JP2008210730A - Battery pack, and its welding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide: a battery pack capable of obtaining excellent welding quality and a welding part high in tensile strength, small in connection resistance between battery electrodes, capable of reducing current-carrying loss in battery charging/discharging, and effective in improvement of battery life; and its welding method. <P>SOLUTION: In a battery pack in which multiple battery cells are housed in one or multiple rows in an electrically insulating housing case and an electrode of each battery cell is coupled to an electrode of another battery cell through each connecting metallic plate, the connecting metallic plates 3 made of copper are disposed on both surfaces of a positive electrode part 6 of each battery cell 2 and a negative electrode part 7 of another battery cell 2 to respectively form lap joints, wherein the battery pack includes welding parts 5 each formed in one specific positions on the connecting metallic plate 3 above the positive electrode part 6 and on the other specific positions on the connecting metallic plate 3 above the negative electrode part 7 by applying arc spot welding. The depth h of weld penetration in the welding part 5 is larger than the thickness T1 of the connecting metallic plate 3 and smaller than the thickness T1 plus the thickness T2 of the positive electrode part 6 or the negative electrode part 7, and is formed in a range satisfying T1<h≤(T1+T2×4/5). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an assembled battery in which positive and negative electrodes of a plurality of single cells are connected by a connecting metal plate and a welding method thereof.

  An assembled battery (also referred to as a battery module) used for a hybrid vehicle, an electric vehicle, a portable device, or the like is required to charge and discharge a large current, and thus several tens of cells need to be connected in series. If the connection resistance (electrical resistance) is large, the energization loss due to the voltage drop increases, the heat generation amount increases, and the battery characteristics deteriorate and the service life decreases. For this reason, several methods for reducing the connection resistance of the assembled battery and connecting the battery electrodes have been proposed.

  In the cylindrical battery and the assembled battery described in Patent Document 1, a current collecting terminal made of a conductive material having a surface portion in which a female screw hole is bored or a male screw portion is erected via a leg portion that supports the surface portion. It has been proposed to connect and fix to the positive electrode portion and the negative electrode portion, respectively.

  In the assembled battery described in Patent Document 2, the plate made of electrically insulating resin disposed on the positive caps of the two unit cells is smaller than the outer periphery of the assembled battery, and has a polygonal shape in the valley space between the unit cells. It has been proposed that a protrusion having a recess is provided and a metal bus bar for mechanically and electrically connecting the cells is disposed on the plate surface.

  In Patent Document 3, metal lead plates protruding outside the first electrode unit and the second battery unit are fixed to the opposing electrode terminals of the cells arranged in a column, and the surfaces of the metal lead plates are in contact with each other. It is proposed to connect in such a state.

  Moreover, in the assembled battery described in Patent Document 4, one of the two types of protrusions of the connection member is welded onto the sealing body of one unit cell, and the other protrusion is the bottom surface of the outer can of the other unit cell. It has been proposed to be welded.

  In the sealed battery and its manufacturing method and sealed battery lid plate described in Patent Document 5, the back surface of the lid plate that seals the opening of the battery container is formed so that the vicinity of the injection hole is thinner than the outer peripheral portion. It has been proposed that the injection hole is sealed by melting the formed portion and the sealing plug.

  Further, in the method of manufacturing a battery having spiral electrodes described in Patent Document 6 (Japanese Patent Publication No. 61-8539), a current collector made of a substantially disc-shaped metal plain plate at the upper and lower electrode protruding ends of the spiral electrode body. It is proposed to wrap the battery in a battery case after welding the current collector and the electrode protruding end that intersects with the current collector at right angles by arc spot welding.

  In the case of the above-mentioned patent document 1, since the current collector terminal attached to the positive and negative electrode parts of the battery and the connection body for connecting the batteries are fastened with bolts, the number of parts is large and the cost is increased. The legs of the current collector terminal are provided with cuts and protrusions, and spot welding (resistance welding) is performed on the positive and negative electrode parts of the battery. However, there are 8 welding points, which increases the number of welding steps. is there. The current collector terminal is made of a conductive material such as nickel and can be spot welded (resistance welding). However, even if the plate thickness is made slightly thicker, the electrical resistance of the nickel material can be reduced. Since it is larger than the electrical resistance of copper material, there is a limit to the reduction in connection resistance. Nickel materials are more expensive than copper materials. Copper materials with low electrical resistance cannot be used for the current collector terminals because it is difficult to perform Joule heating type resistance welding, and arc welding (arc spot welding) is different from the resistance welding method. Not applied.

  In the case of Patent Document 2, T-shaped and cross-shaped metal bus bars are arranged on a plate made of an electrically insulating resin, and spot welding (resistance welding) is performed on the positive electrode terminal and the negative electrode terminal of the unit cell. Although the material of the metal bus bar is not described, it is considered to be a conductive material such as nickel as in the above-mentioned Patent Document 1. In addition, a copper material having a small electric resistance cannot be used for the current collector metal bus bar because it is difficult to perform resistance welding by the Joule heating method. Further, arc welding (arc spot welding) which is different from the resistance welding method is not applied.

  In the case of Patent Document 3, the protruding portions of the metal lead plates that connect the upper first battery unit and the lower second battery unit are soldered or spot welded (resistance welding). Further, the lead plates that connect the electrodes of the plurality of single cells are also spot-welded (resistance welding). Although the structure of the assembled battery is different, arc welding (arc spot welding), which is different from resistance welding and method, is not applied as in Patent Documents 1 and 2. Also, a copper material having a small electrical resistance cannot be used for the metal lead plate and the lead plate because it is difficult to perform resistance welding by the Joule heating method.

  In the case of the above-mentioned Patent Document 4, the upper unit cell and the lower unit cell are connected via a connection member having two types of protrusions, and one protrusion is connected to the lower unit cell positive electrode surface. Welding (resistance welding) is performed, and the other protrusion is welded to the upper cell negative electrode surface (resistance welding). Since the lead part for attaching the welding electrode at the time of welding protrudes from the connecting member, it is necessary to cut or bend the lead part after the end of welding, and there is a problem that extra man-hours increase. Since there is no space for inserting the welding torch, other welding methods such as arc welding different from resistance welding cannot be applied.

  In the case of the above-mentioned Patent Document 5, arc welding is performed on the thin portion of the cover plate and the sealing plug to perform hole sealing (melt bonding), but this is a technique for sealing and welding the hole of the rectangular battery. It does not connect and weld the electrodes of a plurality of single cells. The material of the lid plate and the sealing plug of the square battery is aluminum, not copper or nickel. If the material and the shape are different, the appropriate conditions for welding are completely different, so that the aluminum welding conditions cannot be applied as they are.

  In the case of the above-mentioned Patent Document 6, arc spot welding is performed on the disk-shaped current collector and the protruding end of the spiral electrode body on the lower side, and this is a technique for welding the electrode portion of the round battery. It does not connect and weld the poles of a single cell. The material of the current collector and the spiral electrode body is a steel plate with nickel plating, not copper or nickel. Similar to the above-mentioned Patent Document 5, if the material and shape are different, the appropriate conditions for welding are completely different, so that the welding conditions for the steel sheet cannot be applied as they are.

JP-A-8-287898 JP 2004-164981 A JP 2000-133227 A JP 2001-266843 A Japanese Patent Application Laid-Open No. 2004-2559584 Japanese Patent Publication No. 61-8539

  The present invention provides an assembled battery and a welding method that are effective in improving battery life by obtaining a welded portion having good welding quality and high tensile strength, having low connection resistance between battery electrodes, and reducing current loss during battery charging and discharging. The purpose is to provide.

  In order to achieve the above object, the present invention provides an assembled battery in which a plurality of single cells are stored in one or a plurality of rows in an electrically insulating storage case, and the electrodes of each single cell are connected by connecting metal plates. The connection metal plate made of copper is disposed on both surfaces of the positive electrode part of each unit cell and the negative electrode part of another unit cell to form lap joints, and one of the connection metals on the upper side of the positive electrode unit It is characterized by comprising welded portions each formed by performing arc spot welding at a specific position of the plate and a specific position of the other connecting metal plate above the negative electrode portion.

  In particular, the penetration depth h of the welded portion is larger than the plate thickness T1 of the connection metal plate and smaller than the value obtained by adding the plate thickness T2 of the positive electrode portion or the negative electrode portion, and T1 <h ≦ (T1 + T2 × 4/5). ).

  In the lap joint, a copper material having an upper plate thickness T1 corresponding to the connecting metal plate of 0.5 mm to 1.5 mm and a lower plate thickness T2 corresponding to the positive electrode portion or the negative electrode portion is 0. It is a dissimilar joint with a steel material of .5 mm or more and 1.5 mm or less, and nickel plating is preferably formed on the front and back surfaces of the steel material.

  Further, in order to achieve the above object, the present invention is a set in which a plurality of single cells are stored in one or a plurality of rows in an electrically insulating storage case, and the electrodes of each single cell are connected by each connecting metal plate. In the battery welding method, the connection metal plate made of copper is disposed on both surfaces of the positive electrode part of each unit cell and the negative electrode part of another unit cell to form lap joints, and above the positive electrode part And a step of performing arc spot welding at a specific position of one of the connecting metal plates in the above and a specific position of the other connecting metal plate above the negative electrode part.

  In particular, in the welding step, when the plate thickness of the connecting metal plate is T1 and the plate thickness of the positive electrode portion or the negative electrode portion is T2, the arc is within the range where the penetration depth h satisfies the following formula (1). Spot welding is performed.

T1 <h ≦ (T1 + T2 × 4/5) (1)
That is, in the battery pack of the present invention, the connection metal plate made of copper is disposed on both surfaces of the positive electrode part of each unit cell and the negative electrode part of another unit cell to form lap joints, By including a welded portion formed by performing arc spot welding at a specific position of one of the connecting metal plates on the upper side and a specific position of the other connecting metal plate on the upper side of the negative electrode part, An assembled battery can be obtained in which the connection resistance between the battery electrodes is small and the energization loss during charging and discharging of the battery is small. In particular, the electrical resistance of copper is higher than that of nickel or steel (Cu: 1.55 <Ni:
6.58 <Fe: 8.71 (× 10 ⁻⁶ Ω · cm)) Since it is much smaller, the connection resistance can be reduced by using a copper connection metal plate, and at a lower cost than nickel material. Can be produced. Moreover, even if it is a copper connection metal plate, it can melt-join reliably by arc spot welding. In the conventional Joule heating type resistance welding (spot welding), it is difficult to weld copper having a small electric resistance, and it cannot be applied.

  The penetration depth h of the welded portion is larger than the plate thickness T1 of the connection metal plate, and smaller than the value obtained by adding 4/5 of the plate thickness T2 of the positive electrode portion or the negative electrode portion to T1, T1 <h ≦ (T1 + T2 By forming in the range of x4 / 5), the welding part of the depth which does not melt to the back side of a lap joint can be obtained reliably. If the penetration depth h is shallower than the upper plate thickness T1, welding will be insufficient. Conversely, if the penetration depth h is greater than (T1 + T2 × 4/5), back-melting is likely to occur and corrosion resistance is increased. This is not preferable because there is a problem of reduction and battery leakage.

The lap joint has a copper material having an upper plate thickness T1 corresponding to the connecting metal plate of 0.5 mm to 1.5 mm and a lower plate thickness T2 corresponding to the positive electrode portion or the negative electrode portion of 0.5 mm. This is a dissimilar joint with a steel material of 1.5 mm or less, and nickel plating is formed on the front and back surfaces of the steel material, so that Cu having a low melting point and Fe having a high melting point are combined and cracked using Ni plating as a medium. As a result, a very thin Cu / Fe mixed layer with no weld is formed, and a weld with good weld quality and high tensile strength can be obtained. Moreover, even if it is steel or low carbon steel, corrosion resistance can be improved by Ni plating. The thickness of Ni plating should just be 1 micrometer or more and 10 micrometers or less, dissimilar material welding of copper and steel with Ni plating can be performed, and the favorable weld part without a crack can be obtained.

  If the thickness T1 of the connecting metal plate is less than 0.5 mm, the strength of the material itself is low, the strength of the welded portion is low and the structure is weak against vibration, and conversely, the thickness T1 is 1.5 mm. A thicker thickness is not preferable because arc spot welding cannot be performed due to an increase in heat dissipation to the connecting metal plate. On the other hand, if the plate thickness T2 of the positive electrode portion or the negative electrode portion of the unit cell is less than 0.5 mm, the strength of the material itself is low, the strength of the welded portion is low, and the structure is weak against vibration. If the thickness is larger than 1.5 mm, it is not preferable because deep drawing becomes difficult, the weight increases, and arc welding becomes difficult. On the other hand, if the thickness of the Ni plating is thinner than 1 μm, the steel surface is exposed due to slight scratches and the corrosion resistance tends to be lowered. Conversely, if it is thicker than 10 μm, not only the plating process takes time but also arc welding. It is not preferable because sometimes insufficient bonding is likely to occur.

  Further, in the assembled battery welding method of the present invention, the step of forming the lap joint by disposing the connecting metal plate made of copper on both surfaces of the positive electrode portion of each unit cell and the negative electrode unit of another unit cell; And a step of performing arc spot welding at a specific position of one of the connection metal plates above the positive electrode portion and a specific position of the other connection metal plate above the negative electrode portion, respectively. Thus, the lap joint can be melt-bonded, and a weld with good welding quality and high tensile strength can be obtained. In addition, it is possible to obtain an assembled battery having a small connection resistance between the battery electrodes and a small current loss during charging / discharging of the battery, and can be manufactured at a lower cost than a nickel material by using a connection metal plate made of copper.

  In particular, in the welding step, the penetration depth h with respect to the plate thickness T1 of the connection metal plate and the plate thickness T2 of the positive electrode portion or the negative electrode portion is formed in the range of T1 <h ≦ (T1 + T2 × 4/5). By performing the arc spot welding, as described above, a weld portion having a depth that does not melt to the back side of the lap joint can be reliably obtained.

  According to the assembled battery and the welding method of the present invention, a welded portion having good welding quality and high tensile strength can be obtained, the connection resistance between the battery electrodes is small, the current loss during charging / discharging of the battery can be reduced, and the battery life It can contribute to improvement.

  Hereinafter, preferred embodiments of the assembled battery and the welding method of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory view showing an example of the arrangement of unit cells and the connection between the battery positive and negative electrodes and the current path for the assembled battery of the present invention. 2 is a top view showing an embodiment of the connection state between the battery positive electrodes shown in FIG. 1, and FIG. 3 is a cross-sectional view showing the connection state between the battery positive electrodes shown in FIG. FIG. 4 is a procedure and cross-sectional view showing one embodiment of the connecting metal plate arranging step and the arc spot welding step according to the assembled battery and the welding method of the present invention.

  As shown in FIG. 1, a set of 40 unit cells 2 are stored in a plurality of rows in an electrically insulating storage case 1. The arrangement may be changed to another arrangement, or when the number of single cells is small, they may be arranged in a line, and when a multiple of 80 is required, two sets may be arranged. Each unit cell 2 is a cylindrical lithium battery, in which battery positive electrode parts 6 and other battery negative electrode parts 7 are arranged alternately adjacent to each other, and are connected in series by connecting metal plates 3. When the battery is operating, a high current can be output in the direction of the current path 12.

  As shown in FIGS. 2 to 4, the connection metal plate 3 made of copper is disposed on both surfaces of the battery positive electrode portion 6 of the unit cell 2 and the battery negative electrode unit 7 (battery bottom surface) of the other unit cell 2. Each of the joints is formed, and arc spot welding is performed at a specific position of one of the connection metal plates 3 above the battery positive electrode portion 6 and at a specific position of the other connection metal plate 3 above the battery negative electrode portion 7. Welded portions 5 each formed by construction are provided. The battery positive electrode portion 6 and the battery negative electrode portion 7 are made of steel, and Ni plating is formed on the steel back surface in order to improve corrosion resistance. On the surface portion of each connecting metal plate 3, two welded portions 5 by arc spot welding are formed on the battery positive electrode portion 6 side and two points on the other battery negative electrode portion 7 side. The specific position where the two welded portions 5 should be formed may be, for example, a position about w / 4 from both end faces with respect to the plate width w of the connection metal plate 3 or a position near this. It is also possible to change to another position where welding is easy. Moreover, when forming the welding part 5 one point at a time at the battery positive electrode part 6 side and the battery negative electrode part 7 side, what is necessary is just to make it the approximate center position of the board width w, or this vicinity position. Even with a small number of welding points, a welded portion with good welding quality and high tensile strength can be obtained, the battery positive and negative electrodes can be securely fastened, and at the same time, the number of welding steps can be reduced.

Thus, by forming the welded part 5 by arc spot welding, an assembled battery can be obtained in which the connection resistance between the battery electrodes is small and the energization loss during battery charging and discharging is small. In particular, the electrical resistance of copper is higher than that of nickel or steel (Cu: 1.55 <Ni: 6.58 <
Fe: 8.71 (× 10 ⁻⁶ Ω · cm)) Because it is much smaller, the connection resistance can be made much smaller by using the copper connection metal plate 3, and it can be manufactured at a lower cost than nickel materials. You can also. Moreover, even if it is the connection metal plate 3 made from copper, it can melt-join reliably by arc spot welding, and the welding part 5 with favorable welding quality and high tensile strength can be obtained. Note that conventional Joule heating type resistance welding (spot welding) cannot be applied because it is difficult to weld copper with low electrical resistance.

  The penetration depth h of the welded portion 5 is larger than the plate thickness T1 of the connection metal plate 3 (upper side), and smaller than the value obtained by adding the plate thickness T2 of the battery positive electrode portion 6 or the battery negative electrode portion 7 (lower side). By forming in the range of <h <= (T1 + T2 * 4/5), the welding part 5 of the depth which does not melt to the back side of a lap joint can be obtained reliably.

  The unit cell 3 or the assembled battery of the embodiment shown in FIG. 1 to FIG. 3 is a lithium battery, but may be another battery such as a nickel metal hydride battery. As described above, a welded portion 5 having good welding quality and high tensile strength can be obtained, and a battery assembly having a low connection resistance between battery electrodes and a small current loss during battery charge / discharge can be obtained. Further, two or more bent portions 4 are formed in the upper direction in the connection metal plate 3 at a location away from the position of the welded portion 5. By forming the bent portion 4, it is possible to suppress the stress applied to the welded portion 5 due to restraint due to the integration of the assembled battery, vibration due to operation of mounting on a vehicle, or the like.

  As shown in FIG. 4, the cell arranging step 21 is a step of arranging a predetermined number of the cells 2 in an insulating storage case, attaching a detection signal such as an output voltage, and attaching various necessary parts. It is. In the next connecting metal plate arranging step 22, the copper connecting metal plate 3 is arranged on both surfaces of the battery positive electrode portion 6 of the unit cell 2 and the battery negative electrode unit 7 of the other unit cell 2 to form lap joints. It is a process. Each cell 2 is sealed with a thin insulating sheet (omitted) on the outer periphery except for the battery positive electrode portion 6 and the battery negative electrode portion 7, and is preliminarily divided by an insulating material block frame 8 to perform arc welding. The battery positive electrode portion 6 and the battery negative electrode portion 7 are exposed so as to be able to. The lap joint has a copper material having an upper plate thickness T1 corresponding to the connection metal plate 3 of 0.5 mm to 1.5 mm and a lower plate thickness T2 corresponding to the battery positive electrode portion 6 or the battery negative electrode portion 7. This is a dissimilar joint with steel material of 0.5 mm or more and 1.5 mm or less. The container of the unit cell 2, the battery positive electrode part 6 and the battery negative electrode part 7 are formed with nickel plating on the front and back surfaces of the steel material in order to improve the corrosion resistance. The thickness of the Ni plating is 1 μm or more and 10 μm or less, and enables arc welding of a dissimilar joint between copper and Ni-plated steel.

  The next arc spot welding process 23 is a process in which the lap joint between the connection metal plate 3 and the battery positive electrode part 6 or the battery negative electrode part 7 is melt-bonded 11 by the non-consumable electrode type arc 10. In particular, in this welding step 23, the penetration depth h with respect to the plate thickness T1 of the connecting metal plate 3 and the plate thickness T2 of the battery positive electrode portion 6 or the battery negative electrode portion 7 is in the range of T1 <h ≦ (T1 + T2 × 4/5). Arc spot welding is performed to form. Details will be described with reference to FIG.

  FIG. 5 is a cross-sectional view showing a step of arc spot welding of a lap joint between battery electrodes and a diagram showing a relationship between welding current and time, (1) arc heating of the upper connecting metal plate, (2) The melting of the connecting metal plate, (3) fusion bonding with the lower battery positive electrode part or negative electrode part, and (4) the state of the current waveform over time are shown. The arc heat source used in this embodiment is an arc 10 using a non-consumable tungsten welding electrode 9 and outputs predetermined welding conditions (current and welding time) set in a welding power source. An arc 10 is generated in an atmosphere of shielding gas (Ar gas) flowing out (not shown), and a current I (A) for a predetermined time T (ms) is output as shown in FIG. As shown in FIGS. 5 (1) and 5 (2), the upper connecting metal plate 3 is first arc-heated to be melt-bonded 11, and then, as shown in FIG. The upper molten portion and the lower battery positive electrode portion 6 or the battery negative electrode portion 7 are melt-bonded 11 by the arc force. It is a short time stop welding that does not melt to the back side of the lower plate, solidifies immediately after the arc is erased, and a welded part 5 with good quality free from back melting and cracking can be obtained. At the time of welding, the upper connecting metal plate 3 may be pressed so as to be in close contact with the lower plate (battery positive electrode portion 6 or battery negative electrode portion 7) using a holding jig (omitted). Although it is better that there is no gap in the joint portion, even if there is a slight gap, it can be easily melt-bonded by the arc force.

Moreover, even when welding a dissimilar lap joint between the copper connecting metal plate 3 and the steel battery positive electrode portion 6 or the battery negative electrode portion 7, it can be surely melt-bonded, particularly with Ni plating as a medium. Cu having a low melting point and Fe having a high melting point are combined (melting point of metal: Cu: 1083 <Ni: 1455 <Fe: 1539 ° C.), and an excellent ultrathin Cu / Fe mixed layer without cracking is formed, which is good A welded portion 5 having high welding quality and high tensile strength can be obtained. If the back surface of the battery positive electrode part 6 or the battery negative electrode part 7 made of steel is Ni-plated, the connection metal plate 3 on the upper plate side remains made of copper (without Ni plating) or with Ni plating, and the arc Dissimilar material welding by welding can be performed, and a welded portion 5 having good quality without cracks can be obtained. If the thickness of the Ni plating is less than 1 μm, the steel surface is exposed due to slight scratches and the corrosion resistance tends to be lowered. Conversely, if the thickness is more than 10 μm, not only the plating process takes time, but also arc welding. It is not preferable because sometimes insufficient bonding is likely to occur.

By forming the penetration depth h of the welded portion 5 in the range of T1 <h ≦ (T1 + T2 × 4/5), it is possible to obtain a welded portion 5 with good quality without back melting or cracking, The Ni plating remains and the corrosion resistance can be maintained. For dimension stop welding without back-melting, it is only necessary to select in advance appropriate welding conditions that result in shallow penetration or heat input conditions corresponding thereto, and to output the welding conditions. In addition, if the penetration depth h is shallower than the upper plate thickness T1, welding will be insufficient. Conversely, if the penetration depth h is greater than (T1 + T2 × 4/5), back-melting is likely to occur, resulting in reduced corrosion resistance. And there is a problem of battery leakage. On the other hand, if the thickness T1 of the connecting metal plate 3 is less than 0.5 mm, the strength of the material itself is low, the strength of the welded portion 5 is low and the structure is weak against vibration, and conversely, the thickness T1 is 1. If it is thicker than 5 mm, it is not preferable because arc spot welding cannot be performed due to an increase in heat dissipation to the connecting metal plate 3. On the other hand, if the plate thickness T2 of the battery positive electrode portion 6 or the battery negative electrode portion 7 of the unit cell 2 is less than 0.5 mm, the strength of the material itself is low, the strength of the welded portion is low, and the structure is weak against vibration. In addition, if the plate thickness T2 is greater than 1.5 mm, it is not preferable because the deep drawing process becomes difficult and not only the weight increases but also arc welding becomes difficult.

  The connecting metal plate 3 at the welded portion is flat, but a connecting metal plate having protrusions (convex portions) formed on the back surface may be used. As described above, the connecting metal plate 3 is good by performing the welding method of the present invention. A welded portion 5 having high welding quality and high tensile strength can be obtained, and an assembled battery with low connection resistance between battery electrodes and low current loss during battery charge / discharge can be obtained.

  Table 1 is one example of the results of measuring the connection resistance between the positive and negative electrodes of the battery, and the one obtained by arc welding the connection metal plate of the Ni-plated copper material and the one obtained by resistance welding the connection metal plate of the nickel material Is shown. A high tester was used to measure the connection resistance, and as shown in FIG. 2, the resistance value between the positive and negative electrodes (between points AB) of the unit cell 2 was measured by the AC four-terminal method. As shown in Table 1, the connection resistance (average value of three measurements) between the positive and negative electrodes obtained by two-point welding (arc welding) of a copper connection metal plate is 0.27 mΩ, and the connection metal plate made of Ni is It is about 1/3 of the connection resistance (0.76 mΩ) between the positive and negative electrodes subjected to four-point welding (conventional resistance welding), and even in the case of one-point welding, the result is as small as 0.39 mΩ. As the reason why the connection resistance between the two-point welding and the one-point welding is different, a difference in the size of the joint cross-sectional area is considered. Thus, by using a copper connection metal plate, the connection resistance between the positive and negative electrodes of the battery is reduced, the current loss during battery charging and discharging in the assembled battery shown in FIG. 1 can be greatly reduced, and the battery life is improved. Can contribute. Moreover, it can be manufactured at a lower cost than nickel materials.

図６は、電池溶接におけるアーク溶接の電流とアーク電圧，適正時間及び入熱量の関係を示す一実施例である。板厚０.８mm の接続金属板３（Ｎｉメッキ付銅）と板厚０.８mm の電池正極部６（Ｎｉメッキ付鋼）との異材溶接であり、裏溶けのない溶融接合１１が可能な適正条件を示している。アークスポット溶接では、高い電流Ｉを使用すると短時間及び低入熱量で溶融接合し、低い電流Ｉを使用すると、アーク力及び熱伝導の低下により、溶融接合可能な適正時間Ｔ及び入熱量Ｑが増加している。アーク電圧Ｖａは電流Ｉの大きさに応じて上昇している。入熱量Ｑ（Ｊ）は、電流Ｉ（Ａ）とアーク電圧Ｖａ（Ｖ）及び時間Ｔ（ｍｓ）から算出（Ｑ＝Ｉ×Ｖａ×Ｔ／１０００）することができる。

FIG. 6 is an example showing the relationship between arc welding current, arc voltage, appropriate time, and heat input in battery welding. This is a dissimilar material welding of a 0.8 mm thick connecting metal plate 3 (Ni plated copper) and a 0.8 mm thick battery positive electrode 6 (Ni plated steel), enabling fusion bonding 11 without melting back. Appropriate conditions are shown. In arc spot welding, when a high current I is used, melt bonding is performed in a short time and with a low heat input, and when a low current I is used, an appropriate time T and heat input Q that can be melt-bonded due to a decrease in arc force and heat conduction. It has increased. The arc voltage Va rises according to the magnitude of the current I. The amount of heat input Q (J) can be calculated from the current I (A), the arc voltage Va (V), and the time T (ms) (Q = I × Va × T / 1000).

  When the battery positive electrode 6 or battery negative electrode 7 having a thickness of less than 0.8 mm is melt-bonded, an appropriate time shorter than the relationship between current and time of arc welding shown in FIG. In addition, when the plate thickness is increased to 1 mm, the appropriate time may be set longer. By performing welding using welding conditions suitable for the plate thickness to be used, it is possible to obtain a welded part 5 with good quality without melting back or cracking. Further, even if there is a slight gap in the joint portion, it can be easily melt-bonded by the arc force.

FIG. 7 is an example showing the relationship between the cross-sectional area and the tensile strength of a two-point welded part that has been arc spot welded. The cross-sectional area S is a value calculated by measuring the dimensions from the fracture surface after the tensile test, changing the welding current and time. As shown in FIG. 7, the tensile strength F (breaking load) of the two-point welded portion increases substantially in proportion to the size of the cross-sectional area S. If the bonding surface S is less than 5 mm ^2, peeled fractured from the joining surfaces, the tensile strength F is low (less than 650 N), in the case of 5 ≦ S ≦ 8 mm ² is broken from the upper plate melting unit, high tensile strength (650 ≦ F ≦ 1200 N) can be obtained. When the joint surface S is larger than 8 mm ² , the tensile strength further increases, but the back melt occurs due to excessive heat input.

  Thus, according to the assembled battery and the welding method thereof of the present invention, the connection resistance between the battery electrodes is small, and the energization loss during battery charging / discharging can be reduced. Moreover, even if it is welding of the copper material with which resistance welding is difficult, and welding of the dissimilar lap joint of copper and steel materials, a welding part with favorable welding quality and high tensile strength can be obtained by arc spot welding.

It is explanatory drawing which shows one Example of the arrangement | sequence of the cell concerning the assembled battery of this invention, the connection between battery positive / negative electrodes, and a current pathway. It is a top view which shows one Example of the connection state between the battery positive electrode concerning the assembled battery of this invention, and its welding method. It is sectional drawing which shows the connection state between the battery positive / negative electrodes shown in FIG. It is the procedure and sectional drawing which show one Example of the arrangement | positioning process and arc spot welding process of the connection metal plate which concern on the assembled battery of this invention, and its welding method. It is sectional drawing which shows the process of carrying out the arc spot welding of the lap joint part between battery electrodes, and the diagram which shows the relationship between welding current and time. It is one Example which shows the relationship between the electric current of arc welding in battery welding, an arc voltage, appropriate time, and a heat input. It is one Example which shows the relationship between the cross-sectional area of two-point welding part which carried out the arc spot welding, and tensile strength.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Storage case 2 Single cell 3 Connection metal plate 4 Bending part 5 Welding part 6 Battery positive electrode part 7 Battery negative electrode part 8 Block frame 9 Tungsten welding electrode 10 Arc 11 Fusion joining

Claims (5)

In a battery pack in which a plurality of cells are housed in a storage case in a row or a plurality of rows, and the electrodes of the plurality of cells are connected by a connecting metal plate,
The connecting metal plate includes copper;
The connecting metal plate is disposed on both surfaces of the positive electrode part of the unit cell and the negative electrode part of another unit cell to form a lap joint, and the upper side of the one of the connecting metal plate and the negative electrode part above the positive electrode part. A battery assembly comprising a welded portion formed by performing arc spot welding on the other connecting metal plate.   The penetration depth h of the welded portion is larger than the plate thickness of the connection metal plate, and is smaller than the value obtained by adding 4/5 of the plate thickness of the positive electrode portion or the negative electrode portion to the plate thickness of the connection metal plate. The assembled battery according to claim 1, wherein the battery pack is formed.   The lap joint has a copper material having an upper plate thickness of 0.5 mm to 1.5 mm corresponding to the connecting metal plate and a lower plate thickness of 0.5 mm to 1 corresponding to the positive electrode portion or the negative electrode portion. The assembled battery according to claim 1, wherein the assembled battery is a dissimilar joint with a steel material of .5 mm or less, and nickel plating is formed on the front and back surfaces of the steel material. In a method for welding assembled batteries in which a plurality of cells are stored in a row or a plurality of rows in a storage case, and the electrodes of the plurality of cells are connected by a connecting metal plate,
The connecting metal plate includes copper;
The connection metal plate is disposed on both surfaces of the positive electrode part of the unit cell and the negative electrode part of the other unit cell to form lap joints,
Applying arc spot welding to one of the connection metal plates above the positive electrode portion and the other connection metal plate above the negative electrode portion;
A method for welding an assembled battery, comprising:   In the welding step, the penetration depth h with respect to the plate thickness of the connection metal plate and the plate thickness of the positive electrode portion or the negative electrode portion is larger than the plate thickness of the connection metal plate, and the plate thickness of the positive electrode portion or the negative electrode portion. 5. The method for welding an assembled battery according to claim 4, wherein the arc spot welding is performed so as to be formed in a range smaller than a value obtained by adding 4/5 to a thickness of the connection metal plate.

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