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

Abstract

A primary object of the present disclosure is to provide a positive electrode active material that can suppress an increase in resistance associated with charging and discharging. [Solution] The present disclosure solves the above problem by providing a positive electrode active material having crystalline primary particles containing Li, TM (TM is a transition metal), and O, and being an aggregate composed of a plurality of the primary particles, the primary particles in the aggregate having an average particle size of 0.5 μm or more, and having a pore size distribution obtained by mercury intrusion porosimetry that has a peak in the range of 65 nm to 300 nm.

Description

[Technical Field]

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

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

[0003] For example, Patent Document 1 discloses a positive electrode active material for all-solid-state lithium-ion batteries, in which the pore diameter (D75) seen from the micropore diameter side at 25% accumulation in a cumulative pore distribution curve obtained by mercury intrusion porosimetry is 7 μm or less. Patent Document 2 discloses a positive electrode active material for lithium secondary batteries, in which the pore distribution obtained by mercury intrusion porosimetry has a pore peak in the pore radius range of 10 nm to 200 nm. Patent Document 3 discloses lithium composite oxide particles, in which the pore radius measured by mercury intrusion porosimetry has a subpeak with a peak top at a pore radius of 80 nm to 300 nm. Patent Document 4 discloses a porous metal oxide-based electrochemical energy storage material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-114411 [Patent Document 2] Japanese Patent Application Publication No. 2018-174106 [Patent Document 3] Japanese Patent Application Laid-Open No. 2005-123179 [Patent Document 4] Japanese Patent Publication No. 2022-537567 Summary of the Invention [Problem to be solved by the invention]

[0005] From the viewpoint of improving battery performance, it is required to suppress the increase in resistance due to charging and discharging. The main object of the present invention is to provide a positive electrode active material that can suppress the increase in resistance due to charging and discharging. [Means for solving the problem]

[0006] [1] A positive electrode active material, the positive electrode active material has crystalline primary particles containing Li, TM (TM is a transition metal), and O; the positive electrode active material is an aggregate composed of a plurality of the primary particles, the average particle size of the primary particles in the aggregate is 0.5 μm or more; A positive electrode active material having a pore size distribution obtained by mercury intrusion porosimetry, the pore size distribution having a peak in the range of 65 nm to 300 nm.

[0007] [2] The positive electrode active material according to [1], wherein the pore size distribution has a peak in the range of 90 nm or more and 220 nm or less.

[0008] [3] The positive electrode active material according to [1] or [2], wherein the pore volume at the peak is 0.010 mL / g or more.

[0009] [4] The positive electrode active material according to any one of [1] to [3], wherein the pore volume at the peak is 0.025 mL / g or more.

[0010] [5] The positive electrode active material according to any one of [1] to [4], wherein the primary particles contain at least Ni as the TM.

[0011] [6] The positive electrode active material according to [5], wherein the proportion of the Ni is 0.50 parts by mol or more when the TM is taken as 1 part by mol.

[0012] [7] The positive electrode active material according to [5], wherein the proportion of the Ni is 0.90 parts by mol or more when the TM is taken as 1 part by mol.

[0013] [8] The positive electrode active material according to any one of [1] to [7], wherein the primary particles contain at least one of Co and Mn as the TM.

[0014] [9] The positive electrode active material according to any one of [1] to [8], wherein the primary particles have a layered rock salt type crystal structure.

[0015]

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

[0016]

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

[10] .

[0017]

[12] A method for producing a positive electrode active material according to any one of [1] to [9], a calcination step of calcining a mixture containing the transition metal hydroxide containing the TM, a Li source, and lithium hydroxide as a molten salt to obtain a calcined body; a crushing step of crushing the fired body; and In the mixture, the molar ratio of Li in the molten salt to the TM is 0.1 or more and less than 0.6.

[0018]

[13] the Li source is lithium hydroxide;

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

[12] , wherein in the mixture, a molar ratio of Li in the Li source to the TM is 1.0.

[0019]

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

[12] or

[13] , further comprising, after the pulverization step, a granulation step of granulating the pulverized product of the fired body. [Effects of the Invention]

[0020] The present disclosure has an effect of providing a positive electrode active material that can suppress an increase in resistance associated with charge and discharge. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a schematic cross-sectional view illustrating a positive electrode active material according to the present disclosure. [Figure 2] FIG. 1 is a schematic cross-sectional view illustrating a conventional positive electrode active material. [Figure 3] FIG. 1 is a schematic cross-sectional view illustrating a battery according to the present disclosure. [Figure 4] FIG. 1 is a flow diagram illustrating a method for producing a positive electrode active material according to the present disclosure. [Figure 5] 1 shows the results of measurements performed by mercury porosimetry on the positive electrode active materials obtained in Examples 1 to 4 and Comparative Examples 1 and 2. [Figure 6] 1 shows the results of the capacity retention rates of the batteries obtained in Example 1 and Comparative Examples 1 and 2. DETAILED DESCRIPTION OF THE INVENTION

[0022] Below, embodiments will be described with reference to the drawings etc. However, the present disclosure can be implemented in many different forms and is not limited to the description of the embodiments exemplified below. Furthermore, to clarify the explanation, the drawings may show the width, thickness, and shape of each part schematically compared to the actual form, but this is merely an example and should not be construed as limiting.

[0023] A. Positive electrode active material FIG. 1 is a schematic cross-sectional view illustrating a positive electrode active material according to the present disclosure. As shown in FIG. 1, the positive electrode active material 10 has crystalline primary particles 1 containing Li, TM (TM is a transition metal), and O. The positive electrode active material 10 is an aggregate composed of a plurality of primary particles 1. The average particle size of the primary particles 1 in the aggregate is 0.5 μm or more. The pore size distribution obtained by mercury intrusion porosimetry has a peak in the range of 65 nm to 300 nm.

[0024] According to the present disclosure, the primary particles in the aggregates have a large average particle size, and the pore size distribution has a peak within a predetermined range, resulting in a positive electrode active material that can suppress an increase in resistance associated with charge and discharge. Conventionally, polycrystalline active materials and single-crystalline active materials have been known as positive electrode active materials. For example, as shown in FIG. 2(a), polycrystalline active materials typically have multiple primary particles 1 (very fine primary particles 1) densely packed together. While polycrystalline active materials are relatively easy to manufacture, they are prone to increasing resistance over time. This is because repeated charge and discharge cycles cause cracks in the polycrystals, and the newly formed surfaces created by the cracks react with the electrolyte, generating resistance components.

[0025] On the other hand, as shown in Figure 2(b), in single-crystal active materials, large primary particles 1 do not aggregate but exist as individual particles. Single-crystal active materials are less likely to crack even after repeated charge and discharge compared to polycrystalline active materials. This has the advantage of being able to suppress the increase in resistance over time caused by the reaction of newly formed surfaces with the electrolyte. On the other hand, single-crystal active materials have a larger specific surface area compared to polycrystalline active materials, so repeated charge and discharge easily causes resistance components to accumulate, leading to an increase in resistance over time.

[0026] Thus, although the reasons are different, both polycrystalline and single-crystalline active materials have the problem of being prone to resistance increases over time. In response to this, in the present disclosure, aggregates are formed from large-sized primary particles (primary particles close to single crystal). This provides the advantage of being less susceptible to cracking even with repeated charge and discharge compared to polycrystalline active materials. Furthermore, the aggregates can have a smaller specific surface area compared to single-crystalline active materials. As a result, the accumulation of resistance components due to repeated charge and discharge can be suppressed. Thus, the positive electrode active material in the present disclosure is an aggregate formed by appropriately aggregating large-sized primary particles (conventional single-crystalline active materials), and is therefore a positive electrode active material that can suppress resistance increases associated with charge and discharge.

[0027] In the present disclosure, the degree of aggregation of primary particles is defined by the pore size distribution obtained by mercury intrusion porosimetry. Specifically, it is defined that the pore size distribution has a peak in the range of 65 nm to 300 nm. That is, as shown in FIG. 1 , it is defined that microvoids (voids with a pore size of 65 nm to 300 nm) exist within the aggregates of primary particles 1. The presence of microvoids also has the effect of improving ionic conductivity within the aggregates, especially when an electrolyte solution is used. Furthermore, as the aggregation of primary particles becomes denser, the peak position in the pore size distribution shifts toward the smaller pore size side. Furthermore, in general single-crystal active materials, large primary particles do not aggregate and exist as individual particles, so microvoids do not usually exist.

[0028] As mentioned above, Patent Document 2 discloses a positive electrode active material for lithium secondary batteries, in which a pore distribution obtained by mercury intrusion porosimetry has a pore peak in the pore radius range of 10 nm to 200 nm. Patent Document 3 also discloses lithium composite oxide particles, in which a pore radius measured by mercury intrusion porosimetry has a subpeak with a peak top at a pore radius of 80 nm to 300 nm. However, Patent Documents 2 and 3 do not describe or suggest the average particle size of the primary particles in the aggregates. Furthermore, the examples in Patent Document 2 use lithium carbonate as the Li source, and do not use the molten salt described below. Therefore, it is presumed that a polycrystalline active material is obtained. Furthermore, the examples in Patent Document 3 use LiOH as the lithium carbonate Li source, but the amount of LiOH used is approximately stoichiometric. Furthermore, it is presumed that the primary particles do not grow sufficiently under the firing conditions of 950°C and 12 hours, resulting in a polycrystalline active material. That is, Patent Documents 2 and 3 are premised on the use of polycrystalline active materials, and there is no motivation to prepare the positive electrode active material of the present disclosure.

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

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

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

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

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

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

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

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

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

[0038] 2. Aggregates The positive electrode active material in the present disclosure is an aggregate composed of a plurality of primary particles. As shown in FIG.

[0039] The average particle size of the primary particles in the aggregates is usually 0.5 μm or more, and may be 0.6 μm or more, 0.8 μm or more, 1 μm or more, 2 μm or more, or 5 μm or more. On the other hand, the average particle size of the primary particles in the aggregates is, for example, 20 μm or less, 15 μm or less, or 10 μm or less. The average particle size of the primary particles (positive electrode active material) can be determined, for example, by SEM cross-sectional observation.

[0040] The number of primary particles constituting the aggregate is usually 2 or more, and may be 5 or more, or 10 or more. On the other hand, the number of primary particles constituting the aggregate is, for example, 100 or less. The average particle size of the aggregate is, for example, more than 0.5 μm and 30 μm or less, or may be 0.8 μm or more and 25 μm or less, or 1 μm or more and 20 μm or less, or 2 μm or more and 15 μm or less. The shape of the aggregate is, for example, particulate.

[0041] When the pore size distribution of the positive electrode active material according to the present disclosure is measured by mercury intrusion porosimetry, a peak is present in the range of 65 nm to 300 nm. This peak also includes an inflection point (e.g., Example 4 in FIG. 5). The peak may be present in the range of 75 nm to 220 nm, 80 nm to 200 nm, 85 nm to 180 nm, or 90 nm to 150 nm.

[0042] The pore volume at the peak may be, 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. Meanwhile, the pore volume at the peak may be, 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. Furthermore, the pore size distribution may have a minimum point (a downwardly convex point) in the range of 100 nm to 300 nm. The minimum point may be in the range of 150 nm to 300 nm, or in the range of 150 nm to 250 nm.

[0043] 3.Cathode active material The positive electrode active material in the present disclosure has crystalline primary particles containing Li, TM (TM is a transition metal), and O. The positive electrode active material is an aggregate composed of a plurality of primary particles. The positive electrode active material is typically used in batteries. The method for producing the positive electrode active material is not particularly limited, but examples thereof include the method described in "D. Method for producing positive electrode active material" below.

[0044] The present disclosure also provides a positive electrode active material powder, which contains a plurality of crystalline primary particles containing Li, TM (TM is a transition metal), and O as the positive electrode active material, at least a portion of the primary particles forming aggregates, the primary particles in the aggregates having an average particle size of 0.5 μm or more, and a pore size distribution of the aggregates obtained by mercury intrusion porosimetry exhibiting a peak in the range of 65 nm to 300 nm. Some of the primary particles may form a single-crystalline active material. The proportion of the aggregates relative to the total positive electrode active material in the positive electrode active material powder is, for example, 5% by mass or more, 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.

[0045] B. Cathode composite The positive electrode mixture in the present disclosure contains the above-described positive electrode active material.

[0046] According to the present disclosure, the use of the above-described positive electrode active material results in a positive electrode composite that can suppress an increase in resistance associated with charge and discharge. The positive electrode composite may contain other materials (e.g., a conductive material, a binder) in addition to the positive electrode active material. The positive electrode composite may also contain the above-described positive electrode active material powder. The positive electrode composite may also be in the form of a powder or a slurry containing a dispersion medium.

[0047] The proportion of the positive electrode active material in the solid content of the positive electrode mixture is, for example, 20% by mass or more, or may be 30% by mass or more, or 40% by mass or more. If the proportion of the positive electrode active material is too low, sufficient energy density may not be obtained. On the other hand, the proportion of the positive electrode active material in the solid content of the positive electrode mixture is, for example, 95% by mass or less, or may be 70% by mass or less, or may be 60% by mass or less. If the proportion of the positive electrode active material is too high, ionic conductivity and electronic conductivity may relatively decrease.

[0048] The positive electrode mixture may contain a conductive material. The addition of a conductive material improves electronic conductivity. Examples of conductive materials include carbon-based conductive materials, metal particles, and conductive polymers. Examples of carbon-based conductive materials include particulate materials such as acetylene black (AB) and ketjen black (KB), and fibrous materials such as vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and carbon nanofibers (CNF).

[0049] The proportion of the conductive material in the solid content of the positive electrode mixture is, for example, 0.1% by mass or more. If the proportion of the conductive material is too low, there is a possibility that the electron conduction path will be insufficient. On the other hand, the proportion of the conductive material in the solid content of the positive electrode mixture is, for example, 5% by mass or less. If the proportion of the conductive material is too high, there is a possibility that the proportion of the positive electrode active material will be relatively low, resulting in a low energy density.

[0050] The positive electrode mixture may contain a binder. Addition of the binder makes it possible to obtain a positive electrode active material layer in which the positive electrode active material is less likely to fall off. Examples of binders include rubber-based binders such as styrene-butadiene rubber (SBR) and butadiene rubber (BR), polycarboxylic acid-based binders such as carboxymethyl cellulose, and fluoride-based binders such as polyvinylidene fluoride (PVdF).

[0051] The proportion of the binder in the solid content of the positive electrode mixture is, for example, 0.5% by mass or more. If the proportion of the binder is too low, it may not be possible to sufficiently prevent the positive electrode active material from falling off. On the other hand, the proportion of the binder in the solid content of the positive electrode mixture is, for example, 15% by mass or less. If the proportion of the binder is too high, the proportion of the positive electrode active material will be relatively low, which may result in a low energy density.

[0052] C.Battery Fig. 3 is a schematic cross-sectional view illustrating a battery according to the present disclosure. The battery 20 shown in Fig. 3 includes a positive electrode active material layer 11, a negative electrode active material layer 12, an electrolyte layer 13 disposed between the positive electrode active material layer 11 and the negative electrode active material layer 12, a positive electrode current collector 14 that collects current from the positive electrode active material layer 11, and a negative electrode current collector 15 that collects current from the negative electrode active material layer 12. In the present disclosure, the positive electrode active material layer 11 contains the positive electrode composite described above in "B. Positive Electrode Composite."

[0053] According to the present disclosure, by using the above-described positive electrode composite, a battery can be obtained in which an increase in resistance due to charging and discharging is suppressed.

[0054] 1.Cathode active material layer The positive electrode active material layer contains at least a positive electrode active material. The positive electrode active material layer may also contain a conductive material and a binder. The positive electrode active material, conductive material, and binder are the same as those described above in "A. Positive electrode active material" and "B. Positive electrode composite."

[0055] The positive electrode active material layer may contain an electrolyte. The electrolyte is, for example, an electrolytic solution described below. On the other hand, the positive electrode active material layer may contain a solid electrolyte. The thickness of the positive electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less, or may be 1 μm or more and 500 μm or less, or may be 30 μm or more and 100 μm or less.

[0056] The method for producing the positive electrode active material layer is not particularly limited, but may include, for example, a method in which a positive electrode slurry containing a positive electrode active material and a dispersion medium is applied to a positive electrode current collector and then dried. The dried positive electrode active material layer may be subjected to a press treatment. The press treatment improves the density of the positive electrode active material layer.

[0057] 2.Negative electrode active material layer The negative electrode active material layer contains at least a negative electrode active material, such as a carbon-based active material, a Li-based active material, a Si-based active material, or an oxide-based active material.

[0058] Examples of carbon-based active materials include graphite, soft carbon, and hard carbon. Graphite may be natural graphite or artificial graphite. Examples of Li-based active materials include Li and Li alloys. Examples of Li alloys include Li-Si alloys. Examples of Si-based active materials include Si, SiC composite active materials, Si alloys, and Si oxides. Examples of SiC composite active materials include active materials in which Si or Si alloys are supported on a carbon support. Examples of oxide-based active materials include Li4Ti5O 12 Lithium titanates such as those mentioned above are also included.

[0059] The proportion of the negative electrode active material in the negative electrode active material layer is, for example, 20% by mass or more, or alternatively, 30% by mass or more, or even 40% by mass or more. If the proportion of the negative electrode active material is too low, sufficient energy density may not be obtained. On the other hand, the proportion of the negative electrode active material in the negative electrode active material layer is, for example, 95% by mass or less, or alternatively, 70% by mass or less, or alternatively, 60% by mass or less. If the proportion of the negative electrode active material is too high, the ionic conductivity and electronic conductivity of the negative electrode active material layer may relatively decrease.

[0060] The negative electrode active material layer may contain at least one of a conductive material, a binder, and an electrolyte. Details of the conductive material, the binder, and the electrolyte are the same as those described above in "1. Positive electrode active material layer." The thickness of the negative electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less, or may be 1 μm or more and 500 μm or less, or may be 30 μm or more and 100 μm or less.

[0061] The method for producing the negative electrode active material layer is not particularly limited, but may include, for example, a method in which a negative electrode slurry containing a negative electrode active material and a dispersion medium is applied to a negative electrode current collector and then dried. The dried negative electrode active material layer may be subjected to a press treatment. The press treatment improves the density of the negative electrode active material layer.

[0062] 3. Electrolyte layer The electrolyte layer is a layer disposed between the positive electrode active material layer and the negative electrode active material layer, and contains at least an electrolyte, such as a liquid electrolyte (electrolytic solution).

[0063] An example of the electrolyte is a non-aqueous electrolyte. The non-aqueous electrolyte contains, for example, a lithium salt and a non-aqueous solvent. Examples of the lithium salt include inorganic lithium salts such as LiPF, LiBF, LiClO, and LiAsF; and organic lithium salts such as LiCF, LiN(SOCF), LiN(SOCF) and LiC(SOCF).

[0064] Examples of non-aqueous solvents include carbonate-based solvents such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The non-aqueous solvent may be a mixture of a cyclic carbonate such as EC or PC, which has a high dielectric constant and high viscosity, and a chain carbonate such as DMC, DEC, or EMC, which has a low dielectric constant and low viscosity. The concentration of the lithium salt in the non-aqueous electrolyte solution is, for example, 0.3 M or more and 5 M or less. The non-aqueous electrolyte solution may also contain an ionic liquid. Examples of ionic liquids include sulfonium salts, ammonium salts, pyridinium salts, piperidinium salts, pyrrolidinium salts, morpholinium salts, phosphonium salts, and imidazolium salts.

[0065] Another example of the electrolyte solution is an aqueous electrolyte solution. The aqueous electrolyte solution is an electrolyte solution containing water as the main solvent component. The ratio of water to the total solvent is, for example, 50% by mass or more, and may be 70% by mass or more. Examples of the lithium salt used in the aqueous electrolyte solution include imide-based electrolytes such as lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide. The concentration of the lithium salt in the aqueous electrolyte solution is, for example, 1 M or more and 25 M or less.

[0066] The electrolyte layer may include a separator impregnated with the above-mentioned electrolytic solution. The provision of the separator can suppress the occurrence of internal short circuits. The separator may be, for example, a porous membrane. Examples of materials for the separator include resins such as polyethylene, polypropylene, polyester, polyvinyl alcohol, cellulose, and polyamide. The electrolyte layer may also contain a solid electrolyte. Examples of the solid electrolyte include organic solid electrolytes such as polymer electrolytes and gel electrolytes; and inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, and halide solid electrolytes.

[0067] 4.Battery The battery according to the present disclosure preferably has a positive electrode current collector that collects current from the positive electrode active material layer and a negative electrode current collector that collects current from the negative electrode active material layer. Examples of materials for the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. On the other hand, examples of materials for the negative electrode current collector include SUS, copper, nickel, and carbon. The battery according to the present disclosure may also have an exterior housing that houses the power generating elements (positive electrode active material layer, electrolyte layer, and negative electrode active material layer). Examples of the exterior housing include a case-type exterior housing and a laminate-type exterior housing.

[0068] The type of battery in the present disclosure is not particularly limited, but is typically a lithium-ion battery. The battery in the present disclosure may be a primary battery or a secondary battery, with secondary batteries being preferred. This is because secondary batteries can be repeatedly charged and discharged and are useful, for example, as automotive batteries. Examples of uses for batteries include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. In particular, batteries are preferably used as driving power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric vehicles (BEVs). Furthermore, batteries may also be used as power sources for mobile objects other than vehicles (e.g., railways, ships, and aircraft), and may also be used as power sources for electrical appliances such as information processing devices.

[0069] D. Method for manufacturing positive electrode active material Fig. 4 is a flow diagram illustrating a method for producing a positive electrode active material according to the present disclosure. In Fig. 4, first, a mixture containing a transition metal hydroxide containing TM, a Li source, and lithium hydroxide as a molten salt is fired to obtain a fired body (firing step). Next, the fired body is pulverized (pulverization step). In the mixture, the molar ratio of Li in the molten salt to TM is 0.1 or more and less than 0.6.

[0070] According to the present disclosure, a positive electrode active material capable of suppressing an increase in resistance during charge and discharge can be obtained by using a mixture containing a molten salt and performing a predetermined pulverization process. The molten salt functions as a flux and promotes the growth of primary particles.

[0071] 1. Firing process The calcination step is a step of calcining a mixture containing the transition metal hydroxide containing the TM, a Li source, and lithium hydroxide as a molten salt to obtain a calcined body.

[0072] The transition metal hydroxide contains TM (TM is a transition metal). The transition metal hydroxide corresponds to a precursor of the positive electrode active material. The transition metal hydroxide typically does not contain Li, but may contain Li.

[0073] The synthesis method of the transition metal hydroxide is not particularly limited, and examples thereof include the following methods. First, a raw material aqueous solution of the transition metal hydroxide is prepared. Examples of methods for preparing the raw material aqueous solution include dissolving a water-soluble transition metal compound in water. Examples of the transition metal compound include metal salts such as sulfates and nitrates. Examples of Ni sources include NiSO4 and Ni(NO3)2. Examples of Co sources include CoSO4, Co(NO3)2, and Co(NO3)3. Examples of Mn sources include MnSO4 and Mn(NO3)2. The composition of the raw material aqueous solution is appropriately adjusted according to the desired positive electrode active material.

[0074] Next, an aqueous sodium hydroxide solution is added to the reaction vessel, and while maintaining the pH at an alkaline level (e.g., pH 11.3 to 12.0), the raw material aqueous solution and the NH3 aqueous solution are added dropwise. The reaction temperature is not particularly limited, but is, for example, 50°C or higher and 65°C or lower. After the reaction is complete, the transition metal hydroxide is preferably removed by filtration, washed with water, and then dried.

[0075] In the calcination step, a mixture containing a transition metal hydroxide, a Li source, and a molten salt of lithium hydroxide is prepared. Examples of the Li source include lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, lithium oxide, and lithium chloride. The Li source may be lithium hydroxide or a Li-containing compound other than lithium hydroxide. The molar ratio of Li in the Li source to TM contained in the transition metal hydroxide is, for example, 0.8 to 1.2, or 0.9 to 1.1, or even 1.0.

[0076] The mixture typically contains lithium hydroxide, which is a molten salt. The molar ratio of Li contained in the molten salt to TM contained in the transition metal hydroxide (Li / TM) is typically 0.1 or more and less than 0.6. Li / TM may be 0.15 or more, 0.2 or more, or even 0.25 or more. On the other hand, Li / TM may be 0.55 or less, or 0.5 or less.

[0077] The mixture may contain lithium hydroxide as the Li source and molten salt. The molar ratio (Li' / TM) of Li contained in the Li source and molten salt to TM contained in the transition metal hydroxide is, for example, 1.1 or more, or may be 1.15 or more, or may be 1.2 or more. On the other hand, Li' / TM may be, for example, less than 1.6, or may be 1.55 or less, or may be 1.5 or less.

[0078] In the firing step, the mixture is fired to obtain a fired body. The firing temperature in the firing step is, for example, 650°C or higher, or may be 700°C or higher, or may be 750°C or higher. If the firing temperature is too low, it becomes difficult to sufficiently grow the primary particles. On the other hand, the firing temperature is, for example, 1100°C or lower, or may be 1000°C or lower, or may be 950°C or lower. If the firing temperature is too high, side reactions are likely to occur.

[0079] The firing time in the firing step is not particularly limited, but may be, for example, 5 hours or more, 7 hours or more, or 9 hours or more. On the other hand, the firing time in the firing step is, for example, 15 hours or less, or may be 13 hours or less. The atmosphere in the firing step is usually an atmosphere in which oxygen is present. Examples of firing methods in the firing step include methods using a firing furnace such as a muffle furnace or an electric furnace.

[0080] 2. Crushing process The pulverization step is a step of pulverizing the sintered body. Examples of methods for pulverizing the sintered body include a hammer mill, a laboratory mill, and a ball mill. The pulverization conditions are adjusted so as to obtain the positive electrode active material described above in "A. Positive electrode active material."

[0081] 3. Other processes The method for producing a positive electrode active material according to the present disclosure may or may not include a re-firing step of re-firing the sintered body between the firing step and the pulverization step. Re-firing can further increase the particle size of the primary particles, thereby controlling the pore size distribution.

[0082] The firing temperature in the re-firing step is preferably lower than the firing temperature in the above-mentioned firing step. The firing temperature in the re-firing step is, for example, 400°C or higher and 600°C or lower, and may be 450°C or higher and 550°C or lower. The firing time in the re-firing step is preferably shorter than the firing time in the above-mentioned firing step. The firing time in the re-firing step is, for example, 1 hour or higher and 5 hours or lower, and may be 2 hours or higher and 4 hours or lower. The atmosphere in the re-firing step is usually an atmosphere in which oxygen is present. Examples of firing methods in the re-firing step include methods using a firing furnace such as a muffle furnace or an electric furnace.

[0083] The method for producing a positive electrode active material according to the present disclosure may or may not include a granulation step of granulating the pulverized sintered body after the pulverization step. Granulation can produce large aggregates, thereby controlling the pore size distribution. Examples of methods for granulating the pulverized sintered body include spray drying. In the spray drying method, for example, the pulverized sintered body is dispersed in water, and the resulting dispersion is sprayed using a spray drying device. The heating temperature of the spray drying device is, for example, 150°C or higher and 250°C or lower.

[0084] 4.Cathode active material The positive electrode active material obtained by each of the above steps is the same as that described above in "A. Positive electrode active material."

[0085] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0086] [Example 1] (Preparation of raw material aqueous solution) First, a raw material aqueous solution was prepared by dissolving NiSO4, CoSO4, and MnSO4 in ion-exchanged water. The molar ratio of Ni, Co, and Mn in the raw material aqueous solution was adjusted to Ni:Co:Mn=92:5:3. The concentration of the raw material aqueous solution (the number of moles of raw materials (total solutes) relative to the raw material aqueous solution) was set to 0.2 mol%.

[0087] (Precipitation and Calcination) A specified amount of NH3 aqueous solution was placed in a reaction vessel, and the atmosphere inside the vessel was replaced with nitrogen while stirring with a stirrer. NaOH was added to the reaction vessel to adjust the pH of the aqueous solution to alkaline. The raw material aqueous solution was added dropwise while maintaining a constant pH inside the reaction vessel and controlling the temperature, thereby precipitating transition metal hydroxides. After the precipitation reaction was completed, the precipitate was dehydrated and calcined under the following temperature and pressure conditions. ·Temperature: 120℃ Duration: 8 hours Pressure: 0.2MPa

[0088] (precursor recovery) After the calcination, the precipitate was washed with water. The washed precipitate was filtered to extract the transition metal hydroxide. Next, the precipitate was dried at 110°C for 12 hours to evaporate the water (dried product). This prepared a precursor.

[0089] (Mixing Li raw material and molten salt) The obtained precursor (transition metal hydroxide) and LiOH as a Li source were mixed in a mortar. The LiOH as a Li source was mixed so that the ratio (molar ratio) of Li contained in the Li source to the total amount of transition metal species (Ni, Co, Mn) contained in the transition metal hydroxide was 1.0. Furthermore, LiOH as a molten salt was mixed so that the ratio (molar ratio) of Li contained in the molten salt to the total amount of transition metal species contained in the transition metal hydroxide was 0.2. As a result, the presence of excess LiOH during firing promotes single crystallization of the primary particles.

[0090] (Firing) The mixture was subjected to heat treatment (firing). It was fired in a muffle furnace at 780°C for 12 hours (firing step). Next, the fired body was crushed in an agate mortar to a particle size of 0.2 mm or less, dispersed in 500 mL of pure water, and vigorously stirred for 1 minute to obtain a slurry. The slurry was filtered using a Buchner funnel and filter paper, rinsed with 500 mL of pure water, and the obtained cake was vacuum dried at 90°C. The obtained dry powder was fired in an oxygen stream at 500°C for 3 hours (re-firing). The fired body was pulverized in a hammer mill and crushed to a predetermined particle size (pulverization). This produced a positive electrode active material.

[0091] (Preparation of positive electrode) A positive electrode composite paste containing the above particles as the positive electrode active material and N-methylpyrrolidone (NMP) as the solvent was applied to a metal foil positive electrode current collector using a film applicator with a film thickness adjustment function (All Good Co., Ltd.). After application, the coating was dried on a hot plate at 80°C for 5 minutes to evaporate the NMP solvent, forming a positive electrode active material layer on the positive electrode current collector. This resulted in a positive electrode having a positive electrode current collector and a positive electrode active material layer.

[0092] (Battery construction) A negative electrode composite paste containing natural graphite as the negative electrode active material was applied to the surface of a metal foil negative electrode current collector using a film applicator with a film thickness adjustment function (manufactured by Allgrid Corporation). The mixture was then dried in a dryer at 80°C for 5 minutes to produce a negative electrode with a negative electrode active material layer on the negative electrode current collector. A 1M LiPF solution containing LiPF as the electrolyte and ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a ratio of EC / DMC / EMC = 3 / 4 / 3 vol% was prepared as the electrolyte solution. The positive electrode, separator, and negative electrode were stacked, and the separator was impregnated with the electrolyte solution. A battery (small laminate cell) was produced in which the power generating element was housed in an Al laminate film pouch.

[0093] [Example 2] Except for not performing re-baking, a positive electrode active material was obtained in the same manner as in Example 1. Except for using the obtained positive electrode active material, a battery was obtained in the same manner as in Example 1.

[0094] [Example 3] A positive electrode active material was obtained in the same manner as in Example 1, except that LiOH as a molten salt was mixed so that the ratio (molar ratio) of Li contained in the molten salt to the total amount of transition metal species contained in the transition metal hydroxide was 0.1. A battery was obtained in the same manner as in Example 1, except that the obtained positive electrode active material was used.

[0095] [Example 4] A sintered body was obtained in the same manner as in Example 1, except that LiOH was used as the molten salt, and the ratio (molar ratio) of Li contained in the molten salt to the total amount of transition metal species contained in the transition metal hydroxide was 0.6. The obtained sintered body was pulverized using a hammer mill and crushed to a predetermined particle size (pulverization). 30 g of the pulverized material was then dispersed in 100 mL of pure water, and sprayed at 200°C using a Buchi spray dryer, to obtain a granulated positive electrode active material. A battery was obtained in the same manner as in Example 1, except that the obtained positive electrode active material was used.

[0096] [Comparative Example 1] A positive electrode active material was obtained in the same manner as in Example 1, except that no molten salt was used and the firing temperature was changed to 730° C. A battery was obtained in the same manner as in Example 1, except that the obtained positive electrode active material was used.

[0097] Comparative Example 2 A positive electrode active material was obtained in the same manner as in Example 1, except that LiOH as a molten salt was mixed so that the ratio (molar ratio) of Li contained in the molten salt to the total amount of transition metal species contained in the transition metal hydroxide was 0.6. A battery was obtained in the same manner as in Example 1, except that the obtained positive electrode active material was used.

[0098] [evaluation] (XRD measurement) X-ray diffraction measurements (XRD) using CuKα radiation were performed on the positive electrode active materials obtained in Examples 1 to 4 and Comparative Examples 1 and 2. As a result, it was confirmed that the positive electrode active materials obtained in Examples 1 to 4 and Comparative Examples 1 and 2 all had a layered rock-salt crystalline phase belonging to the space group R-3m. In other words, it was confirmed that the primary particles containing Ni, Co, and Mn had a layered rock-salt crystalline phase.

[0099] (SEM observation) The cross sections of the positive electrode active materials obtained in Examples 1 to 4 and Comparative Examples 1 and 2 were observed with a scanning electron microscope (SEM). As a result, it was confirmed that the positive electrode active materials obtained in Examples 1 to 4 and Comparative Example 1 were aggregates in which multiple primary particles were aggregated. In contrast, the positive electrode active material obtained in Comparative Example 2 was confirmed to be a single-crystal positive electrode active material in which primary particles existed alone. Furthermore, the average particle sizes of the primary particles in the aggregates obtained in Examples 1 to 4 were 8.2 μm, 7.9 μm, 2.3 μm, and 1.5 μm, respectively.

[0100] (Pore size distribution measurement) Pore ​​size distribution measurement was performed by mercury intrusion porosimetry on the positive electrode active materials obtained in Examples 1 to 4 and Comparative Examples 1 and 2. Specifically, the pore size distribution of the positive electrode active material was measured by injecting mercury into a sample tube sealed with 1 g of the positive electrode active material using a mercury intrusion porosimetry analyzer from Micromeritics. The results are shown in Figure 5.

[0101] As shown in Figure 5, it was confirmed that the positive electrode active materials obtained in Examples 1 to 4 and Comparative Example 1 each had one peak in the pore diameter range of 300 nm or less. On the other hand, no peak was confirmed in the pore diameter range of 300 nm or less for the positive electrode active material obtained in Comparative Example 2. The peak position and pore volume are shown in Table 1.

[0102] (resistance increase measurement) The resistance increase before and after the cycle test was measured using the batteries obtained in Examples 1 to 4 and Comparative Examples 1 and 2. First, the initial resistance of the battery was determined. Specifically, the battery was charged to 4.25 V and then discharged to 3.7 V. Then, the voltage drop (V) and current (I) were measured when the battery was discharged for 0.1 seconds at 25°C, and the initial resistance (IV resistance) was determined.

[0103] Next, a cycle test was carried out under the following conditions. Ambient temperature: 60°C Number of cycles: 100 Current rate: 0.3C Voltage range: 4.25V to 2.5V

[0104] After the cycle test, the resistance after 100 cycles (IV resistance) was determined in the same manner as above. The difference between the resistance after 100 cycles and the initial resistance was calculated as the resistance increase (Ω). The results are shown in Table 1.

[0105] (Capacity retention rate measurement) The capacity retention rate was measured using the batteries obtained in Examples 1 to 4 and Comparative Examples 1 and 2. First, the initial discharge capacity of each battery was determined. Specifically, each battery was charged to 4.25 V and discharged at 0.1 C to 2.5 V, and the initial discharge capacity was determined at 25°C.

[0106] Next, a cycle test was carried out under the following conditions. Ambient temperature: 60°C Number of cycles: 100 Current rate: 0.3C Voltage range: 4.25V to 2.5V

[0107] After the cycle test, the discharge capacity after 100 cycles was determined in the same manner as above. The capacity retention rate was calculated by dividing the discharge capacity after 100 cycles by the initial discharge capacity. The results are shown in Table 1.

[0108] Furthermore, the changes in capacity retention rate for the batteries obtained in Example 1 and Comparative Examples 1 and 2 are shown in Figure 6. In Figure 6, the capacity was checked every 25 cycles using CCCV at 60°C and 0.2C, and in the other cycles, CC charge / discharge was performed at 60°C and 0.3C. Note that the capacity retention rates in Table 1 and those shown in Figure 6 do not match because the measurement temperatures were different.

[0109] [Table 1]

[0110] As shown in Table 1, it was confirmed that Examples 1 to 4 were able to suppress the increase in resistance associated with charge and discharge compared to Comparative Examples 1 and 2. Furthermore, Examples 1 to 4 had capacity retention rates equal to or higher than Comparative Examples 1 and 2. Furthermore, as shown in FIG. 6, Comparative Example 2 (single crystal) had a better capacity retention rate than Comparative Example 1 (polycrystal). Furthermore, Example 1 (aggregate) had a notable effect of having a better capacity retention rate than Comparative Example 2 (single crystal). [Explanation of symbols]

[0111] 1…Primary particle 10...Cathode active material 11...Cathode active material layer 12...Negative electrode active material layer 13...electrolyte layer 14...Positive electrode current collector 15...Negative electrode current collector 20...battery

Claims

1. A positive electrode active material, the positive electrode active material has crystalline primary particles containing Li, TM (TM is a transition metal), and O, the positive electrode active material is an aggregate composed of a plurality of the primary particles, the average particle size of the primary particles in the aggregate is 0.5 μm or more; A positive electrode active material, in which a pore size distribution obtained by mercury intrusion porosimetry has a peak in the range of 65 nm or more and 300 nm or less.

2. The positive electrode active material according to claim 1 , wherein the pore size distribution has a peak in the range of 80 nm to 200 nm.

3. 2. The positive electrode active material according to claim 1, wherein the pore volume at the peak is 0.010 mL / g or more.

4. The positive electrode active material according to claim 1 , wherein the pore volume at the peak is 0.025 mL / g or more.

5. The positive electrode active material according to claim 1 , wherein the primary particles contain at least Ni as the TM.

6. The positive electrode active material according to claim 5 , wherein the proportion of the Ni is 0.50 parts by mol or more when the TM is taken as 1 part by mol.

7. The positive electrode active material according to claim 5 , wherein the proportion of the Ni is 0.90 parts by mol or more when the TM is taken as 1 part by mol.

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

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

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

11. A battery having a positive electrode active material layer containing a positive electrode active material, a negative electrode active material layer containing a negative electrode active material, and an electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, A battery, wherein the positive electrode active material layer contains the positive electrode mixture according to claim 10.

12. A method for producing a positive electrode active material, comprising producing the positive electrode active material according to any one of claims 1 to 9, a firing step of firing a mixture containing the transition metal hydroxide containing the TM, a Li source, and lithium hydroxide as a molten salt to obtain a fired body; a crushing step of crushing the fired body; and In the mixture, a molar ratio of Li in the molten salt to TM is 0.1 or more and less than 0.

6.

13. the Li source is lithium hydroxide; 13. The method for producing a positive electrode active material according to claim 12, wherein in the mixture, a molar ratio of Li in the Li source to TM is 1.

0.

14. The method for producing a positive electrode active material according to claim 12 , further comprising, after the pulverization step, a granulation step of granulating the pulverized product of the fired body.

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