JP2018133151A - Square secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a square secondary battery capable of suppressing internal micro short-circuit (low voltage) generated by the incorporation of conductive foreign matter.SOLUTION: Disclosed is a square secondary battery which includes: a wound electrode group around which a separator and an electrode on which an electrode active material mixture layer is coated and which has a metal foil exposed part at one end are wound; and a current collector plate connected to the metal foil exposed part. The metal foil exposed part has a configuration which is sandwiched and joined with the current collector plate and a first plate-like metal member, and the separator is arranged at a position opposite to the first plate-like metal member.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a prismatic secondary battery.

In a lithium ion secondary battery, a prismatic battery comprising a wound electrode group formed by winding a belt-like positive electrode and a negative electrode over a separator and containing an electrolyte, that is, a prismatic lithium ion secondary battery is known. Yes. As a prismatic lithium-ion secondary battery that mainly requires high output, such as a car-mounted prismatic lithium ion secondary battery, the uncoated parts of the positive electrode and negative electrode protrude at both ends in the winding axis direction of the electrode winding group, By connecting the coating part to the current collector plate, a simple configuration is possible, and the current path to the electrode terminals and current collector plate is shortened, and the connection resistance is reduced to achieve high output. Various things have been proposed.

  A method of connecting the uncoated portion to the current collector plate is ultrasonic welding (hereinafter abbreviated as USW). The USW is a welding method in which bonding is performed by applying horizontal ultrasonic vibration while pressing metals. However, due to ultrasonic vibration, metal foreign objects are likely to be generated during welding, and if metal foreign objects jump into the wound group and reach the coated part, there is a possibility of causing a short circuit and causing a problem with the battery. is there.

  Patent Document 1 uses a separator having a low static friction coefficient, and has a structure in which a short-circuit between positive and negative electrodes can be suppressed by sliding a direct tab on the surface of the separator.

JP 2009-187724

  In the technique described in Patent Document 1, a separator having a static friction coefficient of 0.6 or less is used. Even if the electrode direct tab is twisted and contacts the separator, the direct tab can slide on the surface of the separator, thereby suppressing a short circuit between the positive and negative electrodes. In this method, the direct tab of the positive electrode has a part of the metal foil facing the negative electrode through the separator, so that the separator can be prevented from being damaged and short-circuited. The positional relationship of the parts cannot be determined, and a short circuit due to the intrusion of metal foreign matter cannot be prevented.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a prismatic secondary battery that can suppress an internal fine short-circuit (voltage drop) that occurs due to the mixing of conductive foreign matter.

  In order to solve the above problems, a prismatic secondary battery according to the present invention includes a wound electrode group in which an electrode active material mixture layer is applied and an electrode having a metal foil exposed portion at one end and a separator are wound, and the metal A current collector plate connected to the foil exposed portion, wherein the metal foil exposed portion is sandwiched and joined by the current collector and the first plate metal member, and the separator is the first It is arrange | positioned in the position facing 1 plate-shaped metal member.

This invention is made | formed in view of the said subject, and can suppress the internal fine short circuit (voltage drop) generate | occur | produced by mixing of a conductive foreign material.

The external appearance perspective view of a square secondary battery. The disassembled perspective view of a square secondary battery. The exploded perspective view of an electrode winding group. Assembly drawing of electrode winding group, battery cover, current collector plate, and ribbon. The figure explaining the structure of an electrode winding group. The schematic diagram which shows the structure of the junction part of the conventional metal foil exposed part and an electrical power collector. The schematic diagram which shows the structure of the junction part of the metal foil exposed part of this embodiment, and an electrical power collector. The schematic diagram which shows the structure of the junction part of the metal foil exposed part of this embodiment, and an electrical power collector. The schematic diagram which shows the modification of the junction part of the metal foil exposure part of this embodiment, and an electrical power collector. The figure explaining a foreign material removal method.

[Example 1]
FIG. 1 is an external perspective view of a prismatic secondary battery.

FIG. 2 is an exploded perspective view of the prismatic secondary battery.
The prismatic secondary battery 100 includes a battery can 1 and a lid (battery lid) 6. The battery can 1 has a side surface and a bottom surface 1d having a pair of opposed wide side surfaces 1b having a relatively large area and a pair of opposed narrow side surfaces 1c having a relatively small area, and an opening 1a above the side surface 1d. Have
In the battery can 1, the electrode winding group 3 is accommodated, and the opening 1 a of the battery can 1 is sealed by the battery lid 6. The battery lid 6 has a substantially rectangular flat plate shape, and is welded so as to close the upper opening 1 a of the battery can 1 to seal the battery can 1. The battery lid 6 is provided with a positive external terminal 14 and a negative external terminal 12. The wound group 3 is charged through the positive external terminal 14 and the negative external terminal 12, and power is supplied to the external load. The battery cover 6 is integrally provided with a gas discharge valve 10, and when the pressure in the battery container rises, the gas discharge valve 10 opens to discharge gas from the inside, and the pressure in the battery container is reduced. Thereby, the safety of the prismatic secondary battery 100 is ensured.

  The battery can 1 of the prismatic secondary battery 100 includes a rectangular bottom surface 1d, square cylindrical side surfaces 1b and 1c rising from the bottom surface 1d, and an opening 1a opened upward at the upper ends of the side surfaces 1b and 1c. Have. An electrode winding group 3 is accommodated in the battery can 1 via an insulating protective film 2.

  Since the electrode winding group 3 is wound in a flat shape, the electrode winding group 3 has a pair of opposed curved portions having a semicircular cross section and a plane portion formed continuously between the pair of curved portions. doing. The electrode winding group 3 is inserted into the battery can 1 from one curved portion side so that the winding axis direction is along the lateral width direction of the battery can 1, and the other curved portion side is arranged on the upper opening side.

  The positive electrode foil exposed portion 34 c of the electrode winding group 3 is electrically connected to the positive external terminal 14 provided on the battery lid 6 via a positive current collector (current collector terminal) 44. Further, the negative electrode foil exposed portion 32 c of the electrode winding group 3 is electrically connected to the negative external terminal 12 provided on the battery lid 6 via a negative current collector plate (current collector terminal) 24. Thereby, electric power is supplied from the electrode winding group 3 to the external load via the positive electrode current collecting plate 44 and the negative electrode current collecting plate 24, and the electrode winding group 3 is obtained via the positive electrode current collecting plate 44 and the negative electrode current collecting plate 24. Externally generated power is supplied to and charged.

  In order to electrically insulate the positive electrode current collector plate 44 and the negative electrode current collector plate 24, and the positive electrode external terminal 14 and the negative electrode external terminal 12 from the battery lid 6, a gasket 5 and an insulating plate 7 are provided on the battery lid 6. It has been. Moreover, after injecting electrolyte solution into the battery can 1 from the liquid injection port 9, a liquid injection stopper 11 is joined to the battery lid 6 by laser welding to seal the liquid injection port 9, and the rectangular secondary battery 100 is sealed. To do.

  Here, examples of the material for forming the positive electrode external terminal 14 and the positive electrode current collector plate 44 include an aluminum alloy, and examples of the material for forming the negative electrode external terminal 12 and the negative electrode current collector plate 24 include a copper alloy. Examples of the material for forming the insulating plate 7 and the gasket 5 include resin materials having insulating properties such as polybutylene terephthalate, polyphenylene sulfide, and perfluoroalkoxy fluororesin.

Further, the battery lid 6 is provided with a liquid injection hole 9 for injecting an electrolytic solution into the battery container. The liquid injection hole 9 is an injection stopper after the electrolytic solution is injected into the battery container. 11 is sealed. Here, as the electrolytic solution injected into the battery container, for example, a non-aqueous electrolytic solution in which a lithium salt such as lithium hexafluorophosphate (LiPF ₆ ) is dissolved in a carbonic acid ester-based organic solvent such as ethylene carbonate is used. Can be applied.

  The positive external terminal 14 and the negative external terminal 12 have a weld joint that is welded to a bus bar or the like. The weld joint has a rectangular parallelepiped block shape protruding upward from the battery lid 6, and has a configuration in which the lower surface faces the surface of the battery lid 6 and the upper surface is parallel to the battery lid 6 at a predetermined height position. Have.

  The positive electrode connecting portion 14a and the negative electrode connecting portion 12a have a cylindrical shape that protrudes from the lower surfaces of the positive electrode external terminal 14 and the negative electrode external terminal 12 and can be inserted into the positive electrode side through hole 46 and the negative electrode side through hole 26 of the battery lid 6. Have. The positive electrode connection portion 14 a and the negative electrode connection portion 12 a penetrate the battery lid 6 and are more inside the battery can 1 than the positive electrode current collector plate 44, the positive electrode current collector plate base 41 of the negative electrode current collector plate 24, and the negative electrode current collector plate base 21. The positive electrode external terminal 14, the negative electrode external terminal 12, the positive electrode current collector plate 44, and the negative electrode current collector plate 24 are integrally fixed to the battery lid 6. A gasket 5 is interposed between the positive electrode external terminal 14 and the negative electrode external terminal 12 and the battery cover 6, and an insulating plate is interposed between the positive electrode current collector plate 44, the negative electrode current collector plate 24 and the battery cover 6. 7 is interposed.

  The positive electrode current collector plate 44 and the negative electrode current collector plate 24 are a rectangular plate-shaped positive electrode current collector plate base 41, a negative electrode current collector plate base 21, and a positive electrode current collector plate base 41 that are arranged to face the lower surface of the battery lid 6. The negative electrode current collector plate 21 is bent at the side end and extends toward the bottom surface along the wide surface of the battery can 1 to form the positive electrode foil exposed portion 34c and the negative electrode foil exposed portion 32c of the wound group 3. It has a positive electrode side connection end portion 42 and a negative electrode side connection end portion 22 which are connected in a state of being opposed to each other. The positive electrode current collector plate base 41 and the negative electrode current collector plate base 21 are respectively formed with a positive electrode side opening hole 43 and a negative electrode side opening hole 23 through which the positive electrode connection part 14a and the negative electrode connection part 12a are inserted.

An insulating protective film 2 is wound around the electrode winding group 3 with the direction along the flat plane of the electrode winding group 3 and the direction orthogonal to the winding axis direction of the electrode winding group 3 as the central axis direction. Yes. The insulating protective film 2 is made of a single sheet made of synthetic resin such as PP (polypropylene) or a plurality of film members, and is parallel to the flat surface of the electrode winding group 3 and orthogonal to the winding axis direction. It has a length that can be wound around the direction as the winding center.
FIG. 3 is an exploded perspective view showing a state in which a part of the electrode winding group 3 is developed.

  The electrode winding group 3 is configured by winding the negative electrode 32 and the positive electrode 34 in a flat shape with separators 33 and 35 interposed therebetween. In the winding group 3, the outermost electrode is the negative electrode 32, and the separators 33 and 35 are wound outside thereof. The separators 33 and 35 have a role of insulating between the positive electrode 34 and the negative electrode 32.

  The portion of the negative electrode 32 to which the negative electrode active material mixture layer 32b is applied is larger in the width direction than the portion of the positive electrode 34 to which the positive electrode active material mixture layer 34b is applied, and thus the positive electrode active material mixture layer 34b. The portion to which is applied is always sandwiched between the portions to which the negative electrode active material mixture layer 32b is applied. The positive foil exposed portion 34c and the negative foil exposed portion 32c are bundled at a plane portion and connected by welding or the like. The separators 33 and 35 are wider than the portion where the negative electrode active material mixture layer 32b is applied in the width direction, but at positions where the metal foil surface at the end is exposed at the positive electrode foil exposed portion 34c and the negative electrode foil exposed portion 32c. Because it is wound, it does not hinder bundled welding.

  The positive electrode 34 has a positive electrode active material mixture on both sides of a positive electrode foil that is a positive electrode current collector, and a positive electrode foil in which the positive electrode active material mixture is not applied to one end in the width direction of the positive electrode foil An exposed portion 34c is provided.

  The negative electrode 32 has a negative electrode active material mixture on both sides of a negative electrode foil that is a negative electrode current collector, and the negative electrode foil in which the negative electrode active material mixture is not applied to the other end in the width direction of the positive electrode foil An exposed portion 32c is provided. The positive electrode foil exposed portion 34c and the negative electrode foil exposed portion 32c are regions where the metal surface of the electrode foil is exposed, and are wound so as to be disposed on one side and the other side in the winding axis direction.

  Regarding the negative electrode 32, 10 parts by weight of polyvinylidene fluoride (hereinafter referred to as PVDF) is added as a binder to 100 parts by weight of amorphous carbon powder as a negative electrode active material, and N as a dispersion solvent. -A negative electrode mixture in which methylpyrrolidone (hereinafter referred to as NMP) was added and kneaded was prepared. This negative electrode mixture was applied to both surfaces of a 10 μm thick copper foil (negative electrode electrode foil) leaving a welded portion (negative electrode uncoated portion). Then, the negative electrode 32 with a negative electrode active material application part thickness of 70 micrometers which does not contain copper foil was obtained through drying, a press, and a cutting process.

  In this embodiment, the case where amorphous carbon is used as the negative electrode active material is exemplified, but the present invention is not limited to this. Natural graphite capable of inserting and removing lithium ions and various artificial graphite materials Carbonaceous materials such as coke, compounds such as Si and Sn (for example, SiO, TiSi2 etc.), or composite materials thereof may be used, and the particle shape is particularly limited, such as scaly, spherical, fibrous, or massive Is not to be done.

  Regarding the positive electrode 34, 10 parts by weight of flaky graphite as a conductive material and 10 parts by weight of PVDF as a binder are added to 100 parts by weight of lithium manganate (chemical formula LiMn 2 O 4) as a positive electrode active material. A positive electrode mixture in which NMP was added and kneaded as a dispersion solvent was prepared. This positive electrode mixture was applied to both surfaces of an aluminum foil (positive electrode foil) having a thickness of 20 μm leaving a welded portion (positive electrode uncoated portion). Thereafter, a positive electrode 31 having a thickness of 90 μm in the thickness of the positive electrode active material coating portion not including an aluminum foil was obtained through drying, pressing, and cutting processes.

  Further, in the present embodiment, the case where lithium manganate is used as the positive electrode active material is exemplified, but other lithium manganate having a spinel crystal structure or a lithium manganese composite oxide or layered in which a part is substituted or doped with a metal element A lithium cobalt oxide or lithium titanate having a crystal structure, or a lithium-metal composite oxide obtained by substituting or doping a part thereof with a metal element may be used.

Moreover, in this embodiment, although the case where PVDF was used as a binder of the coating part in a positive electrode and a negative electrode was illustrated, polytetrafluoroethylene (PTFE), polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber, styrene Use polymers such as butadiene rubber, polysulfide rubber, nitrocellulose, cyanoethyl cellulose, various latexes, acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, chloroprene fluoride, acrylic resins, and mixtures thereof. In addition, as the shaft core, for example, a structure formed by winding a resin sheet having higher bending rigidity than any of the positive electrode foil 31a, the negative electrode foil 32a, and the separator 33 can be used.
FIG. 4A is an exploded perspective view of the electrode winding group, the current collector plate, and the ribbon (plate-like metal members 30 and 40). FIG. 4B is an exploded perspective view of a state in which the electrode winding group, the current collector plate, and the ribbon (plate-like metal members 30 and 40) are connected.

  The electrode winding group 3 is configured by winding the negative electrode 32 and the positive electrode 34 in a flat shape with separators 33 and 35 interposed therebetween. The positive electrode foil exposed portion 34 c of the electrode winding group 3 is connected by being ultrasonically sandwiched between the positive electrode current collector plate 44 and the positive electrode side ribbon 40. Further, the negative electrode foil exposed portion 32 c of the electrode winding group 3 is connected by ultrasonic welding with the negative electrode current collector plate 24 and the negative electrode side ribbon 30 sandwiched therebetween.

  When ultrasonically welding the negative electrode current collector plate 24 and the negative electrode foil exposed portion 32c of the electrode winding group 3 and the positive electrode current collector plate 44 and the positive electrode foil exposed portion 34c of the electrode group 3, the negative electrode foil exposed portion of the electrode winding group 3 The flat portion of the exposed portion 34c or 32c is sandwiched between the negative ribbon 30 and the negative current collector 24 or the positive ribbon 40 and the positive current collector 44. When ultrasonic welding is performed, the positive electrode foil exposed portion 34c, the positive electrode current collector plate 44, the positive electrode side ribbon 40, the negative electrode electrode foil exposed portion 32c of the electrode winding group 3, the negative electrode current collector plate 24, and the negative electrode side ribbon Since 30 receives ultrasonic vibration, metal foreign objects are likely to be generated between the metal electrode foils.

  FIG. 5A shows the structure of a conventional electrode winding group 3. FIG. 5B is an enlarged view of the dotted line portion A in FIG. 5A. Further, an enlarged view of the dotted lines a and b in FIG. 5B is a lower view of FIG. The conventional electrode winding group 3 has a structure in which the separators 33 and 35 do not reach the narrow portion a1 of the negative electrode foil exposed portion 32c in the left diagram in the lower diagram of FIG. For this reason, there is a gap between the electrode and the separator, and entry of foreign matter cannot be prevented. Note that the right diagram in the lower diagram of FIG. 5B shows the positive electrode side and is basically the same as the left diagram in the lower diagram in FIG.

  Next, the mechanism by which foreign matter enters will be described with reference to FIGS. 6 (a) and 6 (b).

  For example, when a metal foreign object jumps into a gap between the exposed portion of the electrode foil and the separator, it accumulates in the gap. The metal foreign matter that has not been removed by suction is left as it is, and is inserted into the battery can together with the wound group, and the liquid injection process is started. In the injection, the air in the battery can 1 is drawn out and the inside of the battery can is evacuated to inject the electrolyte. At that time, the metal foreign matter left on the exposed portion of the electrode foil is caused to flow by the electrolytic solution and reaches the coated portion of the electrode. If the battery enters the previous process and is charged as it is, there may be a problem that the battery voltage drops such that the metal undergoes a dissolution and precipitation reaction, causing a short circuit between the electrodes.

  Next, a description will be given of a portion serving as a point for suppressing an internal fine short-circuit (voltage drop) that occurs due to the inclusion of foreign matter in the prismatic lithium secondary battery of the present embodiment.

  FIG. 7 is a conceptual schematic diagram in which the joint of the positive electrode foil exposed portion 34c, the positive current collector 44, and the positive side ribbon 40 is enlarged. FIG. 7 shows a state before bonding. The positive electrode foil exposed portion 34 c of the electrode winding group 3 is sandwiched between the positive electrode current collector plate 44 and the positive electrode side ribbon 40, and ultrasonic welding is performed at the position of the weld 50. Are joined together.

  The prismatic lithium secondary battery of the present embodiment is characterized in that the separator 35 is disposed at a position facing the plate-like metal member (positive electrode side ribbon 40). In other words, the plate-like metal member is disposed so as to cover the separator 35. Here, in the winding axis direction of the electrode winding group 3, the separator 35 that covers the distance L1 from the end of the positive electrode active material mixture layer 34b to the end of the opposing plate-like metal member, and the positive electrode foil exposed portion 34c. Each member is placed and ultrasonic welding is performed such that the relationship between the width L2 of the positive electrode active material mixture layer 34b and the distance L3 from the end of the positive electrode active material mixture layer 34b to the welded portion satisfies L1 <L2 <L3.

FIG. 8 shows a schematic diagram after joining. As shown in FIG. 7, the separator 35 is disposed at a position facing the (positive electrode side ribbon 40), thereby eliminating a gap between the exposed portion of the electrode foil and the separator 35 as shown in FIG. 8A. be able to. As a result, it is possible to block the path through which the metal foreign matter generated during ultrasonic bonding enters the gap between the exposed portion of the electrode foil and the separator 35, and the contamination of the foreign matter can be greatly reduced.
7 and 8 (a), the positive electrode side has been described as an example. However, as shown in FIG. 8 (b), the relative positions of the separator 33 and the plate-shaped metal member are configured similarly on the negative electrode side. As a result, the mixing of foreign matters can be greatly reduced.

  The positive side ribbon 40 ribbon and the negative side ribbon 30 are plate-like metal members that are thinner than the current collector plate and have flexibility. Therefore, the separator end can be covered along the curved shape of the portion where the electrode foil exposed portions are bundled.

[Example 2]
FIG. 9 shows a modification of the configuration of the electrode foil exposed portion, current collector plate, and ribbon connecting portion. FIG. 9A is a conceptual schematic diagram on the positive electrode side, and FIG. 9B is a conceptual schematic diagram on the negative electrode side.

  As shown in FIGS. 9A and 9B, in this embodiment, between the positive current collector plate 44 and the positive electrode foil exposed portion 34c, between the negative current collector plate 24 side and the negative electrode foil exposed portion 32c. The positive electrode side ribbon 40 and the negative electrode side ribbon 30 are also arranged therebetween. Explaining the positive electrode side as an example, the joining portion is joined by the arrangement of the first positive electrode side ribbon 40 / the plurality of positive electrode foil exposed portions 34c / second positive electrode side ribbon 40 / positive electrode side current collector plate 44. . Both the first positive electrode side ribbon and the second positive electrode side ribbon are arranged so as to cover the end portion of the separator 35. In this way, by covering the separator with the plate-shaped metal members (first positive side ribbon, second positive side ribbon) on both sides in the joining direction, the intrusion of the metallic foreign matter is blocked as compared with the first embodiment and foreign matter is mixed. Can be prevented. Although the positive electrode side has been described, the same applies to the negative electrode side.

Example 3
Although it is possible to greatly reduce the mixing of metal foreign matter by the configurations of the first and second embodiments, a small amount of foreign matter may be mixed. Therefore, it is preferable to carry out a step of removing the metallic foreign matter. FIG. 10 shows an example of the method for removing metallic foreign matter. Metal foreign matter generated by ultrasonic welding is concentrated outside the winding group. In order to remove those foreign substances, as shown in FIG. 10, the wound group side to which suction is applied is directed obliquely downward, and a high frequency vibration is applied in the left-right direction. Move the metal foreign matter that has entered the gap between the electrodes to the left and right sides. Further, it is possible to remove metallic foreign matters by applying strong suction to the gaps at both ends of the welded portions of the negative electrode ribbon 30 and the negative electrode current collector plate 24, and the positive electrode ribbon 40 and the positive electrode current collector plate 44.

1: battery can, 1a: opening, 1b: wide surface, 1c: narrow surface, 1d: bottom surface,
2: insulation protective film, 3: wound electrode group, 5: gasket,
6: Battery cover, 7: Insulating plate, 9: Injection port, 10: Gas discharge valve, 11: Injection plug,
12: negative electrode external terminal, 12a: negative electrode connection part, 14: positive electrode external terminal,
14a: positive electrode connection part, 21: negative electrode current collector base part, 22: negative electrode side connection end part,
23: negative electrode side opening hole, 24: negative electrode current collector, 26: negative electrode side through hole,
30: Negative electrode side ribbon, 32: Negative electrode, 32a: Negative electrode foil,
32b: negative electrode mixture coating part, 32c: negative electrode foil exposed part, 33: separator,
34: positive electrode, 34a: positive foil, 34b: positive electrode mixture coating part,
34c: positive electrode foil exposed portion, 40: positive electrode side ribbon, 41: positive electrode current collector base,
42: positive electrode side connection end, 43: positive electrode side opening, 44: positive electrode current collector,
46: Positive electrode side through hole, 50: Porous film,
100: Square lithium ion secondary battery

Claims (3)

An electrode active material mixture layer is applied, and an electrode having a metal foil exposed portion at one end, a wound electrode group wound with a separator, and a current collector plate connected to the metal foil exposed portion In the next battery,
The metal foil exposed portion has a configuration in which the current collector and the first plate-shaped metal member are sandwiched and joined,
The prismatic secondary battery, wherein the separator is disposed at a position facing the first plate-like metal member.   2. The prismatic secondary battery according to claim 1, wherein the first plate-shaped metal member is disposed so as to cover an end portion of the separator. In Claim 1, it has the 2nd plate-like metal member arranged between the metal foil exposure part and the current collection object,
The square secondary battery, wherein the separator is disposed at a position facing the first plate-like metal member and the second plate-like metal member.

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