JP2009301982A - Stacked battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stacked battery capable of preventing damage of a joining site with restraint of heat generation at the joining site at the time of large-current conduction. <P>SOLUTION: A tandem battery 20 has two unit cells provided with an anode lead plate electrically connected with an electrode group and a metal-made inner bottom surface of the battery vessel 17 jointed in spot welding connected by bus bars 4 electrically and mechanically connecting the unit cells. One side of a metal heat dissipation member 10 is fixed to one of the welding part 4A of the bus bars 4, and the other side of the heat dissipation member 10 is in contact with an outer bottom surface on the opposite surface side to a welding site 30 of the inner bottom surface side of the battery vessel 17 jointed in spot welding. Even if the joining site 30 generates heat at large-current conduction of the tandem battery 20, heat is transmitted to the bus bars 4 through the heat dissipation member 10, so that the temperature at the joining site 30 is decreased to enable to prevent damage at the joining site 30. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an assembled battery, and in particular, a plurality of secondary batteries in which a conductive member electrically connected to an electrode group and an inner bottom surface of a metal battery can are joined by spot welding, and the secondary battery is electrically connected. The present invention relates to an assembled battery including a bus bar that is mechanically and mechanically connected.

  In recent years, multiple large-current discharges have been used as power sources for mobile vehicles such as electric motor-powered bicycles, hybrid electric vehicles (HEV), and genuine electric vehicles (PEV), or as power sources for stationary power storage systems such as solar thermal power generation and wind power generation. Collective batteries (assembled batteries) in which unit cells are connected in series or series-parallel are used. These assembled batteries are usually called a bus bar, and a conductive member that electrically and mechanically connects the cells is connected to, for example, a metal battery lid that serves as one electrode of one cell. By joining the bottom of the battery can, which is the other electrode of the other unit cell, with series spot welding, two unit cells are connected in series (or in series-parallel), and this is repeated for the number of unit cells required, The required output voltage of the assembled battery is obtained (see, for example, Patent Document 1).

  Direct spot welding is usually used on the inner bottom surface side of the battery can for connection between the battery can of the unit cell and the internal power generation unit (conductive member electrically connected to the electrode group). In addition, the bus bar for connecting to other single cells avoids the direct spot welds (joint points) described above, and series spots are provided at multiple locations on the outer bottom side of the battery can so that it can withstand large current flow. Welding has been done.

JP 2004-152706 A

  In the assembled battery, in order to reduce the resistance of the joint as much as possible, it is effective to increase the number of welding points, increase the joint area, and shorten the distance between the bus bar joint and the can bottom joint. However, at the joint location between the battery can and the power generation unit, it is difficult to increase the number of joint locations and increase the area in order to improve the volume density inside the battery. For this reason, in the conventional secondary battery, when a large current is passed, the joint portion between the battery can and the power generation unit is likely to generate heat, and in the worst case, the joint portion may be red-hot and the joint portion may be melted.

  An object of the present invention is to provide an assembled battery that can suppress heat generation at a joint portion and prevent damage at the joint portion even when a large current is applied.

  In order to solve the above-described problems, the present invention is an assembled battery, and a plurality of secondary batteries in which a conductive member electrically connected to an electrode group and an inner bottom surface of a metal battery can are joined by spot welding. A bus bar that electrically and mechanically connects between the secondary batteries, one side abuts on the outer bottom surface opposite to the inner bottom surface of the battery can joined by spot welding, and the other side is both ends of the bus bar And a metal heat dissipating member fixed to at least one end.

  In the assembled battery of the present invention, a plurality of secondary batteries in which a conductive member electrically connected to an electrode group and an inner bottom surface of a metal battery can are joined by spot welding are electrically mechanically connected between the secondary batteries. It is connected with the bus bar that connects to. The other side of the metal heat dissipating member is fixed to at least one end of both ends of the bus bar, and one side of the heat dissipating member is on the outer bottom surface opposite to the inner bottom surface of the battery can joined by spot welding. It is in contact. For this reason, even when a large current is applied, even if the joint between the conductive member and the inner bottom surface of the battery can generates heat, this heat is transmitted to the bus bar via the heat dissipation member, and the temperature at the joint decreases, resulting in damage to the joint. Can be prevented.

  In this invention, it is preferable that a thermal radiation member has a thermal conductivity larger than the battery can of a secondary battery. Moreover, it is desirable that one side of the heat radiating member is in contact with a portion on the outer bottom surface side corresponding to a joint portion of the inner surface of the battery can by spot welding. As such a heat radiating member, for example, a plug or rivet-like member press-fitted from the bus bar side or a screw-like member screwed from the bus bar side can be used, and the bottom surface of the head of the plug or rivet-like member or screw-like member May be in contact with the upper surface of at least one of the both ends of the bus bar. Moreover, the heat radiating member may be integrally formed with the bus bar.

  Further, in the present invention, at least one end portion of the both ends of the bus bar is provided at a plurality of locations on the outer bottom surface of the battery can so as to avoid locations on the outer bottom surface corresponding to the joining locations of the inner surface of the battery can by spot welding. And may be joined by spot welding. Further, slits for spot welding are formed at both ends of the bus bar, and the secondary battery has an exhaust port formed at the center of the upper surface of the battery cover, and the exhaust port is at least the other end of the bus bar. It is preferable to be positioned immediately below the slit at the end. Of the both ends of the bus bar, one end is joined to the negative battery can of the secondary battery constituting the assembled battery, and the other end is connected in series to the secondary battery. It may be joined to a positive battery lid of another secondary battery. Furthermore, it is preferable that the center part between the both ends of the bus bar has a step with respect to the both ends of the bus bar.

  According to the present invention, one side is in contact with the outer bottom surface opposite to the inner bottom surface of the battery can joined by spot welding, and the other side is made of metal fixed to at least one end portion of both ends of the bus bar. Since a heat dissipation member is provided, even when a large current is applied, even if the joint between the conductive member and the inner bottom surface of the battery can generates heat, this heat is transmitted to the bus bar via the heat dissipation member, and the temperature at the joint decreases. The effect that the damage of a location can be prevented can be acquired.

(First embodiment)
Hereinafter, a first embodiment in which the present invention is applied to a juxtaposed tandem battery will be described with reference to the drawings.

  As shown in FIGS. 1 and 2, the tandem battery (collective battery) 20 according to the present embodiment includes two unit cells 1 and 5 arranged in parallel so that the polarities are opposite to each other in series by a metal bus bar 4. It is connected.

  As the unit cells 1 and 5, for example, a lithium ion secondary battery using a lithium manganese complex oxide as a positive electrode active material and a carbon material capable of releasing and occluding lithium ions as a negative electrode active material can be used.

  Referring to FIG. 4, the lithium ion secondary battery of the present embodiment will be described. The single cells 1 and 5 each have a bottomed cylindrical battery container 17 made of nickel plated steel. In the central portion of the battery case 17, an electrode group 16 is accommodated in which a strip-shaped positive electrode plate and a negative electrode plate are disposed on a hollow cylindrical shaft core 26 made of polypropylene with a separator interposed therebetween. In this example, the battery container 17 has an outer diameter of 40 mm and an inner diameter of 39 mm.

In this example, in order to produce a positive electrode plate, first, a lithium-manganese-cobalt-nickel composite oxide (LiMn _0.33 Co _0.33 Ni _0.33 O having an average particle size of 1 to 2 μm as a positive electrode active material. ₂ ), graphite powder having an average particle diameter of 0.5 μm as a conductive material, and polyvinylidene fluoride (PVDF) as a binder are dispersed in a solvent N-methyl-2-pyrrolidone (NMP) to form a slurry. A solution of was prepared. This solution was applied to both surfaces of an aluminum foil having a thickness of 20 μm by roll-to-roll method transfer, dried, and then pressed to be integrated. The thickness of the positive electrode plate was 160 to 165 μm, and the density of the positive electrode active material layer was 2.8 g / cm ³ . Further, an uncoated portion of the solution was formed on one side in the longitudinal direction of the aluminum foil, the uncoated portion was cut out in a comb shape, and the remaining portion of the notch was formed as the positive electrode lead piece 15.

On the other hand, for the negative electrode plate, an amorphous carbon powder as a negative electrode active material and PVDF as a binder were dispersed in NMP as a solvent at a weight ratio of 90:10 to prepare a slurry solution. This solution was applied to both sides of a rolled copper foil having a thickness of 10 μm by a roll-to-roll method transfer, dried, and then pressed to be integrated. The thickness of the negative electrode plate was 160 to 165 μm, and the density of the negative electrode active material layer was 1.05 g / cm ³ . Further, an uncoated part of the solution was formed on one side in the longitudinal direction of the rolled copper foil, the uncoated part was cut out in a comb shape, and the remaining part of the notch was formed as the negative electrode lead piece 13.

  The positive electrode plate and the negative electrode plate are wound in a cross-sectional spiral shape around the shaft core 26 through a porous polyethylene separator having a thickness of 30 μm so that the two electrode plates do not come into direct contact with each other. ing. The positive electrode lead piece 15 and the negative electrode lead piece 13 described above are disposed on opposite sides of the electrode group 16 and protrude a predetermined length (for example, 4 mm) from the end of the separator. The electrode group 16 is set to a predetermined inner diameter (for example, 9 mm) and a predetermined outer diameter (for example, 38 ± 0.1 mm) by adjusting the lengths of the positive electrode plate, the negative electrode plate, and the separator.

  A copper negative electrode current collecting ring 27 for collecting the electric potential from the negative electrode plate is disposed below the electrode group 16. The outer peripheral surface of the lower end portion of the shaft core 26 is fixed to the inner peripheral surface of the negative electrode current collecting ring 27. Further, the end of the negative electrode lead piece 13 led out from the negative electrode plate is joined to the outer peripheral edge of the negative electrode current collecting ring 27 by ultrasonic welding. A negative electrode lead plate 18 made of copper and serving as a conductive member is disposed below the negative electrode current collecting ring 27. The negative electrode lead plate 18 is joined by direct spot welding at the center of the inner bottom of the battery container 17 that also serves as a negative electrode external terminal. Yes. Hereinafter, for the sake of convenience, this spot welding location is referred to as a joint location 30.

  On the other hand, on the upper side of the electrode group 16, an aluminum positive electrode current collecting ring 14 for collecting the electric potential from the positive electrode plate is disposed on a substantially extension line of the shaft core 26. The positive electrode current collecting ring 14 is fixed to the upper end portion of the shaft core 26. The edge part of the positive electrode lead piece 15 led out from the positive electrode plate is joined to the periphery of the collar part integrally protruding from the periphery of the positive electrode current collecting ring 14 by ultrasonic welding.

  A battery lid that also serves as a positive electrode external terminal is disposed above the positive electrode current collecting ring 14. The battery cover is made of a metal cover case 22 having a communication hole, a metal cover cap 23 having a cross-sectional hat shape and a circular hole 23A formed in the center of the hat portion, and a valve retainer that keeps airtightness. 24 and a metal cleavage valve 21 that is cleaved when the internal pressure rises. These are laminated and assembled by caulking and fixing the periphery of the lid case 22. Therefore, when the internal pressure of the single cells 1 and 5 becomes a predetermined value or more, the cleavage groove of the cleavage valve 21 is broken, and the gas in the single cells 1 and 5 flows through the communication hole formed in the lid case 22 and the cleavage valve 21. It is discharged to the outside of the cells 1, 5 through the cleavage groove and the exhaust port 23 </ b> A of the lid cap 23. One side of the two positive electrode lead plates 19 formed by laminating ribbon-like aluminum foils is joined to the upper surface of the positive electrode current collecting ring 14. The other side of the positive electrode lead plate 19 is joined to the lower surface of the lid case 22. The other ends of the two positive electrode lead plates 19 are joined to each other.

The battery lid is caulked and fixed to the upper part of the battery container 17 via an insulating and heat resistant EPDM resin gasket 25. For this reason, the inside of the single cells 1 and 5 is sealed. In addition, a nonaqueous electrolytic solution (not shown) that can infiltrate the entire electrode group 16 is injected into the battery container 17. Examples of the non-aqueous electrolyte include hexafluorophosphoric acid as a lithium salt in a solvent in which a volume ratio of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) is mixed at a ratio of 30:50:20. Lithium (LiPF ₆ ) dissolved at 1 mol / liter can be used. In addition, the side peripheral surface except the both end surfaces of the single cells 1 and 5 is covered with a heat-shrinkable shrink tube (not shown). The rated capacity of the single cells 1 and 5 is 4.0 Ah.

  As shown in FIGS. 1 and 2, the bus bar 4 is disposed on the other side (left side in FIG. 1) and on the other side (left side in FIG. 1). Further, it is constituted by a substantially disk-shaped welded portion 4B and a plate-like connecting portion (center portion) 4C that is arranged at a level higher than the welded portions 4A and 4B by a step and connects the welded portions 4A and 4B. In the welded portions 4A and 4B, projections (projections) 7 project toward the unit cells 1 and 5 so as to form square four corners at positions serving as welding points. A cross-shaped slit 8 for spot welding is formed between the projections 7.

  In the present embodiment, in order to connect the cells 1 and 5 in series, the welded portion 4 </ b> A of the bus bar 4 avoids the joint portion 30 on the inner bottom surface side of the battery container 17 on the outer bottom surface of the battery container 17 of the battery cell 5. Thus, the electromechanical joining is performed by direct spot welding at the positions of the four projections 7. On the other hand, the welded portion 4B of the bus bar 4 is connected to the battery lid (lid cap 23) of the unit cell 1 so that the exhaust port 23A formed in the lid cap 23 is positioned at the center of the cross of the slit 8 (of the exhaust port 23A). The four projections 7 are electromechanically joined by direct spot welding (to avoid position). That is, the exhaust port 23A is positioned directly below the slit 8 of the welded portion 4B.

  As shown in FIG. 2, a rivet-shaped heat radiation member 10 made of metal is fixed to the center of the cross of the slit 8 of the weld 4A. The heat dissipating member 10 of this example is press-fitted through the slit 8 from the welded part 4B side after the unit cell 5 and the welded part 4B are joined, and is on one side (leg section side with a T-shaped cross section). Is in contact with the outer bottom surface of the battery case 17 corresponding to the joint location 30, and the other side (the arm portion (head) bottom surface side having a T-shaped cross section) is in contact with the upper surface of the welded portion 4B.

  As a material of the heat radiating member 10, for example, a metal material such as copper, copper alloy, aluminum, aluminum alloy, nickel, iron, and stainless steel can be selected. A material having a large thermal conductivity is more preferable.

(Action etc.)
Next, the operation and the like of the tandem battery 20 of this embodiment will be described.

  In the tandem battery 20 of the present embodiment, two unit cells 1 and 5 in which the negative electrode lead plate 18 electrically connected to the electrode group 16 and the inner bottom surface of the battery container 17 are joined by spot welding are unit cells. 1 and 5 are connected by a bus bar 4 which electrically and mechanically connects them. The other side of the heat radiating member 10 is fixed to one welded portion 4A of both ends of the bus bar 4, and one side of the heat radiating member 10 is opposite to the welded portion 30 on the inner bottom surface side of the battery case 17 joined by spot welding. It is in contact with the outer bottom surface on the surface side. Therefore, even if the joining point 30 generates heat when the tandem battery 20 is energized, heat is transmitted to the bus bar 4 through the heat radiating member 10 so that the temperature at the joining point 30 is lowered and damage to the joining point 30 is prevented. Can do. At this time, if the thermal conductivity of the heat radiating member 10 is larger than the thermal conductivity of the battery container 17, the heat generation temperature at the joint 30 can be efficiently lowered.

  In the tandem battery 20 of the present embodiment, the side surface portion of the heat radiating member 10 is in contact with the welded portion 4B, and the bottom surface of the T-shaped arm portion of the heat radiating member 10 is also in contact with the upper surface of the welded portion 4B. Therefore (see FIG. 2), the area for heat dissipation can be increased, and the reliability for preventing damage to the joint 30 due to heat generation can be increased.

  Further, in the tandem battery 20 of the present embodiment, the outer bottom surface of the battery container 17 is such that the welded portion 4B avoids a position on the outer bottom surface side corresponding to the joint part 30 of the inner surface of the battery container 17 joined by spot welding. 4 (see FIG. 1), compared with the case where spot welding is performed on the outer bottom surface side of the battery case 17 corresponding to the joint location 30 (when two welding histories are given to the battery case 17). In addition, it is possible to prevent an influence (perforation or the like) due to poor bonding due to fluidization of the joint location 30 or weakening of the battery container 17.

  Further, in the tandem battery 20 of the present embodiment, the exhaust port 23A is positioned immediately below the center of the cross of the slit 8 of the welded part 4B (see FIG. 1). Even if the internal pressure of the battery becomes equal to or higher than a predetermined value and the cleavage groove of the cleavage valve 21 is cleaved, the gas in the unit cell 1 passes through the exhaust port 23A formed in the lid cap 23A and the slit 8 formed with the weld 4B. And is smoothly discharged outside the unit cell 1. Therefore, the situation where the unit cell 1 bursts does not occur.

  Furthermore, in the tandem battery 20 of the present embodiment, the connecting portion 4C of the bus bar 4 is arranged at a position higher than the welded portions 4A and 4B by a step. For this reason, when heat is transmitted to the bus bar 4 through the heat radiating member 10, the deformation of the bus bar 4 is absorbed by the step, and a short circuit between the welded portion 4 </ b> B and the battery container of the unit cell 1 due to the deformation is prevented. Can do.

  In the present embodiment, a lithium ion secondary battery is exemplified as the secondary battery, but the present invention is not limited to this, and can be applied to, for example, a nickel metal hydride battery. Further, in this embodiment, a tandem battery in which two unit cells are connected in series is illustrated, but the present invention is not limited to this, and an assembled battery (assembled battery) or unit cell in which three or more unit cells are connected in series. It cannot be overemphasized that it is applicable also to the assembled battery which connected in parallel or series-parallel. Furthermore, although the rivet-shaped thing was illustrated for the heat radiating member 10, you may make it use a plug-shaped thing. Alternatively, a screw hole may be provided in the slit 8 and a screw-like member may be used for the heat radiating member 10.

(Second Embodiment)
Next, a second embodiment in which the present invention is applied to a juxtaposed tandem battery will be described. The tandem battery of this embodiment is obtained by integrally forming the heat dissipation member 10 of the first embodiment with the bus bar 4. In the present embodiment, the same members as those in the first embodiment are denoted by the same reference numerals, the description thereof is omitted, and only different portions will be described below.

  As shown in FIG. 3, the welded portion 4 </ b> A in the present embodiment is a plate spring-like member 11 that is obliquely arranged from a part where the slit 8 of the first embodiment is formed to the lower side (unit cell 5 side). have. The distal end portion of the leaf spring-shaped member 11 is in contact with the outer bottom surface on the opposite side to the welded portion 30 on the inner bottom surface side of the battery container 5, and the base portion of the leaf spring-shaped member 11 is fixed to the welded portion 4A. According to this embodiment, the same effects as those of the first embodiment can be obtained, and the number of components can be reduced, the cost can be reduced, and the battery can be reduced in weight.

  In this embodiment, when welding the welded portion 4A to the unit cell 5, the welding spring 4A is pressed against the urging force of the leaf spring-like member 11, and spotted by four projections 7 on the outer bottom surface of the battery container 17. Even if welding is performed, after spot welding, the leaf spring-like member 11 is bent so that the front end portion comes into contact with the outer bottom surface on the opposite surface side of the inner bottom side of the battery container 5. Good. In order to increase the contact area with the battery container 17, the leaf spring-like member 11 may be bent so that the tip part thereof is along the battery container 17 by the biasing force. Further, the welded portion 4A may have a plurality of leaf spring members 11 instead of only one as shown in FIG.

  In accordance with the above-described embodiment, the tandem battery 20 of the example was manufactured and an energization test was performed. In addition, it describes together about the battery of the comparative example produced for the comparison.

(Example)
In Example 1, the tandem battery 20 of the first embodiment (see FIGS. 1 and 2) described above was produced. In Example 2, the tandem battery 20 of the second embodiment (see FIG. 3) was produced.

(Comparative example)
In the comparative example, the heat dissipating member 10 of the first embodiment described above was lacked, that is, a conventional tandem battery was produced.

(test)
The produced tandem batteries of Examples 1 and 2 and the comparative example were charged to 8.2 V (4.1 V at the unit cell level), then connected to an electronic load device, and discharged to 4.0 V by 200 A energization. Visual observation of the state of the container 17 (joint location 30) and energization time were evaluated. The results are shown in Table 1 below.

  As is clear from Table 1, the tandem batteries of Examples 1 and 2 can suppress heat generation at the welded portion 30 and are suitable for continuous discharge of a large current.

  The present invention provides an assembled battery that can suppress the generation of heat at the joining portion even when a large current is applied, and can prevent damage to the joining portion. Therefore, the present invention contributes to the manufacture and sale of the collecting battery, and thus has industrial applicability. .

It is a top view before the press-fit of the heat radiating member of the tandem battery of 1st Embodiment which can apply this invention. It is an upper part side view of the tandem battery of a 1st embodiment. It is a top view of the tandem battery of 2nd Embodiment which can apply this invention. It is sectional drawing of the lithium ion secondary battery which comprises a tandem battery.

Explanation of symbols

1, 5 Single battery (secondary battery)
4 Busbar 4A Welded part (one end)
4B welded part (the other end)
4C connection part (central part)
8 Cross-shaped slit (slit)
10 Heat Dissipation Member 16 Electrode Group 17 Battery Container (Battery Can)
18 Negative lead plate (conductive member)
20 Tandem battery (collective battery)
23 Lid cap (part of battery lid)
23A Exhaust port

Claims (10)

A plurality of secondary batteries in which the conductive member electrically connected to the electrode group and the inner bottom surface of the metal battery can are joined by spot welding;
A bus bar that electrically and mechanically connects the secondary batteries;
A metal heat dissipating member that is in contact with the outer bottom surface on the opposite side to the inner bottom surface of the battery can joined by spot welding on one side, and the other side is fixed to at least one end portion of both ends of the bus bar,
An assembled battery with   The assembled battery according to claim 1, wherein the heat radiating member has a thermal conductivity larger than that of the battery can of the secondary battery.   2. The assembled battery according to claim 1, wherein one side of the heat radiating member is in contact with a portion on the outer bottom surface side corresponding to a joint portion of the inner surface of the battery can by spot welding.   2. The assembled battery according to claim 1, wherein the heat radiating member is a plug or a rivet-like member press-fitted from the bus bar side or a screw-like member screwed from the bus bar side.   The assembled battery according to claim 4, wherein a bottom surface of the head of the plug or rivet-shaped member or screw-shaped member is in contact with an upper surface of at least one of the both ends of the bus bar.   The assembled battery according to claim 1, wherein the heat radiating member is formed integrally with the bus bar.   At least one end of the both ends of the bus bar is spot welded at a plurality of locations on the outer bottom surface of the battery can so as to avoid locations on the outer bottom surface corresponding to the joint location of the inner surface of the battery can by spot welding. The assembled battery according to claim 3, wherein the assembled battery is joined at a joint.   A slit for spot welding is formed at both ends of the bus bar, and the secondary battery has an exhaust port formed at the center of the upper surface of the battery lid, and the exhaust port is at least of both ends of the bus bar. The assembled battery according to claim 7, wherein the assembled battery is positioned immediately below the slit at the other end.   Of both ends of the bus bar, one end is joined to a negative battery can of the secondary battery constituting the assembled battery, and the other end is connected in series to the secondary battery. The assembled battery according to claim 1, wherein the assembled battery is joined to a positive battery cover of another secondary battery.   The assembled battery according to claim 1, wherein a central portion between both end portions of the bus bar has a step with respect to both end portions of the bus bar.

Images