JP2003327839A - Polymer film and separator for electrochemical device - Google Patents

Abstract

An object of the present invention is to provide a polymer film excellent in heat resistance and productivity and a separator for an electrochemical element using the polymer film and having excellent affinity for an electrolytic solution. I do. A matrix containing a non-swellable polymer that is an amorphous thermoplastic resin and at least one polymer selected from a monomer, a copolymer, and a cross-linked polymer containing a polyalkylene oxide group are provided. A polymer film comprising a matrix comprising a swellable polymer comprising a coalesced polymer, and a mixture obtained by dissolving a non-swellable polymer in a solvent and polymerizing the swellable polymer in the solution. A polymer film produced by forming a sheet into a sheet and removing the solvent. A separator for an electrochemical device using the polymer film.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polymer film and a separator for an electrochemical device using the polymer film.

[0002]

2. Description of the Related Art In recent years, lighter weight, higher energy and safety have been required for lithium secondary batteries and capacitors used in portable electronic equipment power supplies, electric vehicles, power storage power supplies and the like. A lithium secondary battery or a capacitor has a separator provided between the positive and negative electrodes to prevent a short circuit. As this separator, an insulating porous substrate is used so that the ions contained in the electrolytic solution can move.

High-capacity lithium secondary batteries and capacitors use a non-aqueous electrolyte, but when the battery is damaged, the electrolyte leaks or the electrolyte is vaporized due to overcharging. I had a problem with. In particular, the polyolefin-based separator that is mainly used in lithium secondary batteries has a problem that the affinity for the polar solvent in the electrolytic solution is low, liquid drainage occurs, and the battery life is short.

In order to solve such problems of safety and affinity, Japanese Patent Application Laid-Open No. 7-320713 discloses that a polymer matrix and a polymer matrix in the polymer matrix are phase-separated and continuously. Then, there has been proposed a battery separator composed of ion conductive paths formed in a three-dimensional mesh shape. In addition, JP-A-11-40128,
Japanese Patent Laid-Open No. 2002-47372 proposes a battery separator manufactured by stretching a mixture of a polymer electrolyte capable of holding an electrolyte solution and a resin such as polyolefin.

Such a battery separator has an improved affinity for an electrolytic solution due to an ionic conduction path or a polymer electrolyte. However, in the conventional method,
The dispersibility of the polymer matrix and the ionic conduction path or the polymer electrolyte and the polyolefin resin was poor, and the ionic conduction path and the polymer electrolyte were sometimes unevenly distributed.

Further, in a lithium secondary battery and a capacitor using a non-aqueous electrolytic solution, if water is mixed in the element, electrochemical stability is deteriorated and the life of the battery or the capacitor is shortened. Therefore, to remove water from the materials used in batteries and capacitors during assembly,
A drying process may be provided. Since the polymer fine particles and the polyolefin resin used conventionally have low heat resistance, there is a problem that the drying temperature cannot be raised, and it takes time and cost to remove water.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polymer film excellent in affinity of electrolyte solution, heat resistance, and productivity, and a separator for electrochemical device using the polymer film. It is in.

[0008]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that a matrix containing a non-swelling polymer and a matrix containing a swelling polymer. It has been found that the non-swelling polymer in the polymer film made of is a non-crystalline thermoplastic resin. Amorphous aromatic polyesters, amorphous thermoplastics such as polyarylate are excellent in heat resistance,
Productivity can be improved. Further, the swelling polymer is a homopolymer containing a polyalkylene oxide group,
When the polymer film of the present invention is used as a separator for an electrochemical device, it has excellent affinity with an electrolytic solution by containing at least one polymer selected from a copolymer and a cross-linked polymer. Therefore, a high-performance electrochemical device can be obtained.

Further, the non-swelling polymer is dissolved in a solvent, and the mixture obtained by polymerizing the swelling polymer in the solution is formed into a sheet, and then the solvent is removed. Since a molecular entanglement occurs between the matrix containing the molecule and the matrix containing the swelling polymer, the non-swelling polymer is not unevenly distributed and is uniform in mechanical strength. It has been found that an excellent polymer film can be provided.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below. An amorphous thermoplastic resin is used as the non-swelling polymer relating to the polymer film of the present invention. As the amorphous thermoplastic resin, aromatic polycarbonate resin, amorphous polyarylate resin, cyclic polyolefin resin typified by polynorbornene resin, polysulfone resin, polyether sulfone resin, hydrogenated polystyrene resin, and modified products thereof Is mentioned. Further, it is preferable to use a heat-resistant amorphous thermoplastic resin having a glass transition point (Tg) of preferably 140 ° C., more preferably 160 ° C. or higher.

Polycarbonate resin is a carbonic acid ester of glycol or divalent phenol, and is --OCO.
It has an O-polar group. Typical compositions include, for example, bis (oxyphenyl) ethane (dioxydiphenylethane), bis (oxyphenyl) isobutane (dioxydiphenylisobutane), bis (oxyphenyl).
Cyclohexane (dioxydiphenylcyclohexane)
Etc.

The polyarylate resin is an aromatic polyester, and a typical example thereof is a polyester obtained from bisphenol A and an aromatic dicarboxylic acid such as terephthalic acid.

As the cyclic polyolefin resin, for example, a polyolefin resin having a norbornene skeleton, a tetracyclododecene derivative or a polymer obtained by metathesis polymerization with an unsaturated cyclic compound copolymerizable with the tetracyclododecene is hydrogenated. There is a polymer thus obtained.

A typical composition of the polysulfone resin is a polymer containing a sulfone group consisting of bisphenol A and biphenyl sulfone. The polyether sulfone resin is a polymer having an ether group and a sulfone group, and examples thereof include polyether sulfone which is a polymer of biphenyl sulfone and oxygen.

Examples of the swelling polymer relating to the polymer film of the present invention include polyacrylonitrile, polyalkyl (meth) acrylate, copolymers of acrylonitrile and polyalkyl (meth) acrylate, copolymers of acrylonitrile and styrene, Polystyrene, polyvinyl chloride, polyvinylidene fluoride, polysaccharide polymer, polysilane, polycarbosilane, polysiloxane and the like can be used. When the straight chain or side chain of these polymers contains a polyalkylene oxide group, high ionic conductivity can be exhibited. Examples of such a polymer include WO96 / 08051 and JP-A-2000-
No. 123632, JP-A-2000-188130, JP-B-6-52671, JP-A-11-35765, JP-B-8-21389, JP-A-2000-154254,
Examples thereof include polymers described in JP 2001-323069 A.

The method of polymerizing the swelling polymer relating to the polymer film of the present invention is not particularly limited, but radical polymerization,
Cationic polymerization, anionic polymerization, polyaddition reaction, polycondensation reaction, hydrosilylation reaction and the like can be used.

An electrolyte salt may be added to the swelling polymer related to the polymer film of the present invention at the time of polymerization. As described above, when the swelling polymer contains an electrolyte salt, there is an advantage that the electrolyte solution or the solvent can be injected quickly when the electrochemical element is assembled. Examples of such electrolyte salts include metal cations,
A cation selected from ammonium ion, amidinium ion, and guanidinium ion, and fluorine ion,
Chlorine ion, bromine ion, iodine ion, perchlorate ion, hypochlorite ion, thiocyanate ion, tetrafluoroborate ion, tetraphenylborate ion, nitrate ion, organic acid ion, permanganate ion,
Phosphate ion, sulfate ion, nitrate ion, thiosulfate _{^{ion, AsF 6 -, PF 6 -}} , stearyl sulfonate ion,
Octyl sulfonate ion, dodecylbenzenesulfonate ion, naphthalenesulfonate ion, dodecyl naphthalenesulfonate ion, 7, 7, 8, 8-tetracyano -p- quinodimethane ^{_{ion, X 1 SO 3 -, [}} (X 1 SO
₂ ) (X ₂ SO ₂ ) N] ^- , [(X ₁ SO ₂ ) (X ₂ SO ₂ )
_{(X 3 SO 2) C]} - and _{[(X 1 SO 2) (} X 2 SO 2)
And a compound consisting of an anion selected from YC] ⁻ . Here, X ₁ , X ₂ , X ₃ and Y are electron withdrawing groups. Preferably, X ₁ , X ₂ and X ₃ are each independently a perfluoroalkyl group or a perfluoroaryl group having 1 to 6 carbon atoms, Y is a nitro group, a nitroso group,
It is a carbonyl group, a carboxyl group, or a cyano group.
X ₁ , X ₂ and X ₃ may be the same or different.

In the method for producing a polymer film of the present invention, the solvent for dissolving the non-swelling polymer varies depending on the kind of the non-swelling polymer, but is a sulfur compound such as thiophene, diethyl sulfide, dimethyl sulfoxide, sulfolane. , Nitrogen compounds such as acetonitrile, diethylamine and aniline, ketones such as acetone, 2-butanone and cyclohexanone, esters, phenols, toluene, xylene, isoparaffin, hydrocarbons such as benzene, halogenated hydrocarbons, dimethylpolysiloxane, tetrahydrofuran, 2 -Methoxytetrahydrofuran, 1,3-dioxolane, 1,2-dimethoxyethane, 1,2-ethoxyethane, ether compounds such as 1,3-dioxane, alcohols such as methanol, ethanol, 2-propanol, butanol Germany or in combination can be used. The swelling polymer is in a non-swelling polymer solution,
By polymerizing, a molecular entanglement occurs between the non-swelling polymer and the swelling polymer, and it is possible to provide a separator for an electrochemical element that is uniform and excellent in mechanical strength.

In the method for producing a polymer film of the present invention, a method of obtaining a sheet-like separator after polymerizing a swelling polymer in a non-swelling polymer solution includes roll coating, curtain coating, It can be manufactured by a bar coating method, a spray coating method, a spin coating method, an electrodeposition method, a solvent casting method or the like. As a post process, a post process such as heating or irradiation with an actinic ray such as a photoelectron beam may be performed.

When the polymer film of the present invention is used as a separator for an electrochemical device, its basis weight is not particularly limited, but is preferably 5 to 50 g / m ² . Although the thickness is not particularly limited, it is preferably thin in order to miniaturize the electrochemical element, and is preferably 10 to 200 μm, more preferably 15 to 100 μm. The thickness of the separator can be adjusted by a super calendar, a machine calendar, a thermal calendar, a soft calendar, or a thermal soft calendar treatment.

By incorporating the separator for electrochemical device using the polymer film of the present invention into a cell such as a lithium secondary battery or a capacitor, and injecting a solvent or an electrolytic solution into the cell, the swelling polymer becomes an electrolyte. Includes salts and solvents to develop ionic conductivity. Examples of the solvent include thionyl chloride, sulfuryl chloride, inorganic solvents such as liquid ammonia, sulfur compounds such as thiophene and diethyl sulfide, nitrogen compounds such as acetonitrile, diethylamine and aniline, fatty acids such as acetic acid and butyric acid, and acid anhydrides thereof. , Ethers, acetals, ketones such as cyclohexanone, esters, phenols, alcohols, hydrocarbons,
Halogenated hydrocarbon, dimethyl polysiloxane, etc. can be used. Particularly, purified sulfur compounds such as dimethyl sulfoxide and sulfolane, ester compounds having a carbonyl bond such as propylene carbonate, ethylene carbonate, γ-butyrolactone, dimethyl carbonate and diethyl carbonate, tetrahydrofuran, 2-methoxytetrahydrofuran, and 1,3-dioxolane. ,
1,2-dimethoxyethane, 1,2-ethoxyethane,
Examples thereof include ether compounds such as 1,3-dioxane and the like, and mixtures thereof. Moreover, the above-mentioned thing can be used as an electrolyte salt of electrolyte solution.

[0022]

EXAMPLES The present invention will be described below with reference to examples.

Example 1 Aromatic polycarbonate (Z20 which is a non-swelling polymer)
0: Mitsubishi Gas Chemical Co., Ltd.) 40 parts by weight was dissolved in 360 parts by weight of tetrahydrofuran. Methoxy polyethylene glycol acrylate (130A:
Kyoeisha Chemical Co., Ltd.) 42 parts by weight, triethylene glycol diacrylate 18 parts by weight, azobisisobutyronitrile 1 part by weight, (C ₂ H ₅ ) ₄ NBF ₄ 0.6 parts by weight,
The swelling polymer was polymerized by heating at 80 ° C. for 3 hours under a nitrogen atmosphere. This polymer liquid was cast on an aluminum sheet by a bar coating method and dried at 130 ° C. for 2 hours to obtain a separator A for electrochemical element. The electrochemical device separator A had a weight of 52 g / m ² and a thickness of 48 μm.

20 mmφ separator A for electrochemical device
0.8M (C₂H_Five)_FourNBF_Four/ Propylene Carbone
Impregnated with a platinum electrolytic solution, sandwiched between platinum electrodes of the same area, and
Ion conductivity was measured using Ratron SI1280B.
When determined, 7.6 × 10 ^-3S / cm (20 ° C)
It was.

80 parts by weight of highly active activated carbon having a specific surface area of 2000 m ² / g and an average particle size of 8 μm, 10 parts by weight of acetylene black, N-of polyvinylidene fluoride (PVDF)
100 parts by weight of a methyl-2-pyrrolidone (NMP) solution (Kureha KF Polymer L # 1120: manufactured by Kureha Chemical Industry Co., Ltd.) and 150 parts by weight of NMP were mixed to prepare an activated carbon-containing liquid. This containing liquid was applied on an aluminum foil and dried to manufacture an electrode for electric double layer capacitor. After sandwiching the electrochemical device separator A between these electrodes and incorporating it into a capacitor cell, 0.8 M (C ₂ H ₅ ) ₄ NBF ₄
/ Propylene carbonate electrolyte was injected, the cell was sealed, and an electric double layer capacitor was manufactured. The capacitance of this electric double layer capacitor was 12 μF. In this electric double layer capacitor, charging to 2.5 V,
The electrostatic capacity after repeating the continuous charge / discharge test for discharging to V 1000 times was 11 μF.

Example 2 Polyarylate resin (U-10, which is a non-swelling polymer)
0: Unitika) 50 parts by weight of tetrahydrofuran 35
It dissolved in 0 parts by weight. To this solution, at room temperature, 45 parts by weight of a copolymer having a hydrosilyl group at both ends, a polyalkylene oxide part in the main chain, and a hydrosilyl group at both ends (molecular weight about 3000), pentaerythritol tetra Allyl ether 15 parts by weight, platinum catalyst 0.00
5 parts by weight was added and heated at 60 ° C. for 3 hours in a nitrogen atmosphere to polymerize the swelling polymer. This polymer liquid
It was cast on an aluminum sheet by a roll coating method and dried at 120 ° C. for 3 hours to obtain a separator B for electrochemical element. The electrochemical device separator B is 53
It was g / m ² and 51 μm.

20 mmφ separator B for electrochemical device
Was impregnated with a 1.0 M LiPF ₆ ethylene carbonate / diethyl carbonate electrolytic solution, sandwiched between platinum electrodes having the same area, and the ion conductivity was measured using the same apparatus as in Example 1. ^-3 S / cm (20 ° C)
Met.

20 parts by weight of lithium cobalt oxide, 2 parts by weight of acetylene black, N of PVDF used in Example 1
18 parts by weight of MP solution and 12 parts by weight of NMP were mixed, applied on an aluminum foil and dried to manufacture a positive electrode for a lithium secondary battery. 20 parts by weight of carbon powder, PVDF
17.5 parts by weight of NMP solution and 12 parts by weight of NMP were mixed, coated on a copper foil, and dried to manufacture a negative electrode for a lithium secondary battery. The electrochemical device separator B is sandwiched between the positive electrode and the negative electrode, and lithium is incorporated into the cell for the next battery, and then 0.8 M (C ₂ H ₅ ) ₄ NBF ₄ / propylene carbonate electrolytic solution is injected. The cell was sealed and a lithium secondary battery was manufactured. The capacity of this lithium secondary battery is 3
It was 80 mAh. In this lithium secondary battery,
The capacity after repeating a continuous charge / discharge test in which the battery was charged to 3.0 V and discharged to 1.0 V 300 times was 330 mAh.

Comparative Example 1 40 parts by weight of polyethylene, 20 parts by weight of polyethylene oxide (PEO-18: manufactured by Sumitomo Seika) and 100 parts by weight of liquid paraffin were uniformly mixed in a slurry form at 160 ° C. This kneaded product was sandwiched between aluminum plates and pressure-treated until a thickness of 50 μm was reached. The sheet was desolvated with heptane and then dried at 90 ° C. for 7 hours to obtain a separator X for electrochemical element.

In the electrochemical device separator X, the swelling polymer was unevenly distributed, and some voids were visually confirmed.
The ionic conductivity measured by the same method as in Example 1 was 4.1 × 10 ⁻³ S / cm (20 ° C.), which was lower than that of the electrochemical device separator A of the present invention. .

An electric double layer capacitor was manufactured in the same manner as in Example 1 except that the separator X for electrochemical device was used as the separator. The electrostatic capacity of the electric double layer capacitor was 5 μF, which was lower than that of Example 1. Further, a continuous charge / discharge test of this electric double layer capacitor was conducted in the same manner as in Example 1. In the electrochemical device separator X, the swelling polymer was unevenly distributed, and thus the electrostatic capacity was 3 μF. Was low.

Comparative Example 2 10 parts by weight of a styrene / butadiene copolymer (styrene / butadiene composition ratio = 2/8) was dissolved in 100 parts by weight of toluene. Polyethylene oxide (P
EO-18: manufactured by Sumitomo Seika Co., Ltd.)
After being cast on an aluminum sheet by a bar coating method, it was dried at 90 ° C. for 5 hours to obtain a separator Y for electrochemical devices (48 g / m ² , 50 μm). Since the styrene / butadiene copolymer was used as the non-swelling polymer for the separator Y for electrochemical device, the drying time was long.

In the electrochemical device separator Y, the swelling polymer was unevenly distributed, and some voids were visually confirmed.
The ionic conductivity measured by the same method as in Example 2 was 1.9 × 10 ⁻³ S / cm (20 ° C.), which was lower than that of the separator B for electrochemical device of the present invention. .

A lithium secondary battery was manufactured in the same manner as in Example 2, except that the separator Y for electrochemical device was used as the separator. The initial capacity of the lithium secondary battery was 290 mAh, which was lower than that in Example 2. Further, when a continuous charge / discharge test of this lithium secondary battery was carried out in the same manner as in Example 2, in the separator Y for an electrochemical element, the swelling polymer was unevenly distributed, so that the capacity was as low as 200 mAh. It was a thing.

[0035]

As described above, since the separator for electrochemical device of the present invention is excellent in productivity and uniform and has excellent affinity for the electrolyte, it is possible to obtain a high-performance electrochemical device. It has the excellent effect of being able to.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01M 10/40 H01G 9/00 301C F term (reference) 4F071 AA30 AA33 AA48 AA50 AA51 AC19 AE19 AF42 AF45 AG02 AG34 AH15 BA02 BB02 BC02 4J002 AB00X BC02W BC03X BC06X BD03X BD14X BG05X BG10X CE00W CF16W CG01W CN03W CP01X CP03X GQ00 5H021 AA06 BB02 BB13 EE02 EE15 EE17 5H029 AJ02 AK03J1212

Claims (4)

[Claims] 1. In a polymer film comprising a matrix containing a non-swelling polymer and a matrix containing a swelling polymer, the non-swelling polymer is an amorphous thermoplastic resin. Polymer film characterized by. 2. A polymer film characterized in that the swelling polymer contains at least one polymer selected from a homopolymer, a copolymer and a crosslinked polymer containing a polyalkylene oxide group. . 3. A polymer produced by dissolving a non-swelling polymer in a solvent, polymerizing the swelling polymer in the solution to form a mixture into a sheet, and then removing the solvent. the film. 4. A separator for an electrochemical element, which comprises the polymer film according to claim 1.