Method of manufacturing battery pack and battery pack

A method of manufacturing a battery pack including battery cells that have electrode tabs protruding from an outer surface includes stacking the battery cells and housing the battery cells in a case so that the electrode tabs protrude from slits in the case, bending the electrode tabs protruding from the slits so that the electrode tabs of adjacent battery cells are folded and overlap each other, and welding the folded and overlapping portion of the electrode tabs.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a 371 application of International Patent Application Serial No. PCT/JP2018/036927, filed Oct. 2, 2018, which claims priority to and the benefit of Japanese Patent Application No. 2017-193809 filed Oct. 3, 2017, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a method of manufacturing a battery pack and to a battery pack.

BACKGROUND

A chargeable/dischargeable battery module that includes a plurality of battery cells is known. For example, patent literature JP4877373B2 discloses stacking battery cells and joining the positive electrode tab and negative electrode tab of each battery cell to a bus bar by ultrasonic welding or the like.

SUMMARY

To prevent the tabs of each layer from interfering during ultrasonic welding when the tabs of the stacked battery cells are welded to the bus bar in JP4877373B2, the tabs are trimmed so as not to overlap in plan view. If the tabs of the battery cell are trimmed, however, then current collects at the remaining tip of the tab, increasing heat generation and possibly leading to shorter cell life.

In light of these considerations, the present disclosure aims to provide a method of manufacturing a battery pack and a battery pack that enable welding without trimming the tabs of battery cells.

To resolve the aforementioned problem, a method according to an embodiment of the present disclosure is a method of manufacturing a battery pack including a plurality of battery cells that have electrode tabs protruding from an outer surface, the method including:

stacking the plurality of battery cells and housing the plurality of battery cells in a case so that the electrode tabs protrude from slits in the case;

bending the electrode tabs protruding from the slits so that electrode tabs of adjacent battery cells are folded and overlap each other; and

welding a folded and overlapping portion of the electrode tabs.

A battery pack according to an embodiment of the present disclosure includes:

a plurality of battery cells having electrode tabs protruding from an outer surface; and

a case housing the plurality of battery cells in a stacked state;

wherein the case includes a plurality of slits through which the electrode tabs protrude;

wherein the electrode tabs of adjacent battery cells are bent so that portions protruding from the slits are folded and overlap each other; and

wherein a folded and overlapping portion of the electrode tabs is welded outside the case.

The method of manufacturing a battery pack and the battery pack according to embodiments of the present disclosure enable welding without trimming the tabs of battery cells.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described below with reference to the attached drawings. The front-back, left-right, and up-down directions in the description below take the directions of the arrows in the figures as a reference. The stacking direction of the plurality of battery cells10in the example below is the up-down direction, but this example is not limiting. The stacking direction of the plurality of battery cells10may match any other direction.

First Embodiment

FIG.1is a perspective view illustrating the appearance of a battery pack1according to a first embodiment of the present disclosure.FIG.2is an exploded perspective view of each component inside the battery pack1illustrated inFIG.1. The battery pack1includes six battery cells10, an insulating sheet20, a first case40, and a second case50as major constituent elements.

The six battery cells10are stacked in the up-down direction. The six stacked battery cells10are referred to below as the battery cells10a,10b,10c,10d,10e,10fin order from bottom to top. The battery cells are referred to collectively as battery cells10when no distinction therebetween is made. Each battery cell10has two outer surfaces11formed by a front surface and a back surface that are substantially parallel in the up-down direction. Each battery cell10has one pair of electrode tabs12pand12nthat protrude in opposite directions from the two outer surfaces11in a direction substantially perpendicular to the stacking direction, in particular in the front-back direction. Each battery cell10is stacked with the pair of electrode tabs12pand12naligned in the front-back direction.

The insulating sheet20is formed as a substantially flat plate by an electrically insulating material such as polyethylene (PE) or polypropylene (PP) resin. The insulating sheet20is disposed to abut against the upper surface of the battery cell10fpositioned at the top of the stacked battery cells10. The insulating sheet20is provided to secure electrical insulation between the restraining plate30abutting against the upper surface of the battery pack1and the battery cells10inside the battery pack1.

A restraining plate30is disposed to abut against the upper surface of the insulating sheet20. The restraining plate30is fixed to the upper surfaces of the engaged first case40and second case50by a suitable method, such as screwing. For example, the restraining plate30is fixed to the top of the engaged first case40and second case50by screwing screws into hole portions provided at the four corners of the restraining plate30and aligned with two screw holes provided at the left and right front edges of the first case40and two screw holes provided at the left and right back edges of the second case50. The restraining plate30clamps the battery cells10to the first case40and the second case50in a state that restrains outer surfaces13that are formed by the upper and lower surfaces of the battery cells10and that are perpendicular to the stacking direction. At the same time, the restraining plate30supports the battery cells10.

The first case40and the second case50engage with each other to support the stacked battery cells10therein. In other words, the stacked battery cells10are mounted on a bottom surface40aof the first case40and a bottom surface50aof the second case50. When engaged, the first case40and the second case50have an opening O formed on the top surface opposite the bottom surface. Connection surfaces S1of the first case40and the second case50that are connected to each other are substantially parallel to the outer surfaces11of the battery cells10on the electrode tab12por12nside. In other words, the connection surfaces S1are parallel to the up-down direction. In this way, the first case40and the second case50engage or separate in the protruding direction of the electrode tabs12pand12nof the battery cells10.

Among the stacked battery cells10, adjacent battery cells10may be adhesively fixed to each other by an adhesive such as a bonding agent or double-sided tape. For example, adjacent battery cells10may be adhesively fixed to each other by any method, such as applying a bonding agent to the upper surface of each battery cell10. Similarly, the battery cell10fand the insulating sheet20may be adhesively fixed to each other by adhesive. Furthermore, the insulating sheet20and restraining plate30may similarly be adhesively fixed to each other by adhesive.

FIGS.3A and3Billustrate only the battery cell10ofFIG.2.FIG.3Ais a top view of the battery cell10.FIG.3Bis a side view of the battery cell10. As an example,FIGS.3A and3Billustrate the battery cell10bdisposed as inFIG.2. The other battery cells10are also configured similarly to the battery cell10billustrated inFIGS.3A and3B.

The battery cell10is formed as a substantially flat plate when viewed from the top. An exterior member14of the battery cell10is formed by a laminated film. The outermost layer of the exterior member14is made of resin to secure electrical insulation. The upper and lower surfaces of the exterior member14form the outer surfaces13. The outer surfaces11protrude one step farther outward in the central region than at the left and right edges. In other words, the outer surfaces11are formed to be convex when viewed from the top. The electrode tab12por12nprotrudes from the portion of the outer surface11that protrudes one step outward. The electrode tabs12pand12nnormally protrude as a flat plate but protrude towards the outside in opposite directions in order to contact the electrode tab of another battery cell10and the like adjacent in the up-down direction. For example, the electrode tab12pprotrudes linearly outward along the front-back direction. The electrode tab12nprotrudes linearly outward along the front-back direction. In the example below, the electrode tab12pprotruding backward is a positive electrode terminal, and the electrode tab12nprotruding forward is a negative electrode terminal, but this example is not limiting. The electrode tabs12pand12nmay be configured so that the positive electrode and negative electrode roles are reversed.

FIGS.4A and4Billustrate only the restraining plate30ofFIG.2.FIG.4Ais a perspective view, from the top, of the restraining plate30.FIG.4Bis a cross-sectional view along the I-I line ofFIG.4A.

The restraining plate30is suitably made of any highly rigid material. For example, the restraining plate30is suitably made exclusively of a metal material. This example is not limiting, and the restraining plate30may be made of a resin material or a metal material provided with an electrically insulating material, such as PET resin, on the surface thereof. The restraining plate30is formed as a substantially flat plate. The restraining plate30has a substantially rectangular recess32formed at the substantially central region and recessed one step inward along the up-down direction. Four hole portions31protrude from the four corners of the outer edge of the restraining plate30that surrounds the recess32. The surface of the recess32is, for example, formed linearly to be substantially parallel to the surface of the outer edge of the restraining plate30. The surface of the recess32is not limited to this configuration and may, for example, be formed as a linear or curved surface that is inclined to protrude farther inward towards the central region thereof. The battery pack1can firmly fix the battery cells10therein by pressure from the recess32. The restraining plate30is not limited to a configuration such as the recess32. For example, the recess32may be omitted, and the restraining plate30may be formed so that the surface thereof is a linear or curved surface inclined to protrude gradually inward from the outer edge towards the central region thereof. Instead of the recess32, the restraining plate30may have at least one rib that protrudes from the lower surface in the central region, for example.

FIG.5Aillustrates the front surface of the first case40inFIG.2.FIG.5Billustrates an enlargement of a portion of the front surface of the first case40.

The first case40is made of a resin material or a metal material provided with an electrically insulating material, such as PET resin, on the surface thereof. The first case40may be made of any highly rigid material. The central region on the front surface of the first case40is formed to protrude one step outward. Six substantially rectangular slits42that pass through the front surface extend in the left-right direction in the central region of the front surface. The slits42are formed to allow the electrode tabs12pand12nof the battery cell10to protrude through the slits42. The six slits42are arranged in a line in the up-down direction so that the positions of the left and right ends are aligned.

Like the first case40, the second case50is made of a resin material or a metal material provided with an electrically insulating material, such as PET resin, on the surface thereof. The second case50may be made of any highly rigid material. The second case50is preferably made of the same material as the first case40with which the second case50engages. The central region on the back surface of the second case50is formed to protrude one step outward. Six substantially rectangular slits52that pass through the back surface extend in the left-right direction in the central region of the back surface. The slits52are formed to allow the electrode tabs12pand12nof the battery cell10to protrude through the slits52. The six slits52are arranged in a line in the up-down direction so that the positions of the left and right ends are aligned.

FIGS.6A through6Dare schematic diagrams respectively illustrating representative first through fourth steps for assembling the battery pack1.FIGS.7A and7Bare schematic diagrams illustrating the inside of the first case40and the second case50at the time of the third and fourth steps ofFIGS.6C and6D.FIG.7Aillustrates an enlargement of a portion in a cross-section of the central region on the front surface of the first case40.FIG.7Billustrates an enlargement of a portion in a cross-section of the central region on the back surface of the second case50.

In the first step illustrated inFIG.6A, the six stacked battery cells10are inserted in the second case50. In this state, the first case40is fitted onto the second case50, which is holding the battery cells10and the insulating sheet20, from the front. In the second step illustrated inFIG.6B, the electrode tabs12pand12nof the battery cells10are caused to protrude from the slits42of the first case40and the slits52of the second case50. In the third step illustrated inFIG.6C, the electrode tabs12pand12nprotruding from the slits42of the first case40and the slits52of the second case50are bent so that the electrode tabs of adjacent battery cells10are folded and overlap each other.

In the fourth step illustrated inFIG.6D, a laser for welding irradiates the folded and overlapping portion of the electrode tabs12pand12n, which are the welding spots, to weld the electrode tabs12pand12ntogether. Similarly, the electrode tab12pand a total plus bus bar60aare welded together, and the electrode tab12nand a total minus bus bar60bare welded together.

The restraining plate30is fixed to the upper surfaces of the engaged first case40and second case50by a suitable method, such as screwing, after the fourth step illustrated inFIG.6D. This completes the assembly of the battery pack1.

As illustrated inFIG.7A, the first case40includes four housing portions47ato47d. The back portion of the front central region of the first case40is divided in the up-down direction into the four housing portions47ato47dby three insulating portions46ato46c. The electrode tab12pof the battery cell10ais disposed in the housing portion47a. The electrode tab12nof the battery cell10badjacent to the upper portion of the battery cell10ais disposed in the housing portion47b. Similarly, the electrode tab12pof the battery cell10cadjacent to the upper portion of the battery cell10bis disposed in the housing portion47b. The electrode tabs12pand12nat the front of the battery cells10d,10e, and10fare similarly arranged alternately in the housing portions47cand47d. Consequently, one, two, two, and one electrode tabs are respectively housed in the four housing portions47of the first case40from bottom to top, with the electrode tabs12pand12nbeing arranged alternately.

The electrode tab12pof the battery cell10aprotrudes outside the first case40through the slit42aand is bent by the third step so as to overlap the total plus bus bar60a. In other words, the electrode tab12pof the battery cell10aprotrudes from the slit42a, bends downwards at approximately 90 degrees, and abuts against the total plus bus bar60anear the slit42a. The laser for welding is irradiated onto the abutting portion, and the electrode tab12pand the total plus bus bar60aare welded together.

The electrode tabs12pand12nof the battery cells10bto10eprotrude outside the first case40through the slits42bto42eand are bent by the third step so as to be folded and overlapping each other. Specifically, the electrode tab12pprotrudes from the slit42, bends downwards at approximately 90 degrees, and abuts against the electrode tab12nof the downwardly adjacent battery cell10near the slit42. The electrode tab12nprotrudes from the slit42, bends upwards at approximately 90 degrees, and abuts against the electrode tab12pof the upwardly adjacent battery cell10near the slit42. The laser for welding is irradiated onto the abutting portion, and the electrode tabs12pand12nare welded together.

The electrode tab12nof the battery cell10fprotrudes outside the first case40through the slit42fand is bent by the third step so as to overlap the total minus bus bar60b. In other words, the electrode tab12nof the battery cell10fprotrudes from the slit42f, bends upwards at approximately 90 degrees, and abuts against the total minus bus bar60bnear the slit42f. The laser for welding is irradiated onto the abutting portion, and the electrode tab12nand the total minus bus bar60bare welded together.

As illustrated inFIG.7B, the second case50includes four housing portions57ato57d. The back portion of the front central region of the second case50is divided in the up-down direction into the four housing portions57ato57dby three insulating portions56ato56c. The electrode tab12nof the battery cell10ais disposed in the housing portion57a. The electrode tab12pof the battery cell10badjacent to the upper portion of the battery cell10ais disposed in the housing portion57b. The electrode tab12pof the battery cell10cadjacent to the upper portion of the battery cell10bis disposed in the housing portion57b. The electrode tabs12pand12nat the back of the battery cells10d,10e, and10fare similarly arranged alternately in the housing portions57cand57d. Consequently, one, two, two, and one electrode tabs are respectively housed in the four housing portions57of the second case50from bottom to top, with the electrode tabs12pand12nbeing arranged alternately.

The electrode tabs12pand12nof the battery cells10ato10fprotrude outside the second case50through the slits52ato52fand are bent by the third step so as to be folded and overlapping each other. Specifically, the electrode tab12pprotrudes from the slit52, bends downwards at approximately 90 degrees, and abuts against the electrode tab12nof the downwardly adjacent battery cell10near the slit52. The electrode tab12nprotrudes from the slit52, bends upwards at approximately 90 degrees, and abuts against the electrode tab12pof the upwardly adjacent battery cell10near the slit52. The laser for welding is irradiated onto the abutting portion, and the electrode tabs12pand12nare welded together.

By thus being bent in vertically opposite directions, the electrode tabs12pand12nof each battery cell10are each connected to the electrode tab of opposite polarity of the adjacent battery cell10. Ultimately, the six battery cells10are connected in series.

As described above, the electrode tab12por12nis bent at substantially 90 degrees so that electrode tabs of adjacent battery cells are folded and overlapping with each other near the slit42or52. As illustrated inFIG.8, recesses43may be provided near the slits42on the outer wall of the first case40. The recesses43are recessed towards the inner perimeter of the first case40. The electrode tabs12pand12nprotruding from the slits42are bent towards the recesses43. This configuration enables the electrode tabs12pand12nto bend 90 degrees or more. Weldability can thereby be improved, even when the electrode tabs12pand12nhave a large spring back. As in the first case40, recesses53may also be provided in the second case50near the slits52on the outer wall of the second case50. The recesses43inFIG.7Aare shaped to increase in depth closer to the protruding electrode tabs12pand12n(i.e. the cross-sectional shape is triangular), but this configuration is not limiting. For example, the cross-sectional shape may be rectangular. The recesses43may have any shape that provides a space allowing bending to an angle of 90 degrees or more.

As also illustrated inFIG.8, a metal plate44may be formed by insertion molding near the slits42(between slits42) on the outer wall of the first case40. The metal plate44is formed by insertion molding inside the outer wall that faces the folded and overlapping portion of the electrode tabs12pand12n, as illustrated inFIG.8. If the laser penetrates the electrode tabs at the time of welding, this configuration can receive the laser with the metal plate44to protect the battery cells10. As in the first case40, a metal plate may also be formed by insertion molding in the second case50near the slits52(between slits52) on the outer wall of the second case50.FIG.8illustrates an example of the recess43and the metal plate44being provided in the outer wall of the case, but a configuration that provides only one of the recess43and the metal plate44may be adopted.

FIGS.9A through9Cillustrate the battery pack1housed in a body80.FIG.9Ais a perspective view, from the top, illustrating a cross-section of the body80supporting the battery pack1.FIG.9Bis a cross-sectional view along the IV-IV line ofFIG.9A.FIG.9Cillustrates an enlargement of the portion surrounded by a dashed line inFIG.9B.

The body80is suitably configured by a metal material such as aluminum. This configuration is not limiting, and the body80may be made of any highly rigid material. For example, the body80may be made of a highly rigid resin material or a metal material provided with an electrically insulating material, such as PET resin, on the surface thereof.

The battery pack1is fixed to the inside of the body80by a suitable method, such as screwing. In greater detail, the battery pack1is housed inside the body80with the bottom surface40aof the first case40and the bottom surface50aof the second case50abutting against a bottom surface80aof the body80. At this time, the bottom surface80aof the body80functions as a restraining member for restraining the stacked battery cells10from below, like the upper restraining plate30. The stacked battery cells10are thus restrained indirectly by the bottom surface80aas a result of abutting against the bottom surface40aof the first case40and the bottom surface50aof the second case50, which abut against the bottom surface80a. This configuration is not limiting, however. The bottom surface80aneed not abut against the bottom surface40aof the first case40and the bottom surface50aof the second case50if, for example, the bottom surface40aand the bottom surface50athemselves can function as a restraining member with sufficient rigidity.

As illustrated inFIGS.9A through9C, fixing portions F of the first case40and the second case50relative to the body80are provided farther inward than the bottom surface80aof the body80. The fixing portions F are thus positioned above the bottom surface80ato be closer to the center of gravity of a battery cell assembly100formed by six stacked battery cells10.

The fixing portions F may, for example, be configured as follows. The two screw holes41of the first case40may be configured to penetrate from the upper surface to the lower surface of the first case40, for example. Similarly, the two screw holes51of the second case50may be configured to penetrate from the upper surface to the lower surface of the second case50, for example. To support the two screw holes41and the two screw holes51, the body80includes supports81protruding inward from the bottom surface80aat corresponding positions. Screw holes81aare provided on the upper surface of the supports81. The screws inserted from above through the two screw holes41and the two screw holes51are screwed into the screw holes81a. For example, the first case40and the second case50may be fixed to the body80by screws being inserted into the screw holes41and the screw holes51and screwed into the screw holes81a. The fixing portion F may thus be formed by the screw hole41or the screw hole51together with the screw hole81a.

In this way, the bottom surface of the battery pack1is fixed in a state of abutment against the bottom surface80aof the body80. Accordingly, the bottom side of the battery pack1is firmly restrained from below by the bottom surface80aof the body80. If the top side of the battery pack1were only configured by the first case40, the second case50, and the insulating sheet20, then the restraining force would be weaker than at the bottom side. This problem is addressed by the restraining plate30being fixed to the first case40and the second case50to cover the battery cell assembly100from one side in the stacking direction, i.e. from above, while the battery pack1is fixed to the body80. As described above, the restraining plate30includes the recess32that is recessed one step towards the upper surface of the battery cell assembly100. The insulating sheet20is disposed between the restraining plate30and the upper surface of the battery cell assembly100at this time. The insulating sheet20abuts against the recess32of the restraining plate30and the upper surface of the battery cell assembly100. On the other hand, the bottom surface40aof the first case40and the bottom surface50aof the second case50abut against the bottom surface80aof the body80. In other words, the upper surface of the battery cell assembly100is pressed from above by the restraining plate30while, simultaneously, the lower surface of the battery cell assembly100is supported by the bottom surface80aof the body80via the abutment against the bottom surface40aof the first case40and the bottom surface50aof the second case50. The position of each battery cell10in the up-down direction is thereby regulated. At this time, gas produced inside the battery cells10due to deterioration over time tends to collect around the battery cells10due to pressure in the stacking direction. In other words, the internal gas collects at a location away from the electrodes formed in the central region.

Typically, the battery characteristics of the battery cell10and the pressure in the stacking direction of the battery cells10are correlated. Specifically, the electrode spacing inside the battery cells10stabilizes when a predetermined pressure is applied. The internal resistance therefore lowers, and the battery characteristics of the battery cells10improve. On the other hand, application of excessive pressure impedes the chemical reaction itself inside the battery cell10, and the battery characteristics worsen. Therefore, when the battery pack1is assembled, the restraining plate30is preferably fixed to apply pressure within a predetermined pressure range in order to obtain good battery characteristics that are stable over time. Even if the battery cells10swell due to deterioration over time, which by reaction would increase the pressure in the stacking direction of the battery cells10, an optimal pressure capable of maintaining battery characteristics can still be secured.

In the above-described battery pack1according to the first embodiment, the electrode tabs12pand12nof the battery cells10are caused to protrude through the slits42,52of the first case40and the second case50. The electrode tabs12pand12nprotruding through the slits42,52are then bent so that electrode tabs of adjacent battery cells10are folded and overlap each other, and the folded and overlapping portion is welded. The electrode tabs12pand12nof the battery cells10can thereby be welded without being trimmed.

The battery pack1according to the first embodiment enables bending towards the recesses43,53provided on the outer wall of the first case40and second case50near the slits42,52. The electrode tabs12pand12ncan therefore bend 90 degrees or more. Weldability can thereby be improved, even when the electrode tabs12pand12nhave a large spring back.

The outer surface13perpendicular to the stacking direction of the battery cells10is restrained by the restraining plate30in the battery pack1. Swelling in the stacking direction of the battery cells10can thereby be suppressed if an internal gas is produced during use of the battery pack1, during charging/discharging, or by deterioration over time. When the restraining plate30is made of a metal material, the rigidity thereof increases, and the battery pack1can effectively suppress swelling of the battery cells10.

Provision of the insulating sheet20and the restraining plate30on only one side of the stacked battery cells10can reduce the number of components and increase productivity of the battery pack1. In this way, the battery pack1is advantageous in terms of the number of components and productivity as compared to a known battery pack in which a cell cover is provided for each battery cell, for example, to protect the battery cells. The simplified configuration of the battery pack1can, in other words, contribute to improving productivity and reducing costs. By the battery cells10being fixed together, the battery cell10and the insulating sheet20being fixed together, and the insulating sheet20and restraining plate30being fixed together by adhesive, the resistance of the battery pack1to vibration or shock improves. For example, when the battery pack1is mounted in a vehicle, the relative displacement between components due to vibration, shock, or the like when the vehicle is moving can be prevented. In this way, the components inside the battery pack1are firmly fixed to each other to prevent damage to the internal components from vibration or shock.

The battery pack1can achieve a smaller size and a lower profile while suppressing swelling of the stacked battery cells10. Specifically, swelling in the stacking direction of the battery cells10can be suppressed in the battery pack1by the upper surface of the battery cell assembly100being pressed from one side in the stacking direction by the restraining plate30while the lower surface is abutted against the bottom surface40aof the first case40and the bottom surface50aof the second case50. At the same time, only one restraining plate30is used, providing the battery pack1with a smaller size, a lower profile, and a lighter weight than a conventional battery module that includes a plurality of restraining plates. Similarly, the battery pack1can contribute to reducing the number of components and the cost.

The battery pack1can suppress deterioration of the first case40and the second case50by including the opening O. If the opening O were omitted, and the restraining plate30were provided directly on the upper surface of the first case40and the second case50, then the restraining plate30would apply pressure directly on these cases, causing the cases to deform and accelerating deterioration. Accordingly, the battery pack1can prevent damage to the case due to such degradation over time.

The configuration of the recess32of the restraining plate30in the battery pack1enables suitable application of pressure to the central region of the outer surface13of the battery cell10that is perpendicular to the stacking direction. The battery pack1can thereby further suppress swelling in the stacking direction of the battery cells10. The application of pressure with the restraining plate30enables suitable retention of the battery cell assembly100inside the first case40and the second case50, thereby making retention more reliable in the battery pack1. In other words, the battery pack1can more firmly fix the battery cell assembly100by the pressure from the recess32. Application of pressure within an optimal range capable of maintaining good battery characteristics in the battery pack1can stabilize the internal resistance in the battery cells10. The pressure in the battery pack1releases internal gas from near the electrodes to the outer periphery of the battery cells10, thereby suppressing degradation of the battery cells10. In other words, the battery pack1suppresses the degradation of battery characteristics that occurs when internal gas is present between electrodes. In particular, the battery pack1can concentrate more pressure on the central region of the outer surface13of the battery cells10and more effectively suppress swelling of the battery cells10in the stacking direction by the surface of the recess32being formed to protrude further inward towards the central region. In this case, the battery pack1can more efficiently collect the internal gas at the outer periphery of the battery cells10.

By the arrangement of the insulating sheet20, the battery pack1can secure electrical insulation between the restraining plate30and the internal battery cells10.

The battery cell assembly100can also be further supported in the battery pack1by the bottom surface40aof the first case40and the bottom surface50aof the second case50abutting against the bottom surface80aof the body80. In particular, the battery pack1includes the restraining plate30on the upper surface side, whereas the bottom surface of the battery pack1abuts against the bottom surface80aof the body80. The battery cell assembly100is thereby firmly restrained from both sides in the up-down direction. Furthermore, as a result of the restraint provided by the restraining plate30and the bottom surface80ain the up-down direction, the first case40and the second case50tend not to warp even when supporting the battery cell assembly100. In other words, warping of the first case40and the second case50is regulated by the restraining plate30and the bottom surface80a.

The battery pack1can fix the battery cell assembly100, which is a heavy load, in a balanced manner by the fixing portions F being arranged closer to the center of gravity of the battery cell assembly100. For example, when the battery pack1is mounted in a vehicle, the stress occurring due to vibration, shock, or the like when the vehicle is moving can be relieved. Consequently, the battery pack1can contribute to improving product reliability. This arrangement in the battery pack1can also contribute to lowering the profile.

The first case40and the second case50in the battery pack1are made of a resin material or a metal material provided with an electrically insulating material on the surface thereof. Electrical insulation can thereby be secured between components external to the battery pack1, such as electrical components, and the battery cells10inside the battery pack1.

The electrical insulation in the battery pack1can be further improved by forming the restraining plate30from a metal material coated with an electrically insulating material or a resin material, like the first case40and the second case50. In this case, the restraining plate30can be reduced in weight, and the battery pack1can be manufactured at a low cost. This contributes to a reduction in weight and cost of the battery pack1itself.

Second Embodiment

FIG.10Ais a perspective view illustrating the appearance of a second case50of a battery pack1according to a second embodiment of the present disclosure.FIG.10Ais a perspective view of the second case50.FIG.10Billustrates an enlargement of the central region on the back surface of the second case50.FIG.10Cschematically illustrates the inside of the central region on the back surface of the second case50. The battery pack1according to the second embodiment differs from the first embodiment in the use of tab connecting bus bars55for connection between cells. The configuration that is the same as in the first embodiment is labeled with the same reference signs below. A description of this configuration is omitted to focus on the differences from the first embodiment.

As illustrated inFIG.10B, the battery pack1according to the second embodiment includes tab connecting bus bars55in the central region on the back surface of the second case50. The tab connecting bus bars55are referred to below as the tab connecting bus bars55a,55b,55c, in order from bottom to top. The tab connecting bus bar55ais provided on the outer wall between the slit52aand the slit52b. The tab connecting bus bar55bis provided on the outer wall between the slit52cand the slit52d. The tab connecting bus bar55cis provided on the outer wall between the slit52eand the slit52f.

As illustrated inFIG.10C, the electrode tab12por the electrode tab12nprotrudes from each slit52. The protruding electrode tabs12pand12nare bent so that the electrode tabs of adjacent battery cells10are folded and overlap each other. Specifically, the electrode tab12pprotrudes from the slit52, bends downwards at approximately 90 degrees, and abuts against the electrode tab12nof the downwardly adjacent battery cell10near the slit52. The electrode tab12pfurther abuts against the tab connecting bus bar55. The electrode tab12nprotrudes from the slit52, bends upwards at approximately 90 degrees, and abuts against the electrode tab12pof the upwardly adjacent battery cell10near the slit52. The laser for welding is irradiated onto the abutting portion, and the electrode tabs12p,12nand the tab connecting bus bar55are welded together.

Tab connecting bus bars45are similarly provided in the first case40.FIGS.11A and11Bschematically illustrate the inside of the central region on the front surface of the first case40.FIG.11Aschematically illustrates a portion where the tab connecting bus bar45is provided, andFIG.11Bschematically illustrates a portion connected to the total minus bus bar60b.

As illustrated inFIG.11A, the electrode tab12por the electrode tab12nprotrudes from each slit42of the first case40. The protruding electrode tabs12pand12nare bent so that the electrode tabs of adjacent battery cells10are folded and overlap each other. Specifically, the electrode tab12pprotrudes from the slit42, bends downwards at approximately 90 degrees, and abuts against the electrode tab12nof the downwardly adjacent battery cell10near the slit52. The electrode tab12pfurther abuts against the tab connecting bus bar45. The electrode tab12nprotrudes from the slit42, bends upwards at approximately 90 degrees, and abuts against the electrode tab12pof the upwardly adjacent battery cell10near the slit52. The laser for welding is irradiated onto the abutting portion, and the electrode tabs12p,12nand the tab connecting bus bar45as a metal member are welded together.

As illustrated inFIG.11B, the electrode tab12nof the battery cell10fprotrudes outside of the first case40from the slit42fand is bent so as to overlap the total minus bus bar60b. In other words, the electrode tab12nof the battery cell10fprotrudes from the slit42f, bends upwards at approximately 90 degrees, and abuts against the total minus bus bar60bnear the slit42f. The laser for welding is irradiated onto the abutting portion, and the electrode tab12nand the total minus bus bar60bare welded together.

FIGS.12A through12Care schematic diagrams respectively illustrating representative first through third steps for assembling the battery pack1according to the second embodiment. In the first step illustrated inFIG.12A, the six stacked battery cells10are inserted in the second case50. In this state, the first case40is fitted onto the second case50, which is holding the battery cells10and the insulating sheet20, from the front. In the second step illustrated inFIG.12B, the electrode tabs12pand12nof the battery cells10are caused to protrude from the slits42of the first case40and the slits52of the second case50. In the third step illustrated inFIG.12C, the electrode tabs12pand12nprotruding from the slits42of the first case40and the slits52of the second case50are bent to abut against the tab connecting bus bars45,55. UnlikeFIGS.10A to10C,FIG.11A, andFIG.11B, the protruding electrode tabs12pand12ninFIGS.12A to12Care not folded to overlap with each other. Cells can be connected by the tab connecting bus bars45,55when the tab connecting bus bars45,55are used in this way. The electrode tabs12pand12ntherefore do not necessarily need to be folded and overlapping with each other. The laser for welding is irradiated onto the electrode tabs12pand12nin this state, welding the electrode tabs12pand12nto the tab connecting bus bars45,55.

The above battery pack1according to the second embodiment achieves similar effects to those described in the first embodiment.

Modification

In the first and second embodiments, the electrode tabs12pand12nprotruding from the slits42of the first case40and the slits52of the second case50may be pressed against the outer walls of the first case40and the second case50by a jig70(pressing member70).FIGS.13A and13Billustrate an example of using the jig70. The jig70illustrated inFIG.13Aincludes windows71positioned facing the folded and overlapping portion of the electrode tabs12pand12n. The windows71are substantially rectangular and extend in the left-right direction. The windows71are referred to below as the windows71a,71b, and71cin order from bottom to top.FIG.13Billustrates the electrode tabs12pand12nbeing pressed against the outer walls of the first case40and the second case50by the jig70. In this state, a laser is irradiated from the windows71a,71b,71cto weld the electrode tabs12pand12n. In this way, the electrode tabs12pand12ncan be reliably abutted, and the gap therebetween can be reduced to secure weldability.

The jig70is made of metal or heat-resistant resin and is covered by an electrically insulating material. Hence, a short-circuit can be prevented and dissolution of the jig at the time of welding can be suppressed when the electrode tabs12pand12nare abutted against the outer walls of the first case40and the second case50.

An insulating cover72(window housing portion72) may further be provided on the jig70. The insulating cover72is, for example, attached to the lower portion of the jig70to be openable, as illustrated inFIGS.13A and13B. After the electrode tabs12pand12nare welded, the windows71a,71b,71care covered by the insulating cover72. This configuration can secure insulation of the welded portion and improve the reliability of the battery pack1.

Furthermore, a jig may be used to bend the electrode tabs12pand12n.FIGS.14A to18illustrate an example of a pressing member700that serves both to bend and press the electrode tabs12pand12n. Like the jig70, the pressing member700includes windows701positioned facing the folded and overlapping portion of the electrode tabs12pand12n. The windows701are referred to below as the windows701a,701b, and701cin order from bottom to top.FIG.14Aillustrates the state in which the electrode tabs12pand12nprotrude from the slits52but are not yet bent.FIG.14Billustrates the state in which the electrode tabs12pand12nare bent by the pressing member700and are pressed against the outer wall of the second case50. Fitting portions56for positioning the pressing member700may be provided on the second case50, as illustrated inFIG.14A. In this case, fitting holes that fit onto the fitting portions56are provided in the pressing member700.

FIGS.15A and15Bcorrespond toFIGS.14A and14Band illustrate the pressing member700being used to bend the electrode tabs12pand12n. The pressing member700includes recesses703for bending the electrode tabs12pand12n. Guides704and705are also provided for the electrode tabs12pand12nto be folded and overlap each other. The inner angles R of the guides704,705are offset, so that the electrode tab12pbends further inward than the electrode tab12n, whereas the electrode tab12nbends further outward than the electrode tab12p. A protrusion may be provided near the center of the recess703, for example. This configuration enables the electrode tabs12pand12nto bend 90 degrees or more. Weldability can thereby be improved, even when the electrode tabs12pand12nhave a large spring back.

The pressing member700may be fixed to the case by a fixing member. A fixing clamp removeable from the case, for example, may be used as the fixing member.FIG.16illustrates an example of fixing the pressing member700to the second case50with a fixing clamp710. While the pressing member700is fixed by the fixing clamp710, a laser is irradiated through the windows701a,701b,701cto weld the electrode tabs12pand12n. The position at which the pressing member700is fixed by the fixing clamp710can be set freely. For example, the pressing member700may be fixed at two opposite corners thereof, or at four locations along the perimeter. Other than the fixing clamp710, a clip or the like may also be used as the fixing member. Fixing the pressing member700with a fixing member in this way can secure weldability and improve productivity.

An insulating cover702(window housing portion702) may further be provided on the pressing member700. The insulating cover702is, for example, attached to the lower portion of the pressing member700to be openable, as illustrated inFIG.17A. After the electrode tabs12pand12nare welded, the insulating cover702is closed as illustrated inFIG.17Bto cover the windows701a,701b,701c. Protrusions58for attaching the insulating cover702may be provided on the second case50. In this case, engaging holes706are provided in the insulating cover702at positions corresponding to the protrusions58. When the windows701a,701b,701care covered in this way by the insulating cover702, insulation of the welded portion can be secured, and the reliability of the battery pack can be improved. The second case50has been described inFIGS.14A to18, but the pressing member700can similarly be used in the first case40as well.

As in the first embodiment, a metal plate44may be formed by insertion molding near the slits42(between slits42) on the outer wall of the first case40in the second embodiment. The metal plate44is formed by insertion molding inside the outer wall that faces the folded and overlapping portion of the electrode tabs12pand12n, as illustrated inFIG.18. If the laser penetrates the electrode tabs at the time of welding, this configuration can receive the laser with the metal plate44to protect the battery cells10. A metal plate may also be formed by insertion molding near the slits52(between slits52) on the outer wall of the second case50.

Instead of the tab connecting bus bar being provided in the first case40or the second case50, the second embodiment may be structured so that a bus bar module90provided with a tab connecting bus bar is abutted against and attached to the outer walls of the first case40and the second case50.FIG.19schematically illustrates an example of the bus bar module90. The bus bar module90includes slits91that pass through the bus bar module90at positions corresponding to the slits42of the first case40. The slits91are substantially rectangular, extend in the left-right direction, and are formed to allow the electrode tabs12pand12nof the battery cell10to protrude through the slits91. The bus bar module90includes a tab connecting bus bar92between the slits91. As illustrated inFIG.19, the electrode tab12por12nprotrudes from each slit91and is bent so that the electrode tabs of adjacent battery cells10are folded and overlap each other. Specifically, the electrode tab12pprotrudes from the slit91, bends downwards at approximately 90 degrees, and abuts against the electrode tab12nof the downwardly adjacent battery cell10near the slit91. The electrode tab12pfurther abuts against the tab connecting bus bar92. The electrode tab12nprotrudes from the slit91, bends upwards at approximately 90 degrees, and abuts against the electrode tab12pof the upwardly adjacent battery cell10near the slit91. The laser for welding is irradiated onto the abutting portion, and the electrode tabs12p,12nand the tab connecting bus bar92are welded together. The bus bar module90may further include an insulating cover93. The insulating cover93is, for example, attached to the lower portion of the bus bar module90to be openable, as illustrated inFIG.19. After the electrode tabs12pand12nare welded, the welded portion is covered by the insulating cover93. This configuration can secure insulation of the welded portion and improve the reliability of the battery pack. The bus bar module90is attached to the first case40inFIG.19, but the bus bar module90may similarly be attached to the second case50.

The shape of the tab connecting bus bar included in the bus bar module90may be changed.FIG.20illustrates an example of using a tab connecting bus bar94that has a substantially C-shaped cross-section. Use of the tab connecting bus bar94allows the electrode tab12por12nprotruding from each slit91to abut against the tab connecting bus bar94without bending. The laser for welding is irradiated onto the abutting portion to weld the electrode tab12pand the tab connecting bus bar94together, or to weld the electrode tab12nand the tab connecting bus bar94together.

It will be apparent to a person of ordinary skill in the art that the present disclosure can be embodied in forms other than the above embodiment without departing from the spirit or essential features of the present disclosure. Accordingly, the description above is only a non-limiting example. The scope of the present disclosure is defined not by the description above, but by the appended claims. Among all possible modifications, the modifications within the range of equivalents are to be considered encompassed by the claims.

A restraining plate30may also be provided along with the opening O at the lower surface side of the battery cell assembly100in the battery pack1. The battery cell assembly100is thereby sandwiched from both above and below by rigid restraining plates30, further improving the pressure retention.

Similarly, an insulating sheet20may also be provided at the lower surface side of the battery cell assembly100in the battery pack1. The electrical insulation in the battery pack1can thereby be further improved.

The number of battery cells10and the number of windows71and701are not limited to the above configurations. Any number of battery cells10may be included. The windows71and701may be provided in an appropriate form corresponding to the number of battery cells10.

REFERENCE SIGNS LIST