JP2002110156A - Manufacturing method of positive pole active material for nonaqueous lithium secondary battery, and its positive pole active material and nonaqueous lithium secondary battery using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the charge and discharge capacity of a nonaqueous lithium secondary battery, which uses transition metal oxide lithium positive pole active material in a positive pole, larger than traditional one. SOLUTION: The lithium transition metal oxide is produced by mixing and baking at least one type from compound of Co, Mn, etc., and lithium compound. The baked particle is heat-treated in oxygen atmosphere on coagulating and balling after melting the surface by heat-treating the baked particle by plasma, for example. The positive pole active material produced by returning the crystal structure to the one of the lithium transition metal oxide exhibits large charge and discharge capacity.

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 non-aqueous lithium secondary battery and a method for producing the same, and more particularly to an improvement in output discharge characteristics and cycle stability of the positive electrode active material and miniaturization of the secondary battery. It is.

[0002]

2. Description of the Related Art In recent years, global warming due to fossil fuel dependence,
Environmental problems such as air pollution by exhaust gas CO ₂ and NOx have become apparent, and various regulations are being studied or implemented in each country.
In the latter half of the 21st century, energy shortages due to depletion of petroleum resources are of concern.

[0003] For this reason, studies have been made to improve energy use efficiency and shift to a society in which the oil dependency ratio is reduced. For example, in the case of automobiles, various hybrid automobiles using a gasoline engine and a motor have been developed, and the energy efficiency has been increased by about 50% compared to a gasoline engine alone. Also, an efficient fuel cell has been developed as a power source, and its practical use as a home power source or a power source for electric vehicles is being studied.

For energy storage of these hybrid vehicles, lithium secondary batteries having a higher battery voltage and a higher energy density than other secondary batteries are suitable and are being actively developed. In particular, high power density is required for energy storage of hybrid vehicles, and high power discharge characteristics and high cycle stability are required.

In general, a lithium secondary battery has a structure in which a positive electrode, a negative electrode, and a separator are arranged in a container, and is filled with a non-aqueous electrolyte using an organic solvent. The positive electrode active material is obtained by applying a positive electrode active material to a current collector such as an aluminum foil and press-molding the same. Lithium cobalt oxide (L
iCoO ₂ ), lithium nickelate (LiNiO ₂ ), spinel type lithium manganate (LiMn ₂ O ₄ ), and other complex oxides of lithium and transition metal (hereinafter referred to as lithium transition metal oxide Is mainly used, and its production method is disclosed in detail in, for example, JP-A-8-17471. The synthesis of these positive electrode active materials is generally carried out using lithium compound (LiOH, Li ₂ CO ₃ etc.) powder and transition metal compound (M
A method in which powders such as nO ₂ , CoO, and NiO are mixed and fired to form a lithium transition metal oxide is widely used. In order to apply the positive electrode active material to the current collector, carbon powder of about several% to several tens% by weight is mixed with the positive electrode active material, and further, PVDF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene) or the like is added. A positive electrode is formed by kneading with a binder, forming a paste, applying the resulting paste on a current collector foil to a thickness of 20 μm to 100 μm, drying and pressing.

In general, the positive electrode active material has an electric conductivity of 10 ^-1 to 10 ^-1 .
10 ^-6 S / cm ² lower than ordinary conductors. The electrical conductivity and the state of electrical contact between the aluminum current collector and the positive electrode active material greatly affect the cycle characteristics and discharge rate characteristics of the battery. Therefore, a conductive auxiliary material such as carbon powder having higher electric conductivity than the positive electrode active material is used so as to further increase the electric conductivity between the aluminum current collector and the positive electrode active material or between the active materials. Looking at the particle morphology of the positive electrode active material after the conventional spinel-type lithium manganate positive electrode active material is applied to the current collector foil, the particle size is composed of secondary particles in which primary particles on the order of submicrons are aggregated. . Usually, the particle morphology has various sizes and shapes, and the secondary particle diameter varies from about 0.1 μm to about 100 μm due to the variation of the aggregation method, and the distribution is not uniform.
As the positive electrode active material, attempts have been made to apply it to the electrode surface in a state where it is exclusively ground to reduce the particle size and increase the specific surface area.

[0007]

Lithium cobalt oxide (LiCoO ₂ ), which is a commonly used positive electrode active material, has a large charge / discharge capacity and a spinel type lithium manganate (LiMn ₂ O ₄ )
Has a relatively small charge / discharge capacity. It is preferable to use a positive electrode active material having a large charge / discharge capacity as a secondary battery used as a power source for an electric vehicle, but a large electrode area is required to extract a large current from the secondary battery, and thus a large amount of the positive electrode active material Will be used. Since lithium cobaltate (LiCoO ₂ ) uses expensive cobalt, using these as a positive electrode active material increases the price of a secondary battery. Therefore, it is desired that the charge / discharge capacity of the secondary battery using lithium cobaltate (LiCoO ₂ ) as a positive electrode active material be further increased to reduce the size of the secondary battery.

It is desirable to use spinel-type lithium manganate (LiMn ₂ O ₄ ), which uses relatively inexpensive manganese, as the positive electrode active material, but it is well known that LiMn ₂ O 4 ₄ Secondary batteries using positive electrode active materials
The charge / discharge capacity is smaller than that using a positive electrode active material such as LiCoO ₂ . Therefore, it is also desirable to increase the charge / discharge capacity of a secondary battery using LiMn ₂ O ₄ and use LiMn ₂ O ₄ as a power source for an electric vehicle.

Accordingly, the present invention provides a positive electrode active material capable of increasing the charge / discharge capacity of a non-aqueous lithium secondary battery using a positive electrode active material comprising a lithium transition metal oxide as a positive electrode, as compared with the conventional one. And a positive electrode active material thereof.

Further, the present invention provides a secondary battery in which the charge / discharge capacity is less reduced even when charge / discharge is repeatedly performed.
It is another object of the present invention to provide a method for producing a positive electrode active material for a non-aqueous lithium secondary battery and to provide the positive electrode active material.

Another object of the present invention is to provide a method for producing a positive electrode active material and a positive electrode active material for the non-aqueous lithium secondary battery, which have a small deterioration in characteristics even in large current discharge.

Further, the present invention provides a non-aqueous lithium secondary battery using a relatively inexpensive spinel-type lithium manganate (LiMn ₂ O ₄ ) positive electrode active material, which has a larger charge / discharge capacity than conventional batteries. It is another object of the present invention to provide a method for producing a positive electrode active material and a positive electrode active material.

Another object of the present invention is to provide a non-aqueous lithium secondary battery using the improved positive electrode active material.

[0014]

According to the method for producing a positive electrode active material for a non-aqueous lithium secondary battery of the present invention, a transition metal compound and a lithium compound, each of which becomes an oxide by firing, are mixed at a predetermined ratio, and the mixture is mixed. After firing to form a composite oxide of lithium and a transition metal, at least the surface of the particles made of the composite oxide of lithium and the transition metal is melted and solidified, and then the particles are heat-treated.

Further, in the method for producing a positive electrode active material for a non-aqueous lithium secondary battery according to the present invention, at least one of a manganese compound and a cobalt compound, each of which becomes an oxide by firing, and a lithium compound are mixed at a predetermined ratio. After firing to form a composite oxide of lithium and a transition metal, at least the surface of the particles made of the composite oxide of lithium and the transition metal is melted and solidified, and then the particles are heat-treated.

Further, in the method for producing a positive electrode active material for a non-aqueous lithium secondary battery according to the present invention, a manganese compound and a lithium compound, each of which becomes an oxide by firing, are mixed at a predetermined ratio, and the mixture is fired to form a spinel type positive electrode. After forming lithium manganate, at least the surface of the particles made of the spinel-type lithium manganate is melt-solidified, and then the particles are heat-treated.

Preferably, the melt-solidification is a thermal plasma treatment, wherein the thermal plasma treatment is performed at a temperature equal to or higher than the melting point of the composite oxide of lithium and transition metal, with an atmosphere of argon, oxygen, air or nitrogen, and a pressure of It is good to carry out at 50KPa to atmospheric pressure.

Preferably, the crystal structure altered by the melt-solidification is returned to the original crystal structure of the composite oxide of lithium and transition metal by the heat treatment, and the heat treatment is performed in an air or oxygen atmosphere at a temperature of 500 to 900. It is good to carry out at ° C.

The positive electrode active material for a non-aqueous lithium secondary battery of the present invention is a particle comprising a composite oxide of lithium and a transition metal, and at least the surface thereof is melt-solidified to be spherical. .

The positive electrode active material for a non-aqueous lithium secondary battery of the present invention is preferably particles composed of at least one of spinel-type lithium manganate and lithium cobaltate. It is characterized by having been done.

Further, the positive electrode active material for a non-aqueous lithium secondary battery of the present invention is more preferably particles composed of spinel-type lithium manganate, and at least the surface thereof is formed into a spherical shape by melt coagulation. And

It is preferable that the spheroidization by the melt solidification is performed by exposing to thermal plasma.

The particle size distribution range of the particles is 0.5 to 100 μm.
m, the average particle size is preferably 0.6 to 50 μm, and the spheroidization ratio of the particles is preferably 3% or more. Further, the limited particle ratio of the particles (circularity of 0.9 to 1.0,
The volume ratio of particles in the particle size range of 5 to 15 μm) is preferably 7% or more.

The non-aqueous lithium secondary battery of the present invention
Of positive electrode active material composed of composite oxide of chromium and transition metal
Lithium secondary battery with a positive electrode formed on the body
Thus, the composite oxide of lithium and a transition metal is at least
Are particles that have been melt-solidified and are spherical.
The density of the positive electrode active material attached to the conductor is 2.54 × 10 ^ThreeKg/
m^ThreeIt is characterized by the above.

The composite oxide of lithium and the transition metal is preferably at least one of spinel-type lithium manganate and lithium cobaltate, and particularly preferably spinel-type lithium manganate.

[0026]

DETAILED DESCRIPTION OF THE INVENTION The lithium transition metal oxide in the present invention is useful as a positive electrode active material for a non-aqueous lithium secondary battery. For example, spinel lithium manganate and lithium cobalt oxide are suitable. When using as a positive electrode active material, the charge and discharge characteristics of the secondary battery become particularly large, and even when using spinel-type lithium manganate using inexpensive manganese as the positive electrode active material, a larger charge and discharge compared to the conventional case Characteristics are obtained.

According to the present invention, for a non-aqueous lithium secondary battery
The positive electrode active material is manufactured according to the flowchart of FIG.
You. First, in step 1, as a raw material,
Compounds of transition metals such as cobalt and manganese (eg,
For example, Co_ThreeO_Four, CoO_Two, Mn_ThreeO_Four, MnCO _Three), And acid by baking
Lithium compound (for example, Li_TwoCO_Three, LiOH) and
Mix at a predetermined ratio. I want to make this mixture
And transition metals in lithium transition metal oxides
Stoichiometric atomic ratio with
A slightly higher proportion of transition metals, for example LiMn_TwoO_FourWhen making
Sets Li / Mn to 0.58. These powders are mixed with water in step 2.
And mixed in a resin ball mill for, for example, 50 hours.
You. The charge / discharge characteristics of the raw materials should be
Oxides and glass-forming substances of Cr, Al, Co, Ni to improve
As B_TwoO_Three, Bi_TwoO_Three, V_TwoO_Five, PbO, etc. can be added
You. The PVA solution is converted into a solid content of 1 w
It is preferable to add around t%.

In step 3, the mixture is granulated with a spray dryer and dried to produce granules of 10 to 100 μm. The granules only need to have a particle size that allows firing. Step 4 is calcination, and the raw material used by this calcination is converted into an oxide, and becomes a lithium transition metal oxide such as spinel-type lithium manganate and lithium cobalt oxide. The firing is performed at 700 ° C. to 1100 ° C. in air or oxygen for several hours to 10 hours. If the particle diameter of the fired particles is large, when applied as a positive electrode active material on a current collector foil, irregularities may occur on the positive electrode or scratches may occur. Crushing (crushing) and sieving (step 5).

Next, the particles are subjected to a thermal plasma treatment in step 6, and at least their surfaces are melted and then solidified to form spheroids. Since the particles sieved in step 5 are crushed, their surfaces are crushed and angular particles, but are instantaneously exposed to a temperature of 5000K to 10000K by thermal plasma treatment, and the particle surface is reduced to several 1000K. Become. As a result, at least the surface of the particles is melted, so that tension is generated on the surface of the particles and the particles become spherical, and then cooled and solidified (hereinafter sometimes referred to as melt-solidification). Thereafter, the particles subjected to the thermal plasma treatment are subjected to a heat treatment in step 7. The heat treatment is performed at a temperature of 500 ° C. to 900 ° C. in the air or oxygen atmosphere. This heat treatment is preferably performed for 2 hours or more. The particles of the lithium transition metal oxide subjected to the thermal plasma treatment have a structure deviating from the intended crystal structure of the lithium transition metal oxide because oxygen is released and a double phase occurs during the thermal plasma treatment. Therefore, the above heat treatment is performed to restore the lithium transition metal oxide having the original crystal structure. In addition, since sudden cooling may cause distortion or the like in the crystal, it is considered that such distortion can be removed.

For the thermal plasma processing in the flowchart of FIG. 1, for example, a high-frequency thermal plasma generator as shown in FIG. 2 can be used. The generator 20 of FIG.
A high-frequency induction coil 21 is wound around the outer periphery, and a thermal plasma is generated inside the coil by high-frequency electromagnetic induction. A material supply port 22 for supplying a material to be subjected to thermal plasma processing and a carrier gas, and a plasma supply gas supply port 23 for generating plasma are provided at an upper portion of the generator 20. The exhaust port 2 is provided on the side wall of the generator 20.
4 are provided.

The conditions for generating the thermal plasma are as follows: a frequency of 0.5 to 20 MHz, particularly 1 to 15 MHz, and an input power of 3 to
The pressure may be 50 KW, and the pressure is 50 KPa to 100 KP.
It is preferable to be about a (atmospheric pressure). As the plasma gas to be introduced, Ar, nitrogen, oxygen, air and the like are preferable, and these may be mixed. As carrier gas,
Argon, nitrogen, or the like can be used.

When a plasma 25 is generated in the generator 20 and the lithium transition metal oxide particles are supplied into the plasma 25 together with the carrier gas while controlling the internal pressure by sucking from the exhaust port 24, the surface of the particles is Are melted and then cooled to produce spheroidized particles 26. The particles subjected to the thermal plasma treatment are subjected to a heat treatment in step 7 in FIG.

Instead of the thermal plasma treatment in the flowchart of FIG. 1, a laser beam or an electron beam may be applied to the particles to melt and solidify at least the surface of the particles to make them spherical. Alternatively, a flame melting method in which particles are melted by a flame of about 1800 ° C. in which a mixed gas of combustible gas and oxygen is burned, and then spheroidized by gas convection may be used.

The particles of the positive electrode active material comprising a lithium transition metal oxide of the present invention preferably have a particle size distribution of 0.5 μm to 100 μm. The lower limit of the desirable particle size distribution is 1 μm and the upper limit is 100 μm. A more desirable range is a lower limit of 2 μm and an upper limit of 30 μm. If the volume frequency is partly prominent and the particle size is high, the packing property of the particles will decrease, so the volume frequency is as low as possible on average and the distribution like a flat mountain is good, for example, the highest value of the volume frequency is the whole Of 1
It is good to be 0% or less. More preferably, it is 5% or less.

The average particle diameter D50 is not less than 0.6 μm and not more than 100 μm.
m, preferably between 3 and 20 μm. A more desirable range is 5 to 10 μm.

Because of such a relatively wide particle size distribution and particle size, the particles can easily enter between the particles when coated on the current collector foil, and the packing density increases. Also,
It can be evenly applied to a uniform thickness.

As the positive electrode active material becomes more spherical, the friction between particles is reduced, and the packing ratio is improved. The effect was not confirmed when the spheroidization ratio was 3% or less, and the effect was confirmed when the spheroidization ratio was 3% or more. Desirably, it is 10% or more. The limited particle ratio is preferably 7% or more, more preferably 20% or more, and further preferably 40% or more.

FIG. 3 is a flow chart showing a process for producing a positive electrode of a non-aqueous lithium secondary battery using the positive electrode active material of the present invention. In this flowchart, step 31 is a raw material, and the positive electrode active material, the carbon-based conductive material, and the binder are weighed and mixed in step 32. As the carbon-based conductive material, carbon black, graphite, acetylene black, or another compound having conductivity can be used, and the used amount is about 1 to 15 wt%, specifically, for example, 5.5.
wt%. As the binder, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTF)
E), polyvinyl fluoride (PVF) and the like, and the amount thereof is 3 to 20% by weight.
5 wt%. The positive electrode active material, the carbon-based conductive material, and the binder are sufficiently mixed in a mortar in step 32, and the thickness is increased by a doctor blade method or the like in step 33 on a separately prepared aluminum current collector foil (eg, 15 μm thick). To a thickness of 100 μm. This is dried in step 34, and a pressure of about 1.5 ton / cm ² is applied in step 35 to form a positive electrode as in step 36.

The positive electrode using the positive electrode active material comprising the spheroidized lithium transition metal oxide of the present invention can be packed at a high density, but is practically preferably at least 2.54 × 10 ³ Kg / m ^3. . It is preferably at least 2.8 × 10 ³ Kg / m ^3, more preferably at least 3.0 × 10 ³ Kg / m ³ . Since the specific surface area of the lithium transition metal oxide of the present invention is minimized due to spheroidization, manganese elution of the electrolytic solution, which is a problem with spinel-type lithium manganate, for example, can be reduced. In addition, the coating resistance is small and smooth, and the coating is easy without any streaking.

FIG. 4 shows a non-aqueous lithium secondary battery for evaluating the charge / discharge characteristics of the positive electrode active material and the positive electrode made therefrom according to the present invention. A beaker is used as a container of the secondary battery 40, and an electrolyte 41 is filled therein. In the electrolyte 41, a positive electrode 42 and a negative electrode 43 are arranged to face each other. The positive electrode 42 is prepared using the positive electrode active material of the present invention according to the flowchart of FIG. For the negative electrode 43, a lithium electrode is used instead of a normal carbon-based material. Between the leads of the positive electrode 42 and the negative electrode 43, a charging power source 44, a load resistor 45, and a voltmeter 46 are inserted in parallel.
A changeover switch 47 for changing over is provided.

The electrolyte 41 can be adjusted by dissolving a lithium-containing electrolyte in a non-aqueous solvent. As such an electrolytic solution, a commercially available one can be used. For example, specifically, a mixed solvent of ethyl carbonate and dimethyl carbonate using 1.2 M LiPF ₆ as an electrolyte can be used.

The secondary battery 40 shown in FIG. 4 is connected to a power supply 44 for charging, and then connected to a load resistor to discharge at 0.33 C (initial discharge capacity of 3.2 hours and a cutoff potential of 3.2 hours).
(Discharge amount per unit weight of the positive electrode active material when discharged to V), discharge capacity at the 50th cycle, discharge capacity when discharged at 2C (cutoff potential 3.2 V in 30 minutes)
(Discharge amount per unit weight of the positive electrode active material when discharge is performed), and the volume capacity representing the discharge capacity per volume calculated from the electrode density and the initial discharge capacity.

Experiment 1 In this experiment, manganese dioxide and lithium carbonate were used as raw materials according to the flowchart of FIG.
The mixture was weighed so that the i / Mn ratio became 0.58, and mixed by a wet method using a resin ball mill for 50 hours. The mixture is PVA
After the addition of the solution, the mixture was granulated by a spray dryer, and the granulated powder was dried to prepare granules having a particle size of 10 to 80 μm. The prepared granules were then processed under the conditions shown in Table 1.

[0044]

[Table 1]

The apparatus for generating thermal plasma for spheroidization is as shown in FIG. 2. In operation, the inside of the apparatus is replaced with Ar gas in advance and the frequency is 13.56 MHz, 5 kW.
Was supplied to the coil to generate thermal plasma of several thousand K, and then a powder sample was supplied into the apparatus using Ar gas as a carrier gas. The supply amount of the powder was adjusted at the time of the supply so that the particles did not come into contact with each other when the particle surface was melted in the plasma and large particles were generated. Result 1
About 200 g could be processed in an hour.

FIG. 5 is an SEM image of the positive electrode active material prepared in the above-described steps. True spherical particles can be confirmed from the materials of Example 1 and Comparative Example 1 which were subjected to the thermal plasma treatment. Each S in FIG.
Comparing the EM images, it is considered that the particle surfaces of Example 1 and Comparative Example 1 were smooth, and the material was heated to the melting point of about 1500 ° C. by the thermal plasma, and at least the surface of the particles was melted and made spherical by the surface tension.

FIG. 6 shows a particle size distribution analyzer (L, manufactured by Horiba, Ltd.)
A-920) shows the measured particle size distribution of each sample. FIG. 6 shows that Example 1 and Comparative Example 1 in which the thermal plasma treatment was performed did not generate coarse particles, and had the same particle size distribution as Comparative Example 2 in which the thermal plasma treatment was not performed. On the other hand, Comparative Example 3, which was not crushed after firing, had coarse particles.

FIG. 7 shows an X-ray diffraction of these samples.
This is the result. After performing the thermal plasma processing of Example 1
LiMn when heat-treated_TwoO_FourIs a single phase of
You. However, Comparative Example 1, in which no heat treatment was performed, was aimed.
LiMn_TwoO_FourOther than LiMnO_Two, Mn_TwoO _Three, Mn_ThreeO_FourConfirm phases such as
it can. The samples of Comparative Example 2 and Comparative Example 3 were the same as in Example 1.
LiMn_TwoO_FourWas a single phase. The lattice constant is shown in the figure.
Posted. Example 1, Comparative Example 2 and Comparative Example 3 have the same case.
It was a child constant. LiMn for Comparative Example 1_TwoO_FourPeak of
It was the same value when it calculated only about. Comparative Example 2 and
Sample No. 3 was prepared by spinel-type lithium manganate
Although at least the surface of these samples is heated,
Comparative Example 1, which was melt-solidified and spheroidized by plasma, was Li
Mn_TwoO_FourOther crystals are generated. Sample of Comparative Example 1 in air
In Example 1 in which the heat treatment was performed at 600 ° C. for 10 hours, LiMn
_TwoO_FourOther crystals disappear, LiMn_TwoO_FourBack to single phase,
Moreover, it can be seen that the peak intensity has increased.

In producing the positive electrode in order to evaluate the characteristics of the positive electrode active material, the following steps were taken according to the flowchart of FIG.
The respective positive electrode active materials, carbon-based conductive materials, and binders of the present example were expressed in terms of% by weight, respectively, and were mixed at a ratio of 90: 5.5: 4.5 (wt%). Was dried at 90 ° C. and pressed with a press at 1.5 tons / cm ² to form a coating film having a thickness of about 100 μm.

A non-aqueous lithium secondary battery for testing shown in FIG. 4 was manufactured using the positive electrode manufactured here. Normally, a carbon-based material is used for the negative electrode of the lithium secondary battery. Here, the lithium electrode 43 was used so that the characteristics of the negative electrode were not taken into consideration in the evaluation results. As the electrolytic solution 41, a mixed solvent of ethyl carbonate and dimethyl carbonate using 1.2 M LiPF ₆ as an electrolyte was used. Table 2 shows the density of the positive electrode active material in the positive electrode, the initial discharge capacity when discharged at 0.33C, the discharge capacity at the 50th cycle, the discharge capacity when discharged at 2C, the electrode density, and the initial discharge capacity. The volume capacity indicates the discharge capacity per volume.

[0051]

[Table 2]

From the data in Table 2, the characteristics of the material obtained in Example 1 were the initial discharge capacity, the discharge capacity at the 50th cycle, 2C
The discharge capacity retention ratio in Example 1 was higher than that in Comparative Examples 1 to 3, and after performing melt solidification by thermal plasma to perform spheroidization, heat treatment was performed to restore the original crystal structure. It can be seen that is obtained. Further, it can be seen that the volume capacity of Example 1 is higher than Comparative Examples 1 to 3 by 10% or more.
This means that the capacity of the battery has been improved by 10% or more.

In the sample of Example 1, since at least the particle surface is melted and solidified by the thermal plasma to form a sphere, the composition tends to be uniform, and the component is hardly segregated because it is cooled (quenched) in a short time. . Since it is heat-treated, the crystals are uniform and the peak intensity is higher than that of the material that has not been subjected to thermal plasma treatment (see FIG. 7). After that, Mn ₂ O ₃ and Mn ₃ O ₄ which do not contribute to charge and discharge are eliminated by the heat treatment, and a single phase of LiMn ₂ O ₄ is obtained. From these facts, it is considered that desirable results were obtained.

Experiment 2 In order to prepare a positive electrode active material having a different particle size distribution, mixed granules of manganese dioxide and lithium carbonate having a particle size of 10 to 80 μm were used as in Experiment 1, and the subsequent steps are shown in Table 3. The treatment was performed as shown.

[0055]

[Table 3]

Since it was known from Experiment 1 that the particle size distribution before the thermal plasma treatment was reflected in the particle size distribution after the thermal plasma treatment, large particles were caught when the electrode was applied, and streaks were formed on the application surface. After firing, the mixture was passed through a 106 μm sieve so that the problem described above did not occur. Comparative Examples 4, 2 and 3 passed through the sieve easily, but in Examples 4 and 5, there were portions that did not pass through the sieve. This is because the samples of Comparative Examples 4 and 2 and 3 passed through the sieve without any grain growth because the firing temperature was low, but the samples of Examples 4 and 5 had high firing temperature and had grain growth during firing. It is thought that it was. Here, the thermal plasma treatment was performed in the same manner as in Experiment 1.

FIG. 8 shows the particle size distribution of each sample prepared under the conditions shown in Table 3. The particle size distribution was measured in the same manner as in Experiment 1. The particle size distribution of Comparative Example 4 having a low firing temperature was 0.2 to 4 μm. Example 2 is 0.5 to 10 μm
m, Example 3 is 1 to 100 μm, Example 4 is 0.5 to 4 μm
Since it is 0 μm and Example 5 is 0.5 to 70 μm, it is found that when these are put together, good characteristics are exhibited at a particle size of 0.5 to 100 μm.

Each of the samples obtained here was applied on an aluminum current collector foil according to the flow chart of FIG. 3 in the same manner as in Experiment 1, and each sample was used as a positive electrode and each sample was used as a positive electrode active material. The battery characteristics were evaluated using the battery. Table 4
Is the density of the positive electrode active material, the initial discharge capacity when discharged at 0.33C, the discharge capacity at the 50th cycle, the discharge capacity when discharged at 2C, the discharge capacity per volume calculated from the electrode density and the initial discharge capacity. Shows the expressed volume capacity.

[0059]

[Table 4]

From the data shown in FIG. 8 and Table 4, in Comparative Example 4 in which the lower limit of the particle size distribution was as small as 0.2 μm, the discharge capacity at the 50th cycle was lowered and it was not practical.
Examples 2, 3, 4, and 5 having m or more are preferable. The upper limit is preferably 100 μm or less so that large particles are not caught when applying the electrode and a problem such as streaking on the applied surface does not occur. A suitable average particle size D50 is determined from the data in FIG.
Between 6 μm and 11 μm, but about 0.6 μm
The range of about 50 μm is good. The higher the electrode density, the more the positive electrode material can be filled in the battery, but practically, the discharge capacity at the 50th cycle is preferably not less than 2.54 × 10 ³ Kg / m ^{3 in} Example 2.

Experiment 3 Here, as an experiment for determining the heat treatment conditions after the thermal plasma treatment, the heat treatment conditions of the spinel-type lithium manganate thermal plasma treated spherical particles produced in the same manner as in Example 1 are shown in Table 5. By changing and processing, a positive electrode active material was produced. Since it was found from Experiment 1 that the characteristics greatly changed depending on the presence or absence of heat treatment, the heat treatment temperature was changed from 400 ° C. to 1000 ° C., and the atmosphere was oxygen in Example 8.

[0062]

[Table 5]

Each sample obtained here was coated on an aluminum current collector foil according to the flow chart of FIG. 3 in the same manner as in Experiment 1 to produce a positive electrode, and each sample was used as a positive electrode active material in the nonaqueous system shown in FIG. Battery characteristics were evaluated using a lithium secondary battery.
The evaluation was performed on the initial discharge capacity when discharging at 0.33C and the discharge capacity at the 50th cycle. The results are shown in Table 6.

[0064]

[Table 6]

From the data in Tables 5 and 6, the heat treatment temperature at 400 ° C. in Comparative Example 5 is too low for practical use because both the initial discharge capacity and the discharge capacity at the 50th cycle are too low. On the other hand, at the heat treatment temperature of 1000 ° C. in Comparative Example 6, there is no problem in the initial discharge capacity,
At the cycle, the discharge capacity decreased by about 30%. Since a lithium secondary battery is used for 500 cycles or more, this cycle characteristic is not practical. From this result, the heat treatment temperature was 5
It turned out that the range of 00-900 degreeC is good. The heat treatment time in Example 1 was 10 hours, but in Example 6
As can be seen from FIG. It was also found that the atmosphere during the heat treatment was better in oxygen in Example 8 than in air in Example 7.

Experiment 4 Here, an experiment was performed to determine the thermal plasma processing conditions for melting and solidifying the surface of the spinel type lithium manganate particles to form a spheroid.
A positive electrode active material was prepared in the same manner as described above. Table 7 shows the thermal plasma processing conditions for each sample. The firing was all performed at 900 ° C. for 5 hours in the atmosphere.

[0067]

[Table 7]

As the spheroidization ratio (%) of each of the obtained samples, the number ratio of the spheroidized particles was calculated using an image processing device after photographing the particle morphology by SEM. In order to evaluate the shape of the granules, the granules were examined with a flow particle image analyzer FPIA-2100 manufactured by Sysmex Corporation. This device is C
Thousands of particles are photographed using a CD camera, and the projected area and perimeter of each particle are measured to calculate the equivalent circle diameter and circularity. The equivalent circle diameter is calculated by Equation 1, and the circularity is calculated by Equation 2. Here, the equivalent circle diameter is the diameter of a perfect circle having the projected area of the particles obtained by measurement, and the circularity is the ratio of the circumference measured from the diameter to the circumference of the projected image.

[0069]

(Equation 1)

[0070]

(Equation 2)

FIG. 9 is a graph showing an example of the measurement, showing the circularity of the particles of Example 11 and Comparative Example 7 in relation to the circle equivalent diameter. The horizontal axis is the equivalent circle diameter and the vertical axis is the circularity, and the data of each particle is indicated by a dot in the figure. This apparatus can graph and digitize the distribution state of the spherical particles, which is a feature of the present invention. Particularly characteristic is the volume ratio of particles having a circle-equivalent diameter (particle diameter) of 5 to 15 μm and a circularity of 0.9 to 1.0. This volume ratio is expressed as a limited particle ratio in this specification. In the lower diagram, SE
In Comparative Example 7 where the spheroidization was 0% and the equivalent circle diameter (particle diameter) was 5%.
Almost no particles having a circularity of 0.9 to 1.0 at １５15 μm, while in Example 11 where spheroidization was confirmed, the particle distribution can be confirmed. The limited particle ratio of Comparative Example 7 was 1.2%.
In Example 11, the value was 16.0%. Table 8 shows the values of the limited particle ratios for other samples obtained in the same manner.

Each of the samples obtained here was coated on an aluminum current collector foil according to the flow chart of FIG. 3 in the same manner as in Experiment 1 to serve as a positive electrode, and each sample was used as a positive electrode active material in the nonaqueous lithium secondary battery shown in FIG. The characteristics of the secondary battery were evaluated and the results are shown in Table 8.

[0073]

[Table 8]

In Comparative Example 7 and Examples 10 to 14, the effects on the spheroidization ratio and the electrode characteristics were examined by changing the input power. From the results in Tables 7 and 8, no spheroidization was observed at 1 KW in Comparative Example 7, but the supply power was increased and
It could be confirmed that spheroidization was achieved by setting the KW or more. Even in Example 10 having a spheroidization rate of 3%, an improvement of 8.5% in volume capacity was obtained as compared with Comparative Example 7 of 0%, so that the spheroidization rate may be 3% or more. Understand. Further, in the sample in which the input power was increased, the electrode density increased and the volume capacity increased as the spheroidization rate increased. A desirable spheroidization ratio is 20% or more, and a more desirable spheroidization ratio is 50% or more.

As in the case of the spheroidization ratio, the correlation between the limited particle ratio and the volume capacity is improved as the limited particle ratio is higher, and the characteristics are improved in Example 10 in which the limited particle ratio is 7% or more. Can be confirmed. Desirable limited particle ratio (circularity of 0.9 to
1.0 and a particle size of 5 to 15 μm) is 20% or more, and a more desirable spheroidization ratio is 40% or more. The sample of Comparative Example 7 was S
Although it was not confirmed by EM that the particles were spherical, it is considered that the numerical value of the limited particle ratio was accidentally obtained.

Example 15 examines the effect of replacing the thermal plasma processing apparatus and changing the frequency of the input power from 13.56 MHz to 4 MHz. From the results of Tables 7 and 8, the sample having a frequency of 4 MHz (Example 15) has a lower spheroidization rate, a limited particle rate, an electrode density, and a volume capacity as compared with Example 12 having a frequency of 13.56 MHz, which has the same input power. However, as compared with Comparative Example 7 in which the spheroidizing treatment was not performed, the effect of the spheroidizing by the thermal plasma treatment was confirmed.

Further, Embodiment 16, Embodiment 17, Embodiment 1
8 was carried out with the atmosphere in the apparatus changed to air, oxygen, and nitrogen, respectively, and the effect of improving the volume capacity was confirmed as in the case of the argon atmosphere. Example 19 is to investigate the effect of lowering the pressure in the apparatus. Table 8 shows that the spheroidization rate, electrode density, and volume capacity are lower than atmospheric pressure, but the effect of spheroidization by thermal plasma treatment was confirmed as compared with Comparative Example 7 in which spheroidization did not occur. Using cobalt tetroxide and lithium carbonate as
It was weighed so that the Li / Co ratio was 1.00 in atomic ratio, and was mixed by a resin ball mill in a wet manner for 50 hours. After adding the PVA solution to the mixture, the mixture was granulated by a spray drier and dried to prepare granules of 10 to 80 μm. The prepared granules were fired at 900 ° C. in the air, crushed with a raikai machine, and passed through a sieve having an opening of 32 μm to obtain a mixture of Example 20 and Comparative Example 8.
Was used for the sample. The sample of Example 20 was subjected to thermal plasma treatment at 13.56 MHz and power of 5 kW in an Ar atmosphere at atmospheric pressure and heat treatment at 600 ° C. in the atmosphere for 10 hours in the same manner as in Example 1. It is confirmed that it is done. For the sample of Comparative Example 8, only heat treatment was performed at 600 ° C. in the air for 10 hours without performing thermal plasma treatment.

The obtained sample was evaluated as a positive electrode active material in the same manner as in Experiment 1, and the electrode density and the initial discharge capacity and volume capacity when discharged at 0.33 C were measured.
Is shown in

[0079]

[Table 9]

From the results, the sample of Example 20 which was subjected to the thermal plasma treatment was compared with Comparative Example 8 which did not perform the thermal plasma treatment.
It was confirmed that the electrode density and the initial discharge capacity were improved and the volume capacity was improved by 15% as compared with that of the above, and it was found that the electrode was effective as a Co-based positive electrode active material.

[0081]

As described in detail above, the positive electrode active material obtained by the production method of the present invention is one in which at least the surface of the lithium transition metal oxide particles is melted and solidified to form a sphere, which is heat-treated. The initial discharge capacity is about 10% as compared with a conventional positive electrode active material (for example, Comparative Examples 2 and 3).
And the decrease in the discharge capacity at the 50th cycle is small. In addition, it is a positive electrode active material with less deterioration in characteristics even in large current discharge. The volume capacity is improved by 15% or more compared to the conventional product.

Similarly, when lithium cobaltate was used as the positive electrode active material, a large charge / discharge capacity was obtained.

[Brief description of the drawings]

FIG. 1 shows a flowchart for producing a positive electrode active material according to the present invention.

FIG. 2 is a schematic configuration diagram of a high-frequency thermal plasma generator used for performing thermal plasma processing in the present invention.

FIG. 3 shows a flowchart for manufacturing a positive electrode using the positive electrode active material of the present invention.

FIG. 4 is a schematic configuration diagram of a non-aqueous lithium secondary battery.

FIG. 5 is an SEM photograph showing a particle structure of a positive electrode active material.

FIG. 6 is a graph showing a particle distribution of a positive electrode active material.

FIG. 7 is an X-ray diffraction chart of a positive electrode active material.

FIG. 8 is a graph showing a particle distribution of a positive electrode active material.

FIG. 9 is a graph showing the circularity of the particles of Example 11 and Comparative Example 7 in relation to the circle equivalent diameter.

[Explanation of symbols]

 20 High-frequency thermal plasma generator 21 High-frequency induction coil 22 Material supply port 23 Gas supply port for plasma operation 24 Exhaust port 25 Plasma 26 Spherical particles 40 (non-aqueous lithium) secondary battery 41 Electrolyte 42 Positive electrode 43 Negative electrode 44 (for charging) power supply 45 load resistance 46 voltmeter 47 selector switch

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Akio Uchikawa 70-2, Minamisakaemachi, Tottori-shi, Tottori Prefecture F-term (reference) 4G048 AA04 AB01 AB05 AC06 AD04 AE05 5H029 AJ03 AJ05 AJ14 AK03 AM03 AM05 AM07 CJ02 CJ08 DJ16 DJ17 HJ01 HJ05 HJ13 HJ14 5H050 AA02 AA07 AA08 AA19 BA17 CA09 FA17 FA19 GA02 GA10 HA01 HA05 HA13 HA14

Claims (17)

[Claims] A mixture of a transition metal compound and a lithium compound, each of which becomes an oxide upon firing, is mixed at a predetermined ratio, and the mixture is fired to form a composite oxide of lithium and a transition metal. A method for producing a positive electrode active material for a non-aqueous lithium secondary battery, comprising melting at least the surface of particles of a composite oxide, coagulating the particles, and then heat treating the particles. 2. A method according to claim 1, wherein at least one of a manganese compound and a cobalt compound, each of which becomes an oxide upon firing, is mixed with a lithium compound at a predetermined ratio, and the mixture is fired to form a composite oxide of lithium and a transition metal. A method for producing a positive electrode active material for a non-aqueous lithium secondary battery, characterized by melting at least the surface of particles comprising a composite oxide of lithium and a transition metal, coagulating the particles, and then heat treating the particles. 3. A manganese compound and a lithium compound, each of which becomes an oxide by firing, are mixed at a predetermined ratio, and the mixture is fired to obtain spinel-type lithium manganate. A method for producing a positive electrode active material for a non-aqueous lithium secondary battery, wherein at least the surface is melt-solidified, and then the particles are heat-treated. 4. The method for producing a positive electrode active material for a non-aqueous lithium secondary battery according to claim 1, wherein said melt-solidification is a thermal plasma treatment. 5. The thermal plasma treatment is performed at a temperature equal to or higher than the melting point of the composite oxide of lithium and transition metal, with an atmosphere of argon, oxygen, air or nitrogen, and a pressure of 50 KPa to atmospheric pressure. A method for producing a positive electrode active material for a non-aqueous lithium secondary battery according to claim 4. 6. The crystal structure altered by the melt-solidification is returned to the original crystal structure of the composite oxide of lithium and transition metal by the heat treatment.
6. The method for producing a positive electrode active material for a non-aqueous lithium secondary battery according to any one of 5. 7. The method for producing a positive electrode active material for a non-aqueous lithium secondary battery according to claim 6, wherein the heat treatment is performed at a temperature of 500 to 900 ° C. in the air or an oxygen atmosphere. 8. A positive electrode active material for a non-aqueous lithium secondary battery, comprising particles comprising a composite oxide of lithium and a transition metal, wherein at least the surface thereof is melt-solidified and spherical. 9. A positive electrode active material for a non-aqueous lithium secondary battery, comprising particles comprising at least one of spinel type lithium manganate and lithium cobaltate, at least the surface of which is melted and solidified to be spherical. material. 10. A positive electrode active material for a non-aqueous lithium secondary battery, comprising particles made of spinel-type lithium manganate, wherein at least the surface of the particles is formed into a spheroid by melting and solidifying. 11. The positive electrode active material for a non-aqueous lithium secondary battery according to claim 8, wherein the spheroidization by melting and solidification is performed by exposing to thermal plasma. 12. The particle size distribution range of the particles is 0.5 to 10
The positive electrode active material for a non-aqueous lithium secondary battery according to any one of claims 8 to 11, wherein the positive electrode active material has a particle size of 0.6 to 50 µm at 0 µm. 13. The positive electrode active material for a non-aqueous lithium secondary battery according to claim 8, wherein a spheroidization ratio of the particles is 3% or more. 14. The limited particle ratio of the particles (circularity of 0.9 to 0.9).
1.0, the volume ratio of particles in the range of 5 to 15 μm) is 7
The positive electrode active material for a non-aqueous lithium secondary battery according to any one of claims 8 to 13, wherein 15. From a composite oxide of lithium and a transition metal
With a positive electrode formed by forming a positive electrode active material
In the lithium secondary battery, the composite oxide of lithium and a transition metal is at least
Particles whose surface has been melted and solidified to form spheroids.
The density of the positive electrode active material attached to is 2.54 × 10 ^ThreeKg / m^ThreeLess than
A non-aqueous lithium secondary battery characterized by the above. 16. The non-aqueous lithium secondary battery according to claim 15, wherein the composite oxide of lithium and a transition metal is at least one of spinel-type lithium manganate and lithium cobaltate. 17. The non-aqueous lithium secondary battery according to claim 16, wherein the composite oxide of lithium and a transition metal is spinel-type lithium manganate.