JP2003151546A - Positive electrode active substance for lithium ion secondary battery and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active substance which is superior especially in a filling property, which has a high capacity and which is superior in a load property and a charging-discharging cycle property, and provide its manufacturing method. SOLUTION: This substance leas such a constitution that the positive electrode active substance for a lithium ion secondary battery has a particle shape of a hexagonal pillar and satisfies 0.5<=(2c)/(a+b)<=1 (in the formula, a shows the average longer shaft diameter of the base face, b shows the average shorter shaft diameter and c shows the average particle height). Further, the positive electrode active substance for the lithium ion secondary battery can be manufactured by a method of baking a raw material mixture in an atmosphere of oxygen density 0.5 to 5 vol.% or by a method of baking the raw material mixture at 700 deg.C or less and of carrying out a process of baking and crushing twice or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode active material for a lithium ion secondary battery, and particularly to a positive electrode active material having excellent filling properties, high capacity, and excellent load characteristics and cycle charge / discharge characteristics, and a method for producing the same. Regarding

[0002]

2. Description of the Related Art Lithium ion secondary batteries are characterized by a high operating voltage of about 3.5 V and a high energy density. Since mobile electronic devices typified by mobile phones and notebook computers are required to be small and lightweight, lithium ion secondary batteries are widely used as power sources for mobile electronic devices. In recent years, various functions have been added to mobile electronic devices such as mobile phones, and along with this, the lithium ion secondary battery as a power source has further improved capacity, load characteristics, cycle characteristics such as cycle charge / discharge characteristics. Improvement is required.

As a positive electrode active material of a lithium ion secondary battery, there is a lithium transition metal composite oxide represented by lithium cobalt oxide (LiMO ₂ (M is a transition metal element)). The lithium-transition metal composite oxide has a hexagonal crystal structure, and Li ions are inserted and desorbed from the a and b axis directions of the crystal structure with charge and discharge. This lithium-transition metal composite oxide is likely to undergo selective crystal growth in the a and b axis directions, and tends to form plate-like particles as shown in FIG. The grain shape reflects the crystal structure. The height direction of the plate-like particles corresponds to the c-axis direction of the crystal structure, and the in-plane direction of the bottom surface of the plate-like particles corresponds to the a and b-axis directions of the crystal structure. It is thought that

When the plate-like particles are used as a positive electrode plate, they are shown in FIG.
As shown in (3), the a and b axis directions of the crystal structure are easily oriented so as to be the in-plane direction of the positive electrode plate. For this reason, it is considered that the plate-like particles come into contact with each other in the a-axis and b-axis directions, so that it becomes difficult to insert and release Li ions, and the Li ion migration resistance at the particle interface becomes high. This causes a problem that load characteristics and cycle charge / discharge characteristics are deteriorated.

Generally, when the positive electrode active material is made of polycrystalline spherical particles, the a and b axis directions of the crystal structure are distributed on the entire surface of the particle without depending on the particle shape, and the insertion and desorption of Li ions are carried out on the surface of the particle. It can be done on the whole surface. Therefore, by using spherical particles, the diffusion of Li ions at the particle interface is improved and the cycle charge / discharge characteristics can be improved. However, the spherical particles have a poor filling property, and when used as a positive electrode plate, there is a problem that the density of the electrode plate is difficult to increase. It is necessary to press the positive electrode plate with a strong pressure in order to obtain a predetermined electrode plate density, and it is considered that the pressing causes cracks or chips of particles, or stress is applied to the crystal, which lowers the initial discharge capacity. Become.

[0006]

As described above, the technology that satisfies both the improvement of the load characteristics and the cycle charge / discharge characteristics and the increase of the discharge capacity as described above has not been sufficiently established at present. Therefore, the object of the present invention has been made in view of the above circumstances. That is, it has excellent filling properties, high capacity,
Another object of the present invention is to provide a positive electrode active material having excellent load characteristics and cycle charge / discharge characteristics and a method for producing the same.

[0007]

Means for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the present inventor has found that the positive electrode active material has a hexagonal columnar shape and the particle shape and the particle size are optimized. The inventors have found that the above problems can be improved, and completed the present invention.

That is, the object of the present invention is to:
This can be achieved by the configuration of (6).

(1) The particle shape is a hexagonal column, and 0.5 ≦ (2c) / (a + b) ≦ 1 (wherein a is the average major axis diameter of the bottom surface, b is the average minor axis diameter of the bottom surface, c is the average particle height.) is a positive electrode active material for a lithium ion secondary battery.

(2) The positive electrode active material for a lithium ion secondary battery according to (1) above, wherein 0.5 ≦ b / a ≦ 1.

(3) The lithium ion ion according to the above (1) or (2), wherein the average major axis diameter of the bottom surface, the average minor axis diameter of the bottom surface, and the average particle height are 1 to 20 μm. Positive electrode active material for secondary batteries.

(4) The positive electrode active material for a lithium ion secondary battery according to any one of (1) to (3) above, which has a tap density of 2.2 g / cm ³ or more.

(5) For the lithium ion secondary battery according to any one of (1) to (4), wherein the raw material mixture is fired in an atmosphere having an oxygen concentration of 0.5 to 5% by volume. Method for producing positive electrode active material.

(6) The lithium ion secondary battery according to any one of (1) to (4) above, wherein the raw material mixture is fired at 700 ° C. or lower, and the firing and crushing steps are performed twice or more. A method for producing a positive electrode active material for a battery.

That is, in the present invention, the particle shape of the positive electrode active material is standardized. In the above (1), a scanning electron microscope (SE
According to M), the positive electrode active material particles are observed. As shown in FIG. 2 (a), regarding the contour corresponding to the bottom surface of the particle, the smallest interval when sandwiched by two parallel lines in contact with the contour is defined as the minor axis diameter of the bottom surface, and then perpendicular to the minor axis diameter. The distance measured in this direction is defined as the major axis diameter of the bottom surface. Further, the particle diameter corresponding to the thickness of the particle in the direction perpendicular to the bottom surface of the particle is defined as the particle height. Particles at a predetermined number of points were measured in the same manner, and the average value was calculated to obtain the average major axis diameter of the bottom surface (a), the average minor axis diameter of the bottom surface (b), and the average particle height (c), and (2c) / ( Calculate a + b).

As described in (1) above, the particle shape is a hexagonal column shape, and (2c) / (a + b) is standardized to 0.5 to 1, whereby the packing property is excellent, the capacity is high, and the load characteristics are high. A positive electrode active material having excellent cycle characteristics can be obtained.

In the above (2), the b / a is standardized to 0.5 to 1 so that the particles have uniform particle properties and excellent crystallinity, whereby the discharge capacity and the cycle charge / discharge characteristics can be further improved. .

In the above (3), the average major axis diameter of the bottom surface, the average minor axis diameter of the bottom surface, and the average particle height obtained by the above-described method are standardized to 1 to 20 μm to obtain sufficiently grain-grown particles. Thereby, the discharge capacity and the cycle charge / discharge characteristics can be further improved.

Further, in the above (4), A. B. D Tap density is measured using a powder measuring instrument. 100c with positive electrode active material powder passed through a sieve and a funnel-shaped joint attached
c Put in a stainless steel container, drop tap 200 times, scrape off the positive electrode active material powder, measure the powder weight of 100 cc, and obtain the density. As described in (4) above, by standardizing the tap density to 2.2 g / cm ³ or more and making the powder excellent in filling property, it is possible to further increase the discharge capacity.

In the present invention, the raw material mixture is fired in an atmosphere having an oxygen concentration of 0.5 to 5% by volume as described in (5) above, or the raw material mixture is prepared as described in (6) above. The positive electrode active material described in (1) to (4) above can be produced by a method of firing at 700 ° C. or lower and performing the firing and pulverization steps twice or more.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the positive electrode active material for a lithium ion secondary battery of the present invention will be described in detail. The positive electrode active material of the present invention has the general formula LiMO ₂ (M is Co, Ni, Fe,
At least one of Mn and Cr) and has a hexagonal crystal structure. A composition in which a part of the constituent elements is replaced with another element may be used.

In particular, the positive electrode active material of the present invention has a hexagonal columnar particle shape as shown in FIG. 2 (a). It may contain a part of irregularly shaped particles with some corners and sides missing. As described above, in the present invention, the particle shape is standardized by the average major axis diameter of the bottom surface (a), the average minor axis diameter of the bottom surface (b), and the average particle height (c), which are geometric particle diameters. The particle shape is observed and evaluated by an image analysis method. For the preparation of the observation sample, a dry sprinkling method, a wet dispersion method, a filter filtration method, or the like can be applied, and attention is paid to overlapping particles, orientation of particles, and dispersion / crushing of aggregates. Next, the particle shape is observed with a scanning electron microscope (SEM). You may take a picture of the particle shape and manually measure the above-mentioned geometric particle diameter.Also, you can perform the binarization processing with image analysis software, separate the particles, and measure the geometric particle diameter. I don't mind.

The load characteristics of the test battery prepared in the example,
The relationship between the cycle charge / discharge characteristics and 2c / (a + b) of the positive electrode active material is shown in FIG. 2c / (a + b) is 0.5 to 1
It can be seen that excellent load characteristics and cycle charge / discharge characteristics can be obtained at. It is considered that the grain shape reflects the hexagonal crystal structure, and the height direction of the grain corresponds to the c-axis direction of the hexagonal crystal structure, and the in-plane direction of the bottom surface is a, b of the crystal structure.
It is considered to correspond to the axial direction. When the hexagonal columnar particles of the present invention are used as a positive electrode plate, it is considered that there are many particles whose bottom surface in-plane direction faces the surface of the electrode plate as shown in FIG. 2 (b). During charge and discharge, Li ions are inserted and desorbed from the a and b axis directions of the crystal structure. Therefore, by filling as shown in FIG. 2B, Li ions are easily inserted and desorbed on the surface of the positive electrode plate, and It is considered that the movement resistance can be reduced. Therefore, as shown in FIG. 3, the hexagonal columnar particles of the present invention are excellent in load charge characteristics and cycle charge / discharge characteristics.

Further, when 2c / (a + b) is 0.5 to 1, it can be seen that the particles have a high tap density and excellent filling properties as shown in FIG. The positive electrode active material is mixed with a conductive agent and a binder, coated on a current collector, dried, and pressed to form a positive electrode plate. It can be seen that when the positive electrode active material has a high tap density, a positive electrode plate having a high electrode plate density can be obtained as shown in FIG. 5 when pressed at a predetermined pressure. For this reason, it is possible to obtain a predetermined electrode plate density even with a weak pressure, and it is possible to minimize damage to crystals and particles due to pressing. This makes it possible to achieve an excellent discharge capacity when used as a battery. As shown in FIG. 5, the tap density is preferably 2.2 g / cm ³ or more. At this time, the filling property is excellent, a particularly high electrode plate density is obtained, and an excellent initial discharge capacity is obtained in a battery.

When 2c / (a + b) is less than 0.5, the particles have a plate shape as shown in FIG. 1 (a). As described above, when the plate-like particles become the positive electrode plate, they are filled as shown in FIG. It is considered that since the particles come into contact with each other in the a-axis direction and the b-axis direction, it becomes difficult to insert and release Li ions, and the migration resistance of Li ions at the particle interface increases. As a result, as shown in FIG. 3, the load characteristics and cycle charge / discharge characteristics deteriorate, which is not preferable.

If 2c / (a + b) is greater than 1, then
Grain growth in the grain height direction must be sufficiently performed, and firing must be performed for a long time. In general, coarse particles are formed with grain growth. When the number of coarse particles is large, when the positive electrode plate is formed, irregularities are formed on the surface of the electrode plate. When the surface of the electrode plate is poor in smoothness, insertion and desorption of Li ions on the surface of the electrode plate are unevenly performed, which promotes the generation of dendrites on the surface of the negative electrode. For this reason, when 2c / (a + b) is larger than 1, it contains a large amount of coarse particles and the surface smoothness when used as a positive electrode plate is poor, and as shown in FIG. However, it is not preferable. Further, as shown in FIG. 4, when 2c / (a + b) is larger than 1, the tap density is small because a large amount of coarse particles are contained, and thus the electrode plate density is small and the initial discharge capacity is small.
Not preferable.

The relationship between the initial discharge capacity and cycle charge / discharge characteristics of the test battery and b / a of the positive electrode active material is shown in FIG. b
/ A is preferably 0.5 to 1, at which time excellent initial discharge capacity and cycle charge / discharge characteristics can be realized. b / a is 0.
When it is 5 or more, the particle properties are adjusted and the particles have excellent crystallinity. Therefore, the initial discharge capacity is large, and the crystals are less likely to collapse even after repeated charge / discharge, and excellent cycle charge / discharge characteristics can be realized.

The characteristics of the positive electrode active material obtained in this example are shown in Tables 1 and 2. The average major axis diameter of the bottom surface, the average minor axis diameter of the bottom surface, and the average particle height are preferably 1 to 20 μm, and at this time, the tap density is high and the filling property is excellent, and the initial discharge capacity, load characteristics, and cycle charge / discharge are excellent. It can be seen that the characteristics can be obtained.

[0029]

[Table 1]

[0030]

[Table 2]

When either the average major axis diameter of the bottom surface, the average minor axis diameter of the bottom surface, or the average particle height is smaller than 1 μm,
Grain growth is not sufficient and the grain height (c) is particularly small. As a result, the particles become plate-like particles, the filling property is poor, and the initial discharge capacity, load characteristics, and cycle charge / discharge characteristics are poor, which is not preferable. When either the average major axis diameter of the bottom surface, the average minor axis diameter of the bottom surface, or the average particle height is greater than 20 μm,
It contains a large amount of coarse particles generated with grain growth,
As described above, the initial discharge capacity is lowered and the surface of the electrode plate when used as a positive electrode plate is poor in smoothness, and in particular, load characteristics and cycle charge / discharge characteristics are deteriorated, which is not preferable.

Table 3 shows the characteristics of the spherical particles produced in this example. Compared with the hexagonal columnar particles of the present invention in Table 1, the spherical particles have a small tap density and poor packing properties. It is necessary to press with a strong pressure when forming the positive electrode plate, which shows that the initial discharge capacity is small. Therefore, a spherical positive electrode active material cannot realize a lithium ion secondary battery having high capacity and excellent cycle charge / discharge characteristics and load characteristics.

[0033]

[Table 3]

Next, a method for producing the lithium-transition metal composite oxide powder, which is the positive electrode active material of the present invention, will be described.

(Production of Raw Material Mixture) The raw material mixture is selected according to the elements constituting the desired composition. A lithium compound, a compound of at least one metal element represented by Co, Ni, Fe, Mn, and Cr, and in the case of substituting with another element, a compound of a substituting element is used as a raw material.

The lithium compound used as a raw material in the present invention is not particularly limited, but for example, Li ₂ CO ₃ or Li
OH, LiOH · H ₂ O, Li ₂ O, LiCl, LiN
O ₃ , Li ₂ SO ₄ , LiHCO ₃ , Li (CH ₃ CO
O) or the like is used.

As the compound of at least one metal element represented by Co, Ni, Fe, Mn, and Cr and the compound of the substitution element, a compound which becomes a composite oxide containing the target metal element by firing, For example, hydroxides, nitrates, carbonates, chloride salts and the like can be used. When a plurality of metal elements are used here, the metal compound as a raw material may be a mixture of compounds of each metal element or a compound containing a plurality of metal elements such as a coprecipitate.

Further, a boron compound, a phosphorus compound or a sulfur compound which is generally used as a flux may be added to a raw material compound and used. B ₂ as a boron compound
O ₃ , H ₃ BO ₃ can be used. Phosphoric acid can be used as the phosphorus compound. As the sulfur compound, Li ₂ S
O ₄ , MnSO ₄ , (NH ₄ ) ₂ SO ₄ , Al ₂ (SO
₄ ) ₃ , MgSO _{4 and the} like are preferably used. In addition, a compound containing a halogen element can be used to improve the particle properties. NH ₄ as a compound containing a halogen element
F, NH ₄ Cl, NH ₄ Br, NH ₄ I, LiF, Li
Cl, LiBr, LiI, MnF ₂ , MnCl ₂ , Mn
Br ₂ , MnI ₂ or the like can be used.

The above compounds are mixed so that the constituent elements have a predetermined composition ratio. At this time, the powdery compound may be mixed as it is, or may be mixed as a slurry by using water or an organic solvent. The slurry-like mixture is dried to obtain a raw material mixture.

(Firing and Grinding of Raw Material Mixture) Next, the raw material mixture obtained by the above method is fired. Two types of methods can be applied here. One has an oxygen concentration of 0.5 to 5% by volume.
It is a method of firing in the atmosphere. Oxygen concentration of 0.5
An inert gas such as N ₂ or Ar gas may be introduced into the furnace in order to adjust the content to ˜5% by volume, or a mixed gas of O ₂ gas and an inert gas adjusted to a predetermined oxygen concentration in advance may be used. You can use it. The firing temperature is not particularly limited and can be appropriately determined depending on the composition, characteristics, intended use, etc. of the positive electrode active material to be produced. Further, it may be crushed after firing.

Another method is to bake below 700 ° C.,
Moreover, it is a method in which the steps of firing and crushing are performed twice or more. The firing atmosphere is not particularly limited as long as oxygen is supplied, and the atmosphere or an oxidizing gas such as O ₂ gas, N ₂ , Ar
An inert gas such as gas may be used. After firing under the conditions described above, a raft mortar, ball mill, vibration mill,
Grind with a jet mill. By performing the above-mentioned firing and crushing steps twice or more, particles having excellent crystallinity and a regular particle shape can be obtained.

At least one of the above two methods
It is considered that crystal growth in the a- and b-axis directions of the hexagonal crystal structure of the lithium-transition metal composite oxide can be suppressed by the production according to the method of the present invention. Hexagonal columnar particles can be generated.

[0043]

EXAMPLES Examples of the present invention will be described below.
The present invention is not limited to the specific examples. [Example 1] Lithium carbonate (L
i ₂ CO ₃ ) and tricobalt tetroxide (Co ₃ O ₄ ) as Li
The raw material mixture was prepared by weighing so as to have a composition ratio of CoO ₂ and dry-mixing. While flowing a N ₂ / O ₂ mixed gas having an oxygen concentration of 3% by volume into the furnace, the raw material mixture was mixed with 900
It was baked at 10 ° C for 10 hours. After firing, the mixture was crushed with a raikai machine and passed through a # 200 sieve to obtain the hexagonal columnar Li of the present invention.
CoO ₂ powder was prepared.

Example 2 A raw material mixture was prepared in the same manner as in Example 1. The raw material mixture was fired in the air at 670 ° C. for 5 hours. After firing, it was crushed with a raikai machine. The firing and crushing steps were performed 5 times. Through a # 200 sieve,
A hexagonal columnar LiCoO ₂ powder of the present invention was produced.

[Examples 3 to 10] N ₂ flowing into the furnace
Various hexagonal columnar LiCoO ₂ powders were produced in the same manner as in Example 1 or 2 except that the oxygen concentration of the / O ₂ mixed gas, the firing temperature, and the number of firing and crushing steps were set to predetermined values.
In the case that the flow of _N 2 / _{O 2} gas mixture in the furnace, the oxygen concentration was 0.5 to 5% by volume. When firing in air, the firing temperature was 700 ° C. or lower, and the firing and crushing steps were performed twice or more.

[Comparative Example 1] N ₂ having an oxygen concentration of 20% by volume
While flowing the / O ₂ mixed gas into the furnace,
L was prepared in the same manner as in Example 1 except that firing was performed at 00 ° C. for 6 hours.
An iCoO ₂ powder was prepared.

[Comparative Example 2] A raw material mixture was placed in the atmosphere at 800 ° C.
Li in the same manner as in Example 2 except that firing is performed for 2.5 hours.
CoO ₂ powder was prepared.

[Comparative Examples 3 to 8] N flowing into the furnace_Two/
O_TwoOxygen concentration of mixed gas, firing temperature, firing and crushing process
Similar to Comparative Example 1 or 2 except that the number of times is set to a predetermined value.
Various LiCoO _TwoA powder was made. The acid in the furnace
Elemental concentration is higher than 5% by volume and firing temperature is 700 ° C
Went higher than.

[Comparative Examples 9 to 12] Comparative Examples 3 to 8 were carried out in the same manner as Comparative Examples 3 to 8 except that monodisperse tricobalt tetroxide (Co ₃ O ₄ ) powder having secondary particles of substantially spherical shape was used as a raw material.
Various spherical LiCoO ₂ powders were made.

The particle shape and tap density of the obtained LiCoO ₂ powder were measured by the following methods. A test battery was prepared and each evaluation was performed. (Evaluation of particle shape) The particle shape was observed with a scanning electron microscope (SEM). The particle shape was evaluated using the image processing software attached to the SEM device. Select the particles to be measured, and from the particle outline corresponding to the bottom of the hexagon,
The minor axis diameter and the major axis diameter were measured. As described above, the minor axis diameter is defined as the smallest interval when sandwiched by two parallel lines in contact with the contour of FIG. 2 (a), and the interval measured in the direction perpendicular to the minor axis diameter is the major axis of the bottom surface. Specified as the diameter. Next, the particle diameter in the direction perpendicular to the bottom surface of the particle was measured as the particle height. Particle 100
Individually selected, the minor axis diameter, major axis diameter, and particle height were measured. The average values of the measured minor axis diameter, major axis diameter, and particle height were determined, and they were defined as the average major axis diameter of the bottom surface (a), the average minor axis diameter of the bottom surface (b), and the average particle height (c). Then (2c) /
(A + b) and b / a were calculated. The minor axis diameter and major axis diameter of the spherical particles obtained in Comparative Examples 9 to 12 were also measured using image processing software.

(Measurement of Tap Density) The measurement of tap density is performed by B. D powder measuring device (manufactured by Tsutsui Rikagakuki Co., Ltd.,
A. B. D-72 type). Pass the LiCoO ₂ powder through a sieve and attach a funnel-shaped joint 1
It was put in a 00cc stainless steel container. Stroke 19m
m, tapped once per second and dropped 200 times. The positive electrode active material powder was ground and the weight of 100 cc of LiCoO ₂ powder was measured to determine the density, which was defined as the tap density.

(Production of Positive Electrode Plate) LiC as a positive electrode active material
90 parts by weight of oO ₂ powder, 5 parts by weight of carbon powder as a conductive agent, and a solution of normal methylpyrrolidone containing 5 parts by weight of polyvinylidene fluoride were kneaded to prepare a paste, which was applied to a positive electrode current collector. Then, it was dried to obtain a positive electrode plate.

(Measurement of Density of Electrode Plate) The positive electrode plate was pressed twice with a roll press machine at a pressure of 1 ton / cm ² . The obtained positive electrode plate was cut into a size of 5 cm ² , and the electrode plate weight and the electrode plate thickness were measured. Then, the density of the coated surface of the positive electrode plate after pressing was calculated and used as the electrode plate density. Next, the positive electrode plate was further pressed to a predetermined thickness to prepare a positive electrode plate for a test battery.

(Preparation of test lithium-ion secondary battery)
The sheet-shaped positive electrode plate, negative electrode plate, and separator were wound and housed in a metal cylindrical battery case to produce a cylindrical lithium ion secondary battery. A carbon material was used as the negative electrode active material, a porous propylene film was used as the separator, and a solution prepared by dissolving LiPF ₆ at a concentration of 1 mol / l in a mixed solvent of ethylene carbonate: diethyl carbonate = 1: 1 (volume ratio) was used as an electrolytic solution. Using.

(Measurement of Initial Discharge Capacity) The test battery was subjected to aging charge / discharge under predetermined conditions. Next, at 25 ° C, the current was 1.
Constant current constant voltage charging up to 4.2V at 6A, current 1.6A
Discharged to 2.75V. The discharge capacity obtained at this time was defined as the initial discharge capacity.

(Measurement of load characteristics) Current of 1.6 at 25 ° C.
A was charged at a constant current and a constant voltage up to 4.2 V, and then discharged at a current of 3.2 A to 2.75 V. The discharge capacity obtained at this time was defined as the load characteristic.

(Measurement of Cycle Charge / Discharge Characteristics) The test battery was charged at a constant current of 1.6 A at a constant current of 1.6 A at 25 ° C. and then discharged at a constant current of 1.6 A to 2.75 V for 300 cycles. Then, the capacity retention rate (%) at the 300th cycle was calculated from the following formula (I).

[0058]

[Equation 1]

[0059]

As described above, the hexagonal column-shaped positive electrode active material powder of the present invention has excellent filling properties, high discharge capacity, and excellent cycle charge / discharge characteristics and load characteristics. As a result, a lithium-ion secondary battery with a high discharge capacity, which could not be achieved in the past, can be put to practical use and can be applied to various fields. The positive electrode active material powder having the excellent battery characteristics can be easily provided by the manufacturing method of the present invention.

[Brief description of drawings]

FIG. 1A is a schematic view showing plate-shaped positive electrode active material particles. (B) A schematic view showing a state in which plate-shaped positive electrode active material particles are filled.

FIG. 2 (a) is a schematic view showing hexagonal columnar positive electrode active material particles of the present invention. (B) A schematic view showing a state in which the hexagonal columnar positive electrode active material particles of the present invention are filled.

FIG. 3 shows load characteristics, cycle charge / discharge characteristics and 2c / (a +
The figure which shows the relationship with b).

FIG. 4 is a diagram showing a relationship between tap density and 2c / (a + b).

FIG. 5 is a diagram showing a relationship between electrode plate density, initial discharge capacity and tap density.

FIG. 6 is a diagram showing a relationship between initial discharge capacity, cycle charge / discharge characteristics, and b / a.

Claims (6)

[Claims] 1. The particle shape is hexagonal columnar, and 0.5 ≦
(2c) / (a + b) ≦ 1 (wherein a is the average major axis diameter of the bottom surface, b is the average minor axis diameter of the bottom surface, and c is the average particle height). Positive electrode active material for secondary batteries. 2. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein 0.5 ≦ b / a ≦ 1. 3. The positive electrode for a lithium ion secondary battery according to claim 1, wherein the average major axis diameter of the bottom surface, the average minor axis diameter of the bottom surface, and the average particle height are 1 to 20 μm. Active material. 4. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the tap density is 2.2 g / cm ³ or more. 5. The raw material mixture is fired in an atmosphere having an oxygen concentration of 0.5 to 5% by volume.
5. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of 1. 6. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the raw material mixture is fired at 700 ° C. or lower, and the steps of firing and crushing are performed twice or more. Method of manufacturing substance.