BATTERY PACK

A battery pack disclosed herein includes: a plurality of single cells each having an electrode body and a battery case housing the electrode body, and arrayed in a predetermined direction; and one or more spacers each disposed between two of the single cells that are adjacent to each other in the predetermined direction. The spacer has, on at least one of surfaces facing the single cells, a convex portion that protrudes toward the single cell. The convex portion is in contact with the battery case of the single cell. A contact portion of the battery case that is a portion in contact with the convex portion protrudes into the battery case so as to be able to stop the electrode body from moving in a direction toward the contact portion.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2019-208837 filed on Nov. 19, 2019, incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The disclosure relates to a battery pack.

2. Description of Related Art

To achieve higher outputs, secondary batteries that are used as onboard power sources, such as lithium-ion secondary batteries and nickel-metal hydride secondary batteries, are commonly used in the form of a battery pack in which a plurality of single cells is connected in series.

Typically, a battery pack has a configuration in which a plurality of single cells is arrayed (stacked) in a predetermined direction, with a spacer interposed between the single cells, and a binding load is applied to the battery pack (e.g., see Japanese Patent Application Publication No. 2015-041484). In JP 2015-041484 A, spacers are each disposed at a central part of a flat surface of a single cell, and the central part of the flat surface of the single cell is dented by a load into a shape matching the outline of the spacer. According to JP 2015-041484 A, this configuration can reduce the likelihood that a welded area between a lid and a main body of a battery case may undergo fatigue deterioration when the internal pressure of the battery case rises.

SUMMARY

However, a thorough review by the inventors has found that when a vehicle equipped with the battery pack of the related art represented by the above one is subjected to external impact, for example, as the vehicle runs over a bump in the road, the electrode bodies inside the single cells move, which may result in damage, such as internal short-circuit or internal disconnection of terminals. In this respect, there is room for improvement.

An object of the disclosure is therefore to provide a battery pack that is less prone to damage due to external impact.

A battery pack disclosed herein includes: a plurality of single cells each having an electrode body and a battery case housing the electrode body, and arrayed in a predetermined direction; and one or more spacers each disposed between two of the single cells that are adjacent to each other in the predetermined direction. The spacer has, on at least one of surfaces facing the single cells, a convex portion that protrudes toward the single cell. The convex portion is in contact with the battery case of the single cell. A contact portion of the battery case that is a portion in contact with the convex portion protrudes into the battery case so as to be able to stop the electrode body from moving in a direction toward the contact portion.

Thus configured, the battery pack provided by the disclosure is less prone to damage due to external impact.

In one aspect of the battery pack disclosed herein, the contact portion is located so as to face an end portion of the electrode body.

The battery pack thus configured is even less prone to damage due to external impact.

In another aspect of the battery pack disclosed herein, an electrode terminal is mounted on the battery case, and the contact portion is located so as to face an end portion of the electrode body on the side of the electrode terminal.

The battery pack thus configured is much less prone to damage due to external impact.

In yet another aspect of the battery pack disclosed herein, the spacer further has, on at least one of the surfaces facing the single cells, a second convex portion that protrudes toward the single cell; a contact portion of the battery case that is a portion in contact with the second convex portion protrudes into the battery case so as to be able to stop the electrode body from moving in a direction toward the contact portion in contact with the second convex portion; and the contact portion in contact with the second convex portion is located so as to face an end portion of the electrode body on the opposite side from the electrode terminal.

The battery pack thus configured is far less prone to damage due to external impact.

In yet another aspect of the battery pack disclosed herein, each of the spacers has a convex portion on each surface, and contact portions of the battery case of the single cell sandwiched between the spacers that are portions in contact with the convex portions protrude into the battery case and keep the electrode body in place by holding the electrode body from both sides.

The battery pack thus configured is even less prone to damage due to external impact.

DETAILED DESCRIPTION OF EMBODIMENTS

A preferred embodiment of a battery pack disclosed herein will be described below with reference to the drawings as necessary. The embodiment described here is, of course, not intended to particularly limit the disclosure. The battery pack disclosed herein can be implemented based on the contents disclosed in this specification and the technical common knowledge in this field.

In the drawings referred to below, those members and parts that have the same workings may be denoted by the same reference signs to omit or simplify an overlapping description. Reference signs U, D, F, Rr, L, and R in the drawings mean up, down, front, rear, left, and right, respectively. Reference signs X, Y, and Z in the drawings mean an array direction of single cells, a width direction of a long-side wall of the single cell, and a vertical direction of the long-side wall of the single cell, respectively. However, these directions are merely for the convenience of description and do not in any way limit the form of installation of the battery pack. The dimensional relationships (lengths, widths, thicknesses, etc.) in the drawings do not reflect the actual dimensional relationships.

FIG. 1is a perspective view schematically showing a battery pack1that is one example of embodiments according to the disclosure. The battery pack1includes a plurality of single cells10and a plurality of spacers40. The battery pack1further includes a binding mechanism. Specifically, the battery pack1includes, for example, a pair of end plates50A,50B, a plurality of binding bands52, and a plurality of screws54as shown inFIG. 1. The pair of end plates50A,50B is disposed at both ends of the battery pack1in a predetermined array direction X (a front-rear direction inFIG. 1). Each binding band52is mounted on the pair of end plates50A,50B like a bridge therebetween. The single cells10are arrayed in the array direction X. The spacers40are each disposed between two of the single cells10that are adjacent to each other in the array direction X. Two end spacers60are disposed respectively between the single cell10and the end plate50A and the single cell10and the end plate50B. The number of the single cells10is not particularly limited as long as the number is not smaller than two. When the battery pack1has two single cells10, the battery pack1has one spacer40.

The end plates50A,50B sandwich the single cells10, the spacers40, and the two end spacers60in the array direction X. The binding bands52are fixed to the end plates50A,50B with the screws54. Each binding band52is mounted so as to apply a specified binding pressure in the array direction X. The binding bands52are mounted, for example, such that a contact pressure on an area of the single cell10that is pressed by the spacer40is roughly 90 to 600 kgf/cm2, for example, about 200 to 500 kgf/cm2. Thus, a load is applied to the single cells10, the spacers40, and the two end spacers60from the array direction X, so that the battery pack1is integrally held. In the shown example, the binding mechanism is composed of the end plates50A,50B, the binding bands52, and the screws54, but the binding mechanism is not limited to this example.

FIG. 2is a plan view schematically showing the single cell10.FIG. 3is a vertical sectional view schematically showing the single cell10. The single cell10is typically a secondary battery capable of charging and discharging repeatedly, for example, a lithium-ion secondary battery, a nickel-metal hydride battery, or an electric double-layer capacitor. The single cell10includes an electrode body20, an electrolyte (not shown), and a battery case30.

The battery case30is a case housing the electrode body20and the electrolyte. The battery case30is made of, for example, metal, such as aluminum or steel. The battery case30in the shown example has a rectangular outer shape with a bottom (rectangular parallelepiped shape). The battery case30is composed of a lid and a case main body. The lid and the case main body are joined together by welding, such as laser welding.

The battery case30has an upper wall30u, a bottom wall30bfacing the upper wall30u, and a pair of short-side walls30nand a pair of long-side walls30was side walls continuing from the bottom all30b. The lid of the battery case30is formed by the upper wall30u, and the case main body thereof is formed by the bottom wall30b, the pair of short-side walls30n, and the pair of long-side walls30w. The case main body is formed, for example, by performing deep drawing on one metal sheet. The pair of short-side walls30nand the pair of long-side walls30weach have a flat part. The thicknesses (plate thicknesses) of the bottom wall30b, the pair of short-side walls30n, and the pair of long-side walls30ware roughly 1 mm or less, typically 0.5 mm or less, for example, 0.3 to 0.4 mm. The pair of long-side walls30wof each battery case30faces the spacers40, except at end portions of the battery pack1. At each end portion of the battery pack1, the pair of long-side walls30wof the battery case30faces the spacer40and the end spacer60.

The upper wall30uof the battery case30is provided with a thin safety valve32that is set to release the internal pressure of the battery case30when the internal pressure has risen to or beyond a predetermined level. The upper wall30uof the battery case30is further provided with a filling port (not shown) through which the electrolyte is poured. A positive-electrode terminal12T and a negative-electrode terminal14T for external connection are mounted on the upper wall30uof the battery case30. The positive-electrode terminal12T of one single cell10and the negative-electrode terminal14T of an adjacent single cell10are electrically connected to each other through a bus bar18. Thus, the single cells10are electrically connected in series. However, the shape, size, number, arrangement, connection method, etc. of the single cells10forming the battery pack1are not limited to those in the aspect disclosed herein but can be changed as necessary. For example, some or all of the single cells10of the battery pack1may be electrically connected in parallel.

The configuration of the electrode body20and the electrolyte housed inside the battery case30may be the same as a conventional one and is not particularly limited. The electrolyte is, for example, a nonaqueous electrolyte containing a nonaqueous solvent and a supporting electrolyte. The nonaqueous solvent is, for example, carbonate, such as ethylene carbonate (EC), dimethyl carbonate (DMC), or ethyl methyl carbonate (EMC). The supporting electrolyte is, for example, lithium salt, such as LiPF6or LiBF4.

FIG. 4is an exploded view schematically showing the electrode body20. In the shown example, the electrode body20is a rolled electrode body. The electrode body20is formed by laminating a band-shaped positive electrode12and a band-shaped negative electrode14so as to be insulated from each other by band-shaped separators16, and rolling this laminate around a rolling axis WL.

The positive electrode12includes a positive-electrode current collector and a positive-electrode active material layer12aanchored to a surface of the positive-electrode current collector. The positive-electrode active material layer12acontains a positive-electrode active material that can reversibly occlude and release charge carriers, for example, lithium transition metal composite oxide. The negative electrode14includes a negative-electrode current collector and a negative-electrode active material layer14aanchored to a surface of the negative-electrode current collector. The negative-electrode active material layer14acontains a negative-electrode active material that can reversibly occlude and release charge carriers, for example, a carbon material. The separators16are porous members through which charge carriers can pass and which insulate the positive-electrode active material layer12aand the negative-electrode active material layer14afrom each other.

In a width direction Y of the electrode body20, a width W3of the separator16is larger than a width W1of the positive-electrode active material layer12aand a width W2of the negative-electrode active material layer14a. The width W2of the negative-electrode active material layer14ais larger than the width W1of the positive-electrode active material layer12a. Thus, W1, W2, and W3meet a condition W1<W2<W3. In the range of the width W1of the positive-electrode active material layer12a, the positive-electrode active material layer12aand the negative-electrode active material layer14aface each other while being insulated from each other.

An exposed positive-electrode current collector portion12nis provided at a right end of the electrode body20in the width direction Y. A positive-electrode current collector plate12cfor a current collecting foil is attached to the exposed positive-electrode current collector portion12n. The positive electrode12of the electrode body20is electrically connected to the positive-electrode terminal12T through the positive-electrode current collector plate12c. An exposed negative-electrode current collector portion14nis provided at a left end of the electrode body20in the width direction Y. A negative-electrode current collector plate14cfor a current collecting foil is attached to the exposed negative-electrode current collector portion14n. The negative electrode14of the electrode body20is electrically connected to the negative-electrode terminal14T through the negative-electrode current collector plate14c.

The electrode body20has a flattened appearance. As seen in a cross-section orthogonal to the rolling axis WL, the electrode body20has a pair of flat roll portions20fand a pair of round roll portions20rinterposed between the pair of flat roll portions20fA pair of end portions of the electrode body20in the width direction Y is open, and an inside and outside of the electrode body20communicate with each other at the end portions in the width direction Y.

In the single cell10, one of the pair of round roll portions20rof the electrode body20is disposed on the side of the bottom wall30bof the battery case30, while the other is disposed on the side of the upper wall30uof the battery case30. In other words, the round roll portions20rof the electrode body20are disposed one above the other in a vertical direction Z. The pair of end portions of the electrode body20in the width direction Y is disposed so as to face the pair of short-side walls30nof the battery case30. The pair of flat roll portions20fof the electrode body20is disposed so as to face the pair of long-side walls30wof the battery case30. In other words, the pair of flat roll portions20fof the electrode body20is disposed along the array direction X.

While the electrode body20is a rolled electrode body in the shown example, the form of the electrode body20is not limited to this example. The electrode body20may be a laminated electrode body in which a plurality of sheet-shaped positive electrodes and a plurality of sheet-shaped negative electrodes are alternately laminated.

FIG. 5is a schematic partial sectional view of a rear part of the battery pack1taken along a stacking direction and an up-down direction. The spacer40is interposed between two adjacent single cells10. The spacer40is made of, for example, a resin material, such as polypropylene (PP) or polyphenylene sulfide (PPS), or a metal material having high heat conductivity.

In the shown example, the spacer40has a plurality of ribs42on each surface. A form of the spacer40not having the ribs42is also possible. The ribs42may have the same configuration as the ribs of a spacer of a commonly known battery pack. In the shown example, the ribs42face the electrode body20(particularly the flat roll portion200. Since a binding load is applied to the battery pack1, the ribs42press the battery case30with the binding load. As the battery case30is pressed, expansion, etc. of the electrode body20can be restricted.

In the shown example, the ribs42are arranged in a comb-like row to allow a cooling fluid (e.g., air) to pass through a gap between the spacer40and the battery case30. Having such ribs42, the spacer40functions as a heat dissipating member that dissipates heat generated inside the single cell10. The arrangement of the ribs42is not limited to this example.

The spacer40has, on a surface facing the right single cell10, a convex portion44R that protrudes toward the single cell10. The spacer40further has, on a surface facing the left single cell10, a convex portion44L that protrudes toward the single cell10.

In the following, the spacer40and the single cell10on the right side thereof will be specifically described. The convex portion44R is in contact with the battery case30of the single cell10. A contact portion34of the battery case30that is a portion in contact with the convex portion44R protrudes into the battery case30. The contact portion34serves as a stopper when the electrode body20moves in a direction toward the contact portion34(i.e., in the upward direction U inFIG. 5). Thus, the contact portion34protrudes into the battery case30so as to be able to stop the electrode body20from moving in the direction toward the contact portion34.

In the shown example, the contact portion34protrudes into the battery case30as the long-side wall30wdeforms under the binding load into a shape corresponding to the convex portion44R of the spacer40. The contact portion34is concave when seen from an outer surface side of the single cell10and convex when seen from an inner surface side of the single cell10. Since the contact portion34can be protruded into the battery case30by deforming the battery case30by the binding load, the long-side wall30wof the battery case30of the single cell10before assembly of the battery pack1may be flat. Alternatively, to make it easy to position the convex portion44R of the spacer40and the battery case30, a portion of the long-side wall30wof the battery case30that is to come into contact with the convex portion44R of the spacer40may be deformed before assembly of the battery pack1so as to become concave when seen from the outer surface side of the single cell10. In this case, that portion of the long-side wall30wmay be deformed into a shape corresponding to the convex portion44R of the spacer40, but it is preferable that the amount of deformation be smaller than that so as not to hinder insertion of the electrode body20into the battery case30.

The contact portion34has a protrusion protruding into the battery case30. The dimension of this protrusion can be determined as appropriate according to the design of the single cell10and the electrode body20. The dimension of the protrusion in the protruding direction (i.e., the height of the protrusion; specifically, the dimension from an inner surface of the battery case30to the apex of the protrusion in the array direction X) is preferably not smaller than 0.5% nor larger than 15%, and more preferably not smaller than 2% nor larger than 10%, of the thickness of the electrode body20.

In the shown example, the contact portion34is located so as to face an end portion of the electrode body20. In this case, the electrode body20can be effectively stopped from moving, so that damage due to external impact is less likely to occur. However, the position of the contact portion34is not limited to this example and can be set as appropriate according to the outer shape of the electrode body20. For example, when the electrode body20has an outer shape with a depression at a central part, the contact portion34may be provided at a position in the battery case30facing the depression at the central part of the electrode body20.

It is advantageous that, as in the shown example, the contact portion34faces that end portion of the electrode body20that is on the side of the electrode terminals (i.e., the positive-electrode terminal12T and the negative-electrode terminal14T). Internal disconnection of the terminals is more likely to occur when the electrode body20moves in a direction toward the electrode terminals. This configuration can restrict movement of the electrode body20in the direction toward the electrode terminals, so that damage due to external impact is less likely to occur. In the shown example, the positive-electrode terminal12T and the negative-electrode terminal14T are mounted on the lid, and the lid and the case main body are welded together. This configuration can reduce the likelihood of fatigue deterioration of the weld between the lid and the case main body.

FIG. 6schematically shows a more preferred form of the single cell. In the more preferred form, the spacer40further has, on at least one of the surfaces facing the single cells10, a second convex portion that protrudes toward the single cell10, and a contact portion (second contact portion)34′ of the battery case30that is a portion in contact with the second convex portion protrudes into the battery case30so as to be able to stop the electrode body20from moving in a direction toward the second contact portion34′, and the second contact portion34′ is located so as to face an end portion of the electrode body20on the opposite side from the electrode terminals. Thus, when the first contact portion34and the second contact portion34′ are respectively provided at both end portions of the electrode body20as shown inFIG. 6, movement of the electrode body20can be further restricted, so that damage due to external impact is even less likely to occur.

In the shown example, the contact portion34protruding into the battery case30is in contact with the electrode body20. However, the contact portion34need not be in contact with the electrode body20. The smaller the distance between the contact portion34and the electrode body20is, the further the movement of the electrode body20can be restricted. In particular, it is advantageous that the contact portion34is in contact with the electrode body20. The contact portion34may be directly in contact with the electrode body20, or when the electrode body20is covered with an insulation film, the contact portion34may be indirectly in contact with the electrode body20through the insulation film.

The spacer40has, also on a surface facing the left single cell10, a convex portion44L that protrudes toward the single cell10. The configuration of the surface of the spacer40facing the left single cell10and the left single cell10is the same as that described above. Specifically, the convex portion44L is in contact with the battery case of the left single cell10, and similarly, a contact portion of the battery case that is a portion in contact with the convex portion44L protrudes into the battery case so as to be able to stop the electrode body from moving in a direction toward the contact portion. However, the spacer40may have the convex portion on only one of the surfaces.

It is advantageous that, as in the shown example, the spacer40has the convex portions44R,44L on the respective surfaces, and that the contact portions of the battery case30of the single cell10sandwiched between the spacers40that are portions in contact with these convex portions protrude into the battery case30of the single cell10and keep the electrode body20in place by holding the electrode body20from both sides. This configuration can firmly fix the electrode body20and thereby further restrict the movement of the electrode body20, so that damage due to external impact is even less likely to occur. In particular, it is more advantageous when the electrode body20is a rolled electrode body as in the shown example, because then the round roll portions20rare provided at the end portions of the electrode body20, which makes it easy to keep the electrode body20in place by holding the end portions thereof from both sides.

A surface of the end spacer60facing the end plate50B is flat. On the other hand, the end spacer60has ribs62on a surface facing the single cell10. Like the ribs42of the spacer40, the ribs62are arranged in a comb-like row. The end spacer60may have the same configuration as a commonly known end spacer disposed between an end plate and a single cell. However, it is advantageous that the end spacer60further has a convex portion64on the surface facing the single cell10as in the shown example. Like the convex portion44R of the spacer40, the convex portion64is in contact with the battery case30of the single cell10, and a contact portion36of the battery case30that is a portion in contact with the convex portion64protrudes into the battery case30so as to stop the electrode body from moving toward the contact portion36. This configuration makes it less likely that the single cell10located at the end of the battery pack1may get damaged due to external impact. Alternatively, a configuration of the end spacer60not having the convex portion64can be adopted.

The battery pack1configured as has been described above is less prone to damage due to external impact, such as internal short-circuit or internal disconnection of the terminals. Moreover, the battery pack1is less prone to fatigue deterioration of the weld between the lid and the case main body of the battery case. The battery pack1can be used for various applications. For example, the battery pack1can be suitably used as a power source (driving power source) for a motor mounted in a vehicle. While the type of the vehicle is not particularly limited, the vehicle is typically an automobile, for example, a plug-in hybrid vehicle (PHV), a hybrid vehicle (HV), or an electric vehicle (EV). The battery pack1can also be used as an industrial or household electricity storage device.

To demonstrate the effects of the battery pack disclosed herein, the inventors have actually conducted simple tests using a single cell and a pair of spacers. Examples of these tests will be described below, but these test examples do not in any way limit the disclosure.

Production of Test Pieces

A single cell110having a rolled electrode body120housed inside a battery case130as shown inFIG. 7was prepared. The configuration of the rolled electrode body120of the single cell110was the same as that of a common lithium-ion secondary battery. The battery case130was composed of a case main body and a lid, which were joined together by laser welding. Terminals (not shown) were mounted to the single cell110as inFIG. 2andFIG. 3.

A pair of spacers140having ribs142and a convex portion144on one surface as shown inFIG. 7was prepared. The spacers140were made of PP. The single cell110was sandwiched between the pair of spacers140such that the surfaces having the convex portion144and the ribs142face the single cell110. This set was further sandwiched between a pair of stainless-steel binding plates and a binding load was applied. The area of contact between the binding plate and the spacer140was 13 cm2, and the load applied was 50 N. Thus, a test piece for Test Example 1 was produced. In the test piece for Test Example 1, contact portions of the battery case130that were portions in contact with the convex portions were deformed by the binding load and protruded into the battery case130, and a dimension h of the protrusion in the protruding direction (h inFIG. 7) was 0.2 cm.

For Test Example 2, a test piece was prepared in which the dimension of the convex portion144was changed and the dimension h (inFIG. 7) of the contact portion in the protruding direction was 0.4 cm.

A pair of spacers240having ribs242and no convex portion as shown inFIG. 8was prepared. The spacers240were also made of PP. Each spacer240had the ribs242also at a part corresponding to the part of the spacer140where the convex portion144was provided. The single cell110was sandwiched between the pair of spacers240such that the surfaces having the ribs242face the single cell110. This set was further sandwiched between a pair of stainless-steel binding plates and a binding load was applied. The area of contact between the binding plate and the spacer240was 13 cm2, and the load applied was 50 N. Thus, a test piece for Test Example 3 was produced. In the test specimen for Test Example 3, the dimension h (inFIG. 7) in the protrusion direction was equivalent to 0 cm.

Impact Resistance Test

The test pieces for Test Examples 1 to 3 were subjected to impact directed upward (in the U-direction in the drawings). The test pieces having been subjected to the impact were observed by X-ray transmission and checked as to whether movement of the electrode body120and internal disconnection occurred. In the impact resistance test, the strength of the impact was varied from 10 G to 100 G. The result is shown in Table 1. [Table 1]

The result in Table 1 shows that providing the convex portions on the spacers and protruding the contact portions of the battery case in contact with the convex portions into the battery case can reduce the likelihood of movement of the electrode body and internal disconnection.

Test on Resistance of Weld of Battery Case to Fatigue Deterioration

The internal pressure of each single cell of the test pieces for Test Examples 1 to 3 was changed by introducing air into the cell through a side surface portion thereof. The initial internal pressure of the cell was 0.25 MPa, and a change in the internal pressure of ±0.20 MPa was counted as one cycle. The internal pressure was repeatedly changed, and the number of cycles at which air leaked through the weld between the lid and the main body of the battery case130was obtained. Further, the number of cycles at which air leaked through the weld, with a change in the internal pressure of ±0.15 MPa counted as one cycle, and the number of cycles at which air leaked through the weld, with a change in the internal pressure of ±0.10 MPa counted as one cycle, were also obtained. The result is shown inFIG. 9.

The result inFIG. 9shows that providing the convex portions on the spacers and protruding the contact portions of the battery case in contact with the convex portions into the battery case can reduce the likelihood of fatigue deterioration of the weld between the lid and the main body of the battery case.

While specific examples of the disclosure have been described in detail above, these examples are merely illustrative and do not limit the scope of the claims. The technique described in the claims include various modifications and changes made to the specific examples illustrated above.