JP3927638B2 - Aprotic electrolyte thin film and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an aprotic electrolyte thin film and a method for producing the same, and more particularly to an aprotic electrolyte thin film in which an aprotic electrolyte solution is immobilized on a polyolefin porous thin film and a method for producing the same.
[Prior art]
The electrolyte thin film can be widely used in fields requiring low mechanical resistance and excellent mechanical strength, such as fuel cells, salt electrolysis, primary batteries, secondary batteries, facilitated transport separation membranes, electrochromic devices, and sensors. Especially, it can utilize as polymer solid electrolytes, such as a lithium-type secondary battery.
[0002]
The solid polymer electrolyte lithium secondary battery solves the short-circuit damage and ignition problem of the battery by preventing the formation of lithium metal dendrite, and there is no liquid leakage compared to the solution type secondary battery. Development has been desired because it enables a large area.
[0003]
A polymer electrolyte in which a lithium salt such as LiClO ₄ is dissolved in a polyether such as polyethylene oxide or polypropylene oxide, polyester, polyimide, or a polyether derivative has been developed, and the ionic conductivity is 10 ⁻⁵ to 10 ⁻³ S /. cm cannot be exhibited unless the temperature is sufficiently higher than room temperature.
In order to reduce the effective resistance, as an example of thinning, a liquid ionic conductor is immobilized using capillary condensation in a fine pore of 0.1 μm or less of a solid polymer porous thin film of 50 μm or less. Although there is a method (Japanese Patent Laid-Open No. 1-158051), the problem of the operating temperature has not been fundamentally solved.
[0004]
Furthermore, as a gel polymer in which a polymer matrix is impregnated with a solution of a salt and a solvent similar to a conventional liquid type lithium battery, a technique using a cross-linked polyalkylene oxide as an electrolyte (USP 4,303,748), polyarylate The technique (USP4,830,939) which gels and uses for electrolyte is proposed. Recently, a technique (USP 5,296,318) using a polymer gel impregnated with a carbonate-based solution in which a lithium salt is dissolved in a copolymer of polyvinylidene fluoride and hexafluoropropylene as an electrolyte has been proposed and considered promising. However, there is a problem of bleeding of the electrolyte due to gel contraction at a high temperature, and there is a problem in solvent retention.
[0005]
[Problems to be solved by the invention]
The present invention eliminates the above-mentioned problems, is easy to reduce the film thickness, increase the area, etc., has excellent aprotic electrolyte solvent retention in a wide temperature range, and has improved long-term stability and mechanical strength. It is to provide a protic electrolyte thin film and a method for producing the same.
[0006]
[Means for Solving the Problems]
As a result of intensive studies in view of the above problems, the present inventors have a polymer having a functional group having a main skeleton composed of a polyolefin excellent in solvent resistance and having an affinity for an electrolyte solvent used for a terminal chain. It was discovered that by impregnating a porous thin film made of a polyolefin composition with an electrolyte solution, the aprotic electrolyte solution was fixed to the film, and an aprotic electrolyte thin film having excellent solvent retention was obtained, and the present invention was conceived. . That is, the aprotic electrolyte thin film of the present invention is one in which an aprotic electrolyte solution is immobilized on a polyolefin porous thin film comprising a polyolefin composition containing terminal-modified polypropylene and a different polyolefin .
[0007]
[Means for Solving the Problems]
In addition, the method for producing an aprotic electrolyte thin film of the present invention comprises the step of impregnating an immobilized aprotic electrolyte solution into a polyolefin porous thin film comprising a polyolefin composition containing terminal-modified polypropylene and a different polyolefin. It is something to be made.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
In the aprotic electrolyte thin film of the present invention, the main skeleton is composed of a polyolefin porous thin film excellent in solvent resistance. This polyolefin porous thin film is composed of a polyolefin resin composition containing a terminal-modified polymer having a functional group having an end chain on the electrolyte solution used, and the electrolyte is dissolved in the pores of the porous thin film. It is a thin film filled with an electrolyte solution and stably held. Hereinafter, the present invention will be described in detail.
[0009]
(1) Polyolefin porous thin film The polyolefin porous thin film used in the present invention is a porous thin film composed of a polyolefin composition containing terminal-modified polypropylene and a different polyolefin .
[0010]
1. Polyolefin composition a. Examples of the solvent-resistant polyolefin which is a polyolefin main skeleton include crystalline homopolymers or copolymers obtained by polymerizing ethylene, propylene, 1-butene, 4-methyl-pentene-1, 1-hexene and the like. However, considering the design of porous structure and thinning, among these, polypropylene, polyethylene (particularly high density polyethylene), and compositions thereof are preferable.
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 low molecular weight components occurs and the strength of the entire thin film is lowered, which is not preferable.
[0011]
As long as the polyolefin has the above molecular weight and molecular weight distribution, it may be either multistage polymerization or a composition of two or more polyolefins.
[0012]
The polyolefin containing the ultra-high molecular weight component as described above may contain various additives such as an antioxidant, an ultraviolet absorber, an anti-blocking agent, a pigment, a dye, and an inorganic filler as necessary. It can be added as long as the purpose is not impaired.
[0013]
b. 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.
[0014]
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.
[0015]
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.
[0016]
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.
[0017]
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.
[0018]
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.
[0019]
As described above, living polypropylene having a number average molecular weight of about 800 to 400,000 and close to monodispersion can be produced.
[0020]
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.
[0021]
These monomers are appropriately selected depending on the solvent of the electrolytic solution used in the production of the electrolyte thin film. Specifically, the Hansen parameter, which is one of the solubility parameters representing the solubility, is selected in consideration. The Hansen parameter is a parameter that is a three-dimensional representation of the solubility parameter divided into three components: an effect δ _d due to nonpolar interaction, an effect δ _p due to polarization, and an effect δ _h due to hydrogen bonding. Values have been investigated (CM Hansen, et al., Encyclopedia of Chemical Technology, NY, p. 889, 1971). In addition, when Hansen parameters of highly soluble solvent (good solvent) and poor solvent for a specific polymer are plotted on the three-dimensional spatial coordinates formed by δ _d , δ _p , and δ _h , the Hansen parameter of the good solvent is Experience has shown that it is located within a certain size sphere. That is, when a three-dimensional spatial coordinate (δ _d , δ _p , δ _h ) distance between a certain solvent and the polymer is short, it can be regarded as a good solvent for the polymer.
[0022]
In the present invention, the blending amount of a single monomer or a plurality of monomers forming the living polymer is adjusted according to the Hansen parameter of 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 made of the resin composition containing the terminal-modified living polymer selectively takes in the electrolyte solution solvent having affinity for the living polymerization functional group covering the surface and the pore surface, Since the main skeleton is made of polyethylene having excellent solvent resistance, the swelling as a whole is moderately suppressed, and large deformation and strength reduction can be prevented.
[0023]
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.
[0024]
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.
[0025]
c. Composition ratio of polyolefin and terminal-modified polypropylene The composition ratio of polyolefin and terminal-modified living-polymerized polypropylene is 1 to 50% by weight, preferably 3 to 30% by weight of the living polymer. 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.
[0026]
2. Method for Producing Polyolefin Porous Thin Film In the method for producing a polyolefin porous thin film of the present invention, a solution is prepared by heating and dissolving the above-described polyolefin composition in a solvent. Examples of the solvent include aliphatic or cyclic hydrocarbons such as nonane, decane, decalin, p-xylene, undecane, dodecane, and liquid paraffin, or mineral oil fractions having boiling points corresponding to these.
[0027]
The dissolution by heating is carried out by stirring at a temperature at which the polyolefin composition is completely dissolved in the solvent, or by uniformly mixing and dissolving in an extruder. When dissolving with stirring in a solvent, the temperature varies depending on the polymer and solvent used, but in the case of a polyethylene composition, for example, it is in the range of 140 to 250 ° C. When producing a porous thin film from a high-concentration solution of a polyolefin composition, it is preferably dissolved in an extruder.
[0028]
The blending ratio of the polyolefin composition and the solvent is 10 to 50% by weight, preferably 10 to 40% by weight, and 90 to 50% by weight of the solvent, with the total of the polyolefin composition and the solvent being 100% by weight. %, Preferably 90 to 60% by weight. When the polyolefin composition is less than 10% by weight (when the solvent exceeds 90% by weight), when forming into a sheet, swell and neck-in are large at the die outlet, making it difficult to form and self-support the sheet. . On the other hand, when the polyolefin composition exceeds 50% by weight (when the solvent is less than 50% by weight), the moldability is lowered.
[0029]
Next, the heated solution of the polyolefin composition thus melt-kneaded is extruded from a die or the like through an extruder and molded.
As the die, a sheet die having a rectangular base shape is usually used, but a double cylindrical hollow fiber die, an inflation die, or the like can also be used. When a sheet die is used, the die gap is usually 0.1 to 5 mm, and it is heated to 140 to 250 ° C. during extrusion molding. In this case, the extrusion speed is usually 20-30 cm / min to 5-10 m / min.
The solution extruded from the die in this way is formed into a gel-like molded article by rapid cooling. Cooling is preferably performed at a rate of at least 50 ° C./min.
[0030]
Next, the gel-like molded product is stretched. Stretching is performed at a predetermined magnification by heating the gel-like molded article and using a normal tenter method, roll method, inflation method, rolling method, or a combination of these methods. The stretching may be uniaxial stretching or biaxial stretching, but biaxial stretching is preferred. In the case of biaxial stretching, either longitudinal or transverse simultaneous stretching or sequential stretching may be used.
[0031]
The stretching temperature is the melting point of the polyolefin + 10 ° C. or less, preferably in the range from the crystal dispersion temperature of the polyolefin to less than the crystal melting point. For example, in the case of polyethylene, it is in the range of 90 to 140 ° C, preferably 100 to 130 ° C.
[0032]
Moreover, although a draw ratio changes with thickness of an original fabric, in uniaxial stretching, 2 times or more are preferable, More preferably, it is 3 to 30 times. In biaxial stretching, the surface magnification is preferably 10 times or more, more preferably 15 to 400 times. If the surface magnification is less than 10 times, stretching is insufficient and a highly elastic, high-strength microporous film cannot be obtained. On the other hand, when the surface magnification exceeds 400 times, a restriction occurs in a stretching operation or the like.
[0033]
The stretched molded product is washed with a solvent to remove the remaining solvent. Cleaning solvents include hydrocarbons such as pentane, hexane and heptane, chlorinated hydrocarbons such as methylene chloride and tetrasalt carbon, fluorinated hydrocarbons such as ethane trifluoride, and ethers such as diethyl ether and dioxane. Volatile ones can be used.
[0034]
It is desirable to dry the washing solvent after extraction and heat-set in the temperature range of the crystal dispersion temperature to the melting point.
The polyolefin porous thin film produced as described above preferably has a breaking strength of 200 kg / cm ² or more. By setting it to 200 kg / cm ² or more, the deformation resistance against swelling when the solvent of the electrolytic solution is dissolved in the living polymerization functional group is sufficient. The thickness is preferably 0.1 to 100 μm, more preferably 0.2 to 50 μm. When the thickness is less than 0.1 μm, the mechanical strength of the film is small and it is difficult to put it to practical use. On the other hand, if it exceeds 100 μm, it is too thick and is not preferable in terms of manufacturing small batteries and capacitors. The porosity and the hole diameter are not particularly limited, but the porosity and the hole diameter are preferably within a range that does not impair the ionic conduction in the state where the electrolyte solution is introduced. Moreover, the porosity and the hole diameter of the range which does not produce an internal short circuit in the same state are preferable.
The obtained polyolefin porous thin film can be further subjected to surface modification such as plasma irradiation, surfactant impregnation, and hydrophilic treatment such as surface grafting as necessary.
[0035]
(2) Electrolyte solution 1) Electrolyte As the electrolyte used in the present invention, 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 , LiPF ₆ , NaSCN and the like can be mentioned.
[0036]
2) Electrolytic Solution Solvent The aprotic solvent for dissolving the electrolyte of the present invention 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. Further, as described above, the functional group of the terminal-modified polypropylene is selected so as to have an affinity for the solvent used in the present invention.
[0037]
(3) Manufacturing method of electrolyte thin film A method of introducing an electrolyte solution in which an electrolyte is dissolved in an electrolyte solvent into a polyolefin porous film to form an aprotic electrolyte thin film is a method of impregnating, coating or spraying a polyolefin thin film with an electrolyte solution. Alternatively, they can be used in combination, and since the terminal functional group of the terminal-modified polypropylene has affinity for the aprotic solution, the polyolefin porous thin film is easily impregnated and fixed. The electrolyte solution may be introduced before being incorporated into the battery, during the battery assembly, or during the final battery assembly process. Above all, from the viewpoints of handling at the time of battery assembly, prevention of wrinkles, adhesion to the surface of the positive and negative electrode plates and the conventional battery assembly process can be applied as they are, the electrolyte solution can be used during the battery assembly process or the final battery assembly process. The method of introducing is preferred.
[0038]
The battery obtained in this way uses the same electrolyte as the conventional aprotic liquid electrolyte, but in addition to fixing by capillary condensation by introducing it into the polyolefin thin film, it is fixed by dissolving and swelling the electrolyte. As a result, there is no risk of liquid leakage, and the vapor pressure is significantly reduced, making it difficult to burn. Further, since the immobilized electrolytic solution works in the same manner as the liquid state in ionic conductivity, the operating temperature can be avoided.
[0039]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not particularly limited to the examples. In addition, the test method in an Example is as follows.
(1) Film thickness: The cross section was measured with a scanning electron microscope.
(2) Porosity: measured by gravimetric method.
(3) Tensile strength at break: Measured according to ASTM D882.
[0040]
Example 1
Living polymerization having 5% by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 2 × 10 ⁶ , 20% by weight of high density polyethylene having a weight average molecular weight of 4 × 10 ⁵ , and a methyl acrylate group at the terminal having a weight average molecular weight of 50,000 To a mixture of 5% by weight of polypropylene and 70% by weight of liquid paraffin (64 cst / 40 ° C.), 0.375 parts by weight of an antioxidant was added per 100 parts by weight of the polyolefin composition, and kneaded by heating with a twin screw extruder.
[0041]
This was discharged from a die having a rectangular base and taken up with a chill roll adjusted to 30 ° C. to obtain a 0.5 mm thick sheet. This sheet was simultaneously biaxially stretched 5 × 5 times at 115 ° C. using a batch type biaxial stretching machine, 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 porous thin film.
[0042]
The obtained polyethylene porous thin film (film thickness 25 μm, porosity 38.5%, tensile breaking strength 875 kg / cm ² ) was immersed in a γ-butyrolactone solution containing 1 mol% of LiBF ₄ at 25 ° C. for 10 hours. An aprotic electrolyte thin film was obtained. After removing the adhering liquid on the surface of the aprotic electrolyte thin film, the change in the weight of the membrane with time was measured immediately, and the weight increase rate obtained by extrapolation after 0 seconds was 65%. Further, as a result of measuring the change with time of the weight starting from the weight extrapolated after 0 seconds in the state of being left in the air at 25 ° C., the weight reduction rate after 1 hour was 0.5% or less.
[0043]
Furthermore, this aprotic electrolyte thin film is punched out to a diameter of 10 mm, and this is sandwiched with a platinum black electrode. The electrical resistance value of the thin film is measured with an alternating current of 1 KHz, and the ionic conductivity of the thin film is calculated from the thickness and area of the thin film. Then, it was 7 × 10 ⁻³ s / cm.
[0044]
Comparative Example 1
In Example 1, a polyethylene microporous membrane (film thickness 25 μm, porosity 43.5%, tensile breaking strength 1049 kg / cm ² ) 10 × obtained in the same manner as in Example 1 except that terminal-modified polypropylene is not used. A 10 mm square was immersed in a γ-butyrolactone solution containing 1 mol% of LiBF ₄ at 25 ° C. for 1 hour to obtain an aprotic electrolyte thin film. After removing the adhering liquid on the surface of the aprotic electrolyte thin film, the change in the membrane weight with time was measured immediately, and the weight increase rate obtained by extrapolation after 0 seconds was 49%. In addition, as a result of measuring the change with time of the weight starting from the weight extrapolated after 0 seconds in the state left at 25 ° C. in the atmosphere, the weight reduction rate after 1 hour was 2.5%.
[0045]
Furthermore, this aprotic electrolyte thin film is punched out to a diameter of 10 mm, and this is sandwiched with a platinum black electrode. The electrical resistance value of the thin film is measured with an alternating current of 1 KHz, and the ionic conductivity of the thin film is calculated from the thickness and area of the thin film. Then, it was 7 × 10 ⁻³ s / cm.
[0046]
【The invention's effect】
The aprotic electrolyte thin film of the present invention uses a polyolefin porous thin film containing living polypropylene having a functional group at its terminal as a base material, and immobilizes the electrolyte solution with the functional group of the terminal chain, and the polyolefin porous thin film main chain skeleton By suppressing the excessive swelling, the electrolyte solution can be stably held in a wide temperature range, and the evaporation rate of the electrolyte solvent can be kept extremely low. Further, by controlling the type and length of the functional group, the ionic conductivity can be easily controlled according to the purpose of use. That is, the safety in overcharging can be improved without significantly reducing the ionic conductivity.
[0047]
In particular, when an ultra-high molecular weight polyethylene component is used as the polyolefin, the aprotic electrolyte thin film has excellent mechanical strength and durability, and primary batteries, secondary batteries, capacitors using aprotic electrolytes, lithium primary batteries, lithium It is suitably used for a secondary battery.

Claims (7)

An aprotic electrolyte thin film in which an aprotic electrolyte solution is immobilized on a polyolefin porous thin film comprising a polyolefin composition containing a terminal-modified polypropylene and a polyolefin different from this .   The aprotic electrolyte thin film 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 aprotic electrolyte thin film according to claim 1 or 2. A method for producing an aprotic electrolyte thin film, comprising impregnating and immobilizing an aprotic electrolyte solution in a polyolefin porous thin film comprising a polyolefin composition containing a terminal-modified polypropylene and a different polyolefin .   The method for producing an aprotic electrolyte thin film according to claim 4, 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 method for producing an aprotic electrolyte thin film according to claim 4 or 5.   The lithium battery using the aprotic electrolyte thin film in any one of Claims 1-3.