JP2011009207A - Rolled copper foil for lithium battery collector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper foil suitable for a collector of a lithium battery that attains high adhesiveness, with respect to an active material layer.SOLUTION: A rolled copper foil for a lithium battery collector satisfies the relations: 0.01 μm≤Ra≤0.10 μm and RSm≤20 μm regarding surface roughness, in a direction parallel to the rolling direction of the upper and the lower surfaces.

Description

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

  Copper foil is mainly used in the electronic industry such as printed wiring boards, electromagnetic wave shields, and lithium secondary batteries. At this time, the copper foil has good adhesiveness with resin and other materials. May be required.

  For example, in a negative electrode for a lithium secondary battery, adhesion between a copper foil as a current collector and a negative electrode active material is required. Therefore, in general, in order to improve the adhesion between the current collector copper foil for the negative electrode of the lithium secondary battery and the active material layer, a surface treatment that forms an unevenness on the surface of the copper foil, called a roughening treatment in advance. It has been done. 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 the adhesion by the anchoring effect, or to change the volume 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, Japanese Patent No. 3733067).

In Japanese Patent No. 3733065, a preferable surface property is specifically specified by a roughness parameter, and a current collector and an active material are obtained by using a copper foil having a large surface roughness Ra as a current collector. It is described that the adhesiveness to the surface is improved (paragraph 0209). The surface roughness Ra of the current collector is preferably 0.01 μm or more, more preferably 0.01 to 1 μm, and further preferably 0.05 to 0.5 μm (paragraph 0021 and the like). ). The surface roughness Ra of the current collector and the average interval S between the local peaks are preferably 100Ra ≧ S (paragraph 0022 and the like). The shape of the convex and concave portions on the surface of the current collector is preferably a cone (paragraph 0023 and the like).
Such surface morphology is obtained by electrolytic copper foil (paragraph 0044), roughening the surface by electrolytically depositing copper on the surface of the rolled copper foil (paragraph 0045), and polishing with emery paper. (Paragraph 0205).

Japanese Patent No. 3733067 Japanese Patent No. 3733065

  Thus, according to the conventional knowledge, in order to improve the adhesion between the copper foil and the active material layer, a roughened copper foil having a large surface roughness Ra is preferred, and in particular, an electrolytic copper foil has been mainly employed. 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 copper foil and the active material layer.

  Then, this invention makes it a subject to provide suitable copper foil as a collector of a lithium battery which can implement | achieve high adhesiveness with an active material layer. Another object of the present invention is to provide a lithium battery using the copper foil according to the present invention as a current collector.

  In order to solve the above-mentioned problems, the present inventor conducted research on the surface properties of copper foil, and in general, rolled copper foil having a smoother surface property than the electrolytic copper foil that has been considered preferable so far. The possibility of a solution was sought. And when manufacturing rolled copper foil, rather than roughening as in the past, the rolling conditions are appropriately controlled, and by forming finer irregularities on the surface, the adhesion with the active material is significant. It was found to increase. The state of this fine unevenness can be defined by Ra and RSm. Therefore, it was found that by optimizing Ra and RSm, a rolled copper foil having significantly improved adhesion to the negative electrode active material can be obtained.

  The present invention completed on the basis of the above knowledge, in one aspect, the lithium battery current collector satisfying 0.01 μm ≦ Ra ≦ 0.10 μm and RSm ≦ 20 μm with respect to the surface roughness in the rolling parallel direction of the upper and lower surfaces It is a rolled copper foil for body.

  In one embodiment of the rolled copper foil for a lithium battery current collector according to the present invention, RSk ≦ −0.3.

  In another embodiment of the rolled copper foil for a lithium battery current collector according to the present invention, RSm / Ra ≦ 200.

  In still another embodiment of the rolled copper foil for a lithium battery current collector according to the present invention, at least one of the upper and lower surfaces is subjected to silane coupling treatment.

  In still another embodiment of the rolled copper foil for a lithium battery current collector according to the present invention, it is for a negative electrode current collector of a lithium ion secondary battery.

  In another aspect, the present invention is a lithium battery using the rolled copper foil as a current collector.

  The copper foil which concerns on this invention has high adhesiveness with an active material. Therefore, it can be suitably used as a current collector for a lithium battery.

  In the present invention, “copper foil” includes copper alloy foil. There is no restriction | limiting in particular as a material of copper foil, What is necessary is just to select suitably according to a use or a required characteristic. For example, but not limited to, Cu-Ni-Si based copper alloy with addition of high purity copper (oxygen-free copper, tough pitch copper, etc.), Sn-containing copper, Ag-containing copper, Ni, Si, etc., Cr, Examples thereof include a copper alloy such as a Cu—Cr—Zr copper alloy to which Zr or the like is added.

  The advantage of the rolled copper foil compared with the electrolytic copper foil will be described. When used as a current collector for a lithium secondary battery, it is possible to obtain a battery having a higher capacity by reducing the thickness of the copper foil. However, if the thickness is reduced, there is a risk of breakage due to a decrease in strength. 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 the electrolytic copper foil, 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 are produced due to the manufacturing process. Although both have different surface properties and different adhesion to the active material, a lithium secondary battery generally has a stack structure in which a large number of positive and negative electrodes are laminated. In this case, both sides of the copper foil are active. It is required to have high adhesion with a substance. Therefore, it is desirable that the upper and lower surfaces of the copper foil have the same surface properties. In this respect, the rolled copper foil is advantageous because the upper and lower surfaces can have substantially the same surface properties.

  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 secondary battery, a battery having a higher capacity can be obtained by thinning the copper foil. From such a viewpoint, it is typically 2 to 50 μm, more typically about 5 to 20 μm.

  In the present invention, lithium batteries include lithium primary batteries and lithium secondary batteries that use metallic lithium as a negative electrode, as well as lithium ion primary batteries that do not contain metallic lithium in the battery but lithium ions in the electrolyte are responsible for electrical conduction. And lithium ion secondary batteries. The negative electrode active material of the lithium battery is not limited, but is tin oxide in which carbon, silicon, tin, germanium, lead, antimony, aluminum, indium, lithium, tin oxide, lithium titanate, lithium nitride, and indium are dissolved. , Indium-tin alloy, lithium-aluminum alloy, lithium-indium alloy, and the like.

  The copper foil according to the present invention satisfies 0.01 μm ≦ Ra ≦ 0.10 μm and 5 μm ≦ RSm ≦ 20 μm with respect to the surface roughness in the rolling parallel direction of the upper and lower surfaces. Ra is a value obtained by folding the roughness curve from the center line and dividing the area obtained by the roughness curve and the center line by the length L, and RSm is a mountain valley obtained from the intersection where the roughness curve intersects the average line -Average period interval. Both are measured according to JIS B0601: 2001. 0.01 μm ≦ Ra ≦ 0.10 μm is a characteristic that is not normally obtained on the M-plane of the electrolytic copper foil. This is because the M surface of the electrolytic copper foil generally has Ra of more than 0.10 μm. Further, 5 μm ≦ RSm ≦ 20 μm is a characteristic that is not normally obtained from the M surface as well as the S surface in the electrolytic copper foil. This is because the electrolytic copper foil generally has an RSm of more than 20 μm.

  Moreover, even if it is a rolled copper foil, as described in Patent Document 2, copper is deposited on the surface by an electrolytic method to roughen the surface, or the surface is actively polished by emery paper. If roughened, the surface properties of the copper foil become rough enough to be comparable to the M-plane of the electrolytic copper foil. Therefore, also in this case, Ra exceeds 0.10 μm and RSm exceeds 20 μm.

  That is, it can be said that the unevenness | corrugation of the surface of the rolled copper foil which concerns on this invention is fine compared with the M surface normally employ | adopted as an adhesive surface with electrolytic copper foil, and the roughened rolled copper foil. The adhesiveness of the rolled copper foil according to the present invention with the negative electrode active material is superior to that of the electrolytic copper foil or the roughened rolled copper foil. Although the present invention is not intended to be limited by theory, the following reasons can be considered. Compared with general surface roughening treatment, the surface irregularities due to oil pits are much finer, which increases the surface area of the material, that is, the effect of increasing the contact area between the binder and the material surface There is. Further, it is considered that the anchoring effect is increased by increasing the number of irregularities per unit area, and the adhesion is increased.

  The condition of 0.01 μm ≦ Ra ≦ 0.10 μm is that when Ra is less than 0.01 μm, the surface is smooth, and when it exceeds 0.10 μm, there are few fine irregularities, so that it adheres to the negative electrode active material. This is because the property tends to deteriorate. Ra is preferably 0.03 ≦ Ra ≦ 0.08, more preferably 0.04 ≦ Ra ≦ 0.06.

  The reason for RSm ≦ 20 μm is that when RSm exceeds 20 μm, the adhesion with the negative electrode active material tends to deteriorate. Preferably, RSm ≦ 16 μm. The lower limit is not particularly limited, but RSm is typically 5 μm ≦ RSm, more typically 8 μm ≦ RSm because it is technically difficult to stably produce RSm of less than 5 μm industrially. is there.

In a preferred embodiment of the rolled copper foil according to the present invention, RSk representing skewness satisfies RSk ≦ −0.3. RSk is also measured according to JIS B0601: 2001. Qualitatively speaking, the shape of the convex and concave portions is not sharp but rounded like a bell. This is different from the idea of Patent Document 2 in which a cone shape is preferable. The reason why RSk ≦ −0.3 is preferable is not intended to limit the present invention by theory, but the following reasons are conceivable.
RSk is a parameter whose value is determined by the shape of the unevenness, and the larger the value, the sharper the tip of the convex portion and the wider the end of the concave portion. On the other hand, the smaller the value, the wider the front end of the convex part and the sharper the end of the concave part. The feature of such a shape indicates that the smaller the value of RSk is, the more difficult it is to peel off the active material that has reached the concave end of the material, that is, the smaller the RSk, the better the adhesion of the active material. The threshold at which this tendency appears remarkably is RSk ≦ −0.3.
Preferably, RSk ≦ −0.5, more preferably RSk ≦ −0.6, and even more preferably RSk ≦ −0.7.

  In another preferred embodiment of the rolled copper foil according to the present invention, RSm / Ra ≦ 200. The increase in RSm / Ra means that the unevenness on the surface of the copper foil becomes gentle and does not have a very good influence on the adhesion with the negative electrode active material. Therefore, RSm / Ra ≦ 200 is preferable, and RSm / Ra ≦ 100 is more preferable.

  The manufacturing method of the rolled copper foil which concerns on this invention is demonstrated. The surface property of the rolled copper foil according to the present invention can be constructed by controlling the surface irregularity caused by the oil pits without performing a roughening treatment such as polishing treatment or electrodeposition grain plating. . The oil pit is a fine recess in which rolling oil confined by a rolling roll and a material to be rolled within a roll bite is partially generated on the surface of the material to be rolled. If the roughening treatment is performed, fine unevenness of the oil pit is lost, which is not preferable. Since the roughening process is omitted, there is also an advantage that economic efficiency and productivity are improved.

  The shape of the oil pit of the rolled copper foil, that is, the surface properties, is controlled by adjusting the surface roughness of the rolling roll, the rolling speed, the viscosity of the rolling oil, the rolling reduction per pass (especially the rolling reduction of the final pass), etc. Is possible. For example, if a rolling roll having a large Ra is used, Ra of the rolled copper foil obtained is also increased. Conversely, if a rolling roll having a small Ra is used, the Ra of the rolled copper foil obtained is likely to be reduced. In addition, by increasing the rolling speed, increasing the viscosity of the rolling oil, or decreasing the rolling reduction per pass, the amount of oil pits generated increases and RSm tends to decrease. Conversely, by reducing the rolling speed, lowering the viscosity of the rolling oil, or increasing the rolling reduction per pass, the amount of oil pits decreases and RSm tends to increase. RSk indicates a value peculiar to oil pits due to rolling, and generally satisfies the above-described conditions as long as the rolling conditions generate oil pits.

  As a method of adhering the rolled copper foil whose surface properties are controlled in this way to the negative electrode active material, there is a method of adhering the copper foil surface to the active material after silane coupling treatment. It is preferable for obtaining high adhesion with the active material. In the silane coupling treatment, at least one surface of the upper and lower surfaces of the copper foil that requires adhesion to the negative electrode active material is brought into contact with the silane coupling agent by dipping, coating, spraying, etc., and then dried to allow silane coupling. This can be done by fixing the agent to the copper foil surface.

  A silane coupling agent is an organosilicon compound having simultaneously a functional group reactively bonded to an organic material and a functional group reactively bonded to an inorganic material in the molecule. Examples of functional groups reactively bonded to organic materials include vinyl groups, epoxy groups, styryl groups, acryloxy groups, methacryloxy groups, amino groups, N-phenylaminopropyl groups, ureido groups, chloropropyl groups, mercapto groups, and isocyanate groups. , Sulfide groups, hexyl groups and the like, and amino groups, vinyl groups, epoxy groups and hexyl groups are preferred. Examples of the functional group reactively bonded to the inorganic material include a halogen group such as a chloro group, an alkoxy group, an acetoxy group, and an isopropenoxy group. Two or more silane coupling agents can be used in combination.

  The silane coupling agent can be used by dissolving in a solvent such as ethanol or water, and the concentration is preferably 0.01% by mass or more from the viewpoint of improving the adhesion between the copper foil and the negative electrode active material.

  A lithium battery can be produced by conventional means using a negative electrode composed of a current collector made of the rolled copper foil according to the present invention and an active material layer formed thereon.

  EXAMPLES Examples of the present invention will be described below, but these are provided for better understanding of the present invention and are not intended to limit the present invention.

Example 1
About various rolled copper foil and electrolytic copper foil, the adhesiveness with a negative electrode active material was evaluated. The surface roughness of the rolled copper foil was changed by adjusting the rolling speed of the final pass. The electrolytic copper foil obtained the commercial item from which surface roughness differs.
[Manufacture of rolled copper foil]
A tough pitch copper ingot having a thickness of 200 mm and a width of 600 mm was manufactured and rolled to 10 mm by hot rolling. Next, annealing and cold rolling are repeated, and finally, by cold rolling, the work roll diameter is 60 mm, the work roll surface roughness Ra is 0.03 μm, and in the final pass, the rolling speed is 50 to 400 m / min and the reduction rate is 20%. It finished to 10 μm. The viscosity of the rolling oil was 9.0 cSt (25 ° C.).
[Surface roughness measurement]
The copper foil was placed on a glass plate and fixed, and the surface roughness of the rolled copper foil in the rolling parallel direction and the electrolytic copper foil in the longitudinal direction of the product were measured using a laser tech confocal microscope HD100D. About the rolled copper foil, although the measurement result about one side was described among upper and lower surfaces, both surfaces had the same surface property. Ra, RSm, and RSk were measured using HD100D manufactured by Lasertec in accordance with JIS B0601: 2001.
[Silane coupling treatment]
After immersing the rolled copper foil having a thickness of 10 μm produced as described above and two types of electrolytic copper foils having different surface roughness in aminopropyltrimethoxysilane having a concentration of 0.5 mass% for 3 seconds and drying with a dryer, Application of the active material and adhesion evaluation were performed as follows.
[Application of active material and evaluation of adhesion]
(1) Artificial graphite having an average diameter of 9 μm and polyvinylidene fluoride are mixed at a weight ratio of 1: 9, and this is dispersed in a solvent N-methyl-2-pyrrolidone to prepare an active material dispersion.
(2) The active material dispersion is applied to the surface of the copper foil that is the current collector.
(3) The copper foil coated with the active material dispersion is heated at 90 ° C. for 30 minutes in a dryer.
(4) After drying, cut into 20 mm squares and apply a load of 1.5 ton / mm ² × 20 seconds.
(5) The sample is cut into a grid pattern with a cutter, a commercially available adhesive tape (registered trademark: cello tape) is applied, and a 2 kg weight roller is placed to reciprocate once to pressure-bond the adhesive tape.
(6) The active material remaining on the copper foil is peeled off and the surface image is taken into a PC and the residual rate of the active material is calculated by binarization. The residual rate was an average value of three samples. In the determination of the active material adhesion, a residual rate of 0 to 50% was “x”, 50 to 70% was “Δ”, 70 to 90% was “◯”, and 90% or more was “◎”.

The results are shown in Table 1.

No. In 1-1 to 1-4, Ra and RSm are within the specified range due to oil pits by rolling, and therefore, the remaining ratio of the active material is good. RSk was also in the preferred range. Further, the smaller the surface roughness RSm, the higher the residual rate.
No. 1-5 to 1-6 are rolled copper foils. Since the rolling speed is low compared with 1-4, there are few oil pits by rolling, and since RSm exceeds the prescribed range, the residual ratio of the active material is low. The value of RSk is also not preferable.
No. 1-7 is an electrolytic copper foil, and Mk has a preferable range of RSk, but since Ra and RSm exceed the specified range, the residual ratio of the active material is low. On the S surface, Ra is in the specified range, but since RSm and RSk exceed the specified range, the residual ratio of the active material is low.
No. 1-8 is an electrolytic copper foil. On the M surface, Ra and RSm exceed the specified ranges, and RSk is also inappropriate. Therefore, the residual ratio of the active material is low. In the S plane, Ra and RSk are in a preferable range, but since the RSm exceeds the specified range, the residual ratio of the active material is low.
In general, the surface roughness of the electrolytic copper foil has large irregularities, and fine irregularities such as oil pits of the rolled copper foil are not formed, so that the residual ratio of the active material is low.

Example 2
About various rolled copper foil, the adhesiveness with an active material was evaluated. The rolled copper foil changed the surface roughness by adjusting the surface roughness of the work roll.
[Manufacture of rolled copper foil]
A tough pitch copper ingot having a thickness of 200 mm and a width of 600 mm was manufactured and rolled to 10 mm by hot rolling. Next, annealing and cold rolling are repeated, and finally, by cold rolling, the work roll diameter is 60 mm and the work roll surface roughness Ra is 0.01 to 0.12 μm. In the final pass, the rolling speed is 250 m / min and the reduction rate is 20%. To a thickness of 10 μm. The viscosity of the rolling oil was 9.0 cSt (25 ° C.).
[Surface roughness measurement]
Measurement was performed in the same manner as in Example 1. The measurement results for one of the upper and lower surfaces were described, but both surfaces had the same surface properties.
[Silane coupling treatment]
Silane coupling treatment was performed in the same manner as in Example 1.
[Application of active material and evaluation of adhesion]
The active material dispersion was applied in the same manner as in Example 1, and the adhesion was evaluated.

The results are shown in Table 2.

  No. 2-1 to 2-3 are rolled work rolls having a surface roughness of 0.01 to 0.09 μm, and in the case of a rolling speed of 250 m / min, Ra and RSm are within the specified ranges due to the occurrence of oil pits due to rolling. In both cases, the residual ratio of the active material is good. RSk was also in the preferred range. Moreover, the tendency for the active material residual rate to become large was seen, so that work roll roughness was small.

  No. Since 2-4 and 2-5 have a larger work roll roughness than the examples, there are few oil pits due to rolling, and Ra and RSm exceed the specified range, so the residual ratio of the active material is low. The value of RSk is also not preferable.

Example 3
About the rolled copper foil formed with various copper alloys, the adhesiveness with an active material was evaluated. The rolled copper foil changed the surface roughness by adjusting the surface roughness of the work roll.
[Manufacture of rolled copper foil]
Various alloy components shown in Table 3 were added to an oxygen-free copper melt having an oxygen concentration of 10 ppm or less to produce a tough pitch copper ingot having a thickness of 200 mm and a width of 600 mm, and rolled to 10 mm by hot rolling. Next, annealing and cold rolling are repeated, and finally, by cold rolling, the work roll diameter is 60 mm, the work roll surface roughness Ra is 0.03 μm, 0.12 μm, and the rolling speed is 250 m / min and the reduction rate is 10 to 10 in the final pass. It finished to 6-20 micrometers in thickness as 20%. The viscosity of the rolling oil was 9.0 cSt (25 ° C.).
[Surface roughness measurement]
Measurement was performed in the same manner as in Example 1. The measurement results for one of the upper and lower surfaces were described, but both surfaces had the same surface properties.
[Silane coupling treatment]
Each copper alloy foil having a thickness of 10 μm produced as described above was immersed in N- (2-aminoethyl) -3-aminopropyltrimethoxysilane having a concentration of 0.5 mass% for 5 seconds and dried with a dryer. Then, application of the active material and adhesion evaluation were performed as follows.
[Application of active material and evaluation of adhesion]
The active material dispersion was applied in the same manner as in Example 1, and the adhesion was evaluated. The residual rate was an average value of three samples. In the determination of the active material adhesion, a residual rate of 0 to 50% was “x”, and 50% or more was “◯”.

The results are shown in Table 3.

No. 3-1 to 3-6 are rolled copper foils. Since RSm and RSk are in the specified ranges due to oil pits by rolling, the remaining ratio of the active material was good.
No. As for 3-7 and 3-8, since the surface roughness of a rolling work roll is large compared with an Example, there are few oil pits by rolling, RSm and RSk exceed the prescribed | regulated range, and the residual rate of an active material Was low.

Claims (6)

  A rolled copper foil for a lithium battery current collector that satisfies 0.01 μm ≦ Ra ≦ 0.10 μm and RSm ≦ 20 μm with respect to the surface roughness in the rolling parallel direction of the upper and lower surfaces.   The rolled copper foil according to claim 1, wherein RSk ≦ −0.3.   The rolled copper foil according to claim 1, wherein RSm / Ra ≦ 200.   The rolled copper foil according to any one of claims 1 to 3, wherein at least one surface of the upper and lower surfaces is subjected to silane coupling treatment.   It is for lithium ion secondary battery negative electrode collectors, The rolled copper foil as described in any one of Claims 1-4.   A lithium battery using the rolled copper foil according to claim 1 as a current collector.