JP5821722B2 - Positive electrode material for lithium ion battery, positive electrode for lithium ion battery and lithium ion battery - Google Patents

Description

  The present invention relates to a positive electrode material for a lithium ion battery, a positive electrode for a lithium ion battery, and a lithium ion battery, and in particular, a positive electrode material for a lithium ion battery suitable for use in an in-vehicle battery excellent in high-speed charge / discharge characteristics, and the like The present invention relates to a positive electrode for a lithium ion battery containing a positive electrode material for a lithium ion battery, and a lithium ion battery including the positive electrode for a lithium ion battery.

In recent years, non-aqueous electrolyte secondary batteries such as lithium ion batteries have been proposed and put into practical use as batteries that are expected to be reduced in size, weight, and capacity.
Among them, lithium ion batteries are characterized by being lighter and smaller and having higher energy than secondary batteries such as conventional lead batteries, nickel cadmium batteries, and nickel metal hydride batteries. Yes.
Lithium transition metal oxides such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , or composite oxides thereof have been put to practical use as electrode active materials used for the positive electrode material of this lithium ion battery, and these are used. The large-capacity lithium-ion battery, which is mounted mainly on mobile devices such as portable information terminals, contributes greatly to reducing the size and weight of the devices.
On the other hand, as new applications of lithium ion batteries, studies are being made on applications for large-scale batteries for power storage and in-vehicle batteries such as EVs, and future development is expected.
However, electrode active materials such as lithium transition metal oxides have a characteristic that oxygen release starts at a temperature of 200 to 300 ° C. when heated in a charged state. Lithium ion batteries use a flammable organic electrolyte as the electrolyte, so when oxygen release begins, there is a risk of the organic electrolyte igniting or exploding. It is not easy to apply to large batteries or in-vehicle batteries from the viewpoint of ensuring safety.

On the other hand, electrode active materials having an olivine structure typified by LiFePO ₄ and LiMnPO ₄ are known as electrode active materials excellent in safety that do not release oxygen even at 350 ° C.
Electrode active materials having these olivine structures have expected properties such as sufficient theoretical capacity and high-speed charge / discharge characteristics in addition to safety, but unlike lithium transition metal oxides, they have poor electronic conductivity. The lithium ion insertion / desorption rate is slow, and it is difficult to obtain a high battery capacity.
Therefore, in order to solve such problems, a technique (Patent Document 1) has been proposed in which an electrode active material is covered with a carbonaceous film generated by thermal decomposition of an organic substance to improve electron conductivity. In addition, a technique has been proposed in which the electrode active material is made into fine particles and a high battery capacity is obtained even when the insertion / desorption rate is slow (Patent Document 2).

By the way, when the electrode active material is made into fine particles, the surface area of the electrode active material fine particles increases. Therefore, when the electrode active material fine particles are bonded onto the current collector to form an electrode active material layer, a large amount of particles are formed. As a result, there is a problem that the amount of electrode active material in the electrode active material layer is reduced or the electron conductivity is hindered by the binder that wraps around between the fine particles. There was a problem that the capacity was reduced. In addition, when the amount of the binder is reduced in order to compensate for these drawbacks, there are problems such as cracking in the molded electrode active material layer and peeling off of the electrode active material layer itself.
In order to solve these problems, a technique has been proposed in which the specific surface area is reduced by using an electrode active material that has been atomized as an aggregate to reduce the amount of binder (Patent Document 3).

In general, as a method for improving the volume density of the aggregate obtained by aggregating the primary particles of the electrode active material, there is a method of widening the particle size distribution of the primary particles. In this case, low electron conductivity or lithium ion If the primary particles are made fine for the purpose of solving the low insertion / release rate, the particle size distribution becomes narrow, resulting in a problem that the volume density of the aggregates decreases.
When considering increasing the capacity of the positive electrode of a lithium ion battery and improving the high-speed charge / discharge characteristics, the electrode active material particles can be reduced by reducing the primary particles of the electrode active material to several hundred nm or less and increasing the specific surface area. It is necessary to sufficiently shorten the distance of movement of electrons and lithium ions that move inside, and to increase the surface of the electrode active material that causes the insertion / extraction reaction of lithium ions. However, in this case, the volume density of the aggregate is significantly reduced, and as a result, the carbonaceous film covering the primary particles of the electrode active material becomes non-uniform, resulting in a decrease in battery capacity. Invite. Accordingly, there has been a demand for further improvement to increase the volume density of the aggregate obtained by agglomerating the primary particles while miniaturizing the primary particles of the electrode active material.

Therefore, by changing the aggregation state of the LiFePO ₄ particles as a positive electrode material having few pores as a positive electrode material made of an aggregate focusing on the particle size of the primary particles of the electrode active material, the electrode active material in the electrode A technique for increasing the density has been proposed (Patent Document 4).
According to this technique, by grinding the LiFePO ₄ lumpy obtained in the primary firing 5μm or less, to obtain a LiFePO ₄ particles with no space formed by the primary particles, such as a resin in this LiFePO ₄ particles A carbon precursor is mixed, granulated to form an aggregate, and the aggregate is subjected to secondary firing to obtain a positive electrode material composed of an aggregate composed of LiFePO ₄ particles and carbon. By using it, high filling of the positive electrode material into the electrode is achieved.

Further, as a positive electrode material in which primary particles of fine electrode active materials having a size of several hundred nm are aggregated, an aggregate composed of a lithium phosphate compound having an olivine structure with a primary particle size of 50 nm or more and 500 nm or less A positive electrode material has been proposed (Patent Document 5).
This agglomerate is obtained by dispersing primary particles of an electrode active material having a carbonaceous film formed on the surface in advance, or primary particles of an electrode active material and a carbon raw material in a solvent, and dispersing the resulting slurry in a high-temperature atmosphere. It is obtained by spraying.
According to this technique, by controlling the pore diameter between primary particles of the electrode active material constituting the aggregate to 0.1 times or more and 0.9 times or less the average particle diameter of the primary particles, The binder is prevented from penetrating between the primary particles to suppress a decrease in electronic conductivity, thereby realizing both high battery capacity and load characteristics.

Furthermore, a technology has been proposed in which a porous lithium oxide microparticle comprising a porous lithium oxide nanoparticle having a carbonaceous film formed and a particle diameter of 100 nm to 500 nm and conductive fibers is used as a positive electrode material (patent) Reference 6).
The porous lithium oxide nanoparticles are formed into a 10-100 nm nanocrystalline porous body via carbon by granulating and firing an electrode active material precursor. By granulating a conductive agent such as a carbon material, porous lithium oxide microparticles having a large specific surface area and high conductivity are obtained. This porous lithium oxide microparticle is suitable for high power applications.
According to this technique, it is possible to aggregate while maintaining the specific surface area of the primary particles of the refined electrode active material.

JP 2001-15111 A Japanese Patent No. 4190912 Japanese Patent No. 3047827 JP 2006-32241 A JP 2009-152188 A JP 2009-158489 A

  By the way, in the technique of patent document 4, since the calcination temperature in primary baking is 700-900 degreeC, the particle growth of an electrode active material particle cannot be suppressed, but the electrode active material after primary baking is used. Primary particles of the electrode active material having a size of μm are included. The primary particles having a size of μm are not only large, but are often solid particles. Therefore, the volume ratio of the primary particles of the electrode active material in the aggregate is increased, and the aggregate is apparently formed. The volume density of becomes higher. When such primary particles of the electrode active material having a size of μm are used as the positive electrode material of the lithium ion battery, the capacity is low and the high-speed charge / discharge characteristics are inferior, and the primary particles of the electrode active material are fine. However, there was a problem that the carbonaceous film could not be made uniform.

In the technique described in Patent Document 5, since the carbonaceous film covering the primary particles of the electrode active material becomes non-uniform, there is a possibility that the electron conductivity of the electrode active material is inferior. Therefore, there is a problem that the bond between the primary particles becomes weak. Moreover, since the contact of each particle is likely to be a point contact, there is a problem that the electron conductivity may be inferior.
In this way, the primary particles of the electrode active material are not bonded in a cervical shape and are likely to be in point contact, so that the binder easily permeates between the primary particles of the electrode active material, and thus the electrons The conductivity improvement is insufficient.

In the technique described in Patent Document 6, since the porous lithium oxide nanoparticles having a low volume density are used, it is inevitable that the volume density of the porous lithium oxide microparticles is reduced. There is a problem that the carbonaceous film that is present may be non-uniform in thickness.
Moreover, since the carbon material is only added to the porous lithium oxide microparticles, the carbon particles are simply adsorbed on the surface of the porous lithium oxide nanoparticles. Therefore, there has been a problem that the film thickness of the carbonaceous film formed on the surface of the primary particles of the electrode active material is not uniform. This non-uniform film thickness of the carbonaceous film cannot sufficiently obtain the electron conductivity and the lithium ion insertion / extraction reaction, which causes a decrease in battery capacity.
As described above, the technique described in Patent Document 6 is effective as a technique for forming secondary particles while keeping the primary particles of the refined electrode active material at a high specific surface area. It cannot be made uniform, the electron conductivity becomes insufficient, and this contributes to a decrease in battery capacity.

  The present invention has been made to solve the above-mentioned problems, and by improving the electron conductivity of the electrode active material, the battery capacity can be improved and the high-speed charge / discharge characteristics are excellent. It aims at providing the positive electrode material for lithium ion batteries, the positive electrode for lithium ion batteries, and a lithium ion battery.

  As a result of intensive studies to solve the above problems, the present inventors have aggregated primary particles of the electrode active material covered with the carbonaceous film and primary particles of the electrode active material 2 The carbonaceous coated secondary particles in which the secondary particles are coated with a carbonaceous coating are mixed to form a mixture. The mixture is further aggregated to form an aggregate. The aggregate further solidifies the aggregate. By containing a porous aggregate having a volume density of 50% by volume or more and 80% by volume or less of the volume density of the case, sufficient electron conductivity and insertion / extraction reaction of lithium ions in the carbonaceous film can be obtained. When the positive electrode material for a lithium ion battery is used for the positive electrode of a lithium ion battery, the internal resistance of the positive electrode is lowered, and as a result, the battery capacity is improved and the present invention has been completed. .

That is, the positive electrode material for a lithium ion battery of the present invention is an aggregate obtained by further aggregating a mixture of primary particles of an electrode active material and secondary particles obtained by agglomerating the primary particles of the electrode active material. The particles and the secondary particles are coated with a carbonaceous film having a uniform film thickness , and the aggregate is 50% by volume or more and 80% by volume or less of the volume density when the aggregate is solid. and also contains a porous agglomerates having a volume density, the electrode active material, Ri phosphate der having an olivine structure, in the porous agglomerate during the primary particles, the secondary Between the particles, the primary particles and the secondary particles are bonded to each other by a cervical joint portion in which a part of the carbonaceous coating is cervical, and a gap between them is lithium. A pore that allows diffusion and penetration of ions is formed. The average particle diameter of primary particles is characterized by at and 0.5μm or less than 0.03 .mu.m.

Before SL aggregates surface is preferably comprising the secondary particles of solid in which formed by agglomerating said primary particles coated by carbonaceous coating.
The number average pore diameter (D50) at 50% of the cumulative pore diameter distribution measured by the mercury intrusion method is preferably 10 nm or more and 300 nm or less.
The average film thickness A of the carbonaceous film at the outer periphery of the aggregate and the average film thickness B of the carbonaceous film at the center of the aggregate are expressed by the following formula (1).
0.7 ≦ B / A ≦ 1.3 (1)
It is preferable to satisfy.

  The positive electrode for a lithium ion battery of the present invention is characterized in that the positive electrode material for a lithium ion battery of the present invention is contained in a positive electrode layer.

  The lithium ion battery of the present invention comprises the positive electrode for a lithium ion battery of the present invention.

  According to the positive electrode material for a lithium ion battery of the present invention, a mixture of primary particles of the electrode active material and secondary particles obtained by aggregating the primary particles of the electrode active material is further aggregated to form aggregates. Since the primary particles and the secondary particles are coated with a carbonaceous film, the insertion / release reaction of lithium ions can be sufficiently obtained by increasing the surface area, and the inside of the primary particles of the electrode active material can be diffused. The movement distance of lithium ions and the movement distance of electrons moving inside the primary particles can be shortened.

  Further, since the aggregate contains a porous aggregate having a volume density of 50 volume% or more and 80 volume% or less of the volume density when the aggregate is solid, the carbonaceous coating film The organic substance decomposition gas generated during the thermal decomposition of the organic substance during the formation of the particles becomes difficult to escape from the aggregate, and the concentration of the organic substance decomposition gas in the vicinity of the surface of the primary particles of the electrode active material can be increased. The film thickness of the carbonaceous film covering the surface of the primary particles of the substance can be made uniform.

  According to the positive electrode for a lithium ion battery of the present invention, since the positive electrode material for a lithium ion battery of the present invention is contained in the positive electrode layer, the internal resistance of the positive electrode can be reduced and the battery capacity can be improved.

  According to the lithium ion battery of the present invention, since the positive electrode for the lithium ion battery of the present invention is provided, the internal resistance of the positive electrode can be reduced, the battery capacity can be improved, and high-speed charge / discharge characteristics can be achieved. It will be excellent.

It is a schematic diagram which shows the porous aggregate contained in the positive electrode material for lithium ion batteries of one Embodiment of this invention. It is a transmission electron microscope (TEM) image which shows the aggregate of Example 1 of this invention. It is a figure which shows the charging / discharging characteristic of Example 1, 3, 5, 8 and Comparative Example 1 of this invention. It is a figure which shows the charging / discharging characteristic of Example 5, 6, 7 of this invention, and Comparative Examples 1 and 3, respectively.

A positive electrode material for a lithium ion battery, a positive electrode for a lithium ion battery, and a form for carrying out the lithium ion battery of the present invention will be described.
This embodiment is specifically described for better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

[Positive electrode material for lithium ion batteries]
The positive electrode material for a lithium ion battery according to this embodiment is an aggregate obtained by further aggregating a mixture of primary particles of an electrode active material and secondary particles obtained by agglomerating the primary particles of the electrode active material. And the secondary particles are coated with a carbonaceous coating, and the aggregate has a porosity of 50% by volume or more and 80% by volume or less of the volume density when the aggregate is solid. It is a positive electrode material containing the aggregate.

FIG. 1 is a schematic view showing a porous aggregate contained in a positive electrode material for a lithium ion battery of the present embodiment. The positive electrode material 1 for a lithium ion battery includes primary particles 2 of an electrode active material, and The mixture with the secondary particles 3 in which the primary particles 2 of the electrode active material are agglomerated is a further agglomerated aggregate, and the primary particles 2 and the secondary particles 3 are covered with a carbonaceous film 4 having a uniform film thickness. Has been.
Between these primary particles 2, between the secondary particles 3, and between the primary particles 2 and the secondary particles 3 are bonded by a cervical connecting portion 5 in which a part of the carbonaceous coating is cervical. At the same time, the gaps between these are pores 6.

And, between these primary particles 2, between secondary particles 3, and between primary particles 2 and secondary particles 3 are joined by cervical joint portion 5, so that the contact portion between these particles is It is a porous agglomerate in a cervical shape with a small cross-sectional area and firmly connected.
As a result, pores 6 capable of diffusing and penetrating lithium ions are formed between these particles, and the carbonaceous coating 4 has a density that does not hinder electronic conduction. In addition, lithium ions can reach the surface of the electrode active material, and lithium ion insertion / release reaction can be efficiently performed. Moreover, since each particle | grain is couple | bonded by the neck-shaped coupling | bond part 5, electronic conduction is easy. Therefore, battery capacity can be improved. Further, by connecting the respective particles by the neck-like connecting portion 5, it is possible to prevent the influence between the particles due to the penetration of the binder and to maintain the electronic conductivity.

The volume density of the porous aggregate can be measured using a mercury porosimeter, and is preferably 50% by volume or more and 80% by volume or less of the volume density when the aggregate is solid, more preferably It is 55 volume% or more and 75 volume% or less. Here, the solid aggregate is an aggregate having no voids at all, and the density of the solid aggregate is equal to the theoretical density of the electrode active material.
The reason why the volume density of the porous aggregate is 50% by volume or more and 80% by volume or less of the volume density when the aggregate is solid is that this range is an organic substance when forming a carbonaceous film. The organic substance decomposition gas generated during the thermal decomposition of is difficult to escape from the aggregate, and the volume density of the porous aggregate is set to 50% by volume or more and 80% by volume or less of the solid volume density. The concentration of the organic substance decomposition gas in the vicinity of the surface of the primary particle 2 of the electrode active material can be increased, and the film thickness of the carbonaceous film covering the surface of the primary particle of the electrode active material can be made uniform.

The aggregate of this embodiment may contain solid secondary particles formed by agglomerating primary particles whose surfaces are coated with a carbonaceous film, in addition to the porous aggregate described above.
Thus, by containing solid secondary particles, the volume density of the whole aggregate can be improved, and the carbonaceous film can be made uniform.
There are voids between the primary particles constituting the solid secondary particles, and these voids are spaces that do not contain anything other than air between the particles, and are the primary particles of the electrode active material. The pores 6 of the carbonaceous film in between are not included.

The average particle diameter of the aggregate of the present embodiment, that is, the aggregate including the porous aggregate and the solid secondary particles is preferably 0.5 μm or more and 100 μm or less, more preferably 1 μm or more and 20 μm. It is as follows.
Here, the reason why the average particle diameter of the aggregate is in the above range is that when the average particle diameter is less than 0.5 μm, the aggregate is too fine to be easily handled, and is handled when preparing an electrode coating paste. On the other hand, if the average particle diameter exceeds 100 μm, there is a high possibility that an aggregate having a size exceeding the thickness of the electrode after drying is present when a battery electrode is produced. Therefore, the uniformity of the electrode film thickness cannot be maintained.

The aggregate of the present embodiment has a number average pore diameter (D50) (hereinafter sometimes referred to simply as “average pore diameter”) at 50% of the cumulative pore diameter distribution measured by the mercury intrusion method of 10 nm or more and 300 nm or less. It is preferable that
Here, if the number average pore diameter (D50) is less than 10 nm, it is not preferable because penetration of the electrolyte solution may be hindered, and if it exceeds 300 nm, the volume density of the aggregate is decreased, which is not preferable.

The agglomerates are mixed with a solvent, a binder, a conductive auxiliary agent, etc. at the time of forming the positive electrode, applied onto the current collector, dried, and then compressed by a press. Condensed or distorted. Here, if the number average pore diameter (D50) of the aggregate is 10 nm or more and 300 nm or less, the binder can be prevented from entering the pores of the aggregate to some extent, and the binder is used as the current collector. Can be effectively used for bonding between the electrode material and the electrode material, and problems such as peeling of the electrode active material layer of the electrode and cracks can be prevented. In addition, when the binder that has penetrated into the pores of the aggregates covers the inner walls of the pores, the primary particles of the electrode active material or the bonds between the secondary particles due to carbon are cracked due to condensation or distortion. Even so, the particles can be firmly bonded to each other, and the electronic conductivity between the electrode active materials can be prevented from being impaired.
If the number average pore diameter (D50) is less than 10 nm, penetration of the electrolyte solution may be hindered, and if it exceeds 300 nm, the volume density of the aggregate decreases, which is not preferable.

The specific surface area of the aggregate is preferably in the range of 5 m ² / g or more and 50 m ² / g or less as measured by the BET method because the surface area of the electrode active material in the aggregate increases.
Here, if the specific surface area is less than 5 m ² / g, the surface area of the electrode active material in the aggregate is too small, the particle size of the electrode active material is too large, and the diffusion distance of lithium ions becomes too long. On the other hand, if the specific surface area of the aggregate exceeds 50 m ² / g, the particle size of the primary particles of the electrode active material becomes too small, and it is difficult to control the degree of aggregation of the dispersion liquid described above. This is not preferable.

_Examples of the electrode active material that is the main component of the aggregate of the present embodiment include lithium cobaltate, lithium nickelate, lithium manganate, lithium titanate, and Li _x A _y D _z PO ₄ (where A is Co, Mn, One or more selected from the group of Ni, Fe, Cu, Cr, D is Mg, Ca, S, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y, one or more selected from the group of rare earth elements, one selected from the group of 0 <x <2, 0 <y <1.5, 0 ≦ z <1.5) as a main component It is preferable that

Here, for A, Co, Mn, Ni, and Fe are for D, and for D, Mg, Ca, Sr, Ba, Ti, Zn, and Al are in terms of high discharge potential, abundant resources, safety, etc. preferable.
Here, the rare earth elements are 15 elements of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu which are lanthanum series.

The average particle diameter of primary particles of this electrode active material is preferably 0.03 μm or more and 0.5 μm or less.
Here, the reason why the range of the average particle diameter of the primary particles is the above range is that this range makes it easy to control the degree of aggregation in the dispersion in which the electrode active material is dispersed in the dispersion medium, and lithium ions This is because it is easy to control the surface area of the electrode active material in which the insertion / desorption reaction is performed and the diffusion distance at which lithium ions diffuse into the particles.
If the average particle size is less than 0.03 μm, it is difficult to control the degree of aggregation of the dispersion, the width of the particle size distribution of the obtained aggregate becomes narrow, and it becomes difficult to improve the volume density of the aggregate. Therefore, if it exceeds 0.5 μm, the surface area of the electrode active material is reduced, the diffusion distance of lithium ions becomes too long, and the battery capacity when charging / discharging at high speed is reduced. This is not preferable.

The average particle size of the secondary particles of this electrode active material is 0.05 μm or more and 0.7 μm or less, so that the width of the particle size distribution of the dispersion and the pore size of the aggregates formed between the secondary particles can be kept moderate. It is preferable because it is possible.
Here, when the average particle diameter is less than 0.05 μm, the width of the particle size distribution of the dispersion is not preferable because it is narrow, and when it exceeds 0.7 μm, the pore diameter of the aggregate may exceed 300 nm. This is not preferable.

In this electrode active material, when used as an electrode material of a lithium ion battery, in order to uniformly carry out a reaction related to lithium ion desorption / insertion over the entire surface of the electrode active material, 80% or more of the surface of the electrode active material, preferably 90 % Or more is preferably coated with a carbonaceous film.
The coverage of a carbonaceous film can be measured using a transmission electron microscope (TEM) and an energy dispersive X-ray spectrometer (EDX). Here, when the coverage of the carbonaceous film is less than 80%, the coating effect of the carbonaceous film is insufficient, and the carbonaceous film is formed when the lithium ion deinsertion reaction is performed on the surface of the electrode active material. This is not preferable because the reaction resistance related to lithium ion desorption / insertion is increased at a portion where the discharge is not performed, and the voltage drop at the end of discharge becomes remarkable.

The amount of carbon in the carbonaceous film is preferably 0.6 parts by mass or more and 10 parts by mass or less, more preferably 0.8 parts by mass or more and 2.5 parts by mass with respect to 100 parts by mass of the electrode active material. Or less.
Here, the reason why the carbon content in the carbonaceous film is limited to the above range is that when the carbon content is less than 0.6 parts by mass, the coverage of the carbonaceous film is less than 80%, and a battery is formed. This is because the discharge capacity at the high-speed charge / discharge rate is low, and it is difficult to realize sufficient charge / discharge rate performance. On the other hand, when the amount of carbon exceeds 10 parts by mass, the amount of the carbonaceous film increases with respect to the electrode active material, and therefore, carbon is included in an amount more than necessary to obtain the necessary conductivity, and when the aggregate is formed. This is because the mass and volume density of carbon are lowered, and as a result, the electrode density is lowered and the battery capacity of the lithium ion battery per unit volume is lowered.

The average film thickness A of the carbonaceous film at the outer periphery of the aggregate and the average film thickness B of the carbonaceous film at the center of the aggregate are expressed by the following formula (1).
0.7 ≦ B / A ≦ 1.3 (1)
It is preferable to satisfy.
In this aggregate, the relationship between the average film thickness A of the carbonaceous film in the outer peripheral portion and the average film thickness B of the carbonaceous film in the central portion satisfies the above formula (1). This can reduce the ease of the lithium ion insertion / release reaction and the unevenness of the carbon film electronic conductivity. Therefore, the internal resistance of the positive electrode can be reduced, and as a result, the battery capacity can be improved.

The tap density of the positive electrode material is preferably 1.0 g / cm ³ or more. Here, when the tap density is less than 1.0 g / cm ³ , when the aggregate is dispersed in the dispersion medium to prepare the electrode slurry, the amount of the solvent retained in the gap inside the aggregate and the gap between the aggregates is small. Since it will increase too much, the density | concentration of the solid content in an electrode slurry will fall, therefore, since the time required for drying of the coating film obtained by apply | coating an electrode slurry becomes long, it is unpreferable.

[Method for producing positive electrode material]
The method for producing a positive electrode material of the present embodiment is obtained by dispersing electrode active material particles in a dispersion medium to obtain an electrode active material dispersion, and adding an organic compound that becomes a carbon precursor to the electrode active material dispersion. The ratio (D90 / D10) of the particle diameter (D90) when the cumulative volume percentage is 90% and the particle diameter (D10) when the cumulative volume percentage is 10% in the particle size distribution of the electrode active material in the slurry is 5 By adjusting the slurry so as to be 30 or less and granulating and drying the slurry, the positive electrode material for a lithium ion battery of the present embodiment, that is, primary particles of the electrode active material and primary particles of the electrode active material The mixture with the secondary particles aggregated is a further aggregated aggregate, and the primary particles and the secondary particles are coated with a carbonaceous film, and the volume density of the aggregate is as follows: Is it 50% by volume or more of the volume density? A method of obtaining a positive electrode material is 80 vol% or less.

As the electrode active material, as described in the above positive electrode material, lithium cobaltate, lithium nickelate, lithium manganate, lithium titanate and Li _x A _y D _z PO ₄ (where A is Co, Mn , Ni, Fe, Cu, Cr selected from the group of one or more, D is Mg, Ca, S, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc Y, Y, one or more selected from the group of rare earth elements, mainly one selected from the group of 0 <x <2, 0 <y <1.5, 0 ≦ z <1.5) It is preferable to use as a component.

Here, for A, Co, Mn, Ni, and Fe are for D, and for D, Mg, Ca, Sr, Ba, Ti, Zn, and Al are in terms of high discharge potential, abundant resources, safety, etc. preferable.
Here, the rare earth elements are 15 elements of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu which are lanthanum series.

Examples of the compound represented by _{Li x A y D z PO 4} , may be used a solid phase method, liquid phase method, those produced by a conventional method such as vapor-phase process.
Examples of the compound include a Li source selected from the group consisting of lithium salts such as lithium acetate (LiCH ₃ COO) and lithium chloride (LiCl), or lithium hydroxide (LiOH), and iron (II) chloride (FeCl ₂ ), divalent iron salts such as iron (II) acetate (Fe (CH ₃ COO) ₂ ), iron (II) sulfate (FeSO ₄ ), phosphoric acid (H ₃ PO ₄ ), ammonium dihydrogen phosphate A slurry-like mixture obtained by mixing a phosphoric acid compound such as (NH ₄ H ₂ PO ₄ ) or diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ) with water is used with a pressure-resistant sealed container. A compound obtained by hydrothermal synthesis and washing the resulting precipitate with water to produce a cake-like precursor material and calcining this cake-like precursor material can be suitably used.

  Examples of the organic compound include polyvinyl alcohol, polyvinyl pyrrolidone, cellulose, starch, gelatin, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, polyacrylic acid, polystyrene sulfonic acid, polyacrylamide, polyvinyl acetate, glucose, and fructose. Galactose, mannose, maltose, sucrose, lactose, glycogen, pectin, alginic acid, glucomannan, chitin, hyaluronic acid, chondroitin, agarose, polyether, polyhydric alcohols.

The compounding ratio of the electrode active material and the organic compound is preferably 0.6 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the electrode active material, when the total amount of the organic compound is converted into the amount of carbon. More preferably, they are 0.8 mass part or more and 2.5 mass parts or less.
Here, when the compounding ratio in terms of carbon amount of the organic compound is less than 0.6 parts by mass, the coverage of the carbonaceous film is less than 80%, and the discharge capacity at the high-speed charge / discharge rate is low when a battery is formed. Therefore, it is difficult to realize sufficient charge / discharge rate performance. On the other hand, when the compounding ratio in terms of carbon amount of the organic compound exceeds 10 parts by mass, the compounding ratio of the electrode active material is relatively low, and when the battery is formed, the capacity of the battery is reduced and the carbonaceous film Due to the excessive loading, the electrode active material becomes bulky. Therefore, the electrode density is lowered, and the decrease in the battery capacity of the lithium ion battery per unit volume cannot be ignored.

These electrode active materials and organic compounds are dissolved or dispersed in water to prepare a uniform slurry. In the dissolution or dispersion, a dispersant may be added, and the organic compound that is a carbon source may have a function as a dispersant.
The method for dissolving or dispersing the electrode active material and the organic compound in water is not particularly limited as long as the electrode active material is dispersed and the organic compound is dissolved or dispersed. For example, dispersion such as ball mill and sand mill A method using an apparatus is preferred.

  In this dispersion, the dispersion conditions of the slurry, for example, the dispersion medium such as zirconia beads used in the dispersion apparatus, the concentration of the electrode active material and the organic compound in the slurry, the dispersion time, etc. are adjusted. The ratio (D90 / D10) can be adjusted to be 5 or more and 30 or less.

Next, this slurry is sprayed in a high-temperature atmosphere, for example, air of 70 ° C. or higher and 250 ° C. or lower and dried.
The average particle size of the droplets at the time of spraying is preferably 0.05 μm or more and 100 μm or less, more preferably 1 μm or more and 20 μm or less.
By setting the average particle size of the droplets during spraying within the above range, a dried product having an average particle size of 0.5 μm or more and 100 μm or less, preferably 1 μm or more and 20 μm or less is obtained.

Next, the dried product is fired in a non-oxidizing atmosphere at a temperature in the range of 500 ° C. to 1000 ° C., preferably 600 ° C. to 900 ° C. for 0.1 hours to 40 hours.
As this non-oxidizing atmosphere, an inert atmosphere such as nitrogen (N ₂ ) or argon (Ar) is preferable, and when it is desired to suppress oxidation more, a reducing atmosphere containing a reducing gas such as hydrogen (H ₂ ) is used. preferable. Further, in order to remove organic components evaporated in the non-oxidizing atmosphere at the time of firing, it is possible to introduce a flammable gas such as oxygen (O ₂ ) and a combustible gas into the inert atmosphere.

  Moreover, the reason for setting the firing temperature to 500 ° C. or more and 1000 ° C. or less is that when the firing temperature is less than 500 ° C., decomposition and reaction of the organic compound contained in the dried product is insufficient, and carbonization of this organic compound is insufficient. As a result, a high-resistance organic matter decomposition product is generated in the obtained aggregate. On the other hand, when the firing temperature exceeds 1000 ° C., Li in the electrode active material evaporates. Not only does the composition of the electrode active material shift, but also the grain growth of the electrode active material is promoted. As a result, the discharge capacity at a high speed charge / discharge rate is lowered, and it is difficult to realize sufficient charge / discharge rate performance. Because it becomes.

Here, the particle size distribution of the obtained aggregate can be controlled by appropriately adjusting the conditions for firing the dried product, for example, the rate of temperature rise, the maximum holding temperature, the holding time, and the like.
As described above, the positive electrode material of the present embodiment, that is, a mixture of the primary particles of the electrode active material and the secondary particles obtained by agglomerating the primary particles of the electrode active material is an aggregate obtained by further aggregating the primary particles and 2 The secondary particles are coated with a carbonaceous film, and a positive electrode material having a volume density of 50% by volume or more and 80% by volume or less of the volume density of the aggregate is obtained.

[Positive electrode for lithium ion batteries]
The positive electrode for lithium ion batteries of this embodiment contains the positive electrode material for lithium ion batteries of this embodiment in the positive electrode layer.
This positive electrode layer is obtained by applying a mixture of the positive electrode material for a lithium ion battery of this embodiment and a binder onto a metal foil such as aluminum and drying it to form a sheet. The lithium ion battery of this embodiment By including the positive electrode material, the internal resistance of the positive electrode is lowered and the battery capacity is also improved.

[Lithium ion battery]
The lithium ion battery of this embodiment includes the positive electrode for a lithium ion battery of this embodiment.
This lithium ion battery includes a positive electrode for a lithium ion battery of the present embodiment, a negative electrode using a graphite-based carbon material, a separator made of porous polypropylene or the like that partitions the positive electrode and the negative electrode, and an electrolytic solution having lithium ion conductivity. By using the positive electrode for a lithium ion battery according to this embodiment, the internal resistance of the positive electrode is reduced, the battery capacity is improved, and the high-speed charge / discharge characteristics are excellent.

  As described above, according to the positive electrode material for a lithium ion battery of this embodiment, the mixture of the primary particles of the electrode active material and the secondary particles in which the primary particles of the electrode active material are aggregated is further aggregated. Thus, the aggregate and the primary particles and the secondary particles are coated with the carbonaceous film, so that the surface area of the aggregate can be increased, and the insertion / release reaction of lithium ions can be sufficiently obtained. As a result, the moving distance of lithium ions diffusing inside the primary particles of the electrode active material and the moving distance of electrons moving inside the primary particles can be shortened.

  Further, since the aggregate contains a porous aggregate having a volume density of 50 volume% or more and 80 volume% or less of the volume density when the aggregate is solid, the carbonaceous coating film The organic substance decomposition gas generated during the thermal decomposition of the organic substance when forming the organic substance is difficult to escape from the aggregate, and therefore the concentration of the organic substance decomposition gas in the vicinity of the surface of the primary particles of the electrode active material can be increased. The film thickness of the carbonaceous film covering the surface of the primary particles of the electrode active material can be made uniform.

  According to the positive electrode for a lithium ion battery of the present embodiment, since the positive electrode material for the lithium ion battery of the present embodiment is contained in the positive electrode layer, the internal resistance of the positive electrode can be reduced and the battery capacity can be improved. .

  According to the lithium ion battery of the present embodiment, since the positive electrode for the lithium ion battery of the present embodiment is provided, the internal resistance of the positive electrode can be reduced, the battery capacity can be improved, and high-speed charge / discharge can be achieved. Excellent characteristics.

Hereinafter, a detailed explanation of the present invention by Examples 1 12 and Comparative Examples 1, 3, 4, the present invention is not intended to be limited to these examples.
For example, in this embodiment, metal Li is used for the negative electrode in order to reflect the behavior of the electrode material itself in the data. However, a negative electrode material such as a carbon material, a Li alloy, or Li ₄ Ti ₅ O ₁₂ may be used. . A solid electrolyte may be used instead of the electrolytic solution and the separator.

"Example 1"
(Production of positive electrode material)
4 mol of lithium acetate (LiCH ₃ COO), 2 mol of iron (II) sulfate (FeSO ₄ ), and 2 mol of phosphoric acid (H ₃ PO ₄ ) were mixed in 2 L (liter) of water to prepare a raw material slurry.
Next, ethylene glycol is added to this raw material slurry so that it becomes 3 parts by mass with respect to 100 parts by mass of raw materials other than water, and water is further added so that the total amount is 4 L (liter). The mixture was adjusted.
Subsequently, this mixture was accommodated in a pressure-resistant sealed container having a capacity of 8 L, and hydrothermal synthesis was performed at 120 ° C. for 1 hour. Next, the obtained precipitate was washed with water to obtain a cake-like electrode active material.

A small amount of sample was taken from the cake-like electrode active material, and the powder was vacuum-dried at 70 ° C. for 2 hours and identified using an X-ray diffractometer. As a result, single-phase LiFePO ₄ was produced. It was confirmed that Further, when the sample was observed using a transmission electron microscope (TEM), it was confirmed that fine plate-like particles having an average primary particle diameter of 70 nm were generated. Here, the average particle diameter of the primary particles is the length of 10 primary particles randomly selected from the field of view of a transmission electron microscope (TEM) image and measured in the major axis direction. It is an average value obtained by averaging.

Next, 150 g of this electrode active material (in terms of solid content), a polyvinyl alcohol aqueous solution obtained by dissolving 20 g of polyvinyl alcohol as an organic compound in 200 g of water, and 500 g of zirconia balls having a diameter of 5 mm as medium particles are put into a ball mill, and the electrode in the slurry The ball mill stirring time was adjusted so that D90 / D10 of the particle size distribution of the active material particles was 7, and the dispersion treatment was performed.
Next, the obtained slurry was sprayed into an air atmosphere at 180 ° C. and dried to obtain a dried product. Next, the obtained dried product was baked at 700 ° C. for 1 hour under an inert atmosphere made of nitrogen (N ₂ ) gas to obtain a positive electrode material (A1) for a lithium ion battery of Example 1.

When the aggregate constituting the obtained positive electrode material (A1) was observed using a scanning electron microscope (SEM), the aggregate was a spherical porous aggregate having an average particle diameter of 6 μm.
Further, when this aggregate was observed using a transmission electron microscope (TEM), primary particles having an average particle diameter of 100 nm were bonded to each other through a cervical bonding portion formed of a carbonaceous film, and the average particle diameter was 200 nm. It was confirmed that the secondary particles aggregated to form an aggregate. A transmission electron microscope (TEM) image of the aggregate is shown in FIG.
Here, the average particle diameter of the secondary particles is the measurement of the length in the major axis direction of 10 secondary particles randomly selected within the field of view of the scanning electron microscope (SEM) image. It is the average value of the lengths in the major axis direction of 50 secondary particles when performed in the field of view.

(Evaluation of positive electrode material)
Volume density of this positive electrode material, number average pore diameter (average pore diameter) D50 inside the aggregate, ratio of average film thickness of carbonaceous coating (thickness of central carbonaceous coating / thickness of outer peripheral carbonaceous coating), ratio Each surface area was evaluated.
The evaluation method is as follows.

(1) Volume density of positive electrode material It measured using the mercury porosimeter.
(2) Average pore diameter inside the aggregate (D50)
Measurement was performed using a mercury porosimeter.
(3) Ratio of average film thickness of carbonaceous film The carbonaceous film of the aggregate is observed using a transmission electron microscope (TEM), and the thickness of the carbonaceous film in the central part of the aggregate and the carbonaceous material in the outer peripheral part. Measure the thickness of each coating at five points, calculate the average value of each, and based on these average values, the ratio of the average thickness of the carbonaceous coating (the thickness of the central carbonaceous coating / the carbonaceous coating of the outer periphery) Thickness) was calculated.

(4) Specific surface area Specific surface area meter The specific surface area (m ² / g) of the positive electrode material was measured using Belsorb II (manufactured by Nippon Bell Co., Ltd.).
These evaluation results are shown in Table 1.

(Production of lithium ion battery)
The positive electrode material (A1), polyvinylidene fluoride (PVdF) as a binder, and acetylene black (AB) as a conductive additive are mixed so that the mass ratio is 90: 5: 5, and further N as a solvent. -Methyl-2-pyrrolidinone (NMP) was added to impart fluidity to produce a slurry.
Next, this slurry was applied onto an aluminum (Al) foil having a thickness of 15 μm and dried. Then, it pressurized by the pressure of 600 kgf / cm < ² >, and the positive electrode of the lithium ion battery of Example 1 was produced.

Lithium metal was disposed as a negative electrode with respect to the positive electrode of the lithium ion battery, and a separator made of porous polypropylene was disposed between the positive electrode and the negative electrode to obtain a battery member.
On the other hand, ethylene carbonate and diethyl carbonate were mixed at 1: 1 (mass ratio), and a 1M LiPF ₆ solution was added to prepare an electrolyte solution having lithium ion conductivity.
Next, the battery member was immersed in the electrolyte solution, and a lithium ion battery of Example 1 was produced.

(Evaluation of lithium-ion battery)
The lithium ion battery was evaluated for discharge capacity, charge / discharge characteristics, and internal resistance.
The evaluation method is as follows.
(1) Discharge capacity The above lithium ion battery charge / discharge test was performed at room temperature (25 ° C.) with a constant voltage of a cut-off voltage of 2-4.5 V, a charge / discharge rate of 0, 1 C, and 1 C. Table 2 shows the initial discharge capacity at each charge / discharge rate.
(2) Charging / discharging characteristics It was carried out at room temperature (25 ° C.) under a constant current (cutting for 1 hour and discharging for 1 hour) with a cut-off voltage of 2-4.2 V and a charge / discharge rate of 1C. The charge / discharge characteristics are shown in FIG.

(3) Internal resistance In the charge / discharge characteristics described above, the voltage drop observed at the end of discharge indicates the magnitude of unevenness of the carbonaceous film on the surface of the positive electrode material, that is, the internal resistance. Therefore, a sample in which a voltage drop was recognized remarkably was judged as a sample having a high internal resistance.
Here, a sample with no voltage drop or a small voltage drop was evaluated as “◯”, and a sample with a noticeable voltage drop was evaluated as “x”.
These evaluation results are shown in Table 2.

"Example 2"
A positive electrode material (A2) of Example 2 was obtained according to Example 1, except that the stirring time of the ball mill was adjusted so that D90 / D10 of the particle size distribution of the electrode active material particles in the slurry was 15. . The obtained positive electrode material (A2) was a spherical aggregate having an average particle diameter of 6 μm, and it was confirmed that secondary particles having an average particle diameter of 120 nm were bonded to each other through carbon.
Evaluation of this positive electrode material (A2) was performed according to Example 1. The evaluation results are shown in Table 1.

A lithium ion battery of Example 2 was produced according to Example 1 using the positive electrode material (A2).
This lithium ion battery was evaluated according to Example 1. The evaluation results are shown in Table 2.

"Example 3"
Electrode active material particles having an average primary particle size of 130 nm were obtained in the same manner as in Example 1 except that the addition amount of ethylene glycol was 1 part by mass with respect to 100 parts by mass of raw materials other than water.
Next, Example 3 according to Example 1 except that this electrode active material particle was used and the stirring time of the ball mill was adjusted so that D90 / D10 of the particle size distribution of the electrode active material particle in the slurry was 8. A positive electrode material (A3) was obtained. The obtained positive electrode material (A3) was a spherical aggregate having an average particle diameter of 6 μm, and it was confirmed that secondary particles having an average particle diameter of 150 nm were bonded to each other through carbon.
Evaluation of this positive electrode material (A3) was performed according to Example 1. The evaluation results are shown in Table 1.

A lithium ion battery of Example 3 was produced according to Example 1 using the positive electrode material (A3).
This lithium ion battery was evaluated according to Example 1. The charge / discharge characteristics are shown in FIG. 3, and the evaluation results are shown in Table 2.

Example 4
A positive electrode material (A4) of Example 4 was obtained according to Example 1 except that the stirring time of the ball mill was adjusted so that D90 / D10 of the particle size distribution of the electrode active material particles in the slurry was 16. The obtained positive electrode material (A4) was a spherical aggregate having an average particle diameter of 6 μm, and it was confirmed that secondary particles having an average particle diameter of 180 nm were bonded to each other through carbon.
Evaluation of this positive electrode material (A4) was performed according to Example 1. The evaluation results are shown in Table 1.

A lithium ion battery of Example 4 was produced according to Example 1 using the above positive electrode material (A4).
This lithium ion battery was evaluated according to Example 1. The evaluation results are shown in Table 2.

"Example 5"
Electrode active material particles having an average primary particle size of 210 nm were obtained in the same manner as in Example 1 except that ethylene glycol was not added.
Next, Example 5 was applied in accordance with Example 1, except that the electrode active material particles were used and the stirring time of the ball mill was adjusted so that D90 / D10 of the particle size distribution of the electrode active material particles in the slurry was 7. A positive electrode material (A5) was obtained. The obtained positive electrode material (A5) was a spherical aggregate having an average particle diameter of 6 μm, and it was confirmed that secondary particles having an average particle diameter of 230 nm were bonded to each other through carbon.
Evaluation of this positive electrode material (A5) was performed according to Example 1. The evaluation results are shown in Table 1.

A lithium ion battery of Example 5 was produced according to Example 1 using the positive electrode material (A5).
This lithium ion battery was evaluated according to Example 1. The charge / discharge characteristics are shown in FIGS. 3 and 4, and the evaluation results are shown in Table 2.

"Example 6"
The positive electrode material of Example 6 according to Example 1 except that ethylene glycol was not added and the stirring time of the ball mill was adjusted so that D90 / D10 of the particle size distribution of the electrode active material particles in the slurry was 15. (A6) was obtained. The obtained positive electrode material (A6) was a spherical aggregate having an average particle diameter of 6 μm, and it was confirmed that secondary particles having an average particle diameter of 260 nm were bonded to each other through carbon.
Evaluation of this positive electrode material (A5) was performed according to Example 1. The evaluation results are shown in Table 1.

A lithium ion battery of Example 6 was produced according to Example 1 using the above positive electrode material (A6).
This lithium ion battery was evaluated according to Example 1. The charge / discharge characteristics are shown in FIG. 4, and the evaluation results are shown in Table 2.

"Example 7"
The positive electrode material of Example 7 according to Example 1, except that ethylene glycol was not added and the stirring time of the ball mill was adjusted so that D90 / D10 of the particle size distribution of the electrode active material particles in the slurry was 25 (A7) was obtained. The obtained positive electrode material (A7) was a spherical aggregate having an average particle diameter of 6 μm, and it was confirmed that secondary particles having an average particle diameter of 390 nm were bonded together via carbon.
Evaluation of this positive electrode material (A7) was performed according to Example 1. The evaluation results are shown in Table 1.

A lithium ion battery of Example 7 was produced according to Example 1 using the positive electrode material (A7).
This lithium ion battery was evaluated according to Example 1. The charge / discharge characteristics are shown in FIG. 4, and the evaluation results are shown in Table 2.

"Example 8"
The positive electrode material (A8) of Example 8 was obtained in the same manner as in Example 1 except that the hydrothermal synthesis was performed at 170 ° C. for 1 hour and ethylene glycol was not added. The obtained positive electrode material (A8) was a spherical aggregate having an average particle diameter of 6 μm, and it was confirmed that secondary particles having an average particle diameter of 340 nm were bonded to each other through carbon.
Evaluation of this positive electrode material (A8) was performed according to Example 1. The evaluation results are shown in Table 1.

A lithium ion battery of Example 8 was produced according to Example 1 using the positive electrode material (A8).
This lithium ion battery was evaluated according to Example 1. The charge / discharge characteristics are shown in FIG. 3, and the evaluation results are shown in Table 2.

"Example 9"
The conditions for hydrothermal synthesis are set to 170 ° C. for 1 hour, ethylene glycol is not added, and the ball mill stirring time is adjusted so that the D90 / D10 of the particle size distribution of the electrode active material particles in the slurry is 14. The positive electrode material (A9) of Example 9 was obtained according to Example 1. The obtained positive electrode material (A9) was a spherical aggregate having an average particle diameter of 6 μm, and it was confirmed that secondary particles having an average particle diameter of 540 nm were bonded together via carbon.
Evaluation of this positive electrode material (A9) was performed according to Example 1. The evaluation results are shown in Table 1.

A lithium ion battery of Example 9 was produced according to Example 1 using the above positive electrode material (A9).
This lithium ion battery was evaluated according to Example 1. The evaluation results are shown in Table 2.

"Example 10"
Instead of iron sulfate (II) (FeSO ₄ ) serving as an iron source, manganese sulfate (II) (MnSO ₄ ) was used as a manganese source, and from a single-phase LiMnPO ₄ having an average particle diameter of 50 nm according to Example 1. A cake-like electrode active material was obtained.
Next, 142.5 g of this electrode active material (in terms of solid content), an aqueous polyvinyl alcohol solution obtained by dissolving 50 g of polyvinyl alcohol as a carbonizing agent in 500 g of water, lithium acetate, iron citrate and phosphoric acid as a carbonization catalyst, iron phosphate 7.5 g in terms of lithium and 500 g of zirconia balls having a diameter of 5 mm as medium particles are put into a ball mill, and the ball mill agitation time is adjusted so that D90 / D10 of the particle size distribution of the electrode active material particles in the slurry is 7. And distributed processing.

Subsequently, the obtained slurry was processed according to Example 1, and the positive electrode material (A10) for lithium ion batteries of Example 10 was obtained. The obtained positive electrode material (A10) was a spherical aggregate having an average particle diameter of 6 μm, and it was confirmed that secondary particles having an average particle diameter of 65 nm were bonded together via carbon.
Evaluation of this positive electrode material (A10) was performed according to Example 1. The evaluation results are shown in Table 1.

A lithium ion battery of Example 10 was produced according to Example 1 using the positive electrode material (A10).
This lithium ion battery was evaluated according to Example 1. The evaluation results are shown in Table 2.

"Example 11"
Instead of iron sulfate (II) (FeSO ₄ ) serving as an iron source, manganese sulfate (II) (MnSO ₄ ) was used as a manganese source, and from a single-phase LiMnPO ₄ having an average particle diameter of 50 nm according to Example 1. A cake-like electrode active material was obtained.
Next, 142.5 g of this electrode active material (in terms of solid content), an aqueous polyvinyl alcohol solution obtained by dissolving 50 g of polyvinyl alcohol as a carbonizing agent in 500 g of water, lithium acetate, iron citrate and phosphoric acid as a carbonization catalyst, iron phosphate 7.5 g in terms of lithium and 500 g of zirconia balls having a diameter of 5 mm as medium particles are charged into a ball mill, and the ball mill agitation time is adjusted so that D90 / D10 of the particle size distribution of the electrode active material particles in the slurry is 27. And distributed processing.

Subsequently, the obtained slurry was processed according to Example 1, and the positive electrode material (A11) for lithium ion batteries of Example 11 was obtained. The obtained positive electrode material (A11) was a spherical aggregate having an average particle diameter of 6 μm, and it was confirmed that secondary particles having an average particle diameter of 100 nm were bonded to each other through carbon.
Evaluation of this positive electrode material (A11) was performed according to Example 1. The evaluation results are shown in Table 1.

A lithium ion battery of Example 11 was produced according to Example 1 using the positive electrode material (A11).
This lithium ion battery was evaluated according to Example 1. The evaluation results are shown in Table 2.

"Comparative Example 1"
The positive electrode material of Comparative Example 1 according to Example 1, except that ethylene glycol was not added and the stirring time of the ball mill was adjusted so that D90 / D10 of the particle size distribution of the electrode active material particles in the slurry was 3. (B1) was obtained. The obtained positive electrode material (B1) is an aggregate having an average particle diameter of 6 μm, primary particles having an average particle diameter of 230 nm are bonded to each other through carbon, and secondary particles bonded by carbon are almost present. It was confirmed that they did not.
Evaluation of this positive electrode material (B1) was performed according to Example 1. The evaluation results are shown in Table 1.

A lithium ion battery of Comparative Example 1 was produced according to Example 1 using the positive electrode material (B1).
This lithium ion battery was evaluated according to Example 1. The charge / discharge characteristics are shown in FIGS. 3 and 4, and the evaluation results are shown in Table 2.

" Example 12 "
The positive electrode material ( A12 ) of Example 12 was obtained in the same manner as in Example 1 except that hydrothermal synthesis was performed at 230 ° C. for 1 hour and ethylene glycol was not added. The obtained positive electrode material ( A12 ) was a spherical aggregate having an average particle diameter of 6 μm, and it was confirmed that secondary particles having an average particle diameter of 920 nm were bonded to each other through carbon.
Evaluation of this positive electrode material ( A12 ) was performed according to Example 1. The evaluation results are shown in Table 1.

A lithium ion battery of Example 12 was produced according to Example 1 using the positive electrode material ( A12 ).
This lithium ion battery was evaluated according to Example 1. The evaluation results are shown in Table 2.

“Comparative Example 3”
150 g of the positive electrode material (A1) prepared according to Example 1 (in terms of solid content), 200 g of water, and 500 g of zirconia balls having a diameter of 5 mm as medium particles are put into a ball mill, and the particle size of the electrode active material particles in the slurry Grinding was performed until D90 / D10 of the distribution became 3 or less, and a slurry composed of carbon-coated electrode active material particles was obtained.

A small amount of sample was collected from this slurry and observed with a transmission electron microscope (TEM). As a result, fine plate-like particles having an average particle size of 230 nm whose surface was covered with a carbonaceous film were mainly used. It was confirmed that secondary particles, which are components and bonded by carbon, were almost absent.
Next, the slurry was sprayed into an air atmosphere at 180 ° C. and dried to obtain a dried product. Next, the obtained dried product was baked at 700 ° C. for 30 minutes under an inert atmosphere made of nitrogen (N ₂ ) gas to obtain a positive electrode material (B3) for lithium ion battery of Comparative Example 3.

The obtained positive electrode material (B3) is an aggregate having an average particle diameter of 6 μm, and primary particles having an average particle diameter of 230 nm coated on the surface with a carbonaceous film are aggregated. Bonding by carbon was not recognized.
Evaluation of this positive electrode material (B3) was performed according to Example 1. The evaluation results are shown in Table 1.

A lithium ion battery of Comparative Example 3 was produced according to Example 1 using the positive electrode material (B3).
This lithium ion battery was evaluated according to Example 1. The charge / discharge characteristics are shown in FIG. 4, and the evaluation results are shown in Table 2.

“Comparative Example 4”
Instead of iron sulfate (II) (FeSO ₄ ) serving as an iron source, manganese sulfate (II) (MnSO ₄ ) was used as a manganese source, and from a single-phase LiMnPO ₄ having an average particle diameter of 50 nm according to Example 1. A cake-like electrode active material was obtained.
Next, 142.5 g of this electrode active material (in terms of solid content), an aqueous polyvinyl alcohol solution obtained by dissolving 50 g of polyvinyl alcohol as a carbonizing agent in 500 g of water, lithium acetate, iron citrate and phosphoric acid as a carbonization catalyst, iron phosphate 7.5 g in terms of lithium and 500 g of zirconia balls having a diameter of 5 mm as media particles are put into a ball mill, and the stirring time of the ball mill is adjusted so that the D90 / D10 of the particle size distribution of the electrode active material particles in the slurry is 3. And distributed processing.

Subsequently, the obtained slurry was processed according to Example 1, and the positive electrode material (B4) for lithium ion batteries of Comparative Example 4 was obtained. The obtained positive electrode material (B4) is a spherical aggregate having an average particle diameter of 6 μm, primary particles having an average particle diameter of 52 nm are bonded to each other through carbon, and secondary particles bonded by carbon are It was confirmed that there was almost no existence.
Evaluation of this positive electrode material (B4) was performed according to Example 1. The evaluation results are shown in Table 1.

A lithium ion battery of Comparative Example 4 was produced according to Example 1 using the positive electrode material (B4).
This lithium ion battery was evaluated according to Example 1. The evaluation results are shown in Table 2.

According to the above evaluation results, in Examples 1 to 12 , the internal resistance of the positive electrode is reduced, the battery capacity is improved, and the high-speed charge / discharge characteristics are compared with Comparative Examples 1 , 3 and 4. It turned out to be excellent.

  The positive electrode material of the present invention is an aggregate obtained by further agglomerating a mixture of primary particles of the electrode active material and secondary particles obtained by aggregating the primary particles of the electrode active material. The primary particles and the secondary particles are carbonaceous. The aggregate is covered with a film, and the aggregate contains a porous aggregate having a volume density of 50 volume% or more and 80 volume% or less of the volume density when the aggregate is solid. By increasing the surface area, lithium ion insertion / desorption reaction can be sufficiently obtained, and the movement distance of lithium ions diffusing inside the primary particles of the electrode active material, and the movement inside the primary particles Therefore, it is possible to improve the discharge characteristics of lithium-ion batteries as well as the next generation, which is expected to be smaller, lighter, and higher in capacity. Next battery And it is also possible to apply, for a next-generation secondary battery, the effect is very large.

DESCRIPTION OF SYMBOLS 1 Positive electrode material for lithium ion batteries 2 Primary particle of electrode active material 3 Secondary particle 4 Carbonaceous film 5 Neck-like joint 6 Pore

Claims (6)

A mixture of primary particles of the electrode active material and secondary particles obtained by agglomerating the primary particles of the electrode active material is an aggregate obtained by further agglomeration;
The primary particles and the secondary particles are coated with a carbonaceous film having a uniform film thickness ,
The aggregate contains a porous aggregate having a volume density of 50% by volume or more and 80% by volume or less of a volume density when the aggregate is solid,
The electrode active material, Ri phosphate der having an olivine structure,
In the porous aggregate, a part of the carbonaceous film is necked between the primary particles, between the secondary particles, and between the primary particles and the secondary particles. While being joined by the neck-like joint, pores capable of diffusing and penetrating lithium ions are formed in the gap between them,
The positive electrode material for a lithium ion battery, wherein the primary particles have an average particle size of 0.03 μm or more and 0.5 μm or less . 2. The lithium ion battery according to claim 1 , wherein the aggregate includes solid secondary particles obtained by agglomerating the primary particles whose surfaces are coated with a carbonaceous film. Positive electrode material. The positive electrode material for a lithium ion battery according to claim 1 or 2 carbon average pore size at 50% of the cumulative pore size distribution (D50) is characterized by at 10nm or more and 300nm or less as measured by mercury porosimetry. The average film thickness A of the carbonaceous film at the outer periphery of the aggregate and the average film thickness B of the carbonaceous film at the center of the aggregate are expressed by the following formula (1).
0.7 ≦ B / A ≦ 1.3 (1)
It claims 1 and satisfies a to the positive electrode material for a lithium ion battery according to any one of 3. A positive electrode for a lithium ion battery comprising the positive electrode material for a lithium ion battery according to any one of claims 1 to 4 in a positive electrode layer. A lithium ion battery comprising the positive electrode for a lithium ion battery according to claim 5 .