JPH10241656A - Battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery which is superior quick discharge characteristics and capable of significantly expecting capacitor improvement in a same volume. SOLUTION: A separator, consisting of an insulation material particle aggregated layer in which insulation substance particles are coupled with a binder is fixed to active material layers of a positive electrode and/or a negative electrode. A distribution in size of voids between insulation material particles of this insulation material particle aggregated layer is a dimension in which a peak diameter of a differential void capacity curve (curve B) at the void capacity reference is generated at ranges of 0.05 micrometers or more and 0.5 micrometers or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery provided with a special separator.

[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. Batteries include single-use primary batteries and secondary batteries that can be used repeatedly by recharging.Examples of the former include manganese batteries and alkaline manganese batteries, which have become widespread with improvements. ing. Examples of the latter include lead-acid batteries, nickel-cadmium batteries, nickel-hydrogen batteries, and the like.Recently, lithium-ion secondary batteries using non-aqueous electrolytes have recently been used at high voltage, high capacity, and high output. Although it is light in weight, it is building a large market.

In such a lithium ion secondary battery,
Generally, a positive electrode sheet having a positive electrode active material layer adhered to a metal foil and a negative electrode sheet having a negative electrode active material layer adhered to a metal foil,
With the two active material layers facing each other across the separator,
Electrode plate laminates such as a wound type, a laminated type, a multi-layered type, and a ninety-nine fold type are manufactured and housed in an airtight container together with an electrolytic solution.

Here, as the electrolyte, a non-aqueous electrolyte (a solution in which an electrolyte is dissolved in a non-aqueous solvent) is used in order to achieve a high voltage. It is low in nature.

As the separator, a microporous membrane made of a polyolefin resin such as polyethylene or polypropylene is used. Such a microporous membrane is, for example, as described in JP-A-3-105585,
It is manufactured by melting a composition containing a polyolefin resin and extruding it into a sheet, extracting and removing substances other than the polyolefin resin to form fine pores therein, and stretching this sheet. .

[0006] Since such a separator must be handled alone, the thickness of the separator cannot be reduced to a certain degree or more.

[0007]

Therefore, such a lithium ion secondary battery uses a non-aqueous electrolyte having poor ionic conductivity, and thus has insufficient discharge characteristics at a large current (rapid discharge characteristics). There is a problem. Further, in a battery such as a lithium ion secondary battery in which a number of unit battery layers including a positive electrode, a separator, and a negative electrode are stacked or wound, the thickness of the separator cannot be reduced to a certain extent or more. Since the length of the unit battery layer that can be stored in the battery can is limited, there is a limit in improving the battery capacity in the same volume.

The present invention has been made in view of such a point, and it is an object of the present invention to provide a battery which has excellent rapid discharge characteristics and can be expected to greatly improve the capacity in the same volume.

[0009]

Means for Solving the Problems To solve the above-mentioned problems, the present inventors have proposed that the thickness of the separator is smaller than that of the conventional separator.
It is considered that the structure should have a three-dimensional network void structure, and the insulating material particle aggregate layer in which the insulating material particles are bonded to each other with a binder is fixed on the electrode, and this functions as a separator. Tried to let. As a result, in the distribution of the size of the pores generated between the insulating material particles of the insulating material particle aggregate layer, the above-described problem is solved, and the viewpoint of the workability at the time of assembling the battery has an appropriate range. The inventors have completed the present invention.

That is, the present invention provides a battery provided with an electrode plate laminate comprising a positive electrode, a negative electrode, and a separator interposed between the two electrodes, wherein the separator between the positive electrode active material and the negative electrode active material is: Consisting of an insulating material particle aggregate layer fixed to at least one of the positive electrode active material and the negative electrode active material, the insulating material particle aggregate layer binds the insulating material particles and the insulating material particles. The distribution of the size of the pores formed between the binder and the insulating substance particles is such that the peak diameter of the differential pore volume curve based on the pore volume is in a range of 0.05 μm or more and 0.5 μm or less. Disclosed is a battery characterized by being distributed.

Separator (Insulating substance particle aggregate layer)
May be one in which a plurality of insulating material particles are arranged in the film thickness direction, or only one in the film thickness direction if the insulating material particles are densely arranged in the film surface. They may be arranged.

[0012] Insulating properties constituting the insulating material particle aggregate layer
The material particles may be inorganic or organic.
Is also good. As the inorganic insulating substance particles, for example, L
i_TwoO, BeO, B_TwoO_Three, Na_TwoO, MgO, Al_Two
O_Three, SiO_Two, P_TwoO_Five, CaO, Cr_TwoO_Three, Fe
_TwoO_Three, ZnO, ZrO_Two, And TiO_TwoOxidation of etc.
Material, zeolite, BN, AlN, Si_ThreeN_Four, And B
a_ThreeN_TwoSuch as nitride, silicon carbide (SiC), zircon
(ZrSiO_Four), MgCO_ThreeAnd CaCO_ThreeEtc charcoal
Acid salt, CaSO_FourAnd BaSO_FourEtc. sulphate, porcelain
Steatite (MgO.SiO)_Two), Fol
Stellite (2MgO ・ SiO_Two), Cordierite
(2MgO.2Al_TwoO_Three・ 5SiO_Two), Etc.
Substance particles.

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 resins such as polyethylene oxide and polypropylene oxide, epoxy resin, acetal resin, AS resin,
Resin particles such as ABS resin are exemplified.

Of these insulating substance particles, oxide particles and resin particles are preferable, and oxide particles are particularly preferable.
The thickness of the separator is not particularly limited.
μm or less, preferably 10 μm or less. That is,
This separator is fixed to at least one of the positive electrode active material and the negative electrode active material as an insulating material particle assembly layer, and it is not necessary to handle the separator alone, so that the film thickness can be extremely thin.

As a method of fixing the insulating material particle aggregate layer, the insulating material particles and a binder are dispersed in a solvent, and the resultant is uniformly applied to the surface of the positive electrode active material layer and / or the negative electrode active material layer. Later, there is a method of evaporating the solvent.

In this case, usable binders include latex (eg, styrene-butadiene copolymer latex, acrylonitrile-butadiene copolymer latex), cellulose derivatives (eg, sodium salt of carboxymethylcellulose), and fluororubber (eg, , A copolymer of vinylidene fluoride, hexafluoropropylene and tetrafluoroethylene), and a fluororesin (eg, polyvinylidene fluoride, polytetrafluoroethylene). Of these, fluorine-based binders such as fluororubber and fluororesin are preferred.

As the solvent, ethyl acetate, 2-ethoxyethanol (ethylene glycol monoethyl ether), N-methylpyrrolidone (NMP), N, N-
Examples include dimethylformamide (DMF), dimethylsulfoxide (DMSO), tetrahydrofuran (THF), and water.

Here, the differential pore volume curve based on the pore volume will be described with reference to FIG. Curve A in FIG. 1 is a pore volume in which the horizontal axis represents the diameter of the pores and the vertical axis represents the value obtained by adding the volumes of pores having the sizes from the larger side to the diameter (pore volume addition value). A curve B obtained by differentiating the pore volume addition value of the curve A with the pore diameter is a differential pore volume curve.

The differential pore volume curve can be obtained by measuring the pore volume addition value using a mercury porosimeter and performing differentiation by the pore diameter. Alternatively, the diameter can be obtained by measuring the diameters of all holes using an electron microscope, calculating the added value of the hole volume using the measured values, and differentiating the added value with the hole diameter.

In the present invention, the distribution of the size of the pores between the insulating substance particles is defined as a distribution in which the peak diameter of the differential pore volume curve is in the range of 0.05 μm to 0.5 μm. In order to obtain such a distribution, as the insulating substance particles, the 50% average particle diameter (D50) is 0.1 to 0.5%.
It is preferable to use one having a size of 3 μm. The amount of the binder is 1/500 of the volume of the insulating substance particles in volume ratio.
３ to と, more preferably 1/500 to 、, even more preferably 1/500.
To １ ／.

The peak diameter of the differential pore volume curve is 0.05
If it is less than μm, it becomes difficult for the electrolyte to permeate during assembly. In addition, when a high current load is applied, the resistance increases and the battery characteristics deteriorate. On the other hand, when the thickness exceeds 0.5 μm, when the insulating material particle aggregate layer is thinned, pinholes are likely to be generated, and the insulating characteristics deteriorate.

In the pore size distribution, the peak diameter is preferably in the range of 0.08 μm or more and 0.3 μm or less.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As an embodiment of the present invention, for example, an electrode plate laminate on which electrodes and separators are wound is housed in a battery can for each battery layer 10 shown in FIG.
A cylindrical lithium ion secondary battery in which a nonaqueous electrolyte is sealed in the battery can is exemplified.

As a positive electrode active material of a lithium ion secondary battery, Li _X capable of storing and releasing lithium in an ionic state is used.
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.

Examples of the non-aqueous electrolyte for the lithium ion secondary battery include LiBF ₄ , LiClO ₄ , and LiAsF.
₆ , CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ N · Li,
An electrolyte such as LiPF ₆ dissolved in an organic solvent alone or in combination of two or more can be used.

As the organic solvent of the non-aqueous electrolyte, 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, and any one of them 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.

The battery layer 10 includes a positive electrode 11 in which a material containing a lithium-containing composite oxide is applied as a positive electrode active material layer 11b on one surface of a current collector foil 11a made of aluminum;
A negative electrode 12 in which a material containing carbon particles is applied as a negative electrode active material layer 12b on one surface of a current collector foil 12a made of copper;
A separator (insulating material particle assembly layer) 13A interposed between the positive electrode active material layer 11b and the negative electrode active material layer 12b,
13B and an insulating film 14 interposed between the positive and negative current collector foils 11a and 12a.
Is fixed on the surface of the positive electrode active material layer 11b, and the separator 13B is fixed on the surface of the negative electrode active material layer 12b.

Then, a positive electrode strip 1 having a separator 13A fixed to a positive electrode 11 as shown in FIG. 3 and a negative electrode strip 2 having a separator 13B fixed to a negative electrode 12 as shown in FIG. The separators 13A and 13B are made to face each other, and the insulating film 14 is arranged between the current collector foils 11a and 12a, and further wound with the positive electrode side outside. Thus, an electrode plate laminate can be manufactured.

Hereinafter, embodiments of the present invention will be described with reference to specific examples. The following seven types of Al ₂ O ₃ powders having different particle size distributions were prepared as insulating substance particles. As a binder, polyvinylidene fluoride (PVD)
F) (Kureha Chemical Industry Co., Ltd.)
-Methylpyrrolidone (NMP) was prepared. <Al ₂ O ₃ powder> No. 1: D50 = 5.0 μm No. 2: D50 = 3.0 μm No. 3: D50 = 2.0 μm No. 4: D50 = 0.7 μm No. 5: D50 = 0.5 μm No. 6: D50 = 0.2 μm No. 7: D50 = 0.013 μm Each Al ₂ O ₃ and PVDF were mixed in a powder state such that the weight ratio became 100: 5, and NMP was added thereto. Was added and mixed to obtain a slurry having a solid content of 56.8% by weight.

The slurry is placed in an aluminum cup and
The solid was dried at 50 ° C. for 1 hour and crushed into small pieces each having a side of about 5 mm. The small piece was subjected to a mercury porosimeter to obtain a differential pore volume curve based on the pore volume, from which the peak diameter was read.

The slurry was applied to a copper foil in various thicknesses using a doctor blade and dried at 120 ° C. for 15 minutes. Thus, the minimum thickness (thickness after drying) that can be uniformly applied was examined.

Further, a cylindrical lithium ion secondary battery was manufactured as follows, and the battery characteristics were examined. First,
An electrode plate laminate having the battery layer 10 shown in FIG. 2 as a unit was produced. First, LiCoO ₂ was prepared as a positive electrode active material, flaky graphite and acetylene black were used as a filler, and fluororubber was used as a binder.

These were prepared by adding LiCoO ₂ : flaky graphite: acetylene black: fluoro rubber = 100:
2.5: 2.5: 1.96 (weight ratio), added to a mixed solvent of ethyl acetate and 2-ethoxyethanol (by volume, ethyl acetate: 2-ethoxyethanol = 1: 3). And mixed to form a paste.

This paste was applied on an aluminum foil (current collector foil) 11a having a thickness of 15 μm, dried, and pressed to form a positive electrode active material layer 11b having a thickness of 87 μm.

Next, each of the above-mentioned slurries is uniformly applied on the positive electrode active material layer 11b using a die coater.
This is dried for 2 minutes in a drying oven at 120 ° C., whereby a separator 13A comprising an insulating material particle aggregate layer is formed.
Was fixed on the positive electrode active material layer 11b to produce a positive electrode strip 1. The thickness of the separator 13A is, Al ₂ using
For each O ₃ , the thickness was set to the minimum thickness that can be uniformly applied as described above except for No. 6, and No. 6 was set to 10 μm. Preparation of Negative Electrode Band First, as the negative electrode active material, mesophase pitch carbon fiber graphite and flaky graphite were prepared. Carboxymethyl cellulose was prepared as a dispersant, and latex was prepared as a binder.

These were prepared by mixing mesophase pitch carbon fiber graphite: flake graphite: carboxymethylcellulose: latex = 90: 10: 1.
It was added to purified water so as to have a ratio of 4: 1.8 (weight ratio) and mixed to form a paste.

This paste was applied on a copper foil (collector foil) 12a having a thickness of 12 μm, dried, and pressed to form a negative electrode active material layer 12b having a thickness of 81 μm. Next, each of the above-mentioned slurries was uniformly applied on the negative electrode active material layer 12b using a die coater.
By drying in a drying oven for 2 minutes, a thickness of 12 μm
The separator 13B composed of the insulating material particle aggregate layer was fixed on the negative electrode active material layer 12b to produce the negative electrode strip 2. The thickness of the separator 13B depends on the used Al ₂ O
_For each of the _three samples, the minimum thickness was set to be uniform as described above except for No. 6, and No. 6 was 10 μm.

These strips 1 and 2 are connected to both separators 1
3A and 13B, and both collector foils 11a and 12
An electrode plate laminate was produced by interposing an insulating film 14 between the electrodes a and winding the electrode with the positive electrode side outward. Insulating film 1
As No. 4, a polypropylene film having a thickness of 12 μm was used.

In this manner, an electrode plate laminate in which the positive electrode strip 1 having a width of 38.75 mm and the negative electrode strip 2 having a width of 40.25 mm were wound at a predetermined length was prepared, and an electrolytic solution having the following composition was prepared. A lithium ion secondary battery having a battery can size of 17 mm in diameter and 5 cm in height was assembled. Here, the lengths of the positive electrode strip 1 and the negative electrode strip 2 wound as the electrode plate laminate differ depending on the thickness of the separator used.

Further, as a conventional example, the separators 13A and 13B composed of the insulating material particle aggregate layer are not fixed to both the positive and negative active material layers 11b and 12b, and the two active material layers 11b and 12b are not fixed.
b and 12b, a polyethylene microporous membrane used in a conventional lithium ion secondary battery was disposed as a separator, and in all other respects, a lithium ion secondary battery was assembled in the same manner as described above (No. . 8 and No.
9).

No. 8 used a polyethylene microporous membrane having a thickness of 25 μm, and No. 9 used a polyethylene microporous membrane having a thickness of 34 μm. Using these batteries, a charge / discharge cycle test was performed under the following conditions. <Composition of Electrolyte> Electrolyte: LiPF ₆ Solvent: Ethylene carbonate (EC) and diethyl carbonate (DEC), EC: DEC = 1: 1 (volume ratio)
What was mixed in.

Electrolyte concentration: 1.0 mol / l <Charging / discharging conditions> Charging: 1st cycle Upper limit voltage: 4.2 V, current density: 1.0 mA / cm ² , constant current constant voltage charging for 6 hours in total, 2nd cycle and after Constant-current constant-voltage charging with a maximum voltage of 4.2 V and a current density of 3.0 mA / cm ² for a total of 3 hours. Discharge: Up to 14 cycles. Constant-current discharging with a current density of 1.5 mA / cm ² and a final voltage of 2.7 V. 15th cycle Constant current discharge up to a final voltage of 2.7 V at a current density of 9.0 mA / cm ² and a discharge capacity (battery capacity) of the first cycle and 14
The change rate (%) of the discharge capacity between the cycle and the 15th cycle was examined. The larger this value is in the negative direction, the worse the battery characteristics are.

The results are shown in Table 1 below.

[0045]

[Table 1]

As can be seen from the results, No. 2 to No. 6 having a peak diameter of the differential pore volume curve in the range of 0.05 μm to 0.5 μm are the separators (No. 9) 30 thinner than the thickness (34 μm)
The coating could be applied uniformly with a thickness of less than μm. Therefore, in comparison with No. 9, the length of the unit battery layer housed in the battery can was increased, the battery capacity was increased, and the rate of change in discharge capacity was also reduced.

In particular, No. 3 to No. 3 in which the peak diameter of the differential pore volume curve is in the range of 0.08 μm or more and 0.3 μm or less.
In No. 5, the slurry had good coatability and could be uniformly coated with a thickness of 20 μm or less. That is, a separator having a thickness smaller than the thickness (25 μm) of the conventionally used thinnest separator (No. 8) could be obtained. Thereby, the length of the unit battery layer housed in the battery can was longer than that of the conventional battery, and the effect of increasing the battery capacity and the effect of reducing the rate of change in the discharge capacity were also large.

Although No. 6 had a separator as thin as No. 3 to 5 or more, the applicability and stability of the slurry were not better than those of Nos. 3 to 5. On the other hand, the peak diameter of the differential pore volume curve is 0.05 μm
No. 1 out of the range of 0.5 μm or less could not be applied uniformly and thinly, and No. 7 had poor slurry applicability and could not be applied uniformly.

In the above embodiment, the separator made of the insulating material particle aggregate layer is fixed to both the positive electrode active material layer 11b and the negative electrode active material 12b. Good.

Further, in the above embodiment, in both the positive electrode and the negative electrode, the active material layer is formed only on one side of the current collector foil, and the insulating material particle aggregate layer is formed on the active material layer. The insulating film 14 is interposed between the positive and negative current collector foils. However, the battery of the present invention is not limited to such a configuration. As shown in FIG.
Active material layers 11b and 12b may be formed on both surfaces of the active material layers 1a and 12a, and the insulating material particle aggregate layer 13 may be fixed on both the active material layers 11b of the positive electrode. Since the body foils do not contact each other, there is no need to interpose the insulating film 14 as in the case of FIG. In addition, as shown in FIG. 6, the insulating material particle aggregate layer 13 may be fixed on the negative electrode active material layer 12b.

As shown in FIG. 7, both the positive electrode and the negative electrode have active material layers 11b, 11b on both surfaces of current collector foils 11a, 12a.
12b, the positive electrode and the negative electrode are both active material layers 11
b, 12b, the insulating material particle assembly layers 13A, 13
B may be fixed.

In the above embodiment, a battery having a wound electrode plate laminate is described. However, the present invention is not limited to this. The present invention is also applicable to a battery having an electrode plate laminate having another known structure.

In the above embodiments, the lithium ion secondary battery has been described. However, the present invention relates to a secondary battery and a primary battery using a non-aqueous electrolyte, and a secondary battery using an aqueous solution as an electrolyte. Also, the present invention can be applied to a primary battery.

[0054]

As described above, according to the present invention,
A useful battery which has excellent rapid discharge characteristics and can be expected to greatly improve capacity in the same volume can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing a differential pore volume curve (A) on a pore volume basis.

FIG. 2 is a cross-sectional view showing a battery layer serving as a unit of an electrode plate laminate of a lithium ion secondary battery which is an embodiment of the battery of the present invention.

FIG. 3 is a cross-sectional view showing a positive electrode band forming the battery layer.

FIG. 4 is a cross-sectional view showing a negative electrode strip constituting the battery layer.

FIG. 5 is a cross-sectional view showing a battery layer corresponding to another embodiment.

FIG. 6 is a cross-sectional view illustrating a battery layer corresponding to another embodiment.

FIG. 7 is a sectional view showing a battery layer corresponding to another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode strip 2 Negative electrode strip 10 Battery layer 11 Positive electrode 11a Current collector foil on the positive electrode side 11b Positive electrode active material 12 Negative electrode 12a Current collector foil on the negative electrode side 12b Negative electrode active material 13 Separator (aggregate layer of insulating material particles) 13A Separator (insulating material particle aggregate layer) 13B Separator (insulating material particle aggregate layer) 14 Insulating film

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01M 10/40 H01M 10/40 Z

Claims (1)

[Claims] 1. A battery provided with an electrode plate laminate comprising a positive electrode, a negative electrode, and a separator interposed between the two electrodes, wherein the separator between the positive electrode active material and the negative electrode active material is:
Consisting of an insulating material particle aggregate layer fixed to at least one of the positive electrode active material and the negative electrode active material, the insulating material particle aggregate layer binds the insulating material particles and the insulating material particles. It is composed of a binder and the distribution of pore sizes between the insulating material particles is such that the peak diameter of the differential pore volume curve based on the pore volume is 0.05 μm.
A battery characterized by a distribution occurring in a range of not less than 0.5 μm and not more than 0.5 μm.