JP2020166963A - Secondary battery - Google Patents

Abstract

To provide a secondary battery in which degradation in the durability of a resin case can be suppressed.SOLUTION: A secondary battery comprises: an electrode plate group in which rectangular positive electrode plates and rectangular negative electrode plates are laminated via a separator; electrolyte; and a resin battery case 100b which houses the electrode plate group and the electrolyte. In the secondary battery, two lateral sides of the electrode plate group each fixed by the collector plates have a first thickness in a lamination direction, while a portion sandwiched by the two lateral sides of the electrode plate group has a second thickness thicker than the first thickness and expanding in an arc in the lamination direction. An inner surface 111 of the battery case 100b facing the lamination direction of the electrode plate group has an arc-shaped surface which corresponds to the arc shape of the electrode plate group expanding in the lamination direction.SELECTED DRAWING: Figure 4

Description

The present invention relates to a secondary battery.

In general, a nickel-metal hydride secondary battery, which is a secondary battery having high energy density and excellent reliability, is widely used as a power source for portable devices and portable devices, and as a power source for electric vehicles and hybrid vehicles. In a nickel-metal hydride secondary battery, a positive electrode plate containing nickel hydroxide as a main component, a negative electrode plate containing a hydrogen storage alloy as a main component are laminated via a separator, and an alkaline electrolytic solution is used as a case. It consists of being contained.

In a nickel-metal hydride secondary battery, a hydrogen storage alloy expands due to charging to store hydrogen, so that a case accommodating a group of electrode plates is pressed outward and expands. For example, Patent Document 1 describes an example of a secondary battery corresponding to expansion.

The secondary battery described in Patent Document 1 has a battery pack capable of absorbing the expansion of the battery that occurs during the charge / discharge cycle of the square battery. The battery pack has a resin case in which a plurality of square elementary batteries are arranged at predetermined positions on the same plane via positioning ribs. A recess is formed on the inner surface of the resin case at a position facing the side surface of the square battery to absorb the bulge of the square battery. The recess has a substantially arcuate cross section and is formed between the positioning ribs. This prevents the outer shape and appearance of the battery pack from changing due to swelling due to an increase in internal pressure during the battery charge / discharge cycle.

JP-A-10-340710

In the secondary battery, the expansion pressure from the electrode plate group is applied to the resin case for accommodating the electrode plate group each time the electrode plate group expands due to charging and discharging. Such repeated stress concentration in the resin case may reduce the durability of the resin case.

It should be noted that these problems are not limited to the nickel-metal hydride secondary battery, but the same applies to other secondary batteries such as a lithium ion secondary battery in which the electrode plate group expands due to charging / discharging or the like.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a secondary battery capable of suppressing a decrease in durability of a resin case.

The secondary battery for solving the above-mentioned problems accommodates a group of electrode plates in which a rectangular positive electrode plate and a rectangular negative electrode plate are laminated via a separator, an electrolytic solution, the electrode plate group, and the electrolytic solution. The two side surfaces of the electrode plate group, which are provided with a resin case and are fixed to each other by a current collector plate, have a first thickness in the stacking direction and are sandwiched between the two side sides of the electrode plate group. The portion has a second thickness that is thicker than the first thickness and bulges in an arc shape in the stacking direction, and the facing surface of the case facing the stacking direction of the electrode plate group bulges in the stacking direction. It has an arcuate surface corresponding to the arcuate shape of the electrode plate group.

According to such a configuration, before charging / discharging with little bulge of the electrode plates, the facing surface of the case facing the stacking direction of the electrode plates is recessed in the center corresponding to the arc shape which is the bulge of the electrode plates. By forming the surface, a wide contact area is secured between the portion sandwiched between the two side surfaces of the electrode plate group and the facing surface of the case. Then, after charging / discharging in which the swelling of the electrode plates becomes large, the expansion force due to the expansion of the electrode plates is dispersed and received over the entire facing surface of the case. Therefore, since the pressing force from the electrode plate group is received over a wide range of the case, the load per unit area applied to the case is reduced. As a result, the decrease in durability of the resin case is suppressed.

Further, since a wide contact area between the facing surface of the case and the electrode plate group can be secured from before charging / discharging to after charging / discharging, a high heat dissipation effect can be obtained.
As a preferred configuration, of the distance between the two facing surfaces facing each other in the case, the distance between the portions accommodating the two side sides of the plate group is set as the first distance, and the distance between the two side sides of the plate group is set as the first distance. When the interval is the second interval, the first interval is longer than the first thickness and shorter than the second thickness, and the second interval is substantially equal to the second thickness.

According to such a configuration, the arc shape of the electrode plate group and the arc shape of the facing surface of the case are close to each other. Therefore, it is possible to suppress a decrease in the durability of the case. In addition, the heat dissipation effect is easily exhibited.

As a preferred configuration, the inner surface of the outer wall of the case is the arc-shaped facing surface, and the outer surface of the outer wall is a linear surface.
According to such a configuration, the outer wall of the case is thick at the portion accommodating the two side sides of the electrode plate group and thin at the center between the two side sides of the electrode plate group. That is, the inside of the case is an arc shape, and the outer surface of the case is a straight plane. According to such a configuration, the expansion force inward of the case is distributed in the stacking direction and the surface direction of the facing surface. Therefore, stress concentration on the end of the outer wall of the case is suppressed.

As a preferred configuration, a battery module including the plurality of cases is provided, and the battery module is partitioned between two adjacent cases by a partition wall.
According to such a configuration, the stress concentration on the connection portion between the outer wall of the case and the partition wall is relaxed in the case partitioned by the partition wall.

As a preferred configuration, the cross section of the connecting portion between the facing surface and the side surface parallel to the stacking direction in the portion accommodating the two side sides of the electrode plate group of the case is a surface having a first arc. In the portion accommodating between the two side sides of the electrode plate group, the cross section of the facing surface is a surface having a second arc having a diameter larger than the first arc corresponding to the arc shape of the electrode plate group.

According to such a configuration, in addition to distributing the pressing force, the position where the stress is concentrated can be changed from the connecting portion between the facing surface and the side surface of the case to the facing surface side away from the connecting portion. it can. As a result, stress concentration is relaxed.

According to the present invention, it is possible to suppress a decrease in the durability of the resin case.

The front sectional view which shows one Embodiment of a secondary battery. The cross-sectional view which shows the enlarged cross-sectional structure of the electrode plate group of the same embodiment. The schematic diagram which shows typically the top view structure before the electric tank insertion of the electrode plate group of the same embodiment. The schematic diagram which shows typically the top view structure before the electrode plate group insertion of the case of the same embodiment. Explanatory drawing explaining the force applied to the partition wall and the side wall of the same embodiment. FIG. 6 is a schematic view schematically showing a top view structure of the case before inserting the battery case for other embodiments of the secondary battery.

An embodiment of the secondary battery will be described with reference to FIGS. 1 to 5.
As shown in FIG. 1, the secondary battery of the present embodiment is a square sealed battery formed by electrically connecting a plurality of nickel-metal hydride secondary batteries (cell batteries) in series.

Here, this square sealed battery has a rectangular parallelepiped square case 300 composed of an integrated battery 100 capable of accommodating a plurality of single batteries and a lid 200 for sealing the same battery 100. ing. As the square case 300, a resin case can be used. A plurality of irregularities (not shown) are formed on the surface of the square case 300 in order to improve heat dissipation when the battery is used.

The integrated electric tank 100 constituting the square case 300 is made of a synthetic resin material having resistance to an alkaline electrolytic solution such as polypropylene or polyethylene. A partition wall 110 is formed inside the integrated battery 100 in the form of partitioning a plurality of cells, and the portion partitioned by the partition 110 becomes the battery 100b for each cell. The integrated electric tank 100 has, for example, six electric tanks 100b, and FIG. 1 shows four of them.

In the electric tank 100b partitioned in this way, the electrode plate group 140, the positive electrode current collectors 150 and the negative electrode current collectors 160 joined to both sides thereof are housed together with the electrolytic solution.
As shown in the enlarged cross-sectional structure of the cell as seen from the upper surface of FIG. 2, the electrode plate group 140 is configured by laminating a rectangular positive electrode plate 141 and a negative electrode plate 142 via a separator 143. At this time, the direction in which the positive electrode plate 141, the negative electrode plate 142, and the separator 143 are laminated is the stacking direction (the direction of the first thickness D1 and the second thickness D2 in FIG. 2). The positive electrode plate 141 and the negative electrode plate 142 of the electrode plate group 140 are formed by the lead portion 141a of the positive electrode plate 141 and the lead portion 142a of the negative electrode plate 142 by projecting to the side portions opposite to each other in the direction of the plate surface. The current collector plates 150 and 160 are joined to the side edge edges of the lead portions 141a and 142a, respectively. Further, outer peripheral separators 144 are provided on both side surfaces of the electrode plate group 140 so as to sandwich the electrode plate group 140 in the stacking direction. The electrode plate group 140 has a width W1 in the width direction from one current collector plate 150 to the other current collector plate 160. Further, the electrode plate group 140 has a first thickness D1 on each side side 140S close to each of the current collector plates 150 and 160 in the stacking direction, and is a central portion in the width direction which is a portion sandwiched between the two side sides. The 140C has a second thickness D2.

Further, as shown in FIG. 1, a through hole 170 used for connecting each electric tank 100b is formed in the upper part of the partition wall 110. In the through hole 170, two connection protrusions 151 and 161 of the connection protrusion 151 protruding from the upper part of the current collector plate 150 and the connection protrusion 161 protruding from the upper part of the current collector plate 160 are connected to each other. By welding and connecting through the through hole 170, the electrode plate group 140 of the adjacent electric tanks 100b is electrically connected in series. Of the through holes 170, the through holes 170 located outside each of the electric tanks 100b at both ends are equipped with a positive electrode connection terminal 120 or a negative electrode connection terminal (not shown) above the end side wall of the integrated electric tank 100. The connection terminal 120 of the positive electrode is welded and connected to the connection protrusion 151 of the current collector plate 150. The connection terminal of the negative electrode is welded and connected to the connection protrusion 161 of the current collector plate 160. The electrode plate group 140 connected in series in this way, that is, the total output of the plurality of cell cells is taken out from the positive electrode connection terminal 120 and the negative electrode connection terminal.

On the other hand, the lid 200 constituting the square case 300 includes an exhaust valve 210 that releases gas to release the internal pressure when the internal pressure of the square case 300 exceeds a predetermined valve opening pressure, and an electric tank 100b. A sensor mounting hole 220 for mounting a sensor for detecting the internal temperature of the lid is provided. The sensor mounting hole 220 makes it possible to measure the temperature of the electrode plate group 140 by a hole extending to the vicinity of the electrode plate group 140.

The exhaust valve 210 is for maintaining the internal pressure in the square sealed battery below an acceptable threshold value, and when the value of the internal pressure exceeds the allowable threshold value and exceeds the valve opening pressure. When the valve is opened, the gas generated inside the battery is discharged. As a result, the square sealed battery discharges gas until the internal pressure becomes equal to or lower than the threshold value, and the internal pressure is maintained below the allowable threshold value.

(Pole plate group 140)
As shown in FIG. 2, the positive electrode plate 141 is composed of nickel hydroxide and cobalt as active materials. Specifically, to nickel hydroxide, add an appropriate amount of a conductive agent such as cobalt hydroxide or metallic cobalt powder, and if necessary, a thickener such as carboxymethyl cellulose or a binder such as polytetrafluoroethylene to form a paste. Process. Then, the paste-like processed product is applied or filled in a core material such as a three-dimensional foamed nickel porous body, and then dried, rolled, and cut to form a plate-shaped positive electrode plate 141. As the three-dimensional porous body of nickel foam, one in which the urethane foam skeleton surface is nickel-plated and then the urethane foam is burnt down is used.

The negative electrode plate 142 is composed of, for example, a hydrogen storage alloy containing mischmetal, nickel, aluminum, cobalt, and manganese, which are a mixture of rare earth elements such as lanthanum, cerium, and neodymium, as an active material. For details, add a conductive agent such as carbon black to this hydrogen storage alloy, and if necessary, a thickener such as carboxymethyl cellulose and a binder such as a styrene-butadiene copolymer to make a paste. Process. Then, the hydrogen storage alloy processed into a paste in this way is applied or filled in a core material such as a punching metal (active material support), and then dried, rolled, and cut to obtain a plate-shaped negative electrode plate 142. To form.

As the separator 143, a non-woven fabric made of an olefin resin such as polypropylene, or, if necessary, a non-woven fabric obtained by subjecting it to a hydrophilic treatment such as sulfonization can be used.
The positive electrode plate 141, the negative electrode plate 142, and the separator 143 are formed by alternately stacking the positive electrode plate 141 and the negative electrode plate 142 on opposite sides of each other via the separator 143 to form a rectangular parallelepiped electrode plate group 140. Constitute. Then, the outer edge of the lead portion 141a of each positive electrode plate 141 protruding and laminated on one side and the current collector plate 150 are joined by spot welding or the like, and the lead portion 142a of each negative electrode plate 142 protruding and laminated on the other side is joined. The outer edge of the current collector plate 160 and the current collector plate 160 are joined by spot welding or the like.

The welded electrode plate group 140 of the current collector plates 150 and 160 is housed in each electric tank 100b in the square case 300, and the positive electrode current collector plate 150 and the negative electrode current collector plate 160 of the adjacent electrode plate group 140 are accommodated. The electrode plate group 140 adjacent to each other is electrically connected in series by being connected by spot welding or the like between the connecting protrusions 151 and 161 projecting above them.

A predetermined amount of an alkaline aqueous solution (electrolyte solution) containing potassium hydroxide as a main component is injected into each of the battery 100b, and the lid 200 seals the opening of the integrated battery 100 to form a plurality of batteries. For example, a square sealed battery having a rated capacity of "6.5 Ah" is constructed of a single battery (nickel-metal hydride secondary battery).

As shown in FIGS. 2 and 3, since both the positive electrode current collector plate 150 and the negative electrode current collector plate 160 are metal plates that do not expand and contract substantially, each side side 140S of the electrode plate group 140 with respect to the stacking direction. Is fixed to the first thickness D1. Further, when the positive electrode plate 141, the negative electrode plate 142 and the separator 143 are laminated while being pressed, the electrode plate group 140 has a first thickness D1 of each side side 140S and a second thickness of the central portion 140C in the width direction. The thickness is adjusted to be substantially the same as that of D2.

Further, referring to FIG. 1, a restraining tape for suppressing the swelling of the electrode plate group 140 in the stacking direction is provided on a part of the upper part of the electrode plate group 140 facing the lid body 200. Further, at least a part of the lower portion of the electrode plate group 140 facing the lid 200 is provided with a restraining tape for suppressing the swelling of the electrode plate group 140 in the stacking direction. Therefore, the upper part and the lower part of the electrode plate group 140 have a strong force to restrain the first thickness D1, while the force to restrain the central portion 140C in the vertical direction of the electrode plate group 140 to the first thickness D1 or less is weak.

Then, the electrode plate group 140 released from pressing by the completion of lamination expands to some extent by the positive electrode plate 141, the negative electrode plate 142, and the separator 143 in which the elastic deformation due to pressing is restored. At this time, the electrode plate group 140 has a small amount of restoration at the side side 140S having a strong binding force from the positive electrode current collecting plate 150 and the negative electrode current collecting plate 160, and at the upper and lower portions where the restraining tape is provided. The amount of restoration is large in the central portion 140C in the width direction and the vertical direction where the binding force is weak. Therefore, the electrode plate group 140 released from pressing has a shape in which the second thickness D2 of the central portion 140C is larger than the first thickness D1 of each side side 140S, that is, both side sides 140S. In comparison, the central portion 140C has a bulging shape, in other words, the both side sides 140S have a contracted shape as compared with the central portion 140C.

Further, the electrode plate group 140 in which the central portion 140C in the width direction is expanded is housed in the electric tank 100b, and then the inner surface 111 of the electric tank 100b is pressed by the expansion pressure 14F due to expansion due to charge / discharge or use. become.

(Electric tank 100b)
As shown in FIGS. 3 and 4, the electric tank 100b has an inner surface 111 having a shape corresponding to the shape of the bulging electrode plate group 140 of the central portion 140C, which is released from the pressing during stacking immediately before being inserted into the electric tank. have. Therefore, it is easy to accommodate the electrode plate group 140, which is manufactured separately from the electric tank 100b and whose central portion 140C is swollen, in the electric tank 100b. Further, the gap between the inner surface 111 of the electric tank 100b and the accommodated electrode plate group 140 can be reduced.

More specifically, the electric tank 100b has a rectangular parallelepiped accommodating space 103 accommodating the electrode plate group 140. The accommodation space 103 is partitioned by a pair of outer walls 101 facing in the stacking direction, a pair of partition walls 110 facing in the width direction, and a bottom surface 102 provided below, and the upper opening of the accommodation space 103 is sealed with a lid 200. It is sealed by being stopped.

By accommodating the electrode plate group 140 in the electric tank 100b, the pair of outer walls 101 each face the outer peripheral separator 144 of the electrode plate group 140, and the pair of partition walls 110 each face the outer peripheral separator 144 of the electrode plate group 140 in the width direction of the electrode plate group 140. It faces the current collector plates 150 and 160 provided on the side sides.

The accommodation space 103 has a shape that swells in the stacking direction at the central portion 112 in the width direction of the outer wall 101. More specifically, the distance between the pair of outer walls 101 facing each other is wider in the second distance D12 in the central portion 112 than in the first distance D11 in the end portion 113 near the partition wall 110. Therefore, in the outer wall 101 whose outer surface 101a is flat, the first plate thickness T11 of the end portion 113 is thicker than the second plate thickness T12 of the central portion 112, so that the inner surface 111 of the electric tank 100b is formed at both ends. The central portion 112 is formed in an arc shape in which the central portion 112 is curved outward with respect to 113.

(Action)
The arc shape of the accommodation space 103 is formed so as to correspond to the bulging shape of the electrode plate group 140 accommodated in the accommodation space 103. The electrode plate group 140 formed by laminating the same positive electrode plate 141, negative electrode plate 142, and separator 143 can calculate or measure the swelling immediately before the insertion of the electric tank after laminating. That is, the arc shape of the accommodation space 103 is designed based on the bulge of the electrode plate group 140 immediately before the insertion of the electric tank, which is acquired or calculated in advance.

At this time, the arc shape of the accommodation space 103 reduces the distance between the accommodating space 103 and the electrode plate group 140. That is, the difference between the second interval D12 at the central portion 112 of the pair of outer walls 101 and the second thickness D2 of the electrode plate group 140 is a difference that allows the electrode plate group 140 to be accommodated in the accommodation space 103. The interval D12 is approximately equal to the second thickness D2. For example, the "second interval D12 / second thickness D2" is "0.9 or more and 1.1 or less", and more preferably "0.95 or more and 1.05 or less". When "second interval D12 / second thickness D2 <1", the electrode plate group 140 in which the central portion 140C is pressed so that the second thickness D2 is compressed, and the central portion 112 has the second interval D12. It is inserted into the accommodation space 103.

Similarly, the difference between the first spacing D11 at the end 113 of the pair of outer walls 101 and the first thickness D1 of the electrode plate group 140 is as small as possible to accommodate the electrode plate group 140 in the accommodation space 103. is there. Therefore, the first interval D11 is longer than the first thickness D1 of the electrode plate group 140 and shorter than the second thickness D2. For example, the "first interval D11 / first thickness D1" is "1.01 or more and 1.1 or less", and more preferably "1.01 or more and 1.05 or less".

As a result, when the electrode plate group 140 is accommodated in the accommodation space 103 of the electric tank 100b, a wide range of the outer peripheral separator 144 of the electrode plate group 140 abuts on a wide range of the inner surface 111 of the electric tank 100b, or a small difference. Oppose with. Then, when expansion due to charge / discharge or expansion due to deterioration occurs, the expansion pressure 14F of the electrode plate group 140 presses the inner surface 111 of the electric tank 100b outward from the facing surface of the electrode plate group 140. At this time, since the expansion pressure 14F is dispersed in a wide range, the concentration of stress on the inner surface 111 of the electric tank 100b is suppressed, and the deformation and deterioration of the outer wall 101 are suppressed.

Further, when a wide range of the electrode plate group 140 abuts or faces the inner surface 111 of the electric tank 100b with a small difference, the heat transfer efficiency of the electrode plate group 140 to the outer wall 101 is enhanced and the heat dissipation effect is exhibited. It becomes easier and the temperature rise of the electrode plate group 140 is suppressed.

As a result, it becomes possible to suppress the stress concentration of the secondary battery and suppress the temperature rise at the same time.
Further, as shown in FIG. 5, since the plate thickness of the outer wall 101 is thick at the end portion 113, it is possible to suppress the concentration of stress on the connecting portion 115 between the outer wall 101 and the partition wall 110.

Normally, when the outer wall 101 is pressed outward, a tension acts on the connecting portion 115 so as to widen the boundary portion 114, which is the boundary between the outer wall 101 and the partition wall 110, at an angle of 45 °, and the outer wall 101 and the outer wall 101. A force that causes a crack acts between the partition wall 110 and the partition wall 110.

In this respect, since the outer wall 101 has a thick end portion 113 close to the partition wall 110, when the central portion 112 receives an expansion pressure 14F, the connection portion 115 has a compression pressure 10F in the width direction and a tension in the stacking direction. The force is divided into 11F, and the force to widen the boundary portion 114 is reduced. Therefore, the decrease in durability of the boundary portion 114, which is likely to deteriorate due to stress concentration, is suppressed, and the decrease in durability of the resin case is also suppressed.

According to this embodiment, the effects described below can be obtained.
(1) Before charging / discharging with little bulge of the electrode plate, the inner surface 111 of the electric tank 100b facing the stacking direction of the electrode plate group 140 is recessed in the center corresponding to the arc shape which is the bulge of the electrode plate group 140. By forming a surface, a wide contact area is secured between the portion sandwiched between the two side sides of the electrode plate group 140 and the inner surface 111 of the electric tank 100b. Then, after charging / discharging in which the swelling of the electrode plate becomes large, the expansion pressure 14F due to the expansion of the electrode plate group 140 is dispersed and received over the entire inner surface 111 of the electric tank 100b. Therefore, since the expansion pressure 14F from the electrode plate group 140 is received in a wide range of the electric tank 100b, the load per unit area applied to the case is reduced. As a result, the decrease in durability of the resin case is suppressed.

Further, since the contact area between the inner surface 111 of the electric tank 100b and the electrode plate group 140 can be secured widely from before charging / discharging to after charging / discharging, a high heat dissipation effect can be obtained.
(2) The arc shape of the electrode plate group 140 and the arc shape of the inner surface 111 of the electric tank 100b are close to each other. Therefore, it is possible to suppress a decrease in the durability of the battery case 100b. In addition, the heat dissipation effect is easily exhibited.

(3) The outer wall 101 of the electric tank 100b is thick at the end 113 as a portion accommodating the two side sides of the electrode plate group 140, and is thin at the central portion 112 between the two side sides of the electrode plate group 140. That is, the inner surface 111 of the electric tank 100b is an arc shape, and the outer surface 101a side of the electric tank 100b is a straight plane. Therefore, the expansion pressure 14F on the inner surface 111 of the electric tank 100b is divided in the stacking direction and the surface direction (width direction) of the inner surface 111. Therefore, stress concentration on the end 113 of the outer wall 101 of the electric tank 100b is suppressed.

(4) In the electric tank 100b partitioned by the partition wall 110, the stress concentration on the connection portion 115 between the outer wall 101 of the electric tank 100b and the partition wall 110 is relaxed.
The above embodiment can be modified and implemented as follows. The above-described embodiment and the following modified examples can be implemented in combination with each other within a technically consistent range.

In the above embodiment, a case where the connection portion between the outer wall 101 and the partition wall 110 has a boundary portion 114 close to a right angle on the inner surface 111 of the electric tank 100b has been illustrated. However, the present invention is not limited to this, and the joint portion between the outer wall 101 and the partition wall 110 may be shaped so that stress concentration is difficult to concentrate, or the position where stress concentration occurs may be shifted from the boundary portion 114.

For example, as shown in FIG. 6, when the electric tank 100b is viewed from above, the inner surface 111 of the electric tank 100b is connected to the boundary portion 123 between the outer wall 101 and the partition wall 110 by a first arc having a radius R1. .. Further, the inner surface 111 of the electric tank 100b is connected between the two boundary portions 123 by a second arc 122 having a radius R2. The radius R1 is a radius capable of suppressing stress concentration, is "radius R1 << radius R2", and the radius R2 has a shape corresponding to the bulge of the electrode plate group 140 opposite to the shape of the second arc 122. It is a value to be approximated.

The boundary portion 123 has no corner at which stress concentration is likely to occur because the inner surfaces of the outer wall 101 and the partition wall 110 that intersect at substantially right angles are connected by an arc. Therefore, in the connecting portion 124 where stress concentration is likely to occur, it is difficult to cause stress concentration at a specific position, and the stress is also dispersed in a wide range.

Further, the outer wall 101 is a connecting portion in which the thick plate thickness T21 changes toward the thin plate thickness T22 at the position where stress concentration occurs in the connecting portion 124 by extending the portion of the thick plate thickness T21 from the partition wall 110 in the width direction. It can be changed to the vicinity of a position away from 124. As a result, stress concentration is relaxed.

Even at the displaced stress concentration position, since the boundary portion 123 of the outer wall 101 has a thick plate thickness T21, when the expansion pressure 24F is applied to the second arc 122, the compression pressure 20F in the width direction and the tension in the stacking direction are applied. The force is divided into 21F, and the force to expand the boundary portion 123 is reduced. Therefore, the decrease in durability of the boundary portion 123, which is likely to be deteriorated due to stress concentration, is suppressed, and the decrease in durability of the resin case is also suppressed.

-In the above embodiment, the case where the electrode plate group 140 has a laminated structure in which the positive electrode plate 141 and the negative electrode plate 142 are laminated via the separator 143 is illustrated. However, the present invention is not limited to this, and may be appropriately changed depending on the shape of the secondary battery and the purpose of use. For example, it is a winding type structure in which a long positive electrode plate and a long negative electrode plate are flatly wound via a long separator.

-In the above embodiment, the case where the restraint tape is provided on the upper part and the lower part of the electrode plate group 140 is illustrated, but the present invention is not limited to this, and the restraint tape is provided on one of the upper part and the lower part of the electrode plate group. Alternatively, the restraint tape may not be provided on both the upper part and the lower part of the electrode plate group.

-In the above embodiment, the case where the secondary battery is a square sealed battery has been illustrated, but the present invention is not limited to this, and any nickel hydrogen secondary battery using a sealed hydrogen storage alloy can be applied. it can.

-In the above embodiment, the case where the secondary battery is a nickel hydrogen secondary battery has been illustrated, but the secondary battery is not limited to this, and the secondary battery is a lithium ion secondary battery that repeatedly expands and contracts due to charging and discharging, and other batteries. It may be a secondary battery.

100 ... integrated electric tank, 100b ... electric tank, 101 ... outer wall, 101a ... outer surface, 102 ... bottom surface, 103 ... accommodation space, 110 ... partition wall, 111 ... inner surface, 112 ... central part, 113 ... end part, 114 ... boundary part , 115 ... connection part, 120 ... connection terminal, 123 ... boundary part, 124 ... connection part, 140 ... electrode plate group, 141 ... positive electrode plate, 141a ... lead part, 142 ... negative electrode plate, 142a ... lead part, 143 ... separator , 144 ... outer peripheral separator, 150 ... current collector plate, 151 ... connection protrusion, 160 ... current collector plate, 161 ... connection protrusion, 170 ... through hole, 200 ... lid, 210 ... exhaust valve, 220 ... sensor mounting hole , 300 ... Square case.

Claims (5)

A group of electrode plates in which a rectangular positive electrode plate and a rectangular negative electrode plate are laminated via a separator, an electrolytic solution, and a resin case for accommodating the electrode plate group and the electrolytic solution are provided.
The two side sides of the electrode plate group fixed by the current collector plates each have a first thickness in the stacking direction.
The portion of the electrode plate group sandwiched between the two sides has a second thickness that is thicker than the first thickness and bulges in an arc shape in the stacking direction.
A secondary battery having an arcuate surface corresponding to the arcuate shape of the electrode plate group bulging in the stacking direction as a facing surface of the case facing the stacking direction of the electrode plate group. Of the distance between the two facing surfaces facing each other in the case, the distance between the portions accommodating the two side sides of the electrode plate group is set as the first distance, and the central distance between the two side sides of the plate group is set as the second distance. When set as an interval
The first interval is longer than the first thickness and shorter than the second thickness.
The secondary battery according to claim 1, wherein the second interval is substantially equal to the second thickness. The inner surface of the outer wall of the case is the arc-shaped facing surface.
The secondary battery according to claim 1 or 2, wherein the outer surface of the outer wall is a straight surface. A battery module with a plurality of the above cases
The secondary battery according to any one of claims 1 to 3, wherein the battery module is partitioned between two adjacent cases by a partition wall. In the portion of the case that accommodates the two side surfaces of the electrode plate group, the cross section of the connecting portion between the facing surface and the side surface parallel to the stacking direction is a surface having a first arc.
In the portion of the case that accommodates between the two side sides of the electrode plate group, the cross section of the facing surface is a second arc having a diameter larger than the first arc corresponding to the arc shape of the electrode plate group. The secondary battery according to any one of claims 1 to 4.