JP2005149862A - Sealed battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sealed battery stabilizing large current discharge at normal time and securing safety at abnormalities of the battery, at low cost. <P>SOLUTION: Sealed cylindrical lithium ion secondary battery is provided with a top lid 21 having an explosion-proof mechanism. The explosion-proof mechanism is equipped with a dish-shaped conductive diaphragm having a flat part at the center, and a splitter 18 electrically connected to an electrode group and equipped with a thin part lifted up toward the diaphragm 2 side in a planate shape at the center. The thin part of the splitter 18 is jointed to the flat part of the diaphragm 2. An outer diameter of the thin part at the diaphragm 2 side is larger than that at a rear face side opposite to the diaphragm 2. The jointed part of the splitter 18 and the diaphragm 2 is kept adhered. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention provides a plate-shaped conductive diaphragm having a flat portion at the center, a connecting member connected to the power generation element, and a thin flat portion that is electrically connected to the connecting member and is raised to the diaphragm side in the center. The present invention relates to a sealed battery having an explosion-proof mechanism in which a flat surface portion of a diaphragm and a thin flat surface portion of a conductive member are joined to each other.

  Conventionally, sealed batteries have been widely used in home appliances, and recently, lithium secondary batteries have been used in particular, among sealed batteries. Since the lithium secondary battery has a high energy density, the lithium secondary battery is being developed as a power source for vehicles such as an electric vehicle (EV) and a hybrid vehicle (HEV), and a stationary power source for offices and homes. However, when the sealed battery falls into an abnormal battery state such as overcharging due to a failure of the charging device, the internal pressure of the battery may extremely increase. For this reason, a sealed battery having an explosion-proof mechanism inside the battery has been proposed (see, for example, Patent Document 1 and Patent Document 2).

  Further, the present inventors have proposed a sealed battery provided with the explosion-proof mechanism shown in FIG. Briefly describing this explosion-proof mechanism, the upper lid 20 has a disc-shaped upper lid cap 1 made of, for example, iron and plated with nickel. The upper lid cap 1 has a hat shape having a cylindrical protrusion whose center protrudes upward, and an opening is formed at the center of the protrusion. The peripheral portion of the upper lid cap 1 is caulked and fixed to the peripheral portion of the dish-shaped diaphragm 2 made of, for example, an aluminum alloy. The diaphragm 2 has a flat portion at the center of the bottom. Between the flat part and the peripheral part of the diaphragm 2, there is formed a thinned cleavage groove 8 that is torn when the battery internal pressure reaches a predetermined pressure (see, for example, Patent Document 3).

  An insulating ring 3 made of, for example, resin and having a substantially T-shaped cross section is disposed below the peripheral edge of the diaphragm 2 to support the diaphragm 2. A plurality of (for example, three) support claws 15 formed integrally with the insulating ring 3 are formed at the lower part on the inner surface side of the insulating ring 3. By these support claws 15, the outer peripheral portion of a flat donut-shaped splitter 4 connected to a lead piece (not shown) electrically connected to the electrode group is supported at a predetermined interval from the bottom surface of the diaphragm 2. The splitter 4 is made of, for example, an aluminum alloy, and is formed with a plurality of through holes 9 for discharging gas in the battery when the battery is abnormal such as overcharge. The central portion of the splitter 4 is made of, for example, a polypropylene resin and an annular spacer 5, and a peripheral portion of a connection plate 6 made of, for example, an aluminum alloy having a projection formed above and having a flat portion at the center of the projection, and the diaphragm 2. It is sandwiched between the flat part. The spacer 5 has a flange portion, and this flange portion is in contact with the flat portion of the diaphragm 2.

  The upper surface of the peripheral edge portion of the connection plate 6 and the lower surface of the central portion of the splitter 4 are laser bonded. Further, the central plane portion of the connection plate 6 and the plane portion at the center of the bottom portion of the diaphragm 2 are electrically and mechanically joined to form a joint portion 7. In this explosion-proof mechanism, the planar areas of the planar portions of the connection plate 6 and the diaphragm 2 are wide, and the planar portions can be stably joined (without variation) using a jig, and the internal pressure of the battery is kept at a predetermined pressure. Then, the diaphragm 2 is reversed and the connection between the connecting plate 6 and the diaphragm 2 at the joint 7 is cut off, so that the battery safety is ensured when the battery is abnormal such as overcharge (when it is not normal). be able to.

JP-A-7-105933 JP-A-8-007866 JP 2003-217544 A

  However, in the above explosion-proof mechanism, since there is no variation in the joint 7, it is possible to stably ensure a large current discharge at normal times, but the splitter 4, the connecting plate 6, and the spacer 5 are separate members. Since the splitter 4 and the connection plate 6 are electrically connected by laser bonding, the cost of the sealed battery is high, and it is difficult to reduce the cost because of the structure.

  In view of the above-described case, an object of the present invention is to provide a sealed battery that can stabilize high-current charging / discharging at normal time and can ensure safety in the event of battery abnormality at low cost.

  In order to solve the above-described problems, the present invention provides a dish-shaped conductive diaphragm having a flat portion in the center, a connecting member connected to a power generation element, and electrically connected to the connecting member. In a sealed battery comprising an explosion-proof mechanism in which the flat surface portion of the diaphragm and the thin flat surface portions of the conductive member are joined to each other, the conductive member has a thin flat surface portion protruding on the diaphragm side. The outer diameter of the thin flat surface portion on the diaphragm side is larger than the outer diameter of the rear surface side of the thin flat surface portion, and is formed integrally with the connection member.

  In the present invention, at the time of battery abnormality such as overcharge, due to an increase in battery internal pressure, the dish-shaped diaphragm having a flat part at the center is reversed, and the flat part of the diaphragm and the thin flat part of the conductive member are disconnected, The conductive path between the power generation element and the diaphragm is interrupted. On the other hand, since the outer diameter of the thin flat portion on the diaphragm side is larger than the outer diameter on the back side of the thin flat portion, the flat surface of the thin flat portion raised on the diaphragm side can be secured stably. Variations can be eliminated and the number of members can be reduced because the conductive member is formed integrally with the connecting member.

  In the present invention, if the thin flat portion raised to the diaphragm side is formed so as to raise the meat on the back side of the thin flat portion, the plane area of the thin flat portion raised to the diaphragm side can be increased. Therefore, the close contact state with the flat portion of the diaphragm can be kept good, and both can be stably bonded.

  According to the present invention, since the conductive path between the power generation element and the diaphragm is interrupted by the reversal of the diaphragm due to the increase in the battery internal pressure, the safety at the time of battery abnormality can be ensured, and the thin wall raised on the diaphragm side Since the flat surface of the flat part can be secured stably and the variation in joining with the flat part of the diaphragm can be eliminated, large current charging and discharging can be secured stably in normal times, and the conductive member is integrated with the connecting member. Since it is formed, a low-cost sealed battery with a small number of members can be obtained.

  Embodiments in which the present invention is applied to a sealed cylindrical lithium ion secondary battery will be described below with reference to the drawings. In the present embodiment, the same members as those shown in FIG. 5 are denoted by the same reference numerals, description thereof is omitted, and only different portions will be described.

  As shown in FIG. 1, a lithium ion secondary battery 30 (hereinafter abbreviated as a battery 30) of the present embodiment includes an electrode group 11. The electrode group 11 is housed in the center of a bottomed cylindrical battery can 10 that also serves as a negative electrode terminal, and the positive electrode and the negative electrode are wound around a resin shaft through a polyethylene microporous separator. Has been.

The positive electrode is, for example, a LiMnO ₂ having a spinel structure or a layered rock salt structure, a lithium manganese transition metal composite oxide powder in which lithium sites or manganese sites of LiMn ₂ O ₄ are substituted or doped with other metal elements, conductive materials A positive electrode active material mixture obtained by mixing carbon material, polyvinylidene fluoride (PVDF) as a binder and n-methylpyrrolidone as a viscosity adjusting solvent, and uniformly dispersing and kneading with Cornell Despa is applied to both surfaces of the aluminum foil. It is obtained by uniformly coating, pressing, drying, and cutting to a predetermined size. In addition, rectangular cutouts are formed at predetermined intervals on one side in the longitudinal direction of the aluminum foil, and the remainder of the cutout serves as a positive electrode tab for current collection.

  On the other hand, the negative electrode is prepared by mixing, for example, graphite or carbon, PVDF as a binder and n-methylpyrrolidone as a viscosity adjusting solvent, uniformly dispersing and kneading with Cornell Despa, and using the negative electrode active material mixture of rolled copper foil. It was obtained by uniformly coating, pressing, drying and cutting to a predetermined size on both surfaces. Note that rectangular cutouts are formed at predetermined intervals on one side in the longitudinal direction of the rolled copper foil, and the remainder of the cutout is a negative electrode tab for current collection.

  The positive electrode tab and the negative electrode tab are arranged so as to be positioned on both end surfaces of the electrode group 11 opposite to each other. A negative electrode current collecting ring for current collection is fixed to the lower end of the shaft core, and a negative electrode tab is ultrasonically welded to the peripheral edge of the negative electrode current collecting ring. The negative electrode current collector ring is resistance-welded to the battery can 10. A reduced diameter portion of a positive current collecting ring 14 for current collection is inserted and fixed at the upper end of the shaft core, and a positive electrode tab is ultrasonically welded to the peripheral portion of the positive current collecting ring 14. In order to allow a large current, one end of a positive electrode lead plate 16 formed by overlapping a plurality of aluminum ribbons is welded to the positive electrode current collecting ring 14. The other end of the positive electrode lead plate 16 is welded to the bottom surface of the upper lid 21.

  As shown in FIG. 2, the upper lid 21 of the present embodiment has a splitter 18 in which these are integrated instead of the connection plate 6 and the splitter 4 compared to the upper lid 20 shown in FIG. 5. The difference is that the spacer 5 is omitted. Further, the splitter 18 is not formed with a hole in the central portion like the splitter 4, but as shown in FIG. 3 (A), the central portion of the splitter is crushed by a press and shown in FIG. 3 (B). As described above, the thin-walled portion LW is formed as a thin-walled flat portion raised in a planar shape on the diaphragm 2 side. The thickness of the thin portion LW is set to be thinner than the thickness of the flat portion at the center of the bottom of the diaphragm 2.

  In general, the volume of metal does not decrease even when a strong press process is performed, so the meat of the pressed part must be released somewhere. In the present embodiment, as shown in FIG. 3 (B), the thin wall LW is formed so as to rise from the back side opposite to the diaphragm 2 of the thin wall portion LW, so that the thin wall is raised by the thickness T1 on the diaphragm 2 side. The meat is released to the periphery A of the part LW, and the area of the flat part of the thin part LW is increased. The outer diameter D1 raised to the diaphragm 2 side due to the meat escape is larger than the outer diameter D2 on the back side of the thin wall portion LW.

  As shown in FIG. 1, the peripheral portion of the upper lid 21 and the battery can 10 are caulked and fixed via a gasket 13, and the inside of the battery 30 is sealed. In the battery 30, for example, a nonaqueous electrolytic solution in which lithium hexafluorophosphate or lithium tetrafluoroborate is dissolved in a mixed organic solvent such as ethylene carbonate or dimethyl carbonate at a rate of about 1 mol / liter is poured. The electrode group 11 is infiltrated with a non-aqueous electrolyte. The positive electrode lead plate 16 is bent in a curved shape, and the other end is welded to the back side of the splitter 18 constituting the bottom surface of the upper lid 21 (the side opposite to the splitter 2).

  Next, the operation and the like of the battery 30 of the present embodiment will be described.

  In the battery 30 of the present embodiment, the shape of the splitter 18 is (outer shape D1)> (outer shape D2), so that the diaphragm 2 and the splitter 18 are fixed by jigs 21 and 22 as shown in FIG. When the flat surface portions at the center of the diaphragm 2 and the splitter 18 are bound together by, for example, the friction stir welding tool 23, the close contact state between the flat surface portions is maintained well, and stable bonding can be performed.

  As shown in FIG. 4A, in press work, meat is generally often released to the back side of the splitter 19. In such press working, the outer diameter D1 raised to the diaphragm 2 side is usually the same as or slightly smaller than the outer diameter D2 on the back side of the thin wall portion LW (D1 ≦ D2). In FIG. 4 (A), the meat escapes to the peripheral portion B on the back side of the thin-walled portion LW. However, in actual pressing, the diaphragm 2 side of the thin-walled portion LW is slightly raised, and the diaphragm 2 Variations in the flatness of the side. According to such a general press work, as shown in FIG. 4B, when the diaphragm 2 and the splitter 19 are restrained by the jigs 21 and 22 at the time of friction stir welding, the central thin portion LW is bent and flat. The property cannot be ensured, and a gap is easily formed between the diaphragm 2 and the diaphragm 2. For this reason, the diaphragm 2 and the splitter 19 are not sufficiently joined to each other, causing a problem that a stable operating pressure cannot be obtained as an explosion-proof mechanism.

  As described above, in the battery 30 of the present embodiment, the thin portion LW is allowed to escape to the portion A (see FIG. 3B), and (outer diameter D1)> (outer diameter D2). In addition, the area of the thin-walled portion LW protruding in a flat shape can be widened, and the close contact state (planar property) with the flat portion at the center of the bottom of the diaphragm 2 can be maintained well. Therefore, in the battery 30 of the present embodiment, there is no variation in the joining of the joint portion 7 between the diaphragm 2 and the splitter 18, so that large current charging / discharging can be stably secured during normal times.

  In the battery 30 of this embodiment, the flat portions of the diaphragm 2 and the splitter 18 are joined by friction stir welding. For this reason, since refinement | miniaturization of the crystal | crystallization by plastic flow arises, the stability of the junction part 7 improves, and the explosion-proof mechanism with a fixed operating pressure of the diaphragm 2 can be obtained. Furthermore, when the diaphragm 2 and the splitter 18 are joined by friction stir welding, they can be joined at a lower temperature than conventional welding. For this reason, since the deformation of the diaphragm 2 and the splitter 18 at the time of friction stir welding can be suppressed, it is possible to obtain an explosion-proof mechanism that is less deformed, in other words, has less variation in operating pressure and is excellent in reliability.

  Furthermore, when the battery 30 of this embodiment falls into an abnormal battery state such as overcharging, the nonaqueous electrolyte is decomposed and gas is generated in the battery can 10 at an accelerated rate. Although the internal pressure of the battery is increased by this gas, the diaphragm 2 maintains the junction with the splitter 18 up to a predetermined pressure (for example, 0.5 to 2.5 MPa) determined by the shape, dimensions, material, and the like of the diaphragm 2 (diaphragm 2 Maintain a dish-like shape up to a predetermined pressure.) When the battery internal pressure exceeds a predetermined pressure, the diaphragm 2 instantly reverses and disconnects the junction with the splitter 18. As a result, the conductive path from the electrode group 11 is blocked. At this time, since the thickness of the thin portion LW of the splitter 18 is thinner than the thickness of the flat portion at the center of the bottom of the diaphragm 2, the thin portion LW is broken first, so that no hole is opened in the diaphragm 2.

  When the internal pressure of the battery further increases, the cleavage groove 8 of the diaphragm 2 is cleaved, and the gas in the battery 30 passes through the through hole 9 formed in the splitter 18, the cleavage groove 8, and the opening formed in the upper lid cap 1. It is opened and the battery 30 can be safely disabled. In this case, since the working pressure of the diaphragm 2 is larger than the atmospheric pressure, once the diaphragm 2 is reversed, the diaphragm 2 does not return to the original dish shape at the atmospheric pressure, and the diaphragm 2 and the splitter 18 are electrically connected again. Without contact.

  Further, the battery 30 of this embodiment uses the splitter 18 in which the connection plate 6 and the splitter 4 shown in FIG. 5 are integrated, and does not use the spacer 5. Therefore, the upper lid 21 can be configured with a small number of parts, and the joining of the connection plate 6 and the splitter 4 is not necessary, so that a low-cost battery 30 can be obtained.

  In the present embodiment, the joint portion 7 formed by friction stir welding is illustrated as a joint between the flat portions of the diaphragm 2 and the splitter 18. However, the above-described effects are not requirements specific to the friction stir welding. The same applies when the diaphragm 2 and the splitter 18 are joined by, for example, a laser instead of the friction stir welding.

  Moreover, in this embodiment, although the cylindrical battery 30 was illustrated, this invention is not limited to this, For example, you may make it apply to a square battery. Furthermore, in the present embodiment, an example in which an aluminum alloy is used as the material of the diaphragm 2 and the splitter 18 is shown, but the present invention is not limited to this, and other conductive materials such as aluminum, nickel alloy, and conductive plastic are used. It may be used. Further, in the present embodiment, an example in which the opening of the upper cap 1 is formed at the center of the protrusion has been shown, but instead, for example, a plurality of openings may be formed at the protrusion rising portion. Furthermore, in the present embodiment, the overcharge has been mainly described as an example when the battery is abnormal. However, the present invention is not limited to this, and the same effects can be achieved, for example, in the case of concentrated load or piercing to the battery. .

  Next, examples of the battery 30 created according to the above-described embodiment will be described. In addition, it describes together about the battery of the comparative example created for the comparison. In addition, the capacity | capacitance of the battery of an Example and a comparative example was made the same.

(Example)
A battery 30 having a capacity of 6 Ah was manufactured using the upper lid 21. The diaphragm 2 was made of A3003-H14 having a thickness of 0.6 mm and formed into a dish shape by pressing. The splitter 18 was made of A3003-H14 having a thickness of 1 mm. Further, a thin portion LW having a thickness of 0.5 mm was formed in the center of the splitter 18 by pressing. At this time, the outer diameter D2 on the back side of the thin-walled portion LW was 4 mm, the meat of the thin-walled portion LW was allowed to escape to the portion A in FIG. 1, and the outer diameter D1 raised on the diaphragm 2 side was 8 mm. The height T1 raised upward was set to about 0.25 mm.

(Comparative Example 1)
A battery of Comparative Example 1 was fabricated using the conventional upper cover 20 shown in FIG. A3003-H14 having a thickness of 0.5 mm was used for the connection plate 6, and the connection plate 6 and the splitter 4 were joined by a YAG laser. In addition, it was set as the structure same as an Example except the upper cover 20. FIG.

(Comparative Example 2)
A battery of Comparative Example 2 was fabricated using the splitter 19 shown in FIG. The outer diameter D1 raised to the diaphragm 2 side is 3.8 mm, the height T1 is about 0.25 mm, the outer diameter D2 on the back side of the thin wall portion LW is 4 mm, and the height T2 of the downward bulge is about 0.3 mm. there were. In addition, it was set as the structure same as an Example except an upper cover.

  The batteries of Example and Comparative Examples 1 and 2 were each made 100, and when the internal pressure of the battery rose due to overcharging, the pressure when the diaphragm 2 was reversed, that is, the stability of the operating pressure as an explosion-proof mechanism was compared. . The results are shown in Table 1 below.

  There was no substantial difference between the batteries of Example and Comparative Example 1, and good operation was obtained in both cases. However, it was found that the upper lid of the battery of Comparative Example 2 had a large variation in operating pressure and the operation was unstable. Therefore, it was confirmed that the explosion-proof mechanism of the battery of Comparative Example 2 was inferior to the battery of Example and Comparative Example 1. Moreover, when the point of cost and performance (stability) was considered, it became clear that the battery of an Example was superior to the battery of the comparative example 1.

  The present invention is industrially applicable because it relates to a sealed battery that can stabilize high-current discharge at normal times and can ensure safety when the battery is abnormal, at low cost.

It is sectional drawing of the airtight cylindrical lithium ion secondary battery of embodiment which can apply this invention. It is sectional drawing of the upper cover of the battery of embodiment. It is sectional drawing of the splitter which comprises the battery upper cover of embodiment, (A) shows the cross-sectional shape of the splitter before forming a thin part, (B) shows the cross-sectional shape of the splitter after forming a thin part. (C) shows the state when a splitter and a diaphragm are joined using a jig. It is sectional drawing of the splitter which made meat escape on the back side, (A) shows the splitter used for the battery of the comparative example 2, (B) is the state when joining a splitter and a diaphragm using a jig | tool. Indicates. It is sectional drawing of the upper cover by a prior art.

Explanation of symbols

2 Diaphragm 4 Splitter (connection member)
6 Connection plate (conductive member)
11 Electrode group (power generation element)
18 Splitter (connection member, conductive member)
20, 21 Upper lid 30 Sealed cylindrical lithium ion secondary battery (sealed battery)

Claims (2)

  A plate-shaped conductive diaphragm having a flat portion in the center, a connecting member connected to the power generation element, and a conductive member electrically connected to the connecting member and having a thin flat portion raised on the diaphragm side in the center. A sealed battery including an explosion-proof mechanism in which the flat portion of the diaphragm and the thin flat portion of the conductive member are joined to each other, the conductive member has an outer diameter of the thin flat portion on the diaphragm side. A sealed battery having a larger outer diameter on the back side of the thin flat portion and formed integrally with the connection member.   2. The sealed battery according to claim 1, wherein the thin flat surface portion protruding to the diaphragm side is formed so as to bulge the back side of the thin flat surface portion.