JP2006049158A - Lithium polymer battery and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium polymer battery using a composite electrode fully satisfying the mechanical properties and having a low impedance and high capacity, and to provide a manufacturing method of the lithium polymer battery. <P>SOLUTION: In the lithium polymer battery having a fused salt polymer electrolyte layer sandwiched between the positive electrode and the negative electrode, an active material of at least one electrode of the positive electrode and the negative electrode is dispersed in a continuous phase of a fused salt polymer electrolyte together with a conductive material, and the continuous phase is integrated with the fused salt polymer electrolyte layer arranged between the electrodes. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a lithium polymer battery using a polymer electrolyte comprising a room temperature molten salt and a method for producing the same.

In the lithium ion battery, a non-aqueous electrolyte containing a lithium salt is generally used. This solution was prepared by dissolving a lithium salt in an aprotic polar solvent such as carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate, lactones such as γ-butyrolactone, and ethers such as tetrahydrofuran. Is. However, these organic solvents are volatile, flammable, and have safety problems during overcharge, overdischarge, short circuit, and the like. Also, the liquid electrolyte is difficult to handle when sealing the battery in a liquid-tight manner. The use of the gelled non-aqueous electrolyte does not solve the problem of volatilization of organic solvents and the danger of ignition, and the problem that the electrolyte separated from the gel leaks still remains.

Recently, a lithium secondary battery using a non-aqueous electrolyte in which a lithium salt is dissolved in a room temperature molten salt containing a quaternary ammonium cation has been proposed. For example, see JP-A-10-92467, JP-A-10-265675, JP-A-11-92467, and JP-A-2002-11230. Room temperature molten salt is safe because it is liquid at room temperature but is non-volatile and non-flammable, but it contains liquid as a gel due to the matrix polymer, and its mechanical properties are insufficient, and the liquid undergoes phase separation. As such, handling and battery design issues still remain.

There has also been a proposal for producing an all solid polymer electrolyte by introducing a vinyl group into an imidazolium salt forming an ion conductive molten salt and polymerizing the monomer. See Japanese Patent Application Laid-Open Nos. 10-83821 and 2000-11753. However, this polymer electrolyte also does not have sufficient mechanical strength.

Thus, there remains a need for safe polyelectrolytes with high ionic conductivity and satisfactory mechanical properties.

On the other hand, when producing a lithium secondary battery using a polymer electrolyte, there are the following problems.

That is, in the case of a battery using a conventional organic electrolyte, a positive electrode or a negative electrode obtained by pressure-molding a mixed powder composed of an active material, a conductive agent, and a binder is used, and a gap formed finely in the inside is used. The electrolyte solution penetrates to form an electrochemical interface with the active material. At this time, each particle is in close contact with each other and maintains a path for electron conduction, so that a good electrochemical interface is formed between the liquid electrolyte and the active material in the electrode. The impedance based on electron conduction is small.

However, when the polymer electrolyte is applied to the positive electrode or negative electrode of a battery, the electrolyte tends to exist between the particles formed on the composite electrode, and therefore, unstable electrochemistry is caused between the polymer electrolyte and the active material in the electrode. As a result, the conductivity between the particles is inferior and the impedance is larger than that of the positive electrode or the negative electrode, which causes an increase in IR loss during battery operation. Further, in order to reduce the impedance, it is necessary to increase the conductive agent. However, the increase in the amount of the active material in the electrode decreases, resulting in a decrease in electrode capacity.

Furthermore, in order to solve the above problems, for example, it has been proposed to use a polymer electrolyte made of a cyclic ether polymer described in JP-A-8-287949.

This polymer electrolyte is a solid electrolyte having a polymer obtained by ring-opening polymerization of a cyclic ether as a basic skeleton, and the electrolyte before polymerization is a normal organic electrolytic solution in which a supporting salt is dissolved in at least the cyclic ether. This liquid is poured into the positive electrode, and then polymerized and cured by a chemical method or an electrochemical method to obtain a polymer electrolyte composite positive electrode.

However, it cannot be said that this polymer electrolyte has sufficient mechanical properties. Therefore, development of a composite positive electrode and a composite negative electrode having sufficiently high mechanical properties and low impedance and high capacity is awaited. It was.
JP-A-8-287949 Japanese Patent Laid-Open No. 10-83821 Japanese Patent Laid-Open No. 10-92467 JP-A-10-265673 JP-A-11-92467 JP 2000-11754 A JP 2002-11230 A

SUMMARY OF THE INVENTION An object of the present invention is to propose a lithium polymer battery using a composite positive electrode and a composite negative electrode having sufficiently high mechanical properties and low impedance and high capacity, and a method for producing the same.

The present invention provides a lithium battery including a molten salt polymer electrolyte layer sandwiched between a positive electrode and a negative electrode, wherein at least one active material of the positive electrode and the negative electrode is dispersed in a continuous phase of the molten salt polymer electrolyte together with a conductive material. And the continuous phase achieves the above object by providing a lithium battery integrated with the molten salt polymer electrolyte layer disposed between the electrodes.

At this time, the continuous phase is preferably formed on both the positive electrode side and the negative electrode side in order to obtain an electrochemically good interface.

Further, in order to obtain a polymer electrolyte according to the present invention having sufficiently satisfactory mechanical properties, a quaternary ammonium salt containing a polymerizable functional group and a quaternary ammonium containing no polymerizable functional group, including a lithium salt. It is preferably a polymer of a salt mixture, and more preferably contains an electrochemically inert polymer reinforcing material in order to further improve the mechanical properties of the polymer electrolyte.

Specifically, the polymer electrolyte according to the present invention is:
a) 1-ethyl-3-vinylimidazolium, N- (2- (meth) acryloyloxyethyl) -N, N, N-trimethylammonium, N- (3- (meth) acryloyloxypropyl) -N, N A quaternary ammonium cation selected from the group consisting of N, N-trimethylammonium, N- (4-vinylbenzyl) -N, N, N-trimethylammonium, and N, N-diallyl-N, N-dimethylammonium; 10 to 20% by weight of a polymerizable molten salt monomer comprising a salt with a fluorine-containing anion selected from bis [(trifluoromethyl) sulfonyl] amide anion or tetrafluoroborate anion,
b) N-methyl-N-propylpiperidinium or N- (2-methoxyethyl) -N, N, N-triethylammonium or N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium 30 to 40% by weight of a non-polymerizable molten salt comprising a salt with a quaternary ammonium cation selected from: bis [(trifluoromethyl) sulfone] amide anion or tetrafluoroborate anion
c) 20-30% by weight of polyvinylidene fluoride, and d) 20-30% by weight of a lithium salt selected from LiBF ₄ or Li (CF ₃ SO ₂ ) ₂ N,
The object of the present invention is achieved by utilizing a composite polymer electrolyte for a lithium battery produced by polymerizing a solution containing.

Moreover, what contains the carbon-carbon double bond can also be used for the said polyvinylidene fluoride.

In order to obtain a higher capacity electrode, the positive electrode active material used in the present invention is V ₂ O ₅ , V ₆ O _{13 + y} (0 ≦ y ≦ 0.16), LiCoO ₂ , LiNiO ₂ , LiMnO ₂ and Li _x. Preferably, the material is selected from Mn ₂ O ₄ (0.1 <x <0.5), and the negative electrode active material is a material that can electrochemically occlude and release lithium, such as graphite, or It is preferably selected from metallic lithium and lithium-containing alloys.

A method for producing a lithium battery comprising a molten salt polymer electrolyte layer sandwiched between a positive electrode and a negative electrode according to the present invention comprises:
a) Molten salt polymer electrolyte containing a quaternary ammonium salt having a polymerizable functional group, a quaternary ammonium salt not containing a polymerizable functional group, a lithium salt, an electrochemically inactive polymer reinforcing material, and a polymerization initiator Preparing a precursor polymerization solution;
b) On the current collector of each electrode, in order to produce a composite electrode having an active material layer composed of a dispersed phase of an active material and a conductive material and a continuous phase of a molten salt polymer electrolyte, in the presence of the active material and the conductive material Thermally polymerizing the precursor polymerization liquid simultaneously with drying;
c) depositing the precursor polymerization solution on a molten salt polymer electrolyte membrane;
d) Each of the composite electrodes obtained in step b) and the molten salt polymer electrolyte membrane obtained in step c) are integrated with the molten salt polymer electrolyte membrane in a continuous phase of the molten salt polymer electrolyte in the composite electrode. Heat fusion and thermal polymerization step,
It is characterized by including.

At this time, step b) is performed by applying a dispersion of the active material and the conductive material in the precursor polymerization liquid to the electrode current collector, and thermally polymerizing the film of the dispersion simultaneously with drying.

Further, in step b), the precursor polymerization liquid may be impregnated into an active material and a conductive material that are fixed to the electrode current collector in advance using a binder polymer, and thermal polymerization may be performed simultaneously with drying. .

As a result, at the same time as the polymerization of the polymer electrolyte, it is combined with the electrode, so that a good electrochemical interface is formed between the polymer electrolyte and the active material in the electrode.

The drying and thermal polymerization in step b) are preferably performed in consideration of the shape controllability and temperature controllability of the composite electrode to be produced. The heating in step b) may be performed under vacuum, and the temperature is preferably 100 ° C. or higher and 200 ° C. or lower.

In a more preferred embodiment, the electrode containing the cured composite polymer electrolyte can be further heat-pressed under vacuum, and at least most of the pores contained in the coating layer are crushed by this treatment. Therefore, the internal resistance can be reduced.

In step d), in order to form a better electrochemical interface between the polymer electrolyte and the active material in the electrode, the composite positive electrode and negative electrode and the polymer electrolyte are thermally polymerized using a vacuum heat press. It is preferable to perform integral molding while heat-sealing.

As described above, according to the present invention, a composite electrode is formed simultaneously with the polymerization of the polymer electrolyte, so that a good electrochemical interface is formed between the polymer electrolyte and the active material in the electrode. Can be manufactured.

As a result, according to the present invention, it is possible to provide a lithium battery using a polymer electrolyte that sufficiently satisfies the mechanical properties and achieves reduction in impedance and increase in capacity of the composite positive electrode and composite negative electrode.

The characteristics of the molten salt polymer electrolyte used in the present invention and the production method thereof will be described.

The cationic species of the polymerizable molten salt monomer used in the present invention is 1-ethyl-3-vinylimidazolium, N- (2- (meth) acryloyloxyethyl) -N, N, N-trimethylammonium, N- ( 3- (meth) acryloyloxypropyl) -N, N, N-trimethylammonium, N- (4-vinylbenzyl) -N, N, N-trimethylammonium, or N, N-diallyl-N, N-dimethylammonium Chosen from. The anionic species is selected from bis [(trifluoromethyl) sulfonyl] amide or tetrafluoroborate anions.

A polymer of a polymerizable molten salt monomer supporting only a lithium salt is not satisfactory in ionic conductivity and mechanical strength. Therefore, a non-polymerizable molten salt having a wide electrochemical window is used by blending with a polymerizable molten salt monomer. Examples thereof are N-methyl-N-propylpiperidium, N- (2-methoxyethyl) -N, N, N-triethylammonium or N, N-diethyl-N-methyl-N- (2-methoxyethyl). A salt of a cationic species selected from ammonium and an anionic species selected from bis [(trifluoromethyl) sulfonyl] amide or tetrafluoroborate.

In order to improve the ionic conductivity of the polymer electrolyte, it is effective to combine polyvinylidene fluoride with the polymer electrolyte. Compounding is achieved by adding polyvinylidene fluoride as a solution to the precursor solution before polymerization of the polyelectrolyte. When polyvinylidene fluoride modified so as to include a carbon-carbon double bond is used, the polymerizable molten salt monomer is graft-polymerized to the double bond, and the ionic conductivity is improved.

The precursor solution before polymerization must contain a lithium salt and a polymerization initiator. Suitable lithium salts are fluorine-containing lithium salts such as LiBF ₄ , Li (CF ₃ SO ₂ ) ₂ N. In the present invention, the polymerization of the polymerizable molten salt monomer and the removal of the solvent are performed by heating, so that the polymerization initiator uses a thermal polymerization initiator such as benzoyl peroxide or 2,2′-azobisisobutyronitrile. be able to.

In order to obtain an optimal balance between the ionic conductivity of the molten salt electrolyte and the reinforcing effect of the polyvinylidene fluoride, the weight ratio of polyvinylidene fluoride / polymerizable molten salt monomer / non-polymerizable molten salt / lithium salt It has been found that the ratio needs to be in the range of 20-30 / 10-20 / 30-40 / 20-30.

In the production of the composite polymer electrolyte of the present invention, polyvinylidene fluoride is dissolved in a suitable solvent such as dimethylacetamide, and other components are added thereto in the above proportions, a polymerization initiator is added, and a precursor solution is prepared. Prepare. Next, this solution is spread out on a support substrate such as a glass plate by a method such as casting or coating, and heated while being supported on the substrate, and polymerization and solvent drying are simultaneously performed. Heating may be performed under vacuum, and the temperature is preferably 100 ° C. or higher and 200 ° C. or lower. The film of the composite polymer electrolyte cured and dried on the substrate can be peeled off from the substrate after cooling and stored until the battery is assembled.

In a more preferred embodiment, the cured composite polymer electrolyte can be heat-pressed under vacuum before peeling from the substrate. By this treatment, at least most of the vacancies contained in the membrane are crushed and the membrane is made compact, so that the ionic conductivity can be further improved.

Next, the manufacturing method of the polymer electrolyte composite positive electrode and composite negative electrode according to the present invention will be described.

The polymer electrolyte used for the composite of the positive electrode and the negative electrode according to the present invention is the same as the molten salt polymer electrolyte described above, in which polyvinylidene fluoride is dissolved in a suitable solvent such as dimethylacetamide, A composite polymer electrolyte precursor solution prepared by adding the components in the above-described proportions and adding a polymerization initiator is used. When this solution is poured into the positive electrode and / or negative electrode, heated, polymerized and dried, a polymer electrolyte composite positive electrode and / or composite negative electrode in which a layer made of the electrolyte composition is formed not only inside the electrode but also on the surface is obtained. It is done.

Also, since this precursor solution is a low-viscosity liquid, an active material coating slurry in which an active material is mixed with this solution is prepared, and the obtained active material coating slurry is applied to the surface of the electrode current collector. Then, the polymer electrolyte composite positive electrode and composite negative electrode can also be produced by heating and polymerizing and drying.

As a result, at the same time as the polymerization of the polymer electrolyte, it is combined with the electrode, so that a good electrochemical interface is formed between the polymer electrolyte and the active material in the electrode.

The conditions for heating and polymerizing and drying the electrode into which the precursor solution has been injected or the active material coating slurry applied to the surface of the electrode current collector are polymerized and dried. It is preferable that the temperature controllability is taken into consideration, and the heating may be performed under vacuum, and the temperature is preferably 100 ° C. or higher and 200 ° C. or lower.

In a more preferred embodiment, the electrode containing the cured composite polymer electrolyte can be further heat-pressed under vacuum, and at least most of the pores contained in the coating layer are crushed by this treatment. Therefore, the internal resistance can be reduced.

Finally, the polymer electrolyte membrane according to the present invention, the composite positive electrode and the composite electrode are alternately laminated and laminated, and this laminate is integrally formed by vacuum heat pressing, and then enclosed in a case made of a metal foil laminate film. A lithium polymer battery can be constructed.

In the following, the present invention is illustrated by means of non-limiting examples. Although these examples are intended for lithium polymer battery composite electrodes and electrolytes, those skilled in the art can readily modify these examples for application to other electrochemical devices by changing the charge transfer ion source. be able to.

All parts and percentages in the examples are by weight unless otherwise specified. Moreover, the measurement in an Example was performed with the following method.

Battery resistance (Ω): An AC four-terminal method and 1 kHz were performed using a digital resistance meter 3566 made by TSURUGA.

Battery discharge capacity (mAh / g): 20 ° C., constant current 0.5 mA / cm ² , cut voltage 3 to 4.2 V, discharge capacity calculated by the weight of positive electrode active material, using an electrochemical measuring device 1255WB manufactured by Solartron went.

Ionic conductivity (σ) of polymer electrolyte membrane: The polymer electrolyte membrane was sandwiched between gold-plated nickel electrodes, and measured using an impedance measuring instrument 4192 manufactured by Hewlett-Packard Co. at 10 mA, 5 Hz to 1300 kHz, and 20 ° C. . However, σ (S / cm) = L / (R × S), S is the area (cm ² ) of the sample, and L is the thickness (cm) of the sample.

Tensile strength (MPa): Measured using a tensile tester Tensilon RT 1350 manufactured by A & D under conditions of 23 ° C. and 5 cm / min. In addition, the compound synthesize | combined in the Example was identified by IR spectrum and NMR spectrum.

(1) Production of polymer electrolyte composite positive electrode

FIG. 1 is a longitudinal sectional view of a lithium polymer battery manufactured according to the present invention. In FIG. 1, 1 is a composite positive electrode, 2 is a polymer electrolyte membrane, and 3 is a composite negative electrode. Among these, 1 is a pressure-molded mixed powder composed of 85% by weight of LiMnO _{2 as the} positive electrode active material 4, 7% by weight of ketjen black as a conductive agent, and 8% by weight of polyvinylidene fluoride as a binder. The positive electrode 1.

Reference numeral 5 denotes a polymer electrolyte filled in fine pores in the positive electrode 1. This electrolyte comprises, as a polymer, polyvinylidene fluoride (abbreviated as PVdF); a polymerizable molten salt monomer (PIL); a diallyl-dimethylammonium salt (abbreviated as DAA); a non-polymerizable molten salt (IL), N -Methyl-N-propylpiperidium salt (abbreviated as MPP); bis [(trifluoromethyl) sulfonyl] amide lithium (abbreviated as LiTFSI) as a lithium salt, PVdF: 14 g, DAA: 10.5 g A precursor solution prepared by dissolving MPP: 10.5 g and LiTFSI: 15 g in dimethylacetamide 113 g, and adding 0.21 g of benzoyl peroxide to this was poured into one positive electrode, and 110 ° C. together with the positive electrode 1 at 110 ° C. It was produced by performing vacuum drying for 30 minutes and simultaneously performing drying and polymerization reaction. Subsequently, vacuum heat pressing was performed for 10 minutes under the condition of 90 ° C. × 21 kg / cm ² to prepare a composite positive electrode 1 having a thickness of 90 μm in which a polymer electrolyte phase was formed on the electrode surface.

(2) Preparation of polymer electrolyte composite negative electrode

In FIG. 1, 3 is a pressure-molded mixed powder composed of 88% by weight of natural graphite as the negative electrode active material 6, 4% by weight of ketjen black as a conductive agent, and 8% by weight of polyvinylidene fluoride as a binder. Negative electrode 3.

7 is a polymer electrolyte filled in fine pores in the negative electrode 3. This electrolyte comprises, as a polymer, polyvinylidene fluoride (abbreviated as PVdF); a polymerizable molten salt monomer (PIL); a diallyl-dimethylammonium salt (abbreviated as DAA); a non-polymerizable molten salt (IL), N -Methyl-N-propylpiperidium salt (abbreviated as MPP); bis [(trifluoromethyl) sulfonyl] amide lithium (abbreviated as LiTFSI) as a lithium salt, PVdF: 14 g, DAA: 10.5 g A precursor solution prepared by dissolving MPP: 10.5 g and LiTFSI: 15 g in dimethylacetamide 113 g and adding 0.21 g of benzoyl peroxide to this was poured into the negative electrode 3, and at 110 ° C. together with the negative electrode 3 It was produced by performing vacuum drying for 30 minutes and simultaneously performing drying and polymerization reaction. Subsequently, vacuum heat pressing was performed for 10 minutes under the condition of 90 ° C. × 21 kg / cm ² to prepare a composite negative electrode 3 having a thickness of 40 μm in which a polymer electrolyte phase was formed on the electrode surface.

(3) Preparation of polymer electrolyte membrane

2 is a polymer electrolyte layer. This electrolyte layer 2 is composed of polyvinylidene fluoride (abbreviated as PVdF) as a polymer, like the composite polymer electrolytes 5 and 7 used for the composite of the positive electrode 1 and the negative electrode 3 and the polymer; As monomer (PIL), diallyl-dimethylammonium salt (abbreviated as DAA); as non-polymerizable molten salt (IL), as N-methyl-N-propylpiperidium salt (abbreviated as MPP); as lithium salt; [(Trifluoromethyl) sulfonyl] amide / lithium (abbreviated as LiTFSI), PVdF: 14 g, DAA: 10.5 g, MPP: 10.5 g, LiTFSI: 15 g were dissolved in dimethylacetamide 113 g, and benzoyl This is a precursor solution prepared by adding 0.21 g of peroxide, and this solution is made of glass having a thickness of 3 mm. It is applied to a thickness of 25~50μm using an applicator on. Next, the applied composite polymer electrolyte was vacuum-dried at 110 ° C. for 30 minutes together with a glass plate, and dried and subjected to a polymerization reaction. Subsequently, the cured film was vacuum heat pressed on a glass plate for 10 minutes under the condition of 90 ° C. × 21 kg / cm ² , and peeled from the glass plate to produce a polymer electrolyte membrane 2 having a thickness of 30 μm.

The ionic conductivity of the polymer electrolyte membrane 2 produced at this time was 1.8 × 10 ⁻³ S / cm at 20 ° C., and the tensile strength was 4.7 MPa.

(4) Fabrication of lithium polymer secondary battery

Finally, the polymer electrolyte membrane 2 according to the present invention, the composite positive electrode 1 and the composite negative electrode 3 are laminated alternately and laminated, and this laminate is heat-sealed by vacuum heat pressing at 150 ° C. × 10 kg / cm ² for 30 minutes. -The lithium polymer secondary battery of Example 1 was constituted by integrally molding by thermal polymerization and then enclosing it in a case made of a metal foil laminate film.

(1) Fabrication of polymer electrolyte composite positive electrode

The cross-sectional structure of the lithium polymer battery in Example 2 is the same as the cross-sectional structure of the lithium polymer battery in Example 1 shown in FIG. That is, 1 is a composite positive electrode, 2 is a polymer electrolyte membrane, and 3 is a composite negative electrode, in which 1 is 85% by weight of LiMnO ₂ that is the positive electrode active material 4 and 7% by weight of ketjen black that is a conductive agent. It is a positive electrode obtained by pressure-molding a mixed powder composed of 8% by weight of polyvinylidene fluoride as a binder.

Reference numeral 2 denotes a polymer electrolyte filled in fine pores in the positive electrode 1. This electrolyte has, as a polymer, polyvinylidene fluoride (abbreviated as PVdF); as a polymerizable molten salt monomer (PIL); as a methacryloyloxyethyl-trimethylammonium salt (abbreviated as MOETMA); as a non-polymerizable molten salt (IL). Diethyl-methyl-methoxyethylammonium salt (abbreviated as DEME); bis [(trifluoromethyl) sulfonyl] amido lithium (abbreviated as LiTFSI) as the lithium salt, PVdF: 14 g, DAA: 10.5 g, A precursor solution prepared by dissolving MPP: 10.5 g and LiTFSI: 15 g in dimethylacetamide 113 g, and adding 0.21 g of benzoyl peroxide to this was poured into one positive electrode, and 110 ° C. together with the positive electrode 1 at 110 ° C. Dry and polymerize at the same time by vacuum drying for 30 minutes. It was generated by. Subsequently, vacuum heat pressing was performed for 10 minutes under the condition of 90 ° C. × 21 kg / cm ² to prepare a composite positive electrode 1 having a thickness of 90 μm in which a polymer electrolyte phase was formed on the electrode surface.

(2) Preparation of polymer electrolyte composite negative electrode

In FIG. 1, 3 is a pressure-molded mixed powder composed of 88% by weight of natural graphite as the negative electrode active material 6, 4% by weight of ketjen black as a conductive agent, and 8% by weight of polyvinylidene fluoride as a binder. Negative electrode 3.

7 is a polymer electrolyte filled in fine pores in the negative electrode 3. This electrolyte has, as a polymer, polyvinylidene fluoride (abbreviated as PVdF); as a polymerizable molten salt monomer (PIL); as a methacryloyloxyethyl-trimethylammonium salt (abbreviated as MOETMA); as a non-polymerizable molten salt (IL). Diethyl-methyl-methoxyethylammonium salt (abbreviated as DEME); bis [(trifluoromethyl) sulfonyl] amido lithium (abbreviated as LiTFSI) as the lithium salt, PVdF: 14 g, DAA: 10.5 g, A precursor solution prepared by dissolving MPP: 10.5 g and LiTFSI: 15 g in dimethylacetamide 113 g and adding 0.21 g of benzoyl peroxide to this was poured into the negative electrode 3, and at 110 ° C. together with the negative electrode 3 Dry and polymerize at the same time by vacuum drying for 30 minutes. It was generated by. Subsequently, vacuum heat pressing was performed for 10 minutes under the condition of 90 ° C. × 21 kg / cm ² to prepare a composite negative electrode 3 having a thickness of 40 μm in which a polymer electrolyte phase was formed on the electrode surface.

(3) Preparation of polymer electrolyte membrane

2 is a polymer electrolyte layer. This electrolyte layer is composed of polyvinylidene fluoride (abbreviated as PVdF) as a polymer, as in the case of the composite polymer electrolyte used for combining the positive electrode 1 and the negative electrode 3 with the polymer; polymerizable molten salt monomer (PIL) Diallyl-dimethylammonium salt (abbreviated as DAA); non-polymerizable molten salt (IL); N-methyl-N-propylpiperidium salt (abbreviated as MPP); lithium salt as bis [(trifluoro Methyl) sulfonyl] amide lithium (abbreviated as LiTFSI), PVdF: 14 g, MOETMA: 10.5 g, DEME: 10.5 g, LiTFSI: 15 g were dissolved in dimethylacetamide 80 g, and benzoyl peroxide 0. 15 g of a precursor solution prepared by adding a 3 mm thick glass plate It is applied to a thickness of 25~50μm using applicator. Next, the applied composite polymer electrolyte was vacuum-dried at 110 ° C. for 30 minutes together with a glass plate, and was produced by drying and polymerization reaction. Subsequently, the cured film was vacuum heat pressed on a glass plate for 10 minutes under the condition of 90 ° C. × 21 kg / cm ² , and peeled from the glass plate to produce a polymer electrolyte membrane 2 having a thickness of 30 μm.

The ionic conductivity of the polymer electrolyte membrane 2 produced at this time was 1.9 × 10 ⁻³ S / cm at 20 ° C., and the tensile strength was 3.5 MPa.

(4) Fabrication of lithium polymer secondary battery

Finally, the polymer electrolyte membrane 2 according to the present invention, the composite positive electrode 1 and the composite negative electrode 3 are laminated alternately and laminated, and this laminate is heat-sealed by vacuum heat pressing at 150 ° C. × 10 kg / cm ² for 30 minutes. Then, the lithium polymer secondary battery of Example 2 was constructed by enclosing it in a case made of a metal foil laminate film.

Comparative example

(1) Production of polymer electrolyte composite positive electrode

The cross-sectional structure of the lithium polymer battery in the comparative example is the same as the cross-sectional structure of the lithium polymer battery of Examples 1 and 2 shown in FIG. However, unlike the first and second embodiments, the following method is used in the method for manufacturing the composite positive electrode. First, a liquid in which 90% by weight of LiMnO ₂ that is the positive electrode active material 4, 3% by weight of acetylene black that is a conductive agent, and 7% by weight of a complex of polyethylene oxide and LiBF ₄ that is a polymer electrolyte is prepared in acetonitrile is prepared. Next, this suspension was poured onto an aluminum foil, and acetonitrile was evaporated to obtain a composite positive electrode 1 having a sheet thickness of 90 μm. Moreover, the composite cathode 1 of the produced comparative example was not subjected to vacuum heat press.

(2) Preparation of polymer electrolyte composite negative electrode

In the method for producing a composite negative electrode, first, 90% by weight of natural graphite as negative electrode active material 4, 3% by weight of ketjen black as a conductive agent, 7% by weight of a complex of polyethylene oxide and LiBF ₄ as a polymer electrolyte are mixed with acetonitrile. Adjust the liquid suspended in Next, this suspension was poured onto a copper foil, and acetonitrile was evaporated to obtain a sheet-like composite negative electrode 3 having a thickness of 40 μm. Moreover, the composite negative electrode 3 of the produced comparative example was not subjected to vacuum heat press.

(3) Preparation of polymer electrolyte membrane

The polymer electrolyte membrane 2 is prepared by adjusting a liquid in which a complex of polyethylene oxide, which is a polymer electrolyte, and LiBF ₄ is suspended in acetonitrile. Next, this suspension was poured onto a glass plate having a thickness of 3 mm, and acetonitrile was evaporated to produce a sheet-like polymer electrolyte membrane 2. Subsequently, the cured film was peeled off from the glass plate without heat pressing to produce a polymer electrolyte membrane 2 having a thickness of 30 μm.

The ionic conductivity of the polymer electrolyte membrane 2 produced at this time was 0.1 × 10 ⁻³ S / cm at 20 ° C., and its tensile strength was 5.1 MPa.

(4) Fabrication of lithium polymer secondary battery

Finally, the produced polymer electrolyte membrane 2, the composite positive electrode 1 and the composite negative electrode 3 were laminated alternately and laminated, and this laminate was integrally formed by vacuum heat pressing for 30 minutes at 150 ° C. × 10 kg / cm ² . Then, a lithium polymer secondary battery of a comparative example was constructed by enclosing it in a case made of a metal foil laminate film.

Conditions other than the above are the same as in Examples 1 and 2 and the comparative example. Table 1 shows the battery resistance and discharge capacity of the composite positive electrode and composite negative electrode obtained in Comparative Example and Examples 1 and 2.

In Examples 1 and 2, DAA or MOETMA was used as the polymerizable molten salt monomer (PIL), but this is not limited to 1-ethyl-3-vinylimidazolium, N- (3- (meth) acryloyloxy. A quaternary ammonium cation selected from the group consisting of propyl) -N, N, N-trimethylammonium and N- (4-vinylbenzyl) -N, N, N-trimethylammonium; and bis [(trifluoromethyl) A polymerizable molten salt monomer composed of a salt with a fluorine-containing anion selected from a [sulfonyl] amide anion or a tetrafluoroborate anion.

Further, MPP or DEME was used as the non-polymerizable molten salt (IL), which is a quaternary ammonium cation composed of N- (2-methoxyethyl) -N, N, N-triethylammonium, bis [(tri Fluoromethyl) sulfone] amide anion or tetrafluoroborate anion or non-polymerizable molten salt may be used. Specifically, N, N, N-triethyl-N-methoxyethylammonium bis [( Trifluoromethyl) sulfonyl] amide (abbreviated as TEME TFSI).

Polyvinylidene fluoride (abbreviated as PVdF) was used as the polymer, but the polymer reinforcing material is electrochemical / chemical such as oxidation resistance, reduction resistance, solvent resistance, low water absorption, and flame resistance. Any polymer that has excellent temperature characteristics such as stability, heat resistance, and cold resistance, as well as excellent mechanical properties (strong elongation, flexibility) and excellent workability, such as fluorine-based polymers such as polytetrafluoroethylene. Polymers, polyolefins such as polyethylene and polypropylene, vinyl polymers such as polyacrylonitrile and polystyrene, polysulfone polymers such as polysulfone and polyethersulfone, polyetherketone polymers such as polyetherketone and polyetheretherketone, polyethers Polyimide-based poly, such as imide, polyamide-imide, and polyimide It can be exemplified by chromatography (both containing copolymer).

Further, although bis [(trifluoromethyl) sulfonyl] amide lithium (abbreviated as LiTFSI) is used as the lithium salt, this may be a lithium salt made of Li (CF ₃ SO ₂ ) ₂ N.

1 is a partial cross-sectional view of a lithium polymer secondary battery according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polymer electrolyte composite positive electrode 2 Polymer electrolyte membrane 3 Polymer electrolyte composite negative electrode 4 Positive electrode active material 5 Polymer electrolyte 6 Negative electrode active material 7 Polymer electrolyte

Claims (16)

In a lithium battery including a molten salt polymer electrolyte layer sandwiched between a positive electrode and a negative electrode, at least one active material of the positive electrode and the negative electrode is dispersed in a continuous phase of the molten salt polymer electrolyte together with a conductive material, and the continuous A lithium battery, wherein the phase is integral with the molten salt polymer electrolyte layer disposed between the electrodes. The lithium battery according to claim 1, wherein the continuous phase is formed on both the positive electrode side and the negative electrode side. 3. The lithium according to claim 1, wherein the molten salt polymer electrolyte is a polymer of a mixture of a quaternary ammonium salt containing a polymerizable functional group containing a lithium salt and a quaternary ammonium salt containing no polymerizable functional group. battery. The lithium battery according to any one of claims 1 to 3, wherein the molten salt polymer electrolyte includes an electrochemically inactive polymer reinforcing material. The molten salt polymer electrolyte is
a) 1-ethyl-3-vinylimidazolium, N- (2- (meth) acryloyloxyethyl) -N, N, N-trimethylammonium, N- (3- (meth) acryloyloxypropyl) -N, N A quaternary ammonium cation selected from the group consisting of N, N-trimethylammonium, N- (4-vinylbenzyl) -N, N, N-trimethylammonium, and N, N-diallyl-N, N-dimethylammonium; 10 to 20% by weight of a polymerizable molten salt monomer comprising a salt with a fluorine-containing anion selected from bis [(trifluoromethyl) sulfonyl] amide anion or tetrafluoroborate anion,
b) N-methyl-N-propylpiperidinium or N- (2-methoxyethyl) -N, N, N-triethylammonium or N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium 30 to 40% by weight of a non-polymerizable molten salt comprising a salt with a quaternary ammonium cation selected from: bis [(trifluoromethyl) sulfone] amide anion or tetrafluoroborate anion
c) 20-30% by weight of polyvinylidene fluoride, and d) 20-30% by weight of a lithium salt selected from LiBF ₄ or Li (CF ₃ SO ₂ ) ₂ N,
The lithium battery according to claim 1, which is produced by polymerizing a polymerization solution containing The lithium battery according to claim 5, wherein the polyvinylidene fluoride includes a carbon-carbon double bond. The positive electrode active material is V ₂ O ₅ , V ₆ O _{13 + y} (0 ≦ y ≦ 0.16), LiCoO ₂ , LiNiO ₂ , LiMnO ₂ and Li _x Mn ₂ O ₄ (0.1 <x <0.5). The lithium battery according to any one of claims 1 to 6 selected from. The lithium battery according to any one of claims 1 to 7, wherein the negative electrode active material is selected from a material capable of electrochemically inserting and extracting lithium, or a metal lithium and an alloy containing lithium. A method for producing a lithium battery comprising a molten salt polymer electrolyte layer sandwiched between a positive electrode and a negative electrode,
a) Molten salt polymer electrolyte containing a quaternary ammonium salt having a polymerizable functional group, a quaternary ammonium salt not containing a polymerizable functional group, a lithium salt, an electrochemically inactive polymer reinforcing material, and a polymerization initiator Preparing a precursor polymerization solution;
b) On the current collector of each electrode, in order to produce a composite electrode having an active material layer composed of a dispersed phase of an active material and a conductive material and a continuous phase of a molten salt polymer electrolyte, in the presence of the active material and the conductive material Thermally polymerizing the precursor polymerization liquid simultaneously with drying;
c) depositing the precursor polymerization solution on a molten salt polymer electrolyte membrane;
d) Each of the composite electrodes obtained in step b) and the molten salt polymer electrolyte membrane obtained in step c) are integrated with the molten salt polymer electrolyte membrane in a continuous phase of the molten salt polymer electrolyte in the composite electrode. Heat fusion and thermal polymerization step,
A method for producing a lithium battery, comprising: The step b) is performed by applying a dispersion of an active material and a conductive material in the precursor polymerization liquid to a current collector, and thermally polymerizing a film of the dispersion simultaneously with drying. Method. The step b) is performed by impregnating an active material and a conductive material previously fixed to a current collector using a binder polymer with the precursor polymerization liquid and performing thermal polymerization simultaneously with drying. the method of. The molten salt polymer electrolyte is
a) 1-ethyl-3-vinylimidazolium, N- (2- (meth) acryloyloxyethyl) -N, N, N-trimethylammonium, N- (3- (meth) acryloyloxypropyl) -N, N A quaternary ammonium cation selected from the group consisting of N, N-trimethylammonium, N- (4-vinylbenzyl) -N, N, N-trimethylammonium, and N, N-diallyl-N, N-dimethylammonium; 10 to 20% by weight of a polymerizable molten salt monomer comprising a salt with a fluorine-containing anion selected from bis [(trifluoromethyl) sulfonyl] amide anion or tetrafluoroborate anion,
b) N-methyl-N-propylpiperidinium or N- (2-methoxyethyl) -N, N, N-triethylammonium or N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium 30 to 40% by weight of a non-polymerizable molten salt comprising a salt with a quaternary ammonium cation selected from: bis [(trifluoromethyl) sulfone] amide anion or tetrafluoroborate anion
c) 20-30% by weight of polyvinylidene fluoride, and d) 20-30% by weight of a lithium salt selected from LiBF ₄ or Li (CF ₃ SO ₂ ) ₂ N,
The method according to claim 9, which is produced by polymerizing a polymerization solution containing The method according to claim 12, wherein the polyvinylidene fluoride contains a carbon-carbon double bond. The positive electrode active material is V ₂ O ₅ , V ₆ O _{13 + y} (0 ≦ y ≦ 0.16), LiCoO ₂ , LiNiO ₂ , LiMnO ₂ and Li _x Mn ₂ O ₄ (0.1 <x <0.5). 14. A method according to any one of claims 9 to 13 selected from. 15. The method according to any one of claims 9 to 14, wherein the negative electrode active material is selected from materials capable of electrochemically inserting and extracting lithium, or metal lithium and an alloy containing lithium. The method according to any one of claims 9 to 15, wherein the step of integrally forming the positive electrode and the negative electrode with a polymer electrolyte accompanied by thermal polymerization uses a vacuum heat press.

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