Positive electrode active material and method for manufacturing the same

Abstract

This invention provides an efficient method for producing a positive electrode active material consisting of primary particles having a predetermined particle size. [Solution] A method for producing a positive electrode active material to obtain a lithium transition metal composite oxide by heat-treating a lithium mixture containing precursor particles containing a transition metal compound including nickel and oxygen, and a lithium source, at a temperature T (°C) defined by the following formula (1). The precursor particles include precursor particles having voids in cross-section, and the median porosity of the precursor particles having voids, which is the ratio of the total area of ​​voids to the cross-sectional area of ​​the precursor particles, is 3 to 35%. The lithium transition metal composite oxide has a ratio of the number of moles of nickel to the total number of moles of metals other than lithium of 0.3 to 0.99, and an average particle size DSEM based on electron microscope observation is 1 to 7 μm. T = -289x + K(1) (where x is the ratio of moles of nickel to the total number of moles of metal in a transition metal compound containing nickel and oxygen, and K satisfies 1050 ≤ K ≤ 1150.)

Description

[Technical Field]

[0001] This disclosure relates to a positive electrode active material and a method for producing the same. [Background technology]

[0002] As a positive electrode active material for lithium secondary batteries, the use of single crystals or secondary particle positive electrode active materials composed of a small number of primary particles is being considered. For example, Patent Document 1 describes a method for producing a positive electrode active material by pulverizing porous oxide particles obtained by heat-treating a nickel metal precursor having pores inside and a lithium precursor. Patent Document 2 describes a method for producing lithium transition metal composite oxide particles having a hollow structure by calcining a lithium compound with transition metal composite hydroxide particles, which consist of secondary particles composed of a core made of polymer particles and an outer shell made of primary particles of a transition metal composite oxide, in an oxidizing atmosphere. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-36062 [Patent Document 2] Japanese Patent Publication No. 2016-31854 [Overview of the project] [Problems that the invention aims to solve]

[0004] One aspect of this disclosure aims to provide an efficient method for producing a positive electrode active material consisting of primary particles having a predetermined particle size. [Means for solving the problem]

[0005] The first embodiment is a method for producing a positive electrode active material, comprising: preparing precursor particles containing a transition metal compound including nickel and oxygen; and heat-treating a lithium mixture containing the precursor particles and a lithium source at a heat treatment temperature T (°C) defined by the following formula (1) to obtain a lithium transition metal composite oxide. The precursor particles include precursor particles having voids in cross-sectional view, and the median porosity of the void-containing precursor particles, which is the ratio of the total area of ​​voids to the cross-sectional area of ​​each precursor particle, is 3% or more and 35% or less. The lithium transition metal composite oxide has a composition in which the ratio of the number of moles of nickel to the total number of moles of metals other than lithium is 0.3 or more and 0.99 or less, and the average particle size D based on electron microscope observation is SEM The particle size is between 1 μm and 7 μm. T = -289x + K (1)

[0006] In equation (1), x is the ratio of the number of moles of nickel to the total number of moles of metal in the transition metal compound containing nickel and oxygen, and K satisfies 1050 ≤ K ≤ 1150.

[0007] The second embodiment is a positive electrode active material manufactured by the method for manufacturing a positive electrode active material of the first embodiment, wherein, in a cross-sectional view, the median porosity, which is the ratio of the total area of ​​voids to the cross-sectional area of ​​the positive electrode active material, is smaller than the median porosity of the precursor particles. [Effects of the Invention]

[0008] According to one aspect of this disclosure, an efficient method for producing a positive electrode active material consisting of primary particles having a predetermined particle size can be provided. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows an example of the relationship between the volume-average particle size D50 of precursor particles and the average particle size DSEM of lithium transition metal composite oxides based on electron microscopy observations. [Figure 2A] This figure shows an example of the relationship between the heat treatment temperature of precursor particles and the average particle size obtained by electron microscopy (DSEM). [Figure 2B] This figure shows an example of the relationship between the nickel ratio in the composition of precursor particles and the heat treatment temperature. [Figure 3A] This figure shows an example of a scanning electron microscope (SEM) image of a cross-section of a precursor particle in Example 1A. [Figure 3B] This figure shows an example of an SEM image of a cross-section of a lithium transition metal composite oxide in Example 1A. [Figure 4A] This figure shows an example of an SEM image of a cross-section of a precursor particle in Comparative Example 1A. [Figure 4B] This figure shows an example of an SEM image of a cross-section of a lithium transition metal composite oxide in Comparative Example 1A. [Modes for carrying out the invention]

[0010] In this specification, the content of each component in a composition means the total amount of multiple substances present in the composition, unless otherwise specified, if multiple substances corresponding to each component are present in the composition. Furthermore, the upper and lower limits of the numerical ranges described herein can be arbitrarily selected and combined from the numerical values ​​exemplified as numerical ranges. Embodiments of this disclosure will now be described in detail. However, the embodiments shown below are illustrative examples of positive electrode active materials and methods for producing them to embody the technical concept of this disclosure, and this disclosure is not limited to the positive electrode active materials and methods for producing them shown below.

[0011] Method for manufacturing positive electrode active material The method for producing a positive electrode active material includes a precursor particle preparation step of preparing precursor particles containing a transition metal compound including nickel and oxygen, and a synthesis step of heat-treating a lithium mixture containing the prepared precursor particles and a lithium source at a predetermined heat treatment temperature T (°C) to obtain a lithium transition metal composite oxide, and may further include other steps as needed. The prepared precursor particles may be a group of precursor particles containing multiple precursor particles. The group of precursor particles includes at least precursor particles having voids in a cross-sectional view. The precursor particles having voids may have a median porosity of 3% or more and 35% or less, which is the ratio of the total area of ​​voids to the cross-sectional area of ​​each precursor particle in a cross-sectional view. The synthesized lithium transition metal composite oxide may have a composition in which the ratio of the number of moles of nickel to the total number of moles of metals other than lithium is 0.3 or more and 0.99 or less, and the average particle size D based on electron microscope observation. SEM The particle size may be between 1 μm and 7 μm. The heat treatment temperature T (°C) in the synthesis process is defined by the following formula (1). In formula (1), x is the ratio of the number of moles of nickel to the total number of moles of metal contained in the transition metal compound containing nickel and oxygen. K satisfies 1050 ≤ K ≤ 1150. T = -289x + K (1)

[0012] A mixture of precursor particles having internal voids and a lithium source is heat-treated at a heat treatment temperature corresponding to the composition of the transition metal compounds contained in the precursor particles, thereby obtaining a predetermined particle size, for example, the average particle size D based on electron microscopy observation. SEM A positive electrode active material containing secondary particles made of primary particles of lithium transition metal composite oxide having a particle size of 1 μm to 7 μm can be efficiently manufactured. This is thought to be because, for example, a lithium source penetrates into the voids of the precursor particles, and lithium is supplied from both inside and outside the precursor particles, thereby promoting the crystal growth of the primary particles containing the lithium transition metal composite oxide, and efficiently forming primary particles with a predetermined particle size. Here, the average particle size D based on electron microscope observation is used. SEM This may correspond to the particle size of the primary particles constituting the positive electrode active material.

[0013] In a non-aqueous electrolyte secondary battery, the positive electrode active material is composed of secondary particles made up of primary particles containing lithium transition metal composite oxides, and the particle size of the primary particles (for example, the average particle size D based on electron microscope observation) is important. SEM When the particle size (for example, 1 μm or larger, preferably 1.8 μm or larger) is of a certain size, durability, cycle characteristics in charge and discharge tend to improve. However, as will be described later, when a lithium mixture containing precursor particles containing a transition metal compound with a large ratio of moles of nickel to the total number of moles of metal contained (for example, 0.6 or larger) and a lithium compound is heat-treated to produce a positive electrode active material containing secondary particles made of primary particles containing a lithium transition metal composite oxide, if the volume average particle diameter of the precursor particles increases, the particle diameter of the primary particles (for example, the average particle size D based on electron microscope observation) tends to improve. SEM The volume average particle diameter of the primary particles tends to decrease. However, as in the method for producing a positive electrode active material according to this disclosure, by using precursor particles having a predetermined void portion as precursor particles and heat-treating a lithium mixture at a predetermined heat treatment temperature, the particle diameter of the primary particles can be increased compared to the case where conventional precursor particles are used. Note that increasing the particle diameter of the primary particles means that the particle diameter of the primary particles increases under conditions in which the composition of the transition metal compound constituting the precursor particles, the volume average particle diameter of the precursor particles, and the heat treatment conditions (e.g., temperature, atmosphere such as oxygen concentration, flux material, etc.) are substantially the same.

[0014] The positive electrode active material produced by the method for producing positive electrode active material may contain a lithium transition metal composite oxide obtained in the synthesis step, or it may consist solely of a lithium transition metal composite oxide. Furthermore, the positive electrode active material produced by the method for producing positive electrode active material may be a positive electrode active material for a non-aqueous electrolyte secondary battery. The non-aqueous electrolyte may be a liquid electrolyte (electrolyte solution) or a solid electrolyte.

[0015] In the precursor particle preparation step, a group of precursor particles is prepared that includes precursor particles containing a transition metal compound (hereinafter also simply referred to as "transition metal compound") containing nickel and oxygen atoms, and having voids in cross-section. Precursor particles having voids in cross-section can also be called precursor particles having voids inside. The group of precursor particles prepared may consist only of precursor particles having voids in cross-section, or it may include precursor particles that do not have voids in cross-section in addition to precursor particles that have voids in cross-section. Here, precursor particles having voids in cross-section means that the cross-section of the observed precursor particle is composed of a region where the transition metal compound exists (hereinafter also referred to as the metal compound region) and a region where the transition metal compound does not exist (void region). The shape of the void in the cross-section of the precursor particle is not particularly limited and may be approximately circular, approximately elliptical, polygonal, or a combination thereof. In addition, there may be multiple voids in the cross-section of the precursor particle. The voids may be located near the center of the precursor particle relative to its outer edge, or they may be distributed uniformly or non-uniformly across the entire cross-section of the precursor particle. Furthermore, the voids may extend to the outer edge of the cross-section of the precursor particle. When observing the cross-section of the precursor particle, for example, using a scanning electron microscope, the metal compound portion and the voids may be identified as regions with different contrasts.

[0016] The median porosity (%) of the precursor particles having voids, which is the ratio of the total area of ​​voids to the cross-sectional area of ​​each precursor particle, may be, for example, 3% to 35%, preferably 4% or more, or 6% or more, or 30% or less, or 20% or less. When the median porosity (%) of the precursor particles is 3% or more, the crystal growth of primary particles containing lithium transition metal composite oxide is promoted, and primary particles having a predetermined particle size tend to be efficiently formed. Furthermore, when the median porosity (%) of the precursor particles is 35% or less, aggregation of precursor particles can be reduced, and defects in the particle structure of the lithium transition metal composite oxide after heat treatment tend to be less likely to occur. The median porosity is calculated using the porosity calculated for each of 10 to 20 (preferably 20) precursor particles having a predetermined amount of voids as the population.

[0017] The porosity of individual precursor particles is calculated as the ratio (%) of the total area of ​​voids to the cross-sectional area of ​​the precursor particle by image analysis of cross-sectional images obtained using a scanning electron microscope (SEM) of the precursor particles. Specifically, the porosity is calculated as follows: Precursor particles (e.g., 1g) are embedded in resin (e.g., 1g), and a sample that allows for cross-sectional observation is prepared by cross-section polishing or other methods. In the observation image obtained with a scanning electron microscope, the diameter of the cross-section approximated as a circle using image analysis software (e.g., Image-J) is the 50% particle size (D) in the volume-based cumulative particle size distribution of the precursor particles. 50Fifty precursor particles are arbitrarily selected that are within ±20% of the specified value. The porosity is calculated for each of the selected precursor particles, and 10 to 20 precursor particles with a porosity of 2% or more are selected as precursor particles having a predetermined void area and used to calculate the median porosity. In calculating the porosity of individual precursor particles, the cross-sectional area of ​​the precursor particle is calculated using image analysis software as the area surrounded by the outer edge of the observed precursor particle cross-section. If the void area extends to the outer edge of the precursor particle cross-section, the cross-sectional area of ​​the precursor particle is calculated based on a hypothetical outer edge calculated assuming that the void area does not exist. Specifically, the area of ​​the polygon surrounded by 20 partition points set at approximately equal intervals along the outer edge of the precursor particle is taken as the cross-sectional area of ​​the precursor particle. The total area of ​​the void area is calculated using image analysis software as the sum of the areas of each region identified as a void area. The specific method for calculating the total area of ​​the void area will be described later.

[0018] In a cross-sectional view, the precursor particles having voids may include precursor particles having a hollow structure. Here, the hollow structure means a structure in which a cavity of a predetermined size is formed inside the precursor particles. That the precursor particles have a hollow structure can be determined from the presence of a void of a predetermined size in addition to the metal compound part in the cross-section of the precursor particles. The group of precursor particles prepared in the precursor particle preparation step may include, in a cross-sectional view, precursor particles (precursor particles having a hollow structure) having at least one void (hereinafter also referred to as a "hollow part") having an area of, for example, 2% or more and 50% or less of the cross-sectional area of the precursor particles. Further, the group of precursor particles may include at least one precursor particle having a hollow structure. The precursor particles having a hollow structure may have a ratio of the area of the hollow part of the precursor particles to the cross-sectional area of the precursor particles of 3% or more, 4% or more, or 10% or more, and 40% or less, 35% or less, or 20% or less in a cross-sectional view. The hollow part in the precursor particles may be, for example, near the center of the precursor particles in a cross-section passing near the center of the precursor particles. Here, the vicinity of the center of the precursor particles may be a position within a range of 50% or less, preferably 30% or less of the radius obtained by approximating the precursor particles as a sphere from the geometric center or the center of gravity of the precursor particles.

[0019] The precursor particles have a 50% particle size D in the volume-based cumulative particle size distribution obtained by the laser scattering method. 50 may be, for example, 2 μm or more and 13 μm or less, preferably 4 μm or more or 10 μm or less. When the 50% particle size D, which is the average particle size of the precursor particles, is within the above range, there is a tendency to be able to manufacture a cathode active material having a predetermined primary particle size more efficiently. 50

[0020] The transition metal compound contained in the precursor particles contains nickel and oxygen atoms. The transition metal compound may be an oxide, hydroxide, or mixture thereof containing nickel, and may contain at least a nickel oxide. In addition to nickel, the transition metal compound may contain other metallic elements. Examples of other metals include cobalt (Co), manganese (Mn), aluminum (Al), titanium (Ti), niobium (Nb), zirconium (Zr), tungsten (W), etc., and may contain at least one selected from the group consisting of these, and may contain at least one selected from the group consisting of at least cobalt (Co), manganese (Mn), and aluminum (Al).

[0021] The transition metal compound may have a composition in which the ratio of the number of moles of nickel to the total number of moles of metal contained in the transition metal compound (hereinafter also referred to as the "nickel ratio") is, for example, 0.3 or more, and preferably 0.3 to 0.99. In one embodiment, the composition of the transition metal compound may have a ratio of the number of moles of nickel to the total number of moles of metal of 0.4 or more or 0.5 or more, and may be 0.8 or less or 0.7 or less. In another embodiment, the composition of the transition metal compound may have a ratio of the number of moles of nickel to the total number of moles of metal of 0.8 or more or 0.9 or more, and may be 0.99 or less, 0.98 or less, or 0.97 or less.

[0022] If the transition metal compound contains cobalt as a metal element other than nickel, the ratio of the number of moles of cobalt to the total number of moles of metal contained in the transition metal compound may be, for example, 0.001 or more and 0.50 or less, 0.01 or more or 0.02 or more, 0.2 or less, 0.1 or less or 0.05 or less. If the transition metal compound contains manganese as a metal element other than nickel, the ratio of the number of moles of manganese to the total number of moles of metal contained in the transition metal compound may be, for example, 0.001 or more and 0.50 or less, 0.005 or more, 0.01 or more or 0.03 or more, 0.4 or less, 0.1 or less or 0.02 or less. If the transition metal compound contains aluminum as a metal element other than nickel, the ratio of the number of moles of aluminum to the total number of moles of metal contained in the transition metal compound may be, for example, 0.001 or more and 0.05 or less, 0.01 or more or 0.03 or less. When the transition metal compound contains at least one of manganese and aluminum, the ratio of the total number of moles of manganese and aluminum to the total number of moles of metals other than lithium may be, for example, greater than 0 and 0.3 or less, and preferably 0.01 or more or 0.03 or less.

[0023] Precursor particles having voids in cross-section can be prepared by a coprecipitation method to obtain transition metal compounds. This method involves preparing a solution by dissolving raw material compounds (such as hydroxides and carbonate compounds), adjusting the temperature and pH, adding complexing agents, etc., to obtain a precursor precipitate having the desired composition, and then heat-treating these precursor precipitates as needed. For details on this method of obtaining transition metal compounds, see, for example, Japanese Patent Publication No. 2003-292322 and Japanese Patent Publication No. 2011-116580 (US Patent Application Publication No. 2012 / 270107).

[0024] The method for preparing precursor particles may include a crystallization step of contacting polymer particles with a nickel-containing metal source solution to obtain polymer particles to which a metal compound is attached, and a heat treatment step of heat-treating the polymer particles to which the metal compound is attached at a temperature of 270°C to 600°C to obtain precursor particles.

[0025] The nickel-containing metal source solution used in the crystallization process may further contain other metal ions in addition to nickel ions. Examples of other metal ions include cobalt ions, manganese ions, aluminum ions, titanium ions, niobium ions, zirconium ions, and tungsten, and may contain at least one selected from the group consisting of cobalt ions, manganese ions, and aluminum ions. The metal source solution may have a composition in which the ratio of moles of nickel ions to the total number of moles of metal ions is, for example, 0.3 or more and 0.99 or less. In one embodiment, the composition of the metal source solution may have a ratio of moles of nickel ions to the total number of moles of metal ions of 0.4 or more or 0.5 or more, and may be 0.8 or less and 0.7 or less. In another embodiment, the composition of the metal source solution may have a ratio of moles of nickel ions to the total number of moles of metal ions of 0.8 or more and 0.9 or more, and may be 0.99 or less and 0.98 or less.

[0026] The polymer particles may be composed of organic polymer compounds. Examples of polymer compounds constituting the polymer particles include poly(meth)acrylate and polystyrene, and mixtures thereof may also be used. The average particle size of the polymer particles may be, for example, 1 μm or more and 8 μm or less, or 2 μm or more or 7 μm or less. Here, the average particle size of the polymer particles is the volume-average particle size, and the 50% particle size D corresponds to the cumulative 50% from the smallest diameter side in the volume-based cumulative particle size distribution. 50 The volume-based cumulative particle size distribution is measured under wet conditions using a laser diffraction particle size distribution analyzer. When the average particle size of the polymer particles is within the above range, it tends to be possible to obtain a group of precursor particles having the desired porosity. This promotes the crystal growth of primary particles containing lithium transition metal composite oxides, allowing for the efficient formation of primary particles with a predetermined particle size, and also tends to reduce the likelihood of defects in the particle structure of the lithium transition metal composite oxide after calcination. In this specification, (meth)acrylate is a general term referring to acrylate, methacrylate, and mixtures thereof.

[0027] The surface of polymer particles may be hydrophilized. Hydrophilization of the polymer particle surface improves the dispersibility of the polymer particles and tends to facilitate the formation of a hydroxide layer on the polymer particle surface. Methods for hydrophilizing polymer particles include oxidation treatment, plasma treatment, etc., to impart hydrophilic functional groups to the polymer particle surface.

[0028] The ratio of the total number of moles of metal ions in the metal source solution that comes into contact with the polymer particles to the number of polymer particles is, for example, 1.0 × 10⁻⁶. -13 The above 1.0 × 10 -8 The following may be used, preferably 1.0 × 10 -12 or more, or 1.0 × 10 -9 The following is acceptable:

[0029] Contact between the metal source solution and polymer particles can be achieved, for example, by adding a metal source solution containing nickel ions and, if necessary, other metal ions, to a dispersion of polymer particles while maintaining its pH in the range of, for example, 7.5 to 13, preferably 11.5 to 13. The addition time of the metal source solution may be, for example, 1 to 24 hours, preferably 3 to 18 hours. The temperature in the crystallization process can be, for example, 40°C to 80°C. The atmosphere in the crystallization process may be a low-oxidizing atmosphere, and for example, the oxygen concentration may be maintained at 10% by volume or less. pH adjustment in the crystallization process can be achieved using acidic aqueous solutions such as sulfuric acid aqueous solution and nitric acid aqueous solution, or alkaline aqueous solutions such as sodium hydroxide aqueous solution and ammonia aqueous solution.

[0030] In the crystallization process, it is desirable to control the particle size of the polymer particles to which the metal compound is attached. Particle size can be controlled by adjusting the temperature, pH, and stirring speed of the reaction field. These conditions can be appropriately adjusted according to actual conditions such as the shape of the container housing the reaction field, the starting materials, and the rate at which the starting materials are introduced into the reaction field. Furthermore, particle size can be controlled by the maturation time and stirring speed after the start of metal compound precipitation on the polymer particles. These conditions can also be appropriately adjusted according to actual conditions, as the particle growth rate and shape differ depending on the shape of the reaction vessel. The particle size of the polymer particles to which the metal compound is attached may be, for example, 2 μm to 13 μm, preferably 4 μm to or 10 μm. The standard deviation of the particle size may be, for example, 0.05 to 0.20, preferably 0.08 to or 0.15. The particle size of the polymer particles to which the metal compound is attached is the volume-average particle size and is measured in the same manner as described above.

[0031] In the heat treatment process, precursor particles are obtained by heat treatment of polymer particles to which the metal compound obtained in the crystallization process is attached. The heat treatment removes the polymer components and forms voids inside the precursor particles. Alternatively, the metal compound may be changed to a metal oxide or the like by heat treatment. The heat treatment temperature may be, for example, 270°C to 600°C, preferably 400°C or higher, or 500°C or lower. The heat treatment time may be, for example, 0.5 hours to 48 hours, preferably 5 hours to 24 hours. The heat treatment atmosphere may be air or an oxygen-containing atmosphere. The heat treatment may be carried out using, for example, a box furnace, rotary kiln furnace, pusher furnace, roller hearth kiln furnace, etc.

[0032] The porosity of precursor particles obtained from polymer particles to which metal compounds are attached can be calculated, for example, as follows: 50% particle size D of the precursor particles based on volume. 50 From the 50 precursor particles selected based on this, the volume-average particle size D of the polymer particles used 50Precursor particles are selected in which the presence of voids with a diameter between 70% and 100% of the specified size can be confirmed. The diameter of the void is calculated as the diameter of a circular shape drawn to be equivalent in size to the void using the circular shape drawing function of image analysis software. Next, for the selected precursor particles having voids of the specified size, a circular shape equivalent in size to the void present in the cross-section of the precursor particle is drawn. The porosity of each individual precursor particle is calculated by dividing the sum of the areas of the drawn circular shapes by the cross-sectional area of ​​the precursor particle calculated as described above. If the presence of a precursor particle with a void of the specified size cannot be confirmed, the porosity of the precursor particle is considered to be 0%.

[0033] Precursor particles having voids in cross-section can also be prepared by obtaining a precursor precipitate from a metal source solution by adjusting the pH in two stages, instead of using polymer particles in the crystallization process. Changing the pH in two stages during the crystallization process alters the rate of precursor precipitate formation. This change in formation rate creates a difference in growth rate between the inside and outside of the precursor precipitate, allowing for the formation of a precursor precipitate with internal voids. The first stage is, for example, a void formation stage, where the pH is controlled from 11.5 to 12.0. The second stage is, for example, a growth stage, where the pH is adjusted to a lower level than the first stage, from 10.5 to 11.9. The difference in pH between the first and second stages may be, for example, 0.1 to 1.5. By drying the resulting precursor precipitate and heat-treating it as needed, precursor particles with internal voids can be obtained. For details on a method for obtaining precursor particles having internal voids by adjusting the pH, see, for example, Japanese Patent Application Publication No. 2023-36062 (U.S. Patent Application Publication No. 2023 / 0082796).

[0034] The porosity of precursor particles obtained by adjusting the pH can be calculated, for example, as follows: In the cross-sectional image of each precursor particle, image analysis software is used to distinguish and detect regions identified as voids and regions identified as metal compounds by binarizing the cross-sectional image. The total area of ​​the regions identified as voids is calculated using image analysis software, and the porosity of each individual precursor particle is calculated by dividing this by the cross-sectional area of ​​the precursor particle calculated as described above.

[0035] In the synthesis process, a lithium mixture containing prepared precursor particles and a lithium source is heat-treated at a predetermined heat treatment temperature T to obtain a lithium transition metal composite oxide. The synthesis process may include a mixing step of mixing prepared precursor particles and a lithium source to obtain a lithium mixture, and a heat treatment step of heat-treating the lithium mixture to obtain a lithium transition metal composite oxide.

[0036] Examples of lithium sources to be mixed with precursor particles include lithium hydroxide, lithium carbonate, and lithium oxide. The particle size of the lithium source used for mixing may be, for example, 0.1 μm to 100 μm as a volume average particle size, and preferably 2 μm to 20 μm.

[0037] The ratio of the total number of moles of lithium to the total number of moles of metal elements constituting the precursor particles in the lithium mixture may be, for example, 0.95 or more and 1.2 or less. Mixing of the precursor particles and the lithium source can be carried out, for example, using a high-speed shear mixer.

[0038] The lithium mixture may further contain other metallic elements besides lithium and the metallic elements constituting the precursor particles. Examples of other metallic elements include aluminum (Al), silicon (Si), zirconium (Zr), titanium (Ti), magnesium (Mg), tantalum (Ta), niobium (Nb), molybdenum (Mo), tungsten (W), yttrium (Y), etc., and may contain at least one selected from this group. For example, if the lithium mixture contains tungsten, niobium, etc. as other metallic elements, the output characteristics of the resulting battery containing the lithium transition metal composite oxide will be improved. For example, if the lithium mixture contains aluminum, zirconium, etc., it is suitable for further improvement of the cycle characteristics of the resulting battery containing the lithium transition metal composite oxide. For example, if the lithium mixture contains titanium, silicon, etc., it is suitable for further improvement of the cycle characteristics under high voltage in the resulting battery containing the lithium transition metal composite oxide. When the lithium mixture contains other metallic elements, the lithium mixture can be obtained by mixing the other metallic elements in their elemental form or as a metallic compound together with the precursor particles and the lithium source. Examples of metal compounds containing other metal elements include oxides, hydroxides, chlorides, nitrides, carbonates, sulfates, nitrates, acetates, and oxalates. Mixing can be carried out, for example, using a high-speed shear mixer.

[0039] If the lithium mixture contains other metal elements, the ratio of the total number of moles of other metal elements to the total number of moles of metal elements contained in the precursor particles may be, for example, 0.0001 or more and 0.1 or less, preferably 0.0005 or more or 0.001 or more, and may be 0.03 or less or 0.01 or less.

[0040] The lithium mixture may further contain at least one metal compound (hereinafter also referred to as a specific metal compound) selected from the group consisting of sodium compounds, potassium compounds, calcium compounds, strontium compounds, and barium compounds. These specific metal compounds may be inert fluxes and may be metal compounds that can lower the heat treatment temperature of the lithium mixture. The specific metal compounds may be, for example, hydroxides, oxides, carbonates, acetates, nitrates, fluorides, chlorides, etc., and may contain at least one selected from the group consisting of these. The melting point of the specific metal compound may be, for example, 800°C or less or 365°C or less, or 200°C or more or 280°C or more. The particle size of the specific metal compound may be, for example, 0.1 μm or more and 100 μm or less as a volume average particle size, preferably 2 μm or more and 20 μm or less. The content of the specific metal compound in the lithium mixture may be, for example, 0.03 or more and 0.15 or less, as the ratio of the number of moles of metal elements contained in the specific metal compound to the total number of moles of metal elements contained in the precursor particles, and preferably 0.055 or more and 0.1 or less.

[0041] The mixing step may involve simultaneously mixing the precursor particles, the lithium compound, and other metal elements or metal compounds as needed, along with the specific metal compound. Alternatively, the specific metal compound may be mixed after mixing the precursor particles, the lithium compound, and other metal elements or metal compounds as needed. Mixing can be carried out, for example, using a high-speed shear mixer.

[0042] In the heat treatment step, the lithium mixture is heat-treated to obtain a lithium transition metal composite oxide. The heat treatment temperature of the lithium mixture may be, for example, 400°C or more and 1000°C or less, preferably 700°C or more, 760°C or more or 800°C or more, and 990°C or less, 960°C or less or 900°C or less. In the lithium transition metal composite oxide obtained within the above range, the average particle size D based on predetermined electron microscope observations is obtained. SEMThis tends to be obtained. The heat treatment temperature in the heat treatment process may preferably be a heat treatment temperature T (°C) selected according to the composition of precursor particles contained in the lithium mixture. The heat treatment temperature T (°C) is selected from temperatures that satisfy the following formula (1), where x is the ratio of the number of moles of nickel to the total number of moles of metal contained in the transition metal compound containing nickel and oxygen, and K is between 1050°C and 1150°C.

[0043] T = -289x + K (1)

[0044] x may be between 0.3 and 0.99. K may preferably be between 1055°C and 1130°C.

[0045] Formula (1) is used for precursor particles having a predetermined porosity, and is calculated by the ratio of nickel in the precursor particles and the average particle size D based on predetermined electron microscope observations. SEM This is an empirical formula derived from the relationship with the obtained heat treatment temperature. By heat-treating the lithium mixture at a temperature that satisfies formula (1), a positive electrode active material having a predetermined primary particle size can be efficiently produced. In one embodiment, the nickel ratio in the precursor particles may correspond to the ratio of the number of moles of nickel to the total number of moles of metals other than lithium in the lithium transition metal composite oxide.

[0046] In one embodiment, if the nickel ratio in the transition metal compound contained in the precursor particles is 0.9 or more and 0.99 or less, the heat treatment temperature T may be 760°C or more and 820°C or less. In another embodiment, if the nickel ratio in the transition metal compound contained in the precursor particles is 0.5 or more and 0.7 or less, the heat treatment temperature T may be 900°C or more and 980°C or less.

[0047] The heat treatment of the lithium mixture may be performed at a single temperature, or at multiple temperatures from the viewpoint of discharge capacity at high voltage. When heat treatment is performed at multiple temperatures, for example, the first temperature may be held for a predetermined time, and then the temperature may be raised or lowered to a second temperature which may be held for a predetermined time. At least one of the first and second temperatures should be selected from the heat treatment temperature T (°C) represented by formula (1), preferably the higher temperature should be selected from the heat treatment temperature T (°C) represented by formula (1). The first temperature may be, for example, 400°C to 800°C, and the second temperature may be, for example, 700°C to 1000°C. The temperature difference between the first and second temperatures may be, for example, 10°C to 500°C. In one embodiment, the first temperature may be, for example, 760°C to 800°C, and the second temperature may be, for example, 740°C to 780°C, and the first temperature may be 10°C to 20°C higher than the second temperature. In one embodiment, the first temperature may be, for example, 400°C or more and 500°C or less, and the second temperature may be, for example, 850°C or more and 950°C or less, and the second temperature may be 400°C or more and 500°C higher than the first temperature.

[0048] When a lithium mixture is heat-treated at a single temperature, the heat treatment time may be, for example, 6 hours or more and 40 hours or 14 hours or 28 hours or less. When a lithium mixture is heat-treated at multiple temperatures, the heat treatment time at the first temperature may be, for example, 1 hour or more and 12 hours or 2 hours or 8 hours or less. The heat treatment time at the second temperature may be, for example, 3 hours or more and 20 hours or 4 hours or 12 hours or less.

[0049] The heat treatment atmosphere may be in the open air or an oxygen-containing atmosphere. The heat treatment can be carried out using, for example, a box furnace, rotary kiln, pusher furnace, roller hearth kiln, etc.

[0050] The lithium transition metal composite oxide obtained in the synthesis process may be subjected to crushing, dispersion, washing, and surface coating treatments as needed.

[0051] positive electrode active material The positive electrode active material may be manufactured by the positive electrode active material manufacturing method described above. In a cross-sectional view, the median porosity of the positive electrode active material, which is the ratio of the total area of ​​voids to the cross-sectional area of ​​the positive electrode active material, may be smaller than the median porosity of the precursor particles used in the manufacture of the positive electrode active material. By making the median porosity of the positive electrode active material smaller than the median porosity of the precursor particles, for example, the electrode density of the formed electrode can be improved.

[0052] The positive electrode active material may consist solely of positive electrode active material having voids in cross-section, or it may include positive electrode active material that does not have voids in cross-section. Here, positive electrode active material having voids in cross-section means that the observed cross-section of the positive electrode active material is composed of a region where lithium transition metal composite oxide exists (hereinafter also referred to as the metal compound region) and a region where lithium transition metal composite oxide does not exist (void region). The shape and distribution of the voids in the positive electrode active material are the same as those of the voids in the precursor particles. When observing the cross-section of the positive electrode active material, for example using a scanning electron microscope, the metal compound region and the void region may be identified as regions with different contrasts.

[0053] The method for calculating the porosity of the positive electrode active material may be the same as the method for calculating the porosity of the precursor particles. For positive electrode active materials having voids, the median porosity (%), which is the ratio of the total area of ​​voids to the cross-sectional area of ​​each positive electrode active material particle, may be, for example, 0% or more and 40% or less, preferably 0% or more or 30% or less. The difference between the median porosity of the positive electrode active material and the median porosity of the precursor particles used in the manufacture of the positive electrode active material may be, for example, greater than 0% and 35% or less, preferably greater than 0% and 30% or less.

[0054] The composition of the lithium transition metal composite oxide contained in the positive electrode active material may have a ratio of the number of moles of nickel to the total number of moles of metals other than lithium that is, for example, 0.3 or more and less than 1, preferably 0.3 or more and 0.99 or less. In one embodiment, the composition of the lithium transition metal composite oxide may have a ratio of the number of moles of nickel to the total number of moles of metals other than lithium that is 0.4 or more or 0.5 or more, and may be 0.8 or less or 0.7 or less. In another embodiment, the composition of the lithium transition metal composite oxide may have a ratio of the number of moles of nickel to the total number of moles of metals other than lithium that is 0.8 or more or 0.9 or more, and may be 0.99 or less, 0.95 or less or 0.93 or less.

[0055] Lithium transition metal composite oxides may contain cobalt. When lithium transition metal composite oxides contain cobalt, the ratio of the number of moles of cobalt to the total number of moles of metals other than lithium may be, for example, greater than 0 and 0.3 or less, preferably 0.001 or more and 0.3 or less, 0.01 or more or 0.02 or more, 0.2 or less, 0.1 or less or 0.05 or less. Lithium transition metal composite oxides may contain manganese. When lithium transition metal composite oxides contain manganese, the ratio of the number of moles of manganese to the total number of moles of metals other than lithium may be, for example, greater than 0 and 0.3 or less, preferably 0.001 or more and 0.3 or less, 0.005 or more, 0.01 or more or 0.03 or more, 0.2 or less, 0.1 or less or 0.02 or less. Lithium transition metal composite oxides may contain aluminum. When the lithium transition metal composite oxide contains aluminum, the ratio of the number of moles of aluminum to the total number of moles of metals other than lithium may be, for example, greater than 0 and 0.1 or less, preferably between 0.001 and 0.05, or between 0.01 and 0.03. When the lithium transition metal composite oxide contains at least one of manganese and aluminum, the ratio of the total number of moles of manganese and aluminum to the total number of moles of metals other than lithium may be, for example, greater than 0 and 0.3 or less, preferably between 0.01 and 0.03.

[0056] The lithium transition metal composite oxide may have, for example, a composition represented by the following formula (2). Li (1+p) Ni (1-x-y) Co x Mn y M z O2(2)

[0057] In the formula, the following conditions are satisfied: -0.05 ≤ p ≤ 0.2, 0.01 ≤ x + y ≤ 0.7, 0 ≤ x ≤ 0.3, 0 ≤ y ≤ 0.3, and 0 ≤ z ≤ 0.1. M is at least one element selected from the group consisting of Al, Si, Zr, Ti, Mg, Ta, Nb, Mo, W, and Y.

[0058] In one embodiment, p, x, y, and z may satisfy 0 ≤ p ≤ 0.2, 0.02 ≤ x + y ≤ 0.4, 0.01 ≤ x ≤ 0.1, 0.01 ≤ y ≤ 0.1, and 0 ≤ z ≤ 0.1. Also in one embodiment, p, x, y, and z may satisfy 0.01 ≤ p ≤ 0.15, 0.3 ≤ x + y ≤ 0.98, 0.01 ≤ x ≤ 0.2, 0.01 ≤ y ≤ 0.3, and 0 ≤ z ≤ 0.05.

[0059] Electrodes for lithium-ion batteries The electrode for the lithium-ion battery comprises a current collector and a positive electrode active material layer disposed on the current collector, which contains the positive electrode active material described above or a positive electrode active material manufactured by the manufacturing method described above.

[0060] Examples of materials for the current collector include aluminum, nickel, and stainless steel. The positive electrode active material layer can be formed by applying an electrode composition obtained by mixing the above-mentioned positive electrode active material, conductive material, binder, etc., with a solvent onto the current collector, and then performing drying, pressurizing, etc. Examples of conductive materials include natural graphite, artificial graphite, and acetylene black. Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, and polyamide acrylic resin. Examples of solvents include N-methyl-2-pyrrolidone (NMP).

[0061] Lithium-ion battery A lithium-ion battery comprises the above-mentioned electrodes for lithium-ion batteries. In addition to the electrodes for lithium-ion batteries, a lithium-ion battery is composed of a negative electrode for lithium-ion batteries, a non-aqueous electrolyte, a separator, etc. For the negative electrode, non-aqueous electrolyte, separator, etc. in a lithium-ion battery, for example, those for lithium-ion batteries described in Japanese Patent Publication No. 2002-075367, Japanese Patent Publication No. 2011-146390, Japanese Patent Publication No. 2006-12433 (the entire disclosures of these are incorporated herein by reference), etc., can be used as appropriate.

[0062] The invention relating to this disclosure may encompass, for example, the following embodiments: [1] Preparing precursor particles containing nickel and an oxygen-containing transition metal compound, The process involves heat-treating a lithium mixture containing the precursor particles and a lithium source at a heat treatment temperature T (°C) defined by the following formula (1) to obtain a lithium transition metal composite oxide. The precursor particles include precursor particles having voids in cross-section, and the median porosity of the precursor particles having voids, which is the ratio of the total area of ​​the voids to the cross-sectional area of ​​each precursor particle, is 3% or more and 35% or less. The lithium transition metal composite oxide has a composition in which the ratio of the number of moles of nickel to the total number of moles of metals other than lithium is 0.3 or more and 0.99 or less, and the average particle size D based on electron microscope observation. SEM A method for producing a positive electrode active material having a diameter of 1 μm or more and 7 μm or less. T = -289x + K (1) (In equation (1), x is the ratio of the number of moles of nickel to the total number of moles of metal contained in the transition metal compound containing nickel and oxygen, and K satisfies 1050 ≤ K ≤ 1150.)

[0063] [2] The manufacturing method according to [1], wherein the precursor particle comprises a precursor particle having at least one void having an area of ​​2% to 50% of the cross-sectional area in a cross-sectional view.

[0064] [3] The manufacturing method according to [1] or [2], wherein the heat treatment temperature T is 765°C or higher and 820°C or lower, and the lithium transition metal composite oxide has a ratio of the number of moles of nickel to the total number of moles of metals other than lithium of 0.9 or higher and 0.99 or lower.

[0065] [4] The manufacturing method according to [1] or [2], wherein the heat treatment temperature T is 900°C or more and 980°C or less, and the lithium transition metal composite oxide has a ratio of the number of moles of nickel to the total number of moles of metals other than lithium of 0.5 or more and 0.7 or less.

[0066] [5] The precursor particles have a 50% particle size D in the volume-based cumulative particle size distribution. 50 A manufacturing method according to any one of [1] to [4], wherein the particle size is 2 μm or more and 13 μm or less.

[0067] [6] The lithium mixture further comprises at least one metal compound selected from the group consisting of sodium compounds, potassium compounds, calcium compounds, strontium compounds and barium compounds. [1] to [5] The method of production according to any one of these.

[0068] [7] The manufacturing method according to any one of [1] to [6], comprising preparing the precursor particles by contacting polymer particles with a metal source solution containing nickel to obtain polymer particles to which a metal compound is attached, and heat-treating the polymer particles to which the metal compound is attached at a temperature of 270°C to 600°C.

[0069] [8] The polymer particles are manufactured according to the method described in [7], wherein the surface of the polymer particles is hydrophilized.

[0070] [9] A positive electrode active material manufactured by a manufacturing method described in any of [1] to [8], wherein, in a cross-sectional view, the median porosity, which is the ratio of the total area of ​​voids to the cross-sectional area of ​​the positive electrode active material, is smaller than the median porosity of the precursor particles. [Examples]

[0071] The present disclosure will be described in detail below with reference to examples, but the present disclosure is not limited to these examples.

[0072] Reference Example 1A Preparation of each solution A metal source solution (first solution) was prepared by mixing nickel sulfate solution, cobalt sulfate solution, and manganese sulfate solution in a molar ratio of 96:3:1 for the metal elements, with a combined concentration of nickel, cobalt, and manganese of 1.36 mol / kg. The total number of moles of metal elements in the metal source solution was 470.26 mol. A 25% by mass sodium hydroxide aqueous solution was prepared as a basic aqueous solution. A 12.5% ​​by mass ammonia aqueous solution (second solution) was prepared as a complex ion forming solution.

[0073] Preparation of the liquid medium 30 liters of water were prepared in the reaction vessel, and sodium hydroxide solution was added to bring the pH to 12.5. Then, aqueous ammonia solution was added to bring the ammonia concentration to 1.5%. Nitrogen gas was introduced to replace the nitrogen in the reaction vessel and prepare the liquid medium.

[0074] Seed crystal generation process While stirring the liquid medium, 0.26 moles of the first solution were added to the liquid medium, representing the total number of moles of metal elements, to precipitate a composite hydroxide containing nickel, cobalt, and manganese.

[0075] Crystallization process While stirring the liquid medium containing the composite hydroxide obtained above, 470 moles of the first solution, an aqueous sodium hydroxide solution, and an aqueous ammonia solution (second solution) were supplied separately and simultaneously, maintaining a basic pH (12.2 to 12.6), to promote the growth of composite hydroxide particles. The liquid was supplied continuously for 13 hours, with a portion of the liquid in the reaction vessel being filtered to continuously concentrate the slurry. The temperature of the liquid medium was controlled to approximately 70°C during the crystallization process. The generated polymer-encapsulated composite hydroxide particles were washed with water and recovered by filtration.

[0076] The volume-average particle size of the obtained composite hydroxide particles was 7.8 μm, and the standard deviation was 0.07.

[0077] Heat treatment process The obtained composite hydroxide particles were subjected to heat treatment at 450°C for 16 hours in an atmospheric environment to convert them into composite oxide particles, which were then recovered.

[0078] The volume-average particle size of the recovered composite oxide particles was 7.5 μm. The median porosity in the particle cross-section of the recovered composite oxide particles was calculated as described below and found to be 0%.

[0079] Synthesis process The obtained composite oxide particles were mixed with lithium hydroxide, aluminum hydroxide, and zirconium oxide in a molar ratio of Li:(Ni+Co+Mn):Al:Zr=1.10:1:0.005:0.0015. Strontium carbonate was then added at a concentration of 0.2 mol% relative to the total number of moles of Ni, Co, and Mn contained in the composite oxide particles to obtain a lithium mixture. The obtained lithium mixture was heat-treated in an oxygen atmosphere at two different temperatures. In the first stage, it was heat-treated at 780°C for 6 hours, and in the second stage, at 765°C for 10 hours. After the heat treatment, it was dispersed to obtain a lithium transition metal composite oxide.

[0080] Average particle size D based on electron microscopy observation of the obtained lithium transition metal composite oxide SEM The particle size was 1.3 μm, and the median porosity was 0%. It also had the following composition: Li 1.10 Ni 0.96 Co 0.03 Mn 0.01 Al 0.005 Zr 0.0015 O2

[0081] Reference example 1B Lithium transition metal composite oxides were obtained in the same manner as in Reference Example 1A, except that the total number of moles of metal elements in the metal source solution was set to 470.52 moles in the preparation of each solution, and 0.52 moles of the first solution were added in the seed crystal generation step, representing the total number of moles of metal elements.

[0082] The volume-average particle size of the obtained composite hydroxide particles was 4.8 μm, with a standard deviation of 0.11, while the volume-average particle size of the composite oxide particles was 4.9 μm. Furthermore, the average particle size D of the obtained lithium transition metal composite oxide was determined based on electron microscopy observations. SEM The porosity was 1.8 μm, and the median porosity was 0%.

[0083] Reference example 1C Lithium transition metal composite oxides were obtained in the same manner as in Reference Example 1A, except that the total number of moles of metal elements in the metal source solution was set to 470.416 moles during the preparation of each solution, and 0.416 moles of the first solution were added as the total number of moles of metal elements during the seed crystal generation process.

[0084] The volume-average particle size of the obtained composite hydroxide particles was 5.9 μm, with a standard deviation of 0.08, while the volume-average particle size of the composite oxide particles was 5.8 μm. Furthermore, the average particle size D of the obtained lithium transition metal composite oxide was determined based on electron microscopy observations. SEM The porosity was 1.6 μm, and the median porosity was 0%.

[0085] Volume-average particle size D of composite hydroxide particles obtained in Reference Examples 1A to 1C 50 And, average particle size D based on electron microscopy observation of lithium transition metal composite oxides SEM The relationship is shown in Figure 1.

[0086] Figure 1 shows the volume-average particle size D of the composite hydroxide particles that serve as precursor particles. 50 And, based on electron microscopy observation of the lithium transition metal composite oxide obtained therefrom, the average particle size D SEM This is inversely proportional. The volume-average particle size D of composite hydroxide particles and the composite oxide particles obtained by heat treatment of them are 50Since they are considered to be approximately equal, the volume-average particle size D of the composite oxide particles that will become precursor particles 50 And, based on electron microscopy observation of the lithium transition metal composite oxide obtained therefrom, the average particle size D SEM It can be considered that they are inversely proportional.

[0087] Reference example 2A It contains nickel, cobalt, and manganese in a molar ratio of Ni:Co:Mn = 35:35:30, with a volume-average particle size D 50 Precursor particles were prepared consisting of composite oxide particles with a diameter of 4 μm and a median porosity of 0%. A lithium mixture was obtained by mixing lithium hydroxide, the prepared composite oxide particles, and zirconium oxide in a molar ratio of Li:(Ni+Co+Mn):Zr=1.09:1:0.005. The obtained lithium mixture was heat-treated in an oxygen atmosphere at two different temperatures. The first stage was 880°C for 3 hours, and the second stage was 980°C, 1000°C, 1020°C, or 1040°C for 5 hours. After heat treatment, the mixture was dispersed to obtain a lithium transition metal composite oxide.

[0088] Average particle size D based on electron microscopy observation of the obtained lithium transition metal composite oxide SEM The average particle size D was 1.32 μm (980°C), 1.85 μm (100°C), 2.36 μm (1020°C), and 2.44 μm (1040°C), respectively. SEM The relationship is shown in Figure 2A as circles and solid lines.

[0089] Reference example 2B It contains nickel, cobalt, and manganese in a molar ratio of Ni:Co:Mn = 60:20:20, with a volume-average particle size D 50Precursor particles were prepared consisting of composite oxide particles with a diameter of 4 μm and a median porosity of 0%. A lithium mixture was obtained by mixing lithium hydroxide, the prepared composite oxide particles, and zirconium oxide in a molar ratio of Li:(Ni+Co+Mn):Zr=1.06:1:0.005. The obtained lithium mixture was heat-treated in an oxygen atmosphere at two different temperatures. In the first stage, it was heat-treated at 450°C for 2 hours, and in the second stage, it was heat-treated at 850°C, 900°C, or 920°C for 5 hours. After heat treatment, it was dispersed to obtain a lithium transition metal composite oxide.

[0090] Average particle size D based on electron microscopy observation of the obtained lithium transition metal composite oxide SEM The average particle size D was 0.56 μm (850°C), 1.09 μm (900°C), and 1.91 μm (920°C), respectively. SEM The relationship is shown in Figure 2A as a triangle and a dotted line.

[0091] From Figure 2A, if the Ni composition ratio (Ni ratio) in the precursor particles is the same, the heat treatment temperature of the lithium mixture and the average particle size D based on electron microscopy observation of the resulting lithium transition metal composite oxide are similar. SEM This shows that there is a proportional relationship. Also, since the approximate lines for each with a different Ni ratio of precursor particles are roughly parallel to each other, the same average particle size D SEM It is thought that there is a proportional relationship between the heat treatment temperature at which the result is obtained and the Ni ratio of the precursor particles. Therefore, in the approximate straight line in Figure 2A, the average particle size D of 1.8 μm is considered to be SEM Calculating the heat treatment temperature at which the desired result can be obtained, the result is 997.9°C for Reference Example 2A with a Ni ratio of 35% and 925.6°C for Reference Example 2B with a Ni ratio of 60%. Based on these results, the average particle size D of 1.8 μm is calculated. SEM The relationship between the heat treatment temperature at which the desired result is obtained and the Ni ratio of the precursor particles is illustrated in Figure 2B.

[0092] Example 1A Preparation of each volume A metal source solution (first solution) was prepared by mixing nickel sulfate solution, cobalt sulfate solution, and manganese sulfate solution in a molar ratio of 96:3:1 for the combined concentration of nickel, cobalt, and manganese at 1.36 mol / kg. The total number of moles of metal elements in the metal source solution was set to 575 moles. A 25% by mass sodium hydroxide aqueous solution was prepared as a basic aqueous solution. A 12.5% ​​by mass ammonia aqueous solution (second solution) was prepared as a complex ion forming solution. Techpolymer XX-7031Z (manufactured by Sekisui Chemical Co., Ltd., Dm=2μm) was prepared as polymer spherical particles.

[0093] Preparation of the liquid medium 30 liters of water were prepared in a reaction vessel, 307 g of polymer spherical particles were added, and an aqueous ammonia solution was added to achieve an ammonia concentration of 1%. Nitrogen gas was introduced to replace the nitrogen in the reaction vessel and prepare the liquid medium.

[0094] Crystallization process While stirring the liquid medium, 575 moles of the first solution, an aqueous sodium hydroxide solution, and an aqueous ammonia solution (second solution) were supplied separately and simultaneously, maintaining a basic pH (12.2 to 12.7). Using polymer spherical particles as nuclei, composite hydroxides were precipitated on their surfaces, allowing the composite hydroxide particles to grow. A portion of the liquid in the reaction vessel was filtered to continuously concentrate the slurry, while each solution was supplied continuously for 13 hours. During the crystallization process, the temperature of the liquid medium was controlled to approximately 70°C. The resulting composite hydroxide particles containing polymer spherical particles were washed with water and recovered by filtration.

[0095] The composite hydroxide particles obtained by this crystallization process were measured using a laser diffraction scattering particle size distribution analyzer (Shimadzu Corporation, SALD2300), and the volume-average particle size (D 50 The diameter was 7.4 μm, and the standard deviation was 0.07.

[0096] Heat treatment process The composite hydroxide particles containing the obtained polymer spherical particles were heat-treated at 450°C for 16 hours in an atmospheric environment to eliminate the contained polymer spherical particles and convert them into composite oxide particles, thereby recovering the precursor particles. The volume-average particle size D of the recovered precursor particles was... 50 It was 7.3 μm.

[0097] SEM observation was performed on a sample prepared for cross-sectional observation by embedding 1g of recovered precursor particles in 1g of resin and processing it with a cross-section polisher. In the SEM image, the diameter of the particle cross-section corresponds to the volume-average particle size D of the precursor particles. 50 Fifty precursor particles were arbitrarily selected that were within ±20% of the specified value. Next, from the selected precursor particles, those in which voids of 70% to 100% of the Dm of the polymer spherical particles used were selected. Here, the size of the void was defined as the size of the circle drawn to match the void using the circular drawing function of the image analysis software. Next, for each of the selected precursor particles having the specified void, the cross-sectional area S1 of the precursor particle and the area S2 of the void were measured, and the value obtained by dividing the area S2 of the void by the cross-sectional area S1 of the precursor particle (S2 / S1) was defined as the porosity of that precursor particle. The cross-sectional area of ​​the precursor particle was defined as the area of ​​the polygon enclosed by 20 partition points set at approximately equal intervals along the outer edge of the precursor particle using the image analysis software. Furthermore, for each void in the cross-section of each precursor particle, a circle was drawn to match the void using the circular drawing function of the image analysis software, and the sum of the areas of the drawn circles was defined as the void area. The porosity was calculated for each of 10 to 20 precursor particles, and the median porosity was found to be 6.8%. The minimum porosity of the obtained precursor particles was 3.5%, and the maximum was 32.9%.

[0098] Synthesis process Lithium hydroxide, the obtained precursor particles, aluminum hydroxide, and zirconium oxide were mixed in a molar ratio of Li:(Ni+Co+Mn):Al:Zr=1.10:1:0.005:0.0015 to obtain a lithium mixture. The obtained lithium mixture was heat-treated in an oxygen atmosphere at two different temperatures. In the first stage, it was heat-treated at 780°C for 6 hours, and in the second stage, at 765°C for 10 hours. After the heat treatment, it was dispersed to obtain a lithium transition metal composite oxide.

[0099] Composition analysis The obtained lithium transition metal composite oxide was dissolved in an inorganic acid and then chemically analyzed by inductively coupled plasma (ICP) emission spectroscopy. The composition of the obtained lithium transition metal composite oxide is shown below. Li 1.10 Ni 0.96 Co 0.03 Mn 0.01 Al 0.005 Zr 0.0015 O2

[0100] D SEM measurement The average particle size D of the obtained lithium transition metal composite oxide was determined based on electron microscopy observation. SEM We obtained it as follows: (1) Using a scanning electron microscope (SEM), an SEM image was obtained by setting the magnification to such that there were 10 to 20 secondary particles in which the outline of the primary particle could be confirmed. Here, the particle size was the 10% particle size D based on volume. 10 Secondary particles, which make up less than half of the total, were excluded from the measurement. (2) The particle size observed at the above magnification was D 10 For more than half of the secondary particles, and for all secondary particles whose primary particle contours could be confirmed, the contour length of each primary particle was determined by tracing the contour of the primary particle that constitutes each secondary particle using image processing software, and the spherical equivalent diameter was calculated from the contour length. (3) The above steps (1) and (2) were repeated until the number of primary particles for which the spherical equivalent diameter was calculated exceeded 100. The average particle size D was calculated as the arithmetic mean of the spherical equivalent diameters of the obtained primary particles. SEMThey sought it.

[0101] Average particle size D based on electron microscopy observation of lithium transition metal composite oxide obtained in Example 1A SEM It was 1.3 μm.

[0102] The median porosity of the obtained lithium transition metal composite oxide was calculated in the same manner as described above, and it was found to be 0%.

[0103] Example 1B A lithium transition metal composite oxide was obtained in the same manner as in Example 1A, except that in the synthesis process, strontium carbonate was added as a strontium compound (Sr compound) at a concentration of 0.2 mol% relative to the total number of moles of Ni, Co, and Mn contained in the composite oxide particles to obtain a lithium mixture.

[0104] Average particle size D based on electron microscopy observation of the obtained lithium transition metal composite oxide SEM The porosity was 1.8 μm, and the median porosity was 0%.

[0105] Example 2A Composite hydroxide particles were obtained in the same manner as in Example 1, except that the total number of moles of metal elements in the metal source solution was set to 305 moles, Techpolymer XX-7032Z (manufactured by Sekisui Chemical Co., Ltd., Dm=5μm) was prepared as polymer spherical particles, the amount of polymer spherical particles added to the liquid medium was 1392g, and the supply time of each solution in the crystallization step was set to 7.3 hours.

[0106] The volume-average particle size of the obtained composite hydroxide particles was 11.4 μm, and the standard deviation was 0.09. Furthermore, the median porosity of the precursor particles containing the composite oxide, obtained by heat-treating the obtained composite hydroxide particles in the same manner as in Example 1A, was 28.0%. The minimum porosity of the obtained precursor particles was 14.2%, and the maximum was 34.8%.

[0107] A lithium transition metal composite oxide was obtained in the same manner as in Example 1A, except that the precursor particles obtained above were used. The average particle size D of the obtained lithium transition metal composite oxide was determined based on electron microscopy observation. SEM The particle size was 1.0 μm, and the median porosity was 23%. It also had the following composition: Li 1.10 Ni 0.96 Co 0.03 Mn 0.01 Al 0.005 Zr 0.0015 O2

[0108] Example 2B A lithium transition metal composite oxide was obtained in the same manner as in Example 2A, except that in the synthesis process, 0.2 mol% of strontium carbonate was added relative to the total number of moles of Ni, Co, and Mn contained in the precursor particles to obtain a lithium mixture.

[0109] Average particle size D based on electron microscopy observation of the obtained lithium transition metal composite oxide SEM The porosity was 1.3 μm, and the median porosity was 21.4%.

[0110] Comparative Example 1A Preparation of each solution The procedure was the same as in Example 1A, except that the total number of moles of metal elements in the metal source solution was set to 470.26 moles and polymer spherical particles were not prepared.

[0111] Preparation of the liquid medium 30 liters of water were prepared in the reaction vessel, and sodium hydroxide solution was added to bring the pH to 12.5. Then, aqueous ammonia solution was added to bring the ammonia concentration to 1.5%. Nitrogen gas was introduced to replace the nitrogen in the reaction vessel and prepare the liquid medium.

[0112] Seed crystal generation process While stirring the liquid medium, 0.26 moles of the first solution were added to the liquid medium, representing the total number of moles of metal elements, to precipitate a composite hydroxide containing nickel, cobalt, and manganese.

[0113] Crystallization process While stirring the liquid medium containing the composite hydroxide obtained above, 470 moles of the first solution, an aqueous sodium hydroxide solution, and an aqueous ammonia solution (second solution) were supplied separately and simultaneously, maintaining a basic pH (12.2 to 12.6), to promote the growth of the composite hydroxide particles. The liquid was supplied continuously for 13 hours, with a portion of the liquid in the reaction vessel being filtered to continuously concentrate the slurry. The temperature of the liquid medium was controlled to approximately 70°C during the crystallization process. The generated composite hydroxide particles were washed with water and recovered by filtration.

[0114] The volume-average particle size of the obtained composite hydroxide particles was 7.8 μm, and the standard deviation was 0.07.

[0115] Heat treatment process The obtained composite hydroxide particles were subjected to heat treatment at 450°C for 16 hours in an atmospheric environment to convert them into composite oxide particles, and the precursor particles were recovered.

[0116] Since no voids of the specified size were observed in the particle cross-section of the recovered precursor particles, the median porosity of the precursor particles was considered to be 0%.

[0117] Synthesis process The obtained precursor particles were mixed with lithium hydroxide, aluminum hydroxide, and zirconium oxide in a molar ratio of Li:(Ni+Co+Mn):Al:Zr=1.10:1:0.005:0.0015 to obtain a lithium mixture. The obtained lithium mixture was heat-treated in an oxygen atmosphere at two different temperatures, as in Example 1A. The first stage involved heat treatment at 780°C for 6 hours, and the second stage involved heat treatment at 765°C for 10 hours. After heat treatment, the mixture was dispersed to obtain a lithium transition metal composite oxide.

[0118] Average particle size D based on electron microscopy observation of the obtained lithium transition metal composite oxide SEM The particle size was 0.9 μm, and the median porosity was 0%. It also had the following composition: Li 1.10 Ni0.96 Co 0.03 Mn 0.01 Al 0.005 Zr 0.0015 O2

[0119] Comparative example 1B A lithium transition metal composite oxide was obtained in the same manner as in Comparative Example 1A, except that in the synthesis process, 0.2 mol% of strontium carbonate was added relative to the total number of moles of Ni, Co, and Mn contained in the precursor particles to obtain a lithium mixture.

[0120] Average particle size D based on electron microscopy observation of the obtained lithium transition metal composite oxide SEM The porosity was 1.3 μm, and the median porosity was 0%.

[0121] Comparative example 2A Composite hydroxide particles were obtained in the same manner as in Example 1A, except that the total number of moles of metal elements in the metal source solution was set to 47 moles, Techpolymer XX-7032Z (manufactured by Sekisui Chemical Co., Ltd., Dm=5μm) was prepared as polymer spherical particles, the amount of polymer spherical particles added to the liquid medium was 609g, and the supply time of each solution in the crystallization step was set to 2.1 hours.

[0122] The volume-average particle size of the obtained composite hydroxide particles was 7.8 μm, and the standard deviation was 0.07. Furthermore, the median porosity of the precursor particles obtained by heat-treating the obtained composite hydroxide particles in the same manner as in Example 1A was 38.8%. The minimum porosity of the obtained precursor particles was 23.2%, and the maximum was 47.9%.

[0123] The obtained precursor particles exhibited strong aggregation and were in an unresolved state. Although the synthesis process was carried out using the obtained precursor particles in the same manner as in Comparative Example 1A, it was not possible to obtain an evaluable lithium transition metal composite oxide.

[0124] Comparative Example 2B The synthesis process was carried out in the same manner as in Comparative Example 2A, except that 0.2 mol% of strontium carbonate was added relative to the total number of moles of Ni, Co, and Mn contained in the precursor particles to obtain a lithium mixture. However, it was not possible to obtain an evaluable lithium transition metal composite oxide.

[0125] Example 3A Preparation of each solution A metal source solution (first solution) was prepared by mixing nickel sulfate solution, cobalt sulfate solution, and manganese sulfate solution in a molar ratio of 6:1:3 for the metal elements, with a combined concentration of nickel, cobalt, and manganese of 1.36 mol / kg. The total number of moles of metal elements in the metal source solution was 470 mol. A 25% by mass sodium hydroxide aqueous solution was prepared as a basic aqueous solution. A 12.5% ​​by mass ammonia aqueous solution (second solution) was prepared as a complex ion forming solution. Techpolymer XX-7031Z (manufactured by Sekisui Chemical Co., Ltd., Dm=2 μm) was prepared as polymer spherical particles.

[0126] Preparation of the liquid medium 30 liters of water were prepared in a reaction vessel, 1366 g of polymer spherical particles were added, and an aqueous ammonia solution was added to achieve an ammonia concentration of 0.8%. Nitrogen gas was introduced and the reaction vessel was purged with nitrogen to prepare the liquid medium.

[0127] Crystallization process While stirring the liquid medium, 470 moles of the first solution, an aqueous sodium hydroxide solution, an aqueous ammonia solution (second solution), and carbon dioxide were supplied separately and simultaneously, maintaining a basic pH (11.4 to 11.6). Using polymer spherical particles as nuclei, composite hydroxides were precipitated on their surfaces, allowing the composite hydroxide particles to grow. A portion of the liquid in the reaction vessel was filtered to continuously concentrate the slurry, while each solution was supplied continuously for 42 hours. During the crystallization process, the temperature of the liquid medium was controlled to approximately 70°C. The resulting composite hydroxide particles containing polymer spherical particles were washed with water and recovered by filtration.

[0128] The volume average particle size of the obtained composite hydroxide particles was 5.3 μm, and the standard deviation was 0.09.

[0129] Heat treatment process The obtained composite hydroxide particles encapsulating polymer spherical particles were heat-treated at 450 °C for 16 hours in an air atmosphere to remove the encapsulated polymer spherical particles and convert them into a composite oxide to recover precursor particles.

[0130] The median value of the porosity of the obtained precursor particles was 16.1%. The minimum value of the porosity of the obtained precursor particles was 13.8%, and the maximum value was 35.2%.

[0131] Synthesis process Lithium hydroxide, the obtained precursor particles, zirconium oxide, and yttrium oxide were mixed so that the molar ratio was Li:(Ni+Co+Mn):Zr:Y = 1.08:1:0.003:0.0015 to obtain a lithium mixture. The obtained lithium mixture was volume heat-treated at two stages in a 60% oxygen atmosphere. In the first stage, heat treatment was performed at 450 °C for 3 hours, and in the second stage, heat treatment was performed at 950 °C for 6 hours. After heat treatment, dispersion treatment was performed to obtain a lithium transition metal composite oxide.

[0132] Composition analysis The composition of the obtained lithium transition metal composite oxide is shown below. Li 1.08 Ni 0.6 Co 0.1 Mn 0.3 Zr 0.003 Y 0.0015 O2

[0133] The average particle size D based on the electron microscope observation of the obtained lithium transition metal composite oxide SEM was 1.8 μm.

[0134] Example 3B A lithium transition metal composite oxide was obtained in the same manner as in Example 3A, except that in the synthesis process, 0.2 mol% of strontium carbonate was added relative to the total number of moles of Mn, Co, and Mn contained in the precursor particles to obtain a lithium mixture.

[0135] Average particle size D based on electron microscopy observation of the obtained lithium transition metal composite oxide SEM It was 2.7 μm.

[0136] Comparative example 3A Preparation of each solution The preparation was the same as in Example 3A, except that polymer spherical particles were not prepared.

[0137] Preparation of the liquid medium 30 liters of water were prepared in the reaction vessel, and sodium hydroxide solution was added to bring the pH to 12.5. Nitrogen gas was introduced and the reaction vessel was purged with nitrogen to prepare the liquid medium.

[0138] Seed crystal generation process While stirring the liquid medium, 1.63 moles of the first solution were added to the liquid medium, representing the total number of moles of metal elements, to precipitate a composite hydroxide containing nickel, cobalt, and manganese.

[0139] Crystallization process Except for using the liquid medium obtained above, composite hydroxide particles that did not contain polymer spherical particles were recovered in the same manner as the crystallization step in Example 3A.

[0140] The volume-average particle size of the obtained composite hydroxide particles was 5.0 μm, and the standard deviation was 0.07.

[0141] Heat treatment process Precursor particles were obtained in the same manner as the heat treatment step in Example 3A, except that the composite hydroxide particles obtained above were used.

[0142] The median porosity of the obtained precursor particles was 0%.

[0143] Synthesis process A lithium transition metal composite oxide was obtained in the same manner as in the synthesis process of Example 3A, except that the precursor particles obtained above were used.

[0144] Composition analysis The composition of the obtained lithium transition metal composite oxide is shown below. Li 1.08 Ni 0.6 Co 0.1 Mn 0.3 Zr 0.003 Y 0.0015 O2

[0145] The average particle diameter D based on the electron microscope observation of the obtained lithium transition metal composite oxide SEM was 1.7 μm.

[0146] Comparative Example 3B In the synthesis process, a lithium transition metal composite oxide was obtained in the same manner as in Comparative Example 3A, except that strontium carbonate was added at 0.2 mol% to the total number of moles of Mn, Co, and Mn contained in the precursor particles to obtain a lithium mixture.

[0147] The average particle diameter D based on the electron microscope observation of the obtained lithium transition metal composite oxide SEM was 2.5 μm.

[0148] The above results are summarized in Table 1. In Table 1, the “+” and “-” in the Sr compound column indicate the presence or absence of strontium carbonate added to the lithium mixture. Also, the “-” in D SEM and porosity indicates that it was not evaluated.

[0149]

Table 1

Claims

1. The preparation of precursor particles containing a transition metal compound including nickel and oxygen, The lithium mixture containing the precursor particles and the lithium source is heat-treated at a heat treatment temperature T (°C) defined by the following formula (1) to obtain a lithium transition metal composite oxide, and the method is as follows: The aforementioned precursor particles include precursor particles having voids in cross-section, and the median porosity of the precursor particles having voids, which is the ratio of the total area of ​​the voids to the cross-sectional area of ​​each precursor particle, is 3% or more and 35% or less. The lithium transition metal composite oxide has a composition in which the ratio of the number of moles of nickel to the total number of moles of metals other than lithium is 0.3 or more and 0.99 or less, and the average particle size D based on electron microscope observation. ＳＥＭ A method for producing a positive electrode active material having a diameter of 1 μm or more and 7 μm or less. T=-289x+K (1) (In equation (1), x is the ratio of the number of moles of nickel to the total number of moles of metal contained in the transition metal compound containing nickel and oxygen, and K satisfies 1050 ≤ K ≤ 1150.)

2. The manufacturing method according to claim 1, wherein the precursor particle comprises a precursor particle having at least one void portion having an area of ​​2% to 50% of the cross-sectional area in a cross-sectional view.

3. The heat treatment temperature T is 765°C or higher and 820°C or lower. The manufacturing method according to claim 1, wherein the lithium transition metal composite oxide has a ratio of the number of moles of nickel to the total number of moles of metals other than lithium of 0.9 or more and 0.99 or less.

4. The heat treatment temperature T is 900°C or higher and 980°C or lower. The manufacturing method according to claim 1, wherein the lithium transition metal composite oxide has a ratio of the number of moles of nickel to the total number of moles of metals other than lithium of 0.5 or more and 0.7 or less.

5. The precursor particles have a 50% particle size D in the volume-based cumulative particle size distribution. ５０ The manufacturing method according to claim 1, wherein the particle size is 2 μm or more and 13 μm or less.

6. The manufacturing method according to claim 1, wherein the lithium mixture further comprises at least one metal compound selected from the group consisting of sodium compounds, potassium compounds, calcium compounds, strontium compounds, and barium compounds.

7. Preparing the aforementioned precursor particles is The process involves contacting polymer particles with a nickel-containing metal source solution to obtain polymer particles to which a metal compound is attached, The manufacturing method according to claim 1, further comprising heat-treating polymer particles to which the metal compound is attached at a temperature of 270°C to 600°C.

8. The manufacturing method according to claim 7, wherein the polymer particles are subjected to a hydrophilic treatment on their surface.

9. A positive electrode active material manufactured by the manufacturing method described in any one of claims 1 to 8, A positive electrode active material in which, in a cross-sectional view, the median porosity, which is the ratio of the total area of ​​voids to the cross-sectional area of ​​the positive electrode active material, is smaller than the median porosity of the precursor particles.

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