JP2002033101A - Lithium-manganese oxide and lithium secondary battery using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Li-Mn spinel compound having an excellent rate characteristic in relation to a Li ion battery positive electrode. SOLUTION: The composition of this lithium-manganese oxide is Li1+x Mn2-x-yMhyO4, where x=0.03-0.15 and y=0.005-0.05, the specific surface area thereof is 0.5-0.8 m2/g, and the content of sodium thereof is 1000 ppm or less. This lithium secondary battery uses the lithium-manganese oxide as a positive electrode material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium-manganese oxide and a lithium secondary battery using the same.

[0002]

2. Description of the Related Art In recent years, portable personal computers and telephones have become portable.
With the rapid progress of cordless technology, the demand for secondary batteries as power sources for driving them is increasing. Among them, non-aqueous electrolyte secondary batteries are particularly expected because of their small size and high energy density. As the positive electrode material of the nonaqueous electrolyte secondary battery, there are lithium cobaltate (LiCoO2), lithium nickelate (LiNiO2), lithium manganate (LiMn2O4) and the like. These composite oxides
Since it has a voltage of 4 V or more with respect to lithium,
The battery has a high energy density.

[0003] However, when a lithium secondary battery is manufactured using these positive electrode materials, there is a problem that an excellent rate characteristic cannot be obtained.

[0004]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a lithium-manganese-based oxide having excellent rate characteristics as a cathode material for a Li-ion battery.

[0005]

Therefore, according to the present invention, the composition of Li1 + xMn2-x-yMgyO4 (x = 0.03-0.15, y = 0.005-0.0
5) The lithium-manganese-based oxide having a specific surface area of 0.5 to 0.8 m2 / g and a sodium content of 1000 ppm or less. Further, there is provided a lithium secondary battery using the lithium-manganese-based oxide as a positive electrode material.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The specific surface area of the lithium-manganese-based oxide having excellent rate characteristics is in the range of 0.5 to 0.8 m2 / g. If it is smaller than this, the area in which Li is desorbed / inserted during charging / discharging becomes small, so that the rate characteristics deteriorate. On the other hand, if the specific surface area is larger than this, the electrical network with the conductive agent becomes insufficient, the electrical resistance increases, and the rate characteristics deteriorate. Further, when the amount of the conductive agent is increased to increase the conductivity, the capacity of the positive electrode itself decreases. Therefore, it is necessary to use a spinel having a specific surface area in this range in order to improve the rate characteristics.

[0007] In previous patents we have reported patents on Mg replacements. This time, we have found that, among them, the Mg-substituted spinel under the conditions described in claim 1 has excellent rate characteristics. Examples of a method for controlling the specific surface area include a method for controlling the firing temperature and time, the type of the raw material, and the particle size of the raw material. Electrolytic manganese dioxide of about 10 μm,
When using lithium carbonate and magnesium oxide as raw materials,
To obtain a spinel with the above specific surface area, 825-8
Firing at 75 ° C for 20 hours is appropriate. If the firing temperature is higher or the firing time is longer, the specific surface area becomes smaller, and if the firing temperature is lower or the firing time is shorter, the specific surface area becomes larger. The temperature shifts to a lower temperature when the raw material particle diameter is increased, and shifts to a higher temperature when chemically synthesized manganese dioxide is used. When Mn2O3, Mn3O4, or the like is used as a raw material, the optimum firing temperature range is determined by the powder characteristics.

When the specific surface area of the lithium-manganese-based positive electrode material is controlled within the above range, the above-mentioned lithium and magnesium substitution amounts are appropriate for achieving both cycle characteristics and capacity. If the Li substitution amount is smaller than this, the cycle characteristics deteriorate, and if the substitution amount is large, the capacity decreases.

The Li—Mn spinel compound of the present invention comprises:
Mixing lithium material, Mg oxide, and Mn oxide,
Obtained by firing. Examples of the lithium raw material include lithium carbonate (Li2CO3), lithium nitrate (Li2NO3), lithium hydroxide (LiOH) and the like.

[0010] In order to obtain a larger reaction area, these raw materials are preferably ground before or after mixing the raw materials. The weighed and mixed raw materials may be used as they are or may be granulated and used. The granulation method may be wet or dry.

[0011] These raw materials are put into a firing furnace, and 600
By calcining at a temperature in the range of ° C to 1000 ° C, the lithium-manganese-based oxide of the present invention is obtained. Examples of the firing furnace used here include a rotary kiln and a stationary furnace. The firing time is 1 to obtain a uniform reaction.
The time is at least an hour, preferably 5 to 20 hours. The Li—Mn-based spinel compound synthesized here is used as a positive electrode material of a lithium secondary battery.

Here, regarding the lithium secondary battery, the positive electrode material, a conductive material such as carbon black, and a binder such as Teflon (polytetrafluoroethylene) binder are mixed to form a positive electrode mixture, For the negative electrode, a lithium alloy or a material capable of desorbing and occluding lithium such as carbon is used. As the non-aqueous electrolyte, a lithium salt such as lithium hexafluorophosphate (LiPF6) is used such as ethylene carbonate-dimethyl carbonate. Those dissolved in a mixed solvent or those obtained by converting them into a gel electrolyte are used.

[0013]

EXAMPLES Example 1 Electrolytic manganese dioxide: lithium carbonate: magnesium oxide adjusted to about 10 μm after neutralizing and washing with ammonia
990 g: 228.0 g: 4.43 g were mixed and fired at 850 ° C. for 20 hours.
The lithium-manganese oxide obtained in this way is
80 wt%, a conductive agent 15 wt%, and a binder 5 wt% were mixed to form a sheet, which was used as a positive electrode. Metal Li for negative electrode, microporous polypropylene for separator, 1M LiPF for electrolyte
A mixed solvent of EC: DMC = 1: 1 in which 6 was dissolved was used.

The charge / discharge test was conducted at 20 ° C. at a current density of 0.5 m
A / cm2, voltage range 3-4.3V. 4.3V high temperature storage test
Discharge after storing the battery charged to 80 ° C for 3 days,
The capacity at this time was expressed as a maintenance ratio with respect to the initial capacity. In the cycle test, the capacity after 100 cycles was expressed as a maintenance ratio with respect to the initial capacity. The rate test was performed by measuring a potential drop from OCV when discharging at 2C for 5 seconds after full charge. Table 1 shows the obtained results.

[0015]

[Table 1]

Example 2 Electrolytic manganese dioxide: lithium carbonate: magnesium oxide, which was neutralized and washed with ammonia and adjusted to about 10 μm =
The same treatment as in Example 1 was carried out except that 990 g: 221.6: 4.43 g was mixed.

Example 3 Aqueous electrolytic manganese dioxide: lithium carbonate: magnesium oxide adjusted to about 10 μm after neutralizing and washing with ammonia
The same treatment as in Example 1 was carried out except that 990 g: 251.2 g: 4.43 g were mixed.

Example 4 Aqueous electrolytic manganese dioxide: lithium carbonate: magnesium oxide adjusted to about 10 μm after neutralizing and washing with ammonia
The same treatment as in Example 1 was carried out except that 997.5 g: 228.0 g: 1.11 g were mixed.

Example 5 Electrolytic manganese dioxide: lithium carbonate: magnesium oxide was adjusted to about 10 μm after neutralizing and washing with ammonia.
The same treatment as in Example 1 was carried out except that 975 g: 228.0: 11.1 g was mixed.

Example 6 Electrolytic manganese dioxide: lithium carbonate: magnesium oxide was adjusted to about 10 μm by neutralizing and washing with ammonia.
990 g: 228.0 g: 4.43 g were mixed and fired at 825 ° C. for 20 hours.

Example 7 Electrolytic manganese dioxide: lithium carbonate: magnesium oxide was adjusted to about 10 μm by neutralizing and washing with ammonia.
990 g: 228.0 g: 4.43 g were mixed and fired at 875 ° C. for 20 hours.

COMPARATIVE EXAMPLE 1 Electrolytic manganese dioxide: lithium carbonate: magnesium oxide = 990 after soda neutralization and washing, and adjusted to about 10 μm.
g: 228.0 g: 4.43 g were mixed and baked at 850 ° C. for 20 hours.

Comparative Example 2 Electrolytic manganese dioxide: lithium carbonate: magnesium oxide was adjusted to about 10 μm by neutralizing and washing with ammonia.
The same treatment as in Example 1 was carried out except that 990 g: 218.0 g: 4.43 g were mixed.

Comparative Example 3 Electrolytic manganese dioxide: lithium carbonate: magnesium oxide was adjusted to about 10 μm by neutralizing and washing with ammonia.
The same treatment as in Example 1 was carried out except that 1000 g: 268.5 g: 4.43 g was mixed.

Comparative Example 4 Electrolytic manganese dioxide: lithium carbonate: magnesium oxide was adjusted to about 10 μm by neutralizing and washing with ammonia.
975 g: 261.7 g: 16.7 g were mixed and 850 ° C. for 20 hours.
Except for baking, the same treatment as in Example 1 was performed.

Comparative Example 5 Electrolytic manganese dioxide: lithium carbonate: magnesium oxide was adjusted to about 10 μm by neutralizing and washing with ammonia.
990 g: 228.0 g: 4.43 g were mixed and fired at 800 ° C. for 20 hours, and treated in the same manner as in Example 1.

Comparative Example 6 Electrolytic manganese dioxide: lithium carbonate: magnesium oxide was adjusted to about 10 μm by neutralizing and washing with ammonia.
990 g: 228.0 g: 4.43 g were mixed and fired at 900 ° C. for 20 hours, and treated in the same manner as in Example 1.

The lithium secondary batteries obtained in Examples 1 to 6 have a specific surface area in a relatively narrow range of 0.50 to 0.78 m2 / g, and as described above, the rate characteristic is 56 to 59 mV in this specific surface area range. And the cycle maintenance rate is maintained as high as 92.3 to 97.1%. The battery capacity of Example 3 was relatively low at 85.0 mAh / g, but the other examples showed a high discharge capacity of 112 mAh / g or more.

In Comparative Example 1, it can be seen that the rate characteristics were greatly reduced by an increase in the sodium content.
In Comparative Example 2, it can be seen that the cycle maintenance ratio was reduced by reducing x to 0.02, which was outside the range of 0.03 to 0.15. Comparative Example 3
It can be seen that the capacity was reduced by increasing x to 0.17, which was outside the range of 0.03 to 0.15. In Comparative Example 4, y was 0.005 to
It can be seen that the capacity was reduced by increasing to 0.07, which is out of the range of 0.05. It can be seen that in Comparative Example 5, the specific surface area was increased and the rate characteristics were reduced because the firing temperature was lower than in Example 1. Comparative Example 6 shows that the specific surface area was reduced due to an increase in the firing temperature as compared with Example 1, and that the rate characteristics and the cycle retention were reduced.

[0030]

According to the present invention, a lithium-manganese-based oxide having excellent rate characteristics can be provided for a positive electrode of a Li-ion battery.

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Claims (2)

[Claims] (1) The composition is Li1 + xMn2-x-yMgyO4 (x = 0.03 to 0.3).
15, y = 0.005 to 0.05), and the specific surface area is 0.5 to 0.8 m2 / g
Lithium-manganese oxides with a sodium content of 1000 ppm or less 2. A lithium secondary battery using the lithium-manganese oxide according to claim 1 as a positive electrode material.