Secondary battery

Abstract

A secondary battery according to one embodiment of the present invention includes an electrode assembly and a pouch case in which the electrode assembly is housed. The pouch case includes a first case portion having a first housing portion in which a portion of the electrode assembly is housed, and a second case portion having a second housing portion in which the remaining portion of the electrode assembly is housed. The first case portion and the second case portion are in contact with each other at edges surrounding the first and second housing portions and are sealed by a band-shaped sealing portion formed on at least a portion of the edge. The sealing portion includes a first sealing portion having a first width and a second sealing portion having a second width smaller than the first width. A longitudinal center of the second sealing portion coincides with a center of a long side of the electrode assembly.

Description

[Technical field]

[0001] Cross-reference to related applications This application claims the benefit of priority based on Korean Patent Application No. 10-2020-0148820 filed on November 9, 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 secondary battery, and more specifically, to a pouch-type secondary battery having improved safety. [Background technology]

[0003] As technological development and demand for mobile devices increases, the demand for secondary batteries as an energy source is rapidly increasing. As a result, much research is being conducted on secondary batteries that can meet various demands.

[0004] Secondary batteries have attracted much attention not only for use in mobile devices such as mobile phones, digital cameras, and notebook computers, but also as energy sources for power plants such as electric bicycles, electric cars, and hybrid electric cars.

[0005] Small devices such as mobile phones and cameras use small battery packs containing a single battery cell, while medium- to large-sized devices such as laptops and electric cars use medium- to large-sized battery packs containing two or more battery cells connected in parallel and / or series.

[0006] There is a high demand for prismatic and pouch-type secondary batteries, which are thin in shape and can be used in products such as mobile phones. Prismatic lithium secondary batteries are advantageous in protecting the electrode assembly from external impact and have an easy liquid injection process, but their shape is fixed and it is difficult to reduce their volume. On the other hand, pouch-type lithium secondary batteries have the advantages of being suitable for manufacturing thin cells without restrictions on shape and size, being easy to assemble by heat fusion, and being highly safe as it is easy to discharge gas or liquid when abnormal behavior occurs.

[0007] However, in such pouch-type secondary batteries, electrolyte decomposition may occur due to factors such as overcharging, exposure to high temperatures, and internal short circuits, which may result in the generation of a large amount of gas. In this case, the generation of gas within the battery case may cause a swelling phenomenon in which the battery case bulges.

[0008] Such swelling may induce high pressure inside the sealed battery case, further accelerating decomposition of the electrolyte and ultimately causing the explosion of the battery cell. In addition, the gas may cause the center of the battery case to swell, causing deformation of the battery cell, which may result in an electrical short circuit.

[0009] Therefore, in order to solve these problems, when the swelling phenomenon occurs, it is necessary to efficiently exhaust the gas generated inside the battery case to the outside to ensure safety. Summary of the Invention [Problem to be solved by the invention]

[0010] The embodiment is directed to providing a pouch-type secondary battery that can safely discharge gas in a desired direction to prevent explosion even if a large amount of gas is generated inside the battery.

[0011] However, the problems to be solved by the embodiments of the present invention are not limited to the above problems, and can be variously expanded within the scope of the technical ideas included in the present invention. [Means for solving the problem]

[0012] According to an embodiment of the present invention, there is provided a secondary battery comprising: an electrode assembly; and a pouch case in which the electrode assembly is housed; the pouch case comprises a first case portion having a first storage portion in which a portion of the electrode assembly is housed; and a second case portion having a second storage portion in which a remaining portion of the electrode assembly is housed. The first case portion and the second case portion are in contact with each other at edges surrounding the first and second storage portions and are sealed by a sealing portion formed in a band shape on at least a portion of the edges. The sealing portion comprises a first sealing portion having a first width and a second sealing portion having a second width smaller than the first width. A longitudinal center of the second sealing portion coincides with a center of a long side of the electrode assembly.

[0013] The sealing portion may further include a first inclined portion that connects the first sealing portion and the second sealing portion and has a shape inclined from the outside of the pouch case toward the electrode assembly, and a second inclined portion that connects the first sealing portion and the second sealing portion and has a shape inclined from the electrode assembly toward the outside of the pouch case.

[0014] The first inclined portion may have a length greater than a length of the second inclined portion.

[0015] The second width may be less than or equal to 1 / 4 of the first width.

[0016] The width of the edge is maintained constant at a portion where the first sealing portion is located and at a portion where the second sealing portion is located.

[0017] The first case part and the second case part each include a base material layer, a metal layer, and a sealing layer, and the sealing part may be a region where the sealing layer of the first case part and the sealing layer of the second case part are heat-sealed to each other to form an integral unit.

[0018] The sealing layer may comprise a thermoplastic resin.

[0019] The electrode assembly may include a pair of long sides facing each other, and the second sealing portion may be disposed corresponding to only one of the pair of long sides.

[0020] The electrode assembly may include a pair of long sides facing each other, and the second sealing portions may be disposed corresponding to both long sides of the pair of long sides.

[0021] The second sealing portion acts as a vent for gas generated when thermal runaway occurs inside the pouch case.

[0022] A battery module according to another embodiment of the present invention may include the above-described secondary battery. Effect of the Invention

[0023] According to the embodiment, in a pouch-type secondary battery, even if a large amount of gas is generated inside, the gas can be safely guided to be discharged in an intended direction to prevent explosion, thereby providing a secondary battery with improved safety. [Brief description of the drawings]

[0024] [Figure 1] 1 is an exploded perspective view showing a secondary battery according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a diagram showing the secondary battery of FIG. 1 in an assembled state. [Diagram 3] FIG. 3 is an enlarged cross-sectional view showing a portion A in FIG. 2. [Figure 4]3 is a diagram showing a schematic front view of the secondary battery shown in FIG. 2. FIG. [Diagram 5] FIG. 3 is a cross-sectional view taken along the line BB' in FIG. [Figure 6] 1 is a graph showing the results of a high-temperature storage experiment performed on secondary batteries according to an embodiment of the present invention and a comparative example. [Figure 7] FIG. 13 is a schematic front view of a secondary battery according to another embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention may, however, be embodied in various different forms and is not limited to the embodiments set forth herein.

[0026] In order to clearly explain the present invention, parts that are not necessary for the explanation will be omitted, and the same reference numerals will be used throughout the specification to refer to the same or similar components.

[0027] In addition, the size and thickness of each component shown in the drawings are arbitrarily shown for convenience of explanation, and the present invention is not necessarily limited to those shown in the drawings. In the drawings, thicknesses are enlarged to clearly express various layers and regions. In the drawings, thicknesses of some layers and regions are exaggerated for convenience of explanation.

[0028] In addition, when a part such as a layer, film, region, or plate is said to be "on" or "above" another part, this includes not only the case where it is directly on top of the other part, but also the case where there is another part in between. Conversely, when a part is said to be "directly on" another part, it means that there is no other part in between. In addition, being "on" or "above" a reference part means being located above or below the reference part, and does not necessarily mean being located "on" or "above" the direction against gravity.

[0029] Additionally, throughout the specification, when a part is said to "comprise" a certain element, this means that it may further include other elements, but not excluding other elements, unless specifically stated to the contrary.

[0030] Also, throughout the specification, a reference to "in a plane" means a view of the part as viewed from above, and a reference to "in cross section" means a view of the part as viewed from the side through a vertical cut.

[0031] FIG. 1 is an exploded perspective view showing a secondary battery according to one embodiment of the present invention, FIG. 2 is a view showing the secondary battery of FIG. 1 in an assembled state, FIG. 3 is an enlarged cross-sectional view of part A of FIG. 2, FIG. 4 is a schematic view showing the secondary battery of FIG. 2 as viewed from the front, and FIG. 5 is a cross-sectional view taken along line B-B' of FIG. 2.

[0032] 1 and 2, a secondary battery 10 according to an embodiment of the present invention includes a pouch case 100 and an electrode assembly 200. The pouch case 100 includes a first case part 110 and a second case part 120. In FIG. 1, the first case part 110 and the second case part 120 are illustrated as being connected to each other and integrally formed, but the first case part 110 and the second case part 120 may be separated from each other. The shape of the pouch case 100 is not limited to that illustrated in FIG. 1, and any shape is possible as long as it can accommodate and seal the electrode assembly 200.

[0033] The electrode assembly 200 may be configured in such a way that a positive electrode plate and a negative electrode plate are disposed with a separator between them. In this case, the electrode assembly 200 may have a structure in which one positive electrode plate and one negative electrode plate are wound with a separator between them, or a structure in which a number of positive electrode plates and a number of negative electrode plates are stacked with a separator between them. The positive electrode plate and the negative electrode plate may each be formed as a structure in which an active material slurry is applied to an electrode current collector, and the slurry is usually formed by stirring an active material, a conductive material, a binder, a plasticizer, etc., in a state where a solvent is added.

[0034] In the electrode assembly 200, there may be uncoated areas where the slurry is not applied to the electrode plates, and electrode tabs corresponding to the respective electrode plates may be formed in the uncoated areas. Specifically, as shown in Fig. 1, a positive electrode tab 310 may be attached to the positive electrode plate of the electrode assembly 200, and a negative electrode tab 410 may be attached to the negative electrode plate of the electrode assembly 200. The positive electrode tab 310 and the negative electrode tab 410 are electrically connected to a positive electrode lead 320 and a negative electrode lead 420 to form electrode terminals 300, 400. At this time, the positive electrode lead 320 and the negative electrode lead 420 may be drawn out to the outside of the pouch case 100, as shown in Fig. 2.

[0035] The first case part 110 and the second case part 120 in FIG. 1 respectively include a first storage part 110s and a second storage part 120s having a recessed shape, and the electrode assembly 200 and the electrolyte are stored in the first storage part 110s and the second storage part 120s.

[0036] The secondary battery 10 of FIG. 2 exemplarily illustrates a pouch-type secondary battery in which the first case part 110 and the second case part 120 shown in FIG. 1 are bonded to each other and sealed.

[0037] 3 is an enlarged view of part A in FIG. 2, and FIG. 4 is a front view of the secondary battery 10 in FIG. 2. Referring to FIG. 3, the first case part 110 and the second case part 120 constituting the pouch case 100 according to an embodiment of the present invention include a sealing part 140 formed on an edge part 130 of the pouch case 100 surrounding the first receiving part 110s and the second receiving part 120s in which the electrode assembly 200 in FIG. 1 is received. The sealing part 140 is formed in a band shape on at least a part of the edge part 130 along the edge of the pouch case 100, thereby joining the first case part 110 and the second case part 120. The first case part 110 and the second case part 120 are heat-sealed to form the sealing part 140, thereby sealing the pouch case 100.

[0038] Fig. 5 is a cross-sectional view taken along line B-B' of Fig. 2. As shown in Fig. 5, the first case part 110 includes a first base layer 113, a first metal layer 112, and a first sealing layer 111, which are stacked in order from the outside, and the second case part 120 includes a second base layer 123, a second metal layer 122, and a second sealing layer 121, which are stacked in order from the outside.

[0039] The first base layer 113 and the second base layer 123 may be made of an insulating material such as polyethylene terephthalate (PET) resin or nylon resin to ensure insulation between the secondary battery and the outside and formability. The first metal layer 112 and the second metal layer 122 may include one selected from the group consisting of copper, aluminum, nickel, iron, carbon, chromium, manganese, and alloys thereof. The first sealing layer 111 and the second sealing layer 121 may include a thermoplastic resin such as polypropylene (PP).

[0040] The first case part 110 and the second case part 120 are attached together such that the first sealing layer 111 and the second sealing layer 121 are in contact with each other at the edge part 130. In this state, the first sealing layer 111 and the second sealing layer 121 are bonded together by applying pressure and heat sealing using a heated mold or the like corresponding to the sealing part 140, thereby forming the sealing layer 140 and sealing the pouch case 100.

[0041] In this case, the sealing portion 140 may include a first sealing portion 141 having a first width W1 and a second sealing portion 142 having a second width W2 smaller than the first width W1. Also, the second sealing portion 142 may be formed such that a center of its length h2 coincides with a center of the length h1 of the long side of the electrode assembly 200 accommodated in the first housing portion 110s and the second housing portion 120s. That is, in FIG. 3, the center of the long side of the electrode assembly 200 and the center of the length of the second sealing portion 142 are all located on the center line C.

[0042] The second sealing part 142 acts as a vent for gas generated when the temperature rises inside the pouch case 100. That is, when exposed to high temperature conditions, the separator inside the electrode assembly 200 shrinks, and the electrolyte vaporizes, causing the battery to expand or the electrodes to deform, resulting in a short circuit between the positive and negative electrodes. In particular, when the electrodes and the current collectors come into contact with each other, a thermal runaway state occurs in which heat generation exceeds heat release, causing the battery to ignite. However, in this case, even if a short circuit occurs between the positive and negative electrodes, if the electrolyte inside the battery is completely discharged, the movement of ions and electrons inside the battery is restricted, preventing ignition. That is, safety can be improved by inducing the electrolyte to evaporate and be discharged at a faster time than in conventional batteries.

[0043] In this embodiment, the other sealing part, i.e., the second sealing part 142 having a smaller width than the first sealing part 141, acts as a vent part to rapidly vent the vaporized electrolyte, thereby preventing fire and explosion and improving safety. That is, when a battery expands, the part where deformation and expansion occur most frequently is the center part C in the longitudinal direction of the electrode assembly 200, and the second sealing part 142 is disposed corresponding to this, so that venting through the second sealing part 142 can be induced more quickly.

[0044] At this time, the second sealing part 142 may be disposed so as to be offset from the width direction center of the first sealing part 141 toward the electrode assembly 200. That is, as shown in Fig. 3, the sealing part 140 includes a first inclined part 143 that connects the first sealing part 141 and the second sealing part 142 and has a shape inclined from the outside of the pouch case 100 toward the electrode assembly 200, and also includes a second inclined part 144 that connects the first sealing part 141 and the second sealing part 142 and has a shape inclined from the electrode assembly 200 toward the outside of the pouch case 100. At this time, the length of the first inclined part 143 may be formed longer than the length of the second inclined part 144.

[0045] With this structure, the second sealing portion 142 is disposed relatively close to the inside, so that even if the width W2 is small, a sufficient sealing effect can be obtained. Also, by including the second inclined portion 144 on the inside, the gas generated inside can be more easily guided to that portion, i.e., the side of the second inclined portion 144 having a recessed shape, so that the damage of the second sealing portion 142 and the discharge of the gas can be more rapidly induced.

[0046] The second width W2 of the second sealing portion 142 may have a value of 1 / 4 or less of the first width W1 of the first sealing portion 141, but is not particularly limited thereto. If the width is too small, the sealing performance may be reduced, so the width may be preferably 1 / 8 or more and 1 / 4 or less.

[0047] Also, as described above, the second sealing part 142 is not obtained by deforming the edge part 130, such as by cutting or trimming it, but by deforming only the pressurized shape of the relevant part during the sealing process by heat sealing, i.e., by reducing the width of the mold. Therefore, the width of the edge part 130 is the same for the first sealing part 141 and the second sealing part 142, and the second sealing part 142 can be easily obtained by simply deforming the width to be heat sealed, i.e., the width of the sealing part 140.

[0048] An experiment was carried out by exposing the secondary battery 10 according to the embodiment of the present invention and a secondary battery of a comparative example to high temperatures, and the results are shown in FIG.

[0049] FIG. 6 is a graph showing the results of a high-temperature storage experiment on secondary batteries according to the embodiment of the present invention and a comparative example.

[0050] In the secondary battery 10 according to the embodiment, the second sealing part 142 is formed as shown in FIGS. 2 to 4, but in the secondary battery according to the comparative example, such a second sealing part 142 is not formed, and all sealing parts have a uniform width.

[0051] When the battery was left at a temperature of 140° C., it was confirmed that an explosion occurred after about 30 minutes in the comparative example, as shown in FIG 6. In contrast, no explosion occurred after 80 minutes in the secondary battery 10 of the embodiment, which confirmed that safety was improved by the rapid discharge of electrolyte even when exposed to high temperatures.

[0052] FIG. 7 is a schematic front view of a secondary battery according to another embodiment of the present invention.

[0053] In the secondary battery 11 according to the second embodiment of the present invention, only the number of second sealing parts 142 is different, and the remaining configuration is the same as that of the secondary battery 10 according to the first embodiment, so a description of the overlapping configuration will be omitted.

[0054] 7, in a secondary battery 11 according to another embodiment, second sealing parts 142 are positioned corresponding to both long sides of a pair of opposing long sides of an electrode assembly 200. In this case, even if gas is suddenly generated inside the secondary battery 11, gas venting occurs simultaneously on both sides, so that the electrolyte can be discharged more quickly. Therefore, explosion at high temperatures can be prevented, and safety can be improved.

[0055] Meanwhile, a plurality of pouch-type secondary batteries according to the present invention may be assembled to form a battery module, and one or more of such battery modules may be packaged in a pack case to form a battery pack.

[0056] The battery module and the battery pack including the battery module may be applied to various devices, such as vehicles including electric bicycles, electric cars, and hybrid cars, but the present invention is not limited thereto and may be applied to various devices that can use the battery module and the battery pack including the battery module, which also fall within the scope of the present invention.

[0057] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also belong to the scope of the present invention. [Explanation of symbols]

[0058] 100: Pouch case 200: Electrode assembly 130: Edge 140: Sealing part 141: First sealing part 142: Second sealing part

Claims

1. electrode assembly; The electrode assembly is accommodated in a pouch case. the pouch case includes a first case portion having a first storage portion in which a portion of the electrode assembly is housed, and a second case portion having a second storage portion in which a remaining portion of the electrode assembly is housed, The first case portion and the second case portion are in contact with each other at edges surrounding the first storage portion and the second storage portion, and are sealed by a sealing portion formed in a band shape on at least a part of the edges, the sealing portion includes a first sealing portion having a first width and a second sealing portion having a second width smaller than the first width, a center of the second sealing portion in a longitudinal direction coincides with a center of a long side of the electrode assembly; the second sealing portion is disposed to be offset toward the electrode assembly from a width direction center of the first sealing portion, a width of the edge portion is maintained constant at a portion where the first sealing portion is located and a portion where the second sealing portion is located; the sealing portion further includes a first inclined portion that connects the first sealing portion and the second sealing portion and is inclined from an outside of the pouch case toward the electrode assembly, and a second inclined portion that connects the first sealing portion and the second sealing portion and is inclined from the electrode assembly toward the outside of the pouch case, The second sealing portion acts as a vent for gas generated when thermal runaway occurs inside the pouch case.

2. The secondary battery according to claim 1 , wherein the first inclined portion has a length greater than a length of the second inclined portion.

3. The secondary battery according to claim 1 , wherein the second width is equal to or smaller than ¼ of the first width.

4. each of the first case portion and the second case portion includes a base layer, a metal layer, and a sealing layer; The secondary battery according to claim 1 , wherein the sealing portion is a region in which a sealing layer of the first case portion and a sealing layer of the second case portion are integrally formed by heat-sealing each other.

5. The secondary battery according to claim 4 , wherein the sealing layer comprises a thermoplastic resin.

6. The electrode assembly includes a pair of long sides facing each other, The secondary battery according to claim 1 , wherein the second sealing portion is located corresponding to only one of the pair of long sides.

7. The electrode assembly includes a pair of long sides facing each other, The secondary battery according to claim 1 , wherein the second sealing portion is located in correspondence with both long sides of the pair of long sides.

8. A battery module comprising the secondary battery according to claim 1 .

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