Patent Description:
The present disclosure relates to an electrode for lithium secondary battery and a method of 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 mobile phones, notebook computers, and camcorders, or electric vehicles. In particular, a lithium secondary battery has an operating voltage of about <NUM>. 6V, has about three times the capacity of a nickel-cadmium battery or a nickel-hydrogen battery which is often used as a power source for electronic equipment, and has a high energy density per unit weight. Therefore, the use of the lithium secondary battery is explosively increasing.

In order to implement a battery cell with a high capacity and a high density of the battery during a manufacturing process of the secondary battery, a rolling process is important in an electrode process. The rolling process refers to a process in which an electrode passes between a pair of rollers in an electrode process and is pressed to a design thickness of a target battery cell.

However, in the rolling process, wrinkles and fractures due to partial deformation of the electrode increase, which greatly affects quality and productivity of the products, and thus improvement is required. <CIT> relates to the technical field of manufacturing electrode plates of secondary batteries,.

One aspect of the present disclosure provides an electrode for lithium secondary battery with improved structure and a method of manufacturing the same.

Another aspect of the present disclosure provides an electrode for lithium secondary battery with improved quality and a method of manufacturing the same.

In order to achieve the above-described and other objects, in one aspect of the present disclosure, there is provided an electrode for lithium secondary battery comprised of an electric collector formed of a metal and a slurry coated on a portion of the electric collector, the electrode for lithium secondary battery comprising a coated part including the portion of the electric collector, on which the slurry is coated, and the slurry; and an uncoated part including a remaining portion of the electric collector on which the slurry is not coated, wherein the uncoated part includes a first uncoated part extended from the coated part; and a second uncoated part extended from the first uncoated part, the second uncoated part including 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 <NUM> to <NUM>.

In another aspect of the present disclosure, there is provided a method (S100) of manufacturing an electrode for lithium secondary battery comprised of an electric collector formed of a metal and a slurry coated on a portion of the electric collector, the method (S100) comprising a slurry coating step (S110) of coating the slurry on at least one surface of the electric collector and dividing the electrode for lithium secondary battery into a coated area on which the slurry is coated and an uncoated area on which the slurry is not coated, wherein the uncoated area includes a first uncoated part adjacent to the coated area, a tab connection portion connected to the first uncoated part and coupled to an electrode tab, and a cut portion extended from the tab connection portion; a heating step (S120) of heating the cut portion; and a rolling step (S130) of rolling the heated electrode, wherein a ratio of a tensile strength of the first uncoated part to a tensile strength of the electric collector of the coated area is <NUM> to <NUM>. The scope for which protection is sought in defined in claim <NUM>, directed to an electrode for a lithium secondary battery and claim <NUM>, a method of manufacturing an electrode for a lithium secondary battery.

According to one aspect of the present disclosure, the present disclosure can minimize generation of electrode wrinkles in a battery cell.

According to one aspect of the present disclosure, the present disclosure can prevent a sticking problem in a process of connecting an electrode tab to an electrode of a battery cell.

According to one aspect of the present disclosure, the present disclosure can minimize a fracture of an electrode of a battery cell in a rolling process.

According to one aspect of the present disclosure, the present disclosure can prevent an electrode failure of a battery cell.

The accompanying drawings, which are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of the disclosure, illustrate embodiments of the disclosure and together with the description serve to explain the principle of the disclosure.

The detailed description and specific examples such as embodiments of the present disclosure are given merely by way of example, since various changes and modifications within the 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 throughout the drawings to refer to the same or like parts or components.

Terms used in the present disclosure are used to explain embodiments and are not intended to limit and/or restrict the present disclosure. A singular expression can include a plural expression as long as it does not have an apparently different meaning in context. In the present disclosure, terms "include" and "have" should be understood to be intended to designate that illustrated features, numbers, steps, operations, components, parts or combinations thereof are present and not to preclude the existence of one or more different features, numbers, steps, operations, components, parts or combinations thereof, or the possibility of the addition thereof.

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 for the purpose of distinguishing 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 referred to as a first component in the same manner. The term "and/or" includes a combination of items related to plurality or some of items related to plurality.

In addition, term such as "part", "device", "block", "member", and "module" may refer to a unit processing at least one function or operation. For example, the terms may mean at least one hardware such as field-programmable gate array (FPGA)/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 are used to help easily understand various technical features, and it should be understood that embodiments presented herein are not limited by the accompanying drawings.

Referring to <FIG>, an electrode <NUM> according to an embodiment of the present disclosure may be included in a battery cell. The electrode <NUM> may be referred to as an "electrode for lithium secondary battery". The electrode <NUM> may be a positive electrode and/or a negative electrode.

The electrode <NUM> may include an electric collector <NUM>. The electric collector <NUM> may be referred to as an "electrode electric collector". The electric collector <NUM> may include a metal. For example, the electric collector <NUM> may be a metal foil. The electric collector <NUM> may be formed to extend in one direction. For example, the electric collector <NUM> may be formed to extend in a longitudinal direction.

The electrode <NUM> may include a slurry <NUM>. The slurry <NUM> may be referred to as an "electrode material". The slurry <NUM> may be coated on a portion of the electric collector <NUM>.

The electrode <NUM> may be divided or partitioned into an area of the electric collector <NUM> on which the slurry <NUM> is coated, and a remaining area. For example, the electrode <NUM> may include a coated part <NUM> and an uncoated part <NUM>.

The coated part <NUM> may refer to a portion of the electrode <NUM> in which the slurry <NUM> is coated on the electric collector <NUM>. For example, the coated part <NUM> may include the slurry <NUM>. For example, the coated part <NUM> may include a portion of the electric collector <NUM> on which the slurry <NUM> is coated.

The uncoated part <NUM> may include a portion of the electric collector <NUM> on which the slurry <NUM> is not coated. That is, the uncoated area <NUM> may indicate a portion of the electrode <NUM> excluding the coated part <NUM>. The coated part <NUM> and the uncoated part <NUM> may be disposed along the length direction of the electric collector <NUM>.

A rolling process is important to implement a battery cell with high capacity and high density 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 <NUM>. The rolling process refers to a process of pressing the electrode in a thickness direction by passing the electrode <NUM> between a pair of rolling rollers.

A thickness of the coated part <NUM> may be greater than a thickness of the uncoated part <NUM> due to the slurry <NUM>. Therefore, in the process of rolling the electrode <NUM>, a pressure may be applied to the coated part <NUM>, and the pressure may not be applied to the uncoated part <NUM>. Hence, the electric collector <NUM> of the coated part <NUM> may be stretched by the pressure, whereas the electric collector <NUM> of the uncoated part <NUM> may not be stretched. The electric collector <NUM> of the coated part <NUM> may indicate a portion of the electric collector <NUM> on which the slurry <NUM> is coated.

For this reason, the electric collector <NUM> may be deformed at a boundary between the coated part <NUM> and the uncoated part <NUM>. The deformation of the electric collector <NUM> may lead to fracture of the electric collector <NUM>. In general, as the electrode density increases and/or a thickness of the electric collector <NUM> decreases, the probability that the electric collector <NUM> is deformed or the probability that the electric collector <NUM> is fractured may increase. The electrode density may indicate a density of the slurry <NUM>.

Due to this, a yield and an operating rate in the rolling process are reduced. In order to solve this, the present disclosure can reduce the tensile strength by heating the uncoated area <NUM> prior to the rolling process, and thus can suppress the deformation and/or fracture of the electric collector <NUM> at the boundary between the coated part <NUM> and the uncoated part <NUM>.

However, if a temperature of the uncoated part <NUM> is raised too high, there may occur a sticking in which the uncoated part <NUM> sticks to an ultrasonic heating mold in a process of bonding the uncoated part <NUM> to an electrode tab through an ultrasonic welding.

When the temperature of the uncoated part <NUM> is relatively raised to a low level, in the process of bonding the uncoated part <NUM> to the electrode tab through the ultrasonic welding, the probability of sticking may decrease, but the probability that the electric collector <NUM> is deformed and/or fractured in the rolling process may increase.

By optimizing output power and configuration of a heating device <NUM> (see <FIG>) for heating the uncoated part <NUM>, the present disclosure can simultaneously solve the fracture of the electrode <NUM> in the rolling process and the sticking in the connecting process of the electrode tab.

The electrode density of the electrode <NUM> may be <NUM>/cc to <NUM>/cc. The electrode density is a mass density of the slurry <NUM>, and may indicate a mass density of the slurry <NUM> that goes through the rolling process.

The slurry <NUM> 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 for used for a negative electrode. The active material may indicate at least one of the cathode active material and the anode active material.

The slurry <NUM> may indicate at least one of a cathode slurry and an anode slurry. The cathode slurry may include the cathode active material, and the anode slurry may include the anode active material.

The electric collector <NUM> may indicate at least one of a cathode electric collector and an anode electric collector. The cathode electric collector may be an electric collector used for the positive electrode. The anode electric collector may be an electric collector for used for the negative electrode. The electric collector <NUM> may be formed of a metal foil.

The uncoated part <NUM> may include a first uncoated part <NUM> and a second uncoated part <NUM>. The first uncoated part <NUM> may be connected to the coated part <NUM>. The second uncoated part <NUM> may be spaced apart from the coated part <NUM>. The first uncoated part <NUM> may be disposed between the coated part <NUM> and the second uncoated part <NUM>. The first uncoated part <NUM> may connect the coated part <NUM> and the second uncoated part <NUM>.

The first uncoated part <NUM> may be formed to extend from the coated part <NUM>. The first uncoated part <NUM> may be configured to have a set tensile strength. For example, the first uncoated part <NUM> may have the set tensile strength by applying heat to the second uncoated part <NUM>. The tensile strength of the first uncoated part <NUM> may be 17kgf/mm<NUM> to 24kgf/mm<NUM>. For example, the tensile strength of the first uncoated part <NUM> may be <NUM> kgf/mm<NUM>.

The second uncoated part <NUM> may be formed to extend from the first uncoated part <NUM>. The second uncoated part <NUM> may be coupled to an electrode tab <NUM> (see <FIG>). The second uncoated part <NUM> may be heat treated so that the first uncoated part <NUM> has the set tensile strength. Through a heat treatment by the heating process, the tensile strength of the uncoated part <NUM> may sequentially decrease as it goes from the first uncoated part <NUM> to the second uncoated part <NUM>.

The second uncoated part <NUM> may include a tab connection portion 52a and a cut portion 52b. The tab connection portion 52a may be connected to the first uncoated part <NUM> and may be coupled to the electrode tab <NUM> (see <FIG>). The tab connection portion 52a may be configured to have a set tensile strength. The set tensile strength of the first uncoated part <NUM> 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 the second tensile strength through the heat treatment of the second uncoated part <NUM>. The tensile strength of the uncoated part <NUM> may decrease as it goes from the first uncoated part <NUM> toward an end portion of the second uncoated part <NUM>. The first uncoated part <NUM> may be configured to have the set tensile strength.

That is, the tensile strength of the first uncoated part <NUM> may be greater than the tensile strength of the tab connection portion 52a, and the tensile strength of the tab connection portion 52a may be greater than a tensile strength 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>). The tab connection portion 52a may be referred to as a "second uncoated area". The cut portion 52b may be referred to as a "third uncoated area". The first uncoated part <NUM> may be referred to as a "first uncoated area".

<FIG> illustrates an electrode and a heating device according to an embodiment of the present disclosure. <FIG> illustrates that the uncoated part <NUM> is partitioned into a plurality of areas for convenience of description, but the scope of the present disclosure regarding the uncoated part <NUM> is not limited to <FIG>. For example, the respective areas of the uncoated part <NUM> may be consecutively connected without being partitioned.

Referring to <FIG>, the heating device <NUM> may heat the electrode <NUM>. The heating device <NUM> may heat the uncoated part <NUM> before the electrode <NUM> is rolled. The heating device <NUM> may heat the uncoated part <NUM> by induction heating annealing (IHA). The induction heating may refer to a method of heating a metal object using electromagnetic induction. The heating device <NUM> may control the temperature of the uncoated part <NUM> by adjusting the output power.

The heating device <NUM> may be controlledly interlocked with a device for rolling the electrode <NUM> (hereinafter, referred to as a "rolling device"). For example, the output power of the heating device <NUM> may depend on the processing speed of the rolling device. Further, the output power of the heating device <NUM> may vary depending on the material and the type of the electrode <NUM>.

The heating device <NUM> may include an induction heating unit <NUM> and a shielding member <NUM>.

The induction heating unit <NUM> may allow an induced current to flow through the electrode <NUM> using an electromagnetic induction action. When an induced current flows in the electrode <NUM>, heat may be generated in the electrode <NUM>. The induction heating unit <NUM> may include a coil. The induction heating unit <NUM> may form a high frequency current.

At least a portion of the shielding member <NUM> may be disposed between the induction heating unit <NUM> and the electrode <NUM>. For example, at least a portion of the shielding member <NUM> may be disposed between the induction heating unit <NUM> and the coated part <NUM>. For example, at least a portion of the shielding member <NUM> may be disposed between the induction heating unit <NUM> and the first uncoated part <NUM>. For example, at least a portion of the shield member <NUM> may be disposed between the induction heating unit <NUM> and the tab connection portion 52a.

The shielding member <NUM> may have an effect of shielding a magnetic flux generated in the induction heating unit <NUM>. For example, at least a portion of the magnetic flux (or magnetic field) incident on the shielding member <NUM> may no longer travel by the shielding member <NUM>. For example, at least a portion of the magnetic flux that is generated in the induction heating unit <NUM> and is directed toward the coated part <NUM> may be shielded by the shielding member <NUM>. For example, at least a portion of the magnetic flux that is generated in the induction heating unit <NUM> and is directed toward the first uncoated part <NUM> may be shielded by the shielding member <NUM>. For example, at least a portion of the magnetic flux that is generated in the induction heating unit <NUM> and is directed toward the tab connection portion 52a may be shielded by the shield member <NUM>.

A predetermined portion of the electrode <NUM> may be heated by the induction heating unit <NUM>. For example, the cut portion 52b may be heated by an induction heating unit <NUM>. The induction heating unit <NUM> may mainly heat the cut portion 52b. A relative permeability of the shielding member <NUM> may be equal to or greater than <NUM>. For example, the shielding member <NUM> may be formed of a material including a ferromagnetic material.

The shielding member <NUM> may include an exposed portion <NUM>. The exposed portion <NUM> may form an exposure space <NUM>. The induction heating unit <NUM> may be exposed to the uncoated part <NUM> through the exposure space <NUM>. For example, the exposure space <NUM> may be positioned between the cut portion 52b and the induction heating unit <NUM>. The exposed portion <NUM> may be referred to as a "magnetic field exposed portion".

The magnetic flux generated by the induction heating unit <NUM> may pass through the exposed portion <NUM> and may be incident on the electric collector <NUM>. For example, the magnetic flux passing through the exposure space <NUM> may be incident on at least a portion of the uncoated part <NUM>. Through this configuration, the heating device <NUM> can mainly heat a specific area of the electrode <NUM>.

For example, the heating device <NUM> may be configured to mainly heat the second uncoated part <NUM>. For example, heat generated in the cut portion 52b may be transferred to the first uncoated part <NUM>. For example, the heating device <NUM> may be configured to mainly heat the cut portion 52b.

The induction heating unit <NUM> may face the cut portion 52b through the exposure space <NUM>. For another example, the induction heating unit <NUM> may face a space outside the cut portion 52b through the exposure space <NUM>. The heating device <NUM> may locally heat the cut portion 52b through induction heating. Heat generated in the cut portion 52b may be heat-conducted to the first uncoated part <NUM>.

The following is a content of an experiment to know changes in the tensile strength, etc. of the electrode <NUM> according to the heating process. The content is described with reference to <FIG> and Table <NUM>. <FIG> is a photograph illustrating the electrode <NUM> depending on the electrode density and the tensile strength after going through the rolling process. The tensile strength illustrated in <FIG> may indicate the tensile strength of the first uncoated part <NUM>.

Referring to <FIG>, a length of the first uncoated part <NUM> may be a first length L1, a length of the tab connection portion 52a may be a second length L2, and a length of the cut portion 52b may be a third length L3. A length of the uncoated part <NUM> may be measured based on a direction in which the uncoated part <NUM> extends from the coated part <NUM>.

For example, a total length of the uncoated part <NUM> may be <NUM>. The first length L1 may be <NUM>. A length of the second uncoated part <NUM> is a sum of the second length L2 and the third length L3, and may be <NUM>. For example, the second length L2 may be <NUM>, and the third length L3 may be <NUM>. The first length L1, the second length L2, and the third length L3 are not limited to the above examples, and can be changed within a range without departing from the purpose of the present disclosure.

Table <NUM> shows, when an intensive heating area and a maximum heating temperature of the uncoated part <NUM> change, the tensile strength and the wrinkle state of the uncoated part <NUM> after the rolling process, the number of stickings generated in the ultrasonic welding process (per <NUM> ultrasonic welding operations), and the number of fractures of the electrode <NUM> after the rolling process (in the process of transporting the electrode <NUM>). In Table <NUM>, the tensile strength of the uncoated part <NUM> before heating the uncoated part <NUM> is <NUM> kgf/mm<NUM>. In Table <NUM>, the electrode density of the electrode <NUM> after the rolling process is <NUM>/cc. In Table <NUM>, the tensile strength of the uncoated part <NUM> before heating may be the same as a tensile strength of the electric collector <NUM> of the coated part <NUM> before heating.

Referring to <FIG> and Table <NUM>, even if only a specific area of the uncoated part <NUM> is selectively heated, the tensile strengths of all the areas of the uncoated part <NUM> may change. This may be due to the thermal conductivity of the uncoated part <NUM>.

The wrinkle of the uncoated part <NUM> may occur at the first uncoated part <NUM> adjacent to the boundary between the coated part <NUM> and the uncoated part <NUM> due to a difference between an elongation of the coated part <NUM>, to which the pressure is directly applied, and an elongation of the uncoated part <NUM> to which the pressure is not applied. In this instance, the tensile strength of the first uncoated part <NUM> may affect the generation of wrinkle.

When comparing an embodiment <NUM> with a comparative example <NUM>, in the embodiment <NUM>, the cut portion 52b, which is an end portion of the uncoated part <NUM>, was intensively heated, and a tensile strength of the first uncoated area <NUM> was <NUM> kgf/mm<NUM>, and in the comparative example <NUM>, the first uncoated part <NUM> was intensively heated, and a tensile strength of the first uncoated part <NUM> was <NUM> kgf/mm<NUM>. Although the tensile strength of the first uncoated part <NUM> in the comparative example <NUM> was significantly less than the tensile strength of the first uncoated part <NUM> in the embodiment <NUM>, a wrinkle state in the embodiment <NUM> was better than a wrinkle state in the comparative example <NUM>.

As in the comparative example <NUM>, when the first uncoated part <NUM> is intensively heated, heat generated in the first uncoated part <NUM> is transferred to the electric collector <NUM> of the coated part <NUM>, and hence a difference between the tensile strength of the electric collector <NUM> at the coated part <NUM> and the tensile strength of the first uncoated part <NUM> may not be large. If the difference between the tensile strength of the electric collector <NUM> at the coated part <NUM> and the tensile strength of the first uncoated part <NUM> is not large, the first uncoated area <NUM> may be more likely to be deformed in the rolling process. When comparing the comparative example <NUM> with a comparative example <NUM>, although a tensile strength (<NUM> kgf/mm<NUM>) of the first uncoated part <NUM> in the comparative example <NUM> was greater than the tensile strength (<NUM> kgf/mm<NUM>) of the first uncoated part <NUM> in the comparative example <NUM>, a wrinkle state in the comparative example <NUM> was better than the wrinkle state in the comparative example <NUM>.

Since the intensive heating area in the comparative example <NUM> was the entire uncoated part <NUM> and the intensive heating area in the comparative example <NUM> was the first uncoated part <NUM>, the heat transferred to the electric collector <NUM> of the coated part <NUM> in the comparative example <NUM> was less than the heat transferred to the electric collector <NUM> of the coated part <NUM> in the comparative example <NUM>. Thus, a difference in the tensile strength between the electric collector <NUM> of the coated part <NUM> and the first uncoated part <NUM> in the comparative example <NUM> was greater than a difference in the tensile strength between the electric collector <NUM> of the coated part <NUM> and the first uncoated part <NUM> in the comparative example <NUM>. As a result, it could be seen that the wrinkle state in the comparative example <NUM> was better than the wrinkle state in the comparative example <NUM>.

As in the embodiment <NUM>, when the cut portion 52b, which is the end portion of the uncoated part <NUM>, was intensively heated, heat generated in the cut portion 52b may reach the first uncoated part <NUM> via the tab connection portion 52a. Since heat is provided to the first uncoated part <NUM> through heat conduction, a temperature of a portion of the first uncoated part <NUM> adjacent to the tab connection portion 52a may be higher than a temperature of a portion of the first uncoated part <NUM> adjacent to the coated part <NUM>. That is, compared to the comparative example <NUM>, even if the tensile strength of the first uncoated part <NUM> becomes lower, the tensile strength of the electric collector <NUM> of the coated part <NUM> may be relatively slightly reduced.

A method of preventing the deformation of the first uncoated part <NUM> may be to maintain the tensile strength of the electric collector <NUM> at the coated part <NUM> while reducing the tensile strength of the first uncoated part <NUM> by increasing the temperature of the first uncoated part <NUM>. As in the embodiment <NUM>, if heat is conducted from a portion opposite to the coated part <NUM> in the first uncoated part <NUM>, the wrinkle state may be good.

Since heat is conducted from a portion opposite to the coated part <NUM> in the first uncoated part <NUM> toward the coated part <NUM>, the tensile strength of the electric collector <NUM> at the coated part <NUM> may be greater than the tensile strength of the first uncoated part <NUM>, the tensile strength of the first uncoated part <NUM> may be greater than the tensile strength 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.

When comparing a comparative example <NUM> with a comparative example <NUM>, in the comparative example <NUM>, a tensile strength of the first uncoated part <NUM> was <NUM> kgf/mm<NUM>, and a wrinkle state was slightly severe, and in the comparative example <NUM>, a tensile strength of the first uncoated part <NUM> was <NUM> kgf/mm<NUM>, and a wrinkle state was good. Even if the entire uncoated part <NUM> is intensively heated in the comparative examples <NUM> and <NUM>, a difference between the tensile strength of the electric collector <NUM> of the coated part <NUM> and the tensile strength of the first uncoated part <NUM> in the comparative example <NUM> may be less than a difference between the tensile strength of the electric collector <NUM> of the coated part <NUM> and the tensile strength of the first uncoated part <NUM> in the comparative example <NUM> by heat transferred to the electric collector <NUM> of the coated part <NUM> at the first uncoated part <NUM>.

It can be seen from Table <NUM> that in the electrode <NUM> with the electrode density of <NUM>/cc, a degree of wrinkle generation of the uncoated part <NUM> is sever when the tensile strength of the first uncoated part <NUM> is less than <NUM> kgf/mm<NUM>. That is, referring to <FIG>, in the comparative examples1, <NUM> and <NUM>, the tensile strength of the first uncoated part <NUM> was less than <NUM> kgf/mm<NUM>, and the wrinkle state was not good.

On the other hand, in the comparative example <NUM> and the embodiments <NUM>, <NUM>, and <NUM>, the tensile strength of the first uncoated part <NUM> is between <NUM> kgf/mm<NUM> and <NUM> kgf/mm<NUM>, and the wrinkle state is good. That is, when the tensile strength of the first uncoated part <NUM> is between <NUM> kgf/mm<NUM> and <NUM> kgf/mm<NUM>, the wrinkle of the first uncoated part <NUM> can be improved.

From a correlation between the tensile strength and the wrinkle state shown in Table <NUM>, it may be understood that when the tensile strength of the first uncoated part <NUM> is reduced to a predetermined level or less, the uncoated part <NUM> is softened and is vulnerable to the wrinkle generation.

However, as can be seen from <FIG>, in the electrode with the lower electrode density of <NUM>/cc, as the pressure applied to the coated part <NUM> decreases, a difference in the elongation between the coated part <NUM> and the uncoated part <NUM> decreases. Hence, the wrinkle difference depending on the tensile strength of the first uncoated part <NUM> can be relatively reduced compared to the electrode with the higher electrode density.

Referring to <FIG>, the electrode <NUM> with the electrode density of <NUM>/cc in the rolling process may be provided with the relatively less pressure than the electrode <NUM> with the electrode density of <NUM>/cc. Therefore, a difference in the elongation between the coated part <NUM> and the uncoated part <NUM> in the electrode <NUM> with the electrode density of <NUM>/cc may be less than a difference in the elongation between the coated part <NUM> and the uncoated part <NUM> in the electrode <NUM> with the electrode density of <NUM>/cc.

For this reason, the wrinkle state generated in the electrode <NUM> with the lower electrode density may be better than the wrinkle state generated in the electrode <NUM> with the higher electrode density.

If the tensile strength of the first uncoated part <NUM> is within a predetermined range and is greater than the tensile strength of the tab connection portion 52a, the wrinkle state of the uncoated part <NUM> may be good. For example, when comparing the embodiments <NUM>, <NUM> and <NUM> and the comparative example <NUM> with the comparative examples <NUM>, <NUM> and <NUM>, the wrinkle state of the uncoated part <NUM> may be good when the tensile strength of the first uncoated part <NUM> is within a range greater than <NUM> kgf/mm<NUM> and less than <NUM> kgf/mm<NUM>. In other words, when a ratio of the tensile strength of the first uncoated part <NUM> to the tensile strength of the electric collector <NUM> of the coated part <NUM> is <NUM> to <NUM>, the wrinkle state of the uncoated part <NUM> may be good.

The tensile strength of the electric collector <NUM> of the coated part <NUM> may not change by the heating process. For example, in Table <NUM>, when the intensive heating area is the cut portion 52b, the heat transferred to the coated part <NUM> may be insignificant since heat is transferred to the coated part <NUM> via the tab connection portion 52a and the first uncoated part <NUM>. Therefore, the tensile strength of the electric collector <NUM> of the coated part <NUM> may not change by the heating process.

In the sticking generated in the ultrasonic welding process, the ultrasonic welding is performed on the tab connection portion 52a, and thus the tensile strength of the tab connection portion 52a may be important. As can be seen from Table <NUM>, in the embodiments <NUM> to <NUM> and the comparative examples <NUM> and <NUM> in which the tensile strength of the tab connection portion 52a is <NUM> kgf/mm<NUM> or more, no sticking occurred in ten tests. On the other hand, in the comparative examples <NUM> and <NUM> in which the tensile strength of the tab connection portion 52a is less than <NUM> kgf/mm<NUM>, the sticking occurred. As the tensile strength of the tab connection portion 52a decreases, the number of stickings may increase.

When the tensile strength of the tab connection portion 52a is not greater than the tensile strength of the first uncoated part <NUM>, the wrinkle state of the uncoated part <NUM> is not very severe. Therefore, a condition in which the tensile strength of the tab connection portion 52a is less than <NUM> kgf/mm<NUM> may be a necessary condition for the wrinkle state of the uncoated part <NUM> to be good. That is, a condition in which the tensile strength of the tab connection portion 52a is between <NUM> kgf/mm<NUM> and <NUM> kgf/mm<NUM> may be a necessary condition for the uncoated part <NUM> in which the number of stickings decreases and the wrinkle state is good. In other words, when a ratio of the tensile strength of the tab connection portion 52a to the tensile strength of the electric collector <NUM> of the coated part <NUM> is <NUM> to <NUM>, the sticking can be suppressed.

The fracture generated in the rolling process may be most affected by the tensile strength of the cut portion 52b. In Table <NUM>, in the embodiments <NUM> and <NUM> and the comparative example <NUM> in which the tensile strength of the cut portion 52b is <NUM> kgf/mm<NUM> or less, no fracture occurred. This is because the fracture occurring in the rolling process starts at the cut portion 52b, on which a stress is concentrated, and the fracture probability decreases if the tensile strength of the cut portion 52b is reduced.

When comparing the embodiment <NUM> with the embodiment <NUM>, in the embodiment <NUM>, the tensile strength of the tab connection portion 52a was <NUM> kgf/mm<NUM> and no fracture occurred, whereas in the embodiment <NUM>, the tensile strength of the tab connection portion 52a was <NUM> kgf/mm<NUM> and the fracture occurred four times. Hence, it can be seen that a condition in which the tensile strength of the tab connection portion 52a is equal to or less than <NUM> kgf/mm<NUM> is advantageous in terms of fracture.

Combining the above results, in the electrode <NUM> with the electrode density of <NUM>/cc, when the tensile strength of the first uncoated part <NUM> is between <NUM> kgf/mm<NUM> and <NUM> kgf/mm<NUM>, and the tensile strength of the tab connection portion 52a is between <NUM> kgf/mm<NUM> and <NUM> kgf/mm<NUM> while the cut portion 52b is intensively heated, the wrinkle state, the sticking, and the fracture of the uncoated part <NUM> can be improved.

In other words, in the electrode <NUM> with the electrode density of <NUM>/cc, when a ratio of the tensile strength of the first uncoated part <NUM> to the tensile strength of the electric collector <NUM> of the coated part <NUM> is <NUM> to <NUM>, and a ratio of the tensile strength of the tab connection portion 52a to the tensile strength of the electric collector <NUM> of the coated part <NUM> is <NUM> to <NUM> while the cut portion 52b is intensively heated, the wrinkle state, the sticking, and the fracture of the uncoated part <NUM> can be improved.

Conditions in which the tensile strength of the first uncoated part <NUM> is greater than the tensile strength 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 may be the most advantageous conditions for the wrinkle state, the sticking, and the fracture of the uncoated part <NUM>.

The second length L2 which is the length of the tab connection portion 52a may be greater than the first length L1 which is the length of the first uncoated part <NUM>. When the second length L2 is greater than the first length L2, the cut portion 52b is mainly intensively heated, and thus a difference between the tensile strength of the tab connection portion 52a and the tensile strength of the first uncoated part <NUM> can be effectively formed.

Since the cut portion 52b is removed before attachment of the electrode tab <NUM> (see <FIG>), the cut portion 52b may not directly affect a performance of the battery cell. However, the cut portion 52b may have an effect on improving the fracture in the rolling process.

A method of processing an electrode of the battery cell is described below. A method S100 of manufacturing an electrode according to an embodiment of the present disclosure may be referred to as a method of manufacturing an electrode for lithium secondary battery.

Referring to <FIG>, a method S100 of manufacturing an electrode according to an embodiment of the present disclosure may comprise a slurry coating step S110. In the step S110, a slurry <NUM> may be coated on at least one surface of an electric collector <NUM>.

The electric collector <NUM> may be formed of a conductive metal thin plate. The electric collector <NUM> may include a thin metal plate. For example, the thin metal plate may be formed of aluminum. The slurry <NUM> may be coated on one surface or both surfaces of the electric collector <NUM>. Through the step S110, an electrode <NUM> may be divided into a coated part <NUM> and an uncoated part <NUM>.

The area of the electrode <NUM> may be divided into an area in which the coated part <NUM><NUM> is positioned and an area in which the uncoated part <NUM> is positioned. The coated part <NUM> may be referred to as a "coated area". The uncoated part <NUM> may be referred to as a "uncoated area". For example, the electrode <NUM> may be divided into a coated area <NUM> and an uncoated area <NUM>.

The method S100 of manufacturing the electrode according to an embodiment of the present disclosure may comprise a hating step S120. In the step S120, a heating device <NUM> may heat the electrode <NUM>. For example, in the step S120, the heating device <NUM> may mainly heat a cut portion 52b. In other words, in the step S120, the heating device <NUM> may mainly heat an end portion of the uncoated part <NUM>. That is, in the step S120, the heating device <NUM> may mainly heat the end portion of the uncoated area <NUM>.

The heating step S120 may comprise a step S121 of forming an exposed portion. In the step S121, an exposure space <NUM> may be formed through a shielding member <NUM> so that a magnetic flux generated by an induction heating unit <NUM> travels while being limited to a predetermined range. In the step S121, a magnetic field formed by the induction heating unit <NUM> may be distributed while being limited to a predetermined range.

The heating step S120 may comprise a step S122 of heating an uncoated part. In the step S122, a portion of the magnetic flux generated by the induction heating unit <NUM> may be shielded by the shielding member <NUM>, and other portion may pass through the exposure space <NUM> and may be incident on the uncoated part <NUM>. For example, in this step S122, the induction heating unit <NUM> may mainly heat the cut portion 52b that is the end portion of the uncoated part <NUM>.

In the heating step S120, the induction heating unit <NUM> may heat the uncoated part <NUM> so that a portion of the uncoated part <NUM> has a set tensile strength. For example, the cut portion 52b may be heated so that a 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 a first uncoated part <NUM> 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 <NUM> has the first tensile strength and the tab connection portion 52a has the second tensile strength.

The method S100 of manufacturing the electrode according to an embodiment of the present disclosure may comprise a rolling step S130. The rolling step S130 may be a step of compressing the electrode <NUM> to increase an adhesive force between the slurry <NUM> and the electric collector <NUM>. Through the rolling step S130, the electrode <NUM> may be compressed to a set thickness.

The method S100 of manufacturing the electrode according to an embodiment of the present disclosure may comprise a cutting step S135 of cutting the cut portion 52b. In the step S135, the cut portion 52b may be separated from the tab connection portion 52a.

The method S100 of manufacturing the electrode according to an embodiment of the present disclosure may comprise a tab connection step S140. The tab connection step S140 may be performed after the rolling step S130. In the tab connection step S140, an electrode tab <NUM> (see <FIG>) may be connected to the uncoated part <NUM>. In the tab connection step S140, the electrode tab <NUM> (see <FIG>) may be connected to the uncoated area <NUM>. In the step S140, the tab connection portion 52a may be connected to the electrode tab <NUM> (see <FIG>).

<FIG> illustrates that the respective areas of the uncoated part <NUM> are partitioned by dotted lines for convenience of description, by way of example, but the respective areas may not be partitioned and may be consecutively connected.

Referring to (a) and (b) of <FIG>, the plurality of second uncoated parts <NUM> may be laminated and welded. Referring to (c) of <FIG>, the cut portion 52b may be separated and removed from the tab connection portion 52a. Referring to (d) of <FIG>, the tab connection portion 52a may be connected or coupled to the electrode tab <NUM> through the welding in a state where the cut portion 52b is removed from the second uncoated part <NUM>. Hence, the electrode <NUM> and the electrode tab <NUM> may be connected.

Claim 1:
An electrode for lithium secondary battery comprised of an electric collector formed of a metal and a slurry coated on a portion of the electric collector, the electrode for lithium secondary battery comprising:
a coated part including the portion of the electric collector, on which the slurry is coated, and the slurry; and
an uncoated part including a remaining portion of the electric collector on which the slurry is not coated,
wherein the uncoated part includes:
a first uncoated part extended from the coated part; and
a second uncoated part extended from the first uncoated part, the second uncoated part including 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 <NUM> to <NUM>.