EP-4742312-A2 - CATHODE FOR SECONDARY BATTERY AND METHOD FOR MANUFACTURING SAME

EP4742312A2EP 4742312 A2EP4742312 A2EP 4742312A2EP-4742312-A2

Abstract

Proposed is a cathode for a secondary battery, which includes a cathode collector and a cathode mixture layer on the cathode collector, includes: a coating section at which the cathode mixture layer is formed with a uniform thickness; a non-coating section that is disposed on at least one edge of the coating section on the cathode collector and at which the cathode mixture layer is not formed; and a cushioning section at which the cathode mixture layer is formed with a thickness smaller than a thickness of the coating section at a location between the coating section and the non-coating section.

Inventors

LEE, DONG HOON
KIM, MIN HWAN
YANG, JUNG MIN

Assignees

SK On Co., Ltd.

Dates

Publication Date: 20260513
Application Date: 20211012

Claims (5)

A cathode for a secondary battery which includes a cathode collector and a cathode mixture layer on the cathode collector, the cathode comprising: a coating section at which the cathode mixture layer is formed with a uniform thickness; a non-coating section that is disposed on at least one edge of the coating section on the cathode collector and at which the cathode mixture layer is not formed; and a cushioning section at which the cathode mixture layer is formed with a thickness smaller than a thickness of the coating section at a location between the coating section and the non-coating section, wherein a boundary between the non-coating section and the cushioning section is a first point, a boundary between the cushioning section and the coating section is a second point, a third point is positioned between the first point and the second point, the cushioning section has two regions having different slopes, a thickness of the cushioning section gradually increases with a uniform slope from the first point toward the third point and gradually increases with a uniform slope from the third point toward the second point, the thickness of the cathode mixture layer at the third point existing between the first point and the second point in the cushioning section is 30% to 80% of the thickness of the cathode mixture layer in the coating section, and the third point is spaced apart from the first point by 20% to 60% of a length from the first point to the second point on the collector.
The cathode of claim 1, wherein density of the cathode mixture layer in the coating section is 3.5 g/cc or more.
The cathode of claim 1, wherein loading of the cathode mixture layer in the coating section is 16.0 mg/cm 2 or more.
The cathode of claim 1, wherein a thickness of the cathode collector is 15 µm or less.
The cathode of claim 1, wherein tensile strength of the collector corresponding to the non-coating section is 12 kgf/mm 2 or more.

Description

CROSS REFERENCE TO RELATED APPLICATION The present application claims priority to Korean Patent Application No. 10-2020-0142435, filed October 29, 2020, the entire contents of which is incorporated herein for all purposes by this reference. BACKGROUND OF THE INVENTION Field of the Invention The present disclosure relates to the cathode for a secondary battery and a method for manufacturing same and, more particularly, to a cathode structure of a secondary battery which minimizes irregular wrinkling or folding, electrode fracture, etc., and a method for manufacturing the cathode structure. Description of the Related Art A secondary battery that can be charged and discharged is widely used as the energy source or an assistant power device of mobile devices. Further, a secondary battery is spotlighted as a power source for an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (plug-in HEV), etc. that have been proposed as measures for solving air pollution generated by existing gasoline vehicles, diesel vehicles, etc. that use fossil fuels, etc. Recently, it is required to develop a secondary battery having higher energy density to increase the distance-to-empty of electric vehicles. A secondary battery is manufactured with an electrode assembly put in an electrode case together with an electrolyte. The electrode assembly, which is a structure composed of a cathode, an anode, and a separator, is classified into a stack type, a folding type, and a stack-folding type, etc., depending on the manufacturing method. There is a need for a process of applying an electrode active material to one or both sides of a metal collector, manufacturing an electrode sheet by drying the electrode active material, rolling the electrode sheet, and slitting the electrode sheet into the unit of an electrode interval in order to manufacture the cathode and the anode of an electrode assembly. A cathode collector is composed of a coating section to be coated with a cathode active material and a non-coating section that is disposed at both sides of the coating section in the longitudinal direction of the coating section and is not applied with a cathode mixture layer. The cathode mixture layer is applied to the coating section of the collector and the applied cathode mixture layer is rolled into a desired thickness. As for rolling, an electrode sheet is generally continuously rolled by cylindrical rolling rollers and this process is repeated to obtain desired electrode thickness and electrode density. An electrode is rolled at a high rolling ratio to manufacture a secondary battery having a high energy density. However, when an electrode sheet is rolled by rolling rollers, especially, when an electrode is rolled at a high rolling ratio, little pressure is applied to the non-coating section of a collector. Accordingly, waves or wrinkles are generated on the collector due to a difference of a collector elongation between the coating section and the non-coating section, and if severe, fracture occurs. When waves or wrinkles are formed on an electrode, a gap is easily generated between the cathode mixture layer and the collector and the gap may considerably deteriorate of the performance of the electrode by causing separation of the cathode mixture layer. Further, if waves or wrinkles are severe, the entire electrode is fractured during rolling. When facture occurs, productivity and yield may be remarkably decreased, and if severe, rolling may not be performed at a desired thickness. A technology of reducing the difference of an elongation between a coating section and a non-coating section during rolling by softening the non-coating section through IHA heating has been developed in the related art, but IHA output should be increased to sufficiently solve the problem of fracture. However, in this case, there is a problem that the quality is made poorer in the following processes such as welding due to excessive softening of a collector. Accordingly, it is highly required to develop a technology that can fundamentally solve this problem. Documents of Related Art (Patent Document 1) KR10-2016-0141448 A SUMMARY OF THE INVENTION The present disclosure has been made in an effort to solve the problems described above and an objective of the present disclosure is to optimize the thickness of an active material layer in the longitudinal direction of a collector after a rolling process with minimum fracture by minimizing the difference of an elongation between a coating section and a non-coating section, and to minimize the difference of an elongation between the coating section and the non-coating section in the rolling process by optimally designing a cushioning section between the coating section and the non-coating section before the rolling process. A cathode for a secondary battery according to an embodiment of the present disclosure, which includes a cathode collector and a cathode mixture layer on the c