JP2512241B2 - Non-aqueous electrolyte secondary battery and method for producing positive electrode active material thereof - Google Patents

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 secondary battery and a method for producing a positive electrode active material thereof.

[0002]

2. Description of the Related Art A non-aqueous electrolyte secondary battery having lithium or a lithium compound as a negative electrode is expected to have a high voltage and a high energy density, and many studies have been conducted for practical use.

Up to now, V ₂ O ₅ , Cr ₂ O ₅ , MnO ₂ , TiS ₂ , etc. have been known as positive electrode active materials for non-aqueous electrolyte secondary batteries, and recently, LiM by Tacley et al.
It was reported that n ₂ O ₄ could be a positive electrode active material for the battery system. (Material Research Bulletin 1983
(Vol. 18, pp. 461-472) In the figure, the potential curve has flat parts near 4.0V and 2.8V, and has two stages. Here, in order to obtain a high energy density, it is necessary to set the charge / discharge voltage range from 4.5 V to 3 V and perform the charge / discharge cycle using the potential flat portion around 4.0 V. However, using the above potential flat portion, the voltage range is 4.5V.
When charging / discharging up to 3 V, the cycle life of charging / discharging is short, and the discharge capacity decreases to less than half in about 50 cycles.

Therefore, the positive electrode active material LiMn ₂ O ₄ was improved so that Li _x M _y Mn _(2-y) O ₄ (M is Co, Cr, Ni,
At least one element selected from Fe, and 0.85
≦ x ≦ 1.15, and by using 0.02 ≦ y ≦ 0.5), cycle characteristics were improved. Also,
It was found that those having a range of 0.3 <y ≦ 0.5 had excellent over-discharge characteristics.

[0005]

However, as described above, in order to improve the overdischarge characteristics, the positive electrode active material LiMn ₂ O _{4 is used.}
By substituting at least one element selected from Co, Cr, Ni, and Fe for 15% or more of Mn of
The capacity is reduced by about 20%. The present invention solves such a problem, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery that improves over-discharge characteristics and a method for producing a positive electrode active material thereof without reducing the capacity of the battery. .

[0006]

[Means for Solving the Problem] To solve this problem
Manufacture of non-aqueous electrolyte secondary battery of the present invention and its positive electrode active material
The manufacturing method uses lithium manganese composite oxide as the positive electrode active material.
Thing Li_xMn_(2-y)Al _yO_Four(0.85 ≦ x ≦ 1.15,
0.02 ≦ y ≦ 0.5) is used.

Further, when synthesizing the lithium manganese composite oxide, aluminum chloride, aluminum bromide or aluminum nitrate is used as a starting material of Al.

[0008]

With this structure, the method for producing the non-aqueous electrolyte secondary battery and the positive electrode active material thereof according to the present invention is based on Mn in LiMn ₂ O _4.
By substituting a part of Co with Cr, Ni, Fe, the charging / discharging cycle property can be remarkably improved. Further, when the substitution amount is more than 15% and 25% or less, the charge / discharge capacity is not lowered. However, the over-discharge characteristics could be improved. Taking the example of substituting Co for Mn, Li
The lattice constant of Mn ₂ O ₄ is 8.25 Å, while Co
In the case of 5% replacement, 8.23Å, in the case of 15% replacement 8.20Å, and in the case of 25% replacement, 8.15Å. As described above, the lattice constant of the active material tends to decrease as the substitution amount increases. Further, in LiCo _y Mn _(2-y) O ₄ , the crystal lattice of the active material shrinks as the y value increases in the range of 0.3 <y ≦ 0.5, and excess Li ions due to overdischarge are generated. It has been found that a positive electrode active material having excellent over-discharge characteristics can be obtained by suppressing the intrusion of hydrogen. However, an increase in y value causes a decrease in charge / discharge capacity. In the present invention, LiMn ₂ O ₄
By substituting a part of Mn in Al with Al having an ionic radius smaller than Co, Cr, Ni, and Fe, the contraction ratio of the crystal lattice is increased, and the substitution amount is decreased, so that the capacity is reduced. In addition, an active material having excellent overdischarge characteristics can be obtained.

[0009]

EXAMPLE A method for producing a non-aqueous electrolyte secondary battery and a positive electrode active material thereof according to an example of the present invention will be described in detail below with reference to the drawings.

Example 1 In this example, Li _x was obtained by substituting a part of Mn of LiMn ₂ O ₄ with Al as a positive electrode active material.
Mn _(2-y) Al _y O ₄ (0.85 ≦ x ≦ 1.15, 0.0
2 ≦ y ≦ 0.5) was examined. As a comparative example, LiMn _(2-y) Co _y O ₄ (y = 0.5) was used.

LiMn ₂ O ₄ was prepared by the following method. L
After thoroughly mixing 4 mol of Mn ₃ O ₄ with 3 mol of i ₂ CO ₃ , the mixture was heated in the air at 900 ° C. for 10 hours to obtain a positive electrode active material LiMn ₂ O ₄ .

LiMn _1.5 Co _0.5 O ₄ was prepared by the following method. Using Li ₂ CO ₃ , CoCO ₃ and Mn ₃ O ₄ , the number of Li atoms is 1 and the number of Mn atoms is 1.
5, weigh and mix so that the number of Co atoms is 0.5,
Positive electrode active material LiM by heating in air at 900 ° C. for 10 hours
n _1.5 Co _0.5 O ₄ was obtained.

LiMn _(2-y) Al _y O ₄ (0.02≤y≤
0.5) was produced by the following method. Li ₂ CO ₃ and M
Using n ₃ O ₄ and aluminum nitrate, the number of Li atoms is 1, the number of Mn atoms is (2-y), and the number of Al atoms is y.
(Y = 0.1, 0.2, 0.3, 0.5, 0.8, 1.
0) Weigh and mix so that
And heating time positive electrode active material _{LiMn (2-y) Al y} O 4 (y =
0.1, 0.2, 0.3, 0.5, 0.8, 1.0) was obtained. However, among these, by powder X-ray diffraction, A
Those in which the substitution amount y of 1 exceeded 0.5 were not obtained as a single phase. Moreover, when the lattice constant is examined, for example, y =
For 0.2, 8.19Å was obtained. Next, a battery manufacturing method and charge / discharge conditions will be described. The above positive electrode active material, acetylene black as a conductive agent, and polytetrafluoroethylene resin as a binder in a weight ratio of 7:
The mixture was mixed at a ratio of 2: 1 to obtain a positive electrode mixture. Further, 0.1 gram of the positive electrode mixture was press-molded into a diameter of 17.5 mm at 2 ton / cm ² to obtain a positive electrode. In FIG. 2, the molded positive electrode 1 is placed in the case 2. A porous polypropylene film was placed as the separator 3 on the positive electrode 1. Negative electrode 4
As a result, a lithium plate having a diameter of 17.5 mm and a thickness of 0.3 mm was pressure-bonded to the sealing plate 5 provided with the polypropylene gasket 6. As the non-aqueous electrolyte, a propylene carbonate solution in which 1 mol / l lithium perchlorate is dissolved is used,
This was added on the separator 3 and the negative electrode 4. Thereafter, the battery was sealed. LiMn _1.9 Al _0.1 as the positive electrode active material
A coin-type battery using O ₄ (A), LiMn _1.8 Al
_The one using _0.2 O ₄ is (B), LiMn _1.7 Al _0.3 O ₄
(C), and LiMn _1.5 Al _0.5 O ₄
The coin-type battery using was designated as (D). Further, as a comparative example, a coin battery using LiMn ₂ O ₄ as an active material was designated as (E), and a coin battery using LiMn _1.5 Co _0.5 O ₄ was designated as (F).

The overdischarge characteristic test of the battery was conducted by the following method. 2. Charge the battery to 4.5V with a constant current of 2mA.
Discharge to 0V. After repeating charging / discharging for about 5 cycles in this voltage range, the voltage range is switched to 4.5V to 0V, charging / discharging is performed for 50 cycles, and 3.0V ~ again.
Charging and discharging were repeated in the voltage range of 4.5V. This test was performed on the batteries (A) to (F) using each active material, and the subsequent charge / discharge behaviors were compared. For comparison, the value obtained by dividing the discharge capacity after the over-discharge cycle by the discharge capacity before the over-discharge cycle was defined as the discharge capacity retention rate, and the durability against over-discharge was evaluated by this value. That is, it can be said that the larger the discharge capacity maintenance rate, the more excellent the over-discharge characteristics the battery has.

In FIG. 1, this is the battery (A),
The charge-discharge curves before and after the over-discharge cycle are shown for (D), (E), and (F). The X-axis scale on the discharge curve side shows the discharge capacity of the battery, and the X-axis scale on the charge curve side shows the remaining uncharged capacity of the battery. In the battery (E) which is a comparative example, the capacity is remarkably reduced after the overdischarge cycle. The battery (F), which is another comparative example, has a capacity decrease of about 5% before and after the over-discharge cycle, but the initial charge / discharge capacity is about 25% lower than that of the battery (E). On the other hand, in the batteries (A) and (D) of this example, compared with the battery (E), the initial capacity and the capacity decrease before and after the over-discharge cycle were
It can be seen that there is almost no evidence that the initial capacity is increasing. Also, in (Table 1), batteries (A) to (F)
The discharge capacity and the discharge capacity retention rate before and after the over-discharge cycle were shown.

[0016]

[Table 1]

By substituting a part of Mn in LiMn ₂ O ₄ with Al as described above, a battery excellent in over-discharge characteristics can be obtained without lowering the capacity. In addition, the substitution element A
Since 1 is an element lighter than Mn, it is understood that the battery (C) has the largest initial discharge capacity and the battery having the best over-discharge characteristics.

Example 2 Next, LiMn _(2-y) Al _y O
₄ (0.02 ≦ y ≦ 0.5) was investigated. Here, the active material LiMn _1.8 Al _0.2 O ₄ will be described in detail.

LiMn _1.8 Al _0.2 O ₄ was prepared by the following method. Li ₂ CO ₃ and Mn ₃ O ₄ are used, and aluminum chloride, aluminum bromide, aluminum nitrate, or aluminum hydroxide is used as a starting material of Al.
The number of atoms is 1, the number of Mn atoms is 1.8, and the number of Al atoms is 0.2, and the mixture is wet-mixed with water as a solvent, and the temperature is 900 ° C. for 10 hours. and heated to give a positive electrode active material LiMn _1.8 Al _0.2 O _4. In order to evaluate the active material thus obtained, a coin-type battery was produced in the same manner as in Example 1. Here, as a starting material of Al,
A battery made of an active material using aluminum nitrate (G), a battery using aluminum chloride (H), a battery using aluminum bromide (I), and a battery using aluminum hydroxide (J). ).

These batteries (G) to (J) were subjected to a charge / discharge test at a constant current of 2 mA in a voltage range of 4.5 V to 3.0 V, and the initial discharge capacities were compared. The results are shown in (Table 2).

[0021]

[Table 2]

Aluminum nitrate has the largest discharge capacity as a starting material of Al, and then aluminum chloride,
Followed by aluminum bromide. From this result aluminum hydroxide appears to be less suitable as a raw material. This seems to be due to the solubility of the raw material in water. When a material having a high solubility in water is used as a starting source of Al, the raw materials are mixed more uniformly,
It is considered that the raw material was dispersed well and a finer positive electrode active material could be obtained. Therefore, it seems that the discharge capacity of the battery increased.

In this embodiment, metallic lithium is used as the negative electrode material of the battery, but the same results are obtained when a lithium alloy or a lithium compound capable of absorbing and releasing lithium is used as the negative electrode material. It has gained.

Further, instead of lithium carbonate, lithium compounds such as lithium hydroxide and lithium nitrate are used,
Similar results were obtained when Mn compounds such as Mn ₂ O ₃ and manganese nitrate were used instead of Mn ₃ O ₄ .

[0025]

As is apparent from the above description of the embodiments,
The method for producing a non-aqueous electrolyte secondary battery and a positive electrode active material thereof according to the present invention is a non-aqueous electrolyte containing lithium, a lithium alloy or a lithium compound capable of absorbing and releasing lithium in the negative electrode, and a lithium salt in the electrolyte. using the formula _{Li x Mn (2-y)} Al y O 4 (0.85 ≦ x ≦ 1.1 as a positive electrode active material
5, 0.02 ≦ y ≦ 0.5), it is possible to provide a positive electrode active material excellent in over-discharge characteristics without lowering the capacity, which has great industrial significance.

[Brief description of drawings]

[1] LiMn _(2-y) of Example 1 of the non-aqueous electrolyte secondary battery and a positive electrode active material of the production process of the present invention Al _y O _{4 (y}
= 0.1, 0.5) and a charge / discharge curve of LiMn ₂ O ₄ and LiMn _1.5 Co _0.5 O ₄ which are comparative examples.

FIG. 2 is a vertical cross-sectional view of coin-shaped batteries used in the tests in Examples 1 and 2;

FIG. 3 is a graph showing a relationship between an x value in a Li _x Mn ₂ O ₄ positive electrode active material and an open circuit voltage of a non-aqueous electrolyte secondary battery using the same.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Yasuhiko Mito 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Yoshinori Toyokuchi 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co. In the company

Claims (2)

(57) [Claims] 1. A negative electrode is made of lithium, a lithium alloy or a lithium compound capable of absorbing and releasing lithium.
Solution using a nonaqueous electrolyte containing lithium salt in the electrolyte, wherein _{Li x Mn (2-y)} Al y O 4 as a positive electrode active material (0.85 ≦ x ≦
1.15, 0.02 ≦ y ≦ 0.5) A non-aqueous electrolyte secondary battery using a substance. 2. A negative electrode containing lithium, a lithium alloy, or a lithium compound capable of inserting and extracting lithium,
Solution using a nonaqueous electrolyte containing lithium salt in the electrolyte, wherein _{Li x Mn (2-y)} Al y O 4 as a positive electrode active material (0.85 ≦ x ≦
1.15, 0.02 ≦ y ≦ 0.5) in a non-aqueous electrolyte secondary battery using a substance represented by the above formula Li _x Mn
_(2-y) Al _y O ₄ (0.85 ≦ x ≦ 1.15, 0.02 ≦
y ≦ 0.5) In the synthesis of the positive electrode active material,
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the starting material of Al is aluminum chloride, aluminum bromide or aluminum nitrate.