KR20130102849A - Current collector for lithium secondary battery and method for producing the same - Google Patents

Abstract

PURPOSE: A current collector for a lithium secondary battery is provided to prevent the loss of discharging capacity maintenance of a lithium secondary battery while obtaining sufficient binding force with an active material. CONSTITUTION: A current collector for a lithium secondary battery (10) includes a copper foil which has a shiny surface (11b) corresponding to one side and a matte surface (11a) corresponding to the opposite side. The maximum difference (ΔGmax) between glossiness values at two different random points in the width direction of the matte surface is 50 or less. A manufacturing method of the current collector for a lithium secondary battery includes a step of manufacturing an electrolytic copper foil in a lactic acid copper-plating liquid in which 2-50 ppm of a sulfide including a propylene group is dissolved.

Description

Current collector for lithium secondary battery and its manufacturing method {Current collector for lithium secondary battery and method for producing the same}

The present invention relates to a current collector for a lithium secondary battery and a method for manufacturing the same, and specifically, to a current collector for a lithium secondary battery and a method for manufacturing the same, which can improve the binding strength with the active material and the discharge cycle life characteristics of the lithium secondary battery. It is about.

Lithium secondary battery has many advantages such as high energy density, high operating voltage and excellent storage and lifespan characteristics compared to other secondary batteries, which can be used for personal computers, camcorders, portable phones, portable CD players, PDAs, etc. Widely used in portable electronic devices.

In general, a lithium secondary battery has a structure including a positive electrode and a negative electrode disposed with an electrolyte interposed therebetween, wherein the positive electrode has a structure in which a positive electrode active material is attached to a positive electrode current collector, and the negative electrode has a negative electrode active material attached to a negative electrode current collector. Has a structure.

In the lithium secondary battery, an electrolytic copper foil is mainly used as a material of the negative electrode current collector, and typically, the electrolytic copper foil is coated with an active material of a carbon-based slurry. Here, the electrolytic copper foil is manufactured through the electroplating process by the electroplating method, a shiny surface having a relatively low roughness is formed on one surface of the manufactured electrolytic copper foil, and the other surface is formed by a so-called mountain structure. As a result, a mat surface having a high roughness is formed.

In the lithium secondary battery, the bonding strength with the active material and the yield of the battery may vary greatly depending on the surface state of the electrolytic copper foil used as the current collector. In particular, when the binding force between the current collector and the active material is low, problems such as an internal short circuit may occur because the active material is dropped from the current collector during use of the secondary battery.

In order to solve this problem, a technique of securing the bonding force between the current collector and the active material by forming a roughness on the surface of the electrolytic copper foil by a mechanical or chemical method is widely used.

However, when the surface nonuniformity caused by the roughness of the surface of the electrolytic copper foil is too large, there is a problem in that the discharge capacity retention rate of the lithium secondary battery is lowered. have.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object thereof is to provide a current collector for a lithium secondary battery that does not reduce the discharge capacity retention rate of the lithium secondary battery while securing sufficient bonding force with the active material.

In order to achieve the above object, the current collector for a lithium secondary battery according to the present invention includes an electrolytic copper foil having a Shiny surface corresponding to one side and a Matt surface corresponding to the other side. As a current collector for a lithium secondary battery, a maximum difference (ΔG _max ) of glossiness values measured at any two points different from each other in the width direction of the mat surface may be 50 or less.

Preferably, the average glossiness G _mean of the mat surface may be 40 to 350.

Preferably, the current collector further includes a protective layer formed on the surface of the electrolytic copper foil, and the protective layer may be made of at least one selected from chromate, benzotriazole, and silane coupling agent.

Preferably, the electrolytic copper foil may be prepared from a lactic acid copper plating solution in which a sulfur compound including a propylene group is dissolved at a concentration of 2 to 50 ppm.

On the other hand, in order to achieve the above object, a method for manufacturing a current collector for a lithium secondary battery according to the present invention, (a) a copper oxide in an acid copper plating solution in which a sulfur compound containing a propylene (Propylene) group is dissolved at a concentration of 2 to 50ppm Preparing a; . ≪ / RTI >

Preferably, the method for producing a current collector for a lithium secondary battery includes (b) forming a protective layer on the surface of the electrolytic copper foil by treating at least one selected from chromium treatment, BTA (benzotriazole) treatment, and silane coupling agent treatment. It may further comprise a step.

The current collector for a lithium secondary battery according to the present invention ensures a sufficient bonding force with the active material coated on the surface and at the same time has the effect of maintaining a constant discharge capacity even if the charge / discharge is repeated.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and form a part of the specification, illustrate preferred embodiments of the invention and, together with the description of the invention given above, serve to further the understanding of the technical idea of the invention. And should not be construed as limiting.
1 is a cross-sectional view showing the structure of a current collector for a lithium secondary battery according to the present invention.
It is a figure which shows the surface of the electrolytic copper foil when (DELTA) G _max value is 20. FIG.
It is a figure which shows the surface of the electrolytic copper foil when (DELTA) G _max value is 75. FIG.
4 is a flowchart illustrating a manufacturing process of a current collector for a lithium secondary battery according to the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor should appropriately interpret the concept of the term appropriately in order to describe its own invention in the best way. It should be interpreted in accordance with the meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined. Therefore, the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible.

Referring to Figure 1 will be described the configuration of the current collector for a lithium secondary battery according to the present invention. 1 is a cross-sectional view showing the structure of a current collector for a lithium secondary battery according to the present invention.

Referring to FIG. 1, the current collector 10 for a lithium secondary battery according to the present invention includes an electrolytic copper foil 11 and a protective layer 12 selectively formed on a surface of the electrolytic copper foil 11.

It is preferable that the said electrolytic copper foil 11 is used as a negative electrode electrical power collector of a lithium secondary battery. That is, in a lithium secondary battery, a foil made of aluminum (Al) is used as a positive electrode current collector to be bonded to a positive electrode active material, and a foil made of copper (Cu) is used as a negative electrode current collector to be bonded to a negative electrode active material. to be. Therefore, in the present invention, a case where the current collector 10 for a lithium secondary battery according to the present invention in which the electrolytic copper foil 11 is used is a negative electrode current collector will be described.

The electrolytic copper foil 11 produced by electroplating has a relatively low surface roughness and has a relatively shiny Shiny surface 11a and the opposite side thereof, which is called a mountain structure. It is made of a mat surface (11) that is relatively high in surface roughness and not much gloss.

The glossiness of the shiny surface 11a of the two surfaces is determined by the degree of polishing of the surface contacting the electrolytic copper foil 11 of the rotating cathode, while the glossiness of the mat surface 11b of the electrolytic copper foil 11 In the manufacturing process, it is possible to adjust by changing the composition of the material constituting the plating liquid, the current density during the electrolytic reaction, and the like.

On the other hand, when the glossiness measured on the mat surface 11b of the copper foil 11 is too high, that is, when the roughness of the mat surface 11b is too low, the bonding force between the copper foil 11 and the active material is difficult to be secured. Therefore, it is preferable that the mat surface 11b has a glossiness of a predetermined value or less. However, when the glossiness is too low, that is, when the roughness of the mat surface 11b is too high, it is difficult to make the contact between the active material and the copper foil 11 uniformly, so that the discharge capacity retention rate of the lithium secondary battery is lowered. have.

Therefore, by adjusting the glossiness of the mat surface 11b to an appropriate range, it is possible to secure both excellent properties of the copper foil 11 as the current collector 10, that is, excellent bonding strength with the active material and high discharge capacity retention rate.

Preferably, the maximum difference ΔG _max of glossiness measured at any two points different from each other in the width direction of the mat surface 11b is formed to be 50 or less. This means that when the maximum difference of the glossiness (ΔG _max ) exceeds 50, the difference in the structure of the copper foil 11 present in the interface portion where the gloss difference is large is large, and thus the bonding force between the copper foil 11 and the active material is secured. Because it is difficult to be. 2 and 3 show a case where the maximum difference (ΔG _max ) of the glossiness is 20 (FIG. 2) and 75 (FIG. 3), respectively. The copper foil shown in FIG. In comparison, the bonding force with the active material becomes better.

In addition, the average glossiness G _mean of the mat surface 11b is preferably determined within the range of 40 to 350. When the average glossiness G _mean exceeds 350, the roughness of the mat surface 11b is too low to secure a bonding force with the active material, and when it is less than 40, the roughness of the mat surface 11b is too high. It is because there exists a problem that the discharge capacity retention rate of a secondary battery falls because the surface nonuniformity becomes large.

As shown in Table 1 below, the glossiness of the mat surface 11b may be adjusted by changing the components of the plating liquid, the current density, the drum buffing, and the like in the manufacturing of the copper foil 11.

On the other hand, the glossiness is measured by selecting a 60 ° incidence angle, which is known to be widely measured from a relatively low gloss sample to a high gloss sample, and measured using a VG700 model type, which is a gloss meter from Nippon Deoshoku, Japan. It is done .

The protective layer 12 is formed of at least one selected from chromate (Chromate), BTA (Benzotriazole) and silane coupling agents formed on the surface of the copper foil 11. The protective layer 12 plays a role of imparting anti-rusting and heat resistance properties to the copper foil 11 and / or increasing bonding strength with the active material.

Next, a method of manufacturing a current collector for a lithium secondary battery according to the present invention will be described with reference to FIG. 4. 4 is a flowchart illustrating a manufacturing process of a current collector for a lithium secondary battery according to the present invention.

Referring to FIG. 4, the method of manufacturing a current collector for a lithium secondary battery according to the present invention includes a copper foil manufacturing step S1 and a protective layer forming step S2 that may be selectively performed.

The copper foil manufacturing step (S1) is a brighter or a leveler that broadens the plating range so that the surface of the plating is polished in an electrolyte in which a sulfur compound including a propylene group is dissolved at a concentration of about 2 to 50 ppm. After adding an additive such as a suppressor to allow the plating to proceed evenly, the process of electrodepositing copper (Cu) on the drum surface of the mill is performed at a current density of approximately 30 to 80 (A / dm 2). This is the step of manufacturing the copper foil (11).

The glossiness of the mat surface 11b is adjusted to an appropriate range as described above by changing the composition of the material constituting the plating liquid for manufacturing the copper foil 11 or the current density during the electrolytic reaction in the copper foil manufacturing step (S1). As a result, excellent characteristics of the copper foil 11 as the current collector 10, that is, excellent bonding strength with the active material and high discharge capacity retention rate can be obtained.

The protective layer forming step S2 may be performed by performing one or more of a chromate treatment, a Benzotriazole treatment, and a silane coupling agent treatment on the mat face 11b of the copper foil 11. It is a step which provides the copper foil 11 with the antirust property, heat resistance characteristic, and / or the adhesive force increase characteristic with an active material.

Next, with reference to [Table 1] below, an experimental example of measuring the active material detachment and the discharge capacity retention rate for the current collector for a lithium secondary battery according to the present invention will be described.

First, the method of determining whether the negative electrode active material is detached through the experiment and the evaluation method of the discharge capacity retention rate will be described.

<Method and condition of judgment>

1. Anode active material Tally  Judgment

2 parts by weight of SBR (styrene butadiene rubber) and 2 parts by weight of CMC (carboxymethyl cellulose) are mixed with respect to 100 parts by weight of carbon commercially available for the negative electrode active material, and a slurry is prepared by using distilled water as a solvent. The negative electrode active material is applied to a current collector according to the present invention with a doctor blade at a thickness of 20 to 60 μm, dried at 120 ° C. and pressed at a pressure of 1 ton / cm 2. After pressing, the sample is cut into a size of 10 cm * 10 cm, and the resin tape (3M CAT132) is brought into close contact with the negative electrode material coating surface, and then the tape is peeled off to count the number of carbon desorbed on the tape surface. If there are more than 10 points, it is judged as NG)

2. Battery Cycle  Life rating

-Cathode plate manufacturing method

It prepared by the same method as described in the negative electrode active material desorption.

-Method of preparing electrolyte

1 M of LiPF ₆ was dissolved as a solute in a non-aqueous organic solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a ratio of 1: 2. The basic electrolyte was 99.5% by weight of the basic electrolyte and succinic anhydride ( Succinic anhydride) 0.5% by weight to prepare a non-aqueous electrolyte.

-Bipolar plate manufacturing method

Li _{1 .1} to the lithium manganese oxide of Mn _{1 .85} Al _{0 .05} O ₄ lithium manganese oxide and o-LiMnO ₂ of orthorhombic crystal structure mixed in a 90: 10 (weight ratio) to prepare a positive electrode active material. A slurry was prepared by mixing the positive electrode active material and carbon black with PVDF [Poly (vinylidene fluoride)] as a binder and NMP as an organic solvent at 85: 10: 5 (weight ratio). The slurry was applied to both sides of Al foil having a thickness of 20 µm and dried to prepare a positive electrode.

-Measurement of discharge capacity retention rate

In the battery manufactured as described above, the capacity per gram of the positive electrode was measured at 4.3 V charge / 3.4 V discharge operating voltage, and in order to evaluate the high temperature life, 50 charge / discharge experiments were performed at a current density of 0.2 C at a high temperature of 50 ° C. Was performed to calculate the discharge capacity retention rate, and the results are shown in Table 1. ( Discharge capacity retention rate (%) = (50th discharge capacity / 1th discharge capacity) x 100, and when discharge capacity retention rate is 90% or less, it is not suitable as a negative electrode current collector for batteries)

Next, referring to Table 2 below, look at the results of the experiment according to the determination method and conditions as described above. Looking at Table 2 below, it can be seen that the adhesion between the current collector 10 and the active material and the cycle life characteristics of the battery vary according to the glossiness of the mat surface 11b.

Comparing the results of Example 2 and Comparative Example 1, when the ΔG _max value exceeds 50, the difference between the copper foil 11 and the active material is due to the excessive structure difference of the copper foil 11 present in the interface portion having a large gloss difference. It can be seen that the number of the leaving part greatly increased by the decrease in the binding force of (ΔG _max ). Is the maximum difference in glossiness measured at any two different points in the width direction of the mat face)

On the other hand, when comparing the result of Example 3 and the comparative example 2, even if (DELTA) G _max value exists in the range of 50 or less, G _mean. If the value is less than 40, the roughness of the mat surface 11b is too high, so that the contact between the active material and the copper foil 11 is not uniform, so that the discharge capacity retention rate is greatly reduced.

Similarly, when comparing the results of Example 4 and Comparative Example 3, even if ΔG _max value is in the range of 50 or less, G _mean If the value exceeds 350, it can be seen that the number of the securing parts desorption difficult to bonding between the roughness of the matte surface (11b) is too low, the active material and the copper foil 11 is also significantly increased. (G _mean : Average glossiness of the mat surface)

Therefore, the ΔG _max value and G _mean measured on the mat surface 11b of the copper foil 11b of the secondary battery current collector 10 according to the present invention from the above experimental results. It can be seen that the value is maintained within a certain range, not only ensuring sufficient adhesive force with the active material, but also having excellent discharge cycle characteristics.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not to be limited to the details thereof and that various changes and modifications will be apparent to those skilled in the art. And various modifications and variations are possible within the scope of the appended claims.

10: current collector for lithium secondary battery 11: electrolytic copper foil
11a: Matte surface 11b: Shiny surface
12: protective layer

Claims (6)

In the current collector for a lithium secondary battery comprising an electrolytic copper foil having a shiny surface corresponding to one side and a mat surface corresponding to the other side,
The maximum difference (ΔG _max ) of the glossiness value measured at any two different points in the width direction of the mat surface is 50 or less, the current collector for a lithium secondary battery. The method of claim 1,
Average glossiness (G _mean ) of the mat surface is a lithium secondary battery collector, characterized in that 40 to 350. The method of claim 1,
The current collector further includes a protective layer formed on the surface of the electrolytic copper foil,
The protective layer is a current collector for a lithium secondary battery, characterized in that at least one selected from Chromate, BTA (benzotriazole) and a silane coupling agent. The method of claim 1,
The electrolytic copper foil is a current collector for a lithium secondary battery, characterized in that the sulfur compound containing a propylene (Propylene) group is produced in a lactic acid copper plating solution is dissolved in a concentration of 2 to 50ppm. A method for manufacturing a current collector for a lithium secondary battery according to any one of claims 1 and 2,
(A) a method for producing a current collector for a lithium secondary battery comprising the step of producing an electrolytic copper foil in a lactic acid copper plating solution in which a sulfur compound containing a propylene (Propylene) group is dissolved in a concentration of 2 to 50ppm. The method of claim 5,
(b) forming a protective layer on the surface of the electrolytic copper foil by forming at least one of chromium treatment, BTA (benzotriazole) treatment, and silane coupling agent treatment. Method of preparation.

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