JP2016184482A - Secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery having high reliability in welding.SOLUTION: A secondary battery according to the present invention includes a power generation element in which an electrode including a metal foil provided with a mixture layer is wound. The metal foil includes crystal grains which have sizes different from each other on one surface and the other surface of the metal foil. The electrode is arranged such that a surface of the metal foil having larger crystals faces an outer peripheral side of the power generation element.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a secondary battery.

  In recent years, secondary batteries with large capacity have been developed as power sources for hybrid electric vehicles, pure electric vehicles, etc. Among them, lithium ion secondary batteries with high energy density (Wh / kg) are attracting attention. . A lithium ion secondary battery is configured by storing a power generation element formed by overlapping and winding a positive electrode, a negative electrode, and a separator for insulating each in a rectangular or cylindrical battery can. Yes.

  In the cylindrical secondary battery, one electrode of the power generation element is electrically connected to an external terminal provided on the battery lid via a current collecting member. In order to weld the current collector and the metal foil of the negative electrode, it is necessary to push the current collector into the power generation element.

  Patent Document 1 discloses that the current collecting member is pushed into the power generation element after the electrodes are deformed in order to easily push the current collection member into the power generation element.

JP 2002-203547 A

  However, in the method described in Patent Document 1, the expanding member is inserted into the metal foil to deform the metal foil. However, in this method, the metal foil is wound around the expanding member and bent, which may cause poor welding with the current collecting member.

  In view of the above problems, an object of the present invention is to provide a secondary battery with high welding reliability.

  In order to solve the above problems, the secondary battery according to the present invention has a power generation element in which an electrode having a mixture layer provided on a metal foil is wound, and the metal foil has one surface and the other surface. The size of the crystal grains is different, and the electrode is disposed on the outer peripheral side of the power generation element with the large crystal face of the metal foil facing.

  By using the above invention, it is easy to insert the jig into the power generation element without increasing the number of steps, and the effect of reducing welding defects can be obtained.

Cross section of cylindrical secondary battery Exploded perspective view of cylindrical secondary battery Exploded sectional perspective view of power generation element Cross section of electrolytic copper foil (A)-(c) is a perspective view of each electric power generation element before convex part brazing (A) And (b) is a perspective view which shows the convex part brazing process of each electric power generation element. (A) And (b) is a production process diagram of a power generation element according to the present invention. Enlarged view of part B in Fig. 7 (a) Process flow diagram from electrode coating to convex welding

  Hereinafter, embodiments will be described with reference to the drawings. In this embodiment, a cylindrical secondary battery and a manufacturing method thereof will be described.

Hereinafter, embodiments of a power storage device according to the present invention will be described with reference to the drawings.
FIG. 1 is an enlarged cross-sectional view showing an embodiment of a cylindrical secondary battery.

  The cylindrical secondary battery 1 includes a battery case 4 including a cylindrical battery can 2 having a bottom and an upper opening, and a hat-type battery lid 3 that seals the top of the battery can 2. Inside the battery container 4, constituent members for power generation described below are accommodated, and a non-aqueous electrolyte 5 is injected.

  In the cylindrical battery can 2, a groove 2 a protruding to the inside of the battery can 2 is formed on the opening 2 b provided on the upper end side.

  A power generation element 10 is arranged inside the battery can 2. The power generation element 10 includes an elongated cylindrical shaft core 15 having a hollow portion along the axial direction, and a positive electrode and a negative electrode wound around the shaft core 15. The hollow portion of the cylindrical shaft core 15 has a different cross-sectional shape in a plane perpendicular to the axial direction in the axial direction (vertical direction in the drawing). The cross-sectional shape above the hollow portion is a track shape formed by parallel portions and curved portions. The cross-sectional shape below the hollow portion is a circle having a diameter smaller than the width of the upper parallel portion. A cylindrical positive current collecting ring 27 is press-fitted into the upper hollow portion 15a. The positive electrode current collecting ring plate 27 includes a disk-shaped base portion 27a, a lower cylindrical portion 27b that protrudes toward the shaft core 15 side at the inner peripheral portion of the base portion 27a, and press-fitted into the inner surface of the shaft core 15, and an outer peripheral edge. And an upper cylindrical portion 27c protruding toward the battery lid 3 side. The positive electrode current collecting ring 27 is fixed and supported on the upper end portion of the shaft core 15 by the lower cylindrical portion 27b.

  The positive electrode convex portion 16 of the positive electrode is welded to the upper cylindrical portion 27 c of the positive electrode current collecting ring 27. The positive electrode current collecting ring 27 is formed of, for example, an aluminum metal, and the positive electrode convex portion 16 of the positive electrode and the pressing member 28 are welded to the outer periphery of the upper cylindrical portion 27c. A number of the positive electrode protrusions 16 are brought into close contact with the outer periphery of the upper cylindrical part 27c of the positive electrode current collecting ring 27, and a pressing member 28 is wound around the outer periphery of the positive electrode protrusion 16 in a ring shape and temporarily fixed. Joined by sonic welding.

  A step portion 15b having a small outer diameter is formed on the outer periphery of the lower end portion of the shaft core 15, and a negative electrode current collecting ring 21 is press-fitted and fixed to the step portion 15b. The negative electrode current collector ring 21 is formed of, for example, a copper-based metal, and an opening 21b that is press-fitted into the step portion 15b of the shaft core 15 is formed in a disk-shaped base portion 21a. An outer peripheral cylindrical portion 21c that protrudes toward is formed. An opening 21 d (see FIG. 2) for allowing the nonaqueous electrolytic solution 5 injected into the hollow shaft of the shaft core 15 to penetrate into the power generation element 10 is formed in the base portion 21 a of the negative electrode current collecting ring 21.

  The negative electrode convex portion 17 of the negative electrode is joined to the outer peripheral cylindrical portion 21 c of the negative electrode current collecting ring 21. The negative electrode convex portion 17 of the negative electrode and the pressing member 22 are welded to the outer periphery of the outer peripheral cylindrical portion 21 c of the negative electrode current collecting ring 21. A number of negative electrode protrusions 17 are brought into close contact with the outer periphery of the outer peripheral cylindrical portion 21c of the negative electrode current collector plate 21, and the holding member 22 is wound around the outer periphery of the negative electrode protrusion 17 in a ring shape and temporarily fixed. Is done. A connection lead plate 50 is joined to the base 21a of the negative electrode current collecting ring 21 by resistance welding, laser welding, or the like.

  Many positive electrode convex parts 16 are welded to the positive electrode current collection ring 27, and many negative electrode convex parts 17 are welded to the negative electrode current collection ring 21, whereby the positive electrode current collection ring 27, the negative electrode current collection ring 21, and the power generation element A power generation unit 20 in which 10 is unitized is configured. A predetermined amount of non-aqueous electrolyte 5 is injected into the battery can 2. As an example of the nonaqueous electrolytic solution 5, a solution in which a lithium salt is dissolved in a carbonate-based solvent is raised.

  FIG. 2 is an exploded perspective view of the cylindrical secondary battery.

  A cylindrical positive current collecting ring 27 is press-fitted above the hollow portion of the cylindrical shaft core 15. The positive electrode current collector ring 27 is made of, for example, an aluminum-based metal. An opening 27d for releasing gas generated inside the battery is formed in the base 27a of the positive electrode current collecting ring 27. The opening 27 e formed in the positive electrode current collection ring 27 is for inserting an electrode rod (not shown) for welding the connection lead plate 50 to the battery can 2. The electrode rod is inserted into the hollow portion of the shaft core 15 from the opening portion 27e formed in the positive electrode current collecting ring 27, and the connecting lead plate 50 is pressed against the inner surface of the bottom portion 2c of the battery can 2 at the tip portion to perform resistance welding. Thus, the power generation unit 20 is fixed to the bottom 2c of the battery can 2. Further, the bottom surface of the battery can 2 connected to the negative electrode current collecting ring 21 acts as one output terminal, and the electric power stored in the power generation element 10 can be taken out from the battery can 2. A flexible connecting member 33 formed by laminating a plurality of aluminum foils is joined to the upper surface of the base portion 27a of the positive electrode current collecting ring 27 by welding one end thereof.

  A battery lid unit 30 is disposed on the upper cylindrical portion 27 c of the positive electrode current collecting ring 27. The battery lid unit 30 includes a ring-shaped insulating plate 34, a connecting plate 35 fitted in an opening 34a provided in the insulating plate 34, a diaphragm 37 welded to the connecting plate 35, and a diaphragm 37 by caulking and welding. The battery cover 3 is fixed.

  The insulating plate 34 has a ring shape made of an insulating resin material having a circular opening 34 a, and is placed on the upper cylindrical portion 27 c of the positive electrode current collecting ring 27.

  The insulating plate 34 has an opening 34a and a side 34b protruding downward. A connecting plate 35 is fitted in the opening 34 a of the insulating plate 34. The other end of the connection member 33 is welded and joined to the lower surface of the connection plate 35.

  The connection plate 35 is made of an aluminum-based metal and has a substantially dish shape that is substantially uniform except for the central portion and is bent to a slightly lower position on the central side. A projection 35a that is thin and formed in a dome shape is formed at the center of the connection plate 35, and a plurality of openings 35b are formed around the projection 35a. The opening 35b has a function of releasing gas generated inside the battery. The protrusion 35 a of the connection plate 35 is joined to the bottom surface of the center portion of the diaphragm 37 by resistance welding or friction stir welding. The diaphragm 37 is formed of an aluminum-based metal, and has a circular cut 37 a centering on the center portion of the diaphragm 37. The cut 37a is formed by crushing the upper surface side into a V shape by pressing and thinning the remainder. The diaphragm 37 is provided for ensuring the safety of the battery, and has a function of cleaving at the cut 37a and releasing the internal gas when the internal pressure of the battery increases.

  The diaphragm 37 fixes the peripheral edge of the battery lid 3 at the peripheral edge. As shown in FIG. 2, the diaphragm 37 initially has a side wall 37 b erected vertically at the peripheral portion toward the battery lid 3 side. The battery lid 3 is accommodated in the side wall 37b, and the side wall 37b is bent and fixed to the upper surface side of the battery lid 3 by caulking.

  The battery lid 3 is made of iron such as carbon steel, nickel plated on both front and back surfaces, a disc-shaped peripheral edge 3a that contacts the diaphragm 37, and a cylindrical portion 3b that protrudes upward from the peripheral edge 3a. Having a hat shape. An opening 3c is formed in the cylindrical portion 3b. The opening 3c is for releasing gas to the outside of the battery when the diaphragm 37 is cleaved by the gas pressure generated inside the battery. The battery lid 3 acts as one power output end, and the stored electric power can be taken out from the battery lid 3.

  A gasket 43 made of an insulating member that covers the caulked portion between the diaphragm 37 and the battery lid 3 is provided. The gasket 43 is made of rubber, and is not intended to be limited, but one example of a preferable material is a fluorine-based resin.

  The gasket 43 has a shape having an outer peripheral wall portion 43b that is formed to rise substantially vertically toward the upper direction at the peripheral edge of the ring-shaped base portion 43a.

  Then, the outer peripheral wall 43b of the gasket 43 is bent together with the battery can 2 by pressing or the like, and the diaphragm 37 and the battery lid 3 are crimped by the base 43a and the outer peripheral wall 43b so as to be pressed in the axial direction. Thereby, the battery lid unit 30 in which the battery lid 3, the diaphragm 37, the insulating plate 34 and the connection plate 35 are integrally formed is fixed to the battery can 2 via the gasket 43, and the insulating plate 34 is attached to the power generation unit 20. The power generation unit 20 is pressed against the bottom side of the battery can 2 in contact with the positive electrode current collecting ring 27.

  FIG. 3 is an exploded cross-sectional perspective view showing details of the structure of the power generation element 10.

  The power generating element 10 has a structure in which a positive electrode 11, a negative electrode 12, and first and second separators 13 and 14 are wound around an axis 15.

  The shaft core 15 is formed of an insulating material such as PP (polypropylene) and has a hollow cylindrical shape. A first separator 13, a negative electrode 12, a second separator 14, and a positive electrode 11 are sequentially laminated and wound on the shaft core 15. Inside the innermost negative electrode 12, the first separator 13 and the second separator 14 are wound several times (one turn in FIG. 3). The first separator 13 and the second separator 14 are formed of an insulating porous body.

  In the innermost circumference (axial core side), the beginning of the negative electrode 12 extends in the circumferential direction from the beginning of the positive electrode 11. Further, at the outermost periphery (battery can side), the negative electrode 12 is wound more outward than the positive electrode 11, and the end of the negative electrode 12 is extended in the circumferential direction from the end of the positive electrode 11. Yes. A second separator 14 is wound around the outer periphery of the outermost negative electrode 12. The end of the second separator 14 on the outermost periphery is stopped with an adhesive tape 19. In some cases, the first separator 13 and the second separator 14 are wound several times on the outermost periphery and then stopped by the adhesive tape 19.

  The positive electrode 11 is formed of an aluminum foil, has a long shape, and includes a positive electrode metal foil 11a and a positive electrode mixture layer 11b in which a positive electrode mixture is applied to both surfaces of the positive electrode metal foil 11a. The upper side edge extending in the longitudinal direction of the positive electrode metal foil 11a is a positive electrode foil exposed portion 11c where the positive electrode mixture is not applied and the positive electrode metal foil 11a is exposed. A large number of positive electrode protrusions 16 protruding upward along the axis of the shaft core 15 are integrally formed on the positive electrode foil exposed portion 11c at equal intervals.

  The positive electrode mixture includes a positive electrode active material, a positive electrode conductive material, and a positive electrode binder. Examples of the positive electrode active material include lithium oxides such as cobalt, manganese, and nickel.

  Examples of the positive electrode binder include polyvinylidene fluoride (PVDF) and fluororubber.

  Examples of the method for applying the positive electrode mixture to the positive electrode metal foil 11a include a roll coating method and a slit die coating method. A slurry obtained by kneading a dispersion solution in a positive electrode mixture is uniformly applied to both surfaces of an aluminum foil having a thickness of 20 μm, dried, pressed, and cut. An example of the coating thickness of the positive electrode mixture is about 40 μm on one side. When the positive electrode metal foil 11a is cut, the positive electrode protrusions 16 are integrally formed. All the positive electrode convex portions 16 have substantially the same length.

  The negative electrode 12 includes a negative electrode metal foil 12a formed of an electrolytic copper foil and having a long shape, and a negative electrode mixture layer 12b in which a negative electrode mixture is applied to both surfaces of the negative electrode metal foil 12a. The side edge on the lower side extending in the longitudinal direction of the negative electrode metal foil 12a is a negative electrode foil exposed portion 12c where the negative electrode mixture is not applied and the copper foil is exposed. A large number of negative electrode protrusions 17 extending in the direction opposite to the positive electrode protrusions 16 along the axis of the axial core 15 are integrally formed on the negative electrode foil exposed part 12c at equal intervals.

  The negative electrode mixture includes a negative electrode active material, a negative electrode binder, and a thickener. An example of the negative electrode active material is graphite carbon.

  Examples of the method for applying the negative electrode mixture to the negative electrode metal foil 12a include a roll coating method and a slit die coating method.

  A slurry obtained by kneading a dispersion solvent in a negative electrode mixture is uniformly applied to both surfaces of an electrolytic copper foil having a thickness of 10 μm, dried, and then cut. An example of the coating thickness of the negative electrode mixture is about 40 μm on one side. When the negative electrode metal foil 12a is cut by pressing, the negative electrode protrusion 17 is integrally formed.

  In the present invention, the thickness of the electrolytic copper foil is 10 μm. However, if the thickness of the electrolytic copper foil is too thick, there is a possibility that a warping amount described later cannot be secured sufficiently. Therefore, the thickness of the electrolytic copper foil is preferably 20 μm or less, more preferably 10 μm or less, which can ensure a sufficient amount of warpage.

  On the other hand, in order to make full use of the warp of the electrolytic copper foil, the length of the negative electrode protrusion 17 is also important. If the negative electrode protrusion 17 protrudes from the end of the negative electrode mixture layer 12b, the negative electrode protrusion 17 warps, but in order to secure a sufficient amount of warpage, the length of the negative electrode protrusion 17 is 20 mm or more. It is preferable to ensure.

  The widths of the first and second separators 13 and 14 are larger than the width of the negative electrode mixture layer 12 b of the negative electrode 12. The width of the negative electrode mixture layer 12 b of the negative electrode 12 is larger than the width of the positive electrode mixture layer 11 b of the positive electrode 11. The width and length of the negative electrode mixture layer 12b are made larger than the width and length of the positive electrode mixture layer 11b, and the entire region of the positive electrode mixture layer 11b is covered with the negative electrode mixture layer 12b. In the case of a lithium ion secondary battery, lithium, which is a positive electrode active material, is ionized, penetrates the separator, and is occluded by the negative electrode active material. In this case, if the negative electrode active material is not formed on the negative electrode side and the negative electrode metal foil 12a is exposed, lithium is deposited on the negative electrode metal foil 12a, causing an internal short circuit. As described above, by covering the entire region of the positive electrode mixture layer 11b with the negative electrode mixture layer 12b, it is possible to prevent such an internal short circuit due to lithium deposition.

  The first separator 13 and the second separator 14 are each formed of, for example, a polyethylene porous film having a thickness of 40 μm.

  Next, the metal foil that is a feature of the present invention will be described. The negative electrode 12 includes a negative electrode metal foil 12a formed of an electrolytic copper foil and having a long shape, and a negative electrode mixture layer 12b in which a negative electrode mixture is applied to both surfaces of the negative electrode metal foil 12a. FIG. 4 is a cross-sectional view of the negative electrode metal foil 12a. Since the electrolytic copper foil used in the present invention is manufactured by electrodeposition, the crystal grain is different between the surface on which the crystal is deposited on the electrolytic drum and the surface on which the crystal grows from the deposited surface. The surface on which crystals precipitate is a surface 12d with small crystal grains, and the surface on which crystals grow is a surface 12e with large crystal grains, and the internal stress generated when each crystal grain is precipitated and grown is different. For this reason, the crystal grains warp to the large surface 12e side due to the influence of internal stress.

  In the present invention, as shown in FIG. 3, the negative electrode metal foil 12 a is arranged on the outer peripheral side of the power generation element 10 so that the surface 12 e with large crystal grains faces. By disposing the negative electrode metal foil 12a in this way, the negative electrode convex portion 17 spreads to the outer peripheral side of the power generation element 10, and is caught by the pieces 51 and 52 at the time of battery production, and the negative electrode convex portion 17 is caught and bent. Disappears. Therefore, the reliability of welding between the negative electrode current collector plate 21 and the negative electrode convex portion 17 is improved.

  FIG. 5 is a perspective view of the power generation element 10 before the convex portion is brazed. FIGS. 5A, 5B, and 5C show a power generation element 10a that uses a negative electrode metal foil 12a (rolled copper foil) that is not an electrolytic copper foil, and a power generation element 10b that has a surface 12d with a smaller crystal grain facing outward. And the electric power generation element 10c which turned the surface 12e of the side with a large crystal grain to the outer side is shown. The power generation element 10a in which the negative electrode protrusion 17 in FIG. 5A is not curved depending on the state of the crystal grains of the negative electrode protrusion 17, and the power generation element in which the negative electrode protrusion 17 in FIG. 10b, the negative electrode convex part 17 of FIG.5 (c) becomes three forms of the electric power generation element 10c which curved and spread outside.

  6 and 7 are diagrams for explaining a process of expanding the negative electrode protrusion 17 in order to insert the negative electrode current collector plate 21. The power generation element 10 needs to be formed by pushing a top 52 having a large taper angle into the central opening 17a of the negative electrode protrusion 17 in order to form an annular protrusion 17b for inserting a negative electrode current collector plate 21 described later. is there. However, in the power generation element 10a in which the negative electrode convex portion 17 is not curved as shown in FIG. 6A, when the top 52 having a large taper angle is pushed, the tip of the negative electrode convex portion 17 is caught by the top 52, and the negative electrode convex portion When the portion 17 is pushed into the opening 17a while being caught by the top 52, the negative electrode convex portion 17 is caught inside the opening 17a. In such a situation, the negative electrode protrusion 17 that is involved is bent and welded without being properly arranged on the outer periphery of the negative electrode current collector plate 21, which may cause poor welding.

  On the other hand, in the power generation element 10b in which the negative electrode protrusion 17 is curved and narrowed inward as shown in FIG. 6B, there is a higher possibility that the negative electrode protrusion 17 is caught on the opening 17a side. End up. For this reason, in the configuration as shown in FIG. 6B, instead of using 52 having a large taper angle, the negative electrode convex portion 17 is pushed out to the outer peripheral side without being caught inside the opening portion 17a, so that a coma having a small taper angle is formed. 51, it is necessary to perform preliminary brazing on the base of the negative electrode protrusion 17. In other words, after the top 51 having a small taper angle is once pushed into the central opening 17 a of the negative electrode convex portion 17, the top 52 having a large taper angle is pushed into the central opening 17 a of the negative electrode convex portion 17. Since it is necessary to braze the root, the brazing process becomes two stages. Therefore, in the form of the power generation element 10a in which the negative electrode convex portion 17 is not curved and the power generation element 10b in which the negative electrode convex portion 17 is curved and narrowed inward, if the battery is manufactured by simplifying the process, the negative electrode current collector The possibility of causing poor welding between the plate 21 and the negative electrode protrusion 17 is increased.

  On the other hand, as shown in FIG. 5 (c), in the power generation element 10 c in which the surface 12 e with a large crystal of the negative electrode metal foil 12 a is arranged toward the outside of the power generation element 10 when the power generation element 10 is formed, the negative electrode protrusion 17 Is intentionally created with the power generating element 10c curved outward. Therefore, as shown in FIG. 7A, the power generation element 10c in which the negative electrode convex portion 17 curves and spreads outward has a negative opening because the central opening 17a of the negative electrode convex portion 17 curves and spreads outward. The convex portion 17 is not caught by the tapered portion of the top 52 having a large taper angle. Accordingly, since the negative electrode convex portion 17 is not caught inside the power generation element 10 and is not broken, the possibility that the negative electrode current collecting plate 21 and the negative electrode convex portion 17 cause poor welding is reduced, and a coma with a small taper angle is formed. Since the top 52 having a large taper angle can be pushed in without the preliminary brazing process of pushing 51, the spare brazing process can be reduced.

  FIG. 7B is a view showing a state after the negative electrode convex portion 17 is brazed until the negative electrode current collector plate 21 and the negative electrode convex portion 17 are welded. The negative electrode protrusion 17 of the power generation element 10 is formed with an annular protrusion 17b having a size that allows the negative electrode current collector plate 21 to be inserted by a piece 52 having a large taper angle. The negative electrode current collector plate 21 is inserted into the annular projecting portion 17b, the negative electrode convex portion 17 is brought into close contact with the outer peripheral cylindrical portion 21c of the negative electrode current collector plate 21, and the pressing member 22 is wound around the outer periphery of the negative electrode convex portion 17 in a ring shape. It is fixed and welded in this state.

  FIG. 8 is an enlarged view of a portion B in the AA cross section of FIG. The negative electrode protrusion 17 has a large crystal surface 12 e disposed outside the power generation element 10. The negative electrode convex portion 17 is curved at the inner peripheral portion of the power generation element 10 because the R portion is tight, and only the tip portion is curved outward of the power generation element 10. On the other hand, since the R portion is loose at the outer peripheral portion of the power generation element 10, the bending is not suppressed, and the negative electrode convex portion 17 is curved to the outside of the power generation element 10. In order to facilitate the insertion of the top 52, it is necessary that the negative electrode protrusion 17 bends toward the outside of the power generation element 10. However, if the outermost negative electrode convex portion 17 is warped too much, it may interfere with a jig required in the step of inserting the top 52, and the productivity of the power generating element 10 may be reduced. Therefore, by suppressing the curvature of the negative electrode convex portion 17 on the inner peripheral side as in the present invention, the influence on the curvature of the negative electrode convex portion 17 on the outermost periphery can be reduced, and the negative electrode convex portion 17 interferes with the jig. This can be suppressed.

  A process flow from electrode coating to convex welding of the battery according to the present invention will be described.

  First, in step S1, the negative electrode 12 is produced by applying a negative electrode mixture on both surfaces of a negative electrode metal foil 12a using an electrolytic copper foil produced by electrodeposition.

  In step S2, the negative electrode protrusion 17 is formed by cutting the negative electrode metal foil 12a by pressing. At this time, the negative electrode convex portion 17 can be curved toward the surface 12e where the crystal is large due to the difference in stress that the negative electrode metal foil 12a has.

  Subsequently, in step S3, the power generation element 10 is produced by winding the positive electrode 11, the negative electrode 12, and the first and second separators 13 and 14 around the shaft core 15. At this time, the negative electrode 12 is wound with the surface 12 e on which the crystal of the negative electrode metal foil 12 a grows facing the outside of the power generation element 10. By creating the power generation element 10 in this way, it is possible to create a state in which the negative electrode protrusion 17 is curved toward the outer peripheral side of the power generation element 10 and the opening 17a is pushed and spread.

  In step S <b> 4, the annular protrusion 17 b is formed by pushing a piece 52 having a large taper angle into the negative electrode protrusion 17 of the power generation element 10.

  Thereafter, the process proceeds to step S5, and the negative electrode current collector plate 21 is inserted into the annular protrusion 17b.

  Finally, in step S6, the negative electrode protrusion 17 is brought into close contact with the outer peripheral cylindrical portion 21c of the negative electrode current collector plate 21 inserted into the annular protrusion 17b, and the holding member 22 is wound around the outer periphery of the negative electrode protrusion 17 in a ring shape. Weld after fixing.

  By performing these six steps, it is possible to manufacture the power generation element 10 in which the surface 12e with large crystal grains of the negative electrode convex portion 17 is arranged outward of the power generation element 10, and the negative electrode convex portion 17 is curved outward of the power generation element 10. A cylindrical secondary battery having stress can be manufactured.

  In the present embodiment, the example using the electrolytic copper foil has been described as a representative example. However, even when the positive electrode metal foil has different crystal grains on the front and back sides, There is a similar effect.

  In the present embodiment, the negative electrode metal foil 12a using an electrolytic copper foil has been described as a representative example. However, a copper foil other than the electrolytic copper foil has different crystal grain sizes on the front and back sides. In this case, the same effect as described above can be obtained.

  In the present invention, the cylindrical secondary battery in which the negative electrode convex portion 17 is provided on the negative electrode metal foil 12a has been described as a representative example. However, the present invention may be applied to a power generation element of a square secondary battery. When applied to a power generation element of a square secondary battery, a force is applied to the curved portions provided at both ends of the power generation element, so that the amount of warpage of the metal foil of the cylindrical secondary battery is reduced, but the power generation element By making the metal foil warp on the outer peripheral side, it becomes easy to insert a welding jig into the opening of the power generation element when welding the current collector plate and the metal foil. Therefore, the possibility that the welding jig wraps the metal foil and causes poor welding between the current collector plate and the metal foil is reduced, and the welding reliability is improved.

  The present invention will be briefly described above. The secondary battery according to the present invention has a power generation element (10) in which an electrode (12) provided with a mixture layer (12b) is provided on a metal foil (12a), and the metal foil (12a) is The crystal grain size is different between one surface (12c) and the other surface (12e), and the electrode (12) is arranged on the outer peripheral side of the power generation element 10 with the surface (12e) having a large metal foil crystal facing. Is done. By adopting such a structure, since the electrode convex portion spreads on the outer peripheral side of the power generation element 10, a jig can be inserted without bending the metal foil. Therefore, the welding reliability between the metal foil and the current collecting member is improved.

  Further, the secondary battery described in the present invention has a structure in which the warpage of the metal foil (12a) is larger on the outer peripheral side than on the inner peripheral side of the power generation element 10. By adopting such a structure, since the electrode convex portion does not extend too far outside the power generation element 10, the electrode convex portion and the jig do not interfere with each other, and the productivity is improved.

  In the secondary battery according to the present invention, the thickness of the metal foil is 20 μm or less. With such a structure, the metal foil can be sufficiently warped, so that interference between the jig and the metal foil can be suppressed. Therefore, the metal foil can be welded to the current collector plate without bending, and the welding reliability is improved.

  In the secondary battery described in the present invention, the length of the copper foil protruding from the mixture layer is 20 mm or more. By adopting such a structure, the metal foil can be sufficiently warped, and as a result, the welding reliability is improved.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various designs can be made without departing from the spirit of the present invention described in the claims. It can be changed. For example, the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to one having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Furthermore, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

DESCRIPTION OF SYMBOLS 1 Cylindrical secondary battery 2 Battery can 2a Groove 2b Opening part 3 Battery cover 3a Peripheral part 3b Cylindrical part 3c Opening part 4 Battery container 5 Non-aqueous electrolyte 10 Electric power generation element 10a Electric power generation element 10b Negative electrode convex part 17 is not curving 10b Negative electrode Power generation element 10 c with convex portion 17 constricted inward Power generation element with negative electrode convex portion 17 spreading outward 11 Positive electrode 11 a Positive metal foil 11 b Positive electrode mixture layer 11 c Positive foil exposed portion 12 Negative electrode 12 a Negative metal foil 12 b Negative electrode Mixture layer 12c Negative electrode foil exposed portion 12d Surface with small crystal 12e Surface with large crystal 13 First separator 14 Second separator 15 Core 15a Upper hollow portion 15b Step portion 16 Positive electrode convex portion 17 Negative electrode convex portion 17a Negative electrode convex portion Opening 17b in the center of the part 17 Annular protrusion 19 Adhesive tape 20 Power generation unit 21 Negative electrode current collector 21a Base 21b 21c outer peripheral cylinder part 21d opening part 22 holding member 27 positive electrode current collector plate 27a base part 27b lower cylinder part 27c upper cylinder part 27d opening part 27e opening part 28 holding member 30 battery cover unit 33 connecting member 34 insulating plate 34a opening part 34b side part 35 Connection plate 35a Protrusion 35b Opening 37 Diaphragm 37a Notch 37b Side wall 43 Gasket 43a Base 43b Outer peripheral wall 50 Connection lead plate 51 Top with small taper angle 52 Top with large taper angle

Claims (6)

In a secondary battery having a power generation element in which an electrode provided with a mixture layer on a metal foil is wound,
The metal foil has different crystal grain sizes on one side and the other side,
The secondary battery according to claim 1, wherein the electrode is disposed on an outer peripheral side of the power generation element such that a surface having a large crystal of the metal foil faces. The secondary battery according to claim 1,
The secondary battery is characterized in that the warpage of the metal foil is larger on the outer peripheral side than on the inner peripheral side of the power generating element. The secondary battery according to claim 2,
The secondary battery, wherein the metal foil is a copper foil prepared by electrodeposition. The secondary battery according to claim 3,
The secondary battery is characterized in that a thickness of the copper foil is 20 μm or less. The secondary battery according to claim 3 or 4,
The length of the copper foil which protruded from the said mixture layer is 20 mm or more, The secondary battery characterized by the above-mentioned. In a method for producing a secondary battery having a power generation element in which an electrode provided with a mixture layer on a metal foil is wound,
The metal foil has a step in which the size of crystal grains is different between one surface and the other surface, and the large surface of the metal foil is wound so that the large surface of the metal foil faces the outer peripheral side of the power generation element. A method for producing a secondary battery.