WO2016006793A1

WO2016006793A1 - Electrolytic copper foil and manufacturing method therefor, current collector for lithium secondary battery comprising electrolytic copper foil, and lithium secondary battery

Info

Publication number: WO2016006793A1
Application number: PCT/KR2015/002986
Authority: WO
Inventors: 전검배; 김영태; 전상현; 이현우; 이상우; 정은선; 김동우
Original assignee: 엘에스엠트론 주식회사
Priority date: 2014-07-10
Filing date: 2015-03-26
Publication date: 2016-01-14
Also published as: JP2017526115A; CN106536791A; KR20160007047A; TWI639731B; KR101737028B1; TW201602418A

Abstract

An electrolytic copper foil according to one embodiment of the present invention is used as a current collector for a lithium secondary battery, and the electrolytic copper foil has a fracture characteristic coefficient (f) ranging from 5.0 to 18.0 after the electrolytic copper foil is annealed at 190°C for an hour, wherein the fracture characteristic coefficient (f) is defined as f={(C-B)/A}×1000 where A denotes stress of the electrolytic copper foil at a moment when the fracture of the electrolytic copper foil is initiated, B denotes elongation at a moment when the fracture of the electrolytic copper foil is initiated, and C denotes elongation at a moment when the fracture of the electrolytic copper foil is terminated in a tension test of the electrolytic copper foil, wherein the moment when the fracture of the electrolytic copper foil is initiated corresponds to the moment when the stress, which has increased with an increase of the elongation of the electrolytic copper foil, begins to decrease in the tension test, and the moment when the fracture of the electrolytic copper foil is terminated corresponds to the moment when the electrolytic copper foil is broken into two or more fragments.

Description

An electrolytic copper foil, a production method thereof, and a current collector for a lithium secondary battery including the electrolytic copper foil and a lithium secondary battery

The present invention relates to an electrolytic copper foil, a production method thereof, a current collector for a lithium secondary battery including the electrolytic copper foil, and a lithium secondary battery. More specifically, And an electrolytic copper foil containing the electrolytic copper foil, a production method thereof, and a current collector for a lithium secondary battery including the electrolytic copper foil and a lithium secondary battery.

The present application claims priority based on Korean Patent Application No. 10-2014-0086970, filed on July 10, 2014, the entire contents of which are incorporated herein by reference.

The lithium secondary battery has many advantages such as high energy density, high operating voltage and excellent preservation and life characteristics compared to other secondary batteries. Thus, the lithium secondary battery can be used for a variety of purposes such as a personal computer, a camcorder, a portable telephone, a portable CD player, a PDA And is widely used in portable electronic devices.

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

In the lithium secondary battery, an electrolytic copper foil is mainly used as a material of the negative electrode current collector. Such an electrolytic copper foil is used to maintain the performance of the secondary battery even if severe conditions are repeatedly formed in the secondary battery due to charging / discharging of the secondary battery. It should have excellent physical properties.

Examples of physical properties that the electrolytic copper foil should have include cracks are not likely to be generated even when severe conditions due to charging and discharging are repeated, rate of decrease in discharge capacity retention rate due to progress of charging and discharging is not too fast, There is no fear of performance deterioration and / or safety accident of the secondary battery due to overheating.

On the other hand, the excellent physical properties of the electrodeposited copper foil can be ensured by controlling various factors, and it is difficult to find out the desired properties by controlling what factors are within a certain range.

DISCLOSURE Technical Problem The present invention has been made in view of the above problems, and it is an object of the present invention to find an important factor for exhibiting excellent performance of a lithium secondary battery and to control the electrolytic copper foil so that the electrolytic copper foil has properties for exhibiting excellent performance of a lithium secondary battery do.

It is to be understood, however, that the technical scope of the present invention is not limited to the above-mentioned problems, and other technical subjects not mentioned above can be understood by those skilled in the art from the description of the invention described below.

The present inventors have repeatedly conducted research and experiments to solve the above technical problems. As a result, it has been found that by applying an electrolytic copper foil having a properly adjusted breaking coefficient to a current collector for a lithium secondary battery, Can be maintained excellent.

The electrolytic copper foil according to an embodiment of the present invention which can maintain the characteristics of a lithium secondary battery as described above is an electrolytic copper foil applied as a current collector for a lithium secondary battery. When the electrolytic copper foil is annealed at 190 ° C for 1 hour (F) corresponding to a range of 5.0 to 18.0.

The breaking property coefficient f is defined as f = {(CB) / A} x1000, wherein A is an elongation at break of the electrolytic copper foil at the time when the breaking of the electrolytic copper foil is started in the tensile test on the electrolytic copper foil Wherein B represents an elongation at the time when fracture of the electrolytic copper foil starts, and C represents an elongation at the time when the breakage of the electrolytic copper foil is terminated, wherein C represents the elongation at the time of breakage of the electrolytic copper foil Corresponds to a time point at which stress that has been increased as the elongation percentage of the electrolytic copper foil increases in the tensile test, and when the breakage of the electrolytic copper foil is terminated, the electrolytic copper foil is broken and separated into two or more pieces Time.

The electrolytic copper foil may have a protective layer formed on the surface thereof, and the protective layer may be formed of at least one selected from the group consisting of chromate, benzotriazole (BTA), and silane coupling agent.

The electrolytic copper foil may have a thickness of less than 20 mu m.

The electrolytic copper foil may have a surface roughness (Rz) of more than 0 and 2 mu m or less.

Meanwhile, the electrolytic copper foil may be manufactured by the electrolytic copper foil manufacturing method according to one embodiment of the present invention. In the electrolytic copper foil manufacturing method according to one embodiment of the present invention, when annealed at 190 ° C for 1 hour (A) a copper sulfate aqueous solution having a copper concentration of 70 g / L to 80 g / L and a sulfuric acid concentration of 80 g / L to 110 g / L, the method comprising the steps of: Lt; / RTI > And (b) electrodepositing copper (Cu) on the surface of the drum of the making machine at a current density of 40 A / m ² to 70 A / m ² at a temperature of 40 ° C to 45 ° C using the aqueous solution of copper sulfate as an electrolyte.

The electrolytic copper foil manufacturing method may include (c) forming a protective layer made of at least one selected from the group consisting of chromate, benzotriazole, and silane coupling agent on the surface of the electrodeposited copper layer.

On the other hand, the technical problem described above can be achieved not only by the electrode current collector for a lithium secondary battery made of the electrolytic copper foil mentioned above, but also by a lithium secondary battery including the electrode current collector for the lithium secondary battery.

According to the present invention, it is possible to minimize the phenomenon in which the capacity retention rate of the lithium secondary battery is reduced and / or the occurrence of ignition due to internal overheating, even if the severe conditions generated in the secondary battery are repeated by charging and discharging the lithium secondary battery This makes it possible to improve the performance of the secondary battery and / or to secure safety in the use of the secondary battery.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and, together with the description of the invention given below, 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 an electrolytic copper foil according to an embodiment of the present invention.

2 is a view showing a process in which the electrolytic copper foil is broken in a tensile test on the electrolytic copper foil.

3 is a stress-elongation graph for explaining the breaking property coefficient.

Hereinafter, preferred 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 concepts of the terms appropriately 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 the present specification and the configurations shown in the drawings are only some of 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.

1, the construction of an electrolytic copper foil 10 according to an embodiment of the present invention will be described.

Referring to FIG. 1, an electrolytic copper foil 10 according to an embodiment of the present invention includes a copper layer 11 and a protective layer 12 selectively formed on the surface of the copper layer 11.

The electrolytic copper foil 10 is preferably used as an anode current collector of a lithium secondary battery. That is, in the lithium secondary battery, the electrolytic copper foil 10 is preferably used as the negative electrode current collector to be combined with the negative electrode active material. On the other hand, a foil made of aluminum (Al) is generally used as the positive electrode current collector to be combined with the positive electrode active material.

Accordingly, in the present invention, the case where the electrolytic copper foil 10 is used as a current collector for a secondary battery according to an embodiment of the present invention corresponds to an anode current collector will be described as an example.

When the electrolytic copper foil 10 is used as a collector of a lithium secondary battery, the electrolytic copper foil 10 receives a force due to the volume expansion of the electrode due to repetitive charging and discharging. In this case, even if a tensile force exceeding the breaking strength of the electrolytic copper foil 10 is applied It does not immediately break.

That is, referring to FIG. 2, the electrolytic copper foil 10 is completely broken through a necking step, a void generating step, a growth and bonding step of voids, and a shearing step at the surface.

3, the electrodeposited copper foil 10 shows an increase in elongation after the stress of the electrolytic copper foil reaches the breaking strength in the stress-elongation graph showing such ductile fracture As a result, the stress tends to decrease gradually, resulting in complete fracture.

The value obtained by dividing the change amount of the elongation until the stress reaches the breaking strength and the complete elongation of the after-electrolytic copper foil 10 divided by the stress value at the beginning of the fracture, i.e., the breaking strength value is multiplied by 1000, (f).

Referring to FIG. 3, such a breaking characteristic coefficient f can be expressed by the following equation:

f = {(C-B) / A} x 1000

Herein, A, B and C are the stresses of the electrolytic copper foil at the time when the breakage of the electrolytic copper foil is started in the tensile test on the electrolytic copper foil, the elongation at the time when the breakage of the electrolytic copper foil is started, And the elongation at the time point at which the fracture of the steel sheet is terminated.

The time point at which the electrolytic copper foil starts to break corresponds to a point corresponding to a point P1 at which a stress that increases together with an increase in elongation in the stress-elongation graph of Fig. 3 starts to decrease.

The time point at which the electrolytic copper foil ends the fracture is a point corresponding to the point P2 at which the stress decreased as the elongation rate increases in the stress-elongation graph of Fig. 3, and at this point, The copper foil is destroyed and separated into two or more pieces.

When the breaking property coefficient f has a too small value, the electrolytic copper foil 10 tears in a short time when it is torn by an external force, and thus the electrolytic copper foil 10 is used as a collector of the lithium secondary battery There is a problem in that it is difficult to maintain the performance of the secondary battery in a severe condition in the secondary battery due to repetitive charging and discharging.

On the contrary, when the breaking characteristic coefficient f has an excessively large value, an unstable state may be maintained for a long time in a situation where the electrolytic copper foil 10 is torn by an external force, so that excessive heat may be generated, And it may be difficult to secure safety in use of the secondary battery.

Therefore, the breaking characteristic coefficient f should be maintained in an appropriate range, preferably in the range of 5.0 to 18.0.

Such a breaking characteristic coefficient f is measured in a state where the electrolytic copper foil 10 is annealed at 190 캜 for one hour. Such annealing is performed in the process of manufacturing a lithium secondary battery by applying the electrolytic copper foil 10 as a current collector So that the high-temperature conditions to be applied are applied.

The fracture characteristics factor f is determined by the change in the concentration of copper and sulfuric acid contained in the plating liquid for electrolytic plating in the course of manufacturing the electrolytic copper foil 10 and various additives (inorganic additives, Brightener, etc.), changes in the current density during plating, and changes in the temperature of the plating solution.

On the other hand, the electrolytic copper foil 10 manufactured by electroplating has a shiny surface 11a having a relatively low surface roughness (Rz) and a so-called mountain surface as a surface opposite thereto, And a matte surface 11b having a relatively high surface roughness Rz due to the structure.

The surface roughness Rz of the matte surface 11a is determined by the degree of polishing of the cylindrical drum on which the copper is precipitated while the surface roughness Rz of the matte surface 11b is determined by the thickness of the surface of the electrolytic copper foil 10 It can be controlled by changing the composition of the material constituting the plating liquid and the current density during the electrolysis reaction.

On the other hand, when the surface roughness Rz of the matte surface 11b of the electrolytic copper foil 10 is too high, it is difficult for the active material and the electrolytic copper foil 10 to contact each other uniformly, . Therefore, it is necessary to adjust the surface roughness Rz to an appropriate level. It is preferable to suppress the surface roughness Rz of the matte surface 11b of the electrolytic copper foil 10 to approximately 2 탆 or less.

The protective layer 12 is selectively formed on the surface of the copper layer 11 for the anticorrosive treatment of the electrolytic copper foil 10 and is formed of chromate, benzotriazole (BTA), silane coupling agent Or the like. The protective layer 12 may not only provide an anticorrosive property to the electrolytic copper foil 10 but also impart heat resistance and / or bonding strength to the active material.

1. 전해 동박의 제조1. Manufacture of electrolytic copper foil

Table 1

The electrolytic copper foil according to an embodiment of the present invention is a copper electrolytic copper foil which is obtained by electrodepositing copper on a cylindrical cathode surface rotated by supplying a plating solution between a cylindrical negative electrode rotating at a constant speed using an aqueous solution of copper sulfate, (The thinner the electrolytic copper foil is, the more the current collector with the active material can enter into the secondary battery, which is advantageous for high capacity, while the thicker the electrolytic copper foil is, the more the thickness of the electrolytic copper foil is applied to the secondary battery , It is preferable that the thickness of the electrolytic copper foil does not exceed 20 탆). The respective conditions applied in the examples and comparative examples were as follows:

Generally, the electrolytic copper foil produced by electrolytic plating has two different sides. That is, in the electrolytic copper foil, there are a shiny side (S side) contacting with the negative electrode drum and a side (Matt side, M side) located in the direction in which crystal grains are grown by precipitation. The surface roughness (Rz) of the S-plane and M-plane of the electrolytic copper foil was formed in a range of approximately 2 탆 or less.

(Example)

As shown in Table 1, a plating solution having a copper concentration of 70 to 80 g / L and a sulfuric acid concentration of 80 to 110 g / L was prepared, and various additives (inorganic metal, leveler, brightener) An electrolytic copper foil was prepared with a current density of about 40 to 70 ASD (although this is not necessarily limited to this range, it can be suitably adjusted within a range that can achieve the object of the present invention).

As the inorganic additive, Fe, W, Zn, Mo and the like were applied. As the leveler, gelatin, collagen and PEG (polyethylene glycol) were used. As brighteners, bis (3-sulfopropyl) disulfide, MPS mercapto-propane sulphonic acid and DPS (3-N, N-dimethylaminodithiocarbamoyl-1-propanesulphonic acid).

On the other hand, the surface of the electrolytic copper foil produced according to the above process conditions was subjected to chromate treatment for protection (rust prevention, etc.).

(Comparative Example)

As shown in Table 1, various additives (the same additives as those of the example) were added to the plating solution having a copper concentration of 70 to 80 g / L and a sulfuric acid concentration of 95 to 105 g / L, and a current of about 50 to 70 ASD The electrodeposited copper foil was prepared under the density condition.

2. 파단 특성계수의 측정2. Measurement of rupture coefficient

(F) of the electrolytic copper foil according to the embodiment of the present invention produced according to the above-mentioned process conditions and the electrolytic copper foil according to the comparative example were measured.

The fracture characteristics factor (f) of electrolytic copper foil was measured by UTM, which is a standardized measurement method. The UTM conditions applied were a gauge length of 50 mm, a width of 12.7 mm, and a measurement speed of 2 mm / min.

The measurement of the rupture modulus (f) for the electrolytic copper foil was carried out under the same conditions as in Example 1, except that electrolytic copper foil according to the example / RTI ID = 0.0 > annealing. &Lt; / RTI > That is, the lithium secondary battery may be subjected to a process of maintaining a high-temperature state for a predetermined period of time during its manufacture, and annealing the electrolytic copper foil to make similar conditions.

The results of the measurement of the rupture coefficient (f) of the electrolytic copper foil subjected to the annealing process are shown in Table 2 below.

Table 2

Referring to the results of Table 2, the electrolytic copper foils of Examples 1 to 6 exhibited the breaking property coefficient values in the range of 5.0 to 18.0, while the electrolytic copper foils of Comparative Examples 1 to 3 showed the breaking property coefficient values of less than 5.0, The electrolytic copper foil of Comparative Example 4 exhibited a breaking property coefficient value exceeding 18.0.

33 . 리튬 이차전지의 제조. Manufacture of lithium secondary battery

- - 양극판 및 음극판의 제조Manufacture of positive and negative plates

(Composition of cathode material mixture)

Anode material (LiCoO2): 85 wt%

Conductive material (acetylene black): 8 wt%

Binder (polyvinylidene fluoride): 7 wt%

(Composition of anode material mixture)

Negative electrode material (graphite or carbon material): 95 ~ 98wt%

Binder (polyvinylidene fluoride): 2 to 5 wt%

N-methylpyrrolidone is added to the above material to form a slurry, which is then applied to the surface of a negative electrode current collector made of a positive electrode current collector made of aluminum foil and an electrolytic copper foil to evaporate the solvent, followed by rolling and slitting in a predetermined size To prepare a positive electrode plate and a negative electrode plate.

- - 리튬 이차전지의 조립Assembly of lithium secondary battery

A positive electrode plate, a separator (hydrophilic porous polyethylene film), and three negative electrode plates were sequentially laminated and wound up, and this was placed in a container to inject / seal the electrolyte, thereby completing a cylindrical battery. The standard of the battery was 18650, which is a general cylindrical type.

Here, as the electrolytic solution, 1 M LiPF ₆ was dissolved in a solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 1: 1.

4. 충방전 시험4. Charging and discharging test

A lithium secondary battery (a secondary battery according to an embodiment of the present invention) manufactured by using the negative electrode current collector to which the electrolytic copper foil according to Examples 1 to 6 shown in Table 1 was applied among the lithium secondary batteries fabricated according to the above- Thereby preparing a lithium secondary battery according to Examples 1 to 6, respectively.

Likewise, the lithium secondary batteries fabricated using the negative electrode current collector to which the electrolytic copper foil according to Comparative Examples 1 to 4 shown in Table 1 were applied were the lithium secondary batteries according to Comparative Examples 1 to 4, respectively.

The lithium secondary batteries thus prepared were subjected to 500 repetitive charging and discharging tests. At this time, charging was performed under the same conditions as CCCV (constant current constant voltage) mode, charging voltage was 4.3 V, and charging current was 0.2 C (current which can be fully charged by charging for 5 hours) Mode, a discharge voltage of 3.0 V, and a discharge current of 0.5 C (a current which can be completely discharged in two hours).

After completion of the repetitive charging and discharging, the capacity retention and heat generation rate of the lithium secondary battery and the occurrence of cracks in the electrolytic copper foil constituting the current collector were measured and shown in Table 3.

Table 3

Referring to Table 3, the lithium secondary batteries (Examples 1 to 6) according to the embodiment of the present invention, in which the rupture coefficient f of the electrolytic copper foil is in the range of 5.0 to 18.0, No crack was generated in the current collector, and the capacity retention rate was maintained as high as about 84% to 93% of the initial capacity (500 charge / discharge cycles, usually about 80% to 90% capacity retention, If there is a problem in the secondary battery, it suddenly falls off, which is a big difference from the normal value.

In addition, the lithium secondary batteries of Examples 1 to 6 have a surface temperature in the normal temperature range of about 25 ° C to 28 ° C (within a normal temperature range of about 30 ° C or less) in the exothermic measurement conducted in such a manner that charge- , And even if the temperature rises temporarily, it does not exceed 40 ° C unless there is a particular abnormality).

On the other hand, in the lithium secondary batteries (Comparative Examples 1 to 3) according to the comparative example in which the breaking property coefficient f of the electrolytic copper foil was less than 5.0, cracks were generated in the current collector due to repeated charge and discharge, To about 24% to 42% as compared with that of the secondary battery. Cracks generated in the current collector cause detachment of the electrode active material adhered to the current collector, so that occurrence of such cracks directly affects the capacity retention rate.

On the other hand, in the lithium secondary battery according to the comparative example (Comparative Example 4) in which the breaking property coefficient (f) of the electrolytic copper foil exceeded 18.0, cracks were not generated in repeated charging and discharging and the capacity retention ratio was maintained at a relatively high level. Which was about 41 ° C, which was far exceeded by 30 ° C, which is normally found in the normal range. Such an abnormal heating phenomenon may not only lower the performance of the lithium secondary battery but also increase the risk of safety accidents.

If the fracture characteristic coefficient f of the electrolytic copper foil 10 is maintained within a certain range (5.0 to 18.0) from the above experimental results, it is possible to maintain the performance of the secondary battery even under severe conditions by repetitive charging and discharging, It can be clearly seen that stability in use can be ensured.

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.

Claims

An electrolytic copper foil as a current collector for a lithium secondary battery,

Wherein the electrolytic copper foil has a breaking characteristic coefficient (f) in the range of 5.0 to 18.0 when annealed at 190 DEG C for 1 hour,

f = {(C-B) / A} x 1000,

A represents the stress of the electrolytic copper foil at the time when the electrolytic copper foil starts to break in the tensile test on the electrolytic copper foil,

B represents the elongation at the time when the electrolytic copper foil starts to break,

C represents an elongation at the time when the fracture of the electrolytic copper foil is terminated,

The time point at which the electrolytic copper foil starts to break corresponds to the time point at which the increased stress is started to decrease as the elongation percentage of the electrolytic copper foil increases in the tensile test,

Wherein the time when the breakage of the electrolytic copper foil is completed corresponds to a time point when the electrolytic copper foil is broken and separated into two or more pieces.
The method according to claim 1,

The electrolytic copper foil,

And a protective layer formed on the surface,

Wherein the protective layer is made of at least one selected from the group consisting of chromate, BTA (benzotriazole), and silane coupling agent.
The method according to claim 1,

The electrolytic copper foil,

Wherein the copper foil has a thickness of less than 20 占 퐉.
The method according to claim 1,

The electrolytic copper foil,

And a surface roughness (Rz) of more than 0 and 2 mu m or less.
A method for producing an electrolytic copper foil having a breaking factor coefficient (f) in the range of 5.0 to 18.0 when annealed at 190 占 폚 for 1 hour,

(a) preparing an aqueous solution of copper sulfate having a copper concentration of 70 g / L to 80 g / L and a sulfuric acid concentration of 80 g / L to 110 g / L; And

(b) electrodepositing copper (Cu) on the surface of the drum of the pre-charging machine at a current density of 40 A / m 2 to 70 A / m 2 at a temperature of 40 ° C to 45 ° C using the aqueous solution of copper sulfate as an electrolyte, &Lt; / RTI >
6. The method of claim 5,

(c) forming a protective layer made of at least one selected from the group consisting of chromate, benzotriazole (BTA) and silane coupling agent on the surface of the electrodeposited copper layer.
An electrode collector for a lithium secondary battery comprising the electrolytic copper foil according to any one of claims 1 to 4.
A lithium secondary battery comprising the electrode current collector for a lithium secondary battery according to claim 7.