JPH09320587A - Nonaqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide at low cost a nonaqueous electrolyte battery for use as a large battery with a battery characteristic that ensures excellent charge and discharge. SOLUTION: A double oxide given as Fe2 (XO4 )3 (containing at least one kind or more selected from S and metal elements in Group VIa as X) is contained as a positive electrode active material 6, an alkali metal or a material that can store and release alkali metal is used as a negative electrode active material 4, and a material that allows ions of the alkali metal to migrate for electrochemical reactions with the positive electrode active material and the negative electrode active material 4 is used as an electrolytic material. Therefore, a nonaqueous electrolyte secondary battery having a large capacity, a long cycle life, and therefore high serviceability can be constructed at low cost, and has the advantage of having applications over a wide range of fields.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte battery, and more particularly to a chargeable / dischargeable non-aqueous electrolyte secondary battery, and particularly to the improvement of the positive electrode active material, aiming at increasing the charge / discharge capacity of the battery. Is.

[0002]

2. Description of the Related Art A non-aqueous electrolyte battery using an alkali metal such as lithium and an alloy or compound thereof as a negative electrode active material is produced by insertion or intercalation reaction of negative metal ions into the positive electrode active material. It has both large discharge capacity and charge reversibility. Conventionally, as a secondary battery using lithium as a negative electrode active material, V _{2 which} can be an intercalation host for lithium has been used.
Batteries using layered or tunnel oxides such as O ₅ , LiCoO ₂ and LiNiO ₂ for the positive electrode have been proposed, but these metal oxides use rare metals with extremely small Clark numbers as the central metal. However, problems remain in terms of cost due to mass production and increase in size.

On the other hand, Fe ₂ O ₃ and FePS ₃ have been proposed as iron-based compound positive electrodes which have no resource problems and are highly economical. However, they have low cycle life and flatness and low discharge voltage. There were many practical difficulties. In addition, ferric sulfate (Fe ₂ (S ₂
O ₄ ) ₃ ) has been proposed, and a flat discharge voltage of 3.6 V has been obtained, but the theoretical discharge capacity due to the redox reaction of trivalent / divalent iron is 134 mAh / g, which is still sufficient. With no capacity, electronic conductivity is also insufficient.

[0004]

SUMMARY OF THE INVENTION The present invention has been proposed to improve the above-mentioned problems, and an object of the present invention is to provide a non-aqueous electrolyte battery for a large battery having battery characteristics excellent in charge / discharge characteristics. At low cost.

[0005]

In order to achieve the above object, the inventors of the present invention have conducted various improvements and studies on ferric sulfate, and as a result, have the same composition formula as Fe ₂ sulfate, Fe ₂ (XO ₄ )
_In place of sulfur, which is a non-metal element, represented by ₃ , at least one or more of Group VIa metal elements in the periodic table including molybdenum, which is a transition metal element, are partially or completely substituted. The positive electrode active material includes the selected substance, and the negative electrode active material is a substance capable of occluding and releasing alkali metal or alkali metal, and the ions of the alkali metal cause an electrochemical reaction with the positive electrode active material and the negative electrode active material. It is characterized in that an electrolyte material is used as a material capable of carrying out the transfer.

The present invention will be described in more detail below.

In the lithium secondary battery of the present invention, as described above, as the positive electrode active material constituting the positive electrode, Fe ₂
It is characterized in that (XO ₄ ) ₃ (wherein X is at least one of S and Group VIa elements) is used.

As shown in FIG. 1, the monoclinic crystal unit cell of Fe ₂ (XO ₄ ) ₃ has oxygen atoms at each corner and Fe ^{3+ at the} center.
With two octahedral FeO ₆ with oxygen atoms in each corner,
It consists of three XO ₄ having S and VIa group metal elements in the center, and one oxygen atom is shared by one octahedral group and one tetrahedral group. The crystal unit cell has a β-iron sulfate structure similar to NASICON, in which the crystal axes are inclined to each other.

Fe ³⁺ in such an octahedral coordination field forms the closest oxygen 2p orbital and the Fe-O hybrid orbital as shown in FIG. In Fe ³⁺ , the bond orbits of σ and π are Fe ³⁺
Completely occupied by the 5 3d electrons of Fe ^{3 + / 2 +}
The redox level of exists on the π ^* antibonding orbital level. Here, since the π ^* antibonding orbital level goes up and down due to the covalent bond between Fe and O, -Fe-O-
Fe ₂ (XO ₄ ) having only X-O-Fe-elemental bonds
_{In the three-} crystal structure, the electronegativity of X is a key parameter that determines the covalent bond of Fe—O, and thus the discharge voltage of this positive electrode material.

Iron sulfate having an electronegativity as large as 2.6, which has sulfur as an anion group, has the highest discharge voltage of 3.6 V as an Fe ^{3 + / 2 +} redox type positive electrode. However, since there are no Fe ⁺ ions, if the discharge continues for two or more electron reactions, the discharge potential drops sharply to 1.5 V or less, and irreversible iron precipitation begins.

The cathode active material of the present invention, Fe ₂ (XO ₄ ).
₃ is characterized in that, as X, a Group VIa metal element such as molybdenum is partially or completely substituted for sulfur. M, which is a typical Group VIa metal element
Since both o and W have an electronegativity of 2.4, which is slightly smaller than that of sulfur, Fe ₂ (MoO ₄ ) ₃ and Fe ₂ (WO ₄ ) ₃
The discharge voltage of the two-electron reaction corresponding to the Fe ^{3 + / 2 +} redox reaction is 3 V, which is slightly lower than that of iron sulfate (Rev. Chim. Miner, 21, No. 4, 5).
37 (1984)). However, by further discharging this positive electrode active material, the inventors of the present invention reduce the hexavalent metal element of Group VIa contained in the XO ₄ anion to pentavalent metal by itself before the precipitation of iron occurs. It was confirmed that a reversible insertion reaction of five Li ions was made possible, and it was discovered that a large-capacity iron compound positive electrode of about 200 mAh / g was discovered.

Examples of such a metal element X include:
In addition to Mo and W, one or more of Group VIa metal elements such as Cr can be cited.

Fe ₂ used as the positive electrode active material in the present invention
(XO ₄ ) ₃ can be synthesized by a known method. For example, Fe ₂ (S _1-x Mo _x O ₄ ) ₃ can be converted to ferric oxide (Fe ₂ O ₃ ) and molybdenum oxide (MoO ₃ ) by ferric sulfate hydrate (Fe ₂ (SO ₄ ) ₃ ·. nH ₂ O) or iron sulfate ammonium salt _{((NH 4) 2 Fe (} SO 4) 2 · 6H
It can be preferably produced by mixing ₂ O) in a predetermined ratio and then firing it in an oxygen-containing atmosphere. Alternatively, ferric nitrate or an aqueous solution of ferric chloride is added to an aqueous solution of ammonium molybdate to obtain a colloidal suspension, which is then dried and baked in an oxygen atmosphere, and then ferric sulfate hydrate ( _{Fe 2 (SO 4) 3 ·} nH 2 O) or iron sulfate ammonium salt _{((NH 4) 2 Fe (} SO 4) 2 · 6H 2
It can also be obtained by mixing and firing with O) at a predetermined ratio.

In any of the synthesis methods, no harmful by-products such as NO _x and SO _x are generated, and even if the water of crystallization remains, its influence can be easily eliminated by heat treatment or the like, so that no Pollution, simple manufacturing, and inexpensive manufacturing are possible.

To form a positive electrode using this positive electrode active material, a mixture of the compound powder and a binder powder such as polytetrafluoroethylene is pressure-molded on a support such as stainless steel, or such a mixture is formed. A conductive powder such as acetylene black is mixed to impart conductivity to the powder, and a binder powder such as polytetrafluoroethylene is further added to the powder as needed, and the mixture is put in a metal container, or It is formed by means such as press-molding the above mixture on a support such as stainless steel, or dispersing the above mixture in a solvent such as an organic solvent to form a slurry and coating it on a metal substrate.

Lithium, which is the negative electrode active material, is formed into a sheet as in the case of a general lithium battery, and the sheet is pressure-bonded to a conductor network of nickel, stainless steel or the like to form a negative electrode. As the negative electrode active material, in addition to lithium, lithium alloys and lithium compounds, other conventionally known alkali metals such as sodium, potassium, and magnesium, and their alkali metal alloys, Li _2.5 Co capable of occluding and releasing alkali metal ions can be used. _0.5 N, Li ₄ Ti ₅ O
Alkali-containing metal materials such as ₁₂ can be used.

Examples of the electrolytic solution include dimethoxyethane, 2-methyltetrahydrofuran, ethylene carbonate, methyl formate, dimethylsulfoxide, propylene carbonate, acetonitrile, butyrolactone, dimethylformamide, dimethyl carbonate, diethyl carbonate, sulfolane, ethyl methyl carbonate and the like. A non-aqueous electrolyte solvent in which a Lewis acid containing an alkali metal ion is dissolved, a solid electrolyte, or the like can be used. Furthermore, various conventionally known materials can be used for other elements such as structural materials such as a separator and a battery case, and there is no particular limitation. The shape of the battery is also not particularly limited, and various shapes and sizes such as a cylindrical shape, a square shape, and a coin shape can be used.

[0018]

EXAMPLES The method of the present invention will be described more specifically with reference to the following examples, but the present invention is not limited thereto. In the examples, preparation and measurement of the battery were performed in a dry box under an argon atmosphere.

[0019]

EXAMPLE 1 FIG. 3 is a cross-sectional view of a coin-type battery, which is one specific example of the battery according to the present invention, in which 1 is a sealing plate, 2 is a gasket, 3 is a positive electrode case, 4 is a negative electrode, and 5 is a separator. , 6 are positive electrode material mixture pellets.

The positive electrode active material includes gamma ferric oxide (Fe
₂ O ₃ ) and molybdenum oxide (MoO ₃ ) with Fe: Mo =
After mixing in a molar ratio of 2: 3, it was obtained by baking in air at 780 ° C. for 1 day. From the powder X-ray diffraction pattern shown in FIG.
It was confirmed to be monoclinic Fe ₂ (MoO ₄ ) ₃ . This sample is designated as a.

This sample a was crushed into powder, mixed with a conductive agent (acetylene black) and a binder (polytetrafluoroethylene), and then roll-molded to form a positive electrode mixture pellet 6 (thickness 0.5 mm, The diameter was 15 mm).

Next, a metallic lithium negative electrode 4 placed under pressure on a stainless steel sealing plate 1 is inserted into a recess of a polypropylene gasket 2, and a polypropylene microporous separator 5 is placed on the negative electrode 4. After arranging the positive electrode material mixture pellets 6 in this order and injecting an appropriate amount of a 1N solution of LiCiO ₄ dissolved in an equal volume mixed solvent of propylene carbonate and dimethoxyethane as an electrolytic solution to impregnate it,
A coin type lithium battery having a thickness of 2 mm and a diameter of 23 mm was produced by covering and crimping the positive electrode case 3 made of stainless steel.

[0023]

Example 2 cathode active material, the sample a and iron sulfate ammonium salt _{((NH 4) 2 Fe (} SO 4) 2 · 6H 2 O) S: Mo = 1: mixed so that the 2 molar ratio After that, it was obtained by rebaking at 500 ° C. for 6 hours in the air. This sample is designated as b.

Example 1 was repeated except that Fe ₂ (SO ₄ ) (MoO ₄ ) ₂ prepared as described above was used as the positive electrode active material.
A coin-type lithium battery was produced in the same manner as.

[0025]

Example 3 As the positive electrode active material, the sample a was mixed with an ammonium iron sulfate salt ((NH ₄ ) ₂ Fe (SO ₄ ) ₂ .6H ₂ O) in a molar ratio of S: Mo = 2: 1. After mixing, it was obtained by rebaking at 500 ° C. for 6 hours in the air. This sample is designated as c.

Example 1 except that Fe ₂ (SO ₄ ) ₂ (MoO ₄ ) prepared as described above was used as the positive electrode active material.
A coin-type lithium battery was produced in the same manner as.

[0027]

The Comparative Example 1 positive electrode active material, in the air iron sulfate ammonium salt _{((NH 4) 2 Fe (} SO 4) 2 · 6H 2 O), 5
Recalcination was performed at 00 ° C. for 6 hours to obtain anhydrous ferric sulfate. This sample is referred to as d.

A coin type lithium battery was prepared in the same manner as in Example 1 except that the anhydrous ferric sulfate Fe ₂ (SO ₄ ) ₃ prepared as described above was used as the positive electrode active material.

0.25 mA / cm of sample d as a comparative example
A pseudo open-circuit potential curve at a current density of ² is shown in FIG. As an example, FIG. 6a shows a voltage regulation charge / discharge curve between 4V and 2.5V at a current density of 0.5 mA / cm ² of sample a.
Similarly, FIG. 6b shows a voltage regulation charge / discharge curve between 4.5 V and 1.5 V at a current density of 0.5 mA / cm ² of the sample a.
Shown in

In the case of anhydrous ferric sulfate Fe ₂ (SO ₄ ) ₃ which has not been subjected to the substitution treatment with a hexavalent metal element, S does not cause a reversible valence change, and therefore, as shown in FIG.
When the two-electron reaction accompanying the valence / 2 valence redox is exceeded, a deposition potential of iron of 1 V or less is rapidly exhibited, and structural destruction occurs at this time. On the other hand, iron molybdate Fe ₂ (MoO ₄ ) ₃ completely substituted by Mo is shown in FIG.
Under the voltage regulation condition between 4V and 2.5V shown in, iron trivalent / 2
It shows a reversible two-electron reaction with valence redox. If this voltage regulation condition is expanded to 4.5V-1.5V,
As shown in FIG. 6b, a 3-electron reaction accompanying the redox reaction of Mo6 valence / 5 valence occurs around 1.5 V, and a convenient 5 electron reaction is possible. However, Fe ₂ (S _1-x Mo _x O ₄ ) ₃ having a NASICON-like structure has four Li atoms per formula weight.
Since I only have a site, the five Li insertions are
It can be seen that a large lattice modulation is brought to the NASICON-like structure, and the discharge curve from the second cycle is changed to a monotonically decreasing curve accordingly.

Table 1 shows F in order to obtain the optimum substitution amount of Mo.
₃ is a comparison of the discharge capacities and cycle characteristics of e ₂ (S _1-x Mo _x O ₄ ) ₃ samples a to d.

2.5 corresponding to Fe ^{3 + / 2 +} redox
The V capacity decreases as the molecular weight increases with the amount of Mo substitution, but the V capacity is 1.5, which corresponds to the redox of Mo ^{6 + / 5 +.}
The V capacity increases with the Mo substitution amount. However, 1.
Fe ₂ (MoO ₄ ) ₃ has the maximum initial discharge capacity at the end of 5 V, but when comparing the cycle capacities at the 50th cycle under the deep charge / discharge condition of the end of 1.5 V, it was found that the amount of inserted Li was positive. Fe ₂ (S _1-x Mo _x O ₄ ) ₃ (2/3 ≧ x will be limited to 4 Li or less per active material)
It can be seen that the composition of> 0) is good.

[0033]

[0034]

As described above, according to the present invention,
A non-aqueous electrolyte secondary battery with low cost, large capacity, and long cycle life and high practicability can be constructed, and it has an advantage that it can be used in various fields.

[Brief description of drawings]

1 is an example of the present invention, monoclinic Fe ₂ (Mo
Crystal structure diagram of O ₄ ) ₃ .

FIG. 2 is a monoclinic Fe ₂ (Mo) according to one embodiment of the present invention.
Energy diagram of Fe-O hybrid orbital showing Fe ^{3 + / 2 +} redox level of O ₄ ) ₃ .

FIG. 3 is a structural cross-sectional view of a coin battery which is a specific example of the present invention.

FIG. 4 is a monoclinic Fe ₂ (Mo) according to one embodiment of the present invention.
X-ray diffraction pattern of O ₄ ) ₃ .

FIG. 5 is anhydrous ferric sulfate Fe, which is a comparative example of the present invention.
₂ is a characteristic diagram showing a pseudo open-circuit potential curve of ₂ (SO ₄ ) ₃ .

FIG. 6a is an embodiment of the present invention Fe ₂ (MoO ₄ ) ₃
FIG. 4 is a characteristic diagram showing a charge / discharge curve during a voltage regulation test between 4 V and 2.5 V in FIG.

FIG. 6b is an embodiment of the present invention Fe ₂ (MoO ₄ ) ₃
FIG. 5 is a characteristic diagram showing a charge / discharge curve at the time of the 4.5V-1.5V voltage regulation test.

[Explanation of symbols]

 1 Stainless steel sealing plate 2 Polypropylene gasket 3 Stainless steel positive electrode case 4 Lithium negative electrode 5 Polypropylene separator 6 Positive electrode material pellet

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahisa Masahiro 3-19-3 Nishishinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Youji Sakurai 3-chome, Nishishinjuku, Shinjuku-ku, Tokyo 19 No. 2 inside Nippon Telegraph and Telephone Corporation (72) Inventor Junichi Yamaki 3-19-3 Nishishinjuku, Shinjuku-ku, Tokyo Inside Nippon Telegraph and Telephone Corporation

Claims (2)

[Claims] 1. The general formula, Fe ₂ (XO ₄ ) ₃ (X,
Containing S and at least one or more of Group VIa metal elements) as a positive electrode active material,
An electrolyte material is a substance capable of occluding and releasing an alkali metal or an alkali metal as a negative electrode active material, and the ions of the alkali metal capable of moving to cause an electrochemical reaction with the positive electrode active material and the negative electrode active material. A non-aqueous electrolyte secondary battery characterized in that 2. In X in the Fe ₂ (XO ₄ ) ₃ ,
A group VIa metal element is Mo, and a compound represented by the general formula Fe ₂ (S _{1-n Mn} O ₄ ) ₃ (1 ≧ n> 0) is included as a positive electrode active material. The non-aqueous electrolyte secondary battery according to claim 1.