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 having a good storage capacity retention rate. [Solution] The present disclosure solves the above problem by providing a positive electrode active material, the positive electrode active material having crystalline primary particles containing Li, TM (TM is a transition metal), and O, the positive electrode active material being a single-crystalline active material constituted from the primary particles, the positive electrode active material having, on the surfaces of the primary particles, compound A containing La, Ni, and O, and compound B containing Li, W, and O, and La and W present inside the primary particles.

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 describes a compound having the chemical formula Li a Ni x Co y Mn 1-x-y W b Disclosed is a W-containing high-nickel ternary positive electrode material that is McO2, characterized in that the high-nickel ternary positive electrode material simultaneously contains spherical secondary particles and single-crystal particles, the single-crystal particles essentially do not contain W element inside, and the spherical secondary particles are doped with W element.

[0004] Patent Document 2 describes a single crystal multi-component positive electrode material, in which the ratio of the length of the longest diagonal to the length of the shortest diagonal measured by SEM for single crystal particles of the single crystal multi-component positive electrode material is defined as the circularity R, and R is 1 or more, and the D of the single crystal particles of the single crystal multi-component positive electrode material is 10 , D 50 and D 90 But, K 90 =(D 90 -D 10 ) / D 50 and K 90 A single crystal multi-element positive electrode material is disclosed, characterized in that the product of R and Cr is 1.20 to 1.40. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2022-542774 [Patent Document 2] Special Publication No. 2024-511223 Summary of the Invention [Problem to be solved by the invention]

[0006] From the viewpoint of improving battery performance, an improvement in storage capacity retention rate is required. The present disclosure has been made in view of the above-described circumstances, and a main object of the present disclosure is to provide a positive electrode active material having a good storage capacity retention rate. [Means for solving the problem]

[0007] [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 a single-crystal active material composed of the primary particles, The positive electrode active material has a compound A containing La, Ni, and O and a compound B containing Li, W, and O on the surfaces of the primary particles, and La and W are present inside the primary particles.

[0008] [2] The positive electrode active material according to [1], wherein the primary particles have a particle size of 0.5 μm or more.

[0009] [3] The positive electrode active material according to [1] or [2], wherein the primary particles contain at least one of Ni, Co, and Mn as the TM.

[0010] [4] The positive electrode active material according to any one of [1] to [3], wherein the primary particles have a layered rock salt type crystal structure.

[0011] [5] The positive electrode active material according to any one of [1] to [4], wherein the compound A is in a particulate form.

[0012] [6] The positive electrode active material according to any one of [1] to [5], wherein the compound B is in the form of a film.

[0013] [7] A positive electrode mixture containing the positive electrode active material according to any one of [1] to [6].

[0014] [8] 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 [7].

[0015] [9] A method for producing a positive electrode active material according to any one of [1] to [6], a first firing step of firing a first mixture containing the transition metal hydroxide containing the TM, a Li source, a La source, a W source, and a Ni source at a temperature T1 to obtain a first fired body; a second firing step of firing the first fired body at a temperature T2 to obtain a second fired body; The temperature T2 in the second baking step is lower than the temperature T1 in the first baking step, The temperature T1 is 500°C or higher and 800°C or lower, The temperature T2 is 400°C or higher and 600°C or lower.

[0016]

[10] The method for producing a positive electrode active material according to [9], wherein the transition metal hydroxide contains at least Ni as the TM and also serves as the Ni source. [Effects of the Invention]

[0017] The present disclosure has an effect of providing a positive electrode active material having a good storage capacity retention rate. [Brief explanation of the drawings]

[0018] [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 battery according to the present disclosure. [Figure 3] FIG. 1 is a flow diagram illustrating a method for producing a positive electrode active material according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0019] 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.

[0020] 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 a single-crystal active material composed of the primary particles 1. The positive electrode active material 10 also has, on the surface of the primary particles 1, a compound A containing La, Ni, and O, and a compound B containing Li, W, and O. Furthermore, La and W are present inside the primary particles 1.

[0021] According to the present disclosure, the presence of La and W inside the primary particles results in a positive electrode active material with good storage capacity retention. It is believed that the presence of La and W inside the primary particles improves the thermal stability of the positive electrode active material. Furthermore, in the present disclosure, the presence of compound A (a compound containing La, Ni, and O) with good electronic conductivity on the surface of the primary particles can reduce resistance. Furthermore, in the present disclosure, the presence of compound B (a compound containing Li, W, and O) with good ionic conductivity on the surface of the primary particles can also reduce resistance. Furthermore, the presence of compound B can suppress an increase in resistance over time. The reason for this is believed to be as follows. While compound A has good electronic conductivity and can reduce resistance, it is believed that side reactions due to electronic conduction cause the accumulation of resistance components (decomposition products), resulting in an increase in resistance over time. In contrast, compound B has moderately low electronic conductivity and therefore can suppress the accumulation of resistance components (decomposition products) in the positive electrode active material, thereby suppressing an increase in resistance over time.

[0022] In addition, in Example 3 of the above-mentioned Patent Document 1, Li 1.0029 Ni 0.83 Co 0.11 Mn 0.06 W 0.0009 La 0.002 Patent Document 1 discloses a positive electrode material represented by formula (I) and (II) O2. More specifically, it describes firing a mixture containing precursor A containing Ni, Co, and Mn but not W, precursor B containing Ni, Co, Mn, and W, LiOH, and La2O3 at a high temperature of 880°C. However, Patent Document 1 does not describe or suggest compound A (a compound containing La, Ni, and O) in this disclosure.

[0023] In addition, in the above-mentioned Patent Document 2, Li 1+a (Ni x Co y Mn z G b )M c O 2-dIn Patent Document 2, a positive electrode material represented by the formula (I) is disclosed, in which G is one or more of Ti, W, V, Ta, Zr, La, Ce, Er, Sr, Si, Al, B, Mg, Co, F, and Y. That is, La is disclosed as one option for G. However, Patent Document 2 does not disclose any examples using La.

[0024] 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.

[0025] La and W are present inside the primary particles. That is, the primary particles contain La and W as constituent elements. "La is present inside the primary particles" means that, when observing the cross section of the primary particle, La is present at a position 1 nm or more inside the outer edge of the primary particle in the direction from the outer edge toward the center of the primary particle. The presence of La can be confirmed by line analysis using transmission electron microscope-energy dispersive X-ray spectroscopy (TEM-EDX). The same applies to "W is present inside the primary particles."

[0026] In the primary particles, the molar ratio of La to the total of La and W is, for example, 20 mol% or more and 80 mol% or less, or alternatively 30 mol% or more and 70 mol% or less, or 40 mol% or more and 60 mol% or less.

[0027] 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.

[0028] 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.

[0029] 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 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.

[0030] The primary particles may or may not contain Co. When the total amount of transition metals 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.

[0031] The primary particles may or may not contain Mn. When the total amount of transition metals 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.

[0032] 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.

[0033] 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 of the periodic table. Examples of the metals belonging to groups 12 to 14 include Zn, Al, Si, Ga, Ge, In, and Sn.

[0034] 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 La d W e 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. "d" may be 0.001 or more, 0.003 or more, 0.005 or more, 0.010 or more, or 0.020 or more, or may be 0.100 or less, 0.075 or less, or 0.050 or less. "e" may be 0.001 or more, 0.003 or more, 0.005 or more, 0.010 or more, or 0.020 or more, or may be 0.100 or less, 0.075 or less, or 0.050 or less.

[0035] The positive electrode active material in the present disclosure is typically a single-crystalline active material composed of the above primary particles. A single-crystalline active material is not a polycrystalline active material (an active material in which a large number of primary particles are tightly packed together). A single-crystalline active material is typically not aggregated but exists as a single independent particle. It is preferable that no grain boundaries are observed in single-crystalline active materials when observed with a scanning electron microscope (SEM) (magnification: approximately 10,000 to 30,000 times). A single-crystalline active material has the advantage of being less susceptible to deterioration over time than a polycrystalline active material.

[0036] The particle size of the primary particles is, for example, 0.5 μm or more, and may be 0.6 μm or more, 0.8 μm or more, or 1.0 μm or more. If the particle size of the primary particles is too small, the particles may not grow sufficiently, making it difficult to produce a single crystal. On the other hand, the particle size of the primary particles is, for example, 20 μm or less, or may be 15 μm or less, 10 μm or less, or 5 μm or less. The particle size of the primary particles is determined, for example, as the longest diameter in SEM observation. Furthermore, for example, when the positive electrode active material layer contains primary particles (positive electrode active material), the particle size (longest diameter) of the primary particles may be determined from a cross-sectional image of the positive electrode active material layer.

[0037] 2. Compound A Compound A in the present disclosure contains La, Ni, and O. Compound A usually has high electronic conductivity, and therefore the presence of compound A on the surface of the primary particles can reduce resistance. Compound A may be disposed directly on the surface of the primary particles or may be disposed via another layer (another compound), with the former being preferred.

[0038] Compound A contains at least La, Ni, and O. Compound A may be composed of only La, Ni, and O, or may further contain other elements. Examples of other elements include Li. That is, compound A may or may not contain Li. An example of the composition of compound A is La. a Ni b O c (0.8≦a≦1.2, 0.8≦b≦1.2, 2.8≦c≦3.2). For example, LaNiO3 is a typical perovskite composition and has good electronic conductivity. Another example of the composition of compound A is La a Li b Ni c O d (3.5≦a≦4.5, 0.5≦b≦1.5, 0.5≦c≦1.5, 7.5≦d≦8.5). For example, La4LiNiO8 is known to have good electronic conductivity and is thought to have a crystalline phase similar to perovskite.

[0039] Compound A may be crystalline or amorphous, but the former is preferred because it provides good electronic conductivity. "A compound is crystalline" means that peaks derived from the target compound are observed by X-ray diffraction using CuKα radiation. On the other hand, "a compound is amorphous" means that peaks derived from the symmetric compound are not observed by X-ray diffraction using CuKα radiation. Note that when the target compound is amorphous, a halo pattern may be observed instead of a peak.

[0040] Compound A preferably has a crystalline phase of perovskite or a crystalline phase similar to perovskite. Compound A preferably has a crystalline phase of at least one of LaNiO3 or La4LiNiO8, because this provides good electronic conductivity. The above crystalline phases include crystalline phases in which some of the constituent atoms (e.g., some O atoms) are missing, and crystalline phases in which some of the constituent atoms (e.g., some La atoms) are present in excess.

[0041] It is preferable that compound A is in a particulate form. "Compound A is in a particulate form" means that, in a cross-sectional image of a primary particle, when the length of compound A in the normal direction to the surface of the primary particle is L1 and the length of compound A in the direction perpendicular to the normal direction is L2, the ratio of L2 to L1 (L2 / L1) is 3.0 or less. The cross-sectional image of a primary particle is, for example, an SEM cross-sectional image.

[0042] When all transition metals contained in the primary particles are taken as 1 molar part, the proportion of La contained in compound A is, for example, 0.001 molar parts or more, or alternatively 0.003 molar parts or more, or even 0.005 molar parts or more. On the other hand, the proportion of La contained in compound A is, for example, 0.100 molar parts or less, or alternatively 0.080 molar parts or less, or alternatively 0.060 molar parts or less.

[0043] The coverage of the compound A with respect to the primary particles is not particularly limited, but may be, for example, 10% or more and 90% or less, 20% or more and 80% or less, or 30% or more and 70% or less. The coverage of the compound A can be determined, for example, by outermost surface analysis using XPS (X-ray photoelectron spectroscopy). For example, when the primary particles contain Ni, Co, and Mn as transition metals TM, the amount of La and the amount of each TM (Ni amount, Co amount, Mn amount) can be determined by outermost surface analysis using XPS, and La / (La+TM) can be used as the coverage. The coverage of the compound B can also be determined in a similar manner. In addition, the electronic conductivity of the compound A is usually higher than that of La2O3. The electronic conductivity of the compound A at 25°C is, for example, 5.0 × 10 -4 S / cm or more, 1.0×10 -3 It may be S / cm or more.

[0044] 3. Compound B The positive electrode active material of the present disclosure has compound B containing Li, W, and O on the surface of the primary particles. Compound B usually has high ionic conductivity, so the presence of compound B on the surface of the primary particles can reduce resistance. Furthermore, the presence of compound B on the surface of the primary particles can suppress an increase in resistance over time. Compound B may be disposed directly on the surface of the primary particles or via another layer (another compound), with the former being preferred.

[0045] Compound B contains at least Li, W, and O. Compound B may be composed of only Li, W, and O, or may further contain other elements. An example of the composition of compound B is Li a W b O c (5.5≦a≦6.5, 0.5≦b≦1.5, 5.5≦c≦6.5). Compound B having the above composition is typically Li6WO6. Other examples of the composition of compound B include Li a W b O c(1.5≦a≦2.5, 0.5≦b≦1.5, 3.5≦c≦4.5). Compound B having the above composition is typically Li2WO4. Another example of the composition of compound B is Li a W b O c (3.5≦a≦4.5, 0.5≦b≦1.5, 4.5≦c≦5.5). Compound B having the above composition is typically Li4WO5. Another example of the composition of compound B is Li a W b O c (1.5≦a≦2.5, 1.5≦b≦2.5, 6.5≦c≦7.5) Compound B having the above composition is typically Li2W2O7.

[0046] Compound B may be crystalline or amorphous. Compound B is preferably film-like. "Compound B is film-like" means that, in a cross-sectional image of a primary particle, the length of compound B in the normal direction to the surface of the primary particle is L3, and the length of compound B in the direction perpendicular to the normal direction is L4. The ratio of L4 to L3 (L4 / L3) is greater than 3.0. The cross-sectional image of the primary particle is, for example, a cross-sectional image obtained by a transmission electron microscope (TEM). The thickness (length L3) of compound B is not particularly limited, but may be, for example, 0.5 nm or more and 20 nm or less, or 1 nm or more and 15 nm or less. The thickness of compound B is determined as the average value of measurements taken at least five times during TEM observation.

[0047] When all transition metals contained in the primary particles are taken as 1 molar part, the proportion of W contained in compound B is, for example, 0.001 molar parts or more, or alternatively, 0.003 molar parts or more, or even 0.005 molar parts or more. On the other hand, the proportion of W contained in compound B is, for example, 0.100 molar parts or less, or alternatively, 0.080 molar parts or less, or alternatively, 0.060 molar parts or less.

[0048] The coverage of the primary particles with compound B is not particularly limited, but may be, for example, 10% to 90%, or 20% to 80%, or 30% to 70%. The ionic conductivity of compound B is usually higher than that of W2O3. The ionic conductivity of compound B at 25°C is, for example, 1.0 × 10 -5 S / cm or more, 1.0×10 -4 It may be S / cm or more.

[0049] 4.Cathode active material The positive electrode active material in the present disclosure is a single-crystal active material composed of crystalline primary particles containing Li, TM (TM is a transition metal), and O. Furthermore, the positive electrode active material has compound A and compound B on the surface of the primary particles. Furthermore, La and W are present inside the primary particles. The positive electrode active material is typically used in batteries. Furthermore, the method for producing the positive electrode active material is not particularly limited, and examples thereof include the method described below in "D. Method for producing positive electrode active material."

[0050] The present disclosure also provides a positive electrode active material powder, which contains a plurality of single-crystal active materials composed of crystalline primary particles containing Li, TM (TM is a transition metal), and O as the positive electrode active material, and at least some of the single-crystal active materials have compound A containing La, Ni, and O and compound B containing Li, W, and O on the surfaces of the primary particles, and single-crystal active material X in which La and W are present inside the primary particles. The single-crystal active material X is the same as the positive electrode active material described above. The proportion of single-crystal active material X relative to all the positive electrode active materials in the positive electrode active material powder is, for example, 5% by mass or more, or may be 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.

[0051] B. Cathode composite The positive electrode mixture in the present disclosure contains the above-described positive electrode active material.

[0052] According to the present disclosure, the use of the above-described positive electrode active material results in a positive electrode composite having a good storage capacity retention rate. 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.

[0053] 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.

[0054] 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).

[0055] 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.

[0056] 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).

[0057] 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.

[0058] C.Battery Fig. 2 is a schematic cross-sectional view illustrating a battery according to the present disclosure. The battery 20 shown in Fig. 2 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."

[0059] According to the present disclosure, by using the above-described positive electrode mixture, a battery having a good storage capacity retention rate can be obtained.

[0060] 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."

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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).

[0069] 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).

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] D. Method for manufacturing positive electrode active material FIG. 3 is a flow diagram illustrating a method for producing a positive electrode active material according to the present disclosure. In FIG. 3, a first mixture containing a transition metal hydroxide containing TM, a Li source, a La source, a W source, and a Ni source is first fired at a temperature T1 to obtain a first fired body (first firing step). Next, the first fired body is fired at a temperature T2 to obtain a second fired body (second firing step). This results in a positive electrode active material. According to the present disclosure, the temperature T2 in the second firing step is lower than the temperature T1 in the first firing step. Furthermore, the temperatures T1 and T2 are each within a predetermined range.

[0076] According to the present disclosure, a positive electrode active material having a good storage capacity retention rate can be obtained by performing the first firing step and the second firing step.

[0077] 1. First firing process The first firing step is a step of firing a first mixture containing the transition metal hydroxide containing the TM, a Li source, a La source, a W source, and a Ni source at a temperature T1 to obtain a first fired body.

[0078] The transition metal hydroxide contains TM (TM is a transition metal). The transition metal hydroxide corresponds to a precursor of a positive electrode active material. The transition metal hydroxide typically does not contain Li, but may contain Li. The transition metal hydroxide may or may not contain La. The transition metal hydroxide may or may not contain W. The transition metal hydroxide may or may not contain Ni.

[0079] 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.

[0080] 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.

[0081] In the first firing step, a first mixture containing a transition metal hydroxide, a Li source, a La source, a W source, and a Ni source is prepared. Examples of Li sources include lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, lithium oxide, and lithium chloride. The Li source may be lithium hydroxide or a Li-containing compound other than lithium hydroxide. The 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.

[0082] Examples of La sources include hydroxides; and metal salts such as sulfates and nitrates. Examples of La sources include La(OH)3, LaSO4, and La(NO3)3. Examples of W sources include H2WO4. For example, when the transition metal hydroxide contains Ni, the transition metal hydroxide may also serve as the Ni source. On the other hand, when the transition metal hydroxide does not contain Ni, a separate Ni source must be used. Examples of Ni sources include Ni(OH)2, NiSO4, and Ni(NO3)2. The amounts of the La source, W source, and Ni source added are appropriately adjusted according to the desired positive electrode active material.

[0083] The first mixture preferably contains a molten salt. The molten salt functions as a flux, thereby enabling the primary particles to grow sufficiently. The molten salt may contain Li. An example of the molten salt is lithium hydroxide. The molar ratio of Li contained in the molten salt to TM contained in the transition metal hydroxide (Li / TM) is, for example, 0.01 or more, or may be 0.05 or more, or 0.10 or more, or may be 0.15 or more. On the other hand, Li / TM is, for example, 0.60 or less, or may be 0.50 or less, or may be 0.40 or less, or may be 0.30 or less.

[0084] The first mixture may contain lithium hydroxide as a Li source and a molten salt. The molar ratio (Li' / TM) of Li contained in the Li source and the molten salt to TM contained in the transition metal hydroxide is, for example, 1.01 or more, or may be 1.05 or more, or 1.10 or more, or 1.15 or more. On the other hand, Li' / TM is, for example, 1.60 or less, or may be 1.50 or less, or 1.40 or less, or 1.30 or less.

[0085] In the first firing step, the first mixture is fired at temperature T1 to obtain a first fired body. Temperature T1 is typically 500°C or higher and 800°C or lower, and may be 550°C or higher and 750°C or lower. If temperature T1 is too high, La2O3 is likely to be produced instead of compound A containing La, Ni, and O, making it difficult to reduce resistance. If temperature T1 is too high, La is likely to be unevenly distributed on the surface of the primary particles and is less likely to be present inside the primary particles. If temperature T1 is too high, W2O3 is likely to be produced instead of compound B containing Li, W, and O, making it difficult to reduce resistance. On the other hand, if temperature T1 is too low, it is difficult to sufficiently grow the primary particles.

[0086] The firing time in the first firing step is not particularly limited, but may be, for example, 5 hours or more and 15 hours or less, or 8 hours or more and 12 hours or less. The atmosphere in the first firing step is usually an atmosphere in which oxygen is present. Examples of firing methods in the first firing step include methods using a firing furnace such as a muffle furnace or an electric furnace.

[0087] 2. Second firing process The second firing step is a step of firing the first fired body at temperature T2 to obtain a second fired body. Temperature T2 in the second firing step is usually lower than temperature T1 in the first firing step. By setting temperature T2 lower than temperature T1, compound A containing La, Ni, and O, rather than La2O3, is more likely to be produced, thereby reducing resistance. Similarly, by setting temperature T2 lower than temperature T1, compound B containing Li, W, and O, rather than W2O3, is more likely to be produced, thereby reducing resistance.

[0088] The difference between temperatures T1 and T2 is, for example, 50°C or more, and may be 75°C or more, or 100°C or more. Temperature T2 is typically 400°C or more and 600°C or less, and may be 450°C or more and 550°C or less. If temperature T2 is too high, La2O3 may be more likely to be produced. On the other hand, if temperature T2 is too low, the effect of improving electronic conductivity due to compound A may not be sufficiently obtained. The firing time in the second firing step is not particularly limited, but may be, for example, 3 hours or more and 7 hours or less, or 4 hours or more and 6 hours or less. The firing time in the second firing step may be shorter than the firing time in the first firing step. The atmosphere in the second firing step is typically an atmosphere containing oxygen. Examples of firing methods in the second firing step include methods using a firing furnace such as a muffle furnace or an electric furnace.

[0089] 3.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."

[0090] 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]

[0091] [Comparative Example 1] (Preparation of positive electrode active material) NiSO4, CoSO4, and MnSO4 were prepared as raw materials and dissolved in ion-exchanged water to prepare a raw material aqueous solution. The molar ratio of Ni, Co, and Mn in the raw material aqueous solution was Ni:Co:Mn=8:1:1. The concentration of the raw material aqueous solution (the ratio of all raw materials to the raw material aqueous solution) was 30% by mass.

[0092] A certain amount of NH3 aqueous solution was then placed in the reaction vessel, and the atmosphere inside the vessel was replaced with nitrogen while stirring with a stirrer. NaOH aqueous solution was added to the reaction vessel, and the pH was kept alkaline (pH = 12). While controlling the temperature at a constant level, the raw material aqueous solution and NH3 aqueous solution were added dropwise to precipitate the transition metal hydroxide. The reaction temperature was 60°C, and the reaction time was 10 hours. Next, the precipitated transition metal hydroxide was filtered out, and washed with water by adding ion-exchanged water and dispersing it with a spoon. After washing, the transition metal hydroxide was dried at 120°C for 16 hours to obtain the precursor transition metal hydroxide.

[0093] Thereafter, a Li source (LiOH) was added to the obtained precursor and mixed in an agate mortar to obtain a first mixture. The amount of Li source added was adjusted so that the molar ratio (Li / NCM) of Li contained in the Li source to the total (NCM) of Ni, Co, and Mn contained in the precursor was 1.1. The obtained first mixture was fired in a firing furnace at 900°C in an oxygen atmosphere for 10 hours to obtain a fired body. The obtained fired body was crushed using a jet mill to adjust the particle size, and a positive electrode active material was obtained.

[0094] (Battery construction) A battery was fabricated using the resulting positive electrode active material. Specifically, a positive electrode composite paste containing the positive electrode active material, a conductive material (acetylene black), and a binder (polyvinylidene fluoride) in a mass ratio of positive electrode active material:conductive material:binder = 88:10:2 was applied to the surface of a metal foil positive electrode current collector using a film applicator with a film thickness adjustment function (manufactured by Allgrid Corporation). The resulting paste was then dried in a dryer at 80 °C for 5 minutes to obtain a positive electrode having a positive electrode current collector and a positive electrode active material layer.

[0095] Next, a negative electrode composite paste containing a negative electrode active material (natural graphite) and binders (SBR and CMC) 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 resulting mixture was then dried in a dryer at 80°C for 5 minutes to obtain a negative electrode current collector and a negative electrode with a negative electrode active material layer. Next, a 1M LiPF solution was prepared as the electrolyte. The solvent for the electrolyte was a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of EC:DMC:EMC = 3:4:3. A wound cylindrical battery was obtained using the above positive electrode, negative electrode, and electrolyte.

[0096] Comparative Example 2 A precursor (transition metal hydroxide) was obtained in the same manner as in Comparative Example 1. A Li source (LiOH), a La source (La(OH)), and a W source (HWO) were added to the obtained precursor and mixed in an agate mortar to obtain a first mixture. The amount of the Li source added was adjusted so that the molar ratio (Li / NCM) of Li contained in the Li source relative to the total (NCM) of Ni, Co, and Mn contained in the precursor was 1.1. The amount of the La source added was adjusted so that La / NCM was 0.005, and the amount of the W source added was adjusted so that W / NCM was 0.005. A positive electrode active material and a battery were obtained in the same manner as in Comparative Example 1, except that the obtained first mixture was used.

[0097] [Example 1] A first mixture was obtained in the same manner as in Comparative Example 2. The obtained first mixture was fired in a firing furnace under conditions of 650°C, oxygen atmosphere, and 10 hours to obtain a first fired body. The obtained first fired body was pulverized using a jet mill, and then fired in a firing furnace under conditions of 500°C, oxygen atmosphere, and 5 hours to obtain a second fired body. The obtained second fired body was pulverized using a jet mill to adjust the particle size, and a positive electrode active material was obtained. A battery was obtained in the same manner as in Comparative Example 1, except that the obtained positive electrode active material was used.

[0098] [Examples 2 and 3] A positive electrode active material and a battery were obtained in the same manner as in Example 1, except that the amounts of the La source and the W source added were changed as shown in Table 1. In Table 1, synthesis method 1 is a method in which a single firing step was performed, as in Comparative Examples 1 and 2, and synthesis method 2 is a method in which a two-step firing step was performed, as in Examples 1 to 3.

[0099] [evaluation] (SEM-EDX measurement) The positive electrode active materials obtained in Examples 1 to 3 were subjected to cross-sectional observation and elemental analysis using a scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX). As a result, it was confirmed that the primary particles in Examples 1 to 3 contained Ni, Co, and Mn. Furthermore, in Examples 1 to 3, particulate compounds were confirmed on the surfaces of the primary particles, and mapping images confirmed that the particulate compounds contained La, Ni, and O.

[0100] (TEM-EDX measurement) Cross-sectional observation and elemental analysis were performed by transmission electron microscope-energy dispersive X-ray spectroscopy (TEM-EDX) on the positive electrode active materials obtained in Examples 1 to 3. As a result, film-like compounds were confirmed on the surfaces of the primary particles in Examples 1 to 3, and mapping images confirmed that the film-like compounds contained W and O.

[0101] Furthermore, line analysis was performed from the edge of the primary particle toward the inside (center) of the primary particle for the positive electrode active materials obtained in Examples 1 to 3. As a result, it was confirmed that La and W were present 1 nm or more inward from the edge of the primary particle.

[0102] (XRD measurement) X-ray diffraction measurements (XRD) using CuKα radiation were performed on the positive electrode active materials obtained in Examples 1 to 3 and Comparative Examples 1 and 2. As a result, it was confirmed that the positive electrode active materials obtained in Examples 1 to 3 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.

[0103] Furthermore, a peak derived from a LaNiO-based crystalline phase (La4LiNiO8) was observed in the positive electrode active materials obtained in Examples 1 to 3. This confirmed that compound A present on the surfaces of the primary particles was crystalline. On the other hand, no peak derived from a LiWO-based crystalline phase was observed in the positive electrode active materials obtained in Examples 1 to 3. This suggests that compound B present on the surfaces of the primary particles is amorphous.

[0104] On the other hand, in the positive electrode active material obtained in Comparative Example 2, no peaks derived from a LaNiO-based crystalline phase were observed, but peaks derived from La2O3 and W2O3 were observed. That is, in the positive electrode active material obtained in Comparative Example 2, Compound A and Compound B according to the present disclosure were not formed.

[0105] (initial resistance) The initial resistance was measured using the batteries obtained in Examples 1 to 3 and Comparative Examples 1 and 2. Specifically, the batteries were charged to 4.3 V and then discharged to 3.7 V. The voltage drop (V) was measured after 10 seconds of discharge at 0°C and C rates of 0.1 C, 0.3 C, 0.5 C, 0.7 C, and 1.0 C. The relationship between the voltage drop (V) and the current value was plotted, and the slope of the linearly approximated line was taken as the resistance (IV resistance). The results are shown in Table 1. The initial resistance values ​​in Table 1 are relative values ​​when the initial resistance of Comparative Example 1 is set to 100%.

[0106] (Storage capacity maintenance rate) The storage capacity retention rate was measured using the batteries obtained in Examples 1 to 3 and Comparative Examples 1 and 2. Specifically, 200 cycles were performed under the conditions of a voltage range of 3.0 V to 4.3 V, a C rate of 2 C, a CC charge / discharge mode, and a temperature of 50° C. The storage capacity retention rate was calculated by dividing the discharge capacity at the 200th cycle by the discharge capacity at the 1st cycle. The results are shown in Table 1.

[0107] [Table 1]

[0108] As shown in Table 1, it was confirmed that Examples 1 to 3 had higher storage capacity retention rates than Comparative Examples 1 and 2. This is presumably because the presence of La and W inside the primary particles improved the thermal stability of the positive electrode active material. It was also confirmed that Examples 1 to 3 had lower initial resistances than Comparative Examples 1 and 2. This is presumably because the presence of compound A (compound A containing La, Ni, and O) with good electronic conductivity on the surface of the primary particles facilitated smooth electron migration. Similarly, it is presumed that the reason for the lower initial resistance was because the presence of compound B (compound B containing Li, W, and O) with good ionic conductivity on the surface of the primary particles facilitated smooth ion migration. [Explanation of symbols]

[0109] 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 a single-crystal active material composed of the primary particles, the positive electrode active material has, on the surfaces of the primary particles, a compound A containing La, Ni, and O, and a compound B containing Li, W, and O; The positive electrode active material, wherein La and W are present inside the primary particles.

2. The positive electrode active material according to claim 1 , wherein the primary particles have a particle size of 0.5 μm or more.

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

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

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

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

7. A positive electrode mixture containing the positive electrode active material according to any one of claims 1 to 6.

8. 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 7 .

9. A method for producing a positive electrode active material, comprising producing the positive electrode active material according to any one of claims 1 to 6, A first mixture containing the transition metal hydroxide containing the TM, a Li source, a La source, a W source, and a Ni source is heated to a temperature T １ a first firing step of firing the mixture to obtain a first fired body; The first fired body is heated to a temperature T ２ a second firing step of firing the mixture to obtain a second fired body; The temperature T in the second baking step ２ is the temperature T in the first baking step １ Lower, The temperature T １ is 500°C or more and 800°C or less, The temperature T ２ The method for producing a positive electrode active material, wherein the temperature is 400°C or higher and 600°C or lower.

10. The method for producing a positive electrode active material according to claim 9 , wherein the transition metal hydroxide contains at least Ni as the TM and also serves as the Ni source.

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