Positive Electrode Active Material for Lithium Ion Secondary Battery and Method for Producing the Same

Abstract

To provide a positive electrode active material for a lithium ion secondary battery and a manufacturing method of the same, which can sufficiently increase the energy density per unit volume at low temperatures.SOLUTION: A positive electrode active material for a lithium ion secondary battery includes (A) 60 mass% to 90 mass% of particles A represented by LiNiaCobMncM1wO2 and (B) 10 mass% to 40 mass% of particles B in which the surface of particles b represented by LifMngFehM2xPO4 is coated with carbon, the surface of particles b has a carbon coverage of 20% to 80%, and the maximum thickness of the carbon coating is 3 nm or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a positive electrode active material for a lithium ion secondary battery and a method for manufacturing the same.

Background Art

[0002] Layered lithium composite oxides such as layered lithium nickel cobalt manganese composite oxide (NMC) have a layered crystal structure in which lithium atom layers and transition metal atom layers are alternately stacked via oxygen atom layers. Such layered lithium composite oxides are used as positive electrode active materials that can constitute high-output and high-capacity lithium ion secondary batteries.

[0003] In a lithium ion secondary battery using such a layered lithium composite oxide as a positive electrode active material, charging and discharging are performed by desorbing and inserting lithium ions into the layered lithium composite oxide. However, unnecessary elution of the transition metal component of the lithium composite oxide and collapse of the crystal structure may occur, leading to a decrease in battery characteristics. Therefore, various developments have been made to use highly useful layered lithium composite oxides.

[0004] For example, Patent Document 1 discloses a positive electrode for a secondary battery including a lithium nickel cobalt manganese composite oxide in which the number of cobalt atoms is specified and lithium iron manganese phosphate in which the number of manganese atoms is specified in order to obtain a secondary battery with excellent energy density, aiming to improve the initial Coulomb efficiency.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, even with the technology described in the above literature, no consideration has been given to the energy density per unit volume when exposed to a low-temperature environment, and there is still sufficient room for improvement.

[0007] Therefore, an object of the present invention is to provide a positive electrode active material for a lithium-ion secondary battery and a method for manufacturing the same, which can sufficiently increase the energy density per unit volume at low temperatures.

Means for Solving the Problems

[0008] Therefore, as a result of intensive studies to solve the above problems, the present inventor has found that by containing a specific amount of Li-Ni-Co-Mn oxide particles (so-called NCM particles) and particles in which carbon is coated on the surface of an olivine-type lithium transition metal phosphate compound containing both manganese (Mn) and iron (Fe) (so-called LMFP particles) under specific conditions, a positive electrode active material for a lithium-ion secondary battery that can effectively increase the energy density per unit volume at low temperatures is obtained.

[0009] That is, the present invention includes the following components (A) and (B): (A) 60% to 90% by mass of particle A represented by the following formula (a) LiNi a Co b Mn c M 1 w O2···(a) (In formula (a), M 1 represents one or more elements selected from Mg, Ti, Nb, Fe, Cr, Si, Al, Ga, V, Zn, Cu, Sr, Mo, Zr, Sn, Ta, W, La, Ce, Pb, Bi, and Ge. a, b, c, w are numbers satisfying 0.3 ≦ a < 1, 0 < b ≦ 0.7, 0 < c ≦ 0.7, 0 ≦ w ≦ 0.3, and 3a + 3b + 3c + (valence of M 1 ) × w = 3. ) (B) 10% to 40% by mass of particles B in which the surface of particles b represented by the following formula (b) is coated with carbon, the carbon coating rate is 20% to 80% on the surface of particles b, and the maximum thickness of the carbon coating is 3 nm or more Li f Mn g Fe h M 2 x PO4···(b) (In formula (b), M 2 represents one or more elements selected 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 satisfy 0 < f ≤ 1.2, 0.2 ≤ g ≤ 0.7, 0.4 ≤ h ≤ 0.9, 0 ≤ x ≤ 0.3, and 0.25 ≤ g / h ≤ 1.5, and f + (valence of Mn) × g + (valence of Fe) × h + (valence of M 2 ) × x = 3. ) The present invention provides a positive electrode active material for a lithium ion secondary battery containing the same.

[0010] Further, the present invention includes the following steps (I) to (V): (I) A step of adding a lithium compound, a metal compound containing at least a manganese compound and / or an iron compound, a phosphoric acid compound, and water to obtain slurry water i, and then subjecting it to a hydrothermal reaction to obtain preliminary particles b' of particles b (II) A step of adding the obtained preliminary particles b' of particles b, a carbon coating agent C, a carbon coating inhibitor D, and water to obtain slurry water ii (III) A step of subjecting the obtained slurry water ii to spray drying to obtain granulated body Y (IV) A step of firing the obtained granulated body Y to obtain particles B of component (B) (V) A step of mixing the obtained particles B of component (B) and particles A of component (A) comprising The carbon coating agent C is a water-insoluble carbon material, and The carbon coating inhibitor D is a water-soluble carbon material having polarity and a boiling point of 400 °C or lower, and the present invention provides a method for producing the positive electrode active material for a lithium ion secondary battery.

Advantages of the Invention

[0011] According to the positive electrode active material for a lithium ion secondary battery of the present invention, it is possible to realize a lithium ion secondary battery that effectively increases the discharge capacity even when exposed to a low temperature environment and maintains a high energy density per unit volume.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0013] Hereinafter, the present invention will be described in detail. The positive electrode active material for a lithium ion secondary battery of the present invention comprises the following components (A) and (B): (A) 60% to 90% by mass of particles A represented by the following formula (a) LiNi a Co b Mn c M 1 w O2 ··· (a) (In formula (a), M 1 represents one or more elements selected from Mg, Ti, Nb, Fe, Cr, Si, Al, Ga, V, Zn, Cu, Sr, Mo, Zr, Sn, Ta, W, La, Ce, Pb, Bi, and Ge. a, b, c, w satisfy 0.3 ≦ a < 1, 0 < b ≦ 0.7, 0 < c ≦ 0.7, 0 ≦ w ≦ 0.3, and 3a + 3b + 3c + (valence of M 1 ) × w = 3.) (B) 10% to 40% by mass of particle B, in which the surface of particle b represented by the following formula (b) is coated with carbon, the carbon coating rate is 20% to 80% on the surface of particle b, and the maximum thickness of the carbon coating is 3 nm or more Li f Mn g Fe h M 2 x PO4···(b) (In formula (b), M 2 represents one or more elements selected 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 satisfy 0 < f ≤ 1.2, 0.2 ≤ g ≤ 0.7, 0.4 ≤ h ≤ 0.9, 0 ≤ x ≤ 0.3, and 0.25 ≤ g / h ≤ 1.5, and f + (valence of Mn) × g + (valence of Fe) × h + (valence of M 2 represents a number that satisfies × x = 3.).

[0014] Thus, the positive electrode active material for a lithium-ion secondary battery of the present invention contains, as the above component (A), NMC particle A, and, on the surface of particle b which is LMFP particle, particle B of the above component (B) composed of particle b showing a value in the range of 20% to 80% of carbon coating rate and showing a high value of 3 nm or more of the maximum thickness of carbon coating, in specific amounts respectively. Thereby, the electron conductivity of the positive electrode active material is improved, the absorption rate of the solvent of the electrode slurry is reduced, the uniformity and the electrode density of the obtained electrode are effectively increased, and the energy density per unit volume can be improved while increasing the discharge capacity at low temperature.

[0015] The positive electrode active material for a lithium-ion secondary battery of the present invention contains 60% to 90% by mass of particle A represented by the following formula (a) as component (A). LiNi a Co b Mn c M 1 w O2···(a) (In formula (a), M 1represents one or more elements selected from Mg, Ti, Nb, Fe, Cr, Si, Al, Ga, V, Zn, Cu, Sr, Mo, Zr, Sn, Ta, W, La, Ce, Pb, Bi, and Ge. a, b, c, and w are numbers satisfying 0.3 ≦ a < 1, 0 < b ≦ 0.7, 0 < c ≦ 0.7, 0 ≦ w ≦ 0.3, and 3a + 3b + 3c + (valence of M 1 × w = 3. )

[0016] The particle A represented by the above formula (a) of the component (A) is a Li-Ni-Co-Mn oxide particle (NCM particle), a so-called lithium composite oxide particle, a particle having a layered rock salt structure, and a secondary particle formed by aggregation of primary particles. By containing such a component (A) in the above amount, it is possible to contribute to an improvement in the energy density per unit volume at low temperatures.

[0017] M in formula (a) 1 represents one or more elements selected from Mg, Ti, Nb, Fe, Cr, Si, Al, Ga, V, Zn, Cu, Sr, Mo, Zr, Sn, Ta, W, La, Ce, Pb, Bi, and Ge. Further, a, b, c, and w in the above formula (a) are numbers satisfying 0.3 ≦ a < 1, 0 < b ≦ 0.7, 0 < c ≦ 0.7, 0 ≦ w ≦ 0.3, and 3a + 3b + 3c + (valence of M 1 × w = 3.

[0018] In the particle A represented by the above formula (a), Ni, Co, and Mn are known to be excellent in electron conductivity and contribute to battery capacity and output characteristics. Also, from the viewpoint of cycle characteristics, it is preferable that a part of such transition elements is substituted by another metal element M 1 . By being substituted by these metal elements M 1 , the crystal structure of the particle A represented by the formula (a) is stabilized, so that destruction of the crystal structure can be suppressed even when charge and discharge are repeated, and it is considered that a high energy density per unit volume can be ensured at low temperatures.

[0019] Specific examples of the particle A represented by the above formula (a) include, for example, LiNi0.33 Co 0.33 Mn 0.34 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.33 Co 0.31 Mn 0.33 Mg 0.03 O2, or LiNi 0.33 Co 0.31 Mn 0.33 Zn 0.03 O2, etc. are mentioned. Among them, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.33 Co 0.33 Mn 0.34 O2, LiNi 0.33 Co 0.31 Mn 0.33 Mg 0.03 Particles composed of O2 are preferred.

[0020] Furthermore, two or more types of particles A represented by the above formula (a) with different compositions may form a core-shell structure having a core part (inside) and a shell part (surface layer part). By making the particles A form this core-shell structure, NCM-based composite oxide particles with a high Ni concentration that are easily eluted into the electrolytic solution can be arranged in the core part, and NCM-based composite oxide particles with a low Ni concentration can be arranged in the shell part in contact with the electrolytic solution. Therefore, the elution of metal components (Ni, Mn, Co, M 1 ) from the particles A into the electrolytic solution can be suppressed. At this time, the core part may be a single phase, or may be composed of two or more phases with different compositions. As an aspect in which the core part is composed of two or more phases, a structure in which a plurality of phases are laminated in a concentric circular layer shape may be used, or a structure in which the composition changes transitionally from the surface of the core part toward the center part may be used. Furthermore, the shell part may be formed outside the core part, and may be a single phase like the core part, or may be composed of two or more phases with different compositions.

[0021] As particle A formed by forming a core-shell structure with two or more kinds of NCM particles having different compositions, specifically, (core part)-(shell part) is, for example, (LiNi 0.8 Co 0.1 Mn 0.1 O2)-(LiNi 0.2 Co 0.4 Mn 0.4 O2), (LiNi 0.8 Co 0.1 Mn 0.1 O2)-(LiNi 0.33 Co 0.33 Mn 0.34 O2), or (LiNi 0.8 Co 0.1 Mn 0.1 O2)-(LiNi 0.33 Co 0.31 Mn 0.33 Mg 0.03 O2) and the like.

[0022] Furthermore, the particle A represented by the above formula (a) may be coated with a metal oxide, a metal fluoride, or a metal phosphate. By coating the NCM particles with these metal oxides, metal fluorides, or metal phosphates, the elution of metal components (Ni, Mn, Co, M 1 ) from the NCM particles into the electrolytic solution can be suppressed. As such a coating material, one or more selected from CeO2, SiO2, MgO, Al2O3, ZrO2, TiO2, ZnO, RuO2, SnO2, CoO, Nb2O5, CuO, V2O5, MoO3, La2O3, WO3, AlF3, NiF2, MgF2, LiF, Li3PO4, Li4P2O7, LiPO3, Li2PO3F, and LiPO2F2, or a composite of these can be used.

[0023] The average particle diameter of the primary particles of the particle A represented by the above formula (a) is 50 nm to 500 nm, more preferably 50 nm to 300 nm, from the viewpoint of suppressing the expansion and contraction amount of the primary particles accompanying the insertion and desorption of lithium ions and effectively preventing particle cracking, and from the viewpoint of handling. Further, the average particle diameter of particle A, which is a secondary particle formed by aggregation of the primary particles (simply referred to as "average particle diameter of particle A"), is preferably 3 μm to 20 μm, more preferably 5 μm to 15 μm, from the viewpoints of obtaining a battery excellent in ensuring energy density per unit volume at low temperature and handling. Here, the "average particle diameter" of particle A means the D value (particle diameter at cumulative 50% (median diameter)) obtained from the volume-based particle size distribution based on the laser diffraction / scattering method. 50 It means the value (particle diameter at cumulative 50% (median diameter)) obtained from the volume-based particle size distribution based on the laser diffraction / scattering method.

[0024] The tap density of particle A represented by the above formula (a) is preferably 1.5 g / cm 3 ~ 3.5 g / cm 3 and more preferably 2.0 g / cm 3 ~ 3.0 g / cm 3 from the viewpoints of obtaining a battery excellent in ensuring energy density per unit volume at low temperature and handling. Note that the tap density means the "tapped bulk density" measured by the method defined in JIS R 1628 "Method for Measuring Bulk Density of Fine Ceramics Powder" in the same manner as below.

[0025] The angle of repose of particle A represented by the above formula (a) is preferably 30° to 60°, more preferably 35° to 55°, from the viewpoints of obtaining a battery excellent in ensuring energy density per unit volume at low temperature and handling.

[0026] Note that the angle of repose is the angle of the ridge line of the mountain formed when the powder is dropped and deposited, and means the value (°) measured by the method defined in JIS R 9301-2-2 "Alumina Powder - Part 2: Physical Property Measurement Methods - 2: Angle of Repose". Specific measurement devices that can be used include powder property evaluation devices, for example, Powder Tester PT-X (manufactured by Hosokawa Micron Corporation).

[0027] The content of component (A) (particle A) is 60% by mass to 90% by mass, preferably 65% by mass to 85% by mass, and more preferably 70% by mass to 80% by mass in the positive electrode active material for a lithium ion secondary battery of the present invention from the viewpoint of increasing the discharge capacity at low temperature and effectively improving the energy density per unit volume.

[0028] Note that particle A can be obtained, for example, by the following production method. Specifically, it is a production method including step (Ia) of preparing slurry water a by adding a nickel compound, a cobalt compound, a manganese compound, and water, and filtering and drying such slurry water a to obtain mixture A, and step (IIa) of adding a lithium compound to the obtained mixture A, mixing, and then firing.

[0029] Examples of the nickel compound used in step (Ia) include nickel sulfate and nickel acetate. These may be used alone or in combination of two or more. Among them, nickel sulfate is preferable from the viewpoint of enhancing battery characteristics. Examples of the cobalt compound include cobalt acetate, cobalt nitrate, and cobalt sulfate. These may be used alone or in combination of two or more. Among them, cobalt sulfate is preferable from the viewpoint of enhancing battery characteristics. Examples of the manganese compound include manganese acetate, manganese nitrate, and manganese sulfate. These may be used alone or in combination of two or more. Among them, manganese sulfate is preferable from the viewpoint of enhancing battery characteristics. In addition to these nickel compounds, cobalt compounds, and manganese compounds, metal (M 1 ) compounds other than these compounds may be used. Examples of the lithium compound include hydroxides (for example, LiOH·H2O, LiOH), carbonates, sulfates, and acetates. Among them, carbonates are preferable.

[0030] In step (Ia), when obtaining the slurry water a, it is preferably adjusted to a pH of 8 to 13, and for example, it may be adjusted by dropping ammonia water.

[0031] In step (IIa), when firing, first pre-firing is carried out at 500°C to 1000°C, preferably 600°C to 900°C for 1 hour to 15 hours, preferably 1 hour to 6 hours, and then main firing is carried out at 500°C to 1000°C, preferably 600°C to 900°C for 1 hour to 15 hours, preferably 5 hours to 13 hours. Also, it is preferably pulverized after pre-firing and then subjected to main firing.

[0032] The positive electrode active material for a lithium ion secondary battery of the present invention contains, as component (B), particles B in which the surface of particles b represented by the following formula (b) is coated with carbon, the carbon coating rate is 20% to 80% on the surface of the particles b, and the maximum thickness of the carbon coating is 3 nm or more, in an amount of 10% by mass to 40% by mass. Li f Mn g Fe h M 2 x PO4···(b) (In formula (b), M 2 represents one or more elements selected 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 satisfy 0 < f ≦ 1.2, 0.2 ≦ g ≦ 0.7, 0.4 ≦ h ≦ 0.9, 0 ≦ x ≦ 0.3, and 0.25 ≦ g / h ≦ 1.5, and f + (valence of Mn) × g + (valence of Fe) × h + (valence of M 2 represents a number that satisfies ) = 3. )

[0033] That is, the particle b represented by the above formula (b) is a so-called olivine-type lithium transition metal phosphate compound (LMFP particle) containing at least both manganese (Mn) and iron (Fe) as transition metals, and is a secondary particle formed by aggregation of primary particles. And the particle B of the component (B) is a particle composed of the particle b in which carbon is unevenly distributed and coated on the surface of the LMFP particle (particle b) constituting the particle B, while showing a value in a limited range where the carbon coating rate is 20% to 80%, and the maximum thickness of the carbon coating in the particle b shows a high value of 3 nm or more. If the positive electrode active material for a lithium ion secondary battery of the present invention containing such a particle B in a specific amount is used as a positive electrode material, in the obtained lithium ion secondary battery, even when exposed to a low temperature environment, a high discharge capacity can be ensured and the energy density per unit volume can be effectively improved.

[0034] Note that the "LMFP particle (particle b)" is a particle (secondary particle) formed by aggregation of preliminary particles b' (hereinafter also referred to as "preliminary particles b'") of LMFP particles corresponding to the primary particles of the so-called particle b. Such preliminary particles b' are particles obtained by step (I') in the manufacturing method of particle B described later. Therefore, the "surface of particle b" corresponds to the surface of the preliminary particle b' excluding the surface where the preliminary particles b' are joined or bonded to each other by aggregation existing inside the particle b, and regardless of the presence or absence of carbon coating.

[0035] In the above formula (b), M 2 represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd, and from the viewpoint of increasing the energy density per unit volume at low temperature, Mg, Al, Ti, Zn, Nb, Co, Zr, or Gd is preferable. Further, in the above formula (X), from the viewpoint of improving the discharge capacity at low temperatures and increasing the energy density per unit volume, for f, 0.6 ≦ f ≦ 1.2 is preferable, 0.65 ≦ f ≦ 1.15 is more preferable, and 0.7 ≦ f ≦ 1.1 is even more preferable. For g, 0.2 ≦ g ≦ 0.6 is preferable, 0.25 ≦ g ≦ 0.55 is more preferable, and 0.3 ≦ g ≦ 0.5 is even more preferable. For h, 0.4 ≦ h ≦ 0.8 is preferable, 0.45 ≦ h ≦ 0.75 is more preferable, and 0.5 ≦ h ≦ 0.7 is even more preferable. For x, 0 ≦ x ≦ 0.2 is preferable, 0 ≦ x ≦ 0.15 is more preferable, and 0 ≦ x ≦ 0.1 is even more preferable. And, the molar ratio of Mn to Fe that constitutes particle b, g / h, is preferably 0.34 ≦ g / h ≦ 1.2, and more preferably 0.42 ≦ g / h ≦ 1.0, from the viewpoint of enhancing the electron conductivity and improving the energy density per unit volume at low temperatures.

[0036] Specifically, for example, LiMn 0.2 Fe 0.8 PO4, LiMn 0.3 Fe 0.7 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.5 Fe 0.5 PO4, Li 1.2 Mn 0.53 Fe 0.37 PO4, Li 0.68 Mn 0.6 Fe 0.56 PO4, etc. may be mentioned. Among them, LiMn 0.4 Fe 0.6 PO4, LiMn 0.5 Fe 0.5 PO4 is preferable.

[0037] The particle b represented by the above formula (b) has carbon coated on its surface. Such carbon is formed by carbonizing a carbon coating agent C, which is one or more carbon materials selected from saccharides, into carbon, and this carbon coats the surface of the above particle b. Carbon coating agent C is a water-insoluble carbon material. Specific examples of such carbon coating agent C include one or more selected from cellulose and cellulose derivatives. More specifically, for example, nitrocellulose, acetyl cellulose, cellulose microfibril, cellulose nanofiber, lignocellulose nanofiber, cellulose nanocrystal, bacterial nanofiber, etc. may be mentioned. Among them, cellulose nanofiber is preferable from the viewpoint of effectively suppressing the decrease in the electron conduction path, effectively increasing the tap density, and contributing to the improvement of the energy density per unit volume at low temperature in the obtained battery. In addition to the carbon formed by carbonizing the carbon coating agent C on the surface of the particle b, the surface of the particle b may be coated with carbon formed by carbonizing a water-soluble carbon material other than the carbon coating inhibitor D that can be used as required.

[0038] The carbon coating rate on the surface of the particle b is 20% to 80%, preferably 30% to 70%, more preferably 35% to 60%, and still more preferably 40% or more and less than 50% from the viewpoint of controlling such a value within a limited range, unevenly distributing carbon on the surface of the particle b to reduce the absorption rate of the solvent of the electrode slurry, improving the uniformity and electrode density of the electrode, and effectively increasing the energy density per unit volume at low temperature.

[0039] In addition, the "carbon coating rate (%)" on the surface of the particle b means a value obtained by the following method. Specifically, as also shown in FIG. 1, first, the surface of the particle b is observed in one field of view in which the particle B is photographed by TEM electron microscope observation, and the surface of the particle b not coated with carbon and the surface of the particle b coated with carbon are specified. Next, the perimeter xn of the surface of the particle b not coated with carbon and the perimeter xc of the surface of the particle b coated with carbon in such a field of view are measured, and xn and xc are added together to obtain the total perimeter xB of the surface of the particle b. The values of "the total perimeter length xB of the surface of particle b" and "the perimeter length xc of the surface of particle b coated with carbon" obtained are introduced into the following formula (1) to calculate the carbon coating rate (%) in one field of view, and the values obtained in 50 fields of view are averaged to obtain the carbon coating rate (%) on the surface of particle b. Carbon coating rate (%) = [(perimeter length xc of the surface of particle b coated with carbon) / (total perimeter length xB of the surface of particle b)] × 100 ··· (1)

[0040] The maximum thickness of the carbon coating on the surface of particle b is 3 nm or more, preferably 4 nm or more, more preferably 5 nm or more, and even more preferably 6 nm or more from the viewpoint of effectively suppressing the generation of by-products during charge and discharge of the lithium-ion secondary battery and effectively increasing the energy density per unit volume at low temperature, while controlling the carbon coating rate within a limited range. There is no particular limitation on the upper limit value, but it is preferably 100 nm or less.

[0041] Note that the "maximum thickness of the carbon coating" on the surface of particle b means the value obtained by the following method. Specifically, first, observe the surface of particle b in one field of view where particle B is photographed by TEM electron microscope observation, and identify the point P on the surface of the positive electrode active material for the lithium-ion secondary battery where carbon is recognized to be the thickest coated in such a field of view. Next, draw a straight line perpendicular to the tangent line including point P, identify the intersection point Q where this straight line intersects the surface of particle B, and measure the distance between point P and intersection point Q as the carbon coating thickness (nm) in one field of view, and average the values obtained in 50 fields of view to obtain the maximum thickness of the carbon coating (nm) on the surface of particle b. Note that a carbon coating thickness of less than 1 nm is regarded as the measurement limit in TEM electron microscope observation.

[0042] The carbon content in particle B corresponds to the content of carbon formed by carbonizing carbon coating agent C. When a water-soluble carbon material other than carbon coating inhibitor D is used as necessary, it corresponds to the total amount with the content of carbon formed by carbonizing the water-soluble carbon material. In particle B, it is preferably 0.7% by mass to 3.2% by mass, more preferably 0.8% by mass to 3.0% by mass, and still more preferably 1.0% by mass to 2.8% by mass.

[0043] In addition, the carbon contained in particle B is carbon formed by carbonizing carbon coating agent C present on the surface of particle b, and carbon formed by carbonizing a water-soluble carbon material other than carbon coating inhibitor D that can be used as necessary, that is, it corresponds to the amount in terms of atoms of carbon coating agent C. When a water-soluble carbon material other than carbon coating inhibitor D is used as necessary, it corresponds to the total amount with the amount in terms of atoms of the water-soluble carbon material, and is determined by measurement using a carbon-sulfur analyzer.

[0044] The average particle diameter of particle b corresponding to the primary particle of particle B is 70 nm to 200 nm, more preferably 90 nm to 170 nm, from the viewpoints of suppressing the amount of expansion and contraction of the primary particle accompanying the insertion and desorption of lithium ions and effectively increasing the energy density per unit volume at low temperature, and from the viewpoint of handling. In addition, the average particle diameter of particle B corresponding to the secondary particle having primary particles formed by aggregation of particle b as particle b is preferably 10 μm to 30 μm, more preferably 12 μm to 20 μm, from the viewpoints of obtaining a battery excellent in ensuring the energy density per unit volume at low temperature and from the viewpoint of handling. Here, the "average particle diameter" of particle b means a value obtained by calculating the crystallite diameter using the XRD / Ruland method for the X-ray diffraction pattern. The "average particle diameter" of particle B means the D 50 value (particle diameter at cumulative 50% (median diameter)) obtained from the volume-based particle size distribution based on the laser diffraction / scattering method.

[0045] Furthermore, from the perspective of increasing the electrode density by approximating the closest packing in the resulting electrode and ensuring a high energy density per unit volume at low temperatures, Particle B preferably has a moderately broad particle size distribution. More specifically, the D 10 value (particle size at 10% cumulative) and the D 50 value ratio (D 10 / D 50 ) is preferably 0.35 to 0.55, more preferably 0.38 to 0.52. Also, the D 90 value (particle size at 90% cumulative) and the D 50 value ratio (D 90 / D 50 ) is preferably 1.65 to 2.10, more preferably 1.68 to 2.07.

[0046] From the perspective of improving the electrode density, increasing the discharge capacity at low temperatures, and effectively increasing the energy density per unit volume, the tap density of Particle B is preferably 1.0 g / cm 3 to 1.6 g / cm 3 , more preferably 1.2 g / cm 3 to 1.6 g / cm 3 .

[0047] From the perspective of improving the uniformity of the electrode and the electrode density and effectively increasing the energy density per unit volume at low temperatures, the angle of repose of Particle B is preferably 30° to 45°, more preferably 30° to 40°.

[0048] The positive electrode active material for a lithium ion secondary battery of the present invention uses the above component (A) (Particle A) and the following steps (I) to (V): (I) A step of adding a lithium compound, a metal compound containing at least a manganese compound and / or an iron compound, a phosphoric acid compound, and water to obtain slurry water i, and then subjecting it to a hydrothermal reaction to obtain preliminary particles b' of Particle b (II) A step of adding the obtained preliminary particles b' of Particle b, a carbon coating agent C, a carbon coating inhibitor D, and water to obtain slurry water ii (III) Subjecting the obtained slurry water ii to spray drying to obtain granulated product Y (IV) Firing the obtained granulated product Y to obtain particles B of component (B) (V) Mixing the obtained particles B of component (B) and particles A of component (A) comprising wherein the carbon coating agent C is a water-insoluble carbon material, and the carbon coating inhibitor D is a water-soluble carbon material having a polarity and a boiling point of 400 °C or lower, and can be obtained by a production method

[0049] In step (I) included in the production method of the present invention, after adding a lithium compound, a metal compound containing at least a manganese compound and / or an iron compound, a phosphoric acid compound, and water to obtain slurry water i, it is subjected to a hydrothermal reaction to obtain preliminary particles b' of particles b

[0050] Examples of the lithium compound that can be used include hydroxides (such as LiOH·H2O, LiOH), carbonates, sulfates, and acetates. Among them, hydroxides are preferred Examples of the manganese compound that can be used include manganese acetate, manganese nitrate, manganese sulfate, etc. These may be used alone or in combination of two or more. Among them, from the viewpoint of improving battery characteristics, manganese sulfate is preferred Examples of the iron compound that can be used include iron acetate, iron nitrate, iron sulfate, etc. These may be used alone or in combination of two or more. Among them, from the viewpoint of improving battery characteristics, iron sulfate is preferred In addition, together with these manganese compounds and iron compounds, a metal (M 2 :M 2 is synonymous with M in formula (b) 2 ) compound other than the manganese compound and the iron compound may also be used Examples of usable phosphoric acid compounds include orthophosphoric acid (H3PO4, phosphoric acid), metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, ammonium phosphate, ammonium hydrogen phosphate, etc. Among these, it is preferable to use phosphoric acid, and it is preferably used as an aqueous solution with a concentration of 70% to 90% by mass.

[0051] More specifically, step (I) includes step (i-1) of mixing a phosphoric acid compound into slurry water i' containing a lithium compound to obtain a precursor ib', subjecting the obtained precursor ib' and slurry water i containing a metal compound containing at least a manganese compound and an iron compound to a hydrothermal reaction to obtain preliminary particles b' of particles b (step (i-2)). It is preferably provided with.

[0052] In step (i-1), the content of the lithium compound in slurry water i' is preferably 5 parts by mass to 50 parts by mass, more preferably 7 parts by mass to 45 parts by mass, based on 100 parts by mass of water. Before adding the phosphoric acid compound to slurry water i', it is preferable to stir slurry water i' in advance. The stirring time of such slurry water i' is preferably 1 minute to 15 minutes, more preferably 3 minutes to 10 minutes. Also, the temperature of slurry water a' is preferably 20°C to 90°C, more preferably 20°C to 70°C.

[0053] In such step (I), when mixing phosphoric acid into slurry water i', it is preferable to dropwise add phosphoric acid while stirring the slurry water. The dropping rate of phosphoric acid into the above slurry water i' is preferably 15 mL / min to 50 mL / min, more preferably 20 mL / min to 45 mL / min, still more preferably 28 mL / min to 40 mL / min. Also, the stirring time of slurry water i' while dropping phosphoric acid is preferably 0.5 hour to 24 hours, more preferably 3 hours to 12 hours. Further, the stirring speed of slurry water i' while dropping phosphoric acid is preferably 200 rpm to 700 rpm, more preferably 250 rpm to 600 rpm, still more preferably 300 rpm to 500 rpm. When stirring the slurry water i', it is preferably cooled to a temperature equal to or lower than the boiling point temperature of the slurry water i'. Specifically, it is preferably cooled to 80°C or lower, more preferably cooled to 20°C to 60°C.

[0054] The slurry water i' after mixing the phosphate compound preferably contains 2.0 to 4.0 moles of lithium per mole of phosphoric acid, more preferably contains 2.0 to 3.1 moles of lithium. The above lithium compound and phosphate compound may be used so as to obtain such an amount. More specifically, the slurry water i' after mixing the phosphate compound preferably contains 2.7 to 3.3 moles of lithium per mole of phosphoric acid, more preferably contains 2.8 to 3.1 moles of lithium.

[0055] By purging nitrogen into the slurry water i' after mixing the phosphate compound, the reaction in such slurry water is completed, and the precursor ib' of the preliminary particle b' constituting the particle b represented by the above (b) is obtained as a slurry. When nitrogen is purged, the reaction can proceed in a state where the dissolved oxygen concentration in the slurry water i' is reduced, and the dissolved oxygen concentration of the slurry water containing the obtained precursor ib' is also effectively reduced. Therefore, the oxidation of the metal compound added in the next step can be suppressed. In the slurry water i' containing such a precursor ib', the precursor of the particle represented by the above (A) exists as fine dispersed particles. Such a precursor ib' is obtained as trilithium phosphate (Li3PO4).

[0056] Next, in step (i-2), the precursor ib' obtained in step (i-1) and the slurry water i containing a metal compound containing at least a manganese compound and an iron compound are subjected to a hydrothermal reaction to obtain a preliminary particle b' of the particle b.

[0057] The molar ratio of the manganese compound to the iron compound used (manganese compound: iron compound) is preferably from 20:80 to 60:40, more preferably from 25:75 to 55:45, and still more preferably from 30:70 to 50:50. Further, the total addition amount of these metal compounds is preferably from 0.99 mol to 1.01 mol, more preferably from 0.995 mol to 1.005 mol, per 1 mol of phosphate ions contained in the slurry water i.

[0058] The amount of water used when subjecting to the hydrothermal reaction is preferably from 10 mol to 50 mol, more preferably from 12.5 mol to 45 mol, per 1 mol of phosphate ions contained in the slurry water i, from the viewpoints of the solubility of the metal compound, ease of stirring, and synthesis efficiency, etc.

[0059] The addition order of the manganese compound, iron compound and metal (M 2 ) compound is not particularly limited. Further, while adding these metal compounds, an antioxidant may be added as necessary. As such an antioxidant, sodium sulfite (Na2SO3), sodium hydrosulfite (Na2S2O4), aqueous ammonia, etc. can be used. The addition amount of the antioxidant is preferably from 0.01 mol to 1 mol, more preferably from 0.03 mol to 0.5 mol, per 1 mol in total of the manganese compound, iron compound and the metal (M 2 ) compound used as necessary.

[0060] The content of the precursor ib' in the slurry water i obtained by adding the manganese compound, iron compound and, as necessary, the metal (M 2 ) compound-containing metal compound and adding an antioxidant or the like as necessary is preferably from 10 to 50% by mass, more preferably from 15 to 45% by mass, and still more preferably from 20 to 40% by mass.

[0061] The hydrothermal reaction may be carried out at 100°C or higher, preferably at 130°C to 180°C. The hydrothermal reaction is preferably carried out in a pressure-resistant container. When the reaction is carried out at 130°C to 180°C, the pressure at this time is preferably 0.3 MPa to 0.9 MPa. When the reaction is carried out at 140°C to 160°C, the pressure is preferably 0.3 MPa to 0.6 MPa. The hydrothermal reaction time is preferably 0.1 hour to 48 hours, more preferably 0.2 hour to 24 hours. The obtained preliminary particles b' are isolated by washing with water and drying after filtration. Freeze drying and vacuum drying are used as the drying means.

[0062] Step (II) included in the production method of the present invention is a step of adding preliminary particles b' of particles b obtained in step (I), a carbon coating agent C, a carbon coating inhibitor D, and water to obtain slurry water ii. The carbon coating agent C is a water-insoluble carbon material as described above. Specifically, the same materials as those described above can be used. Among them, cellulose nanofibers are preferable from the viewpoint of effectively suppressing the decrease in the electronic conduction path, effectively increasing the tap density, and contributing to the improvement of the energy density per unit volume at low temperature in the obtained battery.

[0063] The carbon coating inhibitor D is a water-soluble carbon material having polarity and a boiling point of 400°C or lower. Thus, in step (II), by adding the carbon coating inhibitor D together with the carbon coating agent C, the carbon coating inhibitor D acts like a flocculant to appropriately aggregate the carbon coating agent C without collapsing or overly pulverizing it, and appropriately suppress the coating on the particles b, so that the carbon coating rate and the maximum thickness of the carbon coating on the surface of the particles B can be controlled within the above ranges. It should be noted that through steps (IV) to (IV) described later, the carbon coating agent C is carbonized and coated on the surface of the particles b as carbon, while the carbon coating inhibitor D is burned out and does not remain in the particles B or the positive electrode active material for lithium ion secondary batteries.

[0064] Examples of the water-soluble carbon material having polarity and a boiling point of 400°C or lower include one or more selected from amines and amides. Such a carbon coating inhibitor D acts like a flocculant to moderately aggregate the carbon coating agent C without collapsing or excessively pulverizing it, and moderately suppresses the coating on the particles b. More specifically, examples of such a carbon coating inhibitor D include aliphatic amines such as diethylamine, ethylenediamine, and triethanolamine; heterocyclic amines such as imidazole and pyridine; amides such as formamide, acetamide, and N,N-dimethylformamide; and polyamides such as polyacrylamide and poly-N-vinylacetamide. Among them, ethylenediamine is preferred.

[0065] The order of adding the preliminary particles b' of the particles b, the carbon coating agent C, the carbon coating inhibitor D, and water is not particularly limited, and they may be added all at once. However, it is preferable to add and mix the carbon coating agent C, the carbon coating inhibitor D, and water in advance, and then mix the resulting mixture and the preliminary particles b' of the particles b.

[0066] The addition amount (in terms of carbon atom conversion amount) of the carbon coating agent C is preferably 1.0 to 10 parts by mass, more preferably 1.5 to 7.0 parts by mass, and still more preferably 2.0 to 5.0 parts by mass with respect to 100 parts by mass of the preliminary particles b' of the particles b.

[0067] The addition amount of the carbon coating inhibitor D is preferably 1.5 to 10 parts by mass, more preferably 4.0 to 9.0 parts by mass, and still more preferably 6.0 to 8.0 parts by mass with respect to 100 parts by mass of the preliminary particles b' of the particles b.

[0068] The mass ratio (C / D) of the addition amount (in terms of carbon atom conversion amount) of the carbon coating agent C to the addition amount of the carbon coating inhibitor D is preferably 0.12 to 1.0, more preferably 0.14 to 0.8, and still more preferably 0.16 to 0.6.

[0069] The solid content concentration of the slurry water ii is preferably 30% by mass to 70% by mass, more preferably 35% by mass to 65% by mass, and even more preferably 40% by mass to 60% by mass.

[0070] After adding water, it is preferable to stir the slurry water b in advance before transferring to step (III). The stirring time of such slurry water b is preferably 1 minute to 30 minutes, more preferably 5 minutes to 20 minutes. Also, the temperature of the slurry water b is preferably 10°C to 50°C, more preferably 15°C to 35°C.

[0071] Step (III) included in the production method of the present invention is a step of subjecting the slurry water ii obtained in step (III) to spray drying to obtain granulated product Y. Thereby, while the preliminary particles b' aggregate to form the particles b, as passing through the subsequent steps (IV) to (V), while a part of the surface of the particles b is not coated with the carbon coating inhibitor D, the coating of the carbon coating agent C is moderately inhibited, and the carbon coating rate and the maximum thickness of the carbon coating on the surface of the particles b can be controlled within the above ranges.

[0072] In step (III), in spray drying, the operating conditions may be appropriately set according to the apparatus used. For example, as the processing conditions in a micro mist dryer (MDL-050M manufactured by Fujisaki Electric Co., Ltd.) equipped with a four-fluid nozzle, the hot air temperature is preferably 110°C to 300°C, more preferably 150°C to 250°C. Also, the ratio of the supply amount of hot air to the supply amount of slurry water (supply amount of hot air / supply amount of slurry water) is preferably 500 to 10000, more preferably 1000 to 9000.

[0073] Step (IV) included in the production method of the present invention is a step of firing the granulated product Y obtained in step (III). The firing conditions of the granulated product Y in such step (IV) are preferably in a reducing atmosphere or an inert atmosphere, the firing temperature is preferably 500°C to 1000°C, more preferably 550°C to 900°C, the firing time is preferably 0.5 hours to 12 hours, more preferably 1 hour to 6 hours.

[0074] In addition, from the viewpoint of effectively increasing the tap density value or decreasing the angle of repose value of the fired granule Y obtained in step (IV) compared to other particles, thereby effectively enhancing the uniformity and electrode density of the resulting electrode and effectively improving the energy density per unit volume at low temperatures, the manufacturing method may further include the following steps (IVa) and (IVb).

[0075] That is, the above steps (I) to (IV) are provided, and further,[[]] (IVa) A step of applying a load with an integrated energy of 0.15 kJ / g to 0.30 kJ / g to the fired granule Y obtained in step (IV) using a dry mixer to obtain a consolidated body Y'. (IVb) A step of firing the obtained consolidated body Y' to obtain component (B). It is desirable to be a manufacturing method including these steps.[[]] By applying such a load to the fired granule Y, the fired granule Y is once compacted, effectively enhancing the uniformity and electrode density of the resulting electrode. By going through the subsequent step (IVb), the energy density per unit volume at low temperatures can be effectively improved.[[]]

[0076] The firing conditions of the granule Y in step (IVa) are preferably in a reducing atmosphere or an inert atmosphere. The firing temperature is preferably 500°C to 1000°C, more preferably 550°C to 900°C. The firing time is preferably 0.5 hour to 12 hours, more preferably 1 hour to 6 hours.[[]]

[0077] The dry mixer that can be used in step (IVa) is not particularly limited. For example, an MP mixer (manufactured by Nippon Coke Co., Ltd.) can be used.[[]]

[0078] The integrated energy applied to the fired granule Y is 0.15 kJ / g to 0.30 kJ / g, preferably 0.17 kJ / g to 0.30 kJ / g, more preferably 0.20 kJ / g to 0.30 kJ / g.[[]]

[0079] The average particle size of the obtained compact Y' is preferably 10 μm to 30 μm, more preferably 12 μm to 20 μm.

[0080] Step (IVb) included in the production method of the present invention is a step of firing the compact Y' obtained in step (IVa) to obtain particles B of component (B). The firing temperature in step (IVb) is preferably 200°C to 750°C, more preferably 200°C to 600°C, and even more preferably 200°C to 400°C. The firing time is preferably 15 minutes to 180 minutes, more preferably 30 minutes to 120 minutes. Further, the firing atmosphere is preferably a reducing atmosphere or an inert atmosphere.

[0081] Here, it is desirable that at least one of the firing in step (IVa) and the firing in step (IVb) is at a temperature of 600°C to 750°C. Thereby, while further compacting the compact Y', defects in the crystallinity of carbon or the like derived from particles B and the carbon coating agent C that may occur in part are repaired or revived as the process progresses, and appropriate strength is imparted to the particles B, while contributing to the improvement of the energy density per unit volume at low temperature. From such a viewpoint, it is preferable that the temperature in the firing in step (IVb) is lower than the temperature in the firing in step (IVa). More specifically, for example, the firing temperature in step (IVa) is 600°C to 750°C, and the firing temperature in step (IVb) is 200°C to 400°C.

[0082] Step (V) included in the production method of the present invention is a step of mixing particles B of component (B) obtained in step (IV) and particles A of component (A). By passing through such step (V), the positive electrode active material for a lithium ion secondary battery of the present invention can be obtained. The production method of the particles A is as described above. In step (V), after adjusting these particles A and particles B to the amounts having the above contents, they may be mixed by a conventional method.

[0083] The positive electrode active material for a lithium-ion secondary battery of the present invention is a material used as a positive electrode active material for a lithium-ion secondary battery. Specifically, for example, the positive electrode active material for a lithium-ion secondary battery of the present invention is kneaded with acetylene black, ketjen black, polyvinylidene fluoride, N-methyl-2-pyrrolidone, etc. to prepare a positive electrode slurry, and then applied to a current collector and then press-molded to produce a positive electrode. As the lithium-ion secondary battery to which the positive electrode obtained by using the positive electrode active material for a lithium-ion secondary battery of the present invention can be applied, there is no particular limitation as long as it has a positive electrode, a negative electrode, an electrolytic solution, and a separator, or a positive electrode, a negative electrode, and a solid electrolyte as essential components.

[0084] If it is the positive electrode active material for a lithium-ion secondary battery of the present invention, together with particle A, while maintaining an appropriate carbon coating rate, the thickness of the carbon coating is large, and it is composed of particle B composed of particles b in which carbon is moderately unevenly distributed and present on the surface, and thus a highly useful positive electrode capable of effectively increasing the energy density per unit volume at low temperature can be obtained.

[0085] Here, regarding the negative electrode, as long as it can occlude lithium ions during charging and release them during discharging, its material composition is not particularly limited, and a material composition known in the art can be used. For example, carbon materials such as lithium metal, graphite, silicon-based (Si, SiOx), lithium titanate, or amorphous carbon can be used. And it is particularly preferable to use an electrode formed of an intercalation material capable of electrochemically occluding and releasing lithium ions, especially a carbon material. Further, two or more of the above negative electrode materials may be used in combination. For example, a combination of graphite and silicon-based can be used.

[0086] The electrolytic solution is a solution in which a supporting salt is dissolved in an organic solvent. The organic solvent is not particularly limited as long as it is an organic solvent usually used in the electrolytic solution of a lithium-ion secondary battery. For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, oxolane compounds, etc. can be used.

[0087] The supporting salt is not particularly limited in type, but is preferably at least one of inorganic salts selected from LiPF6, LiBF4, LiClO4 and LiAsF6, derivatives of the inorganic salts, organic salts selected from LiSO3CF3, LiC(SO3CF3)2 and LiN(SO3CF3)2, LiN(SO2C2F5)2 and LiN(SO2CF3)(SO2C4F9), and derivatives of the organic salts.

[0088] The separator electrically insulates the positive electrode and the negative electrode and serves to hold the electrolytic solution. For example, a porous synthetic resin film, particularly a porous film of a polyolefin-based polymer (polyethylene, polypropylene) may be used.

[0089] The solid electrolyte electrically insulates the positive electrode and the negative electrode and exhibits high lithium ion conductivity. For example, La 0.51 Li 0.34 TiO 2.94 、Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li7La3Zr2O 12 、50Li4SiO4·50Li3BO3, Li 2.9 PO 3.3 N 0.46 、Li 3.6 Si 0.6 P 0.4 O4, Li 1.07 Al 0.69 Ti 1.46 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, Li 10 GeP2S 12 、Li 3.25 Ge 0.25 P 0.75 S4, 30Li2S·26B2S3·44LiI, 63Li2S·36SiS2·1Li3PO4, 57Li2S·38SiS2·5Li4SiO4, 70Li2S·30P2S5, 50Li2S·50GeS2, Li7P3S 11 、Li 3.25 P 0.95 S4 may be used.

[0090] The shape of the lithium ion secondary battery having the above configuration is not particularly limited, and may be various shapes such as coin type, cylindrical type, square type, etc., or an irregular shape enclosed in a laminated exterior body.

Examples

[0091] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples.

[0092] Each particle was produced according to the description of each production example. The physical properties of the obtained particles are shown in Table 1.

[0093] 《Measurement of average particle size of primary particles (or particle b)》 Measurement was performed using an X-ray diffractometer (D8 ADVANCE A-25, manufactured by Bruker AXS). The measurement conditions were set as follows: target CuKα, tube voltage 50 kV, tube current 350 mA, scanning range 10 to 80° (2θ), step width 0.0234°, and scan speed 0.13° / step. The XRD pattern was analyzed using the XRD / Ruland method to calculate the crystallite size, and this value was taken as the average particle size as primary particles.

[0094] 《Measurement of average particle size etc. of particle A or particle B (secondary particles)》 The average particle size etc. of the particles (D 50 , D 10 , D 90 ) was measured using a laser diffraction particle size analyzer (Microtrac MT3000II, manufactured by Microtrac BEL). The measurement conditions were as follows: particle permeability: transmission, particle shape: non-spherical, particle refractive index: 1.52. Ethanol was used as the solvent, and the solvent refractive index was 1.36.

[0095] 《Tap density (g / cm 3 )》 The tapped bulk density was measured according to the method specified in JIS R 1628 "Method for Measuring Bulk Density of Fine Ceramic Powders", and this was taken as the tapped density (g / cm 3 ).

[0096] 《Angle of repose (°)》 Using a powder property evaluation apparatus Powder Tester PT-X (manufactured by Hosokawa Micron Corporation), the angle of repose (°) was measured according to the method specified in JIS R 9301-2-2 "Alumina Powder - Part 2: Methods for Measuring Physical Properties - 2: Angle of Repose".

[0097] 《Carbon content of the positive electrode active material particles for lithium-ion secondary batteries》 Using a carbon and sulfur analyzer (EMIA-220V2, manufactured by Horiba, Ltd.), the carbon content of the obtained positive electrode active material particles for lithium-ion secondary batteries was measured.

[0098] 《Carbon coating rate and maximum thickness of carbon coating on the surface of particle b》 Using TEM (JEM-ARM200F, manufactured by JEOL Ltd.), according to the above method, the carbon coating rate and the maximum thickness of the carbon coating in each obtained particle b were determined.

[0099] [Production Example 1: Production of Particle A-1 (NCM Particle)] 473 g of nickel sulfate hexahydrate, 169 g of cobalt sulfate heptahydrate, 145 g of manganese sulfate pentahydrate, and 3 L of water were mixed so that the molar ratio of Ni:Co:Mn was 6:2:2. Then, 25% aqueous ammonia was added dropwise to the resulting mixture at a dropping rate of 300 mL / min to obtain a slurry a1 containing a metal composite hydroxide with a pH of 11. Next, the slurry a1 was filtered and dried to obtain a mixture b1 of metal composite hydroxides. Then, 37 g of lithium carbonate was mixed with the mixture b1 using a ball mill to obtain a powder mixture c1. The obtained powder mixture c1 was calcined and crushed at 800 °C for 4 hours in an air atmosphere, and then calcined at 800 °C for 11 hours in an air atmosphere as the final firing to obtain Particle A-1 (LiNi 0.6 Co 0.2 Mn 0.2 O2, average primary particle size = 250 nm).

[0100] [Production Example 2: Production of Particle B-1] 1272 g of LiOH·H2O and 4 L of water were mixed to obtain Slurry x1. Next, while maintaining the temperature of the obtained Slurry x1 at 25°C and stirring for 3 minutes, 1153 g of an 85% phosphoric acid aqueous solution was dropped at a rate of 35 mL / min, and the mixture was stirred at a speed of 400 rpm for 12 hours to obtain Slurry y1 containing Li3PO4. After purging the obtained Slurry y1 with nitrogen to make the dissolved oxygen concentration of Slurry y1 0.5 mg / L, 964 g of MnSO4·5H2O and 1668 g of FeSO4·7H2O were added to the entire amount of Slurry y1 to obtain Slurry z1. The molar ratio of the added MnSO4 to FeSO4 (manganese compound: iron compound) was 40:60. Next, the obtained Slurry z1 was charged into an autoclave and subjected to a hydrothermal reaction at 180°C for 1 hour. The pressure inside the autoclave was 1.0 MPa. After the hydrothermal reaction, the produced crystals 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 b-1.

[0101] 1000 g of the obtained preliminary particles b-1 were separated, and added to a slurry in which 338 g of cellulose nanofibers (Wma-10002, manufactured by Sugino Machine, fiber diameter 4 to 20 nm) (3.0 parts by mass in terms of carbon atom amount per 100 parts by mass of the preliminary particles b-1) and 67.6 g of ethylenediamine were previously mixed in 2 L of water to obtain Slurry water ii-1. The obtained Slurry water ii-1 was subjected to a dispersion treatment with an ultrasonic stirrer (T25, manufactured by IKA) for 1 minute to uniformly color the whole, and then spray-dried (nozzle air flow rate 35 L / min, supply air temperature 160°C) using a spray dryer (MDL-050M, manufactured by Fujisaki Electric Co., Ltd.) to obtain granulated body Y-1. The obtained granulated body Y-1 was fired at 700°C for 1 hour in an argon-hydrogen atmosphere (hydrogen concentration 3%) to obtain Particle B-1.

[0102] [Production Example 3: Production of Particle B-2] Except that 338 g of cellulose nanofibers was changed to 139 g (1.2 parts by mass in terms of carbon atom relative to 100 parts by mass of the preliminary particles b-1), particles B-2 were obtained in the same manner as in Production Example 2.

[0103] [Production Example 4: Production of Particles B-3] Except that 338 g of cellulose nanofibers was changed to 635 g (5.5 parts by mass in terms of carbon atom relative to 100 parts by mass of the preliminary particles b-1), particles B-3 were obtained in the same manner as in Production Example 2.

[0104] [Production Example 5: Production of Particles B-4] Except that the spray drying conditions (nozzle air flow rate: 35 L / min, supply air temperature: 160°C) were changed to (nozzle air flow rate: 40 L / min, supply air temperature: 155°C), particles B-4 were obtained in the same manner as in Production Example 2.

[0105] [Production Example 6: Production of Particles B-5] Except that the spray drying conditions (nozzle air flow rate: 35 L / min, supply air temperature: 160°C) were changed to (nozzle air flow rate: 25 L / min, supply air temperature: 170°C), granulated body Y-5 was obtained in the same manner as in Production Example 2. Next, the obtained granulated body Y-5 was fired at 650°C for 30 minutes in an argon-hydrogen atmosphere (hydrogen concentration: 3%) to obtain sintered body Y-5. 300 g of the obtained sintered body Y-5 was taken, and using an MP mixer (manufactured by Nippon Coke Co., Ltd.), a compressive force and a shearing force were applied at a load of 0.4 kW for 3 minutes to the powder (integrated energy loaded: 0.24 kJ / g) to obtain consolidated body Y'-5. Further, the obtained consolidated body Y'-5 was fired at 200°C for 30 minutes in an argon-hydrogen atmosphere (hydrogen concentration: 3%) to obtain particles B-5.

[0106] [Production Example 7: Production of Particles B-6] Except that the hydrothermal synthesis conditions (180°C for 1 hour) were changed to (200°C for 5 hours), particles B-6 were obtained in the same manner as in Production Example 2.

[0107] [Production Example 8: Production of Particles B-7] Particle B-7 was obtained in the same manner as in Production Example 2, except that the hydrothermal synthesis conditions (180 °C for 1 hour) were changed to (150 °C for 2 hours).

[0108] [Production Example 9: Production of Particle B-8] Particle B-8 was obtained in the same manner as in Production Example 2, except that 964 g of MnSO4·5H2O was changed to 482 g and 1668 g of FeSO4·7H2O was changed to 2224 g.

[0109] [Production Example 10: Production of Particle B-9] Particle B-9 was obtained in the same manner as in Production Example 2, except that 964 g of MnSO4·5H2O was changed to 1446 g and 1668 g of FeSO4·7H2O was changed to 1112 g.

[0110] [Production Example 11: Production of Particle B-10] Particle B-10 was obtained in the same manner as in Production Example 2, except that 338 g of cellulose nanofiber was changed to 79 g (0.7 part by mass in terms of carbon atom amount with respect to 100 parts by mass of preliminary particle b-1).

[0111] [Production Example 12: Production of Particle B-11] Particle B-11 was obtained in the same manner as in Production Example 2, except that 338 g of cellulose nanofiber was changed to 695 g (6.2 parts by mass in terms of carbon atom amount with respect to 100 parts by mass of preliminary particle b-1).

[0112] [Production Example 13: Production of Particle B-12] Particle B-12 was obtained in the same manner as in Production Example 2, except that 964 g of MnSO4·5H2O was changed to 241 g and 1668 g of FeSO4·7H2O was changed to 2502 g.

[0113] [Production Example 14: Production of Particle B-13] Particle B-13 was obtained in the same manner as in Production Example 2, except that 964 g of MnSO4·5H2O was changed to 1687 g and 1668 g of FeSO4·7H2O was changed to 834 g.

[0114] [Production Example 15: Production of Particle B-14] Except for not using 34 g of ethylenediamine at all, Particle B-14 was obtained in the same manner as in Production Example 2.

[0115]

Table 1

[0116] [Examples 1 to 11, Comparative Examples 1 to 6] According to the formulations shown in Table 1, using a planetary mixer (PLM-2, manufactured by Inoue Seisakusho Co., Ltd.), the particles of each component were mixed to obtain a positive electrode active material. Next, using the obtained positive electrode active material, each evaluation was carried out according to the following method. The results are shown in Table 2.

[0117] 《Evaluation of Battery Characteristics》 Using each of the obtained positive electrode active materials as a positive electrode material, a positive electrode of a lithium-ion secondary battery was fabricated. Specifically, each of the obtained positive electrode active materials, acetylene black, and polyvinylidene fluoride were mixed at a mixing ratio of 90:5:5 by mass, and N-methyl-2-pyrrolidone was added thereto and thoroughly kneaded to prepare a positive electrode slurry. The positive electrode slurry was applied to a current collector made of an aluminum foil with a thickness of 20 μm using a coater, and vacuum dried at 80 °C for 12 hours. Then, it was punched into a disk shape with a diameter of 14 mm and pressed at 16 MPa for 2 minutes using a hand press to obtain a positive electrode.

[0118] Next, a coin-type secondary battery was constructed using the above positive electrode. As the negative electrode, a lithium foil punched into a disk shape with a diameter of 15 mm was used. As the electrolytic solution, a solution in which LiPF6 was dissolved at a concentration of 1 mol / L in a mixed solvent obtained by mixing ethylene carbonate and ethyl methyl carbonate at a volume ratio of 3:7 was used. As the separator, a polymer porous film was used. These battery components were incorporated and housed by a conventional method in an atmosphere with a dew point of -50 °C or lower to obtain a coin-type secondary battery (CR-2032).

[0119] Using the obtained coin-shaped secondary battery, the discharge capacity at a current density of 170 mA / g in an environment with a temperature of 10°C was measured with a discharge capacity measuring device (HJ-1001SD8, manufactured by Hokuto Denko Corporation). Next, the electrode density was calculated by the following formula (y), and this was introduced into the following formula (z) to calculate the energy density per unit volume. Electrode density (g / cm 3 ) = Mass of the positive electrode active material in the positive electrode (g) / Electrode volume (cm 3 )(φ14 mm × thickness (μm)) ···(y) Energy density per unit volume of the positive electrode in a 10°C environment (Wh / L) = Discharge capacity at 10°C (mAh / g) × Average voltage (V) × Electrode density (g / cm 3 ) ···(z)

[0120]

Table 2

Claims

1. The following components (A) and (B): (A) 60% to 90% by mass of particle A represented by the following formula (a) LiNi a Co b Mn c M 1 w O 2 ···(a) (In formula (a), M 1 represents one or more elements selected from Mg, Ti, Nb, Fe, Cr, Si, Al, Ga, V, Zn, Cu, Sr, Mo, Zr, Sn, Ta, W, La, Ce, Pb, Bi, and Ge. a, b, c, and w are numbers satisfying 0.3 ≤ a < 1, 0 < b ≤ 0.7, 0 < c ≤ 0.7, 0 ≤ w ≤ 0.3, and 3a + 3b + 3c + (valence of M 1 ) × w = 3.) (B) 10% to 40% by mass of particle B in which the surface of particle b represented by the following formula (b) is coated with carbon, and on the surface of particle b, the carbon coating rate is 20% to 80%, and the maximum thickness of the carbon coating is 3 nm or more Li f Mn g Fe h M 2 x PO 4 ···(b) (In formula (b), M 2 represents one or more elements selected 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 are numbers satisfying 0 < f ≤ 1.2, 0.2 ≤ g ≤ 0.7, 0.4 ≤ h ≤ 0.9, 0 ≤ x ≤ 0.3, and 0.25 ≤ g / h ≤ 1.5, and f + (valence of Mn) × g + (valence of Fe) × h + (valence of M 2 ) × x = 3.) A method for producing a positive electrode active material for a lithium-ion secondary battery containing the following, wherein the production method includes the following steps (I) to (V): (I) A step of adding a lithium compound, a metal compound containing at least a manganese compound and / or an iron compound, a phosphoric acid compound, and water to obtain slurry water i, and then subjecting it to a hydrothermal reaction to obtain preliminary particles b' of particle b (II) A step of adding the obtained preliminary particles b' of particle b, a carbon coating agent C, a carbon coating inhibitor D, and water to obtain slurry water ii (III) A step of subjecting the obtained slurry water ii to spray drying to obtain granulated body Y (IV) A step of firing the obtained granulated body Y to obtain particle B of component (B) (V) A step of mixing the obtained particle B of component (B) and particle A of component (A) comprising the carbon coating agent C is a water-insoluble carbon material, and the carbon coating inhibitor D is a water-soluble carbon material having polarity and a boiling point of 400°C or lower, a method for producing a positive electrode active material for a lithium-ion secondary battery.

2. The method for manufacturing a positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the carbon content is 0.7% by mass to 3.2% by mass.

3. The method for manufacturing a positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, wherein the average particle diameter of the particles A of the component (A) is 3 μm to 20 μm and the average particle diameter of the component (B) is 10 μm to 30 μm.

4. The tap density of the particles B of the component (B) is 1.0 g / cm 3 to 1.6 g / cm 3 The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 3, wherein the tap density is as described above.

5. The method for manufacturing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 4, wherein the angle of repose of the component (B) is 30° to 45°.

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