JPH1192119A - Oxide powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain oxide powder having characteristics of a plurality of oxides and capable of suppressing the formation of aggregates owing to the rugged surface shape. SOLUTION: Nuclear particles 70 of an oxide are prepd. and fine oxide particles 71 different from the nuclear particles 70 in compsn. are stuck to the surfaces of the nuclear particles 70 to obtain the objective oxide powder 7. The nuclear particles 70 may be particles of lithium manganese double oxide and the fine oxide particles 71 may be fine particles of LiMO2 (M is a transition metal such as Co, Ni, Fe, Cr, Ti or V).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a specially shaped oxide powder having fine particles adhered to the surface.

[0002]

2. Description of the Related Art Oxides such as metal oxides and metal composite oxides are used in various fields, and are used, for example, as positive electrode materials for lithium secondary batteries that have recently attracted attention. As a conventional positive electrode material for a lithium secondary battery, LiCoO ₂ having an ordered layered rock salt structure has been used.
However, in terms of resource quantity and price, this material is considered to be a spinel-structured lithium manganese composite oxide (LiM
n ₂ O ₄ ).

[0003] LiMn ₂ O ₄ has the disadvantages that the diffusion rate of lithium is lower and the conductivity is lower than that of LiCoO ₂ . Therefore, when charging and discharging are performed at a high current density, it is difficult to obtain a large discharge capacity, and the capacity deterioration is large.
Therefore, ideally, the above LiMn ₂ O ₄ and LiCo
An oxide powder having both advantages of O ₂ is desirable as the cathode material.

[0004]

In order to solve the above-mentioned drawback of the charge / discharge characteristics of LiMn ₂ O _{4 at} a high current density, a powder having high crystallinity and a small particle size has been conventionally proposed.
For example, the spray combustion synthesis disclosed in JP-A-7-81905 corresponds to this. However, even with this improvement, LiC
Properties comparable to oO ₂ have not been obtained.

[0005] Powders having a small particle size generally have the disadvantage that they are bulky and do not increase the filling rate. This is because the interparticle adhesion becomes relatively large with respect to the particle weight.
A decrease in the filling factor causes a decrease in the electrode density, that is, a decrease in the battery capacity. In addition, there is a disadvantage that the moldability when forming an electrode is poor due to the adhesion between particles.

Therefore, the present inventors have solved these two problems: (1) a decrease in charge / discharge capacity at a high current density due to a low conductivity or a low lithium diffusion rate;
(2) Intensive investigations were made to solve the problem of the decrease in the filling factor due to the adhesion between particles and the decrease in moldability during electrode fabrication. As a result, we considered that oxide fine powders having different characteristics were arranged on the surface of the core oxide particles in irregular shapes. If this is realized, the adhesion between particles will be reduced due to the effect of unevenness, the filling property and moldability can be improved, and an oxide powder having excellent properties that cannot be obtained with a single oxide will be obtained. Can be.

[0007] In the case of LiMn ₂ O ₄ described above, the conductivity is low or the lithium diffusion rate is low because the conductive oxide fine powder or the oxide fine powder having a high lithium diffusion rate is disposed. In addition, it is possible to suppress a decrease in charge / discharge capacity at a high current density, and also to suppress a decrease in a filling factor and a decrease in moldability at the time of electrode production due to interparticle adhesion.

The present invention has been made in view of such a conventional problem, and has the characteristics of a plurality of oxides.
An object of the present invention is to provide an oxide powder capable of reducing the interparticle adhesion due to the unevenness of the surface.

[0009]

According to the present invention, there is provided an oxide powder comprising oxide particles having a different composition adhered to the surface of core particles made of oxide.

The most remarkable point in the present invention is that each of the particles constituting the oxide powder is obtained by adhering the oxide fine particles on the surface of the core particles, and further comprising the core particles and the oxide fine particles. Means that they are composed of oxides having different compositions.

The particle size of the oxide fine particles is such that they adhere to the surface of the core particles, that is, 1 / the particle size of the core particles.
It is preferable to set the range of 5 to 1/100. When the particle size of the oxide fine particles exceeds the above range, there is a problem that a clear uneven shape cannot be formed on the surface of the core particles in any case.

Next, the operation of the present invention will be described. The oxide powder of the present invention is obtained by adhering the oxide fine particles to the surface of the core particles. Therefore, on the particle surface of the oxide powder, a concavo-convex shape is formed by a portion where the oxide fine particles adhere and a portion where the oxide fine particles do not adhere. The irregular shape of the particle surface exerts an effect of reducing the adhesion of the particles to each other, and can greatly suppress the formation of aggregates. Therefore, the oxide powder of the present invention can greatly improve the bulk density when molded into, for example, a green compact. In addition, the powder's fluidity,
Moldability is also improved.

[0013] The oxide powder is composed of two different oxides, the core particles and the oxide fine particles. Therefore, the excellent properties of the core particles and the excellent properties of the oxide fine particles are simultaneously obtained. Therefore, according to the present invention, it is possible to provide an oxide powder that has the properties of a plurality of oxides and can suppress the formation of aggregates due to the surface irregularities.

Next, the core particles are a lithium manganese composite oxide, and the oxide particles are LiCoO ₂
LiMO ₂ (M = Co, Ni, Fe, C
transition metals such as r, Ti, and V). Thus, the oxide powder can be used as an excellent cathode material in a lithium secondary battery.

That is, in this case, a large number of LiCoO 2 particles are formed on the surface of the core particles of the lithium manganese composite oxide.
LiMO ₂ represented by ₂ is formed in a state adhered. Therefore, the excellent conductivity of the oxide fine particles can be added to the inexpensive and resource-rich core particles. In addition, the filling rate in the case of forming the positive electrode can be improved as compared with the related art due to the effect of suppressing the aggregates having the uneven shape.

Further, this LiMO ₂ is LiMn ₂ O ₄
If charge and discharge are possible in the same voltage range as above, the overall capacity will not be significantly reduced. Therefore, when this oxide powder is applied to the positive electrode material of a lithium secondary battery, it is excellent in high discharge capacity, particularly, increase in charge / discharge capacity at high current density, increase in charge / discharge capacity per volume, etc. It has the effect.

Next, as a method for producing the above-mentioned excellent oxide powder, there is a method for producing an oxide powder obtained by adhering oxide fine particles having a different composition to the surface of core particles made of oxide. A raw material aqueous solution containing the raw material ions of the oxide fine particles is prepared, the core particles are dispersed in the raw material aqueous solution, and then the raw material aqueous solution is emulsified in a flammable liquid to form an emulsion. There is a method for producing an oxide powder, which comprises spraying the emulsion in the form of droplets and burning a combustible liquid in the droplets to synthesize the oxide powder.

The most remarkable point in this production method is that the core particles are dispersed in the raw material aqueous solution in advance, and a spray combustion synthesis method is performed using the raw material aqueous solution.

As the core particles, those having a particle size of 0.5 to 5 μm are used. When the particle size is less than 0.5 μm, there is a problem that it is difficult to form irregularities on the surface of the core particles. On the other hand, when the particle size exceeds 5 μm, it is difficult to perform the spray combustion synthesis method. There is a problem. The above-mentioned core particles can be produced by various methods such as a conventional spray combustion synthesis method and a solid phase reaction method.

The raw material aqueous solution contains the raw material ions of the oxide fine particles, that is, the raw material element of the oxide fine particles to be obtained in an ion state. For example, in the case where oxide fine particles of a lithium-cobalt composite oxide are precipitated on the core particle surface, the raw material aqueous solution contains lithium ions and cobalt ions.

The raw material aqueous solution is emulsified in a combustible liquid to form an emulsion. As the flammable liquid used at this time, kerosene, light oil, heavy oil, gasoline, or the like is used. As the emulsifier for forming an emulsion, one containing no metal ion, particularly a nonionic surfactant is desirable, and glycerin fatty acid ester is used.

The combustion flame temperature of the emulsion in the reaction tower during the spray combustion synthesis of the emulsion is set according to the type of oxide powder to be synthesized. For example, when depositing oxide fine particles of lithium cobalt composite oxide on the surface of core particles of lithium manganese composite oxide, the temperature is preferably set to 600 to 900 ° C. 600 ° C
If it is less than 3, there is a problem in combustion stability. On the other hand, when the temperature exceeds 900 ° C., there is a problem that the lithium manganese composite oxide is decomposed.

Next, the operation of the present invention will be described. In the present invention, the core particles are dispersed in the raw material aqueous solution in advance, and the raw material aqueous solution is made into the above-mentioned emulsion state to perform spray combustion synthesis. Therefore, an oxide powder obtained by adhering oxide powders having different compositions to the surface of the core particles can be easily produced.

That is, in the present production method, an emulsion obtained by emulsifying the raw material aqueous solution substantially uniformly in a flammable liquid is sprayed in the form of droplets. The sprayed droplet contains a raw material aqueous solution having a substantially uniform size in a state of being wrapped in a combustible liquid. Further, each raw material aqueous solution contains core particles dispersed in advance.

[0025] Each of the sprayed droplets undergoes the process of desolvation, thermal decomposition, and crystal growth for each raw material aqueous solution enclosed by the combustion of the combustible liquid.
Specifically, new oxide fine particles synthesized from the raw material aqueous solution precipitate and adhere to the surface of the core particles already existing in the oxide state.

Therefore, the obtained oxide powder becomes an oxide powder having irregularities in which a large number of oxide fine particles are adhered to the surface of the core particles, and exhibits the above-mentioned excellent effects. In the present production method, not all the obtained particles are particles having such a structure, but may include oxide fine particles or particles in a single state of core particles.

As described above, according to the present production method, there is obtained a method for producing an oxide powder, which has the characteristics of a plurality of oxides and can suppress the formation of agglomerates due to the unevenness of the surface.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 An oxide powder according to an embodiment of the present invention and a method for producing the same will be described with reference to FIGS. In this example, as shown in FIG. 1, LiCoO ₂ was deposited on the surface of lithium manganese composite oxide core particles 70 having a composition of Li _1.03 Mn _1.97 O ₄ by the spray combustion synthesis method according to the production method of the present invention. An oxide powder 7 was prepared by adhering oxide fine particles 71 of a lithium-cobalt composite oxide having a composition (Sample E1).

For comparison, a lithium manganese composite oxide powder (sample C1) having a composition of Li _1.03 Mn _1.97 O _{4 was obtained} by two kinds of production methods, a conventional spray combustion synthesis method and a conventional solid phase method. , C2).

First, FIG. 2 shows an outline of the spray combustion synthesizing apparatus. This equipment is a metering pump 1 for supplying emulsion.
An atomizer 2 for spraying an emulsion, a pilot burner 3 for ignition, and a cylindrical combustion reaction tower 4
And a collector 5 for collecting particles. The metering pump 1 is connected to a mixing tank 11 containing the emulsion 110. Samples E1 and C1 were prepared using this apparatus. Sample E1 is an example of the present invention, and sample C1 is a comparative example.

(Production of Sample E1) Lithium nitrate (LiNO ₃ ) as a lithium ion source and cobalt nitrate (Co (NO ₃ ) ₂ .6H ₂ O) as a cobalt ion source
Was dissolved at a molar ratio of Li: Co at a ratio of 1: 1 to adjust the cobalt ion concentration to 0.05 mol / liter to obtain a raw material aqueous solution.

Next, 48.9 g per liter of lithium manganese composite oxide fine particles having a particle size of about 1 μm were added to the raw material aqueous solution, and mixed and dispersed. These fine particles have a composition of Li _1.03 Mn _1.97 O ₄ . Next, the raw material aqueous solution in which the oxide fine particles are dispersed is suspended in kerosene as a combustible liquid in which glycerin fatty acid ester as an emulsifier is dissolved,
An emulsion 110 was prepared in the mixing tank 11.

Next, the emulsion 110 was supplied to the atomizer 2 by the metering pump 1 and sprayed with oxygen gas from the surroundings to be sprayed into the combustion reaction tower 4 in the form of droplets. Then, a flame of a mixed gas of hydrogen and oxygen was supplied from the pilot burner 3, thereby igniting the combustible liquid in the emulsion and performing spray combustion synthesis in the combustion reaction tower 4.

The flame temperature of the emulsion subjected to the spray combustion synthesis was about 900 ° C. During the combustion, air was forcibly supplied to the reaction tower from the outside so as not to run out of oxygen. The oxide powder synthesized by combustion was collected in the collector 5. This was designated as Sample E1.

(Preparation of Sample C1) Lithium nitrate (LiNO ₃ ) as a lithium ion source and manganese nitrate hexahydrate (Mn (NO ₃ ) ₂ .6) as a manganese ion source
An aqueous solution of H ₂ O) dissolved in a molar ratio of Li: Mn of 1.03: 1.97 was adjusted to a manganese ion concentration of 1.97 mol / l, and the raw material aqueous solution was adjusted to 1.97 mol / l. did. The raw material aqueous solution was used without adding the above-mentioned oxide fine particles. Other than that, the lithium manganese composite oxide particles were produced in the same manner as in the production method of Sample E1. This was designated as Sample C1.

(Production of Sample C2) Sample C2 was produced by a conventional solid-phase reaction method. Lithium carbonate (L
i ₂ CO _3), using the particles of manganese dioxide (MnO _2), Li at a molar ratio: Mn 1.03 were mixed so that the 1.97. Mixing was performed with a planetary ball mill using ethanol as a solvent. After drying, the mixed particles were pressed into a pellet and heat-treated at 800 ° C. for 8 hours in oxygen. The pellet was sufficiently pulverized to obtain lithium manganese composite oxide particles of Li _1.03 Mn _1.97 O ₄ having the same composition as above. This was designated as Sample C2.

Next, in this example, the above three samples E
The particle shapes of 1, 1, and 2 were evaluated by SEM observation. In addition, in order to quantitatively evaluate the filling property of the synthetic particles, a sample of 10 g, a die inner diameter of φ30 mm, and a pressure of 1 to
Under the condition of n, the pressure bulk density was measured.

The results of the SEM observation are shown in FIGS. FIG. 3 is an SEM photograph of the sample E1 according to an example of the present invention. FIG. 4 shows an SEM of sample C1 according to a conventional comparative example.
It is a photograph. Each is a 5000 × photograph. As is known from these figures, the particles of the sample E1 formed a surface state of a concavo-convex shape in which a large number of oxide fine particles adhered around the core particles.

On the other hand, the sample C1 had almost the same particle diameter as the sample E1, but had little irregularities on the surface. Further, the shape of the sample C1 varied, and a large number of irregularly shaped particles such as burst particles were observed. Although no SEM photograph is shown for the particles of sample C2, they have a particle size that is one order larger than that of samples E1 and C1, as is conventionally known.

Next, Table 1 shows the measurement results of the bulk density under pressure. As can be seen from Table 1, it can be seen that the sample E1 has the highest bulk density, and that the formation of the irregularities directly contributes to the improvement of the bulk density. The low bulk density of the sample C1 is considered to be due to the large number of irregularly shaped particles such as hollow particles.

[0041]

[Table 1]

Embodiment 2 In this embodiment, a lithium secondary battery was assembled using each of the three samples (E1, C1, C2) manufactured in Embodiment 1 as a positive electrode material, and the characteristics thereof were evaluated.

First, the structure of the lithium secondary battery will be described. In making the positive electrode of the lithium secondary battery, first, the oxide powder of the samples E1, C1, and C2 was mixed with 85%
wt%, 7 wt% of carbon as a conductive agent, and 8 wt% of polyvinylidene fluoride (PVdF) as a binder.
These are dissolved in N-methyl-2-pyrrolidone (NM)
P) and wet mixing to obtain a positive electrode mixture paste. Next, this positive electrode mixture paste was applied to an aluminum foil with a thickness of 0.2 mm, dried, and then pressurized at 2.7 ton / cm ² to prepare a positive electrode.

On the other hand, a metal Li having a thickness of 0.4 mm
One foil was used. A polypropylene nonwoven fabric was interposed between the positive electrode and the negative electrode as a separator. further,
The electrolyte in the lithium secondary battery is 1N Li
A PF ₆ solution was used. The solvent of this electrolyte is a 1: 1 mixture of ethylene carbonate and diethyl carbonate.

Next, in order to evaluate the characteristics of the lithium secondary battery, a charge / discharge test was performed as follows in order to simultaneously evaluate the cycle characteristics and the high discharge capacity. First, each lithium 2
The charging condition of the secondary battery is 1 mA / cm until it reaches 4.3 V.
After the battery was charged with the constant current of ² , and after the voltage reached 4.3 V, the condition was set such that constant voltage charging was performed at this voltage. The total of the above charging times was 4 hours.

The discharge conditions of each lithium secondary battery are as follows:
A constant current discharge was performed, and when the voltage reached 3.5 V, the discharge was terminated. The discharge current density of the constant current discharge was changed every three cycles. Specifically, 0.5 mA for 1-3 cycles
/ Cm ^2, 4~6 cycle is 1mA / cm ^2, 7~9 cycle 2mA / cm ^2, 10~12 cycle 4mA
/ Cm ² , 0.5 mA / cm for 13-15 cycles again
^{And 2} .

FIG. 5 shows the results of the above charge / discharge test. In the figure, the horizontal axis represents the number of charge / discharge cycles, and the vertical axis represents the active material discharge capacity (mAh / g). The respective discharge current densities are shown above the plotted data. According to FIG.
By comparing the data group of three cycles to the data group of 10 to 12 cycles, the high discharge capacity of each lithium secondary battery can be evaluated. The cycle characteristics (durability) can be evaluated by comparing the data group of 1 to 3 cycles with the data group of 13 to 15 cycles.

As a result, both the samples E1 and C1 of the present invention and the conventional spray combustion synthesis method exhibited higher discharge capacity and cycle characteristics than the sample C2 of the solid phase reaction method. As for the high discharge capacity at 4 mA / cm ² , the sample E1 of the present invention showed much better performance than the sample C1.

Samples E1 and C1 were sample C obtained by the solid-phase reaction method.
It is considered that the reason why the performance superior to 2 was exhibited is that the lithium manganese composite oxide particles have good homogeneity, small particle size, and large specific surface area. Further, the reason why the sample E1 which is an example of the present invention exhibited better electrode performance than the sample C1 was because the effect of improving the bulk density by the above-mentioned uneven shape and the effect of improving the conductivity by LiCoO ₂ of the oxide fine particles were exhibited. It is considered to be.

[0050]

As described above, according to the present invention, it is possible to provide an oxide powder having both the properties of a plurality of oxides and suppressing the formation of aggregates due to the unevenness of the surface.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an oxide powder according to a first embodiment.

FIG. 2 is a schematic explanatory view of a spray combustion synthesizing apparatus according to the first embodiment.

FIG. 3 is a SEM photograph (magnification: 5,000 times) showing a particle shape of a sample E1 in Embodiment Example 1 instead of a drawing.

FIG. 4 is a SEM photograph (magnification: 5,000) used as a substitute for a drawing, showing the particle shape of sample C1 in the first embodiment.

FIG. 5 is an explanatory diagram showing a result of a charge / discharge test of a lithium secondary battery in Embodiment 2.

[Explanation of symbols]

 1. . . 1. metering pump, . . Atomizer, 3. . . 3. pilot burner, . . Combustion reaction tower, 5. . . Collector, 7. . . Oxide powder, 70. . . Nuclear particle, 71. . . Oxide fine particles,

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Naoyoshi Watanabe 41-Cho, Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside Toyota Central R & D Laboratories Co., Ltd. (72) Inventor Tatsuo Noriku, Nagakute-cho, Aichi-gun, Aichi Prefecture 41, Yokomichi, Toyota Central Research Laboratory Co., Ltd. (72) Inventor Jun Sugiyama Ochi, Chukuji, Nagakute-cho, Aichi-gun, Aichi Prefecture, Japan 41-Toyota Central Research Laboratory Co., Ltd. (72) Tatsuya Hatanaka Aichi Prefecture 41 Toyota-Chuo R & D Co., Ltd.

Claims (1)

[Claims] 1. An oxide powder comprising oxide fine particles having a different composition adhered to the surface of a core particle made of an oxide.