JP2015106497A - Electrode material and electrode, and lithium ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode material low in internal resistance and excellent in high-speed charge/discharge rate characteristics, a method for producing the electrode material, an electrode, and a lithium ion battery.SOLUTION: An electrode material of the present invention comprises an agglomerated particle obtained by binding a plurality of primary particles each of which includes an electrode active material particle having a surface coated with a carbonaceous coat, the electrode active material particle comprising LiADPO(where, A represents one or two or more selected from the group consisting of Co, Mn, Ni, Fe, Cu and Cr, D represents one or two or more selected from the group consisting of Mg, Ca, S, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y and a rare earth element, and 0<x≤2, 0<y≤1.5 and 0≤z≤1.5 are satisfied). The primary particles have a part where the primary particles are bound to each other by fibrous carbon having an average diameter Dc of 1 nm or more and 100 nm or less and an average length Lc of 2 nm or more and 1 μm or less.

Description

  The present invention relates to an electrode material, an electrode, and a lithium ion battery, and in particular, a positive electrode material for a battery, an electrode material suitable for use in a positive electrode material for a lithium ion battery, and an electrode containing the electrode material, In addition, the present invention relates to a lithium ion battery including a positive electrode made of this electrode.

Conventionally, lithium ion batteries have been put into practical use as power sources for portable information devices and portable information terminals, and in recent years, have also been put into practical use as high-output power sources for electric vehicles, electric tools, and the like.
Conventionally, LiCoO ₂ or the like has been used as an electrode active material used for the positive electrode of these lithium ion batteries. From the viewpoint of stable supply of resources and the like, as an electrode active material replacing these electrode active materials, LiMnPO 4 is used. ₄ , olivine-based electrode materials having an olivine structure such as LiFePO ₄ have been studied.
However, such an olivine-based electrode material has a problem that the electron conductivity is low, and therefore, an olivine-based electrode material with improved electron conductivity has been studied and proposed.

As such an olivine-based electrode material, a first conductive material made of a carbon material such as carbon fiber or carbon nanotube is attached to the surface of the electrode active material particles, and the first conductive material is made of a fibrous carbon material. An electrode material combined with a second conductive material has been proposed (Patent Document 1). With this electrode material, the internal resistance of the battery can be reduced, the discharge characteristics due to a large current are good, and the life characteristics are also good.
In addition, fibrous carbon having a length of 0.5 to 5 μm and a diameter of 0.1 to 0.7 μm derived from the thermal decomposition of alcohol exists inside the aggregate obtained by agglomerating active material particles made of a lithium phosphate transition metal compound. An electrode material has been proposed (Patent Document 2). In this electrode material, it is said that high-rate charge / discharge performance is excellent by disposing fibrous carbon derived from the thermal decomposition of alcohol inside the aggregate.

Further, a film-like body containing carbon is attached to the surface of the active material particles containing lithium manganese phosphate, and these active material particles are carbonaceous protrusions derived from thermal decomposition of an organic substance containing an OH group and having a molecular weight of 500 or more. A connected electrode material has been proposed (Patent Document 3). This electrode material is obtained by adding ascorbic acid during hydrothermal synthesis of lithium manganese phosphate, adding polyvinyl alcohol, granulating and firing, and ascorbic acid-derived carbonaceous film and polyvinyl alcohol-derived carbonaceous protrusion. It is said that you can get things.
In this electrode material, it is said that the discharge capacity can be increased by connecting the active material particles with carbonaceous protrusions derived from the thermal decomposition of organic matter.

JP 2009-043514 A JP 2008-117749 A JP 2010-092599 A

Even in conventional olivine-based electrode materials, further improvement in electron conductivity is required. However, in the electrode material described in Patent Document 1, it is difficult to uniformly disperse the fibrous carbon material between the electrode active material particles, and thus it is difficult to further reduce the internal resistance of the electrode material. was there. In addition, carbon materials such as carbon fibers and carbon nanotubes are expensive, and thus there is a problem that the manufacturing cost is likely to be high and the use is limited.
Moreover, in the electrode material described in Patent Document 2, fibrous carbon having a length of 0.5 to 5 μm and a diameter of 0.1 to 0.7 μm derived from the thermal decomposition of alcohol is present inside the aggregate. However, there is a limit in reducing the internal resistance of the electrode material, and thus there is a problem that it is difficult to further reduce the internal resistance of the electrode material.

  Furthermore, also in the electrode material described in Patent Document 3, a film-like body containing carbon is attached to the surface of the active material particles containing lithium manganese phosphate, and the active material particles are separated from each other by carbon decomposition derived from thermal decomposition of organic matter. Since they are connected by protrusions, they can inhibit aggregation of active material particles and suppress grain growth during thermal decomposition, but there is still a limit to lowering the internal resistance of the electrode material. There is a problem that it is difficult to further reduce the internal resistance of the electrode material.

  The present invention has been made in order to solve the above-described problems, and an object thereof is to provide an electrode material having a small internal resistance and excellent in high-speed charge / discharge rate characteristics, a manufacturing method thereof, an electrode, and a lithium ion battery. And

As a result of intensive studies to solve the above problems, the present inventors have determined that the electrode material is Li _x A _y D _z PO ₄ (where A is a group of Co, Mn, Ni, Fe, Cu, Cr). One or more selected from D, 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 Primary particles obtained by coating the surface of electrode active material particles composed of one or more of the above, 0 <x ≦ 2, 0 <y ≦ 1.5, 0 ≦ z ≦ 1.5) with a carbonaceous film A part in which primary particles are bound by fibrous carbon having an average diameter Dc of 1 nm to 100 nm and an average length Lc of 2 nm to 1 μm. Can further reduce the internal resistance of the electrode material. It has been found that the high-speed charge / discharge rate characteristics can be further improved, and the present invention has been completed.

That is, the electrode material of the present invention is Li _x A _y D _z PO ₄ (where A is one or more selected from the group of Co, Mn, Ni, Fe, Cu, Cr, D is Mg, One or more selected from the group consisting of Ca, S, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y, and rare earth elements, 0 <x ≦ 2, 0 <Y ≦ 1.5, 0 ≦ z ≦ 1.5) composed of aggregated particles formed by combining a plurality of primary particles obtained by coating the surface of electrode active material particles with a carbonaceous film, The particles are characterized by having a portion bonded by fibrous carbon having an average diameter Dc of 1 nm to 100 nm and an average length Lc of 2 nm to 1 μm.

The average particle diameter Da of the primary particles is 0.01 μm or more and 4 μm or less. The average particle diameter Da and the average diameter Dc of the fibrous carbon are expressed by the following formula (1).
0.05 ≦ Dc / Da ≦ 0.5 (1)
It is preferable to satisfy.

The electrode of the present invention is characterized by containing the electrode material of the present invention.
The lithium ion battery of the present invention includes a positive electrode comprising the electrode of the present invention.

According to the electrode material of the present invention, Li _x A _y D _z PO ₄ (where A is one or more selected from the group of Co, Mn, Ni, Fe, Cu, Cr, D is Mg, One or more selected from the group consisting of Ca, S, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y, and rare earth elements, 0 <x ≦ 2, 0 <Y ≦ 1.5, 0 ≦ z ≦ 1.5) The primary particles formed by coating the surfaces of the electrode active material particles with a carbonaceous film have an average diameter Dc of 1 nm to 100 nm and an average Since the aggregated particles have a portion bonded by fibrous carbon having a length Lc of 2 nm or more and 1 μm or less, the internal resistance can be further reduced, and the high-speed charge / discharge rate characteristics can be further improved.

  According to the electrode of the present invention, since the electrode material of the present invention is contained, the internal resistance can be further reduced, and the high-speed charge / discharge rate characteristics can be further improved.

  According to the lithium ion battery of the present invention, since the positive electrode comprising the electrode of the present invention is provided, the internal resistance can be further reduced, and the high-speed charge / discharge rate characteristics can be further improved. Therefore, a lithium ion battery with excellent reliability can be provided.

It is a scanning electron microscope (SEM) image which shows the electrode material of Example 1 of this invention.

The electrode material of the present invention, its manufacturing method, the electrode, and the form for carrying out the lithium ion battery 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.

[Electrode material]
The electrode material of the present embodiment is Li _x A _y D _z PO ₄ (where A is one or more selected from the group of Co, Mn, Ni, Fe, Cu, and Cr, and 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, 0 <x ≦ 2, 0 < The surface of electrode active material particles (hereinafter sometimes simply referred to as Li _x A _y D _z PO ₄ particles) composed of y ≦ 1.5 and 0 ≦ z ≦ 1.5) is covered with a carbonaceous film. An electrode material composed of aggregated particles formed by combining a plurality of primary particles. The primary particles are in the form of fibers having an average diameter Dc of 1 nm to 100 nm and an average length Lc of 2 nm to 1 μm. It has a portion bonded by carbon.
Here, the bonded primary particles are preferably 5% or more, more preferably 10% or more, and further preferably 15% or more.
If the bonded primary particles are less than 5%, it may be difficult to obtain the effect of electron conductivity.

"Primary particles"
Li _x A _y D _z PO ₄ particles serving as nuclei of primary particles are one or more selected from the group of Co, Mn, Ni, Fe, Cu, Cr for A, Mg for D, One or two or more selected from the group of Ca, S, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y, and rare earth elements, 0 <x ≦ 2, It can take a range satisfying 0 <y ≦ 1.5 and 0 ≦ z ≦ 1.5, but for A, Co, Mn, Ni, Fe, for D, Mg, Ca, Sr, Ba, Ti, Zn and Al are preferable from the viewpoints of high discharge potential, abundant resources, safety, and the like.
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 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 500 ° C. or higher in a non-oxidizing atmosphere. In addition, when fired in a temperature range of 1000 ° C. or lower, crystallization occurs.

The average primary particle diameter of the Li _x A _y D _z PO ₄ particles is preferably 10 nm or more and 4000 nm or less, more preferably 20 nm or more and 1000 nm or less.
Here, the reason for limiting the average primary particle diameter of the _Li x _A y _D z PO ₄ particles within the above range, the average primary particle size of less than 10 nm, the surface of the _Li x _A y _D z PO ₄ particles It is difficult to sufficiently cover with a thin film-like carbonaceous film, the discharge capacity at a high speed charge / discharge rate is lowered, and it is difficult to realize sufficient charge / discharge rate performance. When the particle diameter exceeds 4000 nm, the internal resistance of the Li _x A _y D _z PO ₄ particles increases, and therefore, the discharge capacity at a high-speed charge / discharge rate becomes insufficient.

The shape of the Li _x A _y D _z PO ₄ particles is not particularly limited, but an electrode material composed of spherical, particularly spherical, aggregated particles can be easily formed. Therefore, the shape of the Li _x A _y D _z PO ₄ particles Also, a spherical shape, particularly a true spherical shape is preferable.
Here, the reason that the shape of the Li _x A _y D _z PO ₄ particles is preferably spherical is that the surface of the Li _x A _y D _z PO ₄ particles is made of carbon in order to improve the slipperiness between the spherical particles. The viscosity of the positive electrode paste in which an electrode material composed of agglomerated particles formed by combining a plurality of primary particles coated with a porous coating, a binder, and a solvent can be reduced, and this positive electrode paste This is because coating on the current collector becomes easy.

Further, if the shape of the Li _x A _y D _z PO ₄ particles is spherical, the surface area of the Li _x A _y D _z PO ₄ particles is minimized, and the amount of the binder added to the positive electrode paste is minimized. This is preferable because the internal resistance of the positive electrode obtained by this positive electrode paste can be reduced.
Furthermore, if the shape of the Li _x A _y D _z PO ₄ particles is spherical, the primary particles obtained by coating the surface of the Li _x A _y D _z PO ₄ particles with a carbonaceous film can be packed most closely. Thus, 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, which is preferable.

In the Li _x A _y D _z PO ₄ particles, in order to uniformly perform the reaction related to the desorption of lithium ions on the entire surface of the Li _x A _y D _z PO ₄ particles when used as an electrode material of a lithium ion battery, The entire surface of the Li _x A _y D _z PO ₄ particles is preferably covered with a carbonaceous film.
The thickness of the carbonaceous coating film of the _Li x _A y _D z surface of PO ₄ particles is preferably 0.1nm or more and 20nm or less.
Here, if the thickness of the carbonaceous film is less than 0.1 nm, the thickness of the carbonaceous film is too thin, and the surface of the Li _x A _y D _z PO ₄ particles is covered with the carbonaceous film. However, if the thickness of the carbonaceous film exceeds 20 nm, battery activity, for example, battery capacity per unit mass of the electrode material may be reduced. It is not preferable.

The average primary particle diameter of the primary particles, that is, Li _x A _y D _z PO ₄ particles whose surfaces are coated with a carbonaceous film is preferably 0.01 μm or more and 4 μm or less, more preferably 0.02 μm. Above and below 1 μm.
Here, the reason why the average primary particle diameter of the primary particles is limited to the above range is that when the average primary particle diameter is less than 0.01 μm, the primary particles are too small and the discharge capacity at the high-speed charge / discharge rate is low. The average primary particle diameter exceeds 4 μm, which increases the internal resistance of the primary particles, and therefore, high-speed charge / discharge. This is not preferable because the discharge capacity at the rate becomes insufficient.

"Agglomerated particles"
Aggregated particles are particles formed by combining a plurality of primary particles obtained by coating the surface of Li _x A _y D _z PO ₄ particles with a carbonaceous film, and the average particle diameter of the aggregated particles, that is, The average secondary particle diameter 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 secondary particle size of the aggregated particles is limited to the above range is that when the average secondary particle size is less than 0.5 μm, the aggregated particles are too fine to be easily produced, and a positive electrode paste is produced. On the other hand, when the average secondary particle diameter exceeds 100 μm, when the positive electrode (electrode) for a battery is produced, the diameter exceeds the thickness of the positive electrode after drying. This is because there is a high possibility that the agglomerated particles are present, and therefore, the uniformity of the film thickness of the electrode cannot be maintained.

The volume density of the aggregated particles is preferably 50% by volume or more and 80% by volume or less, more preferably 55% by volume or more and 75% by volume or less of the volume density when the aggregated particles are solid. 60 volume% or more and 75 volume% or less.
Here, the solid aggregated particles are aggregated particles having no voids. The density of the solid aggregated particles is obtained by coating the surface of Li _x A _y D _z PO ₄ particles with a carbonaceous film. It is assumed that it is equal to the theoretical density of the primary particles.

  The volume density of the agglomerated particles can be measured using a mercury porosimeter, and is calculated from the mass of the entire electrode material constituted by the agglomerated particles and the volume of the gap between the particles constituting the agglomerated particles. It is what is done. In other words, it is calculated from the particle gap inside the agglomerated particles obtained by removing the gap between the particles from the total volume of the particle gaps constituting the agglomerated particles, and the mass of the entire electrode material constituted by the agglomerated particles. It is the density of the aggregated particles to be formed.

In this aggregated particle, by setting the volume density to 50% by volume or more and 85% by volume or less, unevenness in the amount of the carbonaceous film formed on the surface of the Li _x A _y D _z PO ₄ particle can be reduced. Therefore, unevenness of the electronic conductivity of the aggregated particles can be reduced. Then, by using the aggregated particles with reduced electronic conductivity unevenness as the electrode material of the lithium ion battery, the reaction related to the desorption / insertion of lithium ions can be performed uniformly on the entire surface of the aggregated particles. Resistance can be reduced.

  Here, the above-mentioned “internal resistance” means a reaction resistance related to lithium ion desorption / insertion in the aggregated particles in which the carbonaceous film is not formed on the surface or the carbonaceous film is thin. A high point. Specifically, when this aggregated particle is used as an electrode active material of a lithium ion battery, it appears as the magnitude of the voltage drop at the end of discharge. That is, in the aggregated particles in which lithium ion deintercalation reaction is uniformly performed throughout the particles, the voltage drop at the end of discharge is small, while in the aggregated particles having high lithium ion deinsertion reaction resistance in a part of the surface, The voltage drop at the end of discharge becomes significant.

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 aggregated particles (the thickness of the carbonaceous film in the inner peripheral part / the thickness of the carbonaceous film in the outer peripheral part) is 0.7 or more and 2 0.0 or less is preferable.
Here, the ratio of the average film thickness of the carbonaceous film in the outer peripheral part and inner peripheral part of the outer shell of the aggregated particles (the thickness of the carbonaceous film in the inner peripheral part / the thickness of the carbonaceous film in the outer peripheral part) is within the above range. If it is outside, the thickness of the carbonaceous film on the outer peripheral part or inner peripheral part of the outer shell of the aggregated particles becomes thin, and the electric resistance of the carbonaceous film becomes higher depending on the location. This is not preferable because the internal resistance of the agglomerated particles uniformly performed on the entire surface of the particles is increased.

"Fibrous carbon"
The fibrous carbon is a net-like carbon in which at least a part of the primary particles are bonded to each other, and is generated when excess organic substances and the like at the time of forming the carbon coating layer are thermally decomposed. Examples of the carbon material close to fibrous carbon include single-walled carbon nanotubes (SCNT), double-walled carbon nanotubes (DCNT), multi-walled carbon nanotubes (MCNT), and carbon fibers (CF).
These carbon materials are sometimes used as additives for improving electrode characteristics (conductivity, etc.), but the fibrous carbon in the present embodiment is obtained by thermal decomposition of organic matter during the production of the carbon coating layer. Because it occurs, it differs from simply added carbon, and by bonding with the carbon coating layer, the contact resistance is lowered, the electron conductivity is easily improved, and there is an adhesion effect between the primary particles. .

The average diameter Dc of the fibrous carbon is 1 nm to 100 nm, more preferably 30 nm to 70 nm, and the average length Lc is 2 nm to 1 μm, more preferably 3 nm to 250 nm.
Here, the reason why the average diameter Dc of the fibrous carbon is in the above range is that if the average diameter Dc of the fibrous carbon is less than 1 nm, the fibrous carbon is too thin and the electrical conductivity is low. On the other hand, if the average diameter Dc of the fibrous carbon exceeds 100 nm, the fibrous carbon is too thick, so that it becomes difficult to enter between the primary particles (gap), and it does not contribute to the improvement of the conductivity between the primary particles. This is because it is not preferable.
The reason why the average length Lc of the fibrous carbon is in the above range is that when the average length Lc of the fibrous carbon exceeds 1 μm, the fibrous carbon is too long, and adhesion between primary particles. This is because the strength is weak and it is not preferable because it tends to collapse when granulated. Moreover, if the average length Lc of fibrous carbon is less than 2 nm, there is a possibility that the network cannot be maintained and flexibility cannot be obtained.

The average diameter Dc of the fibrous carbon and the average particle diameter Da of the primary particles are expressed by the following formula (2)
0.05 ≦ Dc / Da ≦ 0.5 (2)
It is preferable to satisfy.
Here, the reason why the average diameter Dc of the fibrous carbon and the average particle diameter Da of the primary particles satisfy the above formula (2) is that the range satisfying the formula (2) is around the primary particles. Is surrounded by fibrous carbon, and electrical conductivity is imparted by the fibrous carbon, so that the internal resistance of the agglomerated particles as the battery material can be made smaller than before, and the high-speed charge / discharge rate characteristics are further improved. This is because it can be improved.
Here, when Dc / Da is less than 0.05, the electron conductivity is lowered, which is not preferable. On the other hand, when Dc / Da exceeds 0.5, the ionic conductivity is inhibited. Therefore, it is not preferable.

[Method for producing electrode material]
The manufacturing method of the electrode material of this embodiment is Li _x A _y D _z PO ₄ (where A is one or more selected from the group of Co, Mn, Ni, Fe, Cu, Cr, and 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, 0 <x ≦ 2 , 0 <y ≦ 1.5, 0 ≦ z ≦ 1.5), obtained by spraying and drying a slurry containing an electrode active material or a precursor thereof, an organic compound, and a surfactant. The dried powder is baked in a temperature range of 500 ° C. or more and 1000 ° C. or less in a non-oxidizing atmosphere.

Next, this manufacturing method will be described in detail.
"Production of slurry"
First, an electrode active material composed of the above Li _x A _y D _z PO ₄ or a precursor thereof and an organic compound are dissolved or dispersed in a solvent to obtain a uniform slurry. In the dissolution or dispersion, a surfactant is preferably added, and a dispersant may be added.
The electrode active material composed of the above Li _x A _y D _z PO ₄ or a precursor thereof is not particularly limited as long as it becomes Li _x A _y D _z PO ₄ particles in the final step.

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.
As this compound, for example, a lithium source selected from the group consisting of lithium salts such as lithium acetate (LiCH ₃ COO), lithium chloride (LiCl), or hydroxides such as lithium hydroxide (LiOH), and Co, Mn, Ni such as divalent iron salts such as iron chloride (II) (FeCl ₂ ), iron acetate (II) (Fe (CH ₃ COO) ₂ ), iron sulfate (II) (FeSO ₄ ), etc. , Fe, Cu, or Cr, one or more metal salts selected from the group consisting of phosphoric acid (H ₃ PO ₄ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), and hydrogen phosphate dihydrogen A slurry mixture obtained by mixing a phosphate compound such as ammonium ((NH ₄ ) ₂ HPO ₄ ) and water is hydrothermally synthesized using a pressure-resistant sealed container, and the resulting precipitate is washed with water. To produce cake-like precursor material And a compound consisting of Li _x A _y D _z PO ₄ obtained by firing the cake of the precursor material is preferably used.

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

Surfactants include various types of cationic, anionic, amphoteric, and nonionic surfactants, but they do not affect battery characteristics and are easy to handle. An agent is preferably used. Examples of such surfactants include polyoxyethylene lauryl ether, polyoxyethylene tridecyl ether, polyoxyalkylene tridecyl ether, fatty acid sorbitan ester, fatty acid diethanolamide, alkyldimethylamine oxide, and alkylcarboxybetaine. It is done.
The mixing ratio of the surfactant to the organic compound is preferably 0.1 parts by mass or more and 12 parts by mass or less with respect to 100 parts by mass of carbon of the organic compound when the total amount of the organic compound is converted into the carbon amount. More preferably, it is 5.0 parts by mass or more and 7.0 parts by mass or less.

  As the solvent, water is preferable, but organic solvents such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol: IPA), butanol, pentanol, hexanol, octanol, diacetone alcohol and the like, acetic acid Esters such as ethyl, butyl acetate, ethyl lactate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, γ-butyrolactone, diethyl ether, ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (ethyl) Cellosolve), ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monomethyl ether, diethylene glycol monoethyl Ethers such as ether, acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), ketones such as acetylacetone and cyclohexanone, amides such as dimethylformamide, N, N-dimethylacetoacetamide and N-methylpyrrolidone, ethylene glycol And glycols such as diethylene glycol and propylene glycol. These may be used alone or in combination of two or more.

The compounding ratio of the electrode active material or its precursor and the organic compound is 0.6 parts by mass or more and 10 parts by mass with respect to 100 parts by mass of the electrode active material or its precursor when the total amount of the organic compound is converted into the amount of carbon. The amount is preferably not more than part by mass, more preferably not less than 0.8 part by mass and not more than 2.5 parts by mass.
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 on the surface of the Li _x A _y D _z PO ₄ particles obtained by synthesis is less than 80%. In other words, when the battery is configured, the discharge capacity at the high-speed charge / discharge rate becomes low, and it becomes 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 or its precursor is relatively low, and when the battery is configured, the capacity of the battery is reduced, Due to the excessive loading of the carbonaceous film, 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 or their precursors, organic compounds, and surfactants as necessary are dissolved or dispersed in a solvent to form a uniform slurry. In this dissolution or dispersion, it is more preferable to add a dispersant.
The method for dissolving or dispersing these in a solvent is not particularly limited as long as the electrode active material or its precursor is dissolved or dispersed and the organic compound and the surfactant are dissolved or dispersed. It is preferable to use a medium agitation type dispersion apparatus that agitates medium particles at high speed, such as a ball mill, a vibration ball mill, a bead mill, a paint shaker, and an attritor.

  In this dissolution or dispersion, it is preferable to disperse the electrode active material or its precursor as primary particles and then stir so as to dissolve the organic compound and the surfactant. In this way, the surface of the primary particles of the electrode active material or its precursor is coated with the organic compound, and the organic compound is interposed between the primary particles. As a result, the electrode active material Alternatively, carbon derived from an organic compound is uniformly interposed between primary particles of the precursor.

"Spraying and drying of slurry"
Next, this slurry is sprayed in a high-temperature atmosphere, for example, in the air of 70 ° C. or more and 250 ° C. or less and dried.
The average particle diameter of the droplets during the 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 dry powder 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.

The ambient temperature during spraying / drying affects the evaporation rate of the solvent in the slurry. Thereby, the evaporation rate of the solvent in the slurry can be controlled by controlling the atmospheric temperature, and thus the structure of the obtained dry powder can be controlled.
For example, the closer the ambient temperature is to the boiling point of the solvent in the slurry, the longer it takes to dry the droplets, and the resulting dry powder will shrink sufficiently. Therefore, it becomes difficult for the dry powder sprayed and dried near the boiling point of the solvent in the slurry to have a hollow structure.
On the other hand, when spraying / drying is performed at an atmospheric temperature considerably higher than the boiling point temperature of the solvent in the slurry, the droplets are instantaneously dried and the dry powder cannot be sufficiently contracted. Therefore, the obtained dry powder easily takes a hollow structure.

For example, when the solvent is water, the boiling point of water is 100 ° C. Therefore, in order to obtain a dry powder having a hollow structure, the atmospheric temperature should be set to 200 ° C. to 300 ° C., which is considerably higher than the boiling point of water. preferable.
The drying time can be controlled not only by the ambient temperature but also by a solvent having a different boiling point. As such a solvent, the above-described organic solvent having a boiling point different from that of water may be added to water, or a plurality of the above-described organic solvents having different boiling points may be mixed.
Thus, the drying obtained by appropriately adjusting the conditions of the particle size of the droplet during spraying, for example, the concentration of the electrode active material or its precursor in the slurry, the spraying pressure, the spraying speed, the ambient temperature, etc. It is possible to control the particle size distribution of the powder.

"Baking dry powder"
The dry powder obtained as described above is subjected to a temperature range of 500 ° C. or higher and 1000 ° C. or lower, preferably a temperature range of 600 ° C. or higher and 900 ° C. or lower, for 0.1 hour or longer and 40 hours in a non-oxidizing atmosphere. Hereinafter, firing is performed.
As this non-oxidizing atmosphere, an inert atmosphere made of an inert gas such as nitrogen (N ₂ ) or argon (Ar) is preferable. When it is desired to further suppress oxidation, hydrogen (H ₂ ) or the like is used as the inert gas. A reducing atmosphere to which about several percent of the reducing gas is added is preferable.
In addition, for the purpose of removing organic components evaporated in the non-oxidizing atmosphere at the time of firing, a flame-supporting or flammable gas such as oxygen (O ₂ ) may be introduced into the inert atmosphere as necessary. .

Here, 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., the decomposition / reaction of the organic compound contained in the dry powder does not proceed sufficiently, and therefore the carbonization of the organic compound As a result, high resistance organic matter decomposition products are present in the aggregated particles obtained by firing the dry powder, while the firing temperature is 1000 ° C. Exceeding this causes the Li in the dry powder to evaporate, resulting in not only compositional deviation in the resulting aggregated particles, but also grain growth in the aggregated particles, resulting in a low discharge capacity at a fast charge / discharge rate. This is because it becomes difficult to realize sufficient charge / discharge rate performance.
Moreover, it is possible to control the particle size distribution of the obtained aggregates by appropriately adjusting the conditions for firing the dry powder, for example, the rate of temperature rise, the maximum holding temperature, the holding time, and the like.

In this baking step, as a pretreatment step of this baking step, a step of holding the dry powder at a temperature considerably higher than room temperature (25 ° C.) is provided to generate network-like carbon between the primary particles. be able to.
In this step, in the same non-oxidizing atmosphere as described above, a (second) temperature range of 120 ° C. or more and 400 ° C. or less, preferably a (second) temperature range of 200 ° C. or more and 300 ° C. or less. Therefore, it is preferable to hold for 0.5 hours or more and 2 hours or less.

The reason why the holding temperature is set to 120 ° C. or more and 400 ° C. or less is considered to be that the film composed of the organic compound and the surfactant changes in a network shape so as to surround the primary particles in this temperature range. Because.
This change from film to network is considered to be due to shrinkage caused by dehydration and modification of the organic compound.
Here, when the holding temperature is less than 120 ° C., no change from a film shape to a mesh shape occurs, and when the holding temperature exceeds 400 ° C., the network structure is destroyed due to a rapid temperature change.

The holding time is the same as the holding temperature.
That is, when the holding time is less than 0.5 hours, no change from a film shape to a mesh shape occurs, whereas when the holding time exceeds 3 hours, the shape is caused by excessive dehydration due to being held at a high temperature for a long time. As a result of the change, the network structure is not destroyed and remains.

As described above, the surface of the electrode active material particles made of Li _x A _y D _z PO ₄ is coated with carbon generated by thermal decomposition of the organic compound in the dry powder, and a mesh-like structure is formed between the electrode active material particles. Agglomerated particles having a hollow structure in which the carbon atoms are interposed are obtained.
Therefore, the electrode material of this embodiment can be obtained.

[electrode]
The electrode of the present embodiment is an electrode containing the electrode material of the present embodiment.
In order to produce the electrode of this embodiment, the above-mentioned electrode material, a binder composed of a binder resin, and a solvent are mixed to prepare an electrode-forming paint or electrode-forming paste. At this time, a conductive aid such as carbon black may be added as necessary.
As the binder, that is, the binder resin, for example, polytetrafluoroethylene (PTFE) resin, polyvinylidene fluoride (PVdF) resin, fluororubber, and the like are preferably used.
The mixing ratio of the electrode material and the binder resin is not particularly limited. For example, the binder resin is 1 part by mass or more and 30 parts by mass or less, preferably 3 parts by mass or more and 20 parts by mass with respect to 100 parts by mass of the electrode material. Part or less.

  The solvent used for the electrode-forming paint or electrode-forming paste may be appropriately selected according to the properties of the binder resin. For example, water, methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol: IPA) , Butanol, pentanol, hexanol, octanol, diacetone alcohol and other alcohols, ethyl acetate, butyl acetate, ethyl lactate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, esters such as γ-butyrolactone, diethyl ether , Ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (ethyl cellosolve), ethylene glycol monobutyl ether (butyl celloso) B), ethers such as diethylene glycol monomethyl ether and diethylene glycol monoethyl ether, ketones such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), acetylacetone and cyclohexanone, dimethylformamide, N, N-dimethylacetoacetamide, N -Amides such as methylpyrrolidone, and glycols such as ethylene glycol, diethylene glycol, and propylene glycol. These may be used alone or in combination of two or more.

Next, this electrode-forming paint or electrode-forming paste is applied to one side of the metal foil, and then dried to form a coating film comprising a mixture of the above electrode material and binder resin on one side. Get a metal foil.
Next, this coating film is pressure-bonded and dried to produce a current collector (electrode) having an electrode material layer on one surface of the metal foil.
In this way, the electrode of this embodiment can be produced.
With this electrode, the internal resistance can be further reduced, and the high-speed charge / discharge rate characteristics can be further improved.

[Lithium ion battery]
The lithium ion battery of this embodiment includes a positive electrode made of the electrode of this embodiment, a negative electrode made of metal Li, Li alloy, Li ₄ Ti ₅ O ₁₂ , a carbon material, etc., and an electrolyte solution and a separator or a solid electrolyte. Yes.
In this lithium ion battery, the internal resistance can be further reduced and the high-speed charge / discharge rate characteristics can be further improved by producing an electrode using the electrode material of the present embodiment. Therefore, a lithium ion battery with excellent reliability can be provided.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely by Examples 1-6 and Comparative Examples 1-4, this invention is not limited by these Examples.

"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 airtight container having a capacity of 8 L, and hydrothermal synthesis was performed at 200 ° 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 in which 20 g of polyvinyl alcohol (PVA: polymerization degree 1500) as an organic compound was dissolved in 200 g of water, and the total amount of polyvinyl alcohol were converted to carbon. A nonionic surfactant polyoxyethylene lauryl ether in an amount corresponding to 6% by mass of the amount of carbon at the time and 500 g of zirconia balls having a diameter of 5 mm as media particles are placed in a ball mill for dispersion treatment to obtain a precursor slurry. It was.

Next, this precursor slurry was sprayed into an air atmosphere at 210 ° C. and dried to obtain a dry powder having an average particle diameter of 7 μm.
Next, this dry powder was held at 250 ° C. for 1 hour in a nitrogen atmosphere, and then fired at 700 ° C. for 1 hour to obtain an aggregate having an average particle size of 7 μm, which was used as the electrode material of Example 1 .
When this electrode material was observed with a scanning electron microscope (SEM), the average particle diameter Da of the primary particles was 200 nm. Moreover, when the aggregate was observed, it was found that fibrous carbon having an average diameter of 60 nm and an average length of 0.5 μm was contained.
From these numerical values, it was found that the ratio (Dc / Da) of the average diameter Dc of the fibrous carbon to the average particle diameter Da of the primary particles was 0.3.
FIG. 1 shows a scanning electron microscope (SEM) image of this electrode material.

(Preparation of positive electrode)
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, and the mixture was kneaded for 30 minutes at a revolution of 1200 rpm and a rotation of 800 rpm using a kneader Awatori Netaro (manufactured by Sinky) to prepare a positive electrode paste.

In this positive electrode paste, the viscosity of the positive electrode paste and the film thickness of the obtained electrode vary depending on the amount of N-methyl-2-pyrrolidinone (NMP) added. Therefore, the amount of N-methyl-2-pyrrolidinone (NMP) added was adjusted so as to have a constant film thickness (μm).
Next, this positive electrode paste was applied onto an aluminum (Al) foil having a thickness of 15 μm as a current collector 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.

(Preparation of negative electrode)
Artificial graphite powder as a negative electrode active material and polyvinylidene fluoride (PVdF) as a binder are mixed at a mass ratio of 95: 5, and N-methyl-2-pyrrolidinone (NMP) is added as a solvent. The mixture was kneaded at a revolution of 1200 rpm and a rotation of 800 rpm for 30 minutes using a kneader Mazerustar (Kurabo Co., Ltd.) to prepare a negative electrode paste.
Subsequently, this negative electrode paste 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 produced the negative electrode of the lithium ion battery of Example 1. FIG.

(Production of lithium ion battery)
The above negative electrode was disposed with respect to the above positive electrode, 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 above battery member was immersed in the above electrolyte solution and laminated to produce a lithium ion battery of Example 1.
Here, there is a column for comparison with the conventional product, but the conventional product has no fibrous carbon between the particles, and Comparative Example 2 corresponds to this in this embodiment.

(Evaluation)
Each of the charge / discharge characteristics and rate characteristics of the lithium ion battery was evaluated.
The evaluation method is as follows.
(1) Charging / discharging characteristics The charging / discharging test of the above 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 0.1 C (after charging for 10 hours, 0.1 hour discharge). As a result, the initial discharge capacity was 160 mAh / g.
Here, the case where it was superior to the initial discharge capacity of the conventional lithium ion battery was indicated as “◯”, and the case where it was equal or less than that was indicated as “X”.

(2) Rate characteristics The above lithium ion battery rate characteristics evaluation test was conducted at room temperature (25 ° C) with a cutoff voltage of 2-4.5 V, a charge rate of 0.1 C, and a discharge rate of 3 C (after 10 hours of charging). , 20 minutes discharge).
Here, the rate ratio was evaluated by the capacity ratio of 3C discharge and 0.1C discharge (0.1C / 3C). As a result, the capacity ratio (0.1C / 3C) was 0.91.
Here, the case where it was superior to the initial discharge capacity of the conventional lithium ion battery was indicated as “◯”, and the case where it was equal or less than that was indicated as “X”.

(3) Handling property Handling property of each of the positive electrode paste and the coating film was evaluated. Here, the viscosity of the positive electrode paste and the adhesion of the coating film obtained by applying this positive electrode paste were evaluated.
In general, if the viscosity of the positive electrode paste is too high, it becomes difficult to handle simply, and the mixing step in producing the positive electrode paste tends to be insufficient, and thus the uniformity of the coating film is lost. Moreover, when the viscosity of the positive electrode paste is too low, an electrode having a desired film thickness cannot be obtained.
Moreover, when the adhesiveness of a coating film is low, an electrode will peel off during the process of producing a battery, or during charging / discharging evaluation, and charging / discharging will become impossible.

Therefore, the viscosity of the positive electrode paste was compared with that of a conventional positive electrode paste, which was widely used.
In addition, the adhesion of the coating film is “O” when the electrode is in close contact with the current collector when the lithium ion battery after the evaluation of the charge / discharge characteristics and the rate characteristics is disassembled, and the electrode is the current collector. The case where it was peeled off was designated as “x”.
These evaluation results are shown in Table 1.

"Example 2"
A dry powder was obtained according to Example 1 and used as the dry powder of Example 2.
Next, this dry powder was held at 200 ° C. for 0.5 hours in a nitrogen atmosphere, and then fired at 700 ° C. for 1 hour to obtain an aggregate having an average particle diameter of 7 μm. The electrode material of Example 2 It was.
When this electrode material was observed with a scanning electron microscope (SEM), the average particle diameter Da of the primary particles was 200 nm. Moreover, when the aggregate was observed, it was found that fibrous carbon having an average diameter of 10 nm and an average length of 0.3 μm was contained.
From these numerical values, it was found that the ratio (Dc / Da) of the average diameter Dc of the fibrous carbon to the average particle diameter Da of the primary particles was 0.05.

(Production of lithium ion battery)
Using the above electrode material, a lithium ion battery of Example 2 was produced according to Example 1, and evaluated according to Example 1.
These evaluation results are shown in Table 1.

"Example 3"
A dry powder was obtained according to Example 1 and used as the dry powder of Example 3.
Subsequently, this dry powder was held at 300 ° C. for 0.5 hours in a nitrogen atmosphere, and then fired at 700 ° C. for 1 hour to obtain an aggregate having an average particle diameter of 7 μm. The electrode material of Example 3 It was.
When this electrode material was observed with a scanning electron microscope (SEM), the average particle diameter Da of the primary particles was 200 nm. Moreover, when the aggregate was observed, it was found that fibrous carbon having an average diameter of 100 nm and an average length of 0.8 μm was contained.
From these numerical values, it was found that the ratio (Dc / Da) of the average diameter Dc of the fibrous carbon to the average particle diameter Da of the primary particles was 0.5.

(Production of lithium ion battery)
Using the electrode material described above, a lithium ion battery of Example 3 was produced according to Example 1, and evaluated according to Example 1.
These evaluation results are shown in Table 1.

Example 4
A dry powder was obtained according to Example 1 and used as the dry powder of Example 4.
Next, the dried powder was held at 250 ° C. for 0.5 hours in a nitrogen atmosphere, and then fired at 700 ° C. for 1 hour to obtain an aggregate having an average particle size of 7 μm. The electrode material of Example 4 It was.
When this electrode material was observed with a scanning electron microscope (SEM), the average particle diameter Da of the primary particles was 200 nm. Moreover, when the aggregate was observed, it was found that fibrous carbon having an average diameter of 30 nm and an average length of 1 μm was contained.
From these numerical values, it was found that the ratio (Dc / Da) of the average diameter Dc of the fibrous carbon to the average particle diameter Da of the primary particles was 0.15.

(Production of lithium ion battery)
Using the above electrode material, a lithium ion battery of Example 4 was produced according to Example 1, and evaluated according to Example 1.
These evaluation results are shown in Table 1.

"Comparative Example 1"
The precursor slurry and dry powder of Comparative Example 1 were obtained in the same manner as Example 1 except that no polyvinyl alcohol was added.
Next, this dry powder was held at 250 ° C. for 1 hour in a nitrogen atmosphere, and then fired at 700 ° C. for 1 hour to obtain an aggregate having an average particle size of 7 μm, which was used as the electrode material of Comparative Example 1. .
When this electrode material was observed with a scanning electron microscope (SEM), the average particle diameter Da of the primary particles was 200 nm. Moreover, when the aggregate was observed, fibrous carbon was not present inside.

(Production of lithium ion battery)
Using the electrode material described above, a lithium ion battery of Comparative Example 1 was produced according to Example 1, and evaluated according to Example 1.
These evaluation results are shown in Table 1.

"Comparative Example 2"
The precursor slurry and dry powder of Comparative Example 2 were obtained in the same manner as in Example 1 except that the nonionic surfactant was not added.
Next, this dry powder was held at 250 ° C. for 1 hour in a nitrogen atmosphere, and then fired at 700 ° C. for 1 hour to obtain an aggregate having an average particle diameter of 7 μm, which was used as the electrode material of Comparative Example 2. .
When this electrode material was observed with a scanning electron microscope (SEM), the average particle diameter Da of the primary particles was 200 nm. Moreover, when the aggregate was observed, fibrous carbon was not present inside.
In addition, as above-mentioned, since this comparative example 2 does not have fibrous carbon, it is equivalent to the conventional general electrode material.

(Production of lithium ion battery)
Using the electrode material described above, a lithium ion battery of Comparative Example 2 was produced according to Example 1, and evaluated according to Example 1.
Since this comparative example 2 is a standard for evaluation as a conventional product, in Table 1 showing the evaluation results, evaluation by “◯” and “×” is not performed, and all evaluation items are set to “−”.

“Comparative Example 3”
A dry powder was obtained according to Example 1 and used as the dry powder of Comparative Example 3.
Next, this dry powder was held at 200 ° C. for 3 hours in a nitrogen atmosphere, and then fired at 700 ° C. for 1 hour to obtain an aggregate having an average particle diameter of 7 μm, which was used as the electrode material of Comparative Example 3. .
When this electrode material was observed with a scanning electron microscope (SEM), the average particle diameter Da of the primary particles was 200 nm. Moreover, when the aggregate was observed, it was found that fibrous carbon having an average diameter of 4 nm and an average length of 0.1 μm was contained.
From these numerical values, it was found that the ratio (Dc / Da) of the average diameter Dc of the fibrous carbon to the average particle diameter Da of the primary particles was 0.02.

(Production of lithium ion battery)
Using the above electrode material, a lithium ion battery of Comparative Example 3 was produced according to Example 1, and evaluated according to Example 1.
These evaluation results are shown in Table 1.

“Comparative Example 4”
A cake-like electrode active material precursor was obtained according to Example 1.
Next, 150 g of this electrode active material precursor (in terms of solid content), a polyvinyl alcohol aqueous solution in which 20 g of polyvinyl alcohol (PVA: polymerization degree 1500) as an organic compound is dissolved in 200 g of water, an average diameter of 1.5 nm, an average length A single-walled carbon nanotube (SCNT) having a thickness of 1 μm and 500 g of zirconia balls having a diameter of 5 mm as medium particles were placed in a ball mill for dispersion treatment to obtain a precursor slurry.

Next, using this precursor slurry, an electrode material of Comparative Example 4 was obtained according to Example 1.
When this electrode material was observed with a scanning electron microscope (SEM), the average particle diameter Da of the primary particles was 200 nm. Moreover, when the aggregate was observed, fibrous carbon was present inside, but the primary particles were not bound to each other.

(Production of lithium ion battery)
Using the electrode material described above, a lithium ion battery of Comparative Example 4 was produced according to Example 1, and evaluated according to Example 1.
These evaluation results are shown in Table 1.

"Comparative Example 5"
The precursor slurry and dry powder of Comparative Example 5 were obtained in the same manner as in Example 1 except that ascorbic acid was used instead of polyvinyl alcohol (PVA).
Next, this dry powder was held at 250 ° C. for 1 hour in a nitrogen atmosphere, and then fired at 700 ° C. for 1 hour to obtain an aggregate having an average particle diameter of 7 μm, which was used as the electrode material of Comparative Example 5. .
When this electrode material was observed with a scanning electron microscope (SEM), the average particle diameter Da of the primary particles was 200 nm. Moreover, when the aggregate was observed, fibrous carbon was not present inside.

(Production of lithium ion battery)
Using the electrode material described above, a lithium ion battery of Comparative Example 5 was produced according to Example 1, and evaluated according to Example 1.
These evaluation results are shown in Table 1.

According to said evaluation result, in the electrode material of Examples 1-4, it turned out that internal resistance can be made still smaller and a high-speed charge / discharge rate characteristic can be improved further.
On the other hand, in the electrode material of Comparative Example 1, since polyvinyl alcohol (PVA) was not added, both the initial discharge capacity and the high-speed charge / discharge rate characteristics were significantly reduced.
In the electrode material of Comparative Example 2, since the nonionic surfactant was not added, the initial discharge capacity was not inferior to that of Examples 1 to 4, but the high-speed charge / discharge rate characteristics were significantly reduced.
In the electrode material of Comparative Example 3, since the average diameter of the fibrous carbon was outside the range of the present invention, the initial discharge capacity was not inferior to that of Examples 1 to 4, but the high-speed charge / discharge rate characteristics were significantly reduced. It was.
In the electrode material of Comparative Example 4, since the fibrous carbon was not a fibrous carbon derived from polyvinyl alcohol, the viscosity of the positive electrode paste was high and the adhesion of the coating film was low.
In the electrode material of Comparative Example 5, since ascorbic acid was used instead of polyvinyl alcohol (PVA), the initial discharge capacity was not inferior to that of Examples 1 to 4, but the high-speed charge / discharge rate characteristics were significantly reduced.

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.

Electrode material of the present _{invention, Li x A y D z PO} 4 ( where, A is Co, Mn, Ni, Fe, Cu, 1 or two or more elements selected from a group consisting of 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, 0 <x ≦ 2, 0 <y ≦ 1.5, 0 ≦ z ≦ 1.5), the primary particles formed by coating the surfaces of the electrode active material particles with a carbonaceous film have an average diameter Dc of 1 nm to 100 nm and an average length. By making the agglomerated particles having portions bonded by fibrous carbon having an Lc of 2 nm or more and 1 μm or less, the internal resistance can be further reduced, and the high-speed charge / discharge rate characteristics can be further improved. Because it is smaller, lighter, and higher volume The present invention can be applied to a next-generation secondary battery that is expected to be quantified. In the case of a next-generation secondary battery, the effect is very large.

Claims (4)

Li _x A _y D _z PO ₄ (where A is one or more selected from the group of Co, Mn, 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, 0 <x ≦ 2, 0 <y ≦ 1.5, 0 ≦ z ≦ 1.5) consisting of agglomerated particles formed by combining a plurality of primary particles obtained by coating the surfaces of electrode active material particles with a carbonaceous film,
The electrode material, wherein the primary particles have a portion bonded by fibrous carbon having an average diameter Dc of 1 nm to 100 nm and an average length Lc of 2 nm to 1 μm. The average particle diameter Da of the primary particles is 0.01 μm or more and 4 μm or less,
The average particle diameter Da and the average diameter Dc of the fibrous carbon are expressed by the following formula (1).
0.05 ≦ Dc / Da ≦ 0.5 (1)
The electrode material according to claim 1, wherein:   An electrode comprising the electrode material according to claim 1 or 2.   A lithium ion battery comprising a positive electrode comprising the electrode according to claim 3.