Positive electrode current collector for lithium secondary battery, method for manufacturing same, and lithium secondary battery comprising same

Abstract

A positive electrode current collector for a lithium secondary battery according to an embodiment of the present invention 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. Therefore, even when a high-density positive electrode active material layer is formed on the positive electrode current collector, deformation or breakage of the positive electrode current collector can be prevented, and thus the life of the secondary battery can be improved.

Description

Technical Field

[0001] The present invention relates to a positive electrode current collector for a lithium secondary battery, a method for manufacturing the positive electrode current collector for a lithium secondary battery, and a lithium secondary battery comprising the positive electrode current collector for a lithium secondary battery. Background Art

[0002] Secondary batteries are batteries that can be repeatedly charged and discharged, and with the development of information communication and display industries, secondary batteries are widely used as a power source for portable electronic communication devices such as camcorders, mobile phones, notebook computers, etc. In addition, battery packs including secondary batteries are being developed in recent years and used as a power source for environmentally friendly vehicles such as hybrid vehicles.

[0003] Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Among them, lithium secondary batteries have high operating voltage and energy density per unit weight, and are advantageous in terms of charging speed and light weight, and therefore are being actively developed and used.

[0004] For example, a lithium secondary battery may include: an electrode assembly including a positive electrode, a negative electrode and a separator (separation membrane); and an electrolyte impregnated with the electrode assembly. The lithium secondary battery may also include an outer packaging material such as a soft pack type outer packaging material that accommodates the electrode assembly and the electrolyte.

[0005] In the lithium secondary battery, a positive electrode active material may be coated on a positive electrode current collector and then dried and rolled to form a positive electrode. The positive electrode active material is filled in the lithium secondary battery at a high density, so that the positive electrode active material has high capacity and high power characteristics.

[0006] However, if the density of the positive active material is increased, the positive current collector may be deformed such as wrinkled or broken due to expansion and contraction caused by charge and discharge of the positive active material layer.

[0007] For example, Korean Patent No. 10-2283842 discloses an electrode current collector for a lithium secondary battery including a novel conductive agent. Summary of the invention

[0008] 1. Technical issues to be resolved

[0009] A technical problem of the present invention is to provide a positive electrode current collector for a lithium secondary battery having improved durability.

[0010] A technical problem of the present invention is to provide a method for manufacturing the positive electrode current collector for a lithium secondary battery.

[0011] One technical problem of the present invention is to provide a lithium secondary battery including the positive electrode current collector for the lithium secondary battery.

[0012] (II) Technical Solution

[0013] The positive electrode current collector for a lithium secondary battery according to an exemplary embodiment may include: an aluminum layer; an aluminum-copper alloy layer formed on at least one surface of the aluminum layer; and a copper layer formed on the aluminum-copper alloy layer.

[0014] In some embodiments, the aluminum-copper alloy layer may contain at least one of Al 2 Cu, AlCu, and AlCu 2 in it.

[0015] In some embodiments, the aluminum-copper alloy layer may be an AlCu-containing layer.

[0016] In some embodiments, the aluminum-copper alloy layer may include a stacked structure of an Al 2 Cu layer and an AlCu-containing layer.

[0017] In some embodiments, the Al 2 Cu layer and the AlCu-containing layer may be sequentially provided from the aluminum layer.

[0018] In some embodiments, the aluminum-copper alloy layer may include the Al 2 Cu layer, the AlCu-containing layer, and a stacked structure of an AlCu 2 -containing layer.

[0019] In some embodiments, the Al 2 Cu layer, the AlCu-containing layer, and the AlCu 2 -containing layer may be sequentially provided from the aluminum layer.

[0020] In some embodiments, the copper concentration (atomic %) of the aluminum-copper alloy layer may increase as it gets closer to the copper layer.

[0021] In some embodiments, the thickness of the aluminum layer may be 3 μm to 20 μm, the thickness of the copper layer may be 1 μm to 15 μm, and the thickness of the aluminum-copper alloy layer may be 0.1 μm to 3 μm.

[0022] In some embodiments, the aluminum-copper alloy layer and the copper layer may be sequentially provided on both surfaces of the aluminum layer.

[0023] In some embodiments, the aluminum-copper alloy layer and the aluminum layer may be sequentially provided on both surfaces of the copper layer.

[0024] A lithium secondary battery according to an exemplary embodiment may include a positive electrode including a positive electrode current collector and a positive electrode active material layer formed on at least one surface of the positive electrode current collector; and a negative electrode disposed opposite to the positive electrode.

[0025] In a method for manufacturing a positive electrode current collector for a lithium secondary battery according to an exemplary embodiment, a copper foil may be hot-rolled on an aluminum foil to form a first preliminary current collector including an aluminum-copper alloy layer. The first preliminary current collector may be heat-treated.

[0026] In some embodiments, the aluminum-copper alloy layer may be formed between the aluminum foil and the copper foil.

[0027] In some embodiments, the step of forming the first preliminary current collector may include rolling the aluminum foil and the copper foil to form a first preliminary alloy layer, hot-rolling the first preliminary alloy layer to form a second preliminary alloy layer including an aluminum-copper alloy layer, and homogenizing the second preliminary alloy layer to form the aluminum-copper alloy layer.

[0028] In some embodiments, the step of heat-treating the first preliminary current collector may include first cold-rolling the first preliminary current collector to form a second preliminary current collector, performing a first annealing process on the second preliminary current collector to form a third preliminary current collector, second cold-rolling the third preliminary current collector to form a fourth preliminary current collector, and performing a second annealing process on the fourth preliminary current collector to form a positive electrode current collector.

[0029] In some embodiments, the second annealing process may include cooling the fourth preliminary current collector to 25°C.

[0030] (III) Beneficial effects

[0031] According to an exemplary embodiment, a positive electrode current collector for a lithium secondary battery may include an aluminum layer, an aluminum-copper alloy layer, and a copper layer. Therefore, even if the thickness of the positive electrode current collector is reduced, high conductivity can be maintained, and thus the energy density of the secondary battery can be increased.

[0032] In addition, even if a high-density active material layer is formed on the positive electrode current collector through a copper layer having a high theoretical capacity, deformation or fracture of the positive electrode current collector can be prevented.

[0033] In some embodiments, the composition of the aluminum-copper alloy in the aluminum-copper alloy layer may change sequentially. Therefore, the aluminum-copper alloy layer plays a buffering role between the aluminum layer and the copper layer, thereby preventing peeling caused by a sharp change in composition. Description of the drawings

[0034] Figures 1 to 5 is a schematic cross-sectional view showing a positive electrode current collector for a lithium secondary battery according to an exemplary embodiment.

[0035] Figure 6 and Figure 7 is a schematic flowchart for explaining a method of manufacturing a positive electrode current collector for a lithium secondary battery according to an exemplary embodiment.

[0036] Figure 8 is a schematic cross-sectional view showing a positive electrode for a lithium secondary battery according to an exemplary embodiment.

[0037] Fig. 9 and Fig.10 are a schematic plan view and a cross-sectional view showing a lithium secondary battery according to an exemplary embodiment. DETAILED DESCRIPTION

[0038] Exemplary embodiments of the present invention provide a positive electrode current collector for a lithium secondary battery including aluminum and copper and a method of manufacturing the same. In addition, a lithium secondary battery including the positive electrode current collector for a lithium secondary battery is provided.

[0039] Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. However, the drawings in this specification are used to illustrate preferred embodiments of the present invention and serve to further understand the technical idea of the present invention together with the above-described content of the invention. Therefore, it should not be construed that the present invention is limited to the content described in the drawings.

[0040] Figures 1 to 5 is a schematic cross-sectional view showing a positive electrode current collector for a lithium secondary battery according to an exemplary embodiment.

[0041] Referring to Figure 1 , the positive electrode current collector 105 may include an aluminum (Al) layer 110, an aluminum-copper alloy layer 120 formed on the aluminum layer 110, and a copper (Cu) layer 130 formed on the aluminum-copper alloy layer 120.

[0042] Accordingly, even when the thickness of the positive electrode current collector 105 is thinned, high conductivity can be maintained, and thus the energy density of the positive electrode 100 can be increased. In addition, by disposing copper having a high theoretical capacity on the outermost layer, even when a high-density positive electrode active material layer is formed on the positive electrode current collector 105, deformation and breakage of the positive electrode current collector 105 can be suppressed.

[0043] Referring to Figure 2 , the positive electrode current collector 105 may include an aluminum layer 110, aluminum-copper alloy layers 120 formed on both surfaces of the aluminum layer 110, and copper layers 130 formed on each of the aluminum-copper alloy layers 120.

[0044] Therefore, even if a high-density active material layer is formed on the positive electrode current collector 105, breakage can be prevented from occurring.

[0045] In some embodiments, the positions of the copper layer 130 and the aluminum layer 110 may be interchanged.

[0046] Referring to Figure 3 , the positive electrode current collector 105 may include a copper layer 130, aluminum-copper alloy layers 120 formed on both surfaces of the copper layer 130, and an aluminum layer 110 formed on the aluminum-copper alloy layers 120.

[0047] Therefore, the conductivity of the positive electrode current collector 105 can be improved, and price competitiveness can be ensured.

[0048] According to an exemplary embodiment, the aluminum-copper alloy layer 120 may contain at least one of Al 2 Cu, AlCu, and AlCu 2 . For example, the aluminum-copper alloy of the aluminum-copper alloy layer 120 may contain at least one of the alloys represented by Al 2 Cu, AlCu, and AlCu 2 .

[0049] In some embodiments, the aluminum-alloy layer 120 may have a single composition. For example, the aluminum-alloy layer 120 may be formed as a single layer containing AlCu.

[0050] In some embodiments, the composition of the aluminum-copper alloy of the aluminum-copper alloy layer 120 may change sequentially. For example, the aluminum concentration and the copper concentration in the aluminum-copper alloy layer 120 may change in the direction from the aluminum layer 110 to the copper layer 130. The term "concentration" used in this specification may refer to, for example, the mutual molar ratio or atomic ratio (atomic %) of aluminum and copper.

[0051] In some embodiments, the copper concentration of the aluminum-copper alloy layer 120 may increase as it approaches the copper layer 130. In some embodiments, the aluminum concentration of the aluminum-copper alloy layer 120 may decrease as it approaches the copper layer 130.

[0052] Referring to Figure 4 , the aluminum-copper alloy of the aluminum-copper alloy layer 120 in the positive electrode current collector 105 may contain alloys represented by Al 2 Cu and AlCu.

[0053] According to an exemplary embodiment, the aluminum-copper alloy layer 120 may include a stacked structure including an Al 2 Cu layer 122 and an AlCu layer 124.

[0054] In some embodiments, the aluminum-copper alloy layer 120 may be sequentially provided with an Al-containing layer starting from the aluminum layer 110 2 Cu layer 122 and an AlCu-containing layer 124. For example, the positive electrode current collector 105 may be formed as an aluminum layer 110, an Al-containing 2 Cu layer 122 formed on both surfaces of the aluminum layer 110, an AlCu-containing layer 124 formed on the Al-containing 2 Cu layer 122, and a copper layer 130 formed on the AlCu-containing layer 124.

[0055] Therefore, deformation and fracture of the positive electrode current collector 105 can be prevented, and the energy density of the positive electrode can be increased.

[0056] In some embodiments, the aluminum-copper alloy layer 120 may be sequentially provided with an AlCu-containing layer starting from the copper layer 130 2 layer 126 and an AlCu-containing layer 124. For example, the positive electrode current collector 105 may be formed as a copper layer 130, an AlCu-containing 2 layer 126 formed on both surfaces of the copper layer 130, an AlCu-containing layer 124 formed on the AlCu-containing 2 layer 126, and an aluminum layer 110 formed on the AlCu-containing layer 124.

[0057] Therefore, deformation and fracture of the positive electrode current collector 105 can be prevented, and the energy density of the positive electrode can be increased.

[0058] See Figure 5 , the aluminum-copper alloy of the aluminum-copper alloy layer 120 in the positive electrode current collector 105 may include alloys represented by Al 2 Cu, AlCu, and AlCu 2 indicates the alloy.

[0059] According to an exemplary embodiment, the aluminum-copper alloy layer 120 may include a stacked structure of an Al-containing 2 Cu layer 122, an AlCu-containing layer 124, and an AlCu-containing 2 layer 126.

[0060] In some embodiments, an Al-containing 2 Cu layer 122, an AlCu-containing layer 124, and an AlCu-containing 2 layer 126 may be sequentially provided starting from the aluminum layer 110. For example, the positive electrode current collector 105 may be formed as an aluminum layer 110, an Al-containing 2 Cu layer 122 formed on both surfaces of the aluminum layer 110, an AlCu-containing layer 124 formed on the Al-containing 2 Cu layer 122, an AlCu-containing layer 126 formed on the AlCu-containing layer 124, and an AlCu-containing 2 layer 126 formed on the AlCu-containing layer 126 and formed on the AlCu-containing 2The copper layer 130 on the layer 126.

[0061] including Al-containing 2 Cu layer 122, AlCu-containing layer 124, and AlCu 2 The aluminum-copper alloy layer 120 including the layer 126 can achieve a gradual alloy composition change for the compositional changes of the aluminum layer 110 and the copper layer 130.

[0062] Therefore, the aluminum-copper alloy layer 120 can buffer the compositional change between the aluminum layer 110 and the copper layer 130, and can prevent the aluminum layer 110 and the copper layer 130 from detaching from each other.

[0063] In some embodiments, the AlCu 2 layer 126, the AlCu-containing layer 124, and the Al 2 Cu layer 122 can be sequentially provided from the copper layer 130. For example, the positive electrode current collector 105 can be formed as the copper layer 130, the AlCu 2 layer 126 formed on both surfaces of the copper layer 130, the AlCu 2 layer 126 formed on the AlCu 2 layer 126, the AlCu-containing layer 124 formed on the AlCu layer 124, the Al 2 Cu layer 122 formed on the AlCu

[0064] Therefore, even if the copper layer 130 is disposed between the aluminum layers 110, peeling caused by a gradual compositional change can be prevented.

[0065] In some embodiments, the thickness of the aluminum layer 110 can be 3 μm to 20 μm, 3 μm to 15 μm, or 4 μm to 10 μm. Within the above ranges, even if the copper layer 130 is formed, the thickness of the positive electrode current collector 105 can not be too thick.

[0066] In some embodiments, the thickness of the aluminum-copper alloy layer 120 can be 0.1 μm to 3 μm or 0.5 μm to 1.5 μm. Within the above ranges, sufficient buffering for the compositional changes of the aluminum layer 110 and the copper layer 130 can be achieved.

[0067] In some embodiments, the thickness of the copper layer 130 can be 1 μm to 15 μm, 1 μm to 10 μm, or 3 μm to 7 μm. Within the above ranges, while ensuring the price competitiveness of the positive electrode current collector 105, even if a high-density active material layer is formed, due to the high theoretical capacity of the copper layer 130, deformation or fracture of the positive electrode current collector 105 can be suppressed.

[0068] Figure 6 and Figure 7It is a schematic flowchart for explaining a method of manufacturing a positive electrode current collector for a lithium secondary battery according to an exemplary embodiment. Figure 7 is Figure 6 a detailed flowchart of the S20 process.

[0069] Referring to Figure 6 and Figure 7 , an aluminum foil can be prepared (e.g., the S10 process).

[0070] According to an exemplary embodiment, the aluminum foil can be manufactured by homogenizing and hot-rolling an aluminum ingot.

[0071] In one embodiment, the aluminum ingot can be cast from an aluminum alloy.

[0072] The aluminum alloy can be put into a furnace and heated above the melting point of aluminum for melting. For example, the aluminum alloy can be heated above 700 °C or above 800 °C to melt the aluminum inside the aluminum alloy. The molten aluminum is put into a mold, and the mold can be cooled below the melting point of aluminum. Thus, an aluminum ingot of high-purity aluminum can be cast from the aluminum alloy.

[0073] In some embodiments, the aluminum ingot can be homogenized by heat treatment.

[0074] For example, the aluminum ingot can be homogenized by heat treatment at 350 °C to 600 °C or 400 °C to 550 °C. Within the above range, segregation within the aluminum grains can be effectively removed, and the aluminum grains can be refined.

[0075] In some embodiments, the homogenized aluminum ingot can be hot-rolled to prepare the aluminum foil.

[0076] For example, the homogenized aluminum ingot can be heat-treated at 350 °C to 500 °C or 400 °C to 450 °C for hot-rolling. Within the above range, the aluminum grains are recrystallized without forming segregation inside the aluminum grains, thereby forming the aluminum foil.

[0077] According to an exemplary embodiment, a copper foil can be adhered to the aluminum foil prepared through the above process, followed by hot-rolling and homogenization to form a first preliminary current collector including an aluminum-copper alloy layer (e.g., the S20 process).

[0078] In some embodiments, a copper foil can be placed on the aluminum foil and rolled to form a first preliminary alloy layer (e.g., the S22 process).

[0079] For example, a copper foil can be placed on the aluminum foil and the aluminum foil and the copper foil can be bonded by a roll-to-roll process. The roll-to-roll process can be carried out at, for example, 250°C to 450°C or 300°C to 400°C. Within the above ranges, the aluminum foil and the copper foil can be recrystallized and bonded without cracks caused by high or low temperatures.

[0080] In some embodiments, the first preliminary alloy layer can be hot-rolled to form a second preliminary alloy layer (e.g., S24 process).

[0081] By hot-rolling the first preliminary alloy layer, aluminum and copper can be recrystallized at the portion where the aluminum foil and the copper foil are in contact. Through the recrystallization of aluminum and copper, an aluminum-copper alloy represented by, for example, Al 2 Cu, AlCu, and / or AlCu 2 can be formed.

[0082] For example, hot-rolling can be started by heat-treating the bonded aluminum foil and copper foil at 500°C to 700°C or 550°C to 650°C. Within the above ranges, the aluminum foil and the copper foil do not melt and recrystallization occurs, so that an aluminum-copper alloy can be formed.

[0083] For example, hot-rolling can be terminated at 300°C to 450°C or 300°C to 400°C. Within the above ranges, recrystallization can be completed without generating ridging marks, so that an aluminum-copper alloy can be formed.

[0084] In some embodiments, the second preliminary alloy layer can be homogenized to form a first preliminary current collector including an aluminum-copper alloy layer (e.g., S26 process).

[0085] For example, homogenization can be started by heat-treating the first preliminary current collector including the aluminum-copper preliminary alloy layer at 300°C to 500°C or 350°C to 450°C. Within the above ranges, the aluminum-copper alloy can be recrystallized without segregation.

[0086] For example, homogenization can be terminated by heat-treating the first preliminary current collector including the aluminum-copper preliminary alloy layer at 250°C to 450°C or 300°C to 400°C. Within the above ranges, recrystallization is completed without generating ridging marks, so that a first preliminary current collector including an aluminum-copper alloy layer can be formed.

[0087] According to an exemplary embodiment, the first preliminary current collector can be heat-treated to manufacture the positive current collector 105 (e.g., S30 process and S40 process).

[0088] In some embodiments, the first preliminary current collector can be subjected to a first cold rolling to form a second preliminary current collector with a reduced thickness.

[0089] For example, the ratio of the thickness of the second preliminary current collector to the thickness of the first preliminary current collector can be from 0.4 to 0.6 or from 0.45 to 0.55. Thus, cracks caused by excessive rolling can be prevented while forming the second preliminary current collector.

[0090] For example, the first cold rolling can be carried out at 10°C to 120°C or at 25°C to 100°C. Within the above range, the mechanical strength and hardness of the second preliminary current collector can be improved.

[0091] In some embodiments, the second preliminary current collector can be subjected to a first annealing process to form a third preliminary current collector.

[0092] For example, the first annealing process can be carried out on the second preliminary current collector at 300°C to 450°C or at 350°C to 400°C. Within the above range, the internal stress of the second preliminary current collector can be removed and it can be softened.

[0093] For example, when the first annealing process is carried out on the second preliminary current collector, it can be carried out for 1 hour to 3 hours or 1 hour to 2 hours. Within the above range, copper and aluminum - copper alloys can also be softened by annealing.

[0094] In some embodiments, the third preliminary current collector can be subjected to a second cold rolling to form a fourth preliminary current collector with a reduced thickness.

[0095] For example, the ratio of the thickness of the fourth preliminary current collector to the thickness of the first preliminary current collector can be from 0.02 to 0.1 or from 0.04 to 0.06. Thus, a fourth preliminary current collector with improved mechanical strength and reduced thickness can be formed.

[0096] For example, the second cold rolling can be carried out at 10°C to 120°C or at 25°C to 100°C. Within the above range, the mechanical strength and hardness of the fourth preliminary current collector can be improved.

[0097] In some embodiments, the fourth preliminary current collector can be subjected to a second annealing to form the positive electrode current collector 105.

[0098] For example, the second annealing process can be carried out on the fourth preliminary current collector at, for example, 200°C to 450°C or at 200°C to 400°C. Within the above range, the internal stress of the fourth preliminary current collector can be removed and it can be softened, thereby enabling the refinement of metal crystals.

[0099] For example, performing a second annealing process on the fourth preliminary current collector can be carried out for, for example, 3 hours to 24 hours or 5 hours to 20 hours. Within the above ranges, aluminum, aluminum-copper alloy, and copper can be fully annealed and softened, and impurities (e.g., rolling oil) can volatilize and be removed.

[0100] In some embodiments, the fourth preliminary current collector can be cooled to room temperature (25 °C) at, for example, 40 °C / hour (hr) to 60 °C / hour or 45 °C / hour to 55 °C / hour, thereby forming the positive electrode current collector 105. Thus, the positive electrode current collector 105 can have improved ductility and strength.

[0101] Figure 8 is a schematic cross-sectional view showing a positive electrode for a lithium secondary battery according to an exemplary embodiment.

[0102] Referring to Figure 8 , the positive electrode 100 can include a positive electrode current collector 105 and a positive electrode active material layer 140, and the positive electrode active material layer 140 is provided by coating a positive electrode active material on the positive electrode current collector 105.

[0103] The positive electrode 100 can be manufactured by coating a positive electrode paste on the positive electrode current collector 105 and then performing rolling and drying. The positive electrode paste can be prepared by mixing and stirring the positive electrode active material with a binder, a conductive material, and / or a dispersing material, etc. in a solvent.

[0104] According to an exemplary embodiment, the positive electrode current collector 105 can include the above-mentioned aluminum layer 110, aluminum-copper alloy layer 120, and copper layer 130.

[0105] In some embodiments, the aluminum-copper alloy layer 120 can include an Al 2 Cu layer 122, an AlCu layer 124, and / or an AlCu 2 layer 126. Thus, even when the amount of the positive electrode active material contained in the positive electrode active material layer 140 increases, the positive electrode current collector 105 will not be deformed or broken.

[0106] According to an exemplary embodiment, the positive electrode active material can include a compound that can reversibly intercalate and deintercalate lithium ions. The positive electrode active material can include lithium-transition metal composite oxide particles. For example, the lithium-transition metal composite oxide particles contain nickel (Ni), and can further include at least one of cobalt (Co) or manganese (Mn).

[0107] For example, the lithium-transition metal composite oxide particles can be represented by the following Chemical Formula 1.

[0108] [Chemical Formula 1]

[0109] Li x Ni 1-y M y O 2+z

[0110] In Chemical Formula 1, 0.9 ≤ x ≤ 1.1, 0 ≤ y ≤ 0.7, and -0.1 ≤ z ≤ 0.1. M may represent one or more elements 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, Sn, or Zr.

[0111] The positive electrode binder may include, for example, an organic binder such as a vinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, etc., or an aqueous binder such as styrene - butadiene rubber (SBR), and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0112] For example, a PVDF - based binder may be used as the positive electrode binder. In this case, the amount of the binder used to form the positive electrode active material layer can be reduced and the amount of the positive electrode active material can be relatively increased, so that the power and capacity of the secondary battery can be improved.

[0113] The conductive material may be included to promote electron migration between the active material particles. For example, the conductive material may include a carbon - based conductive material such as graphite, carbon black, graphene, carbon nanotubes, etc. and / or a metal - based conductive material including perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO 3 , LaSrMnO 3 etc.

[0114] Fig. 9 and Fig.10 are a schematic plan view and a cross - sectional view, respectively, showing a lithium secondary battery according to an exemplary embodiment. Fig.10 is Fig. 9 a cross - sectional view taken along the I - I' line of

[0115] Referring to Fig. 9 and Fig.10 , the lithium secondary battery may include a positive electrode 100 including the above - mentioned positive electrode current collector 105 and a negative electrode 150 opposite to the positive electrode.

[0116] According to an exemplary embodiment, the negative electrode 150 may include a negative electrode current collector 155 and a negative electrode active material layer 160, and the negative electrode active material layer 160 is formed by coating a negative electrode active material on the negative electrode current collector 155.

[0117] The negative electrode active material may be a well-known negative electrode active material in the art that can intercalate and deintercalate lithium ions without particular limitation. For example, the negative electrode active material may be a carbon-based material such as crystalline carbon, amorphous carbon, carbon composite, carbon fiber, etc.; a lithium alloy; silicon or tin, etc. As an example of the amorphous carbon, hard carbon, coke, mesocarbon microbead (MCMB) calcined at 1500 °C or lower, mesophase pitch-based carbon fiber (MPCF), etc. may be cited.

[0118] As an example of the crystalline carbon, graphite-based carbon such as natural graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc. may be cited. As the elements contained in the lithium alloy, aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium, etc. may be cited.

[0119] The silicon-based active material may include SiO x (0 < x < 2) or SiO containing a lithium compound x (0 < x < 2). SiO containing a Li compound x may be SiO containing a lithium silicate x . The lithium silicate may be present in at least a part of the SiO x (0 < x < 2) particles. For example, it may be present inside and / or on the surface of the SiO x (0 < x < 2) particles. In one embodiment, the lithium silicate may include Li 2 SiO 3 , Li 2 Si 2 O 5 , Li 4 SiO 4 , Li 4 Si 3 O 8 etc.

[0120] The silicon-based active material may also contain a silicon-carbon composite compound such as silicon carbide (SiC), etc.

[0121] The negative electrode current collector 155 may include, for example, gold, stainless steel, nickel, aluminum, titanium, copper, or their alloys. In one embodiment, the negative electrode current collector 155 may include copper or a copper alloy.

[0122] For example, the negative electrode active material can be mixed and stirred together with the above-mentioned binder, conductive material, thickening agent, etc. in a solvent to prepare a slurry form. After the slurry is coated on at least one surface of the negative electrode current collector 155, calendering and drying are performed to manufacture the negative electrode 150 including the negative electrode active material layer 160.

[0123] As the binder and the conductive material, substances substantially the same as or similar to the above-mentioned substances can be used. In some embodiments, for the compatibility with the carbon-based active material, the binder used to form the negative electrode can include, for example, an aqueous binder such as styrene-butadiene rubber (SBR), and can be used together with a thickening agent such as carboxymethyl cellulose (CMC).

[0124] A separator 170 can be inserted between the positive electrode 100 and the negative electrode 150. The separator 170 can include a porous polymer film prepared from a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer, etc. The separator 170 can also include a non-woven fabric formed from glass fibers with a high melting point, polyethylene terephthalate fibers, etc.

[0125] In some embodiments, the area (e.g., the area in contact with the separator 170) and / or volume of the negative electrode 150 can be larger than that of the positive electrode 100. Therefore, lithium ions generated from the positive electrode 100 can migrate smoothly to the negative electrode 150, for example, without precipitation in the middle. Therefore, the effect of simultaneously improving power and stability can be more easily achieved by the above-mentioned composite hydroxide particles or in combination with the positive electrode active material.

[0126] According to an exemplary embodiment, a battery cell is defined by the positive electrode 100, the negative electrode 150, and the separator 170, and a plurality of battery cells can be stacked to provide an electrode assembly 180.

[0127] The electrode assembly 180 can be accommodated in a housing 190 together with an electrolyte to define a lithium secondary battery. According to an exemplary embodiment, the electrolyte can use a non-aqueous electrolyte.

[0128] The non-aqueous electrolyte contains a lithium salt as an electrolyte and an organic solvent. The lithium salt is represented, for example, by Li + X - , and as the anion (X - ) of the lithium salt, F - , Cl - , Br - , I - , NO 3 - , N(CN) 2 - , BF 4 - , ClO4 - , PF 6 - , (CF 3 ) 2 PF 4 - , (CF 3 ) 3 PF 3 - , (CF 3 ) 4 PF 2 - , (CF 3 ) 5 PF - , (CF 3 ) 6 P - , CF 3 SO 3 - , CF 3 CF 2 SO 3 - , (CF 3 SO 2 ) 2 N - , (FSO 2 ) 2 N - , CF 3 CF 2 (CF 3 ) 2 CO - , (CF 3 SO 2 ) 2 CH - , (SF 5 ) 3 C - , (CF 3 SO 2 ) 3 C - , CF 3 (CF 2 ) 7 SO 3 - , CF 3 CO 2 - , CH 3 CO 2 - , SCN - and (CF 3 CF 2 SO 2 )2 N - etc.

[0129] The organic solvent that can be used includes, 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, and tetrahydrofuran, etc. These can be used alone or in combination of two or more.

[0130] As Fig. 9 As shown, the tabs (the positive tab and the negative tab) can protrude from the positive current collector 105 and the negative current collector 155 belonging to each electrode unit and extend to one side portion of the housing 190. The tabs can be fused with the one side portion of the housing 190 and form electrode leads (the positive lead 107 and the negative lead 157) extending to the outside of the housing 190 or exposed to the outside of the housing 190.

[0131] The lithium secondary battery can be made into, for example, a cylindrical shape using a can, a prismatic shape, a pouch type, or a coin shape, etc.

[0132] Hereinafter, specific experimental examples for helping to understand the present invention are presented, but these are only for illustrating the present invention and are not used to limit the claims. Various variations and modifications can be made to the embodiments within the scope and technical concept of the present invention, which is clear to those skilled in the art, and such variations and modifications are naturally within the scope of the claims.

[0133] Examples and Comparative Examples

[0134] Example 1

[0135] 1) Manufacture of the positive current collector

[0136] A positive current collector (with a thickness of 15 μm) is manufactured by an aluminum layer with a thickness of 4 μm, and aluminum-copper alloy layers with a thickness of 1.5 μm are respectively formed on both sides of the aluminum layer, and copper layers with a thickness of 4 μm are respectively formed on the aluminum-copper alloy layers.

[0137] Specifically, by a roll-to-roll process, copper foils are bonded to both sides of an aluminum foil. The metal foil with the bonded aluminum foil and copper foil is hot-rolled at 600 °C, and a preliminary aluminum-copper alloy layer is formed through the recrystallization of aluminum and copper. The preliminary aluminum-copper alloy layer is homogenized heat-treated at 450 °C to form an aluminum-copper alloy layer. Thereafter, the cold rolling and annealing processes can be repeated twice to manufacture a positive current collector including the aluminum-copper alloy layer. A protrusion for forming a positive electrode tab is provided on one side of the positive current collector.

[0138] The aluminum-copper alloy layer is sequentially formed with an Al 2 Cu layer, an AlCu layer, and an AlCu 2 layer from the aluminum at the center.

[0139] 2) Manufacture of the positive electrode

[0140] LiNi as the positive electrode active material 0.6 Co 0.2 Mn 0.2 O 2 , carbon black as the positive electrode conductive material, and polyvinylidene fluoride (PVDF) as the positive electrode binder are mixed at a weight ratio of 95:3:2 to prepare a positive electrode slurry. Then, the positive electrode slurry is coated on the area of the positive current collector except for the protrusion (positive electrode tab), and dried and calendered to form a positive electrode active material layer.

[0141] 3) Manufacture of the negative electrode

[0142] The negative electrode active material obtained by mixing artificial graphite and natural graphite at a weight ratio of 7:3, styrene-butadiene rubber, and carboxymethyl cellulose are dispersed in distilled water at a weight ratio of 97:1:2 to prepare a negative electrode slurry.

[0143] The negative electrode slurry is coated on the area of a copper foil with a protrusion (negative electrode tab) on one side except for the protrusion, and dried and calendered to manufacture a negative electrode.

[0144] 4) Manufacture of the secondary battery

[0145] A polyethylene separator (with a thickness of 20 μm) is inserted between the positive electrode and the negative electrode to form a unit electrode assembly. The unit electrode assemblies are stacked to have a capacity of 80 Ah to form an electrode assembly. A positive electrode lead and a negative electrode lead are respectively welded to the positive electrode tab and the negative electrode tab for connection.

[0146] Prepare 1 M of LiPF 6A solution (30:70 v / v EC / EMC mixed solvent), and then additives are added such that fluoroethylene carbonate (FEC) is 1 wt% based on the total 100 wt% of the electrolyte, vinylethylene carbonate (VC) is 0.3 wt%, lithium difluorophosphate (LiPO 2 F 2 ) is 1 wt%, 1,3-propane sultone (PS) is 0.5 wt%, and prop-1-ene-1,3-sultone (PRS) is 0.5 wt% to prepare the electrolyte.

[0147] The electrode assembly is accommodated inside a pouch (case) such that partial regions of the positive electrode lead and the negative electrode lead are exposed to the outside, and three surfaces other than the electrolyte injection portion surface are sealed.

[0148] The electrolyte is injected into the pouch and the electrolyte injection portion surface is sealed to manufacture a lithium secondary battery.

[0149] Example 2

[0150] A lithium secondary battery is manufactured by the same method as in Example 1, except that an aluminum layer with a thickness of 4 μm is used, and aluminum-copper alloy layers with a thickness of 1 μm are respectively formed on both surfaces of the aluminum layer, and copper layers with a thickness of 1.5 μm are respectively formed on the aluminum-copper alloy layers to manufacture a positive electrode current collector (with a thickness of 9 μm).

[0151] Example 3

[0152] An aluminum layer with a thickness of 4 μm is used, and aluminum-copper alloy layers with a thickness of 1 μm are respectively formed on both surfaces of the aluminum layer, and copper layers with a thickness of 1.5 μm are respectively formed on the aluminum-copper alloy layers to manufacture a positive electrode current collector (with a thickness of 9 μm).

[0153] The metal foil bonding the aluminum foil and the copper foil is hot-rolled at 500 °C, and except for the above content, a lithium secondary battery is manufactured by the same method as in Example 1.

[0154] Example 4

[0155] An aluminum layer with a thickness of 4 μm is used, and aluminum-copper alloy layers with a thickness of 1 μm are respectively formed on both surfaces of the aluminum layer, and copper layers with a thickness of 1.5 μm are respectively formed on the aluminum-copper alloy layers to manufacture a positive electrode current collector (with a thickness of 9 μm).

[0156] The metal foil bonding the aluminum foil and the copper foil is hot-rolled at 700 °C. Except for the above, a lithium secondary battery is manufactured by the same method as in Example 1.

[0157] Example 5

[0158] A positive electrode current collector (with a thickness of 9 μm) is manufactured by forming an aluminum-copper alloy layer with a thickness of 1 μm on each of the two surfaces of an aluminum layer with a thickness of 4 μm, and forming a copper layer with a thickness of 1.5 μm on each of the aluminum-copper alloy layers.

[0159] The aluminum-copper preliminary alloy layer is subjected to homogenization heat treatment at 300 °C. Except for the above, a lithium secondary battery is manufactured by the same method as in Example 1.

[0160] Example 6

[0161] A positive electrode current collector (with a thickness of 9 μm) is manufactured by forming an aluminum-copper alloy layer with a thickness of 1 μm on each of the two surfaces of an aluminum layer with a thickness of 4 μm, and forming a copper layer with a thickness of 1.5 μm on each of the aluminum-copper alloy layers.

[0162] The aluminum-copper preliminary alloy layer is subjected to homogenization heat treatment at 500 °C. Except for the above, a lithium secondary battery is manufactured by the same method as in Example 1.

[0163] Comparative Example 1

[0164] A lithium secondary battery is manufactured by the same method as in Example 1, except that a 15-μm aluminum foil is used as the positive electrode current collector.

[0165] Comparative Example 2

[0166] A lithium secondary battery is manufactured by the same method as in Example 1, except that a 9-μm aluminum foil is used as the positive electrode current collector.

[0167] Experimental Example

[0168] (1) Measurement of fracture compaction density

[0169] When manufacturing the positive electrode of the lithium secondary battery according to the examples and comparative examples, the positive electrode paste is coated on the positive electrode current collector with a loading amount of 20 mg / cm 2 . Then, the positive electrode paste is initially rolled at a density of 3.7 g / cm 3 . If there is no fracture, the compaction density is increased by 0.05 g / cm at intervals of 100 m 3 to measure the critical fracture density of the first fracture.

[0170] (2) Measurement of the resistance of the positive electrode current collector

[0171] Using an electrode resistance measuring instrument (the electrode resistance measuring instrument of HIOKI E.E. CORPORATION), a constant current is applied to the surface of the battery electrode, and the volume resistivity of the composite layer and the interfacial resistance between the composite layer and the current collector are calculated from the potential distribution, thereby measuring the average resistance of the positive current collector.

[0172] (3) Measurement of the battery resistance of the secondary battery

[0173] At the point where the state of charge (SOC) of the secondary batteries according to the examples and comparative examples is set to 50%, a current of 1C is applied for 10 seconds and the change in voltage is calculated, thereby measuring the battery resistance.

[0174] The evaluation results are shown in Table 1 below.

[0175] [Table 1]

[0176]

[0177] Referring to Table 1, in the examples using the positive current collector formed of an aluminum layer, an aluminum-copper layer, and a copper layer, the fracture compaction density and the adhesion strength are improved, and the resistances of the positive current collector and the secondary battery are reduced. In Examples 2 to 6 in which the thickness of the copper layer is reduced, the fracture compaction density and the adhesion strength are slightly reduced, and the resistances of the positive current collector and the secondary battery are slightly increased.

[0178] In Example 3 in which the hot rolling temperature is reduced, the fracture compaction density is slightly reduced.

[0179] In Example 5 in which the temperature of the homogenization heat treatment is reduced, the resistances of the positive current collector and the secondary battery are slightly increased.

[0180] In Example 6 in which the temperature of the homogenization heat treatment is increased, the resistances of the positive current collector and the secondary battery are slightly increased.

[0181] Comparative Example 1 using only aluminum foil as the positive current collector has a lower fracture compaction density and adhesion strength, and an increased resistance of the positive current collector and the secondary battery compared to Example 1 having the same thickness.

[0182] Comparative Example 2 using only aluminum foil as the positive current collector has a lower fracture compaction density and adhesion strength, and an increased resistance of the positive current collector and the secondary battery compared to Example 2 having the same thickness.

Claims

1. A positive electrode current collector for a lithium secondary battery, which comprises: an aluminum layer; an aluminum-copper alloy layer formed on at least one surface of the aluminum layer; and a copper layer formed on the aluminum-copper alloy layer.

2. The positive electrode current collector for a lithium secondary battery according to claim 1, wherein, The aluminum-copper alloy layer contains Al 2 Cu, AlCu, and AlCu 2 at least one of which 3. The positive electrode current collector for a lithium secondary battery according to claim 2, wherein, the aluminum-copper alloy layer is an AlCu-containing layer.

4. The positive electrode current collector for a lithium secondary battery according to claim 2, wherein, The aluminum-copper alloy layer includes an Al 2 Cu layer and a stacked structure including an AlCu layer.

5. The positive electrode current collector for a lithium secondary battery according to claim 4, wherein, The Al-containing layer is sequentially provided from the aluminum layer 2 Cu layer and the AlCu-containing layer.

6. The positive electrode current collector for a lithium secondary battery according to claim 2, wherein, The aluminum-copper alloy layer includes an Al 2 Cu layer, an AlCu layer, and a stacked structure including an AlCu 2 layer.

7. The positive electrode current collector for a lithium secondary battery according to claim 6, wherein, The Al-containing layer is sequentially disposed from the aluminum layer 2 Cu layer, the AlCu-containing layer, and the AlCu 2 layer.

8. The positive electrode current collector for a lithium secondary battery according to claim 1, wherein, the copper concentration (atomic %) of the aluminum-copper alloy layer increases as it gets closer to the copper layer.

9. The positive electrode current collector for a lithium secondary battery according to claim 1, wherein, the thickness of the aluminum layer is 3 μm to 20 μm, the thickness of the copper layer is 1 μm to 15 μm, and the thickness of the aluminum-copper alloy layer is 0.1 μm to 3 μm.

10. The positive electrode current collector for a lithium secondary battery according to claim 1, wherein, the aluminum-copper alloy layer and the copper layer are sequentially provided on both surfaces of the aluminum layer.

11. The positive electrode current collector for a lithium secondary battery according to claim 1, wherein, the aluminum-copper alloy layer and the aluminum layer are sequentially provided on both surfaces of the copper layer.

12. A lithium secondary battery, which comprises: a positive electrode including the positive electrode current collector according to claim 1 and a positive electrode active material layer formed on at least one surface of the positive electrode current collector; and a negative electrode disposed opposite to the positive electrode.

13. A method for manufacturing a positive electrode current collector for a lithium secondary battery, which comprises the following steps: hot-rolling an aluminum foil and a copper foil to form a first preliminary current collector including an aluminum-copper alloy layer; and heat-treating the first preliminary current collector.

14. A method for manufacturing a positive electrode current collector for a lithium secondary battery, wherein, the aluminum-copper alloy layer is formed between the aluminum foil and the copper foil.

15. The method for manufacturing a positive electrode current collector for a lithium secondary battery according to claim 13, wherein, the step of forming the first preliminary current collector includes: rolling the aluminum foil and the copper foil to form a first preliminary alloy layer, hot-rolling the first preliminary alloy layer to form a second preliminary alloy layer containing an aluminum-copper alloy, homogenizing the second preliminary alloy layer to form the aluminum-copper alloy layer.

16. The method for manufacturing a positive electrode current collector for a lithium secondary battery according to claim 13, wherein, the step of heat-treating the first preliminary current collector includes: performing first cold rolling on the first preliminary current collector to form a second preliminary current collector, performing a first annealing process on the second preliminary current collector to form a third preliminary current collector, performing second cold rolling on the third preliminary current collector to form a fourth preliminary current collector, A second annealing process is performed on the fourth preliminary current collector to form a positive electrode current collector.

17. The method for manufacturing a positive electrode current collector for a lithium secondary battery according to claim 16, wherein, the second annealing process includes cooling the fourth preliminary current collector to 25 °C.

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