JP2020042958A - Negative electrode current collector foil of secondary battery and manufacturing method thereof, negative electrode of secondary battery, and manufacturing method thereof - Google Patents

Abstract

To provide a negative electrode current collector foil of a secondary battery and a manufacturing method thereof, a negative electrode of a secondary battery and a manufacturing method thereof capable using a high capacity negative electrode active material by having a suitable elastic limit stress σwhile making a cladding material with a low electrical resistivity (volume resistivity) Cu layer on both sides of a stainless steel layer composed of a precipitation hardening stainless steel into a foil with small thickness.SOLUTION: A negative electrode current collector foil (negative electrode current collector foil 5b) of a secondary battery includes a first Cu layer 51, a stainless steel layer 52 made of precipitation hardening stainless steel, and a second Cu layer 53, in this order, and the thickness is 20 μm or less, and the elastic limit stress σis 820 MPa or more.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a negative electrode current collector foil for a secondary battery and a method for manufacturing the same, and a negative electrode for a secondary battery and a method for manufacturing the same.

  BACKGROUND ART Conventionally, as a negative electrode current collector foil of a secondary battery, a clad material in which a Cu layer is pressed against both surfaces of a Ni-based alloy layer is known (see Patent Document 1).

  On the other hand, in recent years, in order to further improve the battery capacity of a secondary battery, there is a tendency to use a Si-based alloy or a Sn-based alloy having a large capacity instead of a conventional carbon-based material for a negative electrode active material. When a Si-based alloy or a Sn-based alloy is used as a negative electrode active material, the volume change of the Si-based alloy or the Sn-based alloy due to charge and discharge is larger than that of a conventional carbon-based material. As a result, the stress applied to the negative electrode current collector becomes larger than before.

Therefore, when a clad material having a Ni-based alloy layer as disclosed in Patent Document 1 is used for a negative electrode current collector foil and a Si-based alloy or a Sn-based alloy is used as a negative electrode active material, the negative electrode active Since the stress applied to the negative electrode current collector due to the volume change during charge / discharge of the substance exceeds the elastic limit stress σ _0.01 of the clad material, the clad material as the negative electrode current collector undergoes wrinkle-like deformation. There is a problem.

  Therefore, it has been proposed to use a clad material made of precipitation hardening stainless steel used for the terminal of the connector disclosed in Patent Document 2 for the negative electrode current collector. The clad material disclosed in Patent Literature 2 is configured by joining Cu or a Cu-based alloy to both surfaces of a precipitation hardening stainless steel before heat treatment, and has a thickness of about 0.1 mm to 1 mm. Further, in Patent Document 2, a SUS630 having a thickness of 1 mm is sandwiched from both sides by Cu (oxygen-free copper) having a thickness of 0.5 mm, and a clad material having a total thickness of 2 mm is repeatedly rolled to a thickness of 0.2 mm. It is disclosed to make a cladding material.

Japanese Patent No. 5329290 JP 2008-123964 A

Here, in recent years, it has been required to reduce the thickness of the negative electrode current collector used for the secondary battery into a foil shape of 20 μm or less. Therefore, the present inventor studied rolling the clad material disclosed in Patent Document 2 to a foil-like thickness of 20 μm or less, and found that the 0.1 mm-thick clad material in the rolled state had a thickness of 20 μm or less. The rolling reduction for rolling into a thick clad material is 80% or more, and the clad material may be broken. Therefore, it is necessary to appropriately perform annealing (softening annealing) for the purpose of softening while rolling the thickness of the clad material from 0.1 mm to 20 μm or less to prevent the clad material from breaking during rolling. However, when soft annealing is performed under general conditions, the metal element constituting the core material diffuses from the core material (precipitation hardening stainless steel) to the surface layer (Cu or Cu-based alloy), thereby increasing the thickness of the surface layer. It has been found that the ratio of the diffusion distance of the metal element to the cladding material increases, and the electrical resistivity (volume resistivity) of the clad material increases. In order to improve the mechanical strength of the clad material rolled to a thickness of 20 μm or less while performing soft annealing as described above, general aging treatment conditions for the precipitation hardening stainless steel constituting the core material are used. It was unclear whether a negative electrode current collector foil having appropriate electric resistance and elastic limit stress σ _0.01 was obtained when heat treatment was performed.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an electric resistivity (volume resistivity) on both surfaces of a stainless steel layer made of precipitation hardening stainless steel. The negative electrode of a secondary battery capable of using a high-capacity negative electrode active material by having a suitable elastic limit stress σ _0.01 while making the clad material provided with the Cu layer having a small An object of the present invention is to provide an electrical conductor foil and a method for manufacturing the same, and a negative electrode for a secondary battery and a method for manufacturing the same.

The inventor of the present application has made intensive studies to solve the above-described problems, and as a result, adjusted the thickness of a clad material having a Cu layer provided on both sides of a stainless steel layer made of precipitation hardening stainless steel to a foil shape of 20 μm or less. Later, it has been found that by performing heat treatment under specific conditions, the elastic limit stress σ _0.01 of the clad material can be made 820 MPa or more. Then, the present invention has been completed.

That is, the negative electrode current collector foil of the secondary battery according to the first aspect of the present invention includes a first Cu layer made of Cu or a Cu-based alloy, and a stainless steel layer made of precipitation hardening stainless steel, A second Cu layer made of Cu or a Cu-based alloy is arranged in this order, the overall thickness is 20 μm or less, and the elastic limit stress σ _0.01 is 820 MPa or more.

In the negative electrode current collector foil of the secondary battery according to the first aspect of the present invention, as described above, the thickness of the negative electrode current collector foil is 20 μm or less, and the elastic limit stress σ _0.01 is 820 MPa. That is all. With such a configuration, plastic deformation is not performed with a stress of less than 820 MPa, and thus deformation of the high-capacity negative electrode active material due to a stress caused by a volume change during charge and discharge can be suppressed. Thereby, it is possible to provide a negative electrode current collector foil for a secondary battery that can use a high-capacity negative electrode active material while having a foil-like small thickness of 20 μm or less. Here, the present inventor has confirmed in an experiment described later that the elastic limit stress σ _0.01 of the negative electrode current collector foil of the secondary battery is 820 MPa or more. The “elastic limit stress σ _0.01 ” means not only a stress at which a permanent strain remaining on the negative electrode current collector foil after unloading in a tensile test becomes 0.01%, but also a plastic deformation (permanent strain). When the foil for a negative electrode current collector is broken in a state of substantially elastic deformation of less than 0.01%, this is a broad concept meaning the stress (tensile strength) when the foil for a negative electrode current collector breaks. .

In the foil for a negative electrode current collector of a secondary battery according to the first aspect, preferably, the elastic limit stress σ _0.01 is 906 MPa or more. Here, the inventor of the present application has confirmed in an experiment described later that the elastic limit stress σ _0.01 of the negative electrode current collector foil of the secondary battery is 906 MPa or more. Thereby, even if the stress applied to the negative electrode current collector foil is increased by using a high capacity negative electrode active material, plastic deformation of the negative electrode current collector foil can be sufficiently suppressed.

  In the foil for a negative electrode current collector of a secondary battery according to the first aspect, preferably, the precipitation-hardening stainless steel constituting the stainless steel layer contains 15% by mass to 19% by mass of Cr, 6% by mass to 9% by mass. Wt% or less Ni, 0.5 wt% or more and 2.0 wt% or less Al, 0.01 wt% or more and 0.3 wt% or less C, and 0.01 wt% or more and 0.3 wt% or less N , The balance being Fe and unavoidable impurities. With this configuration, the precipitation-hardened stainless steel is subjected to heat treatment to generate fine precipitates of Al and Ni in the structure of the stainless steel layer and fix dislocations by C and N. Thereby, the elastic limit stress σ0.01 of the stainless steel layer and the negative electrode current collector foil can be improved.

  In the foil for a negative electrode current collector of a secondary battery according to the first aspect, the metal element constituting the precipitation hardening stainless steel is diffused into the first Cu layer and the second Cu layer, and a part of the diffused metal element is diffused. Present as precipitates. With this configuration, a part of the metal element diffused in the first Cu layer and the second Cu layer is changed from a solid solution state to a precipitated state, so that the electric resistance of the negative electrode current collector foil can be further reduced.

  In the foil for a negative electrode current collector of a secondary battery according to the first aspect, the volume resistivity is preferably 6 μΩ · cm or less. With this configuration, since the volume resistivity is low, the conductivity of the negative electrode current collector foil can be improved. Therefore, it is possible to provide a negative electrode current collector foil for a secondary battery having a thickness of 20 μm or less and having a sufficient elastic limit and conductivity.

In the foil for a negative electrode current collector of a secondary battery according to the first aspect, preferably, the first Cu layer, the stainless steel layer, and the second Cu layer are formed of a clad material that is stacked and joined in this order. ing. According to this structure, the negative electrode current collector foil in which the first Cu layer and the second Cu layer and the stainless steel layer are joined with a strong adhesive force by diffusion bonding has a thickness of 20 μm or less, and It is possible to provide a negative electrode current collector foil having an elastic limit stress σ _0.01 .

In the foil for a negative electrode current collector of a secondary battery according to the first aspect of the present invention, preferably, the first Cu layer and the second Cu layer are plating layers. With such a configuration, the thickness of the first Cu layer and the second Cu layer can be easily reduced, so that the thickness of the secondary battery having a thickness of 20 μm or less and having a sufficient elastic limit stress σ _0.01 is reduced. A foil for a negative electrode current collector can be easily provided.

In the negative electrode of the secondary battery according to the second aspect of the present invention, a negative electrode active material made of a Si-based alloy or a Sn-based alloy is fixed to the surface of the negative electrode current collector foil according to the first aspect. With this configuration, since the negative electrode current collector foil has a sufficient elastic limit stress σ _0.01 , the charge / discharge of a high-capacity negative electrode active material made of a Si-based alloy or a Sn-based alloy can be performed. Can withstand large volume changes. Therefore, even when a high-capacity negative electrode active material such as a Si-based alloy or a Sn-based alloy is used, it is possible to suppress wrinkle-like deformation of the negative electrode current collector foil constituting the negative electrode.

A method for manufacturing a negative electrode current collector foil for a secondary battery according to a third aspect of the present invention includes a first Cu layer made of Cu or a Cu-based alloy, and a stainless steel layer made of a precipitation hardening stainless steel. , And a second Cu layer made of Cu or a Cu-based alloy are laminated in this order to produce a Cu-coated foil having a first thickness exceeding 20 μm. After rolling to the following second thickness, heat treatment is performed at a temperature of 280 ° C. or more and less than 400 ° C. for 1 hour or more and 20 hours or less, and a Cu-coated foil having an elastic limit stress σ _0.01 of 820 MPa or more Get. In the present invention, the case of heating in a low temperature range (for example, less than 400 ° C.) for the purpose of improving the mechanical strength of the precipitation hardening stainless steel is referred to as “heat treatment”, and in a high temperature range (for example, 800 ° C. or more). The case where heating is performed by is referred to as annealing (diffusion annealing, softening annealing), and the two are used separately.

  In the method for producing a negative electrode current collector foil for a secondary battery according to the third aspect of the present invention, as described above, after the Cu-coated foil is rolled to have a second thickness of 20 μm or less, the temperature is 280 ° C. or higher. Heat treatment is performed at a temperature of less than 400 ° C. for 1 hour to 20 hours. With such a configuration, the obtained negative electrode current collector foil does not undergo plastic deformation with a stress of less than 820 MPa, and thus deforms with a stress caused by a volume change during charge and discharge of a high-capacity negative electrode active material. Can be suppressed. Therefore, a negative electrode current collector foil for a secondary battery that can use a high-capacity negative electrode active material while having a foil-like small thickness of 20 μm or less can be easily manufactured.

In the method for manufacturing a negative electrode current collector foil for a secondary battery according to the third aspect, preferably, the heat treatment is performed to obtain a Cu-coated foil having an elastic limit stress σ _0.01 of 906 MPa or more. According to this structure, the heat treatment generates fine precipitates of Al and Ni in the structure of the stainless steel layer, and causes dislocations to be fixed by C and N. Thereby, the elastic limit stress σ _0.01 of the stainless steel layer and the negative electrode current collector foil can be easily improved.

In the method for producing a negative electrode current collector foil for a secondary battery according to the third aspect, preferably, the heat treatment is performed for 3.5 hours or more and 20 hours or less. Here, the inventor of the present application has found that a Cu-coated foil having an elastic limit stress σ _0.01 of 820 MPa or more can be produced by performing the heat treatment for 3.5 hours or more. Therefore, with this configuration, a Cu-coated foil having an elastic limit stress σ _0.01 of 820 MPa or more can be reliably manufactured.

  In the method for producing a negative electrode current collector foil for a secondary battery according to the third aspect, preferably, the metal element constituting the precipitation hardening stainless steel is diffused into the first Cu layer and the second Cu layer of the Cu-coated foil. At the same time, a part of the diffused metal element is deposited as a precipitate. With this configuration, a part of the metal element diffused in the first Cu layer and the second Cu layer is changed from a solid solution state to a precipitated state, so that the electric resistance of the negative electrode current collector foil can be further reduced.

In the method for manufacturing a negative electrode current collector foil for a secondary battery according to the third aspect, preferably, a Cu plate composed of Cu or a Cu-based alloy, and a stainless steel plate material composed of a precipitation hardening stainless steel , And a Cu plate made of Cu or a Cu-based alloy are laminated in this order, rolled so as to have a first thickness, and then annealed, so that a Cu-coated foil formed of a clad material and having a first thickness Is prepared. According to this structure, the negative electrode current collector foil in which the first Cu layer and the second Cu layer and the stainless steel layer are joined with a strong adhesive force by diffusion bonding has a thickness of 20 μm or less, and A negative electrode current collector foil having an elastic limit stress σ _0.01 can be produced.

In the method for producing a negative electrode current collector foil for a secondary battery according to the third aspect, preferably, Cu or a Cu-based alloy is plated on both surfaces of a stainless steel sheet material composed of precipitation-hardened stainless steel, A Cu-coated foil in which a first Cu layer and a second Cu layer formed of a Cu plating layer made of Cu or a Cu-based alloy on both surfaces of a stainless steel layer is prepared. With such a configuration, the thickness of the first Cu layer and the second Cu layer can be easily reduced, so that the thickness of the secondary battery having a thickness of 20 μm or less and having a sufficient elastic limit stress σ _0.01 is reduced. A foil for a negative electrode current collector can be easily produced.

  In the method for manufacturing a negative electrode of a secondary battery according to the fourth aspect of the present invention, the first Cu layer made of Cu or Cu-based alloy, the stainless steel layer made of precipitation hardening stainless steel, A second Cu layer made of an alloy is arranged in this order, and a negative electrode active material made of a Si-based alloy or a Sn-based alloy, a binder, and a binder are provided on the surface of a negative electrode current collector foil having an overall thickness of 20 μm or less. Is placed, and heat treatment is performed at a temperature of 280 ° C. or more and less than 400 ° C. for 1 hour or more and 20 hours or less to fix the negative electrode active material to the surface of the negative electrode current collector foil.

In the method for manufacturing a negative electrode of a secondary battery according to the fourth aspect of the present invention, as described above, the negative electrode current collector foil having a thickness of 20 μm or less is heated at a temperature of 280 ° C. or more and less than 400 ° C. for 1 hour to 20 hours. The holding heat treatment is performed below. With such a configuration, the elastic limit stress σ _0.01 is improved by the heat treatment, and the electric resistance is reduced. Therefore, the electrical resistance and the elastic limit stress σ _0.01 of the negative electrode current collector foil can be set to appropriate ranges. As a result, a high capacity negative electrode having a high elastic limit stress σ _0.01 and using a negative electrode active material such as a Si-based alloy or a Sn-based alloy can be obtained.

In the method for manufacturing a negative electrode of a secondary battery according to the fourth aspect of the present invention, preferably, the heat treatment is performed for 3.5 hours or more and 20 hours or less. With such a configuration, the electrical resistance and the elastic limit stress σ _0.01 of the negative electrode current collector foil can be set in more appropriate ranges. Here, the inventors of the present application have confirmed in an experiment described later that the elastic limit stress σ _0.01 can be set in an appropriate range.

According to the present invention, as described above, a clad material in which a Cu layer having a small electric resistivity (volume resistivity) is provided on both surfaces of a stainless steel layer made of precipitation hardening stainless steel is reduced to a foil-like small thickness. While having a suitable elastic limit stress σ _0.01 , a negative electrode current collector foil of a secondary battery capable of using a high capacity negative electrode active material and a method of manufacturing the same, a negative electrode of a secondary battery and manufacture thereof A method can be provided.

FIG. 3 is a schematic sectional view showing a battery using the negative electrode current collector foil according to the first and second embodiments of the present invention. FIG. 2 is a cross-sectional view illustrating a negative electrode using the negative electrode current collector foil according to the first embodiment of the present invention. It is a mimetic diagram for explaining the manufacturing method of the negative electrode current collector foil according to the first embodiment of the present invention. FIG. 6 is a cross-sectional view illustrating a negative electrode using a negative electrode current collector foil according to a second embodiment of the present invention. It is a schematic diagram for explaining the manufacturing method of the negative electrode current collector foil according to the second embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
First, the structure of the battery 100 using the negative electrode current collector foil 5b according to the first embodiment of the present invention will be described with reference to FIGS.

(Battery structure)
The battery 100 using the negative electrode current collector foil 5b according to the first embodiment of the present invention is a so-called cylindrical (also called can-type) lithium ion secondary battery as shown in FIG. The battery 100 includes a cylindrical housing 1, a cover member 2 that seals an opening of the housing 1, and a power storage element 3 disposed in the housing 1.

  The housing 1 contains the electricity storage element 3 and an electrolyte (not shown). The lid member 2 is made of an aluminum alloy or the like, and also serves as a positive electrode terminal of the battery 100 (battery positive electrode). The electric storage element 3 is manufactured by winding a positive electrode 4, a negative electrode 5, and an insulating separator 6 disposed between the positive electrode 4 and the negative electrode 5. The positive electrode 4 includes a positive electrode active material such as lithium cobalt oxide and a positive electrode current collector (positive electrode current collector foil) made of aluminum foil. On the surface of the positive electrode current collector (positive electrode current collector foil), a positive electrode active material is fixed with a binder or the like. Further, a positive electrode lead member 7 for electrically connecting the lid member 2 and the positive electrode 4 is fixed to the positive electrode 4. The negative electrode 5 is an example of the “negative electrode of a secondary battery” in the claims.

  As shown in FIG. 2, the negative electrode 5 includes a negative electrode active material 5a, a negative electrode current collector (hereinafter, referred to as a negative electrode current collector foil 5b), and a binder 5c for fixing the negative electrode active material 5a to the negative electrode current collector foil 5b. Contains. The negative electrode active material 5a is made of a Si-based alloy or a Sn-based alloy, which is a material into which lithium can be inserted and desorbed. A Si-based alloy or a Sn-based alloy has a larger charge / discharge capacity than a carbon-based material, and a high-capacity battery can be obtained by using a Si-based alloy or a Sn-based alloy. The negative electrode active material 5a expands and contracts according to insertion and desorption of lithium, respectively. The binder 5c may be made of, for example, at least one of polyimide, polyamide, and polyamideimide. As shown in FIG. 1, a negative electrode lead member 8 for electrically connecting the inner bottom surface 1 a of the housing 1 and the negative electrode 5 is fixed to the negative electrode 5. The negative electrode current collector foil 5b is an example of the “foil for a negative electrode current collector of a secondary battery” in the claims.

(Configuration of negative electrode current collector)
Here, in the first embodiment, the negative electrode current collector foil 5b is made of a first Cu layer 51 made of Cu or Cu-based alloy, a stainless steel layer 52 made of precipitation hardening stainless steel, and Cu or Cu-based alloy. And a second clad layer 53 having a three-layer structure. Note that some of the metal elements constituting the stainless steel layer 52 are annealed for the purpose of strengthening the bonding between the first Cu layer 51 and the second Cu layer 53 described below and the stainless steel layer 52 (diffusion annealing shown in FIG. 3). In the annealing for the purpose of softening (softening annealing shown in FIG. 3), the stainless steel layer 52 diffuses into the first Cu layer 51 and the second Cu layer 53. At this time, some of the metal elements constituting the stainless steel layer 52 diffused at the bonding interface 52a between the stainless steel layer 52 and the first Cu layer 51 are combined with Cu (element) constituting the first Cu layer 51. Further, some of the metal elements constituting the stainless steel layer 52 diffused at the bonding interface 52b between the stainless steel layer 52 and the second Cu layer 53 are combined with Cu (element) constituting the second Cu layer 53. Thereby, the first Cu layer 51 and the second Cu layer 53 and the stainless steel layer 52 are joined with strong adhesion. In addition, some of the metal elements diffused from the stainless steel layer 52 into the first Cu layer 51 and the second Cu layer 53 are subjected to a first Cu treatment by a heat treatment for improving mechanical strength (particularly 0.01% proof stress) described later. It is deposited in the layer 51 and the second Cu layer 53.

The precipitation hardening type stainless steel constituting the stainless steel layer 52 generates fine precipitates by performing the heat treatment, and the elastic limit stress σ _0, which is a kind of mechanical strength, is generated by generating the fine precipitates. _.01 can be increased. Examples of the precipitation hardening stainless steel include SUS630 and SUS631 based on JIS G4305. The precipitation hardening stainless steel is composed of 15% by mass to 19% by mass of Cr (chromium), 6% by mass to 9% by mass of Ni (nickel), and 0.5% by mass to 2.0% by mass. It is composed of Al (aluminum), 0.01% to 0.3% by mass of C (carbon), 0.01% to 0.3% by mass of N (nitrogen), balance Fe and inevitable impurities. It is preferably stainless steel.

  When SUS631 or stainless steel having the above composition is used as the precipitation hardening stainless steel, fine particles of Al or Ni-containing intermetallic compound are generated as precipitates in the stainless steel layer 52. And disperse.

  The first Cu layer 51 and the second Cu layer 53 are layers formed using Cu plate materials (the first Cu plate material 151 and the second Cu plate material 153) containing 99% by mass or more of Cu, and are mainly made of Cu (copper). (See FIG. 3). Further, the first Cu layer 51 and the second Cu layer 53 contain a part of the metal elements constituting the stainless steel layer 52. As described above, the annealing described below causes diffusion of the metal element mainly in the region on the stainless steel layer 52 side of the first Cu layer 51 and the second Cu layer 53. Therefore, part of the diffused metal element is formed as a precipitate by heat treatment. It is present in the first Cu layer 51 and the second Cu layer 53. Thereby, a part of the metal element diffused in the first Cu layer 51 and the second Cu layer 53 is changed from a solid solution state to a precipitated state, so that the electric resistance of the negative electrode current collector foil can be further reduced.

  Specifically, when SUS631 or a precipitation-hardening stainless steel having the above composition is used as the precipitation-hardening stainless steel constituting the stainless steel layer 52, for example, the first Cu layer 51 and the second Cu layer 53 include: Al, Fe, Cr and Ni are diffused. When SUS630 is used as the precipitation hardening stainless steel constituting the stainless steel layer 52, for example, Fe and Cr are diffused in the first Cu layer 51 and the second Cu layer 53.

In the first embodiment, the elastic limit stress σ _0.01 of the negative electrode current collector foil 5b is 820 MPa or more. Thus, when a stress of less than 820 MPa is applied to the negative electrode current collector foil 5b, the negative electrode current collector foil 5b undergoes almost no plastic deformation but only elastic deformation. As a result, even when the battery 100 is repeatedly charged and discharged, it is possible to sufficiently suppress the occurrence of wrinkle-like irregularities on the negative electrode current collector foil 5b. The elastic limit stress σ _0.01 of the negative electrode current collector foil 5b is more preferably 906 MPa or more. The upper limit may be, for example, 1200 MPa or less, 1100 MPa or less, 1000 MPa or less, or less than 1000 MPa as needed.

  Further, as shown in FIG. 2, the length (thickness) t1 of the Cu coating foil 50 constituting the negative electrode current collector foil 5b in the Z direction is 20 μm or less. Note that the thickness t1 is preferably 10 μm or less.

  In the Z direction, the thickness ratio of the first Cu layer 51, the stainless steel layer 52, and the second Cu layer 53 (the thickness t2 of the first Cu layer 51: the thickness t3 of the stainless steel layer 52: the thickness t4 of the second Cu layer 53) is , For example, 1: 3: 1.

  In the first embodiment, the negative electrode current collector foil 5b has a volume resistivity (electric resistance per unit volume) of 6 μΩ · cm or less. Thereby, the conductivity of the negative electrode current collector foil 5b becomes 28.7% IACS or more. In addition, “the conductivity of the negative electrode current collector foil 5b is 28.7% IACS or more” means that the conductivity of the international standard soft copper having a volume resistivity of 1.7241 μΩ · cm is 100%. This means that the electrical conductivity of the electrofoil 5b is 28.7 (= 1.7241 (μΩ · cm) / 6 (μΩ · cm) × 100)% IACS or more.

(Configuration of negative electrode)
As shown in FIG. 2, the negative electrode 5 has a surface 51 a of the negative electrode current collector foil 5 b opposite to the side joined to the stainless steel layer 52 of the first Cu layer 51, and a stainless steel layer 52 of the second Cu layer 53. The negative electrode active material 5a is fixed to the surface 53a on the side opposite to the side to be joined with the binder 5c.

(Manufacturing process of negative electrode current collector foil)
Next, a manufacturing process of the negative electrode current collector foil 5b in the first embodiment will be described with reference to FIGS.

  First, as shown in FIG. 3, a stainless steel plate member 152 made of precipitation hardening stainless steel, a first Cu plate member 151 containing 99% by mass or more of Cu and a second Cu plate member 153 containing 99% by mass or more of Cu are prepared. . Here, the thickness ratio of the first Cu plate 151, the stainless steel plate 152, and the second Cu plate 153 (thickness of the first Cu plate 151: thickness of the stainless steel plate 152: thickness of the second Cu plate 153) is "1: 3: The stainless steel plate 152, the first Cu plate 151, and the second Cu plate 153 are prepared so as to be “1”. In addition, the thickness of the stainless steel plate 152, the first Cu plate 151, and the second Cu plate 153 is more than 20 μm in order to be easily prepared and to suppress occurrence of breakage or the like in rolling described later. Is preferred. For example, the thickness of the stainless steel plate 152 is 0.50 mm, and the thickness of both the first Cu plate 151 and the second Cu plate 153 is 0.17 mm.

  The first Cu plate 151 and the second Cu plate 153 are both oxygen-free copper containing 99.96% by mass or more of Cu, phosphorus deoxidized copper containing 99.75% by mass or more of Cu, or 99.9% by mass of Cu. % Or more. The first Cu plate 151 and the second Cu plate 153 may be made of Cu plates having the same composition, or may be made of Cu plates having different compositions.

  Then, in a state where the stainless steel plate member 152 is sandwiched in the thickness direction between the first Cu plate member 151 and the second Cu plate member 153, the roll bonding is performed using the rolling roll 101 under cold conditions (room temperature, for example, about 20 ° C. to about 40 ° C.). I do. As a result, a Cu-coated intermediate material 150a having a first thickness exceeding 20 μm, in which the first Cu plate material 151 and the second Cu plate material 153 are respectively joined in layers on both surfaces of the stainless steel plate material 152, is produced. Thereafter, the Cu-coated intermediate material 150a is rolled under cold (room temperature) using the rolling rolls 102 to produce the Cu-coated foil 150b (first rolling step). At this time, the rolling reduction is set, for example, to 50% or more and 80% or less.

  Then, annealing (diffusion annealing) is performed on the Cu-coated foil 150b for the purpose of strengthening the bonding between the first Cu plate 151 and the second Cu plate 153 and the stainless steel plate 152 in a state of being pressed in layers. Specifically, the Cu-coated foil 150b is passed through the annealing furnace 103 in a non-oxidizing atmosphere such as a nitrogen atmosphere. At this time, the temperature is maintained in the annealing furnace 103 set at a temperature of 830 ° C. to 1050 ° C. (preferably 830 ° C. to 950 ° C.) for 30 seconds to 5 minutes (preferably 30 seconds to 90 seconds). The Cu-coated foil 150b is placed in the annealing furnace 103 so as to be processed.

  Thus, a Cu-coated foil 150c made of a clad material in which the first Cu layer 51 made of the first Cu plate material 151 and the second Cu layer 53 made of the second Cu plate material 153 are joined to both surfaces of the stainless steel layer 52 made of the stainless steel sheet material 152 is formed. It is made. In addition, due to diffusion annealing, a part of the metal element forming the stainless steel layer 52 is diffused at the bonding interface 52a between the stainless steel layer 52 and the first Cu layer 51, and the Cu (element) forming the first Cu layer 51 is diffused. At the same time, they are diffused at the joint interface 52b between the stainless steel layer 52 and the second Cu layer 53, and are combined with Cu (element) constituting the second Cu layer 53.

  Further, in the Cu-coated foil 150c subjected to the diffusion annealing, a part of the metal element contained in the stainless steel sheet material 152 constituting the stainless steel layer 52 becomes part of the first Cu layer 51 and the second Cu layer 53 due to the heat during the diffusion annealing. Has spread to. For example, the stainless steel layer 52 has 15% to 19% by mass of Cr, 6% to 9% by mass of Ni, 0.5% to 2.0% by mass of Al, and 0.01% by mass or more. When composed of precipitation hardened stainless steel composed of 0.3 mass% or less of C and 0.01 mass% or more and 0.3 mass% or less of N, balance Fe and inevitable impurities, or SUS631. In Al, Fe, Cr, and the like are diffused in the first Cu layer 51 and the second Cu layer 53. When the stainless steel layer 52 is made of, for example, SUS630, Fe and Cr are diffused into the first Cu layer 51 and the second Cu layer 53.

  Then, the Cu-coated foil 150c having the first thickness exceeding 20 μm subjected to the diffusion annealing is rolled under cold conditions (room temperature) using the rolling rolls 104 to produce the Cu-coated foil 150d. (Second rolling step). At this time, the rolling is performed such that the rolling reduction in the rolling roll 104 is, for example, 30% or more and 50% or less.

  Annealing (softening annealing) for the purpose of softening is performed on the rolled Cu-coated foil 150 d having a thickness exceeding 20 μm. Specifically, the Cu-coated foil 150d is passed through the annealing furnace 105 in a non-oxidizing atmosphere such as a nitrogen atmosphere. At this time, for example, in the annealing furnace 105 set at a temperature of 800 ° C. to 1050 ° C. (preferably 800 ° C. to 950 ° C.) for 30 seconds to 5 minutes (preferably 30 seconds to 90 seconds) The Cu-coated foil 150d is placed in the annealing furnace 105 so that

  In the Cu-coated foil 150d subjected to the soft annealing, the stainless steel layer 52 is softened by the heat during the soft annealing, so that the rolling can be performed again without causing the foil to break or the edge crack.

  Then, the Cu-coated foil 150e having a thickness of more than 20 μm that has been subjected to the soft annealing is rolled under cold conditions (room temperature) using the rolling rolls 106 to produce the Cu-coated foil 150f (third). Rolling process). At this time, by adjusting the rolling reduction in the rolling roll 106 to be, for example, 30% or more and 80% or less, the Cu-coated foil 150f has a second thickness of 20 μm or less.

  Then, a heat treatment is performed on the Cu-coated foil 150f having a second thickness of 20 μm or less using the heat treatment furnace 107. Specifically, the inside of the heat treatment furnace 107 set to a non-oxidizing atmosphere such as a nitrogen atmosphere and set at a temperature of 280 to 400 ° C. (preferably 280 to 350 ° C.) is heated for one hour by Make it pass for no less than 20 hours. The inside of the heat treatment furnace 107 is preferably set to a non-oxidizing atmosphere such as a nitrogen atmosphere, but may be set to an oxidizing atmosphere (under ordinary air) or a hydrogen atmosphere. As a result, in the first Cu layer 51 and the second Cu layer 53, a part of the metal element constituting the stainless steel layer 52 that has diffused from the stainless steel layer 52 to the first Cu layer 51 and the second Cu layer 53 changes to a precipitate. Therefore, the electric resistance can be reduced. Further, in the stainless steel layer 52, fine precipitates are formed by Al and Ni constituting the stainless steel layer 52, and dislocation of C and N is fixed, so that the mechanical strength is improved.

Thus, a negative electrode current collector foil 5b (see FIG. 2) having a thickness (second thickness) of 20 μm or less and made of the Cu-coated foil 50 with improved elastic limit stress σ _0.01 is produced.

At the holding temperature of the heat treatment (280 ° C. or more and less than 400 ° C.), the negative electrode active material 5a is formed of a resin (for example, polyimide, polyamide, or polyamideimide) used to fix the negative electrode active material 5b to the negative electrode current collector foil 5b. The binder 5c is cured. Therefore, when performing the above-described heat treatment on the Cu-coated foil 150f having the second thickness of 20 μm or less, the Cu-coated foil 150f is used as the negative electrode current collector foil 5b, and the surface of the Cu-coated foil 150f is Si-based. An anode active material 5a made of an alloy or a Sn-based alloy and a composition containing, for example, a binder 5c made of at least one of polyimide, polyamide and polyamideimide are arranged, and the anode active material 5a is collected by the anode current collector. It can be fixed to the surface of the foil 5b (Cu-coated foil 150f). As a result, as shown in FIG. 2, the surface of the negative electrode current collector foil 5b composed of the Cu-coated foil 150f having an overall thickness of 20 μm or less and having an elastic limit stress σ _0.01 of 820 MPa or more, The negative electrode 5 of the secondary battery to which the negative electrode active material 5a made of an alloy or a Sn-based alloy is fixed can be manufactured.

Also, the heat treatment is described to be performed on the Cu-coated foil 150f after the third rolling step, but the Cu-coated foil 150b after the first rolling step or the Cu-coated foil 150d after the second rolling step has a second thickness of 20 μm or less. When it is possible to have a thickness, the above-mentioned heat treatment is performed on the Cu-coated foil 150b after the first rolling step or the Cu-coated foil 150d after the second rolling step, and the overall thickness is 20 μm or less, and the elastic limit The negative electrode current collector foil 5b having a stress σ _0.01 of 820 MPa or more (the upper limit value may be, for example, 1200 MPa or less, 1100 MPa or less, 1000 MPa or less, or less than 1000 MPa) may be produced. it can. That is, the Cu-coated foil 150b after the first rolling step may have the second thickness, and the Cu-coated foil 150d after the second rolling step may have the second thickness. In the manufacturing process of the negative electrode current collector foil 5b, the rolling reduction of the Cu-coated foil 150 from immediately after the rolling joining process to immediately before the heat treatment process may be 80% or more, and softening annealing is performed to increase the rolling reduction. And then rolling.

  In the heat-treated negative electrode current collector foil 5b (Cu-coated foil 50), the volume resistivity of the first Cu layer 51 and the second Cu layer 53 caused by the metal element diffused into the first Cu layer 51 and the second Cu layer 53 during annealing. The effect of the rise has been reduced. Thereby, the volume resistivity of the negative electrode current collector foil 5b is reduced to 6 μΩ · cm or less.

  In addition, in 1st Embodiment, as shown in FIG. 3, manufacture of the negative electrode current collector foil 5b is performed continuously by the roll-to-roll method. That is, the roll-shaped negative electrode current collector foil 5b is continuously manufactured using the roll-shaped stainless steel plate 152, the roll-shaped first Cu plate 151, and the roll-shaped second Cu plate 153. Further, the annealing furnace 103, the annealing furnace 105, and the heat treatment furnace 107 are all continuous furnaces.

  The roll-shaped negative electrode current collector foil 5b is cut into a desired length when used as the negative electrode current collector foil of the battery 100.

<Effect of First Embodiment>
In the first embodiment, the following effects can be obtained.

In the first embodiment, as described above, in the negative electrode current collector foil 5b, the first Cu layer 51, the stainless steel layer 52 made of precipitation hardening stainless steel, and the second Cu layer 53 are arranged in this order. The thickness of the negative electrode current collector foil 5b is 20 μm or less, and the elastic limit stress σ _0.01 is 820 MPa or more. By doing so, since plastic deformation is not performed with a stress of less than 820 MPa, deformation of the high-capacity negative electrode active material 5a due to a stress caused by a volume change during charging and discharging can be suppressed. Accordingly, it is possible to provide a negative electrode current collector foil for a secondary battery, which can use the high capacity negative electrode active material 5a while having a foil-like small thickness of 20 μm or less. The negative electrode 5 of the secondary battery having the high-capacity negative electrode active material 5a on the surface of the body foil can be provided.

In the first embodiment, the elastic limit stress σ _0.01 is 906 MPa or more. Accordingly, when the negative electrode 5 of the secondary battery is formed using the high-capacity negative electrode active material 5a, the stress applied to the negative electrode current collector foil 5b by having the high-capacity negative electrode active material 5a is larger. Also, the plastic deformation of the negative electrode current collector foil 5b can be sufficiently suppressed.

In the first embodiment, the precipitation hardening stainless steel constituting the stainless steel layer 52 is composed of 15% by mass or more and 19% by mass or less of Cr, 6% by mass or more and 9% by mass or less of Ni, and 0.5% by mass or more. 2.0 mass% or less of Al, 0.01 mass% to 0.3 mass% of C, 0.01 mass% to 0.3 mass% of N, balance Fe and inevitable impurities. preferable. As a result, the precipitation-hardening stainless steel is subjected to heat treatment, thereby generating fine precipitates of Al and Ni in the structure of the stainless steel layer 52 and fixing dislocations by C and N. Thereby, the elastic limit stress σ _0.01 of the stainless steel layer 52 and the negative electrode current collector foil 5b can be improved.

  In the first embodiment, the first Cu layer 51 and the second Cu layer 53 are diffused with a metal element constituting the precipitation hardening stainless steel, and a part of the diffused metal element is present as a precipitate. Thereby, a part of the metal element diffused into the first Cu layer 51 and the second Cu layer 53 is changed from a solid solution state to a precipitated state, so that the electric resistance of the negative electrode current collector foil 5b can be further reduced.

  In the first embodiment, the volume resistivity is 6 μΩ · cm or less. Thereby, since the volume resistivity is low, the conductivity of the negative electrode current collector foil 5b can be improved. Therefore, it is possible to provide the negative electrode current collector foil 5b of the secondary battery having a thickness of 20 μm or less and having a sufficient elastic limit and conductivity.

  In the first embodiment, the first Cu layer 51, the stainless steel layer 52, and the second Cu layer 53 are formed of a clad material that is stacked in this order and joined. Thus, the negative electrode current collector foil 5b in which the first Cu layer 51 and the second Cu layer 53 and the stainless steel layer 52 are joined with a strong adhesive force by diffusion bonding, has a thickness of 20 μm or less, and has a sufficient elasticity. The negative electrode current collector foil 5b having a limit can be provided.

In the first embodiment, the negative electrode active material 5a made of a Si-based alloy or a Sn-based alloy is fixed to the surface of the negative electrode current collector foil 5b. Thereby, since the negative electrode current collector foil 5b has a sufficient elastic limit stress σ _0.01 , a large volume change during charging and discharging of the high capacity negative electrode active material 5a made of a Si-based alloy or a Sn-based alloy can be achieved. Can withstand. Therefore, even if a high-capacity negative electrode active material 5a such as a Si-based alloy or a Sn-based alloy is used, wrinkle-like deformation of the negative electrode current collector foil 5b constituting the negative electrode 5 can be suppressed.

  In the first embodiment, as described above, after the Cu-coated foil 50 is rolled so as to have the second thickness of 20 μm or less, it is held at a temperature of 280 ° C. or more and less than 400 ° C. for 1 hour or more and 20 hours or less. Heat treatment is performed. As a result, the obtained negative electrode current collector foil 5b does not undergo plastic deformation with a stress of less than 820 MPa, so that it is possible to suppress deformation of the high-capacity negative electrode active material 5a due to a volume change at the time of charging and discharging. it can. Therefore, the negative electrode current collector foil 5b of the secondary battery which can use the high capacity negative electrode active material 5a while having a foil-like small thickness of 20 μm or less can be easily manufactured.

In the first embodiment, the Cu-coated foil 50 having an elastic limit stress σ _0.01 of 906 MPa or more can be obtained by performing a heat treatment after rolling to a second thickness of 20 μm or less. As a result, fine precipitates of Al and Ni are generated in the structure of the stainless steel layer 52, and dislocation is fixed by C and N. Thereby, the elastic limit stress σ _0.01 of the stainless steel layer 52 and the negative electrode current collector foil 5b can be easily improved.

In the first embodiment, the heat treatment performed after rolling to the second thickness of 20 μm or less is preferably performed for 3.5 hours or more and 20 hours or less. Thereby, the Cu-coated foil 50 having an elastic limit stress σ _0.01 of 820 MPa or more can be reliably manufactured.

  In the first embodiment, diffusion annealing, softening annealing, and heat treatment are performed to diffuse metal elements constituting the precipitation hardening stainless steel into the first Cu layer 51 and the second Cu layer 53 of the Cu-coated foil 50. Then, a part of the diffused metal element is deposited as a precipitate. Thereby, a part of the metal element diffused into the first Cu layer 51 and the second Cu layer 53 is changed from a solid solution state to a precipitated state, so that the electric resistance of the negative electrode current collector foil 5b can be further reduced.

In the first embodiment, a first Cu plate 151 made of Cu or Cu-based alloy, a stainless steel plate 152 made of precipitation hardening stainless steel, and a second Cu plate made of Cu or Cu-based alloy 153 are laminated in this order, rolled to have a first thickness exceeding 20 μm, and then annealed (diffusion annealing) to form a Cu-coated foil having a first thickness exceeding 20 μm constituted by a clad material. 50 is manufactured. Thereby, the first Cu layer 51 and the second Cu layer 53 are bonded to the stainless steel layer 52 with a strong adhesion by diffusion bonding by performing a heat treatment after rolling to have a second thickness of 20 μm or less in a subsequent process. A negative electrode current collector foil 5b having a small electric resistance and a thickness of 20 μm or less and having a sufficient elastic limit stress σ _0.01 can be produced.

In the first embodiment, in the method for manufacturing the negative electrode 5 of the secondary battery, as described above, the negative electrode current collector foil 5b having a thickness of 20 μm or less is heated at a temperature of 280 ° C. or more and less than 400 ° C. for 1 hour to 20 hours. The holding heat treatment is performed below. Thereby, the elastic limit stress σ _0.01 is improved by the heat treatment, and the electric resistance is reduced. Therefore, the electric resistance and the elastic limit stress σ _0.01 of the negative electrode current collector foil 5b can be set to appropriate ranges. As a result, a high capacity negative electrode 5 having a high elastic limit stress σ _0.01 and using the negative electrode active material 5 a such as a Si-based alloy or a Sn-based alloy can be obtained.

In the first embodiment, the heat treatment is performed for 3.5 hours or more and 20 hours or less. Thereby, the electric resistance and the elastic limit stress σ _0.01 of the negative electrode current collector foil 5b can be set to more appropriate ranges.

[Second embodiment]
Next, with reference to FIGS. 1, 4 and 5, a negative electrode current collector foil 205b according to a second embodiment of the present invention will be described. In the second embodiment, an example will be described in which a first Cu plating layer 251 and a second Cu plating layer 253 are used instead of the first Cu layer 51 and the second Cu layer 53 of the negative electrode current collector foil 5b of the first embodiment. Note that the negative electrode current collector foil 205b is an example of “a negative electrode current collector foil of a secondary battery” in the claims.

(Battery structure)
The battery 200 according to the second embodiment of the present invention includes a power storage element 203 including a negative electrode 205 as shown in FIG. As shown in FIG. 4, the negative electrode 205 includes a negative electrode active material 5a, a negative electrode current collector foil 205b, and a binder 5c.

(Configuration of negative electrode current collector)
Here, in the second embodiment, the negative electrode current collector foil 205b is formed by plating a stainless steel layer 252 made of a precipitation hardening stainless steel and both surfaces 252a and 252b in the thickness direction (Z direction) of the stainless steel layer 252, respectively. A Cu-coated foil 250 composed of the first Cu plating layer 251 and the second plating layer 253 thus formed. That is, the negative electrode current collector foil 205b has a three-layer structure. In addition, a surface 251a of the first Cu plating layer 251 opposite to the side on which the stainless steel layer 252 is disposed, and a surface 253a of the second Cu plating layer 253 opposite to the side on which the stainless steel layer 252 is disposed. Each has a negative electrode active material 5a fixed via a binder 5c. The first Cu plating layer 251 and the second Cu plating layer 253 are examples of the “first Cu layer” and the “second Cu layer” in the claims.

  The first Cu plating layer 251 and the second Cu plating layer 253 are mainly composed of Cu (copper). Further, the first Cu plating layer 251 and the second Cu plating layer 253 contain a part of the metal elements constituting the stainless steel layer 252. This part of the metal element is diffused from the stainless steel layer 252 to the first Cu plating layer 251 and the second Cu plating layer 253 in the later-described annealing (the annealing step and the softening annealing step shown in FIG. 5), whereby the first Cu plating is performed. The layer 251 and the second Cu plating layer 253 are mainly included in the region on the stainless steel layer 252 side. Note that an underlayer (for example, a Ni plating layer) may be provided on the stainless steel layer 252, and the first Cu plating layer 251 and the second Cu plating layer 253 may be provided on the underlayer. Thereby, the adhesion between the stainless steel layer 252 and the first Cu plating layer 251 and the second Cu plating layer 253 can be increased.

In the second embodiment, the elastic limit stress σ _0.01 of the negative electrode current collector foil 205b is 820 MPa or more, preferably, the elastic limit stress σ _0.01 is 906 MPa or more. The upper limit may be, for example, 1200 MPa or less, 1100 MPa or less, 1000 MPa or less, or less than 1000 MPa as needed.

  Further, the volume resistivity (electric resistance value per unit volume) of the negative electrode current collector foil 205b is 6 μΩ · cm or less. The length (thickness) t11 of the Cu coating foil 250 constituting the negative electrode current collector foil 205b in the Z direction is 20 μm or less. Note that the thickness t11 is preferably 10 μm or less. The other configuration of the second embodiment is the same as that of the first embodiment.

(Manufacturing process of negative electrode current collector foil)
Next, a manufacturing process of the negative electrode current collector foil 205b according to the second embodiment will be described with reference to FIGS.

  First, as shown in FIG. 5, a stainless steel sheet 152 made of precipitation hardening stainless steel having a thickness exceeding 20 μm is prepared. Then, the first Cu plating layer 251 and the second Cu plating layer 253 (see FIG. 4) are formed on both surfaces of the stainless steel plate 152 by performing plating (hoop plating) on the stainless steel plate 152. Thereby, the Cu-coated intermediate material 250a in which the first Cu plating layer 251, the stainless steel plate material 152, and the second Cu plating layer 253 are laminated in this order can be manufactured.

  Specifically, the first Cu plating layer 251 and the second Cu plating layer 253 are formed by passing the stainless steel sheet material 152 through the electroplating bath 201. In the electroplating bath 201, a plating solution (for example, an aqueous solution of copper sulfate) and a Cu plate material 201a arranged in the plating solution and connected to an appropriate position to form an anode by connecting an electrode are arranged. . Then, in a state where the stainless steel sheet material 152 is configured to be a cathode, electricity is supplied between the stainless steel sheet material 152 and the Cu plate material 201a, so that copper ions in the plating solution are applied to both surfaces of the stainless steel sheet material 152. Precipitates as copper, producing a Cu coating.

  This Cu film gradually grows on the first Cu plating layer 251 and the second Cu plating layer 253 because copper ions gradually dissolve into the plating solution from the Cu plate material 201a and continuously deposit on both surfaces of the stainless steel plate material 152. In this manner, a pair of first Cu plating layers 251 and second Cu plating layers 253 are formed on both surfaces of the stainless steel sheet material 152 to a predetermined thickness, respectively, and the first Cu plating layer 251 and the stainless steel sheet material 152 (the later stainless steel layer 252) And the second Cu plating layer 253 are arranged in this order to produce a Cu-coated intermediate material 250a having a first thickness exceeding 20 μm. Although not shown in FIG. 5, at least the stainless steel sheet material 152 is washed before plating, and at least the Cu-coated intermediate material 250a is washed and dried after plating.

  Thereafter, the Cu-coated intermediate member 250a is rolled using the rolling roll 102 under cold conditions (room temperature, for example, about 20 ° C. or more and about 40 ° C. or less), thereby producing the Cu-coated foil 250b (first). Rolling process). At this time, the rolling reduction is set, for example, to 50% or more and 80% or less.

  Then, the Cu-coated foil 250b is subjected to annealing (annealing step shown in FIG. 5) using the annealing furnace 103 in the same manner as in the diffusion annealing step of the first embodiment (see FIG. 3). Thus, a Cu-coated foil 250c in which the annealed first Cu plating layer 251 and second Cu plating layer 253 are arranged on both surfaces of the stainless steel layer 252 made of the stainless steel sheet material 152 is produced.

  Further, in the Cu-coated foil 250c that has been annealed in the same manner as in the diffusion annealing step of the first embodiment, part of the metal elements constituting the stainless steel sheet material 152 are reduced by the heat during annealing. 251 and the second Cu plating layer 253. When an underlayer (Ni plating layer) formed by Ni plating is provided, diffusion from the underlayer to the first Cu plating layer 251 and the second Cu plating layer 253 (mainly diffusion of Ni) also occurs due to heat during annealing. I do.

  Then, the Cu-coated foil 250c having undergone the annealing step shown in FIG. 5 is rolled under cold (room temperature) using the rolling roll 104 in the same manner as in the first embodiment, to thereby obtain the Cu-coated foil 250d. Is prepared. At this time, the rolling is performed such that the rolling reduction in the rolling roll 104 is, for example, 30% or more and 80% or less (second rolling step).

  Softening annealing is further performed on the rolled Cu-coated foil 250d. Specifically, the Cu-coated foil 250d is passed through the annealing furnace 105 in a non-oxidizing atmosphere such as a nitrogen atmosphere. The temperature in the annealing furnace 105 is, for example, 850 ° C. or more and 1000 ° C. or less.

  Then, the Cu-coated foil 250e that has been subjected to the soft annealing is rolled under cold conditions (room temperature) using the rolling rolls 106 to produce a Cu-coated foil 250f (third rolling step). At this time, the rolling is performed such that the rolling reduction in the rolling roll 106 is, for example, 30% or more and 80% or less. Note that the Cu-coated foil 250 is rolled to a second thickness of 20 μm or less from after the plating process shown in FIG. 5 to before the heat treatment using the heat treatment furnace 107.

  Then, a heat treatment is performed on the Cu-coated foil 250f using the heat treatment furnace 107 in the same manner as in the first embodiment. Specifically, it is held in a heat treatment furnace 107 set at a temperature (heat treatment temperature) of 280 ° C. or more and less than 400 ° C., for example, 280 ° C. or more and 350 ° C. or less, for a holding time of 1 hour or more and 20 hours or less. The Cu-coated foil 250f is placed in the heat treatment furnace 107. The inside of the heat treatment furnace 107 is preferably set to a non-oxidizing atmosphere such as a nitrogen atmosphere, but may be set to an oxidizing atmosphere (under ordinary air) or a hydrogen atmosphere. Thereby, in the first Cu plating layer 251 and the second Cu plating layer 253, some of the metal elements constituting the stainless steel layer 252 that have diffused from the stainless steel layer 252 to the first Cu plating layer 251 and the second Cu plating layer 253 are removed. Since it changes into a precipitate, the electric resistance can be reduced. In the stainless steel layer 252, fine precipitates are formed by Al and Ni constituting the stainless steel layer 252, and dislocations of C and N are fixed, so that the mechanical strength is improved.

Thus, a negative electrode current collector foil 205b (see FIG. 5) having a thickness (second thickness) of 20 μm or less and including the Cu-coated foil 250 with improved elastic limit stress σ _0.01 is produced.

At the holding temperature of the heat treatment (280 ° C. or more and less than 400 ° C.), a resin (for example, at least one of polyimide, polyamide, and polyamideimide) used for fixing negative electrode active material 5a to negative electrode current collector foil 205b. And the like, the binder 5c is hardened. Therefore, when performing the above-described heat treatment on the Cu-coated foil 250f having the second thickness of 20 μm or less, the Cu-coated foil 250f is used as the negative electrode current collector foil 205b, and the surface of the Cu-coated foil 250f is A composition including a negative electrode active material 5a made of an alloy or a Sn-based alloy and a binder 5c composed of at least one of polyimide, polyamide and polyamideimide is disposed, and the negative electrode active material 5a is used as the negative electrode current collector foil 205b. (Cu-coated foil 250f). Thereby, as shown in FIG. 4, the surface of the negative electrode current collector foil 205b composed of the Cu-coated foil 250f having an overall thickness of 20 μm or less and having an elastic limit stress σ _0.01 of 820 MPa or more, The negative electrode 205 of the secondary battery to which the negative electrode active material 5a made of an alloy or a Sn-based alloy is fixed can be manufactured.

Further, the heat treatment is described to be performed on the Cu-coated foil 250f after the third rolling step, but the Cu-coated foil 250b after the first rolling step or the Cu-coated foil 250d after the second rolling step has a second thickness of 20 μm or less. If it is possible to have a thickness, the above-described heat treatment is performed on the Cu-coated foil 250b after the first rolling step or the Cu-coated foil 250d after the second rolling step, and the overall thickness is 20 μm or less, and the elastic limit To produce the negative electrode current collector foil 205b having a stress σ _0.01 of 820 MPa or more (the upper limit may be, for example, 1200 MPa or less, 1100 MPa or less, 1000 MPa or less, or less than 1000 MPa). Can be. That is, the Cu-coated foil 250b after the first rolling step may have the second thickness, and the Cu-coated foil 250d after the second rolling step may have the second thickness. In the manufacturing process of the negative electrode current collector foil 205b, the rolling reduction of the Cu-coated foil 250 from immediately after the plating process to immediately before the heat treatment process may be 80% or more, and softening annealing is performed to increase the rolling reduction. And then rolling.

  Here, in the heat-treated negative electrode current collector foil 205b (Cu-coated foil 250), the first Cu plating layer 251 and the second Cu plating layer 251 caused by the metal element diffused into the first Cu plating layer 251 and the second Cu plating layer 253 during annealing. The effect of the increase in the volume resistivity of the plating layer 253 is reduced. Thereby, the volume resistivity of the negative electrode current collector foil 5b is reduced to 6 μΩ · cm or less.

  In the second embodiment, the negative electrode current collector foil 205b is continuously manufactured by a roll-to-roll method as shown in FIG. That is, the roll-shaped negative electrode current collector foil 205b is continuously manufactured using the roll-shaped stainless steel sheet material 152. The electroplating bath 201 is a so-called electroplating bath apparatus for hoop plating, and the annealing furnace 103, the annealing furnace 105, and the heat treatment furnace 107 are all continuous furnaces. The roll-shaped negative electrode current collector foil 205b is cut into a desired length when used as the negative electrode current collector foil 205b of the battery 200.

  Other configurations of the second embodiment are the same as those of the first embodiment.

<Effect of Second Embodiment>
In the second embodiment, the following effects can be obtained.

In the second embodiment, the negative electrode current collector foil 205b includes a first Cu plating layer 251, a stainless steel layer 252 composed of precipitation hardening stainless steel, and a second Cu plating layer 253 arranged in this order, and has a thickness of 20 μm or less, and the elastic limit stress σ _0.01 is 820 MPa or more. With such a configuration, plastic deformation is not performed with a stress of less than 820 MPa, so that deformation of the high-capacity negative electrode active material 5a due to a volume change during charge and discharge can be suppressed. Accordingly, it is possible to provide a negative electrode current collector foil 205b of a secondary battery capable of using a high-capacity negative electrode active material 5a while having a foil-like small thickness of 20 μm or less. The negative electrode 205 of the secondary battery having the high-capacity negative electrode active material 5a on the surface of the foil for use can be provided.

In the second embodiment, the negative electrode current collector foil 205b has a first Cu plating layer 251 and a second Cu plating layer 253. Thereby, the thickness of the Cu layer (first Cu plating layer 251 and second Cu plating layer 253) constituting negative electrode current collector foil 205b can be easily reduced, so that the thickness is not more than 20 μm and the elasticity is sufficient. The negative electrode current collector foil 205b of the secondary battery having the critical stress σ _0.01 can be easily provided, and the negative electrode of the secondary battery having the high capacity negative electrode active material 5a on the surface of the negative electrode current collector foil 205b 205 can be provided. The other effects of the second embodiment are the same as those of the first embodiment.

[Example]
Next, an experiment performed to confirm the effect of the first embodiment will be described.

(Preparation of Cu coated foil for test material)
First, a Cu-coated foil of a test material was manufactured based on the manufacturing method of the first embodiment. Specifically, a general stainless steel plate 152 corresponding to SUS631, which is a precipitation hardening stainless steel, and a pair of first Cu plate 151 and second Cu plate 153 made of oxygen-free copper of C1020 (based on JIS H0500). Was prepared. In addition, SUS631 is 16 mass% or more and 18 mass% or less of Cr, 6.50 mass% or more and 7.75 mass% or less of Ni, 0.75 mass% or more and 1.50 mass% or less of Al, 0.09 mass%. % Of C, 1.00% by mass or less of Si (silicon), 1.00% by mass or less of Mn (manganese), 0.040% by mass or less of P (phosphorus), 0.030% by mass or less of S ( It is a stainless steel composed of sulfur), balance Fe and inevitable impurities. The thickness of the stainless steel plate 152 is 0.50 mm, and the thicknesses of the first Cu plate 151 and the second Cu plate 153 are both 0.17 mm.

  Then, the stainless steel plate 152 is sandwiched in the thickness direction between the first Cu plate 151 and the second Cu plate 153, and is roll-bonded under cold (room temperature) using the rolling roll 101, thereby forming the stainless steel plate 152. The first Cu plate member 151 and the second Cu plate member 153 were joined to both surfaces, respectively, to produce a Cu-coated intermediate member having a thickness of 0.353 mm. Thereafter, the Cu-coated intermediate material was rolled under cold (room temperature) using a rolling roll 102 to produce a Cu-coated foil having a thickness of 0.135 mm. The Cu-coated foil was further held in an annealing furnace 103 at 900 ° C. for 1 minute to perform diffusion annealing. Furthermore, a Cu-coated foil having a thickness of 0.05 mm was produced by rolling under cold (room temperature) using the rolling roll 104 and softening annealing using the annealing furnace 105. The Cu-coated foil was further rolled under cold (room temperature) using a rolling roll 106 to produce a 0.01-mm (10 μm) -thick Cu-coated foil.

  Then, a heat treatment was performed on the Cu-coated foils of the plurality of test materials thus produced by changing the heat treatment temperature and the heat treatment time.

  In Example 1, the heat treatment temperature was set to 280 ° C., and the heat treatment time was set to 20 hours. In Example 2, the heat treatment temperature was set to 300 ° C., and the heat treatment time was set to 3.5 hours. In Example 3, the heat treatment temperature was set to 300 ° C., and the heat treatment time was set to 20 hours. In Example 4, the heat treatment temperature was set to 350 ° C., and the heat treatment time was set to 3.5 hours. In Example 5, the heat treatment temperature was set to 350 ° C., and the heat treatment time was set to 20 hours.

  In Comparative Example 1, no heat treatment was performed. In Comparative Example 2, the heat treatment temperature was set to 250 ° C., and the heat treatment time was set to 20 hours. In Comparative Example 3, the heat treatment temperature was set to 300 ° C., and the heat treatment time was set to 50 minutes.

Then, the elastic limit stress σ _0.01 and the volume resistivity of the produced Cu-coated foil were measured. The elastic limit stress σ _0.01 is a stress value corresponding to a position where strain is 0.01% in a stress-strain curve (graph) obtained by a tensile test. The volume resistivity was measured based on a four-terminal method based on JIS C2525. Specifically, a circuit to which the four-terminal method based on JIS C 2525 is applied is constructed in a room temperature environment, a test piece cut from a Cu-coated foil is arranged in the circuit, a current is applied, and a voltage is measured. did. The volume resistivity of the Cu-coated foil was determined from the voltage (average value), the volume (thickness and width) of the test specimen, the distance between the contacts of the voltage terminals (the distance between the terminals), and the applied current.

(Measurement result)
Table 1 shows the measurement results of the fabricated Examples 1 to 5, Comparative Example 1, Comparative Example 2, and Comparative Example 3, respectively.

As measurement results, in Comparative Example 1 is a clad material which was not subjected to the heat treatment, to the elastic limit stress sigma _0.01 of a 813MPa, in Example 1 was subjected to heat treatment, the elastic limit stress sigma _0.01 Is 830 MPa, in Example 2, the elastic limit stress σ _0.01 is 820 MPa, in Example 3, the elastic limit stress σ _0.01 is 906 MPa, and in Example 4, the elastic limit stress σ _0.01 is 840 MPa. In No. 5, the elastic limit stress σ _0.01 was 924 MPa, which was a high value.

In Comparative Example 2, the heat treatment was performed at a heat treatment temperature of 250 ° C. for 20 hours, but the elastic limit stress σ _0.01 was 725 MPa, which is lower than the elastic limit stress σ _0.01 813 MPa of Comparative Example 1 in which the heat treatment was not performed. Got lower. On the other hand, in Example 1 in which the heat treatment was performed at a heat treatment temperature of 280 ° C. for 20 hours, the elastic limit stress σ _0.01 was 830 MPa, which was higher than the elastic limit stress σ _0.01 813 MPa of Comparative Example 1. Therefore, the inventor of the present application has found that by performing the heat treatment at 280 ° C. or higher, the elastic limit stress σ _0.01 is improved as compared with the case where the heat treatment is not performed.

In Comparative Example 3, the heat treatment was performed at a heat treatment temperature of 300 ° C. for 50 minutes, but the elastic limit stress σ _0.01 was 800 MPa, which was lower than the elastic limit stress σ _0.01 813 MPa of Comparative Example 1. On the other hand, in Example 2 in which the heat treatment was performed at a heat treatment temperature of 300 ° C. for 3.5 hours, the elastic limit stress σ _0.01 was 820 MPa, which was higher than the elastic limit stress σ _0.01 of Comparative Example 1 of 813 MPa. Therefore, even in the case of performing the heat treatment at a temperature of 280 ° C. or more and less than 400 ° C., the inventor sets the time of the heat treatment at 1 hour or more to 20 hours in order to improve the elastic limit stress σ _0.01. We have found that it is necessary to select appropriately within the following range.

Further, in Example 2 and Example 3, the heat treatment temperature was set to 300 ° C., and in Example 2, the heat treatment time was set to 3.5 hours, whereas in Example 3, it was set to 20 hours. As a result, in Example 2, the elastic limit stress σ _0.01 was 820 MPa, whereas in Example 3, it was as high as 906 MPa. Further, in Example 4 and Example 5, the heat treatment temperature was set to 350 ° C., and in Example 4, the heat treatment time was set to 3.5 hours, whereas in Example 5, it was set to 20 hours. As a result, in Example 4, the elastic limit stress σ _0.01 was 840 MPa, whereas in Example 5, it was as high as 924 MPa. From the above results, the inventors of the present application have found that the longer the heat treatment time, the higher the elastic limit stress σ _0.01 .

  In Comparative Example 1 where no heat treatment was performed, the volume resistivity was 6.39 μΩ · cm, whereas in Example 1 where the heat treatment was performed, the volume resistivity was 5.74 μΩ · cm, and in Example 2, , The volume resistivity is 5.84 μΩ · cm, in Example 3, the volume resistivity is 5.82 μΩ · cm, in Example 4, the volume resistivity is 5.72 μΩ · cm, and in Example 5, the volume resistivity is Both values were as low as 5.8 μΩ · cm. Based on the above findings, the inventor of the present application has learned the optimal heat treatment temperature and heat treatment time, and has completed the present invention.

[Modification]
It should be noted that the embodiments and examples disclosed this time are illustrative in all respects and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description of the embodiments and examples, and includes all modifications (modifications) within the scope and meaning equivalent to the terms of the claims.

  For example, in the first and second embodiments, the negative electrode current collector foil 205b composed of the Cu-coated foil 50 (250) (the negative electrode current collector foil of the secondary battery) is connected to the lithium ion secondary battery (battery 100). Although the example which applied to this was shown, this invention is not limited to this. In the present invention, the negative electrode current collector foil composed of the negative electrode current collector foil of the secondary battery may be applied to a secondary battery other than the lithium ion secondary battery. For example, the negative electrode current collector foil may be applied to a sodium ion secondary battery, a magnesium secondary battery, or the like.

  Also, an example is shown in which the negative electrode current collector foil 5b composed of the Cu-coated foil 50 (a negative electrode current collector foil of a secondary battery) is applied to a lithium ion secondary battery (battery 100). , An example in which the negative electrode current collector foil 205b composed of a Cu-coated foil 250 (a negative electrode current collector foil of a secondary battery) was applied to a lithium ion secondary battery (battery 200), but the present invention is not limited thereto. Not limited. In the present invention, a so-called laminate type lithium ion secondary battery may be used.

  In the first embodiment, an example is shown in which a Cu-coated foil 50 made of a clad material having a three-layer structure of a first Cu layer / a stainless steel layer / a second Cu layer is used as the negative electrode current collector foil 5b. Although an example in which the Cu-coated foil 250 having a three-layer structure of the first Cu plating layer / stainless steel layer / second Cu plating layer is used as the negative electrode current collector foil 205b has been described, the present invention is not limited to this. In the present invention, the negative electrode current collector foil (Cu-coated foil) is not limited to the three-layer structure. For example, a Ni layer or the like that suppresses oxidation of the Cu layer (or the Cu plating layer) may be formed on the surface of the clad material opposite to the Cu layer or the stainless steel layer of the Cu plating layer. Further, as described in the second embodiment, an underlayer (for example, a Ni layer) having a small thickness may be disposed between the Cu plating layer and the stainless steel layer. This underlayer can also be applied to a Cu-coated foil made of a clad material. The thickness of the layers other than the Cu layer (or Cu plating layer) and the stainless steel layer is sufficiently smaller than the thickness of each of the Cu layer (or Cu plating layer) and the stainless steel layer from the viewpoint of miniaturization of the secondary battery. Is preferred. In this case, the thickness of the negative electrode current collector foil having a four-layer structure or more is preferably 20 μm or less.

  In the second embodiment, an example in which a pair of Cu plating layers 251 and 253 are formed on both surfaces of the stainless steel sheet material 152 (the later stainless steel layer 52) by the electroplating bath 201 as the electrolytic plating process is shown. However, the present invention is not limited to this. In the present invention, a pair of Cu plating layers may be formed on both surfaces of the stainless steel layer by electroless plating.

  Further, in the first and second embodiments, the first Cu layer 51 and the second Cu layer 53 (Cu plating layers 251 and 253) are mainly composed of Cu (copper). Not limited to In the present invention, a pair of first Cu plate material and second Cu plate material for producing the first Cu layer and the second Cu layer are made of a Cu-based alloy such as a Cu-Fe alloy such as C1940, a Cu-Ni alloy, and a Cu-Zr alloy. Alternatively, the Cu plate material for producing the first Cu plating layer and the second Cu plating layer may be made of a Cu-based alloy such as a Cu-Fe alloy such as C1940, a Cu-Ni alloy, or a Cu-Zr alloy. Good.

  In the first and second embodiments, the heat treatment is performed on the Cu-coated foil in a state where the first Cu layer, the stainless steel layer, and the second Cu layer are laminated in this order, but the present invention is not limited thereto. Not limited. In the present invention, the Cu-coated foil may be wound into a coil after the third rolling, and the heat treatment may be performed using a batch-type heat treatment furnace.

5, 205 Negative electrode 5a Negative electrode active material 5b, 205b Negative electrode current collector foil (Foil for negative electrode current collector of secondary battery)
5c Binder 50, 250 Cu-coated foil 51 First Cu layer 52, 252 Stainless steel layer 53 Second Cu layer 251 First Cu plating layer (first Cu layer)
253 second Cu plating layer (second Cu layer)

Claims (16)

A first Cu layer made of Cu or Cu-based alloy, a stainless steel layer made of precipitation hardening stainless steel, and a second Cu layer made of Cu or Cu-based alloy are arranged in this order,
A negative electrode current collector foil for a secondary battery having an overall thickness of 20 μm or less and an elastic limit stress σ _0.01 of 820 MPa or more. The foil for a negative electrode current collector of a secondary battery according to claim 1, wherein the elastic limit stress σ _0.01 is 906 MPa or more.   The precipitation hardening stainless steel constituting the stainless steel layer includes 15% by mass to 19% by mass of Cr, 6% by mass to 9% by mass of Ni, and 0.5% by mass to 2.0% by mass of Al. 3. The foil for a negative electrode current collector of a secondary battery according to claim 1, comprising 0.01 to 0.3 mass% of C, the balance of Fe, and inevitable impurities. 4.   The first Cu layer and the second Cu layer, wherein a metal element constituting the precipitation hardening stainless steel is diffused, and a part of the diffused metal element is present as a precipitate. The foil for a negative electrode current collector of the secondary battery according to any one of the preceding claims.   The foil for a negative electrode current collector of a secondary battery according to claim 1, wherein the foil has a volume resistivity of 6 μΩ · cm or less.   The secondary according to any one of claims 1 to 5, wherein the first Cu layer, the stainless steel layer, and the second Cu layer are formed of a clad material laminated and joined in this order. Foil for negative electrode current collector of battery.   The foil for a negative electrode current collector of a secondary battery according to any one of claims 1 to 5, wherein the first Cu layer and the second Cu layer are plating layers.   A negative electrode for a secondary battery, wherein a negative electrode active material made of a Si-based alloy or a Sn-based alloy is fixed on the surface of the negative electrode current collector foil according to claim 1. By laminating a first Cu layer made of Cu or Cu-based alloy, a stainless steel layer made of precipitation hardening stainless steel, and a second Cu layer made of Cu or Cu-based alloy in this order, Producing a Cu-coated foil having a first thickness exceeding 20 μm,
After rolling the produced Cu-coated foil to a second thickness of 20 μm or less, heat treatment is performed at a temperature of 280 ° C. or more and less than 400 ° C. for 1 hour or more and 20 hours or less. A method for producing a negative electrode current collector foil for a secondary battery, wherein the Cu-coated foil having σ _0.01 of 820 MPa or more is obtained. The method for producing a negative electrode current collector foil for a secondary battery according to claim 9, wherein the Cu-coated foil having an elastic limit stress σ _0.01 of 906 MPa or more is obtained by performing the heat treatment.   The method according to claim 9, wherein the heat treatment is performed for 3.5 hours to 20 hours. 12.   The metal element constituting the precipitation hardening stainless steel is diffused in the first Cu layer and the second Cu layer of the Cu-coated foil, and a part of the diffused metal element is deposited as a precipitate. 12. The method for producing a negative electrode current collector foil for a secondary battery according to any one of 9 to 11.   A Cu plate made of Cu or Cu-based alloy, a stainless steel plate material made of the precipitation hardening stainless steel, and a Cu plate made of Cu or Cu-based alloy are laminated in this order, The secondary battery according to any one of claims 9 to 12, wherein the Cu-coated foil formed of a clad material and having the first thickness is produced by rolling after rolling to have a thickness of? A method for producing a negative electrode current collector foil.   By plating Cu or a Cu-based alloy on both surfaces of a stainless steel sheet material composed of the precipitation hardening stainless steel, the stainless steel layer is formed of a Cu plating layer composed of Cu or a Cu-based alloy on both surfaces of the stainless steel layer. The method for producing a foil for a negative electrode current collector of a secondary battery according to any one of claims 9 to 12, wherein the Cu-coated foil on which the 1Cu layer and the second Cu layer are produced is produced.   A first Cu layer composed of Cu or a Cu-based alloy, a stainless steel layer composed of a precipitation hardening type stainless steel, and a second Cu layer composed of a Cu or Cu-based alloy are arranged in this order. A composition containing a negative electrode active material made of a Si-based alloy or a Sn-based alloy and a binder is placed on the surface of a negative electrode current collector foil having a thickness of 20 μm or less, and is placed at a temperature of 280 ° C. or more and less than 400 ° C. for 1 hour. A method for producing a negative electrode for a secondary battery, wherein a heat treatment for holding the negative electrode active material for at least 20 hours is performed to fix the negative electrode active material to the surface of the negative electrode current collector foil. The method according to claim 15, wherein the heat treatment is performed for 3.5 hours or more and 20 hours or less.

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