JP5571616B2 - Rolled copper 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 (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 commercially available as secondary battery negative electrode plate materials are made of tough pitch copper (JIS-C1100) or oxygen-free copper (JIS-C1020). 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%). Oxygen-free copper is pure copper whose oxygen concentration is adjusted to 0.001% or less, and the copper content is standardized to 99.96% or more.
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.

The conventional rolled copper foil made of tough pitch copper or oxygen-free copper is softened by recrystallization in the (2) drying step, and the tensile strength is reduced to 250 MPa or less.
On the other hand, 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. Softened copper foil is easily deformed when subjected to repeated stress. Due to this deformation, the copper foil is fatigued or the active material applied to the surface of the copper foil is peeled off, thereby shortening the charge / discharge cycle life of the battery.

  In order to suppress the softening of the copper foil in the drying step or the like, a rolled copper alloy foil has been proposed in which an alloy element is added to tough pitch copper or oxygen-free copper to improve heat resistance. For example, Japanese Patent Laid-Open No. 2000-303128 (Patent Document 1) discloses a copper alloy foil obtained by adding 0.005 or 0.01% of Cr, Zr, Ag, Cd, Sn, Sb, or Bi to oxygen-free copper. . However, when an alloying element is added to pure copper, the electrical conductivity decreases, and heat generation and voltage loss occur when energized. In addition, the manufacturing process becomes complicated and the manufacturing cost increases.

  Moreover, in Unexamined-Japanese-Patent No. 11-88672 (patent document 2) and Unexamined-Japanese-Patent No. 2002-198054 (patent document 3), as a raw material of a rolled copper foil, oxygen concentration is 0.002% or less and 0.0005 to 0.002%, respectively. Although the pure copper adjusted to 1 is proposed, it aims at the fall of the tensile strength with time of copper foil.

  On the other hand, in the field of rolled copper foil for flexible printed circuit boards (FPC), examples of copper foils with excellent flexibility include, for example, JP 2000-212661 (Patent Document 4) and JP 2000-212660 (Patent Document 5). ) And JP-A 2000-355720 (Patent Document 6) disclose a copper foil in which a cubic texture is developed by recrystallization by annealing at 200 ° C. for 30 minutes, and this copper foil is a flexible print such as an electrode of a lithium ion battery. It is also suitable for uses other than circuits.

JP 2000-303128 A JP-A-11-88672 JP 2002-198054 A JP 2000-212661 A JP 2000-212660 A JP 2000-355720 A

  By the way, all of patent documents 1-6 paid attention to the charge-and-discharge cycle life of the softened copper foil, there is no suggestion of the measure to improve this, and each solved a different subject.

  An object of the present invention is to improve a rolled copper foil made of tough pitch copper or oxygen-free copper, thereby being suitable as a negative electrode current collector material for secondary batteries including lithium ion secondary batteries, and a charge / discharge cycle It is to provide a rolled copper foil having a long life, and a negative electrode current collector, a negative electrode plate and a secondary battery using the same.

  Pure copper is characterized by the development of the Cube orientation {001} <100> (synonymous with cubic texture) when recrystallized. The present inventors have found that the cycle life of a battery is improved by using a copper foil with an expanded Cube orientation as a negative electrode current collector. Also, the Brass orientation {110} <112> and the Copper orientation {112} <111> are harmful to the cycle life, and the Cube orientation has been developed by suppressing the development of the Brass orientation and the Copper orientation. It has been found that the cycle life of the copper foil is further improved.

  Here, the recrystallized grains in the Brass orientation and the Copper orientation were distributed along the shear band of the copper foil surface layer portion. This shear band was introduced at the time of rolling, and was formed starting from an oil pit on the surface of the copper foil. It was found that the greater the number of oil pits, the greater the Brass orientation and Copper orientation.

  Next, a measure for reducing the Brass orientation and Copper orientation using the oil pit as an index was studied, and it was found that the oil pit was reduced when a roll having a small surface roughness was used in the final rolling. However, on the other hand, by rolling using a roll having a small roughness, the surface roughness of the obtained copper foil is lowered, and the adverse effect is insufficient adhesion between the copper foil and the active material, as expected. The knowledge that cycle life is not improved was also obtained. This was considered that the adhesiveness of the active material to the copper foil surface was lowered.

  And we studied this solution diligently, and in each pass before the final pass, we used a roll with a small surface roughness to suppress the formation of oil pits, and a roll with a large surface roughness in the final pass used a copper foil By appropriately increasing the surface roughness, the Brass orientation and Copper orientation were suppressed, the adhesiveness to the active material was good, and a copper foil having an excellent cycle life was successfully developed. Completed.

The present invention has been completed based on the above technical knowledge,
(1) By annealing at 200 ° C. for 30 minutes, the tensile strength decreases to 250 MPa or less, and when measured after heating at 200 ° C. for 30 minutes, the Cube orientation {001} <100> area ratio is 30% or more. The crystal orientation of the Brass orientation {110} <112> area ratio is 20% or less, the Copper orientation {112} <111> area ratio is 20% or less , and the oil pit area ratio is 3 to 20%. wherein the arithmetic flat Hitoshiara Ra of the direction perpendicular to the rolling direction is 0.05～0.12Myuemu, the negative electrode current collector foil of the secondary battery.
(2) The copper foil for a negative electrode current collector of the secondary battery according to (1), characterized by using tough pitch copper or oxygen-free copper as a material.
(3) One or more alloy elements selected from the group consisting of Ag, Sn, Cr, Fe, Zn and Zr are contained in a total amount of 0 to 0.1% by mass, and the balance is made of copper and inevitable impurities. The copper foil for a negative electrode current collector of a secondary battery according to (1), characterized in that the material is made of tough pitch copper or oxygen-free copper.
(4) Tensile strength is 250 MPa or less, Cube orientation {001} <100> area ratio is 30% or more, Brass orientation {110} <112> area ratio is 20% or less, Copper orientation {112} <111> It has a crystal orientation area ratio is 20% or less, 3 to 20 percent the area ratio of the oil pits, an arithmetic flat Hitoshiara Ra of the direction perpendicular to the rolling direction is 0.05~0.12μm A copper foil for a negative electrode current collector of a secondary battery.
(5) The copper foil for a negative electrode current collector of a secondary battery according to (4), characterized in that the material is made of tough pitch copper or oxygen-free copper.
(6) 0 to 0.1% by mass in total of one or more alloy elements selected from the group consisting of Ag, Sn, Cr, Fe, Zn and Zr, with the balance being from copper and inevitable impurities The copper foil for a negative electrode current collector of the secondary battery according to (4), characterized in that the material is made of tough pitch copper or oxygen-free copper.
(7) A negative electrode current collector composed of the rolled copper foil according to any one of (4) to (6).
(8) 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 according to (7).
(9) 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 according to (7). A negative electrode plate having a material layer.
(10) An electrode plate group in which the negative electrode plate according to (8) or (9) is insulated and disposed through a separator having a lithium transition metal composite oxide as a main component of a positive electrode active material and a separator, non-aqueous electrolysis And a battery case containing the electrode plate group and the non-aqueous electrolyte.
(11) After the ingot is hot-rolled, it includes a step of repeating cold rolling and annealing, and finishing to a predetermined thickness by final cold rolling, in which the rolling degree is 90% or more in the final cold rolling, and the final pass In each previous pass, a rolling roll having an arithmetic average roughness Ra of 0.02 to 0.04 μm was used, and in a final pass, a rolling roll having an arithmetic average roughness Ra of the rolled material surface of 0.07 to 0.14 μm was used. It uses, The manufacturing method of the copper foil as described in any one of (1)-(3) characterized by the above-mentioned.
(12) After the ingot is hot-rolled, it includes a step of repeating cold rolling and annealing, finishing to a predetermined thickness by final cold rolling, and then recrystallizing the copper foil by heat treatment, and rolling in the final cold rolling The degree of work is 90% or more, and a rolling roll having an arithmetic average roughness Ra of 0.02 to 0.04 μm is used in each pass before the final pass, and the arithmetic average roughness Ra of the rolled material surface is 0 in the final pass. A method for producing a copper foil according to any one of (4) to (6), wherein a rolling roll of 0.07 to 0.14 μm is used.

  ADVANTAGE OF THE INVENTION According to this invention, the rolled copper foil which is suitable as a negative electrode collector material of secondary batteries including a lithium ion secondary battery, and is excellent in charging / discharging cycle life, and a negative electrode collector and negative electrode plate using the same And a secondary battery.

It is the schematic which shows the structure of a general secondary battery. It is a figure which shows typically the oil pit formed on copper foil. It is a figure which shows typically the optical microscope image of the copper foil sample surface obtained when evaluating the area ratio of an oil pit. It is a figure which shows typically the binarization processing image in the same position of the optical microscope image of FIG.

(1) Components of Copper Foil The material of the copper foil of the present invention is JIS-1100 defined tough pitch copper or JIS-C1020 defined oxygen-free copper.
A copper foil made of tough pitch copper or oxygen-free copper generally has a tensile strength of 400 to 550 MPa after rolling. This copper foil is recrystallized in the drying process during the production of the negative electrode plate, and the tensile strength is reduced to 250 MPa or less. The heat load in the drying process typically corresponds to a heat treatment at 200 ° C. for 30 minutes (see JP 2000-303128 A).

  The effect of the present invention is tough tough pitch copper or oxygen-free copper as long as it is a copper foil that softens in the drying step during the production of the negative electrode plate, that is, when the tensile strength decreases to 250 MPa or less when heated at 200 ° C. for 30 minutes. It appears even in copper foil added with a small amount of alloying elements. That is, in one embodiment of the present invention, one or more alloy elements selected from the group consisting of Ag, Sn, Cr, Fe, Zn and Zr are contained in a total amount of 0.1% by mass or less, and the balance Can be made of tough pitch copper or oxygen-free copper consisting of copper and inevitable impurities. As an example, for the purpose of preventing softening during storage at room temperature, tough pitch copper added with 0.01 to 0.05% by mass of Ag (for example, Japanese Patent Laid-Open No. 2000-212661), Sn is 0.001 to 0.001%. An oxygen-free copper added in an amount of 0.01% by mass (for example, JP-A-2008-106313) can be mentioned.

  When one or more elements of Sn, Cr, Fe, Zn, and Zr, which are easier to oxidize than Cu, are employed, an oxygen-free copper melt is used in order to prevent the additive element from forming an oxide in copper. It is common to add in. Since Ag is less susceptible to oxidation than Cu, it can be added both in the tough pitch copper melt and in the oxygen free copper melt.

(2) Crystal orientation of copper foil When the Cube orientation is large and the Brass orientation and Copper orientation are small in the metal structure of the copper foil, fatigue failure of the copper foil when the battery is subjected to repeated stress due to charging / discharging is suppressed. Cycle life is improved.
Here, the Cube orientation is a state in which the (001) plane faces the rolling surface normal direction (ND) and the (100) plane faces the rolling direction (RD), and is an index of {001} <100>. Indicated. The Brass orientation is a state in which the (110) plane faces the ND and the (112) plane faces the RD, and is indicated by an index of {110} <112>. The Copper orientation is a state in which the (112) plane faces the ND and the (111) plane faces the RD, and is indicated by an index of {112} <111>.

When the area ratio of the Cube orientation is 30% or more, the cycle life of the battery is improved. In addition, when both the area ratio in the Copper orientation and the area ratio in the Brass orientation are 20% or less, the cycle life of the battery is further improved.
More preferably, the area ratio of the Cube orientation is 50% or more, and the area ratios of the Copper orientation and the Brass orientation are each 10% or less. In this case, a good battery cycle life can be obtained more stably.

  The upper limit value of the Cube orientation area ratio is not restricted from the viewpoint of battery characteristics, but the Cube orientation area ratio does not practically exceed 99.9%. Similarly, the lower limit value of the area ratio of the Brass orientation and the Copper orientation is not restricted from the viewpoint of battery characteristics, but the area ratio of the Brass orientation and the Copper orientation is never practically less than 0.1%.

(3) Surface properties of the rolled copper foil When the copper foil material is cold-rolled, the surface irregularities of the rolling roll are transferred to the surface of the rolled material (roll surface transfer), and the lubrication enclosed between the rolling roll and the rolled material. The roughness of the rolled copper foil surface is formed by the dent (oil pit) generated on the rolled material surface by the oil.

The surface of the rolling roll is polished in the circumferential direction by applying a grinding wheel while rotating the roll, and the unevenness of the roll surface is constituted by this polishing mark. Therefore, the unevenness | corrugation of the copper foil surface by roll surface transcription | transfer is observed as a precise | minute streaky pattern extended in parallel with a rolling direction. The degree of unevenness formed by roll surface transfer can be evaluated by measuring the arithmetic average roughness Ra in a direction orthogonal to the rolling direction using a contact roughness meter in accordance with JIS-B0601.

  On the other hand, as schematically shown in FIG. 2, the oil pit is observed as a crack extending perpendicular to the rolling direction, and a shear band is developed obliquely from the bottom. The degree of oil pit generation can be evaluated, for example, by measuring the area ratio of recesses on the copper foil surface (hereinafter referred to as oil pit area ratio) using a confocal microscope.

(3-1) Oil Pit Area Ratio Crystal grains of Brass orientation and Copper orientation are generated along the shear band when the copper foil is recrystallized. For this reason, the oil pit area ratio in the copper foil after rolling shows a good correlation with the area ratios of the Brass orientation and Copper orientation in the copper foil after recrystallization. In other words, by appropriately adjusting the rolling conditions using the oil pit area ratio on the surface of the rolled copper foil as an index, the copper foil can be imparted with a property in which the Brass orientation and the Copper orientation are not easily generated during recrystallization.

  When the area ratio of the oil pit exceeds 20%, either the Brass orientation or the Copper orientation exceeds 20%, and the cycle life of the battery decreases. On the other hand, the oil pit also has an effect of improving the adhesion strength between the copper foil surface and the active material. When the oil pit area ratio decreases, the adhesion strength between the copper foil surface and the active material decreases. If the oil pit area ratio is less than 3%, the desired adhesion strength cannot be obtained no matter how Ra is adjusted. As a result, the active material peels from the surface of the copper foil when subjected to repeated stress due to charging / discharging of the battery, and the cycle life of the battery is reduced. Therefore, the area ratio of the oil pit is specified to be 3 to 20%. A more preferable area ratio of the oil pit is 6 to 15%.

(3-2) Surface roughness Ra in the direction perpendicular to rolling
When Ra in the direction perpendicular to rolling is increased, the adhesion strength between the copper foil surface and the active material is improved. In order to obtain a desired adhesion strength under a condition where the oil pit area ratio is 3 to 20%, it is necessary to adjust Ra to 0.05 μm or more. When the Ra is less than 0.05 μm, the active material peels from the surface of the copper foil when subjected to repeated stress due to charging / discharging of the battery, and the cycle life of the battery is reduced. On the other hand, when the Ra exceeds 0.12 μm, when the battery is subjected to repeated stress due to charging / discharging, the notch on the surface of the copper foil acts as a starting point for fatigue cracks, and the cycle life of the battery is reversed. descend. Therefore, Ra is specified to be 0.05 to 0.12 μm. The more preferable Ra is 0.07 to 0.11 μm.

(4) Manufacturing method of copper foil The molten copper which adjusted oxygen concentration is cast, and an ingot is manufactured. The oxygen concentration of the molten copper can be adjusted by techniques known to those skilled in the art, such as carbon deoxidation. 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, the cold rolling is performed to a predetermined thickness.

  Although the effect of the present invention can be obtained regardless of the thickness of the copper foil, the thickness of the copper foil provided for practical use is generally 35 to 5 μm. If the thickness is less than 5 μm, the copper foil tends to break in the battery manufacturing process, and if it exceeds 35 μm, the negative electrode plate becomes thick, making it 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 above-described method for controlling the area ratio of the Cube orientation, the area ratio of the oil pit (which has a strong correlation with the area ratio of the Copper and Brass orientations), and Ra in the rolling orthogonal direction is not limited to a specific method. For example, it can be controlled by adjusting the final cold rolling conditions.

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.
When the workability r of the final cold rolling is increased, the Cube orientation develops when the copper foil is recrystallized in the battery manufacturing process, and the area ratio increases. In order to increase the Cube orientation area ratio to 30% or more, r must be 90% or more. More preferable r is 95% or more. Here, the working degree 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: after final cold rolling. Thickness).

  As a measure for suppressing the development of oil pits, it is effective to use a rolling roll having a small surface roughness in the final rolling. On the other hand, in order to increase the adhesion strength between the copper foil and the active material, it is necessary to increase Ra in the rolling orthogonal direction on the surface of the copper foil after final rolling, and this is achieved by using a rolling roll having a large surface roughness. It becomes possible. That is, a smaller roll roughness is preferable for suppressing oil pits, and a larger roll roughness is preferable for active material adhesion strength.

  As a solution to the contradictory problem of suppressing the oil pit and increasing the Ra of the copper foil surface, the present inventors used a roll having a small roughness in each pass before the final pass (hereinafter referred to as an intermediate pass). We found a strategy to use a roll with a large roughness in the final pass.

Specifically, a roll having Ra of 0.02 to 0.04 μm is used in the intermediate pass, and a roll having Ra of 0.07 to 0.14 μm is used in the final pass. Here, Ra of a rolling roll is arithmetic mean roughness measured in the direction orthogonal to the circumferential direction of a roll based on JIS-B0601 using a contact roughness meter.

If Ra of the intermediate pass roll exceeds 0.04 μm, it is difficult to adjust the oil pit area ratio to 20% or less. When Ra of the intermediate pass roll is less than 0.02 μm, it is difficult to adjust the oil pit area ratio to 3% or more.
If Ra of the final pass roll exceeds 0.14 μm, it becomes difficult to adjust the Ra of the copper foil surface to 0.12 μm or less. When Ra of the final pass roll is less than 0.07 μm, it is difficult to adjust the Ra of the copper foil surface to 0.05 μm or more.

(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. In addition, a typical secondary battery includes, for example, a positive electrode plate in which a negative electrode plate is mainly composed of a lithium transition metal composite oxide as a main component of a positive electrode active material, an electrode plate group insulatively arranged via a separator, and a nonaqueous electrolyte. And a battery case containing the electrode plate group and the non-aqueous electrolyte.

(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. Examples thereof include 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 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)
The molten copper with adjusted oxygen concentration was cast into an ingot having a width of 500 mm and a thickness of 200 mm. In some ingots, Ag or Sn was added to the molten copper. In addition, about 0.001% of Ag is contained in tough pitch copper and oxygen-free copper as an unavoidable impurity even if not intentionally added.
The ingot was heated at 850 ° C. for 3 hours, processed into a plate having a thickness of 10 mm by hot rolling, and the oxidized scale on the surface was removed by grinding. Thereafter, recrystallization annealing and cold rolling were repeated, and the final rolling finished to a thickness of 18 to 6 μm.

In order to change the workability r in the final cold rolling, the thickness of the plate to which the final recrystallization annealing (annealing immediately before the final cold rolling) was performed was adjusted. The final recrystallization annealing was performed using a continuous annealing line. The temperature of the furnace 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 15 to 30 μm.
In the final cold rolling, the processing degree per pass is 20 to 30%, the material is passed through the rolling rolls a plurality of times, and the copper foil sample is finally formed to the processing degree described in Table 1. Produced. Also, the surface roughness of the rolling roll used in the intermediate pass and the final pass was variously changed.
The following evaluation was performed about the obtained copper foil sample.

(component)
The oxygen concentration in the copper foil 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 taken from a 1.5 mm plate was used for oxygen (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, for example, the metal structure of the sample is observed and no oxide particles are present (oxide particles having a diameter of 2 μm or more are present). 0.01 piece / mm ² or less) may be confirmed. Further, in order to determine that the foil is based on tough pitch copper, for example, the metal structure of the sample is observed, and copper oxide particles having a diameter of 1 to 5 μm are distributed at a frequency of 100 particles / mm ² or more. You can confirm. The diameter of a particle here refers to the diameter of the smallest circle that can surround the particle.

(Tensile strength)
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 after final cold rolling. 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 tensile strength was similarly calculated | required also about the sample after heating the rolled copper foil sample for 30 minutes at 200 degreeC imitating the drying process of a negative electrode active material.

(Measurement of crystal orientation of products)
On the surface of the copper foil sample after heating at 200 ° C. for 30 minutes, the area ratios of the Cube orientation, Copper orientation, and Brass orientation were measured by EBSD. Here, EBSD (Electron Back Scatter Diffraction: Electron Back Scattering Diffraction) refers to reflected electron Kikuchi line diffraction (Kikuchi pattern) that occurs when a sample is irradiated with an electron beam in a SEM (Scanning Electron Microscope). This is a technique for analyzing crystal orientation.
The sample surface was finished to a mirror surface by electrolytic polishing, and the crystal orientation distribution was measured by scanning the area of 1000 μm × 1000 μm in steps of 5 μm. Then, a crystal orientation density function analysis was performed, and the area of crystal grains having an orientation within 15 ° from each of the Cube orientation, Copper orientation, and Brass orientation was divided by the measurement area to obtain an area ratio. OSL Analysis 5.3 of TSL was used for the above analysis. Note that the information obtained in the azimuth analysis by EBSD includes azimuth information up to a depth of several tens of nanometers at which the electron beam penetrates into the sample, but is sufficiently small with respect to the area being measured. Described.

(Area ratio of oil pit)
On the surface of the copper foil sample after final rolling, the oil pit area ratio was measured for an area of 300 μm × 300 μm using a confocal microscope (manufactured by Lasertec, model number: HD100D). The sample was moved in the optical axis direction within the measurement visual field, and an image (Focus Scan Memory image) having a depth of 10 nm was captured from the copper foil surface. And the binarization process was performed considering the part deeper than 10 nm from the copper foil surface as an oil pit. As an example, FIGS. 3 and 4 show an optical microscope image of the sample surface and a binarized image at the same position, respectively. The bright part in the binarized image is an oil pit. The area of this bright color was obtained using commercially available image processing software, and was divided by the measurement area to obtain the oil pit area ratio.

(Ra of copper foil surface)
On the surface of the copper foil sample after the final rolling, the arithmetic average roughness Ra was measured in a direction orthogonal to the rolling direction using a contact roughness meter in accordance with JIS-B0601.

(Cycle life)
A cylindrical lithium ion secondary battery shown in FIG. 1 was produced by the following procedure for a copper foil having a thickness of 10 μm, 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 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) 50 parts by weight of LiCoO ₂ powder as a positive electrode active material, 1.5 parts by weight of acetylene black as a conductive agent, 7 parts by weight of PTFE 50% aqueous dispersion as a binder, 41.5% aqueous solution of carboxymethyl cellulose as a thickener A weight part 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 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 400 times or more.

The evaluation results are shown in Table 1.
Inventive Examples 1 to 16 and Comparative Examples 1 to 8 verify the effects of the present invention on a copper foil having a foil thickness of 10 μm. Inventive Examples 1 to 16 adjust the copper foil component so that the tensile strength after annealing at 200 ° C. for 30 minutes is 250 MPa or less, and in the final rolling, the working degree is 90% or more, and the Ra of the intermediate pass roll is 0.02 The final pass roll Ra was 0.07 to 0.14% and rolled to a thickness of 10 μm. As a result, the oil pit area ratio was 3 to 20%, the Ra of the copper foil sample surface was 0.05 to 0.12 μm, the Cube orientation was 30% or more, and the Copper and Brass orientation was 20% or less. In these inventive examples, a good cycle life exceeding 400 times was obtained.

In Comparative Example 1, since the final rolling degree was less than 90%, the Cube orientation was less than 30%, and the cycle life was reduced due to fatigue failure of the copper foil.
In Comparative Example 2, since the Ra of the intermediate pass roll was less than 0.02 μm, the oil pit area ratio was less than 3%. As a result, the cycle life decreased due to the peeling of the active material.
In Comparative Example 3, since the Ra of the intermediate pass roll exceeded 0.04 μm, the oil pit area ratio exceeded 20%. As a result, the Copper orientation exceeded 20%, and the cycle life was reduced due to fatigue failure of the copper foil.
In Comparative Example 4, Ra of the intermediate pass roll is further increased beyond 0.04 μm, the oil pit area ratio is further increased, the Copper and Brass orientations are over 20%, and the Cube orientation is less than 30%. The cycle life was significantly reduced.
In Comparative Example 5, since the Ra of the final pass roll was less than 0.07 μm, the Ra of the copper foil surface was less than 0.05 μm, and the cycle life was reduced due to the peeling of the active material.
In Comparative Example 6, since Ra of the final pass roll exceeded 0.14 μm, Ra on the surface of the copper foil exceeded 0.12 μm, and the cycle life decreased due to fatigue failure of the copper foil.
Since Comparative Example 7 had an excessive amount of Ag added to Tufucci Copper, and Comparative Example 8 had an excessive amount of Sn added to oxygen-free copper, the tensile strength after annealing at 200 ° C. for 30 minutes was high. It exceeded 250 MPa. That is, since recrystallization was not sufficiently performed by annealing at 200 ° C. for 30 minutes, the Cube orientation was less than 30%, the Copper and Brass orientations were over 20%, and the cycle life was reduced.

  Inventive Examples 17 to 19 and Comparative Examples 9 to 11 have oil pit area ratio, Ra on the copper foil sample surface, Cube, Copper and Brass, by adjusting the degree of processing in the final rolling and the Ra of the rolling roll even at different foil thicknesses. It has been verified that the area ratio in each direction can be controlled, thereby improving the cycle life. Similar results were obtained when the foil thickness was 10 μm.

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 (12)

By annealing at 200 ° C. for 30 minutes, the tensile strength decreases to 250 MPa or less, and when measured after heating at 200 ° C. for 30 minutes, the Cube orientation {001} <100> area ratio is 30% or more, and the Brass orientation {110} <112> area ratio of 20% or less, has a crystal orientation Copper orientation {112} to <111> area ratio is 20% or less, the area ratio of the oil pit is 3-20%, the rolling direction wherein the orthogonal directions of the arithmetic flat Hitoshiara Ra of a 0.05～0.12Myuemu, the negative electrode current collector foil of the secondary battery.   The copper foil for a negative electrode current collector of a secondary battery according to claim 1, wherein the material is made of tough pitch copper or oxygen-free copper.   Tough pitch copper containing 0 to 0.1% by mass in total of one or more alloy elements selected from the group consisting of Ag, Sn, Cr, Fe, Zn and Zr, with the balance being copper and unavoidable impurities 2. The copper foil for a negative electrode current collector of a secondary battery according to claim 1, wherein the material is oxygen-free copper. Tensile strength is 250 MPa or less, Cube orientation {001} <100> area ratio is 30% or more, Brass orientation {110} <112> area ratio is 20% or less, Copper orientation {112} <111> area ratio is It has a crystal orientation consisting of 20% or less, 3 to 20 percent the area ratio of the oil pits, and wherein the arithmetic flat Hitoshiara Ra of the direction perpendicular to the rolling direction is 0.05~0.12μm A copper foil for a negative electrode current collector of a secondary battery.   The copper foil for a negative electrode current collector of a secondary battery according to claim 4, wherein the material is made of tough pitch copper or oxygen-free copper.   Tough pitch copper containing 0 to 0.1% by mass in total of one or more alloy elements selected from the group consisting of Ag, Sn, Cr, Fe, Zn and Zr, with the balance being copper and unavoidable impurities 5. The copper foil for a negative electrode current collector of a secondary battery according to claim 4, wherein the material is oxygen-free copper.   The negative electrode electrical power collector comprised from the rolled copper foil as described in any one of Claims 4-6.   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 7.   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 7. A negative electrode plate.   10. A negative electrode plate according to claim 8 or 9, wherein the negative electrode plate group comprises a positive electrode plate having a lithium transition metal composite oxide as a main component of the positive electrode active material and a separator, a non-aqueous electrolyte, and the electrode. A secondary battery having a plate group and a battery case containing the non-aqueous electrolyte.   After the ingot is hot-rolled, it includes a step of repeating cold rolling and annealing, and finishing to a predetermined thickness by final cold rolling, with the rolling degree being 90% or more in the final cold rolling, before the final pass A rolling roll having an arithmetic average roughness Ra of 0.02 to 0.04 μm is used in each pass, and a rolling roll having an arithmetic average roughness Ra of 0.07 to 0.14 μm on the surface of the rolled material is used in the final pass. The manufacturing method of the copper foil as described in any one of Claims 1-3 characterized by the above-mentioned.   After the ingot is hot-rolled, it includes a step of repeating cold rolling and annealing, finishing to a predetermined thickness by final cold rolling, and then recrystallizing the copper foil by heat treatment. It is 90% or more, and a rolling roll having an arithmetic average roughness Ra of 0.02 to 0.04 μm is used in each pass before the final pass, and an arithmetic average roughness Ra of the rolled material surface is 0.07 to 0.07 in the final pass. A method for producing a copper foil according to any one of claims 4 to 6, wherein a 0.14 µm rolling roll is used.