JP2007059329A - Secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a secondary battery capable of securing strength at a welding point between a metallic cap and a metallic bus bar at a desired value. <P>SOLUTION: A unit cell 1 has an exhaust outlet 6 formed at the upper surface center of a cap 5, and is serially connected to another unit cell 1 through a bus bar 2. In the bus bar 2, a slit 7 is formed at a position corresponding to the exhaust outlet 6 of the cap 5 and projections 4 used as welding points are arranged at positions of four corners of a square. The diagonal two points (4a, 4c), (4b, 4d) of the bus bar 2 are respectively series-spot-welded. The resistance value of the diagonal two points is set not smaller than 150E+3 [Ω], and tensile strength of ≥500 N is ensured as strength at the welding points. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a secondary battery, and more particularly to a connection structure using a metal bus bar for a secondary battery having a metal cap.

  In recent years, an assembled battery in which a plurality of single cells are connected in series has been used as a driving source for various electric tools, electric assist bicycles, bicycles with electric motors, electric vehicles, and the like. There are various types of connection, for example, an elongated columnar shape connected in parallel in the axial direction of a single battery (secondary battery) (for example, refer to Patent Document 1), or a single battery connected in parallel. (For example, refer to Patent Documents 2 and 3).

  Further, a metal bus bar is known as a conductive member that electrically and mechanically connects the cells. Two ends of the metal bus bar are each spot-welded to a metal cap that is one electrode of one unit cell and a battery can bottom that is the other electrode of the other unit cell. The batteries are connected in series, and this is repeated for the required number of single cells to obtain the required output voltage of the assembled battery (see, for example, Patent Documents 2 and 3).

  Note that some cells have a metal cap with a cleavage valve to prevent rupture during overcharge, etc., and an exhaust port is formed in the center of the top surface of this metal cap. The metal bus bar to be used must be placed so as not to close the exhaust port.

JP-A-10-106533 JP 2004-152706 A JP 2004-164981 A

  However, as in Patent Document 1, when the assembled battery is an elongated cylindrical structure, it is necessary to manage the overall shape of the assembled battery, the length and parallelism of each unit cell with high accuracy, When used in an environment that vibrates as a drive source for electric motor-driven bicycles, electric vehicles, etc. The welding point between the bus bar and the unit cell may come off.

  In this regard, as in Patent Documents 2 and 3, in the case of a structure in which single cells are juxtaposed, the metal bus bar is placed in a state where the metal cap and the battery can bottom serving as one electrode are bridged. For this reason, there is no possibility of problems such as poor bonding in terms of workability because the connection is made by series spot welding in a supported stable posture. However, in series spot welding, if the distance between the two welding points is narrow, or if a suitable slit is not provided in the metal bus bar, there is a risk of ineffective diversion during welding, resulting in poor bonding. The desired welding strength cannot be ensured.

  An object of the present invention is to provide a secondary battery capable of ensuring a desired strength at a welding point between a metal cap and a metal bus bar.

  In order to solve the above-described problems, the present invention provides a secondary battery having a metal cap, wherein the metal cap is series spot welded so as to form a plurality of welding points on the upper surface thereof. A slit is formed between the welding points of the metal bus bar, and series slit welding is performed between two welding points at which the resistance between the welding points is greater than or equal to a required resistance by the slit. It is characterized by being.

  When the secondary battery is used in a vibrating environment as a power source for a moving body such as a bicycle with an electric motor or an electric vehicle, it is desirable to ensure a tensile strength of 500 N or more as a sufficient welding strength of the welding point. . In the present invention, slits are formed between the welding points of the metal bus bar, and the resistance value between the welding points can be set by the slits. The relationship between the tensile strength and the resistance value between the welding points is a proportional relationship that can be approximated by a linear line, and series spot welding is performed between two welding points where the resistance between the welding points exceeds the required resistance by the slit. Thus, the tensile strength at the welding point can be set to a desired value (for example, 500 N described above). According to the present invention, since it is possible to set the resistance value between the welding points by the slit, the series spot welding is performed between the two welding points where the resistance between the welding points has a value equal to or higher than the required resistance. A secondary battery in which the strength at the welding point between the metal cap and the metal bus bar is ensured at a desired strength can be obtained.

  In the present invention, each welding point is formed so as to be positioned at the four corners of the square, and if the two points to be series spot welded are two diagonal points, the welding points become four points positioned at the four corners of the square, By performing series spot welding at two diagonal points that can maximize the welding point interval, it is possible to prevent an invalid diversion during welding, thereby avoiding poor bonding. In addition, the metal cap has a cleavage valve, an exhaust port is formed at the center of the upper surface, and the metal bus bar is series spot welded so as to form a plurality of welding points at the peripheral edge of the exhaust port. If the slit is formed at the position corresponding to the exhaust port between the weld points of the metal bus bar, the secondary battery will not be sealed by the slit without sealing the exhaust port in the center of the upper surface of the cap. Even when an abnormal state such as charging occurs, the rupture valve and the exhaust port of the secondary battery communicate with each other to prevent rupture during overcharging.

  According to the present invention, since it is possible to set the resistance value between the welding points by the slit, the series spot welding is performed between the two welding points where the resistance between the welding points has a value equal to or higher than the required resistance. The effect that the secondary battery which ensured the intensity | strength in the welding point of a metal cap and a metal bus bar in desired intensity | strength can be obtained can be acquired.

  Hereinafter, an embodiment in which the present invention is applied to a juxtaposition tandem battery used as a power source of an electrically assisted bicycle will be described with reference to the drawings.

(Constitution)
As shown in FIGS. 1 and 2, in the tandem battery 3 of the present embodiment, two unit cells 1 arranged in parallel with opposite polarities are connected in series by a metal bus bar 2. The two single cells 1 are fixed so as not to move with a frame (not shown) in preparation for use as a power source for a moving body.

  The unit cell 1 is a high-performance lithium secondary battery in which lithium manganate or the like is a main constituent material of a positive electrode mixture and amorphous carbon or the like is a main constituent material of a negative electrode mixture. A winding group wound in a spiral shape is disposed in the center of the cylindrical bottomed battery can with high thermal conductivity, and the winding group is infiltrated with a non-aqueous electrolyte. A positive electrode lead and a negative electrode lead are led out from the upper and lower ends of the winding group, respectively. The positive electrode lead is connected to the bottom surface (lower lid cap described later) of the metal cap 5 serving as the positive electrode terminal, and the negative electrode lead is connected to the battery can serving as the negative electrode terminal. The unit cell 1 is sealed by caulking and fixing the cap 5 to the opening of the battery can via a gasket. In addition, the side peripheral surface except the both end surfaces of the cell 1 is coat | covered with the heat-shrinkable shrink tube.

  The cap 5 is a disc-shaped upper lid cap that protrudes upward and serves as a positive electrode terminal, a disc-shaped lower lid cap having a communication hole communicating with the inside of the unit cell 1, and a disc-shaped plate-shaped member. It is comprised as a unit body which has the cleavage valve in which the groove | channel was formed, and the cleavage valve is accommodated in the cap 5 by the crimping | fixing of the periphery of an upper cover cap and a lower cover cap. A circular hole-like exhaust port 6 is formed in the center portion protruding upward of the upper lid cap. Therefore, when the internal pressure of the unit cell 1 exceeds a predetermined value, the cleavage groove of the cleavage valve is broken, and the gas in the unit cell 1 flows into the communication hole of the lower lid cap, the cleavage groove of the cleavage valve, and the exhaust port 6 of the upper lid cap. To the outside of the unit cell 1. Note that the upper lid cap, the cleavage valve, and the lower lid cap are made of a metal member.

  The bus bar 2 includes a substantially disk-shaped welded portion disposed at both ends thereof and a plate-shaped connection portion that is formed with a step higher than the welded portion and connects the welded portions. In the welded portion, projections (protrusions) 4a, 4b, 4c, and 4d are projected toward the unit cell 1 so as to form the four corners of the square at positions serving as welding points. Between the projections, a slit 7 is formed at a position corresponding to the exhaust port 6 of the cap 5 (upper cap) of the unit cell 1. In other words, the projections 4a, 4b, 4c, and 4d are projected toward the peripheral edge of the exhaust port 6. The slit 7 is formed by four arcs, and has a shape in which a space between the arcs is cut toward the outer peripheral side of the welded portion. For convenience, the portion of the slit 7 formed so as to cut the welded portion is referred to as a cut portion 9.

  For the welded portion of the cap 5 (upper cap) and the bus bar 2, the combination of the welding points (4x, 4y) of the series spot welding is the two diagonal points of the projection (4a, 4c), (4b, 4d) ). The resistance value between the welding points depends on the slit 7. In this embodiment, since the tandem battery 3 is used in an environment in which it vibrates, the welding strength at the welding point between the bus bar 2 and the upper lid cap needs to have a tensile strength of 500 N or more. For this reason, the size and shape of the slit 7 were examined, and the resistance value between the welding points (4a, 4c) and the welding points (4b, 4d) was set to 150E + 3 [Ω] or more. Similarly, the other welded portion of the bus bar 2 and the battery can bottom of another unit cell 1 constituting the tandem battery 3 are series spot welded.

  Tandem batteries B, C, and D are produced by series spot welding with unit cell 1 using bus bar B, bus bar C, and bus bar D in which the size of slit 7 of bus bar 2 is changed to change the resistance between welding points. did. The tensile strength at the weld point between these and the tandem battery 3 of the above embodiment (hereinafter referred to as tandem battery A in the examples) was measured. Each measurement was performed 5 times. FIG. 3 shows the average value of the tensile strength. By the way, when the tandem battery 3 is used in a vibration environment as a power source for an electrically assisted bicycle, sufficient welding strength is required. For example, the tensile strength of 500 N or more is preferable for the welding point between the bus bar 2 and the unit cell 1. As shown in FIG. 3, the tensile strength at the welding point of the tandem batteries A and B was 500 N or more, and the resistance value between the welding points was 150E + 3 [Ω] or more. From this, it can be said that the resistance between the welding points of the tandem battery A needs to be 150E + 3 [Ω] or more, which is a resistance value that can secure a tensile strength of 500 N or more at the welding point.

  As described above, the combination (4x, 4y) of the two points of series spot welding of the tandem battery A of the embodiment is (4a, 4c), (4b, 4d) which is two diagonal points. Thus, a tandem battery E having a combination of two adjacent points (4a, 4b) and (4c, 4d) was produced. When series spot welding is performed, since the welding points are close to each other, for example, the above-described cut portion 9 may be burned out. It seems that invalid shunting occurs as a welding condition. Further, the tensile strength of the tandem battery E was measured, but 500 N could not be secured.

  In the tandem battery A of the embodiment, the slit 7 is formed at a position corresponding to the exhaust port 6 in the center of the upper surface of the cap 5. On the other hand, a tandem battery F in which the slit 7 is sealed is manufactured, Confirmed the safety. Each test was performed 5 times. In the tandem battery A, the cleavage valve of the unit cell 1 was operated, gas was quickly generated from the exhaust port 6, and no smoke or ignition occurred. On the other hand, in the tandem battery F, gas stays in the exhaust port 6, and smoke and ignition may occur.

(Action etc.)
As described above, since the tandem battery 3 according to the present embodiment is used as a power source for an electrically assisted bicycle, it is desirable that a sufficient welding strength at a welding point has a tensile strength of 500 N or more. As shown in FIG. 3, the relationship between the tensile strength and the resistance value between the welding points is a relationship that can be approximated by a linear line, and the resistance between the welding points is greater than the required resistance by the slit 7 (150E + 3 [Ω ] Can be set to a desired value (tensile strength of 500 N or more) at a welding point. For this reason, the tandem battery 3 according to the embodiment has a sufficient vibration-proof structure even when used in a vibration environment as a power source for an electrically assisted bicycle.

  Further, the tandem battery 3 of the present embodiment is formed such that each welding point is located at the four corners of a square, and two points to be series spot welded are two diagonal points (two diagonal points 4a and 4c and two diagonal points) 4b, 4d diagonal 2 points), the welding points are four points located at the four corners of the square, the welding point interval can be maximized, and the invalid diversion during welding can be prevented. Defects can be avoided.

  Further, in the tandem battery 3 of the present embodiment, the cap 5 has a cleavage valve, the exhaust port 6 is formed at the center of the upper surface, and a plurality of welding points are formed at the peripheral edge of the exhaust port 6. The bus bar 2 is series spot welded, and a slit 7 is formed at a position corresponding to the exhaust port 6 between the welding points of the bus bar 2. For this reason, the unit cell 1 does not seal the exhaust port 6, and even if the unit cell 1 falls into an abnormal state such as overcharge, the cleavage valve of the unit cell 1 and the exhaust port 6 communicate with each other at the time of overcharge. Can be prevented from bursting.

  In addition, although the example applied to the tandem battery 3 in which two unit cells are juxtaposed has been shown in the above embodiment, the present invention is not limited to this and can be applied to a battery pack in which a plurality of unit cells are juxtaposed. Needless to say. Examples of such connection forms are also shown in Patent Documents 2 and 3 exemplified in the Background Art section. Further, the present invention is not limited to the series connection between the single cells 1, and it cannot be overemphasized that it can be applied to the parallel connection.

  Since the present invention provides a secondary battery capable of ensuring the desired strength at the weld point between the metal cap and the metal bus bar, it contributes to the manufacture and sale of the secondary battery. Has availability.

It is a top view of the juxtaposition type tandem battery of an embodiment to which the present invention is applicable. It is a side view of the tandem battery of an embodiment. It is a graph which shows the relationship between the tensile strength in the welding point of the tandem battery of an Example, and the resistance between welding points.

Explanation of symbols

1 Single battery (secondary battery)
2 Busbar 5 Cap 6 Exhaust port 7 Slit

Claims (3)

  A secondary battery comprising a metal cap, wherein the metal cap is a series bus welded with a metal bus bar so as to form a plurality of welding points on the upper surface thereof, and the metal bus bar is welded. A secondary battery characterized in that a slit is formed between the points, and series spot welding is performed between the two welding points where the resistance between the welding points has a value equal to or higher than a required resistance.   2. The secondary battery according to claim 1, wherein each welding point is formed so as to be positioned at four corners of a square, and the two points to be series spot welded are two diagonal points.   The metal cap has a cleavage valve, an exhaust port is formed in the center of the upper surface, and the metal bus bar is series spot welded so as to form the plurality of welding points at a peripheral portion of the exhaust port. The secondary battery according to claim 1, wherein the slit is formed at a position corresponding to the exhaust port between welding points of the metal bus bar.

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