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

Abstract

The main purpose of the present disclosure is to provide a positive electrode active material having reduced resistance.　The present disclosure provides a positive electrode active material that has crystalline primary particles containing Li, TM (TM is a transition metal), and O, that is a single crystal active material comprising the primary particles, and that has a compound A containing La, Ni, and O on the surfaces of the primary particles.

Description

Positive electrode active material, positive electrode composite material, battery, and method for manufacturing positive electrode active material

[0001] The present disclosure relates to a positive electrode active material, a positive electrode composite material, a battery, and a method for manufacturing a positive electrode active material.

[0002] In recent years, the development of batteries has been actively carried out. For example, in the automotive industry, the development of batteries used in battery electric vehicles (BEV), plug-in hybrid electric vehicles (PHEV), or hybrid electric vehicles (HEV) has been promoted. As positive electrode active materials used in batteries, active materials containing transition metals such as Ni, Co, and Mn are known.

[0003] For example, in Patent Document 1, the chemical formula is Li ａ Ni ｘ Co ｙ Mn １－ｘ－ｙ W ｂ McO ２ A W-containing high-nickel ternary positive electrode material, wherein the high-nickel ternary positive electrode material contains spherical secondary particles and single-crystalline particles at the same time, and basically no W element is contained inside the single-crystalline particles, and the spherical secondary particles are doped with the W element. A W-containing high-nickel ternary positive electrode material is disclosed.

[0004] In Patent Document 2, a single-crystalline multi-component positive electrode material, wherein the ratio of the length of the longest diagonal line to the length of the shortest diagonal line measured by SEM for the single-crystalline particles of the single-crystalline multi-component positive electrode material is defined as the circularity R, and R is 1 or more, and the D １０ 、D ５０ and D ９０ satisfy K ９０ = (D ９０ - D １０ ) / D ５０ and the product of K ９０ and R is 1.20 to 1.40. A single-crystalline multi-component positive electrode material is disclosed.

[0005] Japanese Patent Application Laid-Open No. 2022-542774 Japanese Patent Application Laid-Open No. 2024-511223

[0006] From the perspective of improving battery performance, there is a need to reduce resistance. This disclosure has been made in view of the above circumstances, and its main purpose is to provide a positive electrode active material with reduced resistance.

[0007] [1] A positive electrode active material, wherein the positive electrode active material has crystalline primary particles containing Li, TM (where TM is a transition metal), and O, the positive electrode active material is a single-crystal active material composed of the primary particles, and the positive electrode active material has a compound A containing La, Ni, and O on the surface of the primary particles.

[0008] [2] The positive electrode active material is the positive electrode active material according to [1], wherein the surface of the primary particles has a compound B containing Li, W, and O.

[0009] [3] The positive electrode active material according to [1] or [2], wherein the particle size of the primary particles is 0.5 μm or larger.

[0010] [4] The positive electrode active material according to any one of [1] to [3], wherein the primary particles contain at least one of Ni, Co and Mn as TM.

[0011] [5] The primary particles are a positive electrode active material according to any one of [1] to [4], having a layered rock salt type crystal structure.

[0012] [6] Compound A is a particulate positive electrode active material according to any one of [1] to [5].

[0013] [7] Compound B is a film-like positive electrode active material according to any one of [1] to [6].

[0014] [8] The positive electrode active material according to any one of [1] to [7], wherein the positive electrode active material has a compound C containing Me (where Me is at least one of Co, Al, Ce, Y, and Ti) and O on the surface of the primary particles.

[0015] [9] A positive electrode composite containing the positive electrode active material described in any of [1] to [8].

[0016]

[10] A battery comprising 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, wherein the positive electrode active material layer contains the positive electrode composite material described in [9].

[0017]

[11] A method for producing a positive electrode active material according to any one of [1] to [8], comprising: a first mixture containing a transition metal hydroxide containing the above TM, a Li source, a La source and a Ni source, at a temperature T １ A first firing step in which the first fired body is fired at a temperature T ２ The process includes a second firing step in which the body is fired at a temperature T in the second firing step to obtain a second fired body, and ２ This refers to the temperature T in the first firing process described above. １ Lower than the above temperature T １ The temperature is between 500°C and 800°C, and the above temperature T ２ This is a method for producing a positive electrode active material, wherein the temperature is between 400°C and 600°C.

[0018]

[12] The method for producing a positive electrode active material according to

[11] , wherein the transition metal hydroxide contains at least Ni as the TM and also serves as the Ni source.

[0019]

[13] The method for producing a positive electrode active material according to

[11] or

[12] , wherein the first mixture contains a W source.

[0020]

[14] The method for producing the positive electrode active material is to add a Me source (Me is at least one of Co, Al, Ce, Y, and Ti) to the second calcined body to produce a second mixture, and then heat the second mixture at a temperature T ３ The process includes a third firing step in which the primary particles are fired at a temperature T in the third firing step to form compound C on the surface of the primary particles, and the temperature T in the third firing step is T ３ The temperature T in the second firing process described above is ２ Lower than the above temperature T ３ A method for producing a positive electrode active material according to any one of

[11] to

[13] , wherein the temperature is 350°C or higher and 550°C or lower.

[0021] This disclosure offers the advantage of providing a positive electrode active material with reduced resistance.

[0022] This is a schematic cross-sectional view illustrating the positive electrode active material in this disclosure. This is a schematic cross-sectional view illustrating the positive electrode active material in this disclosure. This is a schematic cross-sectional view illustrating the positive electrode active material in this disclosure. This is a schematic cross-sectional view illustrating the battery in this disclosure. This is a flowchart illustrating a method for manufacturing the positive electrode active material in this disclosure.

[0023] The embodiments will be described below with reference to the drawings, etc. However, this disclosure can be implemented in many different ways and is not limited to the embodiments described below. In addition, the drawings may schematically represent the width, thickness, and shape of each part compared to the actual form in order to make the explanation clearer, but this is merely an example and should not be interpreted as limiting.

[0024] A. Positive Electrode Active Material Figures 1 to 3 are schematic cross-sectional views illustrating the positive electrode active material in this disclosure. As shown in Figure 1, the positive electrode active material 10 has crystalline primary particles 1 containing Li, TM (where TM is a transition metal), and O. The positive electrode active material 10 is a single-crystal active material composed of primary particles 1. The positive electrode active material 10 also has compound A containing La, Ni, and O on the surface of the primary particles 1. As shown in Figure 2, the positive electrode active material 10 may also have compound B containing Li, W, and O on the surface of the primary particles 1. As shown in Figure 3, the positive electrode active material 10 may also have compound C containing Me (at least one of Co, Al, Ce, Y, and Ti) and O on the surface of the primary particles 1.

[0025] According to this disclosure, a positive electrode active material with reduced resistance can be obtained by having compound A (a compound containing La, Ni, and O) with good electronic conductivity on the surface of the primary particles. Furthermore, in this disclosure, it is preferable that compound B (a compound containing Li, W, and O) with good ionic conductivity be present on the surface of the primary particles. The presence of compound B also reduces resistance. Moreover, the presence of compound B suppresses the increase in resistance over time. The reason for this is presumed to be as follows: Although compound A has good electronic conductivity and can reduce resistance, it is presumed that side reactions due to electronic conductivity cause the accumulation of resistive components (decomposition products), leading to an increase in resistance over time. In contrast, compound B has moderately low electronic conductivity, so it is presumed that the accumulation of resistive components (decomposition products) in the positive electrode active material can be suppressed, thereby suppressing the increase in resistance over time. Furthermore, in this disclosure, it is preferable that compound C (a compound containing Me and O) be present on the surface of the primary particles. This is because it improves the battery's storage capacity retention rate. The reason for this is presumed to be that the presence of compound C on the surface of the primary particles improves the thermal stability of the positive electrode active material.

[0026] Furthermore, in the above-mentioned Patent Document 1, Example 3, Li １．００２９ Ni ０．８３ Co ０．１１ Mn ０．０６ W ０．０００９ La ０．００２ O ２ A positive electrode material represented by is disclosed. More specifically, a precursor A containing Ni, Co and Mn but not W, a precursor B containing Ni, Co, Mn and W, LiOH and La ２ O ３ The invention describes calcining a mixture containing the above at a high temperature of 880°C. However, Patent Document 1 neither describes nor suggests compound A (a compound containing La, Ni, and O) in this disclosure.

[0027] Furthermore, the aforementioned Patent Document 2 contains Li １＋ａ (Ni ｘ Co ｙ Mn ｚ G ｂ ) Mｃ O ２－ｄ A positive electrode material represented by is disclosed, where 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 of the options for G. However, Patent Document 2 does not disclose any examples using La.

[0028] 1. Primary Particles The primary particles in this disclosure are crystalline particles containing Li, TM (where TM is a transition metal), and O. Examples of the crystalline structure of the primary particles include layered rock salt type and spinel type, with the layered rock salt type being preferred. The primary particles may also have a crystalline structure that belongs to space group R-3m.

[0029] The primary particles contain Li, TM (where TM is a transition metal), and O. The primary particles may contain one transition metal, two transition metals, three transition metals, or four or more transition metals.

[0030] Transition metals are metals belonging to groups 3 through 11 of the periodic table. The transition metals included in the primary particles may be metals belonging to the third, fourth, or fifth period. Examples of transition metals include Ti, V, Cr, Mn, Fe, Co, Ni, Zr, Nb, La, and W.

[0031] The primary particles preferably contain at least Ni, as this allows for the creation of a positive electrode active material with good capacitance characteristics. When the total amount of transition metal contained in the primary particles is considered as 1 mole, the proportion of Ni in the primary particles may be, for example, 0.25 moles or more, 0.33 moles or more, 0.50 moles or more, 0.75 moles or more, 0.80 moles or more, or 0.90 moles or more. Increasing the proportion of Ni improves the capacitance characteristics.

[0032] The primary particles may or may not contain Co. When the total amount of transition metal in the primary particles is considered as 1 mole, the proportion of Co in the primary particles may be, for example, 0 moles or more, 0.05 moles or more, or 0.10 moles or more. On the other hand, the proportion of Co in the primary particles may be, for example, 0.40 moles or less, or 0.20 moles or less.

[0033] The primary particles may or may not contain Mn. When the total amount of transition metal in the primary particles is considered as 1 mole, the proportion of Mn in the primary particles may be, for example, 0 moles or more, 0.05 moles or more, or 0.10 moles or more. On the other hand, the proportion of Mn in the primary particles may be, for example, 0.40 moles or less, or 0.20 moles or less.

[0034] The primary particles preferably contain at least one of Ni, Co, and Mn. When all the metals (excluding Li) contained in the primary particles are considered as 1 mole, the total proportion of Ni, Co, and Mn contained in the primary particles is, for example, 0.80 moles or more, may be 0.90 moles or more, or 0.95 moles or more. Note that "total of Ni, Co, and Mn" also includes cases where the proportion of one or two of Ni, Co, and Mn is 0.

[0035] The primary particles consist of Li and TM, as well as other metals other than Li and TM. １ It may contain (metalloids). Other metals M １ Examples include metals belonging to groups 12 through 14 of the periodic table. Examples of metals belonging to groups 12 through 14 include Zn, Al, Si, Ga, Ge, In, and Sn.

[0036] The composition of the primary particles is not particularly limited, but for example, Li ｘ Ni ａ Co ｂ Mn ｃ O ｙThe composition may be represented by (0.1 ≤ x ≤ 1.5, 0.5 ≤ a ≤ 1.0, 0 ≤ b ≤ 0.3, 0 ≤ c ≤ 0.3, a + b + c = 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, and 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, and may be 2.0 or less. "a" may be 0.6 or greater, 0.7 or greater, 0.8 or greater, or 0.85 or greater, and may be 0.9 or less. "b" may be 0.01 or greater, 0.02 or greater, 0.03 or greater, 0.04 or greater, 0.05 or greater, 0.06 or greater, 0.07 or greater, or 0.075 or greater, and may be 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 greater, 0.02 or greater, 0.03 or greater, 0.04 or greater, 0.05 or greater, 0.06 or greater, 0.07 or greater, or 0.075 or greater, and may be 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.

[0037] The positive electrode active material in this disclosure is typically a single-crystal active material composed of the above-mentioned primary particles. A single-crystal active material is not a so-called polycrystalline active material (an active material in which many primary particles are aggregated without gaps). A single-crystal active material is usually not aggregated and exists as a single independent particle. It is preferable that no grain boundaries are observed in the single-crystal active material when observed with a scanning electron microscope (SEM) (magnification: approximately 10,000 to 30,000 times). A single-crystal active material has the advantage of being less prone to degradation over time compared to a polycrystalline active material.

[0038] The particle size of the primary particles is, for example, 0.5 μm or larger, but may also be 0.6 μm or larger, 0.8 μm or larger, or 1.0 μm or larger. If the particle size of the primary particles is too small, the particles may not grow sufficiently, making it difficult to produce them as single crystals. On the other hand, the particle size of the primary particles is, for example, 20 μm or less, but may also be 15 μm or less, 10 μm or less, or 5 μm or less. The particle size of the primary particles is determined, for example, by the longest diameter observed by SEM. Also, for example, if the positive electrode active material layer contains primary particles (positive electrode active material), the particle size (longest diameter) of the primary particles may be determined from a cross-sectional image of the positive electrode active material layer.

[0039] 2. Compound A Compound A in this disclosure contains La, Ni, and O. Compound A usually has high electronic conductivity, so the presence of compound A on the surface of primary particles can reduce resistance. Compound A may be directly placed on the surface of primary particles or placed via other layers (other compounds), but the former is preferred.

[0040] Compound A contains at least La, Ni, and O. Compound A may consist only of La, Ni, and O, or it 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) are examples. For example, LaNiO ３ This 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) are examples. For example, La ４ LiNiO ８ It is known to have good electronic conductivity and is assumed to have a crystalline phase similar to that of perovskite.

[0041] Compound A may be crystalline or amorphous, but the former is preferred because it provides good electronic conductivity. "A compound is crystalline" means that a peak originating from the compound is detected by X-ray diffraction using CuKα rays. On the other hand, "a compound is amorphous" means that no peak originating from the symmetric compound is detected by X-ray diffraction using CuKα rays. Note that if the compound is amorphous, a halo pattern may be observed instead of a peak.

[0042] Compound A preferably has a perovskite crystalline phase or a crystalline phase similar to a perovskite. Compound A is LaNiO ３ Or La ４ LiNiO ８ It is preferable to have at least one of the crystalline phases, because good electronic conductivity can be obtained. The above crystalline phases include crystalline phases in which some of the constituent atoms (for example, some of the O atoms) are missing, and crystalline phases in which some of the constituent atoms (for example, some of the La atoms) are in excess.

[0043] Compound A is preferably in particulate form. "Compound A is particulate" means that, in a cross-sectional image of a primary particle, the length of compound A in the direction normal to the surface of the primary particle is L. １ Let L be the length of compound A in the direction perpendicular to the normal direction. ２ In that case, L １ L ２ Ratio (L ２ / L １ This means that the value is 3.0 or less. The cross-sectional image of the primary particle is, for example, an SEM cross-sectional image.

[0044] When the total amount of transition metal contained in the primary particles is considered to be 1 mole, the proportion of La contained in compound A is, for example, 0.001 moles or more, may be 0.003 moles or more, or may be 0.005 moles or more. On the other hand, the above proportion of La contained in compound A is, for example, 0.100 moles or less, may be 0.080 moles or less, or may be 0.060 moles or less.

[0045] The coverage of compound A on the primary particles is not particularly limited, but for example, it may be 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 compound A can be determined, for example, by surface analysis by XPS (X-ray photoelectron spectroscopy). For example, if the primary particles contain Ni, Co, and Mn as transition metals TM, the amount of La and the amount of each TM (amount of Ni, amount of Co, amount of Mn) can be determined by surface analysis by XPS, and La / (La+TM) can be used as the coverage. The coverage of compounds B and C can be determined in the same way. In addition, the electronic conductivity of compound A is usually La ２ O ３ It is higher than the electronic conductivity of compound A. The electronic conductivity of compound A is, for example, 5.0 × 10 at 25°C. －４ It is S / cm or more, and 1.0 × 10 －３ The ratio may be S / cm or higher. Compound A (a compound containing La, Ni, and O) is placed on the surface of the primary particles. The primary particles may or may not contain La.

[0046] 3. Compound B The positive electrode active material in this disclosure may have 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. In addition, the presence of compound B on the surface of the primary particles can suppress the increase in resistance over time. Compound B may be directly arranged on the surface of the primary particles or arranged via other layers (other compounds), but the former is preferred.

[0047] Compound B contains at least Li, W, and O. Compound B may consist only of Li, W, and O, or it may further contain other elements. An example of the composition of Compound B is Li ａ W ｂ O ｃ Examples include (5.5 ≤ a ≤ 6.5, 0.5 ≤ b ≤ 1.5, 5.5 ≤ c ≤ 6.5). Compound B having the above composition is typically Li ６ WO ６is as follows. Another example of the composition of Compound B is Li ａ W ｂ O ｃ where (1.5 ≤ a ≤ 2.5, 0.5 ≤ b ≤ 1.5, 3.5 ≤ c ≤ 4.5). Compound B having the above composition is typically Li ２ WO ４ is. Another example of the composition of Compound B is Li ａ W ｂ O ｃ where (3.5 ≤ a ≤ 4.5, 0.5 ≤ b ≤ 1.5, 4.5 ≤ c ≤ 5.5). Compound B having the above composition is typically Li ４ WO<​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​When the total amount of transition metals contained in the primary particles is considered to be 1 mole, the proportion of W contained in compound B is, for example, 0.001 moles or more, may be 0.003 moles or more, or may be 0.005 moles or more. On the other hand, the above proportion of W contained in compound B is, for example, 0.100 moles or less, may be 0.080 moles or less, or may be 0.060 moles or less.

[0050] The coverage of compound B on the primary particles is not particularly limited, but for example, it may be 10% or more and 90% or less, 20% or more and 80% or less, or 30% or more and 70% or less. Also, the ionic conductivity of compound B is usually W ２ O ３ Its ionic conductivity is higher than that of compound B. The ionic conductivity of compound B is, for example, 1.0 × 10⁻⁶ at 25°C. －５ It is S / cm or more, and 1.0 × 10 －４ The ratio may be S / cm or higher. Compound B (a compound containing Li, W, and O) is placed on the surface of the primary particles. The primary particles may or may not contain W.

[0051] 4. Compound C The positive electrode active material in this disclosure may have a compound C containing Me (where Me is at least one of Co, Al, Ce, Y, and Ti) and O on the surface of the primary particles. The presence of compound C on the surface of the primary particles provides a positive electrode active material with good storage capacity retention. Furthermore, Me is an element that can stably take on a +3 valence. Compound C may be directly arranged on the surface of the primary particles or arranged via other layers (other compounds), but the former is preferred.

[0052] Compound C contains at least Me and O. Compound C may consist only of Me and O, or it may further contain other elements. Examples of other elements include Li. That is, compound C may or may not contain Li.

[0053] An example of the composition of compound C is Li ａ Me ｂ O ｃExamples include (0.5 ≤ a ≤ 1.5, 0.5 ≤ b ≤ 1.5, 1.5 ≤ c ≤ 2.5). Compound C having the above composition is typically LiMeO ２ That is the case.

[0054] When the total amount of transition metal contained in the primary particles is considered to be 1 mole, the proportion of Me contained in compound C is, for example, 0.001 moles or more, may be 0.005 moles or more, or may be 0.010 moles or more. On the other hand, the above proportion of Me contained in compound C is, for example, 0.100 moles or less, may be 0.080 moles or less, or may be 0.060 moles or less.

[0055] Compound C may be crystalline or amorphous. Compound C may also be particulate or film-like. The definitions of particulate and film-like are the same as above. The coverage of compound C on the primary particles is not particularly limited, but for example, it may be 10% or more and 90% or less, 20% or more and 80% or less, or 30% or more and 70% or less. Compound C (a compound containing Me) is placed on the surface of the primary particles. The primary particles may or may not contain Me.

[0056] 5. Positive Electrode Active Material The positive electrode active material in this disclosure is a single-crystal active material composed of crystalline primary particles containing Li, TM (where TM is a transition metal), and O. Furthermore, the positive electrode active material has at least compound A on the surface of the primary particles. The positive electrode active material may also have compound B on the surface of the primary particles. In addition, the positive electrode active material may have compound C on the surface of the primary particles. The positive electrode active material is typically used in batteries. The method for manufacturing the positive electrode active material is not particularly limited, but examples include the method described in "D. Method for Manufacturing the Positive Electrode Active Material" below.

[0057] Furthermore, this disclosure also provides a positive electrode active material powder in which the positive electrode active material powder contains a plurality of single-crystal active materials composed of crystalline primary particles containing Li, TM (where TM is a transition metal), and O as the positive electrode active material, and at least a portion of the plurality of single-crystal active materials is a single-crystal active material X having compound A containing La, Ni, and O on the surface of the primary particles. The single-crystal active material X is the same as the positive electrode active material described above and may further contain at least compound B and compound C. The ratio of the single-crystal active material X to all positive electrode active materials in the positive electrode active material powder is, for example, 5% by mass or more, may be 10% by mass or more, may be 20% by mass or more, may be 30% by mass or more, may be 40% by mass or more, may be 50% by mass or more, may be 60% by mass or more, or may be 70% by mass or more.

[0058] B. Cathode Compound The cathode compound in this disclosure contains the cathode active material described above.

[0059] According to this disclosure, by using the above-described positive electrode active material, a positive electrode composite material with reduced resistance is obtained. The positive electrode composite material may contain other materials (e.g., conductive material, binder) in addition to the positive electrode active material. The positive electrode composite material may also contain the above-described positive electrode active material powder. Furthermore, the positive electrode composite material may be in powder form or in slurry form containing a dispersion medium.

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

[0061] The positive electrode composite material may contain a conductive material. Adding a conductive material improves the 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 Ketjenblack (KB), and fibrous materials such as vapor-processed carbon fiber (VGCF), carbon nanotubes (CNT), and carbon nanofibers (CNF).

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

[0063] The positive electrode composite material may contain a binder. Adding a binder provides a positive electrode active material layer that is less prone to the detachment of the positive electrode active material. Examples of binders include rubber-based binders such as styrene-butadiene rubber (SBR) and butadiene rubber (BR), polycarboxylic acid-based binders such as carboxymethylcellulose, and fluoride-based binders such as polyvinylidene fluoride (PVdF).

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

[0065] C. Battery Figure 4 is a schematic cross-sectional view illustrating a battery in this disclosure. The battery 20 shown in Figure 4 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 for collecting current from the positive electrode active material layer 11, and a negative electrode current collector 15 for collecting current from the negative electrode active material layer 12. In this disclosure, the positive electrode active material layer 11 contains the positive electrode mixture described in "B. Positive Electrode Mixture" above.

[0066] According to this disclosure, by using the above-mentioned positive electrode composite material, a battery with reduced resistance can be obtained.

[0067] 1. Positive Electrode Active Material Layer The positive electrode active material layer contains at least 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 in "A. Positive Electrode Active Material" and "B. Positive Electrode Compound" above.

[0068] The positive electrode active material layer may contain an electrolyte. The electrolyte is, for example, an electrolyte solution as described later. 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, and may be 1 μm or more and 500 μm or less, or 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 one example is to coat a positive electrode slurry containing the positive electrode active material and a dispersion medium onto a positive electrode current collector and then dry it. The positive electrode active material layer may be subjected to a press treatment after drying. 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. Examples of negative electrode active materials include carbon-based active materials, Li-based active materials, Si-based active materials, and oxide-based active materials.

[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 alloy is supported on a carbon support. Examples of oxide-based active materials include Li ４ Ti ５ O １２ Examples include lithium titanate.

[0072] The proportion of negative electrode active material in the negative electrode active material layer is, for example, 20% by mass or more, may be 30% by mass or more, or 40% by mass or more. If the proportion of negative electrode active material is too low, a sufficient energy density may not be obtained. On the other hand, the proportion of negative electrode active material in the negative electrode active material layer is, for example, 95% by mass or less, may be 70% by mass or less, or 60% by mass or less. If the proportion of negative electrode active material is too high, the ionic conductivity and electronic conductivity in 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, binder, and electrolyte are the same as those described in "1. Positive Electrode Active Material Layer" above. The thickness of the negative electrode active material layer may be, for example, 0.1 μm or more and 1000 μm or less, 1 μm or more and 500 μm or less, or 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 one example is to coat a negative electrode slurry containing the negative electrode active material and dispersion medium onto a negative electrode current collector and then dry it. The negative electrode active material layer may be subjected to a press treatment after drying. The press treatment improves the density of the negative electrode active material layer.

[0075] 3. Electrolyte Layer The electrolyte layer is a layer placed between the positive electrode active material layer and the negative electrode active material layer, and contains at least an electrolyte. The electrolyte is, for example, a liquid electrolyte (electrolyte solution).

[0076] An example of an electrolyte is a non-aqueous electrolyte. A non-aqueous electrolyte contains, for example, a lithium salt and a non-aqueous solvent. An example of a lithium salt is LiPF4. ６ LiBF ４ LiClO ４ LiAsF ６ Inorganic lithium salts such as LiCF ３ SO ３ , LiN (SO ２ CF ３ ) ２ , LiN (SO ２ C ２ F ５ ) ２ , LiC (SO ２ CF ３ ) ３ Examples of organolithium salts include the following.

[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 cyclic carbonates such as EC and PC, which have high dielectric constant and high viscosity, and linear carbonates such as DMC, DEC, and EMC, which have low dielectric constant and low viscosity. The concentration of lithium salt in the non-aqueous electrolyte is, for example, 0.3 M or more and 5 M or less. The non-aqueous electrolyte 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 an electrolyte is an aqueous electrolyte. An aqueous electrolyte is an electrolyte that contains water as the main component of the solvent. The proportion of water to the total solvent is, for example, 50% by mass or more, and may be 70% by mass or more. Examples of lithium salts used in aqueous electrolytes 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 is, for example, 1 M or more and 25 M or less.

[0079] The electrolyte layer may include a separator impregnated with the aforementioned electrolyte. Providing a separator can suppress the occurrence of internal short circuits. The separator is, for example, a porous membrane. Examples of separator materials include polyethylene, polypropylene, polyester, polyvinyl alcohol, cellulose, polyamide, and other resins. The electrolyte layer may also contain a solid electrolyte. Examples of solid electrolytes 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 in this disclosure preferably has a positive electrode current collector for collecting current from the positive electrode active material layer and a negative electrode current collector for collecting 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 in this disclosure may also have an outer casing that houses the power generation elements (positive electrode active material layer, electrolyte layer, and negative electrode active material layer). Examples of outer casings include a case-type outer casing and a laminate-type outer casing.

[0081] The type of battery described herein is not particularly limited, but is typically a lithium-ion battery. The battery described herein may be a primary battery or a secondary battery, but is preferably a secondary battery because it can be repeatedly charged and discharged and is useful, for example, as an in-vehicle battery. Examples of battery applications include powering vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric electric vehicles (BEVs), gasoline cars, and diesel cars. In particular, it is preferable to use the battery as a power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric vehicles (BEVs). The battery may also be used as a power source for mobile devices other than vehicles (e.g., railways, ships, aircraft), or as a power source for electrical products such as information processing devices.

[0082] D. Method for producing the positive electrode active material Figure 5 is a flowchart illustrating the method for producing the positive electrode active material in this disclosure. In Figure 5, first, a first mixture containing a transition metal hydroxide containing TM, a Li source, a La source, and a Ni source is heated to a temperature T １ The first fired body is fired at a temperature T ２ The material is then fired to obtain a second fired body (second firing step). This yields a positive electrode active material. In this disclosure, the temperature T in the second firing step is ２ This refers to the temperature T in the first firing process. １ Lower. Furthermore, temperature T １ and temperature T ２ Each of these falls within a specified range.

[0083] According to this disclosure, a positive electrode active material with reduced resistance can be obtained by performing a first firing step and a second firing step.

[0084] 1. First firing step The first firing step involves firing a first mixture containing the above TM, a transition metal hydroxide, a Li source, a La source, and a Ni source at a temperature T １ This is the process of firing to obtain the first fired body.

[0085] Transition metal hydroxides contain TM (where TM is a transition metal). Transition metal hydroxides are precursors to positive electrode active materials. Transition metal hydroxides typically do not contain Li, but may contain Li. Transition metal hydroxides may also contain La, or may not contain La. Transition metal hydroxides may also contain W, or may not contain W. Transition metal hydroxides may also contain Ni, or may not contain Ni.

[0086] The method for synthesizing transition metal hydroxides is not particularly limited, but examples include the following: First, an aqueous solution of the transition metal hydroxide raw materials is prepared. A method for preparing the aqueous solution of the raw materials is, for example, to dissolve a water-soluble transition metal compound in water. Examples of transition metal compounds include metal salts such as sulfates and nitrates. As a Ni source, for example, NiSO4 is used. ４ Ni (NO ３ ) ２ Examples include CoSO4. ４ Co(NO ３ ) ２ Co(NO ３ ) ３ Examples include MnSO4. ４ , Mn(NO ３ ) ２ These are some examples. The composition of the raw material aqueous solution is adjusted as appropriate to suit 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 (for example, pH 11.3 to 12.0), the aqueous raw material solution and NH are added. ３ The aqueous solution is added dropwise. The reaction temperature is not particularly limited, but for example, it is between 50°C and 65°C. After the reaction is complete, it is preferable to filter out the transition metal hydroxide, wash it with water, and then dry it.

[0088] In the first calcination step, a first mixture containing a transition metal hydroxide, a Li source, a La source, and a Ni source is prepared. Examples of Li sources 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 or more and 1.2 or less, and may be 0.9 or more and 1.1 or less, or 1.0.

[0089] Examples of La sources include hydroxides; metal salts such as sulfates and nitrates. Another example of a La source is La(OH) ３ LaSO ４ , La (NO ３ ) ３ For example, if the transition metal hydroxide contains Ni, the transition metal hydroxide may also serve as a Ni source. On the other hand, if the transition metal hydroxide does not contain Ni, a separate Ni source is required. An example of a Ni source is Ni(OH) ２ NiSO ４ Ni (NO ３ ) ２ Examples include H ２ WO ４ These include the following. The amounts of La source, Ni source, and W source added are appropriately adjusted according to the desired positive electrode active material.

[0090] The first mixture preferably contains a molten salt. The molten salt functions as a flux, allowing primary particles to grow sufficiently. The molten salt may contain Li. Examples of molten salts include lithium hydroxide. The molar ratio of Li in the molten salt to TM in the transition metal hydroxide (Li / TM) is, for example, 0.01 or more, may be 0.05 or more, may be 0.10 or more, or may be 0.15 or more. On the other hand, Li / TM is, for example, 0.60 or less, may be 0.50 or less, may be 0.40 or less, or may be 0.30 or less.

[0091] The first mixture may contain lithium hydroxide as the Li source and molten salt. The molar ratio of Li contained in the Li source and molten salt to TM contained in the transition metal hydroxide (Li' / TM) is, for example, 1.01 or more, may be 1.05 or more, may be 1.10 or more, or may be 1.15 or more. On the other hand, Li' / TM is, for example, 1.60 or less, may be 1.50 or less, may be 1.40 or less, or may be 1.30 or less.

[0092] In the first firing process, the first mixture is heated to a temperature T １ The material is fired at temperature T to obtain the first fired body. １ The temperature is usually between 500°C and 800°C, but may also be between 550°C and 750°C. １ If the value is too high, instead of compound A containing La, Ni, and O, La ２ O ３ This makes it easier for the material to be generated, making it difficult to reduce resistance. Similarly, at temperature T １ If the concentration is too high, it will be W, rather than compound B which contains Li, W, and O. ２ O ３ This makes it easier for the material to be generated, making it difficult to reduce resistance. On the other hand, at temperature T １ If the temperature is too low, it becomes difficult to allow primary particles to grow sufficiently.

[0093] The firing time in the first firing process 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 process is usually an atmosphere in which oxygen is present. As for the firing method in the first firing process, for example, a method using a firing furnace such as a muffle furnace or an electric furnace can be mentioned.

[0094] 2. Second firing process The second firing process involves firing the first fired body at a temperature T ２ This is a process of firing to obtain a second fired body. The temperature T in the second firing process. ２ Typically, the temperature T in the first firing process is １ Lower. Temperature T ２ temperature T １ By making it lower, La ２ O ３Instead, compound A containing La, Ni, and O is more easily formed, which can reduce resistance. Similarly, at temperature T ２ temperature T １ By making it lower, W ２ O ３ Instead, compound B containing Li, W, and O is more easily formed, which can reduce resistance.

[0095] Temperature T １ and temperature T ２ The difference is, for example, 50°C or more, may be 75°C or more, or may be 100°C or more. Also, temperature T ２ The temperature is usually between 400°C and 600°C, but may also be between 450°C and 550°C. ２ If it is too high, La ２ O ３ This may make it easier for it to be generated. On the other hand, temperature T ２ If the temperature is too low, the effect of compound A in improving electronic conductivity may not be sufficiently obtained. The firing time in the second firing step is not particularly limited, but for example, it may be 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 usually an atmosphere in which oxygen is present. As for the firing method in the second firing step, for example, a method using a firing furnace such as a muffle furnace or an electric furnace can be mentioned.

[0096] 3. Third firing process The method for producing the positive electrode active material in this disclosure involves adding an Me source (Me is at least one of Co, Al, Ce, Y, and Ti) to the second firing body to produce a second mixture, and then heating the second mixture at a temperature T ３ The process may include a third firing step in which compound C is formed on the surface of the primary particles by firing. Forming compound C improves the battery's storage capacity retention rate.

[0097] Examples of Me sources include metal salts such as nitrates and sulfates. Me is at least one of Co, Al, Ce, Y, and Ti. Examples of Co sources include Co(NO ３ ) ２ Co(NO３ ) ３ CoSO ４ Examples include Al(NOx). ３ ) ３ Al ２ (SO ４ ) ３ Examples include Ce (NOx). ３ ) ３ Ce ２ (SO ４ ) ３ Examples include Y (NO ３ ) ３ , Y ２ (SO ４ ) ３ Examples include Ti(NO). ３ ) ３ Ti ２ (SO ４ ) ３ These include the following. The amount of Me source added is adjusted as appropriate according to the desired cathode active material.

[0098] Temperature T in the third firing process ３ Typically, the temperature T in the second firing process is ２ Lower. Temperature T ３ temperature T ２ By lowering the temperature, compound C can be formed while suppressing the alteration of compound A, which contains La, Ni, and O. Similarly, temperature T ３ temperature T ２ By lowering the concentration further, compound C can be formed while suppressing the alteration of compound B, which contains Li, W, and O.

[0099] Temperature T ２ and temperature T ３ The difference is, for example, 50°C or more, may be 75°C or more, or may be 100°C or more. Also, temperature T ３ The temperature is usually between 350°C and 550°C, but may also be between 400°C and 500°C. ３ If the temperature is too high, compound A may be altered. On the other hand, temperature T ３If the temperature is too low, the effect of compound C in improving the storage capacity retention rate may not be sufficiently obtained. The firing time in the third firing step is not particularly limited, but for example, it may be 2 hours or more and 8 hours or less, or 3 hours or more and 7 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 in which oxygen is present. As for the firing method in the third firing step, for example, a method using a firing furnace such as a muffle furnace or an electric furnace can be mentioned.

[0100] 4. Positive electrode active material The positive electrode active material obtained by each of the above processes is the same as described in "A. Positive electrode active material" above.

[0101] This disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of this disclosure and achieves similar effects is included within the technical scope of this disclosure.

[0102] [Comparative Example 1] (Preparation of positive electrode active material) NiSO4 as raw material ４ CoSO ４ and MnSO ４ The following were prepared and dissolved in deionized water to prepare the 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.

[0103] Subsequently, NH into the reaction vessel ３ A fixed amount of aqueous solution was added, and while stirring with a stirrer, the reaction vessel was purged with nitrogen. NaOH aqueous solution was added to the reaction vessel, maintaining the pH at an alkaline level (pH = 12), and while controlling the temperature, the raw material aqueous solution and NH were added. ３ An aqueous solution was 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 removed by filtration and washed with deionized water by dispersing it with a spoon. The washed transition metal hydroxide was dried at 120°C for 16 hours to obtain the precursor transition metal hydroxide.

[0104] Subsequently, a Li source (LiOH) was added to the obtained precursor and mixed in an agate mortar to obtain the first mixture. The amount of Li source added was adjusted so that the molar ratio of Li in the Li source to the total amount of Ni, Co, and Mn in the precursor (NCM) was 1.1 (Li / NCM). The obtained first mixture was calcined in a calcination furnace at 900°C in an oxygen atmosphere for 10 hours to obtain a calcined body. The obtained calcined body was crushed using a jet mill to adjust the particle size and obtain a positive electrode active material.

[0105] (Battery Fabrication) A battery was fabricated using the obtained positive electrode active material. Specifically, a positive electrode composite paste containing the positive electrode active material, conductive material (acetylene black), and binder (polyvinylidene fluoride) in a mass ratio of positive electrode active material:conductive material:binder = 88:10:2 was coated onto the surface of a metal foil, which served as the positive electrode current collector, using a film applicator with a film thickness adjustment function (manufactured by AllGrid Co., Ltd.). The mixture 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.

[0106] Next, a negative electrode composite paste containing negative electrode active material (natural graphite) and binder (SBR and CMC) was coated onto the surface of the metal foil, which was the negative electrode current collector, using a film applicator with a film thickness adjustment function (manufactured by AllGrid Co., Ltd.). After that, it was dried in a dryer at 80°C for 5 minutes to obtain a negative electrode having a negative electrode current collector and a negative electrode active material layer. Next, a 1 M LiPF was used as the electrolyte. ６ A solution was prepared. The electrolyte solvent 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. Using the above positive electrode, negative electrode, and electrolyte, a wound cylindrical battery was obtained.

[0107] [Comparative Example 2] A precursor (transition metal hydroxide) was obtained in the same manner as in Comparative Example 1. The obtained precursor was given a Li source (LiOH) and a La source (La(OH) ３ ) and W source (H ２ WO ４The following were added and mixed in an agate mortar to obtain the first mixture. The amount of Li source added was adjusted so that the molar ratio of Li in the Li source to the total amount of Ni, Co, and Mn in the precursor (NCM) (Li / NCM) was 1.1. The amount of La source added was adjusted so that La / NCM was 0.005, and the amount of 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.

[0108] [Example 1] 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. The obtained second fired body was crushed using a jet mill to adjust the particle size and obtain 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.

[0109] [Examples 2-4] The positive electrode active material and battery were obtained in the same manner as in Example 1, except that the amounts of La source and W source added were changed as shown in Table 1. In Table 1, synthesis method 1 is a method that involves a single firing step, as in Comparative Examples 1 and 2, and synthesis method 2 is a method that involves a two-step firing step, as in Examples 1-4.

[0110] [Evaluation] (SEM-EDX measurement) Cross-sectional observation and elemental analysis were performed on the positive electrode active materials obtained in Examples 1 to 4 using scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX). As a result, it was confirmed that the primary particles in Examples 1 to 4 contained Ni, Co, and Mn. In addition, particulate compounds were observed on the surface of the primary particles in Examples 1 to 4, and mapping images confirmed that the particulate compounds contained La, Ni, and O.

[0111] (TEM-EDX measurement) Cross-sectional observation and elemental analysis were performed on the positive electrode active materials obtained in Examples 1 to 3 using transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX). As a result, a film-like compound was confirmed on the surface of the primary particles in Examples 1 to 3, and mapping images confirmed that the film-like compound contained W and O.

[0112] (XRD Measurement) X-ray diffraction (XRD) measurements using CuKα rays were performed on the positive electrode active materials obtained in Examples 1-4 and Comparative Examples 1 and 2. As a result, it was confirmed that the positive electrode active materials obtained in Examples 1-4 and Comparative Examples 1 and 2 all have a layered rock salt type crystalline phase belonging to space group R-3m. That is, it was confirmed that the primary particles containing Ni, Co, and Mn have a layered rock salt type crystalline phase.

[0113] Furthermore, in the positive electrode active materials obtained in Examples 1 to 4, the LaNiO-based crystalline phase (La ４ LiNiO ８ A peak originating from the crystalline phase was observed. Therefore, it was confirmed that compound A present on the surface of the primary particles is crystalline. On the other hand, no peak originating from the LiWO-based crystalline phase was observed in the positive electrode active materials obtained in Examples 1 to 4. Therefore, it is presumed that compound B present on the surface of the primary particles is amorphous.

[0114] On the other hand, in the positive electrode active material obtained in Comparative Example 2, no peaks originating from the LaNiO-based crystalline phase were observed, and La ２ O ３ and W ２ O ３ A peak originating from [the specified component] was observed. In other words, compounds A and B in this disclosure were not formed in the positive electrode active material obtained in Comparative Example 2.

[0115] (Initial Resistance) The initial resistance was measured using the batteries obtained in Examples 1 to 4 and Comparative Examples 1 and 2. Specifically, the batteries were charged to 4.3V and then discharged to 3.7V. After that, the voltage drop (V) was measured when the batteries were discharged for 10 seconds at 0°C under conditions of C rates of 0.1C, 0.3C, 0.5C, 0.7C, and 1.0C. The relationship between the voltage drop (V) and the current value was plotted, and the slope of the approximate straight line drawn using a linear function was defined as the resistance (IV resistance). The results are shown in Table 1. Note that the initial resistance values ​​in Table 1 are relative values ​​with the initial resistance of Comparative Example 1 set to 100%.

[0116] (Cycle Resistance Increase Rate) The cycle resistance increase rate was measured using the batteries obtained in Examples 1 to 4 and Comparative Examples 1 and 2. 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 voltage range: 3.0V-4.3V, C rate: 0.3C, mode: CC charge / discharge, and temperature: 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.

[0117]

[0118] As shown in Table 1, Example 4 was found to have lower initial resistance compared to Comparative Examples 1 and 2. This is presumed to be because the presence of compound A (containing La, Ni, and O), which has good electronic conductivity, on the surface of the primary particles made electron movement smoother. Furthermore, Examples 1 to 3 were found to have lower initial resistance compared to Example 4. This is presumed to be because the presence of compound B (containing Li, W, and O), which has good ionic conductivity, on the surface of the primary particles made ion movement smoother. In addition, Examples 1 to 3 were found to have a lower rate of increase in cycle resistance compared to Example 4. This is presumed to be because the presence of compound B (containing Li, W, and O), which has moderately low electronic conductivity, on the surface of the primary particles suppressed the accumulation of resistance components (decomposition products) due to side reactions caused by electron conduction.

[0119] [Comparative Example 3] A precursor (transition metal hydroxide) was obtained in the same manner as in Comparative Example 1. The obtained precursor was given a Li source (LiOH) and a La source (La(OH) ３ ), W source (H ２ WO ４ ) and Co source (Co (NO ３ ) ３ The following were added and mixed in an agate mortar to obtain the first mixture. The amount of Li source added was adjusted so that the molar ratio of Li in the Li source to the total amount of Ni, Co, and Mn in the precursor (NCM) (Li / NCM) was 1.1. The amount of La source added was adjusted so that La / NCM was 0.005, and the amount of W source added was adjusted so that W / NCM was 0.005. The amount of Co source added was adjusted so that Co / NCM was 0.030. 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.

[0120] [Example 5] 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. The obtained second fired body was crushed using a jet mill, and then Co source (Co(NO) ３ ) ３ A second mixture was obtained by adding the Co source. The amount of Co source added was adjusted so that the molar ratio of Co in the Co source to the total amount of Ni, Co, and Mn in the precursor (NCM) (Co / NCM) was 0.030. The obtained second mixture was calcined in a calcination furnace at 450°C, in an oxygen atmosphere, for 5 hours to obtain a third calcined body. The obtained third calcined body was crushed using a jet mill to adjust the particle size and obtain 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.

[0121] [Example 6] Co source (Co(NO) ３ ) ３ Instead of ), Al source (Al(NO ３ ) ３A positive electrode active material and a battery were obtained in the same manner as in Example 5, except that the following was used. Note that in Table 2, synthesis method 3 is a method that involves a three-stage calcination process, as in Examples 5 and 6.

[0122] [Evaluation] (XRD measurement) X-ray diffraction (XRD) measurements using CuKα rays were performed on the positive electrode active materials obtained in Examples 5 and 6. As a result, a peak attributable to crystalline Co was confirmed in Example 5, and a peak attributable to crystalline Al was confirmed in Example 6.

[0123] (Storage Capacity Retention Rate) The storage capacity retention rate was measured using the batteries obtained in Examples 1, 5, and 6 and Comparative Examples 1 and 3. Specifically, 200 cycles were performed under the conditions of voltage range: 3.0V-4.3V, C rate: 2C, mode: CC charge / discharge, and temperature: 50°C. The storage capacity retention rate was determined by dividing the discharge capacity at the 200th cycle by the discharge capacity at the 1st cycle. The results are shown in Table 2.

[0124]

[0125] As shown in Table 2, Examples 5 and 6 were found to have a higher storage capacity retention rate compared to Example 1 and Comparative Examples 1 and 3. This is presumed to be because the presence of compound C containing Co or Al improved the thermal stability of the positive electrode active material.

[0126] 1...Primary particles 10...Positive electrode active material 11...Positive electrode 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, wherein the positive electrode active material has crystalline primary particles containing Li, TM (where TM is a transition metal), and O; the positive electrode active material is a single-crystal active material composed of the primary particles; and the positive electrode active material has a compound A containing La, Ni, and O on the surface of the primary particles.

2. The positive electrode active material according to claim 1, wherein the positive electrode active material has a compound B containing Li, W, and O on the surface of the primary particles.

3. The positive electrode active material according to claim 1, wherein the particle size of the primary particles is 0.5 μm or larger.

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

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

6. The positive electrode active material according to claim 1, wherein compound A is in particulate form.

7. The positive electrode active material according to claim 1, wherein compound B is in the form of a film.

8. The positive electrode active material according to claim 1, wherein the positive electrode active material has a compound C containing Me (where Me is at least one of Co, Al, Ce, Y, and Ti) and O on the surface of the primary particles.

9. A positive electrode composite containing the positive electrode active material according to any one of claims 1 to 8.

10. A battery comprising 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, wherein the positive electrode active material layer contains the positive electrode composite material described in claim 9.

11. A method for producing a positive electrode active material according to any one of claims 1 to 8, comprising: a first mixture containing a transition metal hydroxide containing TM, a Li source, a La source, and a Ni source, at a temperature T １ A first firing step in which the first fired body is fired at a temperature T ２ The process includes a second firing step in which the body is fired at a temperature T to obtain a second fired body, and the second firing step is performed at a temperature T ２ The temperature T in the first firing step is １ Lower than the aforementioned temperature T １ The temperature is between 500°C and 800°C, and the temperature T ２ This is a method for producing a positive electrode active material, wherein the temperature is between 400°C and 600°C.

12. The method for producing a positive electrode active material according to claim 11, wherein the transition metal hydroxide contains at least Ni as TM and also serves as a Ni source.

13. The method for producing a positive electrode active material according to claim 11, wherein the first mixture contains a W source.

14. The method for manufacturing the positive electrode active material includes adding a Me source (Me is at least one of Co, Al, Ce, Y, and Ti) to the second fired body to prepare a second mixture, and firing the second mixture at a temperature T ３ to form a third firing step of forming a compound C on the surface of the primary particles. The temperature T ３ in the third firing step is lower than the temperature T ２ in the second firing step, and the temperature T ３ is 350°C or higher and 550°C or lower. The method for manufacturing the positive electrode active material according to claim 11.

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