Electrode assembly for lithium secondary battery and lithium secondary battery including same

Abstract

Disclosed herein are an electrode assembly for a lithium secondary battery and a lithium secondary battery including the same. The electrode assembly includes: a negative electrode including a negative electrode current collector having one end portion on which a negative electrode tab is formed, and a negative electrode active material layer positioned on at least one surface of the negative electrode current collector; and a positive electrode including a positive electrode current collector having one end portion on which a positive electrode tab is formed, and a positive electrode active material layer positioned on at least one surface of the positive electrode current collector, a region having a high current density and a region having a low current density are present in each of the negative electrode and the positive electrode, and a pore area ratio in the region having the high current density is greater than a pore area ratio in the region having the low current density.

Description

[0001] This application claims the priority and benefit of Korean Patent Application No. 10-2023-0192250, filed with the Korean Intellectual Property Office on December 27, 2023, the entire disclosure of which is incorporated herein by reference. Technical Field

[0002] The present invention relates to an electrode assembly for a lithium secondary battery, an electrode included in the electrode assembly, and a lithium secondary battery including the electrode assembly. Background Art

[0003] Recently, with the rapid popularization of electronic devices using batteries, such as mobile phones, laptop computers, and electric vehicles, the demand for secondary batteries with high energy density and high capacity is rapidly increasing. Accordingly, research and development for improving the performance of lithium secondary batteries are being actively conducted.

[0004] A lithium secondary battery is a battery including a positive electrode, a negative electrode, and an electrolyte, where the positive electrode and the negative electrode each contain an active material capable of intercalating and deintercalating lithium ions, and when lithium ions intercalate and deintercalate from the positive electrode and the negative electrode, the lithium secondary battery generates electrical energy due to oxidation and reduction reactions.

[0005] Tab pieces are provided on each of the positive electrode and the negative electrode. The tab pieces are provided in a part of each of the positive electrode and the negative electrode. Accordingly, in the positive electrode and the negative electrode, an imbalance in current density may occur between a region adjacent to the tab piece and a region not adjacent to the tab piece. By resolving such imbalance, battery capacity and battery life can be improved. Summary of the Invention

[0006] The present invention aims to provide an electrode assembly for a lithium secondary battery, which suppresses deterioration of an electrode plate by resolving an imbalance in current density on the surface of the electrode plate, increases battery capacity, and improves battery life.

[0007] The present invention also aims to provide an electrode included in the electrode assembly.

[0008] The present invention also aims to provide a lithium secondary battery including the electrode assembly for a lithium secondary battery.

[0009] According to an aspect of the present invention, there is provided an electrode assembly for a lithium secondary battery, the electrode assembly including: a negative electrode including a negative electrode current collector having one end on which a negative electrode tab piece is formed and a negative electrode active material layer positioned on at least one surface of the negative electrode current collector; and a positive electrode including a positive electrode current collector having one end on which a positive electrode tab piece is formed and a positive electrode active material layer positioned on at least one surface of the positive electrode current collector.

[0010] When a voltage is applied to the electrode assembly, regions with high current density and regions with low current density may exist in each of the negative electrode and the positive electrode, and the pore area ratio in the region with high current density may be greater than the pore area ratio in the region with low current density.

[0011] According to another aspect of the present invention, there is provided an electrode included in the electrode assembly.

[0012] According to another aspect of the present invention, there is provided a lithium secondary battery including an electrode assembly for a lithium secondary battery.

[0013] The electrode assembly for a lithium secondary battery according to an embodiment can increase the battery capacity and improve the battery life by solving the current density imbalance on the surface of the electrode plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The above and other objects, features and advantages of the present invention will become more apparent to those of ordinary skill in the art by referring to the following detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings, in which: Figure 1 is an exploded view showing an electrode assembly for a lithium secondary battery according to an embodiment; Figure 2A and Figure 2B shows a diagram showing Figure 1 regions with high current density and regions with low current density in the positive electrode current collector and the negative electrode current collector, where Figure 2A shows the positive electrode current collector, Figure 2B shows the negative electrode current collector; Figure 3 is an exemplary diagram showing the temperature distribution when a voltage is applied; Figure 4 is a conceptual diagram for describing the distribution of pores in the region with high current density in FIG. 2; Figure 5 is a conceptual diagram for describing the distribution of pores in the region with low current density in FIG. 2; Figure 6A and Figure 6B are conceptual diagrams of an electrode assembly for a lithium secondary battery according to another embodiment, where Figure 6A shows the positive electrode current collector, Figure 6B shows the negative electrode current collector; Figure 7A and Figure 7B are conceptual diagrams of an electrode assembly for a lithium secondary battery according to still another embodiment, where Figure 7A shows the positive electrode current collector, Figure 7Bshows a negative electrode current collector; and Figures 8 to 11 is a schematic cross-sectional view showing a lithium secondary battery according to an embodiment. Detailed Description

[0015] Hereinafter, exemplary embodiments of the present invention will be described in detail. However, the following embodiments are presented by way of example, and the present invention is not limited thereto and is defined by the scope of the appended claims.

[0016] Unless specifically stated herein, when a first portion of a layer, film, region, plate, etc. is referred to as being "on" a second portion, this includes not only the case where the first portion is "directly on" the second portion, but also the case where a third portion is present between the first portion and the second portion.

[0017] Unless specifically stated herein, the singular form may also include the plural form. Additionally, unless specifically stated herein, "A or B" may mean "including A, including B, or including both A and B".

[0018] As used herein, the term "a combination thereof" may mean a mixture, stack, composite, copolymer, alloy, blend, or reaction product of components.

[0019] Unless otherwise defined herein, the particle size may be an average particle size. Additionally, the particle size may be an average particle size (D50), and the average particle size (D50) is the diameter of the particles at which the cumulative volume is 50 volume% in the particle size distribution. The average particle size (D50) can be measured by methods known to those skilled in the art (e.g., using a particle size analyzer, transmission electron microscopy images, or scanning electron microscopy images). As another method, the average particle size (D50) value can be obtained by using a measuring instrument device utilizing dynamic light scattering, performing data analysis, counting the number of particles in each particle size range, and calculating the average particle size (D50). Optionally, the average particle size (D50) can be measured using the laser diffraction method. More specifically, when measuring by the laser diffraction method, the average particle size (D50) based on the 50% particle size distribution in the measuring instrument can be calculated by dispersing the particles to be measured in a dispersion medium, introducing the particles into a commercially available laser diffraction particle size measuring instrument (e.g., MT 3000 of Microtrac) and irradiating with ultrasonic waves at an irradiation frequency of about 28 kHz with a power of 60W.

[0020] In an electrode assembly for a lithium secondary battery according to an embodiment, as the energy density of a single cell increases with the recent demand for high capacity of lithium secondary batteries, the degree of degradation is balanced by unevenly designing the electrode plate design density to make the lithium ion concentration on the opposite surfaces of the electrode plate uneven, coating a slurry on the pores of the current collector, creating a connection channel for deactivated lithium, allowing lithium to move in two directions, and thus balancing the state of charge (SoC).

[0021] Due to the pores, the capacity of the battery is increased by 5% to 10% compared to the case where no pores are formed. The degradation rate is reduced due to the uneven design of the electrode plate, and the lithium to be deactivated is minimized through the connection channels of the pores, resulting in an effect of increased capacity.

[0022] An electrode assembly for a lithium secondary battery according to an embodiment includes: a negative electrode having a negative electrode current collector with one end formed with a negative electrode tab and a negative electrode active material layer positioned on at least one surface of the negative electrode current collector; and a positive electrode having a positive electrode current collector with one end formed with a positive electrode tab and a positive electrode active material layer positioned on at least one surface of the positive electrode current collector. When a voltage is applied to the electrode assembly, the negative electrode and the positive electrode each have a region with a high current density and a region with a low current density, and the pore area ratio in the region with a high current density is higher than that in the region with a low current density.

[0023] In an electrode assembly for a lithium secondary battery, the pore area ratio in the region with a high current density can be increased compared to the region with a low current density, so that the effective active material amount can be increased, and the degree of ion transfer in two directions through the pores is increased, so that the degradation rate of the positive electrode current collector and the negative electrode current collector according to the application of voltage can be reduced. The reduction of the degradation rate can increase the life of the current collector according to the use of the battery and increase the safety of the battery by reducing the fire risk. In addition, in the region with a high current density, when forming the active material layer, more slurry for the active material layer is coated compared to the region with a low current density, the movement of lithium through the pores is increased, and the deactivated lithium is minimized, so that the capacity of the battery can be increased. In addition, by providing a uniform current density within the electrode plate, the degradation of the electrode plate is delayed, so that the life of the battery can be improved.

[0024] First, the region with a high current density and the region with a low current density will be described.

[0025] When a voltage is applied to the electrode assembly, regions with high current density and regions with low current density can be relatively determined by the temperature gradient. Here, the applied voltage can be in the range of 3V to 4.5V. For the electrode plate, since it is difficult to directly measure the current density, in the present invention, the current density is evaluated by using temperature instead of current density.

[0026] When a voltage is applied, the region with high current density can be a region where the temperature is 10°C or more (e.g., 10°C to 30°C) higher than the minimum value among the temperatures measured at the positive electrode and the negative electrode.

[0027] In a specific example, the region with high current density can be a region where the temperature is 60°C or higher (e.g., 60°C to 80°C) when the voltage is applied. For example, the region with high current density of the positive electrode can be a region where the temperature is in the range of 60°C to 70°C when the voltage is applied. For example, the region with high current density of the negative electrode can be a region where the temperature is in the range of 70°C to 80°C.

[0028] When a voltage is applied, the region with low current density can be a region where the temperature difference is 10°C or less (e.g., the temperature difference is 0°C or more and less than 10°C) compared to the minimum value among the temperature values measured at the positive electrode and the negative electrode.

[0029] In a specific example, the region with low current density can be a region where the temperature is less than 60°C (e.g., 50°C to 59°C) when the voltage is applied.

[0030] When a voltage is applied to the current collector, the temperature can be measured after attaching an infrared camera or a thermocouple to the electrode assembly or the cell including the electrode assembly, but the present invention is not limited thereto.

[0031] According to one example, the region with high current density can be a region among the multiple regions obtained by equally dividing the negative electrode and the positive electrode into n regions, in which a negative electrode tab or a positive electrode tab is formed. Here, n can be an integer from 4 to 20, for example, 4, 6, 9, 12, or 16.

[0032] In the region with high current density, there can be regions where the pore area ratios are different from each other, and in the region with low current density, there can also be regions where the pore area ratios are different from each other.

[0033] According to one example, the region with low current density can be the remaining regions of the negative electrode and the positive electrode except for the regions with high current density.

[0034] In a specific example, the area of the positive electrode having a high current density may range from 5% to 50% (e.g., 10% to 30%, or 10% to 25%) of the positive electrode area including pores.

[0035] In a specific example, the area of the negative electrode having a high current density may range from 5% to 50% (e.g., 10% to 30%, or 10% to 25%) of the negative electrode area including pores.

[0036] Next, the pore area ratio will be described.

[0037] When the area of the region having a high current density including pores is A and the total pore area is B, the pore area ratio of the region having a high current density can be calculated by B / A×100.

[0038] Regarding the pore area ratio in the region having a low current density, when the area of the region having a low current density including pores is C and the total pore area is D, the pore area ratio of the region having a low current density can be calculated by D / C×100.

[0039] According to one example, in the region having a high current density, the pore area ratio may be 15% or more (e.g., 15% to 50%, or 20% to 35%) of the pore area ratio of the region having a low current density.

[0040] According to one example, the pore area ratio in the region having a high current density may range from 20% to 40%, for example, it may range from 20% to 30%. The pore area ratio in the region having a low current density may range from 0% to 10%, for example, it may range from 0% to 5%. In the above ranges, deterioration of the current collector can be suppressed, and the degree of reduction in battery capacity due to pore formation can be reduced.

[0041] In a specific example, when the current collector is equally divided into n regions (where n is an integer from 4 to 20, such as 4, 6, 9, 12, or 16), the region having a high current density may be a single region having one area or may have multiple regions having the same area. In this case, when the region having a high current density is multiple regions having the same area, the pore area ratio in the range of 20% to 40% may be the average of the pore area ratios calculated for the same area. The pore area ratios calculated for the same area may be different from each other or may be the same.

[0042] In a specific example, when the current collector is equally divided into n regions (where n is an integer from 4 to 20, for example, 4, 6, 9, 12, or 16), the region with a low current density can be a single region with a certain area or can consist of multiple regions with the same area. In this case, when the regions with a low current density are multiple regions with the same area, the pore area ratio within the range of 0% to 10% can be the average of the pore area ratios calculated for the same area. The pore area ratios calculated for the same area can be different from each other or can be the same.

[0043] In a specific example, the pore area ratio in the region with a high current density of the negative electrode can be higher than that in the region with a high current density of the positive electrode. This is because when the same voltage is applied to the positive electrode and the negative electrode, the temperature around the tab of the negative electrode current collector is higher than that around the tab of the positive electrode current collector. In this way, the electrode assembly can significantly reduce the deterioration rate of the current collector, thereby increasing the safety and lifespan of the battery.

[0044] For example, in the region with a high current density of the negative electrode, the pore area ratio can be 5% or more higher than that in the region with a high current density of the positive electrode, for example, 5% to 20% or 5% to 10% higher. Within the above range, the deterioration rates of both the positive electrode and the negative electrode can be significantly reduced, and the lifespan of the battery can be improved to a greater extent.

[0045] In a specific example, in the electrode assembly, pores are formed in the positive electrode current collector and the negative electrode current collector, and no pores are formed in the positive electrode active material layer and the negative electrode active material layer.

[0046] In a specific example, in the electrode assembly, the pore area ratio in the region at the 40% point of the length of the positive electrode in the length direction from the positive electrode tab to the electrode assembly can be within the range of 20% to 40%, and the pore area ratio in the remaining region can be within the range of 0% to 10%.

[0047] In a specific example, in the electrode assembly, the pore area ratio in the region at the 40% point of the length of the negative electrode in the length direction from the negative electrode tab to the electrode assembly can be within the range of 20% to 40%, and the pore area ratio in the remaining region can be within the range of 0% to 10%.

[0048] In each of the region with a high current density and the region with a low current density, the pore area ratio can be achieved by adjusting the diameter and / or the density of the pores.

[0049] In this specification, a "hole" may be a region having a longest diameter of 300 μm or less (e.g., greater than 0 μm and 300 μm or less, or in the range of 1 μm to 300 μm, 100 μm to 300 μm, or 200 μm to 300 μm), and the interior of the hole may be hollow. When the cross-section of the hole is circular, the "longest diameter" may be the diameter, and when the cross-section of the hole is not circular, the "longest diameter" may be the longest diameter.

[0050] Holes are formed in regions with high current density. The diameters of the holes in the regions with high current density may be the same or different from each other.

[0051] Holes may or may not be formed in regions with low current density. The diameters of the holes in the regions with low current density may be the same or different from each other.

[0052] The diameters of the holes in the regions with high current density may be the same or different from the diameters of the holes in the regions with low current density.

[0053] In one specific example, the diameters of the holes in the regions with high current density may be the same as the diameters of the holes in the regions with low current density.

[0054] In another specific example, the diameters of the holes in the regions with high current density may be smaller than the diameters of the holes in the regions with low current density.

[0055] In yet another specific example, the diameters of the holes in the regions with high current density may be larger than the diameters of the holes in the regions with low current density.

[0056] In one specific example, the diameter of the hole may become smaller from the region with high current density to the region with low current density.

[0057] In one specific example, the diameter of the hole may become larger from the region with high current density to the region with low current density.

[0058] In one specific example, the cross-section of the hole may have a circular shape, an elliptical shape, or an amorphous shape.

[0059] In one specific example, the hole may be a through-hole that penetrates from one surface of the current collector to another surface opposite to the one surface.

[0060] In one specific example, the longest diameter of the hole may be 10 to 20 times the thickness of the current collector, e.g., 10 to 15 times. In the above range, the effects of the present invention can be easily achieved.

[0061] In this specification, "hole density" may be the ratio of the number of holes per unit area of a corresponding region, and here "unit area" may be width × height (1 mm × 1 mm).

[0062] In a specific example, the hole density in a region with a high current density may be higher than the hole density in a region with a low current density.

[0063] In a specific example, the hole density may decrease from a region with a high current density to a region with a low current density.

[0064] In a specific example, holes may be formed by conventional methods known to those skilled in the art. For example, holes may be formed by physical punching, etching, or stamping.

[0065] Figure 1 is an exploded view showing an electrode assembly for a lithium secondary battery according to an embodiment.

[0066] Refer to Figure 1 , the electrode assembly for a lithium secondary battery includes a positive electrode and a negative electrode. The positive electrode has a positive electrode current collector 11 and a positive electrode active material layer 12 positioned on one surface of the positive electrode current collector 11. The negative electrode has a negative electrode current collector 21 and a negative electrode active material layer 22 positioned on one surface of the negative electrode current collector 21.

[0067] A positive electrode tab 13 is formed at one end of the positive electrode current collector 11. A negative electrode tab 23 is formed at one end of the negative electrode current collector 21. The positive electrode tab 13 and the negative electrode tab 23 are formed so as not to face each other.

[0068] The positive electrode active material layer 12 may be further formed on the other surface of the positive electrode current collector 11. The negative electrode active material layer 22 may be further formed on the other surface of the negative electrode current collector 21.

[0069] A separator 30 may be further formed between the positive electrode active material layer 12 and the negative electrode active material layer 22.

[0070] The positive electrode active material layer 12, the negative electrode active material layer 22, and the separator 30 may be impregnated with an electrolyte (not shown in Figure 1 ).

[0071] Figure 2A and Figure 2B show diagrams showing regions with high current density and regions with low current density in the positive electrode current collector and the negative electrode current collector when a voltage is applied to the electrode assembly of Figure 1 .

[0072] Refer to Figure 2A, the positive electrode current collector can be equally divided into six regions. Among the six regions, region 11A with a high current density can be the region where the positive electrode tab is formed, and region 11B with a low current density can be the remaining region except for the region of the positive electrode current collector with a high current density.

[0073] Referring to Figure 2B , the negative electrode current collector can be equally divided into six regions. Among the six regions, the region with a high current density can be the region where the negative electrode tab is formed, and the region with a low current density can be the remaining region except for the region of the negative electrode current collector with a high current density.

[0074] For example, as Figure 2A shown in, the surface on which the positive electrode tab 13 is formed is one surface 11a of the positive electrode current collector, the surface opposite to the one surface 11a of the positive electrode current collector is the other surface 11b, and the surfaces connecting the one surface 11a and the other surface 11b are the first side surface 11c and the second side surface 11d. In the positive electrode current collector, the one surface (or the other surface) can be equally divided into three regions, and the first side surface (or the second side surface) can be equally divided into two regions, so six regions 11A, 11B can be obtained. Among the six regions 11A, 11B, the region 11A where the positive electrode tab is formed can be the region with a high current density.

[0075] For example, as Figure 2B shown in, the surface on which the negative electrode tab is formed is one surface 21a of the negative electrode current collector, the surface opposite to the one surface 21a of the negative electrode current collector is the other surface 21b, and the surfaces connecting the one surface 21a and the other surface 21b are the first side surface 21c and the second side surface 21d. In the negative electrode current collector, the one surface (or the other surface) can be equally divided into three regions, and the first side surface (or the second side surface) can be equally divided into two regions, so six regions 21A, 21B can be obtained. Among the six regions 21A, 21B, the region 21A where the negative electrode tab is formed can be the region with a high current density.

[0076] Figure 3 is an exemplary diagram showing the temperature distribution when a voltage is applied to the Figure 1 electrode assembly.

[0077] Referring to Figure 3 , it can be confirmed that the temperature of the positive electrode tab region II is 66.5 °C, the temperature of the negative electrode tab region I is 72.1 °C, the temperature of the bottom IV is 52.6 °C, and the temperature of the central part III is 57.7 °C, so a temperature gradient appears.

[0078] Figure 4 is a conceptual diagram for describing the distribution of holes 1 in regions 11A and 21A with high current density in FIG. 2. Figure 5 is a conceptual diagram for describing the distribution of holes 2 in regions 11B and 21B with low current density in FIG. 2.

[0079] Referring to Figure 4 and Figure 5 the gap distance between holes in the region with high current density can be narrower than the gap distance between holes in the region with low current density. Additionally, referring to Figure 4 in the region with high current density, the gap distance between holes can become smaller toward the positive electrode tab or the negative electrode tab.

[0080] In a specific example, the gap distance between holes in the region with high current density can be the same or different, and can be 50 μm or less, for example, 10 μm to 40 μm. In a specific example, the gap distance between holes in the region with low current density can be the same or different, and can be 100 μm or more, for example, 100 μm to 500 μm. Here, the "gap distance" represents the gap distance between one hole and the hole closest to that one hole.

[0081] Figure 6A and Figure 6B are conceptual diagrams of an electrode assembly for a lithium secondary battery according to another embodiment.

[0082] Referring to Figure 6A the positive electrode current collector can be equally divided into nine regions. Among the nine regions, the region with high current density can be the region where the positive electrode tab is formed, and the region with low current density can be the remaining regions other than the region with high current density of the positive electrode current collector.

[0083] Referring to Figure 6B the negative electrode current collector can be equally divided into nine regions. Among the nine regions, the region with high current density can be the region where the negative electrode tab is formed, and the region with low current density can be the remaining regions other than the region with high current density of the negative electrode current collector.

[0084] For example, as Figure 6AAs shown in [figure], the surface on which the positive electrode tab 13 is formed is one surface 11a of the positive electrode current collector 11, the surface opposite to the one surface 11a of the positive electrode current collector 11 is the other surface 11b, and the surfaces connecting the one surface 11a and the other surface 11b are the first side surface 11c and the second side surface 11d. In the positive electrode current collector, the one surface (or the other surface) can be equally divided into three regions, and the first side surface (or the second side surface) can be equally divided into three regions, so nine regions 11A, 11B can be obtained. Among the nine regions 11A, 11B, the region 11A in which the positive electrode tab is formed can be a region with a high current density.

[0085] For example, as Figure 6B shown in [figure], the surface on which the negative electrode tab 23 is formed is one surface 21a of the negative electrode current collector 21, the surface opposite to the one surface 21a of the negative electrode current collector 21 is the other surface 21b, and the surfaces connecting the one surface 21a and the other surface 21b are the first side surface 21c and the second side surface 21d. In the negative electrode current collector, the one surface (or the other surface) can be equally divided into three regions, and the first side surface (or the second side surface) can be equally divided into three regions, so nine regions 21A, 21B can be obtained. Among the nine regions 21A, 11B, the region 21A in which the positive electrode tab is formed can be a region with a high current density.

[0086] Figure 7A and Figure 7B are conceptual diagrams of an electrode assembly for a lithium secondary battery according to another embodiment.

[0087] Referring to Figure 7A , the positive electrode current collector can be equally divided into four regions. Among the four regions, the region with a high current density can be the region in which the positive electrode tab is formed, and the region with a low current density can be the remaining region except for the region of the positive electrode current collector with a high current density.

[0088] Referring to Figure 7B , the negative electrode current collector can be equally divided into four regions. Among the four regions, the region with a high current density can be the region in which the negative electrode tab is formed, and the region with a low current density can be the remaining region except for the region of the negative electrode current collector with a high current density.

[0089] For example, as Figure 7AAs shown in the figure, the surface on which the positive electrode tab 13 is formed is one surface 11a of the positive electrode current collector 11. The surface opposite to the one surface 11a of the positive electrode current collector 11 is the other surface 11b. The surfaces connecting the one surface 11a and the other surface 11b are the first side surface 11c and the second side surface 11d. In the positive electrode current collector, the one surface (or the other surface) can be equally divided into two regions, and the first side surface (or the second side surface) can be equally divided into two regions, so that four regions 11A and 11B can be obtained. Among the four regions 11A and 11B, the region 11A in which the positive electrode tab is formed can be a region with a high current density.

[0090] For example, as Figure 7B shown in the figure, the surface on which the negative electrode tab 23 is formed is one surface 21a of the negative electrode current collector 21. The surface opposite to the one surface 21a of the negative electrode current collector 21 is the other surface 21b. The surfaces connecting the one surface 21a and the other surface 21b are the first side surface 21c and the second side surface 21d. In the negative electrode current collector, the one surface (or the other surface) can be equally divided into two regions, and the first side surface (or the second side surface) can be equally divided into two regions, so that four regions 21A and 21B can be obtained. Among the four regions 21A and 21B, the region 21A in which the positive electrode tab is formed can be a region with a high current density.

[0091] Hereinafter, each component of the electrode assembly will be described in detail.

[0092] Positive electrode current collector and positive electrode active material layer The positive electrode for a lithium secondary battery may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector.

[0093] The positive electrode active material layer includes a positive electrode active material, and may further include a binder and / or a conductive material. As an example, the positive electrode may further include an additive used as a sacrificial positive electrode.

[0094] Based on 100 wt% of the positive electrode active material layer, the content of the positive electrode active material may be in the range of 90 wt% to 99.5 wt%, and based on 100 wt% of the positive electrode active material layer, the contents of the binder and the conductive material may each be in the range of 0.5 wt% to 5 wt%.

[0095] A compound capable of reversibly inserting and extracting lithium (lithiation insertion compound) can be used as the positive electrode active material. Specifically, one or more of composite oxides of lithium and metals selected from cobalt, manganese, nickel, and combinations thereof can be used.

[0096] The composite oxide may be a lithium transition metal composite oxide. As a specific example, the composite oxide may include lithium nickel-based oxides, lithium cobalt-based oxides, lithium manganese-based oxides, lithium iron phosphate-based compounds, cobalt-free lithium nickel manganese-based oxides, or combinations thereof.

[0097] As an example, a compound represented by any of the following formulas may be used: Li a A 1-b X b O 2-c D c (0.90, may be used by, 0.90, may, 0.90, may make); Li a Mn 2-b X b O 4-c D c (0.90, may be used by, 0.90, may, 0.90, may make); Li a Ni 1-b-c Co b X c O 2-α D α (0.90c may be used by, 0.90c may, 0.90c may, 0 < α < 2); Li a Ni 1-b- c Mn b X c O 2-α D α (0.90c may be 1.8, 0.90c may, 0.90c may, 0 < α < 2); Li a Ni b Co c L 1 d G e O2 (0.90c may be 1.8, 0.90c may, 0.90c may, 0.90c may, 0.90c may); Li a NiG b O2 (0.90c may be 1.8, 0.001 may be 1.8 below); Li a CoG b O2 (0.901 may be 1.8, 0.001 may be 1.8 below); Li a Mn 1-b G b O2 (0.901 may be 1.8, 0.001 may be 1.8 below); Li a Mn2G b O4 (0.901 may be 1.8, 0.001 may be 1.8 below); Li a Mn 1-g Gg PO4 (0.901 can be 1.8, 0.g ≤ 0.5); Li (3-f) Fe2(PO4)3 (0POf)); and Li a FePO4 (0.90).51.8).

[0098] In the above formula, A represents Ni, Co, Mn, or a combination thereof, X represents Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, or a combination thereof, D represents O, F, S, P, or a combination thereof, G represents Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof, and L 1 represents Mn, Al, or a combination thereof.

[0099] As an example, the positive electrode active material can be a high-nickel type positive electrode active material. In the high-nickel type positive electrode active material, based on the metals other than lithium in 100 mol% of the lithium transition metal composite oxide, the nickel content is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, 94 mol% or more, and 99 mol% or less. The high-nickel type positive electrode active material can achieve high capacity and can be applied to high-capacity and high-density lithium secondary batteries.

[0100] The positive electrode active material layer includes the positive electrode active material and may further include a binder and / or a conductive material.

[0101] The binder is used to adhere the positive electrode active material particles to each other and is also used to adhere the positive electrode active material to the current collector. Representative examples of the binder may include at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, and polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon, but the present invention is not limited thereto.

[0102] The conductive material is used to provide conductivity to the electrode, and in the battery being constructed, any electrically conductive material can be used as long as it does not cause a chemical change. Examples of the conductive material may include: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powders or metal fibers containing copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0103] An Al thin film or aluminum foil can be used as the positive electrode current collector, but the present invention is not limited thereto.

[0104] Negative electrode current collector and negative electrode active material layer The negative electrode for a lithium secondary battery may include a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material and may further include a binder and / or a conductive material.

[0105] For example, the negative electrode active material layer may include 90 wt% to 99 wt% of a negative electrode active material, 0.5 wt% to 5 wt% of a binder, and 0.5 wt% to 5 wt% of a conductive material.

[0106] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0107] The material capable of reversibly intercalating / deintercalating lithium ions is a carbon-based negative electrode active material and may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon may include graphite such as natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical, or fibrous, and examples of amorphous carbon may include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0108] An alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used as the alloy of lithium metal.

[0109] A Si-based negative electrode active material or a Sn-based negative electrode active material can be used as the material capable of doping and dedoping lithium. The Si-based negative electrode active material can be silicon, a silicon-carbon composite, SiO x (0 < x < 2), a Si-Q alloy (Q is an alkali metal), an alkaline earth metal, a Group 13 element, a Group 14 element (excluding Si), a Group 15 element, a Group 16 element, a transition metal, a rare earth element, or a combination thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0110] The silicon-carbon composite can be a composite of silicon and amorphous carbon. According to one example, the silicon-carbon composite can be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, the silicon-carbon composite may include secondary particles (cores) in which silicon primary particles are combined and an amorphous carbon coating layer (shells) located on the surface of the secondary particles. The amorphous carbon may also be located between the silicon primary particles, and for example, the silicon primary particles may be coated with amorphous carbon. The secondary particles may exist by being dispersed in an amorphous carbon matrix.

[0111] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer positioned on the surface of the core.

[0112] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with a carbonaceous negative electrode active material.

[0113] The binder is used to adhere the negative electrode active material particles to each other and is also used to adhere the negative electrode active material to the current collector. A non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof can be used as the binder.

[0114] Examples of the non-aqueous binder may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, and combinations thereof.

[0115] The aqueous binder can be one selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, epichlorohydrin rubber, polyphosphazene, poly(meth)acrylonitrile, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0116] When the aqueous binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included. One or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or their alkali metal salts can be mixed and used as the cellulose-based compound. Na, K, or Li can be used as the alkali metal.

[0117] The dry binder is a polymer material capable of being fibrillated and can be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or combinations thereof.

[0118] A conductive material is used to provide conductivity to the electrode, and in the battery being constructed, any electrically conductive material can be used as long as it does not cause a chemical change. Specific examples of the conductive material may include: carbonaceous materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powders or metal fibers containing copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0119] One kind selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof can be used as the negative electrode current collector.

[0120] Electrolyte The electrolyte for a lithium secondary battery contains a non-aqueous organic solvent and a lithium salt.

[0121] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0122] The non-aqueous organic solvent can be a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, an aprotic solvent, or a combination thereof.

[0123] Dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), or butylene carbonate (BC) can be used as the carbonate solvent.

[0124] Methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, or caprolactone can be used as the ester solvent.

[0125] Dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, or tetrahydrofuran can be used as the ether solvent. Additionally, cyclohexanone can be used as the ketone solvent. Ethanol or isopropyl alcohol can be used as the alcohol solvent, and nitriles such as R-CN (R is a hydrocarbon group having a straight-chain, branched-chain, or cyclic structure with 2 to 20 carbon atoms and may include double bonds, aromatic rings, or ether groups), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane and 1,4-dioxolane, or sulfolane can be used as the aprotic solvent.

[0126] The non-aqueous organic solvent can be used alone or in combination of two or more thereof.

[0127] Additionally, when using a carbonate solvent, the cyclic carbonate and the chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate can be mixed at a volume ratio of 1:1 to 1:9.

[0128] A lithium salt is a material that is dissolved in an organic solvent and serves as a source of lithium ions in a battery so that a lithium secondary battery can operate basically and promote the movement of lithium ions between a positive electrode and a negative electrode. Representative examples of lithium salts may include one or more selected from LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI)), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+ 1SO2) (where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluoro bis(oxalate) phosphate (LiDFOP), lithium difluoro bis(oxalate) borate (LiDFOB), and lithium bis(oxalate) borate (LiBOB).

[0129] Separator Depending on the type of lithium secondary battery, a separator may be present between the positive electrode and the negative electrode. Polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used as the separator. Of course, hybrid multilayer films such as polyethylene / polypropylene bilayer separators, polyethylene / polypropylene / polyethylene trilayer separators, and polypropylene / polyethylene / polypropylene trilayer separators can be used.

[0130] The separator may include a porous substrate material and a coating layer containing an organic material, an inorganic material, or a combination thereof, located on one or both surfaces of the porous substrate material.

[0131] The porous substrate material may be any polymer selected from polyolefins (such as polyethylene and polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate), polyacetals, polyamides, polyimides, polycarbonates, polyether ketones, poly(aryl ether ketones), polyetherimides, polyamideimides, polybenzimidazoles, polyethersulfones, polyphenylene ethers, cycloolefin copolymers, polyphenylene sulfides, polyethylene naphthalate, glass fibers, Teflon, and polytetrafluoroethylene, or a polymer film formed from a copolymer or mixture of two or more of them.

[0132] The organic material may include polyvinylidene fluoride-based polymers or (meth)acrylic polymers.

[0133] The inorganic material may include inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof, but the present invention is not limited thereto.

[0134] The organic material and the inorganic material may be mixed in a coating layer or may exist in a stacked form of a coating layer containing the organic material and a coating layer containing the inorganic material.

[0135] In another example, an electrode included in an electrode assembly for a lithium secondary battery is provided.

[0136] In a specific example, the electrode may be a positive electrode for a lithium secondary battery.

[0137] In a specific example, the positive electrode for a lithium secondary battery may include a positive electrode current collector and a positive electrode active material layer positioned on at least one surface of the positive electrode current collector. As described above, in the positive electrode current collector, there are regions with a high current density and regions with a low current density, and the pore area ratio in the region with a high current density is greater than the pore area ratio in the region with a low current density. Since this is basically the same as that described above, detailed description will be omitted here.

[0138] In another specific example, the electrode may be a negative electrode for a lithium secondary battery.

[0139] In another specific example, the negative electrode for a lithium secondary battery may include a negative electrode current collector and a negative electrode active material layer positioned on at least one surface of the negative electrode current collector. As described above, in the negative electrode current collector, there are regions with a high current density and regions with a low current density, and the pore area ratio in the region with a high current density is greater than the pore area ratio in the region with a low current density. Since this is basically the same as that described above, detailed description will be omitted here.

[0140] In yet another example, a lithium secondary battery including an electrode assembly for a lithium secondary battery is provided.

[0141] According to the battery shape, the lithium secondary battery may be classified into a cylindrical battery, a prismatic battery, a pouch battery, and a coin-shaped battery. Figures 8 to 11 is a schematic diagram showing a lithium secondary battery according to an embodiment, Figure 8 shows a cylindrical battery, Figure 9 shows a prismatic battery, and Figure 10 and Figure 11 shows a pouch battery. Refer to Figures 8 to 11, the lithium secondary battery 100 may include an electrode assembly 40 having a separator 30 disposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is embedded. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). As Figure 8 shown, the lithium secondary battery 100 may include a sealing member 60 for sealing the case 50. Additionally, in Figure 9 it, the lithium secondary battery 100 may include a positive electrode lead tab 31, a positive electrode terminal 32, a negative electrode lead tab 41, and a negative electrode terminal 42. As Figure 10 and Figure 11 shown, the lithium secondary battery 100 may include electrode tabs 70 that serve as electrical channels for leading out the current formed in the electrode assembly 40 to the outside, that is, a positive electrode tab 71 and a negative electrode tab 72.

[0142] The lithium secondary battery according to an embodiment of the present invention may be applied to vehicles, mobile phones, and / or various types of electronic devices, and the present invention is not limited thereto.

[0143] Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are only examples of the present invention, and thus the present invention is not limited to the following examples.

[0144] Example 1 Manufacturing the positive electrode current collector Multiple holes are formed in an aluminum foil (thickness of 20 μm) using a punching method. The holes have the same diameter of 250 μm, and the cross-section of the holes has a circular shape. The positive electrode current collector is manufactured by adjusting the hole area ratio in the area of the aluminum foil where the tab is expected to be attached to 30% and the hole area ratio in the remaining area other than the area of the aluminum foil where the tab is expected to be attached to 10%. Figure 2A of the positive electrode current collector.

[0145] Manufacturing the positive electrode A positive electrode active material slurry is prepared by mixing 97 wt% of LiCoO2, 1.5 wt% of carbon black powder as a conductive material, and 1.5 wt% of polyvinylidene fluoride (PVdF), placing the mixture in an N-methyl-2-pyrrolidone solvent, and stirring the mixture and the N-methyl-2-pyrrolidone solvent for 30 minutes using a mechanical stirrer. The manufactured aluminum current collector is coated with the slurry using a doctor blade, dried in a hot air dryer at a temperature of 100 °C for 0.5 hours, dried again in a vacuum condition at a temperature of 120 °C for 4 hours, and the aluminum current collector coated with the slurry is roll-pressed to manufacture the positive electrode.

[0146] Manufacturing the negative electrode current collector Multiple holes are formed in a copper foil (with a thickness of 20 μm) using a punching method. The holes have the same diameter of 250 μm, and the cross-section of the holes has a circular shape. The negative electrode current collector is manufactured by adjusting the hole area ratio in the area where the tab is expected to be attached to the copper foil to 40% and the hole area ratio in the remaining area other than the area where the tab is expected to be attached to the copper foil to 10%. Figure 2B of the negative electrode current collector.

[0147] Manufacturing the negative electrode The negative electrode for the lithium secondary battery is manufactured by coating the manufactured negative electrode current collector with a negative electrode active material slurry and drying the negative electrode active material slurry. The negative electrode active material slurry is prepared by mixing 97 wt% of graphite particles with an average particle size of 25 μm, 1.5 wt% of styrene-butadiene rubber (SBR) binder, and 1.5 wt% of carboxymethyl cellulose (CMC), putting the mixture into distilled water, and stirring the mixture and the distilled water for 60 minutes using a mechanical stirrer.

[0148] Manufacturing the battery The electrode assembly core is prepared by interposing a separator between the positive electrode and the negative electrode manufactured as described above and winding the electrode assembly. The core is inserted into a bag, an electrolyte is injected into the bag, and the bag is vacuum-sealed. An electrolyte in which 1.3 M of LiPF6 is dissolved in a mixed solvent of EC, EMC, and DEC with a volume ratio of 3:5:2 is used. The lithium secondary battery is manufactured by pressing the core inserted into the bag at a temperature of 80 °C for 3 minutes while applying a pressure of 11.7 kgf / cm 2 .

[0149] When a voltage of 4.5 V is applied to the manufactured battery, the current density is evaluated with respect to the temperature distribution. The current density ratio between the region where the hole area ratio of the positive electrode current collector is 30% and the region where the hole area ratio of the positive electrode current collector is 10% is 2:1. The current density ratio between the region where the hole area ratio of the negative electrode current collector is 40% and the region where the hole area ratio of the negative electrode current collector is 10% is 2:1. Since the current density ratio becomes lower, the current density imbalance is resolved, thereby suppressing the deterioration of the electrode plate, increasing the battery capacity, and improving the battery life. According to Example 1, the current density ratio is low, thereby suppressing the deterioration of the electrode plate, increasing the battery capacity, and improving the battery life.

[0150] Example 2 Manufacturing the positive electrode current collector Multiple holes are formed in an aluminum foil (with a thickness of 20 μm) using a punching method. The holes have the same diameter of 250 μm, and the cross-section of the holes has a circular shape. The positive electrode current collector is manufactured by adjusting the hole area ratio in the area where the tab is expected to be attached to the aluminum foil to 30% and the hole area ratio in the remaining area other than the area where the tab is expected to be attached to the aluminum foil to 5%. Figure 2A of the positive electrode current collector.

[0151] Manufacture the negative electrode current collector Multiple holes are formed in a copper foil (with a thickness of 20 μm) using a punching method. The holes have the same diameter of 250 μm, and the cross-section of the holes has a circular shape. The negative electrode current collector is manufactured by adjusting the hole area ratio in the area where the tab is expected to be attached to the copper foil to 40% and the hole area ratio in the remaining area other than the area where the tab is expected to be attached to the copper foil to 5%. Figure 2B of the negative electrode current collector.

[0152] Using the manufactured current collectors, a lithium secondary battery is manufactured in the same manner as in Example 1.

[0153] When a voltage of 4.5 V is applied to the manufactured battery, the current density is evaluated with respect to the temperature distribution. The current density ratio between the area where the hole area ratio of the positive electrode current collector is 30% and the area where the hole area ratio of the positive electrode current collector is 5% is 2:1. The current density ratio between the area where the hole area ratio of the negative electrode current collector is 40% and the area where the hole area ratio of the negative electrode current collector is 5% is 2:1. According to Example 2, the current density ratio is low, so that the deterioration of the electrode plate can be suppressed, the battery capacity can be increased, and the battery life can be improved.

[0154] Example 3 Manufacture the positive electrode current collector Multiple holes are formed in an aluminum foil (with a thickness of 20 μm) using a punching method. The cross-section of the holes has a circular shape. The hole area ratio in the area where the tab is expected to be attached to the aluminum foil is 30%, and the diameter of the holes is 300 μm or less. The hole area ratio in the remaining area other than the above area is 5%, and the diameter of the holes is 300 μm or less. In this case, the diameter of the holes in the area where the tab is expected to be attached is larger than the diameter of the holes in the remaining area other than the above area.

[0155] Manufacture the negative electrode current collector Multiple holes are formed in a copper foil (with a thickness of 20 μm) using a punching method. The cross-section of the holes has a circular shape. The hole area ratio in the area where tabs are expected to be attached to the copper foil is 30%, and the diameter of the holes is 300 μm or less. The hole area ratio in the remaining area other than the above area is 5%, and the diameter of the holes is 300 μm or less. In this case, the diameter of the holes in the area where tabs are expected to be attached is larger than the diameter of the holes in the remaining area other than the above area.

[0156] Using the manufactured current collector, a lithium secondary battery is manufactured in the same manner as in Example 1.

[0157] When a voltage of 4.5 V is applied to the manufactured battery, the current density is evaluated with respect to the temperature distribution. The current density ratio between the area where the hole area ratio of the positive electrode current collector is 30% and the area where the hole area ratio of the positive electrode current collector is 5% is 2:1. The current density ratio between the area where the hole area ratio of the negative electrode current collector is 30% and the area where the hole area ratio of the negative electrode current collector is 5% is 2:1. According to Example 3, the current density ratio is low, so that deterioration of the electrode plate can be suppressed, the battery capacity can be increased, and the battery life can be improved.

[0158] Example 4 Manufacture of the positive electrode current collector Multiple holes are formed in an aluminum foil (with a thickness of 20 μm) using a punching method. The cross-section of the holes has a circular shape. The hole area ratio in the area where tabs are expected to be attached to the aluminum foil is 30%, and the diameter of the holes is 300 μm or less. The hole area ratio in the remaining area other than the above area is 5%, and the diameter of the holes is 300 μm or less. In this case, the diameter of the holes in the area where tabs are expected to be attached is smaller than the diameter of the holes in the remaining area other than the above area.

[0159] Manufacture of the negative electrode current collector Multiple holes are formed in a copper foil (with a thickness of 20 μm) using a punching method. The cross-section of the holes has a circular shape. The hole area ratio in the area where tabs are expected to be attached to the copper foil is 30%, and the diameter of the holes is 300 μm or less. The hole area ratio in the remaining area other than the above area is 5%, and the diameter of the holes is 300 μm or less. In this case, the diameter of the holes in the area where tabs are expected to be attached is smaller than the diameter of the holes in the remaining area other than the above area.

[0160] Using the manufactured current collector, a lithium secondary battery is manufactured in the same manner as in Example 1.

[0161] When a voltage of 4.5 V is applied to the fabricated battery, the current density is evaluated with respect to the temperature distribution. The current density ratio between the region where the hole area ratio of the positive electrode current collector is 30% and the region where the hole area ratio of the positive electrode current collector is 5% is 2:1. The current density ratio between the region where the hole area ratio of the negative electrode current collector is 30% and the region where the hole area ratio of the negative electrode current collector is 5% is 2:1. According to Example 4, the current density ratio is low, thereby suppressing the deterioration of the electrode plate, increasing the battery capacity, and improving the battery life.

[0162] Comparative Example 1 Fabricate the positive electrode current collector Use the punching method to form a plurality of holes in an aluminum foil (thickness of 20 μm). The holes have the same diameter of 250 μm, and the cross-section of the holes has a circular shape. Fabricate the positive electrode current collector by adjusting the hole area ratio in the region where the tab is expected to be attached to the aluminum foil to 30% and the hole area ratio in the remaining region other than the region where the tab is expected to be attached to the aluminum foil to 60%. Figure 2A of the positive electrode current collector.

[0163] Fabricate the negative electrode current collector Use the punching method to form a plurality of holes in a copper foil (thickness of 20 μm). The holes have the same diameter of 250 μm, and the cross-section of the holes has a circular shape. Fabricate the negative electrode current collector by adjusting the hole area ratio in the region where the tab is expected to be attached to the copper foil to 40% and the hole area ratio in the remaining region other than the region where the tab is expected to be attached to the copper foil to 60%. Figure 2B of the negative electrode current collector.

[0164] Use the fabricated current collectors to fabricate a lithium secondary battery in the same manner as in Example 1.

[0165] When a voltage of 4.5 V is applied to the fabricated battery, the current density is evaluated with respect to the temperature distribution.

[0166] The current density ratio between the region where the hole area ratio of the positive electrode current collector is 30% and the region where the hole area ratio of the positive electrode current collector is 60% is 6:1. The current density ratio between the region where the hole area ratio of the negative electrode current collector is 40% and the region where the hole area ratio of the negative electrode current collector is 60% is 6:1. Compared with Example 1 and Example 2, Comparative Example 1 has a higher current density ratio, so the expected effect of solving the current density imbalance on the surface of the electrode plate is relatively low.

[0167] As described above, although the exemplary embodiments of the present invention have been described in detail, the present invention is not limited to these embodiments, and various modifications can be practiced within the scope of the appended claims, and the detailed description, drawings, and these modifications of the present invention also fall within the scope of the present invention.

Claims

1. An electrode assembly for a lithium secondary battery, the electrode assembly comprising: a negative electrode including a negative electrode current collector having a negative electrode tab formed on one end thereof and a negative electrode active material layer positioned on at least one surface of the negative electrode current collector; as well as a positive electrode including a positive electrode current collector having a positive electrode tab formed on one end thereof and a positive electrode active material layer positioned on at least one surface of the positive electrode current collector, wherein, when a voltage is applied to the electrode assembly, a region having a high current density and a region having a low current density exist in each of the negative electrode and the positive electrode, and The pore area ratio in the region with high current density is larger than the pore area ratio in the region with low current density.

2. The electrode assembly according to claim 1, wherein: When a voltage of 3V to 4.5V is applied to the electrode assembly, in the negative electrode and the positive electrode, The temperature of the region having a high current density is 60° C. or higher; and The temperature of the area with low current density is below 60°C.

3. The electrode assembly according to claim 1 or claim 2, wherein: The region of the negative electrode having a high current density is a region where the negative electrode tab is formed among a plurality of regions obtained by evenly dividing the negative electrode current collector into n regions, and the region of the negative electrode having a low current density is a remaining region of the negative electrode excluding the region having a high current density, wherein n is an integer of 4 to 20; and The region with high current density of the positive electrode is a region where the positive electrode tab is formed among a plurality of regions obtained by evenly dividing the positive electrode current collector into n regions, and the region with low current density of the positive electrode is a remaining region except the region with high current density of the positive electrode, wherein n is an integer from 4 to 20.

4. The electrode assembly according to claim 3, wherein: In each of the negative electrode and the positive electrode, regions having pore area ratios different from each other exist in a region having a high current density, and regions having pore area ratios different from each other exist in a region having a low current density.

5. The electrode assembly according to claim 3, wherein: In each of the negative electrode and the positive electrode, a pore area ratio in a region having a high current density is larger than a pore area ratio in a region having a low current density by 15% or more.

6. The electrode assembly according to claim 3, wherein: In each of the negative electrode and the positive electrode, a pore area ratio in a region having a high current density is in a range of 20% to 40%; and The pore area ratio in the region with low current density is in the range of 0% to 10%.

7. The electrode assembly according to claim 3, wherein: A pore area ratio in a region of the negative electrode having a high current density is greater than a pore area ratio in a region of the positive electrode having a high current density.

8. The electrode assembly according to claim 3, wherein: In each of the negative electrode and the positive electrode, the pores are formed in each of the negative electrode current collector and the positive electrode current collector.

9. The electrode assembly according to claim 8, wherein: In each of the negative electrode and the positive electrode, a diameter of pores in a region having a high current density is the same as or different from a diameter of pores in a region having a low current density.

10. The electrode assembly according to claim 9, wherein: In each of the negative electrode and the positive electrode, a diameter of pores in a region having a high current density is smaller than or larger than a diameter of pores in a region having a low current density.

11. The electrode assembly according to claim 9, wherein: In each of the negative electrode and the positive electrode, the diameter of the pores becomes smaller or larger from a region having a high current density toward a region having a low current density.

12. The electrode assembly according to claim 8, wherein: In each of the negative electrode and the positive electrode, the longest diameter of the pores is 300 μm or less.

13. The electrode assembly according to claim 8, wherein: In each of the negative electrode and the positive electrode, a pore density in a region having a high current density is greater than a pore density in a region having a low current density.

14. The electrode assembly according to claim 13, wherein: In each of the negative electrode and the positive electrode, pore density becomes lower from a region having a high current density toward a region having a low current density. 15 . A lithium secondary battery, comprising the electrode assembly for a lithium secondary battery according to claim 1 .

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