JP2001035523A - Manufacture of film exterior trimming battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery minimized in deformation by charge and discharge, having less possibility of deformation or breakage of the battery, even if the internal pressure is raised, superior in stability and particularly suitable for a thin lightweight one by including at least one preliminary charging process for performing a charging, while applying pressure. SOLUTION: In preliminary charging process, pressurization is performed by putting a battery between two opposed plates and applying a pressure from both sides thereof, and the pressure is preferably applied to the plates nipping the battery via an elastic body. Otherwise, in the preliminary charging process, the pressurizing is performed by utilizing hydrostatic pressure, and the battery before preliminary charging is suitably put in an insulating liquid followed by pressurization. The pressure applied in the preliminary charging process is preferably 0.05 MPa or higher. A battery (prior to charging) with a generating element trimmed with an exterior film 7 is put between two opposed plates 8, and an external extraction electrode is charged at a fixed current and a fixed voltage, while applying a pressure to the plates 8 via a spring 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a film-covered battery in which a power generating element including a positive electrode, a negative electrode, and a separator is covered with a heat-fusible film. The present invention relates to a method for producing a film-covered battery having excellent properties.

[0002]

2. Description of the Related Art With the rapid market expansion of notebook personal computers, mobile phones, and the like, there is an increasing demand for batteries having high output and excellent stability used in these computers. In order to respond to this demand, secondary batteries have been developed using an alkali metal ion such as lithium ion as a charge carrier and utilizing an electrochemical reaction accompanying the charge transfer. In such a secondary battery, the active material layers of the anode and the anode are separated by a separator made of a porous film, wound or laminated, and sealed in a metal can or the like to constitute a battery.

Further, prismatic secondary batteries that can be efficiently mounted on various electronic devices have also been developed. This prismatic battery is formed by winding an electrode / separator layer flat, press-molding using a flat plate, and enclosing in a prismatic metal can. However, in recent years, the demand for smaller and lighter electronic devices has been increasing for outer packaging materials, and thinner and lighter packages have also been required. It is difficult to respond to such a demand because it is heavy due to the necessity, and it is difficult to reduce the thickness to 4 mm or less due to problems in molding the can.

[0004] Therefore, a case using a heat-fusible film has been studied. This film consists of a metal foil such as aluminum and a resin with high mechanical strength, such as nylon and polyester, on the outer surface, and a resin that is thermally stable and chemically stable, such as polyethylene and polypropylene, on the inner surface. is there. Then, the battery is manufactured by separating the active material layers of the positive electrode and the negative electrode therein by a separator made of a porous film, winding or laminating the batteries, and laminating the inner surfaces thereof and heat-sealing them.

However, in a battery packaged with a heat-fusible film, the film itself does not have the power to suppress the deformation of the power generating element as compared with a metal can case, and even a slight expansion of the power generating element or an increase in internal pressure causes deformation. There was a problem. In general, it is important for the battery characteristics such as energy density, capacity, current density, impedance, and cycle life that the positive electrode active material and the negative electrode active material are in close and uniform contact with each other via a separator. Therefore, when the power generation element expands or deforms, the impedance increases, the discharge capacity decreases, and the charge / discharge cycle characteristics deteriorate.

To solve this problem, see, for example, Japanese Patent Laid-Open No. 5-182.
Japanese Patent Application Publication No. 649 discloses a method in which the inside of a heat-fusible film is maintained at an atmospheric pressure or less to maintain the closeness of a power generating element including a positive electrode, a negative electrode, an electrolyte, and a separator and suppress deformation. However, even if the inside of the heat-sealing film is maintained at a pressure lower than the atmospheric pressure, the force for holding down the power generation element is at most 1 atm, which is insufficient to prevent deformation, and the internal pressure rises due to gas generation or the like. If you do, the effect will be lost.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and there is little deformation due to charge / discharge and the possibility of battery deformation or destruction even when the internal pressure rises. An object of the present invention is to provide a simple method for producing a film-covered battery which is excellent in small stability and is particularly suitable for a thin and lightweight battery.

[0008]

SUMMARY OF THE INVENTION The present invention provides a positive electrode, a negative electrode,
The present invention relates to a method for manufacturing a film-covered battery, which includes a preliminary charging step of charging while applying pressure at least once, in a method for manufacturing a film-covered battery in which a power generation element including at least an electrolyte and a separator is covered with a film.

According to the study of the present inventors, it has been found that when a power generating element is covered with a heat-fusible film and then charged while applying pressure at least once or more, deformation due to charge and discharge due to subsequent use is small. Was. This is considered to be due to the fact that in the film-covered battery manufactured by the method of the present invention, internal distortion due to charging is averaged over the entire battery, and deformation is suppressed even in subsequent charging and discharging. For this reason, the current collector and the electrode layer, or the electrode layer and the separator, or the separator are broken due to the deformation of the power generating element, and the resulting impedance rises, the capacity, the charge / discharge efficiency drops, the internal short circuit, etc. Can be reduced.

As described above, according to the present invention, it is possible to easily manufacture a film-covered battery excellent in stability and safety in which the possibility of deformation or destruction of the battery is small even when the internal pressure is increased by use. . The manufacturing method of the present invention is extremely effectively used particularly when manufacturing a thin and lightweight battery.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a power generating element includes a positive electrode, a negative electrode, and a separator, each of which is made of a material conventionally known as a constituent of a secondary battery.

For example, the cathode is not particularly limited as long as it absorbs positive ions or discharges negative ions at the time of discharge. LiMnO ₂ , LiMn ₂ O ₄ , Li
Conventionally known cathode materials for secondary batteries such as metal oxides such as CoO ₂ and LiNiO ₂ , conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene, and polyparaphenylene and derivatives thereof, and disulfide compounds can be used. .

The negative electrode is not particularly limited as long as it is a material capable of storing and releasing cations. Crystalline carbon such as graphitized carbon obtained by heat-treating natural graphite, coal or petroleum pitch at a high temperature, etc. Conventionally known negative electrode active materials for a secondary battery, such as amorphous carbon obtained by heat-treating coal, petroleum pitch coke, acetylene pitch coke, and the like, and lithium alloys such as metallic lithium and AlLi can be used.

Further, in the present invention, when forming an electrode, these electrode active materials can be mixed with a suitable binder or a functional material to form an electrode layer. As the binder, a halogen-containing polymer such as polyvinylidene fluoride or the like is used. As the functional material, a conductive polymer such as acetylene black, polypyrrole, or polyaniline for securing electron conductivity; And a composite thereof for ensuring the above.

In the present invention, the current collector is not particularly limited.
For example, a metal foil or a metal mesh having high conductivity and excellent malleability is used. As such a current collector, for example, an aluminum foil is preferable for a positive electrode, and a copper foil is preferable for a negative electrode. The thickness is, for example, 5 to 50 μm. An active material is bonded to these current collectors with a binder.

As the electrolyte contained in the power generating element of the present invention, for example, a conventionally known material as an electrolyte for a secondary battery such as an electrolyte solution, a polymer solid electrolyte, and a polymer gel electrolyte can be used. The electrolyte salt contained in the electrolyte includes ClO ₄ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , CF ₃ SO ₃ ⁻ , (CF ₃ S
O ₂ ) ₂ N ⁻ , (C ₂ F ₅ SO ₂ ) ₂ N ⁻ , (CF ₃ SO ₂ )
^{_{3 C -, (C 2 F}} 5 SO 2) 3 C - halogen-containing compound anions such as Li, K, and alkali metal salts such as Na. These electrolyte salts can be used alone or in combination.

As the electrolyte solution, ethylene carbonate, propylene carbonate, butylene carbonate,
A solution in which the above-mentioned electrolyte salt is dissolved in a non-aqueous solvent such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, acetonitrile, dimethoxyethane, sulfolane, tetrahydrofuran, γ-butyrolactone, N-methyl-2-pyrrolidone, dimethylformamide, etc. Can be

Examples of the solid polymer electrolyte include polyether polymers such as polyethylene oxide and polypropylene oxide containing the above-mentioned electrolyte salt.

Further, as the polymer gel electrolyte, the above-mentioned electrolyte salts and the solvents listed as the non-aqueous solvents usable in the above-mentioned electrolyte solution may be obtained by mixing polyvinylidene fluoride,
Fluorine-based polymers such as polyhexafluoropropylene and polytetrafluoroethylene; acrylate-based polymers such as polymethyl methacrylate and polymethyl acrylate; and polymers included in polymers such as polyacrylonitrile. These solvents or polymers can be used alone or in combination of two or more. In particular, a polymer compounded by copolymerization or the like can be used.

As the porous separator used in the present invention, a microporous separator is generally used, but a woven fabric or a nonwoven fabric can be used as long as the effects of the present invention can be obtained. As the microporous separator, for example, a pore diameter of 0.1 to 5 μm, a porosity of 30 to 70%, and a thickness of 1
５０50 μm can be used. As the material of the separator, a polyolefin-based resin such as polyethylene or polypropylene, polyester, or the like can be used.

In the present invention, the shape of the power generating element is not particularly limited and may be a cylindrical shape. However, a flat shape is preferable for reasons such as thinness and weight reduction and ease of sealing. As shown in FIG. The square shape includes a stacked type in which a large number of positive electrodes and negative electrodes are stacked with a separator interposed therebetween, and a wound type in which a positive electrode, a negative electrode, and a separator are wound.

The battery manufactured according to the present invention is a thin and lightweight battery having such a power generation element covered with a film. As the film used for the exterior, a film that can seal the periphery after the power generation element is put therein is preferable, and a film that can be heat-sealed at least at the sealing portion is preferable. For example, the entire film may be formed of a heat-fusible film made of a polyolefin-based resin such as polyethylene and polypropylene, or the film may have a multilayer structure if necessary, and the innermost layer may be a heat-fusible resin layer. Preferred examples of such a multilayer film include at least three layers of a surface protective layer, an intermediate metal layer, and a heat sealing layer,
A resin that does not melt at the heat-sealing temperature, for example, a resin layer of polyethylene terephthalate, nylon, polyimide, or the like is used for the surface protective layer. In addition, it is preferable to use a metal that has few cracks or pinholes and does not transmit various gases, such as aluminum, nickel, or gold, for the intermediate metal layer. In the present invention, the thickness of the intermediate metal layer is not particularly limited, but if it is too thin, pinholes are likely to be generated. Therefore, it is generally used in the range of 0.015 to 0.1 mm. The heat-sealing layer is not particularly limited as long as it is hardly eroded by the electrolyte solution, is thermoplastic and can be heat-sealed in the range of 150 to 250 ° C., and a polyolefin-based resin such as polyethylene and polypropylene, and a polyimide resin. , Ionomers and the like are used.

In the present invention, the adhesive strength between the thermoplastic resin film and the metal foil can be increased by using an adhesive layer or by performing a surface modification treatment of the metal foil.

Next, an example of the manufacturing method of the present invention will be described with reference to the drawings.

In this example, as shown in FIGS. 1 and 2, a power generation element 1 including a positive electrode 4, a negative electrode 5, and a separator 6 is first packaged with a package film 2, and the periphery (heat fusion region 4) is thermally fused. To wear. At this time, the external lead electrodes 3a and 3b are drawn out from the positive electrode 4 and the negative electrode 5, respectively.

In the pre-charging step of the present invention, the pre-charged battery thus formed is charged while applying pressure.

One example is shown in FIG. In this method, a battery (before charging) 7 in which a power generation element is covered with an outer film is sandwiched between two opposing flat plates 8, and a constant current and a constant current are applied to the external extraction electrodes while applying pressure to the flat plates via a spring 9. Charge with voltage.

The material used for the flat plate sandwiching the battery (before charging) is not particularly limited, and a flat plate such as metal, glass, plastic, or the like is used. Glass, plastic, and metal plates coated with plastic are preferred. In the present invention, the thickness and shape of these flat plates are not particularly limited, and can be appropriately selected according to the shape of the power generating element or the force to be deformed.

In the present invention, the pressure applied to the battery can be selected according to the capacity and shape of the battery. The operation is performed within a range that is sufficient to suppress deformation of the power generation element during charging and that does not destroy the separator in the power generation element. Generally, it is preferable to apply a large pressure to a power generation element that is easily deformed. For example, a battery having a large number of stacked electrodes is applied with a large pressure. To reduce the deformation of the power generating element,
Pressure of 0.05MPa or more is required, and 10MPa
a or less is preferable.

The specific pressure is, for example, a capacity of 600 mAh used for a cellular phone or the like in which the power generating element is less deformed.
For a battery with a size of about 30 × 60 mm, 0.05MP
A pressure range of a to 1 MPa is preferred. Further, in the case of a battery having a capacity of about 1600 mAh and a size of about 35 × 65 mm used for a notebook computer or the like in which the power generating element is easily deformed, the pressure range is preferably 0.5 MPa to 10 MPa.

In order to prevent an excessive pressure from being applied to the power generating element during the charging, and to prevent the electrode layer and the separator from being destroyed as a result, means for mitigating an excessive increase in the pressure are provided. Preferably. For example, it is desirable that the gap between the flat plates is not fixed so that excessive pressure is not applied even when the battery expands.
It is preferable that an elastic body such as a hydraulic cylinder or a spring is interposed between the flat plate and the pressure generating device.

As a pressurizing method in the preliminary charging step, a method using hydrostatic pressure may be used in addition to the method using such a flat plate. That is, this is a method in which a fluid is used to apply pressure to the battery in a vertical direction from the interface with the fluid. For example, it can be performed by placing a battery before charging in a pressure vessel or the like, filling it with a liquid or gas, and pressurizing the battery. The pressure to be applied is the same as in the case of using a flat plate even in the case of such other methods, and can be appropriately changed depending on the capacity / shape of the battery, but it is necessary to use a pressure that can suppress deformation. Necessary, 0.05MPa
The above is preferred. At the same time, the pressure needs to be low enough not to crush the separator in the power generation element.
For example, a battery having a capacity of about 600 mAh and a size of about 30 × 60 mm used for a mobile phone or the like has a similar capacity of 0.05 M
It is performed in a pressure range of Pa to 1 MPa. The liquid used to apply the hydrostatic pressure is not particularly limited as long as it is a liquid stable at the temperature at which the battery is manufactured.
Insulating liquids such as silicon oil and ultrapure water are preferred. And while immersing in such a liquid and applying hydrostatic pressure,
What is necessary is just to supply a predetermined current and voltage to the external extraction electrode and charge the same.

[0033]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

<Example 1> Lithium cobaltate, acetylene black, polyvinylidene fluoride and N-methyl-2-pyrrolidone having an average particle size of 5 µm were mixed at a ratio of 10: 1: 1: 30.
And mixed at a weight ratio of This was uniformly applied on one side of an aluminum foil using a wire bar, and vacuum dried at 100 ° C. for 2 hours to remove the solvent. The obtained thin layer was cut into an appropriate size to prepare a positive electrode layer having a capacity of about 25 mAh. A polyethylene separator film having a thickness of 25 μm and a porosity of 50% was laminated on the positive electrode layer. Further, a slurry obtained by mixing polyvinylidene fluoride, N-methyl-2-pyrrolidone (hereinafter, NMP), petroleum coke powder, and acetylene black at a weight ratio of 1: 30: 20: 1 was cast thereon, and a wire was cast. The mixture was uniformly molded with a bar, and dried under vacuum at 100 ° C. for 2 hours to form a negative electrode layer. Next, a copper foil having the same area as the aluminum foil of the positive electrode was placed on the negative electrode layer as a current collector, wound, and lead terminals were connected to obtain an electrode laminate of a lithium ion secondary battery.

Thereafter, the electrode laminate was sandwiched between a laminate film having a nylon film as a surface protective layer and a polypropylene film as a heat sealing layer on the front and back of an aluminum foil having a thickness of 25 μm. The heater bar was press-bonded and heat-sealed. At this time, before closing the last side, LiP is used as an electrolyte salt.
An electrolyte solution composed of a mixed solution of ethylene carbonate and propylene carbonate containing F ₆ (mixing ratio 50/50) was impregnated to obtain a thin battery before preliminary charging.

With respect to the thin battery (before charging) assembled in this manner, 1 kg / cm
4.2 V at a constant current of 112 mA while applying a pressure of ^2.
The battery was then charged at a constant voltage of 4.2 V for a total of 10 hours to complete a thin battery.

When a charge / discharge test was performed on the obtained thin battery, the initial discharge capacity was 685 mAh, which was the designed value, and the discharge capacity after 150 cycles was 625 mA.
% Decrease. Also, the battery thickness is 1
After 0 cycles, a 5% increase was found, indicating excellent stability.

Example 2 A lithium manganate powder having a spinel structure, a carbonaceous conductivity-imparting material, and polyvinylidene fluoride were mixed and dispersed in NMP at a weight ratio of 90: 5: 5 to form a slurry by stirring. The amount of NMP was adjusted so that the slurry had an appropriate viscosity. Using a doctor blade, this slurry was used as a positive electrode current collector to a thickness of 20 μm.
Uniformly on one side of aluminum foil
Vacuum dried for hours. Similarly, the slurry was applied to the other surface and dried under vacuum. This sheet was roll-pressed to form a positive electrode active material layer.

Next, amorphous carbon powder and polyvinylidene fluoride were mixed with NMP at a weight ratio of 91: 9, dispersed and stirred to form a slurry. The amount of NMP was adjusted so that the slurry had an appropriate viscosity. Using a doctor blade, this slurry was used as a negative electrode current collector to a thickness of 10 μm.
Was uniformly applied on one side of a copper foil and vacuum dried at 100 ° C. for 2 hours. At this time, the theoretical capacity per unit area of the negative electrode layer and the theoretical capacity per unit area of the positive electrode layer were adjusted to be 1: 1. Similarly, the slurry was applied to the other surface and dried under vacuum. This sheet was roll-pressed to form a negative electrode active material layer adhered to both surfaces of the negative electrode current collector.

A microporous separator having a three-layer structure of polypropylene / polyethylene / polypropylene between these positive and negative electrodes (manufactured by Hoechst Celanese Co., Ltd.)
Cellguard 2300) was sandwiched, and the positive electrode / separator / negative electrode was integrally wound to form an electrode laminate.

This electrode laminate was filled with an electrolyte and covered with a film in the same manner as in Example 1 to obtain a thin battery before charging.

A flat plate was applied to the assembled thin battery while applying a pressure of 1 kg / cm ^{2 to} both sides of the battery.
The battery was charged to 4.2 V at a constant current of 2 mA, and then charged at a constant voltage of 4.2 V for a total of 10 hours to complete a thin battery.

A charge / discharge test was performed on the obtained thin battery. As shown in FIG. 4, the initial discharge capacity was 645 mAh as designed, and the discharge capacity after 150 cycles was 5 times.
89 mA, which was a 10% reduction. In addition, as shown in FIG.
% Increase, which proved to be excellent in stability.

<Comparative Example 1> In Example 2, the battery before pre-charging was used as a sample, and a charge / discharge test was performed on this thin battery without applying pressure. As shown in FIG. 4, the initial capacity is reduced to 400 mAh and 60% of the designed value.
Further, the capacity after 150 cycles was also 330 mAh. The thickness of the battery also increased by 15% after 10 cycles, as shown in FIG. It is considered that the deformation due to charge / discharge is non-uniform, and the adhesion surface is peeled off.

The method of manufacturing a thin battery, which includes a step of applying pressure to a thin battery having a power generation element covered with a film while applying pressure, is not limited to manufacturing a secondary battery. It can be applied in the field where deformation etc. may occur when applying voltage.In the manufacturing method of electric double layer capacitor, electrolytic capacitor, various sensors, etc., it is formed by applying voltage or current while applying pressure. By doing so, a product with excellent stability can be manufactured.

[0046]

According to the present invention, even when the internal pressure rises due to use, the possibility of deformation or destruction of the battery is small, and the stability of the battery is reduced with deterioration of various characteristics, particularly, the deterioration of cycle characteristics.
A film-covered battery having excellent safety can be easily manufactured.

[Brief description of the drawings]

FIG. 1 is a view showing a state in which a power generation element is covered with a heat sealing film.

FIG. 2 is a cross-sectional view showing a state where a power generation element is covered with a heat sealing film.

FIG. 3 is a diagram showing a state in which charging is performed while applying pressure from both sides of the battery at the time of preliminary charging.

FIG. 4 is a graph showing repetitive cycle characteristics of discharge capacity of a battery obtained by the manufacturing method of the present invention and a conventional battery.

FIG. 5 is a graph showing a comparison between the thickness of the battery obtained by the manufacturing method of the present invention and a conventional battery in terms of the number of repeated cycles.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Film-covered battery battery element 2 Package film 3a, 3b External lead-out electrode 4 Positive electrode 5 Negative electrode 6 Separator 7 Battery (before charging) 8 Flat plate 9 Spring

Continuation of the front page (72) Inventor Nobuhide Oyama 2-5-5 Shin-Yokohama, Kohoku-ku, Yokohama-shi, Kanagawa Prefecture Inside NEC Mori Energy Co., Ltd. (72) Inventor Masato Shirakata 5-7-1 Shiba, Minato-ku, Tokyo No. Within NEC Corporation (72) Inventor Yuichi Kumeuchi 5-7-1 Shiba, Minato-ku, Tokyo F-term within NEC Corporation 5H028 AA07 BB04 BB10 CC12 HH09 5H029 AJ12 AK03 AK16 AL06 AL07 AL08 AL12 AM00 AM03 AM04 AM07 AM16 BJ04 BJ14 BJ15 CJ03 CJ16 DJ02 EJ12 HJ15

Claims (7)

[Claims] 1. A method of manufacturing a film-covered battery in which a power generating element including at least a positive electrode, a negative electrode, an electrolyte, and a separator is packaged with a film, at least one preliminary charging step of charging while applying pressure.
A method for producing a film-covered battery, comprising: 2. The film-covered battery according to claim 1, wherein the method of applying pressure in the pre-charging step is a method of sandwiching the battery between two opposing flat plates and applying pressure from both sides. Manufacturing method. 3. A pressure is applied to the flat plate sandwiching the battery via an elastic body when applying pressure from both sides with the battery sandwiched between the two opposed flat plates. Item 3. A method for producing a film-covered battery according to Item 2. 4. The method for manufacturing a film-covered battery according to claim 1, wherein the method of applying pressure in the preliminary charging step is a method of utilizing hydrostatic pressure. 5. The method of manufacturing a film-covered battery according to claim 4, wherein in the method using hydrostatic pressure, the battery before precharge is put in an insulating liquid to apply pressure. 6. The method according to claim 1, wherein a pressure applied in the preliminary charging step is 0.05 MPa or more. 7. The method according to claim 1, wherein the positive electrode and the negative electrode are wound with a separator interposed therebetween.