Electrode current collector

Abstract

An electrode current collector according to an embodiment of the present invention includes a polymer film and a conductive material formed on at least one of the upper and lower surfaces of the polymer film. The conductive material may include a thinner portion and a thicker portion.

Description

Technical Field

[0001] The present invention relates to a collector for an electrode, and more specifically, to a collector for an electrode in which a portion of a conductive material metal formed on a polymer film is thinner than other portions, thereby preventing overheating of the battery or performing an electrochemical fuse function such as disconnecting the short-circuit current path in the event of a short circuit. Background Art

[0002] As the demand for secondary batteries has been rapidly increasing, lithium secondary batteries having high energy density, high operating potential, and low self-discharge rate have been commercialized among these secondary batteries.

[0003] Lithium metal secondary batteries are the first commercialized secondary batteries that use lithium metal as the negative electrode. However, lithium metal secondary batteries have problems with battery volume expansion, capacity and energy density due to the lithium resin phase formed on the surface of the lithium metal negative electrode, short circuits due to the continuous growth of the resin phase, reduced cycle life, and battery stability problems (explosion and fire). Production was discontinued only a few years after commercialization. Therefore, instead of lithium metal, a more stable carbon negative electrode that can stably store lithium in an ionic state in a grid or empty space is used. By using the above-mentioned carbon negative electrode, lithium secondary batteries can be truly commercialized and popularized.

[0004] So far, lithium secondary batteries are mainly prepared from carbon-based negative electrode materials or non-carbon-based negative electrode materials. Most of the negative electrode material research and development is concentrated on carbon (graphite, hard carbon, soft carbon, etc.) and non-carbon (silicon, tin, titanium oxide, etc.) materials.

[0005] On the other hand, with the recent miniaturization of portable electronic devices and information communication devices, the use of lithium secondary batteries as ultra-small power supply systems for driving them is highly anticipated.

[0006] In particular, recent research and development have been actively conducted on polymer electronic devices and devices that utilize advantages such as flexibility, low cost, and ease of production. Therefore, for use in miniaturized devices, it is necessary to reduce the thickness and weight of lithium secondary batteries while maintaining their energy density and performance.

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

[0008] In particular, for large-capacity lithium secondary batteries that can store energy for more than 24 hours, there is a further demand for battery safety technologies for reducing or disconnecting short-circuit current in the event of a short circuit.

[0009] In order to solve the above-mentioned problems, the present applicant has proposed the present invention. Summary of the Invention

[0010] Technical issues

[0011] The object of the present invention is to provide an electrode current collector that can be reduced in thickness or weight compared to a current collector made of foil, and at the same time acts as a fuse or the like when an internal short circuit or an external short circuit occurs, thereby preventing temperature rise and increasing battery stability.

[0012] Furthermore, another object of the present invention is to provide an electrode current collector that, when used in a large lithium secondary battery, can prevent the short-circuit current from being unable to be interrupted due to surface contact between the positive electrode current collector and the negative electrode current collector in the event of a short circuit.

[0013] Another object of the present invention is to provide an electrode current collector that can prevent the short-circuit current from being interrupted due to incomplete corrosion or rupture of the aluminum conductive material in the thickness direction when a short circuit occurs.

[0014] Technical Solution

[0015] The electrode collector of one embodiment of the present invention for achieving the above-mentioned purpose may include: a polymer film; and a conductive material formed on at least one of the upper surface or the lower surface of the above-mentioned polymer film, and the above-mentioned conductive material may include a thinner portion and a thicker portion.

[0016] The conductive material may include a thinner portion, and the thinner portion performs the function of an electrochemical fuse or a function of disconnecting a short-circuit current.

[0017] The conductive material may include a portion having a relatively thin thickness formed along a plane direction of the polymer film or a portion having a relatively thin thickness formed along a direction perpendicular to the plane direction of the polymer film.

[0018] The thinner portion of the conductive material may be formed on a horizontal surface of a recessed portion formed from the surface of the conductive material by intaglio etching or a vertical surface of a protruding portion formed from the surface of the conductive material by embossing etching.

[0019] The polymer film may include recessed portions formed from the surface of the conductive material by intaglio etching or protruding portions formed from the surface of the polymer film by embossing etching.

[0020] The conductive material formed on the horizontal surface of the recessed portion formed by negative etching from the surface of the polymer film or the conductive material formed on the vertical surface of the protruding portion formed by positive etching from the surface of the polymer film can be formed thinner than other portions.

[0021] The protrusions formed from the surface of the polymer film by embossing may include a polymer formed on a height difference portion of the polymer film or attached to the surface of the polymer film.

[0022] In the conductive material, the thinner portion may have a thickness of 70% or less compared to the thickness of other portions.

[0023] In the conductive material, the thinner portion may have a thickness of 0.4 μm or less.

[0024] In the conductive material, when the conductive material formed on the polymer film is viewed from above, the thinner portion may be formed into a closed curve or a closed polygon.

[0025] Effects of the Invention

[0026] In the electrode collector of the present invention, a polymer film made of a non-conductor is used instead of metal foil, and a conductive material is coated or a plating layer is formed on the surface of the polymer film. Therefore, the thickness can be further reduced compared to the collector made of metal foil.

[0027] When a short circuit occurs, the electrode collector of the present invention has a resistance value greater than that of a collector made of metal foil, and can be disturbed by the flow of current due to the electrochemical reaction generated in the thinner portion of the conductive material formed on the surface of the polymer film. Therefore, the short-circuit current can be reduced when a short circuit occurs, and the safety of the battery can be improved by preventing the temperature of the battery from rising.

[0028] When a short circuit occurs, the thinner portion of the electrode current collector of the present invention in the aluminum conductive material passes through the entire thickness, causing the conductive material to be completely corroded or broken. Therefore, the short circuit current can be interrupted by increasing resistance.

[0029] The electrode current collector of the present invention can increase the energy density and safety of a secondary battery, and can ensure the safety of a large-capacity secondary battery when a short circuit occurs. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a perspective view showing an electrode assembly including an electrode current collector according to one embodiment of the present invention.

[0031] Figure 2 FIG1 is an exploded perspective view showing an electrode assembly according to an embodiment of the present invention.

[0032] Figure 3 1 is a perspective view showing an electrode current collector according to one embodiment of the present invention.

[0033] Figure 4This is a cross-sectional view showing a state where a lead tab is connected to an electrode current collector according to one embodiment of the present invention.

[0034] Figure 5 and Figure 6 1 and 2 are a top view and a cross-sectional view of an electrode current collector according to an embodiment of the present invention.

[0035] Figure 7 and Figure 8 This is a cross-sectional view of an electrode current collector according to another embodiment of the present invention.

[0036] Figure 9 and Figure 10 It is a plan view showing a comparative electrode current collector and an electrode current collector according to another embodiment of the present invention for comparing short-circuit current interruption performance.

[0037] Figures 11 to 13 For comparison Figure 9 and Figure 10 Experimental results of voltage and temperature changes during external short circuit in a lithium secondary battery including a comparative electrode current collector and a lithium secondary battery including an electrode current collector according to another embodiment of the present invention. DETAILED DESCRIPTION

[0038] 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 restricted to these embodiments. The same reference numerals shown in the various drawings represent the same components.

[0039] Figure 1 This is a perspective view showing an electrode assembly including an electrode current collector according to one 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 perspective view showing an electrode current collector according to one embodiment of the present invention. Figure 4 This is a cross-sectional view showing a state where a lead tab is connected to an electrode current collector according to one embodiment of the present invention. Figure 5 and Figure 6 1 is a top view and a cross-sectional view of an electrode current collector according to an embodiment of the present invention. Figure 7 and Figure 8 This is a cross-sectional view of an electrode current collector according to another embodiment of the present invention.

[0040] Figure 1 and Figure 2 FIG. 1 shows an electrode assembly 10 including an electrode current collector 100 of the present invention. Figure 1 and Figure 2 In the embodiment, the electrode current collector 100 of the present invention is a positive electrode current collector. In order to use the electrode current collector 100 of the present invention in the electrode assembly 10 , it is necessary to coat the surface of the electrode current collector 100 with a positive electrode active material 103 .

[0041] On the other hand, the negative electrode current collector 200 may be formed by coating the negative electrode active material 203 on the negative electrode metal foil 201 , and may be connected to a negative electrode lead tab 290 at one end in the longitudinal direction.

[0042] A separator 300 may be disposed between the negative electrode current collector 200 and the electrode (positive electrode) current collector 100 of the present invention. Figure 2 The state shown is as follows: the negative electrode current collector 200 and the positive electrode current collector 100 are stacked in this order above and below with the separator 300 interposed therebetween. Figure 1 The electrode assembly 10 is shown.

[0043] Hereinafter, for convenience of description, the positive electrode current collector 100 is referred to as an electrode current collector.

[0044] Figure 3 An electrode current collector 100 according to an embodiment of the present invention is shown. Unlike the negative electrode current collector 200 mentioned above, the electrode current collector 100 does not use a metal foil.

[0045] like Figure 3 As shown, the electrode collector 100 (CURRENT COLLECTOR FOR ELECTRODES) of one embodiment of the present invention has a resistance value greater than that of a collector made of metal foil. Therefore, the limiting current value of the current flowing in the collector can be adjusted, and the current flow may be disturbed due to damage to the polymer film. Therefore, when an internal short circuit of the secondary battery occurs, the short circuit current or heat generation can be reduced.

[0046] A lithium secondary battery (Lithium Secondary Battery) having the electrode current collector 100 of the present invention can have the characteristics or concept of a maximum current limited battery (MCLB). The electrode current collector of the present invention that can realize a maximum current limited battery is described below.

[0047] The electrode collector 100 of one embodiment of the present invention serves as a positive electrode collector and has a resistance value greater than that of the positive electrode collector made of metal foil of an existing battery. Therefore, the limiting current can be adjusted. Moreover, when an internal short circuit occurs, the current path can be disconnected or collapsed to reduce the short-circuit current, or the safety of the battery can be improved by reducing the heat generated during the short circuit.

[0048] The electrode current collector 100 according to one embodiment of the present invention does not use a metal foil, but may use a polymer film 101 as a base material, and a thin metal is coated or applied on the polymer film 101 .

[0049] Reference Figure 3 and Figure 4 In one embodiment of the present invention, a current collector 100 for an electrode may include: a polymer film 101; and a conductive material 102 formed on at least one of the upper surface or the lower surface of the polymer film 101.

[0050] 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.

[0051] On the other hand, at least one metal sheet 120 may be formed above the conductive material 102 formed on at least one of the upper and lower surfaces of the polymer film 101 . In other words, the conductive material 102 may be formed between the polymer film 101 and the metal sheet 120 .

[0052] The polymer film 101 can be in the form of a strip having a predetermined length. Preferably, the polymer film 101 is made of a non-conductive material such as polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), or polyethylene terephthalate (PET).

[0053] The polymer film 101 has a thickness of 50 μm or less, preferably 1.4 μm to 50 μm or less. Compared to conventional current collectors using metal foil, the electrode current collector 100 according to one embodiment of the present invention can further reduce the thickness or weight of the battery. By using the non-conductive polymer film 101 having a thickness of 1.4 μm to 50 μm or less as the basic structure of the current collector 100, the overall thickness or weight of the lithium secondary battery including the electrode current collector 100 according to one embodiment of the present invention can be reduced.

[0054] On the other hand, metal sheet 120 is fixed to the opposite side of the side to which lead tab 190 is attached, or to both sides of polymer film 101, and lead tab 190 is welded and fixed to metal sheet 120. If polymer film 101 does not melt at a temperature lower than the welding temperature of lead tab 190, lead tab 190 cannot be bonded to polymer film 101. Therefore, polymer film 101 should preferably have a melting point that allows it to melt during the welding process of lead tab 190.

[0055] Reference Figure 3 and Figure 4 , a metal sheet 120 can be formed to contact or electrically connect with the conductive material 102 formed on the surface of the polymer film 101. Figure 4 As shown, the metal sheet 120 may be formed on one side or both sides of the polymer film 101 .

[0056] On the polymer film 101 , the metal sheet 120 may be used to secure a position for welding the lead tab 190 . That is, the metal sheet 120 may function as a connection portion of the lead tab 190 .

[0057] Preferably, the metal sheet 120 has a thickness of 5 μm or more.

[0058] As mentioned above, the metal sheet 120 is preferably a metal film or metal foil with a thickness of 5 μm or more, but is not limited thereto. That is, the metal sheet 120 can be in the form of a film, foil, or mesh.

[0059] Preferably, the metal sheet 120 may be aluminum foil or SUS 316L metal foil.

[0060] On the other hand, the electrode current collector 100 according to one embodiment of the present invention may include a polymer film 101 and / or a conductive material 102 formed on the surface of the polymer film 101. In this case, the surface of the polymer film 101 on which the conductive material 102 is formed may include recessed portions formed by intaglio or raised portions formed by embossing.

[0061] 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 may also be referred to as the outermost conductive layer forming the electrode current collector 100 .

[0062] The conductive material 102 can be formed to adjust or reduce the limiting current or maximum current of the electrode current collector 100. In other words, the conductive material 102 refers to aluminum metal plated or coated onto the recessed surface or raised surface of the polymer film 101 (formed by negative etching) to control the conductivity of the electrode current collector 100. When the conductive material 102 is plated or coated onto the surface of the polymer film 101 and / or the metal sheet 120, the conductive material 102 may also be referred to as a conductive layer. It should be noted that the term "conductive material 102" encompasses the concept of a conductive layer.

[0063] The maximum amount of current flowing in the electrode collector 100 can be controlled or reduced by adjusting the coating amount or coating thickness of the conductive material 102 plated (coated) or formed on the surface of the polymer film 101. This can improve the safety of the lithium secondary battery and ensure the safety of the battery when a short circuit occurs.

[0064] In other words, the limiting current or maximum current flowing through the electrode current collector 100 can be adjusted by adjusting the thickness or amount of the conductive material 102 formed on the surface of the polymer film 101. As described above, 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 maximum current limited battery (MCLB) of a lithium secondary battery.

[0065] Furthermore, when a physical internal short circuit or external short circuit occurs, the polymer film 101 may be melted, thereby preventing a sudden current from flowing, thereby improving the safety of the battery.

[0066] The conductive material 102 can be formed on the surface of the polymer film 101 by various methods. For example, if the conductive material 102 is aluminum, it can be formed on the surface of the polymer film 101 by sputtering or evaporation coating. Since aluminum is easily oxidized, it is difficult to form the conductive material 102 on the surface of the polymer film 101 by electroplating.

[0067] Since the conductivity of the electrode current collector 100 or the safety of the battery can be controlled by the amount (weight) or thickness of the coated conductive material 102, when plating or coating is performed, it is necessary to use a method that can control or adjust the thickness or weight of the conductive material 102.

[0068] The conductive material 102 may be formed on one side or both sides of the polymer film 101. In this case, the conductive material 102 should preferably be formed to have a thickness of 0.5 μm in terms of minimum cross-section and 2.5 μm in terms of maximum cross-section.

[0069] The electrode current collector 100 of one embodiment of the present invention allows current to flow through the conductive material 102. Therefore, the conductive material 102 coated on the surface of the polymer film 101 should be kept in good condition. To this end, the surface of the polymer film 101 is preferably treated to improve the adhesion between the conductive material 102 and the polymer film 101.

[0070] If the adhesive force between the conductive material 102 and the polymer film 101 is poor, the conductive material 102 may separate or detach from the surface of the polymer film 101 when the electrolyte is injected. Therefore, it is particularly important to improve the adhesive force between the conductive material 102 and the polymer film 101.

[0071] The surface of the polymer film 101 may be subjected to a surface treatment for improving the bonding strength or adhesive force with the conductive material 102 .

[0072] Preferably, in order to improve the adhesion between the conductive material 102 and the polymer film 101 , the surface of the polymer film 101 is subjected to corona treatment.

[0073] On the other hand, the electrode current collector 100 according to one embodiment of the present invention may include a lead tab 190 for connecting to an external device.

[0074] Conventional electrode current collectors made of metal foil can have lead tabs welded directly to the metal foil. However, since the structure corresponding to conventional metal foil in the electrode current collector 100 according to one embodiment of the present invention is the polymer film 101, it is not possible to weld lead tabs directly to the polymer film 101. The electrode current collector 100 according to one embodiment of the present invention solves this problem by attaching additional metal tabs to both sides of the polymer film 101, or on the side opposite to the side connected to the lead tab 190, and welding the lead tab 190 to the metal sheet 120.

[0075] In the electrode current collector 100 according to an embodiment of the present invention, the lead tab 190 may be welded to the metal sheet 120 by ultrasonic welding, laser welding, or spot welding.

[0076] like Figure 4 As shown, one of the metal sheets 120 formed on the upper and lower surfaces of the polymer film 101 can be connected to the lead tab 190. Although not shown, the lead tab 190 is connected to one side of the polymer film 101, and a metal sheet 120 can also be formed on the other side of the polymer film 101 facing the lead tab 190. In this case, the conductive material 102 is located between the polymer film 101 and the metal sheet 120 or between the polymer film 101 and the lead tab 190. Specifically, after the conductive material 102 is plated or coated on the upper and lower surfaces of the polymer film 101, the metal sheet 120 is fixed above the conductive material 102 in a manner that electrically connects to the conductive material 102 or is in contact with the conductive material 102.

[0077] When the lead terminal 190 is welded to one of the metal sheets 120 formed on both sides of the polymer film 101, as the polymer film 101 is melted, the metal sheets 120 formed on both sides of the polymer film 101 are connected. As a result, the lead terminal 190 can be electrically connected to the conductive material 102 formed on both sides of the polymer film 101 at the same time.

[0078] When metal sheets 120 and conductive material 102 are formed on both the upper and lower surfaces of polymer film 101, when lead tab 190 is welded to metal sheet 120 formed on the upper surface of polymer film 101 by ultrasonic welding, laser welding, or spot welding, a portion of polymer film 101 may be melted. If the welding heat generated when welding lead tab 190 exceeds the melting point of polymer film 101, polymer film 101 may melt during the welding process.

[0079] As described above, since the polymer film 101 is absent in the melted portion, the upper and lower metal sheets 120 can directly contact each other. In this case, since the metal sheets 120 are also molten by the welding heat, the upper and lower metal sheets 120 are joined. Since the upper and lower metal sheets 120 are directly melted and bonded in the portion where the polymer film 101 has melted and disappeared, in addition to the upper and lower metal sheets 120, the lead tabs 190 welded to either metal sheet 120 can also achieve electrical connection with the conductive material 102 formed on the upper and lower surfaces of the polymer film 101.

[0080] Even if a portion of the polymer film 101 is melted by welding heat, the electrode current collector 100 according to one embodiment of the present invention maintains the metal sheet 120 and the polymer film 101 connected, and thus the lead tab 190 can be connected.

[0081] However, depending on circumstances, the lead tab 190 may be welded to the metal sheet 120 even in a state where the polymer film 101 is not melted.

[0082] On the other hand, the electrode current collector 100 of one embodiment of the present invention is used as a current collector for the positive electrode of a secondary battery. Unlike conventional current collectors made of metal foil, it can improve the safety of the secondary battery. This is because the conductive material 102 coated or applied to the polymer film 101 functions like a fuse to interrupt short-circuit currents.

[0083] Typically, when a secondary battery experiences an internal or external short circuit, the short-circuit current generates heat, causing the secondary battery to heat up, potentially leading to battery explosion. In contrast, a secondary battery using the electrode current collector 100 according to an embodiment of the present invention as a positive electrode can prevent the secondary battery from heating up even if an internal or external short circuit occurs, and the short-circuit current can be cut off, ensuring battery safety.

[0084] The conductive material 102 coated or applied to the polymer film 101 will perform the function of a current path. When a short circuit occurs, if the conductive material 102 is crushed by reacting with the electrolyte, as if corroded, the current path will be disconnected, and therefore the short-circuit current will not be able to flow further.

[0085] When a short circuit occurs in a secondary battery including the positive electrode collector 100 according to an embodiment of the present invention, the current path can be disconnected because a thinner portion exists in the conductive material 102 formed on the surface of the polymer film 101. Since an electrochemical reaction occurs in the thinner portion and causes an increase in resistance, the short-circuit current path can be disconnected.

[0086] Reference Figure 5 and Figure 6 The electrode collector 100 of one embodiment of the present invention includes: a polymer film 101; and a conductive material 102, formed on at least one of the upper or lower surfaces of the polymer film 101, and the conductive material 102 can have the function of an electrochemical fuse or the function of disconnecting short-circuit current.

[0087] As described above, the conductive material 102 includes a thinner portion 102 b , and the thinner portion 102 b can perform the function of an electrochemical fuse or a function of disconnecting a short-circuit current.

[0088] Figure 5 This is a top view of the conductive material 102 formed on the upper surface of the polymer film 101, as viewed from above. Figure 6 Based on Figure 5 Sectional view of cutting line AA in. Figure 5 and Figure 6 The conductive material 102 formed on the upper surface of the strip-shaped polymer film 101 along the transfer direction S may include a thinner portion 102 b and a thicker portion 102 a .

[0089] Most of the conductive material 102 is a thicker portion 102a, and the remaining portion may be a thinner portion 102b. Figure 5In the conductive material 102 , the thinner portions 102 b may be uniformly formed in a lattice shape, and the thinner portions 102 b may be formed with the same thickness.

[0090] Different from Figure 5 and Figure 6 In the case of the conductive material 102, instead of uniformly forming the thinner portion 102b throughout the entire conductive material 102, the thinner portion 102b may be formed only in a portion of the conductive material 102. For example, the conductive material 102 may be thinner only in the portion connected to the lead tab 190.

[0091] like Figure 5 and Figure 6 As shown, when an internal short circuit occurs in a lithium secondary battery including the electrode current collector 100 according to an embodiment of the present invention, an electrochemical reaction can easily occur in the thinner portion 102 b of the conductive material 102 .

[0092] In the event of a short circuit in a lithium secondary battery using an electrode collector 100 according to an embodiment of the present invention, as the potential of the positive electrode collector 100 in which aluminum metal is coated or applied as the conductive material 102 on the polymer film 101 decreases and approaches the negative electrode potential (i.e., <0.3 volt, negative electrode lithium (Li) metal), if the conductive material 102 is crushed by reacting with the electrolyte, as if corroded, the short circuit current can be disconnected.

[0093] The conductive material 102 coated or applied to the polymer film 101 will perform the function of a current path. When a short circuit occurs, if the conductive material 102 is crushed by reacting with the electrolyte, as if corroded, the current path will be disconnected, and therefore the short-circuit current will not be able to flow further.

[0094] When a short circuit occurs in a lithium secondary battery including the electrode current collector 100 according to an embodiment of the present invention, the conductive material 102 reacts with the electrolyte and is corroded or broken throughout the entire thickness, thereby disconnecting the short-circuit current path.

[0095] However, in the thick portion 102a of the conductive material 102, the conductive material 102 is fractured to a predetermined extent along its thickness direction (depth direction). However, due to its low resistance, current can still flow. Even if a short circuit occurs in the thick portion 102a of the conductive material 102, the conductive material 102 is unlikely to corrode or fracture along its entire thickness, and thus the path of the short-circuit current cannot be interrupted.

[0096] However, in the electrode collector 100 of one embodiment of the present invention, there is a thinner portion 102b in the conductive material 102. When a short circuit occurs, the thinner portion 102b of the conductive material 102 will easily be completely corroded or broken along the thickness direction over the entire thickness, resulting in an increase in resistance in this portion, thereby disconnecting the path of the short-circuit current.

[0097] As described above, the conductive material 102 of the electrode collector 100 of one embodiment of the present invention performs the function of an electrochemical fuse or the function of disconnecting the short-circuit current in the thinner portion 102b. Therefore, when a short circuit occurs, the battery temperature can be prevented from rising and the short-circuit current can be disconnected to ensure the safety of the battery.

[0098] Reference Figure 5 and Figure 6 In the conductive material 102, a thinner portion 102b is formed along the surface direction of the polymer film 101. Figure 6 In the conductive material 102, a thinner portion 102b is formed along the upper surface (surface) of the polymer film 101. Figure 5 and Figure 6 In the embodiment, the conductive material 102 may include a recessed portion 102b formed from the surface thereof by intaglio etching. The recessed portion 102b formed by intaglio etching has a relatively thin thickness, and thus, this portion can cut off the short-circuit current.

[0099] After forming a thick portion 102a of the conductive material 102 on the surface of the polymer film 101, the conductive material 102 may be scraped or removed to a predetermined depth to form a thinner portion 102b of the conductive material 102. Alternatively, the thinner portion 102b may be formed by laser patterning the thicker portion 102a of the conductive material 102. Furthermore, when the conductive material 102 is applied or evaporated onto the surface of the polymer film 101, the thicker portion 102a and the thinner portion 102b may be formed simultaneously.

[0100] In such Figure 5 In the illustrated electrode current collector 100, if a short circuit occurs, the thinner portion 102b along the edge of any one of the lattice-shaped conductive material 102 sections will completely corrode or break, effectively interrupting the current flowing through the other lattice sections. In other words, when a short circuit occurs, the short-circuit current can be interrupted from flowing through the entire conductive material 102 by electrically isolating the lattice sections.

[0101] In the conductive material 102, when the conductive material 102 formed on the polymer film 101 is viewed from above, the thinner portion 102b may be formed into a closed curve or a closed polygon. Figure 5As shown, the thinner portion 102b can be formed into a quadrilateral. Like this, the thinner portion 102b should be formed into a closed curve or a closed polygon. Only in this way can the current flowing in the conductive material 102 surrounded by the thinner portion 102b be cut off from flowing to other parts when a short circuit occurs.

[0102] In the conductive material 102, the thinner portion 102b may be formed to have a thickness of 70% or less compared to the thickness of the other portion 102a. Figure 6 Preferably, in the conductive material 102, if the thickness of the thinner portion 102b is set to T1 and the thickness of the thicker portion 102a is set to T2, then the ratio T1 / T2 of the conductive material 102 is 0.7 or less. Furthermore, preferably, the thinner portion 102b of the conductive material 102 has a thickness of 0.4 μm or less.

[0103] like Figure 5 and Figure 6 As shown, in addition to the recessed manner formed by intaglio etching, a thinner portion in the conductive material 102 may also be formed by protruding from the surface of the conductive material 102 by embossing etching.

[0104] Figure 7 and Figure 8 FIG. 1 is a cross-sectional view of an electrode current collector according to another embodiment of the present invention. Figure 7 and Figure 8 As shown, the entire portion 102d is raised from the surface of the conductive material 102 in a positive manner.

[0105] like Figure 7 As shown, polymer film 101 includes height difference portion 101b and non-height difference portion 101a. Height difference portion 101b is a portion protruding from the surface of non-height difference portion 101a. As described above, when conductive material 102 is applied or evaporated onto the surface of polymer film 101 including height difference portion 101b and non-height difference portion 101a, conductive material 102 is formed not only on the surfaces of non-height difference portion 101a and height difference portion 101b, but also on the thickness surface of height difference portion 101b.

[0106] When the conductive material 102 is applied to the surface of the polymer film 101 by sputtering, the conductive material 102 is sputtered from top to bottom in a direction perpendicular to the surface of the polymer film 101 . Figure 7The arrow SP in the figure indicates the sputtering direction of the conductive material 102. The sputtered conductive material 102 is applied to the surfaces of the non-height difference portion 101a and the height difference portion 101b of the polymer film 101, as well as the side surfaces (thickness surfaces) of the height difference portion 101b. In this case, the conductive material 102 applied to the side surfaces of the height difference portion 101b flows along the surface direction of the non-height difference portion 101a. Therefore, compared to the thickness of the conductive material 102a formed on the surface of the non-height difference portion 101a and the conductive material 102d formed on the surface of the height difference portion 101b, the thickness of the conductive material 102c formed on the side surfaces of the height difference portion 101b is necessarily thinner.

[0107] If the thickness of the conductive material 102a formed on the surface of the non-height difference portion 101a of the polymer film 101 and the thickness of the conductive material 102d formed on the surface of the height difference portion 101b are set to T4, and the thickness of the conductive material 102c formed on the side of the height difference portion 101b is set to T3, then T4 is greater than T3.

[0108] on the other hand, Figure 8 The shape of the polymer film 101 shown is similar to Figure 7 The difference is that in Figure 7 In the embodiment, the height difference portion 101b is also formed by the polymer film 101, but Figure 8 In FIG. 1 , the level difference portion 104 is not formed by the polymer film 101 .

[0109] Figure 8 The electrode current collector 100 shown may include a polymer 104 attached to the surface of the polymer film 101. The polymer 104 is attached to the surface of the polymer film 101 and forms a height difference portion. A binder (not shown) for attachment may be formed between the polymer 104 and the polymer film 101. Preferably, the thickness T5 of the polymer 104 including the binder is about 100 mm. Figure 7 The height difference portions 101b have the same thickness.

[0110] and Figure 7 Similarly, the thickness of the conductive material 102c formed on the side surface (thickness surface) of the polymer 104 is thinner than the thickness of the conductive material 102a formed on the surface of the polymer film 101 and the thickness of the conductive material 102d formed on the surface of the polymer 104 .

[0111] As described above, the conductive material 102 may include a thin portion 102 c formed in a direction perpendicular to the surface direction of the polymer film 101 .

[0112] In another embodiment of the electrode collector 100 of the present invention, there is a thinner portion 102c in the conductive material 102. When a short circuit occurs, the thinner portion 102c of the conductive material 102 is easily completely corroded or broken along the thickness direction over the entire thickness. As a result, the resistance of this portion increases, thereby disconnecting the path of the short-circuit current.

[0113] As described above, the conductive material 102 of the electrode collector 100 in another embodiment of the present invention performs the function of an electrochemical fuse or the function of disconnecting the short-circuit current in the thinner portion 102c. Therefore, when a short circuit occurs, the safety of the battery can be ensured by preventing the battery temperature from rising and disconnecting the short-circuit current.

[0114] exist Figure 7 and Figure 8 In the embodiment, the thickness of the thinner portion 102c of the conductive material 102 may be less than 70% of the thickness of the other portions 102a and 102d. Figure 7 Preferably, in the conductive material 102, if the thickness of the thinner portion 102c is set to T3 and the thickness of the thicker portions 102a and 102d is set to T4, then T3 / T4 of the conductive material 102 is 0.7 or less. Furthermore, preferably, the thinner portion 102c of the conductive material 102 has a thickness of 0.4 μm or less.

[0115] Table 1 shows the experimental results of determining whether the temperature rises during an external short circuit based on the thickness of the thinner portion 102 c of the conductive material 102 .

[0116] The battery used in the experiment had a capacity of approximately 350Ah to 400mAh, using lithium cobalt oxide (LCO) as the positive electrode active material and graphite as the negative electrode active material. A single layer of PE (7μm) was used as the separator, and the electrolyte was VS, FEC, PS, and SN added to 1.1M LiPF6 in EC / EMC.

[0117] Table 1

[0118] T4 thickness T3 thickness Does the temperature rise during external short circuit? T5 thickness Condition 1 0.5μm 0.3~0.35μm no 12μm positive etching Condition 2 0.6μm 0.35~0.4μm no 12μm positive etching Condition 3 1.0μm ~0.4μm no 20μm positive etching

[0119] As shown in Table 1, when the thickness T3 of the thinner portion 102c of the conductive material 102 is less than 0.4 μm, the temperature of the lithium secondary battery does not rise even when an external short circuit (~60 mOhm) occurs. This is because when an external short circuit occurs, the thinner portion 102c of the conductive material 102 corrodes or breaks throughout its entire thickness, interrupting the short-circuit current due to increased resistance.

[0120] If viewed from above Figure 7and Figure 8 The conductive material 102 shown in FIG. 1 is formed in a quadrilateral shape at the edge (side) of the height difference portion 101b or the polymer 104. Figure 5 and Figure 6 As described above, in the conductive material 102 , when the conductive material 102 formed on the polymer film 101 is viewed from above, the thinner portion 102 c may be formed into a closed curve or a closed polygon.

[0121] like Figures 5 to 8 As shown, the polymer film 101 may include a recessed portion formed from its surface by intaglio or a protruding portion formed by embossing, and the conductive material 102 may also include a recessed portion 102b formed from its surface by intaglio or protruding portions 102c and 102d formed from its surface by embossing. The conductive material 102c formed on the side surfaces (thickness surfaces) of the protruding portions 102c and 102d formed by embossing is thinner than other portions. That is, in the polymer film 101, the conductive material 102b formed on the horizontal surface of the recessed portion formed by intaglio or the conductive material 102c formed on the vertical surface of the protruding portion formed by embossing can be thinner than other portions.

[0122] Alternatively, instead of forming the height difference 101b on the polymer film 101, an intaglio pattern or scratches can be formed on the surface of the polymer film 101 where the conductive material 102 is applied or vapor-deposited, and then the thinner portion 102b can be formed by applying or vapor-depositing the conductive material 102. If the intaglio pattern or scratches are formed on the surface of the polymer film 101, the portion will be recessed, creating a vertical surface in the depth direction. The thickness of the conductive material 102 applied to this vertical surface is thinner than that of the other portions. If a short circuit occurs, the thinner conductive material 102 will fracture or corrode throughout its thickness, thus interrupting the short-circuit current path.

[0123] As described above, in the electrode collector 100 of the present invention, there are thinner portions 102b and 102c in the conductive material 102 formed in the polymer film 101. Therefore, when a short circuit occurs, the thinner portions 102b and 102c can disconnect the path of the short-circuit current by performing the function of an electrochemical fuse or the function of disconnecting the short-circuit current.

[0124] In order to confirm the safety based on the thickness of the conductive material, the present inventors Figure 9 and Figure 10 The lithium secondary battery including the electrode current collector shown was subjected to external short circuit and other experiments, and the results confirmed that the electrode current collector 100 of the present invention can ensure the safety of the battery through the thinner portion of the conductive material 102. Figures 9 to 13 Explain the results of the external short-circuit test.

[0125] Figure 9 and Figure 10 1 is a top view showing a comparative electrode current collector and an electrode current collector according to another embodiment of the present invention for comparing short-circuit current interruption performance. Figures 11 to 13 For comparison Figure 9 and Figure 10 Experimental results of voltage and temperature changes during external short circuit in a lithium secondary battery including a comparative electrode current collector and a lithium secondary battery including an electrode current collector according to another embodiment of the present invention.

[0126] In order to implement the method of reducing the current path, the present inventors prepared an electrode current collector that reduces the conductive material area or the current path length (see Figure 9 ), electrode collector with reduced thickness of conductive material (refer to Figure 10 ).

[0127] Figure 9 The electrode current collector shown is constructed by placing lead tabs 190 on both sides of a polymer film and welding them together to electrically connect the lead tabs 190 to the conductive material 102. The polymer film is made of polyethylene terephthalate (PET) and has a thickness of 7 μm. Aluminum is applied to the conductive material 102 to a thickness of less than 0.6 μm. The current path is reduced by removing a portion 102e of the conductive material 102 between the positive electrode active material 103 and the lead tab 190. In this case, the length L1 of the remaining conductive material 102 is set to 5 mm and 10 mm. That is, the length L1 of the current path is 5 mm and 10 mm. Figure 9 The electrode current collector does not reduce the thickness of the conductive material 102, but only reduces the length of the current path.

[0128] Figure 10 The electrode current collector shown is Figure 8 The electrode current collector 100 of another embodiment of the present invention is shown. Specifically, before applying the aluminum conductive material 102 to the surface of the polymer film 101, a polymer 104 is bonded to the polymer film 101, and the conductive material 102 is applied in this state. Polyethylene terephthalate is used as polymer 104, and the thickness of the polymer 104 and the binder (not shown) is 12 μm. A thinner conductive material 102c can be formed on the side of the polymer 104 (same as condition 2 in Table 1).

[0129] Figure 11 and Figure 12 They include Figure 9The external short-circuit test results of the secondary battery with the electrode current collector having the length L1 of the remaining conductive material 102 in the electrode current collector, that is, the length L1 of the current path, of 5 mm and 10 mm, Figure 13 To include Figure 10 Results of external short-circuit tests on secondary batteries using the electrode current collectors in the experiment. The secondary batteries used in the experiment were pouch-type secondary batteries with a polyethylene (PE) separator having a thickness of 7 μm and a capacity of 350 mAh to 400 mAh.

[0130] Reference Figure 11 and Figure 12 If the thickness of the conductive material 102 formed on the polymer film 101 is not reduced and only the current path length L1 is reduced, if a short circuit occurs, the battery temperature will rise rapidly because the current is not disconnected.

[0131] On the contrary, refer to Figure 13 When a short circuit occurs in the case where a thin portion 102 c exists in the conductive material 102 formed in the high-resolution film 101 , it is known that the short circuit current is interrupted due to an increase in resistance.

[0132] As described above, when a short circuit occurs in a secondary battery using the electrode collector 100 of the present invention, the thinner parts 102b and 102c in the conductive material 102 are broken or corroded throughout the entire thickness, thereby disconnecting the short circuit. Ultimately, the battery can be prevented from exploding and the safety of the battery can be ensured.

[0133] As described above, in one embodiment of the present invention, specific matters such as specific structural elements and limited embodiments and drawings are used to illustrate. This is provided only to help understand the present invention as a whole, and the present invention is not limited to the above-described embodiments. A person skilled in the art of the present invention can make various modifications and variations based on the above description. Therefore, the concept of the present invention is not limited to the described embodiments, and all embodiments with equivalent or equivalent variations to the scope of the invention, including the scope of the invention, fall within the scope of the concept of the present invention.

Claims

1. A current collector for an electrode, characterized in that: include: polymer films; and A conductive material is formed on at least one of the upper surface or the lower surface of the polymer film. The conductive material includes a relatively thin portion and a relatively thick portion. In the above conductive material, the relatively thin portion is formed to have a thickness of 70% or less compared to the relatively thick portion, and is formed to have a thickness of 0.4 μm or less. When a short circuit occurs, the conductive material is corroded or broken along the thickness direction over the entire thickness, thereby performing the function of an electrochemical fuse or a function of disconnecting a short-circuit current. In the conductive material, when the conductive material formed on the polymer film is viewed from above, the thin portion is formed into a closed curve or a closed polygonal shape. When a short circuit occurs, the thin portion is completely corroded or broken along the edge of any grid portion of the grid-shaped conductive material, thereby disconnecting the short-circuit current flowing in the conductive material of the grid portion surrounded by the thin portion from flowing to the conductive material of other grid portions, thereby disconnecting the short-circuit current from flowing through the entire conductive material.

2. The electrode current collector according to claim 1, characterized in that The conductive material includes a thin portion formed along a plane direction of the polymer film or a thin portion formed along a direction perpendicular to the plane direction of the polymer film.

3. The electrode current collector according to claim 2, characterized in that The thin portion of the conductive material is formed on a horizontal surface of a recessed portion formed from the surface of the conductive material by negative etching or a vertical surface of a protruding portion formed from the surface of the conductive material by positive etching.

4. The electrode current collector according to claim 3, characterized in that The polymer film includes recessed portions formed from the surface of the conductive material by intaglio etching or raised portions formed from the surface of the polymer film by embossing etching.

5. The electrode current collector according to claim 4, characterized in that The conductive material formed on the horizontal surface of the recessed portion formed from the surface of the polymer film by negative etching or the conductive material formed on the vertical surface of the protruding portion formed from the surface of the polymer film by positive etching is thinner than other portions.

6. The electrode current collector according to claim 5, characterized in that The protrusions formed from the surface of the polymer film by embossing include a polymer formed on a height difference portion of the polymer film or attached to the surface of the polymer film.

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