JP5345974B2 - Rolled copper alloy foil, and negative electrode current collector, negative electrode plate and secondary battery using the same - Google Patents

Description

  The present invention relates to a rolled copper foil suitable as a negative electrode current collector material for a secondary battery such as a lithium ion secondary battery, and a negative electrode current collector, a negative electrode plate and a battery using the rolled copper foil.

With the widespread use of portable devices such as mobile phones and notebook computers, the demand for small, high-capacity secondary batteries is growing. In addition, demand for medium- and large-sized secondary batteries used in electric vehicles, hybrid vehicles, and the like is also increasing rapidly. Among secondary batteries, lithium ion secondary batteries are used in many fields because of their light weight and high energy density.
As a lithium ion secondary battery, an aluminum foil coated with a compound such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ is used as a positive electrode, and a copper foil coated with a carbonaceous material or the like as an active material is used as a negative electrode. What is used is known (a structure of a general secondary battery is shown in FIG. 1).

Copper foil includes rolled copper foil and electrolytic copper foil. The rolled copper foil is excellent as a material for the secondary battery negative electrode plate in terms of strength, fatigue characteristics, and the like. Many of the rolled copper foils marketed as secondary battery negative electrode plate materials are made of tough pitch copper (JIS-C1100). Tough pitch copper is pure copper containing 0.01 to 0.05 mass% oxygen, and the copper content is standardized to 99.90 mass% or more (hereinafter, mass% is expressed as%).
In the manufacturing process of the rolled copper foil, a tough pitch copper ingot is hot-rolled, and then cold-rolling and annealing are repeated, and finally it is finished to a predetermined thickness in the range of, for example, 35 to 5 μm by final cold-rolling.

Generally, a copper foil negative electrode plate is manufactured by the following process using electrolytic copper foil or rolled copper foil.
(1) A paste obtained by kneading and dispersing an active material and a binder in a solvent is applied to one side or both sides of a copper foil serving as a current collector to form a negative electrode plate material.
(2) Heat and dry at a temperature of 150 to 300 ° C. for several tens of minutes to several tens of hours.
(3) Pressurize the negative electrode plate material as necessary.
(4) A shearing process is performed to form a negative electrode plate having a predetermined shape.
Examples of shearing include punching with a press, cutting with shearing, and cutting with a round blade slitter.

In the conventional rolled copper foil made of tough pitch copper or oxygen-free copper, recrystallization occurs in the above (2) drying step, the copper foil strength is reduced (softened), and the tensile strength is reduced to nearly 200 MPa. Such a soft copper foil is subject to high tension load during winding of the negative electrode plate in the battery manufacturing process and manufacturing of the electrode plate group by winding, and the foil easily breaks.
In the lithium ion secondary battery, lithium ions move from the positive electrode to the negative electrode during charging, and lithium ions move from the negative electrode to the positive electrode during discharging. Since the negative electrode active material expands and contracts as the lithium ions move, the copper foil is subjected to mechanical repeated stress due to charge and discharge. Therefore, the softened copper foil is deformed by repeated mechanical stress due to charging / discharging, and the active material applied to the surface of the copper foil is easily peeled off, and the copper foil itself is easily damaged.

With the miniaturization of secondary batteries, the copper foil, which is a negative electrode current collector, is becoming thinner. When the copper foil is thinned, the foil is more likely to be cut, deformed, damaged, etc., and thus the demand for a copper foil that does not soften due to thermal history is further increased.
In order to deal with such problems, a rolled copper foil made of a copper alloy (hereinafter referred to as copper alloy foil) has been proposed instead of a rolled copper foil made of tough pitch copper.

  Japanese Unexamined Patent Publication No. 2000-303128 (Patent Document 1) discloses a copper alloy foil obtained by adding 0.005 or 0.01% of Cr, Zn, Ag, Ca, Sn, Sb or Bi to oxygen-free copper. Japanese Unexamined Patent Application Publication No. 2003-286528 (Patent Document 2) discloses a copper alloy foil containing 0.063 to 0.231% of Sn and appropriately adjusting the hydrogen concentration and the oxygen concentration. This copper foil has improved pinholes and flex life, and can be used as a negative electrode current collector of a lithium ion secondary battery.

On the other hand, for the purpose of improving the characteristics and manufacturability of the secondary battery, various studies have been made on the crystal orientation of the copper foil. JP-A-2003-142106 (Patent Document 3) increases the elongation and strength of the copper foil by adjusting I ₍₂₀₀₎ / I ₍₁₁₁₎ of the copper foil to 0.3 to 4.0, and the negative electrode active material Improved adhesion. Here, I _(hkl) is the integrated intensity of the (hkl) plane obtained by X-ray diffraction with respect to the copper foil surface. However, the copper foil which the Example of this invention has disclosed is an electrolytic copper foil. Similarly, in JP 2009-4370 (Patent Document 4), I ₍₂₀₀₎ / I ₍₁₁₁₎ is adjusted to 0.5 to 1.5 with respect to the electrolytic copper foil to improve the adhesion with the active material. .
In JP-A-11-310864 (Patent Document 5), I ₍₂₀₀₎ / I ₍₂₂₀₎ of the copper foil is adjusted to 0.3 or more to improve the adhesion with the active material. The disclosed copper foil is a rolled copper foil using tough pitch copper as a raw material and a final cold rolling degree of 20 to 99%. In Japanese Patent Application Laid-Open No. 2007-142106 (Patent Document 6), the stress due to expansion and contraction of the negative electrode active material is relaxed by adjusting I ₍₂₀₀₎ / I ₍₂₂₀₎ of the copper foil to 0.4 or more. Although this copper foil can be manufactured by an electrolytic method or a rolling method, details of the manufacturing method are not disclosed.

JP 2000-303128 A JP 2003-286528 A JP 2003-142106 A JP 2009-4370 A JP-A-11-310864 JP 2007-142106 A

  In the rolled copper foil for secondary battery negative electrode current collectors, there has been a problem that has not been solved yet, although it has been a factor in yield reduction in the negative electrode plate manufacturing process. This is a problem that the surface of the copper foil is plastically deformed by shearing pressure during the shearing process. FIG. 2 shows a cross section of the copper foil after the shearing process in which a shearing force is applied from the upper left side to the lower side of the copper foil. The sagging not only reduces the production efficiency, but also inhibits the adhesion between the negative electrode active material and the copper foil to lower the battery performance. However, the conventional technique has not been recognized as a problem.

The occurrence of sagging is promoted by the softening of the copper foil in the thermal history of the drying process. In order to suppress the softening, the rolled copper foil material may be made into a copper alloy as proposed in the patent document. However, the effect of reducing the sagging with respect to the tough pitch copper foil or the oxygen-free copper foil is recognized only by copper alloying and suppressing softening, but the sagging is not improved to a sufficiently small level.
The present invention improves the occurrence of sagging during shearing, and a rolled copper alloy foil suitable as a negative electrode current collector material for secondary batteries including lithium ion secondary batteries, and a negative electrode current collector using the same, An object is to provide a negative electrode plate and a secondary battery.

The inventor diligently studied a method for reducing the sag during shearing of the copper alloy rolled foil. As a result, even in a copper alloy rolled foil that is hardly softened by the heat treatment of the conventional drying process, sagging is likely to occur through the heat treatment under the specific conditions of the present invention, and the size of the sagging at this time is determined after the heat treatment. It has been found that the copper alloy foil shows a good correlation with the crystal orientation of the copper alloy foil, and that the copper alloy foil which does not easily sag after the heat treatment exhibits a good cycle life. Therefore, in order to optimize the crystal orientation after the heat treatment, the composition of the copper alloy foil and the production conditions were adjusted to arrive at the present invention.
That is, the present invention has the following configuration.
(1) A rolled copper alloy for a negative electrode current collector of a secondary battery containing 0.05 to 0.22% by mass of Sn and containing a balance of Cu and impurities and having an electric conductivity of 80% IACS or more. It is a foil, and the crystal orientation after heating at 300 ° C. for 30 minutes is
10 ≦ (5 · I ₍₂₂₀₎ / I _{0 (220)} + 2 · I ₍₁₁₁₎ / I _{0 (111)} + I ₍₃₁₁₎ / I _{0 (311)} ) ≦ 20
I _(hkl) : Integrated strength of (hkl) plane obtained by X-ray diffraction with respect to copper alloy foil surface I _{0 (hkl)} : Relation of integral strength of (hkl) plane obtained by X-ray diffraction with respect to copper powder And a tensile strength after heating at 300 ° C. for 30 minutes is 400 MPa or more.
(2) The rolled copper alloy foil according to (1), further containing 0.1% by mass or less of Ag.
(3) A negative electrode current collector composed of the rolled copper alloy foil according to (1) or (2).
(4) A negative electrode plate having a negative electrode active material layer mainly composed of a carbonaceous material on at least one surface of the negative electrode current collector described in (3) above.
(5) An active material containing at least one selected from the group consisting of metallic lithium, metallic tin, tin compounds, simple silicon, and silicon compounds on at least one surface of the negative electrode current collector described in (3) above A negative electrode plate having a layer.
(6) An electrode plate group in which the negative electrode plate described in (4) or (5) above is insulated and disposed via a separator and a positive electrode plate having a lithium transition metal composite oxide as a main component of the positive electrode active material, non-aqueous electrolysis A secondary battery comprising a liquid and a battery case containing an electrode plate group and a non-aqueous electrolyte.

It is the schematic which shows the structure of a general secondary battery. It is the schematic which shows the copper foil cross section after a shearing process.

  In the present invention, by optimizing the crystal orientation, strength (tensile strength before rolling) and heat resistance (tensile strength after heat treatment) of the copper alloy foil, the sagging during shearing is reduced, and the battery is further reduced. Improved charge / discharge cycle life after incorporation. Further, as a means for optimizing the crystal orientation, strength and heat resistance, an alloy obtained by adding Sn to oxygen-free copper was used as a material for the copper alloy foil, and its Sn concentration and rolling process conditions were controlled. Hereinafter, the details of the characteristics of the copper alloy foil such as the target crystal orientation, strength, and heat resistance, the components of the copper alloy foil as its means, and the manufacturing conditions such as rolling will be described in detail.

(Crystal orientation)
The copper foil negative electrode plate is formed by applying an active material paste and undergoing a heat treatment in a drying process, followed by a shearing process. Therefore, in the rolled copper alloy foil of the present invention intended to prevent sagging during shearing, the crystal orientation after the heat treatment is a problem. The heat load level in the heat treatment assumed by the present invention corresponds to a heat treatment at 300 ° C. for 30 minutes. This is a condition that is extremely stricter than the conventional condition such as 30 minutes at 200 ° C. (patent document 1), which is the standard for heat load. The above-mentioned patent documents that refer to the crystal orientation of the copper foil all examined the crystal orientation before the heat treatment, and were not aware of the sag at the time of shearing, so the crystal orientation after the heat treatment was It was not examined.

The copper alloy foil heat-treated at 300 ° C. for 30 minutes was experimentally examined for the relationship between the crystal orientation of the plate surface and sag during shearing. The most effective component for sag reduction was (220) The next effective orientation is (111), and a slight effect was also observed for the (311) orientation. Further, it has been found that K given by the following equation has a good correlation with the size of the sagging, and that sagging is improved by controlling K to 10 to 20, preferably 10 to 18. Here, I _(hkl) is the integrated intensity of the (hkl) plane obtained by X-ray diffraction with respect to the copper foil surface.
K = 5 · I ₍₂₂₀₎ / I _{0 (220)} + 2 · I ₍₁₁₁₎ / I _{0 (111)} + I ₍₃₁₁₎ / I _{0 (311)}

  When K after heating at 300 ° C. for 30 minutes is less than 10, dripping increases (hereinafter, K is a value after heating at 300 ° C. for 30 minutes). The large sagging hinders the adhesion between the negative electrode active material and the copper foil and shortens the charge / discharge cycle life of the battery. On the other hand, if K exceeds 20, the copper alloy foil becomes brittle, so that the copper alloy foil is easily cracked when subjected to charge / discharge stress, and the charge / discharge cycle life of the battery is also shortened.

(Heat resistance related to the strength of copper alloy foil)
As the heat resistance required for the copper alloy foil of the present invention, the tensile strength after heating at 300 ° C. for 30 minutes is defined as 400 MPa or more. When the tensile strength after heating is less than 400 MPa, the copper foil is deformed by charge / discharge stress, and the charge / discharge cycle life of the battery is shortened. More preferably, the tensile strength after heating at 300 ° C. for 30 minutes is 450 MPa or more.
Here, in order to maintain a tensile strength of 400 MPa or more after heating at 300 ° C. for 30 minutes, it is preferable to have a tensile strength of 480 MPa or more in a rolled state. A more preferable tensile strength after rolling is 520 MPa or more.

(Conductivity of copper alloy foil)
The conductivity of a conventional rolled copper foil made of tough pitch copper is about 100% IACS. However, when the material is made of a copper alloy, the conductivity of the copper foil is lowered and the battery performance tends to be lowered. The electrical conductivity of the rolled copper foil containing Sn of the present invention is 80% IACS or more, preferably 83% IACS or more, and battery performance does not deteriorate at this level.

(component)
Sn contained in the copper alloy foil of the present invention is 0.05 to 0.22%, preferably 0.10 to 0.17%. By making Sn 0.05% or more, it becomes possible to adjust the tensile strength after rolling to 480 MPa or more, the tensile strength after heating at 300 ° C. for 30 minutes to 400 MPa or more, and further K to 10 or more. . By making Sn 0.10% or more, it becomes possible to adjust the tensile strength after rolling to 520 MPa or more and the tensile strength after heating at 300 ° C. for 30 minutes to 450 MPa or more.
On the other hand, by setting Sn to 0.22% or less, it becomes possible to adjust the conductivity to 80% IACS or more and K to 20 or less. By making Sn 0.17% or less, the conductivity can be adjusted to 83% IACS or more and K to 18 or less.

Pure copper materials commonly used by those skilled in the art include oxygen-free copper standardized by JIS-C1020, tough pitch copper standardized by JIS-C1100, and phosphorous deoxidized copper standardized by JIS-C1201, C1220, and C1221. The oxygen concentration of the oxygen-free copper melt is usually 0.001% or less, and the oxygen concentration of the tough pitch copper melt is usually 0.01 to 0.05%. Phosphorus deoxidized copper contains 0.004 to 0.04% P. In the copper alloy foil of the present invention, Sn is added to the oxygen-free molten copper. Therefore, the oxygen concentration of the copper alloy foil of the present invention is 0.001% or less, and the oxygen concentration can be adjusted by techniques known to those skilled in the art, such as carbon deoxidation of molten metal.
On the other hand, when Sn is added to tough pitch copper, Sn forms oxide particles, and not only the effects of Sn on strength, heat resistance and crystal orientation are obtained, but also when the oxide particles are subjected to charge / discharge stress. It becomes the starting point of the crack and the charge / discharge cycle life of the battery is shortened. Moreover, when Sn is added to phosphorous deoxidized copper, conductivity and stress corrosion cracking resistance are insufficient.

  The copper alloy foil of the present invention can contain 0.1% or less of Ag. By adding Ag, the heat resistance can be improved without lowering the electrical conductivity. When Ag exceeding 0.1% is added, the heat resistance is further improved, but in addition to an increase in production cost, ductility is lowered and rolling into a foil becomes difficult. A more preferable Ag concentration is 0.06% or less. In addition, the electrolytic copper used as the melting material of the copper foil usually contains about 0.001% of Ag as an unavoidable impurity.

(Manufacturing method of copper foil)
In the melting of an ingot, first, the oxygen concentration in molten copper is lowered to 0.001% or less by utilizing a deoxidation reaction with carbon, and then an alloy element is added. Next, the ingot is made into a plate having a thickness of about 10 mm by hot rolling, and then cold rolling and recrystallization annealing are repeated, and finally finished to a predetermined thickness (generally 35 to 5 μm) by cold rolling. When the thickness is 5 μm or less, it tends to break even if the tensile strength per unit area is high. On the other hand, if it exceeds 35 μm, the negative electrode plate becomes thick, and it becomes difficult to reduce the size of the secondary battery.

Recrystallization annealing is performed under the conditions that the furnace temperature is in the range of 300 to 800 ° C., the annealing time is in the range of several seconds to several hours, and the crystal grain size after annealing is a predetermined size (usually 3 to 30 μm). Is called. The material after annealing is pickled using a sulfuric acid aqueous solution or the like in order to remove the surface oxide film generated during the annealing.
The method of controlling K is not limited to a specific method, but can be controlled, for example, by adjusting the final cold rolling conditions as follows.

In the final cold rolling after the final recrystallization annealing, the material is repeatedly passed between a pair of rolling rolls to finish the target foil thickness. K is influenced by the total degree of work in the final cold rolling and the degree of work per pass. Here, the total workability R is a sheet thickness reduction rate in the final cold rolling, and R = (T ₀ −T) / T ₀ (T ₀ : thickness before final cold rolling, T: final cold rolling) Later thickness). Further, the processing degree r per pass is a sheet thickness reduction rate when the rolling roll passes once, and r = (t ₀ -t) / t ₀ (t ₀ : thickness before passing the rolling roll, t: thickness after passing through the rolling roll).

In a pass where the working degree r exceeds 40%, shear deformation occurs in the metal structure of the copper alloy foil, and this shear deformation acts to increase K. In the final rolling, K can be adjusted to 10 or more by performing passes in which r exceeds 40% three times or more. The upper limit of the number of passes is not restricted from the point of K, but it is difficult to adjust the rolling shape (flatness) of the foil when the number of passes with a high workability with r exceeding 40% increases. Set to 5 or less. On the other hand, if r exceeds 60%, shear deformation occurs excessively and K exceeds 20. In other words, it is effective in reducing sagging that the pass of r exceeding 40% and not more than 60% is performed 3 to 5 times.
In addition, when rolling to ultrathin foil in the final cold rolling, if the degree of processing per pass is increased, the copper alloy foil is likely to break during rolling. Therefore, conventionally, r is set relatively low with emphasis on rollability, and even if a pass exceeding 40% is performed, it is only performed once in the initial stage where the plate thickness is thick.

  The total workability R of the final cold rolling is preferably 81 to 97%, more preferably 85 to 94%. If R is less than 81%, it becomes difficult to adjust K to 10 or more even if r is controlled, and it becomes difficult to obtain a tensile strength of 400 MPa or more after heating at 300 ° C. for 30 minutes.

(Battery configuration)
The negative electrode plate and the secondary battery according to the present invention are characterized by using the above copper foil as a negative electrode current collector, and other configurations are not limited, and commonly used known ones are used. Can be used.

(Negative electrode)
A negative electrode is comprised from the negative electrode collector of this invention, and the negative electrode active material formed in the single side | surface or both surfaces of a negative electrode collector. Examples of the negative electrode active material include carbonaceous materials capable of occluding and releasing lithium, metals, metal compounds (metal oxides, metal sulfides, metal nitrides), lithium alloys, and the like.
Examples of the carbonaceous material include carbonaceous materials such as graphite, coke, carbon fiber, spherical carbon, pyrolytic vapor phase carbonaceous material, and resin fired body; thermosetting resin, isotropic pitch, mesophase pitch carbon, and mesophase pitch. And carbonaceous materials obtained by subjecting carbon fibers, mesophase microspheres and the like to heat treatment at 500 to 3000 ° C., and the like.
Examples of the metal include lithium, aluminum, magnesium, tin, and silicon.
Examples of the metal oxide include tin oxide, silicon oxide, lithium titanium oxide, niobium oxide, and tungsten oxide. Examples of the metal sulfide include tin sulfide and titanium sulfide. Examples of the metal nitride include lithium cobalt nitride, lithium iron nitride, and lithium manganese nitride.
Examples of the lithium alloy include a lithium aluminum alloy, a lithium tin alloy, a lithium lead alloy, and a lithium silicon alloy.

The negative electrode active material-containing layer can contain a binder. Examples of the binder include a mixture containing carboxymethyl cellulose (CMC) and styrene butadiene (SBR). By using a binder containing CMC and SBR, the adhesion between the negative electrode active material and the current collector can be further increased.
The negative electrode active material-containing layer can contain a conductive agent. Examples of the conductive agent include acetylene black, graphite such as powdered expanded graphite, pulverized carbon fiber, pulverized graphitized carbon fiber, and the like.

(Positive electrode)
The positive electrode includes a positive electrode current collector and a positive electrode active material-containing layer formed on one or both surfaces of the positive electrode current collector.
Examples of the positive electrode current collector include an aluminum plate and an aluminum mesh material.
The positive electrode active material-containing layer contains, for example, an active material and a binder. Examples of the positive electrode active material include chalcogen compounds such as manganese dioxide, molybdenum disulfide, LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ . These chalcogen compounds may be used in a mixture of two or more. As the binder, a fluoroelastomer resin, a polyolefin resin, a styrene resin, a thermoplastic elastomer resin such as an acrylic resin, or a rubber resin such as fluororubber can be used.
The active material-containing layer may further contain acetylene black, graphite such as powdered expanded graphite, carbon fiber pulverized material, graphitized carbon fiber pulverized material, and the like as a conductive auxiliary material.

(Separator)
A separator or a solid or gel electrolyte layer can be disposed between the positive electrode and the negative electrode. As the separator, for example, a polyethylene porous film or a polypropylene porous film having a thickness of 20 to 30 μm can be used.

(Nonaqueous electrolyte)
As the non-aqueous electrolyte, those having a liquid, gel or solid form can be used. The non-aqueous electrolyte preferably includes a non-aqueous solvent and an electrolyte that is dissolved in the non-aqueous solvent.
Examples of the non-aqueous solvent include ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, and γ-butyrolactone. The kind of nonaqueous solvent to be used can be one kind or two or more kinds.
Examples of the electrolyte include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenide (LiAsF ₆ ), and the like. The electrolyte can be used alone or in the form of a mixture.

(Production of rolled copper foil)
After adding an alloy element to the molten copper whose oxygen concentration was adjusted by carbon deoxidation, it was cast into an ingot having a width of 600 mm and a thickness of 200 mm. The ingot was heated at 850 ° C. for 3 hours and formed into a plate having a thickness of 10 mm by hot rolling. Next, the oxide scale on the surface was removed by grinding, and a 1.5 mm plate was formed by cold rolling. Then, recrystallization annealing and cold rolling were repeated, and the thickness was finished to 17 to 7 μm by final rolling.
The final recrystallization annealing (annealing immediately before the final cold rolling) was performed using a continuous annealing line. The furnace temperature was set to 700 ° C., and the material passing speed (residence time in the furnace) was adjusted so that the crystal grain size after annealing was 10 μm.
In order to change the total workability (R) in the final cold rolling, the thickness of the plate to be subjected to final recrystallization annealing was adjusted in advance. In the final cold rolling, the degree of processing (r) per pass was variously changed.

(component)
The oxygen concentration in the copper alloy matrix was analyzed by an inert gas melting-infrared absorption method, and the alloy elements were analyzed by ICP-mass spectrometry. Here, a copper foil sample was used for the analysis of the alloy element, but a sample taken from a 1.5 mm plate was used for the O analysis. This is because the ratio of the surface area to the mass of the foil sample is very large (for example, in the case of a 1 g sample, the surface area of a 1.5 mm thick plate is 1.5 cm ² while the surface area of a 10 μm thick foil is 220 cm. ² ) When oxygen is analyzed using a copper foil sample, oxygen in the surface oxide film and adsorbed water film is added, and the oxygen analysis value is increased by about 0.005% from the oxygen concentration in the copper foil. . In addition, in order to determine that this is an oxygen-free copper-based foil using a foil sample, the metal structure of the sample is observed, and no oxide particles are present (the oxide particles having a diameter of 2 μm or more are 0. (01 / mm ² or less) may be confirmed.

(Tensile strength, conductivity)
The copper alloy foil sample was heated at 300 ° C. for 30 minutes to simulate the drying process of the negative electrode active material. The tensile strength was calculated | required according to IPC (Institute for Interconnecting and Packaging Electronics Circuits) specification, IPC-TM-650; Method 2.4.19 with respect to the sample before and behind a heating. The test piece was 12.7 mm in width and 150 mm in length, and was collected so that the length direction of the test piece was parallel to the rolling direction. The pulling speed was 50 mm / min. Moreover, the electrical conductivity in 20 degreeC was calculated | required with the four-terminal method using the test piece for a tension test with respect to the sample of final cold rolling completion (before heating for 30 minutes at 300 degreeC).

(Crystal orientation)
The copper alloy foil sample was heated at 300 ° C. for 30 minutes to simulate the drying process of the negative electrode active material. The X-ray intensity of each surface of (220), (111) and (311) on the copper foil surface was determined by X-ray diffraction for the heated sample. Fine powder of copper this value measured in advance (Kanto Chemical Co., copper (powder), deer first grade,> 99.85%, 100-200 mesh) divided by the integrated intensity of each surface in, I _{( 220)} / I _{0 (220)} , I ₍₁₁₁₎ / I _{0 (111)} and I ₍₃₁₁₎ / I _{0 (311)} were determined. X-ray diffraction is performed using a Co tube, and the integrated values of peak intensities are (220): 2θ = 86-91 °, (111): 2θ = 47-55 °, (311): 2θ = 107-113. Measurements were made in the range of ° (θ is the diffraction angle).

(Dare evaluation)
The copper alloy foil sample was heated at 300 ° C. for 30 minutes to simulate the drying process of the negative electrode active material. Next, a circular sample was punched out by press punching. The die hole diameter was 5.000 mm. The punch was cylindrical and the diameter was as follows according to the sample thickness. 17 μm thick sample: 4.995 mm, 12 μm thick sample: 4.996 mm, 10 μm thick sample: 4.997 mm, 7 μm thick sample: 4.998 mm. The punching speed was 10 mm / min, and no material pressing was performed.
The fracture surface of the punched sample was observed from the cross section, and the size of the sagging shown in FIG. 2 was measured. The measurement position was a fracture surface portion parallel to the rolling direction. When the sagging was 1/5 or less of the foil thickness, it was determined that good shear workability was obtained.

(Cycle life)
For a sample having a thickness of 10 μm, a cylindrical lithium ion secondary battery shown in FIG. 1 was prepared by the following procedure, and the cycle life was measured.
(1) A thickener aqueous solution dissolved in 99 parts by weight of water with respect to 50 parts by weight of flaky graphite powder as a negative electrode active material, 5 parts by weight of styrene butadiene rubber as a binder, and 1 part by weight of carboxymethylcellulose as a thickener. 23 parts by weight was kneaded and dispersed to obtain a negative electrode paste. This negative electrode paste was applied on both sides of the rolled copper foil sample surface to a thickness of 200 μm by a doctor blade method, heated at 300 ° C. for 30 minutes, and dried. After pressurizing to adjust the thickness to 160 μm, the negative electrode plate 6 was obtained by molding by shearing.
(2) LiCoO ₂ powder 50 parts by weight as a positive electrode active material, acetylene black 1.5 parts by weight as a conductive agent, PTFE 50% by weight aqueous dispersion 7 parts by weight, and carboxymethyl cellulose 1% by weight aqueous solution 41 as a thickener .5 parts by weight was kneaded and dispersed to obtain a positive electrode paste. This positive electrode paste was applied on both sides to a thickness of about 230 μm by a doctor blade method on a current collector made of an aluminum foil having a thickness of 30 μm, heated at 200 ° C. for 1 hour and dried. After pressurizing and adjusting the thickness to 180 μm, it was molded by shearing to obtain a positive electrode plate 5.
(3) A battery case 8 accommodates an electrode group wound in a spiral shape in a state where the positive electrode plate 5 and the negative electrode plate 6 are insulated through a separator 7 made of a polypropylene resin microporous film having a thickness of 20 μm. .
(4) The negative electrode lead 9 connected from the negative electrode plate 6 was electrically connected through the case 8 and the lower insulating plate 10. Similarly, the positive electrode lead 3 connected from the positive electrode plate 5 was electrically connected to the internal terminal of the sealing plate 1 via the upper insulating plate 4. After these, a non-aqueous electrolyte is injected, and the sealing plate 1 and the battery case 8 are caulked and sealed through the insulating gasket 2 to form a cylindrical lithium ion having a diameter of 17 mm, a height of 50 mm and a battery capacity of 780 mAh. A secondary battery was produced.
(5) The electrolytic solution was obtained by dissolving 1.0 mol of lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte in a mixed solvent of 30% by volume of ethylene carbonate, 50% by volume of ethyl methyl carbonate, and 20% by volume of methyl propionate. A predetermined amount of electrolyte was injected. The electrolytic solution was impregnated in the positive electrode active material layer and the negative electrode active material layer.

  Charge / discharge cycle characteristics were evaluated using the produced batteries. Charging / discharging was performed in an environment of 20 ° C., the discharge capacity at the third cycle was taken as the initial capacity, the number of cycles was counted until the discharge capacity was reduced to 80% of the initial capacity, and this was taken as the cycle life. Charging conditions: Constant current-constant voltage charging at 4.2V for 2 hours, and after 550mA (0.7CmA) constant current charging until the battery voltage reaches 4.2V, the current value further attenuates To 40 mA (0.05 CmA). Discharge conditions: Discharge was performed at a constant current of 780 mA (1 CmA) to a discharge end voltage of 3.0 V. It was determined that good cycle characteristics were obtained when the cycle life was 600 times or more, and particularly good cycle characteristics were obtained when the cycle life was 700 times or more.

The evaluation results are shown in Tables 1 and 2. Table 3 shows the degree of processing of each pass for each method employed in the final cold rolling of each example and comparative example.
In Invention Examples 1 to 10 and 15 to 23 having a foil thickness of 10 μm, 0.05 to 0.22% Sn and 0.1% or less of Ag are added to oxygen-free copper, and the total processing degree R is 81 to 97. %, The number of passes in which r exceeds 40% was 3 to 5, and r was 60% or less. As a result, an electrical conductivity of 80% IACS or higher and a tensile strength of 480 MPa or higher were obtained. Tensile strength after heating at 300 ° C. for 30 minutes was 400 MPa or higher, and K after heating at 300 ° C. for 30 minutes was 10-20. became. For this reason, sagging was as small as 1/5 or less of the foil thickness, and a good cycle life of 600 times or more was obtained.
Among these, in Invention Examples 3 to 6, 15 to 17, and 19 to 22 with Sn of 0.10 to 0.17% and R of 85 to 95%, a conductivity of 83% IACS or more and a tensile of 520 MPa or more Strength was obtained, the tensile strength after heating at 300 ° C. for 30 minutes was 450 MPa or more, K after heating at 300 ° C. for 30 minutes was 18 or less, and a very good cycle life of 700 times or more was obtained.
For Invention Examples 31 to 38 having a foil thickness different from 10 μm, the tensile strength after heating at 300 ° C. for 30 minutes is 400 MPa or more and K is 10 to 20 by adjusting the alloy components and rolling conditions in the same manner. It was confirmed that sagging was improved to 1/5 or less of the foil thickness.

Comparative Example 11 is a conventional oxygen-free copper, and Comparative Example 12 is a sample in which Sn is added to oxygen-free copper and the amount added is less than 0.05%. In these, since K after heating at 300 ° C. for 30 minutes became less than 10, the sagging exceeded 1/5 of the foil thickness, and sufficient adhesion between the copper foil and the active material could not be obtained. Moreover, since the tensile strength decreased to less than 400 MPa by heating at 300 ° C. for 30 minutes, the copper foil was deformed by repeated charge and discharge stress. As a result, the active material peeled off under repeated charge / discharge stress, and the cycle life was less than 600 times.
In Comparative Example 13, Sn exceeding 0.22% was added. The copper foil became brittle because K after heating at 300 ° C. for 30 minutes exceeded 20, and the copper foil cracked when subjected to repeated stress, and the cycle life was less than 600 times. Furthermore, since the conductivity was less than 80% IACS, heat generation and voltage loss could not be ignored, and the intended secondary battery could not be manufactured.
In Comparative Example 14, since oxygen exceeded 0.001%, a part of the added Sn was oxidized to become oxidized Sn. As a result, when subjected to repeated charge and discharge stress, the copper foil cracked starting from Sn oxide, and the cycle life was less than 600 times. Also, oxidized Sn does not contribute to the improvement of the heat resistance and crystal orientation of Cu, and therefore K and tensile strength after heating at 300 ° C. for 30 minutes are lower than Example 3 to which the same amount of Sn was added. It was.

In Comparative Examples 24-27, the number of passes in which the degree of processing r per pass exceeds 40% was less than three. The sagging exceeded 1/5 of the foil thickness, and sufficient adhesion between the copper foil and the active material could not be obtained. As a result, the active material peeled off under repeated charge / discharge stress, and the cycle life was less than 600 times. Also in Comparative Examples 34 and 39 having a foil thickness different from 10 μm, the number of passes in which r exceeded 40% was less than 3, and the sagging exceeded 1/5 of the foil thickness.
In Comparative Example 28, a pass in which r exceeds 60% was performed. The copper foil became brittle because K after heating at 300 ° C. for 30 minutes exceeded 20, and the copper foil cracked when subjected to repeated stress, and the cycle life was less than 600 times.
In Comparative Example 29, the total degree of processing R was less than 81%. Since K after heating at 300 ° C. for 30 minutes was less than 10, sagging exceeded 1/5 of the foil thickness, and sufficient adhesion between the copper foil and the active material could not be obtained. Moreover, since the tensile strength decreased to less than 400 MPa by heating at 300 ° C. for 30 minutes, the copper foil was deformed by repeated charge and discharge stress. As a result, the plastic active material peeled due to repeated charge and discharge stress, and the cycle life was less than 600 times.
In Comparative Example 30, the total degree of processing R exceeds 97%. The copper foil became brittle because K after heating at 300 ° C. for 30 minutes exceeded 20, and the copper foil cracked when subjected to repeated stress, and the cycle life was less than 600 times.

1: Sealing plate 2: Insulating gasket 3: Positive electrode lead 4: Upper insulating plate 5: Positive electrode plate 6: Negative electrode plate 7: Separator 8: Battery case 9: Negative electrode lead 10: Lower insulating plate

Claims (6)

It is a rolled copper alloy foil for a negative electrode current collector of a secondary battery having an electric conductivity of 80% IACS or more based on oxygen-free copper base containing 0.05 to 0.22% by mass of Sn and the balance being Cu and impurities. The crystal orientation after heating at 300 ° C. for 30 minutes is
10 ≦ (5 · I ₍₂₂₀₎ / I _{0 (220)} + 2 · I ₍₁₁₁₎ / I _{0 (111)} + I ₍₃₁₁₎ / I _{0 (311)} ) ≦ 20
I _(hkl) : Integrated intensity of (hkl) plane obtained by X-ray diffraction with respect to copper alloy foil surface I _{0 (hkl)} : Relation of integral intensity of (hkl) plane obtained by X-ray diffraction with respect to copper powder A rolled copper alloy foil having a tensile strength of 400 MPa or more after heating at 300 ° C. for 30 minutes.   Furthermore, 0.1 mass% or less of Ag is contained, The rolled copper alloy foil of Claim 1 characterized by the above-mentioned.   A negative electrode current collector composed of the rolled copper alloy foil according to claim 1.   The negative electrode plate which has the negative electrode active material layer which has a carbonaceous material as a main component on the at least single side | surface of the negative electrode collector of Claim 3.   A negative electrode having an active material layer containing at least one selected from the group consisting of metallic lithium, metallic tin, a tin compound, a silicon simple substance, and a silicon compound on at least one surface of the negative electrode current collector according to claim 3. Board.   6. An electrode plate group in which the negative electrode plate according to claim 4 or 5 is insulatively arranged via a separator having a lithium transition metal composite oxide as a main component of a positive electrode active material and a separator, and an electrode plate group And a battery case containing a non-aqueous electrolyte.

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