JP6316095B2 - Rolled copper foil and negative electrode current collector of lithium ion secondary battery - Google Patents

Description

The present invention relates to a rolled copper foil, and more particularly to a rolled copper foil for a negative electrode current collector of a lithium ion secondary battery.

The rolled copper foil is used for a negative electrode current collector such as a lithium ion battery. For example, the rolled copper foil is used by applying a carbon-based active material. Such a negative electrode current collector is manufactured by applying an active material to a rolled copper foil by a roll press. However, in the press using a roll, there is a problem that the copper foil is deformed and the active material is dropped or the yield is lowered due to the shape defect. In recent years, the current collector has been made thinner, and this problem has become more prominent.

In order to improve the adhesion between the current collector copper foil for the negative electrode of the lithium ion secondary battery and the active material layer, a surface treatment for forming irregularities on the surface of the copper foil, called a roughening treatment, is performed in advance. ing. As the method of roughening treatment, methods such as blasting, rolling with a rough surface roll, mechanical polishing, electrolytic polishing, chemical polishing, and plating of electrodeposited grains are known, and among these, electrodeposited grain plating is particularly preferred. It is used a lot. This technology uses a copper sulfate acidic plating bath to deposit a large number of copper in a dendritic or small spherical shape on the surface of the copper foil to form fine irregularities, aiming to improve adhesion by the anchoring effect, or volume change It is carried out with the aim of preventing peeling due to stress concentration at the current collector interface by concentrating stress on the concave portion of the active material layer during expansion of the large active material to form a crack (for example, Patent Document 1).

In Patent Document 2, a preferable surface property is specifically specified by a roughness parameter, and a copper foil having a large value of surface roughness Ra is used as a current collector. It is described that adhesion is improved. The surface roughness Ra of the current collector is preferably 0.01 μm or more, more preferably 0.01 to 1 μm, and still more preferably 0.05.
It is said that it is -0.5 micrometer. The surface roughness Ra of the current collector and the average interval S between the local peaks are 100.
It is preferable to have a relationship of Ra ≧ S. The shape of the uneven portions on the surface of the current collector is preferably a cone shape. And it is described that such a surface form can be obtained by electrolytically depositing copper on the surface of electrolytic copper foil and rolled copper foil to roughen the surface and polishing with emery paper. ing.

On the other hand, in patent document 3, when manufacturing a rolled copper foil, the roughening process is not performed as in the prior art, but the rolling conditions are appropriately controlled, and the active material is formed by forming finer irregularities on the surface. It has been found that the adhesion of is significantly increased. The state of this fine unevenness is defined by Ra and RSm.

International Publication WO2001 / 031720A1 International Publication WO2001 / 029912A1 JP 2011-9207 A

Thus, the conventional knowledge has disclosed the rolled copper foil which controlled the surface state, in improving the adhesiveness of copper foil and an active material layer. However, it is difficult to say that the surface properties of the copper foil have been optimized, and it is considered that there is room for improvement in the adhesion between the rolled copper foil and the active material layer. Then, this invention makes it a subject to provide a rolled copper foil suitable as a collector of a lithium ion secondary battery which can implement | achieve high adhesiveness with an active material layer.

As a result of studying the surface state of the rolled copper foil, the present inventors have rolled the surface roughness (form) of the rolled copper foil so as to be within a certain range, so that the depth and size of the oil pits on the surface are obtained. Has been found to be controlled within a suitable range, and the adhesion between the rolled copper foil and the active material is improved.
The present invention is based on this finding.

The present invention is as follows.
(1) In the surface properties of the rolled copper foil, the Rsk in the rolling direction and the vertical direction of the rolling are both −
1.00 or less, both Rku are 6.00 or less, Rz in the rolling direction is Rza, and Rz in the vertical direction of rolling is Rzb, both Rza and Rzb are 0.60 μm or more, and Rza / Rzb Is a rolled copper foil characterized by being 1.15 or more.
(2) When RSm in the rolling direction is RSma and RSm in the vertical direction of rolling is RSmb, RSma is 20 μm or less, and RSma / RSmb is 0.50 or less.
The rolled copper foil described in 1.
(3) A lithium ion secondary battery negative electrode current collector using the rolled copper foil according to (1) or (2).

In the rolled copper foil of the present invention, the shape of the opening of the oil pit on the surface is sufficiently enlarged, and the anchor effect is obtained by filling the oil pit (recess, depression, valley) with the negative electrode active material and the binder. Therefore, the adhesion of the active material is high. And since the lithium ion secondary battery negative electrode collector using the rolled copper foil of the present invention has high adhesion between the rolled copper foil (current collector) and the active material, it is highly reliable for long-term use. Become.

In the present invention, “rolled copper foil” includes copper alloy rolled foil. There is no restriction | limiting in particular as a composition of a rolled copper foil, What is necessary is just to select suitably according to a use and a required characteristic. For example, pure copper (OFC
: Oxygen-free copper and TPC: tough pitch copper, etc.), Cu-Sn alloys, Cu-Ag alloys, C
Examples include copper alloys such as u-Ni-Si alloys, Cu-Co-Si alloys, Cu-Cr alloys, and Cu-Zr copper alloys. These are examples, and the rolled copper foil of the present invention is not limited to these. There is no restriction | limiting in particular in the thickness of copper foil, What is necessary is just to select suitably according to a required characteristic. Generally, the thickness is 1 to 100 μm, but when used as a current collector for a negative electrode of a lithium ion secondary battery, a battery having a higher capacity can be obtained by thinning the copper foil. From such a viewpoint, 2-50 micrometers is suitable and 5-20 micrometers is more suitable.

When using rolled copper foil as a current collector for a lithium ion secondary battery, it is possible to obtain a battery with a higher capacity by reducing the thickness of the copper foil. There is a risk of breakage due to. In this respect, it is advantageous to use a rolled copper foil having higher strength than the electrolytic copper foil. The rolled copper foil is also excellent in that it has high bending resistance. Moreover, in a lithium ion secondary battery, it is common to take the stack structure which laminated | stacked many positive electrodes and negative electrodes, and in this case, both surfaces of copper foil are calculated | required to have high adhesiveness with an active material. Therefore, it is desirable that the upper and lower surfaces of the copper foil have the same surface properties. The rolled copper foil is advantageous because the upper and lower surfaces can have substantially the same surface properties. In addition, the electrolytic copper foil has a smooth and glossy S surface on the side in contact with the cathode, and a rough and matte M surface on the opposite side for convenience of the manufacturing process. Due to the different properties, the adhesiveness to the active material is also different.

  The surface properties of the rolled copper foil of the present invention will be described.

(1) The Rsk in the rolling direction and the vertical direction of the rolled copper foil of the present invention are both -1.00 or less. The rolling direction of the rolled copper foil is the rolling parallel direction or RD (Rolling Di).
It is also referred to as “rection” and refers to the direction of elongation of the copper foil rolled by the rolling roll. The rolling vertical direction is also referred to as a width direction or TD (Transverse Direction), and indicates a direction perpendicular to the rolling direction. The direction perpendicular to the rolled surface of the copper foil (the direction perpendicular to the rolled surface, ND (Normal Direction)) is distinguished. Rs
k (skewness of the roughness curve) is one of indices indicating surface properties, and is JIS B 06.
01: 2013. Rsk represents the degree of distribution of the convex and concave portions with respect to the reference surface in the roughness curve. If the value of Rsk is negative, the cross-sectional shape of the surface is in a state in which slow curved concave portions are continuously present. In the present invention, since the value of Rsk is negative, the surface area can be increased without increasing the thickness of the copper foil and the irregularities forming the anchor ring can be obtained. Any Rsk in the vertical direction of rolling is set to -1.00 or less. The value of Rsk may be −1.00 or less, but is practically −2.00 or more. The value of Rsk is preferably -1.50 to -1.
00.

(2) Both the rolling direction and the vertical direction Rku of the rolled copper foil of the present invention are 6.00 or less. Rku (crutosis of roughness curve) is one of indices indicating surface properties, and is also defined in JIS B 0601: 2013. Rku is an index indicating the degree of sharpness of the convex part and the concave part in the roughness curve. It can be said that the smaller the value of Rku, the fewer the sharp parts. When the rolling passes are repeated a plurality of times, the depth of the oil pit increases, so that Rku tends to exceed 6.00. However, when the rolling passes further, the individual oil pit openings start to expand, so that the vicinity of the top becomes gentle and the value of Rku can be made 6.00 or less. When the value of Rku is 6.00 or less, the surface of the rolled copper foil is easily filled with the active material slurry. Therefore, both the Rku in the rolling direction and the vertical direction of the rolled copper foil are 6.
00 or less. The value of Rku may be 6.00 or less, but is practically 3.00 or more. The value of Rku is preferably 4.00 to 6.00.

(3) Rz (Rza) in the rolling direction and Rz in the vertical direction of the rolled copper foil of the present invention
(Rzb) is 0.60 μm or more. Rz indicates the maximum height roughness of the contour curve, and is also defined in JIS B 0601: 2013. The height Z of the roughness curve
It is also expressed as the sum of the maximum value of p and the maximum value of valley depth Zv. In this specification, the Rz value in the rolling direction is defined as Rza, and the Rz in the rolling vertical direction is defined as Rzb. In order for the oil pit depth to effectively act on the anchor ring even if the above-mentioned Rsk and Rku are satisfied, it is necessary that both Rza and Rzb of the rolled copper foil are 0.60 μm or more. . The values of Rza and Rzb may be 0.60 μm or more.
0 μm or less. The values of Rza and Rzb are preferably 0.60 to 1.50, respectively.
μm.

(4) Rza / Rzb of the rolled copper foil of the present invention is 1.15 or more. The roughness of the rolled copper foil surface in the rolling direction changes due to the formation of oil pits during rolling, while the roughness of the rolled copper foil surface in the vertical direction of rolling includes oil pit elements, but grinding of the rolling roll Mainly transcription of muscle. This is because the oil pits of the rolled copper foil are formed as valley-shaped depressions orthogonal to the rolling direction. The oil pits on the surface of the rolled copper foil are sufficiently increased to become the main element of the surface roughness, and Rz (R in the rolling direction of the rolled copper foil is used as an index indicating the state in which the effect of the present invention can be obtained.
The ratio of za) to Rz (Rzb) in the vertical direction of rolling needs to be 1.15 or more.

(5) The rolled copper foil of the present invention has an RSm in the rolling direction (referred to as RSma) of 20 μm or less, and a ratio RSma / RSmb to an RSm in the vertical direction of rolling (referred to as RSmb) of 0.50 or less. Is preferred. RSm is one of the indices indicating surface properties, and is also JIS B
0601: 2013. RSm can be said to be the average value of the intervals of one mountain and valley obtained from the intersection where the roughness curve intersects the average line. In this specification, RS in the rolling direction
The value of m is defined as RSma, and RSm in the vertical direction of rolling is defined as RSmb. RSma can be said to be an index representing the density around the area of oil pits formed on the surface of the rolled copper foil. As an index indicating the number of oil pits in a certain area sufficient to improve the adhesion to the active material, the rolled copper foil of the present invention preferably has an RSm (RSma) in the rolling direction of 20 μm or less. Rsma
The value of may be 20 μm or less, but is actually 10 μm or more. The value of Rsma is preferably 10 to 20 μm.

Since RSmb is measured in the same direction as the valley with respect to the oil pit of the rolled copper foil, which is a valley-like depression perpendicular to the rolling direction, detection of the deepest part is slower than RSma. RSma / RSmb is 0.50 or less as an indicator that the oil pit size on the copper foil surface is sufficient and that the roughness element is mainly oil pits rather than the transfer of grinding stripes on the roll surface. Preferably there is.

The rolled copper foil that satisfies the surface properties described above has a sufficiently enlarged surface oil pit opening, and the negative electrode active material and the binder are filled in the recesses of the oil pit to obtain an anchor effect. The adhesion of the substance is improved.

An example of the manufacturing method of the rolled copper foil of this invention is shown. The rolled copper foil of the present invention has, for example, a work roll diameter in a rolling process of φ100 to 150 mm and a rolling oil viscosity of 2 to 6 cSt (40 ° C.
), The total rolling processing rate is 80% or more, the total number of rolling passes is 10 passes or more, and the single pass processing rate is 20% or less (preferably 15% or less) when the foil pressure is 35 μm or less. When the speed is within a foil pressure of 35 μm or less, it can be produced at 200 m / min or more. Furthermore, in order to adjust the roughness factor, there is an increase in the diameter of the work roll, the use of high viscosity rolling oil, an increase in the rolling speed, and a reduction in the one-pass processing rate, which are introduced as appropriate to obtain the desired surface properties. It is possible.

  Specific examples of the present invention will be described below.

(Examples and Comparative Examples)
Rolled copper foil was obtained by rolling a strip (plate material) of alloy EFTEC-64T manufactured by Furukawa Electric Co., Ltd. The composition of this alloy is Cu-0.25% Cr-0.25% Sn-0.22% Zn. The work roll diameter in the rolling process is φ113 mm, and the rolling oil viscosity is 4 cSt.
Using a rolling oil of (40 ° C.), the total rolling processing rate is 84%, the total number of rolling passes is 12 passes, the single pass processing rate is 10 to 20% within the range of the foil pressure of 35 μm or less, and the rolling speed is 35 μm. The following range was performed at 260 to 500 m / min or more. The final foil thickness of the rolled copper foil thus obtained is
It was 8 μm. In addition, the rolling copper foil of the comparative example which does not satisfy | fill the prescription | regulation of this invention was also produced by changing rolling conditions.

<Surface roughness parameter measurement>
The rolled copper foil was wound around a φ20 mm glass tube and fixed, and the surface roughness was measured using a surf coder SE3500 manufactured by Kosaka Laboratory. Moreover, the roughness curve obtained by the measurement is Cross Section Polisher SM-090 manufactured by JEOL Ltd.
It was confirmed that the surface shape observed in the cross section of the rolled copper foil prepared according to 10 was sufficiently reproduced.

<Peel strength>
An active material made of natural graphite and acetylene black and using polyvinylidene fluoride (PVDF) as a binder was applied to the rolled copper foil to produce an electrode (negative electrode). The electrode thickness was 70 μm and the electrode density was 1.5 g / cm ³ . In order to measure the adhesion between the current collector (rolled copper foil) and the active material, a peel test was performed with a sample shape of 10 mm × 60 mm and a test speed of 50 mm / min. AG-1S manufactured by Shimadzu Corporation was used as the peel tester.

Table 1 shows the results of the surface roughness and the peel strength. Here, RD indicates the rolling direction of the rolled copper foil, and TD indicates the rolling vertical direction of the rolled copper foil.

From Examples 1 to 3 in Table 1, it can be seen that the rolled copper foil of the present invention has high adhesion to the active material (high peel strength). Moreover, it turns out that the rolled copper foil of Comparative Examples 1-3 which does not satisfy | fill the prescription | regulation of this invention is inferior to adhesiveness with an active material (peel strength is inferior). In addition, this is not restricted to the alloy (EFTEC-64T) made from Furukawa Electric Co., Ltd., and similar trends could be confirmed in rolled copper foils having other alloy compositions.

Therefore, it turns out that the rolled copper foil which has a predetermined | prescribed surface property like this invention is suitable for a lithium ion secondary battery negative electrode collector. According to the lithium ion secondary battery negative electrode current collector using the rolled copper foil of the present invention, the reliability of the lithium ion secondary battery can be improved.

Claims (2)

In the surface properties of the rolled copper foil, the Rsk in the rolling direction and the vertical direction of the rolling are both -1.00 or less, and both Rku are 6.00 or less,
The rolling direction of Rz and Rza, when the Rz of the rolling vertical and Rzb, both the Rza and Rzb are at 0.60μm or more state, and are Rza / Rzb is 1.15 or more,
The rolling direction RSm and RSMA, when the rolling vertical RSm and RSMB, RSMA is at 20μm or less, RSMA / RSMB 0.50 der Ru rolled copper lithium ion secondary battery negative electrode current collector for the body below Foil. A lithium ion secondary battery negative electrode current collector using the rolled copper foil according to claim 1 .