JP2017117739A - battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery which is high in connection strength of a tab and a lead, and low in rejection rate.SOLUTION: A battery is provided according to an embodiment, which comprises: an electrode group 5 including a positive electrode 6 and a negative electrode 7; an exterior package material in which the electrode group 5 is encased; a positive electrode terminal 3 provided on the exterior package material; a negative electrode terminal 4 provided on the exterior package material; a positive electrode lead 10 for electrically connecting the positive electrode 6 with the positive electrode terminal 3; and a negative electrode lead 11 for electrically connecting the negative electrode 7 with the negative electrode terminal 4. The battery further comprises collecting tabs 6c, 7c for electrically connecting the positive electrode 6 with the positive electrode lead 10, or electrically connecting the negative electrode 7 with the negative electrode lead 11. The collecting tabs 6c, 7c each include a piece of foil, and a protection film 6b or 7b covering at least part of a surface of the piece of foil and having a thickness of 0.01-10 μm.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to a battery.

  In recent years, vehicles such as electric vehicles and hybrid electric vehicles have been widely used. In such vehicles, lithium ion batteries are frequently used as power source batteries. The manufacturing process of a lithium ion battery is composed of various processes, and improvement in productivity is always required.

JP2012-84523A

  The problem to be solved by the present invention is to provide a battery having a high connection strength between a tab and a lead and a low defect rate.

  According to the embodiment, an electrode group including a positive electrode and a negative electrode, an exterior material containing the electrode group, a positive electrode terminal provided on the exterior material, a negative electrode terminal provided on the exterior material, a positive electrode and a positive electrode terminal, There is provided a battery including a positive electrode lead for electrically connecting the negative electrode lead and a negative electrode lead for electrically connecting the negative electrode and the negative electrode terminal. The battery further includes a current collecting tab for electrically connecting the positive electrode and the positive electrode lead or for electrically connecting the negative electrode and the negative electrode lead. The current collecting tab includes a foil and a protective film having a thickness of 0.01 μm or more and 10 μm or less covering at least a part of the surface of the foil.

It is a disassembled perspective view of the nonaqueous electrolyte battery which concerns on embodiment. The perspective view which shows the external appearance of the battery of FIG. The expansion | deployment perspective view of the electrode group used for the battery of FIG. The top view of a positive electrode and a negative electrode. The expanded sectional view which looked at the cross section along the VV line of FIG. 1 from the arrow direction. FIG. 6 is an enlarged sectional view of one layer of the tab shown in FIG. 5. The schematic diagram which shows the ultrasonic welding process performed at the manufacturing process of the battery of FIG. Sectional drawing which shows another example of the electrode group used for the battery of FIG.

  The battery of the embodiment will be described with reference to the drawings.

  The battery shown in FIGS. 1 and 3 is a sealed prismatic non-aqueous electrolyte battery. The nonaqueous electrolyte battery includes an outer can 1, a lid 2, a positive external terminal 3, a negative external terminal 4, and an electrode group 5. An exterior material is composed of the exterior can 1 and the lid 2.

  The outer can 1 has a bottomed rectangular tube shape, and is formed of a metal such as aluminum, an aluminum alloy, iron, or stainless steel, for example.

  As shown in FIG. 3, the flat electrode group 5 has a positive electrode 6 and a negative electrode 7 wound in a flat shape with a separator 8 therebetween. The positive electrode 6 includes a strip-shaped positive electrode current collector made of, for example, a foil, a positive electrode current collector tab having one end parallel to the long side of the positive electrode current collector, and at least a positive electrode current collector tab. And a positive electrode material layer (positive electrode active material-containing layer) 6a formed thereon. On the other hand, the negative electrode 7 is a negative electrode current collector except for a strip-shaped negative electrode current collector made of, for example, a foil, a negative electrode current collector tab having one end parallel to the long side of the negative electrode current collector, and at least the negative electrode current collector tab portion. And a negative electrode material layer (negative electrode active material-containing layer) 7a formed on the electric body. As shown in FIG. 4, the protective film 6b covers both main surfaces of the positive electrode current collecting tab, and the protective film 7b covers both main surfaces of the negative electrode current collecting tab. The main surface of the positive and negative current collecting tabs is a joint surface for ultrasonic metal welding. The thicknesses of the protective films 6b and 7b are preferably 0.01 μm or more and 10 μm or less.

  As shown in FIG. 3, the separator 8 is disposed between the negative electrode material layer 7a and the positive electrode material layer 6a, and each electrode is spirally wound so that the short side of each electrode is parallel to the winding axis. When turned, the electrode group 5 is obtained. In the electrode group 5, a positive electrode current collecting tab wound in a spiral shape protrudes from one end face, and a negative electrode current collecting tab wound in a spiral form protrudes from the other end face. The separator 8 is disposed between the positive electrode material layer and the negative electrode material layer. An electrolytic solution (not shown) is impregnated in the electrode group 5.

  Either the positive electrode 6 or the negative electrode 7 can be wound first, but when the negative electrode 7 is wound before the positive electrode 6, that is, when the negative electrode 7 is located at the innermost circumference, The width of the negative electrode material layer 7 a (the width in the direction parallel to the winding axis) is made wider than that of the positive electrode material layer 6 a of the positive electrode 6, and the positive electrode material layer 6 a can all face the negative electrode material layer 7 a through the separator 8. It is desirable to arrange so that. When the positive electrode 6 is wound before the negative electrode 7, it is desirable that the separator 8 covers the positive electrode material layer 6 a.

  As shown in FIG. 5, the positive electrode current collecting tab 6c and the negative electrode current collecting tab 7c wound in a spiral shape are each divided into two bundles with the vicinity of the winding center of the electrode group as a boundary. The conductive clamping member 9 includes first and second clamping parts 9a and 9b that are substantially U-shaped, and a connecting part that electrically connects the first clamping part 9a and the second clamping part 9b. 9c. Each of the positive and negative electrode current collecting tabs 6c and 7c has one bundle (laminate) sandwiched by the first sandwiching portion 9a and the other bundle (laminate) sandwiched by the second sandwiching portion 9b. As shown in FIG. 6, each of the positive and negative electrode current collecting tabs 6c and 7c is covered with protective films 6b and 7b on both surfaces perpendicular to the thickness direction and on the front end surface. As a result, the protective films 6b and 7b are positioned between the positive and negative current collecting tabs 6c and 7c held in the first holding part 9a and the second holding part 9b, respectively.

  The positive electrode lead 10 includes a substantially rectangular support plate 10a, a through hole 10b opened in the support plate 10a, a bifurcated bifurcated branch from the support plate 10a, and a strip-shaped current collector 10c, 10d extending downward. Have On the other hand, the negative electrode lead 11 includes a substantially rectangular support plate 11a, a through hole 11b opened in the support plate 11a, a bifurcated branch from the support plate 11a, and a strip-shaped current collector 11c extending downward. 11d.

  The materials of the positive and negative electrode leads 10 and 11 and the clamping member 9 are not particularly specified, but are preferably the same material as the positive and negative electrode external terminals 3 and 4. For the positive electrode external terminal 3, for example, aluminum or an aluminum alloy is used, and for the negative electrode external terminal 4, for example, aluminum, an aluminum alloy, copper, nickel, nickel-plated iron, or the like is used. For example, when the material of the external terminal is aluminum or an aluminum alloy, the lead material is preferably aluminum or an aluminum alloy. In addition, when the external terminal is copper, it is desirable that the material of the lead is copper.

  The rectangular plate-like lid 2 is seam welded to the opening of the outer can 1 by, for example, a laser. The lid 2 is made of a metal such as aluminum, aluminum alloy, iron or stainless steel, for example. The lid 2 and the outer can 1 are preferably formed from the same type of metal. The positive external terminal 3 is electrically connected to the support plate 10 a of the positive electrode lead 10, and the negative external terminal 4 is electrically connected to the support plate 11 a of the negative electrode lead 11. The insulating gasket 12 is disposed between the positive and negative external terminals 3 and 4 and the lid 2 and electrically insulates the positive and negative external terminals 3 and 4 and the lid 2. The insulating gasket 12 is preferably a resin molded product.

  The positive electrode lead 10 sandwiches the clamping member 9 between the current collectors 10c and 10d. The current collector 10 c is disposed in the first clamping part 9 a of the clamping member 9. The current collector 10d is disposed in the second clamping unit 9b. The current collectors 10c and 10d, the first and second clamping portions 9a and 9b, and the positive electrode current collector tab 6c are joined by, for example, ultrasonic metal welding. Thereby, the positive electrode 6 and the positive electrode lead 10 of the electrode group 5 are electrically connected via the positive electrode current collection tab 6c.

  The negative electrode lead 11 sandwiches the clamping member 9 between the current collectors 11c and 11d. The current collector 11 c is disposed in the first clamping part 9 a of the clamping member 9. On the other hand, the current collection part 11d is arrange | positioned at the 2nd clamping part 9b. The current collectors 11c and 11d, the first and second clamping portions 9a and 9b, and the negative electrode current collector tab 7c are joined by, for example, ultrasonic metal welding. Thereby, the negative electrode 7 and the negative electrode lead 11 of the electrode group 5 are electrically connected via the negative electrode current collection tab 7c.

  An example of ultrasonic metal welding is shown in FIG. The arrangement relationship between the horn and the anvil may be either inside or outside, but in FIG. 7, the horn 21 is arranged inside and the anvil 22 is arranged outside. The joining interface by ultrasonic metal welding includes the contact surfaces between the current collecting portions 10c, 11c of the positive and negative electrode leads 10, 11 and the holding member 9, the positive and negative current collecting tabs 6c, 7c held in the holding member 9, and This is a contact surface between the positive and negative current collecting tabs 6 c and 7 c and the holding member 9. Examples of the foil used for the positive electrode current collecting tab 6c and the negative electrode current collecting tab 7c include a metal foil such as an aluminum foil and an alloy foil such as an aluminum alloy foil. An oxide film may exist on the surface of the aluminum foil or aluminum alloy foil. According to the ultrasonic metal welding method, the metal parts to be joined are set on the anvil, and ultrasonic vibration is generated while pressing the horn, so that the oxide film at the joining interface is removed and the crystal grains are interatomic distances. By approaching until a bond is created.

  Protective films 6b and 7b having a thickness of 0.01 μm or more and 10 μm or less are disposed between the positive electrode current collecting tab 6c and the negative electrode current collecting tab 7c. Since the positive electrode current collecting tab 6c and the negative electrode current collecting tab 7c are reinforced by the protective films 6b and 7b, a force is uniformly applied to the positive electrode current collecting tab 6c and the negative electrode current collecting tab 7c at the time of ultrasonic bonding. Can be high. Moreover, since it is possible to avoid the positive electrode current collecting tab 6c or the negative electrode current collecting tab 7c from being broken and causing a product defect, the yield can be improved and the productivity can be improved. Further, since the uniformity of the bonding strength between the current collecting tab and the lead is improved, the resistance between the current collecting tab and the lead can be reduced, and the battery performance such as the discharge capacity and the rate performance can be improved.

  If the thickness of the protective films 6b and 7b is less than 0.01 μm, the current collecting tab cannot be reinforced, and the positive current collecting tab 6c or the negative current collecting tab 7c is broken during ultrasonic bonding, resulting in a product defect. The case increases. On the other hand, if the thickness exceeds 10 μm, the charge / discharge performance (discharge capacity, rate performance, etc.) of the battery is impaired due to the increase in resistance. Moreover, the protective film with a thickness exceeding 10 μm prevents ultrasonic welding. Therefore, the thickness is preferably 0.01 μm or more and 10 μm or less.

  The method for measuring the thickness of the protective film is as follows. The protective film on the foil is cut by the ion milling method along the thickness direction together with the foil, the obtained cross section is observed with a scanning electron microscope (SEM), and the thickness of the protective film is measured.

  The protective film is preferably insulative. Examples of the insulating protective film include inorganic sheets such as alumina particles, and organic sheets such as porous bodies and nonwoven fabrics. The protective film preferably contains an organic component. Examples of the organic component include engineering plastics, super engineering plastics, thermoplastic resins (for example, polyvinyl alcohol), and maleic anhydride-isobutylene copolymers. Examples of engineering plastics include polyamide, polyacetal, polybutylene terephthalate, polyethylene terephthalate, syndiotactic polystyrene, polycarbonate, modified polyphenylene ether, and the like. Examples of super engineering plastics include polyphenylene sulfide, polyetheretherketone, liquid crystal polymer, polyvinylidene fluoride, polytetrafluoroethylene (PTFE), polyethernitrile, polysulfone, polyethersulfone, polyarate, polyether Examples include imide, plastic polyimide, and polyvinylidene fluoride (PVdF). The kind of the organic substance component can be one kind or two kinds or more.

  The organic component is preferably formed of fibers. The protective film is preferably a sheet containing organic fibers. The organic fiber may be a fiber of the organic component described above, and preferably contains at least one of engineering plastic and super engineering plastic as a component. Examples of engineering plastics and super engineering plastics include those described above. The kind of organic fiber component can be one kind or two or more kinds. Among the components constituting the organic fiber, polyamideimide is preferable.

  The sheet containing organic fibers may be formed from one or more fibers having a fiber diameter of 10 μm. The fiber diameter is a fiber diameter of a fiber photographed when an arbitrary portion of the protective film on the current collecting tab is observed with a scanning electron microscope (SEM).

  The average fiber diameter of the organic fibers is desirably 2 μm or less. Thereby, the protective film can be made thin and dense. Moreover, the influence which a protective film has on ultrasonic welding can be made small. A more preferable range is 1 μm or less. The fiber diameter of the organic fiber can be measured by electron microscope (scanning electron microscope; SEM) observation, scanning probe microscope (SPM), transmission electron microscope (TEM), scanning transmission electron microscope (STEM), or the like. Further, the length of the organic fiber is obtained based on the length measurement by SEM observation.

  In FIG. 1, both the positive electrode current collecting tab and the negative electrode current collecting tab are coated with the protective film. However, even when only one of the positive electrode current collecting tab and the negative electrode current collecting tab is coated with the protective film, the bonding is also possible. Improvements in strength and productivity can be expected.

  Further, in FIG. 1, both surfaces of the positive electrode current collecting tab and the negative electrode current collecting tab are covered with the protective film. However, even in the case of one surface, it is possible to expect improvement in bonding strength and productivity. When covering both sides, when covering one side, in any case, it is desirable that the thickness of the protective film located between the tab layers be in the range of 0.01 μm to 10 μm.

  In FIG. 1, a positive electrode current collecting tab is provided on one side of the positive electrode, and a negative electrode current collecting tab is provided on one side of the negative electrode. Instead of these, a plurality of foils can be used as a positive electrode current collecting tab or a negative electrode current collecting tab, and a protective film can be provided on at least one surface of at least one foil.

Hereinafter, the separator, the negative electrode, the positive electrode, the nonaqueous electrolyte, and the exterior material will be described.
(1) Separator The separator can have, for example, a porous membrane structure or a non-woven fabric structure. It is more preferable that the separator has a nonwoven fabric structure in which Li ions can move linearly. The separator can include, for example, one or more materials selected from the group consisting of polyamideimide, polyamide, polyolefin, cellulose, polyethylene, polyester, polypropylene, polyvinylidene fluoride (PVdF), and aramid. The separator can have a thickness of 20 μm or less. The nonaqueous electrolyte battery according to the embodiment having a thickness of 20 μm or less can provide a higher energy density and can further suppress an increase in internal resistance. In consideration of an internal short circuit, the thickness is preferably 1 μm or more.

The separator may be a free-standing film independent of the positive electrode and the negative electrode as illustrated in FIG. 3, or may be integrated with the positive electrode, the negative electrode, or both electrodes. An example of an electrode group including a separator integrated with an electrode is shown in FIG. In the electrode group 5 shown in FIG. 8, both surfaces of the negative electrode material layer 7a of the negative electrode 7, one surface of the negative electrode current collecting tab 7c, the negative electrode end surface from which the negative electrode current collecting tab 7c protrudes, and the negative electrode end surface located on the opposite side to the negative electrode end surface The insulating layer 23 is integrated with each other. The negative electrode current collecting tab 7c is composed of one end parallel to one side of the negative electrode current collector 7d, and the insulating layer 23 integrated on one side functions as the protective film 7b. On the other hand, the positive electrode current collecting tab 6c of the positive electrode 6 is composed of one end parallel to one side of the positive electrode current collector 6d, and the insulating layer 23 integrated on one side functions as the protective film 6b. The insulating layer 23 can be a sheet containing organic fibers.
(2) Negative Electrode A negative electrode current collector and a negative electrode material layer included in the negative electrode will be described.

  As the negative electrode current collector, for example, a foil of aluminum, aluminum alloy, copper, or the like can be used.

The negative electrode material layer can further include a negative electrode conductive additive and a binder in addition to the negative electrode active material. The negative electrode active material includes a lithium titanium composite oxide. An example of the lithium titanium composite oxide is lithium titanate. Examples of the lithium titanate include lithium titanate Li _{4 + x} Ti ₃ O ₁₂ (0 ≦ x ≦ 3) having a spinel structure. The negative electrode active material can include one or more lithium-titanium composite oxides.

  The negative electrode material layer can also contain one or more additional negative electrode active materials other than the lithium titanium composite oxide. Examples of the further negative electrode active material include carbon materials such as graphite, and tin and silicon-based alloy materials.

  The average particle diameter of the primary particles of the negative electrode active material is preferably in the range of 0.001 to 1 μm.

  Examples of the negative electrode conductive assistant that can be included in the negative electrode material layer include acetylene black, carbon black, graphite, and graphite.

The binder that can be included in the negative electrode material layer can bind the negative electrode active material and the negative electrode conductive additive. Examples of the binder include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF).
(3) Positive electrode The positive electrode can include a positive electrode current collector and a positive electrode material layer formed on both surfaces or one surface of the positive electrode current collector. The positive electrode current collector can include a portion where the positive electrode material layer is not formed on the surface, and this portion can serve as a positive electrode current collecting tab.

  As the positive electrode current collector, for example, a foil made of aluminum, an aluminum alloy, or the like can be used.

  The positive electrode material layer can contain a positive electrode active material that can be charged and discharged by a combination with lithium titanate contained in the negative electrode. In addition to the positive electrode active material, the positive electrode material layer can further include a positive electrode conductive additive and a binder.

As the positive electrode active material that can be included in the positive electrode material layer, for example, a lithium transition metal composite oxide can be used. Examples of the lithium-transition metal composite oxide, for _{example, LiCoO 2, LiNi 1-x} Co x O 2 (0 <x <0.5), LiMn x Ni y Co z O 2 (0 <x <0.5 , 0 <y <0.5, 0 <z <0.5), LiMn _2−x M _x O ₄ (M is at least one selected from the group consisting of Li, Mg, Co, Al and Ni) , 0 <x <0.2), LiMPO ₄ (M is at least one selected from the group consisting of Fe, Co, and Ni).

  Examples of the positive electrode conductive assistant that can be contained in the positive electrode material layer include acetylene black, carbon black, graphite, and graphite.

  The binder that can be included in the positive electrode material layer can bind the positive electrode active material and the positive electrode conductive additive. Examples of the binder include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF).

The positive electrode material layer can be formed, for example, by applying a slurry containing a positive electrode active material, a positive electrode conductive additive and a binder on the positive electrode current collector and drying the slurry.
(4) Non-aqueous electrolyte The non-aqueous electrolyte can be impregnated in an electrode group including, for example, a negative electrode, a separator, and a positive electrode.

The non-aqueous electrolyte can include a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Alternatively, the non-aqueous electrolyte may include a polymer dissolved in a non-aqueous solvent.
The non-aqueous solvent is not particularly limited, but propylene carbonate (PC), ethylene carbonate (EC), 1,2-dimethoxyethane (DME), γ-butyrolactone (GBL), tetrahydrofuran (THF), 2- Examples include methyltetrahydrofuran (2-MeHF), 1,3-dioxolane, sulfolane, acetonitrile (AN), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and dipropyl carbonate (DPC). . These solvents may be used alone or in combination of two or more.
Examples of the electrolyte salt include LiPF ₆ , LiBF ₄ , Li (CF ₃ SO ₂ ) ₂ N (bistrifluoromethanesulfonylamide lithium; commonly known as LiTFSI), LiCF ₃ SO ₃ (commonly known as LiTFS), and Li (C ₂ F ₅ SO ₂ ). ₂ N (bis pentafluoroethanesulfonyl amide lithium; called _{LiBETI), LiClO 4, LiAsF 6} , LiSbF 6, bisoxalato Lato lithium borate _{(LiB (C 2 O 4)} 2 ( known as LiBOB)), difluoro (tri-fluoro-2 And lithium salts such as -oxide-2-trifluoro-methylpropionate (2-)-0,0) lithium borate (LiBF ₂ (OCOOC (CF ₃ ) ₂ ) (commonly known as LiBF ₂ (HHIB))). . These electrolyte salts may be used alone or in combination of two or more. In particular, it is preferable to use LiPF ₆ or LiBF ₄ .
The electrolyte salt concentration is preferably in the range of 1M to 3M. Thereby, the performance when a high load current is passed can be improved.

In addition, the non-aqueous electrolyte can further include an additive. Although it does not specifically limit as an additive, Vinylene carbonate (VC), vinylene acetate (VA), vinylene butyrate, vinylene hexanate, vinylene crotonate, catechol carbonate, propane sultone, etc. are mentioned. The concentration of the additive is preferably in the range of 0.1 wt% to 3 wt% with respect to 100 wt% of the nonaqueous electrolyte. A more preferable range is 0.5% by weight or more and 1% by weight or less.
(5) Exterior Material The nonaqueous electrolyte battery according to the embodiment can further include an exterior material for housing the electrode group and the nonaqueous electrolyte solution.

  As an exterior material, for example, as shown in FIG. 1, an exterior can formed from aluminum, an aluminum alloy, iron, stainless steel, or the like can be used. The plate thickness of the container is preferably 0.5 mm or less, and more preferably 0.2 mm or less.

  Or as an exterior material, it is also possible to use the exterior container formed from the laminate film instead of the exterior can. As the laminate film, it is preferable to use a multilayer film composed of a foil and a resin film covering the foil. Polymers such as polypropylene (PP), polyethylene (PE), nylon, polyethylene terephthalate (PET) can be used as the resin. Examples of the foil include aluminum and an aluminum alloy. The thickness of the laminate film is desirably 0.2 mm or less.

  Note that various shapes such as a rectangular shape, a cylindrical shape, a thin shape, and a coin shape can be adopted as the shape of the exterior material depending on the application.

  In addition, the non-aqueous electrolyte battery according to the embodiment can further include a lead electrically connected to the electrode group. For example, the nonaqueous electrolyte battery according to the embodiment may include two leads. One lead can be electrically connected to the positive current collecting tab. The other lead can be electrically connected to the negative electrode current collecting tab.

  The lead material is not particularly limited, and for example, the same material as the positive electrode current collector and the negative electrode current collector can be used.

  The nonaqueous electrolyte battery according to the embodiment may further include a terminal electrically connected to the lead and drawn out from the exterior material. For example, the nonaqueous electrolyte battery according to the embodiment can include two terminals. One terminal can be connected to a lead electrically connected to the positive current collector tab. The other terminal can be connected to a lead electrically connected to the negative electrode current collecting tab.

  Although the material of a terminal is not specifically limited, For example, the same material as a positive electrode collector and a negative electrode collector can be used.

  The structure of the electrode group is not limited to a structure wound around a flat spiral, and for example, a structure wound around a cylindrical spiral or a laminated structure can be used.

  According to the first embodiment described above, the current collecting tab for electrically connecting the electrode and the lead has a thickness covering the foil and at least a part of the surface of the foil of 0.01 μm or more and 10 μm. The following protective film is included. The protective film reinforces the current collecting tab. At the same time, the protective film does not interfere with ultrasonic metal welding of the current collecting tab and the lead. As a result, since the force of ultrasonic metal welding is evenly applied to the current collecting tab, it is possible to reduce defects such as the current collecting tab being torn or broken. Further, since the uniformity of the bonding strength between the current collecting tab and the lead is improved, the resistance between the current collecting tab and the lead can be reduced, and the battery performance such as the discharge capacity and the rate performance can be improved.

Hereinafter, embodiments will be described with reference to the drawings.
Example 1
First, a lithium titanate Li ₄ Ti ₅ O ₁₂ powder having a spinel structure was prepared. The average particle size of this lithium titanate was 0.5 μm. This lithium titanate powder was put into N-methylpyrrolidone (NMP) as a solvent together with graphite as a conductive agent and polyvinylidene fluoride (PVdF) as a binder. At this time, the weight ratio of lithium titanate powder: graphite: PVdF was 100: 5: 5. A slurry for preparing a negative electrode was prepared by sufficiently stirring the mixture.

Next, this negative electrode preparation slurry was applied to both surfaces of a strip-shaped aluminum foil except for one end portion parallel to the longitudinal direction. The basis weight at the time of application was 50 g / m ^{2 on} one side.

  Subsequently, the coating film was dried and pressed at 50 kN. Thus, a negative electrode comprising a negative electrode current collector that was an aluminum foil and a negative electrode material layer formed thereon was obtained.

  Subsequently, a separator made of organic fibers was formed on the surface of the negative electrode material layer of the negative electrode by electrospinning, and was integrated with the surfaces of the negative electrode material layer and the negative electrode current collecting tab. The formation conditions are as follows.

  Polyamideimide (PAI) having excellent insulating properties, heat resistance, and solvent resistance was used as the organic fiber material. Dimethylacetamide (DMAc) was used as the solvent. A raw material solution was prepared by dissolving 15% by weight of polyamideimide in this solvent. This raw material solution was supplied from the spinning nozzle to the negative electrode surface at a supply rate of 5 μL / min. At this time, a voltage of 40 kV was applied to the spinning nozzle using a high voltage generator. The supply was performed using one spinning nozzle, and the spinning nozzle was moved with a width of 100 mm. Furthermore, the raw material solution was supplied while the negative electrode was conveyed at 50 mm / min in a direction perpendicular to the operation direction of the spinning nozzle. A separator made of organic fibers was continuously formed on the negative electrode. After forming the insulating layer, it was cut and a negative electrode having a width of 100 mm was pressed with a load of 1 kN to produce a negative electrode.

  In the obtained negative electrode, the separator covered both surfaces of the negative electrode material layer. A separator that covers one negative electrode material layer and a separator that covers the other negative electrode material layer are connected continuously, covering the end face parallel to the negative electrode long side (the long side that is not the negative electrode current collector tab) Was. Further, the separator covered both surfaces of the negative electrode current collecting tab. The separator that covers both surfaces of the negative electrode current collector tab functions as a protective film. The thickness of the separator and the protective film was 10 μm. The average fiber diameter of the organic fibers constituting the protective film was 0.9 μm.

As a positive electrode active material, a powder of lithium-containing nickel manganese cobalt composite oxide LiMn _0.3 Ni _0.3 Co _0.3 O ₂ was prepared. This lithium-containing nickel manganese cobalt composite oxide was put into NMP as a solvent together with graphite as a conductive agent and PVdF as a binder. At this time, the weight ratio of lithium-containing nickel manganese cobalt composite oxide: graphite: PVdF was 100: 5: 5. A slurry for preparing a positive electrode was prepared by sufficiently stirring the mixture.

Next, this positive electrode preparation slurry was applied to both sides of a rectangular aluminum foil except for one end portion parallel to the long side direction. The basis weight at the time of application was 50 g / m ^{2 on} one side. At the time of application, a portion where the slurry was not applied was left on a part of the aluminum foil.

  Subsequently, the coating film was dried and pressed at 50 kN. Thus, a positive electrode comprising a positive electrode current collector as an aluminum foil and a positive electrode material layer formed thereon was obtained.

  Then, the protective film which consists of organic fiber was formed on the surface of the positive electrode current collection tab of a positive electrode by the electrospinning method, and was integrated on both surfaces of the positive electrode current collection tab. The formation conditions were the same as those for the negative electrode.

  Using the positive electrode and the negative electrode prepared as described above, the negative electrode was wound before the positive electrode, and the electrode group shown in FIGS. 1 and 3 was prepared so that the negative electrode had 52 turns and the positive electrode had 51 turns. The width of the negative electrode material layer of the negative electrode (width in the direction parallel to the winding axis) is wider than that of the positive electrode material layer of the positive electrode, and the positive electrode material layer is disposed so that all the positive electrode material layers can face the negative electrode material layer through the separator. . The total length of the electrode group was 10 m.

  Subsequently, a clamping member was disposed on each of the positive electrode current collecting tab and the negative electrode current collecting tab. The positive electrode current collecting tab held by the first and second holding portions of the holding member and the positive electrode lead made of an aluminum plate having a thickness of 3 mm were ultrasonically welded as shown in FIG. Further, the negative electrode current collecting tab held by the first and second clamping portions of the clamping member and the negative electrode lead made of an aluminum plate having a thickness of 3 mm were ultrasonically welded as shown in FIG.

One thousand electrode groups bonded to the positive and negative electrode leads described above were produced.
(Examples 2 and 3)
1000 electrodes were bonded to the positive and negative electrode leads in the same manner as in Example 1 except that the thickness of the protective film and the average fiber diameter of the organic fibers were changed to the values shown in Table 1 below.
Example 4
It joined to the positive / negative electrode lead like Example 1 except changing the kind of organic fiber which comprises a protective film, the thickness of a protective film, and the average fiber diameter of an organic fiber into the value shown in following Table 1. 1000 electrode groups were produced.
(Comparative Example 1)
Except not forming a protective film, 1000 electrode groups joined to the positive and negative electrode leads were produced in the same manner as in Example 1.
(Comparative Example 2)
Instead of using the separator and protective film formed by the electrospinning method, the positive and negative electrode material layers and the positive and negative electrode current collecting tabs are covered with a separator made of a cellulose nonwoven fabric having a thickness of 20 μm, in the same manner as in Example 1. 1000 electrode groups bonded to the positive and negative electrode leads were produced.

  Of the 1000 electrode groups produced in each of the examples and comparative examples, the foil was torn and the one welded from the foil was peeled off. Table 1 shows the defect rate in 1000 electrode groups. In addition, a tensile test was performed on the welded portion which did not become defective, and the tensile strength is shown in Table 1. The conditions of the tensile test are shown below.

  Shimadzu Autograph AG 10kNX manufactured by Shimadzu Corporation was used. The welded portion of the lead portion of the electrode group joined to the positive and negative electrode leads is cut out with a width of 20 mm using a nipper or the like. If the sample to be cut out is a negative electrode, 26 sheets are sandwiched between the upper and lower chuck parts, and if the sample is a positive electrode, 26 sheets are sandwiched between the upper chuck part and 25 sheets between the lower chuck part. From this state, a tensile test is performed at a tensile speed of 1 m / min, and the maximum stress value of the stress strain curve is taken as the tensile strength.

  As can be seen from Table 1, the batteries of Examples 1 to 4 each having an organic fiber sheet formed on the current collecting tab have higher tensile strength and lower defect rate than Comparative Examples 1 and 2. From this, it was found that forming a protective film of 0.01 μm to 10 μm on the current collecting tab is extremely effective in increasing the strength of ultrasonic metal welding and reducing the defect rate.

  According to at least one of the embodiments and examples described above, the current collecting tab for electrically connecting the electrode and the lead has a thickness covering the foil and at least a part of the surface of the foil. And a protective film of 0.01 μm or more and 10 μm or less. As a result, the connection failure between the current collecting tab and the lead is reduced, and the bonding strength between the current collecting tab and the lead is improved, so that the resistance between the current collecting tab and the lead can be reduced, and the discharge capacity and rate are reduced. Battery performance such as performance can be improved.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Exterior can, 2 ... Cover, 3 ... Positive electrode external terminal, 4 ... Negative electrode external terminal, 5 ... Electrode group, 6 ... Positive electrode, 6a ... Positive electrode material layer, 6b, 7b ... Protective film, 6c ... Positive electrode current collection tab, 6d ... Positive electrode current collector, 7 ... Negative electrode, 7a ... Negative electrode material layer, 7c ... Negative electrode current collector tab, 7d ... Negative electrode current collector, 8 ... Separator, 9 ... Holding member, 10 ... Positive electrode lead, 11 ... Negative electrode lead, 12 ... Insulating gasket, 21 ... Horn, 22 ... Anvil, 23 ... Insulating layer.

Claims (6)

An electrode group including a positive electrode and a negative electrode;
An exterior material containing the electrode group;
A positive electrode terminal provided on the exterior material;
A negative electrode terminal provided on the exterior material;
A positive electrode lead for electrically connecting the positive electrode and the positive electrode terminal;
A battery including a negative electrode lead for electrically connecting the negative electrode and the negative electrode terminal;
A current collecting tab for electrically connecting the positive electrode and the positive electrode lead, or for electrically connecting the negative electrode and the negative electrode lead;
The current collecting tab includes a foil and a protective film having a thickness of 0.01 μm or more and 10 μm or less that covers at least a part of the surface of the foil.   The battery according to claim 1, wherein the current collecting tab is electrically connected to the positive electrode lead, the negative electrode lead, or both the positive electrode lead and the negative electrode lead by ultrasonic metal welding.   The battery according to claim 2, wherein the protective film contains an organic component.   The battery according to claim 2, wherein the protective film is a sheet containing organic fibers.   The battery according to claim 4, wherein the organic fiber contains at least one of engineering plastic and super engineering plastic.   The battery according to claim 4 or 5, wherein an average fiber diameter of the organic fibers is 2 µm or less.