Battery with proportional collectors, straps, and plates

A battery comprises at least four cells each comprising a bath in the shape of a rectangular parallelepiped having a width direction dimension greater than a thickness direction dimension, and a power generation element, the power generation element being contained in the bath, the thickness direction sides of the cells facing each other, and the width direction sides of the cells being arranged side by side. A coolant for cooling the cells is allowed to flow along the width direction sides of the cells.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a battery and, more particularly, to a battery in which a plurality of cells are linked so as to obtain a required power capacity.

2. Description of the Related Art

Large-capacity batteries comprising a plurality of linked cells, such as nickel-cadmium cells, nickel-hydrogen cells, or hydrogen cells, are used in various electric appliances, electric vehicles, and the like. In such a large-capacity battery, typically, a plurality of cells in the shape of a thin rectangular parallelepiped are arranged close to each other and bound together. In each cell, a plurality of positive electrode plates and a plurality of negative electrode plates are alternately laminated via separators containing electrolytic solution. For such a cell, when the ambient temperature is high or a large amount of current is discharged, heat is not sufficiently dissipated from the electrode plates contained in each cell, causing the temperature of the cell to be increased, potentially leading to a reduction in the life of the battery. In order to avoid such a problem, configurations described below have been proposed for cooling a large-capacity battery comprising a plurality of linked cells.

Japanese Laid-Open Publication No. 2000-164186 discloses a battery. In the battery, a plurality of cells (each cell being in the shape of a rectangular parallelepiped having a width direction dimension greater than a thickness direction dimension) are connected in series so that the sides along the width direction (width direction side) of the cells are located on the same plane. On the width direction side of each cell, a plurality of ribs are provided in a vertical direction. A coolant channel, through which a coolant is forced to flow, is provided between each rib in the vertical direction of the cell. Thereby, each cell is cooled.

Japanese Laid-Open Publication No. 6-215804 discloses a monoblock battery. The battery is in the shape of a rectangular parallelepiped. A side plate is provided along each of the wall surfaces in the width direction of the battery. A coolant channel (fluid circulation space) is provided between the wall surface and the side plate, and a coolant is supplied to the coolant channel.

Japanese Laid-Open Publication No. 2000-251950 discloses another battery. In the battery, a plurality of cells are linked and arranged so that the width direction sides of the cells face each other. A coolant channel is provided between each cell. Another coolant channel is provided on the sides in the thickness direction of the cells for allowing the coolant channels to communicate with each other. A coolant is allowed to flow through the coolant channel.

However, the configuration disclosed in Japanese Laid-Open Publication No. 2000-164186 described above requires an additional structure for distributing the coolant to the coolant channels of the cells. For this reason, the configuration of the entire battery is complicated and therefore the number of assembling steps is increased, causing an increase in cost.

In the configuration of Japanese Laid-Open Publication No. 6-215804 described above, only the sides of the battery comprising a plurality of linked cells are cooled. Therefore, when a great load is applied to the battery and therefore the amount of heat generated is great, it is difficult to obtain a sufficient cooling effect. Therefore, in order to obtain a sufficient cooling effect, the battery requires an additional structure for distributing the coolant to the coolant channels of the cells. As in Japanese Laid-Open Publication No. 2000-164186, the configuration of the entire battery is complicated and therefore the number of assembling steps is increased, causing an increase in cost.

In the configuration of Japanese Laid-Open Publication No. 2000-251950 described above, the coolant is allowed to flow mainly in the thickness direction side of each cell, and the amount of the coolant flowing through the coolant channel provided between each cell is small. In each cell, a plurality of electrode plates are alternately laminated, and the electrode plates are arranged along the width direction side of the cell. In addition, space is provided between the thickness direction side and the electrode plate so as to facilitate production of the battery. In order to obtain higher cooling efficiency, it is necessary to allow the coolant to flow along the width direction side. However, in this configuration, the coolant is allowed to flow mainly along the thickness direction side and therefore a sufficient level of cooling efficiency cannot be obtained.

As described in this publication, a plurality of cells are arranged so that the width direction sides face each other, and are integrally bound. The cells provided on the ends of the battery receive a smaller level of pressure. In such cells, therefore, electrolytic solution is likely to be dried up, so that the life of the cells is significantly smaller than that of the other cells. This situation will be specifically described below.

FIG. 40is a schematic diagram showing a configuration of a conventional battery.FIG. 41is a diagram for explaining expansion of the cell in the conventional battery. Referring toFIG. 40, the conventional battery400comprises 6 cells401,402,403,404,405, and406, each of which is in the shape of a rectangular parallelepiped in which the width direction dimension is greater than the thickness and height direction dimensions. The cells are arranged so that the width direction sides thereof face each other, and are integrally bound. In each cell, a plurality of electrode plates (positive electrode plates and negative electrode plates) are laminated, and arranged along the width direction sides of the cells. In the battery400having the above-described configuration, when discharging cycles are repeated in each cell401to406, each electrode plate expands. Therefore, as shown inFIG. 41, the cells401to406expand in a direction away from the cells403and404provided at the center, toward the outside. In this case, for the cells401to406, the further out the location of the cell, the smaller the binding force applied to the cell, therefore, the greater the expansion of the cell.

When the cells401to406expand in this manner, the outer cells expand to a greater extent. Therefore, the further out the cell, the smaller the pressure acting on the electrode plate. If the pressure acting on the electrode plate becomes small, the distance between adjacent electrode plates becomes great, causing the electrolytic solution to splash so that the electrolytic solution is likely to be dried up.

FIG. 42is a graph showing the life characteristics of cells in a conventional battery. As described above, the further out the cell, the smaller the pressure applied to the cell. Therefore, the pressure acting on the cells401and406located on the ends of the battery are small as compared to that acting on the other cells402to405, whereby the electrolytic solution is likely to be dried up. Consequently, as shown inFIG. 42, the life of the cells401and406on the ends of the battery is significantly smaller than the life of the other cells402to405, causing variations in the life of the cells in the battery.

In order to suppress the expansion of the cells401to406, a configuration has been proposed, in which as shown inFIG. 43, expansion suppressing plates411and412are provided on the respective ends of the battery. The expansion suppressing plates411and412integrally bind all of the cells401to406. Despite this configuration, the expansion of the cells401and406provided on the ends of the battery cannot be sufficiently suppressed.

FIG. 44is a graph showing a temperature distribution of the cells when the battery shown inFIG. 40is employed in an EV (electric vehicle). When the battery ofFIG. 40is applied to an EV in which a large amount of current may be input or output, variations in temperature between each cell401to406are large as shown inFIG. 44. Points401B to406B indicate the temperatures of the cells401to406, respectively. The temperatures of the cells403and404provided at the middle of the battery are high. The closer the location of the cell to the opposite ends of the battery, the lower the temperature of the cell. Thus, the variations in temperature between the cells401to406are large, and the temperatures of the cells provided in the middle are higher. In this case, corrosion of the grid-like electrode plate and degradation of active substances provided in the electrode plate are accelerated, causing an early reduction in the output voltage of the cell, so that the life of the battery is reduced.

In each of the above-described conventional batteries, a liquid coolant, such as water, is used as a coolant for cooling the linked cells at predetermined positions. Power generation elements composed of positive electrode plates, negative electrode plates and separators are completely shielded from the coolant channels in order to prevent the liquid coolant from penetrating into the power generation elements.

For example, in Japanese Laid-Open Publication No. 6-215804 described above, a plastic material case comprising a bath having an open top, which contains power generation elements, such as electrode plates, and a lid attached to a top portion of the bath, seals the power generation elements so that the power generation elements are shielded from the coolant channel.

In Japanese Laid-Open Publication No. 2000-251950 described above, a plurality of cells are integrally linked in series to construct a sealed secondary battery. A lid member is attached to a top portion of the sealed secondary battery, whereby power generation elements in the cells are sealed, and shielded from a cooling channel.

However, in these publications, the lid is attached to the bath containing the cells, although positioning means for attaching the lid to an appropriate position is not provided. Therefore, it is not easy to appropriately position the lid with respect to the bath. If the lid is not correctly positioned with respect to the bath, the cells are not effectively cooled by the coolant. Also, when the battery is used in a situation where wobble or the like may occur, the lid is displaced from the bath, whereby the coolant is likely to penetrate into the power generation element.

The portion of the battery, which generates heat, is not limited to the electrode plate. In particular, when a terminal portion, which is externally connected, excessively generates heat, a portion around the terminal of the bath containing the cells may be melted. However, in the above-described publications, the electrode plate is mainly cooled by the coolant, but the battery is not provided with an arrangement for preventing the heat generation of the terminal portion.

Next, a problem with the internal structure of conventional batteries having a configuration in which positive electrode plates and negative electrode plates are laminated via separators will be described below.

FIG. 45is a perspective view showing an exemplary internal structure of a conventional battery 1.

A battery501has a case body502which is in the shape of a hollow rectangular parallelepiped and has an open top. The internal space of the case body502is divided by a partition503into three in a longitudinal direction and two in a width direction, i.e., 6 cells502ato502f. The cells502ato502feach have a cross section in the shape of a rectangle extending in the longitudinal direction of the case body 2.

The cells502ato502feach contain a unit power generation element having a plurality of positive electrode plates (e.g., PbO2plate), each of which has a similar planar shape, and a plurality of negative electrode plates (e.g., Pb plate), each of which also has a similar planar shape. In the unit power generation element, positive electrode plates and negative electrode plates are alternately laminated via separators made of porous, extremely fine glass fibers holding dilute sulfuric acid, or the like.

At one end of the case body502, the first cell502aand the sixth cell502fare disposed side by side in the width direction of the case body502. The first cell502a, the second cell502band the third cell502aare disposed side by side in a longitudinal direction of the case body502. The third cell502aand the fourth cell502dare disposed side by side in the width direction of the case body502. The fifth cell502eis disposed between the fourth cell502dand the sixth cell502f. The positive electrode plates and the negative electrode plates of the unit power generation element of each cell502ato502feach extend in the longitudinal direction of the case body502.

All of the positive electrode plates of each unit power generation element of the second cell502bto the fifth cell502e(i.e., excluding the first cell502aand the sixth cell502f) are connected to a first strap504provided on one side of the positive electrode plate. All of the negative electrode plates of each unit power generation element are connected to a second strap504provided on a side of the negative electrode plate opposite to the first strap504provided on the side of the positive electrode plate. The first strap504is conductive to all of the positive electrode plates, while the second strap504is conductive to all of the negative electrode plates.

All of the positive electrode plates of the unit power generation element contained in the first cell502aare connected to the strap504, while all of the negative electrode plates are connected to a terminal member505. All of the negative electrode plates of the unit power generation element contained in the sixth cell502fare connected to the strap504, while all of the positive electrode plates are connected to the terminal member505.

The strap504connected to the negative electrode plate of the unit power generation element contained in the first cell502a, is interconnected to the strap504which is connected to the positive electrode plates of unit power generation element contained in the second cell502b, via a through hole provided in the partition503. As shown inFIG. 45, the strap504connected to the negative electrode plates of the unit power generation element in the second cell502b, is interconnected to the strap504connected to the positive electrode plates of the unit power generation element in the third cell502c, via a through hole provided in the partition503. The strap504connected to the negative electrode plates of the unit power generation element in the third cell502c, is interconnected to the strap504connected to the positive electrode plates of the unit power generation element in the fourth cell502d, next to the third cell502cin the width direction of the case body502, via a through hole provided in the partition503.

The strap504connected to the negative electrode plates of the unit power generation element in the fourth cell502d, is interconnected to the strap504connected to the positive electrode plates of the unit power generation element in the fifth cell502e, via a through hole provided in the partition503. The strap504connected to the negative electrode plates of the unit power generation element in the fifth cell502e, is interconnected to the strap504of the positive electrode plates of the unit power generation element in the sixth cell502f, via a through hole provided in the partition503. Thus, the unit power generation elements contained in the cells502ato502fare connected in series. The terminal member505connected to the unit power generation element in the first cell502ais a positive terminal, while the terminal member505connected to the unit power generation element in the sixth cell502fis a negative terminal.

FIG. 45is a front view of an electrode plate510constituting the positive electrode plate or the negative electrode plate contained in the cells502ato502fof the conventional battery501. The electrode plate510has a rectangular electrode plate body513and a rectangular collector511which is provided at a side of the electrode plate body513, and projects from the electrode plate body513upward. The collector511is provided at the side edge of the electrode plate body513, leaving an appropriate spacing with respect to an end of the side of the electrode plate body513, and also leaving an appropriate spacing with respect to the center of the side of the electrode plate body513.

The thus-constructed electrode plate510is used in a manner as shown inFIG. 46A. Specifically, a pair of the electrode plates510are attached together via a separator, where the collectors511are positioned on the opposite sides, i.e., one of the electrode plates510is turned from side to side (by 180°) and is then attached to the other electrode plate510to obtain a positive electrode plate and a negative electrode plate.

In the unit power generation elements contained in the second cell502bto the fifth cell502e, as shown inFIG. 46B, one strap504is connected by welding to the collectors511of all of the electrode plates510constituting the positive electrode plates, while the other strap504is connected to the collectors511of all of the electrode plates510constituting the negative electrode plates.

As shown inFIG. 47, the strap504has an electrode plate connector504a, which is in the shape of a plate and is attached by welding to a top edge of the collector511provided in the electrode plate510, and an inter-cell connector504bwhich is bent extending upward from a side of the electrode plate connector504a. The electrode plate connector504ais attached by welding to the collector511of the electrode plate510constituting a positive electrode plate or a negative electrode plate, where the inter-cell connector504bis disposed along the partition503provided between the adjacent cells.

The collector511provided in the electrode plate510is made of the same material as that of the electrode plate510(e.g., lead (Pb) or lead oxide (PbO2)). Therefore, the collector511has a considerably large weight. It is preferable to reduce the width direction length of the collector511in order to reduce the weight of the collector511.

However, the strap504provided on the top portion of the collector511has to have a width direction length greater than the width direction length of the collector511. If the width direction length of the collector511is excessively smaller than the width direction length of the strap504, damage, such as rupture, may occur around the collector511due to wobble or the like. Therefore, an appropriate ratio of the width direction length of the strap504, to the width direction length of the collector511, is important in order to avoid damage, such as rupture, and to reduce the weight of the battery.

When the width direction length of the strap504provided on the top end of the collector511is excessively small as compared to the width direction length of the electrode plate510, the resistance of the strap504is high and a voltage drop is large in the case of discharging a large amount of current. Therefore, an appropriate ratio of the width direction length of the strap504to the width direction length of the electrode plate510is important in order to prevent a voltage drop.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a battery comprises at least four cells each comprising a bath in the shape of a rectangular parallelepiped having a width direction dimension greater than a thickness direction dimension, and a power generation element, the power generation element being contained in the bath, the thickness direction sides of the cells facing each other, and the width direction sides of the cells being arranged side by side. A coolant for cooling the cells is allowed to flow along the width direction sides of the cells.

In one embodiment of this invention, the flow of the coolant is branched into the thickness direction sides between the adjacent cells.

In one embodiment of this invention, the battery according further comprises a cooling box. The cells are contained in the cooling box, and a coolant channel is formed between an inner wall surface of the cooling box and the width direction sides of the cells, and between the width direction sides of the cells facing each other.

In one embodiment of this invention, a coolant channel is formed between the thickness direction sides of the cells facing each other.

In one embodiment of this invention, a coolant channel is formed between outer bottom sides of the baths and an inner bottom side of the cooling box.

In one embodiment of this invention, the outer bottom side of each bath is provided with a first depression or a first protrusion, and the inner bottom side of the cooling box is provided with a second protrusion or a second depression which is engaged with the first depression or the first protrusion.

In one embodiment of this invention, the inner wall surface of the cooling box facing the width direction sides of the cells is provided with first ribs for forming a coolant la channel. The width direction sides of the cells facing the inner wall surface of the cooling box are provided with second ribs for forming a coolant channel. The first ribs are abutted to the second ribs.

In one embodiment of this invention, the first ribs are attached to the second ribs by welding with sonication.

In one embodiment of this invention, each second rib is a protrusion and the protrusions are provided on the entire width direction side of each cell.

In one embodiment of this invention, the second ribs are arranged to form a channel such that the coolant is allowed to flow uniformly on the entire width direction side of each cell.

In one embodiment of this invention, the second ribs are in the shape of a line and divide the width direction side of each cell into a plurality of regions, and the plurality of regions are in communication with each other.

In one embodiment of this invention, each second rib has a cross section in the shape of any of a rectangle, a triangle, and a curve.

In one embodiment of this invention, the coolant is liquid.

In one embodiment of this invention, the power generation element comprises electrode plates laminated in parallel to the width direction side of the cell.

In one embodiment of this invention, the battery further comprises a battery case and a lid. The cells are integrally bound with the battery case, and are contained in the cooling box. The cooling box is sealed with the lid.

In one embodiment of this invention, the bath, the battery case, the lid and the cooling box are made of a synthetic resin. The bath is attached to the battery case by welding or adhesion. The lid is attached to the battery case and the cooling box by welding or adhesion.

According to another aspect of the present invention, a battery comprises a plurality of cells comprising a power generation element, in which a plurality of positive electrode plates and a plurality of negative electrode plates are alternately laminated via separators in the power generation element, a battery case integrally binding top portions of the cells, in which the cells are electrically connected to each other, a cooling box containing the cells and the battery case, in which a coolant channel is formed on sides of the cells, and a lid attached to a top portion of the cooling box, sealing the cells and the battery case contained in the cooling box. The lid is provided with battery terminals which are respectively connected to a positive terminal and a negative terminal of the cells. The battery case is provided with depressions, and the lid is provided with protrusions, the depressions being engaged with the corresponding protrusions.

In one embodiment of this invention, the battery case is integrally attached to the lid by welding.

In one embodiment of this invention, the battery case is integrally attached to the lid by adhesion.

In one embodiment of this invention, the battery terminals are provided on the lid by insert molding, and are cooled with the coolant in the cooling box.

According to another aspect of the present invention, a battery comprises positive electrode plates, negative electrode plates, and separators. The positive electrode plates and the negative electrode plates are alternately laminated via the separators. The positive electrode plates and the negative electrode plates each comprises an electrode plate body and a collector provided on the electrode plate body, the collectors of the positive electrode plates are attached to a first strap, and the collectors of the negative electrode plates are attached to a second strap. A length A of the collector of each electrode plate, a length W of the first and second straps along the collector, and a length X of the electrode plate body satisfy:

A>W/2, and

Thus, the invention described herein makes possible the advantages of providing: (1) a battery comprising a plurality of linked cells, in which each has a high level of cooling efficiency, cost for cooling each cell is low, and substantially no variation occurs in the life of each cell; (2) a battery, in which a battery case containing cells can be positioned with respect to a lid, and it is possible to prevent heat generation around terminals; and (3) a battery, in which the weight of the battery can be reduced while preventing damage, such as rupture, of a collector, and the width direction lengths of a strap and a collector can be appropriately adjusted so as to prevent voltage drop due to the increased high resistance of the strap.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a battery according to the present invention will be described with reference to the accompanying drawings.

FIG. 1is a perspective view showing a battery100according to Example 1 of the present invention, when viewed in a slanted direction from the front.FIG. 2is a perspective view showing the battery100, when viewed in a slanted direction from the rear. The battery100contains a plurality of cells. The cells are cooled with high cooling efficiency. The battery100comprises a cooling box10for cooling the cells and a lid20for sealing the cooling box10. The cooling box10and the lid20are made of a synthetic resin.

FIG. 3is a perspective view showing a battery100(note that the lid20is removed from the cooling box10). In the cooling box10, 6 cells30, which are arranged in a matrix of 3 rows×2 columns and connected in series, are integrally contained in a frame-like battery case40. The battery case40is made of a synthetic resin. The battery case40is provided with an inlet orifice41and an outlet orifice42, through which cooling water, which is a coolant for cooling the cells30, is injected or drained, at corresponding end portions thereof. The orifices41and42are each in the shape of a cylinder and project upward.

FIG. 4is a perspective view showing the battery case40in which the cells30are arranged in a matrix of 3 rows×2 columns and are integrally linked.FIG. 5is a perspective view showing the cells30in a matrix of 3 rows×2 columns, where the battery case40is removed.

As shown inFIG. 5, each of the cells30comprises a bath31containing a power generation element comprising positive electrode plates, negative electrode plates and separators. Each bath31is in the shape of a thin rectangular parallelepiped having a greater width direction dimension than a thickness direction dimension, and having a thickness direction side32and a width direction side33which has a greater width than that of the thickness direction side32. The bath31is made of a synthetic resin. The bath31contains a power generation element in which a plurality of positive electrode plates and a plurality of negative electrode plates are alternately laminated via grid-like separators holding dilute sulfuric acid or the like. The positive electrode plates and the negative electrode plates are in parallel to the width direction side33. The width direction side33of the bath31is provided with a plurality of protrusions34, which are in the shape of a cylinder and are uniformly distributed with predetermined spacing.

As shown inFIG. 4, the battery case40comprises a pair of width direction side holding portions43and a pair of thickness direction side holding portions44, which form the shape of a rectangular frame, so that top portions of the cells30in a matrix of 3 rows×2 columns are integrally bound. The inner space of the rectangular frame-like battery case40is divided equally into 3 portions in the longitudinal direction by a pair of thickness direction side holding portions44, and is also divided equally into 2 portions in the width direction by a width direction side holding portion43, thereby providing 3×2 hollow portions. The top portions of the cells30are fitted into the corresponding hollow portions. The battery case40is attached to the baths31of the cells30by welding or adhesion.

Referring toFIGS. 4 and 5, the three cells30forming a row are arranged so that the thickness direction sides32face each other, and the two cells30forming a column are arranged so that the width direction sides33face each other.

The four cells30other than the pair of cells30forming a row at an end of the battery are each provided with a positive electrode plate side strap35which is attached to all of the positive electrode plates in the bath31, and a negative electrode plate side strap35which is attached to all of the negative electrode plates in the bath31. Each strap35has an L-shaped cross section. The two cells30of the four cells30adjacent to each other in the column direction are connected in series, where the positive electrode plate side strap35of one of the two cells30is electrically connected to the negative electrode plate side strap35of the other cell30, via a through hole provided in the thickness direction side holding portions44between the cells30.

Among the four cells30, a pair of cells30forming a row at the other end of the battery are connected in series, where the positive electrode plate side strap35of one of the cells30is electrically connected to the negative electrode plate side strap35of the other cell30via a through hole provided in the width direction side holding portions43between the cells.

One of the pair of cells30forming a row at the end of the battery is provided with a positive electrode plate side strap35, which is connected to all of the positive electrode plates contained in the bath31, and a negative electrode plate side terminal36, which is connected to all of the negative electrode plates contained in the bath31, at a top portion thereof. The other cell30is provided with a negative electrode plate side strap35, which is connected to all of the negative electrode plates contained in the bath31, and a positive electrode plate side terminal36, which is connected to all of the positive electrode plates contained in the bath31, at a top portion thereof.

These cells30are connected in series, where the positive electrode side strap35in one of the cells30is electrically connected to the negative electrode side strap35in the other cell30adjacent to the one cell30in the column direction, via a through hole provided in the thickness direction side holding portion44between the cells, and where the negative electrode side strap35of the other cell30is electrically connected to the positive electrode side strap35in the one cell30adjacent to the other cell30in the column direction, via a through hole provided in the thickness direction side holding portions44between the cell. Thus, the 6 cells30arranged in a matrix of 3 rows×2 columns are connected along a U-shape in series.

The inlet orifice41and the outlet orifice42are provided outwardly from the middle of the respective thickness direction side holding portions44at the ends of the battery case40.

FIG. 6is a perspective view showing the cooling box10. The cooling box10is in the shape of a substantially hollow rectangular parallelepiped and has an open top. The 3×2-matrix cells30integrally bound in the battery case40are inserted into the cooling box10through the open top thereof. There is appropriate spacing between the inserted cells30and an inner wall surface11of the cooling box10. On the inner wall surface11of the cooling box10, a plurality of ribs12extending vertically are spaced parallel at appropriate intervals. The protrusions34provided on the width direction side33of the bath31of the cell30contained in the cooling box10are abutted to the vertically-extending ribs12provided on the inner wall surface11of the cooling box10, followed by welding using sonication. Thereby, space extending vertically is formed between the inner wall surface11of the cooling box10and each cell, by the ribs12on the inner wall surface11of the cooling box10and the protrusions34of the cells30.

FIG. 7is a perspective view showing the lid20when viewed from the same direction as that inFIG. 2. On an end of the lid20, two battery terminals21projecting upward are provided for connecting the cells30connected in series in the 3×2 matrix to the outside of the battery100. The battery terminals21are also electrically connected to the respective terminals36of the pair of cells30provided at the end of the cooling box10. The lid20is also provided with orifice holding holes22and23, through which the projecting inlet orifice41and outlet orifice42provided on the battery case40are respectively passed, at respective ends thereof.

After the battery case40containing the 6 cells30bound integrally is inserted into the cooling box10from the top thereof, the lid20is attached to the top of the battery case40in the cooling box10. In this situation, as shown inFIG. 2, the inlet orifice41and the outlet orifice42are passed through the respective orifice holding holes22and23provided in the lid20. The lid20is attached to the battery case40and the cooling box10by welding or adhesion.

FIG. 8is a perspective view showing a longitudinal cross section of the cooling box10in which the battery case40containing the 6 cells30bound integrally is inserted and to which the lid20is attached.FIG. 9shows the longitudinal cross section.FIG. 10is a perspective view showing a longitudinal cross section of an end of the battery, including the inlet orifice41.FIG. 11shows the longitudinal cross section.FIG. 12is a perspective view showing an enlarged cross section of the inlet orifice41and its surroundings.FIG. 13is a perspective view showing a longitudinal cross section and a transverse cross section of the end including the inlet orifice41.

A hollow injection header13is provided across a top outer portion of an end in the longitudinal direction of the cooling box10in the thickness direction. The injection header13has an open top. When the battery case40is inserted into the cooling box10, the inlet orifice41of the battery case40is located at the middle of the injection header13. The injection header13is supplied with a coolant through the inlet orifice41. The injection header13is in communication with space between the cell30contained in the cooling box10and the inner wall surface11of the cooling box10.

A hollow drain header14is provided across a top outer portion of the other end in the longitudinal direction of the cooling box10in the thickness direction. The drain header14has an open top. When the battery case40is inserted into the cooling box10, the outlet orifice42of the battery case40is located at the middle of the drain header14. The drain header14is also in communication with space between the cell30contained in the cooling box10and the inner wall surface11of the cooling box10. The drain header14is supplied with a coolant, which has been used to cool the cells30, from the cooling box10, and the coolant is drained from the outlet orifice42.

Next, a relationship between a depression45provided in the battery case40and a protrusion24provided in the lid20will be described.FIG. 14is a perspective view showing the battery case40contained in the cooling box10according to Example 1 of the present invention.FIG. 15is a perspective view for explaining the depression45provided in the battery case40.FIG. 16is a perspective view showing a substantial portion of the battery case40.FIG. 17is a front view of the battery case40. Two trapezoidal depressions45are provided in the thickness direction side holding portion44, which is the closest to the inlet orifice41of the four thickness direction side holding portions44of the battery case40. The two depressions45are provided at positions of the thickness direction side holding portion44which faces the lid20and correspond to the two cells30provided at the inlet orifice41side.

FIG. 18is a perspective view for explaining the protrusion24provided in the lid20of the battery100according to Example 1 of the present invention.FIG. 19is a front view showing the protrusion24. The lid20is provided with the two protrusions24which are engaged with the two depressions45provided in the thickness direction side holding portion44of the battery case40. The protrusion24has a side in the shape of a trapezoid and the base of the trapezoid contacts the lid20.

When the lid20is attached to the cooling box10containing the battery case40, the two protrusions24provided in the lid20are engaged with the two depressions45provided in the thickness direction side holding portion44, respectively. The inlet orifice41and the outlet orifice42provided in the battery case40are passed through the respective orifice holding holes22and23provided in the lid20.

As described above, according to Example 1, the two protrusions24provided in the lid20are engaged with the two depressions45provided in the thickness direction side holding portion44of the battery case40, respectively, so that the cooling box10containing the battery case40can be positioned with respect to the lid20. Therefore, the cooling box10containing the battery case40can be reliably sealed by the lid20.

In addition, after the protrusions24of the lid20are engaged with the respective depression45of the battery case40so that the lid20seals the battery case40, the battery case40and the lid20may be integrally attached to each other by welding or adhesion. The welding or adhesion can ensure the sealing of the cells30into the cooling box10.

The sealing of the cooling box10and the lid20can be achieved by a simple structure such that the protrusions24provided in the lid20are engaged with the respective depressions45provided in the battery case40. Thus, since there is substantially no excess structure, the cooling efficiency of the cells30contained in the cooling box10can be improved.

Further, with the above-described configuration, the lid20is correctly positioned with respect to the cooling box10so that the lid20can reliably seal the cooling box10. Therefore, even in applications in which the battery experiences strong vibration in an automobile or the like, the lid20is unlikely to be removed from the cooling box10, so that it is possible to prevent the coolant from entering from the coolant channel to the power generation element.

FIG. 20is a perspective view showing a longitudinal cross section of the battery100taken through one of the battery terminals21, in which the battery case40contains the 6 cells30and the lid20is attached to the cooling box10.FIG. 21is a perspective view showing a longitudinal cross section of an end of the battery100, at which one of the two battery terminals21is provided.FIG. 22shows the longitudinal cross section.

When the lid20is attached to the cooling box10, the two battery terminals21are located over the injection header13. Each battery terminal21is in the shape of a bolt, and is integrated with the lid20by insert molding. In this situation, the two battery terminals21are electrically connected to the respective terminals36of a pair of cells30disposed at an end of the 3×2 matrix of the cells30, the pair of cells30constituting a row of the matrix, via a connecting member provided in the lid20. In this manner, the two battery terminals21allow the 3×2 matrix cells30connected in series to connect to the outside.

FIG. 23is a perspective view showing the bath31of the cell30according to Example 1, when viewed from the bottom.FIG. 24is a perspective view of the cooling box10ofFIG. 6cut out vertically along AOA′ ofFIG. 6, when viewed from the top, showing the inner bottom side and the inner wall surface of the cooling box10. Referring toFIG. 23, a plurality of depressions38are provided on the bottom side37of the bath31. The depression38is in the shape of a circle. One depression38is provided at each of the four corners of the bottom side37, and at the middle of each of the two longer sides and the two shorter sides, and further at the center of the bottom side37. That is, a total of nine depressions38are disposed in a matrix of 3 rows×3 columns. The depression38disposed at the center of the bottom side37has a larger diameter than that of the other depressions38. Referring toFIG. 24, 9 protrusions16are provided on the inner bottom side15of the cooling box10, which correspond to the 9 depressions38provided on the bottom side37of the bath31. The 9 protrusions16are fitted and engaged with the respective depressions38. With the depressions38and the protrusions16, the bath31and the cooling box10are positioned with respect to each other, so that the cell30contained in the cooling box10is sealed.

FIG. 25is a top view of the battery100of Example 1, schematically showing the coolant channel. As described above, the cooling box10contains the 6 baths31of the cells30disposed in the 3×2 matrix.

As shown inFIG. 25, a coolant channel51is provided on the opposite sides of the cooling box10by spacing between the inner wall surface11of the cooling box10and the width direction sides33of the cells30facing thereto. The coolant channel51is surrounded by the width direction sides33, the inner wall surface11, the protrusions34(FIG. 4) provided on the width direction sides33, and the ribs12(FIG. 6) provided on the inner wall surface11. A coolant channel52is provided between the width direction sides33facing inwardly of the baths31. The coolant channel52is surrounded by the width direction sides33and the protrusions34(FIG. 4) provided on the width direction sides33. Four coolant channels53are provided between the thickness direction sides32facing each other. The coolant channel53is in communication with the coolant channels51and52. The coolant channels51and52are in communication with the injection header13(FIG. 8) and the drain header14(FIG. 8).

In the battery100having the coolant channels51,52and53, a part of the coolant injected from the inlet orifice41is allowed to flow through the injection header13and then through the central coolant channel52in a direction indicated by arrow55, forcibly cooling the width direction sides33forming the coolant channel52. The remaining part of the coolant injected from the injection header13(FIG. 8) is allowed to flow through the coolant channels51on the opposite sides of the cooling box10in a direction indicated by arrow54, forcibly cooling the width direction sides33forming the coolant channel51. A part of the coolant flowing through the central coolant channel52is branched into the four coolant channels53in a direction indicated by arrow56. The coolant flowing through the coolant channel53is merged with the coolant flowing through the coolant channel51. The coolant flowing through coolant channels51and52are drained through the drain header14(FIG. 8) from the outlet orifice42.

The coolant flowing through the coolant channels51and52forms a main stream, while the coolant flowing through the coolant channel53branched from the coolant channel52forms a branched stream. Thus, the coolant channels51and52are provided so that the main coolant stream runs in a direction a long the width direction side33and perpendicular to the thickness direction side32.

Referring back toFIG. 22, the battery terminals21are provided over the respective injection headers13. The battery terminal21is cooled by heat exchange with the coolant passing through the injection header13below. Thus, the coolant is injected through the injection header13provided below the battery terminal21, is then allowed to flow through the coolant channels, and is finally drained from the drain header14. Therefore, even if a large amount of current flows through the battery terminal21when the battery100is discharged, the battery terminal21can be effectively cooled, thereby making it possible to avoid damages, e.g., to prevent the surroundings of the battery terminal21from being melted by excessive heat generation of the battery terminal21.

According to Example 1 of the present invention, the main coolant stream in the coolant channels51and52flows along the width direction sides33of the cells30. Therefore, the main coolant stream runs in a direction parallel to the electrode plate contained in the bath31. Therefore, the electrode plate is forcibly cooled by the coolant efficiently. As a result, a higher level of cooling efficiency can be obtained.

Further, according to Example 1 of the present invention, the main coolant stream runs in a direction perpendicular to the thickness direction side32. Therefore, the bath31can be cooled with simple structure in which a single inlet orifice41and a single outlet orifice42are provided. Therefore, the battery of the present invention has a simpler structure for cooling the cells30than the above-described conventional structure which requires an arrangement for distributing a coolant to a plurality of coolant channels, leading to a reduction in the number of assembly steps and cost.

FIG. 26is diagram for explaining a current path in the battery100of Example 1 of the present invention.FIG. 27is a diagram for explaining a current path in a battery200as a comparative example. Referring toFIG. 26, as described inFIGS. 4 and 5, the 6 cells30are arranged in a matrix of 3 rows×2 columns. The two central cells30are electrically connected via the straps35to the respective cells30adjacent thereto on the opposite sides of the battery100. The two columns of the cells30are electrically connected to each other via the straps35provided to the two cells30on one end of the battery100. Thus, the 6 cells30are linked to each other in series in substantially a U shape. Therefore, the current path in the battery100of Example 1 is in the substantial U shape indicated by arrow B.

Referring toFIG. 27, in the battery200of the comparative example, the 6 cells230are disposed side by side where the width direction sides thereof face each other, and the straps235are disposed alternately near one thickness direction side and then the other thickness direction side, linking the 6 cells230disposed in a matrix of 1 rows×6 columns in series. Therefore, the current path in the battery200of the comparative example meanders over a long distance in a direction along the width direction side indicated by arrow C.

Thus, the cells30in the battery100of Example 1 are arranged in the 3×2 matrix, linked to each other in series in the U shape. Therefore, the current path is shorter than that in the comparative example. For this reason, loss due to the connecting portions between the cells30can be reduced, thereby reducing heat generation. As a result, high power can be obtained.

FIG. 28is a diagram for explaining expansion of the cells30in the battery100of Example 1. Referring toFIG. 28, the cells30, which expand in a direction perpendicular to the width direction side, are arranged in a matrix of 3 rows×2 columns where the 3 cells in each column have their thickness direction sides facing each other and the two cells in each row have the width direction side facing each other. Thus, in the battery100of Example 1, only two cells30are disposed in a direction perpendicular to the width direction side, i.e., a direction in which the cell30expands. Therefore, as compared to the conventional arrangement shown inFIG. 40in which all 6 cells are lined up in a direction perpendicular to the width direction side, the influence of the expansion of the cell in Example 1 on other cells is small, whereby the total amount of expansion of the cells can be reduced.

FIG. 29is a graph for explaining the expansion of the cells30in the battery100of Example 1. The horizontal axis indicates the reference numerals for the cells inFIG. 28, while the vertical axis indicates the amount of expansion of each cell. As shown inFIG. 29, in the battery100of Example 1, since the influence of expansion of a cell on other cells is small, the amount of expansion of each cell is uniform. As opposed to this, in the conventional arrangement shown inFIGS. 40 and 41, the further out the location of the cell, the larger the amount of expansion of the cell.

FIG. 30is a graph for explaining the life characteristics of the cells30in the battery100of Example 1. The horizontal axis indicates the number of discharging cycles of each cell, while the vertical axis indicates the voltage of each cell. Since, as described inFIG. 29, the amount of expansion of the cells30is uniform, variations in the voltage between each cell are suppressed. Therefore, since the variation in voltage is small, electrolytic solution is not substantially dried up. Thus, as shown inFIG. 30, there is substantially no variation in the lives of a plurality of cells constituting a battery.

FIG. 31is a diagram for explaining a temperature distribution of the cells30in the battery100of Example 1. The horizontal axis indicates the reference numerical of the cells inFIG. 28, while the vertical axis indicates the temperatures of the cells. The arrangement of Example 1 has a higher level of cooling efficiency than that of the conventional arrangement, and all of the cells have the same area contacting the coolant. Therefore, even if the battery100is used in an EV which has a large amount of input and output current, there is substantially no variation in temperature between each cell, unlike the conventional arrangement, as shown inFIG. 31.

The cylindrical protrusions34ofFIG. 4have a rectangular cross section. The cross section of the protrusions34may be in the shape of a cone and may have a triangular or a curved cross section. Moreover, the protrusions34may be in the shape of a polygonal prism, a polygonal pyramid, or the like.

FIG. 32is a perspective view showing another bath131according to Example 1 of the present invention. The width direction side133of the bath131is provided with a plurality of ribs134A and134B which form a coolant channel. The ribs134A and134B are in the shape of a line extending in a vertical direction, and are disposed parallel to each other at appropriate intervals. The rib134A extends upward from the lower end of the width direction side133, but does not reach the upper end thereof. The rib134B extends downward from the upper end of the width direction side133, but does not reach the lower end thereof. A coolant is allowed to flow along the ribs134A and134B in a direction indicated by arrow A, meandering in a vertical direction on the width direction side133. Thus, the arrangement of the ribs134A and134B allows the coolant to flow over the entire width direction side133uniformly. As described above, when the bath131is applied to the battery100of Example 1, the coolant injected from the inlet orifice41meanders vertically on the width direction side133in the bath131and flows uniformly over the entire width direction side133, thereby further improving cooling efficiency.

FIG. 33is a perspective view showing cross sections of the other ribs provided on the width direction side133of the bath131.FIG. 34shows the cross section. Ribs134C,134D,134E and134F, which are in the shape of a vertical line, are provided parallel to each other on the width direction side133. The rib134C has a rectangular cross section taken in a direction perpendicular to the extending direction of the rib134C. The cross section of the rib134C maybe rectangular, or alternatively triangular as is the rib134D, or curved as are the ribs134E and134F.

FIG. 35is a cross sectional view of other ribs provided on the width direction side133of the bath131. The ribs134G,134H,134I and134J are provided on the width direction side133, extending horizontally. The rib134G has a rectangular cross section taken in a direction perpendicular to the extending direction of the rib134G. The cross section of the rib134G may be rectangular, or alternatively triangular as is the rib134H, curved as is the ribs134I, or trapezoidal as is the rib134J.

FIG. 36is a perspective view showing a battery according to Example 2 of the present invention.

A battery301according to Example 2 of the present invention has a case body302in the shape of a hollow rectangular parallelepiped having an open top. The inner space of the case body302is divided with a partition303into first to sixth cells302ato302f. Specifically, the inner space of the case body302is divided into three portions in the longitudinal direction and into two portions in the width direction, forming the 6 cells302ato302f. The cells302ato302feach have a cross section in the shape of a rectangle elongated in the longitudinal direction of the case body302.

The cells302ato302feach comprise a unit power generation element containing a plurality of positive electrode plates (e.g., PbO2plates) having a similar planar shape and a plurality of negative electrode plates (e.g., Pb plates) having a similar planar shape. In the unit power generation element, the positive electrode plates and the negative electrode plates are alternately laminated via separators made of porous, extremely fine glass fibers holding dilute sulfuric acid, or the like.

At one end of the case body302, the first cell302aand the sixth cell302fare disposed side by side in a width direction of the case body302. The first cell302a, the second cell302band the third cell302care disposed side by side in a longitudinal direction of the case body302. The third cell302cand the fourth cell302dare disposed side by side in the width direction of the case body302. The fifth cell302eis disposed between the fourth cell302dand the sixth cell302f. The positive electrode plates and the negative electrode plates of the unit power generation element of each cell302ato302fare each extending in the longitudinal direction of the case body302.

All of the positive electrode plates of each unit power generation element of the second cell302bto the fifth cell302e(i.e., excluding the first cell302aand the sixth cell302f) are connected to a first strap304provided on one side of the positive electrode plate. All of the negative electrode plates of each unit power generation element are connected to a second strap304provided on a side of the negative electrode plate opposite to the first strap304provided on the side of the positive electrode plate. The first strap304is conductive to all of the positive electrode plates, while the second strap304is conductive to all of the negative electrode plates.

All of the positive electrode plates of the unit power generation element contained in the first cell302aare connected to the first strap304, while all of the negative electrode plates are connected to a terminal member305. All of the negative electrode plates of the unit power generation element contained in the sixth cell302fare connected to the second strap304, while all of the positive electrode plates are connected to the terminal member305.

The second strap304connected to the negative electrode plate of the unit power generation element contained in the first cell302ais interconnected to the first strap304which is connected to the positive electrode plates of unit power generation element contained in the second cell302bvia a through hole provided in the partition303. As shown inFIG. 39, the second strap304connected to the negative electrode plates of the unit power generation element in the second cell302bis interconnected to the first strap304connected to the positive electrode plates of the unit power generation element in the third cell302c, via a through hole provided in the partition303. The second strap304connected to the negative electrode plates of the unit power generation element in the third cell302cis interconnected to the first strap304connected to the positive electrode plates of the unit power generation element in the fourth cell302dnext to the third cell302cin the width direction of the case body302via a through hole provided in the partition303.

The second strap304connected to the negative electrode plates of the unit power generation element in the fourth cell302dis interconnected to the first strap304connected to the positive electrode plates of the unit power generation element in the fifth cell302e, via a through hole provided in the partition303. The second strap304connected to the negative electrode plates of the unit power generation element in the fifth cell302eis interconnected to the first strap304of the positive electrode plates of the unit power generation element in the sixth cell302f, via a through hole provided in the partition303. Thus, the unit power generation elements contained in the cells302ato302fare connected in series. The terminal member305connected to the unit power generation element in the first cell302ais a positive terminal, while the terminal member305connected to the unit power generation element in the sixth cell302fis a negative terminal.

FIG. 37is a front view of an electrode plate310constituting the positive electrode plate or the negative electrode plate contained in the cells302ato302fof the battery301of Example 2. The electrode plate310has a rectangular electrode plate body313and a rectangular collector311which is provided at a side of the electrode plate body313and projects from the electrode plate body313upward. The collector311is provided at the side edge of the electrode plate body313, leaving an appropriate spacing with respect to an end of the side of the electrode plate body313and also leaving an appropriate spacing with respect to the center of the side of the electrode plate body313. The collector311has a predetermined length of A.

The thus-constructed electrode plate310is used in a manner as shown inFIG. 38A. Specifically, a pair of the electrode plates310are attached together via a separator, where the collectors311are positioned on the opposite sides, i.e., one of the electrode plates310is turned from side to side and is then attached to the other electrode plate310to obtain a positive electrode plate and a negative electrode plate.

In the unit power generation elements contained in the second cell302bto the fifth cell302e, as shown inFIG. 38B, one strap304is connected by welding to the collectors311of all of the electrode plates310constituting the positive electrode plates, while the other strap304is connected to the collectors311of all of the electrode plates310constituting the negative electrode plates.

In this case, the inner end side of the strap304is substantially continuously adjacent to the inner end side of the collector311.

The strap304has an electrode plate connector304a, which is in the shape of a plate and is attached by welding to a top edge of the collector311provided in the electrode plate310, and an inter-cell connector304b, which is bent extending upward from a side of the electrode plate connector304a. The electrode plate connector304ais attached by welding to the collector311of the electrode plate310constituting a positive electrode plate or a negative electrode plate, where the inter-cell connector304bis disposed along the partition303provided between the adjacent cells.

The length A of the collector311of the electrode plate310is related to the length W of the electrode plate310along the collector311as follows:

Further, the length A of the collector311of the electrode plate310is related to the length (width) X of the electrode plate body310along the collector311as follows:

Next, an example relating to the bonding strength between the unit power generation element and the strap will be described.

As the electrode plate used in the battery301, an electrode plate310having an electrode plate body313, having a height of 115 mm and a width of 100 mm, was used as a positive electrode plate or a negative electrode plate. 15 electrode plates were prepared as negative electrode plates and were arranged so that their collectors311were located at the same side, while 14 electrode plates were prepared as positive electrode plates and were arranged so that their collectors311were located on the opposite side. The negative electrode plates and the positive electrode plates were alternately laminated via separators to obtain a unit power generation element. The electrode plate connector304aof the strap304at one side was attached by welding to the top edges of the collectors311provided on the top ends of the electrode plates310as positive electrode plates, while the electrode plate connector304aof the strap304at the other side was attached by welding to the top edges of the collectors311provided on the top ends of the electrode plates310as negative electrode plates. The electrical capacity of the unit power generation element was assumed to be 60 Ah.

Note that the width direction length of the electrode plate body313along the collector311is represented by X, the length of the collector311is represented by A, and the length of the strap304along the collector311is represented by W.

The electrode plate310had the electrode plate body313in the shape of a rectangle having a constant width direction length (X) of 115 mm and a constant height of 100 mm. The width direction length A of the collector311and the length W of the strap304were changed in various ways. The unit power generation element to which a pair of straps304were attached were subjected to a drop test and a voltage drop test. In the drop test, the unit power generation element was dropped from a predetermined height and thereafter the amount of deformation of the strap304was investigated. In the voltage drop test, after the drop test, the unit power generation element was discharged for a predetermined time from the full charge state and the amount of voltage drop was measured.

In the drop test, the unit power generation element to which the straps304were attached was turned upside down and was dropped from a height of 1 m, and thereafter, the amount of deformation of each strap304was measured. The results are shown in Table 1.

TABLE 1Length ALength W of strapof collectorX/10X/5X3/10X2/5X/2W/10N/AN/AN/A5N/AW/5N/A145N/AW3/10N/A124N/AW2/50012N/AW/20000N/AW3/50000N/AW7/100000N/AW4/50000N/AW9/100000N/AW0000N/AN/A: The battery could not actually be produced.

Referring to Table 1, when the length A of the collector311was greater than ½ the length W of the strap304(i.e., A>W/2), the strap304was not substantially deformed by the drop test. In contrast, when the length A of the collector311was smaller than ½ the length W of the strap304(i.e., A<W/2), the strap304was sometimes deformed by the drop test. The smaller the length A of the collector311, the greater the amount of deformation of the strap304.

Therefore, it is preferable that the length A of the collector311is greater than ½ the length W of the strap304(i.e., A>W/2).

Note that in Table 1, when the length W of the strap304is equal to ½ of the width direction length X of the electrode plate body313, the total of the lengths of a pair of strap304provided on the unit power generation element (W×2) is equal to the width direction length X of the electrode plate body313. In this case, the straps304having such a length needed to be separated from each other on the unit power generation element, generating wasted space. Therefore, such a strap was not produced in this experiment.

When the length W of the strap304is equal to 1/10 the width direction length X of the electrode plate body313and the length A of the collector311is 1/10 to 3/10 the length W of the strap304, the length A of the collector311is equal to 1/10× 1/10 to 3/10× 1/10 the width direction length X of the electrode plate body313, i.e., about 1 mm to about 3 mm in the case of the electrode plate body313of 115 mm×100 mm. It is difficult to produce a collector311having such a small length. Such a collector311was not prepared in this experiment.

Further, when the length W of the strap304is ⅕ or 3/10 the width direction length X of the electrode plate body313and the length A of the collector311is 1/10 the length W of the strap304, the length A of the collector311is very small. In this case, it is similarly difficult to produce a collector311having such a small length. Such a collector311was not prepared in this experiment.

Next, the amount of voltage drop of the unit power generation element after the drop test was measured by discharging at240A for 10 seconds. The results are shown in Table 2. Note that in Table 2, an amount of voltage drop, where the length W of the strap304is ⅖ the width direction length X of the electrode plate body313, and the length A of the collector311is equal to the length W of the strap304, is defined as a reference value (1.00).

TABLE 2Length ALength W of strapof collectorX/10X/5X3/10X2/5X/2W/21.431.161.121.10N/AW4/51.321.091.061.03N/AW1.271.051.021.00N/AN/A: The battery could not actually be produced.

Referring to Table 2, the smaller the length W of the strap304, the greater the amount of voltage drop.

Specifically, when the length W of the strap304was lowered from ⅕ to 1/10 the width direction length X of the electrode plate body313, the amount of voltage drop was particularly significant.

Therefore, according to Table 2, the length W of the strap304is preferably at least ⅕ the width direction length X of the electrode plate body313in terms of prevention of voltage drop.

In summary of the experimental results, the weight of the strap304or the like can be reduced while avoiding damages, such as deformation, provided that the following conditions are satisfied:

A>W/2, and

where A represents the length of the collector311, W represents the length of the strap304along the collector311, and X represents the width direction length of the electrode plate body313. In this case, the strap304can be prevented from having a high resistance, that is, voltage drop due to such a high resistance can be avoided.

The battery301of Example 2 maybe of either an open type or a sealed type. When the battery301is used as a power source for an electric vehicle or the like, the sealed type, which can resist strong wobble, is preferable.

According to the present invention, it is possible to provide a battery comprising a plurality of linked cells, which has a high level of cooling efficiency for cooling the cells.

Further, according to the present invention, it is possible to provide a battery comprising a plurality of linked cells, which can cool the cells with low cost.

Furthermore, according to the present invention, it is possible to provide a battery comprising a plurality of linked cells, in which there is substantially no variation in the lives of the cells.

In the battery of the present invention, a bath is provided with a depression, and a lid is provided with a protrusion, which is to be engaged with the depression. Therefore, by simply fitting and engaging the protrusion of the lid with the depression of the bath, the lid can be correctly positioned with respect to a cooling box, so that the cells contained in the cooling box can be easily sealed.

In the battery of the present invention, the length A of a collector, the length W of a strap along the collector, and the width direction length W of an electrode plate body satisfy the relationships, A>W/2 and X/5≦W<X/2. Therefore, damages, such as deformation of the strap, can be avoided and the weight of the battery can be reduced. Further, the strap can be prevented from having a high resistance, that is, voltage drop due to such a high resistance can be avoided. The battery is preferably used in applications, in which the battery is strongly wobbled, such as an automobile.