Secondary battery

Abstract

The present invention relates to a secondary battery, and more particularly, to a secondary battery including an electrode lead electrically connected to an electrode assembly. The present invention provides a secondary battery including a pouch in which an electrode assembly is accommodated, and an electrode lead electrically connected to the electrode assembly and protruding from an inside of the pouch to an outside thereof, wherein at least one of the corners of the electrode lead located inside the pouch has a radius of curvature.

Description

[Technical field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0003644 filed on January 10, 2022 and Korean Patent Application No. 10-2023-0002807 filed on January 9, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a secondary battery, and more particularly to a secondary battery including an electrode lead electrically connected to an electrode assembly housed in a pouch. [Background technology]

[0003] Recently, with the development of technology and increasing demand for mobile devices, the demand for secondary batteries that can be charged and discharged as energy sources has increased rapidly, and as a result, much research has been conducted on secondary batteries that can meet various needs.

[0004] Secondary batteries are also attracting attention as a power source for electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (Plug-In HEVs), etc., which have been presented as a way to solve problems such as air pollution caused by existing gasoline and diesel vehicles that use fossil fuels.

[0005] Among such secondary batteries, much research has been conducted on lithium secondary batteries having high energy density and discharge voltage, and the lithium secondary batteries have been commercialized and widely used. Lithium secondary batteries can have various structures, but typically, there is a high demand for pouch-type secondary batteries that are thin, easy to stack, and can be partially deformed.

[0006] A pouch-type secondary battery is a battery that has an electrode assembly and an electrolyte contained in a pouch-shaped laminate sheet that can accommodate the electrode assembly. Such a laminate sheet is sometimes called a "pouch" in the narrow sense. The pouch includes a metal layer and a resin layer, and the resin layer can be fused by heat.

[0007] In particular, the pouch-type secondary battery has a structure in which a pouch encases an electrode assembly so that the electrode assembly is not exposed to the outside. As shown in FIG 1, the pouch-type secondary battery has a structure in which the outer periphery of a pouch 1 is sealed with an electrode lead 2 electrically connected to an electrode assembly (not shown) protruding out of the pouch 1.

[0008] Meanwhile, when the above-mentioned pouch-type secondary battery constitutes a secondary battery module, the above-mentioned electrode lead 2 may be bent and coupled to a busbar, etc., provided for sensing in the secondary battery module.

[0009] Here, since the electrode lead 2 usually has a shape with sharp corners (see FIG. 1), when the electrode lead 2 is bent (see FIGS. 2a to 2b), there is a problem that damage such as cracks occurs in the area where the corner of the electrode lead 2 contacts the pouch 1 (area A in FIG. 2b).

[0010] In this case, the resin layer of pouch 1 can easily be damaged, making it highly likely that the metal layer inside pouch 1 will come into contact with electrode lead 2. When such contact occurs, electricity may flow, resulting in poor insulation resistance. Furthermore, corrosion may occur, allowing moisture to penetrate into pouch 1, causing serious problems with the quality of the secondary battery. Technology to solve this problem is now required. Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been devised to solve the above problems, and an object of the present invention is to provide a secondary battery including an electrode lead that prevents damage to the pouch. [Means for solving the problem]

[0012] The present invention provides a secondary battery including a pouch in which an electrode assembly is accommodated, and an electrode lead electrically connected to the electrode assembly and protruding from an inside of the pouch to an outside thereof, wherein at least one of the corners of the electrode lead located inside the pouch has a radius of curvature.

[0013] When the width of the corner in the width direction of the electrode lead is Rx and the width of the electrode lead is W, the conditional expression 1 / 50≦Rx / W≦1 / 20 can be satisfied.

[0014] When the width of the corner in the longitudinal direction of the electrode lead is Ry and the length of the electrode lead is L, the conditional expression 1 / 45≦Ry / L≦1 / 20 can be satisfied.

[0015] When the width of the corner in the width direction of the electrode lead is Rx and the radius of curvature of the corner is R, the condition Rx≦R can be satisfied.

[0016] When the width of the corner in the longitudinal direction of the electrode lead is Ry and the radius of curvature of the corner is R, the condition Ry≦R can be satisfied.

[0017] When the width of the corner in the width direction of the electrode lead is Rx and the width of the corner in the length direction of the electrode lead is Ry, the conditional expression 1 / 2≦Rx / Ry≦2 can be satisfied.

[0018] When the radius of curvature is R, the condition 2 mm≦R≦5 mm can be satisfied.

[0019] When the width of the corner in the width direction of the electrode lead is Rx, the conditional expression of 1 mm≦Rx≦2 mm can be satisfied.

[0020] When the width of the corner in the longitudinal direction of the electrode lead is Ry, the conditional expression of 1 mm≦Ry≦2 mm can be satisfied.

[0021] The center of a circle of curvature having the radius of curvature may be located on the electrode lead.

[0022] The secondary battery according to the present invention may further include a plurality of electrode tabs protruding from the electrodes of the electrode assembly and welded to the electrode leads. Effect of the Invention

[0023] The present invention provides a secondary battery including an electrode lead in which at least one of the corners located inside the pouch has a predetermined radius of curvature, thereby preventing damage to the pouch, thereby improving insulation resistance defects of the secondary battery and improving durability. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is a front view showing a secondary battery having a conventional electrode lead shape; [Diagram 2] 2(a) is a side view showing the secondary battery of FIG. 1 as viewed from the side, illustrating the state before the electrode lead is bent, and (b) is a side view showing the secondary battery of FIG. 1 as viewed from the side, illustrating the state after the electrode lead has been bent. [Diagram 3] 1 is a front view showing a secondary battery having an electrode lead shape according to a first embodiment of the present invention; [Figure 4] 4 is an enlarged front view of an electrode lead of the secondary battery of FIG. 3 as viewed from the front. FIG. [Diagram 5] FIG. 13 is a side view of the electrode lead being tested. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. However, the present invention may be embodied in various different forms and should not be construed as being limited to the following embodiments.

[0026] In order to clearly explain the present invention, detailed descriptions of parts that are not relevant to the description or related known technologies that may obscure the gist of the present invention have been omitted, and when referring to components in each drawing in this specification, the same or similar reference symbols are used throughout the specification for the same or similar components.

[0027] Furthermore, the terms and words used in this specification and the claims should not be interpreted in a limited manner to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept that is consistent with the technical idea of ​​the present invention, based on the principle that inventors can appropriately define the concepts of terms in order to best explain their invention.

[0028] The present invention provides a secondary battery 10 including a pouch 11 in which an electrode assembly (not shown) is housed, and an electrode lead 12 electrically connected to the electrode assembly and protruding from the inside of the pouch 11 to the outside, at least one of the corners of the electrode lead 12 located inside the pouch 11 having a predetermined radius of curvature.

[0029] First, the pouch 11 can have various configurations for housing the electrode assembly.

[0030] Specifically, an electrode assembly may be housed in the pouch 11, and the surrounding area in which the electrode assembly is housed may be sealed to physically and chemically protect the electrode assembly from the outside.

[0031] The electrode assembly housed in the pouch 11 may include an electrode (not shown) and a separator (not shown). Specifically, the electrode assembly may include positive and negative electrodes and a separator interposed between the electrodes. Here, the positive electrode may be formed by applying a positive electrode active material to an electrode collector, and the negative electrode may be formed by applying a negative electrode active material to an electrode collector.

[0032] An electrode tab (not shown) that is coupled to an electrode lead 12 (to be described later) may be protruded from the electrode of the electrode assembly.

[0033] Specifically, the electrode tab may be formed by a notching process on the electrode current collector before the electrode active material is coated thereon, or may be attached to a certain portion of the electrode current collector after the electrode active material is coated thereon, thereby connecting the electrode and protruding from the electrode.

[0034] Such electrode tabs can be connected to the electrode lead 12 in various ways, as described below. For example, the electrode tabs can be welded to the electrode lead 12, and such welding can be performed by ultrasonic welding, laser welding, resistance welding, etc.

[0035] Meanwhile, the electrode lead 12 is electrically connected to the electrode assembly and is formed to protrude from the inside to the outside of the pouch 11, and may have various configurations.

[0036] Specifically, one end of the electrode lead 12 is connected to an electrode tab formed on an electrode, and the other end is formed to protrude outside the pouch 11, so that it can be connected to an electrode lead 12 of another secondary battery 10 or an external device (e.g., a busbar). Thus, the electrode lead 12 can electrically connect the electrode assembly housed inside the pouch 11 to another secondary battery or an external device outside the pouch 11.

[0037] Here, the electrode lead 12 may be connected to the electrode tab by welding as described above. In this case, the area on the electrode lead 12 where the electrode tab is welded may be defined as the weld area.

[0038] Such electrode leads 12 can have a variety of shapes.

[0039] Here, the electrode lead 12 may be provided such that at least one of the corners located inside the pouch 11 has a predetermined radius of curvature in order to prevent damage to the inside of the pouch 11. Here, the center of a circle of curvature having the radius of curvature may be located on the electrode lead 12.

[0040] More specifically, as shown in Fig. 3, the electrode lead 12 is located inside the pouch 11, and the corner of the end connected to the electrode tab may have a curved structure with a predetermined radius of curvature, thereby minimizing stress concentrated on sharp corners, edges, or burrs at the corners, thereby preventing damage to the pouch 11. Here, in Fig. 3, the parts of the electrode lead 12 and an electrode lead film 12' described below that are located outside the pouch 11 are indicated by solid lines, and the parts that are located inside the pouch 11 are indicated by dotted lines.

[0041] Meanwhile, when the corners of the electrode lead 12 are curved excessively or insufficiently, the quality and reliability of the secondary battery 10 may be affected.

[0042] That is, if the corners are curved excessively, the area of ​​the welding region between the electrode tab and the electrode lead 12 is not sufficiently secured, which may result in poor bonding between the electrode tab and the electrode lead 12. If the corners are not curved enough, there will still be areas at the corners where stress is concentrated, which may result in damage to the pouch 11.

[0043] Therefore, in the present invention, in order to secure a sufficient welding area between the electrode tab and the electrode lead 12 and to solve the problem of stress concentration at the corners, the widths Rx and Ry of the curved corners are specifically limited by ratios to the radius of curvature R, the width W of the electrode lead 12, and the length L of the electrode lead 12, which will be described in more detail below.

[0044] The width of the corner may include the width of the corner relative to the width direction of the electrode lead 12 and the width of the corner relative to the length direction of the electrode lead 12.

[0045] Here, the width of the corner with respect to the width direction of the electrode lead 12 can be understood as the horizontal width of the corner corresponding to the width direction of the electrode lead 12 (x direction in Figure 4), and the width of the corner with respect to the length direction of the electrode lead 12 can be understood as the horizontal width of the corner corresponding to the length direction of the electrode lead 12 (y direction in Figure 4).

[0046] First, the ratio of the width of the corner to the width of the electrode lead 12 in the width direction may be limited to a specific numerical range.

[0047] Specifically, damage experiments can be carried out to check whether a certain numerical range is satisfied.

[0048] For example, referring to Fig. 5, an experiment may be conducted in which the electrode lead 12a attached to the pouch 11a is repeatedly bent. Specifically, a pouch 11a and a plurality of electrode leads 12a having different radii of curvature R may be prepared. The plurality of electrode leads 12a having different radii of curvature R are repeatedly bent to 90 degrees with respect to the lower surface of the pouch 11a, and the bent electrode lead 12a may repeatedly damage the area in contact with the pouch 11a.

[0049] The damaged pouch is then placed in a 20% copper sulfate (CuSO4) aqueous solution, and a power source applying a voltage of 6 V can be electrically connected to the pouch and the aqueous solution. In other words, the (+) pole of the power source can be electrically connected to the aqueous solution, and the (-) pole of the power source can be electrically connected to the pouch.

[0050] The power source passes a current through the damaged pouch and the copper sulfate aqueous solution for 30 to 60 minutes, and then the exposed portion of aluminum (Al) can be confirmed by the deposition of copper (Cu). That is, for each electrode lead 12a with a different radius of curvature R, it is possible to confirm how much of the aluminum layer is exposed by damaging the pouch 11a. In other words, when copper is deposited, it means that the aluminum layer of the pouch 11a is exposed, and this allows the degree of damage to the pouch 11a to be confirmed.

[0051] According to the above experiment, when the width of the corner in the width direction of the electrode lead 12 is Rx and the width of the electrode lead 12 is W, Rx and W can be limited to satisfy the condition 1 / 50≦Rx / W≦1 / 20.

[0052] When Rx / W is less than 1 / 50, the corner of the electrode lead 12 is not sufficiently curved, and there may still be a region where stress is concentrated. That is, in the course of an experiment, it can be confirmed that when Rx / W is less than 1 / 50, copper is precipitated and the aluminum layer is exposed. On the other hand, when Rx / W exceeds 1 / 20, the corner of the electrode lead 12 is excessively curved, and the area of ​​the welding region cannot be sufficiently secured, so that a problem of a decrease in the welding strength between the electrode tab and the electrode lead 12 may occur. In consideration of this, when the width W of the electrode lead 12 is 40 mm≦W≦50 mm, the width (Rx) of the corner in the width direction of the electrode lead 12 may be limited to 1 mm≦Rx≦2 mm, or more preferably 1.1 mm≦Rx≦1.9 mm. In this case, it is preferable that Rx is set to 1.5 mm.

[0053] In addition, when the width of the corner in the width direction of the electrode lead 12 is Rx and the radius of curvature is R, Rx and R can be limited to satisfy the conditional expression of Rx≦R. This is because when Rx is larger than R (Rx>R), an excessive amount of area is removed from the electrode lead 12 for processing the curved surface of the corner, and even the welding area for joining the electrode tab and the electrode lead 12 may be removed, resulting in a reduction in the welding area and a decrease in the welding strength between the electrode tab and the electrode lead 12.

[0054] Meanwhile, the ratio of the width of the corner to the length of the electrode lead 12 in the longitudinal direction to the length of the electrode lead 12 can be limited within a specific numerical range.

[0055] Specifically, when the width of the corner in the longitudinal direction of the electrode lead 12 is Ry and the length of the electrode lead 12 is L, Ry and L can be limited to satisfy the condition 1 / 45≦Ry / L≦1 / 20.

[0056] This is because, when Ry / L is less than 1 / 45, the corners of the electrode lead 12 are not sufficiently curved, and there may still be areas where stress is concentrated. Similarly, when Ry / L is less than 1 / 45, it can be confirmed in the above experiment that copper is precipitated and the aluminum layer is exposed. On the other hand, when Ry / L is more than 1 / 20, the corners of the electrode lead 12 are excessively curved, and the area of ​​the welding area cannot be sufficiently secured, which may cause a problem of reduced welding strength between the electrode tab and the electrode lead 12.

[0057] Considering this, when the length L of the electrode lead 12 is 40 mm≦L≦45 mm, the width Ry of the corner in the longitudinal direction of the electrode lead 12 may be limited to 1 mm≦Ry≦2 mm, or more preferably 1.1 mm≦Ry≦1.9 mm. In this case, it is preferable that the Ry is set to 1.5 mm.

[0058] In addition, when the width of the corner in the longitudinal direction of the electrode lead 12 is Ry and the radius of curvature is R, Ry and R can satisfy the conditional formula of Ry≦R. This is because when Ry is larger than R (Ry>R), an excessive amount of area is removed from the electrode lead 12 for processing the curved surface of the corner, and even the welded area may be removed, resulting in a reduced weld area and a reduced weld strength.

[0059] Meanwhile, the width of the corner relative to the width direction of the electrode lead 12 and the width of the corner relative to the length direction of the electrode lead 12 may be formed to have various ratios to each other.

[0060] For example, when the width of the corner in the width direction of the electrode lead 12 is Rx and the width of the corner in the length direction of the electrode lead 12 is Ry, Rx and Ry can be limited to satisfy a conditional expression of 1 / 2≦Rx / Ry≦2. This is because, when Rx / Ry is less than 1 / 2 or exceeds 2, the curved surface of the corner of the electrode lead 12 is formed asymmetrically, which may cause a problem of making it difficult to secure a welding area.

[0061] Considering this, when the width Rx of the corner in the width direction of the electrode lead 12 is 1 mm≦Rx≦2 mm, the Ry can be limited to 1 mm≦R≦2 mm. In this case, the Rx and the Ry can each be set to 1.5 mm.

[0062] Meanwhile, the above-mentioned radius of curvature can be set to various values.

[0063] Here, it is also preferable that the radius of curvature is set within a range capable of preventing interference between the welding area of ​​the electrode lead 12 and the portion to be curved when the corner is curved, and ensuring welding strength.

[0064] Considering this, when the width Rx of the corner in the width direction of the electrode lead 12 and the width Ry of the corner in the length direction of the electrode lead 12 are limited to 1 mm to 2 mm, the radius of curvature R can be set to satisfy the condition 2 mm≦R≦5 mm. More preferably, the radius R can be set to 3 mm.

[0065] In other words, when R is less than 2 mm, it can be confirmed in the above experiment that copper is precipitated and the aluminum layer is exposed, resulting in damage to the pouch. On the other hand, when R is more than 5 mm, the corners of the electrode lead 12 are excessively curved, and the welding area cannot be sufficiently secured, which weakens the welding strength between the electrode tab and the electrode lead 12 and may cause a problem of poor bonding.

[0066] Meanwhile, the corners of the electrode lead 12 may be curved in various ways. For example, the corners of the electrode lead 12 may be curved by chamfering using a laser or the like.

[0067] Also, the electrode lead 12 may be formed to protrude outward from at least one end of the pouch 11. As an example, the electrode lead 12 may be formed to protrude in one direction from one end of the pouch 11. As another example, the electrode lead 12 may be formed to protrude in opposite directions from both ends of the pouch 11.

[0068] In addition, an electrode lead film 12' made of an insulating material may be further attached to at least one surface of the electrode lead 12 in order to improve the sealing property of the pouch 11 and to ensure sufficient electrical insulation.

[0069] In addition, the material of the electrode lead 12 can be any material that is electrically conductive. For example, the material of the electrode lead 12 can include at least one of copper (Cu), aluminum (Al), nickel (Ni), iron (Fe), carbon (C), chromium (Cr), and manganese (Mn). However, the material of the electrode lead 12 is not limited to the above-mentioned materials, and can be selected from various materials in consideration of mechanical strength, flexibility, and workability.

[0070] Although the present invention has been described above using limited embodiments and drawings, the present invention is not limited thereto, and various implementations are possible within the technical spirit of the present invention and the equivalent scope of the claims described below by a person having ordinary knowledge in the technical field to which the present invention belongs. [Explanation of symbols]

[0071] 10 Secondary battery 11 Pouch 12 Electrode Lead 12' electrode lead film Rx Corner width relative to electrode lead width Ry Corner width relative to the length of the electrode lead W Electrode lead width L Electrode lead length R radius of curvature

Claims

1. a pouch in which the electrode assembly is housed; an electrode lead electrically connected to the electrode assembly and protruding from the inside of the pouch to the outside, A secondary battery, wherein at least one of the corners of the electrode lead located inside the pouch has a radius of curvature.

2. 2. The secondary battery according to claim 1, wherein, when a width of the corner in a width direction of the electrode lead is Rx and a width of the electrode lead is W, a conditional expression of 1 / 50≦Rx / W≦1 / 20 is satisfied.

3. 2. The secondary battery according to claim 1, wherein, when a width of the corner in the longitudinal direction of the electrode lead is Ry and a length of the electrode lead is L, a conditional expression of 1 / 45≦Ry / L≦1 / 20 is satisfied.

4. 2 . The secondary battery according to claim 1 , wherein a conditional expression of Rx≦R is satisfied, where Rx is a width of the corner relative to a width direction of the electrode lead, and R is a radius of curvature of the corner.

5. 2 . The secondary battery according to claim 1 , wherein, when a width of the corner in the longitudinal direction of the electrode lead is Ry and a radius of curvature of the corner is R, a conditional expression of Ry≦R is satisfied.

6. 2. The secondary battery according to claim 1, wherein the width of the corner relative to the width direction of the electrode lead is Rx and the width of the corner relative to the length direction of the electrode lead is Ry, satisfying a conditional formula of 1 / 2≦Rx / Ry≦2.

7. 2. The secondary battery according to claim 1, wherein, when the radius of curvature is R, a conditional expression of 2 mm≦R≦5 mm is satisfied.

8. 2. The secondary battery according to claim 1, wherein when the width of the corner relative to the width direction of the electrode lead is Rx, a conditional expression of 1 mm≦Rx≦2 mm is satisfied.

9. 2. The secondary battery according to claim 1, wherein when the width of the corner in the longitudinal direction of the electrode lead is Ry, a conditional expression of 1 mm≦Ry≦2 mm is satisfied.

10. The secondary battery according to claim 1 , wherein a center of the circle having the radius of curvature is located on the electrode lead.

11. The secondary battery according to claim 1 , further comprising a plurality of electrode tabs protruding from the electrodes of the electrode assembly and welded to the electrode leads.

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