winding.

The R shape of the first electrode 20 in the first end side laminated portion 12b or the second end side laminated portion 12c is tighter toward the portion located on the inner peripheral side of the winding and gentler toward the portion located on the outer peripheral side of the winding. is there. Therefore, cracking of the second active material layer 25 is more likely to occur in the portion of the portion constituting the first end side laminated portion 12b or the second end side laminated portion 12c, which is located on the inner peripheral side of the winding. Therefore, by lowering the active material density in the low density portion 25b by the low density portion 25b located on the inner peripheral side of the winding, cracking of the second active material layer 25 can be suppressed.

Further, the capacity of the electrode assembly 12 can be increased by increasing the density of the active material in the low density portion 25b by the low density portion 25b located on the outer peripheral side where cracks are less likely to occur as compared with the inner peripheral side. it can.

○ The first electrode 20 does not have to have a groove 28 in the first active material layer 24. In this case, the groove forming step is omitted in the electrode manufacturing step.
○ In the first embodiment, the second electrode 30 may also have a groove portion in the portion of the first active material layer 34 that constitutes the first end side laminated portion 12b or the second end side laminated portion 12c. In this case, since the second electrode 30 is easily curved by the groove portion, the formation of the first end side laminated portion 12b and the second end side laminated portion 12c becomes easier.

○ The number of the first high-density coating portion 26 and the first low-density coating portion 27 may be appropriately changed according to the actual number of turns of the first electrode 20.
○ In the first electrode 20, the current collector is not limited to the first metal foil 21, and may be, for example, a woven or net-like sheet. Similarly, in the second electrode 30, the current collector is not limited to the second metal foil 31, and may be, for example, a woven or net-like sheet.

○ In the second embodiment, the material used as the negative electrode active material is not limited to the silicon-based material containing Si, and may be, for example, a silicon-based material containing a silicon compound, a material containing Ti, or even carbon. ..

○ Whether or not cracks occur in the portion of the second active material layer 25 that constitutes the first end-side laminated portion 12b or the second end-side laminated portion 12c is determined by, for example, the type of binder contained in the second active material layer 25. It is also affected by the amount, the thickness of the second active material layer 25, and the like. Therefore, when there is a possibility that the active material layer may be cracked due to the influence of the active material contained in the active material layer, the binder, the thickness of the active material layer, etc., the second active material layer 25 has a high density portion 25a and a low density portion 25a. The density portion 25b is formed, and the low density portion 25b constitutes the first end side laminated portion 12b or the second end side laminated portion 12c.

○ In the first embodiment, for example, when there is a risk that the active material layer of the negative electrode may be cracked by increasing the thickness of the active material layer of the negative electrode, the first electrode 20 as the electrode of the positive electrode and the first electrode 20 are used. The electrode assembly 12 may be formed by winding the first electrode 20 as the electrode of the negative electrode and the two separators 40. That is, also for the electrode of the negative electrode, the high density portion 25a and the low density portion 25b are formed on the second active material layer 25, and the low density portion 25b constitutes the first end side laminated portion 12b and the second end side laminated portion 12c. By doing so, the cracking of the second active material layer 25 may be suppressed.

○ In the second embodiment, when it is known that the active material layer of the positive electrode is not cracked, the electrode assembly 12 has a first electrode 20 as a negative electrode and a second electrode as a positive electrode. It may be formed by winding the electrode 30 and the two separators 40.

○ The first terminal structure 17 and the second terminal structure 18 of the above embodiment are examples. The specific structures of the first terminal structure 17 and the second terminal structure 18 may be appropriately changed as long as electricity can be exchanged with the electrode assembly 12.

○ The electrode assembly 12 may be used for a secondary battery other than the lithium ion secondary battery. The other secondary battery refers to a battery in which ions move between the active material for the positive electrode and the active material for the negative electrode and transfer of electric charge.

○ The electrode assembly 12 may be used in a power storage device other than a secondary battery, such as a capacitor.

12 ... Electrode assembly, 12a ... Central laminated portion as first laminated portion, 12b ... First end side laminated portion as second laminated portion, 12c ... Second end side laminated portion as second laminated portion, 20 ... 1st electrode as an electrode, 21 ... 1st metal foil as a current collector, 22a ... 1st surface, 22b ... 2nd surface, 24 ... 1st active material layer, 25 ... 2nd active material layer, 25a ... high Density part, 25b ... Low density part, 28 ... Groove part, 51, 52 ... Press roll, 220 ... Active material mixture.

Claims (6)

A long sheet-shaped current collector, a first active material layer extending in the longitudinal direction of the current collector on the first surface of the current collector, and a side opposite to the first surface of the current collector. The electrode having the second active material layer extending in the longitudinal direction of the current collector on the second surface of the current collector is such that the first surface is located on the inner peripheral side and the second surface is located on the outer peripheral side. Turned around,
An electrode assembly having a first laminated portion in which the electrodes are laminated flat and a second laminated portion in which the electrodes are laminated in a curved state.
The thickness of the second active material layer is constant in the longitudinal direction of the current collector, and is constant.
The second active material layer alternately has high-density parts and low-density parts having a lower active material density in the second active material layer than the high-density parts in the longitudinal direction of the current collector.
An electrode assembly characterized in that the high-density portion constitutes the first laminated portion and the low-density portion constitutes the second laminated portion. The electrode assembly according to claim 1, wherein the active material density in the low density portion is lower in the low density portion located on the inner peripheral side of the winding and higher in the low density portion located on the outer peripheral side of the winding. The electrode assembly according to claim 1 or 2, wherein the electrode has a groove portion extending in the lateral direction of the current collector in a portion constituting the second laminated portion in the first active material layer. The electrode has the electrode of the positive electrode and the electrode of the negative electrode.
At least for the electrode of the positive electrode, the thickness of the second active material layer is constant in the longitudinal direction of the current collector, and the second active material layer has the high-density portion and the low-density portion. The electrode assembly according to any one of claims 1 to 3, wherein the high-density portion constitutes the first laminated portion, and the low-density portion constitutes the second laminated portion. A long sheet-shaped current collector, a first active material layer extending in the longitudinal direction of the current collector on the first surface of the current collector, and a side opposite to the first surface of the current collector. An electrode manufacturing step of manufacturing an electrode having a second active material layer extending in the longitudinal direction of the current collector on the second surface of the current collector.
The electrodes are wound so that the first surface is located on the inner peripheral side and the second surface is located on the outer peripheral side, and the first laminated portion in which the electrodes are laminated flat and the electrodes are A winding step of forming a second laminated portion laminated in a curved state, and
Have,
The electrode manufacturing process is
A coating step of applying an active material mixture to the first surface and the second surface of the current collector, and
By pressing the current collector coated with the active material mixture, the first active material layer is formed from the active material mixture coated on the first surface, and the first active material layer is formed on the second surface. A pressing step of forming the second active material layer from the coated active material mixture, and
It is a manufacturing method of an electrode assembly having
In the coating process, the second surface of the current collector has a portion coated with the active material mixture at the first coating thickness and a second coating thickness thinner than the first coating thickness. The parts coated with the above are alternately formed in the longitudinal direction of the current collector.
In the pressing step, the active material mixture is pressed by a pair of press rolls set at regular intervals to make the thickness of the second active material layer constant in the longitudinal direction of the current collector. A high-density portion is formed from the active material mixture coated with the first coating thickness, and the active material density is higher than that of the high-density portion from the active material mixture coated with the second coating thickness. Form a low density part,
In the winding step, the electrode assembly is characterized in that the high-density portion constitutes the first laminated portion and the low-density portion constitutes the second laminated portion. Production method. In the coating step, the second coating thickness is set to be as thick as the second coating thickness of the active material mixture coated near one end in the longitudinal direction of the current collector, and the current collector is collected. It is set as thin as the second coating thickness of the active material mixture to be applied near the other end in the longitudinal direction of the body.
In the pressing step, the low density portion has an active material density as low as the low density portion closest to one end in the longitudinal direction of the current collector, and the low density portion closest to the other end in the longitudinal direction of the current collector. Formed to be higher in the part,
The fifth aspect of the present invention, wherein in the winding step, the electrode is wound so that one end of the current collector in the longitudinal direction is the winding start side and the other end of the current collector in the longitudinal direction is the winding end side. A method for manufacturing an electrode assembly.

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