JP2001011550A - Copper alloy rolled foil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an inexpensive copper alloy rolled foil for the electrode material of a collector on the negative electrode side of a lithium ion secondary battery high in tensile strength, excellent in heat resistance and having high electric conductivity. SOLUTION: This foil contains, by weight, 0.005 to 0.25% Ag, <=0.002% or 0.01 to O.04% oxygen and <=0.0002% hydrogen, and the balance Cu with inevitable impurities. In the case the content of oxygen is <=0.002%, the value of A defined by the following formula is controlled to 0.01 to 30, and in the case the content of oxygen is 0.01 to O.04%, the value of A defined by the formula of A=[the content(%) of oxygen]×[the content (%) of hydrogen]2×1012 is controlled to 1 to 300.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative electrode current collector electrode material for a secondary battery, more specifically, a lithium ion secondary battery or a polymer battery, an electric wire used for a micromotor coil, or an electronic material such as a flexible printed board. The present invention relates to a rolled copper alloy foil that can be used for parts.

[0002]

2. Description of the Related Art (Negative electrode current collector for lithium ion secondary battery)
The negative electrode current collector of the lithium ion secondary battery has a thickness of 10 to 2
A paste obtained by dissolving polyvinylidene fluoride (PVDF) in N-methylpyrrolidone on a rolled tough pitch copper foil or electrolytic copper foil of about 0 μm, and further mixing powdered graphite as a negative electrode active material with a # 60 bar coater to a thickness of 90 μm It is manufactured by coating at about 130 ° C. for 3 minutes after coating.

The reason why the rolled tough pitch copper foil or the electrolytic copper foil is used as the negative electrode side current collector is that the heat conductivity is large, the heat generated during charging can be quickly removed, and the one having high strength 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). In addition,
The above processes such as application and drying of the active material are continuously performed while unwinding 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 about 30 minutes.

(Coil for Micromotor Coil) Since the volume of a micromotor is smaller than that of a normal motor, a wire having a square or rectangular cross section is used to increase the coil winding density. In addition, this coil is required to have high electrical conductivity. For this reason, rolled foil of tough pitch copper is cut in the sheet width direction to produce a wire having a square or rectangular cross section. The wire thus manufactured is applied as a resin wire to the surface, dried, and then wound up to be used as a wire for a micromotor coil.

[0005]

(Lithium ion secondary battery negative electrode current collector) Tough pitch copper has a high thermal conductivity (conductivity of 98% IACS or more) and a tensile strength of 400 N by increasing the rolling reduction of cold rolling. / Mm ² or more can be obtained relatively easily. However, tough pitch copper contains particles such as cuprous oxide and oxides of impurity elements in the copper foil containing oxygen,
Very few elements dissolved in the matrix and easy recovery and recrystallization at interfaces such as cuprous oxide and oxides of impurities. Sex is considerably reduced. For this reason, even if the draft is increased in the foil manufacturing process and high-strength tough pitch copper is manufactured, recovery occurs 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. Such a softening phenomenon is particularly remarkable in the spring to summer season when the temperature of the storage atmosphere increases.

[0006] Since the tough pitch rolled copper foil which has been softened in this way has a low tensile strength, it is necessary to change the tension applied to the foil in the step of applying and drying 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 with severe softening is used, foil breakage and foil elongation in the above-described process are apt to occur, resulting in a decrease in productivity. Also, even when using a tough pitch copper rolled foil that has not been softened during storage,
Softening is likely to occur due to heating (130 ° C.) in the drying step, and when the dried foil is wound up, the foil may be stretched and the foil may be cut, thereby lowering the yield and productivity.
In particular, 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 not be used as a product. Furthermore, even when the above problems do not occur, 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 breaks due to expansion and contraction of the active material, Peeling occurs and battery performance is degraded.

On the other hand, the electrolytic copper foil has a tensile strength of 320 N /
mm ² , yield strength 250 N / mm ² , elongation 12% (Examples to be described later), can maintain almost the initial mechanical properties even after heating at 130 ° C. for 30 minutes, and have a higher heat resistance than the tough pitch copper rolled foil. Excellent, but the price is more expensive than rolled copper foil,
The conductivity is 95% IACS, which is slightly lower than that of tough pitch copper rolled foil. In view of this situation, in order to manufacture lithium ion secondary batteries that maintain high performance even by repeated charge and discharge with high yield and productivity, the copper foil used as the negative electrode assembly has a tensile strength. Characteristics such as being large, hardly causing softening during storage, electrode manufacturing process and use, and having conductivity comparable to that of tough pitch copper rolled foil have been required more strongly.

(Cable wire for micromotor coil) For the same reason as described above, tough pitch copper having insufficient heat resistance can be used to cut the foil when cutting the foil in the width direction, apply the resin to the wire, and dry the wire in the drying step. It is easy to cause problems such as cutting. Therefore, a demand for a copper alloy foil having high tensile strength, electrical conductivity comparable to that of tough pitch copper, and excellent heat resistance has also been increased in this application.

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

[0010]

The rolled copper alloy foil according to the present invention contains Ag: 0.005 to 0.25%, further contains oxygen, and has a hydrogen content of 0.0002% or less. This is a rolled copper alloy foil composed of the remainder Cu and unavoidable impurities.
Here, the oxygen content is 0.002% or less or 0.01% or less.
In the former case, the value of A defined by the following formula is 0.01 to 30, and in the latter case, the value of A defined by the following formula is 1 It is desirably about 300. A = [content of oxygen (%)] × [content of hydrogen (%)] ² × 10 ¹² This rolled copper alloy foil has a tensile strength of 300 N at room temperature.
/ Mm ² or more and an elongation of 8% or more, and after heating at 130 ° C. for 30 minutes, a tensile strength of 300 N
/ Mm ² or more and elongation of 8% or more.

[0011]

Next, the reasons for limiting the composition of the rolled copper alloy foil according to the present invention will be described. (Ag) The rolled copper alloy foil of the present invention has an Ag content of 0.005 to
Contains 0.25%. If the Ag content is less than 0.005%, the desired strength and heat resistance cannot be obtained. Also, A
When g is contained in excess of 0.25%, the strength and heat resistance are further improved, but the price increases with the improvement in characteristics, and the cost performance decreases. .25%. Desirable Ag content is 0.007 to 0.20%, more preferably 0.01 to 0.20%. Although the rolled copper alloy foil of the present invention further contains oxygen, Ag has a lower affinity for oxygen than Cu, so most of the Ag in the rolled copper alloy foil does not become an oxide, and It contributes to the strength and heat resistance of the rolled alloy foil. Further, Ag hardly decreases its conductivity even when it is dissolved in a copper matrix, and can maintain conductivity similar to that of tough pitch copper.

(Oxygen) In the rolled copper alloy foil according to the present invention, not only strength and heat resistance but also electrical conductivity are important necessary properties. However, when elements such as P, Mg and Si are added and deoxidized, these properties are obtained. Deoxidizing agent remains in the alloy and the electrical conductivity decreases. Therefore, in the copper alloy foil of the present invention, oxygen is contained in the alloy to convert these elements into oxides, thereby ensuring electrical conductivity comparable to that of tough pitch copper. In the copper alloy foil of the present invention, oxygen is dissolved in a matrix, copper oxide particles such as Cu ₂ O and CuO (formed in a melting casting process and a subsequent manufacturing process), or oxidation of an impurity element inevitably contained. (Including those which are complex oxides with Cu or two or more impurity elements).
In the rolled copper alloy foil of the present invention, the amount of oxygen in a processed state of the foil is mainly determined in the melting casting step.

The oxygen content of the molten metal is 0.002.
%, And less than 0.01%, unavoidable impurity elements in the molten metal are both oxidized and non-oxidized. The oxygen content of the molten metal exceeds 0.002%,
If it is less than 0.01%, the oxide particles of the inevitable impurities are less likely to float and separate from the molten metal, and thus tend to remain in the ingot. Inevitable impurity elements remaining in the ingot without being oxidized are
Heating during hot rolling combines with oxygen in the ingot to form oxide particles. When rolling an ingot containing a large number of inclusions as described above, inclusions serve as starting points for cracking, so that plate and foil breakage are likely to occur in the rolling process, and even after being made into a copper alloy foil, during lithium secondary battery production. The foil is likely to break due to the tension applied to the foil. Further, recovery and recrystallization at the oxide particle interface are apt to occur, and the heat resistance is likely to decrease.

When the oxygen content exceeds 0.01%, the inevitable impurities are almost completely oxidized in the molten metal, and most of the formed oxide particles are discharged from the molten metal. Hard to get up. However, when the oxygen content exceeds 0.04%, the volume ratio of cuprous oxide increases, and the ductility and heat resistance of a copper foil are reduced. When the amount of oxygen is 0.002% or less, the ductility is good because both the contained cuprous oxide and oxide particles of unavoidable impurities are small, and the plate breaks during rolling and production of a lithium ion secondary battery,
No foil breakage. In the copper alloy composition of the present invention, in order to reduce the oxygen content to 0.0003% or less, it is necessary to strictly control the atmosphere during melting and casting, and from the viewpoint of manufacturing cost, the oxygen content is 0%. .0003-0.0
A range of 02% is desirable. As described above, the oxygen content in the copper alloy foil of the present invention is desirably 0.002% or less, or 0.01 to 0.04%.

(Hydrogen) In the copper alloy of the present invention, hydrogen penetrates into the copper alloy from the atmosphere in steps such as melt casting, hot rolling and / or annealing. Since this alloy contains oxygen, when hydrogen enters, it generates steam gas, swells in ingots, hot-rolled materials, and cold-rolled materials, and causes subsequent plate or foil breakage by rolling. 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, so that the strength of the grain boundary is reduced, and as a result, the life of the battery is reduced. For these reasons, the content of hydrogen is preferably 0.0002% or less, and more preferably 0.0001% or less.

Further, in relation to the oxygen content, A =
[Oxygen content (%)] x [Hydrogen content (%)] ² x
10 ¹² and the time, when the oxygen content is less than 0.002%, if A = 0.01 to 30, also the oxygen content of 0.01-0.045, A = 1 to 300 In this case, hot rolling cracking and heat cracking are unlikely to occur. When the oxygen content is 0.002% or less, a special refining facility is required to make A less than 0.01, and it takes a long time for refining.
On the other hand, when A exceeds 30, the occurrence of hot rolling cracks and swelling of the plate during heat treatment increases, and the yield is significantly reduced. When the oxygen content is 0.01 to 0.04%, A is set to 1 to 300 for the same reason.

(Impurity element) The unavoidable impurity element in the rolled copper alloy foil according to the present invention is an element inevitably contained in Cu in a raw material or in a melting and casting step, and is Li, Be, B, Mg, Al. , Si, P, S, C
a, Ti, Cr, Mn, Fe, Co, Ni, Zn, A
s, Se, Zr, Cd, In, Sn, Sb, Te, A
u, Pb and the like. In the copper alloy foil of the present invention, the content of these impurity elements present as solid solution, crystallization, precipitation or oxide in the matrix is 0.005 in total.
% Or less does not affect the strength, conductivity, heat resistance, etc. of the rolled copper alloy foil according to the present invention.

Next, a method for producing a rolled copper alloy foil according to the present invention will be described. (Melting Casting) The ingot for producing the rolled copper alloy foil according to the present invention can be made of electrolytic copper, oxygen-free copper, tough pitch copper and scraps thereof as a raw material for melting copper. Ag
Has a lower melting point than Cu, and Cu-
An Ag intermediate alloy may be used. In the rolled copper alloy foil according to the present invention, when the oxygen content is 0.002% or less, application of a method of dissolving oxygen-free copper (melting casting in a CO-CO ₂ mixed atmosphere, vacuum melting, etc.). Or, in a normal melting and casting facility using a shaft furnace, an electric holding furnace, a coreless furnace, etc., it is possible to cover the molten metal surface of the melting furnace, gutter, mold with flux, graphite particles, charcoal, inert gas, etc. .

Further, the content of oxygen is set to 0.01 to 0.04.
%, It is possible to add copper oxide (CuO, Cu ₂ O) to the molten metal, blow dry air, or cover the surface of the molten metal with an oxidizing flux in a melting furnace or a gutter. Casting is performed after confirming that the target oxygen content is achieved by plasma spectroscopic analysis, structure observation (distribution of cuprous oxide), and the like. The same method may be used for monitoring the oxygen content during casting. With respect to the ingot, the oxygen content is analyzed at several points in the casting direction by the same method, and the content of the impurity element is analyzed. The hydrogen content can be reduced to 0.0002% or less by drying the raw material for melting, furnace, gutter, mold, etc., and controlling the dew point of the atmosphere. The analysis of hydrogen may be performed, for example, by collecting a sample from the ingot and performing the method specified in JIS-Z2614. 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.

(Working heat treatment) The ingot for a copper alloy rolled foil according to the present invention formed by the above-described method has good hot rolling properties and cold rolling properties, and has a vertical continuous casting and a Darville casting. Ingots manufactured by such methods as hot rolling, then cold rolling and heat treatment can be combined into foils, or ingots manufactured by methods such as horizontal continuous casting and thin slab continuous casting (thickness of several mm) ~ 3
(About 0 mm) can be formed into a foil by combining cold rolling and heat treatment. As the working heat treatment step of the copper alloy rolled foil according to the present invention, for example, after heating at 700 to 950 ° C., hot rolling is performed to a thickness of 15 to 25 mm, and a predetermined combination of cold rolling and annealing is performed. Rolled foil of thickness. During cold rolling,
Thickness 0.5 to 1.5 mm, and / or 0.15 to 0.3
After annealing at about mm, annealing is performed at a thickness of less than 0.1 mm, and rolling is performed to a target thickness. After the final sheet thickness is obtained, final annealing may be performed under appropriate conditions for the purpose of recovering ductility and removing distortion. In order to reduce the distortion, it is effective to further correct the distortion with a tension leveler or the like.

In the annealing, either a continuous or batch type annealing furnace such as a continuous annealing furnace or a bell type annealing furnace may be used, but the batch annealing of the coiled alloy is performed at a sheet thickness of 0.1 mm or less. In this case, it is desirable to perform annealing at a temperature of 440 ° C. or less in order to prevent adhesion between the plates during annealing. Further, annealing of an alloy having an oxygen content of 0.002% or less is performed by using a KV furnace gas, an ammonia cracking gas,
It is preferably carried out in an inert atmosphere such as _{2 -10vol% H 2} gas. When annealing a copper alloy having an oxygen content of 0.01 to 0.04%, hydrogen embrittlement (hydrogen in the annealing atmosphere and oxygen in the copper alloy react to generate water vapor, and In order to prevent the material from becoming brittle due to blistering, it is desirable to perform annealing in a vacuum, an annealing atmosphere similar to that of tough pitch copper, or in an atmosphere of inertness or weak acidity.
If an oxide film is formed on the surface of the material by these annealings, it is removed by polishing with an acid.

[0022]

EXAMPLES (Example 1) Using electrolytic copper (purity of 99.99% or more) and Ag shot (purity of 99.99% or more) as raw materials, Examples 1 to 4 of the present invention and Comparative Examples 1 to 4 shown in Table 1 were used. A copper alloy ingot (60 mm × 60 mm × 200 mm) was melted in an inert gas atmosphere and cast into a mold. The alloys of Inventive Examples 2 and 4 and Comparative Examples 1 and 4 were adjusted to oxygen concentration by adding powdered Cu ₂ O before casting. The compositions shown in Table 1 were obtained from Comparative Example 3 obtained from a sample taken from a portion having no crack at the stage where hot rolling was stopped, Comparative Example 4 was obtained from a hot-rolled material, and the others were obtained from copper foil. It is a measured value. The oxygen content is determined by an inert gas melting infrared absorption method (JISH1067), and the hydrogen content is determined by JISZ2614. Among the unavoidable impurities, Al, Si, P, Cr, Mn, Fe, Co,
For Ni, Zn, As, Se, Te, the method specified in JIS, and for other elements, ICP-MS, GD
Analysis was performed using -MS, atomic absorption method and the like. As Comparative Example 5, a commercially available high-strength electrolytic foil (0.015 mmt) was used.

[0023]

[Table 1]

The ingots of Inventive Examples 1 to 4 and Comparative Examples 1, 2 and 4 were made into foils of 0.015 mmt in the following steps. 80
Hot rolling (60 mmt → 15 mmt) after heating at 0 ° C x 1 hour,
Cold rolling (→ 1.0 mmt), heat annealing in a salt bath at 500 to 650 ° C. for 20 seconds, pickling and cold rolling (→ 0.15)
mmt), heat annealing in a salt bath at 500 to 650 ° C. for 20 seconds, pickling, cold rolling (→ 0.05 mmt), N ₂
Annealing in gas at 300 to 380 ° C. for 2 hours, pickling, cold rolling (→ 0.015 mmt), 300 to 35 in N ₂ gas
Annealed at 0 ° C x 2 hours, pickled. However, in the ingot of Comparative Example 3, the hydrogen content and the value of A were larger than the ranges of the present invention, and cracks occurred when hot rolling was performed. Therefore, the subsequent steps after cold rolling were not performed. Although the ingot of Comparative Example 4 could be hot-rolled, it had many impurities, so that the sheet was cut, the surface of the foil was cracked, and holes frequently occurred during the rolling of the foil, and the rolling was stopped at a time point of 0.1 mm or less. From the foils of the present invention and the comparative examples, tensile test pieces (JIS No. 5,
n = 2) and conductivity test specimen (width 10 mm, length 3
00 mm, n = 2), and the tensile strength, elongation and conductivity were measured. Table 2 shows the results.

[0025]

[Table 2]

As shown in Table 2, the copper alloy foils of Examples 1 to 4 of the present invention all have a tensile strength of 300 N / mm ² or more,
With an elongation of 8% or more, the conductivity is comparable to that of tough pitch copper. On the other hand, the tough pitch copper foil of Comparative Example 1 and the copper alloy foil of Comparative Example 2 whose Ag content is lower than the lower limit of the present invention have a tensile strength of less than 300 N / mm ² . Further, the tensile strength and elongation of the electrolytic foil of Comparative Example 5 are comparable to those of the copper alloy foil of the present invention, but the electrical conductivity is slightly lower than that of the copper alloy foil of the present invention.

(Example 2) Tough pitch copper having the composition of Comparative Example 1 was cold-rolled from 0.135 mm to 0.015 mm without annealing, and this rolled copper foil was used as Comparative Example 6. . Tensile test pieces (JIS No. 5) were prepared from the rolled copper alloy foils of Invention Examples 1 to 4 and the rolled copper foils of Comparative Examples 5 and 6 so that the tensile direction was parallel to the rolling direction. These test pieces are subjected to 50-500 ° C (50 ° C intervals).
Was held for 30 minutes (in N ₂ gas) after cooling to room temperature, the tensile strength was measured, and a graph showing the softening characteristics due to this heat treatment was prepared for each sample. Next, for each sample, the tensile strength of the unheated specimen and 500
The average value (average tensile strength) of the tensile strength of the heating material was measured at 30 ° C. × 30 minutes. The heating temperature at which the average tensile strength of each sample was determined from the graph of the softening characteristics, and this was defined as the semi-softening temperature. Table 3 shows the results.

[0028]

[Table 3]

As shown in Table 3, the copper alloy rolled foils of the present invention all have a semi-softening temperature significantly higher than 300 ° C., whereas the electrolytic copper foil of Comparative Example 5 has a temperature of 200 ° C. It was found that the tough pitch copper was easily softened at 110 ° C. From this, it is considered that the copper alloy foil of the present invention does not soften even in the drying step in the manufacturing process of the lithium ion secondary battery, so that the foil does not break or the foil does not elongate during the process.

[0030]

The rolled copper alloy foil according to the present invention has high strength,
Since the conductivity has a value equivalent to that of conventionally used tough pitch copper, it is suitable for use as a negative electrode current collector of a lithium ion secondary battery. In particular, since it is excellent in heat resistance, it hardly softens in a drying process in a battery manufacturing process, and greatly contributes to improvement in productivity. Further, even in a charge / discharge cycle after being incorporated in the battery, cutting of the foil, peeling of the active material, and the like hardly occur, which greatly contributes to higher performance and longer life of the lithium ion secondary battery. Furthermore, since the rolled copper alloy foil of the present invention has the above characteristics, it greatly contributes to the improvement of productivity in the production of electronic components such as electric wires for coils of micromotors, and to the enhancement of their performance.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5G301 AA01 AA08 AB02 AB08 AD01 AD10 5H017 AS10 BB02 BB06 BB14 CC01 EE01

Claims (3)

[Claims] 1. Ag: 0.005 to 0.25% (% by weight, the same applies hereinafter), further containing oxygen, hydrogen content of 0.0002% or less, balance Cu and unavoidable impurities Copper alloy rolled foil. 2. The rolled copper alloy foil according to claim 1, wherein the content of oxygen is 0.002% or less, and the value of A defined by the following formula is 0.01 to 30. A = [content of oxygen (%)] × [content of hydrogen (%)] ² × 10 ¹² 3. An oxygen content of 0.01 to 0.04%,
The copper alloy rolled foil according to claim 1, wherein the value of A defined by the following equation is 1 to 300. A = [content of oxygen (%)] × [content of hydrogen (%)] ² × 10 ¹²