JP2003282064A - Compound current collector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compound current collector of resin and a metal in which junctions of lead wires have only to be put on either a front or back face, and which can be made more lightweight than a metallic foil, and moreover, to provide the compound current collector which can respond also to a demand for thinning. <P>SOLUTION: By forming electric conduction treatment layers 12a and 12b on both faces of a resin film 11 with many through-holes 15, and after forming metal-plating layers 13a, 13b and 13c on the electric conduction treatment layers by an electrolysis metal-plating treatment, the compound current collector has a surface electric resistance of 40 mΩ/cm or less, a tensile strength of 0.8 kg/cm, and a front-back resistance of the electric conduction of 100 mΩ/cm or less, and a formula Y1+Y2+Y3≤0.8×(X1+X2+X3)×Y3/X3 is satisfied further. Here, X1 is the thickness of the resin film (μm), X2 is the thickness (μm) of the electric conduction treatment layer, X3 is the thickness (μm) of the metal- plating layer, Y1 is the weight (mg/cm<SP>2</SP>) of the resin film, Y2 is the weight (mg/cm<SP>2</SP>) of the electric conduction treatment layer, and Y3 is the weight (mg/cm<SP>2</SP>) of the metal-plating layer. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite current collector used in a lithium secondary battery or the like, and more particularly to a composite current collector having excellent front and back electrical conductivity.

[0002]

2. Description of the Related Art In recent years, as electronic devices such as telephones, personal computers, and video cameras have become portable, various electronic devices have been downsized, and it has been strongly demanded to reduce the weight of built-in secondary batteries such as lithium or nickel hydride. It became so. For example, a lithium secondary battery is a negative electrode plate obtained by holding the above negative electrode material on a negative electrode current collector that is a support thereof, a positive electrode that reversibly electrochemically reacts with lithium ions like a lithium cobalt composite oxide. It is composed of a positive electrode plate in which an active material is held by a positive electrode current collector which is a support thereof, and a separator which holds an electrolytic solution and is interposed between the negative electrode plate and the positive electrode plate to prevent a short circuit between both electrodes.

In the case of a strip-shaped or cylindrical battery, the positive electrode plate, the separator, and the negative electrode plate are all formed in the order of thin sheets or foils, and are spirally wound into a battery case. It is stored. Therefore, the electrode plate is generally formed by mixing an active material or a host material with an organic binder, a conductive agent and a solvent to form a paste, coating the paste on the surface of the support, drying the paste, and pressing it in the thickness direction together with the support. It is manufactured by molding. Conventionally, a foil of a metal such as copper or aluminum has been used as the collector of the electrode plate because the collector itself needs conductivity.

In order to reduce the weight of such a battery, it is essential to reduce the weight of the current collector, which occupies a considerable portion of the total weight of the battery. For example, in a lithium polymer battery, the negative electrode current collector alone occupies about 20% of the total battery weight, which is about the same as the negative electrode active material, and the weight reduction of the current collector has a great effect on the weight reduction of the battery.

As an attempt to reduce the weight of the current collector, for example, as described in JP-A-5-31494, there has been proposed a method of laminating an ultrathin film on a resin by vapor deposition of metal or sputtering. However, in this method, the upper limit of the metal laminated thickness is about 2000 Å from the viewpoint of economy and heat resistance of the resin, and the conductive layer must be an extremely thin metal layer, and the current collecting ability is obviously poor. Not only is the problem that the ultra-thin metal layer is partially dissolved and disappeared due to corrosion in the battery over time, and the current collecting ability is further reduced.Because a resin film that is an insulator is used for the core, Since the electrical conductivity between the metal plating layers is poor, to connect both the front and back sides to the current collecting surface, the terminal and the lead wire of the current collector can be joined to either one of the front and back surfaces with a general metal foil. Differently, it needs to be done on both sides Say to the process in complex, new problems have arisen.

[0006]

An object of the present invention is to solve the above-mentioned problems of the conventional current collectors.
Similar to the metal foil generally used as a current collector,
The purpose of the present invention is to provide a composite current collector made of resin and metal, which can be connected to only one side of the front and back, and can be lighter than the metal foil. Another object is to provide a composite current collector that can meet the demand for thinning.

[0007]

Means for Solving the Problems The inventors of the present invention have made earnest studies on the above problems, and as a result, provided a resin film with a large number of through holes, and performed conductive treatment on both surfaces of the resin film having the large number of through holes. After forming the layer, by forming an appropriate amount of metal plating layer by electrolytic plating, the front and back metal plating layers conduct electricity to each other, and the lead wire can be bonded on only one of the front and back surfaces, and also has a good current collecting function. It was found that such a complex current collector can be obtained. The reason why the metal plating layers on both sides were electrically connected to each other was as follows.By observing the through-hole portion of the current collector with a microscope, the wraparound during plating and the formation of a conductive treatment layer up to the inside of the hole not only on the front and back sides but also inside the hole. This is probably because the metal plating layers that join the metal plating layers on the front and back sides were formed. It was also found that even if the inside of the hole is filled with a conductive treatment layer, the electric current can be fulfilled to the front and back metal plating layers. Further, the present inventors have found that the conductivity is not only necessary, but the electric resistance between the front and back sides must be below a certain level. Furthermore, the thickness and weight of the resin film, the conductive treatment layer, and the metal plating layer,
By taking into consideration the strength of the material after metal plating and the electric resistance per unit length, it is easy to assemble it as a battery using the current collector, and the lead wires need only be joined to the front and back surfaces. It was discovered that a composite current collector can be obtained that exhibits a sufficient function as a body.

That is, in the composite current collector of the present invention, a conductive treatment layer is formed on both sides of a resin film having a large number of through holes, and a metal plating layer is formed on the conduction treatment layer by electrolytic plating. , Surface electrical resistance of 40 mΩ / cm or less, tensile strength of 0.8 kg / cm, front and back conduction resistance of 100 mΩ
/ Cm or less and further satisfies the following expression (1). Y1 + Y2 + Y3 ≦ 0.8 × (X1 + X2 + X3) × Y3 / X3 (1) where X1: thickness of resin film (μm), X2: thickness of conductive treatment layer (μm), X3: thickness of metal plating layer ( μm), Y1: weight of resin film (mg / cm ² ), Y2: weight of conductive treatment layer (mg / cm ² ), Y3: weight of metal plating layer (mg / cm ² ). The composite current collector according to claim 2 is characterized in that the through hole is filled with a conductive treatment layer. A composite current collector according to a third aspect of the present invention is characterized in that a conductive treatment layer is formed also on the cross section of the through hole, and a metal plating layer is further formed on the conductive treatment layer. The composite current collector according to claim 4, wherein the metal plating layer is Cu, Ni or A.
It is characterized in that it is mainly composed of l. Claim 5
The composite current collector described in (1) is characterized in that the X1, X2, and X3 satisfy the following expression (2). X1 + X2 + X3 ≦ 9 μm (2)

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) The first embodiment of the composite current collector of the present invention will be described in detail.
FIG. 1 is an external perspective view of the composite current collector of the present invention, and FIG. 2 is a cross-sectional view of a main part of the composite current collector in FIG. As shown in FIG. 1, the composite current collector 10 of the present invention has a conductive film 12a, 1a formed on both surfaces of a resin film 11 which is a carrier (core).
2b, metal plating layers 13a and 13b are formed on them, and a lead wire 14 is formed on one surface of the composite current collector 10.

Further, as shown in FIG. 2, a large number of through holes 15 penetrating the resin film 11 are formed in the resin film which is the core forming the composite current collector 10 of the present invention. The 15 surface layers include the front and back conductive treatment layers 12a,
Conductors 16 are formed to provide continuity between the 12b.

Next, examples of the material of the resin film 11 used in the core of the present invention include polyethylene terephthalate (PET), polyethylene naphthalate (PEN),
Preferable examples include polypropylene (PP), polyethylene (PE), and acid-modified olefin resin modified with acrylic acid, maleic acid, etc. However, the present invention is not limited to the above materials, but the type of battery and the required It is determined by the performance etc.

The thickness of the resin film 11 is as follows.
Generally, a material having a range of 2 μm to 20 μm is used, but it is determined in consideration of characteristics required as a current collector of a battery, for example, mechanical strength, light weight, thinness, and the like. It is not limited.

Whether the resin film 11 is stretched or unstretched, or the crystallinity is not particularly limited, but in general, when the collector is required to have mechanical strength, It is preferable to use a stretched film, and when adhesion to the conductive treatment layers 12a and 12b is particularly required, it is preferable to use an unstretched resin film having a low crystallinity.

The resin film 11 as the core used in the present invention has a large number of through holes 15 as shown in FIGS. The through hole 15 serves as a conductive path between the metal plating layers 13a and 13b on the front and back sides, which are formed on the resin film 11 after the conductive treatment layers 12a and 12b are formed on the both surfaces. The hole diameter and number of the through holes 15 should be determined in consideration of the electrical conductivity between the front and back metal plating layers 13a and 13b, mechanical strength, manufacturability, etc., and are not particularly limited here.

The through hole 15 of the resin film 11 can be formed by punching the resin film by press working with an electric discharge machine or a small diameter punch, or by pulling the resin film vertically and horizontally. The through hole 15 of the resin film 11 can also be formed by a means such as pressing a mold provided with a large number of heated needles. However, the through hole 15 can be formed by a method other than the above method, and the processing method thereof is not particularly limited in the present invention.

Next, the conductive treatment layers 12a and 12b formed on the resin film 11 are provided on both sides of the resin film 11 with the metal plating layers 13a and 13b on the front and back sides thereof, with the conductive treatment layers 12a and 12b interposed therebetween. It is provided to form an upper layer. It is preferable to form the conductive treatment layer also in the through hole 15 (cross section) of the resin film 11 because the metal plating layer 13c that electrically joins the metal plating layers 13a and 13b on the front and back is easily formed inside the hole.

The conductive treatment layers 12a and 12b are formed by using an electrically conductive metal such as Cu, Ni, Al or Ag as an ultrathin metal thin film layer by means such as vapor deposition or sputtering. it can. In addition, the conductive treatment layer 1
The formation of 2a and 12b is carried out by using a conductive paint mainly composed of metal powder such as Cu, Ni, Al, Ag, carbon powder of a conductive agent, etc., or a conductive paint obtained by mixing one or more of these. It is also possible to thinly coat the above on the front and back of the resin film 11 in which the through holes 15 are formed to form a conductive coating film layer, but it should be selected depending on the required performance. Further, if necessary, the vapor deposition, on the ultrathin metal thin film layer formed by means such as sputtering, a composite layer in which a conductive coating film layer is formed by means such as coating,
Alternatively, it may be a composite layer in which the ultrathin metal thin film layer is formed on the conductive coating film layer. Also, the through hole 15
After filling (filling) the inside with the metal powder, carbon powder, or the like, an ultrathin metal thin film layer may be formed on the front and back surfaces of the resin film 11 to form the conductive treatment layers 12a and 12b. This is effective in electrically connecting the plating layers 13a and 13b to each other.

The conductive treatment layers 12a and 12b are preferably formed so that the surface electric resistance thereof is 1.3 Ω / cm or less. Surface electrical resistance is 1.3Ω
This is because if it exceeds / cm, it will be difficult to uniformly form the metal plating layers 13a and 13b to be formed thereon as described later.

Next, metal plating layers 13a, 1a, 1b are formed on the conductive treatment layers 12a, 12b by electrolytic plating.
3b is formed. The kind of metal forming the metal plating layer may be a metal such as Cu, Ni or Al electroplated, but it should be selected according to the required performance. When the composite current collector of the present invention is used for a negative electrode as a current collector of a lithium-based secondary battery, Cu is mainly used, and when it is used for a positive electrode, a metal plating layer is formed mainly of Al. When used as a current collector for the positive and negative electrodes of an MH-based secondary battery, it is common to form a metal plating layer mainly containing Ni.

The thickness of these metal plating layers 13a, 13b is such that the surface electric resistance of the metal plating layer after plating is 40 m.
It is preferable that it be Ω / cm or less. The reason is that if the surface electric resistance exceeds 40 mΩ / cm, the battery energy loss due to the resistance is obtained even if the surface electric resistance is used for a small-sized current collector for a secondary battery, that is, even if the used current collector length is short. Is too large to ignore.

The surface electric resistance referred to in the present invention is 1
The resistance per cm width, and the conductive treatment layers 12a and 12b
Or after further forming the metal plating layers 13a and 13b on the measurement surface of the sample having a width of 1 cm, the positive terminal and the negative terminal having an area of 4 mm ² with an interval of 1 cm. Is a value obtained by measuring the electrical resistance by applying a load of 1 kg / cm ² and bringing them into sufficient contact. To measure the surface electric resistance value, it is important to remove the conductive treatment layer and the metal plating layer on the non-measurement surface to eliminate the influence of the non-measurement surface.

Further, in the present invention, the conduction resistance on the front and back sides is set to 100.
It is an important requirement to make it below mΩ. Current resistance is 1
When it exceeds 00 mΩ, when the lead wire 14 is bonded to only one surface of the composite current collector, the current collecting property of the non-bonded surface is remarkably deteriorated, which is a factor of lowering battery performance, which is not preferable.

The conduction resistance referred to in the present invention is 1 cm × 1 c
On one side of the composite current collector in which the + terminal of m size is cut into 1.5 cm × 1.5 cm, the − of 1 cm × 1 cm size is formed.
It is a value obtained by measuring the electrical resistance by applying a load of 1 kg / cm ² to each of the terminals and applying a load of 1 kg / cm ² to each of the other surfaces at the same position as the + terminal. In addition, the composite current collector 10 of the present invention
In, the resin film 11, the conductive treatment layers 12a and 12b, and the metal plating layer 1 which are the constituent elements of the composite current collector 10
Each of 3a and 13b needs to satisfy the relationship of the following expression (1). Y1 + Y2 + Y3 ≦ 0.8 × (X1 + X2 + X3) × Y3 / X3 (1) where X1: the thickness of the resin film (μm), X2: the thickness of the conductive treatment layer (μm), and X3: metal plating Layer thickness (μm), Y1: resin film weight (mg / cm ² ), Y2: conductive treatment layer weight (mg / cm ² ), Y3: metal plating layer weight (mg / cm ² ). cm ² ).

The above formula (1) reduces the weight of the composite current collector of the present invention as compared with the conventional current collector made of only metal by specifying the relationship between the resin film, the conductive treatment layer and the plating layer. It is a conditional expression that can be performed. More specifically, even if the weight of the composite current collector of the present invention is 80% or less with the same thickness, it is possible to realize a weight reduction compared with a mere metal current collector consisting of only metal components of the metal plating layer. is there.

Further, what is required in the present invention is that the composite current collector thus obtained has a tensile strength of 0.8 kg / cm.
That is all. The tensile strength is 0.8 kg / c
If it is less than m, the current collector cannot withstand the tension required for assembling the battery using the current collector,
It is not preferable because the problem of breaking easily occurs. In addition,
The tensile strength referred to here means the yield strength when the composite current collector is cut into a length of 1 cm and a length of 10 cm and pulled at a speed of 20 mm / min. If the collector is required not only to be light but also thin, X1 + X2 + X3 ≦ 9
It is preferable that the conditional expression of μm is satisfied. Generally, it is difficult to stably produce a metal foil having a thickness of 9 μm or less from a single metal, or sufficient tensile strength cannot be obtained in reality, and the composite current collector of the present invention satisfying the conditional expression is satisfied. Is not only lightweight, but also thin, which is very useful. Incidentally, the composite current collector of the present invention need not be limited to a planar shape,
Depending on requirements, it may be corrugated or may have an uneven pattern formed on the surface.

[0026]

Example 1 As a resin film, a 4 μm-thick biaxially stretched PET film (X1 = 4) having 20 μm / mm ² circular through-holes with a diameter of 5 μm was used, and 500 Å each was formed on each side of Cu film. Of the conductive treatment layer (X
2 = 0.1). Furthermore, thickness: 2μ on both sides
Cu of m was plated to form a metal plating layer (X3 = 4) to obtain a composite current collector. Y1 to Y3 in this case are as shown in Table 1.

(Example 2) As a resin film,
20μ with 16 circular through holes of m diameter / mm ² formed
m biaxially stretched PET film (X1 = 20) was used, and an Ag-based paint containing an Ag powder having an average particle diameter of 0.5 μm as a conductive agent was applied to both sides of the PET film and dried to fill the pores. At the same time, a conductive treatment layer (X2 = 1) having a dry thickness of 0.5 μm was formed to obtain a composite current collector. Further, Cu having a thickness of 2 μm was plated on both surfaces thereof to form a metal plating layer (X3 = 4). Y1-Y in this case
3 was as shown in Table 1.

(Example 3) As a resin film, one side 5
9 square holes having a diameter of 0 μm / mm ^{2 were} formed 4
A biaxially stretched PET film (X1 = 4) having a thickness of μm was used, and a Ni-based paint containing Ni powder as a conductive agent was applied to both surfaces of the film and dried to obtain a conductive treatment layer (X2 having a dry thickness of 0.5 μm each). = 1) was formed. Even after the Ni-based paint was applied and dried, the holes were not blocked by the filling of the paint, and through holes were still observed. Furthermore, thickness: 2 on both sides
A Cu metal plate was plated to form a metal plating layer (X3 = 4) to obtain a composite current collector. Y1 to Y3 in this case are shown in Table 1.
It was as shown in.

(Embodiment 4) 1 μm metal plating layer (X3
= 2) was formed, a composite current collector was obtained in the same manner as in Example 1. Y1 to Y3 in this case are as shown in Table 1.

(Embodiment 5) A vapor deposition layer of Cu is formed on each side of a PET resin film by 1000Å, and a conductive treatment layer (X
2 = 0.2), and a composite current collector was obtained in the same manner as in Example 1 except that a Cu plating layer (X3 = 6) of 3 μm was formed on both surfaces. Y1 to Y3 in this case are as shown in Table 1.

Example 6 A composite current collector was obtained in the same manner as in Example 1 except that the resin film was 6 μm biaxially stretched acrylic acid-modified polypropylene (X1 = 12). Y1 to Y3 in this case are as shown in Table 1.

Example 7 A resin film is a 20 μm biaxially stretched PET film (X1 = 20) and 2 μm Al.
A composite current collector was obtained in the same manner as in Example 2 except that the metal plating layer (X3 = 4) was formed on both surfaces by plating. Y1 to Y3 in this case are as shown in Table 1.

(Comparative Example) Non-porous resin film 20
A composite current collector was obtained in the same manner as in Example 2 except that a biaxially stretched PET film (X1 = 20) having a thickness of μm was used. No through holes were observed in the resin film of the composite current collector not only before plating but also after plating.

In the composite current collectors of Examples 1 to 7, all the electric resistances of the conductive treatment layers before Cu or Ni plating were 1.3Ω.
/ Cm or less. Further, the evaluation of the composite current collectors prepared in Examples 1 to 7 was carried out using the electrical resistance and the method described below to form a battery, and the battery capacity obtained when a current collector made of only metal foil of the same thickness was used. To the battery capacity obtained when the composite current collector of the present invention was used. When the value of the percentage (referred to as composite current collector performance index) was 99.8% or more, the current collection performance of the composite current collector was considered good. The electrical resistances of the composite current collectors were all 40 mΩ / cm or less. In addition, as shown in Table 2, the performance indexes of the composite current collectors of the examples were all 99.8% or more, and all the current collection performances were good.

<Evaluation Method of Composite Current Collector Performance Index> 1. Examples 1 to 6 and Comparative Example A positive electrode having a width of 5 cm and a length of 20 cm (20 μm).
m), LiCoO ₂ : acetylene black: PVDF
= 100: 8: 12 (weight ratio), a laminate of active materials (50 mg / cm ² ) having a composition of 50% / cm ² was used, and the width of each of Examples 1 to 6 and Comparative Example was 5 cm and was 20 cm.
Long composite current collector with graphite: PVDF = 100:
11 (weight ratio) active material (20 mg / cm
² ) is used in a laminated manner, and as the electrolytic solution, 1 mol / L of LiClO ₄ is added to a liquid in which propylene carbonate and ethylene carbonate are mixed at an equal weight ratio,
Using a microporous polypropylene-based separator by a conventional method, the width of the end of the current collector of the positive electrode is 8 cm with a width of 0.5 cm.
A lead made of Al (60 μm) having a length of m was joined to a lead made of Cu (60 μm) having a length of 0.5 cm and a length of 8 cm in the widthwise direction of the end of the current collector of the negative electrode. System secondary battery. Place the battery in an atmosphere of 60 ° C for 1
After leaving for a month, charge end voltage = 4.2V, discharge end voltage =
Constant-current charging / discharging was performed under the conditions of 2 V and charge / discharge rate = 0.2 C, and the discharge capacity (= battery capacity 1) was measured.

Further, in place of the composite current collector of the present invention, a current collector made of only a metal having the same composition as the plating metal of the composite current collector and having the same thickness as the composite current collector is used. The discharge capacity (= battery capacity 2) was measured in the same manner as in. The composite current collector performance index (sometimes referred to as the performance index) was calculated by the following formula. Composite current collector performance index (%) = battery capacity 1 / battery capacity 2 x
100 Here, the theoretical capacity of LiCoO ₂ is set to 135 mAh.
/ G, and 0.2 C is a current value for completing charging or discharging in 5 hours, assuming that charging / discharging is performed theoretically. 2. Example 7 Evaluations were made in the same manner as above except that the composite current collector of Example 7 was used as the current collector of the positive electrode instead of the Al foil, and the Cu foil (10 μm) was used as the current collector of the negative electrode.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

INDUSTRIAL APPLICABILITY The composite current collector of the present invention has the same lead as the metal foil generally used as the current collector although the core uses the resin film as the insulator. Only one of the front and back sides needs to be joined to the wire, and the weight and thickness of the metal foil can be reduced. Therefore, when used as a current collector of a battery, it can be a particularly effective material for reducing the weight and thickness of the battery itself.

[Brief description of drawings]

FIG. 1 is an external perspective view of a composite current collector of the present invention.

FIG. 2 is a cross-sectional view of essential parts of the composite current collector in FIG.

[Explanation of symbols]

10: Composite current collector 11: Resin film 12a, 12b: Conductive treatment layer 13a, 13b, 13c: Metal plating layer 14: Lead wire 15: Through hole 16: Conductor

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Claims (5)

[Claims] 1. A conductive film is formed on both sides of a resin film having a large number of through holes, and a metal plated layer is formed on the conductive film by electrolytic plating.
A composite current collector characterized by having mΩ / cm or less, a tensile strength of 0.8 kg / cm, a front and back conduction resistance of 100 mΩ or less, and further satisfying the following formula (1). Y1 + Y2 + Y3 ≦ 0.8 × (X1 + X2 + X3) × Y3 / X3 (1) where X1: thickness of resin film (μm), X2: thickness of conductive treatment layer (μm), X3: thickness of metal plating layer ( μm), Y1: weight of resin film (mg / cm ² ), Y2: weight of conductive treatment layer (mg / cm ² ), Y3: weight of metal plating layer (mg / cm ² ), 2. The composite current collector according to claim 1, wherein the through hole is filled with a conductive treatment layer. 3. The composite current collector according to claim 1, wherein a conductive treatment layer is also formed on the cross section of the through hole, and a metal plating layer is further formed on the conductive treatment layer. . 4. The metal plating layer is Cu, Ni or Al
The composite current collector according to any one of claims 1 to 3, which is mainly composed of. 5. The composite current collector according to claim 4, wherein X1, X2 and X3 satisfy the following expression (2). X1 + X2 + X3 ≦ 9 μm (2)