JP2001332307A - Electrolyte-bearing polymer film, separator for cell, secondary cell using them and method of fabricating it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolyte-bearing polymer film or the like which can hold a large amount of electrolyte, exhibits practically high ion conductivity and does not impair mechanical characteristics. SOLUTION: The electrolyte-bearing polymer film is composed of a terpolymer of vinylidene fluoride, hexafluoropropylene and chlorotrifluoroethylene and has the capacity of bearing the electrolyte of 100-500 parts by weight per 100 parts by weight of the terpolymer. The polymer film has excellent heat resistance (electrolyte-holding ability at high temperature) and mechanical characteristics and is suitable for use in a lithium ion secondary cell of great safety or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolyte-supporting polymer film applicable to electrochemical devices such as non-aqueous secondary batteries such as lithium and lithium ion secondary batteries and electric double layer capacitors, and to the like. The present invention relates to a separator and a non-aqueous secondary battery using the same. In particular, the present invention relates to a method for producing a non-aqueous secondary battery having an aluminum laminate film as an exterior.

[0002]

2. Description of the Related Art Non-aqueous secondary batteries, which obtain an electromotive force by doping / dedoping lithium, have a high energy density and are widely used with the spread of portable electronic devices in recent years. These portable electronic devices are required to be smaller, lighter, and thinner, and non-aqueous secondary batteries used therefor have similar requirements. Against this background, even in non-aqueous secondary batteries, from the viewpoint of freedom of battery shape and reduction of manufacturing cost, attempts have been made to change the battery outer metal can to an aluminum laminate film. Non-aqueous rechargeable batteries with film packaging have been put into practical use, and are especially used in mobile phones and PDAs, which are required to be thinner.

[0003] The biggest difference in the manufacturing process between the aluminum laminate film sheath and the metal can sheath is the necessity of bonding (joining) between the electrode and the separator. In the case of a metal can, even if the electrode and the separator do not have strong adhesiveness, the electrode and the separator can be bonded by can pressure, so that a favorable electrode-separator interface can be easily formed.
On the other hand, in the case of aluminum laminate film exterior,
Since the exterior is soft and can not expect effects like can pressure,
In order to maintain the electrical connection between the electrode and the separator, it is necessary to bond them.

In addition, when an aluminum laminate film is used as an exterior, the risk of liquid leakage is increased, and therefore, a separator having good electrolyte retention is required as a separator.

[0005] Against this background, various techniques for using a polymer such as polyvinylidene fluoride (PVdF) in combination as a gel electrolyte have been studied in order to achieve both electrolyte retention and adhesion to electrodes. I have. For example, US Pat.
No. 0,357 describes a PVdF film formed with a plasticizer.
A technique is described in which after a copolymer thin film is thermally laminated with an electrode, a plasticizer is extracted and replaced with an electrolytic solution. Also, JP-A-10-189054 and JP-A-10-25584
No. 9 describes a technique of applying a polymer such as PVdF as an adhesive layer to the surface of a microporous polyolefin membrane, bonding the polymer to an electrode in a plasticized state, removing a coating solvent by vacuum drying, and injecting an electrolytic solution. I have.

Japanese Patent Application Laid-Open No. H11-195433 describes a technique in which a gel electrolyte layer made of a PVdF copolymer is previously provided on an electrode surface in a dry environment, and the gel electrolyte layer is bonded to a microporous polyolefin membrane. . JP-A-11-283673 discloses that after inserting a positive electrode / polyolefin microporous membrane / negative electrode element into an aluminum laminate film pack, an electrolytic solution containing a thermopolymerizable monomer (acrylate type) and a thermopolymerization initiator is used. A technique for injecting and gelling by thermal polymerization is described.

[0007] As described above, since the adhesion between the microporous polyolefin membrane, which is the separator used in the metal can-covered non-aqueous secondary battery, and the electrode is not sufficient, the aluminum-laminated film-covered non-aqueous secondary battery is used. When manufacturing
A separator with improved adhesion to the electrodes is required,
Attempts have been made to apply polymer gel electrolytes to accomplish this. However, if a microporous polyolefin membrane is to be used, it is necessary to provide an ion-conductive adhesive layer between the electrode and the microporous polyolefin membrane. Therefore, a polymer that swells in an electrolyte such as PVdF is coated on the electrode. Coating on polyolefin microporous membrane
At the present time, it is difficult to achieve both ion conductivity and adhesiveness, so that complicated methods with low productivity are used at present.

In addition, there is a technique in which a thermopolymerizable monomer is contained in an electrolytic solution to carry out polymerization gelation in-situ. However, in this case, a heat treatment step is involved, so that the usable electrolytic solution solvent and electrolyte are limited. However, there is a problem that the productivity is reduced by the processing.

[0009] Various copolymers have also been proposed for PVdF from the viewpoint of achieving both interfacial adhesion, ionic conductivity, heat resistance, and strength. For example, regarding VdF / hexafluoroperylene (HFP) copolymer, U.S. Patent No. 5,296,318
(HFP: 8-25 wt%), JP-A-9-22727 (HFP: 3-40 wt%),
JP-A-10-284127 (HFP: 30-60 wt%), with respect to VdF / chlorotrifluoroethylene (CTFE) copolymer, U.S. Pat.No. 5,571,634
(CTFE: 8-20 wt%), JP-A-10-265635, JP-A-10-28
No. 4123 (CTFE: 25-75wt%), VdF / HFP / tetrafluoroethylene (TFE)
Regarding the copolymer, JP-A-10-284124, JP-A-1
Japanese Patent Application Laid-Open No. Hei 9-289038 discloses a VdF / polyfluoroalkylvinyl ether copolymer.

However, in these PVdF copolymers, when the copolymerization rate is increased for the purpose of improving the adhesiveness, the degree of crystallinity of the resin is reduced along with the copolymerization, and a large drop in the melting point is caused. In addition, there was a problem that the electrolyte retention at high temperature and strength were insufficient.

[0011]

As described above, a non-aqueous secondary battery with an aluminum laminated film is considered to be cheaper than a non-aqueous secondary battery with a metal can because it is easy to package. Unique adhesive layer coating, heat treatment,
At present, it cannot always be manufactured inexpensively due to a process such as a calendar. In particular, the heat treatment step is not preferable because the usable material is sometimes restricted.

[0012] Therefore, there is a need for a separator having good adhesion to an electrode, which can sufficiently withstand a heat treatment step or the like during the manufacturing process of a non-aqueous secondary battery with an aluminum laminated film.

[0013] From such a background, the present invention provides a separator which can be satisfactorily bonded to an electrode without using a complicated bonding step, and also provides an inexpensive method for manufacturing a non-aqueous secondary battery with an aluminum laminated film. The purpose is to:

[0014]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have conducted intensive studies on vinylidene fluoride-based polymers, and as a result, have achieved the object by using a specific vinylidene fluoride-based polymer. They have found that they can do this and have completed the present invention. That is, the present invention

1. Vinylidene fluoride (VdF), hexafluoropropylene (HFP) and chlorotrifluoroethylene (CTFE)
And a polymer matrix containing a terpolymer of the formula (1) with 100 to 500 parts by weight of a non-aqueous electrolyte solution per 100 parts by weight of the copolymer. Furthermore, the present invention includes a battery separator to be a precursor of such a polymer film, a non-aqueous secondary battery using the same, and a method for producing the same, and specifically includes the following inventions. .

2. 2. The polymer film according to 1, wherein the copolymer has a copolymer composition of VdF / HFP (a) / CTFE (b) (a) = 2 to 8% by weight (b) = 1 to 6% by weight. .

3. 3. The polymer membrane according to 1 or 2, wherein the polymer membrane has a porous reinforcing member therein.

4. The reinforcing member has a thickness of 10 to 50 μm.
m, piercing strength 3g / μm or more, air permeability (JIS P8117) 1
4. The polymer film according to 3, wherein the polymer film is a nonwoven fabric thin film of 0 sec / 100 cc · in ² or less.

5. The reinforcing member has air permeability (JIS P8117)
Is a polyolefin microporous membrane of 200 to 500 sec / 100 cc · in ² .

6. Vinylidene fluoride (VdF), hexafluoropropylene (HFP) and chlorotrifluoroethylene (CTFE)
And a terpolymer having a non-aqueous electrolyte carrying capacity of 100 to 500 parts by weight per 100 parts by weight of the copolymer.

7. 7. The separator according to 6, wherein the copolymer has a copolymer composition of VdF / HFP (a) / CTFE (b) (a) = 2-8% by weight (b) = 1-6% by weight.

8. 8. The separator according to 6 or 7, wherein the separator has a porous reinforcing member therein.

9. The reinforcing member has a thickness of 10 to 50 μm.
m, piercing strength 3g / μm or more, air permeability (JIS P8117) 1
9. The separator according to 8, wherein the separator is a nonwoven fabric thin film of 0 sec / 100 cc · in ² or less.

10. The reinforcing member has an air permeability (JIS P811
7. The separator according to 8, wherein (7) is a microporous polyolefin membrane of 200 to 500 sec / 100 cc · in ² .

[11] A positive electrode having a positive electrode material that occludes and releases lithium ions, and a negative electrode having a metal mainly composed of lithium or a carbonaceous negative electrode material that occludes and releases lithium ions are made of vinylidene fluoride (VdF) and hexagonal. Fluoropropylene (HFP) and chlorotrifluoroethylene (CTF
Non-aqueous polymer bonded to a polymer matrix containing a terpolymer with E) via an electrolyte-carrying polymer membrane carrying 100 to 500 parts by weight of a non-aqueous electrolyte with respect to 100 parts by weight of the copolymer Rechargeable battery.

12. 12. The secondary material according to 11, wherein the copolymer has a copolymer composition of VdF / HFP (a) / CTFE (b) (a) = 2-8% by weight (b) = 1-6% by weight. battery.

13. 13. The separator according to 11 or 12, wherein the polymer film has a porous reinforcing member therein.

14. The reinforcing member has a thickness of 10 to 50 μm.
m, piercing strength 3g / μm or more, air permeability (JIS P8117) 1
14. The secondary battery according to 13, wherein the secondary battery is a nonwoven fabric-like thin film of 0 sec / 100 cc · in ² or less.

15. The reinforcing member has an air permeability (JIS P811
14. The secondary battery according to 13, wherein 7) is a microporous polyolefin membrane of 200 to 500 sec / 100 cc · in ² .

16. 16. The secondary battery according to any one of items 11 to 15, wherein at least one of the positive electrode and the negative electrode has an electrode active material bound by a terpolymer of VdF, HFP, and CTFE.

17. The secondary battery according to any one of items 11 to 16, wherein the aluminum laminate film is used as an exterior.

18. A battery element in which a positive electrode, a separator, and a negative electrode are arranged in this order is molded. 1) Inserting the element into an aluminum laminated film container and then sealing it by injecting a non-aqueous electrolyte, or 2) adding a non-aqueous electrolyte to the element. A method for producing a non-aqueous secondary battery using an aluminum laminated film for an exterior, comprising impregnating with a container and sealing the container in an aluminum laminated film container.

19. Claim 6-
19. The method according to 18, wherein the separator according to any one of 10 is used.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below.

A terpolymer of vinylidene fluoride (VdF), hexafluoropropylene (HFP) and chlorotrifluoroethylene (CTFE) is used as the polymer of the polymer matrix of the electrolyte-supporting polymer membrane of the present invention. . In this copolymer, the VdF component becomes a microcrystalline portion and contributes to improving the mechanical properties of the film. Further, the HFP component becomes an amorphous portion and contributes to impregnation and swelling with respect to the non-aqueous electrolyte. Also, CT
The FE component forms an amorphous portion similarly to the HFP component, and contributes to maintaining the heat resistance and adhesiveness of the film. Therefore, by optimizing the ratio of the three, an electrolyte-carrying polymer membrane having excellent swelling / holding properties with respect to the electrolyte, heat resistance, and adhesion to the electrode can be prepared. Suitable copolymer compositions of the terpolymer include VdF / HFP (a) / CTFE (b) (a) = 2-8% by weight (b) = 1-6% by weight. When the VdF copolymerization fraction is more than 97% by weight, the mechanical properties of the film are improved due to improved crystallinity, but the solubility in various coating solvents is reduced and the interaction with the non-aqueous electrolyte is reduced. , It is difficult to develop sufficient ionic conductivity. Further, when the copolymerization fraction of VdF is less than 86% by weight, the crystallinity of the film is lowered and the mechanical properties and heat resistance are lowered, which is not preferable, and the elastic modulus of the film is lowered and a large amount of electrolyte is held. Becomes difficult. Preferred copolymerization fraction of VdF is 97 to
86% by weight.

The copolymerization ratio (a) of HFP is 2 to 8
% By weight is preferred. If the HFP fraction is less than 2% by weight, the degree of swelling with respect to the electrolytic solution is undesirably reduced. On the other hand, if it exceeds 8% by weight, the modulus of elasticity of the film decreases, and a large amount of electrolyte cannot be sufficiently held, and the heat resistance in the state of supporting the electrolyte decreases, which is not preferable.

Further, the copolymerization fraction (b) of CTFE is 1 to
6% by weight is preferred. If the fraction of CTFE is less than 1% by weight, the effect of adding CTFE is not sufficient, and it is difficult to improve the electrolyte retention. On the other hand, if it is more than 6% by weight, the degree of swelling of the matrix in the electrolytic solution decreases, which is not preferable.

The copolymer can be synthesized by a commonly used radical polymerization method. In particular,
Polymerization can be performed by any method such as a solution polymerization method, a suspension polymerization method, an emulsion polymerization method, and a bulk polymerization method, but a suspension polymerization method and an emulsion polymerization method are preferably used. As the polymerization initiator, for example, peroxides such as di-n-propyl peroxide, diisopropyl peroxydicarbonate, di-t-butyl peroxide, heptafluorobutyl peroxide, azobisisobutyronitrile, peroxide Potassium sulfate, ammonium persulfate and the like can be mentioned.

The molecular weight of the copolymer is preferably from 100,000 to 800,000 in terms of weight average molecular weight (Mw). Mw is 1
If it is less than 00,000, a film having sufficient strength tends not to be obtained. When Mw exceeds 800,000, the solubility of the copolymer in a coating solvent decreases, and it tends to be difficult to form a good film. A particularly preferred molecular weight range is Mw 200,00
0 to 600,000.

These copolymers may be used alone or as a mixture of two or more copolymers. Also,
If necessary, polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyethylene oxide (PE
A non-fluoropolymer swellable with an electrolyte such as O) may be mixed.

The electrolytic solution-supporting polymer membrane of the present invention can be formed directly from the copolymer and a non-aqueous electrolytic solution by, for example, a method described below, or a porous thin film of the copolymer.
(Separator) is formed into a film, and 100 to 500 parts by weight of a non-aqueous electrolyte is supported on 100 parts by weight of the copolymer.

The non-aqueous electrolyte used in the present invention is not particularly limited. For example, in the case of application to a lithium or lithium ion secondary battery, a non-aqueous electrolyte prepared by dissolving a lithium salt in a non-aqueous solvent is used. Liquids can be used.
Specific lithium salts include lithium borotetrafluoride (LiB
F ₄ ), lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium arsenic hexafluoride (LiAsF ₆ ), lithium trifluorosulfonate (CF ₃ SO ₃ Li), lithium perfluoro Methylsulfonylimide [LiN (CF ₃ SO ₂ ) ₂ ] and lithium perfluoroethylsulfonylimide [LiN (C ₂ F ₅ SO
₂ ) ₂ ] etc. can be used. The concentration of the lithium salt is preferably in the range of 0.2 to 2 M (mol / l).

As the non-aqueous solvent for dissolving these lithium salts, propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), vinylene carbonate ( VC), methyl ethyl carbonate (M
EC), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), γ-butyrolactone (γ-BL), sulfolane,
A single solvent such as acetonitrile or a mixed solvent obtained by mixing two or more of these can be used. In particular, PC, EC, γ-B
At least one solvent selected from L, DMC, DEC, MEC and DME is preferably used. In the case of application to an electric double layer capacitor or the like, a non-aqueous electrolyte solution in which an ammonium salt is dissolved instead of the lithium salt is preferably used.

Further, the electrolyte-carrying polymer membrane of the present invention and the separator as a precursor thereof are characterized in that the mechanical properties can be further improved by integrating them with a porous reinforcing member provided inside. . As the porous reinforcing member used here, for example, the average film thickness is 10 to 50 μm, preferably 10 to 40 μm.
m, the piercing strength is 3 g / μm or more, preferably 5 g / μm
With the above, the air permeability (JIS P8117) is 10sec / 100cc
in ² or less, preferably 5 sec / 100 cc · in ² or less, a nonwoven fabric thin film having an air permeability (JIS P8117) of 200 to 500 sec / 100
A cc · in ² polyolefin microporous membrane is preferably used. The average thickness of the porous reinforcing member is 50
When the thickness exceeds μm, it is easy to obtain a high-strength reinforcing member, but the thickness of the obtained separator is increased, and the volume energy density when assembled as a battery is reduced.
More preferably, a reinforcing member having a thickness in the range of 10 to 30 μm is suitable. Here, the average film thickness is an average value of 10 film thicknesses measured by a micrometer having a probe having a measured area of 5 mmφ.

The piercing strength of the porous reinforcing member of the nonwoven fabric thin film of the present invention is 3 g / μm or more, preferably 5 g / μm.
Those having a size of μm or more are preferably used. This value is 3 g / μ
If a support lower than m is used, it will be difficult to achieve sufficient piercing strength even after compounding with the electrolyte-carrying polymer membrane, and the safety (short-circuit prevention properties) when assembled as a battery will be reduced. I do.

Here, the piercing strength means a value measured under the following conditions.

The porous reinforcing member is set on a fixed frame of 11.3 mmφ, and a needle having a tip radius of 0.5 mm is pushed vertically to the center of the membrane, and the needle is pushed at a constant speed of 50 mm / min to open a hole in the membrane. This is a value obtained by normalizing the force applied to the needle at the time of contact with the average film thickness of the member.

The air permeability of the porous reinforcing member of the nonwoven fabric-like thin film of the present invention is determined by the Gurley method (JIS P81117; time required for 100 cc of air to permeate an area of 1 in ² at a pressure of 2.3 cmHg).
Shows the values measured by. When the non-woven fabric-like thin film and the reinforcing member, this value is, 10sec / 100cc · in ² or less, is preferably used to indicate the preferred 5sec / 100cc · in ² following high air permeability. When this value is larger than 10 sec / 100 cc · in ^{2 and} has low air permeability, it becomes difficult to composite a polymer film by impregnation and coating from a polymer solution which is considered to be the most advantageous industrially. At the same time, it becomes difficult to sufficiently increase the ion conductivity of the composite electrolyte-carrying polymer membrane.

The material for forming the nonwoven fabric-like thin film is not particularly limited as long as it is non-swellable and strong in a non-aqueous electrolyte and is electrochemically stable. Various materials such as polyamide, polysulfone, and polyimide can be used.
Among them, those having high strength and heat resistance are particularly preferable. Examples include wholly aromatic polyamides (aramids), polyimides, polyphenylene sulfides, polysulfones, wholly aromatic polyesters, and the like. These materials may be used alone or in combination of two or more.

The basis weight is 6 to 35 g /
m ^2, preferably in the range of 8 to 30 g / m ² is suitably used.
When the basis weight is less than 6 g / m ² , it is easy to obtain a reinforcing member having high air permeability, but it is difficult to obtain a piercing strength of 3 g / μm or more, and as a result, short circuit prevention strength It is difficult to obtain an electrolyte-carrying polymer membrane excellent in the above. On the other hand, when the basis weight is more than 35 g / m ² , it is easy to satisfy the piercing strength, but the average film thickness is 50 μm.
It is difficult to obtain a reinforcing member of m or less. Also, if the density is forcibly increased and the film is made thin, the air permeability decreases and the Macmillan number increases, and as a result, it becomes difficult to obtain an electrolyte-carrying polymer membrane having high ionic conductivity.

When a polyolefin microporous membrane is used as the reinforcing member, the air permeability is 200 to 500 sec / 100 cc.
-In ² is preferred. If this value is less than 200 seconds,
The pore diameter becomes large and it becomes difficult to obtain a thermal fuse effect (shutdown effect), and the probability of short circuit increases, which is not preferable. On the other hand, if this value exceeds 500 sec, sufficient ion conductivity cannot be obtained, which is not preferable.

In the electrolyte-supporting polymer membrane having the porous reinforcing member therein and the separator serving as a precursor thereof, the porous reinforcing member is completely embedded in the membrane or the separator, and the surface of the membrane is reduced. It is important that it is covered with the copolymer of the present invention. If the membrane surface is not completely covered with the copolymer and there is a portion where the porous reinforcing member is exposed, it becomes difficult to achieve good interfacial bonding between the positive electrode and the negative electrode. Therefore, the ratio (a / b) of the thickness (a) of the separator carrying the electrolyte-supporting polymer membrane or the precursor thereof to the thickness (b) of the porous reinforcing member is generally 1.05.
２2, preferably 1.05 to 1.5. If this value is 1.05 or less and the thickness of the copolymer layer present on the front and back is too thin, a part where the porous reinforcing member is partially exposed is formed, and the surface unevenness of the positive electrode and the negative electrode is reduced. The gel-like electrolyte-carrying polymer covering the surface of the supported polymer film makes it difficult to absorb, and as a result, it becomes difficult to achieve good interfacial bonding. When the thickness of the electrolyte-carrying polymer membrane is significantly larger than the thickness of the porous reinforcing member, the volume energy density of the battery is reduced.

Next, a method for producing the electrolyte-carrying polymer membrane of the present invention will be described. The electrolyte-carrying polymer membrane of the present invention can be produced by various known methods. Although the manufacturing method is not particularly limited, the manufacturing method can be roughly divided into two methods.

One is a method for directly producing an electrolyte-carrying polymer membrane, for example, the following method. Melt film forming method: The copolymer of the present invention and a high-boiling non-aqueous electrolyte were blended at a predetermined ratio, and a heated and doped dope was applied on a substrate and cooled to support the non-aqueous electrolyte. A method of forming a polymer film directly. Solvent method: A copolymer of the present invention and a non-aqueous electrolyte are mixed at a predetermined ratio, a low-boiling solvent for dissolving the copolymer is added to dissolve the polymer, and the obtained dope is placed on a substrate. A method for obtaining a polymer film carrying a non-aqueous electrolyte by drying and removing a low-boiling-point solvent after coating.

The other is a method in which a separator capable of supporting a non-aqueous electrolyte is formed into a membrane, and the membrane is later impregnated and supported with a non-aqueous electrolyte to form an electrolyte-supporting polymer membrane. And the like. Extraction method: A copolymer of the present invention and a plasticizer are blended in a predetermined ratio, a low-boiling solvent that dissolves the copolymer is added to dissolve the polymer, and the obtained dope is applied to a substrate. Thereafter, the low-boiling-point solvent is removed by drying, a film containing a plasticizer is formed, the plasticizer is extracted with the solvent, and then replaced with a non-aqueous electrolyte to form a non-aqueous electrolyte-supporting polymer film. Wet film forming method: copolymer of the present invention and water-soluble phase separator
(A pore-forming agent) at a predetermined ratio and dissolved, and the obtained dope is discharged from a slit-shaped nozzle such as a T-die, and then poured into a coagulation bath to coagulate the film, followed by washing with water and drying. A method in which a separator made of a copolymer is formed into a film, and the film is impregnated with a non-aqueous electrolyte to form an electrolyte-supporting polymer film.

In particular, when a separator is formed, the above-mentioned wet method is preferably used because the film structure can be easily controlled by the film forming conditions. In the case of this method, the structure of the separator and the average pore diameter can be controlled by the film forming conditions such as the dope concentration and the coagulation bath concentration.For example, a relatively uniform porous structure having communication holes throughout the film, a coagulation surface A so-called asymmetric film in which a dense layer and a finger void layer are formed can be separately formed. Further, when the morphology of the membrane is different, it is difficult to unconditionally define a suitable pore size, but the pore size is 0.1 to 10 μm,
When a dense layer is provided, the pore size of the dense portion may be 0.01 to 0.2 μm.

[Non-Aqueous Secondary Battery] The secondary battery of the present invention comprises:
A positive electrode having a positive electrode material that occludes and releases metal ions (hereinafter, represented by lithium ions) derived from an electrolyte holding a non-aqueous electrolyte; and a lithium holding a metal mainly composed of lithium or a non-aqueous electrolyte. A nonaqueous secondary battery in which a negative electrode having a carbonaceous negative electrode material that absorbs and releases ions is bonded via an electrolyte-supporting polymer film of the present invention.

Hereinafter, each of them will be described in detail.

(Positive Electrode) The positive electrode of the present invention typically comprises an active material that absorbs and releases lithium ions, a non-aqueous electrolyte,
It can be composed of a binder polymer that holds the electrolytic solution and binds the active material, and a current collector.

Examples of the active material include various lithium-containing oxides and chalcogen compounds. As the lithium-containing oxide, lithium-containing cobalt oxide such as LiCoO _2, lithium-containing nickel oxides such as LiNiO _2, lithium-containing manganese composite oxides such as LiMn ₂ O _4,
Examples include lithium-containing nickel cobalt oxide and lithium-containing amorphous vanadium pentoxide. Examples of the chalcogen compound include titanium disulfide and molybdenum disulfide.

As the non-aqueous electrolyte, those similar to those described above for the electrolyte-carrying polymer membrane can be used.

As the binder polymer which holds the non-aqueous electrolyte and binds the active material, polyvinylidene fluoride (PVdF), vinylidene fluoride (VdF), hexafluoropropylene (HFP) or perfluoromethyl vinyl ether ( PFMV)
And a binary copolymer with tetrafluoroethylene (TFE), V
Tertiary copolymer resin containing PVdF as a main component, such as dF / HFP / TFE, VdF / HFP / CTFE, fluorine resin such as polytetrafluoroethylene, fluorine rubber, styrene butadiene copolymer, styrene A hydrocarbon polymer such as an acrylonitrile copolymer and an ethylene-propylene terpolymer, carboxymethylcellulose, and a polyimide resin can be used, but are not limited thereto. These may be used alone or as a mixture of two or more.

The amount of the binder polymer added was 10
The range of 3 to 30 parts by weight relative to 0 parts by weight is preferred. If the amount of the binder is less than 3 parts by weight, it is not preferable because a sufficient binding force for fixing the active material cannot be obtained. Also, when it exceeds 30 parts by weight, the active material density in the positive electrode decreases,
As a result, the energy density of the battery decreases, which is not preferable.

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. As for the shape, a foil shape or a mesh shape can be used.

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 preferred as the conductive additive. The addition amount 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, but the following methods can be employed. A predetermined amount of the active material, the binder polymer, and a volatile solvent that dissolves the binder are mixed and dissolved to prepare an active material paste. After applying the obtained paste on a current collector, a volatile solvent is removed by drying to form a film. A predetermined amount of the active material, the binder polymer, and a water-soluble solvent that dissolves the binder are mixed and dissolved to prepare a paste of the active material. After coating the obtained paste on a current collector, the obtained coating film is immersed in an aqueous coagulation bath to coagulate the binder polymer, and then the film is washed and dried 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 a metal containing lithium as a main component,
Alternatively, it can be composed of a carbonaceous active material that stores and releases lithium ions, a nonaqueous electrolyte, a binder polymer that holds the electrolyte and binds the active material, and a current collector.

Examples of the carbonaceous active material include those obtained by sintering organic polymer compounds such as polyacrylonitrile, phenol resin, phenol novolak resin, and cellulose, those obtained by sintering coke and pitch, artificial graphite and natural graphite. Carbonaceous materials to be used.

As the non-aqueous electrolyte, those similar to those described above for the electrolyte-supporting polymer membrane can be used.

As the binder polymer that holds the nonaqueous electrolyte and binds the active material, the same binder polymer as the above-described positive electrode can be used.

The amount of the binder polymer added was 10
The range of 3 to 30 parts by weight relative to 0 parts by weight is preferred. If the amount of the binder is less than 3 parts by weight, it is not preferable because a sufficient binding force for fixing the active material cannot be obtained. Also, when it exceeds 30 parts by weight, the active material density in the negative electrode decreases,
As a result, the energy density of the battery decreases, which is not preferable.

As the current collector, a material having excellent reduction stability is preferably used. Specific examples include metallic copper, stainless steel, nickel, and carbon.
Particularly preferably, foil and mesh copper are used.

Further, the negative electrode of the present invention may contain artificial graphite, carbon black (acetylene black), nickel powder and the like as a conductive additive.

The method for producing the negative electrode of the present invention is not particularly limited, but the same method as that described for the positive electrode can be employed.

(Exterior) For the exterior of the non-aqueous secondary battery of the present invention, an aluminum laminate film is preferably used in addition to a generally used can made of stainless steel, aluminum or the like.
There are various types of aluminum laminate films, but there is no particular limitation as long as they are used for non-aqueous secondary batteries.

[Production Method of Nonaqueous Secondary Battery] The electrolytic solution-carrying polymer membrane of the present invention and the separator which is a precursor thereof have good adhesion to electrodes, and are particularly good without a heat treatment / compression bonding step. It is characterized by the ability to perform an excellent interfacial bonding. Therefore, it is possible to provide an easy joining method in a method for manufacturing a nonaqueous secondary battery having an aluminate film exterior that requires electrode / separator adhesion.

The method for producing a non-aqueous secondary battery using an aluminum laminate film for an outer package provided by the present invention uses a separator which is a precursor of the electrolytic solution-supporting polymer film of the present invention as a separator, and contains a non-aqueous electrolytic solution. The positive electrode / separator / negative electrode is arranged in this order without any
After molding the battery element composed of the negative electrode, 1) Insert the element into an aluminum laminated film container and then inject and seal a non-aqueous electrolytic solution. 2) Or impregnate the element with the electrolytic solution and seal it in an aluminum laminated film container. It is characterized by. The aluminum laminated film container used here can be the same as that conventionally used in the method of manufacturing a non-aqueous secondary battery with an aluminum laminated film exterior, and can be used in the above methods 1) and 2). The shape is not limited as long as it is possible.

This manufacturing method is a general method for manufacturing a non-aqueous secondary battery having a metal can exterior. However, it has not been conventionally applied as a method for producing a non-aqueous secondary battery with an aluminum laminated film. In an aluminum-laminated film-covered battery, the separator and the electrode cannot be bonded due to the can pressure, so an adhesive layer between the separator and the electrode is necessary. It is considered that the manufacturing method could not be applied to the method of manufacturing a non-aqueous secondary battery with an aluminum laminated film. However, since the separator of the present invention has good adhesiveness to the electrode while supporting the non-aqueous electrolyte, the non-aqueous secondary battery of the aluminum laminate film-covered type can be used without the electrode / separator lamination step. Can be manufactured. Further, the structure of the battery element can be implemented in either a stack or a wound.

The method for producing a non-aqueous secondary battery with an aluminum laminated film of the present invention has the following advantages, and facilitates the production of a non-aqueous secondary battery with an aluminum laminated film. 1) The process that requires strict water management is from the injection of the electrolytic solution to the sealing of the exterior. 2) The processes (application of an adhesive layer, heat treatment, calendering, etc.) specific to a non-aqueous secondary battery with an aluminum laminated film necessary for bonding the electrode and the separator are unnecessary. 3) The production line for metal can nonaqueous secondary batteries can be used almost as it is.

[0080]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the contents of the present invention will be described in detail using embodiments.

[Example 1] <Synthesis of polymer> In a pressure vessel made of stainless steel, 1.2 g of hexafluoropropylene (HFP), 30 ml of trichlorotrisulfoloethane (CFC113), and heptafluorobutyl peroxide were prepared.
After charging 1 ml of a 5% CFC113 solution and purging the container with nitrogen,-
Cool to 78 ° C and create a vacuum, in which vinylidene fluoride (VdF)
8.5 g, 0.8 g of chlorotrifluoroethylene (CTFE)
The polymerization was carried out with stirring at room temperature for 20 hours. The obtained reaction product was dissolved in heavy DMSO, and the copolymer composition ratio was analyzed by NMR.
The copolymer composition ratio was VdF / HFP / CTFE = 89.1 / 5.1 / 3.8 weight ratio. The molecular weight measured by the GPC method was Mw = 530,000.

<Membrane Production> Propylene carbonate (PC) / ethylene carbonate (EC) in which 1M LiBF4 was dissolved as a non-aqueous electrolyte solution in 100 parts by weight of the obtained copolymer.
300 parts by weight (1/1 weight ratio) was added, and then tetrahydrofuran (THF) was added as a coating solvent, followed by heating at 50 ° C. to dissolve, thereby preparing a coating dope having a polymer concentration of 12 wt%. The obtained dope was coated on a PET film that had been subjected to a release treatment, and then dried to produce a polymer film carrying an electrolytic solution having a thickness of 50 μm. The obtained polymer membrane was evaluated for tensile properties, ionic conductivity and heat resistance.

<Tensile Properties> The obtained electrolyte-carrying polymer film was cut into 1 cm × 3 cm strips, and the tensile strength and the elongation at break were measured using Tensilon.

<Ion conductivity> The obtained electrolyte-carrying polymer membrane was cut into 20 mmφ, and sandwiched between two SUS electrodes.
Conductivity was calculated from AC impedance at Hz.

<Evaluation of Heat Resistance> The obtained electrolyte-carrying polymer film was cut into 20 mmφ, sandwiched between two SUS plates, and heated to 0.5 kgf /
After pressing under the condition of cm ² , heat treatment was performed at 90 ° C. for 1 hour. After the heat treatment, the electrolyte-carrying polymer film was taken out, excess electrolyte exposed on the surface was wiped off, and the electrolyte retention was calculated by a gravimetric method. Electrolyte retention rate (%) = (Electrolyte carried amount after treatment / Electrolyte carried amount before treatment) × 100

Example 2 The copolymer of Example 1 was mixed with a mixed solvent of N, N-dimethylacetamide (DMAc) and polypropylene glycol (PPG) having an average molecular weight of 400 at 6/4 (weight ratio) at 50 ° C. And a dope for film formation having a polymer concentration of 15% by weight was prepared. After coating the obtained dope on a PET film subjected to a release treatment, it was then immersed in a 40% by weight aqueous solution of DMAc to coagulate the film. Next, washing and drying were performed to prepare a 50 μm-thick porous thin film (separator) made of a terpolymer.

The obtained separator was immersed in the non-aqueous electrolyte used in Example 1 for 10 minutes to impregnate and carry the non-aqueous electrolyte on the separator. Next, the membrane was drawn out, and the non-aqueous electrolyte adhering excessively to the surface was wiped off, and the amount of the carried electrolyte was determined by a gravimetric method. The electrolyte carrying amount of this membrane is 260
phr.

With respect to the obtained electrolyte-carrying polymer membrane,
The tensile properties, ionic conductivity and heat resistance were evaluated.

Example 3 The same procedure as in Example 1 was conducted except that a copolymer having a weight ratio of VdF / HFP / CTFE = 90.0 / 7.5 / 2.5 and Mw = 470,000 was used as the vinylidene fluoride copolymer. Perform film formation,
An electrolyte-carrying polymer membrane was formed, and its tensile properties, ionic conductivity, and heat resistance were evaluated.

Example 4 The same procedure as in Example 2 was carried out except that a copolymer having a weight ratio of VdF / HFP / CTFE = 92.2 / 4.4 / 3.4 and Mw = 410,000 was used as the vinylidene fluoride copolymer. A film was formed, and a 50 μm-thick porous thin film (separator) was formed. Next, the electrolyte was impregnated in the same manner as in Example 2, and the characteristics of the electrolyte-carrying polymer film were evaluated.

Comparative Example 1 About 10% by weight of hexafluoropropylene (HFP) as a vinylidene fluoride copolymer with respect to VdF.
Copolymerized polymer (KYNAR2801; manufactured by Elf Atochem)
Was used to form a membrane in the same manner as in Example 1, and a polymer membrane carrying an electrolytic solution was prepared, and its tensile properties, ionic conductivity, and heat resistance were evaluated.

[Comparative Example 2] Perfluoromethylvinyl ether (PFMV) was added to VdF as a vinylidene fluoride copolymer in an amount of 10%.
Except for using a polymer copolymerized by weight%, a membrane was formed in the same manner as in Example 1 to prepare an electrolyte-carrying polymer membrane.
The tensile properties, ionic conductivity and heat resistance were evaluated.

Example 5 The basis weight of m-aramid short fiber having a fineness of 0.9 dtex as a porous reinforcing member was 1
A nonwoven sheet of 5 g / m ² was used. The average thickness of this sheet was 30 μm, the piercing strength was 8.3 g / μm, and the air permeability was 0.02 sec / 100 cc · in ² . After impregnating and applying the dope used in Example 1 to this reinforcing member, drying was performed in the same manner as in Example 1 to produce a 40 μm-thick electrolyte-carrying polymer film composited with the reinforcing member. The degree and heat resistance were evaluated.

Example 6 The porous reinforcing member of Example 5 was impregnated with the dope of Example 2 and then solidified and treated in the same manner as in Example 2.
Washing and drying were performed to produce a porous thin film (separator) in which a reinforcing member having a thickness of 35 μm was combined. The coating amount of the copolymer was 12 g / m ² . In the same manner as in Example 2, this separator was immersed in an electrolytic solution to obtain an electrolytic solution-supporting polymer membrane. At this time, the amount of the supported electrolyte was 280 parts by weight based on 100 parts by weight of the copolymer. The obtained electrolyte-carrying polymer membrane was evaluated for tensile properties, ionic conductivity, and heat resistance.

Example 7 As a porous reinforcing member, a fineness of 0.
A non-woven sheet made of 55 dtex polyethylene terephthalate short fiber and having a basis weight of 12 g / m ² was used. The average thickness of this sheet is 30 μm, and the piercing strength is 5.3 g /
μm and air permeability were 0.01 sec / 100 cc · in ² . In the same manner as in Example 5, using the dope of Example 2, a porous thin film (separator) having a thickness of 35 μm was formed by combining a reinforcing member by a wet method. The coating amount of the copolymer was 12 g / m ² . The electrolyte carrying amount of this membrane was 290 parts by weight based on 100 parts by weight of the copolymer. The obtained electrolyte-carrying polymer membrane was evaluated for tensile properties, ionic conductivity, and heat resistance.

Example 8 A microporous polypropylene membrane (Celgard # 2400, 25 μm thick) was used as a porous reinforcing member.
m, air permeability 350sec / 100cc ・ in ² , basis weight 1
4 g / m ² ), and the polymer of Example 4 was used as the copolymer of the present invention. The polymer was dissolved in a mixed solvent of DMAc / PPG = 6/4 by weight at 50 ° C. to prepare a 14 wt% membrane-forming tough. The obtained dope was applied to the front and back of Celgard # 2400, and then solidified, washed with water and dried to obtain a 35 μm-thick separator having a porous layer of a copolymer on the front and back. The coating amount of the copolymer was 9 g / m ² . This membrane was impregnated with an electrolytic solution in the same manner, and the amount of the electrolytic solution carried on the front and back copolymers was determined. The amount of the supported electrolyte in the porous portion of the copolymer was 280 phr. The obtained electrolyte-carrying polymer membrane was evaluated for tensile properties, ionic conductivity, and heat resistance.

Table 1 summarizes the results of the examples and comparative examples.

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[Table 1]

As is clear from the examples, VdF / HFP / CTFE
When the terpolymer was used, an electrolyte-carrying polymer film having good heat resistance (retention of the electrolyte at high temperatures) could be prepared. Further, by combining this copolymer with a porous reinforcing member, an electrolyte-carrying polymer membrane having more excellent mechanical properties and heat resistance could be prepared.

Example 9 “Positive electrode”: 89.5 parts by weight of lithium cobalt oxide (LiCoO ₂ , manufactured by Nippon Chemical Industry Co., Ltd.) powder, 4.5 parts by weight of acetylene black, and 6 parts by weight of dry weight of PVdF. A positive electrode paste was prepared using a 6 wt% PVdF N-methyl-pyrrolidone (NMP) solution.
The obtained paste was applied on an aluminum foil having a thickness of 20 μm, dried and pressed to obtain a positive electrode having a thickness of 97 μm.

“Negative electrode” Mesophase carbon microbeads (MCMB, Osaka Gas Chemical Co., Ltd.)
6) so that 87 parts by weight of powder, 3 parts by weight of acetylene black and 10 parts by weight of dry weight of PVdF are obtained.
A negative electrode agent paste was prepared using a weight percent PVdF NMP solution. The obtained paste was applied on a copper foil having a thickness of 18 μm, dried and pressed to prepare a negative electrode having a thickness of 90 μm.

"Non-aqueous secondary battery equipped with aluminum laminated film" The above positive electrode, the separator prepared in Example 7, and the above negative electrode were sequentially laminated to form a battery element comprising a positive electrode / separator / negative electrode. The battery element was placed in an aluminum laminated film pack, an electrolyte was injected under reduced pressure, and the aluminum laminated film pack was sealed. Here, 1 M LiPF ₆ EC /
DEC / MEC (1/1/1 weight ratio) was used.

The capacity of the manufactured battery was set to a charging current of 0.2.
C, 4.2V constant current / constant voltage charge, discharge current 0.2
C was 650 mAh when confirmed by constant current discharge at a cutoff of 2.75 V. The Coulomb efficiency of the first charge / discharge cycle was 89%.

The above battery was charged at a charging current of 0.2 C, 4.2
V constant current / constant voltage charge, discharge current 0.2C, 2.75
When a charge / discharge cycle test was performed under the condition of constant current discharge at a V cutoff, 88% of the discharge capacity in the first cycle was maintained at the 100th cycle.

The above battery was charged with a charging current of 0.2 C,
4.2V constant current / constant voltage charge, discharge current 2C, 2.7
When the battery was charged and discharged under the condition of constant current discharge with a cutoff of 5 V, a capacity of 90% of the discharge capacity at 0.2 C was obtained. Further, when the battery after this test was disassembled, it was found that each electrode and the electrolyte-carrying polymer film were well bonded.

Example 10 A separator prepared in Example 8 was used instead of the separator in Example 9 except that
A battery was prepared in the same manner as in Example 9, and the characteristics were evaluated.

The discharge capacity at 0.2 C was 655 mAh, and the initial coulomb efficiency was 89%. The capacity retention rate at the 100th cycle was 88%, and the discharge capacity at 2C was 0.2C.
86% of the capacity of The capacity maintenance ratio at the 100th cycle was 88%. Further, when the battery after this test was disassembled, it was found that each electrode and the electrolyte-carrying polymer film were well bonded.

Comparative Example 3 An aluminum laminated film nonaqueous secondary battery was produced in the same manner as in Example 9 except that the separator was replaced by a microporous polypropylene film (Celgard # 2400) not coated with the copolymer of the present invention. .

The capacity of the manufactured battery was set to a charging current of 0.2.
C, 4.2V constant current / constant voltage charge, discharge current 0.2
C was 645 mAh when confirmed by constant current discharge at a cutoff of 2.75 V. The Coulomb efficiency of the first charge / discharge cycle was 88%.

The above battery was charged at a charging current of 0.2 C, 4.2
V constant current / constant voltage charge, discharge current 0.2C, 2.75
When a charge / discharge cycle test was performed under the condition of constant current discharge at a V cutoff, at the 100th cycle, only 40% of the discharge capacity at the first cycle was maintained.

The difference between the results of Example 10 and Comparative Example 3 is considered to reflect the adhesion between the separator and the electrode, and it can be seen that the separator of the present invention has sufficient adhesion to the electrode. In addition, it can be seen that a practical aluminum laminated film-covered non-aqueous secondary battery can be produced without using a separator having good adhesion as in the present invention without steps such as heat treatment and calendering.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 27/12 C08L 27/12 27/16 27/16 27/20 27/20 H01G 9/02 H01M 2 / 16 P H01M 2/16 H01G 9/00 301C

Claims (18)

[Claims] 1. A polymer matrix containing a terpolymer of vinylidene fluoride (VdF), hexafluoropropylene (HFP) and chlorotrifluoroethylene (CTFE), and 100 to 100 parts by weight of the copolymer. An electrolyte-carrying polymer membrane in which 500 parts by weight of a non-aqueous electrolyte is supported. 2. A copolymer composition of the copolymer, wherein VdF / HFP (a) / CTFE (b) (a) = 2-8% by weight (b) = 1-6% by weight The polymer film according to claim 1. 3. The polymer membrane according to claim 1, wherein the polymer membrane has a porous reinforcing member therein. 4. The reinforcing member has a thickness of 10 to 50 μm, a puncture strength of 3 g / μm or more, and an air permeability (JIS P8117) of 10 seconds.
4. The polymer film according to claim 3, wherein the polymer film is a nonwoven fabric-like thin film having c / 100 cc · in ² or less. 5. The reinforcing member having an air permeability (JIS P8117) of 2
Polymer film of claim 3, wherein the polyolefin microporous membrane of 00~500sec / 100cc · in ^2. 6. A ternary copolymer of vinylidene fluoride (VdF), hexafluoropropylene (HFP) and chlorotrifluoroethylene (CTFE), and a non-aqueous electrolyte carrying capacity of 100% by weight of the copolymer. 100 to 500 parts by weight per part by weight of the battery separator. 7. A copolymer composition of the copolymer, wherein VdF / HFP (a) / CTFE (b) (a) = 2-8% by weight (b) = 1-6% by weight The separator according to claim 6. 8. The separator according to claim 6, wherein the separator has a porous reinforcing member therein. 9. The reinforcing member has a thickness of 10 to 50 μm, a puncture strength of 3 g / μm or more, and an air permeability (JIS P8117) of 10 seconds.
9. The separator according to claim 8, wherein the separator is a nonwoven fabric-like thin film having c / 100 cc · in ² or less. 10. The separator according to claim 8, wherein the reinforcing member is a microporous polyolefin membrane having an air permeability (JIS P8117) of 200 to 500 sec / 100 cc · in ² . 11. A positive electrode comprising a positive electrode material for inserting and extracting lithium ions, and a negative electrode comprising a metal mainly composed of lithium or a carbonaceous negative electrode material for inserting and extracting lithium ions, are vinylidene fluoride. (VdF) and a polymer matrix containing a terpolymer of hexafluoropropylene (HFP) and chlorotrifluoroethylene (CTFE), 100 to 500 parts by weight of a non-aqueous electrolyte solution per 100 parts by weight of the copolymer A non-aqueous secondary battery joined via an electrolyte-carrying polymer membrane carrying a polymer. 12. A copolymer composition of the copolymer, wherein VdF / HFP (a) / CTFE (b) (a) = 2-8% by weight (b) = 1-6% by weight The secondary battery according to claim 10. 13. The polymer film having a thickness of 1
0 to 50 μm, piercing strength 3 g / μm or more, air permeability (JIS P
13. The secondary battery according to claim 11, wherein the secondary battery has a porous reinforcing member made of a nonwoven fabric thin film having a thickness of 10 sec / 100 cc · in ² or less. 14. The polymer membrane has an air permeability inside.
(JIS P8117) 200-500sec / 100cc ・ i
The secondary battery according to claim 11 or 12, wherein further comprising a porous reinforcing member made of a polyolefin microporous membrane of n ^2. 15. At least one of the positive electrode and the negative electrode
The electrode active material is bound by a terpolymer of VdF, HFP, and CTFE.
The secondary battery according to any one of the above. 16. The secondary battery according to claim 11, wherein an aluminum laminate film is used as an exterior. 17. A battery element in which a positive electrode, a separator and a negative electrode are arranged in this order is molded. 1) Inserting the element into an aluminum laminate film container and then sealing it by injecting a non-aqueous electrolyte, or 2) The element. A method for producing a non-aqueous secondary battery using an aluminum laminated film for an exterior, comprising impregnating a non-aqueous electrolytic solution into a container and sealing the container in an aluminum laminated film container. 18. The separator according to claim 6, wherein the separator is
The method according to claim 17, wherein the separator according to any one of claims 1 to 3 is used.