JP2011071019A - Manufacturing method for lithium ion battery positive active material, and positive active material for lithium ion battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a positive active material of a lithium ion battery, capable of enhancing quick charge and discharge characteristics by controlling an amount of trivalent Fe (Fe(III)) contained in a LiFePO<SB>4</SB>fine particle, and to provide the positive active material for the lithium ion battery. <P>SOLUTION: This manufacturing method for the positive active material for the lithium ion battery: dissolves Li<SB>3</SB>PO<SB>4</SB>, or a Li source and a phosphorous source, and a Fe source, into a solvent containing water as a main component; adds an oxidant to an obtained mixture; and generates the LiFePO<SB>4</SB>fine particle, by pressurizing and heating the mixture containing the oxidant. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a method for producing a lithium ion battery positive electrode active material and a lithium ion battery positive electrode active material, and more particularly, by controlling the amount of trivalent Fe (Fe (III)) in LiFePO ₄ fine particles. The present invention relates to a method for producing a lithium ion battery positive electrode active material capable of improving capacity, and a lithium ion battery positive electrode active material obtained by this production method.

Non-aqueous lithium-ion batteries have higher energy density and can be easily miniaturized compared to conventional aqueous batteries such as Ni-Cd batteries and Ni-H batteries. Widely used in portable devices such as computers. As a positive electrode material for this non-aqueous lithium ion battery, LiCoO ₂ is currently in practical use and is generally used.
By the way, in the field of a hybrid battery, an electric vehicle, a large battery mounted on an uninterruptible device, etc. expected in the future, when LiCoO ₂ is directly applied to a positive electrode material of a non-aqueous lithium ion battery, there are various problems as follows. There was a point.
One of the problems is that LiCoO ₂ uses rare metal cobalt (Co), so that it is difficult to obtain a large amount of cobalt (Co) stably in terms of resources and cost. It is.
In addition, LiCoO ₂ releases oxygen at a high temperature, so there is a risk of explosion when abnormal heat is generated or when the battery is short-circuited. Therefore, there is a point that the risk of applying LiCoO ₂ to a large battery is great. .

Therefore, in recent years, a cathode material having a phosphoric acid skeleton that is inexpensive and has low risk has been proposed in place of the cathode material using LiCoO ₂ . Among them, LiFePO ₄ having an olivine structure is attracting attention as a positive electrode material having no problem in terms of resources and costs, based on safety, and has been researched and developed worldwide (for example, patent literature) 1, non-patent literature 1 etc.).
Since the olivine-based positive electrode material typified by LiFePO ₄ uses iron (Fe), it is abundant in nature and inexpensive compared to cobalt and manganese in terms of resources. The olivine structure is a material excellent in safety because it does not release oxygen at a high temperature like a cobalt system such as LiCoO ₂ due to the covalent bond between phosphorus and oxygen.

However, it has been pointed out that LiFePO ₄ having such advantages also has problems in terms of characteristics.
One problem is that the conductivity is low. In this regard, the conductivity is improved by recent improvements, in particular, by combining LiFePO ₄ and carbon, or coating the surface of LiFePO ₄ with carbon. There have been many attempts.
Another problem is that the diffusibility of lithium ions during charging and discharging is low. For example, in a compound having a layered structure such as LiCoO ₂ or a spinel structure such as LiMnO ₂ , the diffusion direction of lithium during charge / discharge is bi-directional or tri-directional, whereas an olivine structure such as LiFePO ₄ is used. In the compound, the diffusion direction of lithium is limited to one direction. In addition, since the electrode reaction during charging / discharging is a two-phase reaction in which conversion is repeated between LiFePO ₄ and FePO ₄ , LiFePO ₄ is considered disadvantageous for high-speed charging / discharging.

The most effective method for solving these problems is to reduce the LiFePO ₄ particle size. That is, even if the diffusion direction is one direction, if the diffusion distance is shortened by reducing the particle size, it can be considered that the charge / discharge speed can be increased.
Conventionally, a solid phase method has been used as a method for synthesizing LiFePO _{4. In} this solid phase method, LiFePO ₄ raw materials are mixed in a stoichiometric ratio and fired in an inert atmosphere. If the conditions are not properly selected, LiFePO ₄ having the intended composition cannot be obtained, and it is difficult to control the particle size and it is difficult to reduce the particle size. Therefore, a liquid phase synthesis method utilizing a hydrothermal reaction has been studied as a method for reducing the particle size of the LiFePO ₄ particles.

The advantage of a hydrothermal reaction is that a product with a much higher purity can be obtained at a lower temperature than in a solid phase reaction. However, also in this hydrothermal reaction, the particle size is largely controlled by factors relating to reaction conditions such as reaction temperature and time. In addition, when controlled by these factors, there are many parts that depend on the performance of the manufacturing apparatus itself, and reproducibility is difficult.
Therefore, as a method for producing LiFePO ₄ fine particles by a hydrothermal reaction, a method of synthesizing organic acids and ions such as CH ₃ COO ⁻ , SO ₄ ²⁻ , Cl ^{− and the} like by simultaneously containing them in a solvent, and this hydrothermal reaction There has been proposed a method of obtaining single-phase LiFePO ₄ fine particles by adding excess Li at the time (for example, see Patent Document 2, Non-Patent Document 2, etc.). A method of obtaining LiFePO ₄ fine particles having a small particle diameter by mechanically pulverizing a reaction intermediate has also been proposed (Patent Document 3).

Japanese Patent No. 3484003 JP 2008-66019 A Special table 2007-511458 gazette

A. K. Padi et al., “Phospho-Olibin as Positive-Electrode Material for Rechargeable Lithium Batteries”, Journal of the Electrochemical Society, 1997, Vol. 144, No. 4, p. 1188 (AKPadhi et al., “ Phosph0-olivine as Positive-Electrode Material for Rechargeable Lithium Batteries ", J. Electrochem. Soc., 144, 4, 1188 (1997)) Keisuke Shiraishi, Yoon Ho, Kiyoshi Kanamura, “Synthesis of LiFePO4 Cathode Active Material for Rechargeable Lithium Battery by Hydrothermal Reaction”, Journal of the Ceramic Society of Japan, 2004, Vol. 112, No. 1305, No. 1 S58-S62 (Keisuke Shiraishi, Young Ho Rho and Kiyoshi Kanamura, "Synthesis of LiFePO4 cathode active material for Rechargeable Lithium Batteries by Hydrothermal Reaction", J. Ceram. Soc. Jpn., Suppl. 112, S58-S62 (2004)

Incidentally, in the method of producing the LiFePO ₄ particles by conventional hydrothermal reaction, certainly LiFePO ₄ particles is obtained, although also improved load characteristics of interest, the initial discharge capacity is decreased, and further high-speed charge There was a problem that the discharge characteristics deteriorated.
This phenomenon is considered to be caused by the generated LiFePO ₄ fine particles having a wide particle size distribution. That is, when the LiFePO ₄ fine particles have a wide particle size distribution, the proportion of amorphous ultrafine particles that do not contribute to charge / discharge increases, resulting in a decrease in initial discharge capacity, and also high-speed charge / discharge characteristics. Will be reduced.

The present invention was made in view of the above circumstances, not just control the primary particle size of LiFePO ₄ particles, the amount of trivalent Fe contained in LiFePO ₄ in the microparticles (Fe (III)) It aims at providing the manufacturing method of the positive electrode active material for lithium ion batteries and the positive electrode active material for lithium ion batteries which can improve a high-speed charge / discharge characteristic by controlling.

Lithium present inventors have, as a result of intensive studies to solve the above problems, using the amount of trivalent Fe contained in LiFePO ₄ in the microparticles (Fe (III)), the LiFePO ₄ particles It has been found that there is a close relationship between the charge / discharge characteristics of the ion battery, particularly the high-speed charge / discharge characteristics, and the present invention has been completed.

That is, the method for producing a positive electrode active material for a lithium ion battery of the present invention was obtained by dissolving Li ₃ PO ₄ or a Li source and a phosphoric acid source and an Fe source in a solvent containing water as a main component. An oxidizing agent is added to the mixture, and the mixture containing the oxidizing agent is pressurized and heated to produce LiFePO ₄ fine particles.

The oxidizing agent is preferably one or more selected from the group consisting of hydrogen peroxide, nitric acid, sodium hypochlorite, metachloroperbenzoic acid, and potassium permanganate.
The addition amount of the oxidizing agent is preferably 0.01 mol% or more and 6 mol% or less with respect to the total mol amount of the Fe source.

The positive electrode active material for lithium ion batteries of the present invention is a lithium ion battery positive electrode active material obtained by the method for producing a positive electrode active material for lithium ion batteries of the present invention,
The LiFePO ₄ particles of trivalent Fe (Fe (III)) and mol of the ratio of the mol amount of the total Fe in the LiFePO ₄ microparticles (Fe (III) / total Fe) is represented by the following formula (1)
0 mol% <Fe (III) / total Fe <7.0 mol% (1)
It is characterized by satisfying.

In the positive electrode active material for a lithium ion battery of the present invention, the specific surface area is preferably larger than 3 m ² / g and 16 m ² / g or less.

According to the method for producing a positive electrode active material for a lithium ion battery of the present invention, Li ₃ PO ₄ , or a Li source and a phosphoric acid source, and an Fe source were dissolved in a solvent containing water as a main component. Since the oxidizing agent is added to the mixture and the mixture containing the oxidizing agent is pressurized and heated, in addition to controlling the primary particle size, the amount of trivalent Fe (Fe (III)) contained Controlled LiFePO ₄ fine particles can be easily produced. Therefore, LiFePO ₄ fine particles in which the primary particle diameter and the amount of trivalent Fe (Fe (III)) are controlled can be easily produced.
Furthermore, by applying the LiFePO ₄ fine particles to an electrode for a lithium ion battery, the high-speed charge / discharge characteristics of the lithium ion battery can be improved.

According to the positive electrode active material for lithium ion batteries of the present invention, the mol amount of the trivalent Fe of LiFePO ₄ particles (Fe (III)), the ratio of the mol amount of the total Fe in the LiFePO ₄ in the microparticles (Fe (III ) / Total Fe) in the following formula (2)
0 mol% <Fe (III) / total Fe <7.0 mol% (2)
Therefore, the charge / discharge characteristics, particularly the high-speed charge / discharge characteristics, of the lithium ion battery using the LiFePO ₄ fine particles can be improved.

It is a figure which shows the charging / discharging curve of Example 4 and Comparative Example 2 of this invention.

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

"Method for producing positive electrode active material for lithium ion battery"
In the method for producing a positive electrode active material for a lithium ion battery according to this embodiment, Li ₃ PO ₄ , or a Li source and a phosphoric acid source, and an Fe source are dissolved in a solvent containing water as a main component, and the resulting mixture is obtained. In this method, an oxidizing agent is added to the mixture, and a mixture containing the oxidizing agent is pressurized and heated to produce LiFePO ₄ fine particles.

When the LiFePO ₄ fine particles are synthesized by hydrothermal reaction, a method using a Li source such as a Li salt, a Fe source such as a Fe (II) salt, a phosphoric acid source such as a PO ₄ salt as a synthesis raw material, a Li source and phosphorus There are a method using Li ₃ PO ₄ reacted with an acid source, and a method using Fe ₃ (PO ₄ ) ₂ reacted with an Fe source and a phosphate source.
However, since Fe ₃ (PO ₄ ) ₂ is easily oxidized and difficult to handle, it is preferable to use Li ₃ PO ₄ and Fe sources such as Fe (II) as raw materials.

Note that the method using Li source, Fe source and phosphoric acid source is equivalent to the method using Li ₃ PO ₄ because Li ₃ PO ₄ is generated at the initial stage of the reaction. Therefore, a method is preferred in which Li ₃ PO ₄ is first synthesized, and then Li ₃ PO ₄ and Fe source are hydrothermally reacted to synthesize LiFePO ₄ fine particles.

Here, the reason for using the hydrothermal reaction is as follows.
As another synthesis method of LiFePO ₄ , there is a solid phase method in which a raw material and a carbon source are mixed and baked in an inert atmosphere or a reducing atmosphere.
Although it is possible to control the oxidation of Fe by this method as well, for that purpose, it is necessary to control the oxygen partial pressure in the atmosphere at the time of firing with high accuracy, and such control is actually extremely difficult. .
On the other hand, since the hydrothermal reaction separates the production process and the firing process of LiFePO ₄ fine particles, the oxidation of Fe in the production process can be easily controlled by the hydrothermal reaction.

Next, a method for producing the LiFePO ₄ fine particles will be described in detail.
1. Preparation of Lithium Phosphate (Li ₃ PO ₄ ) Slurry First, a Li source and a phosphoric acid source are introduced into water, and these Li source and phosphoric acid source are reacted to produce lithium phosphate (Li ₃ PO ₄ ). And a lithium phosphate (Li ₃ PO ₄ ) slurry.

The Li source is preferably a Li hydroxide or a Li salt. For example, the Li hydroxide may be lithium hydroxide (LiOH). Further, as the Li salt, lithium inorganic acid salts such as lithium carbonate (Li ₂ CO ₃ ) and lithium chloride (LiCl), lithium organic acid salts such as lithium acetate (LiCH ₃ COO) and lithium oxalate ((COOLi) ₂ ) And hydrates thereof, and one or more selected from these groups are preferably used.

Examples of phosphoric acid sources include phosphoric acid such as orthophosphoric acid (H ₃ PO ₄ ) and metaphosphoric acid (HPO ₃ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), and diammonium hydrogen phosphate ((NH ₄ )). ₂ HPO ₄ ), ammonium phosphate ((NH ₄ ) ₃ PO ₄ ) and one or more selected from the group of these hydrates are preferably used. Among them, orthophosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate are preferable because of their relatively high purity and easy composition control.

2. Preparation of mixture of lithium phosphate (Li ₃ PO ₄ ) and Fe source To the lithium phosphate (Li ₃ PO ₄ ) slurry described above, an Fe source and a reducing agent are added to form a mixture.
The Fe source is preferably an Fe salt, such as iron chloride (II) (FeCl ₂ ), iron sulfate (II) (FeSO ₄ ), iron acetate (II) (Fe (CH ₃ COO) ₂ ), and water thereof. One or more selected from the group of Japanese products are preferably used.

The reaction concentration, that is, the concentration of Li ₃ PO ₄ and Fe source in this mixture when converted to LiFePO ₄ is preferably 0.5 mol / L or more and 1.5 mol / L or less, more preferably 0.7 mol / L or more and 1.2 mol / L or less.
The reason is that when the reaction concentration is less than 0.5 mol / L, LiFePO ₄ having a large particle size is likely to be produced, and the load characteristics are deteriorated for the reason already described, while the reaction concentration is 1.5 mol / L. by weight, it can not be performed stirring sufficiently, therefore, the reaction does not proceed sufficiently, will remain unreacted materials becomes as a result, difficult to LiFePO ₄ single phase is obtained, used as a battery material It is not possible.

3. Addition of oxidizing agent to the above mixture An oxidizing agent is added to the above mixture to form a mixture containing the oxidizing agent.
The oxidizing agent is preferably one or more selected from the group consisting of hydrogen peroxide, nitric acid, sodium hypochlorite, metachloroperbenzoic acid, and potassium permanganate, for example.
Here, when an oxidizing agent containing metal ions such as sodium hypochlorite and potassium permanganate is used, the metal ions remain in the positive electrode active material, and in some cases, shorten the battery life. Because there is a fear, attention is necessary. Considering this point, hydrogen peroxide, nitric acid, and metachloroperbenzoic acid, which are oxidizing agents not containing metal ions, are preferable.

The addition amount of the oxidizing agent is preferably 0.01 mol% or more and 6 mol% or less, more preferably 1 mol% or more and 6 mol% or less, and further preferably 3 mol%, with respect to the total mol amount of the Fe source contained in the mixture. It is above and below 6 mol%.
Here, if the addition amount of the oxidizing agent is less than 0.01 mol%, the addition amount of the oxidizing agent to the Fe source in the mixture is too small, and therefore trivalent Fe (Fe (Fe) generated in the course of the hydrothermal reaction). The amount of (III)) cannot be controlled, and as a result, the high-speed charge / discharge characteristics of the lithium ion battery to which the obtained LiFePO ₄ fine particles are applied are deteriorated, while the addition amount of the oxidizing agent is 6 mol%. If the amount exceeds 1, the amount of trivalent Fe (Fe (III)) produced during the hydrothermal reaction process can be controlled, but excess oxidant tends to remain as impurities, and as a result This is not preferable because high-speed charge / discharge characteristics of a lithium ion battery to which LiFePO ₄ fine particles are applied are deteriorated.

  In addition, about this oxidizing agent, substances, such as an air atmosphere containing oxygen gas, are also included. In addition, it is preferable to control the gas phase part in the autoclave during the hydrothermal reaction to an oxidizing atmosphere instead of adding the oxidizing agent, since there is no possibility that the oxidizing agent itself becomes an impurity.

3. Hydrothermal synthesis of the mixture The mixture containing the above oxidizing agent is reacted (hydrothermal synthesis) under high-temperature and high-pressure conditions to obtain a reaction product containing LiFePO ₄ fine particles.
The conditions of the high temperature and high pressure in this reaction (hydrothermal synthesis) are not particularly limited as long as the temperature, pressure, and time are within the range of producing LiFePO ₄ fine particles, but the reaction temperature is, for example, 120 ° C. or more and 250 ° C or lower is preferable, more preferably 150 ° C or higher and 220 ° C or lower.

  Further, the pressure during the reaction is preferably, for example, 0.2 MPa or more and 4.0 MPa or less, and more preferably 0.4 MPa or more and 2.5 MPa or less. Although depending on the reaction temperature, the reaction time is preferably, for example, 1 hour to 24 hours, more preferably 3 hours to 12 hours.

4). The reactions containing LiFePO ₄ particles separated above LiFePO ₄ particles, decantation, centrifugation, by filtration or the like, is separated into LiFePO ₄ particles and Li-containing waste solution (solution containing Li unreacted).
The separated LiFePO ₄ fine particles are dried at 40 ° C. or higher for 3 hours or longer using a drier or the like.
As described above, in addition to controlling the primary particle diameter, LiFePO ₄ fine particles in which the amount of trivalent Fe (Fe (III)) contained is controlled can be produced efficiently and easily.

"Positive electrode active material for lithium-ion batteries"
The LiFePO ₄ fine particles, which are the positive electrode active material for a lithium ion battery produced by the above production method, have a controlled amount of trivalent Fe (Fe (III)) contained therein.
In the LiFePO ₄ fine particles, the amount of oxidant added and the amount of trivalent Fe (Fe (III)) in the synthesized LiFePO ₄ are not necessarily stoichiometric, but the trivalent Fe (Fe The amount of (III)) tends to be greater than the amount of added oxidizing agent. The reason is that the surface of the LiFePO ₄ fine particles is naturally oxidized by being exposed to the atmosphere.

The LiFePO ₄ particles of trivalent Fe (Fe (III)) ratio of the mol amount, the mol amount of the total Fe in the LiFePO ₄ micro particles (Fe (III) / total Fe) is represented by the following formula (3)
0 mol% <Fe (III) / total Fe <7.0 mol% (3)
Preferably, the following formula (4) is satisfied.
0.5 mol% <Fe (III) / total Fe <5 mol% (4)
More preferably, the following formula (5) is satisfied.
1.0 mol% <Fe (III) / total Fe <4 mol% (5)
Is to satisfy.

  Here, when the ratio (Fe (III) / total Fe) exceeds 7.0 mol%, excessive trivalent Fe acts as an impurity in the positive electrode active material, and the initial capacity is reduced and the charge / discharge polarization is increased. Since it occurs, it is not preferable. In view of facilitating Li diffusion, the ratio (Fe (III) / total Fe) is preferably more than 0.5 mol%.

The LiFePO ₄ fine particles preferably have a specific surface area of greater than 3 m ² / g and no greater than 16 m ² / g, more preferably greater than 3 m ² / g and no greater than 12 m ² / g, and even more preferably 5 m ^2. Greater than / g and less than or equal to 10 m ² / g.
Here, when the specific surface area is 3 m ² / g or less, the LiFePO ₄ fine particles are coarsened and the particle size distribution is not sharp. As a result, when applied to a lithium ion battery, the initial discharge characteristics vary. On the other hand, when it exceeds 16 m ² / g, the LiFePO ₄ fine particles are excessively fined. As a result, when applied to a lithium ion battery, the discharge voltage This is because the desired charge / discharge characteristics cannot be obtained.

"Electrode for lithium ion battery and lithium ion battery"
In order to use the above-described positive electrode active material for a lithium ion battery as a positive electrode active material for a lithium ion battery, particularly a positive electrode of a lithium ion secondary battery, it is necessary to cover the surface of LiFePO ₄ fine particles with carbon.
This is because if the surface is not coated with carbon, the conductivity, which is the problem of LiFePO ₄ already described, is not improved, and good results as battery characteristics cannot be obtained.

As a carbon coating method, for example, LiFePO ₄ fine particles are mixed with a water-soluble monosaccharide, polysaccharide, or water-soluble polymer compound that is a carbon source, followed by evaporation to dryness, vacuum drying, or spray drying. , using the drying method such as freeze drying method, homogeneously film is formed on the surface of the LiFePO ₄ particles, then in an inert atmosphere, then fired at a temperature that produces a carbon carbon source is decomposed, LiFePO ₄ particles A conductive carbon film is formed on the surface.

The firing temperature depends on the type of carbon source, but is preferably 500 ° C to 1000 ° C, more preferably 700 ° C to 800 ° C.
At a low temperature of less than 500 ° C., the carbon source is not sufficiently decomposed and a conductive carbon film is not sufficiently formed, which becomes a resistance factor in the battery and adversely affects battery characteristics. On the other hand, at a high temperature exceeding 1000 ° C., the growth of LiFePO ₄ fine particles progresses and becomes coarse, and the high-speed charge / discharge characteristics due to the Li diffusion rate, which is a problem of LiFePO ₄ particles, are remarkably deteriorated.
Thus, by covering the LiFePO ₄ fine particles, which are the above-described positive electrode active material for lithium ion batteries, with carbon, it becomes suitable as a positive electrode active material for positive electrodes of lithium ion batteries, particularly lithium ion secondary batteries.

A lithium ion battery can be obtained by using the electrode formed using the carbon-coated LiFePO ₄ fine particles as a positive electrode, and further including a negative electrode, an electrolyte, and a separator.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited by these Examples.

"Example 1"
To 1 L of pure water, 3 mol of lithium chloride (LiCl) and 1 mol of phosphoric acid (H ₃ PO ₄ ) were added and stirred to obtain a lithium phosphate (Li ₃ PO ₄ ) slurry.
Next, 1 mol of iron (II) chloride (FeCl ₂ ) was added to the slurry, and water was further added to obtain a raw material liquid having a total amount of 2 L. The reaction concentration of this raw material liquid was converted to LiFePO ₄ and was 0.5 mol / L.

Next, this raw material liquid is put into an autoclave, evacuated using a diaphragm pump, N ₂ gas is introduced, and then hydrogen peroxide is added in an amount of 0.01 mol% with respect to the total amount of Fe in the raw material liquid. The reaction was conducted at 180 ° C. for 6 hours. Then, it filtered and separated into solid and liquid.
Subsequently, the same amount of water as the mass of the separated solid was added and suspended, and the operation of solid-liquid separation by filtration was performed three times for washing.

The obtained cake-like LiFePO ₄ is pulverized and dispersed for 12 hours in a ball mill using 5 mm diameter zirconia beads as a medium after adding 5 g of polyethylene glycol and 150 g of pure water to 150 g in terms of solid content. A slurry was prepared.

  Next, the slurry was sprayed into an air atmosphere at 180 ° C. and dried to obtain a granulated body having an average particle size of about 6 μm. This granulated body was fired at 750 ° C. for 1 hour under an inert atmosphere to prepare a positive electrode active material for a lithium ion battery of Example 1.

"Examples 2 to 8"
A total of seven raw material liquids prepared in accordance with Example 1 were put in each autoclave, and after evacuating them using a diaphragm pump, N ₂ gas was introduced into each autoclave, and then an oxidizing agent and its The addition amount was introduced so as to have the composition and addition amount shown in Table 1, and the reaction was conducted by heating at 180 ° C. for 6 hours, followed by filtration and solid-liquid separation to produce each solid matter of Examples 2 to 8. .
Subsequently, using these solid materials, positive electrode active materials for lithium ion batteries of Examples 2 to 8 were prepared according to Example 1.

“Comparative Example 1”
The raw material solution prepared in accordance with Example 1 was put into an autoclave and evacuated using a diaphragm pump. Then, N ₂ gas was introduced into the autoclave, heated at 180 ° C. for 6 hours, and then filtered. Then, solid-liquid separation was performed to produce the solid material of Comparative Example 1.
Next, a positive electrode active material for a lithium ion battery of Comparative Example 1 was produced according to Example 1 using this solid material.

"Comparative Example 2"
The raw material solution prepared according to Example 1 was put into an autoclave, evacuated using a diaphragm pump, N ₂ gas was introduced, and then hydrogen peroxide was added in an amount of 7 mol with respect to the total Fe amount of the raw material solution. % Was added and reacted by heating at 180 ° C. for 6 hours, followed by filtration and solid-liquid separation to produce a solid material of Comparative Example 2.
Next, a positive electrode active material for a lithium ion battery of Comparative Example 2 was produced according to Example 1 using this solid material.

"Evaluation of positive electrode active materials for lithium-ion batteries"
For each of the positive electrode active materials of Examples 1 to 8 and Comparative Examples 1 and 2, measurement of specific surface area and determination of trivalent Fe ions were performed by the following methods.
(1) Specific surface area Specific surface area meter The specific surface area (m < ² > / g) of the positive electrode active material was measured using Belsorb II (made by Nippon Bell Co., Ltd.).
(2) Quantification of trivalent Fe ion It was carried out according to Japanese Industrial Standard JIS K 0102 57.1 “phenanthroline spectrophotometry”.

"Production of lithium ion secondary battery"
The positive electrode active materials of Examples 1 to 8 and Comparative Examples 1 and 2 were each subjected to the following treatments to produce lithium ion secondary batteries of Examples 1 to 8 and Comparative Examples 1 and 2, respectively.
First, 90 parts by mass of the positive electrode active material, 5 parts by mass of acetylene black as a conductive auxiliary agent, 5 parts by mass of polyvinylidene fluoride (PVDF) as a binder, and N-methyl-2-pyrrolidinone (NMP) as a solvent were mixed. .
Next, these were kneaded using a three-roll mill to produce a positive electrode active material paste.

Next, this positive electrode active material paste was applied onto an aluminum current collector foil having a thickness of 30 μm, and then dried under reduced pressure at 100 ° C. to produce a positive electrode having a thickness of 60 μm.
Next, this positive electrode was punched into a 2 cm ² disk shape, dried under reduced pressure, and then a lithium ion secondary battery was produced using a stainless steel 2016 type coin cell in a dry argon atmosphere.
Here, metallic lithium was mixed in the negative electrode, a porous polypropylene film was mixed in the separator, and 1 mol of LiPF ₆ was mixed in the electrolyte with a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a ratio of 1: 1. The mixture was used.

"Battery charge / discharge test"
A battery charge / discharge test was performed using the lithium ion secondary batteries of Examples 1 to 8 and Comparative Examples 1 and 2.
Here, the cutoff voltage was 2.0 V to 4.0 V, and the initial discharge capacity was measured by charging at 0.1 C and discharging at 0.1 C. The other discharge capacities were measured by charging at 0.2C and measuring the discharge capacities at 1C, 2C, 3C, and 5C.
The ratio (%) between the discharge capacity at 3C and the discharge capacity at 0.1C was defined as the discharge maintenance ratio (3C / 0.1C maintenance ratio).

Table 1 shows the discharge capacities and discharge retention rates (3C / 0.1C retention rate) of Examples 1 to 8 and Comparative Examples 1 and 2.
Moreover, the charging / discharging curve of Example 4 and Comparative Example 2 is shown in FIG. 1, A shows the charge / discharge curve of Example 4, and B shows the charge / discharge curve of Comparative Example 2, respectively.

According to Table 1, in the positive electrode active materials of Examples 1 to 8, the ratio (Fe (III) / total Fe) is represented by the following formula: 0 mol% <Fe (III) / total Fe <7.0 mol% (6)
Meets a surface area ^3m 2 / g large and since it is less ^16m 2 / g than the ratio, improved discharge capacity and discharge retention rate compared with Comparative Example 1,2 (3C / 0.1C maintenance rate) It was confirmed that the charge / discharge characteristics were improved and the initial discharge capacity was secured.

In the method for producing a positive electrode active material for a lithium ion battery according to the present invention, Li ₃ PO ₄ , or a Li source and a phosphoric acid source, and an Fe source are dissolved in a solvent containing water as a main component. By adding an oxidizing agent and pressurizing and heating the mixture containing this oxidizing agent, LiFePO ₄ fine particles in which the primary particle diameter and the amount of trivalent Fe (Fe (III)) are controlled are easily produced. Therefore, by applying the obtained positive electrode active material for a lithium ion battery to a positive electrode of a lithium ion battery, particularly a lithium ion secondary battery, it is possible to improve the charging / discharging characteristics and secure the initial discharge capacity. The industrial significance is extremely large.

Claims (5)

Li ₃ PO ₄ , or Li source and phosphoric acid source, and Fe source are dissolved in a water-based solvent, an oxidizing agent is added to the resulting mixture, and the mixture containing this oxidizing agent is pressurized - heating, method for producing a lithium ion battery positive electrode active material and generating a LiFePO ₄ particles.   The oxidizing agent is one or more selected from the group consisting of hydrogen peroxide, nitric acid, sodium hypochlorite, metachloroperbenzoic acid, and potassium permanganate. Manufacturing method of a lithium ion battery positive electrode active material.   The method for producing a positive electrode active material for a lithium ion battery according to claim 1 or 2, wherein the addition amount of the oxidizing agent is 0.01 mol% or more and 6 mol% or less with respect to the total mol amount of the Fe source. . A lithium ion battery positive electrode active material obtained by the method for producing a positive electrode active material for a lithium ion battery according to any one of claims 1 to 3,
The LiFePO ₄ particles of trivalent Fe (Fe (III)) and mol of the ratio of the mol amount of the total Fe in the LiFePO ₄ microparticles (Fe (III) / total Fe) is represented by the following formula (1)
0 mol% <Fe (III) / total Fe <7.0 mol% (1)
The positive electrode active material for lithium ion batteries characterized by satisfy | filling. 5. The positive electrode active material for a lithium ion battery according to claim 4, wherein the specific surface area is larger than 3 m ² / g and 16 m ² / g or less.

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