JP2001266942A - Electrolyte-supported polymer membrane and secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid polymer electrolyte membrane having high strength, heat resistance and excellent safety which can be applied to lithium and lithium ion secondary batteries. .05S /
m or more, the piercing strength is 100 g or more, and the mechanical heat-resistant temperature of the membrane is 200 ° C. or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrolyte-supporting polymer membrane having high strength, heat resistance, and excellent safety during overcharge applicable to lithium and lithium ion secondary batteries.
The present invention relates to a so-called gel electrolyte membrane, a porous membrane serving as a precursor thereof, and a secondary battery using the same.

[0002]

2. Description of the Related Art In recent years, with the development of electronic devices, it has been desired to develop a secondary battery which is small and lightweight, has a high energy density and a large number of repetitive chargings. As this type of battery, lithium and lithium ion secondary batteries using an organic electrolyte (non-aqueous electrolyte) instead of an aqueous electrolyte are attracting attention.

In the case of a solution type lithium secondary battery using lithium and a lithium alloy as a negative electrode, a string-like lithium crystal (dendrite) is formed on the negative electrode due to repeated charging and discharging, and short-circuiting or the like is caused. Further, development of a solid electrolyte membrane having characteristics as a separator is desired.

In a lithium ion secondary battery commercialized by solving the problem of dendrite of the lithium secondary battery, the separator itself used for preventing short-circuiting of the electrodes does not have sufficient holding capacity for the electrolyte, and the It is indispensable to use a metal can as the exterior because the liquid is easily leaked. As a result, not only the manufacturing cost of the battery is increased, but also the weight of the battery cannot be sufficiently reduced. From such a background, development of a highly safe electrolyte membrane which also has a function as a separator is desired from the viewpoint of eliminating electrolyte leakage in a lithium ion secondary battery and reducing the weight of the battery.

[0005] From such a background, studies on an electrolyte membrane system satisfying both high ionic conductivity and safety have been vigorously conducted. One of the approaches is a so-called intrinsic polymer electrolyte approach in which a polymer does not contain a liquid component (a solvent or a plasticizer), and a solid electrolyte is prepared using only a polymer and an electrolyte. Since this type of electrolyte does not contain any liquid component, a relatively strong membrane can be obtained, but the limit of ionic conductivity is as low as about 10 ^-5 S / cm, and the electrode active material layer At present, it has not yet been put to practical use, despite the fact that it has been studied for a long time, for reasons such as insufficient bonding with the steel.

On the other hand, as a system for compensating for the drawbacks of the intrinsic polymer electrolyte, such as low ionic conductivity and insufficient interfacial bonding, energetically, a liquid component (solvent or solvent) is added to the intrinsic polymer electrolyte. (A plasticizer). In the case of this system, the ionic conductivity of the gel electrolyte membrane depends on the amount of the contained liquid component, and by containing a considerable amount of the liquid component, 10 ⁻³ S / cm which is considered to be practically sufficient. Several systems exhibiting the above ionic conductivity have been reported. However, in most of these systems, the mechanical properties of the membrane were rapidly impaired with the addition of the liquid component, and the solid electrolyte inherently had a safety function as a separator was lost.

Under such circumstances, US Pat.
No. 96,318 describes a system in which the strength and the ionic conductivity of a gel electrolyte membrane are compatible. This is a gel electrolyte membrane using a copolymer of vinylidene fluoride (VdF) and hexafluoropropylene (HFP) as a polymer, and has attracted attention as a gel electrolyte having a characteristic mechanical characteristic that should be distinguished. However, even with this system, the piercing strength, which is one indicator of the separator function for a secondary battery, is one order of magnitude lower than that of a general-purpose separator.
Moreover, the mechanically heat-resistant temperature (melt flow temperature) of the gel electrolyte membrane is slightly higher than 100 ° C., which is about 50 ° C. lower than that of a normal polyolefin-based separator, and it cannot necessarily guarantee the safety of a lithium ion secondary battery. It is not at present. This is considered to be due to the fact that the gel electrolyte membrane described in the publication is crystalline in view of the copolymerization ratio of HFP, but has a relatively low crystallinity.

Further, in US Pat. No. 5,418,091, for the purpose of improving the heat resistance of these electrolyte membranes, a membrane is formed together with a polyfunctional acrylate, and a crosslinked structure is introduced by irradiation with an electron beam or the like. A technique for performing this is disclosed. However, in the case of this method, it is necessary to extract the plasticizer from the initially formed film, and there is a problem that the manufacturing method is complicated.
In order to solve this problem, Japanese Patent Application Laid-Open No. H11-66948
In the publication, VdF and tetrafluoroethylene (TF
A technique is disclosed in which a copolymer with E) and a polyfunctional acrylate are blended to form a film, then a porous body is formed by a stretching method, and then a crosslinked structure is introduced by electron beam irradiation. However, even when this technique is used, it is hard to say that it has practically sufficient mechanical properties and heat resistance.

On the other hand, various gel electrolytes using a support as a polyolefin-based synthetic resin reinforcing material have been proposed for the purpose of compensating for the mechanical properties which are considered to be insufficient with the gel electrolyte membrane. For example, JP-A-9-22724 and U.S. Pat. No. 5,603,982 disclose a technique using a polyolefin-based fiber nonwoven fabric and a technique disclosed in JP-A-7-22076.
No. 1 discloses a technique using a polyolefin microporous membrane. By using these reinforcing materials together,
Although the mechanical properties are certainly improved, the heat resistance is at most about 160 ° C. due to the use of the polyolefin-based resin, which is not always sufficient.

[0010]

As described above, various attempts have been made to develop an electrolyte-carrying polymer membrane having both high ionic conductivity and a safety function as a separator. High ionic conductivity and sufficient mechanical properties as a separator, and
At present, a practical electrolyte-carrying polymer membrane that has higher heat resistance than current polyolefin-based separators and that can be formed into a thin film and has excellent safety has not been found yet.

As a result of intensive studies in view of such a situation,
Practical high ionic conductivity, strong short-circuit prevention strength as a separator, and a highly safe electrolyte-supporting polymer membrane that combines high heat resistance with respect to short-circuit prevention and a porous membrane that is a precursor thereof, and A secondary battery using them has been developed, and the present invention has been completed. The object of the present invention is
Ion conductivity, strength, and heat resistance
An object of the present invention is to provide an electrolyte-supporting polymer membrane, a so-called gel electrolyte membrane and a porous membrane which is a precursor thereof for a lithium ion secondary battery with high safety at the time of overcharge, and a secondary battery using the same.

[0012]

According to the present invention, there is provided a porous reinforcing member (A) made of a high-strength heat-resistant resin and having a thickness of 100 μm or less, and a repetition derived from vinylidene fluoride held by the porous reinforcing member. A vinylidene fluoride copolymer (B) comprising 50 to 99 mol% of a unit and 1 to 50 mol% of a repeating unit derived from tetrafluoroethylene, having a melting point of 80 ° C. or more and a crystallinity of 20 to 80%. And an electrolyte (C) comprising a polar organic solvent (c1) and an electrolyte (c2), which are integrated with the vinylidene fluoride-based copolymer to form a gel, and have a thickness of not more than 200 μm and an ionic conductivity. Degree 0.05S / m or more, piercing strength 100
g of a polymer membrane carrying an electrolyte having a mechanical heat-resistant temperature of 200 ° C. or more; a porous reinforcing member (A) made of a high-strength heat-resistant resin having a thickness of 100 μm or less, and vinylidene fluoride held by the porous reinforcing member. It comprises 50 to 99 mol% of repeating units derived from 1 to 50 mol% of repeating units derived from tetrafluoroethylene, and has a melting point of 80%.
A porous membrane for a battery, comprising a vinylidene fluoride copolymer (B) having a crystallinity of 20 to 80% or more and a thickness of 200 µm or less, a puncture strength of 100 g or more, and a mechanical heat resistance temperature of 200 ° C or more; It is a secondary battery using them.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The present invention has a thickness of 100 made of a high-strength heat-resistant resin.
μm or less of a porous reinforcing member (A), 50 to 99 mol% of a repeating unit derived from vinylidene fluoride held on the porous reinforcing member, and 1 to 50 mol% of a repeating unit derived from tetrafluoroethylene. A vinylidene fluoride copolymer (B) having a melting point of 80 ° C. or higher and a crystallinity of 20 to 80%, and a gelled polar organic solvent integrated with the vinylidene fluoride copolymer ( c1)
Having a thickness of 200 μm or less and an ionic conductivity of 0.05 S / m.
(25 ° C.) or more, a piercing strength of 100 g or more, and a mechanically heat-resistant temperature of 200 ° C. or more.

Here, the ionic conductivity is obtained by interposing a solid electrolyte-carrying polymer membrane between SUS electrodes of 20 mmφ and analyzing the frequency dependence of impedance in the range of 1 mm (m) Hz to 65 KHz by an alternating current impedance method. 10K
It is obtained from the impedance value of Hz. If this value is higher than 5 × 10 ⁻⁴ S / cm, the impedance when assembled as a battery does not increase, and the capacity during high-rate charging and discharging does not decrease.

The electrolyte-supporting polymer membrane of the present invention is also characterized in that the piercing strength is as high as 100 g or more, preferably 200 g or more. The piercing strength is a physical property that is used in the evaluation of the separator as an index representing the short-circuit prevention strength of the current solution-type lithium ion secondary battery separator.In the present invention, the value measured under the following conditions is used. The piercing strength was used. 11.3 mm electrolyte polymer-supported polymer membrane
Set on a fixed frame of φ, push a needle with a tip radius of 0.5 mm vertically to the center of the membrane, push the needle at a constant speed of 50 mm / min, and hang on the needle when a hole is opened in the membrane The force was used as the piercing strength.

This value is 100 g or more, preferably 200 g
In the above case, when assembled as a battery, the probability of occurrence of a short circuit between the electrodes is suppressed, and safety (short-circuit prevention characteristics) when assembled as a battery is sufficiently ensured. Further, the electrolyte-carrying polymer membrane of the present invention has 20
It is characterized by having a mechanically heat-resistant temperature of 0 ° C. or more. Here, the mechanical heat-resistant temperature means a value measured under the following conditions.

A film thickness of about 45 μm, a width of 5 mm, and a length of 25 mm
A load of 1 g is applied to the strip-shaped electrolyte-carrying polymer membrane of
The temperature was increased at a rate of 10 ° C./min, and a thermomechanical property analysis (TMA) was performed.
The temperature at which 0% elongation was reached was defined as the mechanical heat-resistant temperature. When this temperature is 200 ° C. or higher, a short circuit between the electrodes can be sufficiently prevented when the internal temperature of the battery rises rapidly due to an abnormal reaction of the battery, which is preferable from the viewpoint of safety.

The electrolyte-carrying polymer membrane of the present invention has strength,
It is a composite of a porous reinforcing member characterized by heat resistance and an electrolyte-carrying polymer having practically sufficient ionic conductivity. At that time, the content of the electrolyte-carrying polymer in the electrolyte-carrying polymer film is preferably in the range of 30 to 85% by weight. When the content of the electrolyte-carrying polymer is 30% by weight or more, the influence on the conductivity of the porous reinforcing member is not so much a problem, and the composite electrolyte-carrying polymer membrane has sufficient ionic conductivity. If the content is too large, the strength of the electrolyte-carrying polymer membrane tends to decrease, or the thickness of the electrolyte-carrying polymer membrane may increase unnecessarily, which may be undesirable.

Further, in the electrolyte-carrying polymer membrane of the present invention,
It is particularly preferred that the porous reinforcing member is almost completely embedded in the inside of the membrane and the surface of the membrane is covered with the gel electrolyte-carrying polymer. If the surface of the composite membrane is not covered with the gel-like electrolyte-carrying polymer and the porous reinforcing member is more exposed, good interfacial bonding between the positive electrode and the negative electrode is performed when the battery is formed Tends to be difficult. Therefore, the ratio (a / b) of the thickness (a) of the electrolyte-carrying polymer membrane to the thickness (b) of the porous reinforcing member is generally 1 to 3.
3, preferably 1.05 to 2.0. When the thickness of the electrolyte-carrying polymer membrane is thinner than the thickness of the porous reinforcing member,
A portion where the porous reinforcing member is partially exposed is formed, and it becomes difficult for the surface irregularities of the positive electrode and the negative electrode to be absorbed by the gel electrolyte-carrying polymer covering the surface of the electrolyte-carrying polymer film. It becomes difficult to perform 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.

The high-strength heat-resistant resin forming the porous reinforcing member (A) in the electrolytic solution-carrying polymer membrane of the present invention has a Young's modulus of at least 1,000 MPa, preferably at least 3,000 MPa.
It can be composed of an organic polymer compound having a heat resistance of at least 0 MPa and a heat resistance of at least 200 ° C, preferably at least 300 ° C. A typical example thereof is an aromatic polyamide so-called aramid resin. Regarding the molecular structure of the aromatic polyamide polymer, it can be used in the present invention irrespective of meta-type or para-type. Here, as the meta system, a wholly aromatic polyamide having m-phenylene isophthalamide as a main structural unit is exemplified, and as the para system, a wholly aromatic polyamide having p-phenylene terephthalamide as a main structural unit. Polyamides are typical. These may be mixed.

The porous reinforcing member of the present invention has an average thickness of 10 to 100 μm, preferably 10 to 50 μm,
The piercing strength is 100 g or more, preferably 200 g or more,
A high-strength, high-air-permeability thin film having an air permeability (JIS P8117) of 10 seconds or less, preferably 5 seconds or less is suitably used. If the average film thickness exceeds 100 μm, it becomes easy to obtain a high-strength support, but the thickness of the obtained composite film is increased, and the volume energy density when assembled as a battery is reduced.

The piercing strength of the porous reinforcing member of the present invention is preferably 100 g or more. When a support having a value of less than 100 g is used, it is difficult to achieve a puncture strength of 100 g or more even after the electrolyte-supporting polymer is compounded, and the safety when assembled as a battery (short circuit prevention) Characteristics).

The air permeability of the porous reinforcing member of the present invention is determined by the Gurley method (JIS P81117;
(the time required for permeating the area of in ² at a pressure of 2.3 cmHg). As the porous reinforcing member of the present invention, a support having a high air permeability of 10 seconds or less, preferably 5 seconds or less is suitably used. When a support having a low air permeability larger than 10 seconds is used, it becomes difficult to impregnate and composite the electrolyte-carrying polymer by a coating method from a polymer solution which is considered to be the most advantageous industrially, It tends to be difficult to sufficiently increase the ionic conductivity of the composite electrolyte-carrying polymer membrane.

The shape of the porous reinforcing member that satisfies the above characteristics includes a nonwoven fabric, a woven fabric,
Alternatively, there may be mentioned a breathable paper-like sheet in which the synthetic pulp of the polymer is dispersed in the interstices of the fibers, or a breathable film having a large number of holes made of the resin. Any of these shapes can be used in the present invention as long as the characteristics as the porous reinforcing member are satisfied.However, in consideration of air permeability, a non-woven sheet is most preferable. It is preferably used. The basis weight is 8 to 35 g / m ^2, preferably 10 to ³ g / m ^2.
A range of 0 g / m ² is preferably used. 8g weight
/ M ² , it is easy to obtain a porous reinforcing member having high air permeability, but it is difficult to obtain a piercing strength of 100 g or more, and as a result, a solid with excellent short-circuit prevention strength is obtained. It becomes difficult to obtain a type electrolyte membrane. On the other hand, when the basis weight is more than 35 g / m ² , it is easy to satisfy the piercing strength, but it is difficult to obtain a porous reinforcing member with an average film thickness of 100 μm 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.

The porous reinforcing member (A) has a thickness of 10
0 μm or less, preferably 50 μm or less, more preferably 4 μm or less
0 μm or less, piercing strength is 100 g or more, preferably 200 g or more, air permeability is 10 seconds or less, preferably 5 seconds or less, and the inside is formed in a three-dimensional mesh-like thin film. The three-dimensional network-like thin film is not necessarily required to be from the beginning because it is sufficient that the three-dimensional network-like thin film is formed in the electrolyte-carrying polymer film, but is preferably a nonwoven fabric, a woven fabric, an intertwined two-dimensional fiber, or paper. A three-dimensional network-like thin film may be used from the beginning, such as a sheet. They are preferably in the form of a nonwoven sheet having a basis weight of 8 to 35 g / m ² . Further, the porous reinforcing member (A) does not necessarily have to be derived from fibers, and may be a porous film-like thin film having a Macmillan number of 7 or less.

Next, the electrolyte-supporting polymer to be impregnated and composited with the porous reinforcing material of the present invention will be described. The electrolyte-supporting polymer used in the present invention is characterized in that it is a vinylidene fluoride copolymer (B) having appropriate crystallinity, and specifically, a repeating unit derived from vinylidene fluoride having a molecular weight of 50 to 50%. A vinylidene fluoride copolymer comprising 99 mol%, 1 to 50 mol% of a repeating unit derived from tetrafluoroethylene, having a melting point of 80 ° C. or higher and a crystallinity of 20 to 80% is used.

The vinylidene fluoride copolymer (B) has a melting point of 80 ° C. or higher, preferably 100 ° C. or higher, more preferably 100 to 170 ° C., and particularly preferably 110 to 160 ° C.
It is in the range of ° C. Here, the melting point means the melting point determined by DSC.

The copolymer composition of the vinylidene fluoride copolymer (B) is such that the repeating unit derived from vinylidene fluoride (VdF) is 50 to 99 mol%, preferably 75 to 95 mol%, more preferably 77-95 mol%
And a repeating unit derived from tetrafluoroethylene (TFE) of 1 to 50 mol%, preferably 5 to 25 mol%.
Mol%, more preferably 5 to 23 mol%. Also,
A monomer copolymerizable as long as the crystallinity and melting point of the copolymer are not impaired may be copolymerized as a third component, if necessary, in an amount of 0 to 10 mol%. Specific monomers include, for example, those described in WO 99/28916.

The vinylidene fluoride copolymer has a molecular weight of 50,000 to 500,000, preferably 10 to 500,000.
The range from 000 to 300,000 is preferred. Here, the molecular weight indicates a molecular weight in terms of polystyrene by a GPC method using an NMP solvent. The vinylidene fluoride copolymer (VdF / TFE) of the present invention can be prepared by a known technique (VdF / H).
Since the crystallinity is higher than that of FP), it is characterized in that the mechanical properties are hardly impaired even when the electrolyte is impregnated and retained, and that the electrolyte retention in a high temperature region is improved.

As the electrolytic solution for impregnating the vinylidene fluoride copolymer for the gel electrolyte, a polar organic solvent (non-aqueous solvent (plasticizer)) in which an electrolyte (eg, lithium salt) is dissolved (hereinafter referred to as “non-aqueous electrolytic solution”) Is sometimes used). At this time, it is preferable that the amount of the electrolyte carried on the polymer carrying the electrolyte is 100 parts by weight or more of the electrolyte with respect to 100 parts by weight of the polymer. If the amount of the electrolytic solution is smaller than this, it is difficult to secure a sufficient ionic conductivity when combined with the porous reinforcing member.

As the polar organic solvent to be used, a polar organic solvent having 10 or less carbon atoms generally used for lithium and lithium ion secondary batteries, for example, propylene carbonate (PC), ethylene carbonate (EC),
Butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DE
E), γ-butyrolactone (γ-BL), sulfolane, acetonitrile, tetrahydrofuran, dioxane, ethyl acetate and the like. The polar organic solvents may be used alone or as a mixture of two or more. In particular, PC, EC, γ-BL, DMC, DE
At least one liquid selected from C, MEC and DME is preferably used.

Suitable electrolyte soluble in this polar organic solvent
Quaternary ammonium salts, lithium salts,
Alkali metal salts such as um salt and potassium salt, calcium
Salts and alkaline earth metal salts such as magnesium salts.
Lithium, especially for lithium secondary batteries
As the salt, lithium perchlorate (LiClO_Four), Hexafluoride
Lithium phosphate (LiPF₆), Lithium borotetrafluoride
(LiBF_Four), Lithium arsenide hexafluoride (LiAsF)₆),
Lithium trifluorosulfonate (CF_ThreeSO_ThreeLi),
Lithium perfluoromethylsulfonylimide [LiN
(CF_ThreeSO_Two) _Two] And lithium perfluoroethyls
Ruphonylimide [LiN (C_TwoF_FiveSO_Two)_Two]
However, the present invention is not limited to this. Also these
May be used in combination. Lithium salt soluble
The concentration is preferably in the range of 0.2 to 2 M (mol / l).
Appropriately used.

Next, a method for producing the electrolyte-carrying polymer membrane of the present invention will be described. The electrolyte-carrying polymer film of the present invention has, for example, an average film thickness of 100 μm or less, preferably 50 μm or less.
μm or less, and the piercing strength is 100 g or more, preferably 20
A polar organic solvent in which an electrolyte (for example, a lithium salt) (c2) is dissolved in a high-strength, high-air-permeable porous reinforcing member (A) of 0 g or more and having an air permeability of 10 seconds or less, preferably 5 seconds or less. A gel electrolyte in which the electrolyte (C) comprising (c1) is held in an amount of 100 parts by weight or more with respect to 100 parts by weight of the vinylidene fluoride copolymer (hereinafter also referred to as polymer) (B) (Polymer) in an impregnated state. At this time, a method of impregnating and complexing the gel electrolyte is not particularly limited, but a method of directly impregnating and coating a porous reinforcing member with a polymer in a fluid (solution) state is industrially easy and preferred. . Examples of such a method include the following method.

The vinylidene fluoride copolymer (B) and the electrolytic solution (C) are mixed and dissolved by heating, and the dope in the solution state is directly applied to and impregnated into the porous reinforcing member, and then cooled and solidified to form a composite. How to

The vinylidene fluoride copolymer (B), the electrolytic solution (C) and a volatile solvent for dissolving the polymer resin are mixed and dissolved, and the dope in the solution state is directly applied to the porous reinforcing member. A method of impregnating and then removing and drying the volatile solvent to form a composite.

The vinylidene fluoride copolymer (B), a solvent that dissolves the polymer and is compatible with water, and a phase separating agent (gelling agent or pore-forming agent) are mixed and dissolved, and the solution state is obtained. Dope is directly coated and impregnated on the porous reinforcing member,
Subsequently, the membrane is immersed in an aqueous coagulation bath to solidify the polymer, followed by washing and drying to produce a porous membrane which is a precursor of the electrolyte-carrying polymer membrane. ) To gel the polymer to form a composite film.

The porous membrane for a battery according to the present invention (contents of claim 12) can be obtained, for example, by the above method. The porous reinforcing member (A), the vinylidene fluoride copolymer (B) in the porous membrane for a battery, the thickness thereof,
Preferable examples of the piercing strength and the mechanical heat-resistant temperature are the same as those of the above-mentioned electrolyte-carrying polymer membrane.

Next, the secondary battery of the present invention will be described.

The secondary battery of the present invention comprises: a positive electrode having a positive electrode material that holds a nonaqueous electrolyte and absorbs and releases electrolyte-derived metal ions (hereinafter represented by lithium ions); This is a polymer secondary battery in which the electrolyte-carrying polymer film of the present invention is arranged between a negative electrode having a carbonaceous negative electrode material that inserts and absorbs lithium ions while retaining the above.

Hereinafter, each of them will be described in detail. (Positive Electrode) The positive electrode of the present invention typically comprises an active material that stores and releases lithium ions, a non-aqueous electrolyte, a binder polymer that holds the electrolyte and binds the active material, and a current collector. Can be configured.

As the active material, various lithium-containing materials may be used.
Oxides and chalcogen compounds can be mentioned. Lichi
Li-containing oxides such as LiCoO_TwoSuch as lithium
Containing cobalt oxide, LiNiO_TwoSuch as lithium containing
Nickel oxide, LiMn_TwoO _FourSuch as lithium-containing man
Gun complex oxide, lithium-containing nickel cobalt oxide
Products, lithium-containing amorphous vanadium pentoxide, etc.
be able to. In addition, as a chalcogen compound, disulfur
Titanium nitride, molybdenum disulfide, etc.
You.

As the non-aqueous electrolyte, those similar to those described above for the electrolyte-carrying polymer membrane can be used. Binder polymers that hold the nonaqueous electrolyte and bind the active material include polyvinylidene fluoride (PVdF), VdF and hexafluoropropylene (HF).
P), VdF copolymer resins such as copolymers with perfluoromethylvinylether (PFMV) and tetrafluoroethylene (TFE), fluoropolymers such as polytetrafluoroethylene and fluororubber, and styrene Butadiene copolymer, styrene-acrylonitrile copolymer,
A hydrocarbon polymer such as ethylene-propylene-terpolymer, carboxymethylcellulose, a polyimide resin, or the like can be used, but is not limited thereto. These may be used alone or as a mixture of two or more.

The amount of the binder polymer to be added is as follows.
The range is preferably 3 to 30 parts by weight with respect to 00 parts by weight.
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. On the other hand, if it exceeds 30 parts by weight, the active material density in the positive electrode decreases, and 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. Further, the positive electrode of the present invention may contain artificial graphite, carbon black (acetylene black), nickel powder, or the like as a conductive additive. 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 for dissolving the binder are mixed and dissolved to prepare a paste of the active material. A method in which the obtained paste is applied onto a current collector, and the film from which the volatile solvent has been dried and removed is immersed in a non-aqueous electrolyte to retain the electrolyte. 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 the current collector, the obtained coating film is immersed in an aqueous coagulation bath to coagulate the binder polymer, then the membrane is washed and dried, and the membrane is washed with a non-aqueous electrolyte. To retain the electrolyte by impregnating it.

A predetermined amount of an active material, a binder polymer, a low-boiling volatile solvent that dissolves the binder, and a non-aqueous electrolyte are mixed and dissolved to prepare an active material paste. A method in which the obtained paste is applied on a current collector, and only a volatile solvent having a low boiling point is dried and removed to directly form a positive electrode holding an electrolyte. (Negative Electrode) Next, the negative electrode of the present invention will be described. The negative electrode of the present invention typically comprises 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. Can be done.

Examples of the carbonaceous active material include those obtained by sintering organic polymer compounds such as polyacrylonitrile, phenolic 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 polymer as the above-described positive electrode can be used. The amount of binder polymer added is
The range is preferably 3 to 30 parts by weight based on 100 parts by weight of the active material. 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. On the other hand, if it exceeds 30 parts by weight, the active material density in the negative electrode decreases, and 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-shaped metallic copper is used. Also,
The negative electrode of the present invention may contain artificial graphite, carbon black (acetylene black), nickel powder, or the like as a conductive additive. Although the method for producing the negative electrode of the present invention is not particularly limited, the same method as that described for the above-described positive electrode can be employed. (Production of Battery) Next, a method for producing the polymer electrolyte secondary battery of the present invention will be described.

The method for producing the polymer electrolyte secondary battery of the present invention is not particularly limited, and a known method can be employed. Specifically, by laminating the cathode / electrolyte-carrying polymer film / negative electrode and then laminating by thermocompression bonding, an element in which the electrode and the electrolyte-carrying polymer film are bonded can be produced. Further, in the above method, the secondary battery of the present invention can be obtained by using the porous membrane of the present invention instead of the electrolyte-supporting polymer membrane. At this time, the electrodes and the porous membrane may be thermocompression-bonded dry (in a state where the electrolyte is not included) and then impregnated with the electrolyte to form an active element. In addition, if necessary, an ionic conductive adhesive is disposed between the electrode and the electrolytic solution-carrying polymer film, so that the adhesiveness can be improved.

[0051]

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

Example 1 <Aramid Porous Reinforcing Member> A crystallized m-aramid short fiber having a thickness of 1.38 dtex was added to a 3.3 dtex thickness.
Of non-crystallized m-aramid filaments were added as a binder, and a film was formed at a basis weight of 19 g / m ² by a dry papermaking method and calender rolled to obtain a non-woven sheet. The properties of the obtained support were as follows. Average thickness 36μ
m, density 0.53 g / cm ³ , porosity 62%, air permeability 0.04 sec / 100 cc · in ² , piercing strength 33
0g, Macmillan number 2.4. <Polymer synthesis: VdF / TFE = 80/20 molar ratio>
Ion exchange water 1800m in autoclave of 6L
After charging l, vacuum / nitrogen substitution was repeated three times at room temperature.
Next, after introducing 1500 ml of perfluorocyclobutane,
The temperature was raised to 40 ° C. (internal pressure 0.5 MPa). Then, a monomer gas obtained by mixing VdF and TFE at a molar ratio of 92/8 (initial mixed monomer gas) was used at an internal pressure of 1.3M.
It blew until it became Pa. Thereafter, 5 g of a 50% by weight methanol solution of normal propyl peroxide was added as an initiator under nitrogen pressure, and polymerization was started with stirring. When the internal pressure drops to 1.25 MPa, V
An additional monomer gas in which dF and TFE were mixed at a molar ratio of 80/20 was blown, and the internal pressure was returned to 1.3 MPa. While maintaining the polymerization temperature at 40.degree.
The polymerization was repeated once and the polymerization was completed. After removing perfluorocyclobutane and returning the internal pressure to normal pressure, the polymer was taken out. The obtained polymer is made of a large amount of ion-exchanged water (50
C.) and dried at 110.degree.

The crystallinity determined by X-ray diffraction is 40%,
The melting point determined by the DSC method was 128 ° C., and the molecular weight in terms of polystyrene determined by the GPC method was 300,000. <Composite Gel Electrolyte> PC / EC (1/1) in which 1M LiBF ₄ was dissolved with respect to 100 parts by weight of the polymer.
(1 weight ratio) An electrolytic solution was added in an amount of 300 parts by weight, and tetrahydrofuran (THF) as a solvent was further added and mixed and dissolved to prepare a dope having a polymer concentration of 12% by weight. Impregnating the obtained dope into the aramid porous reinforcing member
By coating and removing the THF by drying at 50 ° C., an electrolyte-carrying polymer film was produced.

Comparative Example 1 A dope for a gel electrolyte used in Example 1 was coated on a silicon-coated release film without using an aramid porous reinforcing member, and was made of an electrolyte-supporting polymer. A film was prepared.

Comparative Example 2 The same procedure as in Example 1 was repeated except that the amount of the electrolytic solution was changed to 80 parts by weight with respect to 100 parts by weight of the polymer. Was prepared.

[Example 2] A film was formed in the same manner as in Example 1 except that a polymer having a VdF / TFE = 90/10 molar ratio was used as in Example 1, to produce an electrolyte-carrying polymer film. . The synthesis of the polymer is described in Example 1.
In the above, the initial mixed monomer gas was VdF / TFE = 9
7/3 molar ratio, additional mixed monomer gas was VdF / TFE
= 90/10, except that the molar ratio was changed. The obtained polymer had a crystallinity of 42%, a melting point of 138 ° C. and a molecular weight of 250,000.

[Comparative Example 3] A single membrane made of an electrolyte-supporting polymer was prepared in the same manner as in Example 2, except that the aramid porous reinforcing member was not used.

Example 3 The procedure of Example 1 was repeated, except that a polymer having a VdF / TFE = 75/25 molar ratio was used as the polymer, and the amount of the electrolyte added was 150 parts by weight per 100 parts by weight of the polymer. Film formation was performed in the same manner as in Example 1 to prepare an electrolyte-carrying polymer film. In the synthesis of the polymer, in Example 1, the initial mixed monomer gas was VdF
The procedure was performed in the same manner as in Example 1 except that the / TFE = 87/13 molar ratio and the additional monomer mixture gas were VdF / TFE = 75/25 molar ratio. The obtained polymer has a crystallinity of 42%, a melting point of 140 ° C. and a molecular weight of 130,000.
Met.

Example 4 The procedure of Example 1 was repeated, except that a polymer having a VdF / TFE = 70/30 molar ratio was used as the polymer, and the amount of the electrolyte added was 150 parts by weight based on 100 parts by weight of the polymer. Film formation was performed in the same manner as in Example 1 to prepare an electrolyte-carrying polymer film.

In the synthesis of the polymer, in Example 1, the initial mixed monomer gas was VdF / TFE = 85/15 molar ratio, and the additional mixed monomer gas was VdF / TFE = 70/3.
The procedure was performed in the same manner as in Example 1 except that the molar ratio was changed to 0. The obtained polymer has a crystallinity of 45% and a melting point of 14%.
At 1 ° C., the molecular weight was 120,000.

Comparative Example 4 In Example 1, the polymer was VdF / HFP = 95/5 molar ratio (KYNAR2
801; manufactured by Elf Atochem)
A film was formed in the same manner as in Example 1 except that the amount of the electrolyte solution was changed to 150 parts by weight with respect to parts by weight, to thereby form an electrolyte-carrying polymer film.

[Comparative Example 5] A method similar to that of Comparative Example 1 was used except that the amount of the electrolytic solution added to 100 parts by weight of the polymer was changed to 300 parts by weight without using the aramid porous reinforcing member. A single membrane made of an electrolyte-supported polymer was prepared.

Example 5 <Aramid Porous Reinforcing Member> A nonwoven fabric having a basis weight of 14 g / m ^{2 in} the same manner as in Example 1 using crystallized m-aramid short fibers having a thickness of 0.9 dtex. A sheet in the shape of a letter was obtained. The properties of the obtained support were as follows. Average thickness 29 μm, density 0.58 g / cm ³ , porosity 59
%, Air permeability 0.02 sec / 100 cc · in ² , piercing strength 220 g, Macmillan number 3.2. <Polymer: VdF / TFE = 90/10 molar ratio> The polymer prepared in Example 2 was used. <Composite Gel Electrolyte> The polymer was dissolved at 50 ° C. in a 6/4 (weight ratio) mixed solvent of N, N-dimethylacetamide (DMAc) and polypropylene glycol (PPG) having an average molecular weight of 400. An 18% by weight dope was prepared. After impregnating and applying the obtained dope to the aramid porous reinforcing member, the DMAc / PPG
It was poured into a 40% by weight aqueous solution composed of (6/4) to coagulate the membrane, and then washed and dried to form a composite porous membrane (precursor). The obtained porous membrane was added to the electrolyte solution for 30 minutes.
After immersion for a minute, the electrolyte adhering excessively to the surface was wiped off to form an electrolyte-carrying polymer film. Table 1 shows the measurement results of the above Examples and Comparative Examples.

[0064]

[Table 1]

Example 6 [Positive Electrode] The dry weight of lithium cobalt oxide (LiCoO2; manufactured by Kansai Catalyst) powder of 85 parts by weight, carbon black of 5 parts by weight, and polyvinylidene fluoride (PVdF) was adjusted to 10 parts by weight. A positive electrode material paste was prepared using an N-methyl-pyrrolidone (NMP) solution of 8% by weight of PVdF. The obtained paste was applied on an aluminum foil having a thickness of 20 μm and dried to prepare a positive electrode coating having a thickness of 120 μm. Then, the obtained positive electrode was dissolved in 1M LiBF ₄ dissolved PC /
It was immersed in EC (1/1 weight ratio) to obtain a positive electrode holding an electrolytic solution.

[Negative Electrode] As a carbonaceous negative electrode material, an NMP solution of 10 wt% PVdF was used so that 90 parts by weight of mesophase carbon microbeads (MCMB; Osaka Gas Chemicals) powder and 10 parts by weight of PVdF were dried. Then, a negative electrode material paste was produced. The obtained paste was coated to a film thickness of 18
The resultant was coated on a μm copper foil and dried to prepare a negative electrode coating film having a thickness of 125 μm. The obtained negative electrode was immersed in PC / EC (1/1 weight ratio) in which 1M LiBF ₄ was dissolved, to prepare a negative electrode holding an electrolyte.

[Battery Production] Each of the positive electrode, the negative electrode, and the electrolyte-carrying polymer membrane prepared in Example 1 was 3 cm × 6 c
m, cut into a positive electrode, an electrolyte-carrying polymer film, and a negative electrode in this order.
Thermocompression bonding was performed at 0 ° C. When a 180 ° peel test was performed on the battery element (positive electrode / electrolyte-supporting polymer film / negative electrode laminate) similarly manufactured, the positive electrode and the electrolyte-supporting polymer film were 22 gf / cm, and that of the negative electrode was 20 gf / cm.
It adhered with a peel force of gf / cm, and it was found that good interfacial bonding was achieved. A stainless sheet terminal was attached to each current collector of the obtained battery element, and laminated with a polyethylene / aluminum / polyethylene terephthalate laminated sheet (film thickness 50 μm) to produce a sheet-shaped battery. About the obtained battery, 1
Charge / discharge was performed at a current density of mA / cm ² . At this time, charging was performed up to 4.2 V, and discharging was cut at 2.7 V. The current efficiency of the initial discharge was 80%, and repeated charging and discharging were possible. Further, the discharge amount per negative electrode weight at that time was 200 mAh / g.

[0068]

As described in detail above, according to the present invention, the safety useful for polymer secondary batteries, which has high ionic conductivity, short-circuit prevention strength, and high mechanical heat resistance, is provided. It has become possible to provide an excellent electrolyte-carrying polymer membrane.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroyuki Motomoto 2-1 Hinode-cho, Iwakuni-shi, Yamaguchi Prefecture Teijin Co., Ltd. Inside the Iwakuni Research Center (72) Inventor Satoshi Nishikawa 2-1 Hinode-cho, Iwakuni-shi, Yamaguchi Prefecture Teijin Inside the Iwakuni Research Center Co., Ltd. (72) Hiromasa Minematsu 2-1 Hinodemachi, Iwakuni-shi, Yamaguchi Teijin Co., Ltd. (72) Inventor Tadashi Ino 1-1-1, Nishi-Itsuya, Settsu-shi, Osaka Daikin Industrial Co., Ltd. (72) Inventor Kenji Ichikawa 1-1, Nishiichitsuya, Settsu-shi, Osaka Daikin Industry Co., Ltd. (72) Inventor Tetsuo Shimizu 1-1-1, Nishiichitsuya, Settsu-shi, Osaka Daikin Industry Co., Ltd. F term in the factory (reference) 5H021 CC01 CC02 EE07 HH00 HH02 HH03 HH06 5H029 AJ12 AK03 AL06 AM00 AM03 AM 04 AM07 AM16 DJ04 DJ09 EJ12 EJ14 HJ00 HJ02 HJ04 HJ14

Claims (21)

[Claims] 1. A high-strength heat-resistant resin having a thickness of 100 μm
m or less, from 50 to 99 mol% of a repeating unit derived from vinylidene fluoride held on the porous reinforcing member, and from 1 to 50 mol% of a repeating unit derived from tetrafluoroethylene. A vinylidene fluoride copolymer (B) having a melting point of 80 ° C. or higher and a crystallinity of 20 to 80%, and a gelled polar organic solvent integrated with the vinylidene fluoride copolymer ( comprising an electrolytic solution (C) comprising c1) and an electrolyte (c2).
200 μm or less in thickness, ionic conductivity 0.05 S / m (2
5 ° C) or more, piercing strength 100 g or more, mechanical heat resistance temperature 2
An electrolyte-carrying polymer membrane of 00 ° C or higher. 2. The vinylidene fluoride copolymer (B) comprises:
Repeating unit 7 derived from vinylidene fluoride
5 to 95 mol%, 5 to 25 mol% of repeating units derived from tetrafluoroethylene, and having a melting point of 100
2. The electrolyte-carrying polymer membrane according to claim 1, wherein the polymer is a copolymer having a crystallinity of 20 to 50% at a temperature of not less than 0. 3. The electrolyte-carrying polymer membrane according to claim 1, wherein the vinylidene fluoride copolymer (B) has a molecular weight of 50,000 to 500,000 (NMP solvent, in terms of polystyrene). 4. The electrolyte-carrying polymer membrane according to claim 1, wherein the high-strength heat-resistant resin is an aromatic polyamide. 5. The porous reinforcing member (A) having a thickness of 10 to 10.
50 μm, puncture strength 100 g or more, air permeability (JIS P
The electrolyte-carrying polymer membrane according to any one of claims 1 to 4, wherein 8117) is derived from a three-dimensional network-like thin film of 10 seconds or less. 6. The porous reinforcing member (A) is a non-woven fabric, a woven fabric or an intertwined two-dimensional fiber.
The polymer solution-carrying polymer membrane according to any one of the above. 7. The porous reinforcing member (A) having a basis weight of 8 to
7. The electrolyte-carrying polymer membrane according to claim 6, which is a 35 g / m ² nonwoven sheet. 8. The electrolyte-carrying polymer membrane according to claim 5, wherein said porous reinforcing member (A) is a porous thin film having a Macmillan number of 7 or less. 9. The polar organic solvent (c1) is propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate,
The solvent is at least one selected from methyl ethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane and γ-butyrolactone.
9. The electrolyte-carrying polymer membrane according to any one of items 1 to 8. 10. The electrolyte (c2) is selected from lithium perchlorate, lithium hexafluorophosphate, lithium borotetrafluoride, lithium trifluorosulfonate, lithium perfluoromethylsulfonylimide and lithium perfluoroethylsulfonylimide. The electrolyte-carrying polymer membrane according to any one of claims 1 to 9, which is at least one or more kinds of electrolytes. 11. An electrolytic solution (C) supporting 100 phr or more of said vinylidene fluoride copolymer (B).
11. The electrolyte-carrying polymer membrane according to any one of items 10 to 10. 12. A thickness of 100 made of a high-strength heat-resistant resin.
μm or less of a porous reinforcing member (A), 50 to 99 mol% of a repeating unit derived from vinylidene fluoride held on the porous reinforcing member, and 1 to 50 mol% of a repeating unit derived from tetrafluoroethylene. A battery comprising a vinylidene fluoride copolymer (B) having a melting point of 80 ° C. or more and a crystallinity of 20 to 80%, a thickness of 200 μm or less, a puncture strength of 100 g or more, and a mechanical heat resistance temperature of 200 ° C. or more. For porous membrane. 13. The vinylidene fluoride copolymer (B)
Consists of 75 to 95 mol% of repeating units derived from vinylidene fluoride and 5 to 25 mol% of repeating units derived from tetrafluoroethylene, and has a melting point of 1
The porous membrane for a battery according to claim 12, which is a copolymer having a crystallinity of 20 to 50% or more at 00C or higher. 14. The vinylidene fluoride copolymer (B) having a molecular weight of 50,000 to 500,000 (NMP solvent,
The porous membrane for a battery according to claim 12 or 13, which is in terms of polystyrene. 15. The battery porous membrane according to claim 12, wherein the high-strength heat-resistant resin is an aromatic polyamide. 16. The porous reinforcing member (A) having a thickness of 10
５０50 μm, piercing strength 100 g or more, air permeability (JISP
The porous membrane for a battery according to any one of claims 12 to 15, wherein 8117) is derived from a three-dimensional network-like thin film of 10 seconds or less. 17. The non-woven fabric, comprising: the porous reinforcing member (A);
13. A woven fabric or an intertwined two-dimensional fiber.
17. The electrolyte-carrying polymer membrane according to any one of items 16 to 16. 18. The porous reinforcing member (A) having a basis weight of 8
Battery porous membrane potential of claim 17 wherein the nonwoven sheet ~35g / m ^2. 19. The battery porous membrane according to claim 16, wherein said porous reinforcing member (A) is a porous thin film having a Macmillan number of 7 or less. 20. A positive electrode having a positive electrode material that stores and releases lithium ions, holding a non-aqueous electrolyte, and a carbonaceous negative electrode material that stores and releases lithium ions, holding a non-aqueous electrolyte. A polymer electrolyte secondary battery in which the electrolyte-carrying polymer film according to claim 1 is disposed between the anode and the negative electrode. 21. A method according to claim 12, further comprising a positive electrode having a positive electrode material for storing and releasing lithium ions and a negative electrode having a carbonaceous negative electrode material for storing and releasing lithium ions.
20. A secondary battery in which the porous membrane according to any one of 19 is arranged.