JP7675541B2 - Positive electrode active material particle mixture for lithium ion secondary batteries - Google Patents

Description

The present invention relates to a mixture of positive electrode active material particles for lithium ion secondary batteries to obtain lithium ion secondary batteries that are high capacity and have excellent safety.

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. As a positive electrode material for such lithium ion secondary batteries, lithium manganese iron phosphate particles such as LiMn _x Fe _1-x PO ₄ are considered promising due to their high safety and large capacity. On the other hand, lithium manganese iron phosphate particles have low electrical conductivity, and still require improvement in order to sufficiently improve the battery characteristics of the resulting lithium ion secondary battery, so various developments have been made in the past.

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 of a lithium-ion secondary battery than when lithium manganese iron phosphate is contained alone.

JP 2011-159388 A

However, with 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 the lithium manganese iron phosphate in order to achieve high capacity in the resulting lithium-ion secondary battery, it is difficult to ensure safety (thermal stability, hereafter the same) and improvements are still required.

Therefore, the object of the present invention is to provide a positive electrode active material particle mixture for lithium ion secondary batteries that uses lithium manganese iron phosphate-based particles and can sufficiently improve the capacity and safety of lithium ion secondary batteries.

The inventors conducted extensive research to solve the above problems and discovered that by combining specific lithium manganese iron phosphate particles with many voids inside the particles with two types of lithium-nickel-cobalt-manganese particles with different nickel contents, it is possible to obtain a positive electrode material that can realize a lithium-ion secondary battery that has high capacity and excellent safety.

That is, the present invention relates to a compound represented by the following formula (A):
Li _a Mn _b Fe _c M ¹ _x PO ₄ ...(A)
(In 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 represent 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 of Mn)×b+(valence of Fe)×c+(valence of ^M1 )×x=3.)
Particles (A) having a tap density of 0.3 g/cm ³ to 1.2 g/cm ³ and a pore volume of 0.2 mL/g to 0.7 mL/g at pore diameters of 10 nm to 3000 nm;
The following formula (B):
_{LiNidCoeMnfM2yO2 ... (} ^B _{) ​}
(In formula (B), ^M2 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 represent numbers satisfying 0.6≦d≦0.95, 0<e≦0.4, 0<f≦0.4, 0≦y≦0.3, and 3d+3e+3f+(valence of ^M2 )×y=3.)
Particles (B) represented by
The following formula (C):
LiNi _g Co _h Mn _i M ³ _z O ₂ ...(C)
(In formula (C), ^M3 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 represent numbers satisfying 0.3≦g<0.6, 0<h≦0.7, 0<i≦0.7, 0≦z≦0.3, and 3g+3h+3i+(valence of ^M3 )×z=3.)
Particles (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 positive electrode active material particle mixture for lithium ion secondary batteries of the present invention contains particles (A), which are lithium manganese iron phosphate-based particles that have many voids inside the particles and exhibit good disintegration properties during the pressing step in the battery manufacturing process, and therefore closely and effectively entangles with particles (B) and (C), which are two types of lithium-nickel-cobalt-manganese-based particles with different nickel contents, making it possible to realize a lithium ion secondary battery that effectively increases capacity while also being excellent in safety (thermal stability).

The present invention will be described in detail below.
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 PO ₄ ...(A)
(In 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 represent 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 of Mn)×b+(valence of Fe)×c+(valence of ^M1 )×x=3.)
Particles (A) having a tap density of 0.3 g/cm ³ to 1.2 g/cm ³ and a pore volume of 0.2 mL/g to 0.7 mL/g at pore diameters of 10 nm to 3000 nm;
The following formula (B):
_{LiNidCoeMnfM2yO2 ... (} ^B _{) ​}
(In formula (B), ^M2 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 represent numbers satisfying 0.6≦d≦0.95, 0<e≦0.4, 0<f≦0.4, 0≦y≦0.3, and 3d+3e+3f+(valence of ^M2 )×y=3.)
Particles (B) represented by
The following formula (C):
LiNi _g Co _h Mn _i M ³ _z O ₂ ...(C)
(In formula (C), ^M3 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 represent numbers satisfying 0.3≦g<0.6, 0<h≦0.7, 0<i≦0.7, 0≦z≦0.3, and 3g+3h+3i+(valence of ^M3 )×z=3.)
Particles (C) represented by
It consists of:

In this manner, 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.
Particle (A) has many voids therein so that the tap density and pore volume are within the above-mentioned specific ranges. Therefore, the particles (A) are appropriately collapsed during the pressing step in the battery production process, and are well and uniformly mixed with particles (B) and particles (C), and the particles are closely and effectively entangled with each other. In the obtained lithium ion secondary battery, the capacity can be effectively increased while effectively suppressing destruction of the crystal structure of each particle even when charging and discharging are repeated, and it is possible to combine excellent safety.

The positive electrode active material particle mixture for a lithium ion secondary battery of the present invention contains particles (A) represented by the following formula (A):
Li _a Mn _b Fe _c M ¹ _x PO ₄ ...(A)
(In 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 represent 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 of Mn)×b+(valence of Fe)×c+(valence of ^M1 )×x=3.)
The particle includes particles represented by:

The particles (A) represented by the above formula (A) are olivine-type lithium manganese iron phosphate particles containing at least manganese (Mn) or iron (Fe), and are secondary particles formed by agglomeration of primary particles. 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, and is preferably Mg or Zr. a is 0<a≦1.2, preferably 0.6≦a≦1.2, more preferably 0.65≦a≦1.15, and even more preferably 0.7≦a≦1.1. b is 0≦b≦1.2, preferably 0.25≦b≦0.8, and more preferably 0.35≦b≦0.8. c is 0≦c≦1.2, preferably 0.2≦c≦0.75, and more preferably 0.2≦c≦0.65. These b and c satisfy b+c≠0. x is 0≦x≦0.3, preferably 0≦x≦0.15, and more preferably 0≦x≦0.1. These 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 _{LiMnPO4 , LiFePO4} , _{LiMn0.8Fe0.2PO4} , _{LiMn0.1Fe0.9PO4 , LiMn0.8Fe0.1Mg0.1PO4 , LiMn0.8Fe0.1Zr0.05PO4 , and the like .}

The tap density of the particles (A) is, from the viewpoint of effectively suppressing unnecessary elution of metals while exhibiting good disintegrability, 0.3 g/cm ³ to 1.2 g/cm ³ , preferably 0.3 g/cm ³ to 1.0 g/cm ³ , and more preferably 0.3 g/cm ³ to 0.8 g/cm ³ .
In the following description, the tap density means the "tap bulk density" measured by the method specified in JIS R 1628 "Method for measuring bulk density of fine ceramic powders."

The pore volume of the particles (A) having a pore diameter of 10 nm to 3000 nm is, in combination with the tap density, 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 allowing the particles (A) to exhibit good disintegratability and effectively enhancing the safety of the resulting battery.
The pore volume refers to a value measured by a mercury intrusion porosimeter.

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 means the D ₅₀ value (particle size at 50% cumulative (median size)) obtained from the volume-based particle size distribution based on the laser diffraction/scattering method.

In addition, from the viewpoint of ensuring an excellent 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 1,000 nm and they have good dispersibility in water, so 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.

When carbon derived from cellulose nanofibers and carbon derived from a water-soluble carbon material are supported on the surface of the particles (A), the sum of the atomic equivalent amount of carbon derived from the cellulose nanofibers and the atomic equivalent amount of carbon derived from the water-soluble carbon material, i.e., the sum of the supported amount of carbon derived from the cellulose nanofibers and the supported 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 the particles (A).
The atomic equivalent amount (supported amount) of carbon derived from the cellulose nanofibers present in the particles (A) and the atomic equivalent amount (supported amount) of carbon derived from the water-soluble carbon material refer to values determined by measurement using a carbon/sulfur analyzer.

From the viewpoint of achieving high capacity and excellent safety in the resulting battery, the content of the 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 the particles (A) support carbon derived from cellulose nanofibers and/or carbon derived from a water-soluble carbon material on their surfaces, the content of the particles (A) also includes the amount of these carbons supported.

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) A step of 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) It can be obtained by a production method including a step of firing the obtained granules b.

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.

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.
As the metal compound containing a manganese compound and/or an iron compound, in addition to manganese compounds and iron compounds, metal (M ¹ ) compounds can be used.
Examples of the manganese compound 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 the 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.
Examples of the metal (M ¹ ) compound include sulfates and nitrates containing a metal having the same meaning as M ¹ in the above formula (A).
Examples of the phosphoric acid compound include orthophosphoric acid (H ₃ PO ₄ , phosphoric acid), metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, ammonium phosphate, ammonium hydrogen phosphate, etc. Among these, it is preferable to use phosphoric acid, and it is preferable to use it as an aqueous solution with a concentration of 70% by mass to 90% by mass.

In 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, relative to 100 parts by mass of water.

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 the 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.

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, 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 the slurry water to a temperature below its boiling point, specifically, to 80° C. or below, and more preferably to 20° C. to 60° C.

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 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.

By purging nitrogen into the slurry water after mixing with the phosphoric acid compound, the reaction in the slurry water is completed to obtain a powder a', which is a precursor of the particles (A), 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 (Li ₃ PO ₄ ).

Next, a manganese compound and an iron compound are 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 even more 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, per mol of phosphate ions contained in the slurry water.

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 these lithium compounds, the metal compound containing a manganese compound and/or an iron compound, the phosphate compound, and the water have the quantitative relationship described above, and it is not necessary for trilithium phosphate ( _Li3PO4 ) as a precursor of particles ( _A ) to be present in the slurry water i.

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.

The order of addition of the manganese compound, iron compound, and metal (M ¹ ) compound is not particularly limited. In addition to adding these metal compounds, an antioxidant may be added as necessary. As such an antioxidant, sodium sulfite (Na ₂ SO ₃ ), sodium hydrosulfite (Na ₂ S ₂ O ₄ ), aqueous ammonia, etc. can be used. The amount of the antioxidant added is preferably 0.01 mol to 1 mol, more preferably 0.03 mol to 0.5 mol, per 1 mol of the total of the manganese compound, iron compound, and metal (M ¹ ) compound used as needed.

When slurry water i' is used, the content of powder a' in the slurry water i obtained by adding a manganese compound, an iron compound and a metal (M ¹ ) compound, and optionally adding an antioxidant, etc., is preferably 10% by mass to 50% by mass, more preferably 15% by mass to 45% by mass, and even more preferably 20% by mass to 40% by mass.

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

The amount of water used in the hydrothermal reaction is preferably 10 to 50 moles, and more preferably 12.5 to 45 moles, per mole of phosphate ions contained in the slurry water i (or slurry water i'), from the standpoints of the solubility of the metal compound, ease of stirring, and synthesis efficiency.

The hydrothermal reaction may be carried out at a temperature of 100° C. or higher, preferably 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.

In step (II), the powder a obtained in step (I), a foaming agent, and water are added and mixed to obtain slurry water ii, which is then spray-dried to obtain granules b. The use of a foaming agent here generates gas, which then becomes present in the granules b. The gas present in the granules b is burned off through step (III) described below, and can be made to exist as voids in the resulting particles (A).

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 forming many voids inside the particles (A).

The solids concentration of the slurry water ii is preferably 35% to 65% by mass, more preferably 40% to 65% by mass, and even more preferably 45% 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 are within the above-mentioned specific ranges.

After the water is added, 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 addition, from the viewpoint of ensuring 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 may 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.

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, as treatment conditions in a micromist dryer equipped with a four-fluid nozzle (MDL-050M manufactured by Fujisaki Electric Co., Ltd.), 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.

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.

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):
_{LiNidCoeMnfM2yO2 ... (} ^B _{) ​}
(In formula (B), ^M2 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 represent numbers satisfying 0.6≦d≦0.95, 0<e≦0.4, 0<f≦0.4, 0≦y≦0.3, and 3d+3e+3f+(valence of ^M2 )×y=3.)
The particle (C) is represented by the following formula (C):
LiNi _g Co _h Mn _i M ³ _z O ₂ ...(C)
(In formula (C), ^M3 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 represent numbers satisfying 0.3≦g<0.6, 0<h≦0.7, 0<i≦0.7, 0≦z≦0.3, and 3g+3h+3i+(valence of ^M3 )×z=3.)
The particle includes particles represented by:

Both of the above particles (B) and particles (C) 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. They are secondary particles formed by agglomeration 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) with different nickel contents in combination, combined with the fact that these particles are uniformly mixed with fine particles (A) that have been appropriately disintegrated during the pressing process in the battery manufacturing process.

In the above formula (B) representing the particle (B), ^M2 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 represents 0.6≦d≦0.95, preferably 0.7≦d≦0.9, and e, f, and y represent numbers satisfying 0<e≦0.4, 0<f≦0.4, and 0≦y≦0.3, and 3d+3e+3f+(valence of ^M2 )×y=3.

_{Specific examples} of _the particles (B) represented by _{the above} formula (B ₎ include _{LiNi0.94Co0.03Mn0.03O2 , LiNi0.9Co0.05Mn0.05O2 , LiNi0.8Co0.1Mn0.1O2 , and LiNi0.6Co0.2Mn0.2O2 . Of these , LiNi0.8Co0.1Mn0.1O2 and LiNi0.6Co0.2Mn0.2O2 are preferred .}

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 favorably and uniformly mixing with the particles (A) that disintegrate appropriately during the pressing step in the battery production process, together with the particles (C).
As with the particles (A), the average particle size refers to the D ₅₀ value (particle size at 50% cumulative (median size)) obtained from the volume-based particle size distribution based on the laser diffraction/scattering method.

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.

In the above formula (C) representing the particle (C), ^M3 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, preferably 0.32≦g≦0.5. h, i and z represent numbers that satisfy 0<h≦0.7, 0<i≦0.7, 0≦z≦0.3 and 3g+3h+3i+(valence of ^M3 )×z=3.

_Specific examples of the particles (C) represented by _{the above formula ( C ) include LiNi0.33Co0.33Mn0.34O2 , LiNi0.4Co0.3Mn0.3O2 , LiNi0.5Co0.2Mn0.3O2 , LiNi0.33Co0.31Mn0.33Mg0.03O2 , LiNi0.33Co0.31Mn0.33Zn0.03O2 , and the like . Of these , LiNi0.33Co0.33Mn0.34O2 and LiNi0.33Co0.31Mn0.33Mg0.03O2 are preferable .}

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 favorably and uniformly mixing with the particles (A) that disintegrate appropriately during the pressing step in the battery production process, together with the particles (B).
As with particles (A) and (B), the average particle size refers to the _D50 value (particle size at 50% cumulative (median diameter)) obtained from a volume-based particle size distribution based on a laser diffraction/scattering method.

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% by mass to 40% by mass, more preferably 10% by mass to 30% by mass, and even more preferably 10% by mass to 20% by mass, from the viewpoint of achieving high capacity and excellent safety in the resulting battery.

The above-mentioned 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-mentioned particles (A). Furthermore, these particles (B) and particles (C) may be produced by known methods, for example, by the methods described in the Examples.

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 (B) and particles (C) together with the above particles (A) in a conventional manner.

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 having a positive electrode, a negative electrode, an electrolyte, and a separator, or a positive electrode, a negative electrode, and a solid electrolyte as essential components. 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, or the like to prepare a positive electrode slurry, which is then applied to a current collector and press-molded to produce a positive electrode.
In the case of the positive electrode active material particle mixture for a lithium ion secondary battery of the present invention, the above-mentioned particles (A) disintegrate appropriately, and are intimately and effectively entangled with the above-mentioned particles (B) and particles (C) contained in the positive electrode active material particle mixture for a lithium ion secondary battery, so that they are well and uniformly mixed together, and the particles (A) disintegrate so as to cover these particles and become finely divided are scattered, so that a highly useful positive electrode that can exhibit high capacity and excellent safety can be obtained.

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 intercalating material that can electrochemically absorb and release lithium ions, particularly a carbon material. Furthermore, two or more of the above negative electrode materials may be used in combination, for example, a combination of graphite and silicon-based materials can be used.

The electrolyte is a solution of a supporting salt dissolved in an organic solvent. The organic solvent is not particularly limited as long as it is an organic solvent that is normally used in electrolytes for lithium ion secondary batteries. For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, oxolane compounds, etc. can be used.

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 _.

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

The solid electrolyte electrically insulates the positive electrode and the negative electrode and exhibits high lithium ion conductivity. For example, La _0.51 Li _0.34 TiO _2.94 , Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ , Li ₇ La ₃ Zr ₂ O ₁₂ , 50Li ₄ SiO ₄・50Li ₃ BO ₃ , Li _2.9 PO _3.3 N _0.46 , Li _3.6 Si _0.6 P _0.4 O ₄ , Li _1.07 Al _0.69 Ti _1.46 (PO ₄ ) ₃ , Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ , Li ₁₀ GeP ₂ S ₁₂ , _{Li3.25Ge 0.25} P _0.75 S ₄ , 30Li ₂ S・26B ₂ S ₃・44LiI, 63Li ₂ S・36SiS ₂・1Li ₃ PO ₄ , 57Li ₂ S・38SiS ₂・5Li ₄ SiO ₄ , 70Li ₂ S・30P ₂ S ₅ , 50Li ₂ S·50GeS ₂ , Li ₇ P ₃ S ₁₁ , and Li _3.25 P _0.95 S ₄ may be used.

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

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

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

<Measurement of tap density (g/cm ³ )>
The tapped bulk density was measured according to the method specified in JIS R 1628 "Method for measuring bulk density of fine ceramic powders", and this was taken as the tapped density (g/cm ³ ).

Measurement of pore volume (mL/g)
The pore volume of the particles was measured by mercury intrusion porosimeter (AutoPoreIV9520, manufactured by Micrometrics) by mercury intrusion method. 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 size range of 10 nm to 3000 nm was obtained.

[Production Example 1: Production of Particles (A-1)]
LiOH.H ₂ O 1272g and water 4L were mixed to obtain slurry water xi. Next, the obtained slurry water xi was stirred for 3 minutes while maintaining the temperature at 25 ° C., while 1153g of 85% phosphoric acid aqueous solution was dropped at 35mL / min, followed by adding 1650g of cellulose nanofiber (Celish KY-100G, manufactured by Daicel FineChem, fiber diameter 4nm to 100nm) and stirring at a speed of 400 rpm for 12 hours to obtain slurry water yi containing Li ₃ PO _4. The obtained slurry water yi was purged with nitrogen to adjust the dissolved oxygen concentration of the slurry water yi to 0.5mg / L, and then 1610g of MnSO _{4.5H 2} O and 834g of FeSO _{4.7H 2} O were added to the total amount of the slurry water yi to obtain slurry water zi. The molar ratio of added _MnSO4 to _FeSO4 (manganese compound:iron compound) was 70:30.

The obtained slurry water zi was then put into an autoclave and subjected to a hydrothermal reaction at 180 ° C. for 1 hour. The pressure inside the autoclave was 1.0 MPa. After the hydrothermal reaction, the 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, 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 whole, 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 fired 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 PO ₄ ).
The resulting particles (A-1) had a tap density of 1.0 g/cm ³ , a pore volume of 0.3 mL/g, an average particle size of 14 μm, and a carbon loading of 4.5% by mass.

[Production Example 2: Production of Particles (A-2)]
Particles (A-2) (LiMn _0.7 Fe _0.3 PO _{4 ) were obtained in the same manner as in Production Example 1, except that the amount of ammonium carbonate added to powder a1 was 12.2 g (1.22 parts by mass per 100 parts by mass of powder a1} ).
The resulting particles (A-2) had a tap density of 0.3 g/cm ³ , a pore volume of 0.7 mL/g, an average particle size of 15 μm, and a carbon loading of 4.5% by mass.

[Production Example 3: Production of particles (A-3)]
Particles (A-3) (LiMn _0.7 Fe _0.3 PO _{4 ) were obtained in the same manner as in Production Example 1, except that the amount of ammonium carbonate added to powder a1 was 0.06 g (0.006 part by mass per 100 parts by mass of powder a1} ).
The resulting particles (A-3) had a tap density of 1.2 g/cm ³ , a pore volume of 0.2 mL/g, an average particle size of 13 μm, and a carbon loading of 4.5% by mass.

[Production Example 4: Production of particles (A-4)]
Particles (A-4) (LiMn _0.7 Fe _0.3 PO _{4 ) were obtained in the same manner as in Production Example 1, except that the amount of ammonium carbonate added to powder a1 was 15.2 g (1.52 parts by mass per 100 parts by mass of powder a1} ).
The resulting particles (A-4) had a tap density of 0.2 g/cm ³ , a pore volume of 0.8 mL/g, an average particle size of 15 μm, and a carbon loading of 4.5% by mass.

[Production Example 5: Production of Particles (A-5)]
Particles (A-5) (LiMn _0.7 Fe _0.3 PO _{4 ) were obtained in the same manner as in Production Example 1, except that the amount of ammonium carbonate added to powder a1 was 0.03 g (0.003 part by mass per 100 parts by mass of powder a1} ).
The resulting particles (A-5) had a tap density of 1.4 g/cm ³ , a pore volume of 0.1 mL/g, an average particle size of 13 μm, and a carbon loading of 4.5% by mass.

[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 having a pH of 11.
The resulting slurry was then filtered and dried to obtain a mixture of metal composite hydroxides, which was then mixed with 111 g of lithium carbonate in a ball mill to obtain a powder mixture. The resulting 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 to obtain particles (B-1) ( _{LiNi0.8Co0.1Mn0.1O2 ,} average particle size _{: 10} μm).

[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% aqueous ammonia was added dropwise to the mixture at a rate of 300 mL/min to obtain a slurry containing a metal composite hydroxide having a pH of 11.
The resulting slurry was then filtered and dried to obtain a mixture of metal composite hydroxides, which was then mixed with 111 g of lithium carbonate in a ball mill to obtain a powder mixture. The resulting 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 to obtain particles (C-1) ( _{LiNi0.5Co0.2Mn0.3O2} , average particle size _{: 10 μm} ).

[Examples 1 to 6, Comparative Examples 1 to 6]
According to the formulations shown in Tables 1 and 2, the specified 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.

<Characteristics of lithium-ion batteries>
The positive electrode of a lithium ion secondary battery was prepared by using each of the obtained positive electrode active material particle mixtures as a positive electrode material. Specifically, each of the obtained positive electrode active material particle mixtures, Ketjen black, and polyvinylidene fluoride were mixed in a mass ratio of 90:5:5, and N-methyl-2-pyrrolidone was added thereto and thoroughly kneaded to prepare a positive electrode slurry. The positive electrode slurry was applied to a current collector made of aluminum foil having a thickness of 20 μm using a coating machine, and vacuum dried at 80° C. for 12 hours. Thereafter, the mixture was pressed at 20 kN using a roll press, and punched into a disk shape of φ14 mm to obtain a positive electrode.

Next, a coin-type secondary battery was constructed using the above positive electrode. A lithium foil punched to φ15 mm was used for the negative electrode. The electrolyte was a mixed solvent of ethylene carbonate and ethyl methyl carbonate 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 for 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).

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).
In addition, the electrode density was calculated by the following formula (x).
Electrode density (g/cm ³ )=
Mass of positive electrode active material particle mixture in positive electrode (mg) / electrode volume (φ14 mm × thickness (μm))
... (x)
The obtained coin-type secondary battery was charged at a constant current of 0.2 C (34 mA/g) and an upper limit voltage of 4.3 V in an environment at an air temperature of 30° C., and then the coin-type secondary battery was disassembled and the positive electrode was washed with 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 a differential scanning calorimeter (DSC, DSC3100SR manufactured by NETZSCH) using the obtained positive electrode composite. 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.

Claims (4)

The following formula (A):
Li _a Mn _b Fe _c M ¹ _x PO ₄ ...(A)
(In 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 represent 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 of Mn)×b+(valence of Fe)×c+(valence of ^M1 )×x=3.)
Particles (A) having a tap density of 0.3 g/cm ³ to 1.2 g/cm ³ and 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):
_{LiNidCoeMnfM2yO2 ... (} ^B _{) ​}
(In formula (B), ^M2 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 represent numbers satisfying 0.6≦d≦0.95, 0<e≦0.4, 0<f≦0.4, 0≦y≦0.3, and 3d+3e+3f+(valence of ^M2 )×y=3.)
Particles (B) having a content of 50% by mass to 80% by mass ;
The following formula (C):
LiNi _g Co _h Mn _i M ³ _z O ₂ ...(C)
(In formula (C), ^M3 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 represent numbers satisfying 0.3≦g<0.6, 0<h≦0.7, 0<i≦0.7, 0≦z≦0.3, and 3g+3h+3i+(valence of ^M3 )×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. 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. 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 . 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.