JPH06283207A - Nonaqueous electrolyte battery - Google Patents

Abstract

(57) [Summary] [Purpose] The purpose is to construct a small-sized high-energy-density lithium battery having a large reversible capacity at low cost. A composition, a material represented by FePO ₄ is included as a positive electrode active material 6, an alkali metal or a compound thereof is used as a negative electrode active material 4, and it is chemically stable to the positive electrode active material and the negative electrode active material. In addition, a non-aqueous electrolyte battery in which an electrolyte substance is a substance capable of moving alkali metal ions to cause an electrochemical reaction with a positive electrode active material or a 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 non-aqueous electrolyte secondary battery that can be charged and discharged, and is particularly related to the improvement of the positive electrode active material to increase the charge and discharge capacity of the battery. It is what

[0002]

2. Description of the Related Art A non-aqueous electrolyte battery using an alkali metal such as lithium and its alloys and compounds 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. It has both chargeability. Conventionally, as a secondary battery using lithium as a negative electrode active material, V ₂ O ₅ or LiC that can serve as an intercalation host for lithium is used.
Although batteries using layered or tunnel oxides such as oO ₂ and LiNiO ₂ for the positive electrode have been proposed, these metal oxides have practical difficulties in terms of cost.

[0003]

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

[0004]

To achieve the above object, the present invention uses a compound represented by the composition formula FePO ₄ as a positive electrode active material and lithium or other alkali metal or a compound thereof as a negative electrode active material. An electrolyte material is an active material and a material that is chemically stable to the negative electrode active material and is capable of moving alkali metal ions to cause an electrochemical reaction with the positive electrode active material or the negative electrode active material. A non-aqueous electrolyte battery characterized by the above is the subject of the invention.

[0005]

The positive electrode active material, which is an iron compound of the present invention, is known to be 4
L, which is the cheapest Mn oxide among V-class high-voltage positive electrodes
Even if compared with iMn ₂ O ₄ , the cost can be reduced to half or less.

[0006]

EXAMPLES Next, examples of the present invention will be described. In the present invention, FePO ₄ was obtained by heat treating FePO ₄ .nH ₂ O. The result of thermal analysis is shown in FIG. From the results of thermogravimetric analysis in FIG. 1, it is found that heat treatment at least at 250 ° C. or higher is required to completely remove the water of crystallization from the commercially available FePO ₄ .nH ₂ O reagent. Curve A shows weight loss,
Curve B shows exotherm or endotherm. Also at room temperature and 250
FIG. 2 shows the X-ray diffraction result of the heat-treated product for 24 hours at each temperature of ° C, 550 ° C, 600 ° C, and 750 ° C. The sample heat-treated at 250 ° C is amorphous, and the sample heat-treated at 550 ° C to 750 ° C is hexagonal. To form a positive electrode using this positive electrode active material, a mixture of FePO ₄ compound powder and a binder powder such as polytetrafluoroethylene is pressure-molded on a support such as nickel or stainless steel. Alternatively, in order to impart conductivity to the mixed substance powder, a conductive powder such as pyrolytic graphite or acetylene black is mixed, and a binder powder such as polytetrafluoroethylene is further added to this, if necessary, The mixture is placed in a metal container, or the mixture is pressure-molded on a support made of nickel, stainless steel or the like.
Lithium, which is the negative electrode active material, is formed into a sheet shape like that of a general lithium battery, or is formed as a negative electrode by pressing the sheet onto a conductor network of nickel, stainless steel or the like. Further, as the negative electrode active material, in addition to lithium, conventionally known materials such as lithium alloys, lithium compounds, and sodium and potassium can be used. As an electrolyte,
For example, in an organic solvent such as dimethoxyethane, 2-methyltetrahydrofuran, ethylene carbonate, methyl formate, dimethyl sulfoxide, propylene carbonate, acetonitrile, butyrolactone, dimethylformamide, LiAsF ₆ , LiBF ₄ , LiPF ₆ ,
A non-aqueous electrolyte solution in which a Lewis acid such as LiAlCl ₄ or LiClO ₄ is dissolved can be used. Further, conventionally known various materials can be used for other elements such as a separator and structural materials (battery case, etc.), and there is no particular limitation. Hereinafter, the method of the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto. In the examples, the production and measurement of the battery were performed in a dry box under an argon atmosphere.

Example 1 FIG. 3 is a cross-sectional view of a coin-type battery which is a specific example of the battery according to the present invention, in which 1 is a stainless steel sealing plate, 2 is a polypropylene gasket,
3 is a positive electrode case made of stainless steel, 4 is a lithium negative electrode, 5 is a microporous separator made of polypropylene, and 6 is a positive electrode material mixture pellet. The positive electrode active material is FePO ₄ · nH ₂ O 2
The one obtained by heat treating at 50 ° C. for 36 hours to dehydrate FePO ₄ was used. The obtained anhydrous FePO ₄ was mixed with a conductive agent (acetylene black powder) and a binder (polytetrafluoroethylene) at a weight ratio of 70: 25: 5, and then roll-formed, and the positive electrode mixture pellet 6 (thickness: 0.5 mm, diameter 17 mm, 200 mg / cell). First, the metallic lithium negative electrode 4 placed under pressure on the sealing plate 1
Insert into the recess of the gasket 2 and place the separator 5 and the positive electrode material mixture pellet 6 in this order on the metal lithium negative electrode 4.
LiCl in an equal volume mixed solvent of propylene carbonate (PC) and 2-dimethoxyethane (DME) as an electrolytic solution.
A proper amount of 1N solution in which O ₄ was dissolved was injected and impregnated thereinto, respectively, and then the positive electrode case 3 was covered and crimped to manufacture a coin type battery having a thickness of 2 mm and a diameter of 23 mm. About the lithium secondary battery of Example 1, 0.5 m
A charge / discharge test under a voltage regulation of 4.5 V> 1 V with a discharge current density of A / cm ² was performed, and it was found that a good characteristic diagram shown in FIG. 4 was obtained and reversible charge / discharge was possible. In FIG. 4, the vertical axis represents the cell voltage and the horizontal axis represents the charging / discharging time. The curve on the lower right shows discharge and the curve on the upper right shows the state of charge.

Comparative Example 1 Commercial FePO ₄ .nH ₂ O
A coin-type battery having the same structure as in Example 1 was assembled except that the reagent was vacuum dried at 90 ° C. and then used as a positive electrode. Therefore, regarding the lithium secondary batteries of Example 1 and Comparative Example 1, the discharge current density of 0.5 mA / cm ² was 4.
When the charge / discharge test under the voltage regulation of 5V> 1V was conducted,
FIG. 5 shows the deterioration behavior of the discharge capacity with the number of charge / discharge cycles. From the comparison of the two, simply use the commercially available reagent FePO ₄
Only by vacuum drying nH ₂ O at 90 ° C., the water contained in the crystals cannot be completely removed, and good cycle characteristics cannot be obtained. It can be seen that the dehydration-treated product of FePO ₄ · nH ₂ O by heat treatment is effective for improving the high voltage capacity of FePO ₄ .

[Embodiment 2] In order to investigate the influence of the crystal system depending on the heat treatment temperature, the same coin-type battery as in Embodiment 1 was used and the FePO ₄ .nH ₂ O heat treatment conditions were set to 600 ° C. and 24 ° C., respectively.
The charge / discharge characteristics were measured under the same conditions as in Example 1 except that the time was changed. Hexagonal FePO obtained under these heat treatment conditions
The charge / discharge curve of No. ₄ is shown in FIG. Even if crystallized by high temperature heat treatment, the charge and discharge curves after the second cycle are similar to those of the amorphous heat treated product of Example 1, and there is almost no difference in battery characteristics.

[0010]

As described above, according to the present invention,
A small high energy density lithium battery having a large reversible capacity can be constructed at an extremely low cost, and the battery of the present invention has an advantage that it can be used in various fields such as a coin battery.

[Brief description of drawings]

FIG. 1 is an embodiment of the present invention FePO ₄ .nH ₂ O
The thermogravimetric analysis and the differential-thermal-analysis characteristic figure of are shown.

FIG. 2 is an embodiment of the present invention FePO ₄ .nH ₂ O
The X-ray-diffraction characteristic figure in each heat processing temperature of is shown.

FIG. 3 is a cross-sectional view showing a configuration example of a coin battery in one embodiment of the present invention.

FIG. 4 is a characteristic diagram showing a 4.5V> 1V voltage-regulated charge / discharge curve of a heat-treated FePO ₄ product as an example of the present invention at a charge / discharge current of 0.5 mA / cm ² .

FIG. 5: 0.5 mA / cm of FePO ₄ heat-treated product (present invention) and untreated product (conventional product) which are examples of the present invention.
² is a characteristic diagram showing the deterioration behavior of the discharge capacity at the time of charge / discharge current with the number of charge / discharge cycles.

FIG. 6 is a characteristic diagram showing a 4.5V> 1V regulated charge / discharge curve of anhydrous FePO ₄ crystal according to an example of the present invention at a discharge current of 0.5 mA / cm ² ;

[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 mixture pellet

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Shoji Shibata 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (72) Inventor Masahiro Ichimura 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo No. Japan Telegraph and Telephone Corporation

Claims (2)

[Claims] 1. A compound represented by the composition formula FePO ₄ is used as a positive electrode active material, lithium or other alkali metal or a compound thereof is used as a negative electrode active material, and chemically stable with respect to the positive electrode active material and the negative electrode active material. And a substance capable of moving alkali metal ions to cause an electrochemical reaction with the positive electrode active material or the negative electrode active material as an electrolyte substance. 2. The Fe as a positive electrode active material according to claim 1.
PO ₄ is a non-crystal electrolyte obtained by thermally decomposing FePO ₄ .nH ₂ O, which is a non-aqueous electrolyte battery.