Battery cell

Abstract

The battery cell comprises: an electrode assembly, wherein the electrode assembly comprises a positive electrode, a negative electrode and a diaphragm; and an outer material accommodating the electrode assembly therein, in which the outer material includes: a first portion forming an accommodating space in which the electrode assembly is accommodated; a second portion integrally formed with the first portion; and a groove portion formed by recessing at least a portion of the second portion and having a resolidification layer on an exterior of the second portion, and wherein the second portion includes a plurality of crystal grains, the plurality of crystal grains of the second portion including an equiaxial microstructure.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the priority of Korean Patent Application No. 10-2023-0120405 filed on September 11, 2023, and Korean Patent Application No. 10-2023-0155172 filed on November 10, 2023, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference in their entirety. Technical Field

[0002] The present application generally relates to a battery cell. Specifically, the present application relates to a battery cell, wherein different regions of an exterior material have different tensile strengths. Background Art

[0003] Secondary batteries are used to convert electrical energy into chemical energy and store energy so that it can be reused many times by charging and discharging. Secondary batteries are widely used in various industrial fields due to their economical and environmentally friendly characteristics. Specifically, among secondary batteries, lithium secondary batteries are widely used in the entire industrial field, including portable devices that require high-density energy.

[0004] The working principle of lithium secondary batteries is electrochemical redox reaction. In other words, the principle is to generate electricity through the movement of lithium ions and charge in the reverse process. In the case of lithium secondary batteries, the phenomenon that lithium ions in the negative electrode (anode) escape from the negative electrode and move to the positive electrode (cathode) through the electrolyte and the separator is called discharge. In addition, the opposite process of this phenomenon is called charging.

[0005] As the charging and discharging processes of the secondary battery are repeated, a swelling phenomenon may occur in which the internal pressure increases and a large amount of heat is generated. Since this swelling phenomenon may cause explosion or fire, a method of controlling the internal pressure of the secondary battery is required. Summary of the invention

[0006] The problem that the present application aims to solve is to provide a battery cell in which the internal pressure is controlled to improve stability.

[0007] In addition, another problem that the present application aims to solve is to provide a method for manufacturing a battery cell, in which a notch portion is integrally manufactured with an external material to improve production efficiency.

[0008] The battery of the present application can be widely used in the field of green technology, such as electric vehicles using batteries, battery charging stations, solar power generation and wind power generation. In addition, the battery cell of the present application can be used in environmentally friendly electric vehicles, hybrid vehicles, etc. to prevent climate change by suppressing air pollution and greenhouse gas emissions.

[0009] According to one embodiment of the present application, a battery cell may include: an electrode assembly, the electrode assembly including a positive electrode, a negative electrode and a separator; and an external material, the external material accommodating the electrode assembly therein, wherein the external material includes: a first part, the first part forming a accommodating space for accommodating the electrode assembly; a second part, the second part is formed integrally with the first part; and a groove part, the groove part is formed by recessing at least a portion of the second part and having a re-solidification layer on the outside of the second part, and wherein the second part includes a plurality of crystal grains, and the plurality of crystal grains of the second part include an equiaxed microstructure.

[0010] The first portion may include a plurality of grains, and the plurality of grains of the first portion may be formed in an anisotropic structure.

[0011] The groove portion may be formed by recessing an outer surface of the outer material toward the inside of the battery cell, and may have a groove shape.

[0012] The groove portion may further include a bottom portion forming a bottom surface, and a furrow provided inside the outer material at a deeper level than the bottom portion.

[0013] A ten-point average roughness of a surface of the groove portion may be higher than a ten-point average roughness of a peripheral portion.

[0014] The ten-point average roughness of the surface of the groove portion may exceed 20.

[0015] At least one of the plurality of dies may be partially cut.

[0016] The second portion may include an overlapping portion and a covering portion, wherein the overlapping portion overlaps the groove portion along a recess direction of the groove portion; the covering portion is located outside the groove portion along a width direction of the groove portion, and the covering portion is formed perpendicular to the recess direction of the groove portion.

[0017] A standard deviation of sizes of the plurality of grains included in the overlapping portion may be 20 or less.

[0018] A standard deviation of sizes of the plurality of grains included in the covering portion may be 20 or less.

[0019] An absolute difference between an average value of sizes of the plurality of grains included in the overlapped portion and an average value of sizes of the plurality of grains included in the covered portion may be 3% or less.

[0020] The external material may also include: a body portion and a cap portion, the body portion accommodating the electrode assembly and having a first portion and a second portion; the cap portion including a cell tab electrically connecting the electrode assembly to the outside and covering the body portion, wherein the groove portion may be provided in the body portion.

[0021] The outer material may further include a venting portion formed by recessing at least one of an inner surface of the outer material and an outer surface disposed in an opposite direction of the inner surface, wherein the recessed portion and the venting portion may be disposed to overlap along a recessed direction, the at least one surface being recessed in the recessed direction.

[0022] The shape of the groove portion may be deformed based on the internal pressure of the external material.

[0023] When the internal pressure of the external material increases, the groove portion may be opened.

[0024] The groove portion may be integrally formed with the outer material.

[0025] The resolidified layer may include vacancy defects.

[0026] The number of vacancy defects in the resolidified layer may be equal to or greater than the number of vacancy defects in the second portion.

[0027] The number of vacancy defects in the second portion may be equal to or greater than the number of vacancy defects in the first portion.

[0028] The thickness of the resolidified layer in the direction from the inside to the outside of the exterior material may be 5 μm or more.

[0029] The first portion may include a plurality of grains, and the plurality of grains of the first portion may be formed in an anisotropic structure.

[0030] The problem that the present application aims to solve is to provide a battery cell in which the internal pressure is controlled to exhibit improved stability.

[0031] Furthermore, another problem that the present application aims to solve is to provide a battery cell manufacturing method in which a groove portion is integrally manufactured with an external material to exhibit improved production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 and Figure 2 A battery cell according to one embodiment of the present application is shown.

[0033] Figure 3 A method for manufacturing an exterior material according to one embodiment of the present application is shown.

[0034] Figure 4 and Figure 5 Heating of the outer material is shown.

[0035] Figure 6 The machining of the groove portion in the outer material is shown.

[0036] Figure 7 and Figure 8 An enlarged view of the groove portion of the present application is shown.

[0037] Fig. 9 An enlarged view of the first portion of the present application is shown.

[0038] Figures 10 to 12 Various embodiments of battery cells are shown.

[0039] Figures 13A to 13C Various embodiments of the groove portion of the present application are shown. DETAILED DESCRIPTION

[0040] Hereinafter, the present application will be described in detail with reference to the accompanying drawings. This is merely illustrative, and the present application is not limited to the specific embodiments described herein.

[0041] Specific terms used in this specification are for convenience of explanation only and are not intended to limit the illustrated embodiments.

[0042] For example, expressions such as “the same” and “are the same” indicate not only a strictly identical state but also a state in which there is a difference in tolerance or degree of obtaining the same function.

[0043] For example, expressions indicating a relative or absolute arrangement such as "in a certain direction", "along a certain direction", "side by side", "vertically", "at the center", "concentric", or "coaxial" not only strictly indicate the arrangement but also indicate a state of relative displacement with a tolerance, or an angle or distance to obtain the same function.

[0044] Various embodiments of the present application will be described below based on a spatial orthogonal coordinate system orthogonal to each other, namely, the X, Y, and Z axes. The directions of the axes (X, Y, and Z) refer to two directions in which the axes extend.

[0045] The X direction, Y direction, and Z direction mentioned below are for the purpose of explanation so that the present application can be clearly understood. Depending on where a reference is placed, directions may be defined differently.

[0046] The terms "first, second and third" used before the components mentioned below are only to avoid confusion about the components they refer to, and have nothing to do with the order, importance or master-slave relationship between the components, etc. For example, the invention including only the second component but not the first component can also be implemented.

[0047] As used in this specification, a singular expression includes a plural expression unless the context clearly dictates otherwise.

[0048] Figure 1 and Figure 2 A battery cell 10 according to one embodiment of the present application is shown; Figure 3 A method for manufacturing an exterior material according to one embodiment of the present application is shown.

[0049] The battery cell 10 described in this specification refers to a secondary battery that can be repeatedly used by charging and discharging. For example, the battery cell may be a lithium secondary battery cell, but is not limited thereto.

[0050] The battery cell 10 may include various shapes. For example, the battery cell 10 may be classified into a pouch-type secondary battery, a prismatic secondary battery, or a cylindrical secondary battery according to its shape. Figure 1 , the battery cell 10 according to one embodiment of the present application may include a prismatic secondary battery. However, the embodiment of the present application is not limited thereto.

[0051] The battery cell 10 of the present application may include: an electrode assembly 150 and an external material 12, the electrode assembly 150 includes a positive electrode, a negative electrode and a separator; the external material 12 accommodates the electrode assembly 150 therein, wherein the external material 12 may include: a first part 19, the first part 19 forms a receiving space in which the electrode assembly 150 is received; a second part 20, the second part 20 may be formed integrally with the first part 19, wherein a preset region of the first part 19 may be heated and cooled; and a groove part 30, the groove part 30 is formed by recessing at least a portion of the second part 20 and having a resolidified layer 25 on the outside, and wherein the second part 20 may include a plurality of grains, and the plurality of grains of the second part may be formed into an equiaxed microstructure.

[0052] The battery cell 10 may include an electrode assembly 150. Figure 2 , the electrode assembly 150 may include a positive electrode 151, a negative electrode 153, and a separator 152. The electrode assembly 150 may be classified into a stacking type, a winding type, a stack-folding type, and a Z-stacking type according to a method of stacking the positive electrode 151, the negative electrode 153, and the separator 152.

[0053] The type of the electrode assembly 150 included in the battery cell 10 of the present application is not limited. In other words, the electrode assembly 150 included in the battery cell of the present application may be an electrode assembly 150 manufactured by any one of stacking type, winding type, stacking folding type and Z stacking type.

[0054] The positive electrode 151 and the negative electrode 153 may include a current collector. The positive electrode 151 may include a positive electrode 151 current collector, and the negative electrode 153 may include a negative electrode 153 current collector. The current collector may include a known conductive material, which does not cause a chemical reaction in the lithium secondary battery to a certain extent. For example, the current collector may include any one of stainless steel, nickel (Ni), aluminum (Al), titanium (Ti), copper (Cu) and their alloys, and may be provided in various forms such as a film, a sheet and a foil.

[0055] The positive electrode 151 and the negative electrode 153 may include active materials. The positive electrode 151 may include a positive active material, and the negative electrode 153 may include a negative active material. The positive active material may be a material in which lithium ions can be inserted and extracted, and the negative active material may be a material in which lithium ions can be adsorbed and extracted. For example, the positive active material may be a lithium metal oxide, and the negative active material may be a carbon-based material such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers, a lithium alloy, any one of silicon (Si) and tin (Sn).

[0056] In addition, the positive electrode 151 and the negative electrode 153 may further include a binder and a conductive material to improve mechanical stability and conductivity, respectively.

[0057] The separator 152 may be configured to prevent an electrical short circuit between the positive electrode 151 and the negative electrode 153 and allow ions to flow through its structure. The separator 152 may be disposed between the positive electrode 151 and the negative electrode 153, the separator physically separating the positive electrode 151 and the negative electrode 153 but allowing ions to flow. The type of the separator is not particularly limited, but may include a porous polymer film. For example, the separator may include a porous polymer film or a porous nonwoven fabric.

[0058] The electrolyte may include an electrolyte. The electrolyte may be a non-aqueous electrolyte. The electrolyte may include a lithium salt and an organic solvent. The electrolyte may also include an additive. The additive may form a film on the positive electrode or the negative electrode through a chemical reaction inside the battery. For example, a cathode interface film may be formed on the positive electrode, and a cathode interface film may be formed on the negative electrode.

[0059] In one embodiment, the outer material 12 can be manufactured using extrusion. Figure 3 , one area of ​​the exterior material body 130 may be extruded to form an empty space in the inner area. Then, the exterior material body 130 may be cut at preset intervals to manufacture a plurality of exterior materials 12.

[0060] In another embodiment, the exterior material 12 may be manufactured by a press process. As long as the exterior material 12 can protect the battery cell from external impact, the method of manufacturing the exterior material is not particularly limited.

[0061] The exterior material 12 may include a body portion 13 accommodating the electrode assembly 150 and a cover portion 14 covering the body portion 13. The cover portion 14 may include a cell tab 11 electrically connecting the electrode assembly 150 to the outside.

[0062] Refer again Figure 2, the main body portion 13 may include an opening portion 15. The main body portion 13 may be open on both sides. The main body portion 13 may be open on each of two opposite sides.

[0063] Meanwhile, the body portion 13 may include a first portion 19 and a second portion 20. The first portion 19 may form a receiving space in which the electrode assembly may be received. The first portion 19 may be formed in a hexahedral shape having openings on two opposite sides. However, the first portion 19 is not limited to the hexahedral shape, and may include various shapes forming a receiving space for receiving the electrode assembly.

[0064] The second portion 20 may be formed integrally with the first portion 19. The second portion 20 may be a portion where a preset area of ​​the first portion 19 is heated and cooled. The second portion 20 may be an area where a groove portion is formed. For example, the second portion may be formed on the outer surface of the first portion 19. Therefore, the outer surface of the first portion 19 may be heated and cooled to form the second portion 20.

[0065] Reference Figure 2 , both sides of the main body part 13 may be open in the Y-direction. The electrode assembly 150 and the electrolyte may be accommodated inside the external material 12 through the opening part 15. For example, the opening part 15 may be set to a hexahedral shape so that both sides may be opened in the Y-direction. The cover part 14 may cover the two open sides of the main body part 13. The main body part 13 and the cover part 14 may be combined to close the accommodation space of the external material 12.

[0066] The cover parts 14a, 14b may cover the body part 13. In other words, the cover parts 14a, 14b may respectively cover both opening sides of the body part 13 to protect components accommodated inside the body part 13. The body part 13 and the cover parts 14a, 14b may be coupled or sealed to each other.

[0067] The battery cell 10 may further include a battery cell tab 11 protruding to the outside of the external material 12 for electrical connection to the outside. The battery cell tab 11 may be disposed in the cover portion 14. The battery cell 10 may include a plurality of cover portions 14a, 14b and a plurality of battery cell tabs 11a, 11b. The battery cell tabs 11a, 11b may be disposed in each of the plurality of cover portions 14a, 14b.

[0068] The cell tabs 11 may be respectively connected to the positive electrode and the negative electrode of the cell 10. The cell tabs 11 may include a positive electrode tab 11a connected to the positive electrode and a negative electrode tab 11b connected to the negative electrode.

[0069] Refer again Figure 1 and Figure 2, the battery cell 10 of the present application may include a groove portion 30 disposed on the surface of the external material 12. The groove portion 30 may be disposed on the outer surface of the external material 12. The groove portion 30 may be provided in the form of a groove from the outer surface to the inner surface. In other words, the groove portion 30 may be recessed from the outer surface to the inner surface to form a groove.

[0070] The battery cell 10 of the present application can adjust the internal pressure by the groove portion 30. The battery cell 10 can be used multiple times by repeatedly charging and discharging. The internal pressure of the battery cell 10 may increase due to the gas generated in the process. When the gas is continuously left and not discharged, the battery cell 10 may explode. Therefore, in order to safely use the battery cell 10, it is necessary to properly adjust the pressure of the battery cell 10.

[0071] The groove portion 30 may be provided on the side of the exterior material 12 so that the gas may be discharged through the groove portion 30. In other words, the shape of the groove portion 30 may be changed based on the internal pressure of the exterior material 12.

[0072] When the internal pressure of the external material 12 increases and reaches the fracture pressure, the groove portion 30 may be opened. In other words, when the internal pressure of the external material 12 is lower than the fracture pressure, the shape of the groove portion 30 will be maintained. When the internal pressure of the external material 12 increases to above the fracture pressure through continuous use of the battery cell, the shape of the groove portion 30 may change. Specifically, the groove portion 30 may be opened, and the gas formed inside the battery cell may be discharged to the outside, which may cause the internal pressure to drop.

[0073] The groove portion 30 may be provided in a plural number. In this way, the pressure of the battery cell 10 may be rapidly reduced. The groove portion 30 may be provided in the body portion 13 .

[0074] The groove portion 30 may be integrally formed with the exterior material 12. For example, the groove portion 30 may be integrally formed with the body portion 13. In other words, the groove portion 30 may be formed in a predetermined region of the body portion 13 by laser processing, rather than being separately manufactured and then joined to the body portion 13.

[0075] The groove portion 30 may be provided in the body portion so that the gas inside the exterior material may be effectively discharged to the outside.

[0076] Figure 4 and Figure 5 Shows heating of external material; Figure 6 A recessed portion 30 is shown formed in the outer material.

[0077] The second portion 20 of the outer material can be heated by the laser LA1. Figure 4 , the outer surface of the bidirectional battery cell 10 in which both sides of the main body portion 13 are open can be heated by the laser LA1.

[0078] In another embodiment, referring to Figure 5 The outer surface of the one-way battery cell 10 with one side opened can be heated by laser. One side of the outer material can be easily heated by laser.

[0079] As the laser, a fiber laser or a diode laser can be used.

[0080] As a fiber laser, a laser having a wavelength in the range of 780 nm to 2200 nm can be used. The fiber laser has a high peak power, thereby allowing cutting or processing of a base material. In addition, the fiber laser has a small beam size, thereby having a high energy density and allowing energy to be densely transmitted to a narrow area.

[0081] As a diode laser, a laser having a wavelength in the range of 810 nm to 1064 nm can be used. A diode laser has a lower peak power than a fiber laser, but it can transmit energy while minimizing damage to the substrate. This allows heating of the substrate. In addition, a diode laser has a larger beam size than a fiber laser, allowing energy to be transmitted uniformly over a wider area.

[0082] The groove portion 30 may be formed by recessing at least a portion of the second portion 20. Figures 4 to 6 , the second portion 20 may be formed by a laser. At least a portion of the second portion 20 may be recessed to form the groove portion 30. For example, the groove portion 30 may be formed by irradiating laser to the second portion 20. The laser that heats the external material and the laser that forms the groove portion 30 may have different wavelengths.

[0083] For example, the first laser LA1 may heat the external material, and the second laser LA2 having a different wavelength from the first laser LA1 may form the groove portion 30 .

[0084] In one embodiment, the pulse width of the second laser LA2 may be different from the pulse width of the first laser LA1. The pulse width of the second laser LA2 may be shorter than the pulse width of the first laser LA1. Since the shorter the pulse width, the shorter the peak power, the thermal effect of the second laser LA2 on the external material can be minimized, thereby forming a groove and preventing damage to the external material. For example, thermal damage to the external material can be prevented.

[0085] Figure 7 and Figure 8 is an enlarged view of the groove portion 30 of the present application; Fig. 9 An enlarged view of a first portion 19 of the present application is shown.

[0086] Reference Figure 7 , the groove portion 30 may be formed by being recessed from the outer surface of the outer material 12. At least a portion of the groove portion 30 may be formed to extend from the inner surface in one direction. Thus, both sides of the groove portion 30 may be spaced apart so that the gas inside can be easily discharged. The recessed depth of the groove portion 30 may be more than 60% of the thickness of the outer material 12. In other words, referring to Figure 7 , a thickness L1 of the exterior material 12 in which the groove portion 30 is formed may be 40% or less of a thickness L2 of the exterior material 12 in which the groove portion 30 is not formed.

[0087] Specifically, Figure 8 An image of a cross section of the external material 12 obtained by an electron backscatter diffraction (EBSD) method is briefly shown. The electron backscatter diffraction method can install an electron backscatter diffractometer on a scanning electron microscope, inject accelerated electrons into a sample, and detect the electrons to analyze the orientation of the material. Thus, the crystal structure of the external material 12 can be analyzed.

[0088] The second portion 20 may include metal precipitates. The metal precipitates may be formed by solidification inside the outer material 12. In one embodiment, for example, the metal precipitates may include manganese (Mn) and silicon (Si).

[0089] Reference Figure 7 The second portion 20 may include an overlapping portion 21 and a covering portion 22 , wherein the overlapping portion 21 overlaps the groove portion 30 along the recessed direction of the groove portion 30 ; and the covering portion 22 is located outside the groove portion 30 along the width direction of the groove portion 30 .

[0090] In one embodiment, the covering portion 22 may have a thickness equal to the width of the groove portion 30 from both sides of the overlapping portion 21 along the width direction of the groove portion 30. Figure 8 , wherein the concave direction of the groove portion 30 may be referred to as the Z-direction, and the width direction of the groove portion 30 may be referred to as the X-direction. The covering portion 22 may refer to an area extending from both sides of the overlapping portion 21 along the width direction of the groove portion 30 by a length of the width of the groove portion 30.

[0091] As described above, the overlap portion 21 can be heated by a laser. After heating, the overlap portion 21 can include a resolidified layer 25, which is formed when a region of the overlap portion 21 solidifies. The resolidified layer 25 can solidify and discolor after a portion of the outer material 12 is heated. In one embodiment, the solidified region can be distinguished from other regions by color. The resolidified layer 25 can be formed on the outside of the groove portion.

[0092] In one embodiment, the thickness of the resolidified layer 25 in the direction from the inside to the outside of the exterior material 12 may be 5 μm (micrometer) or more. In one embodiment, the thickness of the resolidified layer 25 may be 3 μm or more. The stability of the exterior material 12 may be improved by having the above thickness range.

[0093] More specifically, when a pulse laser having a pulse width of 1 ns (nanosecond) or more is used for the exterior material, the resolidified layer 25 can be formed by melting and resolidifying the exterior material 12. When a pulse laser having a pulse width of less than 1 ns is used, the resolidified layer 25 may not be formed.

[0094] The resolidified layer 25 may include vacancy defects. Specifically, the crystal structure of the resolidified layer 25 may include vacancy defects. A vacancy defect is a point defect within a crystal structure and may be formed depending on external conditions such as heat and pressure. A vacancy defect may occur when atoms escape from a lattice region and leave a hole or vacancy in the lattice.

[0095] Finally, the battery cell of the present application may have a resolidified layer 25 formed by heating and cooling certain regions, and the resolidified layer 25 may include vacancy defects.

[0096] In one embodiment, the outer material 12 may include vacancy defects. In other words, the first portion 19 may also include vacancy defects. At this time, regarding the number of vacancy defects, the number of vacancy defects in the resolidified layer 25 may be equal to or greater than the number of vacancy defects in the first portion 19.

[0097] The number of vacancy defects can be measured by the number of vacancy defects generated per unit volume of material. This may increase exponentially with increasing temperature and can be calculated by the following equation 1.

[0098] Formula 1 N v =Nexp(-Q v / kT)

[0099] Here, N v is the number of vacancy defects; N is the total number of potential defect sites, Q v is the activation energy; T is the temperature in Kelvin; k is the Boltzmann's constant.

[0100] The number of vacancy defects in the resolidified layer 25 calculated by Formula 1 may be equal to or greater than the number of vacancy defects in the second portion. In addition, the number of vacancy defects in the second portion may be equal to or greater than the number of vacancy defects in the first portion 19.

[0101] In addition, the second portion 20 may include a plurality of crystal grains 200. The plurality of crystal grains 200 may be confirmed by observing the second portion 20 with a scanning electron microscope (SEM). The second portion 20 may be formed as an equiaxed microstructure. In other words, the plurality of crystal grains 200 may not have an orientation and may have similar lengths toward three axes. The plurality of crystal grains 200 may have isotropy. This is because the outer material 12 is heated and the crystal grains 200 grow in parallel along the three axes.

[0102] At least one of the plurality of grains 200 of the second portion 20 may be partially cut. This is because the groove portion 30 is formed by laser etching the outer material 12. In other words, the groove portion 30 may be formed by laser etching the outer material 12 while minimizing thermal damage to the outer material.

[0103] Meanwhile, the first portion 19 may further include a plurality of crystal grains 100. As described above, the plurality of crystal grains 100 may be confirmed by observing the first portion with a scanning electron microscope. Fig. 9 , the first portion 19 may be formed to have anisotropy. In other words, a plurality of grains in the first portion 19 may have orientations toward three axes and may have different lengths. This is because a process of heating the first portion 19 after pressurizing the first portion 19 is omitted.

[0104] The standard deviation of the size of the plurality of crystal grains 200 included in the overlapped portion 21 may be 20 or less. In other words, the size of the plurality of crystal grains 200 included in the overlapped portion 21 may be formed to be uniform. This is because the crystal grains 200 are not subjected to external pressure after being grown by heating. In other words, laser etching may form the groove portion 30 by cutting the crystal grains 200 irradiated by the laser, and the size of the crystal grains 200 located inside the external material may not be changed.

[0105] The standard deviation of the sizes of the plurality of grains 200 included in the cover portion 22 may be less than 20. Likewise, the sizes of the plurality of grains 200 included in the cover portion 22 may be formed to be uniform.

[0106] The sizes of the plurality of grains 200 included in the overlapping portion 21 and the plurality of grains 200 included in the covering portion 22 may also be formed to be uniform. The average value of the sizes of the plurality of grains 200 included in the overlapping portion 21 may be formed to have a difference of 3% or less from the average value of the sizes of the plurality of grains 200 included in the covering portion 22. That is, the sizes of the plurality of grains 200 included in the second portion 20 may be formed to be uniform.

[0107] When calculating the sizes of the plurality of die 200 included in the overlapping portion 21 and the covering portion 22 , among the plurality of die 200 , the die 200 overlapping a virtual line distinguishing a boundary between the overlapping portion 21 and the covering portion 22 is considered to be included in the overlapping portion 21 .

[0108] Furthermore, among the plurality of dies 200 , those that are partially cut and damaged are not included in calculating the average size.

[0109] Reference Figure 8 , the groove portion 30 may include a bottom portion 31 forming a bottom surface; and a groove 32 that is recessed deeper inward from the edge of the bottom portion 31. For example, the groove 32 may be recessed deeper in the Z direction at both edges of the bottom portion 31. The outer material 12 may be heated by a laser to form the groove.

[0110] In addition, the ten-point average roughness (Rz) of the surface of the groove part 30 may be higher than the ten-point average roughness (Rz) of the surface of the second portion 20. Here, the surface of the second portion 20 may refer to an outer surface.

[0111] The ten-point average roughness is a value that numerically represents the surface roughness. The roughness of the surface of the groove portion 30 and the roughness of the surface of the second portion 20 can be measured by a known method for measuring roughness. The ten-point average roughness of the surface of the groove portion 30 thus measured may be higher than the ten-point average roughness of the surface of the second portion 20. In other words, the surface of the groove portion 30 may be formed to be rougher than the surface of the second portion 20.

[0112] This is because the groove portion 30 is formed using a laser. When the groove portion 30 is formed using a press method instead of a laser, the pressed surface can be formed to be flat. However, in the present application, the groove portion 30 is formed using a laser, so that the surface of the groove portion 30 is formed to be rough. Specifically, the ten-point average roughness of the surface of the groove portion 30 may exceed 20.

[0113] Figures 10 to 12 Various embodiments of battery cells are shown.

[0114] The area of ​​the exterior material 12 heated by the laser is not particularly limited. Fig. 9 , the area where the outer material 12 is heated by the laser may extend along the X direction on one surface of the main body portion.

[0115] Reference Fig.11 , the battery cell 10 of the present application may further include a vent portion 40. The vent portion 40 may be formed by recessing at least one of the inner surface of the outer material 12 and the outer surface disposed in a direction opposite to the inner surface. The second portion 20 may include the vent portion 40. In other words, the vent portion 40 may be formed in the second portion 20.

[0116] The groove portion 30 and the vent portion 40 may be located overlapping along a concave direction in which the vent portion 40 is concave. In other words, the groove portion 30 may be located inside the vent portion 40. The vent portion 40 is intended to thin the external material 12. Thus, when the internal pressure of the battery cell 10 increases, the groove portion 30 may be easily opened.

[0117] The exterior material 12 may be formed thinner due to the groove portion 30 and the vent portion 40. Thus, when the internal pressure of the battery cell 10 increases and reaches a rupture pressure, the groove portion 30 may be opened.

[0118] Refer again Fig.11, the width of the second portion 20 and the width of the vent portion 40 may be set equal. The width of the vent portion 40 may be defined as a recess start point P1 in the vent portion 40 to a recess end point P2 of the vent portion 40 along the X direction. The area between the recess start point P1 and the recess end point P2 may be heated so that the second portion 20 may be located overlapping with the vent portion 40.

[0119] Thus, the groove portion 30 may be broken earlier than other regions of the battery cell 10. That is, the exterior material 12 may be heated to change its physical properties and may have a thinner thickness so that the groove portion 30 may be opened earliest among other regions when the internal pressure increases.

[0120] In another embodiment, the width of the ventilation portion 40 may be set to be longer than the width of the second portion 20. Fig.12 , only a portion of the region from the depression start point P1 to the depression end point P2 where the exterior material 12 starts to be depressed may be heated. Thus, when the pressure increases, the groove portion 30 may be opened earlier than other regions of the battery cell 10 .

[0121] The groove portion 30 may include the same material as the external material 12. In other words, the groove portion 30 may include an inner adhesive layer, an outer insulating layer, and a metal layer. Thus, the groove portion 30 may perform the same function as the external material 12. For example, the groove portion 30 may protect the electrode assembly from external impact.

[0122] FIG. 13A to FIG. 13C Various embodiments of the groove portion 30 of the present application are shown.

[0123] The groove portion 30 may be provided in various shapes. To this end, the first region may be provided in various shapes. Since the laser is irradiated to the first region to form the groove portion 30, the groove portion 30 may be formed in a shape corresponding to the first region.

[0124] Reference Fig.13A , the groove portion 30 may be provided as a line having a central area extending in one direction and having a curvature at one end and the other end. Fig. 13B , the groove portion 30 may have a central area extending in one direction and one end and the other end having straight lines. Fig. 13C , the groove portion 30 may also include a line having a central area extending in one direction and having an arc shape. The shape of the groove portion 30 is not limited as long as it can be opened on the outer surface of the outer material.

[0125] The present application can be modified and implemented in various forms, and its scope is not limited to the above-mentioned embodiments. Therefore, various modifications and changes can be made without departing from the scope of the present application.

Claims

1. A battery cell, comprising: An electrode assembly, the electrode assembly comprising a positive electrode, a negative electrode and a separator; as well as an outer material that houses the electrode assembly therein, wherein the outer material includes: a first portion forming an accommodation space in which the electrode assembly is accommodated; a second portion formed integrally with the first portion; and a groove portion formed by recessing at least a portion of the second portion and having a resolidified layer on an outer portion of the second portion, and The second portion includes a plurality of grains, and the plurality of grains of the second portion include an equiaxed microstructure. 2 . The battery cell according to claim 1 , wherein the first portion includes a plurality of grains, and the plurality of grains of the first portion are formed in an anisotropic structure. 3 . The battery cell according to claim 1 , wherein the groove portion is formed by recessing an outer surface of the exterior material toward an inside of the battery cell, and has a groove shape. 4 . The battery cell according to claim 3 , wherein the recessed groove portion further comprises a bottom portion and a groove, the bottom portion forming a bottom surface; and the groove is disposed at a deeper level inside the external material than the bottom portion.

5. The battery cell according to claim 1, wherein: The ten-point average roughness of the surface of the groove portion is higher than the ten-point average roughness of the second portion. 6 . The battery cell according to claim 5 , wherein a ten-point average roughness of a surface of the groove portion exceeds 20 μm. The battery cell according to claim 1 , wherein at least one of the plurality of dies is partially cut.

8. The battery cell according to claim 7, wherein the second portion comprises: an overlapping portion and a covering portion, wherein the overlapping portion overlaps the groove portion along a recessed direction of the groove portion; The covering portion is located outside the groove portion in a width direction of the groove portion, and the covering portion is formed perpendicular to a recessed direction of the groove portion. 9 . The battery cell according to claim 8 , wherein a standard deviation of sizes of the plurality of grains included in the overlapping portion is 20 or less. 10 . The battery cell according to claim 8 , wherein a standard deviation of sizes of the plurality of grains included in the covering portion is 20 or less. 11 . The battery cell according to claim 8 , wherein a difference between an average value of sizes of the plurality of crystal grains included in the overlapping portion and an average value of sizes of the plurality of crystal grains included in the covering portion is 3% or less.

12. The battery cell according to claim 1, wherein the external material further comprises: a main body portion accommodating the electrode assembly and having the first portion and the second portion; and a cover portion, the cover portion including a cell tab electrically connecting the electrode assembly to the outside and covering the main body portion, wherein the groove portion is disposed in the main body portion.

13. The battery cell according to claim 1, wherein the external material further comprises a ventilation portion, the ventilation portion being formed by recessing at least one of an inner surface of the external material and an outer surface arranged in an opposite direction of the inner surface, wherein the groove portion and the ventilation portion are arranged to overlap in a recessed direction, and the at least one surface is recessed in the recessed direction. 14 . The battery cell according to claim 1 , wherein a shape of the groove portion is deformed based on an internal pressure of the external material. The battery cell according to claim 13 , wherein the groove portion is broken at a pressure above a breaking pressure. 16 . The battery cell according to claim 1 , wherein the groove portion is integrally formed with the external material.

17. The battery cell of claim 1, wherein the resolidified layer comprises vacancy defects. 18 . The battery cell according to claim 17 , wherein the number of vacancy defects in the resolidified layer is equal to or greater than the number of vacancy defects in the second portion. 19 . The battery cell of claim 18 , wherein the number of vacancy defects in the second portion is equal to or greater than the number of vacancy defects in the first portion. 20 . The battery cell according to claim 1 , wherein a thickness of the resolidified layer in a direction from the inside to the outside of the exterior material is 3 μm or more.

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