KR20220061845A - Electrode for lithium secondary battery and method of manufacturing the same - Google Patents

Abstract

An electrode for a lithium secondary battery according to one embodiment of the present invention, which is an electrode for a lithium secondary battery comprising an electric collector formed of metal and a slurry applied to a part of the electric collector, comprises: a coated part including a part coated with the slurry in the electric collector and the slurry; and a non-coated part including a remaining part not coated with the slurry in the electric collector, wherein the non-coated part comprises: a first non-coated part extending from the coated part; and a second non-coated part extending from the first non-coated part and having a tab connection part coupled to an electrode tab, a tensile strength of the first non-coated part is greater than a tensile strength of the tab connection part, and a ratio of the tensile strength of the first non-coated part to the tensile strength of the part coated with the slurry in the electric collector may be 0.65 to 0.85. According to the present invention, it is possible to minimize wrinkles generated on the electrode of a battery cell.

Description

Electrode for lithium secondary battery and manufacturing method thereof

The present invention relates to an electrode for a lithium secondary battery and a method for manufacturing the same.

A general secondary battery refers to 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 cell phones, notebook computers, camcorders, etc. or electric vehicles. In particular, the lithium secondary battery has an operating voltage of about 3.6V, has about three times the capacity of a nickel-cadmium battery or a nickel-hydrogen battery, which are often used as power sources for electronic equipment, and has a high energy density per unit weight. There is a trend of explosive increase in severity.

During the manufacturing process of the secondary battery, the rolling process is important in the electrode process in order to realize high capacity and high density battery cells of the battery. The rolling process refers to a process in which an electrode is passed between a pair of rollers in the electrode process and pressed to the target battery cell design thickness.

However, in such a process, wrinkles and fractures due to partial deformation of the electrode increase, which greatly affects product quality and productivity, so improvement is required.

Patent Publication KR 10-2017-0137355 A

SUMMARY OF THE INVENTION The present invention aims to solve the above and other problems.

Another object of the present invention is to provide an electrode for a lithium secondary battery that minimizes wrinkling of the electrode in a battery cell, and a method for manufacturing the same.

Another object of the present invention is to provide an electrode for a lithium secondary battery that prevents a problem of burning during an electrode tap connection process with respect to an electrode of a battery cell, and a method for manufacturing the same.

Another object of the present invention is to provide an electrode for a lithium secondary battery that minimizes breakage of the electrode of a battery cell during a rolling process, and a method for manufacturing the same.

Another object of the present invention is to provide an electrode for a lithium secondary battery that prevents electrode failure of a battery cell and a method for manufacturing the same.

According to one aspect of the present invention to achieve the above or other object, an electrode for a lithium secondary battery comprising an electric collector formed of a metal and a slurry applied to a part of the current collector, the current collector an applicator comprising a portion to which the slurry is applied and the slurry from among; and an uncoated portion including the remaining portion of the current collector to which the slurry is not applied, wherein the uncoated portion includes: a first uncoated portion extending from the applying portion; and a second uncoated portion extending from the first uncoated portion and having a tab connection portion coupled to the electrode tab, wherein the tensile strength of the first uncoated portion is greater than the tensile strength of the tab connection portion, and wherein the tensile strength of the first uncoated portion is greater than that of the current collector. A ratio of the tensile strength of the first uncoated region to the tensile strength of the portion to which the slurry is applied is 0.65 to 0.85, an electrode for a lithium secondary battery may be provided.

According to another aspect of the present invention, there is provided a method for manufacturing an electrode for a lithium secondary battery comprising a current collector formed of a metal and a slurry applied to a portion of the current collector, wherein the slurry is applied to at least one surface of the current collector. a slurry application step (S110) of dividing the electrode for a lithium secondary battery into an application region to which the slurry is applied and an uncoated region to which the slurry is not applied; The uncoated region includes a first uncoated region adjacent to the application region, a tab connection portion connected to the first uncoated region and coupled to an electrode tab, and a cut portion extending from the tab connection portion, and heating the cut portion ( S120); and a rolling step (S130) of rolling the heated electrode, wherein the ratio of the tensile strength of the first uncoated region to the tensile strength of the current collector in the application region is 0.65 to 0.85, a method of manufacturing an electrode for a lithium secondary battery (S100) may be provided.

The effect of the electrode for a lithium secondary battery according to the present invention and a manufacturing method thereof will be described as follows.

According to at least one of the embodiments of the present invention, an electrode for a lithium secondary battery that minimizes the generation of wrinkles in the electrode of a battery cell and a method for manufacturing the same may be provided.

According to at least one of the embodiments of the present invention, there may be provided an electrode for a lithium secondary battery and a method of manufacturing the same for preventing a problem of burning during an electrode tab connection process with respect to an electrode of a battery cell.

According to at least one of the embodiments of the present invention, an electrode for a lithium secondary battery that minimizes the breakage of the electrode of a battery cell during a rolling process and a method for manufacturing the same may be provided.

According to at least one of the embodiments of the present invention, there may be provided an electrode for a lithium secondary battery that prevents electrode failure of a battery cell and a method for manufacturing the same.

1 is a cross-sectional view of an electrode according to an embodiment of the present invention.
2 is a view showing an electrode and a heating device according to an embodiment of the present invention.
3 is a photograph showing the electrode according to the electrode density and tensile strength after the rolling process.
4 is a flowchart illustrating a method of manufacturing an electrode according to an embodiment of the present invention.
5 is a diagram illustrating a process of connecting an electrode tab to an electrode according to an embodiment of the present invention.

The configuration shown in the embodiments and drawings described in this specification is only a preferred example of the disclosed invention, and there may be various modifications that can replace the embodiments and drawings of the present specification at the time of filing of the present application.

In addition, the same reference numerals or reference numerals in each drawing of the present specification indicate parts or components that perform substantially the same functions.

In addition, the terminology used herein is used to describe the embodiments, and is not intended to limit and/or limit the disclosed invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present specification, terms such as “comprise” or “have” are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features It does not preclude the possibility of the presence or addition of numbers, steps, operations, components, parts, or combinations thereof.

In addition, terms including ordinal numbers such as “first” and “second” used in this specification may be used to describe various components, but the components are not limited by the terms, and the terms are It is used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, a first component may be referred to as a second component, and similarly, a second component may also be referred to as a first component. The term “and/or” includes any combination of a plurality of related listed items or any of a plurality of related listed items.

In addition, terms such as "~ part", "~ group", "~ block", "~ member", and "~ module" may mean a unit for processing at least one function or operation. For example, the terms may refer to at least one process processed by at least one hardware such as a field-programmable gate array (FPGA)/application specific integrated circuit (ASIC), at least one software stored in a memory, or a processor. there is.

Hereinafter, an embodiment according to the present invention will be described in detail with reference to the accompanying drawings. However, the following drawings attached to the present specification illustrate preferred embodiments of the present invention, and serve to further understand the technical spirit of the present invention together with the above-described content of the present invention, so the present invention is described in such drawings It should not be construed as being limited only to the matters.

Referring to FIG. 1 , an electrode 10 according to an embodiment of the present invention 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 a current collector 20 . The current collector 20 may be referred to as an “electrode current collector”. The current collector 20 may include a metal. For example, the current collector 20 may be a metal foil. The current collector 20 may be formed to extend in one direction. For example, the current collector 20 may be formed to extend in the longitudinal direction.

The electrode 10 may include a slurry 30 . The slurry 30 may be referred to as an “electrode material”. The slurry 30 may be applied to a portion of the current collector 20 .

The electrode 10 may be divided or partitioned into a region in which the slurry 30 is applied to the current collector 20 and the remaining region. For example, the electrode 10 may include an applied part 40 (coated part) and an uncoated part 50 (uncoated part).

The application unit 40 may refer to a portion of the electrode 10 in which the slurry 30 is applied to the current collector 20 . For example, the applicator 40 may include the slurry 30 . For example, the application unit 40 may include a portion of the current collector 20 to which the slurry 30 is applied.

The uncoated region 50 may include a portion of the current collector 20 to which the slurry 30 is not applied. That is, the uncoated region 50 may mean a portion of the electrode 10 excluding the application portion 40 . The application part 40 and the uncoated part 50 may be disposed along the length direction of the current collector 20 .

During the battery cell manufacturing process, the rolling process is important for realizing high capacity and high density battery cells. The rolling process is a process following the process of applying the slurry in the process of processing the electrode 10 , and refers to a process of pressing the electrode in the thickness direction by passing the electrode 10 between a pair of rolling rollers.

The thickness of the application part 40 may be greater than the thickness of the uncoated part 50 due to the slurry 30 . Therefore, in the process of rolling the electrode 10 , the application part 40 may receive pressure and the uncoated part 50 may not receive pressure. For this reason, the current collector 20 of the application part 40 may be stretched by pressure, whereas the current collector 20 of the uncoated part 50 may not be stretched. The current collector 20 of the application unit 40 may mean a portion of the current collector 20 to which the slurry 30 is applied.

For this reason, deformation of the current collector 20 may occur at the boundary between the application part 40 and the uncoated part 50 . A change in the current collector 20 may lead to breakage of the current collector 20 . In general, as the electrode density increases and/or the thickness of the current collector 20 decreases, the probability that the current collector 20 will be deformed or the probability that the current collector 20 will break may increase. The electrode density may mean the density of the slurry 30 .

Due to this, the yield and operating rate in the rolling process are lowered. In order to solve this problem, the coating part 40 is heated by heating the uncoated part 50 prior to the rolling process to lower the tensile strength. ) and the uncoated region 50 , deformation and/or breakage of the current collector 20 may be suppressed.

However, if the temperature of the uncoated area 50 is raised too high, in the process of bonding the uncoated area 50 and the electrode tab through ultrasonic welding, seizure occurs in which the uncoated area 50 sticks to the ultrasonic heating mold. can be

When the temperature of the uncoated region 50 is relatively low, the probability of seizure occurring in the process of bonding the uncoated region 50 and the electrode tab to the electrode tab through ultrasonic welding is reduced, but deformation of the current collector 20 or / and the probability of occurrence of breakage may increase.

By optimizing the output power and configuration of the heating device 70 (refer to FIG. 2) that heats the uncoated region 50, the breaking of the electrode 10 in the rolling process and sintering in the electrode tap connection process are prevented. can be solved at the same time.

The electrode density of the electrode 10 may be 3.6 g/cc to 3.8 g/cc. The electrode density is a mass density of the slurry 30 , and may mean a mass density of the slurry 30 that has passed through a 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 an active material for cathode used for a positive electrode and an active material for anode used for a negative electrode. The active material may mean at least one of a positive active material and a negative active material.

The slurry 30 may mean at least one of a positive electrode slurry and a negative electrode slurry. The positive electrode slurry may include a positive electrode active material. The negative electrode slurry may include a negative electrode active material.

The current collector 20 may mean at least one of a positive electrode current collector and a negative electrode current collector. The positive electrode current collector may be a current collector used in a positive electrode. The negative electrode current collector may be a current collector used in a negative electrode. The current collector 20 may be formed of a metal foil.

The uncoated area 50 may include a first uncoated area 51 and a second uncoated area 52 . The first uncoated area 51 may be connected to the applicator 40 . The second uncoated area 52 may be spaced apart from the application unit 40 . The first uncoated area 51 may be disposed between the application unit 40 and the second uncoated area 52 . The first uncoated area 51 may connect the applicator 40 and the second uncoated area 52 .

The first uncoated area 51 may be formed to extend from the application unit 40 . The first uncoated region 51 may be configured to have a set tensile strength. For example, by applying heat to the second uncoated area 52 , the first uncoated area 51 may have a set tensile strength. The first uncoated region 51 may have a tensile strength of 17 kgf/mm ² to 24 kgf/mm ² . For example, the tensile strength of the first uncoated region 51 may be 17 kgf/mm ² .

The second uncoated area 52 may extend from the first uncoated area 51 . The second uncoated region 52 may be coupled to the electrode tab 80 (refer to FIG. 5 ). The second uncoated area 52 may be heat treated so that the first uncoated area 51 may have a set tensile strength. Through the heat treatment by the heating process, the tensile strength of the uncoated area 50 may decrease sequentially from the first uncoated area 51 to the second uncoated area 52 .

The second uncoated portion 52 may include a tab connection portion 52a and a cut portion 52b. The tab connection part 52a is connected to the first uncoated part 51 and may be coupled to the electrode tab 80 (refer to FIG. 5 ). The tab connection part 52a may be configured to have a set tensile strength. The set tensile strength of the first uncoated portion 51 may be referred to as a first tensile strength, and the set tensile strength of the tab connection portion 52a may be referred to as a second tensile strength.

The tab connection portion 52a may have a second tensile strength through heat treatment of the second uncoated portion 52 . The tensile strength of the uncoated area 50 may decrease from the first uncoated area 51 toward the end of the second uncoated area 52 . The first uncoated region 51 may be configured to have a set tensile strength.

That is, the tensile strength of the first uncoated portion 51 may be greater than that of the tab connection portion 52a , and the tensile strength of the tab connection portion 52a may be greater than that of the cut portion 52b . The cut portion 52b may be cut and separated from the tab connection portion 52a after heat treatment is performed (see FIG. 5 ). The tab connection part 52a may be referred to as a “second uncoated region”. The cut portion 52b may be referred to as a “third uncoated region”. The first uncoated region 51 may be referred to as a “first uncoated region”.

2 is a view showing an electrode and a heating device according to an embodiment of the present invention. In FIG. 2 , the uncoated area 50 is illustrated in which each area is divided for convenience of description, but the scope of the present invention regarding the uncoated area 50 is not limited to FIG. 2 . Each region of the uncoated region 50 may be continuously connected without a partitioned configuration.

Referring to FIG. 2 , the heating device 70 may heat the electrode 10 . The heating device 70 may heat the uncoated region 50 before the electrode 10 is rolled. The heating device 70 may heat the uncoated region 50 by induction heating annealing (IHA). Induction heating may refer to a method of heating a metal object using electromagnetic induction. The heating device 70 may control the temperature of the uncoated area 50 by adjusting the output power.

The heating device 70 may be controlledly interlocked with a device for rolling the electrode 10 (hereinafter, “rolling device”). For example, the output power of the heating device 70 may depend on the processing speed of the rolling device. Also, the output power of the heating device 70 may vary depending on the material and the type of the electrode 10 .

The heating device 70 may include an induction heating unit 72 and a shielding member 74 .

The induction heating unit 72 may use electromagnetic induction action to cause an induced current to flow through the electrode 10 . When an induced current flows in 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 can form a high-frequency current.

At least a portion of the shielding member 74 may be disposed between the induction heating unit 72 and the electrode 10 . For example, at least a portion of the shielding member 74 may be disposed between the induction heating unit 72 and the applicator 40 . For example, at least a portion of the shielding member 74 may be disposed between the induction heating unit 72 and the first uncoated region 51 . For example, at least a portion of the shield member 74 may be disposed between the induction heating unit 72 and the tab connection portion 52a.

The shielding member 74 may have an effect of shielding magnetic flux generated by the induction heating unit 72 . For example, at least a portion of the magnetic flux (or magnetic field) incident on the shielding member 74 may no longer travel by the shielding member 74 . For example, at least a portion of the magnetic flux generated in the induction heating unit 72 and directed toward the applicator 40 may be shielded by the shielding member 74 . For example, at least a portion of the magnetic flux generated by the induction heating unit 72 and directed to the first uncoated region 51 may be shielded by the shielding member 74 . For example, at least a portion of the magnetic flux generated in the induction heating unit 72 and directed to the tab connection portion 52a may be shielded by the shielding member 74 .

A predetermined portion of the electrode 10 may be heated by the induction heating unit 72 . For example, the cut portion 52b may be heated by an induction heating unit 72 . The induction heating unit 72 may mainly heat the cut portion 52b. The relative permeability of the shielding member 74 may be 10 or more. For example, the shielding member 74 may be formed of 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 area 50 through the exposure space 78 . For example, the exposure space 78 may be located between the cut portion 52b and the induction heating unit 72 . The exposed portion 76 may be referred to as a “magnetic field exposure portion”.

Magnetic flux generated by the induction heating unit 72 may pass through the exposed portion 76 and be incident on the current collector 20 . For example, magnetic flux passing through the exposure space 78 may be incident on at least a portion of the uncoated region 50 . Through this configuration, the heating device 70 can mainly heat a specific region of the electrode 10 .

For example, the heating device 70 may be configured to mainly heat the second uncoated region 52 . For example, heat generated in the cut part 52b may be transferred to the first uncoated part 51 . For example, the heating device 70 may be configured to primarily heat the cut 52b.

The induction heating unit 72 may face the cut portion 52b through the exposure space 78 . In another example, the induction heating unit 72 may face the space outside of the cut-out 52b through the exposure space 78 . The heating device 70 may locally heat the cut portion 52b through induction heating. Heat generated from the cut portion 52b may be heat-conducted to the first uncoated portion 51 .

The following is the content of the experiment to know the change of the tensile strength of the electrode 10 according to the heating process. It will be described with reference to FIGS. 1 to 3 and Table 1. 3 is a photograph showing the electrode 10 according to the electrode density and tensile strength after the rolling process. The tensile strength shown in FIG. 3 may mean the tensile strength of the first uncoated region 51 .

1 to 3 , the length of the first uncoated part 51 is the first length L1 , the length of the tab connection part 52a is the second length L2 , and the length of the cut part 52b is It may be the third length L3. The length of the uncoated area 50 may be measured based on a direction in which the uncoated area 50 extends from the application unit 40 .

For example, the total length of the uncoated region 50 may be 15 mm. The first length L1 may be 5 mm. The length of the second uncoated region 52 is the sum of the second length L2 and the third length L3 , and may be 10 mm. For example, the second length L2 may be 7 mm, and the third length L3 may be 3 mm. The first length L1 , the second length L2 , and the third length L3 are not limited to the above examples, and may be changed within a range without departing from the purpose of the present invention.

division intensive heating
area maximum heating
temperature
(℃) By area of Mujibu
Tensile strength (kgf/mm ² ) wrinkle
state for ultrasonic welding
Number of occurrences of seizures
(Based on 10 episodes) break
number
(based on 500m) the 1st branch First uncoated area after heating / First uncoated area before heating Tap connection part after heating Tap connection part after heating / Tap connection part before heating cut after heating Cut after heating/Heated cut Example 1 cut 220 19 0.76 17 0.68 10 0.4 O 0 0 times Example 2 cut 200 20 0.8 18 0.72 12 0.48 O 0 0 times Example 3 cut 180 20 0.8 19 0.76 15 0.6 O 0 4 times Comparative Example 1 Unclear whole 220 14 0.56 10 0.4 10 0.4 Δ 5 0 times Comparative Example 2 Unclear whole 200 16 0.64 14 0.56 14 0.56 Δ 2 3rd time Comparative Example 3 Unclear whole 180 17 0.68 17 0.68 16 0.64 O 0 Episode 7 Comparative Example 4 1st uncoated area 220 10 0.4 17 0.68 19 0.76 X 0 Episode 2

(Crinkle on the cheek area: O means good, Δ means slightly severe, X means very severe)

Table 1 shows the tensile strength and wrinkle state of the uncoated area 50 after the rolling process when the intensive heating area and the maximum heating temperature of the uncoated area 50 are different, and the number of sinterings generated in the ultrasonic welding process (ultrasonic welding 10 times) per), and the number of fractures of the electrode 10 after the rolling process (in the process of transporting the electrode 500 m). In Table 1, the tensile strength of the uncoated area 50 before the uncoated area 50 is heated is 25 kgf/mm ² . In Table 1, the electrode density of the electrode 10 after the rolling process is 3.65 g/cc. In Table 1, the tensile strength of the uncoated portion 50 before heating may be the same as the tensile strength of the current collector 20 of the application portion 40 before heating.

1 to 3 and Table 1, even when only a specific area of the uncoated area 50 is selectively heated, the tensile strength of each area of the uncoated area 50 may all be changed. This may be due to the thermal conductivity of the uncoated region 50 .

Wrinkles of the uncoated area 50 are formed between the coated area 40 and the uncoated area 50 due to a difference between the elongation of the uncoated area 50 that is not subjected to direct pressure and the elongation of the uncoated area 50 that is not subjected to pressure. It may occur in the first uncoated region 51 adjacent to the boundary. In this case, the tensile strength of the first uncoated region 51 may affect the degree of wrinkling.

Comparing Example 1 and Comparative Example 4, in the case of Example 1, the tensile strength of the first uncoated area 51 by heating the cut portion 52b, which is the end of the uncoated area 50, is 19 kgf/mm ² , In Comparative Example 4, the first uncoated area 51 was intensively heated so that the tensile strength of the first uncoated area 51 was 10 kgf/mm ² . Although the tensile strength of the first uncoated region 51 in Comparative Example 4 was significantly lower than the tensile strength of the first uncoated region 51 in Example 1, the wrinkled state in Example 1 was the wrinkled state in Comparative Example 4 better than

As in Comparative Example 4, when the first uncoated area 51 is heated intensively, heat generated in the first uncoated area 51 is transferred to the current collector 20 of the application unit 40 , and the application unit 40 . In , the difference between the tensile strength of the current collector 20 and the tensile strength of the first uncoated region 51 may not be large. If the difference between the tensile strength of the current collector 20 and the tensile strength of the first uncoated area 51 in the application unit 40 is not large, there is a high probability that deformation of the first uncoated area 51 will occur in the rolling process. can Comparing Comparative Example 4 and Comparative Example 1, the tensile strength (14kgf/mm ² ) of the first uncoated area 51 in Comparative Example 1 was the tensile strength (10kgf/mm) of the first uncoated area 51 in Comparative Example 4 ² ) Although higher, the wrinkle state in Comparative Example 1 is better than the wrinkle state in Comparative Example 4.

In Comparative Example 1, since the intensive heating region is the entire uncoated region 50, and in Comparative Example 4, the intensive heating region is the first uncoated region 51. Heat is less than the heat transferred to the current collector 20 of the application unit 40 in Comparative Example 4, and therefore, in Comparative Example 1, the current collector 20 and the first plain fabric of the application unit 40 The difference in tensile strength between the parts 51 was larger than the difference in tensile strength between the current collector 20 and the first uncoated part 51 of the application part 40 in Comparative Example 4, so that the wrinkle state in Comparative Example 1 was 4, it can be seen that it is better than the wrinkle state.

When the cut portion 51b, which is the end of the uncoated area 50, is heated intensively as in Example 1, the heat generated from the cut portion 51b may reach the first uncoated area 51 through the tab connection portion 51a. can Since the first uncoated area 51 receives heat through heat conduction, the temperature of a portion of the first uncoated area 51 adjacent to the tab connection portion 51a is increased to the applied portion 40 of the first uncoated area 51 . It may be higher than the temperature of the adjacent part. That is, compared to Comparative Example 4, even if the tensile strength of the first uncoated portion 51 is lowered, the tensile strength of the current collector 20 of the application portion 40 may be relatively insignificantly lowered.

By increasing the temperature of the first uncoated area 51 to lower the tensile strength of the first uncoated area 51 , while maintaining the tensile strength of the current collector 20 in the application unit 40 , the first uncoated area 51 ) It may be a method of suppressing the deformation of As in Example 1, if heat is conducted from the portion opposite to the application unit 40 in the first uncoated area 51 , the wrinkle state may be good.

Since heat is conducted toward the applicator 40 from the portion opposite to the applicator 40 among the first uncoated section 51 , the tensile strength of the current collector 20 in the applicator 40 is determined by the first uncoated section ( 51), the tensile strength of the first uncoated portion 51 is greater than that of the tab connection portion 52a, and the tensile strength of the tab connection portion 52a may be greater than the tensile strength of the cut portion 52b. .

Comparing Comparative Example 2 and Comparative Example 3, the tensile strength of the first uncoated region 51 in Comparative Example 2 was 16 kgf/mm ² and the wrinkle state was slightly severe, and in Comparative Example 3, the tensile strength of the first uncoated region 51 was The strength is 17kgf/mm ² and the wrinkle condition is good. In Comparative Examples 2 and 3, even when the entire uncoated area 50 is intensively heated, in Comparative Example 2, the coated area ( 40), the difference between the tensile strength of the current collector 20 and the tensile strength of the first uncoated region 51 is the tensile strength of the current collector 20 of the application unit 40 and the tensile strength of the first uncoated region 51 in Comparative Example 3 (51) may be smaller than the difference between the tensile strengths.

As can be seen in Table 1, in the electrode 10 having an electrode density of 3.65 g/cc, when the tensile strength of the first uncoated region 51 is less than 17 kgf/mm ² , the degree of wrinkles in the uncoated region 50 . It can be seen that aggravation of That is, referring to Table 1, in Comparative Examples 1, 2, and 4, the tensile strength of the first uncoated region 51 was less than 17 kgf/mm ² , and the wrinkle state was not good.

On the other hand, in Comparative Examples 3, 1, 2, and 3, the tensile strength of the first uncoated region 51 was 17 kgf/mm ² or more and 24 kgf/mm ² or less, and the wrinkle state was good. That is, when the tensile strength of the first uncoated region 51 is 17 kgf/mm ² to 24 kgf/mm ² , it can be confirmed that the wrinkle improvement of the uncoated region 50 is effective.

From the correlation between the tensile strength and the wrinkle state shown in Table 1, when the tensile strength in the first uncoated area 51 decreases to a certain level or less, the uncoated area 50 becomes soft, and the uncoated area 50 reduces the occurrence of wrinkles. can be understood as being vulnerable.

However, as can be seen in FIG. 3 , in the case of an electrode having a low density of 3.55 g/cc, as the pressure applied to the coating part 40 decreases, the difference in elongation between the coating part 40 and the uncoated part 50 decreases. Accordingly, it can be seen that the difference in wrinkles according to the tensile strength of the first uncoated region 51 is also relatively reduced compared to the electrode 10 having a high density.

Referring to FIG. 3 , the electrode 10 having an electrode density of 3.55 g/cc may receive relatively less pressure in the rolling process than the electrode 10 having an electrode density of 3.65 g/cc. Therefore, in the electrode 10 having an electrode density of 3.55 g/cc, the difference in elongation between the coated portion 40 and the uncoated portion 50 is that of the coated portion 40 and the coated portion 40 in the electrode 10 having an electrode density of 3.65 g/cc. It may be smaller than the difference in elongation rates between the uncoated regions 50 .

For this reason, the state of wrinkles occurring in the electrode 10 having a low electrode density may be better than the state of wrinkles occurring in the electrode 10 having a high electrode density.

When the tensile strength of the first uncoated area 51 is within a certain range and the tensile strength of the first uncoated area 51 is greater than that of the tab connection part 52a, the wrinkle state of the uncoated area 50 may be good. For example, comparing Examples 1, 2, 3 and Comparative Examples 3 and Comparative Examples 1, 2, and 4, the tensile strength of the first uncoated region 51 is greater than 16.5 kgf/mm ² and 20.5 kgf/mm ² In a smaller range, the wrinkle state of the uncoated region 50 may be good. In other words, when the ratio of the tensile strength of the first uncoated region 51 to the tensile strength of the current collector 20 of the application unit 40 is 0.65 to 0.85, the wrinkle state of the uncoated region 50 may be good.

The tensile strength of the current collector 20 of the application unit 40 may not be changed by the heating process. For example, in Table 3, when the concentrated heating region is the cut portion 52b, heat is transferred to the application portion 40 through the tab connection portion 52a and the first uncoated portion 51, and thus the application portion 40 ) is insignificant, so the tensile strength of the current collector 20 of the application unit 40 may not be changed by the heating process.

In the case of seizure occurring in the ultrasonic welding process, since ultrasonic welding is performed in the tab connection part 52a, the tensile strength of the tab connection part 52a may be important. As can be seen in Table 1, in the case of Examples 1 to 3 and Comparative Examples 3 and 4, in which the tensile strength of the tab connection part 52a was 15 kgf/mm ² or more, no seizure occurred in 10 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 , seizure occurs, and when the tensile strength of the tab connection portion 52a is low, the number of seizures increases.

When the tensile strength of the tab connection part 52a is not greater than the tensile strength of the first uncoated part 51, the wrinkle state of the uncoated part 50 is not very severe, so the tensile strength of the tab connection part 52a is less than 20 kgf/mm ² A small condition may be a necessary condition for the wrinkle state of the uncoated area 50 to be good. That is, the condition that the tensile strength of the tab connection part 52a is 14.5 kgf/mm ² or more and 19.5 kgf/mm ² or less may be a necessary condition in which the number of sintering is small and the wrinkle state of the uncoated part 50 is good. In other words, if the ratio of the tensile strength of the tab connection part 52a to the tensile strength of the current collector 20 of the application part 40 is 0.55 to 0.8, the seizure may be suppressed.

For fracture occurring during the rolling process, the tensile strength of the cut portion 52b may have the greatest influence. In Table 1, in the case of Examples 1 and 2, and Comparative Example 1 in which the tensile strength of the cut portion 52b was 13 kgf/mm ² or less, no fracture occurred. This is because the fracture occurring in the rolling process starts at the cut portion 52b where the stress is concentrated, and if the tensile strength of the cut portion 52b is lowered, the fracture probability decreases.

Comparing Example 2 and Example 3, in Example 2, the tensile strength of the tab connection portion 52a was 18 kgf/mm ² and no fracture occurred, whereas in Example 3, the tensile strength of the tab connection portion 52a was 19 kgf /mm ² and fracture occurred 4 times. From this, it can be seen that the condition in which the tensile strength of the tab connection part 52a is 18.5 kgf/mm ² or less is advantageous in terms of fracture.

Taking the above results together, in the electrode 10 having an electrode density of 3.65 g/cc, the cut portion 52b is concentrated and heated, but the tensile strength of the first uncoated portion 51 is 16.5 kgf/mm ² or more 20.5 If kgf/mm ² or less and the tensile strength of the tab connection part 52a are 14.5 kgf/mm ² or more and 18.5 kgf/mm ² or less, wrinkles, seizure, and breakage of the uncoated part 50 may be improved.

In other words, in the electrode 10 having an electrode density of 3.65 g/cc, the cut portion 52b is concentrated and heated, but the first uncoated portion 51 compared to the tensile strength of the current collector 20 of the application portion 40 . When the ratio of the tensile strength of is 0.65 to 0.85, and the ratio of the tensile strength of the tab connection part 52a to the tensile strength of the current collector 20 of the application part 40 is 0.55 to 0.75, the wrinkle of the uncoated part 50, Sedimentation and fracture can be improved.

When the tensile strength of the first uncoated region 51 is greater than that of the tab connection portion 52a, and the tensile strength of the tab connection portion 52a is greater than the tensile strength of the cut portion 52b, the wrinkle of the uncoated region 50, It may be the most favorable condition for sintering and fracture.

The second length L2 that is the length of the tab connection part 52a may be greater than the first length L1 that is the length of the first uncoated part 51 . When the second length l2 is greater than the first length L2, the cut portion 52b is mainly heated to intensively heat the difference between the tensile strength of the tab connection portion 52a and the tensile strength of the first uncoated portion 51 effectively. can be

Since the cut portion 52b is removed before attachment of the electrode tab 80 (refer to FIG. 5 ), the cut portion 52b may not directly affect the performance of the battery cell. However, the cut portion 52b may have an effect on improving the fracture during the rolling process.

Hereinafter, a process of processing the electrode of the battery cell will be described. The electrode manufacturing method ( S100 ) according to an embodiment of the present invention may be referred to as a manufacturing method of an electrode for a lithium secondary battery.

1 to 4 , the electrode manufacturing method ( S100 ) according to an embodiment of the present invention may include a slurry application step ( S110 ). In this step ( S110 ), the slurry 30 may be applied to at least one surface of the current collector 20 .

The current collector 20 may be formed of a conductive metal thin plate. The current collector 20 may include a thin metal plate. For example, the thin metal plate may be formed of aluminum. The slurry 30 may be applied to one or both surfaces of the current collector 20 . Through this step ( S110 ), the electrode 10 may be divided into an applied part 40 and an uncoated part 50 .

The region of the electrode 10 may be divided into a region in which the application part 40 is positioned and a region in which the uncoated part 50 is positioned. The application unit 40 may be referred to as an “application region”. The uncoated area 50 may be referred to as a “uncoated area”. For example, the electrode 10 may be divided into an applied region 40 and an uncoated region 50 .

The electrode manufacturing method ( S100 ) according to an embodiment of the present invention may include a heating step ( S120 ). In this step ( S120 ), the heating device 70 may heat the electrode 10 . For example, in this step (S120), the heating device 70 may mainly heat the cut portion (52b). In other words, in this step ( S120 ), the heating device 70 may mainly heat the end portion of the uncoated region 50 . That is, in this step ( S120 ), the heating device 70 may mainly heat the end portion of the uncoated region 50 .

The heating step ( S120 ) may include a step ( S121 ) of forming an exposed part. In this step ( S121 ), the exposure space 78 may be formed through the shielding member 74 so that the magnetic flux generated by the induction heating unit 72 is limited to a preset range and proceeds. In this step (S121), the magnetic field (magnetic field) formed by the induction heating unit 72 may be distributed limited to a preset range.

The heating step ( S120 ) may include a heating step ( S122 ) of the uncoated area. In this step ( S122 ), some of the magnetic flux generated by the induction heating unit 72 may be shielded by the shielding member 74 , and the other portion may pass through the exposure space 78 to enter the uncoated area 50 . . For example, in this step ( S122 ), the induction heating unit 72 may mainly heat the cut part 52b that is the end of the uncoated part 50 .

In the heating step S120 , the induction heating unit 72 may heat the uncoated area 50 so that a portion of the uncoated area 50 has a set tensile strength. For example, the cut portion 52b may be heated so that the tab connection portion 52a has a second tensile strength that is a set tensile strength. For example, the cut portion 52b may be heated so that the first uncoated portion 51 has a first tensile strength that is a set tensile strength. For example, the cut portion 52b may be heated so that the first uncoated portion 51 has a first tensile strength and the tab connection portion 52a has a second tensile strength.

The electrode manufacturing method ( S100 ) according to an embodiment of the present invention may include a rolling step ( S130 ). The rolling step ( S130 ) may be a step of compressing the electrode 10 so that the adhesive force between the slurry 30 and the current collector 20 is increased. Through the rolling step (S130), the electrode 10 may be compressed to a set thickness.

The electrode manufacturing method ( S100 ) according to an embodiment of the present invention may include a cutting step ( S135 ) of cutting the cutting part ( 52b ). In this step (S135), the cut portion (52b) may be separated from the tab connection portion (52a).

The electrode manufacturing method ( S100 ) according to an embodiment of the present invention may include a tab connection step ( S140 ). The tap connection step ( S140 ) may be performed after the rolling step ( S130 ). In the tab connection step ( S140 ), the electrode tab 80 (refer to FIG. 5 ) may be connected to the uncoated region 50 . In the tab connection step S140 , the electrode tab 80 (refer to FIG. 5 ) may be connected to the uncoated region 50 . In this step ( S140 ), the tab connection part 52a may be connected to the electrode tab 80 (refer to FIG. 5 ).

In FIG. 5 , each region of the uncoated region 50 is divided by a dotted line for convenience of description, but each region of the uncoated region 50 may be continuously connected without a partitioned configuration.

Referring to FIGS. 5A and 5B , a plurality of second uncoated regions 52 may be stacked and welded. Referring to FIG. 5C , the cut portion 52b may be separated from the tab connection portion 52a and removed. Referring to FIG. 5D , in a state in which the cut portion 52b is removed from the second uncoated region 52 , the tab connection portion 52a may be connected to or coupled to the electrode tab 80 through welding. Accordingly, the electrode 10 and the electrode tab 80 may be connected.

In the above, specific embodiments have been shown and described. However, it is not limited only to the above-described embodiment, and those of ordinary skill in the art to which the invention pertains can make various changes without departing from the spirit of the invention described in the claims below. .

10: electrode 20: current collector
30: slurry 40: application part
50: uncoated region 51: first uncoated region
52: second uncoated part 52a: tap connection part
52b: cut

Claims (15)

An electrode for a lithium secondary battery comprising an electric collector formed of a metal and a slurry applied to a part of the current collector,
an applicator comprising a portion of the current collector to which the slurry is applied and the slurry; And
Including a non-coated portion including the remaining portion of the current collector to which the slurry is not applied,
The uncoated part,
a first uncoated part extending from the application part; And
and a second uncoated portion extending from the first uncoated portion and having a tab connection portion coupled to the electrode tab,
The tensile strength of the first uncoated portion is greater than the tensile strength of the tab connection portion,
The ratio of the tensile strength of the first uncoated portion to the tensile strength of the portion to which the slurry is applied in the current collector is 0.65 to 0.85,
An electrode for a lithium secondary battery. According to claim 1,
The ratio of the tensile strength of the tab connection portion to the tensile strength of the portion to which the slurry is applied in the current collector is 0.55 to 0.75,
An electrode for a lithium secondary battery. According to claim 1,
The electrode density of the electrode for the lithium secondary battery is 3.6 to 3.8 g/cc,
The tensile strength of the first uncoated part is 16.5 to 20.5 kgf / mm ² of,
An electrode for a lithium secondary battery. According to claim 1,
The electrode density of the electrode for the lithium secondary battery is 3.6 to 3.8 g/cc,
The tensile strength of the tab connection portion is 14.5 to 18.5 kgf / mm ² of,
An electrode for a lithium secondary battery. According to claim 1,
A length of the first uncoated portion in a direction in which the first uncoated portion extends is,
In a direction in which the second uncoated part is extended, the length of the tab connection part is smaller than that of the tab connection part;
An electrode for a lithium secondary battery. A method for manufacturing an electrode for a lithium secondary battery comprising a current collector formed of a metal and a slurry applied to a part of the current collector,
A slurry application step (S110) of applying the slurry to at least one surface of the current collector to divide the electrode for a lithium secondary battery into an application region to which the slurry is applied and an uncoated region to which the slurry is not applied;
The uncoated region includes a first uncoated region adjacent to the application region, a tab connection portion connected to the first uncoated region and coupled to an electrode tab, and a cut portion extending from the tab connection portion, and heating the cut portion ( S120); And
Including a rolling step (S130) of rolling the heated electrode,
The ratio of the tensile strength of the first uncoated region to the tensile strength of the current collector in the application region is 0.65 to 0.85,
A method of manufacturing an electrode for a lithium secondary battery (S100). 7. The method of claim 6,
In the heating step (S120),
When the induction heating unit generates a high-frequency current, a magnetic field is formed to heat the uncoated region by induction heating,
A method of manufacturing an electrode for a lithium secondary battery (S100). 8. The method of claim 7,
The heating step (S120) is,
A shielding member is disposed between the induction heating unit and the electrode to form a magnetic field in a predetermined range from the induction heating unit to form a magnetic field exposure portion (S121); And
A method of manufacturing an electrode for a lithium secondary battery (S100) comprising heating (S122) an end of the uncoated region through the magnetic field exposure part. 9. The method of claim 8,
In the uncoated area heating step (S122),
The magnetic field formed by the induction heating unit forming a high-frequency current, heating the cut portion through the magnetic field exposure portion,
A method of manufacturing an electrode for a lithium secondary battery (S100). 7. The method of claim 6,
Further comprising the step of cutting the cut portion of the rolled electrode (S135),
A method of manufacturing an electrode for a lithium secondary battery (S100). 11. The method of claim 10,
After the cutting step (S135) further comprising the step (S140) of connecting the electrode tab to the tab connection portion,
A method of manufacturing an electrode for a lithium secondary battery (S100). 7. The method of claim 6,
After the heating step,
The tensile strength of the first uncoated portion is greater than the tensile strength of the tab connection portion,
A method of manufacturing an electrode for a lithium secondary battery (S100). 7. The method of claim 6,
The electrode density of the electrode for the lithium secondary battery is 3.6 to 3.8 g/cc,
The tensile strength of the first uncoated part is 16.5 to 20.5 kgf / mm ² of,
A method of manufacturing an electrode for a lithium secondary battery (S100). 7. The method of claim 6,
The ratio of the tensile strength of the tab connection part to the tensile strength of the current collector in the application area is 0.55 to 0.75,
A method of manufacturing an electrode for a lithium secondary battery (S100). 15. The method of claim 14,
The electrode density of the electrode for the lithium secondary battery is 3.6 to 3.8 g/cc,
The tensile strength of the tab connection portion is 14.5 to 18.5 kgf / mm ² of,
A method of manufacturing an electrode for a lithium secondary battery (S100).

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