Electrode current collector

Abstract

The current collector for an electrode according to one embodiment of the present invention includes a base film; and a conductive material provided on at least one of an upper surface and a lower surface of the base film; and the conductive material may be divided into two or more parts along a longitudinal direction or a lateral direction of the base film.

Description

[Technical Field]

[0001] The present invention relates to a current collector for an electrode, and more particularly, to a current collector for an electrode that can enhance the safety of a battery by removing a portion of a conductive metal provided on a base film, thereby inducing a short circuit only in a portion of the battery in the event of a short circuit, and by blocking the short circuit current path in the remaining portion, thereby exhibiting an electrochemical or physical fuse function, such as preventing overheating of the battery. [Background technology]

[0002] As technological development and demand for mobile devices increases, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries, which exhibit high energy density, working potential, and low self-discharge rate, are being commercialized.

[0003] Lithium metal secondary batteries were the first commercialized secondary batteries and used lithium metal as the anode. However, lithium metal secondary batteries suffered from problems such as cell volume expansion, gradual reductions in capacity and energy density due to lithium dendrites forming on the surface of the lithium metal anode, short circuiting due to the continued growth of dendrites, reduced cycle life, and cell stability (explosions and fires). Production of these batteries was halted just a few years after their commercialization. Therefore, carbon-based anodes, which are more stable than lithium metal and can stably store lithium in an ionic state within the lattice and void spaces, were used. The use of these carbon-based anodes led to the commercialization and widespread use of lithium secondary batteries.

[0004] To date, lithium secondary batteries have been dominated by carbon-based or non-carbon-based anode materials, and most anode material development has focused on carbon-based (graphite, hard carbon, soft carbon, etc.) and non-carbon-based (silicon, tin, titanium oxide, etc.) materials.

[0005] Meanwhile, in recent years, as portable electronic devices and information and communication devices have become smaller, there are high expectations for the use of lithium secondary batteries as ultra-small power supply systems for driving these devices.

[0006] Recently, there has been active research and development into polymer-based electronic devices and elements, taking advantage of their advantages such as flexibility, low cost, ease of fabrication, etc. Therefore, in order to use them in miniaturized devices, it is necessary to reduce the thickness or weight of the battery while maintaining the energy density or performance of the lithium secondary battery.

[0007] Furthermore, even if the thickness or weight of a lithium secondary battery is reduced, the safety of the lithium secondary battery must be improved by cutting off or destroying the current path when a short circuit occurs.

[0008] In particular, in the case of large-capacity lithium secondary batteries capable of storing energy of 2 Ah or more, there is an even greater need for battery safety technology that can reduce or cut off short-circuit current when a short circuit occurs.

[0009] The present applicant has proposed the present invention to solve the above-mentioned problems. Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been proposed to solve the above problems, and provides a current collector for an electrode that can reduce thickness or weight compared to a current collector made of metal foil, and at the same time, can function like a fuse when an internal or external short circuit occurs, preventing temperature rise and improving battery stability.

[0011] The present invention also provides an electrode current collector that, in the event of a short circuit in a large-sized lithium secondary battery, prevents the entire electrode current collector from reacting to the short circuit by isolating or separating the short-circuited portion from other portions, allowing the remaining portions of the electrode current collector excluding the short-circuited portion to operate normally. [Means for solving the problem]

[0012] To achieve the above object, a current collector for an electrode according to one embodiment of the present invention includes a base film; and a conductive material provided on at least one of an upper surface and a lower surface of the base film; and the conductive material may be divided into two or more parts along a longitudinal direction or a lateral direction of the base film.

[0013] The conductive material includes a groove formed over the entire conductive material along the longitudinal or lateral direction of the base film, and the conductive material is not formed in the groove.

[0014] The conductive material includes conductive portions formed alternately with the groove portions along the longitudinal or lateral direction of the base film, and the conductive material exists in the conductive portions.

[0015] The conductive portions and the grooves may be formed symmetrically or asymmetrically on the upper and lower surfaces of the base film.

[0016] The base film may be made of a transparent material.

[0017] The conductive portion may include a metal piece or a lead tab that is provided in a direction intersecting the conductive portion and the groove and that is provided to contact the entire conductive portion.

[0018] The insulating polymer layer may be provided between the metal piece or the lead tab and the conductive portion.

[0019] The insulating polymer layer can be melted by heat to attach the metal piece or the lead tab to the conductive portion, and the portion excluding the melted portion can insulate the conductive portion from the metal piece or the lead tab.

[0020] An electrical connection between the lead tab or the metal piece and the conductive portion is formed only at the melting point formed by melting the insulating polymer layer, and the portion where the insulating polymer layer is not melted insulates between the lead tab or the metal piece and the conductive portion. The melting point is formed smaller than the portion where the insulating polymer layer is not melted, so that a current path can be formed through the melting point.

[0021] If a short circuit occurs in one of the plurality of conductive portions divided by the groove portion, the current path through the melting point formed by the insulating polymer layer in contact with the conductive portion where the short circuit occurred is interrupted, and the short circuit does not affect the other conductive portions except for the conductive portion where the short circuit occurred.

[0022] When a short circuit occurs in one of the conductive portions, the conductive portion where the short circuit occurs can be electrically isolated from the other conductive portions by the grooves formed on both sides of the corresponding conductive portion.

[0023] The plurality of conductive portions separated by the grooves may be connected in parallel to the metal piece or the lead tab so that the grooves formed on both sides of the conductive portion where a short circuit occurs can prevent the influence of the short circuit from being transmitted to other conductive portions.

[0024] The conductive portion on one side of the metal piece or the lead tab may have a step portion where the thickness of the conductive material is thinner than the conductive portion. [Effects of the Invention]

[0025] The current collector for an electrode according to the present invention uses a base film made of a non-conductor instead of a metal foil, and a conductive material is coated or plated on the surface of the base film, so that the thickness can be reduced compared to a current collector made of a metal foil.

[0026] The electrode current collector according to the present invention isolates the part of the electrode current collector where the short circuit occurs from the other parts when a short circuit occurs, thereby cutting off the current in the part where the short circuit occurs, thereby reducing the part of the electrode current collector that is involved in the short circuit.

[0027] The electrode current collector according to the present invention has a structure equivalent to a structure in which a number of divided electrode current collectors are electrically connected in parallel to lead tabs. Therefore, when a short circuit occurs, only the divided electrode current collector is separated to cut off the current. This allows the remaining parts of the electrode current collector to continue to be used, thereby improving safety and extending the service life.

[0028] The electrode current collector according to the present invention functions as an electrochemical fuse or a physical fuse, i.e., only a portion of a plurality of divided electrode current collectors where a short circuit occurs induces a short circuit, and other portions where no short circuit occurs cut off the short circuit current path, thereby preventing overheating of the battery and improving battery safety. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a perspective view showing an electrode assembly including a current collector for an electrode according to an embodiment of the present invention; [Figure 2] 1 is an exploded perspective view showing an electrode assembly according to an embodiment of the present invention; [Figure 3] 1 is a plan view showing a state in which a metal piece and a lead tab are attached to a current collector for an electrode according to an embodiment of the present invention. [Figure 4] 4A and 4B are a plan view and a cross-sectional view showing the electrode current collector according to FIG. 3. [Figure 5] 4A and 4B are a plan view and a cross-sectional view for explaining the function of the electrode current collector to which the metal piece and lead tab according to FIG. 3 are attached. [Figure 6] 6 is a view for explaining a state in which a metal piece and a lead tab are welded to the electrode current collector in FIG. 5. FIG. [Figure 7]7 is a diagram for explaining when a short circuit occurs in the electrode current collector to which the metal piece and lead tab according to FIG. 6 are attached. FIG. [Figure 8] FIG. 4 is a plan view showing a modified example of the electrode current collector shown in FIG. 3. [Figure 9] FIG. 4 is a perspective view showing a current collector for an electrode according to another embodiment of the present invention. [Figure 10] FIG. 10 is a plan view showing a current collector for an electrode according to still another embodiment of the present invention. [Figure 11] FIG. 11 is a cross-sectional view taken along the line CC in FIG. [Figure 12] 1 is a graph showing the results of reducing or cutting off short-circuit current when an external short circuit occurs in a secondary battery according to a method of connecting a lead tab to a current collector for an electrode according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to or constrained by the embodiments. The same reference numerals in the drawings denote the same elements.

[0031] FIG. 1 is a perspective view of an electrode assembly including an electrode current collector according to one embodiment of the present invention. FIG. 2 is an exploded perspective view of an electrode assembly according to one embodiment of the present invention. FIG. 3 is a plan view showing a state in which a metal piece and a lead tab are attached to an electrode current collector according to one embodiment of the present invention. FIG. 4 is a plan view and a cross-sectional view of the electrode current collector according to FIG. 3. FIG. 5 is a plan view and a cross-sectional view illustrating the function of the electrode current collector to which the metal piece and lead tab according to FIG. 3 are attached. FIG. 6 is a diagram illustrating a state in which the metal piece and the lead tab are welded in the electrode current collector according to FIG. 5. FIG. 7 is a diagram illustrating a case in which a short circuit occurs in the electrode current collector to which the metal piece and the lead tab according to FIG. 6 are attached. FIG. 8 is a plan view showing a modified example of the electrode current collector shown in FIG. 3. FIG. 9 is a perspective view of an electrode current collector according to another embodiment of the present invention. FIG. 10 is a plan view of an electrode current collector according to yet another embodiment of the present invention. FIG. 11 is a cross-sectional view taken along line CC of FIG. 10.

[0032] 1 and 2 show an electrode assembly 10 including an electrode current collector 100 according to the present invention. In the case of FIGS. 1 and 2, the electrode current collector 100 according to the present invention is a positive electrode current collector. To be used in the electrode assembly 10, a positive electrode active material 103 must be coated on the surface of the electrode current collector 100.

[0033] Meanwhile, the negative electrode current collector 200 may have a negative electrode metal foil 201 coated with a negative electrode active material 203, and a negative electrode lead tab 290 may be connected to one end of the negative electrode metal foil 201 in the longitudinal direction.

[0034] A separator 300 may be disposed between the negative electrode current collector 200 and the electrode (positive electrode) current collector 100 according to the present invention. When the negative electrode current collector 200 and the positive electrode current collector 100 are stacked in order above and below the separator 300 as shown in FIG. 2, the electrode assembly 10 shown in FIG. 1 is obtained.

[0035] For ease of explanation, the positive electrode current collector 100 will be referred to as an electrode current collector below.

[0036] 3 and 4 show an electrode current collector 100 according to one embodiment of the present invention. Unlike the negative electrode current collector 200 mentioned above, the electrode current collector 100 does not use a metal foil.

[0037] The current collector for electrodes (100) according to one embodiment of the present invention has a resistance value greater than that of a metal foil current collector, and therefore, the limiting current value of the current flowing through the current collector can be adjusted. In addition, when an internal short circuit occurs in a secondary battery, the short circuit current can be reduced or heat generation can be prevented because the flow of current can be obstructed due to damage to the base film.

[0038] A lithium secondary battery including the current collector 100 for an electrode according to the present invention may have the characteristics or concept of a Max Current Limited Battery (MCLB). Hereinafter, the current collector for an electrode according to the present invention, which enables the realization of an MCLB, will be described.

[0039] The electrode current collector 100 according to one embodiment of the present invention is a positive electrode current collector and has a higher resistance than the positive electrode current collector of an existing battery, i.e., a positive electrode current collector made of metal foil. Therefore, it is possible to adjust the limit current and also to cut off or collapse the current path in the event of an internal short circuit, thereby reducing the short circuit current or reducing the heat generation that occurs in the event of a short circuit, thereby improving the safety of the battery.

[0040] One feature of the electrode current collector 100 according to one embodiment of the present invention is that it does not use a metal foil, but uses a base film 101 as the basic material, and a thin metal is applied or coated onto the base film 101.

[0041] Referring to Figures 3 and 4, a current collector 100 for an electrode according to one embodiment of the present invention may include a base film (polymer film) 101; and a conductive material 102 provided on at least one of the upper and lower surfaces of the base film 101.

[0042] Here, the conductive material 102 can function as an electrochemical fuse, thereby preventing short circuits. The electrochemical properties of the conductive material 102 will be described later.

[0043] The base film 101 may be provided in a strip shape having a certain length. Here, the base film 101 is preferably made of a non-conductive material such as polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), or polyethylene terephthalate (PET).

[0044] The base film 101 has a thickness of 50 μm or less, and preferably has a thickness of 1.4 μm to 50 μm. The electrode current collector 100 according to an embodiment of the present invention can reduce the thickness or weight of a battery compared to when a conventional metal foil current collector is used, and by using a non-conductive base film 101 having a thickness of 1.4 μm to 50 μm as the basic component of the current collector 100, the overall thickness or weight of a lithium secondary battery including the electrode current collector 100 according to an embodiment of the present invention can be reduced.

[0045] 3 and 4, a current collector 100 for an electrode according to an embodiment of the present invention may include a base film 101 and a conductive material 102 provided on a surface of the base film 101.

[0046] When the electrode current collector 100 is a positive electrode current collector, the conductive material 102 may be made of aluminum (Al) metal. The conductive material 102 can also be said to be a conductive layer that forms the outermost surface of the electrode current collector 100.

[0047] The conductive material 102 may be formed to adjust or lower the limiting current or maximum current of the electrode current collector 100. In other words, the conductive material 102 is an aluminum metal plated or coated on the recessed or embossed surface of the base film 101 in order to control the conductivity of the electrode current collector 100. When the emphasis is on the state of being deposited or coated (applied) on the surface of the base film 101, the conductive material 102 can also be referred to as a conductive layer. Hereinafter, it will be made clear that the concept of the conductive material 102 includes a conductive layer.

[0048] By adjusting the coating amount or coating thickness of the conductive material 102 plated (coated) or evaporated on the surface of the base film 101, the maximum amount of current flowing through the electrode current collector 100 can be controlled or reduced, thereby improving the safety of the lithium secondary battery and ensuring the safety of the battery in the event of a short circuit.

[0049] In other words, the limit current or maximum current flowing through the electrode current collector 100 can be adjusted depending on the thickness or amount of the conductive material 102 formed on the surface of the base film 101. In this way, the conductive material 102 of the electrode current collector 100 according to one embodiment of the present invention can realize the characteristics or concept of a Max Current Limited Battery (MCLB) of a lithium secondary battery.

[0050] Furthermore, when a physical internal or external short circuit occurs, the base film 101 may melt, preventing the generation of a sudden current, thereby improving the safety of the battery.

[0051] The conductive material 102 can be formed on the surface of the base film 101 by various methods. For example, aluminum metal, which is the conductive material 102, can be formed on the surface of the base film 101 by sputtering or evaporation coating. Because aluminum oxidizes easily, it is not easy to form the conductive material 102 on the surface of the base film 101 by electroplating.

[0052] The amount (weight) or thickness of the conductive material 102 coated can control the conductivity of the electrode current collector 100 or ensure the safety of the battery, so when plating or coating, it is necessary to use a method that can control or adjust the thickness or weight of the conductive material 102.

[0053] The conductive material 102 may be formed on only one surface or both surfaces of the base film 101. In this case, the conductive material 102 is preferably formed to a thickness of 0.3 μm based on the minimum cross section and 2.5 μm based on the maximum cross section.

[0054] In the electrode current collector 100 according to an embodiment of the present invention, current can flow through the conductive material 102, so the conductive material 102 must be well maintained as coated on the surface of the base film 101. For this reason, it is preferable to perform a surface treatment on the base film 101 to increase the bonding strength between the conductive material 102 and the base film 101.

[0055] If the adhesive strength between the conductive material 102 and the base film 101 is poor, the conductive material 102 may separate or detach from the surface of the base film 101 when the electrolyte is injected, so it is important to increase the adhesive strength between the conductive material 102 and the base film 101.

[0056] The surface of the base film 101 may be subjected to a surface treatment to enhance the adhesive strength or bonding strength with the conductive material 102 .

[0057] In order to increase the bonding strength between the conductive material 102 and the base film 101, it is preferable to subject the surface of the base film 101 to a corona treatment.

[0058] Meanwhile, the electrode current collector 100 according to an embodiment of the present invention is a current collector used as a positive electrode of a secondary battery, and unlike existing current collectors made of metal foil, can improve the safety of the secondary battery because the conductive material 102 applied or coated on the base film 101 functions as a fuse to interrupt short-circuit current.

[0059] Generally, when an internal or external short circuit occurs in a secondary battery, a heat generation phenomenon occurs in which the temperature of the secondary battery rises due to the short circuit current, and there is a risk of the battery exploding due to the heat generation. In contrast, in the case of a secondary battery using the electrode current collector 100 according to an embodiment of the present invention as a positive electrode, even if an internal or external short circuit occurs, the temperature of the secondary battery is prevented from rising and the short circuit current is cut off, thereby ensuring the safety of the battery.

[0060] The conductive material 102 applied or coated on the base film 101 functions as a current path, but when a short circuit occurs, the conductive material 102 reacts with the electrolyte and cracks into small pieces as if corroded, cutting off the current path and preventing further short-circuit current from flowing.

[0061] Meanwhile, in the electrode current collector 100 according to one embodiment of the present invention, the conductive material 102 may be divided into two or more parts along the longitudinal or lateral direction of the base film 101. In Fig. 4, an arrow S indicates the feed direction or longitudinal direction of the base film 101. The lateral direction of the base film 101 refers to the relatively shorter direction of the horizontal or vertical directions.

[0062] 4, the conductive material 102 can include grooves 102b formed throughout the conductive material 102 along the longitudinal or lateral direction of the base film 101, and conductive portions 102a formed alternately with the grooves 102b. Fig. 4 shows a case where the conductive portions 102a and grooves 102b of the conductive material 102 are formed along the longitudinal or feed direction S of the base film 101.

[0063] Here, the conductive material 102 is not formed in the recessed groove portion 102b, and the conductive material 102 is present in the conductive portion 102a.

[0064] FIG. 4(a) is a plan view showing the groove portion 102b and the conductive portion 102a formed along the longitudinal direction of the base film 101, and FIG. 4(b) is a cross-sectional view taken along the cutting line AA in FIG. 4(a).

[0065] The grooves 102b formed in the conductive material 102 can be formed by coating or depositing the conductive material 102 over the entire upper or lower surface of the base film 101, and then cutting or patterning the conductive material 102 using a laser. That is, after forming the conductive material 102 on the base film 101, the grooves 102b can be formed by removing the area where the grooves 102b are to be formed using a laser.

[0066] On the other hand, in some cases, the grooves 102b can be formed by using a chemical material or a substance that reacts with the aluminum metal that is the conductive material 102, without using a laser.

[0067] If the base film 101 is made of a transparent material, the laser that formed the groove 102b can pass through the base film 101. As shown in FIG. 6 , when the conductive material 102 is formed on both the top and bottom surfaces of the base film 101, i.e., both surfaces, a laser is irradiated onto the conductive material 102 formed on the top surface of the base film 101, thereby removing the conductive material 102 in the irradiated area and forming the groove 102b. At this time, since there is no conductive material 102 in the area where the groove 102b is formed, the base film 101 is present at the bottom of the groove 102b. The laser irradiated onto the bottom of the groove 102b passes through the transparent base film 101 and reaches the conductive material 102 formed on the bottom surface of the base film 101, forming the groove 102b in the conductive material 102 formed on the bottom surface of the base film 101. At this time, the recessed grooves 102b formed on the upper and lower sides of the base film 101 are symmetrical, and their shapes and positions match each other. Similarly, the upper and lower conductive parts 102a are symmetrical, and their shapes and positions match each other (see FIG. 6(a)).

[0068] If the base film 101 is not made of a transparent material, the laser cannot pass through the base film 101, and therefore the laser must be irradiated separately onto the conductive material 102 formed on the upper and lower surfaces of the base film 101. In this case, the conductive portions 102a and the groove portions 102b formed on the upper and lower surfaces may be asymmetrical, and may not match in shape or position (see FIG. 6(b)).

[0069] Thus, the conductive material 102 can include groove portions 102b formed along the longitudinal or lateral direction of the base film 101 so that no conductive material is present throughout the conductive material 102, and conductive portions 102a formed alternately with groove portions 102b along the longitudinal or lateral direction of the base film 101. Unlike groove portions 102b, conductive material 102 is present in conductive portions 102a.

[0070] In addition, the conductive portion 102a and the groove portion 102b may be formed symmetrically or asymmetrically on the upper and lower surfaces of the base film 101, but may be symmetrical when the base film 101 is made of a transparent material that allows laser light to pass through.

[0071] As shown in FIG. 5, the electrode current collector 100 according to an embodiment of the present invention may include a metal element 120 or a lead tab 190 that is disposed in a direction intersecting the conductive portion 102a and the groove portion 102b and is disposed so as to contact the entire conductive portion 102a.

[0072] 5, it is preferable that conductive portion 102a and groove portion 102b are formed along the longitudinal direction or feed direction of base film 101, while metal piece 120 is disposed along the lateral direction of base film 101. In contrast, lead tab 190 may be provided in the same direction as metal piece 120, or may be provided along the direction in which groove portion 102b or conductive portion 102a is formed.

[0073] The conductive portion 102 a of the conductive material 102 may be located between the base film 101 and the metal piece 120 .

[0074] Because the conductive portions 102a of the conductive material 102 are separated by the grooves 102b, a means for electrically connecting all of the conductive portions 102a is required. The metal piece 120 can serve to connect all of the conductive portions 102a. Therefore, the metal piece 120 must be provided in a position or shape that allows it to contact all of the conductive portions 102a separated by the grooves 102b.

[0075] In order for the metal piece 120 to contact all of the conductive portions 102a, it is preferable that it be arranged in the short direction of the base film 101. When the conductive portions 102a and the groove portions 102b are formed in the horizontal direction as shown in Fig. 5, it is preferable that the metal piece 120 be formed in the vertical direction, but it is not necessary that the metal piece 120 be arranged in the vertical direction; even if it is arranged diagonally, it is sufficient that it is arranged so as to contact all of the conductive portions 102a.

[0076] Meanwhile, the lead tab 190 can be connected by placing the metal piece 120 on the surface opposite to the side where the lead tab 190 is attached or on both surfaces of the base film 101 and welding the lead tab 190 to the metal piece 120. However, the lead tab 190 cannot be connected unless the base film 101 melts at a temperature lower than the welding temperature of the lead tab 190. Therefore, it is preferable that the base film 101 has a melting point high enough to melt the lead tab 190 during the welding process.

[0077] The metal piece 120 may be provided on only one of both surfaces of the base film 101 as shown in FIG. 5, or may be provided on both surfaces of the base film 101 as shown in FIG.

[0078] The metal piece 120 can serve to secure a position on the base film 101 to which the lead tab 190 is to be welded. That is, the metal piece 120 can serve as a connecting portion of the lead tab 190.

[0079] The metal piece 120 is preferably formed to have a thickness of 5 μm or more.

[0080] As described above, the metal piece 120 is preferably in the form of a thin metal film or metal foil having a thickness of 5 μm or more, but is not necessarily limited to this form. That is, the metal piece 120 may be provided in the form of a thin film, foil, or mesh.

[0081] The metal piece 120 is preferably made of aluminum foil or SUS 316L foil.

[0082] 5 and 6, the current collector 100 for an electrode according to an embodiment of the present invention may include a lead tab 190 for connection to an external device.

[0083] In conventional metal foil current collectors, lead tabs can be welded directly to the metal foil, but in the current collector 100 for an electrode according to an embodiment of the present invention, the structure corresponding to the conventional metal foil is the base film 101, so it is not possible to weld the lead tabs directly to the base film 101. The current collector 100 for an electrode according to an embodiment of the present invention solves this problem by further positioning metal pieces 120 on both sides of the base film 101 or on the side opposite to the side to which the lead tabs 190 are connected, and welding the lead tabs 190 to the metal pieces 120.

[0084] In the electrode current collector 100 according to an embodiment of the present invention, the lead tab 190 can be welded to the metal piece 120 by ultrasonic welding, laser welding, or spot welding.

[0085] 6, a lead tab 190 may be connected to one of the metal pieces 120 provided on the upper and lower surfaces of the base film 101. Although not shown, the lead tab 190 may be connected to one surface of the base film 101, and the metal piece 120 may be provided on the other surface of the base film 101 facing the lead tab 190. In this case, the conductive material 102 is positioned between the base film 101 and the metal piece 120 or between the base film 101 and the lead tab 190. In other words, the conductive material 102 may be first applied or coated on the upper and lower surfaces of the base film 101, and then the metal piece 120 may be positioned on the conductive material 102 or may be provided in contact with the conductive material 102 so as to be electrically connected to the conductive material 102.

[0086] When the lead tab 190 is welded to one of the metal pieces 120 provided on both sides of the base film 101, the base film 101 melts, connecting the metal pieces 120 provided on both sides of the base film 101 to each other, and as a result, the lead tab 190 can be electrically connected to the conductive material 102 provided on both sides of the base film 101 at the same time.

[0087] When the lead tab 190 is ultrasonically welded, laser welded, or spot welded to the metal piece 120 on the top surface of the base film 101 with the metal piece 120 and the conductive material 102 provided on both the top and bottom surfaces of the base film 101, a portion of the base film 101 may melt. If the welding heat generated when welding the lead tab 190 is higher than the melting point of the base film 101, the base film 101 may melt during the welding process.

[0088] In this way, in the melted portion of the base film 101, the base film 101 is not present, so the upper and lower metal pieces 120 can come into direct contact with each other. At this time, the metal pieces 120 are also melted by the welding heat, so the upper and lower metal pieces 120 are joined together. Therefore, in the unmelted portion of the base film 101, the upper and lower metal pieces 120 are directly melt-bonded together, so that the lead tab 190 welded to any one of the metal pieces 120 can be electrically connected not only to the upper and lower metal pieces 120 but also to the conductive material 102 formed on the upper and lower surfaces of the base film 101.

[0089] In the electrode current collector 100 according to one embodiment of the present invention, even if a portion of the base film 101 melts due to welding heat, the metal piece 120 remains connected to the base film 101, so that the lead tab 190 can be connected.

[0090] However, in some cases, lead tab 190 can be welded to metal piece 120 even when base film 101 is not melted.

[0091] 5 and 6, an insulating polymer layer 130 may be formed between the conductive material 102 and one surface of the metal piece 120 facing the conductive material 102. The insulating polymer layer 130 serves to attach the metal piece 120 to the surface of the base film 101 or the surface of the conductive material 102, or to insulate the conductive material 102 from the metal piece 120.

[0092] If the lead tab 190 directly contacts the conductive material 102 without the metal piece 120, an insulating polymer layer 130 may be provided between the lead tab 190 and the conductive material 102.

[0093] More precisely, an insulating polymer layer 130 may be formed between the metal piece 120 or lead tab 120 and the conductive portion 102a.

[0094] The insulating polymer layer 130 is preferably made of an adhesive or sticky material, and may be made of a polymer material or in the form of a polymer film.

[0095] When the insulating polymer layer 130 is provided in the form of a polymer film, it is preferable that the thickness is less than 50 μm. If the thickness of the insulating polymer layer 130 exceeds 50 μm, welding may not be smooth and resistance may increase.

[0096] The insulating polymer layer 130 can melt at the same temperature as the base film 101 or at a lower temperature than the base film 101. That is, it is preferable that the insulating polymer layer 130 has the same melting point as the base film 101 or a melting point lower than the melting point of the base film 101.

[0097] The insulating polymer layer 130 may be formed of a polymer material such as polyethylene (PE), polypropylene (PP), polyvinylidene difluoride (PVDF), polyethylene terephthalate (PET), polyimide (PI), or the like, or may be formed of a polymer material having an adhesive component such as ethylene vinyl acetate (EVA) or an acrylate-based compound.

[0098] The insulating polymer layer 130 not only serves to attach the metal piece 120 or the lead tab 190 to the surface of the conductive material 102 or the conductive portion 102a, but also serves as an insulating layer. When the lead tab 190 is welded, the insulating polymer layer 130 melts or dissolves due to the welding heat and is electrically connected to the conductive material 102 or the conductive portion 102a, but the portions other than the melted portion are insulated by the insulating polymer layer 130.

[0099] In the event of an external short circuit, if the electrically connected portion between the lead tab 190 and the conductive material 102 is limited to the melted portion, the conductive material 102 in the melted portion will react to reduce or cut off the current. If the electrically connected portion is wide, it may be difficult to cut off the current because more reactions are required. Therefore, it is preferable to provide an insulating polymer layer 130 having insulating properties between the conductive material 102 and the metal piece 120 or between the conductive material 102 and the lead tab 190.

[0100] Referring to FIG. 6, the insulating polymer layer 130 and the metal piece 120 attached to the conductive material 102 or conductive portion 102a provided on both sides of the base film 101 may be provided at the same positions relative to the base film 101.

[0101] 6(a), the insulating polymer layer 130 located between the metal piece 120 and the conductive portion 102a melts to weld the lead tab 190, and the electrical connection between the lead tab 190 or the metal piece 120 and the conductive portion 102a is made only at the melting point W where the insulating polymer layer 130 melts and connects.

[0102] The melting point W formed when insulating polymer layer 130 and base film 101 are melted by the heat generated during welding is small compared to the size of polymer insulating layer 130. Referring to Figure 6(a), it can be seen that the size G1 of melting point W is also small compared to the width of conductive portion 102a.

[0103] In this manner, when the insulating polymer layer 130 is present, an electrical connection between the lead tab 190 or the metal piece 120 and the conductive portion 102a is formed only at the melting point when the lead tab 190 is welded, and a current path is formed at a very small melting point, so the portion excluding the melting point, i.e., the portion of the insulating polymer layer 130 that does not melt, can insulate the lead tab 190 or the metal piece 120 from the conductive portion 102a. In addition, the remaining portion excluding the melting point may be exposed to the electrolyte or may be easily penetrated by the electrolyte.

[0104] When an insulating polymer layer 130 made of an insulating material is present, the electrical connection of the lead tab 190 is made only at a small melting point (site) formed as the insulating polymer layer 130 melts and connects, which is advantageous for cutting off the current path in the event of a short circuit and can improve the safety of the battery.

[0105] In addition, it is preferable that at least one of the upper and lower surfaces of base film 101 has a structure in which there is a portion to which insulating polymer layer 130 is not attached, so that the electrolyte can easily penetrate (or be impregnated). That is, it is advantageous to have a porous structure that is favorable for electrolyte impregnation, or to have a structure in which insulating polymer layer 130 is provided on only one surface of base film 101, on either metal piece 120 or conductive material 102, so that the electrolyte can penetrate through the side where there is no insulating polymer layer. In addition, if the electrolyte has the property of gelling, this can be advantageous for penetration.

[0106] The positive electrode current collector 100 according to the present invention described above requires metal pieces 120 or lead tabs 190 on both the top and bottom of the base film 101 coated with the conductive material 102 in order to attach the metal pieces 120 and lead tabs 190 while current is passed through both the top and bottom of the base film 101. For example, the base film may have metal pieces on both the top and bottom, or one side of the base film may have a metal piece and the other side may have a lead tab. If the base film has metal pieces or lead tabs on only one side, the adhesive strength or tensile strength of the lead tab welding area may be low, making it difficult to use.

[0107] In addition, to ensure current path interruption performance and enhance battery safety when an external short circuit occurs, an insulating polymer layer 130 made of a polymer that is insulating and soluble is required between the metal piece 120 or lead tab 190 and the conductive portion 102a. In this case, the insulating polymer layer 130 allows electrical connection only at the fusion points formed when the lead tab 190 is welded.

[0108] Meanwhile, in a secondary battery including the electrode current collector 100 according to an embodiment of the present invention, if an external short circuit occurs in one of the conductive parts 102a separated by the groove 102b, the short circuit does not affect the other conductive parts 102a because the current path is cut off at the melting point of the conductive part 102a where the short circuit occurred. This will be described in detail below with reference to the drawings.

[0109] 5 and 6, in an electrode current collector 100 according to an embodiment of the present invention, each conductive portion 102a can function as an individual unit cell (UC). Each conductive portion 102a is completely separated by a groove 102b, and all conductive portions 102a are connected to a single metal piece 120. Therefore, the plurality of conductive portions 102a separated by the groove 102b can be considered to have the same or equivalent shape as those connected in parallel to the metal piece 120 or the lead tab 190.

[0110] Therefore, the electrode current collector 100 according to one embodiment of the present invention has a configuration in which each conductive portion 102a capable of performing the electrical function of an individual current collector is connected in parallel to the metal piece 120 or the lead tab 190 as a unit cell (UC).

[0111] 6(a), each unit cell (UC) is divided by a groove portion 102b, and the unit cell (UC) may include a metal piece 120, an insulating polymer layer 130, a conductive portion 102a, and a base film 101. Here, each unit cell (UC) may include at least one melting point W.

[0112] The electrode current collector 100 shown in FIG. 6(a) is different in that the conductive portion 102a and the groove portion 102b are provided in the same symmetrical shape above and below the base film 101, whereas the electrode current collector 100 shown in FIG. 6(b) is provided in an asymmetrical shape.

[0113] In the case of Figure 6(b), the grooves 102b formed on the upper surface of the base film 101 and the grooves 102b formed on the lower surface of the base film 101 are not positioned on a perpendicular line. In the case of Figure 6(b), the unit cells UC may be divided based on the melting points W. That is, each unit cell UC may be divided to include at least one melting point W and one groove 102b located on the upper surface of the base film 101 and one groove 102b located on the lower surface.

[0114] 7(a) is a diagram illustrating a case where an external short circuit C occurs in the conductive portion 102a located at the lowest position of the conductive material 102. The unit cell (UC) including the conductive portion 102a in which the external short circuit (see C1) occurs is electrically isolated from the other conductive portions by the recessed groove portions 102b formed on both sides of the conductive portion 102a, and therefore the other conductive portions 102a are not affected by the short circuit.

[0115] When a short circuit occurs in one of the conductive parts 102a, the current path formed at the melting point W of the insulating polymer layer 130 located in the unit cell (UC) including the conductive part 102a where the short circuit occurred is cut off, and the short circuit does not affect other conductive parts other than the conductive part 102a where the short circuit occurred. 7(a), when a short circuit occurs in the lowest conductive portion 102a among the conductive portions 102a divided by the groove portion 102b, almost all of the current in the remaining conductive portions 102a flows to the short-circuited conductive portion 102a. When the current flowing through the remaining conductive portions 102a flows to the short-circuited conductive portion 102a, the short-circuit current path is interrupted at the short-circuited conductive portion 102a, and the short-circuited conductive portion 102a is isolated from the remaining conductive portions 102a.

[0116] 7(b), when a short circuit (see C, C2) occurs in the conductive portion 102a, the resistance at the contact point between the insulating polymer layer 130 and the conductive portion 102a is high, and the current instantaneously increases, causing the contact point to melt or the potential at the contact point to drop to near the negative electrode potential (i.e., <0.3 volts, negative electrode Li metal). When the conductive material 102 reacts with the electrolyte, the conductive material 102 cracks as if corroded, thereby reducing (decreasing) or blocking the short-circuit current. At this time, the melting point W at which the current path is formed is very small, and the thickness or amount of the conductive material 102 involved in the current path is also small. If the thin or small conductive material 102 reacts with the electrolyte and cracks into small pieces as if corroded, the current path is blocked, and the short-circuit current decreases (decreasing) or no longer flows.

[0117] In this way, in the electrode current collector 100 according to an embodiment of the present invention, the plurality of conductive portions 102a separated by the grooves 102b are connected in parallel to the metal pieces 120 or the lead tabs 190, so that a short-circuited conductive portion 102a does not affect the other conductive portions due to the grooves 102b formed on both sides of the conductive portion 102a. That is, because the grooves 102b block the flow of short-circuit current to the other conductive portions 102a, side reactions occur only in the short-circuited conductive portion 102a, and not in the remaining conductive portions 102a. Therefore, the remaining unit cells (UCs) that are not short-circuited can function normally, thereby extending the service life of a secondary battery using the electrode current collector 100 according to an embodiment of the present invention.

[0118] Furthermore, in the unit cell (UC) including the corresponding conductive part 102a where the short circuit has occurred, side reactions are concentrated at the part where the insulating polymer layer 130 contacts the conductive material 102, and the short circuit current is blocked, thereby preventing safety accidents such as battery explosion or fire due to temperature rise, and ensuring the safety of the secondary battery.

[0119] As described above, the conductive material 102 of the electrode current collector 100 according to another embodiment of the present invention exhibits an electrochemical fuse function or a short-circuit current interruption function at the relatively thin portion 102c, thereby preventing the battery temperature from rising when a short circuit occurs and interrupting the short-circuit current, thereby ensuring the safety of the battery.

[0120] 8 shows a modified example of an electrode current collector according to an embodiment of the present invention. Unlike the electrode current collector shown in FIG. 7, the grooves 102b may be formed in a curved shape rather than a straight line. The grooves 102b may be formed in various shapes by using a laser after the surface of the base film 101 is completely coated with the conductive material 102. However, it is preferable that the grooves 102b be formed in a shape with a certain direction so that all the conductive portions 102a formed on the base film 101 can be connected to one metal piece 120 or lead tab 190.

[0121] FIG. 9 illustrates an electrode current collector 100 according to another embodiment of the present invention. Referring to FIG. 9, a difference is that grooves are formed not only in the conductive material 102 but also in the positive electrode active material 103 coated on the surface of the conductive material 102. When the conductive material 102 is first coated on the base film 101 and then the positive electrode active material 103 is coated on the conductive material 102 and patterned using a laser or chemical material, not only the conductive material 102 but also the positive electrode active material 103 is removed from the patterned portion, and a removed portion 103b may be formed in the positive electrode active material. The removed portion 103b formed in the positive electrode active material 103b is connected to the groove portion 102b of the conductive material 102. In FIG. 9, reference numeral 103a denotes a remaining portion of the positive electrode active material.

[0122] 10 and 11 show a current collector 100 for an electrode according to still another embodiment of the present invention.

[0123] 10, a step 102c where the thickness of the conductive material 102 is relatively thin may be formed in the conductive material 102 or conductive portion 102a adjacent to one side of the metal piece 120 or lead tab 190. That is, the step 102c is not a portion where the conductive material 102 is completely absent like the groove 102b, but is a portion where the conductive material 102 is thinner than the conductive portion 102a.

[0124] Here, the step portion 102c may have a rectangular cross-sectional shape as shown in Fig. 11(a) or an inverted triangular cross-sectional shape as shown in Fig. 11(b). The step portion 102c may have other shapes in addition to the shape shown in Fig. 11.

[0125] The stepped portion 102c is formed on one side of the metal piece 120 or the lead tab 190, and is preferably formed in a portion where the area of ​​the conductive portion 102a is relatively large. Referring to Fig. 10, since the area of ​​the conductive portion 102a on the left side of the metal piece 120 or the lead tab 190 is larger than that on the right side, the stepped portion 102c may be formed on the left side of the metal piece 120 or the lead tab 190. In this case, the stepped portion 102c is preferably formed as close to the metal piece 120 or the lead tab 190 as possible.

[0126] If a short circuit occurs in one of the conductive portions 102a separated by the groove portion 102b, the current of the remaining conductive portion 102a flows to the shorted conductive portion 102a. However, if the current flowing through the shorted conductive portion 102a becomes large, an electrochemical reaction occurs at the step portion 102c present in the shorted conductive portion 102a, increasing resistance and blocking the short-circuit current path. That is, because the thickness of the conductive material 102 present in the step portion 102c is relatively thin, the step portion 102c can function as an electrochemical fuse or a short-circuit current interrupter.

[0127] When a short circuit occurs in a lithium secondary battery including the electrode current collector 100 according to another embodiment of the present invention, the conductive material 102 reacts with the electrolyte and corrodes or cracks in the thickness direction across the entire thickness of the conductive material 102, thereby reducing (reducing) the short circuit current or blocking the path of the short circuit current.

[0128] In the case of the electrode current collector 100 according to another embodiment of the present invention, the conductive material 102 has a step portion 102c that is relatively thin. When a short circuit occurs, the step portion 102c of the conductive material 102 is easily corroded or cracked along the thickness direction over its entire thickness. As a result, the resistance at the step portion 102c increases, thereby blocking the path of the short-circuit current.

[0129] As described above, the conductive material 102 of the electrode current collector 100 according to another embodiment of the present invention exhibits an electrochemical fuse function or a short-circuit current interruption function at the relatively thin stepped portion 102c, thereby preventing the battery temperature from rising when a short circuit occurs and interrupting the short-circuit current, thereby ensuring the safety of the battery.

[0130] Meanwhile, FIG. 12 is a graph showing the results of reducing or cutting off short-circuit current when an external short circuit occurs in a secondary battery, according to the method of connecting a lead tab to a current collector for an electrode according to the present invention.

[0131] FIG. 12(a) shows the results of an external short circuit test for a secondary battery using an electrode current collector 100 with a step 102c in the conductive portion 102a, as shown in FIGS. 10 and 11. The electrode current collector 100 used a 7 μm-thick PET base film 101, 6 μm-thick EVA polymer insulating layers 130 formed on the top and bottom surfaces of the base film 101, and a 0.5 μm-thick aluminum conductive material 102 coated by sputtering. The thickness of the step 102c was less than 50% of the thickness of the aluminum conductive material 102. An external short circuit test was performed on an aluminum pouch secondary battery using an 8 μm-thick copper foil as the negative electrode current collector and EC / EMC=1 / 2 (v / v) 1.1M LiPF6 (with some additives) as the electrolyte. The secondary battery was first fully charged at 4.2V, and then an external short circuit test was carried out by connecting a 60mOhm resistor at room temperature.

[0132] Referring to FIG. 12(a), it can be seen that even when an external short circuit occurs, the battery temperature (Cell Temp) remains almost unchanged, and no overheating occurs.

[0133] 12(b) shows the results of an external short circuit test for a secondary battery using an electrode current collector 100 according to an embodiment of the present invention, in which the conductive portion 102a has a groove 102b, as shown in FIGS. 3 to 8. The electrode current collector 100 was made of a 7 μm-thick PET base film 101, coated with a 0.5 μm-thick aluminum conductive material 102 by sputtering. An external short circuit test was performed on an aluminum pouch secondary battery using an 8 μm-thick copper foil as the negative electrode current collector and EC / EMC=1 / 2 (v / v) 1.1M LiPF6 (with some additives) as the electrolyte. The electrode current collector 100 and lead tab 190 were connected by placing 5 μm thick polyethylene (PE) polymer insulating layers 130 on both the top and bottom surfaces of the base film 101, placing a 12 μm aluminum metal piece 120 on one polymer insulating layer 130, and placing the lead tab 190 on the other polymer insulating layer 130, and then connecting the lead tab 190 by ultrasonic welding. The secondary battery thus formed, with a capacity of 550 mAh, was first fully charged to 4.35 V, and then connected to a 60 mOhm storage battery at room temperature to conduct an external short circuit test.

[0134] Referring to FIG. 12(b), it was found that even when an external short circuit occurred, the battery temperature (Cell Temp) hardly changed, and no overheating occurred.

[0135] As described above, one embodiment of the present invention has been described using specific details such as specific components and limited examples and drawings, but this is provided merely to facilitate a more comprehensive understanding of the present invention, and the present invention is not limited to the above-described example, and those skilled in the art will appreciate that various modifications and variations can be made from such descriptions. Therefore, the spirit of the present invention should not be limited to the described example, and all equivalents or variations within the scope of the claims, including but not limited to the following claims, are considered to fall within the scope of the spirit of the present invention.

Claims

1. a conductive material provided on at least one of the upper and lower surfaces of the base film; The conductive material is divided into two or more portions along the longitudinal direction or the lateral direction of the base film, the conductive material includes grooves formed over the entire conductive material along the longitudinal or lateral direction of the base film, and conductive portions formed alternately with the grooves along the longitudinal or lateral direction of the base film, the conductive material is not formed in the groove portion and the conductive material is present in the conductive portion, a metal piece or lead tab provided in a direction intersecting the conductive portion and the recessed groove portion and overlapping the conductive portion and the recessed groove portion so as to contact the entire conductive portion separated by the recessed groove portion.

2. The current collector for an electrode according to claim 1 , wherein the conductive portion and the groove portion are formed symmetrically or asymmetrically on the upper and lower surfaces of the base film.

3. The electrode current collector according to claim 2 , wherein the base film is made of a transparent material.

4. The electrode current collector according to claim 1 , further comprising an insulating polymer layer provided between the metal piece or the lead tab and the conductive portion.

5. 5. The electrode current collector according to claim 4, wherein the insulating polymer layer is melted by heat to attach the metal piece or the lead tab to the conductive portion, and a portion excluding the melted portion insulates the conductive portion from the metal piece or the lead tab.

6. an electrical connection between the lead tab or the metal piece and the conductive portion is formed only at a melting point formed by melting the insulating polymer layer; the unmelted portion of the insulating polymer layer insulates the lead tab or the metal piece from the conductive portion; The current collector for an electrode according to claim 5 , wherein the melting point is formed smaller than the insoluble portion of the insulating polymer layer, and a current path is formed through the melting point.

7. 7. The electrode current collector according to claim 6, wherein, when a short circuit occurs in one of the plurality of conductive portions divided by the groove portion, a current path through the melting point formed by melting the insulating polymer layer in contact with the conductive portion where the short circuit occurs is interrupted, and the short circuit does not affect other conductive portions except for the conductive portion where the short circuit occurs.

8. 7. The current collector for an electrode according to claim 6, wherein, when a short circuit occurs in any one of the conductive portions, the short-circuited conductive portion is electrically isolated from the other conductive portions by the groove portions formed on both sides of the conductive portion.

9. 2. The current collector for an electrode according to claim 1, wherein the plurality of conductive portions separated by the grooves are connected in parallel to the metal piece or the lead tab so that the grooves formed on both sides of the conductive portion where a short circuit occurs prevent the influence of the short circuit from being transmitted to other conductive portions.

10. The current collector for an electrode according to claim 1 , wherein a step portion is formed in the conductive portion on one side of the metal piece or the lead tab, the conductive material being thinner than the conductive portion.

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