Patent ID: 12261282

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, various embodiments of the present disclosure will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement them. The present disclosure may be modified in various different ways, and is not limited to the embodiments set forth herein.

Portions that are irrelevant to the description will be omitted to clearly describe the present disclosure, and like reference numerals designate like elements throughout the specification.

Further, in the figures, the size and thickness of each element are arbitrarily illustrated for convenience of description, and the present disclosure is not necessarily limited to those illustrated in the figures. In the figures, the thickness of layers, regions, etc. are exaggerated for clarity. In the figures, for convenience of description, the thicknesses of some layers and regions are shown to be exaggerated.

In addition, it will be understood that when an element such as a layer, film, region, or plate is referred to as being “on” or “above” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, it means that other intervening elements are not present. Further, the word “on” or “above” means disposed on or below a reference portion, and does not necessarily mean being disposed on the upper end of the reference portion toward the opposite direction of gravity.

Further, throughout the specification, when a portion is referred to as “including” a certain component, it means that it can further include other components, without excluding the other components, unless otherwise stated.

Further, throughout the specification, when referred to as “planar”, it means when a target portion is viewed from the upper side, and when referred to as “cross-sectional”, it means when a target portion is viewed from the side of a cross section cut vertically.

FIG.3is a perspective view showing a rolling device according to one embodiment of the present disclosure.

Referring toFIG.3, a method of manufacturing an electrode for a secondary battery according to one embodiment of the present disclosure includes the steps of: coating an active material onto an electrode current collector300to form a coated portion400and an uncoated portion500, and applying a compressive residual stress to the surface of the uncoated portion500. At this time, the step of applying the compressive residual stress to the surface of the uncoated portion500includes a step of performing a peening process on the surface of the uncoated portion500. When performing a peening process on the surface of the uncoated portion500, it is desirable to minimize a physical deformation on the surface of the uncoated portion500. That is, a compressive residual stress must be applied to the surface of the uncoated portion500by an action such as quenching through a peening process, which is different from applying an elongation force. According to this embodiment, there is no physical change on the surface of the uncoated portion500through the peening process, or even if there is a physical change, the change may occur uniformly.

The step of applying a compressive residual stress to the surface of the uncoated portion500is performed before a roll process performed along the moving direction of the electrode current collector300, and the roll process may include at least one of a process of rolling a coated portion400and an uncoated portion500of the electrode current collector300and a process of notching a coated portion400and an uncoated portion500of the electrode current collector300.

FIG.4is a diagram schematically showing a state in which the rolling device ofFIG.3is viewed from the front.FIG.5is a schematic diagram showing a notching device according to one embodiment of the present disclosure.

Referring toFIGS.3and4, the electrode rolling device100according to the embodiment of the present disclosure includes a first roller101which unwinds an electrode plate250having a coated portion400on which a coating material is formed on the electrode current collector300and an uncoated portion500corresponding to a non-coated portion, a second roller102which winds the electrode plate250, and a rolling roll109which is located between the first roller101and the second roller102and rolls the coated portion400and the uncoated portion500of the electrode plate250along the moving direction of the electrode plate250. The uncoated portion500may refer to a region excluding the coated portion400formed on the electrode current collector300.

The first roller101provides the electrode plate250to be rolled to the rolling device100, and moves the electrode plate250in a direction of arrow D1ofFIG.4in accordance with the clockwise rotation. The electrode plate250unwound by the first roller101passes between the rolling rolls109while moving along the direction of the arrow. The rolling rolls109are located on both sides with respect to the electrode plate250, respectively, and the electrode plate250that has passed between the two rolling rolls109is pressed. After that, the electrode plate250that has passed between the two rolling rolls109is rewound on the second roller102.

The method of manufacturing an electrode for a secondary battery according to the embodiment of the present disclosure includes a step of performing a peening process, before the electrode plate250having the coated portion400and the uncoated portion500is unwinded and then rolled by the rolling roll109. The peening process may be performed by a peening device PN located between the first roller101and the rolling roll109in the electrode rolling device100according to this embodiment. The peening process may apply a compressive residual stress to the uncoated portion500according to this embodiment.

Referring toFIG.5, in a modified embodiment, the method of manufacturing an electrode for a secondary battery according to the embodiment of the present disclosure includes a step of performing a shot peening process, before the electrode plate250having the coated portion400and the uncoated portion500is unwinded and then notched by an upper mold210and a lower mold220for notching. The peening process may be performed by a peening device PN located between the first roller201and the notching molds210and220in the electrode notching device200according to the present embodiment.

FIG.6is a schematic cross-sectional view showing a peening process ofFIGS.4and5.FIG.7is a perspective view showing a shot peening process according to an embodiment of the present disclosure.FIG.8is a cross-sectional view showing a state in which a dimple portion is formed by shot peening ofFIG.7.

Referring toFIG.6, the step of applying a compressive residual stress to the surface of the uncoated portion500according to the present embodiment may include a step of performing a shot peening process or a step of performing an ultrasonic peening process. In the following, the step of performing the shot peening process will be mainly described.

Referring toFIGS.6to8, a shot ball600may be thrown onto the surface of the uncoated portion500at high speed to hammer the surface of the electrode current collector300. The shot ball600may be formed of a steel ball such as stainless steel. Specifically, in the shot peening process, the shot ball600collides with the surface of the uncoated portion500at high speed, and a kinetic energy of the shot ball600instantaneously causes a plastic deformation on the surface of the material, and the shot ball600separates from the surface. At this time, the uncoated portion500is formed with a dimple portion DP having an indented shape. According to this embodiment, a thin plastic deformation layer PDL is formed on the surface of the dimple portion DP, and the plastic deformation layer PDL may have a compressive residual stress. In contrast, the inside of the uncoated portion500located outside the plastic deformation layer PDL may have a tensile residual stress. Thus, a force to maintain the stretched surface in a state before stretching is applied to the plastic deformation layer PDL according to this embodiment, and a compressive residual stress and tensile residual stress are formed on the surface and inside of the uncoated portion500on which the dimple portion DP is formed, respectively, thereby achieving equilibrium. By leaving a compressive residual stress on the surface of the uncoated portion500by this shot peening process, the compressive residual stress is gradually canceled when repetitive tension is applied, and the fatigue life can be extended until the compressive residual stress disappears.

The compressive residual stress and tensile residual stress described above can be interpreted as cosine values of the residual stress measured using a residual stress tester.

Referring again toFIG.6, in a modified embodiment, the step of applying a compressive residual stress to the surface of the uncoated portion500may include a step of performing an ultrasonic peening process. In the ultrasonic peening process, an ultrasonic device700is disposed on the upper end of the uncoated part500, so that ultrasonic waves collide with the surface of the uncoated part500at high speed, thereby causing plastic deformation. Specifically, in the ultrasonic peening process, the compressive residual stress can be controlled while ultrasonic energy is transmitted to the surface of the uncoated portion500, and high and low cycle fatigue can be improved. The ultrasonic peening process may be performed while controlling the altitude of the ultrasonic device700shown inFIG.6. Through such an altitude control, the surface roughness of the uncoated portion500may be controlled.

The step of performing an ultrasonic peening process may replace the step of performing the above-described shot peening process. Even in the step of performing the ultrasonic peening process, a dimple portion may be formed on the surface of the uncoated portion500, and a plastic deformation layer having a compressive residual stress is formed on the surface of the dimple portion, and the inside of the uncoated portion located outside the plastic deformation layer may have a tensile residual stress. In the ultrasonic peening process, the physical deformation on the surface of the uncoated portion500may be relatively small compared to the above-described shot peening.

FIG.9is a schematic cross-sectional view showing an aging process according to an embodiment of the present disclosure.

Referring toFIG.9, the method of manufacturing an electrode for a secondary battery according to the embodiment of the present disclosure may include a step of heat-treating the electrode current collector300after performing a peening process on the surface of the uncoated portion500. In the step of heat-treating the electrode current collector300, a heat treatment apparatus800is disposed on the upper end of the uncoated part500so that ultrasonic waves collide with the surface of the uncoated part500at high speed, thereby causing plastic deformation. When aging such as heat treatment is performed in addition to the above-mentioned peening process, a compressive residual stress may be further generated on the surface of the electrode current collector300. Accordingly, the level at which unbalanced plastic deformation occurs due to stress during rolling can be alleviated, and the level of tensile residual stress generated on the surface can be significantly alleviated.

According to the embodiment of the present disclosure, by applying a compressive residual stress of the electrode current collector300through a peening process, the electrode current collector300can be heat-treated in a state in which the fracture strength and fatigue durability are enhanced, thereby manufacturing an electrode for a secondary battery in which the internal grain of the electrode current collector300is stabilized. At this time, the heat treatment temperature can be set to a temperature and time within a range in which a large change in the physical properties of the material does not occur.

Although the preferred embodiments of the present disclosure have been described in detail above, the scope of the present disclosure is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present disclosure defined in the following claims also belong to the scope of rights.

DESCRIPTION OF REFERENCE NUMERALS

300: electrode current collector400: coated portion500: uncoated portion600: shot ballDP: dimple portionPDL: plastic deformation layer