JP2002289188A - Electrode active material for non-aqueous electrolyte secondary battery, electrode and battery containing the same - Google Patents

Abstract

[PROBLEMS] To provide an electrode active material having an unprecedented large charge / discharge capacity, an electrode using the electrode active material, and a non-aqueous electrolyte secondary battery. The polyoxoacid condensed polyacid salt is used as an electrode active material for a non-aqueous electrolyte secondary battery, and the polyatom of the polyacid salt is at least one selected from the group consisting of Mo, W, Nb and V. . The polyacid salt is AxBD ₁₂ O ₄₀ represented by the following chemical formula 1 (1) where A is Cs ⁺ , NH ₄ ⁺ , Pb ⁺ , and B is from P, Si, As and Ge. And D is one selected from the group consisting of Mo, W, Nb, and V.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte battery,
More specifically, the present invention relates to a chargeable / dischargeable non-aqueous electrolyte secondary battery, and more particularly to an improvement in an electrode active material, which aims at increasing the charge / discharge capacity of the battery.

[0002]

2. Description of the Related Art A non-aqueous electrolyte secondary battery in which an alkali metal such as lithium, an alkaline earth metal such as magnesium, or an alloy or compound thereof is used as a negative electrode active material is provided with an insert of negative metal ions into the positive electrode active material. The large discharge capacity and reversibility of the charge are ensured by the reaction or the intercalation reaction.

[0003] In conventional, as a secondary battery using lithium as an anode active material, a tunnel-like oxide layered oxide or the like LiMn ₂ O ₄ of LiCoO _2, LiNiO ₂ or the like which can serve as intercalation host versus lithium A battery used as a positive electrode material has been proposed. The theoretical capacity of these oxides is 274 for LiCoO ₂ and LiNiO ₂ .
mAh / g, 148 mAh / g for LiMn ₂ O ₄ ,
Further, the reversible capacity that can be actually charged and discharged is smaller than the above value. Therefore, development of an electrode active material having a larger capacity is desired.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an electrode active material having an unprecedented large charge / discharge capacity, and an electrode using the electrode active material. Another object of the present invention is to provide a non-aqueous electrolyte secondary battery.

[0005]

Means for Solving the Problems In order to achieve the above object, the present inventors have made various studies and found that a specific polyacid salt formed by condensation of an inorganic acid is used as an electrode active material. By doing so, it has been found that the above-mentioned problem concerning the capacity can be improved.

That is, the present invention provides an electrode active material for a non-aqueous electrolyte secondary battery containing a polyacid salt in which oxo acid is condensed, wherein the polyatom of the polyacid salt is selected from the group consisting of Mo, W, Nb and V. It is intended to provide an electrode active material for a non-aqueous electrolyte secondary battery, which is at least one selected from the group.

Next, the present invention also provides an electrode for a non-aqueous electrolyte secondary battery containing the above-mentioned electrode active material. The present invention also provides a non-aqueous electrolyte secondary battery using the electrode described above. More specifically, a non-aqueous electrolyte secondary battery using the electrode described above as a positive electrode, and further includes, as a negative electrode, at least one negative electrode active material selected from the group consisting of an alkali metal material and an alkaline earth metal material It is intended to provide the above non-aqueous electrolyte secondary battery using electrodes.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

(1) Electrode active material for non-aqueous electrolyte secondary battery:

As described above, the electrode active material of the present invention comprises a polyacid salt obtained by condensing oxo acid, wherein a poly atom is Mo,
A compound characterized by being at least one selected from the group consisting of W, Nb and V.

The poly atom is selected from at least one of Mo, W, Nb, and V. Mo is particularly preferably used.
This is because the oxidation-reduction of Mo among hexavalent, tetravalent, and trivalent states easily proceeds, and the potential is as high as about 2.5 V.

It is also possible to replace a part of the poly atoms with another element. As the substitution element, for example, when Mo is used as a poly atom, examples of the substitution element include W, Nb, and V. Among them, V has a pentavalent and trivalent oxidation-reduction potential near 3.5 V, has an ionic radius close to Mo, and has a high potential flat portion.

The above-mentioned polyacid salts include those obtained by condensing one kind of oxo acid and heteropoly acid salts obtained by condensing two or more kinds of oxo acids. In particular, heteropoly acid salts are preferably used. This is because the heteropolyacid has a stable lattice and the diversity of crystals is large. Heteropolyacid salts usually have a structure containing a small number of oxo acids of different atoms in the condensed structure of oxo acids that form the skeleton. The central atom of the oxo acid that forms the skeleton is called a poly atom, and a small number of hetero atoms are called hetero atoms.

Heteroatoms are usually P, Si, As and G
At least one selected from the group consisting of e, P is particularly preferably used. Further, a part of the hetero atom can be replaced with another element. As the replacement element, for example, an element such as Fe, Co, or Mn is preferably used.

In the heteropolyacid salt, the heteroatom 1
Is usually in the range of 4 to 15.
Preferred within this range is a ratio of heteroatoms to polyatoms of any of 1: 6, 1: 9, 1:12, 2:18, and particularly preferred is the ratio of heteroatoms to polyatoms. This is the case when the ratio is 1:12. This is because the 12-heteropolyacid salt has a stable molecular structure and a pseudo-liquid phase behavior, so that it can be expected that Li intercalation can be performed quickly.

The above heteropolyacid salts can be obtained in various structures by combining a polyanion moiety and a counter cation. The polyanion moiety is called a primary structure, and the three-dimensional structure of a polyanion and a counter cation is called a secondary structure. The properties of the heteropolyacid salt vary depending on the counter cation. For example, by using Cs ⁺ or NH ^{4 +} as the counter cation, the heteropolyacid salt can be made hydrophobic and the thermal stability can be increased.

The electrode active material of the present invention is preferably specifically represented by the following general formula (I).

[0018]

## STR3 ## _{A X BD 12 O 40 (I} )

Here, in the general formula (I), A is Cs ⁺ ,
Rb ⁺ and NH ^{4 +} , preferably Cs ⁺ . B is
At least one selected from the group consisting of P, Si, As, and Ge, but P is preferably used. C is M
At least one selected from the group consisting of o, W, Nb, and V, but Mo and / or V is preferably used. X represents the valence of the polyanion moiety, that is, a number satisfying [BD ₁₂ O ₄₀ ] ^X− .

More preferably, in the formula (I), A is Cs ⁺ , B is P, and part of D is Mo.
It is represented by I).

[0021]

Embedded image Cs _{(3 + Y)} PE _Y Mo _(12-Y) O ₄₀ (II)

Here, in the general formula (II), E is W, N
At least one selected from the group consisting of b and V, V is preferably used. Y is a number satisfying 0 ≦ Y ≦ 4, preferably 0 ≦ Y ≦ 2, and more preferably a number satisfying 0 ≦ Y ≦ 1.

The compound as the active material of the present invention can be produced by a known method, and there are various methods. For example, as one specific example, a raw material aqueous solution having a predetermined molar ratio is stirred while being heated, dried to obtain a polyacid, and then Cs is ion-exchanged in the aqueous solution.
Examples of the production method include precipitation, separation and calcination as salts and ammonium salts.

(2) Electrode of the Present Invention: The electrode of the present invention uses the above-mentioned electrode active material. In this case, the active material may be usually used in a powder form, and the average particle size may be about 1 to 100 μm. The average particle size is a value measured by, for example, a laser diffraction type particle size distribution measuring device. The content of the active material in the electrode may be appropriately set according to the type of the active material to be used, the amount of the binder (binder) and the conductive material used as needed, and the like. Further, in the electrode of the present invention, the above-mentioned electrode active material alone or a mixture with other conventionally known electrode active materials may be used.

The production of the electrode of the present invention may be carried out according to a known method for producing an electrode, except that the above-mentioned electrode active material is used. For example, if necessary, a powder of the above-mentioned active material may be mixed with a known binder (polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, ethylene propylene diene polymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluoro rubber, poly rubber, or the like). Vinyl acetate, polymethyl methacrylate, polyethylene,
Nitrocellulose, etc.) and, if necessary, a known conductive material (acetylene black, carbon, graphite, natural graphite, artificial graphite, needle coke, etc.), and then mixing the obtained powder with a support made of stainless steel. What is necessary is just to press-mold on top and to fill a metal container.

Alternatively, for example, the above mixed powder is mixed with an organic solvent (N-methylpyrrolidone, toluene, cyclohexane, dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, The electrode of the present invention can also be produced by a method such as applying a slurry obtained by mixing with ethylene oxide, tetrahydrofuran, etc.) onto a metal substrate such as aluminum, nickel, stainless steel, or copper.

The thickness of the electrode is usually about 1 to 1000 μm, preferably about 10 to 200 μm. If it is too thick, the conductivity tends to decrease, and if it is too thin, the capacity tends to decrease. The electrode obtained by coating and drying is
The material may be compacted by a roller press or the like in order to increase the packing density of the active material.

(3) Non-aqueous electrolyte secondary battery of the present invention: The non-aqueous electrolyte secondary battery of the present invention comprises a non-aqueous electrolyte such as a known lithium secondary battery, except that the electrode (2) of the present invention is used as an electrode. Components in the electrolyte secondary battery can be employed.

The electrode of the present invention can be usually used as a positive electrode. In this case, a known negative electrode active material can be used as the negative electrode active material, but it is preferable to use at least one selected from the group consisting of an alkali metal material and an alkaline earth metal material.

The alkali metal material referred to in the present invention includes, in addition to alkali metals such as lithium, sodium and potassium, alkali metal compounds and alloys, materials capable of occluding and releasing alkali metal ions (for example, Li). _2.5 C
o _0.5 N, Li ₄ Ti ₅ O ₁₂ , carbon material, etc.).

The alkaline earth metal materials include alkaline earth metals such as magnesium and calcium, compounds and alloys of alkaline earth metals, and materials capable of occluding and releasing alkaline earth metal ions. (Eg, Mg _z
Ti ₂ (PO ₄ ) ₃ (0 <z <4) and the like are also included.

The negative electrode may be manufactured according to a known method, for example, in the same manner as described in the above (2). That is, for example, after mixing the powder of the negative electrode active material with the known binder described in (2) as needed, and further with the known conductive material described in (2) as needed, What is necessary is just to shape | mold into a sheet shape, and to press-bond this to a conductor net (collector) of stainless steel, copper, etc. Further, for example, it can be produced by applying a slurry obtained by mixing the above mixed powder with the known organic solvent described in (2) on a metal substrate such as copper.

As other components, those used in known non-aqueous electrolyte secondary batteries can be used. For example, the following can be exemplified.

The electrolyte usually contains an electrolyte and a solvent. The solvent of the electrolyte is not particularly limited as long as it is a non-aqueous solvent.
For example, carbonates, ethers, ketones, sulfolane compounds, lactones, nitriles, chlorinated hydrocarbons, ethers, amines, esters, amides,
A phosphate compound or the like can be used.

Listing these representative ones,
2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, ethylene carbonate, vinylene carbonate, methyl formate, dimethyl sulfoxide, propylene carbonate, acetonitrile, γ-butyrolactone, dimethylformamide, dimethyl carbonate, diethyl carbonate , Sulfolane, ethyl methyl carbonate, 1,
4-dioxane, 4-methyl-2-pentanone, 1,3
Dioxolane, 4-methyl-1,3-dioxolane,
Diethyl ether, sulfolane, methylsulfolane, propionitrile, benzonitrile, butyronitrile, valeronitrile, 1,2-dichloroethane, trimethyl phosphate, triethyl phosphate and the like can be used. These can be used alone or in combination of two or more.

As the electrolytic solution, these solvents are used in combination with the negative electrode active material.
Alkali metal ions or alkaline earth metals in substances
The ion is the positive electrode active material or the positive electrode active material and the negative electrode active material.
That can move to perform an electrochemical reaction with the
Decomposed substances such as LiClO_Four, LiPF₆, LiBF
_Four, LiCF_ThreeSO_Three, LiAsF₆, LiB (C
₆H_Five) _Four, LiCl, LiBr, CH_ThreeSO_ThreeLi, CF_Three
SO_ThreeLi, LiN (SO_TwoCF _Three)_Two, LiN (SO_TwoC_Two
F_Five)_Two, LiC (SO_TwoCF_Three)_Three, LiN (SO_ThreeC
F_Three)_TwoEtc. can be used. In the present invention,
Known solid electrolyte, for example, LiT having a NASICON structure
i_Two(PO_Four)_ThreeEtc. can also be used.

In the battery of the present invention, conventionally known various materials can be used for components such as a separator, a battery case, and other structural materials, and there is no particular limitation.

For example, when a separator is used between the positive electrode and the negative electrode, a microporous polymer film is used, and nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene, polyethylene And those made of polyolefin polymers such as polybutene. A polyolefin-based polymer is preferred from the viewpoint of the chemical and electrochemical stability of the separator, and is preferably made of polyethylene from the viewpoint of the self-closing temperature, which is one of the purposes of the battery separator.

In the case of a polyethylene separator, ultrahigh molecular weight polyethylene is preferable from the viewpoint of high-temperature shape retention, and the lower limit of the molecular weight is preferably 500,000, more preferably 1,000,000, and most preferably 1.5 million.
On the other hand, the upper limit of the molecular weight is preferably 5,000,000, more preferably 4,000,000, and most preferably 3,000,000. If the molecular weight is too large, the fluidity is too low and the pores of the separator may not be closed when heated.

The battery of the present invention may be assembled using these battery elements according to a known method. In this case, the shape of the battery is not particularly limited, and various shapes and sizes such as a cylindrical shape, a square shape, and a coin shape can be appropriately adopted.

[0041]

The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention.

Example 1 Cs as an electrode active material_ThreePMo₁₂O₄₀Is a commercially available H_ThreePM
o₁₂O₄₀(Wako Pure Chemical Industries, Ltd .: H_Three(PMo₁₂O₄₀) ・ N
H_TwoO) CsNO_ThreeWas obtained by ion exchange. H _ThreePMo
₁₂O₄₀(3.9353 g) Cs in aqueous solution (200 ml)
NO_Three(1.6883 g), stirred at 80 ° C., and precipitated
The resulting precipitate was separated. Then, the obtained powder is
At temperatures (300 ° C, 400 ° C, 500 ° C, 600 ° C)
Each was fired in air for 15 hours.

FIG. 1 shows the result of X-ray diffraction of the obtained Cs ₃ PMo ₁₂ O ₄₀ . From the powder X-ray diffraction pattern shown in FIG. 1, it was confirmed that it was a single phase of Cs ₃ PMo ₁₂ O ₄₀ .

Next, a sample fired at 300 ° C. was used as a positive electrode active material (25 mg), and a conductive agent (acetylene black,
12.5 mg) was added to ethanol, mixed, and then pressed against a stainless steel mesh to obtain a positive electrode. Before creating the battery,
Dry at 200 ° C. for 4 hours.

Metallic lithium as the negative electrode and E as the electrolytic solution
Using C (ethylene carbonate): DMC (dimethyl carbonate) = 1: 2, charging and discharging were performed in a range of 5 to 1 V at a constant current of 0.4 mA / cm ² using a semi-open cell using polypropylene as a separator.

As a result, as shown in FIG. 2, Cs ₃ PMo
₁₂ O ₄₀ corresponds to the pentavalent and hexavalent redox of Mo,
A large capacity is shown in the vicinity, and the reversible capacity is about 300 mAh /
g and an extremely large value were obtained.

[0047] For the electrode active material in Example 1, the Cs4PMo ₁₁ VO ₄₀ with a V one of the twelve Mo ligand was obtained as follows.

H ₃ PO ₄ (0.01 mol), V ₂ O
₅ (0.005 mol) and MoO ₃ (0.11 mol) were stirred in an aqueous solution (150 ml) at 80 ° C. for 3 hours, allowed to stand at room temperature, and filtered to remove insoluble V ₂ O ₅ and MoO ₃ . The obtained filtrate was dried at 85 ° C. for 10 hours. A solid (3.9353 g) obtained by drying was dissolved in water (200 ml), CsNO ₃ (1.6883 g) was added thereto, and the mixture was stirred at 80 ° C., and the deposited precipitate was separated. Thereafter, the obtained precipitate was calcined in an oxygen stream at 300 ° C. for 15 hours to obtain Cs ₄ PVMo ₁₁ O ₄₀ as an object.

A charge / discharge test was carried out in the same manner as in Example 1 except that this was used as the positive electrode active material. As a result, as shown in FIG. A flat portion of the resulting potential was newly observed, and was approximately 340 mAh / g.
And an extremely large value was obtained.

[0050]

According to the present invention, since a specific electrode active material is used, conventionally known LiCoO ₂ , LiNi
Compared with an electrode active material such as O ₂ and LiMn ₂ O _4, a non-aqueous electrolyte secondary battery having a particularly large capacity can be provided.

[Brief description of the drawings]

FIG. 1 shows an X-ray diffraction pattern of Cs ₃ PMo ₁₂ O ₄₀ which is an example of the present invention.

FIG. 2 is a characteristic diagram showing charge / discharge curves of Cs ₃ PMo ₁₂ O ₄₀ and Cs ₄ PMo ₁₁ VO _{40 according to} one embodiment of the present invention.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yusaku Takita 3-4-33 Miyazakidai, Oita City, Oita Prefecture F-term (reference) 5H029 AJ03 AK01 AL01 AL03 AL06 AL12 AL13 AM02 AM03 AM04 AM05 AM07 AM12 HJ02 5H050 AA08 BA15 CA01 CB01 CB03 CB07 CB12 HA02

Claims (15)

[Claims] 1. An electrode active material for a non-aqueous electrolyte secondary battery containing a polyacid salt in which oxo acid is condensed, wherein the polyatom of the polyacid salt is at least one selected from the group consisting of Mo, W, Nb and V. An electrode active material for a non-aqueous electrolyte secondary battery, comprising: 2. The electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the poly atom is Mo. 3. The electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein a part of the poly atoms is substituted with another element. 4. The active material for a non-aqueous electrolyte secondary battery according to claim 3, wherein a part of the poly atoms Mo is substituted with V. 5. The electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the polyacid salt is a heteropolyacid salt. 6. The heteropolyacid salt wherein the heteroatom is P, S
The electrode active material for a non-aqueous electrolyte secondary battery according to claim 5, comprising at least one selected from the group consisting of i, As, and Ge. 7. The electrode active material for a non-aqueous electrolyte secondary battery according to claim 5, wherein a part of the hetero atoms of the heteropolyacid salt is substituted with another element. 8. The electrode active material for a non-aqueous electrolyte secondary battery according to claim 5, wherein the ratio of polyatoms to heteroatoms 1 in the heteropolyacid salt is in the range of 4 to 15. 9. The electrode active material for a non-aqueous electrolyte secondary battery according to claim 5, wherein the heteropolyacid salt is represented by the following general formula (I). Embedded image A _X BD ₁₂ O ₄₀ (I) (In the general formula (I), A is Cs ⁺ , NH ₄ ⁺ , Rb ⁺ , and B is a group consisting of P, Si, As, and Ge At least one selected from the group consisting of: Mo, W, Nb,
And V are at least one selected from the group consisting of:
X represents the valence of the polyanion moiety, ie, [BD ₁₂ O
₄₀ ] is a number that satisfies ^X- . ) 10. The electrode active material for a non-aqueous electrolyte secondary battery according to claim 5, wherein the heteroatom of the heteropolyacid salt is P. 11. The electrode active material for a non-aqueous electrolyte secondary battery according to claim 5, wherein the heteropolyacid salt is represented by the following general formula (II). Embedded image Cs _{(3 + Y)} PE _Y Mo _(12-Y) O ₄₀ (II) (In the general formula (II), E is at least one selected from the group consisting of W, Nb, and V. And Y is a number satisfying 0 ≦ Y ≦ 4.) 12. An electrode for a non-aqueous electrolyte secondary battery, comprising the electrode active material according to claim 1. Description: 13. A non-aqueous electrolyte secondary battery using the electrode according to claim 12. 14. The non-aqueous electrolyte secondary battery according to claim 13, wherein the electrode according to claim 12 is used as a positive electrode. 15. The non-aqueous electrolyte secondary battery according to claim 14, wherein an electrode containing at least one negative electrode active material selected from the group consisting of an alkali metal material and an alkaline earth metal material is used as a negative electrode.