JP2002124258A - Lithium manganate particle powder and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium manganate particle powder used as a positive- electrode active material for a nonaqueous electrolyte secondary battery and giving excellent charging/discharging characteristics to the secondary battery. SOLUTION: This lithium manganate particle powder comprises primary particles of 0.05 to 5.0 μm in average particle diameter and contains LiMn2O4 and Li2MnO3. With respect to peak strength in X-ray diffraction of the powder, the peak strength of a (133) plane of the Li2MnO3 is more than 0 but not more than 0.05 relative to the peak strength of a (400) plane of the LiMn2O4. The powder is obtained by mixing manganese oxide and a lithium compound, primarily baking the mixture at temperatures in the range of 850 to 1,000 deg.C, and then secondarily baking it at temperatures in the range of 700 to 800 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to lithium manganate particles having excellent charge / discharge cycle characteristics of a secondary battery as a positive electrode active material for a nonaqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art In recent years, portable and cordless electronic devices such as AV devices and personal computers have been rapidly advanced, and there is a demand for a small, lightweight, and high energy density secondary battery as a power supply for driving these devices. Is getting higher. Under such circumstances, attention is being paid to a lithium ion secondary battery that has the advantages of high charge / discharge voltage and large charge / discharge capacity.

Conventionally, as a positive electrode active material useful for a high energy type lithium ion secondary battery having a voltage of 4V class, LiMn ₂ O ₄ having a spinel structure and L having a rock salt structure have been used.
iMnO ₂ , LiCoO ₂ , LiCo _1-X Ni
_{X O 2,} LiNiO ₂ or the like are generally known, inter alia although LiCoO ₂ is excellent in that it has a high voltage and high capacity, the manufacturing cost due to the supply amount of the cobalt material less problematic Ya Includes environmental safety issues for waste batteries. Therefore, research is being actively conducted on lithium manganate particles of a spinel structure type (basic composition: LiMn ₂ O ₄ ), which are produced from manganese, which has a large supply amount and is low in cost and has good environmental suitability.

[0004] As is well known, lithium manganate particles can be obtained by mixing a manganese compound and a lithium compound at a predetermined ratio and firing the mixture at a temperature of 700 to 800 ° C.

[0005] However, when lithium manganate particles are used as a positive electrode active material of a lithium ion secondary battery, there is a problem that although they have a high voltage and a high energy density, they have poor charge / discharge cycle characteristics. This is because
The crystal lattice expands and contracts due to the desorption / insertion behavior of lithium ions in the crystal structure due to the repetition of charge / discharge, and lattice destruction occurs due to the volume change of the crystal.
Is to be dissolved.

In a lithium ion secondary battery using lithium manganate particles, it is most demanded at present to suppress deterioration of the charge / discharge capacity due to repeated charge / discharge and to improve charge / discharge cycle characteristics. .

In order to improve the charge / discharge cycle characteristics, the Li / Mn ratio of the lithium manganate particles is set to 1 /
It is necessary to increase Mn from 2 and to suppress the elution of Mn into the electrolytic solution. As a means, a method of controlling the firing temperature to obtain lithium manganate particles of high crystallinity, adding a different element, To strengthen the bonding strength of the crystal
A method of performing surface treatment to suppress the elution of Mn, a method of controlling the particle size distribution of lithium manganate particles, and the like have been performed.

A method for obtaining lithium manganate particles by controlling the firing temperature in two stages is disclosed in Japanese Patent Application Laid-Open No. 10-241.
686, JP-A-10-241687 and JP-A-10-194745 are known.

[0009]

SUMMARY OF THE INVENTION As a positive electrode active material for a non-aqueous electrolyte secondary battery, lithium manganate particles having excellent charge / discharge cycle characteristics of a secondary battery have not yet been obtained.

That is, in Japanese Patent Application Laid-Open Nos. Hei 10-241686 and Hei 10-241687, primary calcination is performed at 700 ° C. or higher for the purpose of obtaining lithium manganate particles containing no impurities. After that, a method of performing the secondary firing at less than 700 ° C. as described above is described. However, as shown in a comparative example below, since the secondary firing temperature is low, the lithium manganate particles having excellent charge / discharge cycle characteristics are provided. Powder is hard to say.

Japanese Patent Application Laid-Open No. Hei 10-194745 discloses a method in which primary firing is performed in a temperature range of 250 to 900 ° C., then pulverized by a ball mill, and then secondary firing is performed in a temperature range of 650 to 800 ° C. However, it is difficult to obtain lithium manganate particles having a high degree of crystallinity after the secondary firing because an intermediate treatment for reducing the crystallinity is performed after the primary firing.

Accordingly, the present invention has high crystallinity, can suppress the elution of Mn into the electrolyte, and has a charge / discharge cycle characteristic of a secondary battery as a positive electrode active material for a nonaqueous electrolyte secondary battery. It is an object of the present invention to provide lithium manganate particles having excellent characteristics.

[0013]

The above technical objects can be achieved by the present invention as described below.

That is, the present invention provides an average particle size of 0.05 to
LiMn composed of 5.0 μm primary particles₂O₄And Li₂
MnO₃Lithium manganate particles containing
The peak of the X-ray diffraction of the lithium manganate particles is
The strength of the LiMn ₂O₄Of the (400) plane
For the peak intensity, the Li₂MnO₃(133) face of
Characterized by having a peak intensity of more than 0 and 0.05 or less
Lithium manganate particles.

The present invention also relates to a method of mixing a manganese oxide and a lithium compound, first firing the mixture at a temperature of 850 to 1000 ° C., and then firing the mixture at a temperature of 700 to 800 ° C. A method for producing the lithium manganate particles according to the present invention.

Next, the configuration of the present invention will be described in more detail.

The average particle diameter of the primary particles of the lithium manganate particles according to the present invention is 0.05 to 5.0 μm. When the average particle size is less than 0.05 μm, the packing density becomes low when manufacturing the positive electrode of the secondary battery, and the energy density of the secondary battery is reduced, for example, it is necessary to increase the amount of the binder. Invite. On the other hand, when it exceeds 5.0 μm, the Li insertion / removal reaction tends to decrease when the current density is increased.

The lithium manganate particles according to the present invention are represented by a composition formula of Li _{1 + x} Mn _2-x O ₄ , wherein Li /
It is preferable that Mn is 0.525 to 0.6. Li
When the / Mn ratio is out of the above range, it is difficult to obtain highly crystalline lithium manganate particles.

The lithium manganate particles according to the present invention
Is LiMn₂O₄And Li₂MnO ₃And Li
₂MnO₃Content of lithium manganate particles
In the diffraction peak intensity of X-ray diffraction of₂O₄
The diffraction intensity of the (400) plane of₂MnO₃of
The ratio of the diffraction intensity of the (133) plane is more than 0 and 0.05 or less.
Below. Li₂MnO₃If it does not contain
Suppress the reaction between the lithium gunate particles and the electrolyte.
I can't do that. When the ratio of diffraction intensity exceeds 0.05
Is not preferred because the charge / discharge capacity decreases. Preferably
Is 0.01 to 0.04.

It should be noted that it may contain a different phase such as Mn ₂ O ₃ , Mn ₃ O ₄ , MnO ₂ which does not contribute to the charge / discharge capacity and cycle characteristics.

The lithium manganate particles according to the present invention preferably have a BET specific surface area of 0.1 to 10 m ² / g. When it is less than 0.1 m ² / g, it is considered that the particles are separated from the electrode plate due to expansion and contraction of the particles due to charge and discharge, and the battery characteristics are reduced. If it exceeds 10 m ² / g, the packing density of the positive electrode active material is reduced, and the reactivity with the electrolyte is excessive, so that the safety is reduced.

The lithium manganate particles according to the present invention preferably have a crystallite size of 600 ° or more. When the crystallite size is less than 600 °, it is difficult to obtain lithium manganate particles having high crystallinity. It is preferably at least 700 °.

The lattice constant of the a-axis is preferably 8.20-8.24 °. When the lattice constant of the a-axis is outside the above range, it becomes difficult to obtain lithium manganate particles having high crystallinity.

Next, a method for producing the lithium manganate particles according to the present invention will be described.

The lithium manganate particles according to the present invention are prepared by uniformly mixing a manganese raw material and a lithium raw material at a predetermined ratio, firing the mixture at 850 to 1000 ° C., cooling it to 700 to 800 ° C., It can be obtained by performing secondary firing at that temperature.

The manganese raw material in the present invention may be any manganese oxide having an average particle size of 0.05 to 5.0 μm, and particularly preferably a manganese oxide having a structure similar to a spinel structure in ionic arrangement. . Specifically, γ-Mn ₂ O ₃ or Mn ₃ O ₄ is preferable. In particular, γ- produced by wet synthesis obtained by neutralizing manganese sulfate
Mn ₂ O ₃ is preferable because it is fine particles and has high reactivity.

As the lithium raw material, lithium hydroxide, lithium nitrate, lithium chloride and the like can be used, but lithium carbonate is preferred.

The mixing ratio of the manganese raw material and the lithium raw material is preferably Li / Mn = 0.525 to 0.6. When it is 0.525 or less, the capacity is high but Jahn
-Charge / discharge cycle characteristics are reduced due to generation of distortion due to the Teller effect. If the ratio is 0.6 or more, the initial capacity is not sufficient.

The manganese raw material and the lithium raw material need to be in a uniform mixed state. If they are not mixed uniformly, the composition ratio will be partially deviated, whereby lithium manganate having different capacity and reversibility will be synthesized, and it will also cause a different phase other than lithium manganate. In the present invention, as a manganese raw material, the average particle size is 0.05 to
Since a manganese oxide of 5.0 μm, preferably γ-Mn ₂ O ₃ synthesized by a wet reaction is used, a uniform mixed state is easily obtained.

The primary firing temperature is 850-1000 ° C. When the temperature is lower than 850 ° C, lithium manganate particles having high crystallinity cannot be obtained. 100
At 0 ° C or higher, the average particle size of the primary particles becomes too large.
De-insertion of i-ion is less likely to occur. Preferably 880
It is 1000 ° C, more preferably 900-1000 ° C.

In the present invention, after the primary firing, the temperature is lowered as it is to the secondary firing temperature.

[0032] The secondary firing temperature is 700 to 800 ° C.
If the temperature is lower than 700 ° C., fine LiMn ₂ O ₄ is generated, and the cycle characteristics at high temperatures are particularly deteriorated. When the temperature exceeds 800 ° C., the content of Li ₂ MnO ₃ increases, which is not preferable. Preferably 720 to
780 ° C.

The firing atmosphere for the primary firing and the secondary firing may be an oxygen-containing gas, for example, air. The sintering time may be selected so that the reaction proceeds uniformly.
Time is preferred.

When firing is performed at a temperature in the range of 850 to 1000 ° C., the residual amount of Li ₂ MnO ₃ is large and the initial capacity is reduced. Further, when firing is performed at a temperature in the range of 700 to 800 ° C., highly crystalline lithium manganate particles cannot be obtained.

After the secondary firing, the powder is pulverized to obtain lithium manganate particles.

When a positive electrode material is produced using the lithium manganate particles according to the present invention as a positive electrode active material for a non-aqueous electrolyte secondary battery, a conductive agent such as acetylene black or carbon black, It can be mixed with a binder such as fluoroethylene, polyvinylidene fluoride or the like and molded into a predetermined shape for use.

The negative electrode active material is not particularly limited.
For example, lithium metal, a lithium alloy, or a substance capable of inserting and extracting lithium can be used, and examples thereof include a lithium / aluminum alloy, a lithium / tin alloy, graphite, and graphite.

The electrolyte is not particularly limited either. For example, lithium perchlorate, tetrafluoroethylene or the like may be used in at least one organic solvent such as carbonates such as propylene carbonate, diethyl carbonate and dimethyl carbonate, and ethers such as dimethoxyethane. A solution in which at least one lithium salt such as lithium borate and lithium hexafluorophosphate is dissolved can be used.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical embodiment of the present invention is as follows.

The identity and crystal structure and crystallite size of the reaction product powder were determined by X-ray diffraction (RIGAKU Cu-Kα).
(40 kV 40 mA).

The morphology of the precursor particles was observed with a transmission electron microscope (manufactured by Hitachi, Ltd.).

The BET specific surface area was measured by the BET method.

<Preparation of Positive Electrode> Lithium manganate particles, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder were mixed at a weight ratio of 85: 10: 5, and N-methyl-2- Pyrrolidone was added to form a paste, the paste was applied to an aluminum foil to a thickness of 0.15 mm, dried, and punched out into a 16 mm-diameter disk to produce a positive electrode.

A lithium foil was used for the negative electrode, and a 16 mm disk was punched out.

<Preparation of Secondary Battery> The separator was made of polyethylene, and was punched into a 19 mm disk shape. The electrolyte used was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 1: 1 using LiPF ₆ as a supporting salt. Then, a coin-type cell battery was manufactured in a glove box in an argon atmosphere.

In the charge / discharge cycle test of the secondary battery, the current density with respect to the positive electrode was 0.5 mA /
cm ^2, and charge / discharge was repeated at a cutoff voltage between 4.5 V and 3.0 V. The measurement was performed at temperatures of 20 ° C and 60 ° C.

<Production of lithium manganate particles> As starting materials, 0.040 mol of γ-Mn ₂ O ₃ prepared by wet synthesis having an average particle size of 0.1 μm and 0.023 mol of lithium carbonate (Li / Mn = 0) .575) using an automatic mortar. The obtained mixed powder is placed in an air stream 9
Primary baking was performed at 50 ° C. for 3 hours.

Next, the temperature was cooled to 750 ° C., and secondary firing was performed at 750 ° C. for 5 hours. After firing, the powder was pulverized to obtain lithium manganate particles. The obtained lithium manganate particles had an average major axis diameter of 1.3 μm, a BET specific surface area of 1.0 m ² / g, and a peak intensity of the (133) plane of the Li ₂ MnO ₃ phase of LiMn ₂ O _4. Was 0.026 with respect to the (400) plane intensity ratio.

Next, a coin cell battery was manufactured using the obtained lithium manganate particles. Battery characteristics are
The initial discharge capacity is 120 m under the above-mentioned condition at 60 ° C.
At Ah / g, the maintenance ratio of the discharge capacity with respect to the initial discharge in the 20th cycle was 97%.

[0050]

The most important point in the present invention is that the lithium manganate particles according to the present invention have high crystallinity and, when used as a positive electrode active material of a secondary battery, have a charge-discharge capacity and a charge-discharge capacity. The point is that the cycle characteristics can be balanced at a high level.

In the present invention, the lithium manganate particles have high crystallinity because lithium manganate having high crystallinity is obtained by firing at a high temperature in the primary firing, and manganese produced by the primary firing is also obtained in the secondary firing. The present inventor believes that by firing in a temperature range that does not reduce the crystallinity of lithium oxide, finally, lithium manganate particles having a large crystallite size can be obtained.

The lithium manganate particles according to the present invention
When used as a positive electrode active material for secondary batteries,
LiMn is excellent in both the amount and the charge / discharge cycle characteristics.
₂O ₄By increasing the content of as much as possible
Electric capacity, and the LiMn₂O₄The crystallinity of
Increased and Li₂MnO₃The charge / discharge capacity is reduced
It can be contained within the range not to be
The present inventor believes that the reaction is suppressed as much as possible.
ing.

[0053]

Next, examples and comparative examples will be described.

Examples 1 to 3 and Comparative Examples 1 to 3 Lithium manganate particles were obtained in the same manner as in the embodiment of the present invention except that the primary firing temperature and the secondary firing temperature were variously changed.

In Comparative Example 1, sintering was performed at 900 ° C. for 10 hours in an air stream using the same mixed powder as in Example 1.
Comparative Example 2 was produced in the same manner as in Example 1 except that the primary firing temperature was 900 ° C. and the secondary firing temperature was 600 ° C. In Comparative Example 3, except that the firing temperature was 750 ° C.
It was produced in the same manner as described above.

Table 1 shows the production conditions at this time, various characteristics of the obtained lithium manganate particles, and the results of battery evaluation.
Shown in

[0057]

[Table 1]

As is evident from Table 1, the batteries of Comparative Examples 1 to 3 have significantly deteriorated capacities during charge / discharge cycles, whereas the batteries of Examples 1 to 5 have reduced capacity. Shows a better charge / discharge cycle retention rate.

[0059]

The lithium manganate particles according to the present invention have high crystallinity and can suppress the elution of manganese into the electrolyte. Therefore, when the lithium manganate particles are used as the positive electrode active material, Can provide a non-aqueous electrolyte secondary battery that achieves a high balance between charge and discharge capacity and cycle characteristics.

[Brief description of the drawings]

FIG. 1 is a diagram showing X-ray diffraction patterns of manganese oxides produced in Examples and Comparative Examples.

FIG. 2 shows manganese oxides prepared in Examples and Comparative Examples.
(BET specific surface area = 20m ²/ G) transmission electron microscope
It is a photograph (30000 times).

FIG. 3 is a view showing an X-ray diffraction pattern of a lithium manganese composite oxide produced in Example 2.

FIG. 4 is a view showing an X-ray diffraction pattern of a lithium manganese composite oxide produced in Comparative Example 1.

FIG. 5 is a view showing an X-ray diffraction pattern of a lithium manganese composite oxide produced in Comparative Example 2.

Continuation of the front page (72) Inventor: Masashi Fujino 1-1-1, Shinoki, Onoda-shi, Yamaguchi Prefecture Inside the Onoda Plant of Toda Kogyo Co., Ltd. (72) Inventor: Hideaki Maeda 1-1-1, Shinoki, Onoda-shi, Yamaguchi Prefecture (72) Inventor Hideaki Sadamura 1-1-1, Shinoki, Onoda City, Yamaguchi Prefecture F-term (reference) 4G048 AA04 AB01 AC06 AD03 AE05 5H050 AA07 AA08 BA17 CA09 CA30 FA17 FA19 GA02 GA10 GA26 HA05 HA13 HA14

Claims (2)

[Claims] 1. A primary particle having an average particle diameter of 0.05 to 5.0 μm.
LiMn consisting of particles₂O₄And Li₂MnO₃And containing
Lithium manganate particles powder,
In the peak intensity of X-ray diffraction of lithium oxide particles,
The LiMn ₂O₄For the peak intensity of the (400) plane
Li₂MnO₃(133) plane has a peak intensity of 0
Manganese acid characterized by being more than 0.05 and not more than 0.05
Lithium particle powder. 2. The method according to claim 1, wherein the manganese oxide and the lithium compound are mixed, and the mixture is first fired in a temperature range of 850 to 1000 ° C., and then second fired in a temperature range of 700 to 800 ° C. Item 6. The method for producing lithium manganate particles according to Item 1.