TW201424107A - Copper foil, negative electrode for non-aqueous electrolyte secondary cell, and non-aqueous electrolyte secondary cell - Google Patents

Abstract

The purpose of the present invention is to provide a copper foil that has excellent cycle properties and is used as a power collector of a negative electrode for a non-aqueous electrolyte secondary cell. The present invention uses a copper foil characterized in that the amount of strain with a load of 300 MPa of stress after one hour of heating at 300 DEG C is 0.2-0.4%. With this copper foil the amount of strain with a load of 300 MPa of stress after one hour of heating at 300 DEG C is preferably 0.2-0.33%. Also, it is preferable for this copper foil to contain 0.005-0.3 mass% of at least one of molybdenum, tellurium, and titanium.

Description

Copper foil, negative electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery Field of invention

The present invention relates to a nonaqueous electrolyte secondary battery comprising: a positive electrode; a negative electrode, a negative electrode active material layer formed on a surface of the negative electrode current collector; and a nonaqueous electrolyte secondary battery; and a negative electrode for forming a nonaqueous electrolyte secondary battery The collector's electrode is excellent in electrolytic copper foil.

Background of the invention

In recent years, as a negative electrode active material of a lithium ion secondary battery, a negative electrode active material of a next generation having a charge and discharge capacity far exceeding the theoretical capacity of a carbon material has been continuously developed. For example, a material containing a metal which can be alloyed with lithium (Li) such as bismuth (Si), germanium (Ge) or tin (Sn) is expected.

In particular, when Si, Ge, Sn, or the like is used for the active material, these materials have a large volume change due to the inhalation of Li during charge and discharge, and it is difficult to maintain the state of the current collector and the active material in a good state. Further, these materials have the disadvantage of being repeatedly expanded and contracted by the charge and discharge cycle, and the active material particles are finely pulverized and detached, so that the cycle deterioration is extremely large.

In order to solve the above disadvantages, in order to improve the adhesion between the active material and the current collector, it is proposed to use a polyimide pigment binder.

Since the curing temperature of the polyimine binder is about 300 ° C, the use of a polyimine binder is expected to occur in a current collector (copper foil) that can withstand this temperature.

In addition, when Si, Ge, and Sn are used to increase the capacity of the active material, the active material layer becomes thick, and it is difficult to spread the electrolyte solution to the entire active material layer. In this case, there is an electrode plate for a non-aqueous electrolyte secondary battery in which the electrolyte solution can be expanded to the side of the current collector (copper foil) of the active material layer, and a void or the like is formed in the active material layer ( Please refer to Patent Document 1).

Advanced technical literature Patent literature

Patent Document 1: Japanese Patent Laid-Open Publication No. 2012-49136

Summary of invention

However, even in the invention disclosed in Patent Document 1, the amount of the electrolytic solution is different after the current collector side of the active material layer is compared with the electrolyte side, and the distance from the electrolyte side of the active material layer is affected. , a stress difference due to expansion and contraction of the active material. Further, the unevenness in the horizontal direction of the amount of the electrolyte reaching the current collector side of the active material layer becomes larger as the above-described stress difference becomes larger, and the stress becomes more uneven. Therefore, the uneven stress between the current collector and the active material is increased, and deformation or breakage of the current collector due to local stress concentration occurs, and the battery characteristics are lowered. On the other hand, when the copper foil is not deformed or broken, the stress caused by the expansion of the active material and the shrinkage is not alleviated. In the state, the internal stress of the active material becomes high, and as a result, the active material is destroyed, and the battery characteristics are lowered.

The present invention has been made in view of the above problems, and an object thereof is to produce a copper foil which can be used as a current collector of a negative electrode for a nonaqueous electrolyte secondary battery and which has excellent cycle characteristics.

In view of the above object, the present inventors have actively reviewed and found that in order to control the deformation caused by the uneven stress applied to the copper foil and the stress increase inside the active material, by controlling the hardened polyimide pigment binder The strain in the stress-strain diagram of the copper foil heated at a temperature can solve the problem of the present invention and achieve the present invention.

In order to achieve the aforementioned object, the following invention is provided.

(1) A copper foil characterized in that the strain at a load of 300 MPa after heating at 300 ° C for 1 hour is 0.2 to 0.4%.

(2) The copper foil according to (1), wherein the strain at a load of 300 MPa after heating at 300 ° C for 1 hour is 0.2 to 0.33%.

(3) The copper foil according to (1) or (2), wherein the copper foil contains 0.005 to 0.3% by mass of at least one element selected from the group consisting of molybdenum, titanium, and niobium.

(4) A negative electrode for a nonaqueous electrolyte secondary battery, characterized in that it has an active material layer containing at least one of lanthanum, cerium and tin on the surface of the copper foil, and the copper foil is characterized by being at 300 ° C After heating for 1 hour, the strain at a load of 300 MPa was 0.2 to 0.4%.

(5) A nonaqueous electrolyte secondary battery using the negative electrode for a nonaqueous electrolyte secondary battery according to (4).

According to the present invention, a copper foil which is used as a current collector of a negative electrode for a nonaqueous electrolyte secondary battery and which has excellent cycle characteristics can be obtained.

1‧‧‧Negative electrode for nonaqueous electrolyte secondary battery

3‧‧‧ copper foil

5‧‧‧Active material layer

31‧‧‧Non-aqueous electrolyte secondary battery

33‧‧‧ positive

35‧‧‧negative

37‧‧‧Parts

39‧‧‧ Electrolytes

41‧‧‧Battery cans

43‧‧‧positive lead

45‧‧‧Negative lead

47‧‧‧ positive terminal

49‧‧‧ Sealing body

Fig. 1 is a cross-sectional view showing a negative electrode 1 for a nonaqueous electrolyte secondary battery according to an embodiment of the present invention.

Fig. 2 is a cross-sectional view showing a nonaqueous electrolyte secondary battery 31 according to an embodiment of the present invention.

Form for implementing the invention

Embodiments of the present invention will be described in detail based on the following drawings.

The negative electrode 1 for a nonaqueous electrolyte secondary battery of the first embodiment will be described.

Fig. 1 is a view showing a negative electrode 1 for a nonaqueous electrolyte secondary battery. The negative electrode 1 for a nonaqueous electrolyte secondary battery has an active material layer 5 on the copper foil 3.

(copper foil 3)

When the copper foil 3 is used as a polyimide adhesive, heat treatment at 300 ° C for 1 hour is usually performed. In this case, after the copper foil 3 is heated at 300 ° C for 1 hour, the strain at a load of 300 MPa at a normal temperature is preferably 0.2 to 0.4%, and more preferably 0.2 to 0.33%. When the strain is less than 0.2%, the stress inside the active material due to expansion and contraction of the active material may not be sufficiently alleviated, and the active material layer is easily destroyed; and when the amount of strain is 0.4% or more, Plastic deformation and breakage of the copper foil are liable to occur, and in either case, the battery characteristics are degraded.

According to the above, the copper foil which satisfies 0.2 to 0.4% of the above strain is most suitable. For this reason, at least one type of copper foil containing, for example, molybdenum, titanium or niobium is suitable. By including these metals in the copper foil, the pinning effect of the grain boundary can be exerted, and the coarsening of the crystal grains can be suppressed in the heat treatment at 300 ° C or higher. Therefore, the strain strain can be made in the stress-strain diagram of the copper foil heated at 300 ° C in the range of 0.2 to 0.4%. The content of the foil of the added element is preferably from 0.005 mass% to 0.3 mass%. If the content is less than 0.005% by mass, the crystal grains are coarsened due to the weak pinning effect, so the above-mentioned strain amount is higher than 0.4%; and if it is more than 0.3% by mass, the above-mentioned strain amount is less than 0.2%. . Moreover, it is also inferior in terms of electrical properties such as a decrease in electrical conductivity.

In addition, in order to exhibit the pinning effect of the grain boundary and to suppress the coarsening of the crystal grains in the heat treatment at 300 ° C or higher, the present invention can be obtained by adding a substance other than molybdenum, titanium or niobium. effect.

Further, the tensile strength of the copper foil 3 at a normal temperature after heating at 300 ° C for 1 hour is preferably 450 MPa or more. When it is 450 MPa or less, plastic deformation and cracking may occur in the copper foil due to stress caused by expansion and contraction of the active material during charge and discharge.

(active material layer 5)

The active material layer 5 is a layer containing at least one of negative electrode active materials of cerium, lanthanum, and tin. The active material layer 5 can be obtained by applying a slurry containing particles of cerium, lanthanum, tin, a conductive auxiliary agent, a binder, or the like to a copper foil and drying it. As the binder, polyimide, polyamidamine, polybenzimidazole or the like can be used. When polyimide or the like is used, a high-temperature heat treatment (for example, 300 ° C or higher) is required in the drying step.

(Method of Manufacturing Copper Foil 3)

The present inventors conducted various experiments on the manufacture of copper foil. Then, it was found that when chlorine is not contained in the electrolyte, metal elements such as molybdenum, titanium, and tantalum can be easily taken in the foil, and the strength of the foil after normalization and heating can be improved. Further, it has been found that even when chlorine is contained in the electrolytic solution, by adding a thiourea-based compound, a metal element such as molybdenum, titanium or ruthenium can be taken up, and the strength of the foil after normal state and heating can be improved. Moreover, it has been found that by adjusting the content of the added elements, the amount of strain under a certain stress in the stress-strain diagram can be controlled.

Based on the results of the above-described experiment, the foil-forming conditions of the electrodeposited copper foil satisfying the desired conditions, the negative electrode for a non-aqueous electrolyte secondary battery, and the non-aqueous electrolyte secondary battery are described below.

The foil is formed in a plating bath in which a copper sulfate-based electrolyte solution is added with a metal element such as molybdenum, titanium or ruthenium, a thiourea-based compound (for example, ethylene thiourea), and chloride ions. The purpose of adding a thiourea-based compound to the electrolytic solution is to absorb a metal element such as molybdenum in the copper foil in the presence of chlorine.

On the other hand, when the thiourea-based compound is not used as an additive to the electrolytic solution, the amount of the chloride ion added to the electrolytic solution is preferably less than 5 ppm.

In the electrolytic copper foil, a metal element such as molybdenum, a thiourea-based compound, or a copper sulphate solution is added as an electrolytic solution, and titanium coated with a noble metal oxide is used as an anode, and a titanium rotating cylinder is used as a cathode, and has a current density of 40. The foil is prepared by electrolytic treatment under conditions of ~55 A/dm ² and a liquid temperature of 45 to 60 °C.

(Characteristics of Negative Electrode 1 for Nonaqueous Electrolyte Secondary Battery)

The copper foil of the present embodiment provides a stress which is caused by expansion and contraction of the active material even after heating at 300 ° C for 1 hour. Since the large amount of expansion and contraction of the active material containing ruthenium, osmium, and tin can maintain the adhesion between the current collector (copper foil) and the active material, and it is difficult to generate the current collector (copper foil). Deformed or broken raw copper foil. The negative electrode for a nonaqueous electrolyte secondary battery using the copper foil of the present embodiment as a current collector and the nonaqueous electrolyte secondary battery using the negative electrode have excellent cycle characteristics.

(non-aqueous electrolyte secondary battery)

Fig. 2 shows an example of a nonaqueous electrolyte secondary battery of the present embodiment. As shown in Fig. 2, the nonaqueous electrolyte secondary battery 31 of the present embodiment is formed by laminating the positive electrode 33 and the negative electrode 35 in the order of the separator-negative electrode separator-positive electrode via the separator 37, and is wound into a positive electrode. 33 is formed on the inner side to form an electrode group, and is inserted into the battery can 41. Then, the positive electrode 33 and the positive electrode terminal 47 are respectively connected by the positive electrode lead 43, and the negative electrode 35 is connected to the battery can 41 by the negative electrode lead 45, and the chemical energy generated inside the nonaqueous electrolyte secondary battery 31 is used as electric energy. Take it out. Then, the battery can 41 is filled with the electrolyte 39 so as to cover the electrode group, and then the sealing body 49 is attached to the upper end (opening) of the battery can 41 via an annular insulating spacer, and the sealing body 49 is manufactured. It is composed of a circular cover plate and a positive electrode terminal 47 at the upper portion thereof, and a safety valve mechanism is built in the inside thereof.

Example

Hereinafter, the present invention will be described in detail based on examples. Further, although molybdenum, titanium, and niobium are used as the additives in the present embodiment, other additives may be used as long as the strain amount at a load of 300 MPa in the stress-strain diagram is 0.2 to 0.4%.

<Examples 1 to 9>

The titanium cylinder is placed in a copper sulfate electrolyte added with copper sulfate, sulfuric acid, chloride ions, ETU (ethylene thiourea), bismuth molybdate, barium titanate, cerium oxide added in the amounts shown in Table 1. The electrolytic copper foil was formed into a film under the following electrolysis conditions. Further, the concentrations of Cu, Mo, Ti, and Te in Table 1 are the mass concentrations of the respective metal elements (Cu, Mo, Ti, Te).

Electrolytic condition

Current density 40~55A/dm ² , temperature 45~60°C

The electrolytic copper foil obtained by the above method was subjected to rustproof treatment under the following conditions.

The foil-formed electrolytic copper foil (untreated copper foil) was immersed in a CrO ₃ ;1 g/L aqueous solution for 5 seconds, subjected to a caseinate treatment, and washed with water and then dried.

Further, although the caseinate treatment is carried out here, it is of course possible to carry out the treatment with a benzotriazole-based treatment or a decane coupling agent or a treatment with a decane coupling agent after the treatment with the butyrate.

<Comparative Examples 1 to 5>

The titanium cylinder was placed in a copper sulfate electrolyte containing copper, sulfuric acid, chlorine, molybdenum, niobium, and ETU (ethylene thiourea) in an amount shown in Table 1, and the electrolytic copper foil was formed into a film under the following electrolysis conditions. .

Electrolytic condition

Current density 40~55A/dm ² , temperature 45~60°C

The copper foil obtained by foiling according to the above method is subjected to the first embodiment. Same surface treatment.

<Example ‧ Evaluation of Comparative Example>

The following tests were carried out on the prepared copper foil.

(Measurement of molybdenum and niobium content in copper foil)

The content of molybdenum, titanium, and niobium is determined by dissolving a certain weight of the electrolytic copper foil with an acid, and the amount of molybdenum, titanium, and niobium in the solution is determined by ICP emission spectrometry.

(Measurement of tensile strength and elongation of copper foil)

According to IPC-TM-650, the copper foil subjected to normal temperature and heat treatment was subjected to a tensile test at room temperature. From the obtained stress-strain line diagram, the tensile strength and the strain at 300 MPa load were calculated. Further, the crosshead speed at the time of measurement was set to 50 mm/min, and the strain was measured using a non-contact camera type extensometer.

(Battery performance test)

‧Preparation of anode for lithium secondary battery

A powdery Si alloy-based active material (having an average particle diameter of 0.1 μm to 10 μm) is mixed with a polyimide resin at a ratio of 10% by weight in a weight ratio of 90% by weight to prepare a negative electrode mixture, and the negative electrode mixture is prepared. The negative electrode mixture was dispersed in N-methylpyrrolidone (solvent) to prepare an active material slurry.

Next, the slurry was applied to both surfaces of a strip-shaped electrolytic copper foil having a thickness of 12 μm produced in the examples and the comparative examples, and after drying, it was heated at 300 ° C for 1 hour, and then compressed by a roll press. And a strip-shaped negative electrode was produced. The strip-shaped negative electrode was formed so that the film thickness of the negative electrode mixture after molding was the same on both sides and was 90 μm in total, and the width was 55.6 mm and the length was 551.5 mm.

‧Preparation of positive electrode for lithium secondary battery

0.5 mol of lithium carbonate and 1 mol of cobalt carbonate were mixed, and fired at 900 ° C for 5 hours in the air to prepare a positive electrode active material (LiCoO ₂ ).

The positive electrode active material (LiCoO ₂ ) was used as a conductive agent, and graphite was 6% by weight as a conductive agent, and polyvinylidene fluoride was mixed at a ratio of 3% by weight as a binder to prepare a positive electrode material, and It was dispersed in N-methyl-2-pyrrolidone to form a slurry.

Then, the slurry was uniformly applied to both surfaces of a strip-shaped positive electrode current collector having a thickness of 20 μm made of aluminum, and after drying, it was compression-molded by a roll press to obtain a strip-shaped positive electrode having a thickness of 160 μm. The strip-shaped positive electrode was formed so that the film thickness of the positive electrode mixture after molding was 70 μm in total and the width was 53.6 mm and the length was 523.5 mm.

‧Preparation of lithium ion secondary battery

A lithium ion secondary battery was prepared as one of the nonaqueous electrolyte secondary batteries. A laminated positive electrode, a strip-shaped negative electrode, and a separator having a thickness of 25 μm and a width of 58.1 mm and composed of a microporous polypropylene film were laminated to form a laminated electrode body. The laminated electrode system has a negative electrode located on the inner side thereof in the longitudinal direction thereof and is wound into a spiral shape in a plurality of turns, and the end portion of the separator is fixed to the outermost periphery by a tape to form a spiral electrode body. The hollow portion of the scroll electrode body was formed to have an inner diameter of 3.5 mm and an outer shape of 17 mm.

The prepared scroll-shaped electrode body is housed in a battery can made of nickel-plated iron in a state in which the insulating plate is placed on the upper and lower surfaces thereof, and is collected from the positive electrode for current collection of the positive electrode and the negative electrode. The anode lead wire made of aluminum is exported and connected to the battery cover, and the negative electrode lead made of nickel is derived from the anode current collector Wire and connect it to the battery can.

The battery can containing the scroll electrode body is filled with 5.0 g of a non-aqueous electrolyte solution having a ratio of 1 mol/L in a volumetric mixed solvent of propylene carbonate and diethyl carbonate. Those with LiPF ₆ dissolved. Next, the airtightness in the battery can is maintained by tightening the battery can by the insulating sealing gas gate coated with the asphalt and fixing the battery cover.

According to the above method, a cylindrical lithium secondary battery having a diameter of 18 mm and a height of 65 mm was produced.

The battery of the lithium ion secondary battery was evaluated at a temperature of 25 ° C by the following method.

(first time condition)

Charging: constant current charging with a current of approximately 0.1 C, and after reaching 4.2 V, constant voltage charging is performed, and is terminated when the charging current is equivalent to 0.05 C.

Discharge: A constant current discharge was performed at a current of approximately 0.1 C, and was terminated at 3.0 V.

(charge and discharge cycle conditions)

After the initial charge and discharge test, the charge and discharge were repeated over a period of 100 cycles with a current of approximately 0.5 C. The cycle characteristics were evaluated by dividing the discharge capacity after 100 cycles by the value of the initial discharge capacity as the capacity retention rate.

As clearly shown in Table 1, the strain amount at 300 MPa load after heating at 300 ° C for 1 hour was within 0.2 to 0.4%, and the lithium ion secondary battery using the copper foil as a current collector also exhibited good. Cycle characteristics. In particular, in Examples 1 to 5, the strain at 300 MPa after heating at 300 ° C for 1 hour is within 0.2 to 0.33%, so that the lithium ion secondary battery using the copper foil as a current collector exhibits a particularly excellent cycle. characteristic.

In Comparative Example 1, the strain amount at the load of 300 MPa after heating was as large as 0.45%, so that the deformation of the copper foil during charging and discharging was intense, and the lithium ion secondary battery using the copper foil as a current collector was inferior in cycle characteristics. result.

In Comparative Example 2, since the amount of strain at the load of 300 MPa after heating was as small as 0.17%, the lithium ion secondary battery using the copper foil as a current collector caused problems such as destruction of the active material layer and dropping of the self-collecting body. Unable to evaluate loop characteristics.

In Comparative Examples 3, 4, and 5, since the tensile strength after heating was less than 300 MPa, the strain amount at the load of 300 MPa could not be calculated. The lithium ion secondary battery using the copper foil as a current collector has a problem that the copper foil is broken or the like before 100 cycles, and thus the cycle characteristics cannot be evaluated.

Although the preferred embodiments of the present invention have been described above with reference to the drawings and drawings, the present invention is not limited to the examples. It is to be understood that, as long as it is a person skilled in the art, various changes or modifications can be made within the scope of the technical knowledge disclosed in the present invention, and it is to be understood that these are also within the technical scope of the present invention.

1‧‧‧Negative electrode for nonaqueous electrolyte secondary battery

3‧‧‧ copper foil

5‧‧‧Active material layer

Claims (5)

A copper foil characterized in that the strain at a load of 300 MPa after heating at 300 ° C for 1 hour is 0.2 to 0.4%. The copper foil of claim 1, wherein after the heating at 300 ° C for 1 hour, the strain at a load of 300 MPa is 0.2 to 0.33%. The copper foil according to claim 1 or 2, wherein the copper foil contains 0.005 to 0.3% by mass of at least one element selected from the group consisting of molybdenum, titanium, and niobium. A negative electrode for a nonaqueous electrolyte secondary battery, characterized in that it has an active material layer containing at least one of lanthanum, cerium and tin on the surface of the copper foil, and the copper foil is characterized in that it is heated at 300 ° C for 1 hour. After that, the strain with a load of 300 MPa is 0.2 to 0.4%. A nonaqueous electrolyte secondary battery using the negative electrode for a nonaqueous electrolyte secondary battery according to claim 4.