JP7612404B2 - Vehicle Battery System - Google Patents

Description

The present invention relates to an in-vehicle battery system equipped with a battery pack containing multiple battery modules.

The following Patent Document 1 discloses an in-vehicle battery system equipped with a battery pack that houses multiple battery modules. Each battery module houses multiple battery cells. The system disclosed in Patent Document 1 uses bus bars that electrically connect the battery modules to each other and to other electrical components. The following Patent Document 2 discloses a bus bar, and also discloses that the intermediate portion between the terminals of the bus bar is covered with a heat-resistant thermosetting elastomer (insulating material).

Currently, nickel-metal hydride batteries or lithium-ion batteries are generally used in on-board battery systems. In particular, battery electric vehicles (BEVs) that do not have an internal combustion engine and run only on power stored in the battery are desired to be equipped with a large-capacity battery pack to achieve a long driving range. For this reason, lithium-ion batteries with high energy density are generally used in BEVs. Lithium-ion batteries have high capacity density and can reduce the volume of the battery pack, improving on-board performance. Furthermore, lithium-ion batteries have excellent output density, making them desirable in terms of vehicle dynamics. As such, lithium-ion batteries have many advantages as on-board batteries, and are therefore widely used not only in BEVs but also in hybrid electric vehicles (HEVs) that also have internal combustion engines. The lithium-ion battery disclosed in the above-mentioned Patent Document 1 is also a lithium-ion battery.

JP 2010-277863 A JP 2012-182043 A

To facilitate vehicle mountability of the battery pack, battery modules and other components are densely packed inside the battery pack. For this reason, insulating materials such as insulating tubes and insulating covers are attached to the intermediate portions between the terminals of the busbar to prevent short circuits. In addition, some busbars carry high-voltage current, and insulating materials are also used to protect against high voltage. In addition, the battery module of a lithium-ion battery has a structure that exhausts high-temperature gas generated inside the module to the outside when it overheats. Therefore, if high-temperature gas exhausted from the battery module is released into the battery pack, there is a concern that it may cause thermal damage to the insulating materials attached to the busbar.

The object of the present invention is to provide an in-vehicle battery system equipped with bus bars that have excellent heat resistance.

The vehicle-mounted battery system according to the present invention includes a battery pack that houses multiple battery modules inside, and a bus bar having at least two terminals that electrically connects the battery modules to each other (or the battery modules to electrical components) within the battery pack. Each battery module houses multiple lithium-ion battery cells. The bus bar includes a bus bar body made of conductive metal on which the above-mentioned terminals are formed, and an insulating member that covers the surface of the intermediate portion between the terminals. An expanded graphite layer containing thermally expandable graphite is formed on the surface of the insulating member.

The present invention provides an in-vehicle battery system equipped with bus bars that have excellent heat resistance.

FIG. 1 is a schematic exploded perspective view of a battery pack of an in-vehicle battery system according to an embodiment. FIG. 2 is a schematic perspective view of a battery module housed in the battery pack. FIG. 3 is a perspective view, partly in section, showing a part of the inside of the battery pack. FIG. 4 is a cross-sectional view of a bus bar of the vehicle-mounted battery system (a cross-sectional view taken along line IV-IV in FIG. 3). FIG. 5 is a cross-sectional view showing a state in which the expanded graphite layer of the bus bar is expanded. FIG. 6 is a cross-sectional view showing a first modified example of the bus bar. FIG. 7 is a cross-sectional view showing a second modified example of the bus bar. FIG. 8 is a cross-sectional view showing a third modified example of the bus bar.

The following describes an in-vehicle battery system according to an embodiment, with reference to the drawings. As shown in FIG. 1, the battery system includes a battery pack 2 that houses multiple battery modules 1 therein. As shown in FIG. 2, each battery module 1 houses multiple lithium-ion battery cells 3 therein. The battery module 1 has connection terminals 4 (see FIG. 3) on its outer surface. The battery module 1 is electrically connected to other battery modules 1 and to other electrical components via the connection terminals 4.

When a lithium-ion battery overheats, it generates high-temperature gas. For this reason, the battery module 1 is formed with vent holes 5 for discharging this high-temperature gas. In FIG. 2, a vent hole 5 is provided for each lithium-ion battery cell 3. Note that as long as the vent hole 5 can discharge the high-temperature gas generated in the lithium-ion battery cell 3 to the outside of the battery module 1, it is not necessary that a vent hole 5 is provided for each lithium-ion battery cell 3, although this depends on the internal structure of the battery module 1.

As shown in FIG. 1, the battery pack 2 has a structure consisting of an upper case 2U and a lower case 2L. A plurality of the above-mentioned battery modules 1 are housed in the internal space formed by the upper case 2U and the lower case 2L. The battery pack 2 is heavy, and is mounted under the passenger compartment floor in order to set the center of gravity of the vehicle low from the viewpoint of vehicle dynamics performance. In addition, in the case of a BEV, many battery modules 1 must be mounted in order to obtain a sufficient driving range, and therefore the volume is large. For this reason, the battery modules 1 and associated electrical components are densely packed inside the battery pack 2 in order to keep the volume as small as possible.

Figure 3 shows an enlarged view of a portion of the inside of the battery pack 2. As shown in Figure 3, bus bars 6 (6A, 6B) are used to electrically connect the battery modules 1 to each other or to the battery modules 1 and electrical components. The bus bar 6A connects adjacent battery modules 1 in series. The bus bar 6B connects a set of battery modules 1 connected in series to each other, or connects the battery module 1 to electronic components.

As shown in FIG. 4, which is a cross-sectional view of line IV-IV in FIG. 3, the busbar 6 includes a busbar body 60 made of a conductive metal (copper) with high electrical conductivity. The busbar body 60 includes terminals 60T (see FIG. 3) at both ends, and is electrically connected to the battery module 1 and electrical components via the terminals 60T. In FIG. 3, the terminal 60T of the busbar 6A is connected to the above-mentioned connection terminal 4 of the battery module 1, and the connection is protected by a cover to prevent short circuits. The terminal 60T of the busbar 6B is connected to other connection terminals such as electronic components inside the support member 7 (7B) made of thermosetting resin that supports the busbar 6B from below (see the support member 7B on the left side in FIG. 3). This connection is disposed inside the support member 7 to prevent short circuits.

Busbar 6B is supported from below by support members 7B not only at its ends but also at other portions (see support member 7B on the right side in Figure 3). Note that Figure 4 is a cross-sectional view taken along line IV-IV in Figure 3, which shows the cross-section of busbar 6B, but busbar 6A also has a similar cross section. Furthermore, busbar 6 (6A, 6B) has at least two terminals 60T, and may have three or more terminals 60T. The middle portion between two adjacent terminals 60T is covered by an insulating member 61, which will be described later, to prevent short circuits. Furthermore, terminals 60T do not necessarily have to be provided at both ends of busbar body 60 (busbar 6).

As described above, the intermediate portion between two adjacent terminals 60T of the busbar body 60 (terminals 60T at both ends of the busbar body 60 in this embodiment) is covered with an insulating member 61. The insulating member 61 covers the surface of the intermediate portion and prevents short-circuiting with other components. In this embodiment, the insulating member 61 is composed of a first cover 61a and a second cover 61b made of a thermosetting resin. The first cover 61a and the second cover 61b are fitted to each other with the busbar body 60 in between to form the insulating member 61 that electrically protects the intermediate portion. By configuring the insulating member 61 as a tubular case in this way, the insulating member 61 can be easily attached to the busbar body 60. The insulating member 61 may be formed as a tube made of heat-resistant resin or rubber instead of a case.

As shown in FIG. 4, an expanded graphite layer 62 containing thermally expandable graphite is formed on the surface of the insulating member 61. In this embodiment, a flexible sheet material containing thermally expandable graphite is formed and attached to the surface of the insulating member 61 to form the expanded graphite layer 62. The expanded graphite layer 62 is formed on the outer peripheral surface of the insulating member 61, and is not formed on the end face or inner peripheral surface of the tubular insulating member 61. In addition, the expanded graphite layer 62 does not have to cover the entire outer peripheral surface of the insulating member 61, and may not be formed, for example, near the terminal 60T (i.e., near the end of the insulating member 61).

Thermally expandable graphite is made by inserting an oxidizer between layers of flake graphite. When it is heated rapidly, the oxidizer burns and gasifies, and the gas spreads the layers apart. For this reason, thermally expandable graphite expands in the direction in which the layers are stacked. The expansion start temperature is between 100 and 200 degrees Celsius, and can be adjusted by the type of oxidizer. The expansion rate can also be adjusted by the oxidizer. Thermally expandable graphite can also be used as a filler (additive to change characteristics) for resin and rubber. As mentioned above, when the lithium-ion battery cell 3 generates high-temperature gas due to overheating, the high-temperature gas is discharged to the outside of the battery module 1 and to the inside of the battery pack 2 through the vent hole 5. Therefore, the expanded graphite layer 62 of the bus bar 6 expands due to the heat of the high-temperature gas as shown in FIG. 5.

The expanded graphite layer 62 has a porous or foam-like structure with many tiny gaps inside, and functions as a heat insulating material. As a result, the insulating member 61 is prevented from being exposed to the heat of the high-temperature gas, and the insulating member 61 is prevented from being thermally damaged and the busbar body 60 is prevented from being exposed. As described above, the insulating member 61 is generally made of a thermosetting resin, which has better heat resistance than a thermoplastic resin. However, depending on the type of thermosetting resin, the temperature of the high-temperature gas generated by the overheating of the lithium-ion battery cell 3 may exceed the heat resistance temperature of the thermosetting resin. Therefore, by expanding the expanded graphite layer 62 in this way, the insulating member 61 can be protected from the high-temperature gas.

Here, the expanded graphite layer 62 is only formed on the surface of the insulating member 61, so it does not make the manufacture of the busbar 6 significantly more difficult. In addition, under normal circumstances, the expanded graphite layer 62 is only formed on the surface of the insulating member 61, and does not significantly increase the size of the busbar 6, nor does it reduce the design freedom of the battery pack 2, which contains a high density of components inside. The expanded graphite layer 62 expands only when the lithium ion battery cell 3 generates high-temperature gas due to overheating, thereby fulfilling the function of protecting the insulating member 61 from the high-temperature gas. As a result, it is possible to reliably prevent the busbar body 60 from being exposed and causing a short circuit (particularly a ground fault).

Next, modified examples of the formation form of the expanded graphite layer 62 will be described. First, in modified example 1 shown in FIG. 6, the expanded graphite layer 62 is configured as a tubular case, similar to the insulating member 61. That is, in this modified example, the expanded graphite layer 62 is configured of a first cover 62a and a second cover 62b. The first cover 62a and the second cover 62b are fitted together with the insulating member 61 in between, thereby forming the expanded graphite layer 62 that protects the insulating member 61.

As described above, thermally expandable graphite can be used as a filler. Therefore, the first cover 62a and the second cover 62b can be injection molded using a resin mixed with thermally expandable graphite as a filler. Note that thermally expandable graphite that does not expand at the temperature during injection molding is used. By configuring the expandable graphite layer 62 in this way in a case shape, the expandable graphite layer 62 can be easily formed by attaching the first cover 62a and the second cover 62b so as to cover the insulating member 61.

Next, in the modified example 2 shown in FIG. 7, the expanded graphite layer 62 is molded integrally with the first cover 61a and the second cover 61b of the insulating member 61. When the first cover 61a is injection molded, the portion that contacts the busbar body 60 is first injection molded with a resin that does not contain thermally expandable graphite. Then, with the injection molded portion set in the mold, the expanded graphite layer 62 is injection molded (mold molded) with a resin that contains thermally expandable graphite. The second cover 61b is molded in the same manner. That is, the insulating member 61 and the expanded graphite layer 62 are molded integrally by insert molding. Note that after molding the expanded graphite layer 62, the portion that contacts the busbar body 60 may be molded integrally with the molded expanded graphite layer 62.

The expanded graphite layer 62 is not formed on the mating surfaces between the first cover 61a and the second cover 61b. Thermally expandable graphite and thermally expandable graphite after expansion (hereinafter referred to as expanded graphite) are conductive. Therefore, the thermally expandable graphite and the expanded graphite are arranged so as not to directly contact the busbar body 60 including the terminal 60T. In this way, when the insulating member 61 and the expanded graphite layer 62 are integrated by insert molding, the number of parts is reduced, and the insulating member 61 and the expanded graphite layer 62 can be formed on the busbar body 60 by a single installation operation. In addition, since the insulating member 61 and the expanded graphite layer 62 are insert molded, even if the thermally expandable graphite in the expanded graphite layer 62 expands, the expanded graphite layer 62 does not peel off or fall off from the insulating member 61. As a result, the insulating member 61 is reliably protected by the expanded graphite layer 62.

Next, modified example 3 shown in FIG. 8 will be described. As described above, the battery module 1 has a vent hole 5 for discharging high-temperature gas. Therefore, the portion of the expanded graphite layer 62 facing the vent hole 5 is most exposed to the high-temperature gas. Therefore, in this modified example, the layer thickness of the portion 62X (the lower surface of the expanded graphite layer 62 as shown in FIG. 3) facing the vent hole 5 of the expanded graphite layer 62 of the bus bar 6B is made thicker than the layer thickness of the other portions. Therefore, the insulating member 61 can be protected more reliably by the expanded graphite layer 62.

As described above, the busbar 6B is supported from below by the support member 7B. If the support member 7B is thermally damaged by high-temperature gas, the busbar 6B will lose its support. In this case, the vicinity of the support member 7B of the busbar 6B may be displaced downward by gravity, causing the busbar body 60 to come into contact with other components, resulting in a short circuit (ground fault). In this embodiment (and its modified example), this does not occur because the busbar body 60 is protected by the expanded graphite layer 62 and the insulating member 61 protected by this expanded graphite layer 62.

However, in such a case, the insulating member 61 and the busbar body 60 can be protected more reliably by making the layer thickness of the expanded graphite layer 62 thicker in the portion that comes into contact with other components than in the other portions. Therefore, in the expanded graphite layer 62 of this modified example, the layer thickness of the lower surface portion 62X near the support member 7B is made thicker than in the other portions. Therefore, the insulating member 61 and the busbar body 60 can be protected more reliably by the expanded graphite layer 62.

Although the busbar 6B has been described as an example here, the same applies to the busbar 6A. For example, consider a case where the member 7A shown in FIG. 3 functions as a support member that supports the busbar 6A from below. In this case, for the busbar 6A as well, by making the layer thickness of the lower surface portion 62X of the expanded graphite layer 62 near the support member 7A thicker than the layer thickness of the other portions, the insulating member 61 and the busbar body 60 can be more reliably protected by the expanded graphite layer 62.

The above describes the embodiment (and its modified examples 1 to 3). In the vehicle-mounted battery system according to the above embodiment, the bus bar 6 includes an insulating member 61 and an expanded graphite layer 62. The insulating member 61 covers the surface of the intermediate portion between (at least) two terminals of the bus bar main body 60 formed of a conductive metal. The expanded graphite layer 62 includes thermally expandable graphite and is formed on the surface of the insulating member 61. Therefore, when the high-temperature gas fills the inside of the battery pack 2 due to overheating of the lithium-ion battery cell 3, the thermally expandable graphite included in the expanded graphite layer 62 expands. Therefore, the expanded expanded graphite layer 62 prevents the insulating member 61 from being exposed to the heat of the high-temperature gas, and prevents the insulating member 61 from being thermally damaged and the bus bar main body 60 from being exposed. That is, according to the vehicle-mounted battery system according to the above embodiment (and its modified examples 1 to 3), it is possible to provide a vehicle-mounted battery system including a bus bar 6 with excellent heat resistance.

Here, the high-temperature gas is discharged to the outside of the battery module 1 and to the inside of the battery pack 2 through the vent hole 5. According to the third modified example (FIG. 8) of the above embodiment, the layer thickness of the expanded graphite layer 62 is made thicker at the portion facing the vent hole 5 than the layer thickness of the other portion 62X. The portion 62X of the expanded graphite layer 62 facing the vent hole 5 is the portion most exposed to the high-temperature gas, but since the layer thickness of this portion is made thicker, the insulating member 61 can be more reliably protected by the expanded graphite layer 62. Note that "the layer thickness of the portion facing the vent hole is made thicker than the layer thickness of the other portion" includes the case where the expanded graphite layer is formed only on the surface facing the vent hole (and not on the other surfaces).

In the above embodiment, the insulating member 61 made of resin is supported by the support member 7. If the support member 7 is thermally damaged by the heat of the high-temperature gas and the expanded graphite layer 62 (i.e., the busbar 6 having the expanded graphite layer 62) loses support, the portion of the busbar 6 near the support member 7 may be displaced downward by gravity. However, according to the modified example 3 of the above embodiment (FIG. 8), in the expanded graphite layer 62, the layer thickness of the lower surface portion 62X near the support member 7 is made thicker than the layer thickness of the other portions. Therefore, even if the portion of the busbar 6 near the support member 7 is displaced downward by gravity and the lower surface portion 62X of the expanded graphite layer 62 comes into contact with other parts, the layer thickness of the portion 62X is made thicker. Therefore, the insulating member 61 and the busbar body 60 are more reliably protected by the expanded graphite layer 62, and the occurrence of a short circuit (ground fault) at the portion 62X is reliably prevented. In addition, "the layer thickness of the lower surface portion near the support member is made thicker than the layer thickness of other portions" includes the case where the expanded graphite layer is formed only on the lower surface near the support member (and not on other surfaces).

Furthermore, according to the second modification of the above embodiment, the resin tubular case-shaped insulating member 61 and the expanded graphite layer 62 formed of resin mixed with thermally expandable graphite as a filler are integrated by insert molding. This reduces the number of parts, and the insulating member 61 and the expanded graphite layer 62 can be formed on the busbar body 60 by a single attachment operation. Furthermore, even if the thermally expandable graphite in the expanded graphite layer 62 expands, the expanded graphite layer 62 does not peel off or fall off from the insulating member 61, so the insulating member 61 is reliably protected by the expanded graphite layer 62.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the vent hole 5 is located below the bus bar 6B, so the layer thickness of the underside portion 62X of the expanded graphite layer 62 of the bus bar 6B (the portion facing the vent hole 5) is made thicker. However, if the portion of the expanded graphite layer 62 facing the vent hole 5 is not the underside but the side, the layer thickness of the side may be made thicker.

In the above embodiment, the support member 7 supports the busbar 6 from below. However, the support member 7 may support the busbar 6 (expanded graphite layer 62) from the side or above. In such a case, if the busbar 6 (expanded graphite layer 62) loses support due to thermal damage to the support member 7, the portion of the busbar 6 (expanded graphite layer 62) near the support member 7 may be displaced downward by gravity. In this case, too, the layer thickness of the lower surface portion 62X of the expanded graphite layer 62 is made thicker, so that the insulating member 61 and the busbar body 60 can be more reliably protected by the expanded graphite layer 62.

REFERENCE SIGNS LIST 1 Battery module 2 Battery pack 3 Lithium ion battery cell 5 Vent hole 6 (6A, 6B) Bus bar 60 Bus bar main body 60T Terminal 61 Insulating member 62 Expanded graphite layer 62X (of expanded graphite layer 62) Part facing vent hole 5/lower surface part 7 (7A, 7B) Support member

Claims (4)

A battery module containing multiple lithium-ion battery cells therein;
a battery pack containing a plurality of the battery modules therein;
In the battery pack, a bus bar having at least two terminals electrically connects the battery modules to each other or electrically connects the battery module to an electrical component.
The battery module has a vent hole for discharging high-temperature gas inside when the battery module overheats,
The bus bar is
a busbar body formed of a conductive metal and having the two terminals;
an insulating member covering a surface of a middle portion of the busbar body between the two terminals;
and an expanded graphite layer including, in part, thermally expandable graphite formed on a surface of the insulating member. The vehicle-mounted battery system according to claim 1 , wherein the expanded graphite layer has a layer thickness in a portion facing the vent hole that is greater than a layer thickness in other portions. the insulating member is made of resin and is supported by a support member via the expanded graphite layer ,
3. The vehicle-mounted battery system according to claim 1, wherein the expanded graphite layer has a layer thickness at a lower surface portion adjacent to the support member that is greater than a layer thickness at other portions. The insulating member is formed as a tubular case from resin by a mold,
the expanded graphite layer is molded from a resin having the thermally expandable graphite mixed therein as a filler,
The vehicle-mounted battery system according to any one of claims 1 to 3, wherein the insulating member and the expanded graphite layer are integrated by insert molding.

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