JP2011159503A - Lithium ion conductive polymer electrolyte and lithium battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluorine-containing copolymer with a high ion conductivity, excellent in retentivity of a solvent even if a low-concentrated electrolyte solution is used when it is used as a polymer electrolyte or a binder in a lithium battery. <P>SOLUTION: The lithium ion conductive polymer electrolyte contains a fluorine-content copolymer containing a polymerization unit based on a fluorine-containing ethylene monomer and a polymerization unit having a -SO<SB>3</SB>Li group as a side chain, and a solvent of a lithium ion coordination. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a polymer electrolyte suitably used for a lithium secondary battery and a lithium battery.

Batteries that use materials capable of occluding and releasing alkali metals and alkali metal ions as electrode active materials are attracting attention as having high energy density. Among them, lithium secondary batteries have particularly high energy density, so Widely used as a power source.

In recent years, measures against leakage caused by using liquid electrolytes for primary and secondary batteries, measures for reducing the ignitability of flammable electrolytes, and improving the ease of incorporation into electronic devices by making the batteries into a film and space From the standpoint of effective use of the polymer, it has been proposed to use a polymer electrolyte (see, for example, Patent Documents 1 and 2).

Among them, the polymer electrolyte made of polyvinylidene fluoride is electrochemically stable and contains fluorine atoms, so that the polymer is difficult to burn. However, when the temperature of the polymer electrolyte is raised, the electrolyte may ooze out from the polymer. As an attempt to solve this problem, it has been proposed to use a vinylidene fluoride / hexafluoropropylene copolymer (see, for example, Patent Document 3).

Patent Document 4, a copolymer comprising polymerization units and _-CF 2 COOLi or polymerized units having a side chain containing a _-CF 2 _SO 3 Li which is based on vinylidene fluoride and matrix contains an organic solvent polymer A lithium battery characterized by being an electrolyte has been proposed.

JP-T 8-507407 Japanese National Patent Publication No. 4-506726 US Pat. No. 5,296,318 Japanese Patent Laid-Open No. 10-284128

As described in Patent Document 3, generally, an organic electrolyte used for a polymer electrolyte is a solution in which a supporting salt such as LiPF ₆ is dissolved in an organic solvent such as carbonate. It was highly toxic and increased the risk of electrolyte leakage.

Also in the lithium ion battery proposed in Patent Document 4, the electrolytic solution used contains LiPF ₆ at a high concentration.

The present invention provides a fluorine-containing copolymer having excellent solvent retention and high ion conductivity even when a low concentration electrolytic solution is used when used in a lithium battery as a polymer electrolyte or a binder. is there.

The present invention includes a fluorine-containing copolymer containing a polymer unit based on a fluorine-containing ethylenic monomer and a polymer unit having a —SO ₃ Li group in the side chain, and a lithium ion coordinating solvent. And a lithium ion conductive polymer electrolyte.

Furthermore, it is preferable to contain a lithium salt having a molecular weight of 1000 or less in a content of 1% by mass or less with respect to the polymer electrolyte.

The fluorine-containing ethylenic monomer is preferably vinylidene fluoride.

The fluorine-containing ethylenic monomer is preferably vinylidene fluoride and at least one monomer selected from the group consisting of tetrafluoroethylene and hexafluoropropylene.

The fluorine-containing copolymer preferably has a molar ratio of 50/50 to 85/15 of a polymer unit based on a fluorine-containing ethylenic monomer and a polymer unit having a —SO ₃ L group in the side chain.

The fluorine-containing copolymer has a molar ratio A / of a polymer unit (A) based on vinylidene fluoride and a polymer unit (B) based on at least one monomer selected from the group consisting of tetrafluoroethylene and hexafluoropropylene. (A + B) is preferably 0.50 to 0.95.

The present invention also provides an electrode for a lithium battery comprising the above-described lithium ion conductive polymer electrolyte.

The present invention is also a lithium battery including the above-described lithium ion conductive polymer electrolyte.

Since the polymer electrolyte of the present invention has the above-described configuration, when used in a lithium battery, it can exhibit high ionic conductivity even when the concentration of the supporting electrolyte is low. Therefore, the amount of the toxic supporting electrolyte used can be significantly reduced, and thus a lithium battery excellent in safety can be realized.

The lithium ion conductive polymer electrolyte of the present invention includes a fluorine-containing copolymer comprising a polymer unit based on at least one fluorine-containing ethylenic monomer and a polymer unit having a —SO ₃ Li group in the side chain, and lithium ion It contains a coordinating solvent.

Examples of the fluorine-containing ethylenic monomer include vinylidene fluoride, tetrafluoroethylene, trifluoroethylene, vinyl fluoride, hexafluoropropylene, perfluoro (methyl vinyl ether), perfluoro (propyl vinyl ether) and the like.

Among these, the fluorine-containing ethylenic monomer is preferably vinylidene fluoride because it becomes a polymer electrolyte that is electrochemically stable and excellent in ion conductivity. When the fluorinated copolymer has polymerized units based on vinylidene fluoride, the dielectric constant of the polymer electrolyte can be increased, and the affinity with the solvent is improved and the ionic conductivity is improved.

Moreover, it is also preferable to use vinylidene fluoride and fluorine-containing ethylenic monomers other than vinylidene fluoride as the fluorine-containing ethylenic monomer.

When a copolymer containing a polymer unit based on vinylidene fluoride is brought into contact with a strongly basic electrode active material, a deHF reaction may occur, which causes a problem of gelation of the electrode paste. Thus, by copolymerizing a fluorine-containing ethylenic monomer other than vinylidene fluoride, the chain of vinylidene fluoride is shortened, thereby reducing the deHF reaction and improving the productivity.

The fluorine-containing ethylenic monomer other than vinylidene fluoride is at least one monomer selected from the group consisting of tetrafluoroethylene and hexafluoropropylene because it is easy to copolymerize and is stable in the battery system. It is preferable that it is tetrafluoroethylene.

The fluorine-containing copolymer has a molar ratio A / (A + B) of a polymerization unit (A) based on vinylidene fluoride and a polymerization unit (B) based on a fluorine-containing ethylenic monomer other than vinylidene fluoride of 0.50 to 0.50. 0.95 is preferable, and 0.60 to 0.90 is more preferable.

If the ratio of vinylidene fluoride is too large, the productivity may deteriorate due to the deHF reaction. If the amount is too small, the ionic conductivity may deteriorate.

The fluorine-containing copolymer has a polymerization unit based on a monomer different from a polymerization unit based on a fluorine-containing ethylenic monomer and a polymerization unit having a —SO ₃ Li group in the side chain, and exceeds 20 mol% of the total polymerization units. It may be a copolymer appropriately contained within a range.

Examples of other monomers include ethylene, propylene, isobutylene, ethyl vinyl ether, vinyl acetate, vinyl benzoate, ethyl allyl ether, cyclohexyl allyl ether, norbornadiene, crotonic acid and esters thereof, acrylic acid and alkyl esters thereof, and methacrylic acid. And alkyl esters thereof.

As a polymerization unit having a —SO ₃ Li group in the side chain, the following formula (2)
^{_{-CF 2 -C (-O- (CF 2}} CFY 1 -O) n - (CFY 2) m -SO 3 Li) F- (2)
(In the formula, Y ¹ represents F, Cl or CF ₃ , Y ² represents F or Cl, and n and m represent integers of 0 to 2.)
It is preferable from the point which can synthesize | combine easily industrially.

The fluorine-containing copolymer preferably has a molar ratio of a polymer unit based on a fluorine-containing ethylenic monomer and a polymer unit having a —SO ₃ L group in the side chain of 50/50 to 97/3.

If the fluorine-containing copolymer has too many polymerized units based on the fluorine-containing ethylenic monomer, the electric conductivity of the polymer electrolyte may be lowered. Moreover, when there are too few polymer units based on a fluorine-containing ethylenic monomer, a softness | flexibility will become high too much and there exists a possibility that intensity | strength may fall.

The fluorine-containing copolymer preferably has a number average molecular weight of 1 to 1,000,000. When the number average molecular weight exceeds 1,000,000, the melt viscosity is remarkably increased, so that the processability is deteriorated and the electric conductivity of the polymer electrolyte is lowered. On the other hand, if it is less than 10,000, the mechanical strength of the polymer electrolyte is remarkably lowered, which is not preferable. The number average molecular weight is particularly preferably 3 to 500,000.

The number average molecular weight is a value measured by a GPC (gel permeation chromatograph) method. For example, the number average molecular weight can be calculated based on standard polystyrene by the following method.
Using TLC HLC-8020 manufactured by TOSOH, three columns of polystyrene gel MIX columns (Tosoh GMH series, 30 cm size), 40 ° C., NMP (containing 5 mmol / L LiBr) solvent flow rate of 0.7 mL / min can be used. . The sample concentration can be 0.1 wt% and the implantation amount can be 500 μL. The number average molecular weight in terms of polystyrene is about 100,000 to 500,000, preferably about 130,000 to 450,000, and more preferably about 160,000 to 400,000.

The fluorine-containing copolymer can be produced by a known method, or can be produced by a novel production method completed by the present inventors as follows.

That is, the fluorine-containing copolymer is obtained by radical polymerization of a fluorine-containing ethylenic monomer and a comonomer having a —SO ₃ Li group or an ionic dissociative sulfonic acid derivative in the side chain in an aqueous medium. It can also be produced by a novel production method including a step of obtaining a polymer.

Examples of the ion dissociable sulfonic acid derivatives include —SO ₃ H, —SO ₃ NR ¹ R ² R ³ R ⁴ , —SO ₂ NR ⁵ R ^6, and —SO ₃ M ¹ _{1 / L.}
(However, R ¹ , R ² , R ³ and R ⁴ are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; R ⁵ represents a hydrogen atom or M ² _{1 / L} ; and R ⁶ Represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a sulfonyl-containing group, M ¹ and M ² are the same or different and represent an L-valent metal, and the L-valent metal is group 1 of the periodic table Represents a metal belonging to Group 2, Group 4, Group 8, Group 11, Group 12 or Group 13 (excluding Li)
It is preferably at least one functional group selected from the group consisting of L is preferably 1, 2 or 3, more preferably 1 or 2.

In the radical polymerization, a comonomer having a —SO ₃ Li group or an ionic dissociative sulfonic acid derivative in the side chain is dissolved in an aqueous medium, and the fluorine-containing ethylenic monomer and the comonomer are radically polymerized. Is preferred.

The aqueous medium is not particularly limited as long as it is liquid and contains water. By being an aqueous medium, it is excellent in environmental load and cost. Also, the dispersion stability is improved. The content of water in the aqueous medium is preferably 10% by mass or more, more preferably 30% by mass or more, further preferably 50% by mass or more, and particularly preferably 90% or more. preferable. Most preferably, the aqueous medium consists essentially of water.

The aqueous medium may contain, together with water, a fluorine-free organic solvent such as alcohol, ether or ketone, a fluorine-containing organic solvent having a boiling point of 40 ° C. or lower, and the like.

The radical polymerization may be performed in the presence of a surfactant. However, since the comonomer possessed by the —SO ₃ Li group or the ion dissociable sulfonic acid derivative is polymerized, the surfactant is not necessarily used. Not necessary. Rather, radical polymerization without using a surfactant is preferable in that a polymer with few impurities can be obtained.

The radical polymerization is preferably performed by adding a polymerization initiator. The polymerization initiator is not particularly limited as long as it can generate radicals at the polymerization temperature, and known oil-soluble and / or water-soluble polymerization initiators can be used. A redox initiator may also be used. The concentration of the polymerization initiator is appropriately determined depending on the molecular weight and reaction rate of the target fluorine-containing copolymer.

Examples of the polymerization initiator include persulfates such as ammonium persulfate and potassium persulfate, and organic peroxides such as disuccinic acid peroxide, diglutaric acid peroxide, and tert-butyl hydroperoxide. As the above redox initiator, a combination of a persulfate or an organic peroxide and a reducing agent such as sodium sulfite, a bisulfite such as sodium hydrogen sulfite, a bromate, diimine, or oxalic acid. Is mentioned.

The radical polymerization can be performed under a pressure of 0.05 to 5.0 MPa. A preferable pressure range is 1.5 to 3.0 MPa. Moreover, radical polymerization can be performed at the temperature of 10-100 degreeC. A preferred temperature range is 50-90 ° C. In radical polymerization, a known stabilizer, chain transfer agent, or the like may be added depending on the purpose.

Further, before radical polymerization, a comonomer having an ion dissociable sulfonic acid derivative (except for —SO ₃ Li) in the side chain is brought into contact with a solution having a pH of 8 or less to form —SO ₃ Li groups. The process of obtaining the comonomer which has may be included.

In the case of radical polymerization of a comonomer having an ion dissociable sulfonic acid derivative in the side chain, the precursor obtained by radical polymerization is brought into contact with a solution having a pH of 8 or less, and the ion dissociable sulfone contained in the precursor A fluorine-containing copolymer can be obtained by converting the acid derivative into a —SO ₃ Li group to obtain a fluorine-containing copolymer. This step is not necessary when a comonomer having a —SO ₃ Li group in the side chain is used.

When comonomers allowed to copolymerization by radical polymerization are those having ionic dissociative acid derivatives, fluorine-containing copolymer through the step to convert the -SO 3 _Li groups is carried out in a very mild conditions Thus, a fluorine-containing copolymer suitable for a lithium battery can be obtained.

The solution having a pH of 8 or less is preferably an aqueous solution of a lithium salt selected from the group consisting of lithium chloride, lithium bromide, lithium nitrate and lithium sulfate.

The polymer electrolyte of the present invention may further contain a lithium salt having a molecular weight of 1000 or less, but the content is preferably 1% by mass or less of the polymer electrolyte. That is, the polymer electrolyte of the present invention preferably does not contain a lithium salt, and even if it contains a lithium salt, its content is preferably 1% by mass or less.

The content of the lithium salt in the polymer electrolyte is preferably 0 to 1% by mass. If it exceeds 1% by mass, the toxicity will increase if the liquid leaks. More preferably, it is 0.5 mass%, More preferably, it is 0 mass%.

In the polymer electrolyte of the present invention, since the fluorine-containing copolymer includes a polymer unit having a SO ₃ Li group in the side chain, ions can be conducted without impregnation with a lithium salt.

As the lithium _{salt, LiCF 3 SO 3, LiBF 4} , LiPF 6, LiAsF 6, LiSbF 6, CF 3 COOLi, Li (CF 3 SO 2) a ₂ N or the like can be used.

As a method for including a lithium salt in a polymer electrolyte, a method in which a solution in which the lithium salt is dissolved in a lithium ion coordination solvent in advance is included in the polymer electrolyte is simple. From the concentration of the solution and the impregnated mass, the concentration of the lithium salt in the polymer electrolyte can be specified.

The lithium ion coordinating solvent is one that stably ionizes lithium salts by coordinating to lithium ions, and mainly uses aprotic polar solvents, ethers, carbonates, carboxylic acid esters , Phosphoric acid esters, sulfoxides and the like are preferably used. Of these, carbonates are preferred because they have a moderately high boiling point and a high coordination ability to lithium ions.

As the carbonate ester, either cyclic or chain can be used, and propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate and the like can be used. Furthermore, some hydrogen atoms may be substituted with fluorine atoms. Moreover, the said carbonate ester can be used individually or in mixture of 2 or more types, and may be used in mixture with another solvent.

The content of the lithium ion coordination solvent in the polymer electrolyte is preferably 30 to 80% by mass. If it is less than 30% by mass, the electrical conductivity may be lowered. If it exceeds 80% by mass, the polymer electrolyte may not be maintained in a solid state. As for content of a lithium ion coordination solvent, 35-70 mass% is more preferable.

The polymer electrolyte of the present invention is obtained by processing the above fluorine-containing copolymer into a film shape, for example, and imparting a function of conducting lithium ions. In order to increase the mobility of lithium ions in the polymer, a method of increasing the lithium ion concentration in the polymer by impregnating the lithium salt, a compound having the property of coordinating to lithium ions (lithium ion coordination solvent) There is a method of impregnating.

The polymer electrolyte of the present invention can be produced by various methods. For example, the fluorine-containing copolymer is dissolved or uniformly dispersed in an organic solvent, and mixed with a lithium ion coordination solvent to obtain a mixed solution for forming a polymer electrolyte. The polymer electrolyte-forming mixture is applied onto a glass plate with a bar coater or doctor blade, cast or spin-coated, and then dried to remove the organic solvent in which the copolymer is mainly dissolved or dispersed, thereby removing the fluorine-containing copolymer. A polymer electrolyte film in which a polymer forms a matrix can be obtained. If some of the lithium ion coordinating solvent evaporates during drying, the film is re-impregnated with the solvent or the film is exposed to the solvent vapor to the desired composition.

Examples of the organic solvent for dissolving or dispersing the fluorine-containing copolymer include tetrahydrofuran (hereinafter referred to as “THF”), methyl ethyl ketone, methyl isobutyl ketone, toluene, xylene, N-methylpyrrolidone, acetone, acetonitrile, dimethyl carbonate, and ethyl acetate. Butyl acetate can be used. From the viewpoint of selectively removing the organic solvent by drying, a volatile organic solvent is preferable, and an organic solvent having a boiling point of 100 ° C. or lower such as THF or acetone is more preferable.

The polymer electrolyte of the present invention processed into a film may optionally include a porous support or reinforcement for the purpose of improving mechanical properties, reducing costs and / or other reasons. The porous support may be formed from a wide variety of materials such as, but not limited to, nonwoven fabrics or woven fabrics using various weaves such as plain weave, oblique weave, leno weave and the like. The porous support can be formed from glass, hydrocarbon polymers such as polyolefins (eg, polyethylene, polypropylene), and perhalogenated polymers such as polychlorotrifluoroethylene. Porous inorganic or ceramic materials can also be used. Due to its resistance to thermal and chemical degradation, the porous support is preferably formed from a fluoropolymer, more preferably a perfluoropolymer. For example, the perfluoropolymer of the porous support is polytetrafluoroethylene (PTFE) or tetrafluoroethylene and CF ₂ = CFC _n F _{2n + 1} (n = 1 to 5) or (CF ₂ = CFO- (CF ₂ CF ( It may be a microporous film of a copolymer with CF ₃ ) O) _m C _n F _{2n + 1} (m = 0-15, n = 1-15).

Microporous PTFE films are known to be suitable for use as a support layer. For example, US Pat. No. 3,664,915 discloses a uniaxially stretched film having at least 40% voids. U.S. Pat. No. 3,953,566, U.S. Pat. No. 3,962,153 and U.S. Pat. No. 4,187,390 disclose porous PTFE films having at least 70% voids. To do.

The porous support or the reinforcing material is coated with the above-mentioned fluorine-containing copolymer so that the entire surface is covered with the coating film on the outer surface and further through the inner holes of the support. Alternatively, it is possible to immerse the porous support in the above-described mixed liquid for polymer electrolyte formation, and further laminate the thin film on one surface or both surfaces of the porous support. If the polar liquid dispersion is coated on a relatively non-polar support such as a microporous PTFE film, a surfactant will promote wetting and intimate contact between the dispersion and the support. It may be used to If a surfactant is used, the support may be pretreated with the surfactant prior to contacting the dispersion, or the surfactant may be added to the dispersion itself.

The present invention is also an electrode for a lithium battery containing the polymer electrolyte of the present invention. The polymer electrolyte of the present invention can be suitably used as one or both of a positive electrode and a negative electrode as a binder. The binder is used for the purpose of maintaining the shape of the electrode by binding the electrode active material. Since the polymer electrolyte of the present invention exhibits lithium ion conductivity even when used as a binder, there is a feature that the battery output is not lowered even if the amount added is increased.

The active material used for the positive electrode is a material that can occlude lithium ions in the case of a primary battery, and a material that can occlude and release lithium ions in the case of a secondary battery. For example, Group 4 Ti, Zr, Hf, Group 5 V, Nb, Ta, Group 6 Cr, Mo, W, Group 7 Mn, Group 8 Fe, Ru, Group 9 Co, Group 10 Ni, Group 11 Cu, Group 12 Zn, Cd, Group 13 Al, Ga, In, Group 14 Sn, Pb, Group 15 Sb, Bi, and Group 16 Te, etc. Oxides and composite oxides, chalcogenides such as sulfides, oxyhalides, phosphates, composite oxides of the metal and lithium, and the like can be used. In addition, conductive polymer materials such as polyaniline derivatives, polypyrrole derivatives, polythiophene derivatives, polyacene derivatives, polyparaphenylene derivatives, and copolymers thereof can also be used.

The lithium-containing compound used as the active material used for the positive electrode includes, in particular, a composite oxide of lithium and manganese, a composite oxide of lithium and cobalt, a composite oxide of lithium and nickel, and LiFePO ₄ having an olivine structure. It is preferable that it is at least one kind selected.

The active material used for the negative electrode is a material capable of releasing lithium ions in the case of a primary battery, and a material capable of inserting and extracting lithium ions in the case of a secondary battery. Although the material which forms these negative electrode active materials is not specifically limited, The carbon material, the periodic table 14, the oxide mainly composed of the metal of the 15th group, a carbon compound, a silicon carbide compound, a silicon oxide compound, titanium sulfide, a boron carbide compound Etc.

As the carbon material, those obtained by pyrolyzing organic substances under various pyrolysis conditions, artificial graphite, natural graphite, soil graphite, expanded graphite, scale-like graphite, and the like can be used. Further, as the oxide mainly composed of metals of Groups 14 and 15 of the periodic table, compounds mainly composed of tin oxide can be used.

When a secondary battery using a material capable of inserting and extracting lithium as a negative electrode active material is used, lithium or lithium is contained in one or both of the negative electrode and the positive electrode. In general, a lithium-containing compound is used during the synthesis of the positive electrode active material, and lithium is contained in the solid matrix of the positive electrode active material. In addition, lithium may be contained in the negative electrode by a chemical or electrochemical method before assembling the battery, or lithium metal may be incorporated in contact with one or both of the negative electrode and the positive electrode during battery assembly. it can.

The positive electrode and the negative electrode in the present invention are preferably obtained by kneading an active material with an organic solvent to form a slurry, and applying the slurry to a metal foil current collector and drying. More preferably, the polymer electrolyte forming liquid mixture is applied to the metal foil current collector or the metal foil current collector is impregnated in the polymer electrolyte forming liquid mixture, and the polymer electrolyte is infiltrated into the electrode layer. Alternatively, the polymer electrolyte forming mixture may be mixed with the slurry and then applied to the metal foil current collector.

In addition, the fluorine-containing copolymer is formed into a porous film without being dissolved or dispersed in an organic solvent, and a slurry containing an active material is applied to a metal foil current collector and dried. It is also possible to form a battery element by sandwiching it and then absorbing the lithium ion coordination solvent.

The present invention is also a lithium battery including one or both of the polymer electrolyte and the lithium battery electrode.

Examples of the lithium battery include so-called lithium ion primary batteries and lithium ion secondary batteries.

There is no restriction | limiting in particular in the shape of the said lithium battery. A sheet shape (so-called film shape), a folded shape, a wound-type bottomed cylindrical shape, a button shape, or the like is selected depending on the application.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[Example 1]
Using a stainless steel autoclave with a stirrer having an internal volume of 3 L, 1500 g of ion exchange water and 300 g of CF ₂ = CFOCF ₂ CF ₂ SO ₃ Li were charged. Next, after the autoclave was purged with nitrogen, vinylidene fluoride was introduced, the gauge pressure was increased to 0.2 MPa, and the temperature was increased to 50 ° C. Then, after further introducing vinylidene fluoride to increase the gauge pressure to 0.3 MPa, a solution in which 3 g of ammonium persulfate was dissolved in 20 g of water was charged to initiate polymerization. As the polymerization progressed, vinylidene fluoride was consumed and the pressure decreased, so additional vinylidene fluoride was supplied so as to maintain a gauge pressure of 0.3 MPa.
Ten hours later, when 200 g of vinylidene fluoride was charged, the pressure in the autoclave was released to complete the polymerization, and an emulsion was obtained.

After diluting 1.5 kg of the above emulsion with 1.5 kg of water, the unreacted water-soluble monomer and water-soluble impurities are removed using a Millipore ultrafiltration device (Pellicon-2 Cassette Biomax-10). It refine | purified by adding pure water so that the whole quantity of an emulsion might be 2.0-3.0 kg. The purification was terminated when the ionic conductivity of the filtrate, which was examined using a handheld ion conductivity meter (compact conductivity meter B-173 type), was 0 S · cm ⁻¹ .

The emulsion was analyzed by NMR (Fourker Transform Nuclear Magnetic Resonance Apparatus (FT-NMR) AC300P manufactured by Bruker), and the polymer composition was examined. Polymer units based on vinylidene fluoride contained in the polymer and CF ₂ = CFOCF ₂ It was confirmed that the molar ratio with the polymerized units based on CF ₂ SO ₃ Li was 63/37.

20 g of dimethyl sulfoxide was added to 50 g of the above emulsion, developed on a glass petri dish, heated to 150 ° C. on a hot plate and dried to obtain a film having a thickness of 90 μm.

On the other hand, 5 g of a mixed solvent of diethyl carbonate and propylene carbonate 1: 1 was prepared in a glove box in an argon atmosphere and heated to 40 ° C. Subsequently, 5 g of the film was immersed in the mixed solvent. After 2 hours, the film had occluded all of the mixed solvent. The film was taken out to obtain a lithium ion conductive electrolyte membrane.

The electrolyte membrane was measured for electric conductivity at 40 ° C. in an argon atmosphere by a four-terminal AC impedance method. The electric conductivity was 4 × 10 ⁻⁴ S / cm.

[Example 2]
50 parts by weight of N-methyl-2-pyrrolidinone was added to 50 parts by weight of the emulsion obtained in Example 1, 85 parts by weight of LiCoO ₂ powder as a positive electrode active material, 5 parts by weight of acetylene black as a conductive material, and a homogenizer. Mixing to obtain a slurry. This slurry was applied to a 20 μm thick aluminum foil with a bar coater and dried to obtain a positive electrode used in a lithium secondary battery.

The lithium ion conductive polymer electrolyte of the present invention can be suitably used as a polymer electrolyte or an electrode constituting a lithium battery.

Claims (8)

A fluorine-containing copolymer comprising a polymer unit based on a fluorine-containing ethylenic monomer and a polymer unit having a —SO ₃ Li group in the side chain; and
Lithium ion coordinating solvent,
A lithium ion conductive polymer electrolyte comprising: The lithium ion conductive polymer electrolyte according to claim 1, further comprising a lithium salt having a molecular weight of 1000 or less in a content of 1% by mass or less based on the polymer electrolyte. The lithium ion conductive polymer electrolyte according to claim 1 or 2, wherein the fluorine-containing ethylenic monomer is vinylidene fluoride. The lithium ion conductive polymer electrolyte according to claim 1, 2 or 3, wherein the fluorine-containing ethylenic monomer is vinylidene fluoride and at least one monomer selected from the group consisting of tetrafluoroethylene and hexafluoropropylene. . The fluorine-containing copolymer has a molar ratio of a polymer unit based on a fluorine-containing ethylenic monomer and a polymer unit having a -SO ₃ L group in the side chain of 50/50 to 85/15. Or the lithium ion conductive polymer electrolyte according to 4; The fluorine-containing copolymer has a molar ratio A / of a polymer unit (A) based on vinylidene fluoride and a polymer unit (B) based on at least one monomer selected from the group consisting of tetrafluoroethylene and hexafluoropropylene. 6. The lithium ion conductive polymer electrolyte according to claim 4, wherein (A + B) is 0.50 to 0.95. A lithium battery electrode comprising the lithium ion conductive polymer electrolyte according to claim 1, 2, 3, 4, 5 or 6. A lithium battery comprising the lithium ion conductive polymer electrolyte according to claim 1, 2, 3, 4, 5 or 6.