Patent Description:
Recently, a demand for an in-vehicle secondary battery has increased against the background of environmental regulations. Among the secondary batteries, since a lithium ion secondary battery usually has a high discharge potential as compared with a lead battery, a nickel hydrogen battery, or the like, the lithium ion secondary battery can be miniaturized or have a higher energy density, and thus, is considered as being promising. For example, further higher energy density, higher output density, longer life, and the like are required for the lithium ion secondary battery for real application. For higher output of a battery, it is effective to input and output a large current from the battery as well as higher potential. However, when a large current is input and output from a battery, heat derived from internal resistance of the battery is produced inside the battery. When the produced heat is not sufficiently removed from the battery, battery temperature is raised. Battery characteristics such as battery capacity or internal resistance of a lithium ion battery have a different deterioration trend depending on a battery temperature, and particularly when the battery temperature is higher, the battery characteristics are often lowered. Thus, development of a technology to improve heat dissipation performance of a battery is needed.

When a plurality of lithium ion unit cells (hereinafter, referred to as unit cells) is combined and used as a battery group (for example, used as a battery module or a battery pack), it is desired to decrease a temperature difference between unit cells of the battery group. This is because when the temperature difference between the unit cells is large, a difference in deterioration between the unit cells easily occurs. Since the characteristics of the battery group tend to be rate-determined by the characteristics of the most deteriorated cell among the unit cells included in the battery group, design of the battery group avoiding a structure in which a specific cell is deteriorated is needed.

Thus, a technology in which in a battery group formed by combining a plurality of unit cells, a temperature difference between unit cells is decreased is being developed. Specifically, PTL <NUM> discloses a storage battery in which an electrolytic bath housing a unit cell is formed of a cuboid composed of a short side having a narrow width and a long side having a wide width, and a plurality of unit cells is linked so as to be adjacent to each other between the short sides of the electrolytic bath to form an aggregate battery having a required power capacity. Furthermore, PTL <NUM> discloses battery having a coolant passage for better cooling efficiency, wherein a frame member is provided which holds an array of unit cells therein, wherein at least one of the frame members is formed to have an inlet for introducing a coolant into the inside of the battery and an outlet for discharging the coolant which has flown through the inside of the battery. PTL <NUM> discloses a a battery module cooling technique and a loading structure thereof, wherein a heat conduction medium having a louver structure is interposed at a thermal interface of a heatsink and the battery module. Eventually, PTL <NUM> discloses a battery system mounted on a vehicle using an electric motor, wherein a heat dissipation equalization means is provided that locally modifies the amount of heat released from the battery assembly to the outside to reduce local variations in the internal temperature of the battery assembly when the battery assembly is subjected to natural heat dissipation.

Meanwhile, when a large current is input and output from a battery, a cross-sectional area of a cable connected to the battery is needed to be increased. As a material used in the cable, a metal represented by copper is used, however, the metal has a high thermal conductivity, and thus, has high heat dissipation performance.

In the technology described in PTL <NUM>, a plurality of ribs is formed on a long side of an electrolytic bath of each unit cell. Then, air and the like are forcibly flowed between the ribs to cool the unit cell. In this configuration, when cooling efficiency is decreased (for example, a flow rate of forcibly flowed air is small, or an input/output current is large and a heating value of the unit cell is large), a battery temperature distribution occurs in a battery group to be configured, and particularly, a battery temperature of the unit cell disposed near a center of the long side of the battery group is high, so that there is a risk of deterioration progression. The present invention has been made in view of the above problem, and an object of the present invention is to provide a battery pack having a small temperature difference between battery groups.

In order to solve the above-mentioned problem, the present invention provides a battery pack according to the appended set of claims. Preferable embodiments are claimed by the dependent claims.

According to the invention, a battery pack having a small temperature difference between battery groups can be provided.

Embodiments of the present invention will be described. However, the embodiments do not limit the following descriptions, and can be optionally modified and carried out within the range not departing from the gist of the present invention.

The present embodiments will be described in detail. As a secondary battery in the present embodiment, a lithium ion secondary battery is used; however, the present configuration can be also applied to other types of storage battery. In addition, the effect can be obtained with any constituent member of the lithium ion secondary battery. That is, in the present invention, an electrode composed of an Al current collector foil and a positive electrode material having a layered structure as a positive electrode, and an electrode composed of a Cu current collector foil and a carbon material as a negative electrode are used, but other configurations may be also used. For example, as described in Examples <NUM> and <NUM>, heat dissipation properties may be improved even in the case of using an Al foil in the negative electrode. A cooling environment is an example, and it can be applied also to the case of using other refrigerants. In addition, as a shape of the lithium ion battery, a rectangular battery was used in the present Example; however, the effect can be obtained even with the battery known as having other shapes, for example, a laminate type, a cylindrical shape, or the like.

When unit cells are used as a battery group, the unit cells are connected to each other in series or in parallel. In this case, for guaranteeing safety, a member capable of securing insulation between batteries may be introduced around the unit cell, for example, as shown in Example <NUM>. The shape of the member is free and the material can be freely selected; however, it is preferred to include a heat transfer member. When the unit cells are connected to each other in series or in parallel, wiring to be used is not particularly limited; however, for example, a bus bar can be used. Whatever the form of serial or parallel connection is, the effect is exhibited when the battery arrangement and the configuration of an external terminal according to the present invention are used. For example, even with a battery group in which six battery groups having two parallel parts are arranged in series, the effect of the present invention is obtained. In addition, it is preferred that in the battery group, in addition to electrically connecting the unit cells to each other in series or in parallel, the unit cells are physically bound to each other using a fixing jig. However, the present invention is not limited to the binding method. For example, the effect was exhibited even when two battery groups are secured using a set of fixing jigs or secured using two sets of securing jigs.

In the present invention, the battery pack is configured using a first battery group and a second battery group which are connected by the above-described means as a basic configuration, and in addition to them, the battery pack may be provided with a control device of a battery (for example, a Battery Management System; BMS or the like can be used) or a safety mechanism (for example, a fuse or the like), and even in the case of connecting them to wiring in the battery group, the effect of the present invention is obtained.

A method of contacting a case bottom surface with the battery group is not particularly limited and the effect of the present invention is exhibited even with for example, adhesion with an adhesive or the like or connection through a fixture using bolts or nuts. The shape of the case is exemplified by a cuboid in the present embodiment, however, the shape is not particularly limited. In addition, the effect of the present invention is not limited to a current application condition to the battery pack or a cooling condition.

Hereinafter, the present invention will be described in detail, based on the Examples and the Comparative Examples. <FIG> is an exploded perspective view of a battery pack <NUM>. In addition, when up, down, left, right, front, or rear is referred to in the following description, it follows the directions as indicated in the lower left in each drawing.

The battery pack <NUM> is composed of a first battery group 10A, a second battery group 10B, and a case <NUM> (5a, 5b) housing the first battery group 10A and the second battery group 10B. The case <NUM> is composed of a case 5a and a cover 5b covering a case opening. In addition, in the present embodiment, a bottom surface 5b is provided as an additional member; however, a structure in which the case 5a is provided with a bottom surface and has an opening on an upper surface, and a cover 5b is disposed on the upper surface may be also used.

<FIG> is a drawing representing a storage battery <NUM> used in the present invention. The storage battery <NUM> is composed of a pair of wide surfaces 1a, a pair of narrow surfaces 1b, a bottom surface 1c, and a cover 1d. The cover 1d is provided with a positive electrode external terminal 2a and a negative electrode external terminal 2b.

Referring back to <FIG>, the first battery group 10A and the second battery group 10B are described, respectively. The first battery group 10A is formed by laminating a plurality of the storage batteries <NUM> (in the present embodiment, six storage batteries) so that the wide surfaces 1a of the storage battery <NUM> face each other. For the second battery group 10B also, like the first battery group 10A, a structure is formed by laminating the storage batteries so that the wide surfaces of the storage battery face each other.

The storage batteries <NUM> constituting the first battery group 10A are connected to each other in series by a bus bar <NUM>. In addition, like the second battery group 10B, the storage batteries <NUM> are connected to each other in series by the bus bar <NUM>. In addition, a structure in which the storage battery <NUM> on a bottom surface 5b side of the first battery group 10A and the storage battery <NUM> on a bottom surface 5b side of the second battery group 10Bno are connected to each other by the bus bar <NUM> is formed. Further, each of the two battery groups 10A and 10B has an external terminal <NUM> which is connected to other electronic components (for example, a junction box or the like) housed in the battery pack <NUM>, disposed on the upper center side of the battery pack <NUM>. A temperature change of the battery pack <NUM> was measured by some settings (<FIG>).

First, Example <NUM> is described. A first battery group and a second battery group were horizontally arranged as shown in <FIG> and then thermally directly connected, and a HV cable made of copper having a diameter of <NUM> was installed at the end of a positive electrode external terminal and a negative electrode external terminal and a current was applied thereto. A heating value from the battery at that time was <NUM> W on average.

In addition, as a cooling condition, air at a wind speed of <NUM>/sec was applied only to a bottom plate with a case in a lower portion of the battery group interposed therebetween. In <FIG>, an upper surface of the case is shown. <FIG> shows the results when the state is almost normal, after applying the condition to the battery pack.

Subsequently, Example <NUM> is described. Example <NUM> is different from Example <NUM> in that after the first battery group and the second battery group were horizontally arranged, a heat transfer member <NUM> (heat conductive member) in a planar shape was interposed therebetween.

In <FIG>, a structure of the present Example is shown. In the present Example, as described above, the heat transfer member <NUM> was disposed between the first battery group 10A and the second battery group 10B. The heat transfer member had two types, one having a thickness of <NUM> and the other having a thickness of <NUM>, and a temperature rise of the battery pack <NUM> was measured when each of the heat transfer members was used. The results are shown in <FIG>. In addition, the cooling condition and the current application condition were identical to those of Example <NUM>.

Subsequently, Example <NUM> is described. Example <NUM> is different from Example <NUM> in that as the material of the negative electrode current collector foil, an aluminum current collector foil was used instead of a copper foil.

Since the detailed structure of the battery pack <NUM> is in the same arrangement as that of <FIG>, the description thereof is omitted. The results of a temperature rise of the battery pack <NUM> are shown in <FIG>. In addition, the cooling condition and the current application condition were identical to those of Example <NUM>.

Subsequently, Example <NUM> is described. Example <NUM> is different from Example <NUM> in that as the material of the negative electrode current collector foil, an aluminum current collector foil was used instead of a copper foil. Since the detailed structure of the battery pack <NUM> is in the same arrangement as the arrangement of <FIG>, the description thereof is omitted. In the present embodiment, as the heat transfer member <NUM>, a member having a thickness of <NUM> is used. The results of a temperature rise of the battery pack <NUM> are described in <FIG>. In addition, the cooling condition and the current application condition were identical to those of Example <NUM>.

Subsequently, Example <NUM> is described. Example <NUM> is different from Example <NUM> in that the first battery group 10A and the second battery group 10B were vertically arranged as in <FIG> and a narrow side surface of the storage battery constituting the battery group was in contact with the bottom surface of the case <NUM> of the battery pack <NUM>. The results of a temperature rise of the battery pack <NUM> are described in <FIG>. In addition, the cooling condition and the current application condition were identical to those of Example <NUM>.

Subsequently, Example <NUM> is described. Example <NUM> is different from Example <NUM> in that the first battery group and the second battery group were vertically arranged as in <FIG>, and a narrow side surface of the storage battery constituting the battery group was in contact with the bottom surface of the case <NUM> of the battery pack <NUM>.

In addition, in the present Example, similarly to Example <NUM>, the heat transfer member <NUM> had two types, one having a thickness of <NUM> and the other having a thickness of <NUM>, and each measurement results are shown in <FIG>. In addition, the cooling condition and the current application condition were identical to those of Example <NUM>.

Subsequently, Example <NUM> is described. Unlike Examples <NUM> to <NUM>, the present Example has a structure in which the first battery group and the second battery group, each of which had <NUM> storage batteries <NUM> connected in series, were connected to each other in series, and the bottom surface of the storage battery <NUM> was in contact with the bottom surface 5b of the case of the battery pack <NUM>. In addition, in the present embodiment also, the heat transfer member <NUM> was disposed between the first battery group 10A and the second battery group 10B. As the heat transfer member <NUM>, an aluminum flat plate having a plate thickness of <NUM> was used. The results of a temperature rise of the battery pack <NUM> are shown in <FIG>. In addition, the cooling condition and the current application condition were identical to those of Example <NUM>.

Subsequently, Comparative Example <NUM> is described. Comparative Example <NUM> is different from Examples <NUM> to <NUM> in that the battery group is not divided into two and is laminated as a single battery group.

<FIG> is a drawing of the battery pack <NUM> of Comparative Example <NUM>. Twelve batteries <NUM> were linked in series to form a single battery group, which was disposed so that the wide surface 1a of the unit cell <NUM> was in contact with the bottom surface 5b of the case <NUM>. The results of a temperature rise of the battery pack <NUM> are shown in <FIG> and <FIG>. In addition, the cooling condition and the current application condition were identical to those of Example <NUM>.

Subsequently, Comparative Example <NUM> is described. Comparative Example <NUM> is different from Examples <NUM> to <NUM> in that the battery group was not divided into two and laminated as a single battery group, and the narrow surface 1b of the unit cell <NUM> was in contact with the bottom surface 5b of the case <NUM>.

<FIG> is a drawing of the battery pack <NUM> of Comparative Example <NUM>. Twelve batteries were linked in series to form a single battery group, which was disposed so that the narrow surface 1b of the unit cell <NUM> was in contact with the bottom surface 5b of the case <NUM>. The results of a temperature rise of the battery pack <NUM> are shown in <FIG> and <FIG>. In addition, the cooling condition and the current application condition were identical to those of Example <NUM>. Hereinafter, the effects of the present patent application will be described based on the results of the Examples and the Comparative Examples.

As a result of imparting the conditions represented in the present Examples and the Comparative Examples to the battery group, when the temperature of the battery group reaches an almost steady state, the battery temperature was raised as compared with the environmental temperature. <FIG> are drawings which show a ratio of a rising temperature of each unit cell of the battery group compared with an environmental temperature to a rising temperature of the unit cell having the smallest temperature rise, for each cell. In the drawings, the cell No. corresponds to the cell No. described in the drawing corresponding to each Example or Comparative Example. Here, for two battery groups in the Examples, the unit cells present in the place where the battery groups face each other had almost the same temperature, and the description thereof is omitted for simplicity. Hereinafter, the result of each drawing will be described in detail.

<FIG> shows a temperature rise ratio of the configurations of Examples <NUM>, <NUM> and Comparative Example <NUM>. It can be seen from the drawing that in the Comparative Example as the conventional configuration, the temperature of cell No. <NUM>, which is disposed at a center of the laminate of a battery, was highest. This is because in the battery near cell No. <NUM>, heat quantity produced from the surrounding battery was not dissipated to raise the temperature of the surrounding battery as well as the temperature of the battery itself, and thus, there was no temperature difference to make heat difficult to flow, resulting in a battery temperature rise. Meanwhile, the unit cell of cell No. <NUM> in contact with the case bottom surface and the battery of cell No. <NUM> having the external terminal had a heat dissipation path to suppress a temperature rise. From the results, since there occurred a difference in the temperature rise between cell No. <NUM> and No. <NUM> and cell No. <NUM>, the temperature rise ratio was greatly changed in the same battery group in Comparative Example <NUM>. Therefore, it can be seen that the temperature difference between the unit cells easily occurred It can be seen that examples <NUM> and <NUM> can reduce the temperature rise rate in the entire cells as compared with the Comparative Example, from the comparison of the temperature rise rates of the batteries in the entire cells present in the same arrangement. In addition, as shown in Example <NUM>, it can be seen that the effect was further exhibited by disposing the heat transfer member between the battery groups, thereby reducing the temperature difference between the batteries. This means that the heat dissipation path was effectively secured by disposing the external terminal in cell No. <NUM> which had the highest temperature. Additionally, it can be seen that in Example <NUM>, an Al plate was introduced to secure the heat dissipation path, and thus, the rising temperature difference between batteries could be effectively reduced.

<FIG> shows the temperature rise rates of the configurations of Examples <NUM>, <NUM> and Comparative Example <NUM>. It can be seen from the drawings that when the negative electrode current collector foil was Al also, the temperature difference between batteries tended to be reduced as illustrated in <FIG>. Heat behavior which occurred in <FIG> is due to the same phenomenon as that occurred in <FIG>.

<FIG> shows the configurations of Examples <NUM>, <NUM> and Comparative Example <NUM>. It can be seen from the drawing that in the Comparative Example as the conventional configuration, the temperature of cell No. <NUM> which is at the center of the laminate of the battery was highest. The temperature rise occurred here is due to the same phenomenon as that in the Comparative Example <NUM> shown in <FIG>.

In addition, it can be seen from the drawing that in the case of vertical arrangement also, the temperature difference between batteries was reduced like <FIG> and <FIG>. Even in the case of the vertical arrangement not the horizontal arrangement, the temperature near the center of the long side tended to be raised. It can be seen that by disposing the external terminal in the portion, the same effect as that in <FIG> and <FIG> was obtained and the rising temperature difference could be reduced.

In <FIG>, the temperature difference of the case of Example <NUM> is compared with the battery configuration of the vertical arrangement like Comparative Example <NUM>. It can be seen from the drawing that example <NUM> also tended to reduce the temperature difference. It can be seen that it is because in Example <NUM> also, the external terminal was installed in cell No. <NUM> which has the highest battery temperature, thereby effectively dissipating heat to the outside of the battery group.

The battery pack includes a first battery group (10A) in which a plurality of storage batteries (<NUM>) having a battery can side surface (1a, 1b) and a battery can bottom surface (1c) linked to the battery can side surface (1a, 1b) are laminated so that the battery can side surfaces (1a, 1b) face each other; a second battery group (10B) in which a plurality of storage batteries (<NUM>) having a battery can side surface (1a, 1b) and a battery can bottom surface (1c) linked to the battery can side surface (1a, 1b) are laminated so that the battery can side surfaces (1a, 1b) face each other; and a case (<NUM>) housing the first battery group (10A) and the second battery group (10B), wherein facing surfaces of the first battery group (10A) and the second battery group (10B) are directly or indirectly thermally connected to each other. By having this structure, a battery pack having a decreased temperature difference between the battery groups can be provided.

In addition, the battery pack has a structure in which wide surfaces (1a) of the two battery groups face the bottom surface of the case (<NUM>). By having this structure, a cooling area is increased to improve cooling performance as compared with the case in which the narrow surface 1b is in contact with the case <NUM>.

In addition, in the battery pack, when the wide surface 1a of the battery <NUM> faces downward, the external terminal <NUM> is at the center side of the battery pack, thereby cooling the center side of the battery pack which is more difficult to dissipate heat through the external terminal. Thus, the heat dissipation properties are further improved, thereby making it possible to provide a battery pack having a decreased temperature difference between the battery groups.

In addition, as shown in <FIG>, in the battery pack, the first heat transfer member (<NUM>) is disposed between the first battery group (10A) and the second battery group (10B), and the heat transfer member (<NUM>) is closely adhered to the first battery group (10A) and the second battery group (10B). By having this structure, thermal diffusion is further promoted by the heat transfer member, thereby providing a battery pack having a decreased temperature difference between the battery groups. In addition, <FIG> is a drawing in which <FIG> is viewed from the upper surface.

In addition, in the battery pack described in the present invention, as shown in <FIG>, the second heat transfer member <NUM> and the third heat transfer member <NUM> are disposed on both sides of the first battery group 10A and the second battery group 10B. In this case, the first battery group 10A is sandwiched between the heat transfer member <NUM> and the second heat transfer member <NUM>, and the second battery group 10B is sandwiched between the heat transfer member <NUM> and the third heat transfer member 10B, so that the heat dissipation properties are improved also on both sides of the battery groups 10A and 10B, thereby providing a battery pack having a further decreased temperature difference between the battery groups.

In addition, the battery pack described in the present invention has a structure in which for both of the second heat transfer member <NUM> and the third heat transfer member <NUM>, those having a larger width, that is, a larger thickness than the first heat transfer member <NUM> are used. By having this structure, the structure becomes large so that the case <NUM> and the heat transfer members <NUM> and <NUM> can be fixed with a screw and the like, so that the case <NUM> and the heat transfer members <NUM> and <NUM> can be more closely adhered. Thus, it becomes easy to transfer heat of the battery <NUM> to the case <NUM>, thereby providing a battery pack having improved cooling performance.

Claim 1:
A battery pack (<NUM>), comprising:
a first battery group (10A) in which a plurality of storage batteries having a battery can wide side surface, a battery can narrow side surface, and a battery can bottom surface linked to the battery can wide side surface and the battery can narrow side surface are laminated so that the battery can wide side surfaces face each other;
a second battery group (10B) in which a plurality of storage batteries having a battery can wide side surface, a battery can narrow side surface, and a battery can bottom surface linked to the battery can wide side surface and the battery can narrow side surface are laminated so that the battery can wide side surfaces face each other; and
a case housing the first battery group (10A) and the second battery group (10B), wherein
the battery can narrow side surfaces of the first battery group (10A) and the second battery group (10B) are disposed to face each other,
a first heat transfer member (<NUM>) is disposed between the first battery group (10A) and the second battery group (10B),
the first heat transfer member (<NUM>) is closely adhered on the battery can narrow side surface of the first battery group (10A) and the battery can narrow side surface of the second battery group (10B),
the first battery group (10A) is interposed between the first heat transfer member (<NUM>) and a second heat transfer member (<NUM>),
the second battery group (10B) is interposed between the first heat transfer member (<NUM>) and a third heat transfer member (<NUM>), and
the battery can wide side surfaces of a storage battery of the first battery group (10A) and a storage battery of the second battery group (10B) are closely adhered on the bottom surface of the case,
characterized in that:
a thickness of the first heat transfer member (<NUM>) is smaller than thicknesses of the second heat transfer member (<NUM>) and the third heat transfer member (<NUM>), and wherein
each of the first, second and third heat transfer member is a solid, flat aluminum plate.