Method for producing a precursor of a positive electrode active material for lithium-ion secondary batteries, and the precursor thereof, and method for producing a positive electrode active material for lithium-ion secondary batteries

Abstract

Provided are a method for manufacturing a positive-electrode active material for a lithium-ion secondary battery that has excellent electrochemical characteristics and makes it possible to reduce the amount of greenhouse gases (GHGs) discharged, a precursor used in the aforementioned method, and a method for manufacturing the precursor.　The present invention is a method for manufacturing a precursor of a positive-electrode active material for a lithium-ion secondary battery, the method having an oxidation step for mixing together a metal nickel powder and a lithium-containing compound, and then oxidizing the metal nickel powder after the mixing, the oxidation step resulting in formation of a precursor including nickel oxide having an oxidation rate of 10-70%, the oxidation rate indicating the proportion of the amount of oxidized nickel to the entire amount of Ni contained.

Description

Technical Field

[0001] The present invention relates to a method for producing a precursor of a positive electrode active material for a lithium ion secondary battery, the precursor thereof, and a method for producing a positive electrode active material for a lithium ion secondary battery.

Background Art

[0002] Lithium ion secondary batteries are widely used in various fields including electronics, automobiles, and infrastructure. Particularly in the automotive industry, lithium ion secondary batteries are used as a power source for electric vehicles (EVs) and have become an important core component. From the perspective of extending cruising range, the energy density of lithium ion secondary batteries has been improving year by year, and high-capacity ternary layered materials are used as the positive electrode active material for batteries. The ternary layered material is a composite oxide of lithium and a metal element such as Ni, Co, Mn, or Al (hereinafter referred to as lithium metal composite oxide). Furthermore, from the perspective of sustaining the global environment, reductions in greenhouse gas (GHG) emissions associated with the production of positive electrode active materials are required.

[0003] Patent Document 1 describes a method for producing a positive electrode active material using a metal hydroxide as a precursor. The process of producing a positive electrode active material by reacting a lithium source with a metal hydroxide is widely adopted. Patent Document 2 also describes a production method in which a nickel source is melted, nickel particles obtained by an atomization method are dissolved in an aqueous sulfuric acid solution to obtain nickel sulfate, then a Ni-containing hydroxide is obtained by a crystallization method, and a positive electrode active material for a secondary battery is obtained by a coprecipitation method using this hydroxide. Furthermore, Patent Document 3 describes a method for producing a positive electrode active material from a nickel raw material containing metallic nickel.

Prior Art Literature

Patent Literature

[0004]

Patent Document 1

[0005] As described in Patent Documents 1 and 2, positive electrode active materials are manufactured by reacting synthesized transition metal hydroxide particles with a Li source via a coprecipitation reaction. In the aforementioned coprecipitation reaction, aqueous solutions such as nickel sulfate are used as raw materials, which are produced by acid dissolving highly purified nickel ingots to avoid impurities. Nickel sulfate is produced by refining nickel from nickel ore mined from mines and then processing it through acid dissolution, resulting in a problem of higher GHG emissions during production compared to metallic nickel. Furthermore, since nickel sulfate is a hexahydrate, its Ni mass% (content) is approximately 20-25%, and its bulk density is low. To compensate for this, the volume handled in the manufacturing process of the positive electrode active material becomes large. At the same time, transportation costs also increase. As a result, a lot of energy is required for transportation and manufacturing, and the manufacturing process becomes complicated and lengthy. Consequently, there is a problem of increased GHG emissions. Furthermore, in Patent Document 3, since the firing is carried out using metallic nickel, there was a risk that it would sinter during the firing process and not be able to maintain its particle state. In addition, the crystal structure of the positive electrode active material was unstable, and therefore the electrochemical properties of the lithium-ion secondary battery were also unstable.

[0006] The present invention aims to provide a method for producing a precursor of a positive electrode active material for lithium-ion secondary batteries that can contribute to reducing GHG emissions, as well as the precursor itself, and a method for producing a positive electrode active material for lithium-ion secondary batteries that has a stable crystal structure and good electrochemical properties. [Means for solving the problem]

[0007] This invention utilizes metallic nickel powder as a nickel source, which has lower GHG emissions during manufacturing compared to conventional nickel sulfate. By using metallic nickel powder as a nickel source, the volume handled during transportation and the manufacturing process of the cathode active material can be reduced, thereby reducing the energy used for transportation and manufacturing, and eliminating the complexity of the manufacturing process. As a result, the invention focuses on reducing GHG emissions associated with the manufacturing of cathode active materials.

[0008] Therefore, the present invention According to one aspect, A method for producing a precursor of positive electrode active material for lithium-ion secondary batteries comprises a mixing step of mixing metallic nickel powder with a lithium-containing compound, and an oxidation step of oxidizing the metallic nickel powder after mixing. The average particle size of the aforementioned metallic nickel powder is 20 μm or less. The oxidation step is characterized by using a precursor having nickel oxide with an oxidation rate of 10% to 70% of the total amount of Ni contained, which indicates the ratio of the amount of nickel that is oxidized to the total amount of Ni contained.

[0010] According to one aspect of the present invention, the invention comprises a mixing step of mixing metallic nickel powder with a lithium-containing compound, and an oxidation step of oxidizing the metallic nickel powder after mixing. The average particle size of the aforementioned metallic nickel powder exceeds 20 μm The oxidation step involves obtaining a precursor having nickel oxide, wherein the oxidation rate, which indicates the ratio of the amount of oxidized nickel to the total amount of Ni contained, is 10% or more and 70% or less. Precursor for positive electrode active material for lithium-ion secondary batteries with a Li conversion rate of 10% or more The characteristic of .

[0011] The oxidation step is preferably carried out in an oxidizing atmosphere below the melting point of the lithium-containing compound.

[0012] Furthermore, in the method for producing the precursor of the present invention, when the amount of lithium compound required for the production of a positive electrode active material for lithium-ion secondary batteries is set to 100% by mass, it is preferable that the amount of the lithium-containing compound mixed in the mixing step is 10% by mass or more and 100% by mass or less.

[0013] In this case, it is preferable that the lithium-containing compound is lithium carbonate.

[0014] The present invention relates to a method for producing a positive electrode active material for lithium-ion secondary batteries, characterized by comprising a calcination step of obtaining a positive electrode active material by calcining a precursor produced by the method for producing a precursor of a positive electrode active material for lithium-ion secondary batteries at a temperature of 700°C to 900°C.

[0015] The method for producing the positive electrode active material is characterized by first mixing the precursor, a lithium-containing compound, and at least one of a compound containing a metal element M other than lithium and nickel to form a mixed powder, and then performing the calcination step.

[0016] In this case, the process includes a grinding step of grinding the mixed powder, and a granulation step of granulating the ground mixed powder to form granulated powder, and the calcination step can be performed on the granulated powder.

[0017] Furthermore, the method for producing the positive electrode active material comprises a grinding step of grinding the mixed powder, and a granulation step of granulating the ground mixed powder to form granulated powder, wherein when the amount of lithium-containing compound mixed in the precursor is less than 100% by mass, the remaining amount of the lithium-containing compound is added after the granulation step to form mixed granulated powder, and the calcination step is performed on the mixed granulated powder. Furthermore, another embodiment of the present invention provides a method for producing a positive electrode active material for a lithium-ion secondary battery, comprising a mixing step of mixing metallic nickel powder with a compound containing lithium, and an oxidation step of oxidizing the metallic nickel powder after mixing, wherein the oxidation step produces a precursor having nickel oxide, the oxidation rate of which the ratio of the amount of oxidized nickel to the total amount of Ni contained is 10% or more and 70% or less, and after mixing the precursor with a compound containing lithium and a metal element M other than nickel to make a mixed powder, a grinding step of grinding the mixed powder, and the grinding of the mixed powder grain and make granulated powder GranulationThe process is characterized by comprising the steps of: when the amount of lithium compound required for the production of a positive electrode active material for a lithium-ion secondary battery is set to 100% by mass, if the amount of lithium-containing compound mixed in the precursor is less than 100% by mass, the remaining amount of the lithium-containing compound is added after the granulation step to form a mixed granulated powder, and the mixed granulated powder is calcined at 700°C to 900°C to obtain a positive electrode active material.

[0018] The grinding process may include a coarse grinding process and a fine grinding process.

[0019] It is preferable that the lithium-containing compound mixed before the oxidation step and the lithium-containing compound added after the granulation step are different compounds, and that the melting point of the lithium-containing compound mixed before the oxidation step is higher than the melting point of the lithium-containing compound added after the granulation step.

[0020] Furthermore, the positive electrode active material for the lithium-ion secondary battery is preferably represented by the following compositional formula (1). Li 1+a Ni b M (1-b) O 2+α ...(1) (However, in formula (1) above, M is a metallic element other than Li and Ni, and a, b, and α are numbers that satisfy -0.1 ≤ a ≤ 0.2, 0.6 ≤ b ≤ 1.0, and -0.2 ≤ α ≤ 0.2.)

[0021] The precursor for the positive electrode active material for lithium-ion secondary batteries of the present invention comprises metallic nickel powder and a lithium-containing compound, and contains nickel oxide with an oxidation rate of 10% to 70% of the total amount of nickel contained, wherein the crystallite size of the nickel oxide is 100 nm or less.

[0022] The precursor for the positive electrode active material for lithium-ion secondary batteries of the present invention comprises metallic nickel powder and a lithium-containing compound, and is characterized by containing nickel oxide with an oxidation rate of 10% to 70% of the total amount of nickel contained, and further containing lithium metal oxide. In the following, the "oxidation rate, which indicates the ratio of oxidized nickel to the total amount of nickel contained," will simply be referred to as "oxidation rate." [Effects of the Invention]

[0023] According to the present invention, by producing a precursor for lithium-ion secondary battery positive electrode active material using metallic nickel powder, the energy used for transportation and manufacturing can be reduced, and the complexity of the manufacturing process can be eliminated. As a result, a precursor for lithium-ion secondary battery positive electrode active material and a method for producing the same can be provided, which can contribute to reducing GHG emissions. Furthermore, the method for producing the lithium-ion secondary battery positive electrode active material can provide a positive electrode active material with a stable crystal structure and good electrochemical properties. [Brief explanation of the drawing]

[0024] [Figure 1] This flowchart shows an example of a method for producing a precursor of the positive electrode active material for lithium-ion secondary batteries of the present invention. [Figure 2] This flowchart shows an example of a method for producing a positive electrode active material for lithium-ion secondary batteries according to the present invention. [Figure 3] This flowchart shows an example of a method for producing a positive electrode active material for lithium-ion secondary batteries according to the present invention. [Figure 4] This flowchart shows an example of a method for producing a positive electrode active material for lithium-ion secondary batteries according to the present invention. [Figure 5] This flowchart shows an example of a method for producing a positive electrode active material for lithium-ion secondary batteries according to the present invention. [Figure 6] This flowchart shows an example of a method for producing a positive electrode active material for lithium-ion secondary batteries according to the present invention. [Figure 7]These are the X-ray diffraction (XRD) patterns of the precursors of the positive electrode active materials for lithium-ion secondary batteries in Examples 1 and 2 and Comparative Examples 1 and 2. [Figure 8] These are the XRD patterns of the positive electrode active materials for lithium-ion secondary batteries of Examples 1 and 2 and Comparative Examples 1 and 2. [Figure 9] This figure shows the relationship between the R value and the oxidation rate. [Figure 10] This is an electron probe microanalyzer (EPMA) mapping image of the particle cross-section of the positive electrode active material for the lithium-ion secondary battery in Example 1. [Figure 11] This figure shows the relationship between the Ni ratio in the center of the positive electrode active material for lithium-ion secondary batteries and the D50 of metallic nickel powder. [Figure 12] This is a scanning electron microscope (SEM) image of a particle cross-section of the positive electrode active material for the lithium-ion secondary battery in Example 3. [Figure 13] This is an SEM image of the particle cross-section of the positive electrode active material for the lithium-ion secondary battery in Example 5. [Figure 14] This is an SEM image of the particle cross-section of the positive electrode active material for the lithium-ion secondary battery in Example 1. [Modes for carrying out the invention]

[0025] [Method for producing metallic nickel powder] Before explaining the method for producing the positive electrode active material, we will illustrate the method for producing metallic nickel powder. In this embodiment, metallic nickel powder produced by methods such as atomization or carbonylation can be used. Atomization and carbonylation are preferred because they allow for the production of metallic nickel powder with a low amount of impurity elements. Furthermore, atomization is preferred for obtaining spherical powder. High-purity raw materials are used in battery components to avoid short circuits. In particular, iron (Fe) is an impurity element that is likely to cause short circuits, so the Fe content of metallic nickel powder is preferably 100 ppm or less. More preferably 30 ppm or less, and even more preferably 10 ppm or less. Furthermore, high-purity briquettes or cathodes of Class I are suitable as a high-purity nickel source. In this embodiment, high-purity metallic nickel powder with few impurities is obtained without acid dissolving these briquettes or cathodes.

[0026] Another method for obtaining metallic nickel powder is the carbonyl process. In the carbonyl process, nickel briquettes are reacted with carbon monoxide gas to obtain gaseous nickel carbonyl, which is then thermally decomposed under reduced pressure and low temperature to obtain metallic nickel powder. High-purity metallic nickel powder can also be obtained using the carbonyl process.

[0027] The average particle size of the metallic nickel powder is preferably in the range of 1 μm to 100 μm. This particle size can be measured using a laser diffraction particle size distribution analyzer. In this specification, D50 is considered to be the average particle size. If the grinding step described later is omitted, the average particle size D50 of the metallic nickel powder is preferably 20 μm or less, and more preferably 8 μm or less. When the average particle size D50 of the metallic nickel powder is 20 μm or less, metallic elements other than lithium and nickel diffuse to the center of the metallic nickel powder, and the composition within the positive electrode active material becomes almost uniform. Furthermore, if the D50 of the metallic nickel powder is 8 μm or less, the composition within the positive electrode active material becomes even more uniform, which is preferable. On the other hand, when a grinding process is performed, the average particle size D50 of the metallic nickel powder should be greater than 20 μm, with no upper limit. However, it is acceptable to set it to, for example, between 20 μm and 100 μm, and grind it after the oxidation process described later. The particle size of the metallic nickel powder can be controlled in the atomization method by the injection pressure of the injected water or gas, and in the carbonyl method by the thermal decomposition conditions. Powders larger than 100 μm can be removed by sieving and returned to dissolution (recycled).

[0028] [Method for producing a precursor of positive electrode active material] The following describes a method for producing a precursor of a positive electrode active material using metallic nickel powder. As shown in the flowchart in Figure 1, metallic nickel powder and all or part of a lithium-containing compound are mixed, and an oxidation process is carried out on this mixed powder. Note that all or part of a compound containing lithium and a metal element M other than nickel may be mixed before the oxidation process. In this embodiment, the positive electrode active material is obtained by calcination in an oxygen-containing atmosphere. However, by introducing a precursor of metallic nickel powder that has undergone the oxidation process, a positive electrode active material with good crystallinity can be produced. Furthermore, a lithium-containing compound (e.g., lithium carbonate) acts as an inclusion, preventing sintering of the metallic nickel powders during the oxidation process, and maintaining the powder state after the oxidation process allows for the acquisition of a powdery precursor. Note that if the metallic nickel powder has caked after the oxidation process, it may be crushed. Additionally, by carrying out the oxidation process together with a lithium-containing compound, lithium metal oxide (lithium nickel oxide) is also produced, and a precursor containing lithium metal oxide can be obtained. Using this precursor yields a positive electrode active material with good crystallinity.

[0029] As described above, this invention uses metallic nickel powder as the nickel raw material, eliminating the need for acid dissolution and coprecipitation processes. Estimates suggest that the CO2 emissions generated during the production of metallic nickel are approximately 30% less than those from nickel sulfate, and using metallic nickel powder reduces the CO2 emissions generated during the production of precursors and cathode active materials. Furthermore, because metallic nickel powder is used as the nickel raw material, the volume handled during transportation and the production of cathode active materials can be reduced compared to compounds such as nickel sulfate and nickel hydroxide. Specifically, expressing the Ni content per unit volume of each compound in mass percent, nickel sulfate (Ni(SO)4·6H2O) has a Ni content of 5%, nickel hydroxide (Ni(OH)2) has a Ni content of 29%, while metallic nickel has a Ni content of 100%, resulting in a higher Ni content per unit volume. As a result, the volume handled during transportation and the manufacturing process of the cathode active material is approximately 1 / 20th of that of nickel sulfate and approximately 1 / 3th of that of nickel hydroxide in this embodiment, which reduces fuel consumption during transportation, improves production efficiency through space saving and reduced driving force during manufacturing, and saves energy. These factors lead to a reduction in GHG emissions, making it possible to manufacture cathode active materials while suppressing GHG emissions.

[0030] The lithium-containing compound mixed with metallic nickel powder before the oxidation process may be a single lithium compound or a mixture of multiple lithium compounds. Even when using a mixture of multiple lithium compounds, the ratio of lithium mass in the lithium-containing compound should be within the following range. The amount of lithium-containing compound mixed with metallic nickel powder is preferably 10% to 100% by mass, where 100% by mass is the amount of lithium-containing compound required for the production of the target positive electrode active material. This is because the presence of the lithium-containing compound can suppress sintering. Mixing 10% or more with metallic nickel powder makes it easier to control the prevention of sintering between the metallic nickel powders during the oxidation process. The amount of lithium-containing compound to be mixed is preferably 50% by mass or less, and more preferably 25% by mass or less. This is because the amount of oxidation treatment in the oxidation process is reduced, the energy consumed in the oxidation treatment is reduced, and costs and GHG emissions can be reduced. Furthermore, if a grinding process is performed during the production of the positive electrode active material as described later, the amount of lithium-containing compound mixed before the oxidation process is preferably 10% to 50% by mass. More preferably 25% by mass or less. Reducing the amount of lithium compound mixed reduces the voids within the secondary particles of the positive electrode active material. As a result, the particle strength of the positive electrode active material increases, leading to improved charge-discharge cycle characteristics. Furthermore, by mixing 10% or more by mass of the lithium-containing compound with metallic nickel powder, lithium metal oxide (lithium nickel oxide) is formed in addition to nickel oxide after the oxidation process. When metallic nickel becomes lithium metal oxide, its volume expands by approximately three times, and the stress generated by this volume change causes cracks in the precursor. Consequently, if a grinding process is not performed, these cracks become diffusion pathways for the elements, making it easier for each element to diffuse uniformly. On the other hand, if a grinding process is performed, these cracks make the material easier to grind.

[0031] The lithium-containing compound can be lithium hydroxide, lithium carbonate, or the like. It is also preferable that its melting point is higher than the thermal oxidation temperature of the oxidation process. A higher melting point of the lithium-containing compound than the thermal oxidation temperature prevents sintering of the metallic nickel powders during the oxidation process. Therefore, lithium carbonate is preferred as the lithium-containing compound used in this manufacturing method. Lithium carbonate has a high melting point of 724°C, making it possible to raise the thermal oxidation temperature to 720°C. Even at an oxidation treatment temperature of 720°C, it remains solid, functioning as an inclusion to prevent contact and sintering of the metallic nickel powders, and shortening the oxidation process time. On the other hand, lithium hydroxide may be used as the lithium-containing compound added after the granulation process, as described later. Lithium hydroxide has a lower melting point of 462°C compared to lithium carbonate, and melts at a lower temperature, making it more likely to react with the precursor. Thus, the lithium-containing compound mixed before the oxidation process and the lithium-containing compound added after the granulation process are different compounds, and in some cases, the lithium-containing compound mixed before the oxidation process has a higher melting point. Furthermore, the average particle size of the lithium-containing compound is preferably 100 nm to 100 μm, and more preferably 1 μm to 50 μm.

[0032] For mixing the aforementioned metallic nickel powder with the lithium-containing compound, a V-type mixer, stirring mixer, attritor, media mill, etc., can be used. To ensure uniform mixing, it is preferable to be able to break down the agglomeration of each raw material powder. The mixing method can be either a dry method, in which only the raw material powders are mixed, or a wet method, in which a liquid is used as a dispersion medium.

[0033] The oxidation process is preferable when performed by thermal oxidation in an oxidizing atmosphere, as this shortens the time required for the oxidation treatment. Furthermore, in the case of thermal oxidation, a temperature of approximately 450 to 720°C is good, preferably 450 to 700°C. This is because a temperature of 450 to 700°C makes it easier to obtain a precursor with the desired oxidation rate. The heat treatment time for the oxidation process is good, preferably 0.5 to 20 hours, preferably 3 to 15 hours, and more preferably 5 to 10 hours. This is because the oxidation reaction is completed by performing the oxidation treatment for 5 to 10 hours, making it easy to stably obtain a precursor with the desired oxidation rate. At this time, the oxidation rate obtained in the oxidation process should be between 10% and 70%. An oxidation rate of 10% or more prevents sintering of metallic nickel powders during the subsequent firing process to obtain the positive electrode active material. In addition, an oxidation rate of 10% or more increases the valence of nickel, which is expected to promote the reaction to lithium metal composite oxide during the firing of the positive electrode active material. On the other hand, if the oxidation rate is 70% or less, a positive electrode active material with good crystallinity can be obtained. This is thought to be because the formation of a layered structure is promoted in the firing process when the positive electrode active material is produced using a precursor with an oxidation rate within the above range, rather than using metallic nickel powder that has undergone excessive oxidation. The preferred oxidation rate is 40-70%, more preferably 49-68%. This is because an oxidation rate of 49% or more results in a higher valence of nickel, which further promotes the reaction with lithium metal composite oxide during firing. On the other hand, an oxidation rate of 68% or less promotes the formation of a layered structure in the firing process compared to metallic nickel powder that has undergone excessive oxidation. Furthermore, it is desirable to generate lithium metal oxide (referring to lithium nickel oxide; the terminology will be omitted hereafter) in the oxidation process. If lithium metal oxide is generated, the reaction between the lithium source and the metal source such as nickel is promoted in the subsequent firing process to obtain the positive electrode active material, promoting the formation of layered crystals and resulting in a positive electrode active material with good crystallinity.

[0034] Next, there is described the case where metallic nickel powder having an average particle diameter D50 of more than 20 µm is used. Mixing a lithium-containing compound and performing an oxidation step of oxidizing the metallic nickel powder after mixing can be carried out by the same means and under the same conditions as those described above. However, the precursor after the oxidation step is in the state of a crude precursor having nickel oxide with an oxidation rate of 10% or more and 70% or less, and it is preferable to pulverize this crude precursor of more than 20 µm to obtain a precursor of 20 µm or less. Therefore, when metallic nickel powder having an average particle diameter D50 of more than 20 µm is used, a pulverizing step is included in the production of the positive electrode active material. By this means, lithium and metal elements other than nickel diffuse to the center of the metallic nickel powder, and the composition within the secondary particles of the positive electrode active material becomes substantially uniform, so that the same effect as that obtained by the above-described method using metallic nickel powder of 20 µm or less can be obtained. Further, only the crude precursor may be pulverized, and then a lithium-containing compound and a compound containing a metal element M other than lithium and nickel may be mixed therewith. It should be noted that even when metallic nickel powder having an average particle diameter D50 of 20 µm or less is used, the pulverizing step may be carried out.

[0035] Incidentally, the oxidation rate can be determined by the means described below. (Oxidation rate) The oxidation rate of the precursor indicates the ratio of the amount of oxidized nickel to the total amount of nickel contained therein, and M is the mass of the metallic nickel powder charged into the oxidation treatment Ni , M is the mass of an inclusion component (a lithium-containing compound or a compound containing the metal element M) i and M is the mass of the precursor (oxidized powder) after the oxidation treatment p was calculated from formula (4) based on the above. Incidentally, M p -(M Ni +M i ) is the amount of mass increase of the metallic nickel powder due to the oxidation treatment, and (M p -(M Ni +M i )) / M Ni is the mass increase rate. The oxidation rate was calculated by dividing this mass increase rate by 29.8%, which is the mass increase rate when all of the metallic nickel powder is oxidized. Oxidation rate=(M p -(MNi +M i )) / M Ni / 0.298 × 100 ···(4)

[0036] [Precursor for positive electrode active material] If a grinding process is not performed on the precursor of the positive electrode active material, the crystallite size of nickel oxide contained in the precursor is preferably 100 nm or less. The lower limit can be, for example, 5 nm or more, and preferably 10 nm or more. When the crystallite size of nickel oxide contained in the precursor is 100 nm or less, a positive electrode active material with good crystallinity can be produced. This is thought to be because the fine crystallite size of nickel oxide in the precursor, which is 100 nm or less, promotes the formation of a layered structure in the calcination process to obtain the positive electrode active material. On the other hand, when the crystallite size is 5 nm or more, a positive electrode active material with an appropriate primary particle size can be obtained.

[0037] Furthermore, the precursor of the positive electrode active material preferably contains a lithium metal oxide. This is because the presence of the lithium metal oxide promotes the reaction between the lithium source and a metal source such as nickel during the calcination process to obtain the positive electrode active material, thereby facilitating the formation of a layered structure. Note that the presence of a lithium metal oxide is attributed to the lithium metal oxide in the peak intensity around 2θ = 43.7~44.0° of the X-ray diffraction (XRD) pattern measured by the method described later. LNO And the peak intensity I around 2θ = 44.4~44.7°, which is attributed to metallic nickel. Ni The intensity ratio I LNO / I Ni This is the case when the value is 0.02 or greater.

[0038] [Method for manufacturing positive electrode active material] The method for producing the positive electrode active material of this embodiment is characterized by using the positive electrode active material precursor described above. This is shown in the flowcharts in Figures 2 to 6. As shown in Figure 2, the positive electrode active material may be produced by calcining the precursor, or as shown in Figure 3, the positive electrode active material may be produced by mixing the precursor with a lithium-containing compound and a compound containing a metal element M other than lithium and nickel, and then calcining the mixture to obtain a positive electrode active material of the desired composition. Furthermore, as shown in Figures 4 and 5, grinding and granulation steps may be added. Figure 5 also includes a step of adding the remaining amount of the lithium-containing compound. Figure 6 includes a coarse grinding step and a fine grinding step. Each embodiment will be described below, and will be explained in detail with the examples.

[0039] If the aforementioned precursor contains all the metallic nickel powder and compounds containing lithium and other metallic elements M necessary for the production of the positive electrode active material, the positive electrode active material can be produced by calcining the precursor, as shown in Figure 2. Details of the calcination process will be described later.

[0040] For mixing the aforementioned precursor with a lithium-containing compound and a compound containing a metal element M other than lithium and nickel, a V-type mixer, stirring mixer, attritor, media mill, etc., can be used. To ensure uniform mixing, it is preferable to be able to break down the agglomeration of each raw material powder. The mixing method may be either a dry method, in which only the raw material powders are mixed, or a wet method, in which a liquid is used as the dispersion medium.

[0041] Lithium hydroxide and lithium carbonate can be used as lithium-containing compounds to be mixed with the precursor. Lithium carbonate is preferred because it has low hygroscopicity and is easy to handle. When the grinding step is omitted during the production of the positive electrode active material, it is preferable to use lithium hydroxide. This is because the diffusion of metal elements other than nickel M into the metallic nickel powder is promoted, and a positive electrode active material with a uniform composition can be produced.

[0042] Next, it is preferable to introduce a grinding and mixing step (referred to as the grinding step) in order to promote the calcination reaction. This is because a positive electrode active material with a high initial capacity and good charge-discharge cycle characteristics can be obtained. Grinding and mixing can be carried out using an attritor, media mill, etc. It is preferable to use a media mill, and more preferable to use a bead mill, because the mixed powder can be ground to submicron size. It is preferable that the D50 of the primary particles of the mixed powder after grinding and mixing (ground mixed powder) is 0.30 μm or less. The calcination reaction is promoted and voids in the positive electrode active material are suppressed. As a result, the particle strength of the positive electrode active material becomes high, and the charge-discharge cycle characteristics become good.

[0043] Furthermore, if the average particle size D50 of the metallic nickel powder is coarse, exceeding 20 μm, it is preferable to divide the grinding process into two stages with different grinding conditions. Specifically, it is preferable to divide the grinding into two stages: first, coarse grinding and mixing to a size of less than 10 μm (coarse grinding stage); and second, fine grinding and mixing to a submicron size (fine grinding stage). It is also preferable to use a media mill for both the coarse grinding and fine grinding stages, and it is preferable that the media size in the fine grinding stage is smaller than the media size in the coarse grinding stage. By grinding in two stages, the inclusion of media components from the media mill can be suppressed, and a positive electrode active material with a desired composition and fewer impurities can be obtained.

[0044] In the manufacturing process of the precursor described above, if the amount of lithium-containing compound mixed is less than 100% of the amount of lithium compound required to produce the target cathode active material, it is preferable to add the remaining lithium-containing compound after the granulation process (post-addition) in the manufacturing process of the cathode active material. If a large amount of lithium-containing compound is present in the granulated powder, a porous structure will be formed after firing, resulting in low particle strength of the cathode active material and deterioration of charge-discharge cycle characteristics. However, by adding the lithium compound after granulation, the amount of lithium-containing compound in the granulated powder can be reduced, resulting in a structure with fewer voids after firing. As a result, the particle strength of the cathode active material becomes high, and consequently, the charge-discharge cycle characteristics become good.

[0045] Next, a firing process will be described in which the mixed powder or pulverized mixed powder is fired to obtain a layered positive electrode active material for lithium-ion secondary batteries. Electric furnaces or gas furnaces are used for firing raw material mixtures or granulated powders. The firing atmosphere preferably contains 20% or more oxygen by volume, and if the Ni content is 80% or more of all metal elements excluding Li, an oxygen concentration of 90% or more is preferable. The firing process should be such that a layered positive electrode active material is obtained by firing at a temperature of 700°C to 900°C. This process may include a pre-firing stage where the temperature is maintained at 450°C to 730°C, and a main firing stage where the temperature is higher than that of the pre-firing stage and maintained at 700°C to 900°C. The preferred firing temperature and holding time should be adjusted according to the composition blended during raw material mixing, and the firing should be carried out so that the various physical properties (specific surface area, etc.) of the desired positive electrode active material are within a suitable range after firing.

[0046] Furthermore, the synthesized lithium metal composite oxide may be subjected to a washing process after the calcination process, in which it is washed with deionized water or the like, for the purpose of removing impurities, and a drying process to dry the washed lithium metal composite oxide. It may also be subjected to a crushing process to break down the synthesized lithium metal composite oxide, and a classification process to classify the lithium metal composite oxide to a predetermined particle size.

[0047] Next, the composition of the positive electrode active material in this embodiment will be described. As mentioned above, the composition of the positive electrode active material in this embodiment is not particularly limited, but preferred compositions are described below. First, the positive electrode active material according to this embodiment is represented by the following formula (1). Li 1+a Ni b M (1-b) O 2+α ...(1) (However, in formula (1) above, M is a metallic element other than Li and Ni, and a, b, and α are numbers that satisfy -0.1 ≤ a ≤ 0.2, 0.6 ≤ b ≤ 1.0, and -0.2 ≤ α ≤ 0.2.)

[0048] The positive electrode active material according to this embodiment has a composition in which the proportion of Ni per total metal elements other than Li is 60 atomic percent or more, thereby achieving high energy density and high initial capacity. The proportion of Ni per total metal elements other than Li can be set to an appropriate value within the range of 60 atomic percent or more and 100 atomic percent or less. Because the positive electrode active material contains a high proportion of nickel, Ni 2+ Ni 3+ It is important that oxidation reactions that oxidize to a certain state proceed efficiently.

[0049] A more preferred specific composition of the positive electrode active material according to this embodiment is represented by formula (2). Li 1+a Ni b Co c M1 d X e O 2+α ...(2) [However, in equation (2), M1 represents at least one selected from Al and Mn, X represents one or more metallic elements other than Li, Ni, Co, Al, and Mn, and a, b, c, d, e, and α are numbers that satisfy -0.1≦a≦0.2, 0.7≦b≦1.0, 0≦c≦0.20, 0≦d≦0.20, 0≦e≦0.1, b+c+d+e=1, and -0.2<α<0.2, respectively.]

[0050] The positive electrode active material represented by formula (2) exhibits a high initial capacity compared to LiCoO2, etc., up to around 4.3V, due to its high Ni content. Furthermore, because of its high Ni content, it is a positive electrode active material with lower raw material costs and readily available raw materials compared to LiCoO2, etc.

[0051] Here, we will explain the significance of the numerical ranges of a, b, c, d, e, and α in equations (1) and (2) above.

[0052] In the above formula, 'a' is between -0.1 and 0.2. 'a' represents the stoichiometric ratio of lithium metal composite oxide represented by the general formula LiM'O2 (where M' represents a metal element such as Ni, Co, or Mn), i.e., the excess or deficiency of lithium from Li:M':O=1:1:2. If there is too little lithium, the initial capacity of the positive electrode active material will be low. On the other hand, if there is too much lithium, the charge-discharge cycle characteristics will deteriorate. If 'a' is within the above numerical range, it is possible to achieve both high initial capacity and good charge-discharge cycle characteristics.

[0053] a may be -0.02 or greater and 0.07 or less. If a is -0.02 or greater, a sufficient amount of lithium is secured to contribute to charging and discharging, so the initial capacity of the positive electrode active material can be increased. Also, if a is 0.07 or less, sufficient charge compensation due to the change in the valence state of the metal element is achieved, so both high initial capacity and good charge-discharge cycle characteristics can be achieved.

[0054] The coefficient b for nickel shall be 0.7 or greater and 1.0 or less. When b is 0.70 or greater, a sufficiently high charge / discharge capacity can be obtained compared to when other metal elements are used. Therefore, if b is within the above numerical range, a positive electrode active material exhibiting a high charge / discharge capacity can be manufactured at a lower cost compared to LiCoO2, etc.

[0055] b is preferably 0.80 or greater and 0.95 or less, and more preferably 0.85 or greater and 0.95 or less. The greater b is above 0.80, the higher the initial capacity that can be obtained. Also, the smaller b is below 0.95, the smaller the lattice distortion or crystal structure change associated with lithium ion insertion and deinsulation, making it less likely for cation mixing, where nickel is mixed into the lithium sites, or a decrease in crystallinity to occur during firing, thus suppressing deterioration of initial capacity and charge-discharge cycle characteristics.

[0056] The cobalt coefficient c should be greater than or equal to 0 and less than or equal to 0.20. The addition of cobalt stabilizes the crystal structure and suppresses cation mixing, which involves nickel contamination at lithium sites. Therefore, it is possible to improve charge-discharge cycle characteristics without significantly reducing charge-discharge capacity. On the other hand, excessive cobalt increases raw material costs, thus increasing the manufacturing cost of the positive electrode active material. If c is within the aforementioned numerical range, it is possible to achieve both high charge-discharge capacity and good charge-discharge cycle characteristics with good productivity.

[0057] c may be 0.01 or greater and 0.20 or less, or 0.03 or greater and 0.20 or less, or 0.04 or greater and 0.20 or less. The larger c is above 0.01, the more sufficiently the effect of cobalt element substitution is obtained, and the better the charge-discharge cycle characteristics become.

[0058] The coefficient d of M1 shall be greater than or equal to 0 and less than or equal to 0.20. If elemental substitution is performed with at least one element (M1) selected from the group consisting of manganese and aluminum, the layered structure will be more stable even if lithium is desorbed during charging. On the other hand, if these elements (M1) are in excess, the proportion of other metallic elements such as nickel will decrease, and the initial capacity of the positive electrode active material will decrease. If d is within the above numerical range, the crystal structure of the positive electrode active material can be kept stable, and good charge-discharge cycle characteristics and thermal stability can be obtained along with a high initial capacity.

[0059] Manganese is particularly preferred as the element represented by M1. When manganese is used as the elemental substitute, a higher initial capacity can be obtained compared to when aluminum is used as the elemental substitute. Furthermore, during the calcination of the lithium composite compound, manganese also reacts with lithium carbonate as shown in formula (3) below. This reaction suppresses grain coarsening and allows the nickel oxidation reaction to proceed at high temperatures, thus enabling the efficient production of a positive electrode active material exhibiting high charge-discharge capacity.

[0060] Li2CO3+2M´O+0.5O2→2LiM´O2+CO2···(3) (However, in formula (3) above, M' represents a metallic element such as Ni, Co, or Mn.)

[0061] The coefficient d of M1 is preferably 0.02 or greater, and more preferably 0.04 or greater. The larger the coefficient d of M1, the more sufficiently the effect of elemental substitution by at least one element selected from the group consisting of manganese and aluminum can be obtained. When M1 is manganese, it becomes possible to proceed with the oxidation reaction of nickel at a higher temperature, and a positive electrode active material exhibiting high initial capacity can be obtained more efficiently. Furthermore, the coefficient d of M1 is preferably 0.18 or less. If the coefficient d of M1 is 0.18 or less, the initial capacity is maintained to be high even if elemental substitution occurs.

[0062] The coefficient e of X is set to be greater than or equal to 0 and less than or equal to 0.1. X represents one or more metallic elements other than Li, Ni, Co, Al, and Mn, but if it is elementally substituted with at least one element selected from the group consisting of magnesium, titanium, zirconium, molybdenum, and niobium, it is possible to improve various performances such as charge-discharge cycle characteristics while maintaining the activity of the positive electrode active material. On the other hand, if these elements (X) are in excess, the proportion of other metallic elements such as nickel will decrease, and the charge-discharge capacity of the positive electrode active material will decrease. If e is within the above numerical range, it is possible to achieve both high initial capacity and good charge-discharge cycle characteristics.

[0063] In equations (1) and (2) above, α is between -0.2 and 0.2. α represents the excess or deficiency of oxygen from the stoichiometric ratio of the lithium metal composite oxide represented by the general formula LiM'O2, i.e., Li:M':O=1:1:2. If α is within the above numerical range, the crystal structure has few defects, resulting in high initial capacity and good charge-discharge cycle characteristics. [Examples]

[0064] The following describes the means for measuring characteristic values ​​and preliminary experiments of the oxidation process, followed by a description of the examples.

[0065] (Average particle size, particle strength) The D50 of the primary particles of the crushed mixed powder and the secondary particles of the calcined positive electrode active material powder were measured using a laser diffraction particle size analyzer. Particle strength was measured using a micro-compression tester "MCT-510" (manufactured by Shimadzu Corporation). The particle strength of five positive electrode active material particles with a secondary particle diameter of approximately 10 μm was measured, and the average value was used as the particle strength.

[0066] (Oil absorption amount) The oil absorption of the powder sample was measured in accordance with JIS K5101-13-1, using NMP (N-methylpyrrolidone) as the solvent. 5.0 g of the powder sample was weighed out and placed in a mound on a flat tray. NMP was drawn up using a polydropper (2 mL capacity) and its mass was measured. Next, NMP was added dropwise to the powder sample while mixing with a spatula, continuing the addition and mixing until the powder sample became clay-like. When there was an excess of NMP, it was possible to visually observe that the droplets were not absorbed by the powder sample and remained on the surface. The amount of NMP added up to this point was converted to the oil absorption amount per 100 g of powder sample.

[0067] (X-ray diffraction pattern) X-ray diffraction (XRD) patterns of precursors and cathode active materials were measured using the X'Pert PRO MPD X-ray diffractometer (PANalytical) under the following conditions: CuKα source, tube voltage 45kV, tube current 40mA, sampling interval 0.02° / step, divergence slit 0.5°, scattering slit 0.5°, receiving slit 0.15mm, and scanning range 15°≦2θ≦80°.

[0068] (crystallite size) Furthermore, the crystallite sizes of nickel oxide, lithium metal oxide (LNO), and metallic Ni contained in the precursor were calculated using the analysis software attached to the X-ray diffractometer based on equation (5), after removing Kα2 from the XRD pattern obtained from the measurement of the precursor. Specifically, the peaks attributed to nickel oxide around 2θ = 43.3~43.5°, the peaks attributed to lithium metal oxide (LNO) around 2θ = 43.7~44.0°, and the peaks attributed to metallic nickel around 2θ = 44.4~44.7° were calculated using equation (5). Crystallite size = Kλ / βcosθ···(5) K: shape factor (0.9), λ: X-ray wavelength (0.154nm), θ: diffraction angle

[0069] (R-value) Furthermore, after removing Kα2 from the XRD pattern obtained by measuring the positive electrode active material, the integrated intensity I of the peaks at the 006 plane around 2θ=36°, the 102 plane around 2θ=37°, and the 101 plane around 2θ=38° was calculated. 006 , I 102 , I 101 The R value was measured and calculated using equation (6). It is known that the R value decreases as the layering of the positive electrode active material progresses, and it was used as an indicator of good crystallinity. In this respect, a desirable R value is 0.500 or less. R value = (I 006 +I 102 ) / I 101 ...(6)

[0070] (Oxidation (Lithization) distance) Line analysis of oxygen elements was performed on the cross-section of the precursor using SEM-EDS, and the distance (depth) from the surface where oxidation and lithium formation occurred simultaneously was measured. The distance at which oxidation (lithization) occurred was measured for three particles, and the average value was defined as the oxidation (lithization) distance. Furthermore, the oxidation (Li-conversion) distance ratio was calculated using equation (7) by dividing the oxidation (Li-conversion) distance by the D50 of the precursor secondary particles and multiplying by 100. Oxidation (Lithization) distance ratio = (Oxidation (Lithization) distance) / D50 × 100 ... (7)

[0071] (Li conversion rate) Carbon content C of raw material mixture powder made by mixing metallic nickel powder and lithium carbonate i And the amount of carbon in the precursor C o The amount was measured, and the proportion of lithium carbonate that decreased during the oxidation process, i.e., reacted with metallic nickel, was calculated using equation (8). The reaction product is lithium metal oxide. It is known that an increase in lithium metal oxide makes it easier for cracks to form in the precursor. In this respect, the li conversion rate can be used as an indicator of how easily it can be crushed. Percentage of lithium carbonate reacted with metallic nickel M Li =(C i -C o ) / C i ...(8) Metallic nickel and lithium carbonate in raw material mixed powder Metal elements Molar ratio (M Li / Ni ) and M Li From this, the proportion of metallic nickel that reacted with Li to become Li (Li conversion rate) was calculated using equation (9). Li conversion rate=M Li / Ni × M Li × 100 ...(9)

[0072] (Residual Li amount) 0.5 g of positive electrode active material and 30 ml of pure water were placed in a 50 ml plastic container. After replacing the contents of the container with argon gas, the mixture was stirred for 1 hour to extract the Li component, and the extract was obtained by suction filtration. 15 ml of the obtained extract was diluted to approximately 40 ml with pure water and titrated with 0.02 M hydrochloric acid to analyze the amounts of Li2CO3 and LiOH components in the extract. An automatic titrator (Hiranuma, COM-1700A) was used for the titration. The titration curve was in two stages; the equivalence point (x) of the first stage represents the reactions of equations (10) and (11), and the equivalence point (y) of the second stage represents the reaction of equation (11). Since the number of moles of Li2CO3 in equation (10) is the same as the number of moles of HCl in equation (12), the amount of residual Li2CO3 was defined as the titration volume between the equivalence points of the first and second stages (yx). The amount of residual LiOH is the titration volume up to the equivalence point of the first stage. However, since equation (11) is also included in the titration volume up to the first stage, we used the amount obtained by subtracting equation (11), i.e., the amount of residual Li2CO3, from (2x-y). We also calculated the amount of Li in the residual Li2CO3 and residual LiOH, i.e., the amount of unreacted Li. We calculated the unreacted Li percentage by dividing the number of moles of unreacted Li by the number of moles of other metal elements contained in the positive electrode active material and multiplying by 100. LiOH + HCl → LiCl + H2O ... (10) Li2CO3+HCl→LiCl+LiHCO3···(11) LiHCO3+HCl→LiCl+CO2+H2O···(12)

[0073] (Metallic Ni residual level) After removing Kα2 from the XRD pattern obtained by measuring the precursor, the peak intensity of NiO around 2θ = 43.2° (I NiO ) and the peak intensity of LiNiO2 around 2θ=43.6° (I LiNiO2 ) and the peak intensity of metallic Ni around 2θ=44.5° (I Ni The remaining amount of metallic Ni was calculated from the above using equation (13). Metallic Ni residual level=I Ni / ( I NiO +I LiNiO2 )···(13)

[0074] [Oxidation process of metallic nickel powder] [Preliminary Experiment 1] D50 was produced using an 8μm water atomization method using metallic nickel powder (manufactured by Nippon Atomize Processing). Li:Ni was weighed in such a molar ratio of 1.03:0.85. A total of 5 kg of these raw material powders was placed in a 45L V-type mixer and mixed for 90 minutes to obtain a raw material mixture. Next, this raw material mixture was heat-treated in an air-filled furnace at 650°C for 10 hours to obtain an oxidized powder. Although some of the oxidized powder was caking, it was possible to obtain an oxidized powder equivalent to the 8μm precursor of D50 by crushing it in a mortar. .

[0075] [Preliminary Experiment 2] The oxidation process was carried out in the same manner as in preliminary experiment 1, except that metallic nickel powder and lithium carbonate were weighed so that the molar ratio of the metal elements was Li:Ni 0.10:0.85. Although some of the oxidized powder caked, it was crushed in a mortar and pestle to obtain oxidized powder with a D50 of 8 μm. Note that a molar ratio of metallic nickel powder to lithium carbonate of Li:Ni 0.10:0.85 means that metallic nickel powder was mixed with 10% by mass of the lithium-containing compound necessary for production. For comparison, in preliminary experiment 1, 100% by mass of the same lithium-containing compound was mixed.

[0076] Preliminary experiments 1 and 2 confirmed that by mixing metallic nickel powder with at least a portion of the lithium-containing compound (in this case, lithium carbonate) necessary for manufacturing, and then performing an oxidation treatment, oxidation could be carried out while preventing the sintering of the metallic nickel powder. This is thought to be because the lithium-containing compound interposed between the metallic nickel powders prevented contact between the powders, and as a result, the sintering of the metallic nickel powder was prevented.

[0077] [Example 1] As raw materials, lithium carbonate, metallic nickel powder, cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide were prepared. Each raw material was weighed so that the molar ratio of the metal elements Li:Ni:Co:Mn:Ti:Al was 0.26:0.85:0.03:0.08:0.03:0.01. In addition, lithium hydroxide was prepared separately and weighed so that the molar ratio of the metal elements Li:metals other than lithium was 0.77:1.00. For the metallic nickel powder, a D50 of 8 μm was used, which was produced by the water atomization method. First, metallic nickel powder and lithium carbonate equivalent to 25% by mass were placed in a V-type mixer and mixed for 90 minutes to obtain a raw material mixture. Next, 100g of the raw material mixture was placed in a 150mm square sagger and subjected to an oxidation treatment (oxidation process) in a firing furnace under an atmospheric atmosphere at 650°C for 10 hours to obtain a precursor containing oxidized metallic nickel powder. The obtained precursor had a mass increase of 17% compared to the raw material mixture. Based on this mass increase rate, it was confirmed that 68% of the metallic nickel powder was nickel oxide. In other words, the oxidation rate was 68%.

[0078] Furthermore, the raw materials for metal element M, consisting of cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide, were pre-ground using a ball mill with Φ5 mm zirconia balls as the grinding medium to obtain pre-ground powder of metal element M. The D50 of the pre-ground powder of metal element M was 1.2 μm. As shown in the flow chart in Figure 3, the above-mentioned precursor, the pre-ground powder of the above-mentioned metal element M, and the above-mentioned lithium hydroxide equivalent to 75% by mass were dry-mixed and calcined in a furnace with an oxygen gas atmosphere at 500°C for 20 hours in an oxygen stream. Subsequently, the mixture was calcined in a furnace with an oxygen gas atmosphere at 840°C for 10 hours in an oxygen stream. A positive electrode active material consisting of a lithium metal composite oxide was obtained.

[0079] [Example 2] The precursor and cathode active material were produced in the same manner as in Example 1, except that the oxidation treatment temperature in the oxidation process was 550°C for 10 hours. The oxidation rate of the precursor was 49%.

[0080] [Comparative Example 1] The precursor and cathode active material were produced in the same manner as in Example 1, except that the oxidation treatment temperature in the oxidation process was 400°C for 10 hours. The oxidation rate of the precursor was 7%.

[0081] [Comparative Example 2] The precursor and cathode active material were produced in the same manner as in Example 1, except that the amount of raw material mixture powder loaded into the sagger during the oxidation process was 500g. The oxidation rate of the precursor was 77%. In this example, the loading amount was changed to observe the change in oxidation rate.

[0082] [Comparative Example 3] In Comparative Example 3, a raw material containing metal element M was used as an inclusion. Metallic nickel powder, cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide were prepared as raw materials, and each raw material was weighed so that the molar ratio of the metal elements Ni:Co:Mn:Ti:Al was 0.85:0.03:0.08:0.03:0.01. In addition, lithium hydroxide was prepared and weighed so that the molar ratio of the metal elements Li:metal elements other than lithium was 1.03:1.00. For the metallic nickel powder, a D50 of 8 μm was used, which was produced by the water atomization method. First, the raw materials for metal element M, consisting of cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide, were pre-ground using a ball mill with Φ5 mm zirconia balls as the grinding medium to obtain pre-ground powder of metal element M. The D50 of the pre-ground powder of metal element M was 1.2 μm. Next, metallic nickel powder and pre-ground metallic element M were placed in a V-type mixer and mixed for 90 minutes to obtain a raw material mixture. Then, 50 g of the raw material mixture was placed in a 150 mm square sagger and subjected to an oxidation treatment (oxidation process) in a firing furnace under an atmospheric atmosphere at 550°C for 10 hours to obtain a precursor containing oxidized metallic nickel powder. The mass of the obtained precursor increased by 7.7% compared to the raw material mixture. Based on this mass increase rate, it was confirmed that 62% of the metallic nickel powder was nickel oxide. In other words, the oxidation rate was 62%.

[0083] The above precursor and the above lithium hydroxide were dry-mixed and calcined in a furnace with an oxygen gas atmosphere at 500°C for 20 hours in an oxygen stream. Subsequently, the mixture was calcined in a furnace with an oxygen gas atmosphere at 840°C for 10 hours in an oxygen stream. A positive electrode active material consisting of a lithium metal composite oxide was obtained.

[0084] [Comparative Example 4] The precursor and cathode active material were produced in the same manner as in Comparative Example 3, except that the oxidation treatment temperature in the oxidation process was 500°C for 10 hours. The oxidation rate of the precursor was 42%.

[0085] Table 1 shows the oxidation rates of the precursors for Examples 1 and 2 and Comparative Examples 1 to 4. X-ray powder diffraction (XRD) measurements were also performed on the precursors and cathode active materials of Examples 1 and 2 and Comparative Examples 1 to 4. Figure 7 shows the XRD patterns of the precursors for Examples 1 and 2 and Comparative Examples 1 and 2, and Figure 8 shows the XRD patterns of the cathode active materials. Furthermore, the crystallite size of nickel oxide contained in the precursors, calculated from the XRD measurements of the precursors and cathode active materials of Examples 1 and 2 and Comparative Examples 1 to 4, and the above-mentioned I NiO , I LNO , I Ni , I LNO / I Ni , ILNO / I NiO Table 1 shows the residual metallic Ni content and the R-value of the positive electrode active material. Figure 9 shows the relationship between the oxidation rate and R-value of Examples 1 and 2 and Comparative Examples 1 and 2. Furthermore, electron probe microanalyzer (EPMA) analysis was performed on the particle cross-section of the positive electrode active material of Example 1. The results are shown in Figure 10. Figure 14 shows a cross-sectional SEM image of the positive electrode active material of Example 1.

[0086] [Table 1-1]

[0087] [Table 1-2]

[0088] From Table 1 (Table 1-1, Table 1-2) and Figure 7, it was confirmed that the precursors of Examples 1 and 2 and Comparative Examples 1-4 were composed of oxidized metallic nickel powder, with a portion being nickel oxide. From Figure 8, the positive electrode active materials of Examples 1 and 2 and Comparative Examples 1-4 all showed peaks attributed to the 003 plane around 2θ=18°, the 101 plane around 2θ=36°, the 006 plane around 2θ=37°, the 012 plane around 2θ=38°, the 104 plane around 2θ=44°, the 015 plane around 2θ=48°, and the 107 plane around 2θ=58°, confirming that they are layered lithium metal composite oxides belonging to space group R3-m.

[0089] Furthermore, as shown in Table 1 and Figure 9, Examples 1 and 2, with oxidation rates of 10% to 70%, had lower R values ​​than Comparative Example 1 (with an oxidation rate of 7%) and Comparative Example 2 (with an oxidation rate of 77%), confirming that good crystallinity was obtained for the positive electrode active material. From this, it was found that an oxidation rate of 10% to 70% is desirable. It was also confirmed that the R value is low when the oxidation rate is 49% or higher and the crystallite size of the nickel oxide contained in the precursor is 100 nm or less. Note that while the oxidation rate in Example 1 was 68%, it was higher in Comparative Example 2 at 77%. The increase in oxidation rate is thought to be due to a change in the atmospheric airflow caused by the change in the amount of material loaded, which increased the amount of oxygen supplied to the metallic nickel powder. Therefore, the oxidation rate of metallic nickel powder can be controlled not only by the oxidation treatment temperature but also by the time and heat treatment atmosphere.

[0090] Table 1 shows that the oxidation rates of the precursors in Examples 1 and 2, which used lithium carbonate as an inclusion, and the precursors in Comparative Examples 3 and 4, which used metal element M as an inclusion, are equivalent. On the other hand, Table 1 shows I LNO / I Ni Furthermore, the precursors of Examples 1 and 2 show the formation of lithium metal oxide (LNO) in addition to Ni(NiO) oxide, while the precursors of Comparative Examples 3 and 4 show almost no formation of lithium metal oxide. In addition, the positive electrode active materials of Examples 1 and 2 have a lower R value of 0.500 or less compared to the positive electrode active materials of Comparative Examples 3 and 4, confirming that good crystallinity can be obtained. That is, despite having the same oxidation rate, using the precursors of Examples 1 and 2, which contain lithium metal oxide, resulted in positive electrode active materials with better crystallinity compared to using the precursors of Comparative Examples 3 and 4, which do not contain lithium metal oxide. From the above, it was found that including lithium metal oxide in the precursor yields positive electrode active materials with good crystallinity. LNO / I Ni It was found that a value of 0.02 or higher is desirable. Furthermore, since it is necessary to use a lithium-containing compound as an inclusion in order to produce lithium metal oxide in the precursor, it was confirmed that a cathode active material with good crystallinity can be produced by using a lithium-containing compound as an inclusion.

[0091] Furthermore, observations in Figure 10 confirmed that nickel and cobalt were uniformly distributed within the positive electrode active material, indicating that cobalt was diffused within the metallic nickel powder. This confirms that, with a suitable precursor, a positive electrode active material with a uniform composition can be produced without a grinding process during manufacturing. This is further confirmed by the SEM image in Figure 14, which shows a dense positive electrode active material with no visible voids, as no grinding process was performed.

[0092] As described above, by using the precursor of the present invention, acid dissolution and coprecipitation steps are unnecessary, and the cathode active material can be manufactured simply. Furthermore, since the cathode active material can be manufactured by oxidation treatment without going through compounds such as nickel sulfate or nickel hydroxide, and without crushing metallic nickel powder, the manufacturing process is shortened and the amount of material transported between manufacturing steps is reduced. Moreover, since metallic nickel powder has a higher nickel content and a higher specific gravity compared to nickel sulfate, nickel hydroxide, etc., the volume to be transported is smaller, and the energy required for transportation (transportation costs, etc.) can be reduced. As a result, greenhouse gas (GHG) emissions can be reduced by about 30-40%, and as a result, the cathode active material can be manufactured while suppressing GHG emissions.

[0093] Furthermore, while water is required for the production of nickel sulfate and nickel hydroxide, the present invention allows for the production of positive electrode active material by oxidation treatment from metallic nickel powder, thereby significantly reducing water usage. Moreover, while the production of nickel hydroxide generates by-products such as sodium sulfate that must be disposed of, the present invention does not produce any by-products, eliminating the need to treat waste and enabling the production of positive electrode active material while minimizing environmental impact.

[0094] Next, we will explain the effect of the particle size of metallic nickel powder on the electrochemical properties of the positive electrode active material, and then describe an example in which a lithium-containing compound is added separately.

[0095] [Reference example 1] A precursor was prepared in the same manner as in Example 1, except that D50 was 30 μm metallic nickel powder, and then a cathode active material was prepared in the same manner as in Example 1.

[0096] [Reference example 2] A precursor was prepared in the same manner as in Example 1, except that D50 was 70 μm metallic nickel powder, and then a cathode active material was prepared in the same manner as in Example 1.

[0097] The XRD of the positive electrode active materials in Reference Examples 1 and 2 was measured, and the R value was calculated. The results are shown in Table 2. In addition, the Ni ratio in the center of the particle cross-section of the positive electrode active material was measured by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), and the results are shown in Table 2. Furthermore, the relationship between the D50 of metallic nickel powder and the Ni ratio in the center of the positive electrode active material is shown in Figure 11. Note that the results for Example 1 are also included in Table 2. Based on the above, the influence of the D50 of metallic nickel powder was evaluated.

[0098] [Table 2]

[0099] Table 2 and Figure 11 show that when the D50 of metallic nickel powder is 30 μm or higher, the R value is high, the crystallinity is low, and the Ni ratio in the center of the positive electrode active material is high. In other words, it can be seen that metallic elements other than nickel and lithium do not easily diffuse to the center. On the other hand, as shown in Figure 11, when the D50 of metallic nickel powder is 20 μm or lower, the Ni ratio in the center of the positive electrode active material becomes about 95%, and it was found that metallic elements other than nickel and lithium diffuse more easily. When metallic elements other than lithium diffuse more, the composition of the positive electrode active material becomes more uniform, and it is preferable because the electrochemical properties expected for the desired composition can be obtained. Therefore, if the D50 of metallic nickel powder is 20 μm or lower, metallic nickel powder can be used directly as a raw material, and there is no need to grind it afterward, so the grinding process can be omitted and the process can be simplified.

[0100] On the other hand, even if the D50 of the metallic nickel powder exceeds 20 μm, if a crude precursor containing nickel oxide with an oxidation rate of 10% to 70% (the precursors in Reference Examples 1 and 2) is pulverized to 20 μm or less and used, then, similar to the examples, metal elements other than nickel and lithium can diffuse to the center during the manufacturing process of the positive electrode active material, resulting in a uniform composition and the acquisition of the desired electrochemical properties.

[0101] [Example 3] As raw materials, lithium carbonate, metallic nickel powder, cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide were prepared. Each raw material was weighed so that the molar ratio of the metal elements Li:Ni:Co:Mn:Ti:Al was 1.03:0.85:0.03:0.08:0.03:0.01. For the metallic nickel powder, a D50 of 8 μm was used, which was produced by the water atomization method. In this example, lithium carbonate and metallic nickel powder equivalent to 100% by mass were placed in a V-type mixer and mixed for 90 minutes to obtain a raw material mixture. Next, this raw material mixture was subjected to an oxidation treatment (oxidation process) in a firing furnace under an atmospheric atmosphere at 650°C for 10 hours to obtain a precursor containing oxidized metallic nickel powder.

[0102] Next, following the flow shown in Figure 4, the obtained precursor was mixed with raw materials of metal element M consisting of cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide, and pure water was added to achieve a solid content ratio of 30% by mass. Then, the mixture was wet-ground in a pulverizer to prepare a raw material slurry with a primary particle D50 of 0.3 μm (grinding step). Subsequently, the obtained raw material slurry was spray-dried using a nozzle-type spray dryer (Okawara Chemical Machinery Co., Ltd., ODL-20 model) to obtain granulated powder with a D50 of approximately 10 μm (granulation step). In this example, since the lithium necessary for the production of the target cathode active material was entirely contained in the precursor, the addition and mixing step of lithium-containing compounds was not performed. Therefore, the dried granulated powder was calcined to obtain a lithium metal composite oxide (calcination step). Specifically, it was calcined in a calcination furnace with an oxygen gas atmosphere, at 700°C for 24 hours in an oxygen stream. Subsequently, a lithium metal composite oxide was obtained by calcining in a furnace with an oxygen gas atmosphere, at 840°C for 10 hours in an oxygen stream. The calcined powder obtained from the calcination process was classified using a sieve with a mesh size of 53 μm, and the powder below the sieve was used as the positive electrode active material.

[0103] [Example 4] As raw materials, lithium carbonate, metallic nickel powder, cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide were prepared. Each raw material was weighed so that the molar ratio of the metal elements Li:Ni:Co:Mn:Ti:Al was 1.03:0.85:0.03:0.08:0.03:0.01. For the metallic nickel powder, a D50 of 8 μm was used, which was produced by the water atomization method. First, 50% by mass of lithium carbonate (pre-added) and metallic nickel powder were placed in a V-type mixer and mixed for 90 minutes to obtain a raw material mixture powder, with the molar ratio of lithium to nickel being 0.52:0.85. Next, this raw material mixture powder was subjected to an oxidation treatment (oxidation process) in a firing furnace under an air atmosphere at 650°C for 10 hours to obtain a precursor containing oxidized metallic nickel powder.

[0104] Next, following the flow shown in Figure 5, the obtained precursor was mixed with raw materials of metal element M consisting of cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide, and pure water was added to achieve a solid content ratio of 30% by mass. Then, the raw material slurry was prepared by wet grinding in a pulverizer to obtain primary particle D50 of 0.30 μm (grinding process). Subsequently, the obtained raw material slurry was spray-dried using a nozzle-type spray dryer (Okawara Chemical Machinery Co., Ltd., ODL-20 model) to obtain granulated powder with a D50 of approximately 10 μm (granulation process). This granulated powder and the remaining 50% by mass of lithium carbonate (added later) were put into a V-type mixer and mixed for 90 minutes to obtain mixed granulated powder. In this example, the addition and mixing process of a lithium-containing compound was performed. Then, this mixed granulated powder was calcined to obtain a lithium metal composite oxide (calcination process). Specifically, it was calcined in a calcination furnace with an oxygen gas atmosphere, at 700°C for 24 hours in an oxygen stream. Subsequently, a lithium metal composite oxide was obtained by calcining in a furnace with an oxygen gas atmosphere, at 840°C for 10 hours in an oxygen stream. The calcined powder obtained from the calcination process was classified using a sieve with a mesh size of 53 μm, and the powder below the sieve was used as the positive electrode active material.

[0105] [Example 5] The precursor and cathode active material were manufactured in the same manner as in Example 4, except that 25% by mass of lithium carbonate and metallic nickel powder were added to a V-type mixer so that the molar ratio of lithium to nickel was Li:Ni 0.26:0.85, and the firing temperature in the main firing was set to 820°C. The reason for lowering the firing temperature is as follows: By mixing 25% by mass of lithium carbonate before the oxidation process and adding the remaining 75% by mass after the granulation process, the amount of lithium carbonate in the mixed granulated powder is reduced. As a result, the oxidized metallic nickel powder particles in the mixed granulated powder come into close proximity, the reaction is promoted, and the appropriate firing temperature is lowered.

[0106] Examples 3 to 5 investigate the effect of pre-addition and post-addition of lithium-containing compounds on the amount of compound mixed. Specifically, when the amount of lithium compound required to produce the target cathode active material is considered to be 100% by mass, the amount of lithium-containing compound mixed before the oxidation process was 100% by mass in Example 3, 50% by mass in Example 4, and 25% by mass in Example 5 (pre-addition). In Examples 4 and 5, the remaining lithium compound was added after the granulation process, representing a post-addition example. Cross-sectional SEM observations were performed on the positive electrode active materials of Examples 3 and 5, which differed significantly in their mixing ratios. A photograph of Example 3 is shown in Figure 12, and a photograph of Example 5 is shown in Figure 13. Furthermore, the oil absorption capacity of the positive electrode active materials and the particle strength of Examples 3-5 were measured. These results are shown in Table 3.

[0107] (Fabrication of the positive electrode) Next, lithium-ion secondary batteries were fabricated using the positive electrode active materials synthesized in Examples 3-5 as the positive electrode material, and the initial capacity and capacity retention rate of the lithium-ion secondary batteries were measured. First, the fabricated positive electrode active material, a carbon-based conductive material, and a binder pre-dissolved in N-methyl-2-pyrrolidone (NMP) were mixed in a mass ratio of 92.5:5:2.5. Then, the uniformly mixed positive electrode mixture slurry was applied to a 15 μm thick aluminum foil positive electrode current collector at a rate of 13 mg / cm². 2 The mixture was applied in this manner. Next, the positive electrode slurry applied to the positive electrode current collector was heat-treated at 120°C to remove the solvent and form a positive electrode slurry layer. After that, the positive electrode slurry layer was pressure-molded using a hot press and punched out into a circular shape with a diameter of 15 mm to form the positive electrode.

[0108] (Initial capacity, charge / discharge cycle characteristics (capacity retention rate)) Next, a lithium-ion secondary battery was fabricated using the prepared positive electrode, negative electrode, and separator. For the negative electrode, metallic lithium punched into a circular shape with a diameter of 16 mm was used. For the separator, a porous polypropylene separator with a thickness of 30 μm was used. The lithium-ion secondary battery was assembled by placing the positive electrode and negative electrode opposite each other in a non-aqueous electrolyte with the separator in between. As the non-aqueous electrolyte, a solution was used in which LiPF6 was dissolved at a concentration of 1.0 mol / L in a solvent prepared by mixing ethylene carbonate and dimethyl carbonate in a volume ratio of 3:7.

[0109] The fabricated lithium-ion secondary battery was charged at 25°C with a constant current / voltage of 38 A / kg (based on the mass of the positive electrode mixture) and an upper potential limit of 4.3 V. Then, it was discharged to a lower potential limit of 2.5 V with a constant current of 40 A / kg (based on the mass of the positive electrode mixture), and the charge and discharge capacities were measured. Subsequently, it was charged again with a constant current / voltage of 190 A / kg (based on the mass of the positive electrode mixture) and an upper potential limit of 4.3 V. This cycle of charging and discharging to a lower potential limit of 2.5 V with a constant current of 190 A / kg (based on the mass of the positive electrode mixture) was repeated for a total of 30 cycles, and the discharge capacity after 30 cycles was measured. The capacity retention rate was calculated as the fraction of the discharge capacity after 30 cycles relative to the initial capacity. The results are shown in Table 3.

[0110] [Table 3]

[0111] From the cross-sectional SEM observation images in Figures 12 and 13, it can be seen that the positive electrode active material of Example 5, in which 25% by mass of lithium carbonate was mixed before the oxidation process, has a more porous structure than the positive electrode active material of Example 3, in which 100% by mass of lithium carbonate was mixed before the oxidation process. We believe that a large amount of lithium carbonate in the granulated powder, with scattered oxidized metallic nickel powder, results in a porous structure after firing. Therefore, in Example 3, where a large amount of lithium carbonate was present in the granulated powder, scattered oxidized metallic nickel resulted in a porous structure after firing. On the other hand, in Examples 4 and 5, where the amount of lithium carbonate mixed before the oxidation process was reduced, the amount of lithium carbonate in the granulated powder decreased, the scattering of oxidized metallic nickel powder was eliminated, and a porous structure was obtained. Therefore, with the decrease in the amount of lithium carbonate mixed before the oxidation process, the amount of oil absorbed decreased. The decrease in oil absorbed indicates a decrease in voids within the positive electrode active material. As a result, it was found that the particle strength became higher.

[0112] Table 3 shows that the positive electrode active materials in Examples 3-5 have high initial capacities of 187 Ah / kg or more. Furthermore, Examples 4 and 5, in which the amount of lithium carbonate mixed before the oxidation process was 50% by mass or less, showed good capacity retention rates of 90% or more. In other words, it was confirmed that by limiting the amount of lithium carbonate mixed before the oxidation process to 50% by mass or less, a positive electrode active material with fewer voids and high strength can be obtained, resulting in good cycle characteristics.

[0113] Next, we will describe preliminary experiments regarding the grinding process of the crude precursor, and then we will describe the examples.

[0114] [Preliminary Experiment 3] For the crude precursor of Reference Example 2, carbon content was measured and cross-sectional SEM observation was performed to calculate the Li conversion rate, oil absorption amount, and oxidation (Li conversion) distance mentioned above. The results are shown in Table 4.

[0115] Next, the crude precursor from Reference Example 2 was mixed with raw materials for metal element M consisting of cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide. 200g of this mixed powder was placed in a plastic pot container, 200g of pure water and 200g of zirconia balls (made by Nikatoh) with a ball diameter of 5mm were added as media, and the mixture was ground at a rotation speed of 90 rpm for 64 hours to obtain a ground slurry (coarse grinding process). After coarse grinding, the D50 was 2.9 μm and the D95 was 10.1 μm. Next, we attempted to finely grind the obtained pulverized slurry using a pulverizer, but we were unable to achieve fine grinding. The reason for this will be explained later.

[0116] [Example 6] As raw materials, lithium carbonate, metallic nickel powder, cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide were prepared. Each raw material was weighed so that the molar ratio of the metal elements Li:Ni:Co:Mn:Ti:Al was 1.03:0.85:0.03:0.08:0.03:0.01. For the metallic nickel powder, a D50 of 70 μm and a D95 of 176 μm was used. 25% by mass of lithium carbonate and metallic nickel powder were added to a V-type mixer so that the molar ratio of lithium to nickel was Li:Ni of 0.26:0.85. The mixture was mixed for 120 minutes to obtain a raw material mixture powder. Next, this raw material mixture powder was subjected to an oxidation treatment (oxidation process) in a firing furnace under an air atmosphere at 700°C for 4 hours to obtain a crude precursor containing oxidized metallic nickel powder. The oxidation rate was 69%. Furthermore, carbon content measurement, cross-sectional SEM observation, and XRD measurement were performed on this crude precursor to determine the Li conversion rate, oil absorption amount, oxidation (Li conversion) distance, oxidation (Li conversion) distance rate, and I LNO / I Ni , I LNO / I NiO、 The following was calculated. The results are shown in Table 4.

[0117] Next, following the flow shown in Figure 6, the obtained crude precursor was mixed with raw materials of metal element M consisting of cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide. 200g of this mixed powder was placed in a plastic pot container, 200g of pure water and 200g of zirconia balls (manufactured by Nikkatoh) with a ball diameter of 5mm were added as media, and the mixture was ground at a rotation speed of 90 rpm for 64 hours to obtain a ground slurry (coarse grinding process). The particle size distribution after coarse grinding was measured. The results are shown in Table 4.

[0118] Next, to finely grind the obtained pulverized slurry, it was wet-ground in a grinder to prepare the raw material slurry so that the D50 was 0.3 μm (fine grinding step). The particle size distribution after fine grinding is shown in Table 4. Subsequently, the obtained raw material slurry was spray-dried using a nozzle-type spray dryer (Okawara Chemical Machinery Co., Ltd., ODL-20 model) to obtain granulated powder with a D50 of approximately 10 μm (granulation step). Then, the dried granulated powder and 75% by mass of the remaining lithium carbonate, such that the molar ratio of lithium to nickel was Li:Ni 1.03:0.85, were put into a V-type mixer to obtain mixed granulated powder. The obtained mixed granulated powder was calcined to obtain lithium metal composite oxide (calcination step). Specifically, it was calcined in a calcination furnace with an oxygen gas atmosphere, at 700°C for 24 hours in an oxygen stream. Subsequently, a lithium metal composite oxide was obtained by calcining in a furnace with an oxygen gas atmosphere, at 820°C for 10 hours in an oxygen stream. The calcined powder obtained from the calcination process was classified using a sieve with a mesh size of 53 μm, and the powder below the sieve was used as the positive electrode active material.

[0119] [Examples 7-9] Except for changing the oxidation treatment time in the oxidation process to 8 hours in Example 7, 10 hours in Example 8, and 30 hours in Example 9, a crude precursor was obtained in the same manner as in Example 6, and a positive electrode active material was produced by the same method. Similarly, the degree of oxidation, Li conversion rate, oil absorption amount, oxidation (Li conversion) distance, oxidation (Li conversion) distance rate, and I were measured for the crude precursor. LNO / I Ni , I LNO / I NiO The residual amount of metallic Ni was calculated. The particle size distribution was also measured after coarse and fine grinding. The results are shown in Table 4.

[0120] Next, to investigate the influence of the precursor powder properties on the powder and electrochemical properties of the positive electrode active material, the residual LiOH content, residual Li2CO3 content, unreacted Li percentage, specific surface area, oil absorption, and R value of the positive electrode active material obtained in Examples 6-9 were determined. These results are shown in Table 5. Furthermore, positive electrodes and lithium-ion secondary batteries were fabricated using the same method as in Examples 3-5, and the initial capacity was measured to evaluate the Coulomb efficiency and charge-discharge cycle characteristics (capacity retention rate). These results are shown in Table 5. Coulomb efficiency is a battery characteristic expressed as discharge capacity / charge capacity, and it indicates the percentage of Li ions that were able to return to the positive electrode material by discharge among the Li ions that were desorbed during the initial charge. A higher value indicates better performance.

[0121] [Table 4-1]

[0122] [Table 4-2]

[0123] [Table 5]

[0124] Table 4 shows that, as in Examples 6-9, even when using metallic nickel powder with a D50 of 70 μm, precursors with an oxidation rate of 65% or higher were obtained while preventing sintering by mixing (pre-adding) lithium carbonate before the oxidation process. Furthermore, the Li conversion rate increased with increasing oxidation treatment time, indicating a decrease in the unreacted Li content, and that the reaction between the lithium source and metal sources such as nickel progressed, leading to the formation of lithium metal oxide. The Li conversion rate can be used as an indicator of ease of pulverization, but an increase in the Li conversion rate suggests that the amount of lithium metal oxide in the precursor increases, and this volume expansion makes it easier for cracks to form within the precursor. In addition, in the precursors of Examples 6-9, where the Li conversion rate was 12% or higher, the oil absorption of the precursor was 16-18 ml / 100g, which is a considerable increase from 8 ml / 100g in Reference Example 2, where the Li conversion rate was 7%. This also indicates an increase in cracks within the precursor. As a result, in Examples 6-9, the D95 after coarse pulverization was 3 μm or less, making fine pulverization possible. On the other hand, the Li conversion rate in Reference Example 2 was low, less than 10%, and it is thought that fine pulverization was not possible because there were few cracks.

[0125] Furthermore, as shown in Table 5, the higher the Li conversion rate of the precursor, the lower the unreacted Li content of the positive electrode active material. This resulted in a positive electrode active material with good crystallinity and an R value of 0.500 or less, yielding excellent results in terms of initial capacity, Coulomb efficiency, and capacity retention. Thus, it can be said that by increasing the Li conversion rate of the precursor to 10% or more, the reaction Li + M + O2 → LiMO2 (M = Ni, Co, Mn, etc.) is promoted, and electrochemical properties such as initial capacity are improved. From these results, it was found that by appropriately reacting metallic nickel powder with a portion of Li during the oxidation process in the precursor manufacturing, a lithium-ion secondary battery with a stable crystal structure and good electrochemical properties can be obtained.

[0126] Next, we will describe an additional example in which the amount of lithium-containing compound mixed (pre-added) before the oxidation process is reduced.

[0127] [Example 10] The precursor and cathode active material were manufactured in the same manner as in Example 8, except that 10% by mass of lithium carbonate and metallic nickel powder were added to a V-type mixer so that the molar ratio of lithium to nickel was Li:Ni 0.10:0.85. Oil absorption, particle strength, initial volume, and volume retention rate were measured. The results are shown in Table 6. In addition, to compare the effect of the amount of lithium carbonate added on oil absorption and particle strength, data from Examples 3-5 and Example 8 are also included in Table 6.

[0128] [Table 6]

[0129] As shown in Table 6, it was confirmed that positive electrode active material can be produced even when the amount of lithium carbonate added before the oxidation process is 10% by mass. Furthermore, as the amount of lithium carbonate added before the oxidation process decreases, the amount of oil absorbed, which is an indicator of void volume, also decreases, indicating that the amount of void volume can be controlled by the amount of lithium carbonate added before the oxidation process. In other words, it was reconfirmed that positive electrode active material with high particle strength can be obtained by reducing the amount of lithium carbonate added beforehand to create a structure with fewer voids. With such high particle strength, for example, it becomes possible to apply strong shear force when manufacturing the positive electrode, shortening the mixing process of the positive electrode mixture slurry, or it becomes possible to manufacture a high-density positive electrode by increasing the press pressure.

Claims

1. Metallic nickel powder and A mixing step of mixing a lithium-containing compound, The process includes an oxidation step in which the metallic nickel powder is oxidized after mixing. The average particle size of the aforementioned metallic nickel powder is 20 μm or less. The method for producing a precursor of a positive electrode active material for a lithium-ion secondary battery, characterized in that the oxidation step produces a precursor having nickel oxide, wherein the oxidation rate, which indicates the ratio of the amount of nickel oxidized to the total amount of Ni contained, is 10% or more and 70% or less.

2. Metallic nickel powder and A mixing step of mixing a lithium-containing compound, The process includes an oxidation step in which the metallic nickel powder is oxidized after mixing. The average particle size of the aforementioned metallic nickel powder exceeds 20 μm. The method for producing a precursor for a positive electrode active material for lithium-ion secondary batteries is characterized in that the oxidation step yields a precursor having nickel oxide, wherein the oxidation rate, which indicates the ratio of the amount of oxidized nickel to the total amount of Ni contained, is 10% or more and the Li conversion rate is 10% or more.

3. The method for producing a precursor of a positive electrode active material for a lithium-ion secondary battery according to any one of claims 1 to 2, characterized in that the oxidation step is performed by oxidizing the compound containing lithium in an oxidizing atmosphere below the melting point.

4. A method for producing a precursor of a positive electrode active material for a lithium-ion secondary battery, as described in any one of claims 1 to 2, characterized in that, when the amount of lithium compound required for the production of a positive electrode active material for a lithium-ion secondary battery is 100% by mass, the amount of the lithium-containing compound mixed in the mixing step is 10% by mass or more and 100% by mass or less.

5. A method for producing a precursor of a positive electrode active material for a lithium-ion secondary battery according to any one of claims 1 to 2, characterized in that the lithium-containing compound is lithium carbonate.

6. A method for producing a positive electrode active material for a lithium-ion secondary battery, characterized by comprising a calcination step of calcining a precursor produced by the method for producing a positive electrode active material for a lithium-ion secondary battery described in any one of claims 1 to 2 at 700°C to 900°C to obtain a positive electrode active material.

7. The aforementioned precursor, A method for producing a positive electrode active material for a lithium-ion secondary battery according to claim 6, characterized in that a mixed powder is obtained by mixing a lithium-containing compound with at least one of a compound containing a metal element M other than lithium and nickel, and then the calcination step is performed.

8. A method for producing a positive electrode active material for a lithium-ion secondary battery according to claim 7, comprising a grinding step of grinding the mixed powder, a granulation step of subsequently granulating the ground mixed powder to form granulated powder, and performing the calcination step on the granulated powder.

9. The method for producing a positive electrode active material for a lithium-ion secondary battery according to claim 8, characterized in that when the amount of lithium-containing compound mixed in the precursor is less than 100% by mass, the remaining amount of lithium-containing compound is added after the granulation step to form a mixed granulated powder, and the calcination step is performed on the mixed granulated powder.

10. The method for producing a positive electrode active material for a lithium-ion secondary battery according to claim 8, characterized in that the grinding step comprises a coarse grinding step and a fine grinding step.

11. The method for producing a positive electrode active material for a lithium-ion secondary battery according to claim 9, wherein the lithium-containing compound mixed before the oxidation step and the lithium-containing compound added after the granulation step are different compounds, and the melting point of the lithium-containing compound mixed before the oxidation step is higher than the melting point of the lithium-containing compound added after the granulation step.

12. The method for producing a positive electrode active material for a lithium-ion secondary battery according to claim 6, characterized in that the positive electrode active material for a lithium-ion secondary battery is represented by the following compositional formula (1). Li １＋ａ Ni ｂ M （１－ｂ） O ２＋α ・・・(1) (However, in formula (1) above, M is a metallic element other than Li and Ni, and a, b, and α are numbers that satisfy -0.1 ≤ a ≤ 0.2, 0.6 ≤ b ≤ 1.0, and -0.2 ≤ α ≤ 0.2.)

13. Metallic nickel powder and A mixing step of mixing a lithium-containing compound, The process includes an oxidation step in which the metallic nickel powder is oxidized after mixing. The oxidation step involves obtaining a precursor having nickel oxide, wherein the oxidation rate, which represents the ratio of the amount of nickel oxidized to the total amount of Ni contained, is 10% or more and 70% or less. The process involves mixing the precursor with a compound containing a metal element M other than lithium and nickel to form a mixed powder, and then grinding the mixed powder. A granulation process in which the crushed mixed powder is granulated to produce granulated powder, When the amount of lithium compound required for the production of a positive electrode active material for lithium-ion secondary batteries is set to 100% by mass, if the amount of lithium-containing compound mixed in the precursor is less than 100% by mass, the remaining amount of the lithium-containing compound is added after the granulation step to form a mixed granulated powder. A method for producing a positive electrode active material for a lithium-ion secondary battery, characterized by comprising a firing step of firing the mixed granulated powder at 700°C to 900°C to obtain a positive electrode active material.

14. The method for producing a positive electrode active material for a lithium-ion secondary battery according to claim 13, characterized in that the grinding step comprises a coarse grinding step and a fine grinding step.

15. A method for producing a positive electrode active material for a lithium-ion secondary battery according to any one of Claim 13, wherein the lithium-containing compound mixed before the oxidation step and the lithium-containing compound added after the granulation step are different compounds, and the melting point of the lithium-containing compound mixed before the oxidation step is higher than the melting point of the lithium-containing compound added after the granulation step.

16. The method for producing a positive electrode active material for a lithium-ion secondary battery according to claim 13, characterized in that the positive electrode active material for a lithium-ion secondary battery is represented by the following composition formula (1). Li 1+a Ni b M (1-b) O 2+α ... (1) (However, in formula (1) above, M is a metallic element other than Li and Ni, and a, b, and α are numbers that satisfy -0.1 ≤ a ≤ 0.2, 0.6 ≤ b ≤ 1.0, and -0.2 ≤ α ≤ 0.2.)

17. A precursor for a positive electrode active material for a lithium-ion secondary battery, comprising metallic nickel powder and a lithium-containing compound, wherein the oxide contains nickel oxide with an oxidation rate of 10% to 70% of the total nickel content, and the crystallite size of the nickel oxide is 100 nm or less.

18. A precursor for a positive electrode active material for a lithium-ion secondary battery, comprising metallic nickel powder and a lithium-containing compound, wherein the oxide contains nickel oxide with an oxidation rate of 10% to 70% of the total nickel content, and further contains lithium metal oxide.

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