Positive electrode active material particle mixture for lithium ion secondary batteries

Abstract

To provide a positive electrode active material particle mixture for a lithium ion secondary battery, which enables the satisfactory enhancement in capacity and safety as to a lithium ion secondary battery while using lithium manganese iron phosphate-based particles while using lithium manganese iron phosphate-based particles.SOLUTION: A positive electrode active material particle mixture for a lithium ion secondary battery comprises: particles (A) given by the formula (A), LiaMnbFecM1xPO4 (A) (in the formula (A), M1 represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd; a, b, c and x are numbers that satisfy 0<a≤1.2, 0≤b≤1.2, 0≤c≤1.2, 0≤x≤0.3 and b+c≠0, and a+(Valence number of Mn)×b+(Valence number of Fe)×c+(Valence number of M1)×x=3) and having a tap density of 0.3-1.2 g / cm3, of which the volume of pores of 10-3000 nm in pore diameter is 0.2-0.7 mL / g; particles (B) of a substance represented by the formula (B), LiNidCoeMnfM2yO2; and particles (C) represented by the formula (C), LiNigCohMniM3zO2.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a positive electrode active material particle mixture for a lithium ion secondary battery, for obtaining a lithium ion secondary battery having a high capacity and excellent safety. [Background technology]

[0002] Secondary batteries such as lithium-ion secondary batteries are used in a wide range of fields, including mobile phones, digital cameras, notebook PCs, hybrid cars, and electric cars. LiMn is a popular positive electrode material for these lithium-ion secondary batteries because of its high safety and large capacity. x Fe 1-x Lithium manganese iron phosphate particles such as PO4 are considered promising. However, the conductivity of the lithium manganese iron phosphate particles is low, and there is still a need to improve the battery characteristics of the resulting lithium-ion secondary battery. Therefore, various developments have been carried out.

[0003] For example, Patent Document 1 discloses a positive electrode for a secondary battery that contains lithium-nickel-cobalt-manganese composite oxide together with lithium manganese iron phosphate in order to obtain a secondary battery with excellent energy density, and is more effective in improving the initial coulombic efficiency in a lithium ion secondary battery than when lithium manganese iron phosphate is contained alone. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2011-159388 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the technology described in the above patent document, when attempting to increase the nickel content of the lithium-nickel-cobalt-manganese composite oxide used in combination with lithium iron manganese phosphate in order to achieve high capacity in the resulting lithium-ion secondary battery, it is difficult to ensure safety (thermal stability, hereinafter the same meaning), and the situation still requires improvement.

[0006] Therefore, an object of the present invention is to provide a positive electrode active material particle mixture for a lithium-ion secondary battery that can sufficiently enhance both capacity and safety in a lithium-ion secondary battery while using lithium iron manganese phosphate-based particles.

Means for Solving the Problems

[0007] Therefore, as a result of intensive studies to solve the above problems, the present inventors have found that by using two types of lithium-nickel-cobalt-manganese-based particles with different nickel contents in combination with specific lithium iron manganese phosphate-based particles having many voids inside the particles, a positive electrode material capable of realizing a lithium-ion secondary battery that exhibits high capacity and excellent safety can be obtained.

[0008] That is, the present invention provides the following formula (A): Li a Mn b Fe c M 1 x PO4···(A) (In formula (A), M 1 represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd. a, b, c, and x satisfy 0 < a ≤ 1.2, 0 ≤ b ≤ 1.2, 0 ≤ c ≤ 1.2, 0 ≤ x ≤ 0.3, and b + c ≠ 0, and a + (valence of Mn) × b + (valence of Fe) × c + (valence of M 1 ) × x = 3. ) represented by, and the tap density is 0.3 g / cm 3 ~1.2 g / cm 3and particles (A) having a pore volume of 0.2 mL / g to 0.7 mL / g at a pore diameter of 10 nm to 3000 nm; The following formula (B): LiNi d Co e Mn f M 2 y O2···(B) (In formula (B), M 2 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. d, e, f, and y are within the range of 0.6≦d≦0.95, 0 <e≦0.4、0<f≦0.4、0≦y≦0.3、かつ3d+3e+3f+(M 2 The number that satisfies the formula (valence of x) x y = 3. A particle (B) represented by The following formula (C): LiNi g Co h Mn i M 3 z O2···(C) (In formula (C), M 3 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. g, h, i, and z are within the range of 0.3≦g<0.6, 0 <h≦0.7、0<i≦0.7、0≦z≦0.3、かつ3g+3h+3i+(M 3 The number satisfies the valence of z × z = 3. Particle (C) represented by and a positive electrode active material particle mixture for a lithium ion secondary battery, the positive electrode active material particle mixture comprising the above. Effect of the Invention

[0009] According to the positive electrode active material particle mixture for a lithium ion secondary battery of the present invention, since it contains particles (A) which are lithium manganese iron phosphate-based particles having many voids inside the particles and showing good collapsibility during the pressing process in the battery manufacturing process, both particles (B) and (C) which are two kinds of lithium-nickel-cobalt-manganese-based particles with different nickel contents are closely and effectively intertwined, and a lithium ion secondary battery excellent in capacity and safety (thermal stability) can be realized while effectively increasing the capacity.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the present invention will be described in detail. The positive electrode active material particle mixture for a lithium ion secondary battery of the present invention has the following formula (A): Li a Mn b Fe c M 1 x PO4···(A) (In formula (A), M 1 represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd. a, b, c, and x satisfy 0 < a ≤ 1.2, 0 ≤ b ≤ 1.2, 0 ≤ c ≤ 1.2, 0 ≤ x ≤ 0.3, and b + c ≠ 0, and a + (valence of Mn) × b + (valence of Fe) × c + (valence of M 1 ) × x = 3. ) represented by, and having a tap density of 0.3 g / cm 3 ~1.2 g / cm 3 and particles (A) having a pore volume of 0.2 mL / g to 0.7 mL / g in a pore diameter of 10 nm to 3000 nm, the following formula (B): LiNi d Co e Mn f M 2 y O2···(B) (In formula (B), M 2represents 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. d, e, f, and y are within the range of 0.6≦d≦0.95, 0 <e≦0.4、0<f≦0.4、0≦y≦0.3、かつ3d+3e+3f+(M 2 The number that satisfies the formula (valence of x) x y = 3. A particle (B) represented by The following formula (C): LiNi g Co h Mn i M 3 z O2···(C) (In formula (C), M 3 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. g, h, i, and z are within the range of 0.3≦g<0.6, 0 <h≦0.7、0<i≦0.7、0≦z≦0.3、かつ3g+3h+3i+(M 3 The number satisfies the valence of z × z = 3. Particle (C) represented by It consists of:

[0011] Thus, the positive electrode active material particle mixture for a lithium ion secondary battery of the present invention is a particle mixture containing three types of particles, including particles (A) which are so-called lithium manganese iron phosphate-based particles represented by the above formula (A), particles (B) which are lithium-nickel-cobalt-manganese-based particles having a high nickel content, and particles (C) which are lithium-nickel-cobalt-manganese-based particles having a low nickel content. Since the particles (A) have many voids inside them such that their tap density and pore volume exhibit values within the above-specified ranges, they moderately collapse during the pressing process in the battery manufacturing process, and mix well and uniformly with both the particles (B) and the particles (C), and the particles are closely and effectively intertwined with each other. In the resulting lithium-ion secondary battery, while effectively increasing the capacity, it is possible to effectively suppress the destruction of the crystal structure of each particle even when charge and discharge are repeated, and it is possible to also have excellent safety.

[0012] The positive electrode active material particle mixture for a lithium-ion secondary battery of the present invention contains, as the particles (A), the following formula (A): Li a Mn b Fe c M 1 x PO4···(A) (In formula (A), M 1 represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd. a, b, c, and x satisfy 0 < a ≤ 1.2, 0 ≤ b ≤ 1.2, 0 ≤ c ≤ 1.2, 0 ≤ x ≤ 0.3, and b + c ≠ 0, and satisfy a + (valence of Mn) × b + (valence of Fe) × c + (valence of M 1 ) × x = 3.) and contains particles represented by

[0013] The particles (A) represented by the above formula (A) are olivine-type lithium manganese iron phosphate-based particles containing at least manganese (Mn) or iron (Fe), and are secondary particles formed by aggregation of primary particles. In formula (A), M 1represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd, preferably Mg or Zr. a satisfies 0 < a ≤ 1.2, preferably 0.6 ≤ a ≤ 1.2, more preferably 0.65 ≤ a ≤ 1.15, and still more preferably 0.7 ≤ a ≤ 1.1. b satisfies 0 ≤ b ≤ 1.2, preferably 0.25 ≤ b ≤ 0.8, more preferably 0.35 ≤ b ≤ 0.8. c satisfies 0 ≤ c ≤ 1.2, preferably 0.2 ≤ c ≤ 0.75, more preferably 0.2 ≤ c ≤ 0.65. And b and c satisfy b + c ≠ 0. x satisfies 0 ≤ x ≤ 0.3, preferably 0 ≤ x ≤ 0.15, more preferably 0 ≤ x ≤ 0.1. And a, b, c and x are numbers that satisfy a + (valence of Mn) × b + (valence of Fe) × c + (valence of M) × x = 3. More specifically, examples of such particles (A) include, for example, LiMnPO4, LiFePO4, LiMn 0.8 Fe 0.2 PO4, LiMn 0.1 Fe 0.9 PO4, LiMn 0.8 Fe 0.1 Mg 0.1 PO4, LiMn 0.8 Fe 0.1 Zr 0.05 PO4 and the like.

[0014] From the viewpoint of effectively suppressing unnecessary elution of metals and exhibiting good disintegrability, the tap density of the particles (A) is 0.3 g / cm 3 ~1.2 g / cm 3 and preferably 0.3 g / cm 3 ~1.0 g / cm 3 and more preferably 0.3 g / cm 3 ~0.8 g / cm 3 . Note that the tap density means the "tapped bulk density" measured by the method specified in JIS R 1628 "Method for Measuring Bulk Density of Fine Ceramic Powders" in the same manner as below.

[0015] The pore volume of the particles (A) at pore diameters of 10 nm to 3000 nm, in combination with the above tap density, is 0.2 mL / g to 0.7 mL / g, preferably 0.3 mL / g to 0.7 mL / g, and more preferably 0.4 mL / g to 0.7 mL / g, from the viewpoint of imparting good disintegrability to the particles (A) and effectively enhancing the safety of the resulting battery. The pore volume refers to a value measured by a mercury intrusion porosimeter.

[0016] The average particle size of the particles (A) is preferably 6 μm to 20 μm, more preferably 8 μm to 20 μm, and even more preferably 10 μm to 20 μm, from the viewpoint of being appropriately disintegrated during the pressing step in the battery production process and being mixed well and uniformly with other particles contained in the positive electrode active material particle mixture for lithium ion secondary batteries. The average particle size 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.

[0017] In order to ensure a high capacity, the particles (A) 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. The fiber diameter of cellulose nanofibers is 1 nm to 1000 nm, and they have good dispersibility in water, so that they can effectively suppress the deterioration of the electronic conductive path and ensure that the resulting battery exhibits excellent capacity. Examples of the water-soluble carbon material include one or more selected from sugars, polyols, polyethers, and organic acids. More specifically, examples of the water-soluble carbon material 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.

[0018] When carbon derived from cellulose nanofibers and carbon derived from a water-soluble carbon material are supported on the surface of particles (A), the sum of the atomic equivalent amount of carbon derived from cellulose nanofibers and the atomic equivalent 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 0.8% by mass to 10.0% by mass, more preferably 1.0% by mass to 7.0% by mass, and even more preferably 1.2% by mass to 5.0% by mass, based on 100% by mass of particles (A). The atomic amount (supported amount) of carbon derived from the cellulose nanofibers present in the particles (A) and the atomic amount (supported amount) of carbon derived from the water-soluble carbon material are values ​​determined by measurement using a carbon / sulfur analyzer.

[0019] From the viewpoint of achieving high capacity and excellent safety in the resulting battery, the content of particles (A) in the positive electrode active material particle mixture for lithium ion secondary batteries of the present invention is preferably 10 mass % to 30 mass %, more preferably 10 mass % to 25 mass %, and even more preferably 10 mass % to 20 mass %. In addition, when particles (A) support carbon derived from cellulose nanofibers and / or carbon derived from a water-soluble carbon material on their surfaces, the content of particles (A) also includes the amount of these carbons supported.

[0020] The particles (A) can be obtained, for example, by the following production method. Specifically, the method comprises the following steps (I) to (III): (I) a step of subjecting a slurry water i obtained by mixing a lithium compound, a metal compound including a manganese compound and / or an iron compound, a phosphate compound, and water, or a slurry water i' obtained by mixing trilithium phosphate particles, a metal compound including a manganese compound and / or an iron compound, and water, to a hydrothermal reaction to obtain a powder a; (II) adding and mixing the obtained powder a, a blowing agent and water to obtain a slurry water ii, and spray-drying the slurry water ii to obtain a granule b; (III) A step of firing the obtained granules b The manufacturing method can be obtained by the method.

[0021] Step (I) is a step of subjecting slurry water i obtained by mixing a lithium compound, a metal compound including a manganese compound and / or an iron compound, a phosphate compound, and water, or slurry water i' obtained by mixing trilithium phosphate particles, a metal compound including a manganese compound and / or an iron compound, and water, to a hydrothermal reaction to obtain powder a, i.e., a step of subjecting slurry water i or slurry water i' to a hydrothermal reaction to obtain powder a.

[0022] When slurry water i is used in step (I), examples of the lithium compound include hydroxides (e.g., LiOH·H2O, LiOH), carbonates, sulfates, and acetates. Of these, carbonates are preferred. Metal compounds containing manganese compounds and / or iron compounds include manganese compounds and iron compounds as well as metals (M 1 ) compounds can be used. 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. 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. Metal (M 1 ) compounds, M in the above formula (A) 1 Examples of the metal salts include sulfates and nitrates containing metals having the same meaning as above. 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.

[0023] In preparing the slurry water i in the step (I), the order of adding the lithium compound, the metal compound containing a manganese compound and / or an iron compound, the phosphate compound, and the water is not particularly limited. The lithium compound, the phosphate compound, and the water may be added first, and then the manganese compound and / or the iron compound may be added. Alternatively, the lithium compound, the metal compound containing a manganese compound and / or an iron compound, the phosphate compound, and the water may be added all at once. The content of the lithium compound in the slurry water i obtained by mixing a lithium compound, a metal compound including a manganese compound and / or an iron compound, a phosphate compound, and water is preferably 5 parts by mass to 50 parts by mass, and more preferably 7 parts by mass to 45 parts by mass, per 100 parts by mass of water.

[0024] For example, when phosphoric acid is used as the phosphate compound in step (I), it is preferable to add phosphoric acid to the slurry water to which a lithium compound and water have been added, and then add a manganese compound and / or an iron compound to obtain slurry water i. In this case, it is preferable to stir the slurry water in advance before adding the phosphate compound. The stirring time for the slurry water is preferably 1 to 15 minutes, more preferably 3 to 10 minutes. The temperature of the slurry water is preferably 20°C to 90°C, more preferably 20°C to 70°C.

[0025] Furthermore, when phosphoric acid is added, it is preferable to drop phosphoric acid while stirring the slurry water. The dropping speed of phosphoric acid into the slurry water 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 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 is stirred, it is preferable to cool it to a temperature equal to or lower than the boiling point of the slurry water. Specifically, it is preferable to cool it to 80°C or lower, and more preferably to 20°C to 60°C.

[0026] The slurry water 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 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.

[0027] By purging nitrogen into the slurry water after mixing with the phosphoric acid compound, the reaction in the slurry water is completed, and powder a', which is the precursor of the particles (A), is obtained as a slurry. Purging nitrogen allows the reaction to proceed in a state where the dissolved oxygen concentration in the slurry water is reduced, and the dissolved oxygen concentration of the resulting slurry water containing the powder a' is also effectively reduced, so that the oxidation of the metal compound to be added next can be suppressed. In the slurry water containing the powder a', the precursor of the particles (A) exists as fine dispersed particles of trilithium phosphate (Li3PO4).

[0028] Next, a manganese compound and an iron compound may be added to the slurry water. The molar ratio of the manganese compound and the iron compound (manganese compound:iron compound) used is preferably 90:10 to 50:50, more preferably 85:15 to 55:45, and further preferably 80:20 to 60:40. 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, relative to 1 mol of phosphate ions contained in the slurry water.

[0029] In addition, when preparing the slurry water i, if the lithium compound, the metal compound containing a manganese compound and / or an iron compound, the phosphate compound, and the water are added all at once, it is sufficient that the lithium compound, the metal compound containing a manganese compound and / or an iron compound, the phosphate compound, and the water have the above-mentioned quantitative relationship, and it is not necessary for trilithium phosphate (Li3PO4) as a precursor of the particles (A) to be present in the slurry water i.

[0030] When slurry water i' is used in step (I), metal compounds including a manganese compound and an iron compound may be added to the slurry water obtained by mixing trilithium phosphate particles and water. The content of trilithium phosphate particles in the slurry water i' is preferably 7% by mass to 60% by mass, more preferably 9% by mass to 50% by mass. The molar ratio of the manganese compound and the iron compound used, and the total amount of the metal compounds added are the same as above.

[0031] Manganese compounds, iron compounds and metals (M 1 The 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 1 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 compounds.

[0032] In the case of using the slurry water i', manganese compounds, iron compounds and metals (M 1 The content of powder a' in the slurry water i obtained by adding the hydroxyl group-containing hydroxyl group-containing compound and, if necessary, an antioxidant, etc., is preferably 10 mass % to 50 mass %, more preferably 15 mass % to 45 mass %, and even more preferably 20 mass % to 40 mass %.

[0033] Next, in step (I), the obtained powder a' and the slurry water i containing metal compounds including at least a manganese compound and an iron compound, or the slurry water i' are subjected to a hydrothermal reaction to obtain powder a.

[0034] 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 i (or slurry water i'), from the viewpoints of the solubility of the metal compound, ease of stirring, and synthesis efficiency.

[0035] 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 powder a is isolated by filtration, washing with water, and drying, for example, by freeze drying or vacuum drying.

[0036] Step (II) is a step of spray-drying slurry water ii obtained by adding and mixing the powder a obtained in step (I), a blowing agent and water to obtain granules b. Here, gas is generated by using a blowing agent, and the gas is present inside the granules b. The gas present inside the granules b is burned off through step (III) described later, and can be made to exist as voids inside the obtained particles (A).

[0037] Specific examples of the foaming agent include one or more selected from ammonium hydrogen carbonate, ammonium carbonate, sodium carbonate, lithium carbonate, and potassium carbonate. Among these, ammonium hydrogen carbonate and ammonium carbonate are preferred from the viewpoint of effectively forming many voids inside the particles (A). The amount of the foaming agent added is preferably 0.005 parts by mass to 1.25 parts by mass, more preferably 0.006 parts by mass to 0.6 parts by mass, and even more preferably 0.01 parts by mass to 0.3 parts by mass, relative to 100 parts by mass of powder a, from the viewpoint of effectively creating many voids inside the particles (A).

[0038] The solids concentration of the slurry water ii is preferably 35% by mass to 65% by mass, more preferably 40% by mass to 65% by mass, and even more preferably 45% by mass to 65% by mass, from the viewpoint of effectively creating many voids inside the particles (A) by the foaming agent so that the tap density and pore volume show values ​​within the above-mentioned specific ranges.

[0039] After adding water, it is preferable to pre-stir the slurry water II before subjecting it to spray drying. The stirring time of the slurry water II is preferably 3 to 60 minutes, more preferably 5 to 30 minutes. The temperature of the slurry water II is preferably 10°C to 60°C, more preferably 20°C to 40°C. In order to ensure excellent capacity, when carbon derived from cellulose nanofibers and / or carbon derived from a water-soluble carbon material is supported on the surface of the particles (A), the cellulose nanofibers and / or the water-soluble carbon material can be added to the slurry water i (or slurry water i') and / or slurry water ii in an amount sufficient to achieve the above-mentioned carbon support amount.

[0040] The resulting slurry water ii is then subjected to spray drying to obtain granules B. 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 110° C. to 180° 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.

[0041] Step (III) is a step of firing the granules b obtained in step (II), thereby obtaining particles (A). The firing conditions in step (III) are preferably a reducing atmosphere or an inert atmosphere, the firing temperature is preferably 500°C to 1000°C, more preferably 550°C to 900°C, and the firing time is preferably 0.5 hours to 12 hours, more preferably 1 hour to 6 hours.

[0042] The positive electrode active material particle mixture for a lithium ion secondary battery of the present invention contains particles (B) represented by the following formula (B): LiNi d Co e Mn f M 2 y O2···(B) (In formula (B), M 2 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. d, e, f, and y are within the range of 0.6≦d≦0.95, 0 <e≦0.4、0<f≦0.4、0≦y≦0.3、かつ3d+3e+3f+(M 2 The number that satisfies the formula (valence of x) x y = 3. The particle (C) is represented by the following formula (C): LiNi g Co h Mn i M 3 z O2···(C) (In formula (C), M 3 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. g, h, i, and z are within the range of 0.3≦g<0.6, 0 <h≦0.7、0<i≦0.7、0≦z≦0.3、かつ3g+3h+3i+(M 3 The number satisfies the valence of z × z = 3. The particle includes particles represented by:

[0043] The above-mentioned particles (B) and particles (C) both have a layered rock salt structure containing at least nickel (Ni), cobalt (Co), and manganese (Mn) and are lithium-nickel-cobalt-manganese-based particles (so-called Li-Ni-Co-Mn oxide particles (NCM particles)) with excellent electronic conductivity, and are secondary particles formed by aggregation of primary particles, with particles (B) having a high nickel content and particles (C) having a low nickel content. In this way, the positive electrode active material particle mixture for lithium ion secondary batteries of the present invention can greatly contribute to increasing the capacity of the resulting battery by using two types of particles (B) and particles (C) having different nickel contents in combination, coupled with the fact that these particles are uniformly mixed with fine particles (A) that are appropriately disintegrated during the pressing step in the battery production process.

[0044] In the above formula (B) representing the particle (B), M 2 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, and d is 0.6≦d≦0.95, preferably 0.7≦d≦0.9. e, f, and y are each 0. <e≦0.4、0<f≦0.4、0≦y≦0.3であり、かつ3d+3e+3f+(M 2 This indicates a number that satisfies (valence of) × y = 3.

[0045] Specific examples of the particles (B) represented by the above formula (B) include LiNi 0.94 Co 0.03 Mn 0.03 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, etc. Among them, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2O2 is preferred.

[0046] The average particle size of the particles (B) is preferably 4 μm to 13 μm, more preferably 6 μm to 13 μm, and even more preferably 8 μm to 13 μm, from the viewpoint of good and uniform mixing with the particles (A) that disintegrates appropriately during the pressing step in the battery manufacturing process, together with the particles (C). The average particle size is the D obtained from the volume-based particle size distribution based on the laser diffraction / scattering method, as with the particles (A). 50 The values ​​shown are the particle diameters (median diameters) at 50% of the cumulative particle size.

[0047] From the viewpoint of achieving high capacity and excellent safety in the resulting battery, the content of particles (B) in the positive electrode active material particle mixture for lithium ion secondary batteries of the present invention is preferably 50% by mass to 80% by mass, more preferably 60% by mass to 80% by mass, and even more preferably 70% by mass to 80% by mass.

[0048] In the above formula (C) representing the particle (C), M 3 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. g is 0.3≦g<0.6, and preferably 0.32≦g≦0.5. h, i, and z are 0. <h≦0.7、0<i≦0.7、0≦z≦0.3であり、かつ3g+3h+3i+(M 3 This indicates a number that satisfies z = 3 (valence of x).

[0049] Specific examples of the particles (C) represented by the above formula (C) include LiNi 0.33 Co 0.33 Mn 0.34 O2, LiNi 0.4 Co 0.3 Mn 0.3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.33 Co 0.31 Mn 0.33 Mg 0.03O2, LiNi 0.33 Co 0.31 Mn 0.33 Zinc 0.03 O2, etc. Among them, LiNi 0.33 Co 0.33 Mn 0.34 O2, LiNi 0.33 Co 0.31 Mn 0.33 Mg 0.03 O2 is preferred.

[0050] The average particle size of the particles (C) is preferably 4 μm to 13 μm, more preferably 4 μm to 11 μm, and even more preferably 4 μm to 9 μm, from the viewpoint of good and uniform mixing with the particles (B) and the particles (A) that disintegrate appropriately during the pressing step in the battery production process. The average particle size is the D obtained from the volume-based particle size distribution based on the laser diffraction / scattering method, as with particles (A) and (B). 50 The values ​​shown are the particle diameters (median diameters) at 50% of the cumulative particle size.

[0051] From the viewpoint of achieving high capacity and excellent safety in the resulting battery, the content of particles (C) in the positive electrode active material particle mixture for lithium ion secondary batteries of the present invention is preferably 10 mass % to 40 mass %, more preferably 10 mass % to 30 mass %, and even more preferably 10 mass % to 20 mass %.

[0052] The above particles (B) and particles (C) may be particles having cellulose nanofiber-derived carbon and / or water-soluble carbon material-derived carbon supported on their surfaces, similar to the above particles (A). These particles (B) and particles (C) may be produced by known methods, for example, by the methods described in the Examples.

[0053] The positive electrode active material particle mixture for a lithium ion secondary battery of the present invention can be obtained by mixing the above particles (A) with the above particles (B) and particles (C) in a conventional manner.

[0054] The positive electrode active material particle mixture 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 particle mixture for lithium ion secondary batteries is kneaded with acetylene black, ketjen black, polyvinylidene fluoride, N-methyl-2-pyrrolidone, etc. 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 particle mixture for lithium ion secondary batteries of the present invention, the above particles (A) disintegrate appropriately, and are intimately and effectively entangled with the above particles (B) and particles (C) contained in the positive electrode active material particle mixture for lithium ion secondary batteries, so that they are well and uniformly mixed together, and the particles (A) disintegrate so as to cover these particles and become finely divided and are scattered throughout, thereby making it possible to obtain a highly useful positive electrode that is capable of exhibiting high capacity and excellent safety.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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).

[0059] 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.

[0060] 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

[0061] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.

[0062] <<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: 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.

[0063] Tap density (g / cm 3 Measurement of 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.

[0064] <Measurement of pore volume (mL / g)> The pore volume of the particles was measured by the mercury intrusion method using a mercury intrusion porosimeter (AutoPoreIV9520, manufactured by Micrometritics). A powder sample cell was used, and the measurement pressure range was atmospheric pressure to 414 MPa. From the obtained pore size distribution, the pore volume in the pore diameter range of 10 nm to 3000 nm was obtained.

[0065] [Production Example 1: Production of Particles (A-1)] LiOH·H2O (1272g) and water (4L) were mixed to obtain slurry water xi. Next, 1153g of 85% phosphoric acid aqueous solution was added dropwise at 35mL / min to the obtained slurry water xi while stirring for 3 minutes while maintaining the temperature at 25°C, followed by adding 1650g of cellulose nanofiber (Celish KY-100G, Daicel FineChem, fiber diameter 4nm~100nm) and stirring at 400rpm for 12 hours to obtain slurry water yi containing Li3PO4. Nitrogen was purged into the obtained slurry water yi to adjust the dissolved oxygen concentration of the slurry water yi to 0.5mg / L, and then 1610g of MnSO4·5H2O and 834g of FeSO4·7H2O were added to the total amount of slurry water yi to obtain slurry water zi. The molar ratio of added MnSO4 and FeSO4 (manganese compound:iron compound) was 70:30.

[0066] The obtained slurry water zi 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 1 part by mass of the crystals. The washed crystals were freeze-dried at -50 ° C for 12 hours to obtain powder a1. 1000 g of the obtained powder a1 was taken out, and 0.3 g of ammonium carbonate (0.03 parts by mass per 100 parts by mass of powder a1) and 800 mL of water were added thereto to obtain slurry water zii. The obtained slurry zii 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 40 L / min, supply air temperature 160 ° C) using a spray dryer (MDL-050M, manufactured by Fujisaki Electric Co., Ltd.) to obtain granules b1. The obtained granules b1 were sintered at 700° C. for 1 hour in an argon-hydrogen atmosphere (hydrogen concentration 3%) to obtain particles (A-1) (LiMn 0.7 Fe 0.3 PO4) was obtained. The tap density of the obtained particles (A-1) was 1.0 g / cm 3 The pore volume was 0.3 mL / g, the average particle size was 14 μm, and the amount of carbon supported was 4.5 mass %.

[0067] [Production Example 2: Production of Particles (A-2)] Particles (A-2) (LiMn 0.7 Fe 0.3 PO4) was obtained. The tap density of the obtained particles (A-2) was 0.3 g / cm 3 The pore volume was 0.7 mL / g, the average particle size was 15 μm, and the amount of carbon supported was 4.5 mass %.

[0068] [Production Example 3: Production of particles (A-3)] Particles (A-3) (LiMn 0.7 Fe 0.3 PO4) was obtained. The tap density of the obtained particles (A-3) was 1.2 g / cm 3 The pore volume was 0.2 mL / g, the average particle size was 13 μm, and the amount of carbon supported was 4.5 mass %.

[0069] [Production Example 4: Production of particles (A-4)] Particles (A-4) (LiMn 0.7 Fe 0.3 PO4) was obtained. The tap density of the obtained particles (A-4) was 0.2 g / cm 3 The pore volume was 0.8 mL / g, the average particle size was 15 μm, and the amount of carbon supported was 4.5 mass %.

[0070] [Production Example 5: Production of particles (A-5)] Particles (A-5) (LiMn 0.7 Fe 0.3 PO4) was obtained. The tap density of the obtained particles (A-5) was 1.4 g / cm 3The pore volume was 0.1 mL / g, the average particle size was 13 μm, and the amount of carbon supported was 4.5 mass %.

[0071] [Production Example 6: Production of particles (B-1)] 631 g of nickel sulfate hexahydrate, 84 g of cobalt sulfate heptahydrate, 72 g of manganese sulfate pentahydrate, and 3 L of water were mixed so that the molar ratio of Ni:Co:Mn was 8:1:1, and then 25% aqueous ammonia was added dropwise to the mixture at a rate of 300 mL / min to obtain a slurry containing a metal composite hydroxide with a pH of 11. Next, the obtained slurry was filtered and dried to obtain a mixture of metal composite hydroxides, and then 111 g of lithium carbonate was mixed with the mixture in a ball mill to obtain a powder mixture. The obtained powder mixture 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 (B-1) (LiNi 0.8 Co 0.1 Mn 0.1 O2, average particle size: 10 μm).

[0072] [Production Example 7: Production of particles (C-1)] 394 g of nickel sulfate hexahydrate, 169 g of cobalt sulfate heptahydrate, 217 g of manganese sulfate pentahydrate, and 3 L of water were mixed so that the molar ratio of Ni:Co:Mn was 5:2:3, and then 25% ammonia water was added dropwise to the mixture at a rate of 300 mL / min to obtain a slurry containing a metal composite hydroxide with a pH of 11. Next, the obtained slurry was filtered and dried to obtain a mixture of metal composite hydroxides, and then 111 g of lithium carbonate was mixed with the mixture in a ball mill to obtain a powder mixture. The obtained powder mixture 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 (C-1) (LiNi 0.5 Co 0.2 Mn 0.3 O2, average particle size: 10 μm).

[0073] [Examples 1 to 6, Comparative Examples 1 to 6] According to the formulations shown in Tables 1 and 2, predetermined particles were mixed using a pestle and mortar to obtain a positive electrode active material particle mixture. Next, a lithium ion battery was produced according to the following method, and the battery characteristics were measured and evaluated. The results are shown in Tables 1 and 2.

[0074] <Characteristics of lithium-ion batteries> The obtained mixture of positive electrode active material particles was used as a positive electrode material to prepare a positive electrode for a lithium ion secondary battery. Specifically, the obtained mixture of positive electrode active material particles, Ketjen 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. After that, the mixture was pressed at 20 kN using a roll press and punched into a disk shape with a diameter of 14 mm to prepare a positive electrode.

[0075] 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).

[0076] The resulting coin-type secondary battery was used to measure the discharge capacity at 0.2 C (34 mA / g) in an environment at an air temperature of 30° C. using a discharge capacity measuring device (HJ-1001SD8, manufactured by Hokuto Denko Corporation). Moreover, the electrode density was calculated by the following formula (x). Electrode density (g / cm 3 )= Mass of the positive electrode active material particle mixture in the positive electrode (mg) / electrode volume (φ14mm × thickness (μm)) (x) The obtained coin-type secondary battery was charged at a constant current of 0.2C (34mA / g) and an upper limit voltage of 4.3V in an environment at 30°C, and then the coin-type secondary battery was disassembled and the positive electrode was washed using dimethyl carbonate and ethanol. Next, the positive electrode composite layer was peeled off from the washed positive electrode, and the thermal stability was measured using the obtained positive electrode composite with a differential scanning calorimeter (DSC, DSC3100SR manufactured by NETZSCH). The measurement conditions for DSC were a temperature rise of 4°C / min and a measurement range of 30 to 400°C. The thermal decomposition onset temperature (°C) at which heat generation began was determined from the obtained DSC profile.

[0077] [Table 1]

[0078] [Table 2]

Claims

1. The following formula (A): Li a Mn b Fe c M 1 x 2O 4 ・・・(A) (In formula (A), M 1 represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. a, b, c, and x satisfy 0<a≦1.2, 0≦b≦1.2, 0≦c≦1.2, 0≦x≦0.3, and b+c≠0, and a+(valence of Mn)×b+(valence of Fe)×c+(valence of Mn)×b+(valence of Mn)×c+(valence of Mn). 1 (valence of x) × x = 3. and the tap density is 0.3 g / cm 3 ~1.2g / cm 3 and a particle (A) having a pore volume of 0.2 mL / g to 0.7 mL / g at a pore diameter of 10 nm to 3000 nm and a content of 10 mass% to 30 mass%; The following formula (B): L)) d Co e Mn f M 2 y O 2 ・・・(B) (In formula (B), M 2 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. d, e, f, and y each satisfy the following conditions: 0.6≦d≦0.95, 0<e≦0.4, 0<f≦0.4, 0≦y≦0.3, and 3d+3e+3f+(M 2 (valence) × y = 3. Particles (B) having a content of 50% by mass to 80% by mass; The following formula (C): L)) g Co h Mn i M 3 z O 2 ・・・(C) (In formula (C), M 3 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. g, h, i, and z are within the range of 0.3≦g<0.6, 0<h≦0.7, 0<i≦0.7, and 0≦z≦0.3, and 3g+3h+3i+(M 3 (valence of x) × z = 3. Particles (C) having a content of 10% by mass to 40% by mass. and a positive electrode active material particle mixture for a lithium ion secondary battery comprising the above.

2. 2. The positive electrode active material particle mixture for a lithium ion secondary battery according to claim 1, wherein the particles (A) have an average particle size of 6 μm to 20 μm.

3. 3. The positive electrode active material particle mixture for a lithium ion secondary battery according to claim 1, wherein the particles (B) have an average particle size of 4 μm to 13 μm, and the particles (C) have an average particle size of 4 μm to 13 μm.

4. The positive electrode active material particle mixture for a lithium ion secondary battery according to any one of claims 1 to 3, wherein the surface of the particles (A) is supported with carbon derived from cellulose nanofibers and / or carbon derived from a water-soluble carbon material.

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