KR102197360B1 - Electrode Assembly Comprising One-sided Coating Electrode of Improved Mechanical Strength - Google Patents

Abstract

The present invention is an electrode assembly having a structure in which a plurality of unit cells are stacked with a separator or a separation sheet interposed therebetween,
The unit cells include bi-cells in which electrodes respectively located on both outer surfaces of each other have the same polarity;
Each of the outermost unit cells of the electrode assembly includes at least one single-sided electrode on which the electrode mixture is applied only to one surface of the current collector, and the remaining unit cells excluding the outermost unit cells are electrodes on both sides of the current collector. It consists of double-sided electrodes coated with a mixture;
The first current collector of the single-sided electrode is for an electrode assembly, characterized in that it has a mechanical strength of 150% to 500% with respect to the second current collector of the double-sided electrode having the same polarity as the single-sided electrode.

Description

Electrode Assembly Comprising One-sided Coating Electrode of Improved Mechanical Strength}

The present invention relates to an electrode assembly including a single-sided electrode of improved mechanical strength.

As technology development and demand for mobile devices increase, the demand for batteries as an energy source is rapidly increasing, and accordingly, many studies on batteries that can meet various demands are being conducted.

Typically, in terms of the shape of the battery, there is a high demand for prismatic secondary batteries and pouch-type secondary batteries that can be applied to products such as mobile phones with a thin thickness, and in terms of materials, it has advantages such as high energy density, discharge voltage, and output stability. There is high demand for lithium secondary batteries such as lithium ion batteries and lithium ion polymer batteries.

Such a lithium secondary battery consists of an electrode assembly formed by stacking a positive electrode plate, a negative electrode plate, and a separator, and a battery case surrounding and sealing the electrode assembly.

In the electrode assembly, the positive electrode plate and the negative electrode plate may be a stacked electrode assembly having a structure in which an electrode mixture is applied to each electrode current collector made of a thin metal plate such as aluminum and copper, and a separator is interposed therebetween. , It may be a lamination electrode assembly bonded to each other in a state where the electrode plates are stacked, a lamination/stack type electrode assembly in which stacked electrode assemblies are bonded, or a structure in which stacked electrode assemblies are positioned in a separate film and wound. It may be a stack/folding type electrode assembly.

In general, a plate-shaped electrode assembly is stored in a pouch-type battery case and then used through an activation process.The pouch-type battery case has a lower strength than that of a rectangular or cylindrical battery case made of a metal material. There is a problem that can be easily deformed.

Therefore, to protect the electrode assembly inside the pouch-type battery case from external pressure, there are attempts to increase the strength or elasticity of the battery case itself, which essentially prevents short circuit due to deformation or breakage of the electrode current collector, or prevents fire and explosion. It is to reduce the risk of

As described above, there is a high need for a technology for a high-efficiency secondary battery capable of increasing the strength of the electrode current collector and preventing an increase in thickness, while maintaining the existing electrical characteristics, and capable of being used in mid- to large-sized devices.

An object of the present invention is to solve the problems of the prior art and technical problems that have been requested from the past.

The inventors of the present application have conducted in-depth research and various experiments, and as will be described later, each of the outermost unit cells includes at least one single-sided electrode on which an electrode mixture is applied only to one side of the current collector. , The remaining unit cells excluding the outermost unit cells are composed of double-sided electrodes coated with an electrode mixture on both sides of the current collector, and the first current collector of the single-sided electrode has high mechanical properties relative to the second current collector of the double-sided electrode. In the case of an electrode assembly configured to have strength, it was found that there is an effect of improving safety against external impact, and the present invention was completed.

The electrode assembly according to the present invention for achieving this purpose is an electrode assembly having a structure in which a plurality of unit cells are stacked with a separator or a separation sheet interposed therebetween, and the unit cells are electrodes located on both outer surfaces of each other. It includes bi-cells having polarity, and each of the outermost unit cells of the electrode assembly includes at least one single-sided electrode on which an electrode mixture is applied only to one surface of the current collector, and the Except for the outermost unit cells, the remaining unit cells are composed of double-sided electrodes coated with an electrode mixture on both sides of the current collector, and the first current collector of the single-sided electrode is a double-sided electrode having the same polarity as the single-sided electrode. The second current collector may have a mechanical strength of 150% to 500%.

As described above, when a single-sided electrode is used for each of the outermost unit cells of the electrode assembly, the single-sided electrode may be in a state in which the electrode active material is not applied to the outer surface, and when an external shock using a needle-shaped conductor is applied. Since direct contact with the conductive active material can be prevented, safety from external impact can be improved.

In addition, the mechanical strength of the first current collector for single-sided electrodes included in the outermost unit cell can be used as having significantly higher strength compared to the mechanical strength of the second current collector for double-sided electrodes. Can solve the problems that may occur.

In the electrode assembly, a first current collector having a thickness thinner than that of the second current collector may be used for the remaining unit cells except for the outermost unit cells, so that the overall thickness of the electrode assembly may be reduced. Accordingly, since the loading amount of the electrode active material corresponding to the decrease in the thickness of the electrode current collector can be increased, an effect of increasing the capacity of the battery can be obtained.

The electrode assembly is a stacked (stacked) electrode assembly in which a plurality of anodes and cathodes cut into units of a predetermined size are sequentially stacked with a separator interposed therebetween, and a predetermined unit of anodes and cathodes are stacked with a separator interposed therebetween A stack-folding electrode assembly in which one bi-cell or full-cell is wound with a separator sheet, or a lamination-stack in a structure in which electrode assemblies are adhered in a state in which stacked electrode assemblies are stacked It may be a type electrode assembly.

In one specific example, in the outermost unit cells, an electrode positioned on an outer surface of the electrode assembly may be a single-sided electrode, and electrodes other than the single-sided electrode may be double-sided electrodes. As described above, since the electrodes other than the electrode located on the outermost side of the electrode assembly are composed of double-sided electrodes, there is an advantage of preventing a reduction in the capacity of the battery compared to the case of using only single-sided electrodes.

On the other hand, the single-sided electrodes respectively located on both outer surfaces of the electrode assembly may be electrodes having the same polarity, and preferably, the single-sided electrodes respectively located on both side outer surfaces of the electrode assembly may be an anode. In this way, when the positive electrode is located on each of the outer surfaces of both sides of the electrode assembly, the design of the manufacturing process can be facilitated, and the strength of the aluminum or stainless foil generally used as the positive electrode current collector is used as the negative electrode current collector. Since it is superior to the strength of the copper foil, there is an advantage in that the mechanical strength of the battery cell is improved.

As described above, it is preferable that a positive electrode is positioned on each of the outermost sides of the electrode assembly, and the first current collector and the second current collector may be a positive electrode current collector, respectively, and the mechanical strength of the first current collector is the second current collector. It is possible to provide an electrode assembly having improved overall strength because it is formed significantly higher than that of the mechanical strength. In addition, since the durability against physical shocks applied from the outside is improved, explosion and ignition caused by this can be prevented.

Since the remaining unit cells excluding the outermost unit cells may be bi-cells composed of double-sided electrodes, it is preferable to use double-sided electrodes in order to prevent a decrease in the capacity of the battery, and electrodes respectively located on both outer surfaces are negative or Since unit cells having the same polarity are used as positive electrodes, errors in electrode direction design can be prevented during the battery cell manufacturing process, thereby facilitating the design of the overall process.

In one specific example, the first current collector has an iron content of 55 atomic% to 75 atomic%, a chromium content of 12 atomic% to 30 atomic%, and a nickel content of 8 atomic% to 20 atomic%. It is made of an alloy, and the second current collector may be made of aluminum or an aluminum alloy.

When the iron content of the first current collector is greater than 75 atomic% or the chromium content is less than 12 atomic%, the increase in corrosion resistance obtained by adding chromium is small, and thus corrosion may easily occur, which is not preferable. .

The first current collector is at least one metal selected from the group consisting of tungsten (W), vanadium (V), copper (Cu), silicon (Si), manganese (Mn), carbon (C), and molybdenum (Mo). The configuration may further include elements, and may be configured to have desired characteristics of a current collector by selectively including these elements.

The content of the added metal element may be 1 atomic% to 10 atomic% based on the total amount of metal elements constituting the first current collector, and specifically, may be 2 to 8 atomic%. When the content of the added metal is less than 1 atomic% based on the content of all metal elements, it is difficult to exert the desired alloy effect such as strength and/or electrical conductivity, and if it is greater than 10 atomic%, It is not preferred because the content of the components is relatively reduced.

In the electrode assembly according to the present invention, when the first current collector and the second current collector have the same thickness, the first current collector has a higher mechanical strength corresponding to 150% to 500% based on the mechanical strength of the second current collector. Since it has strength, in order to increase the capacity of the battery without lowering the overall strength of the electrode assembly, the thickness of the first current collector may be thinner than that of the second current collector. Specifically, the thickness of the first current collector may be 20% to 100% of the thickness of the second current collector, and more specifically, the thickness of the first current collector is 30% to 100% of the thickness of the second current collector. It can be 80%.

When the thickness of the first current collector is less than 20% of the thickness of the second current collector, it is difficult to achieve the purpose of manufacturing an electrode assembly with improved strength, and when it is greater than 100%, the overall thickness of the electrode assembly increases. Because it is not desirable.

On the other hand, in the electrode assembly according to the present invention, when the thickness of the first current collector included in the outermost unit cells and having a mechanical strength higher than the mechanical strength of the second current collector is thicker than the thickness of the second current collector, Effectively, the strength of the electrode assembly can be improved. Accordingly, the thickness of the first current collector may be, for example, 110% to 400% of the thickness of the second current collector, and in detail may be 150% to 300%.

In one specific example, the single-sided electrode has a structure in which the electrode mixture is applied only to one surface of the first current collector, and the electrode mixture is applied to one surface of the first current collector facing the double-sided electrode, and the other surface is opposite to the one surface. It may have a structure facing the outside of the electrode assembly. Therefore, even if there is an external impact on the battery cell using acicular conductors, etc., the use of the first current collector with high mechanical strength prevents direct contact between the electrode mixture and the acicular conductor, thereby reducing the risk of explosion or ignition. I can.

The present invention also provides a secondary battery in which the electrode assembly is embedded in a battery case. The battery case may be made of a laminate sheet including a resin layer and a metal layer, and the metal layer may be made of the same material as the first current collector. In this case, since a battery case including a metal layer of the same material as the first current collector having relatively high mechanical strength is used, the safety of the secondary battery may be further improved.

In addition, the battery case may be made of a laminate sheet including a resin layer and a metal layer, and the metal layer may be made of the same material as the second current collector.

The present invention also provides a battery pack including the secondary battery as a unit cell, and a device including the battery pack as a power source.

Specifically, the battery pack may be used as a power source for devices that require high temperature safety, long cycle characteristics, and high rate characteristics, and detailed examples of such devices include mobile devices and wearable devices. , A power tool that is powered and moved by a battery-based motor; Electric vehicles including electric vehicles (EV), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and the like; Electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (E-scooters); Electric golf cart; Power storage systems, etc., but are not limited thereto.

A medium- to large-sized battery module is composed of a plurality of battery cells, and accordingly, the cost of the members used for manufacturing the battery cell greatly affects the manufacturing cost of the entire battery module, so the secondary battery according to the present invention is It can be particularly preferably applied to the battery module.

Since the structure of these devices and a method of manufacturing them are known in the art, detailed descriptions thereof will be omitted in the present specification.

As described above, in the electrode assembly according to the present invention, each of the outermost unit cells includes at least one single-sided electrode on which the electrode mixture is applied only to one surface of the current collector, excluding the outermost unit cells. The remaining unit cells are composed of double-sided electrodes coated with an electrode mixture on both sides of the current collector, and the first current collector of the single-sided electrode is configured to have high mechanical strength with respect to the second current collector of the double-sided electrode. An improved electrode current collector can be provided, and durability against a physical impact applied from the outside is improved, and thus explosion and fire can be prevented.

In addition, since the electrode current collector with relatively high mechanical strength is used, the thickness of the electrode current collector can be designed to be thin.In this case, when the coating amount of the active material is increased, the capacity is increased even if the overall electrode thickness is the same. Can be obtained.

1 is a schematic side view of an electrode assembly according to an embodiment;
2 is a schematic side view of bicells according to an embodiment;
3 is a schematic side view of bicells according to another embodiment;
4 is a schematic side view of a stack-folding electrode assembly composed of bicells of FIGS. 2 and 3; And
5 is a schematic side view of a lamination-stack type electrode assembly composed of bicells of FIGS. 2 and 3.

Hereinafter, it will be described with reference to the drawings according to an embodiment of the present invention, but this is for an easier understanding of the present invention, and the scope of the present invention is not limited thereto.

1 schematically shows a side view of an electrode assembly according to the present invention.

Referring to FIG. 1, the electrode assembly 100 is an electrode assembly formed by winding seven unit cells 110, 120, 130, 140, 150, 160, 170 while being positioned on a long sheet-shaped separator 181. , The unit cells (110, 120, 130, 140, 150, 160, 170) are composed of bi-cells in which electrodes located on the outer surfaces of both sides are the same as each other as positive or negative electrodes. The electrode assembly 100 is composed of seven unit cells, but the number of unit cells is not particularly limited if the electrodes located at both ends of the electrode assembly are composed of bi-cells composed of anodes.

2 and 3 illustrate bicells according to one specific embodiment. 2 and 3, the bi-cells of FIG. 2 are composed of double-sided electrodes in which an electrode mixture is applied to both sides of an electrode assembly, and the bi-cells of FIG. 3 have an electrode mixture coated on only one side of the electrode assembly. It consists of single-sided electrodes and double-sided electrodes.

The double-sided electrodes shown in FIG. 2 are an A-type bi-cell, a cathode 202, and an anode in which an anode 201, a cathode 202, and an anode 201 are sequentially stacked with a separator 203 interposed therebetween. It is a C-type bi-cell in which 201 and the negative electrode 202 are sequentially stacked, and the positive electrode mixture 211 is coated on both sides of the positive electrode current collector, and the negative electrode mixture 212 is coated on both sides of the negative electrode current collector. have.

The bi-cells shown in FIG. 3 are composed of a single-sided positive electrode 301, a double-sided negative electrode 302, and a double-sided positive electrode 305, in which the mixture is applied only to one side of the current collector, and a single-sided negative electrode 304 and a double-sided positive electrode 303 And a double-sided cathode 302.

The single-sided positive electrode 301 is coated with a positive electrode mixture 312 only on one side of the current collector 311 facing the double-sided negative electrode 302, and the double-sided negative electrode 302 is formed on both sides of the negative electrode current collector 321. 322 is coated, and the positive electrode mixture 312 is coated on both sides of the current collector 313 in the double-sided positive electrode 305. The current collector 311 may be made of a material having a higher strength than the mechanical strength of the current collector 313, and the thickness of the current collector 311 is relatively smaller when compared to the thickness of the current collector 313. Can be made, or can be made with a larger thickness.

The single-sided negative electrode 304 is coated with a negative electrode mixture 322 only on one side of the current collector 321 facing the double-sided positive electrode 305, and the double-sided positive electrode 305 is formed on both sides of the positive electrode current collector 311. 312) is applied, and the negative electrode mixture 322 is coated on both sides of the current collector 323 as the double-sided negative electrode 302. The current collector 321 may be made of a material having a higher strength than the mechanical strength of the current collector 323, and the thickness of the current collector 321 is relatively smaller when compared to the thickness of the current collector 323. Can be made, or can be made with a larger thickness.

4 and 5 schematically show side views of an electrode assembly composed of unit cells disclosed in FIGS. 2 and 3. 4 and 5, the electrode assembly 400 of FIG. 4 is a stack manufactured by placing unit cells 410, 420, 430, 440, and 450 on a long sheet-shaped separator 461 and winding -It is a folding type electrode assembly, and the electrode assembly 500 of FIG. 5 is in a state in which unit cells 510, 520, 530, 540, and 550 are stacked, and a separator 561 is interposed between the unit cells. It is a lamination-stack type electrode assembly manufactured by bonding to each other.

The outermost electrode of the electrode assembly 400 has a positive electrode, the outermost positive electrode is made of a single-sided positive electrode coated with a positive electrode mixture only in the inner direction of the current collector, and the remaining electrodes except for the outermost positive electrode are double-sided electrodes. Done. The current collector of the single-sided positive electrode is made of a material having a relatively high mechanical strength compared to the current collector of the double-sided electrode, may be made of a relatively thin thickness, and may be made of a relatively larger thickness to increase strength.

The outermost electrode of the electrode assembly 500 has a positive electrode, the outermost positive electrode is made of a single-sided positive electrode coated with a positive electrode mixture only in the inner direction of the current collector, and the remaining electrodes except for the outermost positive electrode are double-sided electrodes. Done. The current collector of the single-sided positive electrode is made of a material having a relatively high mechanical strength compared to the current collector of the double-sided electrode, may be made of a relatively thin thickness, and may be made of a relatively larger thickness to increase strength.

Hereinafter, it will be described with reference to the embodiments of the present invention, but this is for easier understanding of the present invention, and the scope of the present invention is not limited thereto.

<Example 1>

The stack-folding electrode assembly of FIG. 4 is manufactured so that cross-sectional anodes are located on both outer sides of the electrode assembly in the outermost unit cell.

LiCoO ₂ was used as a positive electrode active material, and LiCoO ₂ 96 wt%, Super-P (conductive agent) 2.0 wt%, PVdF (binder) 2.0 wt% were added to NMP (N-methyl-2-pyrrolidone) as a solvent. After preparing the positive electrode mixture slurry, it was coated, dried, and pressed on one side of a current collector having a thickness of 10 μm and consisting of 74 atomic% iron, 18 atomic% chromium, and 8 atomic% nickel. A single-sided anode was prepared. In addition, a double-sided positive electrode was prepared by coating, drying, and pressing the positive electrode active material on both surfaces of an aluminum foil having a thickness of 12 μm.

Artificial graphite was used as the negative electrode active material, and 96.3% by weight of artificial graphite, 1.0% by weight of Super-P (conductive agent), and 2.7% by weight of PVdF (binder) were added to NMP as a solvent to prepare a negative electrode mixture slurry, A negative electrode was prepared by coating, drying and pressing on both sides on a copper foil having a thickness of 10 μm.

Manufacturing of secondary battery

After manufacturing a bicell as shown in FIGS. 2 and 3 by interposing a separator between the anode and the cathode, five bicells were placed on a long sheet-shaped separation film so that the bicell of FIG. 3 is located at the outermost side. An electrode assembly was manufactured by sequentially winding, and after the electrode assembly was embedded in a pouch-type battery case, a 1M LiPF ₆ carbonate-based solution electrolyte was injected to complete a secondary battery.

<Example 2>

A secondary battery was manufactured in the same manner as in Example 1, except that the thickness of the single-sided positive electrode current collector was 20 μm.

<Comparative Example 1>

All double-sided positive electrode current collectors constituting the electrode assembly were made of aluminum foil having a thickness of 12 μm, and the single-sided positive electrode current collector was made of aluminum foil having a thickness of 20 μm, and a secondary battery was prepared in the same manner as in Example 1. Was prepared.

<Experimental Example 1>

In order to measure the safety of the secondary batteries prepared in Examples 1 and 2 and Comparative Example 1, it was prepared in a fully charged state of 4.35V. Using a nail penetration tester, a nail with a diameter of 2.5 mm made of iron was passed through the center of the secondary battery from above to measure whether or not ignition.

At this time, the penetration speed of the nail was kept constant at 12 m/min, and the results are summarized in Table 1 below.

Fire or not Example 1 No ignition Example 2 No ignition Comparative Example 1 Ignited

As shown in Table 1, the secondary batteries according to the present invention did not cause a short circuit and thus did not ignite, whereas the secondary battery of Comparative Example 1 had short circuits and ignition.

As described above, since the electrode assembly according to the present invention has a structure including a high-strength current collector in a unit cell located at the outermost side, a secondary battery having high safety against external impact can be provided.

Those of ordinary skill in the field to which the present invention belongs will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

Claims (17)

An electrode assembly having a structure in which a plurality of unit cells are stacked with a separator or a separation sheet interposed therebetween,
The unit cells include bi-cells in which electrodes respectively located on both outer surfaces of each other have the same polarity;
Each of the outermost unit cells of the electrode assembly includes at least one single-sided electrode on which the electrode mixture is applied only to one surface of the current collector, and the remaining unit cells excluding the outermost unit cells are electrodes on both sides of the current collector. It consists of double-sided electrodes coated with a mixture;
The first current collector of the single-sided electrode has a mechanical strength of 150% to 500% with respect to the second current collector of the double-sided electrode having the same polarity as the single-sided electrode;
The first current collector comprises an alloy having an iron content of 55 atomic% to 75 atomic%, a chromium content of 12 atomic% to 30 atomic%, and a nickel content of 8 atomic% to 20 atomic%. Electrode assembly. The electrode assembly of claim 1, wherein the electrode assembly is a stack-type electrode assembly, a stack-folding-type electrode assembly, or a lamination-stack-type electrode assembly. The electrode assembly according to claim 1, wherein in the outermost unit cells, an electrode positioned on an outer surface of the electrode assembly is a single-sided electrode, and other electrodes except for the single-sided electrode are double-sided electrodes. The electrode assembly of claim 3, wherein the cross-sectional electrodes positioned on both outer surfaces of the electrode assembly are electrodes having the same polarity. The electrode assembly of claim 4, wherein cross-section electrodes positioned on both outer surfaces of the electrode assembly are positive electrodes. The electrode assembly of claim 1, wherein the first current collector and the second current collector are each a positive electrode current collector. The electrode assembly of claim 1, wherein the unit cells other than the outermost unit cells are bi-cells composed of double-sided electrodes. The method of claim 1,
The second current collector is an electrode assembly, characterized in that made of aluminum or aluminum alloy. The method of claim 1, wherein the first current collector is in the group consisting of tungsten (W), vanadium (V), copper (Cu), silicon (Si), manganese (Mn), carbon (C), and molybdenum (Mo). Electrode assembly, characterized in that it further comprises at least one metal element selected. The electrode assembly according to claim 9, wherein the amount of the added metal element is 1 atomic% to 10 atomic% based on the total amount of metal elements constituting the first current collector. The electrode assembly of claim 1, wherein the thickness of the first current collector is 20% to 100% of the thickness of the second current collector. The electrode assembly of claim 10, wherein the thickness of the first current collector is 30% to 80% of the thickness of the second current collector. The electrode assembly of claim 1, wherein the thickness of the first current collector is 110% to 400% of the thickness of the second current collector. The electrode assembly according to claim 1, wherein the single-sided electrode is coated with an electrode mixture on one side of the first current collector facing the double-sided electrode, and the other side opposite to the one side faces the outside of the electrode assembly. . A secondary battery, characterized in that the electrode assembly according to claim 1 is incorporated in a battery case. The secondary battery according to claim 15, wherein the battery case is made of a laminate sheet including a resin layer and a metal layer, and the metal layer is made of the same material as the first current collector. The secondary battery according to claim 15, wherein the battery case is made of a laminate sheet including a resin layer and a metal layer, and the metal layer is made of the same material as the second current collector.

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