JP2013069684A - Copper foil of negative electrode collector for lithium ion secondary battery, negative electrode for lithium ion secondary battery, lithium ion secondary battery, and method for manufacturing copper foil of negative electrode collector for lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress falling of roughed particles while maintaining high adhesion to a negative electrode active material layer and also improve weld strength with a tab lead, in a copper foil of a negative electrode collector for a lithium ion secondary battery.SOLUTION: A copper foil of a negative electrode collector for a lithium ion secondary battery includes: a rolled copper foil made of copper or a copper alloy; and a first Cu plating layer, a roughed particle, and a second Cu plating layer which are at least provided in order on the rolled copper foil, and further includes one of a nickel-cobalt alloy plating layer, a nickel plating layer, and a cobalt plating layer. When Cb denotes a binder content Cb (wt.%) in a negative electrode active material layer, the surface roughness Ra of the copper foil satisfies a relation of Cb≥38×Ra×Ra-1.2×Ra (where, 0.10≤Ra≤0.72 and 2≤Cb≤20 are satisfied).

Description

  The present invention relates to a negative electrode current collector copper foil for a lithium ion secondary battery, a negative electrode and a battery including the same, and a method for producing a negative electrode current collector copper foil for a lithium ion secondary battery.

  In recent years, lithium ion secondary batteries have been widely used for mobile device applications. The negative electrode of a lithium ion secondary battery is formed by forming a negative electrode active material layer on a negative electrode current collector copper foil made of, for example, a copper foil or a copper alloy foil. A tab lead made of nickel (Ni) or Ni-plated copper or the like is connected by ultrasonic welding to the portion of the negative electrode current collector copper foil where the negative electrode active material layer is not formed in order to establish electrical connection with the battery extrapolation can. ing.

  Until now, carbon (C) -based materials have been used for the negative electrode active material layer, but it is difficult to significantly improve discharge capacity (maximum capacity) with C-based materials. Therefore, recently, negative electrode active material layers mainly composed of tin (Sn) or silicon (Si) having a larger discharge capacity have been studied.

In such examination, volume expansion and contraction when Sn and Si occlude and release lithium (Li ⁺ ) ions are an obstacle. The negative electrode current collector copper foil is plastically deformed due to expansion and contraction of the negative electrode active material layer, and the negative electrode active material layer falls off from the negative electrode current collector copper foil, or the dimensional stability of the battery is lowered. Therefore, studies have been made to suppress the volume change by alloying or mixing with a substance that does not react with Li ⁺ ions, a substance that does not react with Li ⁺ ions, or with a small volume change even when Li ⁺ ions are occluded. Yes.

As an example of using Sn as an Sn alloy thin film or an Sn compound thin film, for example, Patent Document 1 discloses a technique using Cu ₆ Sn ₅ , which is an Sn alloy, in the negative electrode active material layer. In addition, as an example of using Si as a Si alloy thin film or a Si compound thin film, for example, Patent Document 2 discloses a method in which silicon (Si) powder and conductive metal powder are mixed with a binder and applied onto an electrolytic copper foil. Has been. For example, Patent Document 3 discloses a method in which silicon oxide (SiOx) powder and carbonaceous material are mixed with a binder and applied onto a negative electrode current collector.

  When the negative electrode active material layer mainly composed of Sn or Si is used, heat treatment may be performed at a temperature of 400 ° C. or higher, and the negative electrode current collector copper foil needs to have high heat resistance in order to suppress heat softening. . Therefore, for example, Patent Document 4 discloses a technique for forming a cobalt-nickel (Co—Ni) alloy plating layer on a surface of a copper foil to a thickness of 0.5 μm to 5 μm so as to withstand heat treatment at 400 ° C. for 10 hours. It is disclosed.

  On the other hand, attempts have been made to improve the adhesion between the negative electrode current collector copper foil and the negative electrode active material layer. For example, Patent Document 5 discloses a method of roughening a current collector made of copper foil. According to Patent Document 5, the copper foil obtained by the electrolysis method is further immersed in an electrolytic bath to precipitate copper fine particles on the surface, and both surfaces are roughened.

JP 2004-087232 A Japanese Patent No. 4212263 JP 2004-119175 A Japanese Patent No. 4438541 JP 2008-004462 A

  By the way, in order to accommodate more negative electrode active material layers in the battery and increase the capacity of the battery, the negative electrode current collector copper foil is preferably as thin as possible. Therefore, in order to obtain high heat resistance, instead of introducing a thick plating layer as in Patent Document 4 described above, an alternative solution is desired.

  On the other hand, the adverse effect of the heat treatment at 400 ° C. or higher is not only the softening of the negative electrode collector copper foil. That is, an oxide film is formed on the surface of the negative electrode current collector copper foil by heat treatment at a high temperature for a long time, and when the tab lead is welded, the welding strength may be reduced. If the welding strength is insufficient, the tab lead is peeled off and current cannot be taken out of the battery.

  In addition, as described in Patent Document 5 described above, in the method of adding a granular electrodeposit such as copper fine particles to the surface of the negative electrode current collector copper foil to obtain a roughened surface, the granular electrodeposit may sometimes fall off. There is a possibility of causing a short circuit between the positive and negative electrodes.

  An object of the present invention is a lithium ion secondary that can suppress the dropping of the granular electrodeposit while maintaining high adhesion to the negative electrode active material layer, and can improve the welding strength with the tab lead. It is providing the manufacturing method of the negative electrode current collection copper foil for batteries, the negative electrode and battery provided with the same, and the negative electrode current collection copper foil for lithium ion secondary batteries.

According to the 1st aspect of this invention, it has the negative electrode current collection copper foil for lithium ion secondary batteries, and the negative electrode active material layer which is provided in the said negative electrode current collection copper foil for lithium ion secondary batteries, and contains a binder. A negative electrode for a lithium ion secondary battery,
The negative electrode current collector copper foil for a lithium ion secondary battery includes a rolled copper foil made of copper or a copper alloy, a first Cu plating layer provided at least in order of the rolled copper foil, roughened particles, and a second Cu plating layer. And further comprising either a nickel-cobalt alloy plating layer, a nickel plating layer, or a cobalt plating layer,
When the binder ratio Cb (wt%) is Cb, the surface roughness Ra is
Cb ≧ 38 × Ra × Ra−1.2 × Ra (formula 1)
(However, 0.10 ≦ Ra ≦ 0.72 and 2 ≦ Cb ≦ 20 are satisfied)
A negative electrode for a lithium ion secondary battery is provided.

According to a second aspect of the present invention, there is provided a negative electrode current collector copper foil for a lithium ion secondary battery that is used together with a negative electrode active material layer containing a binder to be a negative electrode for a lithium ion secondary battery,
Rolled copper foil made of copper or copper alloy;
A first Cu plating layer provided at least in order of the rolled copper foil, roughened particles, and a second Cu plating layer,
With a nickel-cobalt alloy plating layer, a nickel plating layer, or a cobalt plating layer,
When the binder ratio Cb (wt%) is Cb, the surface roughness Ra is
Cb ≧ 38 × Ra × Ra−1.2 × Ra (formula 1)
(However, 0.10 ≦ Ra ≦ 0.72 and 2 ≦ Cb ≦ 20 are satisfied)
A negative electrode current collector copper foil for a lithium ion secondary battery is provided.

According to a third aspect of the present invention, a mass thickness of the nickel-cobalt alloy plating layer, the nickel plating layer, and the cobalt plating layer is 20 μg / cm ² or more and 40 μg / cm ² or less. A negative electrode current collector copper foil for a lithium ion secondary battery according to the second aspect is provided.

According to a fourth aspect of the present invention, the copper alloy constituting the rolled copper foil is a high heat-resistant copper alloy. The negative electrode collection for a lithium ion secondary battery according to the second or third aspect, An electrolytic copper foil is provided.

According to a fifth aspect of the present invention, there is provided the negative electrode current collector copper foil for a lithium ion secondary battery according to any one of the second to fourth aspects, wherein the first Cu plating layer is made of pure copper. The

According to the sixth aspect of the present invention, the negative electrode current collector copper foil for the lithium ion secondary battery of the second aspect;
A negative electrode active material layer formed on at least one surface of the negative electrode current collector copper foil for the lithium ion secondary battery;
And a tab lead connected to the negative electrode current collector copper foil for the lithium ion secondary battery.

According to the seventh aspect of the present invention, the negative electrode for a lithium ion secondary battery of the sixth aspect;
A positive electrode for a lithium ion secondary battery;
A separator inserted between the negative electrode for lithium ion secondary battery and the positive electrode for lithium ion secondary battery;
A lithium ion secondary battery comprising: a negative electrode for a lithium ion secondary battery in which the separator is inserted; and a container in which the positive electrode for a lithium ion secondary battery is accommodated and an electrolyte is enclosed. Is provided.

According to the eighth aspect of the present invention, Cu plating is performed using a rolled copper foil made of copper or a copper alloy as a cathode, and a first Cu plating layer, a roughened particle, and a second Cu plating layer are provided at least in the order of the rolled copper foil. A Cu plating step to be provided;
Forming a nickel-cobalt alloy plating layer, a nickel plating layer, or a cobalt plating layer on the second Cu plating layer so as to cover the roughened particles and the second Cu plating layer. A method for producing a negative electrode current collector copper foil for a lithium ion secondary battery is provided.

  ADVANTAGE OF THE INVENTION According to this invention, dropping of a granular electrodeposit can be suppressed, maintaining high adhesiveness with respect to a negative electrode active material layer, and weld strength with a tab lead can be improved.

It is sectional drawing of the negative electrode current collection copper foil for lithium ion secondary batteries which concerns on one Embodiment of this invention. It is a top view of the negative electrode for lithium ion secondary batteries which concerns on one Embodiment of this invention. It is a perspective sectional view of a lithium ion secondary battery concerning one embodiment of the present invention. It is a graph which shows the surface roughness Ra and binder ratio Cb of the negative electrode current collection copper foil for lithium ion secondary batteries which concerns on one Embodiment of this invention, and the relationship of negative electrode active material adhesiveness.

<One Embodiment of the Present Invention>
(1) Schematic Configuration of Lithium Ion Secondary Battery First, a schematic configuration of a lithium ion secondary battery according to an embodiment of the present invention will be described with reference to FIG. 2 and FIG. FIG. 2 is a plan view of the negative electrode 1 for a lithium ion secondary battery according to this embodiment. FIG. 3 is a perspective sectional view of the lithium ion secondary battery 50 according to the present embodiment.

   As shown in FIG. 3, the lithium ion secondary battery 50 includes a battery insertion can 5 as a container in which an electrolyte solution (not shown) is enclosed. The battery insertion can 5 includes a negative electrode 1 for a lithium ion secondary battery (hereinafter simply referred to as “negative electrode 1”) having a tab lead 16 and a positive electrode 2 for a lithium ion secondary battery (hereinafter referred to as “negative electrode 1”). (Also simply referred to as “positive electrode 2”) is accommodated with the separator 3 inserted therebetween.

  As shown in FIG. 2, the negative electrode 1 includes a negative electrode current collector copper foil 10 for a lithium ion secondary battery (hereinafter, also simply referred to as “negative electrode current collector copper foil 10”), for example, a negative electrode formed on both surfaces thereof. Active material layers 15a and 15b are provided. The tab lead 16 described above is directly connected to the exposed region 10 s of the negative electrode current collector copper foil 10. Detailed configurations of the lithium ion secondary battery 50 and the negative electrode 1 for a lithium ion secondary battery will be described later.

(2) Structure of negative electrode current collector copper foil for lithium ion secondary battery Hereinafter, a negative electrode current collector copper foil for lithium ion secondary battery 10 according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view of a negative electrode current collector copper foil 10 for a lithium ion secondary battery according to this embodiment.

   As shown in FIG. 1, a negative electrode current collector copper foil 10 includes, for example, a copper alloy foil 11 as a rolled copper foil made of a copper alloy, and copper (Cu) plating made of pure copper formed on both surfaces of the copper alloy foil 11 respectively. Layers 12a and 12b.

  The copper alloy foil 11 is made of, for example, a high heat resistant solid solution type copper alloy or a precipitation type copper alloy. Examples of the copper alloy foil 11 include a rolled copper foil containing zirconium (Zr), chromium (Cr), zinc (Zn), phosphorus (P) and the like. More specifically, HCL02Z foil (containing 0.015 mass% to 0.030 mass% of Zr) manufactured by Hitachi Cable, Ltd. can be used (HCL is a registered trademark).

  Roughened particles 13a and 13b as granular electrodeposits are attached to the respective surfaces of the first Cu plated layers 12a and 12b, and further, second Cu plated layers 13a ′ and 13b ′ (not shown) are roughened particles 13a and 13b. It is provided sufficiently thin so as to cover 13b. Furthermore, the Ni—Co alloy plating layers 14a and 14b are provided sufficiently thin in such a form as to cover the particles of the roughened particles 13a and 13b (and the second Cu plating layers 13a ′ and 13b ′). When the surface roughness Ra (μm) of the negative electrode current collector copper foil 10 is a ratio Cb (wt%) in the negative electrode active material layers 15a and 15b, Cb ≧ 38 × Ra × Ra−1.2 × Ra (Formula 1) ) Is satisfied. The rough particles 13a and 13b are metal particles containing, for example, Cu, iron (Fe), and the like, and are formed by rough plating or the like. Here, the surface roughness Ra is an “arithmetic average roughness Ra” defined in JIS B0601, and is a value measured after forming Ni—Co alloy plating layers 14a and 14b described later. The arithmetic average roughness Ra (μm) of the negative electrode current collector copper foil 10 after the formation of the Ni—Co alloy plating layers 14a and 14b is almost equal to the roughness of the roughened particles 13a and 13b in the order of the second decimal place. It is equivalent.

The mass thickness of the Ni—Co alloy plating layers 14a and 14b is 20 μg / cm ² or more and 40 μg / cm ² or less. Here, the mass thickness represents the thickness of the Ni—Co alloy layers 14 a and 14 b by the mass of the Ni—Co alloy present per unit area of the surface of the negative electrode current collector copper foil 10. The mass per unit area can be obtained by quantitative analysis using, for example, high frequency inductively coupled plasma emission spectroscopy (ICP emission spectroscopy).

As described above, in the present embodiment, as the copper alloy foil 11, a rolled copper foil made of, for example, a high heat resistant copper alloy is used. High yield strength is obtained by using the copper alloy foil 11 by rolling, for example, even if the negative electrode active material layers 15a and 15b shown in FIG. 2 repeat volume expansion / contraction due to insertion and extraction of Li ⁺ ions, Plastic deformation of the negative electrode current collector copper foil 10 can be suppressed. Therefore, the negative electrode active material layers 15a and 15b are unlikely to drop off from the negative electrode current collector copper foil 10, and the dimensional stability of the lithium ion secondary battery 50 can be improved.

  In order to suppress the volume change due to charge / discharge as described above, for example, even if the above-described Sn or Si alloy or the like is used as the negative electrode active material layer, the increase in charge / discharge capacity and the decrease in volume change during charge / discharge Balancing is difficult. Therefore, in order to achieve a high-capacity lithium ion secondary battery, it is necessary to allow the volume change of the negative electrode active material layer to some extent. The allowable amount of volume change is determined by the yield strength and thickness of the negative electrode current collector copper foil such as a copper foil. As the copper foil, an electrolytic copper foil and a rolled copper foil are known, but no practical copper foil having a high yield strength has been found in the electrolytic copper foil.

  On the other hand, rolled copper foil can easily have high yield strength by work hardening. In addition, in the case of rolling, it is possible to produce a solid solution type copper alloy, a precipitation type copper alloy, etc. by blending additive elements, and relatively easily produce a high strength rolled copper foil made of a copper alloy. be able to.

  Further, as in the present embodiment, the copper alloy foil 11 is made of a highly heat-resistant copper alloy, so that the heat resistance is increased as compared with the case where pure copper or the like is used. In the manufacturing process of the negative electrode 1 for a lithium ion secondary battery containing, it is possible to suppress the negative electrode current collector copper foil 10 from being softened, or to maintain a relatively high yield strength even if softening occurs. it can.

  For example, in the case of the HCL02Z foil, even after heat that softens the pure copper foil is applied, the 1% yield strength can be maintained at 480 MPa, which is equivalent to that immediately after rolling. In addition, even after softening by heat treatment at a high temperature of 400 ° C. or higher and for a long time as described in Patent Document 4 above, it is possible to maintain a yield strength that is 100 MPa or more higher than that of an electrolytic copper foil or pure copper foil. Here, the 1% proof stress is obtained by, for example, the “total elongation method” defined in JIS Z2241.

  Thus, unlike the method of Patent Document 4 in which the heat resistance is improved by increasing the thickness of the composite foil (current collector copper foil), in this embodiment, by using the copper alloy foil 11, high strength resistance and The negative electrode current collector copper foil 10 can be thinly formed while ensuring high heat resistance. Therefore, more negative electrode active material layers 15 a and 15 b can be accommodated in the lithium ion secondary battery 50, which can contribute to an increase in capacity of the lithium ion secondary battery 50.

In the present embodiment, the surface roughness Ra (μm) of the negative electrode current collector copper foil 10 satisfies the following expression in relation to the binder ratio Cb (wt%) in the negative electrode active material layers 15a and 15b.
Cb ≧ 38 × Ra × Ra−1.2 × Ra (formula 1)
However, 0.10 ≦ Ra ≦ 0.72 and 2 ≦ Cb ≦ 20 are satisfied.

  As an example, the surface of the negative electrode current collector copper foil 10 to which the first Cu plating layers 12a and 12b, the roughened particles 13a and 13b, the second Cu plating layers 13a ′ and 13b ′, and the Ni—Co alloy plating layers 14a and 14b are sequentially attached. The roughness Ra (μm) is Cb ≧ 38 × Ra × Ra−1.2 × Ra (Formula 1), where Cb is the binder ratio (wt%) in the negative electrode active material layers 15a and 15b. Thereby, adhesiveness with the below-mentioned negative electrode active material layers 15a and 15b formed on the negative electrode current collection copper foil 10 can be improved.

In the present embodiment, for example, Ni—Co alloy plating layers 14 a and 14 b are formed on the second Cu plating layers 13 a ′ and 13 b ′ with a mass thickness of 20 μg / cm ² or more and 40 μg / cm ² or less. Thereby, the surface of the negative electrode current collection copper foil 10 becomes difficult to be oxidized. That is, it is possible to suppress the formation of an oxide film on the surface of the negative electrode current collector copper foil 10 due to the heat treatment in the manufacturing process of the negative electrode 1 and to improve the welding strength with the tab lead 16.

  In addition, since the Ni—Co alloy plating layers 14 a and 14 b are formed on the second Cu plating layers 13 a ′ and 13 b ′, the roughened particles 13 a and 13 b are difficult to drop off, and the lithium ion secondary battery 50 enters the lithium ion secondary battery 50. It is possible to suppress a short circuit between the positive and negative electrodes due to the mixing of the metal particles such as the roughened particles 13a and 13b.

The effect of the Ni—Co alloy plating layers 14 a and 14 b suppressing the roughening particles 13 a and 13 b from dropping is higher than that of the Cu plating layer and the like. In order to obtain such an effect, the Cu plating layer needs to be about 50 nm, for example, whereas the Ni—Co alloy plating layers 14a and 14b have a thickness of 20 nm or more (corresponding to less than 20 μg / cm ² ), for example. I just need it. On the other hand, if the Ni—Co alloy plating layers 14a and 14b are too thick, for example, 50 nm or more (corresponding to less than 50 μg / cm ² ), the surface of the negative electrode current collector copper foil 10 is flattened, and the negative electrode active material layers 15a, 15b, Adhesiveness with 15b will fall. In the present embodiment, as described above, the mass thickness of the Ni—Co alloy plating layers 14a and 14b is set to 20 μg / cm ² or more and 40 μg / cm ² or less, so the surface of the negative electrode current collector copper foil 10 after Cu plating Roughness Ra is hardly changed, and the thickness is necessary and sufficient to suppress dropping of the roughened particles 13a and 13b.

Also in this respect, the above-mentioned Patent Document 4 in which the Co—Ni alloy plating layer is formed in a thickness of 0.5 μm to 5 μm mainly focusing on the improvement of heat resistance of the composite foil (current collector copper foil), and 40 μg / cm ^2. The purpose and configuration are different from those of the present embodiment in which the Ni—Co alloy plating layers 14 a and 14 b are formed below (about several tens of nm).

  As described above, in this embodiment, it is possible to suppress the falling off of the roughened particles 13a and 13b while maintaining high adhesion to the negative electrode active material layers 15a and 15b, and the welding strength with the tab lead 16 is increased. Can be improved.

(3) Manufacturing method of negative electrode current collection copper foil for lithium ion secondary batteries Next, the manufacturing method of the negative electrode current collection copper foil 10 for lithium ion secondary batteries is demonstrated, referring FIG.

(Rolling process)
First, for example, a highly heat-resistant solid solution type copper alloy or a precipitation type copper alloy is rolled to produce a copper alloy foil 11 as a rolled copper foil shown in FIG. That is, when forming a copper alloy foil 11 such as HCL02Z foil containing Zr made by Hitachi Cable, for example, an oxygen-free copper casting facility is used, and the copper alloy is used in an environment where active metals such as Zr are not oxidized. Is cast into a cake. Next, after hot rolling this cake, it is rolled to a predetermined thickness while repeating cold rolling and annealing, and the rolling oil is removed by washing with a solvent to obtain a copper alloy foil 11.

(Cu plating process)
Next, Cu plating is performed using the copper alloy foil 11 as a cathode, the first Cu plating layers 12a and 12b are formed on, for example, both surfaces of the copper alloy foil 11, and the surface of the first Cu plating layers 12a and 12b is formed as a granular electrodeposit. The roughened particles 13a and 13b are attached. Further, second Cu plating layers 13a ′ and 13b ′ are formed so as to cover the roughened particles 13a and 13b.

That is, roughening by electrolytic Cu plating is performed in three stages on the surface of the copper alloy foil 11 subjected to electrolytic degreasing and acid cleaning while the copper alloy foil 11 is conveyed in a coil-to-coil manner. In the first stage, Cu plating for flattening the surface of the copper alloy foil 11 is performed to form the first Cu plating layers 12a and 12b. Next, in the second stage, small rough particles 13a and 13b with a diameter of about 0.8 μm, for example, are attached as representative values. In the third stage, the second Cu plating layers 13a ′ and 13b ′ are attached so as to cover the periphery of the roughened particles 13a and 13b, and the roughened particles 13a and 13b are enlarged so as to have a representative value of, for example, about 1 μm in diameter. Let Specifically, in the first stage and the third stage, for example, electrolysis is performed using a copper sulfate (CuSO ₄ ) plating solution at a current density of several A / dm ^{2. In} the second stage, for example, iron is added to the copper sulfate plating solution. Electrolysis is performed at a high current density of 20 A / dm ² or more and 40 A / dm ² or less by blending (Fe ²⁺ ) ions. The processing time is, for example, not less than 3 seconds and not more than 12 seconds in each stage.

About the surface roughness Ra (micrometer) of the negative electrode current collection copper foil 10, the following formula | equation is satisfy | filled in relation with the ratio Cb (wt%) of the binder in the negative electrode active material layers 15a and 15b.
Cb ≧ 38 × Ra × Ra−1.2 × Ra (formula 1)
However, 0.10 ≦ Ra ≦ 0.72 and 2 ≦ Cb ≦ 20 are satisfied.

  For example, the negative electrode collector in which the first Cu plating layers 12a and 12b, the roughened particles 13a and 13b, the second Cu plating layers 13a ′ and 13b ′, and the Ni—Co alloy plating layers 14a and 14b are sequentially attached on the copper alloy foil 11. The surface roughness Ra (μm) of the copper foil 10 is Cb ≧ 38 × Ra × Ra−1.2 × Ra (Formula 1), where Cb is the binder ratio (wt%) in the negative electrode active material layers 15a and 15b. It has become. By setting it as such surface roughness Ra, adhesiveness with the negative electrode active material layers 15a and 15b formed on the negative electrode current collection copper foil 10 later can be improved.

  Here, even if it is the copper alloy foil 11 before performing Cu plating, surface roughness Ra is about 0.15 micrometer in the state after rolling. However, in this state, sufficient adhesion to the negative electrode active material layers 15a and 15b cannot be obtained even when the negative electrode active material layer having a binder ratio satisfying the relationship of (Formula 1) is formed. As described above, by attaching the roughened particles 13a and 13b to the surface of the copper alloy foil 11, the adhesion is improved by a wedge-like function (anchor effect) due to the material entering the voids of the uneven surface. .

  At this time, if the amount of Cu plating in the third stage is too large, the size of the roughened particles 13a and 13b becomes too large, and the surface roughness Ra of the negative electrode current collector copper foil 10 becomes too large. As described above, when the surface roughness Ra exceeds the upper limit, not only the effect of improving the adhesion to the negative electrode active material layers 15a and 15b can be obtained, but the adhesion may be lowered. On the other hand, in order to keep the coarse particles 13a and 13b small, the second Cu plating layers 13a ′ and 13b ′ are formed by reducing the third-stage plating amount or omitting the third-stage treatment. Compared to the case, the roughened particles 13a and 13b are more likely to fall off.

  In the present embodiment, the Ni—Co alloy plating layers 14a and 14b having a high effect of preventing the roughening particles 13a and 13b from falling off so as to cover the roughening particles 13a and 13b (or the second Cu plating layers 13a ′ and 13b ′). Are formed, and the drop of the roughened particles 13a and 13b is suppressed without substantially changing the surface roughness Ra set to a desired value by the Cu plating. A method of forming the Ni—Co alloy plating layers 14a and 14b will be described.

(Nickel-cobalt alloy plating process)
While transporting the copper alloy foil 11 in a coil-to-coil manner, electrolytic plating is performed on, for example, both surfaces of the copper alloy foil 11 subjected to Cu plating as described above to form the Ni—Co alloy plating layers 14 a and 14 b. . In such electrolytic plating, for example, a plating solution obtained by mixing a nickel sulfate (NiSO ₄ ) solution, a cobalt sulfate (CoSO ₄ ) solution, and a sodium citrate (Na ₃ (C ₃ H ₅ O (COO) ₃ ) solution is used. Electrolysis is performed at a current density of A / dm ^2. The treatment time is, for example, 3 seconds or more and 12 seconds or less.

Thereby, for example, Ni—Co alloy plating layers 14 a and 14 b having a mass thickness of 20 μg / cm ² or more and 40 μg / cm ² or less are formed. The Ni—Co alloy plating layers 14a and 14b can prevent the roughening particles 13a and 13b from falling off. In addition, the surface of the negative electrode current collector copper foil 10 is less likely to be oxidized, and the adhesion with the tab lead 16 can be improved to improve the welding strength. Moreover, since the mass thickness of the Ni—Co alloy plating layers 14a and 14b is set to 40 μg / cm ² or less, the flatness of the negative electrode current collector copper foil 10 is suppressed, and the adhesion to the negative electrode active material layers 15a and 15b is improved. It can be maintained sufficiently.

As described above, the copper alloy foil 11, the first Cu plated layers 12 and 12b formed on both surfaces of the copper alloy foil 11, the roughened particles 13a and 13b formed on the first Cu plated layers 12a and 12b, and the roughened A second Cu plating layer 13a ′, 13b ′ for covering the particles 13a, 13b and enlarging the roughened particles 13a, 13b; and a Ni—Co alloy plating layer 14a, 14b for covering the second Cu plating layers 13a ′, 13b ′. Regarding the surface roughness Ra (μm) of the negative electrode current collector copper foil 10, the negative electrode current collector for a lithium ion secondary battery that satisfies the following formula in relation to the binder ratio Cb (wt%) in the negative electrode active material layers 15 a and 15 b Copper foil 10 is manufactured.
Cb ≧ 38 × Ra × Ra−1.2 × Ra (formula 1)
However, 0.10 ≦ Ra ≦ 0.72 and 2 ≦ Cb ≦ 20 are satisfied.

(4) Manufacturing method of negative electrode for lithium ion secondary battery Next, the manufacturing method of the negative electrode 1 for lithium ion secondary batteries provided with the structure shown in FIG. 2 is demonstrated.

(Formation process of negative electrode active material layer)
First, a method for forming the negative electrode active material layers 15a and 15b by applying a slurry to the negative electrode current collector copper foil 10 will be described. Such a process is performed using an apparatus such as an applicator that applies slurry to the negative electrode current collector copper foil 10 by, for example, a continuous line of a coil-to-coil system.

  Specifically, for example, a negative electrode active material, a binder solution, and a slurry kneaded with a conductive aid as necessary, are applied to both surfaces of the negative electrode current collector copper foil 10, and are uniformly crimped to a substantially uniform thickness. For example, it is dried at 70 ° C. to 130 ° C. for several minutes to several tens of minutes.

  As the negative electrode active material contained in the slurry, for example, an alloy such as Sn or Si, or a powder such as a compound can be used. The diameter of each powder is, for example, several μm to several tens of μm. As the binder solution, a solution of a precursor of an imide resin such as polyimide (PI) or other resin can be used.

  From the viewpoint of battery capacity, when it is desired to mix as much negative electrode active material as possible, the amount of the binder solution is preferably small. Of the non-volatile components remaining on the negative electrode current collector copper foil 10 after the drying process or the like, the proportion of the binder component (hereinafter referred to as the binder proportion) (wt%) can be set to 2.1 wt%, for example. .

  When the surface roughness Ra of the negative electrode current collector copper foil 10 takes a value larger than Ra defined in (Expression 1) for an arbitrary binder ratio Cb (wt%) defined in (Expression 1), There may be cases where the adhesion with the negative electrode active material layers 15a and 15b is not improved or the adhesion is lowered. As a cause of the adhesion behavior, a small amount of the binder solution with respect to the negative electrode active material can be mentioned. That is, if the surface roughness Ra of the negative electrode current collector copper foil 10 is large and the surface irregularities are deep, the binder solution cannot reach the back, so that the binder solution mainly stays in the vicinity of the convex portion. As a result, the binder It is considered that the contact area between the component and the surface of the negative electrode current collector copper foil 10 is reduced, and the adhesion cannot be increased.

  When the binder ratio can be increased, the surface roughness Ra of the negative electrode current collector foil 10 may be increased within a range that satisfies (Equation 1).

  In the present embodiment, the negative electrode active material layer 10 is subjected to Cu plating so that the surface roughness Ra of the negative electrode current collector copper foil 10 becomes an appropriate value in relation to the binder ratio Cb in the negative electrode active material layers 15a and 15b. By providing the Ni—Co alloy plating layers 14 a and 14 b while maintaining high adhesion with 15 a and 15 b, it is possible to suppress the falling off of the roughened particles 13 a and 13 b.

Next, for example, using an infrared heating furnace or the like, the negative electrode current collector copper foil 10 to which the slurry is pressure-bonded is subjected to heat treatment for a long time at a high temperature. At this time, in order to suppress oxidation of the exposed surface of the negative electrode current collector copper foil 10 welded to the tab lead 16, the heat treatment is performed in a non-oxidizing atmosphere such as nitrogen (N ₂ ) gas or argon (Ar) gas. Do. Thereby, for example, an imidization reaction of a binder component made of a precursor such as an imide resin proceeds and solidifies, and the negative electrode active material containing the negative electrode active material and the imidized binder component on both surfaces of the negative electrode current collector copper foil 10. Material layers 15a and 15b are formed.

  In the above heat treatment, if the second Cu plating layers 13a ′ and 13b ′ of the negative electrode current collector copper foil 10 are exposed, even if the heat treatment is performed in a non-oxidizing atmosphere as described above, it is affected by residual oxygen or the like. The surface may be oxidized. Therefore, in the present embodiment, the surface of the second Cu plating layers 13a ′ and 13b ′ is configured to be covered with the Ni—Co alloy plating layers 14a and 14b. Thereby, even if it heat-processes for a long time and high temperature to the negative electrode current collection copper foil 10, the surface becomes difficult to be oxidized.

  As described above, in this embodiment, for example, Sn or Si alloy or the like is used as the negative electrode active material layers 15a and 15b, and the lithium ion secondary battery 50 is required to have a high temperature and a long-time heat treatment. When forming the negative electrode active material layers 15a and 15b, the oxidation of the negative electrode current collector copper foil 10 formed of Cu is suppressed by the Ni—Co alloy plating layers 14a and 14b. Therefore, it is possible to improve the welding strength with the tab lead and extend the life of the lithium ion secondary battery 50.

(Tab lead welding process)
Next, a method of welding the tab lead 16 to the negative electrode current collector copper foil 10 will be described with reference to FIG.

   As shown in FIG. 2, the negative electrode current collector copper foil 10 having the negative electrode active material layers 15 a and 15 b formed on both sides thereof is an exposed region in which the negative electrode active material layers 15 a and 15 b are not formed on at least one side or one end of both sides. 10s. The tab lead 16 is welded to the exposed region 10 s of the negative electrode current collector copper foil 10 in order to establish electrical connection with the battery insertion can 5 provided in the lithium ion secondary battery 50.

  That is, the exposed region 10 s of the negative electrode current collector copper foil 10 and the tab lead 16 made of, for example, Ni or Ni-plated copper are overlapped, and the predetermined pressure and load energy are applied, for example, with an ultrasonic welding machine. The welding process is performed with a load time of. Thereby, the negative electrode current collection copper foil 10 and the tab lead 16 are welded. In this embodiment, since the oxidation of the negative electrode current collector copper foil 10 surface is suppressed by the Ni—Co alloy plating layers 14 a and 14 b covering the surface of the negative electrode current collector copper foil 10, the tab lead 16 is welded with high welding strength. be able to.

  Thus, in this embodiment, since the welding strength with the tab lead 16 is improved, for example, the tab lead 16 is peeled off when the lithium ion secondary battery 50 is manufactured or used, so that current cannot be taken out from the battery. Problems can be reduced.

Such an improvement in the welding strength with the tab lead 16 is obtained, for example, when the mass thickness of the Ni—Co alloy plating layers 14a and 14b is 20 μg / cm ² or more. By setting the mass thickness to 20 μg / cm ² or more, the lower layer Cu hardly diffuses into the Ni—Co alloy plating layers 14a and 14b even when heat treatment is performed for a long time at a high temperature. This is because the formation of an alloy of Ni or Co with Cu that hinders exposure can be suppressed.

  Further, since the new surface is easily exposed when ultrasonic waves are applied, sufficient welding strength with the tab lead 16 can be obtained even in a relatively short welding time. If the welding time is shortened, the manufacturing throughput is increased, and damage to the negative electrode current collector copper foil 10 during welding can be reduced. Accordingly, it is possible to reduce problems such as the negative electrode current collector copper foil 10 being easily broken.

Further, when the mass thickness of the Ni—Co alloy plating layers 14 a and 14 b is larger than, for example, 40 μg / cm ² , the effect of improving the welding strength with the tab lead 16 is saturated. Therefore, by setting the mass thickness of the Ni—Co alloy plating layers 14a and 14b to 40 μg / cm ² or less, waste of expensive materials such as Ni and Co can be suppressed, and the manufacturing cost can be reduced.

  As described above, the negative electrode current collector copper foil 10 for the lithium ion secondary battery, the negative electrode active material layers 15a and 15b formed on, for example, both surfaces of the negative electrode current collector copper foil 10, and the tab lead connected to the negative electrode current collector copper foil 10 16, and the negative electrode 1 for lithium ion secondary batteries is manufactured.

(5) Manufacturing Method of Lithium Ion Secondary Battery Next, a manufacturing method of the lithium ion secondary battery 50 will be described with reference to FIG. Here, the cylindrical lithium ion secondary battery 50 shown in FIG. 3 will be described as an example, but the lithium ion secondary battery may have other forms such as a square type and a laminate type.

  First, the negative electrode 1 for lithium ion secondary batteries and the positive electrode 2 for lithium ion secondary batteries are overlapped via the separator 3, and the winding body 4 wound around the core which is not shown in figure is manufactured. The positive electrode 2 is connected to a positive electrode current collector metal foil for a lithium ion secondary battery, a positive electrode active material layer formed on, for example, both surfaces of the positive electrode current collector metal foil (both not shown), and the positive electrode current collector metal foil A tab lead 26. The metal which comprises positive electrode current collection metal foil is aluminum (Al), another metal, etc., for example. The positive electrode active material layer is made of, for example, a metal composite oxide containing Li. The separator 3 is made of, for example, a porous resin.

  Next, a lower insulating plate (not shown) and the wound body 4 are accommodated in this order in a battery extrapolation can 5 as a container. Subsequently, after inserting a mandrel (core metal) (not shown) into the center of the wound body 4 and housing the upper insulating plate in the battery outer can 5, the groove 6 is formed (grooved) in the battery outer can 5. . Thereafter, drying is performed to remove moisture in the battery extrapolation can 5. When the inside of the battery extra can 5 is sufficiently dried, an electrolyte solution (not shown) is injected. Next, the gasket 7 is mounted in the vicinity of the groove 6 of the battery outer can 5, the tab lead 16 of the negative electrode 1 is welded to the battery outer can 5, and the tab lead 26 of the positive electrode 2 is welded to the terminal 8 t provided in the cap 8. 8 is crimped (crimped) on the battery extrapolation can 5 to enclose the electrolyte.

  As described above, the lithium ion secondary battery including the battery insertion can 5 in which the negative electrode 1 for the lithium ion secondary battery and the positive electrode 2 for the lithium ion secondary battery with the separator 3 interposed therebetween are accommodated and the electrolyte is enclosed. 50 is manufactured.

<Other Embodiments of the Present Invention>
As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to the above-mentioned embodiment, It can change variously in the range which does not deviate from the summary.

  For example, in the above-described embodiment, the HCL02Z foil manufactured by Hitachi Cable, Ltd. was cited as a specific example of the copper alloy foil 11, but the rolled copper foil made of a copper alloy is not limited to this. When some specific examples are shown from Hitachi Cable, Ltd. products, HCL64T (Cr: 0.20 mass% to 0.30 mass%, Sn: 0.23 mass% to 0.27 mass%, Zn: 0.18 mass% to 0.26 mass%, each contained), HCL305 (2.2 mass% to 2.8 mass% of Ni, 0.3 mass% to 0.7 mass% of Si, and 1. 5 mass% to 2.0 mass%, P is contained 0.015 mass% to 0.06 mass%, respectively (HCL is a registered trademark). In addition to these, a copper alloy foil obtained by adding silver (Ag), Sn, Fe or the like to pure copper can also be used.

  Moreover, in the above-mentioned embodiment, although the copper alloy foil 11 was used as a rolled copper foil, it is also possible to use the rolled copper foil which consists of pure copper. A rolled copper foil made of pure copper is suitable, for example, when the heat treatment included in the negative electrode manufacturing process is relatively gentle.

  In the above embodiment, the negative electrode active material layers 15a and 15b are formed on both surfaces of the negative electrode current collector copper foil 10. However, the negative electrode active material layer may be formed on at least one surface of the negative electrode current collector copper foil. In this case, the Cu plating layer, the roughened particles, the Ni—Co alloy plating layer, and the like may be formed on at least one side of a rolled copper foil such as a copper alloy foil or a copper foil.

  In the above-described embodiment, the second Cu plating layers 13a ′ and 13b ′ are further provided on the roughened particles 13a and 13b at the time of Cu plating. However, the second Cu plating layers 13a ′ and 13b ′ are omitted. May be. Even in this case, in the present application, since the Ni—Co alloy plating layers 14a, 14b and the like are separately provided on the rolled copper foil, it is possible to sufficiently suppress the dropping of the roughened particles 13a, 13b. is there.

  Moreover, in the said embodiment, although Ni-Co alloy plating layer 14a, 14b was formed on the copper alloy foil 11, even if it is Ni plating layer, Co plating layer, etc., adhesiveness with a tab lead is improved, and An effect substantially equivalent to that of the Ni—Co alloy plating layers 14a and 14b, which suppresses the dropping of the granular electrodeposits, can be obtained.

  The evaluation results of the adhesion with the negative electrode active material layer of the negative electrode current collector copper foil for a lithium ion secondary battery according to the example of the present invention, the welding strength with the tab lead, and the retention of the roughened particles will be described below.

(1) Production of negative electrode current collector copper foil First, according to the procedure described below, negative electrode current collector copper foils according to Examples 1 to 8, Comparative Examples 1 to 6, Examples 9 to 33, and Comparative Examples 7 to 16 were prepared. Produced.

  As a copper alloy foil used for evaluation, an HCL02Z foil manufactured by Hitachi Cable Co., Ltd. was manufactured to a thickness of 12 μm and a Zr content of 0.02 mass% by the same method as in the above embodiment. The Zr content is obtained by collecting a part of the cake obtained by melt casting and quantitatively analyzing it by solid-state emission spectroscopy.

  Next, electrolytic degreasing, acid cleaning, Cu plating, and Ni—Co alloy plating are performed on the copper alloy foil by a continuous line of a coil-to-coil method using the same method as in the above-described embodiment. A negative electrode current collector copper foil was produced. In Cu plating and Ni—Co alloy plating, centering on the conditions shown in Table 1 below, omission of predetermined steps or change of current density, processing time, etc. It was set to 16. The Co concentration in the Ni—Co alloy plating was 40% to 60%.

  Moreover, in order to see the effect of plating layers other than a Ni-Co alloy plating layer, what carried out Ni plating and Co plating was made into Example 7 and 8, respectively. The plating was performed by a beaker test on the copper alloy foil after the Cu plating was performed on a continuous line.

(2) Measurement of negative electrode current collector copper foil Various measurements were performed on the negative electrode current collector copper foils according to Examples 1 to 33 and Comparative Examples 1 to 16 manufactured as described above according to the procedures described below.

(Measurement of 1% yield strength)
The negative electrode collector copper foil cut out to 15 mm × 160 mm was heat-treated at 400 ° C. for 10 hours in an N ₂ gas atmosphere by an infrared heating furnace. Such heat treatment simulates the step of forming the negative electrode active material layers 15a and 15b in the above-described embodiment. Thereafter, a “metallic material tensile test” defined in JIS Z2241 was performed on each negative electrode current collector copper foil, and 1% yield strength was determined from the stress-strain diagram by the “total elongation method”.

(Measurement of surface roughness Ra)
Before performing the Ni-Co alloy plating, a part of the copper alloy foil after Cu plating is cut out to 25 mm x 400 mm, the mass is measured, and compared with the mass of the copper alloy foil before Cu plating. The amount of plating was measured. Moreover, using the surface roughness measuring instrument (Keyence Laser Scanning Microscope VK-8700) of the negative electrode current collector copper foil after Ni—Co alloy plating, measurement was performed with an objective lens 100 times, and as data processing, tilt correction and noise were measured. Removal (height cut was set under “normal” conditions) was performed, and “arithmetic mean roughness Ra” in accordance with JIS B0601 was calculated.

(Measurement of mass thickness of nickel-cobalt alloy plating layer)
The negative electrode current collector copper foil cut out to 40 mm × 100 mm was immersed in dilute nitric acid (HNO ₃ ) to dissolve the Ni—Co alloy plating layer, and after appropriate dilution, the plating amount was quantitatively analyzed by ICP emission spectroscopic analysis. From the plating amount, the mass thickness of the Ni—Co alloy plating layer was calculated.

(Measurement of adhesion to negative electrode active material layer)
In Examples 1 to 8 and Comparative Examples 1 to 6, the binder ratio (binder ratio) in the negative electrode active material layers 15a and 15b is 2.1 wt%, and the binder ratio is constant. On the other hand, about Examples 9-33 and Comparative Examples 7-16, the binder ratio is changed.

As an example, Example 1 in which the binder ratio is 2.1 wt% will be described. Simulating the negative electrode active material layers 15a and 15b according to the above-described embodiment, a mixture containing Si was formed on the negative electrode current collector copper foil. That is, a commercially available Si powder having a diameter of 3 μm was mixed with a commercially available polyimide (PI) varnish (an N-methylpyrrolidone (NMP) solution of a PI precursor) at a weight ratio of Si: PI = 9: 1. Then, it apply | coated to 100 micrometers thickness on the said negative electrode current collection copper foil. Next, after drying in the atmosphere at 100 ° C. for 30 minutes to evaporate the solvent, the solution was solidified by heat treatment at 400 ° C. for 10 hours in an N ₂ gas atmosphere in an infrared heating furnace. Note that PI used in the present embodiment was 2.1 wt% in the negative electrode active material layers 15a and 15b generated after drying. When changing the binder ratio, the composition may be determined in consideration of the ratio of the PI that is substantially formed.

  Subsequently, the “cross-cut method” defined in JIS K5600-5-6 was conducted to examine the adhesion with the Si mixture, and the result was schematically taken as the adhesion with the negative electrode active material layer. Specifically, the negative electrode current collector copper foil on which the Si mixture was formed was cut at intervals of 2 mm, and the ratio (%) of the case where the base was not exposed by peeling was obtained, and 72% or more was set as the allowable value.

(Measurement of weld strength with tab lead)
The negative electrode current collector copper foil cut out to 15 mm × 50 mm was subjected to heat treatment at 400 ° C. for 10 hours in an N ₂ gas atmosphere by an infrared heating furnace. Next, a tab lead made of pure Ni having a thickness of 0.1 mm and a size of 4 mm × 50 mm was welded to the negative electrode current collector copper foil using an ultrasonic welder in the same manner as in the above embodiment. The welding conditions are a pressure of 0.2 MPa, a load energy of 20 J, and a load time of 0.29 seconds to 0.35 seconds. A tensile test was performed on the negative electrode current collector copper foil with the tab lead welded to measure the maximum breaking load (gf), and an allowable value was 7 gf or more.

(Measurement of retention of roughened particles)
After rubbing 1 cm while pressing the filter paper against the negative electrode current collector copper foil at a weight of 100 weight grams (gf), ○ (not colored), Δ (slightly colored), × (colored) depending on whether the filter paper is colored ), And only the ○ is the allowable value.

(3) Evaluation results of negative electrode current collector copper foil Table 2 shows the evaluation results of the above measurements.

(Evaluation of rolled copper foil)
In each of Examples 1 to 8 and Comparative Examples 1 to 6 shown in Table 2, the 1% yield strength after heat treatment at 400 ° C. for 10 hours was 300 MPa. This is a yield strength that is 100 MPa or more higher than that of pure copper foil. Thereby, it turned out that the rolled copper foil which consists of copper alloys, such as HCL02Z foil, has high proof stress and high heat resistance.

(Evaluation of Cu plating)
Comparative Examples 1 and 2, Examples 1 to 3, and Comparative Example 3 shown in Table 2 are evaluation results of negative electrode current collector copper foils manufactured by varying the conditions of Cu plating. Here, the quality of each example and comparative example was determined mainly based on adhesion with a negative electrode active material that is easily affected by the state of Cu plating (72% or more is an allowable value).

In Comparative Example 1 in which no Cu plating was performed, the surface roughness Ra was 0.15 μm and was within a predetermined range, but there was no roughening particles, so the adhesion with the negative electrode active material layer was insufficient. doing. Such a lack of adhesion is also observed in Comparative Example 2 (the current density of the second and third stages is 0 A / dm ² ) in which the second and third stages of Cu plating are omitted.

  Examples 1 to 3 and Comparative Example 3 are negative electrode current collector copper foils manufactured by gradually extending the processing time of the Cu plating process from 3 seconds to 12 seconds. In Examples 1 to 3 in which the surface roughness Ra is within the predetermined range, sufficient adhesion with the negative electrode active material layer was obtained, and in Example 2 in which the surface roughness Ra was 0.15 μm, the adhesion was maximized. On the other hand, in the comparative example 3 with the longest processing time, the surface roughness Ra is a value exceeding the predetermined range, and the adhesiveness is rapidly lowered.

  From the above results, when the binder ratio Cb is 2.1 wt%, when the surface roughness Ra of the negative electrode current collector copper foil is 0.10 μm or more and less than 0.30 μm, the negative electrode active material layer It was found that the adhesiveness of the was improved. In Examples 1 to 3 and Comparative Examples 1 to 3, since the mass thickness of the Ni—Co alloy plating layer is set to an appropriate value, both the welding strength with the tab lead and the retention of the roughened particles are all. Good results were obtained.

(Evaluation of nickel-cobalt alloy plating)
Comparative Examples 4 and 5, Examples 4 to 6, and Comparative Example 6 shown in Table 2 are evaluation results of negative electrode current collector copper foils manufactured by variously changing the Ni-Co alloy plating conditions. Specifically, the current density of Ni—Co alloy plating was gradually increased from 0 A / dm ^{2 to} 10 A / dm ² . Here, based on the welding strength (7 gf or more is an allowable value) with a tab lead that is easily affected by the state of Ni—Co alloy plating, the retention of roughened particles (only ○ is an allowable value), The quality of the comparative example was determined.

In Comparative Example 4 in which the Ni—Co alloy plating layer was not formed (current density was 0 A / dm ² ) and in Comparative Example 5 in which the current density was small and the mass thickness of the Ni—Co alloy plating layer was less than the predetermined value, tab lead The welding strength is insufficient. In addition, in both Comparative Examples 1 and 2, some loosening of the roughened particles was observed.

In Examples 4 to 6 in which the mass thickness of the Ni—Co alloy plating layer is within the predetermined range, sufficient welding strength with the tab lead is obtained, and in Example 5 in which the mass thickness is 30 μg / cm ² , the welding strength is maximum. became. Further, in any of Examples 4 to 6, the roughened particles were not removed.

On the other hand, in Comparative Example 6, although the mass thickness of the Ni—Co alloy plating layer was set to 50 μg / cm ² , the weld strength with the tab lead was not improved over that of Examples 4-6. That is, in Comparative Example 6, expensive materials such as Ni and Co are wasted.

From the above results, when the mass thickness of the Ni—Co alloy plating layer is 20 μg / cm ² or more and 40 μg / cm ² or less, the retention of the roughened particles becomes good and the welding strength with the tab lead is improved. It was found that the thickness was necessary and sufficient. In Examples 4 to 6 and Comparative Examples 4 to 6, since the surface roughness Ra by Cu plating was set to an appropriate value, good results were obtained for the adhesion with the negative electrode active material layer. .

(Evaluation of plating layer by Co-Ni alloy plating alternative plating)
In Example 7 having a Ni plating layer and Example 8 having a Co plating layer, as in the case of the Ni—Co alloy plating layer, adhesion to the negative electrode active material layer, welding strength with the tab lead, and roughened particles Good results were obtained for any of the above retention properties.

(Evaluation of adhesion of negative electrode active material when binder ratio is changed)
In Examples 9 to 33 and Comparative Examples 7 to 16 shown in Table 2, (1) Cu plating time is changed for each of the first to third stages of Cu plating. (2) Current density at the time of Cu plating is changed. (3) negative electrode current collector copper having different surface roughness within a range of 0.12 to 0.72 (μm) by performing (3) second or / and third Cu plating a plurality of times, etc. Foil is prepared, and the binder ratio Cb in the negative electrode active material layers 15a and 15b is set to various values of 2 (wt%) to 20 (wt%).

  Examples 9 to 33 show a value of 72% or more in the evaluation of adhesion with the negative electrode active material, and it can be seen that sufficient adhesion is obtained. On the other hand, Comparative Examples 7-16 is less than 72%.

  In Examples 9 to 33 and Comparative Examples 7 to 16, since the mass thickness of the Ni—Co alloy plating layer is set to an appropriate value, the welding strength with the above-described example tab lead and the retention of roughened particles are reduced. In either case, good results were obtained.

As described above, the binder ratio Cb (wt%) and the surface roughness Ra (μm) satisfy the following relationship for those having good adhesion to the negative electrode active material.
Cb ≧ 38 × Ra × Ra−1.2 × Ra (formula 1)
However, 0.10 ≦ Ra ≦ 0.72 and 2 ≦ Cb ≦ 20 are satisfied.

  FIG. 4 shows plots of Examples 9 to 33 and Comparative Examples 7 to 16, with the horizontal axis representing the surface roughness Ra (μm) and the vertical axis representing the binder ratio Cb (wt%). In addition, a curve showing a boundary (threshold) at which the evaluation of adhesion with the negative electrode active material is 72% or more is also shown in FIG.

DESCRIPTION OF SYMBOLS 1 Negative electrode for lithium ion secondary batteries 2 Positive electrode for lithium ion secondary batteries 3 Separator 4 Winding body 5 Battery extrapolation can (container)
6 groove 7 gasket 8 cap 8t terminal 10 negative electrode current collector copper foil for lithium ion secondary battery 11 copper alloy foil (rolled copper foil)
12a, 12b First Cu plating layer 13a, 13b Roughened particles (granular electrodeposits)
13a ', 13b' Second Cu plating layer 14a, 14b Ni-Co alloy plating layer 15a, 15b Negative electrode active material layer 16, 26 Tab lead 50 Lithium ion secondary battery

Claims (8)

A negative electrode for a lithium ion secondary battery comprising a negative electrode current collector copper foil for a lithium ion secondary battery, and a negative electrode current collector copper foil for the lithium ion secondary battery, and a negative electrode active material layer containing a binder,
The negative electrode current collector copper foil for a lithium ion secondary battery includes a rolled copper foil made of copper or a copper alloy, a first Cu plating layer provided at least in order of the rolled copper foil, roughened particles, and a second Cu plating layer. And further comprising either a nickel-cobalt alloy plating layer, a nickel plating layer, or a cobalt plating layer,
When the binder ratio Cb (wt%) is Cb, the surface roughness Ra is
Cb ≧ 38 × Ra × Ra−1.2 × Ra (formula 1)
(However, 0.10 ≦ Ra ≦ 0.72 and 2 ≦ Cb ≦ 20 are satisfied)
A negative electrode for a lithium ion secondary battery. A negative electrode current collector copper foil for a lithium ion secondary battery, which is used as a negative electrode for a lithium ion secondary battery by being used together with a negative electrode active material layer containing a binder,
Rolled copper foil made of copper or copper alloy;
A first Cu plating layer provided at least in order of the rolled copper foil, roughened particles, and a second Cu plating layer,
With a nickel-cobalt alloy plating layer, a nickel plating layer, or a cobalt plating layer,
When the binder ratio Cb (wt%) is Cb, the surface roughness Ra is
Cb ≧ 38 × Ra × Ra−1.2 × Ra (formula 1)
(However, 0.10 ≦ Ra ≦ 0.72 and 2 ≦ Cb ≦ 20 are satisfied)
The negative electrode current collection copper foil for lithium ion secondary batteries characterized by the above-mentioned. 3. The lithium ion secondary material according to claim 2, wherein a mass thickness of the nickel-cobalt alloy plating layer, the nickel plating layer, and the cobalt plating layer is 20 μg / cm ² or more and 40 μg / cm ² or less. Negative electrode current collector copper foil for secondary batteries. The said copper alloy which comprises the said rolled copper foil is a high heat resistant copper alloy, The negative electrode current collection copper foil for lithium ion secondary batteries of Claim 2 or 3 characterized by the above-mentioned. The negative electrode current collector copper foil for a lithium ion secondary battery according to any one of claims 2 to 4, wherein the first Cu plating layer is made of pure copper. A negative electrode current collector copper foil for a lithium ion secondary battery according to claim 2,
A negative electrode active material layer formed on at least one surface of the negative electrode current collector copper foil for the lithium ion secondary battery;
A negative electrode for a lithium ion secondary battery, comprising: a tab lead connected to the negative electrode current collector copper foil for the lithium ion secondary battery. A negative electrode for a lithium ion secondary battery according to claim 6,
A positive electrode for a lithium ion secondary battery;
A separator inserted between the negative electrode for lithium ion secondary battery and the positive electrode for lithium ion secondary battery;
A lithium ion secondary battery comprising: a negative electrode for a lithium ion secondary battery in which the separator is inserted; and a container in which the positive electrode for a lithium ion secondary battery is accommodated and an electrolyte is enclosed. . Cu plating step using a rolled copper foil made of copper or copper alloy as a cathode, and providing a first Cu plating layer, roughened particles, and a second Cu plating layer at least in order of the rolled copper foil,
Forming a nickel-cobalt alloy plating layer, a nickel plating layer, or a cobalt plating layer on the second Cu plating layer so as to cover the roughened particles and the second Cu plating layer. A method for producing a negative electrode current collector copper foil for a lithium ion secondary battery.