JPH1153936A - Polymer electrolyte and secondary battery using the electrolyte - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolyte in a solid state which superior in electrolyte holding property at a high temperature, in which a high ion conductivity and a superior dynamic strength are well-balanced by using a polyvinylidene fluoride compound, having a side chain introduced thereto by electron beam emission for the matrix polymer of a gel polymer electrolyte. SOLUTION: Polyvinylidene fluoride powder is made coexistent with an acrylate compound, and a side chain is introduced thereto by irrading with electron beam. The thus-introduced side chain of the polyvinylidene fluoride compound is introduced in a ratio of 3-40% to the repeating unit of vinylidene fluoride, and an electrolyte consisting of an ionic compound dissolved in a nonaqueous organic solvent is preferably controlled within a range of 30-85 wt.%. Thus, dynamic strength and electrolyte holding property up to a high temperature of about 100 deg.C can be ensured, while enabling keeping high ion conductivity, eliminating the concern of fare of leakage from with the use of the electrolyte in a solid state, and a secondary battery can be made extremely small in thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state polymer electrolyte having high ionic conductivity and excellent mechanical strength. Further, the present invention relates to a solid secondary battery having a high output density, and particularly to a small-sized, large-capacity and highly safe lithium or lithium ion solid secondary battery.

[0002]

2. Description of the Related Art Multimedia technology has rapidly progressed in response to the information age, and the performance of electronic products has been improved.
There is a strong demand for portability. Regarding secondary batteries as an energy source, research and development of new secondary batteries aiming at miniaturization, large capacity and high energy density have been actively conducted. In the early 1990s, so-called lithium ion secondary batteries were commercialized. Was A lithium ion secondary battery has a structure in which a metal oxide is used as a positive electrode, a carbon material having a property of absorbing lithium ions is used as a negative electrode, and a negative electrode and a positive electrode are arranged with a separator and an electrolyte interposed therebetween. It is a secondary battery with an energy density.

[0003] However, since the lithium ion secondary battery uses an electrolytic solution, there is a risk of liquid leakage, and there remains a problem in safety. In addition, a metal can must be used for the exterior to prevent liquid leakage, and it has been difficult to reduce the size and thickness.

[0004] Armand (US Pat. No. 4,303,748; 1981) et al. Disclose that instead of an electrolytic solution, a polyalkylene oxide is replaced with an alkali metal,
Or, it has been proposed from an early stage to apply a solid electrolyte in which an alkaline earth metal is dissolved. However, a solid electrolyte composed of polyethylene oxide, which is an ordinary polyalkylene oxide, or polypropylene oxide,
Not only insufficient ionic conductivity, but also extremely high contact resistance with positive and negative electrodes, not yet adopted
(K. Murata, Electrochimica Acta., Vol. 40, No. 13-14, pp2
177-2184, 1995).

Various attempts have been made to solve these problems. Mizoguchi et al. Disclose an ionic conductive solid composition comprising an organic polymer compound having a relative dielectric constant of 4 or more and an organic solvent having excellent solubility in the organic compound (Japanese Patent Publication Nos. 61-23939 and 61-23947). No. publications). This type of ionic conductor is called a gel electrolyte, and since it is in a solid state, it may be confused with a conventional solid electrolyte and simply called a solid electrolyte.

[0006] In a gel electrolyte, excellent mechanical strength is maintained by a polymer compound serving as a matrix, and high ionic conductivity is considered to be achieved by a solution portion contained at a molecular level in the polymer compound. In this case, the material design of the polymer compound serving as the matrix is important.

The proposal of Mizoguchi et al. Is now widely accepted and variously improved. Gozdz et al. Proposed a polymer gel electrolyte (USP 5,296,318; 1995) in which a copolymer of vinylidene fluoride and 8 to 25% by weight of hexafluoropropylene was impregnated with a non-aqueous electrolyte solution in which a lithium salt was dissolved. Have been. By controlling the content of hexafluoropropylene in the copolymer, it is said that high ionic conductivity and mechanical strength are achieved in a well-balanced manner.

In order to ensure both high conductivity and excellent mechanical strength, Lee et al. Reported that a low molecular weight alkylene oxide crosslinked product having an acrylate end group or an acrylate side chain has a high boiling point and a high polarity. Polymer gel electrolytes (USP 4,830,939; 1989) in which a solution of an organic solvent having a high content and an alkali metal salt are dispersed have been proposed.

[0009]

The use of a polymer gel electrolyte not only dramatically improves the ionic conductivity of the electrolyte, but also greatly reduces the contact resistance between the electrolyte and the electrode. It is expected to be put to practical use.
However, some major challenges still remain. Gozdz et al. Proposed a polymer gel electrolyte comprising a copolymer of vinylidene fluoride and hexafluoropropylene, and a non-aqueous electrolyte solution in which a lithium salt was dissolved (U
SP 5,296,318; 1995) has achieved an ionic conductivity that is nearly an order of magnitude higher than the ionic conductive solid composition of Mizoguchi et al., And has excellent workability and mechanical strength. Retention is not always sufficient.

[0010] In order to ensure high ionic conductivity, it is necessary to impregnate the polymer gel electrolyte with as much electrolyte as possible. The benefits of using are diminished. On the other hand, a crosslinked product of an alkylene oxide is not necessarily mechanically sufficient, and when a crosslinking reaction is performed, electron beam irradiation or ultraviolet irradiation is performed on a polymer precursor serving as a matrix containing an electrolyte solution. Side reactions occur, and various problems still remain practically.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to appropriately balance both high ionic conductivity and excellent mechanical strength. An object of the present invention is to provide a polymer electrolyte and an excellent secondary battery using the electrolyte, which can achieve a solid-state electrolyte which is well achieved and has excellent electrolyte retention at high temperatures by a simple method.

[0012]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to solve the above-mentioned problems, and as a result, a polyvinylidene fluoride compound having an appropriate side chain introduced thereinto by electron beam irradiation has been converted to a gel polymer electrolyte. The use of a matrix polymer not only achieves a good balance between high ionic conductivity and excellent mechanical strength, but also has a high gel state in a solid state that has excellent electrolyte retention at high temperatures. We succeeded in obtaining a molecular electrolyte. By applying this technology, they have found out that the above-mentioned problem can be effectively solved, and have completed the present invention.

According to the present invention, there is provided a solid state solid electrolyte comprising a polyvinylidene fluoride compound having a side chain introduced by irradiation with an electron beam, and an electrolytic solution obtained by dissolving an ionic compound contained therein in a non-aqueous organic solvent. It is a polymer electrolyte.

The side chain introduced by electron beam irradiation according to the present invention is not particularly limited, but a compound containing an ethylenically unsaturated bond can be used. Among them, use of an aliphatic acrylate, particularly a fluorine-based aliphatic acrylate compound is preferred. It is considered that the fluoroaliphatic acrylate has good compatibility with the polyvinylidene fluoride compound, and thus the grafting by electron beam irradiation proceeds uniformly.

Specific examples of the aliphatic acrylate compound include isoamyl acrylate, lauryl acrylate,
Alkylene acrylate compounds such as stearyl acrylate, alkylene oxide acrylate compounds such as ethoxydiethylene glycol acrylate, methoxytriethylene glycol acrylate, and methoxydipropylene glycol acrylate; or cyclohexyl acrylate, isobornyl acrylate, tricyclo {5.2.1.0 ^2.6 } Alicyclic acrylate compounds such as decanyl acrylate;

Specific examples of the fluorinated aliphatic acrylate compound include trifluoroethyl acrylate, tetrafluoropropyl acrylate, octafluoropentyl acrylate and the like. These compounds are 1
Not only the type but also two or more types can be introduced as side chains.

The polymer electrolyte of the present invention is a solid-state polymer electrolyte in which the side chain of the polyvinylidene fluoride compound is introduced in an amount of 3 to 40% with respect to the vinylidene fluoride repeating unit. Depending on the type of side chain to be introduced, in the case of a bulky compound such as tricyclo {5.2.1.0 ^2.6 } decanyl acrylate, the introduction ratio of the side chain may be about 5 to 10%,
In the case of a relatively small compound such as trifluoroethyl acrylate, the introduction ratio of the side chain is preferably about 8 to 20%. Generally, when the content is in the range of 3 to 40%, a polymer electrolyte having excellent film-forming processability and high conductivity can be obtained.

The present invention is a solid-state polymer electrolyte in which the solid-state polymer electrolyte contains 30 to 85% by weight of an electrolyte in which an ionic compound is dissolved in a non-aqueous organic solvent. When the content of the electrolyte is 30% by weight or less, the ionic conductivity rapidly drops to 10 ^-5 S / cm or less, which is not practical. When the electrolyte is 85% by weight or more, the ionic conductivity is as high as 10 ^-3 to 10 ^-2 S / cm, but not only the mechanical strength is reduced but also the electrolyte may ooze at a high temperature. Therefore, it is not practical.

The ionic compound used in the present invention is particularly
Without limitation, the general formula M⁺X^-, M⁺Is Li⁺, N
a⁺Or K⁺And more specifically, LiC
lO_Four, LiBF_Four, LiPF₆, LiCF_ThreeSO_Three, Li (CF_ThreeS
O_Two)_TwoN, Li (C_TwoF_FiveSO_Two) _TwoN, Li (CF_ThreeSO_Two)_Three
C or Li (C_TwoF_FiveSO_Two)_ThreeSelected from C
You.

The non-aqueous compound used in the present invention is not particularly limited. Usually, carbonate solvents (propylene carbonate, ethylene carbonate, butylene carbonate, etc.) and amide solvents (N-methylformamide, N-ethylformamide, N, N- Dimethylformamide, N-
Methylacetamide, N-ethylacetamide, N-methylpyrrolidone, etc.), lactone solvents (γ-butyrolactone, γ-valerolactone, δ-valerolactone, etc.), ether solvents, nitrile solvents and the like are used.

Among them, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate and γ-butyrolactone are particularly preferred. In order to use these solvents effectively, mixed solvents with other low-viscosity solvents are often used.

The polyvinylidene fluoride compound to which a side chain is introduced by electron beam irradiation according to the present invention can be obtained by a conventionally known method (Yoshinori Sakamoto, Electron beam processing for practical use, Shinkobunbunko 27, ( Co., Ltd., Polymer Publishing Association, p98-
101). A side chain can be introduced by irradiating an electron beam with a polyvinylidene fluoride compound powder and an acrylate compound coexisting. Further, after irradiating the polyvinylidene fluoride compound powder with an electron beam, the powder can be brought into contact with an acrylate compound to introduce a side chain. Irradiation with an electron beam is preferably performed in a vacuum or an inert gas as much as possible to prevent side reactions. In addition, the irradiation intensity of the electron beam is not particularly limited, and the introduction of the side chain may proceed smoothly, but the decomposition of the polyvinylidene fluoride compound is minimized as much as possible.
The electron beam irradiation dose is preferably 5 to 15 Mrad.

The solid state polymer electrolyte of the present invention can be formed by various methods. Polyvinylidene fluoride compounds are hardly soluble in ordinary low-boiling organic solvents at room temperature, but the polyvinylidene fluoride compounds of the present invention are soluble in various low-boiling organic solvents due to the introduction of side chains.
Therefore, from the polyvinylidene fluoride compound of the present invention to be a matrix, the electrolytic solution in which the ionic compound is dissolved, and the low-boiling organic solvent in which the polyvinylidene fluoride compound is dissolved, a uniform solution around room temperature of 5 to 30 ° C. Can be prepared. By casting from the solution thus prepared and removing the low-boiling solvent, a uniform and tough solid-state polymer electrolyte thin film can be obtained.

Further, after heating a mixture comprising the polyvinylidene fluoride compound of the present invention and an electrolytic solution in which an ionic compound is dissolved to a uniform solution, a thin film of a polymer electrolyte is formed by a hot pressing method. Can also. Furthermore, a thin film of the polyvinylidene fluoride compound of the present invention may be formed into a thin film by a generally known method, and thereafter, a thin film of a polymer electrolyte may be formed by impregnating an electrolytic solution in which an ionic compound is dissolved. .

According to the present invention, there is provided a secondary battery comprising a positive electrode, an electrolyte and a negative electrode, wherein the electrolyte is the solid-state polymer electrolyte of the present invention. Further, according to the present invention, the positive electrode active material is made of LiMn ₂ O ₄ , LiCoO ₂ or LiNiO ₂ which is a metal oxide, and the negative electrode active material is made of lithium metal or lithium or lithium ion made of a material capable of absorbing lithium ions. It is a secondary battery.

The lithium or lithium ion secondary battery of the present invention having such a configuration uses a solid-state, high-conductivity ionic conductive polymer for the electrolyte, and therefore has a small size and a large capacity. It can provide a highly secure energy source.

The positive electrode active material of the present invention is not particularly limited. In addition to the above metal oxides, a conductive polymer such as a polypyrrole derivative, a polyaniline derivative, a polythiophene derivative, a polyparaphenylene derivative, or a compound represented by the general formula (R ( S)
m) a disulfide compound represented by n (R is an aliphatic group,
An aromatic group, S is sulfur, m is a positive number of 1 or more, and n is a positive number of 2 or more), for example, dithioglycol, 2,5-dimercapto-1,3,4-thiadiazole, S-triazine-
2,4,6-trithiol, 7-methyl-2,6,8-trimercaptopurine and the like can also be used.

The negative electrode active material of the present invention is not particularly limited, and any conventionally known negative electrode active material can be used. For example, materials capable of storing lithium ions include natural graphite, crystalline carbon such as graphitized carbon obtained by heat-treating coal and petroleum pitch at a high temperature, or petroleum pitch coke, coal pitch coke, and acenaphthylene pitch. Amorphous carbon obtained by heat-treating coke can be exemplified.

The positive electrode layer of the present invention can be formed by mixing a positive electrode active material with a suitable pressure-sensitive adhesive. In order to secure the electron conductivity of the positive electrode active material layer, a conductive auxiliary such as appropriate carbonaceous fine particles such as acetylene black may be added. Further, a conductive polymer such as a polyaniline derivative, a polypyrrole derivative, or a polythiophene derivative may be added.

Further, in order to secure the ionic conductivity of the positive electrode active material layer, a conventional ionic conductive polymer electrolyte, preferably, the solid-state ionic conductive polymer electrolyte of the present invention may be combined.

The positive electrode according to the present invention is prepared by, for example, thoroughly dispersing a positive electrode active material, a polyvinylidene fluoride compound of the present invention, an electrolytic solution in which an ionic compound is dissolved, and a conductive auxiliary in a suitable solvent. After coating on,
It can be formed by evaporating the solvent. As the positive electrode current collector, a conventionally known thin film such as stainless steel, copper, nickel, or aluminum, a mesh, or a sheet having another shape can be used.

The negative electrode active material layer and the negative electrode of the present invention can be formed in the same manner as the positive electrode active material layer and the positive electrode.

[0033] The secondary battery of the present invention is constructed by a usual method. After a solid state electrolyte thin film is formed in advance, it is disposed between the positive and negative electrodes to form a secondary battery. Further, the solid electrolyte of the present invention having a predetermined thickness may be coated on the positive electrode active material layer or the negative electrode active material layer, and then the positive and negative electrodes may be arranged so as to sandwich the solid electrolyte.

The form of the lithium secondary battery of the present invention is not particularly limited, and can be mounted on a cylindrical, coin, gum, or flat secondary battery.

[0035]

According to the present invention, there is provided a polymer electrolyte comprising a polyvinylidene fluoride compound having a side chain introduced by electron beam irradiation, and an electrolytic solution in which an ionic compound contained therein is dissolved in a non-aqueous organic solvent. It is.

The most important feature of the present invention is that it is possible to easily introduce various molecularly designed side chains into a polyvinylidene fluoride compound by electron beam irradiation. The solid-state electrolyte using the polyvinylidene fluoride compound obtained in this manner achieves excellent mechanical strength at a practical level and high ionic conductivity of 1.0 mS / cm or more at a practical level. In addition, it can be handled with a low-boiling organic solvent and has excellent workability, and it is expected that full-scale application as an electrolyte for secondary batteries is expected in the future.

Further, the side chain of the polyvinylidene fluoride compound is 3 to 40% of the repeating unit of vinylidene fluoride.
By being introduced, the electrolytic solution in which the ionic compound is dissolved in the non-aqueous organic solvent is controlled in the range of 30 to 85% by weight, thereby maintaining high ionic conductivity.
It has also become possible to secure mechanical strength up to a high temperature nearby and electrolyte solution retention.

Since the secondary battery using the solid-state electrolyte of the present invention has a high ionic conductivity of the electrolyte, a high-output secondary battery having substantially the same level as a secondary battery using a conventional electrolyte is realized. it can. Further, since there is no fear of liquid leakage, safety is high and ultra-thinness is possible.

As described above, the solid-state polymer electrolyte of the present invention has high ionic conductivity and excellent mechanical strength.
And because it is easy to handle and has excellent workability, it is a small, large-capacity, high-output, and high-security solid-state secondary battery.
In particular, it greatly contributes to the realization of a lithium or lithium ion solid-state secondary battery.

[0040]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. Examples 1 to 3 of the present invention show a polyvinylidene fluoride compound in which a side chain is introduced by electron beam irradiation, and a method in which a side chain is introduced. Further, Examples 4 to 8 and Comparative Examples 1 to 4 exemplify the solid state electrolyte of the present invention and the electrolyte not conforming to the present invention, and Examples 9 to 11 and Comparative Example 5 show the second embodiment of the present invention. 1 illustrates a secondary battery and a secondary battery using a conventional solution.

The electron beam irradiation for introducing the side chain of the polyvinylidene fluoride compound was performed using TYPE: CB2 manufactured by Iwasaki Electric Co., Ltd.
A 50/15/180 LEB device was used. Acceleration voltage is 1
It was 60 keV. The electron beam irradiation was performed at room temperature in a nitrogen atmosphere.

The preparation of the solid state electrolyte thin film and the measurement of its ionic conductivity were all performed in a glove box in an argon gas atmosphere. The measurement of the ionic conductivity was performed as follows.

First, a solid electrolyte thin film having a predetermined thickness was formed and then cut into a predetermined size. This electrolyte thin film is sandwiched between two platinum blocking electrodes whose surfaces have been cleaned beforehand, and the lead is pulled out from the platinum electrode and the lead is pulled out of an electrochemical workstation (CH Instruments, Mod.
el-1604) at room temperature. The measurement frequency range was 0.1 Hz to 100 kHz, and the applied voltage was 0.1 V.

In the charge / discharge test, 0.2 C
Charge until the battery voltage reaches 4.5V,
After a minimum pause time, the battery voltage is 2.0 V at the same current density.
Discharged until. Hereinafter, charge and discharge are repeated,
The battery characteristics were evaluated. HJ-201 manufactured by Hokuto Denko Co., Ltd. was used for repeated charge / discharge characteristic measurement of the battery.

[0045]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

Example 1 The average molecular weight was about 35 × 10 ³
Of polyvinylidene fluoride compound in ethanol for 24 hours
After rs extraction, it was dried under reduced pressure. After irradiating 10.0 g of the thus purified polyvinylidene fluoride compound with an electron beam at 5 Mrad at room temperature to form active points, 15, 30,
Contact was made with 20 g of tetrahydrofurfuryl acrylate maintained at 50 or 70 ° C.

The mixture of the thus obtained polyvinylidene fluoride compound and tetrahydrofurfuryl acrylate was allowed to stand for a predetermined time, and then water and ethanol (having a volume ratio of 1: 1) were used.
The mixture was extracted for 24 hrs with the mixed solution of 1) and then dried under reduced pressure. The introduction ratio of the side chain was calculated from the weight ratio of the polyvinylidene fluoride compound before and after the introduction of the side chain.

FIG. 1 shows the relationship between the introduction ratio of side chains at 15 ° C. and the polymerization time. At 15 ° C., it can be seen that the polymerization is almost completed after about 60 minutes. FIG. 2 shows the relationship between the side chain introduction ratio after 60 minutes polymerization and the polymerization temperature. From FIG. 1 and FIG. 2, it is understood that by controlling the polymerization time and the polymerization temperature, it is possible to control the introduction ratio of the side chain to the polyvinylidene fluoride compound.

Example 2 In Example 1, hexafluoropropyl methacrylate was used instead of tetrahydrofurfuryl acrylate. The irradiation dose of the electron beam was 5, 7, and 10 Mrad. Polymerization temperature is 30
C. and the polymerization time was 60 minutes. Otherwise, Example 1
Was performed in the same manner as described above. FIG. 3 shows the change in the introduction rate of the side chain for various electron beam irradiation doses. From FIG. 3,
It can be seen that by controlling the electron beam irradiation dose, it is possible to easily control the introduction rate of side chains into polyvinylidene fluoride.

Example 3 In Example 1, the ratio between the repeating unit of the polyvinylidene fluoride compound and tetrahydrofurfuryl acrylate was about 10: 1.
A polyvinylidene fluoride compound and tetrahydrofurfuryl acrylate were mixed. 13. Mixing the mixture with dimethylformamide to ensure uniform mixing.
A 7% by weight solution was prepared and a uniform solution was obtained with stirring at room temperature for 24 hrs. Thereafter, the mixture was sufficiently dried under reduced pressure to obtain a uniform mixture of a polyvinylidene fluoride compound and tetrahydrofurfuryl acrylate. After the mixture was irradiated with 5 Mrad of electron beam, the polymerization temperature was 30
C. and the polymerization time was 60 minutes. Otherwise, Example 1
Was performed in the same manner as described above. The introduction ratio of side chains was 6.7%.

Example 4 In Example 1, a polyvinylidene fluoride compound having a side chain introduction ratio of about 7% obtained under the polymerization conditions of a polymerization temperature of 15 ° C. and a polymerization time of 60 minutes was used. Usually, polyvinylidene fluoride compounds are hardly soluble in low-boiling organic solvents at room temperature, but the polyvinylidene fluoride compounds of the present invention have general-purpose organic solvents such as ketones and halogens because of the introduction of side chains. It is soluble in For example, in the solubility test, the solubility of the polyvinylidene fluoride compound of this example in tetrahydrofuran is 1
It was 7.5 g. The polyvinylidene fluoride compound, Li
PF ₆ , propylene carbonate, and tetrahydrofuran were mixed at a weight ratio of 5: 1.5: 10: 50, and dissolved with stirring with a magnetic stirrer for about 12 hrs.

The solution thus obtained was cast on a stainless steel plate whose surface was previously cleaned, and then left for 30 minutes in an argon gas atmosphere to evaporate tetrahydrofuran to obtain a 97 μm-thick self-supporting plate. A strong and strong polymer electrolyte thin film was obtained. This polymer electrolyte thin film was cut out into a predetermined shape and used for measuring ionic conductivity and assembling a secondary battery.

Example 5 In Example 4, Li (CF ₃ SO ₂ ) ₂ N was used instead of lithium salt LiPF ₆ . Polyvinylidene fluoride compound, Li (CH ₃ SO ₂ ) ₂
The weight ratio of N, propylene carbonate, and tetrahydrofuran was 5: 2.2: 10: 50. Otherwise, a polymer electrolyte thin film was prepared in the same manner as in Example 4. The thickness of the obtained polymer electrolyte thin film was 86 μm.

Example 6 In Example 4, γ-butyrolactone was used instead of propylene carbonate as a non-aqueous organic solvent. Otherwise, a polymer electrolyte thin film was prepared in the same manner as in Example 4. The thickness of the obtained polymer electrolyte thin film was 101 μm.

Example 7 In Example 4, the weight ratio of the polyvinylidene fluoride compound, LiPF ₆ , propylene carbonate, and tetrahydrofuran was 10: 1.5:
10:80. Otherwise, a polymer electrolyte thin film was prepared in the same manner as in Example 4. The thickness of the obtained polymer electrolyte thin film was 91 μm.

Comparative Example 1 A polyvinylidene fluoride compound having a side chain introduction rate of 1.5% obtained by polymerizing at 15 ° C. for 20 minutes in Example 1 was used. In the solubility test,
The polyvinylidene fluoride compound of this comparative example had low solubility in general-purpose organic solvents. For example, the solubility in tetrahydrofuran was 2.4 g. Therefore, it was difficult to form a film using a low boiling point solvent.

[Comparative Example 2] A polyvinylidene fluoride compound having a side chain introduction rate of 51% obtained by polymerizing at 50 ° C for 60 minutes in Example 1 was used. Otherwise, a polymer electrolyte thin film was prepared in the same manner as in Example 4. The thickness of the obtained polymer electrolyte thin film was 87 μm.

Comparative Example 3 In Example 4, the weight ratio of the polyvinylidene fluoride compound, LiPF ₆ , propylene carbonate, and tetrahydrofuran was 20: 0.7:
5: 150. Otherwise, a polymer electrolyte thin film was prepared in the same manner as in Example 4. The thickness of the obtained polymer electrolyte thin film was 126 μm.

Comparative Example 4 In Example 4, the weight ratio of the polyvinylidene fluoride compound, LiPF ₆ , propylene carbonate, and tetrahydrofuran was 10: 10: 9.
0:80. Otherwise, a polymer electrolyte thin film was prepared in the same manner as in Example 4. However, even at room temperature after evaporation of the tetrahydrofuran, a free-standing film was obtained, but due to the large amount of propylene carbonate, a trace amount of solution was seen on the surface.

Example 8 In Example 2, a polyvinylidene fluoride compound having an electron beam irradiation amount of 7 Mrad and having a side chain introduction rate of about 7.6% was used. In the solubility test, the solubility of the polyvinylidene fluoride compound of this example in tetrahydrofuran was 21.1 g. The polyvinylidene fluoride compound, LiPF ₆ , propylene carbonate, and tetrahydrofuran were added in a ratio of 5: 1.5: 10: 5.
The mixture was mixed at a weight ratio of 0 and dissolved for about 20 hrs while stirring with a magnetic stirrer. Otherwise, in the same manner as in Example 4, a polymer electrolyte thin film was produced. The thickness of the obtained polymer electrolyte thin film was 71 μm.

Table 1 summarizes the ionic conductivity of the polymer electrolyte thin films of Examples 4 to 8 and Comparative Examples 2 to 3. Table 1
From this, it is understood that the polymer electrolyte thin film obtained in the present invention exhibits a sufficiently high ionic conductivity at a practical level.

[0062] Example 9 FIG. 4 shows a polymer electrolyte of the present invention in a thin polymer lithium ion secondary battery using a metal oxide as a positive electrode active material, a polymer electrolyte as an electrolyte, and a lithium ion storage carbonaceous material as a negative electrode. It is the schematic which shows the secondary battery of the Example which applied.

In the battery of this embodiment, the positive electrode active material layer formed on one surface of the positive electrode current collector and the negative electrode active material layer formed on one surface of the negative electrode current collector It has a structure that is laminated via an electrolyte layer. This polymer lithium ion secondary battery was manufactured as follows.

The polyvinylidene fluoride compound of Example 1,
A uniform solution of LiPF ₆ , propylene carbonate, and tetrahydrofuran was prepared at a mixing ratio of 10: 1.5: 10: 100. Then, LiMn ₂ O ₄ was added to this mixed solution.
Of acetylene and acetylene black (weight ratio 92: 8)
And then stirred to form a mixture. In addition,
Here, the ratio of the kneaded product of LiMn ₂ O ₄ and acetylene black to the solution containing the polyvinylidene fluoride compound is such that the weight ratio of the kneaded product to the polyvinylidene fluoride compound is 90:
The ratio was set to 10.

Next, only tetrahydrofuran was volatilized and removed from the mixture, and then formed into a sheet by a roll press, cut into an appropriate size, and cut to about 25 mAh.
A positive electrode active material layer having a capacity of 120 μm and a thickness of 120 μm was formed. Next, the positive electrode current collector made of a stainless steel foil having a thickness of 20 μm was attached to a central portion of one surface. In addition, since the positive electrode active material layer thus formed had adhesiveness, it could be attached to the positive electrode current collector without using a binder.

On the other hand, a kneaded product of petroleum coke powder and acetylene black in a weight ratio of 20: 1 was mixed with the electrolyte solution containing the polyvinylidene fluoride compound used in forming the positive electrode active material layer. Was stirred to form a mixture. Here, the ratio of the kneaded product of powdered petroleum coke and acetylene black to the polyvinylidene fluoride compound was set such that the weight ratio of the kneaded product to the polyvinylidene fluoride compound became 95: 5.

Next, only tetrahydrofuran was volatilized and removed from this mixture, and then formed into a sheet by a roll press, cut into the same size as the positive electrode active material layer, and had a capacity of about 25 mAh and a thickness of 150 μm. A negative electrode active material layer was formed. Next, the negative electrode active material layer was attached to the stainless steel foil of the negative electrode current collector in the same manner as in the positive electrode.

Next, a hot-press type hot melt was placed on the outer periphery of the positive electrode current collector, and then the negative electrode active material layer was formed so as to sandwich the polymer electrolyte layer of Example 4 of the present invention. I joined my body. Then, by heating, the hot melt was completely connected to the outer peripheral portion of the current collector to complete a polymer lithium ion secondary battery. FIG. 5 shows the discharge characteristics of the secondary battery thus manufactured, and FIG. 6 shows the charge / discharge characteristics.

Example 10 In Example 9, LiCoO ₂ was used instead of LiMn ₂ O _{4 as} the positive electrode active material. Otherwise, a polymer lithium ion secondary battery was assembled in the same manner as in Example 9. FIG. 7 shows the discharge characteristics of the secondary battery thus manufactured, and FIG. 8 shows the charge / discharge characteristics.

Example 11 In Example 9, the polymer electrolyte thin film of Example 8 was used as the solid state electrolyte thin film. Otherwise, a polymer lithium ion secondary battery was assembled in the same manner as in Example 9. As a result of evaluating the charge / discharge characteristics of the secondary battery manufactured in this manner, almost the same good characteristics as those in Example 9 were obtained.

Comparative Example 5 FIG. 9 is a schematic diagram showing a coin-type lithium ion secondary battery using a usual electrolyte solution and a separator. The same positive electrode active material layer and negative electrode active material layer as in Example 9 were used. This coin-type lithium ion secondary battery was manufactured as follows. First, the positive electrode active material film was spot-welded in a positive electrode can to a thickness of 20 μm.
m on a positive electrode current collector made of a stainless steel net. Then, an annular gasket made of polypropylene was placed on the outer peripheral end of the positive electrode can. Next, the negative electrode active material film cut into a disk shape having the same diameter as the positive electrode was placed on a negative electrode current collector made of a stainless steel mesh spot-welded in a negative electrode can, and attached by crimping.

Next, 0.05 ml of an electrolyte solution prepared such that the weight ratio of propylene carbonate, dimethyl carbonate and LiPF ₆ was 10: 10: 3 was dropped on the positive electrode active material layer. On top of that, a separator made of a propylene non-woven fabric was gently covered so as to completely cover the surface of the positive electrode active material layer, and further an electrolyte solution 0.05 was added.
Then, the negative electrode can was placed on the electrolyte layer so as to sandwich the electrolyte layer including the separator. Then, the positive electrode can and the negative electrode can were overlapped via an annular gasket, and the outer peripheral portions of both cans were caulked to complete a coin-type lithium ion secondary battery. The discharge characteristics of the secondary battery thus manufactured are shown in FIG.
FIG. 6 shows the charge / discharge characteristics of the secondary battery according to the fourth embodiment of the present invention.

From the results of Examples 9 to 11 and Comparative Example 5, the secondary battery according to the present invention is equivalent to a secondary battery using a conventional solution, although the solid-state electrolyte is used. It can be seen that the battery performance of was obtained.

[0074]

The present invention provides a solid-state polymer electrolyte comprising a polyvinylidene fluoride compound having a side chain introduced by electron beam irradiation, and an electrolytic solution in which an ionic compound contained therein is dissolved in a non-aqueous organic solvent. It is. According to the present invention, the type and introduction rate of the side chain can be easily controlled, so that a polymer electrolyte thin film having excellent ionic conductivity and mechanical strength can be obtained. It is also possible to introduce two or more types of side chains having different functions,
Easy molecular design according to required performance.

The present invention also relates to a secondary battery using the polymer electrolyte, in particular, a lithium or lithium ion secondary battery. Since the polymer electrolyte of the present invention has high electrical conductivity, a secondary battery having almost the same excellent characteristics as a secondary battery using a conventional electrolyte solution can be obtained.

Since the polymer electrolyte of the present invention is in a solid state, its safety is high, there is no fear of liquid leakage, and its exterior can be made simple. A remarkable effect such as becoming.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a side chain introduction rate into a polyvinylidene fluoride compound of Example 1 of the present invention and a polymerization time.

FIG. 2 is a graph showing the relationship between the side chain introduction rate of the polyvinylidene fluoride compound of Example 1 and the polymerization temperature.

FIG. 3 is a graph showing the relationship between the side chain introduction rate of the polyvinylidene fluoride compound of Example 2 and the amount of electron beam irradiation.

FIG. 4 is a schematic view showing a thin polymer lithium ion secondary battery according to Embodiment 9 of the present invention.

FIG. 5 is a graph showing the discharge characteristics of the lithium ion secondary batteries of Example 9 and Comparative Example 5.

FIG. 6 is a graph showing charge and discharge repetition characteristics of the lithium ion secondary batteries of Example 9 and Comparative Example 5.

FIG. 7 is a graph showing the discharge characteristics of the lithium ion secondary battery of Example 10.

FIG. 8 is a graph showing charge / discharge repetition characteristics of the lithium ion secondary battery of Example 10.

FIG. 9 is a schematic diagram showing a coin-type lithium ion secondary battery of Comparative Example 5.

Claims (10)

[Claims] 1. A solid, comprising: a polyvinylidene fluoride compound having a side chain introduced by electron beam irradiation; and an electrolyte solution containing an ionic compound dissolved in a non-aqueous organic solvent. State polymer electrolyte. 2. The method according to claim 1, wherein a side chain of the polyvinylidene fluoride compound is introduced by a radical reaction between the polyvinylidene fluoride compound and an aliphatic acrylate initiated by electron beam irradiation. Polymer electrolyte. 3. The polymer electrolyte according to claim 2, wherein the aliphatic acrylate is a fluorinated aliphatic acrylate. 4. The polyvinylidene fluoride compound according to claim 1, wherein a side chain of the polyvinylidene fluoride compound is 3 to 40 with respect to the vinylidene fluoride repeating unit.
The polymer electrolyte according to any one of claims 1 to 3, wherein the polymer electrolyte is introduced in a range of%. 5. The method according to claim 1, wherein the concentration of the electrolytic solution obtained by dissolving the ionic compound in a non-aqueous organic solvent is in the range of 30 to 85% by weight based on the polyvinylidene fluoride compound. The solid state polymer electrolyte according to any one of the above. 6. The method according to claim 1, wherein the ionic compound is represented by the general formula M ⁺ X ⁻ , wherein M ⁺ is one selected from the group consisting of Li ⁺ , Na ⁺ , and K ^+. 1 to 5
The polymer electrolyte according to any one of the above. 7. The ionic compound is LiClO ₄ , Li
BF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) _{2
N, Li (C 2 F 5} SO 2) 2 N, Li (CF 3 SO 2) 3 C,
7. The polymer electrolyte according to claim 6, wherein the polymer electrolyte is one selected from the group consisting of Li (C ₂ F ₅ SO ₂ ) ₃ C. 8. The method according to claim 1, wherein the non-aqueous organic solvent contains at least one selected from the group consisting of ethylene carbonate, propylene carbonate, diethyl carbonate, methyl ethyl carbonate, and γ-butyrolactone. 8. The polymer electrolyte according to any one of 7. 9. A secondary battery comprising a positive electrode, an electrolyte, and a negative electrode, wherein the electrolyte is the solid-state polymer electrolyte according to any one of claims 1 to 8. battery. 10. A lithium-based or lithium-ion-based secondary battery, wherein the active material of the positive electrode is a metal oxide, such as LiMn ₂ O ₄ , LiCoO ₂ , or LiNiO ₂ ,
The secondary battery according to claim 9, wherein an active material of the negative electrode is made of lithium metal or a material capable of storing lithium ions.