JP2003068304A - Electrode active material for non-aqueous electrolyte secondary battery, electrode and battery containing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode and a secondary nonaqueous electrolyte battery by using the electrode active material whose cycle property is improved. SOLUTION: Vanadium-phosphorous composite compound with ω-VOPO4 crystal structure is used as the electrode active material for the secondary nonaqueous electrolyte battery. The vanadium-phosphorous composite compound is shown on the basis of the composition of VOPO4 by general formula (I). AXV1-y My O1+δ1 P1-z Qz O4+δ2 (I) (A is at least an element selected from alkali metals and alkali earth metals that is preferably lithium. X corresponds the amount of an element A inserted in an lithium site. M is at least one element selected from a group consisting of Al, Fe, Ga, Bi, Sn, Cr, Cu, Zn, Mg, Ti, Ge, Ta, Mo, W, Nb, Ni, Mn and Co. Q at least one element selected from a group consisting of S, As, Si and Ge.).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD 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 particularly to the improvement of the electrode active material to improve the cycle characteristics.

[0002]

2. Description of the Related Art A non-aqueous electrolyte secondary battery using an anode metal such as an alkali metal such as lithium or an alkaline earth metal such as magnesium, or an alloy or compound thereof is used as an intercalator for an anode metal ion to the cathode active material. The large discharge capacity and charge reversibility are ensured by the ionization or intercalation reaction.

Recently, as a secondary battery, a battery using VOPO ₄ which can be an intercalation host for lithium as a positive electrode material has been proposed (N. Dupre et al.
al., Solid State Ionics, 140, pp.209-221 (2001), N.Du
pre et al., J. Power Sources, 97-98, pp.532-534 (200
1)).

[0004]

It is known that there are several polymorphs in the crystal structure of VOPO ₄ , and in the above literature, α, α _II , δ, γ type VOPO ₄ is used as a positive electrode. A secondary battery using an active material or metallic lithium as a negative electrode active material has been proposed. According to the above literature, when metallic lithium is used as the negative electrode, α _II -VOPO ₄ has a current value C / 50,
It has been shown to have an initial capacity of 140 mAh / g at voltages near 4V. However, any of the positive electrode active materials composed of VOPO _{4 having} various crystal structures described in the above-mentioned documents has a problem in cycle characteristics. For example, even in the above α _II -VOPO ₄ having the most excellent cycle characteristics, C
The capacity after 9 cycles at a current value of / 50 is 118 mAh /
g (84%). Therefore, development of an electrode active material having improved cycle characteristics is desired.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an electrode active material having improved cycle characteristics, an electrode using the electrode active material, and a non-aqueous electrolyte secondary battery. Especially.

[0006]

The inventors of the present invention have conducted various studies in order to achieve the above object, and as a result, by using VOPO ₄ having a specific crystal structure as an electrode active material, It was found that the above-mentioned problems regarding cycle characteristics can be improved. That is, the present invention relates to ω-VOPO.
It is intended to provide an electrode active material for a non-aqueous electrolyte secondary battery, which is composed of a vanadium-phosphorus composite compound having a _4- type crystal structure.

Next, the present invention also provides an electrode for a non-aqueous electrolyte secondary battery containing the above 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, as a negative electrode, at least one negative electrode active material selected from the group consisting of alkali metal materials and alkaline earth metal materials. The above non-aqueous electrolyte secondary battery using an electrode is provided.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in more detail below.
To do. (1) Electrode active material for non-aqueous electrolyte secondary battery: In the present invention
As described above, the electrode active material is ω-VOPO._FourType of conclusion
Vanadium-Phosphorus composite characterized by having a crystal structure
It is a compound. VOPO_FourThe crystal structure of VO₆With an octahedron
PO_FourA framework with an open tetrahedron in two or three dimensions
For the insertion of alkali metals and alkaline earths.
It has a suitable structure. VO ₆Octahedron and PO_FourJoining tetrahedra
Α, α, depending on the form_II, Δ, γ and other crystal structures exist
Ω-VOPO in the present invention_FourCrystal structure of mold
The compound having is a kind of this, and specifically, JC
X-ray diffraction written on PDS card 37-0809
It is a compound having a crystal structure that gives a pattern.

In the compound having the ω-VOPO ₄ type crystal structure according to the present invention, normally, due to the redox between the pentavalent and tetravalent vanadium, the metal lithium counter electrode is
Charging / discharging is performed at a potential of about 4V. Therefore, it is possible to control the charge / discharge capacity by substituting vanadium and phosphorus in the crystal structure with another element and controlling the average valence of vanadium. It is also possible to stabilize the crystal structure by substitution. Furthermore, the crystal structure can be stabilized by previously inserting an alkali metal element or an alkaline earth metal element into a part of the site where lithium is inserted.

The vanadium-phosphorus composite compound having the ω-VOPO ₄ type crystal structure of the present invention is usually represented by the following general formula (I) based on the composition of VOPO ₄ .

[0011]

_{Embedded image} A _x V _1-y M _y O _{1 + δ 1} P _1-z Q _z O _{4 + δ 2} (I) In the general formula (I), A is an alkali metal element or an alkaline earth metal element. At least one element selected. Specific examples of A include elements such as Li, Na, K, Mg, and Ca. Lithium is preferred. The value of x corresponds to the amount of element A inserted in the lithium site. When the negative electrode is made of a lithium-containing material, if A is other than lithium, the battery capacity tends to decrease too much when the value of x is too large.
4 or less, preferably 0.2 or less, more preferably 0.1
It is the following. Of course, it is possible to set the value of x to 0.

M is Al, Fe, Ga, Bi, Sn, C
r, Cu, Zn, Mg, Ti, Ge, Ta, Mo, W,
At least one element selected from the group consisting of Nb, Ni, Mn, and Co. The value of y corresponds to the substitution amount of vanadium with the element M. If the value of y is too large, the battery capacity tends to decrease too much, so it is usually 0.4 or less, preferably 0.2 or less, more preferably 0.1 or less. Of course, the value of y can be set to 0.

Q is at least one element selected from the group consisting of S, As, Si and Ge. The value of z corresponds to the substitution amount of phosphorus by the element Q. If the value of z is too large, the stability of the crystal structure may decrease, so it is usually 0.4 or less, preferably 0.2 or less, more preferably 0.1 or less. Of course, the value of z can be set to 0.

Further, δ ₁ and δ ₂ are VOPO, respectively.
_This corresponds to the oxygen deficiency amount or the oxygen excess amount derived from the nonstoichiometry of ₄ . δ ₁ is −0.2 ≦ δ ₁ ≦ 0.2, δ ₂ is −0.2
It is a number that satisfies ≦ δ ₂ ≦ 0.2. The compound which is the active material of the present invention can be produced by a known method,
There are various methods.

For example, as one specific example, there can be mentioned a production method in which a raw material aqueous solution having a predetermined molar ratio is stirred while being heated, then dried and fired. (2) The electrode of the present invention: In the electrode of the present invention, the above electrode active material is used. In this case, the above active material may be usually used in the form of powder, and its average particle size may be about 1-100 μm. The average particle size is a value measured by, for example, a laser diffraction type particle size distribution measuring device. In addition, the content of the active material in the electrode may be appropriately set depending on the type of the active material used, the usage amount of the binder (binder) and the conductive material used as necessary, and the like. Further, in the electrode of the present invention,
The above electrode active material may be used alone or in a mixture with other conventionally known electrode active materials.

The electrode of the present invention may be manufactured according to a known method for manufacturing an electrode except that the above electrode active material is used. For example, the active material powder is a known binder as required (polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, ethylene propylene diene polymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluororubber, poly Vinyl acetate, polymethylmethacrylate, polyethylene,
Nitrocellulose, etc.) and, if necessary, a known conductive material (acetylene black, carbon, graphite, natural graphite, artificial graphite, needle coke, etc.), and the resulting mixed powder is made of a support such as stainless steel. It may be pressure-molded on the top or filled in 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, N, N-dimethylaminopropylamine, The electrode of the present invention can also be produced by a method such as coating a slurry obtained by mixing with ethylene oxide, tetrahydrofuran, etc.) on a metal substrate such as aluminum, nickel, stainless steel, and copper.

The thickness of the electrode is usually 1-1000 μm, preferably 10-200 μm. If it is too thick, the conductivity tends to decrease, and if it is too thin, the capacity tends to decrease. The electrodes obtained by coating and drying are
You may compact by a roller press etc. in order to raise the packing density of an active material. (3) Non-aqueous electrolyte secondary battery of the present invention: The non-aqueous electrolyte secondary battery of the present invention is a non-aqueous electrolyte secondary battery such as a known lithium secondary battery except that the electrode (2) of the present invention is used as an electrode. Components in batteries can be employed.

The electrode of the present invention can usually be used as a positive electrode. In this case, as the negative electrode, a negative electrode active material known as an electrode active material can be used, but it is preferable to use at least one selected from the group consisting of alkali metal materials and alkaline earth metal materials. The alkali metal material referred to in the present invention includes alkali metals such as lithium, sodium and potassium, alkali metal compounds and alloys, as well as materials capable of inserting and extracting alkali metal ions (for example, Li _2.5 Co _0.5 N,
Li ₄ Ti ₅ O ₁₂ , carbon materials, etc.) are also included.

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 inserting and extracting alkaline earth metal ions. (For example, 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, and for example, the negative electrode can be manufactured in the same manner as the method described in (2) above. That is, for example, if necessary, the powder of the negative electrode active material is mixed with the known binder described in (2) and, if necessary, the known conductive material described in (2), and then this mixed powder is mixed. It may be formed into a sheet, and this may be pressure-bonded to a conductor network (current collector) such as stainless steel or copper. Alternatively, for example, the mixed powder may be mixed with the known organic solvent described in (2) to obtain a slurry, and the slurry may be applied on a metal substrate such as copper.

As other constituent elements, those used in known non-aqueous electrolyte secondary batteries can be used. For example, the following can be illustrated. The electrolytic solution usually contains an electrolyte and a solvent. The solvent of the electrolytic solution 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, phosphoric acid ester compounds and the like can be used.

The typical ones are listed as follows:
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, methyl sulfolane, 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, a negative electrode active material is added to these solvents.
Alkali metal ion or alkaline earth metal in the substance
Ions are the positive electrode active material or the positive electrode active material and the negative electrode active material.
The electric charge that can carry out the transfer for electrochemical reaction with the quality.
Degradation material, eg LiClO_Four, LiPF₆, LiBF
_Four, LiCF₃SO₃, LiAsF₆, LiB (C
₆H_Five) _Four, LiCl, LiBr, CH₃SO₃Li, CF₃
SO₃Li, LiN (SO₂CF ₃)₂, LiN (SO₂C₂
F_Five)₂, LiC (SO₂CF₃)₃, LiN (SO₃C
F₃)₂Etc. can be used. In addition, according to the present invention,
Known solid electrolytes such as LiT having a Nasicon structure
i₂(PO_Four)₃Etc. can also be used.

In the battery of the present invention, various conventionally known materials can be used for the separator, the battery case, and other structural materials, and there is no particular limitation. For example, when using a separator between the positive electrode and the negative electrode, a microporous polymer film is used, nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene, polyethylene, polybutene, etc. The above-mentioned polyolefin polymer is used. From the viewpoint of the chemical and electrochemical stability of the separator, a polyolefin-based polymer is preferable, and from the viewpoint of the self-closing temperature which is one of the purposes of the battery separator, polyethylene is preferable.

The polyethylene separator is preferably ultra-high molecular weight polyethylene from the viewpoint of shape retention at high temperature, and the lower limit of its molecular weight is preferably 500,000, more preferably 1,000,000, and most preferably 1,500,000.
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. This is because if the molecular weight is too large, the fluidity is so low that 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.

[0027]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. Example 1 ω-VOPO ₄ was obtained as follows.

V ₂ O ₅ and NH ₂ OH.HCl were weighed so that the molar ratio was 1: 1 and an 85% H ₃ PO ₄ aqueous solution was added to P.
/ V was added so that the molar ratio was 1.1 / 1, water was further added, and the mixture was stirred at 80 ° C. The solution was evaporated to dryness,
The solid obtained is dried at 110 ° C. overnight and 2 times in boiling water.
After being washed with water twice, filtered, dried at 60 ° C. overnight and pulverized to obtain VO (HPO ₄ ) .0.5H ₂ O as a precursor.

The obtained VO (HPO_Four) ・ 0.5H₂O
After baking in nitrogen at 500 ° C for 3 hours, further in oxygen
By firing at 600 ° C at
PO _FourGot The obtained ω-VOPO_FourX-ray diffraction results of
As shown in FIG. From the powder X-ray diffraction pattern shown in FIG.
Ω-VOPO described in CPDS card 37-0809_Four
Was confirmed. Also, redox drops of Fe and Zn
The valency of vanadium determined by the above method was 4.95.

Next, using the obtained ω-VOPO ₄ as a positive electrode active material (25 mg), a conductive material (12.5 mg) consisting of 95% by weight of acetylene black and 5% of polytetrafluorethylene was mixed with ethanol. Then, it was pressure-bonded to a stainless mesh to obtain a positive electrode. Before making the cells, they were dried at 200 ° C. for 4 hours. Metallic lithium as the negative electrode, EC (ethylene carbonate): DM as the electrolyte
C (dimethyl carbonate) = 1: 2, polypropylene was used as a separator, and a semi-open cell was used.
It was charged and discharged at a constant current of 08 mA (C / 50) in the range of 4.3 to 3.2V. As a result, the reversible capacity (charging capacity) at the first cycle was 85 mAh / g, which showed good cycle characteristics as shown in FIG. That is, the publicly known document (N. Dupre et al., Solid State Ionics, 140, pp.209-221).
(2001), N. Dupre et al., J. Power Sources, 97-98, pp. 5
32-534 (2001)), even in α _II -VOPO ₄ , which has the best cycle characteristics, the capacity after 9 cycles at a current value of C / 50 dropped to 84%. According to 2, in the case of ω-VOPO ₄ , 9 under the same conditions
The capacity at the cycle cycle is maintained at 99%.

[0031]

According to the present invention, a specific electrode active material can be used.
Since it is used, the VOPO that has been publicly known _FourRatio with electrode active material
In comparison, we propose a non-aqueous electrolyte secondary battery with good cycle characteristics.
Can be offered.

[Brief description of drawings]

FIG. 1 is an X of ω-VOPO ₄ , which is an embodiment of the present invention.
A line diffraction pattern is shown.

FIG. 2 is a characteristic diagram showing cycle characteristics of ω-VOPO ₄ which is an embodiment of the present invention.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tatsumi Ishihara             No.22, 959, Ohno, Oita City, Oita Prefecture (72) Inventor Bustam Mohammad Azumi             51-2A, 1-chome, Sandaminami-cho, Oita City, Oita Prefecture             -1-25 (72) Inventor Yusaku Takita             3-43 Miyazakidai, Oita City, Oita Prefecture F term (reference) 5H029 AJ05 AK03 AL12 AL13 AM02                       AM03 AM04 AM05 AM07 CJ02                       DJ17 HJ02                 5H050 AA07 BA16 CA07 CB12 GA02                       HA02

Claims (4)

[Claims] 1. An electrode active material for a non-aqueous electrolyte secondary battery comprising a vanadium-phosphorus composite compound having an ω-VOPO ₄ type crystal structure. 2. An electrode for a non-aqueous electrolyte secondary battery containing the electrode active material according to claim 1. 3. A non-aqueous electrolyte secondary battery using the electrode according to claim 2 as a positive electrode. 4. The non-aqueous electrolyte secondary battery according to claim 3, wherein an electrode containing at least one kind of negative electrode active material selected from the group consisting of alkali metal materials and alkaline earth metal materials is used as a negative electrode.