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

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

[Technical Field]

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

[0002] Lithium-ion rechargeable batteries are widely used in various fields such as electronics, automobiles, and infrastructure. In particular, lithium-ion rechargeable batteries are used as the power source for electric vehicles (EVs) and are an important core component. From the perspective of extending driving range, the energy density of lithium-ion rechargeable batteries is improving year by year, and the positive electrode active material used in batteries is a ternary layer material that can obtain high-capacity lithium-ion rechargeable batteries. A ternary layer material is a composite oxide of transition metal elements such as nickel (Ni), cobalt (Co), and manganese (Mn) and lithium (Li) (hereinafter referred to as lithium metal composite oxide). As mentioned above, cathode active materials include metal materials with limited reserves. Furthermore, from the perspective of maintaining a sustainable global environment, there is a need to reduce greenhouse gas (GHG) emissions associated with the production of cathode active materials, even in the extraction of these metal elements from minerals.

[0003] Patent Document 1 describes a method for producing a positive electrode active material for a lithium-ion secondary battery using a transition metal hydroxide such as Ni, Co, or Mn as a precursor. The positive electrode active material is produced by reacting the transition metal hydroxide with a Li source. Furthermore, Patent Document 2 describes a manufacturing method in which a nickel source is melted, nickel particles obtained by atomization are dissolved in an aqueous sulfuric acid solution to obtain nickel sulfate, Ni-containing hydroxide is obtained by crystallization, and a positive electrode active material for secondary batteries is obtained by coprecipitation using this hydroxide. Because these processes utilize the coprecipitation method, water-soluble nickel compounds such as nickel sulfate are used as raw materials, resulting in large quantities of weight and volume being handled during manufacturing.

[0004] On the one hand, Patent Document 3 and Patent Document 4 describe methods for manufacturing a positive electrode active material using a nickel raw material containing metallic nickel. These are powders containing nickel or the like instead of water-soluble nickel compounds as the raw material, and since the nickel content per unit volume is higher than that of water-soluble nickel compounds, the volume to be handled during production is relatively small in terms of weight, and it is expected to contribute to reducing GHG emissions during production.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in Patent Document 3, since firing is performed on the powder of metallic nickel as it is, sintering occurs during the firing process, and the particle state cannot be maintained, making it difficult to pulverize. In addition, the crystal structure of the positive electrode active material is unstable, and therefore the electrochemical characteristics of the lithium-ion secondary battery are also unstable. On the other hand, in Patent Document 4, after mixing at least a powder of a lithium compound with a powder of metallic nickel in which the oxygen content is extremely low and most of which is not oxidized, the mixture is oxidized and then fired. However, there is also a certain demand for manufacturing using oxidized nickel powder that is easy to handle as a starting material. In that case, while using oxidized nickel powder as a starting material and aiming to reduce GHG emissions, a precursor of a positive electrode active material for a lithium-ion secondary battery that can produce a positive electrode active material exhibiting good crystallinity is sought.

[0007] Therefore, the present invention aims to provide a method for producing a precursor of a lithium-ion secondary battery positive electrode active material that contributes to reducing GHG emissions and has good crystallinity, and a method for producing a lithium-ion secondary battery positive electrode active material using the precursor. [Means for solving the problem]

[0008] The present invention provides a method for producing a precursor of a positive electrode active material for a lithium-ion secondary battery, comprising: a first lithium mixing step of mixing oxidized metallic nickel powder with 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. In the first lithium mixing step, the lithium-containing compound powder containing 50% by mass or less of lithium relative to the amount of lithium required for the positive electrode active material for the lithium-ion secondary battery to be manufactured is mixed. It is characterized by doing so.

[0009] In the present invention, the oxidized metallic nickel powder is preferably oxidized metallic nickel powder obtained by oxidizing metallic nickel powder or nickel-based alloy powder while suppressing sintering by moving it. Specifically, this can be carried out using a rotary furnace or a rolling bed furnace. On the other hand, the lithiumization step is preferably carried out using a stationary furnace. 。

[0010] The present invention provides a method for producing a positive electrode active material for lithium-ion secondary batteries, characterized by comprising a calcination step in which a precursor produced by the method for producing a precursor for a lithium-ion secondary battery is mixed with a lithium-containing compound and an M metal compound containing metal elements other than lithium and nickel to obtain a pre-calcination mixed powder, and the pre-calcination mixed powder is calcined to obtain a positive electrode active material.

[0011] The manufacturing method of the positive electrode active material for a lithium ion secondary battery of the present invention includes mixing a precursor produced by the manufacturing method of the precursor of the positive electrode active material for the lithium ion secondary battery with an M metal compound containing a metal element other than lithium and nickel, and pulverizing the mixed powder of the precursor and the M metal compound to obtain a pulverized precursor and M metal compound; a granulation step of granulating the pulverized mixed powder of the precursor and the M metal compound to form granulated powder; a second lithium mixing step of adding a lithium-containing compound to the granulated powder so that the amount of lithium required for the positive electrode active material for the lithium ion secondary battery to be produced is obtained, thereby obtaining a lithium-containing compound-added granulated powder; and a firing step of firing the lithium-containing compound-added granulated powder. It is preferable to perform these steps.

[0012] In the present invention, it is preferable that the positive electrode active material for the lithium ion secondary battery is represented by the following compositional formula (1). Li 1+a Ni b M (1-b) O 2+α ···(1) (However, in 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.) In addition, it is preferable that the positive electrode active material for the lithium ion secondary battery is represented by the following compositional formula (2). Li 1+a Ni b Co c M1 d X e O 2+α ···(2) [However, in the 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 respectively satisfy -0.1 ≦ a ≦ 0.2, 0.5 ≦ b ≦ 1.0, 0 ≦ c ≦ 0.20, 0 ≦ d ≦ 0.30, 0 ≦ e ≦ 0.1, b + c + d + e = 1, and -0.2 < α < 0.2.)

Effects of the Invention

[0013] According to the present invention, it is possible to obtain a precursor for a lithium-ion secondary battery positive electrode active material and a lithium-ion secondary battery positive electrode active material that contributes to reducing GHG emissions and has good crystallinity. [Brief explanation of the drawing]

[0014] [Figure 1] This flowchart shows a method for producing oxidized metallic nickel powder according to one embodiment of the present invention. [Figure 2] This is a flowchart showing one embodiment of a method for producing a precursor of a positive electrode active material for lithium-ion secondary batteries according to the present invention. [Figure 3] This figure shows the reflection intensity distribution against the reflection diffraction angle, obtained from X-ray diffraction (XRD) of a precursor of a positive electrode active material for lithium-ion secondary batteries obtained by a manufacturing method according to one embodiment of the present invention, and a comparative example of oxidized metallic nickel powder. [Figure 4A] This is a scanning electron microscope (SEM) image of oxidized metallic nickel powder and a mapping diagram of oxygen (O) in relation to that SEM image. [Figure 4B] This shows an SEM image of lithium-ionized metallic nickel powder and a mapping diagram of oxygen in relation to that SEM image. [Figure 5A] The relationship between the grinding time and average particle size D50 of the lithium nickel mixed powder obtained by the manufacturing method of one embodiment of the present invention and the lithium nickel mixed powder and oxidized metallic nickel powder is shown. [Figure 5B] The relationship between the grinding time and D95 ​​at 95% of the particle size frequency distribution for lithium nickel mixed powder obtained by a manufacturing method according to one embodiment of the present invention, and for lithium nickel mixed powder and oxidized metallic nickel powder, is shown. [Figure 6] This is a flowchart illustrating a method for producing a positive electrode active material for a lithium-ion secondary battery according to a first embodiment of the present invention. [Figure 7] This is a flowchart showing a method for producing a positive electrode active material for a lithium-ion secondary battery according to a second embodiment of the present invention. [Figure 8]This is a flowchart illustrating a method for producing a positive electrode active material for a lithium-ion secondary battery according to a third embodiment of the present invention. [Figure 9A] The schematic cross-sectional structure of the simultaneously mixed granulated powder 90 before and after the calcination process is shown. [Figure 9B] Figure 7 shows the schematic cross-sectional structure of the granulated powder 99 produced in the granulation process S034 before and after the calcination process. [Modes for carrying out the invention]

[0015] Next, with reference to the drawings, 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 "positive electrode active material") using the precursor will be described.

[0016] In the embodiment of the present invention, a metal nickel powder with low GHG emissions is used as the nickel source. This metal nickel powder is either oxidized to prevent sintering when subjected to various heat treatments, or an already oxidized metal nickel powder is prepared (metal nickel oxide powder preparation step). The oxidized metal nickel powder is then mixed with a lithium-containing compound powder (hereinafter referred to as lithium-containing compound powder) (first lithium mixing step), and the mixture is heat-treated to lithify it (lithification step), thereby generating lithium nickel oxide and causing cracks in the powder. The presence of such lithium nickel oxide in the powder makes it relatively easy to pulverize. The powder, which has become relatively easy to pulverize, is then pulverized in a lithium nickel mixed powder pulverization step to obtain a precursor for the positive electrode active material by achieving the desired particle size. The oxidation step, the first lithium mixing step, the lithification step, and the lithium nickel mixed powder pulverization step may be performed simultaneously and consecutively to obtain the precursor for the positive electrode active material, or each manufacturing step may be performed at different times and locations with flexibility in the execution of the process to obtain the precursor for the positive electrode active material.

[0017] Furthermore, the method for producing oxidized metallic nickel powder described below may be used in place of the preparation step S011 for preparing oxidized metallic nickel powder in the method for producing the precursor of the positive electrode active material in the embodiment of the present invention. That is, although the above example obtains oxidized metallic nickel powder through an oxidation step, it is also possible to purchase and use pre-oxidized metallic nickel powder. However, the method for producing oxidized metallic nickel powder described below, when combined with the method for producing the positive electrode active material in each embodiment of the present invention described later, contributes to reducing GHG emissions in the entire process, from the production of metallic nickel powder to the production of the positive electrode active material for lithium-ion secondary batteries. Therefore, the method for producing oxidized metallic nickel powder used in the production of the precursor of the positive electrode active material for lithium-ion secondary batteries in one embodiment of the present invention will be described first.

[0018] [Method for producing oxidized metallic nickel powder] Figure 1 illustrates a method for producing oxidized metallic nickel powder used in the production of the precursor for the positive electrode active material of the lithium-ion secondary battery in this embodiment. In the method for producing oxidized metallic nickel powder according to this embodiment, metallic nickel powder produced by methods such as atomization or carbonylation can be used. S001 in Figure 1 is a preparation step for preparing metallic nickel powder before oxidation. In the preparation step S001 for preparing metallic nickel powder before oxidation, metallic nickel powder with a low amount of impurity elements can be obtained by atomization or carbonylation. The atomization method is preferable for obtaining spherical powder. High-purity raw materials are used for battery components to avoid short circuits inside batteries produced using this metallic nickel powder. In particular, iron (Fe) is an impurity element that is likely to cause 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 of grade Class I are suitable as a high-purity nickel source. In this embodiment, high-purity metallic nickel powder with few impurities, which can be obtained without acid dissolution of these briquettes or cathodes, was used. In this embodiment, nickel-based alloy powder containing metal elements necessary for the positive electrode active material, such as Co and Mn, may be used instead of metallic nickel powder used in the method for producing the precursor of the positive electrode active material.

[0019] Another method for obtaining metallic nickel powder is the carbonyl process. The carbonyl process involves reacting nickel briquettes with carbon monoxide gas to obtain gaseous nickel carbonyl, which is then thermally decomposed under reduced pressure and low temperature to obtain metallic nickel powder. High-purity metallic nickel powder can also be obtained using the carbonyl process. Furthermore, powdered metallic nickel powder can be used as metallic nickel powder before it is briquetized.

[0020] The average particle size of metallic nickel powder is preferably in the range of 1 μm to 100 μm. This particle size can be measured using a laser diffraction particle size distribution analyzer. In this specification, D50, which is the particle size corresponding to an accumulation frequency of 50 volume% in the cumulative particle size distribution measured by laser diffraction scattering, is considered as the average particle size. In this specification, D95 is the particle size value corresponding to an accumulation frequency of 95 volume% in the cumulative particle size distribution.

[0021] (Metallic nickel powder grinding process S002) Once metallic nickel powder is obtained, a metallic nickel powder grinding step S002 is performed to grind the metallic nickel powder. The average particle size D50 of the metallic nickel powder after the metallic nickel powder grinding step S002 is preferably 20 μm or less, and more preferably 8 μm or less. When the average particle size D50 of the metallic nickel powder is 20 μm or less, metallic elements other than lithium and nickel diffuse to the center of the metallic nickel powder, making it easier to make the composition within the positive electrode active material uniform. Furthermore, if the D50 of the metallic nickel powder is 8 μm or less, the composition within the positive electrode active material becomes even more uniform, which is preferable.

[0022] The metal nickel powder grinding step S002 can be omitted. If the metal nickel powder grinding step S002 is omitted, the average particle size D50 of the metal 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. In addition, in order to improve the uniformity of the composition within the positive electrode active material, it is sufficient to achieve such an average particle size D50 before mixing with a compound containing at least Li and Ni other than those described later and firing, so it is not necessarily required to make the average particle size D50 of the metal nickel powder 20 μm or less at this point. However, making the average particle size D50 of the metal nickel powder 20 μm or less at this point can contribute to shortening the processing time in subsequent steps.

[0023] Furthermore, the particle size of metallic nickel powder can be controlled in the atomization method by the injection pressure of the injected water or gas, and in the carbonyl method by the thermal decomposition conditions. Powder particles larger than 100 μm can be removed by sieving and returned to dissolution (recycled).

[0024] (Oxidation process S003) Next, an oxidation step S003 is performed to oxidize the metallic nickel powder. In the oxidation step S003, a rotary furnace or a rolling furnace is used to heat the metallic nickel powder in an oxidizing atmosphere while rolling it. This movement of the metallic nickel powder during the oxidation reaction suppresses 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 can be oxidized while suppressing sintering by heating it in an oxidizing atmosphere while rolling it. Heat treatment in an oxidizing atmosphere shortens the time required for the oxidation treatment. Furthermore, the temperature during heat treatment is preferably between 400°C and 800°C, and more preferably between 500°C and 750°C. By setting the temperature above 400°C, it becomes easier to produce a precursor with the desired oxidation rate when using the oxidized metallic nickel powder obtained by this manufacturing method to produce a precursor for the positive electrode active material. Also, when the temperature during heat treatment is between 400°C and 800°C, the heat treatment time in oxidation step S003 is preferably between 1 and 20 hours, preferably between 5 and 15 hours, and more preferably between 5 and 10 hours. This oxidation step S003 forms an oxide layer on the surface of the metallic nickel powder. The oxide layer can suppress sintering of the metallic nickel powders in the various heat treatment steps performed thereafter. The thickness of the oxide layer should be 500 nm or more, and preferably 5 μm or more. As mentioned above, the oxidation process only requires the formation of 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, an oxidation rate of 2% or more is preferable, and 15% or more is more preferable. When the particle size of the metallic nickel powder is 40 μm, an oxidation rate of 4% or more is preferable, and 25% or more is more preferable. Furthermore, when the particle size of the metallic nickel powder is 20 μm, an oxidation rate of 15% or more is preferable, and 80% or more is more preferable. By achieving these oxidation rates, the thickness of the oxide layer becomes appropriate, and as a result, sintering of the metallic nickel powders can be suppressed in the process after the oxidation process. Furthermore, the metallic nickel powder used in this invention may be purchased and prepared from a commercially available source, as long as it satisfies the requirements such as the Fe content and average particle size mentioned above.

[0026] [Method for producing a precursor of positive electrode active material] The method for producing the cathode active material precursor according to the embodiment of the present invention shown in Figure 2 will be described below. As shown in the flowchart in Figure 2, first, the aforementioned oxidized metallic nickel powder is prepared (metallic nickel powder preparation step S011). The oxidized metallic nickel powder to be prepared can be oxidized metallic nickel powder produced by the aforementioned method for producing oxidized metallic nickel powder, or commercially available powder that satisfies requirements such as Fe content and average particle size. Furthermore, in the metallic nickel powder preparation step S011, it is sufficient to prepare the materials necessary for carrying out the first lithium mixing step S012 described later. Therefore, if the first lithium mixing step S012 described later is carried out in a rotary furnace or tumbling furnace that has performed the oxidation step S003 described above, no special work is required in this metallic nickel powder preparation step S011, and it is possible to skip this step S011.

[0027] Next, a first lithium mixing step (S012) is performed, in which oxidized metallic nickel powder and lithium-containing compound powder are mixed. Subsequently, a first mixed powder, which is a mixture of oxidized metallic nickel powder and lithium-containing compound powder, is heat-treated to perform a lithiation process (S013) in which at least a portion of it is lithified. This lithiation process S013 forms lithium nickel oxide. The lithium nickel mixed powder in which this lithium nickel oxide has been formed has improved pulverability. Next, a lithium nickel mixed powder grinding step (S014) is performed to grind the lithium nickel mixed powder containing lithium nickel oxide to obtain a powdered precursor (S015). As shown in Figure 2, the method for producing a precursor of positive electrode active material for lithium-ion secondary batteries according to this embodiment consists of at least three steps: a first lithium mixing step S012, a lithiation step S013, and a lithium nickel mixed powder grinding step S014. The following describes each step in detail.

[0028] (First lithium mixing process S012) The first lithium mixing step S012 is a step to obtain a first mixed powder by mixing the aforementioned oxidized metallic nickel powder with a lithium-containing compound 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 single-composition lithium-containing compound powder or a mixture of lithium-containing compound powders of multiple compositions. It is preferable to use a lithium-containing compound powder in powder form.

[0029] The amount of lithium-containing compound added here should be either an amount equivalent to the amount of lithium needed to achieve the composition ratio of the final lithium-ion secondary battery positive electrode active material, or an amount equivalent to a smaller amount of lithium. The amount of lithium-containing compound to add should be determined according to how the positive electrode active material is produced from the precursor produced by this embodiment. Alternatively, it may be determined considering the pulverizability in the lithium-nickel mixed powder pulverization step S014 described later.

[0030] Furthermore, 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, the amount may be in the range of 5% or more, and even near the lower limit. 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, the amount of lithium-containing compound is 10% by mass or more and 100% by mass or less. The presence of the lithium-containing compound can suppress sintering of the powders in subsequent processes. By mixing 10% by mass or more of the lithium-containing compound, which is the amount of 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 powders is suppressed when the lithification process (S013) described later is carried out. On the other hand, the amount of lithium-containing compound mixed in the first lithium mixing process (S012) is preferably 50% by mass or less, and more preferably 25% by mass or less, of the amount of lithium-containing compound containing the required amount of lithium. In the lithiumization process (S013) described later, it is necessary to minimize the amount of lithium remaining in the lithium-containing compound that does not fully react with the oxidized metallic nickel powder. Therefore, it is preferable that the amount of lithium-containing compound be less than the amount of lithium required for the positive electrode active material. For example, it is preferable that the amount be 50% by mass or less, and more preferably 25% by mass or less, of the amount of lithium required for the positive electrode active material. This reduces the amount of lithium treatment in the lithiumization process S013, thereby reducing the energy consumed in the lithiumization treatment and lowering costs and GHG emissions.

[0031] Furthermore, when a pulverization process is carried out during the production of the positive electrode active material as described later, it is preferable that the amount of lithium-containing compound mixed before the lithiation process be 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 precursor of the positive electrode active material is small, the voids in the secondary particles of the positive electrode active material can be reduced by applying the method for producing the positive electrode active material in this embodiment, which will be described later. As a result, the particle strength of the positive electrode active material becomes high, and the charge-discharge cycle characteristics become good. Furthermore, even when using a mixture of powders of multiple lithium-containing compounds, it is preferable that the ratio of lithium mass in the mixed powder of lithium-containing compounds and oxidized metallic nickel powder be within the range described above.

[0032] The lithium-containing compound preferably has a melting point higher than the heat treatment temperature of the lithiumization process. Therefore, the lithium-containing compound is preferably lithium carbonate. The melting point of lithium carbonate is high at 724°C, making it possible to raise the lithiumization temperature to 720°C. This is because it remains solid even at 720°C, functions as an inclusion, suppressing contact between metallic nickel powders and sintering, and shortening the lithiumization 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 the voids in the secondary particles of the positive electrode active material to be manufactured, it is preferable to mix only a small amount of lithium-containing compound with the oxidized metallic nickel powder, and it is necessary to arrange the lithium-containing compound powder between the oxidized metallic nickel powders in order to function as an inclusion for the purpose of suppressing sintering. Therefore, in order to mix only a small amount of lithium-containing compound and to arrange more lithium-containing compound powder between the oxidized metallic nickel powders, 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] The first lithium mixing step S012 uses a V-type mixer, a stirring mixer, attritor, media mill, etc. To ensure uniform mixing, it is preferable to be able to break down the agglomeration of each raw material powder. The mixing method can be either a dry method, in which only the raw material powders are mixed, or a wet method, in which a liquid is used as a dispersion medium.

[0034] (Lithitation process 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, where the oxidized metallic nickel powder is lithified. In the lithiation step S013, further oxidation of the oxidized metallic nickel powder is promoted and lithium nickel oxide is generated (lithification). 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 lithiumization step S013, heat treatment in an oxidizing atmosphere is preferable because it shortens the time required for lithiumization of the oxidized metallic nickel powder. The oxidizing atmosphere can be air, a mixture of nitrogen and oxygen gas, or of course, oxygen gas. Furthermore, the temperature is preferably between 450°C and 720°C, and more preferably between 450°C and 700°C. By setting the temperature between 450°C and 700°C, a precursor of the positive electrode active material having the desired lithiumization rate can be easily obtained. The heat treatment time for the lithiumization process is preferably 0.5 hours or more, more preferably between 3 hours and 20 hours, more preferably between 3 hours and 15 hours, and more preferably between 5 hours and 10 hours. This is because performing the lithiumization treatment for 5 to 10 hours allows the oxidized metallic nickel powder to combine with lithium and the lithiumization reaction to be completed, making it easy to stably obtain a precursor with the desired lithiumization rate.

[0036] This process may be carried out using the same rotary furnace or rolling furnace as the oxidation process S003 in which the metallic nickel powder was oxidized. Furthermore, by carrying out the aforementioned first lithium mixing process S012 using the same rotary furnace or rolling furnace, it is possible to carry out the process from the oxidation process S003 of the metallic nickel powder to the lithiumization process S013 continuously. In this way, fuel consumption required during the production of the cathode active material precursor can be reduced, leading to space savings during production, improved production efficiency through reduced driving force, and energy savings. These factors contribute to a reduction in GHG emissions, making it possible to manufacture cathode active materials while suppressing GHG emissions.

[0037] However, this embodiment is not limited to performing the lithiumization process S013 in the same furnace as the oxidation process S003. In other embodiments, the lithium nickel mixed powder may be heated in an oxidizing atmosphere while remaining still, by changing the time and location from the oxidation process S003 or the first lithium mixing process S012, and the process may be carried out in a static furnace capable of 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 lithiumization process S013 in a rotary furnace, performing the lithiumization process in a stationary furnace is preferable because it reduces the amount of lithium source volatilized and suppresses compositional deviations. Furthermore, it is also preferable because the reduced amount of lithium volatilized means that the amount of lithium consumed and not contained in the precursor of the positive electrode active material can be reduced.

[0038] As mentioned above, the lithiation process S013 promotes lithiation along with further oxidation of the metallic nickel powder, forming lithium nickel oxide in addition to nickel oxide. To confirm the formation of lithium nickel oxide, Figure 3 shows the X-ray diffraction (XRD) measurement results of the lithium nickel mixed powder when the lithiation process S013 was performed by mixing 25% by mass of lithium carbonate powder with the oxidized metallic nickel powder, in an amount equivalent to the amount of lithium required for the composition ratio of the positive electrode active material for the lithium-ion secondary battery to be finally manufactured. For comparison, the X-ray diffraction (XRD) measurement results of the oxidized metallic nickel powder are also shown in Figure 3.

[0039] In Figure 3, the vertical axis represents the intensity value (au) of the X-ray diffracted light, and the horizontal axis represents the X-ray reflection diffraction angle (2θ). The upper graph shows the measurement results for lithium nickel mixed powder, and the lower graph shows the measurement results for oxidized metallic nickel powder. In each graph, peaks with a triangular sign represent nickel oxide, peaks with a circular sign represent metallic nickel, and peaks with a rectangular sign represent lithium nickel oxide (Li x Ni y The peak at O) is shown. As can be seen from Figure 3, when lithium carbonate powder was mixed with oxidized metallic nickel powder to perform lithiation, in addition to the peak for nickel oxide, a peak at 2θ = 43.5° to 44.0°, which is attributed to lithium nickel oxide, could be observed. That is, 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 (SEM) images of oxidized metallic nickel powder before and after the lithiation process S013, and their oxygen (O) mapping diagrams. The left image in Figure 4A shows a cross-section of the oxidized metallic nickel powder before the lithiation process S013, and the right image in Figure 4A is the oxygen mapping diagram of the left image in Figure 4A. On the other hand, the left image in Figure 4B shows a cross-section of the lithium nickel mixed powder after the lithiation process S013, and the right image in Figure 4B is the oxygen mapping diagram of the left image in Figure 4B. This oxygen mapping diagram shows the distribution of oxygen concentration by changing the intensity according to the oxygen concentration. Therefore, areas with a relatively high concentration of oxygen atoms are shown in light gray, and areas with low oxygen levels are shown in dark gray.

[0041] Figure 4A shows that in oxidized metallic nickel powder 1, the oxidized region 1b is located in a very shallow area of ​​the surface. In comparison, Figure 4B shows that in the lithium nickel mixed powder 2 formed after the lithiation process S013, the oxidized region 2b extends into the interior of the particles. This oxidized region 2b is heat-treated in an oxidizing atmosphere while mixed with the lithium-containing compound. Therefore, it is presumed that a large amount of lithium nickel oxide is also generated in this oxidized region 2b.

[0042] Furthermore, while Figure 4A shows almost no cracks in metallic nickel powder 1, Figure 4B reveals that cracks 2b have propagated throughout the powder. The reason for the widespread cracking is presumed to be that when oxidized metallic nickel becomes a lithium nickel mixed powder, the volume of the powder expands by approximately three times, and the stress generated by this volume change causes cracks to form. As these cracks propagate throughout the powder, grinding becomes easier, and the grinding process can be completed in a shorter time. If the grinding process is not performed, these cracks become diffusion pathways for the elements, allowing each element to diffuse more uniformly.

[0043] The oxidation rate of the lithium nickel mixed powder after the lithiation process S013 should preferably be 10% or more and less than 100%, as described later in the examples. An oxidation rate of 10% or more suppresses sintering of the lithium nickel mixed powder particles during the subsequent firing process to obtain the positive electrode active material. Furthermore, an oxidation rate of 10% or more increases the valence of nickel, which is expected to promote the reaction with the lithium metal composite oxide during the 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 with the lithium metal composite oxide during firing. In addition, forming lithium nickel oxide makes it easier to pulverize as described above, and further promotes the reaction between lithium and other metals constituting the positive electrode active material, such as nickel, during the firing process to obtain the positive electrode active material, thereby promoting the formation of layered crystal structures and making it easier to obtain a positive electrode active material with good crystallinity.

[0044] The lithification rate of the lithium nickel mixed powder is preferably 8% or higher in order to obtain good pulverability at the lithification rate described later in the examples. If the average particle size of the oxidized metallic nickel powder prepared in the oxide metallic nickel powder preparation step S011 exceeds 20 μm, then 10% or higher is preferable, preferably 15% or higher, and more preferably 20% or higher. If the lithification rate of the lithium nickel mixed powder is excessively increased in the lithification step S013, and a large amount of lithium carbonate is consumed by reacting it with metallic nickel, then when the positive electrode active material is manufactured using the precursor of the positive electrode active material of this embodiment, the amount of unreacted lithium in the positive electrode active material will increase. This phenomenon occurs because if the lithification rate is excessively increased in the lithification step S013, the amount of lithium-containing liquid phase component generated during the calcination process decreases, and the reaction rate between lithium and other metal elements constituting the positive electrode active material, such as nickel, cobalt, and manganese, which are promoted by the liquid phase reaction, becomes slower compared to a calcination process performed with an appropriate amount of liquid phase. As a result, the firing time is prolonged, and it is thought that the amount of unreacted lithium increases when compared over a constant firing time. In other words, the reaction AO + Li2CO3 → LiAO2 (where A represents a metal element other than Li that constitutes the positive electrode active material, such as Ni, Co, or Mn, and AO represents an oxide of these metal elements) slows down, increasing the amount of Li2CO3 contained in the generated positive electrode active material and relatively reducing the amount of LiNiO2 formed. Therefore, since the amount of impurities that do not function as positive electrode active material increases, the upper limit of the lithiumization rate should be set to, for example, 35% or less, preferably 27% or less, and more preferably 25% or less, taking into consideration obtaining an appropriate amount of liquid phase in the firing process.

[0045] (Lithium nickel mixed powder grinding process S014) The lithium nickel mixed powder produced in the lithification process S013 is then subjected to grinding in the lithium nickel mixed powder grinding process S014. This process yields a precursor of the positive electrode active material with a well-controlled particle size distribution, which is advantageous for the subsequent production of the positive electrode active material. Grinding can be carried out using an attritor, media mill, ball mill, bead mill, agitator, or other similar equipment.

[0046] The graphs shown in Figures 5A and 5B illustrate the relationship between grinding time and particle size. Figure 5A shows the change in the average particle size D50 of lithium nickel mixed powder and lithium nickel mixed powder with oxidized metallic nickel powder over the grinding time, and Figure 5B shows the change in D95, which corresponds to the particle size of lithium nickel mixed powder and lithium nickel mixed powder with oxidized metallic nickel powder, over the grinding time. In both Figures 5A and 5B, the horizontal axis represents the grinding time (in hours), and the vertical axis represents the average particle size D50 or D95 (in micrometers). The dotted lines show the average particle size D50 and D95 ​​values ​​of the metallic nickel powder during step S001, which is the process for obtaining the metallic nickel powder before oxidation, as shown in Figure 1. The values ​​plotted with triangles represent the average particle size for lithium nickel mixed powder at each grinding time, and the values ​​plotted with circles represent the average particle size for oxidized metallic nickel powder at each grinding time. The oxidized metallic nickel powder is produced by performing the oxidation step S003 on metallic nickel powder, and then, without going through the first lithium mixing step S012, further producing the oxidized metallic nickel powder in the same oxidizing atmosphere, at the same processing temperature and for the same processing time as the lithiumization step S013.

[0047] As can be seen from Figures 5A and 5B, the lithium nickel mixed powder can be pulverized in a shorter time compared to oxidized metallic nickel powder without lithium. Regarding the average particle size D50, it takes about 50 hours for oxidized metallic nickel powder without lithium carbonate to reach the average particle size D50 before the oxidation process S003, whereas the lithium nickel mixed powder obtained by adding lithium carbonate and going through the lithiation process S013 can be pulverized in about 10 hours. Similarly, the change in the value of D95 is also similar; without the addition of lithium-containing processed powder, it is difficult to reach D95 before the oxidation process, indicating that pulverization is possible, but the powder itself is not pulverized.

[0048] Thus, if lithium-containing compound powder (lithium carbonate) is not added, 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 method. For this reason, in the subsequent cathode active material manufacturing method, 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, a cathode active material precursor that facilitates the production of a good cathode active material can be obtained (S015). In particular, comparing the difference in average particle size D50 and D95 ​​after approximately 50 hours of pulverization, the cathode active material precursor that has undergone the lithium nickel mixed powder pulverization step S014 has a particle size of about 5 μm, while the oxidized metallic nickel powder has a particle size of 10 μm, a difference of twice as much. As can be seen from this, the cathode active material precursor obtained by the cathode active material precursor manufacturing method according to this embodiment has a small particle size and the variation in particle size is suppressed, so it is thought that the reaction treatment carried out in the subsequent cathode active material manufacturing process will proceed smoothly. Furthermore, metallic elements other than lithium and nickel can easily diffuse to the center of each particle, and when manufacturing a positive electrode active material using the positive electrode active material precursor in this embodiment, it becomes easier to homogenize the composition within the positive electrode active material.

[0049] Therefore, in the method for producing the positive electrode active material described later, the positive electrode active material is obtained by calcining in an oxidizing atmosphere containing oxygen. However, by introducing the precursor produced in the production method of this embodiment, a positive electrode active material with good crystallinity can be produced. Furthermore, in the method for producing the cathode active material precursor of this embodiment, it is even more preferable to perform a classification step after the lithium nickel mixed powder grinding step S014. By performing the classification step after the grinding step S014, a good calcination reaction can be easily achieved in the subsequent production of the cathode active material. The classification method is not particularly limited, but known classification methods such as sieve classification and airflow classification using air may be used. Furthermore, the method for producing a precursor of a positive electrode active material according to the embodiment of the present invention may also include other metal element-containing powders necessary to achieve a desired composition ratio of the positive electrode active material, or lithium-containing compound powders to supplement the amount of lithium that is insufficient in the precursor's composition ratio. At a minimum, lithium nickel oxide is included, and the lithium nickel mixed powder that has been pulverized in the lithium nickel mixed powder pulverization step S014 is included in the mixed powder.

[0050] [Method for manufacturing positive electrode active material] Next, the methods for producing the positive electrode active material in embodiments of the present invention will be described. Examples of the methods for producing the positive electrode active material in these embodiments are shown in the flowcharts in Figures 6 to 8. Figure 6 is a flowchart of the method for producing the positive electrode active material in the first embodiment of the present invention, and Figure 7 is a flowchart of the method for producing the positive electrode active material in the second embodiment of the present invention. Figure 8 is a flowchart of the method for producing the positive electrode active material in the third embodiment of the present invention. The methods for producing the positive electrode active material in the first, second, and third embodiments all use a precursor produced by the method for producing the precursor of the positive electrode active material in these embodiments described above. Therefore, these are methods for producing the positive electrode active material using a precursor that already contains nickel and lithium.

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

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

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

[0054] In this way, after preparing powders of metal element compounds necessary to achieve the desired composition of the positive electrode active material, a deficient element mixing step S022 is performed, in which powders of compounds containing deficient elements, such as M metal compounds and lithium-containing compounds, are mixed with the precursor. (Deficiency element mixing process S022) In mixing step S022, a V-type mixer, stirring mixer, attritor, media mill, etc., are used to mix the precursor and the powder of the compound containing the deficient element. To ensure uniform mixing, it is preferable to be able to break up any agglomeration of each raw material powder. As mentioned above, if the lithium content ratio of the precursor is less than the lithium content ratio of the target composition of the positive electrode active material in molar ratio, the lithium-containing compound powder is also mixed together with the M compound powder. Either a dry mixing method, in which only the raw material powders of the precursor powder, M metal compound powder, and 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, M metal compound powder, and lithium-containing compound powder are dispersed in the liquid and then mixed, may be used. Furthermore, if the method for producing the cathode active material of this embodiment is carried out immediately following the method for producing the cathode active material precursor described above, the lithium nickel mixed powder grinding step S014 performed in the precursor production method may be combined with the mixing step S022 by using a stirring mixer, attritor, media mill, ball mill, or bead mill that can perform grinding and mixing simultaneously.

[0055] Lithium hydroxide and lithium carbonate can be used as lithium-containing compounds to be mixed with the precursor. Lithium carbonate is preferred because it has low hygroscopicity and is easy to handle. On the other hand, if the effect of promoting the diffusion of metal element M into the interior of the precursor is important, lithium hydroxide is preferred because it can produce a positive electrode active material with a uniform composition. The amount of lithium-containing compound powder to be mixed with the precursor should preferably be determined by considering the amount of lithium that is insufficient in the lithium content of the precursor for the desired composition of the positive electrode active material, as well as the amount of lithium that will volatilize in the calcination process S023 described later. Furthermore, prior to the elemental mixing step S021, it is preferable to classify both the lithium-containing compound powder and the M metal compound powder to remove coarse particle size powder.

[0056] Once the precursor is mixed with the powder of the M metal compound and the powder of the lithium-containing compound, a calcination process S023 is carried out to calcine this mixed powder (hereinafter referred to as the pre-calcination mixed powder).

[0057] In the firing process S023, a pre-firing mixed powder of the precursor obtained in the elemental deficiency mixing process S022, the powder of the M metal compound, and the powder of the lithium-containing compound is fired to obtain a layered positive electrode active material for lithium-ion secondary batteries. In the firing process S023, an electric or gas furnace is used. The pre-firing mixed powder is left to stand in a firing saggar and fired. Furthermore, it is preferable to allow the mixed powder before firing to contain a large amount of oxygen gas between each particle by sieving it once in an air atmosphere or an oxygen-containing atmosphere and letting it free-fall, thereby accumulating the mixed powder before firing in an oxygen-containing state, and then letting it stand in a dry atmosphere before firing. Furthermore, by creating multiple groove-like indentations or depressions in the pre-fired powder mixture placed on top of the firing saggar, oxygen-containing gases can more easily pass through to the bottom of the pre-fired powder mixture during firing. This promotes oxidation of the pre-fired powder mixture at the bottom of the firing saggar, resulting in less variation in the firing of the pre-fired powder mixture at the top and bottom of the firing saggar. Furthermore, the present invention also allows for the use of a furnace that rotates the pre-fired mixed powder during firing, such as a rotary kiln, instead of the aforementioned furnace.

[0058] The firing atmosphere preferably contains 20% or more oxygen by volume, and if the Ni content is 80% or more of the total metal elements excluding Li, then an oxygen concentration of 90% or more is preferable. The firing process S023 should be performed at a temperature of 700°C to 900°C to obtain a layered positive electrode active material. This process may include a pre-firing stage where the temperature is maintained at 450°C to 730°C, and a main firing stage where the temperature is higher than that of the pre-firing stage and maintained at 700°C to 900°C. The preferred firing temperature and holding time are adjusted according to the composition blended during raw material mixing, and the firing is performed so that the various physical properties (specific surface area, etc.) of the desired positive electrode active material are within a suitable range after firing.

[0059] Furthermore, the synthesized lithium metal composite oxide may be subjected to a washing process after the calcination process, in which it is washed with deionized water or the like, for the purpose of removing impurities, and a drying process to dry the washed lithium metal composite oxide. It may also be subjected to a crushing process to break down the synthesized lithium metal composite oxide, and a classification process to classify the lithium metal composite oxide to a predetermined particle size.

[0060] As described above, the method for producing a positive electrode active material in the first embodiment of the present invention uses metallic nickel powder as the nickel raw material, thus eliminating the need for acid dissolution and coprecipitation steps. It is estimated that the amount of CO2 emissions generated in the production of metallic nickel is about 30% less than that of nickel sulfate, and by using metallic nickel powder, the amount of CO2 emissions generated in the production of the precursor and positive electrode active material can be reduced. Furthermore, because metallic nickel powder is used as the nickel raw material, the volume handled during transportation and in the production process of the positive electrode active material can be reduced compared to compounds such as nickel sulfate and nickel hydroxide. Specifically, if we express the Ni content per unit volume of each compound in mass%, nickel sulfate (Ni(SO)4·6H2O) is 5%, nickel hydroxide (Ni(OH)2) is 29%, while metallic nickel has a Ni content of 100%, resulting in a higher Ni content per unit volume. As a result, the volume handled during transportation and the manufacturing process of the positive electrode active material is approximately 1 / 20th of that of nickel sulfate and approximately 1 / 3th of that of nickel hydroxide in this embodiment, thereby reducing fuel consumption during transportation, improving production efficiency through space savings and reduced driving force during manufacturing, and saving energy. These factors lead to a reduction in GHG emissions, making it possible to manufacture the positive electrode active material while suppressing GHGs. In addition, since nickel sulfate does not need to be used as a raw material, the possibility of sulfur being incorporated into the positive electrode active material is also reduced, making it possible to obtain a positive electrode active material with good electrochemical properties.

[0061] Next, the method for manufacturing the positive electrode active material, which is the second embodiment, will be described with reference to Figure 7. Note that the steps indicated by the same reference numerals as in Figure 6 are the same as those for manufacturing the positive electrode active material in the first embodiment, so a detailed explanation of those steps will be omitted. The second embodiment of the method for manufacturing a positive electrode active material further includes a granulation step S034 compared to the method for manufacturing a positive electrode active material in the first embodiment. Furthermore, a second lithium mixing step S035 is added after the granulation step S034. By including these steps, it becomes possible to manufacture a positive electrode active material that facilitates the creation of electrodes with high energy density. In particular, pressurizing during positive electrode fabrication makes it easier to obtain a positive electrode with high packing density, resulting in a positive electrode with better performance.

[0062] By the way, in the method for producing the positive electrode active material in this second embodiment, the precursor produced by the method for producing the positive electrode active material precursor of the embodiment of the present invention is prepared in the preparation step S021 for the positive electrode active material precursor. (M metal mixing process S032) Next, in order to supplement the metal elements that are lacking in the desired composition of the positive electrode active material, a mixing step S032 is performed in which powder of an M metal compound containing M metal elements other than lithium and nickel, which are not present in the prepared precursor, is mixed with this precursor. Examples of M metal compound powders include cobalt carbonate powder, manganese carbonate powder, titanium oxide powder, aluminum oxide powder, and mixtures thereof.

[0063] In the first embodiment of the method for producing a positive electrode active material, if the amount of lithium contained in the precursor was less than the amount of lithium required for the target composition of the positive electrode active material, the lithium-containing compound powder was also mixed with the M metal element in the deficient element mixing step S022. However, in the second embodiment of the method for producing a positive electrode active material, even if the amount of lithium contained in the precursor is less than the amount of lithium required for the target composition of the positive electrode active material, it is not necessary to mix the lithium-containing compound powder in the M metal compound mixing step S032. Alternatively, 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 lithium 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 target composition of the positive electrode active material.

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

[0065] The means for mixing can be the same as those used in the mixing step S022 of the method for producing the positive electrode active material in the first embodiment, and either the dry mixing method or the wet mixing method described above may be used. Furthermore, if the method for producing the positive electrode active material of this second embodiment is carried out immediately following the method for producing the precursor of the positive electrode active material described above, the M metal compound mixing step S032, described later, may be started midway through the lithium nickel mixed powder grinding step S014 by using a stirring mixer, attritor, media mill, ball mill, or bead mill that can grind and mix simultaneously.

[0066] (Powdering process S033 for precursor and M metal compound powder) Next, a pulverization step S033 is performed to pulverize the mixed powder of the precursor and the M metal compound powder. Performing the pulverization step S033 of the precursor and the M metal compound powder before the granulation step S034 described later promotes the calcination reaction in the calcination step S023, resulting in a positive electrode active material with a good layered structure, enabling the production of a positive electrode active material with a high initial capacity and good charge-discharge cycle characteristics. Preferably, the average particle size D50 of the primary particles of the mixed powder (pulverized mixed powder) obtained after pulverization in this pulverization step S033 is 0.40 μm or less. By achieving such an average particle size, the calcination reaction in the subsequent granulation step S034 and calcination step S023 is easily promoted, and voids in the positive electrode active material are easily suppressed. This contributes to the ease of producing a positive electrode active material with higher particle strength and good charge-discharge cycle characteristics. The grinding can be carried out using an attritor, media mill, ball mill, bead mill, or agitator. A media mill is preferable, and a bead mill is more preferable, as it can grind the mixed powder of the precursor and M metal compound powder to a submicron size. Of course, by using a grinder that has both grinding and mixing functions, such as an agitator, attritor, media mill, ball mill, or bead mill, the mixing step of the M metal compound powder S032 and the grinding step of the precursor and M metal compound powder S033 may be carried out in the same step.

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

[0068] (Pelletization process S034) As described above, a granulation process S034 is performed to produce granulated powder based on the mixed powder of the precursor and M metal compound obtained through the pulverization process S033 of the precursor and M metal compound. First, a mixed powder slurry is prepared using the mixed powder of the precursor and M metal compound and a solvent. If a wet pulverization method is used in the pulverization process S033 of the precursor and M metal compound, granulation is performed based on the pulverized slurry containing this mixed powder. The granulation method is not particularly limited, but for example, granulated powder may be obtained by spray drying using a nozzle-type spray dryer or a disc-type spray dryer.

[0069] (Second lithium mixing process S035) In this second embodiment of the method for producing a positive electrode active material, the amount of lithium that is insufficient from the amount of lithium contained 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, a 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 with the granulated powder in an amount equivalent to the sum of the amount of lithium insufficient from the amount of lithium contained in the granulated powder relative to the amount of positive electrode active material of the target composition, plus the amount of lithium that volatilizes in the subsequent calcination 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, so it is considered that a reaction is more likely to occur with the precursor contained in the granulated powder. In the second lithium mixing step S035, it is possible to mix the granulated powder and the lithium-containing compound powder using a V-type mixer. By mixing lithium-containing compound powder with granulated powder in this way, the positive electrode active material produced through the subsequent calcination process S023 has a microstructure with fewer voids, which increases the particle strength of the positive electrode active material, resulting in good charge-discharge cycle characteristics.

[0070] The reason why a positive electrode active material with a microstructure that minimizes voids can be obtained by the method for producing the positive electrode active material in this second embodiment will be explained with reference to Figure 9. Figure 9A is a schematic diagram of a co-mixed granulated powder 90 produced by simultaneously mixing lithium-containing compound powder 92 with a precursor 91 and M metal compound powder 93, and a schematic diagram of a positive electrode active material 95 produced by calcining the co-mixed granulated powder 90. On the other hand, Figure 9B is a schematic diagram of a granulated powder 99 produced from a mixed powder of precursor 91 and M metal compound powder 93, a lithium-containing compound-added granulated powder 100 produced by adding lithium-containing compound powder 92 to the granulated powder 99 and granulating it, and a positive electrode active material 110 produced by calcining the granulated powder 100, relating to a method for producing a positive electrode active material, which is the second embodiment of this invention.

[0071] The left side of Figure 9A shows the schematic cross-sectional structure of the simultaneously mixed granulated powder 90, and the right side shows the schematic cross-sectional structure of the positive electrode active material 95 after the calcination process of the simultaneously mixed granulated powder 90. The positive electrode active material 95 is obtained by performing the calcination process S023 on the simultaneously mixed granulated powder 90. On the other hand, the left side of Figure 9B shows the schematic cross-sectional structure of the granulated powder 99 consisting of the precursor 91 and the M metal compound powder 93, the center side of Figure 9B shows the schematic cross-sectional structure of the lithium-containing compound-added granulated powder 100, and the right side of Figure 9B shows the schematic cross-sectional structure of the positive electrode active material 110 obtained by the method for producing the positive electrode active material in the second embodiment after the calcination process of the lithium-containing compound-added granulated powder 100.

[0072] In the right-hand diagram of Figure 9A and the right-hand diagram of Figure 9B, 96 in the diagram schematically represents the primary particles of the positive electrode active material. The co-mixed granulated powder 90, shown in Figure 9A, before the calcination process, contains a large amount of lithium-containing compound powder 92. When the co-mixed granulated powder 90 is calcined in this state, a reaction proceeds between the M metal compound, the lithium-containing compound, and the precursor. During this process, the lithium-containing compound 92 becomes a liquid phase and diffuses into the primary particles 96 generated during the calcination process. Therefore, the more lithium-containing compound powder there is, the more voids the resulting structure will have after calcination. Consequently, the positive electrode active material is produced with a large number of voids. On the other hand, the method for producing the positive electrode active material in this second embodiment makes it possible to reduce the generation of voids that occur when the lithium-containing compound powder 92 disappears due to calcination. The granulated powder produced in the granulation step S034 of the method for producing the positive electrode active material in this second embodiment has a schematic configuration of the granulated powder 99 shown in the left diagram of Figure 9B. The granulated powder 99 consists only of the precursor 91 and a portion of the M metal compound powder 93. When producing a positive electrode active material in which the Ni content ratio is 80% or more in molar ratio, the amount of M metal compound powder 93 contained in the granulated powder 99 is relatively small, and the granulated powder 99 is composed almost entirely of the precursor 91.

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

[0074] Next, in the method for producing the positive electrode active material in this second embodiment, a calcination step S023 is performed on the lithium-containing compound-added granulated powder 100. Through this calcination step S023, the lithium-containing compound-added granulated powder 100 is transformed into a positive electrode active material 110 having the schematic structure shown in the right-hand diagram of Figure 9B, as indicated by arrow C. In the firing process S023, the lithium-containing compound powder 92 becomes a liquid phase during firing, and lithium diffuses into the primary particles 96 generated during the firing process. However, since the lithium-containing compound 92 is on the outside of the granulated powder 99, there are almost no areas inside the positive electrode active material where the lithium-containing compound 92 has disappeared, making it less likely for voids to form as shown in Figure 9A. Furthermore, since the lithium-containing compound powder 92 is arranged to surround the granulated powder 99, penetration into the granulated powder is efficient during firing. In this way, after firing, the positive electrode active material has a structure with few voids.

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

[0076] Next, a third embodiment of the method for manufacturing the positive electrode active material will be described using Figure 8. Steps indicated by the same reference numerals as in Figures 6 and 7 may be carried out in the same manner as in the method for manufacturing the positive electrode active material in the first embodiment or the second embodiment. Alternatively, a multi-step process including a calcination stage and a final calcination stage may be performed. Therefore, a detailed explanation of that step will be omitted.

[0077] In the third embodiment of the method for producing a positive electrode active material, instead of the grinding step S033 of the precursor and M metal compound in the method for producing a positive electrode active material in the second embodiment, it includes a coarse grinding step S0331 of the precursor and M metal compound and a fine grinding step S0332 of the precursor and M metal compound. Thus, the mixed powder of the precursor 91 and the powder 93 of the M metal compound is ground in two grinding steps before the granulation step S034.

[0078] In particular, in the method for producing the precursor, if the average particle size D50 of the precursor 91 of the positive electrode active material or the powder 93 of the M metal compound 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 to reduce the size to less than 10 μm, and then perform a fine pulverization step S0332 of the precursor and M metal compound to finely pulverize and mix the precursor and M metal compound powder 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 is smaller than the media size in the coarse pulverization step S0331. It is preferable to use media with a diameter on the order of millimeters in the coarse pulverization step S0331, and to use media with a diameter on the order of sub-millimeters in the fine pulverization step S0332. In this way, by pulverizing in two stages, such as the pulverization conditions such as the media diameter used, the inclusion of media components from the media mill can be suppressed, and a positive electrode active material with a desired composition and fewer impurities can be obtained.

[0079] By finely grinding the precursor 91 and the M metal compound powder 93 before the granulation process S034, the microstructure of the positive electrode active material calcined after the granulation process S034 becomes one with fewer voids. As a result, the particle strength of the positive electrode active material becomes high, leading to good charge-discharge cycle characteristics. Furthermore, the amount of lithium-containing compound powder added after granulation can be reduced. Therefore, in the calcination process S023, which is performed after the granulation process S034, the process is carried out at a relatively higher temperature than in the lithification process S013 in the precursor manufacturing method, making the lithium in the lithium-containing compound more prone to volatilization. However, according to the method for producing positive electrode active material of the present invention, the amount of lithium-containing compound remaining as powder in the calcination process S023 is relatively small, making it possible to relatively reduce the amount of lithium lost due to volatilization.

[0080] Next, a preferred composition of the positive electrode active material to which the method for manufacturing the positive electrode active material of this embodiment can be applied will be described. As mentioned above, the composition of the positive electrode active material of this embodiment is not particularly limited, but preferred compositions are described below. First, the positive electrode active material according to this embodiment is represented by the following formula (1). Li 1+a Ni b M (1-b) O 2+α ...(1) (However, in formula (1) above, M is a metal element other than Li and Ni, and the coefficients a, b, and α are numbers that satisfy -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 per total metal elements other than Li is 50 atomic percent or more, thereby achieving high energy density and high initial capacity. The proportion of Ni per total metal elements other than Li can be set to an appropriate value within the range of 50 atomic percent to 100 atomic percent. Because the positive electrode active material contains a high proportion of nickel, Ni 2+ Ni 3+ It is important that oxidation reactions that oxidize to a certain state proceed efficiently.

[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) [However, in equation (2), M1 represents at least one element selected from Al and Mn, X represents one or more metallic elements other than Li, Ni, Co, Al, and Mn, and the coefficients a, b, c, d, e, and α are numbers that satisfy -0.1 ≤ a ≤ 0.2, 0.5 ≤ b ≤ 1.0, 0 ≤ c ≤ 0.20, 0 ≤ d ≤ 0.30, 0 ≤ e ≤ 0.1, b + c + d + e = 1, and -0.2 < α < 0.2, respectively.]

[0083] The positive electrode active material represented by formula (2) exhibits a high initial capacitance compared to LiCoO2, etc., in the operating voltage range up to approximately 4.3V, due to its high Ni content. Furthermore, because of its high Ni content, it is a positive electrode active material with lower raw material costs and readily available raw materials compared to LiCoO2, etc.

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

[0085] The lithium coefficient a in equations (1) and (2) above shall be between -0.1 and 0.2. The coefficient a represents the excess or deficiency of lithium from the stoichiometric ratio of the lithium metal composite oxide represented by the general formula LiM'O2 (where M' represents a metal element such as Ni, Co, or Mn), i.e., Li:M':O = 1:1:2. If there is too little lithium, the initial capacity of the positive electrode active material will be low. On the other hand, if there is too much lithium, the charge-discharge cycle characteristics will deteriorate. If the coefficient a is within the above numerical range, it is possible to achieve both high initial capacity and good charge-discharge cycle characteristics.

[0086] The coefficient a may be -0.02 or greater and 0.07 or less. If the coefficient a is -0.02 or greater, a sufficient amount of lithium is secured to contribute to charging and discharging, so the initial capacity of the positive electrode active material can be increased. Also, if the coefficient a is 0.07 or less, sufficient charge compensation due to the change in the valence state of the metal element is achieved, so both high initial capacity and good charge-discharge cycle characteristics can be achieved.

[0087] The coefficient b for nickel shall be 0.50 or greater and 1.0 or less. When the coefficient b is 0.50 or greater, a sufficiently high charge / discharge capacity can be obtained compared to when other metal elements are used. Therefore, if b is within the above numerical range, a positive electrode active material exhibiting a high charge / discharge capacity can be manufactured at a lower cost compared to LiCoO2, etc.

[0088] The coefficient b is preferably 0.80 or greater and 0.95 or less, and more preferably 0.85 or greater and 0.95 or less. The greater the coefficient b is above 0.80, the higher the initial capacity that can be obtained. Also, the smaller the coefficient b is below 0.95, the smaller the lattice distortion or crystal structure change associated with lithium ion insertion and removal, making it less likely for cation mixing, where nickel is mixed into the lithium sites, or a decrease in crystallinity to occur during firing, thus suppressing deterioration of initial capacity and charge-discharge cycle characteristics.

[0089] The cobalt coefficient c should be 0 or greater and 0.20 or less. Preferably, it should be 0 or greater and 0.10 or less. The addition of cobalt stabilizes the crystal structure and suppresses cation mixing, which is the mixing of nickel into the lithium sites. Therefore, it is possible to improve the charge-discharge cycle characteristics without significantly impairing the charge-discharge capacity. On the other hand, if there is an excess of cobalt, the raw material cost will increase, thus increasing the manufacturing cost of the positive electrode active material. If the coefficient c is within the above numerical range, it is possible to achieve both high charge-discharge capacity and good charge-discharge cycle characteristics with good productivity.

[0090] The coefficient c may be 0.01 or greater and 0.20 or less, or 0.03 or greater and 0.20 or less, or 0.04 or greater and 0.20 or less. The larger the coefficient c is above 0.01, the more sufficiently the effect of cobalt elemental substitution is obtained, and the better the charge-discharge cycle characteristics become.

[0091] The coefficient d of M1, which is at least one metal selected from Al and Mn, shall be between 0 and 0.30. Elemental substitution with at least one element (M1) selected from the group consisting of manganese and aluminum allows the layered structure to remain more stable even if lithium is desorbed during charging. On the other hand, if these elements (M1) are in excess, the proportion of other metallic elements such as nickel decreases, reducing the initial capacity of the positive electrode active material. If d is within the above numerical range, the crystal structure of the positive electrode active material can be kept stable, resulting in high initial capacity, good charge-discharge cycle characteristics, and thermal stability.

[0092] Manganese is particularly preferred as the element represented by M1. When manganese is used as the elemental substitute, a higher initial capacity can be obtained compared to when aluminum is used as the elemental substitute. Furthermore, during the calcination of the pre-calcination mixed powder used in the method for producing the positive electrode active material in the first embodiment of the present invention and the lithium-containing compound-added granulated powder used in the method for producing the positive electrode active material in the second embodiment, manganese also reacts with lithium carbonate as shown in formula (3) below. This reaction suppresses grain coarsening and allows the nickel oxidation reaction to proceed at high temperatures, thus enabling the efficient production of a positive electrode active material exhibiting high charge-discharge capacity.

[0093] Li2CO3+2M´O+0.5O2→2LiM´O2+CO2···(3) (However, in formula (3) above, M' represents a metallic element such as Ni, Co, or Mn.)

[0094] The coefficient d of M1, which is at least one metal selected from Al and Mn, is preferably 0.02 or higher, and more preferably 0.04 or higher. The larger the coefficient d of M1, the more fully the effect of elemental substitution by at least one element selected from the group consisting of manganese and aluminum can be obtained. When M1 is manganese, the oxidation reaction of nickel can proceed at a higher temperature, and a positive electrode active material exhibiting high initial capacity can be obtained more efficiently. Furthermore, the coefficient d of M1 is preferably 0.18 or lower. If the coefficient d of M1 is 0.18 or lower, the initial capacity is maintained to be high even if elemental substitution occurs.

[0095] The coefficient e of X is set to be greater than or equal to 0 and less than or equal to 0.1. X represents one or more metallic elements other than Li, Ni, Co, Al, and Mn, but if it is substituted with at least one element selected from the group consisting of magnesium (Mg), titanium (Ti), zirconium (Zr), molybdenum (Mo), and niobium (Nb), it is possible to improve various performances such as charge-discharge cycle characteristics while maintaining the activity of the positive electrode active material. On the other hand, if these elements (X) are in excess, the proportion of other metallic elements such as nickel will decrease, which may reduce the charge-discharge capacity of the positive electrode active material. If e is within the above numerical range, it is possible to achieve both high initial capacity and good charge-discharge cycle characteristics. From these points of view, it is particularly preferable that X be Ti.

[0096] The coefficient α in equations (1) and (2) above shall be between -0.2 and 0.2. α represents the excess or deficiency of oxygen from the stoichiometric ratio of the lithium metal composite oxide represented by the general formula LiM'O2, i.e., Li:M':O=1:1:2. If the coefficient α is within the above numerical range, the crystal structure has few defects, resulting in high initial capacity and good charge-discharge cycle characteristics. [Examples]

[0097] The following describes preliminary experiments on the oxidation process of metallic nickel powder, followed by examples of methods for producing the precursor and cathode active material. The means for measuring characteristic values ​​are as follows.

[0098] (specific surface area) The specific surface area of ​​the calcined 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 m². 2 / g or more, 1.0m 2 It is less than / g.

[0100] (Oil absorption amount) The oil absorption of the powder sample was measured in accordance with JIS K5101-13-1, using NMP (N-methylpyrrolidone) as the solvent. 5.0 g of the powder sample was weighed out and placed in a mound on a flat tray. NMP was drawn up using a polydropper (2 mL capacity) and its mass was measured. Next, NMP was added dropwise to the powder sample while mixing with a spatula, continuing the addition and mixing until the powder sample became clay-like. When there was an excess of NMP, it was possible to visually observe that the droplets were not absorbed by the powder sample and remained on the surface. The amount of NMP added up to this point was converted to the oil absorption amount per 100 g of powder sample. The preferred oil absorption rate of the positive electrode active material is 24 ml / 100g or more and 32 ml / 100g or less.

[0101] (X-ray diffraction spectrum pattern) X-ray diffraction (XRD) patterns of the precursor and cathode active material were measured using the X'Pert PRO MPD X-ray diffractometer (PANalytical) under the following conditions: CuKα source, tube voltage 45kV, tube current 40mA, sampling interval 0.02° / step, divergence slit 0.5°, scattering slit 0.5°, receiving slit 0.15mm, and scanning range 15°≦2θ≦80°.

[0102] (R-value) Furthermore, after removing the Kα2 line spectral 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 using equation (4). It is known that the R value decreases as the layering of the positive electrode active material progresses, and it was used as an indicator of good crystallinity. In this respect, a desirable R value is 0.500 or less. R value = (I 006 +I 102 ) / I 101 ...(4)

[0103] (Residual Li amount) 0.5 g of the positive electrode active material produced by the example described later and 30 ml of pure water were placed in a 50 ml poly container, the contents of the poly container were replaced with argon gas, and the mixture was stirred for 1 hour to extract the Li component. The extract was then obtained by suction filtration. 15 ml of the obtained extract was diluted with pure water to approximately 40 ml and titrated with 0.02 M hydrochloric acid to analyze the amounts of lithium carbonate (Li2CO3) and lithium hydroxide (LiOH) components in the extract. An automatic titrator (Hiranuma, COM-1700A) was used for the titration. The titration curve was in two stages; the equivalence point (x) of the first stage represents the reactions of equations (5) and (6), and the equivalence point (y) of the second stage represents the reaction of equation (6). Since the number of moles of Li2CO3 in equation (5) is the same as the number of moles of HCl in equation (7), the titration volume for residual Li2CO3 was defined as the amount between the equivalence points of the first and second stages (yx). The residual LiOH volume is the titration volume up to the equivalence point of the first stage, but since equation (6) is also included in the titration volume up to the first stage, the amount obtained by subtracting equation (6), i.e., the residual Li2CO3 volume, was used (2x-y). In addition, the amount of Li in residual Li2CO3 and residual 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 percentage. LiOH + HCl → LiCl + H2O ... (5) Li2CO3+HCl→LiCl+LiHCO3···(6) LiHCO3+HCl→LiCl+CO2+H2O···(7) The preferred residual LiOH content of the positive electrode active material is 1.3% by mass or less, and the preferred residual Li2CO3 content is 0.4% by mass or less. Furthermore, the preferred unreacted Li content is 3% or less.

[0104] Furthermore, the oxidation rate and lithiumation rate can be determined by the following methods. (oxidation rate) The oxidation rate of the precursor indicates the oxidized volume of the precursor or metallic nickel powder. Specifically, it was calculated using the following method: Oxygen element mapping was performed on the cross-section of the oxidized metallic nickel powder or precursor, and the thickness of the oxide layer containing oxygen was measured from the resulting oxygen element mapping image. The measured thickness of the oxygen layer L Oand metallic nickel powder, or the average particle size R of the precursor A Based on this, it was calculated from equation (8). The major and minor axes of the precursors were measured from the SEM image, and the two were added together and divided by 2 to obtain the particle diameter R (particle diameter R = (major axis + minor axis) / 2). Then, the particle diameters of 50 arbitrary precursors were measured, and the average particle diameter R was calculated by arithmetic mean of the particle diameters R of the 6th to 44th precursors in ascending order of particle diameter R. A The result 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 preferred cathode active material precursor is as described above.

[0105] (Lithiumization rate) Carbon content C of lithium nickel mixed powder, which is a mixture of metallic nickel powder and lithium carbonate. i And the amount of carbon in the precursor C o The amount was measured, and the proportion of lithium carbonate that decreased during the oxidation process, i.e., reacted with metallic nickel, was calculated using equation (9). The reaction product is lithium nickel oxide. It is known that an increase in lithium nickel oxide makes it easier for cracks to form in the precursor. In this respect, the lithification rate can be used as an indicator of how easily it can be crushed. Percentage of lithium carbonate reacted with metallic nickel M Li =(C i -C o ) / C o ...(9) The molar ratio of metallic nickel to lithium carbonate in the raw material mixture powder (M Ni / Li ) and M Li From this, the ratio of metallic nickel that reacted with Li to become lithium (Li conversion rate) was calculated using equation (10). Li conversion rate=M Ni / Li × M Li ...(10) The preferred lithium nickel mixed powder has the lithification rate described above.

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

[0107] [Preliminary Experiment 2] Metallic nickel powder (manufactured by Glencore) with 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 sintered as a result of the heat treatment, and it was not possible to obtain oxidized powder with good particle size.

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

[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 heat treatment, 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 elemental mapping of oxygen (O), which shows the distribution of oxygen elements, was performed on the photographed cross-section. The results are shown in Figure 3(a).

[0110] Preliminary experiments 1-4 showed that if metallic nickel powder can be moved using a rotary furnace such as a rotary kiln or a rolling bed furnace, oxidation can be suppressed while sintering is inhibited. Furthermore, it was found that properly oxidized metallic nickel powder can be obtained.

[0111] [Preliminary Experiment 5] The nickel oxide powder obtained in preliminary experiment 3 was ground using a ball mill with zirconia balls approximately Φ5 mm in diameter as the grinding medium. The D50 after grinding was 8 μm, the same as the raw material for metallic nickel powder. This indicates that the agglomerated powder could be disintegrated, but the oxidized metallic nickel powder could not be ground.

[0112] [Preliminary Experiment 6] The oxidized nickel powder obtained in preliminary experiment 4 was ground using a ball mill with Φ5 mm zirconia balls as the grinding medium. The D50 after grinding remained at 70 μm, the same as the raw material for metallic nickel powder, indicating that grinding was not possible.

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

[0114] [Example 1] The following describes examples of the method for producing the precursor shown in Figure 2 and the method for producing the positive electrode active material shown in Figure 7. First, lithium carbonate powder, oxidized metallic nickel powder (obtained in preliminary experiment 4 with a D50 of 70 μm and an oxidation rate of 16%), cobalt carbonate powder, manganese carbonate powder, titanium oxide powder, and aluminum oxide powder were prepared. Each powder was 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. This amount of lithium carbonate powder is 25% by mass of the amount of lithium required for the positive electrode active material to be manufactured for lithium-ion secondary batteries. This corresponds to the metallic nickel powder preparation step S011 in Figure 2.

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

[0116] Next, the obtained lithium nickel mixed powder was coarsely ground in a ball mill using Φ5 mm zirconia balls as the grinding medium (lithium nickel mixed powder grinding step S014). In this way, a precursor for the positive electrode active material was obtained (S015). The average particle size D50 of the precursor was 1.0 μm.

[0117] As described above, the following was found by comparing Figure 4A and Figure 4B. Specifically, in the oxidized metallic nickel powder in Figure 4A, only the surface of the particles was oxidized, whereas in the lithium nickel mixed powder in Figure 4B, the oxidation extended to the interior of the particles. Furthermore, while almost no cracks were observed in the particles of the oxidized metallic nickel powder in Figure 4A, cracks were observed throughout the particles of the lithium nickel mixed powder in Figure 4B. From this, it was found that pulverization of the crack-free oxidized metallic nickel powder was difficult, but because the lithium nickel mixed powder, which was created by lithifying the oxidized metallic nickel powder, had cracks in its particles, pulverization of the lithium nickel mixed powder became possible.

[0118] Next, a positive electrode active material for lithium-ion secondary batteries was manufactured using the aforementioned positive electrode active material precursor, based on the manufacturing method of the positive electrode active material of the second embodiment shown in Figure 7. The cobalt carbonate powder, manganese carbonate powder, titanium oxide powder, and aluminum oxide powder, which were weighed as described above, were mixed while being pre-ground in a ball mill using Φ5 mm zirconia balls as the grinding medium to obtain M metal compound powder. The average particle size D50 of the M metal compound powder was 1.2 μm.

[0119] Next, the aforementioned lithium nickel mixed powder and M metal compound powder were placed in the same bead mill apparatus (M metal compound powder mixing step S032). The lithium nickel mixed powder was pulverized to obtain a precursor for the positive electrode active material, and at the same time, the precursor for the positive electrode active material and the M metal compound powder were pulverized while being mixed with the M metal compound powder (precursor and M metal compound pulverization step S033). As a result, the average particle size D50 of the mixed powder of the precursor for the positive electrode active material and the M metal compound powder became 0.3 μm. Subsequently, the mixed powder of the precursor for the positive electrode active material and the M metal compound powder was granulated using a spray dryer to obtain granulated powder (granulation step S034).

[0120] Next, to compensate for the insufficient amount of lithium in the granulated powder to meet the requirements for a positive electrode active material for lithium-ion secondary batteries, lithium carbonate powder was prepared separately. The amount of lithium was weighed so that it contained 0.77 moles of lithium for every 1.00 mole of the 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 positive electrode active material to be manufactured for lithium-ion secondary batteries. The granulated powder and the weighed lithium carbonate powder were then put into a V-type mixer to obtain lithium-containing compound-added granulated powder (second 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 heat-treated at 830°C for 10 hours to produce a positive electrode active material for lithium-ion secondary batteries.

[0122] Then, the residual Li content, unreacted Li percentage, specific surface area, and oil absorption of the lithium-ion secondary battery positive electrode active material obtained as described above were measured, and the R value was calculated from the XRD measurement. As a result, the residual Li content was 0.3 mass% for lithium hydroxide and 0.3 mass% for lithium carbonate. The unreacted Li percentage was 2%. All of these results are 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. Both the oil absorption and specific surface area are within the range in which good positive electrode production can be expected. The R value was 0.45. The low R value suggests that the amount of nickel ions mixed into the lithium sites is small, and it was confirmed that good crystallinity was achieved.

[0123] (Fabrication of the 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 the positive electrode material. First, a lithium-ion secondary battery positive electrode active material, a carbon-based conductive material, and a binder pre-dissolved in N-methyl-2-pyrrolidone (NMP) were mixed in a mass ratio of 92.5:5:2.5. Then, the uniformly mixed positive electrode slurry was applied to a 15 μm thick aluminum foil positive electrode current collector at a rate of 13 mg / cm². 2 The mixture was applied in this manner. Next, the positive electrode slurry applied to the positive electrode current collector was heat-treated at 120°C to remove the solvent and form a positive electrode slurry layer. After that, the positive electrode slurry layer was pressure-molded using a hot press and punched out into a circular shape with a diameter of 15 mm to form the positive electrode.

[0124] (Initial capacity, charge / discharge cycle characteristics (capacity retention rate)) Next, a lithium-ion secondary battery was fabricated using the prepared positive electrode, negative electrode, and separator. For the negative electrode, metallic lithium punched into a circular shape with a diameter of 16 mm was used. For the separator, a porous polypropylene separator with a thickness of 30 μm was used. The lithium-ion secondary battery was assembled by placing the positive electrode and negative electrode opposite each other in a non-aqueous electrolyte with the separator in between. As the non-aqueous electrolyte, a solution was used in which lithium hexafluorophosphate (LiPF6) was dissolved at a concentration of 1.0 mol / L in a solvent prepared by mixing ethylene carbonate and dimethyl carbonate in a volume ratio of 3:7.

[0125] The fabricated lithium-ion secondary battery was charged at 25°C with a constant current / voltage of 38 A / kg (based on the mass of the positive electrode mixture) and an upper potential limit of 4.3 V. Then, it was discharged to a lower potential limit of 2.5 V with a constant current of 40 A / kg (based on the mass of the positive electrode mixture), and the charge and discharge capacities were measured. Subsequently, it was charged again with a constant current / voltage of 190 A / kg (based on the mass of the positive electrode mixture) and an upper potential limit of 4.3 V. This cycle of charging and discharging to a lower potential limit of 2.5 V with a constant current of 190 A / kg (based on the mass of the positive electrode mixture) was repeated for a total of 30 cycles, and the discharge capacity after 30 cycles was measured. The capacity retention rate was calculated as the fraction of the discharge capacity after 30 cycles relative to the initial capacity. The Coulomb efficiency, expressed as discharge capacity / charge capacity, was also determined. As a result, the charge capacity was 219 Ah / kg, the discharge capacity was 186 Ah / kg, the Coulomb efficiency was 85%, and the capacity retention rate was 89%. Coulomb efficiency is a battery characteristic that indicates the percentage of Li ions that were released during the initial charge and were able to return to the positive electrode material through discharge. A higher value indicates better performance. Furthermore, as a lithium-ion secondary battery, it exhibited the expected capacity and capacity retention rate of 186 Ah / kg and 89% capacity retention rate with a nickel ratio of 85%, demonstrating good capacity retention.

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

[0127] The following are additional notes regarding preferred embodiments of this disclosure. 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 comprises 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 lithify at least a portion of it to obtain a lithium nickel mixed powder, and a grinding step of grinding the lithium nickel mixed powder, wherein the oxidation step, the mixing step, the lithiation step, and the grinding step are carried out continuously or intermittently to obtain a precursor containing lithium nickel oxide.

[0128] In this embodiment, the method for producing a precursor of positive electrode active material for lithium-ion secondary batteries uses metallic nickel powder with low GHG emissions as the nickel source, and oxidizes this metallic nickel powder so as not to sinter. Then, the oxidized metallic nickel powder is mixed with a lithium-containing compound and heat-treated to lithify it, causing cracks to form within the powder particles. Because it contains such lithium nickel oxide, it can be pulverized relatively easily. The precursor may be obtained by performing the oxidation step, the first lithium mixing step, the lithification step, and the pulverization step simultaneously and consecutively, or the precursor may be obtained by performing each manufacturing step at different times and in different locations, with flexibility in the execution of each step. In this embodiment, the oxidation step may be replaced with a preparation step of preparing pre-oxidized metallic nickel powder. That is, in the example above, oxidized metallic nickel powder is obtained via the oxidation step, but pre-oxidized metallic nickel powder may be purchased and used.

[0129] In one embodiment of this disclosure, the oxidation step is preferably an oxidation step in which metallic nickel powder is oxidized while suppressing sintering by moving it. Specifically, this can be carried out using a rotary furnace or a rolling bed furnace. On the other hand, the lithiumization step is preferably carried out using a stationary furnace.

[0130] A method for producing a positive electrode active material for a lithium-ion secondary battery according to one aspect of the present disclosure is characterized by comprising a calcination step in which a precursor produced by the method for producing a precursor of a positive electrode active material for a lithium-ion secondary battery is mixed with at least one of a lithium-containing compound and a compound containing a metal element M other than lithium and nickel to form a mixed powder, and then calcining the mixed powder at 700°C to 900°C to obtain a positive electrode active material.

[0131] In one embodiment of the present disclosure, it is preferable to have a grinding step of grinding the mixed powder and a granulation step of subsequently granulating the ground mixed powder to form granulated powder, and to perform the calcination step on the granulated powder.

[0132] Furthermore, in one embodiment of this disclosure, the positive electrode active material for the lithium-ion secondary battery is preferably represented by the following compositional formula (1). Li 1+a Ni b M (1-b) O 2+α ...(1) (However, in formula (1) above, M is a metallic element other than Li and Ni, and a, b, and α are numbers that satisfy -0.1 ≤ a ≤ 0.2, 0.5 ≤ b ≤ 1.0, and -0.2 ≤ α ≤ 0.2.) [Explanation of Symbols]

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

Claims

1. A first lithium mixing step involves mixing oxidized metallic nickel powder with lithium-containing compound powder to obtain a first mixed powder, A lithiation step is performed by heat-treating the first mixed powder to obtain a lithium nickel mixed powder containing lithium nickel oxide, The process includes a lithium nickel mixed powder grinding step for grinding the aforementioned lithium nickel mixed powder, A method for producing a precursor of a positive electrode active material for a lithium-ion secondary battery, characterized in that, in the first lithium mixing step, a lithium-containing compound powder containing an amount of lithium of 50% by mass or less relative to the amount of lithium required for the positive electrode active material to be produced.

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

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

4. The method for producing a precursor of a positive electrode active material for a lithium-ion secondary battery according to claim 1, characterized in that the lithiumization step is carried out using a static furnace.

5. A method for producing a positive electrode active material for a lithium-ion secondary battery, characterized by comprising a calcination step of mixing a precursor produced by the method for producing a positive electrode active material for a lithium-ion secondary battery described in 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-calcination mixed powder, and calcining the pre-calcination mixed powder to obtain a positive electrode active material.

6. A precursor produced by the method for producing a precursor of a lithium-ion secondary battery positive electrode active material according to claim 1 is mixed with an M metal compound containing a metal element M other than lithium and nickel, and the mixed powder of the precursor and the M metal compound is pulverized in a precursor and M metal compound pulverization step. A granulation step in which the crushed precursor and the mixed powder of the M metal compound are granulated to form a granulated powder, A second lithium mixing step involves adding a lithium-containing compound to the granulated powder to obtain lithium-containing compound-added granulated powder, so that the amount of lithium required for the positive electrode active material to be manufactured for lithium-ion secondary batteries. A method for producing a positive electrode active material for a lithium-ion secondary battery, characterized by performing a calcination step of calcining the lithium-containing compound-added granulated powder.

7. The method for producing a positive electrode active material for a lithium-ion secondary battery according to claim 5 or 6, characterized in that the positive electrode active material for a lithium-ion secondary battery is represented by the following compositional formula (1). Li １＋ａ Ni ｂ M (1-b) O ２＋α ・・・(1) (However, in formula (1) above, M is a metallic element other than Li and Ni, and a, b, and α are numbers that satisfy -0.1 ≤ a ≤ 0.2, 0.5 ≤ b ≤ 1.0, and -0.2 ≤ α ≤ 0.2.)

8. The method for producing a positive electrode active material for a lithium-ion secondary battery according to claim 5 or 6, characterized in that 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) [However, in equation (2), M1 represents at least one element selected from Al and Mn, X represents one or more metallic elements other than Li, Ni, Co, Al, and Mn, and the coefficients a, b, c, d, e, and α are numbers that satisfy -0.1 ≤ a ≤ 0.2, 0.5 ≤ b ≤ 1.0, 0 ≤ c ≤ 0.20, 0 ≤ d ≤ 0.30, 0 ≤ e ≤ 0.1, b + c + d + e = 1, and -0.2 < α < 0.2, respectively.]

Images