Positive electrode active material for lithium-ion secondary batteries

Abstract

To provide a positive electrode active material for a lithium-ion secondary battery which can sufficiently increase both the energy density per volume and the rate characteristics.SOLUTION: A positive electrode active material for a lithium-ion secondary battery includes (A) 60 mass% to 90 mass% of particle represented by the following formula (a) of LiNiaCobMncM1wO2, (B) 7 mass% to 36 mass% of particle represented by the following formula (b) of LifMngFehM2xPO4, and (C) 1 mass% to 12 mass% of particle represented by the following formula (c) of LijFekM3yPO4, and the mass ratio ((B) / (C)) between the content of component (B) and the content of component (C) is 2 to 9.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a positive electrode active material for a lithium ion secondary battery, for obtaining a lithium ion secondary battery having a high energy density per volume and excellent rate characteristics. [Background technology]

[0002] Layered lithium composite oxides, such as layered lithium-nickel-cobalt-manganese composite oxide (NMC), have a layered crystal structure in which lithium atomic layers and transition metal atomic layers are alternately stacked with oxygen atomic layers in between. Such layered lithium composite oxides are used as positive electrode active materials that can be used to construct high-power and high-capacity lithium-ion secondary batteries.

[0003] In lithium-ion secondary batteries using such layered lithium composite oxides as the positive electrode active material, charging and discharging are performed by the desorption and insertion of lithium ions into the layered lithium composite oxides. However, as the charge and discharge cycles are repeated, the capacity decreases, and especially when used for a long period of time, the capacity of the battery may decrease significantly. This is thought to be due to the fact that the transition metal components of the lithium composite oxide dissolve into the electrolyte during charging, making the crystal structure more likely to collapse. In particular, the higher the temperature, the more the transition metal dissolves, and the greater the impact on cycle characteristics. In addition, if the crystal structure of the lithium composite oxide collapses, the transition metal components of the lithium composite oxide dissolve into the surrounding electrolyte, which may reduce the thermal stability and compromise safety.

[0004] Under such circumstances, various developments have been made using highly useful layered lithium composite oxides. For example, Patent Document 1 discloses a positive electrode for a secondary battery containing a lithium-nickel-cobalt-manganese composite oxide with a specific number of cobalt atoms and lithium manganese iron phosphate with a specific number of manganese atoms in order to obtain a secondary battery with excellent energy density, and aims to improve the initial coulombic efficiency. Patent Document 2 discloses a positive electrode active material that is a mixture of two positive electrode active material powders with different average particle sizes, such as lithium nickel-manganese cobalt oxide and LiPO4, and attempts are being made to produce a battery with a practical output. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2011-159388 A [Patent Document 2] JP 2010-67499 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, none of the techniques described in these documents has been able to sufficiently increase the energy density per volume and the rate characteristics, and there is still 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 that can sufficiently increase both the energy density per volume and the rate characteristics. [Means for solving the problem]

[0008] Therefore, as a result of intensive studies to solve the above problems, the present inventors have found that a positive electrode active material for a lithium ion secondary battery capable of sufficiently increasing both the energy density per volume and the rate performance can be obtained by containing three specific types of particles represented by specific formulas in specific amounts and mass ratios.

[0009] That is, the present invention relates to the following components (A), (B), and (C): (A) 60% to 90% by mass of particles 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, and 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) 7% to 36% by mass of particles represented by the following formula (b) 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, 0.15 ≤ g ≤ 1.1, 0.08 ≤ h ≤ 0.9, 0 ≤ x ≤ 0.3, and 0.2 ≤ g / h ≤ 9, and f + (valence of Mn) × g + (valence of Fe) × h + (valence of M 2 ) × x = 3. ) (C) 1% to 12% by mass of particles represented by the following formula (c) Li j Fek M 3 y PO4···(c) (In formula (c), M 3 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. j, y, and k are numbers satisfying 0 < j ≤ 1.2, 0 ≤ y ≤ 0.3, 0.5 < k ≤ 1.2, and j + (valence of Fe) × k + (M 3 valence) × y = 3.) Disclosed is a cathode active material for a lithium-ion secondary battery, which contains and has a mass ratio ((B) / (C)) of the content of component (B) to the content of component (C) of 2 to 9.

Advantages of the Invention

[0010] According to the cathode active material for a lithium-ion secondary battery of the present invention, a lithium-ion secondary battery having an effectively increased energy density per unit volume and excellent rate characteristics can be realized.

Embodiments for Carrying Out the Invention

[0011] Hereinafter, the present invention will be described in detail. The cathode active material for a lithium-ion secondary battery of the present invention comprises the following components (A), (B), and (C): (A) 60% to 90% by mass of particles 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, 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 + (M 1 valence) × w = 3.) (B) Particles represented by the following formula (b): 7% by mass to 36% 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, 0.15 ≤ g ≤ 1.1, 0.08 ≤ h ≤ 0.9, 0 ≤ x ≤ 0.3, and 0.2 ≤ g / h ≤ 9, and f + (valence of Mn) × g + (valence of Fe) × h + (valence of M 2 × x = 3. ) (C) Particles represented by the following formula (c): 1% by mass to 12% by mass Li j Fe k M 3 y PO4···(c) (In formula (c), M 3 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. j, y, and k satisfy 0 < j ≤ 1.2, 0 ≤ y ≤ 0.3, 0.5 < k ≤ 1.2, and j + (valence of Fe) × k + (valence of M 3 × y = 3. ) contains, and the mass ratio of the content of component (B) to the content of component (C) ((B) / (C)) is 2 to 9.

[0012] Thus, since the positive electrode active material for a lithium-ion secondary battery of the present invention contains three specific types of particles represented by the above specific formulas in specific amounts, in the obtained lithium-ion secondary battery, the rate characteristics can be improved without unnecessarily reducing the energy density per unit volume, and the energy density per unit volume (hereinafter also abbreviated as "energy density") can be further increased by effectively reducing the voids between the particles.

[0013] The positive electrode active material for a lithium ion secondary battery of the present invention contains, as component (A), 60% by mass to 90% by mass of particles 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, and w are within the range of 0.3≦a<1, 0 <b≦0.7、0<c≦0.7、0≦w≦0.3、かつ3a+3b+3c+(M 1 The number that satisfies (valence of x) × w = 3.

[0014] The particles of component (A) represented by the above formula (a) are lithium composite oxide particles (so-called Li-Ni-Co-Mn oxide particles (NCM particles), hereinafter also referred to as "particles (A)"), which are particles having a layered rock salt structure and are secondary particles formed by aggregation of primary particles. By containing such component (A) having a specific average particle size in the above amount, it is possible to contribute to improving the energy density while maintaining excellent rate characteristics.

[0015] 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. In addition, a, b, c, and w in the above formula (a) are within the range of 0.3≦a<1, 0 <b≦0.7、0<c≦0.7、0≦w≦0.3、かつ3a+3b+3c+(M 1 It is a number that satisfies (valence of x) × w = 3.

[0016] In the particles (A) represented by the above formula (a), Ni, Co and Mn are known to have excellent electronic conductivity and contribute to the battery capacity and output characteristics. In addition, from the viewpoint of rate characteristics, it is known that some of these transition elements are mixed with other metal elements M 1 These metal elements M 1 It is considered that the substitution by stabilizes the crystal structure of the particles (A) represented by formula (a), thereby making it possible to suppress destruction of the crystal structure due to charge and discharge, and thus realizing excellent rate characteristics.

[0017] Specific examples of the NCM particles represented by the above formula (a) include LiNi 0.33 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 0.2 Co 0.4 Mn 0.4 O2, LiNi 0.33 Co 0.31 Mn 0.33 Mg 0.03 O2 or LiNi 0.33 Co 0.31 Mn 0.33 Zinc 0.03 O2, etc. 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 made of O2 are preferred.

[0018] Furthermore, the particles (A) represented by the above formula (a) of two or more different compositions may form a core-shell structure having a core part (inside) and a shell part (surface part). By forming the particles (A) with this core-shell structure, NCM-based composite oxide particles with a high Ni concentration that are easily dissolved in the electrolyte 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 that contacts the electrolyte, so that the suppression of the decrease in the rate characteristics can be further improved. In this case, the core part may be one phase, or may be composed of two or more phases with different compositions. As an embodiment in which the core part is composed of two or more phases, it may be a structure in which a plurality of phases are laminated in a concentric layer shape, or a structure in which the composition changes transitionally from the surface of the core part toward the center part. Furthermore, the shell portion may be any portion formed on the outside of the core portion, and may be a single phase like the core portion, or may be composed of two or more phases with different compositions.

[0019] As the particle (A) having a core-shell structure formed by two or more kinds of NCM particles having different compositions, specifically, the (core portion)-(shell portion) 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 Examples of particles include those made of oxygen (O2).

[0020] Furthermore, the particles (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 metal components (Ni, Mn, Co, Mn) from the NCM particles to the electrolyte can be prevented from being transferred to the electrolyte. 1 As such a coating, 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 thereof, can be used.

[0021] The average particle size of the primary particles of the particles (A) represented by the above formula (a) is preferably 50 nm to 500 nm, more preferably 50 nm to 300 nm, from the viewpoints of suppressing the amount of expansion and contraction of the primary particles accompanying insertion and desorption of lithium ions, effectively preventing particle cracking, and handling. Furthermore, the average particle size of particles (A), which are secondary particles formed by aggregation of the primary particles (simply referred to as "average particle size of particles (A)") is preferably 3 μm to 20 μm, and more preferably 5 μm to 15 μm, from the viewpoint of obtaining a battery with excellent rate characteristics and from the viewpoint of handling. Here, the "average particle size" of the particles (A) is the D obtained from the volume-based particle size distribution based on the laser diffraction / scattering method. 50 The values ​​shown are the particle diameters (median diameters) at 50% of the cumulative particle size.

[0022] The tap density of the particles (A) represented by the above formula (a) is preferably 1.5 g / cm from the viewpoint of obtaining a battery having excellent cycle characteristics and from the viewpoint of handling. 3 ~3.5g / cm 3 and more preferably 2.0 g / cm 3 ~3.0g / cm 3 It is. In the following description, tap density means the "tap bulk density" measured by the method specified in JIS R 1628 "Method of measuring bulk density of fine ceramic powders."

[0023] The angle of repose of the particles (A) represented by the above formula (a) is preferably 30° to 60°, more preferably 35° to 55°, from the viewpoint of obtaining a battery with excellent rate characteristics and from the viewpoint of handling.

[0024] The angle of repose, as in the following description, refers to the angle of the ridgeline formed when powder is dropped and piled up, and means the value (°) measured by the method specified in JIS R 9301-2-2 "Alumina powder - Part 2: Measurement of physical properties - 2: Angle of repose". Specific examples of measuring devices that can be used include a powder property evaluation device, such as Powder Tester PT-X (manufactured by Hosokawa Micron Corporation).

[0025] From the viewpoint of effectively achieving both high energy density and excellent rate characteristics, the content of component (A) (particles (A)) in the positive electrode active material for a lithium ion secondary battery of the present invention is 60 mass % to 90 mass %, preferably 65 mass % to 85 mass %, and more preferably 70 mass % to 80 mass %.

[0026] The particles (A) can be obtained, for example, by the following production method. Specifically, the production method includes a step (Ia) of preparing slurry water a by adding a nickel compound, a cobalt compound, a manganese compound, and water, filtering and drying the slurry water a to obtain mixture A, and a step (IIa) of adding a lithium compound to the obtained mixture A, mixing the mixture, and then calcining the mixture.

[0027] The nickel compound used in step (Ia) includes nickel sulfate, nickel acetate, etc., which may be used alone or in combination of two or more. Among them, nickel sulfate is preferred from the viewpoint of improving the 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 these, cobalt sulfate is preferred from the viewpoint of improving battery characteristics. Examples of manganese compounds include manganese acetate, manganese nitrate, manganese sulfate, etc. These may be used alone or in combination of two or more. Among these, manganese sulfate is preferred from the viewpoint of improving battery characteristics. In addition to these nickel compounds, cobalt compounds, and manganese compounds, metals other than these compounds (M 1 ) compounds may also be used. Examples of lithium compounds include hydroxides (e.g., LiOH·H2O, LiOH), carbonates, sulfates, and acetates. Of these, carbonates are preferred.

[0028] In the step (Ia), when obtaining the slurry water a, the pH is preferably adjusted to 8 to 13, for example by adding aqueous ammonia dropwise.

[0029] In the step (IIa), when firing, it is preferable to first perform pre-firing at 500° C. to 1000° C., preferably 600° C. to 900° C., for 1 to 15 hours, preferably 1 to 6 hours, and then perform main firing at 500° C. to 1000° C., preferably 600° C. to 900° C., for 1 to 15 hours, preferably 5 to 13 hours. In addition, it is preferable to crush the material after pre-firing before performing main firing.

[0030] The positive electrode active material for a lithium ion secondary battery of the present invention contains, as component (B), 7% by mass to 36% by mass of particles represented by the following formula (b). Li f Mn g Fe h M 2 x PO4 (b) (In formula (b), M 2represents 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, 0.15 ≤ g ≤ 1.1, 0.08 ≤ h ≤ 0.9, 0 ≤ x ≤ 0.3, and 0.2 ≤ g / h ≤ 9, and f + (valence of Mn) × g + (valence of Fe) × h + (valence of M 2 represents a number that satisfies ) × x = 3.)

[0031] The particles represented by the above formula (b) of component (B) are olivine-type lithium transition metal phosphate compounds containing at least both manganese (Mn) and iron (Fe) as transition metals (so-called LMFP particles, hereinafter also referred to as "particles (B)"), which are secondary particles formed by aggregation of primary particles. Such component (B) is also a factor that the particles have a specific average particle size and are relatively more deformable than other components. By containing this in the above amount, in combination with the above component (A), the rate characteristics can be effectively enhanced without unnecessarily reducing the energy density.)

[0032] Regarding the above particles (B), from the viewpoint of the average discharge voltage, 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, 0.3 ≤ g ≤ 0.9 is preferable, 0.4 ≤ g ≤ 0.8 is more preferable, and 0.5 ≤ g ≤ 0.8 is even more preferable. For h, 0.1 ≤ h ≤ 0.7 is preferable, 0.2 ≤ h ≤ 0.6 is more preferable, and 0.3 ≤ h ≤ 0.5 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 g / h is the molar ratio of Mn to Fe constituting the so-called particles (B), and 1 ≤ g / h ≤ 9 is preferable, 1.2 ≤ g / h ≤ 5.7 is more preferable, and 1.5 ≤ g / h ≤ 4 is even more preferable.)

[0033] Specifically, for example, LiMn 0.3 Fe 0.7 PO4, LiMn 0.7 Fe 0.3 PO4, LiMn0.9 Fe 0.1 PO4, LiMn 0.8 Fe 0.2 PO4, LiMn 0.75 Fe 0.15 Mg 0.1 PO4, LiMn 0.75 Fe 0.19 Zr 0.03 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.5 Fe 0.5 PO4, Li 1.2 Mn 0.63 Fe 0.27 PO4, Li 0.6 Mn 0.84 Fe 0.36 PO4, etc. Among them, LiMn 0.3 Fe 0.7 PO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.8 Fe 0.2 PO4, LiMn 0.6 Fe 0.4 PO4, Li 1.2 Mn 0.63 Fe 0.27 PO4 or Li 0.6 Mn 0.84 Fe 0.36 PO4 is preferred.

[0034] Furthermore, the particles (B) may form a core-shell structure having a core portion (inside) and a shell portion (surface portion). By forming the particles (B) to have this core-shell structure, LMFP particles having a higher Mn content, which is easily dissolved in the electrolyte, are arranged in the core portion, and LMFP particles having a lower Mn content than the core portion are arranged in the shell portion that contacts the electrolyte, thereby suppressing the decrease in rate characteristics caused by the particles (B). In this case, the core portion may be one phase, or may be composed of two or more phases having different compositions. As an embodiment in which the core portion is composed of two or more phases, it may be a structure in which a plurality of phases are laminated in a concentric layer shape, or a structure in which the composition changes transitionally from the surface of the core portion toward the center portion. Furthermore, the shell portion may be any portion formed on the outside of the core portion, and may be a single phase like the core portion, or may be composed of two or more phases with different compositions.

[0035] As the particle (B) having a core-shell structure formed by two or more kinds of LMFP particles having different compositions, specifically, the (core portion)-(shell portion) is, for example, LiMn 0.9 Fe 0.1 PO4-LiMn 0.6 Fe 0.4 PO4, LiMn 0.8 Fe 0.2 PO4-Li 1.2 Mn 0.63 Fe 0.27 Examples include particles made of PO4, etc.

[0036] The average particle size of the primary particles of the particles (B) represented by the above formula (b) is preferably 70 nm to 200 nm, more preferably 50 nm to 180 nm, from the viewpoints of suppressing the amount of expansion and contraction of the primary particles accompanying insertion and desorption of lithium ions, effectively preventing particle cracking, and handling. Furthermore, the average particle size of particles (B), which are secondary particles formed by aggregation of the above primary particles (simply referred to as "average particle size of particles (B)") is preferably 10 μm to 30 μm, more preferably 11 μm to 25 μm, and even more preferably 12 μm to 20 μm, from the viewpoint of obtaining a battery with excellent rate characteristics and from the viewpoint of handling. Here, the “average particle size” of the particles (B) is, like that of the particles (A), the D 50 The values ​​shown are the particle diameters (median diameters) at 50% of the cumulative particle size.

[0037] The tap density of the particles (B) represented by the above formula (b) is preferably lower than that of the particles (A) from the viewpoint of improving the electronic conductivity of the particles and the handling in the electrode slurry to effectively increase the uniformity and electrode density in the obtained electrode, and from the viewpoint of the secondary particles being relatively more easily deformed than other components, and specifically, is preferably 0.7 g / cm. 3 ~1.3g / cm 3 and more preferably 0.8 g / cm 3 ~1.2g / cm 3 and more preferably 0.9 g / cm 3 ~1.1g / cm 3 It is. The tap density means the "tap bulk density" measured by the method specified in JIS R 1628 "Method of measuring bulk density of fine ceramic powders."

[0038] The angle of repose of the particles (B) represented by the above formula (b) is preferably 30° to 45°, more preferably 30° to 43°, and even more preferably 30° to 40°, from the viewpoint of making the angle of repose smaller than that of other particles, improving the electronic conductivity of the particles and the handleability in the electrode slurry, and effectively increasing the uniformity and electrode density in the obtained electrode.

[0039] The angle of repose is the angle of the ridgeline formed when powder is dropped and piled up, and means the value (°) measured by the method specified in JIS R 9301-2-2 "Alumina powder - Part 2: Measurement method of physical properties - 2: Angle of repose". Specific measuring devices that can be used include a powder property evaluation device, such as Powder Tester PT-X (manufactured by Hosokawa Micron Corporation).

[0040] From the viewpoint of ensuring an excellent discharge capacity, the particles (B) may be particles having carbon derived from cellulose nanofibers and / or carbon derived from a water-soluble carbon material supported on the surface of the particles. Cellulose nanofibers are a skeletal component that accounts for about 50% of all plant cell walls, and are lightweight, high-strength fibers that can be obtained by defibrating the plant fibers that make up such cell walls to nano-size. The fiber diameter of such cellulose nanofibers is 1 nm to 1000 nm, and they also have good dispersibility in water. In addition, a periodic structure of carbon is formed in the cellulose molecular chains that make up the cellulose nanofibers. Therefore, when such cellulose nanofibers are carbonized to become carbon and are firmly supported on the surface of the above-mentioned particles (B), the particles (B) exhibit physical properties that make them easy to crush, but have appropriate strength that easily deforms to avoid collapse and suppress excessive pulverization, and effectively suppress the decrease in the electronic conductive path and effectively increase the degree of compaction, thereby ensuring the expression of excellent discharge capacity in the resulting battery.

[0041] The water-soluble carbon material, like the cellulose nanofibers, is carbonized to become carbon, and when this is supported on the surface of the particles (B), like the cellulose nanofibers, it effectively suppresses the deterioration of the electronic conductive path, and ensures the expression of excellent discharge capacity in the resulting battery. Examples of such water-soluble carbon materials include one or more selected from sugars, polyols, polyethers, and organic acids. More specifically, examples include monosaccharides such as glucose, fructose, galactose, and mannose; disaccharides such as maltose, sucrose, and cellobiose; polysaccharides such as starch and dextrin; polyols and polyethers such as ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, butanediol, propanediol, polyvinyl alcohol, and glycerin; and organic acids such as citric acid, tartaric acid, and ascorbic acid. Among these, from the viewpoint of increasing the solubility and dispersibility in a solvent to effectively function as a carbon material, glucose, fructose, sucrose, and dextrin are preferred, and glucose is more preferred.

[0042] Regarding the carbon derived from the cellulose nanofibers and the carbon derived from the water-soluble carbon material, only the carbon derived from the cellulose nanofibers, only the carbon derived from the water-soluble carbon material, or both the carbon derived from the cellulose nanofibers and the carbon derived from the water-soluble carbon material may be supported. Of these, it is preferable to support the carbon derived from the cellulose nanofibers, from the viewpoint of more effectively increasing the discharge capacity by uniformly depositing the carbon derived from the water-soluble carbon material on the surface of the particles while the carbon derived from the cellulose nanofibers is present on the surface of the particles (B) and filling the interparticle voids of the packing structure formed by the particles (B).

[0043] When carbon derived from cellulose nanofibers and / or carbon derived from a water-soluble carbon material is supported on the surface of particles (B), the sum of the atomic amount of carbon derived from cellulose nanofibers and the atomic amount of carbon derived from the water-soluble carbon material, i.e., the total amount of carbon derived from cellulose nanofibers and the total amount of carbon derived from the water-soluble carbon material, is preferably 0.7% by mass to 3.5% by mass, more preferably 0.9% by mass to 3.0% by mass, and even more preferably 1.0% by mass to 2.5% by mass, based on 100% by mass of particles (B).

[0044] From the viewpoint of effectively achieving both high energy density and excellent rate characteristics, the content of component (B) (particles (B)) in the positive electrode active material for a lithium ion secondary battery of the present invention is 7 mass % to 36 mass %, preferably 10 mass % to 30 mass %, and more preferably 12 mass % to 25 mass %.

[0045] In addition, when component (B) (particle (B)) has carbon derived from cellulose nanofibers and / or carbon derived from a water-soluble carbon material supported on its surface, the content of component (B) (particle (B)) includes the amount of these carbons supported. In addition, the atomic equivalent amount (supported amount) of carbon derived from cellulose nanofibers present in particle (B) and the atomic equivalent amount (supported amount) of carbon derived from water-soluble carbon material are values ​​determined by measurement using a carbon / sulfur analyzer.

[0046] The particles (B) can be obtained, for example, by the following production method. Specifically, the method comprises the following steps (Ib) to (IVb): (Ib) A step of adding a lithium compound, a manganese compound and / or an iron compound, a phosphate compound, cellulose nanofibers, and water to obtain a slurry water b, and then subjecting the slurry water to a hydrothermal reaction to obtain a composite B. (IIb) A step of adding the obtained composite B and water to obtain slurry water c. (IIIb) A step of subjecting the obtained slurry water c to spray drying to obtain granules Z. (IVb) A step of firing the obtained granules Z The manufacturing method includes the steps of:

[0047] The above-mentioned step (Ib) is a step in which a lithium compound, a manganese compound and / or an iron compound, a phosphate compound, cellulose nanofibers, and water are added to obtain slurry water b, which is then subjected to a hydrothermal reaction to obtain composite B.

[0048] As the lithium compound, the same ones as those for the above particles (A) can be used, with hydroxides being preferred. As the manganese compound, the same ones as those for the above particles (A) can be used. Examples of the iron compound include iron acetate, iron nitrate, iron sulfate, etc. These may be used alone or in combination of two or more. Among these, iron sulfate is preferred from the viewpoint of improving the battery characteristics. In addition to these manganese compounds and iron compounds, metals other than manganese compounds and iron compounds (M 2 ) compounds may also be used. Examples of 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 preferable to use it as an aqueous solution with a concentration of 70% by mass to 90% by mass. In addition, when supporting carbon derived from cellulose nanofibers, cellulose nanofibers may be added together with a lithium compound and the like in step (Ib) to obtain slurry water b.

[0049] More specifically, the step (Ib) includes a step (ib-1) of mixing a phosphoric acid compound with a slurry water b' containing a lithium compound to obtain a composite B'; A step (ib-2) of subjecting the obtained composite B' and slurry water b containing metal compounds including at least a manganese compound and an iron compound to a hydrothermal reaction to obtain composite B. It is preferable to provide: When cellulose nanofibers are used, a slurry water b' containing a lithium compound and cellulose nanofibers may be prepared.

[0050] In the step (ib-1), the content of the lithium compound in the slurry water b' is preferably 5 to 50 parts by mass, and more preferably 7 to 45 parts by mass, based on 100 parts by mass of water. When cellulose nanofibers are used, the content thereof in the slurry water b' is preferably 0.2 to 10.6 parts by mass, more preferably 0.5 to 8 parts by mass, and even more preferably 0.8 to 5.3 parts by mass, calculated as the amount of residue from the carbonization treatment, per 100 parts by mass of water. It is preferable to stir the slurry water b' before adding the phosphoric acid compound to the slurry water b'. The stirring time of the slurry water b' is preferably 1 to 15 minutes, more preferably 3 to 10 minutes. The temperature of the slurry water b' is preferably 20°C to 90°C, more preferably 20°C to 70°C.

[0051] In the step (Ib), when phosphoric acid is mixed with the slurry water b', it is preferable to drop phosphoric acid while stirring the slurry water. The dropping speed of phosphoric acid into the slurry water b' is preferably 15 mL / min to 50 mL / min, more preferably 20 mL / min to 45 mL / min, and even more preferably 28 mL / min to 40 mL / min. The stirring time of the slurry water b while dropping phosphoric acid is preferably 0.5 hours to 24 hours, and more preferably 3 hours to 12 hours. The stirring speed of the slurry water while dropping phosphoric acid is preferably 200 rpm to 700 rpm, more preferably 250 rpm to 600 rpm, and even more preferably 300 rpm to 500 rpm. When the slurry water b' is stirred, it is preferable to cool the slurry water b' to a temperature equal to or lower than the boiling point of the slurry water b'. Specifically, it is preferable to cool the slurry water b' to a temperature equal to or lower than 80°C, and more preferably to a temperature in the range of 20°C to 60°C.

[0052] The slurry water b' after mixing with the phosphoric acid compound preferably contains 2.0 to 4.0 moles of lithium per mole of phosphoric acid, more preferably 2.0 to 3.1 moles, and the lithium compound and the phosphoric acid compound may be used in such amounts. More specifically, the slurry water b' after mixing with the phosphoric acid compound preferably contains 2.7 to 3.3 moles of lithium per mole of phosphoric acid, more preferably 2.8 to 3.1 moles.

[0053] By purging nitrogen into the slurry water b' after mixing with the phosphoric acid compound, the reaction in the slurry water is completed, and a composite B', which is a precursor of the particles (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 b' is reduced, and the dissolved oxygen concentration of the resulting slurry water containing the composite B' is also effectively reduced, so that the oxidation of the metal compound to be added in the next step can be suppressed. In the slurry water b' containing the composite B', the precursor of the particles (B) exists as fine dispersed particles. The composite B' is obtained as a composite of trilithium phosphate (Li3PO4) and cellulose nanofibers.

[0054] Next, in step (ib-2), the complex B' obtained in step (ib-1) and the slurry water b containing metal compounds including at least a manganese compound and an iron compound are subjected to a hydrothermal reaction to obtain a complex B.

[0055] The molar ratio of the manganese compound to the iron compound (manganese compound:iron compound) used is preferably 95:5 to 20:80, more preferably 90:10 to 30:70, and further preferably 85:15 to 40:60. The total amount of these metal compounds added is preferably 0.99 mol to 1.01 mol, more preferably 0.995 mol to 1.005 mol, per mol of phosphate ions contained in the slurry water A.

[0056] The amount of water used in the hydrothermal reaction is preferably 10 mol to 50 mol, and more preferably 12.5 mol to 45 mol, per mol of phosphate ion contained in the slurry water b, from the viewpoints of the solubility of the metal compound, ease of stirring, synthesis efficiency, and the like.

[0057] Manganese compounds, iron compounds and metals (M 2The order of addition of the metal compounds is not particularly limited. In addition to adding these metal compounds, an antioxidant may be added if necessary. As such an antioxidant, sodium sulfite (Na2SO3), sodium hydrosulfite (Na2S2O4), aqueous ammonia, etc. can be used. The amount of the antioxidant to be added is determined based on the amount of the manganese compound, the iron compound, and the metal (M 2 The amount is preferably 0.01 mol to 1 mol, and more preferably 0.03 mol to 0.5 mol, relative to 1 mol of the total of the salts.

[0058] Manganese compounds, iron compounds and metals (M 2 The content of complex B' in the slurry water b obtained by adding the above-mentioned fluorine-containing compound and, if necessary, an antioxidant, etc., is preferably 10 to 50 mass %, more preferably 15 to 45 mass %, and even more preferably 20 to 40 mass %.

[0059] The hydrothermal reaction may be carried out at 100° C. or higher, preferably at 130° C. to 200° C. The hydrothermal reaction is preferably carried out in a pressure-resistant vessel, and when the reaction is carried out at 130° C. to 200° C., the pressure is preferably 0.3 MPa to 1.6 MPa, and 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 hours to 48 hours, more preferably 0.2 hours to 24 hours. The obtained complex B is isolated by filtration, washing with water, and drying. The drying method used may be freeze drying or vacuum drying.

[0060] The above step (IIb) is a step of adding water to the composite B obtained in the step (Ib) to obtain a slurry water c. The solid content concentration of the slurry water c is preferably 5% by mass to 30% by mass, more preferably 5% by mass to 20% by mass, and further preferably 5% by mass to 15% by mass.

[0061] After adding water, it is preferable to pre-stir the slurry water c before proceeding to step (IIIb). The stirring time of the slurry water c is preferably 3 to 60 minutes, more preferably 5 to 30 minutes. The temperature of the slurry water c is preferably 10°C to 60°C, more preferably 20°C to 40°C.

[0062] The above step (IIIb) is a step of subjecting the slurry water c obtained in the step (IIb) to spray drying to obtain the granules Z. In the spray drying, the operating conditions may be appropriately set depending on the apparatus used. For example, the treatment conditions for a micromist dryer equipped with a four-fluid nozzle (MDL-050M manufactured by Fujisaki Electric Co., Ltd.) are such that the hot air temperature is preferably 110° C. to 300° C., and more preferably 150° C. to 250° C. The volume 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 10,000, and more preferably 1,000 to 9,000.

[0063] The step (IVb) is a step of calcining the granules Z obtained in the step (IIIb). The calcination conditions in the step (IVb) are preferably a reducing atmosphere or an inert atmosphere, the calcination temperature is preferably 500° C. to 1000° C., more preferably 550° C. to 900° C., and the calcination time is preferably 0.5 hours to 12 hours, more preferably 1 hour to 6 hours.

[0064] The tap density and average particle size of the granules Z after firing obtained in the above step (IVb) can be adjusted by appropriately controlling the above conditions during the process from step (IIb) to step (IVb). However, from the viewpoint of effectively increasing the uniformity and electrode density of the obtained electrode and effectively improving the rate characteristics by increasing the tap density value of the granules Z compared to other particles or decreasing the repose angle value compared to other particles, the manufacturing method for obtaining the particles (B) may further include the following steps (Vb) to (VIb). That is, the method includes the above steps (Ib) to (IVb), and further includes the steps (Ib) to (IVb), (Vb) A step of applying an integrated energy load of 0.15 kJ / g to 0.30 kJ / g to the granules Z obtained by the above step (IVb) using a dry mixer to obtain a compact Z'. (VIb) A step of firing the obtained compact Z' It is preferable that the manufacturing method comprises:

[0065] The step (Vb) is a step of applying a load of an integrated energy of 0.15 kJ / g to 0.30 kJ / g to the granules Z obtained in the step (IVb) by a dry mixer to obtain a compacted body Z'. By applying such a load to the granules Z obtained in the step (IVb), the granules Z obtained in the step (IVb) are once compacted, and then the step proceeds to the step (VIb) described later.

[0066] The dry mixer that can be used is not particularly limited, but for example, an MP mixer (manufactured by Nippon Coke Corporation) can be used.

[0067] The cumulative energy applied to the granules Z after firing is 0.15 kJ / g to 0.30 kJ / g, preferably 0.17 kJ / g to 0.30 kJ / g, and more preferably 0.20 kJ / g to 0.30 kJ / g.

[0068] The average particle size of the resulting compact Z' is preferably 4 μm to 30 μm, and more preferably 8 μm to 26 μm.

[0069] The above step (VIb) is a step of firing the compact Z' obtained in the step (Vb). The firing temperature in step (VIb) is preferably 200° C. to 750° C., more preferably 200° C. to 600° C., and further preferably 200° C. to 400° C. The firing time is preferably 15 minutes to 180 minutes, and more preferably 30 minutes to 120 minutes. The firing atmosphere is preferably a reducing atmosphere or an inert atmosphere.

[0070] Here, it is desirable that at least one of the firing in step (IVb) and the firing in step (VIb) is at a temperature of 600°C to 750°C. Thereby, while further consolidating the consolidated body Z', defects in the crystallinity of particles (B) or carbon derived from cellulose nanofibers that may occur in part are repaired or revived as the process progresses, and particles having a higher tap density value or a smaller angle of repose value than other particles, and particles (B) that exhibit appropriate strength can be produced. From such a viewpoint, it is preferable that the firing temperature in step (VIb) is lower than the firing temperature in step (IVb). More specifically, for example, the firing temperature in step (IVb) is 600°C to 750°C, and the firing temperature in step (VIb) is 200°C to 400°C.

[0071] The positive electrode active material for a lithium ion secondary battery of the present invention contains, as component (C), 1% by mass to 12% by mass of particles represented by the following formula (c). Li j Fe k M 3 y PO4···(c) (In formula (c), M 3 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. j, y, and k are numbers satisfying 0 < j ≤ 1.2, 0 ≤ y ≤ 0.3, 0.5 < k ≤ 1.2, and j + (valence of Fe) × k + (valence of M 3 ) × y = 3.)

[0072] The particles of component (C) represented by the above formula (c) are so-called olivine-type lithium transition metal phosphate compounds (LFP particles, hereinafter also referred to as "particles (C)") that contain at least iron (Fe) as a transition metal and do not contain manganese (Mn), and are secondary particles formed by aggregation of primary particles. By containing such particles (C) having a specific average particle size in the above amount, it is possible to effectively reduce the voids between the particles of the above components (A) and (B) while maintaining excellent rate characteristics, and effectively increase the energy density.

[0073] As the particles (C) represented by the above formula (c), from the viewpoint of effectively improving the rate characteristics, specifically, LiFePO4, LiFe 0.99 Mg 0.01 PO4, LiFe 0.97 Zinc 0.03 PO4, LiFe 0.98 Ni 0.02 PO4 can be used, among which LiFePO4 is preferred.

[0074] The average particle size of the primary particles of the particles (C) represented by the above formula (c) is preferably 100 nm to 300 nm, more preferably 120 nm to 250 nm, from the viewpoints of ensuring excellent rate characteristics and handling. In addition, the average particle size of the particles (C), which are secondary particles formed by aggregation of the primary particles (simply referred to as the "average particle size of particles (C)"), is determined from the viewpoint of effectively achieving compatibility between excellent rate characteristics and high energy density, and from the viewpoint of handling, so that the ratio of the average particle size of the particles (C) to the average particle size of the particles (B) ((C) r / (B) r ) is preferably 0.2 to 0.5, more preferably 0.25 to 0.4 or less. The average particle size of such particles (C) is, specifically, preferably 5 μm to 15 μm, more preferably 5 μm to 12 μm. Here, the “average particle size” of the particles (C) is the D obtained from the volume-based particle size distribution based on the laser diffraction / scattering method, similar to the case of the particles (A). 50 The values ​​shown are the particle diameters (median diameters) at 50% of the cumulative particle size.

[0075] The tap density of the particles (C) represented by the above formula (c) is preferably 0.8 g / cm from the viewpoint of improving the electronic conductivity of the particles and the handleability in the electrode slurry and effectively increasing the uniformity and electrode density in the obtained electrode. 3 ~1.3g / cm 3 and more preferably 1.1 g / cm 3 ~1.3g / cm 3 It is.

[0076] The angle of repose of the particles (C) represented by the above formula (c) is preferably 30° to 50°, and more preferably 30° to 45°, from the viewpoint of improving the electronic conductivity of the particles and the handleability in the electrode slurry and effectively increasing the uniformity and electrode density in the obtained electrode.

[0077] From the viewpoint of effectively achieving both high energy density and excellent rate characteristics, the content of component (C) (particles (C)) in the positive electrode active material for a lithium ion secondary battery of the present invention is 1 mass % to 12 mass %, preferably 2 mass % to 10 mass %, and more preferably 3 mass % to 8 mass %.

[0078] In the positive electrode active material for a lithium ion secondary battery of the present invention, the mass ratio of the content of component (B) to the content of component (C) ((B) / (C)) is 2 to 9, preferably 2.5 to 8, more preferably 3 to 7, and even more preferably 3.5 to 6, from the viewpoint of effectively achieving both high energy density and excellent rate characteristics.

[0079] The particles (C) can be obtained, for example, by the same production method as the production method including the above steps (Ib) to (IVb) for the particles (B).

[0080] The positive electrode active material for lithium ion secondary batteries of the present invention can be obtained by adjusting the amount of the particles of the above-mentioned components (A), (B), and (C) to the above-mentioned content, and then mixing them by a conventional method. There is no particular restriction on the order of adding the particles of the components (A), (B), and (C).

[0081] The positive electrode active material for lithium ion secondary batteries of the present invention can be used as a positive electrode material to construct a lithium ion secondary battery essentially consisting of a positive electrode, a negative electrode, an electrolyte, and a separator, or a positive electrode, a negative electrode, and a solid electrolyte. Specifically, for example, the positive electrode active material for lithium ion secondary batteries of the present invention is kneaded with acetylene black, ketjen black, polyvinylidene fluoride, N-methyl-2-pyrrolidone, or the like to prepare a positive electrode slurry, which is then applied to a current collector and press-molded to produce a positive electrode. In the positive electrode active material for a lithium ion secondary battery of the present invention, the above-mentioned three specific types of particles (A) to (C) are closely associated with each other, and are easily compacted without collapsing even during press molding, thereby increasing the electrode density and providing a highly useful positive electrode that can effectively increase the energy density and rate characteristics.

[0082] Here, the negative electrode is not particularly limited in terms of its material composition, and any known material composition can be used, as long as it can absorb lithium ions during charging and release them during discharging. For example, lithium metal, graphite, silicon-based (Si, SiOx), lithium titanate, or carbon materials such as amorphous carbon can be used. It is preferable to use an electrode formed of an intercalation material capable of electrochemically absorbing and releasing lithium ions, particularly a carbon material. Furthermore, two or more of the above negative electrode materials may be used in combination, and for example, a combination of graphite and silicon-based materials can be used.

[0083] The electrolyte solution is prepared 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 electrolytes for lithium ion secondary batteries, and examples of the organic solvent that can be used include carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, and oxolane compounds.

[0084] 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 such inorganic salts, organic salts selected from LiSO3CF3, LiC(SO3CF3)2, LiN(SO3CF3)2, LiN(SO2C2F5)2, and LiN(SO2CF3)(SO2C4F9), and derivatives of such organic salts.

[0085] The separator serves to electrically insulate the positive and negative electrodes and to retain the electrolyte, and may be, for example, a porous synthetic resin film, particularly a porous film of a polyolefin polymer (polyethylene, polypropylene).

[0086] The solid electrolyte electrically insulates the positive and negative electrodes and exhibits high lithium ion conductivity. 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 S 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 Just use S4.

[0087] The shape of the lithium ion secondary battery having the above-mentioned configuration is not particularly limited, and may be various shapes such as a coin type, a cylindrical type, a square type, or an irregular shape enclosed in a laminate exterior body. EXAMPLES

[0088] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.

[0089] Particles of each component were produced according to the description of each production example. The physical properties of the obtained particles are shown in Table 1.

[0090] <<Measurement of the average particle size of primary particles>> The measurements were carried out using an X-ray diffraction apparatus (D8 ADVANCE A-25, manufactured by Bruker AXS). The measurement conditions were 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 / Lebert method to calculate the crystallite diameter, and this value was used as the average particle diameter of the primary particles.

[0091] <<Measurement of average particle size (secondary particles)>> The particle size distribution of the particles was measured using a laser diffraction device (Microtrac MT3000II, manufactured by MicrotracBEL). The measurement conditions were as follows: particle transmittance: transmission, particle shape: non-spherical, particle refractive index: 1.52. Ethanol was used as the solvent, and the solvent refractive index: 1.36.

[0092] Tap density (g / cm 3 )》 The tapped bulk density was measured according to the method specified in JIS R 1628 "Method of measuring bulk density of fine ceramic powders", and this was defined as the tapped density (g / cm 3 ) was decided.

[0093] 《Angle of repose (°)》 The angle of repose (°) was measured using a powder property evaluation device, Powder Tester PT-X (manufactured by Hosokawa Micron Corporation), according to the method specified in JIS R 9301-2-2 "Alumina powder - Part 2: Measurement of physical properties - 2: Angle of repose".

[0094] [Production Example 1: Production of Particles (A-1) (NCM Particles)] 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, and then 25% ammonia water was added dropwise to the mixture at a rate of 300 mL / min to obtain a slurry a1 containing a metal composite hydroxide having a pH of 11. Next, the slurry a1 was filtered and dried to obtain a mixture b1 of metal composite hydroxides, and then 37 g of lithium carbonate was mixed with the mixture b1 in a ball mill to obtain a powder mixture c1. The obtained powder mixture c1 was pre-calcined at 800°C for 4 hours in an air atmosphere and crushed, and then calcined at 800°C for 11 hours in an air atmosphere as a main calcination to obtain particles (A-1) (LiNi 0.6 Co 0.2 Mn 0.2 O2) was obtained.

[0095] [Production Example 2: Production of Particles (B-1) (LMFP Particles)] LiOH·H2O 1272g and water 4L were mixed to obtain slurry x1. Next, 1153g of 85% phosphoric acid aqueous solution was dropped at 35mL / min into the obtained slurry x1 while stirring for 3 minutes while maintaining the temperature at 25°C, followed by adding 4124g of cellulose nanofiber (Wma-10002, Sugino Machine Co., Ltd., fiber diameter 4-20nm) and stirring at a speed of 400 rpm for 12 hours to obtain slurry y1 containing Li3PO4. The obtained slurry y1 was purged with nitrogen to adjust the dissolved oxygen concentration of the slurry y1 to 0.5mg / L, and then 723g of MnSO4·5H2O and 1946g of FeSO4·7H2O were added to the total amount of slurry y1 to obtain slurry z1. The molar ratio of added MnSO4 and FeSO4 (manganese compound: iron compound) was 30:70.

[0096] The obtained slurry z1 was then placed in 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 generated crystals were filtered and then washed with 12 parts by mass of water per part by mass of the crystals. The washed crystals were freeze-dried at -50°C for 12 hours to obtain a complex Cz1. 1000 g of the obtained complex Cz1 was taken out and 1 L of water was added thereto to obtain a slurry Ez1. The obtained slurry Ez1 was dispersed for 1 minute with an ultrasonic agitator (T25, manufactured by IKA Co., Ltd.) to uniformly color the entire mixture, and then spray-dried (nozzle air flow rate 35 L / min, supply air temperature 190°C) using a spray dryer (MDL-050M, manufactured by Fujisaki Electric Co., Ltd.) to obtain a granule Fz1. The obtained granules Fz1 were calcined at 700°C for 1 hour in an argon-hydrogen atmosphere (hydrogen concentration 3%) to obtain particles (B-1) (LiMn 0.3 Fe 0.7 PO4) was obtained.

[0097] [Production Example 3: Production of particles (B-2) (LMFP particles)] The procedure of Production Example 2 was repeated except that the water for obtaining the slurry x1 was 25 L, the molar ratio of the added MnSO4 and FeSO4 (manganese compound:iron compound) was 90:10, and the amount of the added cellulose nanofiber was 20.62 kg. 0.9 Fe 0.1 PO4) was obtained.

[0098] [Production Example 4: Production of particles (B-3) (LMFP particles)] The cellulose nanofiber-derived carbon-supported particles (B-3) (LiMn 0.7 Fe 0.3 PO4) was obtained.

[0099] [Production Example 5: Production of particles (B-4) (LMFP particles)] The cellulose nanofiber-derived carbon-supported particles (B-4) (LiMn 0.7 Fe 0.3 PO4) was obtained.

[0100] [Production Example 6: Production of particles (B-5) (LMFP particles)] The cellulose nanofiber-derived carbon-supported particles (B-5) (LiMn 0.7 Fe 0.3 PO4) was obtained.

[0101] [Production Example 7: Production of particles (B-6) (LMFP particles)] The same procedure as in Production Example 2 was repeated except that the molar ratio of added MnSO4 and FeSO4 (manganese compound:iron compound) was 70:30, the hydrothermal reaction was carried out at 190°C for 2 hours, and the amount of added cellulose nanofiber was 7070 g. 0.7 Fe 0.3 PO4) was obtained.

[0102] [Production Example 8: Production of particles (B-7) (LMFP particles)] The procedure of Production Example 2 was repeated except that the water used to obtain the slurry x1 was 20 L, the molar ratio of the added MnSO4 and FeSO4 (manganese compound:iron compound) was 70:30, the hydrothermal reaction was carried out at 130°C for 1 hour, and the amount of cellulose nanofiber added was 17.17 kg. 0.7 Fe 0.3 PO4) was obtained.

[0103] [Production Example 9: Production of particles (B-8) (LMFP particles)] The same procedure as in Production Example 2 was repeated except that the molar ratio of the added MnSO4 and FeSO4 (manganese compound:iron compound) was 70:30, the amount of cellulose nanofibers added was 11.78 kg, and the inlet air temperature of the spray dryer was 170°C. 0.7 Fe 0.3 PO4) was obtained.

[0104] [Production Example 10: Production of particles (B-9) (LMFP particles)] LiOH·H2O 1272g and water 4L were mixed to obtain slurry a. Next, 1153g of 85% phosphoric acid aqueous solution was dropped at 35mL / min while stirring the obtained slurry a for 3 minutes while maintaining the temperature at 25℃, followed by adding 7070g of cellulose nanofiber (Wma-10002, Sugino Machine Co., Ltd., fiber diameter 4nm-20nm) and stirring at a speed of 400rpm for 12 hours to obtain slurry b containing Li3PO4. Nitrogen was purged into the obtained slurry b to adjust the dissolved oxygen concentration of slurry b to 0.5mg / L, and then 1688g of MnSO4·5H2O and 834g of FeSO4·7H2O were added to the total amount of slurry b to obtain slurry c. The molar ratio of added MnSO4 and FeSO4 (manganese compound: iron compound) was 70:30. The obtained slurry c was then placed in an autoclave and subjected to a hydrothermal reaction at 180°C for 1 hour. The pressure inside the autoclave was 0.8MPa. After the hydrothermal reaction, the generated 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 a complex d. 1000g of the obtained complex d was taken out and 1L of water was added thereto to obtain a slurry e. The obtained slurry e was dispersed for 1 minute with an ultrasonic agitator (T25, manufactured by IKA Co., Ltd.) to uniformly color the whole, and then spray-dried (nozzle air flow rate 35L / min, supply air temperature 190°C) using a spray dryer (MDL-050M, manufactured by Fujisaki Electric Co., Ltd.) to obtain a granule S1. The obtained granules S1 were sintered at 650°C for 30 minutes in an argon hydrogen atmosphere (hydrogen concentration 3%) to obtain a sintered body X1. 300 g of the obtained sintered body X1 was sampled, and a compressive force and a shear force were applied for 2 minutes at a powder load of 0.4 kW using an MP mixer (manufactured by Nippon Coke Corporation) (accumulated energy applied: 0.16 kJ / g) to obtain a compact Y1. The obtained compact Y1 was then sintered at 200°C for 30 minutes in an argon hydrogen atmosphere (hydrogen concentration 3%) to obtain particles (B-9) (LiMn 0.7 Fe 0.3 PO4) was obtained.

[0105] [Production Example 11: Production of Particles (C-1) (LFP Particles)] Particles (C-1) (LiFePO4) carrying carbon derived from cellulose nanofibers were obtained according to Production Example 2, except that only FeSO4 was added without adding MnSO4, the amount of cellulose nanofibers added was 7070 g, and the nozzle air flow rate for spray drying was 50 L / min.

[0106] [Production Example 12: Production of particles (C-2) (LFP particles)] Particles (C-2) (LiFePO4) carrying carbon derived from cellulose nanofibers were obtained according to Production Example 2, except that only FeSO4 was added without adding MnSO4 and the amount of cellulose nanofibers added was 7070 g.

[0107] [Table 1]

[0108] [Examples 1 to 11, Comparative Examples 1 to 3] According to the formulation shown in Table 2, particles of each component were mixed using a planetary mixer (PLM-2, manufactured by Inoue Seisakusho Co., Ltd.) to obtain a positive electrode active material. Next, the obtained positive electrode active material was used to carry out various evaluations according to the following methods. The results are shown in Table 2.

[0109] <Evaluation of battery characteristics (rate characteristics)> The obtained positive electrode active materials were used as positive electrode materials to prepare positive electrodes for lithium ion secondary batteries. Specifically, the obtained positive electrode active materials, acetylene black, and polyvinylidene fluoride were mixed in a mass ratio of 90:5:5, and N-methyl-2-pyrrolidone was added to the mixture and thoroughly kneaded to prepare a positive electrode slurry. The positive electrode slurry was applied to a current collector made of aluminum foil with a thickness of 20 μm using a coater, and vacuum dried at 80° C. for 12 hours. Thereafter, the mixture was punched into a disk shape of φ14 mm and pressed for 2 minutes at 16 MPa using a hand press to obtain a positive electrode.

[0110] Next, a coin-type secondary battery was constructed using the above positive electrode. A lithium foil punched to φ15 mm was used as the negative electrode. The electrolyte was a mixed solvent of ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7, in which LiPF6 was dissolved at a concentration of 1 mol / L. A polymer porous film was used as the separator. These battery components were assembled 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).

[0111] Using the obtained coin-type secondary battery, the discharge capacities of 0.2C (34mAh / g) and 3C (510mAh / g) were measured in an environment of 30°C using a discharge capacity measuring device (HJ-1001SD8, manufactured by Hokuto Denko Corporation), and the rate characteristic values ​​were calculated using the following formula (x). Rate characteristic = (discharge capacity at 3 C) / (discharge capacity at 0.2 C) (x)

[0112] Calculating energy density per volume Using the obtained coin-type secondary battery, the discharge capacity of 0.2 C (34 mAh / g) was measured in an environment at an air temperature of 30° C. using 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 volume. Electrode density (g / cm 3 )= Mass of positive electrode active material in positive electrode (g) / electrode volume (cm3 )(φ14mm×thickness(μm)) (y) Positive electrode volumetric energy density at 30℃ (Wh / L) = Discharge capacity at 30℃ (mAh / g) × average voltage (V) × electrode density (g / cm 3 ) (z)

[0113] [Table 2]

Claims

1. The following components (A), (B), and (C): (A) Particles represented by the following formula (a): 60% by mass to 90% by mass L)) 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 within the range of 0.3≦a<1, 0<b≦0.7, 0<c≦0.7, and 0≦w≦0.3, and 3a+3b+3c+(M 1 (valence of x) × w = 3. (B) Particles represented by the following formula (b) and having an average particle size of 10 μm to 30 μm: 7% by mass to 36% by mass Li f Mn g Fe h M 2 x 2O 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 satisfy 0<f≦1.2, 0.15≦g≦1.1, 0.08≦h≦0.9, 0≦x≦0.3, and 0.2≦g / h≦9, and f+(valence of Mn)×g+(valence of Fe)×h+(valence of Mn)×g+(valence of Mn). 2 (valence of x) × x = 3. (C) Particles represented by the following formula (c): 1% by mass to 12% by mass Li j Fe k M 3 y PO 4 ・・・(c) (In formula (c), M 3 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. j, y, and k are each 0<j≦1.2, 0≦y≦0.3, 0.5<k≦1.2, and j+(valence of Fe)×k+(M 3 (valence) × y = 3. The ratio of the average particle size of component (C) to the average particle size of component (B) ((C)r / (B)r) is 0.2 to 0.5, and the mass ratio of the content of component (B) to the content of component (C) ((B) / (C)) is 2 to 9. Positive electrode active material for lithium-ion secondary batteries.

2. The tap density of component (B) is lower than the tap density of component (A) and is 0.7 g / cm 3 ~1.3g / cm 3 The positive electrode active material for a lithium ion secondary battery according to claim 1 ,

3. 3. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the average particle size of the component (A) is 3 μm to 20 μm.

4. The positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 3, wherein the component (B) has an angle of repose of 30° to 45°.

5. The positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 4, wherein the surface of the particles of component (B) is supported with carbon derived from cellulose nanofibers.

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