JPH08195200A - Positive electrode active material for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery provided with this active material - Google Patents

Abstract

PURPOSE: To provide a nonaqueous electrolyte secondary battery having a long charge/discharge cycle life. CONSTITUTION: This nonaqueous electrolyte secondary battery is provided with a positive electrode 6 active material for the nonaqueous electrolyte secondary battery expressed by the general formula Lix Mn2-y By O4 (0<x<2, 0.001<=Y<0.02) and a lithium negative electrode 3 active material. A lithium-manganese-boron composite oxide has high stability in the charging state, i.e., the state that lithium ions are partially removed from a crystal structure, the capacity is rarely reduced after repeated charges and discharges, and a long life is attained.

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 provides a non-aqueous electrolyte secondary battery having a long charge / discharge cycle life by using a stable positive electrode active material. is there.

[0002]

2. Description of the Related Art In recent years, with the miniaturization of various electronic devices, there has been a demand for secondary batteries having higher energy density. A secondary battery using a non-aqueous electrolyte has several times the energy density of a battery using a conventional aqueous electrolyte solution,
Its practical application is awaited.

The non-aqueous electrolyte is obtained by dissolving a metal salt as an electrolyte in an aprotic organic solvent. For example,
Regarding lithium salts, LiClO ₄ , LiPF ₆ , LiBF ₄ , Li
AsF ₆ , LiCF ₃ SO _{3 and the} like are mixed with propylene carbonate, ethylene carbonate, 1,2-dimethoxytane, γ-butyrolactone, dioxolane, 2-methyltetrahydrofuran, dier carbonate, dimethyl carbonate, sulfolane and the like as a single solvent or a mixture thereof. What is dissolved in a solvent is used.

These non-aqueous electrolytes are used by injecting them into a battery container. They are impregnated into a porous separator, a high molecular weight resin is added to make them highly viscous, or they are gelled to improve fluidity. It is sometimes used by losing it. Also,
A polymer electrolyte represented by polyethylene oxide is also being studied as an electrolyte for a non-aqueous electrolyte secondary battery.

As a negative electrode active material for a non-aqueous electrolyte battery, various materials have been studied so far, but a lithium-based negative electrode is most suitable because a high energy density is expected. Particularly, as a negative electrode of a non-aqueous electrolyte secondary battery, lithium metal, a lithium alloy, carbon holding lithium ions, and the like have been studied.

As a positive electrode active material for a non-aqueous electrolyte secondary battery, an inexpensive spinel type lithium manganese composite oxide (Li
Mn ₂ O ₄ ) has been actively researched in recent years. The crystal structure of this active material is a spinel type cubic crystal, and the potential curve is
There are two steps with flat parts around 4.0V and 2.8V. Here, in order to obtain high energy density, the charge / discharge potential range should be set to
It is required to charge and discharge from 4.3V to 3.0V using the flat part of 4.0V.

[0007]

The spinel type lithium manganese composite oxide LiMn ₂ O ₄ is stable as it is, but when it is used as a positive electrode active material of a non-aqueous electrolyte battery,
There is a drawback that the capacity is greatly deteriorated as the charge / discharge cycle progresses. LiMn ₂ O ₄ has a property that when Li is released by charging, it becomes unstable in its crystal structure and Mn is lost.

In recent years, a composition formula Li _x Mn _{2- y By} O ₄ (0.85 ≦
X ≤1.15, 0.02 ≤Y ≤0.5) (see Japanese Patent Laid-Open No. 4-237970), and Li _{1 + x} Mn _y B _2-y O ₄ (1.6 ≤Y ≤1.9)
(See Japanese Patent Laid-Open No. 5-290846). However, both have a problem that the capacity at the time of high rate discharge is small.

[0009]

Means for Solving the Problems The present invention solves such a problem by using MnO ₂ having a high surface area as a starting material, adding a specific proportion of boron, and comparing the temperature at 600 to 800 ° C. By synthesizing at an extremely low temperature, an active material having a large discharge capacity even at the time of high rate discharge and a long charge / discharge cycle life can be obtained. Further, by using this active material, it is possible to provide a non-aqueous electrolyte secondary battery which has a large capacity at high rate discharge and has a small capacity deterioration with the progress of cycles.
That is, the present invention, as a positive electrode active material of a non-aqueous electrolyte secondary battery, the general formula Li _x Mn _{2- y By} O ₄ (0 <X <2, 0.001
It is characterized by using a lithium manganese boron composite oxide represented by ≦ Y <0.02).

[0010]

Operation: General formula Li _x Mn _{2- y By} O ₄ (0 <X <2, 0.00
The positive electrode active material composed of the lithium boron composite oxide represented by 1 ≤ Y <0.02) made it possible to fabricate a non-aqueous electrolyte secondary battery having excellent high rate discharge performance and long life.

The crystal structure of the lithium-manganese-boron composite oxide has the same cubic system as the conventional spinel type lithium-manganese composite oxide. The lithium-manganese-boron composite oxide has high stability in a charged state, that is, in a state in which a part of lithium ions has escaped from the crystal structure, and the capacity does not decrease much even if charging and discharging are repeated. The reason for this is not clear, but it seems that the substitution of a part of Mn with B stabilizes the crystal structure in the charged state. In addition, MnO ₂ with a high surface area was used as the starting material, and
When synthesized at a relatively low temperature of 0 to 800 ° C., a large capacity at high rate discharge and a long-life active material can be synthesized. As the type of MnO ₂ , _two types of chemically synthesized manganese dioxide and electromanganese dioxide can be used, but it is preferable to use the former in terms of cost and reactivity.

In the synthesis of the above active material, it was confirmed that lithium and boron were not affected by the types of starting materials. As the lithium salt, lithium hydroxide, lithium nitrate, lithium carbonate and the like can be used, and as the raw material of boron, boric acid, boron oxide, ammonium borate and the like can be used.

[0013]

【Example】

It was synthesized _{LiMn 2-y B y O 4} ( Example 1) First.
Y is 0, 0.001, 0.005, 0.01, 0.0.1, 0.2.
It should be noted that Y = 0 represents a composition in which no boron was added and the composition of the conventional product. The synthesis was performed as follows. Lithium hydroxide LiOH and chemically synthesized manganese dioxide MnO ₂ and boric acid H ₃ BO
₃ and ₃ were mixed at a predetermined molar ratio in a mortar and heat-treated at 700 ° C. for 18 hours. After the heat treatment, it was ground in a mortar. Among these, those having a boron substitution amount Y of 0.02 or more showed a diffraction peak of Li ₂ B ₄ O ₇ by powder X-ray diffraction, and a single phase was not obtained.

Next, a non-aqueous electrolyte secondary battery was assembled using the obtained lithium manganese boron composite oxide LiMn _{2- y By} O ₄ as a positive electrode active material. FIG. 1 is a vertical sectional view of a battery according to an embodiment of the present invention. LiMn _2-y B _y O ₄ positive electrode, using a carbon material for the negative electrode. Reference numeral 1 denotes a case that also serves as a positive electrode terminal made by punching a stainless steel sheet having organic electrolyte resistance with a press, and 2 denotes a sealing plate that also serves as a pole terminal that is punched from the same type of material. The negative electrode 3 is in contact with the inner wall thereof. Reference numeral 5 is a separator made of polypropyne impregnated with an organic electrolyte, and 6 is a positive electrode. The open end of the case 1 also serving as the positive electrode terminal is caulked inward, and the outer periphery of the sealing plate 2 also serving as the negative electrode terminal is tightly sealed via a gasket 4 (made of refluoroalkoxy (PFA)).

The negative electrode was manufactured as follows. A negative electrode mixture paste was prepared by adding 8 parts by weight of polyvinylidene fluoride and N-methyl-2-pyrrolidone as a solvent in appropriate amounts to 92 parts by weight of carbon powder (pyrolytic carbon) and kneading well. This paste was uniformly applied to a 100-mesh copper wire mesh (wire diameter 0.1 mm), dried with hot air at a temperature of 85 ° C., then vacuum-dried at a temperature of 250 ° C., and punched into a disk having a diameter of 16 mm to obtain a negative electrode plate.

The positive electrode was manufactured as follows. First, LiMn
_2-y B _y O ₄ 82 polyvinylidene fluoride 6 relative parts by weight.
5 parts by weight, 10 parts by weight of graphite (Lonza FG6), 1.5 parts by weight of Ketjen Black, and N-methyl-2rollidone as a solvent were added in appropriate amounts and kneaded well to prepare a positive electrode mixture paste. Apply this paste evenly to a 100 mesh aluminum wire mesh (wire diameter 0.1 mm) and dry with hot air at a temperature of 85 ° C.
Then, after vacuum drying at a temperature of 250 ° C., it was punched into a disk having a diameter of 16 mm to obtain a positive electrode plate.

As the electrolytic solution, a mixed solvent of propylene carbonate and ethylene carbonate (volume ratio 1: 1)
LiPF ₆ dissolved in 1 mol / liter was used.

In the battery thus manufactured, Y of LiMn _{2- y By} O ₄ used as the positive electrode active material was 0, 0.0
Batteries A, B, C, D, E, F, G, and H were 01, 0.005, 0.01, 0.02, 0.05, 0.1, and 0.2, respectively. It was charged to a voltage 4.3V at a current value ^{2mA (1mA / cm 2),} 6m
A charging / discharging cycle test was performed under the condition of discharging at a voltage of 3.0 V at A (3 mA / cm ² ). The above discharge conditions correspond to high rate discharge for lithium batteries.

Table 1 shows the discharge capacities at the 10th cycle and the 100th cycle. Active material in the range of _{LiMn 2-y B y O 0.001} ≦ Y contains less boron in ₄ <0.02 has little decrease in discharge capacity at the 10th cycle as compared with the comparison battery A, and the charge-discharge cycle The decrease in discharge capacity with the progress is also suppressed. However, in the active material having a relatively high boron content in the range of 0.02 ≦ Y 0.2, the discharge capacity at the 10th cycle is lower than that of the comparative battery A, and the capacity also decreases with the progress of the discharge cycle. . The reason why the discharge capacity at the 10th cycle decreases is that boron, which is a trivalent non-transition metal, does not contribute to the charge / discharge reaction, and the reason that the life performance decreases is that Li ₂ contained in the active material is included. B
It is possible that ₄ O has an adverse effect.

Comparative Example 1 Next, the effect of manganese species on the discharge performance of LiMn _{2- y By} O ₄ was examined. Boron content Y is 0.01 or 0.05.
An active material was synthesized and a battery was prepared in the same manner as in Example 1 except that Mn ₃ O ₄ was used. In the manufactured battery,
Y of LiMn _{2- y By} O ₄ used as the positive electrode active material was 0.0
Batteries I and J of 1 and 0.05 were respectively tested under the same conditions as in Example 1.

Table 2 shows the discharge capacities at the 10th cycle and 100th cycle. The discharge capacity at the 10th cycle is much lower than that of the comparative batteries D 1 and F 2. The reason for this is not clear, but it is considered that the discharge capacity is reduced because the active material using Mn ₃ O ₄ as the starting material has a small surface area. The decrease in capacity with the progress of the charge / discharge cycle is less than that of Comparative Battery A, but the discharge capacity is small even at the 100th cycle because the capacity at the 10th cycle is small.

Example 2 Next, the influence of the synthesis temperature on LiMn _{2- y By} O ₄ was examined. Y is 0.01 and
A battery was prepared by synthesizing an active material in the same manner as in Example 1 except that the synthesis temperature was set to 0.05 and the synthesis temperature was set to 500, 600, 800, and 850 ° C. In the fabricated battery, Y of LiMn _{2- y By} O ₄ used as the positive electrode active material was 0.01 and the synthesis temperature was 50.
Batteries K, L, and 0, 600, 800, and 850 ℃ respectively
M and N, Y is 0.05, synthesis temperature is 500, 600, 800,
The batteries of 850 ° C. were used as batteries O 1, P 2, Q 3, and R 4, respectively, and tested under the same conditions as in Example 1.

Table 3 shows the discharge capacities at the 10th cycle and the 100th cycle. The active material synthesized at a temperature of 500 ° C has a small discharge capacity. As a result of measuring powder X-ray diffraction, the crystal structure of these active materials was insufficiently developed. Synthesis temperature
At 600 ° C. and 800 ° C., similarly to the results of Example 1, the active material having a boron content of Y = 0.01 showed a higher discharge capacity than that of Y = 0.05.

When the synthesis temperature was as high as 850 ° C., the discharge capacity of the active material decreased. The reason for this is considered to be a decrease in high rate discharge performance due to a decrease in surface area of the active material. In addition, the active material with a boron substitution amount Y = 0.01 is the comparative battery A
Almost the same as the above, the discharge capacity decreases with the progress of the charge / discharge cycle. This is probably because the synthesis temperature was high, so a small amount of boron (Y = 0.01) was volatilized.

In the above embodiment, as the positive electrode active material,
Li X value of _{x Mn 2-y B y O} 4 has described the case of using lithium manganese boron complex oxide is 1, but not particularly limited to 1. The X value is electrochemically 0 <X
It is variable in the range <2 and can be optimized according to the battery design. For example, when a material such as a carbon material that causes capacity loss during initial charging is used for the negative electrode, it is preferably electrochemically reduced, and the X value can be used within the range of 1 ≦ X <2. On the other hand, when a battery is assembled in a charged state using metallic lithium or the like for the negative electrode, it is preferable to electrochemically oxidize, and the X value can be used in the range of 0 <X ≤ 1.

Although the case where pyrolytic carbon is used as the negative electrode has been described, various carbon materials such as artificial graphite, natural graphite and pitch-based spherical graphite can be used.

Further, in the above embodiment, the case where LiPF ₆ is used as the electrolyte has been described, but the kind and concentration of the electrolyte are not basically limited. For example, LiAsF ₆ , LiB
Concentration of one or more of F ₄ , LiCLiCF ₃ SO ₃ etc. of 0.5 to 2
It can be used in the range of about mol / l. Although all the batteries according to the above-mentioned embodiments are button type batteries, the same effect can be obtained by applying the present invention to cylindrical, prismatic or paper type batteries.

[0028]

As described above, in the non-aqueous electrolyte secondary battery, Li _x Mn _2-y containing boron as the positive electrode active material is used.
By using a composite oxide having a composition of B _y O ₄ (0 <X <2, 0.001 ≤ Y <0.02), the charge / discharge cycle characteristics of the degradable secondary battery are improved and a long-life secondary battery is provided. It has become possible. The Y value was effective even at a very small amount of 0.001. When the value of Y was 0.02 or more, the decrease in discharge capacity with the progress of the initial charge / discharge cycle increased. The value of Y is preferably 0.001 ≤ Y <0.02.

The battery of the present invention can be applied to a small button battery to a large battery for an electric vehicle because of little deterioration in charge / discharge cycles, and plays a major role in the practical application of a non-aqueous electrolyte secondary battery. To fulfill.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a structure of a battery in an example of the present invention and a comparative example.

[Explanation of symbols]

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

[Table 1]

[Table 2]

[Table 3]

Claims (3)

[Claims] 1. The general formula Li _x Mn _{2- y By} O ₄ (0 <X
<2, 0.001 ≤ Y <0.02) A positive electrode active material for a non-aqueous electrolyte secondary battery. 2. A non-aqueous electrolyte secondary battery comprising a negative electrode containing lithium as an active material and a positive electrode containing the active material according to claim 1. 3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein a lithium compound, manganese dioxide and a boron compound are mixed and heat-treated at a temperature of 600 ° C. or higher and 800 ° C. or lower. Manufacturing method.