JP2001155728A - Positive electrode active material for use in non-aqueous lithium secondary battery and method of fabricating it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material for a non-aqueous lithium secondary battery that has high output discharge characteristics and stable cycle characteristics with long life and with compact size. SOLUTION: A lithium secondary battery comprises a positive electrode coated with a lithium and manganese complex compound of spinel structure as the active material. The lithium and manganese complex compound consists of primary particles, and secondary particles obtained by condensing the primary particles. The active material applied to the positive electrode as the electricity collector has a density of 2.5 g/cm3 or more after formed under pressure. The primary particles are in a size range of 1-20 μm with the maximum to minimum particle size ratio equal to or greater than 3.0.

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 using a lithium manganese composite oxide having a spinel structure as a positive electrode active material, and a method for producing the same. The present invention relates to improvement of characteristics and cycle stability and miniaturization of a secondary battery.

[0002]

2. Description of the Related Art In recent years, global warming due to fossil fuel dependence,
Environmental problems such as air pollution caused by exhaust gas CO ₂ and NO _X 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. For this reason, studies are underway to improve energy use efficiency and shift to a society where the dependence on oil is reduced. For example, in the case of automobiles, various hybrid automobiles using both 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. As a power source, a highly efficient fuel cell has been developed, and its practical use as a home power source or a power source for an electric vehicle is being studied. For energy storage of these hybrid vehicles, lithium secondary batteries having a higher battery voltage and higher energy density than other secondary batteries are suitable and are being actively developed. In particular, a high output density is required for energy storage of a hybrid vehicle, and high output 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 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. The positive electrode active material is LiCoO ₂ , LiNiO ₂ ,
Powders composed of an oxide of lithium and a transition metal, such as LiMn ₂ O ₄ , are mainly used. For example, Japanese Patent Application Laid-Open No. H8-17471 discloses the production method in detail. The synthesis of these positive electrode active materials is generally performed by mixing lithium salt powder (LiOH, Li ₂ CO _3, etc.) and a transition metal oxide (MnO ₂ , C
(oO, NiO, etc.) A method of mixing and firing powders is widely used. When the positive electrode active material is applied to the current collector, a carbon powder of several to several tens% by weight is mixed with the positive electrode material, and further,
After kneading with a binder such as PVdF (polyvinyl fluoride) and PTFE (polytetrafluoroethylene), it is kneaded into a paste and applied to a current collector foil with a thickness of about 20 to 100 μm, followed by drying and pressing. A positive electrode is manufactured.

Generally, the positive electrode active material has an electric conductivity.
10 ^-1 to 10 ^-6 S / cm ² , lower than ordinary conductors. The electric conductivity and the electrical contact state between the Al current collector and the positive electrode active material greatly affect the cycle characteristics and discharge rate characteristics of the battery. For this reason, a conductive auxiliary material such as carbon powder having better electrical conductivity than the positive electrode active material is used so as to further increase the electrical 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 positive electrode active material composed of a lithium manganese composite oxide 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. ing. Normal,
The particle morphology had various sizes and shapes, and the secondary particle diameter also varied from about 0.1 μm to 100 μm due to the variation of the aggregation method, and the distribution was 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.

For example, Japanese Patent Application Laid-Open No. Hei 10-32227 proposes that the specific surface area of the positive electrode active material, the average particle size of the primary and secondary particles, and the porosity are controlled within predetermined ranges to suppress a decrease in capacity. I have. In addition, Japanese Patent Application Laid-Open
Japanese Patent No. 261415 proposes that the cycle density is improved by controlling the tap density before molding the positive electrode and the electrode density after molding in the respective predetermined ranges.
Also, according to Japanese Patent Application Laid-Open No. H11-149926, it is proposed that the particle shape be octahedral, and the size and specific surface area of the particle be defined to increase the charge / discharge capacity.

[0006]

[0007] Normally, the lithium salt powder (LiOH, Li ₂ CO _3, etc.) a transition metal oxide (MnO2, CoO,
The cathode active material synthesized by mixing and baking powders (NiO, etc.) has a wide range of particle sizes from several microns to several hundred microns. When the electric conductivity between the positive electrode active materials or between the active materials is poor and the discharge current is increased, the discharge capacity falls due to the internal resistance. For this reason, the positive electrode active material is crushed to control the particle size and specific surface area. According to this method, the capacity per weight when the discharge current is increased is improved, but the electrode density is reduced. As a result, the capacity per volume, that is, the volumetric efficiency is reduced. On the other hand, weight efficiency (Wh / K
g) and volumetric efficiency (Wh / l) for miniaturization.
At this point, if the electrode density is low as described above, improvement in volume efficiency cannot be expected, and thus there is a problem in downsizing. still,
Even in the above-mentioned known technology, no consideration for weight reduction and size reduction is disclosed at all, and improvement in this respect has been demanded.

Accordingly, the present invention provides a positive electrode active material for a non-aqueous lithium secondary battery having high output discharge characteristics and cycle stability and high electrode density, and in particular, improves volumetric efficiency and enables downsizing. It is an object of the present invention to provide a positive electrode active material for a non-aqueous lithium secondary battery and a method for producing the same.

[0008]

According to the present invention, a lithium manganese composite oxide is used as a positive electrode active material, and the particle size distribution and volume frequency of the particles after applying to a current collector and pressing are controlled to a required range. By doing so, it was found that good cycle characteristics, discharge rate characteristics and positive electrode density were improved to improve the volumetric efficiency as a battery, leading to the present invention.
That is, the present invention relates to a lithium secondary battery provided with a positive electrode obtained by applying and forming a lithium manganese composite oxide having a spinel structure as a positive electrode active material, wherein the lithium manganese composite oxide has primary particles and secondary particles in which primary particles are aggregated. And a positive electrode density of 2.5 g / cm ³ or more after the positive electrode active material is applied to a current collector and pressed and formed, and the particle size distribution of the primary particles is 1 to 3. 20 μm
And the (maximum particle size / minimum particle size) ≧ 3.0 is a positive electrode active material for a non-aqueous lithium battery. The ratio of (maximum particle size / minimum particle size) is 3.0 or more, but preferably 3.0 to 10. Further, in the particle size distribution of the primary particles, it is desirable that the volume frequency of particles having a particle size between 3 μm and 5 μm is 50% or more. More preferably, the volume frequency of 3 μm to 5 μm is 60% or more.

Even when the positive electrode active material is pulverized to control the particle size and specific surface area to be substantially constant as in the above-mentioned conventional example, as shown in FIG. 8, the width of the particle size distribution is narrow and the particle size is small. Was to concentrate on In the case of the particle form in which the small particle size region shows a steep distribution as described above, repulsive static electricity acts between the small particles, so that the particles repel each other and do not become dense, but a sparse portion is generated. As a result, the particles became bulky and the electrode density could not be increased. Therefore, in the present invention, the range of the particle size distribution and the ratio of the particle size are regulated together with the electrode density, and further, an appropriate particle size distribution and the volume frequency of the particles are specified. That is, large particles and small particles are mixed in a certain particle size range. In this case, gravity is more closely approached than large repulsion static electricity between large particles and small particles, so that bulkiness is loosened. At the same time, small particles are interposed between the large particles and the large particles can be densely filled by filling the space between the particles.

In other words, the particle size distribution of the primary particles is in the range of 1 to 20 μm in the particle size distribution of the primary particles, and (maximum particle size / minimum particle size) ≧ 3.0. The electrode density can be increased to 2.5 g / cm ³ or more by the ratio of the particles having a size of ５5 μm to the entire volume being 50% or more. The electrode density is 2.5g /
When it is not less than cm ^3, the electrical contact state between the positive electrode active material, the conductive additive and the Al current collector becomes good, and the cycle stability and discharge rate characteristics are further improved. Here, the electrode density is more preferably 2.6 g / cm ³ or more. However, the upper limit is limited by the sintering temperature in production, and about 2.
The limit is about 8 g / cm ³ . Therefore, 2.6-2.
8 g / cm ³ is a practically preferable range.

In the present invention, when the particle diameter is smaller than 1 μm, the electrode density is further reduced, which is not practical. Further, when the state after the application is observed by SEM, the dispersibility of the conductive material and the binder is deteriorated, and the electrode characteristics are deteriorated. on the other hand,
When a large number of particles larger than 20 μm are contained, the electrode density simply increases, but the film applied in a paste state is unfavorable because a uniform coating film cannot be obtained when the film is blurred or uneven, and the electrode characteristics are deteriorated. Further, in the present invention, the paste-form raw material is applied to a current collector with a film thickness of about 200 μm, and then pressed using a press pressure equivalent to 1.5 ton / cm ² to 100 μm.
The coating is finished to a uniform thickness of about m, but the pressing force is not limited to this. As described above, since the electrode density can be controlled to a high value, the volume efficiency can be balanced and the electrode material can be reduced, and the secondary battery itself can be reduced in size.

Next, considering the improvement of the output discharge characteristics, that is, the increase in energy that can be taken out of the battery when the discharge current is increased, the lithium manganese composite oxide having a spinel structure has a disadvantage in that the crystal during discharge is reduced. It is necessary to efficiently insert lithium ions. It is necessary to synthesize a lithium manganese composite oxide with high crystallinity, that is, a spinel-type structure with few distortions and lattice defects, because lithium ions are inserted into and desorbed from the crystal during charge / discharge by diffusing inside the crystal. There is. However, the spinel-type lithium manganese composite oxide obtained by ordinary means is synthesized at a low firing temperature of 1000 ° C. or less, and after firing, in order to control the particle size in a pulverizing step,
The particles lacked spherical corners or contained many lattice strains and lattice defects, so that lithium ions could not be efficiently desorbed and inserted.

Therefore, the lithium manganese composite oxide powder of the present invention is composed of primary particles and secondary particles obtained by aggregating the primary particles. It has a substantially octahedral-like (hereinafter sometimes simply referred to as octahedron or octahedral particles) with a high (111) plane grown. It is desirable that at least 3% or more of the area ratio be composed of octahedral particles or particles that were octahedral even after being applied to the current collector and press-molded. Those that satisfy the conditions such as above are most desirable. It was found that the discharge characteristics were particularly excellent when the primary particles of the lithium manganese composite oxide of the present invention were made substantially octahedral. The reason for this is that the octahedron is formed by growing the (111) plane of the crystal and has high crystallinity so that the crystal structure is difficult to be destroyed. It is believed that this is because the function of inserting and removing lithium by charging and discharging is increased due to the good contact of the metal.

A general oxide active material particle is composed of a primary particle that reflects the crystal form of the active material and a particle that aggregates (for example, forms aggregated by electrostatic force or mechanical contact) or It is composed of secondary particles formed by sintering (for example, in a form of crystal connection and growth). In the present invention, the aggregated form, the sintered form, and the like are collectively referred to as “aggregation”. The positive electrode active material is composed of primary particles and secondary particles in which the primary particles are aggregated, and it is desirable that these primary particles have a substantially octahedral shape. It is sufficient that the octahedral particles can be confirmed to have a substantially octahedral shape. For example, even if the vertices or sides are missing, they are included in the shape and are called octahedral-like. Also, in reality, spherical, hexahedral or irregular shaped particles may be included. Further, after application molding, it may not be possible to clearly confirm that it is an octahedron by applying pressure, but it is sufficient if the trace remains in a part. Then, the particle size and the particle size distribution of the positive electrode active material may be in a range of the particle size that satisfies the above conditions after coating and molding.

Next, the positive electrode active material of the present invention is characterized in that secondary particles are easily aggregated. Even if the secondary particles are not pulverized, the primary particles are substantially octahedral primary by the pressure during coating and molding. The primary particles are dispersed so that the particles are loosened and peeled off, and the secondary particles are almost invisible. If the number of octahedral particles per unit area at this time is 3% or less, the above-mentioned effect is small. Therefore, it is preferable that at least 3% or more, and preferably 60% or more, be octahedral particles. Here, regarding the occupancy of octahedral particles, a SEM photograph was taken with a scanning electron microscope manufactured by Hitachi, Ltd., and the number of octahedral particles per unit area in a typical visual field was counted. The ratio was calculated by using The particle size distribution was also obtained by measuring the horizontal length of each particle on a SEM photograph in a representative field of view of the electrode surface, and the volume frequency was calculated from the particle diameter obtained by measuring the volume of each particle. It is converted into the volume of a sphere, and the ratio to the total volume is calculated as a percentage.

Next, a method for producing the positive electrode active material for a non-aqueous lithium secondary battery of the present invention will be described. The important manufacturing processes to control the particle size and particle size distribution in the manufacturing process are:
That is, proper firing was performed. This calcination is also an important step for obtaining octahedral particles. By performing an appropriate heat treatment, the growth of octahedral shaped particles can be promoted, the particle size can be controlled, and the positive electrode density can be increased. That is, the present invention relates to a method for producing a positive electrode active material for a non-aqueous lithium secondary battery comprising a lithium manganese composite oxide having a spinel structure, wherein the calcination of the positive electrode active material is carried out at 1,000 ° C. or more and 1100 ° C. in an air atmosphere. After performing the first baking at the following temperature, the second baking is performed again at a temperature of 600 ° C. ± 100 ° C.
This is a method for producing a positive electrode active material for a non-aqueous lithium secondary battery, which comprises a step of baking.

When the sintering temperature is 600 to 700 ° C., octahedral crystals cannot be confirmed in the primary particles, and the electrode characteristics are poor. Primary particles of the octahedron can be confirmed when the sintering temperature is 800 ° C or higher. When the sintering temperature is increased, the ratio of the octahedron in the primary particles and the particle size increase, but at 1100 ° C or higher, the melting of the crystal starts. The characteristics as a positive electrode active material are reduced.
On the other hand, if the temperature is lower than 1000 ° C., the target particle diameter does not easily grow and the electrode density does not increase. As shown in FIG.
It can be seen that an electrode density of 2.6 g / cm @ 3 can be achieved around 30 DEG C. From the above, the firing temperature is selected from the range of 1000 ° C. or more and 1100 ° C. or less in the atmosphere in the air, and is desirably 1030 to 1080 ° C. More preferably, the temperature is 1050 ° C. The firing time is preferably one hour or more, more preferably four hours or more.

Here, the material which has been subjected to the first baking at 900 ° C. or higher to grow primary particles and form a substantially octahedron needs to be oxidized because the material is reduced and the electrode characteristics are remarkably deteriorated. is there. When reduced during firing, the lattice constant increases. Therefore, it is effective to reduce the lattice constant by reoxidizing by performing the second firing again after the firing. This firing temperature was set at 600 as shown in FIG.
It has been confirmed that the temperature was ± 100 ° C. From the above, octahedral primary particles are obtained, and in order to further suppress the lattice constant of the primary particles, a first baking step performed at a temperature of 1000 ° C. or more and 1100 ° C. or less,
It is important to include a second baking step performed at 0 ° C.
If the second firing is not performed, Li ₂ MnO ₃ , Mn ₃ O _{4, and the} like are likely to remain. Therefore, the second firing is performed at a temperature equal to or higher than the decomposition temperature of Li ₂ MnO ₃ or Mn ₃ O ₄ at 600 ° C. ± 100 ° C. And In the case where firing is performed at 900 ° C. or higher instead of the second heat treatment, reduction of the active material can be prevented by taking a measure of cooling in an oxygen atmosphere thereafter.

Next, in order to obtain a high electrode density with the octahedral particles occupying an area of 3% or more when coated and formed on the positive electrode, the granulation of the powder before the above-mentioned firing is important. After the first heat treatment is performed, the granulation is performed. That is, after mixing the raw material powder, the octahedron is easier to produce when baked after making granules of about 10 to 200μ using a spray dryer or the like after mixing, rather than simply firing. The growth of the primary particles and the particle size distribution can be easily controlled, and the electrode density can be increased. The spray dryer is a slurry in which an organic substance such as PVA (polyvinyl alcohol) and pure water are added to raw material powder to form a slurry, and the slurry is dropped on a rotating disk at a required speed, and the dropped slurry has a Coriolis force. In this way, the particles are scattered from the disk in the outer diameter direction and substantially spherical particles are obtained in the air by their own surface tension. The particle diameter can be controlled by appropriately selecting the number of revolutions of the disk on which the slurry is dropped, and the higher the speed of rotation, the smaller the particle diameter.

If the particles are dried and fired under the above conditions, the primary particles form an octahedral particle form upon completion of the firing, and the primary particles aggregate to form secondary particles.
At this time, the secondary particles have a form in which primary particles having a substantially constant particle size are gathered and aggregated like a grape cluster. Further, when the raw material powder composed of the secondary particles is crushed, the dispersion of the particles proceeds so that the grape particles are broken from the grape clusters, and the primary particles and the secondary particles are mixed. At this time, the secondary particles are in a state in which aggregation is easily dissolved, so that strong pulverization is not required and damage to the octahedron is small. A positive electrode active material having octahedral particles can be obtained by controlling the above-mentioned firing temperature and powder before firing, and a positive electrode having an appropriate particle size distribution and particle size can be obtained after coating and molding.

In order to improve the discharge characteristics and cycle stability of the positive electrode active material, the composition of the particles is important, as in the case of the above-mentioned particles. In the case of a lithium manganese composite oxide having a spinel structure, the composition is generally 0.5 to 0.6 in Li / Mn ratio, which is the ratio of the number of atoms, but in the present invention, particularly, 0.56 ≦ Li / Mn. ≦ 0.62. Li / M
When the n ratio is 0.56 or less, the cycle characteristics are poor, and the charge / discharge capacity becomes less than 70% of the initial value at 500 cycles, which is not practical. On the other hand, if it exceeds 0.62, the charge / discharge capacity becomes 100 mA.
It is known that it is not practical because it is less than h / g. A more preferred range is 0.57 ≦ Li / Mn ≦ 0.59, and still more preferably Li / Mn = 0.58.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to examples. Note that the present invention is not limited to the embodiments described below.

(Example) FIG. 1 shows a SEM photograph (magnification: × 1000) of the surface of the positive electrode when the positive electrode active material of the present invention was coated and pressed, and FIG. 2 is a schematic diagram thereof. still,
The schematic diagram is schematically shown for easy understanding, and its scale and density are different from actual ones. In addition, the particles are not limited to octahedrons, but also include particles partially missing or irregular shapes. Since the positive electrode active material is crushed by pressure, it is difficult to confirm the octahedral particles, but it can be relatively easily confirmed by increasing the magnification. The positive electrode active material 3 is composed of octahedral-grown primary particles having different sizes and small and large octahedral (deformed) primary particles 1 and an electrode structure (conductive material and binder) 2. FIG. 2 shows an ideal state, but the particle size distribution of the primary particles is in the range of 1 to 20 μm, and the particles are uniformly applied so that the small particles enter between the large particles.

In this embodiment, manganese dioxide and lithium carbonate are used as raw materials, weighed so that the Li / Mn ratio becomes 0.58 in atomic ratio, and wet weighed by a ball mill made of resin.
Mix for hours. The PVA solution was added to the mixed solution in an amount of 1 wt% in terms of solid content, mixed and then granulated by a spray dryer and dried to prepare granules of 10 to 100 μm. Next, for the first firing, the temperature was set at 600 ° C., 700 ° C., respectively.
800 ° C, 900 ° C, 1000 ° C, 1050 ° C, 108
The duration was changed to 10 hours at 0 ° C. and 1100 ° C.

Thereafter, the granules produced by a spray dryer are crushed by a raikai machine so that no morphology remains, and then a second heat treatment calcination is carried out in order to correct octahedral particles damaged or deformed during crushing. This was performed under the same conditions as in the firing of No. 1. It is not always necessary to perform the second firing. Further, in the embodiment in which the firing temperature is 900 to 1100 ° C. in the first firing (first heat treatment), the second firing (second heat treatment) at 600 ° C. for 5 hours in order to oxidize and reduce the lattice constant. ) Was done. FIG. 3 shows these manufacturing steps. When the obtained positive electrode active material raw material powder was observed by SEM according to this example, octahedral crystals were confirmed in the examples in which the first firing temperature was 800 ° C. or higher. Table 1 shows the results of measuring the number ratio of primary particles and the ratio of (maximum particle size / minimum particle size), which can be confirmed to be octahedral from the SEM observation image. Here, the primary particles are S particles by a scanning electron microscope manufactured by Hitachi, Ltd.
An EM photograph was taken and the number of primary particles per unit area in a typical visual field was counted to obtain a ratio.
Also, from the particle size distribution obtained by measuring the horizontal length of each particle on a SEM photograph in a representative visual field of the electrode surface,
The ratio of (maximum particle size / minimum particle size) was calculated using the maximum particle size and the minimum particle size.

[0026]

[Table 1]

In preparing a positive electrode for evaluating the characteristics of the positive electrode active material, the positive electrode active material, the carbon-based conductive material, and the binder of the present embodiment were expressed in terms of% by weight, and were respectively 90: 5.5: 4.5 (wt.
%), And the uniformly mixed slurry is applied to a 15 μm thick aluminum current collector foil, dried at 90 ° C, and pressed at 1.5 ton / cm ² to form a 100 μm coating. did.

FIG. 5 shows the electrode density when the pressing pressure is changed. Each diagram in the figure shows the first firing temperature. It can be seen that the higher the firing temperature, the higher the density even with a lower press pressure. However, in general, when the pressing pressure is increased to ² ton / cm ² or more, the applied cathode material particles are damaged, and the cycle characteristics are deteriorated.
range cm ² is desirable, and more preferably is to press at a pressure of about 1.5 ton / cm ^2. Next, this 1.5ton /
FIG. 6 shows the relationship between the first firing temperature at a pressure of cm ² and the electrode density. From this figure, if the firing temperature is set to 1030 ° C. or higher,
It is understood that an electrode density of 2.6 g / cm ³ or more can be obtained. FIG. 7 shows the relationship between the second firing temperature and the lattice constant. At a firing temperature of about ± 100 ° C., more preferably about ± 50 ° C., centered at about 600 ° C., the lattice constant becomes smaller again and the cycle characteristics recover.

Under the above conditions, the particle size distribution and volume frequency of the primary particles of the positive electrode material of Example 2 are shown in FIG. Thus, the particle size distribution of the particles of this example is in the range of about 1.5 to 8 μm,
The ratio (maximum particle size / minimum particle size) was 6.5. It can be seen that the width of the particle size is wider than that of the conventional one shown in FIG. 8 in which the (maximum particle size / minimum particle size) ratio is 2.6 and the electrode density is low. The volume frequency of the particles having a size of 3 μm to 5 μm was 60% or more. According to the measurement from the SEM photograph, the particles are octahedral particles or deformed octahedral particles are about 85% of the total area.
It was confirmed that it occupied. Examples 1, 3,
The particle size distribution of the primary particles of the positive electrode material of No. 4 is 1 to 20 μm
And the (maximum particle size / minimum particle size) ratio was 3.5, 7, and 18, respectively. In addition, it was confirmed that the volume frequency of the particles of 3 μm to 5 μm was 50% or more.

Next, a carbon-based material is usually used as the negative electrode of the lithium secondary battery. In this example, a test battery was prepared using a lithium metal electrode so that the characteristics of the negative electrode were not taken into consideration in the evaluation results. As the electrolytic solution, a mixed solvent of ethyl carbonate and dimethyl carbonate using 1.2 M LiPF6 as an electrolyte was used. Table The initial discharge capacity when the sample prepared in this example creates the simple cell, and the discharge capacity when discharged at a current density of 2.5 mA / cm ^2, and discharged at a current density of 0.5 mA / cm ² It is shown in FIG.

[0031]

[Table 2]

From the data in Tables 1 and 2, in the positive electrode of the example, primary particles of octahedron were confirmed, and the particle size distribution was appropriately widened, that is, the ratio of (maximum particle size / minimum particle size) was 3.0 or more. When the positive electrode active material is used, the electrode density is increased, and the discharge capacity at 2C where the discharge is performed in a short time (1/6 of the time of the initial capacity measurement) is 90% or more of the initial capacity. It can be seen that the material has a higher discharge capacity as compared with a conventional active material which has been made finer in the pulverization step or has been formed at a firing temperature of about 800 ° C. In addition, it is found that excellent discharge characteristics are obtained when primary particles of an octahedron with high crystallinity (111) planes are included, the electrode density is increased, and the discharge capacity per volume is large.

[0033]

As described above, according to the present invention, the lithium manganese composite oxide is used as the positive electrode active material, the particle size distribution of the primary particles after being applied to the current collector and pressed and molded, and the maximum particle size thereof. By controlling the diameter / minimum particle diameter ratio, the volume frequency, and the like to the required ranges, the discharge capacity characteristics and the cycle stability could be improved while the positive electrode density was improved. Also,
The shape of the primary particles is controlled to be substantially octahedral and its occupancy is regulated.
The i / Mn ratio was defined in a required range. As a result, high output discharge characteristics and high cycle characteristics were obtained, and a long-life positive electrode active material for non-aqueous lithium secondary batteries could be provided. Since the positive electrode density, the discharge capacity characteristic and the cycle stability have been improved, the volume efficiency of the electrode can be increased and the size can be reduced. As a result, a nonaqueous lithium secondary battery having a small size and excellent characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is an example of a scanning electron microscope photograph after the positive electrode active material of the present invention has been formed into a positive electrode material.

FIG. 2 is a schematic diagram of the photograph of FIG.

FIG. 3 is a flowchart showing a manufacturing process according to the embodiment of the present invention.

FIG. 4 is a diagram showing a particle size distribution and a volume frequency of primary particles of a positive electrode material according to an example.

FIG. 5 is a diagram showing a relationship between a pressing pressure and an electrode density at each first firing temperature.

FIG. 6 is a diagram showing a relationship between a first baking temperature and an electrode density at a press pressure of 1.5 ton / cm ² .

FIG. 7 is a diagram showing a relationship between a second firing temperature and a lattice constant.

FIG. 8 is a diagram showing an example of a particle size distribution and a volume frequency of primary particles of a conventional positive electrode material.

FIG. 9 is a schematic view showing an example of a conventional positive electrode active material.

[Explanation of symbols]

1: Primary particles of positive electrode active material 2: Conductive aid

Continued on front page F-term (reference) 5H003 AA02 AA04 BA05 BB05 BC00 BC01 BC06 BD01 BD02 BD03 BD05 5H014 AA01 AA06 BB05 BB08 EE10 HH00 HH06 HH08 5H029 AJ03 AJ05 AK03 AL06 AM03 AM05 AM07 CJ03 HJ14

Claims (6)

[Claims] 1. A lithium secondary battery provided with a positive electrode formed by applying and forming a lithium manganese composite oxide having a spinel structure as a positive electrode active material, wherein the lithium manganese composite oxide is composed of primary particles and secondary particles in which the primary particles are aggregated. And a positive electrode density of 2.5 g / cm ³ or more after applying the positive electrode active material to a current collector and press-molding the same, and a particle size distribution of the primary particles of 1 to 20 μm. And (maximum particle size / minimum particle size) ≧ 3.0, wherein the positive electrode active material for a non-aqueous lithium battery is characterized in that: 2. In the particle size distribution of the primary particles, 3 μm
2. The positive electrode active material for a non-aqueous lithium battery according to claim 1, wherein the volume frequency of particles having a particle size of m to 5 [mu] m is 50% or more. 3. The particles of the lithium manganese composite oxide powder are composed of primary particles and secondary particles in which the primary particles are aggregated, and these primary particles have a substantially octahedral-like particle form. In the current collector after the substance is applied to the current collector and pressed, at least 3% or more of the area ratio is composed of substantially octahedral-like or substantially octahedral-like primary particles. The positive electrode active material for a non-aqueous lithium battery according to claim 1 or 2, wherein: 4. The lithium-manganese composite oxide has an atomic ratio of lithium to manganese of 0.56 ≦ Li / Mn.
The positive electrode active material for a non-aqueous lithium secondary battery according to any one of claims 1 to 3, wherein ≤ 0.62. 5. A method for producing a positive electrode active material for a non-aqueous lithium secondary battery comprising a lithium manganese composite oxide having a spinel structure, wherein a mixture of a manganese oxide and a lithium salt such as lithium carbonate is placed in an air atmosphere. 1000 ° C or higher 1
After performing the first baking at a temperature of 100 ° C. or less,
A method for producing a positive electrode active material for a non-aqueous lithium secondary battery, comprising a step of performing a second baking at a temperature of 0 ° C. ± 100 ° C. 6. A step of granulating a mixture of a manganese oxide and a lithium salt such as lithium carbonate into granules, and subjecting the first baking to growing substantially octahedral primary particles, A step of crushing the secondary particles in which the substantially octahedral primary particles are agglomerated to make the secondary particles easier to break. 6. The positive electrode active material for a non-aqueous lithium secondary battery according to claim 4, The method of manufacturing the substance.