ELECTRODE FOR SECONDARY BATTERY WITH IMPROVED SAFETY, MANUFACTURING METHOD THEREOF, AND SECONDARY BATTERY INCLUDING SAME ELECTRODE

Abstract

The present invention relates to an electrode for a secondary battery having improved safety, a method for manufacturing the electrode, and a secondary battery including the electrode. The secondary battery according to the present invention includes a plurality of apertures that penetrate a current collector and an electrode active material layer in a thickness direction. The electrode may improve safety by preventing or minimizing the occurrence of ignition or explosion when a sharp object such as a nail penetrates into the interior of a battery, thereby improving safety of the battery.

Claims

1. An electrode for a secondary battery, comprising: a current collector; and an electrode active material layer formed on one side or both sides of the current collector, wherein a plurality of apertures that penetrate the current collector and the electrode active material layer are formed in a thickness direction, wherein the plurality of apertures have a lateral cross-section of one or more selected from a group consisting of circular, oval, and polygonal cross-sectional shapes and have diameters between 100 m and 5 mm, and wherein the electrode has an elongation of 0.3% to 1.0%.

2. The electrode of claim 1, wherein the diameter of each of the plurality of apertures is 400 m to 1 mm.

3. The electrode of claim 1, wherein the plurality of apertures are arranged in a pattern in which a unit pattern of their array is a rectangle or an equilateral triangle, and the unit pattern is repeatedly arranged.

4. The electrode of claim 3, wherein the unit pattern is a square unit pattern, and an aperture interval in a longitudinal direction of sides in the square unit pattern is 1 mm to 8 mm

5. The electrode of claim 3, wherein the unit pattern is an equilateral triangle, and an aperture interval in a longitudinal direction of sides of a unit pattern of the equilateral triangle is 1 mm to 8 mm.

6. The electrode of claim 1, wherein the electrode is a positive electrode.

7. A method for manufacturing an electrode for a secondary battery, the method comprising the steps of: (1) applying an electrode slurry that contains an electrode active material on an electrode current collector and drying the electrode slurry to form an electrode active material layer; and (2) rolling the electrode active material layer, wherein the method further comprises a step of forming a plurality of apertures that penetrate the electrode current collector and the electrode active material layer in a thickness direction after or simultaneously with the step (2).

8. The method of claim 7, wherein the roller applies pressure during the rolling step, and a perforating means is applied on an outer circumferential surface of the roller to form the plurality of apertures.

9. A secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein one or each of the positive electrode and the negative electrode are an electrode according to claim 1.

10. The secondary battery of claim 9, wherein among the positive electrode and the negative electrode, the positive electrode is the electrode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIGS. 1A and 1B are schematic plan views showing examples of aperture array patterns formed according to an embodiment of the present invention.

[0025] FIG. 2 is a schematic perspective view showing an example of a roller used in the aperture forming step of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, the present invention will be described in detail. It is to be understood that the following detailed description and drawings are merely illustrative of the embodiments of the present invention, and therefore the present invention should not be construed as being limited to the description and contents.

[0027] First, the terms used in the present invention are described below. The elongation rate (%) in the present invention refers to the percentage of the elongation after stretching relative to the original length as in a common definition, but since the present invention is applied to a planar object rather than a linear object, the concept includes both a longitudinal elongation and a lateral elongation. The elongation rate may be different for the longitudinal elongation and for the lateral elongation. In this case, the longitudinal elongation and the lateral elongation are arithmetically averaged. For example, when the longitudinal elongation of the electrode is 2% and the lateral elongation is 4%, the elongation of the electrode is 3%.

[0028] An electrode for a secondary battery according to the present invention is an electrode including a current collector and an electrode active material layer formed on one surface or both surfaces of the current collector and having a plurality of apertures that penetrate the current collector and the electrode active material layer in the thickness direction.

[0029] In a specific embodiment of the present invention, the shape of the apertures is not particularly limited, but the shape of the cross-section may be circular, elliptical, polygonal, or the like, and is preferably a substantially circular cross-section.

[0030] Further, the diameter of the apertures may be preferably 100 m to 5 mm, more preferably 400 m to 1 mm, and the apertures are preferably formed on the entire surface of the electrode at predetermined intervals. Preferably, when viewed in a plan view, the total area of the apertures may be 10 to 70%, more preferably 20 to 40% of the total area of the electrode.

[0031] When the diameter and total area of the apertures are smaller than the above range, the effect of decreasing the elongation is pronounced. On the other hand, when the total diameter and area of the apertures are larger than the above range, the amount of the electrode active material decreases, which may lead to the decrease of the battery capacity.

[0032] The array pattern of the apertures may be regular or irregular, but preferably the unit shape of the array of apertures 11 may be a square (in the case of FIG. 1A) or an equilateral triangle (in the case of FIG. 1B), which may be repeatedly formed on the electrode (10). In this case, it is preferable that the aperture interval Ls in the longitudinal direction of the sides of the square shape and the aperture interval Lt in the longitudinal direction of the sides of the regular triangle shape are 1 to 8 mm, and each aperture is preferably circular shape of a diameter of 100 m to 5 mm.

[0033] Thickness, shape, or the like of electrode current collector, especially positive electrode current collector and negative electrode current collector, the composition of the slurry for forming the electrode active material layer, particularly the positive electrode active material layer and the negative electrode active material layer, type of active material, particle size, porosity of the active material layer, and the like according to the present invention are well known in the art and are not particularly limited. Those skilled in the art can easily use the knowledge to understand and acquire the matters related thereto and for the present invention, and therefore, a detailed description thereof will be omitted. In this regard, for example, Patent Document 1 (Korean Patent Laid-Open Publication No. 10-2017-0034570) and Patent Document 2 (Korean Patent Laid-Open Publication No. 10-2013-0055712), which are patents of the present applicant, can be referred to, and the entire contents of these documents are incorporated herein by reference to the extent not inconsistent with the present invention.

[0034] However, the positive electrode current collector may be made of stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium or silver, but in the present invention, aluminum is preferably used for the purpose of reducing the elongation as much as possible. On the other hand, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, baked carbon, surface of copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, or the like, and considering various aspects, the copper foil, which is widely used as a negative electrode current collector, has a considerably large elongation, and therefore it is not easy to achieve a desired level of elongation by the constitution of the present invention. Therefore, since the above-mentioned aluminum is widely used as a positive electrode material in other aspects, the present invention can be more effective when applied to a positive electrode than a negative electrode.

[0035] As described above, according to the present invention, since a plurality of apertures are formed in the electrode, the elongation rate of the electrode is decreased (this may be because the breaking strength of the electrode is weakened due to a large number of apertures), the effect of decreasing the elongation rate may vary depending on the materials used for the electrodes, the size of the apertures, the formed area, and the like, but according to the present invention, the elongation can be reduced to a level of 50% or less compared to prior to the aperture formation. The electrode of the present invention having the reduced elongation as described above may preferably have an elongation of 1.0% or less, more preferably 0.4% to 0.8%, and most preferably 0.4 to 0.5%. When the elongation is 0% or excessively low, not only it is difficult to realize, but also there is a risk that the electrode may be broken in a process such as rolling. Therefore, the elongation of the electrode is preferably at least 0.3% or more.

[0036] On the other hand, in order to ensure safety against penetration of a sharp object, it is desirable that the elongation of the positive electrode and the negative electrode is small, and the elongation of the separator is large (for example, if the separator has an elongation lower than an elongation of the electrode current collector, the positive electrode and the negative electrode are more likely to come into contact with each other). When the electrode of the present invention as described above is used, if a sharp object such as a nail penetrates into the battery, the resistance of the electrode against the penetration of the sharp object is large, and if exceeding the resistance, the electrode is broken without being elongated, and the possibility of contact and the area of contact between the electrodes and between the electrode and the sharp object is decreased, and therefore the possibility of ignition or explosion is significantly decreased.

[0037] Next, a method of manufacturing an electrode for a secondary battery according to the present invention will be described. According to an embodiment, a method of manufacturing an electrode of the present invention includes the steps of (1) applying an electrode slurry that contains an electrode active material on an electrode current collector, and drying the electrode slurry to form an electrode active material layer; and (2) rolling the electrode active material layer, and the step of forming a plurality of apertures that penetrate through the electrode current collector and the active material layer in the thickness direction may be additionally included.

[0038] The apertures may be formed by any method known in the art. For example, the apertures may be formed by pressing the electrode using a pressing device having a perforation means on the pressing die, but preferably, as shown in FIG. 2, the apertures may be formed by pressing the electrode using a roller 20 on the outer circumferential surface of which the perforation means 21 is formed as used in the electrode rolling process. Such an aperture forming step may be performed after the rolling step of step (2), or may be performed simultaneously with the rolling step using a roller having a perforation means formed on the outer peripheral surface thereof as a roller used in the rolling step. The latter method is preferable in terms of process efficiency.

[0039] The pattern for forming the perforation means in the roller may be formed correspondingly to the pattern of the apertures to be formed in the electrode. The perforation means can be used without particular limitation as long as it can form an aperture by pressing the current collector and the active material layer of the electrode. The perforation means may be, for example, a pin, a needle, a rod, a tube or the like capable of forming an aperture by pressurization.

[0040] In the electrode manufacturing method of the present invention, the electrode active material layer forming step, rolling step, and the like are conventional steps known in the art, and can be applied to the present invention without any particular limitation, and those skilled in the art can easily understand and obtain the present invention, so that detailed description thereof will be omitted. In this regard, for example, Patent Documents 1 and 2 may be referred to as described above.

[0041] The present invention further provides a secondary battery, in which the secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, in which one or both of the positive electrode and the negative electrode is an electrode according to the present invention described herein. In particular, it is preferable that the positive electrode is the electrode according to the present invention for the reasons described above.

[0042] The separator, the electrolyte, and the like that constitute the secondary battery of the present invention are well known in the art and can be used in the present invention without any particular limitation, and those skilled in the art can easily understand and obtain them, and therefore detailed descriptions thereof are also omitted. In this regard, for example, Patent Documents 1 and 2 may be referred to as described above.

[0043] Hereinafter, the present invention will be described in more detail through examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0044] The present invention provides an electrode in which a plurality of apertures that penetrate the current collector and the electrode active material layer in the thickness direction are formed in order to reduce the elongation characteristics. Accordingly, a positive electrode and a negative electrode having an aperture according to the present invention were prepared as follows. On the other hand, as a control group, a positive electrode and a negative electrode were prepared in the same manner except that no aperture was formed.

PREPARATION EXAMPLE OF POSITIVE ELECTRODE

PREPARATION EXAMPLE 1 (POSITIVE ELECTRODE 1)

[0045] An aluminum foil having a thickness of 12 m and an elongation of 2.5% was prepared as a positive electrode current collector.

[0046] In addition, LiNi.sub.0.6Mn.sub.0.2Co.sub.0.2O.sub.2 (average particle diameter: 14 m) as a positive electrode active material, PVDF as a binder and Denka black as a conductive material were dissolved in a solvent of N-methylpyrrolidone (NMP) at the composition ratio of 93:4:3 to prepare a positive electrode slurry for forming a positive electrode active material layer.

[0047] The positive electrode slurry was coated on both sides of the aluminum foil, dried and rolled to produce a positive electrode.

[0048] The positive electrode was pressed with a roller as shown in FIG. 2 to form apertures. In particular, the apertures have a circular cross section with a diameter of 500 m, and the array pattern of the apertures is a square pattern as shown in FIG. 1A, and the aperture interval Ls in the longitudinal direction of the sides is 1 mm.

[0049] The positive electrode thus produced finally had a total thickness of about 125 m (one of the active material layers had a thickness of about 56 m) and a porosity of 25%.

PREPARATION EXAMPLE 2 (POSITIVE ELECTRODE 2)

[0050] A positive electrode was prepared in the same manner as in Example 1 except that the aperture interval (Ls) was 5 mm.

PREPARATION EXAMPLE 3 (POSITIVE ELECTRODE 3)

[0051] A positive electrode was prepared in the same manner as in Example 1 except that the aperture interval (Ls) was 10 mm.

PREPARATION EXAMPLE 4 (POSITIVE ELECTRODE 4)

[0052] A positive electrode was prepared in the same manner as in Example 1 except that no aperture was formed.

PREPARATION EXAMPLE OF NEGATIVE ELECTRODE

PREPARATION EXAMPLE 5 (NEGATIVE ELECTRODE 1)

[0053] A copper foil having a thickness of 10 m and an elongation of 3.5% as a negative electrode current collector was prepared.

[0054] In addition, a slurry for forming a negative electrode active material layer was prepared by mixing natural graphite as a negative electrode active material, SBR and CMC as a binder, and Denka black as a conductive material in water as a solvent at a composition ratio of 97:2:1.

[0055] The negative electrode slurry was coated on both sides of the negative electrode current collector, dried and rolled to produce a negative electrode.

[0056] Apertures were formed in the negative electrode in the same manner as in Preparation Example 1 (positive electrode 1).

[0057] The negative electrode thus produced finally had a total thickness of about 150 m (one of the active material layers had a thickness of about 70 m) and a porosity of 35%.

PREPARATION EXAMPLE 6 (NEGATIVE ELECTRODE 2)

[0058] A negative electrode was prepared in the same manner as in Preparation Example 5 except that no aperture was formed.

Measurement of Elongation of Electrode

[0059] The elongation was measured for the positive electrode and the negative electrode according to the respective preparation examples. In particular, the elongation was measured by UTM equipment, and the longitudinal elongation and lateral elongation were measured at a rate of 0.5 mm/min, and then the arithmetic mean thereof was defined as the elongation of the prepared electrode. The elongation measurement results of the positive electrode and the negative electrode according to each preparation example are shown in Table 1 below.

TABLE-US-00001 TABLE 1 Electrode Diameter of Interval of Elongation of preparation Elongation of apertures apertures prepared example curent collector (m) (mm) electrode Preparation 2.5% 500 1 0.5% Example 1 (positive electrode 1) Preparation 2.5% 500 5 0.8% Example 2 (positive electrode 2) Preparation 2.5% 500 10 1.2% Example 3 (positive electrode 3) Preparation 2.5% 1.5% Example 4 (positive electrode 4) Preparation 3.5% 500 1 2.0% Example 5 (negative electrode 1) Preparation 3.5% 2.5% Example 6 (negative electrode 2)

[0060] As shown in Table 1, in the case of Preparation Example 1 (positive electrode 1) having an aperture interval of 1 mm, the elongation was 0.5%, which was only one fifth of the elongation of the current collector. This is also significantly superior to the experimental result of Korean Patent Laid-Open Publication No. 2017-0034570, which is the prior art of the present applicant.

[0061] However, in the case of the Preparation Example 5 (negative electrode 1) in which apertures were formed in the same pattern as the Preparation Example 1 (positive electrode), the effect for improving the elongation was lower than the positive electrode. Therefore, it is preferable to apply the present technology to a positive electrode rather than a negative electrode, because it is more effective.

SECONDARY BATTERY PREPARATION AND NAIL PENETRATION TEST ACCORDING TO EXAMPLES AND COMPARATIVE EXAMPLES

[0062] The positive electrode and the negative electrode according to each of the above Preparation Examples were combined to prepare a secondary battery according to the procedures of Examples and Comparative Examples shown in Table 2 below, and a nail penetration test was performed after manufacturing the secondary battery to observe whether or not ignition occurred.

Preparation of Pouch Type Mono-Cell

[0063] The secondary batteries according to each of the Examples and Comparative Examples were prepared in the same manner as described below except for the Preparation Example combination of the positive electrode and the negative electrode.

[0064] A positive electrode and a negative electrode of each of Examples and Comparative Examples were selected and used as an electrode according to the Preparation Example shown in Table 2 below. An electrode assembly was prepared by interposing a separator made of polyethylene between the positive electrode and the negative electrode.

[0065] The electrode assembly was housed in a pouch, and then an electrolytic solution composed of ethylene carbonate (EC):dimethyl carbonate (DMC):ethyl methyl carbonate (EMC)=3:4:3 and 1M LiPF.sub.6 was injected to prepare a pouch type mono-cell.

Nail Penetration Test

[0066] The nail penetration test was performed on the mono-cell prepared as described above. Prior to the experiment, each mono-cell was fully charged at a voltage of 4.15 V at 25 C. The mono-cell was pierced through the center at a penetration rate of 80 mm/sec using a nail having a diameter of 3 mm. The results are shown in Table 2 below (O: ignited, X: not ignited).

TABLE-US-00002 TABLE 2 Positive electrode Negative electrode Whether Division Preparation example Elongation Preparation example Elongation ignited Example 1 Preparation Example 1 0.5% Preparation Example 5 2.0% X (positive electrode 1) (negative electrode 1) Example 2 Preparation Example 2 0.8% Preparation Example 5 2.0% X (positive electrode 2) (negative electrode 1) Example 3 Preparation Example 1 0.5% Preparation Example 6 2.5% X (positive electrode 1) (negative electrode 2) Comparative Preparation Example 3 1.2% Preparation Example 5 2.0% Example 1 (positive electrode 3) (negative electrode 1) Comparative Preparation Example 4 1.5% Preparation Example 6 2.5% Example 2 (positive electrode 4) (negative electrode 2)

EXAMPLE 1

[0067] First, a mono-cell was prepared by combining Preparation Example 1 (positive electrode 1) and Production Example 5 (negative electrode 1) having the lowest elongation. Subsequently, a nail penetration test of the above method was performed, and it was observed whether the cell ignited. Because of the low elongation, ignition did not occur even after penetration of a sharp object.

EXAMPLE 2

[0068] Next, a mono-cell was prepared by combining Preparation Example 2 having the elongation of 0.8% (positive electrode 2) and Production Example 5 (negative electrode 1). Subsequently, a nail penetration test of the above method was performed, and it was observed whether the cell ignited. As in Example 1, ignition did not occur.

EXAMPLE 3

[0069] Preparation Example 1 (positive electrode 1) having an elongation of 0.5% and Preparation Example 6 (negative electrode 2) having no decrease in elongation characteristic in which apertures were not formed combined, to thereby carry out an experiment in the same manner as in Example 1. No ignition was observed because of low elongation of the Preparation Example 1 (positive electrode).

COMPARATIVE EXAMPLE 1

[0070] Then, an experiment was carried out in the same manner as in Example 1, using Preparation Example 3 (positive electrode 3 having a higher elongation than Example 2 and Preparation Example 5 (negative electrode 1) having a reduced elongation characteristic. Contrary to expectation, there was an ignition. Although the elongation of the negative electrode is lowered, it is considered that if the elongation of the positive electrode is 1.2% or more, ignition may occur. Therefore, it can be seen that lowering the elongation as much as possible by applying the electrode manufacturing method according to the present invention to the positive electrode is most desirable for improving the stability against a sharp object.

COMPARATIVE EXAMPLE 2

[0071] The experiment was carried out in the same manner as in Example 1 using the Preparation Example 6 (a negative electrode 2) in which no aperture is formed as in the Preparation Example 4 (positive electrode 4) in which no aperture is formed. It was verified that the ignition occurred as expected and that the method according to the present invention may prevent the risk due to a sharp object.

[0072] As can be seen from the above Examples and Comparative Examples, according to the present invention, since a plurality of apertures are formed in the electrode, the elongation of the electrode can be greatly reduced. As such, as a short circuit is prevented or reduced when sharp objects such as nails penetrate into the cell or through the cell, the possibility of ignition or explosion becomes significantly decreased.

INDUSTRIAL APPLICABILITY

[0073] As described in detail above, the present invention can prevent or minimize the occurrence of ignition or explosion of the battery even when a sharp object such as a nail penetrates into the battery, thereby further improving the safety of the battery. Therefore, it is industrially very useful.

[0074] While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention, and it will be apparent to those skilled in the art that addition of components and the like are possible.

[0075] Terms such as approximately and about are not used in the following claims because such terms are not allowed to be used in claims, but terms such as equilateral triangle or rectangle used in the following claims should be understood to mean approximately equilateral triangle or approximately rectangle.

DESCRIPTION OF SYMBOLS

[0076] 10: electrode

[0077] 11: aperture

[0078] 20: roller

[0079] 21: perforation means

[0080] Ls, Lt: aperture intervals