Method for manufacturing precursor of lithium ion secondary battery positive electrode active material, and method for manufacturing lithium ion secondary battery positive electrode active material

Abstract

Provided are: a method for manufacturing a precursor of a lithium ion secondary battery positive electrode active material, the method making it possible to manufacture a lithium ion secondary battery positive electrode active material which contributes to a decrease in the greenhouse gas (GHG) discharge amount and which has good crystallinity; and a method for manufacturing a lithium ion secondary battery positive electrode active material using said precursor.　This method for manufacturing a precursor of a lithium ion secondary battery positive electrode active material comprises: a mixing step for mixing a lithium-containing compound powder with oxidized metal nickel powder to obtain a first mixed powder; a lithiation step for heat-treating the first mixed powder to obtain a lithium-nickel mixed powder containing a lithium nickel oxide; and a pulverizing step for pulverizing the lithium-nickel mixed powder.

Description

Method for producing precursor of positive electrode active material for lithium ion secondary battery, and method for producing positive electrode active material for lithium ion secondary battery

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

[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 the driving range, the energy density of lithium-ion secondary batteries has been improving year by year, and ternary layered materials are used as the positive electrode active material for these batteries, resulting in high-capacity lithium-ion secondary batteries. The ternary layered material is a composite oxide of lithium (Li) and transition metal elements such as nickel (Ni), cobalt (Co), and manganese (Mn) (hereinafter referred to as lithium metal composite oxide). As mentioned above, positive electrode active materials contain metal materials with limited reserves. However, even when extracting these metal elements from minerals, reducing greenhouse gas (GHG) emissions associated with the production of positive electrode active materials is required to maintain a sustainable global environment.

[0003] Patent Document 1 describes a method for producing a positive electrode active material for a lithium-ion secondary battery using a hydroxide of a transition metal such as Ni, Co, or Mn as a precursor. The positive electrode active material is produced by reacting a Li source with the hydroxide of the transition metal. Patent Document 2 also 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, 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. Since these methods use the coprecipitation method and use a water-soluble nickel compound such as nickel sulfate as a raw material, the weight and volume handled during production are large.

[0004] On the other hand, Patent Documents 3 and 4 describe methods for producing a positive electrode active material using a nickel raw material containing metallic nickel. These methods use a powder containing nickel and the like as the raw material, rather than a water-soluble nickel compound, and have a higher nickel content per unit volume than water-soluble nickel compounds, so the volume handled during production is relatively small in weight and is expected to contribute to reducing GHG emissions during production.

[0005] Japanese Patent Application Laid-Open No. 2015-002120 International Publication No. 2020 / 066262 International Publication No. 2010 / 082240 International Publication No. 2022 / 209988

[0006] However, in Patent Document 3, metallic nickel powder is fired as is, resulting in sintering during the firing process and making it difficult to maintain its particle state, making it difficult to pulverize. Furthermore, the crystal structure of the positive electrode active material is unstable, resulting in unstable electrochemical characteristics of lithium-ion secondary batteries. On the other hand, in Patent Document 4, metallic nickel powder with an extremely low oxygen content and almost no oxidation is mixed with at least a lithium compound powder, and the mixture is then oxidized and fired. However, there is a certain demand for production using oxidized nickel powder, which is easy to handle, as a starting material. In this case, there is a need for a precursor of a positive electrode active material for lithium-ion secondary batteries that uses oxidized nickel powder as a starting material to reduce GHG emissions while also enabling the production of a positive electrode active material with good crystallinity.

[0007] Therefore, an object 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 reducing GHG emissions and enables the production of a positive electrode active material for a lithium ion secondary battery having good crystallinity, and a method for producing a positive electrode active material for a lithium ion secondary battery using the precursor.

[0008] The method for producing a precursor of a positive electrode active material for a lithium ion secondary battery of the present invention is characterized by comprising: a first lithium mixing step of mixing an oxidized metallic nickel powder with a lithium-containing compound powder to obtain a first mixed powder; a lithiation step of heat-treating the first mixed powder to obtain a lithium-nickel mixed powder containing lithium-nickel oxide; and a lithium-nickel mixed powder pulverization step of pulverizing the lithium-nickel mixed powder.

[0009] In the present invention, the oxidized metallic nickel powder is preferably an oxidized metallic nickel powder obtained by oxidizing metallic nickel powder or nickel-based alloy powder while suppressing sintering by moving the powder. Specifically, the oxidization can be carried out using a rotary furnace or a rolling hearth furnace. On the other hand, the lithiation step is preferably carried out using a stationary furnace. Furthermore, in the present invention, it is preferable that the lithium compound powder containing 50 mass% or less of lithium relative to the amount of lithium required for the positive electrode active material for a lithium-ion secondary battery to be produced is mixed in the first lithium mixing step.

[0010] The method for producing a positive electrode active material for a lithium ion secondary battery of the present invention is characterized by comprising a firing 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 a lithium-containing compound and an M metal compound containing a metal element other than lithium and nickel to obtain a pre-fired mixed powder, and firing the pre-fired mixed powder to obtain a positive electrode active material.

[0011] The method for producing a positive electrode active material for a lithium ion secondary battery of the present invention preferably includes the following steps: a precursor and M metal compound crushing step of mixing the precursor produced by the method for producing a precursor for a lithium ion secondary battery with an M metal compound containing a metal element other than lithium and nickel, and crushing the mixed powder of the precursor and the M metal compound; a granulation step of granulating the crushed mixed powder of the precursor and the M metal compound to form a granulated powder; a second lithium mixing step of adding a lithium-containing compound to the granulated powder so as to obtain a lithium-containing compound-added granulated powder in an amount sufficient for the lithium amount of the positive electrode active material for a lithium ion secondary battery to be produced; and a firing step of firing the lithium-containing compound-added granulated powder.

[0012] In the present invention, 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.) The positive electrode active material for a lithium ion secondary battery is preferably represented by the following composition 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 the coefficients 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.]

[0013] According to the present invention, it is possible to obtain a precursor for a positive electrode active material for a lithium ion secondary battery, which contributes to a reduction in GHG emissions and enables the production of a positive electrode active material for a lithium ion secondary battery having good crystallinity, and a positive electrode active material for a lithium ion secondary battery.

[0014] FIG. 1 is a flowchart showing a method for producing an oxidized metallic nickel powder according to one embodiment of the present invention. FIG. 2 is a flowchart showing an embodiment of a method for producing a precursor of a positive electrode active material for a lithium ion secondary battery according to the present invention. FIG. 3 is a diagram showing the reflection intensity distribution versus the reflection diffraction angle determined from X-ray diffraction (XRD) of a precursor of a positive electrode active material for a lithium ion secondary battery obtained by the production method of an embodiment of the present invention and an oxidized metallic nickel powder as a comparative example. FIG. 4 is a scanning electron microscope (SEM) image of the oxidized metallic nickel powder and a mapping of oxygen (O) for the SEM image. FIG. 5 is an SEM image of a lithiated metallic nickel powder and a mapping of oxygen for the SEM image. FIG. 6 shows the relationship between the grinding time and the average particle size D50 of a lithium-nickel mixed powder and a lithium-nickel mixed powder and an oxidized metallic nickel powder obtained by the production method of an embodiment of the present invention. FIG. 7 shows the relationship between the grinding time and the average particle size D95 at 95% of the particle size frequency distribution of a lithium-nickel mixed powder and a lithium-nickel mixed powder and an oxidized metallic nickel powder obtained by the production method of an embodiment of the present invention. 7 is a flowchart showing a method for manufacturing a positive electrode active material for a lithium ion secondary battery according to a third embodiment of the present invention. It shows a schematic cross-sectional structure of simultaneously mixed granulated powder 90 before and after a firing process. It shows a schematic cross-sectional structure of granulated powder 99 granulated in granulation step S034 in FIG. 7 before and after a firing process.

[0015] Next, a method for producing a precursor of a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention and a method for producing a positive electrode active material for a lithium ion secondary battery (hereinafter referred to as a positive electrode active material) produced using the precursor will be described with reference to the drawings.

[0016] In the present embodiment, a precursor for a positive electrode active material is produced using a metallic nickel powder with low GHG emissions as a nickel source. This metallic nickel powder is oxidized to prevent sintering when subjected to various heat treatments, or an already oxidized metallic nickel powder is prepared (metallic nickel oxide powder preparation process). The oxidized metallic nickel powder is then mixed with a lithium-containing compound powder (hereinafter referred to as a lithium-containing compound powder) (first lithium mixing process), followed by heat treatment for lithiation (lithiation process), which generates lithium nickel oxide and creates cracks within the powder. The inclusion of such lithium nickel oxide in the powder makes it relatively easy to pulverize. The powder thus obtained is then pulverized to the desired particle state in a lithium-nickel mixed powder pulverization process, thereby obtaining a precursor for a positive electrode active material. The oxidation process, first lithium mixing process, lithiation process, and lithium-nickel mixed powder pulverization process may be performed simultaneously and consecutively to obtain a precursor for a positive electrode active material. Alternatively, each production process may be performed at different times or locations, allowing for flexibility in the execution of the processes.

[0017] The method for producing oxidized metallic nickel powder described below may replace the preparation step S011 of preparing oxidized metallic nickel powder in the method for producing a precursor of a positive electrode active material in an embodiment of the present invention. That is, although the oxidized metallic nickel powder is obtained through an oxidation step in the above example, pre-oxidized metallic nickel powder may also be purchased and used. However, when combined with the method for producing a positive electrode active material in each embodiment of the present invention described below, the method for producing oxidized metallic nickel powder described below also contributes to reducing GHG emissions in all processes, including the production of metallic nickel powder to the production of a positive electrode active material for a lithium-ion secondary battery. Therefore, first, a method for producing oxidized metallic nickel powder used in the production of a precursor of a positive electrode active material for a lithium-ion secondary battery in one embodiment of the present invention will be described.

[0018] [Method for Producing Oxidized Metallic Nickel Powder] FIG. 1 illustrates an example of a method for producing an oxidized metallic nickel powder used in producing a precursor for a positive electrode active material for a lithium-ion secondary battery according to this embodiment. In this method for producing an oxidized metallic nickel powder, metallic nickel powder produced by, for example, an atomization method or a carbonyl method can be used. S001 in FIG. 1 is a preparation step for preparing metallic nickel powder before oxidation. In the preparation step S001 for preparing metallic nickel powder before oxidation, the atomization method or the carbonyl method can produce metallic nickel powder with a low amount of impurity elements. The atomization method is preferred for producing spherical powder. High-purity raw materials are used for battery components to avoid short circuits within batteries produced using this metallic nickel powder. In particular, iron (Fe) is an impurity element that easily causes short circuits, so the Fe content of the metallic nickel powder is preferably 100 ppm or less, more preferably 30 ppm or less, and even more preferably 10 ppm or less. Furthermore, high-purity briquettes or cathodes with a grade of Class I are suitable as high-purity nickel sources. In this embodiment, a high-purity metallic nickel powder with few impurities was used, which can be obtained without dissolving the briquettes or cathodes in acid. Note that in this embodiment, a nickel-based alloy powder containing metal elements necessary for the positive electrode active material, such as Co and Mn, may be used instead of the metallic nickel powder used in the method for producing a precursor of the positive electrode active material.

[0019] 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 at low temperature and reduced pressure to obtain metallic nickel powder. High-purity metallic nickel powder can also be obtained using the carbonyl process. Furthermore, powdered metallic nickel powder can be used as metallic nickel powder before being briquetted.

[0020] 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 a cumulative frequency of 50% by volume in the cumulative particle size distribution measured using a laser diffraction / scattering particle size distribution analyzer. In addition, in this specification, D95 is the particle size value corresponding to a cumulative frequency of 95% by volume in the cumulative particle size distribution.

[0021] (Metallic nickel powder pulverization step S002) Once the metallic nickel powder is obtained, the metallic nickel powder is pulverized in the metallic nickel powder pulverization step S002. The metallic nickel powder after the metallic nickel powder pulverization step S002 preferably has an average particle size D50 of 20 μm or less, more preferably 8 μm or less. When the metallic nickel powder has an average particle size D50 of 20 μm or less, metal elements other than lithium and nickel diffuse to the center of the metallic nickel powder, making it easier to homogenize the composition within the positive electrode active material. Furthermore, when the metallic nickel powder has a D50 of 8 μm or less, the composition within the positive electrode active material becomes more homogenous, which is preferable.

[0022] It is possible to omit the metallic nickel powder pulverization step S002. When the metallic nickel powder pulverization step S002 is omitted, the average particle size D50 of the metallic nickel powder obtained in step S001 is preferably 70 μm or less, more preferably 20 μm or less, and even more preferably 8 μm or less. Furthermore, in order to improve the uniformity of the composition within the positive electrode active material, it is sufficient to adjust the average particle size D50 to such an average particle size D50 at least before mixing with a compound containing a metal element M other than Li and Ni, which will be described later, and firing. Therefore, it is not necessarily necessary to adjust the average particle size D50 of the metallic nickel powder to 20 μm or less at this point. However, adjusting the average particle size D50 of the metallic nickel powder to 20 μm or less at this point can contribute to shortening the processing time in the subsequent steps.

[0023] 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 with a particle size exceeding 100 μm can be removed by sieving and returned to the melt (recycled).

[0024] (Oxidation step S003) Next, the oxidation step S003 is performed to oxidize the metallic nickel powder. In the oxidation step S003, a rotary furnace or a roller furnace is used, and the metallic nickel powder is heated in an oxidizing atmosphere while being rolled. In this way, the metallic nickel powder moves during the oxidation reaction, thereby preventing sintering of the powder particles. In this way, oxidized metallic nickel powder is obtained (S004).

[0025] In the oxidation step (S003), the metallic nickel powder is heated in an oxidizing atmosphere while being rolled, thereby allowing oxidation while suppressing sintering. Heat treatment in an oxidizing atmosphere shortens the time required for the oxidation treatment. Furthermore, the temperature during the heat treatment is preferably 400°C or higher and 800°C or lower, and more preferably 500°C or higher and 750°C or lower. Setting the temperature at 400°C or higher facilitates the production of a precursor of a positive electrode active material with a desired oxidation rate when using the oxidized metallic nickel powder obtained by this production method. Furthermore, when the temperature during the heat treatment is 400°C or higher and 800°C or lower, the heat treatment time in the oxidation step S003 is preferably 1 to 20 hours, preferably 5 to 15 hours, and more preferably 5 to 10 hours. This oxidation step S003 forms an oxide layer on the surface of the metallic nickel powder. This oxide layer can suppress sintering of the metallic nickel powder particles during various subsequent heat treatment steps. The thickness of the oxide layer is sufficient to be 500 nm or higher, and preferably 5 μm or higher. As described above, the oxidation step only needs to form an oxide layer. Therefore, the optimal oxidation rate varies depending on the particle size of the metallic nickel powder. For example, when the particle size of the metallic nickel powder is 70 μm, the oxidation rate is preferably 2% or more, more preferably 15% or more. When the particle size of the metallic nickel powder is 40 μm, the oxidation rate is preferably 4% or more, more preferably 25% or more. When the particle size of the metallic nickel powder is 20 μm, the oxidation rate is preferably 15% or more, more preferably 80% or more. By achieving these oxidation rates, the thickness of the oxide layer becomes appropriate, and as a result, sintering of the metallic nickel powder particles can be suppressed in steps after the oxidation step. The metallic nickel powder used in the present invention may be a commercially available powder, as long as it satisfies the above-mentioned requirements, such as the Fe content and average particle size.

[0026] [Method for Producing a Positive Electrode Active Material Precursor] A method for producing a positive electrode active material precursor according to an embodiment of the present invention, as shown in FIG. 2, is described below. As shown in the flowchart of FIG. 2, first, the oxidized metal nickel powder described above is prepared (metal nickel oxide powder preparation step S011). The prepared oxidized metal nickel powder may be the oxidized metal nickel powder produced by the oxidized metal nickel powder production method described above, or a commercially available powder that satisfies the requirements for Fe content, average particle size, etc. Furthermore, the metal nickel oxide powder preparation step S011 only needs to prepare materials necessary for the first lithium mixing step S012 described below. Therefore, if the first lithium mixing step S012 described below is performed using a rotary furnace or a rolling furnace that has undergone the oxidation step S003, no special operations are required in the metal nickel oxide powder preparation step S011, and this step S011 can be skipped.

[0027] Next, a first lithium mixing step (S012) is performed, in which the oxidized metallic nickel powder and the lithium-containing compound powder are mixed. Then, a lithiation step (S013) is performed, in which the first mixed powder, which is a mixed powder of the oxidized metallic nickel powder and the lithium-containing compound powder, is heat-treated to lithiate at least a portion of the mixed powder. This lithiation step (S013) forms lithium nickel oxide. The lithium nickel mixed powder containing the lithium nickel oxide has improved pulverizability. Next, a lithium nickel mixed powder pulverization step (S014) is performed, in which the lithium nickel mixed powder containing the lithium nickel oxide is pulverized to obtain a powdered precursor (S015). As shown in FIG. 2 , the method for producing a precursor for a positive electrode active material for a lithium-ion secondary battery according to this embodiment comprises at least three steps: the first lithium mixing step (S012), the lithiation step (S013), and the lithium nickel mixed powder pulverization step (S014). Each step is described in detail below.

[0028] (First Lithium Mixing Step S012) The first lithium mixing step S012 is a step for mixing the powder of the lithium-containing compound to be mixed with the oxidized metallic nickel powder described above to obtain a first mixed powder. The lithium-containing compound to be mixed with the oxidized metallic nickel powder is preferably lithium hydroxide or lithium carbonate, but is not limited to these compounds. The lithium-containing compound powder may be a powder of a lithium-containing compound having a single composition, or may be a mixture of powders of lithium-containing compounds having multiple compositions. It is preferable to use a powder of the lithium-containing compound in powder form.

[0029] The amount of lithium-containing compound added here is either an amount of lithium compound corresponding to the amount of lithium necessary to achieve the composition ratio of the positive electrode active material for a lithium-ion secondary battery that is finally produced, or an amount of lithium-containing compound corresponding to a smaller amount of lithium. The amount of lithium-containing compound to be added may be determined depending on how the positive electrode active material is produced from the precursor of the positive electrode active material produced according to this embodiment. Alternatively, the amount may be determined taking into consideration the pulverizability in the lithium-nickel mixed powder pulverization step S014 described below.

[0030] The amount of lithium-containing compound powder to be mixed with the oxidized metallic nickel powder may be very small. For example, when the amount of lithium-containing compound containing the amount of lithium necessary to achieve the desired composition ratio of the positive electrode active material is taken as 100% by mass, it may be in the range of 5% or more, or near the lower limit thereof. More preferably, when the amount of lithium-containing compound containing the amount of lithium necessary to achieve the desired composition ratio of the positive electrode active material is taken as 100% by mass, it is 10% by mass or more and 100% by mass or less. The presence of the lithium-containing compound can suppress sintering of powder particles in subsequent steps. By mixing 10% by mass or more of the lithium-containing compound containing the amount of lithium necessary for the positive electrode active material with the oxidized metallic nickel powder, sintering of the oxidized metallic nickel powder particles during the lithiation step (S013) described below is suppressed. On the other hand, the amount of lithium-containing compound mixed in the first lithium mixing step (S012) is preferably 50% by mass or less, or even 25% by mass or less, of the amount of lithium-containing compound containing the desired amount of lithium. In the lithiation step (S013) described below, it is necessary to reduce as much as possible the amount of lithium remaining in the lithium-containing compound that is unable to completely react with the oxidized metallic nickel powder. Therefore, the amount of the lithium-containing compound is preferably less than the amount of lithium required for the positive electrode active material, for example, 50% by mass or less, more preferably 25% by mass or less, of the amount of lithium required for the positive electrode active material. This reduces the amount of lithiation treatment in the lithiation step S013, thereby reducing the energy consumed in the lithiation treatment and reducing costs and GHG emissions.

[0031] Furthermore, when a pulverization step is performed during the production of the cathode active material described below, the amount of lithium-containing compound mixed before the lithiation step is preferably 10% by mass or more and 50% by mass or less. More preferably, it is 25% by mass or less. If the amount of lithium-containing compound mixed during the production of the cathode active material precursor is small, the voids within the secondary particles of the cathode active material can be reduced by applying the method for producing a cathode active material according to the present embodiment described below. As a result, the particle strength of the cathode active material is increased, resulting in improved charge-discharge cycle characteristics. Even when a mixture of powders of multiple lithium-containing compounds is used, it is preferable that the mass ratio of lithium in the mixed powder of the lithium-containing compound and the oxidized metallic nickel powder be within the above-mentioned range.

[0032] The melting point of the lithium-containing compound is preferably higher than the heat treatment temperature of the lithiation process. Therefore, the lithium-containing compound is preferably lithium carbonate. The melting point of lithium carbonate is as high as 724°C, allowing the lithiation temperature to be as high as 720°C. This is because it remains solid even at 720°C and functions as an inclusion, suppressing contact and sintering between the metallic nickel powders, while shortening the lithiation process. The average particle size of the lithium-containing compound powder is preferably 100 nm to 100 μm, more preferably 1 μm to 50 μm. Furthermore, in order to reduce voids within the secondary particles of the positive electrode active material to be produced, it is preferable to mix a small amount of lithium-containing compound with the oxidized metallic nickel powder. Furthermore, in order to function as an inclusion for the purpose of suppressing sintering, it is necessary to arrange the lithium-containing compound powder between the oxidized metallic nickel powder. Therefore, in order to reduce the amount of lithium-containing compound mixed and to arrange more lithium-containing compound powder between the oxidized metallic nickel powder, it is preferable to make the particle size of the lithium-containing compound smaller than that of the oxidized metallic nickel powder and increase the number of lithium-containing compound particles.

[0033] In the first lithium mixing step S012, a V-type mixer, a stirring mixer, an attritor, a media mill, or the like is used. In order to mix uniformly, it is preferable that the aggregation of each raw material powder can be broken down. The mixing method may be either a dry method in which only the raw material powders are mixed, or a wet method in which mixing is performed using a liquid as a dispersion medium.

[0034] (Lithiation step S013) The first mixed powder obtained in the first lithium mixing step S012 is then subjected to a lithiation treatment in the lithiation step S013 to oxidize the metallic nickel powder. In the lithiation step S013, further oxidation of the oxidized metallic nickel powder is promoted and lithium nickel oxide is produced (lithiation). In this way, a mixed powder containing oxidized metallic nickel and lithium nickel oxide (hereinafter referred to as lithium nickel mixed powder) is produced.

[0035] In the lithiation step S013, heat treatment in an oxidizing atmosphere is preferable because it shortens the time required for lithiation of the oxidized metallic nickel powder. The oxidizing atmosphere may be an air atmosphere, a mixture of nitrogen gas and oxygen gas, or, of course, oxygen gas. Furthermore, 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. By setting the temperature at 450°C or higher and 700°C or lower, a precursor of a positive electrode active material having a desired lithiation rate can be easily obtained. Furthermore, the heat treatment time for the lithiation treatment is preferably 0.5 hours or longer, more preferably 3 hours or higher and 20 hours or lower, more preferably 3 hours or higher and 15 hours or lower, and even more preferably 5 hours or higher and 10 hours or lower. By performing the lithiation treatment for 5 to 10 hours, the oxidized metallic nickel powder combines with lithium, completing the lithiation reaction and making it easier to stably obtain a precursor with the desired lithiation rate.

[0036] This step may be performed using the same rotary furnace or roller furnace as the oxidation step S003, in which the metallic nickel powder is subjected to oxidation treatment. Furthermore, by performing the first lithium mixing step S012 using the same rotary furnace or roller furnace, it is possible to continuously perform the metallic nickel powder oxidation step S003 through the lithiation step S013. This reduces the fuel consumption required for producing the precursor of the positive electrode active material, and improves production efficiency and energy efficiency by saving space and driving force during production. These factors lead to a reduction in GHG emissions, making it possible to produce a positive electrode active material with reduced GHG emissions.

[0037] However, this embodiment is not limited to performing the lithiation step S013 in the same furnace as the oxidation step S003. In another embodiment, the lithiation step S013 may be performed in a static furnace, where the lithium-nickel mixed powder is heated in an oxidizing atmosphere while remaining stationary, by changing the time and location from the oxidation step S003 or the first lithium mixing step S012, thereby oxidizing the lithium-nickel mixed powder. The static furnace may be a batch-type box furnace, a tubular furnace, or a roller hearth kiln. Compared to performing the lithiation step S013 in a rotary furnace, performing the lithiation step in a static furnace is preferable because it reduces the amount of volatilization of the lithium source and suppresses composition deviation. Furthermore, the reduced amount of volatilization of lithium makes it possible to reduce the amount of lithium consumed and not contained in the precursor of the positive electrode active material.

[0038] As described above, the lithiation step S013 promotes lithiation along with further oxidation of the metallic nickel powder, resulting in the formation of lithium-nickel oxide in addition to nickel oxide. To confirm the formation of lithium-nickel oxide, 25% by mass of lithium carbonate powder was mixed with the oxidized metallic nickel powder, relative to the amount of lithium carbonate corresponding to the amount of lithium required for the composition of the finally produced positive electrode active material for a lithium-ion secondary battery. The results of X-ray diffraction (XRD) measurement of the lithium-nickel mixed powder obtained when the lithiation step S013 was performed are shown in Figure 3. For comparison, the results of X-ray diffraction (XRD) measurement of oxidized metallic nickel powder are also shown in Figure 3.

[0039] In FIG. 3, the vertical axis indicates the intensity value (a.u.) of the X-ray diffraction light, and the horizontal axis indicates the X-ray reflection diffraction angle (2θ). The upper graph shows the measurement results of the lithium-nickel mixed powder, and the lower graph shows the measurement results of the oxidized metallic nickel powder. In each graph, the peaks marked with a triangle are those indicating nickel oxide, and the peaks marked with a circle are those indicating metallic nickel. The peaks marked with a square are those indicating lithium-nickel oxide (Li ｘ Ni ｙ 0). As can be seen from FIG. 3, when oxidized metallic nickel powder was mixed with lithium carbonate powder and lithiation was carried out, in addition to the peak of nickel oxide, a peak at 2θ = 43.5° to 44.0° attributed to lithium nickel oxide was confirmed. In other words, the formation of lithium nickel oxide was confirmed. Therefore, it can be confirmed that a lithium nickel mixed powder was produced.

[0040] Next, Figures 4A and 4B show scanning electron microscope images (SEM images) of oxidized metallic nickel powder before and after the lithiation step S013, along with oxygen (O) mapping diagrams for the SEM images. The left photograph in Figure 4A shows a cross section of the oxidized metallic nickel powder before the lithiation step S013, and the right photograph in Figure 4A is an oxygen mapping diagram for the left photograph in Figure 4A. Meanwhile, the left photograph in Figure 4B shows a cross section of the lithium-nickel mixed powder after the lithiation step S013, and the right photograph in Figure 4B is an oxygen mapping diagram for the left photograph in Figure 4B. This oxygen mapping diagram shows the distribution of oxygen concentration by varying the shade depending on the oxygen concentration. Therefore, areas with a relatively large number of oxygen atoms are shown in light gray, and areas with a small amount of oxygen are shown in dark gray.

[0041] 4A shows that the oxidized region 1b is located in a very shallow region on the surface of the oxidized metallic nickel powder 1. In contrast, FIG. 4B shows that the particles of the lithium-nickel mixed powder 2 formed after the lithiation step S013 have an oxidized region 2b extending to the interior of the particles. Note that this oxidized region 2b is heat-treated in an oxidizing atmosphere while mixed with a lithium-containing compound. Therefore, it is presumed that a large amount of lithium-nickel oxide is also produced in this oxidized region 2b.

[0042] Furthermore, while almost no cracks are visible in the metallic nickel powder 1 in the photograph of Figure 4A, it can be seen in Figure 4B that cracks 2b have progressed throughout the powder. The reason these cracks occur so frequently is presumably that when oxidized metallic nickel becomes lithium-nickel mixed powder, the volume of the powder expands by approximately three times, and the cracks are generated by the stress generated by this volume change. As these cracks progress throughout the powder, pulverization becomes easier, and the pulverization process can be completed in a short time. If the pulverization process is not performed, these cracks become diffusion paths for the elements, making it easier for each element to diffuse more uniformly.

[0043] The oxidation rate of the lithium-nickel mixed powder after the lithiation step S013 is preferably 10% or more but less than 100%, as described in the examples below. An oxidation rate of 10% or more can suppress sintering of the lithium-nickel mixed powder particles during the subsequent firing step to obtain a positive electrode active material. Furthermore, an oxidation rate of 10% or more 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. A preferred oxidation rate is 50% or more. This is because an oxidation rate of 50% or more increases the valence of nickel, further promoting the reaction to form a lithium metal composite oxide during firing. Furthermore, forming lithium-nickel oxide not only facilitates pulverization as described above, but also promotes the reaction between lithium and other metals constituting the positive electrode active material, such as nickel, during the firing step to obtain the positive electrode active material, thereby facilitating the formation of layered crystals and making it easier to obtain a positive electrode active material with good crystallinity.

[0044] The lithiation rate of the lithium-nickel mixed powder is preferably 8% or higher to obtain good pulverizability, as described in the Examples below. When the average particle size of the oxidized metal nickel powder prepared in the metal nickel oxide powder preparation step S011 exceeds 20 μm, the lithiation rate is preferably 10% or higher, more preferably 15% or higher, and even more preferably 20% or higher. If the lithiation rate of the lithium-nickel mixed powder is excessively increased in the lithiation step S013, resulting in a large amount of lithium carbonate being consumed by reacting with metal nickel, the amount of unreacted lithium increases when a positive electrode active material is produced using the precursor of the positive electrode active material of this embodiment. This phenomenon occurs because an excessively high lithiation rate in the lithiation step S013 reduces the amount of lithium-containing liquid phase components produced during the firing step, and the reaction rate between lithium and metal elements constituting the positive electrode active material other than lithium, such as nickel, cobalt, and manganese, which is promoted by the liquid phase reaction, is slower than in a firing step performed with an appropriate amount of liquid phase. As a result, the baking time is prolonged, and it is thought that the amount of unreacted lithium increases when compared with a constant baking time. ２ CO ３ →LiAO ２ (A represents a metal element other than Li, such as Ni, Co, or Mn, which constitutes the positive electrode active material, and AO represents an oxide of such a metal element) reaction slows down, and the Li contained in the produced positive electrode active material ２ CO ３ increases, and LiNiO ２ Therefore, the amount of impurities that do not function as a positive electrode active material increases, and therefore the upper limit of the lithiation rate is set to, for example, 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 step.

[0045] (Lithium-nickel mixed powder pulverization step S014) The lithium-nickel mixed powder produced in the lithiation step S013 is then pulverized in the lithium-nickel mixed powder pulverization step S014. This step makes it possible to obtain a precursor of a positive electrode active material with a well-controlled particle size distribution, which is advantageous for the subsequent production of a positive electrode active material. Pulverization can be performed using an attritor, a media mill, a ball mill, a bead mill, an agitator mixer, or the like.

[0046] The graphs shown in Figures 5A and 5B show the relationship between milling time and particle size. Figure 5A shows the change in the average particle size D50 of the lithium-nickel mixed powder and the lithium-nickel mixed powder and oxidized metallic nickel powder versus milling time, and Figure 5B shows the change in D95, a value corresponding to the particle size of the lithium-nickel mixed powder and the lithium-nickel mixed powder and oxidized metallic nickel powder, versus milling time. In both Figures 5A and 5B, the horizontal axis represents milling time (unit: hours), and the vertical axis represents average particle size D50 or D95 (unit: micrometers). The dotted lines also show the average particle size D50 and D95 ​​values ​​of the metallic nickel powder during step S001 of obtaining the unoxidized metallic nickel powder shown in Figure 1. The values ​​plotted with triangles represent the average particle size for each milling time for the lithium-nickel mixed powder, and the values ​​plotted with circles represent the average particle size for each milling time for the oxidized metallic nickel powder. The oxidized metallic nickel powder is an oxidized metallic nickel powder that is produced by subjecting metallic nickel powder to the oxidation step S003, without going through the first lithium mixing step S012, and further in the same oxidizing atmosphere as the lithiation step S013 at the same treatment temperature and for the same treatment time.

[0047] 5A and 5B, the lithium-nickel mixed powder can be pulverized in a shorter time than the oxidized metallic nickel powder without lithium addition. Regarding the average particle size D50, the oxidized metallic nickel powder without lithium carbonate takes about 50 hours to reach the average particle size D50 before the oxidation step S003, whereas the lithium-nickel mixed powder obtained by adding lithium carbonate and going through the lithiation step S013 can be pulverized in about 10 hours. The same is true for the change in the D95 value; when no lithium-containing processed powder is added, it is difficult to reach the D95 value before the oxidation step, and although pulverization is possible, the powder itself is not pulverized.

[0048] Thus, without adding lithium-containing compound powder (lithium carbonate), the crude precursor cannot be pulverized, making it difficult to control the particle size. Therefore, it is difficult to obtain a homogeneous cathode active material in the subsequent cathode active material manufacturing process. Therefore, in the subsequent cathode active material manufacturing process, a cathode active material precursor that facilitates the production of a good cathode active material can be obtained by pulverizing the lithium-nickel mixed powder that has undergone the first lithium mixing step S012 and the lithiation step S013, as in this embodiment (S015). In particular, comparing the difference in average particle diameters D50 and D95 ​​after approximately 50 hours of pulverization, the cathode active material precursor that underwent the lithium-nickel mixed powder pulverization step S014 is approximately 5 μm, while the oxidized metallic nickel powder has a diameter of 10 μm, a difference twice as great. As can be seen from this, the cathode active material precursor obtained by the cathode active material precursor manufacturing process according to this embodiment has a small particle size and reduced particle size variation, which is likely to facilitate the reaction process performed in the subsequent cathode active material manufacturing process. Furthermore, metal elements other than lithium and nickel are more likely to diffuse to the center of each particle, and when a positive electrode active material is produced using the precursor of the positive electrode active material in this embodiment, the composition within the positive electrode active material is more easily homogenized.

[0049] Therefore, in the manufacturing method of a cathode active material described below, a cathode active material is obtained by firing in an oxidizing atmosphere containing oxygen. However, by introducing the precursor produced in the manufacturing method of this embodiment, a cathode active material with excellent crystallinity can be manufactured. In the manufacturing method of a cathode active material precursor of this embodiment, it is further preferable to perform a classification step after the lithium-nickel mixed powder pulverization step S014. By performing the classification step after this pulverization step S014, a good firing reaction can be easily achieved in the subsequent manufacturing of the cathode active material. The classification method is not particularly limited, but known classification methods such as sieve classification and airflow classification can be used. Furthermore, the manufacturing method of a cathode active material precursor of this embodiment may further include powders containing other metal elements necessary to achieve the desired composition ratio of the cathode active material, or powders of lithium-containing compounds to compensate for the lithium amount insufficient in the precursor composition ratio. It is sufficient that at least lithium-nickel oxide is contained in the mixed powder, and the lithium-nickel mixed powder pulverized in the lithium-nickel mixed powder pulverization step S014 is included in the mixed powder.

[0050] [Method for Manufacturing Cathode Active Material] Next, a method for manufacturing a cathode active material according to an embodiment of the present invention will be described. Examples of methods for manufacturing a cathode active material according to this embodiment are shown in the flowcharts of FIGS. 6 to 8. Note that FIG. 6 is a flowchart of a method for manufacturing a cathode active material according to a first embodiment of the present invention, and FIG. 7 is a flowchart of a method for manufacturing a cathode active material according to a second embodiment of the present invention. Finally, FIG. 8 is a flowchart of a method for manufacturing a cathode active material according to a third embodiment of the present invention. The methods for manufacturing a cathode active material according to the first, second, and third embodiments all use a precursor manufactured by the method for manufacturing a precursor for a cathode active material according to the present embodiment described above. Therefore, these methods for manufacturing a cathode active material use a precursor that already contains nickel and lithium.

[0051] In the method for producing a positive electrode active material in the first embodiment, a positive electrode active material precursor produced by the method for producing a positive electrode active material precursor using metallic nickel powder described above is mixed with a powder of a compound containing a metal element M other than lithium and nickel (hereinafter referred to as an M metal compound), followed by firing to produce the positive electrode active material. Note that if the lithium content of the precursor is lower in molar ratio than the content of a positive electrode active material of the target composition, the lithium-containing compound can be mixed with the precursor together with the M metal compound at the time of mixing, and the mixture can be fired to produce a positive electrode active material of the target composition.

[0052] On the other hand, the method for producing a cathode active material in the second embodiment shown in Fig. 7 and the method for producing a cathode active material in the third embodiment shown in Fig. 8 include a granulation step that is not included in the method for producing a cathode active material in the first embodiment shown in Fig. 6. Accordingly, a lithium-containing compound corresponding to the amount of lithium that is insufficient when the lithium content ratio of the precursor of the cathode active material is relative to the lithium content ratio of the cathode active material of the target composition is provided after the granulation step. Next, each step of the method for producing a cathode active material in the first embodiment will be described in detail with reference to Fig. 6.

[0053] First, a precursor of a positive electrode active material (hereinafter referred to as "precursor") obtained by the above-described precursor manufacturing method is prepared (S021). Next, to supplement the metal elements lacking in the positive electrode active material of the target composition, a powder of an M metal compound containing a metal element M other than lithium and nickel that is not contained in the precursor is prepared. Examples of the M metal element contained in the M metal compound include, but are not limited to, cobalt (Co), manganese (Mn), aluminum (Al), and titanium (Ti). Furthermore, if the amount of lithium contained in the precursor is less than the amount corresponding to the lithium content of the positive electrode active material of the target composition in terms of molar ratio, a powder of a lithium-containing compound is also prepared to supplement the missing amount.

[0054] After preparing the powders of compounds of the metal elements necessary to achieve the target composition of the positive electrode active material in this manner, the deficient element mixing step S022 is performed, in which the precursor is mixed with a powder of a compound containing the deficient element, such as an M metal compound or a lithium-containing compound. (Deficient Element Mixing Step S022) In the mixing step S022, a V-type mixer, a stirring mixer, an attritor, a media mill, or the like is used to mix the precursor with the powder of the compound containing the deficient element. To achieve uniform mixing, it is preferable to be able to break down the agglomerations of the raw material powders. As mentioned above, if the lithium content of the precursor is lower in molar ratio than the lithium content of the positive electrode active material of the target composition, the lithium-containing compound powder is also mixed together with the M compound powder. The mixing method may be either a dry mixing method in which only the raw material powders of the precursor powder, the M metal compound powder, and the lithium-containing compound powder are mixed, or a wet mixing method in which a liquid is used as a dispersion medium and the precursor powder, the M metal compound powder, and the lithium-containing compound powder are dispersed in the liquid and mixed. When the method for producing a cathode active material of the present embodiment is carried out successively following the method for producing a precursor of the cathode active material described above, the lithium-nickel mixed powder pulverizing step S014, which is carried out in the precursor production method, may be carried out using an agitation mixer, attritor, media mill, ball mill, or bead mill that can simultaneously perform pulverization and mixing, thereby carrying out the lithium-nickel mixed powder pulverizing step S014 and this mixing step S022.

[0055] Lithium hydroxide, lithium carbonate, etc. can be used as the lithium-containing compound to be mixed with the precursor. Lithium carbonate is preferred because it has low hygroscopicity and is easy to handle. On the other hand, when the effect of promoting the diffusion of the metal element M into the interior of the precursor is important, lithium hydroxide is preferred. This is because it allows the production of a positive electrode active material with a uniform composition. The amount of lithium-containing compound powder to be mixed with the precursor is preferably determined taking into account the amount of lithium that is insufficient in the precursor for the target composition of the positive electrode active material, as well as the amount of lithium that will volatilize in the firing step S023 described below. Furthermore, prior to the deficient element mixing step S021, it is preferable to classify both the lithium-containing compound powder and the M metal compound powder to remove powder with a coarse particle size.

[0056] After the M metal compound powder and the lithium-containing compound powder are mixed with the precursor, a firing step S023 is carried out to fire this mixed powder (hereinafter referred to as pre-fired mixed powder) (firing step S023).

[0057] In the firing step S023, a pre-fired mixed powder of the precursor obtained in the deficient element mixing step S022, an M metal compound powder, and a lithium-containing compound powder is fired to obtain a layered-structure positive electrode active material for lithium-ion secondary batteries. An electric furnace or a gas furnace is used in the firing step S023. The pre-fired mixed powder is placed in a firing sagger and fired. Preferably, the pre-fired mixed powder is 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 left to stand in a dry atmosphere before firing. Furthermore, forming multiple groove-like irregularities or depressions in the pre-fired mixed powder placed on the firing sagger facilitates the passage of oxygen-containing gas through the lower part of the pre-fired mixed powder during firing. This promotes oxidation of the pre-fired mixed powder on the bottom of the firing sagger, and the pre-fired mixed powder on the top and bottom of the firing sagger is fired with less variation.In addition, in the present invention, instead of such a furnace, a furnace such as a rotary kiln in which the pre-fired mixed powder is fired while being rotated can be used.

[0058] 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 S023 may be performed at 700°C or more and 900°C or less to obtain a layered cathode active material. This step may include a pre-firing stage maintained at 450°C or more and 730°C or less, and a main firing stage maintained at a temperature higher than the firing temperature in the pre-firing stage and 700°C or more and 900°C or less. The preferred firing temperature and holding time are adjusted depending on the composition blended during raw material mixing, and firing is performed so that the physical properties (specific surface area, etc.) of the target cathode active material after firing fall within preferred ranges.

[0059] After the calcination 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, etc.

[0060] As described above, according to the method for producing a positive electrode active material in the first embodiment of the present invention, since metallic nickel powder is used as the nickel raw material, the acid dissolution step and the coprecipitation step are not required. 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. ２ 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%, whereas 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. These factors lead to a reduction in GHG emissions, making it possible to manufacture a positive electrode active material with reduced GHG emissions. In addition, because nickel sulfate is not required as a raw material, the possibility of sulfur being incorporated into the positive electrode active material is reduced, making it possible to obtain a positive electrode active material with good electrochemical properties.

[0061] Next, a method for manufacturing a positive electrode active material according to a second embodiment will be described with reference to FIG. 7 . Note that steps denoted by the same reference numerals as in FIG. 6 are the same as those in the method for manufacturing a positive electrode active material according to the first embodiment, and therefore detailed descriptions of those steps will be omitted. The method for manufacturing a positive electrode active material according to the second embodiment further includes a granulation step S034 in addition to the method for manufacturing a positive electrode active material according to the first embodiment. Furthermore, a second lithium mixing step S035 is provided after the granulation step S034. By providing these steps, a positive electrode active material that facilitates the production of an electrode with a high energy density can be manufactured. In particular, the application of pressure during positive electrode production makes it easier to obtain a positive electrode with a high packing density, enabling the production of a positive electrode with better performance.

[0062] In the method for producing a cathode active material according to the second embodiment, a precursor produced by the method for producing a cathode active material precursor according to the present embodiment is prepared in the cathode active material precursor preparation step S021. (M metal mixing step S032) Next, to supplement any metal elements lacking in the cathode active material of the target composition, an M metal compound powder mixing step S032 is carried out, in which an M metal compound powder containing an M metal element other than lithium and nickel that is not contained in the prepared precursor is mixed with the precursor. Examples of the M metal compound powder include cobalt carbonate powder, manganese carbonate powder, titanium oxide powder, aluminum oxide powder, and mixtures thereof.

[0063] In the manufacturing method of a positive electrode active material according to the first embodiment, when the amount of lithium contained in the precursor is less than the amount of lithium in the positive electrode active material of the target composition, a lithium-containing compound powder is also mixed together with the M metal element in the deficient element mixing step S022. However, in the manufacturing method of a positive electrode active material according to the second embodiment, even when the amount of lithium contained in the precursor is insufficient compared to the amount of lithium in the positive electrode active material of the target composition, it is not necessary to mix the lithium-containing compound powder in the M metal compound mixing step S032. The lithium-containing compound powder may be mixed with the M metal compound powder and the precursor in the M metal compound mixing step S032. In this case, it is preferable to add the amount of lithium added in the M metal compound mixing step S032 so that the sum of the amount of lithium contained in the precursor and the amount of lithium added in the M metal compound mixing step S032 is less than the amount of lithium required for the positive electrode active material of the target composition.

[0064] If a lithium-containing compound powder is also mixed in the M metal compound mixing step S032, the amount of the lithium-containing compound powder added must be such that the sum of the amount of lithium already contained in the precursor and the amount of lithium contained in the lithium-containing compound newly added in the M metal compound mixing step S032 is smaller than the amount of lithium required for the positive electrode active material of the target composition. This is one of the differences from the method for producing a positive electrode active material in the first embodiment.

[0065] The mixing means may be the same as that used in the mixing step S022 of the method for producing a cathode active material in the first embodiment, and either the dry mixing method or the wet mixing method may be used. Furthermore, when the method for producing a cathode active material in the second embodiment is carried out consecutively after the method for producing a precursor of the cathode active material described above, the lithium-nickel mixed powder pulverizing step S014 may be performed using an agitation mixer, attritor, media mill, ball mill, or bead mill capable of simultaneously pulverizing and mixing, and the M metal compound mixing step S032, which will be described later, may be started midway through the lithium-nickel mixed powder pulverizing step S014.

[0066] (Precursor and M Metal Compound Powder Pulverization Step S033) Next, the mixed powder of the precursor and M metal compound powder is pulverized in the precursor and M metal compound powder pulverization step S033. By performing the precursor and M metal compound powder pulverization step S033 before the granulation step S034 described below, the sintering reaction in the sintering step S023 is promoted, resulting in a positive electrode active material with a good layered structure, a high initial capacity, and a positive electrode active material with good charge-discharge cycle characteristics. The average particle size D50 of the primary particles of the pulverized and mixed mixed powder (pulverized mixed powder) obtained in this pulverization step S033 is preferably 0.40 μm or less. By achieving such an average particle size, the sintering reaction is easily promoted in the subsequent granulation step S034 and sintering step S023, making it easier to suppress voids in the positive electrode active material. This contributes to the ease of manufacturing a positive electrode active material with higher particle strength and good charge-discharge cycle characteristics. The pulverization can be carried out using an attritor, media mill, ball mill, bead mill, stirring mixer, or the like. A media mill is preferred, and a bead mill is more preferred, because it can pulverize the mixed powder of the precursor and the M metal compound powder to submicron size. Of course, by using a mill that has both the functions of pulverization and mixing, such as a stirring mixer, attritor, media mill, ball mill, or bead mill, the aforementioned M metal compound powder mixing step S032 and precursor and M metal compound powder pulverization step S033 may be carried out in the same step.

[0067] Furthermore, when the method for producing a cathode active material according to the second embodiment is carried out successively following the method for producing a precursor of the cathode active material described above, in the lithium-nickel mixed powder pulverizing step S014 in the precursor production method, a mixing and pulverizing means capable of simultaneously pulverizing and mixing, such as an agitator mixer, attritor, media mill, ball mill, or bead mill, may be used, and the M metal compound powder and the lithium-nickel mixed powder produced in the lithiation step S013 may be fed into the mixing and pulverizing means and the pulverizing and mixing means may be driven, thereby simultaneously carrying out the three steps of the lithium-nickel mixed powder pulverizing step S014, the M metal compound mixing step S032, and the precursor and M metal compound powder pulverizing step S033. In this way, by carrying out the lithium-nickel mixed powder pulverizing step S014 in the method for producing a precursor of the cathode active material and the M metal compound mixing step S032 and the precursor and M metal compound powder pulverizing step S033 in the method for producing a cathode active material using the same pulverizing and mixing means, an improvement in production throughput can be achieved.

[0068] (Granulation Step S034) As described above, a granulation step S034 is carried out to produce a granulated powder from the mixed powder of precursor and M metal compound powder that has been subjected to the precursor and M metal compound pulverization step S033. First, a mixed powder slurry is produced using the mixed powder of precursor and M metal compound powder and a solvent. If a wet pulverization method is used in the precursor and M metal compound powder pulverization step S033 described above, granulation is carried out based on the pulverized slurry containing this mixed powder. The granulation method is not particularly limited, and the granulated powder may be obtained by spray drying using, for example, a nozzle-type spray dryer or a disk-type spray dryer.

[0069] (Second Lithium Mixing Step S035) In this second embodiment of the method for producing a positive electrode active material, the amount of lithium insufficient in the precursor or granulated powder relative to the amount of lithium in the positive electrode active material of the target composition is added after the granulation step S034. Therefore, the second lithium mixing step S035 is performed after the granulation step S034. In the second lithium mixing step S035, a lithium-containing compound powder is mixed into the granulated powder in an amount corresponding to the sum of the amount of lithium insufficient in the granulated powder relative to the amount of positive electrode active material of the target composition and the amount of lithium volatilized in the subsequent firing step S023. The lithium-containing compound to be mixed is preferably lithium carbonate or lithium hydroxide. As mentioned above, lithium hydroxide melts at a lower temperature than lithium carbonate, and is therefore thought to be more likely to react with the precursor contained in the granulated powder. In the second lithium mixing step S035, the granulated powder and the lithium-containing compound powder can be mixed using a V-type mixer. By mixing the lithium-containing compound powder with the granulated powder in this manner, the positive electrode active material produced through the subsequent firing step S023 has a structure with fewer voids, which can increase the particle strength of the positive electrode active material, resulting in good charge-discharge cycle characteristics.

[0070] The reason why a cathode active material having a structure with few voids can be obtained by the manufacturing method of the cathode active material according to the second embodiment will be explained with reference to FIG. 9 . FIG. 9A is a schematic diagram of simultaneously mixed granulated powder 90 produced after simultaneously mixing powder 92 of a lithium-containing compound with powder 93 of a precursor 91 and an M metal compound, and a schematic diagram of a cathode active material 95 produced by firing the simultaneously mixed granulated powder 90. On the other hand, FIG. 9B is a schematic diagram of granulated powder 99 produced from a mixed powder of powder 93 of precursor 91 and an M metal compound, lithium-containing compound-added granulated powder 100 obtained by further adding and mixing powder 92 of a lithium-containing compound to the granulated powder 99, and a cathode active material 110 produced by firing the granulated powder 100. This relates to the manufacturing method of the cathode active material according to the second embodiment.

[0071] The left diagram of FIG. 9A shows a schematic cross-sectional structure of simultaneously mixed granulated powder 90, and the right diagram shows a schematic cross-sectional structure of positive electrode active material 95 after the simultaneously mixed granulated powder 90 is fired and the firing step is performed. By performing firing step S023 on simultaneously mixed granulated powder 90, positive electrode active material 95 is obtained. Meanwhile, the left diagram of FIG. 9B shows a schematic cross-sectional structure of granulated powder 99 made of precursor 91 and M metal compound powder 93, the center diagram of FIG. 9B shows a schematic cross-sectional structure of lithium-containing compound-added granulated powder 100, and the right diagram of FIG. 9B shows a schematic cross-sectional structure of positive electrode active material 110 obtained by firing lithium-containing compound-added granulated powder 100 and the firing step is performed.

[0072] In the right-hand diagrams of Figures 9A and 9B, reference numeral 96 in the diagrams schematically indicates primary particles of the positive electrode active material. The simultaneously mixed granulated powder 90 shown in Figure 9A, which is the granulated powder before the firing step, contains a large amount of lithium-containing compound powder 92. When the simultaneously mixed granulated powder 90 is fired in this state, a reaction occurs between the M metal compound, the lithium-containing compound, and the precursor. During this process, the lithium-containing compound 92 becomes liquid during firing and diffuses into the primary particles 96 generated during the firing step. Therefore, the more lithium-containing compound powder there is, the more voids there are in the structure after firing. Therefore, the positive electrode active material is produced in a state where many voids exist. On the other hand, according to the method for producing a positive electrode active material in this second embodiment, it is possible to reduce the generation of voids that occur when the lithium-containing compound powder 92 disappears during firing. The granulated powder produced in the granulation step S034 of the method for producing a positive electrode active material in this second embodiment has the schematic configuration of granulated powder 99 shown in the left-hand diagram of Figure 9B. Granulated powder 99 is composed only of precursor 91 and a portion of M metal compound powder 93. When producing a positive electrode active material having an Ni content of 80% or more in molar ratio, the amount of M metal compound powder 93 contained in granulated powder 99 is relatively small, and granulated powder 99 is composed almost entirely of precursor 91.

[0073] Next, in the method for producing a positive electrode active material in the second embodiment, powder 92 of a lithium-containing compound is added to granulated powder 99, and as a result, the structure of granulated powder 99 changes to lithium-containing compound-added granulated powder 100, as indicated by arrow A in Fig. 9B. As also shown in the central diagram in Fig. 9B, lithium-containing compound-added granulated powder 100 has a structure in which powder particles 92 of the lithium-containing compound cover the outside of granulated powder 99.

[0074] Next, in the method for producing a positive electrode active material according to the second embodiment, the lithium-containing compound-added granulated powder 100 is subjected to a calcination step S023. The calcination step S023 produces a positive electrode active material 110 having the schematic structure shown in the diagram on the right side of FIG. 9B , as indicated by arrow C, from the lithium-containing compound-added granulated powder 100. In the calcination step S023, the lithium-containing compound powder 92 becomes liquid during calcination, and lithium diffuses into the primary particles 96 produced during the calcination step. However, since the lithium-containing compound 92 is located outside the granulated powder 99, the portions where the lithium-containing compound 92 has disappeared are hardly present within the positive electrode active material, making it difficult for voids to form, as shown in FIG. 9A . Furthermore, since the lithium-containing compound powder 92 is arranged so as to surround the granulated powder 99, it efficiently penetrates into the interior of the granulated powder during calcination. Thus, after calcination, a positive electrode active material having a structure with few voids is obtained.

[0075] In the method for producing a positive electrode active material according to the second embodiment, the firing method and firing conditions in the firing step S023 may be the same as those in the method for producing a positive electrode active material according to the first embodiment. By performing the firing step S023 in this manner, it is possible to produce a positive electrode active material of secondary particles composed of primary particles 96. Lithium hydroxide may be used as the lithium-containing compound powder 92 mixed in the second lithium mixing step S035. This is because lithium hydroxide has a melting point of 462°C, which is lower than that of lithium carbonate, and melts at a low temperature, making it more likely to react with the precursor. The firing step S023 in the method for producing a positive electrode active material according to the second embodiment can be performed under the same conditions as those in the firing step S023 in the method for producing a positive electrode active material according to the first embodiment.

[0076] Next, a method for producing a positive electrode active material according to a third embodiment will be described with reference to FIG. 8. Note that steps indicated by the same reference numerals as those in FIGS. 6 and 7 may be performed in the same manner as in the method for producing a positive electrode active material according to the first embodiment or the second embodiment. Alternatively, a multi-step process including a pre-baking step and a main baking step may be performed. Therefore, detailed descriptions of these steps will be omitted.

[0077] The method for producing a positive electrode active material according to the third embodiment includes a coarsely pulverizing step S0331 of the precursor and the M metal compound and a finely pulverizing step S0332 of the precursor and the M metal compound, instead of the pulverizing step S033 of the method for producing a positive electrode active material according to the second embodiment. In this way, the mixed powder of the precursor 91 and the powder 93 of the M metal compound is pulverized in a two-stage pulverizing process before the granulation step S034.

[0078] In particular, in the precursor manufacturing method, when the average particle size D50 of the cathode active material precursor 91 or the M metal compound powder 93 pulverized in the lithium-nickel mixed powder pulverization step S014 is coarse and exceeds 20 μm, it is preferable to perform a coarse pulverization step S0331 of the precursor and M metal compound powder, in which the precursor and M metal compound powder are coarsely pulverized to a size of less than 10 μm, followed by a fine pulverization step S0332 of the precursor and M metal compound, in which the precursor and M metal compound powder are finely pulverized to a submicron size. It is preferable to use a media mill for both the coarse pulverization step S0331 and the fine pulverization step S0332, and it is preferable that the media size in the fine pulverization step S0332 be smaller than that in the coarse pulverization step S0331. It is preferable to use media with a media diameter on the order of millimeters in the coarse pulverization step S0331, and media with a media diameter on the order of submillimeters in the fine pulverization step S0332. In this way, by dividing the pulverization conditions, such as the media diameter, into two stages, it is possible to suppress the incorporation of media components from the media mill and obtain a cathode active material of the desired composition with few impurities.

[0079] By refining the precursor 91 and the M metal compound powder 93 before the granulation step S034 in this way, the structure of the positive electrode active material sintered through the granulation step S034 becomes a structure with fewer voids. As a result, the particle strength of the positive electrode active material is increased, resulting in improved charge-discharge cycle characteristics. Furthermore, the amount of lithium-containing compound powder added after granulation can be reduced. Therefore, the firing step S023 performed after the granulation step S034 is performed at a relatively higher temperature than the lithiation step S013 in the precursor manufacturing method, which makes lithium in the lithium-containing compound more likely to volatilize. However, according to the manufacturing method of the positive electrode active material of the present invention, the amount of lithium-containing compound remaining as powder in the firing step S023 is relatively small, making it possible to relatively reduce the amount of lithium lost through volatilization.

[0080] Next, a preferred composition of the positive electrode active material to which the manufacturing method of the positive electrode active material of this embodiment can be applied 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 the coefficients 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.)

[0081] 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.

[0082] 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 the coefficients 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.]

[0083] The positive electrode active material represented by the formula (2) has a high Ni content, and therefore, when the operating voltage is in the range of approximately 4.3 V, the positive electrode active material can be easily converted into 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.

[0084] Here, the significance of the numerical ranges of the coefficients a, b, c, d, e, and α in the above formulas (1) and (2) will be explained.

[0085] The coefficient a of lithium in the formulas (1) and (2) is set to be equal to or greater than −0.1 and equal to or less than 0.2. The coefficient a is expressed by the general formula: LiM′O 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 the lithium metal composite oxide represented by Li:M':O = 1:1:2. If the lithium content is too low, the initial capacity of the positive electrode active material will be low. On the other hand, if the lithium content is too high, the charge-discharge cycle characteristics will deteriorate. If the coefficient a is within the above numerical range, it is possible to achieve both a high initial capacity and good charge-discharge cycle characteristics.

[0086] The coefficient a may be set to be -0.02 or more and 0.07 or less. If the coefficient a is -0.02 or more, a sufficient amount of lithium is secured to contribute to charge and discharge, thereby increasing the initial capacity of the positive electrode active material. Furthermore, if the coefficient a is 0.07 or less, charge compensation due to a change in the valence of the metal element is sufficiently achieved, thereby achieving both a high initial capacity and good charge and discharge cycle characteristics.

[0087] The coefficient b of nickel is set to 0.50 or more and 1.0 or less. When the coefficient 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 can be manufactured at a lower cost than the others.

[0088] The coefficient 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 coefficient b is, 0.80 or more, the higher the initial capacity can be obtained. Furthermore, the smaller the coefficient b is, 0.95 or less, the smaller the lattice distortion or crystal structure change associated with the insertion and desorption of lithium ions, and the less likely cation mixing, in which nickel is mixed into the lithium sites, or a decrease in crystallinity occurs during firing, thereby suppressing deterioration of the initial capacity and charge / discharge cycle characteristics.

[0089] The coefficient c of cobalt is 0 or more and 0.20 or less. It is preferably 0 or more and 0.10 or less. The addition of cobalt stabilizes the crystal structure and suppresses cation mixing, which involves the incorporation of nickel into lithium sites. Therefore, the charge-discharge cycle characteristics can be improved without significantly impairing the charge-discharge capacity. On the other hand, excessive cobalt increases raw material costs, thereby increasing the manufacturing cost of the positive electrode active material. When the coefficient c is within the above-mentioned range, high charge-discharge capacity and good charge-discharge cycle characteristics can be achieved with good productivity.

[0090] The coefficient c may be 0.01 or more and 0.20 or less, 0.03 or more and 0.20 or less, or 0.04 or more and 0.20 or less. The larger the coefficient c is, 0.01 or more, the more sufficient the effect of the element substitution with cobalt is obtained, and the more improved the charge-discharge cycle characteristics are.

[0091] The coefficient d of M1, which is at least one metal selected from Al and Mn, is 0 or more and 0.30 or less. When elemental 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, resulting in a decrease in the initial capacity of the positive electrode active material. If d is within the above-mentioned numerical range, the crystalline structure of the positive electrode active material can be maintained stable, and good charge / discharge cycle characteristics, thermal stability, and the like can be obtained in addition to a high initial capacity.

[0092] Manganese is particularly preferred as the element represented by M1. When manganese is substituted, a higher initial capacity can be obtained compared to when aluminum is substituted. Furthermore, when the pre-sintering mixed powder used in the method for producing a positive electrode active material in the first embodiment of the present invention or the lithium-containing compound-added granulated powder used in the method for producing a positive electrode active material in the second embodiment is sintered, manganese also reacts with lithium carbonate as shown in the following formula (3). This reaction suppresses 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 that exhibits a high charge / discharge capacity.

[0093] 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.)

[0094] The coefficient d of M1, which is at least one metal selected from Al and Mn, 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.

[0095] The coefficient e of X is 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 substituted with at least one element selected from the group consisting of magnesium (Mg), titanium (Ti), zirconium (Zr), molybdenum (Mo), and niobium (Nb), 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 will decrease, and the charge-discharge capacity of the positive electrode active material may decrease. If e is within the above numerical range, high initial capacity and good charge-discharge cycle characteristics can be achieved at the same time. From these points of view, it is particularly preferable that X is Ti.

[0096] The coefficient α in the formulas (1) and (2) is set to be equal to or greater than −0.2 and equal to or less than 0.2. α is expressed by the general formula: LiM′O ２ This coefficient α represents the excess or deficiency of oxygen from the stoichiometric ratio of the lithium metal composite oxide, i.e., Li:M':O = 1:1:2. If the coefficient α is within the above-mentioned numerical range, the crystal structure has few defects, and a high initial capacity and good charge-discharge cycle characteristics can be obtained.

[0097] Hereinafter, a preliminary experiment of the oxidation process of metallic nickel powder will be described, followed by an example of a method for producing a precursor and a positive electrode active material. The means for measuring characteristic values ​​are as follows.

[0098] (Specific Surface Area) The specific surface area of ​​the fired powder of the positive electrode active material was measured by the BET method.

[0099] The preferred specific surface area of ​​the positive electrode active material is 0.2 m ２ / g or more, 1.0m ２ / g or less.

[0100] (Oil Absorption) The oil absorption of the powder sample was measured in accordance with JIS K5101-13-1, using NMP (N-methylpyrrolidone) as the solvent. 5.0 g of powder sample was weighed out and placed in a mountain shape on a flat tray. NMP was sucked up using a plastic dropper (2 mL capacity), and the mass was measured. Next, NMP was added dropwise to the powder sample while kneading with a spatula. The addition and kneading were continued until the powder sample became clay-like overall. When NMP was excessive, it was visible that the droplets were not absorbed by the powder sample and remained on the surface. The amount of NMP added up to this point was converted to the oil absorption per 100 g of powder sample. The oil absorption of a preferred positive electrode active material is 24 ml / 100 g or more and 32 ml / 100 g or less.

[0101] (X-ray Diffraction Spectrum Pattern) X-ray diffraction (XRD) patterns in X-ray 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°.

[0102] (R value) Furthermore, after removing the Kα2 ray spectrum component from the XRD pattern obtained by measuring the positive electrode active material, the integrated intensity I of each peak at the diffraction angles corresponding to the 006 plane around 2θ = 36°, the 102 plane around 2θ = 37°, and the 101 plane around 2θ = 38° was calculated. ００６ , I １０２ , I １０１ The R value was calculated from the formula (4). 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 0.500 or less. R value = (I ００６ +I １０２ ) / I１０１ ...(4)

[0103] (Amount of Residual Li) 0.5 g of the positive electrode active material produced in the Examples described below and 30 ml of pure water were placed in a 50 ml plastic container, and the atmosphere in 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 then filtered by suction to obtain an extract. 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 lithium carbonate (Li ２ CO ３ The amounts of the lithium hydroxide (LiOH) and lithium hydroxide (LiOH) components were analyzed. An automatic titrator (Hiranuma COM-1700A) was used for the titration. The titration curve had two stages, and the equivalence point (x) of the first stage represented the reaction of formulas (5) and (6), and the equivalence point (y) of the second stage represented the reaction of formula (6). ２ CO ３ The number of moles of is the same as the number of moles of HCl in formula (7), so the remaining Li ２ CO ３ The amount of residual LiOH is the amount of titration up to the first equivalence point, but since the amount of titration up to the first equivalence point is also included in the amount of titration up to the first equivalence point, the amount of residual LiOH is calculated by the equation (6), that is, the amount of residual LiOH. ２ CO ３ The amount obtained by subtracting the amount of residual Li was (2x-y). ２ CO ３ The amount of Li in the remaining LiOH, i.e., 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 multiplied by 100 to calculate the unreacted Li ratio. LiOH + HCl → LiCl + H ２ O... (5) Li ２ CO ３ +HCl→LiCl+LiHCO ３ ...(6) LiHCO ３ +HCl→LiCl+CO ２ +H ２ O (7) The amount of residual LiOH in the preferred positive electrode active material is 1.3 mass % or less, and the amount of residual Li ２ CO ３ The amount of unreacted Li is preferably 0.4% by mass or less. The unreacted Li content is preferably 3% or less.

[0104] The oxidation rate and lithiation rate can be determined by the following methods. (Oxidation Rate) The oxidation rate of a precursor indicates the oxidized volume of the precursor or metallic nickel powder. Specifically, it was calculated by the following method. Oxygen element mapping is performed on the cross section of the oxidized metallic nickel powder or precursor, and the thickness of the oxide layer containing oxygen is measured from the obtained oxygen element mapping image. The measured oxygen layer thickness L Ｏ and the average particle diameter R of the metallic nickel powder or precursor Ａ The particle diameter R was calculated from the formula (8) based on the above formula. The major and minor diameters of the precursor were measured from the SEM image, and the sum of the major and minor diameters was divided by 2 to obtain the particle diameter R (particle diameter R = (major diameter + minor diameter) / 2). The particle diameters of 50 random precursors were then measured, and the particle diameters R of the precursors from the 6th particle to the 44th particle in order of smallest particle diameter R were arithmetically averaged to obtain the average particle diameter R. Ａ was calculated. Oxidation rate = (((R Ａ / 2) ３ )-((R Ａ / 2-L Ｏ ) ３ ) / (R Ａ / 2) ３ )×100 (8) The oxidation rate of the precursor of the preferred positive electrode active material is as described above.

[0105] (Lithium content) The carbon content C of the lithium-nickel mixed powder obtained by mixing metallic nickel powder and lithium carbonate 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 (9). 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 ... (9) The molar ratio of metallic nickel to lithium carbonate in the raw material mixed powder (M Ｎｉ / Ｌｉ ) and M ＬｉThe ratio of metallic nickel that reacted with Li to be lithiated (lithiation ratio) was calculated from the formula (10). Ｎｉ / Ｌｉ × M Ｌｉ (10) The preferred lithiation rate of the lithium-nickel mixed powder is as described above.

[0106] [Metallic nickel powder oxidation process] [Preliminary experiment 1] Metallic nickel powder (manufactured by Nippon Atomize Co., Ltd.) produced by a water atomization method and having an average particle size D50 of 8 μm was heat treated in a static furnace at 650° C. for 10 hours. The metallic nickel powder was sintered by the heat treatment, and it was not possible to obtain an oxidized powder in a good particle state.

[0107] [Preliminary Experiment 2] Metallic nickel powder (manufactured by Glencore) having an average particle size D50 of 70 μm was heat treated in a static furnace at 700° C. for 10 hours. The metallic nickel powder was sintered by the heat treatment, and it was not possible to obtain an oxidized powder in a good particle state.

[0108] [Preliminary Experiment 3] Metallic nickel powder (manufactured by Nippon Atomize Co., Ltd.) produced by water atomization and having an average particle size D50 of 8 μm was heat treated in a rotary kiln at 650° C. for 10 hours. After the heat treatment, some aggregation occurred, and an oxidized metallic nickel powder having an average particle size D50 of 16 μm was obtained.

[0109] [Preliminary Experiment 4] Metallic nickel powder (manufactured by Glencore) with an average particle size D50 of 70 μm was heat-treated in a rotary kiln at 700°C for 10 hours. After the heat treatment, an oxidized metallic nickel powder with an average particle size D50 of 70 μm was obtained. The oxidation rate was 16%. A cross-section of this oxidized metallic nickel powder (hereinafter referred to as nickel oxide powder) was photographed using a scanning electron microscope (SEM), and at the same time, elemental mapping of oxygen (O) was performed on the photographed cross-section to show the distribution of oxygen elements. The results are shown in Figure 3(a).

[0110] Preliminary experiments 1 to 4 showed that if metallic nickel powder can be moved using a rotary furnace such as a rotary kiln or a rolling furnace such as a rolling bed furnace, it can be oxidized while suppressing sintering, and that appropriately oxidized metallic nickel powder can be obtained.

[0111] [Preliminary Experiment 5] The nickel oxide powder obtained in Preliminary Experiment 3 was pulverized in a ball mill using zirconia balls with a diameter of approximately 5 mm as pulverization media. The D50 after pulverization was 8 μm, the same as that of the raw material nickel metal powder, and although agglomerated powder could be decomposed, oxidized nickel metal powder could not be pulverized.

[0112] [Preliminary Experiment 6] The oxidized nickel powder obtained in Preliminary Experiment 4 was pulverized in a ball mill using zirconia balls with a diameter of 5 mm as a pulverization medium. The D50 after pulverization remained at 70 μm, the same as that of the raw material metallic nickel powder, and pulverization was not possible.

[0113] Preliminary experiments 5 and 6 showed that pulverization cannot be achieved by the oxidation process alone.

[0114] Example 1 Below, an example using the precursor manufacturing method shown in FIG. 2 and the cathode active material manufacturing method shown in FIG. 7 is described. First, lithium carbonate powder, oxidized metal nickel powder with a D50 of 70 μm and an oxidation rate of 16% obtained in Preliminary Experiment 4, cobalt carbonate powder, manganese carbonate powder, titanium oxide powder, and aluminum oxide powder were prepared. The various powders were weighed so that the molar ratio of Li:Ni:Co:Mn:Ti:Al was 0.26:0.85:0.03:0.08:0.03:0.01. The amount of lithium carbonate powder was 25% by mass of the amount of lithium required for the cathode active material for a lithium-ion secondary battery to be manufactured. This corresponds to the metal nickel oxide powder preparation step S011 in FIG. 2.

[0115] Next, the oxidized metallic nickel powder and lithium carbonate powder obtained in Preliminary Experiment 4 were first weighed and placed in a V-type mixer and mixed for 90 minutes to obtain a first mixed powder (first lithium mixing step S012). Next, 100 g of the raw mixed powder was placed in a 150 mm square sagger and subjected to a lithiation heat treatment at 650°C for 10 hours in an air-conditioned furnace (lithiation step S013), obtaining a lithium-nickel mixed powder containing lithium-nickel oxide. It was confirmed that 72% of the lithium-nickel mixed powder was converted to nickel oxide. In other words, the oxidation rate of the lithium-nickel mixed powder in this example was 72%. A cross-sectional SEM image of the lithium-nickel mixed powder and the results of elemental mapping of oxygen (O) are shown in Figure 4B. The lithiation rate of the lithium-nickel mixed powder in this example was 20%.

[0116] Next, the obtained lithium-nickel mixed powder was coarsely pulverized in a ball mill using 5 mm diameter zirconia balls as pulverization media (lithium-nickel mixed powder pulverization step S014). In this way, a precursor of the positive electrode active material was obtained (S015). The average particle size D50 of the precursor was 1.0 μm.

[0117] As described above, by comparing Figures 4A and 4B, the following was found. That is, in the oxidized metallic nickel powder of Figure 4A, only the surface of the particles is oxidized, while in the lithium-nickel mixed powder of Figure 4B, oxidation extends to the interior of the particles. Furthermore, while almost no cracks are observed in the particles of the oxidized metallic nickel powder of Figure 4A, cracks are observed throughout the particles of the lithium-nickel mixed powder of Figure 4B. From this, it was found that pulverization of the crack-free oxidized metallic nickel powder was difficult, but that the lithium-nickel mixed powder, which was obtained by lithiating the oxidized metallic nickel powder, had cracks in the particles, making it possible to pulverize the lithium-nickel mixed powder.

[0118] Next, a positive electrode active material for a lithium ion secondary battery was produced using the precursor of the positive electrode active material described above based on the method for producing a positive electrode active material according to the second embodiment shown in Figure 7. The cobalt carbonate powder, manganese carbonate powder, titanium oxide powder, and aluminum oxide powder weighed as described above were mixed and pre-pulverized in a ball mill using zirconia balls with a diameter of 5 mm as the milling medium, to obtain an M metal compound powder. The average particle size D50 of the M metal compound powder was 1.2 µm.

[0119] Next, the lithium-nickel mixed powder and the M metal compound powder were charged into the same bead mill (Mixing step of M metal compound powder S032). The lithium-nickel mixed powder was pulverized to obtain a precursor of the positive electrode active material, and simultaneously mixed with the M metal compound powder, the precursor of the positive electrode active material and the M metal compound powder were pulverized (Precursor and M metal compound pulverization step S033). As a result, the average particle size D50 of the mixed powder of the positive electrode active material precursor and the M metal compound powder was 0.3 μm. Thereafter, the mixed powder of the positive electrode active material precursor and the M metal compound powder was granulated using a spray dryer to obtain a granulated powder (Granulation step S034).

[0120] Next, to compensate for the insufficient amount of lithium in the granulated powder as a positive electrode active material for a lithium-ion secondary battery, lithium carbonate powder was separately prepared and weighed out to contain 0.77 moles of lithium per 1.00 mole of M metal elements other than lithium (e.g., the total molar amount of Ni, Co, Mn, Ti, and Al) contained in the granulated powder. This amount of lithium carbonate powder was 75% by mass of the amount of lithium required for the produced positive electrode active material for a lithium-ion secondary battery. The granulated powder and the weighed lithium carbonate powder were then charged into a V-type mixer to obtain a lithium-containing compound-added granulated powder (secondary lithium-containing compound mixing step S035).

[0121] This lithium-containing compound-added granulated powder was heat-treated at 700° C. for 24 hours and then at 830° C. for 10 hours to produce a positive electrode active material for a lithium ion secondary battery.

[0122] The residual Li amount, unreacted Li rate, specific surface area, and oil absorption of the positive electrode active material for lithium ion secondary batteries obtained as described above were measured, and the R value calculated from XRD measurement was obtained. As a result, the residual Li amount was 0.3 mass% for lithium hydroxide and 0.3 mass% for lithium carbonate. The unreacted Li rate was 2%. Both results were very low. The specific surface area was 0.9 m2 / g, and the oil absorption was 30 ml per 100 g of positive electrode active material. The oil absorption and specific surface area were also within the range expected to produce a good positive electrode. The R value was 0.45. The small R value suggested that the amount of nickel ions mixed into the lithium sites was small, confirming that good crystallinity was achieved.

[0123] (Fabrication of Positive Electrode) Next, a lithium ion secondary battery was fabricated as follows using the positive electrode active material for lithium ion secondary batteries obtained in the previous example as a positive electrode material. First, the positive electrode active material for lithium ion secondary batteries, 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.

[0124] (Initial capacity, charge-discharge cycle characteristics (capacity retention rate)) 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.

[0125] 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. Then, 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. In addition, the ratio of the discharge capacity after 30 cycles to the initial capacity was calculated as the capacity retention rate. In addition, the coulombic efficiency expressed as discharge capacity / charge capacity was calculated. As a result, the charge capacity was 219 Ah / kg, the discharge capacity was 186 Ah / kg, the coulombic efficiency was 85%, and the capacity retention rate was 89%. Coulombic efficiency is a battery characteristic that indicates the proportion of Li ions that were able to return to the positive electrode material upon discharge among the Li ions that were released during the first charge, and the higher this value, the better the battery characteristic. Furthermore, as a lithium-ion secondary battery, the initial capacity was 186 Ah / kg, and the capacity retention rate was 89%, which is the capacity and capacity retention rate expected for an 85% nickel ratio, and the capacity retention rate was also good.

[0126] It was found that a cathode active material with good crystallinity (powder properties) and electrochemical properties can be produced by preparing a precursor through an oxidation process in which metallic nickel powder is oxidized, a lithiation process in which the oxidized metallic nickel powder is mixed with a lithium-containing compound and at least a portion of the powder is lithiated, and a pulverization process. Furthermore, by using powder containing metallic nickel as a starting material, the cathode active material can be produced without using a water-soluble nickel compound, which has a large volume relative to the Ni content, making it possible to reduce GHG emissions during production.

[0127] A method for producing a precursor of a positive electrode active material for a lithium-ion secondary battery according to one aspect of the present disclosure includes an oxidation step of oxidizing metallic nickel powder, a mixing step of mixing the oxidized metallic nickel powder with a lithium-containing compound to obtain a raw material mixed powder, a lithiation step of heat-treating the raw material mixed powder to lithiate at least a portion of the raw material mixed powder to obtain a lithium-nickel mixed powder, and a pulverization step of pulverizing the lithium-nickel mixed powder, wherein the oxidation step, the mixing step, the lithiation step, and the pulverization step are carried out continuously or intermittently to obtain a precursor containing lithium nickel oxide.

[0128] In this embodiment, a method for producing a precursor for a positive electrode active material for a lithium-ion secondary battery uses metallic nickel powder with low GHG emissions as a nickel source and oxidizes the metallic nickel powder to prevent sintering. The oxidized metallic nickel powder is then mixed with a lithium-containing compound and heat-treated to lithiate the powder, generating cracks within the powder particles. The inclusion of such lithium-nickel oxide allows the precursor to be pulverized relatively easily. The oxidation step, the first lithium mixing step, the lithiating step, and the pulverization step may be performed simultaneously and consecutively to obtain the precursor, or each production step may be performed at different times or locations, allowing for flexibility in the implementation of the steps. In this embodiment, the oxidation step may be replaced with a preparation step of preparing pre-oxidized metallic nickel powder. In other words, although the above example shows the production of oxidized metallic nickel powder via an oxidation step, pre-oxidized metallic nickel powder may also be purchased and used.

[0129] In one aspect of the present disclosure, the oxidation step is preferably an oxidation step in which the metallic nickel powder is oxidized while being moved to prevent sintering. Specifically, the oxidation step can be performed using a rotary furnace or a rolling hearth furnace. On the other hand, the lithiation step is preferably performed using a stationary furnace.

[0130] A method for producing a positive electrode active material for a lithium ion secondary battery in one aspect of the present disclosure is characterized by including a firing 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 produce 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.

[0131] In one aspect of the present disclosure, it is preferable to have a crushing step of crushing the mixed powder, and then a granulation step of granulating the crushed mixed powder to form granulated powder, and to perform the firing step on the granulated powder.

[0132] In one embodiment of the present disclosure, 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.)

[0133] 1: Metallic nickel powder 2: Lithium nickel mixed powder 2b: Crack 90: Simultaneous mixed granulated powder 91: Precursor 92: Powder of lithium-containing compound 93: Powder of M metal compound

Claims

1. a first lithium mixing step of mixing the oxidized metallic nickel powder with a lithium-containing compound powder to obtain a first mixed powder; a lithiation step of heat-treating the first mixed powder to obtain a lithium-nickel mixed powder containing lithium-nickel oxide; a lithium-nickel mixed powder pulverization step of pulverizing the lithium-nickel mixed powder, a lithium-containing compound powder containing 50 mass% or less of lithium relative to the amount of lithium required for the lithium-ion secondary battery positive electrode active material to be produced, wherein the lithium-containing compound powder contains 50 mass% or less of lithium in the first lithium mixing step.

2. 2. The method for producing a precursor of a positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the oxidized metallic nickel powder is obtained by oxidizing metallic nickel powder or nickel-based alloy powder while moving the powder.

3. 3. The method for producing a precursor of a positive electrode active material for a lithium ion secondary battery according to claim 2, wherein the oxidized metallic nickel powder is oxidized using a rotary furnace or a rolling bed furnace.

4. 2. The method for producing a precursor of a positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the lithiation step is carried out using a stationary furnace.

5. 10. A method for producing a positive electrode active material for a lithium ion secondary battery, comprising: a firing 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 according to claim 1 with a lithium-containing compound and an M metal compound containing a metal element M other than lithium and nickel to obtain a pre-fired mixed powder; and firing the pre-fired mixed powder to obtain a positive electrode active material.

6. a precursor and M metal compound pulverization step of mixing an M metal compound containing a metal element M other than lithium and nickel with the precursor produced by the method for producing a precursor of a positive electrode active material for a lithium ion secondary battery according to claim 1, and pulverizing the mixed powder of the precursor and the M metal compound; a granulation step of granulating the pulverized mixed powder of the precursor and the M metal compound to form a granulated powder; a second lithium mixing step of adding a lithium-containing compound to the granulated powder so as to obtain a lithium-containing compound-added granulated powder in an amount necessary for the lithium amount of the positive electrode active material for a lithium ion secondary battery to be produced; A method for producing a positive electrode active material for a lithium ion secondary battery, comprising a calcination step of calcining the lithium-containing compound-added granulated powder.

7. 7. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 5, 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.)

8. 7. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 5, wherein the positive electrode active material for a lithium ion secondary battery is represented by the following composition 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 the coefficients a, b, c, d, e, and α are numbers that satisfy the following relationships: -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.]