JP6738565B2 - Electric storage element and method for manufacturing electric storage element - Google Patents

Description

The present invention relates to a power storage element including an electrode body that is wound in a state where a positive electrode and a negative electrode are overlapped with each other, and a method for manufacturing the power storage element.

Conventionally, a secondary battery including an electrode body in which a positive electrode sheet and a negative electrode sheet are wound in a laminated state is known (see Patent Document 1). In this secondary battery, the positive electrode sheet may have a coated portion coated with an electrode active material on both sides in the thickness direction of the sheet, and an uncoated portion not coated with the electrode active material. There is. The coated portion and the uncoated portion are arranged side by side in the width direction of the positive electrode sheet. Further, the negative electrode sheet has a coated portion and an uncoated portion, like the positive electrode sheet.

In the above secondary battery, in order to secure the battery capacity, the negative electrode sheet is usually longer than the positive electrode sheet, and the positive electrode sheet and the negative electrode sheet are wound when wound together with the positive electrode sheet. It is located on the innermost and outermost circumferences. The innermost peripheral end and the outermost peripheral end in the longitudinal direction of the negative electrode sheet extend so as to protrude from the corresponding edge of the positive electrode sheet. That is, in the electrode body, the longitudinal end portion of the negative electrode sheet does not face the positive electrode sheet.

In such a secondary battery (for example, a lithium secondary battery), the potential of the other portion (the portion facing the positive electrode sheet) excluding the end portion in the negative electrode sheet decreases during charging, Since the potential of the end portion is maintained, a potential difference is generated between the end portion (the portion that does not face the positive electrode sheet) and the other portion. Therefore, in the negative electrode, the lithium ions in the other portion move to the end portion, and the number of lithium ions in the other portion that contributes to charge/discharge is reduced. This decrease in the number of lithium ions becomes remarkable as the charge and discharge are repeated, and as a result, the capacity of the secondary battery is greatly reduced, that is, the capacity of the secondary battery deteriorates.

JP, 2005-56257, A

Therefore, it is an object of the present invention to provide a power storage element with suppressed capacity deterioration and a method for manufacturing the power storage element.

The electricity storage device according to the present invention is
A strip-shaped positive electrode and a negative electrode are provided with an electrode body having a wound body wound in a state of overlapping,
The negative electrode has a sheet-shaped conductive portion and an active material layer overlapping the conductive portion, and is located at the innermost and outermost circumferences of the wound body,
At least one end of the innermost peripheral end and the outermost peripheral end in the winding direction of the negative electrode extends in the winding direction from the corresponding edge of the positive electrode,
The end of the negative electrode extending from the corresponding edge has the active material layer thinner than the active material layer of the other portion of the negative electrode on the surface of the conductive portion facing the corresponding edge. Or, it does not have the active material layer.

According to this structure, the active material layer at the end of the negative electrode (the part extending from the corresponding edge of the positive electrode, that is, the part not facing the positive electrode) is thin or has no active material layer, so that the storage element is charged. During discharge, even if a potential difference occurs between the end portion and the other portion (a portion facing the positive electrode), the number of ions that can move from the other portion to the end portion is suppressed. As a result, it is possible to suppress the capacity deterioration of the storage element due to the movement of ions in the negative electrode.

When the negative electrode has an active material layer thinner than the active material layer of the other portion on the surface of the conductive portion of the end facing the corresponding edge side, the active material on the surface Since the rigidity of the end portion of the negative electrode is higher than that in the case where there is no layer, it is possible to suppress a deviation from a planned position or a short circuit due to bending of the end portion.

Further, in the electric storage element,
An end portion extending from the corresponding edge is provided on the innermost peripheral side portion and the outermost peripheral side portion of the negative electrode,
The negative electrode is a range on the inwardly facing surface of the conductive portion of the innermost peripheral side portion, and reaches a position sandwiched by the positive electrode from the innermost peripheral side edge in the winding direction. And a range on the outermost surface of the conductive portion of the outermost peripheral side portion, from the edge of the outermost peripheral side in the winding direction to the position sandwiched by the positive electrode In the range, the active material layer may be thinner than the active material layer in the other portion, or may not be provided.

According to such a configuration, in the negative electrode, the conductive portion on the innermost (inner side of the winding) side of the conductive portion of the innermost peripheral portion (the portion not facing the positive electrode) and on the outermost peripheral portion. Has a thinner active material layer than the active material layer of the portion facing the positive electrode on the surface (the portion not facing the positive electrode) facing the outside (the side opposite to the winding center). Therefore, at the time of charging/discharging the storage element, the potential difference between the innermost peripheral side portion and the outermost peripheral side portion of the negative electrode and the portion excluding the innermost peripheral side portion and the outermost peripheral side portion. Even if occurs, the movement of ions to the innermost peripheral portion and the outermost peripheral portion is suppressed. As a result, the capacity deterioration of the storage element due to the movement of the ions can be suppressed more effectively.

Further, in the electric storage element,
The end portion of the negative electrode extending from the corresponding end portion of the positive electrode may have the active material layer, which is thinner than the active material layer in other portions of the negative electrode, on both surfaces of the conductive portion.

According to this configuration, since the active material layer is thinner than the active material layer of the other portion on both surfaces of the conductive portion at the end of the negative electrode, respectively, there is no active material layer on both surfaces or The rigidity of the end portion of the negative electrode is higher than that in the case where the thin active material layer is provided only on one surface, and thereby, it is possible to more reliably suppress a shift from a planned position or a short circuit due to bending of the end portion. You can

In addition, the method for manufacturing the electricity storage device according to the present invention,
A thin-walled portion provided at an intermediate position in the longitudinal direction in a strip-shaped negative electrode having a sheet-shaped conductive portion and an active material layer that overlaps the conductive portion, and a thin portion of another portion of the negative electrode on the surface of the conductive portion. Cutting a thin portion having an active material layer thinner than an active material layer or having no active material layer along the lateral direction of the negative electrode,
A state in which the thin portion that constitutes the longitudinal end portion of the negative electrode after the cutting extends in the longitudinal direction from at least one of the one end edge and the other end edge in the longitudinal direction of the strip-shaped positive electrode. And stacking the positive electrode and the negative electrode, and winding the stacked positive electrode and negative electrode from the one edge side.

According to such a configuration, it is possible to obtain a power storage element in which the capacity deterioration due to the movement of ions from the part of the negative electrode facing the positive electrode to the part not facing the positive electrode during charging and discharging is suppressed. Specifically, it is as follows.

According to the above configuration, at least one end of the innermost peripheral end and the outermost peripheral end in the winding direction of the negative electrode extends in the winding direction from the corresponding edge of the positive electrode, and the negative electrode An electrode having an active material layer which is thinner than the active material layer of the other part of the negative electrode on the surface of the conductive portion of the end portion extending from the corresponding edge facing the corresponding edge side, or having no active material layer. An electric storage element having a body is obtained. In this electricity storage device, the active material layer at the end of the negative electrode (the portion extending from the corresponding edge of the positive electrode, that is, the portion not facing the positive electrode) of the electrode body is thin or has no active material layer. Even when a potential difference is generated between the end portion and the other portion (the portion facing the positive electrode) during charge/discharge of the element, the number of ions that can move from the other portion to the end portion is suppressed. To be This suppresses the capacity deterioration of the storage element due to the movement of the ions.

Further, in the method of manufacturing the storage element,
The negative electrode may have an uncoated portion of the active material layer that is continuous in the longitudinal direction.

When the negative electrode having a non-covered portion continuous in the longitudinal direction is cut in the width direction, the total thickness of the negative electrode changes at the boundary between the portion where the active material layer is formed and the non-covered portion. Burrs and chips near the boundary between the portion where the active material layer is formed and the non-covered portion (specifically, burrs and chips caused by the difference between the stress applied to the portion where the active material layer is formed and the stress applied to the non-covered portion). Powder) is easily generated. However, according to the above configuration, a change in the total thickness of the negative electrode at the boundary between the non-covered portion and the portion other than the non-covered portion is cut by cutting the thin-walled portion that is reduced by thinning or eliminating the active material layer. It is possible to suppress the generation of the burr and cutting chips at the time of performing. That is, when the active material layer is thick, the change in the total thickness of the negative electrode at the boundary between the portion where the active material layer is formed and the uncovered portion is large, so that burrs and cutting chips of the conductive portion are easily generated when the negative electrode is cut. However, by suppressing the thickness dimension of the active material layer at the cut portion or eliminating the active material layer as in the above configuration, it is possible to suppress the generation of burrs and chips of the conductive portion at the time of cutting.

in this case,
When the active material layer of the negative electrode contains a component having a Vickers hardness higher than that of the conductive portion, the effect of suppressing the generation of burrs and chips in the conductive portion during cutting of the negative electrode becomes more remarkable.

That is, when the active material layer contains a component having a Vickers hardness larger than that of the conductive portion, the conductive portion is pushed by the component when the negative electrode is cut, so that burrs and chips are more likely to be generated, but the active material layer By suppressing the thickness of the active material layer, generation of burrs and cutting chips in the conductive portion at the time of cutting can be effectively suppressed even when the active material layer contains the component.

As described above, according to the present invention, it is possible to provide a power storage element with suppressed capacity deterioration and a method for manufacturing the power storage element.

FIG. 1 is a perspective view of a power storage element according to this embodiment. FIG. 2 is a sectional view taken along the line II-II in FIG. FIG. 3 is an exploded perspective view of the storage element. FIG. 4 is a perspective view showing a configuration of an electrode body of the storage element. FIG. 5 is a cross-sectional view of a positive electrode forming the electrode body. FIG. 6 is a cross-sectional view of a negative electrode forming the electrode body. FIG. 7 is a schematic diagram for explaining a structure of a wound body that constitutes the electrode body and a positive electrode and a negative electrode that constitute the wound body. FIG. 8 is a perspective view of a current collector of the storage element. FIG. 9 is a perspective view of a pair of clip members in the electricity storage device. FIG. 10 is a perspective view of the pair of clip members. FIG. 11 is a sectional view taken along line XI-XI of FIG. FIG. 12 is a sectional view for explaining the negative electrode before being cut into a predetermined length. FIG. 13 is a diagram showing a positional relationship between the positive electrode and the negative electrode in a stacked state before winding. FIG. 14 is a flowchart of the method for manufacturing the electric storage device. FIG. 15 is a cross-sectional view for explaining the negative electrode before being cut into a predetermined length in another embodiment. FIG. 16 is a perspective view of a power storage device including the power storage element.

Hereinafter, an embodiment of a power storage device according to the present invention will be described with reference to FIGS. 1 to 14. The power storage element includes a primary battery, a secondary battery, a capacitor, and the like. In the present embodiment, a chargeable/dischargeable secondary battery will be described as an example of a power storage element. It should be noted that the names of the respective constituent members (respective constituent elements) of the present embodiment are those of the present embodiment and may differ from the names of the respective constituent members (respective constituent elements) of the background art.

The electricity storage device of this embodiment is a non-aqueous electrolyte secondary battery. More specifically, the power storage element is a lithium-ion secondary battery that utilizes electron transfer that occurs as lithium ions move. This type of power storage element supplies electric energy. The electric storage element is used alone or in plural. Specifically, the storage element is used alone when the required output and the required voltage are small. On the other hand, the power storage element is used in the power storage device in combination with another power storage element when at least one of the required output and the required voltage is large. In the power storage device, a power storage element used in the power storage device supplies electric energy.

As shown in FIGS. 1 to 4, the power storage element includes an electrode body 2 having a wound body 22 in which a strip-shaped positive electrode 23 and a strip-shaped negative electrode 24 are wound in an overlapping state. In addition, the electricity storage device 1 of the present embodiment also includes a case 3 that houses the electrode body 2, an external terminal 4 that is arranged outside the case 3, and a current collector 5 that conducts the electrode body 2 and the external terminal 4 to each other. Have.

The electrode body 2 is a winding body 22 in which a winding core 21, a positive electrode 23, and a negative electrode 24 are wound in a state of being insulated from each other, and is wound (arranged) around the winding core 21. And a body 22. In the electrode body 2, lithium ions move between the positive electrode 23 and the negative electrode 24, so that the storage element 1 is charged and discharged.

The winding core 21 is usually made of an insulating material. The winding core 21 has a tubular shape. The winding core 21 of the present embodiment has a flat tubular shape. The winding core 21 is formed by winding a flexible or thermoplastic sheet.

The sheet is made of synthetic resin and has resistance to an electrolytic solution. The sheet is made of, for example, polypropylene (PP), polyethylene (PE), polyphenylene sulfide (PPS), polyethylene terephthalate (PET). The thickness of the sheet is, for example, 50 μm to 200 μm.

The wound body 22 is formed by winding the positive electrode 23 and the negative electrode 24 around the winding core 21 in a stacked (overlapping) state.

As shown in FIGS. 4 and 5, the positive electrode 23 has a sheet-shaped conductive portion 231 and a positive electrode active material layer 232 overlapping the conductive portion 231. In the positive electrode 23 of the present embodiment, the conductive portion 231 is a strip-shaped metal foil, and the positive electrode active material layer 232 is formed (laminated) on both surfaces of the metal foil 231. The metal foil 231 is, for example, an aluminum foil. The positive electrode 23 has an uncovered portion (that is, a portion not having the positive electrode active material layer 232) 233 of the positive electrode active material layer 232 at one edge portion in the width direction which is the lateral direction of the strip shape. The non-covered portion 233 continuously extends in the longitudinal direction of the positive electrode 23. In FIG. 5, the thicknesses of the metal foil 231 and the positive electrode active material layer 232 are exaggerated. Further, hereinafter, a portion of the positive electrode 23 where the positive electrode active material layer 232 is formed (that is, a portion having the positive electrode active material layer 232) is referred to as a covering portion 234.

The positive electrode active material layer includes a positive electrode active material and a binder.

The positive electrode active material is, for example, lithium metal oxide. Specifically, the positive electrode active material is, for example, a composite oxide (LiaCoyO2, LiaNixO2, LiaMnzO4, LiaNixCoyMnzO2, etc.) represented by LiaMebOc (Me represents one or more transition metals), LiaMeb(XOc)d( Me represents one or more transition metals, and X represents a polyanion compound represented by, for example, P, Si, B, and V (LiaFebPO4, LiaMnbPO4, LiaMnbSiO4, LiaCobPO4F, etc.). The positive electrode active material of this embodiment is LiNi1/3Co1/3Mn1/3O2.

The binder used in the positive electrode active material layer is, for example, polyvinylidene fluoride (PVdF), a copolymer of ethylene and vinyl alcohol, polymethyl methacrylate, polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, polymethacryl. Acid, styrene-butadiene rubber (SBR). The binder of this embodiment is polyvinylidene fluoride.

The positive electrode active material layer may further include a conductive additive such as Ketjen Black (registered trademark), acetylene black, or graphite. The positive electrode active material layer of this embodiment has acetylene black as a conductive additive.

As shown in FIGS. 4, 6 and 7, the negative electrode 24 has a sheet-shaped conductive portion 241 and a negative electrode active material layer (active material layer) 242 overlapping the conductive portion 241. The negative electrode 24 is located at the innermost circumference and the outermost circumference of the wound body 22. That is, the negative electrode 24 is longer than the positive electrode 23. At least one of the innermost end 245 and the outermost end 246 in the winding direction of the negative electrode 24 is arranged in the winding direction from the corresponding end edge (longitudinal end) 235A, 236A of the positive electrode 23. It is extended. The innermost end portion 245 of the negative electrode 24 of the present embodiment is arranged in the winding direction from the innermost end edge 235A of the positive electrode 23 located outside the winding body 22 (on the side opposite to the winding core 21). The end portion 246 that extends (is protruding) and is located on the outermost peripheral side is wound from the outermost peripheral edge (longitudinal edge) 236A of the positive electrode 23 located inside the winding body 22 (on the winding core 21 side). It extends in the turning direction (protrudes). That is, the end portion 245 of the negative electrode 24 extending from the innermost peripheral edge 235A of the positive electrode 23 is provided at the innermost peripheral side portion of the negative electrode 24, and the outermost peripheral edge 236A of the positive electrode 23 of the negative electrode 24 is provided. The extended end portion 246 is provided at the outermost peripheral side portion of the negative electrode 24. In FIG. 6, the thicknesses of the conductive portion 241 and the negative electrode active material layer 242 are exaggerated.

In the negative electrode 24 of the present embodiment, the conductive portion 241 is a strip-shaped metal foil, and the negative electrode active material layer 242 is formed (laminated) on both surfaces of the metal foil 241. The metal foil 241 is, for example, a copper foil. The negative electrode 24 has a non-covered portion of the negative electrode active material layer 242 (that is, a negative electrode active material layer) at the other edge (the side opposite to the non-coated portion 233 of the positive electrode 23) in the width direction which is the lateral direction of the strip shape. (A part not having 242) 243. The non-covered portion 243 continuously extends in the longitudinal direction of the negative electrode 24. The width of the coating portion (portion having the negative electrode active material layer 242) 244 of the negative electrode 24 is larger than the width of the coating portion 234 of the positive electrode 23.

The end portions 245, 246 of the negative electrode 24 are thinner on the surface of the metal foil 241 facing the corresponding edges 235A, 236A of the positive electrode 23 than the negative electrode active material layer 242 of the other part of the negative electrode 24 ( Hereinafter, it is also referred to as a "thin layer portion") 242A. That is, the end portion 245 on the innermost peripheral side of the negative electrode 24 of the present embodiment has the thin layer portion 242A at the portion facing outward (specifically, on the outer surface of the metal foil 241), and the outermost peripheral side thereof. The end portion 246 has a thin layer portion 242A on a portion facing inward (specifically, on a surface facing the inside of the metal foil 241). In FIG. 7, the thicknesses of the metal foils 231, 241, the positive electrode active material layer 232, the negative electrode active material layer 242, and the thin layer portion 242A are exaggerated.

The negative electrode 24 is a range on the innermost surface of the metal foil 241 on the innermost peripheral side, and is sandwiched between the innermost peripheral edge 245A in the winding direction and the positive electrode 23 in the wound body 22. The thin layer portion 242A is provided in the range up to the position where it is reached. The negative electrode 24 is a range on the outermost surface of the metal foil 241 at the innermost peripheral side, and is sandwiched between the positive electrode 23 in the wound body 22 from the outermost peripheral edge 246A in the winding direction. The thin layer portion 242A is provided in the range up to the position where it is reached.

In the wound body 22 of the present embodiment, the innermost end 245 of the negative electrode 24 extends slightly in the winding direction from the corresponding edge 235A of the positive electrode 23 on the surface of the metal foil 241 facing outward. A thin layer portion 242A is provided from the protruding (protruding) position to the edge 245A. Further, on the surface of the end portion 246 on the outermost peripheral side of the negative electrode 24 facing inward in the metal foil 241, the edge from a position slightly extending (protruding) in the winding direction from the corresponding edge 236A of the positive electrode 23. The thin layer portion 242A is provided up to 246A.

The negative electrode 24 may have a configuration without the thin layer portion 242A, that is, a configuration in which the metal foil 241 at that portion of the negative electrode 24 is not covered by the negative electrode active material layer 242 and the thin layer portion 242A.

The negative electrode active material layer 242 includes a negative electrode active material and a binder. The negative electrode active material layer 242 of the present embodiment contains a component having a Vickers hardness higher than that of the metal foil 241.

The negative electrode active material causes an alloying reaction with carbon materials such as graphite, non-graphitizable carbon (hard carbon), and easily graphitizable carbon, or lithium ions such as silicon (Si) and tin (Sn). It is a material. The negative electrode active material of this embodiment is non-graphitizable carbon.

The binder used for the negative electrode active material layer is the same as the binder used for the positive electrode active material layer. The binder of this embodiment is polyvinylidene fluoride.

The negative electrode active material layer may further include a conductive additive such as Ketjen Black (registered trademark), acetylene black, or graphite. The negative electrode active material layer of this embodiment does not have a conductive additive.

As shown in FIG. 4, in the wound body 22 of the present embodiment, the positive electrode 23 and the negative electrode 24 configured as described above are wound in a state of being insulated by the separator 25. That is, in the wound body 22, the positive electrode 23, the negative electrode 24, and the separator 25 are wound in a stacked state. The separator 25 is a member having an insulating property. The separator 25 is arranged between the positive electrode 23 and the negative electrode 24. Thereby, in the electrode body 2 (specifically, the wound body 22), the positive electrode 23 and the negative electrode 24 are insulated from each other. Further, the separator 25 holds the electrolytic solution in the case 3. As a result, during charging/discharging of the storage element 1, lithium ions move between the positive electrodes 23 and the negative electrodes 24 that are alternately stacked with the separator 25 in between.

The separator 25 has a strip shape. The separator 25 is made of, for example, a porous film of polyethylene, polypropylene, cellulose, polyamide or the like. The separator 25 may be formed by providing an inorganic layer containing inorganic particles such as SiO2 particles, Al2O3 particles, and boehmite (alumina hydrate) on a substrate formed of a porous film. The separator 25 of this embodiment is formed of polyethylene, for example. The width (widthwise dimension of the strip shape) of the separator is slightly larger than the width of the covering portion 244 of the negative electrode 24. The separator 25 is arranged between the positive electrode 23 and the negative electrode 24, which are overlapped with each other in a state in which the covering portions 234 and 244 are displaced in the width direction so as to overlap each other. At this time, the uncoated portion 233 of the positive electrode 23 and the uncoated portion 243 of the negative electrode 24 do not overlap. That is, the non-covered portion 233 of the positive electrode 23 projects in the width direction from the overlapping region of the positive electrode 23 and the negative electrode 24, and the non-covered portion 243 of the negative electrode 24 extends in the width direction from the overlapping region of the positive electrode 23 and the negative electrode 24 ( The positive electrode 23 projects in the direction opposite to the uncovered portion 233 of the positive electrode 23. The wound body 22 is formed by winding the positive electrode 23, the negative electrode 24, and the separator 25 in a stacked state. The uncoated laminated portion 26 of the electrode body 2 is configured by a portion where only the uncoated portion 233 of the positive electrode 23 or the uncoated portion 243 of the negative electrode 24 is laminated.

The uncoated laminated portion 26 is a portion of the electrode body 2 that is electrically connected to the current collector 5. As shown in FIG. 3 and FIG. 4, the uncoated laminated portion 26 of the present embodiment has two hollow cathodes, a negative electrode 24, and a separator 25. It is divided into parts (divided uncoated laminated part) 261.

The uncovered laminated portion 26 configured as described above is formed on each electrode of the electrode body 2. That is, the uncoated laminated portion 26 in which only the uncoated portion 233 of the positive electrode 23 is laminated constitutes the positive electrode uncoated laminated portion of the electrode body 2, and the uncoated laminated portion in which only the uncoated portion 243 of the negative electrode 24 is laminated. The reference numeral 26 constitutes an uncoated laminated portion of the negative electrode in the electrode body 2.

1 to 3, the case 3 has a case body 31 having an opening, and a cover plate 32 that closes (closes) the opening of the case body 31. The case 3 accommodates the electrolytic solution in the internal space 33 together with the electrode body 2, the current collector 5, and the like. The case 3 is formed of a metal having resistance to the electrolytic solution. The case 3 of this embodiment is formed of, for example, aluminum or an aluminum-based metal material such as an aluminum alloy. The case 3 may be formed of a metal material such as stainless steel and nickel, or a composite material in which a resin such as nylon is bonded to aluminum.

The electrolytic solution is a non-aqueous solution electrolytic solution. The electrolytic solution is obtained by dissolving an electrolyte salt in an organic solvent. The organic solvent is, for example, cyclic carbonic acid esters such as propylene carbonate and ethylene carbonate, and chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The electrolyte salt is LiClO4, LiBF4, LiPF6, or the like. The electrolytic solution of the present embodiment contains 1 mol/L of LiPF6 in a mixed solvent prepared by mixing propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate at a ratio of propylene carbonate:dimethyl carbonate:ethyl methyl carbonate=3:2:5. It has been dissolved.

The case 3 is formed by joining the opening peripheral edge portion 34 of the case main body 31 and the peripheral edge portion of the lid plate 32 in an overlapped state. Further, the case 3 has an internal space 33 defined by the case body 31 and the cover plate 32. In this embodiment, the opening peripheral edge portion 34 of the case body 31 and the peripheral edge portion of the lid plate 32 are joined by welding.

The case body 31 includes a plate-shaped closing portion 311 and a tubular body portion 312 connected to the peripheral edge of the closing portion 311.

The closing portion 311 is located at the lower end of the case body 31 when the case body 31 is arranged so that the opening faces upward (that is, becomes the bottom wall of the case body 31 when the opening faces upward). ) Part. The closing portion 311 has a rectangular shape when viewed in the normal direction of the closing portion 311.

The body 312 of the present embodiment has a rectangular tube shape. Specifically, the body portion 312 has a flat rectangular tube shape. The body portion 312 has a pair of long wall portions 313 extending from the long side at the peripheral edge of the closing portion 311 and a pair of short wall portions 314 extending from the short side at the peripheral edge of the closing portion 311. That is, the pair of long wall portions 313 are opposed to each other with an interval (specifically, an interval corresponding to the short side at the peripheral edge of the closing portion 311) in the short side direction of the closing portion 311, and the pair of short wall portions 314 are closed. The portions 311 are opposed to each other with a gap (specifically, a gap corresponding to a long side on the peripheral edge of the closing portion 311) in the long piece direction. The short wall portion 314 connects the corresponding end portions of the pair of long wall portions 313 (specifically, the ends facing each other in the short side direction) to form the rectangular tube-shaped body portion 312.

As described above, the case main body 31 has a rectangular tube shape (that is, a bottomed rectangular tube shape) in which one end in the opening direction (Z-axis direction) is closed.

The cover plate 32 is a plate-shaped member that closes the opening of the case body 31. Specifically, the cover plate 32 contacts the case body 31 so as to close the opening of the case body 31. More specifically, the peripheral edge of the cover plate 32 is overlapped with the peripheral edge 34 of the opening of the case body 31 so that the cover plate 32 closes the opening.

The lid plate 32 has a contour shape corresponding to the opening peripheral edge portion 34 of the case body 31 when viewed in the Z-axis direction. That is, the cover plate 32 is a rectangular plate material that is long in the long side direction of the closed portion 311.

The external terminal 4 is a part electrically connected to an external terminal of another power storage element or an external device. The external terminal 4 is formed of a conductive member. For example, the external terminal 4 is formed of a metal material having high weldability such as an aluminum-based metal material such as aluminum or aluminum alloy, or a copper-based metal material such as copper or copper alloy. The external terminal 4 has a surface 41 to which a bus bar or the like can be welded.

The current collector 5 is arranged in the case 3 and is directly or indirectly connected to the electrode body 2 so as to be electrically conductive. The current collector 5 of this embodiment is electrically connected to the electrode body 2 via the clip member 50. That is, the electricity storage device 1 includes the clip member 50 that connects the electrode body 2 and the current collector 5 so as to be able to conduct electricity.

The current collector 5 is formed of a conductive member. The current collector 5 is arranged along the inner surface of the case 3. The current collector 5 of this embodiment connects the external terminal 4 and the clip member 50 shown in FIG. Specifically, as shown in FIGS. 3 and 8, the current collector 5 includes a first connection portion 51 that is electrically connected to the external terminal 4 and a second connection that is electrically connected to the electrode body 2. It has a portion 52 and a bent portion 53 that connects the first connecting portion 51 and the second connecting portion 52. In the current collector 5, the bent portion 53 is arranged near the boundary between the lid plate 32 and the short wall portion 314 in the case 3, the first connecting portion 51 extends from the bent portion 53 along the lid plate 32, and The two connecting portion 52 extends from the bent portion 53 along the short wall portion 314. That is, the current collector 5 is formed in an L shape. The current collector 5 of this embodiment is formed by bending a plate-shaped metal material cut into a predetermined shape.

The current collectors 5 configured as described above are arranged on the positive electrode and the negative electrode of the electricity storage device 1, respectively. In the electricity storage device 1 of the present embodiment, in the case 3, the positive electrode uncoated laminated portion 26 and the negative electrode uncoated laminated portion 26 of the electrode body 2 are respectively connected.

The positive electrode current collector 5 and the negative electrode current collector 5 are made of different materials. Specifically, the positive electrode current collector 5 is made of, for example, aluminum or an aluminum alloy, and the negative electrode current collector 5 is made of, for example, copper or a copper alloy.

The clip member 50 shown in FIGS. 3 and 9 to 11 bundles the positive electrodes 23 or the negative electrodes 24 stacked in the uncoated laminated portion 26 (specifically, the divided uncoated laminated portion 261) of the electrode body 2. Sandwich. As a result, the clip member 50 makes the positive electrodes 23 or the negative electrodes 24 stacked in the non-covered stacked portion 26 conductive. Specifically, the clip member 50 includes a pair of opposing pieces 501 that are opposed to each other with the bisected uncoated laminated portion 261 (the laminated positive electrode 23 or negative electrode 24) interposed therebetween, and the corresponding one end portions of the opposing pieces 501. And a connecting portion 502 for connecting. The clip member 50 is formed of a conductive member. In the present embodiment, the two clip members 50 are arranged in the positive electrode non-coated laminated portion 26 of the electrode body 2, and the two clip members 50 are arranged in the negative electrode uncoated laminated portion 26.

The electricity storage device 1 includes an insulating member 6 that insulates the electrode body 2 and the case 3 from each other. The insulating member 6 of this embodiment is, for example, an insulating cover. As shown in FIGS. 2 and 3, the insulating member 6 is disposed between the case 3 (specifically, the case body 31) and the electrode body 2. The insulating member 6 is formed of an insulating material. The insulating member 6 is composed of a sheet-shaped member. The insulating member 6 of the present embodiment is formed of, for example, a resin such as polypropylene or polyphenylene sulfide. The insulating cover 6 of the present embodiment is formed in a bag shape by bending an insulating sheet-like member cut into a predetermined shape.

In the electricity storage device 1 of this embodiment, the electrode body 2 (specifically, the electrode body 2 and the current collector 5) housed in the bag-shaped insulating member 6 is housed in the case 3.

Next, a method for manufacturing the electricity storage device 1 will be described with reference to FIGS.

First, the positive electrode 23 and the negative electrode 24 are cut into a predetermined length (step S1). Here, the positive electrode 23 before cutting has a constant thickness at each position in the longitudinal direction. On the other hand, the negative electrode 24 before cutting has a thin portion 240 that is thinner than other portions (specifically, the entire thickness dimension of the negative electrode 24 is smaller than the other portions) at an intermediate position in the longitudinal direction. Here, the thin portion 240 is “a portion having the metal foil 241 and the thin layer portion 242A in the negative electrode 24” and “the metal foil 241 is provided in the negative electrode 24, but the negative electrode active material layer 242 (the thin layer portion 242A is (Including) does not have ".

The thin portion 240 of the present embodiment has a negative electrode active material layer (thin layer portion 242A) thinner than the negative electrode active material layer 242 of the other portion of the negative electrode 24 (a portion of the negative electrode 24 excluding the thin portion 240). Specifically, in the thin portion 240 of the negative electrode 24, a portion in the length direction of the thin layer portion 242A in a portion on one side of the negative electrode 24 (on the upper surface of the metal foil 241 in FIG. 12) and the other side of the negative electrode 24. A part of the thin layer portion 242A in the length direction in the portion (on the lower surface of the metal foil 241 in FIG. 12) overlaps in the thickness direction. That is, in the thin portion 240, as shown in FIG. 12, the thin layer portions 242A are provided on both sides of the metal foil 241 at positions where portions in the longitudinal direction overlap in the thickness direction. The thin layer portion 242A of the present embodiment may be formed by thinning a part of the negative electrode active material layer 242 laminated on the metal foil 241 in the longitudinal direction by peeling or grinding. The thin layer portion 242A may be formed by thinly laminating a part in the longitudinal direction when laminating (forming) the negative electrode active material layer 242 on the metal foil 241. Further, in FIG. 12, the thicknesses of the metal foil 241, the negative electrode active material layer 242, and the thin layer portion 242A are exaggeratedly shown.

In the negative electrode 24 configured in this manner, the thin layer portion 242A is cut along the lateral direction at the position (the position α in the example shown in FIG. 12) where the thin layer portions 242A overlap each other in the thickness direction. It The negative electrode active material layer in the range indicated by I in FIG. 12 after the cutting is the metal foil 241 of the end 245 on the innermost peripheral side of the negative electrode 24 in the wound body 22 formed by winding together with the positive electrode 23. The thin layer portion 242A disposed on the outer surface (the surface facing the opposite side of the winding core 21) of the. In addition, the negative electrode active material layer in the range indicated by II is on the inwardly facing surface (the surface facing the winding core 21 side) of the metal foil 241 at the innermost peripheral side of the negative electrode 24 in the wound body 22. Of the thin layer portion 242A (see FIG. 7) provided (arranged) in the range from the innermost peripheral edge 245A to the position sandwiched by the positive electrode 23 in the wound body 22. Constitute. Further, the negative electrode active material layer indicated by III constitutes a thin layer portion 242A arranged on the inward facing surface of the metal foil 241 of the end portion 246 on the outermost peripheral side of the negative electrode 24 in the wound body 22. .. Further, the negative electrode active material layer in the range indicated by IV is a range on the outermost surface of the metal foil 241 in the outermost peripheral side portion of the negative electrode 24 in the wound body 22, and is the outermost peripheral side end. A thin layer portion 242A (see FIG. 7) that is provided (arranged) in the range from the edge 246A to the position where the wound body 22 is sandwiched by the positive electrodes 23 is configured.

Next, in the negative electrode 24, the surface on the side where the thin layer portion 242A is arranged is shorter in the longitudinal direction faces outward at the innermost peripheral end 245 when wound, and the outermost peripheral end 246. Then, the positive electrode 23 and the negative electrode 24 are stacked so as to face inward, and the stacked positive electrode 23 and the negative electrode 24 are wound (step S2). That is, at the winding start side end 245, the short side surface faces the positive electrode 23 side (see FIG. 13), and at the winding end side 246, the short side surface is opposite to the positive electrode 23. The positive electrode 23 and the negative electrode 24 are stacked so as to face the side, and the positive electrode 23 and the negative electrode 24 are wound in this stacked state (see arrow β in FIG. 13 ). Thereby, the electrode body 2 is formed. In FIG. 13, the thicknesses of the metal foils 231, 241, the positive electrode active material layer 232, the negative electrode active material layer 242, and the thin layer portion 242A are exaggerated.

The current collector 5 is bonded to the formed electrode body 2 (step S3). Specifically, the positive electrode 23 (or the negative electrode 24) laminated in the uncoated laminated portion 26 (specifically, the divided uncoated laminated portion 261) of each electrode of the electrode body 2 is sandwiched by the clip member 50 so as to be bundled, The clip member 50 and the current collector 5 are ultrasonically bonded to each other. Thereby, the electrode body 2, the clip member 50, and the current collector 5 are joined.

The current collector 5 to which the electrode body 2 is connected, the external terminal 4 and the like are assembled to the cover plate 32 (step S4), and the electrode body 2 and the current collector 5 and the like are covered with the insulating member 6 and are While inserting the electrode body 2 and the current collector 5 into the case body 31, the opening of the case body 31 is closed by the cover plate 32 (step S5). Then, the storage element 1 is completed by welding (for example, laser welding) the boundary between the case body 31 and the cover plate 32 (step S6).

According to the electricity storage device 1 manufactured by the above manufacturing method, the end portion of the negative electrode 24 (the portion extending (protruding) from the corresponding edge 235A, 236A of the positive electrode 23, that is, the portion not facing the positive electrode 23) ) 245 and 246, the negative electrode active material layer is the thin layer portion 242A. Therefore, when charging and discharging the storage element 1, the ends 245 and 246 of the negative electrode 24 and the other parts of the negative electrode 24 (the parts facing the positive electrode 23: the ends 245 and 246 in the example of the present embodiment). Even if a potential difference occurs between the other part), the number of ions that can move from the other part to the ends 245, 246 is suppressed. As a result, in the storage element 1, the capacity deterioration of the storage element 1 due to the movement of ions in the negative electrode 24 (specifically, the negative electrode active material layer) can be suppressed.

Further, since the negative electrode 24 has the thin layer portion 242A on the surface of the metal foil 241 of the end portions 245, 246 facing the corresponding end edge 235A, 236A side of the positive electrode 23, the negative electrode active surface is formed on the surface. The rigidity of the negative electrode 24 (thin portion 240) is higher than that in the case where there is no material layer. For this reason, in the electricity storage device 1, it is possible to suppress a shift from a planned position or a short circuit due to bending of the end portions 245 and 246 of the negative electrode 24.

In addition, in the electricity storage device 1 of the present embodiment, the negative electrode 24 is in the range on the innermost surface of the metal foil 241 facing the inner side, and is from the innermost peripheral edge 245A in the winding direction. The wound body 22 has a thin layer portion 242A in a range up to a position sandwiched by the positive electrodes 23 (see FIG. 7). Further, the negative electrode 24 is a range on the outermost surface of the metal foil 241 at the outermost peripheral side and reaches a position sandwiched by the positive electrode 23 from the outermost peripheral edge 246A in the winding direction. It has a thin layer portion 242A in the range (see FIG. 7).

According to these configurations, in the negative electrode 24, the innermost surface of the metal foil 241 faces the inner surface (the surface facing the winding core 21: the surface not facing the positive electrode 23) and the outermost surface. The negative electrode active material layer (thin layer portion) 242A on the surface of the metal foil 241 on the outer peripheral side that faces the outside (the surface that faces the side opposite to the winding core 21: the surface that does not face the positive electrode 23) is the positive electrode. It is thinner than the active material layer 242 in the portion facing 23. Thereby, during charging/discharging of the electricity storage device 1, between the innermost peripheral side portion and the outermost peripheral side portion of the negative electrode 24 and the portion excluding the innermost peripheral side portion and the disaster state side portion. Even if a potential difference occurs between the two, it is possible to suppress the movement of ions to the innermost peripheral side portion and the outermost peripheral side portion. As a result, it is possible to more effectively suppress the capacity deterioration of the storage element 1 due to the movement of the ions.

Further, in the electricity storage device 1 of the present embodiment, the end portions 245 and 246 of the negative electrode have thin layer portions 242A on both surfaces of the metal foil 241. Therefore, the end portions 245, 246 of the negative electrode 24 have higher rigidity than in the case where the thin layer portion 242A is not provided on both surfaces of the metal foil 241, or the thin layer portion 242A is provided on only one surface of the metal foil 241. As a result, in the electricity storage device 1, it is possible to more reliably prevent a shift from a planned position or a short circuit due to bending of the end portions 245 and 246.

When the negative electrode 24 having the uncoated portion 244 continuous in the longitudinal direction is cut in the width direction, the entire thickness of the negative electrode 24 changes at the boundary between the portion where the negative electrode active material layer 242 is formed and the uncoated portion 244. Therefore, in the vicinity of the boundary between the portion where the negative electrode active material layer 242 is formed and the uncovered portion 244, burrs and chips (specifically, the stress applied to the portion where the negative electrode active material layer 242 is formed and the uncovered portion 244). Burr and cutting chips) due to the difference in stress applied to In the method of manufacturing the electricity storage device 1 according to the present embodiment, the negative electrode 24 before being cut into a predetermined length has the uncoated portion 243 continuous in the longitudinal direction, but other than the uncoated portion 244 and the uncoated portion. Since the thin portion 240 in which the negative electrode active material layer 242A is thinned is cut by the change in the total thickness of the negative electrode 24 at the boundary with the portion of (2), it is possible to suppress the generation of burrs and chips when cutting. That is, when the negative electrode active material layer 242 is thick, the change in the total thickness of the negative electrode 24 at the boundary between the portion where the negative electrode active material layer 242 is formed and the non-covered portion 244 is large. Although burrs and swarf are likely to be generated, by suppressing the thickness dimension of the negative electrode active material layer 242A at the cut portion as in the method of manufacturing the electricity storage device 1 of the present embodiment, the burrs of the metal foil 241 at the time of cutting are burrs. Also, the generation of chips can be suppressed.

When the negative electrode active material layer 242 of the negative electrode 24 contains a component having a Vickers hardness higher than that of the metal foil 241 (hard carbon in the example of the present embodiment) as in the present embodiment, the cutting of the negative electrode 24 is performed. At this time, the suppression of the generation of burrs and chips in the metal foil 241 becomes more remarkable. That is, when the negative electrode active material layer 242 contains a component having a Vickers hardness higher than that of the metal foil 241, the metal foil 241 has the above-mentioned properties when the negative electrode 24 is cut, as compared with a component having a low Vickers hardness (eg, graphite). Since burrs and chips are more likely to be generated because the component having a high Vickers hardness is pressed, the anode active material layer 242A suppresses the component having a high Vickers hardness by suppressing the thickness of the negative electrode active material layer 242A. Even if it is included, generation of burrs and chips in the metal foil 241 at the time of cutting is effectively suppressed.

The power storage element and the method for manufacturing the power storage element of the present invention are not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the scope of the present invention. For example, the configuration of another embodiment can be added to the configuration of one embodiment, and a part of the configuration of one embodiment can be replaced with the configuration of another embodiment. In addition, some of the configurations of certain embodiments may be deleted.

In the negative electrode 24 of the above-described embodiment, the thin layer portion 242A is provided at both ends 245 and 246 in the longitudinal direction (winding direction), but the configuration is not limited to this. The thin layer portion 242A may be provided only on one end of the negative electrode 24 (the innermost end 245 or the outermost end 246).

Further, in the negative electrode 24 of the above-described embodiment, the thin layer portion 242A is provided on both surfaces (both surfaces in the thickness direction) of the longitudinal end portions 245 and 246, but the configuration is not limited to this. The thin layer portion 242A may be provided on at least one of the outermost portion of the innermost peripheral end 245 and the innermost portion of the outermost peripheral end 246 of the negative electrode 24. Further, in the negative electrode 24, the thin portion 240 may have a configuration that does not have the negative electrode active material layer 242 (including the thin layer portion 242A). Also with these configurations, even when a potential difference occurs between the end portions 245, 246 of the negative electrode 24 and another portion (a portion facing the positive electrode 23) during charging/discharging of the electricity storage device 1, the other difference is generated. Since the number of ions that can move from the portion to the end portions 245 and 246 is small, it is possible to suppress the capacity deterioration of the storage element 1 due to the movement of ions in the negative electrode 24 (specifically, the negative electrode active material layer 242). ..

In addition, in the negative electrode 24 of the above-described embodiment, in the portion facing inward, substantially the entire range from the innermost peripheral edge 245A in the winding direction to the position sandwiched by the positive electrodes 23 in the wound body 22. In addition, although it has the thin layer portion 242A, it is not limited to this configuration. The thin layer portion 242A may be provided in a part of the region facing the inner side of the negative electrode 24 from the edge 245A in the winding direction to the position sandwiched by the positive electrodes 23. Similarly, in the negative electrode 24 of the above-described embodiment, in the portion facing outward, substantially the entire range from the outermost peripheral edge 246A in the winding direction to the position sandwiched by the positive electrodes 23 in the wound body 22. In addition, although it has the thin layer portion 242A, it is not limited to this configuration. The thin layer portion 242A may be provided in a part of the region facing the outer side of the negative electrode 24 in a range from the end edge 246A in the winding direction to the position sandwiched by the positive electrodes 23.

Further, in the negative electrode 24 of the above embodiment, the negative electrode active material layer 242 is directly formed (laminated) on both surfaces of the metal foil 241, but the configuration is not limited to this. The negative electrode active material layer 242 may be configured to be indirectly formed (laminated) on the surface of the metal foil 241. For example, for the purpose of improving adhesion or electronic conductivity between the metal foil 241 and the negative electrode active material layer 242, a conductive layer is formed (laminated) on the surface of the metal foil 241, and the surface of the conductive layer is formed. The negative electrode active material layer 242 may be formed (laminated) thereon.

In the method of manufacturing the electricity storage device 1 of the above-described embodiment, in the thin portion 240 of the negative electrode 24 before being cut to a predetermined length, the thin layer portions 242A provided on both sides with the metal foil 241 sandwiched are partially formed in the longitudinal direction. Are shifted so as to overlap each other in the thickness direction, but are not limited to this configuration. As shown in FIG. 15, in the thin portion 240 of the negative electrode 24, a thin layer portion 242A at one site in the thickness direction of the negative electrode 24 and a thin layer portion 242A at the other site in the thickness direction of the negative electrode 24. However, they may overlap in the thickness direction, that is, the positions in the longitudinal direction may coincide. In FIG. 15, the thicknesses of the metal foil 241, the negative electrode active material layer 242, and the thin layer portion 242A are exaggerated.

Further, in the method for manufacturing the electricity storage device 1 of the above-described embodiment, the thin portion 240 to be cut is the thin layer portion 242A in which the negative electrode active material layer 242 is thinner than other portions, but the thin portion 240 is not limited to this configuration. The thin portion 240 to be cut may have a configuration without the negative electrode active material layer 242. In the case where the negative electrode 24 has a configuration that has the non-covered portion 243 that is continuous in the longitudinal direction, a configuration that does not have the negative electrode active material layer 242 can suppress a change in the overall thickness of the negative electrode 24 in the width direction, It is possible to suppress the generation of burrs and chips when cutting the thin portion 240.

Further, in the above embodiment, the case where the power storage element is used as a chargeable/dischargeable non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery) has been described, but the type and size (capacity) of the power storage element are arbitrary. Is. Further, in the above embodiment, the lithium ion secondary battery has been described as an example of the power storage element, but the present invention is not limited to this. For example, the present invention is also applicable to secondary batteries such as magnesium ion batteries or sodium ion batteries, primary batteries, and storage elements for capacitors such as electric double layer capacitors.

A power storage element (for example, a battery) may be used for a power storage device (a battery module when the power storage element is a battery) 11 as shown in FIG. The power storage device 11 includes at least two power storage elements 1 and a bus bar member 12 that electrically connects the two (different) power storage elements 1 to each other. In this case, the technique of the present invention may be applied to at least one power storage element 1.

DESCRIPTION OF SYMBOLS 1... Storage element, 2... Electrode body, 21... Winding core, 22... Winding body, 23... Positive electrode, 231... Metal foil (conductive part), 232... Positive electrode active material layer, 233... Uncovered part, 234... Covered Part, 235A... Edge on innermost side, 236A... Edge on outermost side, 24... Negative electrode, 240... Thin portion, 241... Metal foil (conductive portion), 242... Negative electrode active material layer, 242A... Thin layer Part, 243... uncoated part, 244... coated part, 245... innermost peripheral side end, 245A... innermost peripheral side edge, 246... outermost peripheral side end, 246A... outermost peripheral side edge , 25... Separator, 26... Uncoated laminated portion, 261... Divided uncoated laminated portion, 27... Hollow portion, 3... Case, 31... Case body, 311... Closure portion, 312... Body portion, 313... Long wall portion 314... Short wall part, 32... Lid plate, 33... Internal space, 34... Opening peripheral part, 4... External terminal, 41... Surface, 5... Current collector, 50... Clip member, 501... Opposing piece, 502... Connection part, 51... First connection part, 52... Second connection part, 53... Bent part, 6... Insulation member (insulation cover), 11... Power storage device, 12... Bus bar member

Claims (4)

A thin-walled portion provided at an intermediate position in the longitudinal direction in a strip-shaped negative electrode having a sheet-shaped conductive portion and an active material layer that overlaps the conductive portion, and a thin portion of another portion of the negative electrode on the surface of the conductive portion. Cutting a thin portion having an active material layer thinner than an active material layer or having no active material layer along the lateral direction of the negative electrode,
A state in which the thin portion that constitutes the longitudinal end portion of the negative electrode after the cutting extends in the longitudinal direction from at least one of the one end edge and the other end edge in the longitudinal direction of the strip-shaped positive electrode. The positive electrode and the negative electrode are overlapped with each other, and the positive electrode and the negative electrode in the overlapped state are wound from the one edge side,
The said negative electrode is a manufacturing method of an electrical storage element which has the non-cover part of the said active material layer which follows the said longitudinal direction. The method of manufacturing an electricity storage device according to claim 1, wherein the active material layer of the negative electrode contains a component having a Vickers hardness higher than that of the conductive portion. The method of manufacturing an energy storage device according to claim 1, wherein the thin portion has an active material layer that is thinner than the active material layer of the other portion. The negative electrode has a pair of the active material layers stacked on the conductive portion from both sides in the thickness direction,
In the thin portion, a portion in the longitudinal direction of the range having the active material layer thinner than the active material layer of the other portion in the portion on one side in the thickness direction of the negative electrode, and the thickness of the negative electrode. A part of the longitudinal direction of the range having the active material layer thinner than the active material layer of the other part in the part on the other side of the direction, overlaps when viewed from the thickness direction,
In the cutting, a range having an active material layer thinner than the active material layer of the other part is cut at a position where the conductive portion is sandwiched and seen from the thickness direction,
In the winding, a portion on the shorter side in the longitudinal direction of an area having an active material layer thinner than the active material layer of the other portion in the portion on the one side and the portion on the other side of the negative electrode is wound. 4. The electric storage device according to claim 3, wherein the positive electrode and the negative electrode are wound so as to be overlapped so as to face outward at the end on the innermost peripheral side or face inward at the end on the outermost peripheral side. Manufacturing method.