JP2024025928A - Positive electrode active material mixture for lithium ion secondary battery and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material mixture for a lithium ion secondary battery, capable of having both high discharge capacity and excellent thermal stability in an obtained lithium ion secondary battery while using a layered lithium-nickel-cobalt-manganese composite oxide (NMC), and a manufacturing method thereof.

SOLUTION: A positive electrode active material mixture for a lithium ion secondary battery is a mixture of a particle A that is represented by formula (A): LiNi_aCo_bMn_cM¹ _wO₂ and a particle B that is represented by formula (B): Li_fMn_gFe_hM² _xPO₄, and that is an aggregate of primary particles b in which carbon covers part of a particle surface and connects between particles, the particle B including a void surrounded by the primary particles b. In a cross section of the particle B, the ratio of an area occupied by carbon in an area of the void surrounded by the primary particles b is 10% or more when the area of the void is made to be 100%, and the content of the particle B in the total amount of the mixture is 10 mass% or more and less than 30 mass%.

SELECTED DRAWING: Figure 2

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a positive electrode active material mixture for a lithium ion secondary battery that can ensure excellent thermal stability while increasing the discharge capacity of the lithium ion secondary battery, and a method for manufacturing the same.

Layered lithium composite oxides such as layered lithium-nickel-cobalt-manganese composite oxides (NMC) have high discharge capacity and mass-energy density, and are widely used as useful positive electrode active materials that can be used to construct lithium-ion secondary batteries. It is used. On the other hand, when such layered lithium composite oxides are used, it is difficult to sufficiently ensure good thermal stability, so technology to further add an olivine-type positive electrode material with high thermal stability is needed. Various types have been developed.

For example, Patent Document 1 discloses a positive electrode comprising a positive electrode active material layer containing NMC and a lithium metal phosphate compound coated with carbon while controlling the average particle diameter and volume resistance; No. 2 discloses a positive electrode having a phosphate-carbon composite consisting of NMC and an olivine-type phosphoric acid compound coated with carbon while controlling the volume resistivity and content, and both of them have thermal stability etc. We are trying to improve this.
Furthermore, Patent Document 3 discloses a mixed positive electrode active material that includes a first positive electrode active material that is NMC and a second positive electrode active material that has an olivine structure, and is intended to exhibit stable output characteristics.

JP2018-037380A International Publication No. 2016/139957 Special table 2015-519005 publication

However, even with the techniques described in any of the above patent documents, the discharge capacity may be lower than that of a positive electrode material using NMC alone, and there is still room for improvement.

Therefore, an object of the present invention is to create a positive electrode active material mixture for lithium ion secondary batteries that can have both high discharge capacity and excellent thermal stability in the resulting lithium ion secondary battery while using NMC. body and its manufacturing method.

Therefore, as a result of intensive studies to solve the above problems, the inventors of the present invention have developed NMC with a Ni content within a specific range and a specific olivine-type lithium transition metal phosphate (LMFP) containing carbon. A positive electrode active material mixture for lithium ion secondary batteries that can exhibit excellent thermal stability while maintaining high discharge capacity in the resulting lithium ion secondary batteries by containing them in a specific quantitative relationship. I found my body.

That is, the present invention provides the following formula (A):
_LiNia Co _b Mn _c M ¹ _w O ₂ ...(A)
(In formula (A), ^M1 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. a, b, c and w are 0.3≦a<1, 0<b≦0.7, 0<c≦0.7, Indicates a number that satisfies 0≦w≦0.3, 3a+3b+3c+(valence of ^M1 )×w=3, and 0.3≦a/(a+b+c)<0.7.)
A particle A represented by
The following formula (B):
Li _f Mn _g Fe _h M ² _x PO ₄ ...(B)
(In formula (B), ^M2 is Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, and Gd. Indicates one or more selected elements.f, g, h and x are 0<f≦1.2, 0.3≦g≦1.2, 0.2≦h≦1.2, Indicates a number that satisfies 0≦x≦0.3 and satisfies f+(valence of Mn)×g+(valence of Fe)×h+(valence of ^M2 )×x=3.)
Particle B is an aggregate of primary particles b, which is represented by carbon covering a part of the particle surface and connecting the particles, and has internal voids surrounded by the primary particles b.
A mixture of
In the cross section of particle B, the area ratio occupied by carbon in 100% of the area of voids surrounded by primary particles b is 10% or more,
The present invention provides a positive electrode active material mixture for a lithium ion secondary battery in which the content of particles B in the total amount of the mixture is 10% by mass or more and less than 30% by mass.

Further, the present invention provides the following steps (I) to (V):
(I) After adding a lithium compound, a metal compound containing at least a manganese compound and an iron compound, a phosphoric acid compound, a carbon coating material X1, and water to obtain slurry water i, it is subjected to a hydrothermal reaction to form primary particles. Step of obtaining preliminary particles bx of primary particles b (II) Step of obtaining slurry water ii by adding preliminary particles bx of the obtained primary particles b, carbon coating agent X2, carbon coating inhibitor Y, and water (III) Step of obtaining slurry water ii of obtained primary particles b A step of spray-drying the slurry water ii to obtain granules bz. (IV) A step of firing the obtained granules bz to obtain particles B. and mixing in an amount such that the content of particles B in the total amount of the positive electrode active material mixture for lithium ion secondary batteries is 10% by mass or more and less than 30% by mass,
Carbon coating agent X1 and carbon coating agent X2 are one or more types of carbon materials selected from saccharides, and the mass ratio of the amount of carbon coating agent X1 added to the amount of carbon coating agent X2 added (X1/X2 ) is 0.05 to 9.0, and the carbon coating inhibitor Y is one or more carbon materials selected from polyols other than sugars, amines, and amides. The present invention provides a method for producing a positive electrode active material mixture for use in the present invention.

According to the positive electrode active material mixture for a lithium ion secondary battery of the present invention, in the obtained lithium ion secondary battery, the discharge capacity by LMFP is fully brought out, and the discharge capacity is comparable or higher than when NMC is used alone. In addition to being able to ensure this, it is also possible to exhibit excellent thermal stability.

3 is a TEM photograph of the surface of primary particles b formed by forming particles B1 obtained in Production Example 3. xn indicates the circumferential length of the surface of primary particle b that is not coated with carbon, and xc indicates the circumferential length of the surface of primary particle b that is coated with carbon. 3 is a TEM photograph showing voids surrounded by primary particles b in a cross section of particles B1 obtained in Production Example 3. g indicates a void surrounded by primary particles b, and cr indicates a region occupied by carbon.

The present invention will be explained in detail below.
The positive electrode active material mixture for lithium ion secondary batteries of the present invention has the following formula (A):
_LiNia Co _b Mn _c M ¹ _w O ₂ ...(A)
(In formula (A), ^M1 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. a, b, c and w are 0.3≦a<1, 0<b≦0.7, 0<c≦0.7, Indicates a number that satisfies 0≦w≦0.3, 3a+3b+3c+(valence of ^M1 )×w=3, and 0.3≦a/(a+b+c)<0.7.)
A particle A represented by
The following formula (B):
Li _f Mn _g Fe _h M ² _x PO ₄ ...(B)
(In formula (B), ^M2 is Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, and Gd. Indicates one or more selected elements.f, g, h and x are 0<f≦1.2, 0.3≦g≦1.2, 0.2≦h≦1.2, Indicates a number that satisfies 0≦x≦0.3 and satisfies f+(valence of Mn)×g+(valence of Fe)×h+(valence of ^M2 )×x=3.)
Particle B is an aggregate of primary particles b, which is represented by carbon covering a part of the particle surface and connecting the particles, and has internal voids surrounded by the primary particles b.
A mixture of
In the cross section of particle B, the area ratio occupied by carbon in 100% of the area of voids surrounded by primary particles b is 10% or more,
The content of particles B in the total amount of the mixture is 10% by mass or more and less than 30% by mass.

As described above, the positive electrode active material mixture for lithium ion secondary batteries of the present invention consists of NMC particles A having a Ni content within a specific range, and primary particles whose surfaces are coated with carbon in a unique form. Since it is a mixture of particles A and particles B that contain a specific amount of LMFP particles B formed by agglomeration of , thermal stability can be effectively increased.

Particles A constituting the positive electrode active material mixture for a lithium ion secondary battery of the present invention are represented by the following formula (A).
_LiNia Co _b Mn _c M ¹ _w O ₂ ...(A)
(In formula (A), ^M1 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. a, b, c and w are 0.3≦a<1, 0<b≦0.7, 0<c≦0.7, Indicates a number that satisfies 0≦w≦0.3, 3a+3b+3c+(valence of ^M1 )×w=3, and 0.3≦a/(a+b+c)<0.7.)

The particles A represented by the above formula (A) are Li-Ni-Co-Mn oxide particles (NMC particles), so-called lithium composite oxide particles, which are aggregates of primary particles, and are layered rock salt particles. They are particles with a structure. Then, as a, b, and c in formula (A) satisfy 0.3≦a/(a+b+c)<0.7, the molar amount of Ni in the total molar amount of Ni, Co, and Mn is 30%. The amount of particles is limited to less than 70%. By containing particles B, which will be described later, in a specific amount together with particles A, thermal stability can be improved while effectively preventing an unnecessary decrease in discharge capacity.

^M1 in formula (A) is Mg, Ti, Nb, Fe, Cr, Si, Al, Ga, V, Zn, Cu, Sr, Mo, Zr, Sn, Ta, W, La, Ce, Pb, Indicates one or more elements selected from Bi and Ge.
In addition, a, b, c, and w in the above formula (A) are 0.3≦a<1, 0<b≦0.7, 0<c≦0.7, 0≦w≦0.3, and 3a+3b+3c+(valence of ^M1 )×w=3, and the number satisfies 0.3≦a/(a+b+c)<0.7.

In particle A, Ni, Co, and Mn are known to have excellent electronic conductivity and contribute to battery capacity and output characteristics. Further, from the viewpoint of thermal stability, it is preferable that a part of the transition element is replaced by another metal element ^M1 . Since the crystal structure of particle A is stabilized by substitution with these metal elements ^M1 , it is thought that destruction of the crystal structure can be suppressed even after repeated charging and discharging, and excellent thermal stability can be ensured. It will be done.
Among these, a, b and c in the above formula (A) preferably satisfy 0.35≦a/(a+b+c)≦0.65, more preferably 0.45≦a/(a+b+c). The number satisfies ≦0.60.

Specifically, such particles A include, for example, LiNi _0.33 Co _0.33 Mn _0.34 O ₂ , LiNi _0.4 Co _0.3 Mn _0.3 O ₂ , LiNi _0.5 Co _0.3 Mn _0.2 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.6 Co _0.19 Mn _0.2 Al _0.01 O ₂ , LiNi _0.6 Co _0.19 Mn _0.2 Mg _0.01 O ₂ , LiNi _0.33 Co _0.31 Mn _0.33 Mg _0.03 O ₂ , or LiNi _0.33 Co _0.31 Mn _0.33 Zn _0.03 O ₂ etc. Can be mentioned. Among them, LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.5 Co _0.3 Mn _0.2 O ₂ , LiNi _0.33 Co _0.33 Mn _0.34 O ₂ , LiNi ₀ Particles consisting of _.33 Co _0.31 Mn _0.33 Mg _0.03 O ₂ are preferred.

Furthermore, the particles A may form a core-shell structure having a core portion (inside) and a shell portion (surface layer portion) having mutually different compositions. By forming particles A with this core-shell structure, NMC-based composite oxide particles with a high Ni concentration that are easily eluted into the electrolyte are arranged in the core part, and the shell part in contact with the electrolyte has a Ni concentration. Since the NMC-based composite oxide particles having a low MC can be arranged, the elution of metal components (Ni, Mn, Co, M ¹ ) from the particles A into the electrolytic solution can be suppressed. At this time, the core portion may be composed of one phase, or may be composed of two or more phases having different compositions. As an embodiment in which the core part is composed of two or more phases, it may be a structure in which a plurality of phases are laminated in concentric circles, or a structure in which the composition changes transitionally from the surface of the core part toward the center part. good.
Further, the shell portion may be formed outside the core portion, and may be formed of one phase like the core portion, or may be formed of two or more phases having different compositions.

Furthermore, particles A may be coated with metal oxides, metal fluorides or metal phosphates. By coating the NMC particles with these metal oxides, metal fluorides, or metal phosphates, it is possible to suppress the elution of metal components (Ni, Mn, Co, M ¹ ) from the NMC particles into the electrolyte. . Such coatings include _CeO2 , _SiO2 , _MgO , _Al2O3 , ZrO2, _{TiO2 ,} ZnO, _RuO2 , _{SnO2 ,} CoO, _Nb2O5 , CuO _{, V2O5} , _MoO3 , 1 selected from La ₂ O ₃ , WO ₃ , AlF ₃ , NiF ₂ , MgF ₂ , LiF, Li ₃ PO ₄ , Li ₄ P ₂ O ₇ , LiPO ₃ , Li ₂ PO ₃ F, and LiPO ₂ F ₂ A species, two or more species, or a composite thereof can be used.

The average particle size of the particles A as primary particles can suppress the amount of expansion and contraction of the primary particles due to insertion and desorption of lithium ions, and from the viewpoint of effectively preventing particle cracking and from the viewpoint of handling, It is 50 nm to 500 nm, more preferably 50 nm to 300 nm.
In addition, the average particle size of particles A (simply referred to as "average particle size of particles A"), which are aggregates (secondary particles) of the above-mentioned primary particles, is determined from the viewpoint of ensuring excellent thermal stability and handling. From this viewpoint, the thickness is preferably 3 μm to 20 μm, more preferably 5 μm to 15 μm.
Here, the "average particle size" of particles A means the D ₅₀ value (particle size at 50% cumulative value (median diameter)) obtained from a volume-based particle size distribution based on a laser diffraction/scattering method.

The tap density of particles A is preferably 1.5 g/cm ³ to 3.5 g/cm 3 , more preferably 2.0 g/cm ³ to ³ , from the viewpoint of ensuring high discharge capacity and handling. .0g/ ^cm3 .
Hereinafter, the tap density means the "tapped bulk density" measured by the method specified in JIS R 1628 "Method for Measuring Bulk Density of Fine Ceramic Powders".

In addition, since the positive electrode active material mixture for lithium ion secondary batteries of the present invention consists of particles A and particles B, the content of particles A in the total amount of the mixture may be the remainder of particles B described below. .

Particles A can be obtained, for example, by the following manufacturing method.
Specifically, a step (Ia) of preparing a slurry water a by adding a nickel compound, a cobalt compound, a manganese compound, and water, filtering and drying the slurry water a to obtain a mixture A, and the obtained mixture This manufacturing method includes a step (IIa) of adding and mixing a lithium compound to A and then firing.

Examples of the nickel compound used in step (Ia) include nickel sulfate and nickel acetate, and these may be used alone or in combination of two or more. Among these, nickel sulfate is preferred from the viewpoint of improving battery characteristics.
Examples of the cobalt compound include cobalt acetate, cobalt nitrate, and cobalt sulfate. These may be used alone or in combination of two or more. Among these, cobalt sulfate is preferred from the viewpoint of improving battery characteristics.
Examples of the manganese compound include manganese acetate, manganese nitrate, manganese sulfate, and the like. These may be used alone or in combination of two or more. Among these, manganese sulfate is preferred from the viewpoint of improving battery characteristics.
In addition, metal (M ¹ ) compounds other than these compounds may be used together with these nickel compounds, cobalt compounds, and manganese compounds.
Examples of lithium compounds include hydroxides (eg, LiOH.H ₂ O, LiOH), carbonates, sulfates, and acetates. Among these, carbonates are preferred.

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

In step (IIa), when firing, first pre-calcinate at 500°C to 1000°C, preferably 600°C to 900°C for 1 hour to 15 hours, preferably 1 hour to 6 hours, and then at 500°C to 1000°C. The main firing is preferably carried out at 600° C. to 900° C. for 1 hour to 15 hours, preferably 5 hours to 13 hours. Further, it is preferable to crush the material after preliminary firing and then subject it to main firing.

Particles B constituting the positive electrode active material mixture for lithium ion secondary batteries of the present invention have the following formula (B):
Li _f Mn _g Fe _h M ² _x PO ₄ ...(B)
(In formula (B), ^M2 is Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, and Gd. Indicates one or more selected elements.f, g, h and x are 0<f≦1.2, 0.3≦g≦1.2, 0.2≦h≦1.2, Indicates a number that satisfies 0≦x≦0.3 and satisfies f+(valence of Mn)×g+(valence of Fe)×h+(valence of ^M2 )×x=3.)
It is an aggregate of primary particles b formed by carbon covering a part of the particle surface and connecting the particles, and contains voids surrounded by the primary particles b. In the cross section of particle B, the area ratio occupied by carbon in 100% of the area of voids surrounded by primary particles b is 10% or more.

That is, the particles B represented by the above formula (B) are so-called olivine-type lithium transition metal phosphate compounds (LMFP particles) containing both manganese (Mn) and iron (Fe) as transition metals, and It is an aggregate of primary particles b. Carbon is unevenly distributed on the surface of primary particle b, covering a part of the surface, and while there are certain voids in particle B, which is formed by agglomeration of primary particle b, the surface of primary particle b is Carbon connects primary particles b and primary particles b. Therefore, in the voids inherent in particle B, there are voids surrounded by primary particles b, and when the cross section of particle B is observed, carbon occupies a proportion of 10% or more, and although carbon is unevenly distributed on the surface of the primary particles b, it widely occupies the space between the primary particles b.
In this way, since particle B is an aggregate of primary particles b in which the carbon covering a part of the surface exists in a unique situation, for example, the particle B uniformly covers the entire surface of the primary particle. It is possible to fully draw out the discharge capacity of the LMFP by increasing the efficiency of the electronic conduction path between the primary particles, and as will be described later, if such particles B are used in combination with particles A in a specific amount, high discharge capacity can be achieved. It becomes possible to secure the following.

In the above formula (B), ^M2 is Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. From the viewpoint of increasing the discharge capacity, Mg, Al, Ti, Zn, Nb, Co, Zr, or Gd is preferable.
In addition, f, g, h, and x in the above formula (B) are 0<f≦1.2, 0.3≦g≦1.2, 0.2≦h≦1.2, 0≦x≦ 0.3 and f+(valence of Mn)×g+(valence of Fe)×h+(valence of ^M2 )×x=3.

In the lithium-based polyanion particles represented by the above formula (B), from the viewpoint of improving discharge capacity, f is preferably 0.6≦f≦1.2, and 0.65≦f≦1.15. More preferably, 0.7≦f≦1.1. Regarding g, 0.4≦g≦0.8 is preferable. Regarding h, 0.2≦h≦0.6 is preferable. Regarding x, 0≦x≦0.2 is preferable, 0≦x≦0.15 is more preferable, and 0≦x≦0.1 is even more preferable.
In particular, from the viewpoint of both high discharge capacity and effective electronic conductivity, g and h preferably satisfy g/(g+h)≦0.8, and 0.2≦g/(g+h)≦ More preferably, the number satisfies 0.8, and even more preferably, the number satisfies 0.3≦g/(g+h)≦0.75.

Specifically, for example, LiMn _0.3 Fe _0.7 PO ₄ , LiMn _0.4 Fe _0.6 PO ₄ , LiMn _0.45 Fe _0.55 PO ₄ , LiMn _0.7 Fe _0.3 PO ₄ , LiMn _0.8 Fe _0.2 PO ₄ , LiMn _{0 .75} Fe _0.15 Mg _0.1 PO ₄ , LiMn _0.75 Fe _0.19 Zr _0.03 PO ₄ , LiMn _0.6 Fe _0.4 PO ₄ , LiMn _0.5 Fe _0.5 PO ₄ , Li _1.2 Mn _0.63 Fe _0.27 PO ₄ , or Li _0.6 Mn _0.84 Examples include Fe _0.36 PO ₄ and the like. Among them, LiMn _0.7 Fe _0.3 PO ₄ and LiMn _0.45 Fe _0.55 PO ₄ are preferred.

A part of the surface of the primary particle b forming the particle B is coated with carbon. Such carbon is obtained by carbonizing one or more carbon materials selected from saccharides to form carbon, which is coated on the surface of the primary particle b. One or more types of carbon materials selected from such saccharides (corresponding to "carbon coating material X1 and carbon coating material and amide (corresponding to "carbon coating inhibitor Y" as described later), the surface of primary particle b is unevenly distributed and coated. .
The carbon coated on the surface of the primary particles b is carbon derived from one or more carbon materials selected from sugars, and one or more carbon materials selected from polyols other than sugars, amines, and amides. Two or more types of carbon materials do not remain in the primary particles b.

Specifically, the one or more carbon materials selected from sugars include monosaccharides such as glucose, fructose, galactose, and mannose; disaccharides such as maltose, sucrose, and cellobiose; and starch, dextrin, and cellulose. Polysaccharides: One or more types selected from polysaccharide nanofibers such as cellulose nanofibers, lignocellulose nanofibers, chitin nanofibers, and chitosan nanofibers.
Among these, cellulose nanofibers, lignocellulose nanofibers, chitin nanofibers, or chitosan nanofibers are preferred, and cellulose nanofibers are more preferred, from the viewpoint of effectively increasing the electron conduction path and ensuring high discharge capacity.

The carbon coverage rate on the surface of the primary particle b is controlled to be low and within a limited range, and carbon is unevenly distributed on the surface of the primary particle b, occupying a wide area in the voids within the particle B. From the viewpoint of effectively increasing the discharge capacity by connecting the electron conduction paths and increasing the efficiency of the electron conduction path, the range is preferably 5% or more and less than 70%, more preferably 5% or more and less than 50%, and even more preferably 10%. 48%, more preferably 15% to 45%.

Note that "carbon coverage (%)" on the surface of primary particles b means a value determined by the following method. Specifically, as shown in FIG. 1, first, the surface of the primary particle b was observed in a field of view 1 in which the particles of the positive electrode active material mixture for a lithium ion secondary battery were photographed by TEM electron microscopy, and The surface of primary particle b that is not coated with carbon and the surface of primary particle b that is coated with carbon are specified. Next, in this field of view, measure the "circumferential length xn of the surface of the primary particle b that is not coated with carbon" and "the circumferential length xc of the surface of the primary particle b that is coated with carbon," The sum of xn and xc is defined as "the total circumferential length xA of the surface of primary particle b."
The obtained values of "total circumferential length xA of the surface of primary particle b" and "peripheral length xc of the surface of primary particle b coated with carbon" are introduced into the following formula (1) to calculate the field of view of 1. The carbon coverage (%) on the surface of the primary particle b is calculated, and the values obtained in 50 visual fields are averaged to determine the carbon coverage (%) on the surface of the primary particle b.
Carbon coverage (%) = {(peripheral length of the surface of particle X coated with carbon xc)/
(Total circumference length of the surface of particle X x A)} x 100...(1)

Primary particles b whose surfaces are partially coated with carbon connect primary particles b, and in particles B formed by agglomeration of such primary particles b, voids surrounded by the primary particles b exist. “Voids surrounded by primary particles b” are those formed by aggregated primary particles b within particles B when the cross section of particles B is observed, as shown by “g” in FIG. It means a void formed by primary particles b blocking all sides among the interparticle gaps. The carbon that covers part of the surface of the primary particles b occupies a wide area in the voids and connects the primary particles b, thus promoting an efficient electron conduction path and contributing to increasing the discharge capacity. can do.
In the cross section of particle B, the area ratio occupied by carbon in 100% of the area of the void surrounded by primary particle b is such that carbon is unevenly distributed on the surface of primary particle b, and the void within particle B has a wide area. 10% or more, preferably 10% to 90%, more preferably 10% to 70%, and even more preferably is 10% to 50%.

In addition, in the cross section of particle B, the area ratio occupied by carbon in 100% of the area of voids surrounded by primary particles b means a value determined by the following method. Specifically, first, through TEM electron microscopy, in a field of view 1 in which a cross section of particles B constituting a positive electrode active material mixture for a lithium ion secondary battery was photographed, it was found that particles B were surrounded by primary particles B, which were present in particles B. Observe the voids formed. Next, select the smallest particle among the primary particles b surrounding the void, select 50 visual fields of voids that occupy an area of 0.3 to 1.5 times the area of the selected particle, and calculate the area of the void. The area ratio occupied by carbon in 100% is calculated and the average value thereof is determined as the area ratio (%) occupied by carbon in 100% of the area of the voids surrounded by the primary particles b.

The average particle diameter of the primary particles b is preferably 70 nm to 200 nm from the viewpoint of being able to suppress the amount of expansion and contraction associated with insertion and desorption of lithium ions, effectively increasing the electron conduction path, and handling. , more preferably 90 nm to 170 nm.
Furthermore, the average particle diameter of particles B formed by agglomeration of primary particles b is preferably 10 μm to 30 μm, more preferably 12 μm to 30 μm, from the viewpoint of obtaining a battery with excellent thermal stability and from the viewpoint of handling. It is 20 μm.
Here, the "average particle diameter" of the primary particles b means a value obtained by calculating the crystallite diameter from an X-ray diffraction pattern using the XRD/Leubert method. In addition, the "average particle size" of particles B means the _D50 value (particle size at 50% cumulative value (median diameter)) obtained from a volume-based particle size distribution based on a laser diffraction/scattering method.

The carbon content in the particles B corresponds to the carbon content obtained by carbonizing the above carbon material in the primary particles b, and is preferably 0.5% by mass to 2.5% by mass in the particles B. The content is more preferably 0.6% by mass to 2.0% by mass, and even more preferably 0.7% by mass to 1.8% by mass.

The carbon contained in the particles B is carbon obtained by carbonizing the carbon material present on the surface of the primary particles b forming the particles, that is, corresponds to the atomic amount of the carbon material. Determined by measurement using a sulfur analyzer.

The tap density of particles B is preferably 0.8 g/cm ^{3 to 1.6 g/cm 3 , more preferably 0.9 g/cm 3 to} 1, from the viewpoint of improving electrode density and increasing discharge capacity. .6g/ ^cm3 .

The positive electrode active material mixture for a lithium ion secondary battery of the present invention is a mixture of particles A and particles B. The content of particles B in the total amount of the mixture is 10% by mass or more and less than 30% by mass, from the viewpoint of ensuring excellent thermal stability while allowing the particles B to sufficiently bring out the discharge capacity of the LMFP. , preferably 12% to 25% by weight, more preferably 14% to 25% by weight.

The positive electrode active material mixture for lithium ion secondary batteries of the present invention uses the above particles A, and the following steps (I) to (V):
(I) After adding a lithium compound, a metal compound containing at least a manganese compound and an iron compound, a phosphoric acid compound, a carbon coating material X1, and water to obtain slurry water i, it is subjected to a hydrothermal reaction to form primary particles. Step of obtaining preliminary particles bx of primary particles b (II) Step of obtaining slurry water ii by adding preliminary particles bx of the obtained primary particles b, carbon coating agent X2, carbon coating inhibitor Y, and water (III) Step of obtaining slurry water ii of obtained primary particles b A step of spray-drying the slurry water ii to obtain granules bz. (IV) A step of firing the obtained granules bz to obtain particles B. and mixing in an amount such that the content of particles B in the total amount of the positive electrode active material mixture for lithium ion secondary batteries is 10% by mass or more and less than 30% by mass,
Carbon coating agent X1 and carbon coating agent X2 are one or more types of carbon materials selected from saccharides, and the mass ratio of the amount of carbon coating agent X1 added to the amount of carbon coating agent X2 added (X1/X2 ) is 0.05 to 9.0, and the carbon coating inhibitor Y is one or more carbon materials selected from polyols other than sugars, amines, and amides. can.

In this way, while using specific carbon coating agent X1, carbon coating agent X2, and carbon coating inhibitor Y, carbon coating agent X1 and carbon coating agent X2 are specified in the above step (I) and step (II). By adding so that the mass ratio (X1 / Therefore, in combination with Particle A, it becomes possible to produce a positive electrode active material mixture for lithium ion secondary batteries that has both high discharge capacity and excellent thermal stability.

Step (I) included in the production method of the present invention includes adding a lithium compound, a metal compound containing at least a manganese compound and an iron compound, a phosphoric acid compound, a carbon coating material X1, and water to obtain slurry water i. This is a step of obtaining preliminary particles bx of primary particles b by subjecting them to a hydrothermal reaction.

Lithium compounds that can be used include hydroxides (eg, LiOH.H ₂ O, LiOH), carbonates, sulfates, and acetates. Among them, hydroxide is preferred.
Manganese compounds that can be used include manganese acetate, manganese nitrate, manganese sulfate, and the like. These may be used alone or in combination of two or more. Among these, manganese sulfate is preferred from the viewpoint of improving battery characteristics.
Examples of iron compounds that can be used include iron acetate, iron nitrate, iron sulfate, and the like. These may be used alone or in combination of two or more. Among these, iron sulfate is preferred from the viewpoint of improving battery characteristics.
In addition, a metal (M ² : M ² is synonymous with M ² in formula (b)) compound other than the manganese compound and the iron compound may be used together with these manganese compounds and iron compounds.
Examples of the phosphoric acid compounds that can be used include orthophosphoric acid (H ₃ PO ₄ , phosphoric acid), metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, ammonium phosphate, ammonium hydrogen phosphate, and the like. Among them, it is preferable to use phosphoric acid, and it is preferable to use it as an aqueous solution having a concentration of 70% by mass to 90% by mass.

The amounts of the lithium compound, the metal compound containing the manganese compound and the iron compound, and the phosphoric acid compound used in the slurry water i may be appropriately determined depending on the composition of the target particles B, and may be prepared according to a conventional method.

The carbon coating material X1 is one or more carbon materials selected from the above-mentioned saccharides, and examples of the carbon coating material X1 include the same carbon material as the carbon coating material X2 used in step (II). Specifically, the same ones as above can be used. Among them, it is preferable to use cellulose nanofibers, lignocellulose nanofibers, chitin nanofibers, or chitosan nanofibers from the viewpoint of effectively increasing the electron conduction path and ensuring high discharge capacity in the obtained battery. Fibers are more preferred.

The amount of carbon coating agent X1 added is determined by the mass ratio (X1/ X2) is 0.05 to 9.0, preferably 0.08 to 6.0, more preferably 0.1 to 3.0.
Further, the amount of carbon coating agent X1 added may be adjusted as appropriate, taking into consideration the carbon content in particles B, in terms of carbon atoms in total with the amount of carbon coating agent X2 added, which will be described later.

The order of addition of these lithium compounds, the metal compound containing at least a manganese compound and an iron compound, the phosphoric acid compound, the carbon coating material X1, and water is not particularly limited. They may be added all at once; It is preferable to add the carbon coating agent X1 after first mixing the acid compound and water.

The solid content concentration of slurry water i is preferably 20 parts by mass to 80 parts by mass, more preferably 30 parts by mass to 70 parts by mass, and even more preferably 40 parts by mass to 60 parts by mass.

After adding water, it is preferable to stir the slurry water i in advance before subjecting it to the hydrothermal reaction. The stirring time of the slurry water i is preferably 1 minute to 30 minutes, more preferably 5 minutes to 20 minutes. Further, the temperature of slurry water ii is preferably 10°C to 50°C, more preferably 15°C to 35°C.

Next, the obtained slurry water i is subjected to a hydrothermal reaction to obtain preliminary particles bx of the primary particles b.
The amount of water used in the hydrothermal reaction is determined based on the solubility of the metal compound, ease of stirring, synthesis efficiency, etc., per mole of phosphate ion contained in slurry water i. , preferably 10 mol to 50 mol, more preferably 12.5 mol to 45 mol.

The hydrothermal reaction is preferably carried out at a temperature of 100°C to 300°C, more preferably a range of 120°C to 250°C. The hydrothermal reaction is preferably carried out in a pressure-resistant container, and when the reaction is carried out at 100°C to 300°C, the pressure at this time is preferably 0.1 MPa to 10 MPa, and when the reaction is carried out at 130°C to 250°C, the pressure is preferably 0.1 MPa to 10 MPa. The pressure is preferably 0.2 MPa to 4.0 MPa. The hydrothermal reaction time is preferably 0.2 hours to 30 hours, more preferably 0.5 hours to 10 hours.
The obtained preliminary particles bx are preferably washed with water after filtration.

Step (II) is a step of adding preliminary particles bx of primary particles b obtained in step (I), carbon coating agent X2, carbon coating inhibitor Y, and water to obtain slurry water ii.
As the carbon coating material X2, as mentioned above, the same carbon material as the carbon coating material X1 can be mentioned.
The amount of the carbon coating material X2 added may be adjusted as appropriate by taking into account the carbon content in the particles B based on the total amount of carbon coating material X1 added in terms of carbon atoms. Specifically, the amount of carbon coating agent X2 added is preferably 0.1 parts by mass to 1.8 parts by mass, more preferably The amount is 0.1 parts by mass to 1.7 parts by mass, more preferably 0.1 parts by mass to 1.5 parts by mass.

The carbon coating inhibitor Y is one or more carbon materials selected from polyols other than sugars, amines, and amides, that is, polyols other than carbon coating agent X1 and carbon coating agent X2, amines, and amides. One or more selected carbon materials. By using such a carbon coating inhibitor Y, after passing through step (II), while a part of the surface of the preliminary particle bx of the primary particle b is coated with the carbon coating inhibitor Y, the carbon coating agent X1 is first applied. The primary particle It becomes possible for carbon to occupy a wide area in the void surrounded by b.
In addition, after going through all the steps, the carbon coating agent X2 is finally carbonized together with the carbon coating agent X1 and coated as carbon on the surface of the primary particles b, while the carbon coating inhibitor Y is burned out and becomes the particle B. will not remain.

Examples of polyols other than saccharides include polyols having two hydroxy groups such as polyethylene glycol with a mass average molecular weight of 1000 or less and polypropylene glycol with a mass average molecular weight of 2000 or less; polyols having three hydroxy groups with a mass average molecular weight of 3000 or less. Examples include polyether polyols having the above. Among them, polyols having a volatilization temperature of 170°C to 400°C are preferred, and more specifically, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, and tetrapropylene glycol. , butanediol, pentanediol, hexanediol, hexanetriol, heptanediol, heptanetriol, octanediol, octanetriol, nonanediol, nonanetriol, decanediol, decanetriol, dodecanediol, and other polyols having two hydroxy groups;
Examples include polyols having three or more hydroxy groups such as glycerin, trimethylolpropane, pentaerythritol, and dipentaerythritol.

As amines and amides, those having a volatilization temperature of 170°C or higher are preferred, and specifically, aliphatic amines such as diethanolamine and triethanolamine, heterocyclic amines such as imidazole; amides such as formamide and acetamide; polyacrylamide , polyamides such as poly-N-vinylacetamide; fatty acid amides such as oleic acid amide and stearic acid amide.

The carbon coating inhibitor Y is preferably ethylene glycol, propylene glycol, glycerin, triethanolamine, or oleic acid amide.

The amount of carbon coating inhibitor Y added is preferably 1.5 parts by mass to 20 parts by mass, more preferably 2.0 parts by mass to 15 parts by mass, based on 100 parts by mass of preliminary particles bx of primary particles b. , more preferably 3.0 parts by mass to 12 parts by mass.
In addition, from the viewpoint of controlling the carbon coating on the surface of the primary particle b to the above-mentioned unique situation, the amount of carbon coating inhibitor Y added is determined by the amount of carbon atoms added in the amount of carbon coating agent X1 and the amount of carbon coating agent X2 added. The mass ratio ((X1+X2)/Y) of the total amount in terms of the amount added to the carbon coating inhibitor Y is preferably 0.05 to 3.00, more preferably 0.10 to 2.00. Yes, more preferably 0.15 to 1.50. Furthermore, the mass ratio (X1/Y) between the amount of carbon coating agent X1 added in terms of carbon atoms and the amount of carbon coating inhibitor Y added is preferably 0.01 to 1.20, more preferably 0. It is .01 to 0.45, more preferably 0.01 to 0.30.

The order of adding the preliminary particles bx of the primary particles b, the carbon coating agent X2, the carbon coating inhibitor Y, and water is not particularly limited, and they may be added all at once, but the preliminary particles bx of the primary particles b, After adding and mixing carbon coating inhibitor Y and water, it is preferable to mix the resulting mixture and carbon coating agent X2.

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

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

Step (III) is a step of subjecting slurry water ii obtained in step (II) above to spray drying to obtain granules bz. Thereby, by coating a part of the surface of the preliminary particle bx of the primary particle b with the carbon coating inhibitor Y, the surface of the preliminary particle bx is appropriately inhibited from being coated with the carbon coating agent X2. Particles bx can be aggregated to form granules bz.

In step (III), in spray drying, operating conditions may be set as appropriate depending on the apparatus used. For example, the processing conditions for a micro mist dryer (MDL-050M manufactured by Fujisaki Electric Co., Ltd.) equipped with a four-fluid nozzle are such that the hot air temperature is preferably 110°C to 300°C, and preferably 150°C to 250°C. is more preferable. Further, the ratio of the supply amount of hot air to the supply amount of slurry water (supply amount of hot air/supply amount of slurry water) is preferably from 500 to 10,000, more preferably from 1,000 to 9,000.

Step (IV) is a step of obtaining particles B by firing the granules bz obtained in step (III) above. The firing conditions for the granules bz in step (IV) are preferably in a reducing atmosphere or inert atmosphere, and the firing temperature is preferably 500°C to 1000°C, more preferably 550°C to 900°C. The firing time is preferably 0.5 to 12 hours, more preferably 1 to 6 hours.

In step (V), particles B obtained in step (IV) above and particles A are mixed so that the content of particles B in the total amount of the positive electrode active material mixture for lithium ion secondary batteries is 10% by mass or more and 30% by mass. This is a step of mixing in an amount less than %. Through this step (V), the positive electrode active material mixture for lithium ion secondary batteries of the present invention can be obtained. Note that the method for producing particles A is as described above. In step (V), these particles A and particles B may be mixed by a conventional method after adjusting the amount of particles B to have the above-mentioned content.

The positive electrode active material mixture for lithium ion secondary batteries of the present invention is a material used as a positive electrode active material of lithium ion secondary batteries. Specifically, for example, a positive electrode slurry is prepared by kneading the positive electrode active material mixture for lithium ion secondary batteries of the present invention with acetylene black, Ketjen black, polyvinylidene fluoride, N-methyl-2-pyrrolidone, etc. After that, it is coated on a current collector and then press-molded to produce a positive electrode.
Lithium ion secondary batteries to which the positive electrode obtained using the positive electrode active material mixture for lithium ion secondary batteries of the present invention can be applied include a positive electrode, a negative electrode, an electrolyte, and a separator, or a positive electrode, a negative electrode, and a solid electrolyte. There is no particular limitation as long as it is an essential configuration.

With the positive electrode active material mixture for lithium ion secondary batteries of the present invention, it is possible to fully draw out the discharge capacity of LMFP, secure a discharge capacity equivalent to or higher than that when NMC is used alone, and it is also excellent. It can also exhibit thermal stability.

Here, the material composition of the negative electrode is not particularly limited as long as it can occlude lithium ions during charging and release them during discharging, and any known material composition can be used. For example, lithium metal, graphite, silicon-based (Si, SiOx), lithium titanate, carbon materials such as amorphous carbon, etc. can be used. It is preferable to use an electrode made 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 may be used.

The electrolytic solution is one in which a supporting salt is dissolved in an organic solvent. The organic solvent is not particularly limited as long as it is an organic solvent normally used in electrolytes of lithium ion secondary batteries, and examples include carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, and lactones. , oxolane compounds, etc. can be used.

The supporting salt is not particularly limited in type, but includes inorganic salts selected from LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ , derivatives of the inorganic salts, LiSO ₃ CF ₃ , LiC(SO ₃ CF ₃ ) ₂ and an organic salt selected from 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 ), and a derivative of the organic salt It is preferable that it is at least one kind of.

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

A solid electrolyte electrically insulates a positive electrode and a 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 , Li _3.25 Ge _0.25 P _0.75 S ₄ , 30Li ₂ S・26B ₂ S ₃・44LiI, 63Li _2S・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 , Li _3.25 P _0.95 S ₄ may be used.

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

Hereinafter, the present invention will be specifically explained based on Examples, but the present invention is not limited to these Examples.
The carbon content of the obtained positive electrode active material particles for lithium ion secondary batteries was measured using a carbon/sulfur analyzer (EMIA-220V2, manufactured by Horiba, Ltd.).
In addition, the coverage of carbon on the surface of each positive electrode active material particle obtained and the area ratio occupied by carbon were determined by photographing each positive electrode active material particle using a TEM (JEM-ARM200F, manufactured by JEOL Ltd.). It was determined according to the method described above.

[Manufacture example 1: Manufacture of particles A1]
After mixing 394 g of nickel sulfate hexahydrate, 254 g of cobalt sulfate heptahydrate, 145 g of manganese sulfate pentahydrate, and 3 L of water so that the molar ratio of Ni:Co:Mn was 5:3:2. 25% ammonia water was added dropwise to the mixed solution 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 metal composite hydroxide mixture b1, and then 37 g of lithium carbonate was mixed into the mixture b1 using a ball mill to obtain a powder mixture c1. The obtained powder mixture c1 was pre-calcined in an air atmosphere at 800°C for 4 hours and then crushed, and then main firing was performed at 800°C in an air atmosphere for 11 hours to form particles A1 (LiNi _0.5 Co _{0 .3} Mn _0.2 O ₂ , average particle size: 12.3 μm, tap density: 2.1 g/cm ³ ).

[Manufacture example 2: Manufacture of particles A2]
Except that 473 g of nickel sulfate hexahydrate, 169 g of cobalt sulfate heptahydrate, 145 g of manganese sulfate pentahydrate, and 3 L of water were mixed so that the molar ratio of Ni:Co:Mn was 6:2:2. Particles A2 (LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , average particle size: 10.9 μm, tap density: 2.2 g/cm ³ ) were obtained in the same manner as in Production Example 1.

[Manufacture example 3: Manufacture of particles B1]
Slurry water i1 was obtained by mixing 1272 g of LiOH·H ₂ O and 4 L of water. Next, 1153 g of an 85% phosphoric acid aqueous solution was added dropwise to the obtained slurry water i1 at a rate of 35 mL/min while stirring for 3 minutes while maintaining the temperature at 25° C., and the mixture was stirred at a speed of 400 rpm for 12 hours to obtain Li ₃ PO. Slurry water i2 containing ₄ was obtained.
The obtained slurry water i2 was purged with nitrogen to make the dissolved oxygen concentration of the slurry water i2 0.5 mg/L, and then 1688 g of _MnSO4.5H2O and _{FeSO4.7H2O were} added to the total amount of slurry water _i2 . 834 g was added to obtain slurry water i3. The molar ratio of added MnSO ₄ and FeSO ₄ (manganese compound: iron compound) was 70:30.

Next, 45 g of cellulose nanofibers (Wma-10002, manufactured by Sugino Machine Co., Ltd., fiber diameter 4 to 20 nm) were added to the obtained slurry water i3, and the mixture was charged into an autoclave and subjected to a hydrothermal reaction at 170° C. for 1 hour. . The pressure inside the autoclave was 0.8 MPa. After the hydrothermal reaction, the produced crystals were filtered and then washed with 12 parts by weight of water per 1 part by weight of the crystals. The washed crystals were freeze-dried at −50° C. for 12 hours to obtain preliminary particles bx ¹ .
1000 g of the obtained preliminary particles bx ¹ were collected, and 1 L of water and 45 g of propylene glycol were added and mixed to obtain slurry water ii5. 135 g of cellulose nanofibers were added to and mixed with the obtained slurry water ii5 to obtain slurry water ii6. The obtained slurry water ii6 was dispersed for 1 minute using an ultrasonic stirrer (T25, manufactured by IKA Co., Ltd.) to uniformly color the whole, and then a spray drying device (MDL-050M, manufactured by Fujisaki Electric Co., Ltd.) was used. Granules bz ¹ were obtained by spray drying. The hot air temperature during spray drying was 200° C., and the ratio of the amount of hot air supplied to the amount of slurry water supplied (the amount of hot air supplied/the amount of slurry water supplied) was 2,500.
The obtained granules bz ¹ were fired at 700° C. for 1 hour in an argon hydrogen atmosphere (hydrogen concentration 3%) to obtain particles B1 (LiMn _0.7 Fe _0.3 PO ₄ , average particle size: 13.6 μm , tap density: 1.1 g/cm ³ ).
FIG. 1 shows a TEM photograph of the surface of the primary particle b formed from the particles B1 obtained in Production Example 3, and FIG. 2 shows a TEM photograph of the cross section of the particle B1.

[Manufacture example 4: Manufacture of particles B2]
Particles B2 (LiMn ^0.7 Fe _{0.3 PO 4} ) was obtained.

[Manufacture example 5: Manufacture of particles B3]
Particles B3 ₍ LiMn ^0.7 Fe _0.3 PO ₄ ) was obtained.

[Manufacture example 6: Manufacture of particles B4]
Particles B4 ₍ LiMn ^0.7 Fe _0.3 PO ₄ ) was obtained.

The physical properties of the obtained particles B1 to B4 are shown in Table 1 below.

[Examples 1 to 6, Comparative Examples 1 to 6]
Using the obtained particles A1-2 and particles B1-B4 as appropriate, these particles were mixed manually using a pestle and mortar according to the formulation shown in Table 3 to obtain each mixture.

《Evaluation of battery characteristics (discharge capacity)》
Each of the obtained mixtures was used as a positive electrode material to produce a positive electrode for a lithium ion secondary battery. Specifically, each of the obtained mixtures, acetylene black, and polyvinylidene fluoride were mixed at a mass ratio of 90:5:5, and N-methyl-2-pyrrolidone was added thereto and thoroughly kneaded. A slurry was prepared. The positive electrode slurry was applied to a current collector made of aluminum foil with a thickness of 20 μm using a coating machine, and vacuum-dried at 80° C. for 12 hours. Thereafter, it was punched out into a disk shape of φ14 mm and pressed using a hand press at 16 MPa for 2 minutes to obtain a positive electrode.

Next, a coin-type secondary battery was constructed using the above positive electrode. A lithium foil punched to a diameter of 15 mm was used as the negative electrode. The electrolytic solution was prepared by dissolving LiPF ₆ at a concentration of 1 mol/L in a mixed solvent of ethylene carbonate and ethyl methyl carbonate at a volume ratio of 3:7. A porous polymer film was used as the separator. These battery parts were assembled and housed in an atmosphere with a dew point of −50° C. or lower by a conventional method to obtain a coin-type secondary battery (CR-2032).
Next, using the obtained coin-shaped secondary battery, the discharge capacity (mAh/g) at 0.2C was measured at a temperature of 30℃ using a discharge capacity measuring device (HJ-1001SD8, manufactured by Hokuto Denko Co., Ltd.). This was taken as the actual measured value.

Furthermore, the discharge capacity (mAh/g) at 0.2C was measured in the same manner when particles A1 to 2 and particles B1 to B4 were each used alone.
Next, based on the content of particles in the mixture, calculate the discharge capacity of each mixture, calculate the ratio (%) of the actual value when the calculated value is 100%, and calculate the discharge capacity. This was used as an evaluation index.

Here, the "calculated value of the discharge capacity as a mixture" means, for example, in the case of Example 1, since particles A1 and particles B1 account for 90% by mass and 10% by mass in 100 mass of the mixture, respectively, from the following formula. means the desired value.
154 (mAh/g) x 0.9 + 132 (mAh/g) x 0.1
=152 (mAh/g)
Therefore, in the case of Example 1, since the actual measured value of the discharge capacity is 154 (mAh/g), the "ratio (%) of the actual measured value to the calculated value of the discharge capacity" means the value obtained by the following formula. do.
{154(mAh/g)/152(mAh/g)}×100=101(%)
For other Examples and Comparative Examples, the calculated values of discharge capacity were determined in the same manner, and the ratio (%) of the actual measured value was calculated when the calculated value was taken as 100%.

Table 2 shows the discharge capacity when particles A1 to 2 and particles B1 to B4 are used alone, and the actual measured value of the discharge capacity as a mixture (mAh/g) and the calculated value of the discharge capacity. Table 3 shows the results regarding the ratio (%).
It should be noted that the higher the ratio of the measured value to the calculated value exceeds 100%, the more excellent the discharge capacity can be evaluated as compared to the case where NMC is used alone.

《Evaluation of thermal stability (measurement of DSC peak temperature)》
Using each of the obtained positive electrode active materials, a DSC curve in a temperature range of 30° C. to 500° C. was obtained by measurement with a differential scanning calorimeter (DSC404 F3, manufactured by NETZSCH). At that time, about 10 mg of the sample was placed in an aluminum pan and measured, and the temperature increase rate was 10° C./min.
Next, the obtained DSC curve was observed and the exothermic peak temperature was determined.
In addition, it can be evaluated that the higher the exothermic peak temperature is, the more excellent the thermal stability is.
The results are shown in Table 3.

Claims (8)

The following formula (A):
_LiNia Co _b Mn _c M ¹ _w O ₂ ...(A)
(In formula (A), ^M1 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. a, b, c and w are 0.3≦a<1, 0<b≦0.7, 0<c≦0.7, Indicates a number that satisfies 0≦w≦0.3, 3a+3b+3c+(valence of ^M1 )×w=3, and 0.3≦a/(a+b+c)<0.7.)
A particle A represented by
The following formula (B):
Li _f Mn _g Fe _h M ² _x PO ₄ ...(B)
(In formula (B), ^M2 is Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, and Gd. Indicates one or more selected elements.f, g, h and x are 0<f≦1.2, 0.3≦g≦1.2, 0.2≦h≦1.2, Indicates a number that satisfies 0≦x≦0.3 and satisfies f+(valence of Mn)×g+(valence of Fe)×h+(valence of ^M2 )×x=3.)
Particle B is an aggregate of primary particles b, which is represented by carbon covering a part of the particle surface and connecting the particles, and has internal voids surrounded by the primary particles b.
A mixture of
In the cross section of particle B, the area ratio occupied by carbon in 100% of the area of voids surrounded by primary particles b is 10% or more,
A positive electrode active material mixture for a lithium ion secondary battery, wherein the content of particles B in the entire mixture is 10% by mass or more and less than 30% by mass. The positive electrode active material mixture for a lithium ion secondary battery according to claim 1, wherein the coverage of carbon on the particle surface of the primary particles b is 5% or more and less than 70%. The positive electrode active material mixture for a lithium ion secondary battery according to claim 1 or 2, wherein the carbon content in the particles B is 0.5% by mass to 2.5% by mass. The positive electrode active material mixture for a lithium ion secondary battery according to claim 1 or 2, wherein g and h in formula (B) are numbers that further satisfy g/(g+h)≦0.8. The positive electrode active material mixture for a lithium ion secondary battery according to claim 1 or 2, wherein the carbon coating the particle surface of the primary particles b is carbon derived from cellulose nanofibers. Next steps (I) to (V):
(I) After adding a lithium compound, a metal compound containing at least a manganese compound and an iron compound, a phosphoric acid compound, a carbon coating material X1, and water to obtain slurry water i, it is subjected to a hydrothermal reaction to form primary particles. Step of obtaining preliminary particles bx of primary particles b (II) Step of obtaining slurry water ii by adding preliminary particles bx of the obtained primary particles b, carbon coating agent X2, carbon coating inhibitor Y, and water (III) Step of obtaining slurry water ii of obtained primary particles b A step of spray-drying the slurry water ii to obtain granules bz. (IV) A step of firing the obtained granules bz to obtain particles B. and mixing in an amount such that the content of particles B in the total amount of the positive electrode active material mixture for lithium ion secondary batteries is 10% by mass or more and less than 30% by mass,
Carbon coating agent X1 and carbon coating agent X2 are one or more types of carbon materials selected from saccharides, and the mass ratio of the amount of carbon coating agent X1 added to the amount of carbon coating agent X2 added (X1/X2 ) is 0.05 to 9.0, and the carbon coating inhibitor Y is one or more carbon materials selected from polyols other than sugars, amines, and amides. A method for producing a positive electrode active material mixture for a lithium ion secondary battery. The method for producing a positive electrode active material mixture for a lithium ion secondary battery according to claim 6, wherein the carbon coating material X1 and the carbon coating material X2 are cellulose nanofibers. The mass ratio ((X1+X2)/Y) of the total amount of the added amount of carbon coating agent X1 and the added amount of carbon coating agent X2 and the added amount of carbon coating inhibitor Y is 0.05 to 3.00. A method for producing a positive electrode active material mixture for a lithium ion secondary battery according to claim 6 or 7.