JPH10116603A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the storage characteristics by adding additives such as Al2 O3 to manganese oxides, thereby deactivating the active portion of the manganese oxide, and making the reaction of the manganese oxide with non-aqueous electrolyte during storage be hardly caused. SOLUTION: In the process of fabricating a positive electrode, alumina (Al2 O3 ) is added to manganese dioxide which has undergone a dehydrating process, and the obtained mixture is mixed with carbon powder as electroconductive aid material and fluororesin powder as a binder, and the resultant material is pressure molded into a disc shape, followed by a heating process. In lieu of alumina, it may be accepted to add to manganese oxide at least one of the additives selected among In2 O2 , Tl2 O3 , LiAlO2 , LiGaO2 , and LiTlO2 . As a result, the active portion of the manganese oxide is deactivated so as to make the reaction of manganese oxide with a non-aqueous electrolyte during storage be hardly caused, and excellent storage characteristics can be established.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery including a positive electrode using manganese oxide as an active material, a negative electrode, and a non-aqueous electrolyte, and more particularly, to improving the storage characteristics thereof. And improvement of the positive electrode.

[0002]

2. Description of the Related Art In recent years,
Lithium secondary batteries have attracted attention because they can achieve higher voltages and higher capacities than conventional alkaline secondary batteries. This is because in the case of a lithium secondary battery that does not use an alkaline electrolyte, it is not necessary to consider the decomposition voltage of water when designing the battery.

As a positive electrode active material of a lithium secondary battery,
Metal oxides are mainly used, and among them, manganese oxide is a material that has attracted attention because it is very inexpensive.

However, in a lithium secondary battery, since the voltage of the positive electrode becomes 3 V or more, when a highly active manganese oxide is used as the positive electrode active material, it reacts with the non-aqueous electrolyte. Therefore, when the battery is stored for a long period of time, there is a problem that discharge characteristics and cycle characteristics are deteriorated. For this reason, suppressing the reaction between the manganese oxide and the non-aqueous electrolyte has become an urgent task toward the practical use of this type of secondary battery.

By the way, in order to improve the storage characteristics of a lithium secondary battery using manganese oxide as a positive electrode active material, manganese containing manganese and boron in a specific atomic ratio, which causes little change in crystal structure during charge / discharge cycles, is provided. -It has been proposed to use a boron composite oxide as a positive electrode active material (Japanese Unexamined Patent Publication No. Hei 3-297058). The technology disclosed in this publication uses a manganese-boron composite oxide, which has little crystal structure collapse during a charge / discharge cycle, as a positive electrode active material, so that water (adhered water and bound water) flows out of the positive electrode active material. To suppress the deterioration of battery characteristics due to the reaction between water and lithium during storage.

However, the above manganese-boron composite oxide also has a high surface activity like manganese dioxide. Therefore, when the battery is stored for a long time or at a high temperature, it gradually reacts with the nonaqueous electrolyte. In addition, the reaction product adheres as a film to the surface of the positive electrode or the negative electrode, and battery characteristics such as discharge characteristics and charge / discharge cycle characteristics are deteriorated. That is, the conventional technology described above does not sufficiently improve storage characteristics.

The present invention has been made in view of the above circumstances, and has been made in view of the fact that a reaction between a manganese oxide and a non-aqueous electrolyte during storage is unlikely to occur, so that lithium having excellent storage characteristics is hardly deteriorated in battery characteristics. It is intended to provide a secondary battery.

[0008]

Means for Solving the Problems A lithium secondary battery (battery of the present invention) according to the present invention for achieving the above object has a positive electrode using manganese oxide as an active material, a negative electrode, and a nonaqueous electrolyte. Wherein the manganese oxide includes Al ₂ O ₃ , In
₂ O ₃ , Ga ₂ O ₃ , Tl ₂ O ₃ , LiAlO ₂ , Li
At least one additive selected from InO ₂ , LiGaO ₂ and LiTlO ₂ is added.

Examples of the manganese oxide include a composite oxide of lithium and manganese and manganese dioxide.
As a composite oxide of lithium and manganese, LiMn
₂ O ₄ is exemplified. In addition, a mixture of lithium material such as lithium hydroxide and manganese dioxide having an atomic ratio of Li: Mn of 1: 9 to 7: 3 as a composite oxide with less collapse of the crystal structure during charge / discharge cycles is 300 to 430. And those obtained by heat treatment at ° C. As the manganese oxide, a manganese-boron composite oxide disclosed in JP-A-3-297058 can be used.

Al ₂ O ₃ , In ₂ O ₃ , Ga ₂ O ₃ , T
l ₂ O ₃ , LiAlO ₂ , LiInO ₂ , LiGaO ₂
LiTlO ₂ and LiTlO ₂ may be used alone or in combination of two or more as needed. The proportion of these additives to manganese oxide is 10% manganese.
The total amount is preferably 0.1 to 30 mol per 0 atom.
If the addition ratio is out of this range, it becomes difficult to obtain sufficient storage characteristics.

The present invention relates to an improvement in a positive electrode of a lithium secondary battery. Therefore, as the members other than the positive electrode, conventionally known members as shown below can be used without particular limitation.

Examples of the negative electrode material include a substance capable of electrochemically absorbing and releasing lithium ions and lithium metal. Specific examples of the substance capable of electrochemically occluding and releasing lithium ions include carbon materials such as graphite, coke, and fired organic materials;
Lithium alloys such as aluminum alloys, lithium-lead alloys, lithium-tin alloys; SnO ₂ , SnO, TiO ₂ , N
A metal oxide having a potential such as b ₂ O ₃ which is lower than that of the positive electrode active material may be used.

Specific examples of the solvent of the nonaqueous electrolyte include a mixed solvent of ethylene carbonate and 1,2-dimethoxyethane, a mixed solvent of ethylene carbonate, propylene carbonate and 1,2-dimethoxyethane, and a mixed solvent of ethylene carbonate and butylene. A mixed solvent of carbonate and 1,2-dimethoxyethane is exemplified. Specific examples of the solute of the non-aqueous electrolyte include LiPF ₆ , LiAsF ₆ ,
LiSbF ₆ , LiClO ₄ , LiCF ₃ SO ₃ are mentioned.

In the battery of the present invention, a specific additive is added to the highly active manganese oxide to inactivate the active portion in the manganese oxide. The reaction with the electrolyte does not easily occur. For this reason, the battery of the present invention has excellent storage characteristics.

[0015]

EXAMPLES The present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples and can be carried out by appropriately changing the scope of the invention without changing its gist. It is something.

(Example 1) [Preparation of positive electrode] Alumina (Al ₂ O ₃ ) was added to manganese dioxide (MnO ₂ ) dehydrated at 400 ° C. at a ratio of 5 mol per 100 atoms of manganese. . The mixture thus obtained, and carbon powder as a conductive agent,
A fluororesin powder as a binder was mixed in a weight ratio of 8: 1: 1.
And press-molded into a disk shape, followed by heat treatment at 250 ° C. to produce a positive electrode.

[Preparation of Negative Electrode] A disk-shaped negative electrode was prepared by punching a lithium-aluminum alloy plate.

[Preparation of Nonaqueous Electrolyte] A nonaqueous electrolyte was prepared by dissolving 1 mol / l of LiPF ₆ in a mixed solvent of ethylene carbonate and 1,2-dimethoxyethane at a volume ratio of 1: 1.

[Assembly of Battery] Using the above positive electrode, negative electrode and non-aqueous electrolyte, a flat lithium secondary battery (Battery A1 of the present invention; battery dimensions: outer diameter 24.0 mm, thickness 3.0 m)
m) was assembled. A microporous film made of polypropylene was used for the separator, and this was impregnated with a non-aqueous electrolyte.

Comparative Example 1 A comparative battery B1 was assembled in the same manner as in Example 1 except that no alumina was added in the preparation of the positive electrode.

Example 2 In the preparation of the positive electrode, a mixture of lithium hydroxide and manganese dioxide in a Li: Mn atomic ratio of 3: 7 was heated at 375 ° C. instead of manganese dioxide as the positive electrode active material. The battery A of the present invention was prepared in the same manner as in Example 1 except that the lithium-manganese composite oxide (hereinafter, referred to as Li-Mn composite oxide) obtained as described above was used.
2 was assembled.

Comparative Example 2 A comparative battery B2 was assembled in the same manner as in Example 2 except that alumina was not added in the production of the positive electrode.

Example 3 In the preparation of the positive electrode, LiMn ₂ O ₄ was used instead of manganese dioxide as the positive electrode active material.
Battery A3 of the present invention was assembled in the same manner as Example 1 except that was used.

Comparative Example 3 A comparative battery B3 was assembled in the same manner as in Example 3 except that alumina was not added in the production of the positive electrode.

<Storage characteristics> Each battery immediately after assembly was stored at 25 ° C.
At a constant resistance of 1 kΩ to determine the discharge capacity C1. Each battery immediately after the assembly was stored at 80 ° C. for 2 months, and then discharged under a constant resistance under the same conditions to obtain a discharge capacity C2. The self-discharge rate (%) of each battery was calculated based on the following equation. Table 1 shows the results.

Self-discharge rate (%) = (1−C2 / C1) × 100

[0027]

[Table 1]

As shown in Table 1, the batteries A1, A of the present invention
2 and A3 have lower self-discharge rates than the comparative batteries B1, B2 and B3, respectively. From this fact, regardless of the type of manganese oxide, by adding alumina,
It can be seen that the storage characteristics are greatly improved.

<Relationship Between Additive Ratio of Additive and Storage Characteristics> In the preparation of the positive electrode, the additive ratio of alumina to the Li.Mn composite oxide was 0.05 mol, 0.1 mol, and 1 mol, 10 mol, 20
Example 2 except that the moles were 30 moles and 40 moles.
In the same manner as in the above, batteries A4 to A10 of the present invention were assembled in this order. Next, a test was performed under the same conditions as described above, and the self-discharge rate of each battery was determined. Table 2 shows the results. In Table 2, the results of Battery A2 of the present invention and Comparative Battery B2 are also transcribed from Table 1.

[0030]

[Table 2]

From Table 2, it can be seen that the addition ratio of alumina to the Li.Mn composite oxide is preferably in the range of 0.1 to 30 mol per 100 atoms of manganese. In addition, other manganese oxides (manganese dioxide and LiMn
_{When using 2} O ₄ ) and other additives,
It was confirmed that the number of moles of the additive relative to 00 atoms is preferably 0.1 to 30.

<Relationship between Type of Additive and Storage Characteristics> In the preparation of the positive electrode, In ₂ O ₃ ,
Ga ₂ O ₃ , Tl ₂ O ₃ , LiAlO ₂ , LiGa
Batteries A11 to A17 of the invention were assembled in the same manner as in Example 2 except that O ₂ , LiInO ₂ , and LiTlO ₂ were added to the Li · Mn composite oxide. Further, in the production of the positive electrode, boric acid (H ₃ BO ₃ ) was added to the Li · Mn composite oxide instead of the mixture obtained by adding and mixing alumina to the Li · Mn composite oxide with respect to 100 atoms of manganese. A comparative battery B4 was assembled in the same manner as in Example 1 except that a mixture heated at 350 ° C. was used after addition and mixing at a ratio of 5 mol. Further, in the preparation of the positive electrode, boric acid was added to manganese dioxide at a ratio of 5 mol based on 100 atoms of manganese, and water was added, and the mixture was sufficiently stirred in place of the mixture obtained by adding and mixing manganese dioxide with alumina. After mixing, a comparative battery B5 was assembled in the same manner as in Example 1 except that a manganese-boron composite oxide (Mn-B composite oxide) obtained by performing a heat treatment at 400 ° C. for 4 hours was used. . This comparative battery B5 is disclosed in
This is a battery corresponding to the conventional battery disclosed in Japanese Patent Application Laid-Open No. 297058. Next, a test was performed under the same conditions as described above, and the self-discharge rate of each battery was determined. Table 3 shows the results. Table 3
5 also shows the results of the comparative battery B2 transcribed from Table 1.

[0033]

[Table 3]

As shown in Table 3, the batteries A11 to A of the present invention
17 has a significantly lower self-discharge rate than the comparative batteries B1, B4, and B5. From this fact, In ₂ O was added to the manganese oxide.
₃ , Ga ₂ O ₃ , Tl ₂ O ₃ , LiAlO ₂ , LiGa
It can be seen that when O ₂ , LiInO _2, or LiTlO ₂ is added, a lithium secondary battery with extremely excellent storage characteristics can be obtained, similarly to the case where alumina is added.

In the above embodiment, the case where one kind of additive is added has been described. However, even when two or more kinds of additives specified in the present invention are added in combination, lithium secondary having extremely excellent storage characteristics can be obtained. It was confirmed that a battery was obtained.

[0036]

In the battery of the present invention, since the active portion of the manganese oxide is inactivated, the reaction between the manganese oxide and the non-aqueous electrolyte during storage hardly occurs. For this reason, the battery of the present invention has excellent storage characteristics.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshiyuki Noma 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Koji Nishio 2-chome Keihanhondori, Moriguchi-shi, Osaka No. 5-5 in Sanyo Electric Co., Ltd.

Claims (3)

[Claims] 1. A lithium secondary battery comprising a positive electrode using a manganese oxide as an active material, a negative electrode, and a non-aqueous electrolyte, wherein the manganese oxide includes Al ₂ O ₃ , In ₂ O ₃ ,
Ga ₂ O ₃ , Tl ₂ O ₃ , LiAlO ₂ , LiIn
A lithium secondary battery comprising at least one additive selected from O ₂ , LiGaO ₂ and LiTlO ₂ . 2. The lithium secondary battery according to claim 1, wherein the manganese oxide is a composite oxide of lithium and manganese or manganese dioxide. 3. An Al ₂ O ₃ , In ₂ O ₃ , Ga ₂ O ₃ , T
l ₂ O ₃ , LiAlO ₂ , LiInO ₂ , LiGaO ₂
And at least one additive selected from among LiTlO ₂ is, with respect to manganese 100 atoms in the manganese oxide, claim is added in an amount of 0.1 to 30 mol 1
Or the lithium secondary battery according to 2.