Method for producing positive electrode active material

Abstract

This method for producing a positive electrode active material comprises: preparing a first mixture by mixing a metal nickel powder and a first compound powder that contains lithium; preparing a first baked product by baking the first mixture; preparing a second mixture by mixing the first baked product, the first compound powder, and a second compound powder that contains a metal element M other than nickel and lithium; and preparing a second baked product by baking the second mixture.

Description

Method for manufacturing positive electrode active material

[0001] This disclosure relates to a method for producing a positive electrode active material.

[0002] Non-patent document 1 describes a method for producing single particles of positive electrode active material by mixing metallic nickel powder, lithium salt, and transition metal salt, calcining the mixture, then performing a final calcination, and crushing the calcined material.

[0003] International Publication No. 2022 / 209988, JP 2023-521317

[0004] Matthew DL Garayt et. al., “Single Crystal Li1+x[Ni0.6Mn0.4]1-xO2 Made by All-Dry Synthesis”, Journal of The Electrochemical Society, Vol 170, No. 6 (2023), 060529

[0005] As a result of diligent research into the conventional methods for producing positive electrode active materials described above, the inventors have discovered a novel manufacturing method that can improve the performance of energy storage devices using positive electrode active materials.

[0006] This disclosure is made in light of these circumstances, and one of its purposes is to provide technology for improving the performance of energy storage devices.

[0007] One aspect of the present disclosure is a method for producing a positive electrode active material. This method includes mixing metallic nickel powder and a first compound powder containing lithium to produce a first mixture, calcining the first mixture to produce a first calcined product, mixing the first calcined product with the first compound powder and a second compound powder containing a metallic element M other than nickel and lithium to produce a second mixture, and calcining the second mixture to produce a second calcined product.

[0008] Any combination of the above components, as well as any conversion of the expressions of this disclosure between methods, apparatus, systems, etc., are also valid forms of this disclosure.

[0009] According to this disclosure, it is possible to improve the performance of energy storage devices.

[0010] This is a process diagram of the method for producing the positive electrode active material according to the embodiment. This diagram shows the production conditions, particle size distribution, and cation mixing amount of the positive electrode active material in each example and comparative example. Figure 3(A) is an SEM image of the positive electrode active material according to Example 1. Figure 3(B) is an SEM image of the positive electrode active material according to Example 2. Figure 3(C) is an SEM image of the positive electrode active material according to Comparative Example 1. Figure 3(D) is an SEM image of the positive electrode active material according to Comparative Example 2. Figure 3(E) is an SEM image of the positive electrode active material according to Comparative Example 3.

[0011] The present disclosure will be described below with reference to the drawings, based on preferred embodiments. The embodiments are illustrative and not limiting, and not all features or combinations thereof described in the embodiments are necessarily essential to the present disclosure. The same or equivalent components, members, and processes shown in each drawing are denoted by the same reference numerals, and redundant descriptions are omitted where appropriate. The scale and shape of each part shown in each drawing are set for convenience to facilitate explanation and are not to be interpreted restrictively unless otherwise specified. Furthermore, where terms such as "first," "second," etc. are used in this specification or claims, unless otherwise specified, these terms do not indicate any order or importance, but are used to distinguish one configuration from another. In addition, some components that are not important for explaining the embodiments are omitted in each drawing.

[0012] First, a power storage device using a positive electrode active material manufactured by the method for manufacturing positive electrode active material according to this embodiment will be described. The power storage device is a rechargeable non-aqueous electrolyte secondary battery, such as a lithium-ion battery. In this embodiment, a positive electrode active material for a lithium-ion battery is used as an example, but the positive electrode active material can be used in other known devices as appropriate. The power storage device comprises an electrode group and an outer casing. The electrode group is, for example, cylindrical and has a wound structure in which a strip-shaped positive electrode plate and a strip-shaped negative electrode plate are stacked with a strip-shaped separator in between and wound in a spiral shape. The separator is, for example, made of polypropylene, polyethylene, or the like, a microporous film that has ion permeability and insulating properties. Leads are attached to the positive electrode plate and the negative electrode plate.

[0013] The electrode group is housed in an outer container along with the electrolyte. The outer container is a bottomed cylindrical metal container. A sealing body is fitted into the opening of the outer container. This seals the electrode group and electrolyte inside the outer container. The leads of the positive electrode plate are electrically connected to the sealing body. Therefore, the sealing body constitutes the positive electrode terminal. The leads of the negative electrode plate are electrically connected to the outer container. Therefore, the outer container constitutes the negative electrode terminal. The structure of the energy storage device can be modified as appropriate. The positive electrode plate and the negative electrode plate each comprise a current collector and an electrode mixture layer. The current collector is made of a strip of metal foil. In the case of a typical lithium-ion secondary battery, the current collector is made of aluminum foil or the like for the positive electrode, and copper foil or the like for the negative electrode. The electrode mixture layer is provided on top of the current collector.

[0014] The electrode mixture layer contains an electrode mixture. An example electrode mixture contains an electrode active material, a conductive material, and a binder. In the case of a typical lithium-ion secondary battery, examples of positive electrode active materials include lithium nickel cobalt manganese composite oxide (NCM), lithium nickel cobalt aluminum composite oxide (NCA), and lithium nickel cobalt manganese aluminum composite oxide (NCMA). Examples of negative electrode active materials include graphite. Examples of conductive materials include carbon black (CB), acetylene black (AB), Ketjenblack, carbon nanotubes (CNT), and graphite. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluororubber.

[0015] Next, a method for producing a positive electrode active material will be described. Figure 1 is a process diagram of a method for producing a positive electrode active material according to an embodiment. In the method for producing a positive electrode active material according to this embodiment, first, in the first mixing step S101, metallic nickel powder and a first compound powder containing lithium element are mixed to produce a first mixture. The mixing of metallic nickel powder and the first compound powder can be carried out using a known mixer such as a rocking mill.

[0016] The mixing ratio of metallic nickel powder and the first compound powder may be adjusted so that the ratio of moles of lithium element to the total number of moles of all metal elements Me other than lithium element (hereinafter, this ratio will be referred to as the Li / Me ratio) is 1.00 or more and 1.10 or less. In the first mixing step S101, theoretically, the only metal element Me other than lithium element is nickel element.

[0017] As examples of metallic nickel powder, those produced by the carbonyl method and the water atomization method can be used. The metallic nickel powder may have a volume-based median diameter D50 of 0.2 μm or more and 20 μm or less. This makes it easier to adjust the particle size of the final positive electrode active material to a size suitable for use in energy storage devices. In this disclosure, the median diameter D50 refers to the particle size at which the cumulative frequency of the smallest particle size accounts for 50% in the volume-based particle size distribution. The particle size distribution can be measured using a laser diffraction particle size distribution analyzer (for example, the MT3000II manufactured by Microtrac-Bell Corporation) with water as the dispersion medium.

[0018] Examples of the first compound powder containing lithium element include lithium hydroxide, lithium hydroxide monohydrate, and lithium carbonate powders. The first compound powder has a volume-based median diameter D50 of 0.01 μm to 100 μm. This makes it easier to adjust the particle size of the final positive electrode active material to a size suitable for use in energy storage devices.

[0019] Next, in the first firing step S102, the first mixture is fired. The firing in the first firing step S102 corresponds to pre-firing. This produces the first fired product. A known electric furnace or gas furnace can be used to fire the first mixture. In firing the first mixture, the first mixture may be heated to a temperature of 700°C to 930°C. This makes it possible to obtain a positive electrode active material suitable for use in energy storage devices. The above temperature is, as an example, the maximum temperature in the first firing step S102. The firing time is, for example, 1 hour to 5 hours.

[0020] The obtained first calcined product is crushed in the first crushing step S103. This produces the first calcined product powder. The crushing of the first calcined product can be carried out using known crushing machines such as ball mills and jet mills. As an example, the first calcined product powder has a particle size of 3 μm to 5 μm LiNiO ２ It contains a single particle.

[0021] Next, in the second mixing step S104, the first calcined powder, the first compound powder, and the second compound powder containing metal elements M other than nickel and lithium are mixed to produce the second mixture. The same type of mixer used in the first mixing step S101 can be used to mix each powder. Although the first compound powder is also mixed in the first mixing step S101, it is necessary to mix it again in the second mixing step S104 in order to obtain single particles of positive electrode active material suitable for use in energy storage devices.

[0022] The mixing ratio of the first calcined powder, the first compound powder, and the second compound powder may be adjusted so that the Li / Me ratio is 1.00 or more and 1.10 or less. In the second mixing step S104, the metal element Me other than lithium is theoretically nickel and the metal element M.

[0023] The metal element M may be a transition metal, and may also be cobalt (Co), manganese (Mn), or aluminum (Al). When the positive electrode active material is lithium nickel cobalt manganese composite oxide (NCM), the second compound powder contains cobalt and manganese as metal element M. When the positive electrode active material is lithium nickel cobalt aluminum composite oxide (NCA), the second compound powder contains cobalt and aluminum as metal element M. When the positive electrode active material is lithium nickel cobalt manganese aluminum composite oxide (NCMA), the second compound powder contains cobalt, manganese, and aluminum as metal element M. Examples of the second compound powder include carbonate, hydroxide, and oxide powders of metal element M. The second compound may also be a pure metal metal element M. The second compound powder has a volume-based median diameter D50 of 0.01 μm or more and 20 μm or less. This makes it easier to adjust the particle size of the final positive electrode active material to a size suitable for use in energy storage devices.

[0024] If there are two or more types of metal element M, the second compound powder may be a separate powder for each type of metal element M. For example, if metal element M is cobalt and manganese, the second compound powder may be a powder of the cobalt compound and a powder of the manganese compound.

[0025] Next, in the second firing step S105, the second mixture is fired. The firing in the second firing step S105 corresponds to the main firing. This produces the second fired product. For firing the second mixture, an electric furnace or gas furnace similar to the one used in the first firing step S102 can be used. In firing the second mixture, the second mixture may be heated to a temperature of 700°C to 870°C. This makes it possible to obtain a positive electrode active material suitable for use in energy storage devices. The above temperature is, as an example, the maximum temperature in the second firing step S105. The firing time is, for example, 3 hours to 15 hours.

[0026] The obtained second fired product is crushed in the second crushing step S106. Thereby, single particles of the positive electrode active material are obtained. For crushing the second fired product, the same crusher as that used in the first crushing step S103 can be used. As an example of the positive electrode active material, Li １＋α Ni ｘ M （１－ｘ） O ２＋α single particles are included.

[0027] The above-mentioned "single particle" in the present disclosure means a particle formed of one primary particle, rather than a secondary particle formed by aggregation of a large number of, for example, 1000 or more primary particles. That is, there is substantially no particle interface of the primary particle inside the particle. Note that a particle formed by aggregation of 10 or fewer primary particles approximates a single particle shape and can be substantially regarded as a single particle. The single particle may be a single crystal particle in which substantially no grain boundary exists inside the particle, or may be a polycrystalline particle in which several grain boundaries exist inside the particle. Further, the median diameter D50 on a volume basis of the single particle is 0.5 μm or more and 5.0 μm or less, and the crystallite size of the single particle is 370 Å or more and 1500 Å or less.

[0028] The positive electrode active material of the present embodiment may contain a metal element other than the nickel element, the lithium element, and the metal element M. Further, in the positive electrode active material, the molar number of the nickel element may be 50 mol% or more with respect to the total molar number of all metal elements Me excluding the lithium element. For example, in the positive electrode active material, the ratio of the nickel element to the total molar number of the nickel element and the metal element M is 50 mol% or more. Further, the manufacturing method according to the present embodiment can be applied to the manufacture of a positive electrode active material in which the ratio of each element in Li １＋α Ni ｘ M （１－ｘ） O ２＋α is arbitrary.

[0029] As described above, in the method for producing a positive electrode active material according to this embodiment, first, in the first step, metallic nickel powder and first compound powder are mixed and calcined to produce a first calcined powder. Then, in the second step, the first calcined powder, first compound powder, and second compound powder are mixed and calcined to produce a second compound powder. As a result, compared to the case in which metallic nickel powder, first compound powder, and second compound powder are mixed and calcined simultaneously, the amount of first compound powder added, or in other words, the amount of lithium added, can be reduced in both the first mixing step S101 and the second mixing step S104. Therefore, the Li / Me ratio during powder mixing can be reduced.

[0030] By reducing the Li / Me ratio, Li loss that occurs during the firing of the mixture can be suppressed. Furthermore, a lower Li / Me ratio suppresses particle fusion and sintering during firing, making the fired material easier to disintegrate. This allows for a relaxation of the disintegration conditions required to obtain single particles of positive electrode active material of a size suitable for use in energy storage devices, for example, a particle size of 3 μm to 5 μm. This suppresses crystal cracking in the single particles of positive electrode active material, thereby suppressing an increase in the specific surface area of ​​the positive electrode active material. As a result, the durability of the positive electrode active material can be improved, thus enhancing the performance of energy storage devices. Additionally, a lower Li / Me ratio allows for an increase in the proportion of nickel elements in the mixture. This promotes crystal growth during firing of the mixture.

[0031] Furthermore, in conventional manufacturing methods in which metallic nickel powder, first compound powder, and second compound powder are simultaneously mixed and fired, the mixture was heated at a high temperature of 925°C to 950°C for about 12 to 20 hours in the main firing process in order to obtain single particles of positive electrode active material with a size of 3 μm to 5 μm. In contrast, in the manufacturing method according to this embodiment, which involves a first stage of mixing and firing metallic nickel powder and first compound powder, and a second stage of mixing and firing first fired powder, first compound powder, and second compound powder, the heating temperature in the second firing step S105, which is the main firing process, can be lowered to 700 to 850°C.

[0032] As described in Non-Patent Document 1, when the heating temperature in the main firing is high, above 900°C, cation mixing is more likely to occur during firing. It is known that positive electrode active materials with a large amount of cation mixing are prone to causing deterioration of energy storage devices. Therefore, by lowering the heating temperature in the second firing step S105 using the manufacturing method according to this embodiment, the occurrence of cation mixing can be suppressed, and the performance of the energy storage device can be improved.

[0033] The embodiments of this disclosure have been described in detail above. The embodiments described above are merely examples of how to implement this disclosure. The content of the embodiments does not limit the technical scope of this disclosure, and many design changes, such as changes, additions, and deletions of components, are possible as long as they do not depart from the spirit of the invention as defined in the claims. A new embodiment with design changes will have the combined effects of both the embodiment and the variation. In the embodiments described above, the content in which such design changes are possible is emphasized with notations such as "of this embodiment" or "in this embodiment," but design changes are also permitted even if there are no such notations. Furthermore, any combination of components included in each embodiment is also valid as an embodiment of this disclosure. The hatching applied to the cross-section in the drawings does not limit the material of the object to which the hatching is applied.

[0034] Embodiments may be specified by the following items: [Item 1] A method for producing a positive electrode active material, comprising: mixing metallic nickel powder and a first compound powder containing lithium element to produce a first mixture; calcining the first mixture to produce a first calcined product; mixing the first calcined product, the first compound powder, and a second compound powder containing a metallic element M other than nickel and lithium element to produce a second mixture; and calcining the second mixture to produce a second calcined product. [Item 2] A method for producing a positive electrode active material according to Item 1, comprising heating the first mixture at a temperature of 700°C to 930°C during the calcination of the first mixture. [Item 3] A method for producing a positive electrode active material according to Item 1 or Item 2, comprising heating the second mixture at a temperature of 700°C to 870°C during the calcination of the second mixture. [Item 4] A method for producing a positive electrode active material according to any of Items 1 to 3, wherein the positive electrode active material has a molar amount of nickel element relative to the total number of moles of all metal elements excluding lithium element of 50 mol% or more. [Item 5] A method for producing a positive electrode active material according to any of Items 1 to 4, wherein the metallic nickel powder has a volume-based median diameter D50 of 0.2 μm or more and 10.0 μm or less.

[0035] The following describes embodiments of the present invention, but these embodiments are merely illustrative examples for suitably illustrating the present invention and do not limit the present invention in any way.

[0036] (Example 1) As raw materials for the positive electrode active material, metallic nickel powder (manufactured by Vale), lithium hydroxide (manufactured by Fujifilm Wako Pure Chemical Industries), and cobalt carbonate (manufactured by Kojunsei Kagaku Co., Ltd.) were prepared. The lithium hydroxide and cobalt carbonate were finely powdered in advance using a ball mill.

[0037] Nickel metal powder and lithium hydroxide were put into a powder processing apparatus (rocking mill: manufactured by Seiwa Kogyo Co., Ltd.) to conduct a first mixing process, and a first mixture was produced. The input amount of each powder was adjusted so that the Li / Me ratio would be 1.00. The obtained first mixture was put into an electric furnace (FT-1200G-300: manufactured by Fulltech Co., Ltd.) and calcined at 930 °C for 3 hours to produce a first calcined product. The obtained first calcined product was put into a ball mill (planetary ball mill premium line PL-7: manufactured by Fritsch Co., Ltd.), and ２ using ZrO balls with a diameter of 5 mm, it was crushed under the conditions of 150 rpm for 1 hour. Thereby, first calcined product powder was obtained.

[0038] The obtained first calcined product powder, lithium hydroxide, and cobalt carbonate were put into a powder processing apparatus (rocking mill: manufactured by Seiwa Kogyo Co., Ltd.) to conduct a second mixing process, and a second mixture was produced. The input amount of each powder was adjusted so that the Li / Me ratio would be 1.00. The obtained second mixture was put into an electric furnace (FT-1200G-300: manufactured by Fulltech Co., Ltd.) and sintered at 800 °C for 10 hours to produce a second calcined product. The obtained second calcined product was put into a ball mill (planetary ball mill premium line PL-7: manufactured by Fritsch Co., Ltd.), and ２ using ZrO balls with a diameter of 5 mm, it was crushed under the conditions of 150 rpm for 1 hour. Thereby, particles of a lithium transition metal composite oxide as a positive electrode active material were obtained.

[0039] Regarding the obtained particles of the positive electrode active material, the volume-based particle size distribution was measured using a laser diffraction type particle size distribution measuring apparatus (Partica LA-960V2: manufactured by Horiba, Ltd.). Then, from the measurement results, the median diameter D50 of the positive electrode active material, the diameter D10 which is the diameter at which the cumulative frequency in the particle size distribution becomes 10% from the smaller particle size side, and the diameter D90 which is the diameter at which the cumulative frequency in the particle size distribution becomes 90% from the smaller particle size side were calculated. Also, regarding the obtained particles of the positive electrode active material, XRD measurement was carried out using an XRD diffractometer (MiniFlex: manufactured by Rigaku Corporation). Then, Rietveld analysis of the obtained XRD diffraction pattern was performed to calculate the cation mixing amount.

[0040] (Example 2) A positive electrode active material was produced in the same manner as in Example 1, except that the temperature during pre-firing was set to 750°C. Measurement of particle size distribution and XRD measurement were carried out, and D10, D50, D90, and the cation mixing amount were calculated.

[0041] (Comparative Example 1) A positive electrode active material was produced in the same manner as in Example 1, except that metallic nickel powder, lithium hydroxide, and cobalt carbonate were simultaneously mixed and firing was not carried out, but firing was carried out at 930°C for 3 hours. Measurement of particle size distribution and XRD measurement were carried out, and D10, D50, D90, and the cation mixing amount were calculated.

[0042] (Comparative Example 2) A positive electrode active material was produced in the same manner as in Example 1, except that metallic nickel powder, lithium hydroxide, and cobalt carbonate were simultaneously mixed and pre-firing was carried out at 670°C for 5 hours, and then firing was carried out at 930°C for 3 hours. Measurement of particle size distribution and XRD measurement were carried out, and D10, D50, D90, and the cation mixing amount were calculated.

[0043] (Comparative Example 3) Metallic nickel powder, lithium hydroxide, and cobalt carbonate were adjusted so that the input amount of each powder had an Li / Me ratio of 1.20 and were simultaneously mixed. After pre-firing was carried out at 670°C for 5 hours, firing was carried out at 930°C for 12 hours. A positive electrode active material was produced in the same manner as in Example 1, except for this point. Measurement of particle size distribution and XRD measurement were carried out, and D10, D50, D90, and the cation mixing amount were calculated.

[0044] Figure 2 shows the manufacturing conditions, particle size distribution, and cation mixing amount of the positive electrode active material for each example and comparative example. As shown in Figure 2, the particles of the positive electrode active material in Examples 1 and 2 were confirmed to have a particle size of 3 μm to 5 μm, based on their D10, D50, and D90 values. On the other hand, the particles of the positive electrode active material in Comparative Examples 1 and 2 were mostly small particles with a particle size of less than 3 μm. In particular, the D50 values ​​of 2.1 and 1.5 indicate insufficient particle growth. Furthermore, the particles of the positive electrode active material in Comparative Example 3 were mostly large particles with a particle size of more than 5 μm. In particular, the D90 value of 12.6 is very large, indicating low disintegration ability. In addition, the cation mixing amount of the positive electrode active material in Examples 1 and 2 was smaller than that of the positive electrode active material in Comparative Examples 1 to 3. The cation mixing amount of Examples 1 and 2 was less than 0.05, which was a very good result.

[0045] Furthermore, the particles of the positive electrode active material for each example and comparative example were imaged using a scanning electron microscope (SEM). Figure 3(A) is an SEM image of the positive electrode active material for Example 1. Figure 3(B) is an SEM image of the positive electrode active material for Example 2. Figure 3(C) is an SEM image of the positive electrode active material for Comparative Example 1. Figure 3(D) is an SEM image of the positive electrode active material for Comparative Example 2. Figure 3(E) is an SEM image of the positive electrode active material for Comparative Example 3.

[0046] SEM images confirmed that the particles of the positive electrode active material in each example were mostly single particles composed of one primary particle. Furthermore, the crystallite sizes of the single particles of the positive electrode active material in each example were 452 Å, 464 Å, 310 Å, 341 Å, and 521 Å, respectively, for Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3. The crystal structure of these single particles was a layered rock salt structure belonging to space group R-3m. On the other hand, the particles of the positive electrode active material in each comparative example exhibited defects such as being too small or too large in particle size. From the above, it was confirmed that the method for manufacturing the positive electrode active material according to this embodiment can produce single particles of positive electrode active material of a size suitable for use in energy storage devices.

[0047] This disclosure can be used in a method for producing a positive electrode active material.

[0048] S101 First mixing step, S102 First firing step, S103 First crushing step, S104 Second mixing step, S105 Second firing step, S106 Second crushing step.

Claims

1. A method for producing a positive electrode active material, comprising: mixing metallic nickel powder and a first compound powder containing lithium to produce a first mixture; calcining the first mixture to produce a first calcined product; mixing the first calcined product with the first compound powder and a second compound powder containing a metallic element M other than nickel and lithium to produce a second mixture; and calcining the second mixture to produce a second calcined product.

2. A method for producing a positive electrode active material according to claim 1, comprising heating the first mixture at a temperature of 700°C to 930°C during calcination of the first mixture.

3. A method for producing a positive electrode active material according to claim 1 or 2, comprising heating the second mixture at a temperature of 700°C to 870°C during calcination of the second mixture.

4. The method for producing a positive electrode active material according to claim 1 or 2, wherein the positive electrode active material has a molar amount of nickel element relative to the total number of moles of all metal elements excluding lithium element of 50 mol% or more.

5. The method for producing a positive electrode active material according to claim 1 or 2, wherein the metallic nickel powder has a volume-based median diameter D50 of 0.2 μm or more and 10.0 μm or less.

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