Positive electrode active material, positive electrode mixture, battery, and method for producing positive electrode active material

Abstract

A primary object of the present disclosure is to provide a positive electrode active material that can reduce resistance and the rate of increase in cycle resistance. [Solution] The present disclosure solves the above problem by providing a positive electrode active material, the positive electrode active material having crystalline primary particles containing Li, TM (TM is a transition metal), and O, the positive electrode active material being an aggregate composed of a plurality of the primary particles, and compound A containing La, Ni, and O, and compound B containing Li, W, and O present on the surfaces of the primary particles.

Description

[Technical Field]

[0001] The present disclosure relates to a positive electrode active material, a positive electrode mixture, a battery, and a method for producing the positive electrode active material. [Background technology]

[0002] In recent years, the development of batteries has been actively pursued. For example, in the automotive industry, development of batteries for use in electric vehicles (BEVs), plug-in hybrid vehicles (PHEVs), and hybrid electric vehicles (HEVs) is underway. Active materials containing transition metals such as Ni, Co, and Mn are known as positive electrode active materials for batteries.

[0003] For example, Patent Document 1 describes a compound having the chemical formula Li a Ni x Co y Mn 1-x-y W b Disclosed is a W-containing high-nickel ternary positive electrode material that is McO2, characterized in that the high-nickel ternary positive electrode material simultaneously contains spherical secondary particles and single-crystal particles, the single-crystal particles essentially do not contain W element inside, and the spherical secondary particles are doped with W element.

[0004] Patent Document 2 describes a single crystal multi-component positive electrode material, in which the ratio of the length of the longest diagonal to the length of the shortest diagonal measured by SEM for single crystal particles of the single crystal multi-component positive electrode material is defined as the circularity R, and R is 1 or more, and the D of the single crystal particles of the single crystal multi-component positive electrode material is 10 , D 50 and D 90 But, K 90 =(D 90 -D 10 ) / D 50 and K 90 A single crystal multi-element positive electrode material is disclosed, characterized in that the product of R and Cr is 1.20 to 1.40. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2022-542774 [Patent Document 2] Special Publication No. 2024-511223 Summary of the Invention [Problem to be solved by the invention]

[0006] From the viewpoint of improving battery performance, reduction in resistance and reduction in the rate of increase in cycle resistance are required. The present disclosure has been made in view of the above circumstances, and has as its main object to provide a positive electrode active material that can reduce resistance and reduction in the rate of increase in cycle resistance. [Means for solving the problem]

[0007] [1] A positive electrode active material, the positive electrode active material has crystalline primary particles containing Li, TM (TM is a transition metal), and O; the positive electrode active material is an aggregate composed of a plurality of the primary particles, A positive electrode active material, in which a compound A containing La, Ni, and O and a compound B containing Li, W, and O are present on the surfaces of the primary particles.

[0008] [2] The positive electrode active material according to [1], wherein a pore size distribution obtained by mercury intrusion porosimetry has a peak in the range of 65 nm to 300 nm.

[0009] [3] The positive electrode active material according to [2], wherein the pore size distribution has a peak in the range of 80 nm or more and 220 nm or less.

[0010] [4] The positive electrode active material according to any one of [1] to [3], wherein the primary particles in the aggregates have an average particle size of 0.5 μm or more.

[0011] [5] The positive electrode active material according to any one of [1] to [4], wherein the primary particles contain at least one of Ni, Co, and Mn as the TM.

[0012] [6] The positive electrode active material according to any one of [1] to [5], wherein the primary particles have a layered rock salt type crystal structure.

[0013] [7] The positive electrode active material according to any one of [1] to [6], wherein at least one of the compound A and the compound B is present at the interface between adjacent primary particles in the aggregate.

[0014] [8] The positive electrode active material according to any one of [1] to [7], wherein the compound A is in a particulate form.

[0015] [9] The positive electrode active material according to any one of [1] to [8], wherein the compound B is in the form of a film.

[0016]

[10] A positive electrode mixture containing the positive electrode active material according to any one of [1] to [9].

[0017]

[11] A battery having a positive electrode active material layer containing a positive electrode active material, a negative electrode active material layer containing a negative electrode active material, and an electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, The battery, wherein the positive electrode active material layer contains the positive electrode mixture according to

[10] .

[0018]

[12] A method for producing a positive electrode active material according to any one of [1] to [9], a first firing step of firing a first mixture containing the transition metal hydroxide containing the TM, a Li source, and a W source at a temperature T1 to obtain a first fired body; a second firing step of firing the first fired body at a temperature T2 to obtain a second fired body; a third firing step of adding a La source to the pulverized product of the second fired body to prepare a second mixture, and firing the second mixture at a temperature T3 to obtain a third fired body; and at least one of the first mixture and the second mixture contains a Ni source; The temperature T2 in the second baking step is higher than the temperature T1 in the first baking step, the temperature T3 in the third baking step is lower than the temperature T2 in the second baking step; The temperature T1 is 500°C or higher and 800°C or lower, The temperature T2 is 600°C or higher and 1000°C or lower, The temperature T3 is 400°C or higher and 600°C or lower in the method for producing a positive electrode active material. [Effects of the Invention]

[0019] The present disclosure has the effect of providing a positive electrode active material that can reduce resistance and the rate of increase in cycle resistance. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic cross-sectional view illustrating a positive electrode active material according to the present disclosure. [Figure 2] 1 is a schematic cross-sectional view illustrating a primary particle according to the present disclosure. FIG. [Figure 3] FIG. 1 is a schematic cross-sectional view illustrating a battery according to the present disclosure. [Figure 4] FIG. 1 is a flow diagram illustrating a method for producing a positive electrode active material according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0021] Below, embodiments will be described with reference to the drawings etc. However, the present disclosure can be implemented in many different forms and is not limited to the description of the embodiments exemplified below. Furthermore, to clarify the explanation, the drawings may show the width, thickness, and shape of each part schematically compared to the actual form, but this is merely an example and should not be construed as limiting.

[0022] A. Positive electrode active material FIG. 1 is a schematic cross-sectional view illustrating an example of a positive electrode active material according to the present disclosure. FIG. 2 is a schematic cross-sectional view illustrating an example of a positive electrode active material according to the present disclosure. As shown in FIG. 1, the positive electrode active material 10 has crystalline primary particles 1 containing Li, TM (TM is a transition metal), and O. The positive electrode active material 10 is an aggregate composed of a plurality of primary particles 1. As shown in FIG. 2, a compound A containing La, Ni, and O and a compound B containing Li, W, and O are present on the surface of the primary particles.

[0023] According to the present disclosure, the presence of compound A (a compound containing La, Ni, and O) with good electronic conductivity on the surface of the primary particles can reduce resistance. Also, in the present disclosure, the presence of compound B (a compound containing Li, W, and O) with good ionic conductivity on the surface of the primary particles can also reduce resistance. Furthermore, the positive electrode active material of the present disclosure has aggregates composed of multiple primary particles, which can reduce the rate of increase in cycle resistance.

[0024] Conventionally, polycrystalline and single-crystalline active materials have been known as positive electrode active materials. Polycrystalline active materials typically consist of multiple densely packed primary particles (very fine primary particles). On the other hand, single-crystalline active materials consist of large primary particles that do not aggregate and exist as individual particles. Compared to polycrystalline active materials, single-crystalline active materials are less likely to crack during charge and discharge and are superior in durability. However, because of their large specific surface area, repeated charge and discharge easily cause resistance components to accumulate, leading to an increase in resistance over time.

[0025] In the present disclosure, a plurality of primary particles constitute an aggregate. Therefore, the specific surface area can be made smaller than that of a single primary particle. As a result, the accumulation of resistance components due to repeated charge and discharge can be suppressed. In other words, the effect of reducing the rate of increase in cycle resistance can be achieved. This effect is particularly pronounced when the particle size of the primary particles is large, as described above.

[0026] In the present disclosure, as will be described later, it is preferable that the pore size distribution obtained by mercury intrusion porosimetry has a peak in the range of 65 nm to 300 nm. That is, it is preferable to adjust the degree of aggregation of the primary particles to such an extent that a peak exists in the above range. Specifically, as shown in FIG. 1, it is preferable that minute voids (voids with a pore size of 65 nm to 300 nm) exist inside the aggregates of primary particles 1. The presence of minute voids has the effect of improving ionic conductivity inside the aggregates, particularly when an electrolyte solution is used.

[0027] In addition, in Example 3 of the above-mentioned Patent Document 1, Li 1.0029 Ni 0.83 Co 0.11 Mn 0.06 W 0.0009 La 0.002 Patent Document 1 discloses a positive electrode material represented by formula (I) and (II) O2. More specifically, it describes firing a mixture containing precursor A containing Ni, Co, and Mn but not W, precursor B containing Ni, Co, Mn, and W, LiOH, and La2O3 at a high temperature of 880°C. However, Patent Document 1 does not describe or suggest compound A (a compound containing La, Ni, and O) in this disclosure.

[0028] In addition, in the above-mentioned Patent Document 2, Li 1+a (Ni x Co y Mn z G b )M c O 2-dIn Patent Document 2, a positive electrode material represented by the formula (I) is disclosed, in which G is one or more of Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, Al, B, Mg, Co, F, and Y. That is, La is disclosed as one option for G. However, Patent Document 2 does not disclose any examples using La.

[0029] 1.Primary particles The primary particles in the present disclosure are crystalline particles containing Li, TM (TM is a transition metal), and O. The crystal structure of the primary particles may be, for example, a layered rock salt type or a spinel type, with the layered rock salt type being preferred. The primary particles may also have a crystal structure belonging to the space group R-3m.

[0030] The primary particles contain Li, TM (TM is a transition metal), and O. The primary particles may contain one type of transition metal, two types of transition metals, three types of transition metals, or four or more types of transition metals.

[0031] Transition metals are metals belonging to groups 3 to 11 in the periodic table. The transition metal contained in the primary particles may be a metal belonging to period 3, period 4, or period 5. Examples of transition metals include Ti, V, Cr, Mn, Fe, Co, Ni, Zr, Nb, La, and W.

[0032] The primary particles preferably contain at least Ni. This is because a positive electrode active material with good capacity characteristics can be obtained. When the total amount of transition metals (TM) contained in the primary particles is 1 molar part, the proportion of Ni contained in the primary particles is, for example, 0.25 molar parts or more, 0.33 molar parts or more, 0.50 molar parts or more, 0.75 molar parts or more, 0.80 molar parts or more, or 0.90 molar parts or more. Increasing the proportion of Ni improves the capacity characteristics.

[0033] The primary particles may or may not contain Co. When the total amount of transition metals (TM) contained in the primary particles is 1 molar part, the proportion of Co contained in the primary particles may be, for example, 0 molar parts or more, 0.05 molar parts or more, or 0.10 molar parts or more. On the other hand, the proportion of Co contained in the primary particles may be, for example, 0.40 molar parts or less, or 0.20 molar parts or less.

[0034] The primary particles may or may not contain Mn. When the total amount of transition metals (TM) contained in the primary particles is 1 molar part, the proportion of Mn contained in the primary particles may be, for example, 0 molar parts or more, 0.05 molar parts or more, or 0.10 molar parts or more. On the other hand, the proportion of Mn contained in the primary particles may be, for example, 0.40 molar parts or less, or 0.20 molar parts or less.

[0035] The primary particles preferably contain at least one of Ni, Co, and Mn. When all metals (excluding Li) contained in the primary particles are taken as 1 molar part, the total proportion of Ni, Co, and Mn contained in the primary particles is, for example, 0.80 molar parts or more, or alternatively 0.90 molar parts or more, or even 0.95 molar parts or more. Note that the "total of Ni, Co, and Mn" also includes cases where the proportion of one or both of Ni, Co, and Mn is 0.

[0036] The primary particles consist of Li and TM, as well as other metals other than Li and TM, M 1 Other metals M (including metalloids) may be contained. 1 Examples of the metals include metals belonging to groups 12 to 14 of the periodic table. Examples of the metals belonging to groups 12 to 14 include Zn, Al, Si, Ga, Ge, In, and Sn.

[0037] The composition of the primary particles is not particularly limited, but may be, for example, a compound represented by the general formula Li x Ni a Co b Mn c O y(0.1≦x≦1.5, 0.5≦a≦1.0, 0≦b≦0.3, 0≦c≦0.3, 0.001≦d≦0.1, 0.001≦e≦0.1, a+b+c+d+e=1.0, 1.5≦y≦2.1). "x" may be 0.4 or greater, 0.6 or greater, 0.8 or greater, 1.0 or greater, or 1.05 or greater, or may be 1.4 or less, or 1.2 or less. "y" may be 1.6 or greater, 1.7 or greater, 1.8 or greater, or 1.9 or greater, or may be 2.0 or less. "a" may be 0.6 or more, 0.7 or more, 0.8 or more, or 0.85 or more, or may be 0.9 or less. "b" may be 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, or 0.075 or more, or 0.25 or less, 0.20 or less, 0.15 or less, 0.10 or less, 0.09 or less, or 0.08 or less. "c" may be 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, or 0.075 or more, or 0.25 or less, 0.20 or less, 0.15 or less, 0.10 or less, 0.09 or less, or 0.08 or less.

[0038] 2. Compound A Compound A in the present disclosure contains La, Ni, and O. Compound A usually has high electronic conductivity, and therefore the presence of compound A on the surface of the primary particles can reduce resistance. Compound A may be disposed directly on the surface of the primary particles or may be disposed via another layer (another compound), with the former being preferred.

[0039] Compound A contains at least La, Ni, and O. Compound A may be composed of only La, Ni, and O, or may further contain other elements. Examples of other elements include Li. That is, compound A may or may not contain Li. An example of the composition of compound A is La.a Ni b O c (0.8≦a≦1.2, 0.8≦b≦1.2, 2.8≦c≦3.2). For example, LaNiO3 is a typical perovskite composition and has good electronic conductivity. Another example of the composition of compound A is La a Li b Ni c O d (3.5≦a≦4.5, 0.5≦b≦1.5, 0.5≦c≦1.5, 7.5≦d≦8.5). For example, La4LiNiO8 is known to have good electronic conductivity and is thought to have a crystalline phase similar to perovskite.

[0040] Compound A may be crystalline or amorphous, but the former is preferred because it provides good electronic conductivity. "A compound is crystalline" means that peaks derived from the target compound are observed by X-ray diffraction using CuKα radiation. On the other hand, "a compound is amorphous" means that peaks derived from the symmetric compound are not observed by X-ray diffraction using CuKα radiation. Note that when the target compound is amorphous, a halo pattern may be observed instead of a peak.

[0041] Compound A preferably has a crystalline phase of perovskite or a crystalline phase similar to perovskite. Compound A preferably has a crystalline phase of at least one of LaNiO3 or La4LiNiO8, because this provides good electronic conductivity. The above crystalline phases include crystalline phases in which some of the constituent atoms (e.g., some O atoms) are missing, and crystalline phases in which some of the constituent atoms (e.g., some La atoms) are present in excess.

[0042] It is preferable that compound A is in a particulate form. "Compound A is in a particulate form" means that, in a cross-sectional image of a primary particle, when the length of compound A in the normal direction to the surface of the primary particle is L1 and the length of compound A in the direction perpendicular to the normal direction is L2, the ratio of L2 to L1 (L2 / L1) is 3.0 or less. The cross-sectional image of a primary particle is, for example, an SEM cross-sectional image.

[0043] When all transition metals contained in the primary particles are taken as 1 molar part, the proportion of La contained in compound A is, for example, 0.001 molar parts or more, or alternatively 0.003 molar parts or more, or even 0.005 molar parts or more. On the other hand, the proportion of La contained in compound A is, for example, 0.100 molar parts or less, or alternatively 0.080 molar parts or less, or alternatively 0.060 molar parts or less.

[0044] The coverage of the compound A with respect to the primary particles is not particularly limited, but may be, for example, 10% or more and 90% or less, 20% or more and 80% or less, or 30% or more and 70% or less. The coverage of the compound A can be determined, for example, by outermost surface analysis using XPS (X-ray photoelectron spectroscopy). For example, when the primary particles contain Ni, Co, and Mn as transition metals TM, the amount of La and the amount of each TM (Ni amount, Co amount, Mn amount) can be determined by outermost surface analysis using XPS, and La / (La+TM) can be used as the coverage. The coverage of the compounds B and C can also be determined in a similar manner. In addition, the electronic conductivity of the compound A is usually higher than that of La2O3. The electronic conductivity of the compound A at 25°C is, for example, 5.0 × 10 -4 S / cm or more, 1.0×10 -3 The surface resistivity may be S / cm or more. Compound A (a compound containing La, Ni, and O) is disposed on the surface of the primary particles. The primary particles may or may not contain La.

[0045] 3. Compound B The positive electrode active material of the present disclosure may have a compound B containing Li, W, and O on the surface of the primary particles. Compound B usually has high ionic conductivity, so the presence of compound B on the surface of the primary particles can reduce resistance. Furthermore, the presence of compound B on the surface of the primary particles can suppress an increase in resistance over time. Compound B may be disposed directly on the surface of the primary particles or via another layer (another compound), with the former being preferred.

[0046] Compound B contains at least Li, W, and O. Compound B may be composed of only Li, W, and O, or may further contain other elements. An example of the composition of compound B is Li a W b O c (5.5≦a≦6.5, 0.5≦b≦1.5, 5.5≦c≦6.5). Compound B having the above composition is typically Li6WO6. Other examples of the composition of compound B include Li a W b O c (1.5≦a≦2.5, 0.5≦b≦1.5, 3.5≦c≦4.5). Compound B having the above composition is typically Li2WO4. Another example of the composition of compound B is Li a W b O c (3.5≦a≦4.5, 0.5≦b≦1.5, 4.5≦c≦5.5). Compound B having the above composition is typically Li4WO5. Another example of the composition of compound B is Li a W b O c (1.5≦a≦2.5, 1.5≦b≦2.5, 6.5≦c≦7.5) Compound B having the above composition is typically Li2W2O7.

[0047] Compound B may be crystalline or amorphous. Compound B is preferably film-like. "Compound B is film-like" means that, in a cross-sectional image of a primary particle, the length of compound B in the normal direction to the surface of the primary particle is L3, and the length of compound B in the direction perpendicular to the normal direction is L4. The ratio of L4 to L3 (L4 / L3) is greater than 3.0. The cross-sectional image of the primary particle is, for example, a cross-sectional image obtained by a transmission electron microscope (TEM). The thickness (length L3) of compound B is not particularly limited, but may be, for example, 0.5 nm or more and 20 nm or less, or 1 nm or more and 15 nm or less. The thickness of compound B is determined as the average value of measurements taken at least five times during TEM observation.

[0048] When all transition metals contained in the primary particles are taken as 1 molar part, the proportion of W contained in compound B is, for example, 0.001 molar parts or more, or alternatively, 0.003 molar parts or more, or even 0.005 molar parts or more. On the other hand, the proportion of W contained in compound B is, for example, 0.100 molar parts or less, or alternatively, 0.080 molar parts or less, or alternatively, 0.060 molar parts or less.

[0049] The coverage of the primary particles with compound B is not particularly limited, but may be, for example, 10% to 90%, or 20% to 80%, or 30% to 70%. The ionic conductivity of compound B is usually higher than that of W2O3. The ionic conductivity of compound B at 25°C is, for example, 1.0 × 10 -5 S / cm or more, 1.0×10 -4 The surface resistivity may be S / cm or more. Compound B (a compound containing Li, W, and O) is disposed on the surface of the primary particles. The primary particles may or may not contain W.

[0050] 4. Aggregates The positive electrode active material in the present disclosure is an aggregate composed of a plurality of primary particles. As shown in FIG.

[0051] The average particle size of the primary particles in the aggregates is, for example, 0.5 μm or more, and may be 0.6 μm or more, 0.8 μm or more, 1.0 μm or more, 2 μm or more, or 5 μm or more. Meanwhile, the average particle size of the primary particles in the aggregates is, for example, 20 μm or less, 15 μm or less, or 10 μm or less. The particle size of each primary particle in the aggregates is determined, for example, as the longest diameter in SEM observation. Furthermore, for example, when the positive electrode active material layer contains aggregates (positive electrode active material), the particle size (longest diameter) of each primary particle in the aggregates may be determined from a cross-sectional image of the positive electrode active material layer.

[0052] The number of primary particles constituting the aggregate is usually 2 or more, and may be 5 or more, or 10 or more. On the other hand, the number of primary particles constituting the aggregate is, for example, 100 or less. The average particle size of the aggregate is, for example, more than 0.5 μm and 30 μm or less, or may be 0.8 μm or more and 25 μm or less, or 1 μm or more and 20 μm or less, or 2 μm or more and 15 μm or less. The shape of the aggregate is, for example, particulate.

[0053] When the pore size distribution of the positive electrode active material of the present disclosure is measured by mercury intrusion porosimetry, a peak preferably exists in the range of 65 nm to 300 nm. The peak also includes an inflection point. The peak may exist in the range of 60 nm to 180 nm, or in the range of 80 nm to 160 nm. The peak may exist in the range of 80 nm to 220 nm, or in the range of 100 nm to 200 nm.

[0054] The pore volume at the peak is, for example, 0.010 mL / g or more, or may be 0.015 mL / g or more, or 0.020 mL / g or more, or 0.025 mL / g or more, or 0.045 mL / g or more, while the pore volume at the peak is, for example, 0.100 mL / g or less, or may be 0.090 mL / g or less, or 0.080 mL / g or less, or 0.060 mL / g or less.

[0055] In the present disclosure, at least one of compound A and compound B may be present at the interface between adjacent primary particles in the aggregate.

[0056] 5.Cathode active material The positive electrode active material in the present disclosure has crystalline primary particles containing Li, TM (TM is a transition metal), and O. The positive electrode active material is an aggregate composed of a plurality of primary particles. The positive electrode active material is typically used in batteries. The method for producing the positive electrode active material is not particularly limited, but examples thereof include the method described in "D. Method for producing positive electrode active material" below.

[0057] The present disclosure also provides a positive electrode active material powder, which contains a plurality of crystalline primary particles containing Li, TM (TM is a transition metal), and O as the positive electrode active material, at least a portion of the plurality of primary particles forming aggregates, and a compound A containing La, Ni, and O and a compound B containing Li, W, and O are present on the surfaces of the primary particles forming the aggregates. Some of the plurality of primary particles may form a single-crystalline active material. The proportion of the aggregates relative to the total positive electrode active material in the positive electrode active material powder is, for example, 5% by mass or more, or may be 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more.

[0058] B. Cathode composite The positive electrode mixture in the present disclosure contains the above-described positive electrode active material.

[0059] According to the present disclosure, the use of the above-described positive electrode active material results in a positive electrode composite that can reduce resistance and the rate of increase in cycle resistance. The positive electrode composite may contain other materials (e.g., a conductive material, a binder) in addition to the positive electrode active material. The positive electrode composite may also contain the above-described positive electrode active material powder. The positive electrode composite may also be in the form of a powder or a slurry containing a dispersion medium.

[0060] The proportion of the positive electrode active material in the solid content of the positive electrode mixture is, for example, 20% by mass or more, or may be 30% by mass or more, or 40% by mass or more. If the proportion of the positive electrode active material is too low, sufficient energy density may not be obtained. On the other hand, the proportion of the positive electrode active material in the solid content of the positive electrode mixture is, for example, 95% by mass or less, or may be 70% by mass or less, or may be 60% by mass or less. If the proportion of the positive electrode active material is too high, ionic conductivity and electronic conductivity may relatively decrease.

[0061] The positive electrode mixture may contain a conductive material. The addition of a conductive material improves electronic conductivity. Examples of conductive materials include carbon-based conductive materials, metal particles, and conductive polymers. Examples of carbon-based conductive materials include particulate materials such as acetylene black (AB) and ketjen black (KB), and fibrous materials such as vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and carbon nanofibers (CNF).

[0062] The proportion of the conductive material in the solid content of the positive electrode mixture is, for example, 0.1% by mass or more. If the proportion of the conductive material is too low, there is a possibility that the electron conduction path will be insufficient. On the other hand, the proportion of the conductive material in the solid content of the positive electrode mixture is, for example, 5% by mass or less. If the proportion of the conductive material is too high, there is a possibility that the proportion of the positive electrode active material will be relatively low, resulting in a low energy density.

[0063] The positive electrode mixture may contain a binder. Addition of the binder makes it possible to obtain a positive electrode active material layer in which the positive electrode active material is less likely to fall off. Examples of binders include rubber-based binders such as styrene-butadiene rubber (SBR) and butadiene rubber (BR), polycarboxylic acid-based binders such as carboxymethyl cellulose, and fluoride-based binders such as polyvinylidene fluoride (PVdF).

[0064] The proportion of the binder in the solid content of the positive electrode mixture is, for example, 0.5% by mass or more. If the proportion of the binder is too low, it may not be possible to sufficiently prevent the positive electrode active material from falling off. On the other hand, the proportion of the binder in the solid content of the positive electrode mixture is, for example, 15% by mass or less. If the proportion of the binder is too high, the proportion of the positive electrode active material will be relatively low, which may result in a low energy density.

[0065] C.Battery Fig. 3 is a schematic cross-sectional view illustrating a battery according to the present disclosure. The battery 20 shown in Fig. 2 includes a positive electrode active material layer 11, a negative electrode active material layer 12, an electrolyte layer 13 disposed between the positive electrode active material layer 11 and the negative electrode active material layer 12, a positive electrode current collector 14 that collects current from the positive electrode active material layer 11, and a negative electrode current collector 15 that collects current from the negative electrode active material layer 12. In the present disclosure, the positive electrode active material layer 11 contains the positive electrode composite described above in "B. Positive Electrode Composite."

[0066] According to the present disclosure, by using the above-described positive electrode composite, a battery with reduced resistance and cycle resistance increase rate can be obtained.

[0067] 1.Cathode active material layer The positive electrode active material layer contains at least a positive electrode active material. The positive electrode active material layer may also contain a conductive material and a binder. The positive electrode active material, conductive material, and binder are the same as those described above in "A. Positive electrode active material" and "B. Positive electrode composite."

[0068] The positive electrode active material layer may contain an electrolyte. The electrolyte is, for example, an electrolytic solution described below. On the other hand, the positive electrode active material layer may contain a solid electrolyte. The thickness of the positive electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less, or may be 1 μm or more and 500 μm or less, or may be 30 μm or more and 100 μm or less.

[0069] The method for producing the positive electrode active material layer is not particularly limited, but may include, for example, a method in which a positive electrode slurry containing a positive electrode active material and a dispersion medium is applied to a positive electrode current collector and then dried. The dried positive electrode active material layer may be subjected to a press treatment. The press treatment improves the density of the positive electrode active material layer.

[0070] 2.Negative electrode active material layer The negative electrode active material layer contains at least a negative electrode active material, such as a carbon-based active material, a Li-based active material, a Si-based active material, or an oxide-based active material.

[0071] Examples of carbon-based active materials include graphite, soft carbon, and hard carbon. Graphite may be natural graphite or artificial graphite. Examples of Li-based active materials include Li and Li alloys. Examples of Li alloys include Li-Si alloys. Examples of Si-based active materials include Si, SiC composite active materials, Si alloys, and Si oxides. Examples of SiC composite active materials include active materials in which Si or Si alloys are supported on a carbon support. Examples of oxide-based active materials include Li4Ti5O 12 Lithium titanates such as those mentioned above are also included.

[0072] The proportion of the negative electrode active material in the negative electrode active material layer is, for example, 20% by mass or more, or alternatively, 30% by mass or more, or even 40% by mass or more. If the proportion of the negative electrode active material is too low, sufficient energy density may not be obtained. On the other hand, the proportion of the negative electrode active material in the negative electrode active material layer is, for example, 95% by mass or less, or alternatively, 70% by mass or less, or alternatively, 60% by mass or less. If the proportion of the negative electrode active material is too high, the ionic conductivity and electronic conductivity of the negative electrode active material layer may relatively decrease.

[0073] The negative electrode active material layer may contain at least one of a conductive material, a binder, and an electrolyte. Details of the conductive material, the binder, and the electrolyte are the same as those described above in "1. Positive electrode active material layer." The thickness of the negative electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less, or may be 1 μm or more and 500 μm or less, or may be 30 μm or more and 100 μm or less.

[0074] The method for producing the negative electrode active material layer is not particularly limited, but may include, for example, a method in which a negative electrode slurry containing a negative electrode active material and a dispersion medium is applied to a negative electrode current collector and then dried. The dried negative electrode active material layer may be subjected to a press treatment. The press treatment improves the density of the negative electrode active material layer.

[0075] 3. Electrolyte layer The electrolyte layer is a layer disposed between the positive electrode active material layer and the negative electrode active material layer, and contains at least an electrolyte, such as a liquid electrolyte (electrolytic solution).

[0076] An example of the electrolyte is a non-aqueous electrolyte. The non-aqueous electrolyte contains, for example, a lithium salt and a non-aqueous solvent. Examples of the lithium salt include inorganic lithium salts such as LiPF, LiBF, LiClO, and LiAsF; and organic lithium salts such as LiCF, LiN(SOCF), LiN(SOCF) and LiC(SOCF).

[0077] Examples of non-aqueous solvents include carbonate-based solvents such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The non-aqueous solvent may be a mixture of a cyclic carbonate such as EC or PC, which has a high dielectric constant and high viscosity, and a chain carbonate such as DMC, DEC, or EMC, which has a low dielectric constant and low viscosity. The concentration of the lithium salt in the non-aqueous electrolyte solution is, for example, 0.3 M or more and 5 M or less. The non-aqueous electrolyte solution may also contain an ionic liquid. Examples of ionic liquids include sulfonium salts, ammonium salts, pyridinium salts, piperidinium salts, pyrrolidinium salts, morpholinium salts, phosphonium salts, and imidazolium salts.

[0078] Another example of the electrolyte solution is an aqueous electrolyte solution. The aqueous electrolyte solution is an electrolyte solution containing water as the main solvent component. The ratio of water to the total solvent is, for example, 50% by mass or more, and may be 70% by mass or more. Examples of the lithium salt used in the aqueous electrolyte solution include imide-based electrolytes such as lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide. The concentration of the lithium salt in the aqueous electrolyte solution is, for example, 1 M or more and 25 M or less.

[0079] The electrolyte layer may include a separator impregnated with the above-mentioned electrolytic solution. The provision of the separator can suppress the occurrence of internal short circuits. The separator may be, for example, a porous membrane. Examples of materials for the separator include resins such as polyethylene, polypropylene, polyester, polyvinyl alcohol, cellulose, and polyamide. The electrolyte layer may also contain a solid electrolyte. Examples of the solid electrolyte include organic solid electrolytes such as polymer electrolytes and gel electrolytes; and inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, and halide solid electrolytes.

[0080] 4.Battery The battery according to the present disclosure preferably has a positive electrode current collector that collects current from the positive electrode active material layer and a negative electrode current collector that collects current from the negative electrode active material layer. Examples of materials for the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. On the other hand, examples of materials for the negative electrode current collector include SUS, copper, nickel, and carbon. The battery according to the present disclosure may also have an exterior housing that houses the power generating elements (positive electrode active material layer, electrolyte layer, and negative electrode active material layer). Examples of the exterior housing include a case-type exterior housing and a laminate-type exterior housing.

[0081] The type of battery in the present disclosure is not particularly limited, but is typically a lithium-ion battery. The battery in the present disclosure may be a primary battery or a secondary battery, with secondary batteries being preferred. This is because secondary batteries can be repeatedly charged and discharged and are useful, for example, as automotive batteries. Examples of uses for batteries include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. In particular, batteries are preferably used as driving power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric vehicles (BEVs). Furthermore, batteries may also be used as power sources for mobile objects other than vehicles (e.g., railways, ships, and aircraft), and may also be used as power sources for electrical appliances such as information processing devices.

[0082] D. Method for manufacturing positive electrode active material FIG. 4 is a flow diagram illustrating a method for producing a positive electrode active material according to the present disclosure. In FIG. 4, a first mixture containing a transition metal hydroxide containing TM, a Li source, and a W source is first fired at a temperature T1 to obtain a first fired body (first firing step). The first fired body is then fired at a temperature T2 to obtain a second fired body (second firing step). The La source is then added to the pulverized second fired body to prepare a second mixture, which is then fired at a temperature T3 to obtain a third fired body (third firing step). This results in a positive electrode active material. According to the present disclosure, at least one of the first mixture and the second mixture contains a Ni source. The temperature T2 in the second firing step is higher than the temperature T1 in the first firing step, and the temperature T3 in the third firing step is lower than the temperature T2 in the second firing step. Furthermore, the temperatures T1, T2, and T3 are each within a predetermined range.

[0083] According to the present disclosure, by performing the first, second, and third firing steps, it is possible to obtain a positive electrode active material that can reduce the resistance and the rate of increase in cycle resistance.

[0084] 1. First firing process The first firing step is a step of firing a first mixture containing the transition metal hydroxide containing the TM, a Li source, and a W source at a temperature T1 to obtain a first fired body.

[0085] The transition metal hydroxide contains TM (TM is a transition metal). The transition metal hydroxide corresponds to a precursor of a positive electrode active material. The transition metal hydroxide typically does not contain Li, but may contain Li. The transition metal hydroxide may or may not contain La. The transition metal hydroxide may or may not contain W. The transition metal hydroxide may or may not contain Ni.

[0086] The synthesis method of the transition metal hydroxide is not particularly limited, and examples thereof include the following methods. First, a raw material aqueous solution of the transition metal hydroxide is prepared. Examples of methods for preparing the raw material aqueous solution include dissolving a water-soluble transition metal compound in water. Examples of the transition metal compound include metal salts such as sulfates and nitrates. Examples of Ni sources include NiSO4 and Ni(NO3)2. Examples of Co sources include CoSO4, Co(NO3)2, and Co(NO3)3. Examples of Mn sources include MnSO4 and Mn(NO3)2. The composition of the raw material aqueous solution is appropriately adjusted according to the desired positive electrode active material.

[0087] Next, an aqueous sodium hydroxide solution is added to the reaction vessel, and while maintaining the pH at an alkaline level (e.g., pH 11.3 to 12.0), the raw material aqueous solution and the NH3 aqueous solution are added dropwise. The reaction temperature is not particularly limited, but is, for example, 50°C or higher and 65°C or lower. After the reaction is complete, the transition metal hydroxide is preferably removed by filtration, washed with water, and then dried.

[0088] In the first firing step, a first mixture containing a transition metal hydroxide, a Li source, and a W source is prepared. Examples of the Li source include lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, lithium oxide, and lithium chloride. The Li source may be lithium hydroxide or a Li-containing compound other than lithium hydroxide. The molar ratio of Li in the Li source to TM contained in the transition metal hydroxide is, for example, 0.8 to 1.2, or 0.9 to 1.1, or even 1.0.

[0089] An example of a W source is H2WO4. The first mixture may or may not contain a Ni source. For example, when the transition metal hydroxide contains Ni, the transition metal hydroxide may also serve as the Ni source. On the other hand, when the transition metal hydroxide does not contain Ni, a separate Ni source must be used. Examples of Ni sources include Ni(OH)2, NiSO4, and Ni(NO3)2. The amounts of the La source, W source, and Ni source added are appropriately adjusted according to the desired positive electrode active material.

[0090] The mixture preferably contains a molten salt. The molten salt functions as a flux, allowing the primary particles to grow sufficiently. The molten salt may contain Li. An example of the molten salt is lithium hydroxide. The molar ratio of Li contained in the molten salt to TM contained in the transition metal hydroxide (Li / TM) is usually 0.1 or more and less than 0.6. Li / TM may be 0.15 or more, 0.2 or more, or 0.25 or more. On the other hand, Li / TM may be 0.55 or less, or 0.5 or less.

[0091] The mixture may contain lithium hydroxide as the Li source and molten salt. The molar ratio (Li' / TM) of Li contained in the Li source and molten salt to TM contained in the transition metal hydroxide is, for example, 1.1 or more, or may be 1.15 or more, or may be 1.2 or more. On the other hand, Li' / TM may be, for example, less than 1.6, or may be 1.55 or less, or may be 1.5 or less.

[0092] In the first firing step, the first mixture is fired at a temperature T1 to obtain a first fired body. The temperature T1 is typically 500°C or higher and 800°C or lower, and may be 550°C or higher and 750°C or lower. If the temperature T1 is too high, W2O3 is likely to be produced instead of the compound B containing Li, W, and O, making it difficult to reduce the resistance. On the other hand, if the temperature T1 is too low, it becomes difficult to sufficiently grow the primary particles.

[0093] The firing time in the first firing step is not particularly limited, but may be, for example, 5 hours or more and 15 hours or less, or 8 hours or more and 12 hours or less. The atmosphere in the first firing step is usually an atmosphere in which oxygen is present. Examples of firing methods in the first firing step include methods using a firing furnace such as a muffle furnace or an electric furnace.

[0094] In the first firing step, a pulverization treatment may be carried out to pulverize the first fired body. Examples of the pulverization method include a hammer mill, a lab mill, and a ball mill.

[0095] 2. Second firing process The second firing step is a step of firing the first fired body at a temperature T2 to obtain a second fired body. The temperature T2 in the second firing step is usually higher than the temperature T1 in the first firing step. By setting the temperature T2 higher than the temperature T1, it becomes easier to obtain an aggregate having a peak at a predetermined position in the pore size distribution.

[0096] The difference between temperature T2 and temperature T1 is, for example, 50°C or more, and may be 75°C or more, or 100°C or more. Temperature T2 is typically 600°C or more and 1000°C or less, and may be 650°C or more and 950°C or less. If temperature T2 is too high, W2O3 may be more likely to be produced. On the other hand, if temperature T2 is too low, aggregates having a peak at a predetermined position in the pore size distribution may not be obtained. The firing time in the second firing step is not particularly limited, but may be, for example, 1 hour or more and 5 hours or less, or 2 hours or more and 4 hours or less. The firing time in the second firing step may be shorter than the firing time in the first firing step. The atmosphere in the second firing step is typically an atmosphere containing oxygen. Examples of firing methods in the second firing step include methods using a firing furnace such as a muffle furnace or an electric furnace.

[0097] In the second firing step, the second fired body is usually pulverized. Examples of the pulverization method include a hammer mill, a laboratory mill, and a ball mill. The pulverization conditions are preferably adjusted so that an aggregate having a peak at a predetermined position in the pore size distribution is obtained.

[0098] 3. Third firing process The third firing step is a step of adding an La source to the pulverized product of the second fired body to prepare a second mixture, and firing the second mixture at a temperature T3 to obtain a third fired body. The temperature T3 in the third firing step is usually lower than the temperature T2 in the second firing step. By setting the temperature T3 lower than the temperature T2, a compound A containing La, Ni, and O is more likely to be produced instead of La2O3, thereby reducing the resistance.

[0099] Examples of the La source include hydroxides, sulfates, nitrates, and other metal salts. Examples of the La source include La(OH)3, LaSO4, and La(NO3)3. The amount of the La source added is appropriately adjusted depending on the desired positive electrode active material. The second mixture may or may not contain a Ni source.

[0100] The difference between temperatures T2 and T3 is, for example, 100°C or more, and may be 150°C or more, or 200°C or more. Temperature T3 is usually 400°C or more and 600°C or less, and may be 450°C or more and 550°C or less. If temperature T2 is too high, La2O3 may be easily produced. On the other hand, if temperature T2 is too low, the effect of compound A in improving electronic conductivity may not be sufficiently obtained.

[0101] The temperature T3 in the third baking step may be lower than the temperature T1 in the first baking step. The difference between the temperature T1 and the temperature T3 is, for example, 50°C or more, or may be 75°C or more, or may be 100°C or more.

[0102] The firing time in the third firing step is not particularly limited, but may be, for example, 3 hours or more and 7 hours or less, or 4 hours or more and 6 hours or less. The firing time in the third firing step may be longer than the firing time in the second firing step. The atmosphere in the third firing step is usually an atmosphere containing oxygen. Examples of firing methods in the third firing step include methods using a firing furnace such as a muffle furnace or an electric furnace.

[0103] In the third firing step, a pulverization treatment may be performed to pulverize the third fired body. Examples of the pulverization method include a hammer mill, a laboratory mill, and a ball mill. The pulverization conditions are preferably adjusted so as to obtain aggregates having a peak at a predetermined position in the pore size distribution.

[0104] 4. Other processes The method for producing a positive electrode active material according to the present disclosure may or may not include a granulation step of granulating the pulverized product of the third sintered body after the third sintering step. Granulation can produce large aggregates, thereby controlling the pore size distribution. Examples of methods for granulating the pulverized product of the sintered body include spray drying. In the spray drying method, for example, the pulverized product of the sintered body is dispersed in water, and the resulting dispersion is sprayed using a spray drying device. The heating temperature of the spray drying device is, for example, 150°C or higher and 250°C or lower.

[0105] 5.Cathode active material The positive electrode active material obtained by each of the above steps is the same as that described above in "A. Positive electrode active material."

[0106] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0107] [Comparative Example 1] (Preparation of positive electrode active material) NiSO4, CoSO4, and MnSO4 were prepared as raw materials and dissolved in ion-exchanged water to prepare a raw material aqueous solution. The molar ratio of Ni, Co, and Mn in the raw material aqueous solution was Ni:Co:Mn=8:1:1. The concentration of the raw material aqueous solution (the ratio of all raw materials to the raw material aqueous solution) was 30% by mass.

[0108] A certain amount of NH3 aqueous solution was then placed in the reaction vessel, and the atmosphere inside the vessel was replaced with nitrogen while stirring with a stirrer. NaOH aqueous solution was added to the reaction vessel, and the pH was kept alkaline (pH = 12). While controlling the temperature at a constant level, the raw material aqueous solution and NH3 aqueous solution were added dropwise to precipitate the transition metal hydroxide. The reaction temperature was 60°C, and the reaction time was 10 hours. Next, the precipitated transition metal hydroxide was filtered out, and washed with water by adding ion-exchanged water and dispersing it with a spoon. After washing, the transition metal hydroxide was dried at 120°C for 16 hours to obtain the precursor transition metal hydroxide.

[0109] Thereafter, a Li source (LiOH) was added to the obtained precursor and mixed in an agate mortar to obtain a first mixture. The amount of Li source added was adjusted so that the molar ratio (Li / NCM) of Li contained in the Li source to the total (NCM) of Ni, Co, and Mn contained in the precursor was 1.1. The obtained first mixture was fired in a firing furnace at 900°C in an oxygen atmosphere for 10 hours to obtain a fired body. The obtained fired body was crushed using a jet mill to adjust the particle size, and a positive electrode active material was obtained.

[0110] (Battery construction) A battery was fabricated using the resulting positive electrode active material. Specifically, a positive electrode composite paste containing the positive electrode active material, a conductive material (acetylene black), and a binder (polyvinylidene fluoride) in a mass ratio of positive electrode active material:conductive material:binder = 88:10:2 was applied to the surface of a metal foil positive electrode current collector using a film applicator with a film thickness adjustment function (manufactured by Allgrid Corporation). The resulting paste was then dried in a dryer at 80 °C for 5 minutes to obtain a positive electrode having a positive electrode current collector and a positive electrode active material layer.

[0111] Next, a negative electrode composite paste containing a negative electrode active material (natural graphite) and binders (SBR and CMC) was applied to the surface of a metal foil negative electrode current collector using a film applicator with a film thickness adjustment function (manufactured by Allgrid Corporation). The resulting mixture was then dried in a dryer at 80°C for 5 minutes to obtain a negative electrode current collector and a negative electrode with a negative electrode active material layer. Next, a 1M LiPF solution was prepared as the electrolyte. The solvent for the electrolyte was a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of EC:DMC:EMC = 3:4:3. A wound cylindrical battery was obtained using the above positive electrode, negative electrode, and electrolyte.

[0112] Comparative Example 2 A precursor (transition metal hydroxide) was obtained in the same manner as in Comparative Example 1. A Li source (LiOH), a La source (La(OH)), and a W source (HWO) were added to the obtained precursor and mixed in an agate mortar to obtain a first mixture. The amount of the Li source added was adjusted so that the molar ratio (Li / NCM) of Li contained in the Li source relative to the total (NCM) of Ni, Co, and Mn contained in the precursor was 1.1. The amount of the La source added was adjusted so that La / NCM was 0.005, and the amount of the W source added was adjusted so that W / NCM was 0.005. A positive electrode active material and a battery were obtained in the same manner as in Comparative Example 1, except that the obtained first mixture was used.

[0113] Comparative Example 3 A first mixture was obtained in the same manner as in Comparative Example 2. The obtained first mixture was fired in a firing furnace at 650°C in an oxygen atmosphere for 10 hours to obtain a first fired body. The obtained first fired body was crushed using a jet mill, and then fired in a firing furnace at 500°C in an oxygen atmosphere for 3 hours to obtain a second fired body.

[0114] [Example 1] A precursor (transition metal hydroxide) was obtained in the same manner as in Comparative Example 1. A Li source (LiOH) and a W source (H2WO4) were added to the obtained precursor and mixed in an agate mortar to obtain a first mixture. The amount of the Li source added was adjusted so that the molar ratio (Li / NCM) of Li contained in the Li source to the total (NCM) of Ni, Co, and Mn contained in the precursor was 1.2. The amount of the W source added was adjusted so that W / NCM was 0.005. The obtained first mixture was fired in a firing furnace at 650°C in an oxygen atmosphere for 10 hours to obtain a first fired body.

[0115] The obtained first sintered body was pulverized using a jet mill and then fired in a firing furnace at 800°C in an oxygen atmosphere for 3 hours to obtain a second sintered body. The obtained second sintered body was pulverized using a jet mill. A La source (La(OH)3) was added to the obtained pulverized material and mixed in an agate mortar to obtain a second mixture. The amount of La source added was adjusted so that the molar ratio of La contained in the La source to the total of Ni, Co, and Mn contained in the pulverized material (NCM) (Li / NCM) was 0.005. The resulting mixture was then fired in a firing furnace at 500°C in an oxygen atmosphere for 5 hours to obtain a third sintered body. The obtained third sintered body was pulverized using a jet mill to adjust the particle size, thereby obtaining a positive electrode active material. A battery was obtained in the same manner as in Comparative Example 1, except that the obtained positive electrode active material was used.

[0116] [Example 2] A third fired product was obtained in the same manner as in Example 1. The fired product obtained was pulverized using a hammer mill and crushed to a predetermined particle size (pulverization). 30 g of the pulverized product was then dispersed in 100 mL of pure water and sprayed at 200°C using a Buchi spray dryer to obtain a granulated positive electrode active material. A battery was obtained in the same manner as in Example 1, except for using the resulting positive electrode active material. In Table 1, synthesis method 1 is a method in which a single firing step was performed, as in Comparative Examples 1 and 2; synthesis method 2 is a method in which a two-step firing step was performed, as in Comparative Example 3; and synthesis method 3 is a method in which a three-step firing step was performed, as in Examples 1 and 2.

[0117] [evaluation] (SEM-EDX measurement) The positive electrode active materials obtained in Examples 1 and 2 and Comparative Examples 1 to 3 were subjected to cross-sectional observation and elemental analysis using a scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX). As a result, it was confirmed that the primary particles in Examples 1 and 2 and Comparative Examples 1 to 3 contained Ni, Co, and Mn. Furthermore, in Examples 1 and 2 and Comparative Example 3, particulate compounds were confirmed on the surfaces of the primary particles, and mapping images confirmed that the particulate compounds contained La, Ni, and O.

[0118] (TEM-EDX measurement) Cross-sectional observation and elemental analysis were performed by transmission electron microscope-energy dispersive X-ray spectroscopy (TEM-EDX) on the positive electrode active materials obtained in Examples 1 and 2 and Comparative Example 3. As a result, film-like compounds were confirmed on the surfaces of the primary particles in Examples 1 and 2 and Comparative Example 3, and mapping images confirmed that the film-like compounds contained W and O.

[0119] (XRD measurement) X-ray diffraction measurements (XRD) using CuKα radiation were performed on the positive electrode active materials obtained in Examples 1 and 2 and Comparative Examples 1 to 3. As a result, it was confirmed that the positive electrode active materials obtained in Examples 1 and 2 and Comparative Examples 1 to 3 all had a layered rock-salt crystalline phase belonging to the space group R-3m. That is, it was confirmed that the primary particles containing Ni, Co, and Mn had a layered rock-salt crystalline phase.

[0120] Furthermore, peaks derived from a LaNiO-based crystalline phase (La4LiNiO8) were observed in the positive electrode active materials obtained in Examples 1 and 2 and Comparative Example 3. This confirmed that compound A present on the surfaces of the primary particles was crystalline. On the other hand, peaks derived from a LiWO-based crystalline phase were not observed in the positive electrode active materials obtained in Examples 1 and 2 and Comparative Example 3. This suggests that compound B present on the surfaces of the primary particles is amorphous.

[0121] On the other hand, in the positive electrode active material obtained in Comparative Example 2, no peaks derived from a LaNiO-based crystalline phase were observed, but peaks derived from La2O3 and W2O3 were observed. That is, in the positive electrode active material obtained in Comparative Example 2, Compound A and Compound B according to the present disclosure were not formed.

[0122] (Pore size distribution measurement) Pore ​​size distribution measurements were performed by mercury intrusion porosimetry on the positive electrode active materials obtained in Examples 1 and 2 and Comparative Examples 1 to 3. Specifically, a Micromeritics mercury intrusion porosimetry analyzer was used to measure the pore size distribution of the positive electrode active material by injecting mercury into a sample tube sealed with 1 g of the positive electrode active material. In Examples 1 and 2, the positive electrode active material obtained was an aggregate, and therefore a peak was present in the range of 65 nm to 300 nm. On the other hand, in Comparative Examples 1 to 3, the positive electrode active material obtained was a single crystal, and therefore no such peak was present. The peak position results are shown in Table 1.

[0123] (initial resistance) The initial resistance was measured using the batteries obtained in Examples 1 and 2 and Comparative Examples 1 to 3. Specifically, the batteries were charged to 4.3 V and then discharged to 3.7 V. The voltage drop (V) was then measured after 10 seconds of discharge at 0°C and C rates of 0.1 C, 0.3 C, 0.5 C, 0.7 C, and 1.0 C. The relationship between the voltage drop (V) and the current value was plotted, and the slope of the linearly approximated line was taken as the resistance (IV resistance). The results are shown in Table 1. The initial resistance values ​​in Table 1 are relative values ​​when the initial resistance of Comparative Example 1 is set to 100%.

[0124] (Cycle resistance increase rate) The cycle resistance increase rate was measured using the batteries obtained in Examples 1 and 2 and Comparative Examples 1 to 3. Specifically, the resistance (IV resistance) was measured before and after the cycle test. The cycle test was performed for 100 cycles under the conditions of a voltage range of 3.0 V to 4.3 V, a C rate of 0.3 C, a CC charge / discharge mode, and a temperature of 50°C, and the cycle resistance increase rate was calculated based on the following formula. Cycle resistance increase rate (%) = (resistance after cycle test) / initial resistance × 100 The results are shown in Table 1.

[0125] [Table 1]

[0126] As shown in Table 1, it was confirmed that Examples 1 and 2 and Comparative Example 3 had lower initial resistances than Comparative Examples 1 and 2. This is presumably because the presence of Compound A (Compound A containing La, Ni, and O) with good electronic conductivity and Compound B (Compound B containing Li, W, and O) with good ionic conductivity on the surface of the primary particles allowed for smooth movement of electrons and ions. It was also confirmed that Examples 1 and 2 had lower cycle resistance increase rates than Comparative Example 3. This is presumably because the positive electrode active materials obtained in Examples 1 to 3 (aggregates) had smaller specific surface areas than the positive electrode active material obtained in Comparative Example 3 (single crystal), which prevented the accumulation of resistance components due to repeated charge and discharge. [Explanation of symbols]

[0127] 1...Primary particle 10...Cathode active material 11...Cathode active material layer 12...Negative electrode active material layer 13...electrolyte layer 14...Positive electrode current collector 15...Negative electrode current collector 20...battery

Claims

1. A positive electrode active material, the positive electrode active material has crystalline primary particles containing Li, TM (TM is a transition metal), and O, the positive electrode active material is an aggregate composed of a plurality of the primary particles, a compound A containing La, Ni, and O and a compound B containing Li, W, and O are present on the surface of the primary particles, The compound B is in the form of a film, The thickness of the compound B is 20 nm or less.

2. A positive electrode active material, the positive electrode active material has crystalline primary particles containing Li, TM (TM is a transition metal), and O, the positive electrode active material is an aggregate composed of a plurality of the primary particles, a compound A containing La, Ni, and O and a compound B containing Li, W, and O are present on the surface of the primary particles, The compound A has a composition of LaaNibOc (0.8≦a≦1.2, 0.8≦b≦1.2, 2.8≦c≦3.2) or LaaLibNicOd (3.5≦a≦4.5, 0.5≦b≦1.5, 0.5≦c≦1.5, 7.5≦d≦8.5).

3. 3. The positive electrode active material according to claim 1, wherein a pore size distribution obtained by mercury intrusion porosimetry has a peak in the range of 65 nm to 300 nm.

4. The positive electrode active material according to claim 3 , wherein the pore size distribution has a peak in the range of 80 nm to 220 nm.

5. 3. The positive electrode active material according to claim 1, wherein the primary particles in the aggregate have an average particle size of 0.5 μm or more.

6. 3. The positive electrode active material according to claim 1, wherein the primary particles contain at least one of Ni, Co, and Mn as the TM.

7. 3. The positive electrode active material according to claim 1, wherein the primary particles have a layered rock salt type crystal structure.

8. 3. The positive electrode active material according to claim 1, wherein at least one of the compound A and the compound B is present at an interface between adjacent primary particles in the aggregate.

9. The positive electrode active material according to claim 1 or 2, wherein the compound A is in a particulate form.

10. The positive electrode active material according to claim 2 , wherein the compound B is in the form of a film.

11. A positive electrode mixture comprising the positive electrode active material according to claim 1 or 2.

12. A battery having a positive electrode active material layer containing a positive electrode active material, a negative electrode active material layer containing a negative electrode active material, and an electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, A battery, wherein the positive electrode active material layer contains the positive electrode mixture according to claim 11.

13. A method for producing a positive electrode active material, comprising: the positive electrode active material has crystalline primary particles containing Li, TM (TM is a transition metal), and O, the positive electrode active material is an aggregate composed of a plurality of the primary particles, a compound A containing La, Ni, and O and a compound B containing Li, W, and O are present on the surface of the primary particles, The method for producing the positive electrode active material includes: A first mixture containing the transition metal hydroxide containing the TM, a Li source, and a W source is heated to a temperature T １ a first firing step of firing the mixture to obtain a first fired body; The first fired body is heated to a temperature T ２ a second firing step of firing the mixture to obtain a second fired body; A La source is added to the pulverized product of the second fired body to prepare a second mixture, and the second mixture is heated to a temperature T ３ a third firing step of firing the mixture to obtain a third fired body; and At least one of the first mixture and the second mixture contains a Ni source; The temperature T in the second baking step ２ is the temperature T in the first baking step １ Higher, The temperature T in the third baking step ３ is the temperature T in the second baking step ２ Lower, The temperature T １ is 500°C or more and 800°C or less, The temperature T ２ is 600°C or more and 1000°C or less, The temperature T ３ The method for producing a positive electrode active material, wherein the temperature is 400°C or higher and 600°C or lower.

Images