JPH1131535A - Battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery, which has high capacity and is superior in safety and for which the yield factor at the time of production is improved. SOLUTION: This battery is provided with a winding-type electrode plates layered body formed of a positive electrode which is formed with a positive electrode active material layer 1b on a collector, a negative electrode which is formed with a negative electrode active material layer 2 on a collector, and a separator which is formed of insulating material grains and a binder for binding these insulating material grains and which is integrally formed on the electrode active material layer. In this case, the separator is integrally formed with the only electrode active material layer, which exists on a surface facing the center of the winding of the collectors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery having a high capacity, excellent safety, and an improved yield during production.

[0002]

2. Description of the Related Art In recent years, the development of high-performance batteries has been actively promoted in accordance with demands for smaller, lighter, multifunctional, and cordless electronic devices. The batteries can be classified into single-use primary batteries and secondary batteries that can be repeatedly used by charging. Examples of the former include a manganese battery, an alkaline manganese battery, and the like, which are widely used with improvements. Examples of the latter include lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, and the like. Recently, lithium ion secondary batteries using non-aqueous electrolytes are particularly high-voltage, high-capacity, and high-output batteries. The fact that it is light in weight makes it a big market.

In a lithium ion secondary battery, lithium ions are released from a positive electrode active material into an electrolyte during charging,
The negative electrode active material may enter into the negative electrode active material through pores in the separator, and at the time of discharge, lithium ions that have entered the negative electrode active material are released into the electrolytic solution, and pass through the pores in the separator into the positive electrode active material. By returning, the charge / discharge operation is performed.

[0004] Such a structure of a lithium ion secondary battery is generally formed by making a positive electrode active material layer and a negative electrode active material layer formed on a metal foil as a current collector face each other with a separator interposed therebetween. Which is housed in a metal can together with a non-aqueous electrolyte. As a separator of a conventional lithium ion secondary battery, a microporous membrane made of a polyolefin resin such as polyethylene and polypropylene is used. Its manufacture, for example,
As described in JP-A-3-1055851, a melt containing a polyolefin-based resin composition is extruded into a sheet, and after extracting and removing substances other than the polyolefin-based resin, the sheet is stretched. Is done in a way.

[0005] By adopting the manufacturing method as described above, the separator is relatively expensive among the battery components. In addition, since mechanical strength is required when the electrode plate laminate is manufactured, it is difficult to reduce the thickness of the separator to a certain extent. Therefore, it is not possible to increase the amount of the electrode active material that can be stored in the battery container, that is, to increase the battery capacity.

Therefore, the present inventors have found that it is very effective to improve the above-mentioned drawbacks by integrally forming an insulating material particle aggregate layer on an electrode to function as a separator. . In this separator,
Voids are formed in the gaps between the insulating material particles, and ions are conducted in the material contained in the holes, and the presence of the insulating material particles electrically short-circuits the positive electrode active material layer and the negative electrode active material layer. Do not let. Furthermore, since the gap between the insulating material particles is three-dimensionally continuous within the separator, compared to a conventional polyolefin resin microporous membrane separator in which the gap is mainly continuous in two-dimensional directions, Ions are easy to conduct. Therefore, it has excellent cycle characteristics and high current density discharge characteristics. And, by integrally forming the insulating material particle aggregate layer which is the separator on the electrode active material layer, it is not necessary to handle it alone,
It is sufficiently possible to make the thickness of the separator less than 25 μm, which is an example of the thickness of the separator of the microporous polyolefin resin membrane. As a result, the amount of the electrode active material that can be stored in the battery container can be increased, that is, the battery capacity can be increased.

Further, when the temperature of the battery rises due to external heating, external short circuit, internal short circuit, etc., the separator of the microporous film made of polyolefin resin completely melts when the temperature exceeds 140 to 160 ° C. Internal short-circuits are enlarged. However, when an aggregate layer of insulating material particles having a high melting point (for example, α-Al ₂ O ₃ having a melting point of 2000 ° C. or more) is used as a separator, internal short-circuiting can be prevented from spreading, and thus safety is excellent.

[0008]

However, in a wound electrode plate laminate, when an insulating material particle aggregate layer is integrally formed on an electrode active material layer and this is used as a separator, a polyolefin resin is used. The frequency of internal short-circuits occurring during manufacturing is higher than when a microporous membrane separator is used. This is considered to be due to cracking when the separator portion is curved during winding. This internal short circuit is caused by integrally forming the insulating material particle aggregate layer on both the opposing positive electrode active material layer and the negative electrode active material layer, so that when using a polyolefin resin microporous membrane separator, Although the frequency of internal short circuits can be reduced to the same level, the thickness of the separator part increases, the amount of electrode active material packed in the same volume battery container decreases, and as a result, the battery capacity decreases. is there. Therefore, it is desirable that the insulating material particle aggregate layer is integrally formed only on one of the opposing electrode active material layers.

[0009]

Means for Solving the Problems To achieve the above object, the invention of claim 1 comprises a positive electrode having a positive electrode active material layer formed on a current collector, and a negative electrode active material layer formed on the current collector. A formed negative electrode, a wound electrode plate laminate comprising insulating material particles and a binder which binds the insulating material particles to each other and integrally formed on the electrode active material layer were provided. A battery, wherein the separator is integrally formed only on an electrode active material layer present on a surface of the current collector facing the center of winding.

Here, the center of the winding refers to a point which is the center of the winding axis when the wound electrode plate laminate is manufactured. The separator is an electrical insulator interposed between the positive electrode active material layer and the negative electrode active material layer facing each other, and is capable of transmitting ions that control the battery reaction.

As an example of the embodiment, as shown in FIG. 2, both the positive electrode and the negative electrode have an electrode active material layer on only one surface of the current collector, and as shown in FIG. Is present, there is a case where the separator is integrally formed only on the electrode active material layer present on the surface of the current collector facing the winding center. Here, in FIG. 2, the separator is integrally formed only on one electrode active material layer (only the positive electrode active material layer in the figure), and in FIG. 3, both the positive electrode and the negative electrode are integrally formed only on one side of the electrode active material layer.

According to the present invention, the rate of occurrence of internal short circuits during manufacturing is greatly reduced, and the amount of the electrode active material packed in the same volume battery container is increased, and as a result, the battery capacity is increased. This insulating material particle aggregate layer may be a layer in which a plurality of insulating material particles are arranged in the film thickness direction, or a film if the insulating material particles are densely arranged in the film plane. Only one may be arranged in the thickness direction.

[0013] The insulating material particles constituting the insulating material particle aggregate layer may be inorganic or organic. As the inorganic insulating substance particles, for example, L
i ₂ O, BeO, B ₂ O ₃ , Na ₂ O, MgO, Al ₂ O ₃ ,
SiO ₂ , P ₂ O ₅ , K ₂ O, CaO, TiO ₂ , Cr
Oxides such as ₂ O ₃ , Fe ₂ O ₃ , ZnO, ZrO ₂ and BaO, zeolites, BN, AlN, Si ₃ N ₄ , and Ba ₃
Nitrides such as N ₂ , silicon carbide (SiC), carbonates such as MgCO ₃ and CaCO ₃ , sulfates such as CaSO ₄ and BaSO ₄ , zircon (ZrO ₂ .Si) which is a kind of porcelain
O ₂ ), mullite (3Al ₂ O ₃ .2SiO ₂ ), steatite (MgO.SiO ₂ ), forsterite (2Mg)
O · SiO _2), cordierite (2MgO · 2Al ₂ O
₃ · 5SiO ₂₎ various inorganic particles, and the like.

Organic insulating particles include fluorine such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polymethyl methacrylate, polyacrylate, polytetrafluoroethylene and polyvinylidene fluoride. Resin, polyamide resin, polyimide resin, polyester resin, polycarbonate resin, polyphenylene oxide resin, silicon resin, phenol resin, urea resin,
Melamine resin, polyurethane resin, polyether resin such as polyethylene oxide and polypropylene oxide, epoxy resin, acetal resin, AS resin, AB
Resin particles such as S resin are exemplified.

Among these insulating substance particles, oxide particles and resin particles are preferable, and oxide particles are particularly preferable.
As a method of fixing the insulating material particle aggregate layer on the electrode, the insulating material particles and a binder are dispersed in a solvent to form a slurry, and the slurry is formed on the surface of the current collector facing the winding center. There is a method of uniformly applying the solution on the surface on the active material layer and then heating to remove the solvent.

Here, examples of the binder that binds the insulating substance particles include latex (for example, styrene-butadiene copolymer latex and acrylonitrile-butadiene copolymer latex), cellulose derivative (for example, sodium carboxymethylcellulose). Salt), fluorine rubber (for example, a copolymer of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene) and fluorine resin (for example, polyvinylidene fluoride and polytetrafluoroethylene), and a fluorine-based resin is preferable. .

Regarding the amount of the binder, the volume ratio of the binder to the insulating material particles is 1/500 to 5/3.
It is preferable to use an amount of 1/500 to 1/2
It is more preferable to use an amount of 1/500 to 1
It is more preferable to use an amount of / 5. Solvents for dispersing the insulating material particles and the binder include ethyl acetate, 2-ethoxyethanol (ethylene glycol monoethyl ether), and N-methylpyrrolidone (NM
P), N, N-dimethylformamide (DMF), dimethylsulfoxide (DMSO), tetrahydrofuran (THF), water and the like.

The removal of the solvent by heating may be performed at a temperature and for a time that does not deform or melt the insulating material particles, and is generally performed at 50 to 200 ° C. for 5 to 30 minutes. The concentration of solids (insulating substance particles) in the slurry is not particularly limited, but is preferably in the range of 40 to 60% by weight. According to a second aspect of the present invention, in the wound electrode plate laminate according to the first aspect, a distance from a winding center to a middle point of a length in a current collector thickness direction of the electrode in which the separator is integrated is R. If the distance from the surface of the separator to the midpoint in the thickness direction of the current collector of the electrode on which the separator is integrated is T, 0.001 ≦ (T /
R) 0.5 is provided.

Here, (T / R) is an index indicating the degree of curvature of the separator with respect to the current collector. When the distance from the winding center to the surface of the separator is r, (2πR−2πr) / (2πR) = (R−r) / (R)
= (T / R) (see FIG. 1). (T /
The range of the value of R) is preferably 0.002 ≦ (T / R)
≦ 0.1, more preferably 0.01 ≦ (T /
R) ≦ 0.05.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The case where the battery of the present invention is applied to a lithium ion secondary battery using a non-aqueous electrolyte will be described below. As a positive electrode active material of a lithium ion secondary battery, L capable of storing and releasing lithium in an ionic state is used.
_{i x CoO 2 (0 <x} ≦ 1.1), Li x NiO 2 (0 <x
≦ 1.1), Li _x Ni _y Co _(1-y) O ₂ (0 <x ≦ 1.
1,0 <y <1), Li _x Mn ₂ O ₄ (0 <x ≦ 1.5,
1.66 <y ≦ 2) and the like.

As the negative electrode active material of the lithium ion secondary battery, carbonaceous materials such as coke, graphite, and amorphous carbon, which can store and release lithium in an ion state,
Metal oxides such as SnO.SiO ₂ are mentioned. Non-aqueous electrolytes used in lithium ion secondary batteries include:
For example, LiBF ₄ , LiClO ₄ , LiAsF ₆ , CF ₃
An electrolyte in which an electrolyte such as SO ₃ Li, (CF ₃ SO ₂ ) 2 N · Li, LiPF ₆ or the like is dissolved alone or in combination of two or more can be used.

Examples of the organic solvent in the non-aqueous electrolyte include:
For example, propylene carbonate, ethylene carbonate, γ-butyrolactone, dimethyl sulfoxide, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, 1,2-
Diethoxyethane, tetrahydrofuran and the like,
Either alone or in combination of two or more (for example,
A mixed solvent of a solvent having a high dielectric constant and a solvent having a low viscosity is used.

Here, the electrolyte concentration in the non-aqueous electrolyte is preferably 0.1 to 2.5 mol / l. Hereinafter, embodiments of the present invention will be further described with reference to Examples, but the present invention is not limited thereto.

[0024]

Example 1 First, LiCoO ₂ was prepared as a positive electrode active material, flaky graphite and acetylene black as a filler, and fluororubber was prepared as a binder. These were prepared as follows: LiCoO ₂ : flaky graphite: acetylene black: fluoro rubber = 100: 2.5: 2.5:
A mixed solvent of ethyl acetate and 2-ethoxyethanol (by volume ratio, ethyl acetate:
2-ethoxyethanol = 1: 3) and slurried by mixing.

This slurry was applied to one surface of an aluminum foil (current collector foil) 1a having a thickness of 15 μm, dried, and pressed to form a cathode active material layer 1b having a thickness of 87 μm. Next, mesophase pitch carbon fiber graphite and flaky graphite were prepared as negative electrode active materials. Carboxymethyl cellulose was prepared as a dispersant, and latex was prepared as a binder.

These were prepared by mixing mesophase pitch carbon fiber graphite: scaly graphite: carboxymethylcellulose: latex = 90: 10: 1.
It was added to purified water so as to be in a ratio of 4: 1.8 (weight ratio) and mixed to form a slurry. This slurry is applied to one side of a copper foil (current collector foil) 2a having a thickness of 12 μm, dried, and then pressed to obtain a thickness of 81 μm.
A negative electrode active material layer 2b of μm was formed.

Next, α-Al _{2 is used} as the insulating material particles.
O ₃ powder (produced by Nippon Light Metal Co., Ltd.) was prepared. Further, polyvinylidene fluoride (PVDF) powder (manufactured by Kureha Chemical Industry Co., Ltd.) was prepared as a binder, and N-methylpyrrolidone (NMP) was prepared as a solvent. 100: 5 by weight
Α-Al ₂ O ₃ and PVDF were mixed in a powder state, NMP was added thereto, and further mixed to obtain a slurry of the insulating material particles having a solid content of 56.8% by weight. .

Then, this slurry is applied to the negative electrode active material layer 2.
b) is uniformly coated using a die coater, and dried in a drying oven at 120 ° C. for 2 minutes to form a 15 μm-thick separator 3B made of an insulating material particle aggregate layer on the negative electrode active material. It was integrally formed on the layer 2b. Next, for the positive electrode, a belt having a width of 38.75 mm, and for the negative electrode (an insulating material particle aggregate layer integrally formed on the active material layer), a belt having a width of 40.25 mm were formed. The electrode plate laminate was prepared by winding the insulating material particle assembly layer so that the layer faced the center of the winding. The surface facing the current collector foil was insulated by winding it together with the insulating film 4 of a 12 μm thick polypropylene film (see FIG. 2). This was mixed with LiPF in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 1: 1.
₆ was sealed in a stainless steel metal can together with an electrolytic solution in which 1.0 mol / l was dissolved.
One hundred lithium ion secondary batteries having a height of 50 mm were assembled to obtain a battery of Example 1.

Also, 100 lithium-ion secondary batteries were assembled in the same manner as in Example 1 except that the insulating material particle aggregate layer on the negative electrode active material layer was wound so as to face the opposite side of the winding center. The battery of Comparative Example 1 was obtained. Furthermore, a lithium ion secondary battery similar to that of Example 1 was used except that a 25 μm-thick polyethylene microporous film was used as a separator without integrally forming an insulating material particle assembly layer on a negative electrode active material layer. Were assembled into a battery of Comparative Example 2.

The battery prepared as described above was charged at a constant current and constant voltage for a total of 6 hours at an upper limit voltage of 4.2 V and a current density of 1.0 mA / cm ² , and then charged at a current density of 1.0
The battery was discharged at a constant current of mA / cm ² to a voltage of 2.7 V throughout. At this time, the number of batteries in which an internal short circuit occurred was two in the battery of Example 1, and was 43 in the battery of Comparative Example 1.

The average discharge capacity of the battery of Example 1 was 860 mAh, while that of the battery of Comparative Example 2 was 800 mAh. As is clear from the above, according to the present invention, the rate of occurrence of internal short-circuits during manufacturing is significantly reduced, and the battery capacity is increased.

[0032]

Example 2 An electrode was produced in the same manner as in Example 1 except that an active material layer was formed on both surfaces of a current collector foil for both a positive electrode and a negative electrode. A separator 3 composed of an insulating material particle aggregate layer was formed on only one side of these electrodes in the same manner as in Example 1.
A and 1B were integrally formed on the electrode active material layers 2a and 2b.

Next, the positive electrode was made into a strip having a width of 38.75 mm, and the negative electrode (integrally formed with the insulating material particle aggregate layer on the active material layer) was made into a strip having a width of 40.25 mm. The electrode plate laminate was fabricated by winding the insulating material particle aggregate layer on the active material layer so as to face the center of the winding (see FIG. 3). In the same manner as in Example 1, 100 lithium-ion secondary batteries having a battery can size of 17 mm in diameter and 50 mm in height were assembled to obtain a battery of Example 2.

The same lithium ion secondary battery as in Example 2 was used except that the insulating material particle assembly layer on the positive and negative electrode active material layers was wound so as to face the opposite side of the winding center.
The battery of Comparative Example 3 was obtained by assembling 00 pieces. Further, a lithium ion secondary battery similar to that of Example 2 was used except that an insulating material particle assembly layer was not integrally formed on the positive electrode and the negative electrode active material layers, and a 25 μm-thick polyethylene microporous film was used as a separator. 100 secondary batteries were assembled to obtain a battery of Comparative Example 4.

The battery fabricated as described above was charged and discharged under the same conditions as in Example 1 (and Comparative Examples 1 and 2). At this time, the number of batteries in which an internal short circuit occurred was four in the battery of Example 2, whereas the number of batteries in Comparative Example 3 was
The number of batteries was 51. The average discharge capacity of the battery of Example 2 was 910 mAh, whereas that of the battery of Comparative Example 4 was 860 mAh.

As is apparent from the above, according to the present invention,
As in the case of the first embodiment, the internal short-circuit occurrence rate during manufacturing is significantly reduced, and the battery capacity is increased.

[0037]

As described above, according to the first aspect, a battery having a high capacity, excellent safety, and an improved yield during production can be obtained. In particular, according to the second aspect, a battery in which the above effects are clearly exhibited can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a battery layer for explaining claim 2;

FIG. 2 is a sectional view showing an embodiment of the battery of the present invention.

FIG. 3 is a sectional view showing an embodiment of the battery of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Positive electrode 1a Current collector foil on the positive electrode side 1b Positive electrode active material 2 Negative electrode 2a Current collector foil on the negative electrode side 2b Negative electrode active material 3A Separator (Insulator material particle aggregate layer fixed on positive electrode active material layer) 3B Separator (Insulating material particle aggregate layer fixed on negative electrode active material layer) 4 Insulating film

Claims (2)

[Claims] 1. A positive electrode in which a positive electrode active material layer is formed on a current collector, a negative electrode in which a negative electrode active material layer is formed on a current collector, insulating material particles, and the insulating material particles are bonded to each other. Battery comprising a wound electrode plate laminate comprising a separator made of a binder and integrally formed on the electrode active material layer, wherein the separator is a surface of the current collector facing the winding center. The battery is formed integrally only on the electrode active material layer present in the battery. 2. In the wound electrode plate laminate, a distance from a winding center to a midpoint of a length in a thickness direction of a current collector of the electrode on which the separator is integrated is R, and the distance from the separator surface is 2. The distance of the electrode integrated with the separator to the midpoint of the length in the thickness direction of the current collector, where T is 0.001 ≦ (T / R) ≦ 0.5. 3. Batteries.