Current collector for positive electrode

Abstract

The present invention relates to a current collector for a positive electrode, which is a current collector for a positive electrode instead of a metal foil, and which comprises: a polymer film made of a non-metal non-conductor material; and an aluminum conductive material that forms the outermost surface of the current collector for the positive electrode by being coated or coated with a thickness of 0.25-0.6 [mu] m on at least one of the upper surface and the lower surface of the polymer film, the conductive material having the function of an electrochemical fuse when an internal short circuit or an external short circuit occurs. Or the function of disconnecting or reducing the short-circuit current is realized.

Description

[0001] This application is a divisional application of an invention patent application with an application date of November 17, 2020, a national application number of 202080086218.7 (international application number PCT / KR2020 / 016146), and an invention name of “Collector for positive electrode”. Technical Field

[0002] The present invention relates to a collector for a positive electrode, and more particularly, to a collector for a positive electrode, which prevents overheating of a battery during a short circuit by plating aluminum metal on a polymer film, or performs the function of an electrochemical fuse that disconnects a short-circuit current path or reduces the short-circuit current. Background Art

[0003] As the technological development and demand for mobile devices increase, the demand for secondary batteries as energy sources has increased dramatically, and among these secondary batteries, lithium secondary batteries having high energy density and operating potential and low self-discharge rate have been commercialized.

[0004] Lithium metal secondary batteries are the first commercialized secondary batteries, using lithium metal as the negative electrode. However, lithium metal secondary batteries have volume expansion of the battery due to the lithium resin phase formed on the surface of the lithium metal negative electrode, a gradual decrease in capacity and energy density, a short circuit due to the continuous growth of the resin phase, a reduction in cycle life and battery stability problems (explosion and fire), and production was stopped 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, and the use of the above-mentioned carbon negative electrode makes lithium secondary batteries truly commercialized and popularized.

[0005] So far, lithium secondary batteries are mainly prepared from carbon-based negative electrode materials or non-carbon-based negative electrode materials, and 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.

[0006] On the other hand, recently, as portable electronic devices and information communication devices have become smaller in size, the use of lithium secondary batteries as ultra-small power supply systems for driving the devices has been expected.

[0007] In particular, recently, polymer electronic devices and devices have been actively developed and studied, taking advantage of their flexibility, low price, ease of preparation, 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.

[0008] Furthermore, even if the thickness or weight of the lithium secondary battery is reduced, when a short circuit occurs, it is still necessary to improve the safety of the lithium secondary battery by disconnecting the current path or reducing the short circuit current.

[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 present invention is proposed to solve the above-mentioned problems. The purpose of the present invention is to provide a collector for a positive electrode as follows: compared with a collector made of metal foil, the thickness or weight can be reduced, and at the same time, when an internal short circuit or an external short circuit occurs, it can act as a fuse, thereby preventing the temperature from rising and increasing the stability of the battery.

[0012] Means of solving the problem

[0013] The positive electrode collector of the present invention for solving the above-mentioned problems is a positive electrode collector that replaces metal foil, and includes: a polymer film made of non-metallic non-conductor material; and an aluminum conductive material, which is coated or applied with a thickness of 0.25 to 0.6 μm on at least one of the upper or lower surfaces of the above-mentioned polymer film to form the outermost surface of the above-mentioned positive electrode collector. When an internal short circuit or an external short circuit occurs, the above-mentioned conductive material can have the function of an electrochemical fuse, or has the function of disconnecting or reducing the short-circuit current.

[0014] Furthermore, the positive electrode collector of the present invention is a positive electrode collector that replaces metal foil, and includes: a polymer film made of a non-metallic non-conductor material; and an aluminum conductive material, which is coated or applied with a thickness of 0.25 to 0.6 μm on at least one of the upper or lower surfaces of the above-mentioned polymer film to form the outermost surface of the above-mentioned positive electrode collector. When an internal short circuit or an external short circuit occurs, the above-mentioned conductive material can react with the electrolyte to corrode or break along the thickness direction over its entire thickness while disconnecting the short-circuit current path or reducing the short-circuit current.

[0015] Furthermore, the positive electrode collector of the present invention is a positive electrode collector that replaces metal foil, and includes: a polymer film made of a non-metallic non-conductor material; and an aluminum conductive material, which is coated or applied with a thickness of 0.25 to 0.6 μm on at least one of the upper or lower surfaces of the above-mentioned polymer film to form the outermost surface of the above-mentioned positive electrode collector. When an internal short circuit or an external short circuit occurs, as the potential of the above-mentioned positive electrode collector drops to the negative electrode potential, the above-mentioned conductive material can corrode or break along the thickness direction over the entire thickness while disconnecting the short-circuit current path or reducing the short-circuit current.

[0016] The present invention may include a metal sheet formed on at least one of the upper surface side or the lower surface side of the polymer film in a manner electrically connected to the conductive material, and the conductive material may be formed between the metal sheet and the polymer film.

[0017] The above-mentioned metal sheet may be formed of aluminum foil or SUS 316L foil.

[0018] A lead tab joined or connected to the metal sheet may be included.

[0019] An insulating polymer layer may be formed between the conductive material and the metal sheet.

[0020] A plurality of nano-sized pores can be formed in the conductive material applied or coated on the surface of the polymer film.

[0021] The above-mentioned metal sheet can be formed on the surface of one side of the above-mentioned conductive material. The above-mentioned conductive material is formed on the upper and lower surfaces of the above-mentioned polymer film and may include: an insulating polymer layer formed on the surface of the above-mentioned conductive material on the side of the upper surface side or the lower surface side of the above-mentioned polymer film facing the above-mentioned metal sheet; and a lead terminal sheet bonded or connected to the above-mentioned insulating polymer layer on the side facing the above-mentioned metal sheet.

[0022] The conductive material may be formed on one of the upper surface or the lower surface of the polymer film, and the conductive material, the insulating polymer layer and the metal sheet may be formed on the same side relative to the upper surface or the lower surface of the polymer film.

[0023] A lead tab bonded or connected to the polymer film may be formed on a surface of the upper surface or the lower surface of the polymer film that faces the metal sheet.

[0024] It may include: a metal sheet, formed on one side of the upper or lower surface of the above-mentioned polymer film in a manner electrically connected to the above-mentioned conductive material; and an insulating polymer layer, formed on the side of the upper or lower surface of the above-mentioned polymer film facing the above-mentioned metal sheet, and the above-mentioned conductive material may be formed between the above-mentioned insulating polymer layer and the above-mentioned polymer film.

[0025] A lead tab bonded or connected to the insulating polymer layer may be included.

[0026] Effects of the Invention

[0027] In the collector for the positive electrode 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 plated on at least one of the upper and lower surfaces of the polymer film, so that the thickness or weight can be reduced compared to the collector made of metal foil.

[0028] The collector for the positive electrode of the present invention has a resistance value greater than that of a collector made of metal foil when an internal short circuit or an external short circuit occurs, and the current may be disturbed as a result of corrosion of the conductive material formed on one side of the polymer film or an electrochemical reaction. 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.

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

[0030] Figure 1 It is a perspective view showing an electrode assembly including the positive electrode current collector of the present invention.

[0031] Figure 2 It is an exploded perspective view showing the electrode assembly of the present invention.

[0032] Figure 3 It is a perspective view showing the positive electrode current collector of the present invention.

[0033] Figure 4 1 is a cross-sectional view showing a positive electrode current collector according to a first embodiment of the present invention.

[0034] Figure 5 1 is a cross-sectional view showing a positive electrode current collector according to a second embodiment of the present invention.

[0035] Figure 6 1 is a cross-sectional view showing a positive electrode current collector according to a third embodiment of the present invention.

[0036] Figure 7 1 is a cross-sectional view showing a positive electrode current collector according to a fourth embodiment of the present invention.

[0037] Figure 8 1 is a graph showing the results of measuring the capacity of a lithium secondary battery including the positive electrode current collector according to the first embodiment of the present invention, measured according to the thickness of the conductive material.

[0038] Fig. 9 The graph shows the results of nail penetration tests of lithium secondary batteries including the positive electrode current collector according to the first embodiment of the present invention, according to the thickness of the conductive material. DETAILED DESCRIPTION

[0039] 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.

[0040] Figure 1This is a perspective view showing an electrode assembly including the positive electrode current collector of the present invention. Figure 2 This is an exploded perspective view showing the electrode assembly of the present invention. Figure 3 This is a perspective view showing a positive electrode current collector of the present invention. Figure 4 1 is a cross-sectional view showing a positive electrode current collector according to a first embodiment of the present invention. Figure 5 2 is a cross-sectional view showing a positive electrode current collector according to a second embodiment of the present invention. Figure 6 2 is a cross-sectional view showing a positive electrode current collector according to a third embodiment of the present invention. Figure 7 2 is a cross-sectional view showing a positive electrode current collector according to a fourth embodiment of the present invention. Figure 8 Graph showing the capacity measurement results of a lithium secondary battery including the positive electrode current collector according to the first embodiment of the present invention measured according to the thickness of the conductive material, Fig. 9 The graph shows the results of nail penetration tests of lithium secondary batteries including the positive electrode current collector according to the first embodiment of the present invention, according to the thickness of the conductive material.

[0041] Figure 1 and Figure 2 FIG. 1 shows an electrode assembly 10 including a positive electrode current collector 100 of the present invention. Figure 1 and Figure 2 In this case, in order to use the positive electrode current collector 100 of the present invention in the electrode assembly 10 , it is necessary to apply the positive electrode active material 103 on the surface of the positive electrode current collector 100 .

[0042] On the other hand, the negative electrode current collector 200 may be formed by coating a negative electrode active material 203 on a negative electrode metal foil 201 and connecting a negative electrode lead tab 290 to one end in the longitudinal direction.

[0043] A separation membrane 300 may be disposed between the negative electrode current collector 200 and the positive electrode current collector 100 of the present invention. Figure 2 In the state shown in FIG. 1 , the negative electrode current collector 200 and the positive electrode current collector 100 are stacked in this order on top and bottom with the separator 300 interposed therebetween. Figure 1 The electrode assembly 10 is shown.

[0044] Figure 3 A positive electrode current collector 100 of the present invention is shown. Unlike the negative electrode current collector 200 described above, the positive electrode current collector 100 does not use a metal foil.

[0045] like Figure 3The collector 100 for the positive electrode of the present invention shown has a resistance value greater than that of a collector made of metal foil, and 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, so that 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 positive electrode current collector 100 of the present invention can have the characteristics or concept of a maximum current limited battery (MCLB). Hereinafter, the positive electrode current collector of the present invention that can realize a maximum current limited battery will be described.

[0047] The positive electrode collector 100 of the present invention has a resistance value greater than that of the positive electrode collector made of metal foil of the existing battery, and therefore, the limiting current can be adjusted. Moreover, when an internal short circuit occurs, the current path can be collapsed, thereby reducing the short circuit current, or reducing the heat generated when a short circuit occurs, thereby improving the safety of the battery.

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

[0049] Hereinafter, various embodiments of the positive electrode current collector 100 of the present invention will be described with reference to the drawings.

[0050] First, refer to Figures 4 to 7 The positive electrode current collector 100, 400, 500, 600 of the present invention may include: a polymer film 101; a conductive material 102 formed on at least one of the upper surface or the lower surface of the polymer film 101; a metal sheet 120 formed on the upper surface side or the lower surface side of the polymer film 101 in a manner electrically connected to the conductive material 102; and a lead terminal 190 tab), formed in a manner of joining with the metal sheet 120, the conductive material 102 or one of the polymer film 101, and electrically connected to the conductive material 102, the conductive material 102 may be located between the metal sheet 120 and the polymer film 101 or between the lead terminal tab 190 and the polymer film 101, the lead terminal tab 190 may be welded to the metal sheet 120 formed on the upper and lower surface sides of the polymer film 101 or to the metal sheet 120 formed on one side of the polymer film 101 facing the lead terminal tab 190.

[0051] In this case, the conductive material 102 may be located between the metal sheet 120 and the polymer film 101 or between the polymer film 101 and the lead terminal sheet 190 .

[0052] The conductive material 102 can perform the function of an electrochemical fuse by reacting with the electrolyte when a short circuit occurs, and thus can have a short circuit prevention function. The electrochemical properties of the conductive material 102 will be described later.

[0053] The polymer film 101 may be in a strip shape with a predetermined length. The polymer film 101 may be supplied or transferred in a roll-to-roll manner along its length direction (i.e., a direction with a relatively long length), thereby forming the electrode assembly 10 described below.

[0054] Preferably, the polymer film 101 is formed of a polymer non-conductive material such as polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI) or polyethylene terephthalate (PET).

[0055] The polymer film 101 has a thickness of 50 μm or less, preferably, a thickness of 1.4 μm or more and 50 μm or less. Compared with the case of using the existing metal foil collector, the positive electrode collector 100 of one embodiment of the present invention can reduce the thickness or weight of the battery, and the polymer film of the non-conductive material with a thickness of 1.4 μm or more and 50 μm or less is used as the polymer film 101, thereby reducing the overall thickness or weight of the lithium secondary battery including the positive electrode collector 100, 400, 500, 600 of the present invention.

[0056] On the other hand, preferably, the polymer film 101 is formed of a material that melts at a temperature lower than 300° C. The lead tab 190 is welded to fix to the polymer film 101. If the polymer film 101 does not melt at a temperature lower than the welding temperature of the lead tab 190, the lead tab 190 cannot be bonded to the polymer film 101. Therefore, preferably, the polymer film 101 should have a melting point that can be melted during the welding of the lead tab 190, and should have a melting point lower than 300° C.

[0057] On the other hand, the positive electrode current collector 100 , 400 , 500 , 600 of the present invention may include a conductive material 102 formed on at least one of the upper surface and the lower surface of the polymer film 101 .

[0058] Preferably, the conductive material 102 may be formed of aluminum, and may be formed in a state of being plated or coated on the surface of the polymer film 101. Therefore, the conductive material 102 may also be referred to as the outermost conductive layer forming the positive electrode current collector 100.

[0059] The conductive material 102 can be formed in a manner to adjust the limiting current or the maximum current of the positive electrode current collector 100, 400, 500, 600. In other words, the conductive material 102 refers to aluminum plated or coated on at least one of the upper surface or the lower surface of the polymer film 101 in order to control the conductivity of the positive electrode current collector 100, 400, 500, 600. In the case where the conductive material 102 is plated or coated on the surface of the polymer film 101, the conductive material 102 can also be called a conductive layer. Hereinafter, the conductive material 102 is a concept including a conductive layer.

[0060] The maximum amount of current flowing in the positive electrode collector 100, 400, 500, 600 can be controlled or reduced by adjusting the coating amount or coating thickness of the conductive material 102 plated or coated on at least one of the upper surface or lower 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.

[0061] In other words, the limiting current or maximum current flowing in the positive electrode current collector 100 can be adjusted by the thickness or amount of the conductive material 102 formed on the surface of the polymer film 101. As described above, the characteristics or concept of the maximum limiting current battery of the lithium secondary battery (Lithium Secondary Battery) can be realized by the conductive material 102 of the electrode current collector 100, 400, 500, 600 of the present invention.

[0062] Furthermore, when a physical internal short circuit or external short circuit occurs, the polymer film 101 may melt, which may interfere with the occurrence of a sharp current, thereby improving the safety of the battery. At the same time, when the thickness of the conductive material 102 is thin, when an internal short circuit or an external short circuit occurs, the potential of the aluminum layer forming the conductive material 102 decreases and guides the electrochemical reaction between the aluminum layer and the electrolyte, thereby reducing the conductivity or disconnecting the current, thereby improving the safety of the battery.

[0063] The conductive material 102 can be formed on the surface of the polymer film 101 in various ways. For example, when the conductive material 102 is a metal, it can be formed on the surface of the polymer film 101 by sputtering or evaporation coating.

[0064] The conductivity of the positive electrode collector 100 or the safety of the battery can be controlled by the amount (weight) or thickness of the conductive material 102 plated or coated. Therefore, 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.

[0065] The thickness of the conductive material 102 plated or coated on the surface of the polymer film 101 can be determined by the length of the lead tab 190 and the electrode (collector). For example, preferably, if the length of the electrode (collector) becomes longer, the plated thickness of the conductive material 102 will also increase.

[0066] 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 is preferably formed on one side of the polymer film 101 with a thickness of at least 0.25 μm and at most 0.6 μm.

[0067] The positive electrode current collector 100, 400, 500, 600 of the present invention allows current to flow through the conductive material 102, and therefore, the conductive material 102 should be well plated or coated on the surface of the polymer film 101. For this purpose, preferably, the adhesive force between the conductive material 102 and the polymer film 101 is improved by performing a surface treatment on the polymer film 101.

[0068] If the adhesive force between the conductive material 102 and the polymer film 101 is poor, the conductive material 102 may be separated or detached from the surface of the polymer film 101 when the electrolyte is injected. Therefore, the adhesive force between the conductive material 102 and the polymer film 101 should be increased.

[0069] The surface of the polymer film 101 may be subjected to a surface treatment for improving the bonding force or adhesive force with the conductive material 102 .

[0070] Preferably, the surface of the polymer film 101 is subjected to corona treatment in order to improve the adhesion between the conductive material 102 and the polymer film 101 .

[0071] On the other hand, the positive electrode current collector 100 , 400 , 500 , 600 of the present invention may include a lead tab 190 for connecting to an external device.

[0072] The existing electrode collector made of metal foil can be directly welded to the metal foil welding lead tab, but the positive electrode collector 100, 400, 500, 600 of the present invention is a thin polymer film 101 corresponding to the existing metal foil, so the lead tab cannot be directly welded to the polymer film 101. That is, the lead tab 190 needs to be welded to the conductive material 102 formed on the upper surface or the lower surface of the polymer film 101. Since the polymer film 101 is thin, the welding part cannot ensure sufficient tensile strength, so that the lead tab 190 is difficult to attach to the polymer film 101. The positive electrode collector 100, 400, 500, 600 of the present invention can weld the lead terminal piece 190 to the metal sheet 120 in a state where the metal sheet 120 of metal material is attached to the upper and lower surfaces of the polymer film 101, or weld the lead terminal piece 190 to the metal sheet 120 in a state where the lead terminal piece 190 is attached to one side, thereby solving the above-mentioned problem.

[0073] In the positive electrode current collector 100 , 400 , 500 , 600 of the present invention, the lead tab 190 may be welded to the metal sheet 120 , the conductive material 102 , or the polymer film 101 by ultrasonic welding, laser welding, or spot welding.

[0074] like Figures 4 to 7 The positive electrode current collectors 100 , 400 , 500 , and 600 of the present invention shown in the figure have metal sheets 120 and lead tabs 190 placed on both the upper and lower surfaces of the polymer film 101 .

[0075] Below, refer to Figures 4 to 7 , the positive electrode current collectors 100 , 400 , 500 , and 600 are described in more detail.

[0076] first, Figure 4 The positive electrode current collector 100 of the first embodiment of the present invention shown may form a conductive material 102 on the upper and lower surfaces of a polymer film 101. Metal sheets 120 are formed on the upper and lower surfaces of the polymer film 101 in such a manner as to be joined or connected to the upper and lower conductive materials 102. That is, the metal sheet 120 may be joined or connected to the conductive material 102 on the upper and lower surfaces of the polymer film 101. The lead tab 190 may be welded to one of the upper and lower metal sheets 120 formed on the polymer film 101, whereby the lead tab 190 may be electrically connected to the metal sheet 120 and the conductive material 102.

[0077] The metal sheet 120 may play a role of securing the position of the lead tab 190 to be welded on the polymer film 101. That is, the metal sheet 120 may play the same role as the connection portion of the lead tab 190.

[0078] Preferably, the metal sheet 120 has a thickness of 5 μm or more. The metal sheet 120 may be formed only on a portion of the polymer film 101. The number or position of the metal sheet 120 formed on the polymer film 101 is not limited. However, preferably, when the lead tab 190 is welded to the metal sheet 120, the position of the metal sheet 120 to which the lead tab 190 is welded is determined in consideration of the shape of the electrode assembly.

[0079] As described above, preferably, the metal sheet 120 has a metal film or metal foil form with a thickness of 5 μm or more, but is not limited thereto. That is, the metal sheet 120 may be in the form of a film, foil or mesh.

[0080] The metal sheet 120 may be formed of aluminum foil or SUS 316L foil.

[0081] As described above, the metal sheet 120 of the positive electrode current collector 100 according to the first embodiment of the present invention can secure the welding position of the lead tab 190 .

[0082] like Figure 4 As shown, conductive material 102 may be formed on the upper and lower surfaces of polymer film 101, and metal sheets 120 may be formed on the upper and lower surfaces of polymer film 101 in a manner of contacting the upper and lower conductive materials 102. Lead tab 190 may be welded to one of the upper and lower metal tabs 120. When welding is performed, polymer film 101 may be melted and electrically connected to conductive material 102, metal sheet 120, and lead tab 190.

[0083] And, refer to Figure 4 The positive electrode current collector 100 of the first embodiment of the present invention shown in the figure may form an insulating polymer layer 130 between the side of the metal sheet 120 facing the conductive material 102 and the conductive material 102. The insulating polymer layer 130 is used to attach the metal sheet 120 to the surface of the polymer film 101 or the surface of the conductive material 102 or to insulate the conductive material 102 from the metal sheet 120. Figure 4 In this case, an insulating polymer layer 130 may be provided between the conductive material 102 and the metal sheet 120 .

[0084] Preferably, the insulating polymer layer 130 is formed of a substance having adhesive or cohesive properties. Also, the insulating polymer layer 130 may be formed of a polymer material or in the form of a polymer film. When the insulating polymer layer 130 is formed in the form of a polymer film, preferably, the thickness is less than 50 μm.

[0085] The insulating polymer layer 130 may melt at the same temperature as the polymer film 101 or at a lower temperature than the polymer film 101. That is, the insulating polymer layer 130 preferably has the same melting point as the polymer film 101 or a melting point lower than that of the polymer film 101.

[0086] The insulating polymer layer 130 can be formed of polymer materials such as polyethylene (PE), polypropylene (PP), polyvinylidene fluoride (PVDF), polyethylene terephthalate (PET), polyimide (PI), etc. In addition, it can be formed of polymer materials with adhesive components such as ethylene vinyl acetate (EVA) or acrylic acid ester (Acrylate) compounds.

[0087] The insulating polymer layer 130 can perform the function of attaching the metal sheet 120 on the surface of the polymer film 101 or the conductive material 102 and the function of the insulating layer. When the lead terminal 190 is welded, the insulating polymer layer 130 melts and is electrically connected to the conductive material 102, and the portion other than the welded portion is insulated by the insulating polymer layer 130. When an external short circuit occurs, in the case where the electrically connected portion is limited to the welded portion, the conductive material 102 of the welded portion can reduce or disconnect the current by reacting. In the case where the electrically connected portion is large, it is not necessary to react a lot, and therefore, it is difficult to disconnect the current. Therefore, preferably, when the metal sheet 120 is attached to the conductive material 102, an insulating polymer layer 130 having insulation is formed between the conductive material 102 and the metal sheet 120.

[0088] Among them, the insulating polymer layer 130 and the metal sheet 120 attached to the conductive material 102 respectively formed on both surfaces of the polymer film 101 can be formed at the same position with respect to the polymer film 101 .

[0089] Figure 5 A positive electrode current collector 400 according to a second embodiment of the present invention is shown. Figure 5The positive electrode collector 400 may include: a conductive material 102 coated on the upper and lower surfaces of the polymer film 101; a metal sheet 120 formed on the surface of the conductive material 102 on one side; a lead terminal 190 formed on the surface of the conductive material 102 on the other side; an insulating polymer layer 130 formed between the conductive material 102 and the metal sheet 120; and an insulating polymer layer 130 formed between the conductive material 102 and the lead terminal 190.

[0090] If Figure 4 Compared with the positive electrode current collector 100 of the embodiment of the present invention, there are differences in that the metal sheet 120 is formed on one side of the polymer film 101, and only the lead tab 190 is formed on the opposite side, and the insulating polymer layer 130 is present between the metal sheet 120 and the conductive material 102, and there is no metal sheet 120 between the insulating polymer layer 130 and the lead tab 190. However, Figure 5 The positive electrode current collector 400 shown is also similar to Figure 4 The positive electrode current collector 100 shown is similar, that is, metal members, namely, a metal sheet 120 and a lead tab 190 are placed on the upper and lower surfaces of a polymer film 101 .

[0091] The metal sheet 120 and the lead tab 190 formed on the upper and lower surfaces of the polymer film 101 , respectively, may be formed at the same position.

[0092] Figure 6 A positive electrode current collector 500 according to a third embodiment of the present invention is shown. Figure 6 The positive electrode collector 500 may include: a conductive material 102, which is coated only on one side of the upper and lower sides of the polymer film 101; a metal sheet 120, which is formed on the surface of the conductive material 102; a lead terminal 190, which is formed on the surface of the polymer film 101 without the conductive material 102; and an insulating polymer layer 130, which is formed between the conductive material 102 and the metal sheet 120.

[0093] and Figure 5 Compared with the positive electrode current collector 400 of FIG. 1 , there are the following differences, namely, the conductive material 102 and the metal sheet 120 are formed only on one side of the polymer film 101, and only the lead tab 190 is formed on the opposite side of the polymer film 101, and the insulating polymer layer 130 is present between the metal sheet 120 and the conductive material 102, and there is no insulating polymer layer 130 between the polymer film 101 and the lead tab 190. However, Figure 6 The positive electrode current collector 500 shown is similar to Figure 4 The current collector 100 shown, Figure 5The positive electrode current collector 400 shown is similar, that is, metal members, namely, a metal sheet 120 and a lead tab 190 are placed on the upper and lower surfaces of a polymer film 101 .

[0094] The metal sheet 120 and the lead tab 190 formed on the upper and lower surfaces of the polymer film 101, respectively, may be formed at the same position.

[0095] exist Figure 6 In the positive electrode current collector 500 of the third embodiment of the present invention, the lead tab 190 is attached to the side of the polymer film 101 not coated with the aluminum conductive material 102. Therefore, when the electrode assembly is formed by folding with the side without the conductive material 102 as the inner side, the lead tab 190 is in contact with the separator and the negative electrode. Therefore, there is an advantage that an additional protective film for preventing the lead tab 190 from short-circuiting is not required.

[0096] Figure 7 A positive electrode current collector 600 according to a fourth embodiment of the present invention is shown. Figure 7 The positive electrode collector 600 may include: a conductive material 102, which is coated only on one side of the upper and lower sides of the polymer film 101; a lead terminal 190, which is formed on the surface of the conductive material 102; a metal sheet 120, which is formed on the surface of the polymer film 101 without the conductive material 102; and an insulating polymer layer 130, which is formed between the conductive material 102 and the lead terminal 190.

[0097] The metal sheet 120 and the lead tab 190 formed on the upper and lower surfaces of the polymer film 101 may be formed at the same position.

[0098] Figure 7 The positive electrode current collector 600 shown in the figure is similar to the positive electrode current collector 600 in that the metal sheet 120 and the lead tab 190 are located opposite to each other. Figure 6 There are differences in the positive electrode current collector 400 shown. However, Figure 7 The positive electrode current collector 600 shown is also similar to Figure 4 The positive electrode current collector 100 shown in FIG. Figure 5 The positive electrode current collector 400 and Figure 6 The positive electrode current collector 500 shown is similar, that is, metal components, that is, metal sheet 120 and lead tab 190 are placed on the upper and lower surfaces of polymer film 101. Therefore, Figure 7 The positive electrode current collector 600 according to the fourth embodiment of the present invention can also ensure sufficient tensile strength at the welding portion of the lead tab 190 and have good electrical conductivity.

[0099] As described above, in the positive electrode collector 100, 400, 500, 600 of the present invention, when an insulating polymer layer 130 formed of a polymer is formed on at least one of the upper or lower surfaces of the polymer film 101, parts formed of metal, i.e., a metal sheet 120 or a lead terminal piece 190, are formed on both sides of the polymer film 101, and therefore, the tensile strength of the portion where the polymer film 101 or the lead terminal piece 190 is welded is good.

[0100] When the lead tab 190 is welded, the insulating polymer layer 130 and the polymer film 101 are melted and bonded to the lead tab 190 at the welded portion, thereby being electrically connected to the conductive material 102 .

[0101] On the other hand, refer to Figure 3 , a metal sheet 120 is placed on the conductive material 102, and a lead tab 190 is placed on the metal sheet 120. In this case, an insulating polymer layer 130 exists between the metal sheet 120 and the conductive material 102. During the welding process of the lead tab 190, the insulating polymer layer 130 and the polymer film 101 melt and form a welding point. That is, in Figure 3 In the case of the insulating polymer layer 130 between the metal sheet 120 and the conductive material 102, the insulating polymer layer 130 melts and welds the lead tab 190, and the electrical connection is achieved only through the welding point where the insulating polymer layer 130 melts and connects. As described above, in the case of the insulating polymer layer 130, when the lead tab 190 is welded, the electrical connection forms a current path (pass) only at a very small part of the welding point, so that the lead tab 190 or the metal sheet 120 and the conductive material 102 can be insulated. In addition, the remaining part except the welding point is exposed to the electrolyte or is in a state where the electrolyte easily penetrates.

[0102] If there is no insulating polymer layer between the lead tab or metal sheet and the conductive material, the lead tab or metal sheet is in direct contact with the conductive material. In this case, both are in physical contact with the conductive material with an area corresponding to the size of the lead tab or metal sheet. As described above, in the welding part of the lead tab, in the case of a positive electrode collector where the lead tab or metal sheet is in physical contact with the conductive material, there is no insulating polymer layer between the metal sheet and the conductive material, so the contact area has the size of the metal sheet, and thus, the area required to react can only be increased. As a result, it is difficult to react all the conductive materials coated on the surface of the polymer film. If an external short circuit occurs in a battery using such a positive electrode collector, the current path (pass) is maintained, so the current cannot be disconnected and the temperature of the battery may rise.

[0103] When a lead terminal 190 is welded to one of the metal sheets 120 formed on both sides of the polymer film 101, the polymer film 101 melts, so that 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.

[0104] When the metal sheet 120 and the conductive material 102 are formed on both upper and lower surfaces of the polymer film 101, a portion of the polymer film 101 may be melted when the metal sheet 120 formed on one side of the polymer film 101 is welded to the lead tab 190 by ultrasonic welding, laser welding, or spot welding. If the welding heat generated when welding the lead tab 190 is higher than the melting point of the polymer film 101, the polymer film 101 may be melted during the welding process.

[0105] As described above, since the polymer film 101 does not exist in the melted portion thereof, the upper and lower metal sheets 120 can directly contact each other. In this case, since the metal sheet 120 is also in a state of being melted by welding heat, the upper and lower metal sheets 120 are joined. Therefore, since the upper and lower metal sheets 120 are directly melted and bonded in the portion where the polymer film 101 is melted and does not exist, the lead tab 190 welded to one metal sheet 120 can be electrically connected to the upper and lower metal sheets 120 and the conductive material 102 formed on the upper and lower surfaces of the polymer film 101.

[0106] In the positive electrode current collector 100 , 400 , 500 , 600 of the present invention, even if a portion of the polymer film 101 is melted by welding heat, the metal sheet 120 and the polymer film 101 are kept connected, so the lead tab 190 can be connected.

[0107] However, depending on circumstances, the lead tab 190 may be welded to the metal tab 120 even in a state where the polymer film 101 is not melted.

[0108] On the other hand, the positive electrode current collector 100, 400, 500, 600 of the present invention is a current collector used as a positive electrode of a lithium secondary battery, and unlike a conventional current collector made of metal foil, can improve the safety of the lithium secondary battery. This is because the conductive material 102 coated or applied to the polymer film 101 performs the function of disconnecting or reducing the short-circuit current like a fuse.

[0109] Generally, when an internal short circuit or an external short circuit occurs in a secondary battery, the temperature of the secondary battery increases due to the short circuit current, and heat generation may cause the battery to explode. In contrast, even if an internal short circuit or an external short circuit occurs in a lithium secondary battery using the positive electrode collector 100, 400, 500, 600 of the present invention as a positive electrode, the temperature of the lithium secondary battery can be prevented from increasing, and the short circuit current can be disconnected or reduced, thereby ensuring the safety of the lithium secondary battery.

[0110] When a short circuit occurs in a lithium secondary battery using the positive electrode collector 100, 400, 500, 600 of the present invention as the positive electrode, if the potential of the positive electrode collector 100, 400, 500, 600 on which aluminum metal is coated as the conductive material 102 or applied on the polymer film 101 is reduced to a level close to the negative electrode potential (i.e., <0.3 volt, negative electrode Li metal), then when the aluminum conductive material 102 reacts with the electrolyte, the conductive material 102 breaks as if corroded, thereby disconnecting the short circuit current or reducing the short circuit current.

[0111] The conductive material 102 coated or applied on the polymer film 101 performs the function of a current path (pass). If the conductive material 102 reacts with the electrolyte and shatters like corrosion when a short circuit occurs, the current path is disconnected, thereby preventing the short-circuit current from flowing or reducing the short-circuit current.

[0112] In the case of the collector 100, 400, 500, 600 for the positive electrode of the present invention, the reason why the current path can be disconnected or the short-circuit current can be reduced when a short circuit occurs is that since the thickness of the aluminum conductive material 102 formed on the surface of the polymer film 101 is very thin, the conductive material 102 reacts with the electrolyte throughout its depth direction or thickness direction and corrodes or breaks, thereby disconnecting the short-circuit current path or reducing the short-circuit current.

[0113] The inventors of the present invention have conducted resistance measurement of lead tabs of conductive materials 102 of different thicknesses, battery capacity measurement, and nail penetration tests on lithium secondary batteries including the positive electrode current collectors 100, 400, 500, and 600 of the present invention, and have found the optimal thickness range of the conductive material 102 that can ensure the safety of the lithium secondary battery. The test results and the optimal thickness range of the conductive material 102 will be described below.

[0114] First, in order to carry out the above experiments, the Figure 4 The positive electrode current collector 100 of the first embodiment of the present invention is shown. Figure 4The positive electrode collector 100 may include: a conductive material 102 plated or coated on at least one of the upper and lower surfaces of the polymer film 101; an insulating polymer layer 130 formed between the metal sheet 120 and the conductive material 102, used to bond the metal sheet 120 to the conductive material 10; and a lead terminal 190 welded to a metal sheet 120.

[0115] The polymer film 101 is formed of polyethylene terephthalate (PET) with a thickness of 7 μm, and the conductive material 102 can be formed on one side of the polymer film 101 by sputtering with a thickness of 0.12 μm, 0.25 μm, 0.4 μm, and 0.6 μm. In addition, the insulating polymer layer 130 is formed of acrylic glue with a thickness of 10 μm, and the metal sheet 120 is formed of aluminum foil with a thickness of 12 μm on both sides of the polymer film 101 at a 90-degree angle. In addition, the lead terminal 190 is formed of aluminum metal with a thickness of 100 μm and a width of 3 mm, and is welded to the metal sheet 120 formed with the conductive material 102 by ultrasonic welding.

[0116] *Measure the resistance between the plated surface of the conductive material and the lead lug

[0117] Table 1 shows the results of measuring the resistance between the plated surface of the conductive material 102 and the lead tab 190 according to the thickness of the conductive material 102. The resistance was measured using a HIOKI 3554 tester.

[0118] Table 1

[0119]

[0120]

[0121] Referring to Table 1, it can be confirmed that the smaller the thickness of the conductive material 102 , that is, the smaller the plating amount of the conductive material 102 , the greater the resistance between the plated surface of the conductive material 102 and the lead tab 190 .

[0122] *Measure the capacity of lithium secondary batteries according to the thickness of conductive materials

[0123] In order to measure the capacity of the lithium secondary battery according to the thickness of the conductive material 102, a lithium secondary battery having the following characteristics was prepared.

[0124] (1) Positive electrode composition: NCM (L&F NE-X6S) / super-P / PVDF (solef5130=92 / 4 / 4

[0125] (2) Negative electrode composition: graphite (BTR518) / SBR (Zeon BM-400B) / CMC (Nippon paper) = 97 / 1.5 / 1.5

[0126] (3) Positive electrode load: 3mAh / cm 2

[0127] (4) Negative electrode collector: Cu foil (8 μm)

[0128] (5) Negative electrode load: 3.1 mAh / cm 2

[0129] (6) Separation membrane: 7umPE (Tonen)

[0130] (7) Electrolyte: EC / EMC 1M LiFP6, with additives

[0131] Preparation of pouch type lithium secondary battery (DNP113um) by winding positive electrode / separator membrane / negative electrode

[0132] (8) Positive electrode size: 3cm×15cm

[0133] (9) Battery capacity: ~120mAh

[0134] Table 2 shows the results of measuring the battery capacity of the lithium secondary battery having the above-described characteristics according to the thickness of the conductive material 102 .

[0135] Table 2

[0136]

[0137] In Table 2, the % in brackets refers to the ratio of the 0.2C capacity of the conductive material 102 of different thicknesses. Referring to Table 2, it can be seen that the less the plating amount of the conductive material 101, that is, the smaller the thickness of the conductive material 102, the smaller the 1.0C capacity. However, the battery works normally.

[0138] However, the battery does not function when the thickness of the conductive material 102 is 0.12 μm. Therefore, it is known that the thickness of the conductive material 102 needs to be 0.25 μm or more in order to function as a battery.

[0139] Figure 8 1 is a graph showing the capacity measurement results of a lithium secondary battery including a positive electrode current collector according to the first embodiment of the present invention measured by the thickness of the conductive material. Figure 8 To show that the thickness of the conductive material in Table 2 is 0.25 μm (refer to Figure 8(a)), 0.4μm (ref. Figure 8 (b)), 0.6μm (ref. Figure 8 (c) of the capacity measurement results. Figure 8 It can be seen that when the thickness of the conductive material 102 of the positive electrode current collector 100 is 0.25 μm, 0.4 μm, and 0.6 μm, the lithium secondary battery functions as a normal battery.

[0140] * Safety test of lithium secondary batteries according to the thickness of conductive materials: nail penetration test

[0141] In order to conduct safety tests on lithium secondary batteries according to the thickness of the conductive material, after the lithium secondary batteries were fully charged to 4.2 V, a nail puncture short circuit test was conducted using a 3 mm diameter SUS nail pierced into the center of the battery at a speed of 150 mm / sec. Table 3 shows the results of the nail puncture test.

[0142] Table 3

[0143]

[0144] Referring to Table 3, when the conductive material 102 was plated with a thickness of 0.25 μm to 0.6 μm, it was confirmed that the safety of the battery was ensured even if an external short circuit occurred, and the battery functioned normally.

[0145] Fig. 9 1 is a graph showing the results of nail penetration tests of lithium secondary batteries including the positive electrode current collector of the first embodiment of the present invention according to the thickness of the conductive material. Fig. 9 To illustrate the conductive material thickness of 0.25 μm (refer to Fig. 9 (b)), 0.4μm (ref. Fig. 9 (c)), 0.6μm (ref. Fig. 9 The temperature and voltage changes of the battery when the lithium secondary battery with a positive electrode current collector of the conventional metal foil positive electrode current collector (refer to Fig. 9 (a) of the figure shows the temperature and voltage changes of the battery during the nail penetration test. Fig. 9 In part (a), in the case of a battery using a metal foil current collector, it can be seen that when the nail is inserted, the battery temperature rises sharply and the voltage drops sharply. In this case, the safety of the battery is extremely deteriorated. Fig. 9As shown in parts (a) to (c) of FIG. 1 , in the case of a battery using the conductive material 102 coated with a thickness of 0.25 μm, 0.4 μm, and 0.6 μm, it can be seen that even when a nail is inserted, the temperature and voltage slowly decrease. Therefore, since the lithium secondary battery using the positive electrode collector of the present invention slowly decreases the temperature and voltage of the battery even when a nail is inserted, the safety of the battery is improved and enhanced.

[0146] On the other hand, in the positive electrode current collector 100, 400, 500, 600 of the present invention, the aluminum conductive material 102 is coated or applied on the surface of the polymer film 101 by sputtering or evaporation, and a plurality of nano-sized pores may be formed in the aluminum conductive material 102 formed in this way, or irregular shapes such as cracks (hereinafter referred to as "pores") may exist on the surface. This is because the aluminum particles sputtered or deposited on the polymer film 101 are not sputtered or deposited in a 100% close-fitting state without gaps, but there are tiny gaps between the aluminum particles, and these gaps become pores. In contrast, in the case of a positive electrode current collector made of an existing metal foil, since the metal foil is a rolled foil, there are no pores at all.

[0147] Among them, in the case of the collector 100, 400, 500, 600 for the positive electrode of the present invention, the electrolyte penetrates into the multiple pores existing in the aluminum conductive material 102, and the electrolyte can be present in the pores over the entire or partial thickness of the conductive material 102. When a short circuit occurs in this state, since the area where the electrolyte existing in the pores of the conductive material 120 reacts with the conductive material 102 becomes wider, the conductive material 102 is easily corroded or broken in the thickness direction, and finally the short-circuit current cannot flow. As described above, the multiple pores existing in the conductive material 102 act like a fuse, so that the flow of the short-circuit current can be disconnected or reduced in the event of a short circuit.

[0148] As described above, in the positive electrode collector 100, 400, 500, 600 of the present invention, the conductive material 102 is formed on the surface of the polymer film 101 with a thickness of 0.25 μm based on the minimum cross-section and a thickness of 0.6 μm based on the maximum cross-section, thereby improving the energy density and safety of the lithium secondary battery using such electrode collector 100, 400, 500, 600 as the positive electrode, and ensuring the safety of the battery when a short circuit occurs.

[0149] As described above, in one embodiment of the present invention, specific matters such as specific structural elements and limited embodiments and drawings are used for explanation, which is only provided to help the overall understanding of the present invention. The present invention is not limited to the embodiments described above, and a person of ordinary skill in the technical field to which the present invention belongs can make various modifications and variations from such descriptions. Therefore, the concept of the present invention is not limited to the described embodiments, and all the equivalent or equivalent variations of the scope of the invention, including the scope of the invention, belong to the scope of the concept of the present invention.

Claims

1. A positive electrode current collector, which is a positive electrode current collector replacing a metal foil, characterized in that: include: Polymer film, made of non-metallic and non-conductive materials; Aluminum conductive material is coated or applied to at least one of the upper surface or the lower surface of the polymer film with a thickness of 0.25 to 0.6 μm to form the outermost surface of the positive electrode collector; and a metal sheet formed on at least one of the upper surface side or the lower surface side of the polymer film so as to be electrically connected to the conductive material; When an internal short circuit or an external short circuit occurs, the conductive material has the function of an electrochemical fuse, or has the function of disconnecting or reducing the short circuit current.

2. A positive electrode current collector, which is a positive electrode current collector replacing a metal foil, characterized in that: include: Polymer film, made of non-metallic and non-conductive materials; Aluminum conductive material is coated or applied to at least one of the upper surface or the lower surface of the polymer film with a thickness of 0.25 to 0.6 μm to form the outermost surface of the positive electrode collector; and a metal sheet formed on at least one of the upper surface side or the lower surface side of the polymer film so as to be electrically connected to the conductive material; When an internal short circuit or an external short circuit occurs, the conductive material reacts with the electrolyte to break the short circuit current path or reduce the short circuit current while being corroded or broken in the thickness direction over the entire thickness thereof.

3. A positive electrode current collector, which is a positive electrode current collector replacing a metal foil, characterized in that: include: Polymer film, made of non-metallic and non-conductive materials; Aluminum conductive material is coated or applied to at least one of the upper surface or the lower surface of the polymer film with a thickness of 0.25 to 0.6 μm to form the outermost surface of the positive electrode collector; and a metal sheet formed on at least one of the upper surface side or the lower surface side of the polymer film so as to be electrically connected to the conductive material; When an internal short circuit or an external short circuit occurs, as the potential of the positive electrode collector drops to the negative electrode potential, the conductive material corrodes or breaks along the thickness direction over the entire thickness, disconnecting the short circuit current path or reducing the short circuit current.

4. The positive electrode current collector according to any one of claims 1 to 3, characterized in that: The conductive material is formed between the metal sheet and the polymer film.

5. The positive electrode current collector according to claim 4, characterized in that: It includes a lead terminal piece joined or connected to the above-mentioned metal sheet.

6. The positive electrode current collector according to claim 4, characterized in that: An insulating polymer layer is formed between the conductive material and the metal sheet.

7. The positive electrode current collector according to any one of claims 1 to 3, characterized in that: The conductive material applied or coated on the surface of the polymer film forms a plurality of nano-sized pores.

8. The positive electrode current collector according to claim 6, characterized in that: The metal sheet is formed on one surface of the conductive material, and the conductive material is formed on the upper and lower surfaces of the polymer film. include: an insulating polymer layer formed on the surface of the conductive material on the upper surface side or the lower surface side of the polymer film facing the metal sheet; and The lead terminal piece is bonded or connected to the insulating polymer layer on the side facing the metal sheet.

9. The positive electrode current collector according to claim 6, characterized in that: The conductive material is formed on one of the upper surface or the lower surface of the polymer film. The conductive material, the insulating polymer layer, and the metal sheet are formed on the same side with respect to the upper surface or the lower surface of the polymer film.

10. The positive electrode current collector according to claim 9, characterized in that: A lead tab bonded or connected to the polymer film is formed on a surface of the upper surface or the lower surface of the polymer film that faces the metal sheet.

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