KR20150035502A - Surface-treated copper foil, method for manufacturing same, electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

A surface-treated copper foil, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery, the productivity of which is improved by improving resistance to resistance welding.
The sum of the elemental content (atomic%) of carbon and nitrogen in the depth direction of the copper foil is the largest at the outermost surface by XPS (X-ray photoelectron spectroscopic analysis), and the sum of the elemental content (atomic% The reduction degree of the total content (atomic%) of carbon and nitrogen in the depth direction of the copper foil is 50% / nm or more at a depth which is half the surface of the copper foil and the reduction degree is 50% / nm or more in JIS-K7194: 1994 Wherein the surface-treated copper foil has a surface resistance of 2.5 to 40 m ?.

Description

TECHNICAL FIELD The present invention relates to a surface-treated copper foil, an electrode for a lithium ion secondary battery, a lithium ion secondary battery, and a lithium ion secondary battery.

The present invention relates to a surface-treated copper foil having excellent resistance to welding, which is obtained by welding a surface-treated copper foil, particularly a copper foil or a metal material different from a copper foil by a resistance welding method, and a method for producing the surface- treated copper foil and an electrode for a lithium ion secondary battery and a lithium ion secondary battery .

BACKGROUND ART [0002] In the case of electronic parts used in automobiles and the like, it is required that the electrical connecting parts have higher reliability in recent years in accordance with the increase in the density. Particularly, junctions between terminals and dissimilar metals such as copper foils are required to be bonded more reliably.

Recently, as a negative electrode collector of a nonaqueous solvent secondary battery such as a lithium ion secondary battery, a strong bonding strength or a highly reliable bonding state is required between the copper foils or between the copper foil and the tab terminals.

One of the welding methods that meet this demand is the resistance welding method.

In this resistance welding method, a fusion portion called a nugget is formed at the joint portion of the dissimilar metals, so that it is possible to stably bond the joint portion with less occurrence of peeling. Especially, in the case of joining large metal parts such as a car body .

In the lithium ion secondary battery field, not only high strength and high reliability are obtained, but friction is not generated between the copper foil for the current collector and the tab for the copper foil-terminal unlike the ultrasonic welding. Therefore, By appropriately adjusting the welding time and selecting a condition that does not generate spatter, it is possible to prevent the generation of copper fine particles and the mixing into the battery cell, thereby contributing to the safety of the lithium ion secondary battery.

The ultrasonic weldability of the copper foil is excellent when the surface of the copper foil is not subjected to the rust-preventive treatment in the case where the pretreatment such as heat drying is not carried out. However, if the anticorrosive treatment is not carried out, the surface of the copper foil is easily oxidized in the atmosphere, so that it is not suitable for practical use irrespective of the pretreatment such as heat drying. In order to prevent oxidation of the surface of the copper foil, a method of forming a chromium hydrated oxide film called a chromate film by performing a chromate treatment in an acid bath (pH 1-2) and a method of immersing in a solution containing a triazole compound and a tetrazole compound Thereby forming an organic rust preventive film.

When the thickness of the rust preventive film is thick, it is difficult to clean the surface even when ultrasonic vibration is applied, and since the pure copper is hard to be exposed on the surface, It is hard to occur and the bonding force is weakened.

As for the copper foil to which the ultrasonic weldability is to be improved, a copper foil in which a chromium hydrated oxide is thinly formed on the surface of a copper foil by the present inventors (see Patent Document 1) or a solution obtained by mixing a triazole type compound and a silane coupling agent A copper foil subjected to anti-corrosive treatment (see Patent Document 2) is proposed.

Japanese Unexamined Patent Application Publication No. 2009-68042 Japanese Laid-Open Patent Publication No. 2011-23303

As described above, many studies have been made to improve the properties of the copper foil used as the current collector of a lithium ion battery to improve the characteristics of the ultrasonic welding, but the examination and the method of the copper foil that exhibits good resistance weldability are not yet known . Therefore, a problem of the present invention is to develop a copper foil having excellent resistance weldability which is expected to increase introduction of a lithium ion battery for automobiles into a current collector.

As a result of intensive investigations to solve this problem, the inventors of the present invention have found clues for solution of rust-preventive treatment with an organic component centering on triazole-based compounds and control of surface resistance value. As a result of studying the rust-preventive treatment conditions, it was found that the total content of nitrogen and carbon contained in the rust-preventive coating was the highest on the outermost surface, and the rust- A rust preventive film characterized by a change in the content ratio of nitrogen and carbon with respect to the depth direction is formed, and furthermore, the concentration of the triazole type compound is controlled to set the surface resistance value measured based on JIS K 7194: 1994 within a certain range , An electrolytic copper foil having good resistance welding characteristics is obtained.

The surface-treated copper foil of the present invention is characterized in that the total amount of carbon and nitrogen element content (atomic%) in the depth direction of the copper foil measured on XPS (X-ray photoelectron spectroscopy) (Atomic%) of the element content of carbon and nitrogen with respect to the depth direction of the copper foil at the depth at which the total of the elemental contents (atomic%) of the carbon and the elemental nitrogen becomes half the value at the outermost surface Is 50% / nm or more and the surface resistance specified in JIS-K7194: 1994 is 2.5 to 40 m OMEGA.

In the method for producing a surface-treated copper foil of the present invention, a rust preventive treatment liquid containing 50 to 700 ppm of a triazole-based compound and having a concentration ratio of 0.05 or more to the total concentration of the triazole-based compound is applied to the copper foil , The sum of carbon and nitrogen element content (atomic%) in the depth direction of the copper foil measured on XPS (X-ray photoelectron spectroscopic analysis) on at least one side of the copper foil is the largest at the outermost surface of the copper foil, The degree of reduction of the total content (atomic%) of carbon and nitrogen in the depth direction of the copper foil is 50% or more at a depth at which the total of elemental contents of carbon and nitrogen (atomic% / Nm and a surface resistance specified in JIS-K7194: 1994 of 2.5 to 40 m ?.

According to the present invention, it is possible to provide a surface-treated copper foil excellent in weldability between copper foils by resistance welding or between copper foil and other metals.

Further, the surface treatment method of a copper foil excellent in resistance welding ability of the present invention can easily produce a surface treated copper foil which is excellent in weldability between copper foils by resistance welding or between copper foil and other metals.

FIG. 1 is a graph showing the sum of atomic% of elements of carbon and nitrogen in a depth direction of a copper foil measured by XPS (X-ray photoelectron spectroscopy) according to an embodiment.
2 is an explanatory diagram schematically showing resistance welding.

(Mode for carrying out the invention)

The surface-treated copper foil of the present invention is characterized in that at least one side of the copper foil (in the present invention, the electrolytic copper foil and the rolled copper foil are collectively referred to as a copper foil when it is not necessary to represent them individually), XPS (Atomic%) in the depth direction of the copper foil is the largest at the outermost surface and the sum of the elemental content (atomic%) of carbon and nitrogen is half the value at the outermost surface, A triazole type compound or a complex compound thereof having a reduction degree of a total content (atomic%) of carbon and nitrogen in the depth direction of the copper foil of 50% / nm or more and a resistance value of 2.5 to 40 m? An organic rust inhibitive coating consisting of a mixture of both compounds (in the present specification, an organic rust inhibitive coating composed of a triazole type compound or a complex compound thereof or a mixture of both of them is referred to as " Ria is also based compounds, and / or, described as "anti-corrosive organic compounds consisting of the complex compounds) are formed.

The resistance value on the surface of the copper foil is measured based on JIS-K7194: 1994.

In the present embodiment, elemental analysis in the depth direction is performed by combining an X-ray photoelectron spectroscopic analyzer (XPS apparatus) and an argon spatter, and carbon and nitrogen in the rust preventive film formed on the surface of the copper foil are detected and quantified.

The anticorrosive coating is a complex of copper and a triazole compound and a mixture with a pure triazole compound, and the volume resistivity of the copper foil main body is on the order of 10 ⁵ to 10 ⁶ times. In general, when an insulating film is attached on a metal surface, the resistance value increases as the thickness of the insulating film increases. As a result, the measured value of the surface resistance of one copper foil based on JIS-K7194: 1994 is adopted as an index of the thickness of the rust-preventive coating.

As a method of confirming the content of carbon and nitrogen in the anticorrosive coating film, it is possible to measure the element content (atomic%) of carbon and nitrogen in the depth direction of the copper foil by XPS (X-ray photoelectron spectroscopy) Of the total content of carbon and nitrogen in the depth position at which the sum of the sum of carbon atoms and nitrogen atoms becomes half the value of the outermost surface is used as [% / nm].

The thickness of the rust preventive coating and the amount of the triazole-based compound deposited, that is, the total amount of carbon and nitrogen derived from the triazole-based compound are determined by the treatment concentration and treatment temperature of the triazole-based compound used for the rust-preventive treatment. Also, the sum of the contents of carbon and nitrogen takes a maximum value near the outermost surface of the film, decreases as it progresses in the depth direction, and finally becomes 0%.

That is, if the reduction rate [% / nm] of the element content at the depth position where the total content of carbon and nitrogen is half the value of the outermost surface is large, most of the carbon and nitrogen originating from the triazole- And the rust-preventive component is densely present on the outermost surface of the rust-preventive coating. On the other hand, when this value is small, the existence ratio of carbon and nitrogen derived from the triazole type compound is not only small between the outermost surface and the center portion of the coating, but also low in the presence ratio of carbon and nitrogen near the outermost surface, It can be considered that the rust-preventive component is not in a dense existence state.

From the above, the degree of reduction [% / nm] of the total content of elements of carbon and nitrogen at the depth position where the sum of the elemental contents of carbon and nitrogen is half the value of the outermost surface, It is a measure of whether the resulting carbon and nitrogen are present in large amounts and in dense form.

When this value is smaller than 50% / nm, carbon and nitrogen derived from the triazole-based compound near the surface of the rust preventive film are insufficient, so that contact between the air and the hot water heated in the heating step of the pre- And the thickness of the oxide film tends to increase, and there is a possibility that satisfactory weldability may not be obtained.

The resistance value of the copper foil surface of the present embodiment is 0.25 to 40 m?. When it is smaller than 0.25 mΩ, the ability to protect the surface of the copper foil from air or moisture at room temperature is lowered, and oxidation or discoloration of the surface tends to occur during storage and transportation. In addition, in the high-temperature environment of 100 to 160 캜 such as the drying step in the production of the negative electrode current collector of the nonaqueous solvent secondary battery, since the strength of the rust preventive film is insufficient for preventing oxidation and the thickness of the oxide film is excessively increased, Is extremely deteriorated. When the resistance value on the surface of the copper foil is larger than 40 m OMEGA, the thickness of the rust preventive film itself is excessive, so that the thermal energy at the time of welding is excessively consumed for removing the rust preventive film, This is because of concerns.

The resistance value on the surface of the copper foil is more preferably in the range of 0.25 to 20 m OMEGA, more easily than in the range of 20 to 40 m OMEGA because the rust preventive film is easily removed at the time of welding.

In the method for producing a surface-treated copper foil of the present embodiment, for example, an anticorrosive treatment liquid containing 50 to 700 ppm of a triazole-based compound and having a concentration ratio of 0.05 or more to the total concentration of the triazole- Is applied to the copper foil to form a rust preventive film on at least one side of the copper foil.

Examples of triazole-based compounds include benzotriazole, tolyl triazole, carboxybenzotriazole, chlorobenzotriazole, ethylbenzotriazole, naphthotriazole, and complex compounds thereof. Examples of the carbonic acid anhydride include acetic anhydride, succinic anhydride, maleic anhydride, propionic anhydride, and phthalic anhydride.

The concentration of the triazole compound in the rust-inhibitive treatment liquid is preferably 50 to 700 ppm. When the content is less than 50 ppm, the resistance value of the surface is less than 2.5 mΩ, and oxidation or discoloration of the surface is liable to occur in heating during the storage, transportation and drying process. On the other hand, if it exceeds 700 ppm, the surface resistance value exceeds 40 mΩ, and the thickness of the rust preventive coating itself becomes excessive, so that the thermal energy at the time of welding is excessively consumed for removing the rust preventive film, There is a fear that it will not be obtained.

The concentration ratio of the anhydrous carbonic acid to the triazole-based compound is preferably 0.05 or more. When the concentration ratio of the anhydrous carbonic acid to the triazole-based compound is lower than 0.05, the degree of reduction of the total content of carbon and nitrogen in the depth position at which the sum of the contents of carbon and nitrogen in the outermost surface is half the value 50% / nm. As a result, the difference between the contents of carbon and nitrogen in the vicinity of the outermost surface of the rust preventive film and the inside thereof becomes small, and the rust-preventive component is insufficient near the outermost surface of the rust preventive film, There is a possibility that sufficient weldability may not be obtained.

Further, in order to ensure the stability of the triazole component, it is preferable to set the temperature of the solution to 35 to 55 DEG C and the pH to 6.5 to 8.0. The immersion time is usually about 0.5 to 30 seconds.

However, the conditions of the method for producing the surface-treated copper foil of the present embodiment are not limited to those described above.

In the method for producing an electrolytic copper foil, for example, the foil is immediately dipped in an organic rust inhibitor solution to form a rust preventive film.

In the case where rust-preventive treatment can not be carried out immediately after lamination, a pickling method in which H ₂ SO ₄ = 5 to 200 g / l as a pretreatment and dipping in diluted sulfuric acid at a temperature of 10 ° C to 80 ° C is effective. In the case of degreasing, the cathode and / or anode electrolytic degreasing is carried out in an aqueous solution of NaOH = 5 to 200 g / l and temperature = 10 to 80 캜 for a current density of 1 to 10 A / dm ² for 0.1 to 5 minutes It is effective.

The 10-point average surface roughness Rz of the copper foil is 2.5 占 퐉 or less, which is more suitable because thermal energy at the time of welding tends to be transmitted between the foils.

Example

[Compounds of copper foil (common to Examples 1 to 9 and Comparative Examples 1 to 10)] [

An electrolytic solution having the composition shown below was prepared, and an electrolytic copper foil having a thickness of 10 탆 was manufactured using a noble metal oxide-coated titanium electrode on the anode and a titanium rotary drum on the cathode at a current density of 50 to 100 A / dm ² .

Copper: 70-130 g / l

Sulfuric acid: 80 to 140 g / l

Additive: Sodium 3-mercapto-1-propanesulfonate = 1 to 10 ppm

Hydroxyethylcellulose = 1 to 100 ppm

Low molecular weight glue (molecular weight 3,000) = 1 to 50 ppm

Chloride ion concentration = 10 to 50 ppm

Temperature: 50 ~ 60 ℃

[Formation of a rust preventive film]

[Examples 1 to 9]

The electrolytically-pulverized copper foil was immediately transferred to a triazole-based compound in the presence of benzotriazole (1,2,3-benzotriazole: hereinafter referred to as BTA), tolyltriazole (5-methyl-1H-benzotriazole: hereinafter referred to as TTA) (5-ethyl-1H-benzotriazole: hereinafter referred to as EBTA), and one kind of anhydrous succinic anhydride, maleic anhydride and anhydrous propionic acid was selected and the total concentration was 50 to 700 ppm. In a rust preventive treatment liquid prepared so that the concentration ratio to the total concentration of the compound was in the range of 0.05 or more, thereby performing rust-preventive coating on the surface of the copper foil. The solution temperature was 35 to 55 DEG C and the pH was 6.5 to 8.0.

[Comparative Examples 1 to 4]

The electrolytically electrified copper foil was immediately subjected to electrification at a total concentration of less than 50 ppm by selecting one to three kinds of triazole type compounds from BTA, TTA and EBTA, and one kind of anhydrous succinic anhydride, maleic anhydride and propionic anhydride was selected, So that a rust preventive film was formed on the surface of the copper foil. The solution temperature was 35 to 55 DEG C and the pH was 6.5 to 8.0.

[Comparative Examples 5 to 6]

The electrolytically electrified copper foil was immediately selected from BTA, TTA, and EBTA triazole type compounds at a total concentration of 50 to 700 ppm, and one kind of anhydrous succinic anhydride, maleic anhydride and propionic anhydride was selected, Based compound to the total concentration of the zirconium compound in the range of less than 0.05, whereby a rust-preventive coating was formed on the surface of the copper foil. The solution temperature was 35 to 55 DEG C and the pH was 6.5 to 8.0.

[Comparative Examples 7 to 9]

The electrolytically electrified copper foil was prepared by immediately selecting one to three kinds of triazole type compounds from BTA, TTA and EBTA to have a total concentration of more than 700 ppm, and one kind of anhydrous succinic anhydride, maleic anhydride and propionic anhydride was selected, So that a rust preventive film was formed on the surface of the copper foil. The solution temperature was 35 to 55 DEG C and the pH was 6.5 to 8.0.

[Comparative Example 10]

The copper foil subjected to electrolytic treatment was left without being coated with the anti-corrosive agent.

[Determination in the depth direction of nitrogen and carbon]

The element content (atomic%) in the depth direction of nitrogen and carbon was measured using an XPS measurement apparatus 5600MC of ULVAC PHI Co., Ltd. under the following conditions.

An ultimate vacuum degree of 1 x 10 < ^-10 > Torr (1 x 10 < ^-8 &

X-ray: X-ray monochromated Al-k? Line, output 300W, detection area 800μm?

Ion line: ion species Ar +, acceleration voltage 3 kV, sweep area 3 x 3 mm 2,

Sample angle of incidence 45 ° (angle between sample and detector),

Spattering rate 2.3 nm / min (in terms of SiO ₂ )

A curved line in which the element content (atomic%) is taken as the ordinate axis and the depth direction is taken as the abscissa axis and a sum of the content ratio of nitrogen and carbon is prepared and a tangent line is created at a depth position which is half the value of the content of the outermost surface, The concentration reduction degree [% / nm] was calculated.

FIG. 1 is a graph showing the sum of atomic% of elements of carbon and nitrogen in a depth direction of a copper foil measured by XPS (X-ray photoelectron spectroscopy) according to an embodiment.

Solid line a in Fig. 1 shows an example of the element content (atomic%) of the total of carbon and nitrogen in the depth direction in Examples 1 to 12.

The broken line b in Fig. 1 shows an example of the element content (atomic%) of the total of carbon and nitrogen in the depth direction of Comparative Examples 1 to 9.

In both the solid line a and the broken line b, the sum of the contents of carbon and nitrogen in the depth direction of the copper foil is the largest at the outermost surface. Here, the degree of reduction of the total content of carbon and nitrogen in the depth direction of the copper foil at the depth at which the sum of the elemental contents of carbon and nitrogen is half the value of the outermost surface is a half value Of the graph shown by the solid line a in the depth shown by the dashed line b and the slope of the tangent line Sb of the graph shown by the dashed line b in the depth of the half line in the broken line b.

The area of the region sandwiched between the solid line a and the x-axis according to the embodiment corresponds to the content of carbon and nitrogen in the rust preventive film of the embodiment. Similarly, the area of the area enclosed by the broken line b and the x-axis according to the comparative example corresponds to the content of carbon and nitrogen in the rust preventive film of the comparative example. In the case of the same rustproof film thickness, the contents of carbon and nitrogen are the same in Examples and Comparative Examples, and the area of the area sandwiched between the solid line a and the x axis and the area of the area sandwiched by the broken line b and the x axis are equal.

[Measurement of surface resistance]

The surface resistance of the copper foil was measured by a four-terminal method based on JIS-K7194: 1994 using the resistance meter RM3544 of Hioki Electric Co.,

[Resistance welding test]

As a pretreatment, the copper foil was dried under reduced pressure at a pressure of 100 Pa for 1 hour at a temperature of 140 캜 in a vacuum dryer (ADP200 of Yamato Scientific).

2 is an explanatory diagram schematically showing resistance welding. A tap copper plate 2 having a thickness of 200 mu m is disposed on a lower electrode (copper stage electrode) 1, and 20 sample copper foils 3 are stacked thereon. An upper electrode (copper-alumina alloy rod electrode, Φ3.2 mm) 4 is applied under pressure to the welded portion of the sample copper foil 3 and a current I flows between the upper electrode 4 and the lower electrode 1 Resistance welding is performed.

A peak value of 2400 A, a pulse current of 4.9 ms, and a pressure of 33 N were applied as a welding machine using NRW-200A manufactured by Abeonics Co., Ltd. to obtain 20 sheets of copper foil having a thickness of 10 탆 Thick tap was welded to the copper plate.

After welding under the above conditions, the welded portion of the copper foil of the outermost layer in contact with the upper electrode was observed with an optical microscope at a magnification of 20 times to confirm that no crack occurred, and the welded copper foil was observed One by one. A case where 15 or more copper foils were broken at a welded portion was evaluated as?, 10 to 14 copper foils were broken at a welded portion as?, 9 pieces of copper foils broken at a welded portion or less, or none at all.

In Examples 1 to 12, both the surface resistance and the content ratio of nitrogen to carbon with respect to copper were all appropriate, and the welding condition was good.

In the comparative examples 1 to 4, the surface resistance is excessively small. As a result, the thickness of the anticorrosive coating film is too small, the copper foil surface is excessively oxidized in the drying and heating process of the pre-welding process, and excessive welding energy is consumed to remove the oxide film.

In Comparative Examples 5 to 6, the degree of reduction of the total content of carbon and nitrogen in the vicinity of the outermost surface with respect to the depth direction was 50% at the depth position where the sum of the elemental contents of carbon and nitrogen was half the value of the outermost surface. / Nm, and the rust-preventive component near the outermost surface is insufficient. As a result, the thickness of the anticorrosive coating is in a sufficient range, but the anticorrosion coating tends to be broken from the outermost surface at the time of heating and the oxidation resistance is insufficient. For this reason, the surface of the copper foil is excessively oxidized in the drying and heating process of the pre-welding process, and excessive welding energy is consumed to remove the oxide film, and a satisfactory welding state can not be obtained.

In Comparative Examples 7 to 9, the surface resistance is excessively large. As a result, the thickness of the anticorrosion coating film becomes excessively large, so that the cleaning of the surface due to the current at the time of welding is insufficient, so that a satisfactory welding condition can not be obtained.

In Comparative Example 10, a rust preventive coating was not formed on the surface of the copper foil, and an oxide film was liable to be generated by heating. As a result, the surface of the copper foil is excessively oxidized in the drying and heating process of the pre-welding process, and excessive welding energy is consumed to remove the oxide film, so that a satisfactory welding condition can not be obtained.

Examples 1 to 12 have excellent resistance weldability, so that it is easy to assemble electronic components and the like, and even when the copper foil is used as a current collector for a non-aqueous liquid secondary battery such as a Li battery, an excellent effect has been obtained.

INDUSTRIAL APPLICABILITY As described above, the present invention can provide a surface-treated copper foil which is excellent in weldability between copper foils by resistance welding or between copper foil and another metal.

Further, the surface treatment method of a copper foil excellent in resistance welding ability of the present invention can easily produce a surface treated copper foil which is excellent in weldability between copper foils by resistance welding or between copper foil and other metals.

The surface-treated copper foil of the present invention can be suitably applied to an electrode for a lithium ion secondary battery by using it as an anode current collector.

Further, the present invention can be suitably applied to a lithium ion secondary battery using an electrode for a lithium ion secondary battery as a cathode.

Claims (6)

(Total atomic percent) of carbon and nitrogen in the depth direction of the copper foil measured by XPS (X-ray photoelectron spectroscopy) is the largest at the outermost surface of the copper foil on at least one side of the copper foil, (Atomic%) with respect to the depth direction of the copper foil is 50% or less at the depth where the total of the element content (atomic%) of the nitrogen and the elemental content (atomic% And a surface-treated film having a surface resistance of 2.5 to 40 m? Specified in JIS-K7194: 1994 is formed on the surface-treated copper foil. (Total atomic percent) of carbon and nitrogen in the depth direction of the copper foil measured by XPS (X-ray photoelectron spectroscopy) is the largest at the outermost surface of the copper foil on at least one side of the copper foil, (Atomic%) with respect to the depth direction of the copper foil is 50% or less at the depth where the total of the element content (atomic%) of the nitrogen and the elemental content (atomic% And a surface-treated film having a surface resistance of 2.5 to 20 m? Specified in JIS-K7194: 1994 is formed on the surface-treated copper foil. The surface-treated copper foil according to claim 1 or 2, which is used as an anode current collector of a lithium ion secondary battery. And a step of applying a rust preventive treatment liquid containing 50 to 700 ppm of a triazole-based compound and having a concentration ratio of 0.05 or more to the total concentration of the triazole-based compound, Wherein the surface-treated copper foil is produced by the method according to any one of claims 1 to 3. An electrode for a lithium ion secondary battery, wherein the surface-treated copper foil according to any one of claims 1 to 3 is used as a negative electrode collector. A lithium ion secondary battery using the electrode for a lithium ion secondary battery according to claim 5 as a cathode.

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