JP2005251548A - Square shape secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a square shape secondary battery with current breaking mechanism which works surely even when battery internal pressure rises rapidly at the time of overcharging. <P>SOLUTION: The square shape secondary battery has a square shape metal case with a bottom, a group of electrode plates which are inserted in the metal case via insulating layers, an opening seal metal plate which hermetically joins with the opening of the metal case, an electrode terminal which is attached to the opening seal metal plate via an insulator, and a lead which connects the electrode of the group of the electrode plates with the electrode terminal. A thin thickness portion is formed on one side of the metal case, a projecting portion is formed on a lead which is connected with another electrode terminal, and the projecting portion is connected to the thin thickness portion through a through-hole of the insulating layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a prismatic secondary battery having an excellent safety mechanism when the battery internal pressure increases.

  Square secondary batteries are used in various applications such as portable devices such as mobile phones and power sources for driving electric vehicles. Among these, prismatic lithium ion secondary batteries are used for portable devices. A prismatic lithium ion secondary battery generally has the following structure. An electrode plate group is inserted into a rectangular metal case with a bottom. The electrode plate group includes a positive electrode plate made of a positive electrode current collector coated with a positive electrode active material, a negative electrode plate made of a negative electrode current collector coated with a negative electrode active material, and a separator interposed between both electrode plates, Is spirally wound. A metal sealing plate is joined to the opening of the metal case to maintain airtightness. A negative electrode terminal is attached to the metal sealing plate via an insulating material, and the negative electrode terminal is connected to the negative electrode current collector through a lead. In such a square secondary battery, as a method for ensuring safety during overcharge, a current blocking mechanism is provided in the metal sealing plate.

  This current interrupting mechanism operates when the battery internal pressure rises, interrupts the electrical connection between the negative electrode plate and the negative electrode terminal, and tries to prevent an abnormal increase in the battery internal pressure. However, there is a problem that it does not operate in the following cases. This is because a relatively high pressure is required to operate the current interrupt mechanism, and the metal case may be deformed before the current interrupting mechanism operates.

In view of this, a structure having the following structure has been proposed as a current interruption mechanism using deformation of a metal case. A contact having a convex shape toward the inside of the battery is provided on the side wall of the metal case. This contact is connected to either one of the positive and negative plates by laser welding. When the internal pressure of the battery rises, the side wall of the metal case is deformed to the outside, the contact that is in contact with the electrode plate is released, and the electrical connection is cut off (Patent Document 1).
JP-A-9-92263

  In such a conventional square secondary battery, when the internal pressure of the battery suddenly increases during overcharge, the deformation of the side wall of the metal case cannot follow the increase in internal pressure, and the current interrupting mechanism may not work. .

  Accordingly, the present invention is to solve such a conventional problem, and an object of the present invention is to provide a prismatic secondary battery having a current interrupting mechanism that operates reliably even when the internal pressure of the battery suddenly increases. .

  In order to solve the above-described problems, the present invention provides a bottomed rectangular metal case, a group of electrode plates inserted through an insulating layer in the metal case, and a metal hermetically bonded to the opening of the metal case. A side plate of the metal case, comprising: a sealing plate; one electrode terminal attached to the metal sealing plate via an insulating material; and a lead connecting the one electrode of the electrode plate group and the electrode terminal. Further, the present invention relates to a rectangular secondary battery in which a thin portion is provided, a protrusion is provided on a lead connected to the other electrode, and the protrusion is connected to the thin portion through a through hole of the insulating layer.

  When the battery pressure rises during overcharge, the current interrupt mechanism can be reliably operated at a predetermined pressure. Therefore, a highly safe prismatic secondary battery can be provided.

  In the prismatic secondary battery of the present invention, an electrode plate group is inserted through an insulating layer into a bottomed prismatic metal case. Preferably, the electrode plate group includes a positive electrode plate made of a positive electrode current collector coated with a positive electrode active material, a negative electrode plate made of a negative electrode current collector coated with a negative electrode active material, and an electrode plate interposed between the two electrode plates. The separator is wound in a spiral. A metal sealing plate is joined to the opening of the metal case to maintain airtightness. A negative electrode terminal is attached to the metal sealing plate via an insulating material, and the negative electrode terminal is connected to the negative electrode current collector by a lead. A thin portion is provided on one side surface of the metal case. The lead connected to the other electrode of the electrode plate group has a protruding portion that is electrically connected to the thin portion through the through hole of the insulating layer.

  In order to electrically connect the lead and the thin-walled portion, it is preferable to connect by welding such as laser welding or resistance welding.

  In the prismatic secondary battery of the present invention, when the battery internal pressure increases during overcharging, the thin wall portion provided on one side surface of the metal case is deformed with a predetermined pressure. Thereby, the connection between the thin portion and the protruding portion provided on the lead connected to the other electrode of the electrode plate group is cut off, and the electric current cut-off mechanism is formed so that the electrical connection can be cut off.

  In a preferred embodiment of the present invention, the metal case has a flat shape having two opposing surfaces as main surfaces, and the thin portion is provided on one of the main surfaces.

  In a small electronic device, for example, a mobile phone, a rectangular lithium ion secondary battery used as a driving power source is a flat type having two surfaces facing each other as a main surface in view of the space given to the battery. Many batteries are used. Therefore, the metal case is preferably a flat shape having two opposite surfaces as main surfaces.

It is preferable that the thin part of the metal case is provided in a recess on the outer surface of the metal case.
For example, a mobile phone is generally mounted as a battery pack in which a battery is put in a pack case. This battery has an advantage that even if the metal case is deformed due to an increase in internal pressure, only the thin part provided in the metal case is deformed, and the thickness of the battery other than the thin part is not changed. By specifying the deformation part of the battery in this way, a battery pack can be designed in consideration of the deformation.

  In a further preferred embodiment of the present invention, the insulating layer is an inner case made of an insulating resin and in close contact with the inner surface of the metal case.

  In the case where the thin wall part is deformed by the increase in internal pressure of the battery, and the connection part between the thin part and the projecting part provided on the lead is disconnected and the electrical connection is interrupted, the insulating layer is attached to the lead along with the deformation of the thin part. The thickness of the inner case is preferably 0.3 to 1.5 mm so that the provided protrusions do not follow. The size of the hole of the inner case is preferably the same as or smaller than that of the thin portion. The reason that the internal pressure of the battery rises during overcharge is that the temperature inside the battery also rises due to decomposition of an electrolyte such as a non-aqueous electrolyte. Even at such temperatures, the heat resistant temperature is preferably 100 ° C. or higher so that the insulating layer does not deform. The insulating layer is preferably made of a material that has heat resistance, can insulate the electrode plate group and the metal case, and does not dissolve in an electrolyte such as a non-aqueous electrolyte. For example, a polypropylene resin or a polyphenylene sulfide resin can be used. Further, the insulating layer may be a tape if the thickness of the lead connected to the thin portion is larger than the thickness of the thin portion. This is because the thickness of the lead connected to the thin portion is larger than the thickness of the thin portion, so that even if the thin portion is deformed, the lead is not deformed due to the strength of the lead itself.

  The battery case used for the driving power source of the mobile phone, for example, a battery having a width of about 20 mm, a height of 50 mm, and a thickness of about 5 mm to a width of about 50 mm, a height of 95 mm, and a thickness of about 10 mm. Is preferably provided in a range from a circle having a diameter of 3 mm to the entire surface with respect to one side surface of the metal case. From the viewpoint of practicality, 50% of the area of one side surface of a circular to metal case having a diameter of 5 mm is preferable. The shape of the thin portion is preferably circular from both viewpoints of ease of processing when the thin portion is provided in the metal case and so that the thin portion is uniformly deformed, but is not limited thereto. For example, a square may be used as long as the area corresponds to a circle with a diameter of 3 mm. Moreover, in the battery used for the drive power supply for electric vehicles larger than the said battery size, the area of the thin part of a metal case is one side of a metal case with respect to one side of a metal case from a practical viewpoint. The range of 20% to the entire area of one side surface is preferable.

  The thickness of the thin part of the metal case is preferably 10 to 50% of the thickness of the base material of the metal case. From the viewpoint of practicality, 20 to 50% is more preferable.

  Examples of the positive electrode active material include composite oxides. As the composite oxide, lithium cobaltate, lithium nickelate, lithium manganate, and modified products thereof are preferable. Some of these modified products contain elements such as aluminum and magnesium. Some include at least two elements of cobalt, nickel and manganese.

  As the negative electrode active material, natural graphite, artificial graphite, aluminum, various alloys mainly composed thereof, metal oxides such as tin oxide, and metal nitrides can be used.

Examples of the electrolyte include a non-aqueous electrolyte and a gel electrolyte obtained by adding a non-aqueous electrolyte to a polymer material. The nonaqueous electrolytic solution is composed of a nonaqueous solvent and a solute. Examples of the solute include lithium salts such as lithium hexafluorophosphate (LiPF ₆ ) and lithium tetrafluoroborate (LiBF ₄ ). As the non-aqueous solvent, cyclic carbonates such as ethylene carbonate and propylene carbonate, and chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferable, but not limited thereto. The non-aqueous solvent may be used alone or in combination of two or more. Examples of the additive include vinylene carbonate, cyclohexyl benzene, and diphenyl ether.

  Examples of the polymer material for the gel electrolyte include polymer matrix materials such as polyethylene oxide, polypropylene oxide, and polyvinylidene fluoride, and derivatives, mixtures, and composites thereof. In particular, a copolymer of vinylidene fluoride and hexafluoropropylene or a mixture of polyvinylidene fluoride and polyethylene oxide is preferable, but not limited thereto.

  The separator is not particularly limited as long as it is an electronically insulating microporous thin film having a large ion permeability and appropriate mechanical strength. In general, a microporous film made of a polyolefin-based resin such as polyethylene or polypropylene can be used. The microporous film may be a single layer film made of one kind of polyolefin resin or a multilayer film made of two or more kinds of polyolefin resin.

  FIG. 1 is a schematic longitudinal sectional view of a prismatic lithium ion secondary battery which is an embodiment of the present invention. FIG. 2 shows a schematic longitudinal sectional view of the lower end portion of the electrode plate group. FIG. 3 shows a perspective view of the battery. 1 is a cross-sectional view taken along line XY in FIG.

  The prismatic lithium ion secondary battery includes a positive electrode plate 5 in which a positive electrode mixture 3 is applied to an aluminum foil current collector 1, a negative electrode plate 6 in which a negative electrode mixture 4 is applied to a copper foil current collector 2, A microporous film 7 made of polypropylene resin having a thickness of 25 μm is disposed as a separator between the two electrodes, and a flat electrode group 8 wound in a spiral shape is provided. A positive electrode lead terminal 9 a provided with a protruding portion 9 b is welded to the outermost peripheral portion of the aluminum foil current collector 1. A negative electrode lead terminal 10 is welded to the copper foil current collector 2. The positive electrode lead terminal 9a is disposed on the side surface of the flat electrode plate group 8 having a large area. The negative electrode lead terminal 10 is disposed on the electrode plate group 8. The electrode group 8 is inserted into a polypropylene inner case 11a having a thickness of 1 mm as an inner case serving as an insulating layer. The inner case 11a is provided with a hole 11b on one of the side surfaces having a large area. The hole 11b of the inner case 11a is located on the positive electrode lead terminal 9a side. The electrode plate group 8 inserted into the inner case 11a is housed in an aluminum metal case 12 having a thickness of 1 mm. A thin portion 13 a is provided on one side surface of the metal case 12. The positive electrode lead terminal 9a is placed on the thin portion 13a side. The thin-walled portion 13a is welded to the protruding portion 9b of the positive electrode lead terminal 9a and the thin-walled portion 13a by a laser from the outside of the thin-walled portion 13a of the metal case 12 so as to be electrically connected to the protruding portion 9b of the positive electrode lead terminal 9a. doing.

  As shown in FIG. 3, the metal sealing plate 14 includes a liquid injection hole 15 (not shown), a pressure regulating valve 16 that discharges gas generated inside the battery to the outside when the internal pressure of the battery rises, and an insulating portion. 17 and has a negative electrode external terminal 18 made of nickel attached through 17. The negative electrode lead terminal 10 arranged in the upward direction of the electrode plate group 8 and the nickel negative electrode external terminal 18 are electrically connected by resistance welding.

  The peripheral portions of the metal case 12 and the metal sealing plate 14 are welded and sealed by laser. Thereafter, a non-aqueous electrolyte is injected from a liquid injection hole 15 (not shown) provided in the metal sealing plate 14 under reduced pressure. The liquid injection hole 15 (not shown) is closed by an aluminum sealing plug 19, and the peripheral edge thereof is welded and sealed with a laser.

  Thus, a square secondary battery having a width of 50 mm, a height of 95 mm, and a thickness of 10 mm was produced. The design capacity of the battery is 3000 mAh.

  A case where the internal pressure of the battery increases and the thin portion 13a is deformed is shown as a thin portion 13b after deformation by a dotted line in FIG. In this way, the thin-walled portion 13a is deformed like the thin-walled portion 13b, so that the welding with the protruding portion 9b of the positive electrode lead terminal 9a is broken.

  The positive electrode plate 5 is produced as follows. As positive electrode mixture 3, 85 parts by weight of lithium cobaltate powder, 10 parts by weight of carbon powder as conductive agent, and polyvinylidene fluoride (hereinafter abbreviated as PVDF) N-methyl-2-pyrrolidone (hereinafter referred to as PVDF) as binder The solution is mixed with 5 parts by weight of PVDF. This mixture is applied to an aluminum foil current collector 1 having a thickness of 15 μm, dried, and then rolled to produce a positive electrode plate 5 having a thickness of 100 μm.

  The negative electrode plate 6 is produced as follows. As negative electrode mixture 4, 95 parts by weight of artificial graphite powder and PVDF NMP solution corresponding to 5 parts by weight of PVDF are mixed as binder. This mixture is applied to a copper foil current collector 2 having a thickness of 10 μm, dried, and then rolled to produce a negative electrode plate 6 having a thickness of 110 μm.

The non-aqueous electrolyte is prepared as follows. As a non-aqueous solvent, ethylene carbonate and ethyl methyl carbonate are mixed at a volume ratio of 1: 1, and as a solute, lithium hexafluorophosphate (LiPF ₆ ) is dissolved at 1 mol / L. 24 ml of the non-aqueous electrolyte prepared in this way is used.
Below, the thin part 13a is demonstrated concretely.

<< Examples 1-6 >>
The size of the thin portion 13a was as shown in Table 1 described below, and the thickness was fixed at 0.2 mm.

<< Examples 7 to 11 >>
The thickness of the thin portion 13a was as shown in Table 1 described below, and its size was fixed at a diameter of 5 mm.

《Comparative example》
Example 1 was performed except that the thin portion 13a was not provided.

  Regarding the batteries of Examples 1 to 11 and Comparative Example described above, the presence or absence of welding breakage of the protruding portion of the positive electrode lead connected to the thin wall portion during high temperature storage and the abnormal temperature rise during the overcharge test were evaluated. .

  100 cells each were used for the high temperature storage test. The battery was charged at 20 ° C. with a constant current of 3 A to an upper limit voltage of 4.2 V, held at a constant voltage of 4.2 V, and then stored at 85 ° C. for 48 hours. About the battery after a preservation | save, the presence or absence of the fracture | rupture of the welding of the protrusion part of the positive electrode lead connected to the thin part used as an electric current interruption mechanism was confirmed.

25 cells each were used for the overcharge test. At 20 ° C., overcharging was further performed from the charged state at a current value of 15 A corresponding to the 5C rate. It was confirmed whether or not the battery would rise abnormally. Here, the case where the battery surface temperature became 130 ° C. or higher was judged as an abnormal temperature rise.
The results are shown in Table 1.

  From the results of Table 1, in the batteries of Examples 1 to 11 and the comparative example, no welding breakage was observed in the protruding portion of the positive electrode lead connected to the thin wall portion serving as a current interruption mechanism during high temperature storage. In the overcharge test, no abnormal temperature rise was observed in the batteries of Examples 2 to 10. An abnormal temperature increase of 2/25 cells was observed for the battery of Example 1, 3/25 cells for the battery of Example 11, and 10/25 cells for the battery of the comparative example. However, the number of batteries in which an abnormal temperature increase was observed was larger in the comparative example.

  From this, it can be said that an abnormal temperature rise of the battery can be suppressed by providing the thin portion as in the embodiment.

  In the batteries of Examples 2 to 10, in the overcharge test, from the relationship between the battery voltage and the battery temperature with respect to the elapsed time, the thin part deforms before the battery rises abnormally, and the thin part and the protruding part of the positive electrode lead It was found that the connection of was disconnected and temperature rise was suppressed. On the other hand, in Examples 1 and 11 in which an abnormal temperature increase was observed, and the batteries of the comparative example, even if the temperature increased, the weld between the thin wall portion and the protruding portion of the positive electrode lead did not come off, resulting in an abnormal temperature increase. I found out that

  For this reason, the size of the thin portion of the metal case is preferably provided on a single side surface of the metal case from a circle of 3 mm to the entire surface. From the viewpoint of practicality, 50% is preferable with respect to the area of one side surface of the circular to metal case having a diameter of 5 mm. The thickness of the thin portion of the metal case is preferably 0.1 to 0.5 mm with respect to 1 mm of the substrate thickness of the metal case, that is, 10 to 50% with respect to the thickness of the metal case. From the viewpoint of practicality, 20 to 50% is more preferable.

  In addition, although the Example demonstrated the square lithium ion secondary battery, it is not limited to this. For example, it can be used for a prismatic alkaline storage battery.

  In the embodiment, the case where the metal case is a flat shape having two surfaces facing each other as the main surface has been described. However, the shape is not limited to this as long as it is square.

  Further, in the examples, the strip-shaped positive electrode plate, the strip-shaped negative electrode plate, and the strip-shaped separator between the two electrodes are described, and the flat electrode plate group wound in a spiral shape is described. The same effect can be obtained when a positive electrode plate, a flat negative electrode plate, and an electrode plate group in which unit cell elements each having a separator disposed between them are stacked are used.

  The prismatic secondary battery according to the present invention can reliably operate the current interrupting mechanism at a predetermined pressure when the battery pressure rises during overcharge. Therefore, a highly safe prismatic secondary battery can be provided. The prismatic secondary battery according to the present invention can be used as a drive power source for electronic devices, for example, in notebook computers, mobile phones, digital still cameras, and the like. Further, the present invention can also be applied to a drive power source such as an electric vehicle that requires large current charge / discharge.

It is a schematic longitudinal cross-sectional view of the square lithium ion secondary battery which is one Example of this invention. It is a schematic longitudinal cross-sectional view of the lower end part of the electrode group of the battery. It is a perspective view of the battery.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Aluminum foil collector 2 Copper foil collector 3 Positive electrode mixture 4 Negative electrode mixture 5 Positive electrode plate 6 Negative electrode plate 7 Microporous film made from polypropylene resin 8 Electrode plate group 9a Positive electrode lead terminal 9b Protrusion part 10 Negative electrode lead terminal 11a Polypropylene Internal case 11b Hole 12 Aluminum metal case 13a Thin portion 13b Deformed thin portion 14 Metal sealing plate 15 Injection hole 16 Pressure regulating valve 17 Insulating portion 18 Nickel negative electrode external terminal 19 Aluminum sealing plug

Claims (4)

A rectangular metal case with a bottom, an electrode plate group inserted into the metal case via an insulating layer, a metal sealing plate hermetically bonded to the opening of the metal case, and an insulating material interposed in the metal sealing plate One electrode terminal attached, and a lead for connecting one electrode of the electrode plate group and the electrode terminal,
A rectangular secondary battery in which a thin portion is provided on one side surface of the metal case, a protrusion is provided on a lead connected to the other electrode, and the protrusion is connected to the thin portion through a through hole of the insulating layer.   2. The prismatic secondary battery according to claim 1, wherein the metal case has a flat shape having two opposite surfaces as main surfaces, and the thin portion is provided on one of the main surfaces.   The prismatic secondary battery according to claim 1, wherein the thin portion is provided in a hollow portion on an outer surface of the metal case.   The prismatic secondary battery according to any one of claims 1 to 3, wherein the insulating layer is made of an insulating resin and is made of an inner case that is in close contact with the inner surface of the metal case.

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