Battery pack

Abstract

To properly discharge, in the case where a low-molecular siloxane contained in a material of a battery is gasified, the low-molecular siloxane gas to outside of a battery case.SOLUTION: A battery pack comprises a battery, a battery case, a vent hole, and a pressure adjustment film. The battery contains a low-molecular siloxane as a composition material. The battery case has a housing space storing the battery and a relay member. The vent hole communicates with outside of the battery case. The vent hole extends from a bottom wall surface, constituting the housing space at a lower part of the battery case, downward in the vertical direction. The pressure adjustment film adjusts the pressure of gas in the housing space. The pressure adjustment film is formed at the point where the vent hole is formed. The pressure adjustment film has a retaining particle diameter greater than a molecular diameter of the low-molecular siloxane contained in the composition material.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a battery pack. [Background technology]

[0002] JP 2019-186039 A discloses a battery pack equipped with a pressure adjustment membrane in the middle of a gas exhaust path. In this conventional battery pack, gas is generated inside each battery cell that constitutes the battery pack due to decomposition or volatilization of the electrolyte. This gas is released from the inside of the battery cell to the outside. A gas exhaust path is provided outside the battery cell, and gas derived from the electrolyte released from the battery cell flows through this gas exhaust path. When the gas pressure on the upstream side of the pressure adjustment membrane is higher than that on the downstream side, the gas derived from the electrolyte passes through the pressure adjustment membrane. This allows the gas derived from the electrolyte to be released outside the battery pack. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-186039 Summary of the Invention [Problem to be solved by the invention]

[0004] The materials that make up a cell may contain low-molecular-weight siloxanes. Low-molecular-weight siloxanes typically refer to low-molecular-weight cyclic siloxanes containing 3 to 20 (D3 to D20) repeating units represented by (Si(CH3)-O-), or low-molecular-weight chain siloxanes containing 2 to 20 (M2 to M20) of these repeating units. Low-molecular-weight siloxanes tend to gasify easily. When gasified low-molecular-weight siloxanes, i.e., gaseous siloxanes, adhere to conductive parts, they can be decomposed by thermal oxidation and converted into silicon dioxide. Because silicon dioxide has insulating properties, silicon dioxide adhering to conductive parts can cause insulation failure.

[0005] A typical conductive part in a battery pack is a relay member. In a battery pack, the relay member is usually housed in a space formed in a battery case that is connected to the space housing the battery assembly. Therefore, it is desirable to protect such a relay member from gaseous siloxane. In this regard, the pressure adjustment membrane of conventional battery assemblies is not designed with gaseous siloxane in mind. Therefore, there is room for development focusing on this point of view.

[0006] One object of the present disclosure is to provide a technology that can appropriately discharge low-molecular-weight siloxane contained in a material constituting a battery to the outside of the battery case when the low-molecular-weight siloxane is gasified. [Means for solving the problem]

[0007] The inventors of this disclosure focused on the molecular diameter of low molecular weight siloxanes and their specific gravity relative to air. For example, the average molecular diameter of siloxane D4 is approximately 13 nm. Therefore, if a pressure-regulating membrane has a retention particle diameter larger than the average molecular diameter of the main low molecular weight siloxanes used in battery materials, the gaseous siloxane can pass through by utilizing the pressure difference between the two spaces separated by this pressure-regulating membrane. Furthermore, low molecular weight siloxanes weigh more than 10 times more than air. Therefore, while gaseous siloxanes move through the internal space of the battery pack due to gas convection generated in this space during battery operation, they are expected to accumulate at the bottom of this internal space when the battery is not in operation. Therefore, a pressure-regulating membrane installed at the bottom of the internal space can efficiently allow low molecular weight siloxanes to pass through, especially when the battery is not in operation.

[0008] Based on this perspective, the inventors of the present disclosure conducted various studies and demonstration experiments, and have completed the present disclosure, which can solve the above-mentioned problems. Specifically, the present disclosure is a battery pack including a battery, a battery case, a vent, and a pressure adjustment membrane. The battery includes a low-molecular-weight siloxane as a component. The battery case has a storage space that houses the battery and a relay member. The vent is connected to the outside of the battery case. The vent is formed at the bottom of the battery case, extending vertically downward from the bottom wall that forms the storage space. The pressure adjustment membrane adjusts the pressure of the gas in the storage space. The pressure adjustment membrane is provided at the location where the vent is formed. The pressure adjustment membrane also has a retention particle diameter larger than the molecular diameter of the low-molecular-weight siloxane contained in the component. [Effects of the Invention]

[0009] According to the present disclosure, a vent hole connecting to the outside of the battery case is formed vertically downward from the bottom wall surface that defines the storage space at the bottom of the battery case. A pressure-regulating membrane having a retention particle diameter larger than the molecular diameter of the low-molecular-weight siloxane is also provided at the location where the vent hole is formed. This allows the gasified low-molecular-weight siloxane (i.e., gaseous siloxane) to be discharged to the outside of the battery case. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram showing an example of the basic configuration of a battery pack common to each embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic diagram showing an example of the configuration of the battery pack according to the first embodiment. [Figure 3] FIG. 3 is a diagram showing the results of a verification experiment regarding the change in concentration of gaseous siloxane over time. [Figure 4] FIG. 4 is a schematic diagram showing an example of the configuration of a battery pack according to the second embodiment. [Figure 5] FIG. 5 is a schematic diagram showing an example of the configuration of a battery pack according to the third embodiment. [Figure 6]FIG. 6 is a schematic diagram showing an example of the configuration of a battery pack according to the fourth embodiment. [Figure 7] FIG. 7 is a schematic diagram showing an example of the configuration of a battery pack according to the fifth embodiment. [Figure 8] FIG. 8 is a schematic diagram showing an example of the configuration of a battery pack according to the sixth embodiment. [Figure 9] FIG. 9 is a schematic diagram showing an example of the configuration of a battery pack according to the seventh embodiment. [Figure 10] FIG. 10 is a schematic diagram showing an example of the configuration of a buoyant body. [Figure 11] FIG. 11 is a view of the buoyancy body seen from above, with the bottom of the battery case cut along the AA cross section shown in FIG. [Figure 12] FIG. 12 is a view of the buoyancy body taken from below, with the bottom of the battery case cut along the BB cross section shown in FIG. [Figure 13] FIG. 13 is a schematic diagram showing an example of the configuration of a battery pack according to the eighth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will be simplified or omitted.

[0012] 1. First embodiment A battery pack according to an embodiment of the present disclosure is mounted on a vehicle such as an electric vehicle or a hybrid vehicle. Fig. 1 is a schematic diagram showing an example of the basic configuration of a battery pack common to each embodiment of the present disclosure. The X-axis shown in Fig. 1 corresponds to the vertical direction, and the Y-axis corresponds to the horizontal direction. More specifically, the positive direction of the X-axis corresponds to the vertically upward direction, and the negative direction of the X-axis corresponds to the vertically downward direction.

[0013] Fig. 1 shows a cross section of a battery case 1 that constitutes a battery pack. As shown in Fig. 1, the battery case 1 includes a ceiling portion 11, a bottom portion 12, side walls 13 and 14, and a partition wall portion 15. Portions of the side walls 13 and 14, together with the ceiling portion 11, constitute an upper case, and the remaining portions of the side walls 13 and 14, together with the bottom portion 12, constitute a lower case.

[0014] A storage space 2 is formed in the battery case 1. The storage space 2 is provided with a plurality of battery packs 3, a junction box 4, and a pressure adjustment membrane 5. Three partition walls 15 are shown in FIG. 1, and four battery packs 3 are housed in four spaces formed by these partition walls 15. Each battery pack 3 is, for example, a modularized lithium-ion cell. Low-molecular-weight siloxane is used as the material constituting the cell (for example, the electrode material).

[0015] The junction box 4 houses a control board 41 and a relay member 42. The relay member 42 is a member that connects elements provided on the control board 41 to each other. The relay member 42 may also be a member that connects multiple wires that are drawn into the housing space 2 from the outside of the battery case 1. The junction box 4 is not an essential component of the battery case 1. Therefore, the junction box 4 may be omitted from illustration in Figure 2 and subsequent figures.

[0016] The pressure adjustment membrane 5 discharges the gas in the storage space 2 to the outside of the battery case 1 when the pressure of the gas in the storage space 2 is higher than that outside of the battery case 1. The pressure adjustment membrane 5 also discharges the specific gas in the storage space 2 to the outside of the battery case 1 when the concentration of the specific gas (e.g., gaseous siloxane) in the storage space 2 is higher than that outside of the battery case 1, even if the pressure of the gas in the storage space 2 is the same as that outside of the battery case 1. To enable discharge based on this pressure difference and concentration difference, the pressure adjustment membrane 5 has a retention particle diameter larger than the average molecular diameter of the main low-molecular-weight siloxane used in the battery pack 3.

[0017] FIG. 2 is a schematic diagram showing an example of the configuration of a battery pack according to the first embodiment. In the example shown in FIG. 2, the storage space 2 includes a junction space 21 and a recessed space 22. The junction space 21 is a space that accommodates the junction box 4 shown in FIG. 1. The recessed space 22 is a space recessed in the negative X-axis direction from the bottom wall surface 12a that constitutes the junction space 21. The bottom wall surface 12b that constitutes the recessed space 22 is provided with a through-hole 16 that extends from the bottom wall surface 12b in the negative X-axis direction and penetrates the bottom 12. The through-hole 16 corresponds to an example of a "vent" in the present disclosure. The pressure adjustment membrane 5 is provided on the bottom wall surface 12b at the opening position of the through-hole 16.

[0018] 2, the recessed space 22 is formed, but the recessed space 22 does not have to be formed. In this case, the through-hole 16 extends from the bottom wall surface 12a in the negative direction of the X-axis and penetrates the bottom 12. The pressure adjusting membrane 5 is provided on the bottom wall surface 12a and at the opening of the through-hole 16.

[0019] However, according to verification experiments conducted by the inventors of the present disclosure, it has been found that the rate at which the concentration of gaseous siloxane in the junction space 21 decreases is higher when the pressure adjustment film 5 is provided below the recess space 22 than when it is provided above the recess space 22 (see FIG. 3). Therefore, from the perspective of increasing the efficiency of discharging gaseous siloxane, it is desirable that the storage space 2 includes the recess space 22, and that the pressure adjustment film 5 is provided on the bottom wall surface 12b and at the opening position of the through-hole 16. In other words, the example shown in FIG. 2 is expected to have more advantageous effects than an example in which the recess space 22 is not formed.

[0020] 2. Second embodiment Fig. 4 is a schematic diagram showing a configuration example of a battery pack according to the second embodiment. In the example shown in Fig. 4, the length (depth) of recessed space 22 in the negative X-axis direction is shorter than in the example shown in Fig. 2. Instead, the length (depth) of through-hole 16 in the negative X-axis direction is longer than in the example shown in Fig. 2.

[0021] In the example shown in FIG. 4, a peripheral groove 17 is formed to surround the outer periphery of the pressure adjusting membrane 5. The direction in which the peripheral groove 17 is formed is parallel to the direction in which the through holes 16 are formed (i.e., the negative X-axis direction). However, the length (depth) of the peripheral groove 17 in the negative X-axis direction is shorter than that of the through holes 16. In the example shown in FIG. 4, a bottom water channel 6 is also formed below the deepest part of the peripheral groove 17. The bottom water channel 6 is part of the cooling water channel for the battery pack 3, and cooling water for the battery pack 3 flows through this cooling water channel 6.

[0022] The water vapor in the storage space 2 may be cooled by the wall surfaces (for example, the bottom wall surface 12a) that form the storage space 2 and condense. The water droplets that form as a result of this condensation may interfere with the gas discharge function of the pressure adjustment membrane 5. In this regard, in the example shown in FIG. 4, an outer circumferential groove 17 is formed. Therefore, even if water droplets are generated in the junction space 21, the water droplets can be collected in the junction space 21.

[0023] 4, a bottom water channel 6 is also formed. Therefore, for example, the area around the bottom water channel 6 can be heated by the cooling water heated during operation of the battery pack, and the water collected in the peripheral groove 17 can be gasified. In other words, the water droplet collection function of the peripheral groove 17 can be restored.

[0024] 3. Third embodiment Fig. 5 is a schematic diagram showing a configuration example of a battery pack according to the third embodiment. In the example shown in Fig. 5, bottom wall surface 12a forms a tapered surface that slopes toward the location where through hole 16 is formed (the location where recessed space 22 is formed). Note that, although the entire bottom wall surface 12a forms a tapered surface in the example shown in Fig. 5, only a portion of bottom wall surface 12a that is connected to the opening of recessed space 22 may form a tapered surface.

[0025] 5, the low-molecular-weight siloxane accumulated on the bottom wall surface 12a can be collected at the installation position of the pressure adjusting membrane 5. Therefore, it is possible to increase the efficiency with which the pressure adjusting membrane 5 discharges the low-molecular-weight siloxane.

[0026] 4. Fourth embodiment FIG. 6 is a schematic diagram showing an example of the configuration of a battery pack according to the fourth embodiment. In the example shown in FIG. 6, the battery pack 3 is attached to the ceiling wall surface 11a that defines the storage space 2. That is, unlike the first to fourth embodiments, the attachment position of the battery pack 3 is reversed in the fifth embodiment. As a result, in the example shown in FIG. 7, the storage space 2 includes a junction space 21 and a battery space 23. The junction space 21 has been described above. The battery space 23 is a space formed below the battery pack 3.

[0027] As already explained, low-molecular-weight siloxane is used as a material for the cells. Therefore, when low-molecular-weight siloxane is gasified, it is expected that the gaseous siloxane will move from the space where the battery pack 3 is installed to the junction space 21. In this regard, in the example shown in FIG. 6, the battery space 23 is formed below the battery pack 3. Therefore, compared to the examples shown in FIGS. 2, 4, and 5, the gaseous siloxane, which is heavier than air, will move more easily to the junction space 21. Therefore, it is possible to improve the efficiency with which the pressure adjusting membrane 5 discharges low-molecular-weight siloxane.

[0028] The inverted mounting of the battery pack 3 described in the fourth embodiment can also be applied to mounting the junction box 4 including the control board 41 and the relay members 42. That is, the mounting position of the junction box 4 in the present disclosure may be the bottom wall surface 12a shown in Figures 2, 4, and 5, or the ceiling wall surface 11a shown in Figure 6.

[0029] 5. Fifth embodiment Fig. 7 is a schematic diagram showing a configuration example of a battery pack according to the fifth embodiment. In the example shown in Fig. 7, the junction box 4 is depicted without omission. A through hole 43 that connects the inside and outside of the junction box 4 is formed in a wall member that constitutes the junction box 4. In the example shown in Fig. 7, the through hole 43 is located below the relay member 42. In this example, the through hole 43 is also located near the opening of the recessed space 22.

[0030] When the junction box 4 is installed in the storage space, gaseous siloxane may enter the internal space of the junction box 4 through gaps in the screws or wall members of the junction box 4. In this regard, according to the example shown in FIG. 7, gaseous siloxane that has entered the internal space of the junction box 4 can be quickly discharged through the through-holes 43. In addition, the gaseous siloxane can be discharged from a position close to the opening of the recessed space 22. Therefore, it is also possible to improve the efficiency with which the pressure adjusting membrane 5 discharges gaseous siloxane.

[0031] 6. Sixth embodiment 8 is a schematic diagram showing an example of the configuration of a battery pack according to the sixth embodiment. In the example shown in FIG. 8, through-hole 16 branches midway. Branch hole 18 extends in the positive direction of the Y-axis within bottom portion 12, changes direction near side wall portion 13, and extends in the positive direction of the X-axis within side wall portion 13. The portion of branch hole 18 extending in the positive direction of the Y-axis is also referred to as "horizontal branch hole 18a," and the portion of branch hole 18 extending in the positive direction of the X-axis is also referred to as "vertical branch hole 18b." Vertical branch hole 18b opens to the surface of ceiling portion 11.

[0032] 2 and 4 to 7, the through hole 16 does not branch, but in the example shown in FIG. 8, the through hole 16 is connected to the branch hole 18. Therefore, even if the battery case 1 is submerged and external water enters the through hole 16, the pressure of the gas inside the through hole 16 can be maintained at atmospheric pressure as long as the water does not reach the connecting position of the through hole 16 and the branch hole 18. This makes it possible to prevent the pressure on the pressure adjustment membrane 5 from becoming too high. From this perspective, the position where the branch hole 18 opens does not have to be the surface of the ceiling portion 11, and may be, for example, the surface of the side wall portion 13.

[0033] 7. Seventh embodiment FIG. 9 is a schematic diagram showing an example of the configuration of a battery pack according to a seventh embodiment. In the example shown in FIG. 9, a buoyant body 7 is provided at the position of the through-hole 16. This buoyant body 7 will be described with reference to FIGS. 10 to 12. FIG. 10 is a schematic diagram showing an example of the configuration of the buoyant body 7. FIG. 11 corresponds to a view of the buoyant body 7 taken along the AA cross section shown in FIG. 10, with the bottom 12 cut, and viewed from the bottom wall surface 12b side. FIG. 12 corresponds to a view of the buoyant body 7 taken along the BB cross section shown in FIG. 10, with the bottom 12 cut, and viewed from the surface (bottom surface) side of the bottom 12.

[0034] As shown in Fig. 10, the through-hole 16 is composed of a small-diameter hole 16a having the same diameter as the opening in the bottom wall surface 12b, and a large-diameter hole 16b having a larger diameter than the small-diameter hole 16a. In the example shown in Fig. 10, the diameter of the large-diameter hole 16b increases from the connection with the small-diameter hole 16a toward the negative direction of the X axis, and then becomes constant from that point on. The buoyant body 7 includes a spherical float 71, which is located in the large-diameter hole 16b. The diameter r71 of the float 71 is larger than the radius r16a of the small-diameter hole 16a and smaller than the maximum radius r16b(max) of the large-diameter hole 16b (see Fig. 11).

[0035] The buoyant body 7 also includes a weight 72 and a connecting portion 73. The weight 72 is provided to stabilize the movement of the float 71. The connecting portion 73 is a portion that is connected to the bottom portion 12 and is provided to restrict the movement of the float 71 in the X-axis direction. As shown in FIG. 12, the connecting portion 73 is composed of an annular portion 73a and four arms 73b that extend toward the center of the annular portion 73a. The annular portion 73a is joined to the wall surface that defines the large diameter hole 16b, thereby connecting the connecting portion 73 to the bottom portion 12. For ease of explanation, the weight 72 is not shown in FIG. 12.

[0036] 10 to 12, the through-hole 16 and buoyancy body 7 allow gaseous siloxane to be discharged to the outside through the periphery of the float 71 under normal circumstances. On the other hand, if the battery case 1 is submerged and external water enters the large-diameter hole 16b, for example, the float 71 moves upward to block the connection between the small-diameter hole 16a and the large-diameter hole 16b. This prevents external water from entering the accommodation space 2, thereby protecting the components accommodated in the accommodation space 2, such as the control board 41.

[0037] 8. Eighth embodiment FIG. 13 is a schematic diagram illustrating a configuration example of a battery pack according to the eighth embodiment. In the example illustrated in FIG. 13, the through-hole 16 illustrated in FIG. 2 and other figures is not formed in the bottom portion 12. Instead, a communication hole 19 is formed in the bottom portion 12. The communication hole 19 is composed of a first vertical hole 19a and a second vertical hole 19b extending in the X-axis direction within the bottom portion 12, a horizontal hole 19c extending in the Y-axis direction within the bottom portion 12 and connecting these vertical holes, and a lateral groove 19d recessed from the side surface of the bottom portion 12 into the inside of the bottom portion 12. The second vertical hole 19b is connected to the lateral groove 19d at the wall surface of the lateral groove 19d located in the negative X-axis direction. The communication hole 19 corresponds to an example of a "vent" in the present disclosure. The pressure adjustment membrane 5 is provided at the opening of the second vertical hole 19b.

[0038] 13, the opening of communication hole 19 in the surface of bottom 12 can be formed on the side of bottom 12. Therefore, if the battery pack is installed in the bottom of a vehicle, even if the bottom surface of bottom 12 is damaged by a flying stone, the pressure adjustment membrane 5 can maintain its function of discharging gaseous siloxane. [Explanation of symbols]

[0039] REFERENCE SIGNS LIST 1 battery case 2 storage space 3 battery pack 4 junction box 5 pressure adjustment membrane 6 bottom waterway 7 buoyancy body 11 ceiling portion 11a ceiling wall surface 12 bottom portion 12a, 12b, 12c bottom wall surface 13, 14 side wall portion 15 partition portion 16 through hole 16a small diameter hole 16b large diameter hole 17 peripheral groove 18 branch hole 18a horizontal branch hole 18b vertical branch hole 19 communication hole 19a first vertical hole 19b second vertical hole 19c horizontal hole 19d side groove 21 junction space 22 recess space 23 battery space 41 control board 42 relay member 43 through hole 71 float 72 weight portion 73 connecting portion

Claims

1. a battery containing a low molecular weight siloxane as a component; a battery case having a storage space for storing the battery and the relay member; a vent hole communicating with the outside of the battery case, the vent hole being formed in a vertically downward direction from a bottom wall surface that constitutes the storage space at the bottom of the battery case; a pressure adjusting membrane that adjusts the pressure of the gas in the storage space, the pressure adjusting membrane being provided at a location where the air vent is formed and having a retention particle diameter larger than the molecular diameter of the low-molecular-weight siloxane contained in the component; A battery pack comprising:

2. the bottom wall surface constituting the accommodation space includes a bottom wall surface constituting a recessed space recessed in the vertically downward direction at a location where the air vent is formed, The pressure adjusting membrane is provided on the bottom wall surface that forms the recessed space and at the opening position of the air vent.

2. The battery pack according to claim 1, wherein the battery pack is a battery pack having a plurality of electrodes.

3. a peripheral groove formed vertically downward from a bottom wall surface that constitutes the storage space at the bottom of the battery case and that surrounds the outer periphery of the pressure adjustment membrane; 3. The battery pack according to claim 1 or 2.

4. Further, a cooling water channel for cooling the battery is provided. the cooling water channel includes a bottom water channel formed in a bottom portion of the battery case, A part of the bottom water channel is located below the deepest part of the outer circumferential groove in the vertically downward direction.

4. The battery pack according to claim 3.

5. The bottom wall surface that constitutes the storage space includes a tapered surface that slopes from the periphery of the location where the vent hole is formed toward the location where the vent hole is formed.

3. The battery pack according to claim 1 or 2.

6. The battery is attached to a ceiling wall surface that defines the storage space, The bottom wall surface that constitutes the storage space includes a bottom wall surface that constitutes a gap space formed below the battery in the vertically downward direction.

3. The battery pack according to claim 1 or 2.

7. the relay member is located in a junction box provided in the accommodation space, the junction box includes a junction box through-hole formed in a wall member constituting the junction box and serving as a through-hole connecting the inside and the outside of the junction box; The junction box through-hole is positioned below the relay member in the vertically downward direction.

3. The battery pack according to claim 1 or 2.

8. The vent hole includes a through-hole that extends vertically downward from a bottom wall surface that forms the storage space and penetrates a bottom portion of the battery case, and a branch hole that branches off midway from the through-hole, passes through the bottom portion of the battery case, and opens into a side wall portion or a ceiling portion of the battery case.

3. The battery pack according to claim 1 or 2.

9. the vent hole extends vertically downward from a bottom wall surface that defines the storage space and penetrates a bottom portion of the battery case, the ventilation hole includes a small diameter hole extending vertically downward from a bottom wall surface that constitutes the accommodation space, and a large diameter hole located below the small diameter hole, The aerial vehicle further includes a buoyant body that is housed in the large diameter hole and has a diameter that is larger than the diameter of the small diameter hole and smaller than the diameter of the large diameter hole.

3. The battery pack according to claim 1 or 2.

10. the air vent includes a lateral groove formed in a direction from a side surface of the battery case toward an inside of the battery case, a first vertical hole extending in the vertically downward direction from a bottom wall surface that constitutes the storage space, a second vertical hole extending in the vertically downward direction from a wall surface that is located in the vertically downward direction among the wall surfaces that constitute the lateral groove, and a horizontal hole connecting the first vertical hole and the second vertical hole, The pressure adjusting membrane is provided at the opening position of the second vertical hole.

2. The battery pack according to claim 1, wherein the battery pack is a battery pack having a plurality of electrodes.

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