Carbon steel material, high-strength metal can, and secondary battery contained therein

Abstract

Provided are a high-strength carbon steel suitable as a material of a can for a secondary battery, a metal can manufactured by processing same, and a secondary battery manufactured by accommodating an electrode assembly in the can. A material for manufacturing the metal can is provided in the form of a metal plate. The metal can is manufactured by deep drawing the metal plate. The metal can is made of a material in which a precipitation strengthening element including Nb is added to a carbon steel in a ratio of more than 0.05 wt.% and 0.100 wt% or less. C is contained in the carbon steel in an amount of 0.01 wt.% or more and 0.100 wt.% or less. Mn is contained in the carbon steel in an amount of 0.1 wt.% or more and 0.5 wt.% or less. Si is contained in the carbon steel in an amount of more than 0.001 wt.% and 0.5 wt.% or less.

Description

Carbon steel material, high-strength metal can and secondary battery contained therein

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0005689, dated January 12, 2024, Korean Patent Application No. 10-2024-0006990, dated January 16, 2024, Korean Patent Application No. 10-2025-0001572, dated January 6, 2025, and Korean Patent Application No. 10-2025-0004275, dated January 10, 2025, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to high-strength carbon steel suitable as a material for a can for a secondary battery, a metal can made of the carbon steel, and a secondary battery using the same.

[0003] Can-shaped battery cells, like cylindrical battery cells, house a jelly-roll-shaped electrode assembly within a metal can. These cells are more resistant to shock and temperature than pouch-shaped batteries. Consequently, demand for can-shaped cells in vehicle battery packs is growing.

[0004] Battery cans are manufactured by deep drawing metal sheets and trimming the leading edge of the side walls.

[0005] Cylindrical battery cells, as previously described, feature an electrode assembly embedded within a metal can. These cells offer sufficient rigidity, and their metal surfaces offer excellent heat transfer efficiency, making them ideal for cooling with a cooling fluid. However, conventional cylindrical battery cells are small, requiring a large number of cells to achieve the electrical capacity required for electric vehicles. However, when installing such a large number of cells in a vehicle, where weight reduction directly impacts mileage, the weight of the metal can itself makes it difficult to achieve lightweight vehicle performance. Furthermore, the need to connect the electrode terminals of numerous small cells via busbars presents a significant challenge.

[0006] To address these inconveniences, the size of cylindrical battery cells has been increasing recently, and in particular, a plan to directly mount can-type battery cells without battery modules in electric vehicle battery packs is being considered.

[0007] As the size of cylindrical battery cells increases, the electric capacity increases by volume, while the area of ​​the battery can increases by area. Therefore, the electric capacity of the electrode assembly relative to the load of the battery can is expected to increase. However, if a thermal runaway occurs in a high-capacity battery cell, the explosive force also increases by volume. Therefore, contrary to this expectation, the metal can thickness must be increased to sufficiently increase the strength of the can. Consequently, the weight of the metal can also increase in proportion to the increase in electric capacity.

[0008] To overcome these technical limitations, one option is to use high-strength steel plates to manufacture large battery cans. However, due to the nature of the can manufacturing method, which involves plastic forming of metal plates through deep drawing, using high-strength steel plates requires a higher-power press for can forming, and the mold itself must be stronger. Consequently, the use of high-strength steel plates increases production costs and complexity.

[0009] Also, as the strength of metal materials generally increases, the elongation tends to decrease accordingly. Therefore, if the high-strength steel plate mentioned above is used as the raw material for cans, the formability of the cans will decrease accordingly.

[0010] Moreover, the environment in which cylindrical battery cells require increased strength is not a typical room-temperature environment, but rather an environment where thermal runaway occurs. Because thermal runaway can raise battery cell temperatures to over 500 degrees Celsius, battery cans must be even stronger in high-temperature environments.

[0011] Additionally, the battery can accommodates electrodes and an electrolyte, which undergo a battery reaction as the secondary battery is repeatedly charged and discharged. Therefore, the battery can must have high corrosion resistance to avoid being affected by these battery reactions.

[0012] Traditionally, tungsten (W) was added to carbon steel in appropriate proportions to enhance corrosion resistance and high-temperature properties. However, tungsten reduces ductility, and its addition deteriorates the formability of battery cans, which require deep drawing of metal plates.

[0013] Furthermore, titanium (Ti) has traditionally been added to improve high-temperature properties by suppressing grain growth at high temperatures. However, titanium increases the recrystallization temperature, reducing heat treatment operability and degrading plating properties.

[0014] The present invention presents the following technical problems based on the problems presented above.

[0015] Large capacity cylindrical battery cans do not require high strength in room temperature or other commonly assumed environments, but rather in thermal runaway environments where high temperatures of over 500 degrees Celsius are generated.

[0016] Because large-capacity cylindrical battery cans are manufactured through deep drawing, they don't require the high strength required by the steel industry at room temperature. In other words, considering the can's workability at room temperature, increased elongation is more important than increased strength.

[0017] On the other hand, when thermal runaway occurs, the pressure inside the can increases rapidly, resulting in extremely large tensile stresses in the circumferential direction of the can. In contrast, the metal structure of the can, which must resist this pressure, has the characteristic of undergoing significant axial plastic deformation due to the deep drawing process. In other words, the metal structure of the deep-drawn can must resist tensile forces in a direction orthogonal to the direction of extreme plastic deformation.

[0018] In other words, what is required for a material for a large-capacity cylindrical battery can is not a material that has remarkably high strength at room temperature. Rather, even if the strength at room temperature is not that high, such strength should not deteriorate rapidly in a high-temperature environment above 500 degrees Celsius. For example, a metal with a room-temperature strength of 700 and a high-temperature strength of 500 is more suitable as a battery can material than a metal with a room-temperature strength of 1000 and a high-temperature strength of 300.

[0019] The present invention seeks to provide a can metal material having excellent formability in a can forming processing environment such as deep drawing and having minimal strength loss in a high-temperature environment of 500 degrees Celsius or higher.

[0020] Through this, the present invention aims to provide a metal can for a secondary battery that can be manufactured by preparing the can metal material in a sheet form and deep drawing it.

[0021] Additionally, secondary battery cans require excellent formability and high-temperature properties, while also being corrosion-resistant and unaffected by the battery reaction of the secondary battery. Furthermore, it is desirable for cans to exhibit superior corrosion resistance, as well as excellent room-temperature formability and high-temperature strength.

[0022] The present invention provides a can metal material having excellent formability, high-temperature properties, and corrosion resistance, a metal can for a secondary battery manufactured using the can, and a secondary battery using the metal can.

[0023] The technical objectives of the present invention are not limited to the purposes mentioned above. Other objectives and advantages of the present invention not mentioned above can be understood through the following description and will be more clearly understood through the embodiments of the present invention. Furthermore, it will be readily apparent that the objectives and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims.

[0024] The present invention, which aims to solve the above-described problem, provides a can material for a battery cell that has excellent high-temperature strength while ensuring the formability of a metal can with guaranteed corrosion resistance.

[0025] The above can material can be provided in sheet form that can be processed by deep drawing forming.

[0026] The present invention inhibits grain growth by adding a precipitation strengthening element capable of delaying the recrystallization temperature to carbon steel used as a material for secondary battery cans. This allows the metal can to maintain high strength even in high-temperature environments of 500 degrees Celsius or higher, a thermal runaway environment for secondary batteries.

[0027] The above precipitation strengthening element may be an element other than the five major elements of carbon steel.

[0028] The above precipitation strengthening element can be added to carbon steel containing at least C (carbon) among the five major elements based on Fe (iron).

[0029] The carbon steel to which the above precipitation strengthening element is added may be a carbon steel that can secure a balance of rollability and strength.

[0030] The above precipitation-strengthening element combines with the carbon (C) in carbon steel to form precipitates, thereby inhibiting grain growth. This not only reduces the brittleness of metal cans and increases their ductility, improving room-temperature strength and formability, but also further enhances high-temperature strength.

[0031] The above C can be added to the above carbon steel in a range of 0.01 wt.% to 0.100 wt.%.

[0032] Preferably, the C may be added to the carbon steel in a range of 0.02 wt.% or more and 0.07 wt.% or less.

[0033] More preferably, the C may be added to the carbon steel in a range of 0.03 wt.% or more and 0.05 wt.% or less.

[0034] If the carbon content exceeds the above range, the rolling properties and formability deteriorate, and if it falls below the above range, it is difficult to secure the required strength.

[0035] The above carbon steel may further contain Mn (manganese).

[0036] The above Mn can be added to the carbon steel in a range of 0.1 wt.% to 0.5 wt.%, and preferably, can be added to the carbon steel in a range of 0.15 wt.% to 0.3 wt.%. Accordingly, strength can be increased and hot cracking can be prevented.

[0037] If the manganese content exceeds the above range, ductility, corrosion resistance, and plating properties may decrease, and if it is below the above range, hot cracking may occur.

[0038] The above carbon steel may further contain Si (silicon).

[0039] The above Si may be added to the carbon steel in a range of more than 0.001 wt.% and less than or equal to 0.5 wt.%, and preferably may be added to the carbon steel in a range of more than 0.01 wt.% and less than or equal to 0.02 wt.%.

[0040] If the silicon content exceeds the above range, there is a risk of reduced ductility.

[0041] The above carbon steel may further contain P (phosphorus).

[0042] The above P can be added to the carbon steel in a range of more than 0.001 wt.% and less than 0.02 wt.%, and preferably can be added to the carbon steel in a range of more than 0.003 wt.% and less than 0.008 wt.%. Accordingly, strength and corrosion resistance can be improved.

[0043] If the phosphorus content exceeds the above range, ductility and plating properties may decrease, and if it falls below the above range, strength and corrosion resistance may decrease.

[0044] The above carbon steel may further contain S (sulfur).

[0045] Low-carbon steel containing the five major elements begins to experience changes in its microstructure from 500 degrees Celsius, which causes a decrease in strength. When the precipitation strengthening element is added to the carbon steel, the added precipitation strengthening element combines with the carbon in the carbon steel to form precipitates, thereby increasing the room temperature ductility of the carbon steel and inhibiting the growth of crystal grains at high temperatures, thereby improving the high temperature strength of the carbon steel.

[0046] The above precipitation strengthening element may be added to the carbon steel in a range of more than 0 wt.% and less than or equal to 0.1 wt.%. Specifically, the above precipitation strengthening element may be added to the carbon steel in a range of more than 0.001 wt.% and less than or equal to 0.100 wt.%.

[0047] The added precipitation strengthening element may be one or more elements selected from Ti (titanium) and Nb (niobium). Accordingly, room temperature strength and high temperature strength can be improved, and room temperature ductility can be increased.

[0048] Preferably, the precipitation strengthening element may include Nb.

[0049] The above-mentioned niobium (Nb) combines with carbon in carbon steel to form precipitates. This enhances the room-temperature formability of carbon steel and suppresses the phenomenon of grain growth and strength reduction in carbon steel in high-temperature environments. In other words, the above-mentioned niobium (Nb) further enhances the room-temperature formability and high-temperature strength of metal cans. In particular, niobium (Nb) enhances the curvature formability, thereby further enhancing the formability of the deep drawing process of carbon steel sheets for forming battery cans.

[0050] In addition, Nb forms a thin oxide layer on the surface of carbon steel, thereby increasing electrolytic resistance and corrosion resistance, thereby greatly improving the corrosion resistance of carbon steel suitable for secondary batteries.

[0051] The above Nb may be added to the carbon steel in a range of more than 0.001 wt.% and less than or equal to 0.100 wt.%. Preferably, the above Nb may be added to the carbon steel in a range of more than 0.003 wt.% and less than or equal to 0.09 wt.%.

[0052] More preferably, the Nb is added in a range of 0.05 wt.% to 0.07 wt.%. Accordingly, the tensile strength at room temperature can be improved while further improving the elongation, and the tensile strength at high temperature can be improved while further improving the elongation.

[0053] When the above Nb exceeds 0.07 wt.%, the effect of improving corrosion resistance is minimal, while the room temperature strength of the carbon steel decreases, so that even if the decrease in the high temperature strength of the carbon steel is suppressed, it is difficult to secure the required high temperature ultimate strength. When the above Nb is less than 0.05 wt.%, the effect of improving the formability of the carbon steel is reduced, and the effect of suppressing grain growth at high temperatures is insufficient, so that grains grow even at temperatures lower than 600 degrees Celsius, failing to meet the required high temperature ultimate strength, and the electrolytic resistance and corrosion resistance are weakened, resulting in lower corrosion resistance.

[0054] Optionally, the precipitation strengthening element may include Ti.

[0055] The above-mentioned Ti preferentially combines with elements such as carbon and nitrogen incorporated in carbon steel to form TiN and TiC carbides, thereby enhancing room-temperature formability. Furthermore, these fine precipitates inhibit grain growth at high temperatures, thereby enhancing high-temperature strength.

[0056] The above Ti may be added to the carbon steel in a range of more than 0.001 wt.% and less than or equal to 0.100 wt.%. Preferably, the above Ti may be added to the carbon steel in a range of more than 0.01 wt.% and less than or equal to 0.07 wt.%.

[0057] More preferably, the Ti may be added in a range of 0.03 wt.% to 0.05 wt.% or less. Accordingly, the tensile strength at room temperature can be further improved while the elongation can be improved, and the tensile strength at high temperatures can be further improved.

[0058] When the above Ti exceeds 0.05 wt.%, the grain growth inhibition effect is no longer increased in the required high-temperature environment of about 600 degrees Celsius, making heat treatment of carbon steel difficult and reducing plating properties. When the above Ti is less than 0.03 wt.%, the grain growth effect is not expressed.

[0059] Carbon steel with the above precipitation strengthening element added can be subjected to alloying heat treatment.

[0060] Specifically, the carbon steel is provided in the form of a metal sheet, and may be provided by plating carbon steel and a different metal on one or both sides of the sheet.

[0061] Additionally, the above-mentioned plated carbon steel can be heat treated.

[0062] The above heterogeneous metal may include Ni (nickel).

[0063] The above metal sheet can be processed by deep drawing forming. Accordingly, the metal sheet can have a bottom portion and a tubular side wall portion connected to the bottom portion and extending in the drawing direction (axial direction).

[0064] The leading edge of the side wall portion is trimmed, thereby allowing the axial dimension of the side wall portion to be regulated.

[0065] The above bottom portion may be pierced, thereby forming a piercing hole in the bottom portion.

[0066] In some examples, the piercing hole may be a charging port for injecting electrolyte into the inside of the battery can.

[0067] The above-mentioned injection port can be sealed after injection of the electrolyte.

[0068] In contrast, the piercing hole may be a terminal fixing hole in which a terminal connected to an electrode of an electrode assembly accommodated inside the battery can is fixed.

[0069] A rivet terminal is fixed in the above terminal fixing hole, and a gasket may be interposed between the rivet terminal and the bottom portion. The rivet terminal and the can may be electrically insulated and sealed by the gasket.

[0070] The open end of the can can be sealed by covering it with a cap while the electrode assembly is accommodated inside the can.

[0071] For this purpose, the leading end of the side wall portion can be sealingly joined to the edge of the cap.

[0072] In one example, a beading portion is provided near the leading edge of the side wall portion, the side wall portion is sunken radially inward, the edge of the cap is placed on the outer surface of the beading portion in the axial direction, and the leading edge of the side wall portion is crimped radially inward, so that the edge of the tab can be pressed axially inward.

[0073] A gasket may be interposed between the edge of the cap and the side wall of the can. The gasket may seal the edge of the cap and the end of the side wall of the can. Optionally, the gasket may electrically insulate the cap and the can.

[0074] In another example, the leading edge of the side wall portion may be joined to the edge of the cap to form a sealing connection.

[0075] The above bonding can be achieved by welding.

[0076] The above welding can be achieved by welding. Specifically, the welding can be seam laser welding.

[0077] The above welding can be achieved by melting at least one of the cap and the can.

[0078] The above welding can be achieved by melting the solder paste.

[0079] The above welding can be achieved by melting the brazing filler metal.

[0080] According to the present invention, by adding a precipitation strengthening element to a carbon steel can material, the recrystallization temperature is slowed, thereby suppressing grain growth. This ensures not only room-temperature strength but also sufficient high-temperature strength of the metal can for secondary batteries manufactured thereby. Consequently, a can for secondary batteries can be provided that is more robust even in thermal runaway environments.

[0081] According to the present invention, by adding a precipitation strengthening element including Ti or Nb to a can material of carbon steel, the room temperature elongation can be improved, thereby improving the processability of the can material.

[0082] In addition, according to the present invention, by adding a precipitation strengthening element including Ti or Nb to the can material of carbon steel, both the room temperature strength and the high temperature strength of the battery can can be increased.

[0083] According to the present invention, by adding a precipitation strengthening element including Nb to a can material of carbon steel, the tensile strength at high temperatures is improved while ensuring high-temperature elongation, thereby maximally suppressing breakage of the battery can in a high-temperature environment due to thermal runaway of the battery cell.

[0084] According to the present invention, by adding a precipitation strengthening element including Nb to a can material of carbon steel, the corrosion resistance of a battery can applied to a secondary battery can can be significantly improved.

[0085] According to the present invention, by adding a precipitation strengthening element including Ti to a can material of carbon steel, the tensile strength at both room temperature and high temperature can be further improved.

[0086] In addition to the effects described above, specific effects of the present invention are described below while explaining specific details for carrying out the invention.

[0087] Figure 1 is a cross-sectional view of a carbon steel plate for manufacturing a battery can.

[0088] Fig. 2 is a cross-sectional view of a battery can formed by deep drawing the plate of Fig. 1.

[0089] Fig. 3 is a cross-sectional view of a battery can with the front end of the side wall of the battery can of Fig. 2 trimmed and cut.

[0090] Figure 4 is a cross-sectional view of the electrode assembly accommodated in the battery can of Figure 3.

[0091] Figure 5 is a cross-sectional view of the open end of the battery can of Figure 4 sealed with a cap assembly.

[0092] Figure 6 is a cross-sectional view of the bottom of the battery can of Figure 3, with a piercing hole formed.

[0093] Fig. 7 is a cross-sectional view of a state in which a rivet terminal is fixed to a piercing hole of the battery can of Fig. 6.

[0094] Figure 8 is a cross-sectional view of the electrode assembly accommodated in the battery can of Figure 7.

[0095] Figure 9 is a cross-sectional view of the battery can of Figure 8 with the open end sealed with a cap.

[0096] Fig. 10 is a cross-sectional view of the electrode assembly accommodated in the battery can of Fig. 7.

[0097] Figure 11 is a cross-sectional view of the battery can of Figure 10 with the open end sealed with a cap.

[0098] Figure 12 is an enlarged photographic image of the metal can structure of the example and comparative example.

[0099] [Explanation of symbols]

[0100] 10: Can 10St: Metal sheet, metal plate 10Ni: Coating part 11: Side wall part 11B: Beading part 11C: Crimping part 12: Bottom part 13: Piercing hole 20: Electrode assembly 21: First collector plate 22: Second collector plate 30: Cap assembly, cap 41: Gasket 42: Gasket 50: Insulator 60: Rivet terminal 91: Blank holder 92: Punch T: Trimming C: Cutting P: Piercing W: Bonding

[0101] The above-described objects, features, and advantages will be described in detail below with reference to the accompanying drawings, so that those skilled in the art can easily practice the technical idea of ​​the present invention. In describing the present invention, if it is determined that a detailed description of known technologies related to the present invention may unnecessarily obscure the gist of the present invention, a detailed description thereof will be omitted. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used to indicate the same or similar components.

[0102] Although terms like "first" and "second" are used to describe various components, these components are not limited by these terms. These terms are used merely to distinguish one component from another, and unless otherwise specified, a "first" component may also be a "second" component.

[0103] Throughout the specification, unless otherwise specifically stated, each element may be singular or plural.

[0104] Hereinafter, the phrase "any configuration is placed on (or below)" a component or "on (or below)" a component may mean that any configuration is placed in contact with the upper surface (or lower surface) of said component, and that other configurations may be interposed between said component and any configuration placed on (or below) said component.

[0105] Additionally, when it is described that a component is "connected," "coupled," or "connected" to another component, it should be understood that the components may be directly connected or connected to one another, but that other components may also be "interposed" between the components, or that each component may be "connected," "coupled," or "connected" through another component.

[0106] As used herein, singular expressions include plural expressions unless the context clearly dictates otherwise. In this application, terms such as "consisting of" or "comprising" should not necessarily be construed to include all of the components or steps described in the specification, and should be construed to mean that some of the components or steps may not be included, or that additional components or steps may be included.

[0107] Throughout the specification, when we refer to "A and / or B", this means A, B, or A and B, unless otherwise stated, and when we refer to "C through D", this means C or more and D or less, unless otherwise stated.

[0108] In describing the embodiment, the axial direction refers to the direction in which the side wall of the can extends as the metal sheet is deep drawn, the radial direction refers to the direction approaching or away from the axis, and the circumferential direction refers to the direction surrounding the axis.

[0109] Hereinafter, an embodiment of a high-strength metal can according to the present invention will be described.

[0110] The process of manufacturing a battery can includes first preparing NPS (Nickel Plated Steel) with nickel (10Ni) plated on the surface of a sheet-shaped metal plate (10St) as shown in FIG. 1, and deep drawing the NPS to form a circular bottom portion (12) and a circular tube-shaped side wall portion (11) connected thereto as shown in FIG. 2.

[0111] Next, as illustrated in FIG. 2, a process is included of finalizing the front end of the side wall portion (11) of the battery can (10) by gripping the front end of the side wall portion (11) remaining in a flange shape with a blank holder (91) and trimming (T) with a punch (92). The height of the battery can (10) may be determined by the trimming process, or may be determined through a process such as cutting (C) that may be additionally performed thereafter.

[0112] Accordingly, the metal can (10) may have a bottom portion (12) and a side wall portion (11) extending in the drawing direction or axial direction from the edge thereof, as shown in FIG. 3.

[0113] Although the example illustrates that the metal plate is a plated plate of a heterogeneous metal, it is not necessary to apply a metal plate in the form of a plated plate. In addition, further alloying heat treatment may be performed as needed.

[0114] The battery cell of the embodiment may be, for example, a cylindrical battery cell having a form factor ratio (defined as the ratio of the diameter (Φ) to the height (H) of the cylindrical battery cell) of greater than about 0.4.

[0115] Here, the form factor refers to a value indicating the diameter and height of a cylindrical battery cell. The cylindrical battery cell may be, for example, a 46800 cell or a 46950 cell. In the numerical value indicating the form factor, the first two numbers indicate the diameter of the cell, the next two numbers indicate the height of the cell, and the last number 0 indicates that the cross-section of the cell is circular.

[0116] The above battery cell may be a cylindrical battery cell having a roughly cylindrical shape, a diameter of approximately 46 mm, a height of approximately 80 mm, and a form factor ratio of 0.575.

[0117] The above battery cell may be a cylindrical battery cell having a roughly cylindrical shape, a diameter of approximately 46 mm, a height of approximately 95 mm, and a form factor ratio of 0.484.

[0118] The above battery cell may be a cylindrical battery cell having a roughly cylindrical shape, a diameter of approximately 46 mm, a height of approximately 110 mm, and a form factor ratio of 0.418.

[0119] The above battery cell may be a cylindrical battery cell having a roughly cylindrical shape, a diameter of approximately 48 mm, a height of approximately 75 mm, and a form factor ratio of 0.640.

[0120] The above battery cell may be a cylindrical battery cell having a roughly cylindrical shape, a diameter of approximately 48 mm, a height of approximately 110 mm, and a form factor ratio of 0.436.

[0121] The above battery cell may be a cylindrical battery cell having a roughly cylindrical shape, a diameter of approximately 48 mm, a height of approximately 80 mm, and a form factor ratio of 0.600.

[0122] The present invention can of course also be applied to battery cells having a form factor ratio of approximately 0.4 or less, such as 18650 cells, 21700 cells, etc. For 18650 cells, the diameter is approximately 18 mm, the height is approximately 65 mm, and the form factor ratio is 0.277. For 21700 cells, the diameter is approximately 21 mm, the height is approximately 70 mm, and the form factor ratio is 0.300.

[0123] Below, a first embodiment of a secondary battery using the above battery can (10) is described.

[0124] Referring to FIG. 4, a jelly-roll-shaped electrode assembly (20) wound in a cylindrical shape is inserted into the metal can (10), and a first electrode tab or first collector plate (21) electrically connected to the first electrode of the electrode assembly (20) is bonded to the bottom portion (12) to electrically connect the first electrode and the can (10). Accordingly, the can (10) can have a polarity corresponding to the first electrode of the electrode assembly (20). If necessary, an annular insulator (50) may be interposed between the first collector plate (21) and the bottom portion (12) to facilitate bonding thereof.

[0125] In addition, as illustrated in FIG. 5, a second electrode tab or second collector plate (22) electrically connected to the second electrode of the electrode assembly (20) may be joined to the cap assembly (30) to electrically connect the second electrode and the cap assembly (30). Accordingly, the cap assembly (30) may have a polarity corresponding to the second electrode of the electrode assembly.

[0126] Referring to Fig. 5, the open end of the can (10) is coupled with and sealed with the cap assembly (30). To this end, the side wall portion (11) of the can (10) is radially inwardly recessed near the tip of the side wall portion (11) to form a beading portion (11B). Then, the cap assembly (30) is placed on the outside of the beading portion (11B) in the axial direction, and the tip of the side wall portion (11) is crimped radially inwardly to form a crimping portion (11C). The crimping portion (11C) presses the edge of the cap assembly (30) axially inward. A gasket (42) is interposed between the edge of the cap assembly (30) and the side wall portion (11) to electrically insulate and seal the edge of the cap assembly (30) and the side wall portion (11).

[0127] Next, a second embodiment of a secondary battery using the above battery can (10) will be described.

[0128] As illustrated in Fig. 3, a piercing (P) process is performed on the bottom of a metal can (10) to form a piercing hole (13) in the bottom portion (12) of the metal can (10), as illustrated in Fig. 6. A rivet terminal (60) can be fixed to the piercing hole (13), as illustrated in Fig. 7. At this time, a first gasket (41) is interposed between the rivet terminal (60) and the bottom portion (12) defining the piercing hole (13). Accordingly, the rivet terminal (60) and the can (10) are electrically insulated and sealed.

[0129] Next, as illustrated in Fig. 8, an insulator (50) is placed on the bottom (12) of the metal can (10) so that the rivet terminal (60) is exposed, and an electrode assembly (20) is inserted. Then, a first collector plate (21) electrically connected to the first electrode of the electrode assembly (20) is joined to the rivet terminal (60), thereby electrically connecting the first electrode and the rivet terminal (60). Accordingly, the rivet terminal (60) can have a polarity corresponding to the first electrode of the electrode assembly (20).

[0130] In addition, as illustrated in FIG. 9, the side wall portion (11) of the can (10) is formed by radially inwardly recessing the side wall portion (11) near the tip portion of the side wall portion (11) to form a beading portion (11B). Then, a second collector plate (22) electrically connected to the second electrode of the electrode assembly (20) is placed on the axial outer surface of the beading portion (11B) and joined as necessary, thereby electrically connecting the second electrode and the can (10). Accordingly, the can (10) can have a polarity corresponding to the second electrode.

[0131] And, a cap (30) is placed on the outer side of the beading portion (11B) in the axial direction, and the tip of the side wall portion (11) is crimped radially inward to form a crimping portion (11C). The crimping portion (11C) presses the edge of the cap (30) axially inward. A second gasket (42) is interposed between the edge of the cap (30) and the side wall portion (11) to electrically insulate and seal the edge of the cap (30) and the side wall portion (11). Accordingly, the cap (30) can be non-polar.

[0132] Next, a third embodiment of a secondary battery using the above battery can (10) will be described.

[0133] In the battery can (10) of FIG. 7, in which a rivet terminal (60) is fixed to the bottom portion (12), an insulator (50) is placed on the bottom portion (12) so that the rivet terminal (60) is exposed as shown in FIG. 10, and an electrode assembly (20) is inserted. Then, a first collector plate (21) electrically connected to the first electrode of the electrode assembly (20) is joined to the rivet terminal (60), so that the first electrode and the rivet terminal (60) are electrically connected, so that the rivet terminal (60) has a polarity corresponding to the first electrode of the electrode assembly (20).

[0134] Next, as illustrated in Fig. 11, the open end of the can (10) is sealed with a cap (30). The edge of the cap (30) can be welded and sealed with the tip of the side wall portion (11). At this time, the second collector plate (22) electrically connected to the second electrode of the electrode assembly (20) can be welded (W) together with the welding portion of the side wall portion (11) and the cap (30), so that the can (10) and the cap (30) can have a second polarity.

[0135] The metal that constitutes the metal plate that is the material of the above battery can (10) may be Fe-based carbon steel.

[0136] The above carbon steel contains C (carbon). The C may be added to the carbon steel in a range of 0.01 wt.% to 0.100 wt.%. Preferably, the C may be added to the carbon steel in a range of 0.02 wt.% to 0.07 wt.%. More preferably, the C may be added to the carbon steel in a range of 0.03 wt.% to 0.05 wt.%. Such low-carbon steel has ductility and elongation required for forming a secondary battery can, and sufficiently has room temperature strength required for a secondary battery can.

[0137] The above carbon steel may contain manganese (Mn). The Mn may be added to the carbon steel in a range of 0.1 wt.% to 0.5 wt.%. Preferably, the Mn may be added to the carbon steel in a range of 0.15 wt.% to 0.3 wt.%.

[0138] Additionally, the carbon steel may include Si (silicon). The Si may be added to the carbon steel in a range of more than 0.001 wt.% and less than or equal to 0.5 wt.%. Preferably, the Si may be added to the carbon steel in a range of more than 0.01 wt.% and less than or equal to 0.02 wt.%.

[0139] Additionally, the carbon steel may include P (phosphorus). The P may be added to the carbon steel in a range of more than 0.001 wt.% and less than 0.02 wt.%. Preferably, the P may be added to the carbon steel in a range of more than 0.003 wt.% and less than 0.008 wt.%.

[0140] Additionally, the carbon steel may include S (sulfur). The S may be added to the carbon steel in an amount of less than 0.001 wt.%. Preferably, the S may be added to the carbon steel in an amount of less than 0.0001 wt.%.

[0141] The above carbon steel contains a precipitation strengthening element (X, Y). The precipitation strengthening element (X, Y) may contain at least one element from a group of elements including Ti and Nb. Preferably, the precipitation strengthening element (X) may be Ti, and the precipitation strengthening element (Y) may be Nb.

[0142] Carbon steel, which contains the five major elements, experiences microstructural changes starting at 500 degrees Celsius, leading to a decrease in strength. In other words, simply adjusting the content of the five major elements in carbon steel has limited strength enhancement potential. Consequently, the high-temperature strength of conventional carbon steel can be significantly reduced compared to its room-temperature strength. This compromises battery cell stability, which is particularly critical during thermal runaway.

[0143] The precipitation strengthening elements (X, Y) added to the carbon steel combine with C of the carbon steel to generate nano-sized precipitates (XC, YC) such as TiC and NbC, thereby inhibiting the growth of crystal grains.

[0144] The above precipitation strengthening elements (X, Y) not only improve the room temperature strength of the can material, but also improve the high temperature strength of the can material. In the embodiment, the high temperature strength means the strength of the material at 500 degrees Celsius or higher.

[0145] Here, the strength improved may be, for example, tensile strength. Accordingly, a cylindrical battery cell manufactured from the above-mentioned can material can have high fracture strength at both room temperature and high temperature.

[0146] At least some (X) of the above precipitation strengthening elements can further improve the high temperature strength of the can material compared to the degree of room temperature strength improvement.

[0147] Accordingly, while ensuring the processability of the can material at room temperature, it is also possible to secure the strength of the metal can that can resist the internal pressure of the battery cell at high temperatures.

[0148] The above precipitation strengthening elements (X, Y) improve the room temperature elongation of the can material.

[0149] Accordingly, the formability for manufacturing a can using the above can material can be further improved.

[0150] At least some (Y) of the above precipitation strengthening elements further improves the high temperature elongation of the can material.

[0151] Accordingly, the metal cans of cylindrical battery cells exposed to high-temperature environments, such as those caused by thermal runaway, can be further expanded to accommodate the high internal pressure. This allows for pressure relief and improved fracture resistance.

[0152] In addition, at least some (Y) of the above precipitation strengthening elements form a thin oxide layer on the surface of carbon steel, thereby increasing electrolytic resistance and corrosion resistance, thereby significantly improving the corrosion resistance of carbon steel suitable for secondary batteries.

[0153] The above precipitation strengthening elements (X, Y) can be added to the carbon steel in a range of more than 0.001 wt.% and less than or equal to 0.100 wt.%. Preferably, the above precipitation strengthening elements can be added to the carbon steel in a range of more than 0.01 wt.% and less than or equal to 0.09 wt.%.

[0154] Preferably, at least a portion (X) of the above precipitation strengthening elements can be added to the carbon steel in a range of 0.01 wt.% to 0.07 wt.%, and more preferably in a range of 0.03 wt.% to 0.05 wt.%. Accordingly, the tensile strength at room temperature can be improved while improving the elongation, and the tensile strength at high temperatures can be further improved.

[0155] When the above X exceeds 0.05 wt.%, the grain growth inhibition effect is no longer increased in the required high-temperature environment of about 600 degrees Celsius, making heat treatment of carbon steel difficult and reducing plating properties. When the above X is less than 0.03 wt.%, the grain growth effect is not expressed.

[0156] Preferably, at least some (Y) of the above precipitation strengthening elements can be added to the carbon steel in a range of 0.03 wt.% or more and 0.09 wt.% or less, and more preferably in a range of 0.05 wt.% or more and 0.07 wt.% or less.

[0157] Accordingly, the tensile strength at room temperature can be improved while further improving the elongation, and the tensile strength at high temperatures can be improved while further improving the elongation.

[0158] When the above Y exceeds 0.07 wt.%, the effect of improving corrosion resistance is minimal, while the room temperature strength of the carbon steel is reduced, so that even if the decrease in the high temperature strength of the carbon steel is suppressed, it is difficult to secure the required high temperature ultimate strength. When the above Y is less than 0.05 wt.%, the effect of improving the formability of the carbon steel is reduced, and the effect of suppressing grain growth at high temperatures is insufficient, so that grains grow even at temperatures lower than 600 degrees Celsius, failing to meet the required high temperature ultimate strength, and the electrolytic resistance and corrosion resistance are weakened, resulting in a decrease in corrosion resistance.

[0159] The structure deformed by the forming process transforms into an equiaxed structure in a high-temperature environment, resulting in a decrease in strength. Therefore, compared to the room-temperature strength of conventional carbon steel, the high-temperature strength is bound to be lower.

[0160] When the carbon steel can material provided in the example is deep-drawn, the metal structure becomes elongated along the length of the can. This metal can's metal structure deforms into a spherical grain structure in a high-temperature environment, resulting in a decrease in strength. The larger the grain size formed by this deformation compared to the original material, the greater the decrease in strength.

[0161] The can material of the example suppresses grain growth by forming precipitates by combining the precipitation strengthening element with carbon at high temperatures. Accordingly, carbon steel with the precipitation strengthening element added as in the example must reach a higher temperature to initiate recrystallization, thereby increasing the recrystallization temperature.

[0162] Accordingly, the metal can of a cylindrical battery cell, which is heated to approximately 500 degrees Celsius due to thermal runaway, can undergo recrystallization only at a higher temperature that is delayed by more than 500 degrees Celsius, thereby suppressing grain growth and thereby suppressing a decrease in high-temperature strength compared to room-temperature strength.

[0163] That is, a cylindrical battery cell using a can manufactured from the above carbon steel material metal plate can have high strength both at room temperature and at high temperature.

[0164] <Embodiment of can material>

[0165] Hereinafter, an embodiment of a can material according to the present invention will be described.

[0166] The alloy compositions of the carbon steel of the first embodiment, the carbon steel of the second embodiment, and the carbon steel of the comparative example are configured as follows.

[0167] Wt.%FeCMnSiTi(X)Nb(Y) Comparative Example Bal. 0.039 0.18 0.013--First Example Bal. 0.034 0.17 0.014 0.043-Second Example Bal. 0.041 0.18 0.014-0.063

[0168] First, C in the carbon steel composition of the comparative example 0.03 Mn0.2 Si 0.01 By adding precipitation strengthening elements (X, Y) respectively, the final C 0.03 Mn 0.2 Si 0.01 Ti(X) 0.05 The composition of and C 0.03 Mn 0.2 Si 0.01 Nb(Y) 0.05 Secondary battery can steel sheets of the first and second embodiments having the composition of were manufactured (S01). Next, the steel sheets were maintained at 500 degrees Celsius for 10 minutes and then cooled in the air to manufacture test pieces. These test pieces were manufactured in the same manner at 550 degrees Celsius, 600 degrees Celsius, and 650 degrees Celsius (S02).

[0169] In order to conduct a tissue analysis of the test pieces manufactured as above, each test piece was cut, molded, polished, and etched to manufacture a test piece for tissue analysis (S03).

[0170] And, using an optical microscope, the above tissue analysis specimen was observed at the same magnification (S04). The tissue thus identified is as shown in Fig. 12.

[0171] Referring to Fig. 12, it can be confirmed that the steel sheet of the comparative example began to recrystallize from 500 degrees Celsius. On the other hand, it can be confirmed that the steel sheets of the first and second embodiments began to recrystallize only when the temperature reached around 600 degrees Celsius. In other words, the steel sheet of the comparative example began to recrystallize around 500 degrees Celsius, which is a temperature that is typically increased by thermal runaway, but the steel sheets of the first and second embodiments began to recrystallize only when the temperature reached an even higher 600 degrees Celsius.

[0172] Meanwhile, it can be confirmed that all alloys of the comparative examples and the first and second embodiments were recrystallized at 650 degrees Celsius. However, in the first and second embodiments, where recrystallization was delayed due to the precipitation strengthening element, it can be confirmed that grain growth was suppressed and grains were refined compared to the comparative examples.

[0173] Next, for the above test pieces, the tensile strength and elongation were measured for the steel plate before heat treatment (S01) and after heat treatment at 500 degrees Celsius (S02), respectively, and the results are as follows.

[0174] Room temperature tensile strength (MPa)Room temperature elongation (%)500℃ tensile strength (MPa)500℃ elongation (%)Comparative example 32225.813855.0First embodiment 355(+33)26.5(+0.7)180(+42)52.0(-3)Second embodiment 348(+26)29.5(+3.7)158(+20)62.0(+7)

[0175] In view of the foregoing, it can be confirmed that, compared to the comparative examples, the room temperature strength and high temperature strength of the can materials of both the first and second embodiments have increased. In addition, compared to the comparative examples, it can be confirmed that the room temperature elongation of the can materials of both the first and second embodiments has increased. In this way, the carbon steel material of the secondary battery can of the example can secure the formability of the material by improving the room temperature strength while not decreasing the room temperature elongation but rather increasing it. In addition, since the high temperature strength can be further increased, the safety of the metal can, which may be subjected to a thermal runaway environment, can be further enhanced.

[0176] Furthermore, the can material of the first embodiment exhibits a higher increase in high-temperature strength than room-temperature strength, confirming that high-temperature strength can be further enhanced despite the increased difficulty in processing the can. Although the high-temperature elongation was slightly lower in the first embodiment, the high-temperature tensile strength was further enhanced, thereby further enhancing the safety required in a thermal runaway environment.

[0177] Meanwhile, the can material of the second embodiment also has a higher increase rate of high-temperature strength than that of room-temperature strength, and not only does the room-temperature elongation increase, but the high-temperature elongation increases even further, thereby increasing the elongation margin of the can against the high can internal pressure occurring in a thermal runaway environment, thereby further securing the can's fracture resistance.

[0178] It should be understood that the above-described embodiments are illustrative in all respects and not restrictive, and the scope of the present invention will be determined by the claims that follow, rather than by the detailed description set forth above. Furthermore, the meaning and scope of the claims that follow, as well as all possible modifications and variations derived from their equivalent concepts, should be construed as encompassing the scope of the present invention.

[0179] Although the present invention has been described with reference to the drawings exemplified above, it is to be understood that the present invention is not limited to the embodiments and drawings disclosed herein, and that various modifications may be made by those skilled in the art within the scope of the technical idea of ​​the present invention. Furthermore, even if the operational effects according to the configuration of the present invention have not been explicitly described while describing the embodiments of the present invention, it is natural that the effects predictable by the corresponding configuration should also be acknowledged.

Claims

1. A metal can sheet for a secondary battery made of carbon steel with Nb added in a ratio of 0.05 wt.% or more and 0.10 wt.% or less.

2. A metal can sheet for a secondary battery, wherein in claim 1, the Nb is added to the carbon steel in a ratio of 0.05 wt.% or more and 0.09 wt.% or less.

3. A metal can sheet for a secondary battery, wherein in claim 2, the Nb is added to the carbon steel in a ratio of 0.05 wt.% or more and 0.07 wt.% or less.

4. A metal can sheet for a secondary battery, wherein the proportion of C contained in the carbon steel in claim 1 is 0.01 wt.% or more and 0.100 wt.% or less.

5. A metal can sheet for a secondary battery, wherein the proportion of C contained in the carbon steel in claim 4 is 0.02 wt.% or more and 0.07 wt.% or less.

6. A metal can sheet for a secondary battery, wherein the proportion of C contained in the carbon steel in claim 5 is 0.03 wt.% or more and 0.05 wt.% or less.

7. In claim 1, the carbon steel further contains Mn, A metal can sheet for a secondary battery, wherein the proportion of manganese contained in the carbon steel is 0.1 wt.% or more and 0.5 wt.% or less.

8. A metal can sheet for a secondary battery, wherein the proportion of manganese contained in the carbon steel according to claim 7 is 0.15 wt.% or more and 0.3 wt.% or less.

9. In claim 1, the carbon steel further contains Si, A metal can sheet for a secondary battery, wherein the proportion of Si contained in the carbon steel is greater than 0.001 wt.% and less than or equal to 0.5 wt.%.

10. A metal can sheet for a secondary battery, wherein the proportion of Si contained in the carbon steel according to claim 9 is 0.01 wt.% or more and 0.02 wt.% or less.

11. A metal can manufactured by deep drawing forming the metal can sheet of any one of claims 1 to 10.

12. The metal can of claim 11; and A secondary battery comprising an electrode assembly built into the above metal can.

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