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

Abstract

The main objective of this disclosure is to provide a positive electrode active material capable of reducing resistance and the rate of increase in cycle resistance. This disclosure addresses the aforementioned problem by providing a positive electrode active material having crystalline primary particles containing Li, TM (TM being a transition metal), and O. The positive electrode active material is a aggregate composed of multiple of the aforementioned primary particles, and on the surface of the primary particles are present a compound A containing La, Ni, and O, and a compound B containing Li, W, and O.

Description

Technical Field

[0001] This disclosure relates to positive electrode active materials, positive electrode composites, batteries, and methods for manufacturing positive electrode active materials. Background Technology

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

[0003] For example, Patent Document 1 discloses a W-containing high-nickel ternary cathode material, characterized in that it has the chemical formula Li a Ni x Co y Mn 1-x-y W b McO2 contains W-containing high-nickel ternary cathode material, which includes both spherical secondary particles and single-crystal particles. The single-crystal particles are essentially free of W, while the spherical secondary particles are doped with W.

[0004] Patent document 2 discloses a single-crystal multi-element cathode material, characterized in that, for the single-crystal particles of the above-mentioned single-crystal multi-element cathode material, the ratio of the length of the longest diagonal to the length of the shortest diagonal, as measured by SEM, is defined as the sphericity R, and R is 1 or more. The D-value of the single-crystal particles of the above-mentioned single-crystal multi-element cathode material is... 10 D 50 and D 90 Satisfying K 90 = (D) 90 -D 10 ) / D 50 K 90 The product of R is 1.20 to 1.40.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Publication No. 2022-542774

[0008] Patent Document 2: Japanese Patent Publication No. 2024-511223 Summary of the Invention

[0009] From the viewpoint of improving battery performance, there is a need to reduce resistance and the rate of increase in cycle resistance. This disclosure is made in view of the above-mentioned realities, and its main objective is to provide a positive electrode active material capable of reducing resistance and the rate of increase in cycle resistance.

[0010] [1] A positive electrode active material having crystalline primary particles containing Li, TM (TM being a transition metal) and O.

[0011] The aforementioned positive electrode active material is a condensed aggregate composed of multiple of the aforementioned primary particles.

[0012] On the surface of the aforementioned primary particles, there exists compound A containing La, Ni, and O, and compound B containing Li, W, and O.

[0013] [2] According to the positive electrode active material described in [1], there is a peak in the range of 65 nm to 300 nm in the fine pore size distribution obtained by mercury porosimetry.

[0014] [3] According to the positive electrode active material described in [2], the above-mentioned peak exists in the range of 80 nm to 220 nm in the above-mentioned pore size distribution.

[0015] [4] The positive electrode active material according to any one of [1] to [3], wherein the average particle size of the primary particles in the above-mentioned aggregate is 0.5 μm or more.

[0016] [5] The positive electrode active material according to any one of [1] to [4], wherein the primary particles contain at least one of Ni, Co and Mn as the above-mentioned TM.

[0017] [6] The positive electrode active material according to any one of [1] to [5], wherein the primary particles have a layered rock salt type crystal structure.

[0018] [7] The positive electrode active material according to any one of [1] to [6], wherein at least one of the above-mentioned compound A and the above-mentioned compound B is present at the interface of adjacent primary particles in the above-mentioned aggregate.

[0019] [8] The positive electrode active material according to any one of [1] to [7], wherein the above compound A is in particulate form.

[0020] [9] The positive electrode active material according to any one of [1] to [8], wherein the above compound B is in the form of a film.

[0021]

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

[0022]

[11] 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.

[0023] The above-mentioned positive electrode active material layer contains the positive electrode composite material described in

[10] .

[0024]

[12] A method for manufacturing a positive electrode active material, used to manufacture any one of [1] to [9], comprising:

[0025] In the first calcination step, a first mixture containing a transition metal hydroxide including the aforementioned TM, a Li source, and a W source is calcined at a temperature T1 to obtain a first calcined body.

[0026] The second calcination step involves calcining the first calcined body at temperature T2 to obtain the second calcined body.

[0027] In the third calcination step, a La source is added to the pulverized material of the second calcined body to prepare a second mixture, and the second mixture is calcined at a temperature T3 to obtain the third calcined body.

[0028] At least one of the first mixture and the second mixture contains a Ni source.

[0029] The temperature T2 in the second calcination step is higher than the temperature T1 in the first calcination step.

[0030] The temperature T3 in the third calcination step is lower than the temperature T2 in the second calcination step.

[0031] The temperature T1 mentioned above is 500℃~800℃.

[0032] The temperature T2 mentioned above is 600℃~1000℃.

[0033] The temperature T3 mentioned above is 400℃~600℃.

[0034] This disclosure demonstrates the ability to provide a positive electrode active material that can reduce resistance and the rate of increase in cycle resistance. Attached Figure Description

[0035] Figure 1 This is a schematic cross-sectional view illustrating the positive electrode active material in this disclosure.

[0036] Figure 2 This is a schematic cross-sectional view illustrating a primary particle in this disclosure.

[0037] Figure 3 This is a schematic cross-sectional view illustrating the battery in this disclosure.

[0038] Figure 4 This is a flowchart illustrating a method for manufacturing the positive electrode active material in this disclosure.

[0039] Symbol Explanation

[0040] 1. Primary particle

[0041] 10 Positive electrode active material

[0042] 11 Positive electrode active material layer

[0043] 12 Negative Electrode Active Material Layer

[0044] 13 Electrolyte layer

[0045] 14 Positive current collector

[0046] 15 Negative current collector

[0047] 20 batteries Detailed Implementation

[0048] 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, for the purpose of clearer explanation, the drawings sometimes schematically show the width, thickness, and shape of each part compared with the actual shape, but this is only an example and is not intended to be limiting.

[0049] A. Positive electrode active material

[0050] Figure 1 This is a schematic cross-sectional view illustrating the positive electrode active material in this disclosure. Figure 2 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 condensed aggregate composed of multiple primary particles 1. Additionally, as... Figure 2 As shown, compound A containing La, Ni and O and compound B containing Li, W and O exist on the surface of the primary particles.

[0051] According to this disclosure, a reduction in 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. Similarly, in this disclosure, a reduction in resistance can be achieved by having a compound B (containing Li, W, and O) with good ionic conductivity on the surface of the primary particles. Furthermore, since the positive electrode active material in this disclosure has a condensed aggregate composed of multiple primary particles, a reduction in the rate of increase in cycle resistance can be achieved.

[0052] Here, as positive electrode active materials, polycrystalline and monocrystalline active materials have been known previously. In polycrystalline active materials, multiple primary particles (very fine primary particles) are usually densely packed together. On the other hand, in monocrystalline active materials, large primary particles do not aggregate but exist as independent particles. Compared with polycrystalline active materials, monocrystalline active materials are less prone to breakage during charging and discharging and have superior durability. However, due to their large specific surface area, resistive components accumulate with repeated charging and discharging, leading to an increase in resistance over time.

[0053] In this disclosure, a condensed mass is composed of multiple primary particles. Therefore, the specific surface area can be reduced compared to a single primary particle. As a result, the accumulation of resistive components caused by repeated charging and discharging can be suppressed. That is, the effect of reducing the rate of increase in cyclic resistance can be achieved. This effect is significant even when the particle size of the primary particles is large, as described above.

[0054] In this disclosure, as described below, in the fine pore size distribution obtained by mercury porosimetry, peaks are preferably present in the range of 65 nm to 300 nm. That is, it is preferable to adjust the degree of primary particle aggregation to a level where peaks exist within the aforementioned range. Specifically, as... Figure 1 As shown, it is preferable that there are tiny voids (pores with a diameter of 65 nm to 300 nm) inside the aggregate of primary particles 1. By having tiny voids, especially when using an electrolyte, the ionic conductivity inside the aggregate can be improved.

[0055] Furthermore, in Embodiment 3 of Patent Document 1 described above, a method using Li is disclosed. 1.0029 Ni 0.83 Co 0.11 Mn 0.0 6W 0.0009 La 0.002 The positive electrode material is represented by O2. More specifically, it describes calcining a mixture containing precursor A (containing Ni, Co, and Mn but not W), precursor B (containing Ni, Co, Mn, and W), LiOH, and La2O3 at a high temperature of 880°C. However, Patent Document 1 neither describes nor implies compound A (a compound containing La, Ni, and O) as used in this disclosure.

[0056] Furthermore, Patent Document 2 disclosed above discloses a material composed of Li 1＋a (Ni) x Co y Mn z G b M c O 2－dThe cathode material disclosed in Patent Document 2 is one or more of Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, Al, B, Mg, Co, F, and Y. Specifically, La is disclosed as one option for G. However, Patent Document 2 makes no disclosure of any embodiments using La.

[0057] 1. Primary particle

[0058] 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.

[0059] Primary particles contain Li, TM (TM is a transition metal), and O. Primary particles can contain one, two, three, or more transition metals.

[0060] Transition metals are metals belonging to Groups IIIB to IB in the periodic table. The transition metals contained in primary particles can belong to periods 3, 4, or 5. Examples of transition metals include Ti, V, Cr, Mn, Fe, Co, Ni, Zr, Nb, La, and W.

[0061] 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 the transition metals (TM) contained in the primary particles are set to 1 mole, the proportion of Ni contained in the primary particles can 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. The capacity characteristics are improved by increasing the proportion of Ni.

[0062] 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 the primary particle may be, for example, 0.40 moles or less, or 0.20 moles or less.

[0063] Primary particles may or may not contain Mn. When all transition metals (TM) contained in a primary particle are set to 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.

[0064] The primary particles preferably contain at least one of Ni, Co, and Mn. When all metals contained in the primary particles (excluding Li) are considered as 1 mole, the total proportion of Ni, Co, and Mn in the primary particles is, for example, 0.80 moles or more, 0.90 moles or more, or 0.95 moles or more. It should be noted that "total proportion of Ni, Co, and Mn" also includes cases where the proportion of one or two of Ni, Co, and Mn is 0.

[0065] Primary particles can contain other metals besides Li and TM, such as M. 1 (Including metalloids). As other metals M 1 For example, metals belonging to Groups IIB to IVA in the periodic table can be cited. Examples of metals belonging to Groups IIB to IVA include Zn, Al, Si, Ga, Ge, In, and Sn.

[0066] The composition of primary particles is not particularly limited; for example, it can be composed of particles of the general formula Li. x Ni a Co b Mn c O y The composition 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).

[0067] "x" can be 0.4 or higher, 0.6 or higher, 0.8 or higher, 1.0 or higher, or 1.05 or higher, or it can be below 1.4 or below 1.2.

[0068] “y” can be 1.6 or higher, 1.7 or higher, 1.8 or higher, or 1.9 or higher, or it can be below 2.0.

[0069] “a” can be 0.6 or higher, 0.7 or higher, 0.8 or higher, or 0.85 or higher, or it can be below 0.9.

[0070] “b” can be greater than or equal to 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, or 0.075, or less than or equal to 0.25, 0.20, 0.15, 0.10, 0.09, or 0.08.

[0071] “c” can be greater than or equal to 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, or 0.075, or less than or equal to 0.25, 0.20, 0.15, 0.10, 0.09, or 0.08.

[0072] 2. Compound A

[0073] Compound A in this disclosure contains La, Ni, and O. Compound A typically has high electronic conductivity, thus a reduction in electrical resistance can be achieved by having compound A present on the surface of the primary particle. Compound A can be disposed directly on the surface of the primary particle or disposed on the surface of the primary particle through other layers (other compounds), with the former being preferred.

[0074] 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 included. 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. Another example of the composition of compound A is La... a Li b Ni c O d (3.5≤a≤4.5, 0.5≤b≤1.5, 0.5≤c≤1.5, 7.5≤d≤8.5). For example, La4LiNiO8 is known to have good electronic conductivity, suggesting that it has a crystal phase similar to perovskite.

[0075] Compound A can be crystalline or amorphous, with the former being preferred. This is because it provides good electronic conductivity. "The compound is crystalline" means that a peak from the target compound can be confirmed using CuKα X-ray diffraction. On the other hand, "the compound is amorphous" means that a peak from the target compound cannot be confirmed using CuKα X-ray diffraction. It should be noted that when the target compound is amorphous, sometimes what is observed is not a peak, but a halo pattern.

[0076] Compound A preferably has a perovskite crystal phase or a perovskite-like crystal phase. Compound A preferably has at least one crystal phase selected from LaNiO3 or La4LiNiO8. This is because it provides good electronic conductivity. It should be noted that the aforementioned crystal phases include those lacking a portion of the constituent atoms (e.g., a portion of O atoms) and those with an excess of a portion of the constituent atoms (e.g., a portion of La atoms).

[0077] Compound A is preferably in particulate form. "Compound A is in particulate form" 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 set as L1, and the length of compound A in the direction perpendicular to the normal direction is set 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.

[0078] When all transition metals contained in a primary particle are set to 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 aforementioned 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.

[0079] The coating percentage of compound A relative to the primary particles is not particularly limited, and can be, for example, 10%–90%, 20%–80%, or 30%–70%. The coating percentage of compound A can be determined, for example, by surface analysis based on XPS (X-ray photoelectron spectroscopy). For instance, when the primary particles contain Ni, Co, and Mn as transition metals (TM), the amount of La and each TM (Ni, Co, Mn) can be determined by surface analysis based on XPS, and La / (La + TM) can be used as the coating percentage. The coating percentages of compounds B and C can be determined similarly. 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 For values ​​above S / cm, it 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.

[0080] 3. Compound B

[0081] 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, thus reducing resistance by having compound B on the surface of the primary particles. Furthermore, the presence of compound B on the surface of the primary particles can suppress the increase in resistance over time. Compound B can be directly disposed on the surface of the primary particles or disposed on the surface of the primary particles through other layers (other compounds), with the former being preferred.

[0082] 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 cited. a W b O c (5.5≤a≤6.5, 0.5≤b≤1.5, 5.5≤c≤6.5). Compound B with the above composition is typically Li6WO6. Another example of the composition of compound B is Li... a W b O c (1.5≤a≤2.5, 0.5≤b≤1.5, 3.5≤c≤4.5). Compound B with the above composition is typically Li₂WO₄. Another example of the composition of compound B is Li₂WO₄. a W b O c (3.5≤a≤4.5, 0.5≤b≤1.5, 4.5≤c≤5.5). Compound B with the above composition is typically Li₄WO₅. Another example of the composition of compound B is Li₂. a W b O c (1.5≤a≤2.5, 1.5≤b≤2.5, 6.5≤c≤7.5). Compound B with the above composition is typically Li2W2O7.

[0083] Compound B can be crystalline or amorphous. Furthermore, compound B is preferably in a film-like state. "Compound B is in a film-like state" 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 direction 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 to 20 nm, or 1 nm to 15 nm. The thickness of compound B is determined as the average value obtained from at least five measurements in a TEM-based observation.

[0084] When all transition metals contained in a primary particle are set to 1 mole, the proportion of W 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 aforementioned proportion of W in compound B is, for example, 0.100 moles or less, 0.080 moles or less, or 0.060 moles or less.

[0085] The coverage ratio of compound B relative to primary particles is not particularly limited, and can be, for example, 10%–90%, 20%–80%, or 30%–70%. 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 For values ​​above S / cm, it can also be 1.0 × 10⁻⁶. -4 S / cm or higher. Additionally, compound B (a compound containing Li, W, and O) is configured on the surface of the primary particles. The primary particles may or may not contain W.

[0086] 4. Cohesion of the collective

[0087] The positive electrode active material in this disclosure is a condensed aggregate composed of multiple primary particles. For example... Figure 1 As shown, the positive electrode active material 10 is composed of multiple primary particles 1.

[0088] The average particle size of primary particles in the aggregate is, for example, 0.5 μm or more, 0.6 μm or more, 0.8 μm or more, 1.0 μm or more, 2 μm or more, or 5 μm or more. On the other hand, the average particle size of primary particles in the aggregate is, for example, 20 μm or less, 15 μm or less, or 10 μm or less. The particle size of each primary particle in the aggregate is determined, for example, as the longest diameter observed in SEM. Furthermore, for example, when the positive electrode active material layer contains an aggregate (positive electrode active material), the particle size (longest diameter) of each primary particle in the aggregate can be determined from a cross-sectional image of the positive electrode active material layer.

[0089] The number of primary particles constituting a condensate is typically 2 or more, but can be 5 or more, or even 10 or more. On the other hand, the number of primary particles constituting a condensate is, for example, 100 or less. Furthermore, the average particle size of the condensate is, for example, greater than 0.5 μm and less than 30 μm, and can be 0.8 μm to 25 μm, 1 μm to 20 μm, or 2 μm to 15 μm. Additionally, the shape of the condensate is, for example, granular.

[0090] When measuring the pore size distribution of the positive electrode active material in this disclosure using mercury porosimetry, peaks are preferably present in the range of 65 nm to 300 nm. These peaks also include inflection points. These peaks can exist in the range of 60 nm to 180 nm, or in the range of 80 nm to 160 nm. These peaks can also exist in the range of 80 nm to 220 nm, or in the range of 100 nm to 200 nm.

[0091] The pore size of the aforementioned peak is, for example, 0.010 mL / g or more, 0.015 mL / g or more, 0.020 mL / g or more, 0.025 mL / g or more, or 0.045 mL / g or more. On the other hand, the pore size of the aforementioned peak is, for example, 0.100 mL / g or less, 0.090 mL / g or less, 0.080 mL / g or less, or 0.060 mL / g or less.

[0092] In this disclosure, at least one of compound A and compound B may be present at the interface of adjacent primary particles in a condensate.

[0093] 5. Positive electrode active material

[0094] The positive electrode active material disclosed herein has crystalline primary particles containing Li, TM (TM being a transition metal), and O. Furthermore, the positive electrode active material is a condensed aggregate composed of multiple primary particles. Positive electrode active materials are commonly used in batteries. Additionally, the manufacturing method of the positive electrode active material is not particularly limited; for example, the method described in "D. Manufacturing Method of Positive Electrode Active Material" described later can be cited.

[0095] Alternatively, this disclosure may also provide a positive electrode active material powder comprising a plurality of crystalline primary particles containing Li, TM (TM being a transition metal), and O as the positive electrode active material. At least a portion of the plurality of primary particles constitutes an aggregate, and a compound A containing La, Ni, and O and a compound B containing Li, W, and O are present on the surface of the primary particles constituting the aggregate. A portion of the plurality of primary particles may constitute a single-crystal active material. Furthermore, the proportion of the aggregate relative to the total positive electrode active material in the positive electrode active material powder 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.

[0096] B. Positive electrode composite material

[0097] The positive electrode material disclosed herein contains the aforementioned positive electrode active material.

[0098] 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.

[0099] 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.

[0100] Positive electrode 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 particulate 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).

[0101] The proportion of conductive material in the solid component of the cathode 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 pathways. On the other hand, the proportion of conductive material in the solid component of the cathode 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 may be relatively low, resulting in a relatively lower energy density.

[0102] The cathode material may contain a binder. By adding a binder, 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), polycarboxylate-based binders such as carboxymethyl cellulose, and fluoride-based binders such as polyvinylidene fluoride (PVdF).

[0103] The proportion of binder in the solid component of the cathode material is, for example, 0.5% by mass or more. If the proportion of binder is too low, it may not be able to adequately suppress the shedding of the cathode active material. On the other hand, the proportion of binder in the solid component of the cathode material is, for example, 15% by mass or less. If the proportion of binder is too high, the proportion of cathode active material may be relatively low, resulting in a relatively low energy density.

[0104] C. Battery

[0105] Figure 3 This is a schematic cross-sectional view illustrating the battery in this disclosure. Figure 3 The battery 20 shown 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 composite material described in "B. Positive Electrode Composite Material" above.

[0106] According to this disclosure, by using the above-described positive electrode composite, a battery with reduced resistance and cycle resistance increase rate is obtained.

[0107] 1. Positive electrode active material layer

[0108] 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.

[0109] 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 to 1000 μm, 1 μm to 500 μm, or 30 μm to 100 μm.

[0110] There are no particular limitations on the method for fabricating the positive electrode active material layer. For example, one method involves coating a positive electrode slurry containing the positive electrode active material and a dispersion medium onto the positive electrode current collector and then drying it. The dried positive electrode active material layer can then be pressed. Pressing increases the density of the positive electrode active material layer.

[0111] 2. Negative electrode active material layer

[0112] 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.

[0113] Examples of carbon-based active materials include, for example, graphite, soft carbon, and hard carbon. Graphite can be natural graphite or artificial graphite. Examples of Li-based active materials include, for example, Li and Li alloys. Examples of Li alloys include, for example, Li-Si alloys. Examples of Si-based active materials include, for example, Si-SiC composite active materials, Si alloys, and Si oxides. Examples of SiC composite active materials include, for example, active materials in which Si or Si alloys are supported on a carbon support. Examples of oxide-based active materials include, for example, Li₄Ti₅O. 12 Lithium titanate, etc.

[0114] The proportion of negative electrode active material in the negative electrode active material layer can be, for example, 20% by mass or more, 30% by mass or more, or 40% by mass or more. If the proportion of negative electrode active material is too low, 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 can be, for example, 95% by mass or less, 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 of the negative electrode active material layer may be relatively reduced.

[0115] 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 to 1000 μm, 1 μm to 500 μm, or 30 μm to 100 μm.

[0116] There are no particular limitations on the method for fabricating the negative electrode active material layer. For example, one method involves coating a negative electrode slurry containing the negative electrode active material and a dispersion medium onto the negative electrode current collector and then drying it. The dried negative electrode active material layer can then be pressed. Pressing increases the density of the negative electrode active material layer.

[0117] 3. Electrolyte layer

[0118] The electrolyte layer is a layer disposed between the positive electrode active material layer and the negative electrode active material layer, and contains at least an electrolyte. The electrolyte is, for example, a liquid electrolyte (electrolyte).

[0119] As an example of an electrolyte, a non-aqueous electrolyte 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.

[0120] 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). The non-aqueous solvent can be a mixture of cyclic carbonates such as EC and PC, which have high dielectric constants and high viscosity, and chain carbonates such as DMC, DEC, and EMC, which have low dielectric constants and low viscosity. The concentration of lithium salt in the non-aqueous electrolyte is, for example, 0.3M to 5M. Furthermore, the non-aqueous electrolyte can contain ionic liquids. Examples of ionic liquids include sulfonium salts, ammonium salts, and pyridine. Salt, piperidine Salt, pyrrolidine Salt, Morpholine Salt, Salt, imidazole Salt.

[0121] Another example of an electrolyte is an aqueous electrolyte. An aqueous electrolyte is an electrolyte whose main component contains water as a solvent. The proportion of water relative to all solvents is, for example, 50% by mass or more, and can be 70% by mass or more. Examples of lithium salts used in aqueous electrolytes include, for example, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide, which are imide-based electrolytes. The concentration of the lithium salt in the aqueous electrolyte is, for example, 1M to 25M.

[0122] The electrolyte layer may include a separator impregnated with the aforementioned electrolyte. By providing the separator, the occurrence of internal short circuits can be suppressed. The separator may be, for example, a porous membrane. Materials for the separator include resins such as polyethylene, polypropylene, polyester, polyvinyl alcohol, cellulose, and polyamide. Furthermore, the electrolyte layer may contain a solid electrolyte. Examples of solid electrolytes include, for example, 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.

[0123] 4. Battery

[0124] 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. Examples of materials for the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. Examples of materials for the negative electrode current collector include SUS, copper, nickel, and carbon. Furthermore, the battery disclosed herein may have an outer casing that houses the power generation components (positive electrode active material layer, electrolyte layer, and negative electrode active material layer). Examples of outer casings include, for example, a box-type outer casing and a laminated outer casing.

[0125] 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 secondary batteries 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-powered vehicles, and diesel-powered vehicles. In particular, it is 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 also be used as a power source for mobile bodies other than vehicles (e.g., railways, ships, aircraft), and as a power source for electrical appliances such as information processing devices.

[0126] D. Methods for manufacturing positive electrode active materials

[0127] Figure 4 This is a flowchart illustrating a method for manufacturing the positive electrode active material in this disclosure. Figure 4 In this process, firstly, a first mixture containing a transition metal hydroxide including TM, a Li source, and a W source is calcined at temperature T1 to obtain a first calcined body (first calcination step). Next, the first calcined body is calcined at temperature T2 to obtain a second calcined body (second calcination step). Next, a La source is added to the pulverized second calcined body to prepare a second mixture, and the second mixture is calcined at temperature T3 to obtain a third calcined body (third calcination step). This yields a positive electrode active material. In this disclosure, at least one of the first mixture and the second mixture contains a Ni source. Furthermore, the temperature T2 in the second calcination step is higher than the temperature T1 in the first calcination step, and the temperature T3 in the third calcination step is lower than the temperature T2 in the second calcination step. Moreover, temperatures T1, T2, and T3 are all within specified ranges.

[0128] According to this disclosure, by performing the first calcination step, the second calcination step, and the third calcination step, a positive electrode active material capable of reducing resistance and reducing the rate of increase in cycle resistance can be obtained.

[0129] 1. First calcination process

[0130] The first calcination step is a step of calcining a first mixture containing a transition metal hydroxide including the above-mentioned TM, a Li source and a W source at a temperature T1 to obtain a first calcined body.

[0131] Transition metal hydroxides contain TM (TM being a transition metal). Transition metal hydroxides are precursors to positive electrode active materials. Typically, transition metal hydroxides do not contain Li, but they may contain Li. Additionally, transition metal hydroxides may or may not contain La. Furthermore, transition metal hydroxides may or may not contain W. Additionally, transition metal hydroxides may or may not contain Ni.

[0132] 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. For example, a method for preparing the aqueous solution can be to dissolve a water-soluble transition metal compound in water. For example, metal salts such as sulfates and nitrates can be cited as transition metal compounds. For example, NiSO4 and Ni(NO3)2 can be cited as Ni sources. For example, CoSO4, Co(NO3)2, and Co(NO3)3 can be cited as Co sources. For example, MnSO4 and Mn(NO3)2 can be cited as Mn sources. The composition of the aqueous solution can be appropriately adjusted according to the target positive electrode active material.

[0133] Next, an aqueous sodium hydroxide solution is added to the reaction vessel to maintain the pH at an alkaline level (e.g., pH 11.3–12.0), and the starting material aqueous solution and an aqueous NH3 solution are added dropwise. The reaction temperature is not particularly limited, but is, for example, 50°C–65°C. After the reaction is complete, it is preferable to filter the solution to remove the transition metal hydroxide, wash it with water, and then dry it.

[0134] In the first calcination step, a first mixture containing a transition metal hydroxide, a Li source, and a W 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 to 1.2, less than 0.9 to 1.1, or 1.0.

[0135] Examples of W sources include H₂WO₄. The first mixture may or may not contain a Ni source. For example, when the transition metal hydroxide contains Ni, the transition metal hydroxide can also serve as a Ni source. On the other hand, 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, W, and Ni sources added can be adjusted appropriately based on the target positive electrode active material.

[0136] The mixture described above preferably contains a molten salt. The molten salt functions as a flux, enabling sufficient grain growth of the primary particles. 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 typically 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.

[0137] The mixture described above may contain lithium hydroxide as a Li source and a molten salt. The molar ratio (Li' / TM) of Li in the Li source and molten salt relative to TM in the transition metal hydroxide is, for example, 1.1 or more, 1.15 or more, or 1.2 or more. On the other hand, the Li' / TM ratio is, for example, less than 1.6, 1.55 or less, or 1.5 or less.

[0138] In the first calcination step, the first mixture is calcined at a temperature T1 to obtain the first calcined body. The temperature T1 is typically 500℃ to 800℃, but can be 550℃ to 750℃. If the temperature T1 is too high, compound B containing Li, W, and O will not be formed, and W2O3 will easily form, making it difficult to reduce electrical resistance. On the other hand, if the temperature T1 is too low, it will be difficult for the primary particles to fully grow into grains.

[0139] The calcination time in the first calcination step is not particularly limited; for example, it can be 5 to 15 hours, or 8 to 12 hours. The atmosphere in the first calcination step is usually an oxygen-containing atmosphere. Examples of calcination methods in the first calcination step include using a muffle furnace, an electric furnace, or other calcination furnaces.

[0140] In the first calcination step, a pulverization process can be performed to crush the first calcined body. Examples of pulverization methods include hammer mills, experimental mills, and ball mills.

[0141] 2. Second calcination process

[0142] The second calcination step is a process of calcining the first calcined body at a temperature T2 to obtain the second calcined body. The temperature T2 in the second calcination step is usually higher than the temperature T1 in the first calcination step. By making the temperature T2 higher than the temperature T1, it is easy to obtain a condensed body with peaks at specified positions in the fine pore size distribution.

[0143] The temperature difference between T2 and T1 can be, for example, 50°C or more, 75°C or more, or 100°C or more. Furthermore, T2 is typically between 600°C and 1000°C, or between 650°C and 950°C. If T2 is too high, W2O3 may be easily formed. On the other hand, if T2 is too low, aggregates with peaks at specified positions in the fine pore size distribution may not be obtained. The calcination time in the second calcination step is not particularly limited, for example, it can be between 1 hour and 5 hours, or between 2 hours and 4 hours. The calcination time in the second calcination step can be shorter than the calcination time in the first calcination step. The atmosphere in the second calcination step is typically an oxygen-containing atmosphere. Examples of calcination methods in the second calcination step include using a muffle furnace, an electric furnace, or other calcination furnaces.

[0144] In the second calcination process, a pulverization process is typically performed to crush the second calcined body. Examples of pulverization methods include hammer mills, experimental mills, and ball mills. The pulverization conditions are preferably adjusted in a manner that yields a condensed body with peaks at specified positions within the fine pore size distribution.

[0145] 3. Third calcination process

[0146] The third calcination step involves adding a La source to the pulverized material of the second calcined body to prepare a second mixture, and then calcining the second mixture at a temperature T3 to obtain the third calcined body. The temperature T3 in the third calcination step is typically lower than the temperature T2 in the second calcination step. By keeping the temperature T3 lower than T2, La₂O₃ is not generated, but a compound A containing La, Ni, and O is readily formed, thus reducing electrical resistance.

[0147] 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. The amount of La source added can be adjusted appropriately based on the target positive electrode active material. Additionally, the second mixture may or may not contain a Ni source.

[0148] The temperature difference between T2 and T3 can be, for example, 100°C or more, 150°C or more, or 200°C or more. Furthermore, temperature T3 is typically between 400°C and 600°C, or between 450°C and 550°C. If temperature T2 is too high, La2O3 may be easily formed. On the other hand, if temperature T2 is too low, the increased electronic conductivity effect brought about by compound A may not be fully realized.

[0149] The temperature T3 in the third calcination step can be lower than the temperature T1 in the first calcination step. The difference between temperature T1 and temperature T3 can be, for example, 50°C or more, 75°C or more, or 100°C or more.

[0150] The calcination time in the third calcination step is not particularly limited; for example, it can be 3 to 7 hours, or 4 to 6 hours. The calcination time in the third calcination step can be longer than that in the second calcination step. The atmosphere in the third calcination step is usually an oxygen-containing atmosphere. Examples of calcination methods in the third calcination step include using a muffle furnace, an electric furnace, or other calcination furnaces.

[0151] In the third calcination step, a pulverization process can be performed to crush the third calcined body. Examples of pulverization methods include hammer mills, experimental mills, and ball mills. The pulverization conditions are preferably adjusted to obtain a condensed body with peaks at specified positions in the fine pore size distribution.

[0152] 4. Other processes

[0153] The method for manufacturing the positive electrode active material in this disclosure may include a granulation step after the third calcination step, in which the pulverized material of the third calcined body is granulated, or it may not. Granulation allows for the formation of large aggregates, thereby enabling control over the pore size distribution. As a method for granulating the pulverized material of the calcined body, spray drying is an example. In spray drying, for example, the pulverized material of the calcined body is dispersed in water, and the dispersion is sprayed using a spray drying apparatus. The heating temperature of the spray drying apparatus is, for example, 150°C to 250°C.

[0154] 5. Positive electrode active material

[0155] The positive electrode active material obtained from the above processes is the same as the content described in "A. Positive Electrode Active Material" above.

[0156] It should be noted that this disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and any embodiment having a substantially the same structure and achieving the same effect as the technical concept described in the claims of this disclosure is included within the technical scope of this disclosure.

[0157] Example

[0158] [Comparative Example 1]

[0159] (Preparation of positive electrode active material)

[0160] NiSO4, CoSO4, and MnSO4 were prepared as raw materials and dissolved in ion-exchanged water to prepare a raw material aqueous solution. The molar ratio of Ni, Co, and Mn in the raw material aqueous solution was Ni:Co:Mn = 8:1:1. Furthermore, the concentration of the raw material aqueous solution (the ratio of all raw materials to the raw material aqueous solution) was 30% by mass.

[0161] Then, a certain amount of NH3 aqueous solution was added to the reaction vessel, and nitrogen replacement was carried out in the reaction vessel while stirring with a stirrer. NaOH aqueous solution was added to the reaction vessel to maintain the pH at alkaline (pH=12). While maintaining a certain 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 10 hours. Next, the precipitated transition metal hydroxide was removed by filtration, and ion-exchanged water was added to disperse it with a spoon before washing with water. The washed transition metal hydroxide was dried at 120℃ for 16 hours to obtain the transition metal hydroxide as a precursor.

[0162] Then, a Li source (LiOH) was added to the obtained precursor and mixed using an agate mortar to obtain the first mixture. The amount of Li source added was adjusted such 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 calcined in a calcining furnace at 900°C under an oxygen atmosphere for 10 hours to obtain a calcined body. The calcined body was then broken down using a jet mill to adjust the particle size, yielding the positive electrode active material.

[0163] (Battery manufacturing)

[0164] The obtained positive electrode active material is used to manufacture a battery. Specifically, a film coater (manufactured by ALL GRIT Co., Ltd.) with film thickness adjustment function is used to coat a positive electrode paste 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 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.

[0165] Next, using a film coater (manufactured by ALL GRIT Co., Ltd.) with a film thickness adjustment function, a negative electrode composite paste 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.

[0166] [Comparative Example 2]

[0167] The precursor (transition metal hydroxide) was obtained by operating 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 the mixture was prepared by mixing using an agate mortar to obtain a first mixture. The amount of Li source added was adjusted such that the molar ratio (Li / NCM) of Li contained in the Li source relative to the total NCM of Ni, Co, and Mn contained in the precursor was 1.1. The amount of La source added was adjusted such that the La / NCM ratio was 0.005, and the amount of W source added was adjusted such that the W / NCM ratio was 0.005. Using the obtained first mixture, except otherwise specified in Comparative Example 1, a positive electrode active material and a battery were obtained.

[0168] [Comparative Example 3]

[0169] The same procedure as in Comparative Example 2 was followed to obtain the first mixture. The obtained first mixture was calcined in a calcining furnace at 650°C in an oxygen atmosphere for 10 hours to obtain the first calcined body. The obtained first calcined body was broken down using a jet mill, and then calcined in a calcining furnace at 500°C in an oxygen atmosphere for 3 hours to obtain the second calcined body.

[0170] [Example 1]

[0171] The precursor (transition metal hydroxide) was obtained by operating in the same manner as in Comparative Example 1. A Li source (LiOH) and a W source (H₂WO₄) were added to the obtained precursor, and the mixture was prepared using an agate mortar to obtain a first mixture. The amount of Li source added was adjusted such that the molar ratio (Li / NCM) of Li contained in the Li source relative to the total NCM of Ni, Co, and Mn contained in the precursor was 1.2. The amount of W source added was adjusted such that the W / NCM ratio was 0.005. The first calcined body was obtained by calcining the first mixture in a calcining furnace at 650°C under an oxygen atmosphere for 10 hours.

[0172] The first calcined body was pulverized using a jet mill, and then calcined in a calcining furnace at 800°C in an oxygen atmosphere for 3 hours to obtain a second calcined body. The second calcined body was pulverized using a jet mill. A La source (La(OH)3) was added to the obtained pulverized material and mixed using an agate mortar to obtain a second mixture. The amount of La source added was adjusted such that the molar ratio (La / NCM) of La contained in the La source relative to the total Ni, Co, and Mn contained in the pulverized material was 0.005. Then, a third calcined body was obtained by calcining in a calcining furnace at 500°C in an oxygen atmosphere for 5 hours. The third calcined body was pulverized using a jet mill, and the particle size was adjusted to obtain a positive electrode active material. Using the obtained positive electrode active material, a battery was obtained in the same manner as in Comparative Example 1.

[0173] [Example 2]

[0174] The third calcined product was obtained by operating in the same manner as in Example 1. The obtained calcined body was pulverized using a hammer mill to break it down into particles of a specified size. Then, 30 g of the pulverized material was dispersed in 100 mL of pure water and sprayed at 200°C using a spray drying apparatus manufactured by BUCHI, thereby obtaining the positive electrode active material as a granulated body. Using the obtained positive electrode active material, a battery was obtained in the same manner as in Example 1, except that... It should be noted that in Table 1, synthesis method 1 is a method involving a one-step calcination process as in Comparative Examples 1 and 2, synthesis method 2 is a method involving a two-step calcination process as in Comparative Example 3, and synthesis method 3 is a method involving a three-step calcination process as in Examples 1 and 2.

[0175] [evaluate]

[0176] (SEM-EDX measurement)

[0177] The positive electrode active materials obtained in Examples 1, 2, and Comparative Examples 1-3 were subjected to cross-sectional observation and elemental analysis using scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX). The results confirmed that the primary particles in Examples 1, 2, and Comparative Examples 1-3 contained Ni, Co, and Mn. Furthermore, in Examples 1, 2, and Comparative Example 3, particulate compounds were identified on the surface of the primary particles, and mapping images confirmed that these particulate compounds contained La, Ni, and O.

[0178] (TEM-EDX measurement)

[0179] The positive electrode active materials obtained in Examples 1, 2, and Comparative Example 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 were identified on the surface of the primary particles in Examples 1, 2, and Comparative Example 3, and the mapping images confirmed that the film-like compounds contained W and O.

[0180] (XRD measurement)

[0181] The positive electrode active materials obtained in Examples 1, 2, and Comparative Examples 1-3 were subjected to X-ray diffraction (XRD) using CuKα rays. The results confirmed that the positive electrode active materials obtained in Examples 1, 2, and Comparative Examples 1-3 all possess a layered rock salt type crystal phase belonging to space group R-3m. That is, it was confirmed that the primary particles containing Ni, Co, and Mn possess a layered rock salt type crystal phase.

[0182] Furthermore, in the positive electrode active materials obtained in Examples 1, 2, and Comparative Example 3, peaks from the LaNiO-based crystalline phase (La4LiNiO8) were identified. Therefore, compound A present on the surface of the primary particles was confirmed to be crystalline. On the other hand, peaks from the LiWO-based crystalline phase were not identified in the positive electrode active materials obtained in Examples 1, 2, and Comparative Example 3. Therefore, compound B present on the surface of the primary particles is presumed to be amorphous.

[0183] On the other hand, in the positive electrode active material obtained in Comparative Example 2, no peaks from the LaNiO system crystal phase were identified, but peaks from La2O3 and W2O3 were identified. That is, compounds A and B of this disclosure were not formed in the positive electrode active material obtained in Comparative Example 2.

[0184] (Determination of pore size distribution)

[0185] The pore size distribution of the positive electrode active materials obtained in Examples 1 and 2 and Comparative Examples 1-3 was determined using mercury intrusion porosimetry. Specifically, a mercury intrusion porosimetry pore size distribution measuring device from Micromeritics was used, and mercury was injected into a sample tube containing 1 g of the positive electrode active material to measure the pore size distribution of the positive electrode active material. In Examples 1 and 2, since the positive electrode active materials were obtained as aggregates, peaks were present in the range of 65 nm to 300 nm. On the other hand, in Comparative Examples 1-3, since the positive electrode active materials were obtained as single crystals, the above-mentioned peaks were not present. The results of the peak positions are shown in Table 1.

[0186] (Initial resistance)

[0187] The initial resistance was measured using the batteries obtained in Examples 1 and 2 and Comparative Examples 1-3. Specifically, the batteries were charged to 4.3V and then discharged to 3.7V. The voltage drop (V) was then measured during 10 seconds of discharge at 0°C and various C-rates of 0.1C, 0.3C, 0.5C, 0.7C, and 1.0C. The voltage drop (V) was plotted against the current value, approximating a straight line using a linear function, and the slope of this line was taken as the resistance (V resistance). The results are shown in Table 1. It should be noted that the initial resistance values ​​in Table 1 are relative to the initial resistance of Comparative Example 1, which is set to 100%.

[0188] (Rate of increase in cyclic resistance)

[0189] The increase rate of cycle resistance was measured using the batteries obtained in Examples 1 and 2 and Comparative Examples 1 to 3. Specifically, the resistance (IV resistance) was measured before and after the cycle test. The cycle test was performed for 100 cycles under the conditions of 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.

[0190] Cyclic resistance increase rate (%) = (resistance after cyclic test) / initial resistance × 100

[0191] The results are shown in Table 1.

[0192] [Table 1]

[0193]

[0194] As shown in Table 1, it was confirmed that the initial resistance of Examples 1, 2, and Comparative Example 3 was lower than that of Comparative Examples 1 and 2. This is presumably because the presence of compound A (containing La, Ni, and O) with good electronic conductivity and compound B (containing Li, W, and O) with good ionic conductivity on the surface of the primary particles facilitates the movement of electrons and ions. Furthermore, it was confirmed that the rate of increase in cycle resistance was lower in Examples 1 and 2 compared to Comparative Example 3. This is presumably because the positive electrode active material obtained in Examples 1-2 (condensed aggregates) has a smaller specific surface area than that obtained in Comparative Example 3 (single crystal), thus suppressing the accumulation of resistive components caused by repeated charge-discharge cycles.

Claims

1. A positive electrode active material having crystalline primary particles containing Li, TM, and O, wherein TM is a transition metal. The positive electrode active material is a condensed aggregate composed of multiple 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.

2. The positive electrode active material according to claim 1, wherein, In the fine pore size distribution obtained by mercury porosimetry, peaks exist in the range of 65 nm to 300 nm.

3. The positive electrode active material according to claim 2, wherein, In the aforementioned pore size distribution, the peak exists in the range of 80 nm to 220 nm.

4. The positive electrode active material according to claim 1, wherein, The average particle size of the primary particles in the aggregate is greater than 0.5 μm.

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

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

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

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

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

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

11. 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 composite material as described in claim 10.

12. A method for manufacturing a positive electrode active material, used to manufacture the positive electrode active material according to any one of claims 1 to 9, comprising: In the first calcination step, a first mixture containing a transition metal hydroxide, a Li source, and a W source is calcined at a temperature T1 to obtain a first calcined body, wherein the transition metal hydroxide contains the aforementioned TM. The second calcination step involves calcining the first calcined body at temperature T2 to obtain the second calcined body. In the third calcination step, a La source is added to the pulverized material of the second calcined body to prepare a second mixture, and the second mixture is calcined at a temperature T3 to obtain the third calcined body; At least one of the first mixture and the second mixture contains a Ni source. The temperature T2 in the second calcination step is higher than the temperature T1 in the first calcination step. The temperature T3 in the third calcination step is lower than the temperature T2 in the second calcination step. The temperature T1 is 500℃~800℃. The temperature T2 is 600℃~1000℃. The temperature T3 is 400℃~600℃.

Images