JP2001279351A - Rolled copper alloy foil and its production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain inexpensive copper alloy rolled foil high in tensile strength, having ductility, high in electric conductivity and also excellent in heat resistance. SOLUTION: This rolled copper alloy foil has a composition containing one or more selected from Co, Ni and Fe of, by mass, 0.005 to 0.05% in total, one or two of 0.005 to 0.025% P and 0.005 to 0.025% B in >=0.005 to 0.025% in total, if required, containing 0.005 to 0.15% Ag, and the balance Cu with inevitable impurities. Co and P are desirably contained therein. The rolled copper alloy foil can be produced by performing annealing in a thickness of 150 to 400% of the foil thickness of the product, next performing cold rolling to a thickness of <=103% of the thickness of the product foil, thereafter performing annealing as well and subsequently performing finish rolling or/and flattening treatment with applied tension.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolled copper alloy foil which can be used as a negative electrode current collector electrode material for a secondary battery, more specifically, a lithium ion secondary battery or a polymer battery.

[0002]

2. Description of the Related Art A negative electrode current collector of a lithium ion secondary battery or a polymer battery is formed on a tough pitch rolled copper foil or an electrolytic copper foil having a thickness of about 10 to 20 μm by forming polyvinylidene fluoride (P).
VDF) is dissolved in N-methylpyrrolidone, and a paste obtained by mixing powdered graphite as the negative electrode active material with a # 60 bar coater is applied to a thickness of about 90 μm, and then dried at 130 ° C. for 3 minutes.

The reason why tough pitch rolled copper foil or electrolytic copper foil is used as the negative electrode current collector is that heat conductivity is large, heat generated during charging can be quickly removed, and high strength steel is relatively easy. In the active material application step and the drying step, which can withstand the tensile stress applied to the copper foil, and the ionization tendency. The negative electrode-side current collector manufactured in this manner is overlapped with a positive electrode-side current collector (a positive electrode active material is coated on an aluminum foil) with a separator interposed therebetween, integrated by pressing, and wound (for details). Omitted).

[0004] Tough pitch copper has a high thermal conductivity (conductivity of 9).
8% IACS or more), increasing the rolling reduction of cold rolling to increase the tensile strength to 450 to 475 N / mm ² and the yield strength to 420 to 450 N.
/ Mm ² and an elongation of 0.4 to ² % can be obtained relatively easily. However, tough pitch copper contains oxygen and contains particles of cuprous oxide and oxides of impurity elements in the copper foil, and very few elements are dissolved in the matrix. Since the recovery and recrystallization are likely to occur at the interface of, the heat resistance is considerably reduced as compared with oxygen-free copper or phosphorous deoxidized copper. For this reason, even if the draft rate is increased in the foil manufacturing process and high strength tough pitch copper is manufactured, recovery and recrystallization occur when stored at room temperature for a long time, and phenomena such as a decrease in strength over time and an increase in elongation occur. I do. Such a softening phenomenon is particularly remarkable in the spring to summer season when the temperature of the storage atmosphere increases.

[0005] Since the tough pitch copper rolled foil thus softened has a low tensile strength, it is necessary to change the tension applied to the foil in the application and drying steps of the active material according to the degree of softening. There is. For this reason, when applying to the coating process, work such as strength confirmation is newly generated in advance, which is very complicated. In addition, when a foil having a high degree of softening is used, the foil is likely to be cut or stretched in the above-mentioned step, which causes a decrease in productivity. Furthermore, if the tough pitch copper rolled foil is softened over time due to heat generated by charging and discharging after being incorporated in the battery, the foil may break due to expansion and contraction of the active material, the active material may peel off, and the battery performance may deteriorate. Would. Therefore, for example, in JP-A-11-86873, a small amount of Ag is added to copper to obtain
No. 86872 proposes to reduce the amount of oxygen contained in copper, thereby suppressing recovery / recrystallization during storage at about room temperature to prevent softening.

[0006]

In the case of using a rolled tough pitch copper foil that has not been softened during storage,
Softening is likely to occur due to heating (130 ° C.) in the drying step after application of the active material, and when the dried foil is wound up, the foil may be stretched and the foil may be cut, thereby lowering yield and productivity. In addition, processes such as active material application and drying are continuously performed while rewinding the coil-shaped copper foil, but if the cutting of the foil or the malfunction of the line occurs during the manufacturing process, the line must be stopped. In such a case, the drying time of the applied active material may be 30 minutes or more. If the foil to be dried stays in the furnace for a long time due to a process trouble in the drying process, the softening becomes larger, and this portion may become unusable as a product. Further, in the case of tough pitch copper rolled foil, the ductility of the foil is reduced, so that the foil may be cut during the rolling process and during the production of the lithium ion secondary battery, which may lead to a reduction in productivity and yield.

In view of the above situation, in order to manufacture a lithium ion secondary battery having high performance even by repeated charging and discharging with high yield and high productivity, a copper foil used as a negative electrode current collector is required to have a tensile strength. In addition to high strength, ductility, and high electrical conductivity, there has been a growing demand for characteristics such that softening hardly occurs during storage, electrode manufacturing process, and use. On the other hand, the electrolytic copper foil has a tensile strength of 320 N / mm ² and a proof stress of 250 N / mm.
^{2. It} shows an elongation of 12%, can maintain almost the initial mechanical properties even after heating at 130 ° C. for 30 minutes, and is superior in heat resistance as compared with the tough pitch copper rolled foil, but has a problem that the price is higher than the rolled copper foil. is there.

Accordingly, an object of the present invention is to provide a rolled copper alloy foil having high tensile strength, ductility, high electrical conductivity, excellent heat resistance, and low cost.

[0009]

The rolled copper alloy foil according to the present invention comprises one or more selected from Co, Ni and Fe in a total amount of 0.005 to 0.05%, P: 0.005%. ~
0.025% and B: One or two of 0.005 to 0.025% are contained in a total amount of 0.005 to 0.025%, with the balance being Cu and unavoidable impurities. A particularly desirable composition of the rolled copper alloy foil is Co: 0.005 to 0.05%,
P: 0.005 to 0.025%, Co and P
Is more than 0.02% and 0.06% or less, S: 0.0
Less than 01% is Cu and unavoidable impurities. Also,
The rolled copper alloy foil further contains Ag: 0.005 to 0.1.
5% can be contained. The rolled copper alloy foil is annealed at a thickness of 150 to 400% of the product foil thickness, then cold rolled to a thickness of 103% or less of the product foil, further annealed, and then finish rolled And / or by performing a flattening treatment with tension. Thereby, tensile strength 300N / mm ² , elongation 8%
As described above, the conductivity is 85% IACS or more and 30 at 130 ° C.
Even after heating for minutes to 2 hours, the mechanical properties can be almost maintained.

[0010]

Next, the reasons for limiting the composition of the rolled copper alloy foil according to the present invention will be described. (Co, Ni, Fe) These elements form a solid solution in the copper matrix or generate and precipitate intermetallic compounds with P to improve the tensile strength and heat resistance of the rolled copper alloy foil. However, when the content of these elements is less than 0.005%, the target tensile strength and heat resistance cannot be obtained, and
If the content exceeds 5%, the electrical conductivity decreases. Therefore,
The content of one or more of these elements is 0.005 to 0.05% in total. When these elements are added together with P, the total amount of P and P exceeds 0.02% to 0.06%.
% Is desirable. The lower limit is for ensuring strength and heat resistance, and the upper limit is for ensuring stable electrical conductivity. Note that Co is an element contained in the positive electrode side active material (LiCoO ₂ ), and does not adversely affect the active material dissolved out of the copper foil. Therefore, it is desirable to use Co as the main component of reinforcement.

(P) P has a deoxidizing action, removes oxygen introduced into the molten metal before casting and absorbed in the molten metal, and forms an intermetallic compound together with Co, Ni and Fe to form a metal having strength and heat resistance. Improve the performance. However, when the residual P contained in the ingot is less than 0.005%, O may exceed 0.002% due to insufficient deoxidation. In this case, Co, N
i and Fe form an oxide, and the strengthening action of these elements is lost. When P exceeds 0.025%,
Lowers the conductivity together with solid solution Co, Ni, Fe,
The target conductivity cannot be obtained. Therefore, the content of P is set to 0.005 to 0.025%. Note that B also has a deoxidizing effect, but P forms an intermetallic compound with Co, Ni, and Fe, the electrolyte contains LiPF ₆ as a main component, and P alone contains P to prevent insufficient deoxidation. Or P and B
Is desirable.

(B) B has an action of removing oxygen in the molten metal, and is added instead of or together with P. B is P
In comparison with the above, the conductivity of the rolled copper alloy foil is not reduced, and the internal oxidation is suppressed during annealing in the atmosphere. The above effect can be obtained by adding a very small amount of 0.005%, but if it exceeds 0.025%, the electrical conductivity is reduced.
0.025%. When the melt becomes insufficiently deoxidized with B alone, deoxidation is achieved by co-adding with P. In this case, the added amount is B: 0.005 to 0.025% and P:
0.005 to 0.025% in the total amount of 0.005
% Or more and 0.025% or less.

(Ag) Ag is added as necessary to improve the strength and heat resistance of the rolled copper alloy foil without substantially lowering the conductivity. However, if the Ag content is less than 0.005%, the effect is small, and if the Ag content exceeds 0.25%, the price rise becomes large, so the content is made 0.005 to 0.25%.

(Impurity Element) (S) S is inevitably mixed from metal, raw material, furnace material, anti-oxidation charcoal, flux and the like. When S is contained in excess of 0.001%, it becomes mainly CuS or Cu ₂ S, but this S tends to be free and segregates at the grain boundaries and defects. In this case, the elongation is reduced particularly in a foil state, and the sheet is easily cut when a stress is applied. Therefore, the content of S is set to 0.001% or less. S is removed by adjusting the composition of the molten metal, deoxidizing with P and / or B, adding Mg or Ca directly to form sulfide, and removing the floating sulfide together with other slag. Can respond.

(Oxygen, hydrogen) In the rolled copper alloy foil according to the present invention, the oxygen content is desirably less than 0.003%. When the oxygen content becomes 0.003% or more,
Cracks are generated at the interface of the oxides present in the foil, and the ductility of the foil is likely to be reduced or cut, and the recovery / recrystallization occurs at the interface, and the heat resistance intended for the present invention is obtained. This is because it will not be possible. The hydrogen content is 0.0
It is desirable to make it less than 002%. Hydrogen content is 0.
If it exceeds 0002%, the foil will swell in the processing and heat treatment step, resulting in defects such as surface cracks and peeling, resulting in poor foil yield and productivity. Further, even after being incorporated in a battery as a current collector of a lithium secondary battery, hydrogen moves to a grain boundary due to a rise in temperature during charging or the like, and the strength of the grain boundary is reduced, resulting in a reduction in battery life. For these reasons, the content of hydrogen is preferably 0.0002% or less, and more preferably 0.0001% or less. In order to reduce the hydrogen content to less than 0.0002%, drying of the raw materials used, furnace material in the melting and casting process, sufficient drying of the mold, atmosphere control, degassing (Ar gas bubbling)
Is important.

(Other Impurities) The unavoidable impurity elements in the rolled copper alloy foil according to the present invention are elements which are unavoidably contained in Cu in the raw material or in the melting and casting step.
Except for S, O and H, Li, Be, Al, Si, T
i, Cr, Mn, Zn, As, Se, Zr, Cd, I
n, Sn, Sb, Te, Au, Pb and the like. In the copper alloy foil of the present invention, if the total content of these other impurity elements present in the matrix as solid solution, crystallization, precipitation or oxide is 0.02% or less, the present invention relates to the present invention. Does not affect the strength, heat resistance, etc. of the rolled copper alloy foil. However, since elements such as P, Si, As, and Sb reduce the conductivity even in a very small amount, each of these elements is less than 0.005% in order to keep the conductivity high.
%.

Next, a method for producing a rolled copper alloy foil according to the present invention will be described. (Melting Casting) Ingots for producing the rolled copper alloy foil according to the present invention can be made of electrolytic copper, oxygen-free copper and scraps thereof as raw materials for melting copper. Ag has a lower melting point than Cu, and Ag base metal or a Cu-Ag intermediate alloy may be used. For the addition of B and P, an intermediate alloy such as Cu-2% B or Cu-15% P may be used in order to improve the addition yield. For Co, Ni, and Fe, the metal may be used, or an intermediate alloy of these elements and Cu may be used.

In the rolled copper alloy foil according to the present invention, when the oxygen content is 0.003% or less, a method for dissolving oxygen-free copper (for example, melting and casting in a CO-CO ₂ mixed atmosphere, vacuum melting, etc.) ) Or in ordinary melting and casting facilities using shaft furnaces, electric holding furnaces, coreless furnaces, etc., after deoxidizing the molten metal, the surface of the molten metal of the melting furnace, gutter, mold is fluxed, graphite particles, charcoal, inert. This is possible by covering with gas or the like. In addition, Cu-2% B, Cu-15% P, etc. are used for deoxidation of molten metal, and M is used for desulfurization.
g, a Cu-Mg intermediate alloy, Ca, a Cu-Ca intermediate alloy, or the like may be used as appropriate. 0.0002% hydrogen content
In order to make the following, drying of melting raw materials, furnaces, gutters, molds, etc.,
This is possible by controlling the dew point of the atmosphere. For analysis of hydrogen, for example, a sample is taken from an ingot and JIS-Z26
It is good to carry out by the method prescribed in 14. In casting, ingot casting can be performed by applying a normal casting method such as vertical continuous casting, horizontal continuous casting, thin slab continuous casting or the like, or a casting method such as Darville casting or die casting.

(Heat treatment of foil) The ingot for rolled copper alloy foil according to the present invention, which has been formed by the above-described method, has good hot rollability and cold rollability, and has a vertical continuous casting. , Ingots manufactured by methods such as Darville casting are hot rolled, and then cold rolling and heat treatment are combined to form a foil, or ingots manufactured by methods such as horizontal continuous casting and thin slab continuous casting ( It is also possible to form a foil by combining cold rolling and heat treatment for a thickness of several mm to about 30 mm). For example, 700 to 9
After heating at 50 ° C, hot rolling is performed to obtain a thickness of 15 to 25 mm.
After that, cold rolling and annealing are combined to obtain a rolled foil having a predetermined thickness. In the middle of cold rolling, after annealing at a thickness of about 0.5 to 1.5 mm and / or about 0.15 to 0.3 mm, cold-roll until the thickness of the product becomes 150 to 400% of the foil thickness. Perform rolling. In the annealing of the foil, any continuous or batch type annealing furnace such as a continuous annealing furnace or a bell-type annealing furnace may be used.

(Foil processing heat treatment) The copper alloy foil according to the present invention is annealed at a thickness of 150 to 400% of the product foil thickness → cold rolled to a thickness of 103% or less of the product foil thickness → Finish rolling to the thickness of the product foil after annealing, 'flattening treatment by applying tension after cold rolling to the thickness of the product foil after annealing,
Or "flattening treatment with tension after annealing (in this case,
Cold rolling is performed to the thickness of the product foil in the step of (2)). The intermediate annealing itself at the time when the foil material becomes several times the product foil thickness as described above is known as described in JP-A-10-230303.

In the case where the thickness to be annealed exceeds 400% of the thickness of the product foil, the subsequent cold-rolling rate becomes large, so that the final annealing (, ′ ″) is severely softened and the desired tensile strength is reduced. If a good combination of strength and elongation cannot be achieved, and if the thickness to be annealed is less than 150%, the subsequent cold-rolling reduction rate becomes small, so that tensile strength after cold-rolling cannot be obtained. Final annealing (, '
)), The tensile strength is further reduced. Therefore, it is desirable to anneal at a thickness of 150 to 400% of the product foil thickness. The purpose of this annealing is to soften the copper alloy foil ground. Either a batch annealing furnace or a continuous annealing furnace may be used.Taking an example of annealing using a batch annealing furnace, the material in the furnace is 250 to 650 ° C.
And then hold for about 30 minutes to 2 hours. When using a continuous annealing furnace, conditions may be set so that the hardness after annealing becomes a value obtained by the batch furnace.

Steps (and) are necessary for providing a well-balanced combination of tensile strength, elongation and heat resistance, or even better flatness to the copper alloy foil. When the cold rolling is completed at a thickness exceeding 103% of the thickness of the product foil, or the rolling of 'increases the reduction in elongation. Therefore, the cold rolling is performed to a thickness of less than 103% of the thickness of the product foil. It is desirable to perform the annealing in “,” in which the material is semi-softened. Due to this semi-softening annealing, the dislocations introduced into the copper alloy of the present invention by cold rolling are extinguished from those that easily disappear by thermal motion, and the rearrangement of the dislocations causes ductility to recover, stabilizing the dislocation structure. Achieved.
The semi-softening means that the hardness (Knoop hardness in the case of foil) of the material before annealing is H ₁ , and the hardness when the material is completely recrystallized (for example, heated at 400 to 600 ° C. × 2 hours). Is H ₀ and ΔH = H ₁ −H ₀ , the hardness of the material after annealing is approximately H = H ₀ + 0.5 × ΔH.
The semi-softening annealing can be performed by a low-temperature annealing using a batch furnace or a continuous annealing furnace. When a batch type annealing furnace is used, for example, after the material in the furnace reaches 150 to 400 ° C.,
What is necessary is just to hold for about 30 minutes to 2 hours. When using a continuous annealing furnace, conditions may be set so that the hardness after annealing becomes a value obtained by the batch furnace.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments, but the present invention is not limited to these embodiments. (Example 1) Under a charcoal coating, electrolytic copper (purity 99.
95% or more) and Ag shot (purity 99.99)
%), Cu-50% Co, Cu-30% Ni, Cu
Using an intermediate alloy such as -10% Fe and Cu-15% P as a raw material, a copper alloy ingot (width 60 mm, thickness 60 mm, length 200 mm) having the composition shown in Table 1 was cast in a mold. Also,
As Comparative Example 13, a rectangular parallelepiped block was cut out of a tough pitch copper continuous ingot and the above dimensions were obtained by lathing. Note that Comparative Example No. 10 is Ca and M after melt deoxidation
Desulfurization by adding g was not performed. In addition, the composition shown in Table 1 is a measured value after forming a copper foil. The content of each element is determined by the method specified in JIS, ICP-MS, GD-MS,
According to a method such as an atomic absorption method, the oxygen content was measured by an inert gas melting infrared absorption method (JISH1067), and the hydrogen content was measured by JISZ2614.

[0024]

[Table 1]

No. The ingots 1 to 12 were processed into a foil having a thickness of 0.015 mm by the following steps. (1) 800
After heating at 1 ° C for 1 hour, hot rolling (60mmt → 15mmt)
(2) Cold rolling (→ 1.0 mmt); (3) Heat annealing in a 500 salt bath for 20 seconds; (4) Cold rolling after pickling (→ 0.
2 mmt), (5) annealing for 20 seconds in a 500 ° C. salt bath, (6) cold rolling after pickling (→ 0.055 mmt),
(7) annealing at 400 ° C. for 2 hours in an inert gas;
(8) cold rolling after pickling (→ 0.0151 mmt); (9) annealing at 300 to 400 ° C. for 2 hours in an inert gas;
(10) Skin pass rolling while applying tension (→ 0.01
50 mmt). In addition, No. In the case of only 13 tough pitch copper, the heating temperature was set to 600 ° C., 150 ° C., and 120 ° C. in the steps (5), (7), and (9), respectively, and the other steps were the same.

From each of the manufactured rolled foils, a tensile test piece (JIS No. 5, n
= 3) and a test piece (JISH0505, width 10 mm, length 300 mm, n = 2) was processed, and tensile strength, elongation and conductivity were measured. Table 2 shows the results. The temperature of the final annealing condition shown in Table 2 is the semi-softening temperature defined above.

[0027]

[Table 2]

As shown in Table 2, Each of the copper alloy foils 1 to 7 satisfies target values in tensile strength, elongation and electrical conductivity. Further, the semi-softening temperature (final annealing temperature) is high, which is not softened even when the line is stopped (maintained at 130 ° C.) in the step of forming the active material on the copper alloy foil, causing problems such as foil elongation and foil breakage. Does not occur.
On the other hand, No. No. 8 has a low Co content, so the tensile strength does not reach the target value. 9 has a low Co conductivity because of a large Co content. No. 10 has an S content of 0.0
Since it is as large as 018%, the elongation is low. No. 11 and N
o. Sample No. 12 has a low conductivity because of excessive amounts of Ni and Fe. No. of tough pitch copper No. 13 has a small elongation and a low semi-softening temperature of 120 ° C. Therefore, when the line stops, 13
When it is kept at 0 ° C., it is softened, and problems such as elongation of the foil and breakage of the foil are likely to occur.

[0029]

The rolled copper alloy rolled foil according to the present invention has a tensile strength of 300 N /
mm ² or more, 8% or more elongation, may comprise an electrical conductivity 85% IACS or more characteristics, since half-softening temperature is high, the degree being heated for 30 minutes to 4 hours, for example 130 ° C. softening Without maintaining the properties, a tensile strength of 300 N / mm ² or more and an elongation of 8% or more can be maintained. Therefore, it is less likely to be softened in a drying step in a manufacturing process of a negative electrode current collector such as a lithium ion secondary battery, greatly contributing to an improvement in productivity, and even in a charge / discharge cycle after being incorporated in a battery. Cutting and peeling of the active material are unlikely to occur, which greatly contributes to higher performance and longer life of the lithium ion secondary battery.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat 参考 (Reference) C22F 1/00 650 C22F 1/00 650A 661 661C 682 682 682 685 686 686 686B 694 694A

Claims (4)

[Claims] 1. One or more selected from Co, Ni and Fe in a total amount of 0.005 to 0.05% (% by mass,
The same applies hereinafter), P: 0.005 to 0.025% and B: 0.
005-0.025% of one or two kinds in a total amount of 0.00
A rolled copper alloy foil containing 5% or more and 0.025% or less, with the balance being Cu and unavoidable impurities. 2. Co: 0.005 to 0.05%, P:
0.005 to 0.025%, and the total amount of Co and P exceeds 0.02% to 0.06% or less, S: 0.001%
% Or less, a rolled copper alloy foil comprising the balance Cu and inevitable impurities. 3. The rolled copper alloy foil according to claim 1, further comprising 0.005 to 0.15% of Ag. 4. The method of manufacturing a foil according to claim 1, wherein the thickness of the foil of the product is 1%.
Annealing at a thickness of 50 to 400%, then cold rolling to a thickness of 103% or less of the product foil, further annealing, and then performing finish rolling or / and flattening treatment with tension The method for producing a rolled copper alloy foil according to any one of claims 1 to 3, wherein