JP4127989B2 - Non-aqueous secondary battery separator and non-aqueous secondary battery - Google Patents

Description

【００５９】
表１より本発明のセパレータにおいては、ポリオレフィン微多孔膜上へ塗工した多孔質層によるイオン伝導性の低下がほとんどないことが分かる。
【００６０】
［実施例４］
実施例３の正極及び負極と実施例１及び２で作製したセパレータを用い、これらを重ね合わせ正極／セパレータ／負極からなる電池エレメントを成型した。この電池エレメントをアルミラミネートフィルムパックに入れ、減圧下で電解液を注入し、アルミラミネートフィルムパックを封止した。ここで、電解液には、１Ｍ ＬｉＰＦ₆ ＥＣ／ＤＥＣ／ＭＥＣ（１／２／１重量比）を用いた。このフィルム外装電池は良好に作動し、充放電測定後電池を解体したところセパレータと電極は十分に接着されていた。
【００６１】
【発明の効果】
以上詳述してきたように本発明によれば、イオン透過性に優れかつ接着性良好な多孔質層をポリオレフィン微多孔膜の表裏に塗工することで、電極との接着性が良好でかつポリオレフィン微多孔膜に比べイオン伝導性の低下がなく、一体化によるハンドリング性に優れたセパレータを提供することが可能となる。本発明は、特にフィルム外装電池のセパレータとして好適である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous secondary battery that obtains an electromotive force by doping or dedoping lithium. In particular, the present invention relates to a separator used for a non-aqueous secondary battery.
[0002]
[Prior art]
Other non-aqueous secondary batteries (lithium ion secondary batteries) that use lithium-containing transition metal oxides for the positive electrode, lithium-doped / dedoped carbon-based materials for the negative electrode, and non-aqueous electrolyte solutions Compared to the secondary battery, it has a feature of having a high energy density. This lithium ion secondary battery meets the demands 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 laptop computers. However, demands for reducing the weight and thickness of portable electronic devices are becoming more and more severe. In view of this, the lithium-ion secondary battery used for this is currently undergoing intense technological development in order to further increase the energy.
[0003]
In the flat lithium ion secondary battery mainly used for mobile phones, technological innovation has been made in recent years to change the exterior from a conventional metal can to an aluminum laminate film in response to demands for thinning and weight reduction. 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, liquid leakage was a concern and there was a problem from the viewpoint of safety. For this reason, the film structure battery cannot be realized with the conventional battery configuration of positive electrode / separator / negative electrode.
[0004]
Nevertheless, this technological innovation has been made possible by the technology of a separator with excellent adhesion to electrodes and electrolyte retention. By using this separator, it was possible to achieve good interface contact between the electrode and the separator and to prevent liquid leakage. For this separator, an organic polymer that swells and holds in the electrolyte is used. Although it was considered that such an organic polymer was used alone as a separator, it was put to practical use in a form that is generally reinforced by a support, not suitable for continuous production due to problems in physical properties.
[0005]
That is, a separator has been proposed in which an adhesive layer made of an organic polymer that swells and retains an electrolyte solution is applied to both surfaces of a support. Polyolefin microporous membranes used as separators in nonwoven fabrics and conventional lithium ion secondary batteries have been proposed for the support, but currently polyolefin microporous membranes are mainly put into practical use from the viewpoint of safety due to shutdown characteristics Has been. In addition, an organic polymer mainly composed of polyvinylidene fluoride (PVdF) is mainly used for the adhesive layer from the viewpoint of durability.
[0006]
In addition, the battery configuration in which the adhesive layer is disposed between the electrode and the separator as described above is not only from the viewpoint of enabling the film exterior, but also from the viewpoint of increasing the energy density of the battery in the conventional metal can exterior. ing. High energy density means that many battery elements are tightly packed 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 are problems. However, there is a possibility that this problem can be solved by disposing a flexible adhesive layer as described above.
[0007]
In the background as described above, a polyolefin microporous membrane separator having adhesive layers on the front and back sides has attracted attention. Among these, from the viewpoint of utilizing the current non-aqueous secondary battery manufacturing process, a separator having an adhesive layer (dry adhesive layer) not containing an electrolytic solution has become an important technical element. Such separators have been proposed in JP-A-9-293518, JP-A-10-189054, JP-A-11-26025, JP-A-2001-118558, and the like.
[0008]
[Problems to be solved by the invention]
JP-A-10-189054 discloses a separator having an adhesive layer by applying a dope obtained by dissolving PVdF in N-methylpyrrolidone (NMP) on a polyolefin microporous film and drying it. Such a system has a problem that the adhesive layer becomes dense and good ionic conductivity cannot be obtained, and the battery characteristics deteriorate. Japanese Patent Application Laid-Open No. 2001-118558 proposes a separator in which an adhesive layer is partially coated on a polyolefin microporous film (surface coverage: 50% or less) in order to solve such problems. Since this system is a partial coating, there are many free electrolytes that are not retained by the separator at the electrode / separator interface, which causes problems such as deterioration in cycle characteristics. Moreover, it is not suitable for film exterior from the viewpoint of reliability of liquid leakage.
[0009]
Japanese Laid-Open Patent Publication No. 9-293518 proposes to obtain a separator having an adhesive layer by preparing an adhesive layer made of PVdF by a wet film forming method and bonding it to a polyolefin microporous film. It is characterized by having no holes. Since the PVdF film as an adhesive layer has low physical properties, the method of bonding with a polyolefin microporous film is problematic from the viewpoint of productivity. In addition, according to the description, the bonding is not simply integrated by simply overlapping, but there may be a problem of peeling of the polyolefin microporous film and the adhesive layer. Furthermore, although it has the feature that there is no substantial through-hole on the surface, since there is no through-hole, ion conduction at the electrode / separator interface also becomes a problem, and a decrease in rate characteristics and the like is expected.
[0010]
In JP-A-11-26025, a separator is obtained by a general wet film forming process in which a dope obtained by dissolving PVdF in NMP is applied onto a polyolefin microporous film, and this is solidified in water. This system has the same problems as described above because the coagulation bath is water and thus solidifies quickly and a dense PVdF layer is formed on the surface and does not have substantial through holes.
[0011]
As described above, in the polyolefin microporous membrane separator having the adhesive layers on the front and back surfaces, a configuration that sufficiently satisfies the required characteristics such as ion conductivity, liquid retention, adhesion, and productivity has not been found at present. 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 polyolefin microporous membrane, which has good ion conductivity and good adhesion to an electrode.
[0012]
[Means for Solving the Problems]
In order to solve the above problems, the present invention
In a separator used in a non-aqueous secondary battery that obtains an electromotive force by doping or dedoping of lithium, the separator is a porous material composed of an organic polymer that swells and retains the electrolyte on the entire front and back surfaces of the polyolefin microporous membrane. A layer is disposed and integrated with the polyolefin microporous membrane,
(1) The porosity of the porous layer is 50 to 90%
(2) The surface of the porous layer is dotted with pores having a pore diameter of 0.05 to 10 μm.
(3) The total thickness of the porous layers on the front and back sides is 20 μm or less, and the thickness of the porous layer is 1 μm or more on each side.
Non-aqueous secondary battery separator
I will provide a.
[0013]
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 invention described above, wherein the surface porosity is 1 to 80%.
(A) The organic polymer is polyvinylidene fluoride (PVdF), a PVdF copolymer, or a PVdF-based polymer mainly composed of these, and the non-aqueous two-component system according to any one of (a) Secondary battery separator.
(C) A non-aqueous secondary battery comprising a positive electrode and a negative electrode capable of reversibly doping / de-doping lithium and a separator, and using a non-aqueous electrolyte, and any of the inventions (a) to (b) as the separator. A non-aqueous secondary battery using the separator according to claim 1.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The contents of the present invention will be described below.
[Separator for non-aqueous secondary battery]
The separator for a non-aqueous secondary battery of the present invention is integrated with the polyolefin microporous membrane by disposing a porous layer made of an organic polymer that swells and holds the electrolyte solution on the entire front and back surfaces of the polyolefin microporous membrane. And
(1) The porosity of the porous layer is 50 to 90%
(2) The surface of the porous layer is dotted with pores having a pore diameter of 0.05 to 10 μm.
(3) The total thickness of the porous layers on the front and back sides is 20 μm or less, and the thickness of the porous layer is 1 μm or more on each side.
It is characterized by that.
[0015]
As the polyolefin microporous film, a known film having a film thickness of 5 to 30 μm proposed as a porous support for a separator for a non-aqueous secondary battery can be suitably used.
Examples of the organic polymer that swells and retains the electrolyte include polyvinylidene fluoride (PVdF), polyethylene oxide (PEO), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), and copolymers thereof. In the present invention, these may be used alone or in combination of two or more.
[0016]
Among these, in consideration of durability and film forming property, PVdF, PVdF copolymer, or PVdF polymer mainly composed of these is preferably used. More preferably, PVdF and PVdF copolymer can be mentioned. Among these, in particular, a terpolymer of vinylidene fluoride (VdF), hexafluoropropylene (HFP), and chlorotrifluoroethylene (CTFE) is swellable / retainable with respect to the electrolyte, heat resistance, and adhesion to the electrode. Is preferable, and as a suitable copolymer composition of this ternary copolymer,
VdF / HFP (a) / CTFE (b)
(A) = 2-8% by weight
(B) = 1-6% by weight
Is mentioned. Further, the molecular weight of the organic polymer is preferably 100,000 to 800,000 in terms of weight average molecular weight (Mw), and particularly preferably 200,000 to 600,000. These PVdF polymers can be synthesized by a known method. In general, it can be synthesized by a radical polymerization method, and specifically, prepared by a method such as solution polymerization, suspension polymerization, emulsion polymerization, bulk polymerization or the like.
[0017]
The separator for a non-aqueous secondary battery of the present invention has a structure in which the porous layer is arranged on the front and back of the polyolefin microporous membrane, and the porosity of the porous layer is 50 to 90%. Is preferable, and 60 to 80% is particularly preferable. The porous layer is coated on the microporous polyolefin membrane for the purpose of providing adhesion to the electrode and electrolyte retention, but if the porosity is low, the ionic conductivity is disadvantageous and the battery characteristics are degraded. It becomes a factor to make. For this reason, the porosity is preferably 50% or more, and more preferably 60% or more. A high porosity is advantageous in terms of conductivity, but is disadvantageous in terms of adhesiveness and electrolyte retention. For this reason, the porosity is preferably 90% or less, and more preferably 80% or less.
[0018]
Here, the porosity (ε) can be 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. . That is, ε = {1− (W / DV)} × 100. Here, the volume of the porous layer is obtained by subtracting the volume of the polyolefin microporous membrane from the volume of the separator. The weight of the organic polymer can be obtained by subtracting the weight of the polyolefin microporous membrane from the weight of the separator.
[0019]
The entire surface of the front and back surfaces of the separator of the present invention is covered with the porous layer. However, the surface (outside) of the porous layer is also dotted with pores of 0.05 to 10 μm. This is a feature of a separator for an aqueous secondary battery. 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 electrode separator interface is entirely covered with the polymer, this portion becomes a large resistance, which is disadvantageous in high-rate discharge or the like. Also, if there are too large pores, the electrolyte retention will not be sufficient. From such a viewpoint, it is preferable that 0.05 to 10 μm holes are scattered on the surface, and it is particularly preferable that 0.1 to 3 μm holes are scattered.
[0020]
The surface porosity of the separator of the present invention is preferably in the range of 1 to 80%. The presence of such holes also works advantageously in adhesion to the electrode due to the roughening effect. The holes scattered on the surface can be observed with a scanning electron microscope (SEM), and the hole diameter and the surface opening ratio can be obtained by a method of image processing the results of SEM observation.
[0021]
The separator for a non-aqueous secondary battery of the present invention is also characterized in that the total thickness of the porous layers on the front and back sides is 20 μm or less, and the thickness of the porous layer is 1 μm or more on each side. The porous layer is disadvantageous in terms of ionic conductivity particularly at a low temperature as compared with the polyolefin microporous membrane, and the thickness should be as thin as possible. However, a thicker one is preferable for ensuring adhesion. From such a viewpoint, the sum of the front and back surfaces is preferably 20 μm or less, and particularly preferably 15 μm or less. 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 battery characteristics, which is disadvantageous in low temperature characteristics and high rate discharge characteristics. Moreover, when the thickness of each surface of the porous layer is 1 μm or less, the adhesion with the electrode is insufficient, which is not preferable.
[0022]
In the case of a three-layer structure such as a porous layer / polyolefin microporous membrane / porous layer such as a separator for a non-aqueous secondary battery of the present invention, the relationship between shrinkage stresses if the material and morphology used to form the porous layer are different on the front and back sides. This causes curling and is not preferable in handling. Although curling depends on the physical properties of the polyolefin microporous membrane at the center, curling tends to occur easily in applications that require thinning, such as a separator for a non-aqueous secondary battery. For these reasons, it is preferable that the materials forming the porous layer are essentially equivalent on the front and back sides. Further, it is preferable that the front and back morphologies are substantially the same. The morphology of the porous layers on the front and back sides can be generally observed by SEM. In addition, when the materials forming the porous layer are essentially the same, it can be said that the morphology of the porous layer is the same on both sides if the separator is not curled.
[0023]
When the material forming the porous layer is essentially the same on the front and back, the morphology of the porous layer on the front and back can be estimated from the film thickness and basis weight of the front and back of the porous layer. In order to prevent curling, {(thickness difference between the porous layers on the front and back sides) / (sum of the thickness of the porous layers on the front and back sides)} × 100 <20%, {(the porous materials on the front and back sides) Layer weight difference) / (sum of the weight of the porous layers on the front and back sides)} × 100 <20%.
The film thickness of the nonaqueous secondary battery separator of the present invention is preferably in the range of 10 to 50 μm from the viewpoint of energy density and safety.
[0024]
The separator for a non-aqueous secondary battery of the present invention is a dope obtained by mixing and dissolving the organic polymer, an organic solvent that dissolves the organic polymer, and a phase separation agent (gelling agent or pore-opening agent). Can be obtained by a wet film forming method in which the film is immersed in a microporous polyolefin, and then the film is immersed in an aqueous coagulation bath to coagulate the organic polymer, followed by washing and drying 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 pore diameter can be easily controlled by the dope composition and the coagulation bath composition. Specific conditions for obtaining the separator of the present invention are specifically described below.
[0025]
The organic solvent for the dope can be suitably used as long as it can dissolve the organic polymer and is compatible with water. When the organic polymer is a PVdF-based polymer mainly composed of polyvinylidene fluoride (PVdF), a PVdF copolymer, and PVdF, a highly polar one is preferable, and N-methylpyrrolidone (NMP), N, N-dimethylacetamide (DMAc), N, N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetonitrile and the like are suitably selected, and these may be used in combination. The organic polymer concentration in the dope is preferably selected from 5 to 25% by weight.
[0026]
The phase separation 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, and a PVdF polymer mainly composed of these, for example, water and alcohols are preferably selected. In particular, propylene glycols including polymers, ethylene glycol, tripropylene, and the like. Glycolic alcohols such as glycol (TPG), 1,3-butanediol, 1,4-butanediol, polyethylene glycol monoethyl ether, methanol, ethanol, glycerin and the like are preferably selected. The concentration of the phase separation agent in the dope is preferably in the range of 0 to 60% by weight in the mixed solvent of the organic solvent and the phase separation agent. Choice It is.
[0027]
As the coagulation bath, a mixed solution of water, an organic solvent solvent of the dope and a phase separation agent is preferably used. The proportion of water is preferably in the range of 30 to 90% by weight, and the amount ratio of the organic solvent and the phase separation agent is preferably combined with these amount ratios in the dope for production.
In the separator of the present invention, the organic polymer, a volatile solvent for dissolving the organic polymer, and a plasticizer are mixed and dissolved, and the dope in a solution state is applied to the polyolefin microporous film, and then dried to remove the volatile solvent. Thereafter, the plasticizer is extracted with a volatile solvent that does not dissolve the plasticizer and does not dissolve the organic polymer, and is then dried to obtain a porous film.
[0028]
Among these, as the method for producing the separator of the present invention, the above-mentioned wet film-forming method is more preferable because the porous layer can be easily controlled to be porous and can be integrated with the polyolefin microporous film at the same time. It is.
[Non-aqueous secondary battery]
The non-aqueous secondary battery of the present invention is a non-aqueous secondary battery including a positive electrode and a negative electrode capable of reversibly doping and dedoping lithium and a separator, and using a non-aqueous electrolyte. A secondary battery separator is used, and other configurations are known. Details will be described below.
[0029]
(Positive electrode)
The positive electrode of the non-aqueous secondary battery of the present invention is typically composed of an active material that absorbs and releases lithium ions, a binder polymer, and a current collector.
Examples of the active material include various lithium-containing oxides and chalcogen compounds. As the lithium-containing oxide, LiCoO ₂ Lithium-containing cobalt oxides such as LiNiO ₂ Lithium-containing nickel oxide such as LiMn ₂ O _Four And lithium-containing manganese composite oxide, lithium-containing nickel cobalt oxide, lithium-containing amorphous vanadium pentoxide, and the like. Examples of the chalcogen compound include titanium disulfide and molybdenum disulfide.
[0030]
As the binder polymer, polyvinylidene fluoride (PVdF); binary copolymer of vinylidene fluoride (VdF) and hexafluoropropylene (HFP), perfluoromethylvinyl-ter (PFMV), tetrafluoroethylene (TFE); Ternary copolymer resins mainly composed of PVdF such as VdF / HFP / TFE and VdF / HFP / CTFE; fluorinated resins such as polytetrafluoroethylene and fluorinated rubber, styrene-butadiene copolymers, styrene Hydrocarbon polymers such as acrylonitrile copolymer and ethylene-propylene terpolymer, carboxymethyl cellulose, polyimide resin, and the like can be used, but are not limited thereto. Moreover, these may be used independently or may be used in mixture of 2 or more types.
[0031]
The amount of the binder polymer added is preferably in the range of 3 to 30 parts by weight with respect to 100 parts by weight of the active material. When the amount of the binder is less than 3 parts by weight, it is not preferable because a sufficient binding force for holding the active material cannot be obtained. Moreover, when it exceeds 30 weight part, the active material density in a positive electrode will fall, as a result, the energy density fall of a battery will be caused and it becomes unpreferable.
[0032]
As the current collector, a material having excellent oxidation stability is preferably used. Specific examples include aluminum, stainless steel, nickel, and carbon. Particularly preferably, foil-like aluminum is used. Moreover, about a shape, a foil shape and a mesh shape can be used.
[0033]
Further, the positive electrode of the present invention may contain artificial graphite, carbon black (acetylene black), nickel powder and the like as a conductive additive. Carbon black is particularly preferable as the conductive assistant. The addition amount is preferably in the range of 0 to 10 parts by weight.
[0034]
The manufacturing method of the positive electrode of this invention is not specifically limited, A well-known method can be used. For example, the following method can be employed.
(1) A predetermined amount of an active material, a binder polymer, and a volatile solvent for dissolving the binder are mixed and dissolved to prepare an active material paste. A method of forming a film by coating the obtained paste on a current collector and then removing the volatile solvent by drying.
(2) A predetermined amount of an active material, a binder polymer, and a water-soluble solvent for dissolving the binder are mixed and dissolved to prepare an active material paste. A method of coating the obtained paste on a current collector, immersing the obtained coating film in an aqueous coagulation bath, coagulating the binder polymer, and then washing and drying the film to form a film.
[0035]
(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 mainly composed of lithium or a carbonaceous active material that absorbs and releases lithium ions, a binder polymer, and a current collector.
Examples of the carbonaceous active material include polyacrylonitrile, phenol resin, phenol novolac resin, those obtained by sintering organic polymer compounds such as cellulose, those obtained by sintering coke and pitch, carbon typified by artificial graphite and natural graphite. A quality material can be mentioned.
[0036]
As a binder polymer, the same thing as the positive electrode mentioned above can be used. The amount of the binder polymer added is preferably in the range of 3 to 30 parts by weight with respect to 100 parts by weight of the active material. When the amount of the binder is less than 3 parts by weight, it is not preferable because a sufficient binding force for holding the active material cannot be obtained. Moreover, when it exceeds 30 weight part, the active material density in a negative electrode will fall, as a result, the energy density fall of a battery will be caused and it becomes unpreferable.
[0037]
As the current collector, a material excellent in reduction stability is preferably used. Specifically, metallic copper, stainless steel, nickel, carbon, etc. can be mentioned. Particularly preferably, copper in the form of foil or mesh is used.
Moreover, the negative electrode of the present invention may contain artificial graphite, carbon black (acetylene black), nickel powder, and the like as a conductive additive.
[0038]
The negative electrode of the nonaqueous secondary battery of the present invention is produced by a known method in the same manner as the positive electrode.
(Non-aqueous electrolyte)
In the non-aqueous secondary battery of the present invention, a non-aqueous electrolyte solution in which a lithium salt is dissolved in a non-aqueous solvent can be used.
[0039]
Specific lithium salts include lithium borotetrafluoride (LiBF). _Four ), Lithium perchlorate (LiClO) _Four ), Lithium hexafluorophosphate (LiPF) ₆ ), Lithium arsenic hexafluoride (LIAsF) ₆ ), Lithium trifluorosulfonate (CF) _Three SO _Three Li), lithium perfluoromethylsulfonylimide [LiN (CF _Three SO ₂ ) ₂ ] And lithium perfluoroethylsulfonylimide [LiN (C ₂ F _Five SO ₂ ) ₂ ] Can be used. The lithium salt concentration is preferably in the range of 0.2 to 2M (mol / l).
[0040]
Examples of non-aqueous solvents for dissolving these lithium salts include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), vinylene carbonate (VC), Single solvents such as methyl ethyl carbonate (MEC), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), γ-butyrolactone (γ-BL), sulfolane, acetonitrile, and two or more of these A mixed solvent obtained by mixing can also be used. In particular, at least one solvent selected from PC, EC, γ-BL, DMC, DEC, MEC and DME is preferably used.
[0041]
(Exterior)
For the exterior of the non-aqueous secondary battery of the present invention, an aluminum laminate film is preferably used in addition to commonly used cans such as stainless steel and aluminum. There are various types of aluminum laminate films, but there are no particular limitations as long as they are used for non-aqueous secondary batteries.
[0042]
(Production method)
The non-aqueous secondary battery of the present invention can be suitably 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 it in an exterior. The electrolytic solution may be injected before the outer enclosure or after the enclosure. In the case of the separator of the present invention, there is no particular problem even if a non-aqueous secondary battery is produced by the above-described production method even in the case of an aluminum laminate film because it has excellent adhesion to the electrode, but the adhesion between the electrode and the separator May be subjected to pressure treatment or heat treatment. This treatment may be performed before or after electrolyte injection. In addition, the adhesiveness can be strengthened by injecting the electrolyte after enclosing and then heat aging. This heating aging may be performed before charging or after charging to an appropriate charging depth.
[0043]
【Example】
Hereinafter, the present invention will be described in detail by way of examples. However, the present invention is not limited to the following examples.
[0044]
[Example 1]
As the organic polymer, a fluoropolymer having a copolymer composition of VdF / HFP / CTFE = 92.0 / 4.5 / 3.5 (weight ratio) and Mw = 410,000 was used. The dope was prepared by dissolving the fluoropolymer in a mixed solvent of DMAc (organic solvent): TPG (phase separation agent) = 6: 4 (weight ratio) to 12 wt%.
[0045]
A polypropylene microporous membrane (Celguard # 2400 manufactured by Celgard) was used as the porous support. This polypropylene microporous membrane has a thickness of 25.6 μm and a basis weight of 14.8 g / m. ² Met.
[0046]
The dope was applied to both the front and back surfaces of a polypropylene microporous membrane. The polypropylene microporous film coated with this dope was immersed in a coagulation bath and coagulated. The coagulation bath composition was water: DMAc: TPG = 5: 3: 2. Next, it was washed with water and dried to form a non-aqueous secondary battery separator of the present invention.
[0047]
The properties of the separator for a non-aqueous secondary battery according to 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. The porosity of the porous layer is 67.2%, the thickness of the separator is 39.5 μm, the total thickness of the porous layer is 14.0 μm, and the thickness of the porous layer on each side is 7.1 μm and 6.9 μm. The basis weight is 4.1 g / m ² 4.0 g / m ² . As a result of SEM observation, it was observed that pores having a pore diameter of 0.1 to 0.5 μm were scattered on the surface, and the surface area ratio was about 10%. Furthermore, the produced separator was not significantly curled.
[0048]
[Example 2]
As the organic polymer, a fluoropolymer having a copolymer composition of VdF / HFP / CTFE = 92.0 / 4.5 / 3.5 (weight ratio) and Mw = 410,000 was used. The dope was prepared by dissolving the fluorine-based polymer in a mixed solvent of DMAc (organic solvent): TPG (phase separation agent) = 55: 45 (weight ratio) to 8 wt%.
[0049]
A polypropylene microporous membrane (Celguard # 2400 manufactured by Celgard) was used as the porous support. This polypropylene microporous membrane has a thickness of 25.6 μm and a basis weight of 14.8 g / m. ² Met.
[0050]
The dope was applied to both the front and back surfaces of a polypropylene microporous membrane. The polypropylene microporous film coated with the dope was immersed in a coagulation bath and coagulated. The coagulation bath composition was water: DMAc: TPG = 5: 3: 2. Next, it was washed with water and dried to form a non-aqueous secondary battery separator of the present invention.
[0051]
The properties of the separator for a non-aqueous secondary battery according to 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. The porosity of the porous layer is 72.9%, the thickness of the separator is 34.2 μm, the total thickness of the porous layer is 8.6 μm, and the thickness of the porous layer on each side is 4.3 μm and 4.3 μm. The basis weight is 2.1 g / m ² 2.0 g / m ² . As a result of SEM observation, it was observed that pores having a pore diameter of 0.1 to 0.5 μm were scattered on the surface, and the surface area ratio was about 20%. Furthermore, the produced separator was not significantly curled.
[0052]
[Comparative Example 1]
A separator for a non-aqueous secondary battery was prepared in the same manner as in Example 1 except that a solution obtained by dissolving the fluoropolymer used in Example 1 in DMAc to 12 wt% was used as a dope and the coagulation bath was used as water. Produced. The surface of the produced separator was observed with SEM, but no holes were observed.
[0053]
[Comparative Example 2]
A solution obtained by dissolving the fluoropolymer used in Example 1 in DMAc so as to be 12% by weight was used as a dope, and this was applied to a polypropylene microporous membrane (Celguard # 2400 manufactured by Celgard) on both sides as in Example 1. Worked. After coating, the membrane was dried and a dense membrane composed of the fluoropolymer was formed on the front and back surfaces of the polypropylene microporous membrane to produce a separator for a non-aqueous secondary battery.
[0054]
[Example 3]
"Positive electrode"
Lithium cobalt oxide (LiCoO ₂ , Manufactured by Nippon Chemical Industry Co., Ltd.) Using a NMP solution of 6% by weight of PVdF so that the dry weight of PVDF was 69.5 parts by weight, powder 89.5 parts by weight, acetylene black 4.5 parts by weight A paste was prepared. The obtained paste was applied onto an aluminum foil having a thickness of 20 μm, dried and pressed to obtain a positive electrode having a thickness of 97 μm.
[0055]
"Negative electrode"
As a negative electrode active material, mesophase carbon microbeads (MCMB, manufactured by Osaka Gas Chemical Co., Ltd.) powder 87 parts by weight, 3 parts by weight of acetylene black, and 6% by weight of PVdF so that the dry weight of PVdF is 10 parts by weight. An NMP solution was used to produce a negative electrode agent paste. The obtained paste was applied onto a copper foil with a thickness of 18 μm, dried and pressed to prepare a negative electrode with a thickness of 90 μm.
[0056]
"Production of button batteries"
A button battery (CR2032) was produced using the separator produced in Examples 1 and 2 and the positive and negative electrodes described above. The electrolyte contains 1M LiPF ₆ EC / DEC / MEC (1/2/1 weight ratio) was used. The button battery was measured for a discharge capacity ratio of 2 C discharge to 0.2 C discharge in 4.2 V constant current / constant voltage charge and 2.75 V constant current discharge. The results are shown in Table 1.
[0057]
[Comparative Example 3]
A button battery was produced in the same manner as in Example 3 using the separator and the polypropylene microporous membrane (Celguard # 2400, manufactured by Celgard) produced in Comparative Examples 1 and 2, and the same measurement was performed. The results are shown in Table 1.
[0058]
[Table 1]

[0059]
From Table 1, it can be seen that in the separator of the present invention, there is almost no decrease in ionic conductivity due to the porous layer coated on the polyolefin microporous membrane.
[0060]
[Example 4]
Using the positive electrode and negative electrode of Example 3 and the separator prepared in Examples 1 and 2, these were laminated to form a battery element composed of positive electrode / separator / negative electrode. This battery element was put in an aluminum laminate film pack, and an electrolytic solution was injected under reduced pressure to seal the aluminum laminate film pack. Here, the electrolyte is 1M LiPF ₆ EC / DEC / MEC (1/2/1 weight ratio) was used. This film-clad battery operated well. When the battery was disassembled after charge / discharge measurement, the separator and the electrode were sufficiently bonded.
[0061]
【The invention's effect】
As described above in detail, according to the present invention, the porous layer having excellent ion permeability and good adhesion is coated on the front and back of the polyolefin microporous film, thereby providing good adhesion to the electrode and polyolefin. Compared to a microporous membrane, there is no decrease in ionic conductivity, and it is possible to provide a separator excellent in handling properties by integration. The present invention is particularly suitable as a separator for a film-clad battery.

Claims (4)

In a separator used in a non-aqueous secondary battery that obtains an electromotive force by doping or dedoping of lithium, the separator is a porous material composed of an organic polymer that swells and retains the electrolyte on the entire front and back surfaces of the polyolefin microporous membrane. A layer is disposed and integrated with the polyolefin microporous membrane,
(1) The porosity of the porous layer is 50 to 90%. (2) The surface of the porous layer is interspersed with pores having a pore diameter of 0.05 to 10 .mu.m. (3) A separator for a non-aqueous secondary battery, wherein the total thickness is 20 μm or less, and the thickness of the porous layer is 1 μm or more on each side.   The separator for a non-aqueous secondary battery according to claim 1, wherein the surface porosity is 1 to 80%.   3. The non-aqueous secondary battery according to claim 1, wherein the organic polymer is polyvinylidene fluoride (PVdF), a PVdF copolymer, or a PVdF-based polymer mainly composed of these. Separator.   The nonaqueous secondary battery according to any one of claims 1 to 3, wherein the separator includes a positive electrode and a negative electrode capable of reversibly doping and dedoping lithium, and a separator, and the separator is a nonaqueous secondary battery using a nonaqueous electrolyte. A non-aqueous secondary battery using a battery separator.