JP2002190320A - Solid electrolyte and battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous secondary battery having excellent battery performance and high discharge capacity retention, a solid electrolyte suitable for use therein, and a non-aqueous secondary battery using the same. SOLUTION: In a solid electrolyte composed of an electrolyte solution and a crosslinked polymer, the ratio of the electrolyte solution in the solid electrolyte and the crosslink density of the polymer component are shown in region 1, region 2 or region 3 in FIG. Solid electrolyte within the specified range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolyte comprising an electrolyte solution containing a salt compound exhibiting ionic conduction in a crosslinked polymer, and an electrochemical device using the solid electrolyte. In particular, a solid electrolyte contained in a crosslinked polymer of a nonaqueous electrolyte in which a lithium salt is dissolved, and a lithium secondary battery using the same.

[0002]

2. Description of the Related Art In recent years, storage batteries with higher energy density have been demanded for miniaturization and portability of portable telephones, video cameras, notebook personal computers and the like, or practical use of electric vehicles and the like. A non-aqueous electrolyte battery capable of outputting 3 V or more by using an electrolyte in which a salt is dissolved in an organic solvent is expected. A typical example is a lithium-ion secondary battery that is already on the market. The positive electrode of these non-aqueous electrolyte batteries is L
a spinel structure compound such as iMn ₂ O ₄ or generally Li
A lithium-containing transition metal composite oxide having an α-NaFeO ₂ structure represented by MO ₂ can be used. Where M
Is a single or two or more metal elements selected from Co, Ni, Al, Mn, Ti, Fe and the like. Further, metal oxides such as MnO ₂ and V ₂ O ₅ into which lithium can be inserted, metal sulfides such as TiS ₂ and ZnS ₂ , π-conjugated polymers such as polyaniline and polypyrrole having electrochemical redox activity, It is also possible to use a disulfide compound utilizing the formation and cleavage of a sulfur-sulfur bond in the molecule. On the other hand, as the negative electrode, metallic lithium, various lithium alloys, various metal oxides such as SnO ₂ , or a carbon material capable of inserting and extracting lithium can be used. As a carbon material, naturally produced graphite or an organic material is fired at a high temperature of 2,000 ° C. or more, and a graphite-based carbon material having a flat potential characteristic with a developed graphite structure or an organic material at a relatively low temperature of 1000 ° C. or less. Baking,
A coke-based carbon material or the like that can be expected to have a larger charge / discharge capacity than a graphite-based material is used.

At present, as a combination of a positive electrode and a negative electrode in a lithium ion secondary battery currently on the market, a lithium-containing transition metal composite oxide such as LiCoO ₂ or LiMn ₂ O ₄ is used for the positive electrode, and various carbons are used for the negative electrode. Materials are often used. These batteries average 3.6-
It operates at a voltage of about 3.8V. In some cases, powder or fibrous metal or carbon is added to the electrode for the purpose of improving the electron conductivity of the electrode. As metal,
Copper, silver, aluminum and the like can be used, and as carbon, graphite, carbon black, acetylene black, Ketjen black and the like can be used. As a method for manufacturing an electrode, a small amount of a polymer material serving as a binder, for example, polyvinylidene fluoride (PVDF) dissolved in a solvent such as 1-methyl-2-pyrrolidone, and various active materials and After applying an electrode mixture made into a paste by dispersing a conductive auxiliary agent composed of fine powder of carbon or metal to both sides or one side of a metal foil having a thickness of several tens of μm serving as an electrode core material, an organic solvent is removed. The way to do it is widely done. Examples of other binders include ethylene-propylene-diene terpolymer (EP
Rubber), various fluororubbers such as vinylidene fluoride-propylene copolymer and vinylidene fluoride-hexafluoropropylene copolymer. Others include polytetrafluoroethylene (PTFE), polymer latex and dispersion such as SBR and NBR, sodium polymethacrylate and carboxymethyl cellulose (CM).
There is also a method of using a binder obtained by adding a water-soluble polymer such as C) as a thickener as a binder. The electrode core material is also called a current collector, and an aluminum foil is generally used on the positive electrode side, and a copper foil is generally used on the negative electrode side. In addition, in the electrode immediately after coating and drying, the solvent may be removed during the drying process, so that voids may be formed in the electrode and the filling rate may be too low. Thereby, the contact between the particles in the electrode mixture becomes weak, and the electron conductivity becomes insufficient. Therefore, in many cases, the filling rate of the electrode is increased by a roll press or the like to improve the electron conductivity of the electrode.

[0004] Usually, the positive electrode and the negative electrode produced by the above-described method are layered so as not to lose their shapes through a polymer microporous film serving as a diaphragm so that they are opposed to each other. After firmly winding it up, inserting it into a metal battery can and finally putting in the electrolyte, caulking it by a mechanical method or completely sealing it by laser welding etc. Manufactured. Here, a microporous membrane made of polypropylene or polyethylene is used as the diaphragm, and a non-aqueous electrolyte in which a lithium salt is dissolved in an organic solvent is usually used as the electrolyte. As the organic solvent, ethylene carbonate, propylene carbonate, γ-butyrolactone, sulfolane, diethyl carbonate, dimethyl carbonate, dimethoxyethane, diethoxyethane, 2-
Methyl-tetrahydrofuran, various glymes, etc. may be used alone or in combination of two or more. Lithium salt has high ionic conductivity when made into electrolyte,
Alternatively, lithium hexafluorophosphate (LiPF) is mainly used because it is electrochemically stable in the use potential range of the battery.
₆ ), lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ) and the like are often used. In recent years, various imide salts such as lithium bis (trifluoromethylsulfonyl) imide (Li (CF ₃ SO ₂ ) ₂ N) have been studied. In non-aqueous electrolyte batteries as described above, such as lithium ion secondary batteries, high capacity and long life are desired, but on the other hand, improvement of safety and freedom of battery shape are required. From the viewpoint of improvement and the like, utilization of a solid or solid electrolyte has been studied. In other words, instead of an electrolyte having fluidity, an electrolyte prepared by dissolving a lithium salt in a polymer compound to have ionic conductivity, or a gel in which the fluidity is suppressed by holding the electrolyte in a polymer crosslinked structure The use of electrolytes in the form of an electrolyte, inorganic ceramics having ionic conductivity, glass, and the like has been studied. By sandwiching a film made of such a solid electrolyte between a positive electrode and a negative electrode to form a battery, it is possible to prevent electrolyte leakage and to make the battery shape itself into a film shape. .

Among such solid or solid electrolytes, gel electrolytes containing an electrolytic solution have been studied in many cases because of their ionic conductivity and film-forming properties at room temperature. That is, in order to operate as a battery at room temperature, it is necessary that the ionic conductivity at room temperature be on the order of 1 mS / cm or a value equivalent thereto, and that a thin film can be formed. Therefore, at present, it is most practical to use a gel electrolyte in which an electrolytic solution is made into a gel with a polymer crosslinked structure. The first conceivable gel electrolyte is a system in which a linear high molecular weight polymer is plasticized with an electrolytic solution. That is, a method of dissolving a polymer in an electrolytic solution at a high temperature, returning to room temperature after forming a film, and gelling, or further diluting a combination of the polymer and the electrolytic solution with a low-boiling solvent so as to have fluidity, and then having a low boiling point It is produced by evaporating a solvent to form a film.In such a system, although the polymer does not have a chemical cross-linking structure, it has extremely high viscosity, or a part of the electrolyte and the polymer component Fluidity is lost due to physical cross-linking due to phase separation, and it can be handled substantially as a solid. Specifically, a gel electrolyte in which a polymer having a relatively large molecular weight such as polyacrylonitrile, polyethylene oxide, ethylene glycol-propylene glycol copolymer, polymethyl methacrylate, or polyvinylidene fluoride is plasticized with an electrolyte is known. I have. These systems are
There are drawbacks such as the necessity of handling a highly viscous solution in production and the lack of a chemical cross-linking structure which causes fluidization at high temperatures.

Next, there is a method of polymerizing various (meth) acrylate monomers and vinyl monomers. That is, this is a method in which a monomer having a polymerizable double bond is dissolved in an electrolytic solution, and the monomer is polymerized using heat, light, radiation, or a radical initiator. At this time, by partially adding a polyfunctional monomer, a crosslinked structure is formed during the polymerization reaction, the fluidity is lost, and the entire system can be solidified while holding the electrolytic solution. Examples of such materials include methyl methacrylate and ethyl methacrylate.
Monomers such as (meth) acrylate monomers, vinyl acetate, styrene and derivatives thereof are dissolved in an electrolytic solution and polymerized. In this case, polyfunctional ethylene glycol dimethacrylate or ethylene dimethacrylate is used. And co-polymerize them to form a crosslinked structure and lose the fluidity of the entire system. In addition, those obtained by polymerizing a macromonomer such as polyethylene glycol ethyl ether methacrylate or polyethylene glycol dimethacrylate in an electrolytic solution are known. Examples of such polymerization methods include photopolymerization by irradiation with ultraviolet rays or electron beams, or thermal polymerization in the presence of a radical initiator such as dibenzoyl peroxide or azobisisobutyronitrile. Similarly, there is a method of solidifying the entire system by forming a crosslinked structure using a polyaddition type chemical reaction such as urethane or epoxy reaction. When preparing a solid electrolyte by polymerization or chemical crosslinking, it is not necessary to use a highly viscous solution, and it is excellent in stability and liquid retention because it solidifies in the final shape and has a chemical crosslinked structure. Also has high heat resistance. By impregnating the undiluted solution in advance into a porous body, a nonwoven fabric, or the like and solidifying it, it is also possible to obtain a thin and strong electrolyte membrane.

In addition, there is a method in which a film is prepared in advance from a polymer having a high affinity for an electrolytic solution, and the electrolytic solution is swelled to impart ionic conductivity. Specifically, a polyvinylidene fluoride copolymer,
It has been studied in systems such as acrylonitrile-butadiene rubber. In these systems, the polymer film may be made porous or crosslinked in advance in consideration of an increase in strength or a change in volume after swelling. These systems are inferior in liquid retention because they are later impregnated with an electrolytic solution, and have a problem of seepage of the electrolytic solution over time.

[0008]

As for a solid electrolyte such as a gel electrolyte produced as described above, it is generally considered that the higher the ionic conductivity, the better. However, what really matters is not the performance of the electrolyte itself, but the performance of the battery when the solid electrolyte is incorporated. An object of the present invention is to obtain an electrolyte that can obtain a high-performance battery when actually incorporated into a battery, not only as an electrolyte alone.

[0009]

According to the present invention, as will be described in detail in the present specification, the performance of a battery when a solid electrolyte is actually assembled into a battery is simply the ion of the solid electrolyte itself. It has been found that not only the value of conductivity and the like but also the balance between the electrolyte solution / polymer component ratio contained in the solid electrolyte and the crosslink density of the crosslinked polymer is important. That is, in the battery using the solid electrolyte, it was found that the battery performance was determined not only by the apparent ionic conductivity of the electrolyte itself but by the crosslinking density of the polymer crosslinked structure. For example, as shown in Tables 1 and 2 below, when the same electrolyte solution / polymer component and almost the same ionic conductivity are used in an actual battery, the crosslink density of the polymer crosslinked structure is When it exceeds a certain level, the battery performance is improved. More specifically, a high-concentration electrolyte component in the solid electrolyte and a high ion conductivity can provide a high-performance battery with a relatively low cross-linking density, but a low electrolyte component ratio and a low ionic conductivity. Even if the battery is relatively low, a high-performance battery can be obtained by introducing a highly crosslinked structure into the polymer crosslinked structure. The present invention has been made based on these findings,
(1) In the solid electrolyte composed of the electrolyte solution and the crosslinked polymer, the ratio of the electrolyte solution in the solid electrolyte and the crosslink density of the polymer component are shown in region 1, region 2 or region 3 in FIG. Solid electrolyte characterized by being in the range,
(2) A polymer prepared by dissolving a low-molecular compound that can be polymerized by heat, light, radiation, a polymerization initiator, or the like in an electrolytic solution in advance, and then performing a polymerization reaction to form a crosslinked polymer. The solid electrolyte according to item (1),
(3) In the item (1) or (2), the cross-link density of the cross-linked polymer is reduced by a combination of a low-molecular compound having a single reaction point and a low-molecular compound having two or more reaction points. (4) The polymerizable low molecular compound is a (meth) acrylate monomer or a combination of a plurality of (meth) acrylate monomers. (5) The method for producing a solid electrolyte as described in (5), (5) and (4).
(6) A method for producing a solid electrolyte, characterized in that ethylene dimethacrylate is contained in the (meth) acrylate monomer according to (6), wherein the solid electrolyte according to (1) or (2) is used. (7) After processing the positive electrode, the negative electrode, and the membrane into the final battery form,
(3) A method for producing a non-aqueous secondary battery, characterized by performing the method for producing a solid electrolyte according to any one of (5) to (5).

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the crosslink density of a crosslinked structure contained in an electrolyte is defined by Formula 1.
That is, in Equation 1, the molecular weight of F _i monomers, s _i is the number of polymerizable double bonds contained in the monomer molecule, also p _i in mixing ratio per weight of the monomers contained in the electrolyte is there. However, p ₁ + p ₂ + p ₃ +... + P _i = 1.

[0011]

(Equation 1)

(S _i -1) in the formula (1) represents the number of crosslinking points generated from the monomer. For example, a monomer having s _i = 1 such as methyl methacrylate or ethyl methacrylate can only give a linear polymer and does not cause a crosslinking point, and a monomer having s _i = 2 such as ethylene dimethacrylate has a crosslinking point. Is generated. Two crosslink points are generated from one molecule of the triacrylate monomer in which s _i = 3.
Therefore, Equation 1 represents how many crosslinking points are present in the chemical formula amount of the crosslinked structure contained in the electrolyte. In other words, it indicates how many moles of crosslinking points are present per unit mass (g) of the crosslinked structure.
That is, mol is independent of the chemical structure of the polymer according to Formula 1.
The crosslink density can be quantified as a value having a dimension of / g. In the present invention, the crosslinking density of the polymer crosslinked structure is defined by the number of crosslinking points per mass in Formula 1,
By using the density of the polymer crosslinked structure, it is easy to convert to the number of crosslinked points per volume. That is,
The density of the polymer compound is generally 0.7 to 2.4 g / cm.
It is about ³ , and if the substance systems are similar, the density does not greatly change depending on the crosslinking density, and there is essentially no difference in the definition of the crosslinking density by the number of crosslinking points per mass or volume. .

In the present invention, the monomer used as a precursor of the polymer crosslinked structure is preferably a (meth) acrylate monomer. Examples of the s = 1 monomer that can be used in the present invention include methyl methacrylate, ethyl methacrylate, butyl methacrylate,
Examples thereof include methyl acrylate, ethyl acrylate, and butyl acrylate. Examples of the monomer having s = 2 include ethylene dimethacrylate, propylene dimethacrylate, and ethylene acrylate. Examples of the monomer having s = 3 include methane trimethacrylate. The polymerization initiator can be appropriately selected depending on the type of the monomer to be used. For example, an azo compound such as azobisisobutyronitrile and an organic peroxide such as dibenzoyl peroxide can be used.

The crosslinking density is controlled, for example, when a low molecular weight compound is polymerized to form a crosslinked product, a monomer having a single reaction point (that is, a monomer which gives a linear polymer by homopolymerization) is crosslinked. By combining monomers having two or more reaction points acting as an agent and, first, changing the ratio thereof, it is possible to change the cross-link density of the polymer cross-linked product easily produced. For example, as shown in the embodiment of the present invention,
In the combination of methyl methacrylate and ethylene dimethacrylate, the higher the ratio of ethylene dimethacrylate, the higher the crosslink density of the crosslinked polymer. Also, the second
It is also possible to change the crosslink density by changing the molecular weight of a monomer having two or more reaction points as an example of the above, but the former method using a combination of a monomer having a single reaction point and a crosslinker Has a wider range in which the range of the crosslink density, the chemical structure of the polymer chain, and the like can be far controlled.

Further, in the present invention, a battery can be manufactured by preparing an electrolyte stock solution having a composition defined in the claims, forming an electrolyte membrane alone, and then sandwiching the electrolyte membrane between the positive electrode and the negative electrode. However, on the other hand, the positive electrode
For a cell in which the negative electrode has been assembled into the final battery form, for example, a cell that has been processed in advance into a battery structure with a swirling structure or a flat structure, inject the undiluted electrolyte solution in the same way as injecting a normal electrolyte solution, and then heat. A non-leakage battery can be easily manufactured by gelling the undiluted electrolyte solution. That is, in this step, there is no need to form an electrolyte membrane or handle the electrolyte membrane alone, which is substantially the same as a battery manufacturing method using a normal electrolyte. In addition, since the electrolyte is gelled only in the pores of the membrane or the electrode, the electrolyte is excellent in integration as a battery.

The electrolyte itself used in the present invention is the same as the usual one, and the components and compositions are not particularly different. Specifically, as described above, a non-aqueous electrolyte obtained by dissolving a lithium salt in an organic solvent is usually used. As an organic solvent, ethylene carbonate, propylene carbonate, γ-butyrolactone, sulfolane, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, dimethoxyethane, diethoxyethane, 2-methyl-tetrahydrofuran, a mixture of two or more kinds of various limes, etc. Is used. As the lithium salt, lithium hexafluorophosphate (LiP) is mainly used because it has a high ionic conductivity when used as an electrolytic solution, or is electrochemically stable in a range of the use potential of a battery.
F ₆ ), lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), and the like are often used. In recent years, various imide salts such as lithium bis (trifluoromethylsulfonyl) imide (LiN (CF ₃ SO ₂ ) ₂ ) have been studied. Also, after injecting the electrolyte undiluted solution into the cell assembled in the battery form as described above,
In a method for producing a battery by gelling an electrolyte stock solution, it is not desirable to use a macromonomer having a polyalkylene oxide structure such as polyethylene oxide. In other words, when a macromonomer having a large molecular weight is used, the viscosity of the electrolyte stock solution increases,
It becomes difficult to inject the electrolyte stock solution into the pores of the electrode or the battery. Therefore, it is desirable that the monomer contained in the electrolyte stock solution has a molecular weight of 1,000 or less,
00 or less, more preferably 20 or less.
0 or less. In addition, since the polyalkylene oxide structure has a strong interaction with lithium ions, the transport number of lithium ions is low, and the mobility of lithium ions themselves required for charging and discharging the battery is often poor.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments. In addition, comparative examples for further clarifying the effects of the present invention are also shown. In the examples and comparative examples, mainly a positive electrode and a negative electrode attached to both surfaces of the diaphragm,
That is, an integrated battery cell in which the positive electrode / diaphragm / negative electrode was completely integrated was used. 1. Preparation of LiCoO ₂ positive electrode 90 g of LiCoO ₂ (manufactured by Nikko Fine Products) as an active material and graphite powder (manufactured by Lonza, Inc.) as a conductive agent
1 g of 7 g of KS-6) and 3 g of PVDF as a binder.
An electrode mixture paste was prepared by kneading 42 g of -methyl-2-pyrrolidone. This paste is 30μ thick
The electrode mixture after drying on one side of
mg / cm ^2, and 1-methyl-2-pyrrolidone was dissipated by heating at 100 ° C.
Thereafter, a LiCoO ₂ electrode was produced by compression molding using a roll press machine. LiC prepared by this method
The oO ₂ electrode is simply referred to as the positive electrode in the following examples. In the actual production of the battery cell, an electrode having a size of 30 × 30 mm, in which the electrode mixture was partially peeled off and a tab was formed, was used. 2. Manufacture of carbon negative electrode Graphite-based carbon active material (manufactured by Petka, trade name M
F14) 1-g with 94 g and 6 g of PVDF as a binder
An electrode mixture paste was prepared by kneading 70 g of methyl-2-pyrrolidone. This paste is 20μm thick
The weight of the electrode mixture after drying on one side of the copper foil of about 10 mg /
The coating is in cm ^2, and dissipates 1-methyl-2-pyrrolidone by heating at 100 ° C.. Thereafter, a carbon electrode was produced by compression molding with a roll press. The carbon electrode produced by this method is simply referred to as a negative electrode in the following examples. In actual battery cell fabrication, the electrode mixture was partially peeled off and a tab was removed.
An electrode having a size of × 31 mm was used. 3. Preparation of Integrated Battery Cell In a glass bottle, 2.5 g of PVDF powder (VP850, manufactured by Daikin Industries, Ltd.) having an average particle size of 6 μm and 47.5 ethanol
g were mixed and irradiated with ultrasonic waves in an ultrasonic cleaner to disperse the PVDF powder. This PVDF powder dispersion was transferred to a glass Petri dish, and a microporous membrane made of hydrophilic PTFE (JGWP membrane filter manufactured by Japan Millipore Co., Ltd.) cut into a size of 35 × 35 mm was immersed to wet both surfaces to adhere PVDF powder. After that, it was taken out, sandwiched between the positive electrode and the negative electrode, and fixed from both sides with a glass plate. After heating and vacuum drying at 60 ° C. to dissipate the ethanol, the mixture was heated in a nitrogen stream at 200 ° C. for 10 minutes to form PV.
By melting the DF powder, the hydrophilic PTFE microporous membrane was bonded to the positive electrode and the negative electrode, to produce a battery cell in which the positive electrode / diaphragm / negative electrode was completely integrated.

4. Preparation of methyl methacrylate electrolyte solution (molecular weight F _{i =} 100.12, the number of polymerizable double bonds s _{i =} 1) and dimethacrylate ethylene (F
_{i = 198.22, s i = 2} ) and appropriately mixing, both the mass ratio of 97.5: 2.5 to 60: providing a monomer mixture of 40, a volume ratio of 1: 1 of ethylene carbonate and An electrolyte in which 1 M of LiBF ₄ was dissolved in a mixture of diethyl carbonate, a monomer mixture, and an electrolyte in a mass ratio of 10:
90-35: 65. Finally, 1000 ppm of azobisisobutyronitrile was added as a polymerization initiator to prepare an electrolyte stock solution. The dew point of the preparation of the electrolyte stock solution and subsequent handling was -60 ° C.
The test was performed in the following dry air or under an argon atmosphere. 5. Preparation of Electrolyte-Only Membrane A 1 mm-thick silicon rubber with a central portion cut out was used as a spacer, sandwiched between two glass plates, and the periphery was fixed with clips to form a mold for preparing an electrolyte membrane. Subsequently, the above-mentioned electrolyte stock solution was poured into the mold using a syringe. It was placed in a closed vessel and heated at 80 ° C. for 2 hours to solidify the electrolyte stock solution to obtain a 1 mm thick electrolyte single membrane. 6. Measurement of ionic conductivity The ionic conductivity of the above-mentioned electrolyte alone membrane was measured. Specifically, a single electrolyte membrane cut out to a diameter of 16 mm
mm between stainless steel electrodes and S made by Solartron
The measurement was performed by a complex impedance method using an I-1260 electrochemical measurement device. As a result, the real part of the resistance value at 20 kHz is defined as a resistance value based on the ionic conduction of the sample,
The ion conductivity was calculated from the value. The results are summarized in Table 1.

[0019]

[Table 1]

[7] FIG. Battery Conversion An undiluted electrolyte solution was injected into the integrated battery cell under reduced pressure. You
That is, put the integrated battery cell in a pressure-resistant container and dry the whole
Reduce the pressure to about 100 kPa using a vacuum pump,
Introduce the electrolyte solution so that the battery is completely immersed,
3 minutes under reduced pressure and return to normal pressure and leave for 10 minutes
Injection of the electrolyte solution into the integrated battery cell
Was. After that, remove the battery cell from the container and remove the terminal
Made of a large aluminum laminate sheet so that it can enter completely
The battery cell was sealed in the bag. In this state, apply at 80 ° C for 2 hours.
Upon heating, the electrolyte stock solution was solidified. Solidify the electrolyte solution
After removing the battery cell from the bag, the solidified electrolyte
The battery and remove excess electrolyte from the battery cell surface.
After removing the terminal, finally remove the terminal part as shown in Fig. 1.
To reduce the number of aluminum laminate sheet exterior materials
By pressurizing the film, the lithium ion battery
A pond was made. This film-shaped lithium ion secondary battery
1 will be described with reference to FIG.
Thus, the exterior material 4 made of an aluminum laminated sheet is made of Li
CoO ₂Electrolysis consisting of positive electrode 1, carbon negative electrode 2, and battery partition 3
The battery cell impregnated with the liquid is sealed under reduced pressure,
A film-like lithium ion secondary battery is formed. FIG.
Among them, 5 is a positive electrode tab, 6 is a negative electrode tab, and 7 is a heat sealing sealing portion
Show. 8. Charge / discharge cycle test method The charge / discharge cycle test is performed in a 25 ° C constant temperature bath.
The upper limit voltage is set to 4.2V and the maximum current is 6mA for 5 hours
Charged. On the other hand, the discharge is a constant current of 6 mA and the battery voltage is
Until it reached 2.7V. Between charge and discharge
Had a 15 minute pause. In addition, these charge / discharge
Table 2 summarizes the results of the cycle test.

[0021]

[Table 2]

COMPARATIVE EXAMPLE Instead of the solid electrolyte of the example, 1M of a mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 1: 1 was added.
By injecting only the electrolytic solution in which LiBF ₄ is dissolved into the battery cell, and sealing it under reduced pressure in an aluminum laminate sheet outer package in such a manner as to take out the terminal portion as shown in FIG. A battery was manufactured. Test Results First, Table 1 summarizes the ionic conductivity values of the solid electrolyte single membranes of various compositions. As can be seen from Table 1, the electrolyte /
If the ratio of the polymer components is the same, it can be seen that the ionic conductivity is a substantially constant value regardless of the blending of the monomers, that is, the crosslinking density. Next, Table 2 shows the discharge capacity at the 30th cycle of the battery using the solid electrolyte. As can be seen from Table 2, even when the ratio of the electrolyte solution / polymer component was the same, the battery performance was greatly different depending on the cross-link density of the solid electrolyte used. That is, even if the ratio of the electrolyte solution / polymer component and the ionic conductivity were almost the same, the battery performance was significantly improved when the crosslinking density was increased to a certain level or more. In more detail, a battery having a high ratio of the electrolytic solution has good battery performance even at a relatively low crosslinking density. On the other hand, even though the ratio of the electrolytic solution was low and the ion conductivity was poor, a battery excellent in battery performance was obtained by introducing a highly crosslinked structure. Although the battery performance was improved by increasing the crosslink density by a certain level or more, a stable high performance battery was obtained even when the crosslink density was further increased. For example, when the electrolytic solution ratio is 80%, the crosslinking density is 7.
When it is increased to 57 × 10 ⁻⁴ (MMA: EdMA = 85: 15), the discharge capacity at the 30th cycle exceeds 90% with respect to the electrolysis-only battery of the comparative example. Similarly, a high-performance battery has been obtained. The above relationship is summarized in FIG. The symbol 放電 indicates that the discharge capacity at the 30th cycle exceeds 95% of that of the battery using only the electrolytic solution of the comparative example, and the symbol ○ indicates that the discharge capacity was 90% to 95%. And the mark is also 80
% To 90%. Those with a cross are 80% or less. Therefore, it can be said from FIG. 2 that the batteries in the regions 1 to 3 have sufficiently high performance as a battery using the solid electrolyte. In particular, the battery in the region 1 is the most excellent, and the batteries in the region 2 and the region 3 are more excellent. . As described above, the actual battery performance is not determined only by the ionic conductivity of the solid electrolyte itself. As in the present invention, the polymer cross-linked body in the solid electrolyte is changed according to the ratio of the electrolyte solution / polymer component. A high-performance battery in which the cross-link density is adjusted to a certain level or more can be obtained.

[0023]

As is clear from the above Examples and Comparative Examples and their experimental results, the technique of the present invention, that is, the high content contained in the solid electrolyte depending on the ratio of the electrolytic solution / polymer component, is considered. By adjusting the crosslink density of the molecular crosslinked product to a certain level or more, it is possible to obtain electrolytes and batteries (discharge capacity retention) that show excellent characteristics (ion conductivity) when actually used for batteries. Becomes In the present specification, an example of a gel electrolyte made of a combination of methyl methacrylate and ethylene dimethacrylate has been shown, but the scope of the present invention is not limited to this, and the electrolyte contained in the electrolyte The same effect can be expected if the ratio of the polymer component and the crosslink density are within the scope of the claims.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a film-shaped lithium ion battery.

FIG. 2 is a graph showing a relationship between an electrolyte solution ratio and a crosslink density of a polymer component in a solid electrolyte composed of a crosslinked polymer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 LiCoO ₂ Positive electrode 2 Carbon negative electrode 3 Battery diaphragm 4 Aluminum laminate film exterior material 5 Positive electrode tab 6 Negative electrode tab 7 Heat sealing sealing part

Claims (7)

[Claims] 1. In a solid electrolyte comprising an electrolytic solution and a crosslinked polymer, the ratio of the electrolytic solution in the solid electrolyte and the crosslink density of the polymer component are adjusted to the region 1, the region 2 or the region 3 in FIG. A solid electrolyte characterized by being in the range shown. 2. A polymer crosslinked product is prepared by dissolving a low molecular weight compound which can be polymerized by heat, light, radiation, a polymerization initiator or the like in an electrolytic solution in advance and polymerizing it to form a crosslinked polymer. The solid electrolyte according to claim 1, wherein 3. The crosslink density of a crosslinked polymer according to claim 1, wherein a low molecular compound having a single reaction point and a low molecular compound having two or more reaction points are combined. And a method for producing a solid electrolyte. 4. The polymerizable low molecular weight compound is a (meth) acrylate monomer or a combination of plural kinds of (meth) acrylate monomers.
The method for producing a solid electrolyte according to the above. 5. A method for producing a solid electrolyte, wherein the (meth) acrylate monomer according to claim 4 contains ethylene dimethacrylate. 6. A non-aqueous secondary battery using the solid electrolyte according to claim 1. 7. The method for producing a solid electrolyte according to claim 3, wherein the positive electrode, the negative electrode, and the diaphragm are processed into a final battery form. Manufacturing method of secondary battery.