JP2015065134A - Positive electrode active material for lithium ion batteries, electrode for lithium ion batteries, lithium ion battery, and method for manufacturing positive electrode active material for lithium ion batteries - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a positive electrode active material for lithium ion batteries which enables the reduction in waste loss; a method for manufacturing such a positive electrode active material for lithium ion batteries; an electrode for lithium ion batteries having such a positive electrode active material for lithium ion batteries; and a lithium ion battery.SOLUTION: A positive electrode active material for lithium ion batteries comprises inorganic particles of a substance expressed by the following general formula: LiMnAO(where A represents one of P and S, or both thereof; and 0.7<x≤2). The inorganic particles have a specific surface area of 15-35 m/g, of which YI(yellowness) is 8-16.

Description

  The present invention relates to a positive electrode active material for a lithium ion battery, an electrode for a lithium ion battery, a lithium ion battery, and a method for producing a positive electrode active material for a lithium ion battery.

  In recent years, non-aqueous electrolyte secondary batteries such as lithium ion batteries have been proposed and put into practical use as small, light, and high capacity batteries.

  Secondary batteries of lithium ion batteries (hereinafter referred to as lithium ion secondary batteries) are lighter, smaller and have higher energy than secondary batteries such as conventional lead batteries, nickel cadmium batteries and nickel metal hydride batteries. . Therefore, it is suitably used as a power source for portable electronic devices such as mobile phones and notebook personal computers. Lithium ion secondary batteries are also being studied as high-output power sources for electric vehicles, hybrid vehicles, electric tools, and the like. In the lithium ion batteries used as these high-output power supplies, high-speed charge / discharge characteristics are required for the electrode active material.

In the development of lithium ion secondary batteries, rare metal-free positive electrode active materials have been studied from the viewpoints of high functionality, high capacity, low cost, and various materials have been studied. Among them, an olivine-based phosphate electrode active material typified by LiFePO ₄ has been attracting attention as an electrode active material having high resource and low cost as well as safety.

Among phosphate-based electrode active materials, lithium manganese phosphate (LiMnPO ₄ ) containing Li as an alkali metal and Mn as a transition metal, and lithium cobalt phosphate (LiCoPO ₄ ) containing Co as a transition metal ) Is known to have a theoretical capacity of about 170 mAh / g which is about the same as LiFePO ₄ . However, it has been pointed out that lithium manganese phosphate and lithium cobalt phosphate have a very poor utilization rate compared to LiFePO ₄ even under low-rate discharge conditions (see Non-Patent Document 1, for example).

A. K. Padhi, K .; S. Nanjundaswami, and J.M. B. Goodenough, J.A. Electrochem. Soc. , Vol. 144, issue 4, 1888-1194 (1997).

  The phosphate-based electrode active material has insufficient electron conductivity. Therefore, in a lithium ion secondary battery using a phosphate-based electrode active material as a positive electrode active material, in order to charge and discharge a large current, the active material particles are made finer, and the active material and the conductive material are combined. Various ideas have been made.

  Examples of the method for refining the particles of the phosphate electrode active material include a method for adjusting pH during synthesis. When the pH at the time of synthesis increases, the nucleation frequency of the phosphate electrode active material increases, and fine particles are likely to be generated. However, if the pH during synthesis is high, the transition metal contained in the raw material of the phosphate-based electrode active material is oxidized as a side reaction, and an oxide of the transition metal is likely to be generated. Further, if the particles are fine, the specific surface area becomes large, so that the oxide of the transition metal is easily generated. In a lithium ion secondary battery using a phosphate-based electrode active material, it is known that battery characteristics deteriorate due to such oxidation of a transition metal.

  Such deterioration of the active material may become apparent only after assembling a lithium ion battery and examining battery characteristics. Then, it is necessary to discard the whole battery, and the subject that disposal loss increases arises.

  If the amount of impurities contained in the phosphate electrode active material is measured in advance, it is expected that the battery characteristics of the lithium ion battery can be estimated without assembling the lithium ion battery. However, it is difficult to measure the amount of impurities contained in a trace amount in the phosphate electrode active material.

  Therefore, among the phosphate-based electrode active materials whose particles are miniaturized in order to enable charge / discharge of a large current, they have similar properties in comparing the specific surface area that is an indicator of miniaturization. Even if it was judged, it included a good product capable of realizing good battery characteristics, and a defective product containing more impurities than the good product and inferior in battery characteristics, which contributed to an increase in waste loss.

  This invention is made | formed in view of such a situation, Comprising: It aims at providing the positive electrode active material for lithium ion batteries which can reduce a disposal loss. Another object of the present invention is to provide a method for producing such a positive electrode active material for a lithium ion battery, a lithium ion battery electrode having such a positive electrode active material for a lithium ion battery, and a lithium ion battery.

One embodiment of the present invention includes inorganic particles represented by the general formula Li _x MnAO ₄ (wherein A is one or both of P and S, and 0.7 <x ≦ 2), The inorganic particles provide a positive electrode active material for a lithium ion battery having a specific surface area of 15 m ² / g or more and 35 m ² / g or less and a YI (yellowness) of 8 or more and 16 or less.

  In one aspect of the present invention, the inorganic particle and a carbonaceous film that covers the surface of the inorganic particle may be used.

  In 1 aspect of this invention, the carbon content of the said carbonaceous film is good also as a structure which is 0.6 to 10 mass parts with respect to 100 mass parts of said inorganic particles.

  One embodiment of the present invention provides an electrode for a lithium ion battery having the above positive electrode active material for a lithium ion battery.

  One embodiment of the present invention provides a lithium ion battery having a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the positive electrode has the above-described electrode for a lithium ion battery.

  One aspect of the present invention is a method for producing the above-described positive electrode active material for a lithium ion battery, wherein a liquid material containing a Li compound, a Mn compound, and one or both of a P compound and an S compound, Provided is a method for producing a positive electrode active material for a lithium ion battery, which comprises a step of adjusting the pH to 5 or more and pH 7 or less and a step of heating the liquid in a sealed container.

  In one aspect of the present invention, the method further comprises the step of drying the slurry containing the reaction product obtained in the heating step and the organic compound, and heat-treating the obtained solid in a non-oxidizing atmosphere. It is good.

  ADVANTAGE OF THE INVENTION According to this invention, the positive electrode active material for lithium ion batteries which can reduce a waste loss can be provided. Moreover, the manufacturing method of such a positive electrode active material for lithium ion batteries, the electrode for lithium ion batteries and a lithium ion battery which have such a positive electrode active material for lithium ion batteries can be provided.

A positive electrode active material for a lithium ion battery, a method for producing a positive electrode active material for a lithium ion battery, an electrode for a lithium ion battery, and a lithium ion battery according to one embodiment of the present invention will be described.
This embodiment is specifically described for better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

[Positive electrode active material for lithium ion batteries]
The positive electrode active material for a lithium ion battery according to this embodiment is represented by the general formula Li _x MnAO ₄ (where A is one or both of P and S, and 0.7 <x ≦ 2). Inorganic particles are included, the inorganic particles have a specific surface area of 15 m ² / g or more and 35 m ² / g or less, and YI (yellowness) is 8 or more and 16 or less.

In the present embodiment, the specific surface area of the inorganic particles refers to a value obtained by measurement by a BET method based on nitrogen (N ₂ ) adsorption. Specifically, a value measured by a BET method based on nitrogen (N ₂ ) adsorption using a specific surface area meter (BELSORP-mini, manufactured by Nippon Bell Co., Ltd.) is employed.

When the specific surface area of the inorganic particles is 15 m ² / g or more, the internal resistance of the primary particles is difficult to increase. As a result, a lithium ion battery using such inorganic particles as a positive electrode active material is preferable because a sufficient discharge capacity at a high-speed charge / discharge rate can be secured.
Further, when the specific surface area of the inorganic particles is 35 m ² / g or less, the surface of the primary particles can be sufficiently covered with a thin film of carbon, and the discharge capacity at a high-speed charge / discharge rate can be increased. it can. As a result, in a lithium ion battery using such inorganic particles as a positive electrode active material, a sufficient charge / discharge rate performance can be realized, which is preferable.

In the present invention, YI (yellowness) means a value calculated based on a calculation formula defined by ASTM E 313 (Calculating Yellowness Indices from Instrumentally Measured Color Coordinates).
Specifically, the reflected light is measured twice using a spectroscopic colorimeter (color analyzer (model number TC-1800), manufactured by Tokyo Denshoku Co., Ltd.), and the obtained tristimulus value is based on the above formula. Means the value calculated by At the time of measurement, the positive electrode active material to be measured is placed on the petri dish without unevenness and measured.

The study of the _inventors, the amount of impurities contained in the inorganic particles represented by Li x MNAO _4, it was found that the inorganic particles YI (yellow index) represented by Li x MNAO _4, there is a correlation .

As an impurity contained in the inorganic particles represented by Li _x MnAO ₄ , an oxide of Mn that is a transition metal is typically given. The amount of impurities contained in the inorganic particles represented by Li _x MnAO ₄ affects the battery characteristics of a battery using the inorganic particles as an active material.

  When the amount of Mn oxide in the inorganic particles increases, it is considered that the YI of the inorganic particles increases due to the color of the Mn oxide. On the other hand, when the amount of Mn oxide increases, the inorganic particles are likely to be coarsened, so that the scattering intensity per volume of the particles increases. Then, it is considered that the YI of the inorganic particles is reduced due to the scattered light during the measurement of YI.

According to the inventor's study, when the YI (yellowness) of the inorganic particles represented by Li _x MnAO ₄ is included in the range of 8 to 16, the amount of impurities contained in the inorganic particles is small, and a good battery It was found that the characteristics can be realized.

  The inorganic particles included in the positive electrode active material for a lithium battery of the present embodiment may be crystalline particles or amorphous particles, and are mixed crystal particles in which crystalline particles and amorphous particles coexist. Also good. The inorganic particles can be produced using a known method such as a solid phase method, a liquid phase method, or a gas phase method.

Although the magnitude | size of the positive electrode active material for lithium batteries of this embodiment is not specifically limited, The average particle diameter of a primary particle diameter is 5 nm or more and 500 nm or less are preferable.
The average primary particle size of the positive electrode active material for a lithium battery is preferably 5 nm or more because there is no fear that the crystal structure is destroyed even if the volume changes due to charge / discharge. Moreover, it is preferable that the average particle diameter of the primary particle diameter is 500 nm or less because the supply amount of electrons to the inside of the particles is hardly insufficient and a decrease in utilization efficiency can be suppressed.

  It is preferable that the positive electrode active material for lithium batteries of this embodiment has inorganic particles and a carbonaceous film that covers the surfaces of the inorganic particles. By coating the surface of the inorganic particles with a carbonaceous film, it is possible to impart good electron conductivity to the electrode without greatly reducing the density of the electrode using the positive electrode active material for a lithium battery.

  The carbon content of the carbonaceous film is preferably 0.6 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the inorganic particles. Moreover, it is preferable that carbon amount is 0.8 mass part or more, and it is preferable that it is 2.5 mass parts or less. These upper limit and lower limit values can be arbitrarily combined.

When the amount of carbon in the carbonaceous film is 0.6 parts by mass or more, the coverage of the carbonaceous film is 80% or more, and when a battery is formed, the discharge capacity at a high-speed charge / discharge rate is increased. Therefore, sufficient charge / discharge rate performance can be realized.
On the other hand, when the amount of carbon is 10 parts by mass or less, the amount of the carbonaceous film does not increase too much with respect to the positive electrode active material. Therefore, it is possible to suppress a decrease in the battery capacity of the lithium ion battery per unit volume without including more carbon than the amount necessary to obtain the necessary conductivity.

In addition, it is preferable that a plurality of positive electrode active materials for lithium batteries whose surfaces of inorganic particles are coated with a carbonaceous film are aggregated to form secondary particles.
Since the positive electrode active material for a lithium battery forms secondary particles, pores capable of diffusing and penetrating lithium ions are formed between the primary particles, so that lithium ions may reach the surface of the positive electrode active material. In addition, the insertion / release reaction of lithium ions can be performed efficiently. Moreover, since each primary particle is couple | bonded by a carbonaceous film, the electronic conduction between particle | grains becomes easy.

  Furthermore, carbon particles such as acetylene black, carbon black, graphite, ketjen black, and graphite may be mixed in the carbonaceous film.

  The positive electrode active material for a lithium ion battery according to the present embodiment has a YI (yellowness) of 8 or more and 16 or less, so that it is easy to manufacture a good lithium ion battery without assembling and actually measuring the lithium ion battery. It can be.

[Method for producing positive electrode active material for lithium ion battery]
The manufacturing method of the positive electrode active material for lithium ion batteries of this embodiment is represented by the general formula Li _x MnAO ₄ (where A is one or both of P and S, 0.7 <x ≦ 2), and YI ( A method for producing a positive electrode active material for a lithium ion battery having a yellowness of 8 or more and 16 or less, comprising a Li compound, a Mn compound, and one or both of a phosphorus compound and a sulfur compound. , Adjusting the pH to 5 or more and pH 7 or less, and heating the liquid in a sealed container.

  In the present embodiment, the “liquid body” includes both a solution and a dispersion (slurry).

  The manufacturing method of the positive electrode active material for lithium ion batteries of this embodiment employs a hydrothermal synthesis method.

  The liquid includes (1) a Li compound, (2) a Mn compound, and (3) one or both of a phosphorus compound and a sulfur compound.

(1) Examples of the Li compound include lithium salts such as lithium acetate (LiCH ₃ COO), lithium chloride (LiCl), and lithium hydroxide (LiOH). These may be used alone or in combination of two or more.

(2) Examples of the Mn compound include manganese salts such as manganese chloride (II) (MnCl ₂ ), manganese (II) acetate (Mn (CH ₃ COO) ₂ ), and manganese (II) sulfate (MnSO ₄ ). be able to. These may be used alone or in combination of two or more.

(3) Examples of the phosphorus compound include phosphoric acid (H ₃ PO ₄ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ), and the like. A lithium salt can be mentioned. These may be used alone or in combination of two or more.

Examples of the sulfur compound include sulfuric acid (H ₂ SO ₄ ), or sulfates such as ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) and lithium sulfate (Li ₂ SO ₄ ). These may be used alone or in combination of two or more.

  The liquid is obtained by mixing these compounds with water. For mixing, a generally known method can be used. In addition, each compound may be mixed by adding a plurality of solid compounds to water, and each aqueous solution or dispersion is mixed with each compound after making each compound an aqueous solution or dispersion. Also good.

Furthermore, in the manufacturing method of the positive electrode active material for lithium ion batteries, a liquid is adjusted to pH 5 or more and pH 7 or less (adjustment process). The pH is preferably adjusted by adding an acidic substance such as phosphoric acid or oxalic acid and a basic substance such as NH ₃ .
When phosphoric acid is used for pH adjustment, the generated phosphate ions are consumed as a raw material for the target LiMnPO ₄ , so that contamination of impurities can be suppressed.
In addition, it is preferable to use oxalic acid or NH ₃ for adjusting the pH because the pH can be adjusted without causing a sudden pH change.

On the other hand, for example, when dilute sulfuric acid is used for pH adjustment, pH adjustment is possible, but there is a possibility that sulfur atoms derived from sulfate ions are mixed as impurities.
In addition, when a strong acid is used for adjusting the pH, the surface of the positive electrode active material particles may be corroded if the pH is too low.

Next, the obtained liquid is heated in a pressure-tight airtight container, and subjected to a hydrothermal reaction under high temperature and high pressure, for example, 120 ° C. or more and 250 ° C. or less, 0.1 MPa or more for 1 hour or more and 24 hours or less. (Heating step). As a result, inorganic particles represented by the general formula Li _x MnAO ₄ (wherein A is one or both of P and S, and 0.7 <x ≦ 2) are obtained as a reaction product.

When the treatment temperature of the hydrothermal reaction is increased, the specific surface area of the obtained inorganic particles tends to be small, and when the treatment temperature is lowered, the specific surface area of the obtained inorganic particles tends to be large.
Further, when the treatment time of the hydrothermal reaction is shortened, the specific surface area of the obtained inorganic particles tends to be large, and when the treatment temperature is lengthened, the specific surface area of the obtained inorganic particles tends to be small.
By controlling these treatment conditions, the specific surface area of the obtained inorganic particles can be adjusted as appropriate. In other words, an infinite number of combinations of processing temperature and processing time are assumed even under processing conditions with the same specific surface area.

On the other hand, when the treatment temperature of the hydrothermal reaction is increased, the YI of the obtained inorganic particles tends to be small, and when the treatment temperature is lowered, the YI of the obtained inorganic particles tends to be large.
In addition, when the treatment time for the hydrothermal reaction is shortened, the YI of the obtained inorganic particles tends to increase, and when the treatment temperature is increased, the YI of the obtained inorganic particles tends to decrease.
This is considered to be because when the specific surface area of the inorganic particles changes, the ease of oxidation of Mn contained in the inorganic particles changes, and as a result, the amount of impurities contained in the inorganic particles changes.

  However, the amount of impurities produced varies depending on the processing temperature and processing time. As described above, even if the processing conditions result in the same specific surface area, an infinite number of combinations of the processing temperature and processing time are assumed, so that even if the specific surface area is the same, inorganic particles having different YI may be generated. Therefore, in this embodiment, among the inorganic particles having a specific surface area in a predetermined range, those containing inorganic particles having a YI value in a desired range are positive electrode active materials for lithium ion batteries having good properties. Deciding.

  Further, in the method for producing a positive electrode active material for a lithium ion battery according to the present embodiment, the slurry containing the reaction product obtained in the heating step and the organic compound is dried, and the obtained solid is non-oxidizing. It is preferable to further include a step of heat-treating in an atmosphere.

  Examples of the organic compound include polyvinyl alcohol, polyvinyl pyrrolidone, cellulose, starch, gelatin, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, polyacrylic acid, polystyrene sulfonic acid, polyacrylamide, polyvinyl acetate, glucose, fructose, and galactose. Mannose, maltose, sucrose, lactose, glycogen, pectin, alginic acid, glucomannan, chitin, hyaluronic acid, chondroitin, agarose, polyether, polyhydric alcohol. Examples of the polyhydric alcohol include polyethylene glycol, polypropylene glycol, polyglycerin, glycerin and the like.

  The above reaction product and the organic compound are dissolved or dispersed in a solvent to prepare a uniform slurry. As the solvent, water can be preferably used.

  Further, the slurry may contain a carbonization catalyst for promoting carbonization of the organic compound in the heat treatment described later.

As the carbonization catalyst, a phosphorus compound or a sulfur compound can be used.
Phosphorus compounds that are carbonization catalysts include yellow phosphorus, red phosphorus, orthophosphoric acid (H ₃ PO ₄ ), phosphoric acid such as metaphosphoric acid (HPO ₃ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), phosphorus Diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ), ammonium phosphate ((NH ₄ ) ₃ PO ₄ ), lithium phosphate (Li ₃ PO ₄ ), dilithium hydrogen phosphate (Li ₂ HPO ₄ ), phosphorus Examples thereof include lithium dihydrogen acid (LiH ₂ PO ₄ ) and hydrates thereof. These may be used alone or in combination of two or more.

Examples of the sulfur compound that is a carbonization catalyst include sulfuric acid (H ₂ SO ₄ ), ammonium sulfate ((NH ₄ ) ₂ SO ₄ ), lithium sulfate (Li ₂ SO ₄ ), and the like. These may be used alone or in combination of two or more.

  When the carbonization catalyst is mixed in advance after being made into an aqueous solution, a slurry in which each compound is uniformly mixed can be obtained.

  When producing a positive electrode active material for a lithium ion battery coated with a carbonaceous film, the slurry thus prepared is first dried.

  A spray pyrolysis method can be suitably used for drying the slurry. For example, using the spray pyrolysis method, the 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 to produce a granulated body.

Next, the obtained granulated body is heat-treated in a non-oxidizing atmosphere (heat-treating step).
Here, “under non-oxidizing atmosphere” means under an inert atmosphere or a reducing atmosphere.

  The temperature condition for the heat treatment is preferably 700 ° C. or higher, and more preferably 800 ° C. or higher. Moreover, it is preferable that it is 1000 degrees C or less, and it is more preferable that it is 900 degrees C or less. These upper and lower limits can be arbitrarily combined.

  The heat treatment time is not particularly limited as long as the organic compound is sufficiently carbonized, and is, for example, 0.1 hours or more and 10 hours or less.

  By setting it as the above manufacturing methods, the positive electrode active material for lithium ion batteries by which the surface of the inorganic particle was suitably coat | covered with the carbonaceous film can be manufactured.

  The manufacturing method of the positive electrode active material for lithium ion batteries of this embodiment can manufacture easily the positive electrode active material for lithium ion batteries which is easy to manufacture a good quality lithium ion battery.

[Electrode for lithium ion battery]
The electrode for lithium ion batteries of this embodiment has the positive electrode material for lithium ion batteries of this embodiment.
The electrode for a lithium ion battery can be manufactured, for example, by applying a mixture of a positive electrode active material for a lithium ion battery of this embodiment and a binder onto a metal foil such as aluminum and drying to form a sheet. it can.

  By using the positive electrode active material for a lithium ion battery according to this embodiment, the electrode for a lithium ion battery according to this embodiment is unlikely to cause a defective product and can be a highly reliable electrode.

[Lithium ion battery]
The lithium ion battery of this embodiment is a lithium ion battery having a positive electrode, a negative electrode, and a nonaqueous electrolyte, and the positive electrode has the electrode for the lithium ion battery of this embodiment.

  The lithium ion battery includes, for example, a lithium ion battery electrode according to the present embodiment, a negative electrode using a graphite-based carbon material, a separator made of porous polypropylene or the like that partitions the positive electrode and the negative electrode, and an electrolyte having lithium ion conductivity. Liquid.

  By using the lithium ion battery electrode of this embodiment, the lithium ion battery of this embodiment is unlikely to be defective and can be a highly reliable battery.

  According to the positive electrode active material for a lithium ion battery having the above-described configuration, it is determined whether or not the active material exhibits suitable battery characteristics by measuring YI. Therefore, in the inspection after assembling the battery. Defective waste can be reduced.

  According to the method for producing a positive electrode active material for a lithium ion battery having the above-described configuration, it is possible to easily produce a positive electrode active material for a lithium ion battery that is easy to produce a good lithium ion battery.

Moreover, the electrode for lithium ion batteries of the above structures can be used as a highly reliable electrode.
Moreover, the lithium ion battery having the above configuration can be a highly reliable battery.

  The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but it goes without saying that the present invention is not limited to such examples. Various shapes, combinations, and the like of the constituent members shown in the above-described examples are examples, and various modifications can be made based on design requirements and the like without departing from the gist of the present invention.

[Example]
Hereinafter, although an example and a comparative example explain the present invention, the present invention is not limited to these examples.

For example, in this embodiment, acetylene black is used as the conductive additive, but carbon materials such as carbon black, graphite, ketjen black, natural graphite, and artificial graphite may be used. Further, although evaluation is made with a battery using Li metal as a counter electrode, naturally, a carbon material such as natural graphite, artificial graphite or coke, or a negative electrode material such as Li ₄ Ti ₅ O ₁₂ or a Li alloy may be used. . In addition, as a nonaqueous electrolyte solution as a nonaqueous electrolyte solution, a mixture of ethylene carbonate containing 1 mol / L LiPF ₆ and diethyl carbonate in a volume percentage of 1: 1 is used, but LiBF ₄ is used instead of LiPF _6. Instead of LiClO ₄ or ethylene carbonate, propylene carbonate or diethyl carbonate may be used. A solid electrolyte may be used instead of the electrolytic solution and the separator.

In this example, the following measurements were performed, and the obtained LiMnPO ₄ powder (hereinafter sometimes simply referred to as powder) was evaluated.

(1. Measurement of yellowness (YI))
The yellowness (YI) of the powder is measured using a spectrophotometer (color analyzer (Model No. TC-1800), manufactured by Tokyo Denshoku Co., Ltd.) and the reflected light is measured twice. A value calculated based on a calculation formula defined in E 313 was used. When measuring the tristimulus value, the powder of the positive electrode active material to be measured was placed evenly on the petri dish and measured.

(2. Measurement of specific surface area of powder)
The specific surface area of the powder was measured by a BET method based on nitrogen (N ₂ ) adsorption using a specific surface area meter (BELSORP-mini, manufactured by Nippon Bell Co., Ltd.).

(3. Measurement of X-ray diffraction)
The crystal structure of the obtained powder was analyzed using an X-ray diffractometer (X'Pert PRO MPD, detector: X'celarator, manufactured by Panalical).

(4. Measurement of Mn valence)
(4-1. Measurement of the ratio of Mn (II))
The total amount of Mn contained in the powder was measured by the periodic acid absorptiometric method described in JIS-K0102.
Moreover, the sum of the amount of Mn (III) and the amount of Mn (IV) contained in the powder was measured by an iodine measurement method.
The amount of Mn (II) contained in the powder was determined by subtracting the sum of the amount of Mn (III) and the amount of Mn (IV) from the total amount of Mn.
Then, the ratio (unit:%) of the amount of Mn (II) with respect to the total amount of Mn contained in the powder was calculated using the value of the total amount of Mn and the value of the amount of Mn (II).

(4-2. Mn valence)
The Mn valence (average valence of Mn) contained in the powder is assumed to be Mn (IV) assuming that Mn (III) and Mn (IV) measured by the iodine measurement method are all Mn (IV). The ratio (unit:%) was calculated and obtained by proportional distribution from the following formula.
Mn valence = {2 × (ratio of Mn (II)) + 4 × (ratio of Mn (IV))} / 100

(5. Measurement of charge / discharge characteristics)
(5-1. Production of lithium ion battery)
An active material obtained in Examples and Comparative Examples described later, acetylene black (AB) as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder, an active material: AB: PVdF = 90: A positive electrode material paste was prepared by mixing with N-methyl-2-pyrrolidinone (NMP) at a mass ratio of 5: 5.
The obtained positive electrode paste was applied onto an Al foil having a thickness of 30 μm. The coating film of the paste was 300 μm. After drying, the electrode plate was pressure-bonded to a thickness of about 100 μm at a pressure of 40 MPa.
The obtained electrode plate was punched into a disk shape with a diameter of 16 mm to produce a test electrode.

The counter electrode was a commercially available Li metal.
As the separator, a porous polypropylene film (# 2500, manufactured by Celgard) was adopted.
As the non-aqueous electrolyte solution, a 1 mol / L LiPF ₆ solution was used. As the solvent used in this LiPF ₆ solution, 1 ethylene carbonate and diethyl carbonate at a volume%: was a mixture in 1.

  Using these test electrodes, counter electrode, separator, non-aqueous electrolyte, and 2032 type coin cell, batteries of Examples and Comparative Examples were produced.

(Measurement of 5-2.3C discharge capacity)
The discharge capacity of the manufactured coin-type lithium ion battery was measured using a discharge capacity measuring device (HJ1010mSM8, manufactured by Hokuto Denko).
The manufactured coin-type lithium ion battery was subjected to constant current charging at 25 ° C. until the charging voltage became 4.2 V at a current value of 0.1 C, and then switched to constant voltage charging to obtain a current value of 0.01 C. At that point, charging was terminated.
Thereafter, discharging was performed at a discharging current of 3 C, and discharging was terminated when the battery voltage reached 2.0V. The discharge capacity at the end of the discharge was measured to obtain a 3C discharge capacity.

(Measurement of 5-3.3C capacity / 0.1C capacity ratio)
About the produced coin-type lithium ion battery, after charging on the above-mentioned conditions, it discharged by discharge current 0.1C, and discharge was complete | finished when the battery voltage became 2.0V. The 0.1 C discharge capacity obtained by measuring the discharge capacity at the end of discharge was taken as the initial capacity.
Thereafter, the 3C capacity / 0.1C capacity ratio was calculated using the obtained initial capacity (0.1 C discharge capacity) and the 3 C discharge capacity obtained by the method described above.

(5-4. Measurement of capacity maintenance rate of 300 cycles)
Moreover, charging / discharging was repeated on the above-mentioned conditions, and the charge retention at one cycle was measured as one cycle, the 0.1C discharge capacity at the 300th cycle was measured, and the capacity retention rate relative to the initial capacity was calculated.

Example 1
Lithium acetate (LiCH ₃ COO) was used as the Li source, manganese (II) sulfate was used as the Mn source, and phosphoric acid (H ₃ PO ₄ ) was used as the P source, and these were in a molar ratio of Li: Mn: P = 1: 1: After dissolving in pure water so as to be 1, the pH was adjusted to 6.6 using LiOH and H ₃ PO ₄ to prepare a 200 ml precursor solution.
Subsequently, the obtained precursor solution was put into a pressure vessel, and hydrothermal synthesis was performed at 170 ° C. for 24 hours.
After the reaction, the reaction product in a cake state was obtained by cooling to room temperature.
The obtained precipitate was sufficiently washed with distilled water several times and kept at a water content of 30% so as not to be dried to obtain a cake-like substance.
A part of this precipitate was collected and vacuum-dried at 70 ° C. for 2 hours. When X-ray diffraction was measured, it was confirmed that single-phase LiMnPO ₄ was formed.

As a result of measuring this LiMnPO ₄ with a color analyzer, the yellowness (YI) was 9.8.
Further, the specific surface area of the obtained LiMnPO ₄ powder was 17.2 m ² / g.
As for the charge / discharge characteristics, the 3C discharge capacity was 114 mAh / g.
Further, the charge / discharge characteristics showed a 3C capacity / 0.1C capacity ratio of 70.7%.

(Example 2)
A powdery single-phase LiMnPO ₄ was produced in the same manner as in Example 1 except that the pH of the precursor solution was adjusted to 5.5 using NH ₃ . It was confirmed by measuring X-ray diffraction that the obtained LiMnPO ₄ was a single phase.

As a result of measuring the obtained LiMnPO ₄ with a color analyzer, the yellowness (YI) was 15.6.
Moreover, the specific surface area of the obtained LiMnPO ₄ powder was 28.4 m ² / g.
Regarding the charge / discharge characteristics of the obtained lithium ion secondary battery using LiMnPO ₄ , the 3C discharge capacity was 117 mAh / g, and the 3C capacity / 0.1C capacity ratio was 77.0%.

(Example 3)
A powdery single-phase LiMnPO ₄ was produced in the same manner as in Example 1 except that the pH of the precursor solution was adjusted to 6.1 using NH ₃ . It was confirmed by measuring X-ray diffraction that the obtained LiMnPO ₄ was a single phase.

As a result of measuring the obtained LiMnPO ₄ with a color analyzer, the yellowness (YI) was 13.6.
Moreover, the specific surface area of the obtained LiMnPO ₄ powder was 24.0 m ² / g.
As for the charge / discharge characteristics of the obtained lithium ion secondary battery using LiMnPO ₄ , the 3C discharge capacity was 102 mAh / g, and the 3C capacity / 0.1C capacity ratio was 75.6%.

(Comparative Example 1)
A powdery single-phase LiMnPO ₄ was produced in the same manner as in Example 1 except that the pH of the precursor solution was adjusted to 4.8 using NH ₃ and oxalic acid. It was confirmed by measuring X-ray diffraction that the obtained LiMnPO ₄ was a single phase.

As a result of measuring the obtained LiMnPO ₄ with a color analyzer, the yellowness (YI) was 7.7.
Moreover, the specific surface area of the obtained LiMnPO ₄ powder was 12.7 m ² / g.
Regarding the charge / discharge characteristics of the obtained lithium ion secondary battery using LiMnPO ₄ , the 3C discharge capacity was 85 mAh / g, and the 3C capacity / 0.1C capacity ratio was 64.4%.

(Comparative Example 2)
A powdery single-phase LiMnPO ₄ was produced in the same manner as in Example 1 except that the pH of the precursor solution was adjusted to 7.5 using NH ₃ . It was confirmed by measuring X-ray diffraction that the obtained LiMnPO ₄ was a single phase.

As a result of measuring the obtained LiMnPO ₄ with a color analyzer, the yellowness (YI) was 17.8.
Moreover, the specific surface area of the obtained LiMnPO ₄ powder was 33.0 m ² / g.
As for the charge / discharge characteristics of the obtained lithium ion secondary battery using LiMnPO ₄ , the 3C discharge capacity was 64 mAh / g, and the 3C capacity / 0.1C capacity ratio was 52.9%.

The results are shown in Tables 1 and 2 for Examples 1 to 3 and Comparative Examples 1 and 2.
In the evaluation, those having a 3C discharge capacity of 100 mAh / g or more and a 3C capacity / 0.1C capacity ratio of 70% or more were determined to be non-defective products.

As a result of evaluation, in Examples 1 to 3, the capacity of 3C discharge was 100 mAh / g or more. Further, the 3C capacity / 0.1C capacity ratio was 70% or more.
On the other hand, in Comparative Examples 1 and 2, the 3C discharge capacity was less than 100 mAh / g, and the 3C capacity / 0.1C capacity ratio was less than 70%.
Therefore, it was found that Examples 1 to 3 showed better battery characteristics than Comparative Examples 1 and 2.

  In Examples 1 to 3, a difference of about 3% occurs in the 300 cycle capacity retention rate, but it can be evaluated that the difference is about 5% in the measurement of the 300 cycle capacity maintenance rate. Therefore, it can be said that Examples 1 to 3 show the same physical properties at a 300 cycle capacity maintenance rate.

  From the above results, it was confirmed that the present invention is useful.

Claims (7)

Inorganic particles represented by the general formula Li _x MnAO ₄ (wherein A is one or both of P and S, and 0.7 <x ≦ 2),
The inorganic particles have a specific surface area of 15 m ² / g or more and 35 m ² / g or less, and a positive electrode active material for a lithium ion battery having a YI (yellowness) of 8 or more and 16 or less.   The positive electrode active material for a lithium ion battery according to claim 1, comprising: the inorganic particles; and a carbonaceous film that covers a surface of the inorganic particles.   3. The positive electrode active material for a lithium ion battery according to claim 2, wherein the carbon amount of the carbonaceous film is 0.6 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the inorganic particles.   The electrode for lithium ion batteries which has a positive electrode active material for lithium ion batteries of any one of Claim 1 to 3.   It is a lithium ion battery which has a positive electrode, a negative electrode, and a nonaqueous electrolyte, Comprising: The said positive electrode is a lithium ion battery which has an electrode for lithium ion batteries of Claim 4. It is a manufacturing method of the positive electrode active material for lithium ion batteries of Claim 1, Comprising:
Adjusting a liquid containing Li compound, Mn compound, and one or both of P compound and S compound to pH 5 or more and pH 7 or less;
And a step of heating the liquid in a sealed container. A method for producing a positive electrode active material for a lithium ion battery.   The lithium ion battery battery according to claim 6, further comprising a step of drying a slurry containing the reaction product obtained in the heating step and the organic compound, and heat-treating the obtained solid in a non-oxidizing atmosphere. A method for producing a positive electrode active material.