JP2020031028A - Mixed positive electrode active material for lithium ion secondary battery and production method of the same - Google Patents

Abstract

To provide a positive electrode active material for a lithium ion secondary battery, which is obtained using a lamellar lithium compound oxide secondary particle and a lithium system olivine type compound oxide secondary particle, and furthermore allows for formation of a positive electrode active material layer having a dense packing structure with a small void ratio, and enables the lithium ion secondary battery to express an excellent cycle characteristic, and to provide a production method of the positive electrode active material for a lithium ion secondary battery.SOLUTION: A mixed positive electrode active material for a lithium ion secondary battery is provided that contains a lithium system olivine type compound oxide secondary particle (A) and a lamellar lithium compound oxide secondary particle (B), and that has an Xof 0.3 g/mto 50 g/m, wherein the Xis obtained by the following formula (1): X=T×|D50-D50+2|...(1) (in the formula (1), Tindicates a tap density (g/cm) of the lithium system olivine type compound oxide secondary particle (A), D50 indicates a mean particle diameter (μm) in an accumulation 50% in a particle size distribution of the lithium system olivine type compound oxide secondary particle (A), and D50 indicates the mean particle diameter (μm) in the accumulation 50% in the particle size distribution of the lamellar lithium compound oxide secondary particle (B).).SELECTED DRAWING: None

Description

  The present invention relates to a mixed positive electrode active material for a lithium ion secondary battery capable of obtaining a lithium ion secondary battery having excellent cycle characteristics and safety, and a method for producing the same.

  Layered lithium composite oxides such as layered lithium-nickel-cobalt-manganese composite oxide (NCM) and layered lithium-nickel-cobalt-aluminum composite oxide (NCA) are composed of a lithium atomic layer and a transition metal atomic layer. Has a layered crystal structure alternately stacked via an oxygen atom layer, and has a so-called layered rock salt structure in which one lithium atom is contained per transition metal atom. Such a layered lithium composite oxide is used as a positive electrode active material that can constitute a high-output and high-capacity lithium-ion secondary battery.

  In a lithium ion secondary battery using such a layered lithium composite oxide as a positive electrode active material, charging and discharging are performed by lithium ions being desorbed and inserted into the layered lithium composite oxide. As the number of discharge cycles increases, the capacity decreases, and particularly when used for a long time, the capacity of the battery may significantly decrease. This is considered to be due to the fact that the transition metal component of the layered lithium composite oxide elutes into the electrolytic solution at the time of charging, so that the collapse of the crystal structure tends to occur. Moreover, the thermal stability of the lithium ion secondary battery may be reduced due to the elution of the transition metal component into the electrolyte, and safety may be impaired.

Under such circumstances, for example, a battery material used for a vehicle-mounted battery must have excellent durability so that a battery capacity of a certain level or more can be maintained even after a number of charge / discharge cycles of 1000 cycles or more. Has been required, and various developments have been made to meet this demand. For example, Patent Document 1 discloses a positive electroactive material including a specific lithium iron manganese phosphate compound that can be doped with Ti, Zr, Nb, and the like, and a lithium metal oxide such as NCM or NCA. Therefore, it is trying to improve thermal stability as a lithium ion battery material. Further, Patent Document 2 consists of _{LiFe x Mn 1-xy M y} PO 4, and the electrode active material volume change due to absorption and desorption of lithium ions is within a specific range, NCM and LMO (lithium manganate) An electrode material for a lithium ion secondary battery, which is a mixture containing an electrode active material composed of a lithium-containing metal oxide such as, has been disclosed, to improve safety when used as an electrode and to improve battery life. I'm trying.

JP 2014-524133 A JP 2018-56037 A

  However, the positive electrode active material layer constituting the secondary battery is required to have a small porosity and a solid filling structure.However, in the positive electrode active material layer obtained using the electrode material described in the above patent document, Due to the volume change that differs depending on the type of oxide used, as the usage time of the secondary battery increases, it becomes difficult to maintain a solid filling structure, and the excellent cycle characteristics of the secondary battery May not be secured.

  Therefore, an object of the present invention is to form a positive electrode active material layer having a small packed structure with a small porosity while using layered lithium composite oxide secondary particles and lithium-based olivine type composite oxide secondary particles. It is an object of the present invention to provide a mixed positive electrode active material for a lithium ion secondary battery capable of exhibiting excellent cycle characteristics in the lithium ion secondary battery and a method for producing the same.

  The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, the lithium-based olivine-type composite oxide secondary particles (A) and the layered-type lithium composite oxide secondary particles (B) contained therein However, they have found that, by satisfying a specific relational expression, a mixed positive electrode active material for a lithium ion secondary battery that can exhibit excellent cycle characteristics in a lithium ion secondary battery can be obtained.

That is, the present invention contains secondary particles of lithium-based olivine type composite oxide (A) and secondary particles of layered lithium composite oxide (B), and has the following formula (1):
_{X A = T A × | D} A 50-D B 50 + 2 | ··· (1)
(In the formula (1), T _A represents the tap density of the lithium olivine-type composite oxide secondary particle ^{(A) (g / cm 3} ), D A 50 is lithium olivine-type composite oxide secondary shows the average particle diameter at cumulative 50% in the particle size distribution of the particles (a) (μm), D B 50 , the average particle at 50% accumulation in the particle size distribution of the layered-type lithium composite oxide secondary particle (B) Diameter (μm).)
The obtained X _A is ^{0.3g / m 2 ~50g / m 2} , there is provided a mixed positive active material for a lithium ion secondary battery.

Further, the present invention provides the following steps (I) to (V):
For (I) layered lithium composite oxide secondary particle (B), step (II) at least one lithium-based olivine-type composite oxide secondary measuring the average particle diameter D _B 50 at 50% cumulative in the particle size distribution particles for (a ^t), a tap density T _a ^t, the step of measuring the average particle diameter D _a ^t 50 at 50% accumulation in the particle size distribution of the lithium olivine-type composite oxide secondary particle (a ^t) (III) The D _B 50 obtained in the step (I) is represented by the following formula (1):
_{X A = T A × | D} A 50-D B 50 + 2 | ··· (1)
(In the formula (1), T _A represents the tap density of the lithium olivine-type composite oxide secondary particle ^{(A) (g / cm 3} ), D A 50 is lithium olivine-type composite oxide secondary shows the average particle diameter at cumulative 50% in the particle size distribution of the particles (a) (μm), D B 50 , the average particle at 50% accumulation in the particle size distribution of the layered-type lithium composite oxide secondary particle (B) X _A represents a value (g / m ² ) serving as an index for selecting the lithium-based olivine-type composite oxide secondary particles (A) to be mixed in the step (IV).)
Introduced to step (IV) lithium olivine-type composite oxide secondary particles from among (A ^t), equation (1) by the X _A for a 0.3g / m ² ~50g / m ² obtained , tap density T _a and D _a lithium olivine-type composite oxide secondary particles selecting a (a) (V) selected lithium olivine-type composite oxide secondary particle (a) and layer-structured lithium having 50 An object of the present invention is to provide a method for producing a mixed positive electrode active material for a lithium ion secondary battery, comprising a step of mixing the composite oxide secondary particles (B).

  According to the mixed positive electrode active material for a lithium ion secondary battery of the present invention, it is possible to form a positive electrode active material layer having a small porosity and a dense filling structure, and to provide a lithium ion secondary battery having excellent cycle characteristics. Can be easily obtained.

Hereinafter, the present invention will be described in detail.
The mixed positive electrode active material for a lithium ion secondary battery of the present invention (hereinafter, also referred to as “mixed positive electrode active material (C)”) includes lithium-based olivine-type composite oxide secondary particles (A) and layered lithium composite oxide. Secondary particles (B), and the following formula (1):
_{X A = T A × | D} A 50-D B 50 + 2 | ··· (1)
(In the formula (1), T _A represents the tap density of the lithium olivine-type composite oxide secondary particle ^{(A) (g / cm 3} ), D A 50 is lithium olivine-type composite oxide secondary shows the average particle diameter at cumulative 50% in the particle size distribution of the particles (a) (μm), D B 50 , the average particle at 50% accumulation in the particle size distribution of the layered-type lithium composite oxide secondary particle (B) Diameter (μm).)
The obtained X _A is ^{0.3g / m 2 ~50g / m 2} .

Thus, mixing a positive electrode active material of the present invention (C), the above equation (1) by lithium olivine-type composite oxide secondary particles having a relationship as determined X _A becomes a specific value (A) By containing the layered lithium composite oxide secondary particles (B), the porosity of the formed positive electrode active material layer can be controlled in an appropriate range. Therefore, the amount of voids that buffer the volume change of the positive electrode active material particles in the charge / discharge cycle can be effectively reduced, and even if the charge / discharge cycle increases, the filling structure of the positive electrode active material layer can be prevented from being disturbed. The energy density of the obtained lithium ion secondary battery can be effectively increased.

The tap density (g / cm ³ ) of the lithium-based olivine-type composite oxide secondary particles (A) contained in the mixed positive electrode active material (C) of the present invention is represented by T _A in the above formula (1). Value. The tap density (T _A ) is an apparent bulk density obtained when a gap between powder particles is broken by tapping and tightly packed, which is obtained according to JIS Z 2512 “Metal powder-Tap density measurement method”. is there.

Specifically, T _A of the lithium-based olivine-type composite oxide secondary particles (A) is preferably 0.7 g / cm ^{3 to} 1.8 g / cm ³ , and more preferably 0.85 g / cm 3. ³ was ~1.8g / cm ^3, particularly preferably from ^{0.9g / cm 3 ~1.5g / cm 3} . If T _A is less than the lower limit, the porosity in the positive electrode active material layer obtained by decreasing the filling property of the mixed positive electrode active material (C) may increase, and the energy density may decrease. When T _A exceeds the above upper limit, the amount of deformation of the lithium-based olivine-type composite oxide secondary particles (A) due to the pressing performed in the production of the positive electrode decreases, and the voids in the positive electrode active material layer are sufficiently reduced. Filling may not be possible, and the elution of transition metal from the layered lithium composite oxide secondary particles (B) may not be sufficiently suppressed.

The D ₅₀ value of the lithium-based olivine-type composite oxide secondary particles (A) is the average particle size (median diameter, μm) at a cumulative 50% in the particle size distribution of the lithium-based olivine-type composite oxide secondary particles (A). , and the that is, a value obtained based on the volume-based particle size distribution based on the laser diffraction scattering method, is a value represented by D _a 50 in the above formula (1).

Such D _A 50 is specifically preferably 3Myuemu～30myuemu, more preferably 5Myuemu～25myuemu, particularly preferably 7Myuemu～20myuemu. When D _A 50 is outside the above range, easy distribution of the dilithium-based olivine-type composite oxide in the obtained positive electrode active material layer primary particles (A) becomes uneven, layered lithium composite oxide secondary particles The transition metal elution from (B) may not be sufficiently suppressed.

Further, lithium olivine-type composite oxide secondary particle (A) is the standard deviation in the particle size distribution (D _A SD) is, preferably 4Myuemu～15myuemu, more preferably 5Myuemu～11myuemu, particularly preferably 6 μm to 10 μm. Here, the standard deviation (D _A SD) in the particle size distribution means the standard deviation of the grain size distribution curve of a logarithmic scale. When such D _A SD is outside the above range, the filling of the resulting mixed cathode active material (C) is decreased, or the porosity is increased in the positive electrode active material layer formed, resulting a gap large diameter Or

Further, lithium olivine-type composite oxide secondary particles (A), BET specific surface area (S _A) is preferably 15m ² / g~50m ² / g, more preferably 16m ² / g~30m ² / g, and particularly preferably from 18m ² / g~25m ² / g. Here, the BET specific surface area is a ratio calculated from the gas adsorption amount of the monolayer obtained by converting the adsorption isotherm obtained using nitrogen gas into a BET plot and the size of the nitrogen gas molecule. Means surface area. When the BET specific surface area (S _A ) is less than the above lower limit, the amount of deformation of the lithium-based olivine-type composite oxide secondary particles (A) due to pressing performed in the production of the positive electrode becomes small, and the positive electrode active material layer There is a possibility that the internal voids may not be sufficiently filled, and the elution of the transition metal from the layered lithium composite oxide secondary particles (B) may not be sufficiently suppressed. When the BET specific surface area (S _A ) exceeds the above upper limit, the viscosity of the positive electrode slurry used at the time of preparing the positive electrode increases, and the lithium-based olivine-type composite oxide secondary particles ( The distribution of A) may become non-uniform, and the elution of transition metal from the layered lithium composite oxide secondary particles (B) may not be suppressed.

The lithium-based olivine-type composite oxide secondary particles (A) are specifically, for example, represented by the following formula (I):
^{_{Li a Mn b Fe c M 1}} d PO 4 ··· (I)
(In the formula (I), M ¹ represents Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd. A, b, c, and d represent 0 <a ≦ 1.2, 0.3 ≦ b ≦ 1, 0 ≦ c ≦ 0.7, and 0 ≦ d ≦ 0.3, and a + (valence of Mn) × b + (valence of Fe) ) × c + (valence of M ¹ ) × d = 3.)
Or the following formula (II):
^{_{Li e Mn f Fe g M 2}} h SiO 4 ··· (II)
(In the formula (II), M ² represents Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, Al, Zn, V or Gd. g and h satisfy 0 <e ≦ 2.4, 0 ≦ f ≦ 1.2, 0 ≦ g ≦ 1.2, 0 ≦ h ≦ 1.2, and f + g ≠ 0, and e + (Mn (Valence) × f + (valence of Fe) × g + (valence of M ² ) × h = 4.)
The particles are represented by The particles represented by the above formula (I) are so-called lithium phosphate-based polyanion particles, and the particles represented by the above formula (II) are so-called lithium silicate-based polyanion particles.

Further, the lithium-based olivine-type composite oxide secondary particles (A) have a carbon (C) surface on the surface thereof from the viewpoint of imparting electron conductivity to the particles and obtaining a useful mixed positive electrode active material (C) having excellent cycle characteristics. It is preferred that the particles have D) supported thereon.
Examples of the carbon source that becomes carbon (D) include one or more selected from cellulose nanofibers (d1), water-soluble carbon materials (d2), and water-insoluble carbon powders (d3).

  The cellulose nanofiber (d1) serving as a carbon source is a skeletal component occupying about 50% of all plant cell walls, and can be obtained by, for example, defibrating plant fibers constituting such cell walls to a nano size. Carbon fiber derived from cellulose nanofiber has a periodic structure. The fiber diameter of such a cellulose nanofiber is 1 nm to 100 nm, and also has good dispersibility in water. Further, in the cellulose molecular chain constituting the cellulose nanofiber, since a periodic structure is formed by carbon, this is firmly supported on the surface of the lithium-based olivine-type composite oxide secondary particles (A) while being carbonized. By doing so, it is possible to effectively impart electron conductivity to such particles.

  The water-soluble carbon material (d2) serving as a carbon source is a carbon material that dissolves in 100 g of water at 25 ° C. in an amount of 0.4 g or more, preferably 1.0 g or more in terms of carbon atoms of the water-soluble carbon material. means. Examples of such a water-soluble carbon material include one or more selected from sugars, polyols, polyethers, and organic acids. More specifically, for example, monosaccharides such as glucose, fructose, galactose and mannose; disaccharides such as maltose, sucrose and cellobiose; polysaccharides such as starch and dextrin; ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, butane Polyols and polyethers such as diol, propanediol, polyvinyl alcohol and glycerin; and organic acids such as citric acid, tartaric acid and ascorbic acid. Among them, glucose, fructose, sucrose, and dextrin are preferable, and glucose is more preferable, from the viewpoint of enhancing the solubility and dispersibility in a solvent and effectively functioning as a carbon material.

Further, the water-insoluble carbon powder (d3) serving as a carbon source is a carbon material different from the carbon (d2) derived from the water-soluble carbon material, and is other than carbon derived from the cellulose nanofiber (d1). It is a carbon powder having water-insoluble conductivity (the amount of dissolution in 100 g of water at 25 ° C. is less than 0.4 g in terms of carbon atoms of the water-insoluble carbon powder (d3)). The water-insoluble carbon powder (d3) is composited with the lithium-based olivine-type composite oxide secondary particles (A) to impart electron conductivity to the lithium-based olivine-type composite oxide secondary particles (A). I do. Examples of the water-insoluble carbon powder (d3) include graphite, amorphous carbon (Ketjen black, acetylene black, etc.), nanocarbon (graphene, fullerene, etc.), conductive polymer powder (polyaniline powder, polyacetylene powder, polythiophene powder, Or polypyrrole powder). Of these, graphite, acetylene black, graphene, and polyaniline powder are preferable, and graphite is more preferable, from the viewpoint of efficiently performing complexing. As the graphite, any of artificial graphite (squamous, massive, earthy, graphene) and natural graphite may be used.
The average particle size of the water-insoluble carbon powder (d3) is preferably 0.5 μm to 20 μm, and more preferably 1.0 μm to 15 μm.

  The amount of carbon supported on the surface of the lithium-based olivine-type composite oxide secondary particles (A) is preferably 0.1% by mass in 100% by mass of the lithium-based olivine-type composite oxide secondary particles (A). % To 20% by mass, more preferably 0.3% to 10% by mass, and particularly preferably 0.5% to 8% by mass. More specifically, in the case of carbon (D) using a cellulose nanofiber (d1) or a water-soluble carbon material (d2) as a carbon source, lithium-based olivine-type composite oxide secondary particles (A) 100% by mass The water-insoluble carbon powder (d3) preferably contains 0.1% by mass to 15% by mass, more preferably 0.3% by mass to 10% by mass, and particularly preferably 0.5% by mass to 8% by mass. In the case of carbon (D) having a carbon source of, preferably 0.5 to 20% by mass, more preferably 1 to 15% by mass, particularly preferably 1.5 to 12% by mass. is there.

The D ₅₀ value of the layered lithium composite oxide secondary particles (B) contained in the mixed positive electrode active material (C) of the present invention is the cumulative 50 in the particle size distribution of the layered lithium composite oxide secondary particles (B). the average particle diameter (median diameter, [mu] m) in% is, that is, a value obtained based on the volume-based particle size distribution based on the laser diffraction scattering method, indicated by D _B 50 in the formula (1) Value.

Such D _B 50 is specifically preferably 3Myuemu～20myuemu, more preferably 3.5Myuemu～17myuemu, particularly preferably 4Myuemu～14myuemu. When D _B 50 exceeds the above upper limit, the layered-type lithium composite oxide secondary particles in the the coarse electrode slurry used to produce the electrode during (B) is excessively present, uniform coating of the electrode slurry May be difficult. Further, D _B 50 is less than the lower limit, the surface area of the layered lithium composite oxide secondary particle (B) ends up increasing, elution of the transition metal is likely to easily occur.

The layered lithium composite oxide secondary particles (B) specifically include, for example, the following formula (III):
^{_{LiNi i Co j Mn k M 3}} l O 2 ··· (III)
(In the formula (III), M ³ is Mg, Ti, Nb, Fe, Cr, Si, Al, Ga, V, Zn, Cu, Sr, Mo, Zr, Sn, Ta, W, La, Ce, Pb, Represents one or more elements selected from Bi and Ge, where i, j, k, and l are 0.3 ≦ i <1, 0 <j ≦ 0.7, 0 <k ≦ 0.7, 0 ≦ l ≦ 0.3, and 3i + 3j + 3k + (valence of M ³⁾ shows a number satisfying × l = 3.)
Or the following formula (IV):
^{_{LiNi m Co n Al o M 4}} p O 2 ··· (IV)
(In the formula (IV), M ⁴ is Mg, Ti, Nb, Fe, Cr, Si, Ga, V, Zn, Cu, Sr, Mo, Zr, Sn, Ta, W, La, Ce, Pb, Bi and Represents one or more elements selected from Ge, where m, n, o, and p are 0.4 ≦ m <1, 0 <n ≦ 0.6, 0 <o ≦ 0.3, 0 ≦ (p ≦ 0.3 and 3m + 3n + 3o + (valence of M ⁴ ) × p = 3)
The particles are represented by

In mixing the positive electrode active material of the present invention (C), D _B of T _A and D _A 50, and a layered-type lithium composite oxide secondary particles of the lithium-based olivine-type composite oxide secondary particle (A) (B) 50 is obtained X _a is 0.3g / m ² ~50g / m ² by the following equation (1).
_{X A = T A × | D} A 50-D B 50 + 2 | ··· (1)
When T _A , D _A 50, and D _B 50 are introduced into the above formula (1), and the X _A obtained is within the above range, the transition metal elution from the layered lithium composite oxide secondary particles (B). Can be sufficiently suppressed, and the filling structure of the positive electrode active material layer can be prevented from being disturbed even when the number of charge / discharge cycles increases. Thus, for example, mixing a positive electrode active first material substance (C), after determining layered lithium composite oxide secondary particle (B) to be used, D _B of such layered lithium composite oxide secondary particle (B) T _A and D are selected from the lithium-based olivine-type composite oxide secondary particles (A ^t ) that can exist in plural types so that X _A obtained by the above formula (1) falls within the above range based on the above formula (1). it can be selected and used lithium olivine type compound oxide secondary particle (a) satisfying _a 50.
X _A obtained by the equation (1) is a ^{0.3g / m 2 ~50g / m 2} , preferably ^{0.35 (g / m 2) ~25} (g / m 2), more preferably ^{0.4 (g / m 2) ~20} (g / m 2).

Furthermore, in the mixed positive electrode active material (C) of the present invention, T _A and D _A 50 of the lithium-based olivine-type composite oxide secondary particles (A) and the layered lithium composite oxide secondary particles (B) in addition to D _B 50, D _a SD and S _a of the lithium olivine-type composite oxide secondary particle (a) is even more the dissolution of transition metal from the layer-structured lithium composite oxide secondary particle (B) effectively suppressed, from the viewpoint of cycle characteristics are effectively prevented from being lowered, the X _B obtained by the following equation ^{(2), 0.15 (g 2} / m 4) ~20 (g 2 / m 4 ) Is preferred.
X _B = X _A × D _A SD / S _A (2)
X _B determined by the above formula (2) is more preferably 0.17 (g ² / m ⁴ ) to 8 (g ² / m ⁴ ), and particularly preferably 0.2 (g ² / m ⁴ ). ⁴ ) to 6 (g ² / m ⁴ ).

  The method for producing the lithium-based olivine-type composite oxide secondary particles (A) is not particularly limited, and a known method, for example, a solid phase method, a sol-gel method, a coprecipitation method, or the like can be used. However, from the viewpoint that those satisfying the above various properties can be easily obtained, a production method using a combination of a hydrothermal method and a spray drying method, or a production method using a spray pyrolysis method is preferable.

In addition, as a method of supporting carbon (D) on the surface of the lithium-based olivine-type composite oxide secondary particles (A), the cellulose nanofiber (d1) or the water-soluble carbon material (d2) is used as a carbon source. In this case, the mixture obtained by adding the cellulose nanofiber (d1) or the water-soluble carbon material (d2) and water to the lithium-based olivine-type composite oxide secondary particles (A) and then spray-drying the mixture is reduced in a reducing atmosphere or The firing may be performed in an inert atmosphere at a firing temperature of 500 ° C. to 800 ° C. for a firing time of 10 minutes to 3 hours.
As a result, these carbon sources are carbonized into carbon (D), which is firmly supported on the surface of the lithium-based olivine-type composite oxide secondary particles (A).

When the water-insoluble carbon powder (d3) is used as a carbon source, the lithium-based olivine-type composite oxide secondary particles (A) and the water-insoluble carbon powder (d3) are mixed while applying compressive force and shear force. To form a composite.
As a result, the water-insoluble carbon powder (d3) is firmly supported as carbon (D) on the surface of the lithium-based olivine-type composite oxide secondary particles (A).

The method for producing the layered lithium composite oxide secondary particles (B) is also not particularly limited, and a known method such as a solid phase method, a coprecipitation method, or a sol-gel method can be used. from the viewpoint of conveniently obtained, thereby satisfying the above D _B 50, is preferably a production method using solid phase method incorporating the grinding process.

The mixed positive electrode active material (C) of the present invention is obtained by mixing these lithium-based olivine type composite oxide secondary particles (A) and layered type lithium composite oxide secondary particles (B). In such a mixed positive electrode active material (C), the mass ratio (A: B) of the content of the lithium-based olivine-type composite oxide secondary particles (A) and the content of the layered-type lithium composite oxide secondary particles (B). Is preferably 0.5: 99.5 to 90:10, more preferably 0.5: 99.5 to 50:50, particularly preferably 0.5: 99.5 to 30:70. The amount of the lithium-based olivine-type composite oxide secondary particles (A) and the amount of the layered-type lithium composite oxide secondary particles (B) are adjusted so that these contents have such a mass ratio. What is necessary is just to mix.
When the mass ratio (A: B) is less than the above lower limit, the content of the lithium-based olivine-type composite oxide secondary particles (A) becomes insufficient, so that the layered lithium composite oxide secondary particles ( Elution of transition metal from B) may not be effectively suppressed. When the mass ratio (A: B) exceeds the above upper limit, the content of the layered lithium composite oxide secondary particles (B) having excellent discharge capacity becomes insufficient, so that the obtained lithium ion secondary There is a possibility that the discharge capacity of the battery is reduced.

The lithium-based olivine type composite oxide secondary particles (A) and the layered type lithium composite oxide secondary particles (B) are obtained by directly mixing only these particles to obtain a mixed positive electrode active material (C). A positive electrode slurry may be prepared by adding and mixing a constituent material of a positive electrode mixture such as a conductive additive, a binder, and a solvent, or these particles may be used as a constituent material of a mixed positive electrode active material (C). At the same time, other positive electrode mixture constituent materials may be used, and the constituent materials may be mixed at once or sequentially mixed to prepare a positive electrode slurry. The positive electrode slurry thus obtained contains, as the mixed positive electrode active material (C), lithium-based olivine-type composite oxide secondary particles (A) and layered lithium composite oxide secondary particles (B) satisfying predetermined requirements. Be done.
Specifically, for example, a mixed positive electrode active material (C) containing lithium-based olivine-type composite oxide secondary particles (A) and layered lithium composite oxide secondary particles (B), and a conductive additive such as carbon black. A positive electrode slurry may be obtained by adding a solvent such as N-methyl-2-pyrrolidone to a binder and a binder such as polyvinylidene fluoride and sufficiently kneading the mixture. Thereafter, a positive electrode slurry is applied on a current collector such as an aluminum foil, and is then compacted and dried by a roller press or the like, whereby a positive electrode of a lithium ion secondary battery can be obtained.

  The apparatus and equipment used for preparing the positive electrode slurry and the order in which the respective positive electrode mixture constituent materials are mixed are not particularly limited, but the lithium-based olivine-type composite oxide secondary particles (A) and the layered lithium composite oxide are used. It is desirable that the material secondary particles (B) be in a highly homogeneous mixed state. For example, when the layered lithium composite oxide secondary particles (B) are mixed while applying a shearing force to such an extent that they do not collapse, the lithium-based olivine type composite oxide secondary particles (A) and the layered lithium composite oxide secondary particles are mixed. (B) can be made into a highly uniform mixed state.

  The uniformity of the mixed state of the lithium-based olivine type composite oxide secondary particles (A) and the layered type lithium composite oxide secondary particles (B) is determined by the positive electrode slurry containing the mixed positive electrode active material (C) of the present invention. When the positive electrode active material layer of the ion secondary battery is formed, it can be evaluated from the distribution state of the mixed positive electrode active material (C) particles in the positive electrode active material layer. Specifically, the SEM photograph (backscattered electron image) of the laminated state of the positive electrode active material layer is binarized at a specific gray level to visualize the interparticle gaps, and whether the distribution of the interparticle gaps is uniform or not. May be visually determined and evaluated.

Further, the mixed positive electrode active material (C) of the present invention is more specifically, for example, in the following steps (I) to (V):
For (I) layered lithium composite oxide secondary particle (B), step (II) at least one lithium-based olivine-type composite oxide secondary measuring the average particle diameter D _B 50 at 50% cumulative in the particle size distribution particles for (a ^t), a tap density T _a ^t, the step of measuring the average particle diameter D _a ^t 50 at 50% accumulation in the particle size distribution of the lithium olivine-type composite oxide secondary particle (a ^t) (III) The D _B 50 obtained in the step (I) is represented by the following formula (1):
_{X A = T A × | D} A 50-D B 50 + 2 | ··· (1)
(In the formula (1), T _A represents the tap density of the lithium olivine-type composite oxide secondary particle ^{(A) (g / cm 3} ), D A 50 is lithium olivine-type composite oxide secondary shows the average particle diameter at cumulative 50% in the particle size distribution of the particles (a) (μm), D B 50 , the average particle at 50% accumulation in the particle size distribution of the layered-type lithium composite oxide secondary particle (B) X _A represents a value (g / m ² ) serving as an index for selecting the lithium-based olivine-type composite oxide secondary particles (A) to be mixed in the step (IV).)
Introduced to step (IV) lithium olivine-type composite oxide secondary particles from among (A ^t), equation (1) by the X _A for a 0.3g / m ² ~50g / m ² obtained , tap density T _a and D _a lithium olivine-type composite oxide secondary particles selecting a (a) (V) selected lithium olivine-type composite oxide secondary particle (a) and layer-structured lithium having 50 It can be obtained by a production method including a step of mixing with the composite oxide secondary particles (B).

The “lithium-based olivine-type composite oxide secondary particles (A ^t )” includes at least one or more or a plurality of types of lithium-based olivine-type composite oxide secondary particles (A). The composite oxide secondary particles are generally referred to. Further, similarly to the lithium olivine type compound oxide secondary particle _(A), ^T A ^t represents a tap density of lithium olivine-type composite oxide secondary particle _{^{(A t), D A t}} 50 , the lithium The average particle diameter at a cumulative 50% in the particle size distribution of secondary olivine-type composite oxide secondary particles (A ^t ) is shown.

Step (I), for the layered type lithium composite oxide secondary particle (B), a step of measuring D _B 50. First, mixed in accordance with the positive electrode active material (C) to be obtained, selecting a layered lithium composite oxide secondary particle (B) to be used, use to measure its D _B 50, the above equation (1) Then, lithium-based olivine-type composite oxide secondary particles (A) are selected in the subsequent steps.

Step (II) is at least about one lithium olivine-type composite oxide secondary particle (A ^t), accumulation in the particle size distribution of the tap density T _A ^t, lithium olivine-type composite oxide secondary particle (A ^t) a step of measuring an average particle diameter D _a ^t 50 at 50%. By measuring each type of T _A ^t and D _A ^t 50 of the lithium-based olivine-type composite oxide secondary particles may be present more (A ^t), in the subsequent step, mixing the positive electrode active material of the present invention In obtaining (C), it is possible to select lithium-based olivine-type composite oxide secondary particles (A) having appropriate T _A and D _A 50. Even when only one kind of lithium-based olivine-type composite oxide secondary particles (A ^t ) is present, it is suitable for obtaining the mixed positive electrode active material (C) of the present invention. It is also possible to evaluate whether or not the particles are secondary particles based on the layered lithium composite oxide secondary particles (B) used.
Incidentally, D _A ^t 50 and T _A for lithium olivine type compound oxide secondary particle (A ^{t) t,} each of the lithium-based olivine type compound oxide secondary particle _(A) D A 50 and T _A Is a value obtained by the same measurement method as that described above.

In the step (III), the D _B50 obtained in the step (I) is converted into the following formula (1):
_{X A = T A × | D} A 50-D B 50 + 2 | ··· (1)
(In the formula (1), T _A represents the tap density of the lithium olivine-type composite oxide secondary particle ^{(A) (g / cm 3} ), D A 50 is lithium olivine-type composite oxide secondary shows the average particle diameter at cumulative 50% in the particle size distribution of the particles (a) (μm), D B 50 , the average particle at 50% accumulation in the particle size distribution of the layered-type lithium composite oxide secondary particle (B) X _A represents a value (g / m ² ) serving as an index for selecting the lithium-based olivine-type composite oxide secondary particles (A) to be mixed in the step (IV).)
This is the step of introducing That is, in this step (III), in the step (I), the D _B 50 of the measured layered lithium composite oxide secondary particle (B) in order to the reference, the value of D _B 50 in the formula (1) by specifically introduced, while the value of X _a as an index in the next step, it is possible to select an appropriate lithium olivine-type composite oxide secondary particle (a).

Step (IV) is, from among lithium olivine-type composite oxide secondary particle (A ^t), for the X _A obtained by the equation (1) and ^{0.3g / m 2 ~50g / m 2} , a step of selecting a lithium olivine type compound oxide secondary particle (a) having a tap density T _a and D _a 50. In this step, specifically, utilizing the value of X _A as an index, utilizing the _DB 50 of the layered lithium composite oxide secondary particles (B) and the above formula (1), an appropriate lithium-based olivine type composite oxide Select the secondary particles (A). More preferable ranges for X _A , T _A and D _A 50 are as described above.

  Step (V) is a step of mixing the selected lithium-based olivine type composite oxide secondary particles (A) and the layered type lithium composite oxide secondary particles (B). The specific mixing method is as described above, whereby the mixed positive electrode active material (C) of the present invention can be obtained.

  As a lithium ion secondary battery to which a positive electrode active material layer obtained by using the mixed positive electrode active material (C) of the present invention can be applied, a lithium ion secondary battery particularly including a positive electrode, a negative electrode, an electrolytic solution, and a separator as essential components is provided. Not limited.

  The negative electrode of the lithium ion secondary battery is not particularly limited in its material configuration as long as it can occlude lithium ions during charging and release lithium ions during discharging, and can use a material having a known material configuration. .

  The electrolytic solution is obtained by dissolving a supporting salt in an organic solvent. The organic solvent is not particularly limited as long as it is an organic solvent used for the electrolyte solution of the lithium ion secondary battery.For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, An oxolane compound or the like can be used.

The type of the supporting salt is not particularly limited, but in the case of a lithium ion secondary battery, an inorganic salt selected from LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ , a derivative of the inorganic salt, LiSO ₃ CF ₃ , an organic material selected from LiC (SO ₃ CF ₃ ) ₂ and LiN (SO ₃ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ and LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ) It is preferably at least one of a salt and a derivative of the organic salt.

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

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

Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples.
Each D _A 50 and D _B 50 is a value measured using a laser diffraction-scattering type particle size distribution measuring apparatus MT3300EXII (manufactured by Microtrac Bell (Ltd.)), BET specific surface area, DesorbIII ((Co. ) Shimadzu Corporation).

[Production Example 1: Production of layered lithium composite oxide secondary particles (B) (NMC-Ba)]
After mixing 263 g of nickel sulfate hexahydrate, 281 g of cobalt sulfate heptahydrate, 241 g of manganese sulfate pentahydrate, and 3 L of water such that the molar ratio of Ni: Co: Mn becomes 1: 1: 1. Then, 25% ammonia water was dropped into the mixture at a dropping 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 a metal composite hydroxide, and then 37 g of lithium carbonate was mixed with the mixture b1 by a ball mill to obtain a powder mixture c1.
The obtained powder mixture c1 was calcined at 800 ° C. for 4 hours in an air atmosphere to be crushed, and then calcined at 800 ° C. for 12 hours in an air atmosphere as main firing to obtain layered lithium composite oxide secondary particles. (NMC-Ba) (LiNi _0.33 Co _0.33 Mn _0.34 O ₂ , D ₅₀ : 12.8 μm) was obtained.

[Production Example 2: Production of layered lithium composite oxide secondary particles (B) (NMC-Bb)]
The same procedure as in Production Example 1 was carried out, except that the preliminary firing of the powder mixture c1 was changed to 800 ° C. × 10 hours in an air atmosphere, and the main firing was changed to 800 ° C. × 5 hours in an air atmosphere. Secondary particles (NMC-Bb) (LiNi _0.33 Co _0.33 Mn _0.34 O ₂ , D ₅₀ : 5.0 μm) were obtained.

[Production Example 3: Production of lithium-based olivine-type composite oxide secondary particles (A) (LMP-Aa)]
1272 g of LiOH.H ₂ O and 4 L of water were mixed to obtain a slurry a3. Next, 1153 g of 85% phosphoric acid aqueous solution was dropped at 35 mL / min while stirring the obtained slurry a3 at a temperature of 25 ° C. for 3 minutes, and subsequently, cellulose nanofibers (Wma-10002, Inc.) Sugino machine, with the addition of fiber diameter 4nm~20nm) 5892g, and stirred at a speed 400 rpm 12 hours to obtain a slurry b3 containing Li ₃ PO _4.
And the resulting nitrogen purge slurry b3, added after the dissolved oxygen concentration of the slurry b3 was 0.5 mg / L, with respect to the slurry b3 total _{amount, MnSO 4 · 5H 2 O 1688g} , the FeSO ₄ · 7H ₂ O 834g Thus, a slurry c3 was obtained. The molar ratio of the added MnSO ₄ to FeSO ₄ (manganese compound: iron compound) was 70:30.
Next, the obtained slurry c3 was put into an autoclave, and a hydrothermal reaction was performed at 170 ° C. for 1 hour. The pressure inside the autoclave was 0.8 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 a complex d3.
1000 g of the obtained composite d3 was collected, and 1 L of water was added thereto to obtain a slurry e3. The obtained slurry e3 was subjected to dispersion treatment with an ultrasonic stirrer (T25, manufactured by IKA Corporation) for 1 minute to uniformly color the whole, and then spray-dried (MDL-050M, manufactured by Fujisaki Electric Co., Ltd.). ) To give a granulated material f3 by spray drying at a spray temperature of 150 ° C.
The obtained granule f3 is calcined at 700 ° C. for 1 hour under an argon hydrogen atmosphere (hydrogen concentration: 3%) to obtain a lithium-based olivine type carrying 2.0% by mass of carbon derived from cellulose nanofibers. Composite oxide secondary particles (A) (LMP-Aa) (LiMn _0.7 Fe _0.3 PO ₄ , amount of carbon = 2.0 mass%, tap density: 1.04 g / cm ³ , D ₅₀ : 15.8 μm, particle size (Standard deviation of distribution: 9.8 μm, BET specific surface area: 18.8 m ² / g).

[Production Example 4: Production of lithium-based olivine-type composite oxide secondary particles (A) (LMP-Ab)]
The slurry c3 obtained in Production Example 3 was charged into an autoclave, and a hydrothermal reaction was performed at 140 ° C. for 1 hour. The pressure inside the autoclave was 0.4 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 a complex d4.
1000 g of the obtained composite d4 was collected, and 1 L of water was added thereto to obtain a slurry e4. The obtained slurry e4 was subjected to dispersion treatment with an ultrasonic stirrer (same as above) for 1 minute to uniformly color the whole, and then subjected to spray drying at a spray temperature of 200 ° C. using a spray drying apparatus (same as above). Thus, a granulated body f4 was obtained.
The obtained granule f4 is calcined at 700 ° C. for 1 hour under an argon hydrogen atmosphere (hydrogen concentration: 3%) to obtain a lithium-based olivine type carrying 2.0% by mass of carbon derived from cellulose nanofibers. Composite oxide secondary particles (A) (LMP-Ab) (LiMn _0.7 Fe _0.3 PO ₄ , amount of carbon = 2.0 mass%, tap density: 1.14 g / cm ³ , D ₅₀ : 10.0 μm, particle size (Standard deviation of distribution: 6.6 μm, BET specific surface area: 22.2 m ² / g).

[Production Example 5: Production of lithium-based olivine-type composite oxide secondary particles (A) (LMP-Ac)]
Slurry b5 was obtained instead of slurry b3 in the same manner as in Production Example 3 except that the amount of cellulose nanofibers (same as above) added to slurry a3 was 7660 g, and the same treatment as that for slurry b3 was performed to obtain a composite. A body d5 was obtained. 1000 g of the obtained composite d5 was collected, and 1.5 L of water was added thereto to obtain a slurry e5. The obtained slurry e5 was subjected to dispersion treatment with an ultrasonic stirrer (same as above) for 1 minute to uniformly color the whole, and then subjected to spray drying at a spray temperature of 170 ° C. using a spray drying apparatus (same as above). Thus, a granulated body f5 was obtained.
The obtained granule f5 is calcined at 700 ° C. for 1 hour in an argon hydrogen atmosphere (hydrogen concentration: 3%), and a lithium-based olivine type supporting 2.6% by mass of carbon derived from cellulose nanofiber is supported. Composite oxide secondary particles (A) (LMP-Ac) (LiMn _0.7 Fe _0.3 PO ₄ , amount of carbon = 2.6 mass%, tap density: 1.04 g / cm ³ , D ₅₀ : 7.14 μm, particle size (Standard deviation of distribution: 6.6 μm, BET specific surface area: 24.8 m ² / g).

[Production Example 6: Production of lithium-based olivine-type composite oxide secondary particles (A) (LMP-Ad)]
1000 g of the composite d3 obtained in Production Example 3 was collected, and 2 L of water was added thereto to obtain a slurry e6. The obtained slurry e6 was subjected to dispersion treatment with an ultrasonic stirrer (same as above) for 1 minute to uniformly color the whole, and then subjected to spray drying at a spray temperature of 150 ° C. using a spray drying apparatus (same as above). Thus, a granulated body f6 was obtained.
The obtained granule f6 is calcined at 700 ° C. for 1 hour under an argon hydrogen atmosphere (hydrogen concentration: 3%), and a lithium-based olivine type carrying 2.0% by mass of carbon derived from cellulose nanofibers is supported. Composite oxide secondary particles (A) (LMP-Ad) (LiMn _0.7 Fe _0.3 PO ₄ , amount of carbon = 2.0 mass%, tap density: 0.98 g / cm ³ , D ₅₀ : 8.31 μm, particle size (Standard deviation of distribution: 7.2 μm, BET specific surface area: 19.9 m ² / g).

[Production Example 7: Production of lithium-based olivine-type composite oxide secondary particles (A) (LMP-Ae)]
200 g of the composite d3 obtained in Production Example 3 was sampled, and granulated at 3900 rpm (30 m / s) for 30 minutes using Mechanofusion (AMS-Lab, manufactured by Hosokawa Micron) to obtain a granule f7. Was.
The obtained granule f7 is calcined at 700 ° C. for 1 hour in an argon hydrogen atmosphere (hydrogen concentration: 3%) to obtain a lithium-based olivine type carrying 2.0% by mass of carbon derived from cellulose nanofibers. Composite oxide secondary particles (A) (LMP-Ae) (LiMn _0.7 Fe _0.3 PO ₄ , amount of carbon = 2.0 mass%, tap density: 1.41 g / cm ³ , D ₅₀ : 16.1 μm, particle size (Standard deviation of distribution: 6.6 μm, BET specific surface area: 20.2 m ² / g).

[Production Example 8: Production of lithium-based olivine-type composite oxide secondary particles (A) (LMP-Af)]
200 g of the composite d3 obtained in Production Example 3 was collected and granulated at 2600 rpm (20 m / s) for 30 minutes using Mechanofusion (same as above) to obtain a granulated body f8.
The obtained granule f8 is calcined at 700 ° C. for 1 hour under an argon hydrogen atmosphere (hydrogen concentration: 3%) to obtain a lithium-based olivine type carrying 2.0% by mass of carbon derived from cellulose nanofibers. Composite oxide secondary particles (A) (LMP-Af) (LiMn _0.7 Fe _0.3 PO ₄ , amount of carbon = 2.0 mass%, tap density: 1.42 g / cm ³ , D ₅₀ : 10.5 μm, particle size (Standard deviation of distribution: 9.8 μm, BET specific surface area: 19.8 m ² / g).

[Production Example 9: Production of lithium-based olivine-type composite oxide secondary particles (A) (LMP-Ag)]
Except that 0, and: the addition to MnSO ₄ · 5H ₂ O 1688g to 2411G, the FeSO ₄ · 7H ₂ O 834 g to 0, the molar ratio of MnSO ₄ and FeSO ₄ was added (manganese compound: iron compound) 100 A slurry c9 was obtained in the same manner as in Production Example 3. The obtained slurry c9 was charged into an autoclave and subjected to a hydrothermal reaction at 140 ° C. for 1 hour. The pressure inside the autoclave was 0.4 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 lyophilized at −50 ° C. for 12 hours to obtain a complex d9.
1000 g of the obtained composite d9 was collected, and 1 L of water was added thereto to obtain a slurry e9. The obtained slurry e9 was subjected to dispersion treatment with an ultrasonic stirrer (same as above) for 1 minute to uniformly color the whole, and then subjected to spray drying at a spray temperature of 180 ° C. using a spray drying apparatus (same as above). Thus, a granulated body f9 was obtained.
The obtained granule f9 is calcined at 700 ° C. for 1 hour in an argon hydrogen atmosphere (hydrogen concentration: 3%), and a lithium-based olivine type carrying 2.0% by mass of carbon derived from cellulose nanofiber is supported. Composite oxide secondary particles (A) (LMP-Ag) (LiMnPO ₄ , amount of carbon = 2.0% by mass, tap density: 1.02 g / cm ³ , D ₅₀ : 16.0 μm, standard deviation of particle size distribution : 9.8 µm, BET specific surface area: 21.0 m ² / g).

[Production Example 10: Production of lithium-based olivine-type composite oxide secondary particles (A) (LMP-Ah)]
Except that: (iron compound, manganese compound) was 30:70, added to MnSO ₄ · 5H ₂ O 1688g to 723 g, and the FeSO ₄ · 7H ₂ O 834 g to 1946G, the molar ratio of MnSO ₄ and FeSO ₄ was added Similarly to Production Example 3, lithium-based olivine-type composite oxide secondary particles (A) (LMP-Ah) (LiMn _0.3 Fe _0.7 PO ₄ ) on which 2.0% by mass of carbon derived from cellulose nanofibers are supported , Amount of carbon = 2.0 mass%, tap density: 1.10 g / cm ³ , D ₅₀ : 15.5 μm, standard deviation of particle size distribution: 9.8 μm, BET specific surface area: 17.6 m ² / g). Obtained.

[Production Example 11: Production of lithium-based olivine-type composite oxide secondary particles (A) (LMP-Ai)]
1000 g of the composite d3 obtained in Production Example 3 was collected, and 1 L of water was added thereto to obtain a slurry e11. The obtained slurry e11 was subjected to dispersion treatment with an ultrasonic stirrer (same as above) for 1 minute to uniformly color the whole, and then subjected to spray drying at a spray temperature of 180 ° C. using a spray drying apparatus (same as above). Thus, a granulated body f11 was obtained.
The obtained granule f11 is calcined at 700 ° C. for 1 hour in an argon hydrogen atmosphere (hydrogen concentration: 3%) to obtain a lithium-based olivine type carrying 2.0% by mass of cellulose nanofiber-derived carbon. Composite oxide secondary particles (A) (LMP-Ai) (LiMn _0.7 Fe _0.3 PO ₄ , amount of carbon = 2.0 mass%, tap density: 0.95 g / cm ³ , D ₅₀ : 10.6 μm, particle size (Standard deviation of distribution: 6.6 μm, BET specific surface area: 23.6 m ² / g).

[Production Example 12: Production of lithium-based olivine-type composite oxide secondary particles (A) (LMP-Aj)]
200 g of the composite d3 obtained in Production Example 3 was collected and granulated at 3250 rpm (25 m / s) for 30 minutes using Mechanofusion (same as above) to obtain a granulated body f12.
The obtained granule f12 is calcined at 700 ° C. for 1 hour in an argon hydrogen atmosphere (hydrogen concentration: 3%) to obtain a lithium-based olivine type carrying 2.0% by mass of cellulose nanofiber-derived carbon. Complex oxide secondary particles (A) (LMP-Aj) (LiMn _0.7 Fe _0.3 PO ₄ , amount of carbon = 2.0 mass%, tap density: 1.42 g / cm ³ , D ₅₀ : 10.9 μm, particle size (Standard deviation of distribution: 7.2 μm, BET specific surface area: 20.0 m ² / g).

[Production Example 13: Production of lithium-based olivine-type composite oxide secondary particles (A) (LMP-Ak)]
The slurry c3 obtained in Production Example 3 was charged into an autoclave, and a hydrothermal reaction was performed at 200 ° C. for 1 hour. The pressure inside the autoclave was 1.6 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 a complex d13. 200 g of the obtained composite d13 was collected and granulated at 3900 rpm (30 m / s) for 4 hours using Mechanofusion (same as above) to obtain a granulated body f13.
The obtained granules f13 are calcined at 700 ° C. for 1 hour in an argon hydrogen atmosphere (hydrogen concentration: 3%) to obtain a lithium-based olivine type carrying 2.0% by mass of carbon derived from cellulose nanofibers. Composite oxide secondary particles (A) (LMP-Ak) (LiMn _0.7 Fe _0.3 PO ₄ , amount of carbon = 2.0 mass%, tap density: 1.80 g / cm ³ , D ₅₀ : 29.8 μm, particle size (Standard deviation of distribution: 6.6 μm, BET specific surface area: 17.7 m ² / g).

[Production Example 14: Production of lithium-based olivine-type composite oxide secondary particles (A) (LMP-Al)]
A lithium-based olivine-type composite oxide having 2.0% by mass of carbon derived from cellulose nanofibers was carried out in the same manner as in Production Example 3 except that the spray temperature of the spray drying apparatus (same as above) was changed to 240 ° C. Secondary particles (A) (LMP-Al) (LiMn _0.7 Fe _0.3 PO ₄ , amount of carbon = 2.0 mass%, tap density: 1.04 g / cm ³ , D ₅₀ : 3.0 μm, standard deviation of particle size distribution : 9.8 µm, BET specific surface area: 18.8 m ² / g).

[Production Example 15: Production of lithium-based olivine-type composite oxide secondary particles (A) (LMS-Aa)]
LiOH · H ₂ O 428g, was obtained _{Na 4 SiO 4 · nH 2 O} 1397g, slurry a15 mixed cellulose nanofibers (ibid) 5892G and water 3.75 L. Then, the resulting slurry a15, and MnSO ₄ · 5H ₂ O 1655g and Zr (SO ₄₎ was added to ₂ · 4H ₂ O 53g obtain a slurry b15. The molar ratio (manganese compound: zirconium compound) of the added MnSO ₄ and Zr (SO ₄ ) ₂ was 97: 3.
Next, the obtained slurry b15 was charged into an autoclave, and a hydrothermal reaction was performed at 170 ° C. for 3 hours. The pressure inside the autoclave was 0.4 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 a complex c15.
500 g of the obtained composite c15 was collected, and 500 mL of water was added thereto to obtain a slurry d13. The obtained slurry d13 was subjected to dispersion treatment with an ultrasonic stirrer (same as above) for 1 minute to uniformly color the whole, and then subjected to spray drying at a spray temperature of 150 ° C. using a spray drying apparatus (same as above). Thus, a granulated body e15 was obtained.
The obtained granule e15 is calcined at 650 ° C. for 1 hour in an argon hydrogen atmosphere (hydrogen concentration: 3%), and a lithium-based olivine type carrying 4.0% by mass of carbon derived from cellulose nanofibers is supported. Composite oxide secondary particles (A) (LMS-Aa) (Li ₂ Mn _0.97 Zr _0.03 SiO ₄ , amount of carbon = 4.0 mass%, tap density: 0.97 g / cm ³ , D ₅₀ : 8.9 μm (Standard deviation of particle size distribution: 7.2 μm, BET specific surface area: 28.3 m ² / g).

[Production Example 16: Production of lithium-based olivine-type composite oxide secondary particles (A) (LFS-Aa)]
Except for changing the addition to MnSO ₄ · 5H ₂ O 1655g was FeSO ₄ · 7H ₂ O 1358g, in the same manner as in Production Example 15, a lithium-based olivine carbon from 4.0% by weight of the cellulose nanofibers, which are carried Composite oxide secondary particles (A) (LFS-Aa) (Li ₂ Fe _0.97 Zr _0.03 SiO ₄ , amount of carbon = 4.0 mass%, tap density: 1.03 g / cm ³ , D ₅₀ : 8.5 μm (Standard deviation of particle size distribution: 7.2 μm, BET specific surface area: 26.1 m ² / g).

Table 1 shows the structure of the lithium-based olivine type composite oxide secondary particles (A) and the layered type lithium composite oxide secondary particles (B) for obtaining each mixed positive electrode active material.
Further, lithium olivine-type composite oxide secondary particle (A) and the above formula with a predetermined physical properties of layered-type lithium composite oxide secondary particle (B) (1) by the obtained X _A and the formula (2 )) _Are also shown in Table 1.

≫Manufacture of positive electrode≫
According to the configuration of each mixed positive electrode active material shown in Table 1, a positive electrode slurry was prepared while using lithium-based olivine-type composite oxide secondary particles (A) and layered lithium composite oxide secondary particles (B).
Specifically, a mixed positive electrode active material (a mixture of lithium-based olivine type composite oxide secondary particles (A) and layered type lithium composite oxide secondary particles (B)) (18 g): acetylene black (2 g): polyfluoride A positive electrode slurry was prepared so as to have a mixing ratio of vinylidene chloride (2 g) = 90: 5: 5 (mass ratio). More specifically, first, acetylene black and polyvinylidene fluoride are kneaded at 2,000 rpm for 10 minutes using a rotation / revolution type mixer (ARE-310, manufactured by Shinky Corporation), and then a mixed positive electrode active material is formed. The layered lithium composite oxide secondary particles (B) were added and kneaded at 2,000 rpm for 5 minutes, and then the layered lithium composite oxide secondary particles (B) constituting the mixed positive electrode active material were added. The mixture was further kneaded at 2,000 rpm for 5 minutes. Thereafter, an appropriate amount of N-methyl-2-pyrrolidone was added thereto and kneaded at 2,000 rpm for 5 minutes to obtain a positive electrode slurry.

  Next, using a doctor blade with a blade interval of 250 μm, the above positive electrode slurry was applied to a current collector made of an aluminum foil having a thickness of 20 μm, followed by vacuum drying at 80 ° C. for 12 hours. Then, it was punched into a disk of φ14 mm and pressed at 16 MPa for 2 minutes using a hand press to obtain a positive electrode.

ＳSEM observation of cross section of positive electrode≫
With respect to the obtained positive electrode, an SEM photograph (backscattered electron image; used device: JSM-7001F, manufactured by JEOL Ltd.) of the cross section was subjected to image analysis, and the amount of interparticle voids, average void diameter (equivalent to a circular area) Diameter), the standard deviation of the average void diameter, and the distribution of voids between particles were evaluated. In the image analysis using the SEM photograph, a range of 50 μm × 50 μm around the arbitrarily selected current collector was targeted. A positive electrode cross section sample for SEM observation was produced by polishing the cross section of the positive electrode after cutting and rough polishing with a diamond paste, and then performing a cross section polisher using an Ar ion beam.
Table 2 shows the image analysis results.
In addition, the distribution state of the interparticle space | gap shown in Table 2 is the result of having evaluated the SEM photograph visually. Specifically, the distribution of voids between particles is observed in the entire SEM photograph, and when it is determined that the voids are uniformly dispersed, “○” indicates that large-sized voids are unevenly distributed near the current collector, and the like. In addition, when it was judged that the voids were not uniformly dispersed, it was evaluated as “×”.

遷移 Amount of transition metal eluted into electrolyte 液
A coin-type secondary battery was constructed using the positive electrode. As the negative electrode, a lithium foil punched into φ15 mm (in the case of a lithium ion secondary battery) was used. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solvent obtained by mixing ethylene carbonate and ethyl methyl carbonate at a volume ratio of 3: 7 was used. As the separator, a known separator such as a polymer porous film such as polypropylene was used. These battery parts were incorporated and housed in a conventional manner in an atmosphere having a dew point of -50 ° C or lower, to obtain a coin-type secondary battery (CR-2032).

The obtained secondary battery was subjected to constant current charging at a current of 170 mA / g and a voltage of 4.5 V.
Thereafter, the secondary battery was disassembled, and the positive electrode taken out was washed with dimethyl carbonate, and then immersed in an electrolytic solution. The electrolyte used at this time was a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solvent obtained by mixing ethylene carbonate and ethyl methyl carbonate at a volume ratio of 1: 1. The electrolyte in which the positive electrode was immersed was placed in a closed container, and left at 70 ° C. for one week.
After standing, the electrolyte from which the positive electrode was taken out was filtered through a 0.45 μm discic filter, and acid-decomposed with nitric acid. Ni, Co, and Mn derived from the layered lithium composite oxide secondary particles (B) contained in the acid-decomposed electrolytic solution were quantified using ICP emission spectroscopy (ULTIMA2, manufactured by Horiba, Ltd.).
Table 3 shows the results.

≫Evaluation of discharge characteristics≫
A charge / discharge test was performed using the obtained secondary battery. Specifically, after a constant current charge at a current density of 85 mA / g and a voltage of 4.25 V, a constant current discharge at a current density of 85 mA / g and a final voltage of 3.0 V was performed, and a discharge capacity measuring device (HJ-1001SD8, Hokuto Denko) The discharge capacity at 0.5 C (85 mAh / g) in a 30 ° C. environment was measured. The charge / discharge cycle was repeated 1,000 times, and the capacity retention (%) was determined by the following equation (X).
Table 3 shows the results.
Capacity retention (%) = (discharge capacity after 1000 cycles) /
(Discharge capacity after one cycle) × 100 (X)

  From Table 3, all the examples using the mixed positive electrode active material of the present invention effectively suppressed the transition metal elution amount, particularly the Ni and Mn elution amount, as compared with Comparative Example 1 or Comparative Example 2. As a result, a secondary battery having a high capacity retention rate was obtained. This is because, as shown in Table 2, the positive electrode manufactured using the mixed positive electrode active material of the present invention has a reduced amount of voids, a small variation in void diameter, and a high uniformity of distribution of the voids. It is considered something.

Claims (9)

It contains a lithium-based olivine type composite oxide secondary particle (A) and a layered type lithium composite oxide secondary particle (B), and has the following formula (1):
_{X A = T A × | D} A 50-D B 50 + 2 | ··· (1)
(In the formula (1), T _A represents the tap density of the lithium olivine-type composite oxide secondary particle ^{(A) (g / cm 3} ), D A 50 is lithium olivine-type composite oxide secondary shows the average particle diameter at cumulative 50% in the particle size distribution of the particles (a) (μm), D B 50 , the average particle at 50% accumulation in the particle size distribution of the layered-type lithium composite oxide secondary particle (B) Diameter (μm).)
The obtained X _A is ^{0.3g / m 2 ~50g / m 2} , mixing the positive active material for a lithium ion secondary battery. D _A 50 in formula (1) is a 3Myuemu～30myuemu, mixed positive active material for a lithium ion secondary battery according to claim 1.   The mass ratio (A: B) between the content of the lithium-based olivine type composite oxide secondary particles (A) and the content of the layered type lithium composite oxide secondary particles (B) is 0.5: 99.5. The mixed positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the ratio is from 90 to 90:10. Further, the following formula (2):
X _B = X _A × D _A SD / S _A (2)
(In the formula (2), D _A SD represents the standard deviation ([mu] m) in particle size distribution of the lithium olivine-type composite oxide secondary particle, S _A is BET of lithium olivine-type composite oxide secondary particles (Specific surface area (m ² / g) is shown.)
The X _B that is ^{required, 0.15 (g 2 / m 4} ) which is ^{~20 (g 2 / m 4)} , mixed positive electrode for a lithium ion secondary battery according to any one of claims 1 to 3 Active material.   The mixed positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 4, wherein the lithium-based olivine-type composite oxide secondary particles (A) are particles having carbon supported on the surface. . The lithium-based olivine type composite oxide secondary particles (A) are represented by the following formula (I):
^{_{Li a Mn b Fe c M 1}} d PO 4 ··· (I)
(In the formula (I), M ¹ represents Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd. A, b, c, and d represent 0 <a ≦ 1.2, 0.3 ≦ b ≦ 1, 0 ≦ c ≦ 0.7, and 0 ≦ d ≦ 0.3, and a + (valence of Mn) × b + (valence of Fe) ) × c + (valence of M ¹ ) × d = 3.)
Or the following formula (II):
^{_{Li e Mn f Fe g M 2}} h SiO 4 ··· (II)
(In the formula (II), M ² represents Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, Al, Zn, V or Gd. g and h satisfy 0 <e ≦ 2.4, 0 ≦ f ≦ 1.2, 0 ≦ g ≦ 1.2, 0 ≦ h ≦ 1.2, and f + g ≠ 0, and e + (Mn (Valence) × f + (valence of Fe) × g + (valence of M ² ) × h = 4.)
The mixed positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 5, which is a particle represented by the following formula: The layered lithium composite oxide secondary particles (B) are represented by the following formula (III):
^{_{LiNi i Co j Mn k M 3}} l O 2 ··· (III)
(In the formula (III), M ³ is Mg, Ti, Nb, Fe, Cr, Si, Al, Ga, V, Zn, Cu, Sr, Mo, Zr, Sn, Ta, W, La, Ce, Pb, Represents one or more elements selected from Bi and Ge, where i, j, k, and l are 0.3 ≦ i <1, 0 <j ≦ 0.7, 0 <k ≦ 0.7, 0 ≦ l ≦ 0.3, and 3i + 3j + 3k + (valence of M ³⁾ shows a number satisfying × l = 3.)
Or the following formula (IV):
^{_{LiNi m Co n Al o M 4}} p O 2 ··· (IV)
(In the formula (IV), M ⁴ is Mg, Ti, Nb, Fe, Cr, Si, Ga, V, Zn, Cu, Sr, Mo, Zr, Sn, Ta, W, La, Ce, Pb, Bi and Represents one or more elements selected from Ge, where m, n, o, and p are 0.4 ≦ m <1, 0 <n ≦ 0.6, 0 <o ≦ 0.3, 0 ≦ (p ≦ 0.3 and 3m + 3n + 3o + (valence of M ⁴ ) × p = 3)
The mixed positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 6, which is a particle represented by the following formula: The following steps (I) to (V):
For (I) layered lithium composite oxide secondary particle (B), step (II) at least one lithium-based olivine-type composite oxide secondary measuring the average particle diameter D _B 50 at 50% cumulative in the particle size distribution particles for (a ^t), a tap density T _a ^t, the step of measuring the average particle diameter D _a ^t 50 at 50% accumulation in the particle size distribution of the lithium olivine-type composite oxide secondary particle (a ^t) (III) The D _B 50 obtained in the step (I) is represented by the following formula (1):
_{X A = T A × | D} A 50-D B 50 + 2 | ··· (1)
(In the formula (1), T _A represents the tap density of the lithium olivine-type composite oxide secondary particle ^{(A) (g / cm 3} ), D A 50 is lithium olivine-type composite oxide secondary shows the average particle diameter at cumulative 50% in the particle size distribution of the particles (a) (μm), D B 50 , the average particle at 50% accumulation in the particle size distribution of the layered-type lithium composite oxide secondary particle (B) X _A represents a value (g / m ² ) serving as an index for selecting the lithium-based olivine-type composite oxide secondary particles (A) to be mixed in the step (IV).)
Introduced to step (IV) lithium olivine-type composite oxide secondary particles from among (A ^t), equation (1) by the X _A for a 0.3g / m ² ~50g / m ² obtained , tap density T _a and D _a lithium olivine-type composite oxide secondary particles selecting a (a) (V) selected lithium olivine-type composite oxide secondary particle (a) and layer-structured lithium having 50 A method for producing a mixed positive electrode active material for a lithium ion secondary battery, comprising a step of mixing the composite oxide secondary particles (B).   In the mixing in the step (V), the mass ratio (A: B) of the lithium-based olivine type composite oxide secondary particles (A) and the layered type lithium composite oxide secondary particles (B) is 0.5: The method for producing a mixed positive electrode active material for a lithium ion secondary battery according to claim 8, wherein the ratio is 99.5 to 90:10.