Pack Case

Abstract

The disclosed pack case includes a lower housing that forms an accommodating space, a lower reinforcing plate that is mounted within the accommodating space of the lower housing and supports at least one or more cell assemblies, and an upper housing that is coupled to the lower housing to seal the accommodating space, wherein the mechanical strength of the lower housing is less than the mechanical strength of the lower reinforcing plate.

Description

[Technical Field]

[0001] The present invention relates to a pack case in which the lower housing of the pack case can expand when thermal runaway occurs, thereby effectively suppressing a sudden increase in internal pressure even in a pack mounting structure in which the upper space is extremely limited due to the vehicle chassis.

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0125115, filed September 19, 2023, and Korean Patent Application No. 10-2024-0125621, filed September 13, 2024, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference. [Background technology]

[0003] Unlike primary batteries, secondary batteries are rechargeable and have the potential to be small and have large capacities, and as such, they have been the subject of much research and development in recent years. Demand for secondary batteries as an energy source is rapidly increasing due to the increasing technological development and demand for mobile devices, as well as the growing importance of electric vehicles and energy storage systems to meet the current environmental protection needs.

[0004] Secondary batteries are classified into coin-type batteries, cylindrical batteries, prismatic batteries, and pouch-type batteries depending on the shape of the battery case. The electrode assembly installed inside the battery case of a secondary battery is a power generating element that can be charged and discharged and has a laminated structure of electrodes and a separator.

[0005] Since secondary batteries are required to be used continuously for a long period of time, it is necessary to effectively control the heat generated during the charging and discharging process.If secondary batteries are not cooled smoothly, a positive feedback chain reaction will occur in which an increase in temperature causes an increase in current, and an increase in current causes another increase in temperature, ultimately leading to a fatal condition known as thermal runaway.

[0006] Furthermore, when secondary batteries are assembled in the form of a cell assembly such as a module or pack, thermal runaway in one secondary battery can cause other surrounding secondary batteries to continuously overheat, resulting in a thermal propagation phenomenon. That is, when thermal runaway occurs in a cell assembly in a battery pack, a large amount of conductive dust, gas, and flames are emitted from the high-voltage terminal of the cell assembly, causing dust to accumulate on the high-voltage terminals of other adjacent cell assemblies, and the heat transfer caused by the gas and flames triggers a thermal propagation phenomenon.

[0007] When a heat propagation phenomenon occurs in a battery pack, the pressure and temperature inside the battery pack rise rapidly. To withstand this sudden rise in pressure and temperature, the battery pack must maintain its structural robustness for a considerable period of time. If the battery pack experiences structural collapse and external air flows inside, the combustion reaction becomes rapidly active, posing a major risk to the outside of the pack, such as fire or explosion.

[0008] The lid that seals the top of the pack case of a battery pack is typically made of a metal plate that is relatively thin compared to the other surfaces of the pack case. This is because the lid expands in response to a sudden increase in internal pressure during an event such as thermal propagation, thereby mitigating the pressure increase. While the pressure increase is delayed by the expansion of the lid, a venting device attached to the pack case operates, thereby achieving normal pressure relief. In other words, the lid, which expands due to internal pressure, ensures the initial response time required for the venting device to operate stably.

[0009] However, when a battery pack is mounted on an electric vehicle chassis, it is common for only very limited clearance space to be provided by various vehicle structures disposed above the battery pack. In this case, the expansion of the lid during heat propagation is spatially restricted, and as a result, the internal pressure of the pack case is not properly increased, which can accelerate the heat propagation phenomenon or cause the pack case to collapse prematurely, resulting in serious safety issues such as fire or explosion. Therefore, it is necessary to provide a method for properly alleviating the internal pressure increase of the pack case early, even when the clearance space above the battery pack is narrow. Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide a pack case that can effectively suppress a sudden increase in internal pressure due to the occurrence of thermal runaway.

[0011] However, the technical problems that the present invention aims to solve are not limited to the above-mentioned problems, and other problems not mentioned can be clearly understood by those skilled in the art from the description of the invention described below. [Means for solving the problem]

[0012] The present invention relates to a pack case, which in one example includes a lower housing that forms a storage space, a lower reinforcing plate that is mounted within the storage space of the lower housing and supports at least one or more cell assemblies, and an upper housing that is coupled to the lower housing to seal the storage space, wherein the mechanical strength of the lower housing is less than the mechanical strength of the lower reinforcing plate.

[0013] The lower strengthening plate may include a sidewall in contact with the lower housing and a bottom plate having at least one ventilation hole formed therein.

[0014] The pressure in the sealed receiving space can act on the lower housing through the ventilation holes of the lower strengthening plate.

[0015] In one embodiment, the side wall of the lower reinforcing plate may be joined to the lower housing.

[0016] The lower strengthening plate may form a gap with the lower housing at least in a portion around the ventilation hole of the bottom plate.

[0017] The ventilation hole may include a corner hole formed by cutting a corner of the lower reinforcement plate.

[0018] In addition, the ventilation hole may further include an inner hole formed by partially cutting the inside of the lower reinforcing plate.

[0019] Here, a plurality of the cell assemblies may be provided, and the inner hole may be formed between adjacent cell assemblies.

[0020] According to the pack case of the present invention, when thermal runaway occurs in the cell assembly and the internal pressure rises, the rising pressure acts on the lower housing, causing the lower housing to expand and alleviate the pressure rise.

[0021] Meanwhile, in some embodiments of the present invention, a foamable fireproof paint may be applied between the lower housing and the lower reinforcing plate.

[0022] The foamable fireproof paint expands in volume due to the high-temperature gas flowing through the ventilation holes, and can form a heat insulating layer that fills the space in the lower housing that expands due to an increase in internal pressure.

[0023] In one embodiment, the lower reinforcement plate may include a bottom plate having a flat shape without side walls and having at least one ventilation hole formed therein, and an edge of the bottom plate may be joined or coupled to the lower housing.

[0024] The bottom surface of the lower housing may include an annular edge portion and a stepped bottom surface extending in a shape that protrudes outward from the edge portion, and the edge of the lower strengthening plate may be joined or coupled to the edge portion.

[0025] In one embodiment, the cell assembly has a lower venting structure, and the lower reinforcement plate includes a bottom plate having at least one ventilation hole formed therein, and the ventilation holes may be aligned to face a venting device provided in the cell assembly.

[0026] In one embodiment, the lower housing may have a thinner bottom surface than the side surfaces.

[0027] The lower housing may have an annular side surface and a flat bottom surface which are manufactured separately and then joined together.

[0028] The lower housing having a two-piece structure may have a bottom surface that is thinner than the side surfaces.

[0029] The side and bottom surfaces of the lower housing may be made of different materials. [Effects of the Invention]

[0030] As described above, the pack case of the present invention has a dual structure consisting of a lower strengthening plate that supports the cell assembly and a lower housing that is less rigid than the lower strengthening plate. As a result, when thermal runaway occurs in the pack case and the internal pressure rises suddenly, the pressure acts on the lower housing through the vent holes in the lower strengthening plate, allowing the lower housing to expand.

[0031] The increased internal pressure due to the volumetric increase caused by the expansion of the lower housing is alleviated, and the venting device operates while the sudden increase in pressure is delayed, allowing for stable depressurization. In this way, the pack case of the present invention can prevent structural collapse by appropriately alleviating the pressure increase at the early stage of thermal runaway. In particular, because the pack case of the present invention has a structure in which the lower housing expands, it may be suitable for installation in electric vehicles, where extremely limited space is provided on the upper side of the pack case due to various structures.

[0032] However, the technical effects that can be obtained by the present invention are not limited to the effects described above, and other effects not mentioned can be clearly understood by those skilled in the art from the description of the invention described below.

[0033] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the detailed description of the invention described below, serve to further understand the technical concept of the present invention, and therefore the present invention should not be interpreted as being limited solely to the matters depicted in such drawings. [Brief explanation of the drawings]

[0034] [Figure 1] 1 is a perspective view of a pack case according to an embodiment of the present invention. [Figure 2] FIG. 2 is an exploded perspective view of the pack case of FIG. 1. [Figure 3] FIG. 2 is a plan view of the pack case with the upper housing removed. [Figure 4] FIG. 2 is a cross-sectional view taken along line "AA" in FIG. [Figure 5] 5 is a diagram showing another embodiment of FIG. 4. [Figure 6] 10 is a view showing the lower housing when thermal runaway occurs. [Figure 7] FIG. 10 is a cross-sectional view according to another embodiment of the present invention. [Figure 8] 8 is a view showing a lower housing when thermal runaway occurs in the pack case of FIG. 7. [Figure 9] 1 is a view showing an embodiment of a pack case including a flat lower strengthening plate; [Figure 10] 10 is a view showing an embodiment of a pack case in which the bottom surface of the lower housing has a two-stage structure. [Figure 11] 1 is a diagram showing one embodiment of a pack case suitable for housing a cell assembly having a bottom venting structure. [Figure 12] 10 is a view showing an embodiment of a pack case having a structure in which the thickness of the bottom surface is thinner than that of the side surfaces of the lower housing; [Figure 13] 1 is a view showing an embodiment of a pack case in which the lower housing has a two-piece structure; DETAILED DESCRIPTION OF THE INVENTION

[0035] Because the present invention can be modified in various ways and can have various embodiments, specific embodiments will be described in detail below.

[0036] However, this is not intended to limit the invention to any particular embodiment, but rather it can be understood to include all modifications, equivalents, or alternatives falling within the spirit and scope of the invention.

[0037] In the present invention, terms such as "comprise" and "have" are intended to specify the presence of features, numbers, steps, operations, components, parts or combinations thereof described in the specification, and can be understood as not precluding the presence or possibility of addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0038] Furthermore, in the present invention, when a layer, film, region, plate, or other portion is described as being "on" another portion, this includes not only the case where it is "directly on" the other portion, but also the case where there is another portion between them. Conversely, when a layer, film, region, plate, or other portion is described as being "under" the other portion, this includes not only the case where it is "directly under" the other portion, but also the case where there is another portion between them. Furthermore, in the present application, being disposed "on" can include not only the case where it is disposed at the top, but also the case where it is disposed at the bottom.

[0039] The present invention relates to a pack case, which in one example includes a lower housing that forms a storage space, a lower reinforcing plate that is mounted within the storage space of the lower housing and supports at least one or more cell assemblies, and an upper housing that is coupled to the lower housing to seal the storage space, wherein the mechanical strength of the lower housing is less than the mechanical strength of the lower reinforcing plate.

[0040] The pressure in the sealed receiving space can act on the lower housing through the ventilation holes of the lower strengthening plate.

[0041] As described above, the pack case of the present invention has a dual structure consisting of a lower strengthening plate that supports the cell assembly and a lower housing that is less rigid than the lower strengthening plate. As a result, when thermal runaway occurs in the pack case and the internal pressure rises suddenly, the pressure acts on the lower housing through the vent holes in the lower strengthening plate, allowing the lower housing to expand.

[0042] The increased internal pressure due to the expansion of the lower housing is alleviated, and the venting device operates while the sudden increase in pressure is delayed, allowing for stable depressurization. Furthermore, by appropriately alleviating the pressure increase in the early stages, the pack case structure can be prevented from collapsing. In particular, since the pack case of the present invention has an expanding lower housing, it may be suitable for application to electric vehicles, which have very limited upper space due to various structures arranged on the upper side of the pack case.

[0043] Hereinafter, specific embodiments of the pack case 10 according to the present invention will be described in detail with reference to the accompanying drawings. For reference, the directions of front, back, up, down, left, and right used in the following description to specify relative positions are intended to aid in understanding the invention, and unless otherwise specified, are based on the directions shown in the drawings.

[0044] (First embodiment) Fig. 1 is a perspective view of a pack case 10 according to one embodiment of the present invention, and Fig. 2 is an exploded perspective view of the pack case 10 of Fig. 1. Referring to the drawings, the pack case 10 according to one embodiment of the present invention may include a lower housing 100, a lower reinforcing plate 200, and an upper housing 300.

[0045] The lower housing 100 and the upper housing 300 are interconnected to form at least one sealed storage space. In particular, the lower housing 100 can form a storage space large enough to accommodate at least the lower reinforcing plate 200 and a plurality of cell assemblies 500. In the illustrated embodiment, the lower housing 100 and the upper housing 300 are each shown as half-joined to form one storage space. However, this is an exemplary embodiment, and the upper housing 300 can also be configured in the form of a flat lid, in which case the lower housing 100 can form most of the storage space of the pack case 10.

[0046] Here, the cell assembly 500 refers to an assembly in which multiple secondary batteries are structurally grouped together. Here, the term "grouping multiple secondary batteries together" does not necessarily mean that the batteries are separated from one another by a structure such as a case, but rather that the cell assemblies 500 have structural independence that allows them to be distinguished from one another. Therefore, the cell assembly 500 may also be referred to as a battery module, a battery block, or the like depending on the specific embodiment, but has a more comprehensive meaning than these. In addition, in the accompanying drawings, the cell assembly 500 and the battery cells 510 are depicted as simple rectangular shapes for the sake of convenience in explanation and illustration, but this is merely an example. Therefore, the pack case 10 according to the embodiment of the present invention should not be interpreted as being limited to a specific form factor, such as a coin-type battery, a cylindrical battery, a prismatic battery, or a pouch-type battery.

[0047] The lower reinforcing plate 200 is a structure that supports at least one cell assembly 500. The lower reinforcing plate 200 is mounted within the receiving space of the lower housing 100. For example, the lower reinforcing plate 200 may include side walls 210 that contact the lower housing 100 and a bottom plate 220 that supports the cell assembly 500. To stably install the lower reinforcing plate 200, the side walls 210 of the lower reinforcing plate 200 may be bonded to the lower housing 100. However, the bottom plate 220 of the lower reinforcing plate 200 is not bonded to the lower housing 100. That is, the bottom plate 220 of the lower reinforcing plate 200 and the inner surface of the lower housing 100 are separated from each other.

[0048] The mechanical strength of the lower housing 100 is less than that of the lower reinforcing plate 200. For example, the thickness of the lower housing 100 may be thinner than that of the lower reinforcing plate 200. Alternatively, the material of the lower housing 100 may be softer than that of the lower reinforcing plate 200. Alternatively, the lower housing 100 may be thinner and softer in both thickness and material. As a result, when the same force is applied, the lower housing 100 deforms more and earlier than the lower reinforcing plate 200. Therefore, in this specification, the phrase "the mechanical strength of the lower housing 100 is less than that of the lower reinforcing plate 200" should be broadly interpreted to mean that the lower housing 100 expands more easily than the lower reinforcing plate 200 when the internal pressure of the pack case 10 increases.

[0049] 2 and 3, at least one ventilation hole 230 is formed in the bottom plate 220 of the lower strengthening plate 200. The ventilation hole 230 serves as a passageway that interconnects the two storage spaces divided by the lower strengthening plate 200. For example, if thermal runaway occurs in one of the cell assemblies 500 supported on the lower strengthening plate 200 and the internal pressure increases, the increasing pressure also acts on the lower housing 100 through the ventilation hole 230.

[0050] The ventilation holes 230 should be configured so that even if thermal runaway occurs in a battery cell 510 of a cell assembly 500 mounted in the pack case 10, or in a cell assembly 500 when multiple cell assemblies 500 are mounted, the resulting pressure increase and high-temperature gas can be quickly transferred to the lower housing 100. For this reason, multiple ventilation holes 230 may be provided.

[0051] An exemplary arrangement of the plurality of ventilation holes 230 is shown in FIG. 3. The plurality of ventilation holes 230 may include corner holes 232 formed by cutting out the corners of the lower reinforcing plate 200. The corner holes 232 may be formed in multiple numbers, one at each of the four corners of the lower reinforcing plate 200, in consideration of a symmetrical arrangement. The corner holes 232 are formed at the corners of the lower reinforcing plate 200 because cutting out the corners of the lower reinforcing plate 200 may have little effect on the structural rigidity required to stably support the cell assembly 500.

[0052] 3, the plurality of ventilation holes 230 may include inner holes 234 formed by partially cutting out the interior of the lower strengthening plate 200. This is because, if the corner holes 232 are located at the corners of the lower strengthening plate 200, a time delay may occur in the flow of high-temperature gas toward the lower housing 100 in the event of thermal runaway occurring in the central region. In this case, the rigidity of the lower strengthening plate 200 needs to be designed to be sufficient to support the cell assemblies 500, taking into consideration the inner holes 234. For example, when a plurality of cell assemblies 500 are mounted, the plurality of inner holes 234 may be uniformly formed in a symmetrical shape passing between adjacent cell assemblies 500.

[0053] Fig. 4 is a cross-sectional view taken along line "AA" in Fig. 1. According to Fig. 4, the side wall 210 of the lower reinforcing plate 200 is joined to the lower housing 100, and the bottom plate 220 of the lower reinforcing plate 200 is spaced apart from the lower housing 100.

[0054] 6 is a view showing the lower housing 100 when thermal runaway occurs. When thermal runaway occurs in the cell assembly 500 mounted in the pack case 10, high-temperature gas is generated and the internal pressure rises, the rising pressure can act on the bottom surface of the lower housing 100 through the corner holes 232 of the lower strengthening plate 200. As described above, the mechanical strength of the lower housing 100 is weaker than that of the lower strengthening plate 200. Therefore, as shown in FIG. 6, the lower housing 100, which has weak rigidity, expands due to the pressure, and as the volume increases due to the expansion of the lower housing 100, the rise in pressure inside the pack case 10 can be alleviated.

[0055] While a sudden pressure rise is delayed due to an increase in volume caused by the expansion of the lower housing 100, a venting device (not shown) operates to steadily release pressure, and the pressure rise is appropriately alleviated at the initial stage of thermal runaway, preventing structural collapse of the pack case 10. In particular, since the pack case 10 according to the embodiment of the present invention has a structure in which the lower housing 100 expands, it is suitable for use in cases where there is little space on the upper side of the pack case 10 due to various structures, as exemplarily shown in Fig. 6. For example, the pack case 10 according to the embodiment of the present invention is suitable for use as a case for a battery pack mounted under the chassis of an electric vehicle, i.e., a battery pack mounted so that the upper housing 300 faces the chassis of the electric vehicle and the lower housing 100 faces the ground.

[0056] Meanwhile, FIG. 5 is a view illustrating another embodiment of the lower reinforcing plate 200 compared to FIG. 4. In the embodiment of FIG. 5, the sidewall 210 of the lower reinforcing plate 200 is bonded to the lower housing 100, and the bottom plate 220 of the lower reinforcing plate 200 is in contact with the lower housing 100. Because the bottom plate 220 of the lower reinforcing plate 200 is in contact with and supported by the lower housing 100, problems such as damage, deformation, or noise generation in the lower housing 100, which has low rigidity, are reduced. However, because the bottom plate 220 of the lower reinforcing plate 200 and the lower housing 100 are in close contact with each other, pressure may not be applied smoothly through the ventilation holes 230. To solve this problem, as shown in the enlarged partial view of FIG. 5, at least a portion of the periphery of the ventilation holes 230 in the bottom plate 220 may be configured to form a gap 236 with the lower housing 100. This gap 236 allows internal pressure to be smoothly applied to the lower housing 100. The configuration of the gap 236 formed around the ventilation hole 230 is one exemplary embodiment, and if the bottom plate 220 of the lower reinforcement plate 200 and the lower housing 100 are not joined together, the gap 236 structure may not be necessary.

[0057] (Second embodiment) As described above, in the pack case 10 according to an embodiment of the present invention, when thermal runaway occurs in the installed cell assembly 500 and the internal pressure rises, the rising pressure acts on the lower housing 100 through the ventilation holes 230, and the lower housing 100, which is subjected to the pressure, expands and widens the internal space, thereby alleviating the pressure rise.

[0058] The lower housing 100, which is designed to have relatively low rigidity, is generally thin, particularly the bottom of the lower housing 100. The thinner the thickness, the easier it is to expand in response to an increase in internal pressure. However, when thermal runaway occurs, not only does the internal pressure of the pack case increase, but the high-temperature gas also generates considerable heat. The high-temperature gas also flows into the bottom side of the lower housing 100 through the ventilation holes 230 of the lower strengthening plate 200. When the bottom of the lower housing 100 expands due to pressure, more high-temperature gas gathers in the expanded space, causing the bottom of the lower housing 100 to become hot. As a result, the lower housing 100 of the pack case 10 can act as a heat source for an external fire.

[0059] The second embodiment of the present invention further includes a configuration for effectively suppressing high temperatures from acting on the outside through the lower housing 100 when the bottom surface of the lower housing 100 expands due to thermal runaway. Figure 7 shows a cross-sectional structure of a lower strengthening plate 200 and the lower housing 100 according to the second embodiment of the present invention.

[0060] Referring to FIG. 7, an intumescent fire-resistant paint 400 is applied between the lower housing 100 and the lower reinforcing plate 200. The intumescent fire-resistant paint 400 has the property of foaming when exposed to heat and can form a dry coating layer under normal conditions. When the dry coating layer of the intumescent fire-resistant paint 400 foams due to heat, the dry coating layer can be transformed into an insulating layer (e.g., a carbonized layer) that expands to several tens of times its original volume. The expanded insulating layer can retard heat transfer for a certain period of time.

[0061] Figure 8 is a view showing the lower housing 100 when thermal runaway occurs in the pack case 10 of Figure 7. If an intumescent fire-resistant paint 400 is applied between the lower housing 100 and the lower reinforcing plate 200, the lower housing 100 expands due to pressure when thermal runaway occurs, and the intumescent fire-resistant paint 400 is exposed to high-temperature gas flowing in through the ventilation holes 230. As a result, the intumescent fire-resistant paint 400 expands to several tens of times its volume due to heat, thereby forming a heat insulating layer 410 that fills the space in the lower housing 100 that expands due to an increase in internal pressure.

[0062] The intumescent heat insulating layer 410 created by the intumescent fire-resistant coating 400 does not prevent pressure from acting on the lower housing 100. Instead, it creates a heat insulating effect against high-temperature gases that gather inside the expanding lower housing 100, thereby preventing the pack case 10 from acting as a heat source that could start an external fire in its surroundings.

[0063] (Third embodiment) 9 shows a pack case 10 according to another embodiment of the present invention. In the embodiment of FIG. 9, the lower reinforcing plate 200 is made of a bottom plate 220 without a side wall 210. In other words, the lower reinforcing plate 200 is flat and includes the above-described ventilation holes 230, except for the absence of the side wall 210. That is, a plurality of ventilation holes 230 may be provided, and may include corner holes 232 and / or inner holes 234.

[0064] The flat lower reinforcing plate 200 has its edge joined to the lower housing 100. For example, a plurality of welding points 240 may be formed along the edge of the lower reinforcing plate 200 by spot welding. The remaining portions of the lower reinforcing plate 200, excluding the welding points 240, are in close contact with the lower housing 100 but are not joined to each other. Therefore, as shown in FIG. 6, if thermal runaway occurs in the cell assembly 500 mounted in the pack case 10, high-temperature gas is generated and the internal pressure increases, the lower housing 100 may expand due to the increasing pressure.

[0065] Here, the edges of the lower reinforcing plate 200 are described as being joined to the lower housing 100 by spot welding, but they may be joined by continuous welding instead of spot welding, or may be interconnected by other fastening mechanisms such as bolts or rivets.

[0066] 10 shows another embodiment of a pack case 10 to which a flat lower reinforcing plate 200 is applied. In the embodiment of FIG. 10, the bottom surface 110 of the lower housing 100 has a two-step structure including an annular edge 112 and a stepped bottom surface 114 that extends outward from the edge 112. In the lower housing 100 having such a two-step structure, the annular edge 112 is the area where the edge of the flat lower reinforcing plate 200 joins or connects, and the stepped bottom surface 114 corresponds to the area of ​​the bottom surface 110 of the lower housing 100 that expands due to an increase in internal pressure. The stepped bottom surface 114 has a structure that forms a gap with the bottom plate 220 of the lower reinforcing plate 200, and this gap allows pressure to smoothly act through the ventilation holes 230.

[0067] (Fourth embodiment) FIG. 11 is a diagram showing one embodiment of a pack case 10 suitable for accommodating a cell assembly 500 having a bottom venting structure. Here, the cell assembly 500 having a bottom venting structure may refer to a cell assembly 500 in which a venting device 512, for example, a rupture disk, provided on one or more battery cells 510 constituting the cell assembly 500 is disposed on the bottom facing the lower housing 100. Alternatively, the cell assembly 500 may refer to a venting structure in which the venting device 512 provided on the battery cell 510 is disposed on another surface, for example, the top surface, rather than the bottom, but the venting device provided on the cell assembly 500 is disposed on the bottom facing the lower housing 100, thereby ultimately discharging high-pressure gas toward the lower housing 100. FIG. 11 shows the venting device 512 of the battery cell 510 disposed on the bottom, which should be understood as one exemplary embodiment. The cell assembly 500 itself may also be provided with a venting device in accordance with the definition of a bottom venting structure described above.

[0068] 11 , the inner holes 234, which are located on the inside of the ventilation holes 230 of the lower strengthening plate 200, are aligned to face the venting device 512 of the battery cell 510 included in the cell assembly 500. Therefore, when the venting device 512 of the battery cell 510 is activated to release high-pressure gas, at least a portion of the gas pressure can act directly on the bottom surface 110 of the lower housing 100. The immediate and direct pressure action causes the bottom surface 110 of the lower housing 100 to expand and deform in a shorter time period, thereby inducing pressure relief from the initial stage of pressure buildup inside the pack case 10.

[0069] The arrangement of the ventilation holes 230 of the lower strengthening plate 200 in consideration of the lower venting structure as shown in FIG. 11 can be widely applied to the first to third embodiments described above.

[0070] (Fifth embodiment) 12 and 13 are views showing other embodiments of the lower housing 100. Specifically, Fig. 12 relates to an embodiment in which the side surface 120 and the bottom surface 110 of the lower housing 100 have different thicknesses, and Fig. 13 relates to an embodiment in which the side surface 120 and the bottom surface 110 of the lower housing 100 have a two-piece structure in which they are separate pieces.

[0071] 12, the bottom surface 110 of the lower housing 100 may be thinner than the side surfaces 120. By making the bottom surface 110 of the lower housing 100 thinner, it becomes easy to relatively reduce the mechanical strength of only the bottom surface while maintaining good mechanical strength of the entire lower housing 100. For example, by press processing using a mold, the lower housing 100 may be manufactured in a one-piece structure in which the bottom surface 110 is thinner than the side surfaces 120.

[0072] 13, an embodiment is also possible in which the side surface 120 and the bottom surface 110 are manufactured from separate parts and then joined together to complete the lower housing 100. In such a two-piece structure, the lower housing 100 includes an annular side surface 120 and a flat bottom surface 110, and the lower housing 100 is formed by joining the edge portions of the annular side surface 120 and the bottom surface 110 together.

[0073] 13 requires an additional process of joining the annular side surface 120 and the flat bottom surface 110, but has the advantage of increasing the design flexibility of the lower housing 100. For example, in order to reduce the mechanical strength of the bottom surface 110 compared to the side surface 120, it is easy to create a structure in which the bottom surface 110 is thinner than the side surface 120 of the lower housing 100 of FIG. 12. Alternatively, the bottom surface 110 and the side surface 120 of the lower housing 100 may be made of different materials. Alternatively, to ensure light weight and rigidity, the side surface 120 may be made of an extrusion molded product having a hollow portion reinforced with ribs, and the bottom surface 110 may be made of a regular metal plate.

[0074] The lower housing 100 having a two-piece structure shown in Fig. 13 must be hermetically bonded when the side surface 120 and the bottom surface 110 are joined together. This is because the entire pack case 10 must be kept airtight. The hermetic bond between the side surface 120 and the bottom surface 110 of the lower housing 100 can be achieved by welding. For example, the side surface 120 and the bottom surface 110 can be joined together by continuous welding. Alternatively, it may be possible to combine a structural bond such as bolts or rivets with an airtight bond such as brazing welding.

[0075] The present invention has been described in more detail above with reference to the drawings and embodiments, etc. However, the configurations shown in the drawings or embodiments in this specification are merely one embodiment of the present invention and do not represent all of the technical ideas of the present invention, and therefore, at the time of filing this application, there may be various equivalents and modifications that can replace them. [Explanation of symbols]

[0076] 10: Pack case 100: Lower housing 110: Bottom 112: Edge 114: Bottom of step 120: Side 200: Lower reinforcement plate 210: Side wall 220: Bottom plate 230: Ventilation hole 232: Corner Hole 234: Inner hole 236: Gap 240: Welding point 300: Upper housing 400: Foaming fireproof paint 410: Heat insulating layer (foam heat insulating layer) 500: Cell assembly 510: Battery cell 512: Venting equipment

Claims

1. a lower housing that forms an accommodation space; a lower reinforcement plate mounted in the receiving space of the lower housing and supporting at least one cell assembly; an upper housing coupled to the lower housing to seal the receiving space; Including, The pack case, wherein the mechanical strength of the lower housing is lower than the mechanical strength of the lower reinforcing plate.

2. The lower strengthening plate is The pack case according to claim 1 , comprising a side wall in contact with the lower housing and a bottom plate having at least one ventilation hole formed therein.

3. The pack case according to claim 2 , wherein the pressure in the sealed storage space acts on the lower housing through the ventilation hole in the lower strengthening plate.

4. The lower strengthening plate is The pack case according to claim 2 or 3, wherein the side wall is joined to the lower housing.

5. The lower strengthening plate is The pack case according to claim 4 , wherein at least a portion of the periphery of the ventilation hole of the bottom plate forms a gap with the lower housing.

6. The ventilation hole is The pack case according to claim 2 or 3, further comprising a corner hole formed by cutting a corner of the lower reinforcing plate.

7. The ventilation hole is The pack case according to claim 6 , further comprising an inner hole formed by partially cutting the inside of the lower strengthening plate.

8. A plurality of the cell assemblies are provided, The pack case according to claim 7 , wherein the inner hole is formed between adjacent cell assemblies.

9. When thermal runaway occurs in the cell assembly and the internal pressure rises, Increasing pressure acts on the lower housing; The pack case according to claim 3 , wherein the lower housing expands to relieve pressure buildup.

10. The pack case according to claim 9 , wherein a foamable fire-resistant paint is applied between the lower housing and the lower reinforcing plate.

11. The intumescent fire-resistant coating material is The pack case according to claim 10, wherein the pack case expands in volume due to high-temperature gas flowing in through the ventilation holes, forming a heat insulating layer that fills the space in the lower housing that expands due to an increase in internal pressure.

12. The lower strengthening plate is It has a flat plate shape with no side walls, The pack case according to claim 1 or 2, comprising a bottom plate in which the at least one ventilation hole is formed, and an edge of the bottom plate is joined or coupled to the lower housing.

13. The bottom surface of the lower housing includes an annular edge portion and a stepped bottom surface that extends outward from the edge portion, The pack case according to claim 12 , wherein an edge of the lower reinforcing plate is joined or bonded to the edge.

14. the cell assembly has a bottom venting structure; the lower strengthening plate includes a bottom plate in which the at least one ventilation hole is formed, The pack case according to claim 1 or 2, wherein the ventilation holes are aligned and opposed to venting devices provided in the cell assemblies.

15. The lower housing includes:

3. The pack case according to claim 1, wherein the thickness of the bottom surface is thinner than that of the side surfaces.

16. The lower housing includes:

3. The pack case according to claim 1, wherein the annular side surface and the flat bottom surface are manufactured separately and then joined together.

17. The lower housing includes: The pack case according to claim 16, wherein the bottom surface is thinner than the side surfaces.

18. The lower housing includes: The pack case according to claim 16, wherein the side surface and the bottom surface are made of different materials.

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