JP2000123633A - Solid electrolyte and electrochemical device using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device with excellent discharge characteristics, excellent high temperature characteristics, and capable of realizing a thin and large area by including electrochemically inactive, inorganic particles, a polymer, and an electrolyte, and specifying the weight ratio of the inorganic particles and the polymer in a specified range. SOLUTION: A solid electrolyte is preferable to have a weight ratio of inorganic particles and a polymer of 55:45 to 99:10, and an average particle size of inorganic particles of 0.2-5 μm. The solid electrolyte has ionic conductivity similar to a gel electrolyte using a PVDF family copolymer, high characteristics, especially has excellent rate characteristics, and less drop in discharge capacity even in high rate discharge current. Compared with the gel electrolyte using PVDF family copolymer, strength is high, and forming of a thin film is made possible. The film thickness of the solid electrolyte is possible to make 60 μm, especially 15 μm or lower. Since the solid electrolyte does not deform, short circuit between a positive electrode and a negative electrode can be prevented. Storage characteristics are excellent at high temperature near 80 deg.C, capacity deterioration is very low, the generation of internal short circuit is decreased, and charge/discharge characteristics at high temperature are enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solid electrolyte suitably used for an electrochemical device such as a battery, a capacitor, a display, a sensor, and the like, and an electrochemical device using the solid electrolyte.

[0002]

2. Description of the Related Art At present, various types of batteries are widely used from the field of electronics to automotive applications or large batteries intended for power storage.

[0003] Usually, a liquid is used as the electrolyte of such a battery, but if the electrolyte can be made solid, it is possible to prevent liquid leakage and to form a sheet. For this reason, batteries using solid electrolytes have attracted attention as next-generation batteries. In particular, if a lithium-ion secondary battery or the like, which has been rapidly used in notebook personal computers, mobile phones, and the like, can be made into a sheet or stacked in a smaller size, it is expected that the range of application will be further expanded.

When such a solid electrolyte is used, a ceramic material, a polymer material, or a composite material thereof has been proposed. Above all, a gel electrolyte plasticized by using a polymer electrolyte and an electrolyte solution has both high liquid-based electrical conductivity and high polymer-based plasticity, and is considered promising in electrolyte development.

One of the advantages of a battery using such a solid electrolyte is that the battery can be made thinner and larger, that is, formed into a sheet. This further accelerates the development of applied applications.

[0006] An example in which a gel polymer solid electrolyte (gel electrolyte) is used in a battery is already disclosed in US Pat. No. 3,985,574. Among them, an example is shown in which a supporting electrolyte such as ammonium perchlorate and a solvent such as propylene carbonate are taken and gelled polyacetal is used for a separator and a positive electrode. Is composed.

In US Pat. Nos. 5,296,318 and 5,418,091, there is disclosed a copolymer of vinylidene fluoride (VDF) and 8 to 25% by weight of propylene hexafluoride (HFP). Polymer [P (VDF-HFP)]
A gel electrolyte containing 20 to 70% by weight of a solution in which a lithium salt is dissolved and a lithium intercalation battery using the same are disclosed. This battery has excellent ionic conductivity and discharge characteristics, and particularly excellent rate characteristics, as compared with a battery using a conventional gel electrolyte. That is, even if the discharge current is increased, the discharge capacity does not decrease so much.

However, such a VDF-HFP
Although a gel electrolyte using a PVDF-based copolymer such as a copolymer has excellent characteristics, it has the following problems.

First, the PVDF copolymer is copolymerized and has a reduced crystallinity, so that it is easily swelled by an electrolytic solution and high characteristics can be obtained.
It is easier to deform and has lower strength than VDF homopolymer. This is believed to be due to the intrinsic properties of the material. As a result, a practically usable film thickness is 60 μm or more. The aforementioned U.S. Pat.
In JP-A-96,318 and JP-A-5,418,091, the film thickness is set to 50 μm. However, sufficient strength cannot be obtained with this film thickness, and the positive electrode and the negative electrode are easily short-circuited. Absent. Therefore, the separator used in the conventional solution-based lithium ion battery is usually 25 μm
However, it is disadvantageous in terms of film thickness, and it has not been possible to make full use of the characteristics of a battery using a solid electrolyte in terms of thinning.

Furthermore, since the strength is weak and soft, the positive electrode and the negative electrode are easily short-circuited. For example, when an expanded metal is used as the current collector, there is a portion where the PVDF-based copolymer electrolyte portion is locally thinned correspondingly because the expanded metal bites into the electrode portion,
The positive electrode and the negative electrode are easily short-circuited, which is a major obstacle in battery production.

[0011] In addition, the PVDF copolymer has a drawback that HFP lowers the crystallinity of PVDF, so that the chemical resistance is lowered and the melting point is lowered. For example, PVDF (homopolymer, trade name KYNAR, manufactured by Elf Atchem)
700 series) has a melting point of 170 ° C. and a VDF-HFP copolymer also manufactured by Elf Atochem, for example, K
The melting point of YNAR2801 is 145 ° C. The decrease in chemical resistance means that the PVDF copolymer impregnated with the electrolyte is stored at a high temperature, and unlike the homopolymer, it dissolves in the electrolyte. I will. When such a VDF-HFP copolymer is used for an electrochemical device such as a lithium ion secondary battery or an electric double layer capacitor, a problem arises in adhesion to an electrode, a current collector, or the like. For example, the VDF-HFP
When a copolymer is used for a battery, the storage characteristics of the battery deteriorate. Battery at room temperature or high temperature (40 ° C, 60 ° C, 80 ° C)
(100.degree. C., 100.degree. C.), capacity deterioration occurs, and internal short-circuiting often occurs. In addition, the lowering of the melting point limits the use at high temperatures and deteriorates the high-temperature storage characteristics as described above.

In summary, the problems of the gel electrolyte using the PVDF copolymer are as follows.

1) Low strength and easy to deform 2) Practically it is impossible to make the film thickness less than 60 μm 3) Positive short circuit between positive electrode and negative electrode 4) Storage characteristics at high temperature and high temperature Charging / discharging characteristics are poor

Further, as a method for producing a gel electrolyte separator, a polymer is dissolved in a solvent, an electrolytic solution and the like are mixed therein, and the mixture is applied to a substrate by various methods to evaporate the solvent. A method for obtaining a gel electrolyte film is generally used. A method has also been proposed in which a polymer is directly dissolved in an electrolytic solution and a gel electrolyte film is produced by coating or extrusion. However, the electrolytic solution used for the electrochemical device generally dislikes water, so when industrially producing a gel electrolyte by using these methods, it is necessary to maintain the entire process in a dry atmosphere, which is expensive. Capital investment and maintenance costs are required, and inventory management in the process is not easy.

In the above-mentioned US Pat. No. 5,418,091, a plasticizer is added to a polymer solution, and after this is applied to a substrate,
A method for producing a separator is described in which a solvent is volatilized to produce a film, a plasticizer is extracted therefrom, and a formed void is impregnated with an electrolytic solution. in this way,
The electrolytic solution is used only in the impregnation process and the encapsulation process. In the processes before that, the work can be performed in a normal environment, so that capital investment and maintenance costs can be greatly reduced. In addition, since the separator can be stocked in a film state after coating / drying or after extracting the plasticizer, inventory management becomes easy. However, in this method, it is necessary to immerse the plasticizer-containing polymer film in a large amount of solvent a plurality of times as an extraction step, and this step greatly reduces productivity and mass productivity, and requires treatment of a large amount of waste solvent. There is also a problem in terms of pollution. Extraction can also be achieved by heating the plasticizer-containing polymer film under reduced pressure. However, in this case, productivity and mass productivity are greatly affected, and introduction of equipment and an increase in cost are inevitable.

As described above, the gel electrolyte also has a problem that productivity and mass productivity are low.

Although a battery has been described as an example, other electrochemical devices such as an electric double layer capacitor are required to have a solid electrolyte which has properties equivalent to that of a gel electrolyte, has higher strength, and can be formed into a thin film. ing.

[0018]

SUMMARY OF THE INVENTION An object of the present invention is to provide high ionic conductivity, excellent discharge characteristics, particularly excellent rate characteristics, high strength, thin film, short circuit, and excellent high temperature characteristics. Another object of the present invention is to provide a solid electrolyte that is excellent in productivity and mass productivity, and an electrochemical device that can be thinned and have a large area by using the solid electrolyte.

[0019]

This and other objects are achieved by the present invention described below.

(1) inorganic particles which are electrochemically inert,
A solid electrolyte containing a polymer and an electrolyte, wherein the weight ratio of the inorganic particles to the polymer is 55:45 to 90:10. (2) The solid electrolyte according to (1), wherein the inorganic particles have an average particle size of 0.2 to 10 μm. (3) The conductivity of the inorganic particles in the bulk is 10 ^−9.
The solid electrolyte according to the above (1) or (2), which has a S · cm ⁻¹ or less. (4) The solid electrolyte according to any one of (1) to (3), wherein the inorganic particles are at least one of silicon oxide, aluminum oxide, titanium oxide, magnesium oxide, and barium titanate. (5) The above (1) to wherein the polymer contains fluorine.
The solid electrolyte according to any of (4). (6) The solid electrolyte according to the above (5), wherein the polymer contains a vinylidene fluoride unit. (7) The solid electrolyte according to any one of the above (1) to (6), wherein the porosity at the time of drying excluding the electrolytic solution is 30% or more. (8) The above (1) to (7) wherein the film thickness is 5 to 60 μm.
Any of the solid electrolytes. (9) An electrochemical device using the solid electrolyte according to any one of (1) to (8). (10) The electrochemical device according to (9), which is a lithium secondary battery. (11) The electrochemical device according to (9), which is an electric double-layer capacitor.

[0021]

The solid electrolyte of the present invention contains inorganic particles, a polymer and an electrolyte which are electrochemically inactive, and the weight ratio of the inorganic particles to the polymer is 55:45 to 90:10. The average particle size of the inorganic particles is preferably from 0.2 to 5 μm.
A conventional polymer solid electrolyte (gel electrolyte) is a polymer obtained by generating microporosity in a polymer with a plasticizer and impregnating the polymer with an electrolytic solution to form a gel. On the other hand, the solid electrolyte of the present invention is a solid electrolyte in which the electrolyte is gelled and solidified by inorganic particles and a polymer, and the electrolyte is held in micropores three-dimensionally formed by the inorganic particles. Thus, a solid electrolyte is formed. The polymer is a binder that binds the inorganic particles, and may not be swelled by the electrolytic solution. Therefore, the presence of inorganic particles and polymers is indispensable,
If either is missing, it will not function as a solid electrolyte. At present, the reason is not clear, but it is considered that the pore size, the surface state of the inorganic particles, and the liquid retaining property of the polymer are involved in the properties. That is, the solid electrolyte according to the present invention cannot be produced because it is not formed into a film by simply mixing the inorganic particles and the electrolytic solution, and the polymer / electrolyte ratio disclosed in the present invention cannot be used to form a self-supporting film. Fabrication is impossible, and it is different from a gelled electrolyte membrane as heretofore shown even if only the composition is considered.

The solid electrolyte of the present invention, having such a structure, has an ion conductivity equivalent to that of a gel electrolyte using a conventional PVDF-based copolymer, and has excellent characteristics. In particular, the rate characteristics are excellent, and the discharge capacity is hardly reduced even when the discharge current is increased. Therefore, a battery having a discharge rate equal to that of the gel electrolyte can be manufactured.

Further, as compared with a gel electrolyte using a conventional PVDF copolymer, the strength is high and a thin film can be formed. The solid electrolyte of the present invention can have a film thickness of 60 μm or less, more preferably 40 μm or less, and especially 15 μm or less. In addition, since the positive electrode and the negative electrode are not deformed, a short circuit between the positive electrode and the negative electrode hardly occurs.

Further, it is not necessary to use a PVDF copolymer having inferior heat resistance and chemical resistance. Even if it is used, a very small amount is required as compared with a conventional gel electrolyte.
(Up to about ° C), the capacity deterioration is very small, and the occurrence of internal short-circuits is small. Moreover,
Excellent charge / discharge characteristics at high temperatures.

Furthermore, since it is not necessary to use a plasticizer to manufacture a solid electrolyte and an electrochemical device such as a battery and a capacitor using the same, it is easier than before.

Note that the aforementioned US Pat. No. 5,418,09
In No. 1, in order to increase the strength of the membrane and improve the impregnation rate of the electrolytic solution, 20 wt% of alumina or silica filler is mixed into the polymer solid electrolyte, but the strength is still higher than the solid electrolyte of the present invention. Is weak. Therefore, the film cannot be thinned, and short-circuits are likely to occur. In addition, as described above, since a polymer having low heat resistance and low chemical resistance is used, high-temperature characteristics are poor. In addition, the method of extracting a plasticizer according to this publication has significant disadvantages in terms of productivity and mass productivity.

Japanese Patent Application Laid-Open No. 9-293636 discloses a separator made of an inorganic fiber sheet bound with a fluorine-containing polymer ion exchange resin. Japanese Patent Application Laid-Open No. 9-293637 discloses a separator in which a glass fiber sheet is bound with a resin (such as polyvinylidene fluoride) which is insoluble in an electrolytic solution. However, since these use fibers, fine pores having an appropriate diameter cannot be obtained as compared with the present invention using granules, and the porosity (porosity of glass fiber sheet: 70 to 90)
%) Is small, and the electrolyte is not sufficiently impregnated, and sufficient ionic conductivity cannot be obtained. Further, the film thickness is 30 to 2
The thickness is 00 μm, and 160 μm in the embodiment, and cannot be made thin as in the present invention.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION <Inorganic Particles> The inorganic particles used in the present invention form pores for impregnating an electrolyte in a solid electrolyte, and may be electrochemically inert. It is not particularly limited. The conductivity in the bulk of the inorganic particles 10 ^-9 S · cm ^-1 or less, particularly 10 ^-15 S · cm ^- is preferably ¹ or less.

The inorganic particles used in the present invention preferably have an average particle size of 0.2 to 10 μm, particularly preferably 0.5 to 5 μm. By using such particles, an appropriate pore diameter and porosity can be obtained, and excellent characteristics can be obtained. If the particle size is too small, the particles will be clogged too much. If the particle size is too large, thinning may be hindered. The particle size of silicon oxide or the like conventionally contained in the solid electrolyte as a filler is much smaller than that of the present invention, and is usually 0.01 to
It is about 0.1 μm. The particle size distribution is preferably relatively narrow because voids having a uniform diameter can be obtained, and it is preferable that 50% by weight or more of all particles exist in 1/2 to 2 times the average particle size.

The shape of the inorganic particles is not particularly limited.
It is sufficient that an appropriate pore is formed, and it may be any of irregular shaped flakes, irregular shapes, and spheres.

The material of such inorganic particles is not particularly limited. For example, silicon oxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), titanium oxide (TiO ₂ ), magnesium oxide (MgO), titanium oxide Barium acid (Ba ₂
TiO ₃ ) and the like, among which silicon oxide and aluminum oxide are preferable. These are 2
More than one species may be used in combination. Note that these may slightly deviate from the stoichiometric composition.

<Polymer> The polymer used in the present invention is:
The binder is not particularly limited as long as the binder binds the inorganic particles. Among them, those containing fluorine are preferred, and those containing vinylidene fluoride units are particularly preferred.

Examples of such fluorine-based polymers include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene (HFP) copolymer [P (VDF-HFP)], vinylidene fluoride-chloride 3
Fluorinated ethylene (CTFE) copolymer [P (VDF-C
TFE)], vinylidene fluoride-hexafluoropropylene fluoro rubber [P (VDF-HFP)], vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene fluoro rubber [P (VDF-TFE-HFP)],
Vinylidene fluoride-tetrafluoroethylene-perfluoroalkyl vinyl ether fluororubber is preferred.
The composition range of vinylidene fluoride-hexafluoropropylene fluororubber, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene fluororubber is approximately VDF-HFP binary copolymer with a VDF of 50 to 85 mol%, Further, this is a composition region in which TFE is added in an amount of 0 to 35 mol%. As the vinylidene fluoride-based polymer, those having a vinylidene fluoride content of 50% by weight or more, particularly 70% by weight or more (the upper limit is about 97% by weight) are preferable. In particular, polyvinylidene fluoride (PVDF), fluorinated Copolymer of vinylidene and hexafluoropropylene [P (VDF-HFP)], vinylidene fluoride and chloride 3
Copolymer with fluorinated ethylene [P (VDF-CTF
E)] is preferred. By using a copolymer, the crystallinity is reduced, so that the electrolyte is easily impregnated and retained. In the present invention, a polymer having a high swelling property or a polymer having a low swelling property such as PVDF may be used. However, since PVDF and the like have low solubility, handling is difficult and workability is poor.

Such a vinylidene fluoride-based polymer is commercially available, and a VDF-CTFE copolymer is available from Central Glass Co., Ltd. under the trade name “Sefuralsoft (G
150, G180) "sold by Solvay Japan Limited under the trade name" Solef 31508 ".
Also, VDF-HFP copolymers are commercially available from Elf Atochem under the trade names “KynarFlex2750 (VDF: HFP = 85: 15wt%)”, “KynarFlex2750”
narFlex2801 (VDF: HFP = 90: 10wt%) ”and other product names from Solvay Japan, Ltd.“ Solef 11008 ”,“ Solef 11010 ”,“ Solef 21508 ”,“ Solef 215 ”
10 "and the like.

In addition, latex, for example, "Nipol AR-32" manufactured by Zeon Corporation, or a urethane polymer material can be used.

The weight ratio between the inorganic particles and the polymer is 55:45.
９０90: 10, particularly preferably 60: 40-85: 15. If the content of the polymer is more than this, sufficient conductivity cannot be obtained because the porosity decreases. When the content of the polymer is lower than this, the inorganic particles cannot be sufficiently bound, sufficient sheet strength cannot be obtained, and it becomes difficult to form a thin film.

<Electrolyte> The electrolyte generally comprises an electrolyte salt and a solvent. Considering the application to a lithium battery, the electrolyte salt needs to contain lithium, and specifically, L
iPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ ,
Electrolyte salts such as LiSO ₃ CF ₃ and LiN (CF ₃ SO ₂ ) ₂ are applicable. When used for an electric double layer capacitor, quaternary ammonium salts such as tetraethylammonium perchlorate and tetraethylammonium borofluoride can be used in addition to the above-mentioned alkali metal salts containing Li. In addition, an electrolyte salt compatible with a solvent described below may be appropriately selected depending on an applied electrochemical device. Such an electrolyte salt may be used alone, or a plurality of salts may be mixed at a predetermined ratio.

The organic solvent for the electrolyte is not particularly limited as long as it has good compatibility with the above-mentioned polymer material and electrolyte salt, but is not limited to an application to electrochemical devices such as lithium batteries and capacitors. In consideration of the above, it is preferable that decomposition does not occur even when a high voltage is applied. For example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, dimethyl carbonate (DMC), diethyl carbonate, ethyl methyl carbonate, etc. Carbonates, cyclic ethers such as tetrahydrofuran (THF) and 2-methyltetrahydrofuran, cyclic ethers such as 1,3-dioxolane and 4-methyldioxolane, lactones such as γ-butyrolactone, sulfolane, 3-methylsulfolane and dimethoxy Ethane, diethoxy Tan, ethoxy methoxy ethane,
Ethyl diglyme or the like can be preferably used. These may be used alone or as a mixture.
In addition, a suitable solvent may be appropriately selected from known solvents according to a device to be applied.

The concentration of the electrolyte salt in the electrolyte is preferably from 0.3 to 5 mol / l, and usually shows the highest conductivity near 1 mol / l.

The content of the electrolyte is 30 to 7% of the solid electrolyte.
It is preferably 0% by weight, particularly preferably 40 to 60% by weight. If the content is higher than this, excess electrolyte increases,
When a battery is manufactured, it becomes disadvantageous in weight. Also,
If the content is less than this, it becomes difficult to obtain sufficient ionic conductivity.

<Solid Electrolyte Membrane> The solid electrolyte of the present invention has a thickness of 5 to 100 μm, more preferably 5 to 60 μm, especially 1
It is preferably from 0 to 40 μm. Since the solid electrolyte of the present invention has high strength, the thickness can be reduced. The solid electrolyte of the present invention can be made thinner than a conventional gel electrolyte which could not be reduced to 60 μm or less in practical use. Further, the solid electrolyte can be thinner than a separator (usually 25 μm) used in a solution type lithium ion battery. Can also be thin.
Therefore, it is possible to form a thin and large area, which is one of the advantages of using a solid electrolyte, that is, to form a sheet.

The porosity at the time of drying before impregnation with the electrolytic solution, that is, in the state where the inorganic particles are bound with the polymer, is preferably 30% or more, particularly preferably 45% or more. If the porosity is less than this, the electrolyte cannot be held sufficiently, and the ionic conductivity and the rate characteristics decrease. The upper limit of the porosity is usually 70% or less. If it is too large, the strength will be insufficient. The porosity can be measured by the Archimedes method.

The average pore diameter is 0.05 to 2 μm
Preferably, the thickness is 0.1 to 0.8 μm. Usually, the pore size is larger than that of a conventional gel electrolyte. If the average pore diameter is larger than this, it becomes difficult to maintain a uniform pore diameter, and lithium dendrites may be generated. If it is smaller than this, a problem may occur in diffusion of Li ions. The pore size can be measured with a mercury porosimeter.

<Manufacturing Method> Next, a specific manufacturing method of the solid electrolyte of the present invention will be described.

First, a polymer and inorganic particles are dissolved in a solvent.
Disperse. The solvent at this time may be appropriately selected from various solvents in which the polymer can be dissolved, and industrially, a solvent having a high boiling point and high safety is preferable. For example, N, N-dimethylformamide (DMF), dimethylacetamide, N-methylpyrrolidone, acetone, methyl ethyl ketone (ME
It is preferable to use K), methyl isobutyl ketone, or the like. The concentration of the polymer in the solvent is preferably 5 to 25.
wt%. In the conventional gel electrolyte, the polymer is usually plasticized, but in the present invention, it is not always necessary to plasticize the polymer.

As a method for dispersing and dissolving, a mixture of a polymer and inorganic particles is added to a solvent, or an inorganic particle is added to a polymer solution, and the mixture is heated at room temperature or, if necessary, by a stirrer such as a magnetic stirrer or a homogenizer. And dispersing using a dispersing machine such as a pot mill, a ball mill, a super sand mill, and a pressure kneader.

Then, a mixed slurry of the polymer, the inorganic particles, and the solvent is applied on a substrate or formed into a film by casting or the like. This substrate may be anything as long as it is smooth. For example, resins such as a polyester film and a polytetrafluoroethylene film, and various types of glass. Means for applying the mixed slurry to the substrate is not particularly limited, and may be appropriately determined according to the material and shape of the substrate. Generally, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, a screen printing method and the like are used. Thereafter, if necessary, a rolling treatment is performed by a flat plate press, a calender roll, or the like.

After the application, if the solvent in the mixed slurry is evaporated, a film in which the inorganic particles are bound by the polymer is completed. The drying method may be drying under reduced pressure or air drying. Moreover, you may heat.

Then, this film is immersed in an electrolytic solution and impregnated with the electrolytic solution to obtain the solid electrolyte of the present invention.

<Electrochemical Device> The SPE of the present invention comprises:
It can be used for electrochemical devices such as lithium secondary batteries, electric double layer capacitors, EC displays and sensors, and can be particularly suitably used for lithium secondary batteries and electric double layer capacitors.

<Lithium Secondary Battery> Although the structure of the lithium secondary battery using the solid electrolyte of the present invention is not particularly limited, it is usually composed of a positive electrode and a negative electrode and the electrolyte of the present invention, It is applied to type batteries.

The electrodes combined with the solid electrolyte are:
The electrode of the lithium secondary battery may be appropriately selected from known ones and used. Preferably, a composition of an electrode active material and a gel electrolyte, and if necessary, a conductive auxiliary is used.

For the negative electrode, a negative electrode active material such as a carbon material, lithium metal, lithium alloy or oxide material is used. For the positive electrode, an oxide or carbon material capable of intercalating / deintercalating lithium ions is used. It is preferable to use such a positive electrode active material as described above. By using such an electrode, a lithium secondary battery having excellent characteristics can be obtained.

The carbon material used as the electrode active material may be appropriately selected from, for example, mesocarbon microbeads (MCMB), natural or artificial graphite, resin fired carbon material, carbon black, carbon fiber and the like. These are used as powders. Above all, graphite is preferred, and its average particle size is preferably 1 to 30 μm, particularly preferably 5 to 25 μm. If the average particle size is too small, the charge / discharge cycle life tends to be short and the variation in capacity (individual difference) tends to be large. If the average particle size is too large, the dispersion of the capacity becomes extremely large, and the average capacity becomes small. It is considered that the capacity variation occurs when the average particle size is large because the contact between the graphite and the current collector and the contact between the graphites vary.

As the oxide capable of intercalating and deintercalating lithium ions, a composite oxide containing lithium is preferable. For example, LiCoO ₂ , LiM
_{n 2 O 4, LiNiO 2,} LiV 2 O 4 and the like.
The average particle diameter of these oxide powders is preferably about 1 to 40 μm.

A conductive assistant is added to the electrode as needed. Preferred examples of the conductive auxiliary agent include metals such as graphite, carbon black, carbon fiber, nickel, aluminum, copper, and silver. Particularly, graphite and carbon black are preferable.

The electrode composition of the positive electrode is as follows: active material: conductive additive: gel electrolyte = 30 to 90: 3 to 10: 1 by weight ratio.
The range of 0 to 70 is preferable. In the negative electrode, active material: conductive auxiliary agent: gel electrolyte = 30 to 90: 0 to 10: 1 by weight ratio.
A range from 0 to 70 is preferred. The gel electrolyte is not particularly limited, and a commonly used gel electrolyte may be used. Also,
An electrode containing no gel electrolyte is also preferably used. In this case, a fluorine resin, a fluorine rubber, or the like can be used as the binder, and the amount of the binder is about 3 to 30 wt%.

In the present invention, the above-mentioned negative electrode active material and / or positive electrode active material, preferably both active materials are mixed in a gel electrolyte or a binder and adhered to the surface of the current collector.

In the production of the electrode, first, an active material and, if necessary, a conductive auxiliary are dispersed in a gel electrolyte solution or a binder solution to prepare a coating solution.

Then, this electrode coating solution is applied to a current collector. The means for applying is not particularly limited, and may be determined as appropriate according to the material and shape of the current collector. Generally, a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, a screen printing method, and the like are used.
Thereafter, if necessary, a rolling treatment is performed by a flat plate press, a calender roll, or the like.

The current collector may be appropriately selected from ordinary current collectors according to the shape of the device used by the battery, the method of arranging the current collector in the case, and the like. Generally, aluminum or the like is used for the positive electrode, and copper, nickel, or the like is used for the negative electrode.
Note that a metal foil, a metal mesh, or the like is generally used as the current collector. Although the metal mesh has lower contact resistance with the electrode than the metal foil, a sufficiently low contact resistance can be obtained even with the metal foil.

Then, the solvent is evaporated to produce an electrode. The coating thickness is preferably about 50 to 400 μm.

The positive electrode, the solid electrolyte, and the negative electrode thus obtained are laminated in this order, and pressed to form a battery body.

<Electric Double Layer Capacitor> The solid electrolyte and electrode of the present invention are also effective for electric double layer capacitors.

The current collector used for the polarizable electrode may be a conductive rubber such as a conductive butyl rubber or the like, or may be formed by spraying a metal such as aluminum or nickel. A metal mesh may be provided.

In the electric double layer capacitor, the above-mentioned polarizable electrode and a solid electrolyte are combined.

As the insulating gasket, an insulator such as polypropylene or butyl rubber may be used.

The structure of the electric double-layer capacitor in which the solid electrolyte of the present invention is used is not particularly limited. However, usually, a pair of polarizable electrodes are arranged via the solid electrolyte, and the polarizable electrode and the periphery of the solid electrolyte are usually arranged. An insulating gasket is arranged in the part. Such an electric double layer capacitor may be any type called a coin type, a paper type, a laminated type, or the like.

[0069]

EXAMPLES The present invention will be specifically described below with reference to examples.

Example 1 The following were used as solid electrolyte components.

Inorganic Particles SiO ₂ (Average Particle Size 1 μm) Polymer (Binder) PVDF Kynar 2801 (VDF: HFP = 90: 10 wt% by Elf Atochem)

Each of the above-mentioned components is SiO ₂ : PVDF in a weight ratio.
= 80: 20, acetone was further added to make acetone: PVDF = 9: 1 (weight ratio), and these were mixed and dissolved at room temperature using a pot mill to obtain a slurry-like electrolyte. A solution was obtained. This slurry is
Only PVDF copolymer is soluble, SiO ₂ was dispersed in the solution.

Then, the electrolyte solution was subjected to polyethylene terephthalate (PET) by a doctor blade method.
The solution was applied to a film, and acetone was evaporated at a temperature in the range of room temperature to 50 ° C. to obtain a solid electrolyte sheet. The film thickness (dry film thickness) of the solid electrolyte sheet was 40 μm. Table 1 shows the porosity measured by the Archimedes method.

Then, an electrolytic solution (abbreviated as EL) 1 M LiPF ₆ / EC + DMC (E
C: DMC = 1: 2 (volume ratio)) to obtain a solid electrolyte of the present invention.

The ionic conductivity of the solid electrolyte at 25 ° C. was measured. The measurement of the ionic conductivity, using an alternating current impedance measurement method, cut out the electrolyte to a diameter of 15 mm,
The measurement was carried out by sandwiching a circular SUS304 electrode having a diameter of 20 mm. The measuring apparatus used was a SI1255 type impedance analyzer manufactured by Solartron. Table 1 shows the results.

[0076]

[Table 1]

Examples 2 to 5 Solid electrolytes were prepared and evaluated in the same manner as in Example 1 except that the weight ratio of the inorganic particles to the polymer was changed as shown in Table 1. Table 1 shows the results.

Example 6 PVDF Kynar 74 was used as a polymer.
1 (made by Elf Atchem Co., Ltd. (PVDF)), and a solid electrolyte was prepared in the same manner as in Example 1 except that the weight ratio of the inorganic particles to the polymer was changed as shown in Table 1. ,evaluated. Table 1 shows the results.

<Comparative Example 1> The following was used as a solid electrolyte component.

Polymer PVDF Kynar 2801 (VDF: HFP = 90: 10wt%, manufactured by Elf Atochem) Plasticizer Dibutyl phthalate (DBP) Filler SiO ₂ (average particle size 16 nm)

Each of the above components is PVDF: DBP:
The weight was weighed so that SiO ₂ = 30: 50: 20, and acetone was further added so that acetone: PVDF = 9: 1 (weight ratio), and these were mixed and dissolved at room temperature to obtain a slurry gel electrolyte. A solution was obtained.

Then, this gel electrolyte solution was mixed with polyethylene terephthalate (PE) by a doctor blade method.
T) It was applied to a film, and acetone was evaporated at room temperature to obtain a gel electrolyte sheet.

Next, the gel electrolyte sheet was immersed in hexane to extract DBP as a plasticizer. The film thickness (dry film thickness) of this gel electrolyte sheet was 40 μm.

Then, an electrolytic solution (abbreviated as EL) 1 M LiPF ₆ / EC + DMC (E
C: DMC = 1: 2 (volume ratio)) to obtain a gel electrolyte.

This gel electrolyte was evaluated in the same manner as in Example 1. Table 1 shows the results.

The ionic conductivity of the solid electrolyte of the present invention was equivalent to that of Comparative Example 1 which is a conventional gel electrolyte. Also, the porosity of the electrolyte was equivalent to the conventional one.

FIG. 1 shows an SEM photograph of the solid electrolyte of Example 1, and FIG. 2 shows an SEM photograph of the gel electrolyte of Comparative Example 1. It can be seen that the solid electrolyte of the present invention has larger inorganic particles (gel electrolyte filler) and a larger pore diameter than the conventional gel electrolyte.

Comparative Example 2 A solid electrolyte was prepared and evaluated in the same manner as in Example 1 except that the weight ratio of the inorganic particles to the polymer was changed as shown in Table 1. Table 1 shows the results.

The solid electrolyte of Comparative Example 2 in which the amount of inorganic particles was smaller than that of the solid electrolyte of the present invention had low porosity and low conductivity.

Comparative Example 3 An attempt was made to produce a solid electrolyte in the same manner as in Example 1 except that the weight ratio of the inorganic particles to the polymer was changed to 95: 5. And the electrolyte could not be produced.

Example 7 Batteries were manufactured using the solid electrolytes of Examples 1 to 6, Comparative Example 2, and the gel electrolyte of Comparative Example 1.

LiCoO ₂ was used as a positive electrode active material, acetylene black was used as a conductive additive, and PVD was used as a binder.
F Kynar 2801 was used.

The weight ratio of LiCoO ₂ : acetylene black: PVDF = 83: 6: 11 was weighed, and acetone: PVDF = 9: 1 (weight ratio).
And mixed at room temperature to obtain a positive electrode slurry.

Also, mesocarbon microbeads (MCMB) were used as the negative electrode active material, and acetylene black was used as the conductive auxiliary.

MCMB: acetylene black by weight ratio:
PVDF was weighed so as to be 85: 3: 12, acetone was further added so that acetone: PVDF = 9: 1 (weight ratio), and these were mixed at room temperature to obtain a slurry for a negative electrode.

In preparing a battery using the gel electrolyte of Comparative Example 1, both the positive electrode slurry and the negative electrode slurry
Furthermore, 5-20 wt% of dibutyl phthalate as a plasticizer
added.

Then, the obtained slurry for the positive electrode and the slurry for the negative electrode were respectively coated on a PET film by a doctor blade method, and acetone was evaporated at room temperature to form a sheet.

The solid electrolyte, the positive electrode and the negative electrode thus obtained were cut into predetermined sizes, the respective sheets were laminated, and heat-laminated at 130 to 160 ° C. Thereafter, the positive electrode was thermally laminated with an aluminum grid previously coated with a conductive adhesive as a current collector, and the negative electrode was thermally laminated with a copper grid previously coated with a conductive adhesive as a current collector. Then, 1M LiPF ₆ / EC + DM was used as an electrolytic solution.
After impregnating C (EC: DMC = 1: 2 (volume ratio)), the resultant was sealed in an aluminum laminate pack to produce a lithium secondary battery.

Table 2 shows the short-circuit occurrence rate of the lithium secondary battery manufactured as described above. The short-circuit occurrence rate was evaluated based on how many batteries out of 30 batteries were short-circuited.

Further, the discharge characteristics of the manufactured batteries were examined.
Table 2 shows the ratio between the 2C discharge capacity (capacity when discharged at a constant current of 800 mA) and the 0.2 C discharge capacity (capacity when discharged at a constant current of 80 mA).

[0101]

[Table 2]

The battery using the solid electrolyte of the present invention had a lower short-circuit occurrence rate than the battery using the gel electrolyte of Comparative Example 1. Further, the ratio of the 2C discharge capacity to the 0.2C discharge capacity was equivalent to that of the battery of Comparative Example 1, and the rate characteristics equivalent to those of the conventional battery were obtained.

Further, the battery using the solid electrolyte of Comparative Example 2 in which the amount of inorganic particles was smaller than that of the solid electrolyte of the present invention was as follows:
No failure due to short circuit occurred during battery fabrication,
Rate characteristics were bad.

When the battery was charged and discharged at 85 ° C., all the batteries of the example did not show any deterioration in capacity, but the battery of Comparative Example 1 was short-circuited.

<Examples 8 to 10> The solid electrolyte and lithium 2 were prepared in the same manner as in Example 1 except that the thickness (dry film thickness) of the solid electrolyte sheet was changed from 40 μm as shown in Table 3.
A secondary battery was prepared, and the short-circuit occurrence rate was evaluated in the same manner. Table 3 shows the results.

[0106]

[Table 3]

Even if the film thickness was reduced to 20 μm, 15 μm, or 10 μm, no short circuit occurred in one of the 30 batteries.

Example 11 Further, an electric double layer capacitor was manufactured using the solid electrolytes of Examples 1 to 6 and the gel electrolyte of Comparative Example 1.

Activated carbon powder is used as the electrode active material, acetylene black is used as the conductive additive, and PVD is used as the binder.
F Kynar 2801 was used.

Activated carbon: acetylene black: P
VDF was weighed so that 7: 1: 2, and acetone was further added so that acetone: PVDF = 9: 1 (weight ratio), and these were mixed at room temperature and sufficiently dispersed. Then, this was applied on an aluminum foil to a thickness of 0.15 mm, and the solvent was removed by drying. This electrode is 30mm long x 4mm wide.
Two pieces were cut out to 0 mm, and a solid electrolyte film cut out to a diameter of 20 mm was sandwiched between the electrodes, inserted into an aluminum laminate bag, and a lead take-out portion was heat-sealed to produce an electric double layer capacitor.

The capacitor of the present invention was confirmed to be charged and discharged between 1 V and ² V at a current density of 1 mA / cm ² , and exhibited a capacitance of 4 F. Also, the leakage current at the time of 2V full charge is 0.
The characteristics were as good as 01 mA or less.

As for the capacitor of the comparative example, 15 out of 30 capacitors could not be charged or discharged.

Further, when the thickness of the solid electrolyte is 20 μm,
Even when the thickness was set to 10 μm or 10 μm, charging and discharging were confirmed, and good characteristics were obtained.

[0114]

As described above, according to the present invention, the ionic conductivity is high, the discharge characteristics, particularly the rate characteristics, are excellent, the strength is strong, the film can be formed into a thin film, the short circuit is difficult, and the high temperature characteristics are excellent. Further, it is possible to provide a solid electrolyte which is excellent in productivity and mass productivity, and an electrochemical device which can be made thin and has a large area by using this solid electrolyte.

[Brief description of the drawings]

FIG. 1 is a drawing substitute photograph, which is an SEM photograph of the solid electrolyte of the present invention.

FIG. 2 is a photograph as a substitute for a drawing, showing a conventional solid electrolyte S
It is an EM photograph.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tetsu Maruyama 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK Corporation (72) Inventor Makoto Kobayashi 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK F term in the company (reference) 5G301 CA02 CA12 CA25 CA30 CD01 5H029 AJ02 AJ11 AK02 AK06 AL02 AL06 AL12 AM03 AM04 AM07 AM16 DJ07 DJ08 DJ09 EJ12

Claims (11)

[Claims] 1. An inorganic electrochemically inert particle, a polymer and an electrolytic solution, wherein the weight ratio of the inorganic particle to the polymer is 55:45 to 9
0:10 solid electrolyte. 2. The inorganic particles have an average particle size of 0.2 to 10.
2. The solid electrolyte according to claim 1, which has a size of μm. 3. The solid electrolyte according to claim 1, wherein the conductivity of the inorganic particles in the bulk is 10 ⁻⁹ S · cm ⁻¹ or less. 4. The solid electrolyte according to claim 1, wherein said inorganic particles are at least one of silicon oxide, aluminum oxide, titanium oxide, magnesium oxide and barium titanate. 5. The method according to claim 1, wherein the polymer contains fluorine.
4. The solid electrolyte according to any one of items 1 to 4. 6. The solid electrolyte according to claim 5, wherein said polymer contains a vinylidene fluoride unit. 7. The porosity at the time of drying excluding the electrolytic solution is 3
The solid electrolyte according to any one of claims 1 to 6, which is 0% or more. 8. A film according to claim 1, wherein said film has a thickness of 5 to 60 μm.
Any of the solid electrolytes. 9. An electrochemical device using the solid electrolyte according to claim 1. 10. The electrochemical device according to claim 9, which is a lithium secondary battery. 11. An electric double layer capacitor.
Electrochemical device.