JP2003077474A - Positive electrode active material for lithium secondary battery and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material that is superior in high temperature standing characteristics at charge and discharge, and its manufacturing method. SOLUTION: This is a positive electrode active material that is mainly made of a lithium manganese composite oxide as expressed by the following formula, Li1+x Mn2-x-y Ay O4 (where A is at least one element selected from Co and Al, and 0<x<0.1, 0<y<0.3). The positive electrode active material of the lithium secondary battery contains Zr more than 0 and 1 wt.% or less in the above composite oxide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode active material for a lithium secondary battery used in a small portable information terminal, a power storage power source, an electric vehicle, etc., and a method for manufacturing the same.
Particularly, the positive electrode active material at high temperature and Li containing the same
The present invention relates to the fact that the reliability of an ion secondary battery can be significantly improved.

[0002]

2. Description of the Related Art Generally, a lithium secondary battery is constructed by arranging a positive electrode, a negative electrode and a separator in a container and filling a non-aqueous electrolytic solution with an organic solvent. The positive electrode material is a current collector such as an aluminum foil coated with a positive electrode active material. Since the electric conductivity of this positive electrode active material is 10 ⁻¹ to 10 ⁻⁶ S / cm ² , which is a low value compared to general conductors, it is between the aluminum current collector and the positive electrode active material or between the active materials. In order to enhance the electric conductivity of the positive electrode active material, a conductive auxiliary material such as carbon powder, which has better electric conductivity than the positive electrode active material, is used (JP-A-10-12).
(See Japanese Patent No. 5323). Actually, carbon powder of about several to several tens% by weight ratio is mixed with the positive electrode material, and further kneaded with a binder such as PVdF (polyvinylidene fluoride) and PTFE (polytetrafluoroethylene), and then paste. The positive electrode is manufactured by kneading the mixture into a shape and applying it to a collector foil with a thickness of about 100 μm, drying, and pressing.

This positive electrode active material is made of an oxide of lithium and a transition metal as represented by lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), and the like. Is mainly used,
For example, JP-A-8-17471 discloses the manufacturing method in detail. Generally, a method of mixing lithium salt powder (LiOH, Li ₂ CO _3, etc.) and transition metal oxide (MnO ₂ , CoO, NiO, etc.) powder and firing the mixture is widely adopted for the synthesis of these positive electrode active materials. . In particular, since LiMn ₂ O ₄ uses Mn as the main raw material, it is possible to reduce the cost compared to LiCoO ₂ and LiNiO _2, and it can be used as a positive electrode material for medium- and large-sized Li-ion batteries that are installed in electricity storage and vehicles. Attention has been paid.

[0004]

However, on the other hand, in LiMn ₂ O ₄ , the crystal lattice is likely to expand and contract due to charge and discharge, and the crystal structure is likely to collapse. Therefore, repeated charge and discharge causes the capacity to decrease and the life to be shortened. There's a problem. To solve these problems, in JP-A-7-228798, Li _{1 + X} Mn _2-X O ₄ (0.02 ≦ X ≦ 0.081), which is an excess composition of Li, is set and in JP-A-4-160769. _X Mn _2-Y M _Y O ₄ (M = C
o, Ni, Fe, at least one selected from Cr, 0 ≦ X ≦ 0.09,
0.01 ≦ Y ≦ 0.3), it is attempted to improve the life by substituting a certain amount of Li, transition metal, or the like into the Mn site. However, even with this, Mn was easily eluted in the electrolytic solution at a high temperature, causing deterioration of the capacity of the battery. Although the degree of capacity deterioration at high temperatures is being improved by the above composition, it has not yet reached the level of practical use.

Therefore, the present invention uses a positive electrode active material mainly composed of a lithium manganese composite oxide, which is highly safe and inexpensive, and has a stable life with less manganese eluting and less deterioration even at high temperatures. It is an object of the present invention to provide a positive electrode active material for a secondary battery, a method for producing the same, and a non-aqueous lithium secondary battery having favorable characteristics.

[0006]

The present invention uses a part of Mn.
It has been found that the inclusion of zirconia in the lithium manganese composite oxide substituted with Co or Al and the regulation of this content suppresses the elution of Mn and has an effect of improving the leaving property particularly at high temperatures. . Also find
At this time, further, in the step of mixing the lithium manganese composite oxide raw material powder, it was found that it is preferable to perform the addition of the zirconia by using balls containing ZrO ₂ as a main component, which led to the present invention. .

That is, the present invention is a positive electrode active material mainly composed of a lithium manganese composite oxide represented by the following formula, wherein Li _{1 + X} Mn _2-X-y A _y O ₄ (where A is At least one element selected from Co and Al, 0 <x <0.1,
0 <y <0.3. ) 1 wt% Zr in the composite oxide
% Or less, it is a positive electrode active material for a lithium secondary battery. Here, Zr is 0.0 in the composite oxide.
It is more preferable to contain 1 or more and 0.5 wt% or less,
More preferably, x is 0.04 ≦ x <0.1, and y is 0.05 ≦
The range of y ≦ 0.2 is more preferable. Therefore, the positive electrode active material of the present invention has a discharge capacity deterioration rate of 3% after being left at 60 ° C. for 20 days.
The following is a positive electrode active material for a lithium secondary battery characterized by the following.

Further, the present invention is a method for producing a positive electrode active material mainly composed of a lithium manganese composite oxide represented by the following formula, wherein Li _{1 + X} Mn _2-XY A _y O ₄ (however, A is
At least one element selected from Co and Al, 0 <
X <0.1 and 0 <Y <0.3. ) Preparation of a positive electrode active material for a lithium secondary battery, characterized in that, when the raw material powders of the complex oxide are mixed, they are mixed using a ball containing ZrO2 as a main component, and the Zr component is added at the time of mixing the raw materials. Is the way.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The positive electrode active material of the present invention and the method for producing the same will be described below. First, an appropriate amount of pure water is added to each of the raw material lithium carbonate, manganese oxide, cobalt oxide or aluminum oxide powder to prepare a slurry. Next, this slurry is mixed in a predetermined amount, and then the raw material powder is put into a resin pot together with a ball containing zirconia (ZrO ₂ ) as a main component, and the resin pot is kept at a predetermined rotation speed for a predetermined time. Rotate. In this step, the Zr component is uniformly added to the raw material due to crushing and mixing of the slurry and abrasion of the ball. The amount of Zr added is controlled by the mixing time. Next, about 1 wt% of PVA (polyvinyl alcohol) is added to this slurry, and a granule having an average particle size of about 100 μm is prepared using a disc sprayer. The granules are fired at a temperature between 800 ° C and 1000 ° C, crushed by a raikai machine, and then fired again. The firing temperature at this time is preferably 500 ° C to 900 ° C.

From the above, the general formula: Li _{1 + X} Mn _2-X-y
A _y O ₄ (where 0 <x <0.1, 0 <y <0.3, A is Co, Al
At least one element selected from
A positive electrode active material containing 1 wt% or less can be used. Here, Co is particularly desirable for A. The reason for this is
Cobalt oxide is more reactive than aluminum oxide added as a raw material, and the synthesis of Li _{1 + X} Mn _2-X-y A _y O ₄ is easy, and as shown in the following examples, the same This is because Co is more excellent in high-temperature storage characteristics than Al in the added amount. The range of X and Y is 0 <x <0.1, 0 <y <
It is selected from 0.3, of which 0.04 ≦ x <0.1, 0.05 ≦
y ≦ 0.2 is preferable. The reason for this is that, as shown in the examples, the excess composition of Li is more excellent in the high temperature storage property, and the addition amount of y balances the high temperature property improvement effect and the cost. The Zr content is set to 1 wt% or less, but 0.01 ≦ Zr ≦ 0.5 wt% is preferable.
The reason for this is that when the addition amount is increased, the initial capacity is lowered as shown in the examples.

The raw material powder is mixed by using a ball-shaped medium containing ZrO ₂ as a main component. If only crushing is performed, the mixing time may be extended with a ball mill or the like, but in the case of the positive electrode active material, mixing of different materials due to abrasion from the medium usually causes characteristic deterioration. Therefore, we examined various media that are less likely to mix different materials due to abrasion, have practically no problem in characteristics even if mixed, and are suitable for crushing and mixing raw materials in a short time. As a result, it was found that zirconium oxide is suitable as a medium having a high density of 6 g / cm ³ and a small amount of wear during grinding. Further, in the case of this medium, it was found that the density and hardness were high, the crushing proceeded to increase the density, and the mixing of zirconium oxide worked to improve the high temperature characteristics. This is because the raw materials (eg
As MnO ₂ and Li ₂ Co ₃ ) are pulverized to promote homogenization of the composition, the addition of Zr has the effect of suppressing the formation of particles that grow partially in large areas, which results in an inhomogeneous composition. It is considered that the decrease in capacity and the deterioration in cycle characteristics due to variations in particle size are reduced. In particular, when a third element such as Al or Co is added, its amount is smaller than that of Li carbonate or manganese oxide which is the main raw material. Thus, it is difficult to uniformly mix those having extremely different compounding ratios. Even in such a case, the mixing using the ball-shaped medium containing ZrO ₂ as a main component of the present invention is effective, and since the composition is less inhomogeneous, the effect of improving the characteristics due to the added element becomes remarkable. . Also, Zr is M
The effect of suppressing n elution has also been confirmed.

(Examples) Examples and comparative examples are shown below together with a sample preparation method and a charge / discharge test method. First, as raw materials, lithium carbonate (Li ₂ CO ₃ ) and manganese dioxide (Mn
O ₂ ), cobalt oxide (Co ₃ O ₄ ) and aluminum oxide (A
A predetermined amount of l (OH) ₃ ) was weighed so that each had an atomic ratio within the range shown in Table 1. For the subsequent mixing, the case of a medium containing zirconia (ZrO ₂ ) as a main component and the case of a medium coated with a metal (polyamide resin) were used. The former zirconia (ZrO ₂ )
In the case of a medium containing as a main component, the ball was put into a ball mill pot made of a resin, and 1 lot each was mixed for 12 hours, 36 hours, and 80 hours by a wet method. The resin media was mixed for 24 hours. After mixing, PVA solution is converted to solid content in the mixed solution and it is 1w.
After adding and mixing t%, the mixture was granulated by a spray dryer and dried to prepare granules of 10 to 100 μm. In addition, the first firing is performed at 960 ° C. in the atmosphere, and after crushing in a mortar,
The second firing was performed again at 600 ° C. in the atmosphere. The firing time is 4 hours, and the firing atmosphere is in the atmosphere.

Table 1 shows the composition and Zr content of the samples prepared. The Zr content in the table is adjusted by the kneading time of the ball mill because the ZrO ₂ balls are uniformly mixed. For example, a content of about 0.02 wt% for 12 hours, about 0.1 wt% for 36 hours, and about 0.3 wt% for 80 hours can be obtained. Further, the amount of Zr contained in the positive electrode active material was measured by ICP (high frequency inductively coupled plasma emission spectroscopy analyzer: SPS1500R manufactured by Seiko Denshi Kogyo).

Next, the charge / discharge test of the prepared sample will be described. In this test, the sample was incorporated into a simple model cell and evaluated. The outline is shown in FIG. The simple model cell comprises a test electrode 1, a Li reference electrode 2 (lithium foil), and a Li counter electrode 3 (lithium foil), and each electrode is immersed in an electrolyte solution 4. A potentiometer 5 is connected to the reference electrode terminal and the test electrode terminal, and a constant current power source 6 is connected to the test electrode terminal and the counter electrode terminal. The test electrode 1 was prepared by kneading the positive electrode active material synthesized in the above-mentioned examples, a conductive auxiliary material such as carbon powder, and a binder such as PVDF (polycarbonate vinylidene) at a predetermined ratio to form a paste. Then, it was applied on an aluminum foil as a current collector, dried, and then pressed with a press to be used. The electrolyte used was 1M LiPF ₆ / EC: DMC = 1: 1.

Charging was performed at a constant current density of 0.5 mA / cm ² by depositing lithium on the test electrode until the potential of the reference electrode against lithium reached 4.3V. Further, in measuring the discharge capacity, the amount of electricity flowing until the potential of the test electrode reached 3.0 V with respect to the lithium reference electrode was measured. After the initial discharge capacity was set to 100 and the battery was charged, the battery was left at 60 ° C. for 20 days, and then the discharge capacity was confirmed again. The deterioration rate was calculated from the capacity before and after standing by the following formula. Table 1 also shows the capacity deterioration rate of each sample.

[0016]

[Table 1]

From the comparative example of Table 1 and Examples 1 to 5, LiMn ₂ O ₄
It can be seen that the deterioration rate is reduced by substituting a part of the inside with Co or Al. At this time, it was found that the deterioration rate was further reduced by making the composition of Li excessive. Further, by adding a small amount of Zr component, the deterioration rate can be further reduced as compared with the case where Co or Al is replaced alone. The reason for this is that Zr has the effect of suppressing grain growth, and when a small amount of Zr is added, the primary particles that grow huge are reduced, and primary particles having a uniform size can be obtained. It is considered that the uniformity of the particles acts as described above and further reduces the deterioration rate.

Next, with respect to the composition of Li _1.08 Mn _1.87 Co _0.05 O ₄ , the change of the initial capacity when the addition amount of the Zr component is changed is shown in FIG. As can be seen from Table 1, when the Zr component is added, deterioration at high temperature is improved. However, if the content is simply increased, as can be seen from FIG.
It was found that the initial capacity tends to decrease from around t%. Therefore, the Zr component content is preferably 0 <Zr content ≦ 1 wt%, and more preferably 0.01 ≦ Zr content ≦ 0.5 wt%.

[0019]

EFFECTS OF THE INVENTION According to the present invention, a lithium manganese composite oxide partially substituted with Co or Al contains zirconia, and by defining the content thereof, a positive electrode excellent in leaving characteristics especially at high temperature. An active material and a lithium secondary battery using the same can be provided. At this time, the manufacturing process can be streamlined by using ZrO ₂ ball in the pulverizing and mixing process using media such as a ball mill, and the amount of zirconia mixed from ZrO ₂ ball can be quantitatively regulated in this process, so that the quality is improved. Stabilize.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a charge / discharge test apparatus used in an example of the present invention.

FIG. 2 is a diagram showing the relationship between the Zr addition amount and the initial capacity in one example of the present invention.

[Explanation of symbols]

1: test pole 2: Li reference electrode 3: Li counter electrode 4: Electrolyte 5: Voltmeter 6: Power supply

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 4G048 AA04 AB01 AB05 AC06 AE05                 5H029 AJ05 AJ12 AK03 AL12 AM03                       AM05 AM07 CJ08 DJ16 DJ17                       HJ01 HJ02 HJ14                 5H050 AA07 AA15 BA15 CA09 CB12                       FA17 FA19 GA05 GA10 HA01                       HA02 HA14 HA20

Claims (4)

[Claims] 1. A positive electrode active material mainly composed of a lithium manganese composite oxide represented by the following formula, wherein Li _{1 + X} Mn _2-X-y A _y O ₄ (where A is Co or Al At least one element selected, 0 <x <0.1, 0 <
y <0.3. ) A positive electrode active material for a lithium secondary battery, wherein the composite oxide contains Zr in an amount of 1 wt% or less. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein Zr is contained in the composite oxide in an amount of 0.01 or more and 0.5 wt% or less. 3. The positive electrode active material according to claim 20,
3. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the deterioration rate of discharge capacity after standing for 3 days is 3% or less. 4. A method for producing a positive electrode active material mainly composed of a lithium manganese composite oxide represented by the following formula, wherein Li _{1 + X} Mn _2-X-y A _y O ₄ (where A is Co , At least one element selected from Al, 0 <x <0.1, 0 <
y <0.3. ) A method of manufacturing a positive electrode active material for a lithium secondary battery, characterized in that, when the raw material powders of the composite oxide are mixed, they are mixed using a ball containing ZrO ₂ as a main component, and the Zr component is added at the time of mixing the raw materials. Method.