Positive electrode active material and battery

Abstract

In the present disclosure, the above problem is solved by providing a positive electrode active material having crystalline primary particles containing Li, TM (TM is a transition metal), and O, the positive electrode active material being a single-crystal system active material composed of the primary particles, a compound A containing La, Ni, and O, and a compound B containing Li, W, and O being present on the surface of the primary particles, the compound A being particulate, the compound B being film-like, the compound B coating the surface of the primary particles and coating the surface of the compound A.

Description

Technical Field

[0001] This disclosure relates to positive electrode active materials and batteries. Background Technology

[0002] In recent years, battery development has been booming. For example, in the automotive industry, batteries for battery electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), or hybrid electric vehicles (HEVs) are being developed. As positive electrode active materials for batteries, active materials containing transition metals such as Ni, Co, and Mn are known.

[0003] For example, Japanese Patent Publication No. 2022-542774 discloses a chemical formula of Li. a Ni x Co y Mn 1-x-y W b M c O2-containing high-nickel ternary cathode material. The high-nickel ternary cathode material simultaneously comprises spherical secondary particles and single-crystal particles. A high-nickel ternary cathode material containing W is disclosed, characterized in that the single-crystal particles are substantially free of W, while the spherical secondary particles are doped with W.

[0004] Japanese Patent Application Publication No. 2024-511223 discloses a single-crystal multi-element cathode material. The roundness R of the single-crystal particles in this material, measured by SEM, is defined as the ratio of the longest diagonal length to the shortest diagonal length, and R is greater than or equal to 1. This single-crystal multi-element cathode material is characterized by the D-value of its single-crystal particles. 10 D 50 and D 90 Satisfying K 90 =(D 90 -D 10 ) / D 50 K 90 The product of R is 1.20~1.40.

[0005] HujunZhanget.al., "Perovskite-coatedsmall-sizesingle-crystallineW-dopedNi-richcathodeswithgreatlyenhancedpowerdensityforLi-ionbatteries", Journal of Materials ChemistryA, Issue 36, 2024, disclosed in LiNi 0.85 Co 0.05 Mn 0.10O2 is used for W doping, followed by coating with perovskite oxide La4NiLiO8. Summary of the Invention

[0006] From the perspective of improving battery performance, there is a demand for reducing resistance and the rate of increase in cycle resistance. This disclosure was made in view of the above-mentioned realities, and its main objective is to provide a positive electrode active material capable of achieving both a reduction in resistance and a reduction in the rate of increase in cycle resistance.

[0007] [1] A positive electrode active material,

[0008] The aforementioned positive electrode active material has crystalline primary particles containing Li, TM (TM is a transition metal) and O. The aforementioned positive electrode active material is a single-crystal active material composed of the aforementioned primary particles. On the surface of the aforementioned primary particles, there are compounds A containing La, Ni and O and compounds B containing Li, W and O. The aforementioned compound A is granular, and the aforementioned compound B is film-like. The aforementioned compound B coats the surface of the aforementioned primary particles and also coats the surface of the aforementioned compound A.

[0009] [2] According to the positive electrode active material described in [1], in the cross section of the positive electrode active material, the proportion of the compound B covering the surface of the compound A is 10% or more.

[0010] [3] According to the positive electrode active material described in [1] or [2], wherein, in the cross section of the positive electrode active material, the thickness of the compound B covering the surface of the compound A is 20 nm or less.

[0011] [4] According to any one of [1] to [3], when the intensity of W is measured by EELS analysis from the surface of the compound B covering the compound A toward the center of the primary particle, firstly, a peak value with a peak intensity α is detected, then a certain intensity β is detected, and then a certain intensity γ is detected, wherein the peak intensity α, the certain intensity β and the certain intensity γ satisfy the relationship α > γ > β.

[0012] [5] 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.

[0013] The above-mentioned positive electrode active material layer contains any one of [1] to [4] positive electrode active materials.

[0014] In this disclosure, the positive electrode active material is provided to reduce resistance and the rate of increase in cycle resistance. Attached Figure Description

[0015] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will now be described in conjunction with the accompanying drawings, wherein the same symbols denote the same elements.

[0016] Figure 1 This is a schematic cross-sectional view illustrating the positive electrode active material in this disclosure.

[0017] Figure 2 This is a schematic cross-sectional view illustrating the positive electrode active material in this disclosure.

[0018] Figure 3 This is a schematic cross-sectional view illustrating the battery in this disclosure.

[0019] Figure 4 This is a flowchart illustrating a method for manufacturing the positive electrode active material in this disclosure. Detailed Implementation

[0020] Hereinafter, embodiments will be described with reference to the accompanying drawings. However, this disclosure can be implemented in many different ways and is not limited to the embodiments illustrated below. In addition, to make the description clearer, the drawings sometimes schematically show the width, thickness, and shape of the parts compared to the actual embodiments, but this is only an example and is not intended to limit the interpretation.

[0021] A. Positive electrode active material

[0022] Figure 1 This is a schematic cross-sectional view illustrating the positive electrode active material in this disclosure. For example... Figure 1 As shown, the positive electrode active material 10 has crystalline primary particles 1 containing Li, TM (TM is a transition metal), and O. Furthermore, the positive electrode active material 10 is a single-crystal active material composed of primary particles 1. Compound A containing La, Ni, and O, and compound B containing Li, W, and O are present on the surface of the primary particles 1. Compound A is granular, and compound B is film-like. Additionally, compound B coats the surface of the primary particles 1 and also coats the surface of compound A.

[0023] According to this disclosure, a reduction in electrical resistance can be achieved by having a compound A (containing La, Ni, and O) with good electronic conductivity on the surface of the primary particles. Furthermore, in this disclosure, a reduction in electrical resistance can also be achieved by having a compound B (containing Li, W, and O) with good ionic conductivity on the surface of the primary particles.

[0024] Furthermore, it is speculated that compound A, due to its good electronic conductivity, can reduce resistance, but resistive components (decomposition products) accumulate due to side reactions based on electronic conduction, resulting in an increase in resistance over time. In contrast, it is speculated that compound B has moderately low electronic conductivity, thus suppressing the accumulation of resistive components (decomposition products) in the positive electrode active material and inhibiting the increase in resistance over time. In this invention, compound B coats the surface of the primary particles and also coats the surface of compound A. Therefore, the accumulation of resistive components (decomposition products) generated by side reactions based on electronic conduction on the surface of compound A can be suppressed, and the rate of increase in cycle resistance can be reduced.

[0025] Alternatively, for example, a mixture containing a transition metal hydroxide as a precursor, a La source, and a W source can be calcined to form compounds A and B. In this case, compounds A and B can be formed on the surface of the primary particles, but it is difficult to form compound B by coating compound A. In contrast, in this disclosure, as described later, compound A is formed on the surface of the primary particles by performing a first calcination step of calcining a first mixture containing a transition metal hydroxide and a La source. Then, by performing a second calcination step of adding a W source and further calcining, compound B can be formed by coating compound A. In order for the W source to form compound B by reacting with Li, it is preferable to also add a Li source in the second calcination step. Furthermore, an oxidizing agent is preferably used to promote the reaction of compound B formed from the W source and the Li source.

[0026] 1. Primary particle

[0027] The primary particles in this disclosure are crystalline particles containing Li, TM (TM being a transition metal), and O. Examples of crystal structures for primary particles include layered rock salt type and spinel type, with layered rock salt type being preferred. Furthermore, the primary particles may have crystal structures belonging to space group R-3m.

[0028] Primary particles contain Li, TM (TM being a transition metal), and O. Primary particles can contain one, two, three, or even four or more transition metals.

[0029] Transition metals are metals belonging to groups 3 through 11 of the periodic table. The transition metals contained in a primary particle can belong to the third, fourth, or fifth period. Examples of transition metals include Ti, V, Cr, Mn, Fe, Co, Ni, Zr, Nb, La, and W.

[0030] The primary particles preferably contain at least Ni. This is because a positive electrode active material with good capacity characteristics can be obtained. When all transition metals (TM) contained in the primary particles are set to 1 mole, the proportion of Ni in the primary particles can be, for example, 0.25 moles or more, or 0.33 moles or more, or 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.

[0031] Primary particles may or may not contain Co. When all transition metals (TM) contained in a primary particle are set to 1 mole, the proportion of Co contained in the primary particle 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 contained in a primary particle may be, for example, 0.40 moles or less, or 0.20 moles or less.

[0032] Primary particles may or may not contain Mn. When all transition metals (TM) contained in a primary particle are set at 1 mole, the proportion of Mn contained in the primary particle 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 contained in a primary particle may be, for example, 0.40 moles or less, or 0.20 moles or less.

[0033] The primary particles preferably contain at least one of Ni, Co, and Mn. When all metals (excluding Li) contained in the primary particles are considered to be 1 mole, the total proportion of Ni, Co, and Mn in the primary particles is, for example, 0.80 moles or more. It can be 0.90 moles or more, or 0.95 moles or more. It should be noted that "the total proportion of Ni, Co, and Mn" also includes cases where the proportion of one or two of Ni, Co, and Mn is 0.

[0034] In addition to Li and TM, primary particles may also contain other metals M besides Li and TM. 1 (Including semi-metals). M as another metal 1 Examples of metals belonging to groups 12 through 14 of the periodic table include Zn, Al, Si, Ga, Ge, In, and Sn.

[0035] The composition of primary particles is not particularly limited; for example, it can be composed of the general formula Li. x Ni a Co b Mn c O yThe composition represented by (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).

[0036] The positive electrode active material in this disclosure is typically a monocrystalline active material composed of the aforementioned primary particles. Monocrystalline active material refers to a material that is not a so-called polycrystalline active material (an active material formed by the seamless aggregation of multiple primary particles). Monocrystalline active materials generally do not aggregate and exist as independent particles. Preferably, monocrystalline active materials do not show grain boundaries when observed with a scanning electron microscope (SEM) (magnification: approximately 10,000 to 30,000 times). Compared to polycrystalline active materials, monocrystalline active materials have the advantage of less degradation over time.

[0037] The particle size of primary particles can be, for example, 0.5 μm or larger, 0.6 μm or larger, 0.8 μm or larger, or 1.0 μm or larger. If the particle size of primary particles is too small, the particles will not grow sufficiently, and it may be difficult to fabricate a single crystal. On the other hand, the particle size of primary particles can be, for example, 20 μm or smaller, 15 μm or smaller, 10 μm or smaller, or 5 μm or smaller. The particle size of primary particles can be determined, for example, as the longest diameter observed in SEM. In addition, for example, when primary particles (positive electrode active material) are contained in the positive electrode active material layer, the particle size (longest diameter) of the primary particles can be determined from the cross-sectional image of the positive electrode active material layer.

[0038] 2. Compound A

[0039] Compound A in this invention contains La, Ni, and O. Compound A typically has high electronic conductivity; therefore, by having compound A on the surface of the primary particle, a reduction in electrical resistance can be achieved. Compound A can be directly disposed on the surface of the primary particle or disposed in between other layers (other compounds), with the former being preferred.

[0040] Compound A contains at least La, Ni, and O. Compound A may consist only of La, Ni, and O, or it may contain other elements. For example, Li can be considered as another element. That is, compound A may or may not contain Li. As an example of the composition of compound A, La can be cited. 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 with good electronic conductivity. Other examples of the composition of compound A include La... a Li b Ni cO d (3.5≦a≦4.5, 0.5≦b≦1.5, 0.5≦c≦1.5, 7.5≦d≦8.5). For example, given that La4LiNiO8 has good electronic conductivity, it is hypothesized that it has a crystal phase similar to perovskite.

[0041] Compound A can be crystalline or amorphous, with the former being preferred due to its superior electronic conductivity. "Crystalline" means that a peak from the target compound was confirmed using CuKα X-ray diffraction. Conversely, "amorphous" means that no peak from the target compound was confirmed using CuKα X-ray diffraction. It should be noted that in the case of an amorphous compound, sometimes a halo pattern is observed instead of a peak.

[0042] Compound A preferably has a perovskite crystal phase or a perovskite-like crystal phase. Compound A preferably has at least one of LaNiO3 or La4LiNiO8 crystal phases. This is because good electronic conductivity can be obtained. It should be noted that the above-mentioned crystal phases include crystal phases with a missing portion of the constituent atoms (e.g., a portion of O atoms) and crystal phases with a remaining portion of the constituent atoms (e.g., a portion of La atoms).

[0043] Compound A is typically granular. The term "compound A is granular" means that in a cross-sectional image of a primary particle, when the length of compound A in the direction normal to the surface of the primary particle is defined as L1, and the length of compound A in the direction perpendicular to the normal is defined as L2, the ratio of L2 to L1 (L2 / L1) is 3.0 or less. A cross-sectional image of a primary particle is, for example, an SEM cross-sectional image.

[0044] When all the transition metals contained in a primary particle are set as 1 mole, the proportion of La contained in compound A is, for example, 0.001 moles or more, 0.003 moles or more, or 0.005 moles or more. On the other hand, the above-mentioned proportion of La contained in compound A is, for example, 0.100 moles or less, 0.080 moles or less, or 0.060 moles or less.

[0045] The coating percentage of compound A relative to the primary particles is not particularly limited; for example, it can be 10% or more and 90% or less, 20% or more and 80% or less, or 30% or more and 70% or less. The coating percentage of compound A can be determined, for example, by 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 amounts of each TM (Ni, Co, Mn) can be determined by surface analysis using XPS, and La / (La+TM) can be used as the coating percentage. The coating percentages of compounds A and B can be determined in the same way. Furthermore, the electronic conductivity of compound A is generally higher than that of La₂O₃. The electronic conductivity of compound A at 25°C is, for example, 5.0 × 10⁻⁶. -4 A value of S / cm or higher can also be 1.0 × 10⁻⁶. -3 S / cm or higher. Additionally, 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.

[0046] 3. Compound B

[0047] The positive electrode active material of this disclosure may have a compound B containing Li, W, and O on the surface of the primary particles. Compound B typically has high ionic conductivity; therefore, by having compound B on the surface of the primary particles, a reduction in resistance can be achieved. Furthermore, by having compound B on the surface of the primary particles, an increase in resistance over time can be suppressed. Compound B can be directly disposed on the surface of the primary particles or disposed in between other layers (other compounds), with the former being preferred.

[0048] Compound B contains at least Li, W, and O. Compound B may consist only of Li, W, and O, or it may contain other elements. As an example of the composition of compound B, Li can be included. 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. Other examples of the composition of compound B include Li₂WO₄. 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. Additionally, as other examples of the composition of compound B, Li₂... 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.

[0049] Compound B can be crystalline or amorphous. Furthermore, compound B is typically in the form of a film. "Compound B is in the form of a film" means that, in a cross-sectional image of a primary particle, when the length of compound B in the direction normal to the surface of the primary particle is defined as L3, and the length of compound B in the direction perpendicular to the normal is defined as 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 transmission electron microscope (TEM) cross-sectional image. The thickness of compound B (length L3) is not particularly limited, and can 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 measured at at least five locations during TEM observation.

[0050] When all the transition metals contained in a primary particle are set as 1 mole, the proportion of W contained in compound B is, for example, 0.001 moles or more, 0.003 moles or more, or 0.005 moles or more. On the other hand, the above-mentioned proportion of W contained in compound B is, for example, 0.100 moles or less, 0.080 moles or less, or 0.060 moles or less.

[0051] The coating percentage of compound B relative to the primary particles is not particularly limited; for example, it can be 10% or more and 90% or less, 20% or more and 80% or less, or 30% or more and 70% or less. Furthermore, the ionic conductivity of compound B is generally higher than that of W₂O₃. The ionic conductivity of compound B at 25°C is, for example, 1.0 × 10⁻⁶. -5 A value of S / cm or higher can also be 1.0 × 10⁻⁶. -4 S / cm or higher. Additionally, 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.

[0052] 4. Positive electrode active material

[0053] In the positive electrode active material, compound B coats the surface of the primary particles and also coats the surface of compound A. In the cross-section of the positive electrode active material, the proportion of compound B coating the surface of compound A (coating ratio) is, for example, 10% or more, 30% or more, or 50% or more. This coating ratio can be determined by TEM observation.

[0054] In the cross-section of the positive electrode active material, the thickness of compound B coating the surface of compound A is not particularly limited; for example, it can be less than 20 nm, or less than 15 nm. On the other hand, the thickness of compound B coating the surface of compound A can be, for example, 0.5 nm or more, or more than 1.0 nm. The thickness of compound B coating the surface of compound A can be determined by TEM observation.

[0055] like Figure 2 As shown, when the intensity of W is determined by EELS (Electron Energy Loss Spectroscopy) analysis from the surface of compound B coating compound A toward the center of primary particle 1, a peak value with a peak intensity α is first detected. Next, a certain intensity β is preferably detected, followed by a certain intensity γ. The aforementioned peak value corresponds to the intensity of W contained in compound B coating compound A. Furthermore, a certain intensity β corresponds to the intensity of W contained in compound A, and a certain intensity γ corresponds to the intensity of W contained in the primary particle. Figure 2 As shown, the peak intensity α, a certain intensity β, and a certain intensity γ preferably satisfy the relationship α > γ > β.

[0056] There are no particular limitations on the manufacturing method of the positive electrode active material. For example, the method described in "D. Manufacturing Method of Positive Electrode Active Material" can be cited later.

[0057] Furthermore, this disclosure also provides a positive electrode active material powder containing a plurality of single-crystal active materials composed of crystalline primary particles containing Li, TM (TM being a transition metal), and O. At least a portion of the plurality of single-crystal active materials is a single-crystal active material X. The single-crystal active material X has on the surface of the primary particles: a granular compound A containing La, Ni, and O, and a film-like compound B containing Li, W, and O. Compound B coats the surface of the primary particles and the surface of compound A. Additionally, the proportion of single-crystal active material X in the positive electrode active material powder relative to the total positive electrode active material is, for example, 5% by mass or more, 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. Positive electrode composite material

[0059] In this disclosure, a positive electrode composite material containing the above-mentioned positive electrode active material may also be provided.

[0060] According to this disclosure, by using the above-described positive electrode active material, a positive electrode composite material capable of reducing resistance and the rate of increase in cycle resistance is obtained. In addition to the positive electrode active material, the positive electrode composite material may also contain other materials (e.g., conductive materials, binders). Furthermore, the positive electrode composite material may contain the above-described positive electrode active material powder. Additionally, the positive electrode composite material may be in powder form or in slurry form containing a dispersion medium.

[0061] The proportion of positive electrode active material in the solid component of the positive electrode composite material is, for example, 20% by mass or more, 30% by mass or more, or 40% by mass or more. If the proportion of positive electrode active material is too low, sufficient energy density may not be obtained. On the other hand, the proportion of positive electrode active material in the solid component of the positive electrode composite material is, for example, 95% by mass or less, 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 be relatively reduced.

[0062] Positive electrode composite materials can contain conductive materials. Adding conductive materials improves electronic conductivity. Examples of conductive materials include carbon-based conductive materials, metal particles, and conductive polymers. Examples of carbon-based conductive materials include granular materials such as acetylene black (AB) and Ketjen black (KB), and fibrous materials such as vapor-phase carbon fiber (VGCF), carbon nanotubes (CNTs), and carbon nanofibers (CNFs).

[0063] Cathode composite materials can contain binders. By adding binders, a cathode active material layer that is not easily detached can be obtained. 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] C. Battery

[0065] Figure 3 This is a schematic cross-sectional view illustrating the battery in this disclosure. Figure 3 The battery 20 shown has 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 active material described in "A. Positive Electrode Active Material" above, or the positive electrode composite material described in "B. Positive Electrode Composite Material" above.

[0066] According to this disclosure, by using the above-described positive electrode active material or positive electrode composite material, a battery with reduced resistance and cycle resistance increase rate is obtained.

[0067] 1. Positive electrode active material layer

[0068] The positive electrode active material layer contains at least a positive electrode active material. Additionally, the positive electrode active material layer may 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 Composite Material" above.

[0069] The positive electrode active material layer may contain an electrolyte. The electrolyte may be, for example, an electrolyte solution described later. Alternatively, the positive electrode active material layer may contain a solid electrolyte. The thickness of the positive 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.

[0070] 2. Negative electrode active material layer

[0071] 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.

[0072] Examples of carbon-based active materials include graphite, soft carbon, and hard carbon. Graphite can be natural or artificial. 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 formed by loading Si or Si alloys onto a carbon support. Examples of oxide-based active materials include Li₄Ti₅O. 12 Lithium titanate, etc.

[0073] The negative electrode active material layer may contain at least one of a conductive material, a binder, and an electrolyte. Details regarding the conductive material, binder, and electrolyte are the same as those described in "1. Positive Electrode Active Material Layer" above. Furthermore, 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] 3. Electrolyte layer

[0075] The electrolyte layer is a layer disposed between the positive electrode active material layer and the negative electrode active material layer, and it contains at least an electrolyte. The electrolyte is, for example, a liquid electrolyte (electrolyte).

[0076] As an example of an electrolyte, non-aqueous electrolytes can be cited. Non-aqueous electrolytes, for example, contain lithium salts and non-aqueous solvents. Examples of lithium salts include inorganic lithium salts such as LiPF6, LiBF4, LiClO4 and LiAsF6, and organic lithium salts such as LiCF3SO3, LiN(SO2CF3)2, LiN(SO2C2F5)2 and LiC(SO2CF3)3.

[0077] Examples of non-aqueous solvents include ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC). Non-aqueous electrolytes may also include ionic liquids. Other examples of electrolytes include aqueous electrolytes. Furthermore, the electrolyte layer may have a membrane impregnated with the aforementioned electrolyte.

[0078] 4. Battery

[0079] The battery disclosed herein preferably has a positive current collector for collecting current in the positive electrode active material layer and a negative current collector for collecting current in the negative electrode active material layer.

[0080] The type of battery disclosed herein is not particularly limited, but lithium-ion batteries are typical. Furthermore, the battery in this disclosure can be a primary battery or a secondary battery, with a secondary battery being preferred. This is because it can be repeatedly charged and discharged, making it useful, for example, as a vehicle battery. Examples of applications for the battery include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline vehicles, and diesel vehicles. It is particularly preferred for use as a power source for driving hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or battery electric vehicles (BEVs). Additionally, the battery can be used as a power source for mobile bodies other than vehicles (e.g., railways, ships, aircraft) and for electrical products such as information processing devices.

[0081] D. Methods for manufacturing positive electrode active materials

[0082] This disclosure may also provide a method for manufacturing the aforementioned positive electrode active material. For example... Figure 4As shown, the method for manufacturing the positive electrode active material preferably includes a first firing step of firing a first mixture containing the aforementioned transition metal hydroxide, Li source, Ni source, and La source at a temperature T1 to obtain a first fired body. The method for manufacturing the positive electrode active material preferably includes a second firing step: adding a W source, a Li source, and an oxidant to the first fired body to prepare a second mixture, and firing the second mixture at a temperature T2 to obtain a second fired body. The temperature T2 is preferably lower than the temperature T1.

[0083] According to this disclosure, by performing a first firing process and a second firing process, a positive electrode active material that can achieve a reduction in resistance and a reduction in the rate of increase in cycle resistance can be obtained.

[0084] 1. First firing process

[0085] The first firing process is to fire a first mixture containing the aforementioned TM transition metal hydroxide, Li source, Ni source and La source at a temperature T1 to obtain a first fired body.

[0086] Transition metal hydroxides contain TM (TM being a transition metal). Transition metal hydroxides act as precursors for positive electrode active materials. Transition metal hydroxides may or may not contain Ni.

[0087] There are no particular limitations on the synthesis method of transition metal hydroxides; for example, the following methods can be cited. First, prepare an aqueous solution of the transition metal hydroxide as a raw material. Methods for preparing the raw material aqueous solution include, for example, dissolving a water-soluble transition metal compound in water. Transition metal compounds include, for example, metal salts such as sulfates and nitrates. Ni sources include, for example, NiSO4 and Ni(NO3)2. Co sources include, for example, CoSO4, Co(NO3)2, and Co(NO3)3. Mn sources include, for example, MnSO4 and Mn(NO3)2. The composition of the raw material aqueous solution can be appropriately adjusted according to the target positive electrode active material.

[0088] Next, an aqueous sodium hydroxide solution is added to the reaction vessel, maintaining the pH at an alkaline level (e.g., pH 11.3–12.0), while simultaneously adding the starting material aqueous solution and an NH3 aqueous solution. The reaction temperature is not particularly limited, but can be, for example, above 50°C and below 65°C. After the reaction is complete, it is preferable to filter to remove the transition metal hydroxide, wash with water, and then dry.

[0089] In the first firing step, a first mixture containing a transition metal hydroxide, a Li source, a Ni source, and a La source is prepared. Examples of Li sources include lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, lithium oxide, and lithium chloride. The Li source can be lithium hydroxide or a Li-containing compound other than lithium hydroxide. The molar ratio of Li in the Li source to the TM contained in the transition metal hydroxide is, for example, 0.8 or more and 1.2 or less, 0.9 or more and 1.1 or less, or 1.0.

[0090] Examples of La sources include hydroxides, sulfates, nitrates, and other metal salts. Examples of La sources include La(OH)3, LaSO4, and La(NO3)3. When the transition metal hydroxide contains Ni, it can also serve as a Ni source. Conversely, when the transition metal hydroxide does not contain Ni, a separate Ni source is required. Examples of Ni sources include Ni(OH)2, NiSO4, and Ni(NO3)2. The amounts of La and Ni sources added are adjusted appropriately based on the target positive electrode active material.

[0091] The mixture described above preferably contains a molten salt. By having the molten salt function as a flux, sufficient grain growth of primary particles can be achieved. The molten salt may contain Li. Examples of molten salts include lithium hydroxide. The molar ratio (Li / TM) of Li in the molten salt relative to the amount of transition metal hydroxide (TM) in the transition metal hydroxide is, for example, 0.1 or more and less than 0.6. The Li / TM ratio may be 0.15 or more, 0.2 or more, or 0.25 or more. On the other hand, the Li / TM ratio may be 0.55 or less, or 0.5 or less.

[0092] In the first firing process, the first mixture is fired at a temperature T1 to obtain a first fired body. The temperature T1 is, for example, 700°C or higher and 1100°C or lower, or 800°C or higher and 1000°C or lower. If the temperature T1 is too high, La2O3 may be easily generated. On the other hand, if the temperature T1 is too low, it is difficult for the primary particles to grow sufficiently.

[0093] There is no particular limitation on the firing time in the first firing step; for example, it can be more than 5 hours but less than 15 hours, or more than 8 hours but less than 12 hours. The atmosphere in the first firing step is usually an oxygen-containing atmosphere. Examples of firing methods in the first firing step include using a muffle furnace or an electric furnace.

[0094] In the first firing process, the first fired body can be pulverized. Examples of pulverization methods include jet mills, hammer mills, laboratory mills, and ball mills.

[0095] 2. Second firing process

[0096] The second firing process involves adding a W source, a Li source, and an oxidant to the first fired body to prepare a second mixture, and firing the second mixture at a temperature T2 to obtain the second fired body.

[0097] Examples of W sources include H₂WO₄. The amount of W source added is adjusted appropriately according to the target positive electrode active material. Regarding the Li source, as described above. In the second mixture, the molar ratio of Li in the Li source to the TM contained in the transition metal hydroxide is, for example, 0.003 or more and 0.100 or less, and can be 0.005 or more and 0.05 or less. Examples of oxidants include KMnO₄. In the second mixture, the molar ratio of the oxidant to the TM contained in the transition metal hydroxide is, for example, 0.5 or more and 1.5 or less, and can also be 0.75 or more and 1.2 or less.

[0098] The temperature T2 in the second firing step is preferably lower than the temperature T1 in the first firing step. The difference between temperature T1 and temperature T2 is, for example, 100°C or more, or 200°C or more. Alternatively, temperature T2 is, for example, 500°C or more and 700°C or less, or 550°C or more and 650°C or less. If temperature T2 is too high, W2O3 may be easily formed.

[0099] The firing time in the second firing step is, for example, more than 1 hour and less than 5 hours, or more than 2 hours and less than 4 hours. The firing time in the second firing step can be shorter than the firing time in the first firing step. The atmosphere in the second firing step is usually an oxygen-containing atmosphere. As a firing method in the second firing step, examples include using a muffle furnace, an electric furnace, or other firing furnaces.

[0100] In the second firing process, the second fired body can be pulverized. Examples of pulverization methods include jet mills, hammer mills, laboratory mills, and ball mills.

[0101] 3. Positive electrode active material

[0102] The positive electrode active material obtained through the above processes is the same as the content described in "A. Positive Electrode Active Material" above.

[0103] Furthermore, this disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and may have a structure that is substantially the same as the technical concept described in the claims of this disclosure and achieves the same effect. Any structure is included within the technical scope of this disclosure.

[0104] Comparative Example 1

[0105] Production of positive electrode active material

[0106] NiSO4, CoSO4, and MnSO4 were prepared as raw materials and dissolved in ion-exchange 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. Furthermore, the concentration of the raw material aqueous solution (the proportion of all raw materials relative to the raw material aqueous solution) was 30% by mass.

[0107] Then, a certain amount of NH3 aqueous solution was added to the reaction vessel, and the mixture was stirred while nitrogen was purged from the gas. NaOH aqueous solution was added to the reaction vessel to maintain an alkaline pH (pH=12). While maintaining a controlled temperature, the raw material aqueous solution and NH3 aqueous solution were added dropwise to precipitate the transition metal hydroxide. The reaction temperature was 60℃, and the reaction time was 3 hours. Next, the precipitated transition metal hydroxide was removed by filtration, and ion-exchanged water was added to disperse it with a spoon, followed by washing. The washed transition metal hydroxide was dried at 120℃ for 16 hours to obtain the transition metal hydroxide as a precursor.

[0108] Then, a Li source (LiOH) was added to the obtained precursor and mixed with 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 in the Li source relative to the total NCM (Ni, Co, Mn) in the precursor was 1.1. The first mixture was then calcined in a furnace at 900°C in an oxygen atmosphere for 10 hours to obtain a calcined body. The calcined body was then crushed using a jet mill, and the particle size was adjusted to obtain the positive electrode active material.

[0109] Battery manufacturing

[0110] Using the obtained positive electrode active material, a battery is manufactured. Specifically, using a coating machine (manufactured by Allgood Co., Ltd.) equipped with a film thickness adjustment function, a positive electrode composite slurry containing 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 is coated onto the surface of a metal foil serving as the positive electrode current collector. Then, it is dried at 80°C for 5 minutes using a dryer to obtain a positive electrode having a positive electrode current collector and a layer of positive electrode active material.

[0111] Next, using a coating machine (manufactured by Allgood Co., Ltd.) with film thickness adjustment function, a negative electrode composite slurry containing negative electrode active material (natural graphite) and binders (SBR and CMC) was coated onto the surface of a metal foil serving as the negative electrode current collector. Then, it was dried at 80°C for 5 minutes using a dryer to obtain a negative electrode with a negative electrode current collector and a layer of negative electrode active material. Next, a 1M LiPF6 solution was prepared as the electrolyte. The electrolyte solvent was a mixed solvent prepared by mixing 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-described positive electrode, negative electrode, and electrolyte, a wound cylindrical battery was obtained.

[0112] Comparative Example 2

[0113] The precursor was obtained in the same manner as in Comparative Example 1. A Li source (LiOH), a La source (La(OH)3), and a W source (H2WO4) were added to the obtained precursor and mixed using 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 in the Li source relative to the total NCM (Ni, Co, Mn) in the precursor was 1.1. Furthermore, the amount of La source added was adjusted to La / NCM of 0.01, and the amount of W source added was adjusted to W / NCM of 0.01. The obtained first mixture was calcined in a calcining furnace at 900°C under an oxygen atmosphere for 10 hours to obtain a calcined body. The calcined body was crushed using a jet mill, and the particle size was adjusted to obtain the positive electrode active material.

[0114] Example 1

[0115] The precursor was obtained in the same manner as in Comparative Example 1. A Li source (LiOH) and a La source (La(OH)3) were added to the obtained precursor and mixed using 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 in the Li source relative to the total NCM (Ni, Co, Mn) in the precursor was 1.1. Furthermore, the amount of La source added was adjusted to a La / NCM ratio of 0.01. The obtained first mixture was calcined in a calcining furnace at 900°C under an oxygen atmosphere for 10 hours to obtain a first calcined body.

[0116] W source (H2WO4), Li source (LiOH), and oxidant (KMnO4) were added to the obtained first calcined body and mixed in an agate mortar to obtain a second mixture. The amount of Li source added was adjusted so that the Li / NCM ratio was 0.005, and the amount of oxidant added was adjusted so that the KMnO4 / NCM ratio was 0.01. The obtained second mixture was calcined in a calcining furnace at 600°C under an oxygen atmosphere for 3 hours to obtain a second calcined body. The obtained second calcined body was crushed using a jet mill, and the particle size was adjusted to 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.

[0117] Example 2

[0118] The amount of Li source added to the second mixture was adjusted to a Li / NCM ratio of 0.01. Otherwise, the positive electrode active material and battery were obtained in the same manner as in Example 1.

[0119] Example 3

[0120] The amount of Li source added to the second mixture was adjusted to a Li / NCM ratio of 0.05. Otherwise, the positive electrode active material and battery were obtained in the same manner as in Example 1.

[0121] evaluate

[0122] SEM-EDX measurement

[0123] The positive electrode active materials obtained in Examples 1-3 were subjected to cross-sectional observation and elemental analysis by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX). As a result, in Examples 1-3, granular compounds were confirmed on the surface of the primary particles, and the mapping images confirmed that the granular compounds contained La, Ni, and O.

[0124] TEM-EDX measurement

[0125] The positive electrode active materials obtained in Examples 1-3 were subjected to cross-sectional observation and elemental analysis using transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX). The results showed that film-like compounds (thickness less than 20 nm) were identified on the surface of the primary particles in Examples 1-3, and the mapping images confirmed that these film-like compounds contained W and O. Furthermore, film-like compounds (compound B, thickness less than 20 nm) were also identified on the surface of the particulate compound (compound A) present on the primary particles, with the proportion of compound B coating the surface of compound A exceeding 10% in both cases.

[0126] TEM-EELS measurement

[0127] The intensity of W was determined for the positive electrode active materials obtained in Examples 1-3 by transmission electron microscopy-electron energy loss spectroscopy (TEM-EELS). Specifically, as... Figure 2 As shown, the intensity W was determined by EELS analysis from the surface of compound B, which coats compound A, toward the center of the primary particle. The results showed that a peak intensity (α) was detected first, followed by a certain intensity β, and then a certain intensity γ, confirming that they satisfy the relationship α > γ > β.

[0128] initial resistance

[0129] The initial resistance was measured using the batteries obtained in Examples 1-3 and Comparative Examples 1 and 2. Specifically, the batteries were charged to 4.3V and then discharged to 3.7V. The voltage drop (V) was then measured during a 10-second discharge at various C-rates: 25°C, 0.1C, 0.3C, 0.5C, 0.7C, and 1.0C. The voltage drop (V) was plotted against the current value, and the slope of the approximate straight line drawn as a linear function was taken as the resistance (V resistance). The results are shown in Table 1. Note that the initial resistance values ​​in Table 1 are relative to the initial resistance of Comparative Example 1, which is set to 100%.

[0130] Cyclic resistance increase rate

[0131] The increase rate of cycle resistance was measured using the batteries obtained in Examples 1-3 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 following conditions: voltage range: 3.0V~4.3V, C rate: 0.3C, mode: CC charge / discharge, and temperature: 50°C. The increase rate of cycle resistance was calculated based on the following formula.

[0132] Cyclic resistance increase rate (%) = (resistance after cyclic test) / initial resistance × 100

[0133] The results are shown in Table 1.

[0134] Table 1

[0135]

[0136] As shown in Table 1, it was confirmed that the initial resistance of Examples 1-3 was lower than that of Comparative Example 1. This is because compound A (containing La, Ni, and O) with good electronic conductivity and compound B (containing Li, W, and O) with good ionic conductivity are present on the surface of the primary particles. It is speculated that this is because the movement of electrons and ions becomes smoother. In addition, it was confirmed that the rate of increase in cycle resistance of Examples 1-3 was smaller than that of Comparative Example 2. It is speculated that this is because by coating the surface of compound A with compound B, the accumulation of resistive components (decomposition products) generated by side reactions based on electronic conductivity on the surface of compound A can be suppressed.

Claims

1. A positive electrode active material, The positive electrode active material has crystalline primary particles containing Li, TM as a transition metal, and O. The positive electrode active material is a single-crystal active material composed of the primary particles. The surface of the primary particles contains compound A, which contains La, Ni, and O, and compound B, which contains Li, W, and O. The compound A is in granular form, and the compound B is in film form. The compound B coats the surface of the primary particles and also coats the surface of the compound A.

2. The positive electrode active material according to claim 1, wherein, In the cross-section of the positive electrode active material, the proportion of compound B covering the surface of compound A is more than 10%.

3. The positive electrode active material according to claim 1, wherein, In the cross-section of the positive electrode active material, the thickness of compound B covering the surface of compound A is less than 20 nm.

4. The positive electrode active material according to claim 1, wherein, When the intensity of W is determined by EELS analysis from the surface of compound B covering compound A toward the center of the primary particle, a peak value with a peak intensity α is detected first, followed by a certain intensity β, and then a certain intensity γ, wherein the peak intensity α, the certain intensity β, and the certain intensity γ satisfy the relationship α > γ > β.

5. 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. The positive electrode active material layer contains the positive electrode active material as described in any one of claims 1 to 4.

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