JP6501014B1 - Positive electrode material for lithium ion secondary battery, method for producing the same, electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode material for lithium ion secondary battery capable of improving Li ion conductivity and electron conductivity, a method for producing the positive electrode material, an electrode for lithium ion secondary battery using the positive electrode material, and charging Provided is a lithium ion secondary battery with improved discharge characteristics. A positive electrode material for a lithium ion secondary battery, which comprises aggregated particles in which a plurality of primary particles of a positive electrode active material represented by the following general formula (1) coated with a carbonaceous film are aggregated, A positive electrode material for a lithium ion secondary battery, wherein the compressive strength per diameter is 1.0 MPa / μm or more and 10.0 MPa / μm or less. LixAyDzPO4 (1) (wherein A is at least one selected from the group consisting of Co, Mn, Ni, Fe, Cu and Cr, D is Mg, Ca, Sr, Ba, Ti, Zn, B, Al, Ga , In, Si, Ge, Sc and Y, at least one selected from the group consisting of 0.9 <x <1.1, 0 <y ≦ 1, 0 ≦ z <1, 0.9 <y + z <1 It is .1) 【Selection figure】 None

Description

  The present invention relates to a positive electrode material for a lithium ion secondary battery, a method of manufacturing the positive electrode material, an electrode for a lithium ion secondary battery using the positive electrode material, and a lithium ion secondary battery provided with the electrode.

Lithium ion secondary batteries have higher energy density and power density than lead batteries and nickel hydrogen batteries, and are used in various applications such as small-sized electronic devices such as smartphones, home backup power supplies, and electric tools. In addition, commercialization of large-capacity lithium ion secondary batteries for renewable energy storage such as solar power generation and wind power generation is in progress.
The lithium ion secondary battery comprises a positive electrode, a negative electrode, an electrolyte and a separator. The electrode material constituting the positive electrode has a property capable of reversibly de-inserting lithium ions such as lithium cobaltate (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium iron phosphate (LiFePO ₄ ), etc. Lithium-containing metal oxides are used, and improvements are being considered from various viewpoints such as high capacity, long life, improved safety, and low cost of batteries.

Lithium iron phosphate (LiFePO ₄ ), which is the electrode material, is a material that is easy to reduce in cost because it is rich in resources and uses inexpensive iron. Lithium iron phosphate has excellent safety that is not outstanding in oxide-based cathode materials represented by lithium cobaltate, such as having excellent safety because there is no oxygen release at high temperature due to strong covalent bond of phosphorus and oxygen Have.
On the other hand, lithium iron phosphate is inferior in the input / output characteristics to the oxide-based positive electrode material because the diffusivity of Li ions and the electron conductivity are low. Since this characteristic difference becomes more pronounced when the battery operating temperature is low, lithium iron phosphate is considered to be unsuitable for in-vehicle applications such as hybrid vehicles where high input / output characteristics are required in the low temperature region. It has

LiMPO ₄ (M is a metal element) having an olivine structure typified by lithium iron phosphate has a low Li ion diffusion property and low electron conductivity, and thus the primary particles of LiMPO ₄ are made finer and individual primary particles thereof The charge and discharge characteristics can be improved by coating the surface with a conductive carbonaceous film.
On the other hand, since the finely divided LiMPO ₄ has a large specific surface area, it requires thickening of the electrode mixture slurry and a large amount of binder, so primary particles coated with a carbonaceous film are granulated to form secondary particles. It is general to improve the properties of the electrode mixture slurry by setting it as above.

  For example, as an electrode material, in Patent Document 1, primary particle crystals aggregate to form spherical secondary particles, and base particles comprising lithium nickel manganese composite oxide having voids on the surface and inside of the secondary particles. There is disclosed a positive electrode active material for a lithium secondary battery, comprising: and a conductive fine powder filled in a part of the voids of the matrix particles. Further, Patent Document 2 discloses a positive electrode active material for a lithium secondary battery, which contains particles having voids inside secondary particles.

JP, 2009-117241, A JP, 2015-018678, A

  The electrode mixture layer is formed by applying, drying, and pressing an electrode slurry obtained by mixing an electrode material, a conductive additive, a binder, and the like on an aluminum current collector. However, in the electrode materials described in Patent Documents 1 and 2, since the secondary particles have voids (hollow secondary particles), the secondary particles are excessively deformed or broken during pressing, or the conductive carbonaceous material Peeling of the coating causes deterioration of the battery characteristics. Moreover, the electrode structure becomes nonuniform due to the voids present in the secondary particles, and the Li ion conductivity and the electron conductivity decrease.

  The present invention has been made in view of such circumstances, and a positive electrode material for lithium ion secondary batteries capable of improving Li ion conductivity and electron conductivity, a method of manufacturing the positive electrode material, and the positive electrode An object of the present invention is to provide an electrode for a lithium ion secondary battery using the material, and a lithium ion secondary battery having improved charge and discharge characteristics.

  MEANS TO SOLVE THE PROBLEM The present inventors discovered that the said subject could be solved by the following invention, as a result of earnestly examining in order to solve said subject.

[1] A positive electrode material for a lithium ion secondary battery comprising aggregated particles in which a plurality of primary particles of a positive electrode active material represented by the following general formula (1) coated with a carbonaceous film are aggregated, which has a unit particle diameter The positive electrode material for a lithium ion secondary battery characterized by having a compressive strength of 1.0 MPa / μm or more and 10.0 MPa / μm or less.
Li _x A _y D _z PO ₄ (1)
(Wherein A is at least one member selected from the group consisting of Co, Mn, Ni, Fe, Cu and Cr, D is Mg, Ca, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si , Ge, Sc and Y, at least one selected from the group consisting of 0.9 <x <1.1, 0 <y ≦ 1, 0 ≦ z <1, 0.9 <y + z <1.1 .)
[2] A particle diameter (D50) of a 50% cumulative percentage in the cumulative particle size distribution of the positive electrode material is 2 μm to 10 μm, and a particle diameter (D90) of a 90% cumulative percentage is 15 μm or less ] The positive electrode material for lithium ion secondary batteries as described in these.
[3] The oil absorption amount using N-methyl-2-pyrrolidone of the positive electrode material is 60 ml / 100 g or less, and the tap density is 1.0 g / cm ³ or more. The positive electrode material for lithium ion secondary batteries as described in 4.
[4] The positive electrode material for a lithium ion secondary battery according to any one of the above [1] to [3], wherein the specific surface area of the positive electrode material is 8 m ² / g to 30 m ² / g.
[5] At least a process selected from the group consisting of a process for producing a positive electrode active material and a positive electrode active material precursor represented by the general formula (1), and a positive electrode active material and a positive electrode active material precursor obtained in the process A slurry preparation step of mixing one kind of positive electrode active material raw material and water to prepare a slurry, a crushing step of crushing the positive electrode active material raw material slurry obtained in the step, and the step An organic compound which is a carbonaceous film precursor is added to the crushed slurry thus obtained, and a granulating step for obtaining a granulated product, and a calcinating step of firing the granulated product obtained in the step under a non-oxidative atmosphere And the ratio of the crystallite diameters of the positive electrode active material particles before and after the crushing treatment (crystallite diameter after crushing / crystallite diameter before crushing) is 0.85 or more. The lithium according to any one of the above [1] to [4], which is 0.96 or less Method for producing a cathode material for ion secondary battery.
[6] An electrode for a lithium ion secondary battery comprising an aluminum current collector and a positive electrode mixture layer formed on the aluminum current collector, wherein the positive electrode mixture layer is any one of the above [1] to An electrode for a lithium ion secondary battery comprising the positive electrode material for a lithium ion secondary battery according to any one of [4].
[7] A lithium ion secondary battery having a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode is an electrode for a lithium ion secondary battery according to the above [6]. Next battery.

  According to the present invention, a positive electrode material for a lithium ion secondary battery capable of improving Li ion conductivity and electron conductivity, a method for producing the positive electrode material, and an electrode for a lithium ion secondary battery using the positive electrode material And a lithium ion secondary battery with improved charge and discharge characteristics.

5 is a graph showing the particle diameter of the positive electrode active material particles of Example 1 and Comparative Example 1 on the horizontal axis, and the cumulative frequency of the positive electrode active material particles with respect to each particle diameter on the horizontal axis on the vertical axis. 5 is a graph showing the particle size distribution of positive electrode active material particles of Example 1 and Comparative Example 1; It is a microscope image which shows the measurement of the compressive strength of the positive electrode material for lithium ion secondary batteries obtained by the Example and the comparative example.

An embodiment of the positive electrode material for a lithium ion secondary battery of the present invention will be described.
The present embodiment is specifically described in order to better understand the spirit of the invention, and does not limit the present invention unless otherwise specified.

<Positive material for lithium ion secondary battery>
The positive electrode material for a lithium ion secondary battery of the present embodiment includes aggregated particles in which a plurality of primary particles of a positive electrode active material represented by the following general formula (1) coated with a carbonaceous film are aggregated. Moreover, it is characterized in that the compressive strength per unit particle size is 1.0 MPa / μm or more and 10.0 MPa / μm or less.
Li _x A _y D _z PO ₄ (1)
(Wherein A is at least one member selected from the group consisting of Co, Mn, Ni, Fe, Cu and Cr, D is Mg, Ca, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si , Ge, Sc and Y, at least one selected from the group consisting of 0.9 <x <1.1, 0 <y ≦ 1, 0 ≦ z <1, 0.9 <y + z <1.1 .)

The positive electrode active material used in the present invention is represented by the above general formula (1).
Here, for A, Co, Mn, Ni and Fe are preferable, and Fe is more preferable. As for D, Mg, Ca, Sr, Ba, Ti, Zn and Al are preferable. When the electrode active material contains these elements, it is possible to obtain a positive electrode mixture layer capable of realizing high discharge potential and high safety. Moreover, it is preferable as a material to be selected because it is abundant in resources.

The average primary particle diameter of the primary particles (carbonaceous coated electrode active material) of the positive electrode active material represented by the above general formula (1) coated with the carbonaceous film is preferably 10 nm or more and 400 nm or less, and more preferably The thickness is 20 nm or more and 300 nm or less, more preferably 20 nm or more and 200 nm or less.
When the average primary particle diameter of the primary particles is 10 nm or more, the increase in the mass of carbon required by the increase in the specific surface area of the primary particles of the positive electrode active material is suppressed, and the charge / discharge capacity per unit mass of the positive electrode material is It is possible to suppress the reduction. In addition, the surface of the primary particles of the positive electrode active material can be easily covered with the carbonaceous film uniformly. As a result, in the lithium ion secondary battery using the positive electrode material for a lithium ion secondary battery of the present embodiment, the discharge capacity in high-speed charge and discharge becomes large, and sufficient charge and discharge performance can be realized. On the other hand, when the average primary particle diameter of the primary particles is 400 nm or less, it is possible to suppress an increase in lithium ion diffusion resistance and electron transfer resistance in the primary particles of the positive electrode active material. As a result, in the lithium ion secondary battery using the positive electrode material for a lithium ion secondary battery of the present embodiment, the discharge capacity in high-speed charge and discharge can be increased.

  Here, the average primary particle size is the number average particle size. The average primary particle size of the above primary particles is obtained by randomly selecting 100 primary particles and measuring the major axis and the minor axis of each primary particle with a scanning electron microscope (SEM). It can be determined as a value.

The carbonaceous film is for imparting desired electron conductivity to the primary particles, and is a pyrolytic carbonaceous film obtained by carbonizing an organic compound which is a carbonaceous film precursor.
The thickness of the carbonaceous film is preferably 0.5 nm or more and 5.0 nm or less, and more preferably 1.0 nm or more and 3.0 nm or less.
If the thickness of the carbonaceous film is 0.5 nm or more, the thickness of the carbonaceous film does not become too thin, and a film having a desired resistance value can be formed. As a result, the conductivity is improved, and the conductivity as the positive electrode material can be secured. On the other hand, when the thickness of the carbonaceous film is 5.0 nm or less, reduction in battery activity, for example, battery capacity per unit mass of positive electrode material can be suppressed.

The amount of carbon contained in the primary particles is preferably 0.5% by mass or more and 5.0% by mass or less, more preferably 0.8% by mass or more and 2.5% by mass or less.
When the amount of carbon is 0.5% by mass or more, the conductivity as a positive electrode material can be ensured, and when a lithium ion secondary battery is formed, the discharge capacity at a high speed charge and discharge rate becomes large, and sufficient charging Discharge rate performance can be realized. On the other hand, when the amount of carbon is 5.0% by mass or less, the amount of carbon does not increase excessively, and the battery capacity of the lithium ion secondary battery per unit mass of the positive electrode material for lithium ion secondary battery decreases more than necessary Can be suppressed.

The coverage of the carbonaceous film with respect to the primary particles is preferably 60% or more, and more preferably 80% or more. The covering effect of a carbonaceous film is fully acquired because the coverage of a carbonaceous film is 60% or more.
In addition, the coverage of the said carbonaceous film can be measured using a transmission electron microscope (Transmission Electron Microscope, TEM), an energy dispersive X-ray analyzer (Energy Dispersive X-ray microanalyzer, EDX) etc.

The density of the carbonaceous film, which is calculated by the carbon content constituting the carbonaceous film, is preferably 0.3 g / cm ³ or more and 1.5 g / cm ³ or less, more preferably 0.4 g / cm ³ or more and 1.0 g or more / Cm ³ or less. The density of the carbonaceous film, which is calculated by the carbon content of the carbonaceous film, is the mass per unit volume of the carbonaceous film, assuming that the carbonaceous film is composed of only carbon.
If the density of the carbonaceous film is 0.3 g / cm ³ or more, the carbonaceous film exhibits sufficient electron conductivity. On the other hand, when the density of the carbonaceous film is 1.5 g / cm ³ or less, since the content of the crystallites of graphite having a layered structure in the carbonaceous film is small, Li ions diffuse in the carbonaceous film. There is no steric hindrance due to graphite crystallites. As a result, the charge transfer resistance does not increase. As a result, the internal resistance of the lithium ion secondary battery does not rise, and the voltage drop at the high-speed charge and discharge rate of the lithium ion secondary battery does not occur.

  The average secondary particle diameter of aggregated particles in which a plurality of primary particles are aggregated is preferably 0.5 μm to 15 μm, and more preferably 1.0 μm to 10 μm. The positive electrode material paste for a lithium ion secondary battery is prepared by mixing the positive electrode material, the conductive auxiliary agent, the binder resin (binder) and the solvent such that the average secondary particle diameter of the aggregated particles is 0.5 μm or more. The compounding quantity of the conductive support agent at the time of preparation and a binder can be restrained, and the battery capacity of the lithium ion secondary battery per unit mass of the positive electrode composite material layer for lithium ion secondary batteries can be enlarged. . On the other hand, when the average secondary particle diameter of the aggregated particles is 15 μm or less, the dispersibility and uniformity of the conductive additive and the binder in the positive electrode mixture layer can be enhanced. As a result, in the lithium ion secondary battery using the positive electrode material for a lithium ion secondary battery of the present embodiment, the discharge capacity in high-speed charge and discharge can be increased.

  Here, the average secondary particle size is a volume average particle size. The average secondary particle diameter of the aggregated particles can be measured using a laser diffraction / scattering type particle size distribution measuring device or the like.

  If the above-mentioned aggregated particles are solid particles, the electrode structure can be made uniform, which is preferable. Here, solid particles mean particles in which substantially no space exists inside the particles, and may include unintended spaces such as pores between primary particles. If the electrode structure is uniform, not only the Li ion conductivity and the electron conductivity can be improved, but also the press pressure at the time of preparation of the positive electrode can be suppressed, and peeling of the carbonaceous film due to the collapse of aggregated particles can be suppressed. In addition, it is possible to prevent the electrode mixture layer from falling off from the aluminum current collector. Thereby, the deterioration of the battery characteristics can be suppressed.

The particle diameter (D50) of cumulative percentage 50% in the cumulative particle size distribution of the positive electrode material containing the aggregated particles is preferably 2 μm to 10 μm, more preferably 2.0 μm to 8.0 μm, further preferably 3.0 μm or more It is 7.0 μm or less. The structure of the positive electrode mixture layer obtained by coating and drying the positive electrode material paste for lithium ion secondary batteries on an aluminum current collector as D50 is 2 μm or more and 10 μm can be made uniform, and the electron conduction of the positive electrode mixture layer And lithium ion conductivity can be improved, and direct current resistance at the time of charge and discharge of the lithium ion secondary battery can be reduced.
In addition, the particle diameter (D90) of the cumulative percentage 90% in the cumulative particle size distribution of the positive electrode material containing the aggregated particles is preferably 15 μm or less, more preferably 13 μm or less, still more preferably 12 μm or less. When D90 is 15 μm or less, the agglomerated particle diameter does not become too large with respect to the thickness of the positive electrode mixture layer, unevenness is not easily generated on the surface of the positive electrode mixture layer, and the structure of the positive electrode mixture layer becomes uniform. The lower limit value of D90 is not particularly limited, but is preferably 3.0 μm or more.
Further, the shape of the above-mentioned aggregated particles for improving the filling property of the positive electrode material in the positive electrode mixture layer and improving the battery capacity per unit volume is not particularly limited, but spherical, particularly spherical is preferable.

The specific surface area of the positive electrode material is preferably 8 m ² / g to 30 m ² / g, more preferably 10 m ² / g to 20 m ² / g, still more preferably 10 m ² / g to 18 m ² / g. . When the specific surface area is 8 m ² / g or more, the lithium ion diffusion resistance and the migration resistance of electrons in the primary particle of the positive electrode material for a lithium ion secondary battery decrease. Therefore, the internal resistance can be reduced, and the output characteristics can be improved. On the other hand, when the specific surface area is 30 m ² / g or less, the specific surface area of the positive electrode material for a lithium ion secondary battery does not increase excessively, the required carbon mass is suppressed, and the unit of the positive electrode material for a lithium ion secondary battery The battery capacity of the lithium ion secondary battery per mass can be improved.
In addition, the said specific surface area can be measured by BET method using a specific surface area meter (For example, the Microtrac bell corporation | Co., Ltd. make, brand name: BELSORP-mini).

The oil absorption amount using N-methyl-2-pyrrolidone (NMP) of the above-mentioned positive electrode material is preferably 60 ml / 100 g or less, more preferably 50 ml / 100 g or less, still more preferably 45 ml / 100 g or less. When preparing the positive electrode material paste for a lithium ion secondary battery by mixing the positive electrode material, the conductive auxiliary agent, the binder resin (binder) and the solvent such that the NMP oil absorption is 60 ml / 100 g or less, It is possible to make it difficult for the adhesive and the solvent to penetrate into the aggregated particles, to suppress an increase in paste viscosity, and to improve the coating property on the aluminum current collector. In addition, a necessary amount of binder can be obtained, and the binding property between the positive electrode mixture layer and the aluminum current collector can be improved.
In addition, the said NMP oil absorption can be measured by the method as described in an Example.

The tap density of the positive electrode material is preferably 1.0 g / cm ³ or more, more preferably 1.1 g / cm ³ or more and 1.5 g / cm ³ or less, still more preferably 1.2 g / cm ³ or more and 1.5 g / cm ³ or more. cm ³ or less. When the tap density is 1.0 g / cm ³ or more, the filling ratio (positive electrode density) of the positive electrode mixture layer obtained by coating and drying the positive electrode material paste for lithium ion secondary battery on an aluminum current collector The battery capacity of the lithium ion secondary battery per unit mass of the positive electrode material for the ion secondary battery can be improved.
In addition, the said tap density can be measured by the method based on JISZ2512, and can be specifically measured by the method as described in an Example.

The positive electrode material for a lithium ion secondary battery of the present embodiment has a compressive strength per unit particle diameter of 1.0 MPa / μm or more and 10.0 MPa / μm or less, preferably 2.0 MPa / μm or more and 8.0 MPa / μm It is below.
When the compressive strength per unit particle size exceeds 10.0 MPa / μm, the coagulated particles contained in the positive electrode mixture layer become too dense, so the permeability and retention of the electrolytic solution decrease, and the battery characteristics are deteriorated. There is a risk of On the other hand, if the compressive strength per unit particle size is smaller than 1.0 MPa / μm, deformation and collapse of the agglomerated particles contained in the positive electrode mixture layer, and the carbonaceous film peels from the agglomerated particle surface, and the battery characteristics are deteriorated. There is a risk of
The compressive strength per unit particle diameter can be measured and calculated according to the following procedure, and specifically, can be determined by the method described in the examples.
The particle diameter of the positive electrode material for a lithium ion secondary battery is measured with a microscope using a micro compression tester (for example, product name: MCT510, manufactured by Shimadzu Corporation). Next, in the compression test mode, the type of indenter, the loading speed, and the test force are set to measure the compression strength. The compressive strength per unit particle size is calculated from the particle diameter and compressive strength of the obtained positive electrode material.

<Method of manufacturing positive electrode material for lithium ion secondary battery>
The method for producing a positive electrode material for a lithium ion secondary battery according to the present embodiment includes the steps of producing the positive electrode active material and the positive electrode active material precursor represented by the general formula (1), and the positive electrode active material obtained in the step And at least one positive electrode active material source selected from the group consisting of a positive electrode active material precursor and water to prepare a slurry, and a positive electrode active material source slurry obtained in the step A crushing step of crushing treatment, an organic compound which is a carbonaceous film precursor is added to the crushed slurry obtained in the step to obtain a granulated product, and a structure obtained in the step And calcinating the grains in a non-oxidizing atmosphere, and in the crushing step, the ratio of the crystallite diameter of the positive electrode active material particles before and after the crushing treatment (crystallite diameter after crushing / It is characterized in that the crystallite diameter) before crushing is 0.85 or more and 0.96 or less To.

(Step of manufacturing positive electrode active material and positive electrode active material precursor)
As a production process of the positive electrode active material and the positive electrode active material precursor represented by the general formula (1), conventional methods such as a solid phase method, a liquid phase method, and a gas phase method can be used. The _Li x _A y _D z PO ₄ obtained in this way, for example, those of the particulate (hereinafter, may be referred to as _"Li x _A y _M z PO ₄ particles".) Can be mentioned.
Li _x A _y D _z PO ₄ particles are prepared, for example, by hydrothermally synthesizing a slurry-like mixture obtained by mixing Li source, A source, P source, water, and optionally D source. It is obtained by According to hydrothermal synthesis, Li _x A _y D _z PO ₄ forms as a precipitate in water. The obtained precipitate may be a precursor of Li _x A _y D _z PO ₄ . In this case, the target Li _x A _y D _z PO ₄ particles can be obtained by firing the Li _x A _y D _z PO ₄ precursor.
It is preferable to use a pressure-resistant closed vessel for the hydrothermal synthesis.

Here, as a Li source, hydroxides such as lithium hydroxide (LiOH); lithium carbonate (Li ₂ CO ₃ ), lithium chloride (LiCl), lithium nitrate (LiNO ₃ ), lithium phosphate (Li ₃ PO ₄₎ And lithium inorganic acid salts such as dilithium hydrogen phosphate (Li ₂ HPO ₄ ) and lithium dihydrogen phosphate (LiH ₂ PO ₄ ); lithium acetate (LiCH ₃ COO), lithium oxalate ((COOLi) ₂ ), etc. It is preferable to use at least one selected from the group consisting of lithium organic acid salts; and hydrates thereof.
Lithium phosphate (Li ₃ PO ₄ ) can also be used as a Li source and a P source.

As the source A, chlorides, carboxylates, sulfates and the like containing at least one selected from the group consisting of Co, Mn, Ni, Fe, Cu and Cr can be mentioned. For example, when A in Li _x A _y D _z PO ₄ is Fe, iron (II) chloride (FeCl ₂ ), iron acetate (II) (Fe (CH ₃ COO) ₂ ), iron sulfate can be used as the Fe source. (II) divalent iron salts such as (FeSO ₄ ). Among these, as the Fe source, it is preferable to use at least one selected from the group consisting of iron (II) chloride, iron (II) acetate and iron (II) sulfate.

  As the D source, chloride, carboxylate containing at least one selected from the group consisting of Mg, Ca, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc and Y And sulfates.

Examples of P sources include phosphoric acid compounds such as phosphoric acid (H ₃ PO ₄ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), and diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ). . Among these, as the P source, it is preferable to use at least one selected from the group consisting of phosphoric acid, ammonium dihydrogen phosphate and diammonium hydrogen phosphate.

(Slurry preparation process)
At this process, the positive electrode active material raw material obtained at the said process is disperse | distributed to water, and a uniform slurry is prepared. When the positive electrode active material is dispersed in water, a dispersant may be added. The method for dispersing the positive electrode active material in water is not particularly limited. For example, a method using a medium stirring type dispersing device for stirring medium particles such as a planetary ball mill, a vibrating ball mill, a bead mill, a paint shaker, and attritor at high speed is used. preferable.

(Crushing process)
In this step, the positive electrode active material raw material slurry obtained in the slurry preparation step is crushed. The method for crushing the positive electrode active material raw material slurry is not particularly limited. For example, a medium stirring type dispersing device for stirring medium particles used at the time of dispersing the positive electrode active material raw material in water in the slurry preparation step at high speed is used. The method of crushing using is mentioned. The slurry preparation step and the crushing step may be performed simultaneously.
When crushing the positive electrode active material raw material slurry, the ratio (D90) of the particle size (D90) of the cumulative percentage of the particle size (D90) in the cumulative particle size distribution of the positive electrode active material raw material in the slurry to 10% of the particle diameter (D10) It is preferable to control so that / D10) is 1 or more and 10 or less, and the particle size distribution is unimodal. By making the ratio (D90 / D10) 1 or more and 10 or less and making the particle size distribution unimodal, the dispersibility of the positive electrode active material particles in the slurry is improved. By improving the dispersibility of the positive electrode active material particles, the necking of the positive electrode active material particles becomes strong, and the compression strength per unit particle diameter of the obtained agglomerated particles can be made within the above range, and the agglomerated particles It is possible to achieve high hardness and high density, and the effects of the present invention can be exhibited.
In order to make the ratio (D90 / D10) 1 or more and 10 or less and to make the particle size distribution unimodal, the ratio of crystallite diameters of positive electrode active material particles before and after the crushing treatment (crystallite diameter after crushing / dissolution The crystallite diameter before crushing is controlled to 0.85 or more and 0.96 or less. If the ratio of the crystallite diameter is smaller than 0.85, the load of the crushing treatment is too strong, so reaggregation of the positive electrode active material in the slurry proceeds and the particle size distribution not only becomes unimodal, but also the positive electrode The crystal structure of the active material particles may be destroyed. If the ratio of crystallite diameter is larger than 0.96, the load of the crushing treatment is too weak, and thus the positive electrode active material particles can not be uniformly dispersed and peptized.
The conditions for crushing the slurry can be adjusted, for example, by the material and diameter of the dispersion medium, the concentration of the positive electrode active material in the slurry, the stirring speed, the stirring time, and the like.

The crystallite diameter of the positive electrode active material particles before and after the crushing treatment can be measured by the following method.
The cathode active material raw material slurry is dried at 120 ° C. in the atmosphere, and the dried product is pulverized in a mortar and then measured using a powder X-ray diffractometer (for example, PANalytical, trade name: X'pert MPD). Measure the diffraction pattern under the conditions.
Radiation source: Cu-Kα
Step size: 0.01 ° / step
Scan speed 3 seconds / step
In the measured diffraction pattern, the crystallite diameter is calculated from the following formulas (i) and (ii) using the peak half width (B) in which 2θ is in the range of 28.8 to 30.8 °.
Crystallite diameter before crushing (nm) = {0.9 × 1.5418 × 0.1} / {β1 (Å) × cos (29.78 / 2 × π / 2)} (i)
β1 = (B1-b)
In the formula, in the diffraction pattern measured for the positive electrode active material particles before crushing, B1 is the half width of the peak in which 2θ is in the range of 28.8 to 30.8 °, and b is the half width of the reference sample Si ( 2θ = 47.3 °).
Crystallite diameter after crushing (nm) = {0.9 × 1.5418 × 0.1} / {β2 (Å) × cos (29.78 / 2 × π / 2)} (ii)
β2 = (B2-b)
In the formula, B2 is the half width of the peak in the range of 28.8 to 28.8 ° in the diffraction pattern measured for the positive electrode active material particles after crushing, and b is the half width of the reference sample Si ( 2θ = 47.3 °).

(Granulation process)
In this step, an organic compound which is a carbonaceous film precursor is mixed with a positive electrode active material material in the crushed slurry to produce a granulated product. The organic compound is not particularly limited as long as it is a compound capable of forming a carbonaceous film on the surface of the positive electrode active material. For example, polyvinyl alcohol (PVA), polyvinyl pyrrolidone, cellulose, starch, gelatin, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose , Hydroxyethyl cellulose, polystyrene sulfonic acid, polyacrylamide, polyacrylic acid, polyvinyl acetate, glucose, fructose, galactose, mannose, maltose, sucrose, lactose, glycogen, pectin, alginic acid, glucomannan, chitin, citric acid, hyaluronic acid, Ascorbic acid, chondroitin, agarose, polyether, dihydric alcohol, trihydric alcohol and the like can be mentioned. Among them, polyvinyl alcohol (PVA), glucose and sucrose are preferable. These may use only 1 type and may mix and use 2 or more types.

  The compounding ratio of the organic compound to the positive electrode active material is 0.5 to 4.0 parts by weight of carbon obtained from the organic compound per 100 parts by weight of the active material obtained from the positive electrode active material. Is preferred. The actual blending amount varies depending on the carbonization amount by heating carbonization (the type of carbon source and carbonization conditions), but is about 0.7 to 7 parts by mass in general.

Granules are preferably solid particles from the viewpoint of exhibiting the effects of the present invention. In addition, a minimum necessary amount of aggregation retention agent can be mixed so that the granulated material does not disintegrate. Here, the aggregation support means a compound that assists aggregation of primary particles and retains the shape of secondary particles in which the primary particles are aggregated. Examples of the aggregation retention agent include organic acids such as citric acid, polyacrylic acid and ascorbic acid.
Moreover, you may use the carbonization catalyst for promoting carbonization of an organic compound in the baking process mentioned later.

  In this step, spherical solid particles are obtained by adjusting the concentration of the positive electrode active material contained in the crushed slurry to preferably 15 to 55% by mass, more preferably 20 to 50% by mass. be able to.

Next, the mixture obtained above is sprayed and dried in a high-temperature atmosphere in which the ambient temperature is equal to or higher than the boiling point of the solvent, for example, in the atmosphere at 100 to 250 ° C.
Here, conditions for spraying, for example, concentration of positive electrode active material in crushed slurry, spraying pressure, speed, and conditions for drying after spraying, for example, temperature rising rate, maximum holding temperature, holding By appropriately adjusting the time or the like, a dried product having an average secondary particle diameter of the above-described aggregated particles in the above range can be obtained.

The atmosphere temperature at the time of spraying and drying influences the evaporation rate of the solvent in the crushed slurry, which can control the structure of the resulting dried product.
For example, the closer the ambient temperature is to the boiling point of the solvent in the crushed slurry, the longer it takes to dry the sprayed droplets, so the resulting dried material shrinks sufficiently during the time required for this drying. It will be done. As a result, the dried product sprayed and dried at an ambient temperature near the boiling point of the solvent in the crushed slurry tends to have a solid structure.

(Firing process)
At this process, the granulated material obtained at the said process is baked by non-oxidative atmosphere. The granulated product is fired in a non-oxidizing atmosphere, preferably at a temperature of 650 ° C. or more and 1000 ° C. or less, more preferably 700 ° C. or more and 900 ° C. or less for 0.1 hour or more and 40 hours or less.

As the non-oxidizing atmosphere, an atmosphere composed of an inert gas such as nitrogen (N ₂ ) or argon (Ar) is preferable. When it is desired to further suppress the oxidation of the mixture, a reducing atmosphere containing about several volume% of a reducing gas such as hydrogen (H ₂ ) is preferable. Further, for the purpose of removing the organic components evaporated in the non-oxidizing atmosphere at the time of firing, a combustion supporting gas such as oxygen (O ₂ ) or a flammable gas may be introduced into the non-oxidizing atmosphere.

  Here, by setting the firing temperature to 650 ° C. or more, the decomposition and reaction of the organic compound contained in the mixture are easily advanced sufficiently, and the carbonization of the organic compound is sufficiently performed. As a result, it is easy to prevent the generation of the decomposition product of the highly resistant organic compound in the obtained aggregated particles. On the other hand, by setting the firing temperature to 1000 ° C. or less, lithium (Li) in the positive electrode active material is difficult to evaporate, and grain growth of the positive electrode active material to a target size or more is suppressed. As a result, when a lithium ion secondary battery provided with a positive electrode including the positive electrode material of the present embodiment is manufactured, it is possible to prevent the decrease in discharge capacity at high speed charge and discharge rates, and lithium having sufficient charge and discharge rate performance An ion secondary battery can be realized.

  From the above, the organic compound in the mixture is carbonized to form primary particles that cover the surface of the positive electrode active material with the carbonaceous film derived from the organic compound, and a plurality of the primary particles are aggregated to form aggregated particles.

<Electrode for lithium ion secondary battery>
The electrode for a lithium ion secondary battery according to the present embodiment includes an aluminum current collector and a positive electrode mixture layer formed on the aluminum current collector, and the positive electrode mixture layer is the above-described lithium ion secondary. It is characterized by containing the positive electrode material obtained by the manufacturing method of the positive electrode material for batteries or the above-mentioned positive electrode material for lithium ion secondary batteries. Since the said positive electrode mixture layer contains the above-mentioned positive electrode material, the electrode for lithium ion secondary batteries of this embodiment is excellent in Li ion conductivity and electron conductivity.

[Method of producing an electrode]
In order to produce an electrode, the above-mentioned positive electrode material, a binder comprising a binder resin, and a solvent are mixed to prepare a paint for electrode formation or a paste for electrode formation. At this time, if necessary, a conductive aid such as carbon black, acetylene black, graphite, ketjen black, natural graphite, artificial graphite or the like may be added.
As a binder, that is, a binder resin, for example, polytetrafluoroethylene (PTFE) resin, polyvinylidene fluoride (PVdF) resin, fluororubber and the like are suitably used.
Although the compounding ratio of positive electrode material and binder resin is not specifically limited, For example, 1 mass part or more and 30 mass parts or less, Preferably 3 mass parts or more and 20 mass parts or less make binder resin with respect to 100 mass parts of positive electrode materials .

The solvent used for the electrode-forming paint or electrode-forming paste may be appropriately selected according to the nature of the binder resin.
For example, alcohols such as water, methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol: IPA), butanol, pentanol, hexanol, octanol, diacetone alcohol, ethyl acetate, butyl acetate, ethyl lactate, propylene glycol Esters such as 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 ), Ethers such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether; acetone, Ketones such as methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), acetylacetone and cyclohexanone; amides such as dimethylformamide, N, N-dimethylacetoacetamide and N-methylpyrrolidone; glycols such as ethylene glycol, diethylene glycol and propylene glycol And the like. These may use only 1 type and may mix and use 2 or more types.

Subsequently, a paint for electrode formation or a paste for electrode formation was applied to one side of an aluminum foil and then dried to form a coating film made of a mixture of the above positive electrode material and a binder resin on one side. Obtain an aluminum foil.
Next, the coated film is pressure-bonded and dried, and a current collector (electrode) having an electrode material layer on one surface of an aluminum foil is produced.
In this manner, an electrode excellent in Li ion conductivity and electron conductivity can be produced.

<Lithium ion secondary battery>
The lithium ion secondary battery of the present embodiment has a positive electrode, a negative electrode, and an electrolyte, and includes the above-described electrode for a lithium ion secondary battery as the positive electrode. Therefore, the lithium ion conductivity and the electron conductivity are excellent, and the charge and discharge characteristics of the lithium ion secondary battery can be improved.

Examples of the negative electrode include those containing a carbon material such as metal Li, natural graphite and hard carbon, and a negative electrode material such as Li alloy and Li ₄ Ti ₅ O ₁₂ and Si (Li _4.4 Si).

The electrolyte is not particularly limited, but is preferably a non-aqueous electrolyte. For example, ethylene carbonate (ethylene carbonate; EC) and ethyl methyl carbonate (ethyl methyl carbonate; EMC) become 1: 1 in volume ratio were mixed so, the resulting mixture lithium hexafluorophosphate in a solvent (LiPF _6), for example, those obtained by dissolving at a concentration 1 mol / dm ^3.

The positive electrode and the negative electrode can be opposed to each other via a separator. For example, porous propylene can be used as a separator.
Also, instead of the non-aqueous electrolyte and the separator, a solid electrolyte may be used.

  Hereinafter, the present invention will be specifically described by way of examples and comparative examples. In addition, this invention is not limited to the form as described in an Example.

[Synthesis of positive electrode material for lithium ion secondary battery]
Example 1
Li: Fe: P = 3: 1: 1 in molar ratio of lithium phosphate (Li ₃ PO ₄ ) as Li source and P source and iron (II) sulfate (FeSO ₄ ) as Fe source Mixed. Furthermore, the distilled water for preparation was mixed, and the raw material slurry of 600 ml was prepared.
Next, the raw material slurry is accommodated in a pressure tight container, hydrothermally synthesized at 180 ° C. for 2 hours, cooled to room temperature (25 ° C.), and cake-like positive electrode activity precipitated in the container Material particles were obtained. The positive electrode active material particles were sufficiently washed with distilled water several times, and then the positive electrode active material particles and distilled water were mixed so that the concentration of the positive electrode active material particles was 60% by mass, to prepare a suspension slurry.
This suspended slurry is introduced into a sand mill together with zirconia balls having a diameter of 0.1 mm, and the ratio of crystallite diameter of positive electrode active material particles before and after crushing (crystallite diameter after crushing / crystallite diameter before crushing) is The crushing speed was adjusted by adjusting the stirring speed and the stirring time of the sand mill so as to be 0.91. The ratio (D90 / D10) of the particle diameter (D90) of cumulative percentage 90% in the cumulative particle size distribution of positive electrode active material particles after crushing processing to the particle diameter (D10) of cumulative percentage 10% is 2, particle size distribution is single It was peaky.
Subsequently, a polyvinyl alcohol (PVA) aqueous solution previously adjusted to 20 mass% is mixed with the slurry subjected to the crushing treatment with respect to the positive electrode active material particles in 3.5 mass% in terms of PVA solid content, and further in the crushed slurry Distilled water was mixed so that the positive electrode active material particle concentration was 30% by mass, and then the mixture was sprayed and dried in an air atmosphere at 180 ° C. to obtain a granulated and dried product of positive electrode active material particles.
Next, the obtained dried product is heat-treated at 750 ° C. for 1 hour in an inert atmosphere to carry carbon on the positive electrode active material particles, and a positive electrode material for lithium ion secondary battery of Example 1 is produced. did.

(Example 2)
When crushing with a sand mill, the ratio of crystallite diameter of positive electrode active material particles before and after crushing (crystal diameter after crushing / crystal diameter before crushing) is 0.93. A positive electrode material for a lithium ion secondary battery of Example 2 was produced in the same manner as in Example 1 except that the stirring speed and the stirring time of the sand mill were adjusted to carry out the crushing treatment. The ratio (D90 / D10) of the particle diameter (D90) of cumulative percentage 90% in the cumulative particle size distribution of positive electrode active material particles after crushing treatment to the particle diameter (D10) of cumulative percentage 10% is 5, particle size distribution is single It was peaky.

(Example 3)
Example 6 was carried out in the same manner as Example 1, except that a glucose aqueous solution previously adjusted to 30 mass% was mixed with the slurry crushed by a sand mill in advance to the positive electrode active material particles at 5.0 mass% in terms of glucose solid content. A positive electrode material for a lithium ion secondary battery of Example 3 was produced.

(Example 4)
Example 6 was carried out in the same manner as Example 2, except that a glucose aqueous solution previously adjusted to 30% by mass was mixed with the positive electrode active material particles 5.0% by mass in terms of glucose solid content in the slurry crushed by a sand mill. A positive electrode material for a lithium ion secondary battery of Example 4 was produced.

(Example 5)
Suspended slurry adjusted so that the concentration of positive electrode active material particles is 60% by mass is charged into a sand mill together with zirconia balls having a diameter of 0.5 mm, and the ratio of crystallite diameter of positive electrode active material particles before and after crushing (crushing The same procedure as in Example 1 was carried out except that the stirring speed and the stirring time of the sand mill were adjusted so as to adjust the subsequent crystallite diameter / crystallite diameter before crushing to 0.88. A positive electrode material for a lithium ion secondary battery of Example 5 was produced. The ratio (D90 / D10) of the particle size (D90) of cumulative percentage 90% of the particle size (D90) of cumulative percentage of cumulative particle size distribution of positive electrode active material particles after crushing process to the particle size (D10) is 8.5, particle size distribution Was unimodal.

(Example 6)
Li: Fe: P = 3: 1: 1 in molar ratio of lithium phosphate (Li ₃ PO ₄ ) as Li source and P source and iron (II) sulfate (FeSO ₄ ) as Fe source Mixed. Furthermore, the distilled water for preparation was mixed, and the raw material slurry of 600 ml was prepared.
Next, the raw material slurry is housed in a pressure tight container, hydrothermally synthesized at 130 ° C. for 2 hours, cooled to room temperature (25 ° C.), and cake-like positive electrode activity precipitated in the container Material particles were obtained. The positive electrode active material particles were sufficiently washed with distilled water several times, and then the positive electrode active material particles and distilled water were mixed so that the concentration of the positive electrode active material particles was 60% by mass, to prepare a suspension slurry.
This suspended slurry is introduced into a sand mill together with zirconia balls having a diameter of 0.1 mm, and the ratio of crystallite diameter of positive electrode active material particles before and after crushing (crystallite diameter after crushing / crystallite diameter before crushing) is The positive electrode material for a lithium ion secondary battery of Example 6 was produced in the same manner as in Example 1 except that the stirring speed and the stirring time of the sand mill were adjusted so as to obtain 0.90 and crushing was performed. did. The ratio (D90 / D10) of the particle size (D90) of cumulative percentage 90% of the particle size (D90) of cumulative percentage of cumulative particle size distribution of positive electrode active material particles after crushing process to particle size (D10) is 1.9, particle size distribution Was unimodal.

(Comparative example 1)
Suspended slurry adjusted so that the concentration of positive electrode active material particles is 60% by mass is introduced into a sand mill together with zirconia balls having a diameter of 1 mm, and the ratio of the crystallite diameter of positive electrode active material particles before and after crushing (after crushing Comparison was carried out in the same manner as in Example 1, except that the stirring speed and the stirring time of the sand mill were adjusted and the crushing process was carried out so that the crystallite diameter / crystallite diameter before crushing was 0.98. A positive electrode material for a lithium ion secondary battery of Example 1 was produced. The ratio (D90 / D10) of the particle size (D90) of cumulative percentage 90% in the cumulative particle size distribution of positive electrode active material particles after crushing processing to the particle size (D10) of cumulative percentage 10% is 44, and the particle size distribution is 2 It was peaky.

(Comparative example 2)
When crushing with a sand mill, the ratio of crystallite diameter of positive electrode active material particles before and after crushing (crystal diameter after crushing / crystal diameter before crushing) is 1.0, A positive electrode material for a lithium ion secondary battery of Comparative Example 2 was produced in the same manner as in Example 1 except that the stirring speed and the stirring time of the sand mill were adjusted to carry out the crushing treatment. The ratio (D90 / D10) of the particle diameter (D90) of cumulative percentage 90% in the cumulative particle size distribution of positive electrode active material particles after crushing treatment to the particle diameter (D10) of cumulative percentage 10% is 71, the particle size distribution is 2 It was peaky.

(Comparative example 3)
When crushing with a sand mill, the ratio of crystallite diameter of positive electrode active material particles before and after crushing (crystal diameter after crushing / crystal diameter before crushing) is 0.81. A positive electrode material for a lithium ion secondary battery of Comparative Example 3 was produced in the same manner as in Example 1 except that the stirring speed and the stirring time of the sand mill were adjusted to carry out the crushing treatment. The ratio (D90 / D10) of the particle size (D90) of cumulative percentage 90% of the particle size (D90) of cumulative percentage of cumulative particle size distribution of positive electrode active material particles after crushing treatment to the particle size (D10) of 10% is 2.6, particle size distribution Was bimodal.

(Comparative example 4)
A positive electrode material for a lithium ion secondary battery of Comparative Example 4 was produced in the same manner as Example 1, except that the suspension slurry adjusted so that the concentration of the positive electrode active material particles was 60 mass% was not crushed. did. The ratio (D90 / D10) of the particle size (D90) of the cumulative percentage 90% in the cumulative particle size distribution of positive electrode active material particles to the particle size (D10) of the cumulative percentage 10% was 194, and the particle size distribution was multimodal .

[Crystalline diameter ratio of positive electrode active material particles before and after crushing (crystallite diameter after crushing / crystallite diameter before crushing)]
The positive electrode active material slurry is dried at 120 ° C. in the atmosphere, and the dried product is crushed in a mortar, and then measured using the powder X-ray diffractometer (manufactured by PANalytical, trade name: X'pert MPD) under the following measurement conditions The diffraction pattern was measured.
Radiation source: Cu-Kα
Step size: 0.01 ° / step
Scan speed 3 seconds / step
In the measured diffraction pattern, the crystallite diameter was calculated from the following formulas (i) and (ii) using a half width (B) of a peak in which 2θ is in the range of 28.8 to 30.8 °.
Crystallite diameter before crushing (nm) = {0.9 × 1.5418 × 0.1} / {β1 (Å) × cos (29.78 / 2 × π / 2)} (i)
β1 = (B1-b)
In the formula, in the diffraction pattern measured for the positive electrode active material particles before crushing, B1 is the half width of the peak in which 2θ is in the range of 28.8 to 30.8 °, and b is the half width of the reference sample Si ( 2θ = 47.3 °).
Crystallite diameter after crushing (nm) = {0.9 × 1.5418 × 0.1} / {β2 (Å) × cos (29.78 / 2 × π / 2)} (ii)
β2 = (B2-b)
In the formula, B2 is the half width of the peak in the range of 28.8 to 28.8 ° in the diffraction pattern measured for the positive electrode active material particles after crushing, and b is the half width of the reference sample Si ( 2θ = 47.3 °).

[Ratio (D90 / D10)]
Particle diameter (D90) with a cumulative percentage of 90% in the cumulative particle size distribution of positive electrode active material particles using a laser diffraction type particle size distribution measuring apparatus (trade name: LA-950V2 manufactured by Horiba, Ltd.) using a positive electrode active material raw material slurry And a cumulative percentage of 10% of the particle size (D10) were measured, and the ratio (D90 / D10) was calculated.
In FIG. 1, the horizontal axis indicates the particle diameter of the positive electrode active material particles of Example 1 and Comparative Example 1, and the vertical axis indicates the cumulative frequency of the positive electrode active material particles with respect to each particle diameter on the horizontal axis.

Particle size distribution
Using the positive electrode active material raw material slurry, the particle size distribution of the positive electrode active material particles was measured by a laser diffraction type particle size distribution measuring apparatus (manufactured by Horiba, Ltd., trade name: LA-950V2).
In addition, the particle size distribution of the positive electrode active material particle of Example 1 and Comparative Example 1 is shown in FIG.

When measuring the ratio (D90 / D10) and the particle size distribution with a laser diffraction type particle size distribution analyzer, the number of times of data acquisition is semiconductor laser (LD) 5000 times and light emitting diode (LED) 1000 times, and data calculation is performed. The conditions were as follows.
<Calculation condition>
(Sample refractive index)
LD real part: 1.70
LD imaginary part: 0.20
LED real part: 1.70
LED imaginary part: 0.20
(Dispersant refractive index)
LD real part: 1.33
LD imaginary part: 0.00
LED real part: 1.33
LED imaginary part: 0.00
(Number of iterations): 15 times (particle diameter standard): volume (calculation algorithm): standard calculation

[Evaluation of positive electrode material]
The obtained positive electrode material for a lithium ion secondary battery (hereinafter, also simply referred to as a positive electrode material) was evaluated by the following method. The results are shown in Table 1.

(1) Compressive Strength Per Unit Particle Size The particle diameter of the positive electrode material was measured with a microscope using a micro-compression tester (trade name: MCT 510, manufactured by Shimadzu Corporation). Next, in the compression test mode, type of indenter: FLAT 50, loading rate: 0.0446 mN / sec, test force: 9.8 mN, as shown in FIG. It was compressed perpendicularly to the plane 3 and the compressive strength was measured.
In the measurement, five samples of positive electrode materials were arbitrarily selected, and the average value of the numerical values calculated from the particle diameter and the compressive strength of each of the five samples was taken as the compressive strength per unit particle size.

(2) Particle size (D50) of 50% of cumulative percentage in cumulative particle size distribution, and particle size (D90) of 90% of cumulative percentage
It measured using the laser diffraction type particle size distribution measuring apparatus (The Horiba, Ltd. make, brand name: LA-950V2). Moreover, when measuring with a laser diffraction type particle size distribution measuring apparatus, the number of data acquisition was set to 5000 semiconductor laser (LD) and 1000 light emitting diode (LED), and the data calculation conditions were as follows.
<Calculation condition>
(Sample refractive index)
LD real part: 1.70
LD imaginary part: 0.20
LED real part: 1.70
LED imaginary part: 0.20
(Dispersant refractive index)
LD real part: 1.33
LD imaginary part: 0.00
LED real part: 1.33
LED imaginary part: 0.00
(Number of repetitions): 15 times (particle diameter standard): volume (calculation algorithm): standard calculation It is to be noted that a dispersion solution subjected to the following pretreatment was used as a measurement sample.
40 g of pure water, 0.12 g of polyvinyl pyrrolidone (PVP), and 0.04 g of the positive electrode material were weighed in a 70 mL mayonnaise bottle. The mayonnaise bottle was manually shaken about 10 times to adjust the positive electrode material, polyvinyl pyrrolidone and pure water. Next, a dispersion solution obtained by sonicating this mixed solution with an ultrasonic homogenizer (trade name: SONIFIER 450, manufactured by BRANSON) for 2 minutes under the conditions of Output 5 and pulse 50% was used as a measurement sample.

(3) Oil absorption using N-methyl-2-pyrrolidone (NMP) (NMP oil absorption)
The oil absorption using N-methyl-2-pyrrolidone (NMP) was measured by replacing linseed oil with NMP according to a method according to JIS K 5101-13 (refined linseed oil method).

(4) Tap density Using a powder tester (manufactured by Hosokawa Micron, trade name: TYPE-PT-E), the number of taps was measured under the condition of 150 times by a method according to JIS Z 2512.

(5) The specific surface area specific surface area meter (MOUNTECH trade name: HM model-1208) using a nitrogen _{(N 2)} was measured by the BET method by adsorption.

[Production of positive electrode]
The obtained positive electrode material, polyvinylidene fluoride (PVdF) as a binder, and acetylene black (AB) as a conductive aid are mixed so that the mass ratio becomes 90: 5: 5, and N-methyl as a solvent -2-Pyrrolidone (NMP) was added to impart fluidity to make a slurry.
Next, this slurry was applied onto a 30 μm thick aluminum (Al) foil (current collector) and dried under reduced pressure at 120 ° C. Then, it cut out in strip shape of application width 35 mm, and it applied repeatedly twice with roll gap: 5 micrometers and roll feed rate: 0.5 m / min with a roll press machine, and produced the positive electrode of each example and comparative example.

[Fabrication of lithium ion secondary battery]
The positive electrode produced by the above method and a negative electrode made of commercially available natural graphite were punched out to a predetermined size, current collecting tabs were welded to each, and placed in an aluminum laminate film through a separator made of a porous polypropylene film. In the above, LiPF ₆ is dissolved to a concentration of 1 mol / dm ³ in a solution in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed so that EC: DEC = 50: 50 (vol%). Then, an electrolyte to which 2% by mass of vinylene carbonate (VC) was further added was injected and sealed to prepare a lithium ion secondary battery for battery characteristic evaluation.

[Evaluation of lithium ion secondary battery]
The obtained lithium ion secondary battery was evaluated by the following method. The results are shown in Table 1.

(6) Load characteristics (discharge capacity ratio)
Charge-discharge test of lithium ion secondary battery, at room temperature (25 ° C), cut-off voltage 2.5 V to 3.7 V, constant current at charge / discharge rate 0.1 C (10 hours charge, then 10 hours discharge) The third cycle was repeated three times, and the third discharge capacity was set to a discharge capacity of 0.1 C. Further, charging was performed at room temperature (25 ° C.) with a cutoff voltage of 2.5 V to 3.7 V at 0.2 C (charging for 5 hours), discharging at 3 C (discharge for 20 minutes), and the discharge capacity was measured.
The ratio of the discharge capacity at 3 C to the discharge capacity at 0.1 C was used as the load characteristic, and was calculated by the following equation (1).
Discharge capacity ratio (%) = (3 C discharge capacity / 0.1 C discharge capacity) × 100 (1)

(8) Direct current resistance (DCR; Direct Current Resistance)
The direct current resistance was measured using a lithium ion secondary battery whose charge depth was adjusted to 50% (SOC 50%) at a constant current of a charge rate of 0.1 C at an environmental temperature of 0 ° C. A lithium ion secondary battery adjusted to SOC 50% at room temperature (25 ° C) is alternately energized for 10 seconds each at 1C, 3C, 5C and 10C rates at an ambient temperature of 0 ° C on the charge side and the discharge side Then, the current value at 10 seconds after each rate is plotted on the horizontal axis, and the voltage value is plotted on the vertical axis, and the slope of the approximate straight line by the least squares method is “charge side = input DCR”, “discharge side = output DCR” did. In addition, the idle time for 10 minutes was each provided at the time of the electricity supply direction change by each electric current, and the time of the change of an electricity supply current.

(9) Cycle characteristics (capacity maintenance rate)
The cycle characteristics are repeated 300 times under an environment temperature of 60 ° C., a cut-off voltage of 2.5 V to 3.7 V and a constant current of charge / discharge rate 1 C (one hour charge and then one hour discharge). The ratio of the discharge capacity of the first time to the discharge capacity of the first time was cycle characteristics, and was calculated by the following equation (2).
Capacity retention rate (%) = (300th discharge capacity / first discharge capacity) × 100 (2)

  Comparison of Examples 1 to 6 in which the compressive strength per unit particle diameter satisfies 1.0 MPa / μm or more and 10.0 MPa / μm or less with Comparative Examples 1 to 4 in which the above-mentioned requirements are not satisfied. The lithium secondary battery provided with the positive electrode for a lithium ion secondary battery using the positive electrode material for a lithium ion secondary battery has a low DC resistance value, excellent load characteristics, and a high capacity retention rate.

1 Positive electrode material (positive electrode material for lithium ion secondary battery)
2 indenter center 3 indenter face

Claims (6)

A positive electrode material for a lithium ion secondary battery, comprising aggregated particles in which a plurality of primary particles of a positive electrode active material represented by the following general formula (1) coated with a carbonaceous film are aggregated,
Compressive strength per unit particle size 1.0 MPa / [mu] m or more 10.0 MPa / [mu] m Ri der less oil absorption capacity using N- methyl-2-pyrrolidone is less 60 ml / 100 g, a tap density of 1.0g / cm ³ or more der Rukoto positive electrode material for a lithium ion secondary battery, characterized.
Li _x A _y D _z PO ₄ (1)
(Wherein A is at least one member selected from the group consisting of Co, Mn, Ni, Fe, Cu and Cr, D is Mg, Ca, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si , Ge, Sc and Y, at least one selected from the group consisting of 0.9 <x <1.1, 0 <y ≦ 1, 0 ≦ z <1, 0.9 <y + z <1.1 .)   The particle diameter (D50) of a 50% cumulative percentage in the cumulative particle size distribution of the positive electrode material is 2 μm to 10 μm, and the particle diameter (D90) of a 90% cumulative percentage is 15 μm or less. Positive electrode material for lithium ion secondary batteries. Positive electrode material for a lithium ion secondary battery according to claim 1 or 2 specific surface area equal to or less than 8m 2 ^{/ g} or more 30 m 2 / ^g of the positive electrode material. A process for producing a positive electrode active material and a positive electrode active material precursor represented by the general formula (1), and at least one selected from the group consisting of a positive electrode active material and a positive electrode active material precursor obtained in the process A slurry preparation step of mixing a positive electrode active material and water to prepare a slurry, a crushing step of crushing the positive electrode active material slurry obtained in the step, and a disintegration step obtained in the step An organic compound which is a carbonaceous film precursor is added to the crushed slurry to obtain a granulated product, and a granulation process for obtaining a granulated product, and a baking process for baking the granulated product obtained in the process under a non-oxidative atmosphere Have
In the above-mentioned crushing process, the ratio (crystallite diameter after crushing / crystallite diameter before crushing) of the positive electrode active material particles before and after crushing is 0.85 or more and 0.96 or less The manufacturing method of the positive electrode material for lithium ion secondary batteries of any one of the Claims 1-3 characterized by the above-mentioned. An electrode for a lithium ion secondary battery comprising an aluminum current collector and a positive electrode mixture layer formed on the aluminum current collector, wherein the positive electrode mixture layer is any one of claims 1 to 3 . An electrode for a lithium ion secondary battery comprising the positive electrode material for a lithium ion secondary battery according to item 1. It is a lithium ion secondary battery which has a positive electrode, a negative electrode, and electrolyte, Comprising: The said positive electrode is an electrode for lithium ion secondary batteries of Claim 5 , The lithium ion secondary battery characterized by the above-mentioned.