JP3422627B2 - Crosslinked polymer solid electrolyte and battery - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polymer solid electrolyte composed of an ion conductive polymer material and an ion transfer medium, and a battery using the same.

[0002]

2. Description of the Related Art A solid-state battery having a solid electrolyte as an ion-moving medium has less liquid leakage than a conventional battery using an electrolytic solution as an ion-moving medium, so that the reliability and safety of the battery are improved and a thin film is formed. It is expected to be easy and easy to form a laminated body, to have a high degree of freedom in battery form, and to be simple and lightweight. As the solid electrolyte material, an ion conductive ceramic material or polymer material has been proposed. Of these, the former ceramic material has a brittle property, has poor workability, and is difficult to form a laminate with an electrode. On the other hand, since the ion conductive polymer material is excellent in processability and flexibility, it is preferable that it can be used as a solid electrolyte material to form a bonded body with an electrode and maintain an interface following a change in electrode volume due to ion exchange of the electrode.

As this polymer solid electrolyte, Wright
Report of an alkali metal salt complex of polyethylene oxide by t (British Polymer Journal)
al, 7P. Since 319 (1975), active researches have been made on materials mainly composed of polyalkylene ether materials such as polyethylene oxide and polypropylene oxide, and solid electrolyte materials having materials such as polyacrylonitrile, polyphosphazene and polysiloxane as a skeleton. There is.

Further, a polymer solid electrolyte using a polyvinylidene fluoride resin as the skeletal polymer has been proposed (for example, US Pat. No. 5,296,318). This electrolyte has high ionic conductivity and high electrochemical stability, and is preferable when used in a battery. This preparation is formed by applying a uniform solution prepared by heating and mixing with a polyvinylidene fluoride resin, a metal salt, a plasticizer, and a swelling solvent, and then removing the swelling solvent. Therefore, as the matrix polymer, a normal linear polymer is used to form a uniform solution. This polymer solid electrolyte material is 85-95.
It is not preferable when applied to a battery because it melts at a temperature of ° C and exhibits fluidity. Therefore, an acrylate ester, a di- or triallyl ester, or a di- or triglycidyl ester as a cross-linkable vinyl monomer is made to coexist in a polyvinylidene fluoride resin together with a plasticizer, and a material in which these polymerizable monomers are cross-linked is prepared, and then A polymer solid electrolyte obtained by impregnating this with an electrolytic solution has been proposed (US Pat. No. 5,429,891).

A solid polymer electrolyte formed by using an ordinary linear polymer as a matrix and solid-dissolving an electrolyte and / or a plasticizer exhibits fluidity because it plasticizes at a temperature considerably lower than the melting point of the linear polymer, and external pressure is applied. Therefore, it is easily deformed, so that the structural change of the battery is a problem. As a matter of course, when the solid electrolyte is exposed to a high temperature, the solid electrolyte undergoes a structural change, so that the high temperature stability is poor.

In order to suppress this plasticity, the electrolytic mass and the amount of plasticizer contained in the solid polymer electrolyte are limited. However, the ionic conductivity of the solid polymer electrolyte having a low plasticizer content remains low, and the battery capacity decreases with the increase of the interelectrode overvoltage of the battery using the same. Electrolytic mass to obtain high ionic conductivity polymer solid electrolyte,
A material having an increased amount of plasticizer can be produced, but has low mechanical strength, making it difficult to manufacture a battery structure and poor in high temperature stability.

Therefore, the conventional polymer solid electrolyte composed of a linear polymer as a matrix has problems in structural stability and battery performance. In order to solve this, there is an attempt to make a crosslinkable polymerizable monomer coexist with a vinylidene fluoride polymer and prepare a crosslinked structure by polymerizing the monomer. However, the polymer in the crosslinked body produced using the glycidyl ether-based monomer is not sufficiently crosslinked. In particular, the vinyl-based polymerizable monomer causes a side reaction in the charging / discharging process due to the residual monomer after the crosslinking treatment, but this cannot be completely removed. Further, the presence of dibutyl phthalate or tributoxyethyl phosphate as a polymer plasticizer during monomer polymerization is not preferable because it may cause a side reaction depending on the crosslinking reaction conditions. Further, the steps of mixing and extracting the plasticizer are complicated, and when the extraction is incomplete, the residual plasticizer causes a side reaction on the electrode surface during charging / discharging, which deteriorates the battery performance. Therefore, there has been a demand for a polymer solid electrolyte that uses a polyvinylidene fluoride-based resin as a matrix, which is suitable for industrial production and has a crosslinked structure that does not adversely affect the battery performance.

[0008]

DISCLOSURE OF THE INVENTION The present invention uses a polymer solid electrolyte having excellent high temperature structural stability and high ionic conductivity, and a polymer solid electrolyte having high battery capacity and high safety. The purpose of the present invention is to provide a battery.

[0009]

Means for Solving the Problems The inventors of the present invention have reached the present invention by conducting research on a polymer solid electrolyte using a polyvinylidene fluoride resin. The present invention is as follows. (1) Bulk crosslinked polyvinylidene fluoride resin
A solid polymer electrolyte obtained by impregnating and / or swelling an electrolyte or a mixture of an electrolyte and a plasticizer into a polyvinylidene fluoride resin molded body that does not contain a crosslinkable monomer unit having a structure . (2) The polymer solid electrolyte as described in 1 above, wherein the polyvinylidene fluoride resin is a polyvinylidene fluoride resin molded product crosslinked by electron beam irradiation. (3) A battery in which electrodes are joined via the polymer solid electrolyte according to 1 or 2 above.

The solid polymer electrolyte of the present invention is formed by impregnating a polyvinylidene fluoride resin molding having a crosslinked structure with an electrolyte or a mixture of an electrolyte and a plasticizer. As explained in the prior art, a solid electrolyte formed by adding an electrolyte and a plasticizer to an ordinary polyvinylidene fluoride linear polymer is an electrolyte and a plasticizer content considering the processability when used in a battery. Is about 70%. The polymer solid electrolyte of the present invention is such an electrolyte,
The feature is that a wide range of contents can be selected without being limited by the plasticizer content. That is, the polyvinylidene fluoride resin molded product of the present invention has a high ionic conductivity and is preferable because it can be used in a composition having an increased amount of electrolyte and plasticizer. Further, the polymer solid electrolyte material of the present invention is also excellent in strength and high temperature stability in a wide composition range.

The constituent elements of the polymer solid electrolyte material of the present invention will be sequentially described below. The polyvinylidene fluoride resin having a crosslinked structure of the present invention will be described. Examples of the polyvinylidene fluoride resin used in the present invention include poly (vinylidene fluoride), poly (hexafluoropropylene-vinylidene fluoride) copolymer, poly (perfluorovinyl ether-vinylidene fluoride) copolymer, poly ( Tetrafluoroethylene-vinylidene fluoride) copolymer, poly (hexafluoropropylene oxide-vinylidene fluoride) copolymer, poly (hexafluoropropylene oxide-tetrafluoroethylene-vinylidene fluoride) copolymer, poly (hexafluoro) Examples thereof include propylene-tetrafluoroethylene-vinylidene fluoride) copolymer, poly (fluoroethylene-vinylidene fluoride) copolymer, and the like, or a mixture of these components.

The polymer solid electrolyte of the present invention is characterized by containing the above-mentioned polyvinylidene fluoride resin and having a structure in which this polyvinylidene fluoride resin is crosslinked.
The crosslinked structure of the present invention is based on the above-mentioned polymer molecules, and is characterized by not containing a crosslinkable monomer unit. When a crosslinkable monomer coexists in the polyvinylidene fluoride resin and is polymerized and crosslinked, an electrochemical side reaction occurs due to the presence of the remaining crosslinkable monomer, which causes deterioration of battery performance, which is not preferable. Although it is possible to remove this residual crosslinkable monomer, the polymer solid electrolyte manufacturing process becomes complicated. Further, in the solid polymer electrolyte containing the crosslinkable monomer unit, depending on the crosslinkable monomer unit, hydrolysis is caused even by an electrochemical side reaction or a small amount of water, which is not preferable.

Here, the crosslinkable monomer is a monomer having two or more polymerizable groups such as vinyl groups and epoxy groups in the molecule, and when contained as a monomer unit, at least one of them contributes to the polymerization. It indicates that Specific examples of such crosslinkable monomers include di- or tri (meth) acrylate esters such as trimethylolpropane trimethacrylate, di- or triallyl compounds such as triallyl isocyanurate, and 1,4-butanediol diglycidyl ether. A di- or triglycidyl compound etc. can be illustrated.

The polyvinylidene fluoride resin usually has a linear structure, and the resin is crosslinked to prepare the matrix polymer of the polyvinylidene fluoride resin of the present invention. Examples of this cross-linking method include irradiation with radiant energy such as electron beams, gamma rays, X-rays, ultraviolet rays and infrared rays,
A method of incorporating a radical initiator for reactive crosslinking, a method of reactively crosslinking reactive groups after alkali treatment (de-HF),
Etc. can be used.

For example, as the crosslinking conditions when using electron beam irradiation, if the irradiation dose is not sufficient, the crosslinking effect will not be sufficient, and if the irradiation dose is too high, the polymer structure will collapse, which is not preferable. This irradiation dose is 5Mrad or more and 100M
It is preferably rad or less, more preferably 5
It is Mrad or more and 80 Mrad or less, and particularly preferably 8 Mrad or more and 50 Mrad or less.

The formation of the crosslinked structure can be confirmed by the solubility in the linear polymer-soluble organic solvent. That is, since the polyvinylidene fluoride resin having the crosslinked structure has a component that does not dissolve in the soluble organic solvent and does not dissolve uniformly, it is possible to determine the formation of the crosslinked structure. The soluble solvent is not limited because it depends on the type of polymer, but for example, N-methylpyrrolidone, chloroform,
It can be determined with a solvent such as dichloromethane, dichloroethane, acetone, tetrahydrofuran, dimethylformamide, dimethylsulfoxide, dimethylacetamide.

As the shape of the polyvinylidene fluoride resin molding of the present invention, any of sheet-like, particle-like, linear, filament, fiber such as staple, woven cloth, non-woven cloth, etc. can be used. The molded body may be produced according to the intended form to be used. As a method for processing the molded body, any of a method of molding and then crosslinking prior to the formation of the crosslinked structure and a method of molding the crosslinked body into a desired shape can be used.

As the structure of the polyvinylidene fluoride resin molding of the present invention, any of a bulk structure, a hollow structure and a porous structure can be used. As an example other than this bulk structure,
Examples thereof include a foam material containing a closed cell structure, a porous material containing a through hole structure or a composite material having a closed cell structure and a through hole structure. The method for producing such a foam material or porous material is not particularly limited, but various known methods can be adopted. For example, in the case of a foam material, the method described in JP-B-4-57704 can be used. That is, a molded body obtained by melt-molding a polymer is partially crosslinked by electron beam irradiation or the like, then impregnated with a foaming agent such as a halogen-based compound or hydrocarbon, and then foamed by a method such as heating to obtain a foamed body. Can be obtained. Also,
For example, if it is a porous material, a method for producing a microfilter or an ultrafilter can be used. For example, the method described in JP-A-3-215535 or the method disclosed in JP-B-61-38207 can be used. 54-
The method described in Japanese Patent No. 16382 can be used. Specific examples thereof include a melting method and a wet method, and the melting method is a method in which a polyvinylidene fluoride-based polymer is melted together with a plasticizer, an inorganic powder and the like, and then press-molded into a flat film shape,
It extracts and removes plasticizers and inorganic powders. In the wet method, a polyvinylidene fluoride-based polymer is dissolved in a solvent together with a surfactant, an additive, etc., and this is immersed in a non-solvent in the form of a liquid film to coagulate it, and the solvent, the surfactant and the addition are added. Agents and the like are removed by washing.

In the present invention, when the polyvinylidene fluoride resin molding is used as a material for holding an electrolyte between electrodes of a battery, it is preferably in a sheet shape, a woven cloth shape, or a non-woven cloth shape. It is also possible to use the polyvinylidene fluoride resin of the present invention as an active material binder when the electrode used in the battery is prepared by coating a particulate active material, and in this case, a particulate, filamentous, staple It is preferably in the form of a shape.

The solid polymer electrolyte of the present invention is formed by impregnating the above polyvinylidene fluoride resin molded product having a crosslinked structure with an electrolyte or a mixture of an electrolyte and a plasticizer. In particular, impregnation and swelling of the electrolyte mixture in the crosslinked polymer leads to high ionic conductivity. Further, when the material to be impregnated is composed of a polymer portion and a pore portion, it is preferable that the pore portion is filled with the electrolyte mixture and the polymer portion is swollen with the electrolyte mixture, thereby providing a high ionic conductivity. A material used for an ordinary battery separator, for example, a polyolefin porous membrane is used in a state where it is not swollen with an electrolyte mixture, and it is used assuming that the separator does not swell with the electrolyte mixture even in the battery structure. However, since the skeleton portion of this separator does not contribute to ionic conduction, it gives only low ionic conductivity as a whole. When the polymer matrix in the polymer solid electrolyte is impregnated and swollen with the electrolyte mixture, the entire polymer matrix can contribute to the ionic conduction, resulting in high ionic conductivity, which is preferable.

The electrolyte content in the polymer solid electrolyte is within a range that allows ion transfer, but is not limited because it varies depending on the type of electrolyte to be impregnated and the type of polymer matrix to be impregnated. The lower limit of the electrolyte content is a requirement that the ionic conductivity is obviously increased by impregnation of the electrolyte, and the ionic conductivity of the polymer solid electrolyte is preferably 10 ^-10 S / cm or more. . In addition, when the electrolyte content is high, the carrier ion concentration capable of ion transfer is increased, which is preferable as a material having high ionic conductivity, but in a solid polymer electrolyte having an extremely high electrolyte content, ionic dissociation is suppressed and ionic conductivity decreases. Will end up. Further, the electrolyte is usually fragile by itself, and when the electrolyte content is extremely high, it lowers the mechanical strength, so that when used in a battery as an ion transfer medium, formability, processability, and structural stability may be impaired. Absent. Therefore, the electrolyte content range in the polymer solid electrolyte is 1 with respect to the impregnated polymer solid electrolyte.
It is in the range of wt% to 90 wt%, preferably in the range of 2 wt% to 85 wt%, and more preferably in the range of 3 wt% to 80 wt%.

As the electrolyte used in the present invention, any of organic acids, organic salts, inorganic acids and inorganic salts can be used. Examples of this include tetrafluoroboric acid, perchloric acid, sulfuric acid, phosphoric acid, hydrofluoric acid, inorganic acids such as hydrochloric acid, trifluoromethanesulfonic acid, trifluoropropylsulfonic acid, bis (trifluoromethanesulfonyl) imidic acid, acetic acid,
Examples thereof include organic acids such as tylfluoroacetic acid and propionic acid, and metal salts of these inorganic acids and organic acids. These may be used alone or as a mixture of a plurality of electrolytes. Further, a perfluorosulfonic acid type polymer, a perfluorocarboxylic acid type polymer, or a metal salt thereof can be used as the electrolyte of the present invention. As the cation of these electrolytes, one kind of cation selected from protons, alkali metal cations, alkaline earth metal cations, transition metal cations, rare earth metal cations, and the like can be used, or a plurality of cations can be mixed and used.

The cation species will depend on the intended use. For example, when the solid polymer electrolyte of the present invention is used in a lithium battery, it is preferable to use a lithium salt as an electrolyte to be added. In particular, when used in a lithium secondary battery, it is preferable to select a lithium salt that is rich in electrochemical stability as the electrolyte because it is necessary to repeatedly charge and discharge, and examples of this include CF ₃ SO ₃ Li and C ₄ F ₉ SO. ₃
Li, (CF ₃ SO ₂ ) ₂ NLi, LiBF ₄ , LiP
F ₆ , LiClO ₄ , LiAsF _{6 and the} like can be mentioned.

Further, the ionic dissociation of the electrolyte impregnated with the solid polymer electrolyte of the present invention is promoted and the impregnation property of the electrolyte is enhanced.
A plasticizer may be contained for the purpose of improving the processability of the solid polymer electrolyte. This plasticizer content is determined in consideration of the mechanical strength of the solid polymer electrolyte, ionic conductivity, etc., but in the solid polymer electrolyte of the present invention, it is compared with the conventionally known linear polyvinylidene fluoride-based solid polymer electrolyte. Moreover, it has a feature that the mechanical strength is not impaired even at a high plasticizer content. The plasticizer content is not limited because it varies depending on the type of plasticizer, the type of polyvinylidene fluoride resin, and the structure, but is not more than 98% by weight of the solid polymer electrolyte. More preferably, it is 97% or less.

Examples of the plasticizer include cyclic carbonates such as ethylene carbonate, propylene carbonate and butylene carbonate, chain carbonates such as dimethyl carbonate, methyl ethyl carbonate and methyl ethyl carbonate, ethers such as tetrahydrofuran and methyl tetrahydrofuran, and γ-butyl. Lactone,
Propiolactone, esters such as methyl acetate, acetonitrile, nitrile compounds such as propionitrile, organic low molecular compounds such as hydrocarbons, silicone oil, oligoethylene glycol, polyethylene oxide, aliphatic etal compounds such as polypropylene oxide, polyacrylonitrile , Polar group-containing high molecular weight organic compounds such as aliphatic polyesters and aliphatic polycarbonates.

The polymer solid electrolyte of the present invention is produced by impregnating and / or swelling the above-mentioned electrolyte and plasticizer with a crosslinked polyvinylidene fluoride resin molding. Next, a battery in which electrodes are joined via the solid polymer electrolyte of the present invention will be described. The battery of the present invention has a structure in which a positive electrode and a negative electrode are joined via the above-mentioned solid polymer electrolyte.

For example, when the battery is a lithium battery, a material capable of inserting and extracting lithium ions is used for the positive electrode and the negative electrode of the electrode. As the positive electrode material, a material having a higher electric potential than the negative electrode, for example, Li _1-x CoO ₂ , L
n _1-x NiO ₂ , Li _1-x Mn ₂ O ₄ , Li _1-x MO ₂
(0 <x <1), M represents a mixture of Co, Ni, Mn, and Fe. ), Li _2-y Mn ₂ O ₄ (0 <y <2), crystalline Li _1-x V ₂ O ₅ , amorphous Li _2-y V ₂ O ₅
(0 <y <2), Li _{1.2-x '} Nb ₂ O ₅ (0 <x'<
1.2) and other oxides, Li _1-x TiS ₂ , Li _1-x M
Organic compounds such as metal chalcogenides such as oS ₂ and Li ₃ -z NbSe ₃ (0 <z <3), polypyrrole, polythiophene, polyaniline, polyacene derivatives, polyacetylene, polythienylene vinylene, polyarylene vinylene, dithiol derivatives, disulfide derivatives A compound can be mentioned.

Further, as the negative electrode, a lower electric potential than the above positive electrode is used.
A material having a unit is used. An example of this is metallic lithium
Aluminum, lithium alloy, magnesium alloy
Metal lithium such as minium-lithium alloy, AlS
b, Mg₂Ge, NiSi₂Intermetallic compounds such as
Carbon-based materials such as fights, cokes, low-temperature baked polymers
Materials, SnM-based oxides (M represents Si, Ge, Pb)
You ), Si_1-yM '_yO_z(M 'is W, Sn, Pb,
Represents B and the like. ) Composite oxide, titanium oxide, iron oxide
Which metal oxide lithium solid solution, Li₇MnN_Four, L
i₃FeN₂, Li_3-xCo _xN, Li_3-xNiN, L
i_3-xCu_xN, Li₃BN₂, Li₃AlN₂, Li
₃SiN₃Ceramics such as nitrides of
It However, the lithium ion is reduced at the negative electrode and the metal
When used as a um, it must be a conductive material.
Therefore, it is not limited to the above.

The positive electrode and the negative electrode used in the battery of the present invention are formed by processing the above materials into a predetermined shape. Either a continuous form or a binder dispersion of powder material can be used in this form. As the former continuous body forming method, electrolytic deposition, electrolytic dissolution, vapor deposition, sputtering, CV
D, melt processing, sintering, compression, etc. are used. In the latter case, the powdery electrode material is mixed with a binder to be molded. As the binder material, polyvinylidene fluoride, polyvinylidene fluoride resin such as poly (hexafluoropropylene-vinylidene fluoride) copolymer, fluorine-based polymer such as polytetrafluoroethylene, styrene-butadiene copolymer, styrene-
Hydrocarbon-based polymers such as acrylonitrile copolymers and styrene-acrylonitrile-butadiene copolymers, polymer precursors, and metals are used, and the polyvinylidene fluoride-based resin having a crosslinked structure of the present invention can also be used as a binder. A current collector may be provided on the electrode composed of the positive electrode or the negative electrode with a material having low electric resistance.
Further, the electrolyte or / and the plasticizer, which are the constituent elements of the present invention, can be introduced into a battery having a structure of positive electrode / solid polymer electrolyte / negative electrode by a method such as impregnation or diffusion.

In the case of a lithium battery, the form of the battery has a structure in which a positive electrode and a negative electrode are joined via a solid polymer electrolyte. For example, a sheet-shaped, roll-shaped, or folded structure can be formed with a unit of positive electrode / polymer solid electrolyte / negative electrode in which a sheet-shaped positive electrode, negative electrode, and solid polymer electrolyte are sequentially laminated. Also, the electrodes of the battery units may be connected in parallel or /
It is also possible to use an assembled battery connected in series.
In particular, in the case of a solid electrolyte battery, since the series connection structure is simple, it is possible to increase the voltage by the number of stacked series connection. In addition, if necessary, current is taken out to the battery electrode, external terminal connection part for injection, current voltage control element, functional element to prevent electrode connection at the time of heat generation, prevention of moisture prevention of electrode unit / laminate, protection of structure etc. Layers can also be provided and packaged.

The polymer solid electrolyte of the present invention is not limited to lithium batteries, but also various batteries such as alkaline batteries, lead batteries, nickel-hydrogen batteries, fuel cells, capacitors, electrochemical sensors, electrochromic display devices, and other ions. It can also be applied as a mobile medium,
This is preferable because a product with high industrial value can be provided.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail with reference to the following examples.

[0033]

Example 1 A poly (hexafluoropropylene-vinylidene fluoride) copolymer resin (hexafluoropropylene content 5% by weight) was heat-extruded to give a film thickness of 10
It was formed into a 0 μm sheet. Irradiation dose of 15 Mr to the molded body
After irradiating the electron beam with an ad, the HF gas generated by vacuum drying at 60 ° C. was removed. Immerse the electron beam irradiated polymer sheet in dimethylsulfoxide and heat at 100 ° C for 5
As a result of heating for time and examining the solubility, it was found that the sheet shape was retained. On the other hand, as a result of similarly examining the solubility using a polymer sheet before electron beam irradiation, uniform dissolution was observed. Therefore, it was found that a crosslinked structure was formed in the polymer sheet irradiated with the electron beam. The polymer sheet after electron beam irradiation was treated with lithium tetrafluoroborate (Li
BF ₄ ) ethylene carbonate (EC) / propylene carbonate (PC) / γ-butyl lactone (γ-B)
L) Mixed solvent (EC / PC / γ-BL = 1/1/2) immersed in a solution (LiBF ₄ concentration 1 mol / liter) and then impregnated at a temperature of 100 ° C. for 3 hours to contain a lithium salt. Was dispersed in a polymer sheet to prepare a solid polymer electrolyte. The film thickness after impregnation was 167 μm. Both sides of the polymer solid electrolyte obtained by impregnation are sandwiched by stainless sheets, and the stainless sheets are used as electrodes for AC impedance analysis (EG & G, 398).
Type impedance measuring device, measuring frequency 100kHz ~
1 Hz) and calculated the ionic conductivity from the real part of the complex impedance of the Nyquist plot. As a result, the ionic conductivity was 2.1 × 10 ⁻³ S / cm.

[0034]

Example 2 A sheet of poly (hexafluoropropylene-vinylidene fluoride) copolymer resin (hexafluoropropylene content 5% by weight) having a film thickness of 50 μm extruded in the same manner as in Example 1 was irradiated with an electron beam ( Irradiation amount 10M
rad), and then impregnated with CFC HFC134a (liquid content 5% by weight), and then heated at 180 ° C. to obtain a film thickness of 72
A white foam having a size of μm (expansion ratio: 3 times) was obtained. The closed cell content of this foam was 68% with respect to the whole foam by an air pycnometer (manufactured by Toshiba Beckman, air-comparison specific gravity meter). The foamed product was mixed with lithium tetrafluoroborate (LiBF ₄ ) ethylene carbonate (EC) / propylene carbonate (PC) / γ-butyl lactone (γ-BL) mixed solvent (EC / PC / γ-).
(BL = 1/1/2) solution (LiBF ₄ concentration 1 mol / l) and then impregnated at a temperature of 100 ° C. for 3 hours to diffuse a mixed solvent containing a lithium salt into a polymer sheet to obtain a polymer solid. An electrolyte was prepared. The film thickness after impregnation was 120 μm. Both sides of 1 cm square of the solid polymer electrolyte obtained by impregnation are sandwiched by stainless sheets (6 mm wide strips), AC impedance analysis is performed in the same manner as in Example 1 using the stainless sheets as electrodes, and a real part of complex impedance of Nyquist plot. As a result of calculating the ionic conductivity from, the ionic conductivity was 3.9 × 10 ⁻³
It was S / cm. Further, in a state where both surfaces of the polymer solid electrolyte sheet are sandwiched by stainless steel sheets, both surfaces are pressed by an alumina plate having a thermocouple embedded therein, and further held by a hydraulic press machine capable of heating, and then an alternating current between stainless steel sheet electrodes. The press die was heated while the impedance was measured to evaluate the temperature dependence of the impedance. Impedance measurement is performed using Hioki Denki LCR meter,
As a result of performing the measurement at a frequency of 1 kHz, the gentle impedance changed in the temperature range from room temperature to 220 ° C. As a result of separating the alumina plate and the stainless steel sheet after the end of the experiment, no deformation of the solid polymer electrolyte was observed. From this, it was found that in the temperature range of at least 220 ° C. or less, melt deformation did not occur and the thermal dimensional stability was excellent.

[0035]

Example 3 The poly (hexafluoropropylene-vinylidene fluoride) copolymer resin (hexafluoropropylene content 5% by weight) used in Example 1 was 22.5% by weight, and polyethylene glycol having an average molecular weight of 200 was 12% by weight. %, Polyoxyethylene sorbitan monooleate (manufactured by Kao Atlas Co., Ltd., trade name Tween 80) at a concentration of 1% by weight was added to a dimethylacetamide solution at 60 ° C.
After heating, the glass plate was coated with a blade having a gap of 100 μm, and then the glass plate was dipped in water at 70 ° C. and dried to prepare a porous film containing through holes. This film thickness is 45 μm, and the volume of pores calculated from the specific gravity is 70%.
Met. The water permeation amount was 40 liter / m ² · hr · atm due to the presence of the through holes. After irradiating the dried porous film with an electron beam at a dose of 20 Mrad, ethylene carbonate (EC) / propylene carbonate (PC)
LiB dissolved in a mixed solvent (mixing ratio; EC / PC = 1)
It was immersed in a 1 mol / liter solution of F ₄ and impregnated at a temperature of 90 ° C. for 3 hours to prepare a solid polymer electrolyte. The ionic conductivity of the obtained solid polymer electrolyte was sandwiched between stainless sheets in the same manner as in Example 1 to perform AC impedance analysis, and the ionic conductivity was calculated from the complex impedance real part of the Nyquist plot. It was 1 × 10 ⁻³ S / cm.

[0036]

Example 4 Lithium cobalt oxide (LiCoO ₂ ; average particle size 10 μm) powder (solid content 85%), carbon black (solid content 8% by weight), polyvinylidene fluoride binder (dry weight 7%) %) As a mixture) dispersed in a polyvinylidene fluoride solution of N-methylpyrrolidone (5% by weight) on an aluminum sheet and dried to form a coating film (positive electrode) having a thickness of 115 μm. On the other hand, N-methylpyrrolidone solution of polyvinylidene fluoride (5% by weight of polymer) was uniformly mixed with needle coke powder having an average particle diameter of 12 μm to prepare a slurry (dry weight mixing ratio; needle coke (92%), polymer). (8%)). The slurry was applied onto a metal copper sheet using a doctor blade to form a coating film (negative electrode) having a dry film thickness of 125 μm. Both sides of the polymer solid electrolyte sheet prepared in Example 1 were sandwiched by sandwiching the positive electrode and the negative electrode prepared as described above on the surface of the coating film to the polymer solid electrolyte to prepare a sheet battery having an electrode size of 4 cm square. Then, the sheet battery was placed in a glass cell with an electrode take-out terminal and filled with argon. Charge and discharge machine (Hokuto Denko 101SM type charge and discharge tester) with the glass cell takeout terminal of this battery
Was connected to and charged and discharged at a current density of 1 mA / cm ² .
Charging is constant current charging (constant potential charging after reaching 4.2V),
The discharge was performed at a constant current of 1 mA / cm ² and a 2.7 V cut. After the charging operation, 4.2V potential convergence was confirmed, and discharging and recharging were able to be repeatedly charged and discharged. The current efficiency of the initial charge / discharge was 79%, and the initial discharge amount was 210 mAh / g per carbon weight of the negative electrode.

[0037]

Example 5 Using the lithium cobalt oxide positive electrode coating film and the carbon negative electrode coating film prepared in Example 4, the positive electrode and the negative electrode were sandwiched on both sides of the polymer solid electrolyte prepared in Example 2 in the same manner as in Example 4. A sheet-shaped electrode laminate was prepared. A stainless steel sheet take-out terminal was connected from the collector side of each electrode, and then laminated with a polyethylene / aluminum / polyethylene terephthalate laminated sheet (film thickness 50 μm) to produce a sheet battery. The stainless sheet terminal was connected to a charging / discharging machine in the same manner as in Example 4 to perform charging / discharging. This battery was confirmed to have 4.2V potential convergence by the charging operation, and could be repeatedly charged and discharged by discharging and recharging. The current efficiency of the initial charge / discharge was 80%, and the initial discharge amount was 212 mAh / g per weight of the negative electrode carbon.

[0038]

Example 6 Poly (hexafluoropropylene-vinylidene fluoride) copolymer resin used in Example 1 (hexafluoropropylene content 5% by weight) was added to pellets at 20 Mra.
Electron beam irradiation was performed at the irradiation dose of d, and after irradiation, pulverization treatment was performed in liquid nitrogen to prepare a powder having an average particle size of 5 μm. The prepared polymer powder was dispersed in N-methylpyrrolidone together with lithium cobalt oxide to form a slurry (polymer content 10% by weight as solid content, LiCoO ₂ content 90% by weight). This slurry was applied onto an aluminum sheet and dried to prepare a lithium cobalt oxide coating film having a dry film thickness of 125 μm. Using the coating film as a positive electrode and the negative electrode coating film used in Example 4, each electrode was sandwiched on both sides of the solid polymer electrolyte sheet prepared in Example 2 to prepare a battery laminate. Then, in the same manner as in Example 5, a polyethylene / aluminum / polyethylene terephthalate laminated sheet (film thickness 50 μm) was laminated to produce a sheet battery. As a result of charging / discharging by connecting the stainless steel sheet terminal to a charging / discharging machine in the same manner as in Example 4, it was confirmed that the battery had a potential convergence of 4.2 V by charging operation, and repeated charging / discharging by discharging and recharging was possible Met. The current efficiency of the initial charge / discharge was 77%, and the initial discharge amount was 208 mAh / g per carbon weight of the negative electrode.

[0039]

Comparative Example 1 Polymer sheet extruded in Example 1
In the same manner as in Example 1, but without electron beam irradiation
Lithium tetrafluoroborate (LiBF_Four) D
Tylene carbonate (EC) / Propylene carbonate
(PC) / γ-butyl lactone (γ-BL) mixed solvent
(EC / PC / γ-BL = 1/1/2) Solution (LiBF
_Four(Concentration 1 mol / liter),
As a result of impregnation at temperature for 3 hours, the polymer sheet became the impregnating liquid.
It dissolved uniformly. Therefore, impregnate the polymer sheet at 60 ℃.
Impregnated for 12 hours with a mixed solvent containing a lithium salt.
Preparation of polymer solid electrolyte by diffusing into polymer sheet
did. Both polymer sheets obtained by impregnation at 60 ° C
The surface is sandwiched between stainless sheets,
AC as an electrode for AC impedance analysis
Ion transmission from the real part of the complex impedance of the plot
As a result of calculating the conductivity, the ionic conductivity is 4 × 10.^-FiveS / cm
I found out.

[0040]

Comparative Example 2 The same procedure as in Example 3 was performed on the porous membrane prepared in Example 3 without electron beam irradiation, and lithium tetrafluoroborate (LiBF ₄ ) was mixed with ethylene carbonate (EC) / propylene carbonate (PC). Solvent (EC / PC = 1/1) solution (LiBF ₄ concentration 1 mol
/ L) at room temperature to prepare a polymer solid electrolyte. Both sides of the porous membrane obtained by room temperature impregnation were sandwiched by stainless steel sheets, and AC impedance analysis was performed using this stainless steel sheet as an electrode, and the ionic conductivity was calculated from the complex impedance real part of the Nyquist plot. It was found to be × 10 ^-4 S / cm. Then, when this porous membrane was immersed in the same LiBF ₄ solution at 90 ° C., it was completely dissolved in 10 minutes.

[0041]

Comparative Example 3 Poly (hexafluoropropylene-vinylidene fluoride) copolymer resin used in Example 1 (hexafluoropropylene content 5% by weight) Pellets 10 g (without electron beam irradiation), acetone 40 g and lithium Tetrafluoroborate (LiBF ₄ ) ethylene carbonate (EC) / propylene carbonate (PC)
/ Γ-butyl lactone (γ-BL) mixed solvent (EC / P
C / γ-BL = 1/1/2) solution (LiBF ₄ concentration 1 m
30 g of ol / liter) was mixed and heated at 60 ° C. for 6 hours to prepare a uniform solution. The solution was applied on a glass plate under an argon gas atmosphere, and then acetone was evaporated to prepare a polymer sheet. Polymer sheet obtained by impregnation Both sides of 1 cm square were sandwiched by stainless sheets (6 mm wide strips), and this stainless sheet was used as an electrode for AC impedance analysis in the same manner as in Example 1 to obtain ions from the complex impedance real part of the Nyquist plot. As a result of calculating the conductivity, the ionic conductivity is 0.9 × 10 ^−3.
It was found to be S / cm. In addition, while sandwiching the stainless steel sheets on both sides of the polymer solid electrolyte sheet, both sides were pressed by an alumina plate having a thermocouple embedded therein, and further held by a heatable hydraulic press machine, and then the AC impedance between the stainless sheet electrodes was measured. The temperature dependence of the impedance was evaluated by heating the press die while performing. The impedance measurement was performed at a measurement frequency of 1 kHz using a Hioki Denki LCR meter.
Although the impedance changed gently in the temperature range of 0 ° C, a drastic resistance decrease was observed at 110 ° C. At the same time, exudation of the melt was observed between the electrodes, and it was found that the resistance was decreased due to the thinning of the polymer sheet due to melt deformation. As a result of separating the alumina plate and the stainless steel sheet after the end of the experiment, it was found that the solid polymer electrolyte was in a melt flow and was poor in thermal stability.

[0042]

The polymer solid electrolyte of the present invention is a material having high ionic conductivity and excellent high temperature structural stability.
A battery constructed using this has excellent battery characteristics and safety.

[Brief description of drawings]

FIG. 1 is an impedance-temperature curve of a polymer solid electrolyte of Example 2.

FIG. 2 is an impedance-temperature curve of a polymer solid electrolyte of Comparative Example 3.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI H01M 10/40 H01M 10/40 B (56) Reference JP-A-9-293518 (JP, A) (58) Fields investigated ( Int.Cl. ⁷ , DB name) H01B 1/06 C08J 9/40 C08L 27/16 H01M 6/18 H01M 10/40

Claims (3)

(57) [Claims] 1. A polyvinylidene fluoride resin is crosslinked.
A polymer solid electrolyte obtained by impregnating and / or swelling an electrolyte or a mixture of an electrolyte and a plasticizer into a polyvinylidene fluoride resin molded body containing no bulky crosslinkable monomer unit. 2. The solid polymer electrolyte according to claim 1, wherein the polyvinylidene fluoride-based resin is a polyvinylidene fluoride-based resin molded product crosslinked by electron beam irradiation. 3. A battery characterized in that electrodes are joined via the solid polymer electrolyte according to claim 1 or 2.