JP5329372B2 - Rolled copper foil, and negative electrode current collector, negative electrode plate and secondary battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolled copper foil suitable as a negative electrode collector material of a secondary battery and a negative electrode collector using this, a negative electrode plate, and a battery. <P>SOLUTION: The rolled copper foil for secondary battery negative electrode collector is a copper alloy foil of oxygen-free copper base which contains Sn of 0.05-0.22 mass% and the rest is Cu and impurities and in which the Sn concentration in the surface oxidized film is 0.16-1.5 mass% and which has excellent cycle characteristics. The copper foil may contain Ag of 0.1 mass% or less and preferably has a tensile strength of 480 MPa or more and a conductivity of 80% IACS or more, and maintains the tensile strength of 400 MPa of more after annealing for 30 minutes at 300&deg;C. The secondary battery using this copper foil as a current collector of the negative electrode plate is superior in charge and discharge cycle life. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

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 as an active material is used as a negative electrode. What is used is known (FIG. 2).

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 oxygen of 100 to 500 mass ppm, and the copper content is standardized to 99.90 mass% or more (hereinafter, mass ppm and mass% are expressed as ppm and%, respectively). ).
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 150 to 300 ° C. for several hours 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 a 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 mechanical repeated 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.

In addition, 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, a high-tension load is applied at the time of application of the active material in battery production, and the foil breakage easily occurs, and the foil breakage due to the softening is more likely to occur. Accordingly, there is a need for a copper foil that has higher tensile strength in the product after final rolling (rolled up) and does not cause foil breakage due to softening.
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 Patent Application Laid-Open No. 2000-303128 (Patent Document 1) discloses a copper alloy foil obtained by adding 50 or 100 ppm of Cr, Zn, Ag, Ca, Sn, Sb or Bi to oxygen-free copper.
Japanese Unexamined Patent Application Publication No. 2000-133276 (Patent Document 2) discloses a copper alloy foil containing Zn in a range of 10 to 35%.
In JP-A-11-339811 (Patent Document 3), Cu-0.1% Fe-0.03% P, Cu-0.3% Cr-0.25% Sn-0.2% Zn and Cu-0. A copper alloy foil made of 1% Ni is disclosed.
Japanese Patent Application Laid-Open No. 2000-328159 (Patent Document 4) contains 0.002 to 0.45% by weight of P, and 0.006 to 0.25% by weight of Fe or / and 0.005 to 0.25. A copper alloy foil with added weight percent Ag is disclosed. These alloys are based on phosphorous-deoxidized copper, and the P concentration is limited so as not to cause adverse effects on the properties of P.
Japanese Patent Application Laid-Open No. 2003-286528 (Patent Document 5) 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.

JP 2000-303128 A JP 2000-133276 A JP 11-339811 A JP 2000-328159 A JP 2003-286528 A

Although the copper alloy foil of Patent Document 1 has a tensile strength of 460 to 480 MPa, its heat resistance is targeted to a tensile strength of 400 to 430 MPa after a thermal history of 30 minutes at 200 ° C., Furthermore, a copper foil that maintains the tensile strength even at high temperatures has not been aimed. In Patent Document 2, the alloy having the highest conductivity among the examples is Cu-10% Zn (JIS-C2200), and the conductivity is only 44% IACS (Japan Copper and Brass Association: Copper Products Data Book). (1997)). In the copper alloy foil in which precipitates such as Fe-P and Cr of Patent Document 3 are formed, higher strength and heat resistance can be obtained, but the foil becomes brittle and it has been difficult to roll into an ultrathin foil. And in the Cu-Fe-P alloy in which Fe-P particles are precipitated and the Cu-Cr-Sn-Zn alloy in which Cr particles are precipitated, a tensile strength of 550 MPa is obtained. The strength is at a level that reaches 500 MPa. Since Ag used in Patent Document 4 is expensive, the amount of addition is limited, and the target is tensile strength after 5 minutes of heat history at 300 ° C. The copper foil to maintain was not intended.
According to the examination results of the present inventors, among the conventional copper alloy foils for negative electrode current collectors, the Cu—Sn alloy based on oxygen-free copper of Patent Document 5 is relatively characteristic, manufacturable, and cost-effective. However, it was not sufficient in terms of charge / discharge cycle characteristics of the secondary battery.

In recent years, the demand for the performance of lithium ion secondary batteries has been advanced. Along with this, the rolled copper foil for the negative electrode current collector is not torn during the manufacturing process where high tension is applied or when it is subjected to secondary battery charging / discharging stress. There is a strong demand for the ability of a substance not to peel off.
The present invention improves the Cu-Sn alloy foil, and is suitable as a negative electrode current collector material for secondary batteries such as lithium ion secondary batteries. An object of the present invention is to provide a negative electrode current collector, a negative electrode plate, and a secondary battery.

As a result of intensive studies to solve the above problems, the present inventor has made the following invention.
(1) An oxygen-free copper-based copper alloy foil containing 0.05 to 0.22 mass% of Sn and the balance being Cu and impurities, and the Sn concentration in the surface oxide film is 0.16 to 1.5 mass % der is, together with a more tensile strength and 80% IACS or more conductivity 480 MPa, it characterized that you keep the tensile strength of at least 400MPa after heating at 300 ° C. 30 min, the secondary battery Rolled copper foil for negative electrode current collectors.
(2) The rolled copper 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 foil described in (1) or (2) above.
( 4 ) A negative electrode plate having a negative electrode active material layer mainly composed of a carbonaceous material or a graphite material on at least one surface of the negative electrode current collector described in ( 3 ) above.
( 5 ) At least one surface selected from the group consisting of metallic lithium, metallic tin, a tin compound, a silicon simple substance, and a silicon compound is contained on at least one surface of the negative electrode current collector described in ( 3 ) above. A negative electrode plate having an active material layer.
( 6 ) An electrode plate group in which the negative electrode plate described in the above ( 4 ) or ( 5 ) 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 profile of the depth direction of Sn and O density | concentration in the sample surface of invention example 6. FIG. It is the schematic which shows the structure of a general secondary battery.

(Copper foil components)
In the present invention, Sn is added to oxygen-free copper in order to improve the strength and heat resistance of the copper foil. When the Sn concentration is 0.05% or more, preferably 0.10% or more, a copper foil excellent in strength and heat resistance can be obtained. On the other hand, if the Sn concentration exceeds 0.22%, the electrical conductivity is lowered and it becomes unsuitable for the negative electrode current collector of the secondary battery. More preferably, it is 0.15% or less, and in this case, a conductivity of 83% IACS or more can be stably obtained.

  The copper alloy foil of the present invention is melted by adding Sn to an oxygen-free copper melt. The oxygen concentration of the oxygen-free copper melt is usually 10 ppm or less. When Sn is added to a molten metal containing 100 to 500 ppm of oxygen such as a tough pitch copper molten metal, Sn is oxidized to form tin oxide, and the effect of improving the heat resistance of Sn cannot be obtained. This is because Sn improves the heat resistance of Cu in a state of being dissolved in Cu, but the Sn component deposited as an oxide does not contribute to the improvement of the heat resistance of Cu. The oxygen concentration can be adjusted by techniques known to those skilled in the art, such as carbon deoxidation of molten metal.

  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 10 ppm of Ag as an inevitable impurity.

(Characteristics of copper foil)
In order to further improve the reliability of the battery without causing deformation of the copper foil due to charge / discharge stress, it is preferable to maintain a tensile strength of 400 MPa or more after the drying process. The heat load level in the drying process required in 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 heat load standard of 200 ° C. for 30 minutes (Patent Document 1) and 300 ° C. for 5 minutes (Patent Document 4).
The rolled copper foil of the present invention has a tensile strength after heating at 300 ° C. for 30 minutes, preferably 400 MPa or more, more preferably 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 necessary to have a tensile strength of 480 MPa or more, preferably 520 MPa or more in the state after rolling.
When the Sn concentration is 0.05% or more, the tensile strength after heating under the above conditions is 400 MPa or more, and when it is 0.10% or more, it becomes 450 MPa or more.

  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 of the present invention is preferably 80% IACS or higher, more preferably 83% IACS or higher, and battery performance does not deteriorate at this level.

(Oxide film of copper foil)
The Sn concentration in the surface oxide film of the present invention is 0.16 to 1.5% by mass.
Since Sn is easier to oxidize than Cu, the Sn concentration in the oxide film is higher than the Sn concentration in the matrix. When tin oxide is present on the surface of the copper foil, the affinity for the negative electrode active material such as a metal compound is increased, so it is predicted that there is an advantage that the working efficiency of the process of manufacturing the negative electrode by applying the negative electrode active material is increased. it can. Therefore, in the prior art, the problem with respect to tin oxide that inevitably exists on the surface of the Sn-containing copper foil has not been particularly recognized. However, the present inventor found that when the Sn concentration in the oxide film exceeds 1.5%, the oxide film becomes brittle and easily peels off from the base metal, and the bondability between the copper foil and the active material is inhibited. I found By controlling the Sn concentration in the oxide film to 1.5% or less, the adhesion between the copper foil and the active material was improved, and the charge / discharge cycle life of the battery was improved.
On the other hand, if an attempt is made to adjust the Sn concentration in the oxide film to less than 0.16%, adverse effects occur in areas other than the adhesion to the active material. For example, as will be described later, if annealing is performed in an oxidizing atmosphere in order not to localize tin oxide on the surface, a thick and non-uniform oxide film is generated, and material fracture frequently occurs in final rolling after pickling.
The thickness of the oxide film of the copper alloy foil of the present invention is 1 to 4 nm. Within this range, the thickness of the oxide film does not affect the adhesion between the copper foil and the active material.
In the present invention, the Sn concentration of the oxide film is determined by measuring the Sn concentration profile by Ar sputtering the sample surface by XPS (X-ray photoelectron spectroscopy), and the obtained profile is more than the baseline corresponding to the matrix concentration. Expressed as the maximum peak concentration present on the surface side. Further, the thickness of the oxide film is expressed as the depth when O concentrated on the surface decreases to the O concentration of the base metal in the XPS O concentration profile.

(Manufacturing method of copper foil)
In the melting of the ingot, first, the oxygen concentration in the molten copper is lowered to 10 ppm or less by utilizing a deoxidation reaction by carbon, and then Sn is added. When Sn is added in a state where the oxygen concentration in the molten copper exceeds 10 ppm, Sn is oxidized, and inclusions of tin oxide are generated. 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 for adjusting the Sn concentration in the copper foil surface oxide film after the final rolling does not limit the present invention. For example, the gas atmosphere in the furnace in the final recrystallization annealing before the final rolling has the following effects. Take control into consideration.
When the atmosphere is highly reducible, the tendency of Sn to be oxidized more easily than Cu is directly a factor, and Cu is not oxidized but Sn is preferentially oxidized to form a Sn-rich oxide film. At the time of pickling after annealing, Cu oxide is easily dissolved in acid, but Sn oxide is hardly dissolved in acid, so that the Sn concentration in the oxide film is further increased. Although the oxide film formed by annealing may be partially cracked or peeled off in the final rolling, most of it remains on the surface of the foil product.
On the other hand, if the atmosphere is highly oxidizable, Sn and Cu are oxidized at a similar rate so that the difference in oxidation tendency between Sn and Cu cannot be distinguished, and the Cu / Sn concentration ratio in the oxide film becomes Cu in the matrix. Although it approaches the Sn concentration ratio, the oxide film grows thick and uneven. For this reason, irregularities and pits are generated on the surface of the material after pickling, and pinholes are formed in the copper foil or the copper foil is broken during rolling to the foil.

A preferable final rolling degree is 80 to 98%, more preferably 85 to 95%. Here, the degree of rolling r is r = (t ₀ -t) / t ₀ (t: thickness after rolling, t ₀ : thickness before rolling). If the degree of work of the final cold rolling is less than 80%, it becomes difficult to adjust the tensile strength after rolling to 480 MPa or more. Moreover, when the workability of final cold rolling exceeds 98%, the heat resistance of the copper foil is lowered, and it becomes difficult to maintain a tensile strength of 400 MPa or more after heating at 300 ° C. for 30 minutes. This is because extremely accumulated processing strain promotes recrystallization.

(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 graphite materials, carbonaceous materials such as graphite, coke, carbon fiber, spherical carbon, pyrolytic vapor phase carbonaceous material, and resin fired body; thermosetting resin, isotropic pitch, and mesophase pitch carbon. And graphite materials or carbonaceous materials obtained by subjecting mesophase pitch-based carbon fibers, mesophase microspheres, etc. to heat treatment at 500 to 3000 ° C.
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 thermoplastic elastomer resin such as a fluorine resin, a polyolefin resin, a styrene resin, or an acrylic resin, or a rubber resin such as a fluorine rubber 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 Sn to the molten copper whose oxygen concentration was adjusted by carbon deoxidation, it was cast into an ingot having a width of 500 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. Thereafter, recrystallization annealing and cold rolling were repeated, and the final rolling finished to a thickness of 18 to 6 μm.
Recrystallization annealing 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 working degree of the final rolling, the thickness of the plate to be subjected to final annealing (annealing immediately before final cold rolling) was adjusted in advance.
The Sn concentration in the oxide film on the copper foil surface was adjusted by appropriately controlling the oxidation-reduction atmosphere of the gas atmosphere in the furnace in the final recrystallization annealing by the following method. The used continuous annealing furnace is a furnace that uses a mixed gas of butane gas and air as a heat source, and the atmosphere in the furnace is a mixed gas of CO, CO ₂ , O ₂ , and N ₂ . The ratio of CO concentration to CO ₂ concentration (CO / CO ₂ ) was adjusted by changing the mixing ratio of butane gas and air. When the CO / CO ₂ ratio is increased, a reducing atmosphere is formed, and when the CO / CO ₂ ratio is decreased, an oxidizing atmosphere is formed. The material after leaving the furnace was pickled with a 10% by mass sulfuric acid aqueous solution. The following evaluation was performed on the rolled copper foil obtained after the final rolling.

(component)
The oxygen concentration in the copper foil matrix was analyzed by an inert gas melting-infrared absorption method, and the Sn and Ag concentrations were analyzed by ICP-mass spectrometry. Here, a copper foil sample was used for Sn and Ag analysis, but a sample collected from a 1.5 mm plate was used for 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 50 ppm 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. Although the analysis limit is 1 ppm, the display in the table is limited to 2 digits after the decimal point of mass%.

(Tensile strength, conductivity)
The rolled copper 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 a heating and after 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.
Using a test piece for a tensile test on the rolled up sample (before heating), the conductivity at 20 ° C. was determined by a four-terminal method.

(Oxide film)
Using XPS (X-ray photoelectron spectroscopy), the O and Sn concentration profiles in the sample surface layer were measured by analyzing O and Sn while sputtering the sample surface with Ar. The measurement conditions are as follows.
Apparatus: ULVAC-PHI Co., Ltd. 5600MC, ultimate vacuum: 1.4 × 10 ⁻⁷ Pa, excitation source: monochromatic AlKα, output: 210 W, detection area: 800 μmφ, incident angle: 45 degrees, take-off angle: 45 degrees No neutralization gun.
(Sputtering conditions) Ion species: Ar +, acceleration voltage: 3 kV, sweep region: 3 mm × 3 mm, rate: 2.0 nm / min in terms of SiO ₂ .
The measurement result in Invention Example 6 to be described later is shown in FIG. The Sn peak value in the Sn concentration profile was 0.8%, and this value was taken as the Sn concentration in the oxide film. Further, when the thickness of the oxide film is read from the profile of O concentration, it becomes 1.8 nm. Here, as shown by the dotted line in the figure, the thickness of the oxide film is a depth at which the tangent line is drawn at the bottom of the O concentration curve, and this tangent line intersects the O concentration of the matrix (in this case, zero mass%). Say it.

(Cycle life)
A cylindrical lithium ion secondary battery shown in FIG. 2 was produced 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.

The evaluation results are shown in Table 1. Invention Examples 3 to 10, 12 to 13, 15 to 18, 20 to 22, and 26 to 30 contain 0.05 to 0.22% by mass of Sn, have a conductivity of 80% IACS or more and a tensile strength of 480 MPa or more. The tensile strength of 400 MPa or more is maintained even after annealing at 300 ° C. for 30 minutes. Further, the Sn concentration in the surface oxide film is 1.5% or less. As a result, a good cycle life of 600 times or more is obtained.
In Comparative Examples 1 and 2, Invention Examples 3 to 10, and Comparative Example 11, the effect of Sn concentration in the copper alloy is examined.
Invention Examples 3 to 10 are Sn concentrations within the range of the present invention, and the intended characteristics were obtained. Inventive Examples 3 and 4 are slightly inferior in tensile strength after thermal history because of low Sn concentration. Inventive Examples 9 and 10 have slightly low electrical conductivity because of high Sn concentration.
Comparative Example 1 is a conventional additive-free oxygen-free copper, and the tensile strength of the copper foil decreased to nearly 200 MPa due to a 30-minute thermal history at 300 ° C. in the active material drying step. In Comparative Example 2, the addition amount of Sn added to oxygen-free copper was less than 0.05%, and the tensile strength was less than 400 MPa after 30 minutes of heat history at 300 ° C. Since the tensile strength after heat history was low, the copper foils of Comparative Examples 1 and 2 were deformed by repeated charge / discharge stress, and the active material applied to the copper foil surface was peeled off. As a result, the cycle life was less than 600 times. On the other hand, in Comparative Example 11, since Sn exceeding 0.22% was added, the conductivity was lower than 80% IACS, and the intended secondary battery could not be manufactured due to heat generation and voltage loss.

Invention Examples 12 and 13 added Ag in a preferable range to improve the heat resistance without lowering the electrical conductivity, and the same amount of Sn was added as the tensile strength after heating at 300 ° C. for 30 minutes. It is higher than Invention Example 9.
In Comparative Example 14, oxygen exceeded 10 ppm, and a part of the added Sn was oxidized to be oxidized. For this reason, the tensile strength after heating at 300 ° C. for 30 minutes was less than 400 MPa. Furthermore, as a result of cracks occurring in the copper foil starting from tin oxide when subjected to repeated charge / discharge stress, the copper foil was deformed and the active material was peeled off. As a result, the cycle life was significantly less than 600 times.
Invention Examples 15 to 18 are intended to be used regardless of the foil thickness as long as the thickness of the oxide film is in the range of 1 to 4 nm even when the foil thickness is 6 μm and 12 μm with respect to the foil thickness of 10 μm of Invention Examples 5 to 7. It shows that the effect to do.

In Comparative Example 19, Invention Examples 20 to 22, and Comparative Examples 23 and 24, the effect of Sn concentration in the surface oxide film is examined.
Invention Examples 20 to 22 are Sn concentrations in the surface oxide film within the range of the present invention, and the intended characteristics were obtained.
In Comparative Example 19, when the CO / CO ₂ ratio in the final annealing was made less than 0.1 and the atmosphere was strongly oxidized, a thick and non-uniform oxide film was formed although the Sn concentration in the surface oxide film was low, Remarkable irregularities were formed on the surface after the oxide film was dissolved by pickling. In the final rolling of the next process, the material broke due to the unevenness, and the characteristics could not be evaluated. “* 1” in the table indicates that evaluation is impossible.
In Comparative Examples 23 and 24, the CO / CO ₂ ratio at the time of final annealing exceeded 0.3, the reducibility of the atmosphere became too strong, and the Sn concentration of the surface oxide film exceeded 1.5%. Since this oxide film is brittle, the bondability between the copper foil and the active material is inhibited, and the active material peels from the copper foil when subjected to repeated charge / discharge stress, and the cycle life is less than 600 times.

In Comparative Example 25, Invention Examples 26 to 30, and Comparative Example 31, the effect of the final rolling work degree is examined.
Inventive Examples 26 to 30 adopted an appropriate final rolling degree of processing, and thus intended characteristics were obtained. Inventive Example 26 has a slightly low workability, and Inventive Example 30 has a slightly high workability, so it is slightly inferior in tensile strength after heat history.
Since the working degree of Comparative Example 25 was less than 80%, the tensile strength after rolling was less than 480 MPa, and due to this influence, the tensile strength after receiving a heat history at 300 ° C. for 30 minutes was less than 400 MPa. . Since the working degree of Comparative Example 31 exceeded 98%, annealing softening was promoted, and the tensile strength after receiving a thermal history at 300 ° C. for 30 minutes was less than 400 MPa. The copper foils of Comparative Examples 25 and 31 were deformed by repeated charge / discharge stress, and the active material applied to the copper foil surface was peeled off. As a result, 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)

An oxygen-free copper-based copper alloy foil containing 0.05 to 0.22% by mass of Sn and the balance being Cu and impurities, and the Sn concentration in the surface oxide film is 0.16 to 1.5% by mass Ri, together with a more tensile strength and 80% IACS or more conductivity 480 MPa, characterized that you maintain 400MPa or more tensile strength after heating at 300 ° C. 30 minutes, the negative electrode current collector for a secondary battery Rolled copper foil for body.   Furthermore, 0.1 mass% or less of Ag is contained, The rolled copper foil of Claim 1 characterized by the above-mentioned. Negative electrode current collector composed of rolled copper foil of claim 1 or 2, wherein. The negative electrode plate which has the negative electrode active material layer which has a carbonaceous material or a graphite material as a main component on the at least single side | surface of the negative electrode collector of Claim 3 . 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 is formed on at least one surface of the negative electrode current collector according to claim 3. A negative electrode plate. 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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