KR20190117669A - Rolled copper foil and lithium ion battery for lithium ion battery collectors - Google Patents

Abstract

Provided is a rolled copper foil for a lithium ion battery current collector having good adhesion with a negative electrode active material and good ultrasonic weldability with a copper foil or a tab terminal. The rolled copper foil for lithium ion battery collectors satisfies the residual oil [mg / m 2] + (60 ° glossiness / 400 in the rolling parallel direction) ≦ 2.5 and 60 ° glossiness ≦ 600 in the 200 ≦ rolling parallel direction.

Description

Rolled copper foil and lithium ion battery for lithium ion battery collectors

This invention relates to the rolled copper foil for lithium ion battery collectors, and a lithium ion battery.

Lithium ion batteries are characterized by high energy density and relatively high voltage, and are widely used for small electronic devices such as notebook computers, video cameras, digital cameras, and cellular phones. In the future, it is also promising to be used as a power source for large devices such as electric vehicles and distributed home type power supplies in general households.

1 is a schematic diagram of a stack structure of a lithium ion battery. The electrode body of the lithium ion battery generally has a stack structure in which the positive electrode 11, the separator 12, and the negative electrode 13 are wound or stacked several tens of times. Typically, the positive electrode is composed of a positive electrode current collector made of aluminum foil and a positive electrode active material made of a lithium composite oxide such as LiCoO ₂ , LiNiO _2, and LiMn ₂ O ₄ provided on the surface thereof, and the negative electrode is made of copper foil. It consists of a negative electrode active material which uses a negative electrode electrical power collector and carbon etc. which were provided in the surface. The positive electrodes and the negative electrodes are welded by the tabs 14 and 15, respectively. In addition, although the positive electrode and the negative electrode are connected with the tab terminal made from aluminum or nickel, this is also performed by welding. Welding is usually performed by ultrasonic welding.

As a characteristic required for the copper foil used as an electrical power collector of a negative electrode, adhesiveness with a negative electrode active material and ultrasonic welding property with a copper foil or a tab terminal are mentioned.

As a general method for improving adhesiveness with an active material layer, the surface treatment which forms an unevenness | corrugation on the copper foil surface called a roughening process previously is mentioned. As a method of roughening processing, methods, such as a blasting process, the rolling by a roughening roll, mechanical polishing, electrolytic polishing, chemical polishing, and plating of electrodeposition particle | grains, are known, Among these, plating of electrodeposition particle | grains is especially used abundantly. This technique uses a copper sulfate acid plating bath to deposit a large amount of copper on a copper foil surface in a resinous or small globular form to form fine concavo-convex, to improve adhesion due to the anchoring effect, or to expand an active material having a large volume change. This is done by forming stress by concentrating stress in the recessed portion of the active material layer and preventing peeling due to concentration of stress at the current collector interface (for example, Japanese Patent No. 3733067).

The ultrasonic weldability has not been a big problem in the past by providing a large welding energy in accordance with the weldability of the material. However, since a large amount of welding energy consumes a lot of consumables used for welding, copper foil having good weldability has been required in recent years even when the welding energy is reduced. As the copper foil of such a structure, Unexamined-Japanese-Patent No. 2009-68042 has prescribed | regulated the coating amount to the copper foil surface of the chromium hydride oxide layer as 0.5-70 microgram-Cr / dm <^2> , or the chromium hydride oxide layer is coat | covered The method of making Rz (ten point average roughness prescribed | regulated to JISB0601-1994) of the surface into 2.0 micrometers or less is described. And the Example describes what made such surface roughness the electrolytic copper foil.

Moreover, although the copper foil used as an electrical power collector of a lithium ion battery apply | coats the active material of Li to the copper foil surface, at this time, the said active material may be thickly apply | coated for the high capacity of a battery. However, when the active material is thickly applied, there is a fear that problems related to adhesion between the copper foil and the active material such as the active material peeled off may occur. Moreover, although the use of Si type active material is considered as another means for the high capacity of a battery, since a Si type active material has expansion expansion shrinkage rate higher than the conventional one, there exists a possibility that a problem may arise in adhesiveness.

Japanese Patent No. 3733067 Japanese Patent Publication No. 2009-68042

Thus, although the technology development for the improvement of the characteristic of the copper foil used as an electrical power collector of a lithium ion battery is performed, there exists still room for the technique which improves adhesiveness and ultrasonic weldability simultaneously. Then, an object of this invention is to provide the rolled copper foil for lithium ion battery collectors which has favorable adhesiveness with a negative electrode active material, and favorable ultrasonic welding with copper foil or a tab terminal.

MEANS TO SOLVE THE PROBLEM This inventor repeated research in order to solve the said subject, and by controlling the relationship between the residual oil of a rolled copper foil and the glossiness of a rolling parallel direction, and also controlling the numerical range of the glossiness of a rolling parallel direction, adhesiveness and It discovered that the rolled copper foil for lithium ion battery collectors which can improve an ultrasonic weldability simultaneously can be provided.

The present invention completed on the basis of the above findings, according to one aspect, the residual oil [mg / m 2] + (60 ° glossiness / 400 in the rolling parallel direction) ≤ 2.5, and 200 ≤ 60 ° glossiness in the rolling parallel direction ≤ It is the rolled copper foil for lithium ion battery collectors which satisfy | fills 600.

In one embodiment, the rolled copper foil for lithium ion battery collectors which concerns on this invention satisfy | fills residual oil [mg / m <2>] + (60 degree glossiness / 400 of rolling parallel direction) <= 2.0.

In another embodiment, the rolled copper foil for lithium ion battery current collector according to the present invention satisfies 60 ° glossiness ≤ 600 in 450 ≤ rolling parallel direction.

The rolled copper foil for lithium ion battery collectors which concerns on this invention is for a lithium ion secondary battery negative electrode collector in another embodiment.

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

According to this invention, the rolled copper foil for lithium ion battery collectors which has favorable adhesiveness with a negative electrode active material and favorable ultrasonic welding with a copper foil or a tab terminal can be provided.

1 shows a schematic diagram of a stack structure of a lithium ion battery.
FIG. 2 is a graph showing the relationship between residual oil in Examples and Comparative Examples and 60 ° glossiness in the rolling parallel direction. FIG.

(Rolled copper foil for lithium ion battery collector)

Rolled copper foil is used for the copper foil base material of the rolled copper foil for lithium ion battery collectors of this invention. Rolled copper alloy foil shall also be contained in the said rolled copper foil. There is no restriction | limiting in particular as a material of rolled copper foil, What is necessary is just to select suitably according to a use and a required characteristic. For example, but not limited to, Cu-Ni-Si-based copper alloys containing Cr-containing copper, Ag-containing copper, Ni, Si, etc., in addition to high-purity copper (oxygen-free copper, tough pitch copper, etc.), Cr, Zr Copper alloys, such as the Cu-Cr-Zr system copper alloy which added etc. are mentioned.

There is no restriction | limiting in particular in the thickness of rolled copper foil, What is necessary is just to select suitably according to a required characteristic. Although it is 1-100 micrometers generally, when using it as an electrical power collector of a lithium secondary battery negative electrode, the thinner the rolled copper foil can obtain a battery with a higher capacity. From such a viewpoint, it is typically 2-50 micrometers, More typically, it is about 5-20 micrometers.

The rolled copper foil for lithium ion battery collectors of this invention satisfy | fills residual oil [mg / m <2>] + (60 degree glossiness / 400 of rolling parallel direction) <= 2.5. By controlling the relationship between the residual oil of the rolled copper foil and 60 ° glossiness in the rolling parallel direction in this manner, good adhesion with the negative electrode active material and good ultrasonic weldability with the copper foil or the tab terminal are obtained. It is preferable that the rolled copper foil for lithium ion battery collectors of this invention satisfy | fills residual oil [mg / m <2>] + (60 degree glossiness / 400 of rolling parallel direction) <= 2.2, and residual oil [mg / m <2>] + It is more preferable to satisfy (60 ° glossiness / 400 in the rolling parallel direction) ≤ 2.0.

The rolled copper foil for lithium ion battery collectors of this invention also satisfy | fills 60 degrees glossiness <= 600 of 200 <= rolling parallel direction. When the 60 ° glossiness in the rolling parallel direction is less than 200, the amount of oil pit on the surface of the rolled copper foil is large, the residual oil increases, and the contact between the overlapped copper foil and the copper foil at the time of ultrasonic welding becomes small, so that the ultrasonic weldability Worsens. Moreover, when 60 degree glossiness of rolling parallel direction exceeds 600, there exists a possibility that anchor effect may be reduced and adhesiveness with a negative electrode active material may deteriorate. It is preferable that the rolled copper foil for lithium ion battery collectors of this invention satisfy | fills 60 degrees glossiness <= 600 of 300 <rolling parallel direction, and it is more preferable to satisfy 60 degrees glossiness <= 600 of 450 <rolling parallel direction. Do.

The rolling copper foil for the lithium ion battery collector of this invention by which the relationship of the residual oil of the above-mentioned rolled copper foil and the glossiness of the rolling parallel direction, and the glossiness of the rolling parallel direction was controlled is a grinding | polishing process and plating of electrodeposition particle | grains. It is possible to construct by controlling the uneven state of the surface resulting from the oil pit without performing the roughening process as described above. An oil pit is a fine recessed part in which the rolled oil enclosed by the rolling roll and the to-be-rolled material in the roll bite partly arises on the surface of a to-be-rolled material. Since the roughening process is omitted, there is an advantage that the economics and productivity are improved.

The shape of the oil pit of the rolled copper foil, that is, the surface property, can be controlled by adjusting the surface roughness of the rolling roll, the rolling speed, the viscosity of the rolling oil, the reduction ratio per pass (particularly, the reduction ratio of the final pass), and the like. For example, when the rolling roll with a large surface roughness is used, the surface roughness of the rolled copper foil obtained will also become large, and, on the contrary, when the rolling roll with a small surface roughness is used, the surface roughness of the rolled copper foil obtained will also become small easily. In addition, the amount of oil pits tends to increase by increasing the rolling speed quickly, increasing the viscosity of the rolling oil, or decreasing the reduction ratio per pass. On the contrary, the amount of oil pits tends to decrease by slowing down the rolling speed, lowering the viscosity of the rolling oil, or increasing the reduction ratio per one pass.

(Lithium ion battery)

A lithium ion battery can be produced by usual means using the negative electrode comprised by the electrical power collector which uses the rolled copper foil which concerns on this invention as a material, and the active material layer formed on it. Lithium ion batteries include lithium ion primary batteries and lithium ion secondary batteries in which lithium ions in the electrolyte are responsible for electric conduction. Examples of the negative electrode active material include, but are not limited to, carbon, silicon, tin, germanium, lead, antimony, aluminum, indium, lithium, tin oxide, lithium titanate, lithium nitride, and indium tin oxide, indium-tin alloy, and lithium. Aluminum alloy, lithium indium alloy, etc. are mentioned.

Example

Hereinafter, although the Example of this invention is shown, these are provided in order to understand this invention better, and it does not intend that this invention is limited.

(Examples 1-9, Comparative Examples 1-6)

[Manufacture of Rolled Copper Foil]

An ingot of tough pitch copper having a width of 600 mm was manufactured and rolled by hot rolling.

Next, annealing and cold rolling are repeated, and finally, in cold rolling, the work roll diameter 60mm and the work roll surface roughness Ra are 0.03 micrometer, and it finishes by the thickness of Table 1 at the rolling speed of 400 m / min of a final pass. It was. The viscosity of the rolling oil was 4.0 cSt (25 degreeC). Ra of the obtained rolled copper foil was 0.04 µm. In this state, oil, such as the rolling oil used by the final cold rolling, adheres to copper foil. This copper foil was wash | cleaned with the solution containing a petroleum solvent and an anionic surfactant, the copper fine powder, rolling oil, etc. which adhered to the copper foil surface were removed, and it air-dried after that.

The rolling oil on the copper foil surface was removed by degreasing treatment using normal paraffin as an organic solvent (degreasing solvent). In Table 1, the immersion time in the organic solvent (degreasing solvent) of the copper foil performed in the said degreasing treatment is shown. Moreover, in Examples 1-9, the relational expression of the residual oil of the copper foil surface at this time, and the 60 degree glossiness of a rolling parallel direction (residual oil content [mg / m <2>] + (60 degree glossiness of a rolling parallel direction / 400) ≤) Control to satisfy 2.5).

Moreover, as a method of removing rolling oil etc. from the copper foil surface, conventionally well-known degreasing treatment or washing process can be employ | adopted, and as an organic solvent (degreasing solvent) to be used, For example, normal paraffin, isopropyl alcohol, etc. Alcohols, acetone, dimethylacetamide, tetrahydrofuran and ethylene glycol.

[60 ° gloss]

60 degree glossiness G60RD is incident angle 60 in the direction parallel to a rolling direction, using various glossmeters, such as the Nippon Denshoku Kogyo Co., Ltd. glossimeter handy gloss meter PG-1, for example based on JISZ8741. It calculated | required by measuring glossiness in degrees.

[Residual oil]

The residual oil was measured by the following method. That is, the copper foil sample of the size of 420 mm x 594 mm was cut out small about 50 mm x 50 mm. Next, the said copper foil sample and the solvent (Horiba Seisakusho make H-997) were put into the beaker, and the ultrasonic cleaning for 2 minutes was performed with the ultrasonic cleaner. Then, the oil concentration was measured using the Horiba Seisakusho oil concentration meter OCMA-555 in a dedicated cell. The solvent was measured using Horiba Seisakusho H-997.

In addition, the said oil content concentration can be measured by a well-known general method other than Horiba Seisakusho oil content concentration meter OCMA-555 used by the present Example. Moreover, also about a solvent, well-known general solvents, such as carbon tetrachloride, can be used besides H-997 by Horiba Seisakusho used in the present Example.

[Adhesion with Active Material]

Adhesiveness with the active material was evaluated in the following order.

(1) Artificial graphite and polyvinylidene fluoride having an average diameter of 9 µm are mixed in a weight ratio of 1: 9, and this is dispersed in solvent N-methyl-2-pyrrolidone.

(2) The said active material is apply | coated to the surface of copper foil.

(3) The copper foil coated with the active material is heated in a drier at 90 ° C for 30 minutes.

(4) After drying, one side is cut into squares of 20 mm, and a load of 1.5 tons / mm 2 × 20 seconds is applied.

(5) The said sample is cut | disconnected in the shape of a board | substrate eye with a cutter, the adhesive tape (Cellopan tape (registered trademark)) which is marketed is affixed, and it reciprocates 1 with a roller of 2 kg in weight, and presses an adhesive tape.

(6) The active material which peeled off the adhesive tape and remained on copper foil introduce | transduces the image of a surface into PC, distinguishes the metal gloss part of a copper surface from the black part in which an active material remains by binarization, and Calculate the remaining rate. The residual ratio was made into the average value of each sample. In determination of active material adhesiveness, less than 50% of residual ratio made "x" and 50% or more of "(circle)".

Ultrasonic weldability

Ultrasonic weldability was evaluated in the following procedures.

(1) The copper foil is cut out to a size of 100 mm x 150 mm, and 30 sheets are stacked.

(2) A horn (pitch 0.8 mm, height 0.4 mm) is installed on the Branson actuator (model number: Ultraweld L20E). Anvil used a 0.2 mm pitch.

(3) The welding conditions were 40 psi, 60 micrometers in amplitude, 20 Hz frequency, and the welding time was 0.1 second.

(4) When the copper foil is peeled off one by one after welding under the above conditions, the case where 11 or more copper foils are ruptured in the welded portion is "○", and the case where 0-10 copper foils are ruptured in the welded portion is " X ". In addition, before peeling a copper foil, the welding part of the copper foil of the outermost layer which contacted the horn was magnified and observed 20 times with a real microscope, and after confirming that a crack did not generate | occur | produce, the peeling test was performed.

Table 1 shows the evaluation conditions and the evaluation results.

Examples 1-9 satisfied residual oil content [mg / m <2>] + (60 degree glossiness / 400 of a rolling parallel direction) <= 2.5, and 200 <= glossiness of 600 <= rolling parallel direction. Therefore, both active material adhesiveness and ultrasonic weldability were favorable.

In Comparative Examples 1 and 2, the 60 ° glossiness in the rolling parallel direction exceeded 600, and the residual oil content [mg / m &lt; 2 &gt;] + (60 ° glossiness / 400 in the rolling parallel direction) exceeded 2.5. This was bad.

In Comparative Example 3, 60 ° glossiness in the rolling parallel direction was less than 200, and ultrasonic weldability was poor. More specifically, Comparative Example 3 has a low gloss, and a lot of irregularities are formed in the copper foil by the oil pit. When the copper foil is overlapped and welded by ultrasonic welding, there are few contacts between the copper foil and the copper foil. . As a result, ultrasonic weldability worsened than copper foil with high gloss.

In Comparative Examples 4-6, since residual oil [mg / m <2>] + (60 degree glossiness / 400 of rolling parallel direction) exceeded 2.5, active material adhesiveness was unsatisfactory.

2, the graph which shows the relationship of the residual oil of an Example and a comparative example and 60 degree glossiness of a rolling parallel direction is shown.

Claims (5)

Residual oil [mg / m 2] + (60 ° gloss / 400 in rolling parallel direction) ≦ 2.5, and
200≤60 ° glossiness in rolling parallel direction≤600
Rolled copper foil for lithium ion battery collectors which satisfy | fills. The method of claim 1,
Residual oil content [mg / m <2>] + (60 degree glossiness / 400 of rolling parallel direction) ≤2.0
Rolled copper foil for lithium ion battery collectors which satisfy | fills. The method according to claim 1 or 2,
450≤60 ° glossiness in rolling parallel direction≤600
Rolled copper foil for lithium ion battery collectors which satisfy | fills. The method according to any one of claims 1 to 3,
Rolled copper foil for lithium ion battery collectors for lithium ion secondary battery negative electrode collectors. The lithium ion battery which used the rolled copper foil for lithium ion battery collectors in any one of Claims 1-4 as an electrical power collector.

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