JPH0562680A - Electrode material for solid battery - Google Patents

Abstract

PURPOSE:To obtain an electrode material to generate an intercalation and deintercalation reactions of lithium ions reversibly by intercalating organic molecules in the crystals. CONSTITUTION:This electrode material is a material in which a substance having a two-dimension layer form structure or a three-dimension mesh form structure intercalates organic molecules in its crystals. And in this case, as a substance having a two-dimension layer form structure, graphite, a transition metal oxide, or a transition metal calcogenide may be used, and as a substance having a three-dimension mesh form structure, a chevrel phase compound can be favorably used. Furthermore, as the organic molecule, an organic molecule selected from propylene carbonate, tetrohydrofuran, butyllactone, and dimethoxy- ethane, or a mixtur of them is preferable. Consequently, the intercalation and deintercalation of lithium ions can be generated reversibly, and a desired property can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state electrochemical device using a solid electrolyte, and more particularly to an electrode material used for an all-solid-state electrochemical device such as an all-solid lithium secondary battery using a lithium ion conductive solid electrolyte. ..

[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,
BACKGROUND ART Lithium batteries are actively researched in various fields as batteries capable of obtaining high energy density because lithium has a small atomic weight and a large ionization energy.

Here, as an electrode material used in the above-mentioned lithium battery, particularly an electrode material used in a lithium secondary battery, a substance having a layered structure such as an oxide or a sulfide or a three-dimensional network structure is used. Much research has been done. When these substances are used as an electrode material, the electrochemical reaction is a topochemical reaction called an electrochemical intercalation / deintercalation reaction of lithium ions to empty sites in the crystal lattice. Since the reversibility of such a topochemical reaction is excellent, a lithium secondary battery using such a substance as an electrode material exhibits excellent charge / discharge cycle characteristics.

On the other hand, since electrochemical devices such as batteries use a liquid as an electrolyte, problems such as electrolyte leakage cannot be eliminated. In order to solve these problems and improve reliability, and to make the device smaller and thinner, attempts have been made in various fields to use a solid electrolyte instead of a liquid electrolyte to make an electrochemical device all solid. In particular, with regard to the lithium battery described above, due to its high energy density, there is a risk that the battery will ignite when an abnormality occurs in the battery. Therefore, in order to ensure the safety of the battery, development of an all-solid-state lithium battery using a solid electrolyte composed of a nonflammable solid is desired.

As active materials used in such batteries, studies have been conducted on materials capable of taking lithium ions in and out of vacant sites in a crystal lattice such as a layered crystal structure. That is, such a material used as an active material in a battery serves as a host lattice, and lithium ions are electrochemically taken in and out of the crystal lattice as a guest.

As a material for such a host lattice,
Graphite, transition metal oxides such as V ₂ O ₅ , TiS ₂ ,
A material having a two-dimensional layered structure such as transition metal 2 chalcogenide such as NbS ₂ or M _x Mo ₆ S ₈ (x = Li, Fe,
Examples thereof include a material having a three-dimensional network structure such as a Chevrel phase compound represented by etc).

[0007]

As a specific example of the problem to be solved by the present invention, an example in which a transition metal oxide having a layered structure having a composition formula of TO _{m is} used as a host lattice will be described.

Generally, an electrochemical intercalation reaction of lithium ions between host lattice layers is performed as in the following (Equation 1).

[0009]

[Equation 1]

That is, the intercalation reaction of lithium ions and the accompanying reduction reaction of transition metal ions. Therefore, the state in which the lithium ions are intercalated means that the positively charged lithium ions are inserted between the layers of the negatively charged host lattice.

Here, since lithium is a metal having a high ionization tendency, a strong electrostatic interaction (attracting force) is exerted between the positively charged lithium ions and the negatively charged host lattice. As a result, even if the intercalation reaction of lithium ions as in (Equation 1) occurs, the reverse deintercalation reaction is unlikely to occur.

Although a transition metal oxide has been described as a substance having a two-dimensional layered structure, graphite, a transition metal chalcogenide, a Chevrel phase compound, etc. are used.
In general, when a material capable of intercalating lithium ions in an empty site in a crystal lattice is used as an electrode active material,
There is a problem that a deintercalation reaction (electrochemical oxidation reaction) is unlikely to occur even if an intercalation reaction (electrochemical reduction reaction) of lithium ions occurs.

An object of the present invention is to solve the above problems and to obtain an electrode material in which an intercalation / deintercalation reaction of lithium ions occurs reversibly.

[0014]

The present invention includes a substance having at least a two-dimensional layered structure or a crystal structure of a three-dimensional network structure, wherein the substance having a crystal structure of the two-dimensional layered structure or the three-dimensional network structure is A material obtained by intercalating at least an organic molecule in the crystal is used as an electrode material.

As the substance having the two-dimensional layered structure, graphite, transition metal oxide, or transition metal chalcogenide may be used, and as the substance having the three-dimensional network structure, a chevrel phase compound is used. Good.

As the organic molecule, it is preferable to use an organic molecule selected from propylene carbonate, tetrohydrofuran, butyl lactone, dimethoxyethane or a mixture thereof.

[0017]

When an organic molecule is intercalated in the crystal of a substance having a two-dimensional layered structure or a three-dimensional network structure, the intercalated lithium ion is solvated with the organic molecule. As a result, the electrostatic interaction between the guest lithium ion and the host lattice becomes small, the lithium ion deintercalation reaction easily occurs, and the lithium ion intercalate / deintercalate is reversible. Will occur.

In addition, graphite, transition metal oxides, transition metal chalcogenides as the substance having the two-dimensional layered structure, and a chevrel phase compound as the substance having the three-dimensional network structure are intercalated with lithium ions solvated. This is preferable because the reaction of deionization and deintercalation is smoothly performed.

As the organic molecule, an organic molecule selected from propylene carbonate, tetrohydrofuran, butyl lactone and dimethoxyethane is preferable because it reduces electrostatic interaction between the lithium ion and the host lattice.

[0020]

EXAMPLES This example will be described in detail below with reference to examples.

Example 1 Graphite was used as a substance having a two-dimensional layered structure, and propylene carbonate (PC) was used as an organic molecule intercalated in the substance having a two-dimensional layered structure. PC intercalated graphite, which is one of the examples, was obtained by the following method.

PC in which 5 g of lithium metal block was wrapped in 5 g of graphite powder in a non-woven fabric made of glass fiber and lithium perchlorate (LiClO ₄ ) was dissolved
Soaked in. After leaving this for 7 days at room temperature, unreacted metallic lithium was removed and suction filtration was performed. The sample thus obtained was dried under reduced pressure at 100 ° C. to obtain graphite in which PC and solvated lithium ions were intercalated.

Next, an all-solid secondary battery was constructed and the characteristics of this electrode material were evaluated. First, as the solid electrolyte, 0.3LiI-0.35Li ₂ S-0.35 in the following manner
A lithium ion conductive amorphous solid electrolyte represented by SiS ₂ was synthesized.

First, a glass base material for synthesizing an amorphous solid electrolyte was synthesized. Lithium sulfide (Li ₂ S) and silicon sulfide (SiS ₂ ) were mixed at a molar ratio of 1: 1 and the mixture was put into a glassy carbon crucible. The crucible was put in a vertical furnace and heated to 950 ° C. in an argon stream to make the mixture in a molten state. After heating for 2 hours, the crucible was dropped into liquid nitrogen and rapidly cooled to 0.5 Li ₂ S-0.5.
A glass base material represented by SiS ₂ was obtained. After crushing the glass base material, lithium iodide (LiI) was added to 0.3 LiI
-0.35Li ₂ S-0.35SiS ₂ are mixed so as to have a composition, and the same heating and quenching as described above are performed to obtain 0.3LiI.
Was obtained -0.35Li ₂ S-0.35SiS lithium ion conductivity is represented by ₂ amorphous solid electrolyte.

The solid electrolyte thus obtained and the lithium ion intercalated graphite obtained by solvating PC obtained above were mixed in a weight ratio of 1: 1 and further mixed with a fluororesin binder. The material was used as the positive electrode material. 200 mg of the positive electrode material obtained in this manner was used for 10 mmφ
Was pressed into a disk shape to obtain a positive electrode pellet.

Metal lithium is used as the negative electrode, and the thickness is 1
A 10 mmφ lithium foil was punched out to obtain a negative electrode.

A cross-sectional view of the constructed all-solid-state secondary battery is shown in FIG. In the figure, 1 is the positive electrode pellet thus obtained,
The foil 2 of this positive electrode pellet and the metallic lithium, a solid electrolyte _{(0.3LiI-0.35Li 2 S-0.35SiS} 2)
3 and was pressure-molded integrally in a plastic tube 4 having an inner diameter of 15 mmφ which is a battery case. Subsequently, the stainless foil 5 as a current collector was bonded with carbon paste,
The lead terminals 6 and 7 were attached.

Using this all-solid-state secondary battery, 3.0-1.
Constant-current charging / discharging was performed in a voltage range of 8 V with a current value of 10 μA. The result is shown in FIG.

From these results, this all solid state secondary battery is 20
It was found that a stable charge / discharge curve was exhibited even after the lapse of cycles, and according to the present invention, an electrode material in which the intercalation / deintercalation reaction of lithium ions was reversibly carried out was obtained.

(Comparative Example 1) The same procedure as in Example 1 was repeated except that graphite not intercalated with lithium ions in which organic molecules were solvated, that is, graphite powder was used alone as the positive electrode active material. A solid secondary battery was constructed.

Using this all-solid-state secondary battery, the same charge and discharge test as in Example 1 was conducted and the results are shown in FIG.

The charge / discharge efficiency of the battery is less than 30%,
It can be seen that the discharge reaction has occurred, but the charge reaction has hardly occurred. That is, it was found that in the reaction at the positive electrode, the intercalation reaction of lithium ions between the graphite layers occurs, but the deintercalation reaction hardly occurs.

Example 2 Vanadium oxide (V) (V ₂ O ₅ ) which is one of transition metal oxides was used as a substance having a two-dimensional layered structure, and was intercalated in the substance having the two-dimensional layered structure. PC as an organic molecule to be calated
V ₂ O ₅ obtained by intercalating a mixture of PC and DME, which is one of the examples of the present invention, was obtained by the following method using a mixture of OH and dimethoxyethane (DME).

PC and DM in place of PC in the first embodiment
By the same method as in Example 1 except that E was mixed in a volume ratio of 80:20, lithium ion intercalated V ₂ O ₅ solvating a mixture of PC and DME was obtained.

Except that V ₂ O ₅ intercalated with the solvated lithium ions was used as the positive electrode active material,
An all-solid secondary battery was constructed in the same manner as in Example 1.

Using this all-solid-state secondary battery, a charge / discharge test was conducted in the same manner as in Example 1. The charge / discharge efficiency was almost 100%. According to the present invention, lithium ion intercalation was performed. -It was found that an electrode material in which the deintercalation reaction was reversibly carried out was obtained.

(Comparative Example 2) As a positive electrode active material, an all solid electrolyte was prepared in the same manner as in Example 2 except that V ₂ O ₅ in which lithium ions in which organic molecules were solvated were not intercalated was used. The next battery was constructed.

Using this all-solid-state secondary battery, the same charge and discharge test as in Example 1 was carried out. As a result, a discharge reaction of the battery occurred, but a charging reaction hardly occurred. It was found that the intercalation reaction of lithium ions occurs, but the deintercalation reaction does not easily occur.

Example 3 Titanium disulfide (TiS ₂ ) which is one of transition metal 2 chalcogenides is used as a substance having a two-dimensional layered structure and is intercalated in the substance having a two-dimensional layered structure. Tetrohydrofuran (THF) was used as the organic molecule, and THF intercalated TiS ₂ , which is one of the examples of the present invention, was obtained by the following method.

TiS ₂ was synthesized by the CVD method using metallic titanium and sulfur as raw materials. Lithium ions solvated with THF were intercalated into this TiS ₂ by an electrolytic method. The structure of the working electrode used in this electrolysis method is shown in FIG. In the figure, 8 is TiS ₂ to which Teflon resin was added as a binder, and was pressed into a pellet form together with a titanium mesh 9 as a current collector. The lead terminal 10 was attached to this titanium mesh by spot welding.

Lithium borofluoride (LiBF ₄ ) was prepared by using metallic lithium as the working electrode and the counter electrode of this TiS ₂ electrode.
An electrolytic cell using THF in which is dissolved as an electrolytic solution is formed, and the TiS ₂ electrode is +1.5 V with respect to the lithium electrode in this cell.
Constant voltage is applied so that electrolysis is performed for 5 hours, and TiS
₂ was intercalated with lithium ion solvated with THF. Then, the TiS ₂ electrode was taken out and dried in an argon stream to obtain TiS _{2 in} which THF and lithium ions were intercalated.

An all-solid secondary battery was constructed in the same manner as in Example 1 except that TiS ₂ intercalated with solvated lithium ions was used as the positive electrode active material.

A charge / discharge test was conducted using this all-solid-state secondary battery in the same manner as in Example 1. The charge / discharge efficiency was almost 100%, and according to the present invention, lithium ion intercalation was performed. -It was found that an electrode material in which the deintercalation reaction was reversibly carried out was obtained.

[0044] (Comparative Example 3) a positive electrode active material, TiS ₂ that the lithium ions and the organic molecules solvated not intercalated, i.e. except that TiS ₂ synthesized by CVD in Example 3 was used as it was carried out An all-solid-state secondary battery was constructed in the same manner as in Example 3.

Using this all-solid-state secondary battery, the same charge-discharge test as in Example 1 was carried out. As a result, a discharge reaction of the battery occurred, but a charge reaction hardly occurred. It was found that the intercalation reaction of lithium ions occurs, but the deintercalation reaction does not easily occur.

(Example 4) An organic molecule intercalated into the substance having a three-dimensional network structure using an iron chevrel phase compound represented by FeMo ₆ S ₈ as a substance having a three-dimensional network structure. Butyl lactone (B
Using L), FeMo ₆ S ₈ intercalated with BL, which is one of the examples of the present invention, was obtained by the following method.

FeMo ₆ S ₈ was prepared by mixing metallic iron powder, metallic titanium powder, and molybdenum disulfide (MoS ₂ ) at a molar ratio of 1: 2: 4, and sealing the mixture in a depressurized quartz tube.
It was synthesized by firing at 72 ° C. for 72 hours.

BL, Li instead of PC in Example 1
Example 1 except that LiAsF ₆ was used instead of ClO _4.
FeMo ₆ S ₈ intercalated with lithium ions solvated with BL was obtained by the same method as described above.

Using this all-solid-state secondary battery, a charge / discharge test was conducted in the same manner as in Example 1. The charge / discharge efficiency was almost 100%, and according to the present invention, lithium ion intercalation was performed. -It was found that an electrode material in which the deintercalation reaction was reversibly carried out was obtained.

In the examples of the present invention, V ₂ O ₅ was used as the transition metal oxide, but TiO ₂ , Nb ₂ O ₅ was used.
The same effect can be obtained by using other transition metal oxides such as LiV ₂ O ₅ or complex oxides including transition metals generally called bronze such as LiV ₂ O ₅ , and the present invention provides V ₂ as the transition metal oxide. It is not limited to O ₅ .

In the embodiment of the present invention, TiS ₂ is used as the transition metal 2 chalcogenide.
Needless to say, the same effect can be obtained by using other transition metal 2 chalcogenides such as S ₂ and MoS ₂ , and the present invention is not limited to TiS ₂ as the transition metal 2 chalcogenide.

Although FeMo ₆ S ₈ was used as a compound having a three-dimensional network structure in the examples of the present invention, other compounds such as Li _x Mo ₆ S ₈ and Li _x Cu ₃ Mo ₆ S ₈ were used. Needless to say, the same effect can be obtained by using a Chevrel phase compound or the like, and the present invention is not limited to FeMo ₆ S ₈ as a compound having a three-dimensional network structure.

In the examples of the present invention, graphite, transition metal oxide, transition metal chalcogenide, and chevrel phase compound were used as the compound having a two-dimensional network structure or a three-dimensional network structure. (CF) _n or its derivative (CF
Needless to say, the same effect can be obtained by using a compound that intercalates other lithium ions such as _0.8 I _0.02 ) _n , and the present invention provides a compound having a two-dimensional layered structure or a three-dimensional network structure. It is not limited to the compounds listed in these examples.

Further, in the examples of the present invention, only organic molecules selected from propylene carbonate, tetrahydrofuran, butyl lactone, dimethoxyethane, or a mixture thereof are described as the intercalating organic molecules. It can be applied to all organic molecules that can intercalate into a material such as a layered structure. Therefore, the present invention is not limited to the organic molecules such as propylene carbonate, tetrahydrofuran, butyl lactone, dimethoxyethane, or a mixture thereof as the organic molecules.

[0055]

As described above, according to the present invention in which organic molecules intercalate in the crystal of a substance having a two-dimensional layered structure or a three-dimensional network structure, according to the present invention, intercalation / deintercalation of lithium ions is performed. Can be generated reversibly.

Further, as the substance having the two-dimensional layered structure, graphite, transition metal oxide, and transition metal chalcogenide are used, and as the substance having the three-dimensional network structure, a chevrel phase compound is used. The characteristics of the period can be obtained.

The organic molecules include propylene carbonate, tetrahydrofuran, butyl lactone,
By using an organic molecule selected from dimethoxyethane, desired properties can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of an all-solid-state secondary battery according to an embodiment of the present invention.

FIG. 2 is a diagram showing a charge / discharge curve of an all-solid secondary battery in one example of the present invention.

FIG. 3 is a diagram showing a charge / discharge curve of an all-solid-state secondary battery in a comparative example of the present invention.

FIG. 4 is a configuration diagram of an electrode used for synthesizing an electrode material by an electrolysis method in an example of the present invention.

[Explanation of symbols]

1 Positive Electrode Pellet 2 Negative Electrode (Lithium Foil) 3 Solid Electrolyte Layer 4 Battery Case (Plastic Tube) 5 Stainless Steel Foil 6,7 Lead Terminal 8 TiS ₂ Pellet with Teflon Resin Added as Binder 9 Titanium Mesh 10 Lead Terminal

Claims (6)

[Claims] 1. A substance containing at least a two-dimensional layered structure or a crystal structure having a three-dimensional network structure, wherein the substance having a two-dimensional layered structure or a crystal structure having a three-dimensional network structure has at least an organic molecule in its crystal. An electrode material for a solid-state battery, characterized in that it is an intercalated material. 2. The electrode material for a solid battery according to claim 1, wherein the substance having a two-dimensional layered structure is graphite. 3. The electrode material for a solid battery according to claim 1, wherein the substance having a two-dimensional layered structure is mainly composed of a transition metal oxide or a metal oxide. 4. The solid battery electrode material according to claim 1, wherein the substance having a two-dimensional layered structure is a transition metal chalcogenide. 5. The solid battery electrode material according to claim 1, wherein the substance having a three-dimensional network structure is a Chevrel phase compound. 6. The electrode material for a solid battery according to claim 1, wherein the organic molecule is any one selected from propylene carbonate, tetrahydrofuran, butyl lactone and dimethoxyethane or a mixture thereof.