JP2023047466A - Positive electrode active material nanoparticle mixture for lithium ion secondary battery, and method of manufacturing lithium ion secondary battery - Google Patents

Abstract

To provide a positive electrode active material nanoparticle mixture for a lithium ion secondary battery, with which rate characteristics of a lithium ion secondary battery can be effectively enhanced while a high discharge capacity in the lithium ion secondary battery is retained, and a method for manufacturing a lithium ion secondary battery utilizing the same.SOLUTION: A positive electrode active material nanoparticle mixture for a lithium ion secondary battery is a mixture of nanoparticles A which are represented by the following formula (a): LifMngFehM1xPO4...(a) and have an average particle size of 50-200 nm, and surfaces of which each are covered with carbon with a coverage of 5-70%, and nanoparticles B which are represented by the following formula (b): LiM2aMnbO4...(b) and have an average particle size of 50 -200 nm, a mass ratio (A:B) of the nanoparticles A and the nanoparticles B in the mixture being 95:5 to 70:30.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a positive electrode active material nanoparticle mixture for a lithium ion secondary battery that improves rate characteristics while maintaining a high discharge capacity, and a method for producing a lithium ion secondary battery using the same.

Secondary batteries such as lithium ion secondary batteries are used in a wide range of fields such as mobile phones, digital cameras, notebook PCs, hybrid vehicles, and electric vehicles. As a positive electrode material for such lithium ion secondary batteries, particles having an olivine type structure such as lithium manganese phosphate and lithium iron phosphate, such as LiMn _x Fe _1-x PO ₄ , are highly safe and dischargeable. Although it is considered promising due to its large capacity, issues remain regarding rate characteristics. On the other hand, particles having a spinel structure such as LiMnO ₂ can contribute to the improvement of rate characteristics, but there remains a problem in securing sufficient discharge capacity.
For this reason, various developments using these particles have been conventionally made in order to try to further improve the battery characteristics.

For example, Patent Document 1 discloses a positive electrode active material comprising a lithium compound containing an iron component such as LiFePO ₄ and a specific lithium compound such as LiMn ₂ O ₄ in a proportion of 5% by mass or less, It is designed to prevent deterioration of lithium-ion batteries. Further, Patent Document 2 discloses a positive electrode for a non-aqueous electrolyte secondary battery in which olivine-type lithium manganese phosphate and spinel-type lithium manganate are mixed, and the mixture ratio of the former is 10 to 90% by mass. , attempts to provide a non-aqueous electrolyte secondary battery with high capacity, safety, and excellent cycle characteristics.

WO2011/096469 JP-A-2006-278256

However, even with the techniques described in Patent Documents 1 and 2, there is still room for improvement in order to effectively improve the rate characteristics while maintaining a high discharge capacity in the resulting lithium ion secondary battery.

Therefore, an object of the present invention is a positive electrode active material nanoparticle mixture for a lithium ion secondary battery that can effectively improve the rate characteristics while maintaining a high discharge capacity in the lithium ion secondary battery, and a mixture that utilizes the same. An object of the present invention is to provide a method for manufacturing a lithium ion secondary battery.

Therefore, as a result of intensive studies to solve the above problems, the present inventors have found that lithium manganese iron phosphate nanoparticles having a specific average particle size and having a surface coated with a specific amount of carbon, and LiMnO By being a mixture at a specific mass ratio with nanoparticles represented by a specific formula such as ₂ , it is possible to improve the rate characteristics while maintaining a high discharge capacity in a lithium ion secondary battery. It was found that a positive electrode active material nanoparticle mixture for lithium ion secondary batteries can be obtained.

That is, the present invention provides the following formula (a):
_{LifMngFehM1xPO4 ( a ) _} ^_
(In formula (a), ^M1 is from Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd and Gd f, g, h and x represent one or more selected elements, where 0<f≦1.2, 0.3≦g≦1.2, 0.2≦h≦1.2, Indicates a number that satisfies 0 ≤ x ≤ 0.3 and f + (valence of Mn) x g + (valence of Fe) x h + (valence of ^M1 ) x = 3.)
and having an average particle size of 50 nm to 200 nm, and a nanoparticle A coated with carbon at a coverage rate of 5% to 70% on the surface;
Formula (b) below:
^LiM2aMnbO4 _{( b )}
(In formula (b), ^M represents one or more elements selected from Ni, Co, Al, Mg, Ti, V, Cr, Fe, Zr, Ga, Cu, and Si. a and b represents a number that satisfies 0≤a≤0.1, 0<b≤2, and (valence of ^M2 ) x a + (valence of Mn) x b = 7.)
Nanoparticles B represented by and having an average particle size of 50 nm to 200 nm
a mixture of
A cathode active material nanoparticle mixture for a lithium ion secondary battery is provided in which the mass ratio (A:B) of nanoparticles A and nanoparticles B in the mixture is 95:5 to 70:30.

The present invention also provides the following formula (a):
_{LifMngFehM1xPO4 ( a ) _} ^_
(In formula (a), ^M1 is from Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd and Gd f, g, h and x represent one or more selected elements, where 0<f≦1.2, 0.3≦g≦1.2, 0.2≦h≦1.2, Indicates a number that satisfies 0 ≤ x ≤ 0.3 and f + (valence of Mn) x g + (valence of Fe) x h + (valence of ^M1 ) x = 3.)
and having an average particle size of 50 nm to 200 nm, and a nanoparticle A coated with carbon at a coverage rate of 5% to 70% on the surface;
Formula (b) below:
^LiM2aMnbO4 _{( b )}
(In formula (b), ^M represents one or more elements selected from Ni, Co, Al, Mg, Ti, V, Cr, Fe, Zr, Ga, Cu, and Si. a and b represents a number that satisfies 0≤a≤0.1, 0<b≤2, and (valence of ^M2 ) x a + (valence of Mn) x b = 7.)
Nanoparticles B represented by and having an average particle size of 50 nm to 200 nm
are blended so that the mass ratio (A:B) of nanoparticles A and nanoparticles B is 95:5 to 70:30, and a conductive aid and a binder are blended to prepare a positive electrode paste. The present invention provides a method for manufacturing a lithium ion secondary battery, including the step of

According to the positive electrode active material nanoparticle mixture for a lithium ion secondary battery of the present invention, it is possible to realize a lithium ion secondary battery that maintains excellent discharge capacity and effectively improves rate characteristics.

The present invention will be described in detail below.
The positive electrode active material nanoparticle mixture for lithium ion secondary batteries of the present invention (hereinafter also simply referred to as "nanoparticle mixture of the present invention") has the following formula (a):
_{LifMngFehM1xPO4 ( a ) _} ^_
(In formula (a), ^M1 is from Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd and Gd f, g, h and x represent one or more selected elements, where 0<f≦1.2, 0.3≦g≦1.2, 0.2≦h≦1.2, Indicates a number that satisfies 0 ≤ x ≤ 0.3 and f + (valence of Mn) x g + (valence of Fe) x h + (valence of ^M1 ) x = 3.)
and having an average particle size of 50 nm to 200 nm, and a nanoparticle A coated with carbon at a coverage rate of 5% to 70% on the surface;
Formula (b) below:
^LiM2aMnbO4 _{( b )}
(In formula (b), ^M represents one or more elements selected from Ni, Co, Al, Mg, Ti, V, Cr, Fe, Zr, Ga, Cu, and Si. a and b represents a number that satisfies 0≤a≤0.1, 0<b≤2, and (valence of ^M2 ) x a + (valence of Mn) x b = 7.)
Nanoparticles B represented by and having an average particle size of 50 nm to 200 nm
a mixture of
The mass ratio (A:B) of nanoparticles A and nanoparticles B in the mixture is 95:5 to 70:30

As described above, the nanoparticle mixture of the present invention comprises ultrafine nanoparticles A represented by a specific formula, having a specific average particle size, and having a surface coated with a specific amount of carbon, and a specific It is a mixture obtained by mixing ultrafine nanoparticles B represented by the formula and having a specific average particle size while maintaining a limited mass ratio. When these nanoparticles A and B are densely mixed, the contribution of the carbon coated in a specific amount on the surface of the nanoparticles A is synergistic, effectively suppressing the reduction of the electronic conduction path, and high discharge. To effectively improve rate characteristics while contributing to capacity retention.

The nanoparticles A constituting the nanoparticle mixture of the present invention have the following formula (a):
_{LifMngFehM1xPO4 ( a ) _} ^_
(In formula (a), ^M1 is from Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd and Gd f, g, h and x represent one or more selected elements, where 0<f≦1.2, 0.3≦g≦1.2, 0.2≦h≦1.2, Indicates a number that satisfies 0 ≤ x ≤ 0.3 and f + (valence of Mn) x g + (valence of Fe) x h + (valence of ^M1 ) x = 3.)
and has an average particle size of 50 nm to 200 nm, and the surface is coated with carbon at a coverage rate of 5% to 70%.

The nanoparticles A represented by the above formula (a) are olivine-type lithium transition metal phosphate compounds containing at least both manganese (Mn) and iron (Fe) as transition metals, and are nanoscale ultrafine particles. is. The nanoparticle mixture of the present invention is a mixture in which these nanoparticles are densely mixed while maintaining a specific mass ratio between the nanoparticles A and the nanoparticles B described later. Therefore, it is possible to effectively improve the rate characteristics while effectively maintaining a high discharge capacity.

As for the nanoparticles A, f is preferably 0.6 ≤ f ≤ 1.2, more preferably 0.65 ≤ f ≤ 1.15, and 0.7 ≤ f ≤ 1 from the viewpoint of the average discharge voltage. .1 is more preferred. As for g, 0.4≦g≦0.8 is preferable, 0.5≦g≦0.8 is more preferable, and 0.7≦g≦0.8 is still more preferable. h is preferably 0.2≦h≦0.6, more preferably 0.2≦h≦0.5, and still more preferably 0.2≦h≦0.3. x is preferably 0≤x≤0.2, more preferably 0≤x≤0.15, and still more preferably 0≤x≤0.1. And g/h is the molar ratio of Mn and Fe constituting so-called nanoparticles A, preferably 0.5 ≤ g/h ≤ 5.0, and 1.0 ≤ g/h ≤ 5.0 More preferably, 2.0≤g/h≤5.0.

_{Specifically , LiMn0.2Fe0.8PO4 , LiMn0.3Fe0.7PO4 , LiMn0.4Fe0.6PO4 , LiMn0.6Fe0.4PO4 , LiMn0.7Fe0.3PO4 , LiMn0.8Fe0.2PO4 , LiMn0.75 _ _ _ _ Fe0.15Mg0.1PO4 , LiMn0.75Fe0.19Zr0.03PO4 , LiMn0.5Fe0.5PO4 , Li1.2Mn0.63Fe0.27PO4 , Li0.6Mn0.84Fe0.36PO4 and the like . _ _ _ _ _} Among them, LiMn _0.7 Fe _0.3 PO ₄ and LiMn _0.8 Fe _0.2 PO ₄ are preferable.

The average particle diameter of the nanoparticles A represented by the above formula (a) is 50 nm to 200 nm, preferably 70 nm to 170 nm, from the viewpoint of effectively promoting the insertion and extraction of lithium ions and from the viewpoint of handling. , more preferably 100 nm to 150 nm, still more preferably 100 nm to 130 nm.
Here, the "average particle size" in the nanoparticles A means the average particle size of 100 particles observed in SEM (JSM-7001F, manufactured by JEOL Ltd.).

The tap density of the nanoparticles A is preferably 0.2 g/cm ³ to 1.0 g/cm 3 , more preferably 0.4 g/cm ³ from the viewpoint of improving the electrode density and effectively enhancing the rate characteristics. cm ³ to 1.0 g/cm ³ .

From the viewpoint of securing an excellent discharge capacity and further improving the rate characteristics, the nanoparticles A are coated with carbon at a coverage rate of 5% to 70% on the surface of the particles. As a result, in a nanoparticle mixture in which nanoparticles A and nanoparticles B are densely mixed at a specific mass ratio, the surface of nanoparticles A is coated with a specific amount of carbon in the nanoparticle mixture. Since they are appropriately dispersed, it is possible to effectively suppress the deterioration of the electron conduction path and effectively improve the rate characteristics while contributing to maintaining a high discharge capacity.

The nanoparticles A are coated with carbon on their surfaces. Such carbon is obtained by carbonizing one or two or more carbon materials selected from sugars to form carbon, and the surfaces of the nanoparticles A are coated with the carbon. One or two or more carbon materials selected from such saccharides (also referred to as "carbon coating agent X" as described later) are carbonized to become carbon, and are selected from polyols other than saccharides, amines, and amides. By interposing a seed or two or more kinds of carbon materials (also referred to as "carbon coating inhibitor Y" as described later), the surfaces of the nanoparticles A are efficiently coated.
The carbon coated on the surface of the nanoparticles A is carbon derived from one or more carbon materials selected from sugars, while one or more selected from polyols other than sugars, amines, and amides. Two or more kinds of carbon materials do not remain in nanoparticles A.

Specific examples of one or more carbon materials selected from saccharides include monosaccharides such as glucose, fructose, galactose and mannose; disaccharides such as maltose, sucrose and cellobiose; Polysaccharides: one or more selected from polysaccharide nanofibers such as cellulose nanofibers, lignocellulose nanofibers, chitin nanofibers and chitosan nanofibers.
Among them, cellulose nanofibers, lignocellulose nanofibers, chitin nanofibers, or chitosan nanofibers are preferable from the viewpoint of effectively suppressing deterioration of electronic conduction paths and contributing to improvement of rate characteristics.

The coverage of carbon on the surface of the nanoparticles A is controlled to a limited range, and the carbon is appropriately dispersed in the nanoparticle mixture to maintain the discharge capacity and effectively improve the rate characteristics. From the viewpoint of increasing, it is 5% to 70%, preferably 10% to 48%, more preferably 15% to 45%.

The “carbon coverage (%)” on the surface of the nanoparticles A means a value obtained by the following method. Specifically, first, by electron microscopic observation of TEM, the surface of the nanoparticle A is observed in one field of view, and the surface of the nanoparticle A not coated with carbon and the nanoparticle A coated with carbon identify the surface of Next, in such a field of view, the "perimeter xn of the surface of the nanoparticle A not coated with carbon" and the "perimeter xc of the surface of the nanoparticle A coated with carbon" are measured, The sum of xn and xc is defined as "the total circumference xA of the surface of nanoparticle A".
The values of the obtained "perimeter xA of the surface of the nanoparticle A" and "perimeter xc of the surface of the nanoparticle A coated with carbon" are introduced into the following formula (1), and one field of view is obtained. Calculate the carbon coverage (%) in , and average the values obtained in 50 fields of view to obtain the carbon coverage (%) on the surface of the nanoparticles A. In addition, in TEM electron microscopic observation, whether or not the surface of the nanoparticles A is coated with carbon is defined as a specific limit of up to 1 nm.
Carbon coverage (%) = [(surface perimeter of nanoparticle A coated with carbon xc)/
(Perimeter length xA of surface of nanoparticle A)]×100 (1)

The carbon content in the nanoparticles A corresponds to the content of carbon obtained by carbonizing the carbon material, and is preferably 0.5% by mass to 5.0% by mass in the nanoparticles A, More preferably 0.6 mass % to 5.0 mass %, still more preferably 0.7 mass % to 5.0 mass %.

The carbon contained in the nanoparticles A corresponds to the carbon obtained by carbonizing the carbon material present on the surface of the nanoparticles A, that is, the amount of the carbon material in terms of atoms. obtained by measurement using
Also, the amount of the nanoparticles A whose surface is coated with carbon includes the amount of carbon obtained by carbonizing the carbon material.

The conductivity of the nanoparticles A is preferably 1.0×10 ⁻⁷ S/cm or more, more preferably 5.0×10 ⁻⁷ S/cm, from the viewpoint of contributing to the improvement of the rate characteristics while increasing the discharge capacity. /cm to 1.0× ^{10 −2} S/cm, more preferably 1.0×10 ⁻⁶ S/cm to 1.0×10 ⁻² S/cm.

Nanoparticles A can be obtained, for example, by the following production method. Specifically, the following steps (Ia) to (IIa):
(Ia) After adding a lithium compound, a metal compound containing at least a manganese compound and an iron compound, a phosphoric acid compound, a carbon coating agent X, a carbon coating inhibitor Y, and water to obtain a slurry water i, a hydrothermal reaction is performed. a step of obtaining preliminary particles a; (IIa) a step of firing the obtained preliminary particles a;
The carbon coating agent X is one or two or more carbon materials selected from sugars, and the carbon coating inhibitor Y is one or two or more carbons selected from polyols, amines, and amides other than sugars. It is the manufacturing method that is the material.

The step (Ia) includes adding a lithium compound, a metal compound containing at least a manganese compound and an iron compound, a phosphoric acid compound, a carbon coating agent X, a carbon coating inhibitor Y, and water to obtain slurry water i, This is a step of obtaining preliminary particles a by hydrothermal reaction.
Lithium compounds to be used include hydroxides (eg, LiOH.H ₂ O, LiOH), carbonates, acetates, and nitrates. Among them, hydroxide is preferable.
Manganese compounds include manganese acetate, manganese nitrate, manganese oxide and the like. These may be used individually by 1 type, and may be used in combination of 2 or more types. Among them, manganese oxide is preferable from the viewpoint of improving battery characteristics.
In addition to these lithium compounds and manganese compounds, metal (M ¹ ) compounds other than manganese compounds and iron compounds may be used as metal compounds.

Phosphoric acid compounds include orthophosphoric acid (H ₃ PO ₄ , phosphoric acid), metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, ammonium phosphate, and ammonium hydrogen phosphate. Among them, it is preferable to use phosphoric acid, and it is preferable to use it as an aqueous solution having a concentration of 70% by mass to 90% by mass.

The carbon coating agent X is one or two or more carbon materials selected from the above sugars, and specifically, the same materials as those described above can be used. Among them, cellulose nanofibers, lignocellulose nanofibers, chitin nanofibers, or chitosan nanofibers are preferably used from the viewpoint of effectively suppressing the deterioration of the electronic conduction path and contributing to the improvement of the rate characteristics of the resulting battery. preferable.

The carbon coating inhibitor Y is one or more carbon materials selected from polyols other than sugars, amines, and amides, i.e., one or more selected from polyols other than the carbon coating agent X, amines, and amides. Two or more carbon materials. Thus, in step (Ia), by adding the carbon coating inhibitor Y together with the carbon coating agent X, through the subsequent step (IIa), the carbon coating inhibitor is partially covered on the surface of the nanoparticles A. It is possible to moderately prevent the carbon coating agent X from being coated while Y is coating, and to control the carbon coating rate on the surface of the nanoparticles A within the above range.
By going through the step (IIa) described later, the carbon coating agent X is carbonized and the surface of the nanoparticles A is coated with carbon, while the carbon coating inhibitor Y is burned off and does not remain on the nanoparticles A. becomes.

Specific examples of polyols other than sugars include polyethylene glycol having a mass average molecular weight of 1000 or less, and polypropylene glycol having a mass average molecular weight of 2000 or less. Polyether polyols having the above are mentioned. Among them, polyols having a volatilization temperature of 170° C. to 400° C. are preferred, and more specifically, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol. , butanediol, pentanediol, hexanediol, hexanetriol, heptanediol, heptanetriol, octanediol, octanetriol, nonanediol, nonanetriol, decanediol, decanetriol, polyols having two hydroxy groups such as dodecanediol;
Examples include polyols having three or more hydroxy groups, such as glycerin, trimethylolpropane, pentaerythritol, and dipentaerythritol.

As amines and amides, those having a volatilization temperature of 170° C. or higher are preferable. Specifically, aliphatic amines such as diethanolamine and triethanolamine, heterocyclic amines such as imidazole; amides such as formamide and acetamide; polyacrylamides. , poly-N-vinylacetamide and the like; fatty acid amides such as oleic acid amide and stearic acid amide.

Ethylene glycol, propylene glycol, glycerin, triethanolamine, or oleic acid amide is preferred as the carbon coating inhibitor Y.

The order of addition of the lithium compound, the metal compound containing at least the manganese compound and the iron compound, the phosphoric acid compound, the carbon coating agent X, the carbon coating inhibitor Y, and water is not particularly limited, and may be added all at once. After mixing the metal compound, the phosphate compound and water first, the carbon coating agent X and the carbon coating inhibitor Y may be added at the same time. Although it is possible to mix first and then add the carbon coating agent X, it is preferable to add it all at once.

The amounts of the lithium compound, the metal compound containing the manganese compound and the iron compound, and the phosphoric acid compound used in the slurry water i are appropriately determined according to the composition of the target nanoparticles A, and are prepared according to an ordinary method. Just do it.

From the viewpoint of controlling the carbon coverage on the surface of the nanoparticles A within the above range, the amount of the carbon coating agent X added is the carbon content in the nanoparticles A while taking into consideration the amount of the carbon coating agent X in terms of carbon atoms. may be appropriately adjusted to an amount within the above range.
In addition, from the viewpoint of controlling the carbon coverage on the surface of the nanoparticles A within the above range, the amount of the carbon coating inhibitor Y to be added is the amount of the carbon coating agent X added in terms of carbon atoms and the amount of the carbon coating inhibitor Y The mass ratio (X/Y) to the added amount in terms of carbon atoms is preferably 0.05 to 3.00, more preferably 0.10 to 2.00, and still more preferably 0.15 to 1.50.

The solid content concentration of the slurry water i is preferably 20 to 80 parts by mass, more preferably 30 to 70 parts by mass, still more preferably 40 to 60 parts by mass.

After adding water, it is preferable to stir the slurry water i in advance before proceeding to step (IIa). The stirring time of the slurry water i is preferably 1 minute to 30 minutes, more preferably 5 minutes to 20 minutes. The temperature of the slurry water ii is preferably 10°C to 50°C, more preferably 15°C to 35°C.

Next, the resulting slurry water i is subjected to a hydrothermal reaction to obtain preliminary particles a.
The amount of water used in the hydrothermal reaction is determined from the viewpoint of the solubility of the metal compound, the ease of stirring, the efficiency of synthesis, etc., relative to 1 mol of phosphate ions contained in the slurry water i. , preferably 10 to 50 mol, more preferably 12.5 to 45 mol.

From the viewpoint of controlling the average particle diameter of the nanoparticles A within the above range, the hydrothermal reaction is preferably carried out at 100°C to 300°C, more preferably 120°C to 250°C. The hydrothermal reaction is preferably carried out in a pressure vessel, and when the reaction is carried out at 100°C to 300°C, the pressure at this time is preferably 0.1 MPa to 10 MPa, and when the reaction is carried out at 130°C to 250°C. is preferably 0.2 MPa to 4.0 MPa. The hydrothermal reaction time is preferably 0.2 hours to 30 hours, more preferably 0.5 hours to 10 hours, from the viewpoint of controlling the average particle size of the nanoparticles A within the above range.
The obtained preliminary particles a are preferably washed with water after filtration.

The step (IIa) is a step of firing the preliminary particles a obtained in the step (Ia). As a result, while a part of the surface of the preliminary particle a is coated with the carbon coating inhibitor Y, the coating of the carbon coating agent X is appropriately inhibited, and the carbon coating rate on the surface of the nanoparticle A is reduced as described above. It is possible to form nanoparticles A with a controlled range.
It should be noted that by going through the step (IIa), the carbon coating agent X is carbonized and the surface of the nanoparticles A is coated with carbon, while the carbon coating inhibitor Y is burned off and does not remain on the nanoparticles A. Become.

The firing temperature is 400° C. to 1100° C., preferably 500° C. to 900° C., more preferably 600° C. to 800° C., from the viewpoint of controlling the average particle size of the nanoparticles A within the above range and carbonizing the carbon. preferable. The firing time is preferably 0.5 hours to 30 hours, more preferably 0.5 hours to 20 hours, further preferably 0.7 hours to 10 hours. The firing atmosphere is preferably an inert atmosphere or a reducing atmosphere.

The nanoparticles B constituting the nanoparticle mixture of the present invention have the following formula (b):
^LiM2aMnbO4 _{( b )}
(In formula (b), ^M represents one or more elements selected from Ni, Co, Al, Mg, Ti, V, Cr, Fe, Zr, Ga, Cu, and Si. a and b represents a number that satisfies 0≤a≤0.1, 0<b≤2, and (valence of ^M2 ) x a + (valence of Mn) x b = 7.)
and has an average particle size of 50 nm to 200 nm.

The nanoparticles B represented by the above formula (b) are particles having a spinel structure. The rate characteristics can be improved by forming the nanoparticle mixture of the present invention together with the nanoparticles A while maintaining a specific mass ratio of the ultrafine nanoparticles B.

Specific examples _of the nanoparticles B represented _by the formula ₍ b) include _LiMn2O4 , _{LiNi0.5Mn1.5O4} , _{LiCoMnO4 , LiCrMnO4} , _LiFeMnO4 , _LiAlMnO4 , and _{LiCu0.5Mn1.5O4 .} can be used. Among them, LiMn ₂ O ₄ is preferred.

The average particle size of the nanoparticles B is 50 nm to 200 nm, preferably 70 nm to 170 nm, more preferably 100 nm to 150 nm, more preferably 100 nm to 150 nm, from the viewpoint of ensuring excellent rate characteristics and handling. is between 100 nm and 120 nm.
Here, the "average particle size" in the nanoparticles B means the average particle size of 100 particles observed in SEM (JSM-7001F, manufactured by JEOL Ltd.).

In addition, the nanoparticles B can be obtained, for example, by the following manufacturing method. Specifically, the following steps (Ib) to (IIIb):
(Ib) Step of mixing a lithium compound and a manganese compound to obtain preliminary particles b (IIb) Step of firing the obtained preliminary particles b in an air atmosphere to obtain preliminary particles b′ (IIIb) It is a manufacturing method comprising a step of pulverizing the preliminary particles b'.

The step (Ib) is a step of mixing a lithium compound and a manganese compound to obtain preliminary particles b.
As the lithium compound, the same one as the nanoparticles A can be used, but among them, carbonate is preferable.
As the manganese compound, the same one as the nanoparticles A can be used.
In addition to these lithium compounds and manganese compounds, metal (M ² ) compounds other than these compounds may also be used.

The amount of the lithium compound, manganese compound, etc. used may be appropriately determined according to the desired composition of the nanoparticles B, and mixed according to an ordinary method.
A device such as a ball mill may be used for mixing these compounds in step (Ib).

The step (IIb) is a step of firing the preliminary particles b obtained in the step (Ib) in an air atmosphere to obtain the preliminary particles b'.
The firing temperature is preferably 300°C to 1100°C, more preferably 500°C to 900°C. The firing time is preferably 3 hours to 40 hours, more preferably 10 hours to 20 hours.

The step (IIIb) is a step of pulverizing the preliminary particles b' obtained in the step (IIb). Since the preliminary particles b' are coarse particles, nanoparticles B whose average particle diameter is controlled within the above range can be obtained by going through the step (IIIb).
A device such as a ball mill may be used to mix these compounds in step (IIIb). The pulverization time is preferably 1 hour to 20 hours, more preferably 5 hours to 20 hours, further preferably 10 hours to 20 hours, from the viewpoint of controlling the average particle diameter of the nanoparticles B within the above range.

The nanoparticles B can also be obtained by other production methods such as a sol-gel method and a hydrothermal synthesis method.

The positive electrode active material nanoparticle mixture for a lithium ion secondary battery of the present invention is a nanoparticle mixture in which nanoparticles A and nanoparticles B are mixed.
In the nanoparticle mixture of the present invention, the mass ratio (A:B) of the nanoparticles A and the nanoparticles B is such that the nanoparticles A and B are closely entangled and composited to effectively improve the rate characteristics. From the viewpoint of improvement, it is 95:5 to 70:30, preferably 90:10 to 75:25, and more preferably 90:10 to 80:20.

In order to mix nanoparticles A and nanoparticles B, a normal mixing method may be adopted. can be added and mixed.
Alternatively, the mixture may be mixed using a dry mixing apparatus other than a dry ball mill, or may be mixed manually using a pestle and mortar.

The positive electrode active material nanoparticle mixture for lithium ion secondary batteries of the present invention is highly useful as a positive electrode material for lithium ion secondary batteries, and a lithium ion secondary battery manufactured using such a nanoparticle mixture is Excellent rate characteristics can be exhibited while maintaining a high discharge capacity.

For example, specifically, the method for producing a lithium ion secondary battery of the present invention comprises the following formula (a):
_{LifMngFehM1xPO4 ( a ) _} ^_
(In formula (a), ^M1 is from Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd and Gd f, g, h and x represent one or more selected elements, where 0<f≦1.2, 0.3≦g≦1.2, 0.2≦h≦1.2, Indicates a number that satisfies 0 ≤ x ≤ 0.3 and f + (valence of Mn) x g + (valence of Fe) x h + (valence of ^M1 ) x = 3.)
and having an average particle size of 50 nm to 200 nm, and a nanoparticle A coated with carbon at a coverage rate of 5% to 70% on the surface;
Formula (b) below:
^LiM2aMnbO4 _{( b )}
(In formula (b), ^M represents one or more elements selected from Ni, Co, Al, Mg, Ti, V, Cr, Fe, Zr, Ga, Cu, and Si. a and b represents a number that satisfies 0≤a≤0.1, 0<b≤2, and (valence of ^M2 ) x a + (valence of Mn) x b = 7.)
Nanoparticles B represented by and having an average particle size of 50 nm to 200 nm
are blended so that the mass ratio (A:B) of nanoparticles A and nanoparticles B is 95:5 to 70:30, and a conductive aid and a binder are blended to prepare a positive electrode paste. including the step of

Nanoparticles A and nanoparticles B are as described above. The nanoparticles A and B may be blended so that the mass ratio (A:B) of the nanoparticles A and B is 95:5 to 70:30, preferably the mass ratio (A: B) should be 90:10 to 75:25, more preferably 90:10 to 80:20 in mass ratio (A:B).
In addition, in blending nanoparticles A and nanoparticles B, they may be blended as a mixture in which they are mixed in advance at the above mass ratio (A:B), that is, the above-mentioned nanoparticle mixture prepared in advance is blended as it is. You may

Then, a conductive aid and a binder are further blended to prepare a positive electrode paste.
Carbon black such as acetylene black and ketjen black can be used as the conductive aid. As the binder, polyvinylidene fluoride, styrene-butadiene rubber (SBR), or the like can be used.
Furthermore, a solvent such as N-methyl-2-pyrrolidone may be blended.
A positive electrode paste is prepared by adding and mixing these nanoparticles A and nanoparticles B, or a nanoparticle mixture, a conductive agent, a binder, a solvent, and the like. These may be mixed all at once, or may be prepared by mixing them one by one as appropriate.

Next, the positive electrode paste obtained through these steps is applied onto a current collector such as an aluminum foil, press-molded by a roller press or the like, and dried to obtain a positive electrode. In such a positive electrode, the ultrafine nanoparticles A and the ultrafine nanoparticles B are densely dispersed while maintaining a limited mass ratio, so that the discharge capacity is effectively increased and the rate characteristics are also improved. A positive electrode with high usefulness that can be effectively enhanced can be obtained.

A lithium ion secondary battery can be constructed from the obtained positive electrode by further comprising a negative electrode, an electrolytic solution and a separator, or a negative electrode and a solid electrolyte as essential components.

Here, as for the negative electrode, as long as it can absorb lithium ions during charging and release lithium ions during discharging, the material composition is not particularly limited, and a known material composition can be used. For example, lithium metal, graphite, silicon-based (Si, SiOx), lithium titanate, carbon materials such as amorphous carbon, and the like can be used. It is preferable to use an electrode made of an intercalate material capable of electrochemically intercalating and deintercalating lithium ions, particularly a carbon material. Furthermore, two or more of the above negative electrode materials may be used in combination, for example, a combination of graphite and silicon can be used.

The electrolytic solution is obtained by dissolving a supporting salt in an organic solvent. The organic solvent is not particularly limited as long as it is an organic solvent that is usually used in the electrolyte of a lithium ion secondary battery, and examples thereof include carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones. , oxolane compounds and the like can be used.

The type of supporting salt is not particularly limited, but inorganic salts selected from LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ , derivatives of the inorganic salts, LiSO ₃ CF ₃ , LiC(SO ₃ CF ₃ ) ₂ and LiN(SO ₃ CF ₃ ) ₂ , LiN(SO ₂ C ₂ F ₅ ) ₂ and LiN(SO ₂ CF ₃ )(SO ₂ C ₄ F ₉ ), and derivatives of said organic salts. is preferably at least one of

The separator serves to electrically insulate the positive electrode and the negative electrode and retain the electrolyte. For example, a porous synthetic resin film, particularly a porous film of polyolefin polymer (polyethylene, polypropylene) may be used.

The solid electrolyte electrically insulates the positive and negative electrodes and exhibits high lithium ion conductivity. _{For example , La0.51Li0.34TiO2.94 , Li1.3Al0.3Ti1.7 ( PO4 ) 3 , Li7La3Zr2O12 , 50Li4SiO4.50Li3BO3 , Li2.9PO3.3N0.46 , Li3.6Si _ _ 0.6P0.4O4 , Li1.07Al0.69Ti1.46 ( PO4 ) 3 , Li1.5Al0.5Ge1.5 ( PO4 ) 3 , Li10GeP2S12 , Li3.25Ge0.25P0.75S4 , 30Li2S . _ 26B2S3.44LiI , 63Li2S.36SiS2.1Li3PO4 , 57Li2S.38SiS2.5Li4SiO4 , 70Li2S.30P2S5 , 50Li2S.50GeS2 , Li7P _ _ _ _ _ 3} S ₁₁ and Li _3.25 P _0.95 S ₄ may be used.

The shape of the lithium-ion secondary battery having the above configuration is not particularly limited, and may be various shapes such as a coin shape, a cylindrical shape, a square shape, or an irregular shape enclosed in a laminated outer package. .

EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.

[Production Example 1: Production of nanoparticles A1]
1272 g of LiOH.H ₂ O and 4 L of water were mixed to obtain slurry water i1. Next, while stirring the resulting slurry water i1 at a temperature of 25 ° C. for 3 minutes, 1153 g of an 85% phosphoric acid aqueous solution is added dropwise at 35 mL / min, followed by the carbon content in the nanoparticles A1 obtained. , 4780 g of cellulose nanofiber (Wma-10002, manufactured by Sugino Machine Co., Ltd., fiber diameter 4 to 20 nm) as carbon coating agent X, and 91 g of propylene glycol as carbon coating inhibitor Y (cellulose nanofiber Amount in terms of carbon atoms/amount in terms of carbon atoms of propylene glycol (X/Y)=1.0) was added all at once, and the mixture was stirred at a speed of 400 rpm for 12 hours to obtain slurry water i2 containing Li ₃ PO ₄ . .
The slurry water i2 thus obtained was purged with nitrogen to adjust the dissolved _oxygen concentration of the slurry water _i2 to _0.5 mg/L _. 834 g was added to obtain slurry water i3. The molar ratio of added MnSO ₄ and FeSO ₄ (manganese compound:iron compound) was 70:30.
Next, the resulting slurry water i3 was put into an autoclave and hydrothermally reacted at 170° C. for 1 hour. The pressure inside the autoclave was 0.8 MPa. After the hydrothermal reaction, the crystals produced were filtered and then washed with 12 parts by mass of water per 1 part by mass of the crystals. The washed crystals were freeze-dried at −50° C. for 12 hours to obtain preliminary particles a ₁ .
The obtained preliminary particles a ₁ were sintered at 700° C. for 1 hour in an argon-hydrogen atmosphere (hydrogen concentration 3%) to obtain nanoparticles A1 (composition: LiMn _0.7 Fe _0.3 PO ₄ ).

[Production Example 2: Production of nanoparticles A2]
Nanoparticles A2 (composition: LiMn _0.7 Fe _0.3 ) were prepared in the same manner as in Production Example 1, except that the amount of propylene glycol added was 606 g (the amount of cellulose nanofibers in terms of carbon atoms/the amount of propylene glycol in terms of carbon atoms = 0.15). _PO4 ) was obtained.

[Production Example 3: Production of nanoparticles A3]
Nanoparticles A3 (composition: LiMn _0.7 Fe _0.3 ) were prepared in the same manner as in Production Example 1, except that the amount of propylene glycol added was 114 g (the amount of cellulose nanofibers in terms of carbon atoms/the amount of propylene glycol in terms of carbon atoms = 0.8). _PO4 ) was obtained.

[Production Example 4: Production of nanoparticles A4]
Nanoparticles A4 (composition: LiMn _0.7 Fe _0.3 ) were prepared in the same manner as in Production Example 1, except that the amount of propylene glycol added was 2273 g (the amount of cellulose nanofibers in terms of carbon atoms/the amount of propylene glycol in terms of carbon atoms = 0.04). _PO4 ) was obtained.

[Production Example 5: Production of nanoparticles A5]
Nanoparticles A5 (composition: LiMn _0.7 Fe _0.3 ) were prepared in the same manner as in Production Example 1, except that the amount of propylene glycol added was 26 g (the amount of cellulose nanofibers in terms of carbon atoms/the amount of propylene glycol in terms of carbon atoms = 3.5). _PO4 ) was obtained.

[Production Example 6: Production of nanoparticles A6]
Nanoparticles A6 (composition: LiMn _0.7 Fe _0.3 PO ₄ ) were obtained in the same manner as in Production Example 1, except that the hydrothermal reaction temperature was 130°C.

[Production Example 7: Production of nanoparticles A7]
Nanoparticles A7 (composition: LiMn _0.7 Fe _0.3 PO ₄ ) were obtained in the same manner as in Production Example 1, except that the hydrothermal reaction time was 3 hours.

[Production Example 8: Production of nanoparticles A8]
Nanoparticles A8 (composition: LiMn _0.7 Fe _0.3 PO ₄ ) were obtained in the same manner as in Production Example 1, except that the hydrothermal reaction time was changed to 6 hours.

[Production Example 9: Production of nanoparticles A9]
Nanoparticles A8 (composition: LiMn _0.7 Fe _0.3 PO ₄ ) were obtained in the same manner as in Production Example 1, except that the hydrothermal reaction time was 6 hours and the firing time was 3 hours.

[Production Example 10: Production of nanoparticles B1]
420 g of LiOH.H ₂ O and 1739 g of MnO ₂ were put into a cylindrical container and mixed for 1 hour in a ball mill to obtain preliminary particles b1. Preliminary particles b1′ were obtained by calcining c1 at 910° C. for 3 hours in an air atmosphere. The preliminary particles b1′ were put into a cylindrical container and pulverized with a ball mill for 2 hours to obtain nanoparticles B1 (composition: LiMn ₂ O ₄ ).

[Production Example 11: Production of nanoparticles B2]
Nanoparticles B2 (composition: LiMn ₂ O ₄ ) were obtained in the same manner as in Production Example 10, except that the pulverization time was 3 hours.

[Production Example 12: Production of nanoparticles B3]
Nanoparticles B3 (composition: LiMn ₂ O ₄ ) were obtained in the same manner as in Production Example 10, except that the pulverization time was 1.5 hours.

[Production Example 13: Production of nanoparticles B4]
Nanoparticles B4 (composition: LiMn ₂ O ₄ ) were obtained in the same manner as in Production Example 10, except that the pulverization time was 1 hour.

[Production Example 14: Production of nanoparticles B5]
Nanoparticles B5 (composition: LiMn ₂ O ₄ ) were obtained in the same manner as in Production Example 10, except that the pulverization time was 0.5 hours.

Tables 1 and 2 show the physical properties of the nanoparticles A1 to A9 and the nanoparticles B1 to B5 obtained.

<<Measurement of Average Particle Size of Nanoparticles A and B>> The average particle size of 100 particles observed in SEM (JSM-7001F, manufactured by JEOL Ltd.) was taken as the value of the average particle size.

<<Coverage of carbon on the surface of nanoparticles A>>
Using a TEM (JEM-ARM200F, manufactured by JEOL Ltd.), the carbon coverage (%) of each nanoparticle A obtained was determined according to the method described above.

<<Carbon content of nanoparticles A>>
The carbon content of the obtained nanoparticles A was measured using a carbon/sulfur analyzer (EMIA-220V2, manufactured by Horiba Ltd.).

[Examples 1 to 14, Comparative Examples 1 to 7]
Using the obtained nanoparticles A and nanoparticles B, these nanoparticles were mixed by a manual method using a pestle and mortar according to the mass ratio (A:B) shown in Table 3 to obtain each mixture.

《Evaluation of battery characteristics (rate characteristics)》
Using each obtained mixture as a positive electrode material, a positive electrode for a lithium ion secondary battery was produced. Specifically, each of the obtained mixtures, acetylene black, and polyvinylidene fluoride were mixed at a mass ratio of 90:5:5, and N-methyl-2-pyrrolidone was added thereto and sufficiently kneaded to obtain a positive electrode. A slurry was prepared. The positive electrode slurry was applied to a current collector made of aluminum foil having a thickness of 20 μm using a coating machine, and vacuum-dried at 80° C. for 12 hours. After that, it was punched into a disk shape of φ14 mm and pressed at 16 MPa for 2 minutes using a hand press to obtain a positive electrode.

Next, a coin-type secondary battery was constructed using the above positive electrode. A lithium foil punched into a diameter of φ15 mm was used as the negative electrode. The electrolytic solution used was obtained by dissolving LiPF ₆ at a concentration of 1 mol/L in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3:7. A polymer porous film was used as the separator. These battery parts were incorporated and housed in an atmosphere with a dew point of -50°C or less by a conventional method to obtain a coin-type secondary battery (CR-2032).

Then, using the obtained coin-type secondary battery, the discharge capacity (mAh / g ) was measured, and the value of the rate characteristic (capacity ratio (%)) was obtained from the following formula (x).
Rate characteristics = [(discharge capacity at 10C)/(discharge capacity at 0.2C)] × 100 (x)
Table 3 shows the results.

In constructing a coin-type secondary battery, instead of manufacturing a positive electrode using each mixture obtained, each nanoparticle A and nanoparticle B are blended in an amount such that the mass ratio is shown in Table 3. Then, when the total amount, acetylene black, and polyvinylidene fluoride were mixed at a mass ratio of 90:5:5, and a positive electrode manufactured in the same manner was used, the same results as those shown in Table 3 were obtained. I made sure I got it.

Claims (5)

Formula (a) below:
_{LifMngFehM1xPO4 ( a ) _} ^_
(In formula (a), ^M1 is from Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd and Gd f, g, h and x represent one or more selected elements, where 0<f≦1.2, 0.3≦g≦1.2, 0.2≦h≦1.2, Indicates a number that satisfies 0 ≤ x ≤ 0.3 and f + (valence of Mn) x g + (valence of Fe) x h + (valence of ^M1 ) x = 3.)
and having an average particle size of 50 nm to 200 nm, and a nanoparticle A coated with carbon at a coverage rate of 5% to 70% on the surface;
Formula (b) below:
^LiM2aMnbO4 _{( b )}
(In formula (b), ^M represents one or more elements selected from Ni, Co, Al, Mg, Ti, V, Cr, Fe, Zr, Ga, Cu, and Si. a and b represents a number that satisfies 0≤a≤0.1, 0<b≤2, and (valence of ^M2 ) x a + (valence of Mn) x b = 7.)
Nanoparticles B represented by and having an average particle size of 50 nm to 200 nm
a mixture of
A positive electrode active material nanoparticle mixture for a lithium ion secondary battery, wherein the mass ratio (A:B) of nanoparticles A and nanoparticles B in the mixture is 95:5 to 70:30. The positive electrode active material nano for a lithium ion secondary battery according to claim 1, wherein the carbon coated on the surface of the nanoparticles A is carbon obtained by carbonizing one or more carbon materials selected from sugars. particle mixture. 3. The positive electrode active material nanoparticle mixture for a lithium ion secondary battery according to claim 1, wherein the carbon content in the nanoparticles A is 0.5% by mass to 5.0% by mass. The positive electrode active material nanoparticle mixture for a lithium ion secondary battery according to any one of claims 1 to 3, wherein g and h in the formula (a) satisfy 0.5 ≤ g / h ≤ 5.0. . Formula (a) below:
_{LifMngFehM1xPO4 ( a ) _} ^_
(In formula (a), ^M1 is from Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd and Gd f, g, h and x represent one or more selected elements, where 0<f≦1.2, 0.3≦g≦1.2, 0.2≦h≦1.2, Indicates a number that satisfies 0 ≤ x ≤ 0.3 and f + (valence of Mn) x g + (valence of Fe) x h + (valence of ^M1 ) x = 3.)
and having an average particle size of 50 nm to 200 nm, and a nanoparticle A coated with carbon at a coverage rate of 5% to 70% on the surface;
Formula (b) below:
^LiM2aMnbO4 _{( b )}
(In formula (b), ^M represents one or more elements selected from Ni, Co, Al, Mg, Ti, V, Cr, Fe, Zr, Ga, Cu, and Si. a and b represents a number that satisfies 0≤a≤0.1, 0<b≤2, and (valence of ^M2 ) x a + (valence of Mn) x b = 7.)
Nanoparticles B represented by and having an average particle size of 50 nm to 200 nm
are blended so that the mass ratio (A:B) of nanoparticles A and nanoparticles B is 95:5 to 70:30, and a conductive aid and a binder are blended to prepare a positive electrode paste. A method for manufacturing a lithium ion secondary battery, comprising the step of