JP2016018675A - Secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate welding of a bus bar and enhance the joint strength and the electrical characteristic between a metal member and an external terminal to which the bus bar is joined as compared with prior arts in secondary batteries having external terminals of a positive electrode and a negative electrode formed of different materials, the second batteries being connected to each other in series by the bus bar formed of the same kind of one of the external terminals.SOLUTION: A secondary battery 100 is formed of a material having excellent weldability to the material of one external terminal 20A of external terminals 20A, 20B of positive and negative electrodes. The secondary battery 100 has a metal member 21 which is ultrasonically press-fitted to the other external terminal 20B of the external terminals 20a, 20B of the positive and negative electrodes, and has a bus bar joint face 21a to which the bus bar B is welded.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a secondary battery, for example, a prismatic secondary battery mounted on a vehicle or the like.

  2. Description of the Related Art Conventionally, a secondary battery having a large capacity has been developed as a power source for, for example, a hybrid electric vehicle or a pure electric vehicle. Among such secondary batteries, a rectangular lithium ion secondary battery is attracting attention as a secondary battery having a high energy density.

  The prismatic lithium ion secondary battery is manufactured, for example, as follows. First, a positive electrode in which a positive electrode active material is applied to a positive electrode foil, a negative electrode in which a negative electrode active material is applied to a negative electrode foil, and a separator that insulates them are overlapped and wound to produce a flat storage element. Next, the power storage element is electrically connected to the positive electrode external terminal and the negative electrode external terminal provided on the battery lid, accommodated in the battery can, and the opening of the battery can is welded and sealed with the battery lid. Then, an electrolytic solution is injected from a liquid injection hole provided in the battery lid, a liquid injection stopper is inserted into the liquid injection hole, and welding sealing is performed by laser welding.

  A plurality of the above-described prismatic lithium ion secondary batteries are arranged, a bus bar is welded to an external terminal of each secondary battery, and the plurality of secondary batteries are connected in series or in parallel to produce an assembled battery. Here, when the material of the positive electrode external terminal and the material of the negative electrode external terminal of the secondary battery are different, it may be difficult to weld the one external terminal to the bus bar. For example, when the material of the positive electrode external terminal is aluminum and the material of the negative electrode external terminal is copper, if an aluminum bus bar is used, welding with the negative electrode external terminal becomes difficult, and if a copper bus bar is used, Welding with the positive external terminal becomes difficult.

  For such a problem, a secondary battery in which a positive electrode connection terminal connected to the positive electrode of the electricity storage element and a negative electrode connection terminal connected to the negative electrode of the electricity storage element are made of different metals, the positive electrode connection terminal and the negative electrode connection An intermediate member welded to one of the connection terminals of the terminal, and an external terminal made of the same metal as the other connection terminal of the positive electrode connection terminal and the negative electrode connection terminal and diffused to the intermediate member Is known (for example, see Patent Document 1 below).

  In Patent Document 1, for example, a rolled clad material is used in which an external terminal, which is an aluminum metal plate, and an intermediate member, which is a nickel metal plate, are rolled and diffusion bonded together. Then, the nickel intermediate member of the rolled clad material and the copper negative electrode connection terminal are overlapped, and the boundary portion between the side end surface of the intermediate member and the side end surface of the negative electrode connection terminal is irradiated with laser light and welded. Yes. According to such a secondary battery, it is possible to reduce the connection resistance of the bus bar as compared to the connection by brazing and caulking and to obtain a highly rigid terminal structure.

International Publication No. 2012/169055

  When connecting a plurality of secondary batteries having positive and negative external terminals made of different materials as described above in series, not only facilitate welding of the bus bar, but also a member bonded to the bus bar and the external terminal, It is required to improve the bonding strength and electrical characteristics between the two. However, in the secondary battery described in Patent Document 1, the bonding strength and electrical properties are reduced by the welded portion at the boundary between the side end surface of the intermediate member of the rolled clad material having a relatively small volume and the side end surface of the negative electrode connection terminal. Characteristics are affected. Therefore, it is difficult to improve the bonding strength and electrical characteristics between the rolled clad material and the negative electrode connection terminal.

  The present invention has been made in view of the above problems, and the object thereof is to provide positive and negative external terminals made of different materials, the same kind as one of the external terminals of the positive and negative electrodes. In the secondary battery connected in series by the bus bar made of the above material, the welding strength of the metal member to which the bus bar is joined and the external terminal are improved as compared with the conventional battery while facilitating the welding of the bus bar. It is in providing the secondary battery which can do.

  In order to achieve the above object, the secondary battery of the present invention includes positive and negative external terminals made of different materials, and is connected in series by a bus bar made of the same material as one of the external terminals of the positive and negative electrodes. A secondary battery connected to the first external terminal made of a material excellent in weldability to the material of the one external terminal, and ultrasonically pressed to the other external terminal of the positive and negative external terminals, A metal member having a bus bar joint surface to which the bus bar is welded is provided.

  According to the secondary battery of the present invention, when a plurality of secondary batteries are connected in series by the bus bar, one end of the bus bar made of the same kind of material as the material of one of the external terminals of the positive electrode and the negative electrode, It is possible to easily and satisfactorily weld the one external terminal. Further, the other end of the bus bar is made of a material excellent in weldability to the same type of material as that of the one external terminal, and is a metal member that is ultrasonically pressed to the other external terminal of the positive and negative external terminals. It can be easily and satisfactorily welded to the bus bar joint surface. In addition, the other external terminal and the metal member are bonded to each other by removing the oxide film or the like on the bonding surface by ultrasonic pressure welding, causing migration of metal atoms by diffusion, and being firmly bonded by solid-layer bonding. As a result, the bonding strength and electrical characteristics between them are improved.

  Therefore, according to the secondary battery of the present invention, when connecting secondary batteries having positive and negative external terminals made of different materials in series, the bus bar is joined while facilitating welding of the bus bar. The bonding strength and electrical characteristics between the member and the external terminal can be improved as compared with the conventional case. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments for carrying out the invention.

1 is an external perspective view showing two secondary batteries according to Embodiment 1 of the present invention. The disassembled perspective view which shows the internal structure of the secondary battery shown in FIG. The disassembled perspective view which expanded a part of winding body shown in FIG. Process drawing which shows the process of joining a metal member with respect to an external terminal. Process drawing which shows the process of joining a metal member with respect to an external terminal. Process drawing which shows the process of joining a metal member with respect to an external terminal. Process drawing which shows the process of forming a bus-bar joining surface in a metal member. Process drawing which shows the process of welding a bus bar to a metal member. Sectional drawing which shows the state by which the bus bar was welded to the metal member. Sectional drawing which shows the external terminal and metal member of a secondary battery which concern on Embodiment 2 of this invention. Sectional drawing which shows the state by which the bus-bar was welded to the metal member shown to FIG. 7A. FIG. 6 is an external perspective view showing a secondary battery according to Embodiment 3.

(Embodiment 1)
Hereinafter, Embodiment 1 of the secondary battery of the present invention will be described with reference to the drawings.

  FIG. 1 is an external perspective view showing two secondary batteries 100 according to Embodiment 1 of the present invention.

  The secondary battery 100 is a rectangular secondary battery including a rectangular box-shaped battery container 10 made of a metal material such as aluminum or an aluminum alloy, for example. The battery container 10 includes a flat bottomed rectangular tube-shaped battery can 11 having an opening at the top, and a rectangular plate-shaped battery lid 12 that seals the opening of the battery can 11. The battery can 11 is formed in a flat bottomed rectangular tube shape, for example, by subjecting the metal material to deep drawing.

  Positive and negative external terminals 20A and 20B made of different materials are provided on the upper surface of the battery lid 12 outside the battery container 10 at both ends in the width direction of the battery container 10, that is, in the longitudinal direction of the battery lid 12. A gasket 13 as an insulating member is disposed between the external terminals 20A and 20B and the battery cover 12, and the external terminals 20A and 20B are electrically insulated from the battery cover 12.

  The positive external terminal 20A is made of, for example, aluminum or an aluminum alloy, and the negative external terminal 20B is made of, for example, copper or a copper alloy. The positive and negative external terminals 20A and 20B are each formed in a substantially cylindrical shape. Note that the shapes of the positive and negative external terminals 20A and 20B are not limited to a cylindrical shape, and may be formed, for example, in a substantially rectangular parallelepiped block shape or a rectangular plate shape.

  The secondary battery 100 includes a metal member 21 made of a material excellent in weldability to the material of one of the external terminals 20A among the positive and negative electrodes 20A and 20B and ultrasonically pressed to the other external terminal 20B. Yes. In the present embodiment, the metal member 21 is, for example, a metal plate-like member having a thickness of about several millimeters, and is made of a material excellent in weldability to the material of the positive external terminal 20A. Ultrasonic pressure contact is made on the upper surface of 20B.

  Here, the weldability of the other material to one material represents the ability of the material to perform good welding when welding one material and the other material by an appropriate welding method. is there. In the present embodiment, the material of the positive external terminal 20A, for example, a material that can obtain the required bonding strength and electrical characteristics when welded to aluminum or an aluminum alloy, such as aluminum, aluminum alloy, nickel, nickel alloy, etc. The material is excellent in weldability to the material of the positive external terminal 20A.

  That is, as the material of the metal member 21, the same kind of metal excellent in weldability to the material of the positive electrode external terminal 20A, such as aluminum or an aluminum alloy, or a different kind of metal, such as nickel or a nickel alloy, can be used. In addition, nickel or nickel alloy is excellent also in the weldability with respect to the copper or copper alloy which is the material of the external terminal 20B of a negative electrode. In the secondary battery 100 of the present embodiment, the metal member 21 is made of the same type of metal as the material of the positive electrode external terminal 20A among the positive electrode and negative electrode external terminals 20A and 20B, that is, aluminum or an aluminum alloy. Yes.

  Also, the metal member 21 and the external terminal 20B are diffusion-bonded at the contact interface by ultrasonic pressure welding, and the bonding layer CL (see FIG. 4D) has a different composition from the material of the metal member 21 and the external terminal 20B at the bond interface. ) Is formed. In the bonding layer CL, the materials of the members to be bonded are in a state of entering each other by plastic flow, for example. The thickness of the bonding layer CL formed by ultrasonic pressure welding is, for example, about 0.1 μm to several μm, or about several μm to several tens of μm. On the other hand, the thickness of the joining layer formed at the joining interface by other welding methods such as resistance welding is, for example, about 0.1 mm to several mm. Therefore, whether or not the metal member 21 and the external terminal 20B are ultrasonically welded is determined by, for example, photographing the cross section in the vicinity of the joint interface between them with a scanning electron microscope or the like, and the form, composition, It can be determined by measuring the thickness or the like.

  The metal member 21 has a bus bar joint surface 21a that is smoothened so that the bus bar B connecting the external terminals 20A and 20B of the adjacent secondary battery 100 can be welded. The height from the upper surface of the battery lid 12 to the bus bar joint surface 21a is equal to the height from the upper surface of the battery lid 12 to the upper surface of the positive external terminal 20A. That is, in the height direction perpendicular to the upper surface of the battery cover 12, the height from the upper surface of the battery cover 12 to the upper surface of the negative external terminal 20B is the height from the upper surface of the battery cover 12 to the upper surface of the positive external terminal 20A. It is lower than the thickness by the thickness of the metal member 21.

  Although details will be described later, when the lower surface of the plate-shaped metal member 21 is ultrasonically pressed to the upper surface of the external terminal 20B, several hundreds of the upper surface opposite to the lower surface of the metal member 21 to be joined to the external terminal 20B, for example, Unevenness of about μm is formed. Thereafter, the bus bar joint surface 21a is provided on the upper surface of the metal member 21 by performing a surface treatment that smoothes the unevenness and reduces the surface roughness, such as a cutting process, a polishing process, or a melt process. ing. From the viewpoint of good welding of the bus bar B, the surface roughness of the bus bar joint surface 21a is, for example, an arithmetic average roughness Ra, preferably 6.3 μm or less, more preferably 3.5 μm or less, and still more preferably 1. 0 μm or less.

  The bus bar B welded to the upper surface of the one external terminal 20A and the bus bar joint surface 21a of the metal member 21 is made of the same material as the material of the one external terminal 20A. That is, in the present embodiment, the bus bar B is a rectangular plate-like member that is made of the same material as the material of the positive external terminal 20A, for example, aluminum or an aluminum alloy and has a thickness equivalent to that of the metal member 21. is there.

  Between the positive and negative external terminals 20A and 20B of the battery lid 12, a gas discharge valve 14 and a liquid injection port 15 are provided. The gas discharge valve 14 is provided, for example, by thinning the battery cover 12 by press working, and further, a cleavage groove 14a is formed. When the internal pressure of the battery container 10 rises above a predetermined value due to, for example, overcharging, the gas discharge valve 14 opens the cleavage groove 14a and releases the gas inside the battery container 10 to reduce the internal pressure. . The liquid injection port 15 is used to inject an electrolytic solution into the battery container 10 and is sealed by welding a liquid injection plug 16b by laser welding, for example.

  For example, when a plurality of secondary batteries 100 are connected in series by a bus bar to form an assembled battery, the secondary batteries 100 are stacked in the thickness direction, and the positive and negative electrodes of the secondary batteries 100 adjacent to each other. The positions of the external terminals 20A and 20B are alternately reversed by 180 °. Then, the positive external terminal 20A of one adjacent secondary battery 100 and the negative external terminal 20B of the other secondary battery 100 are connected by a bus bar B. By repeating this in the stacking direction of the secondary batteries 100, a plurality of secondary batteries 100 stacked in the thickness direction are connected in series. Here, the bus bar B has one end joined to the upper surface of the positive external terminal 20A by welding and the other end joined to the metal member 21 ultrasonically welded to the upper surface of the negative external terminal 20B by welding.

  FIG. 2 is an exploded perspective view showing the internal structure of the secondary battery 100 shown in FIG.

  The battery can 11 is a bottomed rectangular tube-shaped, substantially rectangular parallelepiped container having an open upper end in the height direction and an opening 11a at the top. The battery can 11 has a bottom surface 11b that closes the lower end in the height direction, a pair of large side surfaces 11c that face each other in the thickness direction, and a pair of narrow side surfaces 11d that face each other in the width direction. ing.

  Positive and negative current collecting plates 30 </ b> A and 30 </ b> B are fixed to the lower surface of the battery lid 12 inside the battery container 10 at both ends in the longitudinal direction of the battery lid 12 via insulating members 17. The positive current collecting plate 30A is made of, for example, aluminum or an aluminum alloy, and the negative current collecting plate 30B is made of, for example, copper or a copper alloy. The current collecting plates 30 </ b> A and 30 </ b> B each include a plate-like base portion 31 that is substantially parallel to the battery lid 12 and a plate-like terminal portion 32 that extends from the base portion 31 toward the bottom surface 11 b of the battery can 11. .

  The external terminals 20 </ b> A and 20 </ b> B have a columnar connection portion 22 that extends perpendicularly to the upper surface of the battery lid 12 from the lower surface of the portion formed in a substantially cylindrical shape. Each connection part 22 of the external terminals 20A and 20B is formed in, for example, a cylindrical shape, and the battery cover 12, the gasket 13 and the insulating member 17 disposed above and below the base part 31 of each of the current collector plates 30A and 30B. It penetrates the through hole formed. The gasket 13 and the insulating member 17 are made of an insulating resin material such as polybutylene terephthalate, polyphenylene sulfide, and perfluoroalkoxy fluororesin.

  The connecting portion 22 penetrating through the through hole of each member is expanded in diameter by plastic deformation of the tip portion on the lower surface of the base portion 31 to form a caulking portion. Accordingly, the positive and negative external terminals 20A and 20B are electrically connected to the positive and negative current collector plates 30A and 30B, respectively, and these members are electrically insulated from the battery lid 12 by the gasket 13 and the insulating member 17. In this state, the battery lid 12 is integrally fixed.

  The terminal portions 32 of the positive and negative current collecting plates 30 </ b> A and 30 </ b> B extend from one side of the base portion 31 in the thickness direction of the battery case 10 to the bottom surface 11 b of the battery can 11 along the wide side surface 11 c of the maximum area of the battery can 11. It is formed in the plate shape extended toward. The terminal portions 32 of the positive and negative current collector plates 30A and 30B extend downward from the outer end portion of the base portion 31 in the winding axis A direction of the winding body 40, which will be described later, and are end portions of the winding body 40. Are joined to current collector plate joining portions 41d and 42d. Thereby, the positive current collector 30A is electrically connected to the positive electrode 41 (see FIG. 3) at one end in the winding axis A direction of the wound body 40, and the negative current collector 30B is The other end of the wound body 40 in the winding axis A direction is electrically connected to the negative electrode 42 (see FIG. 3).

  The wound body 40 is fixed to the battery lid 12 via the positive and negative current collector plates 30A and 30B and the insulating members 17 and 17 by being joined to the terminal portions 32 of the positive and negative current collector plates 30A and 30B. ing. Further, the positive and negative external terminals 20A and 20B, the gasket 13, the insulating member 17, the current collector plates 30A and 30B, and the wound body 40 are assembled to the battery lid 12, whereby the lid assembly 50 is manufactured.

  An insulating case 60 that covers the wound body 40 is disposed between the battery can 11 and the wound body 40. The insulating case 60 is an insulating resin such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), tetrafluoroethylene (PFA), polyphenylene sulfide (PPS), etc. It is made of materials.

  At the time of manufacturing the secondary battery 100, the insulating case 60 is arranged so as to cover the periphery of the wound body 40 and the current collector plates 30A and 30B constituting the lid assembly 50. The lid assembly 50 opens the battery can 11 from the curved portion 40b on the lower side of the winding body 40 in a state where the periphery of the winding body 40 and the current collector plates 30A and 30B are covered by the insulating case 60. It is inserted into the part 11a. Thus, the wound body 40 and the current collector plates 30 </ b> A and 30 </ b> B are accommodated in the battery container 10 in a state where the insulating case 60 is disposed between the wound body 40 and the current collector plate 30 </ b> A, 30 </ b> B and is electrically insulated from the battery can 11. .

  The wound body 40 is configured so that the narrow side surface 11d of the battery can 11 is positioned on both sides in the winding axis A direction, and the winding axis A direction is substantially parallel to the bottom surface 11b and the wide side surface 11c of the battery can 11. Housed in a can 11. Thereby, the winding body 40 which is an electrical storage element has one curved portion 40b facing the battery lid 12, the other curved portion 40b facing the bottom surface 11b of the battery can 11, and the flat portion 40a facing the wide side surface 11c. It will be in the opposite state.

  Then, with the battery lid 12 closing the opening 11 a of the battery can 11, for example, the entire circumference of the battery lid 12 is joined to the opening 11 a of the battery can 11 by laser welding. Thereby, the opening 11 a of the battery can 11 is hermetically sealed by the battery lid 12, and the battery container 10 including the battery can 11 and the battery lid 12 is formed.

Thereafter, a nonaqueous electrolytic solution is injected into the battery container 10 through the injection port 15 of the battery lid 12, and a sealing material 16a is inserted into the injection port 15 and press-fitted. For example, the injection plug is formed by laser welding. The battery container 10 is hermetically sealed by joining 16b to the liquid injection port 15 and sealing. Examples of the non-aqueous electrolyte injected into the battery container 10 include lithium hexafluorophosphate (LiPF ₆ ) in a mixed solution in which ethylene carbonate and dimethyl carbonate are mixed at a volume ratio of 1: 2. Can be used at a concentration of 1 mol / liter.

  FIG. 3 is an exploded perspective view in which a part of the wound body 40 shown in FIG. 2 is developed. In addition, in FIG. 3, the state before forming the current collector plate junction parts 41d and 42d shown in FIG.

  The wound body 40 is a wound electrode group in which positive and negative electrodes 41 and 42 stacked with separators 43 and 44 interposed therebetween are wound around an axis parallel to the winding axis A and formed into a flat shape. . The wound body 40 is formed into a flat shape having a flat portion 40 a facing the wide side surface 11 c of the battery can 11 and a curved portion 40 b facing the battery lid 12 and the bottom surface 11 b of the battery can 11. The flat portion 40a is a portion where the electrodes 41, 42 and the separators 43, 44 are laminated flat, and the curved portion 40b is a portion where the electrodes 41, 42 and the separators 43, 44 are bent and laminated in a semi-cylindrical shape. It is.

  The separators 43 and 44 insulate the positive electrode 41 and the negative electrode 42, and the separator 44 is wound around the outer periphery of the negative electrode 42 wound around the outermost periphery of the wound body 40. The separators 43 and 44 are made of, for example, porous polyethylene resin.

  The positive electrode 41 includes a positive electrode metal foil 41a that is a positive electrode current collector, and a positive electrode mixture layer 41b made of a positive electrode active material mixture applied to both surfaces of the positive electrode metal foil 41a. One side in the width direction of the long belt-like positive electrode 41 is a foil exposed portion 41c in which the positive electrode mixture layer 41b is not formed and the positive electrode metal foil 41a is exposed. The positive electrode 41 is wound around the winding axis A such that the foil exposed portion 41 c is arranged on the opposite side of the winding axis A direction of the foil exposed portion 42 c of the negative electrode 42.

  In order to manufacture the positive electrode 41, for example, a positive electrode active material mixture obtained by adding and kneading a conductive material, a binder, and a dispersion solvent to a positive electrode active material is mixed on both surfaces of the positive electrode metal foil 41a except for one side in the width direction. Apply, dry, press and cut. As the positive electrode metal foil 41a, for example, an aluminum foil having a thickness of about 20 μm to 30 μm can be used. The thickness of the positive electrode mixture layer 41b not including the thickness of the positive electrode metal foil 41a is, for example, about 90 μm.

As a material of the positive electrode active material mixture, for example, 100 parts by weight of lithium manganate (chemical formula LiMn ₂ O ₄ ) is used as the positive electrode active material, 10 parts by weight of flaky graphite as the conductive material, and 10% by weight as the binder. Part of polyvinylidene fluoride (hereinafter referred to as PVDF) and N-methylpyrrolidone (hereinafter referred to as NMP) can be used as a dispersion solvent.

  The positive electrode active material is not limited to the above-described lithium manganate. For example, another lithium manganate having a spinel crystal structure, or a lithium manganese composite oxide partially substituted or doped with a metal element may be used. Further, as the positive electrode active material, lithium cobaltate or lithium titanate having a layered crystal structure, and a lithium-metal composite oxide obtained by substituting or doping a part thereof with a metal element may be used.

  The negative electrode 42 includes a negative electrode metal foil 42a that is a negative electrode current collector, and a negative electrode mixture layer 42b made of a negative electrode active material mixture applied to both surfaces of the negative electrode metal foil 42a. One side in the width direction of the long strip-like negative electrode 42 is a foil exposed portion 42c where the negative electrode mixture layer 42b is not formed and the negative electrode metal foil 42a is exposed. The negative electrode 42 is wound around the winding axis A such that the foil exposed portion 42c is arranged on the opposite side of the winding axis A direction of the foil exposed portion 41c of the positive electrode 41.

  In order to manufacture the negative electrode 42, for example, a negative electrode active material mixture kneaded by adding a binder and a dispersion solvent to the negative electrode active material is applied to both surfaces of the negative electrode metal foil 42a except for one side in the width direction. , Dry, press, cut. As the negative electrode metal foil 42a, for example, a copper foil having a thickness of about 10 μm to 20 μm can be used. The thickness of the negative electrode mixture layer 42b not including the thickness of the negative electrode metal foil 42a is, for example, about 70 μm.

As a material for the negative electrode active material mixture, for example, 100 parts by weight of amorphous carbon powder as the negative electrode active material, 10 parts by weight of PVDF as the binder, and NMP as the dispersion solvent can be used. The negative electrode active material is not limited to the above-mentioned amorphous carbon, and natural graphite capable of inserting and removing lithium ions, various artificial graphite materials, carbonaceous materials such as coke, and compounds such as Si and Sn (for example, , SiO, TiSi ₂ or the like), or a composite material thereof. The particle shape of the negative electrode active material is not particularly limited, and a particle shape such as a scale shape, a spherical shape, a fiber shape, or a lump shape can be appropriately selected.

  The binder used for the positive electrode and negative electrode mixture layers 41b and 42b is not limited to PVDF. Examples of the binder include polytetrafluoroethylene (PTFE), polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber, styrene butadiene rubber, polysulfide rubber, nitrocellulose, cyanoethyl cellulose, various latexes, acrylonitrile, and vinyl fluoride. Polymers such as vinylidene fluoride, propylene fluoride, chloroprene fluoride, and acrylic resins, and mixtures thereof may be used.

  In the wound body 40, foil exposed portions 41c and 42c of positive and negative electrodes 41 and 42 stacked at both ends in the winding axis A direction are bundled, respectively, and as shown in FIG. 42d is formed. Then, for example, the positive and negative current collector plates 30A and 30B are joined to the positive and negative current collector plate joint portions 41d and 42d by ultrasonic pressure welding, respectively, so that the positive and negative electrodes 41 and 42 become positive and negative current collectors, respectively. The plates are connected to positive and negative external terminals 20A and 20B through the plates 30A and 30B, respectively.

  Based on the above configuration, the secondary battery 100 according to the present embodiment, for example, supplies power supplied from an external power generator or the like to the winding body 40 via the external terminals 20A and 20B and the current collector plates 30A and 30B. Charging is performed by accumulating between the mixture layers 41 b and 42 b of the positive and negative electrodes 41 and 42. Further, the secondary battery 100 is configured such that the electric power charged between the mixture layers 41b and 42b of the positive and negative electrodes 41 and 42 of the wound body 40 is supplied to the motor via the current collector plates 30A and 30B and the external terminals 20A and 20B. For example, power is supplied to an external load that consumes power.

  Hereinafter, the process of joining the metal member 21 to the negative external terminal 20B of the positive and negative external terminals 20A and 20B included in the secondary battery 100 of the present embodiment will be described.

  4A to 4C are process diagrams showing a process of joining the metal member 21 to the negative external terminal 20B by ultrasonic pressure welding. FIG. 4D is a process diagram illustrating a process of forming the bus bar joint surface 21a on the metal member 21 joined to the negative external terminal 20B by ultrasonic pressure welding. The step of bonding the metal member 21 to the negative electrode external terminal 20B and the step of forming the bus bar bonding surface 21a on the metal member 21 are performed, for example, before the step of fixing the negative electrode external terminal 20B to the battery lid 12 described above. Done.

  When joining the metal member 21 to the negative electrode external terminal 20B by ultrasonic pressure welding, first, as shown in FIG. 4A, the anvil An is brought into contact from the side of the external terminal 20B, and the external terminal 20B is attached. Fix it. The anvil An may have a flat surface that contacts the side surface of the external terminal 20B, but a pair of anvil Ans having a semi-cylindrical curved surface that matches the side surface of the cylindrical external terminal 20B may be used. The external terminal 20B can be fixed by being sandwiched from both sides in the direction in which the horn H is vibrated by a pair of anvils An. When the external terminal 20B has a substantially rectangular parallelepiped block shape, the external terminal 20B is sandwiched and fixed by two pairs of anvils An from the two directions perpendicular to the two mutually perpendicular side surfaces of the external terminal 20B. Also good.

  Next, the metal member 21 is placed on the upper surface of the external terminal 20B fixed by the anvil An. And the unevenness | corrugation Ha of the horn H is pressed on the upper surface of the metal member 21, and the lower surface of the metal member 21 and the upper surface of the external terminal 20B are contacted in a state where the metal member 21 is pressed toward the external terminal 20B by the horn H. Let Thereby, the upper surface of the metal member 21 is plastically deformed, and the unevenness Ha of the horn H is in a state of being bitten.

  Next, as shown in FIG. 4B, the horn H is ultrasonically vibrated to perform ultrasonic pressure contact between the metal member 21 and the external terminal 20B. Specifically, the metal member 21 is pressed toward the external terminal 20B by the horn H, and the lower surface of the metal member 21 and the upper surface of the external terminal 20B are brought into contact with each other at a predetermined surface pressure. The horn H is vibrated ultrasonically along the interface. Here, the frequency of the ultrasonic vibration of the horn H is, for example, about 20 kHz or more.

  In ultrasonic pressure welding, for example, the oxide film and dirt on both members are removed by friction between the lower surface of the metal member 21 that is the contact interface and the upper surface of the external terminal 20B, and diffusion of metal atoms occurs between the materials of both members. Both members are solid-phase bonded by diffusion bonding. Note that, in ultrasonic pressure welding, the residual stress of the negative electrode external terminal 20B may be removed by setting the bonding condition to be equal to or higher than the annealing temperature of the material of the negative electrode external terminal 20B.

  By ultrasonic welding, as shown in FIG. 4C, a bonding layer CL is formed over the entire contact interface between the metal member 21 and the external terminal 20B, and the metal member 21 and the external terminal 20B are bonded firmly and densely. The On the other hand, the unevenness 21b corresponding to the unevenness Ha of the horn H is formed on the upper surface of the metal member 21 opposite to the bonding layer CL. The arithmetic average roughness Ra of the upper surface of the metal member 21 due to the unevenness 21b is, for example, about several hundred μm. It is difficult to satisfactorily weld the bus bar B to the upper surface of the metal member 21 having such irregularities 21b, and it is difficult to ensure sufficient bonding strength and electrical characteristics between the metal member 21 and the bus bar. is there.

  Therefore, in this embodiment, as shown in FIG. 4D, for example, the entire upper surface of the metal member 21 is subjected to surface processing for reducing the surface roughness to form the bus bar joint surface 21a. Here, as the surface processing for reducing the surface roughness, for example, cutting processing, polishing processing, melting processing, or the like can be performed. The side surface of the metal member 21 to which the bus bar B is not welded may not be subjected to surface processing.

  Hereinafter, the operation of the secondary battery 100 of the present embodiment will be described.

  FIG. 5 is a process diagram showing a process of welding the bus bars B and B to the positive external terminal 20A of the secondary battery 100 and the metal member 21 ultrasonically welded to the negative external terminal 20B. FIG. 6 is a cross-sectional view of the external terminal 20 </ b> B, the metal member 21, and the bus bar B showing a state in which the bus bar B is welded to the metal member 21.

  For example, when a plurality of secondary batteries 100 are connected in series to form an assembled battery, as shown in FIGS. 1 and 5, the external side of the positive electrode of one secondary battery 100 adjacent to each other in the thickness direction is used. The terminal 20A and the negative external terminal 20B of the other secondary battery 100 are connected by a bus bar B. Here, in the secondary battery 100 of the present embodiment, the positive and negative external terminals 20A and 20B are made of different materials, and the bus bar B is made of the same material as the positive external terminal 20A. Specifically, the material of the positive external terminal 20A and the bus bar B is aluminum or an aluminum alloy, and the material of the negative external terminal 20B is copper or a copper alloy.

  Therefore, when the bus bar B is welded to the positive and negative external terminals 20A, 20B, the welding of the positive external terminal 20A and the bus bar B is a weld of the same kind of metal that has excellent weldability and is capable of good welding. Sufficient bonding strength and electrical characteristics can be obtained. However, welding of the negative electrode external terminal 20B and the bus bar B results in welding of a dissimilar metal that is inferior in weldability and difficult to weld well, here, copper or a copper alloy and aluminum or an aluminum alloy. It is difficult to obtain bonding strength and electrical characteristics.

  On the other hand, the secondary battery 100 of the present embodiment is made of a material excellent in weldability to the material of one external terminal 20A, and is ultrasonically pressed to the other external terminal 20B and the bus bar B is welded. A metal member 21 having a bus bar joint surface 21a is provided.

  Therefore, one end of the bus bar B is welded to the positive external terminal 20A of one secondary battery 100, and the other end of the bus bar B is welded to the metal member 21 of the other secondary battery 100. Both ends can be welded to a material excellent in weldability with the material of the bus bar B. Therefore, the bus bar B can be easily and satisfactorily welded, and the metal member 21 between the bus bar B and the positive external terminal 20A of one secondary battery 100 and between the bus bar B and the other secondary battery 100. In this case, good bonding strength and electrical characteristics can be obtained.

  By welding the bus bar B to the metal member 21, the bus bar B is connected to the negative external terminal 20 </ b> B of the other secondary battery 100 through the metal member 21. Then, via the bus bar B and the metal member 21, the positive external terminal 20A of one secondary battery 100 and the negative external terminal 20B of the other secondary battery 100 are connected. As a welding method between the bus bar B and the metal member 21, for example, laser welding, electron beam welding, resistance welding, arc welding, or the like can be applied. As a welding method between the bus bar B and the metal member 21, for example, lap welding, butt welding, fillet welding, or the like can be applied.

  Here, the metal member 21 is ultrasonically pressed against the negative external terminal 20B, and is firmly bonded by diffusion bonding over the entire contact interface. Therefore, the metal member 21 and the negative external terminal 20B are compared with the welding of the boundary portion between the side end surface of the intermediate member of the rolled clad material described in Patent Document 1 and the side end surface of the negative electrode connection terminal. , It can be firmly bonded in a wider area. Accordingly, the bonding strength and electrical characteristics between the metal member 21 and the negative external terminal 20B can be improved.

  As shown in FIG. 6, for example, when laser welding is applied and the bus bar B is welded to the metal member 21 by lap welding, the lower end of the weld metal W is applied to the upper surface of the negative external terminal 20B or the bonding layer CL. It is preferable not to reach it. That is, it is preferable to set the welding conditions so that the penetration depth d of the metal member 21 is shallower than the thickness T of the metal member. Thereby, melting at the time of welding of the negative external terminal 20B made of copper or copper alloy can be prevented, and damage to the bonding layer CL due to diffusion bonding between the metal member 21 and the negative external terminal 20B can be prevented. . Accordingly, a decrease in bonding strength between the metal member 21 and the negative external terminal 20B is prevented, and good bonding strength and electrical characteristics can be obtained between the metal member 21 and the negative external terminal 20B.

  The metal member 21 has a bus bar joint surface 21a to which the bus bar B is welded. Therefore, unlike the case where the bus bar B is welded to the unevenness 21b formed on the metal member 21 by the ultrasonic welding horn H, the lower surface of the bus bar B is brought into close contact with the bus bar joining surface 21a, and the bus bar B and the metal member 21 are good. Welding can be performed. Thereby, the joining strength and the electrical property between the metal member 21 in which the unevenness 21b is formed by the ultrasonic pressure welding and the bus bar B can be improved.

  The metal member 21 is made of the same material as that of the one external terminal 20A. Therefore, as a material of the metal member 21, compared to a case of using a different kind of material excellent in weldability with the material of the one external terminal 20A, for example, nickel or a nickel alloy, the metal for the material of the one external terminal 20A The weldability of the member 21 can be further improved. Therefore, the weldability of the metal member 21 to the bus bar B made of the same kind of metal as the material of the one external terminal 20A is further improved, and the bonding strength and electrical characteristics between the metal member 21 and the bus bar B are further improved. Can do.

  In the present embodiment, the material of one external terminal 20A is aluminum or an aluminum alloy, and the material of the other external terminal 20B to which the metal member 21 is ultrasonically welded is copper or a copper alloy. Therefore, welding between the bus bar B made of the same kind of aluminum or aluminum alloy as the material of the one external terminal 20A and the other external terminal 20B made of copper or copper alloy is avoided, and the same kind of aluminum or aluminum alloy as the bus bar B is used. The bus bar B can be welded to the metal member 21 to be formed. Therefore, welding can be easily and satisfactorily performed between the metal member 21 and the bus bar B, and the bonding strength and electrical characteristics can be improved.

  Further, the arithmetic average roughness Ra of the bus bar joint surface 21a of the metal member 21 is set to 6.3 μm or less. As a result, the bus bar joint surface 21a and the bus bar B can be more closely adhered to each other, and the reliability of welding between the bus bar joint surface 21a and the bus bar B can be improved. In addition, if the arithmetic average roughness Ra of the bus bar joint surface 21a is, for example, 3.5 μm or less, the reliability of welding can be further improved. For example, if the arithmetic average roughness Ra is 1.0 μm or less, the reliability of welding is further improved. Can be improved. Moreover, it is preferable that the surface roughness of the lower surface of the bus bar B facing the bus bar bonding surface 21a is equal to that of the bus bar bonding surface 21a.

  As described above, according to this embodiment, in the secondary battery 100 including the positive and negative external terminals 20A and 20B made of different materials and connected in series by the bus bar B, the bus bar B can be easily welded. On the other hand, the bonding strength and electrical characteristics between the metal member 21 to which the bus bar B is bonded and the external terminal 20B can be improved as compared with the conventional case.

(Embodiment 2)
Hereinafter, Embodiment 2 of the secondary battery of the present invention will be described with reference to FIGS. 7A and 7B with reference to FIGS. 1 to 4C.

  FIG. 7A is an enlarged cross-sectional view showing a negative electrode external terminal 20B and a metal member 21A of the secondary battery of the present embodiment. FIG. 7B is an enlarged cross-sectional view showing a state where the bus bar B1 is welded to the metal member 21A shown in FIG. 7A.

  The secondary battery of the present embodiment is different from the secondary battery 100 described in the first embodiment in that a bus bar joining surface 21a is formed on a part of the upper surface of the metal member 21A. Since the other points of the secondary battery of the present embodiment are the same as those of the secondary battery 100 of the first embodiment, the same parts are denoted by the same reference numerals and description thereof is omitted.

  In this embodiment, as shown in FIG. 4C, after the metal member 21A is joined to the negative external terminal 20B by ultrasonic pressure welding, the surface roughness described above is formed on a part of the upper surface of the metal member 21A on which the unevenness 21b is formed. Surface treatment is performed to reduce the thickness. Accordingly, as shown in FIG. 7A, a bus bar joining surface 21a is formed on a part of the upper surface of the metal member 21A. That is, in the present embodiment, the bus bar joint surface 21a is a smooth surface formed on a part of the surface of the metal member 21A on which irregularities are formed by ultrasonic pressure welding. The bus bar joint surface 21a can be formed, for example, at the center of the upper surface of the metal member 21A.

  As described above, when the bus bar joining surface 21a is formed on a part of the upper surface of the metal member 21A on which the unevenness 21b is formed, the upper surface of the metal member 21A is disposed on the lower surface of the bus bar B1 facing the upper surface of the metal member 21A. Convex part Ba which protrudes toward is provided. The convex portion Ba is provided at a position corresponding to the formation position of the bus bar joint surface 21a of the metal member 21, for example, at the center in the width direction of the end portion of the bus bar B1. The lower surface of the convex portion Ba is a welding surface joined to the bus bar joining surface 21a when the bus bar B is welded to the metal member 21A. Here, the height h1 from the lower surface of the bus bar B1 to the lower surface of the convex portion Ba, that is, the protruding amount of the convex portion Ba is the maximum height h2 from the bus bar joint surface 21a of the metal member 21 to the apex of the convex portion of the concave and convex portion 21b. Larger than.

  7B, when the bus bar B1 is welded to the metal member 21A by bringing the convex portion Ba of the bus bar B1 into contact with the bus bar joint surface 21a of the metal member 21A, unevenness on the upper surface of the metal member 21A is achieved. It can be reliably avoided that 21b interferes with the lower surface of the bus bar B1. Therefore, it is possible to satisfactorily weld the bus bar B1 to the metal member 21A while minimizing the range of the bus bar joint surface 21a formed on the upper surface of the metal member 21A. Therefore, according to the secondary battery of the present embodiment, not only the same effect as the secondary battery 100 of the first embodiment described above can be obtained, but also the formation of the bus bar joint surface 21a can be facilitated to improve the productivity. Can do.

(Embodiment 3)
Hereinafter, Embodiment 3 of the secondary battery of the present invention will be described with reference to FIGS. FIG. 8 is a perspective view showing the secondary battery 100A of the present embodiment.

  In the secondary battery 100A of the present embodiment, the metal member 21B is made of a material excellent in weldability with respect to the material of the external terminal 20B of one negative electrode among the external terminals 20A and 20B of the positive electrode and the negative electrode. The secondary battery 100 is different from the secondary battery 100 of the first embodiment in that it is ultrasonically pressed to the external terminal 20A. The bus bar B2 is made of a material excellent in weldability to the material of the external terminal 20B of one negative electrode. Since the other points of the secondary battery 100A of the present embodiment are the same as those of the secondary battery 100 of the first embodiment described above, the same portions are denoted by the same reference numerals and description thereof is omitted.

  In the secondary battery 100A of the present embodiment, the material of one negative external terminal 20B is copper or a copper alloy, and the other positive electrode external terminal 20A is aluminum or an aluminum alloy. The metal member 21B and the bus bar B2 are made of the same kind of copper or copper alloy as the material of the external terminal 20B of one negative electrode.

  Thus, when a plurality of secondary batteries 100A are connected in series to form an assembled battery, one end of the bus bar B2 is welded to the external terminal 20B of the negative electrode of the one secondary battery 100A, and the other end of the bus bar B2 Are welded to the metal member 21B of the other secondary battery 100A, so that both ends of the bus bar B2 can be welded to a material excellent in weldability with the material of the bus bar B2.

  Similarly to the secondary battery 100 of Embodiment 1 described above, one end of the bus bar B2 is welded to the negative external terminal 20B of one secondary battery 100A adjacent in the stacking direction, and the metal of the other secondary battery 100A is welded. By welding the bus bar B2 to the member 21B, the bus bar B2 is connected to the positive external terminal 20A of the other secondary battery 100A through the metal member 21B. Then, the negative external terminal 20B of one secondary battery 100A and the positive external terminal 20A of the other secondary battery 100A are connected via the bus bar B2 and the metal member 21B.

  Similarly to the secondary battery 100 of the first embodiment, the metal member 21B is ultrasonically pressed against the external terminal 20A of the positive electrode and is firmly bonded by diffusion bonding over the entire contact interface. . Similarly to the secondary battery 100 of the first embodiment, the metal member 21B has a bus bar joint surface 21a.

  Therefore, according to the secondary battery 100A of the present embodiment, like the secondary battery 100 of the first embodiment, the positive and negative external terminals 20A and 20B made of different materials are provided and connected in series by the bus bar B2. In the secondary battery 100A, the welding strength and electrical characteristics between the metal member 21B to which the bus bar B2 is joined and the external terminal 20A can be improved as compared with the related art while facilitating the welding of the bus bar B2. In addition, by using a copper or copper alloy bus bar, the electrical resistance between the plurality of secondary batteries 100A can be further reduced.

  The embodiment of the present invention has been described in detail with reference to the drawings, but the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

  For example, the material of the metal member is not limited to aluminum, an aluminum alloy, copper, a copper alloy, nickel, or a nickel alloy, and can be appropriately changed according to the materials of the external terminals of the positive electrode and the negative electrode. Similarly, the material of the bus bar is not limited to aluminum, an aluminum alloy, copper, or a copper alloy, and can be appropriately changed according to the material of the external terminal of the positive electrode and the negative electrode and the material of the metal member.

20A positive external terminal, 20B negative external terminal, 21 metal member, 21a bus bar joint surface, 21b uneven, 100, 100A secondary battery, B, B1, B2 bus bar,

Claims (6)

A secondary battery comprising positive and negative external terminals made of different materials, connected in series by a bus bar made of the same kind of material as one of the external terminals of the positive and negative electrodes,
A metal made of a material excellent in weldability to the material of the one external terminal, and having a bus bar joint surface to which the bus bar is welded while being ultrasonically pressed to the other external terminal of the positive electrode and the negative electrode A secondary battery comprising a member.   The secondary battery according to claim 1, wherein the metal member is made of the same material as the material of the one external terminal. The material of the one external terminal is aluminum or an aluminum alloy,
The secondary battery according to claim 2, wherein the material of the other external terminal is copper or a copper alloy. The material of the one external terminal is copper or a copper alloy,
The secondary battery according to claim 2, wherein the material of the other external terminal is aluminum or an aluminum alloy.   The secondary battery according to claim 1, wherein the arithmetic average roughness Ra of the bus bar joint surface is 6.3 μm or less.   The said bus-bar joining surface is a smooth surface formed in a part of surface of the said metal member in which the unevenness | corrugation was formed by the said ultrasonic pressure welding, The Claim 1 characterized by the above-mentioned. Secondary battery.

Images