Positive electrode active material mixture for lithium-ion secondary batteries and method for manufacturing the same

Abstract

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): LiNiaCobMncM1wO2 and a particle B that is represented by formula (B): LifMngFehM2xPO4, 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

Description

[Technical Field]

[0001] The present invention relates to a lithium-ion secondary battery positive electrode active material mixture that can increase the discharge capacity of the lithium-ion secondary battery while ensuring excellent thermal stability, and to a method for producing the same. [Background technology]

[0002] Layered lithium composite oxides, such as layered lithium-nickel-cobalt-manganese composite oxide (NMC), have high discharge capacity and mass energy density, and are widely used as useful cathode active materials for lithium-ion secondary batteries. On the other hand, using such layered lithium composite oxides makes it difficult to ensure sufficient thermal stability, so various techniques have been developed to further add olivine-type cathode materials with high thermal stability.

[0003] For example, Patent Document 1 discloses a positive electrode comprising a positive electrode active material layer containing a lithium metal phosphate compound coated with NMC and carbon, while controlling the average particle size and volume resistivity. Patent Document 2 discloses a positive electrode having a phosphate-carbon composite consisting of an olivine-type phosphate compound coated with NMC and carbon, while controlling the volume resistivity and content. Both attempt to improve thermal stability and other properties. Furthermore, Patent Document 3 discloses a mixed cathode active material comprising a first cathode active material which is an NMC and a second cathode active material which has an olivine structure, aiming to achieve stable output characteristics. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-037380 [Patent Document 2] International Public Relations No. 2016 / 139957 [Patent Document 3] Special Publication No. 2015-519005 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, even with the technologies described in any of the above patent documents, the discharge capacity may be lower than that of a cathode material using NMC alone, and there is still room for improvement.

[0006] Therefore, the object of the present invention is a positive electrode active material mixture for lithium-ion secondary batteries that can combine high discharge capacity and excellent thermal stability in the lithium-ion secondary battery obtained using NMC, and a method for producing the same. [Means for solving the problem]

[0007] Therefore, the inventors conducted diligent research to solve the above problems and found a positive electrode active material mixture for lithium-ion secondary batteries that can exhibit excellent thermal stability while maintaining a high discharge capacity by containing NMC with a Ni content within a specific range and a specific olivine-type transition metal phosphate lithium (LMFP) containing carbon in a specific quantitative relationship.

[0008] In other words, the present invention relates to the following formula (A): LiRing a Co b Mn c M 1 w O2···(A) (In formula (A), M 1 represents one or more elements selected from Mg, Ti, Nb, Fe, Cr, Si, Al, Ga, V, Zn, Cu, Sr, Mo, Zr, Sn, Ta, W, La, Ce, Pb, Bi, and Ge. a, b, c, and w are 0.3 ≤ a < 1, 0 <b≦0.7、0<c≦0.7、0≦w≦0.3、3a+3b+3c+(M 1 Show a number that satisfies (valence of a) × w = 3 and 0.3 ≤ a / (a+b+c) < 0.7. A particle A, Formula (B): Lif Mn g Fe h M 2 x PO4···(B) (In formula (B), M 2 represents one or more elements selected from the group consisting of Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd and Gd. f, g, h and x satisfy 0 < f ≤ 1.2, 0.3 ≤ g ≤ 1.2, 0.2 ≤ h ≤ 1.2, 0 ≤ x ≤ 0.3, and satisfy f + (valence of Mn) × g + (valence of Fe) × h + (valence of M 2 ) × x = 3.) which is an aggregate of primary particles b in which carbon connects between particles while coating part of the surfaces of the particles, and particles B internally having voids surrounded by the primary particles b which is a mixture with in a cross-section of the particles B, the area ratio of carbon in 100% of the total area of the voids surrounded by the primary particles b is 10% or more, the present invention provides a cathode active material mixture for a lithium ion secondary battery, wherein the content of the particles B in the total amount of the mixture is 10 mass% or more and less than 30 mass%.

[0009] The present invention also provides the following steps (I) to (V): (I) a step of adding a lithium compound, a metal compound including at least a manganese compound and an iron compound, a phosphate compound, a carbon coating agent X1, and water to obtain slurry water i, then subjecting the mixture to a hydrothermal reaction to obtain preliminary particles bx of primary particles b (II) a step of adding the obtained preliminary particles bx of primary particles b, a carbon coating agent X2, a carbon coating inhibitor Y, and water to obtain slurry water ii (III) a step of subjecting the obtained slurry water ii to spray drying to obtain a granulated body bz (IV) a step of firing the obtained granulated body bz to obtain particles B (V) a step of mixing the obtained particles B and particles A in an amount such that the content of particles B in the total amount of the cathode active material mixture for a lithium ion secondary battery is 10 mass% or more and less than 30 mass% comprising: Carbon coating agent X1 and carbon coating agent X2 are one or more carbon materials selected from sugars, and the mass ratio (X1 / X2) of the amount of carbon coating agent X1 added to the amount of carbon coating agent X2 added is 0.05 to 9.0, and The present invention provides a method for producing the above-mentioned positive electrode active material mixture for lithium-ion secondary batteries, wherein the carbon coating inhibitor Y is one or more carbon materials selected from polyols other than sugars, amines, and amides. [Effects of the Invention]

[0010] According to the lithium-ion secondary battery positive electrode active material mixture of the present invention, the resulting lithium-ion secondary battery can fully utilize the discharge capacity of LMFP, secure a discharge capacity equal to or greater than that of NMC alone, and exhibit excellent thermal stability. [Brief explanation of the drawing]

[0011] [Figure 1] This is a TEM image of the surface of primary particle b formed by particle B1 obtained by manufacturing 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. [Figure 2] This is a TEM image showing the void surrounded by primary particle b in a cross-section of particle B1 obtained by manufacturing example 3. g indicates the void surrounded by primary particle b, and cr indicates the region occupied by carbon. [Modes for carrying out the invention]

[0012] The present invention will be described in detail below. The positive electrode active material mixture for lithium-ion secondary batteries of the present invention is defined by the following formula (A): LiRing a Co b Mn c M 1 w O2···(A) (In formula (A), M 1represents one or more elements selected from the group consisting of Mg, Ti, Nb, Fe, Cr, Si, Al, Ga, V, Zn, Cu, Sr, Mo, Zr, Sn, Ta, W, La, Ce, Pb, Bi and Ge. a, b, c and w satisfy 0.3 ≤ a < 1, 0 < b ≤ 0.7, 0 < c ≤ 0.7, 0 ≤ w ≤ 0.3, 3a + 3b + 3c + (M 1 valence) × w = 3, and 0.3 ≤ a / (a+b+c) < 0.7).) particles A represented by, and the following formula (B): Li f Mn g Fe h M 2 x PO4···(B) (In formula (B), M 2 represents one or more elements selected from the group consisting of Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd and Gd. f, g, h and x satisfy 0 < f ≤ 1.2, 0.3 ≤ g ≤ 1.2, 0.2 ≤ h ≤ 1.2, 0 ≤ x ≤ 0.3, and f + (valence of Mn) × g + (valence of Fe) × h + (M 2 valence) × x = 3.) particles B represented by, which are aggregates of primary particles b, wherein carbon covers a part of the surface of the particles and connects the particles, and voids surrounded by the primary particles b are internally present which is a mixture with in a cross-section of the particles B, the area ratio of carbon to 100% of the total area of the voids surrounded by the primary particles b is 10% or more, the content of the particles B in the total amount of the mixture is 10 mass% or more and less than 30 mass%.

[0013] As described above, 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, which contains a specific amount of NMC particles A having a Ni content within a specific range, and LMFP particles B formed by aggregating primary particles each having a unique morphology where carbon is coated on the particle surface. Accordingly, in the resulting lithium ion secondary battery, thermal stability can be effectively improved without unnecessarily decreasing the discharge capacity.

[0014] The particles A constituting the positive electrode active material mixture for lithium-ion secondary batteries of the present invention are represented by the following formula (A). LiRing a Co b Mn c M 1 w O2···(A) (In formula (A), M 1 represents one or more elements selected from Mg, Ti, Nb, Fe, Cr, Si, Al, Ga, V, Zn, Cu, Sr, Mo, Zr, Sn, Ta, W, La, Ce, Pb, Bi, and Ge. a, b, c, and w are 0.3 ≤ a < 1, 0 <b≦0.7、0<c≦0.7、0≦w≦0.3、3a+3b+3c+(M 1 Show a number that satisfies (valence of a) × w = 3 and 0.3 ≤ a / (a+b+c) < 0.7.

[0015] The particle A represented by the above formula (A) is a Li-Ni-Co-Mn oxide particle (NMC particle), also known as a lithium composite oxide particle, which is an aggregate of primary particles and has a layered rock salt structure. Furthermore, as a, b, and c in formula (A) satisfy 0.3 ≤ a / (a+b+c) < 0.7, it is a limited amount of particle in which the molar amount of Ni in the total molar amount of Ni, Co, and Mn is 30% or more and less than 70%. By including such particle A together with particle B, which will be described later, in a specific amount, it is possible to improve thermal stability while effectively preventing an unnecessary decrease in discharge capacity.

[0016] M in equation (A) 1 This 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. Furthermore, in equation (A) above, a, b, c, and w are 0.3 ≤ a < 1, 0 <b≦0.7、0<c≦0.7、0≦w≦0.3、かつ3a+3b+3c+(M 1 It is a number that satisfies the following conditions: (valence of a) × w = 3 and 0.3 ≤ a / (a+b+c) < 0.7.

[0017] In particle A, Ni, Co, and Mn are known to have excellent electronic conductivity and contribute to battery capacity and output characteristics. Furthermore, from the viewpoint of thermal stability, some of these transition elements are other metallic elements M 1 It is preferable that these metal elements M are substituted. 1 By being substituted, the crystal structure of particle A is stabilized, so it is thought that the destruction of the crystal structure can be suppressed even when charging and discharging is repeated, and excellent thermal stability can be ensured. In particular, a, b, and c in formula (A) above are preferably numbers that satisfy 0.35 ≤ a / (a+b+c) ≤ 0.65, and more preferably numbers that satisfy 0.45 ≤ a / (a+b+c) ≤ 0.60.

[0018] Specifically, such particle A could be, for example, LiNi 0.33 Co 0.33 Mn 0.34 O2, LiLiLi 0.4 Co 0.3 Mn 0.3 O2, LiLiLi 0.5 Co 0.3 Mn 0.2 O2, LiLiLi 0.6 Co 0.2 Mn 0.2 O2, LiLiLi 0.6 Co 0.19 Mn 0.2 Al 0.01 O2, LiLiLi 0.6 Co 0.19 Mn 0.2 Mg 0.01 O2, LiLiLi 0.33 Co 0.31 Mn 0.33 Mg 0.03 O2, or LiNi 0.33 Co 0.31 Mn 0.33 Zn 0.03 Examples include O2, among others, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiLiLi 0.5 Co 0.3 Mn 0.2 O2, LiLiLi 0.33 Co 0.33 Mn0.34 O2, LiLiLi 0.33 Co 0.31 Mn 0.33 Mg 0.03 Particles made of O2 are preferred.

[0019] Furthermore, particle A may form a core-shell structure having a core portion (internal) and a shell portion (surface) with different compositions. By forming particle A with this core-shell structure, NMC-based composite oxide particles with a high Ni concentration that easily dissolve in the electrolyte can be placed in the core portion, and NMC-based composite oxide particles with a low Ni concentration can be placed in the shell portion that is in contact with the electrolyte, thus reducing the amount of metal components (Ni, Mn, Co, M) released from particle A into the electrolyte. 1 The elution of ) can be suppressed. In this case, the core portion may be a single phase or may be composed of two or more phases with different compositions. As an embodiment in which the core portion is composed of two or more phases, it may be a structure in which multiple phases are stacked in layers in a concentric circle, or it may be a structure in which the composition changes transitionally from the surface to the center of the core portion. Furthermore, the shell portion only needs to be formed on the outside of the core portion, and like the core portion, it may be a single phase or it may be composed of two or more phases with different compositions.

[0020] Furthermore, particle A may be coated with a metal oxide, metal fluoride, or metal phosphate. By coating the NMC particles with these metal oxides, metal fluorides, or metal phosphates, the metal components (Ni, Mn, Co, M) from the NMC particles are removed from the electrolyte. 1 The elution of ) can be suppressed. As such a coating, one or more selected from CeO2, SiO2, MgO, Al2O3, ZrO2, TiO2, ZnO, RuO2, SnO2, CoO, Nb2O5, CuO, V2O5, MoO3, La2O3, WO3, AlF3, NiF2, MgF2, LiF, Li3PO4, Li4P2O7, LiPO3, Li2PO3F, and LiPO2F2, or a composite thereof, can be used.

[0021] The average particle size of particle A as a primary particle is 50 nm to 500 nm, more preferably 50 nm to 300 nm, from the viewpoint of suppressing the amount of expansion and contraction of the primary particle due to the insertion and deinsertion of lithium ions, effectively preventing particle cracking, and from the viewpoint of handling. Furthermore, the average particle size of particle A, which is an aggregate of the primary particles (secondary particles) described above (simply referred to as "average particle size of particle A"), is preferably 3 μm to 20 μm, and more preferably 5 μm to 15 μm, from the viewpoint of ensuring excellent thermal stability and handling. Here, the "average particle size" of particle A is obtained from the volume-based particle size distribution based on laser diffraction and scattering. 50 This value represents the particle size (median diameter) at a cumulative 50% level.

[0022] From the viewpoint of ensuring high discharge capacity and ease of handling, the tap density of particle A is preferably 1.5 g / cm³. 3 ~3.5g / cm 3 More preferably 2.0 g / cm³ 3 ~3.0g / cm 3 That is the case. Furthermore, tap density, as used below, refers to the "tap bulk density" measured by the method specified in JIS R 1628 "Method for Measuring the Bulk Density of Fine Ceramic Powders".

[0023] Furthermore, since the lithium-ion secondary battery positive electrode active material mixture of the present invention consists of particles A and particles B, the content of particle A in the total amount of such mixture may be the remainder of particle B, as described later.

[0024] Particle A can be obtained, for example, by the following manufacturing method. Specifically, the manufacturing method comprises the steps of (Ia) preparing slurry water a by adding a nickel compound, a cobalt compound, a manganese compound, and water, filtering and drying the slurry water a to obtain mixture A, and (IIa) adding a lithium compound to the obtained mixture A and mixing it, and then calcining it.

[0025] Examples of the nickel compound used in step (Ia) include nickel sulfate, nickel acetate, etc. These may be used alone singly, or may be used in combination of two or more. Among these, nickel sulfate is preferable from the viewpoint of improving battery characteristics. Examples of the cobalt compound include cobalt acetate, cobalt nitrate, cobalt sulfate, etc. These may be used alone singly, or may be used in combination of two or more. Among these, cobalt sulfate is preferable from the viewpoint of improving battery characteristics. Examples of the manganese compound include manganese acetate, manganese nitrate, manganese sulfate, etc. These may be used alone singly, or may be used in combination of two or more. Among these, manganese sulfate is preferable from the viewpoint of improving battery characteristics. Note that together with these nickel compounds, cobalt compounds, and manganese compounds, a metal other than these compounds (M 1 ) compound may also be used. Examples of the lithium compound include hydroxides (e.g., LiOH·H₂O, LiOH), carbonates, sulfates, and acetates. Among these, carbonates are preferable.

[0026] In step (Ia), when obtaining slurry water a, it is preferable to adjust the pH to 8 to 13, and the adjustment may be performed, for example, by dropping ammonia water.

[0027] In step (IIa), when firing, it is preferable to first perform calcination 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 perform main firing at 500°C to 1000°C, preferably 600°C to 900°C, for 1 hour to 15 hours, preferably 5 hours to 13 hours. Further, it is preferable to perform crushing after calcination before subjecting to main firing.

[0028] Particles B constituting the positive electrode active material mixture for a lithium ion secondary battery of the present invention are represented by the following formula (B): Li f Mn g Fe h M 2 x PO₄···(B) (In formula (B), M 2 represents one or more elements selected from the group consisting of Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd and Gd. f, g, h and x satisfy 0<f≤1.2, 0.3≤g≤1.2, 0.2≤h≤1.2, 0≤x≤0.3, and f + (valence of Mn)×g + (valence of Fe)×h + (valence of M 2 )×x = 3.) , which is an aggregate of primary particles b where carbon connects the particles while covering a part of the surface of each particle, and has voids enclosed by the primary particles b therein. In the cross-section of the particle B, the proportion of area occupied by carbon in 100% of the area of the voids enclosed by the primary particles b is 10% or more.

[0029] That is, the particle B represented by formula (B) above is a so-called olivine-type lithium transition metal phosphate compound (LMFP particles) containing both manganese (Mn) and iron (Fe) as transition metals, and is an aggregate of primary particles b. Carbon is unevenly distributed on the surface of the primary particles b to cover a part of the surface, and certain voids exist in the particle B formed by aggregation of the primary particles b, while the carbon on the surface of the primary particles b connects between adjacent primary particles b. Therefore, among the voids inside the particle B, there are voids enclosed by the primary particles b. When observing the cross-section of the particle B, carbon accounts for 10% or more of the total area of the voids enclosed by the primary particles b, meaning that carbon, while unevenly distributed on the surface of primary particles b, widely occupies the space between the primary particles b. As described above, since the particle B is an aggregate of primary particles b in which carbon covering a part of the surface exists in a specific state, it can improve the efficiency of electronic conduction paths between primary particles and sufficiently bring out the discharge capacity of LMFP, compared with, for example, particles that uniformly cover the entire surface of primary particles. As will be described later, when such particle B is used in combination with particle A in a specific amount, a high discharge capacity can be ensured.

[0030] In formula (B) above, M 2represents 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 discharge capacity, Mg, Al, Ti, Zn, Nb, Co, Zr or Gd are preferred. In addition, f, g, h and x in the above formula (B) satisfy 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+(M 2 valence)×x=3.

[0031] As the lithium-based polyanion particles represented by the above formula (B), from the viewpoint of improving discharge capacity, for f, 0.6≦f≦1.2 is preferred, 0.65≦f≦1.15 is more preferred, and 0.7≦f≦1.1 is even more preferred. For g, 0.4≦g≦0.8 is preferred. For h, 0.2≦h≦0.6 is preferred. For x, 0≦x≦0.2 is preferred, 0≦x≦0.15 is more preferred, and 0≦x≦0.1 is even more preferred. Among these, from the viewpoint of achieving both high discharge capacity and effective electron conductivity, it is preferred that g and h are numbers satisfying g / (g+h)≦0.8, more preferred that they are numbers satisfying 0.2≦g / (g+h)≦0.8, and even more preferred that they are numbers satisfying 0.3≦g / (g+h)≦0.75.

[0032] Specifically, for example, LiMn 0.3 Fe 0.7 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.45 Fe 0.55 PO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.8 Fe 0.2 PO4, LiMn 0.75 Fe 0.15 Mg 0.1 PO4, LiMn 0.75 Fe 0.19 Zr 0.03 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.5Fe 0.5 PO4, Li 1.2 Mn 0.63 Fe 0.27 PO4, or Li 0.6 Mn 0.84 Fe 0.36 Examples include PO4, among others. LiMn 0.7 Fe 0.3 PO4, LiMn 0.45 Fe 0.55 PO4 is preferred.

[0033] The primary particle b that forms particle B has a portion of its surface coated with carbon. This carbon is formed by carbonizing one or more carbon materials selected from sugars, and this carbon coats the surface of primary particle b. The one or more carbon materials selected from sugars (corresponding to "carbon coating agent X1 and carbon coating agent X2" as described later) are carbonized to carbon, and through the interposition of one or more carbon materials selected from polyols, amines, and amides other than sugars (corresponding to "carbon coating inhibitor Y" as described later), they become unevenly distributed and coat the surface of primary particle b. Furthermore, the carbon coating on the surface of primary particle b is derived from one or more carbon materials selected from sugars, while one or more carbon materials selected from polyols, amines, and amides other than sugars do not remain on primary particle b.

[0034] Specifically, examples of carbon materials selected from sugars include monosaccharides such as glucose, fructose, galactose, and mannose; disaccharides such as maltose, sucrose, and cellobiose; polysaccharides such as starch, dextrin, and cellulose; and one or more nanofibers of polysaccharides such as cellulose nanofibers, lignocellulose nanofibers, chitin nanofibers, and chitosan nanofibers. In particular, from the viewpoint of effectively enhancing the electronically conductive path and ensuring high discharge capacity, cellulose nanofibers, lignocellulose nanofibers, chitin nanofibers, or chitosan nanofibers are preferred, with cellulose nanofibers being more preferred.

[0035] The carbon coverage on the surface of primary particle b is preferably 5% to less than 70%, more preferably 5% to less than 50%, even more preferably 10% to 48%, and even more preferably 15% to 45%, from the viewpoint of controlling such values ​​to a low and limited range, unevenly distributing carbon on the surface of primary particle b, connecting primary particle b while occupying a wide area in the voids within particle b, and improving the efficiency of the electronically conductive path to effectively increase the discharge capacity.

[0036] The "carbon coverage (%)" on the surface of primary particle b refers to the value obtained by the following method. Specifically, as shown in Figure 1, first, the surface of primary particle b is observed in a field of view 1, in which particles of the lithium-ion secondary battery positive electrode active material mixture are photographed using a TEM electron microscope, and the surface of primary particle b that is not covered with carbon and the surface of primary particle b that is covered with carbon are identified. Next, the "perimeter xn of the surface of primary particle b that is not covered with carbon" and the "perimeter xc of the surface of primary particle b that is covered with carbon" are measured in this field of view, and xn and xc are added together to obtain the "total perimeter xA of the surface of primary particle b". The obtained values ​​of "total circumferential length xA of the surface of primary particle b" and "circumferential length xc of the surface of primary particle b coated with carbon" are introduced into the following formula (1) to calculate the carbon coverage rate (%) in one field of view, and the values ​​obtained over 50 fields of view are averaged to obtain the carbon coverage rate (%) on the surface of primary particle b. Carbon coverage (%) = {(Circumference xc of the surface of particle X, which is coated with carbon) / (Total circumference of particle X's surface xA)} × 100 ... (1)

[0037] Primary particles b, each having a carbon coating on part of its surface, connect to each other. In particle B, formed by the aggregation of such primary particles b, there is an internal void surrounded by primary particles b. The "void surrounded by primary particles b" refers to the void formed by the primary particles b that is completely blocked on all sides, as shown as "g" in Figure 2 when observing the cross-section of particle B. The carbon coating on part of the surface of primary particles b occupies a large area within this void and connects the primary particles b, thus promoting an efficient electron conduction path and contributing to an increase in discharge capacity. Furthermore, in the cross-section of particle B, the area ratio occupied by carbon within 100% of the area of ​​the void surrounded by primary particle b is 10% or more, preferably 10% to 90%, more preferably 10% to 70%, and even more preferably 10% to 50%, from the viewpoint of unevenly distributing carbon on the surface of primary particle b, connecting primary particle b while occupying a wide area in the void within particle B, and improving the efficiency of the electron conduction path.

[0038] In the cross-section of particle B, the area ratio of carbon within 100% of the area of ​​the void surrounded by primary particle b refers to the value obtained by the following method. Specifically, first, using a TEM electron microscope, the cross-section of particle B constituting the positive electrode active material mixture for lithium-ion secondary batteries is photographed, and the voids within particle B that are surrounded by primary particle b are observed in one field of view. Next, the smallest particle among the primary particle b surrounding these voids is selected, and 50 fields of view are selected where the void area is 0.3 to 1.5 times the area of ​​the selected particle. The area ratio of carbon within 100% of the void area is calculated, and the average value is determined as the area ratio (%) of carbon within 100% of the area of ​​the void surrounded by primary particle b.

[0039] The average particle size of primary particles b is preferably 70 nm to 200 nm, more preferably 90 nm to 170 nm, from the viewpoint of suppressing the amount of expansion and contraction associated with the insertion and deinsertion of lithium ions, effectively enhancing the electronically conductive path, and ease of handling. Furthermore, the average particle size of particle B formed by the aggregation of primary particle b is preferably 10 μm to 30 μm, and more preferably 12 μm to 20 μm, from the viewpoint of obtaining a battery with excellent thermal stability and handling. Here, the "average particle size" for primary particle b refers to the value obtained by calculating the crystallite size using the XRD / Leber method from the X-ray diffraction pattern. Furthermore, the "average particle size" for particle B refers to the D value obtained from the volume-based particle size distribution based on laser diffraction and scattering. 50 This value represents the particle size (median diameter) at a cumulative 50% level.

[0040] The carbon content in particle B corresponds to the carbon content obtained by carbonization of the carbon material in primary particle b, and is preferably 0.5% to 2.5% by mass, more preferably 0.6% to 2.0% by mass, and even more preferably 0.7% to 1.8% by mass in particle B.

[0041] The carbon contained in particle B is the carbon obtained by carbonizing the carbon material present on the surface of the primary particle b that forms it, that is, it corresponds to the atomic amount of the carbon material, and can be determined by measurement using a carbon-sulfur analyzer.

[0042] From the viewpoint of improving electrode density and increasing discharge capacity, the tap density of particle B is preferably 0.8 g / cm³. 3 ~1.6g / cm 3 More preferably 0.9 g / cm³ 3 ~1.6g / cm 3 That is the case.

[0043] The positive electrode active material mixture for lithium-ion secondary batteries of the present invention is a mixture of particle A and particle B. The content of particle B in the total amount of such mixture is 10% by mass or more and less than 30% by mass, preferably 12% to 25% by mass, and more preferably 14% to 25% by mass, from the viewpoint of ensuring excellent thermal stability while allowing sufficient discharge capacity by LMFP to be extracted by particle B.

[0044] The lithium-ion secondary battery positive electrode active material mixture of the present invention uses the above particle A and follows the following steps (I) to (V): (I) A step in which a lithium compound, a metal compound containing at least a manganese compound and an iron compound, a phosphate compound, a carbon coating agent X1, and water are added to obtain slurry water i, and then subjected to a hydrothermal reaction to obtain preliminary particles bx of primary particles b. (II) Steps to obtain slurry water ii by adding the obtained primary particle bx, carbon coating agent X2, carbon coating inhibitor Y, and water to the obtained primary particle b. (III) Step of obtaining granules bz by spray drying the obtained slurry water ii. (IV) Step of calcining the obtained granules bz to obtain particles B (V) A step of mixing the obtained particle B and particle A in an amount such that the content of particle B in the total amount of lithium-ion secondary battery positive electrode active material mixture is 10% by mass or more and less than 30% by mass. Equipped with, Carbon coating agent X1 and carbon coating agent X2 are one or more carbon materials selected from sugars, and the mass ratio (X1 / X2) of the amount of carbon coating agent X1 added to the amount of carbon coating agent X2 added 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, and can be obtained by a manufacturing method.

[0045] Thus, by using specific carbon coating agents X1 and X2, and carbon coating inhibitor Y, and adding carbon coating agent X1 and carbon coating agent X2 in a specific mass ratio (X1 / X2) in steps (I) and (II) above, primary particles b in which carbon is coated on the particle surface in the unique form described above can be obtained, and further particles B formed by the aggregation of these primary particles can be obtained. Therefore, in combination with particle A, it becomes possible to manufacture a positive electrode active material mixture for lithium-ion secondary batteries that possesses both high discharge capacity and excellent thermal stability.

[0046] Step (I) of the manufacturing method of the present invention is a step of adding a lithium compound, a metal compound containing at least a manganese compound and an iron compound, a phosphoric acid compound, a carbon coating agent X1, and water to obtain slurry water i, and then subjecting it to a hydrothermal reaction to obtain preliminary particles bx of primary particles b.

[0047] Examples of lithium compounds that can be used include hydroxides (e.g., LiOH·H2O, LiOH), carbonates, sulfates, and acetates. Among these, hydroxides are preferred. Examples of manganese compounds that can be used include manganese acetate, manganese nitrate, and manganese sulfate. These may be used individually 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, and iron sulfate. These may be used individually or in combination of two or more. Among these, iron sulfate is preferred from the viewpoint of improving battery characteristics. Furthermore, along with these manganese and iron compounds, metals other than manganese and iron compounds (M 2 :M 2 M in equation (b) 2 Compounds (synonymous with) may also be used. Examples of usable phosphoric acid compounds include orthophosphoric acid (H3PO4, phosphoric acid), metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, ammonium phosphate, and ammonium hydrogen phosphate. Among these, phosphoric acid is preferred, and it is preferable to use it as an aqueous solution with a concentration of 70% to 90% by mass.

[0048] The amounts of lithium compounds, manganese compounds, iron compounds, and other metal compounds, as well as phosphate compounds, used in slurry water i should be determined appropriately according to the composition of the target particles B, and the mixture should be prepared according to a conventional method.

[0049] The carbon coating agent X1 is one or more carbon materials selected from the above-mentioned sugars, and the carbon material used for the carbon coating agent X1 is the same as the carbon coating agent X2 used in step (II). Specifically, the same materials as described above can be used. In particular, from the viewpoint of effectively enhancing the electron conductivity path and ensuring a high discharge capacity in the resulting battery, it is preferable to use cellulose nanofibers, lignocellulose nanofibers, chitin nanofibers, or chitosan nanofibers, with cellulose nanofibers being more preferable.

[0050] The amount of carbon coating agent X1 added is, from the viewpoint of controlling the carbon coating on the surface of primary particle b to the above-described specific conditions, a mass ratio (X1 / X2) of X1 to X2 of the amount of carbon coating agent X2 added in step (II) described later, of 0.05 to 9.0, preferably 0.08 to 6.0, and more preferably 0.1 to 3.0. Furthermore, the amount of carbon coating agent X1 added can be appropriately adjusted, taking into account the carbon content in particle B, by calculating the carbon dioxide equivalent of the total amount of carbon coating agent X1 added and carbon coating agent X2, which will be described later.

[0051] The order in which these lithium compounds, metal compounds including at least manganese compounds and iron compounds, phosphate compounds, carbon coating agent X1, and water are added is not particularly limited and they may be added all at once, but it is preferable to mix the metal compounds, phosphate compounds and water first, and then add the carbon coating agent X1.

[0052] The solid content concentration of slurry water i is preferably 20 to 80 parts by mass, more preferably 30 to 70 parts by mass, and even more preferably 40 to 60 parts by mass.

[0053] It is preferable to pre-stir the slurry water i after adding water and before subjecting it to the hydrothermal reaction. The stirring time for the slurry water i is preferably 1 to 30 minutes, more preferably 5 to 20 minutes. The temperature of the slurry water ii is preferably 10°C to 50°C, more preferably 15°C to 35°C.

[0054] 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 when subjecting the reaction to the hydrothermal reaction is preferably 10 to 50 moles, and more preferably 12.5 to 45 moles, per mole of phosphate ions contained in slurry water i, from the viewpoint of solubility of the metal compound, ease of stirring, and efficiency of synthesis.

[0055] The hydrothermal reaction is preferably carried out at 100°C to 300°C, and more preferably at 120°C to 250°C. The hydrothermal reaction is preferably carried out in a pressure vessel, and when the reaction is carried out at 100°C to 300°C, the pressure 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 0.2 MPa to 4.0 MPa. The hydrothermal reaction time is preferably 0.2 hours to 30 hours, and more preferably 0.5 hours to 10 hours. The obtained preliminary particles bx should be filtered and then washed with water.

[0056] Step (II) is a step in which preliminary particles bx of the primary particles b obtained in step (I), carbon coating agent X2, carbon coating inhibitor Y, and water are added to obtain slurry water ii. As mentioned above, the carbon material used for carbon coating agent X2 is the same as that used for carbon coating agent X1. The amount of carbon coating agent X2 added can be adjusted as appropriate, taking into account the carbon content in particle B, by calculating the carbon atoms in the total amount of carbon coating agent X2 added along with the amount of carbon coating agent X1 added. Specifically, the amount of carbon coating agent X2 added is preferably 0.1 to 1.8 parts by mass, more preferably 0.1 to 1.7 parts by mass, and even more preferably 0.1 to 1.5 parts by mass, per 100 parts by mass of the preliminary particles bx of the primary particles b, in terms of carbon atoms.

[0057] The carbon coating inhibitor Y is one or more carbon materials selected from polyols other than sugars, amines, and amides, i.e., one or more carbon materials selected from polyols other than carbon coating agents X1 and carbon coating agents X2, and from polyols, amines, and amides. By using such a carbon coating inhibitor Y, after going through step (II), the carbon coating inhibitor Y coats a portion of the surface of the preliminary particle bx of the primary particle b, while moderately inhibiting the further coating of the surface of the preliminary particle bx of the primary particle b, which is surrounded by the carbon coating agent X1 that coats the vicinity of the surface. This makes it possible to unevenly distribute carbon on the surface of the primary particle b while allowing carbon to occupy a large area in the voids surrounded by the primary particle b. Furthermore, after all the steps have been completed, the carbon coating agent X2 is ultimately carbonized together with the carbon coating agent X1 and coats the surface of the primary particle b as carbon, while the carbon coating inhibitor Y is burned away and does not remain on particle B.

[0058] Examples of polyols other than sugars include polyethylene glycol with a mass-average molecular weight of 1000 or less, polypropylene glycol with a mass-average molecular weight of 2000 or less, which have two hydroxyl groups; and polyether polyols with a mass-average molecular weight of 3000 or less, which have three or more hydroxyl groups. Among these, polyols with a volatilization temperature of 170°C to 400°C are preferred, and more specifically, polyols having two hydroxyl groups such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, butanediol, pentanediol, hexanediol, hexanetriol, heptanediol, heptanetriol, octanediol, octantriol, nonanediol, nonanetriol, decanediol, decanetriol, and dodecanediol; Examples include polyols having three or more hydroxyl groups, such as glycerin, trimethylolpropane, pentaerythritol, and dipentaerythritol.

[0059] As amines and amides, those with a volatilization temperature of 170°C or higher are preferred. Specifically, examples include aliphatic amines such as diethanolamine and triethanolamine, heterocyclic amines such as imidazole; amides such as formamide and acetamide; polyamides such as polyacrylamide and poly-N-vinylacetamide; and fatty acid amides such as oleamide and stearamide.

[0060] The carbon coating inhibitor Y is preferably ethylene glycol, propylene glycol, glycerin, triethanolamine, or oleic acid amide.

[0061] The amount of carbon coating inhibitor Y added is preferably 1.5 to 20 parts by mass, more preferably 2.0 to 15 parts by mass, and even more preferably 3.0 to 12 parts by mass, per 100 parts by mass of the reserve particles b of the primary particles b. Furthermore, the amount of carbon coating inhibitor Y added is, from the viewpoint of controlling the carbon coating on the surface of primary particle b to the above-mentioned specific conditions, preferably, 0.05 to 3.00, more preferably 0.10 to 2.00, and even more preferably 0.15 to 1.50, as the mass ratio (X1 / Y) of the total amount of carbon coating agent X1 and carbon coating agent X2 added in terms of carbon atoms to the amount of carbon coating inhibitor Y added.

[0062] The order in which the primary particle b's reserve particles bx, carbon coating agent X2, carbon coating inhibitor Y, and water are added is not particularly limited and they may be added all at once. However, it is preferable to add and mix the primary particle b's reserve particles bx, carbon coating inhibitor Y, and water beforehand, and then mix the resulting mixture with the carbon coating agent X2.

[0063] The solid content concentration of slurry water II is preferably 30% to 70% by mass, more preferably 35% to 65% by mass, and even more preferably 40% to 60% by mass.

[0064] It is preferable to pre-stir the slurry water ii after adding water and before proceeding to step (III). The stirring time for the slurry water ii is preferably 1 to 30 minutes, more preferably 5 to 20 minutes. The temperature of the slurry water b is preferably 10°C to 50°C, more preferably 15°C to 35°C.

[0065] Step (III) is a step in which the slurry water ii obtained in step (II) is subjected to spray drying to obtain granules bz. In this step, the carbon coating inhibitor Y coats a portion of the surface of the preliminary particles bx of the primary particles b, thereby moderately inhibiting the coating of the surface of the preliminary particles bx with the carbon coating agent X2, while causing the preliminary particles bx to aggregate and form granules bz.

[0066] In step (III), the operating conditions for spray drying can be set appropriately depending on the equipment used. For example, when using a micro-mist dryer equipped with four fluid nozzles (MDL-050M manufactured by Fujisaki Electric Co., Ltd.), the hot air temperature is preferably 110°C to 300°C, and more preferably 150°C to 250°C. In addition, the ratio of the hot air supply amount to the slurry water supply amount (hot air supply amount / slurry water supply amount) is preferably 500 to 10000, and more preferably 1000 to 9000.

[0067] Step (IV) is a step in which the granular body bz obtained in step (III) is calcined to obtain particles B. The calcination conditions for the granular body bz in step (IV) are preferably in a reducing atmosphere or an inert atmosphere, the calcination temperature is preferably 500°C to 1000°C, more preferably 550°C to 900°C, and the calcination time is preferably 0.5 hours to 12 hours, more preferably 1 hour to 6 hours.

[0068] Step (V) is a step in which particles B obtained in step (IV) above and particles A are mixed in an amount such that the content of particles B in the total amount of lithium-ion secondary battery positive electrode active material mixture is 10% by mass or more and less than 30% by mass. By going through step (V), the lithium-ion secondary battery positive electrode active material mixture of the present invention can be obtained. The method for producing particles A is as described above. In step (V), particles A and particles B are mixed by a conventional method after adjusting the amount of particles B to the above-mentioned content.

[0069] The lithium-ion secondary battery positive electrode active material mixture of the present invention is a material used as a positive electrode active material for lithium-ion secondary batteries. Specifically, for example, a positive electrode slurry is prepared by kneading the lithium-ion secondary battery positive electrode active material mixture of the present invention with acetylene black, Ketjenblack, polyvinylidene fluoride, N-methyl-2-pyrrolidone, etc., then coating it onto a current collector, and then press-molding to produce a positive electrode. The lithium-ion secondary battery to which the positive electrode obtained using the lithium-ion secondary battery positive electrode active material mixture of the present invention can be applied is not particularly limited as long as it has 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.

[0070] The lithium-ion secondary battery positive electrode active material mixture of the present invention can fully extract the discharge capacity of LMFP and secure a discharge capacity equal to or greater than that of NMC alone, while also exhibiting excellent thermal stability.

[0071] Here, the negative electrode is not particularly limited in its material composition as long as it can absorb lithium ions during charging and release them during discharge; known material compositions can be used. For example, lithium metal, graphite, silicon-based materials (Si, SiOx), lithium titanate, or amorphous carbon materials can be used. It is preferable to use an electrode formed of an intercalate material capable of electrochemically absorbing and releasing lithium ions, especially 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.

[0072] The electrolyte is prepared by dissolving a support salt in an organic solvent. The organic solvent is not particularly limited as long as it is an organic solvent commonly used in the electrolyte of lithium-ion secondary batteries. For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, oxolane compounds, etc., can be used.

[0073] The supporting salt is not particularly limited in type, but is preferably at least one of the following: an inorganic salt selected from LiPF6, LiBF4, LiClO4, and LiAsF6; a derivative of the inorganic salt; an organic salt selected from LiSO3CF3, LiC(SO3CF3)2, LiN(SO3CF3)2, LiN(SO2C2F5)2, and LiN(SO2CF3)(SO2C4F9); and a derivative of the organic salt.

[0074] The separator serves to electrically insulate the positive and negative electrodes and to hold the electrolyte. For example, a porous synthetic resin membrane, particularly a porous membrane made of polyolefin polymers (polyethylene, polypropylene), can be used.

[0075] Solid electrolytes electrically insulate the positive and negative electrodes and exhibit high lithium-ion conductivity. For example, La 0.51 Li 0.34 TiO 2.94 Li 1.3 Al 0.3 Ti 1.7(PO4)3, Li7La3Zr2O 12 , 50Li4SiO4·50Li3BO3, Li 2.9 PO 3.3 N 0.46 Li 3.6 Si 0.6 P 0.4 O4, Li 1.07 Al 0.69 Ti 1.46 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, Li 10 GeP2S 12 Li 3.25 Ge 0.25 P 0.75 S4, 30Li2S 26B2S3 44LiI, 63Li2S 36SiS2 1Li3PO4, 57Li2S 38SiS2 5Li4SiO4, 70Li2S 30P2S5, 50Li2S 50GeS2, Li7P3S 11 Li 3.25 P 0.95 Use S4.

[0076] The shape of the lithium-ion secondary battery having the above configuration is not particularly limited and may be various shapes such as coin-type, cylindrical, or prismatic, or it may be an irregular shape enclosed in a laminate casing. [Examples]

[0077] The present invention will be described in detail below 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.). Furthermore, the carbon coverage rate and the area percentage occupied by carbon on the surface of each obtained positive electrode active material particle were determined by imaging each positive electrode active material particle using a TEM (JEM-ARM200F, manufactured by JEOL Ltd.) and following the method described above.

[0078] [Manufacturing Example 1: Manufacturing of Particle A1] To obtain a slurry a1 containing a metal composite hydroxide with a pH of 11, 394 g of nickel sulfate hexahydrate, 254 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 5:3:2. Then, 25% aqueous ammonia was added dropwise to this mixture at a dropping rate of 300 mL / min. Next, slurry a1 was filtered and dried to obtain a mixture b1 of metal composite hydroxides. Then, 37 g of lithium carbonate was mixed into mixture b1 using a ball mill to obtain powder mixture c1. The obtained powder mixture c1 was calcined at 800°C for 4 hours in an air atmosphere to break it down, and then calcined at 800°C for 11 hours in an air atmosphere to produce particles A1 (LiNi 0.5 Co 0.3 Mn 0.2 O2, average particle size: 12.3 μm, tap density: 2.1 g / cm³ 3 ) was obtained.

[0079] [Manufacturing Example 2: Manufacturing of Particle A2] Particle A2 (LiNi) was prepared in the same manner as in Production Example 1, except that 473g of nickel sulfate hexahydrate, 169g of cobalt sulfate heptahydrate, 145g of manganese sulfate pentahydrate, and 3L of water were mixed so that the molar ratio of Ni:Co:Mn was 6:2:2. 0.6 Co 0.2 Mn 0.2 O2, average particle size: 10.9 μm, tap density: 2.2 g / cm³ 3 ) was obtained.

[0080] [Manufacturing Example 3: Manufacturing of Particle B1] Slurry water i1 was obtained by mixing 1272g of LiOH·H2O with 4L of water. Then, while stirring the obtained slurry water i1 at 25°C for 3 minutes, 1153g of 85% aqueous phosphoric acid solution was added dropwise at a rate of 35mL / min, and the mixture was stirred at a speed of 400rpm for 12 hours to obtain slurry water i2 containing Li3PO4. The obtained slurry water i2 was purged with nitrogen to adjust the dissolved oxygen concentration to 0.5 mg / L. Then, 1688 g of MnSO4·5H2O and 834 g of FeSO4·7H2O were added to the total volume of slurry water i2 to obtain slurry water i3. The molar ratio (manganese compound:iron compound) of the added MnSO4 and FeSO4 was 70:30.

[0081] Next, 45 g of cellulose nanofiber (Wma-10002, manufactured by Sugino Machine Co., Ltd., fiber diameter 4-20 nm) was added to the obtained slurry water i3 and placed in an autoclave, where a hydrothermal reaction was carried out at 170°C for 1 hour. The pressure inside the autoclave was 0.8 MPa. After the hydrothermal reaction, the resulting crystals were filtered and then washed with 12 parts by mass of water per 1 part by mass of crystals. The washed crystals were freeze-dried at -50°C for 12 hours to obtain preliminary particles bx 1 I obtained it. Obtained preliminary particle bx 1 1000g was taken, and 1L of water and 45g of propylene glycol were added and mixed to obtain slurry water ii5. 135g of cellulose nanofiber was added to the obtained slurry water ii5 and mixed to obtain slurry water ii6. The obtained slurry water ii6 was dispersed in an ultrasonic stirrer (T25, manufactured by IKA Corporation) for 1 minute to uniformly color the entire mixture, and then spray-dried using a spray-drying device (MDL-050M, manufactured by Fujisaki Electric Co., Ltd.) to obtain granulated material bz 1 The following was obtained. The hot air temperature during spray drying was set to 200°C, and the ratio of the hot air supply amount to the slurry water supply amount (hot air supply amount / slurry water supply amount) was set to 2500. The resulting granulated material bz 1 The particles B1 (LiMn) were fired at 700°C for 1 hour under an argon-hydrogen atmosphere (hydrogen concentration 3%). 0.7 Fe 0.3 PO4, average particle size: 13.6 μm, tap density: 1.1 g / cm³ 3 ) was obtained. Figure 1 shows a TEM image of the surface of primary particle b formed by the particle B1 obtained in manufacturing example 3, and Figure 2 shows a TEM image of the cross-section of particle B1.

[0082] [Manufacturing Example 4: Manufacturing of Particle B2] Slurry water i3 with 27g of cellulose nanofiber and spare particles bx 1 Except for adding 75g of propylene glycol and 153g of cellulose nanofiber to slurry water ii5, the particle B2 (LiMn) was prepared according to manufacturing example 3. 0.7 Fe 0.3 PO4) was obtained.

[0083] [Manufacturing Example 5: Manufacturing of Particle B3] Slurry water i3 with 90g of cellulose nanofiber and spare particles bx 1 Except for adding 45g of propylene glycol and 90g of cellulose nanofiber to slurry water ii5, particle B3 (LiMn) was prepared according to manufacturing example 3. 0.7 Fe 0.3 PO4) was obtained.

[0084] [Manufacturing Example 6: Manufacturing of Particle B4] Without adding cellulose nanofibers to slurry water i3, the preliminary particles bx 1 Except for not adding propylene glycol and adding 180g of cellulose nanofiber to slurry water ii5, the particle B4 (LiMn) was prepared according to Production Example 3. 0.7 Fe 0.3 PO4) was obtained.

[0085] The physical properties of the obtained particles B1 to B4 are shown in Table 1 below.

[0086] [Table 1]

[0087] [Examples 1-6, Comparative Examples 1-6] The obtained particles A1-2 and B1-B4 were used as appropriate, and these particles were mixed manually using a mortar and pestle according to the formulations shown in Table 3 to obtain each mixture.

[0088] Evaluation of battery characteristics (discharge capacity) Each of the obtained mixtures was used as the positive electrode material to fabricate the positive electrode of a lithium-ion secondary battery. Specifically, each of the obtained mixtures, acetylene black, and polyvinylidene fluoride were mixed in a mass ratio of 90:5:5, and N-methyl-2-pyrrolidone was added and kneaded thoroughly to prepare a positive electrode slurry. The positive electrode slurry was applied to a current collector made of 20 μm thick aluminum foil using a coating machine and vacuum dried at 80°C for 12 hours. After that, it was punched out into a φ14 mm disc shape and pressed with a hand press at 16 MPa for 2 minutes to form the positive electrode.

[0089] Next, a coin-type secondary battery was constructed using the above-mentioned positive electrode. A lithium foil stamped to a diameter of φ15 mm was used as the negative electrode. For the electrolyte, a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7 was used, in which LiPF6 was dissolved at a concentration of 1 mol / L. A porous polymer film was used as the separator. These battery components were assembled and housed in an atmosphere with a dew point of -50°C or lower using a conventional method to obtain a coin-type secondary battery (CR-2032). Next, the obtained coin-type secondary battery was used to measure its discharge capacity (mAh / g) at 0.2C in a 30°C environment using a discharge capacity measuring device (HJ-1001SD8, manufactured by Hokuto Denko Co., Ltd.), and this was recorded as the measured value.

[0090] Furthermore, the discharge capacity (mAh / g) at 0.2C was measured in the same manner when particles A1-2 and particles B1-B4 were used individually. Next, the calculated discharge capacity of each mixture was determined based on the particle content in the mixture. The percentage of the measured value relative to these calculated values ​​(set as 100%) was then calculated and used as an indicator for evaluating the discharge capacity.

[0091] Here, "calculated value of discharge capacity as a mixture" refers to the value obtained from the following formula, for example, in Example 1, where particle A1 accounts for 90% by mass and particle B1 accounts for 10% by mass in 100% of the mixture. 154(mAh / g)×0.9+132(mAh / g)×0.1 = 152 (mAh / g) Therefore, in the case of Example 1, since the measured discharge capacity is 154 (mAh / g), the "percentage of the measured value to the calculated value of the discharge capacity (%)" refers to the value obtained by the following formula. {154(mAh / g) / 152(mAh / g)}×100=101(%) For other examples and comparative examples, the calculated discharge capacity was determined in the same manner, and the percentage of the measured value relative to the calculated value (100%) was calculated.

[0092] Table 2 shows the discharge capacities when particles A1-2 and B1-B4 are used individually, and Table 3 shows the measured values ​​(mAh / g) of the discharge capacity as a mixture, and the percentage of the measured values ​​to the calculated values ​​of the discharge capacity. Furthermore, the higher the ratio of the measured value to the calculated value, the better the discharge capacity can be evaluated compared to when NMC is used alone.

[0093] 《Evaluation of Thermal Stability (Measurement of DSC Peak Temperature)》 Using each of the obtained positive electrode active materials, DSC curves were obtained in the temperature range of 30°C to 500°C by measurement with a differential scanning calorimeter (DSC404 F3, NETZSCH). For each measurement, approximately 10 mg of the sample was placed in an aluminum pan, and the heating rate was set to 10°C / min. Next, the obtained DSC curve was observed, and the exothermic peak temperature was determined. Furthermore, the higher the exothermic peak temperature, the better the thermal stability can be considered to be. The results are shown in Table 3.

[0094] [Table 2]

[0095] [Table 3]

Claims

1. Formula (A) below: L)) ａ Co ｂ Mn ｃ M １ ｗ O ２ ・・・(A) (In formula (A), M １ represents one or more elements selected from Mg, Ti, Nb, Fe, Cr, Si, Al, Ga, V, Zn, Cu, Sr, Mo, Zr, Sn, Ta, W, La, Ce, Pb, Bi, and Ge. a, b, c, and w are 0.3 ≤ a < 1, 0 < b ≤ 0.7, 0 < c ≤ 0.7, 0 ≤ w ≤ 0.3, 3a + 3b + 3c + (M １ This shows a number that satisfies the following conditions: (valence of a) × w = 3, and 0.3 ≤ a / (a + b + c) < 0.

7. A particle A, Formula (B) below: Li ｆ Mn ｇ Fe ｈ M ２ ｘ 2O 4 ・・・(B) (In formula (B), M ２ represents one or more elements selected from Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, and Gd. f, g, h, and x satisfy 0 < f ≤ 1.2, 0.3 ≤ g ≤ 1.2, 0.2 ≤ h ≤ 1.2, and 0 ≤ x ≤ 0.3, and f + (valence of Mn) × g + (valence of Fe) × h + (M ２ Show the number that satisfies (valence of x) × x = 3. Represented as such, particle B is an aggregate of primary particles b, in which carbon covers part of the particle surface while connecting the particles, and contains voids surrounded by primary particles b. A mixture of, In the cross-section of particle B, the area ratio of carbon to the total area of ​​the void surrounded by primary particle b is 10% or more and 23% or less. A positive electrode active material mixture for lithium-ion secondary batteries, wherein the content of particle B in the total amount of the mixture is 10% by mass or more and less than 30% by mass.

2. The positive electrode active material mixture for lithium-ion secondary batteries according to claim 1, wherein the carbon coverage rate on the particle surface of primary particle b is 5% or more and less than 70%.

3. The positive electrode active material mixture for lithium-ion secondary batteries according to claim 1 or 2, wherein the carbon content in particle B is 0.5% by mass to 2.5% by mass.

4. The positive electrode active material mixture for lithium-ion secondary batteries according to claim 1 or 2, wherein g and h in formula (B) are further numbers satisfying g / (g+h) ≤ 0.

8.

5. The positive electrode active material mixture for lithium-ion secondary batteries according to claim 1 or 2, wherein the carbon coating the particle surface of the primary particle b is carbon derived from cellulose nanofibers.

6. Next steps (I) to (V): (I) A step in which a lithium compound, a metal compound containing at least a manganese compound and an iron compound, a phosphoric acid compound, a carbon coating agent X1, and water are added to obtain slurry water i, and then subjected to a hydrothermal reaction to obtain preliminary particles bx of primary particles b. (II) Steps to obtain slurry water ii by adding the obtained primary particle bx, carbon coating agent X2, carbon coating inhibitor Y, and water to the obtained primary particle b. (III) Step of obtaining granules bz by spray drying the obtained slurry water ii. (IV) A step of firing the obtained granule bz to obtain particles B. (V) A step of mixing the obtained particles B and particles A in an amount such that the content of particles B in the total amount of lithium-ion secondary battery positive electrode active material mixture is 10% by mass or more and less than 30% by mass. Equipped with, The carbon coating agent X1 and carbon coating agent X2 are one or more carbon materials selected from sugars, and the mass ratio (X1 / X2) of the amount of carbon coating agent X1 added to the amount of carbon coating agent X2 added is 0.05 to 9.0, and A method for producing a positive electrode active material mixture for lithium-ion secondary batteries, wherein the carbon coating inhibitor Y is one or more carbon materials selected from polyols other than sugars, amines, and amides, The positive electrode active material mixture for lithium-ion secondary batteries is given by the following formula (A): LiNia Co b Mn c M 1 w O 2 ... (A) (In formula (A), M1 represents one or more elements selected from Mg, Ti, Nb, Fe, Cr, Si, Al, Ga, V, Zn, Cu, Sr, Mo, Zr, Sn, Ta, W, La, Ce, Pb, Bi, and Ge. a, b, c, and w represent numbers that satisfy 0.3 ≤ a < 1, 0 < b ≤ 0.7, 0 < c ≤ 0.7, 0 ≤ w ≤ 0.3, 3a + 3b + 3c + (valence of M1) × w = 3, and 0.3 ≤ a / (a ​​+ b + c) < 0.7.) A particle A, Formula (B) below: Li f Mn g Fe h M 2 x PO 4 ... (B) (In formula (B), M² represents one or more elements selected from Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, and Gd. f, g, h, and x represent numbers that satisfy 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.) Represented as such, particle B is an aggregate of primary particles b, in which carbon covers part of the particle surface while connecting the particles, and contains voids surrounded by primary particles b. A mixture of, In the cross-section of particle B, the area ratio of carbon to the total area of ​​the void surrounded by primary particle b is 10% or more. A method for producing a mixture in which the content of particle B in the total amount of the mixture is 10% by mass or more and less than 30% by mass.

7. A method for producing a positive electrode active material mixture for a lithium-ion secondary battery according to claim 6, wherein the carbon coating agent X1 and the carbon coating agent X2 are cellulose nanofibers.

8. A method for producing a positive electrode active material mixture for a lithium-ion secondary battery according to claim 6 or 7, wherein the mass ratio ((X1 + X2) / Y) of the total amount of carbon coating agent X1 and carbon coating agent X2 added to the amount of carbon coating inhibitor Y added is 0.05 to 3.00.

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