JP2003197260A - Lithium series secondary battery and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a safe solid electrolyte lithium series secondary battery and its manufacturing method wherein high output characteristics is realized over a wide temperature range. <P>SOLUTION: The lithium series secondary battery uses a solid electrolyte as the electrolyte, and this solid electrolyte is phase-separated into a support structure phase containing a polymer cross-linked body and an electrolytic solution phase which contains at least one part of the electrolytic solution and the average diameter converted into a sphere is within the range of 10 μm to 1.0 μm, and a negative electrode swells in the initial charging process after manufacturing the battery, and threby, the thickness of the solid gel electrolyte layer after the completion of the charging is decreased from 95% to 80% against the thickness of the solid electrolyte layer before the charging, and the electrolytic solution contains a bispentafluoroethyl sulfonyl imidelithium as at least one part of an electrolyte salt at the concentration from 0.6 mol/L to 2.0 mol/L. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery and a manufacturing method thereof, and more particularly to a lithium secondary battery using a solid electrolyte and a manufacturing method thereof.

[0002]

2. Description of the Related Art Due to recent rapid technological advances in the field of electronics, higher performance, smaller size, and portable electronic equipment are being accelerated. Conventionally, lead batteries, nickel-cadmium batteries, nickel-hydrogen batteries, etc. have been used as secondary batteries mounted on these electronic devices, but in recent years, carbon materials and lithium alloys capable of absorbing and releasing lithium ions have been used. A lithium-ion secondary battery, which is a combination of a negative electrode used as an active material and a positive electrode using a lithium-containing composite oxide as an active material, has been researched and developed, and has already been partially put into practical use. This type of secondary battery has a high battery voltage and has a higher energy density per unit weight and unit volume than the conventional secondary battery. Therefore, the lithium ion secondary battery is currently receiving the most attention among many secondary batteries.

However, a lithium secondary battery represented by a lithium ion secondary battery has a high energy density, and in many cases, a flammable organic electrolytic solution is used as an electrolyte. Therefore, the problem about the safety is pointed out.

As a lithium-based secondary battery that does not cause such a safety problem, for example, a polymer solid electrolyte (authentic polymer electrolyte) lithium-based secondary battery using a polymer solid electrolyte as an electrolyte is known. ing. However, the ion conductivity of the solid polymer electrolyte is lower than that of the electrolytic solution, so that the lithium secondary battery using the solid polymer electrolyte as the electrolyte can only be charged and discharged at a low current of about 0.5 CA or less. Not done. In fact, US Pat. No. 5,112,512 discloses siloxane-based polymers and US Pat. No. 4,840,856 discloses phosphazene-based polymers with the aim of improving the ionic conductivity of polymer solid electrolytes. However, the ionic conductivity achieved with these polymers is insufficient. For this reason, at present, it is considered most practical to use a gel electrolyte as the electrolyte.

Gel electrolytes are classified into non-crosslinked type and crosslinked type. Regarding the non-crosslinked type gel electrolyte, for example, J.Appl.polm.Sci., 27,4192 (1982) describes ethylene carbonate (EC), propylene carbonate (PC), or N, N-dimethylformamide (DM).
Reported that ionic conductivity as high as 7.6 × 10 ^-4 S / cm was achieved by compounding lithium perchlorate and polyacrylonitrile (PAN) using a solvent such as F) to form a gel electrolyte. is doing. However, since such a gel electrolyte is thermoplastic, it fluidizes in a high temperature range, and the original purpose of forming a gel state in such a temperature range cannot be achieved. Also, Solid State Ionics, 66,97 (199
3) reported an example using polymethylmethacrylate (PMMA), and Macrolecutes, 19,347 (1986) reported an example using polyvinylpyrrolidone (PVP). Since the viscosity of the mixed solution is generally high, it is difficult to impregnate the mixed solution with the electrode after forming the electrode in advance.

Further, regarding non-crosslinked type gel electrolyte, polyvinylidene fluoride (PVDF) reported by Electrochem. Acta, 28, 591 (1983) and Solid State Ionic.
s, 86-88,49 (1996) reported a copolymer of polyvinylidene fluoride and hexafluoropropylene (PVDF-HF
The so-called Bellcore technology using P) has recently been put to practical use. However, PVDF and PVDF-H
The FP copolymer originally has a low swelling property in an electrolytic solution,
As reported by Electrochem.Acta, 45, 1347 (2000), P
PV with higher electrolyte retention than VDF monopolymer
PC that easily swells DF-HEP copolymer and PVDF
Even when a 1 M LiBF ₄ solution using as a solvent is combined, the amount of electrolyte retained is no more than about 30%.

[0007] This amount of liquid retention is completely insufficient to realize the electrode capacity per unit area in a lithium secondary battery using an electrolyte that is currently in practical use,
To compensate for this, it is necessary to make the electrolyte layer thicker, increase the electrode area, or allow syneresis to occur. However, when the electrolyte layer is thickened, the internal resistance of the battery is greatly increased and the charge / discharge current characteristics are significantly deteriorated. The original characteristic of the lithium-based secondary battery, which is energy density, is lost. Further, when the synergic liquid is present, it is not possible to achieve the original purpose of using the gel electrolyte, which is to realize high safety by eliminating the flowable electrolytic solution.

Regarding the cross-linking type gel electrolyte, JP-A-7-6787 describes that a gel electrolyte is obtained by mixing a trifunctional compound with a solvent and an electrolyte salt and then crosslinking the mixture. , A trifunctional acryloyl-modified alkylene oxide (molecular weight of 1500 or more) that requires a chain length of 35 or more as a trifunctional compound. Also, Electrochem.Acta, 3
7,1681 (1982) uses ethylene glycol dimethacrylate and trimethylolpropane methacrylate as ultraviolet rays (U
V) has been reported to form a gel by crosslinking by exposure to light, and US Pat. No. 4,830,939 and Polym.Adv.Tech., 4,205 disclose relatively low molecular weight acrylates having a molecular weight of 1,000 or less. It has been reported a gel obtained by crosslinking a methacrylate oligomer by exposing it to UV or electron beam (EB). In addition, JP-A-9-2
Japanese Patent No. 5384 reports that an ion conductive polymer gel electrolyte obtained by polymerizing an acrylate monomer having a molecular weight of 1,000 or less and a general formula LiX (R ¹ SO ₂ ) _n are combined [above-mentioned general In the formula,
X represents N, C, B, O or C (R ² ) _m , R ¹ represents a halogenated alkyl group having 1 to 12 carbon atoms, and n is 1 to 1
Indicates an integer of 3. R ² is a hydrogen atom or has 1 carbon atom
To 12 alkyl groups, and m represents 1 or 2. ]. Further, U.S. Pat. No. 4,792,504
As an example of combining a thermoplastic polymer and a cross-linking polymer, a mixture of trimethylolpropane triacrylate, ethylene glycol dimethacrylate and high molecular weight polyethylene oxide (PEO) is cross-linked by UV irradiation to form a matrix. Reported a gel electrolyte obtained by impregnating this matrix with an electrolytic solution.

However, when a polymer having a polyalkylene oxide represented by PEO is used, the mobility of the Li ion is extremely low because the interaction between the polyalkylene oxide portion and the Li ion is strong. In addition, when an acrylate monomer or a methacrylate monomer is used, the volume change due to cross-linking is large. Therefore, in order to realize sufficient electrical contact between the positive electrode and the electrolyte layer and between the negative electrode and the electrolyte layer, the electrolyte It is necessary to polymerize the polymer-electrolyte solution impregnated in either the layer or the positive and negative electrodes, increase the degree of tightness by group winding or stack, and store in the battery case, and in this case, at least one or more. Since the solid-solid interface of 1 exists, it becomes difficult to form a good interface.

Further, the disclosure of Japanese Patent Application Laid-Open No. 9-25384 mentioned above is a technique focused on obtaining a homogeneous phase gel rich in elasticity, and this homogeneous phase gel has a molecular structure in a crosslinked polymer. Contains electrolyte at a level. When such a homogeneous gel is used in a battery, in addition to steric hindrance due to anion clusters, it is necessary for lithium ion clusters having a predetermined size to migrate in an electrolytic solution held in a complicated and intricate fine network structure. Therefore, the DC resistance of the battery increases, and high voltage characteristics cannot be realized.

Further, the following problems are associated with the cross-linking type gel electrolyte. The polymerization reactions used to form cross-linked gel electrolytes include photopolymerization using ultraviolet light and electron beams, and thermal polymerization in the presence of radical generators such as dibenzoyl peroxide and azobisdibutyronitrile. However, in the case of the photopolymerization of the former, polymerization is difficult in the battery because the light is shielded and dimmed by the battery case, and the manufacturing process of the battery is limited. Moreover, in this case, since at least one solid-solid interface exists, it is difficult to form a good interface. Also, in the latter case of thermal polymerization, it is necessary to sufficiently decompose the radical generator, and thus it is necessary to expose each constituent element of the battery to a high temperature. Therefore, it is necessary to optimize the constituent elements of the battery.

There is also a problem common to the non-crosslinked type and crosslinked type gel electrolytes described above. The gel electrolyte is a technique for solidifying a liquid electrolyte, but the type of electrolyte salt that can be used is limited by the battery configuration, gel polymerization method, and the like. For example, lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), and the like are used as the electrolyte salt of the lithium secondary battery. Since LiPF ₆ has a property of corroding aluminum, it is difficult to use it in a battery using aluminum or an aluminum alloy for the positive electrode current collector, the positive electrode tab, the positive electrode terminal and the like. In addition, LiBF ₄ easily decomposes at the potential at which lithium ions intercalate in the graphite negative electrode, and LiPF 4
_{No. 6} is not suitable for a battery intended for high temperature use because of its low thermal stability, and thermal polymerization at a relatively high temperature (60 ° C. or higher) cannot be performed, so that the manufacturing process and battery configuration are limited.

The above-mentioned Japanese Laid-Open Patent Publication No. 9-25384 discloses aluminum and aluminum alloys and the general formula LiX.
It discloses that the compound represented by (R ¹ SO ₂ ) _n is used at the same time, but mentions that it is necessary to use an inhibitor to prevent corrosion of aluminum or an aluminum-based alloy. There is. However, when LiPF ₆ or LiBF ₄ exemplified as an inhibitor is used, the inhibitors themselves are affected by heat or decomposed at a low potential, which adversely affects the battery characteristics.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and is a solid electrolyte lithium secondary battery which is safe and capable of realizing high output characteristics in a wide temperature range, and a method thereof. It is intended to provide a manufacturing method.

[0015]

In order to solve the above-mentioned problems, the present invention provides a positive electrode, a negative electrode, and an electrolyte supporting material which is interposed between the positive electrode and the negative electrode and electrically insulating, and the electrolyte. A solid electrolyte layer comprising a solid electrolyte supported by a support material is provided, the solid electrolyte comprises an electrolytic solution containing a non-aqueous solvent and an electrolyte salt, and a polymer crosslinked body, and the solid electrolyte Is phase-separated into a supporting structure phase containing the cross-linked polymer and an electrolyte solution phase containing at least a part of the electrolyte solution and having an average diameter converted into spheres of 10 μm to 1.0 μm, The negative electrode expands during the first charging process after the assembly is completed, so that the thickness of the solid electrolyte layer after the charging is 95% to 80% of the thickness of the solid electrolyte layer before the charging. %, The electrolyte is the electrolyte salt Bispentafluoroethylsulfonyl imide lithium as a part of at least 0.6 mo
Provided is a lithium-based secondary battery, which is characterized by containing at a concentration of 1 / L to 2.0 mol / L.

Further, the present invention comprises a positive electrode, a negative electrode, and an electrolyte support material which is interposed between the positive electrode and the negative electrode and is electrically insulating, and a solid electrolyte supported by the electrolyte support material. A solid electrolyte layer, wherein the solid gel electrolyte is a method for producing a lithium-based secondary battery comprising an electrolytic solution containing a non-aqueous solvent and an electrolyte salt and a polymer crosslinked body, wherein the positive electrode and the Forming an electrode group by interposing the electrolyte supporting material between the negative electrode, a step of housing the electrode group in a container and injecting the electrolytic solution and a monomer into the container, and the monomer At least one of a supporting structural phase containing the polymer crosslinked body and the electrolytic solution, wherein the polymer crosslinked body is produced by thermally polymerizing the polymer, thereby obtaining the solid electrolyte. Contains a part and into a sphere The average diameter of the Sun 10μm~1.0
It is formed into a structure that is phase-separated into an electrolyte solution phase in the range of μm, and expands as the negative electrode in the first charging process after completion of assembly, so that the thickness of the solid electrolyte layer after the charging is increased. Is reduced to 95% to 80% with respect to the thickness of the solid electrolyte layer before charging,
The electrolytic solution contains lithium bispentafluoroethylsulfonylimide at least as a part of the electrolyte salt.
Provided is a method for producing a lithium-based secondary battery, which is characterized by containing at a concentration of 6 mol / L to 2.0 mol / L.

The inventors of the present invention have first explained that the conventional solid electrolyte battery is inferior in output characteristics to the electrolytic solution battery.
We focused on the gel electrolyte structure. Conventionally, regarding gel electrolyte batteries, the above-mentioned Bellcore technology (using PVDF)
Except as described in JP-A-9-24384,
Research has been conducted with a focus on how to enhance ionic conductivity while assuming that the gel electrolyte is a “homogeneous phase gel” in order to secure mechanical strength.
On the other hand, the present inventors have taken steps from such a premise, and play a role of giving a gel electrolyte a supporting structure phase that plays a role of imparting mechanical strength to the gel electrolyte, and a role of imparting ion conductivity to the gel electrolyte. By having a structure that is phase-separated from the electrolyte solution phase and having a sufficiently large size for each electrolyte solution phase, it is possible to cause migration of ions by a mechanism substantially similar to that of the electrolyte solution battery, and a solid gel electrolyte battery. It was thought that it was possible to remarkably improve the output characteristics of, and the effect was actually confirmed.

When the gel electrolyte has a structure in which the supporting structure phase and the electrolytic solution phase are separated in this way, the ionic conductivity of the solid electrolyte largely depends on the size of the electrolytic solution phase. That is, when the size of the electrolyte solution phase is excessively small, the ion transport mechanism in the electrolyte becomes similar to the ion transport mechanism in the homogeneous phase gel, so that the above-described effect of phase separation is hardly obtained. According to the experiments by the present inventors, the above effect could be obtained by setting the average diameter converted into spheres of the electrolyte solution phase to 1.0 μm or more.

Even in the conventional homogeneous phase gel, it can be considered that the gel electrolyte is phase-separated into a supporting structure phase and an electrolytic solution phase from an extremely microscopic viewpoint. However, the size of such an electrolytic solution phase is much smaller than the above lower limit value, and it can be considered that a substantially uniform phase is formed. Such a difference can be confirmed not only by actually measuring the size of the electrolytic solution phase, but the gel electrolyte used in the conventional gel electrolyte battery is transparent, whereas it is used in the present invention. It can be confirmed from the fact that the solid electrolyte to be formed is clouded due to light scattering at the interface between the supporting structure phase and the electrolytic solution phase.

The average diameter converted into spheres of the electrolytic solution phase also affects the liquid retention of the solid electrolyte. That is, when the average diameter converted into spheres of the electrolyte solution phase is excessively large, the electrolyte solution may seep out and the safety may be reduced. According to the experiments by the present inventors, in order to realize high liquid retention,
It has been found that it is preferable to set the average diameter converted into spheres of the electrolytic solution phase to 10 μm or less.

When the electrolyte is phase-separated into a supporting structure phase and an electrolytic solution phase, the ionic conductivity and liquid retention of the solid electrolyte also depend on the volume ratio of the electrolytic solution phase to the solid electrolyte. When the solid electrolyte is produced under the condition that the average diameter of the sphere of the electrolyte solution phase is within the above range, the volume ratio of the electrolyte solution phase to the solid electrolyte is usually within the above range.

To make the solid electrolyte into a phase-separated structure, for example, its crosslink density may be increased. Further, the average diameter converted into spheres of the electrolytic solution phase and the volume ratio of the electrolytic solution phase to the solid electrolyte are the above-mentioned crosslinking density and the ratio of the electrolytic solution to the polymer crosslinked body (or the monomer as the raw material) Controllable by. Furthermore, the “average diameter of the electrolytic solution phase converted into spheres” and the “volume ratio of the electrolytic solution phase to the solid electrolyte” can be obtained from, for example, a micrograph of the solid electrolyte.

The solid electrolyte used in the present invention is usually
It tends to be more brittle than a solid electrolyte in a homogeneous phase. In the present invention, since the solid electrolyte and the electrolyte support material (or the separator) are combined, part of the role of preventing damage to the solid electrolyte can be assigned to the electrolyte support material. Even when the solid gel electrolyte is in a uniform phase, when it is applied to a lithium-based secondary battery, for example, the resistance to tension during group winding is improved, or the battery is misused. It is essentially essential to use a non-woven fabric or a porous separator in order to prevent the deposition of dendritic Li metal on the negative electrode due to overcharging which is sometimes observed. Therefore, the use of electrolyte support does not cause any disadvantage.

The solid electrolyte can be obtained by preparing a mixed solution of a monomer and an electrolytic solution and polymerizing the monomer contained therein by a crosslinking reaction. In this case, generally, the volume is greatly reduced after the polymerization as compared with before the polymerization. Therefore, in the manufacturing process of the solid gel electrolyte battery, it is necessary to control the degree of tightness of the electrode group after polymerization to be within an appropriate range. Such control is possible, for example, by filling the respective surfaces and holes of the separator and the electrode with the electrolyte, and then performing group winding or the like. However, according to this method, it is possible to easily achieve a uniform degree of tightness when a stack structure is adopted, but in the case of group winding in a substantially cylindrical shape or in the case of group winding in an elliptic cylinder or an elliptic cylinder. In some cases, it may be difficult to keep the degree of tightness in the electrode group constant between the side close to the winding core and the outer peripheral side, or between the flat portion and the corner portion.

Further, according to this method, when at least one member of the positive electrode, the negative electrode, and the separator cannot hold the electrolyte by itself, the electrolytic solution in the electrolyte diffuses to the above-mentioned at least one member after forming the electrode group. Therefore, the absolute amount of ions and electrolyte in the electrolyte tends to be insufficient. If the ion concentration in the electrolytic solution is increased in advance to prevent this, the viscosity of the mixed solution of the electrolytic solution and the monomer becomes excessively high, and it becomes difficult to fill the electrolyte into the pore structure of the separator or the electrode surface. . On the other hand, when the proportion of the electrolytic solution in the electrolyte is increased,
The electrolyte may leak from the electrolyte. Further, even if all of the positive electrode, the negative electrode, and the separator can hold the electrolyte, the method of group winding or stacking after applying the electrolyte to the electrode and the separator causes an unnecessarily large volume, and the volume energy of the battery is increased. This will reduce the density.

To solve the above-mentioned problems, the electrodes and the separators are group-wound or stacked and housed in a battery container as in the manufacturing process of the electrolyte battery, and the electrolyte and the monomer are stored in the battery container. After injecting the liquid, it is effective to seal the battery container to thermally polymerize the monomer. According to this method
In addition to being able to achieve a uniform degree of tightness, there is no excess of electrolyte between the electrodes and the separator.
Moreover, since the above electrolyte does not diffuse,
It is not necessary to excessively increase the ratio of the electrolytic solution in the mixed solution of the electrolytic solution and the monomer or the ion concentration. However, in this method, since the polymerization is performed after the electrode groups and the like are formed in advance, when the volume decreases due to the polymerization, voids may occur between the electrode groups.

On the other hand, in the present invention, a negative electrode that expands in the first charging process after completion of assembly is used.
In the case where the negative electrode has such a structure, even if voids are generated between the electrode groups after the solid electrolyte is generated, the negative electrodes expand during the first charging process after the assembly is completed, and the voids between the electrode groups are crushed. Be done. Therefore, a good close contact state can be realized, and high ionic conductivity can be obtained.

In order to obtain such an effect, it is important that the degree of expansion of the negative electrode is within an appropriate range. That is, when the degree of expansion of the negative electrode is excessively high, the solid electrolyte layer may be excessively compressed, and the electrolyte solution may seep out, resulting in deterioration of safety and life characteristics. On the other hand, when the expansion degree of the negative electrode is excessively low, the compression degree becomes insufficient, and it becomes difficult to crush the voids between the electrode groups, so that high output characteristics cannot be obtained. According to the experiments by the inventors,
When the thickness of the electrode group is made substantially constant before and after the polymerization, as the negative electrode, the thickness of the solid electrolyte layer after charging is expanded by the expansion in the first charging process after the completion of assembly to the thickness of the solid electrolyte layer before charging. By using a material whose thickness is reduced to 95% to 80%, it is possible to achieve high ionic conductivity without seeping out of the electrolytic solution, and to significantly affect cycle characteristics. It was possible to increase the tightness of the electrode group without giving it. In addition, in general,
An electrode material and an electrode structure with a small volume change are adopted for the electrode of the electrolytic solution battery or the like for the purpose of improving the life characteristics, and a material showing a volume increase enough to obtain the above effect is not used.

The high temperature cycle characteristics and the low temperature characteristics of the solid electrolyte battery are greatly influenced not only by the crosslinked polymer forming the support structure phase but also by the electrolyte salt. An organic lithium salt such as bispentafluoroethylsulfonylimide lithium (LiBETI) used in the present invention is a LiP that is being studied for use in an electrolyte-based lithium secondary battery.
F _6, LiBF _4, and LiClO ₄ compared with like, anions greatly contributes by freezing point depression of electrolytic solution for a large effect of increasing the viscosity of the electrolyte. In addition, LiBET
Organolithium salts such as I include LiPF ₆ , LiBF ₄ ,
And compared to LiClO ₄ etc., ethylene carbonate,
The effect of improving the ionic conductivity of the electrolyte, which has a high ionization degree in the electrolyte solvent generally used in lithium secondary batteries such as propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and dimethoxyethane. Is big. Also, LiB
Organolithium salts such as ETI have excellent thermal stability,
The stability at the time of high temperature use can be improved.

However, the imide system to which LiBETI belongs has the property of dissolving aluminum as described above. LiBETI is a compound having a larger anion size and lower aluminum solubility than lithium bistrifluorosulfonylimide [LiN (SO ₃ CH ₃ ) ₂ ] and the like, but nevertheless, when used in an electrolyte battery. Has a strong ability to corrode aluminum and has a problem in long-term reliability. On the other hand, in the present invention, LiBE
TI is used in a solid electrolyte battery, in which case the anion trapping effect of the electrolyte itself weakens the ability to corrode aluminum. In addition, as a result of the experiments conducted by the present inventors, the LiBETI concentration in the electrolytic solution was 0.6 mol / mol.
It was found that by setting the ratio within the range of L to 2.0 mol / L, it is possible to realize sufficient ionic conductivity and also to realize long-term reliability without using an inhibitor.

In the present invention, a crosslinked polymer (or,
The polymer used as the host polymer) is not particularly limited, but a polymer having a polyalkylene oxide structure such as polyethylene oxide tends to have a very strong interaction with a lithium salt. Therefore, when such a polymer is used, the above phase separation may be difficult to occur. Examples of the material capable of easily causing phase separation include a cross-linked polymer obtained by cross-linking and polymerizing a (meth) acrylate monomer. This crosslinked polymer has an advantage that it is inexpensive in addition to being able to easily cause phase separation. Among the cross-linked polymers obtained by cross-linking and polymerizing the (meth) acrylate monomer, it is particularly preferable to use the cross-linked polymers obtained by cross-linking and polymerizing methyl methacrylate and ethylene dimethacrylate. Since they are hydrophobic, they are easy to handle.

In the present invention, as the non-aqueous solvent, a solvent generally used in electrolyte-based lithium secondary batteries can be used. Examples of such a solvent include ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), sulfolane (SL), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC). , Dimethoxyethane (DME), diethoxyethane (DEE), 2-methyl-tetrahydrofuran (2MeTHF), various glymes, and mixtures thereof. However, in the present invention, it is necessary that the non-aqueous solvent be capable of keeping the LiBETI concentration in the electrolytic solution within the above range. Also, DMC, DM
Since E and DEE have a flash point of room temperature or lower, it is preferable to use a solvent other than those.

In the present invention, the positive electrode is made of LiMn ₂ O ₄
A spinel structure compound such as the above, a lithium-containing transition metal composite oxide having an α-NaFeO ₂ structure represented by the general formula LiMO ₂ , and the like can be used. In the above general formula, M is Co, Ni, Al, Mn, Ti,
At least one metal element selected from Fe and the like is shown. Further, Mn into which lithium can be inserted in the positive electrode
Metal oxides such as O ₂ and V ₂ O ₅ , metal sulfides such as TiS ₂ and ZnS ₂ , π-conjugated polymers such as polyaniline and polypyrrole having electrochemical redox activity, and sulfur in the molecule It is also possible to use disulfide compounds which result in the formation / cleavage of sulfur bonds.

In the present invention, a carbon material capable of inserting and extracting lithium can be used for the negative electrode. Examples of such a carbon material include, for example, a graphite-based carbon material having a flat potential characteristic in which a graphite structure developed by firing naturally produced graphite or an organic raw material at a high temperature of 2000 ° C. or higher, and 1000 ℃ organic raw material
The coke-based carbon material, etc., which is obtained by firing at a relatively low temperature and is expected to have a larger charge / discharge capacity than the graphite-based material, can be given below.

Further, in the present invention, as the electrolyte supporting material, those generally used as a separator can be used, and a nonwoven fabric or a porous sheet made of a polyolefin material is suitable.

[0036]

EXAMPLES Examples of the present invention will be described below. In this example, a solid electrolyte lithium secondary battery was manufactured by the method described below, and the physical properties of the constituent elements and the output characteristics of the battery were examined. In addition, here, a stack structure is adopted, and a rectangular type having a rated capacity of 15 Ah is used.

(A) Preparation of slurry for coating positive electrode active material mixture 90 parts by weight of LiCoO ₂ powder having an average particle size of 10 μm as a positive electrode active material, and polyvinylidene fluoride resin as a binder (Neoflon manufactured by Daikin Industries, Ltd.) VDF V
P-850), 4.0 parts by weight, 5.0 parts by weight of graphite powder as a conductive agent, and 20 parts by weight of N-methylpyrrolidone as a dispersant. Next, the oriented material was stirred and mixed at 8,000 rpm for 20 minutes by a disperser to prepare a slurry for coating a positive electrode active material mixture.

(B) Production of Positive Electrode Plate The coating slurry of the positive electrode active material mixture described above was applied to a thickness of 20 μm.
m of aluminum foil is continuously coated on one side using a die coater and dried at 70 ° C, then heated in an oven at 135 ° C for 2 minutes, and further in an oven at 150 ° C. The mixture was heated for 2 minutes to remove the dispersant, thereby forming a positive electrode active material mixture coating film on the current collector. Next, a positive electrode active material mixture coating film having the same thickness was formed on the other surface of the current collector by the same method. This is 4.9k
Press at a pressure of Pa, size to a specified size,
Further, the positive electrode plate was obtained by removing the active material layer of the terminal connecting portion.

(C) Preparation of slurry for coating negative electrode active material mixture 85 parts by weight of negative electrode active material and 10 parts by weight of polyvinylidene fluoride resin (Neoflon VDF VP-850 manufactured by Daikin Industries, Ltd.) as a binder. And 3 parts by weight of Kayarad R-167 manufactured by Nippon Kayaku Co., Ltd., which is an acrylate monomer, as a compound that reacts with an electron beam, and 225 parts by weight of N-methylpyrrolidone as a dispersant. Then, the oriented material is dispersed by a disperser at 8,000r.
A slurry for coating a negative electrode active material mixture was prepared by stirring and mixing at pm for 20 minutes.

(D) Production of Negative Electrode Plate The coating slurry of the above negative electrode active material mixture was coated to a thickness of 14 μm.
A current collector made of copper foil of m was continuously coated on one side with a die coater and dried at 100 ° C. to form a negative electrode active material mixture coating film on the current collector. Next, a negative electrode active material mixture coating film having the same thickness was formed on the other surface of the current collector by the same method. This was pressed at a pressure of 4.9 kPa, sized to a predetermined size, and the active material layer in the terminal connecting portion was removed to obtain a negative electrode plate.

(E) Assembly of Battery The positive electrode plate and the negative electrode plate produced by the above method are alternately stacked with a polyethylene porous sheet interposed therebetween, and after attaching a current collecting plate and connecting terminals, It was stored in a battery case container of the mold. Next, a top cover was attached to the battery container and they were sealed by welding. Then, a mixed solution containing the electrolytic solution, the monomer and the initiator was poured into the container and heated to thermally polymerize the monomer. A mixed solution containing ethylene carbonate (EC) and diethyl carbonate (DEC) in a ratio of 4: 6 was used as the non-aqueous solvent constituting the electrolytic solution, and LiBETI was used as the electrolyte salt. In addition, here, a plurality of types of samples were prepared by making the LiBETI concentration in the electrolytic solution, the composition of the monomer used to generate the electrolyte, and the negative electrode active material different from each other.

(F) Measurement of Physical Properties of Constituent Elements With respect to each of the samples assembled as described above, the appearance of the solid gel electrolyte was visually observed, and the average diameter of the electrolyte solution phase in the solid gel electrolyte was measured. The ratio (thickness reduction ratio) of the thickness of the solid gel electrolyte layer after charging to the thickness of the solid gel electrolyte layer before the first charging after the completion of assembly was measured. The results are shown in Table 1 below.

[0043]

[Table 1]

In Table 1, "electrolyte composition"
In the column, the monomer composition used to form the crosslinked polymer and the polymer ratio in the electrolyte are shown in the upper column,
The composition of the electrolytic solution is shown in the lower part. Further, in Table 1, "MMA-EdMA" indicates a mixture of methyl methacrylate and ethylene dimethacrylate, and the parentheses thereafter indicate the weight ratio thereof. In addition, sample 10
With respect to the above, "-" entered in the "Appearance of electrolyte" column means that the degree of cross-linking was too high, so that the gel was not formed and collapsed. In addition, “MCMB” is mesophase carbon microbeads, “MCF” is mesophase carbon fiber, “NG” is natural graphite, and “MB” is
"C-NC" indicates hard carbon, respectively.

As shown in Table 1 above, in any of Samples 1 to 7, the LiBETI concentration in the electrolytic solution was 0.
6 mol / L to 2.0 mol / L, the average diameter of the electrolytic solution phase in the solid gel electrolyte is 10 μm to 1.0 μm, and the thickness reduction rate of the solid gel electrolyte layer is 95 to 80%. On the other hand, in Samples 8 to 15, L in the electrolytic solution
At least one of the iBETI concentration, the average diameter of the electrolytic solution phase in the solid gel electrolyte, and the thickness reduction rate of the solid electrolyte layer is out of the above range. That is, Samples 1 to 7 correspond to Examples of the present invention, and Samples 8 to 15 correspond to Comparative Examples.

(G) Evaluation of room temperature output characteristics Next, the 20CA discharge characteristics of the samples 1 to 9 and 11 to 15 in the fully charged state were measured under the temperature condition of 25 ° C. In addition, as for the sample 10, the discharge characteristics were not measured because the solid gel electrolyte layer could not be formed as described above. The measurement results are shown in Table 2 below.

[0047]

[Table 2]

As shown in Table 2, Samples 1 to 9 according to the examples of the present invention have the same output characteristics (874 to 100) as Sample 15, which is an electrolyte-based lithium secondary battery.
3 W / kg). On the other hand, in samples 8 and 9 according to the comparative example in which phase separation is not performed, 426 W / k
g and 468 W / kg, sufficient output characteristics could not be obtained, and the output density was 600 W for both sample 11 according to the comparative example having an excessively low electrolyte salt concentration and sample 12 according to the comparative example having an excessively high electrolyte salt concentration. / Kg. Further, the output density was extremely low in the sample 13 according to the comparative example in which the expansion of the negative electrode was excessively small, and was also low in the sample 14 in the comparative example in which the expansion of the negative electrode was excessively large. From the above results, it was confirmed that according to the present invention, it is possible to realize the high-temperature output characteristics at the same level as the electrolytic solution battery, even though the solid electrolyte is used.

(G) Evaluation of low-temperature output characteristics Next, the discharge capacities of samples 1 to 9 and 11 to 15 in a fully charged state were measured under a temperature condition of -20 ° C. Here again, the discharge capacity of Sample 10 was not measured. The measurement results under the temperature condition of −20 ° C. are shown in Table 3 below as relative values to the measurement results under the temperature condition of 20 ° C.

[0050]

[Table 3]

As shown in Table 3 above, Samples 1 to 7 according to the examples of the present invention have the same low temperature output characteristics (discharge at -20 ° C.) as Sample 15 which is an electrolyte-based lithium secondary battery. The capacity is 70% or more of the discharge capacity at 20 ° C)
showed that. From the above results, it was confirmed that according to the present invention, it is possible to realize the low temperature output characteristics that are as high as those of the electrolytic solution battery, even though the solid electrolyte is used.

(H) Evaluation of high temperature cycle characteristics Next, the high temperature cycle characteristics of the samples 1 to 9 and 11 to 15 were measured. Here, too, the high temperature cycle characteristics of the sample 10 were not measured. Table 4 shows various conditions for measuring the high temperature cycle characteristics, and Table 5 shows the ratio of the capacity at the 300th cycle to the initial capacity as a measurement result.

[0053]

[Table 4]

[0054]

[Table 5]

As shown in Table 5 above, in Samples 1 to 7 according to the examples of the present invention, the capacity retention ratio exceeded 70%. This value is equivalent to the samples 8, 9, 11 to 1 according to the comparative example.
Not only is it higher than the capacity retention rate of No. 4 but also exceeds the capacity retention rate of Sample 15, which is an electrolyte battery. From the above, it was confirmed that according to the present invention, extremely high temperature cycle characteristics can be realized.

(I) Liquid leakage test For samples 1 to 8, 10 and 14, the upper lid portion was opened and the side surface of the battery was pressed at a pressure of 1 kgf for 15 minutes, and the weight change after the pressurization was compared with that before the pressurization. Examined. The amount of weight loss is shown as the amount of liquid leakage in Table 6 below.

[0057]

[Table 6]

As shown in Table 6 above, the leakage amounts of Samples 1 to 7 according to the examples of the present invention were as follows: Sample 10 according to Comparative Example in which the electrolyte collapsed and Sample 10 according to Comparative Example in which the negative electrode expanded excessively. The amount is much smaller than that of Sample No. 14, which is almost the same level as that of Sample 8 according to Comparative Example in which the electrolyte is a homogeneous gel. From the above, it was confirmed that high safety can be realized according to the present invention.

[0059]

As described above, in the present invention, the solid electrolyte contains at least a part of the supporting structure phase containing the crosslinked polymer and the electrolytic solution, and has an average diameter converted to spheres of 1
Since it has a structure in which it is phase-separated into an electrolytic solution phase in the range of 0 μm to 1.0 μm, it is possible to realize high ionic conductivity while preventing exudation of the electrolytic solution. Further, in the present invention, the negative electrode expands in the first charging process after completion of assembly, so that the thickness of the solid electrolyte layer after charging is 95% of the thickness of the solid electrolyte layer before charging. % ~
Since what is reduced to 80% is used, it is possible to realize a good contact by crushing the voids generated by the production of the solid electrolyte. Furthermore, in the present invention, as at least a part of the electrolyte salt, lithium bispentafluoroethylsulfonylimide, which contributes greatly to the freezing point depression of the electrolytic solution, has high ionization degree in the solvent, and is also rich in thermal stability, is used. In addition, since the concentration in the electrolytic solution is within the range of 0.6 mol / L to 2.0 mol / L, it is possible to achieve sufficient ionic conductivity and use an inhibitor. It is possible to achieve long-term reliability. That is, according to the present invention, there is provided a solid electrolyte lithium-based secondary battery that is safe and can realize high output characteristics in a wide temperature range, and a method for manufacturing the same.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masahiro Yamamoto             Fukushima Prefecture Iwaki City Joban Shimo-Funao Pile 23-6               Furukawa Battery Co., Ltd., Iwaki Plant (72) Inventor Koji Hataya             2-6-1, Marunouchi, Chiyoda-ku, Tokyo             Kawa Electric Industry Co., Ltd. F term (reference) 5H029 AJ02 AJ12 AK03 AK16 AL06                       AL07 AM02 AM03 AM04 AM05                       AM07 AM16 CJ02 CJ11 CJ13                       DJ09 HJ04 HJ05 HJ10

Claims (3)

[Claims] 1. A solid electrolyte comprising a positive electrode, a negative electrode, and an electrolyte support material that is interposed between the positive electrode and the negative electrode and is electrically insulating, and a solid electrolyte supported by the electrolyte support material. A layer, the solid electrolyte includes an electrolytic solution containing a non-aqueous solvent and an electrolyte salt and a polymer crosslinked body, the solid electrolyte is a supporting structure phase containing the polymer crosslinked body and the electrolytic solution And a phase-separated into an electrolytic solution phase containing at least a part of and having an average diameter converted into a sphere within a range of 10 μm to 1.0 μm, and the negative electrode expands in the first charging process after completion of assembly, Therefore, the thickness of the solid electrolyte layer after charging is 9 times the thickness of the solid electrolyte layer before charging.
5% to 80%, and the electrolyte solution contains lithium bispentafluoroethylsulfonylimide as an electrolyte of at least a part of the electrolyte salt.
A lithium secondary battery, which is contained at a concentration of 6 mol / L to 2.0 mol / L. 2. The lithium secondary battery according to claim 1, wherein the cross-linked polymer is formed by cross-linking and polymerizing a (meth) acrylate monomer. 3. A solid electrolyte comprising a positive electrode, a negative electrode, and an electrolyte support material that is interposed between the positive electrode and the negative electrode and is electrically insulating, and a solid electrolyte supported by the electrolyte support material. A method for producing a lithium-based secondary battery, comprising a layer, wherein the solid electrolyte comprises a polymer crosslinked body and an electrolytic solution containing a non-aqueous solvent and an electrolyte salt, between the positive electrode and the negative electrode. A step of forming an electrode group with the electrolyte supporting material interposed; a step of housing the electrode group in a container and injecting the electrolytic solution and a monomer into the container; and thermally polymerizing the monomer. A step of producing the crosslinked polymer, thereby obtaining the solid electrolyte, wherein the solid electrolyte contains at least a part of a supporting structure phase containing the crosslinked polymer and the electrolytic solution. And the average diameter converted to sphere The solid electrolyte is formed into a structure that is phase-separated into an electrolyte solution phase in the range of 0 μm to 1.0 μm, and expands as the negative electrode in the first charging process after the assembly is completed, thereby the solid electrolyte after the charging. The thickness of the layer is reduced to 95% to 80% with respect to the thickness of the solid electrolyte layer before charging, and the electrolyte solution is bispentafluoroethyl as at least a part of the electrolyte salt. Lithium sulfonylimide is
A method for manufacturing a lithium-based secondary battery, characterized in that the lithium secondary battery is contained at a concentration of 6 mol / L to 2.0 mol / L.