JP2013069565A - Electrode material and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: an electrode material less in variation of the amount of a carbonaceous coating carried and also capable of improving electronic conductivity when an electrode active material having a carbonaceous coating formed on a surface thereof is used as the electrode material; and a method for producing the electrode material.SOLUTION: An electrode material of the present invention comprises an aggregate formed by an aggregation of an electrode active material particle having a carbonaceous coating formed on a surface thereof. An average particle size of the aggregate is 0.5 μm or more and 100 μm or less. A pore diameter (D50) when a cumulative volume percentage of a pore diameter distribution of the aggregate is 50% is 0.1 μm or more and 0.2 μm or less. A porosity of the aggregate is 15 vol.% or more and 50 vol.% or less with respect to a volume in the case where the aggregate is solid.

Description

  The present invention relates to an electrode material and a method for producing the same, and more particularly to an electrode material suitable for use in a positive electrode material for a battery and further a positive electrode material for a lithium ion battery, and a method for producing the electrode material.

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.
This lithium ion battery is composed of a positive electrode and a negative electrode having a property capable of reversibly inserting and removing lithium ions, and a non-aqueous electrolyte.
As a negative electrode material for a lithium ion battery, a Li-containing metal oxide having a property capable of reversibly inserting and removing lithium ions, such as a carbon-based material or lithium titanate (Li ₄ Ti ₅ O ₁₂ ), as a negative electrode active material. Things are used.
On the other hand, as a positive electrode material of a lithium ion battery, as a positive electrode active material, a lithium-containing metal oxide, such as lithium iron phosphate (LiFePO ₄ ), which has a property capable of reversibly inserting and removing lithium ions, a binder, and the like. The electrode material mixture containing is used. And the positive electrode of a lithium ion battery is formed by apply | coating this electrode material mixture on the surface of metal foil called a collector.

Such a lithium ion battery is lighter and smaller than a conventional secondary battery such as a lead battery, a nickel cadmium battery, or a nickel metal hydride battery, and has high energy. It is used as a power source for portable electronic devices such as personal computers. In recent years, lithium-ion batteries have been studied as high-output power sources for electric vehicles, hybrid vehicles, electric tools, etc., and batteries used as these high-output power sources are required to have high-speed charge / discharge characteristics. Yes.
However, an electrode active material, for example, an electrode material including a Li-containing metal oxide having a property capable of reversibly removing and inserting lithium ions has a problem of low electron conductivity. Therefore, in order to increase the electron conductivity of the electrode material, the surface of the electrode active material particles is covered with an organic component, which is a carbon source, and then carbonized to form a carbonaceous film on the surface of the electrode active material. An electrode material in which carbon of this carbonaceous film is interposed as an electron conductive substance has been proposed (Patent Document 1).

JP 2001-15111 A

By the way, in order to use an electrode active material as a battery material of a lithium ion battery, the electronic conductivity of an electrode active material is indispensable, and the higher the electronic conductivity of this electrode active material, the better.
However, in an electrode material obtained by firing a conventional electrode active material supporting an organic compound or a precursor of an electrode active material in a non-oxidizing atmosphere, an aromatic produced by thermal decomposition of the organic compound during firing A carbonaceous film is formed on the surface of the electrode active material by the condensation of the carbonaceous compound, while the aromatic carbon compound is volatile at a high temperature, particularly at a firing temperature of 500 ° C. or higher and 1000 ° C. or lower. The higher the concentration of the vaporized substance in the aromatic carbon compound, the more the carbonaceous film is supported and the thicker the film is. However, the lower the concentration of the vaporized substance, the more the carbonaceous film is supported. Less and the thickness of the coating is reduced.

  Therefore, in the aggregate of primary particles of the electrode active material, when the electrode active materials are not aggregated, and when the aggregate is an aggregate with many voids, the non-oxidizing atmosphere When firing, the concentration of the vaporized aromatic carbon compound is lowered, the amount of the carbonaceous film supported is reduced entirely or partially, the thickness of the carbonaceous film is reduced, and the carbonaceous film is coated. There was a problem that the rate decreased.

  The present invention has been made to solve the above problems, and when using an electrode active material having a carbonaceous film formed on the surface as an electrode material, the amount of unevenness of the carbonaceous film supported is small, And it aims at providing the electrode material which can improve electronic conductivity, and its manufacturing method.

  As a result of intensive studies to solve the above problems, the present inventors have made electrode active materials in a slurry containing an electrode active material or a precursor of an electrode active material and an organic compound when producing an electrode material. Alternatively, the ratio (D90 / D10) of the particle diameter (D90) when the cumulative volume percentage of the particle size distribution of the precursor of the electrode active material is 90% to the particle diameter (D10) when the cumulative volume percentage is 10% is 5 or more. When the cumulative volume percentage of the pore size distribution of the obtained aggregate is 50%, the pore diameter (D50) is 0.1 μm or more and 0.2 μm or less. The rate can be 15% by volume or more and 50% by volume or less with respect to the volume when the aggregate is solid. Therefore, the concentration of the vaporized substance of the aromatic carbon compound inside the aggregate Can enhance As a result, it was found that a carbonaceous film with little unevenness can be supported on the surface of the electrode active material in the aggregate, and the present invention has been completed.

  That is, the electrode material of the present invention comprises an aggregate formed by aggregating electrode active material particles having a carbonaceous film formed on the surface, and the average particle diameter of the aggregate is 0.5 μm or more and 100 μm or less, When the cumulative volume percentage of the pore size distribution of the aggregate is 50%, the pore diameter (D50) is 0.1 μm or more and 0.2 μm or less, and the porosity of the aggregate is that the aggregate is solid. It is characterized by being 15% by volume or more and 50% by volume or less with respect to the volume of the case.

In the electrode material of the present invention, it is preferable that 80% or more of the surface of the electrode active material is covered with the carbonaceous film.
The aggregate is a shell-shaped aggregate having voids inside, and a ratio of an average film thickness of the carbonaceous film in the outer peripheral portion and the inner peripheral portion of the shell-shaped aggregate (inner peripheral carbon). The thickness of the quality coating / the thickness of the outer peripheral carbonaceous coating) is preferably 0.7 or more and 1.3 or less.
The amount of carbon in the carbonaceous film 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.
The tap density of the aggregate is preferably 1.0 g / cm ³ or more and 1.5 g / cm ³ or less.

Select the electrode active material, lithium cobalt oxide, lithium nickel oxide, lithium manganate, lithium titanate and _{Li x A y D z PO 4} ( where, A is Co, Mn, Ni, Fe, Cu, from the group of Cr 1 or 2 or more, D is selected from the group consisting of Mg, Ca, S, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y, and rare earth elements It is preferable that the main component is one or more species selected from the group of 0 <x <2, 0 <y <1.5, 0 ≦ z <1.5.

  The method for producing an electrode material of the present invention includes an electrode active material or an electrode active material precursor and an organic compound, and a cumulative volume percentage of a particle size distribution of the electrode active material or the electrode active material precursor is 90%. The slurry having a ratio (D90 / D10) of not less than 5 and not more than 30 with respect to the particle diameter (D10) when the cumulative volume percentage of the particle diameter (D90) is 10% is dried. Baking is performed in a non-oxidizing atmosphere of 500 ° C. or higher and 1000 ° C. or lower.

  According to the electrode material of the present invention, the average particle diameter of the aggregate formed by aggregating the electrode active material particles having the carbonaceous film formed on the surface is 0.5 μm or more and 100 μm or less, and the pore size distribution of the aggregate When the cumulative volume percentage is 50%, the pore diameter (D50) is 0.1 μm or more and 0.2 μm or less, and the porosity of the aggregate is relative to the volume when the aggregate is solid. Since the volume is set to 15% by volume or more and 50% by volume or less, it is possible to reduce unevenness in the amount of the carbonaceous film formed on the surface of the electrode active material particles, thereby reducing the electronic conductivity unevenness of the electrode active material. Can be reduced. Therefore, when used as an electrode material for a lithium ion battery, the internal resistance can be reduced.

  And, by using the electrode active material with reduced unevenness of electronic conductivity as the electrode material of the lithium ion battery, it becomes possible to perform the reaction related to the desorption / insertion of lithium ions uniformly over the entire surface of the electrode active material, The internal resistance can be reduced.

  According to the method for producing an electrode material of the present invention, the electrode active material or the precursor of the electrode active material and an organic compound, and the particle size distribution of the electrode active material or the precursor of the electrode active material with respect to D90 of D90 The slurry having a ratio (D90 / D10) of 5 or more and 30 or less is dried, and then the obtained dried product is fired in a non-oxidizing atmosphere of 500 ° C. or more and 1000 ° C. or less. Thus, it is possible to easily manufacture an electrode material that can reduce the unevenness of the amount of the carbonaceous film formed on the electrode and reduce the unevenness of the electronic conductivity of the electrode active material.

It is a figure which shows the charging / discharging characteristic in the room temperature of Example 1 and Comparative Example 1 of this invention.

The electrode material of this invention and the form for implementing the manufacturing method are demonstrated.
This embodiment is specifically described for better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

[Electrode material]
The electrode material of the present embodiment comprises an aggregate formed by aggregating electrode active material particles having a carbonaceous film formed on the surface, and the average particle diameter of the aggregate is 0.5 μm or more and 100 μm or less, When the cumulative volume percentage of the pore size distribution of the aggregate is 50%, the pore diameter (D50) is 0.1 μm or more and 0.2 μm or less, and the porosity of the aggregate is such that the aggregate is solid. It is 15 volume% or more and 50 volume% or less with respect to the volume in the case of doing.
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.

  Here, the aggregate formed by aggregating the electrode active material having the carbonaceous film formed on the surface is formed by aggregating the electrode active materials having the carbonaceous film formed on the surface in a point contact state. It is an agglomerate in a state where a contact portion between electrode active materials is in a neck shape with a small cross-sectional area and is firmly connected. As described above, the contact portion between the electrode active materials has a cervical shape with a small cross-sectional area, so that a channel-like (network-like) void is three-dimensionally expanded in the aggregate.

As the electrode active material, lithium cobalt acid, lithium nickel acid, lithium manganese oxide, lithium titanate and _{Li x A y D z PO 4} ( where, A is Co, Mn, Ni, Fe, Cu, from the group of Cr One or more selected, D is selected from the group of Mg, Ca, S, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y, rare earth elements It is preferable that the main component is one type selected from the group of 1 type or 2 types or more, 0 <x <2, 0 <y <1.5, 0 ≦ z <1.5).

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.

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, preferably 90%, of the surface of the electrode active material. % 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 particle size of the aggregate is preferably 0.5 μm or more and 100 μm or less, more preferably 1 μm or more and 20 μm or less.
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 pore size distribution of the aggregate can be measured using a mercury porosimeter.
The pore diameter (D50) when the cumulative volume percentage of the pore diameter distribution of the aggregate is 50% is preferably 0.1 μm or more and 0.2 μm or less.
Here, the reason why the D50 of the pore size distribution of the aggregate is in the above range is that when the D50 is less than 0.1 μm, the density inside the aggregate becomes too high, and the channel shape (network-like) inside the aggregate is too high. ), And as a result, the tar-like substance generated during carbonization of the organic compound is trapped inside the aggregate, which is not preferable. On the other hand, when D50 exceeds 0.2 μm, The concentration of the vapor of the aromatic carbon compound in the void inside the aggregate of the electrode active material becomes too low, and the film thickness of the carbonaceous film on the inner periphery of the outer shell of the aggregate becomes thin. Since the internal resistance of a substance becomes high, it is not preferable.

The porosity of this aggregate can be measured using a mercury porosimeter as in the case of the above pore diameter distribution.
The porosity of the aggregate is preferably 15% by volume or more and 50% by volume or less, more preferably 20% by volume or more and 45% by volume or less with respect to the volume when the aggregate is solid.
Here, if the porosity of the aggregate is less than 15% by volume with respect to the volume when the aggregate is solid, the density inside the aggregate is too high, and the channel shape inside the aggregate is too high. The (network-like) voids become smaller, and as a result, the tar-like substance generated during carbonization of the organic compound is trapped inside the aggregate, which is not preferable. On the other hand, this aggregate is solid. If the volume exceeds 50% by volume, the concentration of the aromatic carbon compound vapor in the voids inside the aggregate of the electrode active material becomes too low, and in the inner periphery of the outer shell of the aggregate This is not preferable because the carbonaceous film becomes thin and the internal resistance of the electrode active material increases.

  As described above, when the porosity of the aggregate is 50% by volume or less, the aggregate is densified to increase the strength of the aggregate. For example, the electrode active material is mixed with a binder, a conductive additive, and a solvent. When the electrode slurry is prepared, the aggregates are less likely to collapse. As a result, the increase in the viscosity of the electrode slurry is suppressed and the fluidity is maintained, so that the coatability is improved and the electrode slurry is improved. The filling property of the electrode active material in the coating film can also be improved. In addition, when the aggregate collapses during electrode slurry preparation, the necessary amount of the binder that binds the electrode active materials increases, so the viscosity of the electrode slurry increases, the solid content concentration of the electrode slurry decreases, and the electrode occupies the weight of the positive electrode film The active material ratio is lowered, which is not preferable.

The tap density of the aggregate is preferably 1.0 g / cm ³ or more and 1.5 g / cm ³ or less.
Here, when the tap density of the aggregate is less than 1.0 g / cm ³ , the solid content of the electrode slurry is increased because the voids inside the aggregate and the amount of solvent retained in the aggregate gap increase when the electrode slurry is produced. This is not preferable because the concentration decreases, and therefore the time required for drying the coating film coated with the electrode slurry becomes longer. On the other hand, when the tap density of the aggregate exceeds 1.5 g / cm ³ , the filling property of the aggregate in the coating film coated with the electrode slurry becomes too high, and the solvent is difficult to volatilize during drying.

When this aggregate is a shell-shaped aggregate having voids inside, the size of the voids formed inside is preferably 80% or less, more preferably 70% of the diameter of the aggregate particles. It is as follows.
Here, when the size (diameter) of the voids exceeds 80% of the diameter of the aggregate particles, the shell shape of the aggregates cannot be maintained. Therefore, the concentration of the aromatic carbon compound vapor in the voids As a result, the film thickness of the carbonaceous film in the inner peripheral portion of the outer shell of the aggregate becomes thin and the internal resistance of the electrode active material becomes high, which is not preferable.

The ratio of the average film thickness of the carbonaceous film in the outer peripheral part and the inner peripheral part of the outer shell of the shell-like aggregate (the thickness of the inner peripheral carbonaceous film / the thickness of the outer carbonaceous film) is 0.7 or more and 1.3 or less is preferable.
Here, if the ratio of the average film thickness of the carbonaceous film in the outer peripheral part and the inner peripheral part of the outer shell (thickness of the inner peripheral carbonaceous film / thickness of the outer peripheral carbonaceous film) is out of the above range, aggregation occurs. Since the thickness of the carbonaceous film in the outer peripheral part or inner peripheral part of a body outer shell becomes thin and the internal resistance of an electrode active material becomes high, it is not preferable.

  In the electrode material of this embodiment, the porosity of the aggregate is set to 15% by volume or more and 50% by volume or less with respect to the volume when the aggregate is solid. It is possible to reduce the unevenness of the amount of the carbonaceous film formed on the substrate, and hence to reduce the unevenness of the electronic conductivity of the electrode active material. And, by using the electrode active material with reduced unevenness of electronic conductivity as the electrode material of the lithium ion battery, it becomes possible to perform the reaction related to the desorption / insertion of lithium ions uniformly over the entire surface of the electrode active material, The internal resistance can be reduced.

  Here, the above-mentioned “internal resistance” means a portion where a carbonaceous film is not formed on the surface of the electrode active material or a reaction resistance related to lithium ion desorption in a thin carbonaceous film is high. Specifically, it appears as the magnitude of the voltage drop at the end of discharge when used as an electrode active material of a lithium ion battery. That is, in the electrode active material in which the lithium ion desorption reaction is uniformly performed on the entire surface of the electrode active material, the voltage drop at the end of discharge is small, while the lithium ion desorption reaction resistance is partially on the surface of the electrode active material. In an electrode active material having a high value, a voltage drop at the end of discharge becomes significant.

[Method for producing electrode material]
The method for producing an electrode material according to the present embodiment includes an electrode active material or an electrode active material precursor and an organic compound, and the cumulative volume percentage of the particle size distribution of the electrode active material or the electrode active material precursor is 90%. The slurry having a ratio (D90 / D10) of not less than 5 and not more than 30 with respect to the particle diameter (D10) when the cumulative volume percentage of the particle diameter (D90) is 10% is dried. It is a method of firing in a non-oxidizing atmosphere of not lower than 1000 ° C and lower than 1000 ° C.

As the electrode active material, as described in the above 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.

Li _x A _y D compound represented by _z PO ₄ as _{(Li x A y D z PO} 4 particles) is used those produced by the solid phase method, liquid phase method, conventional methods such as vapor phase method be able to.
As the compound _{(Li x A y D z PO} 4 particles), for example, lithium acetate _(LiCH 3 COO), selected from the group consisting of lithium salts such as lithium chloride (LiCl), and lithium hydroxide, (LiOH) Li source, divalent iron salt such as iron chloride (II) (FeCl ₂ ), iron acetate (II) (Fe (CH ₃ COO) ₂ ), iron sulfate (II) (FeSO ₄ ), and phosphoric acid ( A slurry obtained by mixing a phosphate compound such as H ₃ PO ₄ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ), and water. The resulting mixture is hydrothermally synthesized using a pressure-resistant airtight container, and the resulting precipitate is washed with water to produce a cake-like precursor material, and the resulting cake-like precursor material is baked. _(Li x _A y _D z P ₄ particles) can be preferably used.

The Li _x A _y D _z PO ₄ particles may be crystalline particles or amorphous particles, or may be mixed crystal particles in which crystalline particles and amorphous particles coexist. Here, the reason that the Li _x A _y D _z PO ₄ particles may be amorphous particles is that the amorphous Li _x A _y D _z PO ₄ particles are non-oxidized at 500 ° C. or more and 1000 ° C. or less. This is because crystallization occurs when heat treatment is performed in a neutral atmosphere.

The size of the electrode active material is not particularly limited, but the average particle size of the primary particles is preferably 0.01 μm or more and 20 μm or less, more preferably 0.02 μm or more and 5 μm or less.
Here, the reason why the average particle diameter of the primary particles of the electrode active material is limited to the above range is that the surface of the primary particles is sufficiently thin film carbon if the average particle diameter of the primary particles is less than 0.01 μm. It is difficult to coat, and the discharge capacity at a high speed charge / discharge rate is lowered, and it is difficult to realize sufficient charge / discharge rate performance. On the other hand, the average particle size of primary particles is 20 μm. On the other hand, the internal resistance of the primary particles increases, and therefore, the discharge capacity at the high-speed charge / discharge rate becomes insufficient.

The shape of the electrode active material is not particularly limited, but it is easy to produce an electrode material composed of spherical, particularly spherical, secondary particles. Therefore, the shape of the electrode active material is also preferably spherical, particularly true spherical. It is.
Here, the reason why the shape of the electrode active material is preferably spherical is that the amount of solvent when preparing the positive electrode paste by mixing the electrode active material, the binder resin (binder), and the solvent. This is because the positive electrode paste can be easily applied to the current collector.

Moreover, if the shape of the electrode active material is spherical, the surface area of the electrode active material is minimized, and the amount of binder resin (binder) added to the electrode material mixture can be minimized and obtained. This is preferable because the internal resistance of the positive electrode can be reduced.
In addition, since the electrode active material is easily packed most closely, the filling amount of the positive electrode material per unit volume is increased, so that the electrode density can be increased, and as a result, the capacity of the lithium ion battery can be increased. Is preferable.

  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 this dissolution or dispersion, it is more preferable to add 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, a planetary ball mill, a vibration ball mill, A method using a medium agitation type dispersion apparatus that stirs medium particles such as a bead mill, a paint shaker, or an attritor at a high speed is preferable.

In this dissolution or dispersion, it is preferable that the electrode active material is dispersed as primary particles and then stirred so as to dissolve the organic compound. By doing so, the surface of the primary particles of the electrode active material is coated with the organic compound, and as a result, the carbon derived from the organic compound is uniformly interposed between the primary particles of the electrode active material.
Moreover, in the particle size distribution of the electrode active material or the precursor of the electrode active material in the slurry, the particles when the cumulative volume percentage of the particle size (D90) when the cumulative volume percentage of the particle size distribution is 90% is 10%. The dispersion conditions of the slurry, for example, the concentration of the electrode active material and the organic compound in the slurry, the stirring time, the stirring time, etc. are appropriately adjusted so that the ratio (D90 / D10) to the diameter (D10) is 5 or more and 30 or less. Good. Thereby, the tap density of the aggregate obtained by spraying and drying this slurry becomes 1.0 g / cm ³ or more.

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, for the purpose of removing organic components evaporated in the non-oxidizing atmosphere at the time of firing, it is possible to introduce a flammable and combustible gas such as oxygen (O ₂ ) into the inert atmosphere as necessary. .

  Also, the reason for setting the firing temperature to 500 ° C. or more and 1000 ° C. or less is that if the firing temperature is less than 500 ° C., the decomposition / reaction of the organic compound contained in the dried product does not proceed sufficiently, so that the organic compound is not carbonized. This is because, as a result, a high-resistance organic substance 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. As a result, not only composition deviation occurs in the electrode active material, but also the grain growth of the electrode active material is promoted, and as a result, the discharge capacity at a high-speed charge / discharge rate is lowered, and sufficient charge / discharge rate performance can be realized. It will be difficult.

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 surface of the primary particles of the electrode active material is coated with the carbon generated by the thermal decomposition of the organic compound in the dried product, and therefore, the secondary in which carbon is interposed between the primary particles of the electrode active material. Aggregates composed of particles are obtained.
This aggregate serves as an electrode material in the present embodiment.

  According to the electrode material of the present embodiment, the average particle diameter of the aggregate formed by aggregating the electrode active material particles having the carbonaceous film formed on the surface is 0.5 μm or more and 100 μm or less, and the pore diameter of the aggregate When the cumulative volume percentage of the distribution is 50%, the pore diameter (D50) is 0.1 μm or more and 0.2 μm or less, and the porosity of the aggregate is relative to the volume when the aggregate is solid. 15 vol% or more and 50 vol% or less, it is possible to reduce the unevenness of the amount of the carbonaceous film formed on the surface of the electrode active material, thereby reducing the electronic conductivity unevenness of the electrode active material. Can be reduced. Therefore, when used as an electrode material for a lithium ion battery, the internal resistance can be reduced.

  According to the method for manufacturing an electrode material of the present embodiment, the cumulative volume percentage of the particle size distribution of the electrode active material or the electrode active material precursor is 90, including the electrode active material or the electrode active material precursor and the organic compound. The slurry having a ratio (D90 / D10) of 5 or more and 30 or less with respect to the particle diameter (D10) when the cumulative volume percentage of the particle diameter (D90) at 10% is 10% is dried, and then the obtained dried product Is fired in a non-oxidizing atmosphere of 500 ° C. or higher and 1000 ° C. or lower, so that unevenness in the amount of carbonaceous film formed on the surface of the electrode active material can be reduced. An electrode material that can reduce the conductive unevenness can be easily manufactured.

EXAMPLES Hereinafter, although this invention is demonstrated concretely by Examples 1-5 and Comparative Examples 1-3, this invention is not limited by 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 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 with 2 L (liter) of water so that the total amount was 4 L. Thus, a uniform slurry mixture was prepared.
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 precursor.

Next, 150 g of this electrode active material precursor (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 placed in a ball mill, and slurry The ball mill stirring time was adjusted so that D90 / D10 of the particle size distribution of the precursor particles of the electrode active material therein was 7, and dispersion treatment was performed.
Next, the obtained slurry was sprayed into an air atmosphere at 180 ° C. and dried to obtain a dried product having an average particle size of 6 μm.
Next, the obtained dried product was fired in a nitrogen atmosphere at 700 ° C. for 1 hour to obtain an aggregate having an average particle size of 6 μm. This aggregate was used as the electrode material of Example 1.

(Evaluation of electrode material)
The pore size distribution (D50) of the aggregate of this electrode material, the porosity of the aggregate, the ratio of the average film thickness of the carbonaceous coating (the thickness of the inner peripheral carbonaceous coating / the thickness of the outer peripheral carbonaceous coating), tap The density and the coverage of the carbonaceous film were evaluated.
The evaluation method is as follows.

(1) Pore size distribution of aggregate (D50)
Measurement was performed using a mercury porosimeter.
(2) Porosity of aggregate It measured using the mercury porosimeter.
(3) Ratio of average film thickness of carbonaceous film The carbonaceous film of the aggregate is observed with a transmission electron microscope (TEM), and the thickness of the carbonaceous film on the inner periphery of the aggregate and the carbon on the outer periphery. The thickness of the carbonaceous film was measured, and the ratio of the average film thickness of the carbonaceous film (the thickness of the inner peripheral carbonaceous film / the thickness of the outer peripheral carbonaceous film) was calculated.

(4) Tap density Measured according to Japanese Industrial Standard JIS R 1628 "Method for measuring bulk density of fine ceramic powder".
(5) Covering rate of carbonaceous film The carbonaceous film of the aggregate is observed using a transmission electron microscope (TEM) and an energy dispersive X-ray spectrometer (EDX). The ratio of the covered part was calculated and used as the coverage.
The evaluation results are shown in Table 1.

(Production of lithium ion battery)
The above electrode material, 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 N-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 LiPF6 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 charge / discharge characteristics and internal resistance of this lithium ion battery were evaluated.
The evaluation method is as follows.

(1) Charging / discharging characteristics The above-described charging / discharging test of the lithium ion battery was performed at room temperature (25 ° C.) at a constant current of a cutoff voltage of 2-4.5 V and a charging / discharging rate of 1 C (after charging for 1 hour, 1 hour Discharge). The initial discharge capacity is shown in Table 2, and the charge / discharge characteristics are shown in FIG.
(2) Internal Resistance In the discharge curve shown in FIG. 1, the voltage drop observed at the end of discharge indicates the presence of the electrode active material not covered with the carbonaceous film. 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”.
The evaluation results are shown in Table 2.

"Example 2"
The electrode material and the lithium ion battery positive electrode were the same as in Example 1 except that the stirring time of the ball mill was adjusted so that D90 / D10 of the particle size distribution of the precursor particles of the electrode active material in the slurry was 10. Were prepared and evaluated. The evaluation results are shown in Tables 1 and 2.
In Example 2, the same voltage drop at the end of discharge as in Example 1 was observed.

"Example 3"
The electrode material and the lithium ion battery positive electrode were the same as in Example 1 except that the stirring time of the ball mill was adjusted so that D90 / D10 of the particle size distribution of the precursor particles of the electrode active material in the slurry was 20. Were prepared and evaluated. The evaluation results are shown in Tables 1 and 2.
In Example 3, the same voltage drop at the end of discharge as in Example 1 was observed.

Example 4
The electrode material and the positive electrode of the lithium ion battery were the same as in Example 1 except that the stirring time of the ball mill was adjusted so that D90 / D10 of the particle size distribution of the precursor particles of the electrode active material in the slurry was 25 Were prepared and evaluated. The evaluation results are shown in Tables 1 and 2.
In Example 4, the same voltage drop at the end of discharge as in Example 1 was observed.

"Example 5"
The electrode active material of Example 5 was the same as Example 1 except that manganese sulfate (II) (MnSO ₄ ) was used as the manganese source instead of iron sulfate (II) (FeSO ₄ ) serving as the iron source. The precursor of was obtained.
Then, in the same manner as in Example 1, except that the lithium iron phosphate precursor was added to the polyvinyl alcohol aqueous solution as the carbonization catalyst so as to have the same mass as the polyvinyl alcohol solid content in the polyvinyl alcohol aqueous solution. No. 5 electrode material and a lithium ion battery positive electrode were prepared and evaluated. The evaluation results are shown in Tables 1 and 2.
Note that. In Example 5, the same voltage drop at the end of discharge as in Example 1 was observed.

“Comparative Example 1”
The electrode material and the lithium ion battery were the same as in Example 1 except that the stirring time of the ball mill was adjusted so that D90 / D10 of the particle size distribution of the precursor particles of the electrode active material in the slurry was 1.5. A positive electrode was prepared and evaluated. The evaluation results are shown in Tables 1 and 2, and the charge / discharge characteristics are shown in FIG.

“Comparative Example 2”
The electrode material and the lithium ion battery positive electrode were the same as in Example 1 except that the stirring time of the ball mill was adjusted so that the D90 / D10 of the particle size distribution of the precursor particles of the electrode active material in the slurry was 3. Were prepared and evaluated. The evaluation results are shown in Tables 1 and 2.

“Comparative Example 3”
The electrode material and the positive electrode of the lithium ion battery were the same as in Example 1 except that the stirring time of the ball mill was adjusted so that D90 / D10 of the particle size distribution of the precursor particles of the electrode active material in the slurry was 40 Were prepared and evaluated. The evaluation results are shown in Tables 1 and 2.

According to the above result, the electrode material of Examples 1-5 has the ratio of the average film thickness of a carbonaceous film in the range of 0.7-1.3, compared with the electrode material of Comparative Examples 1-3. It was found that the tap density and the coverage of the carbonaceous film were high, and the unevenness of the loading amount of the carbonaceous film formed on the surface of the electrode active material was small. Moreover, the electrode material of Examples 1-5 has low internal resistance compared with the electrode material of Comparative Examples 1-3, and when it is used as an electrode material of a lithium ion battery, internal resistance can be lowered significantly. I understood.
Moreover, according to FIG. 1, it turned out that the electrode material of Example 1 has a high discharge capacity compared with the electrode material of the comparative example 1, and is excellent in discharge characteristics.

  In the electrode material of the present invention, the average particle diameter of the aggregate formed by aggregating the electrode active material particles having a carbonaceous film formed on the surface is 0.5 μm or more and 100 μm or less, and the pore size distribution of the aggregate is accumulated. When the volume percentage is 50%, the pore diameter (D50) is 0.1 μm or more and 0.2 μm or less, and the porosity of the aggregate is relative to the volume when the aggregate is solid. By setting the volume to 15% by volume or more and 50% by volume or less, it is possible to reduce the unevenness of the amount of the carbonaceous film formed on the surface of the electrode active material particles, and to reduce the unevenness of the electronic conductivity of the electrode active material. When used as an electrode material for a lithium ion battery, the internal resistance can be greatly reduced, so that the discharge characteristics of the lithium ion battery can be further improved. Smaller, lighter, it is possible to also apply to next-generation secondary battery that higher capacity can be expected, if the next generation of the secondary battery, the effect is very large.

Claims (7)

It consists of an aggregate formed by aggregating electrode active material particles having a carbonaceous film formed on the surface,
The average particle size of the aggregate is 0.5 μm or more and 100 μm or less,
When the cumulative volume percentage of the pore size distribution of the aggregate is 50%, the pore size (D50) is 0.1 μm or more and 0.2 μm or less,
The electrode material according to claim 1, wherein a porosity of the aggregate is 15% by volume or more and 50% by volume or less based on a volume when the aggregate is solid.   The electrode material according to claim 1, wherein 80% or more of the surface of the electrode active material is covered with the carbonaceous film. The aggregate is a shell-shaped aggregate having voids inside,
The ratio of the average film thickness of the carbonaceous film in the outer peripheral part and the inner peripheral part of the outer shell of the shell-shaped aggregate (the thickness of the inner peripheral carbonaceous film / the thickness of the outer carbonaceous film) is 0.7 or more The electrode material according to claim 1 or 2, wherein the electrode material is 1.3 or less.   The carbon content in the carbonaceous film is 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. Electrode material. 5. The electrode material according to claim 1, wherein a tap density of the aggregate is 1.0 g / cm ³ or more and 1.5 g / cm ³ or less. Select the electrode active material, lithium cobalt oxide, lithium nickel oxide, lithium manganate, lithium titanate and _{Li x A y D z PO 4} ( where, A is Co, Mn, Ni, Fe, Cu, from the group of Cr 1 or 2 or more, D is selected from the group consisting of Mg, Ca, S, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y, and rare earth elements The main component is one or more species selected from the group of 0 <x <2, 0 <y <1.5, 0 ≦ z <1.5). The electrode material according to any one of 5. Accumulation of particle diameter (D90) when electrode active material or electrode active material precursor and organic compound are included, and cumulative volume percentage of particle size distribution of electrode active material or electrode active material precursor is 90% A slurry having a ratio (D90 / D10) to a particle size (D10) of 5% to 30% when the volume percentage is 10% is dried.
Next, the obtained dried product is fired in a non-oxidizing atmosphere of 500 ° C. or higher and 1000 ° C. or lower.

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