Battery pack

Abstract

The objective is to provide a battery pack that minimizes the temperature difference between battery groups. [Solution] The battery pack described in the present invention comprises a first battery group formed by stacking multiple storage batteries, each having a battery can side and a battery can bottom connected to the battery can side, with their battery can sides facing each other; a second battery group formed by stacking multiple storage batteries, each having a battery can side and a battery can bottom connected to the battery can side, with their battery can sides facing each other; and a housing for housing the first battery group and the second battery group, wherein the first battery group and the second battery group are thermally connected to each other, either directly or indirectly, on their opposing surfaces.

Description

Technical Field

[0001] The present invention relates to a battery pack.

Background Art

[0002] In recent years, due to environmental regulations, the demand for in-vehicle secondary batteries has been increasing. Among these, lithium-ion secondary batteries are generally regarded as promising because they can be made smaller and have a higher energy density compared to lead batteries and nickel-metal hydride batteries, etc., since they generally have a higher discharge potential. For full-scale application, requirements for lithium-ion secondary batteries include, for example, further increasing the energy density, increasing the output density, and extending the life. To increase the output of the battery, in addition to increasing the potential, for example, it is effective to input and output a large current from the battery. However, when a large current is input and output from the battery, heat generation due to the internal resistance of the battery occurs inside the battery. If the generated heat cannot be sufficiently removed from the battery, the battery temperature rises. The battery characteristics such as the battery capacity and internal resistance of a lithium-ion battery have different degradation tendencies depending on the battery temperature, and in particular, the higher the battery temperature, the more likely the battery characteristics are to deteriorate. Therefore, there is a need for technological development to improve the heat dissipation performance of the battery.

[0003] When a plurality of lithium-ion single cells (hereinafter referred to as single cells) are combined and used as a battery group (for example, when used as a battery module or a battery pack), it is desirable to reduce the temperature difference between the single cells in the battery group. This is because when the temperature difference between the single cells is large, a difference in degradation is likely to occur between the single cells. The characteristics of the battery group tend to be limited by the characteristics of the most degraded battery among the single cells included in the battery group, so a design of the battery group that avoids a structure in which a specific battery degrades is necessary. Since the characteristics of the battery group tend to be limited by the characteristics of the most degraded battery among the single cells included in the battery group, a design of the battery group that avoids a structure in which a specific battery degrades is necessary.

[0004] Therefore, technologies have been developed to reduce the temperature difference between individual cells in a battery group formed by combining multiple individual cells. Specifically, Patent Document 1 describes a storage battery in which a battery case containing individual cells is formed as a rectangular parallelepiped consisting of a narrow short side and a wide long side, and multiple individual cells are connected adjacently between the short sides of this battery case to form a battery group with the required power capacity.

[0005] On the other hand, when supplying and outputting large currents from a battery, the cross-sectional area of ​​the cable connected to the battery also needs to be large. Metals such as copper are commonly used as materials for cables, and metals generally have high thermal conductivity, resulting in high heat dissipation performance. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2000-164186 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In the technology described in Patent Document 1, multiple ribs are formed on the long side of the battery case of each individual cell. Cooling of the individual cells is performed by forcibly circulating air or the like between these ribs. In such a configuration, if the cooling efficiency decreases (for example, if the flow rate of the air being forcibly circulated is small, or if the input / output current is large and the amount of heat generated by the individual cells is large), a temperature distribution will occur within the battery group, and the temperature of individual cells located near the center of the long side of the battery group will be particularly high, which may lead to accelerated degradation. The present invention has been made in view of the above problem, and aims to provide a battery pack in which the temperature difference between battery groups is small. [Means for solving the problem]

[0008] The battery pack described in the present invention comprises a first battery group formed by stacking multiple storage batteries, each having a battery can side and a battery can bottom connected to the battery can side, with their battery can sides facing each other; a second battery group formed by stacking multiple storage batteries, each having a battery can side and a battery can bottom connected to the battery can side, with their battery can sides facing each other; and a housing for housing the first and second battery groups, wherein the first and second battery groups are thermally connected to each other, either directly or indirectly, on their opposing surfaces. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a battery pack that reduces the temperature difference between battery groups. [Brief explanation of the drawing]

[0010] [Figure 1] A diagram illustrating an example of the specific configuration of the battery group in Example 1. [Figure 2] A diagram illustrating an example of the specific configuration of the battery group in Example 2. [Figure 3] A diagram illustrating an example of the specific configuration of the battery group in Example 5. [Figure 4] A diagram illustrating an example of the specific configuration of the battery group in Example 6. [Figure 5] A diagram illustrating an example of the specific configuration of the battery group in Example 7. [Figure 6] A diagram illustrating an example of the specific configuration of the battery group in Comparative Example 1. [Figure 7] A diagram illustrating an example of the specific configuration of the battery group in Comparative Example 2. [Figure 8] This temperature rise ratio diagram shows the temperature rise of each individual cell from the ambient temperature for the configurations of Examples 1 and 2 and the conventional configuration, expressed as a ratio from the lowest temperature within the cell group. [Figure 9] This temperature rise ratio diagram shows the temperature rise of each individual cell from the ambient temperature for the configurations of Examples 3 and 4 and the conventional configuration, expressed as a ratio from the lowest temperature within the cell group. [Figure 10]Temperature rise ratio diagram showing the temperature rise from the ambient temperature of each single cell in the configurations of Examples 5 and 6 and the conventional configuration, expressed as a ratio from the lowest temperature in the battery pack. [Figure 11] Temperature rise ratio diagram showing the temperature rise from the ambient temperature of each single cell in the configuration of Example 7 and the conventional configuration, expressed as a ratio from the lowest temperature in the battery pack. [Figure 12] View of the battery pack of FIG. 2 as seen from above. [Figure 13] First modification of FIG. 12. [Figure 14] Second modification of FIG. 12. [Figure 15] Perspective view of the secondary battery of the present invention.

Mode for Carrying Out the Invention

[0011] A mode for carrying out the present invention will be described. However, this embodiment is not limited to the following content and can be arbitrarily changed and implemented within the scope not departing from the gist of the present invention.

[0012] This embodiment will be described in detail. In the secondary battery in this embodiment, a lithium ion secondary battery is used, but this configuration can also be applied to other types of storage batteries. Also, any components of the lithium ion secondary battery can achieve the effect. That is, in the present invention, an electrode composed of an Al current collector foil and a cathode material having a layered structure as the cathode, and an electrode composed of a Cu current collector foil and a carbon material as the anode are used, but other configurations may also be used. For example, as described in Examples 3 and 4, heat dissipation can also be improved when an Al foil is used for the anode. The cooling environment is an example and can also be applied when other refrigerants are used. Also, in this embodiment, a rectangular battery is used as the shape of the lithium ion battery, but effects can also be obtained with other known shapes such as laminate type, cylindrical type, etc.

[0013] When using a single battery as a battery pack, the single batteries are connected in series or in parallel. At this time, in order to ensure safety, a member that can ensure insulation between the batteries may be introduced around the single battery, for example, as shown in Example 7. The shape of the member is free, and the material can also be freely selected, but it is preferable that a heat transfer member is included. When connecting single batteries in series or in parallel, the wiring used is not particularly limited, and for example, a bus bar can be mentioned. Regardless of the form of series or parallel connection, the effects of the present invention can be manifested by using the battery arrangement and the configuration of the external terminals according to the present invention. For example, even in a battery pack where two parallel-connected battery groups are connected in six series, the effects of the present invention can be obtained. In addition to electrically connecting single batteries in series or in parallel, it is preferable to physically restrain the single batteries using a fixing jig. However, the present invention is not limited to the method of restraint. For example, even when two battery groups are fixed using one set of fixing jigs, or when fixed using two sets of fixing jigs, the effects are manifested.

[0014] In the present invention, a battery pack is configured with a first battery group and a second battery group connected by the means described above as the basic configuration. In addition to these, the battery pack may further include a battery control device (for example, a Battery Management System; BMS, etc.), and a safety mechanism (for example, a fuse, etc.). Connecting these to the wiring in the battery group can also obtain the effects of the present invention.

[0015] The method of contact between the bottom surface of the housing and the battery groups is not particularly limited. For example, adhesion using an adhesive or connection via a fixing fixture using bolts and nuts can also show the effects of the present invention. In this embodiment, the shape of the housing is exemplified as a rectangular parallelepiped, but the shape is not particularly limited. Also, the effects of the present invention are not limited to the current application conditions and cooling conditions for the battery pack.

[0016] Hereinafter, the present invention will be described in more detail based on examples and comparative examples. FIG. 1 is an exploded perspective view of the battery pack 100 of the present invention. In the following description, when referring to up, down, left, right, front, and back The direction indicated in the lower left corner of each drawing shall be followed.

[0017] The battery pack 100 consists of a first battery group 10A and a second battery group 10B, and a housing 5 (5a, 5b) that houses the first battery group 10A and the second battery group 10B. The housing 5 consists of a case 5a and a lid 5b that closes the opening of the case. In this embodiment, the bottom surface 5b is a separate component, but it is also possible to have a structure in which the bottom surface is provided on the case 5a and the opening is provided on the top surface, with the lid 5b positioned on the top side.

[0018] Figure 15 shows a storage battery 1 used in the present invention. The storage battery 1 consists 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.

[0019] Returning to Figure 1, let's explain the first battery group 10A and the second battery group 10B. The first battery group 10A consists of multiple (six in this embodiment) storage batteries 1 stacked with their wide surfaces 1a facing each other. The second battery group 10B also has a similar structure to the first battery group 10A, with the wide surfaces of the storage batteries stacked facing each other.

[0020] The batteries 1 constituting the first battery group 10A are connected in series with a busbar 2. Similarly, the batteries 1 in the second battery group 10B are also connected in series with a busbar 2. Furthermore, the batteries 1 on the bottom surface 5b side of the first battery group 10A and the batteries 1 on the bottom surface 5b side of the second battery group 10B are connected to each other with a busbar 2. The two battery groups 10A and 10B each have external terminals 3 located on the center side of the top surface of the battery pack 100 that connect to other electronic components (such as a junction box) housed in the battery pack 100. In this invention, the temperature change of the battery pack 100 was measured in several configurations (Figures 1 to 7).

[0021] (Example 1) First, let's describe Example 1. The first and second battery groups were laid flat as shown in Figure 1, then thermally connected directly. After that, copper HV cables with a diameter of 95 mm were attached to the positive and negative external terminals, and current was applied. The average heat generated from the batteries at this time was 3 W.

[0022] Furthermore, as a cooling condition, air at a wind speed of 5 m / sec was applied only to the bottom plate via the casing located below the battery group. Figure 1 shows the top surface of the casing. Figure 8 shows the results after applying these conditions to the battery pack and reaching a near-steady state.

[0023] (Example 2) Next, we will describe Example 2. Example 2 differs from Example 1 in that the first battery group and the second battery group are placed horizontally and then connected via a flat heat conductive member 4.

[0024] Figure 2 shows the structure of this embodiment. In this embodiment, as described above, a heat conductive member 4 was placed between the first battery group 10A and the second battery group 10B. Two types of heat conductive members were prepared, with thicknesses of 3 mm and 15 mm, and the temperature rise of the battery pack 100 was measured when each was used. The results are shown in Figure 8. The cooling conditions and current application conditions were the same as in Embodiment 1.

[0025] (Example 3) Next, we will describe Example 3. Example 3 differs from Example 1 in that the material of the negative electrode current collector foil is changed from copper foil to aluminum foil.

[0026] The specific structure of battery pack 100 is the same as in Figure 1 in terms of arrangement, so the explanation will be omitted. The results of the temperature rise of pack 100 are shown in Figure 9. The cooling conditions and current application conditions were the same as in Example 1.

[0027] (Example 4) Next, we will describe Example 4. Example 4 differs from Example 2 in that the negative electrode current collector foil material is changed from copper foil to aluminum foil. The specific structure of the battery pack 100 is the same as in Figure 2, so we will omit the explanation. In this embodiment, a 15 mm thick material is used for the heat conductive member 4. The result of the temperature rise of the battery pack 100 is shown in Figure 9. The cooling conditions and current application conditions are the same as in Example 1.

[0028] (Example 5) Next, Example 5 will be described. Example 5 differs from Example 1 in that the first battery group 10A and the second battery group 10B are placed vertically as shown in Figure 3, and the narrow sides of the batteries constituting the battery group are in contact with the bottom surface of the housing 5 of the battery pack 100. The result of the temperature rise of the battery pack 100 is shown in Figure 10. The cooling conditions and current application conditions are the same as in Example 1.

[0029] (Example 6) Next, Example 6 will be described. Example 6 differs from Example 2 in that the first and second battery groups are placed vertically as shown in Figure 4, and the narrow sides of the batteries constituting the battery groups are in contact with the bottom surface of the housing 5 of the battery pack 100. In this example, as in Example 2, two heat conductive members 4 were prepared, one with a thickness of 3 mm and the other with a thickness of 15 mm, and the measurement results for each are shown in Figure 10. The cooling conditions and current application conditions are the same as in Example 1.

[0030] (Example 7) Next, we will describe Example 7. Unlike Examples 1 to 6, this example has a structure in which a first battery group and a second battery group, each consisting of six storage batteries 1 connected in series, are connected in series with each other, and the bottom surface of the storage batteries 1 is in contact with the bottom surface 5b of the housing of the battery pack 100. In this example as well, a heat conductive member 4 is placed between the first battery group 10A and the second battery group 10B. An aluminum plate with a thickness of 15 mm is used for the heat conductive member 4. The result of the temperature rise of the battery pack 100 is shown in Figure 11. The cooling conditions and current application conditions are the same as in Example 1.

[0031] (Comparative Example 1) Next, we will explain Comparative Example 1. Comparative Example 1 differs from Examples 1 to 7 in that the battery group is not divided into two, but is stacked as a single battery group.

[0032] Figure 6 shows the battery pack 100 of Comparative Example 1. Twelve batteries 1 are connected in series to form a single battery group, and the wide surface 1a of each individual battery 1 is in contact with the bottom surface 5b of the housing 5. The results of the temperature rise of the battery pack 100 are shown in Figures 8 and 9. The cooling conditions and current application conditions are the same as in Example 1.

[0033] (Comparative Example 2) Next, Comparative Example 2 will be described. Comparative Example 2 differs from Examples 1 to 7 in that the battery group is not divided into two but stacked as a single battery group, and furthermore, the narrow side 1b of the single cell 1 is in contact with the bottom surface 5b of the housing 5.

[0034] Figure 7 shows the battery pack 100 of Comparative Example 2. By connecting 12 batteries in series... A single battery group is used, and it is arranged so that the narrow side 1b of the single cell 1 is in contact with the bottom surface 5b of the housing 5. The results of the temperature rise of the battery pack 100 are shown in Figures 10 and 11. The cooling conditions and current application conditions are the same as in Example 1. The effects of this patent will be explained below based on the results of the example and comparative example.

[0035] When the conditions shown in this example and comparative example were applied to the battery group, the battery temperature rose compared to the ambient temperature when the battery group reached a near-steady state. Figures 8-11 show the ratio of the temperature rise of each individual cell in the battery group relative to the ambient temperature to the temperature rise of the cell with the smallest temperature rise. The cell numbers in the figures correspond to the cell numbers shown in the figures corresponding to each example and comparative example. In this case, for the two battery groups in the example, the temperatures of individual cells located opposite each other in the battery groups were approximately the same, so their descriptions were omitted for simplicity. The results of each figure will be explained in detail below.

[0036] Figure 8 shows the temperature rise ratios for the configurations of Examples 1 and 2, which are examples of applying the present invention to a battery arrangement laid flat, similar to Comparative Example 1. From the figure, it can be seen that in the Comparative Example, which is a conventional configuration, the temperature of cell No. 7, which is the central part of the stacked batteries, is the highest. This is because, in the battery near cell No. 7, the heat generated by the surrounding batteries is not dissipated, so not only the temperature of the cell itself but also the temperature of the surrounding batteries is high, and because there is no temperature difference, heat does not flow easily, and as a result the battery temperature is high. On the other hand, the temperature rise of the single cell No. 1, which is in contact with the bottom surface of the housing, and the cell No. 12, which has external terminals, is suppressed because there is a heat dissipation path. From the above results, a difference in the temperature rise of cells No. 1 and No. 12 and cell No. 7 was observed, so the temperature rise ratio changed significantly even within the same battery group in Comparative Example 1. Therefore, it can be seen that a difference in temperature between individual cells is likely to be observed in Comparative Example 1.

[0037] On the other hand, Figure 8 simultaneously shows an embodiment of the present invention. In the present invention, by comparing the rate of temperature rise between cells in the same arrangement across all cells, it can be seen that the rate of temperature rise can be reduced across all cells compared to the comparative example. Furthermore, as shown in Example 2, the effect is further enhanced by placing a heat transfer member between the battery groups, and it can be seen that the temperature difference between cells is mitigated. This means that by placing the external terminals in cell No. 6, which has the highest temperature, an effective heat dissipation path is secured. In addition, in Example 2, a heat dissipation path can also be secured by introducing an Al plate, so it can be seen that the temperature difference between cells was effectively reduced.

[0038] Figure 9 shows the temperature rise rates of the configurations in Examples 3 and 4, which are examples of applying the present invention to a battery configuration laid flat, similar to Comparative Example 1. From the figure, it can be seen that even when the negative electrode current collector foil is made of Al, the temperature difference between the batteries tends to be mitigated, similar to what was shown in Figure 8. The thermal behavior observed in Figure 9 is due to the same phenomenon observed in Figure 8.

[0039] Figure 10 shows the configurations of Examples 5 and 6, which are examples of applying the present invention to a battery configuration that is vertically oriented, similar to Comparative Example 2. From the figure, it can be seen that in the conventional configuration of Comparative Example, the temperature of cell No. 6, which is the central part of the stacked batteries, is the highest. The temperature rise occurring here is due to the same phenomenon as the behavior shown in Comparative Example 1 in Figure 8.

[0040] Furthermore, the figures show that even when the battery is placed vertically, the temperature difference between the batteries is mitigated, similar to Figures 8 and 9. Even when placed vertically rather than horizontally, the temperature tends to be higher near the center of the long side. By placing the external terminals in that area, the same effect as in Figures 8 and 9 is obtained, and the temperature difference is reduced.

[0041] Figure 11 compares the temperature difference when the present invention is applied to the configuration shown in Example 7, with the battery configuration being vertically oriented, similar to Comparative Example 2. From the figure, it can be seen that the temperature difference tends to be mitigated in the present invention as well. In Example 7, this is because the external terminal was installed on cell No. 6, which had the highest battery temperature, allowing for effective heat dissipation to the outside of the battery group.

[0042] The battery pack described in the present invention comprises a first battery group (10A) formed by stacking multiple storage batteries (1) having side surfaces (1a, 1b) and bottom surfaces (1c) connected to the side surfaces (1a, 1b) with their side surfaces (1a, 1b) facing each other; a second battery group (10B) formed by stacking multiple storage batteries (1) having side surfaces (1a, 1b) and bottom surfaces (1c) connected to the side surfaces (1a, 1b) with their side surfaces (1a, 1b) facing each other; and a housing (5) that houses the first battery group (10A) and the second battery group (10B), characterized in that the first battery group (10A) and the second battery group (10B) are thermally connected to each other's opposing surfaces, either directly or indirectly. By adopting such a structure, it is possible to provide a battery pack that reduces the temperature difference between the battery groups.

[0043] Furthermore, in this invention, the wide surfaces (1a) of the two battery groups are positioned opposite the bottom surface of the housing (5). This structure increases the cooling area, resulting in improved cooling performance compared to having the narrow surface 1b in contact with the housing 5.

[0044] Furthermore, in the battery pack described in the present invention, when the wide surface 1a of the battery 1 is facing downwards, the external terminals 3 are positioned towards the center of the battery pack, allowing cooling of the central part of the battery pack, where heat is less likely to escape, to be performed via the external terminals. As a result, it is possible to provide a battery pack with improved heat dissipation and reduced temperature differences between battery groups.

[0045] Furthermore, as shown in Figure 12, in the battery pack described in the present invention, a first heat transfer member (6) is arranged between the first battery group (10A) and the second battery group (10B), and the heat transfer member (6) is in close contact with the first battery group (10A) and the second battery group (10B). By adopting this structure, the heat transfer member promotes further heat diffusion, and a battery pack with a smaller temperature difference between the battery groups can be provided. Note that Figure 12 is a top view of Figure 2.

[0046] Furthermore, in the battery pack described in the present invention, as shown in Figure 13, a second heat transfer member 61 and a third heat transfer member 62 may be placed on either side 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 6 and the second heat transfer member 61, and the second battery group 10B is sandwiched between the heat transfer member 6 and the third heat transfer member 10B. This improves heat dissipation on both sides of the battery groups 10A and 10B, making it possible to provide a battery pack with a smaller temperature difference between the battery groups.

[0047] Furthermore, in the battery pack described in the present invention, the second heat transfer member 61 and the third heat transfer member 62 are both wider than the first heat transfer member 6. By adopting such a structure, the housing 5 and the heat transfer members 61 and 62 can be fastened together with screws or the like, creating a larger structure, and allowing the housing 5 and the heat transfer members 61 and 62 to be more tightly fitted together. As a result, the heat generated by the battery 1 is more easily transferred to the housing 5, making it possible to provide a battery pack with improved cooling performance.

[0048] Furthermore, in the battery pack described in the present invention, as shown in Figure 14, in another form, the first heat transfer member 6 is thicker than the second heat transfer member 61 and the third heat transfer member 62. By adopting such a structure, heat diffusion is further promoted between the two battery groups where heat dissipation is worst, making it possible to provide a battery pack with improved cooling performance. In addition, in the present invention, the type of battery pack in which the wide surface 1a of the battery 1 is in contact with the bottom surface of the housing 5 is particularly effective when used with natural cooling without flowing cooling air between battery groups or individual cells. Therefore, the present invention is very suitable for a structure in which the battery 1 is placed horizontally. Furthermore, the present invention relates to a battery group comprising a first battery group and a second battery group, each consisting of a rectangular parallelepiped with a wide surface and a narrow surface, stacked with the wide surfaces facing each other, the battery pack comprising a first battery group and a second battery group, the first battery group and the second battery group arranged side by side and housed in a housing such that the narrow surfaces of the batteries face each other, a first heat transfer member disposed between the first battery group and the second battery group, the first heat transfer member in close contact with the first battery group and the second battery group, and in the batteries on the upper surfaces of the first battery group and the second battery group, external terminals are provided on the central side of the battery pack to connect the first battery group and the second battery group to an electronic circuit in the housing, and heat is dissipated through these external terminals. The present invention relates to a battery pack, further comprising a second heat transfer member and a third heat transfer member, wherein the first battery group is sandwiched between the first heat transfer member and the second heat transfer member, the second battery group is sandwiched between the first heat transfer member and the third heat transfer member, and the second heat transfer member and the third heat transfer member are thicker than the first heat transfer member. The present invention also relates to a battery pack, further comprising the first battery group being sandwiched between the first heat transfer member and the second heat transfer member, the second battery group being sandwiched between the first heat transfer member and the third heat transfer member, and the first heat transfer member being thinner than the second heat transfer member and the third heat transfer member.

[0049] Although embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above, and various design modifications can be made without departing from the spirit of the invention as described in the claims. For example, the embodiments described above are described in detail in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations described. Furthermore, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Moreover, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations. [Explanation of symbols]

[0050] 1 single cell 2 Wiring 3 External terminals 4. Bottom of the enclosure 5. Top of the enclosure 6, 61, 62 Heat transfer members

Claims

1. A first battery group is formed by stacking multiple storage batteries, each having a battery can side and a battery can bottom connected to the battery can side, with the battery can sides facing each other. A second battery group is formed by stacking multiple storage batteries, each having a battery can side and a battery can bottom connected to the battery can side, with the battery can sides facing each other. In a battery pack comprising a housing for the first battery group and the second battery group, A battery pack characterized in that the first battery group and the second battery group are thermally connected to each other, either directly or indirectly, on their opposing surfaces.

2. In the battery pack according to claim 1, A first heat transfer member is positioned between the first battery group and the second battery group. The heat transfer member is characterized in that it is in close contact with the first battery group and the second battery group.

3. In the battery pack according to either claim 1 or 2, The battery pack has a second heat transfer member and a third heat transfer member. The first battery group is sandwiched between the first heat transfer member and the second heat transfer member. The second battery group is sandwiched between the first heat transfer member and the third heat transfer member. A battery pack characterized in that the second heat transfer member and the third heat transfer member are thicker than the first heat transfer member.

4. In the battery pack according to any one of claims 1 to 3, The battery pack has a second heat transfer member and a third heat transfer member. The first battery group is sandwiched between the first heat transfer member and the second heat transfer member. The second battery group is sandwiched between the first heat transfer member and the third heat transfer member. The battery pack is characterized in that the first heat transfer member is thinner than the second heat transfer member and the third heat transfer member.

Images