Electrode for lithium secondary batteries

Abstract

An electrode for a lithium secondary battery formed of an electric collector made of a metal and a slurry coated on a part of the electric collector, the electrode for a lithium secondary battery comprising: a coated part including the part of the electric collector on which the slurry is coated and the slurry; and an uncoated part including a remaining part of the electric collector on which the slurry is not coated, the uncoated part including: a first uncoated part extending from the coated part;anda second uncoated portion extending from the first uncoated portion, the second uncoated portion having a tab connection portion connected to an electrode tab, wherein a tensile strength of the first uncoated portion is greater than a tensile strength of the tab connection portion.;

Description

TECHNICAL FIELDThe present disclosure relates to an electrode for a lithium secondary battery.BACKGROUNDA general secondary battery is a battery that can be charged and discharged unlike a primary battery that cannot be charged, and is widely used in electronic devices such as mobile phones, notebooks, and camcorders, or electric vehicles. Specifically, lithium secondary batteries have an operating voltage of about 3.6 V, a capacity about three times as high as a nickel-cadmium battery or a nickel-hydrogen battery, which is frequently used as a power source for electronic devices, and a high energy density per unit weight. Therefore, the use of lithium secondary batteries is explosively increasing.In the manufacture of a secondary battery, in order to realize a battery cell having a high capacity and a high battery density, a rolling process in an electrode process is important. The rolling process refers to a process in which an electrode passes between a pair of rolls in an electrode process and is pressed to a certain thickness of a target battery cell.However, in the rolling process, wrinkles and breakages are increasingly caused by partial deformation of the electrode, which greatly deteriorates the quality and productivity of the products, so that improvement is required.SUMMARYAn aspect of the present disclosure provides an electrode for a lithium secondary battery having an improved structure.Another aspect of the present disclosure provides an electrode for a lithium secondary battery with improved quality.In order to achieve the above-described and other objects, in one aspect of the present disclosure, there is provided an electrode for a lithium secondary battery formed of an electric collector formed of a metal and a slurry coated on a part of the electric collector, wherein the electrode for the lithium secondary battery includes a coated part including the part of the electric collector on which the slurry is coated and the slurry; An uncoated part including a remaining part of the electric collector on which the slurry is not coated, wherein the uncoated part includes a first uncoated part extending from the coated part and a second uncoated part extending from the first uncoated part, wherein the second uncoated part includes a tab connection portion coupled to an electrode tab, wherein a tensile strength of the first uncoated part is greater than a tensile strength of the tab connection portion, and wherein a ratio of the tensile strength of the first uncoated part to a tensile strength of the portion of the electric collector on which the slurry is coated is 0.65 to 0.85.According to an aspect of the present disclosure, the present disclosure may minimize the formation of electrode wrinkles in a battery cell.According to an aspect of the present disclosure, the present disclosure may prevent a problem of sticking in a process of connecting an electrode tab to an electrode of a battery cell.According to an aspect of the present disclosure, the present disclosure may minimize breakage of an electrode of a battery cell in a rolling process.According to an aspect of the present disclosure, the present disclosure may prevent electrode failure in a battery cell.BRIEF DESCRIPTION OF THE DRAWINGSThe accompanying drawings, which are included to provide a further understanding of the disclosure and are part of the disclosure, illustrate embodiments of the disclosure and together with the description serve to explain the principle of the disclosure. FIG. 1 is a cross-sectional view of an electrode according to an embodiment of the present disclosure. FIG. 2 illustrates an electrode and a heater according to an embodiment of the present disclosure. FIG. 3 is a photograph showing an electrode depending on the electrode density and tensile strength after a rolling operation. FIG. 4 is a flow chart showing a system for manufacturing an electrode. FIG. 5 illustrates a process for connecting an electrode tab to an electrode according to an embodiment of the present disclosure.DETAILED DESCRIPTIONThe detailed description and specific examples, such as embodiments of the present disclosure, are given by way of example only, since various changes and modifications within the spirit and scope of the present disclosure will become apparent to those skilled in the art from the detailed description.Wherever possible, the same reference numbers will be used in the drawings to refer to the same or like parts or components.The terms used in the present disclosure are for explaining embodiments, and are not intended to limit and / or limit the present disclosure. A term in the singular may include a term in the plural as long as it does not have an apparently different meaning in the context. In the present disclosure, the terms "include" and "have" are to be understood to mean that the illustrated features, numerals, steps, operations, components, parts, or combinations thereof are present, and do not preclude that there are one or more other features, numerals, steps, operations, components, parts, or combinations thereof, or that they may be added.The terms including an ordinal number such as "first", "second", etc. may be used to describe various components, but the components are not limited by such terms. The terms are used only to distinguish one component from other components. For example, a first component may be referred to as a second component without departing from the spirit and scope of the present disclosure, and a second component may be similarly referred to as a first component. The term "and / or" includes a combination of elements that refer to a plurality, or some of the elements that refer to a plurality.Moreover, terms such as "part", "device", "block", "element", and "module" may refer to a unit that processes at least one function or operation. The terms may refer to, for example, at least one hardware such as a field programmable gate array (FPGA) / an application specific integrated circuit (ASIC), at least one software stored in a memory, or at least one process processed by a processor.Reference will now be made in detail to embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. The accompanying drawings illustrate embodiments of the present disclosure and serve to facilitate understanding of various technical features, and it should be understood that the embodiments presented herein are not limited by the accompanying drawings.As illustrated in FIG. 1, an electrode 10 according to an embodiment of the present disclosure may be included in a battery cell. The electrode 10 may be referred to as an "electrode for a lithium secondary battery". The electrode 10 may be a positive electrode and / or a negative electrode.The electrode 10 may include an electrical collector 20. The electric collector 20 may be referred to as an "electric electrode collector". The electrical collector 20 may include a metal. For example, the electrical collector 20 may be a metal foil. The electric collector 20 may be formed to extend in one direction. For example, the electric collector 20 may be formed to extend in a longitudinal direction.The electrode 10 may include a slurry 30. The slurry 30 may be referred to as "electrode material". The slurry 30 may be coated on a portion of the electrical collector 20.The electrode 10 may be divided or divided into a region of the electric collector 20 on which the slurry 30 is coated and a remaining region. The electrode 10 may include, for example, a coated portion 40 and an uncoated portion 50.The coated portion 40 may refer to a portion of the electrode 10 on which the slurry 30 is coated on the electrical collector 20. The coated portion 40 may include, for example, the slurry 30. The coated portion 40 may include, for example, a portion of the electrical collector 20 on which the slurry 30 is coated.Uncoated portion 50 may include a portion of electrical collector 20 on which slurry 30 is not coated. That is, the uncoated region 50 may indicate a part of the electrode 10 without the coated part 40. The coated part 40 and the uncoated part 50 may be disposed along the longitudinal direction of the electric collector 20.A rolling process is important to realize a high capacity, high density battery cell during a manufacturing process of the battery cell. The rolling process is a process following a process of coating the slurry in a process of processing the electrode 10. The rolling process refers to a process in which the electrode is pressed in a thickness direction by passing the electrode 10 between a pair of rolling rolls.The thickness of the coated part 40 may be greater than the thickness of the uncoated part 50 due to the slurry 30, and therefore, pressure may be applied to the coated part 40 while pressure may not be applied to the uncoated part 50 during rolling of the electrode 10. Consequently, the electric collector 20 of the coated part 40 can be stretched by the pressure, while the electric collector 20 of the uncoated part 50 cannot be stretched. The electrical collector 20 of the coated portion 40 may refer to a portion of the electrical collector 20 on which the slurry 30 is coated.For this reason, the electric collector 20 may be deformed at a boundary between the coated part 40 and the uncoated part 50. The deformation of the electric collector 20 may result in breakage of the electric collector 20. Generally, as the electrode density and / or thickness of the electrical collector 20 increases, the likelihood of deformation of the electrical collector 20 or breakage of the electrical collector 20 may increase. The electrode density may indicate the density of the slurry 30.This reduces the yield and the operation rate in the rolling process. To solve this problem, the present disclosure may reduce the tensile strength by heating the uncoated portion 50 before the rolling process, and thus suppress the deformation and / or the breakage of the electric collector 20 at the boundary between the coated part 40 and the uncoated part 50.However, when the temperature of the uncoated part 50 is too high, sticking may occur in which the uncoated part 50 is stuck to an ultrasonic heating die by ultrasonic welding in a process of bonding the uncoated part 50 to an electrode tab.When the temperature of the uncoated part 50 is raised to a relatively low level in bonding the uncoated part 50 to the electrode tab by ultrasonic welding, the possibility of sticking may decrease, but the possibility of the electric collector 20 being deformed and / or broken during rolling may increase.By optimizing the output and the configuration of a heater 70 (see FIG. 2 ) for heating the uncoated part 50, the present disclosure can simultaneously release the breakage of the electrode 10 in the rolling process and the sticking in the joining process of the electrode tab.The electrode density of the electrode 10 may be 3.6 g / cm 3 to 3.8 g / cm 3. The electrode density is a mass density of the slurry 30, and may indicate a mass density of the slurry 30 that passes through the rolling process.The slurry 30 may be a mixture of an active material, a binder, and a conductive agent. The active material may be divided into a cathode active material used for a positive electrode and an anode active material used for a negative electrode. The active material may refer to the cathode active material and / or the anode active material.The slurry 30 may refer to at least one of a cathode slurry and an anode slurry. The cathode slurry may contain the cathode active material and the anode slurry may contain the anode active material.The electric collector 20 may denote at least one of a cathode collector and an anode collector. The cathode electric collector may be an electric collector used for the positive electrode. The anode collector may be an electric collector used for the negative electrode. The electric collector 20 may be formed of a metal foil.The uncoated portion 50 may include a first uncoated portion 51 and a second uncoated portion 52. The first uncoated part 51 may be connected to the coated part 40. The second uncoated portion 52 may be spaced apart from the coated portion 40. The first uncoated part 51 may be disposed between the coated part 40 and the second uncoated part 52. The first uncoated part 51 may connect the coated part 40 and the second uncoated part 52 to each other.The first uncoated part 51 may be formed to extend from the coated part 40. The first uncoated part 51 may be configured to have a set tensile strength. For example, the first uncoated part 51 may obtain the adjusted tensile strength by applying heat to the second uncoated part 52. The tensile strength of the first uncoated part 51 may be 17 kgf / mm 2 to 24 kgf / mm 2. For example, the tensile strength of the first uncoated part 51 may be 17 kgf / mm 2.The second uncoated part 52 may be formed to extend from the first uncoated part 51. The second uncoated portion 52 may be connected to an electrode tab 80 (see FIG. 5 ). The second uncoated part 52 may be heat treated such that the first uncoated part 51 has the adjusted tensile strength. By heat treatment by the heating process, the tensile strength of the uncoated part 50 may sequentially decrease from the first uncoated part 51 to the second uncoated part 52.The second uncoated part 52 may include a tab connection portion 52 aand a cut portion 52 b. The tab connection portion 52 amay be connected to the first uncoated part 51 and coupled to the electrode tab 80 (see FIG. 5 ). The tab connection portion 52 amay be configured to have a certain tensile strength. The target tensile strength of the first uncoated part 51 may be referred to as a first tensile strength, and the target tensile strength of the tab connection portion 52 amay be referred to as a second tensile strength.The tab connection portion 52 acan obtain the second tensile strength by the heat treatment of the second uncoated part 52. The tensile strength of the uncoated part 50 may decrease from the first uncoated part 51 toward an end portion of the second uncoated part 52. The first uncoated part 51 may be configured to have the set tensile strength.That is, the tensile strength of the first uncoated part 51 may be greater than the tensile strength of the tab connection portion 52 a, and the tensile strength of the tab connection portion 52 amay be greater than the tensile strength of the cut portion 52 b. The cut portion 52 bmay be cut off after the heat treatment and separated from the tab connection portion 52 a(see FIG. 5 ). The tab connection portion 52 amay be referred to as a "second uncoated region". The cut portion 52 bmay be referred to as a "third uncoated region". The first uncoated part 51 may be referred to as a "first uncoated region".FIG. 2 illustrates an electrode and a heater according to an embodiment of the present disclosure. FIG. 2 shows that the uncoated part 50 is divided into a plurality of regions for convenience, but the scope of the present disclosure regarding the uncoated part 50 is not limited to FIG. 2. For example, the respective regions of the uncoated part 50 may be lined up without division.As illustrated in FIG. 2, the heater 70 may heat the electrode 10. The heater 70 may heat the uncoated part 50 before the electrode 10 is rolled. The heater 70 may heat the uncoated part 50 by induction heating annealing (IHA). Induction heating may refer to heating a metal object by electromagnetic induction. The heater 70 can control the temperature of the uncoated part 50 by adjusting the output power.The heater 70 may be controllably coupled to an apparatus for rolling the electrode 10 (hereinafter referred to as "rolling apparatus"). For example, the output of the heater 70 may depend on the processing speed of the rolling apparatus. Further, the output of the heater 70 may vary depending on the material and type of the electrode 10.The heater 70 may include an induction heating unit 72 and a shielding member 74.The induction heating unit 72 may allow an induced current generated by electromagnetic induction to flow through the electrode 10. When an induced current flows through the electrode 10, heat may be generated in the electrode 10. The induction heating unit 72 may include a coil. The induction heating unit 72 may generate a high-frequency current.At least a part of the shielding member 74 may be disposed between the induction heating unit 72 and the electrode 10. For example, at least a part of the shielding member 74 may be disposed between the induction heating unit 72 and the coated part 40. For example, at least a part of the shielding member 74 may be disposed between the induction heating unit 72 and the first uncoated part 51. For example, at least a part of the shielding member 74 may be disposed between the induction heating unit 72 and the tab connection portion 52 a.The shield member 74 may shield the magnetic flux generated in the induction heating unit 72. For example, at least a portion of the magnetic flux (or magnetic field) that impinges on the shield member 74 may no longer flow through the shield member 74. For example, at least a part of the magnetic flux generated in the induction heating unit 72 and directed to the coated part 40 may be shielded by the shielding member 74. For example, at least a part of the magnetic flux generated in the induction heating unit 72 and directed to the first uncoated part 51 may be shielded by the shielding member 74. For example, at least a part of the magnetic flux generated in the induction heating unit 72 and directed to the tab connection portion 52 amay be shielded by the shielding member 74.A predetermined part of the electrode 10 may be heated by the induction heating unit 72. For example, the cut portion 52 bmay be heated by an induction heating unit 72. The induction heating unit 72 can mainly heat the cut portion 52 b. The relative permeability of the shielding member 74 may be equal to or greater than 10. The shield member 74 may be formed of, for example, a material including a ferromagnetic material.The shielding member 74 may include an exposed portion 76. The exposed portion 76 may form an exposure space 78. The induction heating unit 72 may be exposed to the uncoated part 50 through the exposure space 78. For example, the exposure space 78 may be disposed between the cut portion 52 band the induction heating unit 72. The exposed portion 76 may be referred to as a "magnetic field exposed portion.".The magnetic flux generated by the induction heating unit 72 may pass through the exposed portion 76 and strike the electric collector 20. For example, the magnetic flux passing through the exposed region 78 may impinge on at least a portion of the uncoated portion 50. With this configuration, the heater 70 can mainly heat a specific area of the electrode 10.For example, the heater 70 may be configured to mainly heat the second uncoated part 52. For example, the heat generated in the cut portion 52 bmay be transferred to the first uncoated part 51. For example, the heater 70 may be configured to mainly heat the cut portion 52 b.The induction heating unit 72 may face the cut portion 52 bthrough the exposure space 78. In another example, the induction heating unit 72 may face a space outside the cut portion 52 bthrough the exposure space 78. The heater 70 may locally heat the cut portion 52 bby induction heating. The heat generated in the cut portion 52 bmay be transmitted to the first uncoated part 51.The following is a description of the contents of an experiment for detecting changes in the tensile strength, etc. of the electrode 10 depending on the heating process. The contents will be described with reference to Figs. 1 to 3 and Table 1. FIG. 3 is a photograph showing the electrode 10 depending on the electrode density and the tensile strength after the rolling process. The tensile strength illustrated in FIG. 3 may indicate the tensile strength of the first uncoated part 51.Referring to FIGS. 1 to 3, a length of the first uncoated part 51 may be a first length L 1, a length of the tab connection portion 52 amay be a second length L 2, and a length of the cut portion 52 bmay be a third length L 3. The length of the uncoated part 50 can be measured based on a direction in which the uncoated part 50 extends from the coated part 40.The total length of the uncoated part 50 may be, for example, 15 mm. The first length L 1 may be 5 mm. The length of the second uncoated part 52 is the sum of the second length L 2 and the third length L 3 and may be 10 mm. For example, the second length L 2 may be 7 mm and the third length L 3 may be 3 mm. The first length L 1, the second length L 2, and the third length L 3 are not limited to the above examples, and may be changed within a range without departing from the purpose of the present disclosure. [Table 1] Table 1] [Table 1] Table 1]Ex. 1Section section section220190,76170,68100,4O. O00Ex. 2Cut Portion200200,8180,72120,48O. O00Ex. 3Cut Portion180200,8190,76150,6O. O04See, for example. Ex. 1Whole uncoated part220140,56100,4100,4Δ δ Δ50See, for example. Ex. 2Whole uncoated part200160,64140,56140,56Δ δ Δ23See, for example. Ex. 3Whole uncoated part180170,68170,68160,64O. O07See, for example. Ex. 4First uncoated portion220100,4170,68190,76x x x x x x x02(Wrinkles on the uncoated part: O means "good", Δ means "slightly strong", and X means "very strong")Table 1 shows, when an intense heating range and a maximum heating temperature of the uncoated part 50 change, the tensile strength and the wrinkle state of the uncoated part 50 after the rolling operation, the number of adhesions generated in ultrasonic welding (per 10 ultrasonic welding operations), and the number of fractures of the electrode 10 after the rolling operation (during the transportation of the electrode 500 m). In Table 1, the tensile strength of the uncoated part 50 before heating the uncoated part 50 is 25 kgf / mm 2. In Table 1, the electrode density of the electrode 10 after the rolling is 3.65 g / cm 3. In Table 1, the tensile strength of the uncoated part 50 before heating may be the same as the tensile strength of the electric collector 20 of the coated part 40 before heating.Referring to FIGS. 1 to 3 and Table 1, the tensile strengths of all areas of the uncoated part 50 may change even when only a certain area of the uncoated part 50 is selectively heated. This may be due to the thermal conductivity of the uncoated part 50.Wrinkling of the uncoated part 50 may occur at the first uncoated part 51 adjacent to the boundary between the coated part 40 and the uncoated part 50 due to a difference between the strain of the coated part 40 to which the pressure is directly applied and the strain of the uncoated part 50 to which the pressure is not applied. In this case, the tensile strength of the first uncoated part 51 may affect the generation of wrinkles.In the embodiment of Example 1, when Example 1 was compared with Comparative Example 4, the cut portion 52 bwhich is an end portion of the uncoated part 50 was intensively heated, and the tensile strength of the first uncoated portion 51 was 19 kgf / mm 2, and in Comparative Example 4, the first uncoated part 51 was intensively heated, and the tensile strength of the first uncoated part 51 was 10 kgf / mm 2. Although the tensile strength of the first uncoated part 51 in Comparative Example 4 was significantly lower than the tensile strength of the first uncoated part 51 in Embodiment 1, a wrinkle state in Embodiment 1 was better than a wrinkle state in Comparative Example 4.As in Comparative Example 4, when the first uncoated part 51 is intensively heated, the heat generated in the first uncoated part 51 is transferred to the electric collector 20 of the coated part 40, so that the difference between the tensile strength of the electric collector 20 at the coated part 40 and the tensile strength of the first uncoated part 51 may not be large. When the difference between the tensile strength of the electric collector 20 at the coated part 40 and the tensile strength of the first uncoated part 51 is not large, the first uncoated region 51 may be more likely to be deformed in the rolling process. In comparison of Comparative Example 4 with Comparative Example 1, although a tensile strength (14 kgf / mm 2) of the first uncoated part 51 in Comparative Example 1 was larger than the tensile strength (10 kgf / mm 2) of the first uncoated part 51 in Comparative Example 4, a wrinkle state in Comparative Example 1 was better than the wrinkle state in Comparative Example 4.Since the intensive heating area in Comparative Example 1 was the entire uncoated part 50 and the intensive heating area in Comparative Example 4 was the first uncoated part 51, the heat transferred to the electric collector 20 of the coated part 40 in Comparative Example 1 was less than the heat transferred to the electric collector 20 of the coated part 40 in Comparative Example 4. Thus, a difference in tensile strength between the electric collector 20 of the coated part 40 and the first uncoated part 51 in Comparative Example 1 was larger than a difference in tensile strength between the electric collector 20 of the coated part 40 and the first uncoated part 51 in Comparative Example 4.As in the embodiment of Example 1, when the cut portion 52 bwhich is the end portion of the uncoated part 50 has been intensively heated, the heat generated in the cut portion 52 bmay reach the first uncoated part 51 via the tab connection portion 52 a. Since heat is supplied to the first uncoated part 51 by heat conduction, the temperature of a portion of the first uncoated part 51 in the vicinity of the tab connection portion 52 acan be higher than the temperature of a portion of the first uncoated part 51 in the vicinity of the coated part 40.One method of preventing the deformation of the first uncoated part 51 may be to maintain the tensile strength of the electric collector 20 at the coated part 40 while reducing the tensile strength of the first uncoated part 51 by increasing the temperature of the first uncoated part 51. As in the embodiment of Example 1, the wrinkle state may be good when the heat is conducted from a portion opposite to the coated part 40 into the first uncoated part 51.Since heat is conducted from a portion in the first uncoated part 51 opposite to the coated part 40 to the coated part 40, the tensile strength of the electric collector 20 at the coated part 40 may be greater than the tensile strength of the first uncoated part 51, the tensile strength of the first uncoated part 51 may be greater than the tensile strength of the tab connection portion 52 a, and the tensile strength of the tab connection portion 52 amay be greater than the tensile strength of the cut portion 52 b.In comparison of Comparative Example 2 with Comparative Example 3, the tensile strength of the first uncoated part 51 was 16 kgf / mm 2 in Comparative Example 2, and the wrinkle state was slightly marked, and in Comparative Example 3, the tensile strength of the first uncoated part 51 was 17 kgf / mm 2 and the wrinkle state was good. Even when the whole uncoated part 50 in Comparative Examples 2 and 3 is intensively heated, a difference between the tensile strength of the electric collector 20 of the coated part 40 and the tensile strength of the first uncoated part 51 in Comparative Example 2 may be less than a difference between the tensile strength of the electric collector 20 of the coated part 40 and the tensile strength of the first uncoated part 51 in Comparative Example 3 due to the heat transferred to the electric collector 20 of the coated part 40 at the first uncoated part 51.It is apparent from Table 1 that in the electrode 10 having an electrode density of 3.65 g / cm 3 the wrinkling of the uncoated part 50 is highly pronounced when the tensile strength of the first uncoated part 51 is less than 17 kgf / mm 2. That is, referring to FIG. 1, in Comparative Examples 1, 2, and 4, the tensile strength of the first uncoated part 51 was less than 17 kgf / mm 2, and the wrinkle state was not good.On the other hand, in Comparative Example 3 and the embodiments of Examples 1, 2, and 3, the tensile strength of the first uncoated part 51 is between 17 kgf / mm 2 and 24 kgf / mm 2, and the wrinkle state is good. That is, when the tensile strength of the first uncoated part 51 is between 17 kgf / mm 2 and 24 kgf / mm 2 the wrinkling of the first uncoated part 51 can be improved.From the correlation between the tensile strength and the wrinkle state shown in Table 1, it is understood that the uncoated part 50 becomes softer and is liable to wrinkle when the tensile strength of the first uncoated part 51 is reduced to a predetermined level or less.However, as can be seen from FIG. 3, in the electrode having the lower electrode density of 3.55 g / cm 3 with decreasing pressure on the coated part 40, the difference in elongation between the coated part 40 and the uncoated part 50 decreases. Therefore, the difference in wrinkle depending on the tensile strength of the first uncoated part 51 can be relatively reduced as compared to the electrode having the higher electrode density.Referring to FIG. 3, the electrode 10 having an electrode density of 3.55 g / cm 3 may be provided with a relatively lower pressure in the rolling process than the electrode 10 having an electrode density of 3.65 g / cm 3. Therefore, the difference in elongation between the coated part 40 and the uncoated part 50 in the electrode 10 having the electrode density of 3.55 g / cm 3 may be smaller than the difference in elongation between the coated part 40 and the uncoated part 50 in the electrode 10 having the electrode density of 3.65 g / cm 3.For this reason, the folded state generated in the electrode 10 having the lower electrode density may be better than the folded state generated in the electrode 10 having the higher electrode density.When the tensile strength of the first uncoated part 51 is within a predetermined range and is greater than the tensile strength of the tab connection portion 52 a, the folded state of the uncoated part 50 may be good. For example, when comparing the embodiments of Examples 1, 2, and 3 and Comparative Example 3 with Comparative Examples 1, 2, and 4, the folded state of the uncoated part 50 may be good when the tensile strength of the first uncoated part 51 is in a range of more than 16.5 kgf / mm 2 and less than 20.5 kgf / mm 2. In other words, when the ratio of the tensile strength of the first uncoated part 51 to the tensile strength of the electric collector 20 of the coated part 40 is 0.65 to 0.85, the wrinkle state of the uncoated part 50 may be good.The tensile strength of the electric collector 20 of the coated part 40 cannot change by the heating process. For example, in Table 1, when the cut portion 52 bis the intense heating region, the heat transferred to the coated member 40 may be insignificant because the heat is transferred to the coated member 40 via the tab connection portion 52 aand the first uncoated member 51. Therefore, the tensile strength of the electric collector 20 of the coated part 40 cannot change by the heating process.In the bonding generated in the ultrasonic welding process, the ultrasonic welding is performed on the tab connection portion 52 a, and therefore, the tensile strength of the tab connection portion 52 acan be important. As is apparent from Table 1, in the embodiments of Examples 1 to 3 and Comparative Examples 3 and 4 in which the tensile strength of the tab connection portion 52 ais 15 kgf / mm 2 or more, no sticking occurred in ten tests. On the other hand, in Comparative Examples 1 and 2 in which the tensile strength of the tab connection portion 52a is less than 15 kgf / mm 2 bonding occurred. As the tensile strength of the tab connection portion 52 aceeds, the number of bonds may increase.When the tensile strength of the tab connection portion 52 ais not greater than the tensile strength of the first uncoated part 51, the folded state of the uncoated part 50 is not very strong. Therefore, a condition in which the tensile strength of the tab connection portion 52 ais less than 20 kgf / mm 2 may be a necessary condition for the wrinkle state of the uncoated part 50 to be good. That is, a condition in which the tensile strength of the tab connection portion 52 ais between 14.5 kgf / mm 2 and 19.5 kgf / mm 2 may be a necessary condition for the uncoated part 50 in which the number of adhesions decreases and the wrinkle state is good. In other words, when the ratio between the tensile strength of the tab connection portion 52 aand the tensile strength of the electric collector 20 of the coated part 40 is 0.55 to 0.8, the adhesion can be suppressed.The breakage generated in rolling can be most affected by the tensile strength of the cut portion 52 b. In Table 1, no breakage has occurred in the embodiments of Examples 1 and 2 and Comparative Example 1 in which the tensile strength of the cut portion 52 bis 13 kgf / mm 2 or less. This is because the breakage during rolling starts at the cut portion 52 bto which the stress concentrates, and the probability of breakage decreases as the tensile strength of the cut portion 52 bis lowered.When the embodiment of Example 2 was compared with the embodiment of Example 3, in the embodiment of Example 2, the tensile strength of the tab connecting portion 52a was 18 kgf / mm 2 and no breakage occurred, while in the embodiment of Example 3, the tensile strength of the tab connecting portion 52a was 19 kgf / mm 2 and the breakage occurred four times. From this, it can be seen that a condition in which the tensile strength of the tab connection portion 52 ais equal to or less than 18.5 kgf / mm 2 is favorable in terms of breakage.Combining the above results, in the electrode 10 having the electrode density of 3.65 g / cm 3, when the tensile strength of the first uncoated part 51 is between 16.5 kgf / mm 2 and 20.5 kgf / mm 2 and the tensile strength of the tab connection portion 52 ais between 14.5 kgf / mm 2 and 18.5 kgf / mm 2 while the cut portion 52 bis intensively heated, the wrinkle state, adhesion, and breakage of the uncoated part 50 can be improved.In other words, in the electrode 10 having an electrode density of 3.65 g / cm 3 when the ratio between the tensile strength of the first uncoated part 51 and the tensile strength of the electric collector 20 of the coated part 40 is 0.65 to 0.85, and a ratio of the tensile strength of the tab connection portion 52 ato the tensile strength of the electric collector 20 of the coated part 40 is 0.55 to 0.75 while the cut portion 52 bis intensively heated, the wrinkle state, adhesion, and breakage of the uncoated part 50 can be improved.Conditions in which the tensile strength of the first uncoated part 51 is greater than the tensile strength of the tab connection portion 52 aand the tensile strength of the tab connection portion 52 ais greater than the tensile strength of the cut portion 52 bmay be the most favorable conditions for the folded state, the sticking, and the breakage of the uncoated part 50.The second length L 2, which is the length of the tab connection portion 52 a, may be greater than the first length L 1, which is the length of the first uncoated part 51. When the second length L 2 is larger than the first length L 1, the cut portion 52 bis largely intensively heated, and thus a difference between the tensile strength of the tab connection portion 52 aand the tensile strength of the first uncoated part 51 can be effectively formed.Since the cut portion 52 bis removed before the electrode tab 80 is attached (see FIG. 5 ), the cut portion 52 bmay not directly affect the performance of the battery cell. However, the cut portion 52 bmay affect the improvement of the breakage in the rolling process.A process for processing an electrode of the battery cell will be described below. An electrode manufacturing system S 100 may be referred to as an electrode manufacturing system for a lithium secondary battery.Referring to FIGS. 1 to 4, an electrode manufacturing system S 100 may include a slurry coating step S 110. In step S 110, a slurry 30 may be coated on at least one surface of an electric collector 20.The electric collector 20 may be formed of a thin conductive metal plate. The electric collector 20 may include a metal thin plate. The metal thin plate may be formed of aluminum, for example. The slurry 30 may be coated on one surface or both surfaces of the electric collector 20. Through step S 110, an electrode 10 may be divided into a coated part 40 and an uncoated part 50.The area of the electrode 10 can be divided into a region where the coated part 40 is located and a region where the uncoated part 50 is located. The coated portion 40 may be referred to as a "coated portion". The uncoated portion 50 may be referred to as an "uncoated region". For example, the electrode 10 may be divided into a coated region 40 and an uncoated region 50.The system S 100 for manufacturing the electrode may include a heating step S 120. In step S 120, a heater 70 may heat the electrode 10. For example, in step S 120, the heater 70 may mainly heat a cut portion 52 b. In other words, in step S 120, the heater 70 may mainly heat an end portion of the uncoated part 50. That is, in step S 120, the heater 70 may mainly heat the end portion of the uncoated region 50.The heating step S 120 may include a step S 121 of forming an exposed portion. In step S 121, an exposure space 78 may be formed by a shield member 74 so that a magnetic flux generated by an induction heating unit 72 propagates while being limited to a predetermined range. In step S 121, a magnetic field generated by the induction heating unit 72 may be dispersed while being limited to a predetermined range.The heating step S 120 may include a step S 122 of heating an uncoated part. In step S 122, a part of the magnetic flux generated by the induction heating unit 72 may be shielded by the shielding member 74, and another part may pass through the exposure space 78 and impinge on the uncoated part 50. For example, in this step S 122, the induction heating unit 72 may mainly heat the cut portion 52 bwhich is the end portion of the uncoated part 50.In heating step S 120, the induction heating unit 72 may heat the uncoated part 50 such that a portion of the uncoated part 50 has a certain tensile strength. For example, the cut portion 52 bmay be heated such that a tab connection portion 52 ahas a second tensile strength that is a target tensile strength. For example, the cut portion 52 bmay be heated such that a first uncoated part 51 has a first tensile strength corresponding to a target tensile strength. For example, the cut portion 52 bmay be heated such that the first uncoated part 51 has the first tensile strength and the tab connection portion 52 ahas the second tensile strength.The system S 100 for manufacturing the electrode may include a rolling step S 130. The rolling step S 130 may be a step of compressing the electrode 10 to increase an adhesion force between the slurry 30 and the electric collector 20. Through the rolling step S 130, the electrode 10 may be compressed to a certain thickness.The electrode manufacturing system S 100 may include a cutting step S 135 of cutting the cut portion 52 b. In step S 135, the cut portion 52 bmay be separated from the tab connection portion 52 a.The system S 100 for manufacturing the electrode may include a step S 140 for connecting the tabs. The tab bonding step S 140 may be performed after the rolling step S 130. In the tab bonding step S 140, an electrode tab 80 (see FIG. 5 ) may be bonded to the uncoated part 50. In step S 140, the electrode tab 80 (see FIG. 5 ) may be connected to the uncoated region 50. In step S 140, the tab connection portion 52 amay be connected to the electrode tab 80 (see FIG. 5 ).FIG. 5 shows that the respective regions of the uncoated part 50 are divided by broken lines for convenience, but the respective regions may not be divided and arranged one behind another.Referring to (a) and (b) of FIG. 5, the plurality of second uncoated parts 52 may be laminated and welded. As shown in (c) of FIG. 5, the cut portion 52 bmay be separated and removed from the tab connection portion 52 a. As shown in (d) of FIG. 5, the tab connection portion 52 acan be joined or coupled to the electrode tab 80 by welding when the cut portion 52 bhas been removed from the second uncoated part 52. Consequently, the electrode 10 and the electrode tab 80 can be connected.Although the embodiments have been described with reference to a number of illustrative embodiments, numerous other modifications and embodiments may be devised by those skilled in the art that will fall within the scope of the principles of the present disclosure. In particular, various variations and modifications are possible in the components and / or arrangements of the present combination arrangement within the scope of the present disclosure, the drawings and the appended claims. In addition to variations and modifications in the components and / or arrangements, alternative uses will also be apparent to those skilled in the art. The scope of the present disclosure should be determined by rational interpretation of the appended claims, and all modifications within an equivalent scope of the present disclosure are included within the scope of the present disclosure.

Claims

An electrode for a lithium secondary battery formed of an electric collector formed of a metal and a slurry coated on a part of the electric collector, the electrode for a lithium secondary battery comprising: a coated part including the part of the electric collector on which the slurry is coated and the slurry; and an uncoated part including a remaining part of the electric collector on which the slurry is not coated, the uncoated part including: a first uncoated part extending from the coated part; and a second uncoated part extending from the first uncoated part, the second uncoated part having a tab connection portion connected to an electrode tab, wherein a tensile strength of the first uncoated part is greater than a tensile strength of the tab connection portion.The electrode for a lithium secondary battery according to claim 1, wherein the second uncoated part includes a cut portion extending from the tab connection portion, and wherein the tensile strength of the tab connection portion is greater than the tensile strength of the cut portion.The electrode for a lithium secondary battery according to claim 1, wherein the ratio between the tensile strength of the first uncoated part and the tensile strength of the part of the electric collector on which the slurry is coated is 0.65 to 0.85.The electrode for a lithium secondary battery according to claim 1, wherein the ratio between the tensile strength of the tab connection portion and the tensile strength of the part of the electric collector on which the slurry is coated is 0.55 to 0.75.The electrode for a lithium secondary battery according to claim 1, wherein the electrode density of the electrode for a lithium secondary battery is 3.6 to 3.8 g / cm 3 and wherein the tensile strength of the first uncoated part is 16.5 to 20.5 kgf / mm 2.The electrode for lithium secondary battery according to claim 1, wherein the electrode density of the electrode for lithium secondary battery is 3.6 to 3.8 g / cm 3 and wherein the tensile strength of the tab connection portion is 14.5 to 18.5 kgf / mm 2.The electrode for lithium secondary battery according to claim 1, wherein a length of the first uncoated part in a direction in which the first uncoated part extends is shorter than a length of the tab connection portion in a direction in which the second uncoated part extends.The electrode for lithium secondary battery according to claim 1, wherein a length of the uncoated part is the sum of a length of the first uncoated part and a length of the second uncoated part.The electrode for a lithium secondary battery according to claim 1, wherein a length of the uncoated part is 15 mm.The electrode for a lithium secondary battery according to claim 1, wherein a length of the first uncoated part is 5 mm and a length of the second uncoated part is 10 mm.The electrode for a lithium secondary battery according to claim 2, wherein the length of the second uncoated part is the sum of the length of the tab connection portion and the length of the cut portion.The electrode for a lithium secondary battery according to claim 1, wherein a length of the second uncoated part is 10 mm.The electrode for a lithium secondary battery according to claim 2, wherein the length of the tab connection portion is 7 mm and the length of the cut portion is 3 mm.

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