Manufacturing method of secondary battery

Abstract

To provide a manufacturing method of a secondary battery improved in productivity.SOLUTION: A manufacturing method comprises: Step (S1) of making a winding core 210 hold a first separator 32 and a second separator 34; Step (S2) of winding the first separator 32 and the second separator 34 around the winding core 210; Step (S3) of arranging a winding start end 20s of a negative electrode 20 so that the negative electrode 20 is arranged on an inner peripheral side of the first separator 32 in a state where the winding core 210 is stopped, and arranging a winding start end 10s of a positive electrode 10 between an outer peripheral side of the first separator 32 and the second separator 34; and Step (S4) of winding the positive electrode 10 and the negative electrode 20 around the winding core 210.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a secondary battery. [Background technology]

[0002] Conventionally, secondary batteries have been known that include a wound electrode body formed by stacking a strip-shaped first separator, a strip-shaped positive electrode, a strip-shaped second separator, and a strip-shaped negative electrode and winding them around a winding axis (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2022-127948 Summary of the Invention [Problem to be solved by the invention]

[0004] The wound electrode body is produced, for example, by the following steps. That is, first, as shown in FIG. 10A, a winding device having a winding core is prepared. Then, a strip-shaped positive electrode, a strip-shaped negative electrode, and two strip-shaped separators are each wound into a reel and set on the winding device. The winding core has, for example, an adsorption mechanism, and is configured to be able to fix (e.g., fix by adsorption) the separators supported on the winding core. The winding core also has a rotation mechanism, and is configured to be able to rotate at a predetermined rotation speed in a predetermined rotation direction (counterclockwise in this case, the direction of the arrow in FIG. 10A). FIG. 11 schematically shows the rotation speed of the winding core 210 in each step.

[0005] Next, as shown in FIG. 10A, the starting ends of the two strip-shaped separators are adsorbed and fixed to the winding core (holding step). Then, as shown in FIGS. 10A and 11, the winding core is rotated in this state, and the two separators are wound around the winding core to a predetermined length (step Sa; separator initial winding step). Next, as shown in FIG. 10B, the rotation of the winding core 210 is temporarily stopped, and the starting end of the strip-shaped negative electrode is placed between the two separators (step Sb; negative electrode placement step). Then, as shown in FIGS. 10C and 11, the winding core is rotated in this state, and the two separators and the strip-shaped negative electrode are wound around the winding core to a predetermined length (step Sc; negative electrode initial winding step). Next, as shown in FIG. 10D, the rotation of the winding core 210 is temporarily stopped again, and the starting end of the strip-shaped positive electrode is placed between the two separators (step Sd; positive electrode placement step). 10E and 11, the positive electrode, negative electrode, and separator are wound around the winding core by rotating the winding core while supplying the strip-shaped positive electrode and strip-shaped negative electrode so that the negative electrode winds around the positive electrode (step Se; main winding step). In this manner, a cylindrical wound body (cylindrical body) is formed.

[0006] 11, the conventional method stops the rotation of the winding core 210 twice, once when the negative electrode is placed (step Sb) and once when the positive electrode is placed (step Sd), thereby preventing, for example, strong rubbing between the separator and the electrode (negative electrode and / or positive electrode) surfaces and preventing the electrodes from shifting (misaligning) in the stacking. However, this method has the problem of lengthening the takt time for winding the cylindrical body, which ultimately reduces the productivity of secondary batteries.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing a secondary battery with improved productivity. [Means for solving the problem]

[0008] The present invention provides a method for manufacturing a secondary battery having a wound electrode body formed by stacking and winding a strip-shaped first separator, a strip-shaped positive electrode, a strip-shaped second separator, and a strip-shaped negative electrode. This manufacturing method includes: a holding step of holding the first separator and the second separator on a winding core; a first winding step of rotating the winding core at a first rotational speed after the holding step and winding the first separator and the second separator onto the winding core; an arrangement step of, after the first winding step, positioning a winding start end of the negative electrode so that the negative electrode is positioned on the inner circumferential side of the first separator and positioning the winding start end of the positive electrode between the outer circumferential surface of the first separator and the second separator, while the winding core is rotating at a second rotational speed slower than the first rotational speed or is stopped; and a second winding step of winding the positive electrode and the negative electrode around the winding core at a third rotational speed faster than the first rotational speed after the arrangement step.

[0009] In the manufacturing method disclosed herein, in the arrangement step, the negative electrode is arranged on the inner circumferential side of the first separator, and the positive electrode is arranged between the outer circumferential surface of the first separator and the second separator, so that the negative electrode is wound around the positive electrode. This makes it possible to wind the positive electrode and negative electrode approximately simultaneously around the winding core. As a result, the number of times the winding core rotation is slowed or stopped can be reduced from two to one. Therefore, the technology disclosed herein can shorten the winding takt time and efficiently manufacture a highly reliable wound electrode assembly in which lamination misalignment and the like are suppressed. This ultimately improves the productivity of secondary batteries. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view schematically showing a secondary battery according to one embodiment. [Figure 2] FIG. 2 is a schematic vertical cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 3 is a schematic vertical cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a schematic cross-sectional view taken along line IV-IV in FIG. [Figure 5] FIG. 5 is a perspective view that schematically shows a plurality of wound electrode bodies attached to a sealing plate. [Figure 6] FIG. 6 is a schematic cross-sectional view of a wound electrode body. [Figure 7] FIG. 7 is a schematic diagram showing the configuration of a wound electrode body. [Figure 8] 8A to 8E are explanatory diagrams of a winding process according to one embodiment, where FIG. 8A is an explanatory diagram of a holding process, FIG. 8B is an explanatory diagram of a first winding process, FIG. 8C is an explanatory diagram of a placement process, and FIG. 8D is an explanatory diagram of a second winding process. [Figure 9] FIG. 9 is a graph schematically showing the rotation speed of the winding core according to one embodiment. [Figure 10] 10A to 10E are explanatory diagrams of the winding process according to the conventional technology, with FIG. 10A showing the separator initial winding process, FIG. 10B showing the negative electrode arrangement process, FIG. 10C showing the negative electrode initial winding process, FIG. 10D showing the positive electrode arrangement process, and FIG. 10E showing the main winding process. [Figure 11] FIG. 11 is a graph showing a schematic representation of the rotation speed of a winding core according to the prior art. DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments of the technology disclosed herein will be described below with reference to the drawings. It should be noted that matters other than those specifically mentioned in this specification that are necessary for implementing the technology disclosed herein (for example, the general configuration and manufacturing process of a secondary battery that does not characterize the present invention) can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The technology disclosed herein can be implemented based on the content disclosed in this specification and common technical knowledge in the relevant field. In this specification, the expression "A to B" indicating a range includes the meaning of "greater than A" and "smaller than B" as well as "greater than A."

[0012] In this specification, the term "secondary battery" refers to a general electricity storage device that can be repeatedly charged and discharged by the movement of charge carriers between a positive electrode and a negative electrode via an electrolyte. The concept of secondary battery encompasses storage batteries such as lithium ion secondary batteries and nickel-metal hydride batteries, and capacitors such as lithium ion capacitors and electric double layer capacitors. The following describes an embodiment that focuses on a lithium ion secondary battery.

[0013] <1. Structure of secondary batteries> First, a secondary battery 100 manufactured by the manufacturing method disclosed herein will be described. FIG. 1 is a perspective view of the secondary battery 100. FIG. 2 is a schematic longitudinal sectional view taken along line II-II in FIG. 1. FIG. 3 is a schematic longitudinal sectional view taken along line III-III in FIG. 1. FIG. 4 is a schematic transverse sectional view taken along line IV-IV in FIG. 1. In the following description, the symbol X indicates the "depth direction," the symbol Y indicates the "width direction" perpendicular to the depth direction, and the symbol Z indicates the "height direction" perpendicular to the depth and width directions. In addition, the symbol F in the depth direction X indicates "front," and the symbol Rr indicates "rear." In the width direction Y, the symbol L indicates "left," and the symbol R indicates "right." In the height direction Z, the symbol U indicates "up," and the symbol D indicates "down." However, these directions are merely used for convenience of explanation and do not limit the installation form of the secondary battery 100 disclosed herein.

[0014] As shown in Fig. 2, the secondary battery 100 includes a wound electrode assembly 40, a battery case 50 that houses the wound electrode assembly 40, a positive electrode terminal 60, and a negative electrode terminal 65. Although not shown, the secondary battery 100 further includes an electrolyte solution. The secondary battery 100 is preferably a non-aqueous electrolyte secondary battery such as a lithium-ion secondary battery. The secondary battery 100 is characterized by including the wound electrode assembly 40 disclosed herein, and other configurations may be similar to conventional ones.

[0015] The battery case 50 is a housing that houses the wound electrode assembly 40 and the electrolyte. As shown in FIG. 1, the battery case 50 has a flat, bottomed, rectangular parallelepiped (square) outer shape. Any conventionally known material can be used for the battery case 50 without any particular restrictions. The battery case 50 is preferably made of metal. Examples of materials for the battery case 50 include aluminum, aluminum alloys, iron, and iron alloys. As shown in FIGS. 1 and 2, the battery case 50 includes an exterior body 52 and a sealing plate 54. The battery case 50 is preferably a prismatic battery that includes the exterior body 52 and the sealing plate 54.

[0016] As shown in Fig. 2, the exterior body 52 is a flat, bottomed, rectangular container having an opening 52h on its top surface. As shown in Fig. 1, the exterior body 52 includes a bottom wall 52a that is substantially rectangular in plan view, a pair of long side walls 52b that extend upward in the height direction Z from the long sides of the bottom wall 52a and face each other, and a pair of short side walls 52c that extend upward in the height direction Z from the short sides of the bottom wall 52a and face each other. The bottom wall 52a faces the opening 52h. The area of ​​the short side walls 52c is smaller than that of the long side walls 52b.

[0017] As shown in FIG. 2, the sealing plate 54 is a plate-like member that closes the opening 52h of the exterior body 52. ​​The sealing plate 54 has a substantially rectangular shape in a plan view. The periphery of the sealing plate 54 is joined (e.g., welded) to the opening 52h of the exterior body 52. ​​This hermetically seals (closes) the battery case 50. The sealing plate 54 is provided with a liquid injection hole 55, a gas release valve 57, and two terminal insertion holes 58 and 59. The liquid injection hole 55 is a through-hole for injecting electrolyte into the battery case 50 after the sealing plate 54 is assembled to the exterior body 52. ​​The liquid injection hole 55 is sealed with a sealing member 56 after the electrolyte is injected. The gas release valve 57 is a thin-walled portion designed to rupture (open) when the pressure inside the battery case 50 reaches or exceeds a predetermined value, thereby releasing the gas to the outside.

[0018] The electrolyte may be the same as conventional ones and is not particularly limited. The electrolyte is, for example, a non-aqueous electrolyte containing a non-aqueous solvent (organic solvent) and a supporting salt (electrolyte salt). The electrolyte is preferably a non-aqueous electrolyte. Examples of non-aqueous solvents include carbonates such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. Examples of supporting salts include fluorine-containing lithium salts such as lithium hexafluorophosphate (LiPF6). The electrolyte may contain additives as needed.

[0019] The positive electrode terminal 60 is attached to one end of the sealing plate 54 in the width direction Y (the left end in FIGS. 1 and 2). The negative electrode terminal 65 is attached to the other end of the sealing plate 54 in the width direction Y (the right end in FIGS. 1 and 2). As shown in FIG. 2, the positive electrode terminal 60 and the negative electrode terminal 65 extend from the inside to the outside of the sealing plate 54 through terminal insertion holes 58, 59. Resin gaskets 90 are attached to the terminal insertion holes 58, 59 of the sealing plate 54, respectively. This insulates the positive electrode terminal 60 and the negative electrode terminal 65 inserted into the terminal insertion holes 58, 59 from the sealing plate 54.

[0020] As shown in FIGS. 1 and 2, the positive electrode terminal 60 is connected to a plate-shaped positive electrode external conductive member 62 on the outer surface of the sealing plate 54. The negative electrode terminal 65 is connected to a plate-shaped negative electrode external conductive member 67. The positive electrode external conductive member 62 and the negative electrode external conductive member 67 are each insulated from the sealing plate 54 by an external insulating member 92 made of resin. The positive electrode external conductive member 62 and the negative electrode external conductive member 67 are connected to other batteries or external devices via external connection members (such as bus bars).

[0021] As shown in Fig. 2, the lower end 60c of the positive electrode terminal 60 is connected to a positive electrode current collecting member 70 inside the exterior body 52. ​​The positive electrode terminal 60 is connected to the positive electrode 10 (see Fig. 7) of the wound electrode body 40 via the positive electrode current collecting member 70. The lower end 65c of the negative electrode terminal 65 is connected to a negative electrode current collecting member 75 inside the exterior body 52. ​​The negative electrode terminal 65 is connected to the negative electrode 20 (see Fig. 7) of the wound electrode body 40 via the negative electrode current collecting member 75.

[0022] FIG. 5 is a perspective view schematically showing multiple wound electrode assemblies 40 attached to a sealing plate 54. As shown in FIGS. 3 to 5, in the secondary battery 100 of this embodiment, multiple (specifically, three) wound electrode assemblies 40 are housed in a single battery case 50, lined up in the depth direction X. When the secondary battery 100 has multiple wound electrode assemblies 40, the takt time of the wound electrode assemblies 40 is lengthened, which has a significant impact on the productivity of the secondary battery 100. Therefore, applying the technology disclosed herein is particularly effective. However, the number of wound electrode assemblies 40 arranged in a single battery case 50 is not particularly limited and may be two or more (multiple), or may be one. The multiple wound electrode assemblies 40 are housed inside the exterior body 52 while being covered with an electrode assembly holder 98 (see FIG. 3) made of an insulating resin sheet. This prevents direct contact between the wound electrode assemblies 40 and the exterior body 52.

[0023] As shown in FIG. 3, the wound electrode body 40 has a flat outer shape. The wound electrode body 40 preferably has a flat outer shape, as in this embodiment. The flat wound electrode body 40 has a pair of curved portions (R portions) 40r whose outer surfaces are curved, and a flat portion 40f whose outer surface is flat and connects the pair of curved portions 40r. As can be seen from FIGS. 2, 5, and 7, the multiple wound electrode bodies 40 are arranged inside the battery case 50 with their respective winding axes WL (see FIG. 7) oriented parallel to the width direction Y of the secondary battery 100. The pair of curved portions 40r face the bottom wall 52a and the sealing plate 54 of the exterior body 52. ​​The pair of flat portions 40f face the pair of long side walls 52b of the exterior body 52.

[0024] As shown in FIGS. 2 and 4 , a positive electrode tab group 42 is provided at one end (left end) in the width direction Y of the wound electrode assembly 40, and a negative electrode tab group 44 is provided at the other end (right end). A positive electrode current collecting member 70 is attached to the positive electrode tab group 42. The positive electrode tab group 42 is connected to the positive electrode terminal 60 via the positive electrode current collecting member 70. A negative electrode current collecting member 75 is attached to the negative electrode tab group 44. The negative electrode tab group 44 is connected to the negative electrode terminal 65 via the negative electrode current collecting member 75. The secondary battery 100 has a so-called horizontal tab structure in which the positive electrode tab group 42 and the negative electrode tab group 44 are located on the left and right sides of the wound electrode assembly 40. However, in other embodiments, the secondary battery 100 may have a so-called upper tab structure in which the positive electrode tab group 42 and the negative electrode tab group 44 are located above and below the wound electrode assembly 40.

[0025] Fig. 6 is a schematic cross-sectional view showing a cross section perpendicular to the winding axis direction of the wound electrode body 40. Fig. 7 is a schematic diagram showing the configuration of the wound electrode body 40. Note that the symbol X in Fig. 6 also indicates the thickness direction of the wound electrode body 40. Furthermore, the symbol MD in Fig. 7 stands for "machine direction" and indicates the longitudinal direction of the wound electrode body 40 and the separators 32, 34 (i.e., the winding direction).

[0026] 7, the wound electrode body 40 is configured by stacking and winding a strip-shaped first separator 32, a strip-shaped positive electrode 10, a strip-shaped second separator 34, and a strip-shaped negative electrode 20. Such a wound electrode body 40 can be formed, for example, as described in the manufacturing method below, by winding the strip-shaped positive electrode 10, the strip-shaped negative electrode 20, and two strip-shaped separators 32, 34 in the longitudinal direction MD around a winding axis WL.

[0027] As shown in FIG. 6, in the winding start region (winding center region) of the wound electrode assembly 40, the separators 32, 34 are wound before the positive electrode 10 to the negative electrode 20. That is, the start end (near the winding axis WL) of the wound electrode assembly 40 is made up of the separators 32, 34. Neither the positive electrode 10 nor the negative electrode 20 is disposed at the start end of the wound electrode assembly 40. The winding start end 32s of the first separator 32 and the winding start end 34s of the second separator 34 are located on the flat portion 40f here. It is preferable that the winding start end 32s of the first separator 32 and the winding start end 34s of the second separator 34 are aligned in position.

[0028] In the following description, the first bending point from the winding starting ends 32s and 34s of the separators 32 and 34 is referred to as the first bending point P1, the second bending point P2, the third bending point P3, and the fourth bending point P4. The first bending point P1 and the third bending point P3 are located on one side in the height direction Z (upper side in FIG. 6) and are stacked (overlapping). The second bending point P2 and the fourth bending point P4 are located on the other side in the height direction Z (lower side in FIG. 6) and are stacked (overlapping).

[0029] The separators 32, 34 are folded back at the first bending point P1, then folded back to the opposite side at the second bending point P2, forming pleats. In the winding start region, the separators 32, 34 form a Z-shape. This allows for appropriate tension to be applied to the separators 32, 34 in the first winding step (step S2) of the manufacturing method described below, even if the initial winding length of the separators 32, 34 is relatively short, thereby reducing costs. Furthermore, in the arrangement step (step S3) of the manufacturing method described below, a winding method in which the positive electrode 10 wraps around the negative electrode 20 can be suitably adopted. Furthermore, a gap G can be secured near the second bending point P2, improving the impregnation of the electrolyte in the central region of the wound electrode assembly 40 (particularly the central portion in the width direction Y). This ultimately improves battery characteristics (e.g., high-rate cycle characteristics).

[0030] The winding start end 20s of the negative electrode 20 is located closer to the winding start end than the winding start end 10s of the positive electrode 10. Here, the winding start end 20s of the negative electrode 20 is located on a flat portion 40f between the first bending point P1 and the second bending point P2. The winding start end 20s of the negative electrode 20 is located closer to the first bending point P1 than the second bending point P2. The winding start end 20s of the negative electrode 20 is wrapped in the first separator 32 on the winding start end side than the second bending point P2. More specifically, the winding start end 20s is sandwiched between the outer peripheral surface of the first separator 32 folded back at the first bending point P1 and the inner peripheral surface of the first separator 32 folded back at the second bending point P2. Because the separators 32 and 34 are Z-shaped, the negative electrode 20 is sandwiched between the inner peripheral surface of the first separator 32 and the outer peripheral surface of the second separator 34 from around the fourth bending point P4.

[0031] The winding start end 10s of the positive electrode 10 is located closer to the winding termination side (a position further in the winding direction) than the winding start end 20s of the negative electrode 20. Here, the winding start end 10s of the positive electrode 10 is located on the flat portion 40f between the third bending point P3 and the fourth bending point P4. The winding start end 10s of the positive electrode 10 is located closer to the first bending point P1 (and the third bending point P3) than the second bending point P2. The winding start end 10s of the positive electrode 10 is located closer to the winding termination side than the third bending point P3, and is sandwiched between the outer peripheral surface of the first separator 32 folded back at the third bending point P3 and the inner peripheral surface of the second separator 34. The second separator 34 is wound around the outer peripheral side of the positive electrode 10. The negative electrode 20 is wound around the outer periphery of the second separator .

[0032] In the thickness direction of the wound electrode assembly 40 (direction X in FIG. 6 ), the starting end of the negative electrode 20 preferably overlaps the starting end of the positive electrode 10 in a region closer to the winding starting end than the first bending point (here, the third bending point P3). By overlapping the starting end of the positive electrode 10 and the winding starting end 20s of the negative electrode 20 at the boundary between the flat portion 40f and the curved portion 40r, where a difference in surface pressure is likely to occur, it is possible to prevent a large step (depression) from occurring in the flat portion 40f. This reduces the likelihood of a difference in surface pressure occurring even when pressure is applied to the flat portion 40f during the manufacturing process or during use of the secondary battery 100. This reduces the likelihood of current distribution, thereby suppressing uneven charge / discharge reactions. As a result, Li deposition can be suppressed. This in turn prevents micro-short circuits between the positive electrode 10 and the negative electrode 20.

[0033] In the winding direction (longitudinal direction MD), the distance Ds between the winding start end 10s of the positive electrode 10 and the winding start end 20s of the negative electrode 20 is preferably 20 mm or less. This can prevent, for example, a large step (depression) from occurring in the flat portion 40f, and for the reasons described above, can suppress the occurrence of Li deposition. Ultimately, it can prevent a micro-short circuit between the positive electrode 10 and the negative electrode 20. From the viewpoint of charge carrier acceptance, the distance Ds is preferably approximately 10 mm or more, and more preferably 13 mm or more. From the viewpoint of improving Li deposition resistance, the distance Ds is more preferably 17 mm or less.

[0034] The winding end 10e of the positive electrode 10 is located closer to the winding start end than the winding end 20e of the negative electrode 20. In this example, the winding end 10e of the positive electrode 10 is located on the flat portion 40f. The winding end 20e of the negative electrode 20 is located closer to the winding end (a position further in the winding direction) than the winding end 10e of the positive electrode 10. In this example, the winding end 20e of the negative electrode 20 is located on the flat portion 40f. The winding end 20e of the negative electrode 20 is covered from the outer periphery by two separators 32, 34.

[0035] In the wound electrode assembly 40, from the viewpoint of charge carrier acceptance, it is preferable that the negative electrode 20 is always located on the surface facing the positive electrode 10. In other words, it is preferable that the winding start end 20s of the negative electrode 20 is located closer to the winding start end than the winding start end 10s of the positive electrode 10, and that the winding end 20e of the negative electrode 20 is located closer to the winding end than the winding end 10e of the positive electrode 10. This prevents Li extracted from the portion of the positive electrode not facing the negative electrode from concentrating in the portion facing the negative electrode. This therefore suppresses the occurrence of Li deposition. Ultimately, it is possible to prevent a micro-short circuit between the positive electrode 10 and the negative electrode 20.

[0036] The winding end 32e of the first separator 32 and the winding end 34e of the second separator 34 are located closer to the winding end (in the winding direction) than the winding end 10e of the positive electrode 10 and the winding end 20e of the negative electrode 20. The winding end 32e of the first separator 32 and the winding end 34e of the second separator 34 are located on a flat portion 40f in this example. The winding end portion (outermost portion) of the second separator 34 forms the outer peripheral surface of the wound electrode assembly 40. A stop tape 48 is attached to the winding end 32e of the first separator 32 and the winding end 34e of the second separator 34 to prevent loosening of the winding.

[0037] It is preferable that the winding end 32e of the first separator 32 and the winding end 34e of the second separator 34 are aligned. This allows the width of the stop tape 48 to be reduced, thereby preventing twisting when unwrapping or wrinkling when applying. As a result, it is possible to prevent the flat portion 40f from having a locally thick portion (a protruding portion), for example, and for the reasons described above, it is possible to prevent Li deposition. This in turn prevents micro-short circuits between the positive electrode 10 and the negative electrode 20. Furthermore, it is possible to reduce the amount of expensive stop tape 48 used, thereby reducing costs.

[0038] The number of windings of the wound electrode body 40 is preferably adjusted appropriately taking into consideration the performance and manufacturing efficiency of the target secondary battery 100. The number of windings is preferably 20 or more, and more preferably 25 or more. If the number of windings is large, the takt time of the wound electrode body 40 will have a significant impact on the productivity of the secondary battery 100. Therefore, it is particularly effective to apply the technology disclosed herein. The specific configuration of the wound electrode body 40 will be described below.

[0039] The positive electrode 10 may be the same as a conventional one and is not particularly limited. As shown in FIG. 7, the positive electrode 10 is a strip-shaped member. The positive electrode 10 includes a strip-shaped positive electrode core 12, and a positive electrode active material layer 14 and a protective layer 16 fixed to at least one surface of the positive electrode core 12. The positive electrode 10 preferably includes the positive electrode core 12 and the positive electrode active material layer 14. From the viewpoint of increasing capacity, the positive electrode active material layer 14 is preferably formed on both sides of the positive electrode core 12. The protective layer 16 is not essential and can be omitted in other embodiments. A metal foil having a predetermined conductivity can be preferably used for the positive electrode core 12. The positive electrode core 12 is preferably made of, for example, aluminum or an aluminum alloy.

[0040] In the positive electrode 10, a positive electrode tab 12t protrudes outward (to the left in FIG. 7) from one end side in the width direction TD. A plurality of positive electrode tabs 12t are provided at predetermined intervals in the longitudinal direction MD. The positive electrode tab 12t is a portion where the positive electrode active material layer 14 is not formed and where the positive electrode core 12 is exposed (current collector exposed portion). As shown in FIGS. 4 and 7, the plurality of positive electrode tabs 12t are stacked at one end (the left end in FIGS. 4 and 7) in the long side direction Y of the secondary battery 100 to form a positive electrode tab group 42.

[0041] As shown in FIG. 7, the positive electrode active material layer 14 is provided in a strip shape along the longitudinal direction MD of the positive electrode core 12. Here, the positive electrode active material layer 14 is formed on both sides of the positive electrode core 12 from the winding start end 10s to the winding end 10e of the positive electrode 10 in FIG. 6. The positive electrode active material layer 14 contains a positive electrode active material that can reversibly store and release charge carriers. The positive electrode active material layer 14 preferably contains a positive electrode active material, a binder, and a conductive material. The width W1 (see FIG. 7) of the positive electrode active material layer 14 may be approximately 100 to 400 mm, for example, 200 to 350 mm.

[0042] The positive electrode active material is a particulate material capable of reversibly absorbing and releasing charge carriers. The positive electrode active material preferably contains a lithium transition metal composite oxide. A suitable example of the lithium transition metal composite oxide is a lithium transition metal composite oxide represented by the general formula LiMO2 (where M is one or more transition metal elements other than Li). As the M, a lithium transition metal composite oxide containing at least one of Ni, Co, and Mn is preferred, and a lithium transition metal composite oxide containing Ni is particularly preferred.

[0043] The positive electrode binder may be a resin binder conventionally used as a positive electrode binder. Specific examples include vinyl halide resins such as polyvinylidene fluoride (PVdF) and polyalkylene oxides such as polyethylene oxide (PEO). The positive electrode binder may be made of PVdF. In addition to the positive electrode active material and the positive electrode binder, the positive electrode active material layer 14 may contain any component such as a conductive material, a dispersant, etc. Examples of conductive materials include carbon black such as acetylene black (AB) and ketjen black, activated carbon, graphite, carbon fiber, and other carbon materials.

[0044] The protective layer 16 is a layer configured to have lower electrical conductivity than the positive electrode active material layer 14. The protective layer 16 is provided in a region adjacent to the edge of the positive electrode 10 on the positive electrode tab 12t side. The protective layer 16 is formed in a strip shape along the longitudinal direction MD of the positive electrode 10. The provision of the protective layer 16 can prevent direct contact between the positive electrode core 12 and the negative electrode active material layer 24 and an internal short circuit when the separators 32, 34 are damaged. The protective layer 16 preferably contains insulating ceramic particles such as alumina. The protective layer 16 may contain a binder for fixing the ceramic particles to the surface of the positive electrode core 12. However, the protective layer is not an essential component and may be omitted in other embodiments.

[0045] The negative electrode 20 may be the same as a conventional one and is not particularly limited. As shown in FIG. 7, the negative electrode 20 is a strip-shaped member. The negative electrode 20 includes a strip-shaped negative electrode core 22 and a negative electrode active material layer 24 fixed to at least one surface of the negative electrode core 22. The negative electrode 20 preferably includes the negative electrode core 22 and the negative electrode active material layer 24. From the viewpoint of increasing capacity, the negative electrode active material layer 24 is preferably formed on both sides of the negative electrode core 22. For each member constituting the negative electrode 20, conventionally known materials that can be used in general secondary batteries (e.g., lithium-ion secondary batteries) can be used without particular limitation. For example, a metal foil having a predetermined conductivity can be preferably used for the negative electrode core 22. The negative electrode core 22 is preferably made of, for example, copper, a copper alloy, or the like.

[0046] In the negative electrode 20, a negative electrode tab 22t protrudes outward (to the right in FIG. 7 ) from one end side in the width direction TD. A plurality of negative electrode tabs 22t are provided at predetermined intervals in the longitudinal direction MD. The negative electrode tab 22t is a portion where the negative electrode active material layer 24 is not formed and where the negative electrode core 22 is exposed (current collector exposed portion). As shown in FIGS. 4 and 7 , the plurality of negative electrode tabs 22t are stacked at one end (the right end in FIGS. 4 and 7 ) in the long side direction Y of the secondary battery 100 to form a negative electrode tab group 44.

[0047] As shown in FIG. 7, the negative electrode active material layer 24 is provided in a strip shape along the longitudinal direction MD of the negative electrode substrate 22. Here, the negative electrode active material layer 24 is formed on both sides of the negative electrode substrate 22 from the winding start end 20s to the winding end 20e of the negative electrode 20 in FIG. 6. The negative electrode active material layer 24 contains a negative electrode active material capable of reversibly absorbing and releasing charge carriers. The negative electrode active material layer 24 preferably contains a negative electrode active material and a binder. From the viewpoint of charge carrier acceptance, the width W2 of the negative electrode active material layer 24 (see FIG. 7) is preferably equal to or longer than the width W1 of the positive electrode active material layer 14. In relation to the width W1 of the positive electrode active material layer 14, the width W2 of the negative electrode active material layer 24 is preferably 200 mm or more, more preferably 250 mm or more. Here, the negative electrode active material layer 24 covers the positive electrode active material layer 14 at both ends in the width direction TD.

[0048] The negative electrode active material is a particulate material that can reversibly absorb and release charge carriers in relation to the above-mentioned positive electrode active material. The negative electrode active material preferably contains graphite. However, the negative electrode active material may contain materials other than graphite. Specific examples of negative electrode active materials other than graphite include carbon materials such as hard carbon, soft carbon, and amorphous carbon, as well as silicon-based materials.

[0049] The negative electrode binder may be a resin binder conventionally used as a negative electrode binder. Specific examples include rubbers such as styrene butadiene rubber (SBR), celluloses such as carboxymethyl cellulose (CMC), and acrylic resins such as polyacrylic acid (PAA). The negative electrode binder may be composed of SBR and CMC. In addition to the negative electrode active material and the negative electrode binder, the negative electrode active material layer 24 may contain any component, such as a conductive material. As the conductive material, a carbon material such as one exemplified as an optional component that may be contained in the positive electrode active material layer 14 may be used.

[0050] A functional layer may be provided on the surface of the positive electrode 10 and / or the negative electrode 20. The functional layer is a layer that imparts desired functions (such as improvement in heat resistance, adhesiveness, strength, etc.) to the positive electrode 10 and / or the negative electrode 20. Preferred examples of the functional layer include a heat-resistant layer and an adhesive layer. For example, by providing a heat-resistant layer containing an inorganic filler and a binder on the surface of the positive electrode 10 and / or the negative electrode 20, the occurrence of an internal short circuit can be suppressed even when metal foreign matter is mixed in, and the safety of the secondary battery 100 can be improved. Further, according to the manufacturing method disclosed herein, the wound electrode body 40 can be efficiently manufactured while suppressing peeling of the functional layer.

[0051] As shown in FIG. 7, the first separator 32 and the second separator 34 are each strip-shaped members. The separators 32 and 34 are respectively disposed between the positive electrode 10 and the negative electrode 20. The separators 32 and 34 are each insulating sheets in which a plurality of fine through-holes through which charge carriers can pass are formed. By interposing the separators 32 and 34 between the positive electrode 10 and the negative electrode 20, contact between the positive electrode 10 and the negative electrode 20 can be prevented, and charge carriers (for example, lithium ions) can be moved between the positive electrode 10 and the negative electrode 20. The width W3 (see FIG. 7) of the separators 32 and 34 is preferably the same as or longer than the width W2 of the negative electrode active material layer 24. Here, the separators 32 and 34 cover the negative electrode active material layer 24 at both ends in the width direction TD. The width W1 of the positive electrode active material layer 14, the width W2 of the negative electrode active material layer 24, and the width W3 of the separators 32 and 34 satisfy the relationship W1 < W2 < W3.

[0052] The separators 32 and 34 may have the same configuration or different configurations. At least one of the separators 32 and 34 preferably includes a separator base material and one or more functional layers. The functional layer is formed on at least one surface of the separator base material, in other words, on the surface facing the positive electrode 10 and / or on the surface facing the negative electrode 20. The functional layer may be provided only on one surface of the separator base material, or may be provided on both surfaces respectively.

[0053] The separator substrate can be any of those used in conventional battery separators without any particular restrictions. The separator substrate is preferably a porous sheet-like member. The separator substrate may have a single-layer structure or a two- or more-layer, e.g., three-layer structure. The separator substrate is preferably made of a polyolefin resin. This ensures sufficient flexibility of the separators 32, 34 and makes it easier to fabricate the wound electrode assembly 40. As the polyolefin resin, polyethylene (PE), polypropylene (PP), or a mixture thereof is preferred, and PE is more preferred.

[0054] The functional layer is a layer that imparts a desired function to the separator substrate (e.g., improved heat resistance, adhesion, strength, etc.). Suitable examples of functional layers include a heat-resistant layer and an adhesive layer. The functional layer may be a layer with greater surface irregularities and fragility than the separator substrate, but the manufacturing method disclosed herein makes it possible to efficiently manufacture the wound electrode body 40 while suppressing peeling of the functional layer. In a preferred embodiment, the separators 32 and 34 each include a heat-resistant layer formed on one surface of the separator substrate and an adhesive layer formed on the other surface of the separator substrate. However, in other embodiments, for example, the heat-resistant layer and adhesive layer may be laminated in this order on one surface of the separator substrate, or the separator may not include a heat-resistant layer or an adhesive layer.

[0055] The heat-resistant layer contains an inorganic filler and a binder. The heat-resistant layer suppresses thermal shrinkage of the separators 32 and 34, contributing to improved safety of the secondary battery 100. Ceramic particles such as alumina, zirconia, boehmite, aluminum hydroxide, silica, and titania are preferred as inorganic fillers, and aluminum-containing compounds are particularly preferred from the viewpoint of suppressing thermal shrinkage of the separators 32 and 34. The inorganic filler may account for the largest mass percentage in the heat-resistant layer. Examples of binders for the heat-resistant layer include acrylic resins, fluorine-based resins, urethane resins, ethylene vinyl acetate resins, and epoxy resins. Acrylic resins are particularly preferred. The surface roughness Ra of the heat-resistant layer is typically greater than that of the separator substrate, and can be, for example, approximately 0.2 to 1.0 μm.

[0056] The heat-resistant layer preferably faces the positive electrode 10. The heat-resistant layer preferably abuts against the positive electrode 10 (typically the positive electrode active material layer 14). This preferably prevents the separators 32, 34 from thermally shrinking at high temperatures, and also allows gas generated inside the wound electrode body 40 to be smoothly discharged to the outside of the wound electrode body 40, for example, during initial charging or overcharging of the secondary battery 100.

[0057] The adhesive layer contains, for example, an adhesive layer binder at the highest mass ratio. The adhesive layer may further contain other materials (e.g., inorganic filler, etc.). Examples of adhesive layer binders include resins such as fluorine-based resins, acrylic resins, urethane resins, ethylene vinyl acetate resins, and epoxy resins. Among these, fluorine-based resins and acrylic resins are preferred because of their high flexibility. The adhesive layer binder may be the same as or different from the heat-resistant layer binder. The adhesive layer preferably faces the negative electrode 20. The adhesive layer preferably abuts against the negative electrode 20 (typically the negative electrode active material layer 24). In this case, the adhesive layer is bonded to the negative electrode 20, for example, by the press-molding step of the manufacturing method described below. This can suppress stacking misalignment. Furthermore, an increase in thickness of the flat portion 40f of the wound electrode body 40 after press-molding is suppressed, thereby suppressing the occurrence of springback.

[0058] <2. Secondary Battery Manufacturing Method> The secondary battery 100 described above can be manufactured by a manufacturing method including an electrode assembly fabrication step in which a flat wound electrode assembly 40 is fabricated using separators 32, 34 from the positive electrode 10 and the negative electrode 20. Other manufacturing processes may be the same as conventional methods. The manufacturing method disclosed herein may further include other steps at any stage. For example, after the electrode assembly fabrication step, a step of housing the wound electrode assembly 40 and an electrolyte solution in a battery case 50, or a step of sealing the battery case 50 may be included. In this embodiment, the electrode assembly fabrication step includes (1) a winding step and (2) a press-molding step, in this order. After the winding step or the press-molding step, a (3) drying step may further be included. This will be described in detail below with reference to FIGS. 8A to 8E.

[0059] (1) The winding process is a process for producing a cylindrical wound body (cylindrical body) including a strip-shaped positive electrode 10, a strip-shaped negative electrode 20, and strip-shaped separators 32 and 34. A winding device is used in this process. The strip-shaped positive electrode 10, the strip-shaped negative electrode 20, the strip-shaped first separator 32, and the strip-shaped second separator 34 are wound into reels and set in the winding device. The winding device includes, for example, a winding unit 200 as shown in FIG. 8A. The strip-shaped positive electrode 10, the strip-shaped negative electrode 20, the strip-shaped first separator 32, and the strip-shaped second separator 34 are transported to the winding unit 200 along a transport path (e.g., multiple rollers) not shown. A dancer roll mechanism for removing slack, a tensioner for adjusting tension, and the like are appropriately arranged on the transport path. As shown in FIG. 8A, the winding unit 200 has a winding core 210 and a rotation mechanism (not shown) that rotates the winding core 210.

[0060] Here, the winding core 210 has a substantially cylindrical outer shape and a substantially circular side surface as shown in FIG. 8A. However, in other embodiments, the winding core 210 may have a flat side surface. In such cases, the press molding step (2) described later may be omitted. Although not particularly limited, the diameter of the winding core 210 is, for example, approximately 50 to 100 mm, and in one example, 80 mm. The winding core 210 has a first portion 211 and a second portion 212 divided into semicircular shapes. A slit 213 is formed between the first portion 211 and the second portion 212 so as to pass through the axis of the winding core 210. The length of the slit 213 is the same as the diameter of the winding core 210. The width of the slit 213 is formed so that the separators 32 and 34 can be inserted therethrough. Here, the winding core 210 is configured so that the separators 32 and 34 in the slit 213 are attracted and fixed in place by an electrostatic chuck. The electrostatic chuck is configured so that it can be switched on and off by a control device (not shown).

[0061] The winding core 210 further has a suction mechanism that adsorbs components (e.g., separators 32, 34) supported on the winding core 210 to the winding core 210. Although not shown in the figures, in this embodiment, a plurality of suction holes are formed in the side surface of the winding core 210 (specifically, the arc portions of the first portion 211 and the second portion 212). The suction mechanism is configured to include, for example, a suction fan, and to suck air above the winding core 210 through the suction holes, thereby adsorbing and holding the components supported on the winding core 210 to the winding core 210. The suction mechanism is configured to be switchable between ON and OFF by a control device (not shown).

[0062] The rotation mechanism is connected to a control device (not shown) and is configured to rotate the winding core 210 around its axis in a predetermined rotation direction (counterclockwise in this case, the direction of the arrow in FIG. 8B) at a predetermined rotation speed. The rotation mechanism is, for example, a rotary motor, and is configured so that the control device (not shown) can switch the rotation mechanism on and off and control the rotation speed.

[0063] In this embodiment, the winding process includes, in this order, a holding process (step S1), a first winding process (step S2), an arrangement process (step S3), and a second winding process (step S4). Figure 8A is an explanatory diagram of the holding process, Figure 8B is an explanatory diagram of the first winding process, Figure 8C is an explanatory diagram of the arrangement process, and Figure 8D is an explanatory diagram of the second winding process.

[0064] In the holding step (step S1), as shown in FIG. 8A, the first separator 32 and the second separator 34 are held on the winding core 210. In this embodiment, first, the winding start end 32s of the first separator 32 and the winding start end 34s of the second separator 34 are aligned, and the start ends of the first separator 32 and the second separator 34 are passed through the slit 213 of the winding core 210. In other words, the separators 32 and 34 are sandwiched between the first portion 211 and the second portion 212 of the winding core 210. Note that here, the first separator 32 is disposed on the inside (toward the winding core 210), and the second separator is disposed on the outside (above the first separator 32). At this time, the starting end of the first separator 32 and the starting end of the second separator 34 pass through the slit 213 and protrude a predetermined length from the slit 213. The separators 32 and 34 inside the slit 213 are attracted and fixed to the winding core 210 by an electrostatic chuck.

[0065] The portions protruding from the slit 213 are then bent in the direction opposite to the rotation direction of the winding core 210 (clockwise in this case) and curved along the second portion 212 of the winding core 210. As a result, a first bending point P1 and a second bending point P2 are formed at the starting ends of the separators 32, 34, and the separators are bent into a Z shape. In this embodiment, as shown in FIG. 8A , the starting end of the first separator 32 and the starting end of the second separator 34 cover approximately half of the arc of the second portion 212. The separators 32, 34 wound around the winding core 210 are suction-fixed to the winding core 210 by a suction mechanism. In this manner, the separators 32, 34 are held by the winding core 210.

[0066] In the first winding step (step S2), as shown in FIGS. 8B and 9, the winding core 210 is rotated at a first rotation speed V1 in a predetermined rotation direction (counterclockwise in this case, the direction of the arrow in FIG. 8B) while the strip-shaped first separator 32 and the strip-shaped second separator 34 are being supplied. This causes the first separator 32 and the second separator 34 to be wound around the winding core 210 by a predetermined length. This step may be equivalent to the conventional "initial separator winding step." While not particularly limited, the first rotation speed V1 (the fastest rotation speed in this step (in the graph in FIG. 9)) is preferably set to, for example, 150 to 1500 rpm.

[0067] In the arrangement step (step S3), as shown in FIG. 8C , first, the winding core 210 is stopped by the control device (i.e., V2 = 0) or rotated at a second rotation speed V2 slower than the first rotation speed V1. By slowing the rotation speed of the winding core 210 compared to the first winding step, it is possible to suppress stacking misalignment (misalignment) between the positive electrode 10 and the negative electrode 20, thereby producing a highly reliable wound electrode body 40. Furthermore, when inserting the positive electrode 10 and / or the negative electrode 20, for example, it is possible to prevent a situation in which the surfaces of the separators 32, 34 rub strongly against the surfaces of the positive electrode 10 and / or the negative electrode 20, causing, for example, part of the functional layer to fall off. In a preferred embodiment, it is more preferable to stop the winding core 210 (V2 = 0). Although not particularly limited, when the winding core 210 is rotated, it is preferable that the second rotation speed V2 (the fastest rotation speed in this step) is a low speed of, for example, 20 rpm or less. The second rotation speed V2 can be set to, for example, 1 to 10 rpm, or even 1 to 5 rpm.

[0068] Then, when the rotation speed of the winding core 210 decreases (preferably when the winding core 210 stops), the strip-shaped positive electrode 10 and the strip-shaped negative electrode 20 are inserted approximately simultaneously. In other words, the winding of the positive electrode 10 and the negative electrode 20 begins with a single decrease or stop of the rotation speed of the winding core 210. Specifically, the winding start end 20s of the negative electrode 20 is positioned so that the negative electrode 20 is positioned on the inner circumferential surface of the first separator 32 (the surface facing the winding core 210). In addition, the winding start end 10s of the positive electrode 10 is positioned between the outer circumferential surface of the first separator 32 (the surface opposite the winding core 210) and the second separator 34. In this way, by using a winding method in which the negative electrode 20 is arranged on the inner circumferential side of the first separator 32 and the positive electrode 10 is sandwiched between the outer circumferential surface of the first separator 32 and the inner circumferential surface of the second separator 34, and the negative electrode 20 is wound around the positive electrode 10, the negative electrode 20 is positioned more inner than the positive electrode 10. This makes it possible to wind the positive electrode 10 and the negative electrode 20 around the winding core 210 at approximately the same time.

[0069] In addition, as shown in Figure 8C, by shifting the insertion position of the winding starting end 20s of the negative electrode 20 from the insertion position of the winding starting end 10s of the positive electrode 10, the winding direction distance Ds between the winding starting end 10s of the positive electrode 10 and the winding starting end 20s of the negative electrode 20 can be adjusted.

[0070] In this specification, the term "substantially simultaneously" is a term that allows for slight deviations due to, for example, human or mechanical errors, etc. Specifically, the term encompasses cases where the placement of the positive electrode 10 and the placement of the negative electrode 20 are simultaneous (within 0.05 seconds) and cases where there is a slight deviation of about 0.05 to 0.3 seconds.

[0071] In the second winding step (step S4), as shown in FIGS. 8D and 9, the winding core 210 is rotated at a third rotation speed V3 faster than the first rotation speed V1 while supplying the strip-shaped positive electrode 10 and the strip-shaped negative electrode 20. This causes the positive electrode 10 and the negative electrode 20 to be wound around the winding core 210. This step may correspond to the conventional "main winding step." Although not particularly limited, the third rotation speed V3 (the fastest rotation speed in this step (in the graph of FIG. 9)) is preferably faster than the first rotation speed V1 and the second rotation speed V2. The third rotation speed V3 is preferably, for example, 500 to 1500 rpm.

[0072] After the positive electrode 10 and the negative electrode 20 are wound around the winding core 210 a predetermined number of times in this manner, the winding end 10e of the positive electrode 10, the winding end 20e of the negative electrode 20, and the winding end 32e, 34e of the separators 32, 34 are each cut using a cutter or the like. At this time, it is preferable to adjust the winding end 20e of the negative electrode 20 so that it is located closer to the winding end than the winding end 10e of the positive electrode 10, and further, the winding end 32e, 34e of the separators 32, 34 are located closer to the winding end than the winding end 20e of the negative electrode 20. It is also preferable to align the winding end 32e of the first separator 32 and the winding end 34e of the second separator 34. Then, a stop tape 48 (see FIG. 6) is attached to the winding end 32e of the first separator 32 and the winding end 34e of the second separator 34. In this manner, a cylindrical body is produced.

[0073] As described above, the manufacturing method disclosed herein (1) enables the number of times that the rotation of the winding core 210 is slowed or stopped in the winding step to be reduced from two times in the conventional method to one time. In other words, the method does not include a step of accelerating and then decelerating the rotation speed of the winding core 210 between the timing of placing the positive electrode 10 and the timing of placing the negative electrode 20. Therefore, for example, the conventional initial negative electrode winding step can be omitted. This shortens the takt time of the winding step, enabling the efficient manufacture of a highly reliable wound electrode body 40 in which lamination misalignment and the like are suppressed. This in turn improves the productivity of the secondary battery 100.

[0074] (2) In the press-molding step, the cylindrical body prepared as described above is press-molded into a flat shape as shown in FIG. 6 and other figures. The press-molding conditions (e.g., pressure, holding time, etc.) are design factors that can be appropriately adjusted depending on, for example, the number of windings of the wound electrode body 40 and the properties of the separator (presence or absence and configuration of a functional layer). The press-molding may be performed at room temperature or while heating (at a high temperature). By the press-molding, a positive electrode tab group 42 in which positive electrode tabs 12t are stacked is formed at one end of the wound electrode body 40 in the width direction Y, and a negative electrode tab group 44 in which negative electrode tabs 22t are stacked is formed at the other end. Then, a reaction portion in which the positive electrode active material layer 14 and the negative electrode active material layer 24 face each other is formed at the center of the width direction Y of the wound electrode body 40, over a length of width W1. In this manner, a wound electrode body 40 including the positive electrode 10, the negative electrode 20, and the separators 32, 34 is produced.

[0075] In this embodiment, the separators 32, 34 have an adhesive layer on the surface facing the negative electrode 20. Therefore, the adhesive layer of the separators 32, 34 is bonded to the negative electrode 20 by press molding. Specifically, when the cylindrical body is crushed during press molding, a large pressure is applied to each of the positive electrode 10, the negative electrode 20, and the separators 32, 34 located on the flat portion 40f. As a result, the adhesive layer is pressed and deformed to fit the surface of the negative electrode active material layer 24, and the separators 32, 34 and the negative electrode 20 are bonded (press-bonded) together.

[0076] (3) In the drying step, moisture contained in the wound electrode body 40 is removed. As the drying method, for example, conventionally known methods such as ventilation drying, heat drying, vacuum drying, etc. can be appropriately used. When heat drying is used, it is preferable to set the heating temperature to 120°C or less from the viewpoint of suppressing thermal shrinkage of the separators 32, 34 (particularly thermal shrinkage of the separator substrate).

[0077] <3. Uses of secondary batteries> The secondary battery 100 can be used for various purposes, but can be suitably used, for example, as a power source (driving power source) for a motor mounted on a vehicle such as a passenger car, truck, etc. The type of vehicle is not particularly limited, but examples include a plug-in hybrid electric vehicle (PHEV), a hybrid electric vehicle (HEV), and a battery electric vehicle (BEV).

[0078] Although several embodiments of the present invention have been described above, the above embodiments are merely examples. The present invention can be implemented in various other forms. The present invention can be implemented based on the contents disclosed in this specification and the common general technical knowledge in the relevant field. The technology described in the claims includes various modifications and alterations of the above-exemplified embodiments. For example, it is possible to replace part of the above-described embodiments with other modified embodiments, and it is also possible to add other modified embodiments to the above-described embodiments. Furthermore, if a technical feature is not described as essential, it may be deleted as appropriate.

[0079] As described above, specific aspects of the technology disclosed herein include those described in the following sections. Item 1: A method for manufacturing a secondary battery including a wound electrode body formed by stacking and winding a strip-shaped first separator, a strip-shaped positive electrode, a strip-shaped second separator, and a strip-shaped negative electrode, the method comprising: a holding step of holding the first separator and the second separator on a winding core; a first winding step of rotating the winding core at a first rotation speed after the holding step and winding the first separator and the second separator around the winding core; and a second winding step of rotating the winding core at a first rotation speed after the first winding step. a positioning step of positioning a winding start end of the negative electrode so that the negative electrode is positioned on the inner circumferential side of the first separator and positioning a winding start end of the positive electrode between the outer circumferential surface of the first separator and the second separator while the first separator is rotated at a second rotation speed slower than the first rotation speed or while the second separator is stopped; and a second winding step of winding the positive electrode and the negative electrode around the winding core at a third rotation speed faster than the first rotation speed after the positioning step. Item 2: The manufacturing method according to item 1, wherein at least one of the first separator and the second separator comprises a separator substrate and a functional layer provided on at least one surface of the separator substrate. Item 3: The manufacturing method according to item 1 or 2, wherein when the wound electrode body is viewed from the winding axis direction, the first separator and the second separator form a Z-shape in the winding start end region. Item 4: The manufacturing method according to any one of Items 1 to 3, wherein the winding start end of the first separator and the winding start end of the second separator are aligned. Item 5: The manufacturing method according to any one of Items 1 to 4, wherein the winding end of the first separator and the winding end of the second separator are aligned. Item 6: The manufacturing method according to any one of Items 1 to 5, wherein the distance between the winding start end of the positive electrode and the winding start end of the negative electrode in the winding direction is 20 mm or less. [Explanation of symbols]

[0080] 10 positive electrode 20 negative electrode 32, 34 Separator 40 Wound electrode body 50 Battery Case 100 Secondary battery 200 Winding unit 210 Roll Core 211 Part 1 212 Part 2 213 Slit P1 1st bending point P2 2nd bending point P3 3rd bending point P4 4th bending point

Claims

1. A method for manufacturing a secondary battery including a wound electrode body formed by stacking and winding a strip-shaped first separator, a strip-shaped positive electrode, a strip-shaped second separator, and a strip-shaped negative electrode, a holding step of holding the first separator and the second separator on a winding core; a first winding step of rotating the winding core at a first rotation speed after the holding step and winding the first separator and the second separator around the winding core; an arrangement step of, after the first winding step, arranging a winding start end of the negative electrode so that the negative electrode is arranged on the inner circumferential side of the first separator, and arranging a winding start end of the positive electrode between an outer circumferential surface of the first separator and the second separator, while rotating the winding core at a second rotation speed slower than the first rotation speed or while stopping the winding core; a second winding step of winding the positive electrode and the negative electrode around the winding core at a third rotation speed that is faster than the first rotation speed after the disposing step; Including, In the placing step, the negative electrode is supplied to the inner peripheral side of the first separator above a center line that passes through the axis of the winding core and extends horizontally, in a direction that slopes downward as it approaches the winding core, The positive electrode is supplied between the outer peripheral surface of the first separator and the second separator above a center line that passes through the axis of the winding core and extends horizontally, in a direction that slopes downward as it approaches the winding core. A method for manufacturing a secondary battery.

2. In the arranging step, the positive electrode is supplied from above the negative electrode toward the winding core. The method of claim 1.

3. In the arranging step, the timing of arranging the negative electrode on the inner peripheral side of the first separator and the timing of arranging the positive electrode between the outer peripheral surface of the first separator and the second separator are simultaneous or delayed by 0.05 seconds or less. The method according to claim 1 or 2.

4. In the arranging step, a distance between an insertion position of the winding start end of the negative electrode and an insertion position of the winding start end of the positive electrode is 20 mm or less in the winding direction. The method according to claim 1 or 2.

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