Battery pack including heat diffusion suppression structure

Abstract

The present invention relates to a battery pack including a battery module housing that accommodates a plurality of battery cells, a battery pack case that accommodates one or more of the battery module housings, and a water tank that is located on one side of the battery module housing and that accommodates cooling water, wherein the battery module housing is formed so that at least a portion of the surface facing the water tank is open, and in the event of a battery cell ignition, the battery pack can quickly and accurately prevent the flames from the ignited battery cell from spreading.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 2020-0157818 filed on November 23, 2020, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a battery pack including a thermal diffusion suppression structure, specifically a battery pack including a thermal diffusion suppression structure that allows cooling water to be injected directly into a ignited battery cell to prevent the spread of flames that may occur in a battery cell inside the battery pack. [Background technology]

[0003] As a result of continuous research and development into lithium secondary batteries, it has become possible to manufacture and commercialize lithium secondary batteries with increased capacity and improved output. In addition, demand for lithium secondary batteries is increasing as an energy source that can replace fossil fuels, which are problematic for environmental pollution.

[0004] Therefore, the application of lithium secondary batteries to various devices is increasing. For example, lithium secondary batteries are widely used as energy sources for wireless mobile devices, which are multifunctional small products, or wearable devices worn on the body, as well as energy sources or energy storage systems (ESS) for electric vehicles and hybrid electric vehicles, which are presented as alternatives to existing gasoline and diesel vehicles.

[0005] As lithium secondary batteries are used as large-capacity, high-power energy sources, ensuring the safety of the lithium secondary batteries has become an important issue.

[0006] Generally, in the event of a fire occurring in a battery cell housed inside a power storage device, a separate water injection device is used to inject water into the battery module or battery pack.

[0007] However, in this case, facilities and space are required to install the water injection device, and there is a problem that the fire may spread due to the time lag between sensing the gas discharged by venting the battery cell and injecting water.

[0008] Alternatively, a method can be used in which heat insulating material or fire extinguishing agents are placed inside or outside the battery module or battery pack to block heat transfer between battery cells or to cool a ignited battery cell.

[0009] However, when using a heat insulating material, although it can prevent the spread of flames, there is a problem that it cannot perform fire extinguishing function.When using a fire extinguishing agent, the fire extinguishing agent is placed in the empty space inside the battery pack taking into account the energy density, so there is a problem that the fire extinguishing agent is not dispersed accurately at the point where the fire started.

[0010] As such, as a technology for preventing thermal runaway in a battery pack, Patent Document 1 discloses a device in which an envelope containing water is placed on top of the battery, the envelope being made of a material with a relatively low melting point, and when the battery temperature increases, the envelope melts and the water inside is discharged into the battery.

[0011] In Patent Document 1, the entire envelope is made of a material with a low melting point, so when the battery temperature increases, water is not released from only specific parts of the envelope, but rather the envelope melts and all of the water inside is released.

[0012] Therefore, if the envelope is placed below the battery cell, water cannot be injected into the battery cell and the fire extinguishing function cannot be achieved. For this reason, there is a restriction that the container must only be used in a certain direction so that the envelope is placed above the battery cell.

[0013] In Patent Document 2, an inner case and an inner case are housed inside an outer case, a plurality of unit cells are housed in the inner case, a fire extinguishing agent is housed in the inner case, and an injection tube is included for injecting the fire extinguishing agent into the inner case when the unit cells heat up to an upper limit temperature or higher. When the unit cells heat up to an upper limit temperature or higher, the injection tube opens and the fire extinguishing agent housed in the inner case is injected into the inner case.

[0014] Patent Document 2 includes compressed gas for spraying the extinguishing agent, a nozzle used as an injection pipe, and an inner case that houses the extinguishing agent, but additional space is required to accommodate these components, and additional costs are incurred for providing the extinguishing agent and compressed gas.

[0015] Patent Document 3 discloses a battery module including a cell assembly, a heat sink positioned in contact with the outer surface of the cell assembly and having a refrigerant flow path formed therein through which a refrigerant moves, and a heat-shrinkable tube that is heat-shrunk so that the cell assembly and the heat sink are tightly attached to each other.

[0016] In Patent Document 3, the heat sink is placed in close contact with the cell assembly to achieve heat dissipation for the cell assembly, but it cannot prevent the flames from spreading to adjacent battery modules if the cell assembly catches fire.

[0017] As such, there is a strong need for a technology that can minimize the spread of flames when a battery cell housed inside a battery pack catches fire, does not require additional space, and prevents a decrease in energy density. [Prior art documents] [Patent documents]

[0018] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-523622 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-252909 [Patent Document 3] Korean Patent Publication No. 2020-0030964 Summary of the Invention [Problem to be solved by the invention]

[0019] The present invention is intended to solve the above problems, and aims to provide a battery pack that includes a fire extinguishing function and a heat diffusion suppression structure that can extinguish a fire in a battery cell when the battery cell ignites or explodes, and prevent the flame from spreading to adjacent battery cells. [Means for solving the problem]

[0020] To achieve this object, a battery pack according to the present invention includes a battery module housing that accommodates a plurality of battery cells, a battery pack case that accommodates one or more of the battery module housings, and a water tank that is located on one side of the battery module housing and contains coolant, and at least a portion of the surface of the battery module housing that faces the water tank may be open.

[0021] In the battery pack according to the present invention, the water tank may be integrated with a heat sink, and a flow path may be formed inside the water tank to guide the flow of cooling water flowing in and out.

[0022] In the battery pack according to the present invention, the water tank may be formed to a size sufficient to cover the entire upper surface of the battery module housing.

[0023] In the battery pack according to the present invention, the water tank may be attached to the inner surface of the upper surface of the battery pack case.

[0024] In the battery pack according to the present invention, the battery pack case may have an open top, and the water tank may be coupled to the battery pack case in a manner that covers the open top surface of the battery pack case.

[0025] In the battery pack according to the present invention, the battery module housing may be formed in a plate shape and disposed on each of both side surfaces of a battery cell stack formed of the plurality of battery cells.

[0026] In the battery pack according to the present invention, metal straps for fixing the plurality of battery cells may be attached to the upper and lower surfaces of the battery cell stack.

[0027] In the battery pack according to the present invention, the battery module housing may have a structure that encloses the outer surface of the battery cell stack formed of the plurality of battery cells except on both sides where electrode terminals protrude, and an opening may be formed on one side of the battery module housing that faces the water tank.

[0028] In the battery pack according to the present invention, the water tank may have a through hole formed in one surface facing the battery module housing, and a sealing member may be attached to the through hole.

[0029] In the battery pack according to the present invention, the sealing member may be made of a material that melts when exposed to high-temperature gas or a spark emitted from the battery cell.

[0030] In the battery pack according to the present invention, the through-hole may be opened by melting the sealing member, and cooling water stored inside the water tank may be poured into the battery cells through the through-hole.

[0031] In the battery pack according to the present invention, the through-hole may be formed in the form of a plurality of holes uniformly distributed on one surface of the water tank.

[0032] In the battery pack according to the present invention, a partition wall may be added between the battery module housings.

[0033] In the battery pack according to the present invention, the sealing member may include an extension portion that fills the through hole and extends from an outer surface of the water tank further outward than the periphery of the through hole.

[0034] In the battery pack according to the present invention, the battery cells may be pouch-shaped battery cells, prismatic battery cells, or cylindrical battery cells. [Effects of the Invention]

[0035] As explained above, the battery pack according to the present invention includes a water tank inside the battery pack, which not only does not increase the external dimensions of the battery pack but also allows for rapid cooling of ignited battery cells, thereby reliably suppressing thermal runaway in the battery cells.

[0036] In addition, a sealing member is attached to one side of the water tank facing the battery module housing, so if the sealing member melts and is removed, cooling water can be sprayed toward the ignited battery cell regardless of the position and direction of the battery pack.

[0037] Furthermore, since a through hole is formed on one side of the water tank and the sealing member fills the through hole, an increase in the weight of the battery pack due to the addition of the sealing member can be minimized.

[0038] In addition, even if one of the battery cells constituting the battery cell stack catches fire, cooling water can be accurately injected into the ignited battery cell, so the heat diffusion blocking effect can be obtained even when applied to a large-capacity battery pack.

[0039] Furthermore, production costs can be reduced when water is used instead of expensive extinguishing agents. [Brief explanation of the drawings]

[0040] [Figure 1] 1 is a perspective view of a battery pack according to a first embodiment of the present invention; [Figure 2] 1 is an exploded perspective view of a battery pack according to a first embodiment. [Figure 3] 1 is a perspective view of a battery module including a battery module housing having an opening formed on one side thereof facing a water tank; [Figure 4] 2 is a cross-sectional view of the battery pack shown in FIG. 1 taken along line AA'. FIG. [Figure 5] 3A and 3B are schematic diagrams for explaining a situation in which a flame is extinguished when a fire occurs in the battery pack according to the first embodiment. [Figure 6] FIG. 10 is an exploded perspective view of a battery pack according to a second embodiment. [Figure 7] 7 is a cross-sectional view of the battery pack shown in FIG. 6 taken along line AA'. FIG. [Figure 8] 10 is a schematic diagram for explaining a situation in which a flame is extinguished when a fire occurs in the battery pack according to the second embodiment. FIG. [Figure 9] FIG. 10 is an exploded perspective view of a battery pack according to a third embodiment. [Figure 10] 10 is a cross-sectional view of the battery pack shown in FIG. 9 taken along line AA'. FIG. [Figure 11] 10 is a schematic diagram for explaining a situation in which a flame is extinguished when a fire occurs in the battery pack according to the third embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0041] Hereinafter, with reference to the accompanying drawings, a detailed description will be given of embodiments of the present invention that will enable those skilled in the art to easily carry out the present invention. However, in describing the operation principles of the preferred embodiments of the present invention in detail, if it is determined that a detailed description of related well-known functions or configurations may obscure the gist of the present invention, such detailed description will be omitted.

[0042] Furthermore, the same reference numerals are used throughout the drawings for parts that have similar functions and actions. Throughout the specification, when a part is said to be connected to another part, this includes not only a direct connection but also an indirect connection via another element between them. Furthermore, unless otherwise specified, the inclusion of a certain element does not mean the exclusion of other elements, but means that other elements may also be included.

[0043] Furthermore, unless otherwise specified, descriptions that specify elements by limiting or adding components are applicable to any invention and are not limited to descriptions of a specific invention.

[0044] Furthermore, throughout the description of the invention and the claims of this application, the singular includes the plural unless otherwise specified.

[0045] Furthermore, throughout the description of the invention and claims of this application, unless otherwise specified, "or" includes "and." Therefore, "including A or B" means any of the three cases including A, including B, or including both A and B.

[0046] Additionally, all numerical ranges include the endpoints and all intermediate values ​​therebetween unless expressly stated to exclude.

[0047] The present invention will now be described by way of detailed examples with reference to the drawings.

[0048] FIG. 1 is a perspective view of a battery pack according to a first embodiment of the present invention, and FIG. 2 is an exploded perspective view of the battery pack according to the first embodiment.

[0049] 1 and 2, the battery pack according to the present invention includes a battery module housing 210 that houses a plurality of battery cells 220, a battery pack case 100 that houses one or more battery module housings 210, and a water tank 300 that is located on one side of the battery module housing 210 and contains coolant, and at least a portion of the surface of the battery module housing 210 that faces the water tank 300 is open.

[0050] A through hole is formed on the bottom surface of the water tank 300, and a sealing member 320 is attached to prevent the coolant from leaking out through the through hole when the battery pack is in a normal state. The sealing member 320 is attached to the bottom surface of the water tank and cannot be seen from the outside of the battery pack, but is shown in Figures 1 and 2 for ease of explanation.

[0051] In one specific example, the plurality of battery cells 220 may be pouch-shaped battery cells, and the pouch-shaped battery cells may be stacked so that the electrode assembly housing portions are in close contact with each other and arranged so that the bottom of the electrode assembly housing portion is perpendicular to the ground.

[0052] The pouch-shaped battery cell may be a bidirectional battery cell in which the positive and negative electrode leads protrude in opposite directions, or a unidirectional battery cell in which the positive and negative electrode leads protrude in the same direction.

[0053] The water tank 300 is an integrated heat sink type, and a flow path 310 is formed inside the water tank 300 to guide the flow of cooling water flowing in and out, so that the temperature of the cooling water flowing in / out of the water tank 300 can be maintained at a constant level.

[0054] The water tank 300 may be formed in the shape of a rectangular parallelepiped with a lower surface facing the battery module housing 210 and an upper surface facing the opposite direction, and the areas of the upper and lower surfaces are large enough to cover the upper surfaces of all of the battery module housings 210 accommodated in the battery pack case 100.

[0055] In one specific example, the battery pack case 100 may have a box-like shape with the top removed from a rectangular parallelepiped, and the top may be open, and the water tank 300 may be combined with the battery pack case 100 in a shape that covers the open top of the battery pack case 100.

[0056] That is, the water tank 300 is disposed on the top surface of the battery module housing 210, and can function as a lid for the battery pack case with an open top.

[0057] In another specific example, the battery pack case 100 may have a structure including a case body formed in an open shape by removing the top surface from a rectangular parallelepiped, and a top plate coupled to the open top surface. In this case, the water tank may be coupled to the top plate. That is, the water tank may be attached to the inner surface of the top surface of the battery pack case.

[0058] Alternatively, the top plate may be the upper surface of the water tank, and the water tank may be integral with the top plate.

[0059] The battery module housing 210 shown in FIG. 2 is formed in the shape of a plate and is placed on each side of a battery cell stack made up of a plurality of battery cells 220 .

[0060] Additionally, metal straps 240 for fixing the plurality of battery cells 220 are attached to the upper and lower surfaces of the battery cell stack.

[0061] For example, two or more metal straps 240 may be attached to each battery cell stack, and the metal straps 240 may be attached to the upper and lower surfaces of the battery cell stack with plate-shaped battery module housings 210 attached to both sides of the battery cell stack.

[0062] The metal straps 240 attached to the upper surface of the battery cell stack may include extensions that extend downward along both sides of the battery cell stack, and the metal straps 240 attached to the lower surface of the battery cell stack may include extensions that extend upward along both sides of the battery cell stack. By using the metal straps with such extensions, the shape of the battery cell stack can be fixed.

[0063] In addition, since the battery cells 220 are exposed in the portion of the upper surface of the battery cell stack where the metal straps 240 are not attached, the cooling water in the water tank 300 can be sprayed directly onto the battery cells.

[0064] In addition to the expansion and contraction of the electrode assemblies during repeated charge and discharge, gas is also generated as a by-product of the charge and discharge process in the battery cells 220. This can cause the battery module housing to expand, but by adding a partition 110 between the battery module housings 210, the impact of the volumetric expansion of the battery module housing 210 on the adjacent battery module housings can be minimized and the battery module housings 210 can be fixed and supported.

[0065] FIG. 3 is a perspective view of a battery module housing having an opening formed on one side surface facing the water tank.

[0066] Referring to FIG. 3, the battery module housing 210 has a structure that encloses the outer surface of a battery cell stack consisting of a plurality of battery cells 220 except for both sides where electrode terminals 221 protrude, and an opening 230 is formed on one side of the battery module housing 210 that faces the water tank.

[0067] As long as cooling water can be directly injected into all the built-in battery cells through the openings 230 formed in the battery module housing 210, the shape, size, number, etc. of the openings are not particularly limited.

[0068] The battery cells shown in Figures 2 and 3 are pouch-type battery cells, and may be bidirectional battery cells in which the positive and negative leads protrude in opposite directions, or may be unidirectional battery cells in which the positive and negative leads protrude in the same direction.

[0069] FIG. 4 is a cross-sectional view of the battery pack shown in FIG. 1 taken along line A-A', and FIG. 5 is a schematic diagram for explaining how a flame is extinguished when a fire occurs in the battery pack according to the first embodiment.

[0070] 4 and 5, the plate-shaped battery module housing 210 shown in FIG. 2 is used as the battery module housing, and the metal straps are not shown in the cutaway view for ease of explanation.

[0071] A plurality of battery module housings 210 are arranged inside the battery pack case 100, and a plurality of battery cells 220 are arranged inside the battery module housings 210. A water tank 300 is arranged above the plurality of battery module housings 210, and the water tank 300 is filled with cooling water to lower the temperature of battery cells that have generated heat or caught fire.

[0072] A through-hole is formed in the surface of the water tank 300 facing the battery module housing 210, and a sealing member 320 is attached to the through-hole to seal it. The sealing member 320 is made of a material that melts when exposed to high-temperature gas or sparks emitted from the battery cells 220. That is, when the battery cells 220 are in a normal state, the sealing member 320 keeps the through-hole sealed. However, if a battery cell 220′ catches fire, the temperature of the battery cell increases, generating a flame that spreads to adjacent sealing members. This melts the sealing member 320, which has a low melting temperature, and opens the through-hole 330, allowing cooling water in the water tank 300 to be directly injected into the battery cells.

[0073] When a battery cell ignites, the cooling water stored in the water tank 300 vaporizes, its volume increases, and it becomes highly pressurized. When the through-hole 330 is opened, the cooling water can be sprayed with strong pressure toward the ignited battery cell.

[0074] At this time, the sealing member 320 that is not adjacent to the ignited battery cell 220' does not melt and can maintain its shape, so that the cooling water can be sprayed only from the through hole where the sealing member has been removed.

[0075] Considering that the cooling water is injected directly into the pouch-shaped battery cells, it is necessary to prevent the injection of the cooling water from causing a fire or explosion in the pouch-shaped battery cells. Therefore, it is preferable that the additives contained in the cooling water do not contain flammable substances. Alternatively, if a flammable substance is contained as an additive, the amount of the additive may be sufficient to prevent a secondary explosion of the pouch-shaped battery cells and also sufficient to act as an antifreeze to prevent the cooling water from freezing.

[0076] The sealing member may be made of a thermoplastic polymer resin having a melting point of about 200°C or less. For example, the thermoplastic polymer resin may be a material having a melting point of about 100°C or more and 200°C or less, such as polyethylene or polypropylene.

[0077] The sealing member 320 fills the through hole and may include an extension 325 extending from the outer surface of the water tank further outward than the periphery of the through hole. Since the extension 325 extends further from the outer surface of the water tank, it can improve the bonding strength of the sealing member 320 to the water tank under normal conditions, and in the event of a battery cell fire, it can begin to melt from the extension due to an increase in temperature, opening the through hole.

[0078] In lithium secondary batteries, thermal runaway can occur when a battery cell is defective, overcharged, or overheated. When a battery cell enters a thermal runaway state, the temperature of the battery cell can rise to approximately 260°C, the temperature at which gas venting occurs. Furthermore, the temperature of the battery cell can continue to rise even while gas venting is occurring.

[0079] When manufacturing a battery pack by housing multiple battery cells in a battery pack case, if one battery cell experiences thermal runaway, high heat and flames can be transferred to adjacent battery cells, causing the adjacent battery cells to overheat and also experience thermal runaway. Furthermore, the thermal runaway battery cell can heat other adjacent battery cells, causing a chain reaction of thermal runaway. Therefore, if a thermal runaway battery cell occurs within a battery pack case, it can lead to thermal runaway in multiple battery cells, which can spread over a wider area and cause significant damage. When multiple battery cells experience thermal runaway, temperatures can reach or exceed 1,000°C, which can continue until the battery cells are completely burned, putting users in a dangerous situation.

[0080] Therefore, it is very important to extinguish the ignited battery cell before the flame and high heat of the ignited battery cell spread to adjacent battery cells.

[0081] Therefore, the battery pack according to the present invention includes a water tank 300 containing cooling water located adjacent to the top of the battery module housing 210, and a through-hole through which the cooling water flows is sealed with a sealing member having a low melting point, and when the sealing member 320 melts due to a ignited battery cell, the through-hole 330 opens. Therefore, the cooling water contained inside the water tank 300 is directly injected into the battery cell 220 through the through-hole.

[0082] This process allows the pouch-type battery cell that has overheated or caught fire to be quickly extinguished or cooled, thereby preventing the spread of thermal runaway and allowing time for the battery cell fire to be extinguished using external water injection facilities.

[0083] Furthermore, even if the battery pack of the present invention is installed in a position close to the user, such as in an electric vehicle, a fire in the battery cell can be quickly extinguished, ensuring the safety of the user.

[0084] The through-holes 330 formed in the water tank 300 may be formed as a plurality of holes uniformly distributed on one side of the water tank, so that if any battery cell catches fire, the sealing member located adjacent to it can melt. Therefore, even if any battery cell catches fire, cooling water can be directly injected into the ignited battery cell regardless of its position. That is, the number of through-holes formed in the water tank may be designed taking into account the size and number of battery module housings, and the shape, size, and number of battery cells arranged in the battery module housings.

[0085] FIG. 6 is an exploded perspective view of a battery pack according to the second embodiment, FIG. 7 is a cross-sectional view of the battery pack shown in FIG. 6 taken along line A-A', and FIG. 8 is a schematic diagram for explaining how a flame is extinguished when a fire occurs in the battery pack according to the second embodiment.

[0086] 6 to 8, the battery pack includes a battery module housing 210 that houses a plurality of battery cells 220, a battery pack case 100 that houses one or more battery module housings 210, and a water tank 300 located on top of the battery module housing 210, and the battery module housing 210 is formed such that at least a portion of the surface facing the water tank 300 is open.

[0087] The plurality of battery cells 220 may be rectangular battery cells having an overall hexahedral structure, with an electrode assembly housed in a battery case made of a metal material, and the positive and negative terminals may protrude from the upper surface to face the water tank 300. The rectangular battery cells may be closely stacked such that the sides with the larger areas are adjacent to each other.

[0088] In addition, the water tank 300 has a through-hole formed on one side facing the battery module housings, and a sealing member 320 made of a material with a low melting point is attached to the through-hole. Therefore, when a battery cell ignites, the sealing member melts and opens the through-hole, and the cooling water stored inside the water tank can be directly injected into the battery cells 220 through the through-hole.

[0089] In addition, the description of the battery pack according to the second embodiment can be applied to the description of the battery pack according to the first embodiment, and the same reference numerals are used to designate the same components in the first and second embodiments.

[0090] FIG. 9 is an exploded perspective view of a battery pack according to the third embodiment, FIG. 10 is a cross-sectional view of the battery pack shown in FIG. 9 taken along line A-A', and FIG. 11 is a schematic diagram for explaining how a flame is extinguished when a fire occurs in the battery pack according to the third embodiment.

[0091] 9 to 11, the battery pack includes a battery module housing 210 that houses a plurality of battery cells 220, a battery pack case 100 that houses one or more battery module housings 210, and a water tank 300 located on top of the battery module housing 210, and the battery module housing 210 is formed such that at least a portion of the surface facing the water tank 300 is open.

[0092] The plurality of battery cells 220 may be cylindrical battery cells having an overall cylindrical structure in which an electrode assembly is housed in a battery case made of a metal material, and may be arranged such that the positive terminal protrudes upward to face the water tank 300.

[0093] In addition, the water tank 300 has a through-hole formed on one side facing the battery module housings, and a sealing member 320 made of a material with a low melting point is attached to the through-hole. Therefore, when a battery cell ignites, the sealing member melts and opens the through-hole, and the cooling water stored inside the water tank can be directly injected into the battery cells 220 through the through-hole.

[0094] In addition, the description of the battery pack according to the third embodiment can be applied to the description of the battery pack according to the first embodiment, and the same reference numerals are used to designate the same components in the first and third embodiments.

[0095] Those skilled in the art will be able to make various applications and modifications within the scope of the present invention based on the above content. [Explanation of symbols]

[0096] 100 Battery pack case 110 Bulkhead 210 Module Housing 220,220' battery cell 221 Electrode terminal 230 Aperture 240 Metal Strap 300 Water Tank 310 Flow path 320 Sealing material 325 Extension 330 Through hole

Claims

1. A battery module housing accommodating a plurality of battery cells stacked in a first direction perpendicular to the up-down direction; a battery pack case that houses one or more of the battery module housings; and a water tank located on the upper surface of the battery module housing and containing cooling water; Including, the battery module housing is a battery pack formed in such a manner that at least a part of a surface facing the water tank is open, The water tank is integrated with a heat sink, A flow path is formed inside the water tank to guide the flow of cooling water that flows in and out, The water tank has a through hole formed in one surface facing the battery module housing, and a sealing member is attached to the through hole. the sealing member is made of a material that melts when exposed to high-temperature gas or sparks emitted from the battery cell; The through-hole is opened by melting the sealing member, and cooling water stored inside the water tank is poured into the battery cell through the through-hole. The through-hole is formed as a plurality of holes distributed on one surface of the water tank.

2. 2. The battery pack according to claim 1, wherein the water tank is formed to a size that covers the entire upper surface of the battery module housing.

3. 3. The battery pack according to claim 1, wherein the water tank is attached to an inner surface of an upper surface of the battery pack case.

4. The battery pack case has an open top, The battery pack according to claim 1 or 2, wherein the water tank is coupled to the battery pack case in a manner that covers an open upper surface of the battery pack case.

5. 5. The battery pack according to claim 1, wherein the battery module housing is formed of a pair of plates that sandwich both side surfaces of a battery cell stack formed of the plurality of battery cells in a direction perpendicular to both the up-down direction and the first direction.

6. The battery pack according to claim 5 , wherein metal straps are attached to the upper and lower surfaces of the battery cell stack, respectively, for fixing the plurality of battery cells.

7. the battery module housing has a structure that encloses the outer surface of a battery cell stack formed by the plurality of battery cells except on both sides where electrode terminals protrude, 7. The battery pack according to claim 1, wherein an opening is formed in one surface of the battery module housing facing the water tank.

8. The battery pack according to any one of claims 1 to 7, wherein the through-holes are formed as a plurality of holes uniformly distributed on one surface of the water tank.

9. 9. The battery pack according to claim 1, wherein a partition wall is added between the battery module housings.

10. The battery pack according to any one of claims 1 to 8, wherein the sealing member fills the through hole and includes an extension portion that extends further outward from the outer surface of the water tank beyond the periphery of the through hole.

11. The battery pack according to any one of claims 1 to 10, wherein the battery cells are pouch-shaped battery cells, prismatic battery cells, or cylindrical battery cells.

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