Positive electrode current collector for a lithium secondary battery, manufacturing method therefor, and lithium secondary battery containing said current collector

Abstract

A cathode current collector for a lithium secondary battery according to embodiments of the present invention may include a first metal layer including a first region and a second region having a thickness smaller than that of the first region, and a second metal layer disposed on the second region of the first metal layer and having a different composition than the first metal layer. Accordingly, when the cathode current collector is coupled to a cathode tab, etc., heat generation due to a resistance difference at the coupled portion can be prevented.

Description

Technical area

[0001] The present disclosure relates to a positive electrode (“cathode”) current collector for a lithium secondary battery, a method of manufacturing the cathode current collector for a lithium secondary battery, and a lithium secondary battery including the cathode current collector for a lithium secondary battery. State of the art

[0002] A secondary battery is a battery that can be repeatedly charged and discharged. With the rapid advancement of information and communication technology and the display industry, secondary batteries have been used as a power source in various portable electronic telecommunications devices such as camcorders, mobile phones, laptops, and so on. Recently, a battery pack with a secondary battery has also been developed, which is used as a power source in environmentally friendly vehicles such as electric vehicles and hybrid vehicles.

[0003] Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, nickel-hydrogen batteries, and the like. Among these, lithium secondary batteries have a high operating voltage and high energy density per unit weight, making them advantageous in terms of charging speed and lightweight design. In this regard, lithium secondary batteries have been actively developed and applied in various industrial fields.

[0004] The lithium secondary battery may, for example, comprise an electrode assembly with a cathode, an anode, and a separator, as well as an electrolyte impregnated into the electrode assembly. The lithium secondary battery may further include, for example, a bag-like outer casing housing the electrode assembly and the electrolyte.

[0005] In a lithium secondary battery, the cathode can be formed by applying a cathode active material to a cathode current collector, followed by drying and pressing the current collector. The cathode current collector can be connected to a cathode tab and protrude from the outer casing.

[0006] However, when the cathode current collector is coupled to the cathode tab, a resistance difference occurs due to the different composition between the cathode current collector and the cathode tab, and excessive heat may be generated at the connecting portion of the cathode current collector and the cathode tab.

[0007] For example, Korean Patent Application No. 10-2283842 discloses an electrode current collector for a lithium secondary battery containing a novel conductive material. Summary of the inventionProblems to be solved by the invention

[0008] An object of the present disclosure is to provide a cathode current collector for a lithium secondary battery with improved stability.

[0009] Another object of the present disclosure is to provide a method for manufacturing the cathode current collector for a lithium secondary battery.

[0010] Another object of the present disclosure is to provide a lithium secondary battery including the cathode current collector for a lithium secondary battery. Means to solve the problems

[0011] A cathode current collector for a lithium secondary battery according to exemplary embodiments may include: a first metal layer including a first region and a second region having a thickness smaller than that of the first region; and a second metal layer disposed on the second region of the first metal layer and having a different composition than that of the first metal layer.

[0012] In some embodiments, the first metal layer may be a single layer containing aluminum.

[0013] In some embodiments, the second metal layer may include copper.

[0014] In some embodiments, the second metal layer may comprise an aluminum-copper alloy layer disposed on the second region of the first metal layer and a copper layer disposed on the aluminum-copper alloy layer.

[0015] In some embodiments, the aluminum-copper alloy layer may include at least one of Al2Cu, AlCu, and AlCu2.

[0016] In some embodiments, the second metal layer may not be formed on the first region of the first metal layer.

[0017] In some embodiments, the cathode current collector may have a constant overall thickness.

[0018] In some embodiments, the second region may include a distal portion having a constant thickness and an inclined portion extending between the first region and the distal portion, wherein the thickness of the inclined portion may gradually decrease from the first region toward the distal portion.

[0019] In some embodiments, the second metal layer may be formed on both surfaces of the second region of the first metal layer.

[0020] A lithium secondary battery according to exemplary embodiments may include: a cathode including the cathode current collector described above and a cathode active material layer disposed on the cathode current collector; and an anode disposed to oppose the cathode.

[0021] In some embodiments, the cathode current collector may include an active region corresponding to the first region and a connection region corresponding to the second region, and the layer of active cathode material may be disposed on at least a portion of the active region.

[0022] A method for manufacturing a cathode current collector for a lithium secondary battery according to exemplary embodiments may include: forming a preliminary current collector by bonding a second metal foil having a different composition than the first metal foil to a portion of at least one surface of the first metal foil; and heat-treating the preliminary current collector, wherein the preliminary current collector includes a first preliminary metal layer having an active portion and a non-coated portion with a thickness smaller than that of the active portion, and a second preliminary metal layer formed on the non-coated portion.

[0023] In some embodiments, the step of forming a preliminary current collector may include: pressing a portion of the first metal foil to form a groove; and bonding the second metal foil to the groove.

[0024] In some embodiments, the step of forming a preliminary current collector may include: placing the second metal foil on a portion of the first metal foil; and rolling and bonding the first metal foil and the second metal foil.

[0025] In some embodiments, the preliminary current collector may further include a preliminary alloy layer formed between the first preliminary metal layer and the second preliminary metal layer.

[0026] In some embodiments, the step of forming a preliminary current collector may further comprise: hot rolling the first metal foil to which the second metal foil is bonded.

[0027] In some embodiments, the step of heat treating the preliminary current collector may include: cold rolling the preliminary current collector; and annealing the cold-rolled preliminary current collector.

[0028] In some embodiments, the second metal foil may be bonded to a central portion in a width direction of the first metal foil along a longitudinal direction, and the method may further comprise, after the step of heat-treating the preliminary current collector, slitting the central portion in the width direction of the heat-treated preliminary current collector along the longitudinal direction. Beneficial effects

[0029] The cathode current collector for a lithium secondary battery according to exemplary embodiments may include two or more metal layers with different compositions in a partial region. The region where the two or more metal layers are formed may be used as a connection region with a cathode tab. Accordingly, when the cathode tab is connected to the cathode current collector, a homogeneous connection can be established at the connection portion, thereby suppressing heat generation due to a resistance difference.

[0030] In some embodiments, the lithium secondary battery may include the cathode current collector. This may reduce the internal resistance of the secondary battery and improve the capacity characteristics. Brief description of the drawings Fig.1 is a schematic cross-sectional view showing a cathode current collector for a lithium secondary battery according to exemplary embodiments. Fig. 2 is a schematic flowchart for describing a method of manufacturing a cathode current collector for a lithium secondary battery according to exemplary embodiments. Fig. 3 is a schematic cross-sectional view showing a cathode for a lithium secondary battery according to exemplary embodiments. Fig. 4 and Fig. 5 are a schematic plan view and a cross-sectional view showing a lithium secondary battery according to exemplary embodiments. Embodiment of the invention

[0031] Embodiments of the present invention provide a cathode current collector for a lithium secondary battery that includes two or more metal layers in a portion, and a method for manufacturing the same. Furthermore, a lithium secondary battery including the cathode current collector for a lithium secondary battery is provided.

[0032] Hereinafter, the embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, since the drawings accompanying the present disclosure illustrate only one of several preferred embodiments of the present invention, in order to more easily understand the technical spirit of the present invention with the invention described above, it should not be construed as being limited to such a description shown in the drawings.

[0033] Fig.1 is a schematic cross-sectional view showing a cathode current collector for a lithium secondary battery according to exemplary embodiments.

[0034] Referring to Fig. 1, a cathode current collector 105 may include a first metal layer 110 and a second metal layer 130, according to one embodiment. For example, the first metal layer 110 may include a first metal. The second metal layer 130 may, for example, include a second metal with a different composition than the first metal.

[0035] In exemplary embodiments, the first metal layer 110 may include a first region I and a second region II with a thickness smaller than that of the first region I, and the second metal layer 130 may be disposed on the second region II of the first metal layer 110. In this case, the second metal layer 130 may not be disposed on the first region I.

[0036] In some embodiments, the first region I of the first metal layer 110 may correspond to an active region of the cathode current collector 105. The active region may be a region in which a layer of active cathode material 140 is formed.

[0037] In some embodiments, the second region II of the first metal layer 110 may correspond to a connection region of the cathode current collector 105. The connection region may be a region in which the cathode current collector is connected to the cathode tab.

[0038] In some embodiments, the density in the second region II of the first metal layer 110 may differ from the density in the first region I. For example, since the second metal layer 130 is formed on the second region II with a different composition than that of the first metal layer 110, the second region II may have a different density than the first region I.

[0039] For example, the density in the second region II of the first metal layer 110 may be greater than the density in the first region I. For example, the density in the second region II of the first metal layer 110 may be smaller than the density in the first region I.

[0040] In some embodiments, the thickness of the second metal layer 130 may be substantially equal to or greater than the difference between the thickness of the first metal layer 110 in the first region I and the thickness of the second region II.

[0041] In one embodiment, the sum of the thicknesses of the first metal layer 110 and the second metal layer 130 in the second region II may be substantially equal to the thickness of the first metal layer 110 in the first region I.

[0042] Accordingly, the cathode current collector 105 can have a constant thickness overall. Since the thickness of the cathode current collector 105 is constant over the entire area of ​​the cathode current collector 105, for example, the coating property of the active cathode material can be improved and the thickness and volume of the electrode assembly can be reduced when stacking.

[0043] In some embodiments, the second region II may include a distal portion with a constant thickness and an inclined portion extending between the first region I and the distal portion. Accordingly, a bonding area between the first metal layer 110 and the second metal layer 130 may be expanded during bonding, thereby improving the bonding strength of the first metal layer 110 and the second metal layer 130. As a result, it is possible to prevent separation or peeling between the first metal layer 110 and the second metal layer 130.

[0044] In one embodiment, the thickness of the inclined portion may gradually decrease from the first region I to the distal portion. Accordingly, a uniform rolling force can be applied when rolling and bonding the second metal layer 130 to the first metal layer 110, thereby suppressing unevenness in the bonding strength.

[0045] In some embodiments, second metal layers 130 may be disposed on both surfaces of the second region II of the first metal layer 110. Accordingly, when the cathode current collector 105 is connected to the cathode tab, a resistance change at the connection portion between the cathode current collector 105 and the cathode tab may be uniform across the entire connection portion.

[0046] In some embodiments, the compositions of the first metal layer 110 and the second metal layer 130 may be different.

[0047] For example, the first metal layer 110 may be a single layer containing aluminum, and the second metal layer 130 may be a copper-containing metal layer. Furthermore, the first metal layer 110 may be a single layer containing copper, for example, and the second metal layer 130 may be an aluminum-containing metal layer.

[0048] In some embodiments, an alloy layer 120 may be formed between the first metal layer 110 and the second metal layer 130 in the second region II. The alloy from which the alloy layer 120 is formed may, for example, be an alloy of the first metal used to form the first metal layer 110 and the second metal used to form the second metal layer 130.

[0049] Accordingly, the alloy layer 120 can serve as a buffer layer for the composition change between the first metal layer 110 and the second metal layer 130 and prevent the separation between the first metal layer 110 and the second metal layer 130.

[0050] In one embodiment, the alloy layer 120 may be an aluminum-copper alloy layer. The aluminum-copper alloy layer may, for example, include at least one of Al2Cu, AlCu, and AlCu2.

[0051] As described above, when the first metal layer 110 is an aluminum layer and the second metal layer 130 is a copper layer, the cathode current collector 105 may include a stacked structure including an aluminum layer, an aluminum-copper alloy layer formed on the aluminum layer, and a copper layer formed on the aluminum-copper alloy layer in the connection region.

[0052] When the first metal layer 110 is a copper layer and the second metal layer 130 is an aluminum layer, the cathode current collector 105 may include a stacked structure including a copper layer, an aluminum-copper alloy layer formed on the copper layer, and an aluminum layer formed on the aluminum-copper alloy layer in the connection region.

[0053] Fig. 2 is a schematic flowchart for describing a method of manufacturing a cathode current collector for a lithium secondary battery according to exemplary embodiments.

[0054] As in Fig. 2, a preliminary current collector may be formed from a first metal foil and a second metal foil (e.g., method S10).

[0055] In exemplary embodiments, the preliminary current collector may be formed by bonding the second metal foil to a portion of at least one surface of the first metal foil.

[0056] The first metal foil and the second metal foil may have different compositions. For example, the first metal foil may be an aluminum foil and the second metal foil may be a copper foil. For example, the first metal foil may be a copper foil and the second metal foil may be an aluminum foil.

[0057] In some embodiments, the first metal foil and the second metal foil may be joined in a roll-to-roll process.

[0058] In one embodiment, a portion of the first metal foil may be pressed to form a groove, and the second metal foil may be bonded to the groove to form the preliminary current collector. Accordingly, the bonding position of the second metal foil on the first metal foil can be selectively determined in advance, thereby improving the precision of the bonding position.

[0059] In one embodiment, the second metal foil may be placed on a portion of the first metal foil, and the first metal foil and the second metal foil may be rolled and bonded to form the preliminary current collector.

[0060] In this case, the second metal foil can be rolled onto the first metal foil, so that the overall thickness of the preliminary current collector remains constant. Accordingly, the first metal foil and the second metal foil can be bonded by a single roll pressing, thereby improving the processing speed.

[0061] In some embodiments, the region where the second metal foil is joined may be an end portion of the first metal foil.

[0062] In some embodiments, the region where the second metal foil is bonded may correspond to a central portion in the width direction of the first metal foil. Accordingly, the second metal foil may be bonded to the central portion in the width direction of the first metal foil along the longitudinal direction. The term "longitudinal direction" as used herein may refer to a direction perpendicular to the width direction.

[0063] In some embodiments, the preliminary current collector may comprise a first preliminary metal layer including an active portion and a non-coated portion whose thickness is less than that of the active portion, and a second preliminary metal layer formed on the non-coated portion of the first preliminary metal layer.

[0064] The first region I of the first metal layer may be formed from the active part and may correspond to the active region of the cathode current collector 105 on which the layer of cathode active material 140 is formed. Accordingly, the layer of cathode active material 140 may be formed on a single metal layer.

[0065] The second region II of the first metal layer may be formed from the uncoated portion and may correspond to a connection region where the cathode current collector 105 is connected to the cathode tab. Accordingly, the composition of the uncoated portion may be adjusted so that the cathode current collector 105 can be homogeneously connected to the cathode tab.

[0066] In one embodiment, the preliminary current collector may further include a preliminary alloy layer formed between the first preliminary metal layer and the second preliminary metal layer. The preliminary alloy layer may, for example, be formed from an alloy of the first metal used to form the first preliminary metal layer and the second metal used to form the second preliminary metal layer.

[0067] In some embodiments, the preliminary current collector can be manufactured by bonding the second metal foil to the first metal foil, followed by hot rolling the first metal foil to which the second metal foil is bonded. Accordingly, the alloy forming the preliminary alloy layer between the first preliminary metal layer and the second preliminary metal layer can be recrystallized, thereby preventing segregation of the preliminary alloy layer.

[0068] In some embodiments, the first metal used to form the first preliminary metal layer may be aluminum, and the second metal used to form the second preliminary metal layer may be copper.

[0069] In this case, the uncoated portion of the preliminary current collector may include an aluminum layer, an aluminum-copper alloy layer formed on the aluminum layer, and a copper layer formed on the aluminum-copper alloy layer. Accordingly, a homogeneous connection with the cathode current collector 105 formed from the preliminary current collector can be realized even if the cathode tab is made of copper. Therefore, it is possible to suppress heat generation by preventing resistance differences caused by the connection between heterogeneous metals.

[0070] In some embodiments, the first metal used to form the first preliminary metal layer may be copper, and the second metal used to form the second preliminary metal layer may be aluminum.

[0071] In this case, the uncoated portion of the preliminary current collector may include a copper layer, an aluminum-copper alloy layer formed on the copper layer, and an aluminum layer formed on the aluminum-copper alloy layer. Furthermore, the active portion may be a copper layer. Accordingly, the electrical conductivity of the cathode current collector 105 formed from the preliminary current collector can be improved, thereby increasing the energy density of the lithium secondary battery.

[0072] In exemplary embodiments, the preliminary current collector may be heat treated to prepare the cathode current collector 105 (e.g., processes S20 and S30).

[0073] In some embodiments, the preliminary current collector may be cold rolled, and the cold rolled preliminary current collector may be annealed to heat treat the preliminary current collector.

[0074] In one embodiment, the preliminary current collector may be cold-rolled to reduce the thickness of the preliminary current collector. This may improve the mechanical strength and hardness of the preliminary current collector.

[0075] In one embodiment, the cold-rolled preliminary current collector may be annealed to remove internal stresses of the cold-rolled preliminary current collector and to soften it.

[0076] In one embodiment, cold rolling and annealing can be performed repeatedly. This can improve the mechanical strength of the preliminary current collector and refine the metal crystals.

[0077] In some embodiments, as described above, the second metal foil may be bonded to the widthwise central portion of the first metal foil. In this case, after the heat-treatment step, the widthwise central portion of the heat-treated preliminary current collector may be slit along the longitudinal direction to prepare the current collector. Accordingly, a plurality of current collectors can be manufactured in a single process, thereby improving the production yield of the cathode current collector 105.

[0078] In some embodiments, both corners of the uncoated portion of the cathode current collector 105 may be notched.

[0079] In one embodiment, the width of the uncoated portion of the cathode current collector 105, including the uncoated portion where the corners are notched, may be equal to the width of the cathode tab. Accordingly, electrical conductivity may be improved when the uncoated portion and the cathode tab are bonded together.

[0080] Fig. 3 is a schematic cross-sectional view showing a cathode for a lithium secondary battery according to exemplary embodiments.

[0081] Referring to Fig. 3, the cathode 100 may include the cathode current collector 105 and the active cathode material layer 140 formed by depositing an active cathode material onto the cathode current collector 105. The active cathode material layer 140 may be formed on at least a portion of the active region of the cathode current collector 105.

[0082] The layer of active cathode material 140 can be formed by coating the active area of ​​the cathode current collector 105 with a cathode slurry, followed by compacting and drying the slurry. The cathode slurry can be formed by mixing and stirring the active cathode material with a binder, a conductive material, and / or a dispersant in a solvent.

[0083] In exemplary embodiments, the active cathode material may contain a compound capable of reversibly intercalating and deintercalating lithium ions. The active cathode material may contain lithium transition metal composite oxide particles. For example, the lithium transition metal composite oxide particles may contain nickel (Ni) and further contain at least one of cobalt (Co) and manganese (Mn).

[0084] The lithium transition metal composite oxide particles can be represented, for example, by the following formula 1. Li x Ni 1-y M y O 2+z [Formula 1]

[0085] In Formula 1, x can be in a range of 0.9≤x≤1.1, y can be in a range of 0≤y≤0.7, and z can be in a range of -0.1≤z≤0.1. M can be one or more selected from Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, or Sn.

[0086] The cathode binder may contain, for example, an organic binder such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, etc., or an aqueous binder such as styrene-butadiene rubber (SBR) and may be used together with a thickener such as carboxymethylcellulose (CMC).

[0087] For example, a PVDF-based binder can be used as a cathode binder. In this case, the amount of binder used to form the cathode active material layer can be reduced and the amount of cathode active material can be relatively increased, thereby improving the performance and capacity of the secondary battery.

[0088] The conductive material can be used to facilitate electron transfer between the active material particles. The conductive material can, for example, comprise a carbon-based conductive material such as graphite, carbon black, graphene, or carbon nanotubes and / or a metal-based conductive material such as tin, tin oxide, titanium oxide, or a perovskite material such as LaSrCoO3 and LaSrMnO3, etc.

[0089] Fig. 4 and Fig. 5 are a schematic plan view and a cross-sectional view showing a lithium secondary battery according to exemplary embodiments, respectively. Fig.5 is a cross-sectional view on line II' in Fig. 4 in the direction of the thickness of the battery.

[0090] As in Fig. 4 and Fig. 5, the lithium secondary battery may include a cathode 100 having the cathode current collector 105 described above and an anode 150 opposite the cathode.

[0091] According to exemplary embodiments, the anode 150 may include an anode current collector 155 and a layer of active anode material 160 formed by coating the anode current collector 155 with an active anode material.

[0092] The active anode material used in the present invention may comprise any material known in the art as long as it can intercalate and deintercalate lithium ions, without particular limitation. For example, carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, carbon fibers, etc., a lithium alloy, a silicon (Si) compound, or tin, etc., may be used. Examples of amorphous carbon may include hard coal, coke, mesocarbon microbeads (MCMB) calcined at 1600 °C or less, mesophase pitch-based carbon fibers (MPCF), or the like.

[0093] Examples of crystalline carbon may include graphite-based carbon such as natural graphite, graphite coke, MCMB graphite, MPCF graphite, or similar. Other elements contained in the lithium alloy may include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium, among others.

[0094] The silicon-based active material can be SiO x (0 <x<2) oder SiO x (0 <x<2), das eine Lithiumverbindung enthält, enthalten. Das SiO x , which contains the Li compound, SiO x containing lithium silicate. The lithium silicate may be present in at least part of the SiO x (0 <x<2)-Teilchen vorhanden sein, z. B. im Inneren und / oder auf der Oberfläche der SiO x (0 <x<2)-Teilchen. In einer Ausführungsform kann das Lithiumsilikat Li2SiO3, Li2Si2O5, Li4SiO4, Li4Si3O8 usw. enthalten.

[0095] The silicon-based active material may also contain a silicon-carbon compound such as silicon carbide (SiC).

[0096] For example, the anode current collector 155 may include gold, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and in one embodiment, the anode current collector 155 may include copper or a copper alloy.

[0097] For example, a slurry can be prepared by mixing the active anode material with the above-described binder, conductive material, thickener, and the like in a solvent and stirring the mixture. The slurry can be applied to at least one surface of the anode current collector 155 and then compacted and dried to produce the anode 150 including the layer of active anode material 160.

[0098] Materials substantially identical or similar to those described above can be used as the binder and conductive material. For example, in some embodiments, a binder for forming an anode may include an aqueous binder such as styrene-butadiene rubber (SBR) to ensure compatibility with a carbon-based active material, and may be used in conjunction with a thickener such as carboxymethylcellulose (CMC).

[0099] In some embodiments, a separation membrane 170 may be disposed between the cathode 100 and the anode 150. The separation membrane 170 may comprise a porous polymer film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, or ethylene / methacrylate copolymer. The separation membrane 170 may include a nonwoven fabric made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0100] In some embodiments, the anode 150 may have a larger area (e.g., a contact area with the separation membrane 170) and / or a larger volume than that of the cathode 100. This allows lithium ions generated by the cathode 100 to migrate smoothly to the anode 150 without, for example, being precipitated during the process. Accordingly, the effect of simultaneously improving performance and stability can be more easily realized by combining it with the composite hydroxide particles or the active cathode material described above.

[0101] According to exemplary embodiments, an electrode cell is defined by the cathode 100, the anode 150, and the separation membrane 170, and a plurality of electrode cells may be stacked to form an electrode assembly 180.

[0102] The electrode assembly 180 can be housed together with an electrolyte in an outer casing 190 to form a lithium secondary battery. In exemplary embodiments, a non-aqueous electrolyte can be used as the electrolyte.

[0103] The non-aqueous electrolyte may contain a lithium salt of an electrolyte and an organic solvent, wherein the lithium salt is replaced, for example, by Li + X - and is represented as an anion (X - ) of the lithium salt F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C -, CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - , etc. can be cited as examples.

[0104] As the organic solvent, for example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfite, tetrahydrofuran, and the like can be used. These compounds can be used alone or in combination with two or more of them.

[0105] As in Fig.As shown in Figure 4, electrode tabs (a cathode tab and an anode tab) may protrude from the cathode current collector 105 and the anode current collector 155, respectively, belonging to each electrode cell, and extend to one side of the housing 190. The cathode current collector 105 and the anode current collector 155 may comprise the connection region and the active region, respectively, and the electrode tabs (the cathode tab and the anode tab) may be connected to the connection portions and protrude. The electrode tabs may be connected to the electrode tab connection regions. The electrode tabs may be fused to one side of the housing 190 to form electrode lines (a cathode line 107 and an anode line 157) that extend to or are exposed outside the housing 190.

[0106] The lithium secondary battery can be manufactured, for example, in a cylindrical shape using a container, in a prismatic shape, in the shape of a bag, or in the shape of a coin.

[0107] Below, embodiments of the present disclosure will be described in more detail with reference to specific experimental examples. However, the following examples and comparative examples included in the experimental examples are only illustrative of the present disclosure, and those skilled in the art will naturally understand that various changes and modifications are possible within the scope and spirit of the present disclosure. Such changes and modifications are properly encompassed in the appended claims. Examples and comparative examplesExample 11) Manufacturing of the cathode current collector

[0108] A copper foil was bonded to both surfaces of a second portion of aluminum foil in a roll-to-roll process. A metal foil formed by bonding an aluminum foil and a copper foil was hot-rolled at 600°C to form a preliminary aluminum-copper alloy layer by recrystallizing aluminum and copper. An aluminum-copper alloy layer was formed by heat-treating the preliminary aluminum-copper alloy layer at 450°C to achieve homogenization. Then, first cold rolling, first annealing, second cold rolling, and second annealing were performed. After that, the length of the uncoated part including the second portion was notched to match the length of the end of the cathode tab, thereby fabricating a cathode current collector with the bonding portion.

[0109] The aluminum-copper alloy layer was formed in the order of an Al2-Cu layer, an AlCu layer and an AlCu2 layer from the aluminum layer in the center. 2) Production of the cathode

[0110] LiNi 0.6 Co 0.2 Mn 0.2 O2 as the active cathode material, carbon black as the conductive cathode material, and polyvinylidene fluoride (PVDF) as the cathode binder were mixed in a weight ratio of 95:3:2 to prepare a cathode slurry. The cathode slurry was then applied to a portion of the cathode current collector except for a cathode tab connecting portion, followed by drying and pressing to form a cathode active material layer. Afterward, the cathode current collector and the cathode tab were bonded together through the bonding portion to form a cathode.

[0111] The cathode tab was made of copper. 3) Manufacturing the anode

[0112] An active anode material obtained by mixing artificial graphite and natural graphite in a weight ratio of 7:3, styrene-butadiene rubber, and carboxymethyl cellulose were dispersed in distilled water in a weight ratio of 97:1:2 to prepare an anode slurry.

[0113] To prepare an anode, the anode slurry was applied to a portion of a copper foil with a protrusion, excluding the protrusion, and then dried and pressed. The protrusion was then bonded to an anode tab to produce an anode.

[0114] The anode tab was made of copper. 4) Production of the secondary battery cell

[0115] A polyethylene separation membrane (20 µm thick) was inserted between the cathode and anode to form a unit electrode assembly. An electrode assembly was formed by stacking the unit electrode assemblies to achieve a capacity of 80 Ah. A cathode lead and an anode lead were welded and connected to the cathode tab and the anode tab, respectively.

[0116] The cathode line and the anode line were made of copper and had a thickness of 0.3 mm.

[0117] A 1M LiPF6 solution (a mixed solvent of EC and EMC in a volume ratio of 30:70) was prepared, and then 1 wt% of fluoroethylene carbonate (FEC), 0.3 wt% of vinylethylene carbonate (VC), 1 wt% of lithium difluorophosphate (LiPO2F2), 0.5 wt% of 1,3-propanesultone (PS), and 0.5 wt% of prop-1-ene-1,3-sultone (PRS) were added in the amounts described above based on 100 wt% of the total electrolyte to prepare an electrolyte.

[0118] The electrode assembly was placed in a bag (casing) so that some portions of the cathode lead and the anode lead are exposed to the outside of the bag, followed by sealing three sides of the bag except for one side of an electrolyte injection part.

[0119] The electrolyte was injected into the bag, and the side of the electrolyte injection part was sealed to prepare a lithium secondary battery. 5) Manufacturing of the secondary battery module

[0120] The secondary battery leads were connected to a bus bar to interconnect the lithium secondary batteries and form a lithium secondary battery module.

[0121] The bus bar was formed of copper, and 12 lithium secondary batteries were connected to form a package of the secondary battery module. Example 2

[0122] A lithium secondary battery and a lithium secondary battery module were manufactured in the same manner as in Example 1, except that the cathode tab and the cathode lead were formed of aluminum and the thickness of the cathode lead was 0.4 mm. Comparison example 1

[0123] A lithium secondary battery and a lithium secondary battery module were manufactured in the same manner as in Example 1, except that the cathode current collector was formed of aluminum foil, the cathode tab and the cathode lead were formed of aluminum, and the thickness of the cathode lead was 0.4 mm. Experimental example (1) Measurement of the resistance at the welding section between the electrode current collector and the electrode tab

[0124] A resistance meter was connected to both ends of the cathode current collector and the cathode tab, and a microcurrent was applied to measure the resistance at the weld section.

[0125] In addition, the resistance meter was connected to both ends of the anode current collector and the anode tab, and a microcurrent was applied to measure the resistance at the weld section. (2) Measurement of the resistance of the secondary battery cell

[0126] At the point where the state of charge (SOC) of the secondary batteries according to the examples and comparative examples was set to 50%, a current of 1 C was applied for 10 seconds and the cell resistance was calculated by a voltage change. (3) Measurement of the resistance of the secondary battery module

[0127] At the point where the state of charge (SOC) of the secondary battery modules according to the examples and comparative examples was set to 50%, a current of 1 C was applied for 10 seconds and the module resistance was calculated by a voltage change.

[0128] The evaluation results are shown in Table 1.

[148] [TABLE 1] Resistance at the cathode welding section (mΩ) Resistance at the anode welding section (mΩ) Resistance of the secondary battery cell (mΩ) Resistance of the secondary battery module (mΩ) Example 1 0,015 0,017 1,095 13,53 Example 2 0,025 0,017 1,105 14,06 Comparison example 1 0,02 0,017 1,1 13,86

[0129] Referring to Table 1, in Example 1, where both the surface of the connecting portion of the cathode current collector and the cathode tab were formed of copper, the resistance at the cathode tab welding portion, the resistance of the secondary battery cell, and the resistance of the secondary battery module were all reduced. In Example 2, where the surface of the connecting portion of the cathode current collector was formed of copper but the cathode tab was formed of aluminum, the resistance at the cathode welding portion, the resistance of the secondary battery cell, and the resistance of the secondary battery module were all slightly increased.

[0130] In Comparative Example 1, in which both the connecting portion of the cathode current collector and the cathode tab were formed of aluminum, the resistance at the welding portion of the cathode tab, the resistance of the secondary battery cell, and the resistance of the secondary battery module were slightly increased. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] KR 10-2283842

[0007]

Claims

[1] Cathode current collector for a lithium secondary battery, comprising: a first metal layer comprising a first region and a second region having a thickness less than that of the first region; and a second metal layer disposed on the second region of the first metal layer and having a different composition than that of the first metal layer. [2] The cathode current collector for a lithium secondary battery according to claim 1, wherein the first metal layer is a single layer containing aluminum. [3] A cathode current collector for a lithium secondary battery according to claim 2, wherein the second metal layer comprises copper. [4] The cathode current collector for a lithium secondary battery according to claim 3, wherein the second metal layer comprises an aluminum-copper alloy layer disposed on the second region of the first metal layer and a copper layer disposed on the aluminum-copper alloy layer. [5] The cathode current collector for a lithium secondary battery according to claim 4, wherein the aluminum-copper alloy layer comprises at least one of Al2Cu, AlCu and AlCu2. [6] The cathode current collector for a lithium secondary battery according to claim 1, wherein the second metal layer is not formed on the first region of the first metal layer. [7] A cathode current collector for a lithium secondary battery according to claim 1, wherein the cathode current collector has a constant thickness as a whole. [8] A cathode current collector for a lithium secondary battery according to claim 1, wherein the second region comprises a distal part having a constant thickness and an inclined part extending between the first region and the distal part, wherein the thickness of the inclined part gradually decreases from the first region towards the distal part. [9] The cathode current collector for a lithium secondary battery according to claim 1, wherein the second metal layer is formed on both surfaces of the second region of the first metal layer. [10] Lithium secondary battery comprising: a cathode comprising the cathode current collector according to claim 1 and a cathode active material layer disposed on the cathode current collector; and an anode opposite the cathode. [11] The lithium secondary battery according to claim 10, wherein the cathode current collector comprises an active region corresponding to the first region and a connection region corresponding to the second region, and the cathode active material layer is disposed on at least a part of the active region. [12] A method of manufacturing a cathode current collector for a lithium secondary battery, comprising: Forming a preliminary current collector by bonding a second metal foil having a different composition than the first metal foil to a portion of at least one surface of the first metal foil; and Heat treatment of the preliminary current collector, wherein the preliminary current collector comprises a first preliminary metal layer including an active portion and a non-coated portion having a thickness smaller than that of the active portion, and a second preliminary metal layer formed on the non-coated portion. [13] A method of manufacturing a cathode current collector for a lithium secondary battery according to claim 12, wherein the step of forming a preliminary current collector comprises: pressing a portion of the first metal foil to form a groove; and Connecting the second metal foil to the groove. [14] A method of manufacturing a cathode current collector for a lithium secondary battery according to claim 12, wherein the step of forming a preliminary current collector comprises: Placing the second metal foil on a portion of the first metal foil; and Rolling and bonding the first metal foil and the second metal foil. [15] A method of manufacturing a cathode current collector for a lithium secondary battery according to claim 12, wherein the preliminary current collector further comprises a preliminary alloy layer formed between the first preliminary metal layer and the second preliminary metal layer. [16] A method of manufacturing a cathode current collector for a lithium secondary battery according to claim 15, wherein the step of forming a preliminary current collector further comprises: Hot rolling of the first metal foil to which the second metal foil was bonded. [17] A method of manufacturing a cathode current collector for a lithium secondary battery according to claim 12, wherein the step of heat-treating the preliminary current collector comprises: Cold rolling the preliminary current collector; and annealing the cold-rolled preliminary current collector. [18] A method of manufacturing a cathode current collector for a lithium secondary battery according to claim 12, wherein the second metal foil is bonded to a central portion in a width direction of the first metal foil along a longitudinal direction, and further comprising, after the step of heat-treating the preliminary current collector, slitting the central portion in the width direction of the heat-treated preliminary current collector along the longitudinal direction.

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