JPH09134725A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a large-sized secondary battery at a low cost having an excellent charge/discharge characteristic. SOLUTION: A secondary battery concerned includes a positive electrode active material whose main component is iron complex oxide, which contains alkali metal (A) and is expressed as AyFeXO4 , where A is alkali metal, X is an element belonging to Group IV-VII in the periodic table, and (y) is conditioned as 0<y<2, and a negative electrode active material which is a substance capable of absorbing and releasing alkali metal, alkali earth metal, or their ions. The battery also includes an electrolyte which is a substance allowing the alkali metal ions to make movement for generating electrochemical reactions with the positive or negative electrode active material.

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 to increase 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 or an alloy or compound thereof as a negative electrode active material has a large discharge capacity due to an insertion or intercalation reaction of a negative electrode metal ion into the positive electrode active material. Charge reversibility is compatible. Conventionally, as a secondary battery using lithium as a negative electrode active material, V ₂ O ₅ or Li that can be an intercalation host for lithium is used.
Batteries using layered or tunnel oxides such as CoO ₂ and LiNiO ₂ for the positive electrode have been proposed. However, these metal oxides use a rare metal with an extremely small Clark number as the central metal, and therefore cost reduction. There are practical difficulties in that respect.

[0003]

DISCLOSURE OF THE INVENTION The present invention has been proposed in order to solve the above-mentioned problems of the present situation, and its purpose is to provide a non-aqueous electrolyte for a large-sized battery having excellent battery characteristics in charge and discharge characteristics. It is to provide a secondary battery at low cost.

[0004]

The present invention will be described in brief. The present invention relates to a non-aqueous electrolyte secondary battery, which is represented by the general formula: AyFeXO ₄ (A is an alkali metal, X is a group IV of the periodic table). To a group VII element, a substance mainly composed of an alkali metal (A) -containing iron complex oxide represented by 0 <y <2) as a positive electrode active material, and an alkali metal, an alkaline earth metal,
Alternatively, a substance capable of occluding and releasing an alkali metal or alkaline earth metal ion is used as a negative electrode active material, and the ion of the alkali metal can move to cause an electrochemical reaction with the positive electrode active material or the negative electrode active material. Is an electrolyte substance.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The olivine compound, the spinel compound, and the reverse spinel compound all have a composition formula of ABCO ₄ . The difference between the olivine structure and the spinel structure including the reverse spinel is that the oxygen ions are hexagonally close packed or cubic close packed, and the stable structure changes depending on the type of A or X element. For example, LiF
In ePO ₄ , the olivine structure is stable, and in LiFeVO ₄ , the reverse spinel structure is the stable phase. However, in any structure, in the positive electrode active material of the present invention, AyFeXO ₄ , the element X is located at the tetrahedral site, and the alkali metal A is located at the octahedral site together with iron. As described above, the positive electrode active material in the present invention is {X}
-[AyFe] O ₄ (herein, {} indicates a tetrahedral site, and [] indicates an octahedral site), but as such an element X, for example, V, P, As, Sb, B
One or more of the Va group or Vb group elements such as i can be mentioned. The olivine phase or spinel phase of AyFeXO ₄ is mixed with a lithium compound, an iron compound, and an ammonium salt of the element (X), and is then baked in a nitrogen gas stream in order to prevent iron from being trivalently oxidized. It can be easily synthesized. The synthesizing method is not limited to this method. For example, in a reducing atmosphere, a method such as in a hydrogen gas stream or addition of carbon powder is also 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,
Alternatively, a conductive powder such as acetylene black is mixed in order to impart conductivity to such a mixture powder, and a binder powder such as polytetrafluoroethylene is further added thereto as required, and the mixture is placed in a metal container. It is formed by such means as putting in, or 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. It

Lithium, which is the negative electrode active material, is formed into a sheet in the same manner as that 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. Further, as the negative electrode active material, other than lithium, lithium alloys and lithium compounds, other conventionally known alkali metals such as sodium, potassium and magnesium, alkaline earth metals, or alkali metals or alkaline earth metal ions can be occluded and released. Materials such as alloys of the above metals, carbon materials and the like 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 alkali metal. A non-aqueous electrolyte solvent in which a Lewis acid containing ions 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.

[0007]

EXAMPLES The method of the present invention will be described in more detail with reference to the following examples, which should not be construed as limiting the invention thereto. In the examples, the production and measurement of the battery were performed in a dry box under an argon atmosphere.

Example 1 FIG. 1 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, and 3 is a gasket.
Is a positive electrode case, 4 is a negative electrode, 5 is a separator, and 6 is a positive electrode material mixture pellet. Lithium carbonate, iron oxalate dihydrate, and diammonium phosphate were used as the positive electrode active material according to the following reaction formula (Formula 1), and after weighing and mixing, in a nitrogen gas stream at 800 ° C. for several days. LiFePO ₄ obtained by firing
Was used.

[0009]

Reaction formula: Li ₂ CO ₃ + 2FeC ₂ O ₄ 2H ₂
O + 2 (NH ₄ ) ₂ HPO ₄ → 2LiFePO ₄ + 4N
_{H 3 + 5CO 2 + 5H 2} O + 2H 2

The X-ray diffraction pattern of the obtained powder sample is shown in FIG. That is, FIG. 2 shows LiF which is an embodiment of the present invention.
is a diagram showing an X-ray diffraction pattern of ePO _4. In FIG. 2, the vertical axis represents X-ray diffraction intensity (arbitrary unit) and the horizontal axis represents 2θ.
(°) is shown. The X-ray diffraction pattern is LiCoPO
₄ and LiNiPO ₄ and LiMnPO ₄ , just the orthorhombic olivine structure (JCPDS # 40-1499)
It was identified as [Triphylite]. This sample is designated as a. This sample a is crushed into powder, mixed with a conductive agent (acetylene black) and a binder (polytetrafluoroethylene), and roll-formed,
Positive electrode mixture pellet 6 (thickness 0.5 mm, diameter 15 mm)
And Next, a negative electrode 4 made of metallic lithium, which was placed under pressure on a stainless steel sealing plate 1, was inserted into the recess of a polypropylene gasket 2, and a polypropylene-made microporous separator 5 and a positive electrode mixture were placed on the negative electrode 4. After arranging the pellets 6 in this order and injecting an appropriate amount of a 1N solution of LiPF ₆ dissolved in a single solvent of propylene carbonate as an electrolytic solution for impregnation, the positive electrode case 3 made of stainless steel is covered and caulked. Due to the thickness 2mm, diameter 23mm
A coin-type lithium battery was manufactured.

Example 2 As the positive electrode active material, lithium carbonate and iron oxalate dihydrate,
And ammonium vanadate according to the following reaction formula (Formula 2), after weighing and mixing, in a nitrogen gas stream at 600 ° C.
LiFeVO ₄ obtained by firing for 2 weeks was used.

[0012]

Embedded image Reaction formula: Li ₂ CO ₃ + 2FeC ₂ O ₄ 2H ₂
O + 2NH ₄ VO ₃ → 2LiFeVO ₄ + 2NH ₃ +5
CO ₂ + 3H ₂ O + 2H ₂

The X-ray diffraction pattern of the obtained powder sample is shown in FIG. That is, FIG. 3 shows LiF, which is an embodiment of the present invention.
is a diagram showing an X-ray diffraction pattern of EVO _4. 3, the vertical axis and the horizontal axis have the same meaning as in FIG. The X-ray diffraction pattern is LiCoVO ₄ (JCPDS # 38-139).
6) and LiNiVO ₄ (JCPDS # 38-1395)
Was identified as having the same cubic inverse spinel structure as. This sample is designated as b. A coin-type lithium battery was produced in the same manner as in Example 1 except that LiFeVO ₄ produced as described above was used as the positive electrode active material.

Example 3 As the positive electrode active material, lithium carbonate and iron oxalate dihydrate,
LiFe obtained by ammonium vanadate and diammonium phosphate were weighed and mixed according to the following reaction formula (Formula 3), and calcined at 600 ° C. for several days in a nitrogen gas stream.
V _0.5 P _0.5 O ₄ was used.

[0015]

## STR3 ## Reaction formula: Li ₂ CO ₃ + 2FeC ₂ O ₄ 2H ₂
O + NH ₄ VO ₃ + (NH ₄ ) ₂ HPO ₄ → 2LiFe
V _0.5 P _0.5 O ₄ + 3NH ₃ + 5CO ₂ + 4H ₂ O + 2
H ₂

This sample is designated as c. A coin-type lithium battery was produced in the same manner as in Example 1 except that LiFeV _0.5 P _0.5 O ₄ produced as described above was used as the positive electrode active material.

Comparative Example 1 In order to confirm the effect of the present invention, iron oxide, γ-Fe ₂ O ₃ , which is a typical conventional iron compound positive electrode, was used as sample d.
A coin-type lithium battery similar to that in Example 1 was produced. Both samples a (Example 1) and b prepared in this way
A battery using (Example 2), c (Example 3), and d (Comparative Example 1) as a positive electrode active material at a current density of 0.25 mA / cm ^{2 at} a voltage of 1 V after an initial charge of 5.3 V termination. The final discharge capacities are shown in Table 1.

[0018]

[Table 1]

The discharge curves of Samples a, b, and c are similar, but as an example, the discharge curve of Sample a at a current density of 0.25 mA / cm ² after an initial charge of 5.3 V termination is shown in FIG.
FIG. 5 shows the initial discharge curve of Sample d at the same current density of 0.25 mA / cm ² . That is, FIG. 4 is a characteristic diagram showing an initial discharge curve of LiFePO _{4 according to} an embodiment of the present invention after initial charging at 5.3 V, and FIG. 5 is a discharge curve of Fe ₂ O _{3 according to} a comparative example of the present invention. FIG. 4 and 5, the vertical axis represents the battery voltage (V) and the horizontal axis represents the charging / discharging time (hr). Further, as an example showing the cycle reversibility of the present invention, sample a 0.25 mA
FIG. 6 shows a charge / discharge curve during the voltage regulated charge / discharge cycle test between 5.3 V and 2.5 V at a current density of / cm ² . That is, FIG. 6 is a characteristic diagram showing a charge-discharge curve during a voltage regulation test between 5.3 V and 2.5 V of LiFePO ₄ which is an example of the present invention. In FIG. 6, the vertical axis and the horizontal axis have the same meaning as in FIG. As is clear from Table 1 and FIGS. 4 and 5, the LiFeXO ₄ of the present invention is low in cost, but compared with the conventional iron oxide positive electrode, γ-Fe ₂ O ₃ .
Since the discharge voltage is high and flat, the discharge capacity at the end of 2.5 V is about twice that of γ-Fe ₂ O ₃ . Also,
As is clear from FIG. 6, the high voltage portion has good cycleability.

[0020]

As described above, according to the present invention,
A low-cost, high-capacity, high-capacity non-aqueous electrolyte secondary battery can be configured, and has the advantage of being usable in various fields.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a configuration example of a coin-type battery that is an embodiment of the present invention.

FIG. 2 is a diagram showing an X-ray diffraction pattern of LiFePO ₄ which is an example of the present invention.

FIG. 3 is a diagram showing an X-ray diffraction pattern of LiFeVO ₄ which is an example of the present invention.

FIG. 4 is an example of the LiFePO ₄ of the present invention.
It is a characteristic view which shows the initial discharge curve after 3V initial charge.

FIG. 5 is a characteristic diagram showing a discharge curve of Fe ₂ O ₃ which is a comparative example of the present invention.

FIG. 6 is a graph showing 5. of LiFePO ₄ which is an example of the present invention.
It is a characteristic view which shows the charging / discharging curve at the time of a voltage regulation test between 3V and 2.5V.

[Explanation of symbols]

1: Sealing plate, 2: Gasket, 3: Positive electrode case, 4: Negative electrode, 5: Separator, 6: Positive electrode mixture pellet

Front page continuation (72) Inventor Hideaki Otsuka 3-19-3 Nishishinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Youji Sakurai 3-19-3 Nishishinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation Telephone Company (72) Inventor Junichi Yamaki 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (3)

[Claims] 1. AyFeXO ₄ (A is an alkali metal, X is an element of Group IV to Group VII of the periodic table, 0 <y <
2) A substance mainly composed of an alkali metal (A) -containing iron composite oxide represented by 2) is contained as a positive electrode active material, and an alkali metal,
A material capable of occluding and releasing an alkaline earth metal, or an alkali metal or an alkaline earth metal ion is used as a negative electrode active material, and an ion of the alkali metal causes an electrochemical reaction with the positive electrode active material or the negative electrode active material. A non-aqueous electrolyte secondary battery in which a substance capable of moving is an electrolyte substance. 2. The substance in which the alkali metal (A) -containing iron complex oxide, AyFeXO ₄ , contains at least one element selected from the group Va or the group Vb of the periodic table as X. The non-aqueous electrolyte secondary battery according to claim 1, wherein 3. The iron compound oxide containing alkali metal (A), AyFeXO _4, has a spinel structure or an inverse spinel structure having an olivine having a hexagonal close-packed oxygen skeleton or a cubic close-packed oxygen skeleton. Item 1
The non-aqueous electrolyte secondary battery according to.