JP5416077B2 - 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 as an active material is used as a negative electrode. What is used is known (FIG. 2).

Copper foil includes rolled copper foil and electrolytic copper foil. The rolled copper foil is excellent as a material for the secondary battery negative electrode plate in terms of strength, fatigue characteristics, and the like. Many of the rolled copper foils marketed as secondary battery negative electrode plate materials are made of tough pitch copper (JIS-C1100). Tough pitch copper is pure copper containing oxygen of 100 to 500 mass ppm, and the copper content is standardized to 99.90 mass% or more (hereinafter, mass ppm and mass% are expressed as ppm and%, respectively). ).
In the manufacturing process of the rolled copper foil, a tough pitch copper ingot is hot-rolled, and then cold-rolling and annealing are repeated, and finally it is finished to a predetermined thickness in the range of, for example, 35 to 5 μm by final cold-rolling.

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

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

In addition, with the miniaturization of secondary batteries, the copper foil, which is a negative electrode current collector, is becoming thinner. When the copper foil is thinned, a high-tension load is applied at the time of application of the active material in battery production, and the foil breakage easily occurs, and the foil breakage due to the softening is more likely to occur. Accordingly, there is a demand for a copper foil that has a higher tensile strength in a product after final rolling (rolled up) and is less likely to soften during thermal history.
In order to deal with such problems, a rolled copper foil made of a copper alloy (hereinafter referred to as copper alloy foil) has been proposed instead of a rolled copper foil made of tough pitch copper.

Japanese Patent Application Laid-Open No. 2000-303128 discloses a copper alloy foil obtained by adding 50 or 100 ppm of Cr, Zr, Ag, Cd, Sn, Sb, or Bi to oxygen-free copper.
Japanese Unexamined Patent Application Publication No. 2000-133276 (Patent Document 2) discloses a copper alloy foil containing Zn in a range of 10 to 35%.
In JP-A-11-339811 (Patent Document 3), Cu-0.1% Fe-0.03% P, Cu-0.3% Cr-0.25% Sn-0.2% Zn and Cu-0. A copper alloy foil made of 1% Ni is disclosed.
JP-A-2000-328159 (Patent Document 4) contains 0.002 to 0.045% P, and 0.006 to 0.25% Fe or / and 0.005 to 0.25%. A copper alloy foil added with Ag is disclosed. These alloys are based on phosphorous-deoxidized copper, and the P concentration is limited so as not to cause adverse effects on the properties of P.
Japanese Patent Application Laid-Open No. 2003-286528 (Patent Document 5) discloses a copper alloy foil containing 0.063 to 0.231% of Sn and appropriately adjusting the hydrogen concentration and the oxygen concentration. This copper foil has improved pinholes and flex life, and can be used as a negative electrode current collector of a lithium ion secondary battery.

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

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

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

As a result of intensive studies to solve the above problems, the present inventor has made the following invention.
(1) An oxygen-free copper-based copper alloy foil containing 0.05 to 0.22% by mass of Sn and the balance being Cu and impurities, and the angle formed with the rolling direction is 0 degrees, 22.5 degrees, and 45 degrees , 67.5 degrees, and 90 degrees, the Young's modulus is measured, and when Emax / Emin is the maximum value among the five Young's modulus and Emin is the minimum value, Emax / Emin is 1. 3 Ri der hereinafter and having the above tensile strength and 80% IACS or more conductivity 480 MPa, characterized that you keep the tensile strength of at least 400MPa after heating at 300 ° C. 30 min, the secondary battery Rolled copper foil for negative electrode current collector.
(2) The rolled copper foil according to (1), further containing 0.1% by mass or less of Ag.
( 3 ) The negative electrode electrical power collector comprised from the rolled copper foil of the said (1) or (2) description.
( 4 ) 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 ( 3 ).
( 5 ) At least one surface selected from the group consisting of metallic lithium, metallic tin, a tin compound, a silicon simple substance, and a silicon compound is contained on at least one surface of the negative electrode current collector described in the above ( 3 ). A negative electrode plate having an active material layer.
( 6 ) An electrode plate group in which the negative electrode plate described in the above ( 4 ) or ( 5 ) is insulated and disposed through a positive electrode plate having a lithium transition metal composite oxide as a main component of a positive electrode active material and a separator, non-aqueous electrolysis A secondary battery comprising a liquid and a battery case containing an electrode plate group and a non-aqueous electrolyte.

It is the schematic which shows the measurement direction with respect to the rolling direction of the Young's modulus of the rolled copper foil in this invention. It is the schematic which shows the structure of a general secondary battery.

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

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

  The copper alloy foil of the present invention can contain 0.1% or less of Ag. By adding Ag, the heat resistance can be improved without lowering the electrical conductivity. When Ag exceeding 0.1% is added, the heat resistance is further improved, but in addition to an increase in production cost, ductility is lowered and rolling into a foil becomes difficult. A more preferable Ag concentration is 0.06% or less. In addition, the electrolytic copper used as the melting material of the copper foil usually contains about 10 ppm of Ag as an inevitable impurity.

(Characteristics of copper foil)
In order to further improve the reliability of the battery without causing deformation of the copper foil due to charge / discharge stress, it is preferable to maintain a tensile strength of 400 MPa or more after the drying process. The heat load level in the drying process required in the present invention corresponds to a heat treatment at 300 ° C. for 30 minutes. This is a condition that is extremely stricter than the conventional heat load standard of 200 ° C. for 30 minutes (Patent Document 1) and 300 ° C. for 5 minutes (Patent Document 4).
The rolled copper foil of the present invention has a tensile strength after heating at 300 ° C. for 30 minutes, preferably 400 MPa or more, more preferably 450 MPa or more. In addition, when the copper foil of the present invention is completely recrystallized, the tensile strength decreases to nearly 200 MPa, and when the tensile strength of 400 MPa or more is maintained, the copper foil is recrystallized in the metal structure of the copper foil after heating at 300 ° C. for 30 minutes. Has not occurred. This decrease in tensile strength is due to the recovery of the metal structure.
Here, in order to maintain a tensile strength of 400 MPa or more after heating at 300 ° C. for 30 minutes, it is necessary to have a tensile strength of 480 MPa or more, preferably 520 MPa or more in the state after rolling.
When the Sn concentration is 0.05% or more, the tensile strength after heating under the above conditions is 400 MPa or more, and when it is 0.10% or more, it becomes 450 MPa or more.

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

(Young's modulus of copper foil)
The Young's modulus (longitudinal elastic modulus, stress / elongation) of a copper single crystal is anisotropic, and the Young's modulus changes significantly depending on the crystal direction. A rolled copper foil is an aggregate of many crystal grains, and atoms are arranged in a certain direction inside each crystal grain, but the direction differs for each crystal grain. However, each crystal grain is not randomly oriented, and the direction of the crystal grain is biased in the course of the manufacturing process such as solidification, rolling, and recrystallization. Therefore, the Young's modulus of a normal rolled copper foil varies depending on the direction in which stress is applied. That is, even if it is pulled with the same stress, the elongation (elastic elongation) of the copper foil changes depending on the pulling direction. Such a property having different characteristics depending on the direction is called anisotropy.
Conventionally, the mechanical properties of the negative electrode copper foil have been adjusted in consideration of productivity in the battery production line such as prevention of foil breakage. Therefore, with regard to the Young's modulus of the negative electrode copper foil, only the absolute value in the rolling direction in which tension is applied in the line was noted, and the anisotropy was not considered at all. However, when the present inventors used a copper foil having a large Young's modulus anisotropy as a negative electrode current collector, the copper foil wrinkled due to the anisotropy of elongation when subjected to charge / discharge stress. It was found that the active material peels due to this.
As a result of investigations by the present inventors, Young's modulus was measured in five directions in which the angle formed with the rolling direction was 0 degree, 22.5 degrees, 45 degrees, 67.5 degrees, and 90 degrees, and these five Young's moduli were measured. When Emax / Emin is 1.3 or less, preferably 1.25 or less as an index of Young's modulus anisotropy when the maximum value is Emax and the minimum value is Emin, the charge / discharge cycle life is Found significant improvement.
In addition, as above-mentioned, since the copper foil of this invention does not recrystallize in the heat drying process of an active material, the anisotropy of a Young's modulus does not change before and after this drying process.

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

Recrystallization annealing is performed under the conditions that the furnace temperature is in the range of 300 to 800 ° C., the annealing time is in the range of several seconds to several hours, and the crystal grain size after annealing is a predetermined size (usually 3 to 30 μm). Is called. The material after annealing is pickled using a sulfuric acid aqueous solution or the like in order to remove the surface oxide film generated during the annealing.
The method for controlling the anisotropy of the Young's modulus is not limited to a specific method, but can be controlled, for example, by adjusting the final cold rolling conditions as follows.
In the final cold rolling after the final recrystallization annealing, the material is repeatedly passed between a pair of rolling rolls to finish the target foil thickness. The Young's modulus anisotropy is influenced by the total workability in the final cold rolling and the workability per pass. Here, the total workability R is a sheet thickness reduction rate in the final cold rolling, and R = (T ₀ −T) / T ₀ (T ₀ : thickness before final cold rolling, T: final cold rolling) Later thickness). Further, the processing degree r per pass is a sheet thickness reduction rate when the rolling roll passes once, and r = (t ₀ -t) / t ₀ (t ₀ : thickness before passing the rolling roll, t: thickness after passing through the rolling roll).

Increasing the total working degree R increases the tensile strength of the copper foil, but increases the anisotropy of the Young's modulus. By making R preferably 97% or less, more preferably less than 94%, Emax / Emin can be adjusted to 1.3 or less, preferably 1.25 or less. On the other hand, if R is lower than 80%, it becomes difficult to adjust the tensile strength after rolling to 480 MPa or more. Therefore, the total working degree R of the final cold rolling is preferably 80 to 97%, more preferably 85 to 94%.
When rolling to ultrathin foil in the final cold rolling, if the degree of processing per pass is lowered, the rolling time is inevitably increased. Therefore, conventionally, the workability r per pass has been set to be relatively high with an emphasis on the productivity of rolling.
If the working degree r per pass of the final cold rolling is 50% or more, shear deformation occurs in the metal structure of the copper foil. As a result, anisotropy of Young's modulus is promoted, and even if R is 80 to 97%, Ema / Emin exceeds 1.3. Therefore, the maximum working degree r _{max in} all passes in the final cold rolling is preferably less than 50%, more preferably 43% or less. On the other hand, the minimum degree of processing r _min does not affect the tensile strength and Young's modulus of the copper foil of the present invention, but if r is reduced, the number of passes increases and rolling takes time. Therefore, in consideration of productivity, r _min is preferably 10% or more, more preferably 15% 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.

(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. , Graphite materials or carbonaceous materials obtained by subjecting mesophase pitch carbon fibers, mesophase spherules, 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. As the binder, for example, organic solvent-based polyvinylidene fluoride (PVDF), water-dispersed styrene butadiene rubber (SBR), or the like can be used. SBR can be used in combination with, for example, carboxymethylcellulose (CMC) as a thickener. By using a mixture of SBR and CMC, 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.
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.
The positive electrode active material-containing layer can contain a binder. 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. One example is polytetrafluoroethylene (PTFE). As the thickener, for example, CMC can be used in combination with the binder.
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, γ-butyrolactone, and methyl propionate. The kind of nonaqueous solvent to be used can be one kind or two or more kinds.
Examples of the electrolyte include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenide (LiAsF ₆ ), and the like. The electrolyte can be used alone or in the form of a mixture.

(Production of rolled copper foil)
After electrolytic copper was dissolved and the oxygen concentration was adjusted by carbon deoxidation, Sn and Ag were added and cast into an ingot having a width of 500 mm and a thickness of 200 mm. The ingot was heated at 850 ° C. for 3 hours and formed into a plate having a thickness of 10 mm by hot rolling. Next, the oxide scale on the surface was removed by grinding, and a 1.5 mm plate was formed by cold rolling. Thereafter, recrystallization annealing and cold rolling were repeated, and the final rolling finished to a thickness of 18 to 6 μm.
The final recrystallization annealing (annealing immediately before the final cold rolling) was performed using a continuous annealing line. The furnace temperature was set to 700 ° C., and the material passing speed (residence time in the furnace) was adjusted so that the crystal grain size after annealing was 10 μm.
In order to change the total workability (R) in the final cold rolling, the thickness of the plate to be subjected to final recrystallization annealing was adjusted in advance. In the final cold rolling, the degree of processing (r) per pass was variously changed.

(component)
The oxygen concentration in the copper alloy matrix was analyzed by an inert gas melting-infrared absorption method, and the Sn and Ag concentrations were analyzed by ICP-mass spectrometry. Here, a copper foil sample was used for Sn and Ag analysis, but a sample collected from a 1.5 mm plate was used for O analysis. This is because the ratio of the surface area to the mass of the foil sample is very large (for example, in the case of a 1 g sample, the surface area of a 1.5 mm thick plate is 1.5 cm ² while the surface area of a 10 μm thick foil is 220 cm. ² ) When oxygen is analyzed using a copper foil sample, oxygen in the surface oxide film and adsorbed water film is added, and the oxygen analysis value is increased by about 50 ppm from the oxygen concentration in the copper foil. In addition, in order to determine that this is an oxygen-free copper-based foil using a foil sample, the metal structure of the sample is observed, and no oxide particles are present (the oxide particles having a diameter of 2 μm or more are 0. (01 / mm ² or less) may be confirmed. In addition, Sn and Ag density | concentration were calculated | required to 2 digits below the decimal point of the mass%.

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

(Young's modulus)
The Young's modulus of the copper foil sample after final rolling (before heating at 300 ° C. for 30 minutes) was measured by a vibration method. As a measuring device, a cantilever type thin plate Young's modulus measuring device, TE-RT manufactured by Nippon Techno Plus Co., Ltd. was used.
The sample had a strip shape with a width of 3.2 mm and a length of 15 mm, and the vibration length was 10 mm. As shown in FIG. 1, the angle formed by the longitudinal direction of the sample and the rolling direction was α (degrees), and samples were collected from five directions where α = 0, 22.5, 45, 67.5, and 90. The Young's modulus was measured four times for each of the samples in these five directions to obtain an average value, and Emax / Emin was determined by setting Emax as the maximum of the five average values and Emin as the minimum.

(Cycle life)
A cylindrical lithium ion secondary battery shown in FIG. 2 was produced by the following procedure, and the cycle life was measured.
(1) 50 parts by weight of scaly graphite powder as a negative electrode active material, 5 parts by weight of SBR as a binder, and 23 parts by weight of a thickener aqueous solution dissolved in 99 parts by weight of water with respect to 1 part by weight of CMC as a thickener, By kneading and dispersing, a negative electrode paste was obtained. This negative electrode paste was applied on both sides of the rolled copper foil sample surface to a thickness of 200 μm by a doctor blade method, heated at 300 ° C. for 30 minutes, and dried. After pressurizing to adjust the thickness to 160 μm, the negative electrode plate 6 was obtained by molding by shearing.
(2) LiCoO ₂ powder 50 parts by weight as a positive electrode active material, acetylene black 1.5 parts by weight as a conductive agent, PTFE 50% by weight aqueous dispersion 7 parts by weight, CMC 1% by weight aqueous solution 41.5 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 electrolyte is a predetermined amount of an electrolyte prepared by dissolving 1.0 mol of LiPF ₆ as an electrolyte in a mixed solvent of 30% by volume of ethylene carbonate, 50% by volume of methyl ethyl carbonate, and 20% by volume of methyl propionate. did. 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 was 600 times or more.

The evaluation results are shown in Table 1. Table 2 shows the degree of processing of each pass for each method employed in the final cold rolling of each example. Here, in the examples where the Sn or Ag concentration is <0.01%, Sn or Ag is not added, and these concentrations are unavoidable impurity levels.
The inventive example contains 0.05 to 0.22 mass% of Sn, and has a conductivity of 80% IACS or more and a tensile strength of 480 MPa or more. These invention examples maintain a tensile strength of 400 MPa or more after annealing at 300 ° C. for 30 minutes, and Emax / Emin is 1.3 or less. As a result, a good cycle life of 600 times or more is obtained.
Here, the data of Invention Example 2 is shown as an example of the measured value of Young's modulus: 0 degrees: 110.8 GPa, 22.5 degrees: 114.9 GPa, 45 degrees: 117.6 GPa, 67.5 degrees: 125. It was 8 GPa and 90 degrees: 133.5 GPa. Therefore, Emax / Emin = 1.20 from Emax = 133.5 GPa and Emin = 110.8 GPa.

Inventive Examples 1 to 4 and Comparative Examples 5 to 7 have 0.12% Sn-containing oxygen-free copper, the total workability R is 90%, the workability r per pass is variously changed, and the thickness is 10 μm. It is finished. In Comparative Examples 5 to 7 in which the maximum value of the processing degree per pass was 50% or more, Emax / Emin exceeded 1.3. As a result, the copper foil wrinkled when subjected to repeated charge / discharge stress, the active material applied to the copper foil surface peeled off, and the cycle life was less than 600 times.
Inventive Examples 9 to 14 and Comparative Examples 8 and 15 are the oxygen-free copper to which 0.12% of Sn is added, the maximum working degree r _max per pass is about 40%, and the total working degree R is variously changed. The thickness is finished to 7 μm. In Comparative Example 8 in which the total workability was less than 80%, the tensile strength after rolling was less than 480 MPa. Due to this influence, the tensile strength after receiving a heat history at 300 ° C. for 30 minutes was less than 400 MPa, and the copper foil was plastically deformed by charge / discharge stress. In Comparative Example 15 in which the total workability exceeded 97%, Emax / Emin exceeded 1.3, and wrinkles were generated in the copper foil due to charge / discharge stress. Therefore, in Comparative Examples 8 and 15, the active material on the surface of the copper foil was peeled off, and the cycle life was less than 600 times.

  Invention Examples 16 to 18 have a foil thickness of 18 μm, 12 μm and 6 μm with respect to a foil thickness of 10 μm of Invention Examples 1 to 4 and a foil thickness of 7 μm of Invention Examples 9 to 14, and a foil thickness within the scope of the present invention. It shows that the intended effect can be obtained regardless of

Inventive Examples 21-27, 29 and 30 and Comparative Examples 19, 20, 28 and 31 verify the influence of the components of the copper foil.
Invention Examples 21 to 27 show that the intended effect of the present invention can be obtained if the Sn content is in the range of 0.05 to 0.22 mass%.
Comparative Example 19 is conventional oxygen-free copper, and the tensile strength of the copper foil was reduced to nearly 200 MPa due to the heat history at 300 ° C. for 30 minutes in the active material drying step. In Comparative Example 20, the addition amount of Sn added to oxygen-free copper was less than 0.05%, and the tensile strength was less than 400 MPa due to the thermal history at 300 ° C. for 30 minutes. Therefore, the copper foils of Comparative Examples 19 and 20 were plastically deformed by repeated charge / discharge stress, and the active material on the surface of the copper foil was peeled off, and the cycle life was less than 600 times.
In Comparative Example 28, since Sn exceeding 0.22% was added, the conductivity was lower than 80% IACS. If the conductivity is less than 80% IACS, heat generation and voltage loss cannot be ignored, and the intended secondary battery cannot be manufactured.

Inventive Examples 29 and 30 added Ag in a preferable range to improve the heat resistance without lowering the electrical conductivity, and the same amount of Sn was added as the tensile strength after heating at 300 ° C. for 30 minutes. It is higher than Invention Example 26.
In Comparative Example 31, since oxygen exceeded 10 ppm, a part of the added Sn was oxidized to be oxidized Sn. Since the Sn component deposited as an oxide does not contribute to improving the heat resistance of Cu, the tensile strength after heating at 300 ° C. for 30 minutes is less than 400 MPa, and the copper foil is subjected to repeated charge / discharge stress. While the plastic material was deformed and the active material was peeled off, cracks occurred in the copper foil starting from Sn oxide. As a result, the cycle life was significantly less than 600 times.

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

Claims (6)

An oxygen-free copper-based copper alloy foil containing 0.05 to 0.22% by mass of Sn and the balance being Cu and impurities, and the angle formed with the rolling direction is 0 degrees, 22.5 degrees, 45 degrees, and 67. When Young's modulus is measured in five directions of 5 degrees and 90 degrees, and Emax / Emin is 1.3 or less when the maximum value of the five Young's modulus is Emax and the minimum value is Emin. Ah is, which has a higher tensile strength and 80% IACS or more conductivity 480 MPa, characterized that you keep the tensile strength of at least 400MPa after heating at 300 ° C. 30 minutes, the anode current of the rechargeable battery Rolled copper foil for electric bodies.   Furthermore, 0.1 mass% or less of Ag is contained, The rolled copper foil of Claim 1 characterized by the above-mentioned. Claim 1 or 2 negative electrode current collector composed of rolled copper foil according. The negative electrode plate which has the negative electrode active material layer which has a carbonaceous material or a graphite material as a main component on the at least single side | surface of the negative electrode collector of Claim 3 . An active material layer containing at least one selected from the group consisting of metallic lithium, metallic tin, a tin compound, a silicon simple substance, and a silicon compound is formed on at least one surface of the negative electrode current collector according to claim 3. A negative electrode plate. 6. An electrode plate group in which the negative electrode plate according to claim 4 or 5 is insulatively arranged via a separator having a lithium transition metal composite oxide as a main component of a positive electrode active material and a separator, and an electrode plate group And a battery case containing a non-aqueous electrolyte.

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