JP2015049995A - Method for manufacturing positive electrode active material for lithium ion batteries, and positive electrode active material for lithium ion batteries - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a positive electrode active material for lithium ion batteries which makes possible to prepare a positive electrode active material for lithium ion batteries high in voltage, energy density, and load characteristic, and superior in long-term cycle stability and safety, and which makes possible to produce a positive electrode active material in a simple manufacturing process efficiently; and a positive electrode active material for lithium ion batteries.SOLUTION: A method for manufacturing a positive electrode active material for lithium ion batteries comprises: a slurry-preparation step for mixing a Li source and a Mn source which make raw materials of olivine type LiMnPOparticles, and an A source and a P source which make raw materials of olivine type LiAPO(where A represents at least one of Fe and Ni) into a slurry; and a heating treatment step for heating the slurry in a temperature range of 100°C to lower than 150°C in an airtight condition, and further heating the slurry in a temperature range of 150-200°C.

Description

  The present invention relates to a method for producing a positive electrode active material for a lithium ion battery and a positive electrode active material for a lithium ion battery. In particular, a phosphate-based electrode active material having an olivine structure is used as the electrode active material. A method for producing a positive electrode active material for a lithium ion battery suitable for producing a positive electrode for a lithium ion battery having excellent energy density, high load characteristics, and long-term cycle stability and safety, and a positive electrode for a lithium ion battery It relates to active materials.

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.
This lithium ion battery is lighter, smaller and has higher energy than secondary batteries such as conventional lead batteries, nickel cadmium batteries and nickel metal hydride batteries. It is used as a power source for information terminals and portable electronic devices.

In recent years, this lithium ion battery has been studied as a high-output power source for electric vehicles, hybrid vehicles, electric tools, and the like. High-speed charge / discharge characteristics are required for the electrode active materials of batteries used as these high-output power supplies.
Various materials have been studied as a rare metal-free positive electrode active material from the viewpoints of high functionality, high capacity, low cost, and the like of such secondary batteries. Among these, an olivine-type phosphate electrode active material typified by LiFePO ₄ has attracted attention as an electrode active material having high resource and low cost as well as safety.

Among these phosphate-based electrode active materials, lithium manganese phosphate (LiMnPO ₄ ) whose alkaline metal is Li and whose transition metal is Mn has a theoretical capacity of about 170 mAh / g, which is almost the same as LiFePO _4. However, even under low-rate discharge conditions, the utilization factor is very poor compared to LiFePO _4, and there is a problem that it is difficult to charge and discharge a large current due to insufficient electron conductivity. In order to solve these problems, various efforts have been made, such as the refinement of particles and the combination with conductive materials.
For example, as a method for producing a conductive carbon material used for compounding with a conductive substance, a method of carbonizing wood using an iron catalyst such as iron nitrate has been proposed (Patent Document 1). Further, as a positive electrode material for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte comprising a nickel compound or an iron compound on the surface of a base particle made of lithium manganese phosphate and further comprising carbon on the nickel compound or iron compound. A positive electrode material for an electrolyte secondary battery has been proposed (Patent Document 2).

JP 2009-190957 A JP 2010-135305 A

However, in the conventional positive electrode material for a non-aqueous electrolyte secondary battery described above, a nickel compound or an iron compound is formed on the surface of the base particle made of lithium manganese phosphate, and then carbon is formed on the nickel compound or the iron compound. Therefore, the purity and crystallinity of the nickel compound or iron compound and carbon formed on the surface of the base particle are likely to be insufficient, and the load characteristics, cycle characteristics and energy density are excellent. There is a problem that it is difficult to obtain a positive electrode material.
In addition, since the manufacturing process is complicated, it is difficult to efficiently produce the positive electrode material.

  The present invention has been made to solve the above problems, and has a higher voltage, a higher energy density, a higher load characteristic, a long-term cycle stability and a positive electrode active material for lithium ion batteries. The manufacturing method of a positive electrode active material for a lithium ion battery and a positive electrode active material for a lithium ion battery capable of efficiently producing a positive electrode active material with a simple manufacturing process And

As a result of intensive studies to solve the above-mentioned problems, the present inventors formed a film made of olivine-type LiAPO ₄ (where A is at least one of Fe and Ni) on the surface of olivine-type LiMnPO ₄ particles. In a method for producing a positive electrode active material for a lithium ion battery, a slurry obtained by mixing raw materials of LiMnPO ₄ particles and LiAPO ₄ is heat-treated in a sealed state in a temperature range of 100 ° C. or more and less than 150 ° C., and In addition, a film made of LiAPO ₄ (where A is at least one of Fe and Ni) was formed on the surface of LiMnPO ₄ particles by heat treatment in a temperature range of 150 ° C. or higher and 200 ° C. or lower in a sealed state. Particles can be efficiently obtained in large quantities by a single hydrothermal treatment, and therefore higher voltage, higher energy density, higher negative In characteristic, the long-term cycle stability and the positive active material for a lithium ion battery excellent in safety, a simple process, found that can be efficiently produced, and have completed the present invention.

That is, in the method for producing a positive electrode active material for a lithium ion battery according to the present invention, a coating film made of olivine-type LiAPO ₄ (where A is at least one of Fe and Ni) is formed on the surface of olivine-type LiMnPO ₄ particles. A method for producing a positive electrode active material for a lithium ion battery, wherein a slurry is prepared by mixing a Li source and a Mn source as raw materials for the LiMnPO ₄ particles, and an A source and a P source as raw materials for the LiAPO ₄ And a heat treatment step of heat-treating the slurry in a sealed state in a temperature range of 100 ° C. or higher and lower than 150 ° C., and further heat-treating in a temperature range of 150 ° C. or higher and 200 ° C. or lower. It is characterized by that.

The slurry preparation step preferably includes a step of adjusting the molar ratio A / Mn of the A source to the Mn source to be 0.04 or more and 0.20 or less.
After the heat treatment step, a second slurry preparation step in which the LiAPO ₄ -coated LiMnPO ₄ particles obtained in the heat treatment step, an organic compound serving as a carbon source, and a solvent are mixed to form a second slurry. It is preferable to include a second heat treatment step of drying the second slurry and then heat-treating it in a temperature range of 500 ° C. or higher and 1000 ° C. or lower in a non-oxidizing atmosphere.

  The positive electrode active material for lithium ion batteries of the present invention is obtained by the method for producing a positive electrode active material for lithium ion batteries of the present invention.

According to the method for producing a positive electrode active material for a lithium ion battery of the present invention, a slurry obtained by mixing a Li source and a Mn source as raw materials for LiMnPO ₄ particles and an A source and a P source as raw materials for LiAPO ₄ into a slurry. A heat treatment step of heat-treating the slurry in a sealed state in a temperature range of 100 ° C. or higher and lower than 150 ° C., and further heat-treating in a temperature range of 150 ° C. or higher and 200 ° C. or lower. Therefore, particles having an olivine-type LiAPO ₄ film (where A is at least one of Fe and Ni) formed on the surface of the olivine-type LiMnPO ₄ particles can be efficiently obtained in large quantities by one hydrothermal treatment. Can do. Therefore, a positive electrode active material for a lithium ion battery having higher voltage, higher energy density, and higher load characteristics and excellent long-term cycle stability and safety can be efficiently produced in a simple process.

According to the positive electrode active material for a lithium ion battery of the present invention, since it was obtained by the method for producing a positive electrode active material for a lithium ion battery of the present invention, a longer cycle stability with higher voltage, higher energy density, and higher load characteristics. Excellent in safety and safety.
By applying this positive electrode active material for a lithium ion battery to an electrode for a lithium ion battery, a lithium ion battery having higher voltage, higher energy density, and higher load characteristics, and excellent long-term cycle stability and safety is provided. be able to.

It is a figure which shows the measurement result of the element distribution of the depth direction of the positive electrode active material for lithium ion batteries of Examples 1 and 2 and Comparative Examples 1 to 3 of the present invention. It is a figure which shows the charging / discharging curve of each lithium ion battery of Example 1, 2 and Comparative Examples 1-3 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, the surface of olivine-type LiMnPO ₄ particles is coated with a coating made of olivine-type LiAPO ₄ (where A is at least one of Fe and Ni). A method for producing a positive electrode active material for an ion battery, comprising:
A slurry preparation step in which a Li source and a Mn source as raw materials for the LiMnPO ₄ particles and an A source and a P source as raw materials for the LiAPO ₄ are mixed to form a slurry;
A heat treatment step of heat-treating the slurry in a sealed state in a temperature range of 100 ° C. or more and less than 150 ° C., and further in a temperature range of 150 ° C. or more and 200 ° C. or less;
A second slurry preparation step in which the LiAPO ₄ -coated LiMnPO ₄ particles obtained in this heat treatment step, an organic compound serving as a carbon source and a solvent are mixed to form a second slurry;
A second heat treatment step of drying the second slurry and then heat-treating in a temperature range of 500 ° C. or more and 1000 ° C. or less in a non-oxidizing atmosphere;
It is a manufacturing method which has this.
Next, this manufacturing method will be described in detail.

(Slurry preparation process)
In the process of mixing the Li source and Mn source as raw materials for the olivine-type LiMnPO ₄ particles, and the A source and P source as raw materials for the olivine-type LiAPO ₄ (wherein A is at least one of Fe and Ni) into a slurry. is there.

Examples of the Li source include hydroxides such as lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ), lithium chloride (LiCl), lithium nitrate (LiNO ₃ ), and lithium phosphate (Li ₃ PO ₄ ). , Lithium inorganic acid salts such as dilithium hydrogen phosphate (Li ₂ HPO ₄ ), lithium dihydrogen phosphate (LiH ₂ PO ₄ ) and hydrates thereof, lithium acetate (LiCH ₃ COO), lithium oxalate ((COOLi ) ₂ ) and the like, and hydrates thereof, and one or more selected from these are preferably used.
The Mn source is preferably a Mn salt, such as manganese chloride (II) (MnCl ₂ ), manganese sulfate (II) (MnSO ₄ ), manganese acetate (II) (Mn (CH ₃ COO) ₂ ), and water thereof. One or more selected from among Japanese products are preferred.

The A source is preferably a metal salt containing at least one of Fe and Ni, for example, selected from chlorides, sulfates, acetates, nitrates and hydrates containing at least one of Fe and Ni. One type or two or more types are preferred.
Examples of the P source 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 ), lithium phosphate (Li ₃ PO ₄ ), dilithium hydrogen phosphate (Li ₂ HPO ₄ ), lithium dihydrogen phosphate (LiH ₂ PO ₄ ) And one or more selected from these hydrates are preferably used.

Examples of the mixing method of these Li source, Mn source, A source and P source include a method of adding each raw material solid to an aqueous solvent and a method of mixing each aqueous raw material solution, from the viewpoint of uniformly mixing the raw materials. The latter method is preferred.
When mixing these raw materials, it is preferable to prepare such that the molar ratio A / Mn of the A source to the Mn source is 0.04 or more and 0.20 or less.

Here, the reason why the molar ratio A / Mn of the A source to the Mn source is limited to the above range is that this range is higher voltage, higher energy density, higher load characteristics, long-term cycle stability and safety. It is because it is the range which can be compatible.
In addition, when the molar ratio A / Mn is less than 0.04, it is not preferable because the coating of the olivine type LiAPO ₄ (where A is at least one of Fe and Ni) becomes insufficient, while the molar ratio A When / Mn exceeds 0.20, the movement of lithium ions from the electrolytic solution to the olivine-type LiMnPO ₄ particles is inhibited, which is not preferable.

(Heat treatment process)
In this process, the slurry obtained in the above step is heat-treated in a sealed state in a temperature range of 100 ° C. or higher and lower than 150 ° C., and further heat-treated in a temperature range of 150 ° C. or higher and 200 ° C. or lower. .
Each of time in these heat treatment, LiAPO ₄ on the surface of LiMnPO ₄ particles (where, A is Fe, at least one of Ni) 1 times water LiAPO ₄ coated LiMnPO ₄ particles formed by coating a coating composed of What is necessary is just to be able to obtain efficiently in large quantities by heat processing.
Considering these conditions, for example, heat treatment is performed for 1 hour or more and 12 hours or less in a temperature range of 100 ° C. or more and less than 150 ° C., and then for 1 hour or more and 6 hours in a temperature range of 150 ° C. or more and 200 ° C. or less. It is preferable to heat-process below.

In the heat treatment in the initial temperature range of 100 ° C. or higher and lower than 150 ° C., the reaction of LiMnPO ₄ does not proceed at a temperature lower than 100 ° C., and LiAPO ₄ (provided on the surface of LiMnPO ₄ particles at 150 ° C. or higher. LiAPO ₄ coated LiMnPO ₄ particles formed by coating a film made of A is at least one of Fe and Ni), and Mn and A (where A is at least one of Fe and Ni) are contained in the particles. This is not preferable because evenly existing particles are generated.
In the heat treatment in the next temperature range of 150 ° C. or higher and 200 ° C. or lower, the reaction of LiAPO ₄ (where A is at least one of Fe and Ni) does not proceed at temperatures lower than 150 ° C., whereas it is 200 ° C. or higher. In this case, crystal growth proceeds and coarse particles are formed, which is not preferable.

In this heat treatment step, the surface of LiMnPO ₄ particles is subjected to heat treatment in a two-step temperature range of 100 ° C. or higher and lower than 150 ° C., and further 150 ° C. or higher and 200 ° C. or lower. ₄ (wherein A is at least one of Fe and Ni), LiAPO ₄ -coated LiMnPO ₄ particles coated with a coating film can be efficiently obtained in a large amount by one hydrothermal treatment.

After the heat treatment in this two-step temperature range, the mixture is cooled to room temperature (25 ° C.) by standing or cooling, and a precipitated cake-like reaction product is obtained.
Next, this precipitate (= the precipitated cake-like reaction product) is sufficiently washed with distilled water or pure water several times, and then using a hot air dryer, a batch dryer or the like. dry.
Thus, LiAPO ₄ (where, A is Fe, at least one of Ni) on the surface of LiMnPO ₄ particles LiAPO ₄ coated LiMnPO ₄ particles formed by coating a coating film made of, it can be easily and conveniently manufactured.

(Second slurry preparation step)
In this step, the LiAPO ₄ -coated LiMnPO ₄ particles obtained in the heat treatment step are mixed with an organic compound and a solvent to be a carbon source to form a second slurry.
The organic compound that serves as the carbon source is not particularly limited as long as it is an organic compound that generates carbon by heat treatment in a non-oxidizing atmosphere. For example, higher monohydric alcohols such as hexanol and octanol, Examples thereof include unsaturated monohydric alcohols such as allyl alcohol, propynol (propargyl alcohol) and terpineol, and polyvinyl alcohol (PVA).

  Although it does not restrict | limit especially as a solvent which melt | dissolves this organic compound, For example, water, methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol: IPA), butanol, pentanol, hexanol, octanol, diacetone alcohol, etc. Alcohols, ethyl acetate, butyl acetate, ethyl lactate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, esters such as γ-butyrolactone, diethyl ether, ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol Monoethyl ether (ethyl cellosolve), ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monomethyl ether, diethyl Ethers such as ethylene glycol monoethyl ether, ketones such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), acetylacetone, cyclohexanone, amides such as dimethylformamide, N, N-dimethylacetoacetamide, N-methylpyrrolidone And glycols such as ethylene glycol, diethylene glycol, and propylene glycol. These may be used alone or in combination of two or more.

The concentration of the organic compound serving as the carbon source in the slurry is not particularly limited, but in order to uniformly form a coating layer containing carbonaceous matter on the surface of the LiAPO ₄ -coated LiMnPO ₄ particles, 1 mass % To 25% by mass is preferable.

(Second heat treatment step)
The second slurry obtained in the second slurry preparation step is dried to obtain a powder, and this powder is heated in a temperature range of 500 ° C. or higher and 1000 ° C. or lower in a non-oxidizing atmosphere. It is a process to process.
The non-oxidizing atmosphere is preferably an inert gas atmosphere such as a nitrogen gas atmosphere or an argon atmosphere, or a reducing atmosphere containing about several mass% of hydrogen gas in the nitrogen gas.

The time for this heat treatment depends on the temperature at the time of heat treatment, but it may be in the range of time for carbon to be generated from the organic compound as the carbon source, for example, 500 ° C. or more and 1000 ° C. or less in a non-oxidizing atmosphere When the heat treatment is performed in the above temperature range, it is preferably 1 hour or more and 24 hours or less.
As described above, the surface of the LiMnPO ₄ particles is coated with a coating made of LiAPO ₄ (where A is at least one of Fe and Ni), and the surface is further coated with a carbonaceous coating and the LiAPO ₄ coated LiMnPO ₄ Particles can be prepared easily and simply.

[Positive electrode active material for lithium ion batteries]
The positive electrode active material for a lithium ion battery of this embodiment is a positive electrode active material obtained by the method for producing a positive electrode active material for a lithium ion battery of this embodiment, and LiAPO ₄ (provided that A is the surface of LiMnPO ₄ particles). These are carbonaceous and LiAPO ₄ -coated LiMnPO ₄ particles (hereinafter, also simply referred to as surface-coated LiMnPO ₄ particles) coated with a coating composed of at least one of Fe and Ni, and further coated with a carbonaceous coating.

The size of the surface-coated LiMnPO ₄ particles is not particularly limited, but the average primary particle diameter is preferably 20 nm or more and 400 nm or less, more preferably 30 nm or more and 150 nm or less.
Here, if the average primary particle size is less than 20 nm, the LiMnPO ₄ particles themselves may be destroyed by volume change due to charge / discharge, which is not preferable. On the other hand, if the average primary particle size exceeds 400 nm, the particles enter the particle interior. This is not preferable because the supply amount of electrons is insufficient and the utilization efficiency is lowered.
The average primary particle size is the number average particle size. The average primary particle diameter of the particles can be measured using a laser diffraction / scattering particle size distribution measuring apparatus or the like.

The shape of the surface-covered LiMnPO ₄ particles is not particularly limited, but it is preferable that the shape of the surface-coated LiMnPO ₄ particles is spherical, in particular, true spherical, because it is easy to produce an electrode material composed of spherical, particularly spherical secondary particles. .
Here, as the shape of the surface-coated LiMnPO ₄ particles, a spherical shape, particularly a true spherical shape, is preferable because an electrode material composed of the surface-coated LiMnPO ₄ particles, a binder resin (binder), and a solvent are mixed. This is because the amount of solvent in preparing the electrode forming paint or electrode forming paste can be reduced, and the electrode forming paint or electrode forming paste can be easily applied to the current collector.

Further, if the surface-coated LiMnPO ₄ particles have a spherical shape, the surface area of the electrode material produced using the surface-coated LiMnPO ₄ particles is minimized, and the addition of a binder resin (binder) added to the electrode material This is preferable because the amount can be minimized and the internal resistance of the positive electrode obtained can be reduced.
Furthermore, since it is easy to close-pack, the filling amount of the positive electrode material per unit volume is increased, the electrode density can be increased, and as a result, a high capacity lithium ion battery can be provided, which is preferable.

The thickness of the film made of LiAPO ₄ (where A is at least one of Fe and Ni) in the surface-coated LiMnPO ₄ particles is preferably 1 nm or more and 5 nm or less.
The reason why the thickness range of this LiAPO ₄ coating is preferably 1 nm or more and 5 nm or less is that this range is compatible with higher voltage, higher energy density, higher load characteristics, and long-term cycle stability and safety. This is because it is possible. Here, when the thickness is less than 1 nm, the coating of the olivine type LiAPO ₄ (where A is at least one of Fe and Ni) becomes insufficient, which is not preferable. On the other hand, when the thickness exceeds 5 nm, This is not preferable because the movement of lithium ions from the liquid to the olivine-type LiMnPO ₄ particles is inhibited.

The thickness of the carbonaceous film in the surface-coated LiMnPO ₄ particles is preferably 2 nm or more and 10 nm or less.
If the thickness of the carbonaceous film is less than 2 nm, the carbonaceous film is too thin, and it becomes difficult to improve the electronic conductivity of the surface-coated LiMnPO ₄ particles, while the thickness of the carbonaceous film is 10 nm. If it exceeds, battery activity, for example, battery capacity per unit mass of the electrode material may decrease.

[electrode]
The electrode of the present embodiment is an electrode containing the positive electrode active material for a lithium ion battery of the present embodiment.
In order to produce the electrode of this embodiment, the positive electrode active material for lithium ion battery (= surface-coated LiMnPO ₄ particles), a binder composed of a binder resin, and a solvent are mixed, and a coating material for electrode formation is obtained. Alternatively, the electrode forming paste is adjusted. At this time, a conductive aid may be added as necessary.

  Examples of such conductive assistants include thermal black, furnace black, lamp black, acetylene black, ketjen black, carbon nanotubes that are fibrous carbon, and vapor-grown carbon fibers. Particularly, carbon having excellent conductivity is preferably acetylene black or ketjen black. Acetylene black and ketjen black are preferred because they are readily available.

As the binder, that is, the binder resin, for example, polytetrafluoroethylene (PTFE) resin, polyvinylidene fluoride (PVdF) resin, fluororubber, and the like are preferably used.
The blending ratio of the positive electrode active material for lithium ion battery and the binder resin is not particularly limited. For example, the binder resin is added in an amount of 1 part by mass to 30 parts by mass with respect to 100 parts by mass of the positive electrode active material for lithium ion battery. The amount is preferably 3 parts by mass or more and 20 parts by mass or less.

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

Next, this electrode-forming paint or electrode-forming paste is applied to one surface of the metal foil, and then dried, and a coating film made of a mixture of the above-described positive electrode active material for a lithium ion battery and a binder resin is applied. A metal foil formed on the surface is obtained.
Next, this coating film is pressure-bonded and dried to produce an electrode having an electrode material layer on one surface of the metal foil.
In this way, the electrode of this embodiment can be produced.

[Lithium ion battery]
The lithium ion battery of this embodiment includes a positive electrode made of the electrode of this embodiment, a negative electrode made of metal Li, Li alloy, Li ₄ Ti ₅ O ₁₂ , a carbon material, etc., and an electrolyte solution and a separator or a solid electrolyte. Yes.
In this lithium ion battery, by producing an electrode using the positive electrode active material for the lithium ion battery according to the present embodiment, the desorption / insertion of Li is improved, and therefore, higher voltage, higher energy density, and higher load characteristics. And long-term cycle stability and safety can be achieved.

As described above, according to the method for producing a positive electrode active material for a lithium ion battery of the present embodiment, the Li source and Mn source as raw materials for LiMnPO ₄ particles, and the A source and P source as raw materials for LiAPO ₄ are used. A slurry preparation step of mixing and forming a slurry, and the slurry are heat-treated in a sealed state in a temperature range of 100 ° C. or higher and lower than 150 ° C., and further heat-treated in a temperature range of 150 ° C. or higher and 200 ° C. or lower. A heat treatment step, a second slurry preparation step in which the LiAPO ₄ -coated LiMnPO ₄ particles obtained in the heat treatment step, an organic compound serving as a carbon source and a solvent are mixed to form a second slurry, and this After the second slurry is dried, there is a second heat treatment step in which heat treatment is performed in a temperature range of 500 ° C. or higher and 1000 ° C. or lower in a non-oxidizing atmosphere. , The surface of LiMnPO ₄ particles, LiAPO ₄ (where, A is Fe, at least one of Ni) film made is formed, a further surface-coated LiMnPO ₄ particles whose surface is coated with the carbonaceous coating, once It can be efficiently obtained in large quantities by hydrothermal treatment. Therefore, a positive electrode active material for a lithium ion battery having higher voltage, higher energy density, and higher load characteristics and excellent long-term cycle stability and safety can be efficiently produced in a simple process.

According to the positive electrode active material for a lithium ion battery of this embodiment, the surface of LiMnPO ₄ particles is coated with a film made of LiAPO ₄ (where A is at least one of Fe and Ni), and the surface is further coated with a carbonaceous film. Since the surface-coated LiMnPO ₄ particles are coated by the above, it is possible to achieve both higher voltage, higher energy density, higher load characteristics, and long-term cycle stability and safety.
By applying this positive electrode active material for a lithium ion battery to a lithium ion battery, it is possible to provide a lithium ion battery with higher voltage, higher energy density, higher load characteristics, and excellent long-term cycle stability and safety. it can.

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

"Example 1"
LiFePO ₄ -coated LiMnPO ₄ particles were produced by coating the surface of LiMnPO ₄ particles with a coating made of LiFePO ₄ by a hydrothermal synthesis method.
Here, Li ₃ PO ₄ is used as the Li source and P source, an MnSO ₄ aqueous solution is used as the Mn source, an FeSO ₄ aqueous solution is used as the Fe source, and these are molar ratios of Li: P: Mn: Fe = 3: 1: 0. 9: 0.1 to prepare a raw material slurry having a total volume of 200 ml.

Next, this raw material slurry was accommodated in a pressure-resistant airtight container, subjected to a heating reaction at 110 ° C. for 1 hour, and then subjected to a heating reaction at 170 ° C. for 1 hour.
After this reaction, the mixture was cooled to room temperature (25 ° C.) to obtain a cake-like reaction product as a precipitate.
Next, the precipitate was sufficiently washed with distilled water, and then dried at 120 ° C. for 12 hours using a dryer to obtain LiFePO ₄ -coated LiMnPO ₄ particles.

Next, 95 parts by mass of this LiFePO ₄ -coated LiMnPO ₄ particles and 5 parts by mass of an aqueous polyvinyl alcohol solution containing 10% by mass of polyvinyl alcohol (PVA) as an organic compound were mixed to obtain a PVA-containing slurry.
Next, this PVA-containing slurry was dried using a spray dryer, and the obtained dried product was heat-treated at 600 ° C. for 1 hour in a nitrogen gas atmosphere, and the positive electrode active material for lithium ion battery of Example 1 A surface-coated LiMnPO ₄ particle was obtained.

"Example 2"
LiNiPO ₄ -coated LiMnPO ₄ particles were produced by coating the surface of LiMnPO ₄ particles with a coating made of LiNiPO ₄ by a hydrothermal synthesis method.
Here, Li ₃ PO ₄ is used as the Li source and the P source, an MnSO ₄ aqueous solution is used as the Mn source, an NiSO ₄ aqueous solution is used as the Ni source, and these are molar ratios of Li: P: Mn: Ni = 3: 1: 0. 9: 0.1 to prepare a raw material slurry having a total volume of 200 ml.

Next, this raw material slurry was housed in a pressure-resistant airtight container, subjected to a heating reaction at 110 ° C. for 1 hour, and then subjected to a heating reaction at 190 ° C. for 1 hour.
After this reaction, the mixture was cooled to room temperature (25 ° C.) to obtain a cake-like reaction product as a precipitate.
Next, the precipitate was sufficiently washed with distilled water, and then dried at 120 ° C. for 12 hours using a dryer to obtain LiNiPO ₄ -coated LiMnPO ₄ particles.

Next, 95 parts by mass of the LiNiPO ₄ -coated LiMnPO ₄ particles and 5 parts by mass of an aqueous polyvinyl alcohol solution containing 10% by mass of polyvinyl alcohol (PVA) as an organic compound were mixed to obtain a PVA-containing slurry.
Next, this PVA-containing slurry was dried using a spray drier, and the obtained dried product was heat-treated at 600 ° C. for 1 hour in a nitrogen gas atmosphere to obtain a positive electrode active material for a lithium ion battery of Example 2. A surface-coated LiMnPO ₄ particle was obtained.

"Comparative Example 1"
A positive electrode active material for a lithium ion battery was prepared by a hydrothermal synthesis method.
Here, Li ₃ PO ₄ is used as the Li source and P source, an MnSO ₄ aqueous solution is used as the Mn source, an FeSO ₄ aqueous solution is used as the Fe source, and these are molar ratios of Li: P: Mn: Fe = 3: 1: 0. 9: 0.1 to prepare a raw material slurry having a total volume of 200 ml.

Subsequently, this raw material slurry was accommodated in a pressure-resistant airtight container and subjected to a heating reaction at 130 ° C. for 1 hour.
After this reaction, the mixture was cooled to room temperature (25 ° C.) to obtain a cake-like reaction product as a precipitate.
Next, the precipitate was sufficiently washed with distilled water, and then dried at 120 ° C. for 12 hours using a dryer to obtain a powder.

Next, 95 parts by mass of the powder and 5 parts by mass of an aqueous polyvinyl alcohol solution containing 10% by mass of polyvinyl alcohol (PVA) as an organic compound were mixed to obtain a PVA-containing slurry.
Next, this PVA-containing slurry was dried using a spray dryer, and the obtained dried product was heat-treated at 600 ° C. for 1 hour in a nitrogen gas atmosphere, and the positive electrode active material for lithium ion battery of Comparative Example 1 Got.

"Comparative Example 2"
A positive electrode active material for a lithium ion battery was prepared by a hydrothermal synthesis method.
Here, Li ₃ PO ₄ is used as the Li source and P source, an MnSO ₄ aqueous solution is used as the Mn source, an FeSO ₄ aqueous solution is used as the Fe source, and these are molar ratios of Li: P: Mn: Fe = 3: 1: 0. 9: 0.1 to prepare a raw material slurry having a total volume of 200 ml.

Subsequently, this raw material slurry was accommodated in a pressure-resistant airtight container and subjected to a heating reaction at 170 ° C. for 1 hour.
After this reaction, the mixture was cooled to room temperature (25 ° C.) to obtain a cake-like reaction product as a precipitate.
Next, the precipitate was sufficiently washed with distilled water, and then dried at 120 ° C. for 12 hours using a dryer to obtain a powder.

Next, 95 parts by mass of the powder and 5 parts by mass of an aqueous polyvinyl alcohol solution containing 10% by mass of polyvinyl alcohol (PVA) as an organic compound were mixed to obtain a PVA-containing slurry.
Next, this PVA-containing slurry was dried using a spray dryer, and the resulting dried product was heat-treated at 600 ° C. for 1 hour in a nitrogen gas atmosphere, and the positive electrode active material for lithium ion battery of Comparative Example 2 Got.

“Comparative Example 3”
A positive electrode active material for a lithium ion battery was prepared by a hydrothermal synthesis method.
Here, Li ₃ PO ₄ is used as the Li source and P source, an MnSO ₄ aqueous solution is used as the Mn source, an FeSO ₄ aqueous solution is used as the Fe source, and these are molar ratios of Li: P: Mn: Fe = 3: 1: 0. 9: 0.1 to prepare a raw material slurry having a total volume of 200 ml.

Next, this raw material slurry was accommodated in a pressure-resistant airtight container, subjected to a heating reaction at 110 ° C. for 1 hour, and then subjected to a heating reaction at 250 ° C. for 1 hour.
After this reaction, the mixture was cooled to room temperature (25 ° C.) to obtain a cake-like reaction product as a precipitate.
Next, the precipitate was sufficiently washed with distilled water, and then dried at 120 ° C. for 12 hours using a dryer to obtain a powder.

Next, 95 parts by mass of the powder and 5 parts by mass of an aqueous polyvinyl alcohol solution containing 10% by mass of polyvinyl alcohol (PVA) as an organic compound were mixed to obtain a PVA-containing slurry.
Next, this PVA-containing slurry was dried using a spray dryer, and the obtained dried product was heat-treated at 600 ° C. for 1 hour in a nitrogen gas atmosphere, and the positive electrode active material for lithium ion battery of Comparative Example 3 Got.

"Evaluation of positive electrode active materials for lithium-ion batteries"
The positive electrode active materials for lithium ion batteries of Examples 1 and 2 and Comparative Examples 1 to 3 were evaluated.
Evaluation items and evaluation results are as follows.

(1) Element distribution in the depth direction The element distribution in the depth direction of the positive electrode active material for lithium ion batteries was measured using Auger electron spectroscopy.
The measurement results of the element distribution in the depth direction of the positive electrode active materials for lithium ion batteries of Examples 1 and 2 and Comparative Examples 1 to 3 are shown in Table 1 and FIG.

As a result, in the positive electrode active materials for lithium ion batteries of Examples 1 and 2, it was confirmed that Fe and Ni were present on the particle surface, and Mn was clearly unevenly distributed inside.
On the other hand, the presence of Fe could not be confirmed in the positive electrode active material for lithium ion batteries of Comparative Example 1, and it was not possible to confirm that Fe and Mn were unevenly distributed in the positive electrode active materials for lithium ion batteries of Comparative Examples 2 and 3. .

(2) Specific surface area Specific surface area meter Using BELSORP-mini, the specific surface areas of the positive electrode active materials for lithium ion batteries of Examples 1 and 2 and Comparative Examples 1 to 3 were measured. These measurement results are shown in Table 1.
As a result, each of the positive electrode active materials for lithium ion batteries of Examples 1 and 2 and Comparative Examples 1 and 2 had a large specific surface area, but the specific surface area of the positive electrode active material for lithium ion batteries of Comparative Example 3 was greatly reduced. It was. The reason for this is considered to be that the temperature of the heating reaction is as high as 250 ° C., and therefore crystal growth has progressed.

“Production and evaluation of lithium-ion batteries”
Examples 1, 2 and Comparative Examples 1 to 3, positive electrode active materials for lithium ion batteries, acetylene black (AB) as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder (mass) The mixture is mixed so that the ratio of the active material is: AB: PVdF = 80: 10: 10, and N-methyl-2-pyrrolidinone (NMP) is added as a solvent to give fluidity. And it was set as each positive electrode material paste of Comparative Examples 1-3.

  Next, these pastes were applied onto an aluminum (Al) foil having a thickness of 30 μm and dried. Thereafter, pressurization was performed at a predetermined pressure to prepare lithium ion battery electrode plates, and these electrode plates were punched into a disk shape having a diameter of 16 mm. A test electrode was prepared.

For the test electrodes of these lithium ion batteries, lithium (Li) metal was used as the counter electrode, and a porous polypropylene film was used as the separator. In addition, as the non-aqueous electrolyte solution, hexafluoride so as to have a concentration of 1 mol / L in a mixed solution in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a volume ratio of 1: 1. A LiPF ₆ solution in which lithium phosphate (LiPF ₆ ) was dissolved was used.
Next, lithium ion batteries of Examples 1 and 2 and Comparative Examples 1 to 3 were prepared using the test electrode, the counter electrode, the nonaqueous electrolyte solution, and the 2032 type coin cell.

The battery characteristics of these lithium ion batteries were tested.
In the battery characteristic test, constant current charging was performed at a current of 0.1 CA at an environmental temperature of 25 ° C. until the voltage of the test electrode reached 4.3 V with respect to the Li equilibrium voltage, and then the current value at 4.3 V was The constant voltage charge was performed until it became 0.01CA. Then, it was rested for 1 minute, and constant current discharge of 0.1 CA and 1 CA was performed until the voltage of the test electrode became 2.0 V with respect to the Li equilibrium voltage. Table 1 shows the discharge capacities of the lithium ion batteries of Examples 1 and 2 and Comparative Examples 1 to 3, and FIG. 2 shows the charge and discharge curves of the lithium ion batteries of Examples 1 and 2 and Comparative Examples 1 to 3, respectively. Show.

According to these results, the discharge capacity and charge / discharge curve of the lithium ion batteries of Examples 1 and 2 were compared with the discharge capacity and charge / discharge curve of the lithium ion batteries of Comparative Examples 1 to 3, respectively. It was excellent.
This factor is considered to be because the lithium ion batteries of Comparative Examples 1 to 3 had a factor that deteriorated the battery characteristics.
That is, in the lithium ion battery of Comparative Example 1, LiFePO ₄ was not present on the surface of LiMnPO ₄ , and as a result, the battery characteristics were degraded.
In the lithium ion battery of Comparative Example 2, LiMnPO ₄ and LiFePO ₄ are in solid solution, and thus the proportion of LiFePO ₄ present on the surface is reduced. As a result, the characteristic improvement action does not work effectively, and the battery characteristics Had fallen.
In the lithium ion battery of Comparative Example 3, the specific surface area of the particles was greatly reduced, and thus the reaction field between the crystal and Li was reduced, and as a result, the battery characteristics were lowered.

In this embodiment, acetylene black (AB) is used as a conductive additive, but carbon materials such as carbon black, graphite, ketjen black, natural graphite, and artificial graphite may be used. Moreover, although evaluation is made with a battery using lithium (Li) metal as a counter electrode, naturally, carbon materials such as natural graphite, artificial graphite, coke, Li ₄ Ti ₅ O ₁₂ , or lithium (Li) alloy, etc. A negative electrode material may be used.
Further, as the non-aqueous electrolyte solution, a solution in which ethylene carbonate containing 1 mol / L of LiPF ₆ and diethyl carbonate are mixed in a volume ratio of 1: 1 is used, but LiBF ₄ or LiClO ₄ is used instead of LiPF _6. May be used, and propylene carbonate or diethyl carbonate may be used instead of ethylene carbonate.
Moreover, you may use a solid electrolyte instead of electrolyte solution and a separator.

The method for producing a positive electrode active material for a lithium ion battery according to the present invention includes a Li source and a Mn source as raw materials for olivine-type LiMnPO ₄ particles, and a raw material for olivine-type LiAPO ₄ (where A is at least one of Fe and Ni). A slurry preparation step of mixing A source and P source to become a slurry, and heat-treating the slurry in a sealed state in a temperature range of 100 ° C. or higher and lower than 150 ° C., and further 150 ° C. or higher and 200 And a heat treatment step in which heat treatment is performed in a temperature range of less than or equal to ° C., thereby forming a film made of olivine-type LiAPO ₄ (where A is at least one of Fe and Ni) on the surface of the olivine-type LiMnPO ₄ particles. Particles can be efficiently obtained in large quantities by one hydrothermal treatment, so the next generation is expected to be smaller, lighter, and higher in capacity. It is possible to apply also to the secondary battery, when the next generation of the secondary battery, the effect is very large.

Claims (4)

A method for producing a positive electrode active material for a lithium ion battery, in which a film made of olivine-type LiAPO ₄ (where A is at least one of Fe and Ni) is formed on the surface of olivine-type LiMnPO ₄ particles,
A slurry preparation step in which a Li source and a Mn source as raw materials for the LiMnPO ₄ particles and an A source and a P source as raw materials for the LiAPO ₄ are mixed to form a slurry;
A heat treatment step of heat-treating the slurry in a sealed state in a temperature range of 100 ° C. or more and less than 150 ° C., and further in a temperature range of 150 ° C. or more and 200 ° C. or less;
The manufacturing method of the positive electrode active material for lithium ion batteries characterized by having.   The lithium ion according to claim 1, wherein the slurry preparing step includes a step of preparing a molar ratio A / Mn of the A source to the Mn source to be 0.04 or more and 0.20 or less. A method for producing a positive electrode active material for a battery. After the heat treatment step, a second slurry preparation step in which the LiAPO ₄ -coated LiMnPO ₄ particles obtained in the heat treatment step, an organic compound serving as a carbon source, and a solvent are mixed to form a second slurry. ,
A second heat treatment step of drying the second slurry and then heat-treating in a temperature range of 500 ° C. or more and 1000 ° C. or less in a non-oxidizing atmosphere;
The method for producing a positive electrode active material for a lithium ion battery according to claim 1, wherein:   A positive electrode active material for a lithium ion battery 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.

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