JP3086297B2 - Non-aqueous solvent secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a positive electrode active material used for a non-aqueous solvent secondary battery.

[0002]

2. Description of the Related Art In recent years, with the development of electronic equipment, there has been a demand for the development of a secondary battery which is small, lightweight, has a high energy density and can be repeatedly charged and discharged. Known secondary batteries of this type use lithium or a lithium alloy as a negative electrode active material, and use oxides, sulfides, selenides, or the like such as molybdenum, vanadium, titanium, or niobium as a positive electrode active material. Have been.

On the other hand, manganese dioxide is used in non-aqueous solvent primary batteries as a positive electrode active material having a high energy density and a high voltage, and has been put to practical use. Therefore, in a non-aqueous solvent secondary battery having a lithium anode, use of the manganese dioxide as a cathode active material has been studied. However, such non-aqueous solvent secondary batteries have a problem in charge / discharge cycle characteristics. That is, the manganese dioxide has a tunnel structure, and when the battery is discharged, the Li ⁺ ions of the negative electrode enter the tunnel, thereby expanding the MnO ₂ crystal structure. Since the alkali metal ions in the tunnel can easily move, when the battery is charged, the Li ⁺
Is released, and the MnO ₂ crystal structure shrinks accordingly. For this reason, M used in a conventional non-aqueous solvent primary battery
When nO ₂ is used as it is as a positive electrode active material of a secondary battery, the initial discharge capacity is large, but the contraction and expansion of the crystal structure are repeated as the battery is charged and discharged.
There was a problem that the tunnel structure of No. ₂ collapsed and the charge / discharge capacity deteriorated significantly as the charge / discharge cycle progressed.

[0004] In view of the above, Japanese Patent Laid-Open No. 2-1703 is disclosed.
53, as shown in JP-A-2-170354, cycle characteristics can be improved by using a lithium manganese oxide obtained by adding a lithium salt to a manganese oxide obtained by a novel synthesis method and heat-treated. ing.

On the other hand, in a system using lithium as a negative electrode active material, a dendrite phenomenon in which lithium precipitates in a needle-like shape during charging and discharging is caused, and the danger of an internal short circuit or the like is considered at this stage. Therefore, as a negative electrode carrier,
Electrode active materials using the intercalation or doping phenomenon have attracted attention. Since these electrode active materials do not cause a complicated chemical reaction during the charge / discharge reaction, they are expected to have an extremely excellent charge / discharge cycle. In particular, a system using a carbonaceous material as a negative electrode support and using LiCoO ₂ / LiNiO ₂ or the like as a positive electrode active material has been proposed.

[0006]

As described above, a system using a carbonaceous material as a negative electrode carrier is very interesting. At this time, it is important to select a positive electrode active material as a counter electrode. The cycle life of LiCoO ₂ / LiNiO ₂ described above can be improved by its synthesis conditions and the addition of the third component, and when combined with a carbonaceous material, the battery can have excellent cycle characteristics. It has disadvantages such as instability of the product. Further, when a lithium manganese oxide disclosed in Japanese Patent Application Laid-Open No. 2-170354 is combined, the capacity accompanying the cycle is so large that it cannot be put to practical use.

[0007] The present invention has been made to address such a problem, and has as its object to improve the cycle characteristics of lithium manganese oxide.

[0008]

The present invention relates to manganese trioxide and manganese tetroxide obtained by roasting manganese sulfate.
As a positive electrode active material, a lithium manganese-based composite oxide obtained by adding and heating a lithium compound and at least one metal salt selected from magnesium, titanium, vanadium, iron, cobalt, nickel, and zinc is used. By doing so, the above object is achieved.

A method for synthesizing the above-mentioned lithium manganese composite oxide will be described step by step. Mn ₃ O ₄ can be obtained by heating manganese sulfate to obtain anhydrous manganese sulfate and heating it at about 1000 ° C. in the atmosphere. Further, this Mn ₃ O ₄ is oxidized and roasted at about 700 ° C. to form Mn ₂ O 4.
₃ is obtained. Examples of the lithium compound include lithium carbonate (Li ₂ CO ₃ ) and lithium nitrate (LiNO
₃ ) and lithium hydroxide (LiOH). As the third component metal salt, carbonate (MgCO ₃ , Co
CO ₃ , NiCO ₃ , ZnCO ₃ ), sulfate (Fe
₂ (SO ₄ ) ₃ , Ti (SO ₄ ) ₂ ) and ammonium vanadate (NH ₄ VO ₃ ).

The mixing ratio of these compounds is represented by the general formula: Lix
When expressed as MMyMzO ₄ (M: metal component), 0.9 ≦ x
≦ 1.16, 1 ≦ y <2, 0 <z ≦ 1, 1.8 ≦ y + z
The range of ≦ 2.2 is preferred. If the amount of lithium (x) is small, the lower metal oxide is contained in the lithium manganese oxide after the heat treatment, and if it is too large, Li ₂ CO ₃ , Li ₂
O and the like are contained, and in any case, the cycle characteristics may be deteriorated. When the manganese content and the metal component content are out of the specified ranges, there is a possibility that the cycle characteristics of the obtained lithium manganese-based composite oxide may deteriorate. The heating temperature range after the addition of the metal salt is 600 to 95.
A temperature range of 0 ° C. is preferred. If the temperature is lower than 600 ° C., unreacted components are present, and if the temperature exceeds 950 ° C., a lower metal oxide is contained, which may cause deterioration of cycle characteristics.

In the non-aqueous solvent secondary battery of the present invention, a binder may be used to form a positive electrode and a negative electrode. Examples of the binder include a terpolymer of ethylene-propylene-cyclic diene, polytetrafluoroethylene, polyacrylic acid, and polyacrylates.

The electrolyte of the non-aqueous electrolyte used in the non-aqueous solvent secondary battery of the present invention includes LiPF ₆ , LiCl
Lithium salts such as O ₄ , LiBF ₄ , and LiCF ₃ SO ₃ are exemplified. As the solvent for the electrolytic solution, propylene carbonate (PC), ethylene carbonate (E
C), tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, 1,2-dimethoxyethane (DME). These solvents can be used alone or as a mixture of two or more kinds. In particular, from the viewpoint of extending the charge / discharge cycle life, a mixed solvent of propylene carbonate and 1,2-dimethoxyethane, ethylene carbonate and 2-methyltetrahydrofuran , A mixed solvent of ethylene carbonate and 1,2-dimethoxyethane, and a mixed solvent of propylene carbonate and ethylene carbonate.

As the carbonaceous material as the negative electrode carrier, a carbonaceous material obtained by firing an organic compound is preferably used in order to improve battery characteristics. The organic compound serving as a raw material of the carbonaceous material is not particularly limited as long as it is a commonly used one. For example, a phenol resin, particularly a novolak resin, and polyacrylonitrile can be used. It is particularly preferable that the carbonaceous material has the characteristics of an organic compound fired body as shown in Japanese Patent Application No. 1-283086.

[0014]

According to the present invention, manganese trioxide and manganese tetroxide obtained by roasting manganese sulfate are added to a lithium compound and at least one of Mg, Ti, V, Fe, Co, Ni and Zn. By using a lithium manganese-based composite oxide obtained by adding and heat-treating a metal salt, it was possible to suppress capacity deterioration due to charge and discharge when a carbonaceous material was used as a negative electrode support. This is because the third component element replaces manganese in the crystal structure, and therefore L in the crystal structure
This is because the structural change due to the desorption / intrusion of i could be suppressed.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings.
You. Example 1: Manganese sulfate (MnSO₄・ H₂O) 2 kg
Is heated in air at 600 ° C. for 30 minutes to dehydrate to anhydrous salt.
After that, the obtained anhydrous manganese sulfate (MnSO₄) Atmosphere
Baking at 1050 ° C for 20 minutes in Mn₃O₄And
Further, this is oxidized and roasted at 700 ° C. for 10 minutes to obtain Mn₂O₃
Was obtained in an amount of about 1 kg. The reaction formula during this time is shown below. MnSO₄・ H₂O → MnSO₄+ H₂O MnSO₄ → 1 / 3Mn₃O₄+ SO₂+1/30₂  Mn₃O₄+ ／ O₂→ 3 / 2Mn₂O₃  Mn obtained by the above method₂O₃And lithium carbonate and dicarbonate
And Li: Mn: Ni = 1: 1.9: 0.1.
The mixture was weighed in a molar ratio and mixed well in a mortar. This mix
The mixture was heated at 850 ° C, cooled and pulverized again.
Heat to heat lithium manganese composite oxide (LiMn_1.9
Ni_0.1O₄) Got.

90% by weight of this product, 7% by weight of acetylene black as a conductive material and 3% by weight of a terpolymer of ethylene-propylene-cyclic diene as a binder are kneaded in hexane to form a slurry-like positive electrode. A positive electrode mixture was prepared, and this positive electrode mixture was applied on a titanium substrate having a thickness of 15 μm, air-dried, and then pressurized to a constant thickness, followed by heating and drying at 200 ° C. for 10 hours to obtain 0.26 mm A plate-shaped positive electrode having a thick positive electrode mixture layer was produced.

On the other hand, the carbonaceous material as the negative electrode carrier is obtained by firing a novolak resin at 950 ° C. in a nitrogen atmosphere.
It was further manufactured by heating to 2.000 ° C. to carbonize and pulverized to a powder having an average particle size of 10 μm.

A terpolymer of ethylene-propylene-cyclic diene as a binder is dissolved in hexane and dispersed so that the carbonaceous material: the binder = 97: 3. Prepared. This slurry was applied on a stainless steel substrate having a thickness of 10 μm and dried to form a negative electrode mixture layer having a thickness of 0.2 mm.

Using the positive and negative electrodes thus obtained, a non-aqueous solvent secondary battery (A) of AA size as shown in FIG. 1 was assembled. That is, the non-aqueous solvent secondary battery 1 includes the cylindrical stainless steel container 3 having the bottom, on which the insulator 2 is disposed, and which also serves as the negative electrode terminal. The container 3 contains an electrode group 4. The electrode group 4 has a structure in which a strip formed by laminating a negative electrode 5, a separator 6, and a positive electrode 7 in this order is spirally wound so that the negative electrode 5 is located outside. The separator 6 is formed of a polypropylene porous film impregnated with an electrolytic solution. The electrolyte is composed of propylene carbonate and 1,2
Mixed solvent with dimethoxyethane (volume ratio 50: 5
0), lithium hexafluorophosphate (LiP
F ₆ ) in a 0.5 molar concentration. Above the electrode group 4 in the container 3, an insulating plate 8 having an opening at the center is arranged. An insulating sealing body 9 is provided at the upper opening of the container 3.
Are fixed to the container 3 in an airtight manner. A positive electrode terminal 10 is fitted into a central opening of the insulating sealing plate 8. The positive terminal 10 is connected to the positive electrode 7 via a positive electrode lead 11. In addition, the said negative electrode 5
It is connected to the above-mentioned container 3 which is a negative electrode terminal via a negative electrode lead (not shown).

Example 2: Mn ₂ O obtained by the method of Example 1
₃ and lithium carbonate, magnesium carbonate with Li: Mn:
Mg was weighed out in a molar ratio of 1: 1.7: 0.3 and mixed well in a mortar. This mixture was heated at 800 ° C., cooled, mixed again, and heated at 800 ° C. to obtain a lithium manganese composite oxide (LiMn _1.7 Mg _0.3 O ₄ ).
Using this product, a battery (B) similar to that of Example 1 was produced.

Example 3 Mn ₂ O obtained by the method of Example 1
₃ with lithium carbonate, cobalt carbonate and ammonium vanadate, Li: Mn: Co: V = 1.1: 1.2:
It was weighed in a molar ratio of 0.8: 0.1 and mixed well in a mortar. This mixture was heated at 850 ° C., cooled and mixed again, and heated at 850 ° C. to obtain a lithium manganese composite oxide (Li _1.1 Mn _1.2 Co _0.8 V _0.1 O ₄ ).
I got Battery (C) similar to that of Example 1 using this product
It was created.

Comparative Example 1: Mn ₂ O ₃ obtained in Example 1 and lithium carbonate were weighed and mixed at a molar ratio of Li: Mn = 1: 2, and then heated at 850 ° C. to obtain spinel type LiM.
n ₂ O ₄ was obtained. Using this product, a battery (D) similar to that of Example 1 was produced. Comparative Example 2: Mn ₂ O ₃ obtained by heat-treating electrolytic manganese dioxide at 600 ° C., lithium carbonate and nickel carbonate,
Li: Mn: Ni = 1: 1, 9: 0.1 were weighed out, mixed, and then heat-treated at 850 ° C. to obtain a lithium-manganese composite oxide. Using this product, a battery (E) similar to that of Example 1 was produced.

Embodiments 1, 2, 2
3. With respect to the five types of non-aqueous solvent secondary batteries of Comparative Examples 1 and 2, 4.2 V at a constant current of 20 mA and a constant current of 100 mA.
And 2.8 V in the range from 1 to 2.8 V. FIG. 2 shows the discharge capacity retention rate in this charge / discharge evaluation. As is clear from FIG. 2, the non-aqueous solvent secondary batteries A, B, and C of the present invention have smaller capacity deterioration due to the cycle than the comparative batteries D and E. Has good characteristics.

This is because the third component metal element added during the synthesis partially replaces the coordination position of manganese in the spinel-structured LiMn ₂ O ₄ , and partially becomes a lithium compound and is mixed in the active material. Becomes Due to these effects, 4
It is considered that the Li ions in the crystal accompanying the charge / discharge at about V smoothly flow in and out, and the structural change can be suppressed, so that the capacity deterioration is small. Further, the composition of Example 1 and Comparative Example 2 is the same, but the one of this example has better cycle characteristics. This is because the lower manganese oxide (Mn ₂ O ₃ ,
Since Mn ₃ O ₄ ) has a large specific surface area and small particles, the obtained active material has a large specific surface area and a small particle diameter as compared with those of the comparative example, and it is considered that the electrochemical properties are improved.

[0025]

The non-aqueous solvent secondary battery of the present invention is characterized in that manganese sulfate and manganese oxide obtained by roasting manganese sulfate as a positive electrode active material are added to lithium salt, Mg, Fe,
By using a lithium manganese-based active material obtained by adding and heating at least one metal salt composed of V, Ti, Co, Ni, and Zn, charge and discharge can be performed even when a carbonaceous material is used as the negative electrode. Thus, a non-aqueous solvent secondary battery having a long service life can be obtained. The positive electrode active material of the present invention can be used in a system using lithium or a lithium alloy as the negative electrode. In that case, what limits the battery characteristics is deterioration on the negative electrode side. 2-1
Characteristics equivalent to those shown in 70354 are obtained.

[Brief description of the drawings]

FIG. 1 is a half-mounted sectional view showing a non-aqueous solvent secondary battery of Example 1 of the present invention.

2 (A), 2 (B) and 3
FIG. 9C is a characteristic diagram showing a change in discharge capacity with respect to the number of charge / discharge cycles in each of the nonaqueous solvent secondary batteries of Comparative Example 1 (D) and Comparative Example 2 (E).

[Explanation of symbols]

 1: Non-aqueous solvent secondary battery 4: Electrode group 7: Positive electrode

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 4/36-4/62 H01M 10/40

Claims (1)

(57) [Claims] A lithium compound, magnesium, or manganese trioxide (Mn ₂ O ₃ ) or manganese tetroxide (Mn ₃ O ₄ ) obtained by roasting manganese sulfate.
A lithium manganese-based composite oxide obtained by adding and heating one or more metal salts selected from titanium, vanadium, iron, cobalt, nickel and zinc is used as a positive electrode active material. Non-aqueous solvent secondary battery.