JP2003203677A - Nonaqueous electrolyte secondary cell and manufacturing method of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary cell capable of preventing deterioration of the discharging and cycle properties, and to provide a manufacturing method of the same. <P>SOLUTION: Adhering strength between an activator and a current collector is made stronger than that between a separator and the activator. By the above, the current collector is prevented from generating crack and exfoliation from the activator, and the cell with excellent discharging property and cycle property can be provided. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery and a method for manufacturing the same.

[0002]

2. Description of the Related Art Recently, non-aqueous electrolyte secondary batteries (hereinafter, referred to as
(Sometimes simply referred to as "battery"), downsizing,
Higher capacity is required. For this reason, as a battery case, a laminate film exterior material has come to be used in place of the conventionally used metallic battery can. However, when such an exterior material is used, the electric connection between the positive electrode and the negative electrode is ensured by the pressure applied to the power generating element housed inside, as in the case of using a rigid battery can. It becomes difficult to obtain the effect of doing.

Techniques for solving this problem include:
For example, as disclosed in Japanese Unexamined Patent Publication No. 2000-223159, by bonding an adhesive polymer between a positive electrode or a negative electrode and a separator, and integrating the positive electrode, the negative electrode, and the separator, electricity between the positive electrode and the negative electrode is reduced. There is a technology to improve the mechanical bondability.

[0004]

However, in the battery as described above, when a stress is generated between the electrode and the separator due to some factor during assembly or use of the battery, cracks in the active material layer or the collector may occur. May be peeled off. Therefore, there has been a problem that the discharge characteristics and cycle characteristics of the battery deteriorate.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery capable of preventing deterioration of discharge characteristics and cycle characteristics of the battery.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to provide a non-aqueous electrolyte secondary battery capable of preventing the deterioration of initial characteristics and cycle characteristics of the battery and a method for producing the same, and found the following findings. It was

As described above, it has been conventionally considered that the battery performance can be improved by integrating the positive electrode, the negative electrode and the separator to improve the electrical connection between the positive electrode and the negative electrode. Many techniques have been proposed for strengthening the adhesion between the negative electrode and the separator.
However, in the battery in which the electrode and the separator are bonded to each other, swelling-contraction of the active material layer accompanying the battery reaction,
Alternatively, the current collector-
Stress may occur between the active material layers and between the active material layer and the separator. In particular, in a wound type battery, since the degree of bending is different for each layer, the strain between layers tends to increase.

In such a case, if the separator-active material layer is firmly adhered, the generated stress is hardly absorbed between the separator-active material layer and is mainly absorbed between the active material layer-current collector. The Rukoto. Therefore, it is considered that stress is concentrated between the active material layer and the current collector, causing cracks in the active material layer and separation from the current collector, and eventually deterioration of discharge characteristics and cycle characteristics of the battery. Further, in the case of a wound type battery, cracks or peeling from the current collector may occur in the active material layer even during the winding operation of winding the electrode and the separator during the production of the power generation element.

The present inventor has, surprisingly, made the adhesive strength between the active material layer and the current collector higher than that between the separator and the active material layer in order to prevent the deterioration of the discharge characteristic and the cycle characteristic of the battery. Therefore, it was found that it is effective to avoid the concentration of stress between the active material layer and the current collector. In particular,
Adhesion between the active material layer and the current collector rather than the separator and the active material layer when the winding operation is performed after the positive electrode or the negative electrode and the separator are bonded to each other in the case of manufacturing a wound battery. It has been found that increasing the strength is effective.

That is, the present invention provides a positive electrode having a positive electrode active material layer formed on the surface of a positive electrode side current collector, a negative electrode having a negative electrode active material layer formed on the surface of a negative electrode side current collector, and the positive electrode. With a separator interposed between the negative electrode,
A non-aqueous electrolyte secondary battery in which the positive electrode and / or the negative electrode and the separator are bonded to each other, wherein the active material layer and the current collector are more strongly than the adhesive strength between the separator and the active material layer. The adhesive strength between the two is increased.

Adhesion strength between the separator and the active material layer,
And the adhesive strength between the active material layer and the current collector, the characteristics of the separator, the type of adhesive, the composition of the active material layer, the type and amount of the binder, the surface roughness of the current collector, the current collector Since it is affected by various factors such as the mixture application conditions when forming the active material layer on top, it is necessary to set the conditions individually according to the battery design, but as a result, the separator and the active material layer If the adhesive strength between the active material layer and the current collector is higher than the adhesive strength of
The object of the invention is achieved.

As the binder contained in the positive electrode active material layer of the present invention, for example, polyvinylidene fluoride can be used. Further, as the positive electrode active material, for example, lithium cobalt oxide, lithium nickel oxide, spinel lithium manganate, which is a lithium-containing oxide of a transition metal, or a composite oxide thereof can be used. The positive electrode active material is
From the viewpoint of improving discharge characteristics, the average particle size is 1 to 50 μm,
The specific surface area is preferably 0.7 to 3.5 m ² / g. Further, the positive electrode active material layer may contain a conductive agent and other additives, if necessary, in addition to the binder and the positive electrode active material described above. From the viewpoint of improving discharge characteristics and workability during electrode production, the proportion of the positive electrode active material contained in the positive electrode active material layer is 85% by weight to 95% by weight, and the proportion of the binder is 3% by weight to 8%. The ratio of the weight% and the conductive agent is preferably 2% by weight to 7% by weight.

The current collector on the positive electrode side is not particularly limited as long as it is one normally used in non-aqueous electrolyte secondary batteries, but the thickness is 10 to 25 μm and the surface roughness is the center line average roughness. And an aluminum foil having a thickness of 0.14 μm to 2.8 μm can be preferably used.

As the binder contained in the negative electrode active material layer of the present invention, for example, polyvinylidene fluoride, styrene butadiene rubber, or a mixture of styrene butadiene rubber and carboxymethyl cellulose can be used. Further, as the negative electrode active material, for example, graphite,
Carbon black, activated carbon, carbon fiber, carbonaceous materials such as coke, tin oxide, silicon oxide and the like can be used. When a carbonaceous material is used, the ratio of the negative electrode active material contained in the negative electrode active material layer is 95% by weight to 99% by weight,
The proportion of the binder is preferably 1% by weight to 5% by weight.

The negative electrode side current collector is not particularly limited as long as it is one normally used in non-aqueous electrolyte secondary batteries, but the thickness is 5 to 20 μm and the surface roughness is the center line average roughness. And a copper foil having a thickness of 0.14 μm to 2.8 μm can be preferably used.

The separator of the present invention is not particularly limited as long as it is usually used for non-aqueous electrolyte secondary batteries, and for example, a microporous membrane made of polyethylene or polypropylene can be used.

In the present invention, for bonding the positive electrode or the negative electrode and the separator, for example, vinylidene fluoride, 4
-Adhesive polymers such as polymers of fluorinated ethylene can be used. There is no particular limitation on the method of holding the adhesive polymer between the positive electrode or the negative electrode and the separator, for example, an adhesive solution prepared by dissolving the adhesive polymer in a suitable solvent is used to laminate the positive electrode, the negative electrode, and the separator. After impregnating the body, it may be retained by removing the solvent by heating under pressure. Alternatively, the adhesive polymer may be applied to the positive electrode, the negative electrode, or the separator and then sequentially laminated to hold the adhesive polymer. In particular, if the adhesive polymer to be retained is made porous and the electrolyte is retained in the pores, the ionic conductivity is improved and the internal resistance is reduced, which is very preferable in terms of charge / discharge characteristics. As a method of making the adhesive polymer porous, for example, a solvent extraction method as disclosed in JP 2001-126700 A can be adopted.

[0018]

EFFECTS OF THE INVENTION AND EFFECTS OF THE INVENTION According to the present invention, it is possible to prevent the active material layer from being peeled or cracked from the current collector, and to provide a battery having good discharge characteristics and cycle characteristics.

[0019]

EXAMPLES The present invention will be described in detail below with reference to examples.

<Example 1> 1. Preparation of Lithium Ion Secondary Battery 1) Preparation of Positive Electrode Lithium cobalt oxide was used as a positive electrode active material, and polyvinylidene fluoride was used as a binder and graphite was used as a conductive agent in a weight ratio of 91: 5: 4. The mixture was mixed at a ratio and N-methylpyrrolidone was added to prepare a positive electrode mixture paste. This paste was uniformly applied to both sides of a current collector made of an aluminum foil having a thickness of 12 μm and a center line average roughness of 1.0 μm so that the thickness per one side was 100 μm, and dried. After that, hot roll press at 95 ° C. is performed so that the thickness of one surface of the positive electrode active material layer is 85 μ
A strip-shaped positive electrode sheet with m was produced.

2) Preparation of Negative Electrode Graphite was used as a negative electrode active material, and polyvinylidene fluoride as a binder was added to this graphite in a weight ratio of 9
The mixture was mixed at a ratio of 5: 5, and N-methylpyrrolidone was added to prepare a negative electrode mixture paste. This paste, thickness 1
A current collector made of a copper foil having a thickness of 0 μm and a center line average roughness of 1.0 μm was uniformly applied on both surfaces so that the thickness per surface was 85 μm, and dried. Thereafter, a hot roll press at 60 ° C. was applied to produce a strip-shaped negative electrode sheet having a thickness of 75 μm per one surface of the negative electrode active material layer.

3) Production of power generation element Polyvinylidene fluoride was used as an adhesive polymer. 4 parts by weight of this polyvinylidene fluoride was mixed with 96 parts by weight of N-methylpyrrolidone to prepare an adhesive polymer solution.
This adhesive polymer solution was intermittently applied to both surfaces of the negative electrode prepared in 2) above, and a separator was superposed on it. After pressing this laminated body with a roll press, 65
It was dried in a warm air dryer at ℃ for 3 hours. In this way, a negative electrode sheet having separators adhered on both sides was produced. The negative electrode sheet and the positive electrode sheet prepared in 1) were superposed and wound in a flat shape to prepare a power generation element.

4) Preparation of Electrolyte Solution Ethylene carbonate and diethyl carbonate were mixed in a volume ratio of 3: 7 to prepare a non-aqueous solvent. L, which is a lithium salt as an electrolyte, is added to this non-aqueous solvent.
iPF ₆ was added at a concentration of 1.2 mol / l to prepare a non-aqueous electrolytic solution.

5) Preparation of Battery A laminated film in which a polyethylene terephthalate film, an aluminum foil, an adhesive layer, a first modified polyolefin layer, and a second modified polyolefin layer are laminated in this order.
A bag-shaped battery case was prepared by folding back the second modified polyolefin layer side as the inner side and welding the bottom side and the side side. The power generation element was housed in this battery case. Finally, the electrolytic solution prepared in 4) above was injected into the battery case, and the opening was sealed by thermocompression bonding to complete the battery.

2. Peeling test A peeling test was performed on the power generation element manufactured in 3) above. With respect to the negative electrode sheet bonded to the separator, the terminal portion of the negative electrode side current collector and the terminal portion of the separator were pinched with fingers and pulled in opposite directions to be peeled off. It was investigated whether the negative electrode active material layer was attached to the negative electrode side current collector or the separator.

3. High Rate Discharge Test The battery prepared by the above method was charged to 4.1 V at a constant current of 600 mA in an atmosphere of 25 ° C. and then 4.1.
Charging was performed at a constant voltage of V for 2 hours. Then, this battery was discharged at a constant current of 2 CA in an atmosphere of 25 ° C., and the time until the voltage reached 2.75 V (discharge time) was measured.

4. Cycle test The battery prepared by the above method was charged to 4.1 V at a constant current of 600 mA in an atmosphere of 25 ° C. and then 4.1.
Charging was performed at a constant voltage of V for 2 hours. Then, this battery was discharged to 2.75 V at a constant current of 600 mA in an atmosphere of 25 ° C. This was set as one cycle, and 30 cycles were repeated. The time (discharge time) until the voltage reached 2.75 V at the time of discharging in the 30th cycle was measured.

Example 2 The same adhesive polymer solution as in Example 1 was intermittently applied to both sides of the positive electrode prepared in the same manner as in Example 1, and the separator was superposed on it.
This laminate was pressed by a roll press and then dried in a warm air dryer at 65 ° C. for 3 hours. In this way, a positive electrode sheet having separators adhered on both sides was produced. By stacking this positive electrode sheet and a negative electrode sheet produced in the same manner as in Example 1 and winding them in a flat shape,
A power generation element was produced. Using this power generation element, Example 1
A battery was prepared in the same manner as in. The positive electrode sheet adhered to the separator was subjected to a peeling test as in the case of the negative electrode sheet of Example 1. A cycle test was performed on the manufactured battery in the same manner as in Example 1.

Comparative Example 1 The same adhesive polymer solution as in Example 1 was applied over both surfaces of the negative electrode prepared in the same manner as in Example 1, and the separator was superposed thereon. . The coating amount of the adhesive polymer solution was 1 in Example 1.
It was set to 0 times. This laminate was pressed by a roll press and then dried in a warm air dryer at 65 ° C. for 3 hours. In this way, a negative electrode sheet having separators adhered on both sides was produced. The negative electrode sheet and the positive electrode sheet produced in the same manner as in Example 1 were superposed and wound in a flat shape to produce a power generating element. A battery was produced in the same manner as in Example 1 using this power generating element. A peeling test was performed on the negative electrode sheet bonded to the separator in the same manner as in the negative electrode sheet of Example 1. A cycle test was performed on the manufactured battery in the same manner as in Example 1.

Comparative Example 2 The same adhesive polymer solution as in Example 1 was applied over both surfaces of the positive electrode prepared in the same manner as in Example 1, and the separator was superposed on it. The amount of the adhesive polymer solution applied was 8 times that in Example 2. After pressing this laminate with a roll press,
It was dried in a warm air dryer at 65 ° C. for 3 hours. In this way, a positive electrode sheet having separators adhered on both sides was produced. The positive electrode sheet and the negative electrode sheet produced in the same manner as in Example 1 were superposed and wound in a flat shape to produce a power generating element. Using this power generation element,
A battery was prepared in the same manner as in Example 1. The positive electrode sheet adhered to the separator was subjected to a peeling test as in the case of the negative electrode sheet of Example 1. A cycle test was performed on the manufactured battery in the same manner as in Example 1.

<Results and Discussion> 1. Peeling test In Examples 1 and 2, the negative electrode active material layer and the positive electrode active material layer were peeled from the separator following the negative electrode side current collector and the positive electrode side current collector, respectively. On the other hand, in Comparative Example 1, the negative electrode active material layer was separated from the negative electrode side current collector following the separator. In addition, during the winding operation during the production of the power generation element, peeling was partially observed between the negative electrode active material layer and the negative electrode side current collector. Similarly, also in Comparative Example 2, the positive electrode active material layer was separated from the positive electrode side current collector following the separator. Further, during the winding operation for producing the power generation element, peeling was partially observed between the positive electrode active material layer and the positive electrode side current collector.

As described above, the adhesive strength between the active material layer and the current collector can be made higher than the adhesive strength between the separator and the active material layer by adjusting the coating method and the coating amount of the polymer adhesive solution. did it. When the adhesive strength between the active material layer and the current collector is lower than the adhesive strength between the separator and the active material layer, peeling from the current collector occurs in the active material layer during the winding operation. It was found that such peeling can be prevented when the adhesive strength between the active material layer and the current collector is higher than the adhesive strength between the separator and the active material layer.

2. Cycle Test Table 1 shows the discharge time in the high rate discharge test and the cycle test for each of the examples and comparative examples. The discharge time in each test is shown as a relative value with the discharge time in Example 2 as 100.

[0034]

[Table 1]

From Table 1, in both cases of adhering the positive electrode and the separator and adhering the negative electrode and the separator, the adhesive strength between the active material layer and the current collector is higher than the adhesive strength between the separator and the active material layer. When the value is increased (Example 1,
In Example 2), the discharge time is longer than in the case where the adhesive strength between the active material layer and the current collector is lower than the adhesive strength between the separator and the active material layer (Comparative Example 1 and Comparative Example 2). And was excellent in high rate discharge characteristics and cycle characteristics. This is because when the adhesive strength between the active material layer and the current collector is higher than the adhesive strength between the separator and the active material layer, the winding operation during the production of the power generation element, the swelling of the active material layer accompanying the battery reaction- It is considered that peeling of the active material layer from the current collector due to shrinkage or the like was suppressed.

The technical scope of the present invention is not limited to the above-described embodiments, but extends to an equivalent range.

Claims (2)

[Claims] 1. A positive electrode having a positive electrode active material layer formed on the surface of a positive electrode current collector, a negative electrode having a negative electrode active material layer formed on the surface of a negative electrode current collector, and the positive electrode and the negative electrode. A non-aqueous electrolyte secondary battery including a separator interposed between the positive electrode and / or the negative electrode and the separator, the adhesive strength between the separator and the active material layer being higher than that. A non-aqueous electrolyte secondary battery, wherein the adhesive strength between the active material layer and the current collector is increased. 2. A positive electrode having a positive electrode active material layer formed on the surface of a positive electrode current collector, a negative electrode having a negative electrode active material layer formed on the surface of a negative electrode current collector, and the positive electrode and the negative electrode. A method of manufacturing a non-aqueous electrolyte secondary battery comprising a separator interposed between the positive electrode and / or the negative electrode and the separator, the method comprising: a positive electrode side current collector and a negative electrode side current collector. An electrode preparation step of forming a positive electrode active material layer and a negative electrode active material layer on the surface, an adhering step of adhering the positive electrode and / or the negative electrode and a separator, and a positive electrode and / or an electrode adhered to the separator in the adhering step. Or a power generation element manufacturing step of manufacturing a power generation element using a negative electrode, and the adhesive strength between the active material layer and the current collector is more than the adhesive strength between the separator and the active material layer. To Non-aqueous method for producing electrolyte secondary battery characterized by listening.