JP3927645B2 - Immobilized liquid film conductor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an immobilized liquid film conductor and a method for producing the same, and more particularly to an immobilized liquid film conductor obtained by immobilizing an ionic conductor on a porous conductive film having high electronic conductivity and a method for producing the same.
[0002]
[Prior art]
There are a wide range of conductors made of polymer materials such as polyethylene, polypropylene, polyvinyl chloride, polysulfone, butadiene rubber, silicone rubber, ethylene-propylene-diene terpolymer, epoxy resin, etc. and an electronic conductive material such as carbon black. Are known. These conductors are used for antistatic materials, electromagnetic shielding materials, conductive paints, adhesives, IC packaging materials, planar heating elements, surface switches, and the like.
[0003]
Further, in such a conductor, a porous thin film conductor (porous conductive film) that is porous but highly conductive is used extremely effectively as an electrode or an electrode constituent material in a device using a solid polymer electrolyte or a liquid electrolyte. be able to. That is, the contact interface between the electrode and the electrolyte can be enlarged because of the porous structure, and thus, for example, a high-performance battery such as a lithium-based primary battery or a lithium-based secondary battery is manufactured using the interface. It becomes possible.
[0004]
As an example of the development of the thin film conductor, Ketjen Black (trademark of Akzo Chemical) is mixed with a plasticizer solution of polyethylene, and after forming and stretching the sheet, the electrolyte is applied to the porous thin film from which the plasticizer is removed. There is a porous conductive film immobilized using capillary condensing force and a method for producing the same (Japanese Patent Laid-Open No. 3-87096). However, there is a problem with electrolyte retention. On the other hand, recently, a polymer gel impregnated with a carbonate-based solution in which a lithium salt is dissolved by mixing LiMn ₂ O ₄ and carbon black or petroleum coke and carbon black into a copolymer of polyvinylidene fluoride and hexafluoropropylene is used as a battery. Although a technique (USP 5,296,318) used for a positive electrode or a negative electrode is proposed, there is a problem of electrolyte oozing due to gel contraction at a high temperature, which is not a complete solution for electrolyte retention. Therefore, it is desired to develop a thin film conductor that can be easily formed into a thin film and have a large area and has a stable holding ability of an electrolyte solution in a wide temperature range.
[0005]
[Problems to be solved by the invention]
The object of the present invention is to eliminate the above-mentioned problems, to easily reduce the film thickness and increase the area, to have excellent aprotic electrolyte solution retention in a wide temperature range, and to improve long-term stability and mechanical strength. It is to provide an immobilized liquid film conductor and a manufacturing method thereof.
[0006]
[Means for Solving the Problems]
As a result of intensive studies to overcome the problems of the prior art, the present inventors have a functional group having an affinity for an electrolyte solution solvent used for a terminal chain in a polyolefin microporous film containing an electronic conductive material. It has been found that the above object can be achieved by immobilizing the aprotic electrolyte on the membrane by impregnating the polyolefin microporous membrane containing the polymer with the electrolyte solution.
[0007]
[Means for Solving the Problems]
That is, the immobilized liquid membrane conductor of the present invention fixes an aprotic electrolyte solution to a polyolefin microporous membrane composed of a polyolefin composition containing terminal-modified polypropylene , a different polyolefin, and an electronic conductive material. It is a fixed liquid film conductor.
Further, the method of producing immobilized liquid film conductivity of the present invention, a terminal-modified polypropylene, a polyolefin which is different from this, a polyolefin composition containing an electron-conductive material polyolefin microporous membrane in aprotic electrolyte The surface of a polyolefin microporous thin film containing a solution impregnated and immobilized , or an electronically conductive material is coated with terminal-modified polypropylene, and the surface-coated polyolefin microporous membrane is impregnated with an aprotic electrolyte solution, It is to be fixed .
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The immobilized liquid membrane conductor of the present invention comprises a terminal-modified polymer having a functional group having an affinity for the electrolyte solvent used in the polyolefin microporous membrane containing an electronic conductive material as a main skeleton. An electrolyte solution in which an electrolyte is dissolved in a solvent is filled in the pores of the microporous membrane, and the microporous membrane is stably held. Hereinafter, the present invention will be described in detail.
[0009]
1. Polyolefin microporous membrane containing an electronically conductive material and terminal-modified polypropylene and a different polyolefin a. Polyolefin Examples of polyolefin include polyethylene, polypropylene, ethylene-propylene copolymer, polybutene-1, and poly-4-methylpentene-1. Among these, polyethylene is preferable. As this polyethylene, those made of ultra high molecular weight polyethylene, high density polyethylene, and medium to low density polyethylene can be used, but those containing ultra high molecular weight polyethylene or components thereof from the viewpoint of strength, safety, film forming property, etc. Is preferably used. Further, the polyolefin contains 1% by weight or more of an ultrahigh molecular weight component having a weight average molecular weight of 5 × 10 ⁵ or more, preferably 1 × 10 ⁶ to 1 × 10 ⁷ , and has a molecular weight distribution (weight average molecular weight / number average molecular weight). ) Is preferably 10 to 300. When the content of the ultrahigh molecular weight polyolefin component is less than 1% by weight, the portion contributing to the improvement of the stretchability of the film is insufficient. On the other hand, the upper limit is not particularly limited. On the other hand, if the molecular weight distribution exceeds 300, breakage due to a low molecular weight component occurs and the strength of the entire film decreases, which is not preferable.
[0010]
b. Electronic Conductive Material Examples of the electronic conductive material include various metals and semiconductors, oxide-based and sulfide-based electronic conductive materials, and carbon or graphite. These may have any shape such as a particulate shape, a fibrous shape, a fibril shape, and a whisker shape. Particularly preferred are battery positive electrode active materials such as TiS ₃ , TiS ₂ , TiO ₂ , V ₂ O ₅ , NbSe ₃ , MnO ₂ , LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , PbO ₂ , NiOOH, petroleum coke, There are battery negative electrode active materials such as natural graphite, carbon fiber, Pb, and Cd, and conductive agents such as acetylene black, ketjen black (trademark of Akzo Chemical), carbon whisker, graphite whisker, and graphite fibril.
The blending amount of the electronic conductive material is preferably 1 to 200% by weight, particularly 5 to 100% by weight, based on the polyolefin used. When the blending amount is less than 1% by weight, it is difficult to obtain sufficient conductivity, and when it exceeds 200% by weight, it becomes difficult to obtain a practically sufficient film.
[0011]
c. End-modified polypropylene End-modified polypropylene is a polypropylene having a functional group structure at the end. Here, the polypropylene is not limited to a propylene homopolymer, but one or more of propylene and another α-olefin (for example, ethylene, 1-butene, 1-hexene, 4-methyl-1-pentene, etc.). Of the block copolymer rubber.
[0012]
Polypropylene having a functional group structure at the terminal can be produced as follows.
That is, it is produced by reacting a living polypropylene obtained by living polymerization of propylene with a functional group-containing monomer in the presence of a catalyst composed of a specific vanadium compound and an organoaluminum compound.
As the vanadium compound, V (acetylacetonato) ₃ , V (2-methyl-1,3-butanedionato) ₃ , and V (1,3-butanedionato) ₃ are preferable. The organoaluminum compound is an organoaluminum compound having 1 to 18 carbon atoms, preferably 2 to 6 carbon atoms, or a mixture or complex thereof, such as dialkylaluminum monohalide, monoalkylaluminum dihalide, alkylaluminum sesquioxide. Halide etc. are mentioned.
[0013]
The polymerization reaction is preferably performed in a solvent that is inert to the polymerization reaction and that is liquid during polymerization. Such solvents include saturated aliphatic hydrocarbons, saturated alicyclic hydrocarbons, and aromatic hydrocarbons.
The amount of the polymerization catalyst used for the polymerization of propylene is 1 × 10 ^{−4 to} 0.1 mol, preferably 5 × 10 ^{−4 to} 5 × 10 ⁻² mol of vanadium compound per mol of propylene, and 1 organoaluminum compound. × 10 ^{−4 to} 0.5 mol, preferably 1 × 10 ^{−3 to} 0.1 mol. In addition, it is desirable that 4 to 100 moles of the organoaluminum compound is used per mole of the vanadium compound.
[0014]
Living polymerization is normally performed at −100 ° C. to 100 ° C. for 0.5 to 50 hours. The molecular weight of the resulting living polypropylene can be adjusted by changing the reaction temperature and reaction time. By setting the polymerization temperature to a low temperature, particularly −30 ° C. or less, a polymer having a molecular weight distribution close to monodispersion can be obtained. At −50 ° C. or lower, a living polymer having Mw (weight average molecular weight) / Mn (number average molecular weight) of 1.05 to 1.40 can be obtained.
As described above, living polypropylene having a number average molecular weight of about 800 to 400,000 and close to monodispersion can be produced.
[0015]
Next, in order to introduce a functional group structure at the terminal, living polypropylene is reacted with a functional group-containing monomer. As the monomer to be introduced, acrylic acid, methacrylic acid, acrylic acid ester, methacrylic acid ester, acrylamide, acrylonitrile, styrene and derivatives thereof are used. Specifically, for example, acrylic acid esters include methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, stearyl acrylate, ethyl decyl acrylate, ethyl hexadecyl acrylate, 2 -Acrylic monomers such as ethoxyethyl acrylate, tetrahydrofurfuryl acrylate, trimethylolpropane triacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 1,4 butanediol diacrylate, 1,6-hexanediol diacrylate Examples of methacrylic acid esters include methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, Tridecyl acrylic acid, methacrylic acid stearyl, cyclohexyl methacrylate, benzyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, glycidyl methacrylate, methacrylic monomers such as ethylene glycol dimethacrylate. One or more of these types can be selected and used. Moreover, crosslinkable monomers, such as vinyl acrylate, vinyl methacrylate, divinylbenzene, vinyl butyl acrylate, can also be used as needed.
Among the above-mentioned monomers, it is preferable to use a monomer composed of acrylic acid, methacrylic acid or an ester thereof, or an acrylic monomer composed of acrylamide or a derivative thereof.
[0016]
In the present invention, the blending amount of a single monomer or a plurality of monomers forming a living polymer is adjusted according to the solvent of the electrolytic solution. By doing so, it is effectively swollen and gelled in the electrolytic solution and can be firmly fixed. Here, the porous thin film containing the terminal-modified living polymer selectively takes in the electrolyte solvent having affinity for the living polymerization functional group covering the surface and the pore surface, but the main skeleton is solvent resistant. Since it is made of polyethylene having excellent properties, its swelling is moderately suppressed as a whole, and large deformation and strength reduction can be prevented.
[0017]
In the reaction between the living polypropylene and the functional group-containing monomer, the monomer is supplied to the reaction system in which the living polypropylene is present and reacted. The reaction is usually performed at a temperature of −100 ° C. to 150 ° C. for 5 minutes to 50 hours. By increasing the reaction temperature or lengthening the reaction time, the degree of modification of the polypropylene terminal by the monomer unit can be increased. Usually, 1 to 1,000 mol of monomer is used per 1 mol of living polypropylene.
[0018]
The terminal-modified polypropylene obtained as described above has a number average molecular weight (Mn) of about 800 to 500,000, and a very narrow molecular weight distribution (Mw / Mn = 1. 05 to 1.40). Moreover, it has an average terminal structure of 0.1 to 500, preferably 0.5 to 100, of the monomer at its terminal. One feature of the terminal-modified polypropylene produced in this way is that the syndiotactic dyad fraction is 0.6 or more.
The amount of the terminal-modified living polymerized polypropylene used is 1 to 50% by weight, preferably 3 to 30% by weight of the polyolefin. If it is less than 1% by weight, the effect of impregnation and immobilization of the electrolytic solution with the solvent cannot be expected. On the other hand, when it exceeds 50% by weight, the mechanical strength is remarkably lowered.
[0019]
d. Production method As a method for producing a polyolefin microporous film containing an electronically conductive material and terminal-modified polypropylene and a polyolefin different from this , (1) the above-mentioned electronically-conductive material and the above-mentioned terminal-modified polypropylene are blended with polyolefin. There are a method for producing a microporous film from the composition, and (2) a method for producing a microporous film from a composition obtained by blending the above-mentioned electronic conductive material into polyolefin and coating the surface with terminal-modified polypropylene.
[0020]
A method for producing a microporous film from a composition in which the above electronically conductive material and the above-mentioned terminal-modified polypropylene are blended with the polyolefin of (1) is described in JP-A-60-242035 and JP-A-3-64334. It can be done by the method. For example, it can be performed as follows. A composition in which terminal-modified polypropylene is blended with polyolefin containing ultra-high molecular weight polyolefin is heated and dissolved in a solvent such as liquid paraffin in an amount of 10 to 50% by weight to obtain a uniform solution, and an electronically conductive material is uniformly blended therein. To do. A sheet is formed from this solution and cooled to form a gel-like sheet, and then heated at a temperature of the melting point of polyolefin + 10 ° C. or less and stretched to a surface magnification of 3 times or more. For example, the solvent contained in the stretched film may be extracted and removed with a volatile solvent such as methylene chloride, followed by drying and heat setting.
[0021]
(2) A method of producing a microporous film from a composition in which an electronic conductive material is blended with polyolefin and coating the surface with terminal-modified polypropylene is carried out according to the method described in the above patent. 10 to 50% by weight is heated and dissolved in a solvent such as liquid paraffin to make a uniform solution, and an electronic conductive material is uniformly mixed therein. A sheet is formed from this solution and cooled to form a gel-like sheet, and then heated at a temperature of the melting point of polyolefin + 10 ° C. or less and stretched to a surface magnification of 3 times or more. The solvent contained in the stretched film is removed by extraction with a volatile solvent such as methylene chloride, then dried and heat set. By coating the surface of the obtained polyolefin microporous membrane with a solution in which terminal-modified polypropylene is dissolved in a solvent such as aromatic hydrocarbon, paraffin hydrocarbon, chloroform, tetrahydrofuran, etc. by impregnation, coating, spraying, etc. is there.
[0022]
In addition, various additives such as an antioxidant, an ultraviolet absorber, a lubricant, an anti-blocking agent, a pigment, a dye, and an inorganic filler are added to the polyolefin microporous film as necessary, so long as the object of the present invention is not impaired. Can be added.
[0023]
e. Physical Properties A polyolefin microporous film containing an electronically conductive material, terminal-modified polypropylene , and a different polyolefin has a film thickness of 1-1000 μm, preferably 5-500 μm. If the thickness is less than 1 μm, it is difficult to put it to practical use from the viewpoint of mechanical strength and handling. On the other hand, when it exceeds 1000 μm, the effective resistance increases, and the volume efficiency as a conductor is disadvantageous. The porosity of the film is not limited, but is in the range of 30 to 95%, more preferably 50 to 90%. If the porosity is less than 30%, immobilization of the aprotic electrolyte solution may be insufficient. On the other hand, if the porosity exceeds 95%, the mechanical strength of the membrane is reduced and the practicality is inferior. . The average pore diameter is preferably 1 μm or less. Furthermore, the polyolefin microporous film containing the above-described electronic conductive material preferably has a breaking strength of 200 kg / cm ² or more. By setting the breaking strength to 200 kg / cm ² or more, the deformation resistance against swelling when the aprotic electrolyte solution is dissolved is sufficient.
[0024]
2. Immobilization of an aprotic electrolyte solution in a polyolefin microporous membrane containing an electronically conductive material, terminal-modified polypropylene , and a different polyolefin a. Electrolyte solution As the electrolyte of the aprotic electrolyte solution, an alkali metal salt or an alkaline earth metal salt is used. For example, LiF, NaI, LiI, LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , NaSCN Etc. In addition, the aprotic solvent for dissolving the electrolyte of the aprotic electrolyte solution is a solvent that is stable against alkali metals, specifically, propylene carbonate, ethylene carbonate, γ-butyrolactone, dimethoxyethane, acetonitrile, form Aprotic high dielectric constant solvents such as amide, tetrahydrofuran and diethyl ether are used alone or in combination of two or more.
[0025]
b. Immobilization method As a method of immobilizing an aprotic electrolyte solution to a polyolefin microporous membrane containing an electronically conductive material and terminal-modified polypropylene and a different polyolefin, an aprotic electrolyte thin film can be impregnated, coated or coated. A spray etc. can be used individually or in combination. In addition, the electrolyte solution may be fixed before being incorporated in the battery, in the middle of the battery assembly process, or in the final battery assembly process. Above all, from the viewpoints of handling during battery assembly, prevention of fouling, adhesion to positive and negative electrode plate surfaces, and the conventional battery assembly process can be applied as it is, the electrolyte can be used during the battery assembly process or the final battery assembly process. A method of immobilizing the solution is preferred.
[0026]
c. Specific conductivity of immobilized liquid film conductor The immobilized liquid film conductor of the present invention constituted as described above has a specific conductivity of 10 ⁻⁵ Scm ⁻¹ or more, preferably 10 ⁻³ Scm ⁻¹ or more. When the specific conductivity is less than 10 ⁻⁵ Scm ⁻¹ , the effective resistance increases and is not practical. For example, the effective resistance when the film thickness is 1 μm is 1 μm / 10 ⁻⁵ Scm ⁻¹ , that is, 10 Ωcm ² .
[0027]
【Example】
The invention is illustrated in more detail by the following specific examples.
Example 1
5 parts by weight of ultrahigh molecular weight polyethylene (weight average molecular weight 2 × 10 ⁶ ), 20 parts by weight of high density polyethylene (weight average molecular weight 4 × 10 ⁵ ), living polymerized polypropylene each having a methyl acrylate group at the molecular end (weight average molecular weight 5) × 10 ⁴ ) 0.37 parts by weight of antioxidant was added to 100 parts by weight of a mixture containing 5 parts by weight, 30 parts by weight of petroleum coke powder, 3 parts by weight of ketjen black powder (trademark of Akzo Chemical) and 70 parts by weight of liquid paraffin. In addition, the mixture was heated and kneaded with a twin screw extruder. This was extruded from a die having a rectangular base, and was taken up with a chill roll to obtain a 1 mm thick sheet. This sheet was simultaneously biaxially stretched 5 × 5 times at 120 ° C. using a batch type biaxial stretching machine, and the remaining liquid paraffin was washed with n-hexane and then dried at 120 ° C. while fixed to a metal frame. Heat setting was performed to obtain a polyethylene microporous film containing an electronic conductive material and terminal-modified polypropylene.
[0028]
The obtained film (film thickness: 25 μm) was immersed in a propylene carbonate solution containing 1 mol of LiPF ₆ at a temperature of 25 ° C. for 1 hour to obtain an immobilized liquid film conductor having a swelling rate (weight increase rate) of 103%. Obtained.
The obtained immobilized liquid film conductor was punched out to a diameter of 10 mm, sandwiched between platinum black electrodes, and the electrical resistance value was measured with an alternating current at a frequency of 1 kHz, and calculated from this value and the thickness and area of the immobilized liquid film conductor. The specific conductivity was 8 × 10 ⁻² Scm ⁻¹ .
[0029]
Example 2
Ultra high molecular weight polyethylene (weight average molecular weight 2 × 10 ⁶ ) 5 parts by weight, high density polyethylene (weight average molecular weight 4 × 10 ⁵ ) 25 parts by weight, petroleum coke powder 30 parts by weight, and ketjen black powder (trademark of Akzo Chemical) To 100 parts by weight of a mixture containing 3 parts by weight and 70 parts by weight of liquid paraffin, 0.37 parts by weight of an antioxidant was added and heated and kneaded with a biaxial extruder. This was extruded from a die having a rectangular base, and was taken up with a chill roll to obtain a 1 mm thick sheet. This sheet was simultaneously biaxially stretched 5 × 5 times at 120 ° C. using a batch type biaxial stretching machine, and the remaining liquid paraffin was washed with n-hexane and then dried at 120 ° C. while fixed to a metal frame. Heat setting was performed to obtain a polyethylene film containing an electronically conductive material.
[0030]
A living polymerized polypropylene having a methyl acrylate group (weight average molecular weight 5 × 10 ⁴ ) at one end of each molecular chain diluted to 15% by weight with methylene chloride was applied to the obtained film (film thickness 30 μm), and at room temperature. It was allowed to stand for 24 hours and dried to obtain a polyolefin microporous thin film having a filling amount of 46% by weight of living polymerized polypropylene.
0.1 cc of a propylene carbonate solution containing 1 mol of LiPF ₆ was dropped on the 10 × 10 mm square of this membrane at a temperature of 25 ° C., and left in a sealed container for 1 hour to obtain a swelling rate (weight increase rate) of 95. % Of an immobilized liquid film conductor was obtained.
The obtained immobilized liquid film conductor was punched out to a diameter of 10 mm, sandwiched between platinum black electrodes, and the electrical resistance value was measured with an alternating current at a frequency of 1 kHz, and calculated from this value and the thickness and area of the immobilized liquid film conductor. The specific conductivity was 7 × 10 ⁻² Scm ⁻¹ .
[0031]
Comparative Example 1
In Example 2, the polyethylene microporous film before being coated with living polymerized polypropylene was immersed in a propylene carbonate solution containing 1 mol of LiPF ₆ at 25 ° C. for 1 hour, and the swelling rate (weight increase rate) was 81.5%. An immobilized liquid film conductor was obtained.
The obtained immobilized liquid film conductor was punched out to a diameter of 10 mm, sandwiched between platinum black electrodes, and the electrical resistance value was measured with an alternating current at a frequency of 1 kHz, and calculated from this value and the thickness and area of the immobilized liquid film conductor. The specific conductivity was 4 × 10 ⁻² Scm ⁻¹ .
[0032]
【The invention's effect】
The immobilized liquid membrane conductor of the present invention is stable in a wide temperature range by immobilizing the electrolyte solution by the solubility of the graft polymerized polymer and suppressing its excessive swelling by the porous membrane substrate skeleton made of polyolefin. Since the electrolyte solution can be held and the evaporation rate of the electrolyte solution can be kept extremely low, good conductivity can be maintained over a wide temperature range. That is, it is possible to improve safety in overcharging without significantly reducing electronic conductivity. Furthermore, this immobilized liquid film conductor is excellent in mechanical strength due to the skeleton made of polyolefin, and can be applied with almost no change in the conventional battery manufacturing process. Further, since this immobilized liquid film conductor has both ion and electron conductivity, it is useful for electrodes of electrolytes, particularly batteries using liquid electrolytes, electrochromic elements, electric double layer capacitors, liquid crystal elements and the like. Since the ionic conductor in the immobilized liquid film conductor is continuous with the electrolyte between the electrodes and is in close contact with the porous conductive film over a wide area, it is effective as an electrode material for various cells and elements using the electrolyte. .

Claims (8)

An immobilized liquid membrane conductor in which an aprotic electrolyte solution is immobilized on a polyolefin microporous membrane comprising a polyolefin composition containing a terminal-modified polypropylene , a different polyolefin and an electronic conductive material.   The immobilized liquid film conductor according to claim 1, wherein the terminal-modified polypropylene is a terminal functional group-modified polypropylene obtained by a living polymerization method. Polyolefin composition, weight and the polyolefin having an average molecular weight contains 5 × 10 ⁵ or more ultra-high molecular weight polyolefin 1 wt% or more, containing terminal functional group-modified polypropylene obtained by living polymerization method 1-50 wt% The immobilized liquid film conductor according to claim 1 or 2. A terminal-modified polypropylene, a polyolefin which is different from this, impregnated with a non-protonic electrolyte solution microporous polyolefin membrane comprising a polyolefin composition containing an electron-conductive material, immobilized liquid, characterized in that the immobilization A method for producing a membrane conductor.   A surface of a polyolefin microporous thin film containing an electronic conductive material is coated with terminal-modified polypropylene, and the surface-coated polyolefin microporous membrane is impregnated with an aprotic electrolyte solution to be immobilized. A method for producing a conductor.   The method for producing an immobilized liquid film conductor according to claim 4 or 5, wherein the terminal-modified polypropylene is a terminal functional group-modified polypropylene obtained by a living polymerization method.   The electrode using the fixed liquid film conductor in any one of Claims 1-3.   A battery using the immobilized liquid film conductor according to claim 1 as an electrode.