JP4794138B2 - Assembled battery - Google Patents

Description

  The present invention relates to an assembled battery formed by connecting a plurality of unit cells such as alkaline storage batteries.

In recent years, applications of secondary batteries (storage batteries) have been rapidly expanded and are widely used as power sources for personal computers, mobile phones, electric tools, electric vehicles, hybrid vehicles, electric bicycles and the like.
Among these, when used in electric vehicles, hybrid vehicles, electric bicycles, electric tools, etc., a relatively high output and large current are required, and because of the flexibility to respond to changes in the usage environment, etc., good safety An assembled battery is widely used in which a nickel-metal hydride storage battery having a single cell is used as a single battery and a plurality of these batteries are connected in series.
Japanese Patent Laid-Open No. 2001-185102 JP 2003-229102 A Japanese Patent Laid-Open No. 2003-223879

  The assembled battery having the above configuration can extract high output and large current to the outside, but generates a large amount of heat due to the internal resistance of the battery. A part of the heat is radiated from the exterior body covering the assembled battery to the outside, but other heat remains inside the assembled battery. In particular, in the unit cell disposed in the center of the assembled battery, the heat dissipated by the other unit cells adjacent to each other is hindered, so that the temperature around the battery is unlikely to decrease.

  In this way, if the state in which heat dissipation is not successfully performed in a single cell continues, problems such as a decrease in charging efficiency, oxidation of the negative electrode alloy due to generated oxygen, and deterioration due to an increase in internal resistance of the cell become significant. . Further, a decrease in charging efficiency and an increase in self-discharge reaction cause a difference in battery capacity between the individual cells (State of Charge; SOC shifts). When such a battery capacity difference occurs, when each single battery is connected in series like the assembled battery, the supply current to the outside is aligned with the current value of the battery having the lowest capacity among the assembled batteries. The phenomenon occurs. For this reason, the output of the assembled battery is reduced at a relatively early time before reaching the normal cycle life.

Further, if the assembled battery is used as it is, the single battery having a relatively high discharge efficiency is fully charged at the time of charging, but at this time, there is an insufficiently charged single battery in the assembled battery. If the battery pack is used by recognizing this time point as a fully charged state of the battery pack, the battery cell that has not been fully charged falls into an overdischarged state, and deterioration of the battery cell also occurs.
Therefore, due to the presence of the single battery having a reduced capacity as described above, there arises a problem that the life of the assembled battery is shortened as a result.

  The present invention has been made in view of the above problems, and by suppressing variations in the life of each unit cell, it is possible to realize a better cycle life than the conventional one and to exhibit good battery performance. An object is to provide a possible assembled battery.

In order to solve the above-described problem, an assembled battery including a battery module in which four or more unit cells are connected, and the module is compared with the electric resistance between the unit cells in the vicinity of both ends of the battery module. It was set as the structure with small electrical resistance between the single cells in the center side of a longitudinal direction.
Here, the battery module can be configured by connecting the unit cells in series and in a rod shape.

Furthermore, each said single cell was connected through the electrically-conductive member, respectively, and the electrical resistance between the said single cells shall be adjusted with selection of the material of each said electrically-conductive member.
Or the electrical resistance between the said single cells shall be adjusted with the connection area of the said single cell and each said electrically-conductive member.
The electrical resistance can be adjusted by the thickness of the conductive member.

  In the battery pack of the present invention, heat dissipation is achieved by relatively reducing the electrical resistance between adjacent cells in the battery module as compared with the electrical resistance between adjacent cells at both ends of the battery module as described above. This suppresses the generation of Joule heat of the single cell near the center of the battery module, which is difficult to perform, and makes the temperature distribution in the entire assembled battery uniform. By achieving this uniform temperature distribution, the following effects can be obtained.

  That is, in the past, when the battery pack was driven, the heat generated by the single cells near the center of the battery module was not sufficiently dissipated, resulting in variations in the life of the single cells over time. The temperature distribution of the assembled battery is made uniform by adjusting the electric resistance therebetween. For this reason, in the assembled battery of this invention, even if charging / discharging is repeated, generation | occurrence | production of the cell which falls into an overcharge and overdischarge state is suppressed. Therefore, according to the present invention, variations in the life of the single cells are suppressed, the cycle life of the assembled battery as a whole is extended, and good battery performance is exhibited.

In particular, when used in a high temperature environment, the effect is great. On the other hand, even when used in a low temperature environment, battery performance can be stably obtained.
In order to obtain such an effect, in the present invention, various adjustments are made mainly on the configuration of the connection portion between the single cells. In other words, in order to adjust the electrical resistance resistance according to the connection location of each unit cell, it is possible to adjust the electrical resistance by changing the member thickness and conductive characteristics of the conductive member, or increase the number of connection points with the unit cell A method of increasing the area and reducing the electrical resistance in proportion to the number of connection points can be employed.

Hereinafter, embodiments will be described with reference to the drawings.
<Embodiment 1>
The assembled battery 1 according to the first embodiment is formed by connecting a plurality of unit cells 20A to 20D in series and in a rod shape via conductive members 10A to 10C to form a battery module 2, and further, the battery module 2 (See FIG. 4).

Therefore, hereinafter, each configuration of the conductive member, the battery module, and the assembled battery will be described in order.
1. Configuration of Conductive Member FIG. 1 is an assembled view showing the configuration of the conductive member. Here, 10A arranged between the longitudinal directions of the unit cells 20A and 20B is illustrated, but the basic structure (except for the thickness of the member in the present embodiment) is common to all other conductive members 10B to 10C). is doing.

The conductive member (also referred to as “dish tab”) 10A shown in the figure is composed of a predetermined thickness (final thickness of 0.5 mm) made of a steel plate as a core, and subjected to conductive plating such as nickel. The material is pressed into a dish.
On the dish tab 10A, a first flat portion 103 and a second flat portion 102 are formed via a step 103b as a stepped bottom, and a rib 101 is formed so as to surround the second flat portion 102. Has been.

  Among these, convex portions 101 a and 103 a formed by partially deforming the members are provided on the inner surface of the rib 101 and the outer surface of the first flat portion 103, respectively. These are formed as connecting portions (welded portions) of the unit cells 20A and 20B, respectively. The rib 101 is connected to the outer can 201A of the unit cell 20A, and the first flat portion 103 is connected to the sealing plate 202B of the unit cell 20B.

The first flat portion 103 is further provided with a perforated region 104 in the center thereof. This is for inserting the positive terminal 204B of the unit cell 20B.
The first flat portion is formed to have a smaller diameter than the second flat portion, thereby preventing a short circuit from coming into contact with the outer can 201B of the unit cell 20B.
As a material suitable for the conductive member 10A, materials other than those described above, such as stainless steel and copper, may be used. However, the conductive member 10A is made of a material excellent in conductivity (that is, having low electric resistance) and suitable for resistance welding. Is desirable.

In addition, although mentioned later for details, in this invention, it has the characteristics in the point adjusted according to the location which uses the electroconductivity of the said conductive member 10A by changing the material of the said conductive member 10A.
2. Configuration of Battery Module FIG. 2 shows an internal configuration example of a D cell (single type battery) in JIS standard as an example of the single cells 20A and 20B.

  The unit cells 20A and 20B are known cylindrical alkaline secondary batteries (nickel-hydrogen storage batteries), and the positive plates 220A and 220B and the negative plates 221A and 221B are spirally wound through the nonwoven fabric separators 222A and 222B. The spiral electrode body that is rotated is impregnated with an alkaline electrolyte to form power generation elements 210A and 210B, which are housed in cylindrical outer cans 201A and 201B.

The positive plates 220A and 220B are electrode plates in which nickel hydroxide is filled as an active material in a core body made of punching metal. This nickel electrode plate is composed of either a sintered type or a non-sintered type.
The negative plates 221A and 221B are hydrogen storage alloy electrodes in which a core made of punching metal is filled with a hydrogen storage alloy as an active material.

The nonwoven fabric separators 222A and 222B are made of a polypropylene nonwoven fabric subjected to hydrophilic treatment.
Openings of the outer cans 201A and 201B are sealed with sealing plates 202A and 202B via gaskets 223A and 223B.
Positive terminals 204A and 204B are attached to the sealing plates 202A and 202B, and the discharge holes 205A and 205B opened in the sealing plates 202A and 202B are closed with valve plates 207A and 207B pressed by the elastic valves 206A and 206B. Yes. In the unlikely event that the gas pressure inside the battery rises abnormally, the valve plates 207A and 207B are pushed up by the gas pressure, and the gas is allowed to escape from the discharge holes 205A and 205B.

  The positive plates 220A and 220B of the power generation elements 210A and 210B are connected to the sealing plate 302A and the positive terminal 204A via the positive current collectors 309A and 309B, and the negative plates 221A and 221B are packaged via the negative current collectors 211A and 211B. Cans 201A and 201B are connected (the above 202B, 204B, 205B, 206B, 207B, 209B, 211A, and 223B are not shown).

The unit cells 20A and 20B having the above-described configuration are the sealing plate fixed to the plate tab 10A by caulking to the bottom 203A (negative electrode terminal) which is the end face of the cylindrical outer can 201A and the upper portion of the outer can 201B. It is electrically connected to 202B (positive electrode terminal side).
As a specific connection example at this time, first, resistance welding is performed on the sealing plate 202B of the single cell 20B at the convex portion 103a, and then resistance welding is performed on the convex portion 101a around the outer can 201A of the single cell 20A. To do. The welding step may be reversed.

At this time, as resistance welding conditions, for example, the connection is made by energizing the welding current for 3 seconds at a current value of about 4 kA.
By the resistance welding, the cells 20A and 20B are connected with the plurality of convex portions 101a and 103a as connection points, respectively. However, since the connection is achieved with a certain area as a whole, particularly insufficient strength occurs in the connection structure. Never do.

In addition, as a connection means, the connection using solder other than the said resistance welding can also be utilized.
Thus, in this Embodiment, the method of connecting unit cell 20A, 20B via the electrically-conductive member 10A is repeated. As a result, finally, a battery module 2 (see FIG. 3) formed by connecting the four unit cells 20A to 20D with the conductive members 10A to 10C is formed.
In the battery module 2 shown in FIG. 3, as means for electrically connecting to other battery modules 2, fixing tabs 11A and 11B are arranged at both ends in the longitudinal direction, and screws are placed on the fixing tabs 11A and 11B. Module terminals 51 and 52 are provided.

In this configuration example, four battery cells 20A to 20D are connected by a single battery module 2, but of course the present invention is not limited to this number. Also good.
3. Configuration of assembled battery FIG. 4 is a diagram showing a configuration of an assembled battery 1 in which a plurality of the battery modules 2 are provided side by side.

  In the configuration example of this figure, a total of 13 battery modules 2 (that is, a total of 52 single cells) are connected in series using strip-shaped connection members 54 and nuts 55. The connection method and the assembled form of the battery modules 2 may be other than this. Here, since all the battery modules 2 are connected in series, depending on the module at a specific position, as shown at the left end of the figure, the other modules are installed upside down.

The assembled battery 1 having such a structure can be used in a state in which the unit cell is exposed as it is, but it is desirable to use the battery pack in a battery case together with a cooling device such as a dedicated cooling fan.
At this time, if the battery modules 2 can be arranged in a regular hexagonal shape (honeycomb shape), the battery case can be reduced in size and can be configured as a battery system having a high energy density.

4. Effects of the Present Invention Here, the feature of the present invention is that the electrical resistance between the adjacent single cells (20A and 20B, and 20C and 20D) in the vicinity of both ends of the battery module 2 is larger than that of the module longitudinal direction. The point is that the thermal resistance between adjacent cells (20B and 20C) is set to be large near the center.

Specifically, the electric resistance of the plate tab 10B connecting the cells 20B and 20C is adjusted to be smaller than the electric resistance of the plate tabs 10A and 10C connecting the cells 20A and 20B and 20C and 20D, respectively. Has been.
As a means for performing this adjustment, there is a method of adjusting the member thickness of the dish tab 10B so as to be thicker than the member thickness of the dish tabs 10A and 10C (specifically, the member thickness of the dish tabs 10A and 10C). Is 0.5 mm, and the thickness of the plate tab 10B is 1.5 mm). Thus, the Joule heat which generate | occur | produces in the dish tab 10B can be restrained small by making the electrical resistance of the dish tab 10B smaller than the electrical resistance of the dish tabs 10A and 10C.

According to the assembled battery 1 having the above configuration, during driving, the single battery of each battery module 2 generates Joule heat due to internal resistance and generates heat in accordance with the output amount and driving time. This heat generation is normally dissipated to the outside air around the assembled battery 1.
At this time, the vicinity of both ends of the battery module 2 (the vicinity of the dish tabs 10A and 10C) has a property of being relatively easily exposed to the outside air, so that good heat dissipation efficiency is maintained. The battery has a small area in contact with the outside air, and has a property that it cannot easily dissipate heat due to heat generated by other adjacent unit cells. However, in the first embodiment, by providing the dish tab 10B having a thick member near the center of the battery module 2, the electrical resistance between the single cells 20A and 20C sandwiching the dish tab 10B is reduced. Therefore, generation | occurrence | production of Joule heat is suppressed and the emitted-heat amount of cell 20A, 20C is reduced. Furthermore, since the dish tab 10B is composed of a thicker member than the other dish tabs 10A, 10C, the heat sink effect is also exerted by utilizing the thickness of this member, and heat is dissipated further in the vicinity of the center of the battery module 2. The effect is enhanced.

As a result, the assembled battery 1 has a uniform temperature distribution as a whole, and the heat dissipation characteristics of the individual cells (52 in total) constituting the assembled battery 1 are aligned.
Here, when used in a high temperature state, a single battery as a secondary battery has a property that the cycle life characteristics deteriorate at an earlier stage than the normal time. This is because, in an assembled battery using a large number of single cells, the single battery located in the central part of the battery module 2 (particularly, the single battery located in the central part of the battery module 2 located inside the assembled battery) is first. However, this may cause a difference in battery capacity between the single cells, which may reduce the normal cycle life of the assembled battery. Here, when connecting and using a plurality of single cells, because there is a phenomenon that the current supplied to the outside is aligned with the battery with the lowest capacity among the assembled batteries, regardless of the normal cycle life of the assembled battery, Although the phenomenon that the output of the assembled battery decreases with time occurs, in the assembled battery 1 of the present invention, as described above, the occurrence of the problem is suppressed by making the temperature distribution uniform. The cycle life is extended so that good battery performance can be exhibited.

  In addition, if the battery does not dissipate heat well as in the past, each cell will decrease in charging efficiency as the temperature rises, oxidation of the negative electrode alloy due to generated oxygen, deterioration due to increase in battery internal resistance However, in the present invention, since the heat generation amount of the single cells is made uniform, for example, when air cooling is performed by a cooling fan in the case of the battery system, the entire single cells are The effect of cooling with good balance can also be expected. For this reason as well, the present invention is particularly suitable as a battery system for electric vehicles and the like, and has high performance in industrial value.

  In addition, although the structural example which adjusts the thickness of dish tab 10A-10C was shown here, this invention is not limited to this, For example, it is high electroconductivity compared with dish tab 10A, 10C (in other words, electrical resistance is low). ) By using the material as the material of the dish tab 10B, the heat generation amount of the entire assembled battery may be made uniform. In this case, as described above, the dish tabs 10A and 10C are made by applying nickel plating to iron, and the dish tab 10B is made of copper as a material having higher conductivity than iron, and plated according to circumstances. Can be realized.

  Furthermore, in the present invention, in addition to the method of uniforming the heat dissipation amount around the dish tab by the material thickness of the dish tabs 10A to 10C, or the method of selecting the material, the connection area to the single cell (in this embodiment, the convexity By increasing / decreasing the number of connection points), the electric resistance between the single cells via the dish tabs 10A to 10C can be adjusted, and the electric resistance of the battery module 2 can be made uniform.

  Specifically, the number of connection points between the plate tab 10B and the single cells 20B and 20C is the number of connection points between the plate tab 10A and the single cells 20A and 20B, and the connection point between the plate tab 10C and the single cells 20C and 20D. Adjust to be more than the number. Also with this configuration, the electrical resistance can be lowered in proportion to the number of connection points, so that the same effect as described above can be expected.

<Performance comparison experiment>
Here, based on the configuration of the first embodiment, battery modules of examples and comparative examples were actually manufactured and performance comparison experiments were performed. In the first embodiment, a rod-shaped battery module in which four unit cells are connected in series has been described. However, in the example and the comparative example, as a variation of the battery module of the first embodiment, five battery modules are provided. A rod-shaped battery module formed by connecting single cells in series was prepared.

Hereinafter, the production and experimental results of the battery modules of Examples and Comparative Examples will be described.

1. Production of Example 1 First, as a single cell, a cylindrical nickel-metal hydride storage battery ABCDE (a total of five) having a D size and a nominal capacity of 6.0 Ah having the same performance was used.

And the said cell ABCDE (a total of 5 pieces) was connected in series in the same order along the longitudinal direction of the armored can of each cell through the dish tab, and the rod-shaped battery module was produced as a whole.
Here, the thickness of the plate tabs a and d connecting the cells A and B and between the cells D and E was set to 0.5 mm. On the other hand, the thicknesses of the plate tabs b and c connecting the cells B and C and the cells C and D, respectively, were set to 1.5 mm. Accordingly, the electric resistances of the dish tabs a to d were set to 0.9 mΩ, 0.7 mΩ, 0.7 mΩ, and 0.9 mΩ in the same order.

2. Production of Example 2 A battery module was produced with the same configuration and connection form of the unit cells as in Example 1 above.

All the dish tabs interposed between each of the single cells ABCDE (total of 5) were made of the same material with the same thickness (1.5 mm).
In the battery module of Example 2, the number of connection points was changed according to the position of the dish tab. That is, the number of welding points was 2 on the plate tabs a and d, and the number of welding points was 4 on the plate tabs b and c. As a result, the electric resistance between the cells via each dish tab is set to 1.1 mΩ, 0.7 mΩ, 0.7 mΩ, and 1.1 mΩ in the same order between AB, BC, CD, and DE. did.

3. Production of Comparative Example A battery module of a comparative example was produced with the same configuration and connection form of the unit cells as in Examples 1 and 2 above. The dish tabs were all made of the same material with the same thickness (1.5 mm).

In the battery module of the comparative example, all the welding points of the dish tab were set to four points, and all the electric resistances of the dish tab were set to 0.7 mΩ. As the welding conditions, the welding current was set to 0.5 kA.

4. Pulse cycle test For each of the battery modules of Examples 1 and 2 and Comparative Example manufactured as described above, a cycle experiment was performed over a total of 20000 cycles.

The experimental conditions were as follows.
Atmospheric temperature: 28 ° C
Charge / discharge current: 50A
Use capacity range set to 40% to 60% of nominal capacity

5. Battery temperature When the cycle test was completed for 20000 cycles, the cell temperature in each battery module was measured. The results are summarized in Table 1.

6. Remaining capacity measurement When the above cycle test was completed for 20000 cycles, the remaining capacity in each battery module was measured. The results are summarized in Table 2.

7. Battery direct current resistance measurement In the above pulse cycle test, before the start of the third cycle test and after the end of 20000 cycle, after charging 50% of the nominal capacity, charge and discharge at 30, 90, 150A for 10 seconds respectively, The voltage and current at 10 seconds after the start of discharge at the current value were plotted, and the battery DC resistance was estimated from the slope of the approximate curve.

The results are summarized in Table 3.

＜実験結果考察＞
まず表１の結果から明らかなように、実施例１、２では、導電部材である各皿タブの電気抵抗を電池モジュールの両端部から内部に向けて小さく設定することによって、充放電中の組電池では温度分布の均一化が図られることが確認された。一方、比較例では単電池の放熱にバラツキを生じ、温度差が比較的大きくなっている。

<Experimental results consideration>
First, as is clear from the results in Table 1, in Examples 1 and 2, by setting the electrical resistance of each dish tab, which is a conductive member, small from both ends of the battery module toward the inside, It was confirmed that the temperature distribution was made uniform in the battery. On the other hand, in the comparative example, the heat dissipation of the single cells varies, and the temperature difference is relatively large.

Further, in the data shown in Table 2, it can be confirmed that even after the charge / discharge cycle is repeated by a certain amount, the variation in the remaining capacity is suppressed to a smaller extent in each of Examples 1 and 2 than in the comparative example. In particular, in Example 2 in which the number of connection points is adjusted, the variation in the remaining capacity is suppressed to one third or less as compared with the comparative example, and the high effect of the present invention is proved.
Such a result is considered to suggest that in the assembled battery of the present invention, the charging efficiency characteristics and self-discharge amount of each unit cell are kept uniform. Therefore, in the assembled battery of the present invention, the effect of protecting each unit cell from overcharge and overdischarge is exhibited, and it is presumed that the assembled battery of the present invention has a good cycle life. .

Furthermore, from the results in Table 3, it can be seen that Examples 1 and 2 have the effect of reducing the increase in internal resistance compared to the comparative example. As described above, in the present invention, the variation in the performance of each unit cell is suppressed, so that the degree of deterioration of each unit cell becomes uniform, and it can be seen that stable battery performance is exhibited over a long period of time.
<Other matters>
In the above embodiment, a configuration using a nickel hydride storage battery has been described. However, the present invention is not limited to this, and other types of batteries such as a nickel cadmium storage battery and a lithium ion battery may be used.

  In addition, when the number of single cells is five or more, it is desirable that the dish tab arranged on the battery module is adjusted so that the member thickness or the electrical resistance gradually decreases from both ends of the module along the inside of the module. In the present invention, at least the plate thickness of the other plate tab may be thicker or the electric resistance may be smaller than the plate tabs close to both ends of the module.

Furthermore, in the above configuration example, the configuration in which the plate tab is point-welded to the unit cell has been shown, but the shape of the welded portion is not limited to a small area such as a substantial welding “point”, but is welded in a larger area You may do it.
Moreover, in this invention, as a electrically-conductive member which connects the single cells in a battery module, it is not limited to the shape of the dish tab demonstrated in the said embodiment. In addition to this, for example, a ring-shaped tab having approximately the same size as the sealing plate of the unit cell is used, and convex portions are formed on both sides of the tab, and the convex portion is adjacent to the outer can bottom and the sealing plate of the unit cell and resistance welding. It is good also as composition to do. In this case, the welding step can be performed at a time by supplying power from the positive electrode terminal and the negative electrode terminal (exterior can bottom) of the unit cell, and has advantages such as excellent manufacturing efficiency.

  Further, in the battery module of the present invention, the single cells may be directly connected by a method such as resistance welding without using the conductive member such as the dish tab or the ring-shaped tab. Specifically, in the adjacent unit cell, the positive electrode terminal of one unit cell is connected to the negative electrode terminal (outer can bottom) of the other unit cell. In this case, in the battery module, the connection (welding) area between the single cells located on the center side of the battery module is larger than the connection (welding) area between the single cells located at both ends of the battery module. As a result, the electrical resistance associated with the connection between the single cells located on the center side of the battery module can be actively reduced, so that the same effect as in the first embodiment can be expected.

It is also possible to reduce the resistance value of parts such as the sealing plate or outer can of the cell located in the center of the battery module and increase the resistance value of the parts of the cell located at both ends of the battery module. The effect similar to that of the first embodiment can be expected.
In this case, the material of the outer can and sealing plate of the unit cell disposed near the center of the battery module is a material that is more conductive than the outer can and sealing plate of the unit cell used in other positions. The electrical resistance may be adjusted.

  Furthermore, as the battery module constituting the assembled battery of the present invention, the configuration in the form of a rod has been described. However, the “bar shape” referred to here indicates that the overall appearance of the module is a rod shape, The connection method is not limited. For example, a plurality of cylindrical / rectangular cells may be provided side by side so that the side surfaces are in contact with each other, and the battery module as a whole may be arranged in a rod shape.

  Moreover, in the said Embodiment 1, although the example which comprises an assembled battery using a some battery module was shown, the quantity of the battery module used for the assembled battery of this invention should just be at least 1 or more.

The present invention is optimal as an assembled battery that can be used satisfactorily even in extremely high temperature and low temperature environments, and can obtain a high output by combining a large number of single cells while eliminating variations in battery characteristics.
Specifically, the assembled battery of the present invention can be used for a power supply device such as a hybrid electric vehicle, an electric vehicle, a work vehicle, a work robot, or an emergency power supply device for an elevator.

It is a set figure showing composition of a conductive member (dish tab). It is a fragmentary sectional view of a cell and a dish tab. It is a figure which shows the structure of a battery module. It is a figure which shows the structure of an assembled battery.

Explanation of symbols

1 assembled battery 2 battery module 10A to 10C conductive member (dish tab)
20A-20D single battery (nickel metal hydride storage battery)
101 Rib 101a, 103a Convex part 102 First flat part 103 Second flat part 104 Opening region

Claims (4)

An assembled battery including a battery module in which four or more unit cells are connected in series and in a rod shape ,
An assembled battery having a configuration in which the electrical resistance between the single cells on the center side in the module longitudinal direction is smaller than the electrical resistance between the single cells in the vicinity of both ends of the battery module.   Each unit cell is connected via a conductive member,
  The assembled battery according to claim 1, wherein an electrical resistance between the unit cells is adjusted by selection of a material of each of the conductive members.   Each unit cell is connected via a conductive member,
  The assembled battery according to claim 1, wherein an electrical resistance between the unit cells is adjusted by a connection area between the unit cell and each of the conductive members.   Each unit cell is connected via a conductive member,
  The assembled battery according to any one of claims 1 to 4, wherein an electric resistance between the unit cells is adjusted by a thickness of each of the conductive members.

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