JP6981115B2 - Lithium ion secondary battery - Google Patents

Description

The present invention relates to a lithium ion secondary battery, and in particular, at least one of the electrodes of the outermost layer has a structure in which an electrode mixture layer is formed only on the inner surface of the electrode current collector in the stacking direction. Regarding lithium-ion secondary batteries.

A lithium ion secondary battery having a structure in which a plurality of positive electrodes and negative electrodes are laminated is known. In this lithium ion secondary battery, the positive electrode and the negative electrode each have a structure in which an electrode mixture layer containing an active material is formed on both sides of an electrode current collector.

Here, in the electrode of the outermost layer in the stacking direction, the electrode mixture layer formed on the outer surface of the electrode current collector does not contribute to the battery capacity. For this reason, a battery having a structure in which the electrode of the outermost layer is provided with an electrode mixture layer only on the inner surface of the electrode current collector is known.

However, when the electrode mixture layer is provided only on one side of the electrode current collector, when the electrode is pressed during battery manufacturing, the end side with respect to the center of the single-sided electrode is due to the stress difference on both sides of the single-sided electrode. The problem of bending outward in the stacking direction arises.

Therefore, in Patent Document 1, the bending of the single-sided electrode is suppressed by making the thickness of the electrode current collector of the outermost single-sided electrode thicker than the thickness of the electrode current collector of the other electrodes of the same electrode. The batteries that are designed to be used are listed.

Japanese Unexamined Patent Publication No. 2007-149349

However, if the thickness of the electrode current collector of the single-sided electrode of the outermost layer is made thicker than the thickness of the electrode current collector of the other electrodes of the same electrode, the current flowing to the outermost layer side becomes larger than that of the inner layer. .. As a result, when the battery is charged, lithium is likely to be deposited on the negative electrode located on the outermost layer side, which may reduce the life, reliability, and safety of the battery.

The present invention solves the above-mentioned problems, suppresses the bending of the single-sided electrode of the outermost layer in which the electrode mixture layer is formed only on the inner surface of the electrode current collector in the stacking direction, and suppresses the bending of the single-sided electrode on the outermost layer side. It is an object of the present invention to provide a lithium ion secondary battery capable of suppressing the precipitation of lithium on the negative electrode located in.

The lithium ion secondary battery of the present invention is
A lithium ion secondary battery having a laminate in which a plurality of positive electrodes and negative electrodes are alternately laminated.
With the plurality of positive electrodes,
With the plurality of the negative electrodes,
Equipped with
The electrodes other than the electrodes of the outermost layer of the laminated body have an electrode current collector and an electrode mixture layer formed on both sides of the electrode current collector.
At least one of the electrodes in the outermost layer of the laminated body has an electrode current collector and a single-sided electrode mixture layer formed only on the inner surface of the electrode current collector in the stacking direction.
The thickness of the electrode current collector on which the single-sided electrode mixture layer is formed is thicker than the thickness of the electrode current collectors of the other same electrode electrodes.
When the single-sided electrode having the single-sided electrode mixture layer is a positive electrode, the thickness of the single-sided electrode mixture layer is thinner than the thickness of the electrode mixture layer of the other positive electrode.
When the single-sided electrode is a negative electrode, the thickness of the positive electrode mixture layer facing the single-sided electrode mixture layer is thinner than the thickness of the electrode mixture layer of the other positive electrode.
It is characterized by that.

Wherein a capacity ratio of the negative electrode for the positive electrode, and the single-sided electrode, when the volume ratio of the single-sided electrode and the counter electrode X1, the capacity ratio of the positive electrode and the other of the anode and X2, 1 The relationship <X1 / X2 <1.5 can be established.

According to the present invention, the thickness of the electrode current collector on which the single-sided electrode mixture layer is formed is thicker than the thickness of the electrode current collectors of other isopolar electrodes, so that the single-sided electrode located in the outermost layer has a thickness. The bending can be suppressed. When the single-sided electrode is a positive electrode, the thickness of the single-sided electrode mixture layer is thinner than the thickness of the electrode mixture layer of the other positive electrode, and when the single-sided electrode is a negative electrode, the positive electrode faces the single-sided electrode mixture layer. Since the thickness of the electrode mixture layer of is thinner than the thickness of the electrode mixture layer of the other positive electrode, the capacity ratio of the one-sided electrode located in the outermost layer and the electrode facing the one-sided electrode is different. It is larger than the capacity ratio of the negative electrode and the positive electrode. As a result, when charging the lithium ion secondary battery, it is possible to suppress lithium precipitation at the negative electrode located on the outermost layer side where a larger current flows than the inner layer, and the battery life, reliability, and safety can be improved. Can be improved.

Further, in the lithium ion secondary battery according to the present invention, when the single-sided electrode is a negative electrode, the thickness of the single-sided negative electrode mixture layer of the single-sided negative electrode is not made thicker than the thickness of the negative electrode mixture layer of the other negative electrode. The thickness of the electrode mixture layer of the positive electrode facing the single-sided electrode mixture layer is thinner than the thickness of the electrode mixture layer of the other positive electrode. If the thickness of the single-sided negative electrode mixture layer of the single-sided negative electrode is made thicker than the thickness of the negative electrode mixture layer of the other negative electrode, the single-sided negative electrode may be curved. Can be suppressed.

It is sectional drawing of the lithium ion secondary battery which is the lithium ion secondary battery in one Embodiment of this invention, and the electrode of the outermost layer is a negative electrode. (A) is a diagram showing the configuration of a negative electrode other than the single-sided negative electrode located in the outermost layer among a plurality of laminated negative electrodes, and (b) is a diagram showing the configuration of a single-sided negative electrode located in the outermost layer. Is. (A) is a diagram showing the configuration of a positive electrode other than the positive electrode facing the single-sided negative electrode located in the outermost layer among a plurality of laminated negative electrodes, and (b) is a diagram showing the configuration of a single-sided negative electrode located in the outermost layer. It is a figure which shows the structure of the opposite positive electrode. It is sectional drawing of the main part of the lithium ion secondary battery which is the lithium ion secondary battery in one Embodiment of this invention, and the electrode of the outermost layer is a positive electrode. (A) is a diagram showing the configuration of a positive electrode other than the single-sided positive electrode located in the outermost layer among a plurality of laminated positive electrodes, and (b) is a diagram showing the configuration of a single-sided positive electrode located in the outermost layer. Is. FIG. 3 is a cross-sectional view of a main part of a lithium ion secondary battery according to an embodiment of the present invention, wherein one of the electrodes of the outermost layer is a positive electrode and the other is a negative electrode. (A) is a diagram showing the configuration of a positive electrode other than a single-sided positive electrode located in the outermost layer and a positive electrode facing the single-sided negative electrode located in the other outermost layer among a plurality of laminated positive electrodes (b). ) Is a diagram showing the configuration of the positive electrode facing the single-sided negative electrode, and (c) is a diagram showing the configuration of the single-sided positive electrode.

Hereinafter, embodiments of the present invention will be shown, and the features of the present invention will be described in more detail.

In the lithium ion secondary battery of the present invention, a plurality of positive electrodes and negative electrodes are alternately laminated, and at least one of the electrodes of the outermost layer is an electrode mixture only on the inner surface of the electrode current collector in the stacking direction. It has a structure in which layers are formed.

In the following, a configuration example in which the electrode of the outermost layer is a negative electrode will be described first, followed by a configuration example in which the electrode of the outermost layer is a positive electrode, and a configuration example in which one electrode of the outermost layer is a positive electrode and the other is a negative electrode. Will be described.

<When the outermost electrode is the negative electrode>
FIG. 1 is a cross-sectional view of a lithium ion secondary battery 100A according to an embodiment of the present invention, wherein the electrode of the outermost layer is a negative electrode. In the lithium ion secondary battery 100A, a laminate 10 formed by alternately stacking a plurality of positive electrodes 11 and 12 via a separator 13 and a non-aqueous electrolyte 14 are housed in a laminate case 20. Has a structure.

The laminated case 20 which is an exterior body is formed by thermocompression bonding the peripheral portions of a pair of laminated films 20a and 20b to each other.

The positive electrode terminal 16a is led out to the outside from one end side of the laminate case 20, and the negative electrode terminal 16b is led out to the outside from the other end side. The plurality of positive electrodes 11 are connected to the positive electrode terminals 16a via lead wires 15a. Further, the plurality of negative electrodes 12 are connected to the negative electrode terminals 16b via the lead wire 15b.

Of the plurality of laminated negative electrodes 12, the negative electrodes 12a other than the single-sided negative electrode 12b located in the outermost layer, that is, the negative electrodes 12a located inside the single-sided negative electrode 12b in the stacking direction are as shown in FIG. 2A. The negative electrode current collector 31a and the negative electrode mixture layer 32a formed on both sides of the negative electrode current collector 31a are provided.

On the other hand, as shown in FIG. 2B, the single-sided negative electrode 12b located in the outermost layer is a single-sided negative electrode mixture formed only on the inner surface of the negative electrode current collector 31b and the negative electrode current collector 31b in the stacking direction. It includes a layer 32b.

As the negative electrode current collectors 31a and 31b, for example, a metal foil such as copper can be used.

The thickness of the negative electrode current collector 31b of the single-sided negative electrode 12b is thicker than the thickness of the negative electrode current collector 31a of the other negative electrode 12a. Specifically, the thickness of the negative electrode current collector 31b is such that the occurrence of warpage (curvature) of the single-sided negative electrode 12b can be suppressed, and preferably the thickness at which the single-sided negative electrode 12b does not warp. With such a configuration, it is possible to prevent the single-sided negative electrode 12b from being warped when the single-sided negative electrode 12b is pressed in the battery manufacturing process.

The negative electrode mixture layer 32a and the single-sided negative electrode mixture layer 32b contain a negative electrode active material, and may further contain a binder and a conductive auxiliary agent. As the negative electrode active material, for example, artificial graphite can be used. The negative electrode mixture layer 32a and the single-sided negative electrode mixture layer 32b are made of the same material, and their thicknesses are substantially the same.

Among the positive electrodes 11, the positive electrodes 11a other than the positive electrode 11b facing the single-sided negative electrode 12b located in the outermost layer are formed on both sides of the positive electrode current collector 21 and the positive electrode current collector 21 as shown in FIG. 3A. The positive electrode mixture layer 22a is provided.

On the other hand, the positive electrode 11b facing the single-sided negative electrode 12b, that is, the positive electrode 11b located on the outermost side among the plurality of laminated positive electrodes 11, has the positive electrode current collector 21 and the positive electrode current collector 21 as shown in FIG. 3 (b). The positive electrode mixture layer 22a formed on the inner surface of the positive electrode current collector 21 in the stacking direction and the positive electrode mixture layer 22b formed on the outer surface of the positive electrode current collector 21 in the stacking direction are provided. The positive electrode mixture layer 22b faces the single-sided negative electrode mixture layer 32b of the single-sided negative electrode 12b via the separator 13.

As the positive electrode current collector 21, for example, a metal foil such as aluminum can be used. The thickness of the positive electrode current collector 21 of all the positive electrodes 11 is substantially the same.

The positive electrode mixture layers 22a and 22b contain a positive electrode active material, and may further contain a binder and a conductive auxiliary agent. As the positive electrode active material, for example, lithium cobalt oxide can be used. The positive electrode mixture layers 22a and 22b are made of the same material.

The thickness of the positive electrode mixture layer 22b of the positive electrode 11b facing the single-sided negative electrode mixture layer 32b of the single-sided negative electrode 12b is thinner than the thickness of the positive electrode mixture layer 22a of the other positive electrode 11a. More specifically, the thickness of the positive electrode mixture layer 22b of the positive electrode 11b is set to a thickness capable of suppressing lithium precipitation on the single-sided negative electrode 12b of the outermost layer.

That is, by making the thickness of the positive electrode mixture layer 22b of the positive electrode 11b thinner than the thickness of the positive electrode mixture layer 22a of the other positive electrode 11a, the single-sided negative electrode 12b located in the outermost layer and the single-sided negative electrode 12b face each other. The capacity ratio (A / C) of the positive electrode 11b is larger than the capacity ratio of the other negative electrodes 12a and the positive electrode 11a. As a result, when charging the lithium ion secondary battery 100A, it is possible to suppress lithium precipitation at the single-sided negative electrode 12b of the outermost layer in which a larger current flows than that of the inner layer.

Here, in order to make the capacity ratio of the single-sided negative electrode 12b located in the outermost layer and the positive electrode 11b facing the single-sided negative electrode 12b larger than the capacity ratio of the other negative electrode 12a and the positive electrode 11a, the single-sided negative electrode of the single-sided negative electrode 12b is used. It is also conceivable to make the thickness of the mixed material layer 32b thicker than the thickness of the negative electrode mixed material layer 32a of the other negative electrode 12a. However, if the thickness of the single-sided negative electrode mixture layer 32b is increased, the stress difference between both sides of the single-sided negative electrode 12b becomes large, and warpage may occur when the single-sided negative electrode 12b is pressed in the battery manufacturing process.

In the lithium ion secondary battery 100A of the present embodiment, the thickness of the single-sided negative electrode mixture layer 32b of the single-sided negative electrode 12b and the negative electrode mixture layer 32a of the other negative electrode 12a are substantially the same, and the thickness is substantially the same as that of the single-sided negative electrode mixture layer 32b. By making the thickness of the positive electrode mixture layer 22b of the positive electrode 11b facing each other thinner than that of the positive electrode mixture layer 22a of the other positive electrode 11a, the single-sided negative electrode 12b located in the outermost layer and the positive electrode facing the single-sided negative electrode 12b are used. The capacity ratio of 11b is set to be larger than the capacity ratio of the other negative electrode 12a and the positive electrode 11a. As a result, it is possible to suppress lithium precipitation on the single-sided negative electrode 12b of the outermost layer and suppress the occurrence of warpage of the single-sided negative electrode 12b.

Here, if the capacity ratio of the single-sided negative electrode 12b and the positive electrode 11b facing the single-sided negative electrode 12b is made too large, the potential of the positive electrode 11b rises and the oxidative deterioration of the positive electrode 11b is promoted. Therefore, assuming that the capacitance ratio of the single-sided negative electrode 12b and the positive electrode 11b facing the single-sided negative electrode 12b is X1 and the capacitance ratio of the other negative electrode 12a to the positive electrode 11a is X2, X1 / X2 is preferably less than 1.5. .. That is, it is preferable that the relationship of 1 <X1 / X2 <1.5 is established.

<When the outermost electrode is a positive electrode>
FIG. 4 is a cross-sectional view of a main part of the lithium ion secondary battery 100B according to the embodiment of the present invention, wherein the electrode of the outermost layer is a positive electrode. In FIG. 4, the same components as those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted.

Of the plurality of laminated positive electrodes 11, the positive electrodes 11a other than the single-sided positive electrode 11c located in the outermost layer are formed on both sides of the positive electrode current collector 21a and the positive electrode current collector 21 as shown in FIG. 5A. It is provided with a formed positive electrode mixture layer 22a.

On the other hand, as shown in FIG. 5B, the single-sided positive electrode 11c located in the outermost layer is a single-sided positive electrode mixture formed only on the inner surface of the positive electrode current collector 21c and the positive electrode current collector 21c in the stacking direction. It includes a layer 22c.

The thickness of the positive electrode current collector 21c of the single-sided positive electrode 11c is thicker than the thickness of the positive electrode current collector 21a of the other positive electrode 11a. Specifically, the thickness of the positive electrode current collector 21c is such that the occurrence of warpage (curvature) of the single-sided positive electrode 11c can be suppressed, and preferably the thickness at which the single-sided positive electrode 11c does not warp. With such a configuration, it is possible to suppress the warp of the single-sided positive electrode 11c when the single-sided positive electrode 11c is pressed in the battery manufacturing process.

The thickness of the single-sided positive electrode mixture layer 22c of the single-sided positive electrode 11c is thinner than the thickness of the positive electrode mixture layer 22a of the other positive electrode 11a. More specifically, the thickness of the single-sided positive electrode mixture layer 22c of the single-sided positive electrode 11c is set to a thickness capable of suppressing lithium precipitation at the negative electrode 12 facing the single-sided positive electrode 11c.

That is, by making the thickness of the single-sided positive electrode mixture layer 22c of the single-sided positive electrode 11c thinner than the thickness of the positive electrode mixture layer 22a of the other positive electrode 11a, the negative electrode 12 facing the single-sided positive electrode 11c of the outermost layer and one side. The capacity ratio of the positive electrode 11c is larger than the capacity ratio of the other negative electrodes 12 and the positive electrode 11a. As a result, when charging the lithium ion secondary battery 100B, it is possible to suppress lithium precipitation at the negative electrode 12 facing the single-sided positive electrode 11c through which a larger current flows than that of the inner layer.

The configuration of the plurality of laminated negative electrodes 12 is the same as the configuration of the negative electrodes 12a shown in FIG. 2A. That is, the negative electrode 12 includes a negative electrode current collector 31a and a negative electrode mixture layer 32a formed on both sides of the negative electrode current collector 31a.

<When one electrode of the outermost layer is a positive electrode and the other is a negative electrode>
FIG. 6 is a cross-sectional view of a main part of a lithium ion secondary battery 100C according to an embodiment of the present invention, wherein one of the electrodes on the outermost layer is a positive electrode and the other is a negative electrode. Is. In FIG. 6, the same components as those in FIGS. 1 and 4 are designated by the same reference numerals, and detailed description thereof will be omitted.

The plurality of laminated positive electrodes 11 include a single-sided positive electrode 11c located on one outermost layer, a positive electrode 11b facing the single-sided negative electrode 12b located on the other outermost layer, and other positive electrodes 11a.

As shown in FIG. 7A, the positive electrode 11a includes a positive electrode current collector 21a and a positive electrode mixture layer 22a formed on both sides of the positive electrode current collector 21.

On the other hand, as shown in FIG. 7B, the positive electrode 11b facing the single-sided negative electrode 12b has the positive electrode current collector 21a and the positive electrode mixture layer 22a formed on the inner surface of the positive electrode current collector 21a in the stacking direction. And the positive electrode mixture layer 22b formed on the outer surface of the positive electrode current collector 21 in the stacking direction. The positive electrode mixture layer 22b faces the single-sided negative electrode mixture layer 32b of the single-sided negative electrode 12b, which will be described later, via the separator 13.

Further, as shown in FIG. 7C, the single-sided positive electrode 11c located in the outermost layer is a single-sided positive electrode mixture formed only on the inner surface of the positive electrode current collector 21c and the positive electrode current collector 21c in the stacking direction. It includes a layer 22c.

The thickness of the positive electrode current collector 21c of the single-sided positive electrode 11c is thicker than the thickness of the positive electrode current collectors 21a of the other positive electrodes 11a and 11b. Specifically, the thickness of the positive electrode current collector 21c is such that the occurrence of warpage (curvature) of the single-sided positive electrode 11c can be suppressed, and preferably the thickness at which the single-sided positive electrode 11c does not warp. With such a configuration, it is possible to suppress the warp of the single-sided positive electrode 11c when the single-sided positive electrode 11c is pressed in the battery manufacturing process.

Further, the thickness of the single-sided positive electrode mixture layer 22c of the single-sided positive electrode 11c is thinner than the thickness of the positive electrode mixture layer 22a of the positive electrode 11a. More specifically, the thickness of the single-sided positive electrode mixture layer 22c of the single-sided positive electrode 11c is set to a thickness capable of suppressing lithium precipitation at the negative electrode 12a facing the single-sided positive electrode 11c.

That is, by making the thickness of the single-sided positive electrode mixture layer 22c of the single-sided positive electrode 11c thinner than the thickness of the positive electrode mixture layer 22a of the positive electrode 11a, the negative electrode 12a facing the single-sided positive electrode 11c of the outermost layer and the single-sided positive electrode 11c The capacity ratio of is larger than the capacity ratio of the negative electrode 12a and the positive electrode 11a on the inner layer side. As a result, when charging the lithium ion secondary battery 100C, it is possible to suppress lithium precipitation at the negative electrode 12a facing the single-sided positive electrode 11c through which a larger current flows than that of the inner layer.

Of the plurality of laminated negative electrodes 12, the negative electrodes 12a other than the single-sided negative electrode 12b located in the outermost layer are on both sides of the negative electrode current collector 31a and the negative electrode current collector 31a, as shown in FIG. 2A. The negative electrode mixture layer 32a formed is provided.

On the other hand, as shown in FIG. 2B, the single-sided negative electrode 12b located in the outermost layer is a single-sided negative electrode mixture formed only on the inner surface of the negative electrode current collector 31b and the negative electrode current collector 31b in the stacking direction. It includes a layer 32b.

The thickness of the negative electrode current collector 31b of the single-sided negative electrode 12b is thicker than the thickness of the negative electrode current collector 31a of the other negative electrode 12a. Specifically, the thickness of the negative electrode current collector 31b is such that the occurrence of warpage (curvature) of the single-sided negative electrode 12b can be suppressed, and preferably the thickness at which the single-sided negative electrode 12b does not warp. With such a configuration, it is possible to suppress the warp of the single-sided negative electrode 12b when the single-sided negative electrode 12b is pressed in the battery manufacturing process.

Further, the thickness of the positive electrode mixture layer 22b of the positive electrode 11b facing the single-sided negative electrode mixture layer 32b of the single-sided negative electrode 12b is thinner than that of the positive electrode mixture layer 22a of the positive electrode 11a (FIGS. 7A and 7B). reference). More specifically, the thickness of the positive electrode mixture layer 22b of the positive electrode 11b is set to a thickness capable of suppressing lithium precipitation on the single-sided negative electrode 12b of the outermost layer.

That is, by making the thickness of the positive electrode mixture layer 22b of the positive electrode 11b thinner than the thickness of the positive electrode mixture layer 22a of the other positive electrode 11a, the single-sided negative electrode 12b located in the outermost layer and the single-sided negative electrode 12b face each other. The capacity ratio of the positive electrode 11b is larger than the capacity ratio of the negative electrode 12a and the positive electrode 11a located on the inner layer side. As a result, when charging the lithium ion secondary battery 100C, it is possible to suppress lithium precipitation at the single-sided negative electrode 12b of the outermost layer in which a larger current flows than that of the inner layer.

The present invention is not limited to the above embodiment, and various applications and modifications can be added within the scope of the present invention.

In the above description, it is assumed that the electrodes located on both outer sides in the stacking direction are single-sided electrodes, but only one of the electrodes located on both outer sides in the stacking direction may be a single-sided electrode. ..

The present invention is not limited by the materials used for the positive electrode current collector and the negative electrode current collector, nor is it limited by the materials of the positive electrode mixture layer and the negative electrode mixture layer.

The exterior body may be a metal can instead of a laminated case.

10 Laminated body 11 Positive electrode 11a Positive electrode located in the inner layer 11b Positive electrode facing the single-sided negative electrode 11c Single-sided positive electrode 12 Negative electrode 12a Negative electrode located in the inner layer 12b Single-sided negative electrode 13 Separator 14 Non-aqueous electrolyte 16a Positive electrode terminal 16b Negative electrode terminal 20 Laminated cases 21, 21a , 21c Positive Electrode Collector 22a, 22b Positive Electrode Layer 22c Single-sided Positive Electrode Layer 31a, 31b Negative Electrode Collector 32a Negative Electrode Layer 32b Single-sided Positive Electrode Layer 100A, 100B, 100C Lithium Ion Secondary Battery

Claims (2)

A lithium ion secondary battery having a laminate in which a plurality of positive electrodes and negative electrodes are alternately laminated.
With the plurality of positive electrodes,
With the plurality of the negative electrodes,
Equipped with
The electrodes other than the electrodes of the outermost layer of the laminated body have an electrode current collector and an electrode mixture layer formed on both sides of the electrode current collector.
At least one of the electrodes in the outermost layer of the laminated body has an electrode current collector and a single-sided electrode mixture layer formed only on the inner surface of the electrode current collector in the stacking direction.
The thickness of the electrode current collector on which the single-sided electrode mixture layer is formed is thicker than the thickness of the electrode current collectors of the other same electrode electrodes.
When the single-sided electrode having the single-sided electrode mixture layer is a positive electrode, the thickness of the single-sided electrode mixture layer is thinner than the thickness of the electrode mixture layer of the other positive electrode.
When the single-sided electrode is a negative electrode, the thickness of the positive electrode mixture layer facing the single-sided electrode mixture layer is thinner than the thickness of the electrode mixture layer of the other positive electrode.
A lithium-ion secondary battery characterized by this. Wherein a capacity ratio of the negative electrode for the positive electrode, and the single-sided electrode, when the volume ratio of the single-sided electrode and the counter electrode X1, the capacity ratio of the positive electrode and the other of the anode and X2, 1 The lithium ion secondary battery according to claim 1, wherein the relationship <X1 / X2 <1.5 is established.

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