Precursor of positive electrode active material for lithium-ion secondary battery, method for producing same, positive electrode active material for lithium-ion secondary battery, and method for producing same

Abstract

The objective of the present invention is to provide: a method for producing a precursor of a positive electrode active material for a lithium-ion secondary battery which contributes to a reduction in GHG emissions and is easily pulverized; and a method for producing a positive electrode active material for a lithium-ion secondary battery. In addition, the objective of the present invention is to provide: a precursor which can be easily pulverized; and a positive electrode active material for a lithium-ion secondary battery which has a stable crystal structure and good electrochemical characteristics.　The method for producing a precursor of a positive electrode active material for a lithium-ion secondary battery includes: a mixing step for mixing a metallic nickel powder and a lithium-containing compound; and an oxidation step for oxidizing the metallic nickel powder after mixing, wherein the precursor obtained after the oxidation step includes a lithium metal oxide having a peak at 2θ=43.5-44.0° as measured by X-ray powder diffraction.

Description

Precursor of positive electrode active material for lithium ion secondary battery and method for producing same, and positive electrode active material for lithium ion secondary battery and method for producing same

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

[0002] Lithium-ion secondary batteries are widely used in various fields, including electronics, automobiles, and infrastructure. In particular, lithium-ion secondary batteries are used as a power source for electric vehicles (EVs) and are an important core component in automobiles. To extend driving 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 these batteries. These ternary layered materials are composite oxides of lithium (Li) and metal elements such as nickel (Ni), cobalt (Co), manganese (Mn), or aluminum (Al) (hereinafter referred to as lithium metal composite oxides). Furthermore, to maintain a sustainable global environment, there is a need to reduce greenhouse gas (GHG) emissions associated with the production of positive electrode active materials.

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

[0004] JP 2015-002120 A International Publication No. 2020 / 066262 International Publication No. 2010 / 082240 A

[0005] As described in Patent Documents 1 and 2, positive electrode active materials are generally produced by reacting a lithium source with transition metal hydroxide particles synthesized by a coprecipitation reaction. In the coprecipitation reaction, aqueous solutions such as nickel sulfate are used as raw materials, which are produced by dissolving highly purified nickel bullion in acid to avoid impurities. Nickel sulfate is produced by purifying nickel from nickel ore extracted from mines and then processing it through acid dissolution, resulting in high GHG emissions during production. Furthermore, because nickel sulfate is a hexahydrate, its Ni content is approximately 20-25% by mass, making it low in bulk density. To compensate for this, the volume handled in the production process for positive electrode active materials must be large. At the same time, transportation costs are also high. This increases the energy required for transportation and production, and the production process becomes complicated and lengthy. As a result, there is the problem of high GHG emissions. Furthermore, as mentioned above, nickel sulfate is used as an aqueous solution, which consumes a large amount of water resources. In addition, when nickel sulfate or the like is reacted with sodium hydroxide or ammonia as auxiliary materials to produce hydroxide particles as precursors, sulfide-based waste products such as sodium sulfate and waste liquid containing ammonia are generated as by-products. Processing these sulfide-based waste products is also costly. In Patent Document 3, metallic nickel is fired as is, resulting in sintering during the firing process, making it impossible to maintain the particle state and making it difficult to pulverize. Furthermore, the crystal structure of the positive electrode active material is unstable, which results in unstable electrochemical characteristics of lithium-ion secondary batteries.

[0006] The present invention aims to provide a method for producing a precursor of a positive electrode active material for a lithium ion secondary battery, which can contribute to reducing GHG emissions and improving ease of pulverization, and a method for producing a positive electrode active material for a lithium ion secondary battery. Another object of the present invention is to provide a precursor that is easy to pulverize, and a positive electrode active material for a lithium ion secondary battery that has a stable crystal structure and good electrochemical properties.

[0007] The manufacturing method of the present invention uses, as a nickel source, metallic nickel powder, which is a raw material that emits less GHG during production than conventional nickel sulfate, and is characterized by subjecting the metallic nickel powder to an oxidation reaction with a lithium-containing compound.

[0008] The method for producing a precursor of a positive electrode active material for a lithium ion secondary battery of the present invention includes 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, and is characterized in that the precursor obtained after the oxidation step contains a lithium metal oxide having a peak at 2θ = 43.5° or more and 44.0° or less in X-ray powder diffraction measurement.

[0009] The lithiation rate of the precursor, which indicates the proportion of the metallic nickel powder that has reacted with lithium, is preferably 8% or more.

[0010] In the precursor, it is preferable that the metallic nickel powder has an average particle size of more than 20 μm and the lithiation rate of the precursor is 10% or more.

[0011] The precursor obtained after the oxidation step preferably contains nickel oxide having an oxidation rate, which indicates the ratio of the amount of oxidized nickel to the total amount of Ni contained in the precursor, of 10% or more and less than 100%.

[0012] In addition, in the method for producing a precursor of the present invention, when the amount of the lithium compound necessary for producing a positive electrode active material for a lithium ion secondary battery is taken as 100 mass %, it is preferable that the amount of the lithium-containing compound mixed in the mixing step is 10 mass % or more and less than 100 mass %.

[0013] The method for producing a positive electrode active material for a lithium ion secondary battery of the present invention is characterized by comprising a calcination step of mixing a precursor produced by the method for producing a precursor of a positive electrode active material for a lithium ion secondary battery with at least one of a compound containing lithium and a compound containing a metal element M other than lithium and nickel to obtain a mixed powder, and then calcining the mixed powder at 700°C or higher and 900°C or lower to obtain a positive electrode active material.

[0014] In this case, it is preferable to have a pulverization step of pulverizing the mixed powder, and then a granulation step of granulating the pulverized mixed powder to form granulated powder, and to perform the firing step on the granulated powder.

[0015] The method for producing a positive electrode active material includes a crushing step of crushing the mixed powder, and a granulation step of subsequently granulating the crushed mixed powder to form a granulated powder, wherein the amount of the lithium-containing compound mixed in the precursor is less than 100 mass %, and the remaining amount of the lithium-containing compound is added after the granulation step to form a mixed granulated powder, and the firing step is performed on the mixed granulated powder.

[0016] The pulverization step may include a first pulverization step (coarse pulverization step) and a second pulverization step (fine pulverization step) in which the material is pulverized more finely than in the first pulverization step.

[0017] It is preferable that the media size used in the second crushing step is smaller than the media size used in the first crushing step.

[0018] It is preferred 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.

[0019] Furthermore, the positive electrode active material for a lithium ion secondary battery is preferably represented by the following composition formula (1): Li １＋ａ Ni ｂ M (1-b) O ２＋α ... (1) (In the formula (1), M is a metal element other than Li and Ni, and a, b, and α are numbers that satisfy the following: -0.1≦a≦0.2, 0.5≦b≦1.0, and -0.2≦α≦0.2.)

[0020] On the other hand, the precursor of the positive electrode active material for a lithium ion secondary battery of the present invention is characterized by containing nickel and lithium, and including a lithium metal oxide having a peak at 2θ=43.5° or more and 44.0° or less in X-ray powder diffraction measurement of the precursor, and having a lithiation rate of 8% or more.

[0021] The precursor contains a lithium nickel oxide having a peak at 2θ=43.5° or more and 44.0° or less in X-ray powder diffraction measurement, and the peak intensity I LiNiO2and the peak intensity I of the peak at 2θ=44.0° or more and 45.0° or less, which is attributed to metallic nickel. Ni Intensity ratio I LiNiO2 / I Ni is preferably 0.5 or more.

[0022] The positive electrode active material for a lithium ion secondary battery of the present invention is characterized by having a residual lithium hydroxide (hereinafter referred to as residual LiOH) of 0.6 mol % or less, a porosity of 5 vol % to 15 vol % or less, a mode pore diameter of 10 nm to 250 nm, a particle strength of 30 MPa or more, and containing nickel and lithium.

[0023] Intensity I calculated from the integral value of the peak identified as the 006 plane in the X-ray powder diffraction measurement of the positive electrode active material ００６ and the intensity I calculated from the integral value of the peak identified as the 102 plane. １０２ and the intensity I calculated from the integral value of the peak identified as the 101 plane. １０１ It is preferable that the R value calculated by the following formula based on the above is 0.46 or less. R value = (I ００６ +I １０２ ) / I １０１

[0024] In the following, the "oxidation rate indicating the ratio of the amount of oxidized nickel to the total amount of nickel contained in the precursor" will be simply referred to as the "oxidation rate."

[0025] According to the manufacturing method of the present invention, by producing a precursor of a positive electrode active material for a lithium ion secondary battery using metallic nickel powder, it is possible to reduce the energy used for transportation and manufacturing and eliminate the complexity of the manufacturing process. As a result, it is possible to provide a precursor of a positive electrode active material for a lithium ion secondary battery that is easy to pulverize and contributes to reducing GHG emissions, reducing water resource consumption, and reducing waste disposal, and a method for manufacturing a positive electrode active material for a lithium ion secondary battery using the precursor. Alternatively, it is possible to provide a precursor that is easy to pulverize, or a positive electrode active material for a lithium ion secondary battery that has a stable crystal structure and good electrochemical properties.

[0026] 4A shows the relationship between the grinding time and particle size of the precursor in an example of the method for producing a positive electrode active material for a lithium ion secondary battery of the present invention. FIG. 4B shows the change in average particle size D50 (median particle size) with grinding time, and FIG. 4B shows the change in particle size value of cumulative particle size distribution D95 with grinding time. FIG. 4C shows the relationship between the grinding time and particle size of the precursor in an example of the method for producing a positive electrode active material for a lithium ion secondary battery of the present invention. FIG. 4A shows the change in average particle size D50 (median particle size) with grinding time, and FIG. 4B shows the change in particle size value of cumulative particle size distribution D95 with grinding time. FIG. 4B shows the relationship between the grinding time and particle size value of cumulative particle size distribution D95. FIG. 4C shows the relationship between the grinding time and particle size of the precursor in an example of the method for producing a positive electrode active material for a lithium ion secondary battery of the present invention. FIG. 4B shows the relationship between the grinding time and particle size value of cumulative particle size distribution D95. FIG. 4C shows the relationship between the grinding time and particle size value of cumulative particle size distribution D95. FIG. 4D shows the relationship between the grinding time and particle size value of cumulative particle size distribution D95. FIG. 4D shows the relationship between the grinding time and particle size value of cumulative particle size distribution D95. 11A shows a schematic diagram of pre-addition, and FIG. 11B shows a schematic diagram of post-addition. Cross-sectional SEM images of positive electrode active materials according to examples and comparative examples are shown. FIG. 12A shows an SEM image of the positive electrode active material according to Example 8, FIG. 12B shows an SEM image of the positive electrode active material according to Comparative Example 2, and FIG. 12C shows an SEM image of the positive electrode active material according to Comparative Example 3. Cross-sectional SEM images of positive electrode active materials according to examples and comparative examples are shown after charge-discharge cycling. FIG. 13A shows an SEM image of Example 8, FIG. 13B shows an SEM image of Comparative Example 2, and FIG. 13C shows an SEM image of Comparative Example 3. An SEM image of the positive electrode active material according to Example 13 is shown.

[0027] [Method of Manufacturing Metallic Nickel Powder] Before describing one embodiment of the method of manufacturing a positive electrode active material of the present invention, one embodiment of the method of manufacturing metallic nickel powder will be illustrated. In this embodiment, metallic nickel powder manufactured by, for example, the atomization method or the carbonyl method can be used. Needless to say, metallic nickel powder manufactured by reactive crystallization or a gas-phase reduction method other than the carbonyl method can also be used. The atomization method and the carbonyl method are preferable because they can produce metallic nickel powder with a low amount of impurity elements. Furthermore, the atomization method is preferable for producing spherical powder. High-purity raw materials are used for battery components to prevent short circuits. In particular, iron (Fe) is an impurity element that easily causes short circuits. Therefore, the Fe content of the metallic nickel powder is preferably 100 ppm or less by mass, more preferably 30 ppm or less, and even more preferably 10 ppm or less. Furthermore, high-purity briquettes or cathodes with a grade of Class I are suitable as high-purity nickel sources. In this embodiment, metallic nickel powder is produced by the atomization method, the carbonyl method, or the vapor phase reduction method without dissolving the briquettes or cathodes in acid, thereby obtaining metallic nickel powder with few impurities. Note that the metallic nickel powder in this invention refers to powder made of pure nickel metal that contains almost no oxides such as nickel oxide and has a purity of 99% by mass or more.

[0028] Another method for obtaining metallic nickel powder is the carbonyl process. In the carbonyl process, nickel briquettes or the like 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.

[0029] 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, the average particle size is defined as D50, which is the particle size corresponding to 50% of the smallest particle size in the volume integral curve obtained from the particle size distribution (volume basis) obtained using the laser diffraction particle size distribution analyzer. Furthermore, D95, described below, is the particle size corresponding to 95% of the smallest particle size in the volume integral curve obtained using a similar method. In the method for producing a cathode active material precursor and a cathode active material according to this embodiment, the pulverization step, described below, may be omitted. In this case, the average particle size D50 of the metallic nickel powder is preferably 20 μm or less, more preferably 8 μm or less. When the average particle size D50 of the metallic nickel powder is 20 μm or less, metal elements other than lithium and nickel diffuse to the center of the metallic nickel powder, resulting in a substantially uniform composition within the cathode active material. Furthermore, when the D50 of the metallic nickel powder is 8 μm or less, the composition within the cathode active material becomes more uniform, which is preferable. On the other hand, when a pulverization step is performed, the average particle size D50 of the metallic nickel powder is more than 20 μm with no upper limit, but for example, it may be set to more than 20 μm and not more than 100 μm, and pulverization may be performed after the oxidation step described below. The particle size of the metallic nickel powder can be controlled by the injection pressure of the injected water or gas in the atomization method, and by the thermal decomposition conditions in the carbonyl method. Powder exceeding 100 μm can be removed by sieve classification and returned to melting (recycled) as a raw material for the manufacturing method of metallic nickel powder.

[0030] [Method of Manufacturing a Cathode Active Material Precursor] A method of manufacturing a cathode active material precursor using metallic nickel powder according to one embodiment of the present invention will now be described. As shown in the flowchart of FIG. 1 , metallic nickel powder and a lithium-containing compound are mixed, and an oxidation step is performed to oxidize and lithiate the mixed powder. This mixed powder may contain the entire amount of lithium element required for a cathode active material for a lithium-ion secondary battery manufactured using the precursor obtained by the method of this embodiment, or may contain only a small portion of the required amount of lithium element. In the method of manufacturing a cathode active material according to this embodiment, described below, a cathode active material is obtained by firing in an oxygen-containing atmosphere. Here, by introducing a metallic nickel powder precursor that has undergone an oxidation step, a cathode active material with excellent crystallinity can be manufactured. Here, by performing the oxidation step together with a lithium-containing compound, the metallic nickel powder, the lithium-containing compound, and oxygen react to form a compound of nickel, lithium, and oxygen (hereinafter referred to as lithiation), thereby forming a lithium metal oxide (lithium nickel oxide), which improves pulverizability. In this specification, unless otherwise specified, lithium metal oxide refers to an oxide containing lithium and a metal element other than lithium (e.g., nickel, or a metal element M other than lithium and nickel, as described below), and thus refers to a lithium metal composite oxide. Furthermore, lithium-containing compounds (e.g., lithium carbonate, lithium hydroxide) act as inclusions, preventing sintering of the metallic nickel powder particles during the oxidation process. Therefore, the powder state can be maintained even after the oxidation process, and a powdery precursor can be obtained. It is also possible to mix all or part of a compound containing a metal element M other than lithium and nickel (e.g., Mn, Co, Al, titanium (Ti)) before the oxidation process.

[0031] First, as described above, in the present invention, metallic nickel powder is used as the nickel raw material, so the acid dissolution step and coprecipitation step are unnecessary. ２ It is estimated that the amount of CO emitted during the production of precursors and positive electrode active materials is approximately 30% less than that of nickel sulfate. ２This reduces the amount of discharge, the consumption of water resources, and waste. Furthermore, because metallic nickel powder is used as the nickel raw material, the volume handled during transportation and in the manufacturing process of the positive electrode active material can be reduced compared to compounds such as nickel sulfate and nickel hydroxide. Specifically, the Ni content per unit volume of each compound is expressed in mass %, as follows: nickel sulfate (Ni(SO) ４ ・6H ２ O) 5%, nickel hydroxide (Ni(OH) ２ ) is 29%, while the Ni content of metallic nickel is 100%, resulting in a high Ni content per unit volume. As a result, in this embodiment, the volume handled during transportation and the manufacturing process of the positive electrode active material is about 1 / 20 of that of nickel sulfate and about 1 / 3 of that of nickel hydroxide, which reduces fuel consumption during transportation and improves production efficiency and energy conservation by saving space and driving force during manufacturing. Furthermore, when a positive electrode active material is manufactured using the precursor obtained by the precursor manufacturing method of this embodiment, the amount of residual lithium compound after calcination is reduced, which may eliminate the need for a water washing step to wash away residual lithium compound from the positive electrode active material after manufacturing the positive electrode active material. This makes it possible to reduce the energy required for drying after water washing and the amount of water consumption. These factors lead to a reduction in GHG emissions, allowing the manufacturing of a positive electrode active material with reduced GHG and water consumption. In this way, by using metallic nickel powder as a nickel source, the volume handled in transportation and the manufacturing process of the positive electrode active material can be reduced, reducing the energy used for transportation and manufacturing and eliminating the complexity of the manufacturing process. As a result, GHG emissions and water resource consumption during manufacturing of the positive electrode active material are reduced, and the need for auxiliary materials and waste disposal is eliminated. Furthermore, by promoting lithiation through an oxidation reaction between metallic nickel powder and a lithium-containing compound, pulverization is facilitated in the subsequent pulverization process. Therefore, the positive electrode active material manufactured using the precursor of this embodiment can achieve good crystallinity.

[0032] "Mixing Step" The lithium-containing compound mixed with the metallic nickel powder before the oxidation step may be a single lithium compound or a mixture of multiple lithium compounds. Even when multiple lithium compounds are mixed, the mass ratio of lithium in the lithium-containing compound may be within the following range. The amount of the lithium-containing compound mixed with the metallic nickel powder is preferably 10% by mass or more but less than 100% by mass, where 100% by mass is the amount of the lithium-containing compound required to produce the target positive electrode active material. This is because the presence of the lithium-containing compound can suppress sintering. Mixing 10% or more with the metallic nickel powder makes it easier to prevent sintering between the metallic nickel powders during the oxidation step. The amount of the lithium-containing compound mixed is preferably 50% by mass or less, and even more preferably 25% by mass or less. This is because the amount of oxidation treatment in the oxidation step is reduced, reducing the energy consumed in the oxidation treatment and reducing costs and GHG emissions. Furthermore, when a pulverization step is performed during the production of the positive electrode active material described below, the amount of the lithium-containing compound mixed before the oxidation step is preferably 10% by mass or more but less than 50% by mass, more preferably 25% by mass or less. When the amount of the lithium compound mixed is reduced, the voids in the secondary particles of the positive electrode active material are reduced, resulting in higher particle strength of the positive electrode active material and improved charge-discharge cycle characteristics.

[0033] Furthermore, by mixing 10% by mass or more of the lithium-containing compound with metallic nickel powder, the subsequent oxidation step promotes lithiation of the metallic nickel powder along with oxidation, forming lithium metal oxide (referring to lithium nickel oxide, but hereinafter, this description will be omitted). Figure 2 shows X-ray powder diffraction (XRD) measurements of the precursors of lithium nickel oxide obtained by the production method of this embodiment in which lithium carbonate was added (25% by mass relative to the amount of lithium-containing compound required to produce the desired cathode active material) and nickel oxide produced by oxidation without adding a lithium-containing compound. As a result, when lithium carbonate was added, in addition to the nickel oxide peak, a peak at 2θ = 43.5° to 44.0° attributable to lithium nickel oxide was observed. In other words, the formation of lithium nickel oxide was confirmed. Figure 3 shows SEM images of the cross-sectional structure of the metallic nickel powder before and after the oxidation step. The cross-sectional structure of the metallic nickel powder before the oxidation step is shown in Figure 3A. In contrast to the cross-sectional structure shown in FIG. 3A , after the oxidation process, in the case where lithium carbonate was not added, cavities were scattered throughout the metallic nickel powder, as shown in FIG. 3B . However, in the case where the oxidation process was performed after adding lithium carbonate, the cross section of the particles after the oxidation process showed cracks propagating throughout, as shown in FIG. 3C . This can be understood as the fact that 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. As these cracks propagate throughout the powder particles, the precursor becomes easier to pulverize. Furthermore, when the pulverization process is not performed, these cracks become diffusion paths for elements, facilitating more uniform diffusion of each element. On the other hand, when pulverization is performed in a later process, these cracks enable pulverization in a shorter time.

[0034] The lithium-containing compound may be lithium hydroxide, lithium carbonate, or the like. It is preferable that the melting point of the lithium-containing compound is higher than the thermal oxidation temperature of the oxidation step. If the melting point of the lithium-containing compound is higher than the thermal oxidation temperature, sintering of the metallic nickel powder particles during the oxidation step can be prevented. Therefore, the lithium-containing compound used in this manufacturing method is preferably lithium carbonate. The melting point of lithium carbonate is as high as 724°C, allowing the thermal oxidation temperature to be as high as 720°C. This is because it remains solid even at 720°C and functions as an inclusion, preventing contact and sintering of the metallic nickel powder particles, while also shortening the oxidation step. Meanwhile, lithium hydroxide may be used as the lithium-containing compound added after the pulverization step or granulation step during the production of the positive electrode active material, as described below. Lithium hydroxide has a lower melting point of 462°C than lithium carbonate and melts at a lower temperature, which is thought to facilitate reaction with the precursor. In this way, the lithium-containing compound mixed before the oxidation step and the lithium-containing compound added after the granulation step may be different compounds, and the lithium-containing compound mixed before the oxidation step may be selected to have a higher melting point. On the other hand, if the lithium-containing compound mixed before the oxidation step and the lithium-containing compound added after the granulation step are the same compound, the reaction between the precursor and the lithium-containing compound proceeds uniformly during firing, which is effective in homogenizing the crystallinity of the positive electrode active material. In addition, it is effective in controlling inevitable impurities in the positive electrode active material. The average particle size of the lithium-containing compound is preferably in the range of 100 nm to 100 μm, more preferably in the range of 1 μm to 50 μm.

[0035] The metallic nickel powder and the lithium-containing compound are mixed using a V-type mixer, agitator mixer, attritor, media mill, or the like. To achieve uniform mixing, it is preferable to be able to break down the agglomerations of the raw material powders. 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 a dispersion medium. However, considering the subsequent oxidation process, dry mixing is preferred. Dry mixing can reduce the amount of heat required in the oxidation process, which also contributes to reducing GHG emissions.

[0036] "Oxidation Process and Lithium Ionization" The oxidation process is preferably carried out by applying heat in an oxygen-containing atmosphere to oxidize a mixed powder of metallic nickel powder and a lithium-containing compound, since this shortens the time required for the oxidation process. Furthermore, in the case of thermal oxidation, the temperature is preferably 450°C or higher and 720°C or lower, and more preferably 450°C or higher and 700°C or lower. Setting the temperature at 450°C or higher and 700°C or lower makes it easier to obtain a precursor with the desired oxidation rate. Furthermore, the heat treatment time for the oxidation process is preferably 0.5 hours or higher and 20 hours or lower, more preferably 3 hours or higher and 15 hours or lower, and more preferably 5 hours or higher and 10 hours or lower. By performing the oxidation process for 5 hours or higher and 10 hours or lower, the oxidation reaction is completed, making it easier to stably obtain a precursor with the desired oxidation rate. In this case, the oxidation rate of the metallic nickel powder in the oxidation process is preferably 10% or higher and lower than 100%. Setting the oxidation rate to 10% or higher can prevent sintering of the metallic nickel powder particles during the subsequent firing process to obtain the positive electrode active material. Furthermore, an oxidation rate of 10% or higher increases the valence of nickel, which is expected to promote the reaction to form a lithium metal composite oxide during firing of the positive electrode active material. On the other hand, to facilitate obtaining good crystallinity in a positive electrode active material using the precursor of this embodiment, an oxidation rate of less than 100% is sufficient. An oxidation rate of 95% or less, or 90% or less, is preferred, and an oxidation rate of 70% or less makes it easier to obtain a positive electrode active material with good crystallinity. This is believed to be because the formation of a layered structure during the firing process is promoted when a positive electrode active material is produced using a precursor with an oxidation rate within the above range, compared to a metallic nickel powder with excessive oxidation. On the other hand, an oxidation rate of 50% or higher increases the valence of nickel, which further promotes the reaction to form a lithium metal composite oxide during firing. Furthermore, an oxidation rate of 70% or less is even more preferred, as the formation of a layered structure during the firing process is promoted more than a metallic nickel powder with excessive oxidation.

[0037] Furthermore, it is preferable to lithiate the metallic nickel powder in the oxidation process to form and incorporate an appropriate amount of lithium metal oxide. This is because the formation of lithium metal oxide facilitates the aforementioned pulverization. Furthermore, in the subsequent calcination process to obtain the positive electrode active material, the reaction between the lithium source and a metal source such as nickel is promoted, facilitating the formation of layered crystals, resulting in a positive electrode active material with good crystallinity. The lithiation ratio is preferably 8% or more to obtain good pulverization properties. When the average particle size of the metallic nickel powder exceeds 20 μm, it is 10% or more, preferably 15% or more, and more preferably 20% or more. If the lithiation ratio is excessively increased in the oxidation process, causing lithium carbonate to react with metallic nickel and consume much of it, the liquid phase component will decrease in the calcination process, resulting in insufficient grain growth due to liquid phase sintering. As a result, unreacted lithium will increase. In other words, MO+Li ２ CO ３ →LiMO ２ (M = Ni, Co, Mn, etc.) reaction does not proceed, and Li ２ CO ３ The number of LiMO ２ The amount of formation of the positive electrode active material decreases. Therefore, impurities that do not function as a positive electrode active material increase. Therefore, the upper limit of the lithiation rate is set to 35% or less, preferably 27% or less, and more preferably 25% or less, in consideration of obtaining an appropriate amount of liquid phase in the firing process. Furthermore, for powders with an average particle size D50 of 20 μm or less, pulverization itself is not essential, so fewer cracks are sufficient. Therefore, a lithiation rate of less than 8% is sufficient. The presence of cracks is preferable because they mainly serve as diffusion paths for elements, allowing metal elements to diffuse to the center of the metal nickel powder, resulting in a nearly uniform composition within the secondary particles of the positive electrode active material.

[0038] On the other hand, when using metallic nickel powder with an average particle size D50 exceeding 20 μm, a lithiation rate of 10% or higher is preferable. After the oxidation process, the precursor is in the form of a crude precursor with a large particle size. However, by increasing the lithiation rate to 10% or higher, crude precursors exceeding 20 μm can be easily and quickly pulverized, allowing them to be used in the subsequent production of positive electrode active materials. Figure 4 shows the relationship between pulverization time and particle size with and without a lithium-containing compound. Figure 4A shows the change in pulverization time and D50, and Figure 4B shows the change in pulverization time and D95. In both Figures 4A and 4B, the broken line α shows the change in pulverization time and D50 particle size or D95 particle size for a precursor containing lithium carbonate, while the broken line β shows the change in pulverization time and D50 particle size and D95 ​​particle size for a precursor without lithium carbonate. The precursor with lithium carbonate added was pulverized in a shorter time than the precursor without lithium carbonate. Regarding D50, without lithium carbonate, it took approximately 50 hours to reach the D50 value before the oxidation process, whereas with lithium carbonate added, pulverization was achieved in approximately 10 hours. The same is true for D95; without the addition of a lithium-containing compound (lithium carbonate), it is difficult to reach the D95 level before the oxidation process. Although crushing is possible, the difficulty of pulverization increases. Thus, without the addition of a lithium-containing compound (lithium carbonate), pulverization of the crude precursor becomes difficult, making it difficult to apply a method for producing a positive electrode active material that includes a pulverization process. Therefore, lithiation is advantageous in a method for producing a positive electrode active material that includes a pulverization process. As described above, when a metallic nickel powder having an average particle size D50 exceeding 20 μm is used, a pulverization process is performed. However, adding and mixing a lithium-containing compound to the metallic nickel powder and lithiating the metallic nickel powder in the oxidation process facilitates pulverization and shortens the pulverization time. It is also acceptable to perform a pulverization process when a metallic nickel powder having an average particle size D50 of 20 μm or less is used. The means for determining the oxidation rate and lithiation rate will be described in the Examples section.

[0039] "Precursor of Positive Electrode Active Material" The precursor of the positive electrode active material of this embodiment has a peak at 2θ=43.5° or more and 44.0° or less, which is indicated by lithium metal oxide, in X-ray powder diffraction measurement of the precursor, and its lithiation rate is 8% or more. That is, it is preferable that the precursor contains an appropriate amount of lithium metal oxide. The inclusion of the lithium metal oxide causes cracks in the powder particles of the precursor, improving the pulverizability as described above. In addition, this is because the reaction between the lithium source and the metal source such as nickel progresses in the firing step to obtain the positive electrode active material, facilitating the formation of a layered structure. Furthermore, this precursor contains lithium nickel oxide having a peak at 2θ=43.5° or more and 44.0° or less in X-ray powder diffraction measurement, and the peak intensity I of the peak is LiNiO2 and the peak intensity I of the peak at 2θ=44.0° or more and 45.0° or less, which is attributed to metallic nickel. Ni Intensity ratio I LiNiO2 / I Ni It is preferable that the ratio is 0.5 or more. By making the ratio 0.5 or more, the metallic nickel component which is ductile and difficult to crush is reduced, and lithium nickel oxide which is prone to cracking is formed, which improves crushability. In addition, when the average particle size of the metallic nickel powder exceeds 20 μm, the ratio I LiNiO2 / I Ni is preferably 5 or more, more preferably 13 or more, and even more preferably 20 or more. LiNiO2 / I Ni indicates the formation rate of lithium nickel oxide, and is therefore linked to the above-mentioned lithiation rate. The upper limit of this ratio is set to 35 or less, preferably 29 or less, and more preferably 25 or less.

[0040] [Method for Producing Cathode Active Material] The method for producing a cathode active material according to this embodiment is characterized by using the above-described precursor of the cathode active material. An example of an embodiment of the method for producing a cathode active material of the present invention is shown in the flowcharts of FIGS. 5 to 7. As shown in FIG. 5, the cathode active material may be produced by mixing a precursor, a compound containing a metal element M other than lithium and nickel (hereinafter also referred to as the M element compound), and the remaining amount of a lithium-containing compound to obtain a cathode active material of the desired composition, followed by calcination. While FIGS. 5 to 7 include a step of adding the remaining amount of the lithium-containing compound, as shown in FIGS. 6 and 7, the cathode active material may also be produced by adding a pulverization step or a granulation step. FIG. 7 includes a first pulverization step (coarse pulverization step) and a second pulverization step (fine pulverization step). Each embodiment is described below, and more specifically, along with examples.

[0041] "Step of mixing precursors, etc." First, a precursor is prepared by the precursor manufacturing method described above. This precursor is prepared by mixing a lithium-containing compound with metallic nickel powder and oxidizing it, and therefore exhibits an appropriate oxidation rate. A V-type mixer, agitator mixer, attritor, media mill, etc. is used to mix this precursor, the lithium-containing compound, and the M element compound. For uniform mixing, it is preferable to be able to break down the agglomerations 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 a dispersion medium.

[0042] The lithium-containing compound to be mixed with the precursor may be lithium hydroxide, lithium carbonate, or the like. Lithium carbonate is preferred because it has low hygroscopicity and is easy to handle. In addition, lithium carbonate is preferable because it can reduce the CO emitted during the production of lithium carbonate. ２ The amount of lithium is preferably less than that of other lithium-containing compounds such as lithium hydroxide. On the other hand, the use of lithium hydroxide shortens the calcination time, increasing productivity. In addition, the amount of CO emitted by calcination is also low. ２This is preferable because the amount is reduced. When the pulverization step is omitted during the production of the positive electrode active material, lithium hydroxide is preferably used. This is because the diffusion of metal elements M other than nickel into the metallic nickel powder is promoted, allowing the production of a positive electrode active material with a uniform composition. In the precursor production process, the lithium-containing compound mixed with the metallic nickel powder before the oxidation step and the lithium-containing compound mixed with the precursor in this mixing step may be different substances or the same substance. Furthermore, the amount of lithium-containing compound mixed in this step may be the entire amount of the precursor that is insufficient to provide the amount of lithium required to produce the desired positive electrode active material, or only a portion of it. For example, when a granulation step is performed before the firing step to produce a polycrystalline secondary particle positive electrode active material, the lithium-containing compound can be added in the pulverization step (including the first pulverization step (coarse pulverization step) and the second pulverization step (fine pulverization step) described below), or it can be added after the granulation step. Adding the lithium-containing compound after the granulation step can suppress voids, and adding it after the granulation step is preferable. On the other hand, when the granulation step is not performed, it is preferable to mix in the mixing step a lithium-containing compound containing an amount of lithium that is insufficient for the amount of lithium required to produce the target positive electrode active material.

[0043] "Pulverization Step" Next, it is preferable to introduce a pulverization and mixing step (referred to as the pulverization step) for the purpose of promoting the sintering reaction. This is because a positive electrode active material with a high initial capacity and good charge-discharge cycle characteristics can be obtained. The pulverization can be carried out using an attritor, a media mill, or the like. A media mill is preferred, and a bead mill is more preferred, because it can pulverize the mixed powder to submicron size. The D50 of the primary particles of the pulverized mixed powder (referred to as the pulverized mixed powder) is preferably 0.40 μm or less. The sintering 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 is high, resulting in good charge-discharge cycle characteristics.

[0044] Furthermore, when the average particle size D50 of the metallic nickel powder is coarse, exceeding 20 μm, it is preferable to perform the pulverization process in two stages under different pulverization conditions. Specifically, as shown in FIG. 7, the first stage is coarse pulverization to a size of less than 10 μm (first pulverization process (coarse pulverization process)), followed by fine pulverization to submicron size in the second stage (second pulverization process (fine pulverization process)). Furthermore, it is preferable to use a media mill for both the first pulverization process (coarse pulverization process) and the second pulverization process (fine pulverization process), and it is preferable that the media size in the second pulverization process (fine pulverization process) is smaller than the media size in the first pulverization process (rough pulverization process). By performing the pulverization process in two stages, it is possible to suppress the incorporation of media components from the media mill, thereby obtaining a positive electrode active material with the desired composition and fewer impurities.

[0045] Granulation Process: In the precursor production process described above, if the amount of lithium-containing compound mixed is less than 100% of the amount of lithium compound required to produce the desired cathode active material, it is preferable to add the remaining amount of lithium-containing compound after the granulation process (post-addition) in the cathode active material production process. The effect of post-addition will now be described with reference to FIG. 11 . FIG. 11A is a schematic diagram of granulated powder before and after the firing process when the remaining amount of lithium-containing compound is added before the granulation process (pre-addition), and FIG. 11B is a schematic diagram of granulated powder before and after the firing process when the lithium-containing compound is post-added. For the granulated powder shown in FIG. 11A, the cathode active material is obtained by the following process. First, a precursor is produced from a lithium-containing compound containing a partial amount of lithium required for the cathode active material and metallic nickel powder, and a compound containing an M element compound is mixed with the precursor, followed by pulverization to obtain a pulverized slurry. To this pulverized slurry, a lithium-containing compound in an amount insufficient for the amount of lithium required for the cathode active material is added, followed by granulation. In the process shown in FIG. 11A , a lithium-containing compound corresponding to the amount of lithium missing from the lithium-containing compound required for the positive electrode active material is added before granulation. This is referred to as pre-addition. Note that pre-addition also refers to the case where a precursor formed from a lithium-containing compound and metallic nickel powder, which contains the entire amount of lithium required for the positive electrode active material, is used. When pre-addition is performed in this manner, the granulated powder is formed in a state in which particles 111 obtained by mixing the precursor and the M element compound and lithium-containing compound 112 are uniformly mixed with each other, as shown in FIG. 11A . Therefore, a large amount of lithium-containing compound is present in the granulated powder containing oxidized metallic nickel powder. Since lithium-containing compound 112 becomes liquid during firing and diffuses into the primary particles that make up the granulated powder, the more lithium-containing compound there is, the more voids there are in the structure after firing. Therefore, the produced positive electrode active material has a structure with many voids between particles 113 composed of an oxide of lithium, nickel, and metallic element M, which reduces the particle strength of the positive electrode active material and ultimately deteriorates the charge / discharge cycle characteristics.On the other hand, in the positive electrode active material of this embodiment shown in FIG. 11B , a precursor formed from a lithium-containing compound and metallic nickel powder, containing a portion of the lithium required for the positive electrode active material, is mixed with an M element compound and pulverized, and the resulting pulverized slurry is granulated. Then, after the granulated powder is formed, a lithium-containing compound corresponding to the amount of lithium that is insufficient relative to the amount of lithium required for the positive electrode active material is added. This addition of a lithium-containing compound after the granulated powder is formed is referred to as post-addition. With post-addition, the amount of lithium-containing compound in the granulated powder is originally small, so particles 121 of the mixed powder obtained by mixing the precursor and the M element compound are close to each other, preventing gaps from forming. Furthermore, the post-added lithium-containing compound 112 is arranged so as to surround the particles 121, allowing sufficient penetration into the interior of the granulated powder during firing. Thus, after firing, a structure with few voids between particles 113 composed of an oxide of lithium, nickel, and metallic element M is formed. As a result, the particle strength of the positive electrode active material is high, resulting in excellent charge-discharge cycle characteristics. Therefore, it is preferable to add the remaining amount of the lithium-containing compound after the granulation step (post-addition).

[0046] "Firing Step" Next, the firing step of firing the granulated powder, the mixed powder, or the pulverized mixed powder to obtain a layered-structure positive electrode active material for lithium-ion secondary batteries will be described. An electric furnace or a gas furnace is used to fire the mixed powder, the pulverized mixed powder, or the granulated powder. The firing atmosphere preferably contains 20% or more oxygen by volume, and when the Ni content is 80 atomic % or more of all metal elements excluding Li, the oxygen concentration is preferably 90% or more. The firing step may be performed at 700°C to 900°C to obtain a layered-structure positive electrode active material. The firing step may include a pre-firing step maintained at 450°C to 730°C and a main firing step maintained at a temperature higher than the firing temperature in the pre-firing step and at 700°C to 900°C. The preferred firing temperature and holding time are adjusted according to the composition of the raw material mixture, and firing is performed so that the physical properties (specific surface area, etc.) of the target positive electrode active material after firing are within a preferred range. As described above, metallic nickel powder is used as the starting material, and a lithium-containing compound is mixed and oxidized, so the precursor exhibits an appropriate oxidation rate and lithiation rate. Therefore, this firing process results in an appropriate oxidation rate and lithiation rate, making it easy to produce a positive electrode active material with a preferred composition ratio as described below.

[0047] After the firing step, the synthesized lithium metal composite oxide may be subjected to a washing step in which it is washed with deionized water or the like, a drying step in which the washed lithium metal composite oxide is dried, etc., for the purpose of removing impurities, etc. Furthermore, the synthesized lithium metal composite oxide may be subjected to a crushing step in which it is crushed, a classification step in which the lithium metal composite oxide is classified into a predetermined particle size distribution (particle size), etc.

[0048] Furthermore, when it is necessary to set the particle size distribution of the positive electrode active material produced using the precursor produced by the above-described precursor production method to fall within a predetermined range, it is preferable to perform the following treatment in each of the steps of (precursor mixing step, etc.), (pulverization step), (granulation step), and (firing step).

[0049] First, a process for achieving a desired particle size distribution of the positive electrode active material will be described based on the method for producing a positive electrode active material for a lithium ion secondary battery shown in Fig. 5. In the step of mixing precursors and the like, it is preferable to mix the lithium-containing compound with the precursor at different times from the timing of mixing the M element compound.

[0050] For example, by selecting a powder material made of a substance that is difficult to pulverize as the powder material to be initially mixed with the precursor and then pulverizing and mixing it, it becomes possible to reduce the amount of powder material with large particle sizes and perform firing. Specifically, it is preferable to mix a powder material made of an M element compound as the powder material to be initially mixed with the precursor. In this case, as described above, it is preferable to use a V-type mixer, agitator mixer, attritor, media mill, etc. Note that agitator mixers, attritors, and media mills are preferred because they perform mixing and pulverization simultaneously. It is even more preferable to classify the powder material made of the M element compound before mixing it with the precursor, and then mix the precursor and the powder material made of the M element compound after classification. Of course, it is also preferable to classify the precursor using a similar method so that it falls within a predetermined particle size distribution range before mixing. The classification method is not particularly limited, but known classification methods such as sieve classification and airflow classification may be used.

[0051] Furthermore, it is preferable to mix the precursor with a powder material made of an M element compound, and then mix in a powder material made of a lithium-containing compound. In this case, the (mixing) step shown in Fig. 5 corresponds to the step of mixing a powder material made of an M element compound with a precursor first, and then mixing in a powder material made of a lithium-containing compound. Therefore, when it is necessary to make the resulting cathode active material have a particle size distribution within a predetermined range, it is preferable that the mixing step in the method for producing a cathode active material for a lithium-ion secondary battery shown in Fig. 5 be divided into at least two or more steps, and that the mixing step be performed each time a different powder material is mixed into the precursor.

[0052] It is preferable to classify the powder material comprising the lithium-containing compound before mixing it. Furthermore, as described above, the mixing here is also preferable to use a V-type mixer, stirring mixer, attritor, media mill, or the like, since mixing and pulverization can be performed simultaneously. Furthermore, it is preferable to pulverize and mix the powder material comprising the M element compound and the powder material comprising the lithium-containing compound together with the precursor, generate a pre-sintering mixed powder, and then classify it in the same manner as described above, thereby making the particle size distribution of the pre-sintering mixed powder within a predetermined range. In some cases, sieve classification, air flow classification, or the like can also be performed.

[0053] It is preferable to prevent moisture absorption of the powder material consisting of the M element compound, the powder material consisting of the lithium-containing compound, and the precursor before mixing with the precursor, in order to prevent aggregation. For example, it is preferable to store these powder materials in a humidity-controlled container or storage facility, such as in a container positively pressurized with dry gas, until just before being introduced into a mixing device such as a V-type mixer, stirring mixer, attritor, or media mill. It is also preferable to positively pressurize the internal atmosphere of the mixing device with dry gas to prevent the outside atmosphere from entering.

[0054] In addition, using lithium nitrate instead of the aforementioned lithium hydroxide or lithium carbonate as the powder material made of a lithium-containing compound also contributes to facilitating adjustment of the particle size distribution range for the resulting positive electrode active material.

[0055] Next, when a calcination step is carried out after the particle size distributions of the powder material consisting of the precursor and the M element compound and the powder material consisting of the lithium-containing compound are adjusted to a predetermined distribution range, it is preferable to prevent excessive aggregation of the powder materials in the calcination step or to carry out the calcination while maintaining a uniform aggregation state such as in pellet form. First, the calcination step carried out so as to prevent excessive aggregation of the powder materials will be described.

[0056] The pre-fired mixed powder, which is a mixture of a precursor, a powder material consisting of an M element compound, and a powder material consisting of a lithium-containing compound, is preferably placed in a sintering sagger. Furthermore, the pre-fired mixed powder is preferably first sieved in air or an oxygen-containing atmosphere and then allowed to fall freely, so that a large amount of oxygen gas is contained between each particle. The pre-fired mixed powder is then deposited in an oxygen-containing state, and then placed in a dry atmosphere and fired in an electric furnace or gas furnace. The pre-fired mixed powder placed in the sintering sagger is preferably provided with multiple grooves or holes to facilitate the passage of oxygen-containing gas to the lower part of the pre-fired mixed powder during firing. This promotes oxidation of the pre-fired mixed powder at the bottom of the sagger, thereby forming gas channels for ensuring uniform firing of the pre-fired mixed powder at the top and bottom of the sagger. Alternatively, a furnace such as a rotary kiln, which rotates the pre-fired mixed powder during firing, may be used. In either case, it is preferable to use an oxygen-rich atmosphere containing oxygen gas, more preferably an atmosphere with an oxygen concentration of 90% or more, under a pressure higher than atmospheric pressure in order to make the particle size distribution of the positive electrode active material into a predetermined distribution state by allowing the oxygen-containing gas to penetrate into the interior of the pre-sintering mixed powder.

[0057] Next, the firing step, in which the pre-fired mixed powder is fired while maintaining a uniform agglomerated state, will be described. Before the firing step, it is preferable to apply pressure to the pre-fired mixed powder, which is a mixture of a precursor, a powder material consisting of an M element compound, and a powder material consisting of a lithium-containing compound, using a method such as a roller press to form a molded body. After producing the molded body from the pre-fired mixed powder in this manner, firing is preferably performed. Furthermore, before the firing step, pellets of a predetermined size and shape are produced using the pre-fired mixed powder, which is a mixture of a precursor, a powder material consisting of an M element compound, and a powder material consisting of a lithium-containing compound. Regarding the pellet production method, it is preferable to compress the mixture into a mold having the inverted shape of a pellet of a predetermined size and shape. When wet mixing and grinding is performed to mix the powder material consisting of a precursor and an M element compound with the powder material consisting of a lithium-containing compound, it is also possible to produce pellets of a predetermined size and shape by compression molding in a wet state. Furthermore, pellets formed into spherical shapes by rotational molding or rolling a cubic press-molded product, or granules granulated with a spray dryer are also preferable. It is also preferable that the dimensions are adjusted to the dimensions of the positive electrode active material to be produced. After producing pellets from the pre-fired mixed powder in this manner, it is preferable to fire the pellets.

[0058] In addition, when performing the firing process, whether to prevent excessive aggregation of the powder materials or to form the pre-fired mixed powder into pellets and fire while maintaining a uniform aggregation state, it is preferable to fire at a low temperature within the above-mentioned temperature range. Since lowering the firing temperature delays the formation of a layered structure, it is preferable to fire for a relatively long time to ensure sufficient formation of the layered structure. Furthermore, adjusting the oxygen concentration supplied during firing also makes it easier to obtain a positive electrode active material with a particle size distribution within a predetermined range.

[0059] It is also preferable to perform a crushing treatment during or after the firing process. The crushing method here may be either wet crushing or dry crushing. During the firing process, a dry crushing method is more preferable in order to facilitate reaching the minimum temperature at which a layered structure is formed as quickly as possible. Known crushing methods, such as grinders, bead mills, attritors, and jet mills, can be used as the crushing method. Furthermore, in order to set the particle size distribution of the positive electrode active material within a predetermined range, airflow classification, such as air classification, may be performed after crushing. On the other hand, when a wet crushing method is applied after the firing process, known classification methods, such as centrifugation, sedimentation, and classification using a porous membrane, may also be used.

[0060] In this way, it is possible to produce a positive electrode active material consisting of primary particles whose basic structure is precursor particles without performing a granulation step, and to make the particle size distribution of the positive electrode active material fall within a predetermined range.

[0061] In addition, in the production of a positive electrode active material composed of polycrystalline secondary particles, the above-described treatment is also useful for controlling the particle size distribution of the positive electrode active material produced.

[0062] 6 or 7, for example, it is preferable that the powder material consisting of the precursor and the M element compound to be mixed with the precursor be subjected to classification treatment and treatment to prevent moisture absorption before mixing in the same manner as described above. It is also preferable that classification be performed as described above after the pulverization treatment during mixing of the precursor and the powder material consisting of the M element compound to be mixed with the precursor.

[0063] Furthermore, in the granulation step, granulated powder is produced from a powder material consisting of a precursor and an M element compound, and it is preferable to perform a classification process on the produced granulated powder. It is also preferable to perform a classification process on the powder material consisting of a lithium-containing compound that is added to the classified granulated powder. It is also preferable to perform a classification process on the granulated powder to which the powder material consisting of a lithium-containing compound has adhered. It is also preferable to use lithium nitrate instead of the aforementioned lithium hydroxide or lithium carbonate for the powder material consisting of a lithium-containing compound, as this promotes particle growth.

[0064] Next, it is preferable to perform a classification process on the pre-sintering mixed granulated powder, which is a mixture of a powder material made of a lithium-containing compound and the granulated powder, in the same manner as described above, to adjust the particle size distribution range to a predetermined range. Furthermore, the pre-sintering mixed granulated powder may be fired while being treated to prevent excessive aggregation, as described above, or may be fired while maintaining a uniform aggregation state such as pellets. By performing a classification process between each step shown in FIG. 6 or FIG. 7 and simultaneously performing pulverization during mixing, it becomes easier to obtain a positive electrode active material with a controlled particle size distribution.

[0065] (Composition of Positive Electrode Active Material) Next, the composition of the positive electrode active material of this embodiment will be described. As described above, the composition of the positive electrode active material of this embodiment is not particularly limited, but a preferred composition will be 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) (In the formula (1), M is a metal element other than Li and Ni, and a, b, and α are numbers that satisfy the following: -0.1≦a≦0.2, 0.5≦b≦1.0, and -0.2≦α≦0.2.)

[0066] The positive electrode active material according to this embodiment has a composition in which the proportion of Ni relative to all metal elements other than Li is 50 atomic % or more, thereby realizing high energy density and high initial capacity. The proportion of Ni relative to all metal elements other than Li can be an appropriate value within the range of 50 atomic % or more and 100 atomic % or less. Because this is a positive electrode active material containing a high proportion of nickel, Ni ２＋ Ni ３＋ It is important that the oxidation reaction to oxidize to HCl be carried out efficiently.

[0067] 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) [In formula (2), M1 represents at least one selected from Al and Mn, X represents one or more metal elements other than Li, Ni, Co, Al, and Mn, and a, b, c, d, e, and α are numbers satisfying −0.1≦a≦0.2, 0.5≦b≦1.0, 0≦c≦0.20, 0≦d≦0.30, 0≦e≦0.1, b+c+d+e=1, and −0.2<α<0.2, respectively.]

[0068] The positive electrode active material represented by the formula (2) has a high Ni content, and therefore, in the range up to about 4.3 V, LiCoO ２ In addition, since the Ni content is high, LiCoO ２ Compared with the above, the raw material cost is low and the raw material is easily available as a positive electrode active material.

[0069] Here, the meaning of the numerical ranges of a, b, c, d, e and α in the above formulas (1) and (2) will be explained.

[0070] In the formula, a is preferably −0.1 or more and 0.2 or less. ２ (M' represents a metal element such as Ni, Co, or Mn), i.e., the excess or deficiency of lithium from the stoichiometric ratio of Li:M':O = 1:1:2 of the lithium metal composite oxide. If the amount of lithium is too small, the initial capacity of the positive electrode active material will be low. On the other hand, if the amount of lithium is too high, the charge-discharge cycle characteristics will deteriorate. It is preferable to set a within the above-mentioned numerical range to achieve both a high initial capacity and good charge-discharge cycle characteristics.

[0071] a may be -0.02 or more and 0.07 or less. When a is -0.02 or more, a sufficient amount of lithium contributing to charge and discharge is secured, so that the initial capacity of the positive electrode active material can be increased. Furthermore, when a is 0.07 or less, charge compensation due to a change in the valence of the metal element is sufficiently performed, so that both a high initial capacity and good charge and discharge cycle characteristics can be achieved.

[0072] The coefficient b of nickel is preferably 0.50 or more and 1.00 or less. When b is 0.50 or more, a sufficiently high charge / discharge capacity can be obtained compared to the case where other metal elements are used. Therefore, when b is in the above-mentioned numerical range, a positive electrode active material exhibiting a high charge / discharge capacity can be obtained by using LiCoO ２ It is preferable to manufacture it at a low cost compared to the above.

[0073] The value of b is preferably 0.80 or more and 0.95 or less, and more preferably 0.85 or more and 0.95 or less. The larger the value of b, which is 0.80 or more, the higher the initial capacity. Furthermore, the smaller the value of b, which is 0.95 or less, the smaller the lattice distortion or crystal structure change associated with the insertion or desorption of lithium ions. This makes it less likely that cation mixing, in which nickel is mixed into the lithium sites, or a decrease in crystallinity will occur during firing, thereby suppressing deterioration of the initial capacity and charge / discharge cycle characteristics.

[0074] The cobalt coefficient c is preferably 0 or more and 0.20 or less. The addition of cobalt stabilizes the crystal structure and suppresses cation mixing, which involves the incorporation of nickel into lithium sites. This results in improved charge-discharge cycle characteristics without significantly impairing charge-discharge capacity. On the other hand, excessive cobalt increases raw material costs, thereby increasing the manufacturing cost of the positive electrode active material. It is preferable to set c within the above-mentioned range to achieve good productivity, high charge-discharge capacity, and good charge-discharge cycle characteristics.

[0075] The value of c may be 0.01 or more and 0.20 or less, or 0.03 or more and 0.20 or less, or 0.04 or more and 0.20 or less. The larger the value of c is, the more sufficient the effect of the element substitution with cobalt is obtained, and the more improved the charge-discharge cycle characteristics are.

[0076] The coefficient d of M1 is preferably 0 or more and 0.30 or less. When element substitution is performed with at least one element (M1) selected from the group consisting of manganese and aluminum, the layered structure is maintained more stably even when lithium is released during charging. On the other hand, if these elements (M1) are in excess, the proportion of other metal elements such as nickel decreases, and the initial capacity of the positive electrode active material decreases. If d is within the above numerical range, the crystalline structure of the positive electrode active material can be maintained stable, and good charge / discharge cycle characteristics, thermal stability, etc. can be obtained in addition to a high initial capacity.

[0077] As the element represented by M1, manganese is preferred. When manganese is substituted, a higher initial capacity can be obtained compared to when aluminum is substituted. Furthermore, when the lithium composite oxide is calcined, manganese also reacts with lithium carbonate as shown in the following formula (3). This reaction suppresses the coarsening of crystal grains and allows the oxidation reaction of nickel to proceed at high temperatures, making it possible to efficiently obtain a positive electrode active material exhibiting a high charge / discharge capacity. Note that at least one element M1 selected from the group consisting of manganese and aluminum may be selected from manganese and aluminum. In this case, it is preferable to select manganese as at least one element and to increase the molar ratio of manganese relative to the other selected elements.

[0078] Li ２ CO ３ +2M'O+0.5O ２ →2LiM'O ２ +CO ２ ... (3) (In the formula (3), M' represents a metal element such as Ni, Co, or Mn.)

[0079] The coefficient d of M1 is preferably 0.02 or more, and more preferably 0.04 or more. The larger the coefficient d of M1, the more sufficient the effect of element substitution with at least one element selected from the group consisting of manganese and aluminum can be obtained. When M1 is manganese, the oxidation reaction of nickel can be promoted at a higher temperature, and a positive electrode active material exhibiting a 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, a high initial capacity can be maintained even with element substitution.

[0080] The coefficient e of X is preferably 0 or more and 0.1 or less. X represents one or more metal elements other than Li, Ni, Co, Al, and Mn. When X is at least one element selected from the group consisting of tungsten, magnesium, titanium, zirconium, molybdenum, and niobium, various performances such as charge-discharge cycle characteristics can be improved 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 metal elements such as nickel decreases, and the charge-discharge capacity of the positive electrode active material decreases. When e is within the above numerical range, high initial capacity and good charge-discharge cycle characteristics can be achieved at the same time.

[0081] In the formulas (1) and (2), α is preferably −0.2 or more and 0.2 or less. α is represented by the general formula: LiM′O ２ This represents the excess or deficiency of oxygen from the stoichiometric ratio of the lithium metal composite oxide expressed by the formula (1), i.e., Li:M':O = 1:1:2. It is preferable that α is in the above-mentioned numerical range so that there are few defects in the crystal structure and high initial capacity and good charge / discharge cycle characteristics can be obtained.

[0082] Next, the powder characteristics of the positive electrode active material will be described. As described above, the powder characteristics of the positive electrode active material of this embodiment are not particularly limited, but preferred powder characteristics will be described below. The positive electrode active material may be a polycrystalline positive electrode active material having a structure in which primary particles of several hundred nanometers are aggregated to form secondary particles of several micrometers to several tens of micrometers, or a single-crystalline (or single-particle) positive electrode active material having a structure in which a single primary particle of one to several micrometers is aggregated or several primary particles are aggregated.

[0083] The residual LiOH of the positive electrode active material is preferably 0.60 mol % or less, more preferably 0.40 mol % or less. By setting the residual LiOH within the above range, the amount of by-products deposited on the surface (interface) of the positive electrode active material during charge / discharge cycles is reduced, and an increase in interface resistance can be suppressed. As a result, the charge / discharge cycle characteristics are improved. Furthermore, gelation of the positive electrode mixture during positive electrode preparation can be suppressed, making it possible to easily prepare a positive electrode. In addition, the water washing step after firing can be omitted. Note that when a compound containing lithium carbonate is used instead of lithium hydroxide, the residual Li ２ CO ３ is preferably 0.60 mol % or less, more preferably 0.30 mol % or less.

[0084] The oil absorption of the positive electrode active material is preferably 25 ml / 100 g or more and 32 ml / 100 g or less. By setting the oil supply amount to 25 ml / 100 g or more and 32 ml / 100 g or less, excessive voids within the particles of the positive electrode active material are suppressed while the particle strength is high. Because of the high strength, stress due to volume changes associated with charge / discharge cycles can be alleviated, and crack occurrence can be suppressed. As a result, good cycle characteristics are achieved. Therefore, a secondary battery in which the positive electrode material is composed of the positive electrode active material of this embodiment can be expected to have a long life. Furthermore, using a positive electrode active material within the above oil supply amount range is preferable because it reduces the amount of binder used during positive electrode production, making it easier to manufacture the positive electrode.

[0085] The porosity of the positive electrode active material is preferably 5% by volume or more and 15% by volume or less, more preferably 5% by volume or more and 12% by volume or less. By adjusting the porosity to the above range by operations such as post-addition after the granulation process, as described above, excessive voids within the particles of the positive electrode active material can be suppressed while increasing particle strength. Setting the voids to 5% by volume or more can mitigate the accumulation of stress caused by volume changes associated with charge and discharge, which is preferable. On the other hand, setting the porosity to 15% by volume or less results in high particle strength, which is preferable. Setting the porosity to 5% by volume or more and 15% by volume or less can mitigate stress caused by volume changes associated with charge and discharge cycles, and the high particle strength can suppress crack occurrence, resulting in good cycle characteristics. Therefore, a secondary battery comprising a positive electrode material made of the positive electrode active material of this embodiment can be expected to have a long life. Furthermore, using a positive electrode active material with a porosity within the above range is preferable because it reduces the amount of binder used during positive electrode production, making it easier to manufacture the positive electrode.

[0086] The mode (mode pore diameter) of the pore diameter of the positive electrode active material is preferably 10 nm or more and 250 nm or less, more preferably 10 nm or more and 200 nm or less. By setting the mode pore diameter within this range, the pores within the positive electrode active material particles become fine and uniform, resulting in high particle strength. As a result, stress due to volumetric changes accompanying charge-discharge cycles can be alleviated, and the high strength can suppress cracking due to charge-discharge cycles, resulting in good cycle characteristics.

[0087] The particle strength of the positive electrode active material is preferably 30 MPa or more, more preferably 50 MPa or more. If the particle strength is high within the above range, cracking due to charge / discharge cycles can be suppressed, resulting in good cycle characteristics. On the other hand, the upper limit is not particularly limited, but it is preferably 300 MPa or less, for example.

[0088] α-NaFeO in X-ray powder diffraction measurement ２ Crystal structure of type (Li １＋ａ Ni ｂ Co ｃ M1 ｄ X e O ２＋α ) and the intensity I calculated from the integral value of the peak identified as the 006 plane. ００６and the intensity I calculated from the integral value of the peak identified as the 102 plane. １０２ and the intensity I calculated from the integral value of the peak identified as the 101 plane. １０１ Based on this, the R value = (I ００６ +I １０２ ) / I １０１ It is preferable that the R value calculated by the above formula is 0.46 or less. This R value is calculated by the following formula: ２ It was found that the R value depends on the amount of cation mixing, in which nickel ions are mixed into the lithium sites in the crystalline structure of the type. That is, as the R value decreases, the amount of cation mixing decreases, and less nickel ions are mixed into the lithium sites, allowing Li ions to move smoothly within the lithium sites during charge and discharge. This results in low diffusion resistance and high initial capacity. Specifically, an R value of 0.46 or less results in low cation mixing and a high discharge capacity. The upper limit of the R value is preferably 0.45 or less, more preferably 0.44 or less. On the other hand, the lower limit is preferably 0.42 or more. When the R value is 0.42 or more, the primary particle size, which affects the capacity retention rate during charge and discharge cycles, does not become coarse, which is preferable because it can achieve both high capacity and good charge and discharge cycle characteristics.

[0089] Hereinafter, a preliminary experiment of the oxidation step will be described, followed by a method for producing a precursor and the precursor, and then a method for producing a cathode active material and examples of the cathode active material. The means for measuring characteristic values ​​are as follows.

[0090] First, the oxidation rate and lithiation rate can be determined by the following means. (Oxidation rate) The oxidation rate of the precursor indicates the ratio of the amount of oxidized nickel to the total amount of nickel contained, and is calculated by the mass M of the metallic nickel powder introduced into the oxidation treatment. Ｎｉ , the mass M of the inclusion component (a compound containing lithium or a compound containing a metal element M) i and the mass M of the precursor (oxidized powder) after oxidation treatment. ｐ It was calculated from the formula (4) based on the above. ｐ - (M Ni +M i ) is the mass increase of the metallic nickel powder due to the oxidation treatment, and (M ｐ - (MNi +M i )) / M Ｎｉ is the mass increase rate. The oxidation rate was calculated by dividing this mass increase rate by 0.298, which is the mass increase rate when the metallic nickel powder is completely oxidized. Oxidation rate (%) = (M ｐ - (M Ni +M i )) / M Ｎｉ / 0.298 × 100 ... (4)

[0091] (Lithium content (Li content)) In this specification, this is the proportion of metallic nickel that has reacted with lithium. In this example, instead of directly determining the proportion of metallic nickel powder that has reacted with lithium, the carbon content C of the raw material mixed powder obtained by mixing metallic nickel powder and lithium carbonate is calculated. i and the carbon content C of the precursor o The amount of lithium carbonate that decreased during the oxidation process, that is, the proportion of lithium carbonate that reacted with metallic nickel, was calculated using equation (5). The reaction product is lithium nickel oxide. It is known that an increase in lithium nickel oxide makes it easier for cracks to occur within the precursor. In this respect, the lithiation rate can be used as an index of ease of pulverization. The proportion of lithium carbonate that reacted with metallic nickel, M Ｌｉ = (C i -C o ) / C o ... (5) The molar ratio of metallic nickel to lithium carbonate in the raw material mixed powder (M Ｎｉ / Ｌｉ ) and M Ｌｉ The ratio of metallic nickel that reacted with Li to be converted to lithiation (lithiation rate) was calculated from the formula (6). Ｎｉ / Ｌｉ × M Ｌｉ ...(6)

[0092] (Average particle size, particle strength) The D50 of the primary particles of the pulverized mixed powder and the secondary particles of the fired powder of the positive electrode active material (particles formed by aggregation of multiple primary particles due to the granulation process) was measured using a laser diffraction particle size distribution analyzer. The particle strength was measured using a micro-compression tester "MCT-510" (manufactured by Shimadzu Corporation). The particle strength was measured for five particles of the positive electrode active material with a secondary particle diameter of about 10 μm, and the average value was taken as the particle strength.

[0093] (Oil absorption) The oil absorption of a powder sample was measured in accordance with JIS K5101-13-1, using NMP (N-methylpyrrolidone) as the solvent. 5.0 g of powder sample was weighed out and placed in a mountain shape on a flat tray. NMP was sucked up with a poly dropper (2 mL capacity) and the mass was measured. Next, NMP was added dropwise to the powder sample while kneading with a spatula, and the addition and kneading were continued until the powder sample became clay-like overall. When there was an excess of NMP, it was visible that the droplets were not absorbed by the powder sample and remained on the surface, and the amount of NMP added dropwise up to this point was converted to the oil absorption per 100 g of powder sample.

[0094] (X-ray Diffraction Pattern) X-ray diffraction (XRD) patterns in X-ray powder diffraction measurement of the precursor and the positive electrode active material were measured using an X-ray diffractometer "X'Pert PRO MPD" (manufactured by PANalytical) under the conditions of a CuKα radiation source, a tube voltage of 45 kV, a tube current of 40 mA, a sampling interval of 0.02° / step, a divergence slit of 0.5°, a scattering slit of 0.5°, a receiving slit of 0.15 mm, and a scanning range of 15°≦2θ≦80°.

[0095] (Crystallite diameter) The crystallite diameters of nickel oxide, lithium metal oxide (LNO), and metallic Ni contained in the precursor were calculated by removing Kα2 from the XRD pattern obtained by measuring the precursor, and then calculating the half-width β of each peak of 2θ = 43.3 to 43.5 ° and the vicinity thereof attributable to nickel oxide, 2θ = 43.7 to 44.0 ° and the vicinity thereof attributable to lithium metal oxide (LNO) and 2θ = 44.4 to 44.7 ° and the vicinity thereof attributable to metallic nickel based on the formula (7) using the analysis software attached to the X-ray diffractometer. Crystallite diameter = Kλ / β cosθ (7) K: shape factor (0.9), λ: X-ray wavelength (0.154 nm), θ: diffraction angle

[0096] (R value) Furthermore, after removing Kα2 from the XRD pattern obtained by measuring the positive electrode active material, the integrated intensity I of each peak of the 006 plane near 2θ = 36°, the 102 plane near 2θ = 37°, and the 101 plane near 2θ = 38° was calculated. ００６ , I １０２ , I １０１The R value was calculated from the formula (8). It is known that the R value decreases as the layering of the positive electrode active material progresses, and was used as an index of good crystallinity. In this respect, a preferable R value is 0.50 or less. R value = (I ００６ +I １０２ ) / I １０１ ...(8)

[0097] (Oxidation (lithiation) distance) Line analysis of oxygen elements was performed on the cross section of the precursor by SEM-EDS, and the distance (depth) from the surface where oxidation and lithiation occurred simultaneously was measured. The oxidation (lithiation) distance was measured for three particles, and the average value was taken as the oxidation (lithiation) distance. The oxidation (lithiation) distance was divided by the D50 of the precursor and multiplied by 100 to obtain the oxidation (lithiation) distance ratio, which was calculated using formula (9). Oxidation (lithiation) distance ratio = (oxidation (lithiation) distance) / D50 × 100 (9)

[0098] (Residual Li Amount) 0.5 g of the positive electrode active material and 30 ml of pure water were placed in a 50 ml plastic container, and the inside of the plastic container was replaced with argon gas. The container was then 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 with pure water to about 40 ml, and titrated with 0.02 M hydrochloric acid to determine the amount of Li in the extract. ２ CO ３ The amounts of the components and LiOH components were analyzed. An automatic titrator (Hiranuma COM-1700A) was used for the titration. The titration curve has two stages, and the equivalence point (x) of the first stage represents the reaction of formula (10) and formula (11), and the equivalence point (y) of the second stage represents the reaction of formula (11). ２ CO ３ The number of moles of is the same as the number of moles of HCl in formula (12), so the remaining Li ２ CO ３ The titration volume is the volume (y-x) between the first equivalence point and the second equivalence point. The remaining LiOH is the titration volume up to the first equivalence point, but since formula (11) is also included in the titration volume up to the first equivalence point, formula (11), that is, the remaining Li ２ CO ３ The amount obtained by subtracting the amount of Li was (2x-y). ２ CO ３The amount of Li in the remaining LiOH, that is, the amount of unreacted Li, was calculated. The number of moles of unreacted Li was divided by the number of moles of metal elements other than Li contained in the positive electrode active material, and the result was multiplied by 100 to calculate the unreacted Li ratio. Note that for the remaining LiOH, the number of moles of Li in the remaining LiOH was substituted as the moss number of unreacted Li, divided by the number of moles of metal elements other than Li contained in the positive electrode active material, and multiplied by 100 to obtain a value (mol %). LiOH + HCl → LiCl + H ２ O...(10) Li ２ CO ３ +HCl→LiCl+LiHCO ３ ...(11) LiHCO ３ +HCl→LiCl+CO ２ +H ２ O... (12)

[0099] (Metal Ni Residual Degree) After removing Kα2 from the XRD pattern obtained by measuring the precursor, the peak intensity (I ＮｉＯ ) and LiNiO around 2θ = 43.6° ２ Peak intensity (I ＬｉＮｉＯ２ ) and the peak intensity of metallic Ni around 2θ = 44.5° (I Ｎｉ The residual metal Ni content was calculated from the formula (13). Ｎｉ / (I ＮｉＯ +I ＬｉＮｉＯ２ ) ... (13)

[0100] (Porosity and Most Common Pore Diameter) The porosity of the positive electrode active material was determined by measuring the volume of pores having a pore diameter of 0.6 μm or less (pore volume) by mercury intrusion using a pore distribution measurement device "Autopore IV 9520" (manufactured by Shimadzu Corporation-Micromeritics), and dividing the measured volume by the volume of the positive electrode active material. That is, Porosity = Pore Volume / Volume of Positive Electrode Active Material (14) Furthermore, the pore distribution was measured using the pore distribution measurement device, and the most common pore diameter in the range of pore diameters of 0.6 μm or less was defined as the most common pore diameter.

[0101] [Metallic Nickel Powder Oxidation Process] [Preliminary Experiment 1] Metallic nickel powder (Ni purity 99.7% by mass, manufactured by Nippon Atomize Processing Co., Ltd.) produced by a water atomization method with a D50 of 8 μm and lithium carbonate were weighed out so that the molar ratio of metal elements was Li:Ni = 1.03:0.85. A total of 5 kg of these raw material powders was charged into a 45 L V-type mixer and mixed for 90 minutes to obtain a raw material mixed powder. Next, this raw material mixed powder was heat-treated in a sintering furnace in an air atmosphere at 650 °C for 10 hours to obtain an oxidized powder. Although some of the oxidized powder was caked, it was possible to obtain an oxidized powder equivalent to a precursor with a D50 of 8 μm by crushing it in a mortar.

[0102] [Preliminary Experiment 2] The same oxidation process as in Preliminary Experiment 1 was carried out, except that metallic nickel powder and lithium carbonate were weighed out so that the molar ratio of metal elements was Li:Ni 0.10:0.85. Although some of the oxidized powder was caked, oxidized powder with a D50 of 8 μm was obtained by crushing it in a mortar. Note that, when metallic nickel powder and lithium carbonate are mixed in a molar ratio of metal elements Li:Ni 0.10:0.85, metallic nickel powder and 10 mass% of the lithium-containing compound required for production are mixed. Incidentally, in the above-mentioned Preliminary Experiment 1, 100 mass% of the same lithium-containing compound is mixed.

[0103] Preliminary experiments 1 and 2 confirmed that by mixing metallic nickel powder with at least a portion of the lithium-containing compound (here, lithium carbonate) required for production and then performing an oxidation treatment, it was possible to oxidize the metallic nickel powder while preventing sintering. This is thought to be because the presence of the lithium-containing compound between the metallic nickel powder particles prevents contact between the metallic nickel powder particles, and as a result, prevents sintering of the metallic nickel powder.

[0104] [Example 1] As raw materials, lithium carbonate, metallic nickel powder, cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide were prepared, and each raw material was weighed out so that the molar ratio of metal elements Li:Ni:Co:Mn:Ti:Al was 0.26:0.85:0.03:0.08:0.03:0.01. Separately, lithium hydroxide was prepared and weighed out so that the molar ratio of metal elements other than Li:Li was 0.77:1.00. Therefore, the target composition of the positive electrode active material (hereinafter referred to as the charged composition of the positive electrode active material) was Li:Ni:Co:Mn:Ti:Al. １．０３ Ni ０．８５ Co ０．０３ Mn ０．０８ Ti ０．０３ Al ０．０１ O ２ The metallic nickel powder used was a metallic nickel powder with a D50 of 8 μm and a Ni purity of 99.7% by mass, produced by a water atomization method. Hereinafter, in each example, comparative example, and reference example, what is simply referred to as metallic nickel powder refers to a metallic nickel powder with the same nickel purity as in Example 1. First, metallic nickel powder and an amount of lithium carbonate equivalent to 25% by mass, required based on the molar ratio described above, were charged into a V-type mixer and mixed for 90 minutes to obtain a raw material mixed powder. Next, 100 g of the raw material mixed powder was placed in a 150 mm square sagger and subjected to an oxidation treatment (oxidation step) at 650°C for 10 hours in a firing furnace in an air atmosphere to obtain a precursor containing a partially lithiated metallic nickel powder. The mass of the obtained precursor was 17% greater than that of the raw material mixed powder. Calculations based on this mass increase confirmed that 68% of the metallic nickel powder had become nickel oxide. In other words, the oxidation rate was 68%.

[0105] Furthermore, a raw material for metal element M consisting of cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide was pre-pulverized in a ball mill using 5 mm zirconia balls as the milling medium to obtain a pre-pulverized powder of metal element M. The D50 of the pre-pulverized powder of metal element M was 1.2 μm. As shown in the flow chart of FIG. 5 , the precursor described above, the pre-pulverized powder of metal element M, and 75% by mass of the lithium hydroxide were dry-mixed and calcined at 500°C for 20 hours in an oxygen gas flow in a calcination furnace substituted for an oxygen gas atmosphere. The mixture was then calcined at 840°C for 10 hours in an oxygen gas flow in a calcination furnace substituted for an oxygen gas atmosphere. This yielded a positive electrode active material consisting of a lithium metal composite oxide.

[0106] Example 2 A precursor and a positive electrode active material were produced in the same manner as in Example 1, except that the oxidation treatment temperature in the oxidation step was 550° C. for 10 hours. The oxidation rate of the precursor was 49%.

[0107] [Comparative Example 1] In Comparative Example 1, a raw material of metal element M was used as a mixed raw material with metal nickel powder. As raw materials, metal nickel powder, cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide were prepared, and each raw material was weighed so that the molar ratio of metal elements was Ni:Co:Mn:Ti:Al = 0.85:0.03:0.08:0.03:0.01. In addition, lithium hydroxide was prepared and weighed so that the molar ratio of metal elements was Li:metal elements other than lithium = 1.03:1.00. Note that, for the metal nickel powder, metal nickel powder with a D50 of 8 μm produced by a water atomization method was used. In addition, similar to Example 1, the target composition of the positive electrode active material (hereinafter referred to as the charged composition of the positive electrode active material) was Li. １．０３ Ni ０．８５ Co ０．０３ Mn ０．０８ Ti ０．０３ Al ０．０１ O ２First, a raw material of metal element M consisting of cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide was pre-pulverized in a ball mill using 5 mm zirconia balls as the milling medium to obtain a pre-pulverized powder of metal element M. The pre-pulverized powder of metal element M had a D50 of 1.2 μm. Next, the metallic nickel powder and the pre-pulverized powder of metal element M were placed in a V-type mixer and mixed for 90 minutes to obtain a raw material mixed powder. Next, 50 g of the raw material mixed powder was placed in a 150 mm square sagger and oxidized in a firing furnace in an air atmosphere at 550°C for 10 hours (oxidation step), obtaining a precursor containing metallic nickel powder combined with metal element M. The lithium-free precursor obtained had a mass increase of 7.7% compared to the raw material mixed powder. Calculations based on this mass increase confirmed that 62% of the metallic nickel powder had become nickel oxide. In other words, the oxidation rate was 62%.

[0108] The precursor and the lithium hydroxide were dry-mixed and calcined in an oxygen gas atmosphere in a calcination furnace at 500°C for 20 hours in an oxygen stream. The mixture was then calcined in an oxygen gas atmosphere in a calcination furnace at 840°C for 10 hours in an oxygen stream. This yielded a positive electrode active material made of a lithium metal composite oxide.

[0109] The oxidation rates of the precursors of Examples 1 and 2 and Comparative Example 1 are shown in Table 1. The crystallite diameters of the nickel oxide contained in the precursors calculated from XRD measurements of the precursors and the positive electrode active materials of Examples 1 and 2 and Comparative Example 1, and the above-mentioned I ＮｉＯ , I LiNiO2 , I Ｎｉ , I LiNiO2 / I Ｎｉ , I LiNiO2 / I ＮｉＯ The residual amount of metallic Ni and the R value of the positive electrode active material are shown in Table 1 (Table 1-1, Table 1-2).

[0110] Item #1 in Table 1-1 is the average particle size D50 of the metallic nickel powder as the starting material, Item #2 in Table 1-1 is the name of the material mixed with the metallic nickel powder before the oxidation step, Item #3 in Table 1-1 is the oxidation temperature (°C) in the oxidation step, Item #4 in Table 1-1 is the total mass (g) of the metallic nickel powder introduced into the oxidation step and the material mixed with the metallic nickel powder, and Item #5 in Table 1-1 is the oxidation rate of the precursor produced after the oxidation step. Next, Item #6 in Table 1-2 is the crystallite size of the nickel oxide contained in the precursor calculated from the results of XRD measurement performed on the precursor after the oxidation step, and Item #7 in Table 1-2 is the peak intensity (I) of NiO near 2θ = 43.2° after removing Kα2 from the XRD patterns of the precursors of each Example and Comparative Example. ＮｉＯ ) value, and item #8 in Table 1-2 is LiNiO around 2θ = 43.6° after removing Kα2 from the XRD patterns of the precursors of each example and comparative example. ２ Peak intensity (I ＬｉＮｉＯ２ ) value, and item #9 in Table 1-2 is the peak intensity (I) of metallic Ni around 2θ = 44.5° after removing Kα2 from the XRD pattern of the precursor of each example and comparative example. Ｎｉ ) value, and item #10 in Table 1-2 is the I value in the precursors of each example and comparative example. ＬｉＮｉＯ２ Value and I Ｎｉ Item #11 in Table 1-2 indicates the ratio of I in the precursors of each example and comparative example. ＬｉＮｉＯ２ Value and I ＮｉＯ Item #12 in Table 1-2 is the ratio of the oxidation rate to the R value of the precursor of each Example and Comparative Example, calculated by formula (13). Item #13 in Table 1-2 is the R value of the cathode active material of each Example and Comparative Example. EB1 represents Example 1, EB2 represents Example 2, and Rf1 represents Comparative Example 1. The relationship between the oxidation rate and the R value for Examples 1 and 2 and Comparative Example 1 is shown in FIG. 8.

[0111]

[0112]

[0113] 8, it was confirmed that Examples 1 and 2 have lower R values ​​than Comparative Example 1, and that positive electrode active materials with good crystallinity can be obtained. Tables 1-1 and 1-2 show that the oxidation rates are equivalent for the precursors of Examples 1 and 2, which use lithium carbonate as the material to be mixed with the metallic nickel powder before the oxidation step, and the precursor of Comparative Example 1, which uses raw materials for the metal element M consisting of cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide. On the other hand, the peak intensities (I ＬｉＮｉＯ２ ) are 10600, 1400 and LiNiO around 2θ = 43.6°, respectively. ２ Peak intensity (I ＬｉＮｉＯ２ ) was confirmed, but no clear peak actually appeared in the comparative example. ＬｉＮｉＯ２ ) but only presents values ​​around 2θ=43.6°. ＬｉＮｉＯ２ / I Ｎｉ Therefore, the precursors of Examples 1 and 2 contain lithium metal oxide (LiNiO) in addition to Ni oxide (NiO). ２ ) was formed, while no lithium metal oxide was observed in the precursor of Comparative Example 1. Furthermore, the cathode active materials of Examples 1 and 2 had a lower R value of 0.50 or less compared to the cathode active material of Comparative Example 1, confirming that cathode active materials with good crystallinity were obtained. That is, despite the same oxidation rate, the use of the precursors of Examples 1 and 2 containing lithium metal oxide resulted in cathode active materials with good crystallinity compared to the use of the precursor of Comparative Example 1 not containing lithium metal oxide. From the above, it was found that the inclusion of lithium metal oxide in the precursor results in a cathode active material with good crystallinity. Furthermore, since the formation of lithium metal oxide in the precursor requires the use of a compound containing lithium as an inclusion, it was confirmed that the use of a compound containing lithium as an inclusion can produce a cathode active material with good crystallinity. Furthermore, from the XRD patterns of the precursors after the oxidation process in Examples 1 and 2, in addition to the nickel oxide peak, it was confirmed that a peak existed between approximately 43.5° and 44.0°, which is the 2θ angle attributed to lithium nickel oxide.

[0114] Next, the particle size of the metallic nickel powder and its influence on the electrochemical properties of the positive electrode active material will be described, followed by an example in which a lithium-containing compound is added separately.

[0115] Reference Example 1 A precursor was produced in the same manner as in Example 1 except that metallic nickel powder having a D50 of 30 μm was used, and then a positive electrode active material was produced in the same manner as in Example 1.

[0116] Reference Example 2 A precursor was produced in the same manner as in Example 1, except that metallic nickel powder having a D50 of 70 μm was used, and then a positive electrode active material was produced in the same manner as in Example 1.

[0117] XRD was measured for the positive electrode active materials of Reference Examples 1 and 2, and the R values ​​were calculated. The results are shown in Table 2. Item I in Table 2 indicates the average particle size D50 (μm) of the metallic nickel powder used in Example 1 and each Reference Example. Item II in Table 2 indicates the oxidation rate of the precursor obtained by mixing the metallic nickel powder with lithium carbonate and then oxidizing it in each Example and each Reference Example. Item III in Table 2 indicates the R values ​​of the positive electrode active materials in Example 1 and each Reference Example. Item IV in Table 2 indicates the nickel ratio (Ni ratio) at the center of the particles of the positive electrode active material in Example 1 and each Reference Example. EB1 indicates Example 1, Ex1 indicates Reference Example 1, and Ex2 indicates Reference Example 2.

[0118] Incidentally, this Ni ratio was determined by measuring the Ni ratio at the center of the particle cross section of the positive electrode active material using a scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX), and the results are shown in Table 2. The relationship between the D50 of the metallic nickel powder and the Ni ratio at the center of the positive electrode active material is shown in FIG. 9. The results of Example 1 are also shown in Table 2. From the above, the influence of the D50 of the metallic nickel powder was evaluated.

[0119]

[0120] As shown in Table 2 and Figure 9, when the D50 of the metallic nickel powder is 30 μm or more, the R value is high, the crystallinity is low, and the Ni ratio at the center of the positive electrode active material is high. In other words, it can be seen that metal elements other than nickel and lithium are less likely to diffuse to the center. On the other hand, as shown in Figure 9, when the D50 of the metallic nickel powder is 20 μm or less, the Ni ratio at the center of the positive electrode active material is approximately 95%, which indicates that metal elements other than nickel and lithium are more likely to diffuse. Further diffusion of metal elements other than lithium is preferable because it results in a more uniform composition of the positive electrode active material and allows the desired electrochemical characteristics to be obtained with the target composition. From the above, it is possible to directly use the metallic nickel powder as a raw material to produce a positive electrode active material if the D50 of the metallic nickel powder is 20 μm or less.

[0121] On the other hand, even if the D50 of the metallic nickel powder exceeds 20 μm, if it contains lithium metal oxide and has a high lithiation rate, it can be used as a raw material by grinding it to 20 μm or less in a short grinding time (FIG. 4) as described above. As in the examples, it can be said that metal elements other than nickel and lithium can diffuse to the center during the production process of the positive electrode active material, resulting in a uniform composition and enabling the desired electrochemical properties to be obtained.

[0122] [Example 3] As raw materials, lithium carbonate, metallic nickel powder, cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide were prepared, and each raw material was weighed so that the molar ratio of metal elements was Li:Ni:Co:Mn:Ti:Al=1.03:0.85:0.03:0.08:0.03:0.01. Note that metallic nickel powder used was metallic nickel powder with a D50 of 8 μm produced by a water atomization method. Also, similar to Example 1, the target composition of the positive electrode active material (hereinafter referred to as the charged composition of the positive electrode active material) was Li:Ni:Co:Mn:Ti:Al=1.03:0.85:0.03:0.08:0.03:0.01. １．０３ Ni ０．８５ Co ０．０３ Mn ０．０８ Ti ０．０３ Al ０．０１ O ２First, lithium carbonate (pre-added) and metallic nickel powder, in amounts corresponding to 25 mass % required according to the above-mentioned molar ratio so that the molar ratio of lithium to nickel was Li:Ni 0.26:0.85, were charged into a V-type mixer and mixed for 90 minutes to obtain a raw material mixed powder. Next, this raw material mixed powder was subjected to an oxidation treatment (oxidation step) in a firing furnace in an air atmosphere at 650°C for 10 hours to obtain a precursor containing oxidized metallic nickel powder.

[0123] Next, following the flow chart shown in Figure 6, the obtained precursor was mixed with raw materials for the metal element M, consisting of cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide, and pure water was added to the mixture to a solids ratio of 30% by mass. The mixture was then wet-pulverized in a pulverizer to prepare a raw material slurry with a primary particle D50 of 0.30 μm (pulverization process). The obtained raw material slurry was then spray-dried using a nozzle-type spray dryer (Okawahara Chemical Engineering Co., Ltd., ODL-20 model) to obtain a granulated powder with a D50 of approximately 10 μm (granulation process). This granulated powder and the remaining 75% by mass of lithium carbonate (post-added) were placed in a V-type mixer and mixed for 90 minutes to obtain a mixed granulated powder. In this example, the lithium-containing compound was added and mixed. The mixed granulated powder was then calcined to obtain a lithium metal composite oxide (calcination process). Specifically, the mixture was calcined in an oxygen gas atmosphere at 700°C for 24 hours in an oxygen stream in a calciner. Thereafter, the mixture was subjected to main calcination in an oxygen gas flow at 820°C for 10 hours in a calcination furnace whose atmosphere had been replaced with oxygen gas, thereby obtaining a lithium metal composite oxide. The calcined powder obtained by the calcination step was classified using a sieve with an opening of 53 µm, and the powder that fell under the sieve was used as the positive electrode active material.

[0124] In Example 3, the remaining amount of lithium compound was mixed after the granulation step, with 25% by mass being mixed before the oxidation step (pre-addition) and 75% by mass being mixed after the granulation step (post-addition). The oxidation rate and lithiation rate of the precursor in Example 3, as well as the oil absorption and particle strength of the positive electrode active material, were measured. The results are shown in Table 3.

[0125] (Preparation of Positive Electrode) Next, a lithium ion secondary battery was prepared using the positive electrode active material synthesized in Example 3 as the positive electrode material and metallic lithium as the negative electrode material, and the initial capacity and capacity retention rate of the lithium ion secondary battery were measured. First, the prepared 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 positive electrode current collector made of aluminum foil with a thickness of 15 μm in a coating amount of 13 mg / cm. ２ The positive electrode mixture slurry applied to the positive electrode current collector was then heat-treated at 120°C to remove the solvent, thereby forming a positive electrode mixture layer. The positive electrode mixture layer was then pressure-molded using a hot press and punched into a circular shape with a diameter of 15 mm to form a positive electrode.

[0126] (Initial capacity and charge / discharge cycle characteristics (capacity retention rate) by half cell) Subsequently, a lithium ion secondary battery was fabricated using the fabricated positive electrode, negative electrode, and separator. Metallic lithium punched into a circle with a diameter of 16 mm was used as the negative electrode. A porous separator made of polypropylene with a thickness of 30 μm was used as the separator. The positive electrode and negative electrode were opposed to each other in a non-aqueous electrolyte solution via the separator, and a lithium ion secondary battery was assembled. The non-aqueous electrolyte solution was a solvent mixture of ethylene carbonate and dimethyl carbonate in a volume ratio of 3:7, to which lithium hexafluorophosphate (LiPF ) was added at a concentration of 1.0 mol / L. ６ ) was dissolved in a solution.

[0127] The fabricated lithium ion secondary battery was charged at a constant current / constant voltage of 38 A / kg based on the mass of the positive electrode mixture and an upper limit potential of 4.3 V in an environment of 25 ° C. Then, it was discharged to a lower limit potential of 2.5 V at a constant current of 40 A / kg based on the mass of the positive electrode mixture, and the charge capacity and discharge capacity were measured. Thereafter, it was charged at a constant current / constant voltage of 190 A / kg based on the mass of the positive electrode mixture and an upper limit potential of 4.3 V. Then, a total of 30 cycles of discharge to a lower limit potential of 2.5 V at a constant current of 190 A / kg based on the mass of the positive electrode mixture were performed, and the discharge capacity after 30 cycles was measured. The ratio of the discharge capacity after 30 cycles to the initial capacity was calculated as the capacity retention rate. The results are also shown in Table 3.

[0128] Item A in Table 3 is the average particle size D50 (μm) of the metallic nickel powder used in Example 3. Item B in Table 3 is the ratio (mass%) of the amount of lithium carbonate added in the mixing step with the metallic nickel powder before the oxidation step in Example 3 to the amount of lithium carbonate added in the entire process of producing the positive electrode active material. Item C in Table 3 is the ratio (mass%) of the amount of lithium carbonate added between the granulation step and the firing step in Example 3 to the amount of lithium carbonate added in the entire process of producing the positive electrode active material. Item D in Table 3 is the ratio (mass%) of the amount of lithium carbonate added after the oxidation step in Example 3. Item E in Table 3 indicates the lithiation rate of the precursor in Example 3, Item F in Table 3 indicates the oil absorption per 100 g of the positive electrode active material in Example 3 (ml / 100 g), Item G in Table 3 indicates the average particle strength (MPa) of the positive electrode active material in Example 3, Item H in Table 3 indicates the initial discharge capacity (Ah / kg) of the lithium ion secondary battery produced using the positive electrode active material in Example 3, and Item J in Table 3 indicates the capacity retention rate (%) of the lithium ion secondary battery produced using the positive electrode active material in Example 3. Also, EB3 in Table 3 indicates Example 3.

[0129]

[0130] From Table 3, it is believed that the positive electrode active material of Example 3 had a reduced amount of lithium carbonate in the granulated powder, eliminating the scattered oxidized metallic nickel powder and resulting in a structure with fewer voids. In other words, because the amount of lithium carbonate mixed before the oxidation process was small, the oil absorption was reduced, reducing the voids in the positive electrode active material, and as a result, the particle strength was also high. Furthermore, as a lithium-ion secondary battery, the initial discharge capacity was high at 190 Ah / kg. The capacity retention rate was also good, at 90% or more. This is believed to be because the amount of lithium carbonate mixed before the oxidation process was 50% by mass or less, resulting in a positive electrode active material with fewer voids and higher strength. Furthermore, the post-addition of the remaining lithium carbonate allowed for sufficient penetration of the lithium component, resulting in good cycle characteristics.

[0131] Next, a preliminary experiment on the milling process for a crude precursor produced using metallic nickel powder having an average particle size D50 exceeding 20 μm will be described, followed by a description of examples.

[0132] [Preliminary Experiment 3] The carbon content was measured and cross-sectional SEM observation was performed on the crude precursor of Reference Example 2, and the lithiation rate, oil absorption, and oxidation (lithiation) distance were calculated. The results are shown in Table 4 (Table 4-1 and Table 4-2).

[0133] Next, the crude precursor of Reference Example 2 was mixed with the raw material of the metal element M consisting of cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide. 200 g of this mixed powder was placed in a plastic pot, 200 g of pure water and 200 g of zirconia balls (manufactured by Nikkato) with a ball diameter of 5 mm were added as media, and the mixture was pulverized at a rotation speed of 90 rpm for 64 hours to obtain a pulverized slurry (first pulverization step (coarse pulverization step)). After coarse pulverization, the D50 was 2.9 μm and the D95 was 10.1 μm. Next, in order to finely pulverize the obtained pulverized slurry, wet pulverization was performed using a pulverizer, but fine pulverization was not possible. The reason for this will be explained later.

[0134] [Example 4] As raw materials, lithium carbonate, metallic nickel powder, cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide were prepared, and the raw materials were weighed so that the molar ratio of metal elements Li:Ni:Co:Mn:Ti:Al was 1.03:0.85:0.03:0.08:0.03:0.01. As in Example 1, the target composition of the positive electrode active material (hereinafter referred to as the charged composition of the positive electrode active material) was Li: １．０３ Ni ０．８５ Co ０．０３ Mn ０．０８ Ti ０．０３ Al ０．０１ O ２ The metallic nickel powder used had a D50 of 70 μm and a D95 of 176 μm. Lithium carbonate and metallic nickel powder, equivalent to 25% by mass, were charged into a V-type mixer in an amount required according to the molar ratio of lithium to nickel, such that the molar ratio of lithium to nickel was Li:Ni 0.26:0.85. Mixing was performed for 120 minutes to obtain a raw material mixed powder. Next, this raw material mixed powder was oxidized by performing an oxidation treatment (oxidation step) at 700°C for 4 hours in a firing furnace in an air atmosphere, to obtain a crude precursor containing a partially lithiated 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 above-mentioned lithiation rate, oil absorption, oxidation (lithiation) distance, oxidation (lithiation) distance rate, and I. ＬｉＮｉＯ２ / I Ｎｉ , I ＬｉＮｉＯ２ / I ＮｉＯ、 The results are shown in Tables 4-1 and 4-2. In Example 4, in addition to the nickel oxide peak, a peak between approximately 43.5° and 44.0°, which is the 2θ angle attributable to lithium nickel oxide, was also confirmed from the XRD pattern of the precursor after the oxidation step.

[0135] Next, following the flow chart shown in Figure 7, the obtained crude precursor was mixed with raw materials for the metal element M, consisting of cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide. 200 g of this mixed powder was placed in a plastic pot, and 200 g of pure water and 200 g of zirconia balls (manufactured by Nikkato) with a ball diameter of 5 mm were added as media. The mixture was then pulverized at a rotation speed of 90 rpm for 64 hours to obtain a pulverized slurry (first pulverization step (coarse pulverization step)). The particle size distribution after coarse pulverization was measured. The results are shown in Table 4-2.

[0136] Next, the obtained pulverized slurry was wet-pulverized in a pulverizer to prepare a raw material slurry having a D50 of 0.3 μm (second pulverization step (pulverization step)). The particle size distribution after pulverization is shown in Table 4-2. The obtained raw material slurry was then spray-dried using a nozzle-type spray dryer (Okawahara Chemical Engineering Co., Ltd., ODL-20 model) to obtain a granulated powder having a D50 of approximately 10 μm (granulation step). The dried granulated powder and lithium carbonate (75 mass %) required based on the molar ratio of lithium to nickel (Li:Ni) of 1.03:0.85 were then added to a V-type mixer to obtain a mixed granulated powder. The obtained mixed granulated powder was calcined to obtain a lithium metal composite oxide (calcination step). Specifically, the mixture was calcined in an oxygen gas atmosphere at 700°C in an oxygen stream for 24 hours in a calcination furnace substituted with oxygen gas. Thereafter, the mixture was subjected to main calcination in an oxygen gas flow at 820°C for 10 hours in a calcination furnace whose atmosphere had been replaced with oxygen gas, thereby obtaining a lithium metal composite oxide. The calcined powder obtained by the calcination step was classified using a sieve with an opening of 53 µm, and the powder that fell under the sieve was used as the positive electrode active material.

[0137] [Examples 5 to 7] A crude precursor was obtained in the same manner as in Example 4, except that the oxidation treatment time in the oxidation step was changed to 8 hours in Example 5, 10 hours in Example 6, and 30 hours in Example 7, and a positive electrode active material was produced in the same manner. In each example, as in Example 1, the target composition of the positive electrode active material (hereinafter, the charged composition of the positive electrode active material) was Li １．０３ Ni ０．８５ Co ０．０３ Mn ０．０８ Ti ０．０３ Al ０．０１ O ２Similarly, for the crude precursor, the oxidation rate, lithiation rate, oil absorption, oxidation (lithiation) distance, oxidation (lithiation) distance rate, and I derived from the XRD measurement results were ＬｉＮｉＯ２ / I Ｎｉ , I ＬｉＮｉＯ２ / I ＮｉＯ The residual amount of metallic Ni, etc. were calculated. In addition, the particle size distribution after coarse pulverization and after fine pulverization was measured. The results are shown in Table 4 (Table 4-1, Table 4-2). In all of Examples 5 to 7, in addition to the nickel oxide peak, a peak was confirmed in the XRD pattern of the precursor after the oxidation step, between approximately 43.5° and 44.0°, which is the 2θ angle attributed to lithium nickel oxide.

[0138] Next, in order to investigate the influence of the powder characteristics of the precursor on the powder characteristics and electrochemical characteristics of the positive electrode active material, the residual LiOH and residual Li of the positive electrode active materials obtained in Examples 4 to 7 were measured. ２ CO ３ The unreacted Li ratio, specific surface area, oil absorption, and R value were determined. The results are shown in Table 5. Furthermore, a positive electrode and a lithium ion secondary battery were fabricated in the same manner as in Example 3, and the initial capacity was measured, and the Coulomb efficiency and charge / discharge cycle characteristics (capacity retention rate) were evaluated. The results are shown in Table 5. Note that the Coulomb efficiency is a battery characteristic expressed as discharge capacity / charge capacity, and indicates the proportion 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; the higher this value, the better the characteristics.

[0139] Item A1 in Table 4-1 indicates the average particle size D50 (μm) of the metallic nickel powder used in producing the precursors in Reference Example 2 and Examples 4 to 7. Item B1 in Table 4-1 indicates the oxidation treatment temperature (° C.) in the oxidation step performed after mixing the metallic nickel powder with lithium carbonate in Reference Example 2 and Examples 4 to 7. Item C1 in Table 4-1 indicates the oxidation treatment time (hours) in the oxidation step in Reference Example 2 and Examples 4 to 7. Item D1 in Table 4-1 indicates the ratio (% by weight) of the amount of lithium carbonate added in the mixing step with the metallic nickel powder before the oxidation step to the amount of lithium carbonate added in all steps of producing the positive electrode active material. Furthermore, item E1 in Table 4-1 indicates the oxidation rate (%) of the precursors of Reference Example 2 and Examples 4 to 7, item F1 in Table 4-1 indicates the Li conversion rate (%) of those precursors, item G1 in Table 4-1 indicates the oil absorption per 100 g of those precursors (ml / 100 g), item H1 in Table 4-1 indicates the oxidation (Li) conversion distance (μm) of those precursors, and item J1 in Table 4-1 indicates the oxidation distance rate (%) of those precursors.

[0140] On the other hand, item A2 in Table 4-2 shows the peak intensity (I) of metallic Ni after removing Kα2 from the XRD patterns of the precursors of Reference Example 2 and Examples 4 to 7. Ｎｉ ) value, and item B2 in Table 4-2 is the value of LiNiO after removing Kα2 from the XRD pattern of the precursor. ２ Peak intensity (I ＬｉＮｉＯ２ ) value, and Table 4-2, Item C2, is the peak intensity (I) of NiO after removing Kα2 from the XRD pattern of the precursor. ＮｉＯ ) values, Table 4-2, Item D2 shows the I values ​​in their precursors. ＬｉＮｉＯ２ Value and I Ｎｉ The ratio of the I value to the I value in Table 4-2, Item E2, is the I value in those precursors. ＬｉＮｉＯ２ Value and I ＮｉＯ The ratio of the Ni content to the Ni content of the precursors was calculated based on the formula (13). Item F2 in Table 4-2 was calculated based on the formula (13). Item G2 in Table 4-2 was calculated based on the XRD measurement results. The crystallite diameter (nm) of the nickel oxide phase contained in the precursors was calculated based on the XRD measurement results. Item H2 in Table 4-2 was calculated based on the XRD measurement results. ２Item J2 in Table 4-2 is the crystallite diameter (nm) of the metallic Ni phase contained in these precursors, calculated from the XRD measurement results. Item K2 in Table 4-2 is the average particle size D50 (μm) after the precursors of Reference Example 2 and Examples 4 to 7 have been subjected to the first pulverization step (coarse pulverization step), item L2 in Table 4-2 is the particle size D95 (μm) which accumulates from the smallest size based on the particle size distribution of the precursors of Reference Example 2 and Examples 4 to 7 have been subjected to the first pulverization step (coarse pulverization step), item M2 in Table 4-2 is the average particle size D50 (μm) after the precursors of Reference Example 2 and Examples 4 to 7 have been subjected to the first pulverization step (coarse pulverization step) and the second pulverization step (fine pulverization step), item N2 in Table 4-2 is the particle size D95 (μm) which accumulates from the smallest size based on the particle size distribution of the precursors of Reference Example 2 and Examples 4 to 7 have been subjected to the first pulverization step (coarse pulverization step) and the second pulverization step (fine pulverization step).

[0141] Next, item A3 in Table 5 shows the amount of remaining LiOH obtained from the positive electrode active materials of Examples 4 to 7 using a titrator, and item B3 in Table 5 shows the amount of remaining LiOH obtained from the positive electrode active materials of Examples 4 to 7 using a titrator. ２ CO ３ Item C3 in Table 5 is the ratio (%) of the number of moles of unreacted Li contained in the positive electrode active materials of Examples 4 to 7 to the number of moles of metal elements other than Li contained in each positive electrode active material of Examples 4 to 7. Item D3 in Table 5 is the specific surface area (m ２ / g), item E3 in Table 5 is the oil absorption per 100 g of the positive electrode active material of Examples 4 to 7 (ml / 100 g), and item F3 in Table 5 is the R value of the positive electrode active material of Examples 4 to 7. Item G3 in Table 5 is the initial charge capacity (Ah / kg) of the lithium ion secondary battery produced using the positive electrode active material of Examples 4 to 7, item H3 in Table 5 is the initial discharge capacity (Ah / kg) of those lithium ion secondary batteries, item J3 in Table 5 is the coulombic efficiency (%) of those lithium ion secondary batteries, and item K3 in Table 5 is the capacity retention rate (%) of those lithium ion secondary batteries. In Tables 4-1, 4-2, and 5, EB4 corresponds to Example 4, EB5 to Example 5, EB6 to Example 6, EB7 to Example 7, and Ex2 to Reference Example 2.

[0142]

[0143]

[0144]

[0145] As shown in Table 4-1, even when using metallic nickel powder with a D50 of 70 μm, as in Examples 4 to 7, precursors with an oxidation rate of 65% or higher were obtained while preventing sintering by adding lithium carbonate before the oxidation process. Furthermore, the lithium content increased with increasing oxidation time, indicating a decrease in the unreacted lithium content, and the reaction between the lithium source and metal sources such as nickel progressed, resulting in the formation of lithium metal oxide. While the lithium content can be used as an indicator of ease of pulverization, increasing the lithium content increases the amount of lithium metal oxide in the precursor, which can be said to increase the volumetric expansion, making the precursor more susceptible to cracking. Furthermore, for precursors in Examples 4 to 7 with a lithium content of 12% or higher, the oil absorption of the precursor was 16 to 18 ml / 100 g, a significant increase from 8 ml / 100 g in Reference Example 2, which had a lithium content of 7%. This also indicates an increase in cracks within the precursor. As a result, in Examples 4 to 7, the D95 after coarse pulverization was 3 μm or less, making fine pulverization possible. On the other hand, the lithiation rate in Reference Example 2 was low at less than 10%, and it is thought that the small number of cracks prevented fine pulverization. Therefore, when the average particle size of the metallic nickel powder exceeds 20 μm, it is necessary to set the lithiation rate of the precursor to 10% or more.

[0146] Furthermore, as shown in Table 5, the higher the lithiation ratio of the precursor, the lower the unreacted Li ratio of the positive electrode active material. This resulted in a positive electrode active material with good crystallinity and an R value of 0.50 or less, and good results were obtained in terms of initial capacity, Coulombic efficiency, and capacity retention. Figure 10 shows the relationship between the lithiation ratio and initial capacity. It can be seen that the higher the lithiation ratio, the higher the initial capacity. Here, the higher the lithiation ratio, the lower the unreacted Li ratio contained in the positive electrode active material. This indicates that there are fewer unreacted impurities, and it can be said that the higher the lithiation ratio, the lower the unreacted impurities. From this perspective, it can be said that the initial capacity also increases. While the initial capacity was slightly lower in Example 7, this was thought to be due to excessive lithiation before the firing process, resulting in the consumption of lithium carbonate, which reduced the liquid phase component during the firing process and made it difficult for the lithium metal oxide reaction to proceed. For these reasons, by setting the lithiation ratio of the precursor to 10% or more, preferably 15% or more, the Li+M+O ２ →LiMO ２ (M=Ni, Co, Mn, etc.) reaction is promoted, and electrochemical properties such as initial capacity are also improved.

[0147] In addition, in the precursors of Examples 4 to 7, the peak intensity I LiNiO2 and the peak intensity of metallic nickel I Ni Intensity ratio I LiNiO2 / I Ni In Table 4, ＬｉＮｉＯ２ / I Ｎｉ The values ​​are shown as D95, which is a sufficiently large value of 5 to 30. Therefore, sufficient cracks were formed in these precursors, making them highly pulverizable. In fact, the D95 was pulverized to 3.0 μm or less in the first pulverization step (coarse pulverization step), and the D95 was also pulverized to 0.5 μm or less in the second pulverization step (fine pulverization step). Therefore, positive electrodes and lithium ion secondary batteries were successfully fabricated.

[0148] From the above results, it was found that by appropriately reacting metallic nickel powder with a portion of Li in the oxidation step in the production of the precursor, lithiation is promoted, the crystal structure is stabilized, and a lithium-ion secondary battery with good electrochemical properties can be obtained.

[0149] Next, in order to examine the influence of the manufacturing method of the positive electrode active material of the present invention on the powder characteristics and electrochemical characteristics of the positive electrode active material, positive electrode active materials were manufactured according to Example 8 and Comparative Examples 2 and 3, and the amount of residual Li, particle strength, porosity, and mode porosity were measured.

[0150] [Example 8] A positive electrode active material was produced in the same manner as in Example 6, except that the temperature of the main baking was set to 840°C. As in Example 1, the target composition of the positive electrode active material (hereinafter, the charged composition of the positive electrode active material) was Li １．０３ Ni ０．８５ Co ０．０３ Mn ０．０８ Ti ０．０３ Al ０．０１ O ２ It was decided.

[0151] [Comparative Example 2] First, lithium carbonate, nickel hydroxide, cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide were prepared as raw materials. Each raw material was weighed so that the molar ratio of metal elements was Li:Ni:Co:Mn:Ti:Al was 1.03:0.85:0.03:0.08:0.03:0.01, and pure water was added so that the solid content ratio was 30 mass%. Then, wet grinding (wet mixing) was performed using a grinder to prepare a raw material slurry with an average particle size of less than 0.2 μm. This comparative example differs from the examples in that nickel hydroxide is used as a raw material. Also, as in Example 1, the target composition of the positive electrode active material was Li １．０３ Ni ０．８５ Co ０．０３ Mn ０．０８ Ti ０．０３ Al ０．０１ O ２ It was decided.

[0152] The resulting raw material slurry was then spray-dried using a nozzle-type spray dryer to obtain granulated powder with a D50 of approximately 12 μm. The granulated powder was then dehydrated in a continuous conveying furnace at 400°C for 5 hours in an air atmosphere. The granulated powder was then heat-treated in an oxygen gas atmosphere-substituted sintering furnace at 650°C for 22 hours in an oxygen stream, and then pre-fired at 700°C for 30 hours. The granulated powder was then fired in an oxygen gas atmosphere-substituted sintering furnace at 840°C for 10 hours in an oxygen stream, and then heat-treated in an oxygen gas atmosphere-substituted sintering furnace at 740°C for 4 hours in an oxygen stream. When nickel hydroxide is used as the raw material, a heat treatment process is performed to remove adhesion of the raw material powder within the firing furnace and adjust the structure. The fired powder was then classified using a sieve with a mesh size of 53 μm, and the powder that fell through the sieve was used as the positive electrode active material.

[0153] [Comparative Example 3] A positive electrode active material was produced in the same manner as in Comparative Example 2, except that the temperature of the main baking was set to 820°C. In addition, as in Example 1, the target composition of the positive electrode active material was Li １．０３ Ni ０．８５ Co ０．０３ Mn ０．０８ Ti ０．０３ Al ０．０１ O ２ It was decided.

[0154] The residual Li amount, particle strength, porosity, and mode porosity of the positive electrode active materials of Example 8, Comparative Example 2, and Comparative Example 3 were measured. The results are shown in Table 6 (Table 6-1, Table 6-2). Cross-sectional SEM observations of the positive electrode active materials were also performed. FIG. 12A shows a cross-sectional SEM image of Example 8, FIG. 12B shows a cross-sectional SEM image of Comparative Example 2, and FIG. 12C shows a cross-sectional SEM image of Comparative Example 3.

[0155] (Fabrication of Positive Electrode) Next, lithium ion secondary batteries were fabricated using the positive electrode active materials synthesized in Example 8, Comparative Example 2, and Comparative Example 3 as positive electrode materials in the same manner as in Example 3, except that graphite was used for the negative electrode and a square positive electrode measuring 30 mm × 35 mm was used.

[0156] (Initial discharge capacity and charge / discharge cycle characteristics (capacity retention rate, resistance increase rate) in a full cell) Subsequently, a lithium ion secondary battery was fabricated using the fabricated positive electrode, a 35 mm x 40 mm graphite negative electrode, and a separator. A 30 μm thick porous polypropylene separator was used as the separator. The positive electrode and negative electrode were opposed to each other in a non-aqueous electrolyte solution via the separator, and the lithium ion secondary battery was assembled. The non-aqueous electrolyte solution was a mixture of ethylene carbonate and dimethyl carbonate in a volume ratio of 3:7, with LiPF at a concentration of 1.0 mol / L. ６ A solution containing the above was used. Also, 1.5% vinylene carbonate (VC) was added as an additive.

[0157] The fabricated lithium ion secondary battery was charged at a constant current / constant voltage of 40 A / kg based on the mass of the positive electrode mixture and an upper limit potential of 4.2 V in an environment of 25 ° C. Then, it was discharged to a lower limit potential of 2.5 V at a constant current of 40 A / kg based on the mass of the positive electrode mixture, and the charge capacity and discharge capacity were measured. Thereafter, it was charged at a constant current / constant voltage of 190 A / kg based on the mass of the positive electrode mixture and an upper limit potential of 4.2 V. Then, a total of 300 cycles of discharging to a lower limit potential of 2.5 V at a constant current of 190 A / kg based on the mass of the positive electrode mixture were performed, and the discharge capacity after 300 cycles was measured. The ratio of the discharge capacity after 300 cycles to the initial capacity was calculated as the capacity retention rate. Furthermore, the DC resistance was measured at the beginning of the cycle and after 300 cycles, and the ratio of the resistance after 300 cycles to the initial resistance was calculated as the resistance increase rate. The results are also shown in Table 6.

[0158] Item A4 in Table 6-1 indicates the amount of remaining LiOH obtained from the positive electrode active materials of Example 8 and Comparative Examples 2 and 3 using a titrator. Item B4 in Table 6-1 indicates the amount of remaining LiOH obtained from the positive electrode active materials of Example 8 and Comparative Examples 2 and 3 using a titrator. ２ CO ３Item C4 in Table 6-1 is the oil absorption per 100 g (ml / 100 g) of the positive electrode active material of Example 8 and Comparative Examples 2 and 3; Item D4 in Table 6-1 is the porosity (%) of the positive electrode active material of Example 8 and Comparative Examples 2 and 3; Item E4 in Table 6-1 is the most frequent pore size (nm) of the positive electrode active material of Example 8 and Comparative Examples 2 and 3; Item F4 in Table 6-1 is the particle strength (MPa) of the positive electrode active material of Example 8 and Comparative Examples 2 and 3; and Item G4 in Table 6-1 is the R value of the positive electrode active material of Example 8 and Comparative Examples 2 and 3. Item A5 in Table 6-2 is the initial discharge capacity (Ah / kg) in full cells of the lithium ion secondary batteries produced using the positive electrode active materials of Example 8 and Comparative Examples 2 and 3, item B5 in Table 6-2 is the capacity retention rate (%) in full cells of the lithium ion secondary batteries produced using the positive electrode active materials of Example 8 and Comparative Examples 2 and 3, and item C5 in Table 6-2 is the resistance increase rate (%) of the lithium ion secondary batteries produced using the positive electrode active materials of Example 8 and Comparative Examples 2 and 3. In both Tables 6-1 and 6-2, EB8 corresponds to Example 8, Rf2 corresponds to Comparative Example 2, and Rf3 corresponds to Comparative Example 3.

[0159] The batteries were disassembled after the charge-discharge cycles, and cross-sectional SEM images of the positive electrode active materials were observed. The results are shown in Figure 13. Figure 13A shows a cross-sectional SEM image of the positive electrode active material of Example 8, Figure 13B shows a cross-sectional SEM image of the positive electrode active material of Comparative Example 2, and Figure 13C shows a cross-sectional SEM image of the positive electrode active material of Comparative Example 3.

[0160]

[0161]

[0162] From Table 6-1, Example 8 has a lower residual LiOH and residual Li than Comparative Examples 2 and 3. ２ CO ３ In Example 8, after the metallic nickel powder and the lithium-containing compound are reacted, the mixture is further mixed with a lithium-containing compound and calcined. Therefore, the reaction between the transition metal source and the Li source is accelerated, and as a result, the remaining LiOH and Li ２ CO ３ It is thought that this has decreased.

[0163] Furthermore, the porosity of Example 8 was 12%, which was larger than that of Comparative Example 2 and equivalent to that of Comparative Example 3. On the other hand, the most frequent pore diameter was 178 nm, which was smaller than that of Comparative Examples 2 and 3. Furthermore, FIG. 12 shows that Example 8 has a smaller pore diameter and is more uniformly distributed than Comparative Examples 2 and 3. In Example 8, the lithium-containing compound was added twice, before granulation (pre-addition) and after granulation (post-addition), and the amount of lithium-containing compound inside the granulated powder was small. This is thought to be due to the mechanism described in FIG. 11(b) resulting in fewer pores and a smaller pore diameter.

[0164] Furthermore, the particle strength of Example 8 was 59 MPa, which was higher than the 23 MPa of Comparative Example 3, which also had a porosity of 12%. This was the same strength as the 59 MPa of Comparative Example 2, which had a porosity of 4%, and it was confirmed that Example 8 achieved both high porosity and high strength. This is thought to be due to the small mode pore size and uniform pore distribution.

[0165] Next, looking at the electrochemical characteristics in Table 6-2, the initial capacity in the full cell was equivalent in Example 8 and Comparative Examples 2 and 3. On the other hand, the capacity retention rate in the full cell was 80% in Example 8, which was better than 69% in Comparative Example 2 and 71% in Comparative Example 3.

[0166] The reason why the charge-discharge cycle characteristics of the positive electrode active material of Example 8 were good will be considered. From Table 6-2, the resistance increase rate of Example 8 was lower than that of Comparative Examples 2 and 3, and it is thought that the deposition of by-products on the surface of the positive electrode active material in Example 8 was small. This is because the positive electrode active material of Example 8 contained residual LiOH and residual Li. ２ CO ３ 13, no cracks were observed in the positive electrode active material after the charge-discharge cycle in Example 8, whereas cracks were observed at the grain boundaries in Comparative Examples 2 and 3. This is thought to be because the positive electrode active material of Example 8 has a high porosity that can relieve stress associated with the charge-discharge cycle, and has high strength that can prevent the occurrence of cracks such as stress cracking. From the above, it can be seen that the positive electrode active material of Example 8 has a residual LiOH content, a residual Li ２ CO ３It is believed that the low porosity reduces the increase in resistance, and the combination of high porosity and high strength suppresses the occurrence of cracks, resulting in good charge-discharge cycle characteristics.

[0167] From the above, it was found that a lithium ion secondary battery with good electrochemical properties can be obtained by using a positive electrode active material that has a balance of LiOH, high porosity, and high strength.

[0168] [Example 9] A positive electrode active material was produced in the same manner as in Example 8, except that the raw materials were weighed so that the molar ratio of metal elements was Li:Ni:Co:Mn:Ti:Al was 1.03:0.92:0.03:0.00:0.03:0.02. Therefore, the target composition of the positive electrode active material in Example 9 was Li:Ni:Co:Mn:Ti:Al. １．０３ Ni ０．９２ Co ０．０３ Ti ０．０３ Al ０．０２ O ２ It was decided.

[0169] [Example 10] As in Example 8, lithium carbonate and metallic nickel powder were mixed in a V-type mixer so that the lithium and nickel molar ratio was 0.26:0.85, and then oxidized to produce a precursor. Thereafter, a positive electrode active material was produced in the same manner as in Example 8, except that the lithium-containing compound to be mixed with the precursor by post-addition was lithium hydroxide, the pre-baking was omitted, and the main baking temperature was set to 800°C. Note that, as in Example 1, the target composition of the positive electrode active material of Example 10 was Li １．０３ Ni ０．８５ Co ０．０３ Mn ０．０８ Ti ０．０３ Al ０．０１ O ２ It was decided.

[0170] The residual Li amounts and R values ​​of the positive electrode active materials of Examples 9 and 10 were measured and are shown in Table 7. Item A6 in Table 7 indicates the residual LiOH amounts of Examples 9 and 10, and item B6 in Table 7 indicates the residual LiOH amounts of Examples 9 and 10. ２ CO ３Item C6 in Table 7 shows the R values ​​of Examples 9 and 10. Item D6 in Table 7 shows the initial discharge capacity of a lithium ion secondary battery when the positive electrode active material of Example 10 was used to configure the lithium ion secondary battery in the same manner as in Example 3. In Table 7, EB9 corresponds to Example 9, and EB10 corresponds to Example 10.

[0171]

[0172] From Table 7, even if the composition with a high Ni ratio or the lithium compound added later is lithium hydroxide, the remaining LiOH and the remaining Li ２ CO ３ It was confirmed that a positive electrode active material having a low R value and a stable crystal structure could be produced.

[0173] Next, in the manufacturing process shown in FIG. 5 , a single crystal (single particle) positive electrode active material was produced using a manufacturing method that added a first pulverization step (coarse pulverization step) in which the precursor and the M element compound were simultaneously wet-pulverized when mixing them, a second pulverization step (fine pulverization step) in which the pulverized slurry obtained in the first pulverization step (coarse pulverization step) was finely pulverized until the average particle size D50 reached a predetermined particle size before mixing with a lithium-containing compound, and a classification step in which classification was performed after the second pulverization step (fine pulverization step).

[0174] [Example 11] As raw materials, lithium carbonate, metallic nickel powder, cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide were prepared, and the raw materials were weighed so that the molar ratio of metal elements Li:Ni:Co:Mn:Ti:Al was 1.03:0.85:0.03:0.08:0.03:0.01. As in Example 1, the target composition of the positive electrode active material (hereinafter referred to as the charged composition of the positive electrode active material) was Li:Ni:Co:Mn:Ti:Al. １．０３ Ni ０．８５ Co ０．０３ Mn ０．０８ Ti ０．０３ Al ０．０１ O ２The metallic nickel powder used had a D50 of 70 μm and a D95 of 176 μm. Lithium carbonate and metallic nickel powder, equivalent to 25% by mass, were charged into a V-type mixer so that the molar ratio of lithium to nickel was 0.26:0.85. Mixing was performed for 120 minutes to obtain a raw material mixed powder. Next, this raw material mixed powder was oxidized in an air-conditioned furnace at 700°C for 10 hours (oxidation step) to obtain a crude precursor containing partially lithiated metallic nickel powder. The crude precursor was manufactured using the same process as in Example 4. Since the raw materials used were also the same, the oxidation rate was 69%, the same as in Example 4. Furthermore, carbon content measurement, cross-sectional SEM observation, and XRD measurement were performed on this crude precursor to determine the lithiation rate, oil absorption, oxidation (lithiation) distance, oxidation (lithiation) distance rate, and I. ＬｉＮｉＯ２ / I Ｎｉ , I ＬｉＮｉＯ２ / I ＮｉＯ、 The results were also substantially the same as those in Example 4.

[0175] Next, the obtained crude precursor was mixed with raw materials of the metal element M consisting of cobalt carbonate, manganese carbonate, titanium oxide, and aluminum oxide, and 200 g of this mixed powder was placed in a plastic pot, 200 g of pure water and 200 g of zirconia balls (manufactured by Nikkato) with a ball diameter of 5 mm were added as media, and the mixture was pulverized at a rotation speed of 90 rpm for 40 hours to obtain a pulverized slurry (first pulverization step (rough pulverization step)). The particle size distribution after coarse pulverization was measured.

[0176] Next, the obtained pulverized slurry was wet-pulverized in a pulverizer to prepare a raw material slurry having a D50 of 0.3 μm (second pulverization step (pulverization step)). Subsequently, the obtained raw material slurry was dried in a blower dryer, crushed in a mortar, and then classified using a 45 μm mesh sieve. The pulverized powder and lithium carbonate (75 mass %) required for the molar ratio of lithium to nickel (Li:Ni) of 1.03:0.85 were added to a V-type mixer to obtain a mixed pulverized powder. The obtained mixed pulverized powder was calcined to obtain a lithium metal composite oxide (calcination step). Specifically, the mixture was calcined in an oxygen gas atmosphere in a calcination furnace at 700°C for 24 hours in an oxygen stream. The mixture was then calcined in an oxygen gas atmosphere in a calcination furnace at 900°C for 10 hours in an oxygen stream to obtain a lithium metal composite oxide. The fired powder obtained in the firing step was crushed in a mortar and then classified using a sieve with 45 μm openings, and the powder that fell under the sieve was used as the positive electrode active material.

[0177] Example 12 A positive electrode active material was prepared in the same manner as in Example 11, except that the main baking conditions were changed to 900° C. for 20 hours.

[0178] Example 13 A positive electrode active material was prepared in the same manner as in Example 11, except that the main baking conditions were changed to 870° C. for 20 hours.

[0179] [Example 14] A positive electrode active material was prepared in the same manner as in Example 11, except that lithium hydroxide was used as the lithium-containing compound to be mixed with the pulverized powder, and calcination was not performed, but the mixture was fired at 870°C for 20 hours.

[0180] Example 15 A positive electrode active material was prepared in the same manner as in Example 14, except that the firing conditions were changed to 840° C. for 20 hours.

[0181] The residual Li amount, R value, and primary particle diameter of the positive electrode active materials of Examples 11 to 15 were measured and are shown in Table 8. Item A8 in Table 8 is the residual LiOH amount of Examples 11 to 15, and item B8 in Table 8 is the residual LiOH amount of Examples 11 to 15. ２ CO ３Item C8 in Table 8 shows the R values ​​of Examples 11 to 15, and item D8 in Table 8 shows the primary particle diameters of Examples 11 to 15. Item E8 in Table 8 shows the initial discharge capacity of a lithium ion secondary battery when the positive electrode active materials of Examples 11, 13, 14, and 15 were used to configure the lithium ion secondary battery in the same manner as in Example 3. In Table 8, EB11 to EB15 correspond to Examples 11 to 15.

[0182]

[0183] As shown in Table 8, Examples 11 to 15 had an average primary particle size exceeding 1 μm, resulting in so-called single-crystal positive electrode active materials. Furthermore, even without a granulation process, the R value was a relatively low value of 0.48 or less, confirming that a positive electrode active material with relatively good crystallinity could be obtained. An SEM image of the positive electrode active material in Example 13 is shown in Figure 14. It can be seen that the crystal grains of the positive electrode active material themselves were good.

[0184] Furthermore, when the post-added Li-containing compound was lithium hydroxide, the R value tended to be lower. In addition, the average primary particle size was smaller under low temperature or short time firing conditions. The smaller the average primary particle size, the higher the initial capacity tended to be.

[0185] <Preferred Aspects of the Present Disclosure> Preferred aspects of the present disclosure are described below. According to one aspect of the present disclosure, there is provided a method for producing a precursor of a positive electrode active material for a lithium ion secondary battery, the method comprising: a mixing step of mixing metallic nickel powder with a lithium-containing compound; and an oxidation step of oxidizing the metallic nickel powder after the mixing, wherein the precursor obtained after the oxidation step has a peak at 2θ = 43.5° or more and 44.0° or less in X-ray powder diffraction measurement.

[0186] Preferably, the precursor has a lithiation rate of 8% or more, which indicates the proportion of the metallic nickel powder that has reacted with lithium. Preferably, the metallic nickel powder has an average particle size of more than 20 μm, and the precursor has a lithiation rate of 10% or more. Preferably, the precursor obtained after the oxidation step contains nickel oxide having an oxidation rate of 10% or more but less than 100%, which indicates the proportion of oxidized nickel to the total amount of Ni contained in the precursor. Preferably, when the amount of lithium compound necessary for producing a positive electrode active material for a lithium-ion secondary battery is taken as 100% by mass, the amount of the lithium-containing compound mixed in the mixing step is 10% by mass or more but less than 100% by mass.

[0187] According to one aspect of the present disclosure, the method further includes a firing step of mixing the precursor produced by the method for producing a precursor of a positive electrode active material for a lithium ion secondary battery described above with at least one of a compound containing lithium and a compound containing a metal element M other than lithium and nickel to obtain a mixed powder, and then firing the mixed powder at 700°C or higher and 900°C or lower to obtain a positive electrode active material.

[0188] Preferably, the method includes a grinding step of grinding the mixed powder, followed by a granulation step of granulating the ground mixed powder to form a granulated powder, and then performing the firing step on the granulated powder. Preferably, the method includes a grinding step of grinding the mixed powder, followed by a granulation step of granulating the ground mixed powder to form a granulated powder, wherein the amount of the lithium-containing compound mixed in the precursor is less than 100 mass%, and the remaining amount of the lithium-containing compound is added after the granulation step to form a mixed granulated powder, and then performing the firing step on the mixed granulated powder. Preferably, the grinding step includes a first grinding step and a second grinding step in which the mixture is ground more finely than the first grinding step. Preferably, the diameter of the media used in the second grinding step is smaller than the diameter of the media used in the first grinding step.

[0189] Preferably, the lithium-containing compound mixed before the oxidation step and the lithium-containing compound added after the granulation step are different compounds, and the lithium-containing compound mixed before the oxidation step has a higher melting point than the lithium-containing compound added after the granulation step. Preferably, the positive electrode active material for a lithium ion secondary battery is represented by the following composition formula (A): Li １＋ａ Ni ｂ M (1-b) O ２＋α ...(A) (wherein, in the formula (A), M is a metal element other than Li and Ni, and a, b, and α are numbers that satisfy the following: -0.1≦a≦0.2, 0.5≦b≦1.0, and -0.2≦α≦0.2). It is preferably provided in a positive electrode active material represented by the following composition formula (B). Li １＋ａ Ni ｂ Co ｃ M1 ｄ X e O ２＋α ... (B) [In formula (2), M1 represents at least one element selected from Al and Mn, X represents one or more metal 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, 0.5≦b≦1.0, 0≦c≦0.20, 0≦d≦0.30, 0≦e≦0.1, b+c+d+e=1, and −0.2<α<0.2.] Furthermore, it is preferable that M1 contains at least one element selected from the group consisting of tungsten, magnesium, titanium, zirconium, molybdenum, and niobium.

[0190] According to another aspect of the present disclosure, there is provided a precursor for a positive electrode active material for a lithium ion secondary battery having a lithiation rate of 8% or more, the precursor comprising nickel and lithium, and a lithium metal oxide having a peak at 2θ=43.5° or more and 44.0° or less in X-ray powder diffraction measurement of the precursor. Preferably, the precursor comprises a lithium nickel oxide having a peak at 2θ=43.5° or more and 44.0° or less in X-ray powder diffraction measurement of the precursor, and the peak intensity I LiNiO2 and the peak intensity I of the peak at 2θ=44.0° or more and 45.0° or less, which is attributed to metallic nickel.Ni Intensity ratio I LiNiO2 / I Ni is 0.5 or more. Preferably, the positive electrode active material containing lithium and nickel has a residual LiOH content of 0.6 mol % or less, a porosity of 5 vol % to 15 vol %, a mode pore diameter of 10 nm to 250 nm, a particle strength of 30 MPa or more, and contains nickel and lithium. Alternatively, it is preferably provided in the positive electrode active material represented by the above composition formula (A) or the positive electrode active material represented by the following composition formula (B). Li １＋ａ Ni ｂ Co ｃ M1 ｄ X e O ２＋α ... (B) [In formula (2), M1 represents at least one element selected from Al and Mn, X represents one or more metal elements other than Li, Ni, Co, Al, and Mn, and a, b, c, d, e, and α are numbers that satisfy the following conditions: -0.1≦a≦0.2, 0.5≦b≦1.0, 0≦c≦0.20, 0≦d≦0.30, 0≦e≦0.1, b+c+d+e=1, and -0.2<α<0.2.] Furthermore, it is preferable that M1 contains at least one element selected from the group consisting of tungsten, magnesium, titanium, zirconium, molybdenum, and niobium. Preferably, the intensity I calculated from the integrated value of the peak identified as the 006 plane in X-ray powder diffraction measurement is ００６ and the intensity I calculated from the integral value of the peak identified as the 102 plane. １０２ and the intensity I calculated from the integral value of the peak identified as the 101 plane. １０１ The R value calculated by the following formula based on the above is 0.46 or less. R value = (I ００６ +I １０２ ) / I １０１

Claims

1. A method for producing a precursor of 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 precursor obtained after the oxidation step is a precursor containing lithium metal oxide having a peak at 2θ = 43.5° or more and 44.0° or less in X-ray powder diffraction measurement.

2. A method for producing a precursor of a positive electrode active material for a lithium ion secondary battery as described in claim 1, characterized in that the lithium content of the precursor, which indicates the proportion of the metallic nickel powder that has reacted with the lithium, is 8% or more.

3. A method for producing a precursor of a positive electrode active material for a lithium ion secondary battery as described in claim 1, characterized in that the average particle size of the metallic nickel powder exceeds 20 μm and the lithium content of the precursor is 10% or more.

4. The method for producing a precursor of a positive electrode active material for a lithium ion secondary battery as described in claim 1, characterized in that the precursor obtained after the oxidation step contains nickel oxide having an oxidation rate, which indicates the ratio of the amount of oxidized nickel to the total amount of Ni contained, of 10% or more and less than 100%.

5. A method for producing a precursor of a positive electrode active material for a lithium ion secondary battery, as described in claim 1, characterized in that when the amount of lithium compound required for producing a positive electrode active material for a lithium ion secondary battery is 100 mass%, the amount of the lithium-containing compound mixed in the mixing process is 10 mass% or more and less than 100 mass%.

6. A method for producing a positive electrode active material for a lithium ion secondary battery, comprising a calcination step of mixing a precursor produced by the method for producing a precursor of a positive electrode active material for a lithium ion secondary battery described in claim 1 with at least one of a compound containing lithium and a compound containing a metal element M other than lithium and nickel to obtain a mixed powder, and then calcining the mixed powder at a temperature of 700°C or higher and 900°C or lower to obtain a positive electrode active material.

7. A method for producing a positive electrode active material for a lithium ion secondary battery as described in claim 6, characterized in that it comprises a grinding step for grinding the mixed powder, and then a granulation step for granulating the ground mixed powder to form a granulated powder, and the firing step is performed on the granulated powder.

8. A method for producing a positive electrode active material for a lithium ion secondary battery as described in claim 6, characterized in that it comprises a grinding step of grinding the mixed powder, and then a granulation step of granulating the ground mixed powder to form a granulated powder, wherein the amount of the lithium-containing compound mixed in the precursor is less than 100 mass %, and the remaining amount of the lithium-containing compound is added after the granulation step to form a mixed granulated powder, and the firing step is performed on the mixed granulated powder.

9. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 7, characterized in that the pulverizing step includes a first pulverizing step and a step of pulverizing the material finer than that in the first pulverizing step.

10. A method for producing a positive electrode active material for a lithium ion secondary battery as described in claim 9, characterized in that the media size used in the second crushing step is smaller than the media size used in the first crushing step.

11. A method for producing a positive electrode active material for a lithium-ion secondary battery, as described in claim 7, characterized in that the lithium-containing compound mixed before the oxidation process and the lithium-containing compound added after the granulation process are different compounds, and the melting point of the lithium-containing compound mixed before the oxidation process is higher than the melting point of the lithium-containing compound added after the granulation process.

12. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 6, wherein 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) (In the formula (1), M is a metal element other than Li and Ni, and a, b, and α are numbers satisfying -0.1≦a≦0.2, 0.5≦b≦1.0, and -0.2≦α≦0.2.) 13. A precursor for a positive electrode active material for a lithium ion secondary battery, comprising nickel and lithium, and a lithium metal oxide having a peak at 2θ = 43.5° or more and 44.0° or less in X-ray powder diffraction measurement of the precursor, and having a lithiation rate of 8% or more.

14. The precursor contains a lithium nickel oxide having a peak at 2θ=43.5° or more and 44.0° or less in an X-ray powder diffraction measurement, and the peak intensity I LiNiO2 and the peak intensity I of the peak at 2θ=44.0° or more and 45.0° or less, which is attributed to metallic nickel. Ni Intensity ratio I LiNiO2 / I Ni The precursor of a positive electrode active material for a lithium ion secondary battery according to claim 13, wherein the value of is 0.5 or more.

15. A positive electrode active material for a lithium ion secondary battery, characterized in that the residual LiOH is 0.6 mol % or less, the porosity is 5 vol % or more and 15 vol % or less, the most frequent pore diameter is 10 nm or more and 250 nm or less, the particle strength is 30 MPa or more, and the positive electrode active material contains nickel and lithium.

16. Intensity I calculated from the integral value of the peak identified as the 006 plane in X-ray powder diffraction measurement ００６ and the intensity I calculated from the integral value of the peak identified as the 102 plane. １０２ and the intensity I calculated from the integral value of the peak identified as the 101 plane. １０１ The positive electrode active material for a lithium ion secondary battery according to claim 15, characterized in that the R value calculated based on the following formula is 0.46 or less. R value = (I ００６ +I １０２ ) / I １０１

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