JP5219973B2 - Rolled copper foil excellent in shear workability, 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, in particular, a rolled copper foil that does not easily sag in a shearing process, and a negative electrode collector using the same. The present invention relates to an electric body, a negative electrode plate, and a battery.

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 (FIG. 4).

  Copper foil includes rolled copper foil and electrolytic copper foil. The rolled copper foil is excellent in terms of strength, elongation, fatigue characteristics and the like as a material for the secondary battery negative electrode plate because the processing strain due to rolling is stored in the material and is cured. Many of the commercially available rolled copper foils are made of pure copper such as tough pitch copper or oxygen-free copper. In the rolled copper foil manufacturing process, tough pitch copper or oxygen-free copper ingots are hot-rolled, then cold-rolled and annealed repeatedly, and finally in the final cold-rolled thickness of 18, 12, 9, 6 μm, etc. Finish.

Generally, manufacture of a copper foil negative electrode plate is performed in the following process using electrolytic copper foil or rolled copper foil after roughening.
(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 to obtain a negative electrode plate material.
(2) Heat at 150 to 200 ° C. for several hours to several tens of hours to dry.
(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.
The shearing process refers to a processing method in which a plate material is subjected to shear deformation to separate materials, and examples include punching with a press, cutting with shearing, cutting with a round blade slitter, and the like.

  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. When the negative electrode active material is peeled off from the copper foil or cracked in the copper foil due to this stress, the charge / discharge cycle life of the battery is shortened. Therefore, attempts have been made to improve the copper foil for the purpose of improving the cycle life.

In JP-A-2000-303128 (Patent Document 1), an alloying element is added in order to prevent the rolled copper foil from being recrystallized due to the thermal history received in the battery manufacturing process and the strength is lowered (softening). In addition to solid solution, the oxygen content is suppressed to 30 ppm or less in order to prevent oxide formation of the additive element.
In Japanese Patent Application Laid-Open No. 2008-4462 (Patent Document 2), by increasing the crystal grains of the electrolytic copper foil by heat treatment, distortion generated between the crystal grains due to expansion and compression during charge / discharge is reduced, and charge / discharge cycle characteristics are improved. doing.

Various studies have been conducted in the field of rolled copper foil for flexible printed circuit (FPC) substrates to improve the crystal structure level of copper foil. For example, JP 2000-212661 (Patent Document 3) adjusts the amount of Cu ₂ O inclusions by limiting the oxygen concentration in tough pitch copper for the purpose of improving the flexibility and softening characteristics of FPC rolled copper foil. . Japanese Patent Application Laid-Open No. 2000-256765 (Patent Document 4, “0019”) reports that the flexibility is improved by suppressing the amount of inclusions having a diameter of 1 to 5 μm and the amount of inclusions having a diameter of 5 μm or more. Japanese Patent Laid-Open No. 2003-19311 (Patent Document 5, “0029”) prevents the formation of large inclusions for the purpose of smoothing the surface after the ultra-thin etching process.
As described above, in the field of FPC, several inventions focusing on second-phase particles (inclusions) have been disclosed, and the adverse effects of second-phase particles on the characteristics of FPC have been pointed out. Further, the second phase particles generate a pinhole in the copper foil during the rolling process, and this pinhole causes the copper foil circuit breakage of the FPC. Even if pinholes do not occur, abnormalities may occur in the shape of the copper foil circuit due to the presence or loss of the second phase particles. Thus, for FPC applications, the second phase particles are not preferred in principle. Therefore, the total amount of the second phase particles is limited in the prior art, and the second phase particles having a specific size are not actively used for improving the characteristics of the rolled copper foil, particularly the rolled copper foil for battery negative electrode. (Patent Documents 3 to 5).

JP 2000-303128 A JP 2008-4462 A JP 2000-212661 A JP 2000-256765 A Japanese Patent Laid-Open No. 2003-19311

  On the other hand, in the rolled copper foil for the negative electrode current collector of the secondary battery, there is a problem that has not yet been solved while causing a decrease in yield in the negative electrode plate manufacturing process. This is a problem in which the surface of the copper foil is plastically deformed by shearing pressure during shearing (see FIG. 2 showing a cross section of the copper foil after shearing). The sagging not only lowers the production efficiency, but also inhibits the adhesion between the negative electrode active material and the copper foil to lower the battery performance.

The occurrence of sagging is promoted by the softening of the copper foil in the thermal history of the drying process. If only the softening is to be suppressed, the rolled copper foil material may be made into a copper alloy as proposed in Patent Document 1. However, when an alloy element is added to copper, not only the conductivity is lowered, but also the life of the press die and the blade is shortened during the shearing process. Furthermore, there is a problem that the manufacturing cost of the rolled copper foil increases due to alloying. On the other hand, in order to prevent sagging of the rolled copper foil for a negative electrode current collector, it has not been studied so far to control the metal structure of a pure copper material.
Therefore, in the present invention, the copper foil material is not made into a copper alloy, it is a pure copper material, the shear workability is improved, and it is suitable as a negative electrode current collector material for secondary batteries including lithium ion secondary batteries. An object of the present invention is to provide a rolled copper foil excellent in shear workability, and a negative electrode current collector, a negative electrode plate and a secondary battery using the same.

This inventor earnestly researched the policy which improves shear workability about the rolled copper foil softened through the drying process. As a result, if the second phase particles such as non-metallic inclusions, precipitates, and crystallized substances are dispersed in the copper matrix at an appropriate frequency according to the size, form, and composition, the shear workability is improved. I found it to improve. This invention is made | formed based on this discovery, and provides the following rolled copper foil, a negative electrode collector, a negative electrode plate, and a secondary battery.
(1) A copper or copper alloy foil used as a negative electrode current collector of a secondary battery, and among the second phase particles dispersed in the copper or copper alloy matrix, second phase particles having a diameter of 1 to 5 μm There 500-5000 pieces / mm ^2, Ri second phase particles der less than 10 / mm ² having a diameter exceeding 5 [mu] m, more than 90 percent of the second-phase particles having a diameter of 1 to 5 [mu] m, 5.0 or less aspect ratio negative electrode current collector rolled copper foil and having a.
(2 ) The rolled copper foil for a negative electrode current collector according to the above (1 ), wherein 90% or more of the second phase particles having a diameter of 1 to 5 μm are copper oxide.
( 3 ) The rolled copper foil for a negative electrode current collector according to (1) or ( 2), wherein the rolled copper foil is made of tough pitch copper containing 150 to 300 mass ppm of oxygen.
( 4 ) The rolled copper foil for a negative electrode current collector according to ( 3 ) above, wherein the total amount of trace elements excluding oxygen and silver in the tough pitch copper is 25 mass ppm or less.
( 5 ) The rolled copper foil for a negative electrode current collector according to ( 3 ) or ( 4 ) above, wherein the sulfur concentration in the trace element is 10 mass ppm or less.
( 6 ) The negative electrode electrical power collector comprised from the rolled copper foil of any one of said (1)-( 5 ).
( 7 ) 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 as described in said ( 6 ).
( 8 ) An active material 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 described in ( 6 ) above. A negative electrode plate having a layer.
(9) above (7) or the negative electrode plate according to (8), via a separator, the electrode plate group by insulating the lithium transition metal composite oxide as the positive electrode plate composed mainly of the positive electrode active material A secondary battery comprising the electrode plate group in a battery case and injecting a non-aqueous electrolyte.

  The rolled copper foil for a negative electrode current collector of the present invention is less prone to sag during shearing, has a higher production efficiency than conventional rolled copper foil, and has excellent battery performance when used as a secondary battery negative electrode material. It can be secured.

It is a scanning electron micrograph which shows the structure where the 2nd phase particle is disperse | distributing in the base material of a copper alloy. It is the schematic which shows the copper foil cross section after a shearing process. It is the schematic which shows the major axis L2 and the minor axis L1 of 2nd phase particle | grains. It is the schematic which shows the structure of a general secondary battery.

(Size and frequency of second phase particles)
The second phase particles of the present invention are particles that are formed when other elements are contained in copper and that form a phase different from the copper matrix (matrix). The number of second phase particles having a diameter of 1 to 5 μm and a diameter exceeding 5 μm was obtained by arbitrarily selecting 500 mirror-finished copper foil rolled surfaces (surfaces parallel to the rolled surface and perpendicular to the thickness direction). It is obtained by measuring the number of particles in the corresponding diameter range from a scanning electron micrograph (see FIG. 1) having a field of view of 0.002 mm ² . Here, the diameter means the average value of L1 and L2 by measuring the short diameter (L1) and long diameter (L2) of the particles as shown in FIG.

In the present invention, the number of second phase particles having a diameter of 1 μm or more and 5 μm or less is defined as 500 / mm ² or more and 5000 / mm ² or less. When the copper foil contains second phase particles having a diameter of 1 to 5 μm at a frequency of 500 particles / mm ² or more, sagging caused by shearing is reduced. This is because the breakage of copper in the latter half of the shearing process is promoted by the second phase particles acting as crack starting points.
When the number of second phase particles having a diameter of 1 to 5 μm is less than 500 particles / mm ² , the starting point of cracks is reduced, and sagging increases. On the other hand, if it exceeds 5000 / mm ² , cracks are likely to occur in the copper foil when subjected to charge / discharge stress, and the charge / discharge cycle life of the battery is shortened.
The adverse effect on the charge / discharge cycle life increases with larger second phase particles. Therefore, in addition to the above, the number of second phase particles having a diameter exceeding 5 μm is defined to be less than 10 particles / mm ² .

(Form of second phase particles)
There are various types of second phase particles depending on the composition and production history of the copper foil. The form of the second phase particles also affects the shear processability, and the effect of improving the shear processability increases as the isotropic form of the second phase particles.
If the second phase particles having an aspect ratio (ratio of major axis to minor axis) of 5.0 or less in the second phase particles having a diameter of 1 to 5 μm are less than 90%, the second phase particles serving as the starting point of cracks And the effect of improving the shear workability is significantly reduced. Moreover, since the structure is not uniform, the copper foil is easily cracked when subjected to charge / discharge stress, and the charge / discharge cycle life of the battery is shortened. Therefore, it is preferable that 90% or more of the second phase particles having a diameter of 1 to 5 μm have an aspect ratio of 5.0 or less. More preferably, it is 94% or more.
Here, the form of the second phase particles in the present invention is a form observed in a cross section parallel to the rolling surface and perpendicular to the thickness direction. The aspect ratio is the ratio L2 / L1 of the short diameter (L1) to the long diameter (L2), and the aspect ratio of the second phase particles having a diameter of 1 to 5 μm obtained when measuring the number of second phase particles as described above. Is the ratio.

(Composition and production method of second phase particles)
As a method of introducing the second phase particles into the copper foil of the present invention,
(A) a method of adding a metal element having a low solubility in solid copper, such as chromium and zirconium, to pure copper and precipitating it,
(B) a method of generating a compound such as copper oxide or copper sulfide by adding a nonmetallic element such as oxygen or sulfur to pure copper;
(C) a method of simultaneously adding a metallic element and a nonmetallic element to form a compound of both (for example, Ni ₂ Si, MgP, Al ₂ O ₃ , MnS, etc.),
and so on.
Chromium, zirconium, and the like are dissolved in the hot rolling and solution treatment, and are precipitated as fine particles having a diameter of less than 1 μm by the aging treatment, and exhibit precipitation hardening action. In order to form the second phase particles having a diameter of 1 μm or more, the aging treatment may be performed for a long time at a relatively high temperature to grow the precipitate particles, but this is accompanied by a decrease in strength.
When oxygen is added to pure copper, it is easy to control the particle diameter, and it is possible to form copper oxide particles that are hard, hard to deform by rolling, and excellent in isotropy.
Sulfur has very low solubility in copper (about 1 mass ppm at 600 ° C.), and most of the content is copper sulfide. However, copper sulfide tends to extend long by rolling, and it becomes difficult to achieve an aspect ratio of 5.0 or less.
In the case of second phase particles such as Ni ₂ Si, MgP, Al ₂ O ₃ and MnS, coarse particles are likely to be formed during casting. Coarse particles reduce the charge / discharge cycle life. In order to reduce the coarse particles, it is necessary to control the casting conditions to suppress the growth of the particles and to dissolve the particles produced by casting by high-temperature heat treatment.

In order to obtain the size, frequency, and form of the second phase particles, a method of adding oxygen to pure copper to produce copper oxide particles is most preferable among the above methods.
In order to achieve the size, frequency, and morphology of the second phase particles of the present invention using copper oxide particles, the proportion of copper oxide in the second phase particles having a diameter of 1 to 5 μm is more preferably 90% or more. Is preferably adjusted to 96% or more. The second phase particles made of copper oxide are generally present in a copper matrix in an isotropic form and have an appropriate hardness, so that they tend to start cracks in the copper matrix during shearing. is there.

(Copper foil material)
Conventionally used as a material for rolled copper foil includes tough pitch copper (JIS-C1100) and oxygen-free copper (JIS-C1020). Tough pitch copper is pure copper containing 100 to 500 mass ppm of oxygen and 10 to 100 mass ppm of inevitable impurities (excluding oxygen), and the copper content is standardized to 99.90 mass% or more. Oxygen-free copper contains 10 mass ppm or less of oxygen and 10 to 100 mass ppm of inevitable impurities (excluding oxygen). Some of these inevitable impurity elements form second-phase particles (inclusions, crystallized substances, precipitates, etc.) in copper.
By improving the tough pitch copper, it is possible to obtain the size, frequency and form of the second phase particles of the present invention. That is, oxygen is adjusted to 150 mass ppm to 300 mass ppm, the total of trace elements (elements other than copper excluding oxygen and silver) is adjusted to 25 mass ppm or less, and sulfur contained in the trace element is adjusted to 10 mass ppm or less. By doing so, a copper foil material suitable for the present invention is obtained.

Here, when oxygen becomes less than 150 mass ppm, the number of second phase particles having a diameter of 1 to 5 μm is less than 500 particles / mm ² . Further, when the oxygen exceeds 300 mass ppm, the number of second phase particles having a diameter of 1 to 5 μm exceeds 5000 / mm ^2, and when the oxygen exceeds 400 mass ppm, the number of second phase particles having a diameter of 5 μm or more is 10 / mm ² or more.
Trace elements other than oxygen and silver in the copper are mixed in the copper oxide particles existing as the second phase particles and change the size and form of the particles. In addition, trace element oxides, trace element-copper compounds, trace element compounds, and the like are generated as new second-phase particles. Therefore, when the amount of trace elements increases, it becomes difficult to control the size, frequency, and form of the second phase particles. Therefore, in the tough pitch copper of the present invention, the total of trace elements excluding oxygen and silver is preferably 25 mass ppm or less. In addition, since silver is a stable and low reactive element, if it is 0.1% by mass or less, it is not possible to change the properties of the copper oxide particles or to form new second phase particles in the copper. Absent. Accordingly, silver is not added to the trace elements in the present invention. When silver is added to copper, heat resistance and strength can be improved without lowering conductivity. When silver exceeds 0.1 mass%, the ductility of copper foil will fall.

  There is sulfur as a trace element contained in copper at a relatively high concentration. Since sulfur is easily mixed from the oil or the like adhering to the raw material when melting a tough pitch copper ingot, special care is required. When sulfur is mixed, the aspect ratio of the second phase particles is increased. When sulfur exceeds 10 mass ppm, the second phase particles having an aspect ratio of 5.0 or less and having a diameter of 1 to 5 μm are less than 90%.

(Manufacturing method of copper foil)
The method for producing tough pitch copper also affects the size, frequency, and morphology of the second phase particles of the present invention. In the production process of tough pitch copper, pure copper raw materials such as electrolytic copper and copper scrap are dissolved, and after adjusting the oxygen concentration, the molten copper is cooled and solidified to produce an ingot. Copper oxide particles are produced in the copper matrix during the solidification process. When the solidification rate is decreased, the copper oxide particles are increased, and when the solidification rate is increased, the copper oxide particles are decreased.
The ingot is processed into a plate having a thickness of about 10 mm by hot rolling, and then finished by annealing and cold rolling. The copper oxide particles are hard and do not deform by cold rolling, but deform by hot rolling. The higher the hot rolling temperature, the larger the deformation (the aspect ratio becomes larger). When the rolling temperature exceeds 980 ° C., the second phase particles having an aspect ratio of 5.0 or less and a diameter of 1 to 5 μm are adjusted to 90% or more. It becomes difficult to do.

(Battery configuration)
The negative electrode plate and the secondary battery according to the present invention are characterized by using the copper foil as a negative electrode current collector, and are not limited and generally used except for the rolled copper foil of the present invention. Known ones can be used.

(Negative electrode plate)
The negative electrode plate of the present invention is composed of the negative electrode current collector of the present invention and a negative electrode active material attached to one or both surfaces of the negative electrode current collector together with a binder.
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 negative electrode binder include a mixture containing carboxymethyl cellulose (CMC) and styrene butadiene rubber (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 graphites such as acetylene black and powdered expanded graphite, pulverized carbon fibers, and pulverized graphitized carbon fibers.

(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, a positive electrode 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 for the positive electrode, a thermoplastic 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 positive electrode active material-containing layer can further contain, as a conductive auxiliary material, acetylene black, graphite such as powdered expanded graphite, pulverized carbon fiber, pulverized graphitized carbon fiber, and the like.

(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.

(material)
As a raw material for the copper foil, high-quality electrolytic copper was used without using scrap. The oxygen concentration was adjusted by adding cupric oxide. In experiments for examining the effects of trace elements, silver or trace elements were added to high-grade electrolytic copper.
Samples prepared without adding trace elements were subjected to quantitative analysis of all elements by glow discharge mass spectrometry (GD-MS). As a result, the detected elements and their concentrations (mass ppm) were S: 3.2, Fe: 0.8, As: 0.4, Sb: 0.7, Bi: 0.2, Pb: 0.00. 1, Se: 0.2, Te: 0.1, Ag: 8.3. No other elements were detected at the analysis lower limit of 0.1 mass ppm. That is, when silver or a trace element was not added, the total of elements other than copper and oxygen derived from the raw material was 14.0 ppm by mass, and the concentration of the trace element excluding silver was 5.7 ppm by mass.

(Production of rolled copper foil)
Using a high-frequency induction furnace, 3 kg of high-grade electrolytic copper was dissolved in a graphite crucible having an inner diameter of 60 mm, trace elements were added as necessary, and cupric oxide was added. Next, this molten metal was poured into a mold to produce a rectangular parallelepiped ingot having a thickness of 30 mm, a width of 60 mm, and a height of about 150 mm. At that time, in order to change the cooling rate, the casting temperature and the material of the mold were changed as follows.
(1) Casting temperature: It was changed in the range of 1100-1300 ° C. The solidification rate is increased by lowering the casting temperature.
(2) Mold material: Performed under four types of conditions: brick, graphite, cast iron, and pure copper.

Next, this ingot was inserted into a heating furnace maintained at a predetermined temperature in the range of 800 to 1000 ° C. for 3 hours, taken out from the heating furnace, and hot rolled to a thickness of 8 mm. The oxidized scale on the surface of the hot rolled material was removed with a grinder. Then, recrystallization annealing and cold rolling were repeated, and the foil thickness was finished to 18 μm to 6 μm by the final rolling.
The plate thickness of the final annealing was adjusted so that the final rolling workability was 90%. Here, the degree of rolling r is r = (to-t) / to (t: thickness after rolling, to: thickness before rolling).
About the obtained rolled copper foil, the following method evaluated the 2nd phase particle | grains, tensile strength and elongation, shear workability, and cycle life.

(Evaluation of second phase particles)
The rolled copper foil sample was heated at 200 ° C. for 1 hour to simulate the drying process of the negative electrode active material. After the rolled surface was mechanically polished to a mirror surface, the size and number of the second phase particles were measured using a scanning electron microscope. The number of second phase particles having a diameter of 1 to 5 μm and second phase particles having a diameter exceeding 5 μm was measured on 500 micrographs having a visual field of 0.002 mm ² .
The aspect ratio of the second phase particles having a diameter of 1 to 5 μm used in the above measurement was measured, and the ratio of particles having an aspect ratio of 5.0 or less was determined. Further, 50 second-phase particles having a diameter of 1 to 5 μm were arbitrarily selected, and the components were analyzed by EDS (energy dispersive X-ray analyzer) for each to determine the ratio of the copper oxide particles in the 50 particles. Here, the second phase particles having a total copper concentration and oxygen concentration of 90% by mass or more were defined as copper oxide particles.

(Tensile test)
The rolled copper foil sample was heated at 200 ° C. for 1 hour to simulate the drying process of the negative electrode active material. The tensile strength and elongation were 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 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.
(Evaluation method of shear workability)
The rolled copper foil sample was heated at 200 ° C. for 1 hour 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. 18 μm thick sample: 4.994 mm, 12 μm thick sample: 4.996 mm, 9 μm thick sample: 4.997 mm, 6 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.

(Evaluation method of cycle life)
The cylindrical lithium ion secondary battery shown in FIG. 4 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 a rolled copper foil sample surface to a thickness of 200 μm by a doctor blade method, heated at 200 ° C. for 1 hour, 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, carboxymethylcellulose 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, and dried by heating at 200 ° C. for 1 hour. 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 procedures, a non-aqueous electrolyte is injected, the sealing plate 1 and the battery case 8 are caulked and sealed through the insulating gasket 2, and the cylindrical lithium having a diameter of 17 mm, a height of 50 mm and a battery capacity of 780 mAh is used. An ion secondary battery was produced.
(5) The electrolytic solution was prepared 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. This 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 The battery was charged to 40 mA (0.05 CmA). Discharge conditions: Discharge to a discharge end voltage of 3.0 V with a constant current of 780 mA (1 CmA). It was determined that good cycle characteristics were obtained when the cycle life reached 500 times or more.

Example A (effect of oxygen concentration and casting conditions)
The effects of the oxygen concentration and casting conditions on the number of second phase particles having a diameter of 1 to 5 μm are described in Examples 3, 6 to 8, 10, 12 to 14, and 17 to 19 and Comparative Examples 1, 2, 4, 5, 9, 11, 15, 16 and 20-22. The results are shown in Table 1.
Ingots were produced by casting molten metal having various oxygen concentrations at different molds and casting temperatures. The ingot is heated at 900 ° C. for 3 hours, then hot rolled to a thickness of 8 mm, repeated cold rolling and annealing to finish a foil with a thickness of 6 to 18 μm, second phase particles, tensile strength and elongation, shear processability And the cycle life was evaluated. The pure copper mold was water-cooled through a cooling water pipe, and the other molds were air-cooled. As an influence of the mold material, the solidification rate increases in the order of brick <graphite <cast iron <pure copper. Also, the lower the casting temperature, the faster the solidification rate. In this experiment (Example 1), since no trace element was added, silver was 8.3 mass ppm, the total of trace elements excluding oxygen and silver was 5.7 mass ppm, and sulfur was 3.2 mass ppm. It is.

The evaluation results are shown in Table 1. When the casting conditions are the same, the number of second-phase particles having a diameter of 1 to 5 μm increases as the oxygen concentration increases (Comparative Examples 1 and 2, Examples 3, 7, 12 to 14, Comparative Example 15 and 16). Further, when the oxygen concentration is increased, second-phase particles having a diameter of more than 5 μm are generated, and the number thereof increases with an increase in oxygen concentration (Example 14, Comparative Examples 15 and 16). In each sample, among the second phase particles having a diameter of 1 to 5 μm, the proportion of the particles having an aspect ratio of 5.0 or more is 90% or more, and the proportion of the copper oxide particles is 90% or more.
In Examples 3, 6 to 8, 10, 12 to 14 and 17 to 19 in which ingots were produced with an oxygen concentration of 150 to 300 ppm by mass and an appropriate solidification rate, the sizes and numbers defined by the present invention were adjusted. Two-phase particles are obtained, and good shear processability and cycle life are obtained.
In Comparative Examples 1, 2, and 20 to 22 in which the oxygen concentration is less than 150 ppm by mass, the number of particles having a diameter of 1 to 5 μm is less than 500 / mm ² , and as a result, sagging exceeds 1/5 of the foil thickness. .
In Comparative Examples 15 and 16 in which the oxygen concentration exceeds 300 mass ppm, the number of particles having a diameter of 1 to 5 μm exceeds 5000 / mm ² , and in Comparative Example 16, the number of particles having a diameter of more than 5 μm exceeds 10 / mm ² . . As a result, the cycle life of Comparative Examples 15 and 16 is less than 500 times.

In Comparative Example 4 using a pure copper mold and Comparative Example 5 cast at 1100 ° C. immediately above the melting point, since the solidification rate was too high, a lot of fine second-phase particles having a diameter of less than 1 μm that do not contribute to reduction of dripping were precipitated. The number of particles having a diameter of 1 to 5 μm was less than 500 particles / mm ² . For this reason, sagging exceeded 1/5 of foil thickness.
In Comparative Example 9 cast at a high temperature of 1300 ° C. and Comparative Example 11 using a brick mold, the solidification rate was too slow, and thus the second phase particles were significantly coarsened. As a result, the number of particles having a diameter exceeding 5 μm exceeded 10 particles / mm ² , and the cycle life was significantly reduced. Further, in Comparative Example 11, particles having a diameter of 1 to 5 μm were less than 500 particles / mm ² due to the coarsening of the particles, and sagging exceeded 1/5 of the foil thickness.

Example B (Influence of hot rolling conditions)
The effects of hot rolling conditions on the number of second phase particles having a diameter of 1 to 5 μm and a diameter of more than 5 μm were examined in Examples 13, 23 to 26 and Comparative Example 27.
An ingot was manufactured by casting a molten metal whose oxygen concentration was adjusted to about 250 ppm by mass into a cast iron mold at 1200 ° C. The ingot was inserted into a heating furnace maintained at various temperatures (hot rolling temperature) for 3 hours, removed from the heating furnace, and hot rolled to a thickness of 8 mm. Thereafter, recrystallization annealing and cold rolling were repeated, and the thickness was finished to 12 μm for evaluation. In addition, since the trace element is not added, silver is 8.3 mass ppm, the total of trace elements except oxygen and silver is 5.7 mass ppm, and sulfur is 3.2 mass ppm.

The evaluation results are shown in Table 2. As the hot rolling temperature increases, the proportion of second phase particles having an aspect ratio of 5.0 or less and a diameter of 1 to 5 μm is decreasing. In each sample, the ratio of the copper oxide particles in the second phase particles having a diameter of 1 to 5 μm is 90% or more.
In Examples 13, 23 to 26, which were hot-rolled at a temperature of 980 ° C. or less, 90% or more of the second phase particles having a diameter of 1 to 5 μm had an aspect ratio of 5.0 or less, which was favorable. Shear processability and cycle life were obtained.
On the other hand, in Comparative Example 27 in which hot rolling was performed at 1000 ° C. exceeding 980 ° C., the frequency of second phase particles having a diameter of 1 to 5 μm was 500 to 5000 particles / mm ² , but an aspect ratio of 5.0 or less. Second phase particles having a ratio were less than 90%. Since the extended second phase particles not only contribute to the reduction of sagging but also deteriorate the cycle life, the sagging of Comparative Example 27 exceeded 1/5 of the foil thickness, and the cycle life was less than 500 times.
In Example 23 where the hot rolling temperature was as low as 800 ° C., good shear workability and cycle life were obtained, but light cracks occurred on the surface of the ingot during hot rolling. Was removed by chamfering and then processed into a foil. Therefore, stable production was somewhat difficult.

Example C (effect of trace elements)
The effects of trace elements on cycle life were examined in Examples 12, 28-30, 33, 35, 37, 39 and 40 and Comparative Examples 31, 32, 34, 36 and 38 by adding trace elements. .
High-grade electrolytic copper was dissolved, a predetermined amount of element was added, assuming a trace element mixture, and the oxygen concentration was adjusted to about 220 ppm by mass. This molten metal was cast into a cast iron mold at 1200 ° C. to produce an ingot. After heating at 900 ° C. for 3 hours, hot rolling was performed to a thickness of 8 mm, and cold rolling and annealing were repeated to finish the thickness to 12 μm, and the second phase particles, shear workability and cycle life were evaluated.
The evaluation results are shown in Table 3. Here, the trace element total is the total concentration of elements other than copper, oxygen, and silver, and is obtained by adding the amount of added elements to the concentration originally contained (5.7 mass ppm). The total sulfur is obtained by adding the amount of added sulfur to the sulfur concentration (3.2 mass ppm) originally contained.
Examples 28 to 30 and Comparative Examples 31 and 32 are obtained by adding sulfur. Due to the formation of copper sulfide and the mixing of sulfur into copper oxide, the proportion of particles having an aspect ratio of 5.0 or less in the second phase particles having a diameter of 1 to 5 μm is reduced, and the second phase particles having a diameter of 1 to 5 μm are formed. The proportion of copper oxide particles occupied also decreased. In Comparative Examples 31 and 32 where sulfur exceeds 10 ppm by mass, the proportion of particles having an aspect ratio of 5.0 or more of the second phase particles having a diameter of 1 to 5 μm is less than 90%, and the proportion of copper oxide particles is also 90%. Was less than. As a result, sagging exceeded 1/5 of the foil thickness and the cycle life was less than 500 times.

In Example 33 and Comparative Example 34, a small amount of tin was added to the molten metal assuming that copper scrap with tin plating was mixed into the raw material. Due to the formation of tin oxide and the inclusion of tin in the copper oxide, the proportion of the copper oxide particles in the second phase particles having a diameter of 1 to 5 μm was reduced, and the second phase particles were enlarged. As a result, the number of particles having a diameter of 1 to 5 μm decreased, and the number of particles having a diameter exceeding 5 μm increased. In Comparative Example 34 in which the total amount of trace elements other than oxygen and silver exceeds 25 mass ppm, the ratio of the copper oxide particles is less than 90%, the number of particles having a diameter of 5 μm or more exceeds 10 particles / mm ² , and the cycle life is 500 times. It was less than.
In Example 35 and Comparative Example 36, a small amount of zinc was added to the molten metal assuming that brass scrap was mixed into the raw material. Similar results were obtained as when tin was added.
In Example 37 and Comparative Example 38, it was assumed that low-grade electrolytic copper was used as a raw material, and trace elements assumed to be main inevitable impurities of electrolytic copper were added to the molten metal. By increasing the amount of trace elements, the proportion of copper oxide particles decreased, the proportion of particles having an aspect ratio of 5.0 or more in the second phase particles having a diameter of 1 to 5 μm decreased, and the number of particles exceeding 5 μm in diameter increased. In Comparative Example 38 where the total amount of trace elements other than oxygen and silver exceeds 25 mass ppm, the proportion of particles having an aspect ratio of 5.0 or more in the second phase particles having a diameter of 1 to 5 μm is less than 90%, and copper oxide The proportion of particles was also less than 90%. As a result, sagging exceeded 1/5 of the foil thickness, and the cycle life was less than 500 times.
In Examples 39 and 40, silver was added to improve strength and heat resistance. The size and number of second phase particles defined by the present invention are obtained, and good shear workability and cycle life are obtained. It has been shown that the effect of the present invention is exhibited even when a small amount of silver is added.

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 (9)

Of copper or copper alloy foil used as a negative electrode current collector of a secondary battery, among second phase particles dispersed in a copper or copper alloy matrix, second phase particles having a diameter of 1 to 5 μm are 500 to 5000 / mm ^2, Ri second phase particles der less than 10 / mm ² having a diameter exceeding 5 [mu] m, more than 90% of the second-phase particles having a diameter 1~5μm is 5.0 to have the following aspect ratio A rolled copper foil for a negative electrode current collector. The rolled copper foil for a negative electrode current collector according to claim 1, wherein 90% or more of the second phase particles having a diameter of 1 to 5 µm are copper oxide. The rolled copper foil for a negative electrode current collector according to claim 1 or 2 , wherein the rolled copper foil is made of tough pitch copper containing 150 to 300 ppm by mass of oxygen. 4. The rolled copper foil for a negative electrode current collector according to claim 3 , wherein the total amount of trace elements excluding oxygen and silver in the tough pitch copper is 25 mass ppm or less. The rolled copper foil for a negative electrode current collector according to claim 3 or 4 , wherein a sulfur concentration in the trace element is 10 mass ppm or less. The negative electrode electrical power collector comprised from the rolled copper foil of any one of Claims 1-5 . 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 6 . A negative electrode having an active material layer 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 according to claim 6. Board. An electrode plate group is formed by insulating the negative electrode plate according to claim 7 or 8 from a positive electrode plate having a lithium transition metal composite oxide as a main component of the positive electrode active material via a separator, and the electrode plate group is A secondary battery that is housed in a battery case and injected with a non-aqueous electrolyte.

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