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

Abstract

The main object of the present disclosure is to provide a positive electrode active material capable of suppressing an increase in electric resistance accompanying charge and discharge. In the present disclosure, the above object is achieved by providing a positive electrode active material having crystalline primary particles containing Li, TM (TM is a transition metal), and O, the positive electrode active material being an agglomerate composed of a plurality of the primary particles, the average particle diameter of the primary particles in the agglomerate being 0.5 μm or more, and a peak being present in the range of 65 nm or more and 300 nm or less in a pore size distribution obtained by a mercury porosimetry.

Description

Technical Field

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

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

[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) observed from the micropore diameter side at 25% accumulation in the cumulative pore distribution curve obtained by mercury intrusion porosimetry is less than 7 μm. 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 range of pore radius 10 nm or more and 200 nm or less. Patent Document 3 discloses lithium composite oxide particles, in which, in measurements based on mercury intrusion porosimetry, there is a secondary peak with a peak apex in the range of pore radius 80 nm or more and 300 nm or less. Patent Document 4 discloses a porous metal oxide-based electrochemical energy storage material.

[0004] Existing technical documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2021-114411

[0006] Patent Document 2: Japanese Patent Application Publication No. 2018-174106

[0007] Patent Document 3: Japanese Patent Application Publication No. 2005-123179

[0008] Patent Document 4: Japanese Patent Application Publication No. 2022-537567 Summary of the Invention

[0009] From the perspective of improving battery performance, it is necessary to suppress the increase in resistance that occurs during charging and discharging. The main objective of this disclosure is to provide a positive electrode active material capable of suppressing the increase in resistance that occurs during charging and discharging.

[0010] [1]

[0011] A positive electrode active material,

[0012] The aforementioned positive electrode active material contains crystalline primary particles containing Li, TM (TM is a transition metal), and O.

[0013] The aforementioned positive electrode active material is an aggregate composed of multiple primary particles.

[0014] The average particle size of the primary particles in the aforementioned aggregates is greater than 0.5 μm.

[0015] In the fine pore size distribution obtained by mercury porosimetry, peaks exist in the range of above 65 nm and below 300 nm.

[0016] [2]

[0017] According to the positive electrode active material described in [1], in the above-mentioned pore size distribution, the above-mentioned peak exists in the range of 90 nm and 220 nm.

[0018] [3]

[0019] According to the positive electrode active material described in [1] or [2], the pore size of the above peak is 0.010 mL / g or more.

[0020] [4]

[0021] According to any one of [1] to [3], the pore size of the above peak is 0.025 mL / g or more.

[0022] [5]

[0023] According to any one of [1] to [4], the primary particles mentioned above contain at least Ni as the above TM.

[0024] [6]

[0025] According to the positive electrode active material described in [5], when the above-mentioned TM is set to 1 mole, the proportion of the above-mentioned Ni is 0.50 moles or more.

[0026] [7]

[0027] According to the positive electrode active material described in [5], when the above-mentioned TM is set to 1 mole, the proportion of the above-mentioned Ni is 0.90 moles or more.

[0028] [8]

[0029] According to any one of [1] to [7], the primary particles contain at least one of Co and Mn as the above-mentioned TM.

[0030] [9]

[0031] According to any one of [1] to [8], the primary particles have a layered rock salt-type crystal structure.

[0032]

[10]

[0033] A positive electrode mixture containing any one of the positive electrode active substances described in [1] to [9].

[0034]

[11]

[0035] 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.

[0036] The above-mentioned positive electrode active material layer contains the positive electrode compound described in

[10] .

[0037]

[12]

[0038] A method for manufacturing a positive electrode active material, comprising the following steps:

[0039] A firing process comprising firing a mixture containing a transition metal hydroxide, a Li source, and lithium hydroxide as a molten salt to obtain a sintered body, wherein the transition metal hydroxide contains the aforementioned TM; and

[0040] The pulverization process of pulverizing the above-mentioned sintered body.

[0041] In the above mixture, the molar ratio of Li in the above molten salt to the above TM is 0.1 or more and less than 0.6.

[0042]

[13]

[0043] According to the method for manufacturing the positive electrode active material described in

[12] ,

[0044] The aforementioned Li source is lithium hydroxide.

[0045] In the above mixture, the molar ratio of Li in the above Li source to the above TM is 1.0.

[0046]

[14]

[0047] According to the manufacturing method of the positive electrode active material described in

[12] or

[13] , the manufacturing method includes a granulation step after the pulverization step, in which the pulverized material of the sintered body is granulated.

[0048] The present disclosure provides the following effect: it can provide a positive electrode active material that can suppress the increase in resistance associated with charging and discharging. Attached Figure Description

[0049] Figure 1 This is a schematic cross-sectional view illustrating the positive electrode active material of this disclosure.

[0050] Figure 2 This is a schematic cross-sectional view illustrating an existing positive electrode active material.

[0051] Figure 3 This is a schematic cross-sectional view illustrating the battery of this disclosure.

[0052] Figure 4 This is a flowchart illustrating a method for manufacturing the positive electrode active material of this disclosure.

[0053] Figure 5 The results are obtained by mercury porosimetry for the positive electrode active materials obtained in Examples 1-4 and Comparative Examples 1 and 2.

[0054] Figure 6 The results are the capacity retention rates of the batteries obtained in Example 1 and Comparative Examples 1 and 2.

[0055] Explanation of reference numerals in the attached figures

[0056] 1…first particle

[0057] 10… Positive electrode active material

[0058] 11… Positive electrode active material layer

[0059] 12…Negative electrode active material layer

[0060] 13…Electrolyte layer

[0061] 14…Positive current collector

[0062] 15… Negative current collector

[0063] 20… batteries Detailed Implementation

[0064] 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, in order to make the description clearer, the drawings sometimes schematically show the width, thickness, and shape of various parts compared with the actual embodiment; this is ultimately just an example and is not to be interpreted as limiting.

[0065] A. Positive electrode active material

[0066] Figure 1 This is a schematic cross-sectional view illustrating the positive electrode active material of 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 an aggregate composed of multiple primary particles 1. The average particle size of the primary particles 1 in the aggregate is 0.5 μm or more. Additionally, in the fine pore size distribution obtained by mercury intrusion porosimetry, peaks exist in the range of 65 nm or more and 300 nm or less.

[0067] According to this disclosure, the primary particles in the condensate have a large average particle size, and the fine pore size distribution has peaks within a predetermined range, thus making it a positive electrode active material capable of suppressing the increase in resistance associated with charging and discharging. Polycrystalline and monocrystalline active materials are conventionally known as positive electrode active materials. For example... Figure 2 As shown in (a), in polycrystalline active materials, multiple primary particles 1 (very fine primary particles 1) are usually tightly packed. Although polycrystalline active materials are relatively easy to manufacture, they are prone to an increase in resistance over time. This is because, through repeated charging and discharging, cracks are generated in the polycrystalline material, and the newly formed surfaces generated by the cracks react with the electrolyte, thereby generating resistive components.

[0068] On the other hand, such as Figure 2 As shown in (b), in the monocrystalline active material, the large primary particles 1 do not aggregate but exist as independent individual particles. Compared with polycrystalline active materials, monocrystalline active materials are less prone to cracking even with repeated charging and discharging. Therefore, they have the advantage of suppressing the increase in resistance over time due to the reaction between the newly formed surface and the electrolyte. On the other hand, compared with polycrystalline active materials, monocrystalline active materials have a larger specific surface area, so through repeated charging and discharging, resistive components accumulate, and the resistance is more likely to increase over time.

[0069] Thus, despite the different reasons, both polycrystalline and monocrystalline active materials suffer from the problem of resistance increasing over time. In this disclosure, agglomerates composed of large-particle primary particles (approximately the size of monocrystalline primary particles) are used. Therefore, compared to polycrystalline active materials, this method offers the advantage of being less prone to cracking even with repeated charge-discharge cycles. Furthermore, compared to monocrystalline active materials, the agglomerates reduce the specific surface area. As a result, the accumulation of resistive components due to repeated charge-discharge cycles can be suppressed. Thus, the positive electrode active material of this disclosure is an agglomerate formed by moderately agglomerating large-particle primary particles (conventional monocrystalline active materials), thereby becoming a positive electrode active material capable of suppressing the increase in resistance associated with charge-discharge cycles.

[0070] In this disclosure, the degree of primary particle aggregation is defined by the pore size distribution obtained by mercury intrusion porosimetry. Specifically, a peak is defined in the pore size distribution that exists in the range of 65 nm to 300 nm. That is, as... Figure 1As shown, it is specified that micropores (pores with a diameter of 65 nm or more and 300 nm or less) exist within the aggregate of primary particles 1. The presence of these micropores, especially when an electrolyte is used, can improve the ionic conductivity within the aggregate. Furthermore, if the aggregation of primary particles becomes more compact, the peak position in the pore size distribution shifts towards the lower pore size side. In contrast, in typical single-crystal active materials, large primary particles do not aggregate but exist as individual particles, and therefore micropores are usually absent.

[0071] As described above, Patent Document 2 discloses a positive electrode active material for lithium secondary batteries, which, in a pore distribution obtained by mercury intrusion porosimetry, exhibits a pore peak in the range of pore radius 10 nm or more and 200 nm or less. Furthermore, Patent Document 3 discloses lithium composite oxide particles, which, in measurements by mercury intrusion porosimetry, exhibit a secondary peak with a pore radius of 80 nm or more and 300 nm or less. However, Patent Documents 2 and 3 neither describe nor suggest the average particle size of the primary particles in the aggregate. Additionally, in the embodiments of Patent Document 2, since lithium carbonate is used as the Li source and the molten salt described later is not used, a polycrystalline active material is presumed to be obtained. Furthermore, in the embodiments of Patent Document 3, although LiOH is used as the Li source, the amount of LiOH used is approximately stoichiometric. Moreover, under firing conditions of 950°C and 12 hours, the primary particles cannot grow sufficiently, presumably resulting in a polycrystalline active material. In other words, Patent Documents 2 and 3 presuppose a polycrystalline active material, and there is no motivation to produce the positive electrode active material disclosed herein.

[0072] 1. Primary particle

[0073] The primary particles disclosed herein are crystalline particles containing Li, TM (TM is 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. Alternatively, the primary particles may also have crystal structures belonging to space group R-3m.

[0074] Primary particles contain Li, TM (TM is a transition metal), and O. Primary particles can contain one, two, three, or more transition metals.

[0075] Transition metals are metals belonging to groups 3 through 11 of the periodic table. The transition metal contained in a primary particle can also be a metal belonging to period 3, 4, or 5. Examples of transition metals include Ti, V, Cr, Mn, Fe, Co, Ni, Zr, Nb, La, and W.

[0076] The primary particles preferably contain at least Ni. This is because it yields a positive electrode active material with good capacity characteristics. Assuming that all transition metals (TM) contained in the primary particles constitute 1 mole, the proportion of Ni 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. Increasing the proportion of Ni improves the capacity characteristics.

[0077] Primary particles may or may not contain Co. When the total amount of transition metals (TM) contained in a primary particle is 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.

[0078] 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 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 in a primary particle may be, for example, 0.40 moles or less, or 0.20 moles or less.

[0079] The primary particles preferably contain at least one of Ni, Co, and Mn. When all metals (excluding Li) contained in the primary particles are considered to be 1 mole, the total proportion of Ni, Co, and Mn in the primary particles is, for example, 0.80 moles or more, 0.90 moles or more, or 0.95 moles or more. Furthermore, "the total proportion of Ni, Co, and Mn" also includes cases where the proportion of one or two of Ni, Co, and Mn is 0.

[0080] In addition to Li and TM, primary particles can also contain other metals M besides Li and TM. 1 (Including metalloids). As other metals M 1 For example, metals belonging to groups 12 to 14 in the periodic table can be listed. Examples of metals belonging to groups 12 to 14 include Zn, Al, Si, Ga, Ge, In, and Sn.

[0081] The composition of primary particles is not particularly limited; for example, it can also be composed of the general formula Li. x Ni a Co b Mn c O yThe composition represented by (0.1≤x≤1.5, 0.5≤a≤1.0, 0≤b≤0.3, 0≤c≤0.3, a+b+c=1.0, 1.5≤y≤2.1).

[0082] "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 less than 1.4 or less than 1.2.

[0083] "y" can be 1.6 or higher, 1.7 or higher, 1.8 or higher, or 1.9 or higher, and can be below 2.0.

[0084] "a" can be 0.6 or higher, 0.7 or higher, 0.8 or higher, or 0.85 or higher, and can be below 0.9.

[0085] "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, and can be less than or equal to 0.25, 0.20, 0.15, 0.10, 0.09, or 0.08.

[0086] "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, and can be less than or equal to 0.25, 0.20, 0.15, 0.10, 0.09, or 0.08.

[0087] 2. Condensate

[0088] The positive electrode active material disclosed herein is an 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.

[0089] The average particle size of primary particles in condensates is typically 0.5 μm or larger, but can be 0.6 μm or larger, 0.8 μm or larger, 1 μm or larger, 2 μm or larger, or 5 μm or larger. On the other hand, the average particle size of primary particles in condensates can be, for example, 20 μm or smaller, 15 μm or smaller, or 10 μm or smaller. The average particle size of primary particles (positive electrode active material) can be determined, for example, by observation of SEM cross-sections.

[0090] The number of primary particles constituting an agglomerate 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 an agglomerate is, for example, 100 or less. Furthermore, the average particle size of the agglomerate is, for example, greater than 0.5 μm and less than 30 μm, but can be 0.8 μm or more and less than 25 μm, 1 μm or more and less than 20 μm, or 2 μm or more and less than 15 μm. Additionally, the shape of the agglomerate is, for example, particulate.

[0091] For the positive electrode active material of this disclosure, when the pore diameter distribution is determined by mercury intrusion porosimetry, peaks exist in the range of 65 nm to 300 nm. These peaks also include inflection points (e.g., Figure 5 (Example 4). The above peaks can exist in the range of 75nm and above and 220nm, in the range of 80nm and above and 200nm, in the range of 85nm and above and 180nm, or in the range of 90nm and above and 150nm.

[0092] The pore size of the aforementioned peak can 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. Conversely, the pore size of the aforementioned peak can 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, in the pore size distribution, minima (downward-convex points) can exist in the range of 100 nm to 300 nm. These minima can exist in the range of 150 nm to 300 nm, or in the range of 150 nm to 250 nm.

[0093] 3. Positive electrode active material

[0094] The positive electrode active material disclosed herein has crystalline primary particles containing Li, TM (TM is a transition metal), and O. Furthermore, the positive electrode active material is an 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] Furthermore, this disclosure also provides a positive electrode active material powder, which, as a positive electrode active material, contains a plurality of crystalline primary particles containing Li, TM (TM is a transition metal), and O. At least a portion of the plurality of primary particles constitutes an aggregate, and the average particle size of the primary particles in the aggregate is 0.5 μm or more. In the pore size distribution of the aggregate obtained by mercury intrusion porosimetry, a peak exists in the range of 65 nm or more and 300 nm or less. A portion of the plurality of primary particles may also constitute a single-crystal active material. In addition, relative to all the positive electrode active material in the positive electrode active material powder, the proportion of the aggregate 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 mixture

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

[0098] According to this disclosure, by using the aforementioned positive electrode active material, a positive electrode mixture is formed that can suppress the increase in resistance associated with charging and discharging. In addition to the positive electrode active material, the positive electrode mixture may also contain other materials (e.g., conductive materials, binders). Furthermore, the positive electrode mixture may also contain the aforementioned positive electrode active material powder. Additionally, the positive electrode mixture may be in powder form or in slurry form containing a dispersion medium.

[0099] The proportion of the positive electrode active material in the solid components of the positive electrode mixture is, for example, 20% by mass or more, 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 components of the positive electrode mixture is, for example, 95% by mass or less, 70% by mass or less, or 60% by mass or less. If the proportion of the positive electrode active material is too high, ionic conductivity and electronic conductivity may decrease relatively.

[0100] Positive electrode additives can also 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-grown carbon fibers (VGCF), carbon nanotubes (CNTs), and carbon nanofibers (CNFs).

[0101] The proportion of conductive material in the solid components of the positive electrode compound is, for example, 0.1% by mass or more. If the proportion of conductive material is too low, the electron conduction pathway may be insufficient. On the other hand, the proportion of conductive material in the solid components of the positive electrode compound is, for example, 5% by mass or less. If the proportion of conductive material is too high, the proportion of positive electrode active material becomes relatively low, and the energy density may decrease.

[0102] The positive electrode compound may also contain an adhesive. By adding an adhesive, a layer of positive electrode active material that is not easily detached can be obtained. Examples of adhesives include rubber-based adhesives such as styrene-butadiene rubber (SBR) and butadiene rubber (BR), polycarboxylate-based adhesives such as carboxymethyl cellulose, and fluoride-based adhesives such as polyvinylidene fluoride (PVdF).

[0103] The proportion of the binder in the solid components of the positive electrode compound is, for example, 0.5% by mass or more. If the proportion of the binder is too low, it may not be able to adequately suppress the shedding of the positive electrode active material. On the other hand, the proportion of the binder in the solid components of the positive electrode compound 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 becomes relatively low, and the energy density may decrease.

[0104] C. Battery

[0105] Figure 3 This is a schematic cross-sectional view illustrating the battery of 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 agent described in "B. Positive Electrode Agent" above.

[0106] According to this disclosure, by using the above-described positive electrode additive, a battery is formed that suppresses the increase in resistance associated with charging and discharging.

[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 also contain conductive materials and binders. The positive electrode active material, conductive materials, and binders are the same as those described in "A. Positive Electrode Active Material" and "B. Positive Electrode Compound" 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 or more and 1000 μm or less, 1 μm or more and 500 μm or less, or 30 μm or more and 100 μm or less.

[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. Alternatively, the dried positive electrode active material layer can 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 graphite, soft carbon, and hard carbon. Graphite can be natural or artificial. Examples of Li-based active materials include Li and Li alloys. Examples of Li alloys include Li-Si alloys. Examples of Si-based active materials include Si, SiC composite active materials, Si alloys, and Si oxides. Examples of SiC composite active materials include active materials with Si or Si alloys supported on a carbon support. Examples of oxide-based active materials include Li₄Ti₅O. 12 Lithium titanate, etc.

[0114] The proportion of the negative electrode active material in the negative electrode active material layer is, for example, 20% by mass or more, 30% by mass or more, or 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, 70% by mass or less, or 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 decrease relatively.

[0115] The negative electrode active material layer may also contain at least one of a conductive material, a binder, and an electrolyte. Details regarding the conductive material, binder, and electrolyte are the same as those described in "1. Positive Electrode Active Material Layer" above. Furthermore, the thickness of the negative electrode active material layer may be, for example, 0.1 μm or more and 1000 μm or less, 1 μm or more and 500 μm or less, or 30 μm or more and 100 μm or less.

[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. Alternatively, the dried negative electrode active material layer can 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, non-aqueous electrolytes can be cited. Non-aqueous electrolytes may 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). Non-aqueous solvents can also be mixtures 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, 0.3 M or more and 5 M or less. Furthermore, non-aqueous electrolytes may also contain ionic liquids. Examples of ionic liquids include sulfonium salts, ammonium salts, pyridinium salts, piperidine salts, pyrrolidine salts, morpholine salts, etc. Salts and imidazole salts.

[0121] Other examples of electrolytes include aqueous electrolytes. Aqueous electrolytes are electrolytes whose main component contains water as a solvent. The proportion of water to the total solvent is, for example, 50% by mass or more, and may also be 70% by mass or more. Examples of imide-based electrolytes used in aqueous electrolytes include lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide. The concentration of the lithium salt in the aqueous electrolyte is, for example, 1 M or more and 25 M or less.

[0122] The electrolyte layer may also include a membrane impregnated with the electrolyte. By providing a membrane, the occurrence of internal short circuits can be suppressed. The membrane may be, for example, a porous membrane. Materials used for the membrane include resins such as polyethylene, polypropylene, polyester, polyvinyl alcohol, cellulose, and polyamide. Furthermore, the electrolyte layer may also contain a solid electrolyte. Examples of solid electrolytes include organic solid electrolytes such as polymer electrolytes and gel electrolytes; and inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, and halide solid electrolytes.

[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. On the other hand, examples of materials for the negative electrode current collector include SUS, copper, nickel, and carbon. Furthermore, the battery disclosed herein may also have an outer casing housing the power generation elements (positive electrode active material layer, electrolyte layer, and negative electrode active material layer). Examples of outer casings include a shell-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 disclosed herein can be a primary battery or a secondary battery, with a secondary battery being preferred. This is because it can be repeatedly charged and discharged, making it useful, for example, as a vehicle battery. Examples of applications for the battery include power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline vehicles, and diesel vehicles. It is particularly preferred for use as a power source for driving hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or battery electric vehicles (BEVs). Additionally, the battery can be used as a power source for mobile bodies other than vehicles (e.g., trains, ships, airplanes) and 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 of this disclosure. Figure 4 In this process, firstly, a mixture containing a transition metal hydroxide, a Li source, and lithium hydroxide as a molten salt is calcined to obtain a calcined body (calcination step), wherein the transition metal hydroxide contains TM. Next, the calcined body is pulverized (pulverization step). In the mixture, the molar ratio of Li to TM in the molten salt is 0.1 or more and less than 0.6.

[0128] According to this disclosure, a positive electrode active material capable of suppressing the increase in resistance associated with charging and discharging can be obtained by using a mixture containing molten salt and subjecting it to a predetermined pulverization process. The molten salt acts as a flux, promoting the growth of primary particles.

[0129] 1. Firing process

[0130] The sintering process is a process of sintering a mixture containing a transition metal hydroxide, a Li source, and lithium hydroxide as a molten salt to obtain a sintered body, wherein the transition metal hydroxide contains the aforementioned TM.

[0131] Transition metal hydroxides contain TM (TM is a transition metal). Transition metal hydroxides are precursors to positive electrode active materials. Transition metal hydroxides typically do not contain Li, but may contain Li.

[0132] There are no particular limitations on the synthesis methods of transition metal hydroxides; for example, the following methods can be listed. First, prepare an aqueous solution of the transition metal hydroxide as a raw material. Methods for preparing the raw material aqueous solution include, for example, dissolving a water-soluble transition metal compound in water. Transition metal compounds include, for example, metal salts such as sulfates and nitrates. Ni sources include, for example, NiSO4 and Ni(NO3)2. Co sources include, for example, CoSO4, Co(NO3)2, and Co(NO3)3. Mn sources include, for example, MnSO4 and Mn(NO3)2. The composition of the raw material aqueous solution is appropriately adjusted according to the target positive electrode active material.

[0133] Next, an aqueous sodium hydroxide solution is added to the reaction vessel, and the starting material aqueous solution and NH3 aqueous solution are added dropwise while maintaining an alkaline pH (e.g., pH 11.3–12.0). The reaction temperature is not particularly limited, but can be, for example, above 50°C and below 65°C. After the reaction is complete, the transition metal hydroxide is preferably filtered out, washed with water, and then dried.

[0134] In the firing process, a mixture containing a transition metal hydroxide, a Li source, and lithium hydroxide as a molten salt 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 amount of TM contained in the transition metal hydroxide is, for example, 0.8 or more and 1.2 or less, 0.9 or more and 1.1 or less, or 1.0.

[0135] The mixture described above typically contains lithium hydroxide as a molten salt. The molar ratio (Li / TM) of the molten salt to the transition metal hydroxide is typically 0.1 or more and less than 0.6. The Li / TM ratio can be 0.15 or more, 0.2 or more, or 0.25 or more. On the other hand, the Li / TM ratio can be 0.55 or less, or 0.5 or less.

[0136] The mixture described above may also contain lithium hydroxide as a Li source and a molten salt. The molar ratio of Li in the Li source and the molten salt to the TM in the transition metal hydroxide (Li′ / TM) is, for example, 1.1 or more, 1.15 or more, or 1.2 or more. On the other hand, Li′ / TM is, for example, less than 1.6, 1.55 or less, or 1.5 or less.

[0137] In the firing process, the mixture is fired to obtain a fired body. The firing temperature in the firing process is, for example, 650°C or higher, or 700°C or higher. If the firing temperature is too low, it is difficult for the primary particles to grow sufficiently. On the other hand, the firing temperature is, for example, 1100°C or lower, or 1000°C or lower, or 950°C or lower. If the firing temperature is too high, side reactions are likely to occur.

[0138] The firing time in the firing process is not particularly limited; for example, it can be more than 5 hours, more than 7 hours, or more than 9 hours. On the other hand, the firing time in the firing process can be less than 15 hours, or less than 13 hours. The atmosphere in the firing process is usually an oxygen-containing atmosphere. As for firing methods in the firing process, examples include using a muffle furnace, an electric furnace, or other firing furnaces.

[0139] 2. Grinding process

[0140] The pulverization process is the process of pulverizing the aforementioned sintered body. Examples of methods for pulverizing the sintered body include hammer mills, laboratory grinders, and ball mills. Furthermore, the pulverization conditions are adjusted to obtain the positive electrode active material described in "A. Positive Electrode Active Material" above.

[0141] 3. Other processes

[0142] The method for manufacturing the positive electrode active material disclosed herein may or may not include a re-firing step between the firing step and the pulverizing step, in which the fired body is fired again. By performing the re-firing, the particle size of the primary particles can be further increased, thereby enabling control of the pore size distribution.

[0143] The firing temperature in the re-firing process is preferably lower than that in the aforementioned firing process. The firing temperature in the re-firing process is, for example, 400°C or higher and 600°C or lower, or 450°C or higher and 550°C or lower. The firing time in the re-firing process is preferably shorter than that in the aforementioned firing process. The firing time in the re-firing process is, for example, 1 hour or higher and 5 hours or lower, or 2 hours or higher and 4 hours or lower. The atmosphere in the re-firing process is typically an oxygen-containing atmosphere. Examples of firing methods in the re-firing process include using a muffle furnace, an electric furnace, or other similar firing furnaces.

[0144] The method for manufacturing the positive electrode active material disclosed herein may or may not include a granulation step after the pulverization step, in which the pulverized material of the sintered body is granulated. Granulation allows for the production of large aggregates, thereby enabling control over the pore size distribution. Spray drying is a method for granulating the pulverized material of the sintered body, for example. In spray drying, the pulverized material of the sintered 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 or higher and 250°C or lower.

[0145] 4. Positive electrode active material

[0146] The positive electrode active material obtained through the above processes is the same as the content described in "A. Positive Electrode Active Material" above.

[0147] Furthermore, this disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and solutions having substantially the same technical concept as those described in the claims of this disclosure, and solutions that achieve the same effect, are all included within the technical scope of this disclosure.

[0148] Example

[0149] [Example 1]

[0150] (Preparation of raw material aqueous solution)

[0151] First, a raw material aqueous solution is prepared by dissolving NiSO4, CoSO4, and MnSO4 in ion-exchange water. The molar ratio of Ni, Co, and Mn in the raw material aqueous solution is adjusted to Ni:Co:Mn of 92:5:3. The concentration of the raw material aqueous solution (relative to the number of moles of raw material (total solute) in the raw material aqueous solution) is 0.2 mol%.

[0152] (Precipitation and pre-firing)

[0153] A predetermined amount of NH3 aqueous solution was added to the reaction vessel, and nitrogen was purged while stirring the vessel. NaOH was then added to the reaction vessel to adjust the pH of the aqueous solution to alkaline. Maintaining a constant pH within the reaction vessel, the raw material aqueous solution was added dropwise while controlling the temperature, thereby precipitating the transition metal hydroxide. After the precipitation reaction was complete, the precipitate was dehydrated and pre-calcined under the following temperature and pressure conditions.

[0154] Temperature: 120℃

[0155] • Duration: 8 hours

[0156] Pressure: 0.2 MPa

[0157] (Precursor recovery)

[0158] After pre-calcination, the precipitate is washed with water. The washed material is then filtered to remove the transition metal hydroxide. Next, it is dried at 110°C for 12 hours to evaporate the water (dried product). This prepares the precursor.

[0159] (Mixing of Li feedstock and molten salt)

[0160] The obtained precursor (transition metal hydroxide) and LiOH as a Li source were mixed in a mortar. The LiOH was mixed such that the molar ratio (Li content in the Li source relative to the total number of transition metals (Ni, Co, Mn) in the transition metal hydroxide was 1.0. Furthermore, LiOH was mixed as a molten salt such that the molar ratio (Li content in the molten salt relative to the total number of transition metals in the transition metal hydroxide) was 0.2. Thus, during calcination, the presence of excess LiOH promoted the single crystallization of primary particles.

[0161] (Firing)

[0162] The mixture was heat-treated (calcined). It was calcined in a muffle furnace at 780°C for 12 hours (calcination process). Next, the calcined body was pulverized in an agate mortar to a particle size of less than 0.2 mm, then dispersed in 500 mL of pure water and vigorously stirred for 1 minute to obtain a slurry. The slurry was filtered through a Buchner funnel and filter paper, washed with 500 mL of pure water, and the resulting filter cake was vacuum-dried at 90°C. The dried powder was calcined at 500°C for 3 hours under oxygen flow (re-calcination). The calcined body was then pulverized using a hammer mill to break it to a predetermined particle size (pulverization). This yielded the positive electrode active material.

[0163] (The production of the positive electrode)

[0164] A positive electrode paste containing the aforementioned particles as the positive electrode active material and N-methylpyrrolidone (NMP) as a solvent is applied to a metal foil serving as the positive electrode current collector using a film coater (All Good Co., Ltd.) equipped with a film thickness adjustment function. After coating, to allow the NMP solvent to evaporate, a drying process is performed on a hot plate at 80°C for 5 minutes, thereby forming a positive electrode active material layer on the positive electrode current collector. Thus, a positive electrode having a positive electrode current collector and a positive electrode active material layer is obtained.

[0165] (Battery manufacturing)

[0166] A negative electrode paste containing natural graphite as the negative electrode active material was applied to the surface of a metal foil serving as the negative electrode current collector using a film coater (manufactured by All Good Co., Ltd.) with a film thickness adjustment function. Subsequently, it was dried at 80°C for 5 minutes using a dryer to create a negative electrode with a layer of negative electrode active material on the negative electrode current collector. A 1M LiPF6 solution containing LiPF6 as the electrolyte, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) as solvents at a volume percentage of 3 / 4 / 3 (EC / DMC / EMC) was prepared as the electrolyte. The above-mentioned positive electrode, separator, and negative electrode were stacked, and the separator was impregnated with the electrolyte to create a battery (small laminated cell) housing a power generation element in a soft-pack made of Al laminated film.

[0167] [Example 2]

[0168] No further firing was performed, and the positive electrode active material was obtained in the same manner as in Example 1. Using the obtained positive electrode active material, a battery was obtained in the same manner as in Example 1.

[0169] [Example 3]

[0170] LiOH was mixed as a molten salt such that the molar ratio of Li in the molten salt to the total number of transition metals in the transition metal hydroxide was 0.1. Otherwise, the positive electrode active material was obtained in the same manner as in Example 1. Using the obtained positive electrode active material, a battery was obtained in the same manner as in Example 1.

[0171] [Example 4]

[0172] LiOH was mixed as a molten salt such that the molar ratio of Li in the molten salt to the total number of transition metals in the transition metal hydroxide was 0.6. Otherwise, a sintered body was obtained in the same manner as in Example 1. The obtained sintered body was pulverized using a hammer mill to break (crush) it to a predetermined particle size. Then, 30 g of the pulverized material was dispersed in 100 mL of pure water and sprayed at 200°C using a spray dryer manufactured by BUCHI, thereby obtaining a 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.

[0173] [Comparative Example 1]

[0174] The positive electrode active material was obtained in the same manner as in Example 1, except that molten salt was not used and the firing temperature was changed to 730°C. Using the obtained positive electrode active material, a battery was obtained in the same manner as in Example 1.

[0175] [Comparative Example 2]

[0176] LiOH was mixed as a molten salt such that the molar ratio of Li in the molten salt to the total number of transition metals in the transition metal hydroxide was 0.6. Otherwise, the positive electrode active material was obtained in the same manner as in Example 1. Using the obtained positive electrode active material, a battery was obtained in the same manner as in Example 1.

[0177] [evaluate]

[0178] (XRD measurement)

[0179] The positive electrode active materials obtained in Examples 1-4 and Comparative Examples 1 and 2 were subjected to X-ray diffraction (XRD) using CuKα rays. The results confirmed that the positive electrode active materials obtained in Examples 1-4 and Comparative Examples 1 and 2 all possess a layered rock salt-type crystalline phase belonging to space group R-3m. That is, it was confirmed that the primary particles containing Ni, Co, and Mn possess a layered rock salt-type crystalline phase.

[0180] (SEM observation)

[0181] The cross-sections of the positive electrode active materials obtained in Examples 1-4 and Comparative Examples 1 and 2 were observed using a scanning electron microscope (SEM). The results confirmed that the positive electrode active materials obtained in Examples 1-4 and Comparative Example 1 were aggregates formed by the aggregation of multiple primary particles. In contrast, the positive electrode active material obtained in Comparative Example 2 consisted of individual primary particles, confirming it as a single-crystal positive electrode active material. Furthermore, the average particle sizes of the primary particles in the aggregates obtained in Examples 1-4 were 8.2 μm, 7.9 μm, 2.3 μm, and 1.5 μm, respectively.

[0182] (Determination of pore diameter distribution)

[0183] The pore size distribution of the positive electrode active materials obtained in Examples 1-4 and Comparative Examples 1 and 2 was determined using mercury intrusion porosimetry. Specifically, a mercury intrusion porosimetry pore size distribution measuring device from Micromeritics was used to inject mercury into a sample tube containing 1 g of positive electrode active material, thereby measuring the pore size distribution of the positive electrode active material. The results are shown below. Figure 5 .

[0184] like Figure 5 As shown, the positive electrode active materials obtained in Examples 1-4 and Comparative Example 1 each had one peak in the range of pore size below 300 nm. On the other hand, no peak was found in the positive electrode active material obtained in Comparative Example 2 in the range of pore size below 300 nm. The peak positions and pore size are shown in Table 1.

[0185] (Measurement of resistance increase)

[0186] Using the batteries obtained in Examples 1-4 and Comparative Examples 1 and 2, the increase in resistance before and after the cycle test was measured. First, the initial resistance of the batteries was determined. Specifically, the batteries were charged to 4.25V and then discharged to 3.7V. Subsequently, the voltage drop (V) and current (I) during a 0.1-second discharge at 25°C were measured to determine the initial resistance (IV resistance).

[0187] Next, a cyclical test was conducted under the following conditions.

[0188] Ambient temperature: 60℃

[0189] Number of cycles: 100

[0190] Current ratio: 0.3C

[0191] Voltage range: 4.25V to 2.5V

[0192] After the cyclic test, the resistance (IV resistance) after 100 cycles is calculated in the same way as above. The difference between the resistance after 100 cycles and the initial resistance is calculated as the increase in resistance (Ω). The results are shown in Table 1.

[0193] (Volume retention rate determination)

[0194] The capacity retention rate was measured using the batteries obtained in Examples 1-4 and Comparative Examples 1 and 2. First, the initial discharge capacity of the batteries was determined. Specifically, the batteries were charged to 4.25V, discharged at 0.1C to 2.5V, and the initial discharge capacity was determined at 25°C.

[0195] Next, a cyclical test was conducted under the following conditions.

[0196] Ambient temperature: 60℃

[0197] Number of cycles: 100

[0198] Current ratio: 0.3C

[0199] Voltage range: 4.25V to 2.5V

[0200] After the cyclic test, the discharge capacity after 100 cycles was calculated 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.

[0201] in addition, Figure 6 This indicates the change in capacity retention of the batteries obtained in Example 1 and Comparative Examples 1 and 2. Figure 6 In the process, capacity was confirmed every 25 cycles at 60°C and 0.2C under CCCV conditions, while other cycles were performed at 60°C and 0.3C under CC charge-discharge conditions. Furthermore, the capacity retention rate and... (Table 1 shows...) Figure 6 The volume retention rates shown are inconsistent due to different measurement temperatures.

[0202] Table 1

[0203]

[0204] As shown in Table 1, it was confirmed that Examples 1-4, compared with Comparative Examples 1 and 2, were able to suppress the increase in resistance associated with charging and discharging. Furthermore, Examples 1-4 exhibited the same or better capacity retention rate compared with Comparative Examples 1 and 2. Additionally, as... Figure 6 As shown, Comparative Example 2 (single crystal) exhibited better capacity retention compared to Comparative Example 1 (polycrystalline). Furthermore, Example 1 (condensate) showed a significantly better capacity retention compared to Comparative Example 2 (single crystal).

Claims

1. A positive electrode active material, The positive electrode active material has crystalline primary particles containing Li, transition metals, and O. The positive electrode active material is an aggregate composed of multiple primary particles. The average particle size of the primary particles in the aggregate is greater than 0.5 μm. In the fine pore size distribution obtained by mercury porosimetry, peaks exist in the range of above 65 nm and below 300 nm.

2. The positive electrode active material according to claim 1, wherein the peak exists in the pore diameter distribution in the range of 80 nm or more and 200 nm or less.

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

4. The positive electrode active material according to claim 1, wherein the pore size of 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 transition metal.

6. In the positive electrode active material according to claim 5, when the transition metal is set to 1 molar part, the proportion of Ni is 0.50 molar parts or more.

7. The positive electrode active material according to claim 5, wherein when the transition metal is set to 1 molar part, the proportion of Ni is 0.90 molar parts or more.

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

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 substance as described in 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 compound 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 the following steps: A firing process comprising firing a mixture containing a transition metal hydroxide, a Li source, and lithium hydroxide as a molten salt to obtain a fired body, wherein the transition metal hydroxide contains the transition metal; and The pulverizing process of pulverizing the sintered body. In the mixture, the molar ratio of Li in the molten salt to the transition metal is greater than 0.1 and less than 0.

6.

13. The method for manufacturing the positive electrode active material according to claim 12, The Li source is lithium hydroxide. In the mixture, the molar ratio of Li in the Li source to the transition metal is 1.

0.

14. The method for manufacturing the positive electrode active material according to claim 12, wherein the manufacturing method comprises a granulation step of granulating the pulverized material of the calcined body after the pulverization step.

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