JP4017744B2 - Solid-type polymer electrolyte membrane and method for producing the same - Google Patents

Description

【００５６】
実施例１〜５で明らかなように、実施例1で示した平均膜厚、突刺し強度、透気度を満足したアラミド支持体をゲル電解質含浸の支持体として用いることにより、膜厚45μmと薄膜で、しかも400g以上の突刺し強度と5×10^-4S/cm以上のイオン伝導度を示し、かつ400℃以上の力学的耐熱性を有する固体型ポリマー電解質膜が種々のポリマー系および複合化方法で実現できることが分かった。
【００５７】
これに対し、アラミド支持体を併用しなかった場合は、イオン伝導度的には十分なものを得ることは可能であるが、何れの系においても数十g程度の突刺し強度しか得られず、しかも耐熱温度も100℃前後と安全性が優れたものを得ることは出来なかった(比較例1,2,5および7)。
【００５８】
また、実施例１で示した諸物性を満足するアラミド支持体を用いた場合でも、イオン伝導度の低いゲル電解質を含浸複合化させた場合は、満足するイオン伝導度を実現できないことが分かった(比較例３)。
【００５９】
また、アラミド支持体として、目付け量が低く、突刺し強度が十分でないものを用いた場合、ゲル電解質を複合化しても突刺し強度が十分に増加せず、短絡防止の面で安全性の高い固体型ポリマー電解質膜を作製するのは困難であった(比較例４)。また、アラミド支持体の目付け量を高くした場合、突刺し強度は満足できるが、支持体自身の膜厚が厚くなり、薄膜が困難となるとともに膜の透気度が低下するため、その支持体膜中にゲル電解質ドープを十分含浸できなくなった(比較例６)。
【００６０】
以上の結果が示すように、耐熱性の優れた全芳香族ポリアミドを素材として用いた特定の諸物性をしめすアラミド支持体にゲル電解質含浸複合化することにより、イオン伝導度、短絡防止強度、耐熱性の三者を兼ね備えた固体型ポリマー電解質膜を作製出来ることを見出した。
【００６１】
【発明の効果】
以上詳述してきたように本発明によれば、高いイオン伝導度と、強い短絡防止強度と、高い力学的耐熱性とを兼ね備えた、ポリマー二次電池用途に有用な安全性の優れた固体型ポリマー電解質膜を提供することが可能となった。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solid polymer electrolyte membrane having high strength and heat resistance, which is applicable to lithium and lithium ion secondary batteries and excellent in safety.
[0002]
[Prior art]
In recent years, with the development of electronic devices, it has been desired to develop a secondary battery that is small and light, has a high energy density, and has a large number of repeated charging operations. Lithium and lithium ion secondary batteries that use non-aqueous electrolytes instead of aqueous electrolytes are attracting attention as this type of battery.
[0003]
In the case of a solution-type lithium secondary battery using lithium and a lithium alloy as a negative electrode, thread-like lithium crystals (dendrites) are formed on the negative electrode due to repeated charge and discharge, causing a short circuit, etc. Development of a solid polymer electrolyte having the following characteristics is desired.
[0004]
In addition, in lithium ion secondary batteries that have been commercialized by eliminating the problem of dendrites in lithium secondary batteries, the separator itself used to prevent short-circuiting of the electrodes does not have sufficient electrolyte retention, and electrolyte leakage Therefore, it is indispensable to use a metal can as an exterior. Thereby, not only the manufacturing cost of the battery becomes high, but also the weight of the battery cannot be sufficiently reduced. Against this background, development of a highly safe polymer electrolyte that also functions as a separator is desired from the viewpoint of eliminating electrolyte leakage in lithium ion secondary batteries and reducing the weight of the battery.
[0005]
From such a background, polymer electrolyte systems that achieve both high ionic conductivity and safety have been energetically studied. One of the approaches is a so-called intrinsic polymer electrolyte approach that does not include a liquid component (solvent or plasticizer) in a polymer, and attempts to produce a solid electrolyte by using only a polymer and an electrolyte. Since this type of electrolyte does not contain liquid components, it can obtain a relatively strong membrane, but the limit of ionic conductivity is as low as 10 ^-5 S / cm, and the electrode active material layer In spite of the fact that it is not possible to achieve sufficient bonding, the present situation is that it has not yet been put into practical use even though it has been studied for a long time.
[0006]
On the other hand, the intrinsic polymer electrolyte has been studied energetically as a system to compensate for the drawbacks such as low ionic conductivity and inadequate interface bonding, and the intrinsic polymer electrolyte has a liquid component (solvent or plasticizer). So-called gel electrolyte to which is added. In the case of this system, the ionic conductivity of the gel electrolyte membrane depends on the amount of the liquid component contained, and 10 ^-3 S / cm, which is considered practically sufficient by containing a considerable amount of the liquid component. Several systems showing the above ionic conductivity have been reported. However, in most of these systems, the mechanical properties of the membrane are rapidly impaired with the addition of the liquid component, and the safety function as a separator that the solid electrolyte should originally have disappeared.
[0007]
Under such circumstances, US Pat. No. 5,296,318 describes a system in which the gel electrolyte membrane has both strength and ionic conductivity. This is a gel electrolyte membrane using a vinylidene fluoride and hexafluoropropylene copolymer as a polymer, and has attracted attention as a system exhibiting mechanical properties that should be specially characterized as a gel electrolyte. However, even in this system, the puncture strength, which is one index of the separator function for secondary batteries, is an order of magnitude lower than that of general-purpose separators, and the mechanical heat resistance temperature (melt flow temperature) of the gel electrolyte membrane is The current situation is that the safety of the lithium ion secondary battery is not necessarily guaranteed because it is slightly higher than 100 ° C. and about 50 ° C. lower than that of a normal polyolefin separator.
[0008]
Against this background, gel electrolytes that use various supports as reinforcing materials have been proposed for the purpose of supplementing the mechanical properties that are insufficient with gel electrolyte membranes. For example, Japanese Patent Application Laid-Open No. 9-22724 describes a technique in which a synthetic fiber nonwoven fabric such as polyolefin is used in combination as a support during film formation of a coating type polymer gel electrolyte. In order to impregnate a polymer solution having a high viscosity and realize high ionic conductivity, a non-woven fabric having a coarse mesh is required. However, when a polyolefin-based nonwoven fabric is used, it is difficult to reduce the film thickness because the strength of the polyolefin fiber itself is not sufficient. Further, the mechanical heat resistance of the obtained electrolyte membrane was dominated by the polyolefin non-woven fabric, and was about 160 ° C. at most.
[0009]
U.S. Pat. No. 5,603,982 describes a method in which an electrolyte solution and a monomer are impregnated into a nonwoven fabric such as polyolefin having high air permeability in a solution state, and then the monomer is polymerized to form a solid electrolyte . In this method, since the viscosity of the solution to be impregnated into the nonwoven fabric is low, the liquid can be easily impregnated. It was necessary to perform polymerization of the monomers by sandwiching them with the material. Also in this method, not only the manufacturing process is complicated, but also a polyolefin-based non-woven fabric is adopted, so that it is difficult to realize a thin film.
[0010]
Several systems using a polyolefin microporous membrane as a support instead of a nonwoven fabric have been proposed as systems capable of realizing a thinner film than a nonwoven fabric. However, unlike the above-described nonwoven fabric, it is difficult to impregnate a high-viscosity dope made of a polymer solution into a microporous film having a pore size of submicron or less, and a coating method of a polymer solution that is considered to be easy in terms of process is used. It cannot be adopted. As a technique for avoiding this problem, Japanese Patent Laid-Open No. 7-220761 discloses a technique in which a polyolefin microporous film is impregnated with a low-viscosity solution comprising an electrolytic solution and an ultraviolet curable resin, and then the resin is cured by irradiation with ultraviolet rays. Are listed. However, even if a low-viscosity solution that is easily impregnated is used, it is difficult to impregnate the hydrophobic polyolefin microporous membrane with the solution, and not only the hydrophilic treatment of the microporous membrane is necessary, but also by ultraviolet irradiation. At the time of the effect of the resin, it was necessary to sandwich it with a glass plate treated with a fluororesin from both sides of the film, and the production process was complicated. It has also been pointed out that sufficient conductivity cannot be obtained when such a microporous membrane is impregnated with a gel electrolyte (Abraham et al., J. Electrochem. Soc., 142, NO. 3, 1995). .
[0011]
[Problems to be solved by the invention]
As described above, various attempts have been made to develop a polymer electrolyte that achieves both high ionic conductivity and a safety function as a separator. However, the polymer electrolyte exhibits practically high ionic conductivity and is sufficient as a separator. At present, no practical polymer electrolyte membrane which exhibits excellent mechanical properties and has a higher heat resistance than the current polyolefin-based separator and which can be made into a thin film and excellent in safety has not yet been found.
[0012]
As a result of diligent examination in view of such circumstances, a solid polymer electrolyte membrane excellent in safety that combines practical high ionic conductivity, strong short-circuit prevention strength as a separator, and high heat resistance for short-circuit prevention As a result, the present inventors have completed the present invention. An object of the present invention is to provide a solid polymer electrolyte membrane for a lithium ion secondary battery with high safety, which has three factors of ionic conductivity, strength, and heat resistance, and a method for producing the same.
[0013]
[Means for Solving the Problems]
The present invention relates to a breathable paper-like sheet having a structure in which a synthetic pulp, which is a polymer of a wholly aromatic polyamide, is dispersed in a gap between the aramid fibers, which is a nonwoven fabric made of aramid fiber, which is a wholly aromatic polyamide polymer. It is composed of a composite of a porous thin film having a gas permeability of 10 sec / 100 cc · in ² or less and a lithium ion conductive polymer electrolyte, and the ion conductivity is 5 × 10 ⁻⁴ S / cm or more at 25 ° C. A solid polymer electrolyte membrane for a lithium ion battery having a puncture strength of 300 g or more and a mechanical heat resistant temperature of the membrane of 300 ° C. or more, and the lithium in the solid polymer electrolyte membrane for the lithium ion battery The content of the ion conductive polymer electrolyte is preferably 30 to 85% by weight, and the polymer electrolyte is a lithium ion conductive polymer electrolyte having an ion conductivity of 5 × 10 ^{−4 at} 25 ° C. S / cm or more is preferable, and it is a gel electrolyte that holds 100 parts by weight or more of a non-aqueous electrolyte solution in which a lithium salt is dissolved with respect to 100 parts by weight of the polymer resin. A PVdF copolymer comprising vinylidene chloride (PVdF) as a main component, the porous thin film having an average film thickness of 50 μm or less, a puncture strength of 200 g or more, and an air permeability of 10 sec / 100 cc · in ² The following high-strength and high-permeability porous thin film is a non-woven fabric, woven fabric, or aramid fiber composed of aramid fibers that are wholly aromatic polyamide polymers. The air-permeable paper-like sheet has a structure in which synthetic pulp, which is a polymer of wholly aromatic polyamide, is dispersed in the gaps between them, or the porous thin film with high strength and high air permeability is made of wholly aromatic polyamide Polymer weight per unit 12-30 A non-woven sheet of g / m ² is preferable, and the composite is preferably an impregnated integrated composite of a porous thin film and a polymer electrolyte.
[0014]
Such a preferable solid polymer electrolyte membrane is preferably a porous thin film having an average film thickness of 50 μm or less, a puncture strength of 200 g or more, and a high strength / high permeability of air permeability of 10 sec / 100 cc · in ² or less. It can be manufactured by impregnating a support with a gel electrolyte holding 100 parts by weight or more of a non-aqueous electrolyte solution in which a lithium salt is dissolved with respect to 100 parts by weight of a polymer resin, and combining them.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the solid type polymer electrolyte of the present invention and the production method thereof will be described.
The solid polymer electrolyte membrane of the present invention exhibits a practically high ionic conductivity of 5 × 10 ⁻⁴ S / cm or more at 25 ° C. and a puncture strength of 300 g or more sufficient for application to a battery. It is a polymer electrolyte membrane that has both practical ionic conductivity and safety, having a dynamic heat resistance temperature of 300 ° C. or higher. Here, the ionic conductivity is determined by sandwiching a solid polymer electrolyte membrane between 20 mmφ SUS electrodes and analyzing the frequency dependence of impedance in the range of 10 mm (m) Hz to 65 KHz by the AC impedance method. It is what I have requested. When this value is lower than 5 × 10 ⁻⁴ S / cm, the impedance when assembled as a battery becomes high, and the capacity during high-rate charge / discharge decreases, which is not preferable.
[0016]
The solid polymer electrolyte membrane of the present invention is also characterized by a high puncture strength of 300 g or more. The puncture strength is a physical property used for the evaluation of the separator as an index representing the short-circuit prevention strength of the separator of the current solution type lithium ion secondary battery. In the present invention, the value measured under the following conditions is The puncture strength was used.
[0017]
When the support is set on a 11.3 mmφ fixed frame, a needle with a tip radius of 0.5 mm is pushed vertically to the center of the support, the needle is pushed in at a constant speed of 50 mm / min, and a hole is opened in the support The force applied to the needle was defined as the piercing strength.
[0018]
When this value is less than 300 g, the puncture strength of this polymer electrolyte membrane is not sufficient, and when assembled as a battery, the probability of short circuit between electrodes increases, and safety when assembled as a battery (short circuit prevention characteristics) Is not secured sufficiently.
[0019]
In addition, the polymer electrolyte membrane of the present invention is characterized in that it has a mechanical heat resistance of 300 ° C. or higher. Here, the dynamic heat-resistant temperature means a value measured under the following conditions.
[0020]
A 1 g load was applied to a strip-shaped polymer electrolyte membrane with a thickness of about 45 μm, a width of 5 mm, and a length of 25 mm, and the temperature was raised at a rate of 10 ° C./min to perform thermomechanical property analysis (TMA). The temperature at which the film breaks or the film stretches by 10% was defined as the dynamic heat resistant temperature.
[0021]
If this temperature is less than 300 ° C., a short circuit between the electrodes cannot be sufficiently prevented when the internal temperature of the battery suddenly rises due to an abnormal reaction of the battery or the like, which is not preferable for safety.
[0022]
The solid polymer electrolyte membrane of the present invention can be produced by combining a porous support thin film characterized by strength and heat resistance and a polymer electrolyte having practically sufficient ionic conductivity. In this case, the content of the polymer electrolyte in the solid polymer electrolyte membrane is preferably in the range of 30 to 85% by weight. When the content of the polymer electrolyte is less than 30% by weight, it is not preferable because sufficient ionic conductivity cannot be obtained when it is combined with the porous support. On the other hand, when the content exceeds 85% by weight, the strength of the composite membrane decreases, or the thickness of the polymer electrolyte membrane increases, which is not preferable.
[0023]
Next, the polymer electrolyte to be impregnated and composited with the porous support of the present invention will be described. As the polymer electrolyte used in the present invention, a lithium ion conductive polymer electrolyte having an ion conductivity of 5 × 10 ⁻⁴ S / cm or more at 25 ° C. is used. When the conductivity of the polymer electrolyte is lower than this, a practically sufficient ionic conductivity of 5 × 10 ⁻⁴ S / cm or more is not secured when impregnated into the support, which is not preferable.
[0024]
As the type of polymer electrolyte, either an intrinsic polymer electrolyte that does not contain a liquid component or a gel electrolyte that contains a liquid component can be used. However, in consideration of ionic conductivity, a gel electrolyte is more preferable. Adopted. Polymer resins for gel electrolytes include polyethylene oxide (PEO), copolymers of PEO and polypropylene oxide (PPO), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), copolymers of PAN and PMMA, acrylonitrile Copolymer of styrene and styrene (NSR), polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), other sugar polymers such as pullulan, and (meth) acrylate polymer having ethylene oxide skeleton -Although a copolymer etc. can be mentioned, it is not limited to this. However, a polymer of a type that can be directly impregnated and applied to the aramid support from a polymer in a fluid (solution) state is more preferably used because of the ease of the film forming process.
[0025]
In particular, as a preferred polymer resin for gel electrolyte, there can be mentioned a PVdF copolymer mainly composed of PVdF which can be impregnated and has excellent oxidation resistance. Suitable copolymerization components include hexafluoropropylene (HFP), perfluoromethyl vinyl ether (FMVE), chlorotrifluoroethylene (CTFE), vinyl fluoride and tetrafluoroethylene (TFE). A polymer component and an original copolymer or VdF copolymer are suitable as the polymer material of the present invention. A suitable copolymerization ratio of these copolymerization components is in the range of 3 to 10 mol%.
[0026]
As the electrolytic solution impregnated in the polymer resin for gel electrolyte, a nonaqueous solvent (plasticizer) in which a lithium salt is dissolved is preferably used. At that time, the amount of the electrolytic solution impregnated in the polymer resin is required to be 100 parts by weight or more with respect to 100 parts by weight of the polymer. When the amount of the electrolytic solution is less than this, it is not preferable because sufficient ion conductivity cannot be secured when it is combined with the porous support.
[0027]
As the non-aqueous solvent (plasticizer) used, propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), dimethyl carbonate (DMC), which are generally used for lithium and lithium ion secondary batteries, List diethyl carbonate (DEC), methyl ethyl carbonate (MEC), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), γ-butyrolactone (γ-BL), sulfolane, acetonitrile, etc. I can do it. The non-aqueous solvent may be used alone or in combination of two or more. In particular, at least one liquid selected from PC, EC, γ-BL, DMC, DEC, MEC and DME is preferably used.
[0028]
Suitable lithium salts that dissolve in this non-aqueous solvent include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium borotetrafluoride (LiBF ₄ ), lithium arsenic hexafluoride ( LiAsF ₆ ), lithium trifluorosulfonate (CF ₃ SO ₃ Li), lithium perfluoromethylsulfonylimide [LiN (CF ₃ SO ₂ ) ₂ ] and lithium perfluoroethylsulfonylimide [LiN (C ₂ F ₅ SO ₂ ) ₂ ] and the like, but are not limited thereto. The concentration of the lithium salt to be dissolved is preferably in the range of 0.2 to 2M.
[0029]
Next, the porous support thin film used in the present invention will be described. As the porous support thin film of the present invention, a high strength / high air permeability thin film having an average film thickness of 50 μm or less, a piercing strength of 200 g or more and an air permeability of 10 sec / 100 cc · in ² or less is suitable. Used for. If the average film thickness is 50 μm or more, it becomes easy to obtain a high-strength support, but the film thickness of the resulting polymer electrolyte composite film is increased, which preferably reduces the volume energy density when assembled as a battery. Absent.
[0030]
As the puncture strength of the support of the present invention, a stab strength of 200 g or more is preferably used. When a support with a value lower than 200 g is used, it becomes difficult to achieve a puncture strength of 300 g or more even after impregnation with a polymer electrolyte, and safety when assembled as a battery (prevention of short circuit) (Characteristic) is not sufficient, which is not preferable.
[0031]
The air permeability of the support of the present invention is a value measured by the Gurley method (the time required for 100 cc of air to permeate an area of 1 in ² at a pressure of 2.3 cmHg). As the porous support thin film of the present invention, a support having a high air permeability of 10 sec / 100 cc · in ² or less is preferably used. When this value is greater than 10 sec / 100 cc · in ^{2 and} a low air permeability support is used, it becomes difficult to impregnate and combine the polymer electrolyte by a coating method from a polymer solution considered to be the most advantageous industrially. In addition, it is difficult to sufficiently increase the ionic conductivity of the composite polymer electrolyte, which is not preferable.
[0032]
As the material for the high-strength and high-permeability porous thin film support of the present invention, a wholly aromatic polyamide is used from the viewpoint of strength and heat resistance. As the shape of the support, there is a breathability in which a non-woven fabric or a woven fabric made of an aramid fiber which is a polymer of a wholly aromatic polyamide, or a synthetic pulp which is a polymer of a wholly aromatic polyamide is dispersed in the gap between the aramid fibers. Examples thereof include a paper-like sheet or a breathable film having a large number of holes made of an aramid resin which is a polymer of wholly aromatic polyamide. Any of these shapes can be used in the present invention as long as the necessary characteristics as the support are satisfied. However, in consideration of the air permeability, a nonwoven sheet is most preferable. Used for. As the basis weight, a range of 12 to 30 g / m ² is preferably used. If the basis weight is less than 12 g / m ^2, but the is easy to obtain a high air permeability support, piercing it becomes difficult to obtain more than 200g as strength, excellent results in short circuit prevention strength It becomes impossible to obtain a solid electrolyte membrane. On the other hand, when the basis weight is more than 30 g / m ² , it is easy to satisfy the puncture strength, but it becomes difficult to obtain a support having an average film thickness of 50 μm or less. In addition, forcibly increasing the density and reducing the thickness make it difficult to obtain a composite membrane having high ionic conductivity due to a decrease in air permeability.
[0033]
The molecular structure of the wholly aromatic polyamide polymer can be used in the present invention regardless of whether it is meta or para. Here, the meta type is typically a wholly aromatic polyamide whose main constituent unit is m-phenylene isophthalamide, and the para type is a wholly aromatic unit whose main constituent unit is p-phenylene terephthalamide. A typical example is polyamide.
[0034]
Next, the manufacturing method of the solid type polymer electrolyte membrane of this invention is demonstrated. The solid polymer electrolyte membrane of the present invention is a porous thin film having an average film thickness of 50 μm or less, a puncture strength of 200 g or more, and an air permeability of 10 sec / 100 cc · in ² or less. The support is produced by impregnating a gel electrolyte holding 100 parts by weight or more of a non-aqueous electrolyte solution in which a lithium salt is dissolved with respect to 100 parts by weight of a polymer resin. At this time, the method of impregnating and complexing the gel electrolyte is not particularly limited, but a method of impregnating and applying a polymer in a fluid (solution) state that is easy for industrial production directly onto the porous thin film support is more preferable. It is. Examples of such a method include the following method.
[0035]
(1) A method in which a polymer resin for gel electrolyte and an electrolytic solution are mixed and dissolved by heating, and the dope in the solution state is directly applied to and impregnated into a porous thin film support, and then cooled and solidified to form a composite.
[0036]
(2) A polymer resin for gel electrolyte, an electrolytic solution and a volatile solvent for dissolving the polymer are mixed and dissolved, and the dope in the solution state is directly applied to and impregnated into the porous thin film support, and then the volatile solvent. A method of compounding by removing by drying.
[0037]
(3) A polymer resin for gel electrolyte, a solvent in which the polymer is dissolved and compatible with water, and a phase separation agent (gelling agent or pore opening agent) are mixed and dissolved, and the dope in the solution state is supported by the porous thin film. Directly coat and impregnate the body, then immerse the membrane in a water-based coagulation bath to coagulate the polymer, then immerse the composite membrane that has been washed and dried in the electrolyte, and gel the polymer resin to form a composite membrane Method.
[0038]
【Example】
Hereinafter, the contents of the present invention will be described in detail using examples.
[0039]
[Example 1]
<Aramid support>
A non-crystallized m-aramid long fiber having a thickness of 3 de was added as a binder to a crystallized m-aramid short fiber having a thickness of 1.25 de, and a calender roll was formed by a dry papermaking method with a basis weight of 19 g / m ^2. A non-woven sheet was obtained. The characteristics of the obtained support were as follows. Average film thickness 36μm, density 0.53g / cm ³ , porosity 62%, air permeability 0.04sec / 100cc · in ² , puncture strength 330g.
[0040]
<Combination of gel electrolyte>
As a polymer resin for the gel electrolyte, a PVdF copolymer obtained by copolymerizing 5 mol% of hexafluoropropylene (HFP) with PVdF was used. To 100 parts by weight of this polymer, 300 parts by weight of a PC / EC (1/1 weight ratio) electrolyte solution in which 1M LiBF ₄ is dissolved is added, and tetrahydrofuran (THF) is further added as a solvent to mix and dissolve the polymer. A dope having a concentration of 12% by weight was prepared. The obtained aramid support was impregnated and coated with the obtained dope, and THF was dried and removed at 50 ° C. to produce a solid polymer electrolyte membrane.
[0041]
[Comparative Example 1]
Without using an aramid support, the gel electrolyte dope used in Example 1 was coated on a release film coated with silicon to produce a single membrane made of a gel electrolyte.
[0042]
[Comparative Example 2]
In Comparative Example 1, film formation was performed in the same manner as in Comparative Example 1 except that the amount of electrolyte added was 100 parts by weight with respect to 100 parts by weight of the polymer resin for gel electrolyte. Produced.
[0043]
[Comparative Example 3]
In Example 1, a solid type compounded with an aramid support in the same manner as in Example 1 except that the amount of electrolyte added was changed to 80 parts by weight with respect to 100 parts by weight of the polymer resin for gel electrolyte. A polymer electrolyte was prepared.
[0044]
[Comparative Example 4]
In Example 1, an aramid support was produced by the dry papermaking method in the same manner as in Example 1 except that the basis weight at the time of forming the aramid support was 10 g / m ² . Various characteristics of the obtained support were as follows. Average film thickness 20μm, density 0.51g / cm ³ , porosity 63%, air permeability 0.01sec / 100cc · in ² , puncture strength 85g.
[0045]
Using this support, a composite membrane with a gel electrolyte was produced in the same manner as in Example 1.
[0046]
[Example 2]
In Example 1, a polymer obtained by copolymerizing 8.7 mol% of HFP with respect to PVdF was used as the polymer resin for the gel electrolyte, and the amount of the electrolyte added to 100 parts by weight of the polymer resin was changed to 250 parts by weight. Film formation was performed in the same manner as above to prepare a composite solid polymer electrolyte with an aramid support.
[0047]
[Comparative Example 5]
In Example 2, a single membrane made of a gel electrolyte was produced using the same method as in Comparative Example 1 without using an aramid support.
[0048]
[Comparative Example 6]
As the aramid support, crystallized m-aramid short fibers having a thickness of 1.25 de and m-aramid fibrite (synthetic pulp-like particles) are blended at a ratio of 7/3 (weight ratio) to prepare a dilute aqueous slurry. A wet paper was made with a basis weight of 37 g / m ² . The obtained wet paper was placed on a calendar roll to obtain a paper-like sheet. Various physical properties of the obtained support were as follows. Average film thickness 58μm, density 0.62g / cm ³ , porosity 51%, air permeability 29sec / 100cc · in ² , puncture strength 630g.
[0049]
When this aramid support was impregnated with the polymer dope for the gel electrolyte of Example 2, the polymer could not be sufficiently impregnated into the aramid support, and a good composite electrolyte membrane could not be produced.
[0050]
[Example 3]
Using polyacrylonitrile (PAN) as a polymer resin for gel electrolyte, 12 parts by weight of PAN, 55 parts by weight of EC, 27 parts by weight of PC, and 8 parts by weight of LiBF ₄ were quickly mixed and dissolved at 120 ° C. to prepare a dope for coating. . The obtained dope was impregnated and coated on the aramid support of Example 1 at 120 ° C., then cooled to room temperature to gel the dope, and a composite solid polymer electrolyte with the aramid support was produced.
[0051]
[Comparative Example 7]
In Example 3, a PAN gel electrolyte single membrane was prepared without using an aramid support.
[0052]
[Example 4]
As a polymer resin for the gel electrolyte, a PVdF copolymer obtained by copolymerizing 5.3 mol% of perfluorovinyl ether (FMVE) with PVdF is used. With respect to 72 parts by weight of this polymer resin, 262 parts by weight of dimethylacetamide (DMAc) and an average molecular weight are used. 66 parts by weight of 400 polyethylene glycol was added and mixed by heating at 60 ° C. to prepare a dope for coating. The obtained dope was impregnated and coated on the aramid support of Example 1, and the membrane was immersed in a 50% aqueous solution of DMAc to coagulate the membrane. Subsequently, the membrane was washed with water and dried to prepare a dry composite membrane comprising an aramid support / PVdF copolymer. Next, the obtained dry composite membrane was immersed in PC / EC (1/1 weight ratio) in which 1M LiBF ₄ was dissolved, and impregnated with an electrolytic solution to obtain a composite solid type polymer electrolyte.
[0053]
[Example 5]
As a polymer resin for the gel electrolyte, a PVdF copolymer obtained by copolymerizing 9.0 mol% of FMVE with PVdF was used, and a composite solid polymer electrolyte was prepared in the same manner as in Example 4.
[0054]
Table 1 shows the measurement results for the electrolyte membranes of the above Examples and Comparative Examples. In Table 1, the amount of impregnation represents the amount of impregnation of the electrolytic solution with respect to the weight of the solid polymer electrolyte membrane.
[0055]
[Table 1]

[0056]
As apparent from Examples 1 to 5, by using an aramid support that satisfies the average film thickness, puncture strength, and air permeability shown in Example 1 as a support for gel electrolyte impregnation, a film thickness of 45 μm was obtained. Solid polymer electrolyte membranes with thin film, puncture strength of 400g or more, ionic conductivity of 5 × 10 ^-4 S / cm or more, and mechanical heat resistance of 400 ° C or more are various polymer systems and composites. It was found that it can be realized by the conversion method.
[0057]
On the other hand, when an aramid support is not used in combination, it is possible to obtain a sufficient ionic conductivity, but only about several tens of grams of puncture strength can be obtained in any system. Moreover, it was impossible to obtain a heat-resistant temperature of around 100 ° C. and excellent safety (Comparative Examples 1, 2, 5, and 7).
[0058]
In addition, even when an aramid support that satisfies the various physical properties shown in Example 1 was used, it was found that satisfactory ionic conductivity could not be realized when a gel electrolyte having low ionic conductivity was impregnated. (Comparative Example 3).
[0059]
In addition, when an aramid support with a low basis weight and insufficient puncture strength is used, the puncture strength does not increase sufficiently even if the gel electrolyte is combined, and it is highly safe in terms of preventing short circuits. It was difficult to produce a solid type polymer electrolyte membrane (Comparative Example 4). Also, when the basis weight of the aramid support is increased, the piercing strength is satisfactory, but the support itself becomes thicker, making it difficult to form a thin film and lowering the air permeability of the film. The film could not be sufficiently impregnated with the gel electrolyte dope (Comparative Example 6).
[0060]
As shown in the above results, ionic conductivity, short-circuit prevention strength, heat resistance can be obtained by compounding the gel with an aramid support that exhibits specific physical properties using a wholly aromatic polyamide with excellent heat resistance as a material. It has been found that a solid polymer electrolyte membrane having three properties can be produced.
[0061]
【The invention's effect】
As described above in detail, according to the present invention, the solid type having high ionic conductivity, strong short-circuit prevention strength, and high mechanical heat resistance, which is useful for polymer secondary battery applications and excellent in safety. It has become possible to provide a polymer electrolyte membrane.

Claims (9)

A non-woven fabric made of aramid fibers that are wholly aromatic polyamide polymers, a woven fabric, or a breathable paper-like sheet having a structure in which synthetic pulp that is a polymer of wholly aromatic polyamides is dispersed in the gaps between the aramid fibers, and It consists of a composite of a porous thin film with an air permeability of 10 sec / 100 cc · in ² or less and a lithium ion conductive polymer electrolyte, and has an ionic conductivity of 5 × 10 ⁻⁴ S / cm or more at 25 ° C. A solid polymer electrolyte membrane for a lithium ion battery having a strength of 300 g or more and a mechanical heat resistant temperature of the membrane of 300 ° C. or more.   2. The solid polymer electrolyte membrane for a lithium ion battery according to claim 1, wherein the content of the lithium ion conductive polymer electrolyte in the solid polymer electrolyte membrane is 30 to 85% by weight. 3. The solid type polymer electrolyte membrane for lithium ion batteries according to claim 1, wherein the ion conductivity of the lithium ion conductive polymer electrolyte is 5 × 10 ⁻⁴ S / cm or more at 25 ° C.   4. The lithium ion conductive polymer electrolyte is a gel electrolyte that holds 100 parts by weight or more of a non-aqueous electrolyte in which a lithium salt is dissolved with respect to 100 parts by weight of a polymer resin. Solid-type polymer electrolyte membrane for lithium ion batteries.   5. The solid type polymer electrolyte membrane for a lithium ion battery according to claim 4, wherein the polymer resin is a PVdF copolymer mainly composed of polyvinylidene fluoride (PVdF). The porous thin film has an average film thickness 50 μ m Below, the piercing strength is 200g And the air permeability is 10sec / 100cc ・ in ² 6. The solid polymer electrolyte membrane for a lithium ion battery according to claim 1, which is a porous thin film having the following high strength and high air permeability. The high-strength and high-permeability porous thin film has a basis weight. 12 ~ 30g / m ² A solid polymer electrolyte membrane for a lithium ion battery according to claim 6, which is a non-woven fabric sheet. The solid polymer electrolyte membrane for a lithium ion battery according to any one of claims 1 to 7, wherein the composite is an impregnated integrated composite of a porous thin film and a lithium ion conductive polymer electrolyte. Average film thickness 50 The puncture strength is less than μm 200g And the air permeability is 10sec / 100cc ・ in ² Polymer resin is applied to the following high-strength and high-permeability porous thin films 100 Non-aqueous electrolyte with lithium salt dissolved in parts by weight 100 A method for producing a solid polymer electrolyte membrane for a lithium ion battery, comprising impregnating a gel electrolyte retained in an amount of at least parts by weight.