JP2003022839A - Multilayer structure and lithium battery using the same - Google Patents

Abstract

(57) [Problem] To provide a lithium battery having practical characteristics, and a multilayer structure in which electrodes are provided on both main surfaces of a layered lithium ion conductive solid electrolyte molded body. And a lithium ion conductive solid electrolyte molded article, a multilayer structure comprising an inorganic lithium ion conductive solid electrolyte and a crosslink made of a chemically crosslinkable liquid polymer. A battery using the multilayer structure. An inorganic lithium ion conductive solid electrolyte and a chemically cross-linkable liquid polymer are mixed, molded and formed into a layer, and an electrode body is pressure-bonded to both main surfaces of the layer, and the liquid polymer is further cross-linked. A method for producing a multilayer structure that is converted into a multilayer structure. [Effect] A thin all-solid lithium battery can be stably and easily obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium ion conductive solid electrolyte molded body in which a mobile ion species is lithium ion, and a lithium battery using the same.

[0002]

2. Description of the Related Art In recent years, with the development of portable devices such as personal computers and mobile phones, the demand for batteries as a power source thereof has become very large. In particular, a lithium battery is a substance that has a small atomic weight of lithium and a large ionization energy, and thus has been actively researched as a battery that can obtain a high energy density, and is now widely used as a power source for portable devices. Has been.

On the other hand, as lithium batteries become more and more versatile, the internal energy increases due to the increase in the amount of the active material contained therein, and the content of the organic solvent, which is a combustible substance used in the electrolyte, also increases, causing ignition of the battery. In recent years, interest in such risks has been highlighted.

As a method for ensuring the safety of lithium batteries, it is extremely effective to use a solid electrolyte, which is a nonflammable substance, instead of the organic solvent electrolyte, and various inorganic lithium ion conductive solid electrolyte powders are used. The development of all-solid-state lithium batteries with high safety is progressing by applying the.

In the development of the lithium ion conductive inorganic solid electrolyte, the main object has been to increase the lithium ion conductivity in the inorganic solid electrolyte, but when it is applied to a device such as a battery, a high lithium ion conductivity is required. It is important to have excellent processability as well as ionic conductivity. By thinning the solid electrolyte layer, not only the internal impedance can be reduced and the output characteristics can be improved, but the volume ratio of the solid electrolyte layer in the battery is reduced, and the energy density of the battery is also improved. .

Therefore, in order to impart processability, a high concentration of an inorganic salt having a lithium ion conductivity and a rubber-like polymer are used as a "polymer insoler".
In recent years, a proposal of a new solid electrolyte named “in salt)” has been made [CA Angel,
C. Liu, and E. Sanche, "Nature" (C.
A. Angel, C.I. Liu, and E.
Sanchez, Nature,) Volume 632 (1)
993) p. 137], but its conductivity is not sufficient.

Therefore, recently, a composite lithium ion conductive solid electrolyte prepared by mixing a non-rubber-like polymer has been proposed (Taro Inada, Kazunori Takada, Ryohisa Kajiyama, Masaru Takaguchi,
Shigeo Kondo, Tsutomu Watanabe, 26th Annual Meeting of Solid State Ionics Symposium, p114). In this method, the lithium ion conductive solid electrolyte composited mainly by dry mixing without using a solvent shows good conductivity.

However, when mass productivity is taken into consideration in consideration of application to an all-solid-state lithium battery, a wet method typified by a doctor blade method or the like that can easily continuously produce a thin film and a large-area electrolyte layer. Although it is desirable to adopt the method, in the case of the above method, the polymer covers the particle surface of the inorganic lithium ion conductive solid electrolyte in a film shape, so that the ion diffusion in the complex is inhibited and the ion conductivity is reduced. There is a problem that

[0009]

DISCLOSURE OF THE INVENTION The present invention solves the above problems, and the surface of particles of an inorganic lithium ion conductive solid electrolyte is coated with a specific polymer to form a lithium ion conductive solid electrolyte molded body. The purpose of the present invention is to provide a lithium battery having practical characteristics by avoiding the phenomenon that the ion conductivity of the lithium ion battery decreases.

[0010]

That is, the present invention provides a multilayer structure in which electrode bodies are provided on both main surfaces of a layered lithium ion conductive solid electrolyte molded article, wherein the lithium ion conductive solid electrolyte is formed. A multi-layer structure characterized in that the molded body is composed of an inorganic lithium ion conductive solid electrolyte and a crosslinked product of a chemically crosslinkable liquid polymer, and preferably a crosslink of the chemically crosslinkable liquid polymer. The above-mentioned multi-layer structure is characterized in that the body does not break in the Charpy impact test specified in JIS K-7111. The present invention is a battery characterized by using the above-mentioned multilayer structure.

Further, according to the present invention, an inorganic lithium ion conductive solid electrolyte and a chemically crosslinkable liquid polymer are mixed and molded to form a layer, and electrode bodies are pressure-bonded to both main surfaces of the layer. The method for producing a multilayer structure further comprises converting the liquid polymer into a crosslinked body.

The multi-layer structure of the present invention is a multi-layer structure in which electrode bodies are provided on both main surfaces of a layered lithium ion conductive solid electrolyte molded body, wherein the lithium ion conductive solid electrolyte molded body is an inorganic material. A lithium ion conductive solid electrolyte and a crosslinked body made of a chemically crosslinkable liquid polymer,
It has a feature that it is excellent in ion conductivity and that an all-solid-state lithium battery can be easily obtained.

The present inventors have experimentally studied various conditions such as composition and particle state when a lithium ion conductive solid electrolyte and a polymer are mixed to obtain a lithium ion conductive solid electrolyte composite. , When using a chemically crosslinkable liquid polymer as the polymer, not only the ion conductivity of the obtained lithium ion conductive solid electrolyte composite is good, but also the processability, especially the processability into a thin film is excellent. Then, the inventors obtained the finding that the lithium ion conductive solid electrolyte molded body obtained by molding the lithium ion conductive solid electrolyte composite is suitable for a thin all-solid-state lithium ion battery, and arrived at the present invention. Is.

Although the above reason is not clear,
Even if the distribution of the polymer in the lithium ion conductive solid electrolyte composite is in a state of covering the particle surface of the lithium ion conductive inorganic solid electrolyte, it should be pressure-treated with a uniaxial press or a roller. The distribution state of the polymer is changed to such an extent that the contact between the particles of the lithium ion conductive inorganic solid electrolyte is not hindered, and in the resulting lithium ion conductive solid electrolyte molded body, the solid electrolyte particles are It is presumed that the contact is good.

On the basis of the above assumptions, when a lithium ion conductive inorganic solid electrolyte is blended with a polymer having an uncrosslinked structure (hereinafter referred to as an uncrosslinked body) to cause a crosslinking reaction, a lithium ion conductive inorganic solid is obtained. It can be easily inferred that among the substances in which the existence condition of the particle surface of the electrolyte is changed, those which can achieve the object and effect of the present invention are equivalent to the chemically crosslinkable liquid polymer of the present invention.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. Polymers having a cross-linked structure (hereinafter referred to as cross-linked products) are roughly classified into physical cross-linked products such as styrene-butadiene block copolymers that exhibit rubber elasticity due to a higher-order structure in which hard segments and soft segments are entangled, and There is a chemically cross-linked body such as a rubber vulcanizate that exhibits rubber elasticity by a chemical bond generated by a cross-linking reaction. In the present invention,
In order to secure the processability of the obtained lithium ion conductive solid electrolyte composite, a polymer cross-linked product obtained by cross-linking a liquid uncross-linked product, and therefore the latter chemically cross-linked product is selected. Whether or not the polymer is a chemically crosslinked product can be evaluated by whether or not the polymer swells when immersed in a solvent having the same solubility parameter.

As the chemically crosslinkable rubber-like polymer, in addition to silicone rubber, for example, in the hydrocarbon system, natural rubber, synthetic rubber such as isoprene and butadiene are known.
These uncrosslinked materials are known to have various viscosities at room temperature, and some of them may appear solid, but even in that case, they show fluidity called cold flow when left for a long time, but in reality, It is a liquid substance. Among these, the non-crosslinked body of the highly fluid liquid is preferable in order to reduce the coating of the inorganic lithium ion conductive solid electrolyte particles with the polymer.
In this respect, as shown in Examples described later, it can be said that a low-viscosity silicone rubber uncrosslinked body having a viscosity of about 0.8 to 1.0 Pa · s is one of particularly suitable polymers. Further, since the uncrosslinked silicone rubber is excellent in electrochemical stability and electronic insulation, it is suitable for the present invention in view of the characteristics of the obtained crosslinked body.

Further, in the present invention, it is desirable that the crosslinked body composed of the chemically crosslinkable liquid polymer does not break in the Charpy impact test specified in JIS K-7111. However, the presence of the cross-linked product of the chemically cross-linkable liquid polymer can improve the mechanical properties of the lithium-ion conductive solid electrolyte composite and improve the resistance to stress application in actual use. Then, when the above requirements are satisfied, the mechanical and hence electrical reliability of the lithium ion conductive solid electrolyte composite, and thus the lithium battery, can be improved.

As the inorganic lithium ion conductive solid electrolyte used in the present invention, various kinds are known. For example, 0.01Li ₃ PO ₄ .0.63Li ₂ S.0.3.
Sulfide glass having a composition such as 6SiS ₂ [N. Aothani, K.K. Iwamoto, K. Takada, and S.I. Kondou, "Solid State Ionics" (N. Aotan
i, K. Iwamoto, K. Takada, and S. Kondo, Solid Stat
e Ionics,) Volume 68 (1994) p. 35], Li
Lithium germanium thio-phosphate having a composition such as _3.25 Ge _0.25 P _0.75 S ₄ (hereinafter referred to as thio-lysicone) (Masayama Murayama, Ryuji Kanno, Yoji Kawamoto, Takashi Kamiyama, 68th Annual Meeting of the Electrochemical Society of Japan) Abstracts, p183)
Is suitable because of its high conductivity.

In the present invention, the ratio of the crosslinked body made of the chemically crosslinkable liquid polymer to the inorganic lithium ion conductive solid electrolyte is as follows: Percentage is 2-10
% Is preferable. If the cross-linked product of the chemically cross-linkable liquid polymer is less than 2% by volume, it may be difficult to obtain a molded product having excellent workability and flexibility, and if it exceeds 10% by volume, it may sometimes depend on the method of molding and curing. A molded product having sufficient lithium ion conductivity may not be obtained in some cases. If the addition is within the above range, 3 × 10 ⁻⁴ S · cm ⁻¹
The lithium ion conductive solid electrolyte molded body having the above high ionic conductivity can be obtained.

The multi-layer structure of the present invention has a structure in which electrode bodies are provided on both main surfaces of a layered molded body made of the specific lithium ion conductive solid electrolyte molded body described above. The thickness of the layered molded body may be about 20 to 100 μm for an all-solid-state lithium battery. Furthermore, in order to improve the mechanical properties of the molded body, an electrically insulating structure can be used, and for example, a polyester mesh can be placed inside or in contact with the lithium ion conductive solid electrolyte molded body.

The electrode body in the present invention includes a positive electrode body and a negative electrode body. Examples of the positive electrode body include, for example, a positive electrode active material, an inorganic lithium ion conductive solid electrolyte, a mixture containing a conductive auxiliary agent, and the same chemical crosslinkability as that used for the lithium ion conductive solid electrolyte molded body portion of the present invention. The one obtained by adding the liquid polymer is preferable because it is excellent in adhesion with the lithium ion conductive solid electrolyte composite.
The present invention is not limited to this.

Examples of the positive electrode active material include oxides such as lithium cobalt oxide, lithium nickel oxide, and lithium manganate, or those obtained by partially replacing the transition metal with another metal. Examples of the conductive aid include carbon powder such as acetylene black and metal powder such as nickel and iron.

The positive electrode body can be improved in current collecting property and mechanical strength by, for example, applying a slurry of the positive electrode body on a current collector. As the positive electrode current collector, an aluminum foil, a foil made of nickel, or aluminum,
A mesh made of nickel or stainless is available. Aluminum foil is the easiest to handle in order to obtain good workability of the sheet. When applying the positive electrode slurry to an aluminum foil, in order to improve the adhesiveness, the aluminum foil is roughened in advance and / or a composite conductive slurry containing carbon and a resin is applied to form a primer layer. It is also effective to form. This composite conductive slurry may be a commercially available product such as carbon dawtite, or may be self-made by mixing a low melting point terpene resin and carbon in a solvent.

In the case of carbon dautite, since the solvent is a toluene type solvent, the solvent of the positive electrode slurry is preferably a saturated hydrocarbon type solvent containing a small amount of toluene. The surface of the primer is melted with a small amount of toluene, and good adhesion is exhibited. When a terpene resin having a low melting point is used, for example, if a phenol terpene resin is selected, it is insoluble in a saturated hydrocarbon solvent. Therefore, when such a resin is used, the positive electrode slurry is prepared and coated with a saturated hydrocarbon solvent and then heated to 100 ° C. or higher to be bonded by utilizing terpene resin melting. This heat treatment may also serve as a crosslinking reaction of silicone. In that case, a heating temperature of about 150 ° C. is desirable.

As the negative electrode body, for example, the same as that used for the lithium ion conductive solid electrolyte molded body portion of the present invention in a mixture containing a negative electrode active material, an inorganic lithium ion conductive solid electrolyte, and a conductive auxiliary agent. Those obtained by adding a chemically crosslinkable liquid polymer are preferable because they have excellent adhesion to the lithium ion conductive solid electrolyte composite, but the present invention is not limited thereto. Examples of the active material used for the negative electrode body of the present invention include indium foil, lithium foil or alloy foils thereof, or a graphite film formed on the negative electrode current collector. Further, similarly to the case of the positive electrode, it is also possible to apply a slurry on the current collector to the negative electrode body, for example, a negative electrode active material, an inorganic lithium ion conductive solid electrolyte, a conductive auxiliary agent is included. It is effective when a negative electrode body composed of the following mixture is used. Examples of the current collector for the negative electrode include copper foil and stainless mesh.

The multilayer structure of the present invention comprises, for example, mixing an inorganic lithium ion conductive solid electrolyte (hereinafter, simply referred to as an electrolyte) and a chemically crosslinkable liquid polymer and molding the mixture to form a layer. It can be obtained by bonding electrode bodies to both main surfaces and converting the liquid polymer into a crosslinked body. At this time, as described above, if the inorganic lithium ion conductive solid electrolyte and the chemically crosslinkable liquid polymer are mixed in both the positive electrode and the negative electrode, a lithium ion conductive solid electrolyte molded body is obtained. At the time of cross-linking, the chemical cross-linking liquid polymer present in the positive electrode and the negative electrode can also be cross-linked, and the adhesion between the electrode body and the lithium ion conductive solid electrolyte molded body becomes extremely good, which is preferable. . The bonding method may be, for example, a positive electrode current collector, an electrolyte layer (hereinafter, simply referred to as an electrolyte layer), a negative electrode body, and a negative electrode current collector stacked in this order, or a positive electrode current collector. It is also possible to separately manufacture a positive electrode component in which the positive electrode body is stacked and a negative electrode component in which the negative electrode body is stacked on the negative electrode current collector, apply the electrolyte layer to one of the components, and then join the both components. When an alloy foil is used as the active material for the negative electrode, the negative electrode current collector may be joined just before it is sealed in a case. In the case of joining, after the respective parts are stacked, a crosslinking reaction is caused by applying pressure with a uniaxial press or roller and then heat-treating, or by performing heat treatment while applying pressure.

Further, the present invention is a battery using the above-mentioned multilayer structure, which has high safety performance such as fire resistance because it does not contain an electrolytic solution containing an organic solvent. Also,
Since side reactions such as decomposition of the electrolyte do not occur, the storage characteristics are excellent and self-discharge does not occur during long-term storage. The battery of the present invention can be obtained by using the above-mentioned multilayer structure of the present invention, providing a current collector and lead portions on the multilayer structure, and further sealing the case in a case.

[0029]

EXAMPLES The present invention will be described in more detail below with reference to examples. Inorganic lithium ion conductive solid electrolyte is thio-
Rishikon Li _3.25 Ge is _{0.25 P 0. 75 S 4, Li} 2 S,
It was synthesized by heating GeS ₂ and P ₂ S ₅ at 700 ° C. under vacuum. The pulverization of the lithium ion conductive solid electrolyte, mixing of silicone rubber and the like, thinning, preparation of a sample for measuring ionic conductivity, and measurement of ionic conductivity were all performed in a dry argon atmosphere. Regarding the crushing operation, the particle size is 1 to 5 by observation with a scanning electron microscope.
It carried out until it became (micrometer).

Examples 1 to 3 Two-part type silicone (viscosity 0.8 Pa · s), which weighs as shown in Table 1 and cures by an addition reaction, was added to dry heptane at room temperature. Then, 1.47 g of pulverized thio-lysicon was added to the obtained solution to obtain a slurry.
On the indium sheet (thickness 0.1 mm) to be the negative electrode,
The slurry was cast and heptane was distilled off to obtain an electrolyte / negative electrode composite sheet.

On the other hand, 2.4 g of lithium cobalt oxide, 1.4 g of thio-lysicon and 40 mg of acetylene black were dry-mixed to obtain a mixed powder. Then, 10.3 mg of the same silicone uncrosslinked product used for the electrolyte slurry was dissolved in a heptane solution containing 2 wt% toluene, and 1.47 g of the mixed powder was added thereto to obtain a positive electrode slurry. The positive electrode slurry was applied onto an aluminum foil which had been coated with carbon dauite and dried to obtain a positive electrode sheet.

The obtained positive electrode sheet and the above-mentioned electrolyte / negative electrode composite sheet were put together, joined while applying a pressure of 0.1 GPa, and heated in that state at 150 ° C. for 30 minutes to crosslink the uncrosslinked silicone.

Regarding the multilayer structure obtained by the above operation,
When the ionic conductivity was evaluated, it was good as shown in Table 1. Furthermore, when an all-solid-state lithium battery was manufactured using the multilayer structure of Example 1, the secondary battery operating characteristics were shown without any abnormality. Further, it was left for 10 minutes in the flame of the Bunsen burner, but it did not catch fire. Furthermore, it was left at 60 ° C. for 30 days, but no self-discharge occurred.

[0034]

[Table 1]

[0035]

EFFECTS OF THE INVENTION The multilayer structure of the present invention is characterized by being excellent in lithium ion conductivity, and a thin all-solid-state lithium battery can be stably and easily obtained by using the multilayer structure, which is very useful industrially. is there.

   ─────────────────────────────────────────────────── ─── Continued front page    (71) Applicant 000003296             Denki Kagaku Kogyo Co., Ltd.             1-4-1 Yurakucho, Chiyoda-ku, Tokyo (72) Inventor Taro Inada             3-5-1, Asahi-cho, Machida-shi, Tokyo Electrification             Gakkou Central Research Institute (72) Inventor Kazunori Takada             1-2-1 Sengen, Tsukuba-shi, Ibaraki Independent             National Institute for Materials Science (72) Inventor Shigeo Kondo             1-2-1 Sengen, Tsukuba-shi, Ibaraki Independent             National Institute for Materials Science (72) Inventor Watanabe             1-2-1 Sengen, Tsukuba-shi, Ibaraki Independent             National Institute for Materials Science (72) Inventor Ryuji Kanno             1-2-1 Sengen, Tsukuba-shi, Ibaraki Independent             National Institute for Materials Science (72) Inventor Ryohisa Kajiyama             Toda Kogyo, 1-4 Meiji Shinkai, Otake City, Hiroshima Prefecture             Creative Headquarters Co., Ltd. (72) Inventor Hideki Sasaki             Kyoto Prefecture Kyoto City Minami-ku Kichijoin Nishinosho Inono Babacho             No. 1 Research & Development Division, Nippon Battery Co., Ltd. F term (reference) 5H029 AJ06 AJ14 AK03 AL07 AL11                       AL12 AM12 CJ03 CJ05 CJ06                       CJ08 DJ09 EJ03 EJ12

Claims (4)

[Claims] 1. A multilayer structure comprising electrode bodies provided on both main surfaces of a layered lithium ion conductive solid electrolyte molded body, wherein the lithium ion conductive solid electrolyte molded body is an inorganic lithium ion conductive solid electrolyte. And a cross-linked body comprising a chemically cross-linkable liquid polymer. 2. The multi-layer structure according to claim 1, wherein the cross-linked product made of the chemically cross-linkable liquid polymer does not break in the Charpy impact test specified in JIS K-7111. 3. An inorganic lithium ion conductive solid electrolyte and a chemically crosslinkable liquid polymer are mixed and molded to form a layer, and electrode bodies are pressure bonded to both main surfaces of the layer, and the liquid is further formed. A method for producing a multi-layer structure, which comprises converting a polymer into a crosslinked body. 4. A battery using the multilayer structure according to claim 1 or 2.