JPH0766833B2 - Lithium secondary battery - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is applicable to 4 V against lithium.
The present invention relates to a secondary battery (4V class lithium secondary battery) using spinel-type LiMn ₂ O ₄ as a positive electrode active material.

[0002]

2. Description of the Related Art With the rapid miniaturization and weight reduction of electronic equipment, the development of a secondary battery that is smaller, lighter in weight and high in energy density, and that can be repeatedly charged and discharged with respect to the power source battery The demand is increasing. A lithium secondary battery is the most promising as a secondary battery satisfying these requirements. This is because a lithium secondary battery has a high negative voltage because the potential of lithium, which is a negative electrode, is very low, and the volume and weight energy density of lithium are high, so that a high energy density secondary battery can be provided. This is because it has advantages.

As a positive electrode active material for a lithium secondary battery, various materials have been proposed as a result of research. As typical ones, for example, V ₂ O ₅ , spinel type LiMn ₂ O ₄ , L
Examples thereof include iCoO ₂ . Among these, spinel type LiMn ₂ O _{4 which} is rich in resources and has a high potential of about 3 V with respect to lithium has been actively studied as a practical active material.

The electrode reaction of this active material is given by the following equation, and the working potential is about 3 V (Li / Li ⁺ ).

Discharge reaction: LiMn ₂ O ₄ + Li ⁺ + e ⁻ → Li ₂ Mn ₂ O ₄ Charge reaction: Li ₂ Mn ₂ O ₄ → LiMn ₂ O ₄ + Li ⁺ + e ⁻ However, in recent years, spinel type LiMn ₂ O ₄ is LiC
It has been reported that it has a very noble potential of about 4 V with respect to lithium by being further electrochemically oxidized similarly to oO _2, and is reversible with respect to charge and discharge of lithium (as a typical report example). Asahi Glass Industrial Technology Promotion Association Research Report, 53, 107 (1988)).

The electrode reaction of this active material is given by the following equation, and the working potential is about 4 V (Li / Li ⁺ ).

Charge reaction LiMn ₂ O ₄ → 2MnO ₂ + Li ⁺ + e ⁻ Discharge reaction 2MnO ₂ + Li ⁺ + e ⁻ → LiMn ₂ O ₄ This active material has a higher potential than conventional active materials. In addition to the above, since manganese oxide, which is abundant in resources and inexpensive, is used as a raw material, it seems to be most promising as a positive electrode active material for lithium secondary batteries.

Spinel type LiMn ₂ O ₄ generally contains a manganese oxide and a lithium compound at a Li / Mn molar ratio of 1: 1.
It is known that it can be produced by heat treatment after mixing so as to be 1/2. However, it has been reported that the optimum heat treatment conditions as an active material for batteries differ depending on the manganese oxide or lithium compound used. For example,
When manganese dioxide (MnO ₂ ) is used as the manganese oxide and lithium carbonate (Li ₂ CO ₃ ) is used as the lithium compound, the optimum heat treatment temperature is reported to be 430 ° C to 520 ° C (Japanese Patent Laid-Open No. 63-274059). Japanese Patent Laid-Open No. 1-173574
Issue). The test results shown in the conventional report are shown in FIG. 2. The results show that unreacted temperatures below 430 ° C.
It is said that it has been confirmed by experiments that Li ₂ CO ₃ remains, and on the other hand, when the temperature exceeds 520 ° C., the capacity decreases unilaterally as the processing temperature rises.

However, recently, manganese oxide (Mn ₂
There is a report that it is preferable to use O ₃ ).
-170354). Here, when lithium carbonate (Li ₂ CO ₃ ) is used as the lithium compound, 540 ° C. to 950 ° C.
Reports that the heat treatment temperature is optimal. The reason is that when the temperature is lower than 540 ° C, Li ₂ CO ₃ remains in the obtained lithium manganese oxide, whereas when the temperature exceeds 950 ° C, Mn ₃ remains.
This is because O ₄ is generated.

Therefore, according to the above report, L under various conditions
iMn ₂ O ₄ was synthesized, a lithium secondary battery was assembled using these active materials, and a charge / discharge cycle test was performed in an operating region of 4V.

Surprisingly, however, a secondary battery using an active material, which has been conventionally reported to exhibit excellent characteristics in the 3V operating region, has a charge / discharge capacity which increases as the charge / discharge cycle progresses in the 4V operating region. It was found that significant deterioration occurred.

In the above-mentioned report (Research report of Asahi Glass Industrial Technology Promotion Association, 53,107 (1988)), cubic spinel (LiMn ₂ O ₄ ) and tetragonal (Li ₂ Mn ₂ O ₄ ) in the operating region of 3V.
It is reported that intercalation and deintercalation of lithium occurs while maintaining the cubic crystal structure in the 4V operating region, while the crystal change occurs between the two.

This is 3 V against the occlusion and release of lithium.
It is suggested that the stable crystal layer is different between the operating region of 4V and the operating region of 4V. That is, since the active material exhibiting excellent characteristics in the operation range of 3 V is unstable in the operation range of 4 V with respect to lithium, the charge / discharge capacity significantly deteriorates as the cycle progresses. It seems to be.

An object of the present invention is to provide an inexpensive lithium secondary battery having a high voltage of 4V and excellent cycle characteristics.

[0015]

To the lithium according to the invention
In contrast, a lithium secondary battery operating at 4V uses a material capable of inserting and extracting lithium or lithium ions as a negative electrode active material, and at least an amount that can be detected by X-ray diffraction analysis.
Spinel type LiMn ₂ O ₄ containing manganese trioxide
Is used as the positive electrode active material.

[0016]

As a result of studies conducted to achieve the above object, spinel type LiMn ₂ O ₄ characterized by containing manganese trioxide (Mn ₂ O ₃ ) was found to have an operating range of 4 V with respect to lithium. It was found to be stable to charge and discharge.

This active material can be identified by having a diffraction peak of manganese trioxide at a diffraction angle of 32.9 degrees in X-ray diffraction using CuKα radiation.
This active material is obtained by adding lithium carbonate (Li ₂ CO ₃ ) to manganese dioxide (MnO ₂ ) in a ratio of Li / Mn atomic ratio of 1/2 and heating and firing at a temperature of 500 ° C. or higher and 750 ° C. or lower. Can be manufactured by.

The active material obtained by this method exhibits a discharge capacity of 100 mAh / g or more and an excellent capacity retention characteristic in an operating region of 4 V against lithium, but has a discharge capacity of 3 V in the operating region as previously reported. It was found that the discharge capacity was remarkably reduced with the progress of the cycle.

A battery provided with the positive electrode active material of the present invention is 4 V
The reason for having a long cycle life in the operating region of is not clear, but it is considered as follows.

Lithium carbonate is added to manganese dioxide (MnO ₂ ) and the mixture is heated and baked at a temperature of 500 ° C. or higher and 750 ° C. or lower to give manganese dioxide (Mn ₂ O ₃ ).
It is possible to synthesize spinel type LiMn ₂ O ₄ containing.

Conventionally, in a 3 V operating region where a crystal change occurs between cubic spinel (LiMn ₂ O ₄ ) and tetragonal crystal (Li ₂ Mn ₂ O ₄ ), Mn in spinel type LiMn ₂ O ₄ crystals is
It has been reported that the mixture of ₂ O ₃ adversely affects the charge / discharge capacity and the cycle retention characteristics (Japanese Patent Laid-Open No. 2-170354). However, in the 4 V operating region where the absorption and desorption of lithium ions occur while maintaining the cubic crystal structure, manganese trioxide mixed in the crystal seems to stabilize the spinel type LiMn ₂ O ₄ crystal, As a result, it is considered that the battery provided with the positive electrode active material of the present invention exhibited a long cycle life in the operation region of 4V.

This active material uses manganese dioxide, which has a large specific surface area and a large pore volume, as a starting material, and the heat treatment temperature makes it difficult for the crystal size to grow.
Since it is a relatively low temperature of 0 ° C. to 750 ° C., it is considered that it also has the features of large specific surface area and pore volume and small crystal size. The positive electrode active material of the present invention having such characteristics can smoothly occlude and release lithium ions in a 4 V operating region, and can suppress the collapse of the crystal structure due to repeated charging and discharging. As a result, it is considered that a long-life lithium secondary battery with less capacity deterioration with the progress of charge / discharge cycles could be obtained.

Examples of the manganese dioxide include γ-type, β-type or γ-β-type manganese dioxide, and those having a low content of impurities such as sodium and potassium are desirable.

[0024]

EXAMPLES The present invention will be described below with reference to preferred examples. [Example 1] Manganese dioxide and lithium carbonate were used as Li /
After mixing and crushing at a Mn molar ratio of 1/2, 1 ton / c
It was molded into pellets having a diameter of 20 mm and a height of 20 mm at m ² . Each of these pellets is placed in air for 500
It was fired at 8 ° C., 650 ° C. and 750 ° C. for 8 hours. All of these reaction products were dark blue powders, and their X-ray diffraction patterns were examined to obtain the diffraction patterns shown in FIGS. 3, 4 and 5, respectively, and the Li of ASTM No. 35-782 was obtained.
This is in agreement with the data of Mn ₂ O ₄ . Also, in all reaction products, Mn ₂ O ₃ (ASTM No. 3
1-286) peak was confirmed.

To 100 parts by weight of LiMn ₂ O _{4 of} the present invention, 5 parts by weight of acetylene black (conductive aid) and 2 parts by weight of polytetrafluoroethylene (binder) were added and kneaded well. After that, it was dried with hot air at 120 ° C. for 4 hours to prepare a positive electrode mixture. And 108 mg of the positive electrode mixture
Each was weighed and wrapped in a 325-mesh SUS316 wire mesh and pressure-molded at 2 ton / cm ² to obtain a positive electrode. The size of the positive electrode is approximately 16.0 mm in diameter and 0.4 mm in thickness. Before incorporating this positive electrode into a battery, it was vacuum dried again at 120 ° C. for 3 hours.

Lithium metal was used for the negative electrode. The size of the negative electrode is 16 mm in diameter and 0.4 mm in thickness, and the theoretical capacity is about 2
It is 30 mAh.

[0027] A polypropylene microporous separator (trade name "Celguard K274") and a polypropylene non-woven fabric are used as a separator, and the outer diameter is 20.0 mm.
I made a battery with a height of 2.0 mm.

The electrolyte used was ethylene carbonate (EC) and 4
-Methyl 1,3-dioxolane (4-MeDOL) and 1,3
-Dioxolane (DOL) and a volume ratio of 5: 3: 2.
Lithium perchlorate (1 mol / l) was dissolved as an electrolyte in the organic solvent mixed in (7) (LiClO ₄
(1M) / EC + 4-MeDOL + DOL (5: 3: 2.7) mixed solvent).

FIG. 1 is a vertical sectional view of a battery. In this figure, 1 is a case that also serves as a positive electrode terminal, which is formed by punching out a stainless steel sheet having organic electrolyte resistance by a press, and 2
Is a sealing plate that also functions as a negative electrode terminal made by stamping the same kind of material, and the negative electrode active material 3 is pressure-bonded to the inner wall thereof. Reference numeral 5 is a separator made of polypropylene impregnated with an organic electrolyte, 6 is a positive electrode mixture, and the opening end of the case 1 which also functions as a positive electrode terminal is caulked inward, and the inside of the sealing plate 2 which also functions as a negative electrode terminal via a gasket 4. It is hermetically sealed by tightening the circumference.

The present batteries using the positive electrode active material of the present invention are referred to as batteries (A), (B) and (C), respectively. [Comparative Example 1] Manganese dioxide and lithium carbonate were used as Li /
After mixing and crushing at a Mn molar ratio of 1/2, 1 ton / c
It was molded into pellets having a diameter of 20 mm and a height of 20 mm at m ² .

The pellets were respectively heated and calcined in air at 450 ° C. and 850 ° C. for 8 hours. 450
The reaction product at 0 ° C. was a brown powder, and the X-ray diffraction pattern was examined to obtain the diffraction pattern shown in FIG.
This is in agreement with the data of LiMn ₂ O ₄ of STM No. 35-782. On the other hand, the reaction product at 850 ° C. was a dark blue powder, and when the X-ray diffraction pattern was examined, the diffraction pattern was as shown in FIG. 7, which was in agreement with the data of LiMn ₂ O ₄ of ASTM No. 35-782. 33 ° for both active materials
No peak indicating the presence of Mn ₂ O ₃ (ASTM No. 31-286) in the vicinity was confirmed.

A battery similar to that of Example 1 was prepared except that these LiMn ₂ O ₄ were used as the positive electrode active material of the battery. Comparative batteries using this positive electrode active material are referred to as batteries (a) and (a), respectively. [Comparative Example 2] Manganese trioxide (Mn ₂ O ₃ ) and lithium carbonate were mixed and pulverized at a Li / Mn molar ratio of 1/2, and then pulverized into pellets having a diameter of 20 mm and a height of 20 mm at 1 ton / cm ^2. Molded.

The pellets were heated and calcined in air at 650 ° C. and 850 ° C. for 8 hours, respectively. These reaction products were dark blue powders, and their X-ray diffraction patterns were examined to give the diffraction patterns shown in FIGS. 8 and 9, which were in agreement with the data of LiMn ₂ O ₄ of ASTM No. 35-782. Both of these active materials have M around 33 °.
No peak indicating the presence of n ₂ O ₃ (ASTM No. 31-286) was confirmed.

A battery similar to that of Example 1 was prepared except that this LiMn ₂ O ₄ was used as the positive electrode active material of the battery. Comparative batteries using this positive electrode active material are referred to as batteries (C) and (D), respectively.

Regarding the above various batteries, 4.3V to 3.5
Charge and discharge were repeated at a constant current of 1.8 mA between V and the discharge capacity in each cycle was measured. As a typical example, FIG. 10 shows a charge / discharge curve at the 10th cycle of the battery (B).
Shown in.

A battery (A) of the present invention comprising an active material synthesized by using manganese dioxide as a manganese oxide,
(B) and (C) and comparative batteries (a), (a),
FIG. 11 shows the change in discharge capacity with the progress of the charge / discharge cycle of (C) and (D).

The batteries (A), (B) and (C) of the present invention using the positive electrode active material of the present invention are comparative batteries (A),
Compared to (a), (c) and (d), almost no decrease in capacity was observed with the progress of the cycle.

It is considered that the reason why the discharge capacity of the comparative battery (a) is small is that the formation of spinel type LiMn ₂ O ₄ crystals of this battery active material is insufficient.

The reason why the battery provided with the positive electrode active material of the present invention has an excellent cycle life is not clear, but it is considered as follows.

The positive electrode active materials of the batteries (A), (B) and (C) of the present invention showing excellent cycle life in the above test are spinel type LiM containing manganese trioxide.
n ₂ O ₄ . In the 4 V operating region, the positive electrode active material occludes and releases lithium ions while maintaining the cubic crystal structure. At this time, it is considered that the manganese trioxide contained in the crystal prevents the collapse of the spinel type LiMn ₂ O ₄ crystal, and as a result, a comparative battery having an active material containing no manganese trioxide (a) ), (U)
It is considered that the battery provided with the positive electrode active material of the present invention did not show a decrease in discharge capacity with the progress of cycles, as compared with (d) and (d).

The active material of the present invention uses manganese dioxide, which has a large specific surface area and a large pore volume, as a starting material, and the heat treatment temperature makes it difficult for the crystal size to grow.
Since it is a relatively low temperature of 0 ° C. to 750 ° C., it is considered that it also has characteristics that the specific surface area and the pore volume are large and the crystal size is small. In the positive electrode active material of the present invention having such characteristics, the lithium ions can be smoothly absorbed and desorbed in the operation region of 4 V, and the collapse of the crystal structure due to repeated charging and discharging can be suppressed. . As a result, it is considered that a long-life lithium secondary battery with less capacity deterioration with the progress of charge / discharge cycles could be obtained.

Although lithium was used as the negative electrode active material in the above examples, when using the positive electrode of the present invention,
The negative electrode active material is basically not limited, and a conventional material capable of inserting and extracting um ions of an organic electrolyte secondary battery can be used.

Further, the organic solvent which is a lithium ion conductive substance and the solid ionic conductor are not basically limited, and those used in the conventional organic electrolyte secondary battery can be used. Examples of the organic solvent include cyclic esters such as ethylene carbonate which is an aprotic solvent and ethers such as tetrahydrofuran and dioxolane. These can be used alone or in a mixture of two or more kinds. As the solid ionic conductor, any substance having lithium ion conductivity can be used. A typical example thereof is polyethylene oxide.

Also, the supporting electrolyte dissolved in such an organic solvent or solid ionic conductor is not basically limited. For example, LiAsF ₆ , LiClO ₄ , Li
One or more of BF ₄ , LiP _F6 and LiCF ₃ SO ₃ can be used.

Although the batteries according to the above-mentioned embodiments are all button type batteries, the same effect can be obtained by applying the present invention to cylindrical, prismatic or paper type batteries.

[0046]

As described in detail above, according to the present invention, LiMn ₂ O ₄ for a 4V class lithium secondary battery, which is excellent in reversibility for occlusion and release of lithium ions, can be used as a positive electrode active material, It is possible to provide a high energy density 4V class lithium secondary battery having excellent cycle life performance as compared with a conventional battery.

[Brief description of drawings]

FIG. 1 is a diagram showing an internal structure of a button battery which is an example of a 4V class lithium secondary battery.

FIG. 2 is a diagram showing a conventional report example.

FIG. 3 is a diagram showing an X-ray diffraction pattern of LiMn ₂ O ₄ according to this example.

FIG. 4 is a diagram showing an X-ray diffraction pattern of LiMn ₂ O ₄ according to this example.

FIG. 5 is a diagram showing an X-ray diffraction pattern of LiMn ₂ O ₄ according to this example.

FIG. 6 is a diagram showing an X-ray diffraction pattern of LiMn ₂ O ₄ according to a comparative example.

FIG. 7 is a diagram showing an X-ray diffraction pattern of LiMn ₂ O ₄ according to a comparative example.

FIG. 8 is a diagram showing an X-ray diffraction pattern of LiMn ₂ O ₄ according to a comparative example.

FIG. 9 is a diagram showing an X-ray diffraction pattern of LiMn ₂ O ₄ according to a comparative example.

FIG. 10 is a diagram showing charge / discharge curves of the batteries prepared in Examples.

FIG. 11 is a graph showing a change in discharge capacity of a battery according to the present invention and a comparative battery as the charging / discharging cycle progresses.

[Explanation of symbols]

 1 Battery Case 2 Sealing Plate 3 Lithium 4 Gasket 5 Separator 6 Positive Electrode Mixture

Claims (1)

[Claims] 1. A material capable of inserting and extracting lithium or lithium ions is used as a negative electrode active material, and at least X-rays are used.
The <br/> spinel LiMn ₂ O ₄ containing three manganese dioxide in an amount that can be detected by diffraction analysis was the positive electrode active material, lithium
Lithium secondary battery that operates at 4V with respect to battery.