JP2003086162A - Separator for nonaqueous secondary battery and nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a nonaqueous lithium ion secondary battery having a good ion conductivity and good adhesion to electrodes. SOLUTION: The separator for the nonaqueous secondary battery is characterized in that porous layers made of an organic polymer swollen with and retaining an electrolyte are positioned on the entire front and back surfaces of a polyolefin microporous film and integrated with the polyolefin microporous film, the porous layers having a specific void ratio with holes of specific diameters scattered over the surfaces of the porous layers, and the porous layers each having a specified thickness. The nonaqueous secondary battery using the separator is also disclosed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a non-aqueous secondary battery that obtains electromotive force by undoping.
In particular, it relates to a separator used for a non-aqueous secondary battery.

[0002]

2. Description of the Related Art A non-aqueous secondary battery using a lithium-containing transition metal oxide as a positive electrode, a carbon-based material capable of doping and dedoping lithium as a negative electrode, and a non-aqueous electrolytic solution as an electrolytic solution (lithium ion battery The secondary battery is characterized by having a higher energy density than other secondary batteries. This lithium-ion secondary battery meets the requirements of portable electronic devices such as weight reduction and thinning, and is used as a power source for portable electronic devices such as mobile phones and notebook computers. However, demands for weight reduction and thinning of portable electronic devices are becoming more and more severe. Therefore, in the current situation, the lithium-ion secondary battery used for this purpose is also undergoing intense technological development in search of further higher energy.

In flat type lithium-ion secondary batteries mainly used for mobile phones, there is a demand for thinning and weight reduction.
In recent years, technological innovation has been made to replace the conventional metal can with an aluminum laminate film. Since this aluminum laminate film exterior (film exterior) is a flexible exterior unlike a metal can exterior, the external pressure is weak and it is not easy to make contact between the electrode and the separator interface. In addition, there was a risk of liquid leakage, and there was a problem from the viewpoint of safety. Therefore, a film-clad battery cannot be realized with the conventional battery structure of positive electrode / separator / negative electrode.

[0004] Nevertheless, what made this technical innovation possible is the technology of the separator which is excellent in the adhesiveness to the electrode and the electrolyte retaining property. By using this separator, good interfacial contact between the electrode and the separator was made possible, and liquid leakage could be prevented. An organic polymer that swells and holds the electrolyte is used for this separator. It has been considered to use such an organic polymer alone as a separator, but it is not suitable for continuous production due to problems in physical properties, and is practically used in a form of being generally reinforced by a support.

That is, there has been proposed a separator in which an adhesive layer made of an organic polymer which swells and holds an electrolytic solution is coated on both surfaces of a support. Nonwoven fabrics and polyolefin microporous membranes used as separators in conventional lithium-ion secondary batteries have been proposed for the support, but currently polyolefin microporous membranes are mainly used from the viewpoint of safety due to their shutdown characteristics. Has been done. Further, an organic polymer mainly composed of polyvinylidene fluoride (PVdF) is mainly used for the adhesive layer from the viewpoint of durability.

In addition, the battery structure in which the adhesive layer is arranged between the electrode and the separator as described above is not only for the purpose of enabling film packaging, but also for enhancing the energy density of the battery in the conventional metal can packaging. Has been attracting attention. Increasing the energy density means tightly packing many battery elements in a can of a predetermined size. In this case, it is difficult to form a good electrode separator interface, and cycle characteristics and the like have become problems,
This problem may be solved by disposing the flexible adhesive layer as described above.

With the above background, attention has been paid to a polyolefin microporous membrane separator having adhesive layers on the front and back sides. Among these, a separator having an adhesive layer (dry adhesive layer) containing no electrolytic solution has become an important technical element from the viewpoint of utilizing the current non-aqueous secondary battery manufacturing process. Such a separator is disclosed in JP-A-9-2.
No. 93518, Japanese Patent Laid-Open No. 10-189054,
JP-A-11-26025 and JP-A-2001-11
No. 8558 is proposed.

[0008]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In Japanese Patent No. 89054, a separator having an adhesive layer is obtained by coating a dope prepared by dissolving PVdF in N-methylpyrrolidone (NMP) on a polyolefin microporous membrane and drying the dope. Such a system has a problem that the adhesive layer becomes dense and good ionic conductivity cannot be obtained, resulting in deterioration of battery characteristics. Further, Japanese Patent Laid-Open No. 2001-118558 proposes a separator in which an adhesive layer is partially (on a surface coverage of 50% or less) applied onto a polyolefin microporous film in order to solve such a problem. Since this system is a partial coating, a large amount of free electrolytic solution that is not retained by the separator exists at the electrode / separator interface, which causes problems such as deterioration in cycle characteristics. In addition, it is not suitable as a film exterior from the viewpoint of reliability of liquid leakage.

Japanese Unexamined Patent Publication (Kokai) No. 9-293518 proposes that an adhesive layer made of PVdF is produced by a wet film-forming method, and this is attached to a polyolefin microporous film to obtain a separator having an adhesive layer. It is characterized by not having a typical through hole. Since the PVdF film, which is the adhesive layer, has low physical properties, the method of laminating it with the polyolefin microporous film is problematic from the viewpoint of productivity. Further, according to the description, the bonding is not essentially integrated by simply stacking, and the problem of peeling between the microporous polyolefin membrane and the adhesive layer may be considered. Further, it is characterized in that there is substantially no through hole on the surface, but since there is no through hole, ionic conduction at the interface between the electrode and the separator also becomes a problem, and it is expected that the rate characteristics and the like will deteriorate.

In Japanese Patent Laid-Open No. 11-26025, a separator is obtained by a general wet film forming process of coating a dope prepared by dissolving PVdF in NMP on a polyolefin microporous film and solidifying the dope in water. In this system, since the coagulation bath is water, the coagulation is fast and a dense PVdF layer is formed on the surface, and there is substantially no through hole, and there are the same problems as described above.

Thus, in the polyolefin microporous membrane separator having the adhesive layers on the front and back sides, the ion conductivity,
At present, no structure has been found that sufficiently satisfies the required properties such as liquid retention, adhesiveness and productivity. In view of such a current situation, an object of the present invention is to develop a separator in which an adhesive layer is integrated on the front and back of a microporous polyolefin membrane, which has good ion conductivity and good adhesion to electrodes.

[0012]

Means for Solving the Problems In order to solve the above problems, the present invention provides a separator used in a non-aqueous secondary battery that obtains an electromotive force by doping / dedoping lithium. A porous layer made of an organic polymer that swells and retains an electrolytic solution is arranged on the entire front and back surfaces of the porous film and integrated with the polyolefin microporous film, and the porosity of the porous layer is 50 to 90%. The total thickness of the front and back porous layers having pores of 0.05 to 10 μm scattered on the surface of the porous layer is 20 μm or less, and the thickness of the porous layer is 1 μm or more on each side. A separator for a non-aqueous secondary battery is provided.

Here, the porous layer functions as an adhesive layer with the electrode. In addition to the above invention, the present invention also includes the following contents. (A) The separator for a non-aqueous secondary battery according to the above invention, which has a surface porosity of 1 to 80%. (A) The organic polymer is polyvinylidene fluoride (PVd
F), PVdF copolymer, or P mainly containing them
The separator for a non-aqueous secondary battery according to any one of the above inventions and (a), which is a VdF polymer. (C) In a non-aqueous secondary battery that includes a positive electrode and a negative electrode capable of reversibly doping / de-doping lithium and a separator, and uses a non-aqueous electrolyte solution, any one of the above inventions and (A) to (A) as the separator. A non-aqueous secondary battery comprising the separator described in (1) above.

[0014]

DETAILED DESCRIPTION OF THE INVENTION The contents of the present invention will be described below. [Non-Aqueous Secondary Battery Separator] In the non-aqueous secondary battery separator of the present invention, a porous layer made of an organic polymer that swells in and holds an electrolyte solution is arranged on the entire front and back surfaces of a polyolefin microporous membrane. That is integrated with the polyolefin microporous membrane, and the porosity of the porous layer is 50 to 90%, and the surface of the porous layer is interspersed with pores having a pore diameter of 0.05 to 10 μm. The total thickness of the layers is 20 μm or less, and the thickness of the porous layer is 1 μm or more on each side.

As the polyolefin microporous film, a known one having a film thickness of 5 to 30 μm, which is proposed as a porous support for a separator for a non-aqueous secondary battery, can be preferably used. Organic polymers that swell and retain the electrolyte are polyvinylidene fluoride (PVdF), polyethylene oxide (PEO), polyacrylonitrile (PA).
N), polymethylmethacrylate (PMMA) and copolymers thereof. In the present invention, these may be used alone or as a mixture of two or more kinds.

Of these, considering durability and film formability, P
VdF, PVdF copolymers, or PVdF-based polymers mainly containing these are preferably used. More preferably, PVdF and PVdF copolymer can be mentioned. Among these, especially vinylidene fluoride (Vd
The terpolymer of F), hexafluoropropylene (HFP), and chlorotrifluoroethylene (CTFE) is preferable because of its excellent swelling / retaining property in an electrolytic solution, heat resistance, and adhesion to electrodes. Suitable copolymerization composition of the copolymer includes VdF / HFP (a) / CTFE (b) (a) = 2 to 8% by weight (b) = 1 to 6% by weight. The weight average molecular weight (Mw) of the organic polymer is preferably 100,000 to 800,000, and particularly preferably 200,000 to 600,000. These PVdF-based polymers can be synthesized by a known method. Generally, it can be synthesized by a radical polymerization method, and specifically, it is prepared by a method such as solution polymerization, suspension polymerization, emulsion polymerization, bulk polymerization and the like.

The non-aqueous secondary battery separator of the present invention comprises:
The porous layer is arranged on the front and back of the polyolefin microporous membrane to form an integrated structure. The porosity of the porous layer is preferably 50 to 90%, and particularly preferably 60 to 80%. Is. The porous layer is coated on the polyolefin microporous membrane for the purpose of imparting adhesiveness to electrodes and electrolyte retention, but if the porosity is low, it is disadvantageous in terms of ionic conductivity and deteriorates battery characteristics. Will be a factor. Therefore, the porosity is preferably 50% or more, more preferably 60% or more.
Also, a high porosity is advantageous in terms of conductivity, but is disadvantageous in terms of adhesiveness and electrolyte retention. Therefore, the porosity is preferably 90% or less, more preferably 80% or less.

The porosity (ε) is calculated from the volume (V) of the porous layer, the weight (W) of the organic polymer present in the volume and the density (D) of the organic polymer. be able to. That is, ε = {1- (W / DV)} × 10
It is 0. Here, the volume of the porous layer is determined by subtracting the volume of the polyolefin microporous membrane from the separator volume. Further, the weight of the organic polymer is obtained by subtracting the weight of the polyolefin microporous membrane from the weight of the separator.

Almost the entire front and back surfaces of the separator of the present invention are covered with the porous layer, but 0.05 to 10 μm pores may be scattered on the surface (outer side) of the porous layer. This is a feature of the non-aqueous secondary battery separator of the present invention. As described in JP-A-9-293518, those having substantially no through holes on the surface are advantageous from the viewpoint of electrolyte retention. However, since the entire interface of the electrode separator is covered with the polymer, this portion has a large resistance, which is disadvantageous in high rate discharge and the like. Also, if too large pores are present, the electrolyte retention becomes insufficient. From this point of view, it is preferable that the surface is interspersed with pores of 0.05 to 10 μm, and particularly preferably interspersed with pores of 0.1 to 3 μm.

The surface porosity of the separator of the present invention is preferably in the range of approximately 1 to 80%. The presence of such holes also has an advantageous effect on the adhesiveness to the electrode due to the roughening effect. The holes scattered on this surface are scanning electron microscopes (SE
M), and the pore size and surface porosity are SE
The result of M observation can be obtained by a method of image processing or the like.

The non-aqueous secondary battery separator of the present invention comprises:
It is also a feature that the total thickness of the front and back porous layers is 20 μm or less, and the thickness of the porous layer on each side is 1 μm or more. The porous layer is disadvantageous in ion conductivity particularly at low temperatures as compared with the polyolefin microporous membrane, and it is better that the thickness is as thin as possible. However, in order to secure the adhesiveness, a thicker one is preferable. From this point of view, the sum of the front and back sides is 20μ
m or less is preferable, and 15 μm or less is particularly preferable.
Further, the thickness of the porous layer on each side is preferably 1 μm or more. When the sum of the front and back surfaces of the porous layer is 20 μm or more, the resistance of the porous layer portion is remarkably reflected in the battery characteristics, which is disadvantageous in low temperature characteristics and high rate discharge characteristics. Further, if the thickness of each surface of the porous layer is 1 μm or less, the adhesion to the electrode becomes insufficient, which is not preferable.

In the case of a three-layer structure of porous layer / polyolefin microporous film / porous layer such as the separator for a non-aqueous secondary battery of the present invention, shrinkage occurs if the material forming the porous layer and the morphology are different from each other. It causes curling due to stress and is not preferable in handling. Although the curl depends on the physical properties of the polyolefin microporous membrane in the center, the curl tends to occur easily in applications such as a separator for a non-aqueous secondary battery that requires a thin film. For this reason, it is preferable that the materials forming the porous layer are essentially the same on the front and back. Further, it is preferable that the morphology of the front and the back is almost the same. The morphology of the porous layers on the front and back can be generally observed by SEM. Further, when the materials forming the porous layer are essentially the same, the morphology of the porous layer can be said to be the same on the front and back sides unless the separator curls.

When the materials forming the porous layer are essentially the same on the front and back, the morphology of the porous layers on the front and back can be estimated from the film thickness and the basis weight of each of the front and back of the porous layer. In order to prevent curling, {(difference in film thickness between the front and back porous layers) / (sum of film thickness between the front and back porous layers)} × 100
<20%, {(area difference between the front and back porous layers) /
(The unit weight of the porous layers on the front and back sides)} × 100 <20% is preferable. The thickness of the separator for a non-aqueous secondary battery of the present invention is 1 from the viewpoint of energy density and safety.
The range of 0 to 50 μm is preferable.

The non-aqueous secondary battery separator of the present invention comprises:
The organic polymer, an organic solvent that dissolves it and is compatible with water, and a phase-separating agent (gelling agent or pore-forming agent) are mixed and dissolved, and the dope is applied to the polyolefin micropores. It can be obtained by a wet film forming method in which the organic polymer is immersed in an aqueous coagulation bath to coagulate the organic polymer, and then washed and dried to form a porous film. This film-forming method is particularly suitable for controlling the morphology of the separator of the present invention because the porosity and the pore size can be easily controlled by the dope composition and the coagulation bath composition. The suitable conditions for obtaining the separator of the present invention will be specifically described below.

The organic solvent of the dope can be preferably used as long as it can dissolve the organic polymer and is compatible with water. When the organic polymer is a polyvinylidene fluoride (PVdF), a PVdF copolymer, or a PVdF-based polymer containing PVdF as a main component, those having a high polarity are preferable, and N-methylpyrrolidone (NMP), N, N-
Dimethylacetamide (DMAc), N, N-dimethylformamide (DMF), dimethylsulfoxide (DM)
SO), acetonitrile and the like are preferably selected, and these may be mixed and used. The concentration of the organic polymer in the dope is preferably 5 to 25% by weight.

The phase separating agent can be used as long as it is a poor solvent for the organic polymer and is compatible with water. When the organic polymer is PVdF, a PVdF copolymer, or a PVdF-based polymer containing them as a main component, for example, water and alcohols are preferably selected, and in particular, propylene glycols including polymers, ethylene glycol, and tripropylene. Glycol (TPG), 1,3-butanediol, 1,4-butanediol, polyethylene glycol monoethyl ether, polyhydric alcohols such as methanol, ethanol and glycerin are preferably selected. The concentration of the phase separation agent in the dope is suitably selected within the range of 0 to 60% by weight in the mixed solvent of the organic solvent and the phase separation agent.

For the coagulation bath, a mixed solution of water, an organic solvent solvent of the dope and a phase separating agent is preferably used. The proportion of water is 30
The preferred range is from 90 to 90% by weight, and the amount ratio of the organic solvent and the phase separating agent is more preferably the same as the amount ratio of the dope in terms of production. The separator of the present invention is prepared by mixing and dissolving the organic polymer, a volatile solvent that dissolves the organic polymer, and a plasticizer, coating the dope in a solution state on a polyolefin microporous membrane, and then drying to remove the volatile solvent. Alternatively, it can be obtained by a dry film-forming method in which the plasticizer is extracted with a volatile solvent that dissolves the plasticizer and does not dissolve the organic polymer and then dried to form a porous film.

Among these, as the method for producing the separator of the present invention, the above-mentioned wet film-forming method facilitates the control of the porosity of the porous layer and can be integrated with the polyolefin microporous membrane at the same time. Therefore, it is more preferable. [Non-Aqueous Secondary Battery] The non-aqueous secondary battery of the present invention is a non-aqueous secondary battery that includes a positive electrode and a negative electrode capable of reversibly doping and dedoping lithium and a separator, and uses a non-aqueous electrolyte solution. The non-aqueous secondary battery separator of the present invention is used, and other configurations are known. Less than,
The details will be described.

(Positive Electrode) The positive electrode of the non-aqueous secondary battery of the present invention
Is typically an active material that absorbs and releases lithium ions
It is composed of a binder polymer and a current collector. The above
Examples of active materials include various lithium-containing oxides and chalcogenides.
Compounds may be mentioned. Lithium-containing oxide
Then LiCoO₂Lithium-containing cobalt oxide such as
Thing, LiNiO₂Lithium-containing nickel oxide, such as
LiMn₂O _FourLithium-containing manganese composite oxide, such as
Lithium-containing nickel cobalt oxide, lithium-containing non-
Examples thereof include crystalline vanadium pentoxide. Well
Also, as chalcogen compounds, titanium disulfide, disulfide
Examples thereof include molybdenum.

As the binder polymer, polyvinylidene fluoride (PVdF); vinylidene fluoride (Vd)
F) and hexafluoropropylene (HFP), perfluoromethyl vinyl ether (PFMV), tetrafluoroethylene (TFE) binary copolymer; VdF / HFP / TF
E, a terpolymer resin containing PVdF as a main component such as VdF / HFP / CTFE; polytetrafluoroethylene,
Fluorine resin such as fluorine rubber, styrene-butadiene copolymer, styrene-acrylonitrile copolymer,
Hydrocarbon-based polymers such as ethylene-propylene-terpolymer, carboxymethyl cellulose, and polyimide resins can be used, but are not limited thereto. These may be used alone or in combination of two or more.

The amount of binder polymer added depends on the amount of active material 1
A range of 3 to 30 parts by weight is preferable with respect to 00 parts by weight.
If the amount of the binder is less than 3 parts by weight, a sufficient binding force for holding the active material cannot be obtained, which is not preferable. On the other hand, if it exceeds 30 parts by weight, the density of the active material in the positive electrode decreases, resulting in a decrease in the energy density of the battery, which is not preferable.

As the current collector, a material having excellent oxidation stability is preferably used. Specifically, aluminum, stainless steel, nickel, carbon, etc. can be mentioned. Particularly preferably, foil-shaped aluminum is used. Regarding the shape, a foil shape or a mesh shape can be used.

The positive electrode of the present invention may contain artificial graphite, carbon black (acetylene black), nickel powder or the like as a conductive auxiliary material. Carbon black is particularly preferable as the conductive additive. The amount added is preferably in the range of 0 to 10 parts by weight.

The method for producing the positive electrode of the present invention is not particularly limited, and known methods can be used. For example,
The following method can be adopted. A predetermined amount of the active material, the binder polymer, and the volatile solvent that dissolves the binder are mixed and dissolved to prepare a paste of the active material. A method in which the obtained paste is applied onto a current collector, and then the volatile solvent is dried and removed to form a film. A predetermined amount of the active material, the binder polymer, and the water-soluble solvent that dissolves the binder are mixed and dissolved to prepare a paste of the active material. A method of coating the obtained paste on a current collector, immersing the obtained coating film in an aqueous coagulation bath to coagulate the binder polymer, and then washing and drying the film to form a film.

(Negative Electrode) Next, the negative electrode of the present invention will be described. The negative electrode of the present invention is composed of a metal containing lithium as a main component or a carbonaceous active material that absorbs and releases lithium ions, a binder polymer, and a current collector. As the carbonaceous active material, polyacrylonitrile, phenol resin, phenol novolac resin, those obtained by sintering an organic polymer compound such as cellulose, those obtained by sintering coke or pitch, carbon represented by artificial graphite or natural graphite. Quality materials can be mentioned.

As the binder polymer, those similar to the above-mentioned positive electrode can be used. The amount of the binder polymer added is 3 to 30 with respect to 100 parts by weight of the active material.
A range of parts by weight is preferred. If the amount of the binder is less than 3 parts by weight, a sufficient binding force for holding the active material cannot be obtained, which is not preferable. Also, if it exceeds 30 parts by weight,
The active material density in the negative electrode is reduced, resulting in a decrease in the energy density of the battery, which is not preferable.

As the current collector, a material having excellent reduction stability is preferably used. Specific examples thereof include metallic copper, stainless steel, nickel and carbon.
Particularly preferably, foil-shaped and mesh-shaped copper is used. Further, the negative electrode of the present invention may contain artificial graphite, carbon black (acetylene black), nickel powder or the like as a conductive auxiliary material.

The negative electrode of the non-aqueous secondary battery of the present invention is manufactured by a known method like the positive electrode. (Non-Aqueous Electrolyte) In the non-aqueous secondary battery of the present invention, a non-aqueous electrolyte in which a lithium salt is dissolved in a non-aqueous solvent can be used.

Specific lithium salts include lithium borotetrafluoride (LiBF ₄ ) and lithium perchlorate (LiCl
O ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium arsenic hexafluoride (LIAsF ₆ ), lithium trifluorosulphonate (CF ₃ SO ₃ Li), lithium perfluoromethylsulfonyl imide [LiN (CF ₃ SO 4 ₂ ) ₂ ] and lithium perfluoroethylsulfonylimide [Li
N (C ₂ F ₅ SO ₂ ) ₂ ] and the like can be used. Also,
The concentration of the lithium salt is 0.2 to 2M (molar
The range of / l) is preferably used.

As the non-aqueous solvent for dissolving these lithium salts, propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (B
C), dimethyl carbonate (DMC), diethyl carbonate (DEC), vinylene carbonate (VC),
Methyl ethyl carbonate (MEC), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE),
A single solvent such as γ-butyrolactone (γ-BL), sulfolane or acetonitrile, or a mixed solvent obtained by mixing two or more kinds of these can also be used. Especially, PC, EC, γ-B
At least one solvent selected from L, DMC, DEC, MEC and DME is preferably used.

(Exterior) As the exterior of the non-aqueous secondary battery of the present invention, an aluminum laminate film is preferably used in addition to the commonly used cans such as stainless steel and aluminum.
Further, there are various types of aluminum laminated films, but they are not particularly limited as long as they are used for non-aqueous secondary batteries.

(Manufacturing Method) The non-aqueous secondary battery of the present invention can be preferably manufactured by a known non-aqueous secondary battery manufacturing method. That is, a positive electrode, a separator, and a negative electrode are sequentially stacked to produce a battery element of positive electrode / separator / negative electrode. It can be manufactured by enclosing this in an exterior. The electrolytic solution may be injected before or after the enclosure.
In the case of the separator of the present invention, there is no particular problem in manufacturing a non-aqueous secondary battery by the manufacturing method as described above even in the aluminum laminate film exterior because it has excellent adhesiveness to the electrode, but the adhesiveness of the electrode and the separator is good. In order to make the battery stronger, the battery element may be subjected to pressure treatment or heat treatment. This treatment may be performed before or after the electrolytic solution is injected. Further, the adhesiveness can be strengthened by heat aging treatment after injecting the electrolytic solution after enclosing the outer package. This heating aging may be performed before charging or after charging to an appropriate charging depth.

[0043]

The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the following examples.

Example 1 As the organic polymer, the copolymer composition was VdF / HFP / CTFE = 92.0 / 4.5 /
A fluoropolymer having a Mw of 410,000 (weight ratio) of 3.5 was used. The fluorine-containing polymer was dissolved in a mixed solvent of DMAc (organic solvent): TPG (phase separating agent) = 6: 4 (weight ratio) so as to be 12% by weight to adjust the dope.

A polypropylene microporous membrane (Celgard # 2400 manufactured by Celgard) was used as the porous support. The thickness of this polypropylene microporous film is 25.6μ.
m and areal weight was 14.8 g / m ² .

The dope was coated on both front and back surfaces of a polypropylene microporous film. The polypropylene microporous membrane coated with this dope was immersed in a coagulation bath to coagulate. Here, the coagulation bath composition was water: DMAc: TPG = 5: 3: 2. Then
It was washed with water and dried to form a film of the non-aqueous secondary battery separator of the present invention.

The characteristics of the separator for a non-aqueous secondary battery of the present invention in which a porous layer is laminated on almost the entire front and back surfaces of the produced polypropylene microporous membrane and the microporous membrane and the porous layer are integrated are as follows. It was on the street. Porosity of porous layer 67.
2%, the film thickness of the separator was 39.5 μm, the total thickness of the porous layer was 14.0 μm, the thickness of the porous layer on each side was 7.1 μm and 6.9 μm, and the basis weight on each side was 4.
1 g / m ² , 4.0 g / m ² . As a result of SEM observation, it was observed that holes having a pore diameter of 0.1 to 0.5 μm were scattered on the surface, and the surface open area ratio was about 10%. further,
The produced separator did not curl significantly.

Example 2 As the organic polymer, the copolymer composition was VdF / HFP / CTFE = 92.0 / 4.5 /
A fluoropolymer having a Mw of 410,000 (weight ratio) of 3.5 was used. The fluoropolymer was dissolved in a mixed solvent of DMAc (organic solvent): TPG (phase separating agent) = 55: 45 (weight ratio) so as to be 8% by weight to adjust the dope.

A polypropylene microporous membrane (Celgard # 2400 manufactured by Celgard) was used as the porous support. The thickness of this polypropylene microporous film is 25.6μ.
m and areal weight was 14.8 g / m ² .

The dope was applied to both front and back surfaces of a polypropylene microporous film. The polypropylene microporous membrane coated with the dope was immersed in a coagulation bath to coagulate. Here, the coagulation bath composition was water: DMAc: TPG = 5: 3: 2. Then, it was washed with water and dried to form a film of the separator for a non-aqueous secondary battery of the present invention.

The characteristics of the separator for a non-aqueous secondary battery of the present invention in which a porous layer is laminated on almost the entire front and back surfaces of the produced polypropylene microporous membrane and the microporous membrane and the porous layer are integrated are as follows. It was on the street. Porosity of porous layer 72.
9%, the thickness of the separator was 34.2 μm, the total thickness of the porous layer was 8.6 μm, and the thickness of the porous layer on each side was 4.
3μm and 4.3μm, each side has a basis weight of 2.1g
/ M ² , 2.0 g / m ² . As a result of SEM observation, it was observed that holes having a pore diameter of 0.1 to 0.5 μm were scattered on the surface, and the surface open area ratio was about 20%. Furthermore, the produced separator did not curl significantly.

[Comparative Example 1] The same procedure as in Example 1 was repeated, except that the solution prepared by dissolving the fluoropolymer used in Example 1 in DMAc in an amount of 12% by weight was used as the dope and the coagulation bath was water. A non-aqueous secondary battery separator was produced. The surface of the produced separator was observed by SEM, but no hole was observed.

[Comparative Example 2] A solution prepared by dissolving the fluoropolymer used in Example 1 in DMAc in an amount of 12% by weight was used as a dope, which was applied to a polypropylene microporous membrane (Celgard # 2400 manufactured by Celgard). Coating was performed on the front and back in the same manner as in Example 1. A non-aqueous secondary battery separator was produced by coating and drying and then forming a dense film made of the fluoropolymer on the front and back of the polypropylene microporous film.

Example 3 "Positive electrode" 89.5 parts by weight of lithium cobalt oxide (LiCoO ₂ , manufactured by Nippon Kagaku Kogyo Co., Ltd.) powder, 4.5 parts by weight of acetylene black and 6 parts by weight of PVdF dry. As a result, a positive electrode paste was prepared by using a 6 wt% PVdF NMP solution. The resulting paste has a thickness of 20
97μ thickness after coating and drying on aluminum foil of μm
m positive electrode was obtained.

"Negative electrode" Mesophase carbon microbeads (MCMB, Osaka Gas Chemical Co., Ltd.) as a negative electrode active material
Powder), 87 parts by weight of powder, 3 parts by weight of acetylene black, and 10 parts by weight of PVdF dry weight.
A negative electrode paste was prepared using a Nd solution of PVdF in a weight percentage. The obtained paste was applied on a copper foil having a thickness of 18 μm, dried and pressed to produce a negative electrode having a thickness of 90 μm.

[Preparation of Button Battery] A button battery (CR2032) was prepared using the separator prepared in Examples 1 and 2 and the above positive electrode and negative electrode. 1 M L for electrolyte
iPF ₆ EC / DEC / MEC (1/2/1 weight ratio)
Was used. The discharge capacity ratio of 2C discharge to 0.2C discharge at 4.2V constant current / constant voltage charge and 2.75V constant current discharge of this button battery was measured. The results are shown in Table 1.

[Comparative Example 3] Separators and polypropylene microporous membranes produced in Comparative Examples 1 and 2 (manufactured by Celgard)
A button battery was prepared in the same manner as in Example 3 using Cell Guard # 2400), and the same measurement was performed. The results are shown in Table 1.

[0058]

[Table 1]

From Table 1, in the separator of the present invention,
It can be seen that there is almost no reduction in ionic conductivity due to the porous layer coated on the polyolefin microporous membrane.

Example 4 Using the positive electrode and negative electrode of Example 3 and the separator prepared in Examples 1 and 2, these were stacked to form a battery element consisting of positive electrode / separator / negative electrode. This battery element was placed in an aluminum laminate film pack, and an electrolytic solution was injected under reduced pressure to seal the aluminum laminate film pack. Here, 1 M LiPF ₆ EC / DEC / MEC (1
/ 2/1 weight ratio) was used. This film-clad battery worked well, and when the battery was disassembled after the charge / discharge measurement, the separator and the electrode were sufficiently bonded.

[0061]

As described above in detail, according to the present invention, the porous layer having excellent ion permeability and good adhesiveness is coated on the front and back surfaces of the microporous polyolefin membrane to thereby improve the adhesiveness to the electrode. It is possible to provide a separator which is excellent in ionic conductivity and has a lower ionic conductivity than that of the microporous polyolefin membrane, and which is excellent in handleability due to integration. The present invention is particularly suitable as a separator for a film-clad battery.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroki Sano             2-1, Hinodecho, Iwakuni, Yamaguchi Prefecture Teijin Limited             Company Iwakuni Research Center (72) Inventor Takahiro Omido             2-1, Hinodecho, Iwakuni, Yamaguchi Prefecture Teijin Limited             Company Iwakuni Research Center F-term (reference) 5H021 AA06 CC04 EE04 EE10 EE15                       EE27 HH02 HH03                 5H029 AJ00 AK03 AK05 AL06 AL07                       AM02 AM03 AM04 AM05 AM07                       DJ04 DJ13 EJ12 EJ14 HJ00                       HJ04 HJ06 HJ09

Claims (4)

[Claims] 1. A separator used in a non-aqueous secondary battery, which obtains an electromotive force by doping / dedoping lithium,
The separator is provided with a porous layer made of an organic polymer that swells and holds an electrolyte solution on the entire front and back surfaces of the polyolefin microporous membrane, and is integrated with the polyolefin microporous membrane, and the voids of the porous layer are integrated. The total thickness of the porous layers on the front and back sides in which pores having a pore diameter of 0.05 to 10 μm are scattered on the surface of the porous layer having a ratio of 50 to 90% is 20 μm or less, and the thickness of the porous layer is A separator for a non-aqueous secondary battery, characterized in that each side has a thickness of 1 μm or more. 2. The separator for a non-aqueous secondary battery according to claim 1, which has a surface porosity of 1 to 80%. 3. The non-woven fabric according to claim 1, wherein the organic polymer is polyvinylidene fluoride (PVdF), a PVdF copolymer, or a PVdF-based polymer containing them as a main component. Water-based secondary battery separator. 4. A non-aqueous secondary battery comprising a positive electrode and a negative electrode capable of reversibly doping / de-doping lithium, and a separator, wherein the separator is any one of claims 1 to 3. A non-aqueous secondary battery characterized by using the non-aqueous secondary battery separator of.