KR102111116B1 - Electrode assembly and secondary battery comprising the same - Google Patents

Abstract

The present invention relates to an electrode assembly and a secondary battery including the same, and specifically includes a positive electrode, a separator, and a negative electrode, wherein at least one of the positive electrode and the negative electrode is coated with a first active material and a second active material on both sides of a current collector, respectively. It is an electrode comprising a coated layer, the loading amount of the first active material coating layer and the second active material coating layer is 1: 1.25 to 10 relates to a stacked or stacked-folding electrode assembly.
In the electrode assembly according to the present invention, the first active material coating layer and the second active material coating layer have different loading amounts, and thus, without being subjected to physical force from the outside, the electrode assembly has a curved shape due to a difference in volume expansion degree of the active material while being charged. Can have Therefore, the pressurization process in the conventional method for manufacturing a curved secondary battery can be omitted, and it is possible to solve the short circuit problem caused by the destruction of the positive electrode, the negative electrode and the separator and the short circuit caused by the pressurization from the outside, thereby improving the yield. I can do it.

Description

Electrode assembly and secondary battery comprising the same {ELECTRODE ASSEMBLY AND SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to an electrode assembly and a secondary battery comprising the same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing, and many studies have been conducted on lithium secondary batteries with high energy density and discharge voltage among such secondary batteries, and they have been commercialized and widely used. Is being used.

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

As such secondary batteries, electronic devices are becoming smaller and thinner in accordance with the consumer's preference, so to minimize unnecessary waste of space, miniaturization and thinning of the shape of the batteries are also required. Therefore, it is necessary to implement various shapes of the battery according to the shape of the device and to efficiently utilize the internal space of the device.

In particular, in recent years, since the device design itself is a very important factor in the consumer's product selection, various types of designs have been designed to deviate from the flat design considering the conventional productivity. For example, devices such as mobile phones and laptops may be designed with a curved surface for ergonomic design.

As described above, a number of designs with curved surfaces formed on the outer surface may be developed and put into practical use. However, since most of the manufactured batteries are flat, unnecessary space is wasted, and it is difficult to mount the battery stably due to the space. There is a problem that the battery may be damaged by flowing by an external impact.

Accordingly, when a curved surface is formed at a position where a battery is to be mounted in a device, a battery having a curved surface corresponding to a corresponding portion is required to be stably mounted on such a device.

On the other hand, as a related art related to a secondary battery having a curved surface, a battery cell having a curved shape and a battery pack including the same are disclosed in Korean Patent Registration No. 10-1161136. Specifically, as a method of manufacturing a battery cell curved with a radius of curvature (R), the radius of curvature (R) is in the range of 50 mm to 150 mm, and (a) an electrode assembly is mounted on a variable cell case and electrolyte is injected. Sealing in one state to manufacture an upright battery cell, and performing the initial charge and discharge; (b) a process of attaching the upright battery cell to a jig of an upper and lower separation type in which a curved battery cell shape having a radius of curvature (r) smaller than the radius of curvature R is imprinted, and then pressing it; And (c) taking out the battery cell by opening the jig, and then allowing the bending state to partially recover so that the radius of curvature R is made for a predetermined period of time. Gives

However, when manufacturing a battery cell having a curved shape by applying a physical force from the outside as described above, there is a problem that the active material or the separator is damaged.

Accordingly, there is a need to develop an electrode assembly capable of manufacturing a battery having a curved shape without damaging a battery cell.

Republic of Korea Patent Registration No. 10-1382554

The first technical problem to be solved of the present invention is to provide an electrode assembly capable of manufacturing a secondary battery curved in a curved shape with minimal damage to an active material or a separator.

The second technical problem to be solved of the present invention is to provide a secondary battery, a battery pack and a small mobile device including the electrode assembly.

In order to solve the above problems, the present invention includes an anode, a separator and a cathode,

At least one of the positive electrode and the negative electrode is an electrode including a coating layer coated with a first active material and a second active material on both sides of a current collector, and the loading amount of the first active material coating layer and the second active material coating layer is 1: 1.25 to 10 A stacked or stack-folded electrode assembly is provided.

In addition, the present invention includes the stacked or stacked-folding electrode assembly, the secondary battery is curved in a curved shape, the secondary battery, the battery pack is embedded in a pack case curved in a curved shape similar to the secondary battery And a small mobile device including the battery pack.

In the electrode assembly according to the present invention, the first active material coating layer and the second active material coating layer have different loading amounts, and thus, without being subjected to physical force from the outside, the electrode assembly has a curved shape due to a difference in volume expansion degree of the active material while being charged. Can have Therefore, the pressurization process in the conventional method of manufacturing a curved secondary battery can be omitted, and the breakage of the positive electrode, the negative electrode, and the separator that may occur in the pressurized state from the outside and the short circuit caused by this can be solved and the yield is improved. I can do it.

1 is a schematic cross-sectional view of an electrode assembly showing before and after charging of an electrode assembly according to an embodiment of the present invention.
2 is a schematic cross-sectional view of a current collector showing R1 and R2 when the current collector according to an embodiment of the present invention is curved in a curved shape.

Hereinafter, the present invention will be described in more detail to aid understanding of the present invention.

The terms or words used in the present specification and claims should not be interpreted as being limited to ordinary or lexical meanings, and the inventor can appropriately define the concept of terms in order to best describe his or her invention. Based on the principle that it should be interpreted as meanings and concepts consistent with the technical spirit of the present invention.

The terminology used herein is only used to describe exemplary embodiments, and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

In this specification, the terms "comprises", "haves" or "have" are intended to indicate the presence of implemented features, numbers, steps, elements or combinations thereof, one or more other features or It should be understood that the existence or addition possibilities of numbers, steps, elements, or combinations thereof are not excluded in advance.

The conventional curved secondary battery is manufactured by applying an external physical force, such as a pressing process, thereby causing side effects such as destruction of the positive electrode, the negative electrode and the separator, and a short circuit problem.

Accordingly, the present invention is to provide an electrode assembly capable of solving a high defect rate of a conventional secondary battery having a curved shape.

An electrode assembly according to an embodiment of the present invention includes a positive electrode, a separator, and a negative electrode, and at least one of the positive electrode and the negative electrode is an electrode including a coating layer coated with a first active material and a second active material on both sides of a current collector. , The loading amount of the first active material coating layer and the second active material coating layer may be a stacked or stacked-folding electrode assembly having a ratio of 1: 1.25 to 10.

At this time, a schematic diagram of a stacked or stacked-folding electrode assembly according to an embodiment of the present invention is shown in FIG. 1, and the stacked or stacked-folding electrode assembly of the present invention will be described in detail with reference to this.

The electrode assembly of the present invention includes a first active material coating layer and a second active material coating layer on both sides of the current collector. At this time, the loading amount of the first active material coating layer and the second active material coating layer is different, and when the battery is charged, the volume expansion of the second active material coating layer having a higher loading amount is greater than the volume expansion of the first active material coating layer. Therefore, the electrode assembly is bent so that the surface coated with the second active material is convex. As a result, the electrode assembly of the present invention can obtain an electrode assembly having a curved shape itself by charging the battery without receiving physical force from the outside.

The first active material coating layer and the second active material coating layer respectively applied in different amounts on both sides of the current collector and the current collector may be included only in the positive electrode, may be included only in the negative electrode, or may be included in both the positive electrode and the negative electrode. If, when both the positive electrode and the negative electrode include the first active material coating layer and the second active material coating layer, because the volume change of the negative electrode active material is usually larger than the positive electrode active material, the electrode assembly so that the surface coated with the second active material in the negative electrode is convex Can bend.

The loading amount of the first active material coating layer and the second active material coating layer may be 1: 1.25 to 10, preferably 1: 2 to 5. At this time, the loading amount refers to the weight of the active material coated per unit area. Since the amount of the second active material coating layer is larger than that of the first active material coating layer, volume expansion occurs more, so that the electrode assembly may be bent so that the surface coated with the second active material is convex.

If, when the loading amount of the second active material coating layer is less than 1.25 times compared to the loading amount of the first active material coating layer, the difference in volume expansion is not severe enough to bend the current collector, so a curved secondary battery cannot be manufactured. This may occur, and when the loading amount of the second active material coating layer is more than 10 times compared to the loading amount of the first active material coating layer, the separation membrane is distorted or the active material cannot be completely covered due to a difference in excessive volume expansion. A short circuit problem may occur in the secondary battery.

Particularly, in the case of a stacked or stacked-folding electrode assembly, since a large amount of active material can be loaded compared to a wound electrode assembly, there is an advantage of manufacturing a high-loading electrode assembly.

At least one of the first active material and the second active material included in the positive electrode is lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium cobalt-nickel oxide, lithium cobalt-manganese oxide, lithium manganese-nickel oxide and lithium cobalt- It may be one or more selected from the group consisting of nickel-manganese oxide. Specifically, lithium cobalt oxide or lithium cobalt-nickel-manganese oxide having a wide volume expansion during charging may be used.

At least one of the first active material and the second active material included in the negative electrode may be at least one selected from the group consisting of silicon-based materials, carbon-based materials, and silicon-carbon-based composite materials. A wide silicon-based material may be used, and more specifically, Si, SiO _x (0.03≤x≤2) and Si-Z alloy (where Z is an alkali metal, alkaline earth metal, group 13 element, group 14 element, It may be one or more selected from the group consisting of transition metals, rare earth elements, or combinations thereof, and not Si), but the type of the active material used for the positive electrode and the negative electrode is not limited thereto.

The thickness of the separator may be 5 to 20 μm. The current collector may have a thickness of 6 to 30 μm. If the thickness of the current collector is less than 6 μm, a problem that the strength of the manufactured secondary battery decreases may occur, and when the thickness of the current collector exceeds 30 μm, a problem that the secondary battery does not bend well may occur. Specifically, a copper foil of 6 to 20 μm as the negative electrode and an aluminum foil of 8 to 30 μm as the positive electrode may be used.

When the thickness of the separator, the current collector, the first and second positive electrode active material layers, and the first and second negative electrode active material layers is within the above range, the curvature of the secondary battery including the electrode assembly according to the present invention is easily expressed, There is an effect that the performance of the secondary battery is excellent.

As the separator, a sheet or a non-woven fabric made of an olefin-based polymer such as polypropylene such as chemical resistance and hydrophobicity, glass fiber, or polyethylene may be used, and when a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte serves as a separator. It may be, but the type of the membrane is not limited thereto, and a membrane having variability sufficient to accommodate warpage due to volume expansion of the active material may be appropriately selected and used.

As the current collector of the positive electrode and the negative electrode, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or a surface treated with carbon, nickel, titanium, silver, or the like on the surface of aluminum or stainless steel may be used. Specifically, aluminum may be used as the positive electrode current collector, and copper may be used as the negative electrode current collector, but is not limited thereto, and a metal or metal composite that can be varied depending on the volume expansion of the active material may be appropriately selected and used.

The electrode assembly is a stacked or stacked-folding electrode assembly, and may be formed by cutting and stacking electrodes in a certain shape. The electrode assembly may be sequentially superimposed on a full cell in which an anode, a separator, and a cathode are positioned as a basic unit, and a separation film may be interposed in each overlapping portion of the electrode. In addition, the electrode assembly may be an anode, a separator, a cathode, a bicell in which a separator and an anode are positioned, or a bicell in which a cathode, a separator, an anode, a separator, and a cathode are positioned as a basic unit, and the bicell A separation film may be interposed in each of the overlapping portions of.

The secondary battery according to an embodiment of the present invention may include the stacked or stacked-folding electrode assembly and bent in a curved shape.

When the stacked or stacked-folding electrode assembly is centered on a current collector, since the loading amounts of the first active material coating layer and the second active material coating layer on both sides are different, the secondary battery including the electrode assembly has high loading. The surface coated with the positive second active material may have a curved shape to be convex.

As shown in Fig. 2, in the cross section of the current collector in the electrode assembly, R1 is the shortest distance from the center point of the shortest distance between both ends of the current collector to the center point of the distance between both ends on the current collector. , When R2 is half of the shortest distance between both ends of the current collector, R2 / R1 may be 1 to 20, specifically 1 to 5.

If R2 / R1 is less than 1, the curvature of the secondary battery becomes too large, and a short circuit problem may occur. If the R2 / R1 is less than 20, a degree of deflection is insignificant, and thus a problem that cannot be applied to a curved device may occur.

According to an embodiment of the present invention, mounting the electrode assembly of claim 1 in a variable cell case and injecting an electrolyte solution to produce a battery cell (step 1); And charging the battery cell (step 2); provides a method for manufacturing a secondary battery comprising a.

Hereinafter, a method of manufacturing a secondary battery according to the present invention will be described in detail for each step.

In the method of manufacturing a secondary battery according to the present invention, step 1 is a step of manufacturing a battery cell by mounting the electrode assembly of claim 1 in a variable cell case and injecting an electrolyte.

In the electrode assembly of claim 1, the first active material coating layer and the second active material coating layer of different loading amounts are formed on both sides around the current collector, so that the surface coated with the second active material due to a difference in volume expansion through a subsequent filling process It can be convex and curved.

The variable cell case may be a pouch-shaped case made of a metal can or a laminate sheet comprising a metal layer and a resin layer, but is not limited thereto, and freely selecting a metal or resin that can be changed according to the volume expansion of the active material Can be used. The electrolyte is N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyl lactone, 1,2-dimethoxy ethane, tetrahydroxyfran (franc ), 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxorun, formamide, dimethylformamide, dioxorun, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate phosphate, trime Toxic methane, dioxoren derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyropionate, ethyl propionate, etc. can be used. However, it is not limited thereto.

On the other hand, it may further include the step of pressing after mounting the battery cell prepared in step 1 to the jig. Before performing the charging to generate the warpage of the battery cell, a small amount of physical pressure is applied to the battery cell in the same manner as the conventional method of manufacturing a secondary battery of a warped shape, and then the charging may be performed. By adding such a step, the secondary battery that is finally manufactured can easily adjust the degree of variation by being less curved or more curved than when the pressing step is not performed.

In the method of manufacturing a secondary battery according to the present invention, step 2 is a step of charging the battery cell. In the battery cell manufactured in step 1, the first active material coating layer and the second active material coating layer in the battery cell undergo volume expansion while being charged, and since the loading amount of the active material is different, the degree of volume expansion is also different and the second active material is coated. The battery cell itself may be warped so that the face is convex.

The charging of the battery cell is the shortest distance from the center point of the shortest distance between both ends of the current collector to the center point of the distance between both ends on the current collector, in the cross section of the current collector in the electrode assembly. , When R2 is half of the shortest distance between both ends of the current collector, it may be performed until R2 / R1 becomes greater than 0, specifically, 1 ≤ R2 / R1 ≤ 20.

If R2 / R1 is less than 1, the curvature of the secondary battery becomes too large, which may cause breakage and short circuit problems, and if it is more than 20, the degree of warpage may be insignificant and thus a problem that cannot be applied to a curved device may occur.

At this time, the charging of the battery cell may be performed at a temperature of 15 ℃ to 90 ℃. Specifically, it may be performed at room temperature of 20 ° C to 30 ° C, or may be performed in a hot pressurized environment of 45 ° C to 85 ° C.

On the other hand, when the secondary battery manufactured according to the present invention is discharged, the shape of the curve may be relaxed in a direction opposite to that of charging. Therefore, the shape of the secondary battery during charging and discharging can be applied to electronic devices that provide information or require aesthetics by changing the shape of the secondary battery visually and physically.

Or, in the manufacturing method of the secondary battery according to the present invention, further comprising the step of forming a fixed case surrounding the secondary battery curved in a curved shape prepared in step 2, to prevent the change during discharge as described above It might be. At this time, the fixing case is curved in a curved shape similar to that of the secondary battery to prevent the shape change of the secondary battery, and may surround the surface of the secondary battery or a portion close to the surface to securely fix the shape.

As the fixing case, a material having a high strength capable of withstanding the restoring force of the electrode assembly during discharge of the secondary battery may be used, and specifically, a fixing case including iron may be used, but the material of the fixing case is limited thereto. It does not work.

According to an embodiment of the present invention, the secondary battery provides a battery pack embedded in a pack case curved in a curved shape similar to the secondary battery. Since the battery pack includes a secondary battery manufactured by bending itself by varying the loading amount of the active material around the current collector of the electrode, there is little risk of destruction and short circuit, and thus it is possible to exhibit stable and excellent battery characteristics.

In addition, since the mobile devices are evolving into various shapes as minimizing unnecessary waste of space and serving as an aesthetic collection, the battery pack can be applied to the shape of such a small mobile device. The device may be a smart phone, a mobile phone, a notebook, a tablet PC, a watch, a TV, glasses, etc., but the field where the battery pack can be applied is not limited to a small mobile device, and is appropriate for devices having various curved shapes. It can be applied.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art to which the present invention pertains can easily practice. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

<Example 1>

Step 1: First positive electrode active material coating layer: Aluminum current collector: Second positive electrode active material coating layer: Porous polyethylene separator: Second negative electrode active material coating layer: Copper current collector: An electrode assembly in which the first negative electrode active material coating layer was sequentially stacked was prepared. At this time, LiCoO ₂ was used as the first and second positive electrode active materials, and Graphite / SiO was used as the first and second negative electrode active materials. The loading amount of the first positive electrode active material coating layer is 0.260 g / 25 cm ² , and the loading amount of the second positive electrode active material coating layer is 0.52 g / 25 cm ² , and the first negative active material has an N / P ratio with the first positive electrode active material. To be 107%, the second negative active material was prepared by setting the second positive active material to N / P ratio of 107%. (N / P ratio is the value obtained by dividing the discharge capacity per unit area of the cathode by the discharge capacity per unit area of the anode.)

 At this time, the first positive electrode active material coating layer: the loading amount ratio of the second positive electrode active material coating layer is 1: 2, the first negative electrode active material coating layer: the loading amount ratio of the second negative electrode active material coating layer is 1: 2, the first positive electrode active material coating layer: Aluminum current collector: Second positive electrode active material coating layer: Porous polyethylene separator: Second negative electrode active material coating layer: Copper current collector: First negative active material coating layer thickness is 70 μm, 12 μm, 125 μm, 18 μm, 135 μm, 10 μm, respectively. , 75 µm.

Step 2: The electrode assembly prepared in step 1 was placed in a pouch-shaped case made of a laminate sheet comprising an aluminum layer and a polypropylene layer, and a cell was prepared by injecting 1 M of LiPF ₆ dissolved electrolyte into a carbonate solvent.

Step 3: Charge the battery cell in CC / CV mode at room temperature (0.2C / 4.35V, 1 / 20C cut-off), so that in the cross section of the current collector in the electrode assembly, R1 is between both ends of the current collector. The shortest distance from the center point of the shortest distance to the center point of the distance between both ends on the current collector, and when R2 is half of the shortest distance between both ends of the current collector, R2 / R1 is a curved shape of 5 A curved secondary battery was prepared.

<Comparative Example 1>

In step 1 of Example 1, the first positive electrode active material coating layer: the second positive electrode active material coating layer loading amount ratio is 1: 0.5, the first negative electrode active material coating layer: the second negative electrode active material coating layer loading amount ratio is 1: 0.5 A secondary battery was manufactured in the same manner as in Example 1, except for one.

<Comparative Example 2>

In step 1 of Example 1, the first positive electrode active material coating layer: the loading amount ratio of the second positive electrode active material coating layer is 1:15, the first negative electrode active material coating layer: the loading amount ratio of the second negative electrode active material coating layer is 1:15 A secondary battery was manufactured in the same manner as in Example 1, except for one.

<Comparative Example 3>

The secondary battery was performed in the same manner as in Example 1, except that the battery cell manufactured in Step 2 of Example 1 was pressurized with a jig of an upper and lower separation type in which a curved battery cell shape was imprinted, and Step 3 was omitted. It was prepared.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concept of the present invention defined in the following claims are also provided. It belongs to the scope of the invention.

Claims (17)

It includes an anode, a separator and a cathode,
The positive electrode and the negative electrode both include a coating layer coated with a first active material and a second active material on both sides of the current collector,
The loading amount of the first active material coating layer and the second active material coating layer is 1: 1.25 to 10,
First positive electrode active material coating layer: positive electrode current collector: second positive electrode active material coating layer: separator: second negative electrode active material coating layer: negative electrode current collector: the first negative electrode active material coating is sequentially stacked,
A stacked or stacked-folded electrode assembly in which the volume change of the negative electrode active material is larger than that of the positive electrode active material.
According to claim 1,
The current collector has a thickness of 6 to 30 μm, characterized in that the stacked or stacked-folding electrode assembly.
According to claim 1,
At least one of the first active material and the second active material is Si, SiO _x (0.03≤x≤2) and Si-Z alloy (where Z is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal , A rare-earth element or a combination thereof, and not Si), at least one member selected from the group consisting of a stacked or stacked-folded electrode assembly.
According to claim 1,
At least one of the first active material and the second active material is a lithium cobalt oxide or a lithium-cobalt-nickel-manganese oxide stacked or stacked-fold electrode assembly.
A secondary battery comprising the stacked or stacked-folding electrode assembly of claim 1 and curved in a curved shape.
The method of claim 5,
In the cross section of the current collector in the electrode assembly, R1 is the shortest distance from the center point of the shortest distance between both ends of the current collector to the center point of the distance between both ends on the current collector, and R2 is the When half of the shortest distance between both ends, R2 / R1 is a secondary battery, characterized in that 1 to 20.
The method of claim 5,
In the cross section of the current collector in the electrode assembly, R1 is the shortest distance from the center point of the shortest distance between both ends of the current collector to the center point of the distance between both ends on the current collector, and R2 is the When half of the shortest distance between both ends, R2 / R1 is a secondary battery, characterized in that 1 to 5.
Mounting the electrode assembly of claim 1 in a variable cell case and injecting an electrolyte solution to produce a battery cell (step 1); And
A method of manufacturing a secondary battery comprising; charging the battery cell (step 2).
The method of claim 8,
The charging of the battery cell is the shortest distance from the center point of the shortest distance between both ends of the current collector to the center point of the distance between both ends on the current collector, in the cross section of the current collector in the electrode assembly. , When R2 is half of the shortest distance between both ends of the current collector, R2 / R1 is performed until it exceeds 0.
The method of claim 8,
The method of manufacturing a secondary battery, characterized in that charging of the battery cell is performed until 1 ≦ R2 / R1 ≦ 20.
The method of claim 8,
The method of manufacturing a secondary battery, characterized in that the charging of the battery cell is performed at 15 ℃ to 90 ℃.
The method of claim 8,
The method of manufacturing a secondary battery further comprising the step of pressing after mounting the battery cell prepared in step 1 to the jig.
The method of claim 8,
The variable cell case is a method of manufacturing a secondary battery, characterized in that the pouch-shaped case made of a metal can or a laminate sheet comprising a metal layer and a resin layer.
The method of claim 8,
The method of manufacturing a secondary battery further comprising the step of forming a fixed case surrounding the secondary battery curved in a curved shape manufactured in step 2.
A battery pack in which the secondary battery of claim 5 is embedded in a pack case which is curved in a curved shape similar to the secondary battery.
A small mobile device comprising the battery pack of claim 15.
The method of claim 16,
The device is a small mobile device, characterized in that the smart phone, mobile phone, laptop, tablet PC, watch, TV, glasses.

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